INTEGRATION OF WIPED-FILM EVAPORATION AND CROSS-FLOW MICROFILTRATION FOR THE PURIFICATION OF A SILYLENOL ETHER REACTION MIXTURE - PROCESS ISSUES AND SCALEUP

The reaction between p-nitrobenzyl 2-diazoacetoacetate and trimethylch lorosilane (TMS-Cl) produces a toluene-soluble silylenol ether (SEE) p roduct and insoluble byproduct salts (NaCl and triethylammonium hydroi odide). Purification of the SEE solution via removal of the salts and unreacted TMS-Cl is accomplished by integrating two unit operations [c rossflow microfiltration and distillation in a wiped-film evaporator ( WFE)] into a semicontinuous process. The process addresses the critica l scale-up issues of potential exothermic activity near the operating temperature, water sensitivity of the product, and the avoidance of di rect solids handling. Key to its successful scaleup from the laborator y (2 kg scale) to manufacturing (370 kg scale) was the development of a distributed control system which addresses characteristics unique to each of the unit operations. Crossflow operation at all scales exhibi ted a substantial increase and then a decrease in transmembrane pressu re (TMP) which coincided with dissolved solids concentration and conco mitant solution viscosity. Membrane fouling, which became apparent in manufacturing after repeated membrane use, was addressed by operationa l changes to minimize TMP and by incorporating a membrane cleaning pro cedure.