Political, economic and environmental impacts of biofuels: A review

Applied Energy 86 (2009) S108–S117

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Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Political, economic and environmental impacts of biofuels: A review Ayhan Demirbas * Sila Science, Trabzon, Turkey

a r t i c l e

i n f o

Article history: Received 3 January 2009 Received in revised form 21 April 2009 Accepted 22 April 2009 Available online 22 May 2009 This article is sponsored by the Asian Development Bank as part of the Supplement ‘‘Biofuels in Asia’’. Keywords: Biofuel Policy Economy Environment Impacts

a b s t r a c t Current energy policies address environmental issues including environmentally friendly technologies to increase energy supplies and encourage cleaner, more efficient energy use, and address air pollution, greenhouse effect, global warming, and climate change. The biofuel policy aims to promote the use in transport of fuels made from biomass, as well as other renewable fuels. Biofuels provide the prospect of new economic opportunities for people in rural areas in oil importer and developing countries. The central policy of biofuel concerns job creation, greater efficiency in the general business environment, and protection of the environment. Projections are important tools for long-term planning and policy settings. Renewable energy sources that use indigenous resources have the potential to provide energy services with zero or almost zero emissions of both air pollutants and greenhouse gases. Biofuels are expected to reduce dependence on imported petroleum with associated political and economic vulnerability, reduce greenhouse gas emissions and other pollutants, and revitalize the economy by increasing demand and prices for agricultural products. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction It is well known that transport is almost totally dependent on fossil particularly petroleum based fuels such as gasoline, diesel fuel, liquefied petroleum gas, and compressed natural gas. As the amount of available petroleum decreases, the need for alternate technologies to produce liquid fuels that could potentially help prolong the liquid fuels culture and mitigate the forthcoming effects of the shortage of transportation fuels increases. There are several reasons for biofuels to be considered as relevant technologies by both developing and industrialized countries. They include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sectors of all countries in the world. Biofuels have become more attractive recently because of its environmental benefits [1–7]. The benefits of biofuels over traditional fuels include greater energy security, reduced environmental impact, foreign exchange savings, and socioeconomic issues related to the rural sector. Furthermore, biofuel technology is relevant to both developing and industrialized countries. For these reasons, the share of biofuels in the automotive fuel market is expected to grow rapidly over the next decade. Biofuels could be peaceful energy carriers for all countries. They are renewable and available throughout the world. Policy-makers will need to pay more attention to the implications for the transition to biofuel economy. The concept of sustainable devel* Tel.: +90 462 230 7831; fax: +90 462 248 8508. E-mail address: [email protected]. 0306-2619/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.04.036

opment embodies the idea of the inter-linkage and the balance between economic, social and environmental concerns [8–11]. Biofuel is a renewable energy source produced from natural (biobased) materials, which can be used as a substitute for petroleum fuels. The most common biofuels, such as ethanol from corn, wheat or sugar beet and biodiesel from oil seeds, are produced from classic food crops that require high-quality agricultural land for growth. However, ethanol is a petrol additive/substitute that can be produced from plentiful, domestic, cellulosic biomass resources such as herbaceous and woody plants, agricultural and forestry residues, and a large portion of municipal and industrial solid waste streams. Production of ethanol from biomass is one way to reduce both the consumption of crude oil and environmental pollution. There is also a growing interest in the use of vegetable oils for making biodiesel, which is less polluting than conventional petroleum diesel fuel [12,13,5,14–21]. The term biofuel is referred to as solid (bio-char), liquid (ethanol, vegetable oil and biodiesel) or gaseous (biogas, biosyngas and biohydrogen) fuels that are predominantly produced from biomass [22–26]. Liquid biofuels may offer a promising alternative. Liquid biofuels are substitute fuel sources to petroleum; however some still include a small amount of petroleum in the mixture. The biggest difference between biofuels and petroleum feedstocks is oxygen content [27–30]. Biofuels production costs can vary widely by feedstock, conversion process, scale of production and region. For biofuels, the cost of feedstock (crops) is a major component of overall costs. Total biofuel costs should also include a component representing the

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impact of biofuels production on related markets, such as food. In particular, the cost of producing oil-seed-derived biodiesel is dominated by the cost of the oil and by competition from high-value uses like cooking [13,15,31]. In 2004, 3.4 billion gallons of fuel ethanol were produced from over 10% of the corn crop. Ethanol demand is expected to more than double in the next 10 years. For the supply to be available to meet this demand, new technologies must be moved from the laboratories to commercial reality [32]. The world ethanol production is about 60% from feedstock from sugar crops. Biodiesel is a synthetic diesel-like fuel produced from vegetable oils, animal fats or waste cooking oil. It can be used directly as fuel, which requires some engine modifications, or blended with petroleum diesel and used in diesel engines with few or no modifications [33–35,16,36,37]. At present, biodiesel accounts for less than 0.2% of the diesel consumed for transport [38]. Biodiesel has become more attractive recently because of its environmental benefits [39–41]. The cost of biodiesel, however, is the main obstacle to commercialization of the product. With cooking oils used as raw material, the viability of a continuous transesterification process and recovery of high quality glycerol as a biodiesel by-product are primary options to be considered to lower the cost of biodiesel [42–45,34]. Advantages of biofuels are the following: (a) biofuels are easily available from common biomass sources, (b) they represent a carbon dioxide-cycle in combustion, (c) biofuels have a considerable environmentally friendly potential, (d) there are many benefits to the environment, economy and consumers in using biofuels and (e) they are biodegradable and contribute to sustainability [46,47]. The benefits include greenhouse gas reductions including reduced carbon dioxide emissions, which will contribute to domestic and international targets, the diversification of the fuel sector, biodegradability, sustainability, and an additional market for agricultural products. Biofuels help to protect and create jobs. Table 1 shows the major benefits of biofuels. Table 1 Major benefits of biofuels. Economic impacts

Sustainability Fuel diversity Increased number of rural manufacturing jobs Increased income taxes Increased investments in plant and equipment Agricultural development International competitiveness Reducing the dependency on imported petroleum

Environmental impacts

Greenhouse gas reductions Reducing of air pollution Biodegradability Higher combustion efficiency Improved land and water use Carbon sequestration

Energy security

Domestic targets Supply reliability Reducing use of fossil fuels Ready availability Domestic distribution Renewability

The scope of this review is political, economic and environmental impacts of two liquid biofuels (ethanol and biodiesel). 2. Methodology A number of studies with comparisons of gasoline, ethanol and gasoline/ethanol blends; diesel, ethanol and diesel/ethanol blends; and diesel, natural gas and diesel/biodiesel blends bus emissions have been published previously [48–56]. The basis for these comparisons, the choice of vehicles and even the outcome vary significantly. The studies have been conducted to develop a methodology for the generation of driving and duty cycles for refuse vehicles matching the statistical metrics and distributions of the generated cycles to the collected database [57,58]. These cycles can be utilized in the development and computer simulation of future refuse vehicle designs, specifically liquid biofuel fuelled vehicles. Other comparisons include a chassis-based testing program to document emission reduction (NOx, SOx, HC, CO and PM) performance from a fleet of vehicles accumulating mileage or applying standard driving cycles [59,60]. Methodology is also based on land use changes over time. A certain amount of land is needed to meet the required production for biofuel raw materials. The surplus available land can possibly be used for biofuel production. Several theoretical concepts have been applied in the development of the method. A general overview of methodology and data requirement for biofuels is shown in Table 2. 3. Land availability The land availability for producing biofuels in a well-established infrastructure makes an impact in the energy economy. The well-established infrastructure contains a sustainable truck traffic system, where a well-established railroad system is available, trucks would only take the biomass to collection centers and then it would be railed to the biorefinery. Assuming that high yield sugar crop is planted all around the biorefinery, the longest pratical trip a truck would need to make would be a 45 km round trip [14]. 4. Production of ethanol and biodiesel in the world There are two global liquid transportation biofuels that might replace gasoline and diesel fuel; these are ethanol and biodiesel, respectively. Transport is one of the main energy consuming sectors. It is assumed that biodiesel is used as a petroleum diesel replacement and that ethanol is used as a gasoline replacement. The EU production of biofuels amounted to around 2.9 billion liters in 2004, with ethanol totalling 620 million liters and biodiesel the remaining 2.3 billion liters. The feedstocks used for ethanol production are cereals and sugar beet, while biodiesel is manufactured mainly from rapeseeds. In 2004, EU biodiesel production used 27% of EU rapeseed crop. In the same year, ethanol production used 0.4% of EU cereals production and 0.8% of EU sugar beet production. The EU is by far the world’s biggest producer of biodiesel with Germany producing over half of the EU’s biodiesel. France and

Table 2 General overview of methodology and data requirement for biofuels. Inputs Design Literature review

Raw materials Comparisons

Outputs Cost factors Capital cost Feedstock price Chemicals Investment support process Land use subsidy and credit

Data analysis

Political impact

Economic impact

Environmental impact

Cost data

Benefits

Combustion efficiency

Emission reducing

Scenarios Future view

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Italy are also important biodiesel producers, while Spain is the EU’s leading ethanol producer [38]. Fig. 1 shows the world productions of ethanol and biodiesel between 1980 and 2007. Between 1991 and 2001, world ethanol production rose from around 16 billion liters a year to 18.5 billion liters. From 2001 to 2007, production is expected to have tripled, to almost 60 billion liters a year. Brazil was the world’s leading ethanol producer until 2005 when US production roughly equaled Brazil’s. The United States became the world’s leading ethanol producer in 2006. (the) People’s Republic of China holds a distant but important third place in world rankings, followed by India, France, Germany and Spain. Fig. 2 shows the top five ethanol producers in 2006. Between 1991 and 2001, world biodiesel production grew steadily to approximately 1 billion liters. Most of this production was in OECD Europe and was based on virgin vegetable oils. Small plants using waste cooking oils started to be built in other OECD countries by the end of the 1990s, but the industry outside Europe remained insignificant until around 2004. Since then, governments around the world have instituted various policies to encourage development of the industry, and new capacity in North America, south-east Asia and Brazil has begun to come on stream at a brisk

Total world production, billion liters

60

50

Ethanol

40

Biodiesel 30

20

10

0 1979

1984

1989

1994

1999

2004

Years Fig. 1. World production of ethanol and biodiesel, 1980–2007.

5 4.5 4

Billion gallon

3.5 3 2.5 2 1.5 1 0.5 0 USA

Brazil (the) PRC

India

France

Fig. 2. The top five ethanol producers (billion gallons) in 2006.

Table 3 Total biofuel support estimates for US and EU in 2006 (billions of US$).

The United States (US) Europe Union (EU) Total of world

Biodiesel

Ethanol

Total biofuels

0.60 3.11 3.65

5.96 1.61 7.85

6.70 4.82 11.79

Table 4 Fuel economy impacts of biodiesel use. Percent of biodiesel in diesel fuel

% Reduction in miles/gallon

20 100

0.9–2.1 4.6–10.6

rate. As a result, between 2001 and 2007, biodiesel production will have grown almost tenfold, to 9 billion liters. 5. Political impacts of biofuels Policy drivers for renewable liquid biofuels have attracted particularly high levels of assistance in some countries given their promise of benefits in several areas of interest to governments, including agricultural production, greenhouse gas emissions, energy security, trade balances, rural development and economic opportunities for developing countries. Total biofuel support estimates for US and EU in 2006 is given in Table 3 [61]. Ethanol can be used directly in cars designed to run on pure ethanol or blended with gasoline to make ‘‘gasohol”. Anhydrous ethanol is required for blending with gasoline. No engine modification is typically needed to use the blend. Ethanol can be used as an octane-boosting, pollution-reducing additive in unleaded gasoline. World production of ethanol from sugar cane, maize and sugar beet increased from less than 20 billion liters in 2000 to over 40 billion liters in 2005. This represents around 3% of global gasoline use. Production is forecasted to almost double again by 2010 [38]. Biodiesel is a synthetic diesel-like fuel produced from vegetable oils, animal fats or waste cooking oil. It can be used directly as fuel, which requires some engine modifications, or blended with petroleum diesel and used in diesel engines with few or no modifications. At present, biodiesel accounts for less than 0.2% of the diesel consumed for transport [38]. Biodiesel has become more attractive recently because of its environmental benefits. The cost of biodiesel, however, is the main obstacle to commercialization of the product. With cooking oils used as raw material, the viability of a continuous transesterification process and recovery of high quality glycerol as a biodiesel by-product are primary options to be considered to lower the cost of biodiesel [42,43]. The possible impact of biodiesel on fuel economy is positive as given in Table 4 [62]. Many farmers who raise oilseeds use a biodiesel blend in tractors and equipment as a matter of policy, to foster production of biodiesel and raise public awareness. It is sometimes easier to find biodiesel in rural areas than in cities. Additional factors must be taken into account, such as the fuel equivalent of the energy required for processing, the yield of fuel from raw oil, the return on cultivating food, and the relative cost of biodiesel versus petrodiesel. Biodiesel policy should reflect that theme by aggressively eliminating the government imposed barriers to its success. Biodiesel policy should be based firmly in the philosophy of freedom. Given the history of petroleum politics, it is imperative that today’s policy decisions ensure a free market for biodiesel. Producers of all sizes must be free to compete in this industry, without farm subsidies, regulations and other interventions skewing the playing field. The production and utilization of biodiesel are facilitated firstly

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through the agricultural policy of subsidizing the cultivation of non-food crops. Secondly, biodiesel is exempt from the oil tax. 6. Costs, prices and economic impacts of biofuels In previous economic studies of biodiesel production, the main economic factors such as capital cost, plant capacity, process technology, raw material cost and chemical costs were determined [43]. The major economic factor to consider for input costs of biodiesel production is the feedstock, which is about 75–80% of the total operating cost. Other important costs are labor, methanol and catalyst, which must be added to the feedstock [63]. Using an estimated process cost, exclusive of feedstock cost, of US$0.158/l for biodiesel production, and estimating a feedstock cost of US$0.539/l for refined soy oil, an overall cost of US$0.70/l for the production of soy-based biodiesel was estimated [64]. Palm oil is the main option that is traded internationally, and with potential for import in the short term [65]. Costs for production from palm oil are estimated; the results are shown in Table 5 [65]. The oil in the vegetable seeds is converted into biodiesel through oil extraction, oil refining, and transesterification. The cost of biodiesel can be lowered by increasing feedstock yields, developing novel technologies, and increasing economic return on glycerol production by finding other uses for this by-product, which, at the moment, due to oversupply is sold for little or no value. Alternatively, the use of cosolvents, such as tetrahydrofuran, can make the alcohol–oil–ester–glycerol system into a single phase, thereby reducing the processing costs [10]. However, these improvements still would not make biodiesel economically competitive at the current stage. Biofuels production costs can vary widely by feedstock, conversion process, scale of production and region. On an energy basis, ethanol is currently more expensive to produce than gasoline in all regions considered. Only ethanol produced in Brazil comes close to competing with gasoline. Ethanol produced from corn in the US is considerably more expensive than from sugar cane in Brazil, and ethanol from grain and sugar beet in Europe is even more expensive. These differences reflect many factors, such as scale, process efficiency, feedstock costs, capital and labor costs, co-product accounting, and the nature of the estimates. The cost of large-scale production of bio-based products is currently high in developed countries. For example, the production cost of biofuels may be three times higher than that of petroleum fuels, without, however, considering the non-market benefits. Conversely, in developing countries, the costs of producing biofuels are much lower than in the OECD countries and very near to the world market price of petroleum fuel [38]. Average international prices for common biocrude, fat, crops and oils used as feedstock for biofuel production in 2007 are given in Table 6 [10]. The cost of feedstock is a major economic factor in the viability of biodiesel production. Nevertheless, the price of waste cooking oil is 2.5– 3.5 times cheaper than virgin vegetable oils, thus can significantly

Table 6 Average international prices for common biocrude, fat, crops and oilseed as feedstock for biofuel production in 2007 (US$/ton). Biocrude Maize Sugar Wheat Crude palm oil Rapeseed oil Soybean oil Refined cottonseed oil Crude corn oil Crude peanut oil Crude tea seed oil Waste cooking oil Yellow grease Poultry fat

167 179 223 215 543 824 771 782 802 891 514 224 412 256

reduce the total manufacturing cost of biodiesel (Table 6). Biodiesel obtained from waste cooking vegetable oils has been considered a promising option. Waste cooking oil is available with relatively cheap price for biodiesel production in comparison with fresh vegetable oil costs. Economic advantages of a biofuel industry would include value added to the feedstock, an increased number of rural manufacturing jobs, an increased income taxes, investments in plant and equipment, reduced greenhouse gas emissions, reduced a country’s reliance on crude oil imports and supported agriculture by providing a new labor and market opportunities for domestic crops. In the recent years, the importance of non-food crops increased significantly. The opportunity to grow non-food crops under the compulsory set-aside scheme is an option to increase the biofuel production. Renewable liquid fuels such as ethanol, biodiesel, green diesel, and green gasoline are important because they replace petroleum fuels. The renewable liquid fuels are generally considered as offering many priorities, including sustainability, reduction of greenhouse gas emissions, regional development, social structure and agriculture, and security of supply [5]. The socioeconomic impacts on the local economy arising from providing power through renewable resources instead of conventional generation technologies are very important. These impacts include direct and indirect differences in the jobs, income, and gross output. There are significant socioeconomic impacts associated with the investment in a new power plant, including increases in employment, output, and income in the local and regional economy. Increases in these categories occur as labor is directly employed in the construction and operation of a power plant, as local goods and services are purchased and utilized. The potential for reduced costs of renewable liquid fuels and conservation of scarce fuel resources results in significant reductions in fuel usage. In addition to these economic benefits, development of renewable resources will have environmental, health, safety and other benefits.

Table 5 Costs of biodiesel production. Plant size (million liters)

Capital costs

Feedstock

Methanol

Other

Glycerol credit

Distribution and blending

Total

Tallow fat ($/l) 6 23 46 69 137

0.33 0.15 0.11 0.08 0.06

0.40 0.40 0.40 0.40 0.40

0.05 0.05 0.05 0.05 0.05

0.11 0.10 0.09 0.08 0.06

0.12 0.12 0.12 0.12 0.12

0.08 0.08 0.09 0.15 0.15

0.85 0.66 0.61 0.64 0.60

Palm oil ($/l) 60 71 143

0.09 0.08 0.06

0.73 0.73 0.73

0.05 0.05 0.05

0.08 0.08 0.06

0.12 0.12 0.12

0.04 0.04 0.04

0.88 0.86 0.82

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Agriculture ethanol is at present more expensive than synthesis-ethanol from ethylene. The simultaneous production of biomethanol (from sugar juice) in parallel to the production of ethanol, appears economically attractive in locations where hydro-electricity is available at very low cost (0.01 $ Kwh) [66]. Currently there is no global market for ethanol. The crop types, agricultural practices, land and labor costs, plant sizes, processing technologies and government policies in different regions considerably vary ethanol production costs and prices by region. The cost of producing ethanol in a dry mill plant currently totals US$1.65/ gallon. Corn accounts for 66% of operating costs while energy (electricity and natural gas) to fuel boilers and dry DDG represents nearly 20% of operating costs [67]. Ethanol from sugar cane, produced mainly in developing countries with warm climates, is generally much cheaper to produce than ethanol from grain or sugar beet in International Energy Agency (IEA) countries. For this reason, in countries like Brazil and India, where sugar cane is produced in substantial volumes, sugar cane-based ethanol is becoming an increasingly cost-effective alternative to petroleum fuels. Ethanol derived from cellulosic feedstock using enzymatic hydrolysis requires much greater processing than from starch or sugar-based feedstock, but feedstock costs for grasses and trees are generally lower than for grain and sugar crops. If targeted reductions in conversion costs can be achieved, the total cost of producing cellulosic ethanol in OECD countries could fall below that of grain ethanol. Estimates show that ethanol in the EU becomes competitive when the oil price reaches US$70 a barrel while in the United States it becomes competitive at US$50–60 a barrel. For Brazil the threshold is much lower – between US$25 and US$30 a barrel. Other efficient sugar producing countries such as Pakistan, Swaziland and Zimbabwe have production costs similar to Brazil’s [68]. Anhydrous ethanol, blendable with gasoline, is still somewhat more expensive. Prices in India have declined and are approaching the price of gasoline. The generally larger United States conversion plants produce biofuels, particularly ethanol, at lower cost than plants in Europe. Production costs for ethanol are much lower in countries with a warm climate, with Brazil probably the lowest-cost producer in the world. Production costs in Brazil, using sugar cane as the feedstock, have recently been recorded at less than half the costs in Europe. Production of sugar cane ethanol in developing countries could provide a low-cost source for substantial displacement of oil worldwide over the next 20 years. Table 7 shows the top 10 ethanol producers [66]. For biofuels, the cost of crop feedstock is a major component of overall costs. In particular, the cost of producing oil-seed-derived biodiesel is dominated by the cost of the oil and by competition from high-value uses like cooking. The largest ethanol cost component is the plant feedstock. Operating costs, such as feedstock cost, co-product credit, chemicals, labor, maintenance, insurance and taxes, represent about one third of total cost per liter, of which

Table 7 The top 10 ethanol producers (billion gallons). Country

2004

2005

2006

USA Brazil (the) PRC India France Germany Russia Canada South Africa Thailand

3.54 3.99 0.96 0.46 0.22 0.07 0.20 0.06 0.11 0.07

4.26 4.23 1.00 0.45 0.24 0.11 0.20 0.06 0.10 0.08

4.85 4.49 1.02 0.50 0.25 0.20 0.17 0.15 0.10 0.09

the energy needed to run the conversion facility is an important (and in some cases quite variable) component. Capital cost recovery represents about one-sixth of total cost per liter. It has been showed that plant size has a major effect on cost [69]. The plant size can reduce operating costs by 15–20%, saving another $0.02–$0.03 per liter. Thus, a large plant with production costs of $0.29 per liter may be saving $0.05–$0.06 per liter over a smaller plant [70]. Biodiesel from animal fat is currently the cheapest option ($0.4– $0.5/l) while traditional transesterification of vegetable oil is at present around $0.6–$0.8/l [71]. Rough projections of the cost of biodiesel from vegetable oil and waste grease are, respectively, $0.54–$0.62/l and $0.34–$0.42/l. With pre-tax diesel priced at $0.18/l in the United States and $0.20–$0.24/l in some European countries, biodiesel is thus currently not economically feasible, and more research and technological development will be needed [72]. 7. Environmental impacts of biofuels A number of studies with comparisons of diesel, natural gas and diesel/biodiesel blends bus emissions have been published previously [48–50,73–77]. Biodiesel, has a good energy return because of the simplicity of its manufacturing process, and has significant benefits in emissions as well. It could also play an important role in the energy economy if higher crop productivities are attained [10]. Table 8 shows the emissions of biodiesel (B20 and B100) for same model compression–ignition (diesel) vehicles [78]. Emissions of NOx increase with increasing biodiesel amount in the blends. The properties of biodiesel and diesel fuels, in general, show many similarities, and therefore, biodiesel is rated as a realistic fuel alternative to diesel. There are several ways to control NOx in a biodiesel engine run the engine very lean, which lowers the temperature, or very rich, which reduces the oxygen supplies, decrease the burn time or lower the engine. Emissions of NOx increase with the combustion temperature, the length of the high temperature combustion period, and the availability of biodiesel, up to a point. Alcohols have been used as a fuel for engines since the 19th century. Among the various alcohols, ethanol is known as the most suited renewable, bio-based and eco-friendly fuel for spark-ignition (SI) engines. The most attractive property of ethanol as an SI engine fuel is that it can be produced from renewable energy sources such as sugar, cane, cassava, many types of waste biomass materials, corn and barley. In addition, ethanol has higher evaporation heat, octane number and flammability temperature therefore it has positive influence on engine performance and reduces exhaust emissions. The results of the engine test showed that ethanol addition to unleaded gasoline increase the engine torque, power and fuel consumption and reduce carbon monoxide (CO) and hydrocarbon (HC) emissions [55]. The biodiesel impacts on exhaust emissions varied depending on the type of biodiesel and on the type of conventional diesel. Blends of up to 20% biodiesel mixed with petroleum diesel fuels can be used in nearly all diesel equipment and are compatible with most Table 8 Emissions of biodiesel for same model diesel vehicles. Vehicle or engine

Fuel

Peugeot Partner Peugeot Partner Renault Kangoo Renault Kangoo Dacia Pickup Dacia Pickup

B100 B20 B100 B20 B100 B20

Emissions, g/km NOx

CO

CH

PM

SOx

2.05 1.86 2.23 1.92 2.15 1.91

9.37 17.73 9.22 17.36 9.42 18.29

0.54 1.32 0.49 1.26 0.56 1.35

2.68 4.71 3.06 5.63 2.59 4.63

0 0.004 0 0.003 0 0.005

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storage and distribution equipment. Using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter. These reductions increase as the amount of biodiesel blended into diesel fuel increases. In general, biodiesel increases NOx emissions when used as fuel in diesel engine. The fact that NOx emissions increase with increasing biodiesel concentration could be a detriment in areas that are out of attainment for ozone. The pollutant emissions of ethanol–gasoline blends of 0%, 5%, 10%, 15% and 20% were experimentally analyzed in a four-stroke (SI) engine. The concentration of CO and HC emissions in the exhaust pipe were measured and found to be decreased when ethanol blends were introduced. This was due to the high oxygen percentage in the ethanol. In contrast, the concentration of CO2 and NOx was found to be increased when ethanol is introduced [56]. Oxygenated diesel fuel blends have a potential to reduce the emission of particulate matter (PM) and to be an alternative to diesel fuel. Results obtained showed that the addition of ethanol to the diesel fuel may be necessary to decrease diesel PM generation during combustion [54,60]. The total number and total mass of the PM of the ethanol–diesel blend fuels were decreased by about 11.7–26.9% [52]. An experimental investigation was conducted to evaluate the effects of using blends of ethanol with conventional diesel fuel, with 5% and 10% (by vol.) ethanol, on the performance and exhaust emissions of a fully instrumented, six-cylinder, turbocharged and after-cooled, heavy duty, direct injection (DI), Mercedes–Benz engine. Fuel consumption, exhaust smokiness and exhaust regulated gas emissions such as nitrogen oxides, carbon monoxide and total unburned hydrocarbons are measured. The differences in the measured performance and exhaust emissions of the two ethanol–diesel fuel blends from the baseline operation of the engine, i.e. when working with neat diesel fuel, were determined and compared [57]. Diesel emissions were measured from an automotive engine using anhydrous ethanol blended with conventional diesel, with 10% ethanol in volume and no additives. The resulting emissions were compared with those from pure diesel [58]. The results of the statistical analysis suggest that the use of E10 results in statistically significant decreases in CO emissions (16%); statistically significant increases in emissions of acetaldehyde (108%), 1,3-butadiene (16%), and benzene (15%); and no statistically significant changes in NOx, CO2, CH4, N2O or formaldehyde emissions. The statistical analysis suggests that the use of E85 results in statistically significant decreases in emissions of NOx (45%), 1,3-butadiene (77%), and benzene (76%); statistically significant increases in emissions of formaldehyde (73%) and acetaldehyde (2540%), and no statistically significant change in CO and CO2 emissions [59]. Biofuels are important because they replace petroleum fuels. There are many benefits for the environment, economy and consumers in using biofuels. The advantages of biofuels such as biodiesel, vegetable oil, ethanol, biomethanol, biomass pyrolysis oil as engine fuel are liquid nature-portability, ready availability, renewability, higher combustion efficiency, lower sulfur and aromatic content and biodegradability [79]. The biggest difference between biofuels and petroleum feedstocks is oxygen content. Biofuels have oxygen levels from 10% to 45% while petroleum has essentially none making the chemical properties of biofuels very different from petroleum. Oxygenates are just pre used hydrocarbons having structure that provides a reasonable antiknock value. Also, as they contain oxygen, fuel combustion is more efficient, reducing hydrocarbons in exhaust gases. The only disadvantage is that oxygenated fuel has less energy content. The combustion is the chemical reaction of a particular substance with oxygen. Combustion represents a chemical reaction,

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during which from certain matters other simple matters are produced, this is a combination of inflammable matter with oxygen of the air accompanied by heat release. The quantity of heat evolved when one mole of a hydrocarbon is burned to carbon dioxide and water is called the heat of combustion. Combustion to carbon dioxide and water is characteristic of organic compounds; under special conditions it is used to determine their carbon and hydrogen content [80]. During combustion the combustible part of fuel is subdivided into volatile part and solid residue. During heating it evaporates together with a part of carbon in the form of hydrocarbons combustible gases and carbon monoxide release by thermal degradation of the fuel. Carbon monoxide is mainly formed through the following reactions (a) from reduction of CO2 with unreacted C,

CO2 þ C ! 2CO

ð1Þ

and (b) from degradation of carbonyl fragments (–CO) in the fuel molecules at 600–750 K temperature. The combustion process is started by heating the fuel above its ignition temperature in the presence of oxygen or air. Under the influence of heat, the chemical bonds of the fuel are cleaved. If complete combustion occurs, the combustible elements (C, H and S) react with the oxygen content of the air to form CO2, H2O and mainly SO2. If not enough oxygen is present or the fuel and air mixture is insufficient then the burning gases are partially cooled below the ignition temperature and the combustion process stays incomplete. The flue gases then still contain combustible components, mainly carbon monoxide (CO), unburned carbon (C) and various hydrocarbons (CxHy). The standard measure of the energy content of a fuel is its heating value (HV), sometimes called the calorific value or heat of combustion. In fact, there are multiple values for the HV, depending on whether it measures the enthalpy of combustion (DH) or the internal energy of combustion (DU), and whether for a fuel containing hydrogen product water is accounted for in the vapor phase or the condensed (liquid) phase. With water in the vapor phase, the lower heating value (LHV) at constant pressure measures the enthalpy change due to combustion [81]. The heating value is obtained by the complete combustion of a unit quantity of solid fuel in an oxygen-bomb colorimeter under carefully defined conditions. The gross heat of combustion or higher heating value (GHC or HHV) is obtained by oxygen-bomb colorimeter method as the latent heat of moisture in the combustion products is recovered. 7.1. Combustion efficiencies of biofuels Biofuels are oxygenated compounds. The oxygenated compounds such as ethanol, methanol and biodiesel provide more efficient combustion, and cleaner emissions. At a stoichiometric air/ fuel ratio of 9:1 in comparison with gasoline’s 14.7:1, it is obvious that more ethanol is required to produce the chemically correct products of CO2 and water. Ethanol has a higher octane number (108), broader flammability limits, higher flame speeds and higher heats of vaporization than gasoline. These properties allow for a higher compression ratio, shorter burn time and leaner burn engine, which lead to theoretical efficiency advantages over gasoline in an internal combustion engine. The octane number of ethanol allows it to sustain significantly higher internal pressures than gasoline, before being subjected to pre-detonation. Disadvantages of ethanol include its lower energy density than gasoline, its corrosiveness, low flame luminosity, lower vapor pressure, miscibility with water, and toxicity to ecosystems. Methanol also is possible to take advantage of the higher octane number of methyl (114) alcohol and increase the engine compres-

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sion ratio. This would increase the efficiency of converting the potential combustion energy to power. Finally, alcohols burn more completely, thus increasing combustion efficiency. Some technical properties of fuels are presented in Table 9. Biofuels such as ethanol, biomethanol, biohydrogen and biodiesel generally results to lower emissions than those of fossil based engine fuels. Many studies on the performances and emissions of compression–ignition engines, fuelled with pure biodiesel and blends with diesel oil, have been performed and are reported in the literature [82,83]. Vegetable oils have become more attractive recently because of their environmental benefits and the fact that it is made from renewable resources. Dorado et al. [83] describe experiments on the exhaust emissions of biodiesel from olive oil methyl ester as alternative diesel fuel fuelled in a Diesel direct injection Perkins engine [84]. The methyl ester of vegetable oil was evaluated as a fuel in compression-ignition engines (CIE) by researchers [85]. They concluded that the performance of the esters of vegetable oil did not differ greatly from that of diesel fuel. The brake power was nearly the same as with diesel fuel, while the specific fuel consumption was higher than that of diesel fuel. Based on crankcase oil analysis, engine wear rates were low but some oil dilution did occur. Carbon deposits inside the engine were normal, with the exception of intake valve deposits. The results showed the transesterification treatment decreased the injector coking to a level significantly lower than that observed with diesel fuel [86]. Although most researchers agree that vegetable oil ester fuels are suitable for use in CIE, a few contrary results have also been obtained. The results of these studies point out that most vegetable oil esters are suitable as diesel substitutes but that more long term studies are necessary for commercial utilization to become practical. The use of biodiesel to reduce N2O is attractive for several reasons. First, biodiesel contains little nitrogen, as compared with diesel fuel which is also used as a re-burning fuel. The N2O reduction was strongly dependent on initial N2O concentration and only slightly dependent upon temperature, where increased temperature increased N2O reduction. This results in lower N2O production from fuel nitrogen species for biodiesel. In addition, biodiesel contains virtually trace amount of sulfur, so SO2 emissions are reduced in direct proportion to the diesel fuel replacement. Biodiesel is a regenerable fuel; when a diesel fuel is replaced by a biodiesel, there is a net reduction in CO2 emissions. As an energy source used in a diesel engine it reduces the consumption of diesel fuels and thereby reduces the greenhouse effect. Additional effects are a reduction of the ash volume and the SOx and NOx emissions of a biodiesel fuelled CIEs. Neat Biodiesel (BD) and BD blends reduce particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO) emissions and increase nitrogen oxides (NOx) emissions compared with diesel fuel used in an unmodified diesel engine [67]. The emission impacts of 20% by vol. soybean-based biodiesel added to an average base petrodiesel is given in Table 10. The total net emission of carbon dioxide (CO2) is considerably less than that of diesel oil and the amount of energy required for the production of biodiesel is less than that obtained with the final product. In addition, the emission of pollutants is somewhat less.

Table 10 Emission impacts of 20% by vol. soybean-based biodiesel added to an average base petrodiesel. Percent change in emissions NOx (nitrogen oxides) PM (particular matter) HC (hydrocarbons) CO (carbon monoxide)

+2.0 10.1 21.1 11.0

Source: Ref. [86].

Table 11 Average biodiesel emissions (%) compared to conventional diesel, according to Ref. [62]. Emission type

Total unburned hydrocarbons (HC) Carbon monoxide Particulate matter NOx Sulfates Polycyclic aromatic hydrocarbonsa Ozone potential of speciated HC a

Pure biodiesel

20% Biodiesel + 80% petrodiesel

B100

B20

67 48 47 +10 100 80 50

20 12 12 +2 20 13 10

Average reduction across all compounds measured.

CO2, one of the primary greenhouse gasses, is a trans-boundary gas, which means that, after it is emitted by a source, it is quickly dispersed in our atmosphere by natural processes. Biodiesel reduces CO2 emissions. Table 11 shows the average biodiesel emissions compared to conventional diesel, according to US Environmental Protection Agency (EPA) [87]. Table 12 shows the average changes in mass emissions from diesel engines using the biodiesel mixtures relative to the standard diesel fuel. Results indicate that the transformities of biofuels are greater than those of fossil fuels, thus showing that a larger amount of resources is required to get the environmental friendly product. This can be explained by the fact that natural processes are more efficient than industrial ones. On the other hand, the time involved in the formation of the fossil fuels is considerably different from that required for the production of the biomass [88]. Different scenarios for the use of agricultural residues as fuel for heat or power generation are analyzed. Reductions in net CO2 emissions are estimated at 77–104 g/MJ of diesel displaced by biodiesel. The predicted reductions in CO2 emissions are much greater than values reported in recent studies on biodiesel derived from other vegetable oils, due both to the large amount of potential fuel in the residual biomass and to the low-energy inputs in traditional coconut farming techniques. Unburned hydrocarbon emissions from biodiesel fuel combustion decrease compared to regular petroleum diesel. Biodiesel, produced from different vegetable oils, seems very interesting for several reasons: it can replace diesel oil in boilers and internal combustion engines without major adjustments; only a small decrease in performances is reported; almost zero emissions of sulfates; a small net contribution of CO2 when the whole life-cycle is considered; emission of pollutants comparable with that of diesel oil. For these reasons, several campaigns have been

Table 9 Some technical properties of fuels. Fuel property

Gasoline

Diesel no. 2

Isooctane

Methanol

Ethanol

Cetane number Octane number Auto-ignition temperature (K) Lower heating value (MJ/Kg)

– 96 644 44

50 – 588 43

– 100 530 45

5 114 737 20

8 108 606 27

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A. Demirbas / Applied Energy 86 (2009) S108–S117 Table 12 Average changes in mass emissions from diesel engines using the biodiesel mixtures relative to the standard diesel fuel (%). Mixture

CO

NOx

SO2

Particular matter

Volatile organic compounds

B20 B100

13.1 42.7

+2.4 +13.2

20 100

8.9 55.3

17.9 63.2

planned in many countries to introduce and promote the use of biodiesel [88]. The brake power of biodiesel was nearly the same as with diesel fuel, while the specific fuel consumption was higher than that of diesel fuel. Based on crankcase oil analysis, engine wear rates were low but some oil dilution did occur. Carbon deposits inside the engine were normal, with the exception of intake valve deposits. Although most researchers agree that vegetable oil ester fuels are suitable for use in CIE, a few contrary results have also been obtained. The results of these studies point out that most vegetable oil esters are suitable as diesel substitutes but that more long term studies are necessary for commercial utilization to become practical [89]. Several results related to influence of micro nutrition on yield of oil have been reported on soil changes impacts [90–94]. Suitable climatic and soil conditions have increased plant oil yields [93]. Biomethane generated from grass requires four times less land than biodiesel from rapeseed to produce the same gross energy [90]. Grass is a low-energy input crop and it is a carbon negative crop [90,91]. 8. Biofuel regulation issues in EU, including the environmental sustainability criteria Biofuel consumption in the EU is growing rapidly but major efforts will need to be undertaken if the EU’s objectives for 2010 and beyond are to be achieved. Current and future policy support therefore focuses on creating favorable economic or legal frameworks to accelerate the market penetration of biofuels. The Member States of EU will promote specific types of biofuels, depending on their main objectives and natural potentials. This will require complementary instruments such as subsidies for production facilities, user incentives or feedstock subsidies [95]. The main EU directives which have impact on sustainable energy development are directives promoting energy efficiency and use of renewable energy sources, directives implementing greenhouse gas mitigation and atmospheric pollution reduction policies and other policy documents and strategies targeting energy sector. Promotion of use of renewable energy sources and energy efficiency improvements are among priorities of EU energy policy because the use of renewable energy sources and energy efficiency improvements has positive impact on energy security and climate change mitigation [96]. In the EU climate change has been the principal policy driver for promoting the use of energy from renewable resources. The spring European Council of 2007 set ambitious targets by 2020 of a 20% reduction of greenhouse gas emissions (GHG) compared to 1990 levels, a 20% renewables share in the EU’s final energy consumption including a 10% share of biofuels in each Member State. The GHG emission savings from the use of biofuels shall be at least 35% compared to fossil fuel. On January 23, 2008, the Proposal for a Directive of the European Parliament and of the Council on the Promotion of the Use of Energy from Renewable Resources was issued. Article 15 of this proposal defined environmental sustainability criteria that both domestic and imported biofuels must satisfy. These criteria include a minimum GHG reduction requirement, limits on the types of land where conversion toward biofuel crop production is acceptable, and reinforcing best agricultural practices. The first sustainability criterion defined in the European proposal is a 35% reduction in

GHG emissions for biofuels relative to their fossil fuel counterpart. The second sustainability criterion relates to the preservation of diverse ecosystems. The greenhouse gas emission saving from the use of biofuels and other bioliquids shall be at least 35%. Biofuels and other bioliquids shall not be made from raw material obtained from highly biodiverse land and from land with high carbon stock. Agricultural raw materials cultivated in the community and used for the production of biofuels and other bioliquids shall be obtained in accordance with the requirements and standards under the provisions, and in accordance with the minimum requirements for good agricultural and environmental condition. Specifically for biofuels and bioliquids the draft directive establishes environmental sustainability criteria to ensure that biofuels that are to count towards the target are sustainable. They must achieve a minimum level of greenhouse gas emission reduction (35%) and respect a number of binding requirements related to environmental impact and biodiversity. The sustainability criteria aim to reduce greenhouse gas emissions and to prevent loss of valuable biodiversity and undesired land use changes. For the foreseeable future the EU will have to rely on first generation biofuels to achieve the 10% target in 2020: vegetable oils for biodiesel and sugar and starch crops for ethanol. These import requirements may be between 30% and 50%. The sustainability criteria under discussion in the EU constitute an important step forward notwithstanding their shortcomings. They should be implemented in a nondiscriminatory way without conferring undue competitive advantage to domestic producers and allowing developing countries export opportunities for ethanol and biomass. A speedy transition to second generation biofuels is of particular importance. Sustainability criteria should progressively ensure that only advanced biofuels are available for end-users. 9. Conclusion Today, the world is facing three critical problems: (1) high fuel prices, (2) climatic changes and (3) air pollution. Currently there are several important problems to be resolved worldwide: (1) high need for energy, (2) high depletion of non-renewable energy recourses and (3) high local and global environmental pollution [97,98]. Discussions on biofuels include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sector. The biggest difference between biofuels and petroleum feedstocks is oxygen content. Biofuels have oxygen levels from 10% to 45% while petroleum has essentially none making the chemical properties of biofuels very different from petroleum. Oxygenates are just pre used hydrocarbons having structure that provides a reasonable antiknock value [99]. Most traditional biofuels, such as ethanol from corn, wheat, or sugar beets, and biodiesel from oil seeds, are produced from classic agricultural food crops that require high-quality agricultural land for growth. Ethanol is a petrol additive/substitute. Production of ethanol from biomass is one way to reduce both the consumption of crude oil and environmental pollution. Biodiesel is an environmentally friendly alternative liquid fuel that can be used in any diesel engine without modification. There has been renewed interest in the use of vegetable oils for making biodiesel due to its less polluting and renewable nature as against the conventional petroleum diesel fuel.

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Biofuels have become more attractive recently because of its environmental benefits. Ethanol addition to gasoline has increased the engine torque, power and fuel consumption and reduced carbon monoxide (CO) and hydrocarbon (HC) emissions. In general, biodiesel increases NOx emissions when used as fuel in diesel engine. The emissions of biodiesel (B20 and B100) for same model compression–ignition (diesel) vehicles have increased from 1.86 to 2.23, respectively. The fact that NOx emissions increase with increasing biodiesel concentration could be a detriment in areas that are out of attainment for ozone. Oxygenated diesel fuel blends have a potential to reduce the emission of particulate matter (PM) and to be an alternative to diesel fuel. Biofuels production costs can vary widely by feedstock, conversion process, scale of production and region. The major economic factor to consider for input costs of biodiesel production is the feedstock, which is about 75–80% of the total operating cost. Other important costs are labor, methanol and catalyst, which must be added to the feedstock. In particular, the cost of producing oilseed-derived biodiesel is dominated by the cost of the oil and by competition from high-value uses like cooking. On an energy basis, ethanol is currently more expensive to produce than gasoline in all regions considered. Only ethanol produced in Brazil comes close to competing with gasoline. Ethanol produced from corn in the US is considerably more expensive than from sugar cane in Brazil, and ethanol from grain and sugar beet in Europe is even more expensive. The simultaneous production of biomethanol (from sugar juice) in parallel to the production of ethanol, appears economically attractive in locations where hydroelectricity is available at very low cost. Production costs for ethanol are much lower in countries with a warm climate, with Brazil probably the lowest-cost producer in the world. Production costs in Brazil, using sugar cane as the feedstock, have recently been recorded at less than half the costs in Europe. The generally larger US conversion plants produce biofuels, particularly ethanol, at lower cost than plants in Europe. Biofuels, such as ethanol and biodiesel, are two alternative fuels promoted with potential to reduce dependence on fossil fuel imports. They also have the potential to reduce GHG emissions into the atmosphere, although the extent of this reduction is still debated and depends on a variety of factors including the type of crop input used and the choice of production processes. Europe’s sustainability and biodiversity criteria related to biofuels are: The sustainability criteria aimed to ensure:     

A minimum GHG saving. Avoid loss of high biodiversity land. Avoid loss of high carbon-stock land. Environmental requirements for agriculture. Diversification of feedstocks. Biodiversity criteria aimed to ensure: No use of raw material from:

 forest undisturbed by significant human activity,  highly biodiverse grassland,  nature protection areas, unless compatible with nature protection.

References [1] Balat M. New biofuel production technologies. Energy Educ Sci Technol Part A 2009;22:147–61. [2] Demirbas C. The global climate challenge: recent trends in CO2 emissions from fuel combustion. Energy Educ Sci Technol Part A 2009;22:179–93. [3] Humbad A, Kumar S, Babu BV. Carbon credits for energy self sufficiency in rural India – a case study. Energy Educ Sci Technol Part A 2009;22:187–97.

[4] Dincer K. Lower emissions from biodiesel combustion. Energy Sources Part A 2008;30:963–8. [5] Demirbas A, Dincer K. Sustainable green diesel: a futuristic view. Energy Sources Part A 2008;30:1233–41. [6] Hacisaligoglu S. Ethanol–gasoline and ethanol–diesel fuel blends. Energy Educ Sci Technol Part A 2009;22:133–46. [7] Demirbas B. Biofuels for internal combustion engines. Energy Educ Sci Technol Part A 2009;22:117–32. [8] Balat M. An overview of biofuels and policies in the European Union. Energy Sources Part B 2007;2:167–81. [9] Demirbas A. Recent progress in biorenewable feedstocks. Energy Educ Sci Technol 2008;22:69–95. [10] Demirbas A. Economic and environmental impacts of the liquid biofuels. Energy Educ Sci Technol 2008;22:37–58. [11] Demirbas T. Overview of ethanol from biorenewable feedstocks: technology, economics, policy and impacts. Energy Educ Sci Technol Part A 2009;22: 163–77. [12] Demirbas A. Biofuels sources, biofuel policy, biofuel economy and global biofuel projections. Energy Convers Manage 2008;49:2106–16. [13] Demirbas A. Present and future transportation fuels. Energy Sources Part A 2008;30:1473–83. [14] Demirbas A. New liquid biofuels from vegetable oils via catalytic pyrolysis. Energy Educ Sci Technol 2008;21:1–59. [15] Demirbas A. Bio-fuels from agricultural residues. Energy Sources, Part A 2008;30:101–9. [16] Sigar CP, Soni SL, Mathur J, Sharma D. Performance and emission characteristics of vegetable oil as diesel fuel extender. Energy Sources Part A 2009;31:139–48. [17] Demirbas A. The sustainability of combustible renewables. Energy Sources Part A 2008;30:1114–9. [18] Keskin A. Biodiesel production from free fatty acids obtained with neutralization of the crude glycerin. Energy Sources Part A 2009;31:17–24. [19] Demirbas A. Alternatives to petroleum diesel fuel. Energy Sources Part B 2007;2:343–51. [20] Chhetri AB, Islam MR. Towards producing a truly green biodiesel. Energy Sources Part A 2008;30:754–64. [21] Demirbas A. Progress and recent trends in biodiesel fuels. Energy Convers Manage 2009;50:14–34. [22] Kong L, Li G, Zhang B, He W, Wang H. Hydrogen production from biomass wastes by hydrothermal gasification. Energy Sources Part A 2008;30: 1166–78. [23] Demirbas A. Biohydrogen generation from organic wastes. Energy Sources Part A 2008;30:475–82. [24] Balat M. Hydrogen-rich gas production from biomass via pyrolysis and gasification processes and effects of catalyst on hydrogen yield. Energy Sources Part A 2008;30:552–64. [25] Demirbas A. Hydrogen production from carbonaceous solid wastes by steam reforming. Energy Sources Part A 2008;30:924–31. [26] Balat M. Possible methods for hydrogen production. Energy Sources Part A 2009;31:39–50. [27] Demirbas A. Biomethanol production from organic waste materials. Energy Sources Part A 2008;30:565–72. [28] Demirbas A. Conversion of corn stover to chemicals and fuels. Energy Sources Part A 2008;30:788–96. [29] Demirbas A. The importance of ethanol and biodiesel from biomass. Energy Sources Part B 2008;3:177–85. [30] Balat M. Progress in biogas production processes. Energy Educ Sci Technol 2008;22:15–36. [31] Demirbas A. Partial hydrogenation effect of moisture contents on combustion heats of oils via pyrolysis from biomass. Energy Sources Part A 2008;30: 508–15. [32] Bothast RJ. New technologies in biofuel production. Agricultural Outlook Forum (AOF), February, 24, 2005. . [33] Demirbas A. Biodegradability of biodiesel and petrodiesel fuels. Energy Sources Part A 2009;3:169–74. [34] Balat M. Biodiesel fuel production from vegetable oils via supercritical ethanol transesterification. Energy Sources Part A 2008;30:429–40. [35] Demirbas A. Production of biodiesel from algae oils. Energy Sources Part A 2009;31:163–8. [36] Demirbas A. Oils from hazelnut shell and hazelnut kernel husk for biodiesel. production. Energy Sources Part A 2008;30:1870–5. [37] Ilkilic C, Yucesu HS. The use of cottonseed oil methyl ester on a diesel engine. Energy Sources Part A 2008;30:742–53. [38] UN (United Nations). The emerging biofuels market: regulatory, trade and development implications. United Nations conference on trade and development, New York and Geneva, 2006. [39] Demirbas A. Biodiesel production via rapid transesterification. Energy Sources Part A 2008;30:1830–4. [40] Lv P, Wang X, Yuan Z, Tan T. Conversion of soybean oil to biodiesel fuel with immobilized Candida lipase on textile cloth. Energy Sources Part A 2008;30: 872–9. [41] Demirbas MF. Pyrolysis of vegetable oils and animal fats for the production of renewable fuels. Energy Educ Sci Technol 2008;22:59–67. [42] Ma F, Hanna MA. Biodiesel production: a review. Bioresour Technol 1999;70: 1–15.

A. Demirbas / Applied Energy 86 (2009) S108–S117 [43] Zhang Y, Dub MA, McLean DD, Kates M. Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresour Technol 2003;90:229–40. [44] Balat M. Production of biodiesel from vegetable oils: a survey. Energy Sources Part A 2007;29:895–913. [45] Utlu Z. Evaluation of biodiesel fuel obtained from waste cooking oil. Energy Sources Part A 2007;29:1295–304. [46] Puppan D. Environmental evaluation of biofuels. Periodica Polytechnica Ser Soc Man Sci 2002;10:95–116. [47] Demirbas A. Biodiesel fuels from vegetable oils via catalytic and non-catalytic supercritical alcohol transesterifications and other methods: a survey. Energy Convers Manage 2003;44:2093–109. [48] Air Resources Board, California Environmental Protection Agency. Study of CNG and diesel transit bus emissions. Air Resources Board; 2002. . [49] Ozkurt I. Qualifying of safflower and algae for energy. Energy Educ Sci Technol Part A 2009;23:145–51. [50] Ayala A, Kado NY, Okamoto A, Holmén BA, Kuzmicky PA, Kobayashi R, Stiglizt KE. Diesel and CNG heavy-duty transit bus emissions over multiple driving schedules: regulated pollutants and project overview. SAE technical paper, 2002-01-1722. [51] Macedo IC, Seabra JEA, Silva JEAR. Green house gases emissions in the production and use of ethanol from sugarcane in Brazil: the 2005/2006 averages and a prediction for 2020. Biomass Bioenergy 2008;32: 582–95. [52] Kim H, Choi B. Effect of ethanol–diesel blend fuels on emission and particle size distribution in a common-rail direct injection engine with warm-up catalytic converter. Renew Energy 2008;33:2222–8. [53] Yu S, Tao J. Simulation based life cycle assessment of airborne emissions of biomass-based ethanol products from different feedstocks planting areas in (the) PRC. J Cleaner Prod 2009;17:501–6. [54] Ozkurt I. Qualifying of safflower and algae for energy. Energy Educ Sci Technol Part A 2009;23:145–51. [55] Najafi G, Ghobadian B, Tavakoli T, Buttsworth DR, Yusaf TF, Faizollahnejad M. Performance and exhaust emissions of a gasoline engine with ethanol blended gasoline fuels using artificial neural network. Appl Energy 2009;86: 630–9. [56] Rakopoulos DC, Rakopoulos CD, Kakaras EC, Giakoumis EG. Effects of ethanol– diesel blends on the performance and exhaust emissions of heavy duty DI diesel engine. Energy Convers Manage 2008;49:3155–62. [57] Lapuerta M, Armas O, Herreros JM. Emissions from a diesel–ethanol blend in an automotive diesel engine. Fuel 2008;87:25–31. [58] Graham LA, Belisle SL, Baas CL. Emissions from light duty gasoline vehicles operating on low blend ethanol gasoline and E85. Atmos Environ 2008;42:4498–516. [59] Corro G, Ayala E. Ethanol and diesel/ethanol blends emissions abatement. Fuel 2008;87:3537–42. [60] Granda CB, Zhu L, Holtzapple MT. Sustainable liquid biofuels and their environmental impact. Environ Prog 2007;26:233–50. [61] EPA (US Environmental Protection Agency). A comprehensive analysis of biodiesel impacts on exhaust emissions. Draft technical report, EPA420-P-02001, October 2002. [62] Balat M, Balat H. A critical review of bio-diesel as a vehicular fuel. Energy Convers Manage 2008;49:2727–41. [63] Haas MJ, McAloon AJ, Yee WJ, Foglia TA. A process model to estimate biodiesel production costs. Bioresour Technol 2006;97:671–8. [64] Dene T, Hole J. Enabling biofuels: biofuel economics. Final report. Auckland, New Zealand: Minister of Transport, Covec Ltd.; June 2006. [65] Renewable Fuels Association (RFA). Ethanol Industry Statistics, Washington (DC, USA); 2007. [66] Grassi G. Modern bioenergy in the European Union. Renew Energy 1999;16: 985–90. [67] Urbanchuk JM. Economic impacts on the farm community of cooperative ownership of ethanol production, LECG, LLC, Wayne, PA, February 13, 2007. . [68] Dufey A. Biofuels production, trade and sustainable development: emerging issues. Environmental Economics Programme, Sustainable Markets Discussion Paper No. 2, International Institute for Environment and Development (IIED), London, September, 2006. [69] Whims J. Corn based ethanol costs and margins. Attachment 1, AGMRC, Kansas State U, 2002. ].

S117

[70] IEA (International Energy Agency). Biodiesel statistics. IEA energy technology essentials, OECD/IEA, Paris, January; 2007. [71] Bender M. Economic feasibility review for community-scale farmer cooperatives for biodiesel. Bioresour Technol 1999;70:81–7. [72] Tzirakis E, Karavalakis G, Zannikos F, Stournas S. Impact of Diesel/biodiesel blends on emissions from a diesel vehicle operated in real driving conditions. SAE technical paper, 2007-01-0076. [73] Janulis P. Reduction of energy consumption in biodiesel fuel life cycle. Renewable Energy 2004;29:861–71. [74] Krahl J, Knothe G, Munack A, Ruschel Y, Schröder O, Hallier E, et al. Comparison of exhaust emissions and their mutagenicity from the combustion of biodiesel, vegetable oil, gas-to-liquid and petrodiesel fuels. Fuel 2009;88:1064–9. [75] Soltic P, Edenhauser D, Thurnheer T, Schreiber D, Sankowski A. Experimental investigation of mineral diesel fuel, GTL fuel, RME and neat soybean and rapeseed oil combustion in a heavy duty on-road engine with exhaust gas aftertreatment. Fuel 2009;88:1–8. [76] Coronado CR, de Carvalho Jr JA, Silveira JL. Biodiesel CO2 emissions: a comparison with the main fuels in the Brazilian market. Fuel Process Technol 2009;90:204–11. [77] Demirbas AH. Inexpensive oil and fats feedstocks for production of biodiesel. Energy Educ Sci Technol Part A 2009;23:1–13. [78] Demirbas A. Modernization of biomass energy conversion facilities. Energy Sources Part B 2007;2:227–35. [79] Demirbas A. Theoretical heating values and impacts of pure compounds and fuels. Energy Sources, Part A 2006;28:459–67. [80] Jenkins BM, Baxter LL, Miles Jr TR, Miles TR. Combustion properties of biomass. Fuel Process Technol 1998;54:17–46. [81] Laforgia D, Ardito V. Biodiesel fuelled IDI engines: performances, emissions and heat release investigation. Bioresour Technol 1994;51:53–9. [82] Cardone M, Prati MV, Rocco V, Senatore A. Experimental analysis of performances and emissions of a diesel engines fuelled with biodiesel and diesel oil blends. In: Proceedings of MIS–MAC V, Roma; 1998. p. 211–25 [in Italian]. [83] Dorado MP, Ballesteros EA, Arnal JM, Gomez J, Lopez FJ. Exhaust emissions from a Diesel engine fueled with transesterified waste olive oil. Fuel 2003;82:1311–5. [84] Dunn RO. Alternative jet fuels from vegetable-oils. Trans ASAE 2001;44: 1151–757. [85] Shay EG. Diesel fuel from vegetable oils: status and opportunities. Biomass Bioenergy 1993;4:227–42. [86] US Environmental Protection Agency (EPA). A comprehensive analysis of biodiesel impacts on exhaust emissions. Draft technical report, EPA420-P-02001, October 2002. [87] Carraretto C, Macor A, Mirandola A, Stoppato A, Tonon S. Biodiesel as alternative fuel: experimental analysis and energetic evaluations. Energy 2004;29:2195–211. [88] Demirbas A. Global biofuel strategies. Energy Educ Sci Technol 2006;17:27–63. [89] Thamsiriroj T, Murphy JD. Is it better to import palm oil from Thailand to produce biodiesel in Ireland than to produce biodiesel from indigenous Irish rape seed? Appl Energy 2009;86:595–604. [90] Tilman D, Hill J, Lehman C. Carbon-negative biofuels from low-input high diversity grassland biomass. Science 2006;314:1598–600. [91] Thamsiriroj T. Optimal biomass and technology for production of biofuel as a transport fuel. Master Thesis, University College Cork; 2007. [92] Rasamee-thamawong P. Oil palm: sustainable energy production for the future. Bangkok: Petchkarat Publishing; 2007. [93] Nithedpattrapong S, Srikul S, Korawis C, Onthong J. Influence of N, P, K and Mg on yield of oil palm grown on Kohong soil series. Thai Agric Res J 1995;13:164–74. [94] Wiesenthal T, Leduc G, Christidis P, Schade B, Pelkmans L, Govaerts L, et al. Biofuel support policies in Europe: lessons learnt for the long way ahead. Renew Sust Energy Rev 2009;13:789–800. [95] Streimikiene D, Šivickas G. The EU sustainable energy policy indicators framework. Environ Int 2008;34:1227–40. [96] Demirbas A. Energy concept and energy education. Energy Educ Sci Technol Part B 2009;1:85–101. [97] Demirbas A. Future energy sources: part I. Future Energy Source 2009;1:1–95. [98] Ulusarslan D, Gemici Z, Teke I. Currency of district cooling systems and alternative energy sources. Energy Educ Sci Technol Part A 2009;23:31–53. [99] Kan A. General characteristics of waste management: a review. Energy Educ Sci Technol Part A 2009;23:55–69.