Spanning the molecular to industrial scale of the adsorption-based separation of CO2/CH4 by MIL-160(Al)
Marta Bordonhos, Maria Inês Severino Neves, Afsaneh Marandi, Farid Nouar, Miguel Jorge, José R. B. Gomes, Christian Serre, Moisés L. Pinto
Abstract
The microporous bioderived MIL-160(Al) MOF has been investigated for CO₂/CH₄ separation in the context of biogas upgrading, by complementary experimental and computational studies, from the molecular to the industrial process levels. MIL-160(Al) has been synthesised and shaped into beads using silica, without loss of adsorption performance, beyond the expected loss in adsorption capacity due to the presence of nonporous silica. Experimental and GCMC-simulated adsorption isotherms for pure CO 2 and CH 4 align closely, validating the strategies used. The latter have been extended to binary CO 2 :CH 4 mixtures, with results cross-validated with IAST. A detailed model has been developed in Aspen Adsorption that uses the LDF approach to describe adsorption kinetics, and the Extended Virial isotherm for multicomponent equilibrium, achieving close agreement between simulation and experimental results. Industrial PSA/VPSA process simulations based on the classic 2-bed, 4-step Skarstrom cycle and the validated model have shown the VPSA process offers better CH 4 recovery ( ca . 82 vs. 52 %) and similar unit energy consumption when compared to the PSA process ( ca. 12 vs. 11 Wh · mol CH 4 , Prod – 1 ), despite having higher raw energy requirements due to vacuum regeneration ( ca. 92 vs. 33 kWh per cycle). Considering only electricity, a main operation cost factor, the operation cost for the VPSA process is ca. 98 € € · t Upgraded biogas – 1 , which gives an estimated economic return of ca. 725 € € · t Upgraded biogas – 1 , based on the price of natural gas. Consequently, VPSA emerges as a promising industrial-scale process for biogas upgrading with MIL-160(Al) as a promising new adsorbent.