Producing superior biofuel from wood biomass

21 December 2011

Producing superior biofuel from wood biomass

A method developed at Aalto University in Finland makes it possible to use microbes to produce butanol suitable for biofuel and other industrial chemicals from wood biomass. Combining a butanol and pulp plant into a modern biorefinery would provide significant synergy benefits in terms of energy use and biofuel production. This will, for instance, minimize the feed stock cost and help in improving the waste water treatment.

Credit: Mikko Raskinen

Bio-butanol is considered as the most suitable transport fuel due to its higher energy density which is similar to fossil fuels and it is also less corrosive. It can also be blended with petrol or diesel in higher concentrations without any engine modifications.

Most commonly used raw materials in butanol production have so far been starch and cane sugar. The new process has the potential to use hardwood, softwood and recycled fibers.

The study was undertaken with an objective to develop a process suitable for existing pulp and paper mills. Along with cellulose, the Kraft process that is currently used in pulping produces black liquor, which can already be used as a source of energy. It is not, however, suitable for microbes.

In the Aalto University's study, the pulping process was altered so that, in addition to cellulose, the other sugars remain unharmed and can therefore be used as raw material for microbes.

“When wood biomass is boiled in a mixture of water, alcohol and sulphur dioxide, all parts of the wood cellulose, hemicellulose and lignin – are separated into clean fractions,” says Dr. Tom Granström, one of the lead researchers.

“The cellulose can be used to make paper, nanocellulose or other products, while the hemicellulose is efficient microbe raw material for chemical production. Thus, the advantage of this new process is that no parts of the wood sugar are wasted,” Granström says.

The patented process runs now at laboratory-scale. Commercial-scale prosess is expected to be in operation within two years.

Synergy benefits in biofuel production

The new process will help promote the biorefinery concept as this industry already harvests and processes trees at centralized facilities. It would increase the refining value of forest residues that cannot be utilized in, for example, the pulp process.

Estimates indicate that combining a butanol and pulp plant into a modern biorefinery would provide significant synergy benefits in terms of energy use and biofuel production. This will minimize the feed stock cost and also help in improving the current waste water treatment.

“The use of cheap substrate along with continuous mode production makes the process industrially attractive. Further, we developed method for efficient utilization of spent broth to make process more economical,” Granström notes.

In accordance with EU requirements, all fuel must contain 10 percent biofuel by 2020. A clear benefit of butanol is that a significantly large percentage - more than 20 percent of butanol, can be added to fuel without having to make any changes to existing combustion engines.

The nitrogen and carbon emissions from a fuel mix including more than 20 percent butanol are significantly lower than with fossil fuels. For example, the incomplete combustion of ethanol in an engine produces volatile compounds that increase odour nuisances in the environment.

Finland boosts utilization of forest residues

Presently, a basic feedstock for production of commodity chemicals and fuels is petroleum. The depletion of petroleum supplies and increased CO2 emission encouraged to find a replacement for petroleum with renewable resources such as forest biomass that is a potential sustainable source for production of power, biofuels and variety of commodity chemicals.

The project run by Aalto University is part of the BioRefine program of Tekes - the Finnish Funding Agency for Technology and Innovation.

The Biorefine program is developing new competence based on national strengths and related to the refining of biomass.

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