Purification of l-(+)-lactic acid from pre-treated fermentation broth using vapor permeation-assisted esterification

The vapor permeation-assisted esterification of l-(+)-lactic acid and ethanol was investigated using a zeolite membrane. Pervaporation and vapor permeation were initially investigated for dehydration performances, and the latter showed much better results. The molecular sieve property of the membrane resulted in a high separation factor of over 1000 for all conditions. The maximum flux was 10.24 kg/(m² h) at a feed temperature of 145 °C, a water feed concentration of 10 wt%, and a feed pressure of 4.0 bars, respectively. For vapor permeation-assisted esterification using synthetic solutions, the productivity and ethyl lactate yield strongly depended on the dehydration rate. Realistic purifications were performed with fermentation broths of Pediococcus pentosaceus as the lactic acid producer. Experimental results revealed that most of the lactic acid was converted into ethyl lactate at the final stage of the reaction. After distillation and hydrolysis, high purity l-(+)-lactic acid was obtained with more than 95% recovery yields.