Co Hydrogenation in a Microreactor Under Non-Differential Regime: Kinetics, and Impact of Reactor Design and Operational Variables

A kinetic model for CO methanation and the water gas shift reaction, using a commercial catalyst 12 % Ni/γ-Al<inf>2</inf>O<inf>3</inf> powder catalyst, is developed for a wall-coated microreactor to assess the impact of reactor design and operational parameters on catalytic performance. This model incorporates the simultaneous resolution of multidimensional balances of momentum, energy, and species continuity both in the catalytic and the hollow zones within the microchannels. The microreactor consists of 80 microchannels, each with dimensions of 0.45 × 0.15 × 50 mm3 and coated with a catalytic layer with an average thickness of 0.04 mm. Ninety-five experimental assays are carried out in triplicate under various conditions, including temperature (250 – 350 °C), H<inf>2</inf>/CO molar ratio at the inlet (2 – 11) and volumetric flow rates (110 – 140 mL/min). The corrected Akaike Information Criterion (AICc) indicated that a variation of the Champon model accurately described the experimental data of CO conversion and methane selectivity up to the non-differential regime, which generally occurs at an industrial scale. An apparent activation energy of 92.3 and 156 kJ/mol for the CO methanation and water gas shift reactions are calculated, respectively. The impact of operational variables on the methane mass flow, such as reaction temperature, feed composition, and flow rate, is quantified. Considering a mixture close to stoichiometric (H<inf>2</inf>/CO = 3.2), a boundary temperature of 325 °C and GHSV of 88 L/h/g<inf>cat</inf>, a maximum velocity of 1.26 m/s, complete isothermicity in the microchannel and a pressure drop of less than 0.5 kPa were achieved. Experimentally, a 47 % conversion and 93 % selectivity to methane were achieved, which closely approximated the value reported by the selected model. It is determined that the smaller dimensions of the microchannels favored CO conversion and methane formation, and it is verified that the microchannels operate isothermally throughout their entire domain, with pressure losses being negligible (<1%). Additionally, catalyst thickness has a greater impact on methane mass flow rate than the length and number of microchannels. This research contributes to the design of more efficient catalytic and thermal processes for the production of clean synthetic fuels, which is essential for the sustainable development of processes. © 2024 Elsevier Ltd