Biofuels: the future?

 

A sugar cane plantation producing ethanol in the state of Sáo Paulo, Brazil Reproduced by kind permission of the Embassy of Brazil, London

A sugar cane plantation producing ethanol in the state of Sáo Paulo, Brazil Reproduced by kind permission of the Embassy of Brazil, London

The pressure to develop biofuels for powering transport has varied greatly over recent years. Local and international targets have ranged from incremental increases to major changes in the sourcing of biofuels. John Constable, the Director of Policy and Research for the Renewable Energy Foundation, outlines the state-of-play today with the help of Paul Dupree of the Department of Biochemistry at Cambridge University, and Chris Perry a water resources economist.

The use of biological substances to produce liquid transport fuels is far from new. Henry Ford’s design for the Model T specified the use of ethanol, and Rudolf Diesel’s original engine ran on peanut oil. Indeed, Ford referred to ethanol as the “fuel of the future”, and Diesel expected the production of oils for his engine to become one of the foundations of developing agriculture.

Historically, then, it is tempting to see the last century of intense use of liquid fuels derived from fossil oil as a temporary diversion, and the current interest in renewables as a return to first principles. But much has changed since Ford and Diesel, not least the remarkable growth in aviation and in world population, and biofuels are unlikely to displace petroleum very significantly in the medium term.

Challenges involved

This is partly a question of sheer scale. Global transport currently consumes energy amounting annually to 2,637 million tonnes of oil equivalent (Mtoe), of which biofuels constitute just 24 Mtoe, a little less than 1%. Increasing this fraction would clearly present great difficulties, even if bioethanol and biodiesel had no competitors. But in fact, there are other possible alternatives, including hydrogen fuel cells and rechargeable electric batteries, and for some uses, urban transport for example, these may prove to be more economical and appropriate than biofuels.

And with some crops in some places there are also concerns with regard to the energy balance (the energy needed to grow and process the crop to produce fuel, as against the energy contained in the fuel), and the carbon balance (the carbon emitted in the growing emitting and processing, as against the carbon emissions avoided by displacement of fossil fuels).

For Brazilian ethanol from sugarcane these ratios are strongly positive, in the order of ten to one, but in other cases the balances are marginal and not always powerfully convincing. While at present these are serious constraints, the development of Second Generation fuels, discussed later in the article, promises to address these matters.

STAGES IN BIOFUEL DEVELOPMENT

First generation

The so-called ‘first generation’ of biofuels is based on knowledge and technology that in many cases pre-dates the modern petroleum industry. For example, foodstuffs such as wheat, maize, or sugar, can be fermented to produce bioethanol, or oily crops like rapeseed can be processed to make biodiesel.

Second generation

The upcoming generation of biofuels, the second generation, makes increased use of non-food crops like grasses, waste biomass such as the stalks of wheat and corn, and chippings from wood. Many of the technologies and processes to produce second generation biofuels are currently under development, with the goal of improving carbon efficiency and increasing yield (see box: Second Generation Biofuels).

Brazil leads the way

Nevertheless, biofuels have been extremely successful in Brazil, where some 40% of the fuel consumed in gasoline-burning Otto Cycle engines (the standard petrol engine) is now derived from renewable sources, mostly ethanol from sugar cane.Since 2003, Brazilian drivers have been able to purchase flex-fuel vehicles, and these now account for 65% of all new car sales. The engines in these vehicles have been specially adapted to permit them to run on any mixture of biofuel and gasoline, allowing the driver to take advantage of fluctuations in the price of either commodity.

The Brazilian Government believes that the avoided cost of importing oil between 1976 and 2004 exceeded US $60 billion.Economic arguments such as this combine with fuel security concerns to drive the pro-ethanol policy of the United States, while in other countries, notably the European Union, there is intense interest in low carbon fuels as part of attempts to tackle climate change. Indeed, the EU is aiming to derive 10% of transport fuel from renewable sources by 2020.

Public perceptions of this endeavour, however, have varied widely over a short period of time, swinging from the belief that it would protect our societies from the end of oil, to the currently pervasive view that biofuels are unsustainable and will exacerbate global food poverty. In this turbulent atmosphere, it is increasingly difficult to make sense of biofuels’ true potential. We can only begin to understand the matter by teasing out the truth behind the science and the developing relationship between biological feedstocks (raw materials) and industrial processes.

Biodiesel and Bioethanol

Biofuels are already a noticeable though very small share of global transport fuels. In fact, they already occupy globally about 1% of cropped land and account for a similar proportion of crop water consumption. In 2007 the world produced 49.6 billion litres of fuel ethanol, the largest producers being Brazil (19 billion litres) and the USA (24.6 billion litres). Growth in Brazil has been steady since the 1930s, while the United States has achieved a meteoric 300% increase since 2000. For comparison we can note that the EU is the world’s third largest producer with a comparatively modest 2.2 billion litres.

As might be expected, given the much more widespread use of diesel engines for personal transport in Europe, roughly 90% of world production of biodiesel is for the European market, which produces 5 billion litres per year. Most of this is produced in Germany, far and away the largest producer at 2.5 billion litres, France, and Italy.

Most of the Organisation for Economic Co-operation and Development (OECD) states have policies designed to expand the market for biofuels. The US aims to reduce gasoline use by 20% by 2010, through both efficiency gains and biofuel substitution. To supply 15% of US gasoline in 2017 would require 132 billion litres of bioethanol, about five times current output.

The European Union has an ambitious (some argue impractical) policy requiring that 20% of its Final Energy Consumption (the energy used at the point of consumption for heating, transport, and electricity) be obtained from renewable sources by 2020. Transport must contribute by obtaining a minimum of 10% of its fuel from renewables. While the US might be able to achieve its target without imports there is no likelihood that the EU can do so.

Natural advantages

Much of the ethanol needed by the EU, and perhaps part of that required by the USA, is likely to come from Brazil, a country that can use sugar-cane as a feedstock, and is also blessed with very high levels of sunlight and rain. Very little of Brazil’s enormous biofuels industry needs to employ artificial irrigation, a fact of paramount importance making it a very special case. Many of these plantations are clustered in the south of the country, in the state of São Paulo, far from the Amazon rainforest areas in the north, and they currently utilize some 5.5 million hectares of Brazil’s total area of 851 million hectares.

The Brazilian government estimates that 12% of the country could be used for sugar-cane cultivation, roughly twenty times the current figure, without, it argues, unacceptable ecological damage. If biofuels targets persist in the EU, some part of this potential growth may be realised in order to supply the export market. Indeed, this export trend may be rational and ecologically sound because, while ethanol can also be produced from other feedstocks such as maize and wheat, these sources are much less attractive, since they are less productive than sugar-cane and require more intensive agriculture.

The Chemistry of Biodiesel and Bioethanol

Biodiesel is commonly produced from vegetable oils. These oils are made by plants to store energy and nutrition in their seeds by capturing both the energy from sunlight and CO2 captured from the air, aspects which make them attractive as renewable fuels. The oils must first be removed from the seeds by mechanical crushing, and then processed to make them suitable for use in a diesel engine. In this processing the fatty acids in the oils are transesterified, a process in which the alcohol in an ester compound is replaced with another alcohol, usually methanol, to prevent the oils from solidifying. This methanol must be supplied to the process as an input.

After transesterification the biodiesel has properties very similar to petroleum diesel and can be used in unmodified engines if blended with standard diesel up to levels of about 20%. Higher levels require modifications to the engine.

Rapeseed is the major source of oil in Europe, whereas soybean provides most of the oil for the much smaller biodiesel industry in the US. A few percent of global palm oil production is also used. Biodiesel can also be made from waste plant oils and animal fats, but the quantity of these is insufficient to make an impact on fuel usage.

Bioethanol is simply ethanol made through fermentation of sugars by yeast, followed by distillation, technologies well-developed over the centuries. The starch of maize (corn) grains can be easily broken down to glucose by cooking and the introduction of enzymes, after which brewer’s yeast can be added. It is even easier to ferment the sucrose which can be obtained from sugar cane or sugar beet, as this is the normal source of energy for the yeast. The yield of sugars from these crops is much higher than that of oils from oilseeds, so although the conversion of sugars to fuels is more complex, the larger quantity obtained is an incentive for farming these crops.

Competition for Resources

There are widespread concerns about the impact on national and international agricultural economies that would result from the development of biofuel crops on the scale needed to reach the more ambitious governmental targets.

In this respect, the promotion of biofuels is not greatly different from other substantial interventions in agricultural markets, such as the Common Agricultural Policy of the EU, the system of subsidies applied in the United States to various crops, or measures adopted by many developing countries to protect domestic production in pursuit of food security. Rapid development in several large countries, notably India and China, has also dramatically increased the demand for animal feed, which also changes the incentive structure at farm level so that resources (land, labour and water) are diverted from one crop to another.

Water is perhaps the most worrying area of resource competition. Many of the countries where biofuels are thought to offer potential have relatively plentiful sunshine, land and labour resources, but limited water resources.

While several potential biofuel crops such as jatropha are referred to as drought tolerant, what this generally means is that the plant will survive drought, not that the crop is productive if unwatered. Indeed, the physics of plant growth are such that there is close to a linear relationship between water consumption and biomass production. Thus, concerns that promotion of biofuels will increase competition for scarce water supplies are well founded.

Financial implications

Such changes can be seen as damaging to the interests of the poor, because the crop that is driven out is usually a low-value foodgrain, while the crop that expands is oriented to the needs of the better off (be it production of meat or biofuels). However, the effects are rarely simple: while the poor consumer may have to pay more for food, the income of the often equally poor producer is increased by the new crop.

It should also be recalled that some biofuel processes make food as a byproduct; one litre of biodiesel from soybean results in four kilograms of soybean meal, and there appears to be some scope for the promotion of crops such as ‘sweet sorghum’ that provide both a grain and biofuel.

In general, to the extent that biofuel crops compete for resources with existing crops, it is inevitable that prices will rise.Only where a higher price for biofuels induces use of currently unexploited resources (as seems possible in Brazil, for example) is there no impact on the consumers of existing agricultural products.

Farmers, like all businessmen, make decisions in an ever-changing market. Reducing uncertainty improves the likelihood that their decisions will be prudent and durable. While society wants biofuels at low prices, neither society nor producers benefit from prices that do not allow sustained production. And conversion of land from one crop to another is not a short-term decision – especially for the perennial biofuel crops.

Subsidising crops

The economic conditions in which biofuels are produced (meaning the prices of biofuel products, the prices of alternative crops, and the security of those prices over time) will be critical in determining the success of this venture. The Brazilian experience demonstrates that government intervention was necessary initially (indeed for a decade or more) to protect biofuel farmers from the vagaries of oil prices and reassure them that investment was viable in the longer term. All forms of intervention carry risks, but instability is perhaps the worst.

The volatility of energy prices makes it difficult to base the case for biofuels on financial market viability - in any case, for most countries it will probably always be cheaper to buy oil than grow biofuels. However, there may be benefits to society through reduced carbon emissions. Establishing the value of that benefit and setting a floor price for biofuels that reflects this value would allow the most efficient producers to profit from growing these crops. To the extent that the floor price is competitive with food grains, the impact would be to push those prices up, benefiting producers at the expense of consumers.

Second Generation Biofuels

Plants not only store energy in sugars as starch within their seeds, but they also convert fixed carbon from the atmosphere into sugars and use them to build all their structures. Each plant cell is encased in a wall of polysaccharides, including cellulose, which like starch is composed of long chains of glucose.

However, unlike starch, it is not easy to release the energy from cellulose, but this does happen in nature (in cows’ stomachs, for example) and in principle we could do the same, releasing the sugars from biomass like grass and wood.

In one process currently under development, biomass is first ‘cooked’ with steam or treated with acids, and then enzymes are added to release the sugars. These are then fed to strains of yeast that have been specially engineered to grow on the sugars found in the plant biomass. The yeast can ferment these sugars to produce ethanol that is then recovered like conventional biofuels.

This route to biofuels is promising and much discussed, but the science is new and a great deal to be done. Research currently underway is revealing how genetic modification or selective breeding can optimise plants to allow sugars to be more easily released from the cell walls for fermentation, making biofuel recovery cheaper and more energy efficient.

Alternative technologies can involve gasifying the plant material, and using complex chemistry to re-synthesise hydrocarbon fuels. This process requires expensive chemical engineering infrastructure and catalysts, but has the potential to produce all types of fuels, including jet fuel. The wide range of alternative technologies makes this an exciting time for biofuel researchers but difficult for investors, as it is unclear which technologies will turn out to be the cheapest and most energy efficient.

Lignocellulosic and other Biofuels

In this economic context, it is of great importance that the efficiency of biofuel processes are improved as much as possible, and in fact there is significant potential here. The first major step forward will probably be the development of new technologies to use plant materials that are currently unsuitable for conversion. These may be waste plant materials such as straw, or high yielding energy crops such as willow or energy grasses.

An advantage of using these materials is that they give a substantially higher yield per hectare than the seeds currently used for food or biofuels. Moreover, this high yield can be obtained without the energy-intensive use of fertilisers and pesticides needed to produce heavy crops of wheat, maize, and soy. The success of this venture requires the development of novel technologies with much reduced costs (see Box: The Chemistry of Second Generation Biofuels).

Research also shows that algae, which can have very high rates of conversion of sunlight to oils, may provide an alternative to land plants, avoiding competition for land and water needed to grow food. However, this would require development of technologies to grow and harvest algae from areas the size of small countries, which is difficult to envisage at present.

Biochemical Industry

Even with great advances in the science of feedstocks it does not seem reasonable at present to expect that biofuels for transport will provide more than a fraction of total transport needs. However, this could be valuable insofar as it brings real benefits to the countries that grow them, and creates a significant moderating effect on the market price of fossil fuels.

Of course, no one can rule out a sudden advance in a surprising direction, perhaps in conjunction with developments in the mechanical engineering of personal transport, but it would be imprudent at present to bet on a breakthrough in any one area. Indeed, research might well reveal that the most promising avenues are in somewhat different directions.

For example, one other promising line of investigation is the use of biological sources rather than fossil hydrocarbons as feedstocks for the chemicals industry, for plastics and pharmaceuticals for example, and it may be in that sector, ultimately, that much of the science currently focused on biofuels eventually yields dividends.

BIOGRAPHIES – Dr John Constable, Dr Paul Dupree, Chris Perry

Dr John Constable is the Director of Policy and Research for the Renewable Energy Foundation. He is currently responsible for co-ordinating the Foundation’s large circle of practical and academic engineers, and is the principal author of the Foundation’s publications.

Dr Paul Dupree is Reader in Biochemistry at the University of Cambridge. He studies plant growth and plant biomass with the aim of improving the quantity and quality for conversion to second generation ‘lignocellulosic’ biofuels. He is developing technologies to improve the processes of depolymerisation of the biomass.

Chris Perry is a water resources economist, who originally trained as an engineer. He worked for the World Bank for over twenty years, primarily on large-scale irrigation projects in the Middle East and, primarily, Asia; thereafter, he was head of research and Deputy Director General of the International Water Management Institute.

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