A new path to renewable diesel from biomass

November 8, 2012 |

Graduate student Zachary Baer works with a fermentation chamber to separate acetone and butanol (top clear layer) from the Clostridium brew at the bottom.

“Pack Up Your (renewable fuel) Troubles In Your Old Kit Bag”, say Berkeley researchers, who transform an old WWI-era process into a route to renewable diesel.

If the Digest possessed a magic wand and could change just one thing about the production of biofuels in the United States – it would be to give the country a quick, sustainable path around the ethanol “blend wall”.

Here’s the problem. Limited to 10 percent blend rates, it is possible to distribute only 13 billion gallons of ethanol into the current 130 billion gallon gasoline fuel demand. With 15 billion gallons in ethanol production capacity…well, you see the problem. As the Digest posed the question at Advanced Biofuels Markets last week in San Francisco, “where’s all the ethanol going to go?”

It is that very aspect that makes technologies from companies such as Gevo or Butamax so compelling — the opportunity to transition a 100 million gallon ethanol plant that can blend fuels at 10 percent to an 80 million gallon isobutanol production capacity that can blend at up to 16 percent. In this way, the US blend wall would move from around 13 billion gallons of ethanol-equivalent to 19.5 billion gallons.

It’s part of what puts companies such as Solazyme, Virent, LS9 and Amyris routinely near the top of the 50 Hottest Companies in Bioenergy – options for producing drop-in fuels – and especially those that displace diesel instead of just gasoline.

Now we have a new option on the table, for the longer haul.

A team of Berkeley researchers, supported by the Energy Biosciences Institute, have developed a new process to make renewable diesel from starch, sugars, or even cellulosic sugars. Or, rather, transformed an old process that was first developed in the First World War as a means to make cordite, for munitions.

“What I am really excited about is that this is a fundamentally different way of taking feedstocks – sugar or starch – and making all sorts of renewable things, from fuels to commodity chemicals like plastics,” said Dean Toste, UC Berkeley professor of chemistry and co-author of a report on the new development that will appear in today’s issue of Nature. Co-authors include Harvey Blanch and Douglas Clark, UC Berkeley professors of chemical and biomolecular engineering – plus former post-doctoral fellow Pazhamalai Anbarasan, graduate student Zachary C. Baer, postdocs Sanil Sreekumar and Elad Gross and BP chemist Joseph B. Binder.

The breakthrough

The new work is based on the old Weizmann process, which used Clostridium acetobutylicum bacteria to ferment sugars into acetone, butanol and ethanol in a 3:6:1 ratio. Blanch and Clark discovered that several organic solvents, in particular glyceryl tributyrate (tributyrin), could extract the acetone and butanol from the fermentation broth while not extracting much ethanol. Tributyrin is not toxic to the bacterium and, like oil and water, doesn’t mix with the broth.

At the same time, Toste had discovered a catalytic process that preferred exactly that proportion of acetone, butanol and ethanol to produce a range of hydrocarbons, primarily ketones, which burn similarly to the alkanes found in diesel.

More than just starch and sugar – more than just fuels

The process is versatile enough to use a broad range of renewable starting materials, from corn sugar (glucose) and cane sugar (sucrose) to starch, and would work with non-food feedstocks such as grass, trees or field waste in cellulosic processes.

“You can tune the size of your hydrocarbons based on the reaction conditions to produce the lighter hydrocarbons typical of gasoline, or the longer-chain hydrocarbons in diesel, or the branched chain hydrocarbons in jet fuel,” Toste said.

Why Clostridium fell out of favor

According to Blanch, a key challenge with the old Weitzmann process was in the cost of distillation. The process by which the Clostridium bacteria convert sugar or starch to these three chemicals is very efficient. This led him and his laboratory to investigate ways of separating the fermentation products that would use less energy than the common method of distillation.

“The extractive fermentation process uses less than 10 percent of the energy of a conventional distillation to get the butanol and acetone out – that is the big energy savings,” said Blanch. “And the products go straight into the chemistry in the right ratios, it turns out. It looks very compatible with diesel, and can be blended like diesel to suit summer or winter driving conditions in different states.”

“Diesel could put Clostridium back in business, helping us to reduce global warming,” Clark said. “That is one of the main drivers behind this research.”

If viable, then what?

OK, so let’s look at the consequences. First, the process has to move from lab to industrialization. That will take time – especially to figure the extent to which existing infrastructure (e.g. today’s ethanol plants) can be utilized. If Gevo’s experience is any guide, those conversions, we understand involve about a 40-50 cent per gallon CAPEX charge for the separation technology and changes to the fermentation equipment. In this case, there would be a catalysis process on the back-end that needs to be added.

More work on the catalysts are always welcome – to bring down the cost, bring up the activity rates.

How is this different from, say, what LS9 does?

In converting starches and sugars to diesel-range molecules, it’s the similar at the beginning and end, though the new EBI process produces ketones instead of alkanes. The middle is quite different – LS9 is more of a consolidated bioprocessor that directly converts sugars to a target product, whereas this is a three step fermentation, separation and catalysis process. Neither LS9 nor this process use distillation.

Having said that – in its path to commercial scale, LS9 has focused on FAME biodiesel (fuels) and fatty alcohols (for the chemical markets), for now. Its process for producing alkanes from sugars is at the pilot stage – and LS9 has indicated it is focused relentlessly on commercializing its first two molecules now, and will develop others later on.

The challenge? As with any process that takes molecules that have a lot of oxygen, by weight, and produces hydrocarbons – there are going to challenges in making the economics work. Something that the afore-mentioned Solazyme, LS9, Amyris and Virent are all-too familiar with.

The special opportunity? One thing that we know about the old Weitzmann ABE process is how to run it at scale. It’s been done effectively for decades — what failed is not the process, but the economics, given the energy-intensity of distillation. Scale-up risk would be expected to be markedly lower.

The bottom line

This particular discovery could well impact the US renewable fuels outlook before the end of the current RFS2 schedules, which take us now through 2022 — but not much before the end of this decade. We may well see the impact in the chemicals markets, first, as this technology works its way down the cost curve towards parity with fuel costs.

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