(355e) Fabrication of Highly Permeable Matrimid Substrates for a CO2-Selective Composite Membrane | AIChE

(355e) Fabrication of Highly Permeable Matrimid Substrates for a CO2-Selective Composite Membrane

Authors 

Pang, R. - Presenter, The Ohio State University
Chen, K., The Ohio State University
Han, Y., The Ohio State University
Ho, W., The Ohio State University
A more permeable substrate with a higher surface porosity is more desirable to reduce the mass transfer resistance in the substrate and the lateral diffusion resistance in the selective layer of a thin-film composite (TFC) membrane. In this study, highly permeable Matrimid substrates with a bicontinuous surface layer and macrovoids in the bulk were prepared by vapor-induced phase separation to enhance the CO2 permeance of an amine-containing facilitated transport membrane. With the addition of LiCl in the Matrimid (thermoplastic polyimide)/N-methyl-2-pyrrolidone (NMP) casting solution, the casting solution viscosity was increased significantly so that a lower Matrimid concentration could be used for the casting on the nonwoven fabric without causing penetration. In addition, LiCl could decrease the thermodynamic stability of the casting solution significantly. As a result, the phase separation was induced via the spinodal decomposition mechanism, and a bicontinuous surface layer could be formed. The casting solution composition, including Matrimid, LiCl and polyvinylpyrrolidone (hydrophilic additive) concentrations, was optimized with respect to the substrate morphology and CO2 permeance. Compared with a benchmark polyethersulfone substrate that has been previously used for TFC membrane synthesis, the best Matrimid substrate showed a high surface porosity of 20.3% (vs. 13.4% of PES substrate). Also, the new substrate exhibited a high CO2 permeance of 260,057 GPU, which was 11.8 times more permeable than the PES substrate. This high permeance was contributed mainly by the absence of a top dense layer and the presence of macrovoids in the bulk. By using this substrate, the prepared TFC facilitated transport membrane showed a CO2 permeance of 932 GPU, which was 72 GPU higher than the counterpart coated on the PES substrate. Meanwhile, the CO2/N2 selectivity was retained at 158 at 57°C. This permeance improvement can be explained well using the resistance-in-series model, attributing to significant reductions in both substrate and lateral diffusion mass transfer resistances.