Process and apparatus for the preparation of polyester polyols

Abstract

The application provides a preparation method and a process device of polyester polyol. Specifically, a two-stage membrane material assembly device is provided. The first stage is a PSF or PVDF coated base film assembly which is directly connected with a gas phase outlet of a polyester reaction kettle, can intercept small molecule alcohol ester in the gas phase reaction product, and refluxes to the reaction kettle. Water and other components generated by the reaction can pass through and enter the second stage separation membrane. The second stage is an adsorption de-aldehyde component modified pervaporation membrane assembly. The prepared adsorption membrane separation material solves the problems of complex esterification reaction dehydration and impurity removal process, low rectification separation efficiency, and the inability to recover byproducts and three wastes, innovates the traditional intermittent polyester production process with low reaction efficiency and long operation period, and has a wide application prospect in the polyester polyol synthesis field.

Description

Technical Field

[0001] This invention belongs to the field of polyester polyol production technology, specifically relating to a method and apparatus for preparing polyester polyols. Background Technology

[0002] Polyester polyols are one of the important raw materials for polyurethane synthesis, widely used in various industries such as TPU, CPU, PUR, inks, and dry lamination. They are usually produced by the esterification condensation or transesterification reaction of polycarboxylic acids or anhydrides with polyols, and are mostly produced in batch reactors. Conventional polyester polyols can generally be divided into aliphatic polyols and aromatic polyols, as well as polycaprolactone polyols and polycarbonate diols. The structure and properties of polyester polyols often determine the performance of polyurethane materials. With the continuous development and expansion of the application and production capacity of polyester polyols, improving production efficiency and reducing process energy and material consumption have become key to the development of the polyester industry.

[0003] Polyester polyol production generally employs a batch reactor process, with a total operation cycle of 20-40 hours. It can be broadly divided into three stages: feedstock addition, esterification heating, and vacuum polycondensation. Taking butanediol-based polyester as an example, the material undergoes heating and reaction, continuously producing esterification water, along with small-molecule alcohol esters, byproducts such as tetrahydrofuran and acetaldehyde. This gaseous product is separated by a distillation column, and reflux is used to control the column top temperature at around 100°C, allowing the higher-boiling-point small-molecule alcohol esters to return from the bottom of the column to the reactor for further reaction. However, existing technologies suffer from low distillation separation efficiency and poor performance, leading to water reflux inhibiting the forward reaction of the polyester polyol and excessive loss of raw material alcohol, thus extending the operation cycle. Furthermore, the recovery of byproducts such as tetrahydrofuran and acetaldehyde through distillation is complex and costly.

[0004] To address the limitations of traditional distillation separation processes, pervaporation technology is increasingly being applied to treat systems with similar or azeotropic boiling points, achieving organic matter separation and product dehydration. It is a type of membrane separation technology, primarily utilizing the selective permeability of pervaporation membrane materials to drive mass transfer through concentration or pressure differences across the membrane. Widely used molecular sieve membranes offer advantages such as good mechanical strength, hydrothermal stability, chemical stability, and long service life. However, existing technologies generally cannot be integrated with product manufacturing processes, exhibiting limitations such as limited dehydration functionality and high energy consumption.

[0005] Patent CN116515092A discloses a polyester polyol, its preparation method, and its application, representing most current preparation processes. It uses a distillation column to separate water and other substances produced during esterification and polycondensation reactions. However, the unavoidable water content in the alcohol phase removed by vacuum causes the reaction to proceed in reverse, resulting in reduced production efficiency. Patent CN1339516A mentions a method for separating and reusing byproducts, but distillation and stripping alone cannot completely purify various byproducts. The recovered components, after modification, can only be returned to the reactor, resulting in low added value. Patent CN115260131A introduces a pervaporation membrane coupled with pressure swing distillation for tetrahydrofuran dehydration. Compared to distillation separation, this method has lower operating costs, but its function is limited, unable to simultaneously separate macromolecular alcohols, water, and aldehydes produced as byproducts in polyester polyol preparation. Currently, there are no reports on the preparation of composite multifunctional pervaporation membranes or their application in polyester processing and byproduct separation. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, one of the objectives of this invention is to provide a method for preparing polyester polyols. This method changes the distillation process route, which suffers from low separation efficiency of reaction products and difficulty in recovering by-products. It enables rapid and complete separation of distillate water from small molecule alcohol esters, promotes esterification reaction, and allows for the recovery of by-products acetaldehyde and tetrahydrofuran. This significantly improves reaction efficiency, reduces production energy consumption, and transforms waste liquid into value-added chemical products.

[0007] In addition, a process apparatus is provided to improve the production process of polyester polyols, achieve efficient product separation, and promote the improvement of reaction efficiency, which can be used to solve the above-mentioned problems.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a polyester polyol includes the following steps: in a reaction vessel, a dicarboxylic acid and a diol react at a temperature above 110°C, and under the stripping of an inert gas, water, small molecule alcohol esters, tetrahydrofuran, and acetaldehyde escape and are separated by a separation system comprising a primary separation membrane and a secondary separation membrane.

[0010] The dicarboxylic acid described in this invention includes one or more of adipic acid, succinic acid, octanoic acid, terephthalic acid, phthalic acid, isophthalic acid, and phthalic anhydride.

[0011] The diols described in this invention include one or more of ethylene glycol, 1,4-butanediol, 1,2-propanediol, 1,3-propanediol, 1,6-hexanediol, diethylene glycol, and neopentyl glycol.

[0012] The small molecule alcohol esters described in this invention cannot pass through the primary separation membrane and are refluxed back to the reactor; tetrahydrofuran and acetaldehyde enter the secondary separation membrane; water passes through the secondary separation membrane, tetrahydrofuran cannot pass through the secondary separation membrane and is collected; acetaldehyde is adsorbed by the secondary separation membrane.

[0013] As a preferred method, acetaldehyde is desorbed by purging the secondary separation membrane with high-temperature and high-pressure steam.

[0014] As a preferred embodiment, the inert gas described in this invention includes gases such as N2 that do not adversely affect the reaction.

[0015] As a preferred embodiment, the separation system of the present invention uses a vacuum unit to provide differential pressure driving force.

[0016] The primary separation membrane of the present invention uses porous materials such as metal powder sintered filter elements or porous ceramic filter elements as substrates. Polysulfone (PSF) and polyvinylidene fluoride (PVDF) are attached to the surface of the substrate using a phase transfer method to obtain a membrane material with uniform pores. The membrane material is then assembled to obtain a primary separation membrane module.

[0017] As a preferred embodiment, the method for preparing the primary separation membrane includes the following steps:

[0018] (1) Immerse the porous material in sodium hydroxide solution to remove surface impurities, and then wash with water;

[0019] (2) Immerse the product from step (1) in the casting solution for 0.5-1h, then remove it and place it in water.

[0020] The porous material in step (1) of the present invention has a pore size of 1-20 μm, preferably a metal powder sintered filter element or a porous ceramic filter element.

[0021] The casting solution in step (2) of this invention uses N,N-dimethylformamide as the solvent, and polysulfone or polyvinylidene fluoride as the solute, with a concentration of 15-30 wt%.

[0022] In step (2) of the present invention, since the solubility of polysulfone PSF or polyvinylidene fluoride PVDF in water is reduced, it is uniformly attached to the surface of the porous material to form a primary separation membrane with filtration function.

[0023] The secondary separation membrane of the present invention is an amine-modified NaA type molecular sieve membrane. Its preparation method includes the following steps: using macroporous ceramic as a carrier, the amine and silicon-aluminum components are grown and solidified on the surface of the carrier by microwave synthesis, thereby forming a pervaporation molecular sieve membrane with adsorption function.

[0024] As a preferred embodiment, the method for preparing the secondary separation membrane according to the present invention includes the following steps:

[0025] S1: Grind the surface of the large-pore ceramic carrier, ultrasonically clean it with alkaline solution, and dry it;

[0026] S2: The product of S1 is hot-impregnated into a zeolite suspension to pre-coat seed crystals, and then taken out and calcined.

[0027] S3: Mix the solution containing silicon and aluminum components with sodium hydroxide solution and react them, then add amine solution and stir to mix;

[0028] S4: Place the S2 product into a microwave synthesis vessel and inject the S3 product. After in-situ aging and crystallization, remove the product, cool it to room temperature, wash it with water, and dry it.

[0029] In one embodiment of the present invention, the polishing in S1 is done with sandpaper, preferably 800 to 1500 grit.

[0030] In one embodiment of the present invention, the alkali in the alkaline solution S1 comprises sodium hydroxide and / or potassium hydroxide.

[0031] In one embodiment of the present invention, the concentration of the alkaline solution in S1 is 0.1-2 mol / L.

[0032] In one embodiment of the present invention, the ultrasonic cleaning time in S1 is 1-2 hours, and the drying time is 5-24 hours.

[0033] In one embodiment of the present invention, the zeolite in the zeolite suspension in S2 is type A zeolite.

[0034] In one embodiment of the present invention, the concentration of the zeolite suspension in S2 is 2-15 g / L.

[0035] In one embodiment of the present invention, the hot impregnation time in S2 is 2-10h, the calcination temperature is 180-250℃, and the calcination time is 0.5-5h.

[0036] In one embodiment of the present invention, the amine in the amine solution of S3 includes one or more of diethylamine, triethylamine, ethylenediamine, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine.

[0037] In one embodiment of the present invention, the amine solution in S3 is an aqueous solution with a concentration of 0.1%-2wt%.

[0038] In one embodiment of the present invention, the solution containing silicon and aluminum components in S3 is an aqueous solution, and the solute includes one or more of aluminum oxide, sodium aluminate, silicon dioxide, sodium silicate, kaolin, and metakaolin.

[0039] In one embodiment of the present invention, in S3, the concentration of the solution containing the silicon-aluminum component is 5%-30wt%; and the concentration of the sodium hydroxide solution is 0.1-2mol / L.

[0040] In one embodiment of the present invention, the S3 product contains a solution of silicon-aluminum components accounting for 50-70 wt%, a sodium hydroxide solution accounting for 10-20 wt%, and an amine solution accounting for 10-40 wt%.

[0041] In one embodiment of the present invention, the microwave synthesis temperature in S4 is 50-80°C, the in-situ aging time is 2-10 min, the crystallization temperature is 70-95°C, and the crystallization time is 20-60 min.

[0042] In one embodiment of the present invention, the water washing in step S4 needs to reach a pH of 7.

[0043] The present invention also provides a process apparatus for preparing polyester polyols, comprising the following components: a reactor with a stirring function, a primary separation membrane, a secondary separation membrane, a water condenser, a water collection tank, a THF collection tank, an acetaldehyde solution collection tank, and a vacuum unit; wherein the top outlet of the reactor is connected to the inlet of the primary separation membrane, the side outlet of the primary separation membrane is connected to the inlet of the secondary separation membrane, and the unpermeable material from the primary separation membrane flows back to the top of the reactor; the side outlet of the secondary separation membrane is connected to the inlet of the water condenser, the outlet of the water condenser is connected to the inlet of the water collection tank, and the top outlet of the water collection tank is connected to the vacuum unit; of the unpermeable material from the secondary separation membrane, one THF stream is connected to the THF collection tank, and the other stream is connected to the acetaldehyde solution collection tank.

[0044] As a preferred embodiment, the secondary separation membrane is equipped with a high-temperature steam purge inlet to achieve acetaldehyde desorption and membrane regeneration.

[0045] As a preferred embodiment, the temperature of the polyester reactor is 150-260°C.

[0046] As a preferred embodiment, the vacuum unit maintains a reaction pressure range of 0.1-80 kPa and a vacuum operation time of 2-20 h.

[0047] As a preferred embodiment, the steam temperature for the secondary separation membrane desorption is 100-150℃ and the steam pressure is 0.2-1MPaG.

[0048] Compared with the prior art, the positive effects of the present invention are as follows:

[0049] (1) The modified pervaporation membrane module replaces the traditional distillation separation process, which can greatly improve the dehydration efficiency of esterification reaction, avoid energy waste, reduce raw material alcohol loss, and reduce production costs.

[0050] (2) The pervaporation membrane module with adsorption and formaldehyde removal effect can simultaneously remove moisture, adsorb impurities and recover by-products, saving the process steps of treating industrial waste and realizing the green circular upgrade of polyester production process. Attached Figure Description

[0051] Figure 1 This invention describes the process flow for producing polyester polyols using adsorption membrane separation. Detailed Implementation

[0052] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0053] Adipic acid: Industrial product, Beijing Innocare Technology Co., Ltd.;

[0054] 1,4-Butanediol: Beijing Inokai Technology Co., Ltd., purity 99%;

[0055] Ethylene glycol: Beijing Innocare Technology Co., Ltd., purity 99%;

[0056] Tetrabutyl titanate: Beijing Inokai Technology Co., Ltd., purity 99%;

[0057] Kaolin: Industrial product, Beijing Innocare Technology Co., Ltd.;

[0058] Silica sol: Industrial grade, containing 20 wt% SiO2, Aladdin;

[0059] Molecular sieve membrane carrier: Al2O3 ceramic tube, pore size 3μm, porosity 45%;

[0060] Synthetic zeolite: 350 mesh, type A, Thermo Fisher;

[0061] Anhydrous ethanol: Aladdin, analytical grade;

[0062] Sodium hydroxide: analytical grade, Sinopharm Chemical Reagent Co., Ltd.;

[0063] Diethylamine: Beijing Inokai Technology Co., Ltd., purity 99%;

[0064] Triethylamine: Beijing Inokai Technology Co., Ltd., purity 99%;

[0065] m-Phenylenediamine: Beijing Inokai Technology Co., Ltd., purity 99%;

[0066] Sodium silicate: Beijing Innocare Technology Co., Ltd., analytical grade;

[0067] Microwave synthesis reactor: MDS-6, power 600W, Xinyi Microwave Chemical Technology Co., Ltd.;

[0068] Gas chromatograph: Model GC7890T, Column: GDX103, Shanghai Tianmei Scientific Instruments Co., Ltd.

[0069] Example 1

[0070] The secondary modified pervaporation molecular sieve membrane material is prepared using the following steps:

[0071] S1: The molecular sieve membrane carrier is pretreated by polishing the surface with 800-mesh and 1500-mesh sandpaper in sequence, and then ultrasonically cleaning it with 0.1 mol / L NaOH solution. After drying for 24 hours, it is ready for use.

[0072] S2: Prepare a zeolite suspension with a concentration of 15 g / L (350 mesh type A), pre-coat the S1 product with seeds by hot impregnation in the suspension for 8 hours, and then calcine it at a temperature of 200℃ for 4 hours.

[0073] S3: Preparation of amine-modified synthesis solution: Sodium aluminate, silica sol, sodium hydroxide and amine solution are mixed according to the ratio. The amine solution components include diethylamine and m-phenylenediamine, and the concentration of each component is added at 0.5 wt%. The mass concentration ratio of each component of amine solution, sodium aluminate, silica sol and sodium hydroxide solution is 1:20:20:59. Stir for 20 h for later use.

[0074] S4: Place the S2 product into a microwave synthesis vessel, and synthesize it at 80℃. Then inject the S3 amine-modified synthesis solution. After in-situ aging for 10 min and crystallization at 80℃ for 60 min, remove the product and quickly cool it to room temperature. Rinse it with deionized water until neutral and dry it to obtain a pervaporated molecular sieve membrane with adsorption function.

[0075] Example 2

[0076] The secondary modified pervaporation molecular sieve membrane material is prepared using the following steps:

[0077] S1: The molecular sieve membrane carrier is pretreated by polishing the surface with 800-mesh and 1500-mesh sandpaper in sequence, and ultrasonically cleaning it with 0.1 mol / L sodium hydroxide solution. After drying for 24 hours, it is ready for use.

[0078] S2: Prepare a zeolite suspension with a concentration of 5 g / L, pre-coat the S1 product with seeds by hot impregnation in the suspension for 8 h, take it out and calcine it at 200 ℃ for 10 h.

[0079] S3: Preparation of amine-modified synthesis solution: Mix metakaolin, silica sol, sodium hydroxide and amine solution according to the specified ratio. The amine solution components include triethylamine, o-phenylenediamine and p-phenylenediamine, with component concentrations of 0.8wt%, 0.6wt% and 0.6wt% respectively. The mass concentration ratio of each component in the amine solution to metakaolin, silica sol and sodium hydroxide solution is 1:30:30:39. Stir for 20 hours and set aside.

[0080] S4: Place the S2 product into a microwave synthesis vessel, synthesize at 95℃, and inject amine-modified synthesis solution. After in-situ aging for 10 min and crystallization at 80℃ for 60 min, remove and quickly cool to room temperature. Rinse with deionized water until neutral and dry to obtain a pervaporated molecular sieve membrane with adsorption function.

[0081] Example 3

[0082] Polyester production process: Adipic acid and 1,4-butanediol are added to a stirred reactor at a molar ratio of 1:1.2 and the temperature is raised. When the reaction temperature exceeds 110°C, water is generated in the system. Simultaneously, due to the stripping effect of nitrogen, small molecule alcohol esters and byproducts such as tetrahydrofuran and acetaldehyde escape. A vacuum unit provides the pressure difference driving force for the gas phase components to enter the primary and secondary separation membranes. Due to their large molecular size, the small molecule alcohol esters cannot pass through the primary membrane and flow back to the reactor. Tetrahydrofuran and acetaldehyde enter the secondary separation membrane prepared in Example 1. Because the secondary separation membrane has adsorption and selective permeability, water molecules, being small, can pass through the secondary separation membrane and enter the water cooler to obtain an aqueous phase. Tetrahydrofuran molecules, being large, cannot pass through the membrane module, resulting in the separation of high-purity tetrahydrofuran components. Acetaldehyde molecules, being of medium size, can react with the modified amine groups on the surface of the secondary separation membrane and be adsorbed. They can be desorbed by intermittent high-temperature and high-pressure steam purging to form an acetaldehyde solution.

[0083] Example 4

[0084] Polyester production process: Adipic acid and 1,4-butanediol are added to a stirred reactor at a molar ratio of 1:1.2, and the mixture is heated. When the reaction temperature exceeds 110°C, moisture is generated in the system. Simultaneously, due to the stripping effect of nitrogen, small molecule alcohol esters and byproducts such as tetrahydrofuran and acetaldehyde escape. A vacuum unit provides the pressure difference driving force for the gaseous components to enter the primary and secondary separation membranes. Due to their large molecular size, the small molecule alcohol esters cannot pass through the primary membrane and flow back to the reactor. Tetrahydrofuran and acetaldehyde enter the secondary separation membrane prepared in Example 2. Other operations are consistent with Example 3.

[0085] Comparative Example 1

[0086] Referring to the method in Example 3, the difference lies in that the gaseous material from the reactor outlet does not pass through a membrane separation unit; instead, a packed distillation column is used to separate small molecules and water. The specific operating conditions are as follows: the gaseous outlet of the reactor is connected to the feed inlet of the distillation column. Water, small molecule alcohol esters, and byproducts such as tetrahydrofuran and acetaldehyde generated during the reaction enter the distillation column. A reboiler is installed at the bottom of the distillation column to provide heat for vaporization, and a condenser is installed at the top of the column. The temperature at the top of the distillation column is controlled to not exceed 100°C through reflux of the cooling medium. The reactor temperature is maintained at 220°C for 30 hours. Other operations remain unchanged, and the reaction yields a polyester polyol product.

[0087] Comparative Example 2

[0088] Referring to the method in Example 3, the difference is that the primary separation membrane is not used, but other operations remain unchanged, to obtain the polyester polyol product.

[0089] Comparative Example 3

[0090] Referring to the method of Example 3, the difference is that the secondary separation membrane module is not modified with amine solution, and other operations remain unchanged. The polyester polyol product is obtained according to the process flow in Example 1.

[0091] Table 1. Polyester Production Results

[0092]

Claims

1. A method for preparing a polyester polyol, comprising the following steps: In the reaction vessel, the dicarboxylic acid and diol react at a temperature above 110°C. Under the stripping of an inert gas, water, small molecule alcohol esters, tetrahydrofuran, and acetaldehyde are removed, and then separated by a separation system containing a primary separation membrane and a secondary separation membrane.

2. The method according to claim 1, characterized in that, The dicarboxylic acid includes one or more of adipic acid, succinic acid, octanoic acid, terephthalic acid, phthalic acid, isophthalic acid, and phthalic anhydride; the diol includes one or more of ethylene glycol, 1,4-butanediol, 1,2-propanediol, 1,3-propanediol, 1,6-hexanediol, diethylene glycol, and neopentyl glycol.

3. The method according to claim 1 or 2, characterized in that, The primary separation membrane is formed by attaching polysulfone or polyvinylidene fluoride to the surface of a porous material using a phase transfer method; preferably, the porous material is selected from metal powder sintered filter cartridges or porous ceramic filter cartridges.

4. The method according to any one of claims 1-3, characterized in that, The secondary separation membrane is an amine-modified NaA-type molecular sieve membrane.

5. The method according to any one of claims 1-4, characterized in that, The preparation method of the secondary separation membrane includes the following steps: using macroporous ceramic as a carrier, the amine and silicon-aluminum components are solidified and formed on the carrier surface by microwave synthesis.

6. The method according to any one of claims 1-5, characterized in that, The method for preparing the secondary separation membrane, Includes the following steps: S1: Grind the surface of the large-pore ceramic carrier, ultrasonically clean it with alkaline solution, and dry it; S2: The product of S1 is hot-impregnated into a zeolite suspension to pre-coat seed crystals, and then taken out and calcined. S3: Mix the solution containing silicon and aluminum components with sodium hydroxide solution and react them, then add amine solution and stir to mix; S4: Place the S2 product into a microwave synthesis vessel and inject the S3 product. After in-situ aging and crystallization, remove the product, cool it to room temperature, wash it with water, and dry it.

7. The method according to any one of claims 1-6, characterized in that, The zeolite in the zeolite suspension described in S2 is type A zeolite.

8. The method according to any one of claims 1-7, characterized in that, The amine in the amine solution described in S3 includes one or more of diethylamine, triethylamine, ethylenediamine, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine; and / or the solution containing the silicon-aluminum component is an aqueous solution, and the solute includes one or more of alumina, sodium aluminate, silicon dioxide, sodium silicate, kaolin, and metakaolin.

9. The method according to any one of claims 1-8, characterized in that, The microwave synthesis temperature described in S4 is 50-80℃, the in-situ aging time is 2-10 min, the crystallization temperature is 70-95℃, and the crystallization time is 20-60 min.

10. A process apparatus for preparing polyester polyols using the method described in any one of claims 1-9, comprising the following components: a reactor with a stirring function, a primary separation membrane, a secondary separation membrane, a water condenser, a water collection tank, a THF collection tank, an acetaldehyde solution collection tank, and a vacuum unit; wherein the top outlet of the reactor is connected to the inlet of the primary separation membrane, the side outlet of the primary separation membrane is connected to the inlet of the secondary separation membrane, and the unpermeable material from the primary separation membrane is returned to the top of the reactor; the side outlet of the secondary separation membrane is connected to the inlet of the water condenser, the outlet of the water condenser is connected to the inlet of the water collection tank, and the top outlet of the water collection tank is connected to the vacuum unit; of the unpermeable material from the secondary separation membrane, one THF stream is connected to the THF collection tank, and the other stream is connected to the acetaldehyde solution collection tank.

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