Biofuel

DENIS J. MURPHY

Future prospects for biofuels ABSTRACT In recent years, global production of biofuels has increased dramatically, mainly due to a combination of government policy initiatives and increasing oil prices. This phenomenon has been most marked in highly energy consuming regions such as the European Union and North America, and in primary producer regions such as Brazil, Malaysia and Indonesia. In this article the nature of major existing biofuels, such as bioethanol and biodiesel, and their agricultural sources will be discussed. The future prospects for ‘2nd generation’ fuels such as biohydrogen and feedstocks such as lingo-cellulosic biomass will then be examined. Finally, the broader aspects of biofuels and their long-term future will be critically examined in the context of global food production, population growth, fossil carbon substitution, and climate change. INTRODUCTION Biofuels are combustible solid, liquid, or gaseous materials, derived directly from recently produced biological materials (normally of plant origin), that are normally used for power or automotive generation. Most contemporary biofuels are obtained from crops that can be renewable, providing they are managed sustainably via appropriate cycles of harvesting and replanting. In contrast, fossil fuels such as coal, mineral oil, or natural gas, and other non-renewable (in the short term) fuels such as peat, are derived from the remains of long-dead biological organisms (Table 1). In a 1996 article, entitled Biodiesel and its prospects, I wrote: “Although there is undoubtedly a niche market for biodiesel, the long-term future of the product must remain uncertain in view of the ever-changing politico-economic situation regarding oil crops in developed countries … Looking even further ahead to the eventual exhaustion of fossil-derived

hydrocarbons, it is more likely that we will tend to husband our valuable renewable oils for use as lubricants and organic synthols, rather than burn them as fuels.” (1) Why have the prospects for biofuels changed so significantly over the past few years? One answer is that the recent fashion for biofuels is largely a political phenomenon that was amplified by economic factors, such as increases in mineral oil prices (2). The political dimension is shown by recent State of the Union addressed by US president George W Bush where he stated that the country should replace 75% of its imported fuel (>9.2 billion tonnes (3)) by biofuel by 2025; and that total gasoline use should be reduced by 20% (4.1 billion tonnes) by 2017 (4). The fuel shortfall would be replaced by renewables, especially biofuels. However, even using the best biofuel crops, generation of this 4-9 billion tonnes oil equivalent (TOE) would require over a billion hectares, or 5-6 times the US total arable land area (Tables 2 and 3). Over recent years, US policymakers have favoured biofuel production by granting subsidies to farmers and processors and by greatly increasing public and private investment in R&D, especially relating to lingocellulosic biomass (5, 6). Meanwhile, another major global trading bloc, the European Union, has set a minimum 10% obligation for transport biofuel use in the EU27 nations by 2020 (7) In addition to increased imports, especially of palm biodiesel, this obligation will require the use of large amounts of current domestic oilseed production, as well as about 60 million tonnes (MT) of cereals for bioethanol production. So, what are the realistic options for generating this quantity of biofuels? TYPES OF BIOFUELS Many of the biofuels listed below, such as ethanol, diesel and wood, can be produced with existing technologies and are known as 1st generation, or conventional, fuels (Table 2). There is also much interest in developing so-called 2nd generation biofuels produced from biomass, especially lingocellulosic feedstocks which are enzymatically converted on a large scale into fuels such as bioethanol (8). Bioethanol Current bioethanol fuels are most commonly (and most efficiently) obtained from starch- or sugar-rich carbohydrate crops, such as sugar cane or maize, although they can also be derived from other renewable sources such as some grasses and fibrous plants. Conversion of plant carbohydrate to ethanol requires relatively complex and highly energyconsuming fermentation, distillation and dehydration processes and ethanol fuels are less efficient in engines than either diesel or gasoline

Table 1. Balance sheet for fossil carbon production/consumption*

14

Biodiesel Biodiesel is derived from oil-producing crops, normally as triacylglycerols that are already semi refined hydrocarbon-

chimica oggi • Chemistry Today • vol 26 n 1 / Jan-Feb 2008

Biofuel

Oil crops like molecules requiring Oil crops have an adlittle further processing. vantage over carbohydrate Some vehicle engines can crops in that their major run directly on crude products, long-chain vegetable oils (even waste triacylglycerols, are cheoils), but better performance mically much closer to is obtained by catalytic hydrocarbon fuels and transmethylation of the Table 2. Biofuel crop yields and efficiency to energy output from derived fuel hence require less elaborate triacylglycerols to produce and less costly processing. methyl esters. Biodiesel is Typical C16 and C18 triacylglycerol oils from such crops one of the most efficient biofuels, especially if it is derived can be efficiently transesterified to methyl esters for use in from existing high yielding oil crops such as oil palm or virtually all engine types. potential future sources such as microalgae. However, the economic and environmental balance sheet for biodiesel Temperate oilseed crops from lower yielding oilseeds, such as sun or rapeseed is less Oilseed crops, such as rapeseed, sunflower, and soybean promising. are sources of high quality edible vegetable oils but can also be used for biodiesel production. Compared to tropical oil Biohydrogen crops, temperate oilseeds have two major drawbacks as Biohydrogen production is still largely under development biodiesel production platforms. First, they have comparatively although recent progress towards commercial applications low yields of about 1 tonne/ha of oil and, second, they have has been promising. a single annual harvest which necessitates relatively inefficient Conversion of various forms of biomass to hydrogen may batch processing, storage of large quantities of seeds or be achieved using several types of organism, including fuel, and annual replanting of the entire crop. bacteria and microalgae, and can proceed via modified The major European biodiesel crop is rapeseed, with photosynthesis plus several forms of fermentation and/or Germany and France the most important producers. Rapeseed anaerobic digestion. Potential feedstocks range from crops biodiesel is most commonly used as a vehicle fuel and is to organic waste, including sewage. widely promoted for its environmental benefits. However, recent studies imply that oilseed biofuels may not be so Others unequivocally ‘green’ as often claimed, especially in the While the above three are the major biofuel categories context of a full economic/environmental audit or life cycle currently in use or under development, there are several analysis (10). For example, the financial and energy cost other groups of actual or potential biofuels. Additional of planting, weeding, spraying (with energy-requiring bioalcohols include butanol and methanol, both derived chemical inputs), harvesting, transporting, processing an from biomass fermentation. oilseed biofuel crop in a highly energy-consuming economy Other biogases include methane, normally produced by employing an expensive labour force may well exceed the anaerobic digestion of various forms of organic matter gain in using a carbon renewable fuel versus the fossilincluding biomass and waste materials. Solid biofuels include derived alternative. traditional local materials such as wood and charcoal, which in many parts of the world have been harvested continuously Tropical oil crops and sustainably for millennia. Tropical oil crops such as oil palm and coconut produce high yields of oil in the fruits as well as in their seeds. The economics and logistics of tropical oil crops, with their higher MAJOR SOURCES OF BIOFUELS yields, continuous harvesting (on a regional or large plantation scale), and with replanting only every 25 years or so, are Carbohydrate crops much more favourable than those of temperate oilseeds. By The major useful products of carbohydrate crops are fermentable far the most important tropical oil crop is the oil palm, which sugars or starches that can be processed to manufacture fuel-grade ethanol. Sugar crops include cane (tropical) and beet (temperate) but only the more high-yielding sugar cane is viable as a commercial biofuel crop. Sugar crops Brazilian sugar cane was one of the pioneering modern biofuel crops and has been grown on a commercial scale since 1975 (9). The cane sugar is fermented to alcohol and blended in a 24:76 ratio with gasoline into a fuel called gasohol. Starch crops The major fermentable product of maize is starch, which is both lower yielding and significantly more expensive (energetically and financially) to process to ethanol than cane sugar. However, due to its ready availability in the US Corn Belt, and thanks to locally popular (with farmers) federal subsidies, bioethanol from maize has become one of the fastest growing biofuels since 2006. In an open market, the longer-term prospects of maize biofuel are less assured, due to competition from sugar cane for bioethanol production and from oilseed-derived biodiesel fuels, which often have lower net carbon footprints and higher yields.

Table 3 Potential for substitution by biofuels in the transportation sector achieving the 2020 biofuels target would require c.600 million ha land using conventional technology and c.250 million ha with 2nd generation technologies

chimica oggi • Chemistry Today • vol 26 n 1 / Jan-Feb 2008

15

Biofuel 16

can produce up to 5-8 tonnes/ha of oil for transesterification to methyl esters (11). In 2007, the Malaysian Ministry of Plantation Industries and Commodities announced that Malaysia and Indonesia, which together generate over 85% of global palm oil output, would reserve 40% (about 14 million tonnes (12)) of oil for biodiesel markets (13). Already, in 2007, about 25% of palm oil production was for nonfood, mostly biodiesel, use. Another tropical oil crop being developed in countries such as India is Jatropha curcas, whose oil-rich nuts can potentially yield 1.5-2.5 tonnes/ha biodiesel.

WHAT IS THE FUTURE OF BIOFUELS?

Recent criticisms of biofuels Current political targets for biofuel use are driven by a combination of environmental concerns (especially in Europe) about putative impacts of net carbon emissions; and security concerns (especially in the USA) about the reliability and cost of imported fuels. Meanwhile, the economic case for biofuels has been enhanced by the seemingly inexorable increase in crude oil prices to $100/barrel (16). Ironically, however, several environmental groups, NGOs in developing countries, and some scientists have recently begun to question the wisdom of the current rush to biofuels. It has been pointed Lipogenic microalgae out that biofuel production in industrial economies such as Most microalgae have considerably faster growth rates than the EU may generate as much or more carbon than it capture land plants and, providing high-oil varieties can be identified (17), as well as being almost entirely reliant on subsidies and cultured on a sufficiently large scale, they could potentially from public taxation. On the other hand, biofuel production generate very large quantities of biodiesel. For example, in developing economies is claimed to divert productive land researchers at the US National Renewable Energy Lab have away from edible crops and increase food prices for relatively estimated that 1 billion TOE biodiesel could be produced poor consumers (18). Moreover, the conversion of pristine from microalgae grown in ponds over an area of 0.2 million habitats such as rainforest for biofuel production is alleged ha and that sufficient biodiesel to replace all petroleum to have led to environmental transport fuels could be produced degradation and habitat loss, e.g. from 3.8 million ha (14). Although for signature species such as the this is a large land area, many orang utan in parts of the Far microalgae will grow well in East. sunny, warm habitats such as Some of the potential adverse manmade ponds located in arid consequences of an over-hasty areas like the Colorado Desert, adoption of biofuels can be and therefore will not occupy illustrated by the following recent arable land required for food examples. In the USA, the diversion production. of corn (maize) towards bioethanol production in 2007 led to greatly Biomass crops reduced soybean planting and Biomass crops are often relatively price rises for soy oil feedstocks fast-growing fibrous or woody and other staple grains like wheat species that can be harvested and barley. As corn stocks were from existing sources (e.g. cereal diverted to fuel use, prices of edible straw) or coppiced on a regular Figure1. Oil palm plantation in Central Malaysia for either food or biodiesel production (courtesy of United Plantations corn-based products such as tortillas basis (e.g. miscanthus). Before Berhad) increased by 60%, leading to the discover y of fossil fuels, serious civil disorder in Mexico traditional societies largely relied during the ‘tortilla riots’ of early 2007, as well as warnings on coppiced wood for fuel but population increases now about possible global impacts on food prices (19). Even in make it impossible to return to wood as a truly sustainable richer European countries, the impact of biofuel-generated biofuel. food price increases caused public concern as shown by Some biomass crops may be burned directly in small scale calls in Italy for a pasta strike (sciopero della pasta) in protest power plants located close to farms, but the production of against wheat price increases during September 2007. But portable fuels, which are much more useful and flexible than the most serious impact has been in poorer countries, especially raw biomass, requires processing and refining, normally by in parts of Asia where bread prices increased by as much fermentation, to produce bioethanol. as 80% in the latter part of 2007 (20). Many technical and economic criticisms of biofuels are Lingo-cellulosic crops based on analyses of their overall environmental and One of the major drawbacks of much of the existing biofuel economic costs versus their useful outputs (21-26). The technology is that it tends to rely on plant materials that assumptions underlying such calculations have sometimes could also be used as food or animal feed. been questioned by other specialists, but they nevertheless Several major oil companies and research centres are raise concerns about the environmental credentials of therefore investigating the potential conversion of inedible certain biofuels. Some of the criticisms of biofuels from biomass, especially woody or fibrous materials, to fuels non-scientists have been even more forthright, such as their such as bioethanol (15). controversial description in October 2007 as “a crime While there are many challenges in scaling up lab-based against humanity” by UN Special Rapporteur Jean Ziegler processes to commercially feasible dimensions, the scale (27, 28) and the November 2007 report from Oxfam of investment in these technologies makes it likely that there warning that the rush to biofuel crops could harm poorer will be significant progress in developing lingo-cellulosic people in developing countries by reducing food production feedstocks over the next decade. and increasing prices (29). Other sources of biofuels Are these criticisms justified? Traditional sources include wood, charcoal, and dried To what extent can biofuels realistically contribute to global animal/human excrement but none of these feedstocks can fuel requirements currently met by fossil fuels and what are be produced sustainably on a large enough scale to make likely consequences for food production? As shown in Table more than a minor contribution to global biofuel generation. 1, current annual global fossil carbon consumption is 9.5

chimica oggi • Chemistry Today • vol 26 n 1 / Jan-Feb 2008

Biofuel 18

6.3 billion is likely to increase to about 9 billion by 2050, billion TOE (tonnes oil equivalent), derived from oil (41%), it seems inconceivable that such a decrease in edible crop coal (32%), and natural gas (27%) (30). It is impossible for area could occur without serious consequences for global biofuels to satisfy even a fraction of this requirement. For food security, especially for poorer farmers and urban workers example, even if the entire global arable land area were in developing countries. One possible solution being researched devoted to the most efficient and realistic mixed portfolio of in the USA is use of non food-producing land to generate biodiesel (oilseeds and oil palm), bioethanol annual (maize, new biofuel feedstocks, such as desert-grown microalgae cane, wheat etc) and woody perennial crops (miscanthus, or lignocellulosic biomass derived either from existing crop poplar) we could only replace about 35% of current fossil waste or from marginal land unsuitable for pasture or arable carbon consumption – and of course there would be no use (14). room for food crops (Table 3). For this reason, policymakers have focused on the transport sector where substitution by liquid biofuels is more straightforward. CONCLUSIONS However, transport only uses 25% of total fossil carbon consumption. The long-term prospects for biofuels remain uncertain. On This means that even the modest (but still possibly unachievable) the one hand, the current rush to meet often-unrealistic target of 10% replacement by biofuels proposed in the EU policy targets has sometimes distorted agricultural food would, if pursued globally, only offset about 2.5% of annual production and may itself have fossil carbon consumption. significant adverse environmental and Moreover, even this rather small target social consequences. On the other (in terms of mitigating non-renewable hand, new technologies hold the carbon emissions and hence promise of much more efficient biofuels ameliorating putative environmental in the future. However, these consequences such as climate change) technologies remain as yet unrealised, would still require the removal from and may not be operationally or food production of 80-120 million ha commercially viable for another decade or 6-9% of the global arable crop or more. Moreover, we cannot simply area. Among the many alternative base the present case for biofuels on strategies for mitigation of carbon the potential for future scientific emissions is an increased planting of progress. forestry on non-arable land or nonGiven that the current very small, but carbon solutions such as greater use Figure 2. The author at a new oil palm biodiesel rapidly growing, biofuels sector is of nuclear, solar, wind, hydro, or tidal refining facility under construction near Port Klang, already significantly distorting food power generation (10). In short, the Malaysia, 2007 (courtesy of Golden Hope Plantations Berhad) production and food prices in several ability of 1st generation biofuels alone parts of the world, it will be important to substitute for fossil fuels without to perform a calm and measured evidence-based appraisal significant consequences for global food production is distinctly of biofuels that addresses a wide range of socio-economic uncertain. and technological issues, including the following points: – What is the real purpose of biofuels – simple substitution Technological advances of fossil transport fuels or a wider role in ameliorating Much faith has been pinned on advances in plant breeding climate change? and processing technologies to provide improved 2 nd – Can biofuels really make a significant contribution to generation biofuels, e.g. from lignocellulosic biomass. One reducing global fossil carbon consumption? option is to use advanced breeding methods, including DNA – What are their likely short-, medium- and long-term marker-assisted selection, TILLING (Targeting Induced Local impacts on production, of other crops, especially Lesions in Genomes), and transgenesis (genetic engineering) staple foods? to improve existing crops or to adapt new crops for use as – What are the realistic prospects for 2nd generation biofuels. Improved on-farm or centralised processing biofuels that will not need to displace staple crops technologies, including use of genetically enhanced microbes, from food-producing land? could enable more efficient and cost effective fermentation – To what extent are biofuels a ‘public good’ that truly of a range of crop feedstocks to produce fuels such as merits such high levels of taxpayer support? bioethanol and biohydrogen. For example, bacteria or fungi (including yeasts) could be It is apparent that present patterns in biofuel use, and their engineered for improved digestion of plant fibres (31-33) future potential as fossil carbon substitutes, are fraught and beyond (34); plants themselves could be engineered with uncertainty and remain controversial in many quarters to facilitate conversion of their biomass to fuel (35-37); (41). While it will be important to develop improved 2nd the oil yield and fatty acid composition of oil-bearing crops could be altered to make plant oils more suitable for direct generation biofuels, more research on non-carbon alternatives use as fuels, hence avoiding the costly process of methyl is also warranted. As noted by Righelato and Spracklen ester production (38, 39); and finally, microalgae could in a recent article in Science, “In our view, biofuels cannot possibly be engineered to produce hydrogen via anaerobic provide a solution to our energy needs, but by appearing photosynthesis (40). to be a “quick fix,” they may distract us from developing Over the next few decades, the development of more efficient effective, long-term, carbon-free solutions in the time window 2nd generation technologies for biofuel production might available to us” (44). Finally, and as noted in the introduction and elsewhere, double or treble yields and also increase the ratio of energy we should recall that biofuels are only one of many useful output/input in some of the less efficient bioenergy crops food or non-food products available from plants and that such as maize or wheat. But even a three-fold increase in in the longer term, plants might be more appropriately energy crop yield/ha still means that a relatively small 10% regarded as renewable sources of valuable semi-refined biofuel replacement target would still require diversion from chemicals rather than simply as low-grade energy feedstocks food production of 30-40 million ha or 2-3% of the global (1, 42, 43). arable crop area. Since the present human population of

chimica oggi • Chemistry Today • vol 26 n 1 / Jan-Feb 2008

1. 2. 3. 4. 5.

6. 7.

8. 9.

10. 11. 12. 13. 14. 15.

16. 17.

18. 19.

20.

21.

22.

23.

Murphy DJ (1996) Biodiesel and its prospects, NRC-PBI Bulletin, pp 8-10. Saskatoon, Canada. Murphy DJ (2007a) Plant Breeding and Biotechnology: Societal Context and the Future of Agriculture, Cambridge University Press, UK. US Department of Energy (2005) Biofuels for Transportation, Office of Science, http://genomicsgtl.energy.gov/biofuels/transportation. shtml Bush GW (2007) State of the Union Address, Jan 23, 2007, http://www.whitehouse.gov/stateoftheunion/2007/initiatives/sotu2 007.pdf Perlack, R. D., L. L. Wright, A. F. Turhollow, R. L. Graham, B. J. Stokes, and D. C. Erbach. (2005) Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply. Department of Energy/GO-1020052135, ORNL, 2005, http://www1.eere.energy.gov/biomass/pdfs/ final_billionton_vision_report2.pdf National Biofuels Action Plan (2007) US Department of Energy, http://www.biofuelspostureplan.govtools.us/documents/NationalBiof uelsActionPlanWorkshopSummaryReportFinal-5-30-07.pdf EU (2007) ‘In the biofuels directive adopted in 2003, Europe set itself the objectives of replacing 2% of petrol and diesel for transport by biofuels by 2005, and 5.75% by 2010… The Commission therefore proposes reinforcing the legislative framework, with a 10% minimum for the market share of biofuels in 2020.’ http://europa.eu/rapid/ pressReleasesAction.do?reference=MEMO/07/5 Service RF (2007) Biofuel Researchers Prepare To Reap a New Harvest, Science 315, 1488-1491 Szwarc A (2004) Use of biofuels in Brazil, Workshop on Mitigation SBSTA 21 / COP 10, Dec 9, 2004 Buenos Aires, http://unfccc.int/ files/meetings/cop_10/in_session_workshops/mitigation/application /pdf/041209szwarc-usebiofuels_in_brazil.pdf Righelato R and Spracklen DV (2007) Carbon Mitigation by Biofuels or by Saving and Restoring Forests? Science 317, 902 Average palm oil yields are currently about 3.5 tonnes/ha but better performing plantations can readily yield over 6 tonnes/ha and elite breeding material is capable of 8-10 tonnes/ha (see ref 1) USDA (2007) Oilseeds: World Markets and Trade, US Department of Agriculture, Nov 2007 bulletin, http://www.fas.usda.gov/oilseeds/ circular/2007/November/oilseeds1107.pdf The Edge Daily (2007) Palm oil — Fruits of labour, 13 August, 2007, http://www.theedgedaily.com/cms/content.jsp?id=com.tms.cms.artic le.Article_5e184002-cb73c03a-d647d800-e4a57491 Briggs M (2004) Widescale Biodiesel Production from Algae, University of New Hampshire, http://www.unh.edu/p2/biodiesel/ article_alge.html Fales SL et al (2007) Convergence of Agriculture and Energy: II. Producing Cellulosic Biomass for Biofuels, Council for Agricultural Science and Technology, Oct 2007 www.cast-science.org/websiteUploads/publicationPDFs/CAST% 20Commentary%202007-2%207o12145.pdf In 2003, crude oil prices on the New York Mercantile Exchange (NYMEX) were below $25/barrel but by late 2007 they had increased 3.6-fold to over $96/barrel. Patztek TW (2004) Thermodynamics of the Corn-Ethanol Biofuel Cycle, Critical Reviews in Plant Sciences 23, 519-567; updated web version: http://petroleum.berkeley.edu/papers/patzek/CRPS416Patzek-Web.pdf Murphy DJ (2007b) Future prospects for oil palm in the 21st century: Biological and related challenges, Eur. J. Lipid Sci. Technol. 109, 296-306 For tortilla riots see: http://www.zmag.org/content/showarticle. cfm?SectionID=59&ItemID=12030 See also related articles at: How the rising price of corn made Mexicans take to streets http://news.independent.co.uk/world/americas/article2697788.ece ; Biofuels to blame as beer prices soar 40 per cent in Germany http://news.independent.co.uk/business/news/article2699083.ece; Biofuel demand to push up food prices http://environment.guardian. co.uk/food/story/0,,2118876,00.html; Grow food, not fuel, OPEC says http://www.canada.com/edmontonjournal/news/business/ story.html?id=d0b300f5-1f7f-4039-9507-16890f6e06dd BBC (2007) Wheat price rises were also caused by climatic factors in some parts of the world but the biofuels effect was probably a major factor, especially in Asia, http://news.bbc.co.uk/1/hi/world/ 7004409.stm Larson ED (2005) “A Review of LCA Studies on Liquid Biofuel Systems for the Transport Sector” available at http://stapgef.unep.org/docs/ folder.2005-12-07.8158774253/folder.2005-12-08.9446059805/ folder.2005-12-08.0238464777/file.2006-06-21.8962502645 Von Blottnitz H & Curran MA (2007) A review of assessments conducted on bio-ethanol as a transportation fuel from a net energy, greenhouse gas, and environmental life cycle perspective, J. Cleaner Production 15, 607-619 Crutzen PJ, Mosier AR, Smith KA, and Winiwarter W (2007) N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels, Atmospheric Chemistry and Physics 7, 11191-11205 http://www.atmos-chem-phys-discuss.net/7/11191/2007/acpd-711191-2007.html

24. Gilbertson T, Holland N, Semino S and Smith K (2007) Paving the way for Agrofuels, EU policy, sustainability criteria, and climate calculations, 25 September 2007, http://www.tni.org/detail_pub. phtml?&know_id=202 25. Kaltschmitt M, Reinhardt GA and Stelzer T (1997) Life cycle analysis of biofuels under different environmental aspects, Biomass & Bioenergy 12, 121-134 26. Kløverpris J and Wenzel H(2007) Modelling Global Land Use and Social Implications in the Sustainability Assessment of Biofuels, Biofuel Assessment Conference, Copenhagen, 4 June 2007, International Journal of Life Cycle Assessment 12, 204; see also http://www. biofuelassessment.dtu.dk/ 27. BBC website (2007) Biofuels ‘crime against humanity' http://news. bbc.co.uk/1/hi/world/americas/7065061.stm In October 2007, Ziegler (former professor of social science and economics at the universities of Geneva and Paris Sorbonne) called for a five-year moratorium on biofuels, claiming that conversion of crops such as maize, wheat and sugar cane into fuels was driving up food, land and water prices. 28. International Herald Tribune (2007) UN expert calls turning food crops into fuel “a crime against humanity” http://www.iht.com/ articles/ ap/2007/10/26/news/UN-GEN-UN-Food-vs-Biofuel.php#Scene_1

Biofuel

REFERENCES*

For a complete list of references please contact the author at: [email protected] * all websites checked in Dec 2007

DENIS J. MURPHY Biotechnology Unit Division of Biological Sciences University of Glamorgan, CF37 1DL United Kingdom

chimica oggi • Chemistry Today • vol 26 n 1 / Jan-Feb 2008

19