Hydrogen storage and fuel processing strategies

Abstract

It is widely recognised that fossil fuels are finite, and alternatives should be investigated to secure future energy supplies. Much research is directed towards hydrogen as a fuel, but the gas is unmanageable without an effective storage and distribution strategy. This work investigates the Methylcyclohexane-Toluene-Hydrogen (MTH) system of hydrogen storage with a view to providing vehicular fuel or storing energy produced by intermittent producers. Stable liquid-hydrocarbon hydrogen storage enables hydrogen distribution using the existing fossil fuel network, eliminating the need to build a new fuel infrastructure. A literature survey is carried out covering the area of Liquid Organic Hydrogen Carriers (LOHCs). A study of the technoeconomic bottlenecks which would prevent the widespread use of the MTH system is conducted to direct the project research efforts, which reveals that the vehicular on-board dehydrogenation system must be reduced in size to be practical. Process intensification is attempted by dehydrogenating methylcyclohexane in the liquid-phase, which is experimentally demonstrated in this work (an original contribution). However, to be feasible for a vehicle, the liquid-phase dehydrogenation system demands a specific window of conditions, with hydrocarbon vapour pressure, enthalpy of reaction and equilibrium constant all being important factors. No window is possible to satisfy all conditions for the MTH system, which renders this vehicular system infeasible. Alternative liquid carriers are investigated to solve the problem, but no clear candidate carrier is found without using highly experimental and costly molecules. This leads to a new investigation of other applications for the MTH system. MCH for power to a Scottish whisky distillery is investigated, followed by an investment appraisal of the distillery system. The system is technically feasible but attracts a high capital expenditure (almost £16M) and operational cost (£2.4M annually) which is uncompetitive with alternative options such as biomass fuels. Finally, possible future work in the field of LOHC technology is considered.