CO2 separation from biogas with ionic liquid-based hybrid solvents: From properties to process

In this work, ionic liquids (ILs)-based hybrid solvents, consisting of 1-butyl-3-methylimidazolium acetate (BMAC)-propylene carbonate (PC), were developed for CO2 separation from biogas. The impacts of IL mass fraction and temperature on the absorption capacity, viscosity, and density were studied. Feed gases, including pure CO2, pure CH4, and synthetic biogas, were tested, and the results were evaluated and compared. Thermodynamic modeling was used to represent the newly measured results together with literature data, and a systematic process simulation and evaluation were conducted. The measurements show an enhanced CO2 solubility with an increased BMAC mass fraction and decreased temperature. An increased viscosity was observed with increasing BMAC mass fraction and decreasing temperature. In addition, the type of feed gas holds a neglectable effect on CO2 and CH4 absorption capacities. To find an optimal mass fraction of BMAC-PC and quantify the performance, in the process simulation and evaluation, two types of regeneration blocks, i.e., air-blow regeneration and thermal regeneration, were involved. It shows that the process with thermal regeneration block requires less energy and lower capture cost than the process with the air-blow regeneration, which indicates a superior affinity to thermal regeneration when BMAC is presented in the solvent system. Also, the decrease in PC content firstly decreases and then increases the energy demand, and the minimum energy demand of 23.4 kW can be found with w(IL) = 0.3, which reduces by 33.5% compared to pure PC. Similarly, the minimum capture cost of 68 $/ton-CO2 can be found with w(IL) = 0.3, representing a 21% reduction from the case with pure PC. The further analysis concludes a major reduction in the utility cost by 48%.

Automated summary

This study developed ILs-based hybrid solvents for CO2 separation from biogas and investigated the effects of IL mass fraction and temperature on absorption capacity, viscosity, and density. It was found that increasing IL mass fraction and decreasing temperature enhanced CO2 solubility. The process simulation and evaluation showed that thermal regeneration required less energy and had lower capture cost compared to air-blow regeneration. Reducing the PC content also decreased energy demand and capture cost.