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Making liquid fuel from coal generates lots of CO2

Coal is most commonly used to generate electricity, an activity that overall contributes more CO2 to the atmosphere than any other human enterprise.  Coal can also be made into liquid fuels, including synthetic gasoline and diesel, by so-called coal-to-liquids (CTL) processes. But this conversion is water-intensive and can generate substantial CO2 emissions, even before accounting for the emissions from burning the fuel when it is used. Altogether, CTL fuels end up releasing about twice as much CO2 as fuels made directly from petroleum, and more than burning the same amount of coal for electricity. It’s possible to capture the CO2 from the liquefaction process and store it underground — but that still leaves the emissions from the fuel itself, which are about the same as those from conventional gasoline or diesel. (Other pollutants, however, such as sulfur dioxide, would be much lower for CTL diesel than for conventional diesel.) 

An intriguing idea for using coal to make liquids with much lower overall CO2 emissions is to convert some biomass along with the coal in systems using carbon capture and storage. With such technology, it is possible to make liquid fuels with lower CO2 emissions than conventional petroleum-derived fuels – as low as zero emissions.1 2

References
  1. E.D. Larson, G. Fiorese, G. Liu, R.H. Williams, T.G. Kreutz, and S. Consonni, “Co-Production of Synfuels and Electricity from Coal + Biomass with Zero Net Carbon Emissions: An Illinois Case Study,” (Abstract) Energy and Environmental Science, published online, 9 November 2009.
  2. America’s Energy Future Panel on Alternative Liquid Transportation Fuels: Liquid Transportation Fuels from Coal and Biomass: Technological Costs, Status, and Environmental Impacts, (Summary) National Academies Press, Washington DC, 20 May 2009.