Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

Abstract

Natural gas from stranded sources is being predominantly flared, and there is a growing demand for new technologies for its utilisation, where electrification, flexibility, and modularity play an important role. Plasma-activated methane partial oxidation reaction was studied in a designed dielectric barrier discharge ionisation reactor unit, producing value-added platform chemicals, namely, methanol, formaldehyde, intermediate formic acid, acetic acid, and paraformaldehyde at ambient temperature and atmospheric pressure. The effects of various process parameters, such as voltage, total convertible gas flow rate, and reagent ratio relationship, were considered. In addition, coupling of the following catalytic materials with plasma was examined: alumina (Al2O3), chabazite, ferrierite, microporous beta zeolite, silica (SiO2) glass beads, ZSM-5 (MFI), Fe on H-ZSM-5 and Al2O3, Mo on H-ZSM-5, TiO2 and SiO2, and Pd on Al2O3. In the liquid product, 21.5% CH3OH, 20.4% CH2O, 0.3% HCOOH, and 2.4% CH3COOH were measured when using pure plasma, and a maximum aggregate yield of the organic oxygenate compounds of 5.21 mol.% was achieved. The usage of shaped silicate surface increased the selectivity towards synthesised oxygen-containing structures, while the application of alumino-silicate mixture constituents reduced it. It was determined that elementary covalently bonded carbon was formed inside pores when pure zeolites were used. Fe- and Pd-based heterogeneous catalysts favoured the complete exothermic combustion of CH4 feedstock reactant species, and the liquid product consisted only of water in the Pd- case. The utilisation of Mo/H-ZSM-5 resulted in a 46% increased yield of formalin. A mechanism for the role of Mo was proposed, where Mo oxidises methanol to formaldehyde and the metal is reoxidised in plasma.