Method for purifying wastewater
The present invention provides a method for treating water containing phenolic material such as bisphenol A, phenol, para tertiary butyl phenol, and 1,1,1-tris(hydroxyphenyl)ethane, as well as water soluble polycarbonate oligomers, and dispersed polycarbonate particles by extracting the phenolic material from the water using a water immiscible organic liquid containing an amine coupling catalyst. The treated water is then steam stripped to remove residual organic liquid and the amine. The organic liquid, containing the bisphenol A, phenol, para tertiary butyl phenol, and 1,1,1-tris(hydroxyphenyl)ethane, as well as water soluble polycarbonate oligomers and dissolved polycarbonate particles can be fed back to the coupling step of the polycarbonate process without further regeneration or treatment.
1. An improved method for preparing polycarbonate by an interfacial, polycondensation reaction with the steps of:
(a) reacting phosgene and a bisphenol 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 phosgene being dissolved in the organic phase and the bisphenol dissolved as a salt in the aqueous phase;
(b) subsequently reacting the carbonate oligomers in the presence of a coupling catalyst to form a polycarbonate;
(c) separating the aqueous and organic phases; the aqueous phase containing salts formed as by-products of the reaction of bisphenol and phosgene as well as organic liquid and one or more phenolic material(s), including water soluble polycarbonate oligomers and polycarbonate particles, and the organic phase containing the coupling catalyst and polycarbonate product;
(d) treating the separated organic phase with an acidic wash water solution to remove amine coupling agent and then with aqueous liquid to remove inorganic impurities;
(e) recovering the polycarbonate product;
wherein the improvement comprises
(i) treating either or both the separated aqueous phase obtained in step (c) and/or the wash water obtained in step (d) with an organic solution of the coupling catalyst in a halogenated organic liquid to extract the phenolic materials; and
(ii) steam stripping the aqueous solutions treated in step (i) to remove the organic liquid and coupling catalyst.
2. The method of claim 1 wherein the phenolic material comprises bisphenol, a mono functional phenolic terminator, and/or a multifunctional phenolic branching agent; the coupling catalyst is a tertiary aliphatic amine or cyclic amine; and the organic liquid is a chlorinated hydrocarbon.
3. The method of claim 1 wherein the phenol comprises bisphenol A, para tertiary butyl phenol, and 1,1,1tris(hydroxyphenyl)ethane the coupling catalyst is triethylamine, and the organic liquid is dichloromethane.
4. The method of claim 1 wherein the phenolic containing water is contacted with the water immiscible, organic liquid containing a coupling catalyst using countercurrent extraction.
5. The method of claim 1 further comprising the step of recirculating the organic liquid, coupling catalyst and/or phenolic material to the polymerization reaction coupling step (1).