James C. Kuo

Gasification and Indirect Liquefaction

To produce liquid fuels from coal, either direct or indirect liquefaction routes can be used. The discussion of the former route is the subject of Chapter 6; the latter route will be discussed here. The indirect liquefaction route consists of the conversion of coal to synthesis gas (hydrogen plus carbon monoxide), and then the conversion of the synthesis gas to liquid fuels, such as alcohols or hydrocarbons. The major processing steps include the following: Coal gasification using steam and oxygen to form hydrogen and carbon monoxide. Synthesis gas purification to remove particulate matter, carbon dioxide, ammonia, hydrogen sulfide, carbonyl sulfide, and other undesirable impurities. A water-gas shift process to react some carbon monoxide with steam to give hydrogen. The removal of carbon dioxide formed in the water-gas shift process. Synthesis gas conversion to form alcohols or hydrocarbons. Final product upgrading to convert the alcohols or hydrocarbons obtained from the synthesis gas conversion step into some specific marketable products.

Engineering Evaluation of Direct Methane Conversion Processes

Methane is the most stable hydrocarbon. Conventional conversions of methane into other useful chemicals, such as methanol and higher hydrocarbons, require an initial formation of synthesis gases (H2 + CO + CO2) at very high temperatures (800–1400°C).

Evaluation of Direct Methane Conversion Processes

This paper describes evaluation studies on direct CH4 conversion processes. The processes are first classified according to their chemistry and then subjected to preliminary evaluations, including thermochemical calculations and some scoping process calculations. An analysis on selectivity, conversion, and yield shows the importance of achieving high selectivities in all processes. Furthermore, two processes, i.e., a “Direct Partial Oxidation to Methanol” process and an “Oxidative Coupling to Ethylene” process, are selected for engineering evaluations for making liquid fuels. Both are compared against a conventional Natural Gas-to-Methanol via Steam Reforming process. The DPOM process scheme is simple because of simple products and easy product separation and could become competitive if >90% selectivity at 7.5% single-pass conversion or > 80% selectivity at 15% conversion is achieved. The OCE process scheme is relatively complicated and could become competitive if > 88% selectivity at 35% single-pass conversion is accomplished.