Process for preparing a bisphenol

In a process for the preparation of a bisphenol by condensation of a phenolic compound and a carbonyl compound in the presence of an acidic ion exchange resin catalyst, strong acids that leach from the acidic ion exchange resin catalyst into the reaction effluent are scavenged by a carbon adsorbent. The acid scavenging improves the product quality and yield by reducing acid catalyzed cracking of bisphenols during purification and finishing steps.

BACKGROUND OF THE INVENTION 
This invention relates to the preparation of a bisphenol. In one aspect, 
the invention relates to improving purity and yield in a process to 
manufacture a bisphenol employing an acidic ion exchange resin catalyst. 
Bisphenols are used as the starting material in the manufacture of resins 
such as polycarbonate resins and epoxy resins. It is important that the 
bisphenol starting material is as pure as possible in order to avoid 
adverse effects on the properties of resulting resins. 
Bisphenols can be manufactured over a strongly acidic ion exchange resin 
catalyst by condensation of a phenol and a ketone or an aldehyde. If a 
sulfonated organic polymer is used as the acidic ion exchange resin 
catalyst, strong organic acids such as phenol sulfonic acid have been 
found to leach into the reaction product mixture. As an example, typically 
for bisphenol-A (BPA), the product stream from the reaction zone 
containing BPA in solution is passed to a crystallization zone, wherein 
the BPA is crystallized as an adduct with phenol and the remaining 
solution, or "mother liquor," is recycled to the reaction zone. The 
leached acid will remain in the separated product stream with the 
crystallized BPA and cause degradation of the BPA product during 
subsequent process steps, particularly if thermal finishing steps are 
involved. It has been found that the soluble acid leached from the acidic 
ion exchange resin acts as a catalyst for cracking of BPA during the 
thermal finishing step, which results in a lower product purity and a 
decrease in product yield. 
In order to obtain bisphenols with higher purity, it is known to use an 
amine-based organic anion exchange resin to remove acidic impurities from 
the mother liquor. Such amine-based resins are expensive and inherently 
less stable than the catalyst resin, and their use can result in the 
presence of soluble amines or the reaction products of these amines with 
phenol in the product stream, which will decrease product quality. When 
the amine-based resin is used in a recycled system, the soluble amines 
will in turn poison the acidic ion exchange catalyst upon recycle of 
unconverted reactant. Such amine-based organic resins are typically 
regenerated by aqueous base, which is also a poison for the acidic ion 
exchange resin catalyst. 
It is therefore an object of the present invention to provide an acidic ion 
exchange resin catalyzed bisphenol preparation process with improved 
purity and yield. It is another object of the present invention to provide 
a process to remove acidic impurities from a recycled system without 
poisoning the acidic ion exchange resin catalyst. 
SUMMARY OF THE INVENTION 
According to the invention, a process for the production of a bisphenol is 
provided, the process comprising the steps of: 
(A) contacting a carbonyl compound with a stoichiometric excess of a 
phenolic compound in the presence of an effective amount of an acidic ion 
exchange resin catalyst to produce a reaction product mixture comprising a 
bisphenol and a sulfonic acid; 
(B) contacting the reaction product mixture comprising a bisphenol and a 
sulfonic acid with a carbon adsorbent under conditions effective to reduce 
the acidity of the reaction product mixture; and 
(C) recovering bisphenol from the thus treated reaction product mixture.

DETAILED DESCRIPTION OF THE INVENTION 
According to the invention, a high purity bisphenol can be produced in high 
yield by contacting a reaction product mixture containing a bisphenol with 
a carbon guard bed. The reaction product mixture is the effluent of a 
reaction zone wherein a carbonyl compound and a phenolic compound are 
allowed to react in the presence of an effective amount of an acidic ion 
exchange resin catalyst. 
The phenolic compounds employed as the starting material in the production 
of bisphenols according to the invention are any compounds containing a 
hydroxy group linked to a carbon of an aromatic group. Suitable phenolic 
compounds include, for example, phenols and substituted phenols, such as: 
phenol, cresols, xylenols, chlorophenols, thymol, carvacrol, cumenol, 
2-methyl-6-ethylphenol, 2,4-dimethyl-3-ethylphenol, 4-ethylphenol, 
2-ethyl-4-methylphenol, 2,3,6-trimethylphenol, 
2-methyl-4-tertiary-butylphenol, 2,4-ditertiary-butylphenol, 
4-methyl-2-tertiary-butylphenol, 2-tertiary-butyl-4-methylphenol, 
2,3,5,6-tetramethylphenols, 2,6-dimethylphenol, 
2,6-ditertiary-butylphenol, 3,5-dimethylphenol, 3,5-diethylphenol, 
2-methyl-3,5-diethylphenol, o-phenylphenol, p-phenylphenol, the naphthols, 
phenanthrol, their homologues and analogues. Suitable phenolic compounds 
include those containing one or more phenolic groups in each nucleus as 
well as polynuclear compounds. 
The carbonyl compounds employed as the starting material can be any 
compound of the following formula: 
##STR1## 
wherein R.sub.1 can be any aliphatic, cycloaliphatic, aromatic or 
heterocyclic radicaI, and R.sub.2 can be hydrogen or an aliphatic, 
cycloaliphatic, aromatic or heterocyclic radical. Suitable carbonyl 
compounds include ketones and aldehydes. Examples of suitable ketones 
include, for example, acetone, 1,3-dichloroacetone, dimethyl ketone, 
methyl ethyl ketone, diethyl ketone, dibutyl ketone, methyl isobutyl 
ketone, cyclohexanone, propionylphenone, methyl amyl ketone, mesityl 
oxide, cyclopentanone, acetophenone, and examples of suitable aldehydes 
include acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde. 
The specific phenolic compound and carbonyl compound employed as starting 
material will depend upon the specific bisphenol compound desired and may 
be governed to some extent by specific operating conditions employed. The 
invention process is particularly suitable for production of bisphenol-A, 
for which the carbonyl compound is acetone and the phenolic compound is 
phenol. Typically, excess phenol is used for the condensation reaction. 
Preferably the ratio of phenol to carbonyl compound is within the range of 
about 20:1 to 2:1, generally about 12:1 to 2:1. 
Acidic ion exchange resins usable in the condensation reaction of a 
phenolic compound and a carbonyl compound according to the present 
invention include essentially all known acidic ion exchange resins. 
Sulfonated resins are generally preferred. In particular, a sulfonated 
aromatic organic polymer as the ion exchange resin catalyst is quite 
suitable. 
Various acidic ion exchange resins are disclosed, for example, in U.S. Pat. 
Nos. 2,597,438, 2,642,417, 3,172,916, 3,394,089, 3,634,341, 4,045,379, 
4,396,728, 4,455,409 and 4,584,416. Some examples of suitable commercially 
available sulfonated resins are: M-31 and G-26 manufactured by Dow 
Chemical Company; A-15, A-31, A-32, XE-383 and XE-386 manufactured by Rohm 
and Haas; and SC-102 and SC-104 manufactured by Bayer-Lewatit. 
The reaction is preferably executed in the presence of an added promoter 
for the acid-catalyzed reaction. Any known promoters for the acid 
catalyzed condensation of a phenolic compound and a carbonyl compound are 
suitable. Suitable promoters are mercaptan groups which are either free or 
bound to the resin. An alkyl mercaptan and bis-mercapto ethanolamine are 
examples of suitable promoters for the invention process. 
In order to obtain bisphenols with improved yields and higher purities 
according to the invention process, the effluent of the reaction zone is 
contacted with a carbon adsorbent under conditions effective to reduce the 
acidity of the effluent. A portion of the excess phenol is optionally 
removed by flashing prior to or after the acid removal step. The preferred 
adsorbents are any carbons that exhibit a reasonable surface area and 
porosity to act as a viable adsorbent in a liquid-phase system. The carbon 
adsorbent can be in any shape or form. The particle size is preferably 
within the range of about 0.4 to 2.4 mm diameter, and the surface area is 
preferably greater than about 50 m.sup.2 /g. The pore sizes typically 
range from about 20 to 1000 angstroms. Preferred carbons exhibit a low ash 
content, or are acid washed to remove leachable metal contaminants prior 
to use. The carbon should also be prewashed with demineralized water to 
remove fines before use. Typical carbons may be derived from coal, 
coconuts, wood, bone char, peat, or any other suitable source of carbon. 
Alternatively, a carbon layer may be deposited on a suitable non-carbon 
carrier. A suitable binder may optionally be used to maintain integrity of 
the carbon particle. Activation or calcination of the carbon may 
optionally be employed. The preferred carbon is prepared from a bituminous 
coal, calcined with a suitable binder, and acid washed before use. 
The effluent is preferably contacted with a fixed-bed activated carbon in 
either an upflow or downflow configuration at a weight hourly space 
velocity (WHSV) within the range of about 0.2 to 10, preferably about 0.5 
to 3. If an upflow mode is employed, the bed should not be fluidized so 
that back mixing and fines generation are minimized. The WHSV in the acid 
scavenging zone may vary considerably within the scope of the invention 
depending to some extent upon the specific bisphenol products, the 
catalyst, the acid loss rate from the reaction and the adsorbent used, but 
is preferably within the range of about 0.2 to 10 in order to obtain acid 
concentrations of less than about 0.1 ppm in the effluent after treatment. 
For convenience, the invention process will be specifically described in 
terms of its most preferred embodiment, in which acetone and an excess of 
phenol are contacted in a reaction zone in the presence of a sulfonated 
cationic exchange resin catalyst and free mercaptan to produce BPA. The 
reaction is carried out in one or a series of reactors operated at 
temperatures within the range of about 60.degree. to about 95.degree. C. 
The reaction effluent includes bisphenol-A, acetone, water, mercaptan, 
phenol, various phenolic by-products of the reaction, and acids leached 
from the catalyst. After removing a portion of excess phenol by flashing, 
the effluent is passed through a fixed-bed carbon adsorbent to remove 
heavy or non-volatile acids (e.g. sulfonic acids and sulfuric acid) at 
temperatures within the range of about 65.degree. to about 130.degree. C. 
In an optional embodiment of the invention process, the acid removal step 
can be carried out prior to the flashing step. 
Subsequently, BPA can be purified and removed from the adsorbent-treated 
effluent by various methods. Suitable means for recovering bisphenols 
include one or more of such steps as, distillation, solvent extraction, 
stratification, extractive distillation, adsorption, crystallization, 
filtration, centrifugation and thermal liberation. Typically, the BPA is 
isolated by passing the treated reaction product stream containing BPA to 
a crystallization zone, where the stream is cooled to crystallize a 
BPA-phenol adduct or treated with water to crystallize the BPA. Slurries 
of crystallized BPA or crystalline adducts of BPA are separated from the 
remaining solution by filtration or by centrifugation and the remaining 
filtrate or "mother liquor" is recycled to the reaction zone. In a 
finishing zone, BPA isolated as a crystalline adduct is converted to BPA 
by thermally stripping phenol from the adduct and recrystallizing, and the 
water-crystallized BPA is dried. More than one such step can be employed 
in the finishing zone to purify BPA. Subsequently, the purified BPA is 
recovered. 
In an optional embodiment of the invention process, the acid removal step 
is carried out downstream of the crystallization step before recovery of 
the BPA. 
Bisphenols prepared by the invention process have improved purity and 
yield, as thermal cracking of the product is minimized or eliminated. The 
invention process provides a conveniently recyclable system without 
significant risk of contamination of the acidic ion exchange resin 
catalyst. This is advantageous particularly in a system in which the 
mother liquor is recycled to the reactor. 
The following examples demonstrate the acid removal step in a bisphenol 
production process according to the invention process. 
EXAMPLE 1-2 
Phenol doped with varying known concentrations of phenol sulfonic acid was 
contacted with an activated carbon (CALGON, TYPE CAL) prepared from a 
bituminous coal and calcined with a binder before acid washing with HCl. 
The activated carbon was first water washed and dried in a vacuum oven at 
90.degree. C. before use. The ratio of phenol supernatant to carbon 
adsorbent was 20:1. The carbon/phenol mixtures were placed in a shaking 
water bath and allowed to equilibrate at 90.degree. C. for 36 hours. Final 
concentration of acid in the supernatant was determined by potentiometric 
titration with 0.01 or 0.1N potassium hydroxide. The amount of acid 
adsorbed by the carbon was calculated from known initial and measured 
final supernatant acid concentrations, and the known ratio of supernatant 
to carbon. Results are shown in FIG. 1. The Langmuir-like curvature 
(concave downward) is indicative of strong adsorption of the acid by 
carbon. 
The experiment was repeated with water as a supernatant at 25.degree. C. 
The resulting adsorption isotherm was quite similar to that obtained in 
dry phenol at 90.degree. C. This result indicates the adsorption is not 
sensitive to temperature or phenol/water ratio. The strong adsorption 
evident from the curvature of the isotherms in FIG. 1 indicates the carbon 
adsorbent will give a favorable performance if implemented in a fixed bed 
to adsorb acid in a continuous flow process. 
EXAMPLE 3 
A packed bed containing 36 grams of the above carbon was water washed. 
Phenol containing 2207 ppmw of phenol sulfonic acid (PSA) was passed over 
the bed at 90.degree. C. at a weight hourly space velocity (WHSV), defined 
as grams of effluent per gram of carbon per hour, of 10.5. FIG. 2 shows 
acidity in the effluent (normalized by the 2207 ppmw injected 
concentration) versus the cumulative amount of effluent collected 
normalized by the total weight of carbon, or the "bed weights+ of effluent 
produced. Effluent acidities were determined by potentiometric titration 
of effluent samples. These values were confirmed via analysis of PSA by 
liquid chromatography. 
No acid was observed in the effluent until ten bed weights of effluent had 
been produced, while the effluent concentration did not exceed 50% of the 
injected concentration until more than 20 bed weights of effluent had been 
produced. If no adsorption had occurred, the injected concentration of 
acid would have appeared in the effluent after production of only one bed 
weight of effluent. The flow experiment thus demonstrates efficient and 
virtually complete acid removal by the carbon adsorbent, as expected from 
the isotherm studies of examples 1 and 2. It is known that by reducing 
weight hourly space velocity, breakthrough of acid can be further delayed, 
such that the "equilibrium+ breakthrough at 64 bed weights (calculated 
from the above isotherm) can be approached. 
EXAMPLES 4-6 
One gram of bisphenol-A was doped with varying amounts of phenol sulfonic 
acid (PSA) to give the concentrations reported in Table 1. Each sample was 
sealed in a glass ampoule and heated at 180.degree. C for 30 minutes to 
simulate temperatures found in thermal finishing of BPA. Contents of the 
ampoule were then dissolved in acetonitrile solvent for analysis by liquid 
chromatography. The assay was specific for phenol and isopropenyl phenol 
(IPP), which are known products of the acid-catalyzed degradation of 
Bisphenol-A. The amounts of undesired phenol and IPP formed in these tests 
increased with increasing acid content of the sample. These results 
demonstrate the sensitivity of the process to trace concentrations of 
phenol sulfonic acid. Concentrations of phenol and IPP in BPA product 
above 100 ppmw are undesirable. The importance of removal of this acid 
with the carbon adsorbent is thus demonstrated. 
TABLE 1 
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CRACKING OF BISPHENOL-A CATALYZED BY 
PHENOL SULFONIC ACID 
30 MINUTES, 180.degree. C., SEALED AMPOULES 
Acid Phenol IPP 
Run ppm (ppmw) (ppmw) 
______________________________________ 
Example 4 5.8 1400 357 
Example 5 0.5 80 47 
Example 6 0 28 16 
Feed 0 25 16 
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Example #6 = Blank 
IPP = Isopropenyl Phenol 
Feed = Unheated BPA Feed Sample Assay 
EXAMPLE 7 
Phenol was recirculated continuously through a 38-gram packed bed 
containing a sulfonic acid ion exchange resin catalyst followed by a 
35-gram packed bed of the activated carbon adsorbent described above at 
80.degree. C. and at a WHSV of 3. Effluent samples from the catalyst bed 
contained 0.6 ppmw phenol sulfonic acid, at steady state, as determined by 
liquid chromatography. No acidity was detected in the effluent from the 
carbon bed at any time during 38 days of continuous operation. Using the 
0.6 ppmw loss rate from the catalyst bed, a concentration of 17 ppmw PSA 
is calculated as the concentration of acid that would have been realized 
in the closed recirculation system, if acid were not removed by the carbon 
adsorbent. The deleterious impact of acid concentrations between 0.6 ppmw 
and 17 ppmw on bisphenol-A product quality is evident from examples 4-6.