Gasoline from trees

Jan. 7, 2013
KiOR Corp. recently announced the completion of a commercial-scale plant to make gasoline blendstocks from wood. According to the company, the commercial facility at Columbus, Miss., will produce 11 million gal/year of gasoline blendstocks from 183,000 tons of southern yellow pine.

KiOR Corp. recently announced the completion of a commercial-scale plant to make gasoline blendstocks from wood. According to the company, the commercial facility at Columbus, Miss., will produce 11 million gal/year of gasoline blendstocks from 183,000 tons of southern yellow pine. Since the density of southern yellow pine is about 39 lb/cu ft, this mass of wood is equivalent to 9.4 million cu ft.1 The average annual growth of growing stock on commercial timberland in the south is about 65 cu ft/acre.2 Therefore, annual production of 11 million gal of gasoline blendstocks will require that 225 sq miles of timberland be dedicated to fuel production. Note that these 11 million gal of fuel constitute just 0.052% of the 21 billion gal of cellulosic biofuels mandated by the Renewable Fuel Standard.

Commercial timberland (forest land capable of producing at least 20 cu ft/acre/year and not withdrawn for other purposes) in the US covers 514 million acres—about one fourth of the land area of the US.3 If the entire 21 billion gal of cellulosic biofuels were supplied from wood by this technology, 342 million acres, or two thirds of the total commercial timberland in the US would have to be devoted to producing wood for fuel.4 Only a few years ago the major environmental organizations were advocating a ban on all logging in national forests. That, of course, was before renewable energy became fashionable. That said, timber harvesting operations, even when done carefully, result in increased soil erosion and stream sedimentation.

I want to emphasize two important points here. The first is that the 21 billion gal of biofuel constitute only 15% of the US gasoline supply. The second is that in converting the wood into a petroleum feedstock, 40% of the energy in the wood is lost. If wood is to be used as a fuel, a far better alternative is to burn it in a power generating plant.

Donald F. Anthrop
Berkeley, Calif.

References

1. Seely, O., "Physical Properties of Common Woods," csudh.edu/oliver/chemdata/woods.
2. Smith, W., et al., "Forest Resources of the United States," Gen. Tech. Rept., US Department of Agriculture, Forest Service, Washington, DC, 2007, p. 65.
3. Ibid., p. 153.
4. For this calculation, the writer used 52 cu ft/acre for the annual net growth, which is the average net growth for all US commercial timberland (Ref. 2).