(18d) CO2 Capture Using Phase-Changing Bis-Iminoguanidines (BIGs) with Amino Acids; Analysis of a Direct Air Capture Process

CO₂ capture using phase-changing bis-iminoguanidines (BIGs), such as the methyl-glyoxal-bis-iminoguanidine (MGBIG), with aqueous amino acids (e.g., sarcosine) is investigated in this study. The objective is to provide a better understanding of the process and its scaleup for the direct air capture (DAC) of CO₂. DAC processes involving BIGs are of major interest due to their comparatively lower regeneration energy requirements and environmental risks. Unlike in monoethanolamine (MEA), which does not change phase, only the insoluble carbonate precipitate undergoes thermal regeneration instead of the bulk solution, leading to energy savings.

This work explores three main aspects of a DAC process using MGBIG and sarcosine: (i) CO₂ loading of the solvent, (ii) solid-liquid separation of the carbonate precipitate from the slurry through the use of press and vacuum filtration, and (iii) regeneration of the BIG precipitate using processes that employ temperature swing, vacuum-assisted temperature swing, and microwave exposure. A holistic technoeconomic analysis of the entire process is also developed to estimate the capital and operating costs and overall energy requirements for a scaled-up DAC plant capable of sequestering 1 million tonnes of CO₂ annually using MGBIG and sarcosine.

Calorimetric and spectroscopic studies indicate that the proposed DAC system can achieve CO₂ loadings of 0.6 mol CO₂ per mol solvent and will require approximately 8 GJ per tonne of CO₂ for solvent regeneration. Preliminary cost analyses peg the total cost of CO₂ sequestration of the proposed process to be approximately $210 per tonne of CO₂.

These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine solvents that can be used to effectively capture atmospheric CO₂ at scale.