Pilot-Scale CO2 Separation from Simulated Biogas in a Loop Reactor Based on Hydrate Technology

To increase the calorific value and energy density of biogas, the removal of CO2 gas is required to purify biogas. In this work, a tubular loop reactor was designed to enhance the formation of semiclathrate hydrate and separate simulated biogas of 50.0 mol % CO2/50.0 mol % CH4. In the separation process of simulated biogas, the gas hydration ratio was increased to 52.81% with the increase of initial pressure, but the fierce competition between CH4 and CO2 molecules in the hydrate cages prevented CO2 molecules to enter the hydrate cages at high initial pressure, which reduced CO2 separation factor significantly. The CO2 separation factor and CH4 concentration in the gas phase reached optimized values of 7.43 and 72.00%, respectively, at an initial pressure of 3.0 MPa. In addition, the CO2 concentration in the hydrate phase and the CH4 recovery ratio at 5.0 K were more than those at a higher driving force due to the formation of more CO2 hydrate at a low driving force. Through the determination of the sapphire window and the online particle analyzer, the size of hydrate particles and stable flow were observed. In the period of hydrate nucleation and slow growth, the average particle size D50 was 18.9 and 50.2 μm, respectively.