2 Introduction to Renewable Biomaterials
1.2 Comparison of Fossil-BasedversusBio-Based Raw Materials
1.2.1 The Nature of Fossil Raw Materials
The current global economy is very much based on fossil resources to produce energy
(electricity, fuel, heat) and organic chemicals. The initial source of these feedstock
has been biomass transformed through geological processes into crude oil, natural
gas, black coal as well as lignite and peat. What makes these materials valuable for
use in energy and chemistry processes is their high energy as well as carbon content
(Table 1.1). The most valuable fossil resources are the hydrocarbons that consist only
of carbon and hydrogen. Subgroups are, for example, alkanes (saturated hydrocarbons;
CnH 2 n+ 2 ), cycloalkanes (CnH 2 n), alkenes (unsaturated hydrocarbons; CnH 2 n), and
aromatics (ring-shaped molecules) differing in the number of carbon and hydrogen
and molecular structure.
Coal, especially black coal, is the oldest fossil resource. Formed from terrestrial plant
biomass, it has been consolidated between other rock strata and altered to form coal
seams by the combined impact of pressure and heat under low-oxygen conditions over
about 300 million years. Black coal is extracted by open-cast mining as well as deep
mining (up to a depth of 1500 m). It is composed primarily of carbon.
Fossil oil has been formed over a time period of about 100 million years by the
exposure to similar conditions on sedimentation layers of marine organisms such
as algae and plankton. Under such conditions, the long-chain organic molecules of
the vegetable biomass are split into short-chain compounds forming liquid oil. It
accumulates in specific geological formations called crude oil reservoirs.
Some fractions even split down to molecules with only one carbon and become
gaseous methane (CH 4 ). Therefore, oil deposits (and coal mines) always contain
methane of more or less similar age. Methane sources covered by nonpermeable
geological layers lead to real methane deposits. From such geological formations, the
gas can be extracted in the form of natural gas. Natural gas can also be the result of
biological catabolic processes degrading biomass. These deposits are also found under
nonpermeable geological formations but have been formed over a period of about
20 million years.
As oil and gas generation needs high-pressure conditions the corresponding deposits
are highly pressurized. If such sites are drilled, oil and gas escape through the well – a
process called primary recovery allowing to exploit 5–10% of the total oil and gas. By
Table 1.1Composition (%) and heat value (MJ kg−^1 )(Herrmannand
Weber, 2011) of fossil feedstock.
CH NOS MJkg−^1
Natural gas 75–85 9–24 Traces Traces Traces 32–
Mineral oil 83–87 10–14 0.1–2 0.5–6 0.5–6 43
Black coal 60–75 6 Traces 17–34 0.5–3 25–
Lignite 58–73 4.5–8.5 Traces 21–36 3 22
Peat 50–60 5–7 1–4 30–40 0.2–2 15
