Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-11-12
2001-02-20
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S727000
Reexamination Certificate
active
06191316
ABSTRACT:
The present invention relates to a process for working up the residual mother liquors from the production of dihydroxydiarylalkanes (bisphenols) discharged from the process once the bisphenol has been separated.
The production of bisphenols by the acid-catalysed reaction of ketones with phenol is known. There have been a number of different proposals for this (cf, for example, U.S. Pat. No. 2,775,620, EP-A 342 758, EP-A 616 993, EP-A 342 758, DE-OS 3,833,900, U.S. Pat. No. 4,308,404, U.S. Pat. No. 4,308,405, EP-A 630 878, U.S. Pat. No. 4,876,391, U.S. Pat. No.3,242,219).
There is a survey of the older literature on bisphenol production in Ullmann's Encyclopedia of Indust. Chem., 5th. Edition, Vol. A 19, pages 348-52. As a rule bisphenols, especially bisphenol A (BPA), industrially the most important of the bisphenols, are prepared by introducing ketone and phenol into a recirculated mother liquor obtained from the working up of bisphenol, this mixture is passed through acidic ion exchangers and the conversion to bisphenol takes place. Any ketone which may possibly not have reacted is recovered from the reaction mixture and led back into the reaction. The reaction mixture is cooled, the bisphenol is if necessary allowed to crystallise out as phenol adduct, separated off and washed with phenol. The phenol is separated from the adduct by flash distillation and pure bisphenol is recovered. The mother liquor from the crystallisation is passed through acidic ion exchangers and isomers contained therein undergo rearrangement to form bisphenol. The bisphenol thus formed is separated by crystallisation and the crystallisate obtained is passed to the first crystallisation step. A portion (approximately 10 to 20%) of the mother liquor now obtained is set aside; the bulk is returned to the reaction. Phenol is distilled off from the portion set aside and is returned to the reaction. The residue obtained during the distillation is removed from the process and is used, for example, for the preparation of phenol resin.
An appreciable quantity of valuable compounds, such as bisphenol and isomers, are lost in the portion which is set aside and ultimately discharged. This removal from the mother liquor is absolutely essential, so as not to allow the quantity of unusable and interfering compounds to become too great. Attempts have therefore been made to work up and to decompose the discharged portion, in order to recover the valuable materials for use in the production of bisphenol. For this, too, there have been a number of different proposals.
By pyrolysis at about 300° C. it is possible to obtain moderate yields of phenol and alkylphenols, which have still to be thoroughly purified (U.S. Pat. No.2,497,503). A hydrogenation treatment also leads to valuable products, as is disclosed in EP-A 17 852. The decomposition can also be accelerated by acidic and basic compounds. However, only phenol is obtained by using acids such as sulphuric acid or toluenesulphonic acid (U.S. Pat. No. 3,466,337). Basic catalysts, on the other hand, effect a decomposition of the discharged materials into phenol and isoalkenylphenol. Catalysts mentioned are alkali metal compounds, such as NaOH, KOH, NaHCO
3
, Na acetate, Na hypophosphite, K
2
CO
3
, MgO and Al isopropylate (U.S. Pat. No. 4,277,628, U.S. Pat. No. 4,594,459, U.S. Pat. No. 4,131,749).
In this procedure, however, only a part of the discharged material is decomposed, and operation is intermittent or semicontinuous. Wholly continuous processes are unknown.
These processes have been improved, as regards a higher purity of the bisphenol, in that the phenol/isoalkenylphenol mixture from the decomposition is introduced into the first mother liquor after the separation of the first bisphenol portion. The mixture is passed over the acid catalyst and the reaction of isoalkenylphenol with phenol and the rearrangement are allowed to proceed simultaneously. The second bisphenol portion is then separated from the mixture by crystallisation and the second mother liquor is again removed for decomposition. The second bisphenol portion is introduced into the first crystallisation. The purity of the bisphenol is thereby somewhat increased, but the process is rendered more complicated by an additional circulation (U.S. Pat. No. 4,954,661).
It has also been proposed that the second mother liquor in the bisphenol process described above, or the first mother liquor after separation of the first quantity of bisphenol and after the rearrangement, be at least partly worked up by distillation, in order better to utilise the valuable products contained therein. The bisphenol thus obtained is reintroduced into the first crystallisation step and purified there. The low-boiling components containing isomers are introduced into the reaction (WO 94/20445 and EP-A 552 518). The difficulty lies in obtaining at justifiable expense from the mother liquor, which is highly enriched by isomers and by-products, sufficiently pure fractions particularly low in chromans and indans, which are difficult to remove, without excessively increasing the no longer usable residue and diminishing the yield. Because of this, a portion of the distillation products have to be discarded.
The fractions low in bisphenol which are obtained during the distillation may also be decomposed and the decomposition products reintroduced into the process (EP-A 332 203).
It has now been found that the yield from bisphenol synthesis using the above-described process may simply be increased by mixing the discharged portion of the second mother liquor, once the phenol has been removed by distillation, with a basic catalyst and continuously apportioning it as a melt into a reactive rectification stage. During the reactive rectification, this melt is decomposed into a mixture of phenol and isoalkylphenol, obtained as an overhead product, which flows into the reaction, and bottoms which, once acidified, are apportioned into a second reactive rectification stage, where they are decomposed into phenol which, optionally after further purification, is returned to the reaction, and second bottoms which are discarded.
Suitable aromatic hydroxyl compounds for the production of the educts for the process according to the invention are not substituted in the para position and contain no substituents of the second order, such as cyano groups, carboxyl groups or nitro groups; examples which may be mentioned are phenol. o- and m-cresol, 2.6-dimethylphenol, o-tert.-butylphenol, 2-methyl-6-tert.-butylphenol, o-cyclohexylphenol, o-phenylphenol, o-isopropylphenol, 2-methyl-6-cyclopentylphenol o- and m-chlorophenol, 2,3,6-trimethylphenol. Preferred compounds are phenol, o- and m-cresol, 2,6-dimethylphenol, o-tert.-butylphenol and o-phenylphenol; phenol is particularly preferred.
Suitable ketones contain at least one aliphatic group on the carbonyl function: examples which may be mentioned are acetone, methyl ethyl ketone, methyl propyl ketone. methyl isopropyl ketone, diethyl ketone, acetophenone, cyclohexanone, cyclopentanone, methyl-, dimethyl- and trimethylcyclohexanonc, which may also have germinal methyl groups, such as 3,3-dimethyl-5-methylcyclohexanone (hydroisophorone). Preferred compounds are acetone, acetophenone, cyclohexanone and its homologues containing methyl groups: acetone is particularly preferred.
Educts for the process according to the invention are the mother liquors arising during the production of dihydroxydiarylalkanes by the reaction of aromatic hydroxy compounds with ketones and isoalkenylphenols on acid catalysts.
Preferred educts for the process according to the invention are in particular also the mother liquors remaining after separation of the bis(4-hydroxyaryl)alkanes, which, after addition of the consumed hydroxy compounds and optionally removal of a certain proportion in order to avoid the accumulation of unwanted by-products, are returned to the process: in the case of bisphenol A synthesis, such mother liquors contain approx. 78-88 wt. % of phenol and 22-12 wt. % of bisphenol A and by-products of the follow
Buysch Hans-Josef
Fengler Gerd
Fennhoff Gerhard
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Shippen Michael L.
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