Thermochemical reaction between MgH2 and Li2CO3 to produce synthetic CH4

GRASSO, M. L.; AZCONA, SARA ROZAS; APARICIO, SANTIAGO; F C GENNARI

Buenos Aires

Congreso; 11th Word Congress of Chemical Engineering (WCCE11); 2023

Asociación Argentina de Ingenieros Químicos

The conversion of CO2 into value-added products such as synthetic fuels is an interesting alternative to contribute to the mitigation of CO2 emissions. In particular, the use of alkaline earth-metal hydrides and alkaline metal carbonates to CO2 hydrogenation via mechanochemical [1] and thermochemical [2] reaction was reported.In this work, a thermal activated reaction to transform CO2 was explored using the MgH2-Li2CO3 mixture in presence and absence of Ni as a catalyst. Commercial MgH2, Li2CO3 and Ni reagents were used to prepare mixtures with different MgH2:Li2CO3 molar ratio (4:1 and 2:1). The binary and ternary (with 10 wt.%Ni) systems were prepared in a planetary ball mill under Ar, room temperature, during 1 h and 400 rpm. Static thermal treatments were carried out in a stainless steel reactor where the sample was heated under vacuum (350ºC-450ºC) for different times (5-24h). Structural and microstructural characterization of powders were made using XRD, SEM-EDXS, solid-state FTIR and Raman spectroscopy. FTIR and GC were used for gaseous products analysis.For the MgH2:Li2CO3 system after heating at 450°C for 5 h, XRD and solid-state FTIR results suggested the presence of crystalline Mg and MgO and amorphous Li2O for both molar compositions. For 2:1 ratio, crystalline Li2O was also detected. Additionally, Raman spectra indicated the absence of carbon formation during thermal reaction. In the gas products after heating at 400°C and 450 °C, CH4, H2 and superior hydrocarbons (C2 and C3) were detected independently of the initial molar ratio. A maximum CH4 yield of 68.2% was reached after heating at 450°C for 5 h. For the MgH2:Li2CO3:Ni system, MgO, Li2O and Ni were observed as main products. Additionally, Mg2NiH0.3 appeared at 400°C and 450°C for 4:1 molar ratio. According to Raman spectra, the presence of carbon was discarded. H2, CH4 and superior hydrocarbons were also identified. In presence of Ni at 400°C after 5 h, the highest CH4 yield was 92 % and 76.2% for the 2:1 and 4:1 mol ratio, respectively. In the gas products, water was detected by FTIR.Finally, the experimental evidence allow us to propose a reaction mechanism. For MgH2-Li2CO3 system, first Mg is formed due to the MgH2 decomposition. Then, this Mg interacts with Li2CO3 in a rich H2 atmosphere and follow to the formation of MgO/Li2O and CH4. For the MgH2-Li2CO3-Ni system, it is considered a different global process responding to a Sabatier reaction favored by Ni.The present work shows attractive results about a process to produce CH4 using MgH2 and Li2CO3 as portable sources of H2 and CO2, with and without Ni as catalyst.