RU2782457C2 - Processing of residual flows from bisphenol production - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing of residual flows from bisphenol production. A method for processing of a residual flow from bisphenol production by condensation of a phenol compound and a carbonyl compound in one or more condensation reactors is described, wherein the residual flow contains unreacted phenols, bisphenol isomers, triphenols, organic sulfides, and water. The method provides for: (a1) contact of at least part of the residual flow or its product of reaction with an acidic catalyst in an additional reactor separate from condensation reactor(s), under conditions sufficient for provision of acid-catalyzed hydrolysis of organic sulfides in the residual flow to corresponding thiols and obtaining an outcoming flow; and (b1) distillation of at least part of the outcoming flow for extraction of distillate containing phenols and thiols, and obtaining a bottom product containing bisphenol isomers and triphenols and having a smaller content of organic sulfides than the residual flow.

EFFECT: removal of sulfur-containing compounds from residual flows from bisphenol production.

8 cl, 5 dwg, 3 tbl, 16 ex

Description

The field of technology to which the present invention relates

[0001] The present invention relates to the treatment of residual streams from the manufacture of bisphenols, in particular the manufacture of bisphenol-A, in order to remove and recover sulfur-containing compounds.

Background of the Invention

[0002] Bisphenol-A (BPA), also called 2,2-bis(4-hydroxyphenyl)propane or para,p-diphenylolpropane (p,p-BPA), is a commercially significant compound used to make polycarbonates, other engineering thermoplastics and epoxy resins. In particular, polycarbonate applications require high purity BPA due to the stringent requirements for optical clarity and color in the final application. 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 condensation reaction can take place 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 sulphonated ion exchange resin. In recent years, acidic ion exchange resins have become the overwhelming choice as catalysts for the condensation reaction in the manufacture of bisphenols, and strongly acidic sulfonated polystyrene ion exchange resins are particularly suitable in this regard.

[0003] Two different techniques for using heterogeneous acid catalysts in the production of bisphenols predominate in industrial practice. In one technique, the cocatalyst circulates freely in the reactor with the reaction feed. It is used to increase the selectivity and/or activity of the reaction. An alkanethiol such as methyl or ethyl mercaptan or a mercaptocarboxylic acid such as 3-mercaptopropionic acid is commonly used as the free circulating cocatalyst in this technique.

[0004] In a second technique for using heterogeneous acid catalysts in the production of bisphenols, the catalyst is modified by adding co-catalyst agents such as thiazolidines and aminothiols to some of the acid sites on the catalyst. For example, mercapto promoter groups can be attached to the sulfonate ions of the backbone of the cation exchange resin via covalent or ionic nitrogen bonds.

[0005] One problem with the use of sulfur-containing promoters in the manufacture of bisphenols is that thiols, in particular methyl mercaptans, also react with carbonyls and other unsaturated intermediates to form sulfides. These heavier sulfides are found in the reactor product as well as in the residual stream remaining after the desired bisphenol product has been recovered. At present, at least a portion of the residual stream is then distilled to recover the phenol and aqueous distillate, leaving the heavy sulfides in the bottom stream of the distillation process. This not only increases consumption of the thiol promoter, but also fouls the bottom stream, making disposal and/or further processing of the bottom stream more difficult.

[0006] Therefore, in the manufacture of bisphenols using sulfur-containing promoters, a way is required to remove sulfide contaminants from residual streams remaining after recovery of the desired bisphenol product and to recover the thiol promoter from sulfide contaminants.

Brief summary of the present invention

[0007] In one aspect, the present invention relates to a process for treating a bottom stream from the manufacture of bisphenol, wherein the bottom stream contains unreacted phenols, bisphenol isomers, trisphenols, organic sulfides, and water, and the method includes:

(a1) contacting at least a portion of the bottom stream, or reaction product thereof, with an acid catalyst under conditions sufficient to allow acid-catalyzed hydrolysis of the organic sulfides in the bottom stream to the corresponding thiols and produce an effluent; and

(b1) distilling at least a portion of the effluent to recover a distillate containing phenols and thiols and obtaining a bottom product containing bisphenol and trisphenol isomers and having a lower organic sulfide content than the residual stream.

[0008] In a further aspect, the present invention relates to a process for producing bisphenol-A, comprising:

(a2) condensing acetone with a molar excess of phenol in the presence of a thiol-promoted first solid acid catalyst under conditions effective to produce a first effluent containing bisphenol isomers, unreacted phenol, trisphenols, organic sulfides and water;

(b2) recovering bisphenol-A from the first effluent to leave a residual stream containing a mixture of bisphenol isomers depleted in bisphenol-A, unreacted phenol, trisphenols, organic sulfides and water;

(c2) contacting at least a portion of the residual stream with a second catalyst under conditions effective to isomerize the bisphenol isomers to bisphenol-A and to hydrolyze the organic sulfides to the corresponding thiols and produce a second effluent;

(d2) separating the second outlet stream into a recycle stream and a purge stream;

(e2) feeding the recycle stream to step (a2) or step (b2);

(f2) distilling the purge stream or its reaction product to recover distillates containing phenol and thiols and obtain a bottom product containing bisphenol and trisphenol isomers and having a lower content of organic sulfides than the residual stream; and

(g2) supplying the distillates recovered in step (f2) to step (a2).

[0009] In another additional aspect, the present invention relates to a method for producing bisphenol-A, comprising:

(a3) condensing acetone with a molar excess of phenol in the presence of a thiol-promoted first solid acid catalyst under conditions effective to produce a first effluent containing bisphenol isomers, unreacted phenol, trisphenols, organic sulfides and water;

(b3) recovering bisphenol-A from the first effluent to leave a residual stream containing a mixture of bisphenol isomers depleted in bisphenol-A, unreacted phenol, trisphenols, organic sulfides and water;

(c3) separating the residual stream into a first part and a second part;

(d3) contacting the first portion of the residual stream with a second catalyst under conditions effective to isomerize the bisphenol isomers to bisphenol-A and produce a second effluent;

(e3) recycling at least a portion of the second effluent to step (a3) or step (b3);

(f3) contacting the second portion of the residual stream with a third catalyst under conditions sufficient to allow acid-catalyzed hydrolysis of the organic sulfides in the second portion of the residual stream to the corresponding thiols to form a third effluent;

(g3) distillation of the third effluent stream to recover distillates containing phenols and thiols and obtain a bottom product containing bisphenol and trisphenol isomers and having a lower content of organic sulfides than the residual stream; and

(b3) supplying the distillates recovered in step (g3) to step (a3).

Brief description of the figures

[0010] FIG. 1 shows a typical process for treating a residual stream from a bisphenol-A manufacturing process.

[0011] FIG. 2 shows a first embodiment of the method disclosed herein.

[0012] FIG. 3 shows a second embodiment of the method disclosed herein.

[0013] FIG. 4 shows a modification of the second embodiment of the method disclosed herein.

[0014] FIG. 5 shows the relationship of the first order reaction rate constant for reducing the concentration of 4-methyl-4-methylthio-2-pentanone (MOM) as a function of water concentration in the reaction feedstock for a batch reaction of approximately 750 ppm MOM in phenol in the presence of a sulfonated strong acid ion exchanger. resins.

Detailed disclosure of the present invention

[0015] The present invention relates to the production of bisphenols by acid-catalyzed condensation of carbonyl compounds with phenols in the presence of sulfur-containing promoters. In particular, the present invention provides a simple process for treating the residual streams left after the desired bisphenol product has been recovered to convert the sulfide by-products of the condensation reaction to thiols, which can then be recycled back to the condensation reaction.

[0016] The method of the present invention is applicable to an acid-catalyzed condensation reaction between any carbonyl reactant and any phenol reactant to form a bisphenol product. Examples of suitable carbonyl compounds are those represented by the following formula:

where R represents hydrogen or an aliphatic, cycloaliphatic, aromatic or heterocyclic radical, including hydrocarbon radicals such as alkyl, cycloalkyl, aryl, aralkyl, alkaryl, or saturated or unsaturated; n is greater than 0, preferably 1 to 3, more preferably 1 to 2, and most preferably 1; and where n is greater than 1, X is a bond or a multivalent linking group with 1-14 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms; and where n is 1, X is hydrogen or an aliphatic, cycloaliphatic, aromatic, or heterocyclic radical, including hydrocarbon radicals such as alkyl, cycloalkyl, aryl, aralkyl, alkaryl, or saturated or unsaturated, provided that both X and R are not hydrogen.

[0017] Suitable carbonyl compounds for use herein include aldehydes and ketones. These compounds typically contain three to fourteen carbon atoms and are preferably aliphatic ketones. Examples of suitable carbonyl compounds include ketones such as acetone, methyl ethyl ketone, diethyl ketone, dibutyl ketone, isobutyl methyl ketone, acetophenone, methyl and amyl ketone, cyclohexanone, 3,3,5-trimethylcyclohexanone, cyclopentanone, 1,3-dichloroacetone, and the like. Most preferred is acetone.

[0018] Carbonyl compounds react with phenolic compounds. Suitable phenolic compounds for use herein include phenol and phenol homologues and substitution products containing at least one replaceable hydrogen atom directly bonded to the aromatic ring of the phenol. Such groups substituting a hydrogen atom and directly attached to an aromatic nucleus include halogen radicals such as chloride and bromide, and hydrocarbon radicals such as alkyl, cycloalkyl, aryl, alkaryl and aralkyl groups. Suitable phenolic compounds include phenol, cresols, xylenols, carvacrol, cumic alcohol, 2-methyl-6-ethylphenol, 2,4-dimethyl-3-ethylphenol, o-chlorophenol, m-chlorophenol, o-tert-butylphenol, 2.5 -xylenol, 2,5-di-tert-butylphenol, o-phenylphenol, 4-ethylphenol, 2-ethyl-4-methylphenol, 2,3,6-trimethylphenol, 2-methyl-4-tert-butylphenol, 2-tert -butyl-4-methylphenol, 2,3,5,6-tetramethylphenols, 2,6-dimethylphenol, 2,6-di-tert-butylphenol, 3,5-dimethylphenol, 2-methyl-3,5-diethylphenol, o -phenylphenol, p-phenylphenol, naphthols, phenantrol and the like. Most preferred are compositions containing phenol. Mixtures of any of the above compounds can be used.

[0019] Bisphenolic compounds obtained by the condensation reaction of a phenolic compound and a carbonyl compound in the method of the present invention are compounds where the nuclei of at least two phenolic radicals are directly attached by carbon-carbon bonds to the same carbon atom in the alkyl group. An illustrative non-limiting example of a bisphenol compound is represented by the formula:

where each of R ₁ and R ₂ independently represents a monovalent organic radical. Examples of such radicals include hydrocarbon radicals such as aliphatic, cycloaliphatic, aromatic or heterocyclic radicals, more particularly hydrocarbon radicals such as alkyl, cycloalkyl, aryl, aralkyl, alkaryl, or saturated or unsaturated. Preferably, each of R ₁ and R ₂ independently represents an alkyl radical having 1-2 carbon atoms. Most preferably, the bisphenol compound contains 2,2-bis(4-hydroxyphenyl)propane, i. bisphenol-A (BPA).

[0020] The reaction conditions used to carry out the condensation reaction described above will vary depending on the type of phenolic compound, solvent, carbonyl compound, and selected condensation catalyst. In general, phenolic compounds and carbonyl compounds are reacted in a reaction vessel either batchwise or continuously at a temperature ranging from about 20°C to about 130°C, preferably from about 50°C to about 90°C.

[0021] The pressure conditions are not particularly limited, and the reaction may take place under atmospheric pressure, subatmospheric pressure, or superatmospheric pressure. However, it is preferable to carry out the reaction either without any external supply pressure, or at sufficient pressure to force the reaction mixture through the catalyst bed, or to push the reaction mixture up in the vertical reactor, or to keep the contents of the reaction vessel in a liquid state if the reaction is carried out at a temperature above the boiling point of a reactant. The pressure and temperature should be set under such conditions that the reactants remain in the liquid phase in the reaction zone. The temperature may exceed 130°C, but should not be so high that any ingredients in the reaction vessel decompose, and should not be so high that the reaction product decomposes or promotes the synthesis of significant amounts of unwanted by-products.

[0022] The reactants are introduced into the reaction zone under such conditions as to provide a molar excess of the phenolic compound relative to the carbonyl compound. For example, the mole ratio of phenolic compound to carbonyl compound is preferably at least about 2:1, more preferably at least about 4:1, and up to about 25:1.

[0023] The condensation reaction is carried out in the presence of an acidic heterogeneous catalyst promoted with at least one organic sulfur compound. Suitable catalysts include molecular sieves, partially neutralized and insoluble salts of heteropoly acids, and acidic cation exchange resins. Preferred condensation catalysts are cation exchange resins, and especially those having a cation exchange capacity of at least about 0.5 and more preferably greater than about 4.0 meq/g on a dry matter basis. Particularly preferred are sulfonated cation exchange resins such as sulfonated styrene-divinylbenzene copolymers, sulfonated cross-linked styrene polymers, phenol-formaldehyde-sulfonic acid resins, benzene-formaldehyde-sulfonic acid resins, perfluorinated sulfonic acid resins, and the like. These include resins sold under trade names such as Amberlites or Amberlysts (Rohm and Haas Co.), DOWEX (Dow Chemical Co.), Permutit QH (Permutit Co.), Chempro (Chemical Process Co.), catalysts from Purolite, Lewatit® (LANXESS Deutschland GmbH), NAFION® (DuPont) and the like. Strongly acid resins based on a sulfonated styrene-divinylbenzene copolymer are preferred. Suitable cation exchange resins are derived from a sulfonated polymerized styrenic monomer that has been crosslinked with about 1% to about 8% divinylbenzene (resin). Specific examples of suitable sulphonated resins are Amberlyst® 131, Lewatit® K-1221, Purolite® CT-122, Purolite® CT-124, Diaion™ SK104H, Tulsion® 38 and Dowex® 50WX4.

[0024] The catalytic system for condensation also contains at least one organic sulfur-containing promoter, which usually contains at least one thiol, S-H, group. Such thiol promoters may be either ionically or covalently attached to the heterogeneous acid catalyst or not attached to the heterogeneous acid catalyst and added separately to the condensation reaction. Non-limiting examples of linked 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.

[0025] The amount of organic sulfur-containing promoter used in the catalyst system depends on the particular acidic heterogeneous catalyst used and the condensation process to be catalyzed. In general, however, the organic sulfur-containing promoter is used in an amount of 2 to 30 mol. %, for example, from 5 to 20 mol. %, based on the acid group (sulfonic group) in the acid ion exchange resin.

[0026] Where the unbound thiol promoter 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 hydrolysing agent, VMTP dissociates in the reaction zone into methyl mercaptan and acetone as acetone condenses with phenol to form BPA. A convenient hydrolysing agent is water, which can be introduced into any of the batches directly into the reaction zone, or can be produced in situ by a condensation reaction between a carbonyl compound and a phenolic compound. A molar ratio of water to VMTP catalyst promoter in the range of from about 1:1 to about 5:1 is sufficient for proper hydrolysis of the VMTP catalyst promoter. This amount of water is obtained in situ under normal reaction conditions. Thus, no additional water is required to be introduced into the reaction zone, although water may optionally be added as needed.

[0027] Any suitable reactor can be used as the reaction zone. The reaction may take place in a single reactor or in a plurality of reactors connected in series or in parallel. The reactor may be a countercurrent or plug flow reactor and the reaction may be carried out in a continuous or batch mode and the reactor may be oriented so as to receive an upward or downward flow. In the case of a fixed bed flow system, the liquid space velocity of the raw material mixture fed to the reactor is typically 0.2-50 h ⁻¹ . In the case of batch operation of the slurry bed system, the amount of strongly acidic ion exchange resin used, although it varies depending on the reaction temperature and pressure, is usually 20-100 wt. % based on the mixture of raw materials. The reaction time is usually 0.5-5 hours.

[0028] The main products of the condensation reaction are the desired bisphenol isomer, typically bisphenol-A, and water along with various by-products including other bisphenol isomers such as 2-(4-hydroxyphenyl)-2-(2-hydroxyphenyl)propane or o ,p-BPA, trisphenols and other impurities such as chromanes and indanes, as well as unreacted phenol and in some cases unreacted carbonyl compound. In addition, the condensation reaction effluent also contains organic sulfides formed by the condensation of the thiol promoter with carbonyl, carbonyl derivatives, and unsaturated intermediates. One example is 2,2-bis(methylthio)propane (VMTP). Another example of such a sulfide is 4-methyl-4-methylthio-2-pentanone (MOM):

which can be obtained by the reaction of mesityl oxide with methyl mercaptan.

[0029] Any method known to those skilled in the art can be used to recover the desired bisphenol product, typically bisphenol-A, from the condensate effluent. In general, however, the crude effluent from the condensation reaction is fed to a first separator, such as a distillation column, where most of the water and any unreacted carbonyl compound can be removed as overhead, while the desired bisphenol product, other bisphenol isomers, unreacted phenolic compound and heavy by-products (including organic sulfides) are recovered as a bottoms product. This bottom product can be fed into an additional separator. While crystallization is the primary method for separating the bisphenol-A, any known method for isolating the desired bisphenol product from the bottoms product may be used depending on the degree of purity of the bisphenol product desired.

[0030] The liquid phase mixture remaining after separation of the desired bisphenol product from the effluent by condensation or crystallization, or by any other means, is referred to herein as the "residual stream". If the isolation is carried out by crystallization, the residual stream is usually referred to as the mother liquor. The composition of the residual stream can vary widely, but typically after distillation to remove and recycle the added solvent, and optionally to perform partial dehydration, the residual stream contains:

(a) up to 90 wt. %, for example, up to 80 wt. %, for example, up to 75 wt. % unreacted phenolic compound and in most cases at least 60 wt. %, for example, at least 65 wt. %, for example, at least 70 wt. % unreacted phenolic compound;

(b) up to 30 wt. %, for example, up to 25 wt. %, for example, up to 20 wt. %, a mixture of bisphenol isomers depleted in the desired bisphenol isomer, usually bisphenol A, and in most cases at least 10 wt. %, for example, at least 15 wt. %, for example, at least 18 wt. %, the specified mixture of bisphenol isomers;

(c) up to 20 wt. %, for example, up to 16 wt. %, for example, up to 12 wt. %, trisphenolic and heavier aromatic compounds and in most cases at least 4 wt. %, for example, at least 6 wt. %, for example, at least 8 wt. %, trisphenolic and heavier aromatic compounds;

(d) up to 0.6 wt. % (6000 mass parts per million), for example, up to 0.4 mass. %, for example, up to 0.2 wt. %, for example, up to 0.1 wt. % organic sulfides and in most cases at least 0.01 wt. %, for example, at least 0.04 wt. %, for example, at least 0.06 wt. %, organic sulfides; and

(e) up to 1.0 wt. %, for example, up to 0.8 wt. %, for example, up to 0.6 wt. %, water and in most cases at least 0.2 wt. %, for example, at least 0.3 wt. %, for example, at least 0.4 wt. %, water.

[0031] For process economy, the bottom stream is subjected to various treatments to recover and recycle the unreacted phenolic compound and bisphenol isomers. In addition, a portion of the residual stream is typically purged to avoid the accumulation of heavy aromatics in the process recycle loops. The present invention provides a process for converting at least a portion of the organic sulfides present in the bottom stream to thiols before any bottom stream is purged so that loss of the thiol promoter in the purge is minimized and disposal problems of the purge stream are reduced.

[0032] In particular, the process disclosed herein involves contacting at least a portion of the bottom stream, or reaction product thereof, with an acidic hydrolysis catalyst under conditions sufficient to allow acid-catalyzed hydrolysis of the organic sulfides in the bottom stream to the corresponding thiol and carbonyl compound. The liberated carbonyl can then react with phenol in the bottom stream to form the bisphenol isomer and water. The consumption of carbonyl and the production of water contribute to the further conversion of sulfides into thiols and carbonyls. A typical example of a hydrolysis reaction is the hydrolysis of 4-methyl-4-methylthio-2-pentanone, which, as discussed above, can be obtained in the methyl mercaptan-promoted manufacture of bisphenol-A, and which can be hydrolyzed in the presence of an acid catalyst according to the following reaction:

[0033] Mesityl oxide is in equilibrium with acetone. In addition, both carbonyls can be condensed with phenol in the presence of an acidic hydrolysis catalyst to give bisphenols and water.

[0034] Any known hydrolysis catalyst can be used to convert organic sulfides in the bottom stream to the corresponding thiols, although preferred catalysts include acid ion exchange resins, in particular sulphonated acid ion exchange resins. In one embodiment, the hydrolysis catalyst contains an acidic, sulphonated micronetted polystyrene ion exchange resin with 2-6% divinylbenzene crosslinks. Suitable conditions for the hydrolysis reaction include a temperature of 60 to 110°C, such as 75-95°C, and a WHSV of 1-10 h ^-1 . The mole ratio of water to hydrolysable organic sulfide in the hydrolysis reaction feed stream is not critical, but is typically at least 2:1, eg at least 4:1 or greater, eg at least 20:1. Upper limits on the molar ratio of water to hydrolysable organic sulfide are highly practical and may be up to 100:1 or more, for example up to 80:1. Any known reactor design can be used for the hydrolysis reaction, but in one preferred embodiment, the reactor is operated liquid filled with feed downflow through the ion exchange resin catalyst bed.

[0035] The hydrolysis reaction effluent is fed to a distillation column where thiols, which are more volatile than the corresponding sulfides, are recovered in the overhead with water and unreacted phenolic compound. The bottoms product contains bisphenol isomers, trisphenols and heavier aromatics and has a lower organic sulfide content than the bottom stream. Typically, the bottoms product contains less than 100 ppmw, eg less than 10 ppmw, of organic sulfides. All or at least part of the overhead products can then be recycled, usually without further separation, to the bisphenol manufacturing process, in particular to the condensation reactor, while at least part of the bottoms product can be used in the downstream process, subjected to additional treatment to recover more phenol, acetone and/or isopropenylphenol and/or purge for disposal. In the case of obtaining bisphenol-A, suitable operating conditions for the distillation column include a temperature of from 160°C to 220°C and a pressure of 75 mm Hg. st. abs. up to 200 mm Hg. st.abs.

[0036] In one embodiment of the method of the present invention, the residual stream is divided into first and second parts without any initial treatment of the residual stream (except for solvent removal and partial dehydration). The first part of the residual stream is then fed to the isomerization reaction zone as described below, while the second part is fed to the hydrolysis reactor described above. The relative amounts of the first and second parts of the residual stream are not critical, but in some embodiments, the implementation of the second part contains at least 1 wt. %, for example, at least 3 wt. % of the total residual flow, but usually not more than 6 wt. %, for example, not more than 5 wt. % of the total residual flow.

[0037] The isomerization reaction zone used in this one embodiment of the method of the present invention may include any known acid catalyst effective under the conditions in the isomerization reaction zone to isomerize a non-equilibrium mixture of bisphenol isomers, in particular a mixture depleted in the desired bisphenol isomer. A suitable isomerization catalyst comprises an acidic ion exchange resin, in particular a sulphonated acid ion exchange resin. Suitable isomerization conditions include a temperature of 60 to 100°C, eg 75-85°C, and a WHSV of 1-10 h ^-1 . The effluent from the isomerization reaction zone has a higher content of the desired bisphenol isomer, such as p,p-BPA than the bottom stream, and can be recycled to a bisphenol production process, such as a condenser or crystallizer, to selectively recover the desired bisphenol isomer.

[0038] In a further embodiment of the process of the present invention, the entire residual stream is fed to a combined isomerization/hydrolysis reaction zone containing one or more catalysts effective under the conditions in the reaction zone to isomerize a non-equilibrium mixture of bisphenol isomers, in particular a mixture lean in the desired isomer bisphenol, and for the hydrolysis of organic sulfides to the corresponding thiols. Suitable catalysts for carrying out the combined isomerization/hydrolysis reaction include acid ion exchange resins, in particular sulfonated acid ion exchange resins. Suitable isomerization/hydrolysis conditions include a temperature of 60 to 110°C, eg 80-90°C, and a WHSV of 1-10 h ^-1 .

[0039] The effluent from the isomerization/hydrolysis reaction zone has a higher content of the desired bisphenol isomer such as p,p-BPA than the bottom stream and a lower organic sulfide content than the bottom stream. The effluent is then divided into first and second parts, the first part being recycled to the bisphenol manufacturing process, in particular to a crystallizer for selectively recovering the desired bisphenol isomer, and the second part being fed to a distillation column. The relative amounts of the first and second portions of the isomerization/hydrolysis effluent are not critical, but in some embodiments, the second portion contains at least 1 wt. %, for example, at least 3 wt. % of the total output stream, but usually not more than 6 wt. %, for example, not more than 5 wt. % of the total output stream.

[0040] The distillation column that receives the second portion of the isomerization/hydrolysis effluent is operated under such conditions that unreacted phenolic compound, water and thiols are recovered in the overhead while the bottoms product contains bisphenol isomers, trisphenols and heavier aromatics and has lower content of organic sulphides than the residual stream. All or at least part of the overhead products can then be recycled, usually without further separation, to the bisphenol manufacturing process, in particular to the condensation reactor, while at least part of the bottoms product can be used in the downstream process, subjected to additional treatment to recover more phenol, acetone and/or isopropenylphenol and/or purge for disposal. In the case of obtaining bisphenol-A, suitable operating conditions for the distillation column include a temperature of from 160°C to 220°C and a pressure of 75 mm Hg. st. abs. up to 200 mm Hg. st.abs.

[0041] In a modification of a further embodiment of the process of the present invention, the second portion of the isomerization/hydrolysis effluent is fed to an additional hydrolysis reactor prior to being fed to the distillation column. The additional hydrolysis reactor converts additional organic sulfides present in the isomerization/hydrolysis effluent back to thiols for recovery in the distillation column overhead.

[0042] Referring to the figures, in the state of the art, as shown in FIG. 1, a crude product stream from a thiol-promoted bisphenol-A manufacturing process that contains phenol, bisphenol-A and its isomers, trisphenols, and other impurities such as chromanes and indanes, water, and sulfides formed by condensing the thiol promoter with acetone is purified, usually in a crystallizer (not shown) to recover the desired bisphenol-A. As shown in FIG. 1, the bisphenol-A depleted residual stream (11) remaining after separating the solids from the crystallization effluent and distilling to recover any solvent used in the crystallization step is divided into a first part (12) and a second part (13). The first part (12) is then fed into the isomerization reactor (14) where it is contacted with an acidic isomerization catalyst to convert the bisphenol-A depleted mixture of bisphenol isomers in the first part (12) back to equilibrium concentration. The resulting isomerized effluent (15) is then recycled to the condenser or crystallizer to recover more bisphenol-A.

[0043] The second part (13) of the residual stream (11) is fed to a distillation column (20), which separates the second part (13) into a distillate stream (21) containing phenol and water, and a bottoms product (22) containing BPA isomers , trisphenols and other impurities, usually containing from about 0.01 to about 0.60 wt. % organic sulfides.

[0044] Various embodiments of the present invention are shown in FIGS. 2-4, in which like reference numbers are used to identify components like those shown in FIGS. 1. In the first embodiment of the disclosed method shown in FIG. 2, the residual stream (11) is again divided into a first part (12) and a second part (13), the first part (12) being fed into the isomerization reactor (14) for contact with an acidic isomerization catalyst. However, in this first embodiment of the disclosed process, the second part (13) of the residual stream is fed to the hydrolysis reaction zone (25) where the organic sulfides are converted back into carbonyl compounds and thiols. The effluent (26) from the hydrolysis reaction zone (25) is then fed to a distillation column (20) to be separated into a distillate stream (21), which now contains thiols in addition to phenol and water, and a bottom product (22), which contains BPA isomers , trisphenols and other impurities, but less organic sulfides than the residual stream (11).

[0045] A second embodiment of the disclosed method is shown in FIG. 3, in which the entire residual stream (11) is fed to the isomerization/hydrolysis reactor (30) where it is contacted with one or more acidic isomerization and hydrolysis catalysts to convert the bisphenol-A depleted mixture of bisphenol isomers in the residual stream (11) back to equilibrium concentration and for the hydrolysis of at least part of the organic sulfides in the corresponding thiols. The effluent (31) from the isomerization/hydrolysis reactor (30) is then divided into a first part (32), which is recycled back to the bisphenol-A manufacturing process, and a second part (33), which is fed into the distillation column (20).

[0046] In a modification of this second embodiment shown in FIG. 4, the second portion (33) of the isomerization/hydrolysis reactor effluent passes through an additional hydrolysis reactor (34) before being fed to the distillation column (20). Reactor (34) contains an acid catalyst, such as an ion exchange resin, effective to convert at least a portion of any remaining organic sulfides to the corresponding thiol.

[0047] The present invention will now be described more specifically with reference to the following non-limiting examples.

Example 1

[0048] A batch reactor system was used containing a 500 ml jacketed, three-necked round-bottom flask, a two-stage condenser to minimize volatile loss, and an ethylene glycol circulating bath to control the temperature of the reaction mixture. A thermocouple inserted into the reactor controlled the reaction temperature during the experiments. A magnetic stirrer provided constant stirring in the reactor.

[0049] The reactor was initially charged with 170 g of phenol and 30 g of the p,p-BPA isomer. Then, a volume of 4% cross-linked S-DVB ion exchange resin (IER) Diaion™ SK104H, equivalent to 5 g on a dry matter basis, was washed at least 5 times with deionized water. The IER was then air dried overnight in a fume hood. The IER was then dried further with 1000 ml of phenol for 2.5 hours in a Soxhlet extractor before loading into the reactor. The phenol/p,p-BPA/IER mixture (initially at room temperature) was heated to 80° C. by circulating glycol in the reactor jacket. This stage was carried out under a nitrogen atmosphere and with constant stirring of the environment in the reactor to ensure the balancing of the IER and the reaction mixture. During this period, p,p-BPA was isomerized to give an equilibrium mixture of o,p-BPA and BX, and impurities were also formed, usually in the recycle stream of the BPA process. After approximately 14-18 hours, the water content of the treated reaction medium was determined using GC/TCD analysis or a Karl Fischer coulometer and adjusted to 0.50 mass with deionized water. % at least 40 minutes after the last adjustment with water, 0.16 g of MOM was added to the reactor to obtain approx. 800 mass parts per million at the beginning of the reaction. To minimize MOM loss, the nitrogen purge for the reactor was turned off and the reactor vent line was clamped during the reaction period. The duration of the periodic work was 4 hours, and the time of the experiment began with the addition of MOM. The original sample was taken from the reactor before adding MOM. The sampling of the reaction mixture was carried out using a syringe injected through the membrane. Samples were taken from the reactor at 1 hour intervals after the addition of MOM. Each sample was labeled (0-4) and prepared according to internal standard protocols for analysis by HPLC and sulfur composition (GC/SCD). The MOM concentrations in mass parts per million for each sample are shown in Table 1. The initial MOM concentration was calculated based on the added masses of phenol, BPA, water and MOM.

Examples 2-6

[0050] For these examples, the batch reaction described in Example 1 was repeated using the same conditions, except that the measured water concentration in the sample taken immediately before the addition of MOM (sample 0) changed as shown in Table 1.

Examples 7-10

[0051] For these examples, the batch reaction described in example 1 was repeated using the same conditions, except that the reaction temperatures were raised to 95°C for example 7 and example 8, and lowered to 65°C for example 9 and example 10.

Example 11

[0052] For Example 11, the batch reaction described in Example 1 was repeated using a volume of 4% crosslinked S-DVB ion exchange resin equivalent to 10 grams on a dry matter basis rather than 5 grams.

Examples 12-15

[0053] For examples 12-15, the batch reaction described in example 1 was repeated using a volume of 2% crosslinked S-DVB ion exchange resin (Purolite® CT-122) equivalent to 5 grams of dry matter, and not 4% crosslinked S-DVB ion exchange resin.

Example 16

[0054] For example 16, the batch reaction described in example 1 was repeated with 1.345 grams of MOM to obtain an initial concentration of approximately 6300 mass parts per million with a water concentration of 0.29 mass. %.

[0055] The measured concentrations of MOM from Examples 1-6 can be plotted against reaction time to show that the hydrolysis reaction rate is substantially first order with respect to MOM. Experimental reaction rate constant, k _exp. , can then be calculated as shown in the last column of Table 1.

Experimental reaction rate constants for Examples 1-6 are plotted against initial water concentration in FIG. 5, which shows that the reaction rate constant for MOM is inversely proportional to the square of the initial water concentration. Fig. 5 shows that the effective acidity of the ion exchange resin has a strong influence on the MOM reaction rate, and that the hydrolysis reaction rate is not limited by the concentration of water as long as it is present in a stoichiometric excess. The relationship between the initial water concentration and the experimental reaction rate constants for examples 1-6 was used to calculate the corrected experimental reaction rate constant, k _{0.5 wt.%} , at a nominal initial water concentration of 0.5 wt. %. The expected value of k _{0.5 wt.%} based on examples 1-6 is 0.0125. The corrected experimental rate constants for Examples 1-16 are shown in Table 2. The value in the rightmost column represents R, the ratio of the corrected experimental rate constant, k _{0.5 wt%} , to the expected value of 0.0125 obtained from the correlation in FIG. 5. Examples with R values greater than 1 had faster reaction rates than the water corrected rate correlations for temperature, catalyst type, and catalyst loading rate in Examples 1-6. Examples with R values less than 1 had a lower reaction rate than the water corrected rate correlations for temperature, catalyst type, and catalyst loading rate in Examples 1-6.

[0056] Example 16 shows efficient hydrolysis of MOM for concentrations up to 6300 ppmw at a molar ratio of 3.72:1 water to hydrolysable organic sulfides. Table 3 shows the MOM concentrations versus time for Example 16. The concentration of methyl mercaptan (MeSH) was increased to a stoichiometrically equivalent concentration.

[0057] While the present invention has been described and shown with reference to specific embodiments, those skilled in the art will appreciate that the present invention is susceptible to variations not necessarily shown herein. For this reason, therefore, reference will only be made to the appended claims for the purposes of determining the actual scope of the non-present invention.

Claims (9)

1. A process for treating a residual stream from the manufacture of bisphenol by condensing a phenolic compound and a carbonyl compound in one or more condensation reactors, wherein the residual stream contains unreacted phenols, bisphenol isomers, trisphenols, organic sulfides, and water, and wherein the method comprises: (a1) contacting at least a portion of the bottom stream or its reaction product with an acid catalyst in an additional reactor separate from the condensation reactor(s) under conditions sufficient to allow acid-catalyzed hydrolysis of the organic sulfides in the bottom stream to the corresponding thiols and produce an effluent stream; and (b1) distilling at least a portion of the effluent to recover a distillate containing phenols and thiols and obtaining a bottom product containing bisphenol and trisphenol isomers and having a lower organic sulfide content than the residual stream. 2. The method of claim 1, further comprising recycling at least a portion of the distillates to the bisphenol manufacturing process. 3. The method according to claim 1 or 2, wherein the acid catalyst comprises an acid ion exchange resin. 4. A process according to any one of the preceding claims, wherein the acid catalyst comprises a sulfonated acid ion exchange resin with 2-6% crosslinks. 5. The method according to any one of the preceding claims, wherein the recovered thiol is methyl mercaptan. 6. The method according to any one of the preceding claims, wherein the contacting step (a1) is carried out at a temperature of from about 60 to 110°C. 7. A process according to any one of the preceding claims, wherein the bottom stream contains up to 6000 ppm by weight of hydrolysable organic sulfides and sufficient water present such that the mole ratio of water to hydrolysable organic sulfides is at least 4:1. 8. A process according to any one of the preceding claims, wherein the bottom stream comprises a mother liquor stream from the crystallization step for recovering the bisphenol product.

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