The use of fossil fuels as a source of energy and carbon is becoming increasingly unsustainable. While several alternative energy sources for electricity and heat production exist, liquid carbon-based fuels are still necessary in key transportation areas such as aviation. In addition, an alternative source of carbon is needed to produce carbon-based chemicals. Lignocellulosic biomass has the potential to address both needs, but finding conversion routes to jet fuels or commodity chemicals is challenging.
To investigate the combination of biological and catalytic conversion processes for enhancing the biomass derived product diversity and to assess the sustainability along the entire value chain. In a first bioprocess, to convert lignocellulose into carboxylic acids, which are then catalytically upgraded to alpha-olefins or jet-fuel components.
To convert all carbohydrate fractions of lignocellulosic biomass, the project team developed the lactate platform for producing carboxylic acids. Here, an engineered artificial microbial community funnels the heterogeneous feedstock to lactate as central intermediate, which is then further converted into the target acid(s). The feasibility of this concept was exemplified by producing, e.g., 196.5 kg butyric acid per ton beech wood.
In the catalytic upgrading process olefin selectivities > 90% at close to 99% conversion of carboxylic acids were obtained using a Cu/SiO2-Al2O3 catalyst. A sudden selectivity switch from olefins to predominantly alkanes was observed at full conversion. Carboxylic acids were also successfully upgraded in a single step using Cu/ZrO2 to an organic oil composed of C8 – C16 aromatics and cycloalkenes. This oil is compatible as a 10 vol % blend with Jet A-1 fuel in terms of specific energy and distillation properties.
The sustainability analysis showed that the potentially available herbaceous biomass in Switzerland could reach a quantity of 500,000 tons of dry matter per year. With wood, this figure might be several-fold larger. Thus, the feedstock of a potential biorefinery in Switzerland would be a mix of residual wood, herbal biomass from extensive grassland, harvest residues from agriculture and forest wood that could be utilised without causing environmental damage, i.e. reducing soil organic matter. Based on existing laboratory data (basic technologies, yield, rate) the minimum selling price of lignocellulose based jet-fuel, produced in a pilot facility with an annual capacity of 10,000 tons of biomass intake was estimated at 3.6 CHF/litre, which is about twice the current kerosene price but in agreement with price forecasts for other biomass based production routes.
Implications for practice
All three subprojects advanced research in their respective fields considerably and paved the way for new innovative approaches in each respective field. In the biochemical sub-project, solutions for the co-cultivation of microorganisms with different growth requirements were developed. In the sub-project analysing the catalytic upgrading, a selectivity switch phenomenon was discovered which can be employed to control product distributions for alpha-olefin or jet-fuel production. In the life cycle sustainability assessment LCSA sub-project, the methodology and database for assessing and optimising the economic and environmental performance of biorefineries was enhanced and can now be used by other scientists.
Implications for practice
The developed biochemical and catalytical processes showed promising novel approaches for an efficient and sustainable conversion of lignocellulose into alpha-olefins and jet-fuels. However, the analysed technologies are on a low technology readiness level (TRL) and the accompanying industrial advisory board has therefore recommended advancing to pilot-scale and testing the technology in a pilot biorefinery.
Production of fuels and commodity chemicals through subsequent biochemical and catalytic conversion of lignocellulosic biomass
The joint project consists of three research projects
Consolidated bioprocessing of lignocellulosic biomass for production of lactic acid and mixed carboxylic acids as fuel precursor
- Dr. Michael Hans-Peter Studer, Hochschule für Agrar-, Forst- und Lebensmittelwissenschaften, Berner Fachhochschule, Zollikofen
Catalytic upgrading of biomass-derived carboxylic acids for fuel and chemical production
- Prof. Jeremy Luterbacher, Laboratoire des procédés durables et catalytiques Institut des sciences et ingénierie chimique, EPF Lausanne
Sustainability evaluation of biorefinery systems for fuel and commodity chemical generation from plant residues
- Dr. Jan Hendrik Grenz, Hochschule für Agrar-, Forst- und Lebensmittelwissenschaften, Berner Fachhochschule, Zollikofen; Prof. Stefanie Hellweg, Dr. Bernhard Streit
