Biobutanol development makes headway

Debugging biobutanol

23 February 2009 00:00  [Source: ICB]

Developers find the best microbes in order to outdo ethanol in the biofuel race

BUTANOL, ALREADY a widely used industrial chemical, has the potential to outdo ethanol in the biofuels arena.

Biobutanol is said to offer several advantages over ethanol - it has a higher energy density, can be transported in existing pipelines, is easier to mix with gasoline or use alone in internal combustion engines, has a lower vapor pressure that makes it less polluting than ethanol, and can be managed in the existing gasoline distribution network.

The main problem, several biobutanol developers note, is the cost.

"The challenge with biobutanol has always been the low productivity of the fermentation process and the expensive cost of separating the fuel from the water," says Steven Shevick, chief financial officer of US-based Cobalt Biofuel.

"Now there are technologies than can improve fermentation productivity and reduce energy consumption in the separation phase to the extent of making biobutanol very competitive," he adds.

For the first half of the 20th century, biobutanol was produced via acetone-butanol-ethanol (ABE) bacterial fermentation using microbes such as Clostridium acetobutylicum. The ABE process was eclipsed by lower-cost petrochemical routes during the 1950s, says Ron Cascone, manager of biofuels development at US consulting firm Nexant.

While there are still several existing ABE-based biobutanol plants in China, the dominant petrochemical route today is the propylene-based oxo synthesis process.

Butanol has yet to be applied commercially as a fuel. "In practice, biobutanol is a much more attractive biofuel than ethanol, but developers have to go through certain hoops to get it commercialized," Cascone says.

Companies currently working on biobutanol include a joint venture between US chemical firm DuPont and UK-based oil giant BP US start-up firms such as Cobalt Biofuels, Gevo and Tetravitae Bioscience UK-based biotech company Green Biologics, and French biotech firm Metabolic Explorer.

In an investor conference late last year, DuPont vice president and general manager John Ranieri said the company's biobutanol venture with BP, which started in 2006, is on track to have an operational pilot plant this year and a commercial manufacturing process with economics comparable to grain ethanol by 2010.

DuPont won't disclose the microorganism the company uses, but says it already yields more butanol than the traditional process.

BATTLE OF THE BUGS

Biobutanol fermentation differs from bioethanol mainly in the use of bacteria rather than yeast. Yet, Cascone says it is feasible to adapt existing or new grain and sugarcane-based ethanol plants to produce biobutanol.

Most of the technology being developed in the US, Europe and Asia is based on genetically modified versions of the Clostridium to improve butanol tolerance and yield, says Cascone.

A challenge for biobutanol developers is that bacteria are poisoned by the butanol they produce once its concentration rises above around 6%.

Cobalt does not disclose the kinds of Clostridium strains it uses, but said that it can run continuous fermentations over 1,000 hours, making its bioprocessing very efficient. Its organism can also use a wider variety of nonfood feedstock.

"We have refined our bug and our technique for selecting bugs we've run highly efficient and productive fermentations for long periods of time, and we have a very efficient separation technology, which are all now proven at the lab scale," says Shevick.

Cobalt Biofuels expects to build a 10,000-35,000 gal/year pilot plant this year. Between 2010 and 2011, the company hopes to build a demo-scale plant with a capacity between 2m and 10m gals/year, and to proceed to a commercial plant by 2012.

"Our goal is to try to accelerate the timeline in order to produce low-cost biobutanol first for the chemical market, and then to the transportation sector," Shevick adds.

Green Biologics says its microbial platform technology is based on a unique collection of heat-loving bacteria (thermophiles) and thermostable enzymes. The company's fermentation technology can process waste and by-product feedstocks such as molasses, a by-product of sugar production.

"The fluctuating commodity prices are a challenge for any biochemical company," says Green Biologics CEO Sean Sutcliffe. "For butanol producers, a deep insight into the microbial and fermentation processes and ability to switch feedstocks is needed to give good operating performance - and that's an opportunity for us."

Green Biologics says it has already tested its technology up to the 300 liter laboratory scale and is currently working with existing biobutanol producers to incorporate its technology into existing facilities.

Late last year, the company signed a letter of intent for a strategic partnership with a Chinese biobutanol producer. Green Biologics also plans to build a 1,000 tonne/year biobutanol demo scale in India with its partner Laxmi Organic Industries, a biochemical manufacturer.

"The first part of our goal is applying our improved technology to the biobutanol plants that have over 300,000 tonnes of capacity already built in China," says Sutcliffe. "Given the reduction in oil prices, they require our technology to switch to lower-cost by-products such as molasses and in due course, cellulosic feedstocks, to be competitive," he adds.

Green Biologics is currently offering new plant designs that combine its advanced microbial technology with existing process technology. The designs can be applied to retrofit small-scale existing molasses/cane juice/corn ethanol facilities of around 10,000 tonnes/year, to larger scale stand-alone plants with 30,000 tonnes/year or more capacity.

BREWING A BIOFUEL BLOCKBUSTER

More designer biobutanol microbes are expected to come out of the woodwork.

Hans Blaschek, a microbiologist in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois, is working on second generation strains of the soil bacterium Clostridium beijerinckii, which he himself developed 10 years ago at the Illinois laboratory.

The mutant bacterium, which reportedly produces higher concentrations of butanol when added to a vat of plant by-product, is currently the basis for Tetravitae BioScience's biobutanol technology. Tetravitae licensed the strain from the university and is scaling up to use it in larger ethanol plants.

Several scientists from the US Department of Agriculture's Agricultural Research Services (ARS) is also working on the C. beijerinckii bacterium - particularly the strain P260 obtained from the University of Otago in Dunedin, New Zealand.

ARS researcher Nasib Qureshi said the strain was able to convert nearly 430 grams of sugar into 192 combined grams of ABE in a 22-day fed-batch operating period.

"If scaled up further, the process could yield 307 combined kilograms or 99 gallons of ABE from one short ton of wheat straw," said Qureshi in a statement. "The P260 strain produces a specific ratio of the three chemicals but efforts are now under way to develop genetically modified bacteria that will only make biobutanol."

Producing only butanol or other selected alcohols is what Gevo is aiming for with its patented process called Gevo's Integrated Fermentation Technology (GIFT). In 2007, Gevo was able to acquire exclusive license for certain modified E.coli bacteria from the University of California Los Angeles that can produce bio-isobutanol.

"Our technology produces one and only one product - isobutanol," says Gevo CEO Patrick Gruber. "With only one product produced in the fermentation, the economics and purity are improved. We also don't have to build greenfield, as it is simple enough to run it in ethanol plants."

Gevo says its technology can cost less than 30 cents/gal to retrofit an ethanol plant to make isobutanol. Isobutanol can also be converted to gasoline blendstocks for less than an additional 25 cents/gal.

"The production cost of our system is expected to be 50% of the cost of petrochemical-based processes even at modest oil prices like what we have now," says Gruber. "Our production processes are already proven at pilot scale. We have shown high-yield, high-purity isobutanol in a very low capital-cost system."

In November 2008, Gevo partnered with Kansas-based engineering and construction firm ICM to commercialize the technology. Gevo expects to begin operating a 1m gal/year plant in Missouri this summer by retrofitting an ethanol facility. The company aims to produce 20m to 50m gallons/year of isobutanol and other biobased hydrocarbons by 2011.

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By: Doris de Guzman
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