The NILE Project — Advances in the Conversion of Lignocellulosic Materials into Ethanol
Résumé
NILE ("New Improvements for Lignocellulosic Ethanol") was an integrated European project
(2005-2010) devoted to the conversion of lignocellulosic raw materials to ethanol. The
main objectives were to design novel enzymes suitable for the hydrolysis of cellulose to
glucose and new yeast strains able to efficiently converting all the sugars present in
lignocellulose into ethanol. The project also included testing these new developments in
an integrated pilot plant and evaluating the environmental and socio-economic impacts of
implementing lignocellulosic ethanol on a large scale. Two model raw materials – spruce and wheat straw – both preconditioned with similar
pretreatments, were used. Several approaches were explored to improve the saccharification
of these pretreated raw materials such as searching for new efficient enzymes and enzyme
engineering. Various genetic engineering methods were applied to obtain stable xylose- and
arabinose-fermenting Saccharomyces cerevisiae strains that tolerate the toxic compounds
present in lignocellulosic hydrolysates. The pilot plant was able to treat 2 tons of dry
matter per day, and hydrolysis and fermentation could be run successively or
simultaneously. A global model integrating the supply chain was used to assess the
performance of lignocellulosic ethanol from an economical and environmental perspective.
It was found that directed evolution of a specific enzyme of the cellulolytic cocktail
produced by the industrial fungus, Trichoderma reesei, and modification of the composition
of this cocktail led to improvements of the enzymatic hydrolysis of pretreated raw
material. These results, however, were difficult to reproduce at a large scale. A substantial increase in the ethanol conversion yield and in specific ethanol
productivity was obtained through a combination of metabolic engineering of yeast strains
and fermentation process development. Pilot trials confirmed the good behaviour of the
yeast strains in industrial conditions as well as the suitability of lignin residues as
fuels. The ethanol cost and the greenhouse gas emissions were highly dependent on the
supply chain but the best performing supply chains showed environmental and economic
benefits. From a global standpoint, the results showed the necessity for an optimal integration of
the process to co-develop all the steps of the process and to test the improvements in a
flexible pilot plant, thus allowing the comparison of various configurations and their
economic and environmental impacts to be determined.
Domaines
Physique [physics]
Origine : Publication financée par une institution
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