A short review on hydrophobic pervaporative inorganic membranes for ethanol/water separation applications

Inorganic based membranes are promising candidates for a variety of applications, including adsorption and separation due to their large surface area, high pore volume, tunable structure, and strong resistance against aggressive operation conditions, such as high temperature and pressure. Many research groups have investigated zeolite, micro- or mesoporous silica, and hybrid materials (organic and inorganic materials) as advanced membrane configurations in liquid separation applications. Especially, hydrophobic inorganic membranes have potential to separate ethanol from aqueous solution via pervaporation, ultimately producing ethanol, but several important challenges such as reliable synthesis, fabrication, or functionalization are yet to be solved. More specifically, a novel, high throughput process for the fabrication of continuous and defect-free hydrophobic inorganic membranes is required. Then, functionalization of pore structures of the membrane, if necessary, is desirable in order to tailor even more advanced hydrophobic properties for ethanol. Finally, the separation characteristics and performance of inorganic membranes must be further investigated to implement in the industry. Herein, the synthesis and normalized separation performance of diverse hydrophobic inorganic membranes with respect to selective layer material basis, such as zeolite, functionalized mesoporous silica, and mixed matrix, are comprehensively reviewed and the future direction is presented with a focus on ethanol recovery.