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Encyclopedia of Physical Science and Technology EN002G-61 May 19, 2001 19:33

144 Biomass, Bioengineering of

The energy value (heat of combustion) of petroleum is resources. Worldwide, many hundreds of millions of tons
about twice that of biomass (trees have a higher energy of crop residues such as rice straw, sugar cane bagasse
content than grasses) while coal averages about one and a and corn stover are likely to be available at very low cost,
half times the energy value of biomass. The lower energy probably less than $20 per ton. Thus while fossil resources
value of biomass is due to the fact that it contains substan- are relatively inexpensive (even given oil price volatility)
tial oxygen, while petroleum has little or no oxygen. renewable plant resources are equally inexpensive, and in
The lower energy content (i.e., the higher oxygen con- many cases, less expensive. The importance of this fact to
tent) of biomass is both an advantage and a disadvantage biomass processing cannot be overstated.
for this renewable resource. Biomass and the many oxy- Plant raw material costs are crucial for the devel-
genated compounds that can be made from biomass are opment of cost-competitive biobased products. For
inherently more biodegradable and therefore more envi- well-developed processes making commodity chemicals
ronmentally compatible than petroleum and petroleum- and fuels, approximately 50–70% of the total production
derived compounds. Put another way, a large spill of wheat costs are due to the raw material costs. Thus inexpensive
straw is not an environmental disaster, while we are well biomass should eventually lead to inexpensive biobased
aware of the impacts of petroleum spills. Powerful eco- products, if the necessary bioprocessing technologies
nomic considerations tied to raw material use efficiency for converting biomass to biobased products can also be
also direct us toward maintaining the oxygen molecules made inexpensive. In general, we do not yet have inex-
in biobased industrial products. pensive biomass processing technology. However, if the
Petroleum, a liquid, is easier and less expensive to trans- necessary research and development work is done to learn
port and store than solid biomass. One consequence of this how to inexpensively convert biomass to biobased prod-
fact is that much biomass processing will likely be done ucts, there is every reason to believe that these biobased
relatively close to where the biomass is produced. This products can compete on a cost and performance basis
may provide opportunities to integrate biomass produc- with similar products derived from petroleum.
tion with biomass processing and to more easily return to To illustrate, the large chemical companies Dow Chem-
the land the unused or unusable components of biomass. ical and DuPont have recently announced plans to produce
Few such opportunities exist with petroleum processing. monomers for polymer (plastic) production from renew-
In many climates, biomass production takes place only able sugars and starches. These carbohydrates are rela-
during part of the year, so there are additional storage tively inexpensive, and the companies have also devel-
issues that are unique to biomass. Finally, large quanti- oped inexpensive and effective conversion technologies to
ties of biomass can be produced in many, if not most, produce the monomers. For example, Cargill Dow Poly-
countries, while comparatively few countries produce mers (CDP) LLP (Minnetonka, MN) is building the first
significant quantities of petroleum. Thus biomass pro- of up to five large processing plants to convert corn starch
duction is inherently more “democratic” than petroleum into lactic acid and then into polymers (polylactides). Al-
production and is certainly less susceptible to political though biodegradability of the polymers is obviously a
manipulation. benefit, CDP expects its polylactide polymers to compete
on a cost and performance basis with petroleum-derived
competing products. Similarly, DuPont’s carbohydrate-
4. Cost of Biomass versus Fossil Feedstocks
derived product, 1,3 propanediol, is intended to com-
Petroleum costs varied between about $10 and $20 per bar- pete directly with the identical molecule produced from
rel ($65 to $130 per ton) during the decade of the 1990s. petroleum. The chemical industry is therefore beginning
Currently oil prices are about $30 per barrel or roughly to change its raw material base. As technologies improve
$200 per ton. Coal is available for approximately $30 per and bioprocessing costs decrease, there is every reason to
ton. By comparison, corn at $2.50 per bushel, an “average” believe that more such products will follow.
corn price over the last decade, is roughly equivalent to
$90 per ton. Corn is currently less than $2.00 per bushel,
or about $70 per ton, approximately one third the current B. Major Types of Biomass: Their
price of crude oil. Hay crops of different types and quali- Production and Composition
ties are available in very large quantities (tens of millions
1. Sugar Crops
of tons) for approximately $30–$50 per ton and several
million tons per year at least of crop residues such as rice The major sugar crops are sugar cane and sugar beets.
straw and corn stover are available in the United States for Worldwide, approximately 100 million tons per year of
less than $20 per ton. Figure 2 summarizes some of these sugar (sucrose) are produced from sugar cane and sugar
comparisons of the relative prices of biomass and fossil beets. Most of these sugars are used ultimately in human