Carbon molecular sieve membranes for biogas upgrading: Techno-economic feasibility analysis

Biomethane, produced by biogas upgrading, has a great potential to replace part of the fossil fuel natural gas, and may be injected into a gas grid or used as compressed biomethane as vehicle fuel. The state-of-the-art technologies for biogas upgrading in the European region are water scrubbing, pressure swing adsorption and chemical absorption, however, high performance carbon membranes may also have a great potential in this application. In this work, cellulose-derived hollow fiber carbon membranes were tested for CO2/CH4 separation at moderate pressures (5-20 bar), and a CO2/CH4 permeance selectivity >60 was obtained. The developed membranes were evaluated for biogas upgrading in a 1000 m3(STP)/h biogas plant based on HYSYS simulation and cost estimation. The results indicated that carbon membranes can be a promising candidate for biogas upgrading with a low processing cost of 0.078 $/m3 at the feed pressure of 8.5 bar. Increased membrane performance can further reduce the cost. Moreover, a carbon membrane system can be very cost-effective for upgrading of biogas in small-scale plants of around 350 m3(STP)/h.