15-01-2014, 12:06 PM
Bioethanol from Lignocellulose
The Products
Ethanol:
Fuel (crops and residues) 68%
Anhydrous Ethanol, gasoline aditive
Hydroethanol destined for Biofuels
Beverages (crops) 11%
Perfumes & Pharmacology (crops) 21%
Alternative Products:
Sugar Powder (crops)
Biodegradable Plastic (crops)
Polyhydroxybutyrate-PHB
Ethanol cost x Oil cost
The direct cost of 1 l of gasoline in the USA was US$0.21 and the cost of 1 l of ethanol was US$0.34.
The average cost of sugarcane production in Brazil was US$180/t of sugar or US$0.20/L of ethanol.
However, the energy originating from 1 L of ethanol corresponds to 20.5 MJ, and from 1 L of gasoline, 30.5 MJ.
Criteria for microorganisms
Broad substrate utilization
Converting hexose and pentose to ethanol efficiently.
High ethanol yield (>90% of theoretical) and productivity
High tolerance to acids, ethanol, inhibitors and process hardiness.
Can be robust to simple growth medium
Escherichia coli
An important vehicle for the cloning and modification of genes
Ferment hexose and pentose as well with high ethanol yield by recombinant strains
High glycolytic fluxes
Reasonable ethanol tolerance
Saccharomyces cerevisiae
The most common and natural fermentative yeast for ethanol
Only convert glucose to ethanol for wild-type
Limitation of using lignocellulose
Relative high ethanol yield
Can be easily modified by metabolic engineering to ferment pentose
Pre-treatment of Lignocellulose for bioethanol fermentation
It was considered necessary to give a brief overview of this pre-treatment step, since the method employed can have implications for fermentation conditions and the choice of microbe.
The hydrolysis is usually carried out by the use of enzymes or by chemical treatment.
Enzymatic Hydrolysis
This is carried out by cellulose enzymes which are highly specific.
Novozymes is launching three new enzymes which make the production of ethanol from wheat, rye and barley up to 20%
The new enzymes break down components of the grain which would otherwise result in a thick consistency. This saves producers the amount of water and energy that would otherwise be required to dilute and handle the mash. A thinner mash also makes life easier for the enzymes in the next stage of the process, which break the material down into sugars for fermentation into ethanol (alcohol).
Conclusion:
For bioethanol from lignocellulose to be a viable alternative to fossil fuel, then the cost of production will have to be reduced.
The perfect microbe that provides broad substrate utilization, give high ethanol yields and is tolerant to the harsh conditions after chemical pretreatment will have to be engineered
Reduction in process costs, by integrating process engineering tools with metabolic engineering