Page 238 - Synthetic Fuels Handbook

224 CHAPTER EIGHT

accumulate carbon from the atmosphere via photosynthesis and the widespread utilization
of these materials as basic inputs into the generation of power, fuels, and chemicals is a
viable route to reduce greenhouse gas emissions.
Thus, the petroleum and petrochemical industries are coming under increasing pressure
not only to compete effectively with global competitors utilizing more advantaged hydro-
carbon feedstocks but also to ensure that its processes and products comply with increas-
ingly stringent environmental legislation.
The production of fuels and chemicals from renewable plant-based feedstocks utilizing
state-of-the-art conversion technologies presents an opportunity to maintain competitive
advantage and contribute to the attainment of national environmental targets. Bioprocessing
routes have a number of compelling advantages over conventional petrochemical produc-
tion; however, it is only in the last decade that rapid progress in biotechnology has facilitated
the commercialization of a number of plant-based chemical processes. It is widely recog-
nized that further significant production of plant-based chemicals will only be economically
viable in highly integrated and efficient production complexes producing a diverse range of
chemical products. This biorefinery concept is analogous to conventional oil refineries and
petrochemical complexes that have evolved over many years to maximize process synergies,
energy integration, and feedstock utilization to drive down production costs.

8.1.1 Feedstock Types

Plants offer a unique and diverse feedstock for chemicals. Plant biomass can be gasified to
produce synthesis gas, a basic chemical feedstock and also a source of hydrogen for a future
hydrogen economy (Hocevar, 2007). In addition, the specific components of plants such
as carbohydrates, vegetable oils, plant fiber, and complex organic molecules known as pri-
mary and secondary metabolites can be utilized to produce a range of valuable monomers,
chemical intermediates, pharmaceuticals, and the following materials:
Carbohydrates (starch, cellulose, sugars) are readily obtained from wheat and potato,
while cellulose is obtained from wood pulp. The structures of these polysaccharides can
be readily manipulated to produce a range of biodegradable polymers with properties
similar to those of conventional plastics such as polystyrene foams and polyethylene
film. In addition, these polysaccharides can be hydrolyzed, catalytically or enzymati-
cally, to produce sugars, a valuable fermentation feedstock for the production of ethanol,
citric acid, lactic acid, and dibasic acids such as succinic acid.
Vegetable oils are obtained from seed oil plants such as palm, sunflower, and soya. The
predominant source of vegetable oils in many countries is rapeseed oil. Vegetable oils
are a major feedstock for the oleochemical industry (surfactants, dispersants, and per-
sonal care products) and are now successfully entering new markets such as diesel fuel,
lubricants, polyurethane monomers, functional polymer additives and solvents.
Plant fibers (lignocellulosic fibers) are extracted from plants such as hemp and flax, and
can replace cotton and polyester fibers in textile materials and glass fibers in insulation
products.
Specialty products such as highly complex bioactive molecules, the synthesis of which
is often beyond the ability and economics of laboratories, and a wide range of chemi-
cals are currently extracted from plants for a wide range of markets, from crude herbal
remedies to very high value pharmaceutical intermediates.
Fats and greases, the proper categorization may be debatable since those are by-products
of the reduction of animal biomass into component parts. However, most fats and
greases, and some oils, are not available for bioenergy use until after they become a