Reducing the Energy Carbon Content - Energy and Climate: How to Achieve a Successful Energy Transition - page 81

oleaginous plants, fast rotation crops on agricultural areas, etc.) as raw
material would considerably increase the biofuel production potential.
In order to produce liquid fuels from lignocellulosic biomass, we will
nevertheless need to develop 'second generation' technologies, which have
not yet been proven either industrially or economically. Two main
conversion pathways are used:

. The

, under development, consists of con-
verting biomass under the effect of heat into a gaseous or liquid phase.
Liquid fuels can be obtained through gasification followed by
Fischer-Tropsch synthesis. The BTL (biomass to liquids) process is
similar to GTL (gas to liquids) and CTL (coal to liquids) processes
used to produce synthetic fuels from natural gas or coal, which are
described in Chapter 7. It offers the advantage of producing high-
quality liquid fuels, in particular diesel, which can be used directly in
current engines.
Pyrolysis of lignocellulosic biomass in an oxygen-free atmosphere
produces a liquid phase called 'bio-oil'. This product is rich in
oxygenated compounds, making it immiscible with hydrocarbons.
It can be converted into liquid fuels by gasification. Its conversion
into fuel by hydrogenation is also one of the research pathways being
investigated.
. The

thermochemical pathway

requires fractionation of the lignocellu-
losic biomass into its three fractions: cellulose, hemicelluloses and
lignin. Glucose can be obtained from cellulose under the effect of
enzymes. The glucose then undergoes a fermentation step to obtain
ethanol. The aim of current studies is to improve the performance of
this conversion process. The research work also concerns the con-
version of hemicelluloses to obtain other sugars, the pentoses, whose
subsequent conversion into ethanol by fermentation is also being
studied. This conversion, which is more difficult than the case of the
cellulose fraction, has not reached the industrial stage [67]. Lignin is
separated and can be used as a fuel to supply energy. Production of
cellulosic ethanol is still currently more expensive than production of
ethanol fromother sugar plants. In viewof the extensive research and
development work in progress we can expect production to become
more competitive.

biochemical pathway

Large-scale development of biofuels is only acceptable if compatible with
sustainable development criteria. The risks associated with the produc-
tion of biomass intended for use as biofuels must be carefully analysed