Direct Air Capture of CO₂ with Aqueous Amino Acids and Solid Bis-iminoguanidines (BIGs)

Abstract

We report a bench-scale direct air capture (DAC) process comprising CO2 absorption with aqueous amino acid salts (i.e., potassium glycinate, potassium sarcosinate), followed by room-temperature regeneration of the amino acids by reaction with solid meta-benzene-bis(iminoguanidine) (m-BBIG), resulting in crystallization of the hydrated m-BBIG carbonate salt, (m-BBIGH2)(CO3)(H2O)n (n = 3-4). The CO2 is subsequently released by mild heating (60-120 °C) of the carbonate crystals, which regenerates the m-BBIG solid quantitatively. This low-temperature crystallization-based DAC process circumvents the need to heat the aqueous amino acid sorbents, thereby minimizing their loss through thermal and oxidative degradation. The CO2 cyclic capacity for the sarcosine/m-BBIG system, measured over three consecutive absorption/regeneration cycles, is in the range of 0.12-0.20 mol/mol. The regeneration energy of m-BBIG, comprising the enthalpy of CO2 and water release, and the sensible heat, is 360 kJ/mol (8.2 GJ/ton CO2). Alternatively, the aqueous amino acids can be regenerated by boiling under reflux, with measured cyclic capacities of up to 0.64 mol/mol.

Dialing in Direct Air Capture of CO2 by Crystal Engineering of Bisiminoguanidines

“…Finally, converting this fundamental science into a practical DAC technology will require process design and development, including design and testing of a fast and efficient air-liquid contactor and a crystallizer unit that can handle large volumes of solids under continuous crystallization conditions, coupled with an efficient solid-liquid separator, such as a filter press or cyclone. [22]…”

“…Instead, the carbonate salts were precipitated by reaction with Na 2 CO 3 , followed by quantitative CO 2 release from the carbonate solids and conversion into the free bases (Scheme 1). [20][21][22]27,28] and current work.…”

“…[17][18][19] We have recently discovered a new approach to DAC ( Figure 1) involving crystallization of carbonate salts of bis (iminoguanidine)s (BIGs). [20][21][22][23] The CO 2 absorption from air is driven by the extremely low aqueous solubilities of the BIG carbonate salts (on a par with CaCO 3 ), which can be attributed to a large extent to the strong hydrogen bonds involving the carbonate and guanidinium ions, as well as the water molecules included in the crystals. [24] BIGs are a class of anion-coordinating ligands readily accessible by imine condensation of dialdehydes with aminoguanidinium salts.…”

Direct air capture of CO2viacrystal engineering

“…This brings the overall heat of regeneration to 288 kJ mol À1 . 45 In order to understand the structural factors determining the DAC chemistry of BIGs, we initiated a systematic structureproperties relationship study, focusing initially on the very basic series of BIG structures resulting from glyoxal (GBIG) and its simple analogs methylglyoxal (MGBIG) and diacetyl (DABIG) (Fig. 9).…”

“…The rates of CO 2 uptake can be greatly accelerated by combining BIG-CO 3 crystallization with CO 2 absorption by aqueous amino acids or peptides, which work in synergy with BIGs to achieve effective and energyefficient DAC. [44][45][46] As illustrated in Fig. 10, the DAC cycle with amino acids/BIGs comprises the following steps: (i) fast CO 2 absorption by the aqueous amino acid (glycine is shown as a representative example), yielding the corresponding bicarbonate salt (via a carbamate intermediate); (ii) crystallization of the carbonate anions with BIG, which regenerates the amino acid; (iii) CO 2 release from the BIG carbonate solid and BIG regeneration.…”