Xianshe Feng

Integrated membrane/adsorption process for gas separation

Abstract A novel process that incorporates membrane permeation into the cyclic process of pressure swing adsorption (PSA) was proposed to improve gas separation performance. This integration is not a simple combination of the two process components. Unlike in the traditional membrane processes where pressures are kept constant, the pressure in the integrated permeation/adsorption system is changing as the permeation proceeds with time. Permeation processes with varying pressure were analyzed parametrically to study the feasibility of integrating permeation with cyclic PSA processes. Two configurations of the process integration were investigated: membrane-assisted feed gas pressurization, and membrane-assisted co-current depressurization. A bench scale unit comprising of an asymmetric cellulose acetate hollow fiber module and a pair of 5xa0A molecular sieve packed bed adsorbers was assembled and tested for hydrogen purification. It was shown that as compared to the simple adsorption process, both product purity and recovery could be improved by using the integrated process, and the improvement was especially remarkable for the cases where the feed gas mixture contained impurities that were difficult to remove by adsorption.

Improving the performance of TFC membranes via chelation and surface reaction: applications in water desalination

Here we report modification of thin film composite (TFC) membranes via a series of chemical and surface reactions. Initially, the nascent polyamide (PA) active layer was prepared by interfacial polymerization and composited with graphene oxide (GO) nanosheets and then reacted with cupric chloride dihydrate (CuCl2·2H2O). Finally, the composited membrane was treated by a reaction with ammonium hydroxide (NH4OH) solution. The chemical modifications of the PA active layer included the formation of a polyamide–copper–graphene oxide complex (PA–Cu2+–GO), whereas, the surface modifications, mineralization, include the formation of copper hydroxide [Cu(OH)2] on the membrane surface through a reaction between the residual CuCl2·2H2O and NH4OH solution. The results of the compositional analysis of mineralized membranes showed that the active layer is fully cross-linked, with Cu2+ chelated with amide nitrogen and coordinated with the carbonyl groups. The membrane performance was evaluated using a cross-flow apparatus at 2000 mg L−1 NaCl solution, 25 °C and a pressure of 15 bar. The mineralized membrane with optimum concentrations of copper chloride and ammonium hydroxide of 0.125 molar and 0.1%, respectively, and a reaction time of 1 minute showed a higher pure water permeability and solute water flux (44.25, 33.77 L m−2 h−1) compared to the pristine TFC membrane (21.36, 20.2 L m−2 h−1) with an excellent salt rejection (≥98.5%). Moreover, the mineralized membranes were found to resist chlorine attack and fouling adsorption more than the non-treated TFC membrane.

Poly(p-phenylene terephthamide) embedded in a polysulfone as the substrate for improving compaction resistance and adhesion of a thin film composite polyamide membrane

A new approach to improving the compaction resistance and polyamide skin layer adhesion onto the substrate in thin film composite (TFC) membranes was developed. It was based on in situ polymerization of p-phenylene terephthamide (PPTA) in a polysulfone (PSf) solution prior to membrane casting via the phase inversion process, thereby forming a PPTA-embedded PSf substrate. The TFC membrane was prepared by interfacial polymerization on such (PPTA/PSf) substrates. The crystal structure of the PPTA polymerized in the PSf/NMP solution was investigated by XRD and TEM. The immobilization of PPTA in the PSf substrate was confirmed by FTIR and XPS. The surface properties of the PPTA/PSf substrates were characterized by FESEM, AFM and WCA measurements. Incorporating PPTA into the substrates resulted in more open porous structures and a thinner dense layer, as well as a rougher and more hydrophilic surface. Both the compaction resistance of the TFC membrane and the polyamide skin layer adhesion onto the substrates were improved by the presence of PPTA. The TFC membranes exhibited a typical nanofiltration performance with salt rejections in the order of Na2SO4 > MgSO4 > MgCl2 > NaCl.