K₂CO₃-Containing Composite Sorbents Based on Thermally Modified Alumina: Synthesis, Properties, and Potential Application in a Direct Air Capture/Methanation Process

Abstract

In this work, a series of K2CO3-containing composite materials based on alumina supports with different porous structure were synthesized and studied in a direct air capture process. Alumina supports with the modified porous structure were obtained as a result of the thermal treatment of porous γ-Al2O3 at elevated temperatures. Composite materials were synthesized by impregnating the porous support (unmodified or modified alumina) with an aqueous solution of potassium carbonate. All the K2CO3/Al2O3 sorbents were tested in the process of CO2 absorption from the air with a relative humidity of 25% followed by thermal desorption as a result of heating the material to 200 °C. The composite materials were characterized by X-ray diffraction and temperature-programmed desorption methods. Among the materials studied, the composite sorbent based on the porous alumina thermally modified at T = 750 °C demonstrated the highest dynamic CO2 absorption capacity. This composite material was later tested in a direct air capture/methanation process combining CO2 capture from ambient air and methanation via the catalytic Sabatier reaction. The process was implicated using an adsorber and a catalytic reactor connected in series. To regenerate the composite sorbent after the step of CO2 absorption from ambient air, the adsorber was heated to 200 °C in an H2 flow. The desorbed CO2 was converted into methane in the preheated catalytic reactor containing the Ru/Al2O3 methanation catalyst. The optimization of the operating conditions (namely, the catalytic reactor temperature and the inlet H2 flow rate) allowed for obtaining CH4 from carbon dioxide with a yield of 98%. The thermal energy required for heating the new CO2 sorbent from 25 to 200 °C at the desorption/methanation step of the direct air capture/methanation process was estimated to be 9 MJ per 1 m3 (STP) of produced CH4.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

“…Apart from the use of a single solid that incorporates both sorption and methanation functions, the process of integrated CO 2 capture and conversion to methane can be realized via the combination of two different solids that perform these functions individually. Veselovskaya et al published a number of works that incorporated the use of a K 2 CO 3 /Al 2 O 3 sorbent and a Ru/Al 2 O 3 methanation catalyst [126][127][128]. The high CO 2 sorption capabilities of the K 2 CO 3 -based sorbent enabled it to capture CO 2 directly from ambient air (direct air capture or DAC), where its concentration is as low as 400 ppm.…”

“…The sorbent could be regenerated at the mild temperature of 200 • C under H 2 flow and CH 4 was produced at a subsequent catalytic reactor that contained the Ru/Al 2 O 3 methanation catalyst. The whole operation was coined as direct air capture and methanation (DACM) process [128].…”

CO2 Capture and Utilization Editorial

“…Industrial & Engineering Chemistry Research pubs.acs.org/IECR Editorial for subsequent chemical synthesis applications, such as the production of CH 4 by catalytic methanation with H 2 39. …”

Direct CO2 Capture from Air via Crystallization with a Trichelating Iminoguanidine Ligand

“…The simplest materials were aqueous/solid alkaline hydroxides, oxides, and salts such as NaOH, KOH, Ca(OH) 2 , CaO, and K 2 CO 3 , which had high binding energy and showed strong affinity for CO 2 . 18 − 22 However, a high calcination temperature of ∼900 °C for CaCO 3 and ∼1000 °C for Na 2 CO 3 cost huge energy for regeneration of these sorbents to release CO 2 . Amine-based materials have been widely investigated for capturing CO 2 from ambient air.…”