Abstract:

The esterification-hydrolysis method has been reported to be an effective technique for the refining of crude lactic acid product, which based on the principle that lactic acid is easy to react with lower alcohols to form volatile esters, which donate high-purity lactic acid after being hydrolyzed. Under the catalysis of strong acid cation exchange resin bed, the esterification between lactic acid and methanol was performed in the present study. The effects of feed flow rate, reaction temperature and acid/alcohol molar ratio on esterification rate were examined. As the feed flow rate descended, the esterification rate showed a change trend to initially ascend and then keep stable. Increasing reaction temperature led to a higher reaction rate, but the equilibrium esterification rate was kept basically unchanged. With increasing acid/alcohol molar ratio, the equilibrium esterification rate revealed a smaller incremental increase. The reaction rate data were correlated with a kinetic model based on the pseudohomogeneous catalysis. The activation energy, pre-exponential constant and equilibrium constant of the reaction were found to be 33805.56 J/mol, 4856.63 mol-1·L·min-1, and 1.1151, respectively. The mean relative deviation between the experimental and predicted values was 2.74%.

Key words: lactic acid, esterification, fixed bed, pseudo-homogeneous model