Porosity distribution optimization catalyst for methanol decomposition in solar parabolic trough receiver-reactors by the variational method

Abstract

Decomposing methanol to hydrogen and carbon monoxide in solar parabolic trough receiver-reactors is a promising way for solar energy utilization, which converts solar energy to chemical energy. Due to the non-uniform boundary heat flux of receivers and the varying concentration of methanol, the porosity distribution of catalyst should be carefully designed to improve the thermochemical reaction performance. In this contribution, we theoretically analyze the relations of such factors as temperature, mass fraction of gas mixture, porosity distribution, and reaction rate, establish a optimization model by adapting the largest conversion rate of methanol as an optimization objective together with such constraints as the continuity equation, the momentum equation, the energy conservation equation, the species equations, and the fixed total mass of catalyst, apply the variational principle to derive the governing equations for optimization of catalyst porosity distribution, and finally take a solar parabolic trough receiver–reactor with methanol decomposition reaction as an example to show the applications. When the surface heat flux as well as the total mass of porous catalyst are given, solving the newly deduced governing equations directly gives the optimal porosity distribution of catalyst under different working conditions. Meanwhile, the optimized non-uniform porosity distribution of catalyst will effectively improve the conversion rate of the methanol, e.g. from 52.3% to 72.3% when E = 40, which provide a guidance for catalyst design to improve the thermochemical reactions performance.