Effects of operation parameters on the recovery process of lactic acid by reactive batch distillation

Abstract

In this study, lactic acid was recovered through reactive batch distillation with esterification and hydrolysis reaction of this. Various operation parameters were investigated considering the interaction of reaction and separation. Esterification part in this system has difficulty in performing reactive distillation because products of esterification are nodes. At first, heating rate and mole ratio of reactant in feed were investigated as parameters that determine the system feasibility, related to thermodynamic characteristics of system. To operate the esterification part effectively, methanol content more than stoichiometric ratio and efficient removal of product components from reaction mixture are ensured simultaneously. Therefore, due to this inherent conflict in system, there was optimum reactant ratio for each heating rate into the reboiler of esterification part. The recycled methanol flow rate may be used to control the behavior of system with time which is divided into the subdivisions according to the differences in volatility of components and subsequent differences in boilup rates. It was the best policy that in initial part of batch, loss of methanol was compensated sufficiently with somewhat higher temperature of partial condenser, and in latter part to enhance the removal of product, partial condenser temperature was increased. Suitable semi-batch mode operation resulted in reducing the inherent difficulty of operation. Through continuous feeding of light excess reactant, methanol, loss of this component was compensated effectively and the removal of products was not delayed by excess methanol in reboiler residual. When ethanol was used as a reactant of esterification reaction, formation of azeotrope with water decreased efficiency with temperature of partial condenser above this azeotrope. Although ethanol decreased efficiency of system due to lower reaction rate and heavier ester, compared to the case of methanol, feasible performance was ob...