A Semi-Industrial Scale Process to Produce Carbon Membranes for Gas Separation

Abstract

Carbon molecular sieve membranes (CMSMs) are thin carbon barriers, usually in the shape of a film or hollow fibre, that are capable of selectively transporting certain gases. CMSMs are prepared by the thermal decomposition, in a controlled chemical environment, of organic compounds (precursor) that do not melt or soften during carbonization.

The utilization of CMSMs in commercial stage is still unavailable due to expensive precursor materials and a complex multi-step preparation process. The objective of this research work was the preparation of CMSMs from cellulose acetate, which is a relatively cheap, environmentally friendly, and abundant raw material, for gas separation.

A pilot-scale facility with annual production capacity of 700m2 CMSMs was developed and the production process was optimized. The process for precursor fibre preparation involves several steps like spinning, winding, water and chemical treatment, and drying, and these steps were optimized to achieve a mechanically robust cellulose-precursor membrane. These precursor membranes were carbonized at high temperature (550-850°C) and carbonization conditions were optimized to achieve high performance CMSMs for different applications. Prepared CMSMs exhibited significant separation properties for carbon dioxide (CO2) and methane (CH4) and, air separation. Techno-economic evaluation showed that CMSMs have nice potential for applications such as biogas upgrading to vehicle fuel, natural gas separation, and oxygen enriched air. Chemical, thermal, or electrical treatment can be performed effectively to minimize the aging effect.

High separation performance and low operational cost make CMSMs a good candidate for gas separation applications especially where high chemical and/or thermal resistance is required. However, there are only a few manufacturers involved in the production of carbon membranes, and this is because greater costs are involved in producing and making carbon membrane modules. Nevertheless, more research work is needed to produce carbon membranes at a lower price.