Fabrication and testing of carbon molecular sieve membranes for CO2/H2 separation

Most majority of the chemical manufacturing industries depend on separation technologies to produce their products. Considering their unique properties, membranes could be used as an environmentally friendly alternative to conventional methods for separation of gases. Among the various types of membranes, polymeric membranes are one of the most commonly used in the industry. However, some of their shortcomings such as poor chemical and thermal resistance, and limited performance has encouraged researchers to look for alternative materials. Carbon membranes are a group of inorganic membranes that have shown promising results in terms of performance and thermal stability. In this study, Carbon molecular sieve membranes were fabricated by carbonization of cellulose hollow fiber precursor in Argon gas environment. The obtained carbon fibers were then tested in view of their possible use in CO2/hydrogen separation. In particular, using a single-gas permeation rig, the permeability of N2, He, and CO2 and He/CO2 selectivity at 2 bar and 25°C were determined. Helium was used in the experiments instead of hydrogen for safety reasons while nitrogen was included in the tests for a preliminary characterization of the membrane structure. The separation performance of the obtained fibers was evaluated, and the results were compared with Robeson upper bound for He/CO2 as a benchmark. The highest obtained He/CO2 selectivity was equal to 58.9 with He permeability of 18.1 Barrer. The results showed that increasing the final carbonization temperature yields carbon hollow fibers with higher selectivity and lower permeability. This could be utilized to finetune the membrane separation properties according to the specific application needs. Recent findings in the field of carbon molecular sieve membranes were also collected and reviewed.