Page 265 - Synthetic Fuels Handbook

FUELS FROM BIOMASS 251

another engine. In general, newer engines are more sensitive to fuel than older engines, but
new engines are also likely to be designed with some amount of biofuel in mind.
Straight vegetable oil can be used in some (older) diesel engines. Only in the warmest
climates can it be used without engine modifications, so it is of limited use in colder cli-
mates. Most commonly it is turned into biodiesel. No engine manufacturer explicitly allows
any use of vegetable oil in their engines.
Biodiesel can be a direct biofuel. In some countries manufacturers cover many of their
diesel engines under warranty for 100 percent biodiesel use. Many people have run thou-
sands of miles on biodiesel without problem, and many studies have been made on 100 percent
biodiesel. In many European countries, 100 percent biodiesel is widely used and is avail-
able at thousands of gas stations.
Ethanol is the most common biofuel, and over the years many engines have been
designed to run on it. Many of these could not run on regular gasoline. It is open to debate
if ethanol is a direct replacement in these engines though—they cannot run on anything
else. In the late 1990s engines started appearing that by design can use either fuel. Ethanol
is a direct replacement in these engines, but it is debatable if these engines are unmodified,
or factory modified for ethanol.
Butanol is often claimed as a direct replacement for gasoline. It is not in wide spread
production at this time, and engine manufacturers have not made statements about its
use. While it appears that butanol has sufficiently similar characteristics with gasoline
such that it should work without problem in any gasoline engine, no widespread experi-
ence exists.
There is some concern about the energy efficiency of biofuel production. Production of
biofuels from raw materials requires energy (for farming, transport, and conversion to final
product), and it is not clear what the overall efficiency of the process is. For some biofuels
the energy balance may even be negative.
Since vast amounts of raw material are needed for biofuel production, monocultures and
intensive farming may become more popular, which may cause environmental damages
and undo some of the progress made toward sustainable agriculture.

8.6 A BIOREFINERY

Plants are very effective chemical mini-factories or refineries insofar as they produce chem-
icals by specific pathways. The chemicals they produce are usually essential manufacture
(called metabolites) include sugars and amino acids that are essential for the growth of the
plant, as well as more complex compounds.
Biorefining offers a key method to accessing the integrated production of chemicals, mate-
rials, and fuels. The biorefinery concept is analogous to that of an oil refinery (Chap. 3).
In a manner similar to the petroleum refinery, a biorefinery would integrate a variety of
conversion processes to produce multiple product streams such as motor fuels and other
chemicals from biomass. In short, a biorefinery would combine the essential technolo-
gies to transform biological raw materials into a range of industrially useful intermediates.
However, the type of biorefinery would have to be differentiated by the character of the
feedstock. For example, the crop biorefinery would use raw materials such as cereals or
maize and the lignocellulose biorefinery would use raw material with high cellulose con-
tent, such as straw, wood, and paper waste.
In addition, a variety of methods techniques can be employed to obtain different product
portfolios of bulk chemicals, fuels, and materials. Biotechnology-based conversion pro-
cesses can be used to ferment the biomass carbohydrate content into sugars that can then
be further processed. As one example, the fermentation path to lactic acid shows promise