A mixture of carbon monoxide and hydrogen is called synthesis gas, because it can be used to synthesize a variety of useful and valuable products, as explained in Chapter 21. Synthesis gas can be made from virtually any carbon-containing material, including all of the fossil and bio- fuels discussed in this book, and others that are not (such as municipal or agricultural wastes or used tires). Generically, the reaction is

“C”+H2O→CO+H2,

where “C” is used simply to represent a carbon-containing feedstock, not implying it to be pure carbon. The reaction conditions and reactor design, and even different names for the process, are specific to individual feedstocks. Several terms are used, depending on the nature of the feedstock, to describe what is chemically the same process. Conversion of gaseous or light liquid hydrocarbons is called steam reforming. Partial oxidation uses heavy oils from petroleum or oil sands. And, if solid biomass or coal is the feed, the process is called gasification. Regardless of names, the reaction of carbon-containing feedstocks with steam provides immense versatility to produce, and later employ, synthesis gas.

An important aspect of synthesis gas production is the versatility of what can be done with the product: synthesis gas can be used directly as a gaseous fuel; converted to methane (substitute natural gas); converted to methanol, to be used directly as a liquid fuel or converted further to gasoline; or converted to a variety of other liquid hydrocarbon fuels. When using coal as the feedstock, some of the impurities in the coal – notably sulfur and mineral matter – can be removed at the same time. Further, it is easier to capture CO2 from concentrated gas streams associated with synthesis gas processes than from the relatively dilute flue gas streams produced in coal combustion.