阅读说明：本技术 间苯二甲胺型半芳香族聚酰胺及其制备方法 (Metaxylylenediamine type semi-aromatic polyamide and preparation method thereof ) 是由 郑天成 段小超 郭孝乐 于豪 赵丽恒 于 2021-04-14 设计创作，主要内容包括：本发明提供一种制备间苯二甲胺型半芳香族聚酰胺盐溶液的方法(简称成盐方法)以及采用间苯二甲胺型半芳香族聚酰胺盐溶液制备间苯二甲胺型半芳香族聚酰胺的方法(简称聚合方法)。本发明的成盐方法主要利用间苯二甲胺与一种或多种二元酸的水溶液直接混合,制备出稳定的间苯二甲胺型半芳香族聚酰胺盐溶液。本发明的聚合方法采用常压或微正压预聚合的工艺将间苯二甲胺型半芳香族聚酰胺盐溶液制备成间苯二甲胺型半芳香族聚酰胺。(The invention provides a method for preparing a solution of m-xylylenediamine type semi-aromatic polyamide salt (a salifying method for short) and a method for preparing m-xylylenediamine type semi-aromatic polyamide by adopting the solution of m-xylylenediamine type semi-aromatic polyamide salt (a polymerization method for short). The salifying method of the invention mainly utilizes the direct mixing of m-xylylenediamine and one or more than one dibasic acid aqueous solution to prepare the stable m-xylylenediamine type semi-aromatic polyamide salt solution. The polymerization method adopts a normal pressure or micro-positive pressure prepolymerization process to prepare the m-xylylenediamine semi-aromatic polyamide salt solution into the m-xylylenediamine semi-aromatic polyamide.)

1. A process for the preparation of a solution of a semi-aromatic polyamide salt of the isophthalic type, characterized in that it comprises:

(1) providing an aqueous dispersion of a dibasic acid;

(2) mixing a dibasic acid aqueous dispersion with diamine to obtain a crude salt solution with the temperature of 50-140 ℃, the concentration of 30-80 wt% and the pH of 3-7, wherein the diamine comprises m-xylylenediamine;

(3) adjusting the temperature, concentration and/or pH of the crude salt solution to obtain a refined salt solution with the temperature of 50-140 ℃, the concentration of 45-70 wt% and the pH of 4.8-7.5;

wherein the absolute value of the difference in concentration between the refined salt solution and the crude salt solution is not more than 20 wt%.

2. The method of claim 1, wherein the method has one or more of the following features:

the dibasic acid comprises aliphatic dibasic acid and optional aromatic dibasic acid; preferably, the mole fraction of the aliphatic dibasic acid in the dibasic acid is more than or equal to 70 percent; preferably, the aliphatic dibasic acid comprises adipic acid, and the mole fraction of the adipic acid in the aliphatic dibasic acid is preferably more than or equal to 80%;

the concentration of the crude salt solution is 40-70 wt%;

the pH value of the crude salt solution is 3.5-7;

in the step (3), applying pressure of 0-300 KPa to a reaction system;

the absolute value of the concentration difference between the refined salt solution and the crude salt solution is not more than 10 wt%;

the absolute value of the temperature difference between the refined salt solution and the crude salt solution is not more than 40 ℃, preferably not more than 20 ℃;

the diamine in the step (2) is m-xylylenediamine;

the step (3) comprises adding a diamine, preferably comprising m-xylylenediamine, more preferably m-xylylenediamine, to the crude salt solution;

the step (3) does not include a concentration operation;

in the diamine contained in the refined salt solution, the mole fraction of m-xylylenediamine in the diamine is more than or equal to 60 percent, preferably more than or equal to 80 percent; preferably, the diamine contained in the refined salt solution is m-xylylenediamine;

the method further comprises the step (4): storing the refined salt solution, wherein the storage temperature is 50-140 ℃, the storage concentration is 45-70 wt%, and the storage pH value is 4.8-7.5.

3. A salifying device for preparing a m-xylylenediamine-type semi-aromatic polyamide salt solution is characterized by comprising an acid supply unit, a crude salt preparation unit, a refined salt preparation unit and an optional storage unit which are connected in sequence, wherein the acid supply unit supplies an aqueous dispersion of a dibasic acid to the crude salt preparation unit, the crude salt preparation unit is used for mixing the aqueous dispersion of the dibasic acid and a diamine containing m-xylylenediamine to obtain a crude salt solution, the refined salt preparation unit is used for adjusting the temperature, the concentration and/or the pH of the crude salt solution to obtain a refined salt solution, and the storage unit is used for storing the refined salt solution.

4. Salifying apparatus according to claim 3, wherein said salifying apparatus has one or more of the following characteristics:

the crude salt solution is as described in claim 1 or 2;

the refined salt solution is as described in claim 1 or 2;

the acid supply unit comprises a solid acid conveying device, a stirring device, a desalted water pipeline, a dissolving tank, a diacid aqueous solution pipeline and a conveying pump, wherein the solid acid conveying device is provided with a feeding hole and a discharging hole, the stirring device is arranged in the dissolving tank, the dissolving tank is provided with a solid acid feeding hole, a desalted water feeding hole and a discharging hole, the solid acid feeding hole of the dissolving tank is communicated with the discharging hole of the solid acid conveying device, the desalted water feeding hole of the dissolving tank is communicated with the desalted water pipeline, the discharging hole of the dissolving tank is communicated with the diacid aqueous solution pipeline, the conveying pump is arranged on the diacid aqueous solution pipeline, the solid acid conveying device is provided with a metering device, the desalted water pipeline is provided with a metering device, and the dissolving tank is provided with a safety valve, a meter and a temperature control system;

the crude salt preparation unit comprises a m-xylylenediamine pipeline, a desalted water pipeline, a stirring device, a standby acid solution pipeline, a pH detection device, a crude salt reactor, a delivery pump, a filter, a crude salt solution pipeline and a feedback regulation control system, wherein the stirring device and the pH detection device are arranged in the crude salt reactor, the crude salt reactor is provided with a diacid water solution feed inlet, a m-xylylenediamine feed inlet, a desalted water feed inlet, a standby acid solution feed inlet and a discharge outlet which are respectively communicated with the diacid water solution pipeline, the m-xylylenediamine pipeline, the desalted water pipeline, the standby acid solution pipeline and the crude salt solution pipeline, the delivery pump and the filter are arranged on the crude salt solution pipeline, the m-xylylenediamine pipeline is provided with a metering device, and the metering device is connected with the feedback regulation control system and controls the addition amount of diamine, the desalting water pipeline is provided with a metering device, the metering device is connected with a feedback regulation control system to control the addition amount of the desalting water, the standby acid solution pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system to control the addition amount of the binary acid water dispersoid, the crude salt reactor is provided with a safety valve, an instrument and a temperature control system, and the pH detection device is connected with the feedback regulation control system;

the refined salt preparation unit comprises one or more refined salt reactors, one or more spare acid solution pipelines in one-to-one correspondence with the refined salt reactors, one or more m-xylylenediamine pipelines in one-to-one correspondence with the refined salt reactors, one or more stirring devices in one-to-one correspondence with the refined salt reactors, one or more pH detection devices in one-to-one correspondence with the refined salt reactors, a delivery pump, a filter, a refined salt solution pipeline and a feedback regulation control system, wherein the stirring devices and the pH detection devices are arranged in the refined salt reactors, each refined salt reactor is provided with a crude salt solution feed inlet, an m-xylylenediamine feed inlet, a spare acid solution feed inlet and a discharge outlet which are respectively communicated with the crude salt solution pipeline, the m-xylylenediamine pipeline, the spare acid solution pipeline and the refined salt solution pipeline, and the delivery pump and the filter are arranged on the refined salt solution pipeline, the standby acid solution pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of the binary acid water dispersoid, the m-xylylenediamine pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of diamine, the refined salt reactor is provided with a safety valve, an instrument and a temperature control system, and the pH detection device is connected with the feedback regulation control system;

the storage unit comprises a salt solution storage tank, a delivery pump and a filter, wherein the salt solution storage tank is provided with a feed inlet and a discharge outlet, the feed inlet of the salt solution storage tank is communicated with a refined salt solution pipeline, the discharge outlet of the salt solution storage tank is communicated with a pipeline, and the delivery pump and the filter are arranged on the pipeline.

5. A continuous polymerization process for preparing a semi-aromatic polyamide of the isophthalic type, characterized in that it comprises:

(1) prepolymerization reaction: carrying out pressure maintaining and temperature rising on a m-xylylenediamine semi-aromatic polyamide salt solution to carry out amidation reaction, and preparing a polymerization intermediate I with the polymerization degree of 5-20;

(2) pressure release reaction: reducing the pressure and raising the temperature of the polymerization intermediate I to further react and improve the polymerization degree, and preparing a polymerization intermediate II with the polymerization degree of 20-40;

(3) final polymerization reaction: carrying out normal pressure or negative pressure operation on the polymerization intermediate II to further improve the polymerization degree and prepare a finished product of the m-xylylenediamine type semi-aromatic polyamide with the polymerization degree of 40-140;

wherein the prepolymerization reaction, the pressure release reaction and the final polymerization reaction are respectively carried out in three reactors which are sequentially connected in series.

6. The continuous polymerization process of claim 5, wherein the continuous polymerization process has one or more of the following characteristics:

the temperature of the m-xylylenediamine semi-aromatic polyamide salt solution is 50-140 ℃, the concentration is 45-70 wt%, and the pH is 4.8-7.5;

the solution of the semiaromatic polyamide salt of the isophthalic acid type is the refined salt solution described in claim 1 or 2;

in the step (1), the initial reaction temperature is 160-200 ℃, and the final reaction temperature is 210-235 ℃;

in the step (1), the reaction pressure is 0-0.8 MPa;

in the step (1), the reaction time is 0.3-3 h;

the distribution width of the polymerization degree of the polymerization intermediate I is less than or equal to 5;

in the step (2), the initial reaction temperature is 220-235 ℃, and the final reaction temperature is 240-265 ℃;

in the step (2), the reaction pressure is normal pressure;

in the step (2), the reaction time is 0.3-3 h;

in the step (3), the reaction temperature is 240-280 ℃;

in the step (3), the reaction pressure is 0 to-0.1 MPa;

in the step (3), the reaction time is 0.3-3 h;

the width of the distribution of the degree of polymerization of the finished semi-aromatic polyamide of the m-xylylenediamine type is less than or equal to 15.

7. A continuous polymerization device for preparing m-xylylenediamine semi-aromatic polyamide, which is characterized by comprising a salt solution storage tank, an optional first additive tank, a first delivery pump, a static mixer, a pre-polymerization device, an optional second additive tank, a second delivery pump, a pressure-release polymerization lifting device, a third delivery pump, a final polymerization device and a fourth delivery pump, wherein the static mixer is provided with a feed inlet and a discharge outlet, the salt solution storage tank is connected with the feed inlet of the static mixer through a pipeline, the first delivery pump is arranged on a pipeline connecting the salt solution storage tank and the static mixer, the first additive tank is connected with a pipeline connecting the salt solution storage tank and the static mixer through a pipeline, the pre-polymerization device is provided with a feed inlet, an additive inlet and a discharge outlet, and the discharge outlet of the static mixer is connected with the feed inlet of the pre-polymerization device, the device comprises a prepolymerization device, a pressure-release polymerization lifting device, a third conveying pump, a fourth conveying pump and a fourth conveying pump, wherein an additive inlet of the prepolymerization device is connected with a second additive tank, the pressure-release polymerization lifting device is provided with a feed inlet and a discharge outlet, the discharge outlet of the prepolymerization device is connected with the feed inlet of the pressure-release polymerization lifting device through a pipeline, the second conveying pump is arranged on the pipeline connecting the discharge outlet of the prepolymerization device and the feed inlet of the pressure-release polymerization lifting device, the final polymerization device is provided with a feed inlet and a discharge outlet, the discharge outlet of the pressure-release polymerization lifting device is connected with the feed inlet of the final polymerization device through a pipeline, the third conveying pump is arranged on the pipeline connecting the discharge.

8. A batch polymerization process for preparing a semi-aromatic polyamide of the isophthalic type, characterized in that it comprises: in the same polymerization reactor, pre-polymerization reaction is carried out on the m-xylylenediamine semi-aromatic polyamide salt solution to obtain a polymerization intermediate I with the polymerization degree of 5-15, then pressure relief reaction is carried out to obtain a polymerization intermediate II with the polymerization degree of 20-40, and finally final polymerization reaction is carried out to prepare the m-xylylenediamine semi-aromatic polyamide finished product with the polymerization degree of 40-140.

9. The batch polymerization process of claim 8, wherein the batch polymerization process has one or more of the following characteristics:

the temperature of the m-xylylenediamine semi-aromatic polyamide salt solution is 50-140 ℃, the concentration is 45-70 wt%, and the pH is 4.8-7.5;

the solution of the semiaromatic polyamide salt of the isophthalic acid type is the refined salt solution described in claim 1 or 2;

in the prepolymerization reaction, the reaction temperature is 160-230 ℃;

in the prepolymerization reaction, the reaction pressure is 0-0.8 MPa;

in the prepolymerization reaction, the reaction time is 0.3-3 h;

the distribution width of the polymerization degree of the polymerization intermediate I is less than or equal to 8;

in the pressure release reaction, the reaction temperature is 220-260 ℃;

in the pressure release reaction, the reaction pressure is normal pressure;

in the pressure release reaction, the reaction time is 0.3-3 h;

in the final polymerization reaction, the reaction temperature is 240-280 ℃;

in the final polymerization reaction, the reaction pressure is 0 to-0.1 MPa;

in the final polymerization reaction, the reaction time is 0.3-3 h;

the width of the distribution of the degree of polymerization of the finished semi-aromatic polyamide of the m-xylylenediamine type is less than or equal to 15.

10. Semi-aromatic polyamides of the isophthalic acid type prepared by the process according to any one of claims 5 to 6 and 8 to 9.

11. A method for producing a semi-aromatic polyamide of the isophthalic type, characterized in that the method comprises the method for producing a solution of a semi-aromatic polyamide of the isophthalic type of claim 1 or 2 and the continuous polymerization method for producing a semi-aromatic polyamide of the isophthalic type of claim 5 or 6, or the method comprises the method for producing a solution of a semi-aromatic polyamide of the isophthalic type of claim 1 or 2 and the batch polymerization method for producing a semi-aromatic polyamide of the isophthalic type of claim 8 or 9.

Technical Field

The invention belongs to the field of polyamide preparation, and particularly relates to m-xylylenediamine type semi-aromatic polyamide and a preparation method thereof.

Background

As an important variety of semi-aromatic nylon, m-xylylenediamine type semi-aromatic nylon (MX type nylon) has been introduced in the eighties of the last century, and has been popular among people due to its excellent rigidity, excellent processability, and good barrier properties. Among these materials, the most well-known variety is PA MXD6 (poly m-xylylene adipamide), which has many advantages and is widely used.

The PA MXD6 is a semi-crystalline special nylon, has the characteristics of low water absorption, high heat deformation temperature, high tensile strength and bending strength, small molding shrinkage, good barrier property to gases such as oxygen, carbon dioxide and the like, and the excellent properties make the PA MXD6 especially suitable for the application of packaging materials, particularly the high barrier property and the boiling resistance of the PA MXD6 have great application advantages.

At present, the MX type nylon is mainly produced by direct melt polymerization and salt melt polymerization.

The direct melt polymerization is to directly mix and react two raw materials for producing MX type nylon to prepare MX type nylon. Although the method does not need a salt forming step, the raw materials are heated to a higher temperature in the preparation process, so that the raw materials are easily decomposed, and the product has various defects such as fish eyes, yellowing and the like. Formulations modified to address the above disadvantages are also not very demanding. Meanwhile, the method has high requirement on the purity of raw materials. Since the molar ratio is kept stable during the mixing process, the equipment requirements are extremely complicated, and therefore, the scale-up production is difficult. And it is difficult to realize complete continuous production at the present stage.

The production of MX-type nylon by direct melt polymerization mainly has the following technical defects: (1) the requirement on the purity of the raw materials is high, the cost of the raw materials with high purity is high, and the preparation process is complex; (2) in the monomer mixing process, as an additional molar ratio adjusting system is not provided, the requirement on equipment is extremely complex to maintain a stable molar ratio, so that the production cost is higher, the production process of the device is difficult, and the time and cost for equipment debugging, maintenance and repair are higher; (3) the method is semi-continuous production, complete continuous production cannot be realized, and the final polymerization reaction device is a screw rod, so that the precise control of polymerization parameters is difficult.

The salifying melt polymerization is to prepare solid salt by mixing m-xylylenediamine (MXDA) and dibasic acid according to a fixed proportion, and then dissolve the solid salt during polymerization to complete the subsequent polymerization. However, this method involves salt formation and polymerization dissolution, and has problems of large energy consumption, low efficiency, long time consumption, etc. because of the presence of twice temperature rise for water discharge. Meanwhile, the pH value needs to be adjusted again every time the production is carried out, so the defect is obvious.

Patent document CN1931921A discloses a preparation method of an MXD 6/montmorillonite composite material, which adopts a method of first salt formation and then polymerization to prepare an MXD6 modified material, wherein the time consumption of the salt preparation process is long, 1-5h, a phosphoric acid catalyst is used, and the polymerization process is a one-pot method, i.e., the salt preparation and the reaction are carried out in the same container, and the pH value needs to be repeatedly adjusted before each polymerization.

Patent document CN105924358B discloses a method for preparing a nylon salt, which comprises preparing an aqueous solution of a dibasic acid-base compound and a diamine-acid compound, and mixing them to form a soluble salt and a relatively insoluble salt (nylon salt). For example, an aqueous solution of terephthalic acid-sodium hydroxide and an aqueous solution of hexamethylenediamine-hydrochloric acid are prepared and mixed to precipitate a nylon 6T salt. However, the salt prepared by the method needs centrifugal separation, is dissolved again and repeatedly heated when being used, directly increases energy consumption and resource waste, is difficult to store, is difficult to enlarge production, and has no advantage in cost in industrial continuous production.

The MX-type nylon prepared by adopting a salifying melt polymerization method at present mainly has the following technical defects: (1) MXDA and dibasic acid are prepared into a salt aqueous solution according to a fixed proportion, solid salt is prepared by precipitation, separation and drying, and then secondary dissolution is needed before polymerization, so that the problems of large energy consumption, low efficiency, long time consumption and the like caused by twice temperature rise and water removal (one time is during preparation of the solid salt and one time is during polymerization) in the process; (2) salifying melt polymerization is mostly produced and prepared by adopting an intermittent small reaction kettle at present, the device is difficult to amplify, and meanwhile, the method has the inherent defects of uneven performance distribution, low production capacity and low production efficiency of the prepared material; (3) in the existing nylon condensation polymerization, a high-pressure polymerization process is adopted. In general, the pressure during the polycondensation reaction of the polyamide monomer acid and the monomer amine is often higher than 1.5MPa, even close to 2 MPa. For example, in the polymerization of polyamide 66, the reaction pressure in the apparatus is usually 1.75MPa in order to prevent volatilization of aliphatic hexamethylenediamine. The high positive pressure existing in the reaction means that the reactor needs to keep absolute sealing and pressure resistance on the basis of ensuring stable mass and heat transfer in the reaction process of nylon polymerization equipment, so that the manufacturing difficulty of the nylon polymerization equipment is greatly increased. In addition, high pressure in the reaction process is accompanied by explosive high-risk risks, which greatly influences the personal safety of operators to some extent and causes unnecessary potential safety hazards. Meanwhile, the high-pressure polymerization process is greatly restricted by environmental evaluation and land during the examination and approval and the production of the device, which indirectly hinders the development of the nylon industry; (4) in the aspect of the process, the high pressure is mainly generated by high-temperature water vapor and the like. The gas is directly discharged in the polymerization process, and the heat in the polymerization reactor is also taken away while causing environmental hazard, so that unnecessary temperature drop phenomenon is generated in the reaction process, and the energy consumption in the nylon polymerization process is increased.

Disclosure of Invention

Aiming at a series of problems in production of MX-type nylon, the invention provides a method for preparing a solution of m-xylylenediamine type semi-aromatic polyamide salt (MX salt for short) (a salifying method for short) and a method for preparing m-xylylenediamine type semi-aromatic polyamide (MX polyamide for short, MX nylon for short) by adopting the MX salt solution (a polymerization method for short). The salifying method mainly utilizes the direct mixing of the semi-aromatic diamine MXDA and one or more dibasic acid aqueous solutions to prepare the stable semi-aromatic polyamide salt solution. The polymerization method of the invention adopts the pre-polymerization process of normal pressure or micro-positive pressure to prepare MX type polyamide from MX salt solution.

Specifically, the present invention provides a method for preparing a solution of a semi-aromatic polyamide salt of the isophthalic acid type, the method comprising:

(1) providing an aqueous dispersion of a dibasic acid;

(2) mixing a dibasic acid aqueous dispersion with diamine to obtain a crude salt solution with the temperature of 50-140 ℃, the concentration of 30-80 wt% and the pH of 3-7, wherein the diamine comprises m-xylylenediamine;

(3) and adjusting the temperature, the concentration and/or the pH of the crude salt solution to obtain a refined salt solution with the temperature of 50-140 ℃, the concentration of 45-70 wt% and the pH of 4.8-7.5.

In one or more embodiments, the absolute value of the difference in concentration between the refined salt solution and the crude salt solution is no more than 20 wt%.

In one or more embodiments, the diacids include aliphatic diacids and optionally aromatic diacids; preferably, the mole fraction of the aliphatic dibasic acid in the dibasic acid is more than or equal to 70 percent; preferably, the aliphatic dibasic acid comprises adipic acid, and the mole fraction of the adipic acid in the aliphatic dibasic acid is preferably equal to or more than 80%.

In one or more embodiments, the crude salt solution has a concentration of 40 to 70 wt%.

In one or more embodiments, the pH of the crude salt solution is 3.5 to 7.

In one or more embodiments, in step (3), a pressure of 0 to 300KPa is applied to the reaction system.

In one or more embodiments, the absolute value of the difference in concentration between the refined salt solution and the crude salt solution is no more than 10 wt%.

In one or more embodiments, the absolute value of the temperature difference between the refined salt solution and the crude salt solution is no more than 40 ℃, preferably no more than 20 ℃.

In one or more embodiments, the diamine in step (2) is m-xylylenediamine.

In one or more embodiments, step (3) comprises adding a diamine, preferably comprising m-xylylenediamine, more preferably m-xylylenediamine, to the crude salt solution.

In one or more embodiments, the step (3) does not include a concentration operation.

In one or more embodiments, the refined salt solution contains diamine in which m-xylylenediamine accounts for 60% or more, preferably 80% or more, of the diamine in mole fraction; preferably, the diamine contained in the refined salt solution is m-xylylenediamine.

In one or more embodiments, the method further comprises step (4): storing the refined salt solution, wherein the storage temperature is 50-140 ℃, the storage concentration is 45-70 wt%, and the storage pH value is 4.8-7.5.

The invention also provides a salifying device for preparing the m-xylylenediamine semi-aromatic polyamide salt solution, which comprises an acid supply unit, a crude salt preparation unit, a refined salt preparation unit and an optional storage unit which are connected in sequence, wherein the acid supply unit is used for supplying the aqueous dispersion of the dibasic acid to the crude salt preparation unit, the crude salt preparation unit is used for mixing the aqueous dispersion of the dibasic acid and diamine containing m-xylylenediamine to obtain a crude salt solution, the refined salt preparation unit is used for adjusting the temperature, the concentration and/or the pH of the crude salt solution to obtain a refined salt solution, and the storage unit is used for storing the refined salt solution.

In one or more embodiments, the crude salt solution is as described in any embodiment herein.

In one or more embodiments, the crude salt preparation unit is used to mix an aqueous dispersion of a dibasic acid with m-xylylenediamine.

In one or more embodiments, the acid supply unit includes a solid acid delivery device, a stirring device, a desalted water pipe, a dissolving tank, a diacid aqueous solution pipe, and a delivery pump, wherein the solid acid conveying device is provided with a feed inlet and a discharge outlet, the stirring device is arranged in the dissolving tank, the dissolving tank is provided with a solid acid feeding hole, a desalted water feeding hole and a discharging hole, the solid acid feeding hole of the dissolving tank is communicated with the discharging hole of the solid acid conveying device, a desalted water inlet of the dissolving tank is communicated with the desalted water pipeline, a discharge port of the dissolving tank is communicated with the diacid aqueous solution pipeline, the delivery pump is arranged on the diacid aqueous solution pipeline, the solid acid delivery device is provided with a metering device, the desalting water pipeline is provided with a metering device, and the dissolving tank is provided with a safety valve, an instrument and a temperature control system.

In one or more embodiments, the crude salt preparation unit includes a m-xylylenediamine pipeline, a desalted water pipeline, a stirring device, a standby acid solution pipeline, a pH detection device, a crude salt reactor, a transfer pump, a filter, a crude salt solution pipeline, and a feedback regulation control system, the stirring device and the pH detection device are disposed in the crude salt reactor, the crude salt reactor has a diacid aqueous solution feed port, a m-xylylenediamine feed port, a desalted water feed port, a standby acid solution feed port, and a discharge port, and is respectively communicated with the diacid aqueous solution pipeline, the m-xylylenediamine pipeline, the desalted water pipeline, the standby acid solution pipeline, and the crude salt solution pipeline, the transfer pump and the filter are disposed on the crude salt solution pipeline, the m-xylylenediamine pipeline is provided with a metering device, and the metering device is connected with the feedback regulation control system, The system comprises a crude salt reactor, a feedback regulation control system, a standby acid solution pipeline, a desalting water pipeline, a standby acid solution pipeline, a safety valve, a meter and a temperature control system, wherein the addition amount of diamine is controlled, the desalting water pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of desalted water, the standby acid solution pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of a binary acid water dispersion, the crude salt reactor is provided with a safety valve, a.

In one or more embodiments, the refined salt preparation unit includes one or more refined salt reactors, one or more spare acid solution pipelines corresponding to the refined salt reactors one to one, one or more m-xylylenediamine pipelines corresponding to the refined salt reactors one to one, one or more stirring devices corresponding to the refined salt reactors one to one, one or more pH detection devices corresponding to the refined salt reactors one to one, a transfer pump, a filter, a refined salt solution pipeline, and a feedback regulation control system, the stirring devices and the pH detection devices being disposed in the refined salt reactors, the refined salt reactors having a crude salt solution feed inlet, a m-xylylenediamine feed inlet, a spare acid solution feed inlet, and a discharge outlet respectively communicating with the crude salt solution pipeline, the m-xylylenediamine pipeline, the spare acid solution pipeline, and the refined salt solution pipeline, the transfer pump and the filter being disposed on the refined salt solution pipeline, the standby acid solution pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of the binary acid water dispersoid, the m-xylylenediamine pipeline is provided with a metering device, the metering device is connected with the feedback regulation control system and controls the addition amount of diamine, the refined salt reactor is provided with a safety valve, an instrument and a temperature control system, and the pH detection device is connected with the feedback regulation control system.

In one or more embodiments, the storage unit includes a salt solution storage tank having a feed inlet and a discharge outlet, a delivery pump and a filter, the feed inlet of the salt solution storage tank is in communication with a refined salt solution pipeline, the discharge outlet of the salt solution storage tank is in communication with a pipeline, and the delivery pump and the filter are disposed on the pipeline.

The present invention also provides a continuous polymerization process for preparing a semi-aromatic polyamide of the isophthalic acid type, comprising:

(1) prepolymerization reaction: carrying out pressure maintaining and temperature rising on a m-xylylenediamine semi-aromatic polyamide salt solution to carry out amidation reaction, and preparing a polymerization intermediate I with the polymerization degree of 5-20;

(2) pressure release reaction: reducing the pressure and raising the temperature of the polymerization intermediate I to further react and improve the polymerization degree, and preparing a polymerization intermediate II with the polymerization degree of 20-40;

(3) final polymerization reaction: carrying out normal pressure or negative pressure operation on the polymerization intermediate II to further improve the polymerization degree and prepare a finished product of the m-xylylenediamine type semi-aromatic polyamide with the polymerization degree of 40-140;

wherein the prepolymerization reaction, the pressure release reaction and the final polymerization reaction are respectively carried out in three reactors which are sequentially connected in series.

In one or more embodiments, in the step (1), the solution of the semi-aromatic polyamide of the isophthalic acid type has a temperature of 50 to 140 ℃, a concentration of 45 to 70 wt% and a pH of 4.8 to 7.5. In one or more embodiments, in step (1), the solution of the semi-aromatic polyamide salt of the isophthalic acid type is a refined salt solution as described in any of the embodiments herein. In one or more embodiments, in step (1), the reaction starting temperature is 160 to 200 ℃ and the reaction finishing temperature is 210 to 235 ℃. In one or more embodiments, in step (1), the reaction pressure is from 0 to 0.8 MPa. In one or more embodiments, in step (1), the reaction time is 0.3 to 3 hours. In one or more embodiments, the polymerization intermediate I has a breadth of polymerization degree distribution of 5 or less.

In one or more embodiments, in step (2), the reaction starting temperature is 220 to 235 ℃ and the reaction finishing temperature is 240 to 265 ℃. In one or more embodiments, in step (2), the reaction pressure is atmospheric. In one or more embodiments, in step (2), the reaction time is 0.3 to 3 hours.

In one or more embodiments, in step (3), the reaction temperature is from 240 ℃ to 280 ℃. In one or more embodiments, in step (3), the reaction pressure is from 0 to-0.1 MPa. In one or more embodiments, in step (3), the reaction time is 0.3 to 3 hours.

In one or more embodiments, the width of the distribution of the degree of polymerization of the finished semi-aromatic polyamide of the isophthalic acid type is 15 or less.

The invention also provides a continuous polymerization device for preparing m-xylylenediamine semi-aromatic polyamide, which comprises a salt solution storage tank, an optional first additive tank, a first delivery pump, a static mixer, a pre-polymerization device, an optional second additive tank, a second delivery pump, a pressure-release polymerization lifting device, a third delivery pump, a final polymerization device and a fourth delivery pump, wherein the static mixer is provided with a feed inlet and a discharge outlet, the salt solution storage tank is connected with the feed inlet of the static mixer through a pipeline, the first delivery pump is arranged on a pipeline connecting the salt solution storage tank and the static mixer, the first additive tank is connected with a pipeline connecting the salt solution storage tank and the static mixer through a pipeline, the pre-polymerization device is provided with a feed inlet, an additive inlet and a discharge outlet, and the discharge outlet of the static mixer is connected with the feed inlet of the pre-polymerization device, the device comprises a prepolymerization device, a pressure-release polymerization lifting device, a third conveying pump, a fourth conveying pump and a fourth conveying pump, wherein an additive inlet of the prepolymerization device is connected with a second additive tank, the pressure-release polymerization lifting device is provided with a feed inlet and a discharge outlet, the discharge outlet of the prepolymerization device is connected with the feed inlet of the pressure-release polymerization lifting device through a pipeline, the second conveying pump is arranged on the pipeline connecting the discharge outlet of the prepolymerization device and the feed inlet of the pressure-release polymerization lifting device, the final polymerization device is provided with a feed inlet and a discharge outlet, the discharge outlet of the pressure-release polymerization lifting device is connected with the feed inlet of the final polymerization device through a pipeline, the third conveying pump is arranged on the pipeline connecting the discharge.

The present invention also provides a batch polymerization method for preparing a semi-aromatic polyamide of the isophthalic acid type, the method comprising: in the same polymerization reactor, pre-polymerization reaction is carried out on the m-xylylenediamine semi-aromatic polyamide salt solution to obtain a polymerization intermediate I with the polymerization degree of 5-15, then pressure relief reaction is carried out to obtain a polymerization intermediate II with the polymerization degree of 20-40, and finally final polymerization reaction is carried out to prepare the m-xylylenediamine semi-aromatic polyamide finished product with the polymerization degree of 40-140.

In one or more embodiments, the solution of the semi-aromatic polyamide of the isophthalic acid type has a temperature ranging from 50 to 140 ℃, a concentration ranging from 45 to 70 wt% and a pH ranging from 4.8 to 7.5.

In one or more embodiments, the solution of a semiaromatic polyamide of the isophthalic type is a refined salt solution as described in any of the embodiments herein.

In one or more embodiments, the reaction temperature in the prepolymerization reaction is 160 to 230 ℃. In one or more embodiments, the reaction pressure in the prepolymerization reaction is 0 to 0.8 MPa. In one or more embodiments, the reaction time in the prepolymerization is 0.3 to 3 hours. In one or more embodiments, the polymerization intermediate I has a breadth of polymerization degree distribution of 8 or less.

In one or more embodiments, the pressure release reaction is carried out at a reaction temperature of 220 to 260 ℃. In one or more embodiments, the pressure relief reaction is at atmospheric pressure. In one or more embodiments, the pressure release reaction is carried out for a reaction time of 0.3 to 3 hours.

In one or more embodiments, the reaction temperature in the final polymerization reaction is 240 to 280 ℃. In one or more embodiments, the reaction pressure in the final polymerization reaction is from 0 to-0.1 MPa. In one or more embodiments, the reaction time in the final polymerization reaction is 0.3 to 3 hours.

In one or more embodiments, the width of the distribution of the degree of polymerization of the finished semi-aromatic polyamide of the isophthalic acid type is 15 or less.

The invention also relates to the semi-aromatic polyamide of the m-xylylenediamine type prepared by the method of any one of the embodiments.

The present invention also provides a method for producing a semi-aromatic polyamide of the isophthalic type, the method comprising the method for producing a solution of a semi-aromatic polyamide of the isophthalic type as described in any of the embodiments herein and a continuous polymerization method for producing a semi-aromatic polyamide of the isophthalic type as described in any of the embodiments herein, or the method comprising the method for producing a solution of a semi-aromatic polyamide of the isophthalic type as described in any of the embodiments herein and a batch polymerization method for producing a semi-aromatic polyamide of the isophthalic type as described in any of the embodiments herein.

Drawings

FIG. 1 is a schematic diagram of a salifying apparatus of the present invention, with the following reference numbers:

in acid supply unit i: 101 is a solid acid conveying device, 102 is a stirring device, 103 is a desalting water pipeline, 104 is a dissolving tank, 105 is a diacid aqueous solution pipeline, and 106 is a conveying pump;

in crude salt preparation unit ii: 201 is a m-xylylenediamine pipeline, 202 is a desalted water pipeline, 203 is a stirring device, 204 is a standby acid solution pipeline, 205 is a pH detection device, 206 is a crude salt reactor, 207 is a delivery pump, and 208 is a filter;

in refined salt preparation unit III: A301-A3 n are spare acid solution pipelines, M301-M3 n are M-xylylenediamine pipelines, S301-S3 n are stirring devices, R301-R3 n are refined salt reactors, 311 is a delivery pump, and 312 is a filter; wherein n represents the number of refined salt reactors;

in storage unit iv: 400 is a salt solution storage tank, 401 is a delivery pump, 402 is a filter.

FIG. 2 is a schematic view of a continuous polymerization apparatus of the present invention, and reference numerals are described below: 1 is a salt solution storage tank, 2 is an additive tank, 4 is a delivery pump, 5 is a static mixer, 6 is a pre-polymerization device, 7 is the additive tank, 8 is the delivery pump, 9 is a pressure-release polymerization lifting device, 10 is the delivery pump, 11 is a final polymerization device, and 12 is the delivery pump.

FIG. 3 is a schematic view of a batch polymerization apparatus of the present invention, and reference numerals are described below: 1 is a salt solution storage tank, 2 is an additive tank, 4 is a delivery pump, 5 is a static mixer, 6 is a polymerization kettle, and 7 is a delivery pump.

Detailed Description

To make the features and effects of the present invention obvious to those skilled in the art, the terms and words used in the specification and claims are generally described and defined below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.

All features defined herein as numerical ranges or percentage ranges, such as numbers, amounts, levels and concentrations, are for brevity and convenience only. The description of numerical ranges or percentage ranges should be considered to have covered and specifically disclosed all possible subranges and individual numerical values (including integers and fractions) within the ranges. In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification. As used herein, the terms "comprising," "including," or "containing" mean that the various ingredients can be used together in a mixture or composition of the invention. Thus, the terms "consisting essentially of … …" and "consisting of … …" are encompassed by the terms "comprising," including, "or" containing.

The invention provides a method for preparing a m-xylylenediamine type semi-aromatic polyamide salt (MX salt for short) solution and a method for preparing m-xylylenediamine type semi-aromatic polyamide (MX polyamide for short, also called MX nylon) by adopting the MX salt solution.

Salt forming process

The prior art does not present a proposal related to the continuous operation for producing the m-xylylenediamine type semi-aromatic nylon salt solution. The present invention overcomes the deficiencies of the prior art. The method can effectively prepare the MX salt (such as MXD6 salt) which can be stably stored and can be directly used for preparing MX-type nylon by subsequent continuous polymerization. Meanwhile, the invention also provides continuous preparation of the MX complex salt (such as MXD6/MXD10 salt) solution for the first time, and the continuous preparation method can be directly used for continuously preparing the modified MX type copolymerized nylon.

Herein, the polyamide salt refers to a salt formed from a dibasic acid and a diamine. MX salt refers to a salt formed from a diacid and a diamine comprising m-xylylenediamine (MXDA), and the salt-forming diacid includes an aliphatic diacid and/or the salt-forming diamine includes an aliphatic diamine. The MX-type nylon refers to a polymer obtained by polymerizing a dibasic acid and a diamine containing MXDA, and the dibasic acid involved in the polymerization comprises an aliphatic dibasic acid and/or the diamine involved in the polymerization comprises an aliphatic diamine. In the MX salts, the molar fraction of MXDA in the diamine is generally 60% or more, preferably 80% or more, and may be 100%, for example. In MX-type nylons, the proportion of the number of structural units derived from MXDA to the total number of structural units derived from diamines is usually not less than 60%, preferably not less than 80%, and may be, for example, 100%.

The method for preparing the MX salt solution (salifying method for short) mainly utilizes the direct mixing of the semi-aromatic diamine MXDA and one or more types of dibasic acid aqueous solutions to prepare the stable semi-aromatic polyamide salt solution.

The salifying method comprises the step of carrying out salifying reaction on one or more binary acid aqueous solutions and m-xylylenediamine to prepare MX salt solutions.

In the present invention, the salt-forming reaction of the MX salt solution is carried out under stirring and protection of inert gas (e.g. nitrogen).

In some embodiments, the salt formation process of the present invention comprises the steps of:

(1) providing an aqueous dispersion of a dibasic acid;

(2) mixing the aqueous dispersion of the dibasic acid with MXDA to obtain a crude salt solution (crude salt solution for short) of the m-xylylenediamine type semi-aromatic nylon;

(3) and (3) adjusting the temperature, the concentration and/or the pH value of the crude salt solution to obtain an m-xylylenediamine type semi-aromatic nylon refined salt solution (refined salt solution for short).

In step (1), the dibasic acid may be dispersed in water to obtain an aqueous dispersion of the dibasic acid. The aqueous dispersion of the dibasic acid may be an aqueous solution of the dibasic acid. The water suitable for use in the present invention is preferably desalinated water. The diacid in the aqueous diacid dispersion may include one or more diacids. The dibasic acid may be one or more selected from succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, terephthalic acid and isophthalic acid. The mass fraction of the dibasic acid in the dibasic acid water dispersion is less than 50 wt%. The dibasic acid preferably comprises an aliphatic dibasic acid, preferably predominantly an aliphatic dibasic acid, more preferably a molar fraction of aliphatic dibasic acid of not less than 70%, such as not less than 80%, not less than 90%, 100%. The aliphatic dibasic acid may be one or more selected from succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. In some embodiments, the aliphatic dibasic acid is adipic acid. In some embodiments, the aliphatic dibasic acid comprises adipic acid, preferably in a mole fraction of greater than or equal to 80%, such as greater than or equal to 90%, of the aliphatic dibasic acid. In some embodiments, the aliphatic dibasic acid is adipic acid and sebacic acid, and the molar fraction of adipic acid in the aliphatic dibasic acid is preferably 80% or more, e.g., 90% or more, 90% to 95%. When the dibasic acid is dispersed in water, the operation temperature is 20-140 ℃.

The dibasic acid may be provided in powder form, for example, one or more dibasic acid powders may be added directly to the dissolution tank or the blending tank via a powder feeder. The powder feeder comprises a weighing and metering system, and the feeding amount of the powder diacid can be timely regulated and controlled. The blending tank comprises a temperature detection heating and heat preservation system, a stirring device, a feed inlet (comprising one or more powder feed inlets and a desalted water feed inlet), a discharge port, an air inlet, an exhaust port, a pressure gauge and a safety valve. A metering control system is arranged at the desalted water inlet to adjust the water inlet amount in time. The atmosphere in the tank can be replaced through the air inlet and the air outlet.

In the step (2), a crude salt solution is prepared by a salt-forming reaction (amine acid reaction) of a dibasic acid and a diamine. The diamine used in step (2) comprises MXDA and optionally other diamines. In the diamine used in step (2), MXDA accounts for 60% or more, preferably 80% or more, for example 100% or more of the mole fraction of the diamine. The diamine used in step (2) may optionally comprise other aromatic diamines (e.g., p-xylylenediamine) and/or aliphatic diamines (e.g., one or more selected from the group consisting of p-xylylenediamine, hexamethylene diamine, nonanediamine, decamethylene diamine, and dodecane diamine) in addition to MXDA. The temperature of the crude salt solution is preferably controlled to be 50-140 ℃, for example, 120-140 ℃, 130 ℃, 135 ℃. The concentration of the crude salt solution is preferably controlled to be 30 to 80 wt%, more preferably 40 to 70 wt%, for example 55 to 65 wt%, 60 wt%, 61 wt%, 64 wt%. The pH value of the crude salt solution is preferably controlled to be 3-7, such as 3.5-7, 4-6, 4.5, 4.9, 5. Herein, the concentration of the salt solution refers to the mass fraction of the solute dissolved in the salt solution to the total mass of the salt solution. The preparation of the crude salt solves the problems of conveying and metering of the dibasic acid in the salt forming process. Because the solubility of the dibasic acid is lower than that of the salt, the preparation of the crude salt enables the crude salt solution to be more accurately metered although the diacid is excessive at the same temperature, and is beneficial to the control of the quality of the salt solution and the material transportation. The condition parameters for preparing the crude salt solution are similar to those of the refined salt solution, and the refined salt solution is convenient to further prepare.

The dibasic acid aqueous dispersion can be conveyed to a crude salt reactor by a conveying pump, mixed with diamine and reacted to prepare a crude salt solution. The crude salt reactor comprises a temperature detection heating and heat preservation system, a stirring device, a pH detection device, a feeding hole (comprising a plurality of binary acid water dispersion feeding holes, an MXDA feeding hole and a desalted water feeding hole), a discharging hole, an air inlet, an air outlet, a pressure gauge and a safety valve. The pH detection device is linked with the metering systems of the feed inlets, so that the feed amount of the raw materials can be regulated and controlled in time. And a metering system is arranged at the feed inlet of the dibasic acid water dispersion and used for regulating and controlling the feed amount of the dibasic acid. And a metering system is arranged at the MXDA feed inlet and used for regulating and controlling the feed quantity of MXDA. And a metering control system is arranged at the desalted water feeding port and used for regulating and controlling the feeding amount of the desalted water. The atmosphere in the reactor can be replaced through the air inlet and the air outlet. The heat source of the heating and maintaining system can be provided by the heat of the reaction of the amine acid and/or the hot steam discharged in the polymerization reaction.

In the step (3), the temperature of the refined salt solution is preferably controlled to be 50-140 ℃, for example, 120-140 ℃, 130 ℃, 135 ℃. The concentration of the refined salt solution is preferably controlled to be 45 to 70 wt%, for example, 60 to 70 wt%, 65 wt%, 66 wt%, 68 wt%. The pH value of the refined salt solution is preferably controlled to be 4.8-7.5, such as 5.5-6.2, 5.8, 5.9, 6.1. It is understood that at least one of the temperature, concentration and pH of the crude salt solution is different from the temperature, concentration and pH of the refined salt solution. In some embodiments, in step (3), a slight positive pressure is applied to the reaction system to ensure the emission of water vapor. The slight positive pressure may be provided by water vapor itself, or by nitrogen. The micro-positive pressure can be in the range of 0 to 300 KPa. In some embodiments, step (3) comprises: and (3) adjusting the temperature of the crude salt solution to 50-140 ℃, adjusting the concentration of the crude salt solution to 45-70 wt%, and/or adjusting the pH value of the crude salt solution to 4.8-7.5 to obtain a refined salt solution. In some embodiments, step (3) comprises adding a diamine to the crude salt solution. The concentration and pH of the crude salt solution can be adjusted by adding diamine to the crude salt solution. The diamine added in the step (3) preferably comprises MXDA, wherein the molar fraction of MXDA in the diamine is preferably not less than 60%, more preferably not less than 80%; more preferably, the diamine added is m-xylylenediamine.

In step (3), a refined salt solution is obtained by fine-tuning the temperature, concentration and/or pH of the crude salt solution, for example, by supplementing diamine to the crude salt solution and optionally adjusting the temperature of the salt solution. In the present invention, step (3) preferably does not include a concentration operation. Herein, the concentration operation means a concentration operation in the conventional sense that the concentration of the solution is significantly increased, for example, by 20% by weight or more, 15% by weight or more, or 10% by weight or more, by evaporating the solvent by heating. The invention finds that the salt solution obtained by concentration operation in the process of preparing the salt solution has poor storage stability, and the performance (such as color) of MX-type nylon prepared by the salt solution is not ideal. Therefore, in the present invention, the absolute value of the difference in concentration between the refined salt solution and the crude salt solution is not more than 20 wt%, preferably not more than 15 wt%, more preferably not more than 10 wt%, for example not more than 7 wt%, not more than 6 wt%, not more than 5 wt%. In a preferred embodiment, the absolute value of the difference in temperature between the refined salt solution and the crude salt solution does not exceed 40 ℃, preferably does not exceed 20 ℃, such as does not exceed 15 ℃, does not exceed 10 ℃, does not exceed 5 ℃, or the temperature of the refined salt solution and the crude salt solution is the same.

The crude salt solution can enter a refined salt reactor through a delivery pump and a filter, and the refined salt solution with target temperature, concentration and pH is further prepared. The refined salt reactor comprises a temperature detection heating and heat preservation system, a stirring device, a pH detection device, a feeding hole (comprising one or more diacid water dispersion feeding holes, an MXDA feeding hole and a desalted water feeding hole), a discharging hole, an air inlet, an air outlet, a pressure gauge and a safety valve. The refined salt reactor can be used singly or in parallel, so that the production efficiency and the pH regulation accuracy are improved. In some embodiments, the invention adopts a plurality of refined salt reactors, the refined salt blending needs longer time, and the plurality of refined salt reactors are used in parallel, so that the efficiency and the pH regulation and control accuracy can be improved. The pH detection device is linked with the metering systems of the feed inlets, so that the feed amount of the raw materials can be regulated and controlled in time. And a metering system is arranged at the feed inlet of the dibasic acid water dispersion and used for regulating and controlling the feed amount of the dibasic acid. And a metering system is arranged at the MXDA feed inlet and used for regulating and controlling the feed quantity of MXDA. And a metering control system is arranged at the desalted water feeding port and used for regulating and controlling the feeding amount of the desalted water. The atmosphere in the reactor can be replaced through the air inlet and the air outlet. The heat source of the heating and maintaining system can be provided by the heat of the reaction of the amine acid and/or the hot steam discharged in the polymerization reaction.

The salification process of the invention optionally can also comprise a step (4): and storing the refined salt solution. The storage temperature of the refined salt solution is preferably controlled to be 50-140 ℃. The storage concentration of the refined salt solution is preferably 45-70 wt%. The storage pH value of the refined salt solution is preferably controlled to be 4.8-7.5. The above parameters are essentially unchanged during storage of the salt solution according to the invention.

The prepared refined salt solution can enter a salt solution storage tank through a delivery pump and a filter for storage and standby, and can also be directly used for subsequent polymerization. The salt solution storage tank comprises a temperature detection heating and heat preservation system, a pH detection device, a refined salt solution feeding hole, a discharging hole, an air inlet, an air outlet, a pressure gauge and a safety valve. The temperature detection heating heat preservation system and the pH detection device respectively detect the temperature and the pH value in the storage tank in real time.

The salification method of the invention has the following advantages:

1. the salt solution prepared by the salifying method has controllable pH and stable storage, can be directly used for subsequent polymerization, and can be transported in a short distance if necessary. The amine acid molar ratio and the pH value of the product are not changed during storage. The saline solution can be stably stored for at least 2 days, is vital to the stability of the product performance, and simultaneously effectively meets the storage requirement of the saline solution under the accident conditions of parking, overhauling and the like in the production process;

2. the salifying method does not appear in the preparation of the m-xylylenediamine semi-aromatic polyamide, overcomes the defect of high energy consumption caused by secondary dehydration in the existing method, has the characteristics of convenience, low energy consumption, high efficiency and easiness in storage, and is reasonable and easy to industrialize;

3. the salt forming method can be used for preparing MX salt solution with higher concentration (45-70 wt%);

4. the salt solution prepared by the salifying method can be directly used in the subsequent polymerization process without secondary processes such as purification, separation, dissolution and blending, so that the production efficiency is improved, the subsequent continuous production is ensured, and the energy consumption and the waste gas and waste liquid amount are further reduced.

Although other types of semi-aromatic polyamides (such as copolymerized PA6T/66, PA6T/6I, PA6I/6, PA12T, PA 9T) involve methods for preparing solid salts or salt solutions, the other types of semi-aromatic polyamides have different monomer properties and physical properties due to the difference of main monomers between the semi-aromatic polyamides and MX-type polyamides (i.e., m-xylylenediamine has a high boiling point and is not easily volatilized, m-xylylenediamine is in a liquid state at room temperature, the solubility of salts is different, and the solubility of MX salt is small), so that the MX-type polyamides and other types of semi-aromatic polyamides are different in preparation processes.

Polymerization process

The method for preparing the m-xylylenediamine semi-aromatic polyamide by using the MX salt solution (a polymerization method for short) prepares the MX-type polyamide by using the MX salt solution through a normal-pressure polymerization process.

The polymerization method of the invention directly adopts MX salt solution (such as refined salt solution of the invention) to prepare MX nylon through polycondensation.

The polymerization method has diversified production modes, and can realize continuous production and intermittent production.

The continuous production is easy to improve the productivity and enlarge the production, the performance difference between finished product batches is reduced, and the product stability is improved.

In continuous production, the invention can accurately control the polymerization degree of each stage, further control the molecular weight and the distribution of the finished product, and regulate and control the macroscopic property of the finished product.

The continuous polymerization process of the present invention comprises the steps of:

(1) prepolymerization reaction: carrying out pressure maintaining and temperature rising on the salt solution for amidation reaction to prepare a polymerization intermediate I with polymerization degree of 5-20;

(2) pressure release reaction: reducing the pressure and raising the temperature of the polymerization intermediate I to further react and improve the polymerization degree, and preparing a polymerization intermediate II with the polymerization degree of 20-40;

(3) final polymerization reaction: and (3) carrying out normal pressure or negative pressure operation on the polymerization intermediate II to further improve the polymerization degree and prepare the finished MX-type nylon melt with the polymerization degree of 40-140.

The salt solution as a raw material of the polymerization method of the present invention is preferably a refined salt solution prepared by the salt formation method of the present invention.

In the step (1), the temperature of the salt solution is gradually increased, and a certain pressure is maintained, namely the constant-pressure drainage process. The initial temperature of the reaction at this stage is 160-200 ℃, and the final temperature of the reaction is 210-235 ℃, for example, 225 ℃. The step (1) is a prepolymerization step, wherein the prepolymerization is carried out under normal pressure or micro-positive pressure, the reaction time period pressure is constant, and the constant pressure is 0-0.8 MPa, such as 0.45MPa and 0.5 MPa. The reaction time is 0.3-3 h, such as 0.8 h. The polymerization degree distribution width of the polymerization intermediate I is less than or equal to 5. In the step (1), the polymerization degree of the polymerization intermediate I is controlled to be 5-20, and the distribution width of the polymerization degree is less than or equal to 5, which is particularly important and has great influence on the subsequent polymerization process and the product performance. Herein, the breadth of the polymerization degree distribution refers to the difference between the maximum polymerization degree and the minimum polymerization degree.

In some embodiments, in step (1), a continuous reactor is used, wherein the material flows in the reactor, the inlet temperature is 170-200 ℃, and the outlet temperature is 210-235 ℃. The continuous reactor comprises a temperature detection control system, a liquid level detection control system, a pressure detection control system, a flow control system, a feeding hole, a discharging hole, an emergency discharging system, an air inlet, a plurality of air outlets and a safety valve.

In the step (2), the pressure of the polymerization intermediate I is rapidly released after flowing out through the outlet of the reactor in the step (1), and the temperature is increased. And step (2) is a pressure reduction and drainage process. The initial temperature of the reaction at this stage is 220-235 deg.C, and the final temperature of the reaction is 240-265 deg.C, such as 245 deg.C. The pressure is normal pressure. The reaction time is 0.3-3 h.

In the step (3), the temperature of the polymerization intermediate II is further raised or maintained, and the reaction pressure is normal pressure or negative pressure, preferably negative pressure, to further increase the polymerization degree. The reaction temperature in this stage is 240-280 ℃, such as 255 ℃, 260 ℃. The pressure is 0 to-0.1 MPa, for example-0.04 MPa or-0.06 MPa. The reaction time is 0.3-3 h, such as 0.5h and 0.6 h. The polymerization degree distribution width of the finished MX-type nylon is less than or equal to 15.

The continuous polymerization process of the present invention optionally may further comprise step (4): discharging the finished MX-type nylon melt out of the polymerizer to prepare the finished MX-type nylon slice. The process of preparing the chips may include one, more or all of cooling, casting, pelletizing, screening, drying and bagging. These operations are conventional in the production of chips or pellets.

When a batch reactor is used, all steps are carried out in the same reactor, so that no distinct phase boundaries exist.

The batch polymerization process of the present invention comprises: and (3) carrying out prepolymerization reaction on the salt solution to obtain a polymerization intermediate I with the polymerization degree of 5-15, then carrying out pressure release reaction to obtain a polymerization intermediate II with the polymerization degree of 20-40, and finally carrying out final polymerization reaction to prepare the m-xylylenediamine type semi-aromatic polyamide finished product with the polymerization degree of 40-140.

In some embodiments, the salt solution is subjected to pressure and temperature maintaining in the polymerization reactor, amidation reaction is carried out for a period of time, then the pressure is reduced to normal pressure and the temperature is raised, the polymerization degree is further improved, finally, negative pressure operation is carried out, the polymerization degree is further improved, and the finished MX type nylon melt with the target polymerization degree is prepared.

In the polymerization process, sampling can be carried out at any time, the molecular weight and the distribution of the polymerization intermediate are detected, and the process is adjusted to prepare the finished MX-type nylon meeting the requirements.

In the batch polymerization, in a polymerization reactor, the material is firstly heated to 160-230 ℃, for example 220 ℃, the pressure is kept at 0-0.8 MPa, for example 0.5MPa, the reaction time is 0.3-3 h, for example 1.5h, and at the end of the stage, the polymerization degree of the material is 5-15, and the distribution width of the polymerization degree is less than or equal to 8. And then, discharging the pressure in the kettle to the normal pressure, and simultaneously raising the temperature in the kettle to 220-260 ℃ such as 258 ℃, wherein the reaction time is 0.3-3 h, and the polymerization degree range of the materials is 20-40. And finally, carrying out normal pressure or negative pressure operation, preferably negative pressure operation on the polymerization kettle, wherein the pressure is 0-0.1 MPa, such as absolute pressure of 20KPa, the temperature is kept at 240-280 ℃, such as 265 ℃, the reaction time is 0.3-3 h, such as 0.5h, and the MX-type nylon finished product is prepared, the polymerization degree range of the MX-type nylon finished product is 40-140, and the polymerization degree distribution width of the MX-type nylon finished product is less than or equal to 15.

The batch polymerization process of the present invention optionally may further comprise: discharging the finished MX-type nylon melt out of the polymerizer to prepare the finished MX-type nylon slice. The process of preparing the chips may include one, more or all of cooling, casting, pelletizing, screening, drying and bagging. These operations are conventional in the production of chips or pellets.

One of the features of the polymerization process of the present invention is that the polymerization reaction is carried out at a low pressure, and that the volatilization of m-xylylenediamine in a large amount is avoided at the time of low-pressure polymerization. The invention does not adopt a low-pressure process to prepare MX-type nylon before.

The polymerization process of the present invention has the following advantages:

1. the production method can realize the complete continuous industrial production of MX-type nylon (including MX-type copolymerized nylon), greatly improve the production efficiency and the material stability, and control the product performance by controlling the polymerization degree of each stage through the design process conditions;

2. the adopted polymerization intermediate is MX salt solution, the performance is stable, secondary parameter adjustment is not needed, and the limitation of high requirement on the purity of the raw material is overcome;

3. in the existing MXD6 polymerization process, the highest pressure reached in the prepolymerization stage is more than 1MPa, and the highest pressure of some nylon polymerization is even up to 2MPa and more. Compared with the existing high positive pressure polymerization mode of nylon, the polymerization method of the invention adopts micro positive pressure or normal pressure polymerization to produce MX type nylon for the first time in the prepolymerization stage. The polymerization method has the advantages of low requirement on devices, low maintenance cost, less production area limitation, easy amplification and expansion, easy production, low energy consumption and the like, has great significance for reducing the production cost of nylon, and can effectively expand the market and application fields of the nylon;

4. the polymerization method of the invention is adopted to continuously produce MX type copolymerized nylon by normal pressure or micro-positive pressure prepolymerization, and can effectively solve the defects of unstable product performance, higher polymerization pressure, complex equipment requirement and the like faced by copolymerization modification.

The structural composition of MX type polyamide has a significant influence on the properties, especially the influence of the molecular weight and its distribution on the crystallinity of the material. When the MX-type nylon is used for a packaging material, the requirement on the crystallization performance of the MX-type nylon is very high. Therefore, the requirements of the application field require that it satisfy certain performance, and further require that it have certain structure. In order to solve the problem, the invention preferably arranges sampling ports at the key positions of the polymerization equipment (the middle section and the ending section of the prepolymerization reactor, the ending section of the pressure release reactor and the initial section, the middle section and the ending section of the final polymerization reactor), adjusts corresponding polymerization parameters in time, and can adjust related processes to prepare MX-type semi-aromatic polyamide with target molecular weight and distribution thereof in the polymerization process according to requirements.

The present invention will be described in further detail with reference to examples. It should be understood that the following examples are carried out according to the technical scheme of the present invention, and detailed embodiments and specific operation procedures are given, but these examples are merely illustrative, and the scope of the present invention is not limited to the following examples. As to the reagents, methods, conditions and the like used herein and in the examples, conventional reagents, methods and conditions are used unless otherwise indicated.

The following test methods were used in the examples and comparative examples:

polymerization degree: measuring by using Gel Permeation Chromatography (GPC), wherein the solvent is hexafluoroisopropanol;

tensile strength: according to test standard ASTM D638;

relative viscosity: according to test standard ISO 307;

chroma: the polymerized sections were tested directly without treatment using an x-rite Ci7600 colorimeter.

Apparatus example 1

FIG. 1 is a schematic diagram of a salt former apparatus of the present invention. The salifying device comprises an acid supply unit I, a crude salt preparation unit II, a refined salt preparation unit III and an optional storage unit IV.

In the acid supply unit I, 101 is a solid acid transfer device, 102 is a stirring device, 103 is a desalted water pipe, 104 is a dissolving tank, 105 is a diacid aqueous solution pipe, and 106 is a transfer pump. The solid acid transfer device 101 has a feed inlet and a discharge outlet. The agitation device 102 is disposed in the dissolving tank 104. The dissolving tank 104 has a solid acid feed port, a desalted water feed port, and a discharge port. The solid acid feed inlet of the dissolving tank 104 is communicated with the discharge outlet of the solid acid conveying device 101. The desalted water feed port of the dissolving tank 104 communicates with the desalted water pipe 103. The discharge port of the dissolving tank 104 is communicated with a diacid aqueous solution pipeline 105. A transfer pump 106 is provided on the diacid aqueous solution pipe 105. The solid acid transfer device 101 is provided with a metering device. The demineralised water pipe 103 is provided with a metering device. The dissolving tank 104 is provided with a safety valve, an instrument, a temperature control system and the like.

In the crude salt preparation unit ii, 201 is a m-xylylenediamine line, 202 is a desalted water line, 203 is a stirring device, 204 is a standby acid solution line, 205 is a pH detection device, 206 is a crude salt reactor, 207 is a transfer pump, and 208 is a filter. The stirring device 203 and the pH detection device 205 are disposed in the crude salt reactor 206. The crude salt reactor 206 has a diacid aqueous solution feed port, a meta-xylylenediamine feed port, a desalted water feed port, a standby acid solution feed port, and a discharge port, which are respectively communicated with the diacid aqueous solution conduit 105, the meta-xylylenediamine conduit 201, the desalted water conduit 202, the standby acid solution conduit 204, and the crude salt solution conduit. A transfer pump 207 and a filter 208 are provided on the crude salt solution pipe. The m-xylylenediamine pipeline 201 is provided with a metering device, and the metering device is connected with a feedback regulation control system to control the addition amount of diamine. The desalted water pipeline 202 is provided with a metering device, and the metering device is connected with the feedback regulation control system to control the addition amount of desalted water. The standby acid solution pipeline 204 is provided with a metering device, and the metering device is connected with a feedback regulation control system to control the addition amount of the binary acid water dispersoid. The crude salt reactor 206 is provided with safety valves, instruments, temperature control systems, etc. The pH detection device 205 is connected with a feedback regulation control system (not shown in the figure).

In the refined salt preparation unit III, A301-A3 n are spare acid solution pipelines, M301-M3 n are M-xylylenediamine pipelines, S301-S3 n are stirring devices, R301-R3 n are refined salt reactors, 311 are delivery pumps, and 312 are filters. A stirring device S3n and a pH detection device (not shown in the figure) are provided in the refined salt reactor R3 n. The refined salt reactor R3n is provided with a crude salt solution inlet, a M-xylylenediamine inlet, a standby acid solution inlet and an outlet, which are respectively communicated with a crude salt solution pipeline, a M-xylylenediamine pipeline M3n, a standby acid solution pipeline A3n and a refined salt solution pipeline. A transfer pump 311 and a filter 312 are provided on the fine salt solution pipe. The standby acid solution pipeline A3n is provided with a metering device, and the metering device is connected with a feedback regulation control system to control the addition amount of the binary acid water dispersoid. The M-xylylenediamine pipeline M3n contains a metering device, and the metering device is connected with a feedback regulation control system to control the addition amount of diamine. The refined salt reactor R3n is provided with a safety valve, an instrument, a temperature control system and the like. The pH detection device on each refined salt reactor R3n is connected with a feedback regulation control system (not shown in the figure). In A3n, M3n, S3n and R3n, n represents the number of refined salt reactors, for example, when the refined salt preparation unit III includes n refined salt reactors, a301 is a first spare acid solution pipeline, M301 is a first M-xylylenediamine pipeline, S301 is a first stirring device, R301 is a first refined salt reactor, a302 is a second spare acid solution pipeline, M302 is a second M-xylylenediamine pipeline, S302 is a second stirring device, R302 is a second refined salt reactor, and so on, A3n is an n-th spare acid solution pipeline, M3n is an n-th M-xylylenediamine pipeline, S3n is an n-th stirring device, and R3n is an n-th refined salt reactor. The fine salt solution pipeline can be communicated with the polymerization reaction device.

In the storage unit IV, 400 is a salt solution storage tank, 401 is a delivery pump, and 402 is a filter. The salt solution storage tank 400 has a feed inlet and a discharge outlet. The feed inlet of the salt solution storage tank 400 is communicated with a refined salt solution pipeline. The discharge port of the salt solution storage tank 400 may be in communication with a pipe on which the transfer pump 401 and the filter 402 are disposed, and the pipe may be in communication with the polymerization reaction apparatus.

The dissolving tank 104, the crude salt reactor 206, the refined salt reactor R3n, the salt solution storage tank 400 and the pipeline connected with the salt solution storage tank all have temperature control devices.

Device application example 1

The procedure for the preparation of the salt solution using the salification apparatus of equipment example 1 is as follows:

1. adding the dibasic acid powder into a dissolving tank 104 through a solid acid conveying device 101, and simultaneously adding desalted water through a desalted water pipeline 103 to prepare the dibasic acid powder into an aqueous dispersion;

2. conveying the dibasic acid slurry into a crude salt reactor 206 through a diacid aqueous solution pipeline 106, simultaneously adding m-xylylenediamine through an m-xylylenediamine pipeline 201, carrying out online detection and real-time pH change feedback through a pH detection device 205, stopping adding m-xylylenediamine through a feedback regulation control system (not shown in figure 1) when a preset pH value is reached, and conveying the m-xylylenediamine to a refined salt preparation unit III through a pump 207 and a filter 208 after a period of stabilization;

3. simultaneously injecting the crude salt solution and m-xylylenediamine into refined salt reactors R301-R3 n, feeding back pH changes in the refined salt reactors R301-R3 n in real time through a pH detection device and a feedback regulation control system to determine the addition amount of the m-xylylenediamine, and blending the refined salt solution with target pH;

4. the refined salt solution passes through a pump 311 and a filter 312 and then enters the storage unit IV for standby.

By combining diacid supply units, different diacids are added into the crude salt reactor 206 by using the spare acid solution pipeline A3n, compound MXDA salts such as MXD6/MXDT salt, MXD6/MXD10 salt and the like can be synthesized, and continuous production of MXD6 in-situ copolymerization modification can be realized.

Example of apparatus 2

FIG. 2 is a schematic view of a continuous polymerization apparatus of the present invention. The continuous polymerization device comprises a salt solution storage tank 1, an additive tank 2, a delivery pump 4, a static mixer 5, a pre-polymerization device 6, an additive tank 7, a delivery pump 8, a pressure-release polymerization lifting device 9, a delivery pump 10, a final polymerization device 11 and a delivery pump 12. The static mixer 5 has a feed inlet and a discharge outlet. The feed inlet of salt solution storage tank 1 and static mixer 5 passes through the pipeline and links to each other, and delivery pump 4 sets up on the pipeline of connecting salt solution storage tank 1 and static mixer 5, and additive jar 2 passes through the pipeline with the pipeline of connecting salt solution storage tank 1 and static mixer 5 and links to each other. The prepolymerization device 6 is provided with a feed inlet, an additive inlet and a discharge outlet. The discharge port of the static mixer 5 is connected with the feed port of the prepolymerization device 6. The additive inlet of the prepolymerization device 6 is connected with an additive tank 7. The pressure-releasing polymerization riser 9 has a feed port and a discharge port. The discharge port of the prepolymerization device 6 is connected with the feed port of the pressure-release polymerization lifting device 9 through a pipeline. The delivery pump 8 is arranged on a pipeline connecting the discharge port of the pre-polymerization device 6 and the feed port of the pressure-releasing polymerization lifting device 9. The final polymerization device 11 has a feed inlet and a discharge outlet. The discharge port of the pressure-releasing polymerization lifting device 9 is connected with the feed port of the final polymerization device 11 through a pipeline. The delivery pump 10 is arranged on a pipeline between the discharge port of the pressure-release polymerization lifting device 9 and the feed port of the final polymerization device 11. The outlet of the final-focusing device 11 is connected to a pipe, on which a delivery pump 12 is arranged.

Example of apparatus 3

FIG. 3 is a schematic view of a batch polymerization apparatus of the present invention. The batch polymerization device comprises a salt solution storage tank 1, an additive tank 2, a delivery pump 4, a static mixer 5, a polymerization kettle 6 and a delivery pump 7. The static mixer 5 has a feed inlet and a discharge outlet. The feed inlet of salt solution storage tank 1 and static mixer 5 passes through the pipeline and links to each other, and delivery pump 4 sets up on the pipeline of connecting salt solution storage tank 1 and static mixer 5, and additive jar 2 passes through the pipeline with the pipeline of connecting salt solution storage tank 1 and static mixer 5 and links to each other. The polymerizer 6 has a feed port and a discharge port. The discharge port of the static mixer 5 is connected with the feed port of the polymerizer 6. The outlet of the polymerizer 6 is connected to a pipe, and a transfer pump 7 is provided on the pipe.

Example 1

In this example, MXD6 nylon was produced by a continuous process using m-xylylenediamine and adipic acid as raw materials, and the salt formation apparatus of equipment example 1 and the continuous polymerization apparatus of equipment example 2.

The tanks were first evacuated of air using high purity nitrogen, and 500kg of adipic acid and 420kg of demineralized water were formulated as an aqueous adipic acid dispersion in an acid supply unit I. The crude salt solution is conveyed to a crude salt preparation unit II through a pump 106, at the same time, m-xylylenediamine is injected into a crude salt reactor 206 through an m-xylylenediamine pipeline 201 in the crude salt preparation unit II, the addition amount of the m-xylylenediamine is controlled through a pH detection device 205 and a feedback regulation control system, and a crude salt solution with the pH of 4.5 is formed, wherein the temperature in the crude salt reactor is 140 ℃ at the moment, and the concentration of the crude salt is 64 wt%.

The crude salt solution is injected into a refined salt preparation unit III through a delivery pump 207 and a filtering device 208, at the same time, M-xylylenediamine is injected into refined salt reactors R301-R3 n through M-xylylenediamine pipelines M301-M3 n in the refined salt preparation unit III, the addition amount of the M-xylylenediamine is controlled through a pH detection device and a feedback regulation control system, so that a refined salt solution with the pH of 5.9 is formed, and the temperature in the refined salt reactor is 140 ℃. Is transported to the storage unit IV through the transportation pump 311 and the filter 312 for standby. The concentration of the refined salt solution was 70 wt%.

The refined salt solution is sent to a continuous polymerization apparatus through a transfer pump 401 and a filter 402. The temperature of the seminal saline was further heated to 160 ℃ before entering the prepolymerization apparatus 6. In the prepolymerization unit 6, the temperature of the refined salt solution was gradually increased while maintaining the pressure of 0.45MPa for a period of 0.8h and the temperature at the outlet was 235 ℃. At this time, the polymerization degree of the intermediate reactant I was detected to be 9 to 11. After passing through the outlet, the pressure is rapidly released to normal pressure, the temperature is further heated to 245 ℃ in the pressure-releasing polymerization lifting device 9, and a reaction intermediate II is formed at the same time, wherein the polymerization degree is 35-39. And (3) the reaction intermediate II enters a final polymerization device 11, the temperature is further increased to 260 ℃, the pressure is controlled to be-0.04 MPa, the time is 0.5h, and the polymerization degree is further increased to 113-125 through reaction. After cooling, belt casting, granulation, screening, drying and bagging, MXD6 nylon chips with good transparency and high brightness are prepared, the related performance of the materials is tested, and the test results are shown in Table 1.

After the refined salt solution is left for 1 day, the pH value of the solution is tested, and MXD6 nylon chips are obtained by adopting the polymerization method, the related performance of the materials is tested, and the test results are shown in Table 1.

After the refined salt solution is placed for 2 days, the pH value of the refined salt solution is tested, and the MXD6 nylon chips are obtained by adopting the polymerization method, the related performance of the materials is tested, and the test results are shown in Table 1.

Example 2

In this example, MXD6-MXD10 copolymerized nylon was prepared by a continuous process using m-xylylenediamine, adipic acid and sebacic acid as raw materials, and using the salt formation apparatus of facility example 1 and the continuous polymerization apparatus of facility example 2.

The tanks were first evacuated of air using high purity nitrogen, and 450kg of adipic acid, 50kg of sebacic acid and 500kg of desalted water were configured as an aqueous diacid dispersion in an acid supply unit I. The crude salt solution is conveyed to a crude salt preparation unit II through a pump 106, m-xylylenediamine is injected into a crude salt reactor 206 through an m-xylylenediamine pipeline 201 in the crude salt preparation unit, the addition amount of the m-xylylenediamine is controlled through a pH detection device 205 and a feedback regulation control system, and a crude salt solution with the pH of 4.9 is formed, wherein the temperature in the crude salt reactor is 130 ℃ at the moment, and the concentration of the crude salt is 61 wt%.

The crude salt solution is injected into a refined salt preparation unit III through a delivery pump 207 and a filtering device 208, at the same time, M-xylylenediamine is injected into refined salt reactors R301-R3 n through M-xylylenediamine pipelines M301-M3 n in the refined salt preparation unit III, the addition amount of the M-xylylenediamine is controlled through a pH detection device and a feedback regulation control system, so that a refined salt solution with the pH of 6.1 is formed, and the temperature in the refined salt reactor is 140 ℃. Is transported to the storage unit IV through the transportation pump 311 and the filter 312 for standby. The concentration of the refined salt solution was 66 wt%.

The refined salt solution is sent to a continuous polymerization apparatus through a transfer pump 401 and a filter 402. The temperature of the seminal saline was further heated to 160 ℃ before entering the prepolymerization apparatus 6. In the prepolymerization unit 6, the temperature of the refined salt solution was gradually increased while maintaining the pressure of 0.5MPa for a period of 0.8h and the temperature at the outlet was 225 ℃. At this time, the polymerization degree of the intermediate reactant I was detected to be 7 to 9. After passing through the outlet, the pressure is rapidly released to normal pressure, the temperature is further heated to 240 ℃ in the pressure-releasing polymerization lifting device 9, and a reaction intermediate II is formed at the same time, wherein the polymerization degree is 33-39. And (3) the reaction intermediate II enters a final polymerization device 11, the temperature is further raised to 255 ℃, the pressure is controlled to be minus 0.06MPa, the time is 0.6h, and the polymerization degree is further increased to 110-125 through reaction. After cooling, belt casting, granulation, screening, drying and bagging, MXD6-MXD10 copolymerized nylon chips with good transparency and high brightness are prepared, the related performances of the materials are tested, and the test results are shown in Table 1.

After the refined salt solution is placed for 1 day, the pH value of the solution is tested, and MXD6-MXD10 slices are obtained by adopting the polymerization method, the related properties of the materials are tested, and the test results are shown in Table 1.

After the refined salt solution is placed for 2 days, the pH value of the solution is tested, and MXD6-MXD10 slices are obtained by adopting the polymerization method, the related properties of the materials are tested, and the test results are shown in Table 1.

Example 3

In this example, MXD6 nylon was produced by a batch process using m-xylylenediamine and adipic acid as raw materials, and the salt formation apparatus of equipment example 1 and the batch polymerization apparatus of equipment example 3.

The tanks were first evacuated of air using high purity nitrogen, and 500kg of adipic acid and 450kg of demineralized water were prepared as an aqueous adipic acid dispersion in an acid supply unit I. The crude salt solution is conveyed to a crude salt preparation unit II through a pump 106, at the same time, m-xylylenediamine is injected into a crude salt reactor 206 through an m-xylylenediamine pipeline 201 in the crude salt preparation unit II, the addition amount of the m-xylylenediamine is controlled through a pH detection device 205 and a feedback regulation control system, and a crude salt solution with the pH of 4.5 is formed, wherein the temperature in the crude salt reactor is 135 ℃, and the concentration of the crude salt is 61 wt%.

The crude salt solution is injected into a refined salt preparation unit III through a delivery pump 207 and a filtering device 208, at the same time, M-xylylenediamine is injected into refined salt reactors R301-R3 n through M-xylylenediamine pipelines M301-M3 n in the refined salt preparation unit III, the addition amount of the M-xylylenediamine is controlled through a pH detection device and a feedback regulation control system, so that a refined salt solution with the pH of 5.8 is formed, and the temperature in the refined salt reactor is 140 ℃. Is transported to the storage unit IV through the transportation pump 311 and the filter 312 for standby. The concentration of the refined salt solution was 68 wt%.

The refined salt solution is sent to a batch polymerization apparatus through a transfer pump 401 and a filter 402. In the polymerization vessel 6, the contents were heated gradually to 258 ℃ with a concomitant change in pressure during the gradual rise of the contents. Firstly, keeping the pressure in the kettle at 0.5MPa for 1.5 hours, sampling and detecting when the temperature in the kettle is 220 ℃, wherein the polymerization degree of a sample is 9-14 at the moment, gradually relieving the pressure to normal pressure, simultaneously gradually increasing the temperature in the kettle to 258 ℃, sampling and detecting, and the polymerization degree of the sample is 31-39 at the moment. And after the temperature in the kettle is raised to 265 ℃, vacuumizing to the absolute pressure of 20KPa, keeping for 0.5h, and further reacting to improve the polymerization degree to 110-120. After cooling, belt casting, granulation, screening, drying and bagging, MXD6 nylon chips with good transparency and high brightness are prepared, the related performance of the materials is tested, and the test results are shown in Table 1.

After the refined salt solution is left for 1 day, the pH value of the solution is tested, and the MXD6 slices are obtained by adopting the polymerization method, the related properties of the materials are tested, and the test results are shown in Table 1.

After the refined salt solution is left for 2 days, the pH value of the solution is tested, and the MXD6 slices are obtained by adopting the polymerization method, the related properties of the materials are tested, and the test results are shown in Table 1.

Comparative example 1

This comparative example was carried out using m-xylylenediamine and adipic acid as raw materials, a dissolution tank, a salt-forming reactor and the continuous polymerization apparatus of equipment example 2 to prepare MXD6 nylon.

Firstly, each tank body is evacuated of air by adopting high-purity nitrogen, 500kg of adipic acid and 1820kg of desalted water are prepared into adipic acid aqueous dispersion in a dissolving tank, and the adipic acid aqueous dispersion is conveyed to a salt forming reactor. In a salt-forming reactor, m-xylylenediamine with equal molar ratio is added to prepare MXD6 salt solution with 35 wt% of temperature of 60 ℃. Concentrating the salt solution at initial temperature of 110 deg.C, final temperature of 140 deg.C, concentration final concentration of 70 wt%, pH of 5.8, and time of 1 h.

MXD6 chips were prepared by the same process parameters as in example 1, except that the polymerization degree of the intermediate reactant I was 20-34, the polymerization degree of the intermediate reactant II was 45-62, and the polymerization degree of the product was 53-75. The materials were tested for relevant properties and the results are shown in table 1.

After the salt solution having the above concentration of 70 wt% was left to stand for 1 day, its pH value was measured, and MXD6 chips were obtained by the above polymerization method, and the properties related to the materials were measured, and the results of the measurement are shown in table 1.

After leaving the salt solution at the concentration of 70 wt% for 2 days, the pH was measured, and MXD6 chips were obtained by the above polymerization method, and the properties related to the materials were measured, and the results are shown in table 1.

Comparative example 2

This comparative example uses m-xylylenediamine and adipic acid as raw materials, and MXD6 salt solution was prepared using the salt formation apparatus of equipment example 1 and MXD6 nylon was prepared using the continuous polymerization apparatus of equipment example 2.

The refined salt solution of example 1 was first prepared using the process parameters of example 1.

The refined salt solution is sent to a continuous polymerization apparatus through a transfer pump 401 and a filter 402. The temperature of the seminal saline was further heated to 160 ℃ before entering the prepolymerization apparatus 6. In the prepolymerization unit 6, the temperature of the salt solution was gradually increased while maintaining a pressure of 0.7MPa for a period of 1.2h and a temperature of 250 ℃ at the outlet. The polymerization degree of the intermediate reactant I was detected to be 14 to 37. After passing through the outlet, the pressure is rapidly released to normal pressure, the temperature is further heated to 270 ℃ in the pressure-releasing polymerization lifting device 9, and a reaction intermediate II is formed at the same time, wherein the polymerization degree is 52-73. And (3) enabling the reaction intermediate II to enter a final polymerization device 11, further raising the temperature to 285 ℃, controlling the pressure to be normal, and keeping the time for 1.2h, so that the polymerization degree is further increased to 65-87 through further reaction. After cooling, belt casting, granulation, screening, drying and bagging, MXD6 nylon chips were prepared and tested for the relevant properties of the materials, with the test results shown in Table 1.

As can be seen from table 1, the salt solution prepared by the method of comparative example 1 has poor storage stability, and the pH of the salt solution greatly changes after two days of storage. Compared with example 1, the product prepared in comparative example 1 has significantly reduced tensile strength, reduced transparency, poor flowability, significantly poor chromaticity (yellowish), and a broad polymerization degree distribution, which has a large influence on the properties of the material. This shows that the salt solution prepared by the method of the present invention has better storage stability and the product prepared therefrom has better properties including higher tensile strength, better flowability and better transparency and chroma than the salt solution obtained by concentration during the preparation (comparative example 1).

Compared with example 1, the tensile strength of the product prepared in comparative example 2 is significantly reduced, the transparency is reduced, the fluidity is deteriorated, and the chroma is significantly deteriorated. This indicates that the products prepared using the polymerization process of the present invention have better properties, including higher tensile strength, better flow, and better clarity and color.

Table 1: results of Performance test of MX-type nylons obtained in examples 1 to 3 and comparative examples 1 to 2

Injecting: for comparative example 1, this is meant a salt solution of 70% strength by weight in comparative example 1.