Page 326 - Synthetic Fuels Handbook

312 CHAPTER TEN

with methanol. Ethyl-t-butyl ether (ETBE) is made by using ethanol instead of methanol.
Thus either ethanol or methanol from either grain or wood could be a factor in making t-
butyl ether octane enhancers. The characteristics of ethers are generally closer to those of
gasoline than those of alcohols.
Ethers are benign in their effect on fuel system materials and are miscible in gasoline;
therefore, they are not subject to phase separation in the presence of water, as are methanol
and ethanol. Ethers are nonpolar. They are of low volatility and thus give low evaporative
emissions.
Alternative fuels from wood, as well as grain, have a potential for being competitive
with gasoline and diesel motor fuels from petroleum, even without subsidization. Today,
ethanol from grain and a slight amount from wood are competing, but only with a large
Federal and some State subsidies. However, environmental and octane-enhancing benefits
of ethanol and other oxygenated fuels that may be produced from grain and wood may
make them worth more than comparisons on fuel value alone would indicate.
Diesel fuel or gasoline from wood is a possibility through a number of approaches.
The one that appears simplest is to use an exudation or gum from a tropical wood species,
Copaifera, which is said to be directly combustible in a diesel engine. The Fischer-Tropsch
pyrolysis process, used successfully for converting coal to synthesis gas in South Africa
could also be used to make synthesis gas from wood (Fig. 10.3). Synthesis gas could then be
used to make gasoline or diesel fuel. Or methanol could be produced from wood and then,
by a catalyzed reaction known as the Mobil process, be transformed to gasoline.

Product
oil
Gasification

Wood Distillation

Wet Compressor FT
scrubber synthesis
Heat recovery
FIGURE 10.3 Diesel from wood by the Fischer-Tropsch process.

Although, ideally, there should be additional pilot testing for any process to produce
ethanol or methanol from wood commercially, technology for ethanol production has been
developed and subjected to some pilot testing. The technology is available for fairly rapid
implementation, should the need for alternative fuels become pressing as the result of
another global petroleum emergency. Depending on feedstock costs and other variables,
ethanol from wood might or might not be able to compete with ethanol from corn. Another
important consideration is production and marketing of by-products such as high fructose
corn syrup and distillers dry grains from corn and molasses and/or furfural from wood. The
two-stage, dilute sulfuric acid hydrolysis process is a possibility for commercial application
in producing ethanol from low-grade hardwoods.
In the two-stage hydrolysis process, for every 100 kg of oven-dry wood feedstock about
20 kg carbohydrates suitable for processing to ethanol are obtained from the second stage.
There are more carbohydrates derived from the first stage, about 24.9 kg, but many of these
first stage carbohydrates are not necessarily fermentable to ethanol.
Ethanol is a possibility if xylose can be fermented to ethanol economically. Fermentation
of the xylose and glucose from the first stage could result in almost doubling the ethanol