Method for recycling amine catalyst in interfacial polycarbonate manufacturing process
View Patent ↗The present invention relates to an improved process for recycling a coupling catalyst, preferably an amine catalyst in an interfacial polycarbonate manufacturing process. Specifically, the amine catalyst is recycled in an acidic wash water solution.
1. An interfacial process for producing a polycarbonate resin from a dihydric phenol, a carbonate precursor, and a monophenolic chain terminator using an amine coupling catalyst which process comprises the steps of:
(a) reacting the carbonate precursor and the dihydric phenol using a two-phase reaction mixture to form carbonate oligomers; the reaction mixture comprising an aqueous, alkaline phase and an immiscible organic phase, with the carbonate precursor being dissolved in an organic phase and a salt of the dihydric phenol and a salt of the monophenolic chain terminator dissolved in the aqueous phase;
(b) subsequently polymerizing the carbonate oligomers in the presence of a coupling catalyst to form a polycarbonate resin;
(c) separating the aqueous and organic phases; wherein the organic phase comprises the coupling catalyst and polycarbonate resin;
(d) treating the separated organic phase with an acidic wash water solution to remove amine coupling agent by forming a salt of the coupling catalyst which is soluble in the acidic wash water solution;
(e) recovering the polycarbonate resin;
wherein the improvement comprises
(i) treating the acidic wash water solution comprising the salt of the coupling catalyst with a basic material to adjust the solution pH to at least 12 producing an alkaline wash water solution comprising the coupling catalyst; and
(ii) recycling said alkaline wash water solution comprising the coupling catalyst back into the polymerization step (b).
2. The process according to claim 1 wherein the amine coupling catalyst is a tertiary amine.
3. The process of claim 2 wherein the amine coupling catalyst is triethylamine.
4. The process of claim 1 wherein the dihydric phenol is bisphenol-A; the carbonate precursor is phosgene; the monophenolic chain terminator is phenol, para-t-butyl phenol, p-cumyl phenol, or para-t-octyl phenol; and the amine coupling catalyst is triethyl amine.
5. The process of claim 1 further comprising a branching agent providing a branched polycarbonate resin.
6. The process of claim 1 wherein the basic material is a caustic solution.
7. A polycarbonate resin produced by the process of claim 1 or 6 .
8. A branched polycarbonate resin produced by the process of claim 5 .