Environmental Engineering Reference
In-Depth Information
Bacteria strains such as
Zymmomonas mobilis
have been demonstrated as an
alternative to yeats offering several advantages in the fermentation including higher
specific productivity, ethanol yield and alcohol tolerance [3].
Biobutanol
Biobutanol (also denoted as biogasoline) is another interesting candidate that
recently entered the battle of the alcohols and has the potential to become one of
the key biofuels of the future due to its interesting properties [53-56].
The biobutanol is produced via fermentation in which the sugars from the source
(so far from edible feedstocks) are firstly converted to butyrate and hydrogen, then
turned into butanol via fermentation using various bacteria strains [53, 54]. The
process has been reported to work with a wide range of bacteria and biomass
[53-57]. Four main species have been in use, namely
C. acetobutylicum
,
C. bei-
jerinckii
,
C. saccharoperbutylacetonicum
and
C. saccharobutylicum
. Most data are
available from
C. acetobutylicum
that has been widely employed in the fermentation
of starchy raw materials [53, 54].
Dupont and BP announced a partnership in 2006 to develop the next generation
of biofuels, with biobutanol as first product [56, 58, 59]. A biobutanol demonstration
plant has recently started to be built at an existing BP site in the UK that is expected
to start test production of biobutanol by 2009 using sugar beet as feedstock [58, 59].
Similar biobutanol pilot plant projects are also ongoing in the US [60].
8.2.2 Second Generation Biofuels
Alternative feedstocks, generally
non-edible feedstocks
including waste vegetable
oils and fats, non-food crops and biomass sources, and/or technologies were
implemented/developed in an attempt to overcome the major shortcomings of the
production of first generation biofuels. The biofuels obtained from such tech-
nologies have been denoted as second generation biofuels [61]. In theory, these
can solve these problems and can supply a larger proportion of fuel supply
in a more sustainable and reasonably priced way with greater environmental
benefits (Fig. 8.7).
Several advances have been made in the last few years/months. The majority
of the second generation biofuels processing technologies are not yet available on
a fully commercial scale so the biofuels are expected to enter the market within
a few years. Moreover, the development of many other approaches are currently
ongoing and many more are to be reported, so the list included below, far from
being exhaustive, provides the most interesting technologies reported until very
recently. Second generation biofuels will be classified in various groups depend-
ing on the technologies employed for their preparation. In a similar way to those of
the first generation biofuels, these are prepared by
chemical, thermo-chemical and
biological
conversion.
