In this work, an intensified process for capturing CO₂ from air by using an aqueous solution of highly soluble methylglyoxal-bis-iminoguanidine (MGBIG) and sarcosine amino acid in two steps has been investigated utilizing a household humidifier setup. Based on our previous findings, a new generation rotating air contactor (RAC) has been developed and tested for a three-step direct air capture process (DAC) using 1 M potassium sarcosinate solution to increase the CO₂ uptake efficiency from air and further adapt the new design for the intensified direct air capture (IDAC).

An in-depth study of IDAC process has been carried out. The intensified method allows simultaneous CO₂ absorption and precipitation in the form of MGBIG carbonate in the first step followed by quantitative regeneration of MGBIG and the release of captured CO₂. In retrospect, the three-step process utilizes potassium sarcosinate solution for CO₂ absorption and MGBIG for precipitation; therefore, these two steps can only be performed consecutively. Several combinations of MGBIG and sarcosine (molar concentrations: 0.3:0.3, 0.5:0.3, 0.7:0.4, 0.5:0) have been investigated to determine the optimal solvent composition that corresponds to the highest CO₂ uptake capacity for IDAC. The CO₂ absorption and precipitation step is monitored in situ for 24 h to gain insights into MGBIG carbonate crystal formation and phase composition. Furthermore, ten consecutive IDAC cycles with MGBIG and sarcosine molar concentrations of 0.5 and 0.3 M, respectively, have been performed to study the CO₂ cyclic capacity and recyclability of MGBIG and aqueous sarcosine solution. It was determined that the average CO₂ cyclic capacity is 0.23 molCO₂/L corresponding to 49.4% overall CO₂ crystallization yield as MGBIG-carbonate.

In addition, we moved on to next generation rotating air contactor (RAC) and tested it with 1 M potassium sarcosinate solution for DAC under three different climatic conditions: 35 F, 65 F and 95 F at fixed 80% relative humidity. For the RAC, the amino acid solution was fully saturated in 6 hours, that is 3 to 4 times faster than the conventional humidifier. The RAC will be further applied for IDAC process.

Kashif Nawaz

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