Refining method of crude BPA

Abstract

The invention relates to a refining method of crude BPA, which comprises the following steps: 1) crude BPA from an upstream waste PC recovery device enters a dissolving tank, and is dissolved by a solvent to obtain a crude BPA solution; 2) the crude BPA solution treated in the step 1) enters a resin treatment bed, sodium ions are adsorbed and removed, and a low-salt BPA solution is obtained; (3) the low-salt BPA solution obtained in the step (2) enters a water washing tower, sodium ions are further removed, and a refined BPA solution is obtained; (4) mixing the refined BPA solution treated in the step (3) with phenol, feeding the mixture into a rectifying tower, and removing and recovering the solvent to obtain a phenol / BPA solution; and (5) the phenol / BPA solution obtained in the step (4) enters a crystallization unit of a BPA device to be further crystallized and purified, phenol is removed, a BPA product is obtained, the BPA dry basis purity is 99.96% or above, the PTBP content is 20 ppm or below, the phenol content is 15 ppm or below, sodium ions are 1 ppm or below, alcohols are 0.1 ppm or below, carbonic ester is 0.1 ppm or below, and the melting color number is 20 or below.

Description

Technical Field

[0001] The invention belongs to the technical field of BPA preparation and relates to a method for refining crude BPA. Background Art

[0002] Bisphenol A (BPA for short) is an important chemical raw material, mainly used to make polycarbonate and epoxy resin. Polycarbonate has high requirements for raw materials, requiring a purity of more than 99.85% and a melting color number of less than 5. BPA is synthesized by alkylation reaction with phenol and acetone as raw materials, and purified by crystallization process to obtain a high-purity product, which meets the requirements of polycarbonate for raw materials.

[0003] Polycarbonate (PC for short) is an important engineering plastic, with annual consumption increasing year by year, and is expected to reach 3.5 million tons by 2025. In order to actively respond to the national "dual carbon" strategy and achieve sustainable development, it is of great significance to realize the cycle of BPA → PC resin → PC products → BPA.

[0004] CN 116368179A discloses a polycarbonate regeneration and purification route, wherein alcoholysis of BPA is respectively washed with dichloromethane to obtain the residue of diethyl carbonate, dissolved in ethanol, adsorbed by activated carbon, and recrystallized by adding water, and dried to obtain a BPA product. The purity of the BPA product obtained by this process route is only 99.4%, which cannot be directly used in the production of polycarbonate, and it is difficult to achieve a closed-loop circulation of polycarbonate.

[0005] CN 116368098A discloses a polycarbonate regeneration and purification route, wherein alcoholysis BPA is dissolved in toluene, washed with desalted water 5 times, cooled to precipitate BPA crystals, filtered and dried to obtain a BPA product. The BPA obtained by this process has a purity of only 99.8% and a melting color number of 165, and cannot be directly used in polycarbonate production.

[0006] Therefore, it is necessary to develop a purification route for the crude BPA obtained by degradation of PC products. Summary of the invention

[0007] During the research on crude BPA produced by degradation of polycarbonate, the inventors found that secondary brand BPA mainly contains phenol, PTBP, methanol, DMC, and sodium BPA, among which phenol, PTBP, methanol, and DMC entering the polycarbonate production process will cause abnormal molecular weight, affecting its product quality; sodium BPA will produce high color number substances during storage and transportation, which will also affect product quality. Therefore, how to completely remove phenol, PTBP, methanol, DMC, and sodium BPA from crude BPA is the key to realizing the direct use of BPA regenerated from polycarbonate in the production cycle of polycarbonate. Based on this research, the present invention was completed.

[0008] The purpose of the present invention is to provide a method for pre-treating and productizing and recycling crude BPA to achieve chemical recycling of PC products, in order to solve the problem that crude BPA obtained by alcoholysis of waste polycarbonate cannot meet national standards due to its low purity and high impurity content.

[0009] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0010] A method for refining crude BPA comprises the following steps:

[0011] 1) Crude BPA from an upstream waste PC recovery device enters a dissolution tank and is dissolved with a solvent to obtain a crude BPA solution;

[0012] 2) the crude BPA solution after the treatment in step 1) enters a resin treatment bed to remove sodium ions by adsorption to obtain a low-salt BPA solution;

[0013] 3) The low-salt BPA solution obtained in step 2) enters a water washing tower to further remove sodium ions to obtain a refined BPA solution;

[0014] 4) the refined BPA solution treated in step 3) is mixed with phenol and then enters a distillation tower to remove and recover the solvent to obtain a phenol / BPA solution;

[0015] 5) The phenol / BPA solution obtained in step 4) enters the crystallization unit of the BPA device for further crystallization and purification to remove phenol and obtain a BPA product.

[0016] The crude BPA in step 1) contains, by total mass, 0.001%-0.05% phenol, 90%-96% BPA, 0.4%-2.5% PTBP, 0.005%-3% methanol, 0.005%-3% DMC, and 0.1%-2% BPA sodium salt.

[0017] The solvent in step 1) is selected from at least one of methanol, ethanol, butanol, phenol, acetone, MTBE and isopropyl ether, preferably isopropyl ether.

[0018] Preferably, the mass concentration of BPA in the prepared crude BPA solution is 10%-30%, preferably 20%-25%.

[0019] The resin in step 2) is a macroporous cationic resin, preferably one or more of Seplite LX-160, AMBERLITE IR120Na, and D001 resin.

[0020] The feed rate of the resin treatment bed in step 2) is 0.5-5 BV / h, preferably 1-2 BV / h.

[0021] The water washing tower in step 3) is a plate tower, a packed tower or a combination thereof, preferably a plate tower.

[0022] The water-to-oil ratio of the water scrubber in step 3) is 0.1-2, preferably 0.2-0.5, and the oil is one or more of isopropyl ether, methanol, ethanol, butanol, phenol, acetone, and MTBE, preferably isopropyl ether.

[0023] In step 4), the distillation tower is selected from any one of a plate tower, a structured packing tower, and a random packing tower, preferably a plate tower.

[0024] The mass fraction of BPA in the phenol / BPA mixed solution is 20%-40%, preferably 28-35%.

[0025] The number of theoretical plates of the distillation tower is 20-35, preferably 28-32, the reflux ratio is 0.2-2, preferably 1-1.5; the bottom pressure is 10-30 kPa, preferably 18-22 kPa; the bottom temperature is 190-210°C, preferably 196-205°C.

[0026] Step 5) In the crystallization step, the phenol / BPA solution enters a primary crystallizer, and after the BPA is partially crystallized, the crystal liquid enters a secondary crystallizer for further crystallization, and the slurry of the crystals and the crystal liquid in the secondary crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with the second crystal mother liquor to obtain washed crystals, and the mother liquor is sent to the resin reactor.

[0027] The crystals after a stage of washing are heated and melted, and then enter the first flash evaporator, and then the second flash evaporator. The low-phenol BPA solution after flash evaporation enters the stripping tower to obtain the BPA product.

[0028] The heating and melting temperature is 90°C-150°C, preferably 120°C-140°C;

[0029] The temperature of the first stage crystallization is 60-72°C, preferably 64-70°C, the pressure is 65-80kPa, preferably 72-78kPa, and the residence time is 2-4h, preferably 2.5-3h.

[0030] The temperature of the first stage of secondary crystallization is 50-55°C, preferably 53-54°C, the pressure is 22-32 kPa, preferably 27-30 kPa, and the residence time is 2-4 h, preferably 2.5-3 h.

[0031] The first-stage centrifugal pressure is 30-50 kPa, preferably 40-45 kPa, and the ratio of the second-stage crystallization mother liquor to the first-stage crystal is 0.5-1.1, preferably 0.6-0.7.

[0032] The primary flash pressure is 10 kPa-25 kPa, preferably 15 kPa-20 kPa, and the temperature is 155°C-180°C, preferably 160°C-170°C.

[0033] The secondary flash pressure is 1 kPa-3 kPa, preferably 2-2.5 kPa, and the temperature is 158°C-170°C, preferably 160°C-165°C.

[0034] The stripping tower is selected from any one of a plate tower, a structured packing tower, and a random packing tower, preferably a plate tower, with a theoretical plate number of 15-25, preferably 18-20.

[0035] The stripping tower pressure is 8-15 kPa, preferably 10-12 kPa; the stripping temperature is 165°C-175°C, preferably 168°C-170°C; the steam to stripping feed ratio is 0.08-0.12, preferably 0.1-0.11.

[0036] The BPA dry basis purity is above 99.96%, the PTBP content is below 50 ppm, the phenol content is below 15 ppm, the sodium ion content is below 1 ppm, the alcohol content is below 0.1 ppm, and the melting color number is below 20.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The crude BPA obtained by degrading waste polycarbonate in the prior art cannot be directly applied to the high-end polycarbonate industry, resulting in resource waste and product quality degradation. The method of the present invention can transform secondary brand BPA into products with a dry basis purity of more than 99.96%, thereby achieving greater economic benefits and resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention.

[0040] Among them, 1 is crude BPA, 2 is a dissolution tank, 3 is a BPA solution, 4 is a resin treatment bed, 5 is a low-salt BPA solution, 6 is a water washing tower, 7 is phenol, 8 is BPA / phenol solution, 9 is a circulating isopropyl ether, and 10 is a distillation tower.

[0041] Figure 2 Schematic diagram of the production process for BPA

[0042] Among them, 11 phenol, 12 acetone, 13 reactor, 14 BPA reaction liquid, 15 first-stage crystallizer, 16 first-stage second-stage crystallizer, 17 first-stage crystallization liquid, 18 first-stage second-stage crystallization liquid, 19 first-stage centrifuge, 20 first-stage crystal, 21 phenol washing, 22 first-stage flash distillation, 23 second-stage flash distillation, 24 phenol recovery, 25 tail gas, 26 steam, 27 BPA product, 28 stripping tower. DETAILED DESCRIPTION

[0043] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0044] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0045] The crude BPA is obtained by degrading PC products in the presence of alkali solution and methanol, filtering the reaction solution to remove insoluble impurities of the color powder, and then drying to remove methanol and DMC solvents. According to the analysis, the mass content is 0.001%-0.05% phenol, 90%-96% BPA, 0.4%-2.5% PTBP, 0.005%-3% methanol, 0.005%-3% DMC, and 0.1%-2% BPA salt.

[0046] The resin is purchased Seplite LX-160 macroporous cationic resin.

[0047] Isopropyl ether is purchased from Kailing Chemical, with a purity of more than 99.0%

[0048] BPA Testing Method:

[0049] Phenol / BPA / PTBP content test in BPA: Weigh 1 g of solid, accurately weigh the mass, dilute 100 times with acetonitrile, and use liquid phase to analyze the impurity content.

[0050] BPA melting color number test: Weigh 30g of solid and place it in a colorimetric tube, heat it to 170℃ to melt, store it stably for 1h, and place it in a colorimeter to read the color number.

[0051] Test for sodium BPA in BPA: Weigh 1g of solid, record the weight accurately, add it to a nickel dry pot, add 10g of aqua regia to digest at 250℃, dissolve for 30min, then add pure water to dilute to 100ml. Use ICP measurement.

[0052] Methanol / DMC test in BPA: Weigh 10g of solid and place it in a headspace bottle. Heat the solid in the headspace bottle to 110°C and analyze the methanol and DMC content in the gas phase.

[0053] Example 1

[0054] The crude BPA from the previous process, containing 0.001% phenol, 96% BPA, 2.5% PTBP, 0.005% methanol, 0.005% DMC, and 1.489% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and 20kg / h of circulating isopropyl ether is added to prepare a 20% BPA solution.

[0055] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 1 BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with two water washing stages and a water-to-oil ratio of 0.2 to obtain a refined BPA solution.

[0056] The refined BPA solution was fed into a distillation tower, into which 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 20, the reflux ratio was 0.2, the tower bottom pressure was 10 kPa, and the tower bottom temperature was 190° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0057] BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 65kPaG, the temperature controlled at 60℃, and the residence time at 2.5h. After BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 50kPaG, the temperature controlled at 22℃, and the residence time at 2.5h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 0.5, and the centrifugal pressure is controlled at 30kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80℃, the reaction rate at 1BV / h, and the resin service life of 30 months.

[0058] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 10kPa and a temperature of 155°C, and then enter the second flash evaporator at a pressure of 1kPa and a temperature of 158°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with 15 theoretical plates, a pressure of 12kPa, a temperature of 165°C, and a stripping steam ratio of 0.1 to obtain the BPA product.

[0059] The dry basis purity of BPA is 99.96%, the content of PTBP is 1ppm, the content of phenol is less than 5ppm, the content of sodium ion is 1ppm, the content of methanol is 0.1ppm, the content of DMC is 0.1ppm, and the melting color number is less than 10.

[0060] Example 2

[0061] The crude BPA from the previous process, containing 0.05% phenol, 90% BPA, 2.5% PTBP, 3% methanol, 3% DMC, and 1.45% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and 45kg / h of circulating isopropyl ether is added to prepare a 10% BPA solution.

[0062] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 2BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with three water washing stages and a water-to-oil ratio of 0.3 to obtain a refined BPA solution.

[0063] The refined BPA solution was fed into a distillation tower, and 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 35, the reflux ratio was 1, the tower bottom pressure was 15 kPa, and the tower bottom temperature was 200° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0064] BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 72kPaG, the temperature controlled at 64℃, and the residence time at 2h. After BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 27kPaG, the temperature controlled at 53℃, and the residence time at 2h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 0.6, and the centrifugal pressure is controlled at 50kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80℃, the reaction rate at 1BV / h, and the resin service life of 30 months.

[0065] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 20kPa and a temperature of 160°C, and then enter the second flash evaporator at a pressure of 2kPa and a temperature of 160°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with 18 theoretical plates, a pressure of 10kPa, a temperature of 170°C, and a stripping steam ratio of 0.08 to obtain the BPA product.

[0066] The dry basis purity of BPA is 99.96%, the content of PTBP is 3ppm, the content of phenol is below 10ppm, the content of sodium ion is 0.5ppm, the content of methanol is 0.05ppm, the content of DMC is 0.05ppm, and the melting color number is 12.

[0067] Example 3

[0068] The crude BPA from the previous process, containing 0.02% phenol, 92.58% BPA, 0.4% PTBP, 2.5% methanol, 2.5% DMC, and 2% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and is added with 15kg / h of circulating isopropyl ether to prepare a 25% BPA solution.

[0069] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 1.5 BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with two water washing stages and a water-to-oil ratio of 0.4 to obtain a refined BPA solution.

[0070] The refined BPA solution was fed into a distillation tower, into which 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 25, the reflux ratio was 1.5, the tower bottom pressure was 20 kPa, and the tower bottom temperature was 205° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0071] The BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 80kPaG, the temperature controlled at 72°C, and the residence time at 3h. After the BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 30kPaG, the temperature controlled at 54°C, and the residence time at 3h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 0.7, and the centrifugal pressure is controlled at 40kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80°C, the reaction rate at 1BV / h, and the resin service life of 30 months.

[0072] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 22 kPa and a temperature of 175°C, and then enter the second flash evaporator at a pressure of 2.5 kPa and a temperature of 165°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 25, a pressure of 8 kPa, a temperature of 175°C, and a stripping steam ratio of 0.11 to obtain the BPA product.

[0073] The dry basis purity of BPA is 99.97%, the content of PTBP is 1ppm, the content of phenol is below 3ppm, the content of sodium ion is 0.1ppm, the content of methanol is 0.01ppm, the content of DMC is 0.01ppm, and the melting color number is 8.

[0074] Example 4

[0075] The crude BPA from the previous process, containing 0.03% phenol, 95% BPA, 0.5% PTBP, 2.4% methanol, 1.97% DMC, and 0.1% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and is added with 11.7kg / h of circulating isopropyl ether to prepare a 30% BPA solution.

[0076] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 1 BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with three water washing stages and a water-to-oil ratio of 0.5 to obtain a refined BPA solution.

[0077] The refined BPA solution was fed into a distillation tower, into which 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 30, the reflux ratio was 2, the tower bottom pressure was 30 kPa, and the tower bottom temperature was 210° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0078] BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 78kPaG, the temperature controlled at 70℃, and the residence time at 4h. After BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 32kPaG, the temperature controlled at 55℃, and the residence time at 4h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 1.1, and the centrifugal pressure is controlled at 45kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80℃, the reaction rate at 1BV / h, and the service life of the resin is 30 months.

[0079] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 25kPa and a temperature of 180°C, and then enter the second flash evaporator at a pressure of 3kPa and a temperature of 170°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 20, a pressure of 15kPa, a temperature of 168°C, and a stripping steam ratio of 0.12 to obtain the BPA product.

[0080] The dry basis purity of BPA is 99.96%, the content of PTBP is 1ppm, the content of phenol is less than 10ppm, the content of sodium ion is 0.1ppm, the content of methanol is 0.05ppm, the content of DMC is 0.05ppm, and the melting color number is 12.

[0081] Comparative Example 1

[0082] The crude BPA from the previous process, containing 0.01% phenol, 91.91% BPA, 2.5% PTBP, 3% methanol, 1% DMC, and 1.5% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and is added with 20kg / h of circulating isopropyl ether to prepare a 20% BPA solution.

[0083] The BPA solution enters a plate-type water washing tower with one washing stage and a water-to-oil ratio of 0.1 to obtain a refined BPA solution.

[0084] The refined BPA solution was fed into a distillation tower, into which 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 20, the reflux ratio was 0.2, the tower bottom pressure was 10 kPa, and the tower bottom temperature was 190° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0085] BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 65kPaG, the temperature controlled at 60℃, and the residence time at 3.5h. After BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 24kPaG, the temperature controlled at 51℃, and the residence time at 3.5h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 0.8, and the centrifugal pressure is controlled at 35kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80℃, the reaction rate at 1BV / h, and the resin service life of 8 months.

[0086] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 10kPa and a temperature of 165°C, and then enter the second flash evaporator at a pressure of 1kPa and a temperature of 160°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 20, a pressure of 10kPa, a temperature of 165°C, and a stripping steam ratio of 0.08 to obtain the BPA product.

[0087] The dry basis purity of BPA is 99.90%, the PTBP content is 34ppm, the phenol content is below 15ppm, the sodium ion is 30ppm, the methanol is 1ppm, the DMC is 1ppm, and the melting color number is 130.

[0088] It is known in the art that in the absence of resin adsorption, metal ions entering the crystallization process will degrade BPA, and the sodium ion and melt color of the refined BPA product will be significantly deteriorated.

[0089] Comparative Example 2

[0090] The crude BPA from the previous process, containing 0.05% phenol, 94% BPA, 1.5% PTBP, 1.5% methanol, 2% DMC, and 0.95% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and is added with 15kg / h of circulating isopropyl ether to prepare a 25% BPA solution.

[0091] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 5 BV / h in a bottom-in-top-out manner.

[0092] The low-salt BPA solution was fed into a distillation tower, and 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 30, the reflux ratio was 1, the tower bottom pressure was 15 kPa, and the tower bottom temperature was 200° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0093] BPA / phenol solution enters a primary crystallizer, the pressure is controlled at 74kPaG, the temperature is controlled at 65℃, and the residence time is 3h. After BPA is partially crystallized, the crystal liquid enters a secondary crystallizer for further crystallization, the pressure is controlled at 29kPaG, the temperature is controlled at 54℃, and the residence time is 3h. The slurry of crystals and crystal liquid in the secondary crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, the mass ratio of washing liquid to crystal is 0.9, and the centrifugal pressure is controlled at 45kPaG. The mother liquor is sent to the resin reactor, the resin reaction temperature is 80℃, the reaction rate is 1BV / h, and the resin service life is 7 months.

[0094] After a washing, the crystals are heated to 140°C to melt and enter the first flash evaporator at a pressure of 20kPa and a temperature of 170°C, and then enter the second flash evaporator at a pressure of 2kPa and a temperature of 165°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 15, a pressure of 15kPa, a temperature of 168°C, and a stripping steam ratio of 0.1 to obtain the BPA product.

[0095] The dry basis purity of BPA is 99.90%, the PTBP content is 40ppm, the phenol content is below 18ppm, the sodium ion is 32ppm, the methanol is 1ppm, the DMC is 1ppm, and the melting color number is 134.

[0096] It is known in the art that in the absence of water washing, metal ions enter the crystallization process and degrade BPA, and the sodium ion and melt color of the refined BPA product deteriorate significantly.

[0097] Comparative Example 3

[0098] The crude BPA from the previous process, containing 0.02% phenol, 96% BPA, 2% PTBP, 0.6% methanol, 0.6% DMC, and 0.78% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and is added with 17kg / h of circulating isopropyl ether to prepare a 22.7% BPA solution.

[0099] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 1 BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with three water washing stages and a water-to-oil ratio of 0.5 to obtain a refined BPA solution.

[0100] The BPA solution was fed into a distillation tower, and 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 5, the reflux ratio was 1.5, the tower bottom pressure was 20 kPa, and the tower bottom temperature was 205° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0101] BPA / phenol solution enters a primary crystallizer, the pressure is controlled at 78kPaG, the temperature is controlled at 70℃, and the residence time is 2h. After BPA is partially crystallized, the crystal liquid enters a secondary crystallizer for further crystallization, the pressure is controlled at 31kPaG, the temperature is controlled at 55℃, and the residence time is 2h. The slurry of crystals and crystal liquid in the secondary crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, the mass ratio of washing liquid to crystal is 1, and the centrifugal pressure is controlled at 30kPaG. The mother liquor is sent to the resin reactor, the resin reaction temperature is 80℃, the reaction rate is 1BV / h, and the resin service life is 3 months.

[0102] After a washing step, the crystals are heated to 140°C to melt, and then enter the first flash evaporator at a pressure of 15kPa and a temperature of 175°C, and then enter the second flash evaporator at a pressure of 3kPa and a temperature of 170°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 25, a pressure of 8kPa, a temperature of 170°C, and a stripping steam ratio of 0.11 to obtain the BPA product.

[0103] The dry basis purity of BPA is 99.91%, the PTBP content is 45ppm, the phenol content is below 130ppm, the sodium ion is 0.1ppm, the methanol is 4ppm, the DMC is 4ppm, and the melting color number is 90.

[0104] It is known in the art that during the refining process of BPA after PC degradation, when the distillation removal is not thorough, after the organic solvent enters the crystallization process, various indicators such as product organic impurities and melt color number will significantly deteriorate.

[0105] Comparative Example 4

[0106] The crude BPA from the previous process, containing 0.03% phenol, 95% BPA, 0.5% PTBP, 2.4% methanol, 1.97% DMC, and 0.1% BPA sodium salt, enters the dissolution tank at a feed rate of 5kg / h, and 5kg / h of circulating isopropyl ether is added to prepare a 30% BPA solution.

[0107] The BPA solution enters the Seplite LX-160 macroporous resin bed at a rate of 1 BV / h in a bottom-in-top-out manner. The treated low-salt BPA solution enters a plate-type water washing tower with three water washing stages and a water-to-oil ratio of 0.5 to obtain a refined BPA solution.

[0108] The refined BPA solution was fed into a distillation tower, into which 15 kg / h of phenol was introduced. The theoretical plate number of the distillation tower was 30, the reflux ratio was 2, the tower bottom pressure was 30 kPa, and the tower bottom temperature was 210° C. Isopropyl ether was recovered from the top of the tower, and a BPA / phenol solution was obtained in the tower bottom.

[0109] BPA / phenol solution enters a first-stage crystallizer, with the pressure controlled at 78kPaG, the temperature controlled at 70℃, and the residence time at 4h. After BPA is partially crystallized, the crystal liquid enters a second-stage crystallizer for further crystallization, with the pressure controlled at 32kPaG, the temperature controlled at 55℃, and the residence time at 4h. The slurry of crystals and crystal liquid in the second-stage crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals are washed with phenol, with the mass ratio of washing liquid to crystal being 1.1, and the centrifugal pressure is controlled at 45kPaG. The mother liquor is sent to the resin reactor, with the resin reaction temperature at 80℃, the reaction rate at 1BV / h, and the service life of the resin is 30 months.

[0110] After a washing step, the crystals are heated to 140°C to melt, and then enter the first flash evaporator at a pressure of 25kPa and a temperature of 180°C, and then enter the second flash evaporator at a pressure of 3kPa and a temperature of 170°C. The low-phenol BPA solution after flash evaporation enters the stripping tower with a theoretical plate number of 20, a pressure of 15kPa, a temperature of 168°C, and a stripping steam ratio of 0.12 to obtain the BPA product.

[0111] The dry basis purity of BPA is 99.93%, the PTBP content is 20ppm, the phenol content is below 40ppm, the sodium ion is 6ppm, the methanol is 0.05ppm, the DMC is 0.05ppm, and the melting color number is 120.

[0112] It is known to those skilled in the art that when the solubility of crude BPA in isopropyl ether is high, the desalination by water washing is not thorough, and various indicators such as product organic impurities and melt color number are significantly deteriorated.

[0113] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for refining crude BPA, comprising the following steps: 1) Crude BPA from an upstream waste PC recovery device enters a dissolution tank and is dissolved with a solvent to obtain a crude BPA solution; 2) the crude BPA solution after the treatment in step 1) enters a resin treatment bed to remove sodium ions by adsorption to obtain a low-salt BPA solution; 3) The low-salt BPA solution obtained in step 2) enters a water washing tower to further remove sodium ions to obtain a refined BPA solution; 4) the refined BPA solution treated in step 3) is mixed with phenol and then enters a distillation tower to remove and recover the solvent to obtain a phenol / BPA solution; 5) The phenol / BPA solution obtained in step 4) enters the crystallization unit of the BPA device for further crystallization and purification to remove phenol and obtain a BPA product.

2. The purification method according to claim 1, characterized in that The crude BPA in step 1) contains, by total mass, 0.001%-0.05% phenol, 90%-96% BPA, 0.4%-2.5% PTBP, 0.005%-3% methanol, 0.005%-3% DMC, and 0.1%-2% BPA sodium salt.

3. The purification method according to claim 1 or 2, characterized in that: The solvent in step 1) is selected from at least one of methanol, ethanol, butanol, phenol, acetone, MTBE and isopropyl ether, preferably isopropyl ether; and / or, the mass concentration of BPA in the crude BPA solution is 10%-30%, preferably 20%-25%.

4. The refining method according to any one of claims 1 to 3, characterized in that: The resin in step 2) is a macroporous cationic resin, preferably one or more of Seplite LX-160, AMBERLITE IR120 Na, and D001 resin; and / or, the feed rate of the resin treatment bed in step 2) is 0.5-5BV / h, preferably 1-2BV / h.

5. The refining method according to any one of claims 1 to 4, characterized in that: The water-to-oil ratio of the water washing tower in step 3) is 0.1-2, preferably 0.2-0.5, and the oil is one or more of isopropyl ether, methanol, ethanol, butanol, phenol, acetone, and MTBE, preferably isopropyl ether; and / or, the water washing tower in step 3) is one or a combination of a plate tower and a packed tower, preferably a plate tower.

6. The refining method according to any one of claims 1 to 5, characterized in that: In step 4), the distillation tower is selected from any one of a plate tower, a structured packing tower, and a random packing tower, preferably a plate tower; and / or, the mass fraction of BPA in the phenol / BPA mixed solution is 20%-40%, preferably 28-35%; and / or, the theoretical plate number of the distillation tower is 20-35, preferably 28-32, the reflux ratio is 0.2-2, preferably 1-1.5, the bottom pressure is 10-30 kPa, preferably 18-22 kPa; the bottom temperature is 190-210° C., preferably 196-205° C.

7. The refining method according to any one of claims 1 to 6, characterized in that: Step 5) In the crystallization step, the phenol / BPA solution enters a primary crystallizer, and after the BPA is partially crystallized, the crystal liquid enters a secondary crystallizer for further crystallization, and the slurry of the crystals and the crystal liquid in the secondary crystallizer is sent to a centrifuge to separate a mother liquor and a crystal. The crystals of the first stage are washed with the second stage crystallization mother liquor, and the mother liquor of the first stage is sent to the resin reactor.

8. The purification method according to claim 7, characterized in that The crystals after the first stage of washing are heated and melted, and then enter the first-stage flash evaporator, and then enter the second-stage flash evaporator. The low-phenol BPA solution after flash evaporation enters the stripping tower to obtain the BPA product. Preferably, the heating and melting temperature is 90°C-150°C, preferably 120°C-140°C.

9. The purification method according to claim 7 or 8, characterized in that The temperature of the first stage crystallization is 60-72°C, preferably 64-70°C, the pressure is 65-80kPa, preferably 72-78kPa, and the residence time is 2-4h, preferably 2.5-3h; and / or, the temperature of the second stage crystallization is 50-55°C, preferably 53-54°C, the pressure is 22-32kPa, preferably 27-30kPa, and the residence time is 2-4h, preferably 2.5-3h; and / or, the first stage centrifugal pressure is 30-50kPa, preferably 40-45kPa, and the ratio of the second stage crystallization mother liquor to the first stage crystal is 0.5-1.1, preferably 0.6-0.

7. The refining method according to any one of claims 7 to 9, characterized in that The primary flash pressure is 10kPa-25kPa, preferably 15kPa-20kPa, and the temperature is 155℃-180℃, preferably 160℃-170℃; and / or, the secondary flash pressure is 1kPa-3kPa, preferably 2-2.5kPa, and the temperature is 158℃-170℃, preferably 160℃-165℃; and / or, the stripping tower is selected from any one of a plate tower, a structured packing tower, and a random packing tower, preferably a plate tower; and / or, the number of theoretical plates is 15-25, preferably 18-20; and / or, the stripping tower pressure is 8-15kPa, preferably 10-12kPa; the stripping temperature is 165℃-175℃, preferably 168℃-170℃; the steam to stripping feed ratio is 0.08-0.12, preferably 0.1-0.11.

Images