Nature Publishes a Feature on "Biofuelling the Future". (December 28, 2006)

    The journal Nature published a ten-page business feature in its December 7, 2006) issue in which it assesses "[t]he idea of using living plants as a way to capture the all-but-unlimited energy of the Sun..."

For openers you're told that compared to an array of solar cells, plants are very poor transducers of the Sun's energy. Even under the best of plantation management, storing "more than a watt or two per square metre on average" isn't quite attainable. On the other hand under the proper conditions plants can even manufacture themselves and "[t]hey use up carbon dioxide in the process, which is a definite environmental plus — and they turn that carbon, along with the Sun's energy, into stable organic compounds." In short while biofuels can never be a sole energy source, as a carbon-neutral fuel, they show worthwhile potential.

Emma Marris discussed the advantages that Brazil has which allows it to make extensive use of ethanol as a replacement for in whole or part for hydrocarbon fuel. She says simply that "Brazil's sugar-cane ethanol industry is the world's best and able to get better... Brazil's tropical sun makes it a great place for growing sugar cane: it is the largest cane producer in the world, producing more than twice as much as the number two, India. Just crush out the sucrose solution, ferment it into alcohol with the help of yeast and distill it to the desired concentration; burn the 'bagasse' — the fibrous pulp left over when the sugar is squeezed from the cane — to power the process along. Put the alcohol into your gas tank and you are effectively driving it on sunlight."

Ms Marris reports, "In 2004, Isaias de Carvalho Macedo at the University of Campinas did a study for the state of São Paulo that considered energy inputs such as fertilizer manufacture and agricultural machinery in the sugar-cane industry¹. He and his colleagues estimate that the whole shebang costs about 250,000 kilojoules per tonne of cane. That tonne of cane in turn yields about 2 million kilojoules in ethanol and surplus electricity made by burning bagasse. That's an eight-fold return.

"Macedo's analysis suggests that a tonne of cane used as ethanol fuel represents net avoided emissions equivalent to 220.5 kilograms of carbon dioxide when compared with petroleum with the same energy content. The team extrapolates that ethanol use in Brazil reduces greenhouse-gas emissions by the equivalent of 25.8 million tonnes of carbon dioxide equivalent a year. For comparison, Brazil's total carbon dioxide emissions from fossil fuels is 92 million tonnes a year, according to the US Department of Energy. The improvement is thus substantial, if not out-of-this-world."

However, "Last year, a paper by a group at Washington State University in Richland made headlines by claiming that in this broadest perspective, Brazil's ethanol was bad for the environment," but Ms Marris writes that the claim is disputed and the industry continues to become "greener".

And as to the question of decimating the Brazilian rain forests the authorities claim Brazil "is big enough to expand its sugar-cane fields massively without either displacing necessary food crops or getting anywhere near the rainforest that the rest of the world seems to have decided is international property."

In addition Robert Boddey, a soil chemist at Embrapa, the Brazilian agricultural research unit has told Ms Marris, "For [Brazil's] degraded pastures, which are slowly losing carbon, [planting sugar cane] is not such a bad change. And almost 70% of the Cerrado [Latin America's savanna, of which Brazil has some 200 million hectares] has already been cleared." And sugar cane is considered to be more environmentally friendly than palm oil, the most energy-intensive source of biodiesel. Palm-oil plantations for biofuel are having serious effects on the primary forests of Indonesia, but are not as yet big business in Brazil."

Ms Marris concludes her assessment of the use of sugar cane as a feedstock for ethanol production:

To replace a tenth of today's global petrol production, Brazil's ethanol production would have to grow by a factor of 40 or so. Few see that as likely in itself. Even [Eduardo Pereira de Carvalho, president of Unica, the union of cane-growers in São Paulo], who is undeniably bullish, sees only a doubling by 2014, though he does not see that as the end of the story. Enthusiasts for new cane varieties talk of doubling the yield per hectare, but not necessarily going much further.

But a doubling or two is not to be sniffed at, and there is increasing interest in spreading the techniques developed in this most cane-friendly of countries to others in Latin America and elsewhere, with the details changed to fit local conditions. Already, ethanol is becoming a large enough business for the price of sugar on world markets to respond to changes in the oil markets — so the price of your caipirinha is now, in a very small way, susceptible to the manoeuvres of OPEC.

While there is consensus that obtaining ethanol from sugar cane in a tropical environment such as Brazil is a viable partial biofuel alternative to petrol despite its lower energy density, somewhat corrosive properties and a tendency to absorb water, such is not the case when evaluating ethanol production from maize (corn) kernels grown under temperate climatic conditions.

Katharine Sanderson in the second of the three assessments in Nature she points out, "Studies that compare the energy that goes into making ethanol — expended during the harvesting, fertilizing and transporting of the corn to refineries, and then refining it — with the energy that is released when it is burned routinely show that the net gain is at best small. The American Coalition for Ethanol says that ethanol contains twice the amount of energy that is used to make it; critics see no net gain whatsoever," and US President George W Bush in this year's State of the Union address said that In order to improve US energy security, he "intended to make cellulosic ethanol (ethanol made from the rougher and woodier parts of plants) a competitive biofuel within six years."

Most plants convert the sun's energy into cellulose the related polymer, hemicellulose, and in the case of woody plants lignin as well, a complex polymer consisting of various types of substructures which appear to repeat randomly.

To break down these polymers to the point where they can be converted to ethanol requires extensive and costly pre-treatments and despite the building of pilot plants utilising enzymatic treatments it is probably premature to attempt full scale commercial production based on any of the current methods.

Ms Sanderson makes the point, "Companies large enough to afford it are also following the basic research route rather than placing early bets on particular technologies. BP has announced it will invest US$500 million over ten years to fund an Energy Biosciences Institute, which will be a dedicated facility based at a university. The University of Cambridge, Imperial College London, Massachusetts Institute of Technology, Stanford, the University of California, Berkeley, and Lawrence Berkeley National Laboratory have all been mentioned as possible hosts — the final

Credit: Nature - R. Hodgkins

 decision is expected in December."

In addition there is beginning to be given serious consideration to the synthesis of the four carbon alcohol, butanol, and in fact BP and DuPont are working with British Sugar to adapt their ethanol fermentation facility in East Anglia to the synthesis of butanol and Ms Sanderson concludes her article with, "[Matt Drinkwater, market analyst at New Energy Finance in London, UK] thinks that an industry demand for butanol as an end product could actually increase interest in cellulosic approaches. 'Most refiners would be much happier to use butanol than ethanol,' he says. If oil companies become confident in biofuel technologies, investors would in turn be more confident of the biofuels industry as a whole, giving the industry that elusive final shove that it seems to need."

In the last of the three articles Heidi Ledford discusses the "pros and cons" of making "liquid fuel from biomass -- or from coal".

Brian Schweitzer, the Democratic governor of of the north-western US state of Montana is one of the most vocal advocates for converting coal into liquid fuel. As Ms Ledford puts it, "With 8% of the world's [coal] reserves, Montana has enough coal to make 240 billion barrels of diesel fuel, which is in the same ball park as all of the proven reserves claimed by Saudi Arabia."

The proven method used for the conversion is the Fischer–Tropsch process. "Its first major use was during the Second World War, when the blockaded Nazis produced about 90% of their diesel and aviation fuel with the technologies originally developed by Franz Fischer and Hans Tropsch at the Kaiser Wilhelm Institute for Coal Research in 1923. South Africa began liquefying coal in response to apartheid-era sanctions, and in part as a result of its investment back then, continues to derive about 30% of its fuel from liquefied coal."

However, the Fischer–Tropsch process entails considerable expense, and was undertaken in Germany and South Africa as a last resort.

Furthermore, Ms Ledford says, "the Natural Resources Defense Council (NRDC), a US-based environmental group, says that even if 90% of that carbon were captured, producing and using coal-derived fuels would still release 8% more carbon dioxide than petroleum-derived fuels.

[see Williams, R. H., Larson, E. D. & Jim, H. 8th International Conference on Greenhouse Gas Control Technologies, Trondheim, Norway, 19-22 June 2006.]

While critical cost-benefit analyses remain to be determined (after all the technology is still in development) a possibility floated by Ms Ledford  is "plant biomass as a feedstock from which to make synthetic fuel, on the other hand, [would not require] sequestration — the emitted carbon is carbon that came from the air in the first place. If one were to add sequestration to a biomass-to-liquids plant, the result could be 'carbon negative', in that the net effect on the atmosphere would be to draw down the level of carbon dioxide as some of the carbon dioxide fixed by the plant would be sequestered into the planet's crust. What's more, Fischer–Tropsch methods could complement, at the very least, some other biomass technologies. Plant material that contains too much lignin and not enough cellulose for use in cellulosic ethanol projects could still be used in a Fischer–Tropsch system."

And it has been suggested that the Fischer–Tropsch process "could outcompete the fermentation of cellulose more generally". However, Robin Zwart of the Dutch Energy Research Centre in Petten hopes that upcoming improvements in efficiency says that oil prices will still have to exceed $70–80 per barrel to make liquid fuels from, for example, willow trees economical.

Currently the quoted price per barrel is about US$61.