Straw from crops such as
wheat, barley, oats and oilseed rape is seen as a potential source of biomass
for second generation biofuel production. Currently the UK produces around 12
million tonnes of straw. Although much is used for animal bedding, mushroom
compost and energy generation, there still exists a vast surplus. Preliminary
lab findings are pointing at ways that the process of turning straw from
oilseed rape into biofuel could be made more efficient, as well as how the
straw itself could be improved.
The bright yellow fields
of oilseed rape are a familiar sight at this time of year, but for scientists
what lies beneath is just as exciting.
Researchers at the Institute of Food Research are looking
at how to turn straw from oilseed rape into biofuel. Preliminary findings are
pointing at ways the process could be made more efficient, as well as how the
straw itself could be improved.
Straw from crops such as wheat, barley, oats and oilseed rape
is seen as a potential source of biomass for second generation biofuel
production. Currently the UK produces around 12 million tonnes of straw.
Although much is used for animal bedding, mushroom compost and energy
generation, there still exists a vast surplus.
Straw contains a mix of sugars that could be used as a source
of biofuels that do not compete with food production but instead represent a
sustainable way of utilizing waste. However, the sugars are in a form that
makes them inaccessible to the enzymes that release them for conversion into
biofuels, so pre-treatments are needed. The pre-treatments make the complex
carbohydrates more accessible to enzymes that convert them to glucose, in a process
called saccharification. This is then fermented by yeast into ethanol.
Using the facilities at the Biorefinery Centre on the Norwich
Research Park, Professor Keith Waldron and his team have been looking at the
steps needed to unlock the sugars tied up in the tough straw structure. In
particular, they have looked at the pre-treatment stage, focusing on steam
explosion, which involves 'pressure-cooking' the biomass, to drive a number of
chemical reactions. A rapid pressure-release then causes the material to be
ripped open, to further improve accessibility.
They varied the temperature and duration of steam explosion
and then used a variety of physical and biochemical techniques to characterise
what effects varying the pre-treatments had on the different types of sugars
before and after saccharification.
The amount of cellulose converted to glucose increased with
the severity of the pretreatment. Saccharification efficiency is also
associated with the loss of specific sugars, and subsequent formation of sugar
breakdown products.
In a further study funded by the BBSRC / EPSRC Integrated
Biorefining Research and Technology Club, the scientists discovered the key
factors that determine the efficiency of saccharification. One particular
compound, uronic acid, limited the rate at which enzymes worked. The final
sugar yield was closely related to the removal of xylan, a common component of
plant cell walls. The abundance of lignin, a 'woody' cell wall component, was
positively related to the amount of available sugars.
These findings will help improve the efficiency by which
straw can be converted to biofuels. For example, adding enzymes that more
effectively remove xylan should improve yield. Controlling the level of lignin
in the material should also help.
It may even be possible to improve the straw itself, for
example to reduce the uronic acid content in the biomass, as suggested by these
findings. In the main, oilseed rape has been bred to improve oilseed yield and
disease resistance, without paying much attention to the straw. The IFR is
working with colleagues at the University of York and the John Innes Centre to
see whether there are ways of breeding more "biofuel-ready" varieties
of oilseed rape, with the same yields of oilseed but with more amenable straw.
In addition, a full understanding of the polysaccharides and other compounds
made available during pretreatment may mean other valuable co-products, like
platform chemicals, may be viably produced from the surplus straw.
No comments:
Post a Comment