Process for manufacturing bisphenol

Abstract

A process for producing bisphenol A comprises reacting acetone with phenol in the presence of a catalyst system comprising an acidic heterogeneous catalyst and a catalyst promoter comprising at least one organic sulfur-containing compound to produce a reaction effluent containing bisphenol A, water, unreacted acetone, unreacted phenol, and at least a portion of the catalyst promoter. At least a portion of the reaction effluent is distilled to remove the water, catalyst promoter, and unreacted acetone and leave a residue stream containing bisphenol A. At least a portion of the residue stream is then contacted with a basic anion exchange resin to produce a purified stream from which bisphenol A is recovered. [Selected Figure] Figure 1

Description

[Technical field]

[0001] The present invention relates to a process for producing bisphenol A. [Background technology]

[0002] Bisphenol A (BPA), also called 2,2-bis(4-hydroxyphenyl)propane or para,para-diphenylolpropane (p,p-BPA), is a commercially important compound used to make polycarbonates, other engineering thermoplastics, and epoxy resins. BPA is produced commercially by the condensation of acetone and phenol, and in fact, the production of BPA is the largest consumer of phenol. The reaction may be carried out in the presence of a strong homogeneous acid, such as hydrochloric acid, sulfuric acid, or toluenesulfonic acid, or in the presence of a heterogeneous acid catalyst, such as a sulfonated ion exchange resin. In recent years, acidic ion exchange resins have become the overwhelming catalyst of choice for the condensation reaction to produce bisphenols, with strongly acidic sulfonated polystyrene ion exchange resins being particularly useful in this regard.

[0003] Two different technologies using heterogeneous acid catalysts in the production of bisphenols dominate industrial practice. In one technology, a cocatalyst promoter circulates freely through the reactor with the reaction feed. It is used to increase the selectivity and / or activity of the reaction. Alkanethiols, such as methyl or ethyl mercaptan, or mercaptocarboxylic acids, such as 3-mercaptopropionic acid, are typically used as freely circulating cocatalyst promoters in this technology. The acid sites of the resin are left available, i.e., the majority of them are not bound to the promoter. This allows flexibility in adjusting the optimum concentration of the promoter, taking into account the specific reaction conditions in question.

[0004] In a second technique using heterogeneous acid catalysts in the production of bisphenols, the catalyst is modified by the addition of cocatalyst agents, such as thiazolidines and aminothiols, to some of the acidic sites on the catalyst. For example, mercapto promoter groups may be attached to the backbone sulfonate ions of a cation exchange resin by covalent or ionic nitrogen bonds. The fixed promoter technique requires less direct handling and processing of the promoter than the free circulating promoter process, but the ability to refine the process by separate processing of the resin and promoter is greatly reduced.

[0005] Among the requirements for BPA are thermal stability and high purity due to stringent requirements for optical clarity and color in the final application, especially when used in the production of polycarbonate. It is therefore known, for example from U.S. Pat. No. 5,124,490, to improve the color and thermal stability of BPA products by contacting the BPA process stream with a basic anion exchange bed to remove traces of acid leached from a strong acid sulfonated ion exchange resin catalyst used in the acetone / phenol condensation reaction.

[0006] Although treatment with basic anion exchange resins is effective in purifying BPA process streams, it has been found that if the process stream further contains residual mercaptan promoters, such as methyl or ethyl mercaptans, contact with the basic anion exchange resins can convert the mercaptans to dimethyl sulfide, dimethyl disulfide, diethyl disulfide, hydrogen sulfide, or other sulfur species, resulting in an uneconomical loss of the mercaptan promoters as well as the need for additional process steps to remove the undesired sulfur species.

[0007] Therefore, a need exists for improved methods for purifying BPA process streams produced using heterogeneous acid catalysts promoted with organic sulfur-containing compounds. Summary of the Invention

[0008] It has now been discovered in accordance with the present invention that in order to obtain the quality benefits from contacting with an anion exchange bed without losing the mercaptan promoter, the BPA reaction effluent should first be distilled to remove the mercaptan promoter and unreacted acetone prior to contact with the anion exchange bed. Moreover, to maximize capture of trace acidic materials, contact with the anion exchange bed should preferably occur before the distilled stream is subjected to crystallization or other methods to recover BPA.

[0009] Thus, in one aspect, the invention resides in a process for producing bisphenol A, the process comprising the steps of: (a) reacting acetone with phenol in the presence of a catalyst system comprising an acidic heterogeneous catalyst and a catalyst promoter comprising at least one organic sulfur-containing compound to produce a reaction effluent comprising bisphenol A, water, unreacted acetone, unreacted phenol, and at least a portion of the catalyst promoter; (b) distilling at least a portion of the reaction effluent to remove water, catalyst promoter, and unreacted acetone and leaving a remainder stream containing bisphenol A; (c) contacting at least a portion of the retentate stream with a basic anion exchange resin to produce a purified stream; and (d) recovering bisphenol A from the purified stream. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a simplified flow diagram illustrating a process for producing bisphenol A according to one embodiment of the present invention.

[0011] [Diagram 2] 1 is a graph showing the change in diethyl disulfide (DEDS) concentration in the product obtained in Example 1 with time on oil using 10 g (dry basis) of Lewatit™ MP 62 WS anion exchange resin at temperatures of 90° C., 110° C. and 120° C.

[0012] [Diagram 3] 1 is a graph showing the change in diethyl disulfide (DEDS) concentration in the product obtained in Example 1 with time on oil using various amounts of Lewatit™ MP 62 WS anion exchange resin at a temperature of 90° C.

[0013] [Figure 4] 1 is a graph showing the change in diethyl disulfide (DEDS) concentration in the product obtained in Example 1 with time on oil using 10 g (dry basis) of Lewatit™ MP 62 WS anion exchange resin and 10 g (dry basis) of Amberlyst™ A26 anion exchange resin, both at a temperature of 90° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to the production of bisphenol A (BPA) by the condensation of acetone with phenol in the presence of a catalyst system comprising an acidic heterogeneous catalyst and a catalyst promoter comprising at least one organic sulfur-containing compound. The condensation reaction effluent contains a crude BPA product, typically including acidic impurities leached from the catalyst, water, at least a portion of the catalyst promoter, and typically unreacted acetone and phenol. In particular, the present invention provides a simple and effective process for purifying the BPA product while minimizing the loss of the catalyst promoter present in the reaction effluent stream, thereby improving the color and thermal stability of the BPA product.

[0015] Any known reaction system may be used to effect the condensation of acetone with phenol to produce BPA in accordance with the present invention. Generally, acetone and phenol are reacted in a batch or continuous reaction zone at a temperature ranging from about 20° C. to about 130° C., preferably from about 50° C. to about 90° C.

[0016] The pressure conditions are not particularly limited, and the reaction may be carried out at atmospheric, subatmospheric or superatmospheric pressure. However, it is preferred to carry out the reaction without any externally induced pressure, or at a pressure sufficient to force the reaction mixture across the catalyst bed, or to force an upstream reaction mixture into a subsequent vertical reactor, or to maintain the contents in the reaction vessel in a liquid state if the reaction is carried out at a temperature above the boiling point of any of the components. The pressure and temperature should be set under conditions that keep the reactants in the liquid phase in the reaction zone. The temperature may exceed 130° C., but should not be so high as to decompose any of the components in the reaction vessel, nor should it be so high as to decompose the reaction products or promote the synthesis of significant amounts of undesirable by-products.

[0017] The reactants are introduced into the reaction zone under conditions which ensure a molar excess of phenol relative to acetone, for example, the molar ratio of phenol to acetone is preferably at least about 2:1, more preferably at least about 4:1, and up to about 25:1.

[0018] The condensation reaction is carried out in the presence of an acidic heterogeneous catalyst promoted by at least one organic sulfur-containing compound. Suitable catalysts include molecular sieves, partially neutralized and insolubilized salts of heteropolyacids, and acidic cation exchange resins. Preferred condensation catalysts are cation exchange resins, especially those having a cation exchange capacity of at least about 0.5, more preferably greater than about 4.0 meq / g dry weight. Particularly preferred are sulfonated cation exchange resins, such as sulfonated styrene-divinylbenzene copolymers, sulfonated crosslinked styrene polymers, phenol-formaldehyde-sulfonic acid resins, benzene-formaldehyde-sulfonic acid resins, perfluorinated sulfonic acid resins, and the like. These include those sold under trade names such as Amberlite or Amberlyst (Rohm & Haas), DOWEX (Dow Chemical), PermutitQH (Permutit), Chempro (Chemical Process), catalysts from Purolite, Lewatit™ (LANXESS Germany), NAFION™ (DuPont), etc. Strongly acidic sulfonated styrene-divinylbenzene copolymer resins are preferred. Suitable cation exchange resins are made from sulfonated polymerized styrene monomer crosslinked with about 1% to about 8% divinylbenzene (resin). Specific examples of suitable sulfonated resins are Amberlyst™ 131, Lewatit™ K-1221, Purolite™ CT-122, Purolite™ CT-124, Diaion™ SK104H, Tulsion™ 38 and Dowex™ 50WX4.

[0019] The condensation catalyst system also includes at least one organic sulfur-containing promoter, which generally includes at least one thiol group, i.e., SH group. Such thiol promoters are ionically or covalently bound to the heterogeneous acid catalyst, or are not bound to the heterogeneous acid catalyst and are added separately to the condensation reaction. Non-limiting examples of bound promoters include mercaptoalkylpyridines, mercaptoalkylamines, thiazolidines, and aminothiols. Non-limiting examples of unbound promoters include alkyl mercaptans, such as methyl mercaptan (MeSH) and ethyl mercaptan, mercaptocarboxylic acids, such as mercaptopropionic acid, and mercaptosulfonic acids.

[0020] The amount of organic sulfur-containing promoter used in the catalyst system will depend on the particular acidic heterogeneous catalyst used, but generally the organic sulfur-containing promoter is used in an amount of 2 to 30 mole %, for example 5 to 20 mole %, based on the acidic groups (sulfonic acid groups) in the acidic ion exchange resin.

[0021] When the unbound thiol is methyl mercaptan and the carbonyl compound is acetone, 2,2-bis(methylthio)propane (BMTP) is formed in the presence of an acid catalyst. In the presence of a hydrolysis agent, BMTP dissociates in the reaction zone into methyl mercaptan and acetone, while acetone condenses with phenol to form BPA. A convenient hydrolysis agent is water, which may be introduced into either of the feedstock charges or directly into the reaction zone, or may be produced in situ by a condensation reaction between the carbonyl compound and a phenolic compound. A molar ratio of water to BMTP catalyst promoter in the range of about 1:1 to about 5:1 is sufficient to adequately hydrolyze the BMTP catalyst promoter. This amount of water is produced in situ under typical reaction conditions. Thus, no additional water needs to be introduced into the reaction zone, although water may optionally be added if desired.

[0022] Any suitable reactor may be used as the reaction zone. The reaction may be carried out in a single reactor or in multiple reactors connected in series or parallel. The reactor may be a backmixed or plug flow type reactor, the reaction may be carried out in continuous or batch mode, and the reactor may be oriented to produce an upflow or downflow. In the case of a fixed bed flow system, the liquid hourly space velocity of the mixture of raw materials fed to the reactor is typically between 0.2 and 50 h o. -1 In the case of a slurry bed batch apparatus, the amount of the strong acid ion exchange resin used varies depending on the reaction temperature and pressure, but is usually 20-100% by weight based on the mixture of raw materials. The reaction time is usually 0.5-5 hours.

[0023] The primary products of the condensation reaction are the desired bisphenol isomer, i.e., bisphenol A and water, along with various by-products, such as other diphenylolpropane isomers, e.g., 2-(4-hydroxyphenyl)-2-(2-hydroxyphenyl)propane, trisphenols, and other impurities, e.g., chroman and indane. In addition, the effluent of the condensation reaction also contains at least a portion of the organic sulfur-containing promoter, along with unreacted phenol and unreacted acetone.

[0024] The crude condensation reaction effluent also contains traces of polysulfonic acid groups that leach from the sulfonated ion exchange catalyst during the condensation reaction. These polysulfonic acid groups can cause degradation of the BPA product melt, increase color in the melt, and reduce the thermal stability of the BPA product, especially in high transparency polycarbonate applications. These effects can be ameliorated by contacting the crude reaction effluent with a basic anion exchange resin. However, although treatment with a basic anion exchange resin is effective in removing acid groups from the BPA process stream, it has been found that when the process stream also contains residual mercaptan promoters, this treatment also converts the mercaptans to dimethyl sulfide, dimethyl disulfide, diethyl disulfide, hydrogen sulfide, or other sulfur species. This results in the uneconomic loss of the mercaptan promoter as well as the need for additional process steps to remove possible sulfur species.

[0025] To obviate this problem, in the present process, the crude condensation reaction effluent is distilled to remove at least a portion of the catalyst promoter, unreacted acetone, unreacted phenol and water prior to any contact with the basic anion exchange resin, leaving a residual stream containing phenol, BPA, other diphenylolpropane isomers, trisphenols and possible other heavy by-products. Conveniently, the distillation of the crude condensation reaction effluent is carried out at a temperature of 155-185°C and a pressure of 50-85 kPa-a.

[0026] At least a portion of the catalyst promoter, unreacted acetone and unreacted phenol removed by the distillation step is preferably recycled to the condensation reaction.

[0027] The residue stream remaining after the distillation step typically contains less than 1,000 ppm by weight of water, e.g., less than 100 ppm by weight of water, less than 500 ppm by weight of acetone, e.g., less than 50 ppm by weight of acetone, and less than 100 ppm by weight of sulfur-containing catalyst promoter, e.g., less than 10 ppm by weight of sulfur-containing catalyst promoter. The residue stream is then contacted with a basic anion exchange resin to reduce the level of acid groups leached from the strong acid sulfonated ion exchange condensation reaction catalyst and produce a purified stream. The contacting step with the basic anion exchange resin is carried out at a temperature of 80-120°C, e.g., by downflow of the residue stream through a bed of basic anion exchange resin. Suitable anion exchange resins can be strong or weakly basic anion exchange resins, preferably weakly basic anion exchange resins containing primary, secondary or tertiary amine groups. Examples of commercially available basic anion exchange resins are Lewatit™ MP 62, Amberlyst™ A21, Amberlyst™ A26 and Diaion™ WA-21.

[0028] Any method known to those skilled in the art may be used to recover the desired BPA product from the resulting purified stream. One preferred method of BPA recovery is crystallization. The crystallization process can be one of several known techniques for the purification of BPA, preferably the crystallization of an equimolar adduct with phenol. The crystals produced are then separated from the mother liquor by filtration or centrifugation. The separated mother liquor is then recycled to the condensation reactor. In one embodiment, the mother liquor is separately contacted with a strong acidic sulfonation ion exchange reaction catalyst to convert impurities, especially other isomers of diphenylolpropane, to BPA, and then this reaction product is returned to the condensation reactor.

[0029] One embodiment of this process is shown in Figure 1, where fresh acetone is fed by line 11 to condensation reactor 12, which also receives recycled acetone, phenol and organic sulfur-containing promoter via line 13. Condensation reactor 12 contains an acidic heterogeneous catalyst, preferably a sulfonated ion exchange resin, and is operated under conditions such that acetone and phenol react to produce a condensation reaction product that contains BPA and water as well as various by-products such as other isomers of diphenylolpropane, trisphenols and heavy impurities such as chroman and indan.

[0030] The effluent from the condensation reactor 12, containing unreacted acetone and unreacted phenol along with the condensation reaction products and at least a portion of the catalyst promoter, is fed via line 14 to one or more distillation columns 15 operated to remove (i) a first lights stream consisting of most of the unreacted acetone and catalyst promoter, (ii) a second intermediate stream consisting of most of the water in the effluent and some unreacted phenol, and (iii) a third stream consisting primarily of unreacted phenol. The first stream (i) and the third stream (iii) are collected and recycled to the condensation reactor 12 via line 13, while the second lights stream (ii) is collected and fed to wastewater treatment (not shown) via line 16.

[0031] After removal of the first light stream (i), the second intermediate stream (ii) and the third stream (iii), the remaining residue stream, which contains most of the bisphenol components of the condensation reactor effluent and residual unreacted phenol, is fed via line 17 to a bed 18 of basic anion exchange resin for removal of leached polysulfonic acid groups. After leaving bed 18, the purified residue stream is fed to a crystallizer 19, which also receives fresh phenol via line 21. An adduct of BPA and phenol is selectively crystallized in crystallizer 19, separated from the mother liquor by filtration or centrifugation, and fed via line 22 to a melt finisher 23. The adduct crystals are melted in finisher 23 to separate the phenol from the BPA, which is recycled to crystallizer 19 via line 24 and fed to solidifier 25.

[0032] The mother liquor remaining after recovery of the BPA / phenol adduct is removed from crystallizer 19 via line 26 and split into a purge stream 27 and a recycle stream 28, with the recycle stream 28 being returned to condensation reactor 12. In some embodiments, before being returned to condensation reactor 12, the mother liquor recycle stream is separately contacted with a strong acid sulfonation ion exchange catalyst 29 to convert impurities, particularly other isomers of diphenylolpropane, to the preferred BPA isomer.

[0033] The invention will now be described in more detail with reference to the following non-limiting Examples and the accompanying drawings, Figures 2 to 4. EXAMPLES

[0034] A synthetic mixture consisting of 70 wt% phenol, 25 wt% BPA, 2 wt% water, 2 wt% ethyl mercaptan, and 1 wt% acetone was prepared to simulate the effluent from the condensation reaction of phenol with acetone in the presence of a representative alkyl mercaptan promoter, ethyl mercaptan promoter.

[0035] A series of tests was carried out in which 200 g of this synthesis reaction effluent mixture was contacted in a closed autoclave with various amounts of the basic anion exchange resin Lewatit™ MP 62 WS at temperatures of 90° C., 110° C. and 120° C., and with 10 g of the basic anion exchange resin Amberlyst™ A26 at 90° C. In each case the anion exchange resin was washed with 10 bed volumes of deionized water before the tests.

[0036] The autoclave contents were sampled at various times throughout each test, and samples were analyzed by GC-FID / SCD to determine the identity and amount of possible sulfide species produced. The results are summarized in Figures 2-4 and illustrate the production of diethyl disulfide (DEDS) during contact with a basic anion exchange resin in the presence of an ethyl mercaptan promoter. Specifically, the results show that using Lewatit™ MP 62 WS anion exchange resin, the DEDS concentration in the reaction product increased with increasing reaction temperature (Figure 2) and anion exchange resin charge (Figure 3). Figure 4 shows that at the same temperature (90°C), Amberlyst™ A26 anion exchange resin produced more DEDS than Lewatit™ MP 62 WS anion exchange resin, likely reflecting the presence of more strongly basic sites attached to the former. EXAMPLES

[0037] A test similar to that of Example 1 was conducted in which 200 g of a synthetic mixture consisting of 70 wt. % phenol, 28 wt. % BPA, and 2 wt. % ethyl mercaptan was contacted with 10 g of washed Lewatit™ MP 62 WS anion exchange resin in an autoclave at 100° C. Over the course of the 24 hour test, the ethyl mercaptan content of the mixture was found to decrease as an increasing amount of DEDS was detected. This test demonstrates that if an anion exchange resin is not placed downstream of the distillation step to remove the mercaptan from the condensation effluent, there will be a loss of the mercaptan promoter to undesired sulfur species. EXAMPLES

[0038] A synthetic mixture composed of 70 wt. % phenol and 30 wt. % BPA was prepared to simulate the bottoms stream remaining after distillation to remove water, catalyst promoter, and unreacted acetone from the reaction effluent of the condensation of phenol with acetone. 200 g of this synthetic bottoms mixture was contacted with 10 g of washed Lewatit™ MP 62 WS anion exchange resin in an autoclave at 100° C. No DEDS was detected after 24 hours of flow. This demonstrates that no DEDS was produced during contact with the anion exchange resin when the ethyl mercaptan promoter was not present in the mixture.

[0039] When the test was repeated using washed Amberlyst™ A26 anion exchange resin, the same results (no detectable DEDS) were obtained. [Examples 4 to 6]

[0040] The test of Example 3 was repeated using washed Lewatit MP 62 WS anion exchange resin, but with various synthetic mixtures. The various synthetic mixtures consisted of 70% by weight phenol, 28% by weight BPA, and 2% by weight water (Example 4); 70% by weight phenol, 29% by weight BPA, and 1% by weight acetone (Example 5); and 70% by weight phenol, 27% by weight BPA, 2% by weight water, and 1% by weight acetone (Example 6). In each case, no DEDS was detected after 24 hours of running. These examples show that in the absence of ethyl mercaptan promoter, no DEDS was produced during contact with the anion exchange resin, and that the presence of water and / or acetone in the mixture did not change these results.

[0041] Although the present invention has been described and illustrated by reference to specific embodiments, those skilled in the art will recognize that the present invention is amenable to variations not necessarily exemplified herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

1. 1. A process for producing bisphenol A, comprising the steps of: (a) reacting acetone with phenol in the presence of a catalyst system comprising an acidic heterogeneous catalyst and a catalyst promoter comprising at least one organic sulfur-containing compound to produce a reaction effluent comprising bisphenol A, water, unreacted acetone, unreacted phenol, and at least a portion of the catalyst promoter; (b) distilling at least a portion of said reaction effluent to remove water, said catalyst promoter and unreacted acetone and leaving a remainder stream containing bisphenol A; (c) contacting the entire amount of said retentate stream immediately after step (b) with a basic anion exchange resin to produce a purified stream; and (d) recovering bisphenol A from said purified stream.

2. 10. The process of claim 1, wherein the acidic heterogeneous catalyst comprises a sulfonated ion exchange resin.

3. 3. The process of claim 1 or 2, wherein the catalyst promoter comprises at least one organic sulfur-containing compound selected from the group consisting of alkyl mercaptans, mercaptocarboxylic acids, mercaptosulfonic acids, mercaptoalkylpyridines, mercaptoalkylamines, thiazolidines, and aminothiols.

4. 4. The process of any one of claims 1 to 3, wherein the distillation step (b) is carried out at a temperature of from 155 to 185°C and a pressure of from 50 to 85 kPa-a.

5. The process of any one of claims 1 to 4, wherein the remainder stream contains less than 1,000 ppm by weight water, less than 500 ppm by weight acetone, and less than 100 ppm by weight of a sulfur-containing catalytic promoter.

6. 6. The process of any one of claims 1 to 5, wherein at least a portion of the catalyst promoter removed in distillation step (b) is recycled to reaction step (a).

7. The process of any one of claims 1 to 6, wherein the contacting step (c) is carried out at a temperature of from 80 to 120°C.

8. The process of any one of claims 1 to 7, wherein the contacting step (c) is carried out by downflow of the retentate stream through a bed of the basic anion exchange resin.

9. The process of any one of claims 1 to 8, wherein the anion exchange resin is a weakly basic anion exchange resin containing primary, secondary or tertiary amine groups.

10. The process of any one of claims 1 to 9, wherein recovery step (d) comprises crystallization to separate the purified stream into a solid bisphenol A-containing product and a mother liquor stream.

11. 11. The process of claim 10, wherein the mother liquor stream contains other isomers of diphenylolpropane other than bisphenol A and the process further comprises the steps of: (f) contacting said mother liquor with a sulfonated acidic ion exchange catalyst under conditions to convert at least a portion of the other isomers of said diphenylolpropane to bisphenol A to produce an isomerized product stream.

12. The process of claim 11 further comprising the steps of: (g) feeding at least a portion of said isomerized product stream to the reaction of step (a).

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