Biogas upgrading to biomethane with zeolite membranes: Separation performance and economic analysis

Biogas represents an important renewable source alternative to fossil fuels, which can significantly contribute to the reduction of global warming and the gradual decarbonisation. In this work, the purification of CH4 and CO2 from a biogas mixture was investigated using DD3R zeolite membrane modules, as a possible solution to replace the traditional techniques at higher environmental impact (i.e., solvent absorption and cryogenic distillation). Multistage membrane configurations operating at 25°C and 30 bar were proposed and explored to get highly pure biomethane (concentration of 98 %) and carbon dioxide (concentration of 99.5 %), imposing a recovery of both the species higher than 90 %. Then, an economic analysis was carried out, evaluating the economic potential of each configuration as a function of several parameters, such as membrane module cost, biomethane selling price, CO2 permeance, CO2/CH4 selectivity, feed flow rate and pressure. The multistage schemes were found to be promising in a wide range of zeolite membrane module cost (i.e., up to 2000 $/m2), providing positive values of the economic potential, due to the good recovery of both the components, which produced high revenues. The increment of the CO2 permeance and, especially, of the feed flow rate (i.e., plant size) allowed for a more profitable process. In particular, if feed flow rate increased from 100 to 1000 Nm3/h, the economic potential would grow of about 12 times, from 113 to 1370 thousand dollars per year. Hence, this preliminary economic assessment showed that zeolite membranes can be successfully used in biogas treatment to get pure CH4 and CO2. Such an analysis can be applied to any membrane materials, once permeance and selectivity are fixed.