Page 314 - Synthetic Fuels Handbook

300 CHAPTER TEN

Today low cost and accessible energy can no longer be taken for granted. We are back
to a point where many people, including materials scientists and engineers, are beginning
to appreciate the need for renewable resources like wood. This appreciation is heightened
and fed by the fact that the United States finds itself blessed with a timber inventory that
is increasing each year. Unfortunately, much of this is not of the large clear sixes and high
quality to which we are accustomed.
On the other hand, the past abundance of timber and the dispersion of the industry have
worked against advances in technology for the efficient production, conversion, and use of
wood products. Fortunately, and despite its relatively recent origin as a recognized field of
study, wood science has had an appreciable effect on wood technology as well as science
in general. The study of wood chemistry has contributed to our understanding of the prin-
cipal components of wood—cellulose and lignin—and their reactions. Early research on
hydrolysis of cellulose was prompted by fuel needs in World War I, but contributed much
to our knowledge of this form of chemical reaction. Similarly, research on nitrocellulose
was prompted by the needs for explosives. Accompanying studies of saccharification and
fermentation are contributing much to our scientific knowledge in those areas. Engineering
studies of wood as an orthotropic material contributed strongly to the concept of sandwich
construction, now commonly used in aircraft design, as well as to the early development of
glass-fiber-reinforced plastics in the 1950s and 1960s.
Another research focus is on use of wood for fuel, which still plays a big part in man’s
existence. Today about half of the world’s annual wood harvest is burned for those same
products primitive man valued from his wood fire—heat and light. But much of this is in
the less developed countries. In most developed countries, use of wood for fuel peaked in
the last century. But with the energy situation as it is today, even developed countries are
turning to wood for fuel. It is renewable, relatively cheap, low in ash content, and negligible
in sulfur content.
On the other hand, wood is bulky, has less than half the heat of combustion of fuel oil,
and in its green state is heavy to ship. Furthermore the cost of a wood-burning system may
be three to four times that of a gas-burning installation because of fuel storage, handling,
and air quality control systems. These drawbacks have kindled interest in production of
liquid and gaseous fuels from wood. Much research is devoted to improving existing tech-
nology and devising new approaches, but such fuels are still expensive compared with
petroleum-based fuels.
Finally, closely related to the conversion of wood to liquid or gaseous fuel is the
use of the chemical storehouse that is wood to produce a wide range of silvichemicals.
Research has shown how to produce useful products from cellulosic polymers, wood and
bark extractives, oleoresins, and pulping liquors. Many processes of these types already
form the basis of chemical production on a commercial scale. But the potential to use
wood as a chemical feedstock is much greater than has so far been realized. Whole wood
can be gasified, liquefied, or pyrolized in ways comparable with those used for coal to
yield a wide variety of chemicals. Cellulose, as a glucose polymer, can be hydrolyzed
to the glucose monomer by acid or enzymes, and the glucose then fermented to ethanol.
The ethanol can be used as a fuel or as a source of other important chemicals such as
ethylene or butadiene.
As an alternative, use of glucose as substrate for fermentation would make possible
production of antibiotics, vitamins, and enzymes. Hemicelluloses can easily be converted
to simple sugars which can be used to produce ethanol or furfural, a potential raw material
for nylon or other synthetics.
Lignin can be pyrolized, hydrogenated, and hydrolyzed to yield phenols, which can
be further processed to benzene. Once the technology and economics are feasible, future
plants will manufacture a variety of these very significant chemicals from wood, now
derived from petroleum or other resources.