Simulation of the recovery of methane from low-concentration methane/nitrogen mixtures by concentration temperature swing adsorption

In this work, the concentration of methane from low concentration methane/nitrogen mixtures by a concentration thermal swing adsorption (CTSA) process with silicalite as adsorbent and steam as desorbent has been studied by simulation with a theoretical model based on conservation equations. The cycle consists of seven steps: (i) introduction of fresh feed, (ii) receipt of the high concentration mass transfer zone (MTZ), (iii) rinse with methane product, (iv) displacement of methane with steam, (v) displacement of steam with light product (nitrogen), (vi) bed cooling and (vii) receipt of the low concentration MTZ. The proposed CTSA process can concentrate methane from methane/nitrogen mixtures with concentrations of 5-20% methane up to +99% with +99% recovery with productivities of 7.5·10−5-2.7·10−4 mol kg−1 s−1 and thermal energy consumptions of 10-46 MJ/kg (assuming heat integration with other processes). It is found that the heat exchange rate through the bed wall is very important for this process, affecting the energy consumption significantly.