Method and system for separating and purifying bisphenol A through continuous melt crystallization

Abstract

The invention provides a method and system for separating and purifying bisphenol A through continuous melt crystallization, and belongs to the technical field of separation and purification. The method comprises the following steps: 1, carrying out suspension crystallization on a pre-concentrated solution containing bisphenol A and phenol to obtain bisphenol A-phenol adduct crystal mush; step 2, pre-separating the bisphenol A-phenol adduct crystal mush to obtain a suspension crystallization mother solution and a first thick solid phase, and carrying out rotary melting crystallization on the first thick solid phase to obtain a rotary melting crystallization mother solution and a second thick solid phase; and step 3, performing sweating purification on the second thick solid phase to obtain high-purity bisphenol A. Compared with a traditional separation and purification scheme, the method is simple in technological process, low in energy consumption, high in product purity and capable of continuously and stably running for a long time.

Description

Technical Field

[0001] This invention belongs to the field of separation and purification technology, and specifically relates to a method and system for continuous melt crystallization separation and purification of bisphenol A. Background Technology

[0002] Bisphenol A (BPA) is an important organic chemical intermediate used in the production of various polymer materials such as epoxy resins, polycarbonates, and polysulfone resins. Its synthesis methods mainly include the sulfuric acid method, the hydrochloric acid method, and the ion exchange resin method, with the ion exchange resin method being the most widely used.

[0003] The ion exchange resin method uses acetone and phenol as raw materials to produce bisphenol A through dehydration in the presence of an acidic catalyst. The reactor effluent contains the product bisphenol A, unreacted acetone and phenol, water generated during the reaction, impurities from other side reactions, and some acidic catalyst impurities. To obtain bisphenol A products that meet the purity requirements of downstream synthesis, the reaction products must be separated and purified, and crude crystallization is a key step in the bisphenol A separation and purification process.

[0004] Existing technologies for purifying bisphenol A prepared using ion exchange resins primarily employ multiple recrystallization processes. For example, Mitsubishi Chemical, in its patent JP2000133873A, describes using multiple recrystallizations in the crystallization unit to ensure the purity of the bisphenol A-phenol adduct crystals. Chinese invention patent CN105130758A employs a multi-stage suspension crystallization process, followed by negative pressure removal of the phenol solvent and multi-stage falling film crystallization to improve product purity. However, a key limitation to product purity is that the bisphenol A-phenol adduct obtained in the suspension crystallization stage still contains certain impurities. Existing technologies commonly use centrifugation and washing, which can only remove impurities introduced onto the crystal surface due to mother liquor residue, failing to remove impurities embedded within the crystals. Removing impurities embedded within the crystals through recrystallization is inefficient, requiring multiple stages. With each additional stage, operational complexity and energy consumption increase, rendering the process economically unfeasible. Summary of the Invention

[0005] To address the aforementioned problems, this application aims to provide a method for the continuous melt crystallization separation and purification of bisphenol A that is simple to operate, economical, and can significantly improve product purity. The method includes: Step 1: Suspension crystallization of the pre-concentrated solution containing bisphenol A and phenol to obtain bisphenol A-phenol adduct slurry; Step 2: Pre-separate the bisphenol A-phenol adduct slurry to obtain a suspended crystallization mother liquor and a first thick solid phase. Perform melt-crystallization on the first thick solid phase to obtain a melt-crystallization mother liquor and a second thick solid phase. Step 3: Purify the second thick solid phase by sweating to obtain high-purity bisphenol A.

[0006] In one embodiment, the high-purity bisphenol A has a bisphenol A purity greater than 99.95% and a phenol and monoisomeric impurity content of less than 100 ppm, preferably less than 50 ppm.

[0007] In one embodiment, the pre-concentrated solution containing bisphenol A and phenol is obtained by dehydrating and pre-concentrating a product stream prepared by ion exchange resin method.

[0008] In one embodiment, the preparation process of the ion exchange resin method is as follows: a catalytic condensation reaction is carried out in a reactor packed with an acidic ion exchange resin catalyst at 50-80°C and 0.3 MPa. The raw materials are phenol and acetone, and the main products are bisphenol A and water. After the reaction, the material first enters a light-light-removal tower for dehydration and light-light-removal. The water and unreacted acetone generated are removed from the top of the tower, and the bottom liquid is then concentrated under reduced pressure to remove phenol, obtaining the corresponding pre-concentrated liquid.

[0009] In one embodiment, in step one, the pre-concentrated solution containing bisphenol A and phenol comprises 15-55 wt% bisphenol A, 50-85 wt% phenol, 3-15 wt% by-product impurities, 0-8 wt% acetone and 0-10 wt% water.

[0010] It is understood that the byproduct impurities described in this application are impurities generated by side reactions, and typically include the aforementioned isomer impurities, acidic contaminants, polyphenolic compounds, isopropylphenol, polymers, etc., for example, isomers are usually 2,2'-BPA and 2,4'-BPA, etc.

[0011] In one embodiment, the pre-concentrated solution containing bisphenol A and phenol comprises: 25 wt% bisphenol A, 65 wt% phenol, and other impurities totaling approximately 10 wt%.

[0012] In one embodiment, in step one, the temperature of the bisphenol A-phenol adduct slurry in the crystallizer is controlled to be 40~90°C, preferably 45~60°C, and more preferably 50°C.

[0013] In one embodiment, suspension crystallization can be single-stage or multi-stage suspension crystallization. When multi-stage crystallization is used, the crystal slurry is transferred to the next stage one by one, and the crystallization mother liquor is returned to the previous stage one by one. The temperature of each stage of crystallization gradually increases along the direction of crystal slurry transfer.

[0014] In one embodiment, the suspension crystallization can be carried out by using a partition heat exchange method or a vacuum flash solvent method to cool the material and remove the sensible heat of cooling and the enthalpy of phase change during crystallization.

[0015] In one embodiment, in step two, the bisphenol A mass content in the first thick solid phase is greater than or equal to 60%.

[0016] The control of the bisphenol A concentration in the first thick solid phase to be greater than or equal to 60% is determined by the thermodynamic phase equilibrium relationship between bisphenol A crystallization and melting. In actual operation, this parameter can be used to realize the melting process in industry.

[0017] In one embodiment, pre-separation can be performed using existing solid-liquid separation methods, such as hydrocyclones, centrifuges, or filters, to pre-separate the thickened slurry. The moisture content of the thickened slurry is such that the bisphenol A mass content in the stream entering the melting and crystallization step is greater than or equal to 60%.

[0018] In one embodiment, the suspended crystallization mother liquor obtained after pre-separation can be recycled to a reactor that prepares the product using the ion exchange resin method to continue the reaction, or it can be sent to an impurity treatment device for impurity removal.

[0019] In one embodiment, in step two, the transfer crystallization is a primary crystallization, and the material temperature in the crystallizer is controlled at 98~120℃, preferably 105~115℃, and more preferably 110℃.

[0020] In one embodiment, in step two, the transfer crystallization is a two- to five-stage crystallization process, and the material temperature in the crystallizer is controlled to gradually increase within the range of 95~155℃, with a total residence time of greater than or equal to 3 hours.

[0021] For example, in step two, the melting and crystallization is a three-stage crystallization process. The temperature inside the crystallizer for the first-stage crystallization is controlled at 100°C, the temperature inside the crystallizer for the second-stage crystallization is 130°C, and the temperature inside the crystallizer for the third-stage crystallization is 150°C.

[0022] It is understood that the primary crystallization described in this application refers to setting up one transmelting crystallizer, and the multi-stage crystallization refers to setting up multiple transmelting crystallizers in series. For example, the two to five stages of crystallization are two to five transmelting crystallizers in series.

[0023] In one embodiment, during multi-stage melting, the slurry is transferred backward stage by stage, and the mother liquor is returned to the previous crystallizer stage by stage.

[0024] For example, when using a three-stage melt-melt crystallization process, the material temperature in the first-stage crystallizer receiving the bisphenol A-phenol adduct slurry from the continuous suspension crystallization unit is controlled at 100°C. The overflow mother liquor from the first-stage melt-melt crystallizer is returned to the continuous suspension crystallization step, and the slurry is thickened before being transferred to the second-stage melt-melt crystallizer. The material temperature in the second-stage melt-melt crystallizer is controlled at 130°C, the overflow mother liquor is returned to the first-stage melt-melt crystallizer, and the slurry is thickened before being transferred to the third-stage melt-melt crystallizer. The material temperature in the third-stage melt-melt crystallizer is controlled at 150°C, the overflow mother liquor is returned to the second-stage melt-melt crystallizer, and the slurry is thickened before being transferred to the continuous evaporation purification step.

[0025] In one embodiment, in step three, the bottom temperature of the sweating purification process is controlled to be greater than 159°C, and the extraction flow rate is 1~5 t / h.

[0026] In the sweating purification step, the bottom of the sweating tower is heated to melt the bisphenol A crystals, and a high-purity liquid bisphenol A stream is collected from the bottom of the tower. By controlling the heat input and the flow rate collected from the bottom of the tower, the proportion of refluxed molten liquid in the sweating purification unit can be controlled, thereby adjusting the purity of the bisphenol A product at the bottom of the sweating tower.

[0027] In one embodiment, the method further includes the steps of: circulating the suspended crystallization mother liquor to the reactor to continue obtaining the pre-concentrated liquor, and / or, removing impurities and then recovering it.

[0028] In one embodiment, the method further includes the step of: recycling the mother liquor from the melt crystallization process to the suspension crystallization step to continue suspension crystallization.

[0029] In one embodiment, the method further includes the step of: circulating the overflow liquid purified by sweating to the melting and crystallization step for continued melting and crystallization.

[0030] On the other hand, this application also provides a system suitable for the continuous melt crystallization separation and purification method of bisphenol A, the system comprising: A continuous suspension crystallization unit includes a first crystallizer for suspending and crystallizing a pre-concentrated solution containing bisphenol A and phenol to obtain a bisphenol A-phenol adduct slurry. The melt-crystallization unit includes a separator and a second crystallizer for separating the first thick solid phase from the bisphenol A-phenol adduct slurry and performing melt-crystallization on the first thick solid phase; and, The sweating purification unit includes a sweating tower, which is used to sweat and purify the second thick solid phase obtained after melting and crystallization to obtain high-purity bisphenol A.

[0031] In one embodiment, the system further includes a circulation pipeline that can be used to circulate the mother liquor obtained after melting and crystallizing in the second crystallizer to the first crystallizer for continued suspension crystallization, and / or to circulate the overflow liquid purified by sweating in the sweating tower to the second crystallizer for continued melting and crystallizing.

[0032] In one embodiment, the first crystallizer and / or the second crystallizer is selected from any one or more of a forced circulation crystallizer, an OSLO crystallizer, a DTB crystallizer, or a batch crystallizer.

[0033] Preferably, the crystallizer can be a crystallizer with a graded discharge function, which can adjust the suspended density and system concentration in the crystallizer through clear overflow and reversal.

[0034] In one embodiment, the continuous suspension crystallization unit employs a single-stage forced circulation crystallizer with an external tube heat exchanger, using a partitioned heat exchange method to provide cooling to the crystallization liquid.

[0035] This application has at least the following beneficial effects: 1. The method for separating and purifying bisphenol A provided in this application has a simple operation process and low equipment investment. It only requires one step of continuous suspension crystallization, one step of melt crystallization and one step of continuous sweating to obtain high-purity bisphenol A products. It eliminates the distillation or rectification operation steps for solvent removal in traditional processes, reduces the risk of product deterioration, and all equipment can be operated at atmospheric pressure without the need for an auxiliary negative pressure system.

[0036] 2. The system for separating and purifying bisphenol A provided in this application has stable operation and low energy consumption per unit product. The three operation steps involved are continuous series operations. After the system stabilizes, the operating conditions are constant and the temperature gradient gradually increases, avoiding the energy loss caused by continuous heating and cooling during recrystallization or multi-stage falling film crystallization in traditional operations.

[0037] 3. The method and system for separating and purifying bisphenol A provided in this application yield bisphenol A with a purity greater than 99.95%, and a maximum of greater than 99.998%. The content of phenol and single isomer impurities is less than 50 ppm, and the impurity content is significantly reduced. It also has the advantages of high purity, high yield and low energy consumption. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the structure and process flow of the continuous melt crystallization separation and purification system for bisphenol A provided in Example 1. In the diagram: 1. Continuous suspension crystallizer; 2. Transfer melting crystallizer; 3. Solid-liquid pre-separation equipment; 4. Continuous sweating tower; 5. Circulation pipeline; S1, Bisphenol A pre-concentrated solution; S2, Bisphenol A-phenol adduct crystal slurry; S3, Thick stream of Bisphenol A-phenol adduct crystal slurry; S4, Continuous suspension crystallization mother liquor; S5, Melt-transfer crystallization mother liquor; S6, Bisphenol A crystal slurry; S7, Sweat overflow liquid; S8, High-purity Bisphenol A product; Figure 2 This is the solid-liquid equilibrium phase diagram of the phenol + bisphenol A two-component system; Figure 3 The chromatogram of the bisphenol A product in Example 1 is shown below. Figure 4 This is the chromatogram of the bisphenol A product from Example 2. Detailed Implementation

[0040] The present invention is described below through specific embodiments. These embodiments should be understood as illustrative, not limiting, of the scope of the invention, which is primarily defined by the claims. For those skilled in the art, various changes or modifications to the material composition and dosage in these embodiments, without departing from the spirit and scope of the invention, also fall within the scope of protection of the present invention.

[0041] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Test methods in the following examples that do not specify specific experimental conditions are generally performed under conventional experimental conditions or according to the manufacturer's recommended experimental conditions. Unless otherwise specified, the reagents and raw materials used in this invention are commercially available. All chemical reagents involved in this invention are of analytical grade.

[0042] Example 1 This embodiment provides a system for continuous melt crystallization separation and purification of bisphenol A, the system comprising: A continuous suspension crystallization unit is used to perform suspension crystallization on a pre-concentrated solution containing bisphenol A and phenol to obtain a bisphenol A-phenol adduct slurry. A melt-crystallization unit is used to separate the first thick solid phase from the bisphenol A-phenol adduct slurry and to perform melt-crystallization on the first thick solid phase; and, The sweating purification unit is used to sweat and purify the second thick solid phase obtained after melting and crystallization to obtain high-purity bisphenol A.

[0043] See Figure 1 The continuous suspension crystallization unit includes a first crystallizer, which in this embodiment is a continuous suspension crystallizer 1. It can be a single-stage forced circulation crystallizer with an external tube heat exchanger, using a wall-to-wall heat exchange method to provide cooling to the crystallizing liquid. The transfer crystallization unit includes a separator and a second crystallizer, which in this embodiment are a solid-liquid pre-separation device 3 and a transfer crystallizer 2. The sweating purification unit includes a continuous sweating tower 4. The continuous suspension crystallizer 1, the solid-liquid pre-separation device 3, the transfer crystallizer 2, and the sweating tower 4 are sequentially connected by interconnecting pipelines. Furthermore, a circulation pipeline 5 is provided between the transfer crystallizer 2 and the continuous suspension crystallizer 1, and between the sweating tower 4 and the transfer crystallizer 2, to return the overflow liquid from the subsequent stage to the previous stage.

[0044] like Figure 1 As shown, the continuous suspension crystallizer 1 can be connected to the reactor used to prepare bisphenol A via a pipeline to receive the initial product to be purified, namely, the pre-concentrated liquid S1 containing bisphenol A and phenol. The solid-liquid pre-separation device 3 is connected to the continuous suspension crystallizer 1 and the transfer melting crystallizer 2 respectively to receive the bisphenol A-phenol adduct slurry S2 obtained in the continuous suspension crystallizer 1, and to separate the bisphenol A-phenol adduct slurry to obtain the first thick solid phase, namely, the thick stream of bisphenol A-phenol adduct slurry S3, and the continuous suspension crystallization mother liquor S4. Part of the continuous suspension crystallization mother liquor S4 is returned to the reactor for recycling, and part is recovered after removing impurities. The thick stream S3 of the bisphenol A-phenol adduct crystal slurry enters the transfer crystallizer 2 for transfer crystallization. The overflow stream from the top of the transfer crystallizer, namely the transfer crystallization mother liquor S5, flows back to the continuous suspension crystallizer 1 through the circulation pipeline 5 to continue suspension crystallization. The second thick phase obtained by transfer crystallization, namely the bisphenol A crystal slurry S6, is transferred to the continuous sweating tower 4 for sweating purification.

[0045] Furthermore, after the bisphenol A slurry S6 is transferred to the continuous sweating tower 4, solid-liquid separation occurs. The bisphenol A crystals form a stacked crystal bed in the continuous sweating purification tower 4. The mother liquor from the sweating purification, i.e., the sweating overflow liquid S7, overflows from the top of the continuous sweating tower 4 and returns to the melt crystallizer 2. The bottom of the continuous sweating tower 4 is heated to melt the bisphenol A crystals. A high-purity liquid bisphenol A stream S8 is collected from the bottom of the tower. The proportion of reflux melt liquid in the sweating purification unit can be controlled by controlling the heat input and the flow rate collected from the bottom of the tower, thereby adjusting the purity of the bisphenol A product at the bottom of the sweating tower.

[0046] Optionally, the continuous suspension crystallizer 1 and the transfer melting crystallizer 2 can be selected from any one or more of the forced circulation crystallizer, OSLO crystallizer, DTB crystallizer, or batch crystallizer. Among them, the crystallizer is preferably a crystallizer with a staged discharge function, which can adjust the suspension density and system concentration in the crystallizer through clear overflow and backflow.

[0047] Optionally, the solid-liquid pre-separation device 3 can be selected from any one or more of hydrocyclones, centrifuges, or filters.

[0048] In the system provided in the above embodiments, the bisphenol A-phenol adduct undergoes transcrystallization in the transmelting crystallization unit by controlling the equilibrium temperature to form bisphenol A crystals and a bisphenol A phenol solution. The temperature parameters are selected according to... Figure 2 The solid-liquid equilibrium diagram of the bisphenol A-phenol two-component system is set up as shown. Using the apparatus and method provided in the above embodiments, impurities on the surface and inside of the bisphenol A crystals prepared by the ion exchange resin method can be effectively removed, while having the advantages of high purity, high yield and low energy consumption.

[0049] Example 2 This embodiment provides a method for the continuous melt crystallization separation and purification of bisphenol A, using the system provided in Example 1. The specific method steps are as follows: After pretreatment and concentration, the reaction solution contains 25 wt% bisphenol A, 65 wt% phenol, and approximately 10 wt% other impurities. The feed rate of the bisphenol A pre-concentrated solution is approximately 18 t / h, and the temperature of the suspended crystal slurry is controlled at approximately 50℃, corresponding to a bisphenol A concentration of approximately 10% in the continuous suspension crystallization mother liquor. The bisphenol A-phenol adduct slurry is pumped into a continuous centrifuge via a transfer pump, and the thick solid phase is pre-separated before entering the melt crystallizer. The flow rate of the continuous suspension crystallization mother liquor discharged from the separation and purification section is approximately 15 t / h, with a portion returned to the reactor for recycling and a portion sent to the impurity treatment unit. The slurry temperature in the melt crystallizer is controlled at 110℃, at which point the bisphenol A concentration in the melt crystallization mother liquor is approximately 64%, and the designed residence time in the melt crystallizer is 4 hours. The transfer rate from the melt crystallizer to the sweating purification unit is 15 t / h, with a solid suspension density of approximately 40%. The diaphoretic purification unit stably produces bisphenol A at a flow rate of 3 t / h, corresponding to a product purity greater than 99.95%, with phenol and single isomer impurities content less than 100 ppm. Furthermore, the yield, calculated based on the feed and effluent concentrations, is approximately 66.67% (with a feed concentration of 25%, the limiting yield is approximately 84%). Compared to existing purification and separation methods, this approach reduces energy consumption, thus improving economic efficiency.

[0050] Example 3 This embodiment is based on Embodiment 1, and the melting and crystallization unit is operated in the form of a three-stage crystallizer connected in series. The main difference in steps is as follows: The material temperature in the first-stage crystallizer receiving the bisphenol A-phenol adduct slurry from the continuous suspension crystallization unit is controlled at 100°C. The overflow mother liquor from the first-stage melting crystallizer is returned to the continuous suspension crystallization unit, and the slurry is thickened before being transferred to the second-stage melting crystallizer. The material temperature in the second-stage melting crystallizer is controlled at 130°C, the overflow mother liquor is returned to the first-stage melting crystallizer, and the slurry is thickened before being transferred to the third-stage melting crystallizer. The material temperature in the third-stage melting crystallizer is controlled at 150°C, the overflow mother liquor is returned to the second-stage melting crystallizer, and the slurry is thickened before being transferred to the continuous sweating purification unit. The feed flow rate to the continuous sweating purification unit is controlled at approximately 30 t / h, and the solid suspension density is approximately 40%. The total system feed and discharge rates are the same as in Example 1, corresponding to a product purity greater than 99.998%, and phenol and single isomer impurities content less than 50 ppm.

[0051] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for the continuous melt crystallization separation and purification of bisphenol A, characterized in that, The method includes: Step 1: Suspension crystallization of the pre-concentrated solution containing bisphenol A and phenol to obtain bisphenol A-phenol adduct slurry; Step 2: Pre-separate the bisphenol A-phenol adduct slurry to obtain a suspended crystallization mother liquor and a first thick solid phase. Perform melt-crystallization on the first thick solid phase to obtain a melt-crystallization mother liquor and a second thick solid phase. Step 3: Purify the second thick solid phase by sweating to obtain high-purity bisphenol A.

2. The method according to claim 1, characterized in that, In step one, the pre-concentrated solution containing bisphenol A and phenol comprises 15-55 wt% bisphenol A, 50-85 wt% phenol, 3-15 wt% byproduct impurities, 0-8 wt% acetone, and 0-10 wt% water; and / or, In step one, the temperature of the bisphenol A-phenol adduct slurry is controlled to be 40-90℃.

3. The method according to claim 1, characterized in that, In step two, the bisphenol A mass content in the first thick solid phase is greater than or equal to 60%.

4. The method according to claim 1, characterized in that, In step two, the transfer crystallization is a primary crystallization, and the material temperature in the crystallizer is controlled at 98~120℃.

5. The method according to claim 1, characterized in that, In step two, the melting crystallization is a two- to five-stage crystallization process, with the material temperature in the crystallizer gradually increasing from 95 to 155°C, and the total residence time being greater than or equal to 3 hours.

6. The method according to claim 1, characterized in that, In step three, the temperature at the bottom of the sweating purification process is controlled to be greater than 159°C, and the extraction flow rate is 1~5t / h.

7. The method according to claim 1, characterized in that, The method further includes the following steps: circulating the melt crystallization mother liquor to the suspension crystallization step for continued suspension crystallization; and / or, The overflow liquid purified by sweating is recycled to the melting and crystallization step to continue melting and crystallization.

8. A system suitable for the continuous melt crystallization separation and purification method for bisphenol A as described in any one of claims 1-7, characterized in that, The system includes: A continuous suspension crystallization unit includes a first crystallizer for suspending and crystallizing a pre-concentrated solution containing bisphenol A and phenol to obtain a bisphenol A-phenol adduct slurry. The melt-crystallization unit includes a separator and a second crystallizer for separating the first thick solid phase from the bisphenol A-phenol adduct slurry and performing melt-crystallization on the first thick solid phase; and, The sweating purification unit includes a sweating tower, which is used to sweat and purify the second thick solid phase obtained after melting and crystallization to obtain high-purity bisphenol A.

9. The system according to claim 8, characterized in that, The system also includes a circulation pipeline for circulating the mother liquor obtained after melting and crystallization in the second crystallizer to the first crystallizer for continued suspension crystallization; and / or for circulating the overflow liquid purified by sweating in the sweating tower to the second crystallizer for continued melting and crystallization.

10. The system according to claim 8, characterized in that, The first crystallizer and / or the second crystallizer are selected from any one or more of the forced circulation crystallizer, OSLO crystallizer, DTB crystallizer or batch crystallizer.

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