阅读说明：本技术 三聚甲醛和二氧五环联产制备聚甲醛的方法 (Method for preparing polyformaldehyde by coproduction of trioxymethylene and dioxolane ) 是由 张小明 陈洪林 邓聪迩 雷蔚鑫 雷骞 李克景 于 2020-08-14 设计创作，主要内容包括：一种三聚甲醛和二氧五环联产制备聚甲醛的方法,利用乙二醇与三聚甲醛粗品中的甲醛合成半缩醛,分离后用于合成二氧五环,而脱醛的三聚甲醛粗品的后续分离精制过程得以简化。该工艺降低了聚甲醛单体制备过程的稀醛量,降低了制备工艺能耗,提高了聚甲醛单体的产品质量。(A method for preparing polyformaldehyde by coproducing trioxymethylene and dioxolane is characterized in that ethylene glycol and formaldehyde in a trioxymethylene crude product are used for synthesizing hemiacetal, the hemiacetal is used for synthesizing dioxolane after separation, and the subsequent separation and refining processes of the dealdehydized trioxymethylene crude product are simplified. The process reduces the amount of diluted aldehyde in the preparation process of the polyformaldehyde monomer, reduces the energy consumption of the preparation process and improves the product quality of the polyformaldehyde monomer.)

1. A method for preparing polyformaldehyde by coproduction of trioxymethylene and dioxolane is characterized by comprising the steps of preparing a trioxymethylene monomer, preparing a dioxolane monomer and carrying out polymerization reaction to obtain polyformaldehyde.

2. The method according to claim 1, wherein the trioxymethylene monomer preparation process comprises:

the method comprises the following steps: the concentrated formaldehyde aqueous solution reacts under the action of a cyclization catalyst to prepare trioxymethylene, and a trioxymethylene reaction product is extracted from a gas phase and passes through a concentration tower to obtain a trioxymethylene crude product;

step two: and (3) reacting formaldehyde in the trioxymethylene crude product with ethylene glycol in a formaldehyde removal reactor to remove formaldehyde, and then dehydrating and separating by adopting membrane dehydration to obtain a trioxymethylene monomer.

3. The method of claim 2, wherein the dioxolane monomer is prepared by a process comprising:

step three: synthesizing formaldehyde in the ethylene glycol and formaldehyde crude product to obtain hemiacetal, and obtaining a dioxolane crude product at the top of the tower through a reactive distillation tower; finally, dehydrating through a molecular sieve membrane permeation gasification membrane, separating and dehydrating at the permeation side, and obtaining a dioxolane monomer at the retentate side;

the preparation method of the paraformaldehyde comprises the following steps:

step four: trioxymethylene monomer and dioxy pentacyclic monomer are polymerized to prepare polyformaldehyde.

4. The method according to claim 2, wherein in the first step, the concentration of formaldehyde in the concentrated formaldehyde aqueous solution is more than 50%, the cyclization catalyst is a solid acid catalyst, the reaction temperature is 80-150 ℃, and the reaction pressure is-0.1-0.3 MPa.

5. The method as claimed in claim 2, wherein in the second step, in the process of removing formaldehyde from the trioxymethylene crude product, the molar ratio of the added ethylene glycol to the formaldehyde in the trioxymethylene crude product is 1: 1-5: 1.

6. The method according to claim 2, wherein in step two, the membrane is a water permeable molecular sieve membrane; the temperature of the residual side dehydration operation is 80-150 ℃, and the dehydration pressure is 0.1-1.0 MPa; the pressure of the permeation side is-0.05 to-0.1 MPa, the trioxymethylene at the permeation side is recovered by rectification and circulated to the inlet of a membrane dehydration device, and simultaneously, water is separated.

7. The method as claimed in claim 3, wherein in the third step, the solid acid catalyst is resin or molecular sieve, the amount of the solid acid catalyst is 1-15% of the total mass of the hemiacetal, the reaction pressure is-0.05-0.1 MPa, and the reaction temperature is 80-150 ℃.

8. The method as claimed in claim 3, wherein in the third step, before entering the reactive distillation column, the hemiacetal is dehydrated to obtain hemiacetal with low water content;

the hemiacetal with low water content adopts evaporation dehydration operation, the pressure of the evaporation dehydration is-0.08-0.1 MPa, the temperature of the evaporation dehydration is 60-150 ℃, and the evaporation dehydration equipment is falling film evaporation and reduced pressure evaporation equipment;

or the hemiacetal with low water content is subjected to membrane dehydration, the membrane dehydration is a pervaporation process, the used membrane material is a hydrophilic molecular sieve membrane, the hemiacetal with low water content is obtained at the retentate side, water is separated and removed at the permeate side, the pressure at the retentate side of the membrane dehydration is 0-0.5 MPa, the temperature is 60-150 ℃, and the pressure at the permeate side is-0.06-0.1 MPa.

9. The method as claimed in claim 3, wherein in the third step, the crude dioxolane with formaldehyde content of less than 0.1% and water content of less than 15% is obtained from the top of the dioxolane rectifying tower;

the molecular sieve membrane permeable gasification membrane is a hydrophilic NaA molecular sieve membrane, the pressure of the retentate side of the molecular sieve membrane permeable gasification membrane is 0.1-1.0 MPa, the temperature is 80-150 ℃, and the pressure of the permeate side is-0.08-0.1 MPa; dehydrating the residual side to obtain the dioxolane monomer with the water content of less than 0.5 percent.

10. A system for co-production preparation of polyformaldehyde from trioxymethylene and dioxolane is characterized by comprising three units: a trioxymethylene monomer preparation unit, a dioxolane monomer preparation unit and a polyformaldehyde preparation unit;

the trioxymethylene monomer preparation unit comprises a trioxymethylene reactor (R1101), a trioxymethylene concentrating tower (T1101), a trioxymethylene dealdehyder tower (T1102) and a trioxymethylene membrane dehydration device (M1101); the dioxygen pentacyclic monomer preparation unit comprises a dioxygen pentacyclic reaction rectifying tower (R1201) and a dioxygen pentacyclic membrane dehydration device (M1202); the polyformaldehyde preparation unit consists of a polyformaldehyde reactor (R1301);

the trioxymethylene reactor (R1101) is filled with a cyclization catalyst, and the dioxypentacyclic reaction rectifying tower (R1201) is filled with a solid acid catalyst.

Technical Field

The invention relates to a process for preparing polyformaldehyde by co-production of trioxymethylene and dioxolane, and particularly relates to the field of production of polyformaldehyde. The hemiacetal is synthesized by using the ethylene glycol and the formaldehyde in the trioxymethylene crude product, and is used for synthesizing the dioxolane after separation, and the subsequent separation and refining processes of the dealdehydized trioxymethylene crude product are simplified.

Background

Polyoxymethylene is one of five engineering plastics universal in the world, and China has become the biggest polyoxymethylene producing country and consuming country in the world; meanwhile, polyformaldehyde is a chemically important branch in the coal chemical industry C1, and the energy structure in China determines the advantage of industrial large-scale production of polyformaldehyde. However, the current situation of the domestic polyformaldehyde production industry is 'big but not strong', the production device technology is backward, the product structure is single, the quality is unstable, the advanced and mature polyformaldehyde production process is monopolized by foreign companies, and the domestic polyformaldehyde product consumption is seriously dependent on import. The production of trioxymethylene and dioxolane monomers, which are used as the core of a polyformaldehyde process, faces bottleneck problems of small scale, high energy consumption, unstable quality, large pollution, weak investment in research and development and technical innovation, and the like for a long time.

At present, the common synthetic method of trioxymethylene is to synthesize trioxymethylene under the action of an acid catalyst by using 50-65% of high-concentration formaldehyde as a raw material. The reaction is a rapid reversible reaction, but the reaction equilibrium constant is small, the conversion rate of formaldehyde is low, and only trioxymethylene with the equilibrium composition of about 3% is obtained in the reaction liquid. Meanwhile, trioxymethylene, formaldehyde and water form an azeotrope, and a common separation method is difficult to separate. The prior preparation, separation and purification process of the trioxymethylene has the defects of low efficiency, high difficulty, high energy consumption, high pollution and the like.

1) Extraction separation process

CN1136812A discloses a method for separating a mixture of trioxymethylene, formaldehyde and water by using an extraction separation technology. Catalyzing formaldehyde aqueous solution by using cation exchange resin to obtain a balanced solution of trioxymethylene, formaldehyde and water, adding a proper solvent to separate the trioxymethylene from the balanced solution in an extractor, and reducing the concentration of the trioxymethylene in reaction liquid so that the subsequent reaction moves towards the direction of generating the trioxymethylene. CN103328464 discloses a process for preparing trioxymethylene using a reactive distillation column comprising a reactor, a distillation unit and an extraction unit, the extraction unit using a solvent which is a halogenated aliphatic hydrocarbon or a halogenated aromatic hydrocarbon. The above extraction separation technology requires the recovery of the solvent for recycling to the extractive distillation, which inevitably consumes a large amount of energy, and the extraction solvent used is often a hazardous and harmful substance, which inevitably causes environmental pollution.

2) Pressure swing rectification separation

CN101238114A reports a reaction-pressure swing distillation technology to separate trioxymethylene, a mixture of formaldehyde and water and a method for producing trioxymethylene. Trioxymethylene was added at 1bar, formaldehyde and water forming a ternary azeotrope with a mass composition of 69% trioxymethylene, 5% formaldehyde and 26% water. The pressure-variable rectification separation is carried out by different compositions of ternary azeotrope under different pressures. However, the separation and purification process is lengthy and consumes a lot of energy.

3) Membrane separation process

CN1264374 provides a membrane separation technique for separating trioxymethylene from a mixture of trioxymethylene, water and formaldehyde. The method uses a polydimethylsiloxane membrane or a hydrophobic membrane of a polyether amide block copolymer material, and trioxymethylene in a mixture of trioxymethylene, water and formaldehyde selectively permeates a separation membrane. And rectifying and separating the material rich in trioxymethylene on the permeation side to obtain purified trioxymethylene. The dilute trioxymethylene material flow on the residual side enters another separation tower for separation. JP9533762 discloses a membrane separation and production method of trioxymethylene, in which trioxymethylene is separated from a mixture of trioxymethylene, water and formaldehyde by using a hydrophobic separation membrane such as a silicone rubber membrane, a polyacrylic silane membrane, a polyacrylic acrylamide membrane, etc., by a pervaporation technique. Because the ternary azeotropic composition of trioxymethylene, water and formaldehyde contains a large amount of trioxymethylene, the separation membrane area required for the permeation separation of most of trioxymethylene is large and the energy consumption is high, which causes the increase of the separation investment and the operation cost. Meanwhile, the high-concentration trioxymethylene at the permeation side is easy to crystallize under vacuum, so that a separation membrane is blocked, the separation performance of the membrane is reduced, and stable operation is difficult to realize in the actual separation process. Therefore, the membrane separation technology of trioxymethylene mixture cannot show the advantages of high efficiency and low energy consumption of membrane separation, and a more effective membrane separation method is to remove water from trioxymethylene, water and formaldehyde mixed liquid, for example, US5523419 discloses a method for separating trioxymethylene from azeotropic mixture by a pervaporation dehydration method. The mixture of trioxymethylene, formaldehyde and water is rectified and separated to obtain a material consisting of ternary azeotropy, and then a hydrophilic polyvinyl alcohol membrane is adopted to carry out separation and dehydration at 70-120 ℃ under 1-3 bar.

However, in practical application, after the mixture of trioxymethylene, formaldehyde and water is dehydrated, the trioxymethylene and formaldehyde content on the retentate side is increased, and the retentate side needs to be kept at a high temperature to avoid trioxymethylene crystallization and formaldehyde self-polymerization, but the used polyvinyl alcohol film has no thermal stability and chemical stability, so that the stability of separation performance cannot be ensured, and practical application is limited. Meanwhile, the method does not solve the problems of low formaldehyde utilization rate, large pollution in the separation process and the like caused by the recycling of the dilute formaldehyde generated in the membrane separation process.

The comonomer of Dioxolane (DOX) is prepared by the catalytic reaction of 60 percent of concentrated formaldehyde solution and ethylene glycol through concentrated sulfuric acid to generate a crude product. A production section of a coarse product of the dioxolane, wherein paraformaldehyde and ethylene glycol react intermittently under the catalysis of ion exchange resin to produce the dioxolane; and in the refining process of the coarse dioxolane product, the coarse dioxolane product is subjected to rectification, salting out by sodium chloride, dehydration by anhydrous calcium chloride, rectification, adsorption and dehydration by a molecular sieve and other processes to obtain the dioxolane product with the purity of 99.9 percent.

The defects of the existing paraformaldehyde production process are as follows:

first, due to the low equilibrium conversion for trioxane synthesis, a large amount of free formaldehyde is present in the trioxane solution during the separation. Free formaldehyde will condense and polymerize with water, methanol and formaldehyde itself to form hemiacetals and formaldehyde polymers. The relative volatility of part of hemiacetal, polymer of formaldehyde and trioxymethylene is similar and can not be separated by common separation methods. The prior art generally adopts crystallization or extraction method to carry out primary separation on a synthetic product, and refining by rectification, but trioxymethylene with ultra-purity or nearly 100% purity still cannot be obtained, and simultaneously, new solvent is introduced into the extraction process, so that the separation system is more complicated, the energy consumption and the dilute aldehyde recovery are difficult, and a separate dilute aldehyde recovery unit is often needed for recovery.

Secondly, for the existing and the above-mentioned preparation processes of trioxymethylene, the difficulties of large amount of dilute formaldehyde and high energy consumption for recovery exist, for example, about 15% of dilute formaldehyde of about 4 tons can be generated for each 1 ton of trioxymethylene.

Under different formaldehyde concentrations and temperatures, the distribution of the multi-formaldehyde hydrates with different polymerization degrees has a certain amount of long-chain multi-formaldehyde hydrates even in a low-concentration formaldehyde solution, and a 30% formaldehyde aqueous solution can be turbid when stored at room temperature, because the multi-formaldehyde hydrates with large polymerization degrees are easy to precipitate. Therefore, dehydration of formaldehyde solution is a complex physical and chemical process, which results in a very energy-consuming scheme for recovering dilute aldehyde by rectification.

And thirdly, the dioxolane and water can form an azeotrope, the azeotropic point is 70-73 ℃, the water content is 6.7%, the separation difficulty is high, and meanwhile, due to the existence of formaldehyde, the local concentration of a separation unit is too high, a formaldehyde polymer is easily formed, so that the pipeline of the rectifying tower is blocked, and in addition, the existence of formic acid, the equipment and the pipeline are easily corroded. Low efficiency, high difficulty, high energy consumption, large pollution and the like.

Disclosure of Invention

In order to solve the problems, the disclosure provides a green method for preparing polyformaldehyde by coproduction of trioxymethylene and dioxolane, which comprises the processes of preparing trioxymethylene monomers, synthesizing dioxolane monomers and obtaining polyformaldehyde through polymerization reaction.

The method specifically comprises the following steps:

the method comprises the following steps: preparing trioxymethylene from the concentrated aqueous solution of trioxymethylene under the action of a cyclization catalyst, and extracting a trioxymethylene reactant from a gas phase and passing the reactant through a concentration tower to obtain a crude trioxymethylene product;

step two: formaldehyde in the trioxymethylene crude product reacts with ethylene glycol in a dealdehyding reactor to remove formaldehyde, and then membrane dehydration is adopted for dehydration separation to obtain a trioxymethylene monomer;

step three: synthesizing formaldehyde in the ethylene glycol and the crude product of formaldehyde to obtain hemiacetal, and synthesizing a crude product of dioxolane in a reactive distillation tower under the action of a solid acid catalyst; finally, dehydrating through a molecular sieve membrane permeation gasification membrane, separating and dehydrating at the permeation side, and obtaining a dioxolane monomer at the retentate side;

step four: by BF₃The trioxymethylene monomer and the dioxypentacyclic monomer are subjected to polymerization reaction at 70-120 ℃ for 0.1-5 h as a polymerization initiator to prepare the polyformaldehyde.

In the first step, the concentration of formaldehyde in the concentrated formaldehyde aqueous solution is more than 50%, and the concentrated formaldehyde aqueous solution can be obtained by concentrating a formaldehyde aqueous solution prepared by an Ag method or a formaldehyde aqueous solution prepared by an iron-molybdenum method;

in the first step, a cyclization catalyst is used in the cyclization reaction, the reaction temperature is 80-150 ℃, and the reaction pressure is-0.1-0.3 MPa. The cyclization catalyst is preferably an acidic catalyst, the acidic catalyst is preferably a solid acid catalyst, and the solid acid catalyst is one or a mixture of more of resin, a molecular sieve, a supported ionic liquid and alumina.

In the first step, the trioxymethylene reactor is a separate kettle-type reactor or a fixed bed reactor or a fluidized bed reactor, and is integrated with the rectifying tower and is arranged in the rectifying tower kettle or the rectifying tower. When the kettle type device is arranged in the kettle of the rectifying tower, the dosage of the cyclizing catalyst is 0.1-20% of the reaction liquid, and when a fixed bed, a fluidized bed or the device is arranged in the rectifying tower, the volume space velocity of the feeding is 0.2-10 h^-1(ii) a The bottom of the trioxymethylene reactor is provided with a discharge port which can discharge part of reactants and reduce the content of formic acid in the reactor; or partial deactivated cyclizing catalyst can be discharged, and a cyclizing catalyst replenishing port is arranged at the inlet of the trioxymethylene reactor.

In the first step, the concentration is carried out in a trioxymethylene concentration tower, the middle part or the tower kettle of the trioxymethylene concentration tower is provided with a trioxymethylene reactor outlet gas phase inlet, and the trioxymethylene concentration tower is a plate tower, a partition wall tower or a packed tower.

Preferably, in the first step, a trioxymethylene concentrated solution material flow with the trioxymethylene content of more than 50% and the formaldehyde content of less than 10% is obtained at the top of a trioxymethylene concentration tower through rectification concentration, the trioxymethylene content of less than 1% in a formaldehyde aqueous solution material flow at the bottom of the concentration tower, the operation temperature of the concentration tower is 50-180 ℃, and the pressure is-0.1-0.2 MPa.

In the second step, in the process of removing formaldehyde from the trioxymethylene crude product, the molar ratio of the added ethylene glycol to the formaldehyde in the trioxymethylene crude product is 1: 1-5: 1, the temperature is 50-150 ℃, and the pressure is-0.1-0.15 MPa. In a preferable scheme, the glycol and the trioxymethylene crude product can be uniformly mixed and then dealdehydized in a rectifying tower. Or the ethylene glycol and the crude trioxymethylene can be in countercurrent flow in a rectifying tower and are in full contact. The processes are all for the reason that the ethylene glycol and the formaldehyde form hemiacetal, and a ternary azeotropic system formed by trioxymethylene, water and the formaldehyde is broken through. The system is separated into a mixture of trioxymethylene and water with low boiling points, and hemiacetals of ethylene glycol and formaldehyde with high boiling points. Wherein the formaldehyde content of the trioxymethylene and water mixture is less than 0.1%.

In step two, the trioxymethylene concentrate stream is dehydrated through a membrane, for example by pervaporation or gasification permeation, to obtain trioxymethylene monomer having a water content of less than 0.1% on the retentate side.

Preferably, in step two, the membrane is a water-permeable molecular sieve membrane; the temperature of the dehydration operation of the retentate side is 80-150 ℃, and the dehydration pressure is 0.1-1.0 MPa. The pressure of the permeation side is-0.05 to-0.1 MPa, the trioxymethylene at the permeation side can be recovered by rectification and circulated to the inlet of a membrane dehydration device, and simultaneously, water is separated out.

In the third step, the solid acid catalyst is resin or molecular sieve. The resin catalyst can load acidic substances such as sulfonic acid, ionic liquid and the like.

In the third step, the dosage of the solid acid catalyst is 1-15% of the mass of the hemiacetal, the reaction pressure is-0.05-0.1 MPa, and the reaction temperature is 80-150 ℃.

In the third step, the hemiacetal is synthesized into the five-ring dioxide under the action of a solid acid catalyst, and can be carried out in a fixed bed, a kettle type and a reaction rectifying tower.

In the third step, a coarse product of the dioxolane with the formaldehyde content of less than 0.1 percent and the water content of less than 15 percent is obtained at the top of the reactive distillation tower, and a mixture of unreacted raw materials and water produced by the reaction is obtained at the tower bottom, wherein the pressure is-0.1-0.2 MPa, and the temperature is 60-150 ℃.

In the third step, the molecular sieve membrane pervaporation membrane is a hydrophilic NaA molecular sieve membrane, membrane dehydration is a pervaporation process or a gasification pervaporation process, and the crude dioxolane on the retentate side is liquid or gas on the membrane surface;

in the third step, the pressure of the permeation gasification membrane at the permeation side of the molecular sieve membrane is 0.1-1.0 Mpa, the temperature is 80-150 ℃, and the pressure at the permeation side is-0.08-0.1 MPa;

in the third step, the residue side is dehydrated to obtain the dioxolane monomer with the water content of less than 0.1 percent, the dioxolane in the residue side can be recovered by rectification, a dioxolane mixture with the water content of less than 15 percent is obtained at the top of a rectifying tower, and an aqueous solution with the dioxolane content of less than 0.1 percent is obtained at the bottom of the rectifying tower.

More preferably, in the third step, the hemiacetal can also be dehydrated to obtain hemiacetal with low water content, and then the hemiacetal is reacted to synthesize the dioxolane;

the hemiacetal with low water content adopts evaporation dehydration operation, the pressure of the evaporation dehydration is-0.08-0.1 MPa, the temperature of the evaporation dehydration is 60-150 ℃, and the evaporation dehydration equipment is falling film evaporation and reduced pressure evaporation equipment;

or, the hemiacetal with low water content is subjected to membrane dehydration, the membrane dehydration is a pervaporation process, the used membrane material is a hydrophilic molecular sieve membrane, the hemiacetal with low water content is obtained on the retentate side, and water is separated and removed on the permeate side. The pressure of the retentate side of the membrane dehydration is 0-0.5 Mpa, the temperature is 60-150 ℃, and the pressure of the permeate side is-0.06-0.1 Mpa;

the content of formaldehyde in the water separated in the preparation process of the hemiacetal with low water content is 0.1-1%, and the water can be circulated to an absorption tower of a formaldehyde production unit;

after the hemiacetal with low water content is dehydrated, the water content is lower than 5 percent;

the hemiacetal with low water content synthesizes the dioxolane under the action of the solid acid catalyst, and unreacted raw materials and water produced by the reaction are circulated to a trioxymethylene crude product dealdehyding device, so that the utilization rate of the raw materials is improved.

The disclosure also relates to a system for preparing polyformaldehyde by co-production of trioxymethylene and dioxolane, which comprises three units: a trioxymethylene monomer preparation unit, a dioxolane monomer preparation unit and a polyformaldehyde preparation unit.

The trioxymethylene monomer preparation unit comprises a trioxymethylene reactor (R1101), a trioxymethylene concentrating tower (T1101), a trioxymethylene dealdehyder tower (T1102) and a trioxymethylene membrane dehydration device (M1101); the dioxygen pentacyclic monomer preparation unit comprises a dioxygen pentacyclic reaction rectifying tower (R1201) and a dioxygen pentacyclic membrane dehydration device (M1202); the polyoxymethylene preparation unit consists of a polyoxymethylene reactor (R1301).

(1) Trioxymethylene monomer preparation unit

Mixing a formaldehyde aqueous solution material flow 1 with the formaldehyde concentration of more than 50% with a circulating material flow 3 at the bottom of a trioxymethylene concentrating tower (T1101), and then feeding the mixture into a trioxymethylene reactor (R1101) filled with a cyclization catalyst in advance, wherein the filling mass of the resin catalyst is 15% of the reaction liquid, the reaction temperature is 80-150 ℃, and the reaction pressure is-0.1-0.3 MPa. At the outlet of the reactor, a stream 2 of aqueous solution of trioxymethylene and formaldehyde is withdrawn in the gas phase.

And the material flow 2 enters a trioxymethylene concentrating tower (T1101) and the operation pressure is-0.1-0.2 MP. A stream 4 of a concentrated trioxymethylene mixture is obtained at the top of the column and a stream 3 of an aqueous formaldehyde solution is obtained at the bottom of the column, which is recycled to the trioxymethylene reactor (R1101).

Feeding the trioxymethylene mixture material flow 4 and the ethylene glycol material 5 into a trioxymethylene formaldehyde-removing tower (T1102), wherein the molar ratio of the feeding amount of the ethylene glycol to the formaldehyde in the trioxymethylene mixture material flow 4 is 1: 1-5: 1. a stream 7 of a mixture of the trioxymethylenes is obtained at the top of the column, and a stream 6 of hemiacetals of ethylene glycol and formaldehyde is obtained at the bottom of the column.

The stream 7 of the dealdehydised trioxymethylene mixture is dewatered in a trioxymethylene membrane dewatering unit (M1101) to obtain a trioxymethylene monomer stream 10 having a water content of 0.1%, and a permeate side water stream 11.

(2) Dioxo pentacyclic monomer preparation unit

A trioxymethylene concentrating tower (T1101) obtains hemiacetal material flow 6 of ethylene glycol and formaldehyde, the hemiacetal material flow enters a dioxy pentacyclic reaction rectifying tower (R1201), a sulfonic acid solid acid catalyst is pre-loaded in the tower, a dioxy pentacyclic mixture material flow 9 is obtained at the tower top, and an aqueous solution material 8 is obtained at the tower bottom.

The stream 9 of the mixture of the dioxolane enters a dioxolane membrane dehydration unit (M1202) equipped with a molecular sieve membrane, and after dehydration, a stream 12 of the monomer dioxolane and a stream 13 of permeate side water are obtained.

(3) Polyoxymethylene preparation unit

Trioxymethylene monomer material flow 10 and dioxypentacyclic monomer material flow 12 are subjected to polymerization reaction in a polyformaldehyde reactor (R1301) to prepare polyformaldehyde.

Preferably, the dioxygen pentacyclic monomer preparation unit further comprises a low-water content hemiacetal membrane dehydration device, wherein before entering a dioxygen pentacyclic reaction rectifying tower, a hemiacetal stream obtained from a trioxymethylene concentrating tower passes through the low-water content hemiacetal membrane dehydration device to obtain low-water content hemiacetal with the water content of less than 5%, and then enters the dioxygen pentacyclic reaction rectifying tower.

Adopt this disclosed advantage to lie in:

1. the hemiacetal formed by the glycol and the formaldehyde breaks through a unit azeotropic system of trioxymethylene, formaldehyde and water which are difficult to separate, so that the system is separated into a trioxymethylene aqueous solution system with a low boiling point and a hemiacetal system with a high boiling point, and meanwhile, the hemiacetal can be used as a raw material for synthesizing a dioxolane monomer, so that the raw material utilization rate of the whole system is improved, and the separation efficiency is greatly improved.

2. Formaldehyde is removed through the dealdehyding reaction, so that the purification and preparation process of the trioxymethylene monomer becomes easier, the process flow is simplified, and the equipment investment is reduced.

3. According to the preparation process of the dioxolane, provided by the disclosure, through dehydration in a hemiacetal production process, the water content in reactants is reduced, the reaction rate is improved, the subsequent separation difficulty is reduced, and the polymer quality is improved.

4. The solid acid catalyst can improve the conversion rate and selectivity of products, reduce the corrosion of equipment, and has the advantages of easy separation of the catalyst from reaction liquid, mild reaction conditions and avoidance of side effects of polyformaldehyde degradation and low polymerization conversion rate caused by other catalysts.

5. The method adopts multiple dehydration processes, reduces the energy consumption of dehydration and separation, reduces the cost, and is suitable for industrialization.

6. According to the method, trioxymethylene and dioxolane are co-produced to prepare polyformaldehyde, multiple cycles are utilized, the utilization rate and the conversion rate of raw materials are improved, and the energy consumption is reduced.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and together with the description serve to explain the principles of the disclosure.

FIG. 1 is a process flow diagram of example 1.

FIG. 2 is a process flow diagram of example 2.

The device comprises an R1101 trioxymethylene reactor, a T1101 trioxymethylene concentrating tower, a T1102 trioxymethylene dealdehyding tower, an M1101 trioxymethylene membrane dehydration device, an R1201 dioxygen pentacyclic reaction rectifying tower, an M1202 dioxygen pentacyclic membrane dehydration device, an R1301 polyformaldehyde reactor and an M2201 low water content hemiacetal membrane dehydration device.

Detailed Description

The present disclosure will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present disclosure. It should be further noted that, for the convenience of description, only the portions relevant to the present disclosure are shown in the drawings.

It should be noted that the embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.