Effect of Iterative Use of Methylcyclohexane as a Hydrogen Carrier on Catalytic Activity and By-product Formation

Abstract

Methylcyclohexane (MCH) is a candidate liquid organic hydrogen carrier for the storage of renewable energy. The by-products were examined in dehydrogenation and hydrogenation of the MCH/toluene (TOL) pair that forms an energy storage and release system. Pt catalyst was used for the dehydrogenation of MCH, and Ni catalysts were used for the hydrogenation of TOL, and 10 cycles of dehydrogenation/hydrogenation were conducted. Conversion of TOL to MCH greater than 97 % across all cycles, and conversion of MCH to TOL decreased from 90 to 84 %, with increasing cycle number. The original MCH feed contained 0.6 % impurities, and the concentration of by-products ranged from 0.7-0.9 %. More than 70 by-products were identified in the liquid product, and were categorized as the products of six types of side reactions: demethylation, ring-opening, isomerization to form 5-or 6-membered ring compounds, dimerization, and polycyclic compound formation. Demethylation compounds showed remarkable accumulation after 10 cycles.