Professor Aadrian van Heiningen and Tom Granström with a team of scientists at Aalto University in Finland and associated with the University of Maine in the U.S. have developed a process to make fuel grade butanol and other industrial chemicals from wood biomass.
Butanol is particularly suitable as a transport fuel because it is not water-soluble and has higher energy content than ethanol. Moreover there is pressure building in the European Union as new fuel requirements state 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 per cent butanol are significantly lower than with fossil fuels. For one point of comparison, the incomplete combustion of ethanol in an engine produces volatile compounds that increase odor nuisances in the environment. 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.
The significant new breakthrough in the study is to successfully combine modern wood pulp handling – and new biotechnology. Finland’s advanced forest industry provides particularly good opportunities to develop this type of bioprocesses.
Wood biomass is made up of three primary substances, the cellulose, hemicelluloses and lignin. Of these three, cellulose and hemicellulose can be used as a source of nutrition for microbes in a bioprocess. 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. But black liquor is not suitable for feeding microbes. In the Aalto 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.
The most commonly used raw materials in bio based butanol production so far have been starch and cane sugar. In contrast to this, the starting point in the Aalto University study was to use only the lignocellulose, otherwise known as wood biomass, which does not compete with food production. The publication of the results are in Bioresouce Technology.
When wood biomass is boiled in a mixture of water, alcohol and sulfur dioxide, all parts of the wood – cellulose, hemicellulose and lignin – are separated into clean fractions. The cellulose can be used to make paper, nanocellulose or other products, while the hemicellulose is efficient microbe raw material for chemical production. The Finns’ new advantage of this new process is that no parts of the wood sugar are lost or wasted.
The published estimates indicate that combining a butanol process and a pulp plant into a modern biorefinery would provide significant synergy benefits in terms of energy use and biofuel production. The program at Aalto University is developing new skills based on national strengths and related to the refining of biomass. The overall aim of the project is to increase the refining value of forest residues that cannot be utilized in, for example, the pulp process.
The lab results for the process successfully used batch and continuous production of acetone, butanol and ethanol (ABE). Initially, batch experiments were performed using spent liquor to check the suitability for production of ABE. Maximum concentration of total ABE was found to be 8.79 g/l using 4-fold diluted liquor supplemented with 35 g/l of glucose. In completing the course of testing the team returned to batch processing for the highest yields.
The Finn effort looks to have good results that may be applied wherever forests are harvested, especially where paper is made. Butanol is the alcohol most desirable for a drop in gasoline replacement – producers won’t need to look far for customers/
The next step is to come out of the lab for a little real outside world testing. There’s a large stock of black liquor from papermaking that could use a high value process to extract the value in a better way. It looks like the Finn team might have it.