Synthesis gas or syngas, once (early twentieth century) named "manufactured gas" and "town gas" is a gas mixture fuel (CO + H2) produced by pyrolysis. It is a lean gas (twice less energy than natural gas) and dirty, toxic, acidic and corrosive if it has not been thoroughly cleaned (as was the case when used for interior lighting).
Synthesis gas can be produced from almost any carbon source ranging from natural gas and oil products to coal and biomass by oxidation with steam and oxygen. These reactions are characterized by a first step gasification by pyrolysis of an organic material (for example wood or coal) in the presence of an oxidizing agent introduced in sufficient quantity, enough so that there is combustion, but too little for it is complete. Exemplary reactions are shown below with respect to a cellulose repeat unit (C6H10O5) found, for example, in cellulosic feedstocks. Similar reactions can occur with any carbon-containing feedstock.
Steam Reforming C6H10O5+H2O→6CO+6H2
Partial Oxidation C6H10O5+½O2→6CO+5H2
Water-Gas Shift CO+H2O → H2+CO2
The synthesis gas contains mostly steam, hydrogen, methane, carbon monoxide and a bit carbone dioxide with thermolysis residues. Almost all of these residues are toxic compounds, carcinogenic or mutagenic. The present use of syngas is primarily for the manufacture of ammonia and methanol, followed by the use of pure hydrogen for hydrotreating in refineries.