Environmental Engineering Reference
In-Depth Information
8.4.1.6 Synthetic Biofuels
Synthetic biofuels have several advantages as they can be used in unmodified diesel
engines [88, 89] and they are cleaner that traditional fuels due to the removal of all
contaminants to avoid the poisoning of the catalysts used in the processing steps
[3, 105, 106]. These biofuels can have excellent autoignition characteristics as they
have similar energy content, density and viscosity that of fossil diesel as well as
higher cetane number and lower aromatic content (which results in lower particle
emissions). They are also S-, N-free and less corrosive than other biofuels (e.g.
bioethanol and biodiesel) therefore being more environmentally friendly than fuels
produced from crude oil. Some of them (e.g. FT-diesel) have been proved to reduce
the CO, NOx and particulate matter compared to diesel fuel [88, 107, 108].
However, the production of synthetic biofuels faces a similar technological bar-
rier to that of the gasification-derived biofuels (i.e. bioalcohols and other synthetic
biofuels): the production of the synthesis gas has to be adapted to the higher reac-
tivity and different properties of biomass with respect to coal. This includes two key
steps in the process that need thorough improvements: biomass pre-treatment (via
torrefaction and/or pyrolysis) to avoid the aggregation of the biomass particles that
can plug the feeding lines and economically viable inferior temperatures of gasifi-
cation (e.g. via supercritical water gasification) that have been reported to provide
higher efficiencies.
For instance, the FTS biofuel production can be more cost effective reducing
both the capital and the operating costs of the plant [209], being the purification of
the syngas the most expensive section to take into account for costs in an FT plant.
The development of active and selective catalysts and the utilisation of by-products
including electricity, heat and steam are some other inputs that need to be addressed.
8.5 Conclusions
The potential for biofuels has been recognised throughout the twentieth century but
the new century has brought with it a widespread realisation that the petroleum age
is coming to an end. The use of petrol-fuel replacements has generated a lot of con-
troversy; ideally they should contribute to global sustainability, ensuring the energy
supply and meeting the GHG targets (as well as being profitable and cost compet-
itive as much as possible) without compromising the economies, culture, societies
and the environment of our future. More thoughtful analysis is now showing that
many of these so-called first generation biofuels are little better than traditional fuels
in terms of overall carbon footprint and environmental damage. Second generation
biofuels and more widely, biomass exploitation, have a great potential to improve
these values and the future aims should focus on redoubling our efforts to produce
later generation biofuels based on low value and waste biomass, using the greenest
and efficient technologies and with properly measured and reported environmental
impacts. A joint effort from politics, economists, environmentalists and scientists is
needed now, more than ever, to address the issues of the progressive incorporation
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