CN114516793A - Method for producing terephthalic acid ester by continuous esterification - Google Patents
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- 238000005886 esterification reaction Methods 0.000 title claims abstract description 333
- 230000032050 esterification Effects 0.000 title claims abstract description 298
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 23
- -1 terephthalic acid ester Chemical class 0.000 title claims abstract description 16
- 239000002002 slurry Substances 0.000 claims abstract description 152
- 238000000034 method Methods 0.000 claims abstract description 69
- 238000002360 preparation method Methods 0.000 claims abstract description 58
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 38
- 125000005233 alkylalcohol group Chemical group 0.000 claims abstract description 31
- 239000003054 catalyst Substances 0.000 claims abstract description 27
- 239000000463 material Substances 0.000 claims abstract description 24
- 230000008569 process Effects 0.000 claims abstract description 24
- 239000007787 solid Substances 0.000 claims abstract description 6
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 210
- 238000006243 chemical reaction Methods 0.000 claims description 52
- 239000007788 liquid Substances 0.000 claims description 42
- 239000000843 powder Substances 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 22
- 239000000203 mixture Substances 0.000 claims description 14
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 8
- JMXKSZRRTHPKDL-UHFFFAOYSA-N titanium ethoxide Chemical compound [Ti+4].CC[O-].CC[O-].CC[O-].CC[O-] JMXKSZRRTHPKDL-UHFFFAOYSA-N 0.000 claims description 8
- VXUYXOFXAQZZMF-UHFFFAOYSA-N titanium(IV) isopropoxide Chemical compound CC(C)O[Ti](OC(C)C)(OC(C)C)OC(C)C VXUYXOFXAQZZMF-UHFFFAOYSA-N 0.000 claims description 8
- 239000012295 chemical reaction liquid Substances 0.000 claims description 6
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 claims description 4
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 claims description 4
- ZXEKIIBDNHEJCQ-UHFFFAOYSA-N isobutanol Chemical compound CC(C)CO ZXEKIIBDNHEJCQ-UHFFFAOYSA-N 0.000 claims description 4
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 3
- KKEYFWRCBNTPAC-UHFFFAOYSA-L terephthalate(2-) Chemical compound [O-]C(=O)C1=CC=C(C([O-])=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-L 0.000 claims description 3
- QUVMSYUGOKEMPX-UHFFFAOYSA-N 2-methylpropan-1-olate;titanium(4+) Chemical compound [Ti+4].CC(C)C[O-].CC(C)C[O-].CC(C)C[O-].CC(C)C[O-] QUVMSYUGOKEMPX-UHFFFAOYSA-N 0.000 claims description 2
- HKJYVRJHDIPMQB-UHFFFAOYSA-N propan-1-olate;titanium(4+) Chemical compound CCCO[Ti](OCCC)(OCCC)OCCC HKJYVRJHDIPMQB-UHFFFAOYSA-N 0.000 claims description 2
- 230000006837 decompression Effects 0.000 claims 1
- 239000002253 acid Substances 0.000 abstract description 10
- 238000005265 energy consumption Methods 0.000 abstract description 8
- 239000011343 solid material Substances 0.000 abstract description 2
- 239000000047 product Substances 0.000 description 100
- WOZVHXUHUFLZGK-UHFFFAOYSA-N dimethyl terephthalate Chemical compound COC(=O)C1=CC=C(C(=O)OC)C=C1 WOZVHXUHUFLZGK-UHFFFAOYSA-N 0.000 description 48
- 239000002994 raw material Substances 0.000 description 26
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- 239000011344 liquid material Substances 0.000 description 12
- 239000012071 phase Substances 0.000 description 9
- 238000005516 engineering process Methods 0.000 description 8
- 238000011084 recovery Methods 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 7
- 230000009467 reduction Effects 0.000 description 7
- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 6
- URLKBWYHVLBVBO-UHFFFAOYSA-N Para-Xylene Chemical group CC1=CC=C(C)C=C1 URLKBWYHVLBVBO-UHFFFAOYSA-N 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 229920000728 polyester Polymers 0.000 description 6
- YJTKZCDBKVTVBY-UHFFFAOYSA-N 1,3-Diphenylbenzene Chemical group C1=CC=CC=C1C1=CC=CC(C=2C=CC=CC=2)=C1 YJTKZCDBKVTVBY-UHFFFAOYSA-N 0.000 description 5
- 238000009835 boiling Methods 0.000 description 5
- XGZNHFPFJRZBBT-UHFFFAOYSA-N ethanol;titanium Chemical compound [Ti].CCO.CCO.CCO.CCO XGZNHFPFJRZBBT-UHFFFAOYSA-N 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- RLJWTAURUFQFJP-UHFFFAOYSA-N propan-2-ol;titanium Chemical compound [Ti].CC(C)O.CC(C)O.CC(C)O.CC(C)O RLJWTAURUFQFJP-UHFFFAOYSA-N 0.000 description 4
- 239000002699 waste material Substances 0.000 description 4
- 229910010413 TiO 2 Inorganic materials 0.000 description 3
- 229920000180 alkyd Polymers 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 3
- 239000007795 chemical reaction product Substances 0.000 description 3
- 239000012528 membrane Substances 0.000 description 3
- 238000002156 mixing Methods 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 239000013589 supplement Substances 0.000 description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 150000001298 alcohols Chemical class 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- ONIHPYYWNBVMID-UHFFFAOYSA-N diethyl benzene-1,4-dicarboxylate Chemical compound CCOC(=O)C1=CC=C(C(=O)OCC)C=C1 ONIHPYYWNBVMID-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
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- 239000011148 porous material Substances 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- 150000003503 terephthalic acid derivatives Chemical class 0.000 description 2
- PXGZQGDTEZPERC-UHFFFAOYSA-N 1,4-cyclohexanedicarboxylic acid Chemical compound OC(=O)C1CCC(C(O)=O)CC1 PXGZQGDTEZPERC-UHFFFAOYSA-N 0.000 description 1
- LLLVZDVNHNWSDS-UHFFFAOYSA-N 4-methylidene-3,5-dioxabicyclo[5.2.2]undeca-1(9),7,10-triene-2,6-dione Chemical compound C1(C2=CC=C(C(=O)OC(=C)O1)C=C2)=O LLLVZDVNHNWSDS-UHFFFAOYSA-N 0.000 description 1
- YIMQCDZDWXUDCA-UHFFFAOYSA-N [4-(hydroxymethyl)cyclohexyl]methanol Chemical compound OCC1CCC(CO)CC1 YIMQCDZDWXUDCA-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
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- 239000000498 cooling water Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 150000005690 diesters Chemical class 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- IDGUHHHQCWSQLU-UHFFFAOYSA-N ethanol;hydrate Chemical compound O.CCO IDGUHHHQCWSQLU-UHFFFAOYSA-N 0.000 description 1
- 239000012847 fine chemical Substances 0.000 description 1
- 238000005984 hydrogenation reaction Methods 0.000 description 1
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- 238000011031 large-scale manufacturing process Methods 0.000 description 1
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- 239000011268 mixed slurry Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- QQVIHTHCMHWDBS-UHFFFAOYSA-N perisophthalic acid Natural products OC(=O)C1=CC=CC(C(O)=O)=C1 QQVIHTHCMHWDBS-UHFFFAOYSA-N 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
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Classifications
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/08—Preparation of carboxylic acid esters by reacting carboxylic acids or symmetrical anhydrides with the hydroxy or O-metal group of organic compounds
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a method for producing terephthalic acid ester by continuous esterification of purified terephthalic acid, which comprises the following steps: solid powdery purified terephthalic acid and part of esterified products circularly returned from the esterification tower or the flash tank are prepared into slurry, the slurry reacts with superheated alkyl alcohol steam in the esterification tower, a catalyst can be used or not used in the esterification process, part of generated materials are circularly returned to the slurry preparation kettle, and part of the generated materials are used as products and sent to the downstream. The method can continuously and stably convey the pure terephthalic acid solid material, and can simplify the flow, reduce the equipment investment, reduce the total alcohol acid ratio in the esterification process and reduce the material consumption and the energy consumption while ensuring the esterification rate.
Description
Technical Field
The invention belongs to the technical field of chemical industry, and particularly relates to a method for producing terephthalic acid ester by continuous esterification of terephthalic acid.
Background
Terephthalic esters, and in particular dimethyl terephthalate (DMT), have been the primary raw material for the production of polyesters, such as ethylene terephthalate (PET). The air-staged oxidation esterification method for synthesizing DMT by p-xylene was invented by Witten company in Germany and Hercules company in America at the end of the forty years, which was called four-stage method or Imhausen method, and was improved into a two-stage oxidation and two-stage esterification combined two-stage combined oxidation esterification method, which is called Witten method or Hercules method.
The polyester production by DMT is due to the difficulty in producing high-purity terephthalic acid, i.e., purified terephthalic acid (PTA, also known as terephthalic acid, terphthalic acid; pure terephthalic acid; terephthalic acid, 1, 4-phthalic acid) which meets the polymer production requirements by the current paraxylene production technology. Terephthalic acid has low solubility in almost all solvents and sublimes when heated to temperatures above 300 ℃, and is difficult to purify by conventional methods. DMT has stable property, can be dissolved in alcohols such as methanol, ethanol and the like, is easy to purify by adopting a recrystallization or rectification method, and can obtain DMT with high purity and meeting the production requirement of polyester. PTA can be produced by further hydrolyzing high-purity DMT.
In 1965, Amoco company developed a direct hydrorefining technology of crude terephthalic acid, i.e. crude acid was dissolved in hot water at 270 ℃ and 5.5MPa, and hydrogenated under the action of Pd/C catalyst, and then PTA product was recovered by crystallization. With the gradual improvement and maturity of the Amoco PTA technology, the production of PTA can be carried out without DMT, the flow is greatly simplified, and the production cost is reduced. After 90 s in the 20 th century, the production of PET polyester from PTA became the mainstream, and the DMT device of the original Witten method (also called Hercules method) was shut down gradually. Currently, only turkish, usa, korea and japan have a few DMT devices operating.
In addition to polyester production, terephthalate esters can be used to produce fine chemicals such as 1, 4-Cyclohexanedimethanol (CHDM) and 1, 4-cyclohexanedicarboxylic acid (CHDA) by hydrogenation, hydrolysis, and the like. At present, domestic CHDM manufacturers can only solve the problem of raw material source through import, and have high price, long supply period and high risk of being impacted by international supply chains. From 2005, the PTA capacity of a civil polyester enterprise in China is expanded in a large scale upstream, and by the beginning of 2021, the PTA capacity in China exceeds 6300 ten thousand tons/year, and by the year 2023, 2600 ten thousand tons/year PTA capacity is ready to be put in, so that the raw material source is sufficient, guaranteed and the cost is controllable. Therefore, the technology for producing the terephthalate by continuously esterifying the PTA serving as the raw material is developed, the problem that the sources of the terephthalate, especially DMT, in China are limited can be relieved, the downstream application field of the PTA can be expanded, and a new technical route is provided for solving the problem of potential excess PTA capacity.
In addition to the shut-down Witten process plant, there are a few kettle batch processes for the production of terephthalic acid esters using sulfuric acid as catalyst (Jiangsu chemical, 2001, 29(4), 32-34). However, the existing intermittent process is mainly applied to the process of recovering waste terephthalic acid, polyester resin waste chips and waste silk, has small yield, generates a large amount of waste acid and a large amount of washing wastewater in the production process, and has large treatment difficulty, large environmental pollution, serious equipment corrosion and high consumption quota of methanol. In addition, the batch esterification process is suitable for flexible production of various products in small scale. The continuous esterification process is suitable for large-scale production, and has the advantages of low cost, stable product quality, and easy realization of byproduct recovery and comprehensive energy optimization utilization. The technology of producing terephthalic acid ester by using PTA as a raw material and adopting a continuous esterification process is rarely reported.
The traditional Witten process is a continuous multistage oxidation multistage esterification process, esterification is carried out by adopting oxidation reaction products and alcohols, the oxidation reaction products are slurry liquid (Ullmann's Encyclopedia of Industrial Chemistry, Terphtalic acid, dimethyl terephthalate, and isophtalic acid,2000) under reaction conditions, and p-xylene exists in the slurry liquid in a solid form and is conveyed by a high-speed centrifugal pump. When the slurry oxidation reaction product of the esterification raw material is replaced by solid Purified Terephthalic Acid (PTA), the problem of PTA transportation is firstly solved to realize a continuous esterification method. As PTA can not be melted and is difficult to dissolve in almost any solvent, the PTA still needs to be conveyed in a slurry liquid mode, wherein PTA is a dispersed phase in the slurry liquid, and other liquid phases are continuous phases. Liquid alcohol esterified with PTA can be used as a continuous phase, for example, in the 70 s of the 20 th century, researchers have proposed using methanol as a continuous phase to prepare PTA slurry, and the methanol is used for dispersing PTA and also used as a reactant of esterification reaction. However, in order to ensure that the slurry is not blocked during the transportation process, the mass ratio of methanol to terephthalic acid is controlled to be more than 4:1 (petrochemical, 1979, 4, 230-. This results in a molar ratio of alkyd in excess of 20: 1. According to the stoichiometric ratio, the molar ratio of the alcohol acid reaches 2:1, and then the complete esterification of the PTA can be realized. Using methanol as the continuous phase will result in a molar ratio of alkyd of 10 times the stoichiometric ratio. Although the excessive methanol is beneficial to the esterification reaction, the methanol needs to be completely gasified in the esterification process, and the methanol with the stoichiometric ratio exceeding the stoichiometric ratio needs to be condensed and rectified after the reaction and is recovered in a liquid state, so that the ultrahigh ratio of the methanol to the acid causes a large amount of steam and circulating water consumption, and the energy consumption and the cost are increased. More importantly, at high temperature, PTA esterification is an endothermic reaction, and in order to achieve higher esterification rate, the esterification temperature is usually above 250 ℃, that is, the mixed slurry is heated to at least 250 ℃, which exceeds the critical temperature of common esterification solvents such as methanol, ethanol and the like (methanol critical temperature 240 ℃, ethanol critical temperature 243 ℃), so that the system needs to maintain very high pressure at the reaction temperature in order to keep PTA slurry state transportation. The system pressure is higher than 8MPa for methanol and higher than 6.5MPa for ethanol. The requirements on esterification equipment are high, the investment is increased, and the high operation pressure also brings challenges to daily maintenance and safety management.
The PTA slurry is prepared by adopting other high-boiling point solvents, although the preheating problem of the PTA slurry under lower pressure can be realized, the high-boiling point solvents are impurities in a reaction system, so a large amount of impurities not only bring great burden to subsequent product refining and increase investment and energy consumption, but also continuously supplement the solvents due to inevitable loss in the reaction and separation processes, and the material consumption is increased.
Disclosure of Invention
Aiming at the technical problems, the invention provides a continuous esterification technology taking Purified Terephthalic Acid (PTA) and alkyl alcohol as raw materials, which can continuously carry out esterification reaction under the condition of using a catalyst or not using the catalyst, has low esterification pressure, short flow, stable quality and is suitable for large-scale industrialization; compared with the reported technology, the molar ratio of the alkyd is greatly reduced, the energy consumption and material consumption are reduced, and the cost is reduced.
In order to achieve the purpose, the technical method adopted by the invention comprises the following contents:
the PTA powder material is fed into slurry-preparing still in the form of solid state, in the slurry-preparing still the PTA powder material, circulating esterified product (target product terephthalic acid diester whose mass content is greater than 94% and small quantity terephthalic acid monoester and trace unconverted PTA) and catalyst are fully mixed to obtain slurry material, then the above-mentioned slurry material is pressurized by slurry pump, and fed into heat exchanger of esterification tower, after the heat exchange is reached to reaction temperature, the above-mentioned material is fed into upper portion of esterification tower, the lower portion of esterification tower is fed into superheated alkyl alcohol steam, the material is undergone the esterification reaction in the esterification tower, the bottom product of esterification tower is passed through filter to remove TiO produced by catalyst 2After the fine powder is obtained, the pressure is reduced in a flash tank to remove light components (a small amount of alkyl alcohol dissolved in the esterification product under high pressure) dissolved in the fine powder, and part of the light components is recycled to the slurry preparation kettle to prepare slurry and part of the light components goes to the downstream.
In the method, the granularity of the PTA powder is 30-500 μm, preferably 50-250 μm, and more preferably 75-175 μm.
In the method, the mass ratio of PTA to the recycled esterified product in the slurry preparation is 1: 0.8-20, preferably 1: 1-10, and more preferably 1: 2-6.
In the method, the reaction conditions in the esterification tower are as follows: the molar ratio of the superheated alkyl alcohol steam to the PTA in the slurry liquid is 2.2-10: 1, the reaction temperature is 200-320 ℃, the reaction pressure (gauge pressure) is 0.5-5 MPa, and the hourly space velocity of the reaction liquid is 0.05h-1～10h-1Preferred reaction conditions are as follows: the molar ratio of the superheated alkyl alcohol vapor to the PTA in the slurry liquid is 2.5-8: 1, the reaction temperature is 220-300 ℃, the reaction pressure (gauge pressure) is 1-4 MPa, and the hourly space velocity of the reaction liquid is 0.1h-1～5h-1Further preferred reaction conditions are as follows: the molar ratio of the superheated alkyl alcohol vapor to the PTA in the slurry liquid is 3-6: 1, the reaction temperature is 240-285 ℃, the reaction pressure (gauge pressure) is 2-3.5 MPa, and the hourly space velocity of the reaction liquid is 0.2h -1～1.5h-1。
In the above method, the alkyl alcohol may be methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, or the like. Methanol, ethanol and isopropanol are preferred, and methanol and ethanol are further preferred.
In the method, the catalyst can be added at any position between the inlet of the slurry preparation kettle and the inlet of the esterification tower at one time, or added at different positions between the inlet of the slurry preparation kettle and the inlet of the esterification tower at multiple times.
In the above method, the catalyst may be one or a mixture of two or more of tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, and tetraisobutyl titanate. Preferably one or a mixture of two or more of tetraethyl titanate, tetraisopropyl titanate and tetra-n-butyl titanate.
In the method, the ratio of the total mass flow of the catalyst added at one time or in multiple times to the mass flow of the PTA is 0.03-2: 100, and the preferable ratio is 0.1-1: 100.
In the above process, the catalyst may not be used, i.e., no catalyst is used in the entire esterification process. When no catalyst is used, the filter may be omitted.
In the above method, the operating pressure (gauge pressure) of the flash tank is 0.1 to 2MPa, preferably 0.2 to 1 MPa.
In the method, the circulating esterification product can be circulated back to the slurry preparation kettle from the outlet of the flash tank, and can also be pumped out from any position from the outlet of the filter to the inlet of the flash tank and circulated back to the slurry preparation kettle.
In the method, the temperature of the circulating esterification product is 195-345 ℃, preferably 215-295 ℃, and further preferably 235-280 ℃.
In the method, the esterification tower is divided into two or more esterification devices.
The slurry pump can also be a centrifugal pump or a high-speed centrifugal pump or a gear pump;
by adopting the technical scheme of the invention, the method has the following beneficial effects:
the invention discloses a method for preparing terephthalic acid ester by continuous esterification of purified terephthalic acid, which adopts a part of esterified products, mainly terephthalic acid diester with higher boiling point, as a continuous phase to prepare slurry liquid of PTA raw material. In a general chemical process, after a product and unreacted raw materials are separated at an outlet of a reaction device, the unreacted raw materials are recycled to the inlet of the reaction device, so that the total conversion rate and the raw material utilization rate are improved. The method provided by the invention recycles part of the product to the slurry preparation kettle at the outlet of the reaction equipment (esterification tower), thereby reducing the cost of the esterification process and saving the investment while ensuring the continuous and stable transportation of the PTA. Compared with the scheme of preparing slurry liquid by adopting alkyl alcohol as a continuous phase, the method provided by the invention reduces the alcohol-acid ratio in the esterification process, reduces the circulation of excessive alkyl alcohol, saves the consumption of electric power, steam and circulating cooling water, and reduces the operation cost; greatly reduces the pressure of the esterification reaction, thereby reducing the pressure grade of equipment and saving investment. Compared with the scheme of preparing the slurry by adopting other solvents with high boiling points as continuous phases, the method provided by the invention adopts partial products as the continuous phases, and the products are continuously generated in the reaction process without additional supplement or additional separation facilities for recovering the solvents, thereby reducing the investment and the operation cost.
The method can continuously and stably convey the pure terephthalic acid solid material, and can simplify the process, reduce the equipment investment, reduce the total alcohol acid ratio in the esterification process and reduce the material consumption and the energy consumption while ensuring the esterification rate.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention and are not intended to limit the invention.
FIG. 1 is a flow chart of continuous esterification of purified terephthalic acid to produce terephthalic acid esters.
Fig. 2 is a flowchart of comparative example 1.
Fig. 3 is a flowchart of comparative example 2.
The reference numbers in fig. 1 are: 1. a slurry preparation kettle 2, a slurry pump 3, an esterification tower heat exchanger 4, an esterification tower 5, a filter 6 and a flash tank.
The reference numbers in fig. 2 are: 1. the system comprises a slurry preparation kettle 2, a slurry pump 3, a tubular reactor heat exchanger 4, a tubular reactor 5, a throttle valve 6, an esterification tower heat exchanger 7, an esterification tower 8 and a flash tank.
The reference numbers in fig. 3 are: 1. the system comprises a slurry preparation kettle, 2, a slurry pump, 3, an esterification tower heat exchanger, 5, a filter, 6, a flash tank, 7, a solvent recovery tower, 8, a condenser, 9, a reflux tank, 10, a reboiler, 11 and a reflux pump.
Detailed Description
The following examples further illustrate the embodiments of the present invention in detail. The following examples are for the understanding of the present invention and are not to be construed as limiting the process of the present invention.
The apparatus and connection used in the following embodiments of the present invention are shown in fig. 1. According to the flow sequence of materials, the method comprises the following steps: a slurry preparation kettle 1, a slurry pump 2, an esterification tower heat exchanger 3, an esterification tower 4, a filter 5 (when a catalyst is not used, the filter can be omitted), and a flash tank 6; when the device is operated for the first time, the esterification tower does not output the esterified product. The esterification product is terephthalic acid diester with the mass content of more than 98 percent, so that the terephthalic acid diester to be produced corresponding to the used alkyl alcohol raw material can be purchased to replace the circulated liquid esterification product after operation and added into the slurry preparation kettle for the first operation of the device. If the alkyl alcohol is methanol, then dimethyl terephthalate is purchased; for example, the alkyl alcohol is ethanol. Diethyl terephthalate is purchased and so on. During the first operation, molten terephthalic acid diester is used for replacing an esterification product to prepare PTA slurry, the reaction is started, and after the esterification product is produced, circulation can be established. During the shutdown and overhaul period of the device, some esterification products can be reserved for start-up after overhaul.
Example 1
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 16.6kg/h and 66.4kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 19.2kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam to carry out esterification reaction, the operating temperature of the esterification tower is 270 ℃, and the pressure (gauge pressure) of the top of the esterification tower is 2.6MPa, and the liquid hourly space velocity (volumetric flow of slurry liquid divided by volume of esterification tower) is 0.25h-1The surplus methanol steam and water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is an esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, alkyl alcohol which is slightly dissolved in the esterification product under high pressure is removed through pressure reduction in the flash tank, part of the esterification product is circulated back to a slurry preparation kettle at 66.4kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 98.8 percent.
Under the conditions listed in example 1, the plant was operated continuously for 1000h, and no fouling of the esterification column heat exchanger was observed.
Comparative example 1
The apparatus and connection relationship used are shown in fig. 2.
Adding PTA powder with the particle size of 90-140 mu m and methanol into a slurry preparation kettle at the feeding rates of 16.6kg/h and 65.7kg/h respectively to prepare slurry, then pumping the slurry into a pre-esterification heat exchanger by a slurry pump to heat to 260 ℃, reacting the mixed material in a pre-esterification reactor, wherein the temperature is 260 ℃, the pressure (gauge pressure) is 8.0MPa, and the liquid hourly space velocity is 1.5h-1. The material at the outlet of the pre-esterification reactor is decompressed to 2.5MPa (gauge pressure) through a throttle valve, and enters an esterification tower after heat exchange in a heat exchanger of the esterification tower is carried out to 270 ℃; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters an esterification tower from the lower part at the flow rate of 14.1kg/h, liquid materials and the superheated methanol steam are in countercurrent contact for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.5MPa, excessive methanol steam and water generated by the esterification reaction leave the esterification tower from the top, and an esterification product is obtained at the bottom of the esterification tower. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.7 percent, and the selectivity of dimethyl terephthalate is 98.6 percent.
In order to ensure that the esterification of PTA is complete, the molar ratio of methanol to PTA needs to exceed the stoichiometric ratio, in all embodiments and comparative examples, the mixture of alkyl alcohol and water at the top of the esterification tower needs to be recovered, the methanol is separated and recycled, the methanol and water are usually separated by adopting a rectification mode, in order to ensure the separation effect and reduce the loss of the methanol, the methanol at the top of the rectification tower needs to be cooled to 30-40 ℃, the temperature needs to be preheated to more than 200 ℃ before the reaction, energy recovery equipment needs to be arranged, and certain steam, electricity and circulating water are consumed, so that the smaller the excess of the methanol is, the better the esterification effect is ensured. The preparation of slurry with methanol inevitably increases the degree of excess methanol, increases the size of the equipment and increases the energy consumption. In addition, the pressure of the slurry liquid of the methanol and the PTA can be continuously increased to 8MPa in the process of preheating to the reaction temperature, so that the pressure grades of pipelines, valves and equipment are improved, and the investment is increased. Compared with comparative example 1, in example 1, the excessive methanol content is greatly reduced and the high-pressure tubular reactor is omitted. In the case of a slurry with methanol, a high-pressure reactor is required for the pre-esterification.
Comparative example 2
The device and connection relationship used are shown in fig. 3.
Adding PTA powder with the granularity of 90-140 mu m and m-terphenyl into a slurry preparation kettle at the feeding rates of 16.6kg/h and 68.1kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of an esterification tower by a slurry pump, and after heat exchange is carried out to 270 ℃, sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters an esterification tower from the lower part of the esterification tower at the flow rate of 19.2kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.6MPa, and the liquid hourly space velocity is 0.25h-1The excessive methanol steam and water generated by the esterification reaction leave the esterification tower from the top, the effluent at the bottom of the tower is a mixture of terephthalic acid esterification products and m-terphenyl, the pressure of the mixture is reduced to 0.4MPa (gauge pressure) through a flash tank, the mixture enters a solvent recovery tower, the terephthalic acid ester and the m-terphenyl are high-boiling-point substances, the solvent recovery tower adopts the pressure reduction operation to reduce the boiling points of the terephthalic acid ester and the m-terphenyl, the terephthalic acid esterification products are recovered at the top of the tower, the recovered m-terphenyl is recycled to a slurry preparation kettle at the bottom of the tower, and the slurry preparation kettle supplements the solvent lost in the recovery process. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 98.6 percent.
Example 2
Adding PTA powder with the granularity of 250-475 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 16.6kg/h and 66.4kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 19.2kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) of the top of the tower is 2.6MPa, and the liquid hourly space velocity is 0.25h-1The surplus methanol steam and the water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is the esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank (the pressure in the flash tank is reduced to remove a small amount of alkyl alcohol dissolved in the esterification product under high pressure), part of the esterification product is recycled to the slurry preparation kettle at 66.4kg/h, and the rest is the esterification product which is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.0 percent, and the selectivity of dimethyl terephthalate is 97.3 percent.
Example 3
Adding PTA powder with the particle size of 38-75 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 16.6kg/h and 66.4kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 19.2kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) of the top of the tower is 2.6MPa, and the liquid hourly space velocity is 0.25h -1The surplus methanol steam and water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is an esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, alkyl alcohol which is slightly dissolved in the esterification product under high pressure is removed through pressure reduction in the flash tank, part of the esterification product is circulated back to a slurry preparation kettle at 66.4kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 99.3 percent.
Examples 1 to 3 show that too large a PTA particle size results in a decrease in the esterification rate, and that a small particle size of PTA facilitates acceleration of the esterification reaction. The method provided by the invention is feasible when the granularity of PTA powder is 30-500 mu m, and the granularity distribution is narrower, so that the viscosity of slurry is favorably reduced, and the granularity is more preferably 50-250 mu m. The average particle size of commercial PTA is between 100 and 130 μm, and the particle size of small PTA requires additional equipment, such as an airflow crushing mill, to crush the raw material, resulting in increased equipment investment and operation cost. The operation cost and the esterification rate are comprehensively considered, and the thickness is further preferably 75-175 mu m.
Example 4
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 30.0kg/h and 57.3kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 34.7kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.6MPa, and the liquid hourly space velocity is 0.25h -1The surplus methanol vapor and the water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is the esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, the pressure of the esterification product is reduced in the flash tank, a small amount of alkyl alcohol dissolved in the esterification product under high pressure is removed, part of the esterification product is circulated to a slurry preparation kettle at the speed of 57.3kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.7 percent, and the selectivity of dimethyl terephthalate is 98.4 percent.
Under the conditions outlined in example 4, the pressure drop across the esterification column heat exchanger increased significantly (from 70kPa to 200kPa) after 120 hours of plant operation, indicating that the slurry concentration was too high, causing PTA solids to settle within the heat exchanger, resulting in heat exchanger plugging. Under high slurry concentration, the continuous operation can be ensured by adopting a mode of switching after more than 2 heat exchangers are connected in parallel (more than 2 heat exchangers are respectively connected in parallel between a slurry pump and an esterification tower through pipelines), when the pressure drop of the used heat exchanger reaches a set value (such as 200kPa), the heat exchanger is switched to a standby heat exchanger, and the original heat exchanger is disassembled and cleaned and then is reassembled for standby.
Example 5
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 12.6kg/h and 69.0kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters an esterification tower from the lower part of the esterification tower at the flow rate of 14.6kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.6MPa, and the liquid hourly space velocity is 0.25h -1The surplus methanol steam and the water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is an esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, alkyl alcohol which is slightly dissolved in the esterification product under high pressure is removed through pressure reduction in the flash tank, part of the esterification product is circulated to a slurry preparation kettle at the rate of 69.0kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 99.1 percent.
It can be seen from comparison between example 1 and example 4 that the slurry concentration is too high, which can cause the heat exchange equipment and the pipeline elbow to be blocked under the condition of long-time operation, and to ensure continuous operation, backup equipment (such as an esterification tower heat exchanger) needs to be arranged, so that the equipment investment is increased, and the workload of periodical cleaning is increased, which results in the increase of maintenance cost. Comparing example 1 with example 5, it can be seen that reducing the slurry concentration does not result in plugging, but under the same reaction conditions, the throughput of PTA feed is reduced and the plant capacity is reduced. Although the PTA throughput can be increased by increasing the liquid hourly space velocity appropriately, the amount of recycled esterification product increases accordingly, resulting in increased power consumption. The mass ratio of PTA to the circulating esterification product is 1: 0.8-20 when the slurry is prepared, 1: 1-10 is preferable for prolonging the cleaning period and improving the equipment generating capacity, and 1: 2-6 is further preferable for improving the stability and the economical efficiency of the process flow by considering the removal of backup equipment.
Example 6
Adding PTA powder and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at feeding rates of 16.6kg/h and 76.1kg/h respectively, preparing slurry, mixing the slurry with tetraethyl titanate with the flow rate of 65g/h at a slurry pump inlet, arranging a static mixer or other mixing facilities when adding a catalyst at a position outside the slurry preparation kettle, mixing part of slurry liquid flowing out of the slurry preparation kettle with the catalyst, introducing the mixture into the slurry pump inlet to ensure that the catalyst and the slurry liquid flowing out of the slurry preparation kettle are uniformly mixed, pressurizing the slurry pump, sending the mixture into an esterification tower heat exchanger to exchange heat to 270 ℃, sending the mixture into the esterification tower from the middle upper part of the esterification tower, sending superheated ethanol steam with the pressure of 270 ℃, sending the superheated ethanol steam with the pressure of 3.2MPa into the esterification tower from the lower part of the esterification tower at the flow rate of 9.2kg/h, carrying out esterification reaction by countercurrent contact between the liquid material and the superheated ethanol steam in the esterification tower, the operating temperature of the esterification tower is 260 ℃, the pressure (gauge pressure) at the top of the tower is 2.8MPa, and the liquid hourly space velocity is 0.27h-1Excess ethanol vapor and water from the esterification reaction exit the esterification column overhead and the bottoms stream is the esterification product. Catalyst tetraethyl titanate and esterification product water react to generate TiO 2Filtering TiO from the material at the outlet of the esterification tower by a filter2Then the mixture enters a flash tank to be decompressed to 0.2MPa (gauge pressure) (the flash tank is decompressed to remove a small amount of alkyl alcohol dissolved in the esterified product under high pressure), wherein part of the esterified product is recycled to the slurry preparation kettle at 76.1kg/h, and the rest part of the esterified product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 98.5%, and the selectivity of diethyl terephthalate is 94.8%.
Example 7
Adding PTA powder with the granularity of 90-140 mu m, a liquid esterification product circulated by an esterification tower and tetraisopropyl titanate into a slurry preparation kettle at feeding rates of 23.2kg/h, 93.0kg/h and 70g/h respectively, preparing slurry, sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 3.0MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 24.0kg/h, and liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steamThe esterification reaction is carried out, the operating temperature of the esterification tower is 270 ℃, the pressure (gauge pressure) at the top of the tower is 2.6MPa, and the liquid hourly space velocity is 0.35h-1Excess methanol vapor and water from the esterification reaction exit the esterification column overhead and the bottoms stream is the esterification product. Catalyst tetraisopropyl titanate and esterified product water react to produce TiO 2Filtering TiO from the material at the outlet of the esterification tower by a filter2Then, 93.0kg/h of partial esterification product is circulated back to the slurry preparation kettle, and the rest part is decompressed to 0.4MPa (gauge pressure) by a flash tank (the pressure in the flash tank is reduced to remove a small amount of alkyl alcohol dissolved in the esterification product under high pressure), and the product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 99.5 percent.
Example 8
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 16.6kg/h and 66.4kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 240 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 250 ℃ and the pressure of 2.5MPa enters an esterification tower from the lower part of the esterification tower at the flow rate of 19.2kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 250 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.0MPa, and the liquid hourly space velocity is 0.25h-1The surplus methanol steam and water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is an esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, alkyl alcohol which is slightly dissolved in the esterification product under high pressure is removed through pressure reduction in the flash tank, part of the esterification product is circulated back to a slurry preparation kettle at 66.4kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 98.2 percent, and the selectivity of dimethyl terephthalate is 95.3 percent.
Example 9
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 19.9kg/h and 79.7kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 285 ℃, and then carrying out esterificationThe middle upper part of the tower enters an esterification tower; superheated methanol steam with the temperature of 280 ℃ and the pressure of 2.5MPa enters an esterification tower from the lower part of the esterification tower at the flow rate of 23.0kg/h, liquid materials in the esterification tower are in countercurrent contact with the superheated methanol steam for esterification reaction, the operating temperature of the esterification tower is 285 ℃, the pressure (gauge pressure) at the top of the esterification tower is 2.0MPa, and the liquid hourly space velocity is 0.3h-1The surplus methanol steam and the water generated by the esterification reaction leave the esterification tower from the top, the bottom effluent is an esterification product, the pressure of the esterification product is reduced to 0.4MPa (gauge pressure) through a flash tank, alkyl alcohol which is slightly dissolved in the esterification product under high pressure is removed through pressure reduction in the flash tank, part of the esterification product is recycled to a slurry preparation kettle at 79.7kg/h, and the rest of the esterification product is sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.9 percent, and the selectivity of dimethyl terephthalate is 98.4 percent.
As can be seen from the examples 1 and 8 to 9, the esterification rate is reduced and the PTA conversion rate and diester selectivity are reduced due to the reduction of the esterification temperature, the equilibrium conversion rate of PTA is lower than 80% at the temperature of below 200 ℃, and the production capacity of equipment is too low. The esterification rate can be improved by increasing the temperature, the production capacity of equipment is improved, but the esterification temperature exceeds 285 ℃, a small amount of methanol can generate side reaction to generate dimethyl ether, and the dimethyl ether is obviously increased by exceeding 320 ℃. The formation of dimethyl ether leads to an increase in methanol consumption and a complicated flow of the subsequent methanol recovery. The reaction temperature is 200-320 ℃, the method provided by the invention is feasible, the equipment production capacity is considered to be improved, the reaction temperature is preferably 220-300 ℃, the equipment production capacity and the side reaction of methanol are comprehensively considered, and the reaction temperature is further preferably 240-285 ℃.
Example 10
Adding PTA powder with the granularity of 90-140 mu m and a liquid esterification product circulated by an esterification tower into a slurry preparation kettle at the feeding rates of 26.6kg/h and 106.3kg/h respectively to prepare slurry, then sending the slurry into a heat exchanger of the esterification tower by a slurry pump, exchanging heat to 270 ℃, and then sending the slurry into the esterification tower from the middle upper part of the esterification tower; superheated methanol steam with the temperature of 270 ℃ and the pressure of 2.8MPa enters the esterification tower from the lower part of the esterification tower at the flow rate of 30.7kg/h, liquid materials and the superheated methanol steam are in countercurrent contact in the esterification tower for esterification reaction, the operating temperature of the esterification tower is 270 ℃, and the pressure (gauge pressure) of the top of the tower is2.3MPa and liquid hourly space velocity of 0.40h-1Excess methanol vapor and water produced by the esterification reaction leave the esterification tower from the top, the bottom effluent is esterification products, part of the esterification products are recycled to the slurry preparation kettle at 106.3kg/h, and the rest part of the esterification products are decompressed to 0.3MPa (gauge pressure) through a flash tank (the pressure in the flash tank is reduced to remove a small amount of alkyl alcohol dissolved in the esterification products under high pressure), and the esterification products are sent to the downstream. Based on the PTA raw material, the conversion rate of PTA of the bottom product of the esterification tower is 99.6 percent, and the selectivity of dimethyl terephthalate is 96.7 percent.
The results show that the method provided by the invention can reduce the total alcohol acid ratio in the esterification process, simplify the flow, reduce high-pressure equipment and high-energy-consumption solvent recovery equipment, reduce the investment and reduce the circulation of excessive alkyl alcohol and the consumption of steam, electric power and circulating water. The catalyst can accelerate the rate of esterification reaction and improve the production capacity of equipment, but the catalyst reacts with water generated by the esterification reaction to generate TiO 2Therefore, it is necessary to provide a filter, such as a ceramic membrane filter having a pore size in the range of 50 to 500nm (in the embodiment of the present invention, a ceramic membrane filter having a pore size of 300 nm), for removing TiO from the ceramic membrane filter2. The filter can be omitted without the use of a catalyst. Due to the difference of raw materials, compared with the Witten method, the method disclosed by the invention has the advantages that the process is greatly simplified, and compared with other PTA esterification technologies, the energy consumption, the investment and the material consumption can be greatly reduced, so that the method has good economic benefits.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The invention has been described with reference to an exemplary embodiment, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to other means and applications having the same functionality.
Claims (10)
1. A method for producing terephthalate by continuous esterification is characterized in that:
the production of terephthalic acid ester is carried out by adopting an esterification tower, PTA (purified terephthalic acid) powder enters a slurry preparation kettle in a solid state form, the PTA powder and an esterification product circularly returned to the slurry preparation kettle are mixed in the slurry preparation kettle to prepare slurry, the slurry is pressurized by a slurry pump and then sent to a heat exchanger of the esterification tower, the slurry enters the middle part and/or the upper part of the esterification tower after heat exchange is carried out to reaction temperature, superheated alkyl alcohol steam is introduced into the lower part of the esterification tower, and the material is subjected to esterification reaction in the esterification tower; the surplus methanol steam and water generated in the esterification reaction exit the esterification tower from the top, and the bottom effluent is the esterification product produced in the esterification tower;
one part of the bottom effluent is used as an esterification product and circulated back to the slurry preparation kettle, and the rest part is decompressed by the flash tank and is a target esterification product; or, the bottom effluent is decompressed by a flash tank, part of the bottom effluent is used as the esterification product and circulated back to the slurry preparation kettle, and the rest part is used as the target esterification product.
2. The method of claim 1, wherein: the granularity of the PTA powder is 30-500 mu m, preferably 50-250 mu m, and further preferably 75-175 mu m.
3. The method of claim 1, wherein: the mass ratio of PTA to the circulating esterification product in the slurry preparation is 1: 0.8-20, preferably 1: 1-10, and further preferably 1: 2-6.
4. The method of claim 1, wherein: the reaction conditions in the esterification tower are as follows: the molar ratio of the superheated alkyl alcohol steam to the PTA in the slurry liquid is 2.2-10: 1, the reaction temperature is 200-320 ℃, the reaction pressure (gauge pressure) is 0.5-5 MPa, and the hourly space velocity of the reaction liquid is 0.05h-1～10h-1Preferred reaction conditions are as follows: the molar ratio of the superheated alkyl alcohol vapor to the PTA in the slurry liquid is 2.5-8: 1, the reaction temperature is 220-300 ℃, the reaction pressure (gauge pressure) is 1-4 MPa, and the hourly space velocity of the reaction liquid is 0.1h-1～5h-1Further, furtherPreferred reaction conditions are as follows: the molar ratio of the superheated alkyl alcohol vapor to the PTA in the slurry liquid is 3-6: 1, the reaction temperature is 240-285 ℃, the reaction pressure (gauge pressure) is 2-3.5 MPa, and the hourly space velocity of the reaction liquid is 0.2h-1～1.5h-1。
5. The method according to claim 1 or 4, wherein the alkyl alcohol is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, etc.; one or more of methanol, ethanol and isopropanol are preferred, and one or two of methanol and ethanol are further preferred;
the temperature of the superheated alkyl alcohol steam is 200-320 ℃, and the pressure is 1-5.5 MPa; the preferred temperature is 220-300 ℃, and the pressure is 1.5-4.5 MPa; further preferably, the temperature is 240 to 285 ℃ and the pressure is 2.5 to 4.0 MPa.
6. The method of claim 1, wherein: adding a catalyst into an esterification tower of the esterification reaction, wherein the catalyst can be one or a mixture of more than two of tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate and tetraisobutyl titanate; preferably one or a mixture of more than two of tetraethyl titanate, tetraisopropyl titanate and tetra-n-butyl titanate;
the ratio of the total mass flow of the added catalyst to the mass flow of the PTA is 0.03-2: 100, and the preferable ratio is 0.1-1: 100.
Removing TiO produced by catalyst from esterification product flowing out of the bottom of the esterification tower through a filter2After the fine powder is obtained, the fine powder enters a flash tank for decompression; the circulating esterification product can be circulated back to the slurry preparation kettle from the outlet of the flash tank, and can also be pumped out from any position of a connecting pipeline between the outlet of the filter and the inlet of the flash tank to be circulated back to the slurry preparation kettle.
7. The method of claim 6, wherein: the catalyst can be added into the slurry preparation kettle at a material inlet of the slurry preparation kettle or added at any position of a connecting pipeline between the slurry preparation kettle and the material inlet of the esterification tower at one time; or, adding the mixture into the slurry preparation kettle from the material inlet of the slurry preparation kettle, or adding the mixture into the slurry preparation kettle for more than 2 times from the same or different positions of a connecting pipeline between the slurry preparation kettle and the material inlet of the esterification tower.
8. The method of claim 1, wherein: the operating pressure (gauge pressure) of the flash tank is 0.1-2 MPa, preferably 0.2-1 MPa.
9. The method of claim 1, wherein: the temperature of the circulating esterification product introduced into the slurry preparation kettle is 195-345 ℃, preferably 215-295 ℃, and further preferably 235-280 ℃; the circulating esterification product is a target esterification product terephthalic acid diester with the mass content of more than 94 percent; wherein the impurities are terephthalic acid monoester and unconverted PTA generated in the esterification process.
10. The method of claim 1, wherein: the esterification tower is two or more than three esterification tower devices which are connected in parallel or in series-parallel connection between the esterification tower heat exchanger and the flash tank through pipelines;
when the device is operated for the first time, the esterification product added into the slurry preparation kettle is the target esterification product terephthalic acid diester to be produced, the mass content of which is more than or equal to 98%.
Priority Applications (1)
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| CN116589353A (en) * | 2023-05-16 | 2023-08-15 | 杭州迈科瑞科技有限公司 | Method for preparing dibutyl terephthalate by microreactor |
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| CN105111074A (en) * | 2015-07-20 | 2015-12-02 | 浙江大学 | Methyl esterification recycling method of alkali decrement wastewater solid residue |
| CN111635317A (en) * | 2020-06-29 | 2020-09-08 | 福建春达化工有限公司 | Energy-saving technology for esterification reaction of dioctyl terephthalate (DOTP) |
| CN113620804A (en) * | 2021-09-13 | 2021-11-09 | 盐城市春竹香料有限公司 | Continuous esterification process and device for ethyl 2-methylbutyrate |
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| CN105111074A (en) * | 2015-07-20 | 2015-12-02 | 浙江大学 | Methyl esterification recycling method of alkali decrement wastewater solid residue |
| CN111635317A (en) * | 2020-06-29 | 2020-09-08 | 福建春达化工有限公司 | Energy-saving technology for esterification reaction of dioctyl terephthalate (DOTP) |
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