development of polymer blend-based carbon membrane for carbon dioxide separation from natural gas

Abstract

In membrane technology, polymeric membranes are the commonly used commercial membranes for carbon dioxide (CO2) separation. The limitations of commercial polymeric membranes have motivated researchers to study other alternatives, namely inorganic membranes, due to their higher thermal stability, good chemical resistance to solvents, higher mechanical strength and longer lifespan. In this study, novel carbon membranes supported onto porous alumina tubular with superior CO2 separation performance were fabricated via carbonization of P84 co-polyimide (PI) blended with different types of additives such as polyvinylpyrrolidone, microcrystalline cellulose, and nanocrystalline cellulose (NCC). The preparation of this carbon membrane involved three main processes: (a)dope polymeric precursor membrane preparation, (b)coating step, and (c)heat treatment process. The influence of the dope formulation, carbonization conditions, and dip-coating parameters on the gas separation performance of the carbon membranes was evaluated. All membrane samples were characterized using scanning electron microscope, thermal gravimetric analysis, x-ray diffraction meter, raman analysis, mercury porosimetry, and Fourier transform infrared spectroscopy. Pure gas permeation tests of the resultant membranes were also conducted and evaluated by using CO2, and methane (CH4). The effects of additive loadings, carbonization conditions and dip-coating parameters have shown significant improvements toward the physiochemical and gas permeation properties. The incorporation of additives enhanced the gas separation performance in comparison to single polymer-based carbon membranes, where in this case NCC demonstrated the most promising additive with 36% improvement of CO2 permeance. Manipulation of gas environments during carbonization process of argon, helium, and nitrogen have shown that argon environment gives 32% and 12% improvement of CO2 permeance and CO2/CH4 selectivity, respectively. These were due to higher order degree of carbon membrane and significant acceleration of the degradation reaction on carbon membranes. The influence of dip coating-carbonization cycles and dipping time during membrane fabrication resulted in a uniform membrane with pinhole-free particle layer and specific pore diameter. When the soaking time was increased from 30 to 120 min, CO2 permeance and CO2/CH4 selectivity increased up to 180% and 86%, respectively. The study also revealed that membrane PI-based carbon membrane with addition of 7 wt% of NCC featured excellent permeation properties with permeance of 3.13 ± 1.56 GPU and 213.56 ± 2.17 GPU for CH4 and CO2 gases, respectively. PI/NCC carbon membrane exhibited the highest CO2/CH4 selectivity of 68.23 ± 3.27 GPU under argon carbonization environment, 120 min thermal soaking time, two times coating-carbonization cycles, and 45 minutes coating duration.