Process for recovering 2,2-bis(4-hydroxyphenyl)propane from distillation residues from the preparation thereof

A process is disclosed for the recovery of 2,2-bis(4-hydroxyphenyl)propane, herein referred to as bisphenol-A, from residues remaining after purification distillation of bisphenol-A produced from a condensation reaction of phenol and acetone. The process comprises mixing the residues with phenol in the absence of acidic reagents to precipitate a bisphenol-A-phenol crystalline adduct and recovering bisphenol-A from the separated adduct.

This invention concerns a process using phenol in the absence of acidic 
reagents to recover 2,2-bis(4-hydroxyphenyl) propane from residues 
remaining after purification distillation of 2,2-bis(4-hydroxyphenyl) 
propane produced from a condensation reaction of phenol and acetone. 
BACKGROUND OF THE INVENTION 
The use of high purity 2,2-bis(4-hydroxyphenyl) propane, herein referred to 
as bisphenol-A, as a reactant in the preparation of subsequent 
formulations such as the preparations of polycarbonate resins is well 
known in the art. One method for obtaining the purity needed of the 
bisphenol-A is to distill crude bisphenol-A. In such distillations, a 
residue is obtained, comprising various by-products and these primarily 
include higher condensation products of bisphenol-A, condensation products 
of phenol and acetone produced in the original bisphenol-A formation, 
colored substances, isomers of bisphenol-A, and the like. Unfortunately, 
for yield loss purposes, the residues contain 20-60% of bisphenol-A, 
itself. Prahl et al, U.S. Pat. No. 3,290,390, disclose the addition of 
phenol to such residues and simultaneously contacting this resulting 
mixture with an acidic agent such as hydrogen chloride at between room 
temperature and 150.degree. C. to produce thereform bisphenol-A. However, 
the method of Prahl et al requires, according to their examples, 16 hours 
or more reaction time. 
It has now been discovered that it is possible to recover the bisphenol-A 
inherently contained, and in a vastly shorter period of time simply by 
treating the residue with phenol in the absence of an acidic reagent, such 
as hydrogen chloride, sulfuric acid, phosphoric acid, and the like. The 
process of this invention yields bisphenol-A as a solution for subsequent 
recovery such as by cooling to produce crystals of a 1:1 molar phenol 
adduct, from which the bisphenol-A can then be recovered, by procedures 
known per se. 
In practice, commercial plants utilize distillation of bisphenol-A as a 
step in the purification process. The bottoms from the distillation are 
called "tars" and conventionally these are disposed of by burning. This 
represents a serious loss in yield because tars contain from 20-60% 
bisphenol-A plus the isomerizable by-products. Experiments have shown that 
28-71% of the bisphenol-A in a typical tar can be recovered by this 
process. The mother liquor from the crystallization can be stripped of 
phenol (for recycle) in a separate column, and the diminished quantity of 
"tar" remaining can be burned or otherwise utilized. 
DESCRIPTION OF THE INVENTION 
According to the present invention, there is provided a process for the 
production of 2,2-bis(4-hydroxyphenyl) propane from the tarry residue or 
isomer by-product residue which remain after purification distillation of 
2,2-bis(4-hydroxyphenyl) propane comprising: 
(i) forming a warm mixture of said residue and added phenol in the 
substantial absence of an acidic reagent; 
(ii) cooling said mixture to precipitate a crystalline adduct of 
2,2-bis(4-hydroxyphenyl) propane and phenol; 
(iii) separating the adduct; and 
(iv) subsequently recovering said 2,2-bis(4-hydroxyphenyl propane 
therefrom. 
The residues contemplated herein are generally referred to as waste streams 
in commercial purification of bisphenol-A and are many times merely 
disposed of without treatment to reclaim additional bisphenol-A. In 
general, the tar by-products comprise (1) higher condensation products of 
bisphenol-A which are bisphenol-A molecules coupled with themselves and 
which remain as residue in the purification distillation of bisphenol-A, 
and (2) isomer by-products, defined as products of phenol and acetone 
removed with the bisphenol-A fraction during said purification 
distillation. The tars further include colored substances and various 
other unknowns. 
The ratio of phenol to residue can vary, but that which creates a preferred 
mixture is about 0.5-2.0:1 and, most preferably, 1.0-1.2:1 by weight. 
Although the temperature ranges for steps (i) and (ii) can be varied, 
preferably, step (i) will be carried out at a temperature between about 
60.degree. C. and about 85.degree. C., and step (ii) in a temperature 
range of from about 20.degree. C. to about 40.degree. C. 
The residues with which the process is most efficiently utilized comprise 
from about 25 to about 50% by weight of bisphenol-A. 
Also contemplated is a process wherein step (iv) is carried out by heating 
said adduct to cause distillation of phenol therefrom and which includes 
the subsequent step of 
(v) recycling the phenol back into a reactor for condensation of phenol and 
acetone. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following examples are set forth to illustrate more clearly the 
principle and practice of this invention to those skilled in the art. 
Unless otherwise specified, where parts or percents are mentioned, they 
are parts or percents by weight.

EXAMPLE 1 
A tarry residue from distillation of a condensation reaction of acetone and 
phenol, (35 wt.% 2,2-bis(4-hydroxyphenyl) propane), 1500 grams, is heated 
to an initial temperature of 70.degree. C. and 1500 grams of 70.degree. C. 
phenol is added (phenol/tar ratio, 1.0/1.0). The mixture is then reduced 
to a final temperature of 30.degree. C. until formation of a crystalline 
1:1 bisphenol-A/phenol molar adduct is substantially complete. Results of 
gas chromatographic analysis of the adduct thus formed shows 28% of the 
bisphenol-A present in the completed reaction mixture is present in the 
adduct formed. 
EXAMPLE 2 
The procedure of Example 1 is repeated, using phenol in an amount 
sufficient to provide a phenol/tar ratio of 1.2/1.0. The initial 
temperature is 75.degree. C.; the final temperature is 35.degree. C. 
Results of gas chromatographic analysis of the adduct shows 71% of the 
bisphenol-A present in the completed reaction mixture is present in the 
adduct formed. 
EXAMPLE 3 
The procedure of Example 2 is repeated. The initial temperature is 
80.degree. C.; the final temperature is 35.degree. C. This time gas 
chromatographic analysis shows 44% of the bisphenol-A recovered as the 
adduct. 
EXAMPLE 4 
A residue comprising isomer by-products from the distillation purification 
of bisphenol-A made from acetone and phenol (33 wt.% of 
2,2-bis(4-hydroxyphenyl) propane), 1500 grams, is heated to an initial 
temperature of 70.degree. C. and 1500 g of 70.degree. C. phenol is added 
(phenol/residue ratio, 1.0/1.0). The mixture is then reduced to a final 
temperature of 30.degree. C. until formation of a crystalline 1:1 
bisphenol-A/phenol molar adduct is substantially complete. Results of gas 
chromatographic analysis of the adduct thus formed shows 51% of the 
bisphenol-A present in the completed reaction mixture is present in the 
adduct formed. 
Obviously, other modifications and variations of the present invention are 
possible in light of the above teachings. It is, therefore, to be 
understood that changes may be made in the particular embodiments of the 
invention described which are within the full intended scope of the 
invention as defined by the appended claims.