Study on a numerical model and PSA (pressure swing adsorption) process experiment for CH4/CO2 separation from biogas

• We investigated the separation of the CH4/CO2 mixture gas from the biogas.
• The LDF constants of CO2 and CH4 are selected as 0.03 and 0.0005, respectively.
• As the adsorption pressure increases, the purity increases while the recovery decreases.
• The optimum selectivity in the present process conditions is found to be 1.9.

We investigated the separation of the CH4/CO2 (54.9%/45.1%) mixture gas from the biogas through the PSA (pressure swing adsorption) experiment and the numerical simulation. To understand the adsorption characteristics of CH4/CO2, the adsorption equilibrium amount of pure gas is measured and the key parameters of the adsorption equilibrium model are determined using the Langmuir isotherm model. A numerical model is developed through the optimization study of the kinetic parameter and the porosity using the adsorption equilibrium model with the experimental data. The LDF (linear driving force) constants of CO2 and CH4 are selected as 0.03 and 0.0005 for the porosity of 0.3, respectively, and the cyclic steady state of the process is obtained at 13th cycle by the simulation of the PSA process. As the adsorption pressure and purge gas ratio increase, the purity increases while the recovery decreases. On the other hand, as the desorption pressure decreases, the purity increases while the recovery decreases. The recovery decreases in each case because the amount of the product gas increases. The optimum selectivity in the present process conditions is found to be 1.9 [CO2 equilibrium amount adsorbed (2.47 mol/kg-ads)/CH4 equilibrium amount adsorbed (1.30 mol/kg-ads)].