CO₂ Absorption Using Hollow Fiber Membrane Contactors: Introducing pH Swing Absorption (pHSA) to Overcome Purity...

Recently, membrane contactors have gained more popularity in the field of CO₂ removal; however, achieving high purity and competitive recovery for poor soluble gas (H₂, N₂, or CH₄) remains elusive. Hence, a novel process for CO₂ removal from a mixture of gases using hollow fiber membrane contactors is investigated theoretically and experimentally. A theoretical model is constructed to show that the dissolved residual CO₂ hinders the capacity of the absorbent when it is regenerated. This model, backed up by experimental investigation, proves that achieving a purity > 99% without consuming excessive chemicals or energy remains challenging in a closed-loop system. As a solution, a novel strategy is proposed: the pH Swing Absorption which consists of manipulating the acido-basic equilibrium of CO₂ in the absorption and desorption stages by injecting moderate acid and base amount. It aims at decreasing CO₂ residual content in the regenerated absorbent, by converting CO₂ into its ionic counterparts (HCO3- or CO32-) before absorption and improving CO₂ degassing before desorption. Therefore, this strategy unlocks the theoretical limitation due to equilibrium with CO₂ residual content in the absorbent and increases considerably the maximum achievable purity. Results also show the dependency of the performance on operating conditions such as total gas pressure and liquid flowrate. For N₂/CO₂ mixture, this process achieved a nitrogen purity of 99.97% with a N₂ recovery rate of 94.13%. Similarly, for H₂/CO₂ mixture, a maximum H₂ purity of 99.96% and recovery rate of 93.96% was obtained using this process. Moreover, the proposed patented process could potentially reduce energy or chemicals consumption.