Although the demand and price for hydrogen in the USA are currently insufficient to support its generation from any source, its possible role in the future is the subject of considerable speculation. The coal reserves of the USA offer a possible long-term source of energy and chemicals, and perhaps a basis for the generation of hydrogen from water. With that in mind, a preliminary design has been carried out for a process to produce pure hydrogen and pure carbon-dioxide from coal char.

The conversion of coal char and water to CO2 and H2 is endothermic, and the completion of the water-gas-shift phase is limited by equilibrium. A possible alternative without those shortcomings is the CO2–Acceptor Process described in a now expired patent. In the proposed process the coal char is digested in molten caustic. The CO2 is completely converted to Na2CO3 and none escapes as a gas, this enables the water-gas-shift reaction to go to completion, and results in an overall reaction that is very exothermic. The molten alkali/carbonate mixture is catalytic with respect to the coal-char gasification allowing it to be carried out at 500oC as compared to 1000oC in conventional gasifiers. However, a pressure of as much as 50 atm is desirable to increase the concentration of water in the liquid phase. Supplementary processes and equipment are required to recover for re-use the caustic soda from its mixture with sodium carbonate and to separate out the small amount of ash from the coal char for disposal.

This process is attractive because of the purity of both the hydrogen and carbon dioxide streams that are produced. Based on the preliminary design calculations it appears to be technically feasible. However, because of the high pressures, high temperatures, and the extensive need for nickel cladding, a several-fold increase in the price of hydrogen would be required to make it economically attractive.