阅读说明：本技术 一种生产低小分子含量聚酯的高效反应器及方法 (Efficient reactor and method for producing low-small-molecular-content polyester ) 是由 杨勇 朱兴松 常玉 夏峰伟 郭瑞龙 周刚 于 2020-06-10 设计创作，主要内容包括：本发明公开了一种生产低小分子含量聚酯的反应器及方法,反应器上段为圆柱体段,反应器下段为倒锥体段,圆柱体段分为保温区和冷却区,保温区内设有分流板和位于保温区中轴线的出风管,所述出风管上设有若干出风口；所述分流板呈框形,由位于同一平面的多个圆环嵌套而成,所述圆环为空心,圆环上设有若干出风口本发明通过圆形盘管分流板的设计可实现粒子输送过程中的平推流,不易造成返混,热氮气/空气出风管提供稳定气流与球形聚酯颗粒充分进行传热传质,大幅提高聚酯颗粒小分子脱除的效率,反应器的冷却段采用螺旋管换热器,可以实现换热效率高、清洗周期短,产品品质高。(The invention discloses a reactor and a method for producing low-small-molecular-content polyester.A cylinder section is arranged at the upper section of the reactor, an inverted-cone section is arranged at the lower section of the reactor, the cylinder section is divided into a heat insulation area and a cooling area, a flow distribution plate and an air outlet pipe positioned on the central axis of the heat insulation area are arranged in the heat insulation area, and a plurality of air outlets are arranged on the air outlet pipe; the splitter plate is frame-shaped and formed by nesting a plurality of circular rings on the same plane, the circular rings are hollow, and a plurality of air outlets are arranged on the circular rings.)

1. The efficient reactor for producing the polyester with the low small molecular content is characterized by comprising a two-section reactor (2), wherein the upper section of the reactor is a cylindrical section (1), the lower section of the reactor is an inverted-cone section (3), the tail end of the inverted-cone section is a discharge hole (23), and the reactor is also provided with a first air inlet (105) and a second air inlet (31); the cylinder section (1) is divided into a heat preservation area (10) and a cooling area (11), a flow distribution plate (102) and an air outlet pipe (103) located on the central axis of the heat preservation area are arranged in the heat preservation area, and a plurality of air outlets are formed in the air outlet pipe (103); the flow distribution plate (102) is formed by nesting a plurality of circular rings on the same plane, the flow distribution plate (103) is hollow, and a plurality of air outlets are formed in the flow distribution plate; the inlet of the air outlet pipe (103) and the flow distribution plate (102) are connected with a first air inlet (105) through a pipeline.

2. The high efficiency reactor for producing low small molecule content polyesters according to claim 1, characterized in that the dividing plate (102) is provided with at least two layers.

3. The high efficiency reactor for producing low molecular weight polyester according to claim 1, wherein the flow distribution plate (102) is communicated with the air outlet pipe (103).

4. The high-efficiency reactor for producing low-molecular-weight polyester according to claim 1, wherein the first gas inlet (105) is connected with a heat medium system (6), and the heat medium system (6) comprises a heat exchanger and a dryer.

5. The high efficiency reactor for producing polyesters with a low small molecular weight content as claimed in claim 1, characterized in that the reactor cooling zone (11) is provided with a spiral coil heat exchanger (111) consisting of several vertically arranged tube runs (116) and a spiral coil (115) surrounding the outside of the tube runs.

6. The high efficiency reactor for producing low small molecule content polyester according to claim 5, wherein the spiral coil (115) is provided with fins (114) for heat dissipation.

7. The high-efficiency reactor for producing the low-molecular-weight polyester, according to claim 1, is characterized in that the diameters of the air outlets of the air outlet pipe (103) and the disc of the flow distribution plate (102) are smaller than the diameter of the particles.

8. The efficient reactor for producing the polyester with the low small molecular content according to claim 1, wherein the ratio of the surface area of the spiral tube plate of the heat exchanger to the surface area of the reactor is 1: 4-1: 6.

9. The high efficiency reactor for producing low molecular weight polyester as claimed in claim 1, wherein the ratio of the distance between adjacent rings of the splitter plate (102) to the reactor diameter is greater than 1:11, and the thickness of the splitter plate is less than 100 mm.

10. The high efficiency reactor for producing polyesters with a low content of small molecules as claimed in claim 1, characterized in that a reducer (4) is arranged in said inverted cone section (3), said reducer (4) forming an annular space with the outer shell of said inverted cone section (3), and said second gas inlet (31) being arranged in said inverted cone outer shell.

11. A method for producing a low-molecular-weight polyester, which is based on the reactor of any one of claims 1 to 9, and comprises the following steps,

(1) spherical polyester particles enter a heat preservation area of a reactor from a feed inlet at the top of the reactor, hot air or nitrogen dried by a heat medium system is introduced from a first air inlet of the reactor, and the dried hot air or nitrogen enters the reactor through a flow distribution plate and an air outlet pipe to contact the particles to remove micromolecules in the particles;

(2) the polyester granules with most of small molecules removed enter a cooling zone, and are cooled by cooling water and cold air or nitrogen, and the small molecules in the granules are further removed;

(3) the particles are discharged from the outlet and enter the next process.

12. The method for producing low-small-molecule-content polyester according to claim 11, wherein the reactor insulation zone in step (1) is maintained at an internal temperature of 160-190 ℃ by a jacket insulation device, the residence time is 15-40h, and the temperature of hot air or nitrogen is 160-190 ℃.

13. The method for producing a low-molecular-weight polyester according to claim 11, wherein the temperature of the cooling water in the step (2) is 40 ℃ or lower, the circulating flow rate in the tube is 1.0 to 2.0m/s, and the residence time of the pellets in the cooling zone is not more than 3 hours.

14. The method for producing low-molecular-weight polyester according to claim 11, wherein the ratio of the amount of the pellets in the steps (1) and (2) to the amount of the introduced air or nitrogen is 5 to 25.

Technical Field

The invention relates to a high-efficiency reactor and a method for producing low-small-molecular-content polyester.

Background

Polyethylene terephthalate (PET) is a semi-crystalline thermoplastic polyester that is widely used in the manufacture of fibers, films, sheets, and food trays and beverage containers. In the prior art, terephthalic acid (PTA) and Ethylene Glycol (EG) are used as main raw materials to prepare high-viscosity polyester, low-viscosity polyester with the intrinsic viscosity of about 0.65dl/g and the polymerization degree of about 100 is obtained through conventional liquid phase polymerization, and then high-viscosity polyester with the intrinsic viscosity of 0.80dl/g and the average polymerization degree of more than 135 is improved through a solid-phase tackifying process, so that the high-viscosity polyester meets the requirements of subsequent processing.

In polyester packaging products, besides intrinsic viscosity, the content of small molecules is another most important index, particularly acetaldehyde (AA), can permeate into packaged objects to produce adverse effects, and if food is packaged, the taste of food is directly influenced and health risks are caused to human bodies. The sources of acetaldehyde are mainly: in the liquid phase polymerization stage, part of AA with the content of about 100 mu g/g is formed due to high-temperature degradation reaction; partial side reactions occur in the solid phase tackifying stage, and a small amount of AA is produced. AA generated by the two sources can be basically removed in the solid-phase tackifying process, and the final AA content is not more than 1.0 mu g/g. Although the solid-phase tackifying technology is mature, hot nitrogen/air is usually adopted to remove small molecules in polyester solid particles and improve viscosity, the technology has the problems of high energy consumption and material consumption, uneven molecular weight distribution of PET products, much dust and the like. In the existing production technology, the liquid phase tackifying technology is to make PET reach higher intrinsic viscosity (generally above 0.78 dL/g) in a final polycondensation reactor, perform underwater crystallization, cutting and granulation, and then realize the preparation of a final polyester product through a micromolecule removing device. The preparation of polyester chips with low small molecular weight content aiming at the crystallized spherical particles obtained by liquid phase tackifying is of great importance in the structural design and process conditions of the reactor in the production flow.

At present, all existing reactors are designed by tower body structures of conventional cylindrical polyester particles, so that polyester chips fall unevenly by means of dead weight, the stacking density of the polyester particles is low, plug flow cannot be effectively formed, heat exchange is uneven, back mixing is easily caused, the existing tubular heat exchanger at a cooling section has a short cleaning period due to impurity precipitation, the removal efficiency of small molecules in the chips is low, and the replacement period of dust removal bags of a cooler is greatly influenced by the outside.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a high-efficiency reactor and a method for producing low-small-molecular-weight polyester, so as to solve the technical problems.

The technical scheme is as follows: the invention relates to an efficient reactor for producing low-micromolecule-content polyester, which comprises a vertical two-section reactor, wherein the upper section of the reactor is a cylinder, and the lower section of the reactor is an inverted cone; the top of the reactor is provided with a feed inlet and an air outlet, and the reactor is also provided with a first air inlet and a second air inlet; the cylinder body is divided into a heat preservation area and a cooling area, a flow distribution plate and an air outlet pipe located on the central axis of the heat preservation area are arranged in the heat preservation area, and a plurality of air outlets are formed in the air outlet pipe; the flow distribution plate is formed by nesting a plurality of circular rings positioned on the same plane, is hollow and is provided with a plurality of air outlets; the air outlet pipe inlet and the flow distribution plate are connected with the first air inlet through a pipeline.

The high-efficiency reactor for producing the polyester with low small molecular content, which is based on the reactor, comprises the following steps,

(1) spherical polyester particles enter a heat preservation area of a reactor from a feed inlet at the top of the reactor, hot air or nitrogen dried by a heat medium system is introduced from a first air inlet of the reactor, and the dried hot air or nitrogen enters the reactor through a flow distribution plate and an air outlet pipe to contact the particles to remove micromolecules in the particles;

(2) the polyester granules with most of small molecules removed enter a cooling zone, and are cooled by cooling water and cold air or nitrogen, and the small molecules in the granules are further removed;

(3) the particles are discharged from the outlet and enter the next process.

The heat preservation area of the reactor in the step (1) passes through a jacket heat preservation device, the internal temperature is maintained at 190 ℃, the retention time is 15-40h, and the temperature of hot air or nitrogen is 160-190 ℃.

The temperature of the cooling water in the step (2) is less than or equal to 40 ℃, the circulating flow rate in the pipe is 1.0-2.0m/s, and the residence time of the particles in the cooling section is not more than 3 hours.

The ratio of the amount of the particles in the steps (1) and (2) to the amount of the introduced air or nitrogen is 5-25.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:

(1) the heat preservation area is provided with a hollow cylindrical hot nitrogen/air outlet pipe, and the air outlet pipe is connected with a hot nitrogen/air inlet pipe outside the tower through the bottom of the heat preservation area, so that stable airflow in the whole tower is provided to fully perform heat and mass transfer by forward and reverse collision with spherical polyester particles, and each particle can obtain the same contact opportunity.

(2) According to the invention, the circular coil splitter plate is nested at the top and the middle of the nitrogen outlet pipe, so that the uniformity of material distribution in the reactor is fully improved. The gas outlet is arranged on the splitter plate and matched with the gas inlet pipe, so that the contact area of the material and the gas is further increased, the splitter plate is particularly suitable for removing small molecules from granular materials, the problem of back mixing can be solved, the flat plug flow in the conveying process of the slice particles is realized, and the efficiency of removing the small molecules from the polyester slices can be greatly improved.

(3) The cooling area of the invention adopts the design of a spiral coil type heat exchanger, one or more layers of fins are arranged outside the spiral coil and welded on the outer surface of the spiral coil to increase the heat exchange area, and the surface area of the heat exchange tube is as follows: the tube pass surface area is 1: 4-1: 6, the length-diameter ratio is more than or equal to 2, the condensed water performs heat exchange through rotational flow movement of the spiral channel outside the tube, the heat transfer coefficient is high, the space utilization rate is high, fluid in the spiral tube further strengthens convective heat exchange under the action of centrifugal force, impurities in the condensed water are easy to take away, and frequent cleaning of the heat exchanger is avoided. The condensed water is recycled, energy loss of a cooler in the conventional production flow is avoided, and the energy-saving and environment-friendly effects are achieved.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic view of the structure of the splitter plate of the present invention;

FIG. 3 is a schematic view of a partial structure of the spiral coil heat exchanger of the present invention;

fig. 4 is a horizontal cross-sectional view of the spiral coil heat exchanger of the present invention.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

As shown in fig. 1, the tower body of the reactor 2 of the present invention is designed in two vertical sections, including a cylindrical section 1 and an inverted cone section 3. The center of the top of the tower body is provided with a feed inlet 22 and a gas phase outlet 21, and the tail end of the inverted cone at the lower end is provided with a reactor material outlet 23. The cylinder section is divided into a warm-keeping zone 10 and a cooling zone 11. The cooling zone 11 has a smaller diameter than the holding zone 10 in order to ensure that the material has different residence times in the two zones.

A hollow cylindrical hot nitrogen/air outlet pipe 103 is arranged on the central axis of the heat preservation area 10, the air outlet pipe 103 is connected with a first air inlet 105 through a pipeline at the bottom of the heat preservation area, the inlet air is nitrogen or air, a plurality of air outlets are arranged on the air outlet pipe 103, and the diameter of an air outlet hole of the pipe wall is smaller than the diameter of spherical polyester particles.

Be equipped with flow distribution plate 102 in reactor 2, the flow distribution plate nestification is outside air-out pipe 103, and the flow distribution plate is equipped with 1 layer at least. The splitter plate 102 is formed by nesting a plurality of annular disks with different diameters, and the annular disks are all positioned on the same plane and are uniformly distributed in appearance. The disc is hollow, a plurality of air outlets are arranged on the upper surface of the disc, and each layer of splitter plate is connected with a first air inlet 105 through a pipeline, as shown in fig. 2. The splitter plate 102 and the air outlet pipe 103 can be communicated with each other, so that connecting pipelines are saved, the gas flow rate and the temperature are more uniform, and the process control is facilitated.

The outer diameter of the air outlet pipe 103 is the minimum diameter of the inner ring of the circular coil splitter plate, and the joint of the air outlet pipe and the circular coil splitter plate has no dead angle. The upper and lower splitter plates 102 are welded and supported by cylindrical brackets 104, and the disks are also connected by the brackets. The ratio of the distance between the adjacent circular rings of the flow distribution plate 102 to the diameter of the reactor is more than 1:11, and the thickness of the flow distribution plate is less than 100mm, preferably 30-100 mm.

The first air inlet 105 is also connected with a heat medium system 6, and the heat medium system 6 comprises a heat exchanger and a dryer, so that the drying of the inlet air can be further ensured, and the inlet air temperature is kept constant.

The outer wall of the cylinder of the tower body of the heat preservation area 10 is provided with a jacket heat preservation device which can maintain the temperature in the tower.

As shown in fig. 3, a spiral coil heat exchanger 111 is disposed in the cooling zone 11, and the heat exchanger is composed of a plurality of vertically disposed tube passes 116 and a spiral coil 115 surrounding the outside of the tube passes, and a certain gap is formed between the tube passes surrounding the spiral coil. The particles fall from the tube pass of the heat exchanger by gravity or vibration, and cooling water enters from a cooling water inlet 113 arranged below the cooling section, passes through the spiral coil, flows out from a cooling water outlet 112 arranged above the spiral coil, and circulates in the spiral coil outside the tube pass. Surface area of the heat exchange tube: the surface area of the cylinder is 1: 4-1: 6, and the length-diameter ratio is more than or equal to 2. Fins with certain width are horizontally arranged on the outer wall of the spiral coil pipe to increase heat exchange between the spiral coil pipe and the cold air or nitrogen which moves upwards.

A reducing pipe 4 is arranged in the inverted cone 3 at the lower section, and the reducing pipe 4 and the shell of the inverted cone 3 form an annular space which is in a double-top cone design. The outer shell of the inverted cone 3 is provided with a second gas inlet 31, the position of the second gas inlet corresponds to the annular space, dry air or nitrogen enters the tube bundle of the heat exchanger through an annular gap generated by the cone, and particles fall from the reducer 4.

The method for producing the low-small-molecular-weight polyester by adopting the high-efficiency reactor specifically comprises the following steps:

spherical polyester particles enter a first section of heat preservation area of the tower body from a feed inlet at the top of the reactor, wherein the viscosity of the spherical polyester particles at the feed inlet is 0.70-0.80dL/g, the acetaldehyde content is 10-100 mu g/g, the formaldehyde content is 10-50 mu g/g, and the crystallinity is 30-40%. The particles fall to the circular coil pipe splitter plate by means of dead weight and then are split and descend, because the contact area among the spherical polyester particles is small, relative displacement is easy to occur, so that the speed in the falling process is uneven, the stacking density is smaller than that of the cylindrical particles, the design of the splitter plate can keep the descending speed of the middle and the edge of the spherical polyester particles balanced, the plug flow is effectively formed, stable airflow in the whole tower is provided in the hot nitrogen/air outlet pipe, the heat and mass transfer is fully carried out by forward and reverse collision of the spherical polyester particles, each particle can obtain the same contact opportunity, and therefore the micromolecule removal efficiency is improved. The micromolecules are formaldehyde, acetaldehyde, acrolein, benzene, toluene, ethylbenzene, xylene, styrene and the like. The temperature of the jacket of the cylinder is kept at 190 ℃ and 160 ℃ for 15-40 h.

A uniform cooling zone for removing most of small molecular polyester particles, wherein the cooling zone adopts a spiral coil type heat exchanger, cooling circulates from a spiral coil from bottom to top, the particles fall down from the tube pass of the heat exchanger by virtue of gravity, the temperature of cooling water is less than or equal to 40 ℃, the circulating flow rate in the tube is 1.0-2.0m/s, the residence time of the cooling zone is 1-3h, and the temperature of the polyester particles after passing through the cooling zone is about 40 ℃.

The reactor back taper body section adopts the design of a double-top cone, and simultaneously plays the role of a diversion cone, so that the falling speed of spherical particles in the middle of the reactor is balanced with that of the edge of the reactor, and the back mixing of a discharge port is avoided. Dry air or nitrogen is continuously blown into the heat exchanger tube bundle through the annular gap generated by the cone, fully contacts with the spherical particles from top to bottom, and continuously discharges formaldehyde, acetaldehyde, acrolein gas and micromolecules in the tower body. The exhausted air/nitrogen can be recycled after dehumidification and catalyst absorption of moisture, formaldehyde, acetaldehyde and micromolecules. The ratio of the amount of the granules in the whole micromolecule removing process to the air/nitrogen is 5-25, wherein the temperature of the hot air/nitrogen is 160-190 ℃, and preferably 170-185 ℃. Because the reactor is internally provided with the splitter plate and the central air outlet pipe, and the splitter plate is provided with a plurality of air outlets, the efficiency of removing small molecules can be increased, the process can be carried out at a temperature lower than the conventional temperature by 20 ℃, and the reactor is energy-saving and low-carbon.

The polyester particles prepared by the reactor have low micromolecule content, the dust content is lower than 10 mu g/g, the dust proportion is reduced by 80 percent compared with polyester slices produced by a conventional solid-phase tackifying device, the retention time is greatly shortened to 15-30 h, the internal and external viscosity difference of the particles is lower than 0.01dL/g, the molecular weight distribution is less than or equal to 2.2, and the post-processing injection molding temperature of a user is reduced by 10-15 ℃. Compared with the prior art, the reactor has the advantages of low energy consumption and material consumption, low equipment investment, uniform internal and external particle viscosity, less dust and high devolatilization efficiency.

The polyester granules produced by the above reactor, the dust was collected by a cyclone to obtain the dust content, and the molecular weight distribution and the formaldehyde and acetaldehyde contents were also measured with reference to the polyester test standard (GB17931-2003) and the results are shown in the following table:

item	Comparative example (solid phase adhesion promoter)	Example 1	Example 2	Example 3	Example 4
						Nitrogen/air temperature deg.C	210	170	180	190	165
Residence time h	16	30	24	16	30
						Molecular weight distribution PD	2.5	2.09	1.99	2.00	2.20
The content of formaldehyde is mu g/g	0.5	0.46	0.37	0.33	0.49
						Acetaldehyde content of mu g/g	0.8	0.7	0.6	0.7	0.8
Dust content mu g/g	25	8	6	9	9
						Degree of crystallinity%	55	42	46	50	40
Initial viscosity dL/g	0.65	0.75	0.75	0.75	0.75
						Final viscosity dL/g	0.85	0.75	0.76	0.78	0.75
Initial melting temperature of	230	216	219	220	215