The combination of a new PERVAPTM membrane and molecular sieves enhances the ethanol drying process

Abstract

A new commercial polyvinyl alcohol (PVA) membrane (PERVAP™ 4100HF) was characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and contact angle (CA) goniometer. The separation performance of the membrane for drying ethanol by pervaporation was also investigated and compared with a standard membrane (PERVAP™ 4100) under same operating conditions. The results show that the new membrane is thinner and less cross-linked than the standard one. The water permeance in PERVAP™ 4100HF (∼800 GPU) is four-time higher than that in PERVAP™ 4100 (200 GPU) at 70 °C and for <5 wt.% of water concentration in the feed. The water/ethanol selectivity of the new membrane under this operating condition is very high (∼7000). The effect of feed water concentration on the Arrhenius activation energy was also investigated to evaluate the mass transfer through the membrane under other operating conditions, like higher temperatures and lower feed water concentrations. Simulation results confirmed that optimizing the operating temperature, the new membrane exhibits outstanding separation performance for drying ethanol below 500 ppm of water. Lastly, the ethanol drying process using the PERVAP™ membranes is compared with a molecular sieve system. Although the new membrane can easily dry ethanol below 500 ppm of water, a hybrid system consisting of pervaporation followed by molecular sieves leads to an interesting process solution, e.g., for a feed flow of 1000 kg/h, the required membrane area and the quantity of molecular sieves can be reduced from 650 m2 to 250 m2 (2.6 times less), and from 2252 kg to 204 kg (11 times less), respectively. Therefore, the ethanol drying process can be greatly optimized in terms of capital costs and energy when using a hybrid system instead of using pervaporation or molecular sieve system alone.