Second-generation biofuels need work

Fuel trek: the next generation

24 February 2009 15:46  [Source: ICB]

The development of sustainable biofuel options is progressing well. Who will come out the winners?

ONCE SEEN as a promising alternative to gasoline, corn-based ethanol is being supplanted by a second generation of biofuels promising greater sustainability. Cellulosic materials, algae, pyrolysis and directed evolution are all contributing to these developments.

Pyrolysis

A combined pyrolysis/Fischer-Tropsch (FT) route to biofuels from cellulose is being demonstrated by French gas producer Air Liquide's subsidiary Lurgi at the science and engineering research institution Forschungszentrum Karlsruhe in Germany. Lurgi will be building a gasification plant in a joint project with the Karlsruhe Institute for Technology by 2011.

The Lurgi process takes three steps to turn straw to automotive fuel. The first stage uses fast pyrolysis at around 500°C to convert thin-walled plants, such as straw, into an energy-rich slurry.

This slurry is then transported to a central refinery, where it is heated with steam to produce synthesis gas. In the final step, the synthesis gas is converted into fuels by the FT process.

Edmund Henrich, of theForschungszentrum Karlsruhe outlined the process in a presentation at the second European summer school on Renewable Motor Fuels, in 2007.

Henrich says that, on average, the cereal harvest for rural Europe yields around 50 tonnes/km2 of straw that is not needed to maintain soil fertility. Square bales of this straw could be transported economically for between 20-30km (13-19 miles) to a pyrolysis plant.

"Taking the larger radius, the plant would convert around 200,000 tonnes/year," he says. "With a dry ligno-cellulose feed, the output is around 134,000 tonnes/year of a pyrolysis oil/char paste, a sludge or slurry with a density of 1,300kg/m³ and a higher heating value of 6 +/-1 kWh/kg."

Henrich says the output of the pyrolysis paste is about eight times greater than the straw bales and this can make it economical to transport for long distances. Henrich adds that the slurry can contain around 90% of the initial bioenergy and is easily stored in tanks and silos. Because the energy density is much greater than straw, it is economic to transport this by rail to a central refining facility, which can be up to 500km away.

Henrich says about half of the initial biomass energy can be converted into raw FT products, about 80% of the FT raw product energy may be converted into super-clean diesel and gasoline, and he suggests that a synfuel energy yield of 42% is a realistic upper value. Available present-day technology is near 30%. Synthesis pathways via methanol may be more efficient.

How sweet it is

Cellulosic to ethanol via enzymes and fermentation is an area where Swiss-based agricultural chemicals firm Syngenta has been active. The company has partnered with other industrial biotech firms, notably France-based Proteus and US-based Verenium (formerly Diversa), to develop technology.

Proteus and Syngenta announced in January that they will work together to develop novel, high-performing enzymes for next-generation biofuel production.

Both diversity screening and directed evolution methods are to be used for the discovery and the optimization of enzymes for the conversion of biomass into biofuels.

Proteus has a range of technologies and a source of new genes. It also has tools to generate new proteins that enable it to produce tailored enzymes, as well as a protein manufacturing platform to generate them.

Just over two years ago, Syngenta signed up Verenium to develop a range of novel enzymes to economically convert pretreated cellulosic biomass to mixed sugars.

This route to producing ethanol from cellulose is likely to be a long haul. Syngenta says that converting biomass to biofuels requires breakthrough developments in three areas: chemical preparation of the cellulosic biomass (pretreatment), conversion of pretreated cellulosic biomass to fermentable sugars by combinations of enzymes (saccharification), and the development of novel microorganisms to ferment the sugars to ethanol or other fuels (fermentation).

Dutch chemical giant DSM is using its longstanding expertise in industrial processes that use yeast and enzyme technologies to help develop routes to ethanol from cellulose.

"Our focus is on how to bring conversion technology into play, into second-generation, second-wave technology," says John Monks, business director bioproducts. He is not interested in making biofuels as such, but rather in the processes that make them possible.

DSM has partnered with Spain-based biofuels firm Abengoa, and the combination has won a grant from the US Department of Energy to look at ways of turning agricultural residues into biofuels. The firm's focus is wheat straw and corn stover. "Will it be the best feedstock? Who knows?" says Monks, "Whatever is chosen, there are many hurdles to be overcome in getting the fuel from the field. The challenge is in delivering technology, which enables cost-effective production. People have to be broad-minded about what's out and what's in."

Cost effective means biofuel from cellulose that can compete with oil at around $65/bbl. DSM's routes are currently "several orders of magnitude" above that price level, so there is plenty of room for development.

Wood's bioproducts business has pulled in yeast technology from Gist Brocades and a number of processes and ideas to develop yeasts that deliver enzymes capable of handling not only C6 sugars like glucose and fructose but also C5 saccharides produced by the decomposition of cellulose and lignin.

"Yeast classically consumes C6 sugars," says Monks. "Some of the work we're doing in the lab is to change the diet of yeast. Typically it turns its nose up at C5 sugars, and we're trying to persuade it to be more broadminded." This can be done through natural selection, protein engineering, or a combination of the two.

One concern about using field waste as a source of biomass is the effect of removing cellulose on soil structure and fertility. Monks says that research needs to be done to ensure that the right level of cellulose is left on fields to protect the soil below. This is especially important in areas like the US Midwest, where wind erosion can be a problem if soils become too dry and lack organic matter.

Aqueous solution

Algae, grown in freshwater lagoons or the sea, may be one answer. Algae can yield over half their biomass in oil, which can be converted to biodiesel. They also produce sugars that can be fermented to ethanol.

However, there is still some way to go before biofuels produced from algae can become a reality, says Dominique Duvauchelle, chairman and CEO of France-based industrial biotech company Eco-Solution. Duvauchelle puts the current best yield at around 25g/m2 for algae from open ponds. His company, like DSM, sees its niche as providing technology and tools to make biofuels.

Eco-Solutions started with a platform that enables it to stress a range of microbes from bacteria to yeast to algae, encouraging them to respond through accelerated evolution to the environments to which they are subjected.

According to a rule of thumb, bacteria will divide once an hour and algae once every day, says Duvauchelle. Eco-Solutions has a patented method for increasing this rate, so that algae placed in the reactor will mutate faster than naturally. After a short time a natural mutation in the algae will likely have developed to become the dominant form in the reactor, being the fittest for that environment.

Duvauchelle says this process can be repeated as necessary and combined with high throughput screening to rapidly develop algae that will have high yield and high growth rates.

Eco-Solutions has been working for three years to understand algal metabolism in an attempt to tackle algae's problems as a biofuel source.

"It is slow-growing and must be faster," says Duvauchelle. "There are some problems with contamination at the start of growth after the algae has been seeded in open ponds, and the amount of biomass required."

These problems go some way to explaining why the economics are still unclear. "We will need a 1ha (2.5 acre) pond to better define that," he says.

The firm is in discussion with two companies that are interested in CO2 mitigation, he says, and a trial may be possible by the end of 2010.

Duvauchelle believe that a combination of open ponds and glassware might offer the best economics. His current strategy sees algae started in glass and then added to the ponds. But it is important that the biofuel algae grow quickly to minimize the amount of contamination from competitive algae. "There are about 30,000 species of algae," he says. "100 are well known and between 15 and 20 are used for production." So there is plenty of scope for competition.

But the diversity of algae also means that there is scope to produce niche algae for different conditions. He says it is unlikely that there will be single algae that works well in the cold climates, the tropics, salt and fresh water.

All of these technologies could offer considerable range for producing biofuel from nonfood sources. The pyrolysis route looks to be the closest to commercialization, but is some way off. For companies looking to bet for the longer-term enzyme, fermentation and algal routes could still pay off though.

CORN POWER:
Corn-based ethanol still has a future, according to US biofuel company poet

One biofuel company, US-based Poet, claims to be making around 20,000 gals/year (75,700 liters/year) of ethanol using corn cobs as feedstock. Poet has a research center in South Dakota, and it is pursuing an integrated starch and cellulose to ethanol refinery model. The company is supported by DuPont and Novozymes.

Speaking in May 2006, DuPont executive vice president and chief innovation officer Thomas Connelly said: "We have worked over the last three years to develop a technology package that can efficiently break down the complex sugar matrix found in corn stover into ethanol from cellulose at a high yield. We are excited about the progress we have made and, while we still have to complete more research, we are ready to take the next steps to bring cellulosic ethanol to the market."

In 2004,Broin and Novozymes partnered in the development of a new enzyme for Broin's BPX technology, a patent-pending raw starch hydrolysis process that converts starch to sugar, which then ferments to ethanol without heat.

The innovative technology was taken to commercial-scale production after four years of research and development and eliminates the cooking process that has been part of ethanol production for hundreds of years.

The results included higher ethanol yields, increased nutrient quality and flowability in distillers dry grain soluble, reduction in plant emissions and reduced energy costs by up to 15%. During the development phase, Broin obtained from Novozymes a sample of acid fungal amylase enzyme that ultimately became specific to the process.

Simon Robinson is ICIS online editor and writes the Big Biofuels Blog. He takes a nonpartisan but skeptical view of the different technologies, companies and routes to biofuels.


By: Simon Robinson
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