HYDRIDE FORMING MATERIALS FOR CO2 CONVERSION: CO2 METHANATION USING MGH2 AS A PORTABLE HYDROGEN MEDIUM

AMICA, G.; F. C. GENNARI

Cancún

Congreso; XXIX International Materials Research Congress.; 2021

The Materials Research Society (MRS)

The use of solid hydrides as hydrogen source to react with CO2 can be consider a strategy to modify the ΔG0 of the reaction of CO2 to a desired product. When a different and thermodynamically stable final product is formed, the enthalpy and the global Gibbs free energy change can be positively affected promoting its reduction. In this work the feasibility of CO2 conversion into CH4 employing LiAlH4 without catalysts was explored comparatively via mechanochemical and thermochemical process with a relation of H2:CO2 of 4:1. Trough mechanical milling at room temperature of LiAlH4 under CO2 atmosphere for 1, 5 and 24 h, CH4 and CH3OH were detected as the main gaseous products, as well as a small amount of H2O. While short milling times (1 and 5 h) were not sufficient to selectively transform the CO2 to a desirable product, in 24 h no excess of CO2 or CO formation was detected and a methane yield of 21% was obtained. The material was also evaluated by thermochemical processes. Under dynamic conditions, the exposition of LiAlH4 to a CO2 flux from room temperature up to 300ºC, led to mass gain and the formation of lithium carbonate. Under static conditions, the sample was heated up to 250 ºC under a CO2 atmosphere during 1 and 24h. CH4 formation with little excess of CO2 and no sign of CO or other organic compounds were detected as gaseous products. When the length of the treatment increased from 1 to 24 h, the methane yield increased from 10.5 to 22%. Despite mechanical milling is interesting because it is a room temperature process, the energy provided does not seem to be enough to achieve high conversion rates. Our theoretical calculations indicate that from a thermodynamic point of view, to maximize CH4 yield it is desirable to operate the system at low temperatures. However, is not possible to lower the reaction temperature without affecting the molar percentage of CH4 considerably. The use of catalysts or a fluid medium such as a non-polar solvent to enhance transport phenomena can be an interesting strategy to overcome kinetic barriers.