Solvent regeneration by novel direct non-aqueous gas stripping process for post-combustion CO₂ capture

Using an inert, immiscible organic component as the purging gas is an innovative technology in the CO₂ stripping process. It allows stripping at a lower temperature and overcomes the inherent problem of high energy consumption in steam-based CO₂ stripping processes. This work focused on developing a novel, direct non-aqueous gas stripping process and exploiting its potential for energy saving through experiments. An elaborate pre-screening of carrier gases was conducted through hydrocarbon, alcohols, aldehydes, ketones, and their isomers, etc. Pentane, hexane, and cyclohexane were selected as the carrier candidates for their good immiscibility with water/amine, low vaporization energy, mild condensation conditions, and low toxicity. The effects of carrier gas category, carrier gas flow rate, and rich solvent feeding temperature on the stripping performance were investigated. Pentane was found to be the superior carrier gas due to its low heat of vaporization, high regeneration rate, and low energy requirement. A unique phenomenon of water evaporation from the solvent was discovered in the organic gas stripping process, providing a promising approach to break the gas-liquid interface for enhanced diffusion kinetics. The feasibility of low temperature CO₂ stripping was analyzed by varying the rich solvent feeding temperature (70–100 °C). With pentane as the stripping gas, it was interesting to find an optimum rich-feed temperature lower than 90 °C, indicating great potential for a reduction in the overall energy requirement. Under the optimal conditions, the energy consumption during CO₂ regeneration, using pentane as the carrier gas, was 2.38 GJ/t CO₂, 38.8% lower than that of the conventional stripping process. Furthermore, parasitic issues, such as water loss and solvent loss, were discussed. An improved direct non-aqueous gas stripping process with two-stage compression was used to tackle the carrier gas recovery problem. The simulation results show that more than 98% of the carrier gas can be recovered through preliminary separation approaches.