Kinetics of thermal dry reforming of methane for syngas production and solid carbon capture

Dry reforming of CH${}_4$, either by co-feeding CH${}_4$ and CO${}_2$ from waste streams or directly using biogas, has potential as a CO${}_2$-sink. This study investigates entirely thermal, catalyst-free dry reforming in a tubular flow reactor, aiming for syngas production with concurrent carbon capture. Kinetic modelling couples an elementary step-based gas-phase mechanism with a carbon deposition model. One-dimensional numerical simulations of the flow reactor are compared with experimental measurements. For this, operating conditions are widely varied, in particular temperature (1273 K to 1873 K), residence time (1 to 7 seconds), and CH${}_4$ : CO${}_2$ molar feed ratio (1 to 4). Two temperature regimes are identified, with varying dominance of the reverse water-gas shift and CH${}_4$ pyrolysis reactions. Above 1673 K, CO${}_2$ is fully consumed, independent of residence time and feed composition. Optimized operating parameters result in a H${}_2$/CO ratio of 2 in the effluent gas stream, e.g. as commonly desired for methanol and oxo-alcohol synthesis. Notably, under such optimized conditions, only a minor share of carbonaceous species remains in the gas-phase as hydrocarbons, while 33% of the CH${}_4$-borne carbon is transformed into CO and 48% of CH${}_4$-borne carbon is captured as solid carbon.
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By combining numerical simulations and experiments, catalyst-free thermal dry reforming of biogas for sustainable syngas production and solid carbon capture is investigated under industrially viable conditions.