Batch and continuous studies for ethyl lactate synthesis in a pervaporation membrane reactor

Pervaporation process using commercial silica water selective membranes was evaluated to contribute for the ethyl lactate process intensification by continuous pervaporation membrane reactor. Preliminary studies were performed in order to assess the existence of membrane defects and mass transfer limitations, studying the influence of feed pressure and flowrate, respectively. After, in the absence of mass transfer limitations, membrane performance was evaluated experimentally, at different composition and temperature measuring the flux and selectivity of each species in binary mixtures (water/ethanol, water/ethyl lactate and water/lactic acid). Thus, species permeances were obtained for each experiment and correlated in order to account for the effect of temperature and feed composition. Permeances of ethanol and ethyl lactate depend solely on the temperature, following an Arrhenius equation; for water, its permeance follows a modified Arrhenius equation taking into account also the dependence on the feed water content. Mathematical models, considering concentration and temperature polarization, and non-isothermal effects as well, were developed and applied to analyze the performance of batch pervaporation and continuous pervaporation membrane reactor, in both isothermal and non-isothermal conditions. The PVMR with five membranes in series, operating at 70 °C, leads to 98% of lactic acid conversion and 96% of ethyl lactate purity.

Research highlights▶ Selective water membrane for ethyl lactate synthesis by continuous membrane reactor. ▶ Water permeance expression accounting for temperature and water feed content. ▶ Membrane reactor models considering concentration and temperature polarization. ▶ 98% of lactic acid conversion and 96% of ethyl lactate purity obtained at 70 °C.