Advanced BioFuels USA

by Lorenz Bauer (Lee Enterprises Consulting, Inc./Biofuels Digest)  What’s up with C5 and C6 sugars? Given that a significant portion of the several billion dollars spent on renewable fuels spending involves these molecules, it is not surprising that progress is fast and furious. This note provides an overview and snapshot of the technological progress reported in the three months since Biofuels Digest’s 2016 March Madness Webinar on this topic.

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Cellulosic sugars compete against those extracted from corn, sugar beets and other sources. The cost of the cellulosic sugar produced should be equivalent or lower than sugar from traditional sources. As of yet, the cellulosic sugars are not cost competitive, averaging 30-50% above ethanol produced from extracted sugars.   However, these costs are highly variable.   The production cost of cellulosic ethanol in the six commercially operating cellulosic ethanol plants varies by 40%.   As the technology improves it is widely predicted that the goal of matching extractive sugar costs will be achieved in the near future.

The significant contributors to the cost of cellulosic sugar production are feedstock, pretreatment and capital costs with each contributing about 20-40% of the costs. Enzyme costs have been decreasing rapidly. For example, the enzyme cost per pound of cellulosic ethanol has come down 72% between 2008 and 2012 and have continued to fall. Improvements in activity and process technology which allow more effective use of the enzymes.

Capital costs are the other major portion of the cost of cellulosic ethanol production. Again these costs are highly variable depending on plant size, location, and technology.

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The US DOE has set a target feedstock price of $60 per ton which using industry rule of thumb would translate to $0.06 per pound of sugar. This price does not include transportation or pretreatment.   The current cost of woodchips, which are the only commercially marketed biomass, is about $80 per ton at harvest and increases to over $120 per ton when processing and delivery costs are included. This would correspond to sugar production cost of $0.12 per ton based on raw materials alone.   The market price of industrial sugars has varied from $0.11 to $0.19 per pound in the last year.

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As a result, government subsidies and mandates will continue to play a key role in the future in both traditional and cellulosic ethanol.  These subsidies are a reflection of the societal demand for reducing the use of fossil carbon sources rather than economics.

Current subsidies provide up to $2.64 price benefit for cellulosic ethanol. This subsidy more than makes up for increased production costs and is a major driver for short term investment.

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One focus of research is contacting the biomass with catalysts and enzymes   New enzymes that degrade cell walls have been shown to greatly enhance the rate of cellulose conversion.     A recent patent application describes incorporating the genes for expressing these enzymes into plant DNA.

The use of organic solvents to swell biomass and extract selective components continues to be explored.

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Purification of the hydrolase broth containing the sugar with membranes and ion exchange resin was recently disclosed.   A new class of microorganism that selectively metabolizes the lignin derived aromatics in the presence of sugar was reported.     However, these purification steps add to the cost of using cellulosic sugars.

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Another disclosure described methods for adapting existing pulp and paper production equipment to allow continuous enzymatic hydrolysis of cellulose.   Repurposing pulp processing plants is a particularly attractive route to lower the capital required for producing biofuel.

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There is significant progress in identifying more robust enzyme systems capable of continuous operation at higher temperatures, pH, resistance to inhibition.   The ability to operate at higher temperatures is of particular interest because it increases enzyme activity and allows better integration with pretreatments that often involve higher temperatures.

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Microbes that can that use C-5 xylose sugars as a fermentation feed continue to be found.

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The C5 and C6 can be converted to fuels by a number of chemical catalyzed reactions like hydrogenation, dehydration and reforming to yield furfurals, furans, levulunic acid and polyols.   Ethanol itself can be converted to olefins and hydrocarbons, and a number of recent patent disclosure and commercial announcements have recently appeared proposing these approaches.

Downstream carbon-carbon bond formation reactions are needed to produce fuel products.  READ MORE