Evaluation and comparison of aqueous ChCl/Urea and other physical absorbents for biogas upgrading process

Biogas has been considered as an alternative renewable energy, and CO₂ removal from raw biogas (i.e. biogas upgrading) is needed for producing biomethane used as vehicle fuels or injected into the natural gas grid. Biogas upgrading using physical absorbents is a simple and efficient technology with low energy requirements for regeneration. In this work, the conceptual process for biogas upgrading using 4 kinds of physical solvents, i.e. water, dimethyl ether of polyethylene glycol (DEPG), propylene carbonate (PC) and aqueous choline chloride (ChCl) /urea (AQ_DES) was developed and simulated with Aspen Plus. The energy utilization, the amount of recirculated solvent and the diameters of absorber and desorber were analyzed based on equilibrium approach. After that, the rate-based simulation was established to evaluate the specific cost of the process using different solvents. Based on equilibrium approach the comparison between the solvents in respect to the energy utilization for biogas upgrading using different solvents shows the following order: DEPG > water > AQ_DES > PC, whereas the amount of recirculated solvent and the diameters of absorber and desorber follow another order: water > DEPG > AQ_DES > PC. The rate-based results show that the process using PC has the lowest total specific cost, followed by AQ_DES, water and DEPG.