David L. Cresswell

Options for on-Board Use of Hydrogen Based on the Methylcyclohexane–Toluene–Hydrogen System

The methylcyclohexane-toluene-hydrogen (MTH)-system is considered as one of the potential solutions for the successful exploitation of the hydrogen economy. Three options for on-board use of the MTH-system have been considered. A base-case process flowsheet is developed and simulated in Aspen HYSYS®. Thermal pinch analysis is performed to assess the thermal energy deficiency for the dehydrogenation reaction to be carried out. Heat energy requirements and the size of the methylcyclohexane and toluene storage tanks for on-board applications rule out the idea of using the MTH-system in a total replacement of gasoline in an internal combustion engine or a fuel cell with hydrogen from the MTH-system. A hybrid MTH–gasoline system is emerged as a practical solution for the on-board use of hydrogen from the MTH-system.

Dehydrogenation of Methylcyclohexane: Parametric Sensitivity of the Power Law Kinetics

For heterogeneous catalytic reactions, the empirical power law model is a valuable tool that explains variation in the kinetic behavior with changes in operating conditions, and therefore aids in the development of an appropriate and robust kinetic model. In the present work, experiments are performed on 1.0 wt% Pt/Al2O3 catalyst over a wide range of experimental conditions and parametric sensitivity of the power law model to the kinetics of the dehydrogenation of methylcyclohexane is studied. Power law parameters such as order of the reaction, activation energy, and kinetic rate constants are found dependent upon the operating conditions. With H2 in the feed, both apparent order of the reaction and apparent activation energy generally increase with an increase in pressure. The results suggest a kinetic model, which involves nonlinear dependence of rate on the partial pressure of hydrogen and adsorption kinetics of toluene or some intermediate.

MATHEMATICAL MODELING OF A LABORATORY METHYLCYCLOHEXANE DEHYDROGENATION REACTOR AND ESTIMATION OF RADIAL THERMAL CONDUCTIVITIES AND WALL HEAT TRANSFER COEFFICIENTS

A laboratory micro-pilot fixed-bed reactor for the dehydrogenation of methylcyclohexane was modeled. The kinetic model developed in our previous work (Usman et al., 2012) over 1.0 wt.% Pt/γ-Al2O3 was used in modeling the reactor. The experimental data over the same catalyst was compared with the proposed model and reasonable estimates of the data were found. Effective radial thermal conductivity and apparent wall heat transfer coefficient were observed to be a function of the composition of the reaction mixture and varied along the length of the reactor.

Selectivity of the formation of the ring-closed products and methylcyclohexenes in the dehydrogenation of methylcyclohexane to toluene

In our previous publication (Usman et al., 2011), the by-products formation during the dehydrogenation of methylcyclohexane over 1.0 wt% Pt/γ-Al2O3 was studied under wide range of operating conditions. The formation and yield patterns of benzene, cyclohexane, and isomers of xylene were studied. In the present contribution, the formation and yield patterns of the ring-closed products (sum of ethylcyclopentane and dimethylcyclopentanes) and methylcyclohexenes are studied. The yields of both of the ring-closed products (RCPs) and methylcyclohexenes (MCHes) were observed to increase with an increase in pressure. However, the effect of hydrogen concentration was found affecting differently at the low and at the high pressures. The yield patterns of methylcyclohexenes suggested methylcyclohexenes as the reaction intermediate in the formation of toluene.