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: Carbon Membrane Performance: State-of-the-Art

Linfeng LeiJ and Xuezhong Heab

"Department of Chemical Engineering, Norwegian University of Science and Technology hDepartment of Chemical Engineering, Guangdong Technion Israel Institute of Technology (GTIIT)


Carbon membranes with ultra-microporous structures are usually prepared by carbonization of polymeric precursors such as polyimides [1-4] and cellulose derivatives [5-8]. Carbon molecular sieve (CMS) membranes made from polyimide precursors have a potential application in the ultrafine discrimination of molecules that are close in size, due to their high selectivity [3]. However, the production costs of carbon membranes are quite high because of the high cost of polyimide materials. He et al. [5,9] reported that cellulose acetate (CA)-derived carbon membranes showed good performance in CO,/ CH4 and CO,/N, separation processes, and their membranes were upscaled to a pilot-scale system with an annual production capacity of 700 m2 [10]. However, the difficulties in controlling the drying process for the deacety- lated hollow fibers remain a challenge for large-scale production.

Spinning cellulose hollow fibers directly from a cellulose dope solution could be a solution. Recently, novel carbon hollow fiber membranes (CHFMs) have been prepared from cellulose precursors directly spun with a cellulose/ (l-ethyl-3-methylimidazolium acetate (EmimAc) + dimethyl sulfoxide) system. The CHFMs show good performances that are above the Robeson upper bound of CO,/CH4 and 0,/N,. The optimized carbon membrane presents a CO, permeability of 239 barrer and a CO,/CH4 selectivity of 186, based on a pure-gas permeation measurement. Thus, development of cellulose-based CHFMs shows potential for gas separation.

Carbon membranes can be divided into two categories: unsupported and supported. Unsupported membranes have three different configurations: flat- sheet film, hollow fiber, and capillary tubes. Supported carbon membranes have two configurations: flat-sheet and tubular. The unsupported CHFMs are prepared from hollow fiber precursors, which, due to high packing density, could be the only viable configuration when large areas are needed in industrial applications.

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