Dehydrogenation of dicyclohexylamine in gaseous phase over a nickel catalyst: effect of reaction parameters

Abstract

This work deals with a study of the effect of reaction temperature and partial pressure of hydrogen on the product selectivity of the gas-phase dehydrogenation of dicyclohexylamine. Laboratory experiments of dicyclohexylamine dehydrogenation were performed in a glass tubular flow-through reactor with the use of commercial supported nickel Ni/Cr2O3-SiO2 catalyst. The systematic variation in reaction temperature (433–463 K) and partial pressure of hydrogen, i.e. the molar ratio of dicyclohexylamine to H2 and N2 (1:0:30–1:15:0), was used to investigate the dehydrogenation of dicyclohexylamine from the perspective of the formation of products. It was confirmed that the major products of dicyclohexylamine dehydrogenation are imine N-cyclohexylidenecyclohexanamine and aromatic amine N-phenylcyclohexylamine, while the latter is the dominant product. The sequential hydrogenolysis reaction of N-phenylcyclohexylamine was observed to result in the formation of cyclohexylamine and benzene. Furthermore, a significant increase in the concentration of the other six products was observed. The mass spectrometry detection identified these products as N-butylcyclohexanamine, N-pentylcyclohexanamine, N-isopentylcyclohexanamine, N-(2-methylbutyl)cyclohexanamine, N-cyclopentylcyclohexanamine, and N-(3-methylcyclopentyl)cyclohexanamine. The reaction results in the formation of two dehydrogenation products, which are accompanied by other subsequent reactions, such as hydrogenolysis, isomerization, and cyclization.Graphical abstract