Energy Solutions to Air Pollution and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 314

Biodiesel is a liquid diesellike fuel derived from veg-
etable oil or animal fat. Major edible vegetable oil
sources of biodiesel include soybean, rapeseed, mus-
tard, false flax, sunflower, palm, peanut, coconut, cas-
tor, corn, cottonseed, and hemp oils. Inedible vegetable
oil sources include jatropha, algae, and jojoba oils. Ani-
mal fat sources include lard, tallow, yellow grease, fish
oil, and chicken fat. Soybean oil accounts for about 90
percent of biodiesel production in the United States.
Biodiesel derived from soybean oil is referred to as soy
biodiesel .
Biodiesel consists primarily of long-chain methyl,
propyl, or ethyl esters that are produced by the chemi-
cal reaction of an oil or fat (both lipids) with an alcohol.
It is a standardized fuel designed to replace diesel in
standard diesel engines. It can be used as pure biodiesel
or blended with regular diesel. Blends range from 2
percent biodiesel/98 percent diesel ( B2 )to100 percent
biodiesel ( B100 ). Generally, only blends B20 and lower
can be used in a diesel engine without engine modifi-
cation. The use of vegetable oil or animal fat directly
(without conversion to biodiesel) in diesel engines is
also possible; however, it results in more incomplete
combustion, and thus more air pollutant by-products,
as well as a greater buildup of carbon residue in, and
damage to, the engine than biodiesel.
Asignificant effort has been made to produce algae
biodiesel ,which is biodiesel from algae grown from
waste material, such as sewage. However, such efforts
have been hampered by the fact that algae can be grown
efficiently only when they are exposed to the sun. As
such, they cannot be grown efficiently in high density,
with one on top of the other, and require a significant
surface area. Each volume of oil produced from algae
also requires about 100 times that volume of water. Both
factors have limited the growth of the algae biodiesel
industry.
Neither solid nor liquid biofuels of any type are rec-
ommended for a clean energy future . Specifically, solid
biofuels for home heating and cooking and for elec-
tric power generation are not recommended. Liquid
ethanol, butanol, and biodiesel from any sources are
not recommended. The main reasons are that (1) nearly
all biofuels are combusted to generate energy, result-
ing in air pollution similar to or greater than that from
fossil fuels; (2) solid or liquid biofuel does not reduce
global warming-relevant emissions nearly to the extent
as do WWS resources; (3) several biofuels increase
such emissions relative to fossil fuels; (4) many biofu-
els require rapacious amounts of land; (5) many biofu-
els require excessive quantities of water; and (6) many

13.1.4. Why Not Liquid or Solid Biofuels?
Biofuels are solid, liquid, or gaseous fuels derived from
organic matter. Most biofuels are derived from dead
plants or animal excrement. Solid biofuels ,such as
wood, grass, agricultural waste, and dung, are burned
directly for home heating and cooking significantly in
developing countries and for electric power generation
in developed and developing countries. Liquid biofuels
are generally used for transportation as a substitute for
gasoline or diesel. The most common transportation
biofuels are ethanol, used in passenger cars and other
light-duty vehicles, and biodiesel, used in many heavy-
duty vehicles.
Ethanol [C 2 H 5 OH(aq)] is produced in a factory,
generally from corn, sugarcane, wheat, sugar beet, or
molasses. The most common among these sources are
corn and sugarcane, resulting in the production of corn
ethanol and sugarcane ethanol ,respectively. Microor-
ganisms and enzyme ferment sugars or starches in these
crops to produce ethanol, as in Reaction 2.3.
Fermentation of cellulose originating from switch-
grass, wood waste, wheat, stalks, corn stalks, or Mis-
canthus can also produce ethanol, but the process is
more energy intensive because natural enzyme break-
down of cellulose (e.g., as occurs in the digestive
tracts of cattle) is slow. Faster breakdown of cellulose
requires genetic engineering of enzymes. The ethanol
resulting from these sources is referred to as cellulosic
ethanol .
Ethanol may be used on its own, as it is frequently in
Brazil, or blended with gasoline. A blend of 6 percent
ethanol/94 percent gasoline is referred to as E6 .Other
typical blends are E10 , E15 , E30 , E60 , E70 , E85 , and
E100 .Inmany countries, including the United States,
E100 is required to contain 5 percent gasoline as a
denaturant ,which is a poisonous or untasteful chem-
ical added to a fuel to prevent people from drinking it.
As such, E85, for example, contains about 81 percent
ethanol and 19 percent gasoline.
Aproposed alternative to ethanol for transportation
fuel is butanol [C 4 H 9 OH(aq)]. It can be produced
by fermentation of the same crops used to produce
ethanol but with a different bacterium, Clostridium
acetobutylicum .Butanol contains more energy per unit
volume of fuel than does ethanol. However, unburned
butanol also reacts more quickly in the atmosphere with
the OH(g) radical than does unburned ethanol, speed-
ing up ground-level ozone formation relative to ethanol.
On average, ethanol, itself, produces more ground-level
ozone than does gasoline (Section 4.3.8).