Reactor design, modeling and optimization for the high-temperature methane pyrolysis and the reverse water-gas shift reaction

Abstract

In this work, two reactions are studied as a mean to deal with the current CO2 conundrum. The first reaction is the high-temperature pyrolysis of methane. This reaction serves as a way to avoid the stoichiometric production of CO2 when producing hydrogen, which could either be used for energy production or as a base chemical. The second reaction is the reverse Water-Gas Shift (rWGS) reaction. By means of this reaction, CO2 that is unavoidably produced and has been captured, can be activated to the more reactive CO and subsequently mixed with hydrogen to produce syngas. For the methane pyrolysis, liquid- and solid-based reactors are studied. The former are reactor concepts based on the use of molten media. Capillary, falling-film and rotating reactors are introduced as alternatives to carry out the pyrolysis with efficient heat transfer and to avoid carbon deposition. Solid-based reactors, in the form of moving-bed, are studied from a theoretical perspective. First the operation stability of the reactor is investigated by means of bifurcation analysis, and then several heat input strategies are modeled and optimized to determine solutions in the short, mid and long-term. For the rWGS, multifunctional adsorptive reactors are studied as a workaround to the problem of low equilibrium conversion, as well as heat input for more attractive low-temperature rWGS, as compared to the industrially common high-temperature counterpart. Two concepts are investigated; a fixed-bed and a moving-bed reactor. Their potential for optimization is determined, and a comparison between the concepts is achieved.