Process for preparing bisphenol A

Details Process for preparing bisphenol A Process for preparing bisphenol A

2000-11-29

2001-12-11

Shippen, Michael L. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S727000, C521S033000

Reexamination Certificate

active

06329556

ABSTRACT:

FIELD OF TECHNOLOGY
This invention relates to a process for preparing 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A).
BACKGROUND TECHNOLOGY
In recent years, there is an increasing demand for bisphenol A as a principal raw material for engineering plastics such as polycarbonates and epoxy resins. Bisphenol A is usually obtained by the reaction of excess phenol with acetone in the presence of an acidic catalyst. Cation exchange resins are most common for such catalyst and those containing sulfonic acid groups are normally used. Of cation exchange resins containing sulfonic acid groups, sulfonated styrene-divinylbenzene copolymers are put to practical use most widely.
Sulfonated styrene-divinylbenzene copolymers are resins obtained by copolymerizing styrene and divinylbenzene in the presence of a polymerization initiator and introducing sulfonic acid groups to the aromatic rings of the styrene and divinylbenzene in the resulting copolymers with the aid of sulfuric acid and the like. The copolymers in question are considered to have a complex three-dimensional network in which divinylbenzene bridges polystyrene chains to form an irregularly intertwined structure. An increase in the amount of divinylbenzene leads to increased branching of the polystyrene chain and a denser network. Conversely, a decrease in the amount of divinylbenzene leads to decreased branching and a coarser network. The divinylbenzene here plays the role of a knot in the network and is referred to as crosslinking agent. The ratio of the amount of crosslinking agent added to the amount of total monomers used is generally designated as degree of crosslinking.
The aforementioned copolymers ranging widely in the degree of crosslinking have been used as a catalyst for the preparation of bisphenol A and the existence of a significant correlation has been reported between the degree of crosslinking and the catalyst life. For example, Japan Kokai Tokkyo Koho Hei 6-32755 (1994) teaches the use of cation exchange resins with a degree of crossliking of 6 wt. % or less since the life of a cation exchange resin catalyst becomes longer as the degree of crosslinking becomes lower. However, a cation exchange resin catalyst with a lower degree of crosslinking generally contains less sulfonic acid groups per unit volume of catalyst and leads to reduced output of bisphenol A. Moreover, a cation exchange resin catalyst with a lower degree of crosslinking is more susceptible to elastic deformation when subjected to a stress from the outside and, when used in a fixed-bed reactor, may occasionally cause such pressure loss as to render the production difficult on a commercial scale. Thus, elongation of the catalyst life by reducing the degree of crosslinking causes another problem and an improved procedure is desired for development of cation exchange resin catalysts which maintain the production of bisphenol A over a long period of time, resist elastic deformation and possess high strength without decreasing the number of sulfonic acid groups per unit volume of catalyst.
An object of this invention is to provide cation exchange resin catalysts which show high productivity per unit volume of catalyst, have a long life, maintain high productivity of bisphenol A over a long period of time, resist elastic deformation and possess high strength. Another object of this invention is to provide an efficient process for preparing bisphenol A.
DISCLOSURE OF THE INVENTION
The present inventors have conducted intensive studies to accomplish the aforementioned objective, found that divinylbiphenyl is appropriate for use as crosslinking agent for cation exchange resin catalysts and arrived at this invention.
Accordingly, this invention relates to a process for preparing 2,2-bis(4-hydroxyphenyl)propane by the condensation of phenol with acetone in the presence of a cation exchange resin catalyst obtained by sulfonating copolymers of monovinyl monomers mainly comprising of styrenes and divinyl monomers as crosslinking agent which comprises using divinyl monomers containing 20 mol % or more of divinybiphenyl. This invention also relates to the aforementioned cation exchange resin catalysts to be used in the condensation reaction.
The sulfonated copolymers of styrene and divinyl monomers to be used as cation exchange resin catalyst in this invention are prepared in accordance with a known procedure by copolymerizing a mixture of monovinyl monomers mainly comprising of styrenes and divinyl monomers mainly comprising of divinylbiphenyl or divinylbenzene and divinylbiphenyl in the presence of a polymerization initiator and sulfonating the resulting copolymers with sulfuric acid or the like to introduce sulfonic acid groups to the aromatic rings of the styrenes and divinyl monomers.
Styrenes include monovinyl derivatives of aromatic compounds such as styrene, vinyltoluene, a -methylstyrene, vinylxylene, vinylethylbenzene, vinylbiphenyl, methylvinylbiphenyl. Monovinyl monomers other than styrenes include aliphatic olefins. Monovinyl monomers here mainly consist of styrenes, that is, they consist of 50 mol % or more, preferably 80 mol % or more of styrenes.
Divinyl monomers may be 100% divinylbiphenyl or a mixture of divinylbiphenyl with other divinyl monomers if the latter are less than 20 mol %. Such other divinyl monomers include divinylbenzene and divinyltoluene, divinylbenzene being preferable. Divinylbiphenyl accounts for 20 mol % or more, preferably 50 mol % or more, of divinyl monomers. Moreover, divinyl monomers mainly consist of divinylbiphenyl and divinylbenzene and the two together desirably account for 50 mol % or more, preferably 80 mol % or more, of divinyl monomers.
Of several isomers of divinylbiphenyl, 4,4′-divinylbiphenyl or a mixture of isomers mainly consisting of 4,4′-divinylbiphenyl is preferable. Depending on the procedure used for its preparation, 4,4′-divinylbiphenyl occasionally contains the unreacted starting material and intermediates such as 4,4′-diethylbiphenyl, 4,4′-vinylethylbiphenyl and 4-vinylbiphenyl and it can be used together with such intermediates without ill effect. Rather, it is desirable that 4,4′-divinylbiphenyl contains 10-60 mol % of monovinylbiphenyls such as 4,4′-vinylethylbiphenyl and 4-vinylbiphenyl. Monovinylbiphenyls are counted as monovinyl monomer. Likewise, of the isomers of divinylbenzene, 1,4-divinylbenzene or a mixture mainly consisting of 1,4-divinylbenzene is preferable.
As for the ratio of divinylbenzene to divinylbiphenyl in use, more divinylbiphenyl gives a longer catalyst life and higher catalyst strength, which makes it desirable to use as high a proportion of divinylbiphenyl as possible. Concretely, the molar ratio of divinylbiphenyl to divinylbenzene is 10/0-8/2, preferably 10/0-5/5.
The degree of crosslinking, as designated by the weight ratio of divinyl monomers as crosslinking agent to a mixture of all monomers, is not restricted, but it is 0.1-20 wt. %, preferably 1-15 wt. %, more preferably 2-8 wt. %, in consideration of the catalyst life, productivity of bisphenol A and catalyst strength. The degree of crosslinking as designated by the molar ratio of divinyl monomers to the total monomers is 2-50 mol %, preferably 2-40 mol %, more preferably 3-10 mol %. A decrease in this degree of crosslinking lowers the catalyst strength and performance.
A known procedure can be adopted for the copolymerization of monovinyl monomers mainly consisting of styrenes and divinyl monomers. Normally, the copolymerization is carried out at 50-90° C. for 3-30 hours in accordance with a procedure, for example, of introducing water and a dispersant in specified amounts to the polymerization reactor, adding a mixture of monomers in which a polymerization initiator has been dissolved to the water with stirring to form an oil-in-water suspension, and carrying out the polymerization at a specified temperature in a nitrogen atmosphere.
A concrete procedure for the polymerization is as follows. A polymerization initiator is added to a mixture of mono

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