Better recycling of wastewater could drastically reduce the price of biofuel

A pioneering study has proposed a new integrated method for producing aviation fuels from woody feedstock by considering all downstream processing stages and carrying out a detailed economic analysis.

Lignocellulose, a raw material in biomass, can be converted to biofuels and is often considered a long-term alternative to the diminishing supply of fossil fuels. The conversion process involves biomass pretreatment, hydrolysis of constituent carbohydrates and catalytic conversion of platform chemicals. Proposed strategies to convert lignocellulose to aviation fuels have underused components, preventing their commercialisation.

A collaboration between several research groups has taken a hydrolysis-based approach to produce aviation fuel from red maple biomass. The proposed method focuses on synthesising levulinic acid and furfural from lignocellulosic 5- and 6-carbon sugars and catalytically upgrading these to jet fuel range alkanes. This combined techno-economic analysis considers several possible processing options at points throughout the procedure and combines the most viable to create a comprehensive conversion process, which can produce jet fuel priced at $4.75 (£2.88) per gallon. ‘We wanted to understand how the individual processes interlink with each other and how impurities cause problems with downstream processing,’ explains Aniruddha Upadhye, of George Huber’s research group at the University of Wisconsin in the US.

Compared to jet fuel prices today of around $3.00, $4.75 seems a little steep. ‘The researchers are very forthcoming about the current limitations of this approach. With a total capital investment of about $12 per annual gallon of liquid fuel, and 40% of total operating costs devoted to wastewater treatment, additional work is clearly needed,’ says Bruce Dale, a biomass conversion expert at Michigan State University in the US. In fact, the economic analysis flags up several main areas requiring further research to reduce cost. The main operating cost is the treatment of wastewater used in the hydrolysis steps. Improving the recyclability of wastewater and replacing expensive platinum-based catalysts could see the minimum price per gallon drop to a competitive $2.88 against conventional jet fuels.

Upadhye foresees no major problems in scaling up the technologies for commercial use, but further investigation is required into the recovery of products and separation of components to maintain high carbon yields throughout the entire process. ‘It is a critical step in the right direction and many studies in the future will be benchmarked with this work,’ adds Oliver Inderwildi, an expert in biofuels at the University of Oxford, UK.