Lignin conversion breakthrough: SAF gets cost-competitive

opinion

by Fayaz Hussain

February 19, 2024

Charles Cai’s career is dedicated to breaking down walls. Plant walls.

As adjunct professor of chemical and environmental engineering at University of California Riverside he focuses on finding new ways to convert plant waste into renewable fuels and functional materials. He has just published research that may make biomass Sustainable Aviation Fuel (SAF) from second-generation feedstocks like rice straw and wheat straw a lot cheaper.

“We found that we could achieve with the selection of a woody feedstock, selection of converting lignin further into SAF and the selection of ethanol as our alcohol choice, that we were able to achieve a breakeven selling price for SAF of a little over $3 per gallon equivalent,” said Cai when speaking to SAF Investor.

Lignin, nature’s glue, provides structural rigidity to plants but poses a significant challenge for biofuel production. Its complex structure makes it difficult to extract the valuable sugars needed for fermentation. Traditionally, harsh chemicals or energy-intensive processes were required to break down lignin, significantly increasing the cost and environmental footprint of SAF production.

Professor Cai’s team offers a different approach. Its co-solvent enhanced lignocellulosic fractionation (CELF) technology employs tetrahydrofuran (THF) as a catalyst to efficiently break down lignin. This ingenious process not only yields the necessary sugars for SAF production but also simultaneously generates paraffins and olefins, key components of the SAF blend itself.

Furthermore, the researchers implemented a catalytic technology called Athermic Oxygen Removal (AOR) utilising a readily available copper catalyst. This method achieves an impressive 90% conversion rate for lignin, maximising the utilisation of this abundant biomass component.

The high efficiency also allows for the use of woody feedstocks like poplar, which offer both economic and environmental advantages compared with other options.

“The system we have developed is agnostic to biomass feedstock types. We have tried hard woods, soft woods, sugarcane bagasse, rice straw, almond waste, corn stover, several energy crops etc,” he adds.

Professor Cai emphasises the crucial role of processing second-generation feedstocks sustainably and cost-effectively in achieving large-scale SAF production and decarbonising the aviation industry. His team’s innovation addresses both aspects – utilising readily available, non-food sources while significantly reducing production costs.

The promising results have garnered significant attention. The US Department of Energy’s Bioenergy Technology Office has awarded a $2m grant to UCR to develop a pilot-scale SAF plant. This pilot programme aims to showcase the technology’s potential on a practical level and attract further investment from biofuel processors.

You can read the research paper here. Its full title is: “Economics and Global Warming potential of a commercial-scale delignifying biorefinery based on co-solvent enhanced lignocellulosic fractionation to produce alcohols, sustainable aviation fuels, and co-products from biomass.”

It could have been: Break the wall and make airlines pay less for it.