Polishing effect on the alpha- alumina tubes for membrane separation performance

• A new customized, surface polishing system for tubular alumina substrates. • High reproducibility and quality of polished alumina substrate surface properties. • Excellent control of relationships between substrate surface, water transport and gas transfer. • Controlled deposition of polyetherimide membranes for enhanced CO 2 , N 2 , and CH 4 gas selectivities. Nanocomposite membranes have been research focus of numerous gas separation applications. Understanding the interfacial properties between inorganic and organic materials is crucial for enhancing membrane performance. In particular, the design of interface topology, pore texture, and chemistry on membrane support surfaces can have a profound effect on both gas permeance and selectivity. Therefore, careful control of interfacial surface properties between the membrane active layer and the underlying support is challenge. In this study, a newly-customised, automatic, tubular polishing system was designed and implemented to control the surface properties of tubular alumina substrates for gas separation membrane processing. The effects of sandpaper grits, sandpaper pulling speed and tube rotation speed, as well as calcination temperature on surface finishing were thoroughly examined and evaluated for water flux and gas separation performance of nanocomposite membranes. After polishing process, the surface roughness of alumina substrates significant increased from 238 nm to 568 nm. The best polished alumina tubes were treated with a 7000 grits sandpaper, 2.3 s polishing time, 1600 rpm rotation, and a partial sintering temperature of 1200 °C achieved a comparable surface pore diameter of 0.2 µm, 43.4 % porosity, and an average pure water flux of 28.2 ± 1.4 LMH/bar. This combination of alumina substrate pre-conditioning offered the ideal interfacial surface properties for dip-coating of polyetherimide membranes, which produced a competitively high CO 2 /N 2 permselectivity of 21.9 ± 1.0 and CO 2 /CH 4 of 21.1 ± 1.4 for CO 2 separation membrane development.