BioGasol Boosts Cellulosic Ethanol Yield by 7.5%

9 January 2009

BioGasol, a spin-off from Danish Technical University (DTU) in Lyngby, Denmark (earlier post), has improved the C₅ sugar processing capability of the thermophilic anaerobic bacterium used in its cellulosic ethanol production process, thereby increasing the ethanol yield by 7.5%.

The BioGasol process focuses on the full consumption of available carbohydrates in the biomass feedstock to produce a range of products and thus make the entire process much more cost-effective. The primary product is cellulosic bioethanol, but the process also delivers bio-methane via anaerobic digestion and hydrogen (from xylose fermentation) as well as other valuable by-products from the parts of biomass not suitable for ethanol production.

The process also recirculates and reuses all streams produced in the integrated process—process water is reused with the integration of the biogas cycle, for example, further reducing cost and environmental impact of production.

The BioGasol process has four main stages:

1. Pre-treatment. Biogasol uses a combination of combination of steam-explosion and wet oxidation (Wet Explosion). Wet Explosion applies both the addition of oxygen and a pressure release at high temperature (170 °C to 200 °C). Biogasol calculates that this method will deliver more sugar at lower cost than other processes.

2. Hydrolysis and glucose fermentation. The Biogasol process combines hydrolysis and fermentation. The BioGasol Concept produces its enzymes for hydrolysis at the plant using an enzyme-producing fungus strain developed in collaboration with Novozymes A/S.

   The main products from the enzymatic hydrolysis are the sugars glucose (C₆) and xylose (C₅). The glucose is simultaneously fermented into ethanol by yeast. After fermentation the process stream is separated into a solid and a liquid fraction. The liquid fraction then moves to the xylose fermentation reactor.

3. Xylose fermentation. Xylose is the second-most abundant carbohydrate monomer after glucose, and constitutes between 10-40% of the total carbohydrates in lignocellulosic biomass. Fermentation of both xylose and glucose is therefore a crucial step forward in reducing the cost of ethanol production from lignocellulosic raw materials.

   In the Biogasol process, a thermophilic anaerobic bacterium converts both C₆ and C₅ sugars into ethanol or ethanol/hydrogen in an immobilized reactor at 70 °C. Bioethanol is distilled out as a part of the re-circulation loop of the reactor and a fraction of the ethanol can be collected directly from the out-gas stream leaving the reactor due to the high process temperature. This step is unique and one of BioGasol’s patented processes. Wastewater from the xylose fermentation is afterwards transferred to the anaerobic digester.

   BioGasol increased the yield by removing the anaerobe’s natural ability to produce acetic acid and other by-products. Up to 86% of the C₅ sugars in the biomass can now directly be converted into bioethanol.

4. Biogas production and recirculation of the process water. The remaining non-carbohydrate organics move to an anaerobic digester along with the wastewater stream for the production of biomethane.

In contrast to our competitors we are able to convert much more of the C₅ sugars that are present in the biomass into bioethanol. This further emphasizes how unique our technology for cellulosic ethanol production is.

—Prof. Birgitte Ahring, BioGasol CEO