Development of a binarization analysis technique and characteristic for mixed-matrix pervaporation membranes

Pervaporation (PV) is considered a promising energy-efficient process for recovering ethanol from fermentation liquids. In this study, ethanol separation characteristics were elucidated using mixed-matrix pervaporation membranes composed of hydrophobic polymers (PDMS) and high-silica ZSM-5 (HSZ). The selectivity and flux of ethanol/water were both improved when HSZ content in PDMS matrices was increased — at 50 wt% HSZ content the selectivity reached 15 and the flux of ethanol was improved to 0.05 kg/m²/hr. A new method was demonstrated to quantify the local thickness of the PDMS matrices by cross-sectional SEM binarization and inscribed circle analysis. PDMS matrices became more uniform with an increase in the HSZ content. The uniform presence of the PDMS matrices can be interpreted as more uniform dispersion of HSZ particles. An increase in total length of PDMS-HSZ interface resulted in improved ethanol permeability. NMR analysis showed that the molecular mobility of PDMS was restricted. Those results suggest an increase in the physical interaction between PDMS and HSZ. This study demonstrated a new analytical method for understanding the local thickness of the PDMS matrices and the interfacial state of mixed-matrix pervaporation membranes.