CN112111054A - Production method of low-acetaldehyde PET - Google Patents
Production method of low-acetaldehyde PET Download PDFInfo
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- CN112111054A CN112111054A CN202011064971.4A CN202011064971A CN112111054A CN 112111054 A CN112111054 A CN 112111054A CN 202011064971 A CN202011064971 A CN 202011064971A CN 112111054 A CN112111054 A CN 112111054A
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 17
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 127
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 claims abstract description 74
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims abstract description 69
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 53
- 238000000034 method Methods 0.000 claims abstract description 17
- 239000003054 catalyst Substances 0.000 claims abstract description 16
- 238000000746 purification Methods 0.000 claims abstract description 16
- 239000013078 crystal Substances 0.000 claims abstract description 13
- 230000008569 process Effects 0.000 claims abstract description 13
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 claims abstract description 12
- 238000006068 polycondensation reaction Methods 0.000 claims abstract description 9
- KKEYFWRCBNTPAC-UHFFFAOYSA-N Terephthalic acid Chemical compound OC(=O)C1=CC=C(C(O)=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-N 0.000 claims abstract description 8
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- QQVIHTHCMHWDBS-UHFFFAOYSA-N isophthalic acid Chemical compound OC(=O)C1=CC=CC(C(O)=O)=C1 QQVIHTHCMHWDBS-UHFFFAOYSA-N 0.000 claims abstract description 6
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 6
- 238000005886 esterification reaction Methods 0.000 claims abstract description 4
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 239000012299 nitrogen atmosphere Substances 0.000 claims abstract description 4
- 239000003381 stabilizer Substances 0.000 claims abstract description 4
- 230000008719 thickening Effects 0.000 claims abstract description 3
- 239000007921 spray Substances 0.000 claims description 71
- 238000005507 spraying Methods 0.000 claims description 27
- 239000007788 liquid Substances 0.000 claims description 15
- 238000011010 flushing procedure Methods 0.000 claims description 7
- 239000007789 gas Substances 0.000 claims description 4
- 230000007246 mechanism Effects 0.000 claims description 4
- 238000007664 blowing Methods 0.000 claims description 2
- 230000032050 esterification Effects 0.000 claims 1
- 229920000728 polyester Polymers 0.000 abstract description 6
- 229910001873 dinitrogen Inorganic materials 0.000 description 21
- 238000006243 chemical reaction Methods 0.000 description 14
- 239000000047 product Substances 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- IKHGUXGNUITLKF-XPULMUKRSA-N acetaldehyde Chemical compound [14CH]([14CH3])=O IKHGUXGNUITLKF-XPULMUKRSA-N 0.000 description 5
- 239000012535 impurity Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000005265 energy consumption Methods 0.000 description 3
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 3
- 238000005457 optimization Methods 0.000 description 3
- 230000004224 protection Effects 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 235000013361 beverage Nutrition 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 231100000956 nontoxicity Toxicity 0.000 description 2
- 238000004064 recycling Methods 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 230000006750 UV protection Effects 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 235000014171 carbonated beverage Nutrition 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000008157 edible vegetable oil Substances 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 235000013305 food Nutrition 0.000 description 1
- 235000011194 food seasoning agent Nutrition 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000005022 packaging material Substances 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 229920001225 polyester resin Polymers 0.000 description 1
- 239000004645 polyester resin Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/66—Polyesters containing oxygen in the form of ether groups
- C08G63/668—Polyesters containing oxygen in the form of ether groups derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/672—Dicarboxylic acids and dihydroxy compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
- C08G63/785—Preparation processes characterised by the apparatus used
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Polyesters Or Polycarbonates (AREA)
Abstract
The invention discloses a production method of low-acetaldehyde PET in the field of polyester production, which comprises the following steps: A. melt polymerization, mixing terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, a catalyst, a stabilizer and the like, performing esterification reaction under certain conditions, and performing polycondensation reaction to obtain amorphous basic slices; B. crystallizing, namely crystallizing the amorphous basic slice obtained in the step A in a crystallizer in a nitrogen atmosphere to obtain a crystal slice; C. preheating, namely further heating and crystallizing the crystal slices in a preheater, and introducing nitrogen purified by a nitrogen purification system into the preheater; D. thickening, and further polycondensing the heated crystal chips. The invention can solve the problems that the purity of nitrogen used in the process of producing PET in the prior art is insufficient, and the acetaldehyde content in the produced PET is difficult to further reduce.
Description
Technical Field
The invention relates to the field of polyester production, and particularly relates to a production method of low-acetaldehyde PET.
Background
The polyester resin has the excellent characteristics of transparency, no toxicity, no odor, difficult breakage, good barrier property, high ultraviolet resistance, high viscosity, heat resistance and the like, and becomes the best choice of the packaging material required by the development of the modern times. The PET polyester package is closely contacted with people, such as PET polyester bottle flakes, is used in the fields of cold and hot filling beverages, foods and the like, and is suitable for beverage packages such as barreled water, carbonated beverages, mineral water and edible oil packages, seasoning commodity packages, daily chemical product packages and the like. In the production process of PET resin, acetaldehyde (AA) is inevitably generated to influence the quality of polyester packaging products, and the polyester bottle flake with high energy conservation and ultralow acetaldehyde has the advantages of safety, environmental protection, no toxicity, no odor and the like, and is widely demanded by society. Research on a low-acetaldehyde control technology in the polycondensation process effectively inhibits/removes the generation of acetaldehyde in the reaction process, reduces the content of acetaldehyde in a polymer, reduces the reaction temperature, reduces energy consumption, and forms a production system with high product quality and greenness, which is the direction of the development of efforts of various companies at present. Adopt nitrogen gas to carry out inert gas protection and get rid of the micromolecule product among the prior art, conventional production is direct to introduce the preheater recycling behind preheater and the reactor nitrogen gas through the blowback filter, debris are many in the nitrogen gas behind preheater and the reactor, contain low molecular substance such as ethylene glycol, acetaldehyde, moisture, because the reaction that the PET molecular chain increases is reversible reaction, the existence of ethylene glycol in the gas, be unfavorable for going on of reaction, be unfavorable for the increase of PET molecular weight, the people's existence of moisture also can make the PET molecule take place to hydrolyze, simultaneously impure nitrogen gas has brought into acetaldehyde, make PET sliced acetaldehyde content in the preheater can not further reduce all the time.
Disclosure of Invention
The invention aims to provide a method for producing low-acetaldehyde PET, which aims to solve the problems that the purity of nitrogen used in the process of producing PET in the prior art is insufficient, and the acetaldehyde content in the produced PET is difficult to further reduce.
In order to achieve the purpose, the basic technical scheme of the invention is as follows: a low-acetaldehyde PET production method comprises the following steps:
A. melt polymerization, mixing terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, a catalyst, a stabilizer and the like, performing esterification reaction under certain conditions, and performing polycondensation reaction to obtain amorphous basic slices;
B. crystallizing, namely crystallizing the amorphous basic slice obtained in the step A in a crystallizer in a nitrogen atmosphere to obtain a crystal slice;
C. preheating, namely further heating and crystallizing the crystal slices in a preheater, and introducing nitrogen purified by a nitrogen purification system into the preheater;
D. thickening, and further polycondensing the heated crystal chips.
According to the scheme, purified high-purity nitrogen is introduced in the preheating stage of solid-phase polymerization, low-molecular substances such as ethylene glycol and water are taken out from the preheater, so that the reaction is carried out in the positive and negative reaction directions, the molecular weight of PET is improved, the reaction temperature can be properly reduced compared with that before optimization, meanwhile, by-product acetaldehyde in the PET reaction can be taken out by the high-purity nitrogen, the acetaldehyde content in a system is reduced, and the acetaldehyde content in a product is reduced.
Further, the flow rate of nitrogen into the preheater in the step C is 200-280 cubic meters per hour. Preferably, the nitrogen flow rate in this range can be used to promote the forward progress of the PET solid polymerization reaction in the preheater, which is advantageous for increasing the PET molecular weight.
And further, in the step C, an air inlet pipeline for introducing purified nitrogen into the preheater is communicated between the back-blowing filter and the preheater. The preheater intercommunication has the blowback filter among the prior art, directly sends into the preheater with the filterable nitrogen gas of blowback filter, and PET's reaction in its impurity is more influences the preheater is linked to the preheater as the nitrogen gas after this scheme of preferred will purify, provides the preheater with the high-purity nitrogen gas after the purification, can effectively reduce PET sliced acetaldehyde content in the preheater, improves PET molecular weight.
And furthermore, the nitrogen purification system in the step C comprises a spray tower and a demister, an air inlet pipeline is connected with an air outlet of the demister, an air inlet of the demister is communicated with an air outlet of the spray tower, and an air outlet of the back flushing filter is communicated with an air inlet of the spray tower. The circulating nitrogen in the system is sprayed and washed by a spray tower in the nitrogen purification system through ethylene glycol to remove acetaldehyde in the nitrogen, and liquid drops carried by the nitrogen are separated by a demister to ensure that the purity of the nitrogen entering the preheater is high.
Further, a first heater is arranged on the air inlet pipeline, the first heater heats the purified nitrogen to 170 ℃, a second heater is arranged between the air inlet pipeline and the preheater, and the second heater heats the nitrogen to 200-220 ℃. The nitrogen gas that draws as preferredly through the defroster is high in purity, and the dew point is low, and the temperature is low, can heat preliminarily through first heater, again through second heater secondary heating raise the temperature to polycondensation reaction temperature for can be faster after nitrogen gas gets into the preheater promote the reaction go on, improve PET molecular weight, and take away acetaldehyde, but two heaters staged heating intensifies, can improve heater life, reduce the energy consumption.
Furthermore, the spray tower comprises three stages of spray layers, two spray nozzles are arranged in each stage of spray layer, and the spray flow of each spray nozzle in the second stage and the third stage is greater than that of the spray nozzle in the first stage. The spraying efficiency can be improved in a multiple way as the optimization, and the nitrogen circulation requirement of the system is met.
Furthermore, the second stage sprays the layer and the third stage sprays the layer and all is equipped with circulation mechanism in the spray column, and the second stage sprays the layer and sprays the spraying liquid circulation that flows out in the layer with first order, second stage and spray and constantly replaced by the fresh ethylene glycol that the first order let in. As the preferred such spray tower in the first stage sprays fresh ethylene glycol, the second stage, the third stage spray ethylene glycol that recycles, the ethylene glycol that sprays the layer and spray, acetaldehyde washing absorption effect increases progressively in the in-process that nitrogen gas flows, can carry out better acetaldehyde washing to nitrogen gas, more be favorable to improving the purity of nitrogen gas.
Furthermore, the temperature of the first-stage spraying layer spraying liquid and the second-stage spraying layer spraying liquid in the spraying tower is 3-10 ℃, and the temperature of the third-stage spraying layer spraying liquid is 10-35 ℃. Preferably, the heat exchange between the spray liquid and the nitrogen gas is improved, and the spray washing effect on acetaldehyde in the nitrogen gas can be improved.
Furthermore, in the nitrogen purification system, ethylene glycol and acetaldehyde in nitrogen are oxidized by using a catalyst, the temperature of the catalyst is 280-320 ℃, and the catalyst is increased by 50 kg compared with the previous catalyst, so that the catalytic effect is improved, and the catalytic efficiency is improved. Preferably, the effect of oxidizing ethylene glycol and acetaldehyde in nitrogen gas can be improved, and the effect of purifying nitrogen gas can be further improved.
In the prior art, nitrogen gas is directly sent into the preheater by a fan in a back flushing filter, the part of nitrogen gas contains glycol, acetaldehyde, moisture and the like, the purity is crossed at the bottom, impurities are more, the reaction of PET molecular chain growth is reversible reaction, the existence of glycol in the nitrogen gas is not beneficial to the reaction and the growth of PET molecular weight, the existence of moisture can also make the PET molecule generate hydrolysis, the acetaldehyde is still brought in by impure nitrogen gas, and the acetaldehyde amount in the PET is difficult to reduce.
The principle and the advantages of the invention are as follows: 1. compared with the conventional technology in which the nitrogen after the preheater and the reactor is directly introduced into the preheater for recycling after passing through a back-flushing filter, the invention further improves the purity of the nitrogen, and greatly reduces the contents of the acetaldehyde, the ethylene glycol and the moisture in the preheater. 2. According to the invention, the structure of the spray tower for purifying the nitrogen is improved, three-stage spraying is adopted, the flow of spraying liquid is increased step by step, the volume of the spray tower is increased, the nitrogen can be washed and purified in an incremental manner, and the effective purification of the circulating nitrogen is ensured. 3. The nitrogen flow, the nitrogen temperature, the spraying temperature, the catalysis temperature and the dosage are researched and improved, a PET production system with high nitrogen purification rate, high impurity catalysis rate, strong acetaldehyde removal capacity and remarkable energy-saving and consumption-reducing effects is formed, and the high-quality production requirement of PET is met.
Drawings
FIG. 1 is a schematic diagram showing the connection of a preheater and a nitrogen purification system in step C of example 1 of the present invention;
fig. 2 is a schematic structural view of a spray tower in embodiment 1 of the present invention.
Detailed Description
The following is further detailed by way of specific embodiments:
reference numerals in the drawings of the specification include: the system comprises a preheater 1, a back-flushing filter 2, a spray tower 3, a spray nozzle 31, a liquid collecting tank 32, a circulating pump 33, a heat exchanger 34, a demister 4, a fan 5, a first heater 6, a second heater 7, an air supply valve 8, an air inlet valve 9 and an exhaust valve 10.
Example 1, a process for producing low acetaldehyde PET comprising the steps of:
A. melt polymerization, mixing terephthalic acid, ethylene glycol, diethylene glycol, a catalyst, a stabilizer and the like, performing esterification reaction under certain conditions, and performing polycondensation reaction to obtain an amorphous basic slice;
B. crystallizing, namely crystallizing the amorphous basic slice obtained in the step A in a crystallizer in a nitrogen atmosphere to obtain a crystal slice;
C. preheating, namely further crystallizing the crystal slices in a preheater, introducing nitrogen purified by a nitrogen purification system into the preheater, wherein the flow of the nitrogen entering the preheater is 280 cubic meters per hour, and the nitrogen is heated to 220 ℃ before entering the preheater so that the temperature of the crystal slices in the preheater is raised to the corresponding temperature required by the polycondensation reaction, and the slices are kept in the preheater for about 3 hours;
D. tackifying, and further polycondensing the preheated slices, wherein the polycondensation reaction temperature is 200-220 ℃, and the polycondensation reaction time is 10-20 hours (the time is determined according to the yield variety).
Referring to fig. 1, in step C, the preheater 1 is communicated with the blowback filter 2, a blower 5 and an air inlet valve 9 are arranged on a pipeline between the preheater 1 and the blowback filter 2, and an air inlet pipeline for introducing purified nitrogen into the preheater 1 is communicated between the blowback filter 2 and the preheater 1. The nitrogen purification system comprises a spray tower 3 and a demister 4, an air inlet pipeline is connected with an air outlet of the demister 4, an air inlet of the demister 4 is communicated with an air outlet of the spray tower 3, an air outlet of the back flushing filter 2 is communicated with an air inlet of the spray tower 3, and an exhaust valve is arranged on a pipeline between the air outlet of the back flushing filter and the air inlet of the spray tower 3. The air inlet pipeline is provided with a first heater 6, the air inlet pipeline between the first heater 6 and the fan 5 is provided with an inlet air supply valve 8, the first heater 6 heats purified nitrogen to 170 ℃, a second heater 7 is arranged between the air inlet pipeline and the preheater 1, and the second heater 7 heats the nitrogen to 200-220 ℃.
Referring to fig. 2, the spray tower 3 used in the method comprises three stages of spray layers, each stage of spray layer is internally provided with two spray nozzles 31, each spray flow in the second stage and the third stage is larger than that of the first stage, the specific first stage spray layer sprays fresh glycol, the spray flow is adjusted in real time according to the yield, and the spray flow of each nozzle in the second stage spray layer and the third stage spray layer is 90T/H. The second level sprays the layer and the third level sprays the layer and all is equipped with circulation mechanism in spray tower 3, and the second level sprays the layer and includes collecting tank 32, and circulation mechanism is equipped with circulating pump 33 and heat exchanger 34 including connecting the circulation pipeline on collecting tank 32 on the circulation pipeline, and circulating pump 33 sprays the spray liquor that flows out in the layer with first order, second level and supplies to spray 31 circulation after the heat transfer and spray. The whole length of spray column 3 of improvement like this increases than prior art, sprays the ethylene glycol volume and doubles, increases the contact time of ethylene glycol and gas, improves heat exchange efficiency, can effectively spread the low molecular substance in the gas to the ethylene glycol to comprehensive effectual impurity of getting rid of in the nitrogen gas.
In the prior art, the acetaldehyde content of a PET crystal slice in a preheater 1 is about 2.5PPM in the production process, and the acetaldehyde content of a finished product PET is about 0.7 PPM. After the improved process method is adopted, the acetaldehyde content of the PET slices in the preheater 1 can be reduced to be lower than 1.8PPM, the acetaldehyde content of finished PET can be reduced to be lower than 0.6PPM, the viscosity of the product in the production process can be further improved, and the heating temperature can be reduced compared with that before optimization and improvement under the same condition, so that the corresponding energy consumption is reduced.
In the embodiment 2, the temperature of the first-stage spraying layer spraying liquid and the second-stage spraying layer spraying liquid in the spraying tower is 3 ℃, and the temperature of the third-stage spraying layer spraying liquid is 10 ℃. In the nitrogen purification system, ethylene glycol and acetaldehyde in nitrogen are oxidized by using a catalyst, the temperature of the catalyst is 280 ℃, and the amount of the catalyst is increased, so that the content of the catalyst is increased by one third on the basis of the prior art, and the nitrogen purification requirement of the system is met. After such a modification, the acetaldehyde content of the finished PET can be further reduced to below 0.5PPM based on example 1.
Example 3 in this example the flow of nitrogen into the preheater was 240 cubic meters per hour, the second heater heated the nitrogen to 210 ℃, the first and second stage spray levels in the spray tower at 7 ℃ and the third stage spray level at 25 ℃ with a catalyst temperature of 300 ℃.
The foregoing is merely an example of the present invention and common general knowledge in the art of specific structures and/or features of the invention has not been set forth herein in any way. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.
Claims (9)
1. A production method of low-acetaldehyde PET is characterized by comprising the following steps: the method comprises the following steps:
A. melt polymerization, mixing terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, a catalyst and a stabilizer for esterification, and then carrying out polycondensation to obtain an amorphous basic slice;
B. crystallizing, namely crystallizing the amorphous basic slice obtained in the step A in a crystallizer in a nitrogen atmosphere to obtain a crystal slice;
C. preheating, namely further heating and crystallizing the crystal slices in a preheater, and introducing nitrogen purified by a nitrogen purification system into the preheater;
D. thickening, and further polycondensing the heated crystal chips.
2. The process for producing low acetaldehyde PET of claim 1, wherein: the flow rate of the nitrogen entering the preheater in the step C is 200 and 280 cubic meters per hour.
3. The process for producing low acetaldehyde PET of claim 2, wherein: and C, communicating an air inlet pipeline for introducing purified nitrogen into the preheater between the back-blowing filter and the preheater.
4. A process for the production of low acetaldehyde PET as claimed in claim 3, wherein: and the nitrogen purification system in the step C comprises a spray tower and a demister, the air inlet pipeline is connected with an air outlet of the demister, an air inlet of the demister is communicated with an air outlet of the spray tower, and an air outlet of the back flushing filter is communicated with an air inlet of the spray tower.
5. The process for producing low acetaldehyde PET as claimed in claim 4, wherein: the air inlet pipeline is provided with a first heater, the first heater heats purified nitrogen to 170 ℃, a second heater is arranged between the air inlet pipeline and the preheater, and the second heater heats the nitrogen to 200-220 ℃.
6. The process for producing low acetaldehyde PET as claimed in claim 5, wherein: the spray tower comprises three stages of spray layers, two paths of spray nozzles are arranged in each stage of spray layer, and the spray flow of each path in the second stage and the third stage is greater than that of the first stage.
7. The process for producing low acetaldehyde PET of claim 6, wherein: the second stage sprays the layer and the third stage sprays the layer and all is equipped with circulation mechanism in the spray column, and the second stage sprays the layer and sprays the spraying liquid circulation that flows out in the layer with first order, second stage and spray and constantly replace through the fresh ethylene glycol that the first order let in.
8. The process for producing low acetaldehyde PET of claim 7, wherein: the temperature of the first-stage spraying layer spraying liquid and the second-stage spraying layer spraying liquid in the spraying tower is 3-10 ℃, and the temperature of the third-stage spraying layer spraying liquid is 10-35 ℃.
9. The process for producing low acetaldehyde PET of claim 8, wherein: ethylene glycol and acetaldehyde in nitrogen are oxidized by a catalyst in a nitrogen purification system, the temperature of gas entering the catalyst system is heated to be 280 ℃ and 320 ℃, and the catalyst is increased by 50 kilograms.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113461488A (en) * | 2021-07-30 | 2021-10-01 | 重庆万凯新材料科技有限公司 | Ethylene glycol circulating treatment process |
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Application publication date: 20201222 |