Membrane gas permeation systems in the production of renewable gaseous fuels

Increasing scarcity and prices of fossil fuels as also climate changes make the contemporary global society look for sustainable alternatives. Production of renewable gaseous fuels like biomethane and biohydrogen are potential solutions for the provision of energy carriers in the next future. Current well-established and newly establishing state-of-the-art technologies deliver multiple processes for the conversion of biomass to combustible gases. Anaerobic digestion of energy crops and biowaste produces gas mixtures containing principally methane and carbon dioxide with a typical methane content of 50-65 vol.%. Similar gas compositions are obtained in the process combining biomass steam gasification with producer gas methanation. On the other hand, biohydrogen can be produced in the fermentation of biomass. Dark fermentation is likely to yield gas mixtures containing 40-65 vol.% hydrogen. The photo-fermentation produces gas mixtures with hydrogen content of up to 90 vol.%. In both biohydrogen containing mixtures, carbon dioxide is the second most abundant component. Raw producer gas from biomass steam gasification is a promising source of renewable hydrogen. Typical gas mixture contains around 40 vol.% hydrogen with considerable amounts of carbon dioxide, carbon monoxide and methane. The content of hydrogen can be increased further to values above 60 vol.% if AER type of gasification is applied.

All of the aforementioned technologies require an energy efficient and reliable means for the upgrading of the produced gas mixtures. In typical gas utilization scenarios like grid injection or electricity production with fuel cells, bulk gases and minor impurities need to be separated from biomethane and biohydrogen. Membrane gas permeation is a potential separation technology for this task.

Current work discusses membrane gas separation processes for the upgrading of renewable methane and hydrogen. The evaluation focuses on the current state of development of membrane gas permeations systems in the upgrading of gases from several biomass conversion technologies. Especially, crucial gas upgrading parameters like specific energy consumption and gas recovery are in the focus of the discussion. The work correlates these parameters to the current state of membranes’ development and the future development directions to review possible reductions in specific energy consumption for the improvements of process sustainability.