Page 272 - Synthetic Fuels Handbook

258 CHAPTER EIGHT

replace equivalent or identical products currently obtained from crude oil, coal, or gas.
Thus, the biorefinery is analogous to an oil refinery in which crude oil is separated into a
series of products, such as gasoline, heating oil, jet fuel, and petrochemicals.
By producing multiple products, a biorefinery can take advantage of the differences
in biomass components and intermediates and maximize the value derived from the bio-
mass feedstock. A biorefinery might, for example, produce one or several low-volume, but
high-value, chemical products and a low-value, but high-volume liquid transportation fuel,
while generating electricity and process heat for its own use and perhaps enough for sale of
electricity. The high-value products enhance profitability, the high-volume fuel helps meet
national energy needs, and the power production reduces costs and avoids greenhouse gas
emissions.
As a feedstock, biomass can be converted by thermal or biological routes to a wide range
of useful forms of energy including process heat, steam, electricity, as well as liquid fuels,
chemicals, and synthesis gas. As a raw material, biomass is a nearly universal feedstock due
to its versatility, domestic availability, and renewable character. At the same time, it also
has its limitations. For example, the energy density of biomass is low compared to that of
coal, liquid petroleum, or petroleum-derived fuels. The heat content of biomass, on a dry
basis (7000–9000 Btu/lb) is at best comparable with that of a low-rank coal or lignite, and
substantially (50–100 percent) lower than that of anthracite, most bituminous coals, and
petroleum. Most biomass, as received, has a high burden of physically adsorbed moisture,
up to 50 percent by weight. Thus, without substantial drying, the energy content of a bio-
mass feed per unit mass is even less.
These inherent characteristics and limitations of biomass feedstocks have focused the
development of efficient methods of chemically transforming and upgrading biomass feed-
stocks in a refinery. The refinery would be based on two “platforms” to promote different
product slates.
The sugar-base involves breakdown of biomass into raw component sugars using
chemical and biological means. The raw fuels may then be upgraded to produce fuels and
chemicals that are interchangeable with existing commodities such as transportation fuels,
oils, and hydrogen.
Although a number of new bioprocesses have been commercialized it is clear that eco-
nomic and technical barriers still exist before the full potential of this area can be realized.
One concept gaining considerable momentum is the biorefinery which could significantly
reduce production costs of plant-based chemicals and facilitate their substitution into exist-
ing markets. This concept is analogous to that of a modern oil refinery in that the biorefin-
ery is a highly integrated complex that will efficiently separate biomass raw materials into
individual components and convert these into marketable products such as energy, fuels,
and chemicals.
By analogy with crude oil, every element of the plant feedstock will be utilized includ-
ing the low value lignin components. However, the different compositional nature of the
biomass feedstock, compared to crude oil, will require the application of a wider variety
of processing tools in the biorefinery. Processing of the individual components will utilize
conventional thermochemical operations and state-of-the-art bioprocessing techniques.
The production of biofuels in the biorefinery complex will service existing high volume
markets, providing economy-of-scale benefits and large volumes of by-product streams
at minimal cost for upgrading to valuable chemicals. A pertinent example of this is the
glycerol by-product produced in biodiesel plants. Glycerol has high functionality and is
a potential platform chemical for conversion into a range of higher value chemicals. The
high-volume product streams in a biorefinery need not necessarily be a fuel but could also
be a large-volume chemical intermediate such as ethylene or lactic acid.
A key requirement for delivery of the biorefinery concept is the ability to develop pro-
cess technology that can economically access and convert the five- and six- membered ring