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.
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