Page 48 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel feedstocks and their prospects 25

removing CO 2 and minor gases, biomethane may be compressed and used for com-
pressed natural gas (CNG) applications. In the EU, however, only a few cases of
biomethane conversion actually occur for use as fuel or in gas networks. Conversion
of biogas to energy is almost entirely reserved to electricity production while use
in vehicles is still limited [20, 21]. The greatest use as biomethane for transport
occurs in Central and Northern European countries (Switzerland and Sweden, in
particular). In Sweden, new biodigesters fed by organic feedstock are equipped with
postprocessing facilities to upgrade biogas into biomethane for use in vehicles and
pumping in the natural gas network. In that country, 4,000 light-duty vehicles as well
as entire fleets of public transport vehicles are fed by biomethane [22].
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In the EU-27 alone, more than 1.5x10 t of animal manure are produced every
year, with total energy-generation potential of about 830PJ [23]. By the end of
2014, there were more than 17,000 active biogas plants in Europe, with total produc-
tion potential estimated by year 2020 in 770PJ/year, up from 92PJ/year in 2002. The
countries accounting for the largest number of plants are currently Germany and Italy,
while the UK is the largest producer of landfill biogas (84% of its national production)
[24]. It should be noted that landfill-related production is bound to decrease signifi-
cantly in the future while a significant share of these resources will be obtained from
energy crop production on surplus agricultural land. The European Environmental
Agency (EEA) estimates that the land potential for environmentally compatible
energy crop cultivation in the EU-27 results in a total additional energy potential
of 1115TWh in 2020 and 1650TWh in 2030 [25].

2.3.1.1 Syngas

Syngas is the short name for a gasification product, mostly from waste biomasses,
known as “synthesis gas,” consisting of a mixture of H 2 , CO, and CO 2 that could
be used as a potential intermediate in the conversion of biomass into fuel. The primary
use of syngas is in the production of other fuels, namely methanol and diesel fuel. In
some industrial settings (steel milling, petroleum refining, etc.), large amounts of
waste gas with these characteristics are produced.
The production of diesel fuel from syngas relies on the Fischer-Tropsch process, a
series of chemical reactions converting CO and H 2 into liquid hydrocarbon. Methane
from landfills could serve as feedstock for producing diesel fuel, technically consid-
ered biodiesel because it is not derived from fossil fuels. A novel use of syngas is to
directly power hydrogen fuel cells; hydrogen is simply captured from the gas, and
refined for use in fuel cells. Of course, this tends to defeat the “zero emissions”
aim of fuel cells and so is not widely used beyond research.

2.3.2 Liquid biofuels

Biodiesel and bioethanol and are the two main first-generation biofuels, extensively
used as additives in transport sectors worldwide. Currently, the world renewable bio-
fuel market is dominated by bioethanol, with biobutanol gaining attention as an alter-
native due to its superior properties. In the following paragraphs, both conventional