Patent ID: 6979752

Claim:
A transesterification process for converting, on a continuous mode of operation, the diester of polytetramethylene ether (PTMEA) to the corresponding polytetramethylene ether glycol (PTMEG) using two reactors in series and characterized by the following steps: a) introducing the feed comprising PTMEA and an effective amount of C 1 to C 4 alkanol plus an alkali metal oxide, hydroxide or alkoxide catalyst to the first stage of the first multistaged reactor, said first reactor comprising a sequence of stages designed to provide adequate retention time followed by high efficient distillation trays; b) recovering from the overheads of the first reactor vapors of alkanols and of the ester of alkanol formed in the transesterification; c) delivering said vapors of alkanol and of alkanol esters to an azeotropic column to separate overheads the azeotrope of alkanol ester and at bottoms alkanol with a low content of alkanol ester, to be recycled to the process; d) feeding to the last stage of the first reactor vapors of the alkanol separated at the bottoms of said azeotropic column and vapors of methanol from the second reactor to sweep the major part of the alkanol ester formed by transesterification in the first reactor; e) feeding the liquid effluent from the last stage of the first reactor to the first stage of the second multistaged reactor, said second reactor comprising a sequence of stages designed to assure adequate retention time, in combination with high efficient distillation trays; f) recovering from the overheads of the second reactor vapors of alkanol with residual amount of alkanol ester to be transferred to the last stage of the first reactor; g) feeding to the last stage of the second reactor vapors of fresh alkanol and vapors of alkanol recovery from the effluent from the transesterification in an evaporation following the neutralization step; h) adding to the liquid effluent of the last stage of the second reactor a mixture of phosphoric acid and of sodium phosphate monobasic to neutralize the basic catalyst, where the phosphoric acid is in equivalent proportion to the basic catalyst of 3 to the 2.6 to 3.4, and where the sodium phosphate monobasic is in equivalent proportion to the basic catalyst of 2 to from 1.0 to 4.0; i) feeding the neutralization effluent to a crystallizer; j) feeding the crystallizer effluent to a filtration unit; k) feeding the effluent from the filtration to an evaporator to remove vapors of alkanol which are fed to the last stage of the second reactor as per point g) above said two reactors in series operating at nearly atmospheric pressure and at a temperature close to the boiling point of the alkanol.