Technical Challenges

The chart of H/C ratios for various fossil fuels indicates one of the technical challenges facing the advanced fossil fuel technology-namely adding hydrogen to produce the light liquid or gaseous fuels desired. The production of hydrogen, usually by the water-gas reaction, is expensive in both primary energy and dollars. The addition of hydrogen to a solid, low-hydrocarbon-ratio fuel usually requires elevated temperatures and pressures in the presence of catalyst to form a higher-order hydrocarbon. A catalyst second problem with both coal and oil from shale is the organically bound nitrogen and sulfur in coal and oil shale, product that are undesirable in the liquid crude produced. They poison catalyst in refining and are undesirable in finished product because of NOx and SOx emission levels. Hydrogen can also be used to remove these elements but the combination of hydrogen for liquefying plus nitrogen or sulfur removal places enormous demand on the amounts of hydrogen required, affecting both primary resource efficiency and resultant product cost.

The problems associated with producing a liquid hydrocarbon from the kerogen contained in oil shale are different than those in upgrading coal to a liquid product. The kerogen has a much higher H/C ratio (see figure), and for rich oil shales it is the binding agent for the rock which must by pyrolysed thermally or removed by some other process to be available for recovery.