http://www.pre.ethz.ch/
In a number of previous reports, we've documented that Oxygen, concentrated to at least some extent, as opposed to unpurified air, is preferred for use in gasification procedures intended to produce, primarily, a blend of Carbon Monoxide and Hydrogen, a hydrocarbon synthesis gas, from Coal.
The use of purified Oxygen efficiently promotes exothermic reactions with Coal which enable the inclusion of other co-reactants, such as Steam and/or Carbon Dioxide, whose breakdown into their elemental constituents consumes a great deal of thermal energy; and, it does so without promoting or enabling the wasteful formation of Nitrogen Oxide pollutants, as would be the case if unpurified air were to be used.