Biogas Upgrading by Pressure Swing Adsorption with Design of Experiments

Global warming is predominantly caused by methane (CH4) and carbon dioxide (CO2) emissions. CH4 is estimated to have a global warming potential (GWP) of 28–36 over 100 years. Its impact on the greenhouse effect cannot be overstated. In this report, a dual-bed eight-step pressure swing adsorption (PSA) process was used to simulate the separation of high-purity CH4 as renewable energy from biogas (36% CO2, 64% CH4, and 100 ppm H2S) in order to meet Taiwan’s natural gas pipeline standards (>95% CH4 with H2S content < 4 ppm). Three selectivity parameters were used to compare the performance of the adsorbents. In the simulation program, the extended Langmuir–Freundlich isotherm was used for calculating the equilibrium adsorption capacity, and the linear driving force model was used to describe the gas adsorption kinetics. After the basic case simulation and design of experiments (DOE) for the laboratory-scale PSA, we obtained a top product CH4 purity of 99.28% with 91.44% recovery and 0.015 ppm H2S purity, and the mechanical energy consumption was estimated to be 0.86 GJ/ton-CH4. Lastly, a full scale PSA process simulation was conducted for the commercial applications with 500 m3/h biogas feed, and the final CH4 product with a purity of 96.1%, a recovery of 91.39%, and a H2S content of 1.14 ppm could be obtained, which can meet the standards of natural gas pipelines in Taiwan.