Biotechnology for Biofuels

Abstract

Ethanol is a biofuel that is used as a replacement for approximately 3% of the fossil-based gasoline consumed in the world today. Most of this biofuel is produced from sugarcane in Brazil and corn in the United States. We present here the rationale for the ethanol program in Brazil, its present 'status' and its perspectives. The environmental benefits of the program, particularly the contribution of ethanol to reducing the emission of greenhouse gases, are discussed, as well as the limitations to its expansion. Introduction Fuel-grade ethanol, produced from biomass, has been considered as a suitable automotive fuel for nearly a century, particularly for vehicles equipped with spark-ignition engines (technically referred to as Otto cycle engines, but commonly known as gasoline engines). Ethanol was not used in significant amounts until the mid 1970s. The dramatic increase in the cost of oil at the time of the first oil crisis imposed severe foreign exchange burdens on countries dependent upon oil imports, including Brazil. As a leading producer of sugar from sugarcane, Brazil was well situated to explore the option of ethanol as an alternative to gasoline. This led the Government to encourage the redirection of some sugarcane production to generate ethanol as a replacement for gasoline, thus reducing oil imports. Under the Brazilian Government's plan, PETROBRAS, the state-owned oil company, would purchase a guaranteed amount of ethanol from producers. In addition, economic incentives were given to agro-industrial enterprises willing to produce ethanol, in the form of low interest rates. This translated into nearly US$2.0 billion in loans from 1980 to 1985, representing 29% of the total investment needed [1]. On the basis of such policies, ethanol production increased rapidly over the years, reaching 18 billion liters in 2007. Ethanol from sugarcane, produced under proper conditions, is essentially a renewable fuel and has clear advantages over gasoline in reducing greenhouse gas emissions and improving air quality in metropolitan areas. In this paper we review the technological characteristics of ethanol as a fuel, the present 'status' of the ethanol Program in Brazil, the characteristics of ethanol as a renewable fuel, the future perspectives of the ethanol Program in Brazil followed by a discussion on the possibility of expanding ethanol production from sugarcane and conclusions. Technical characteristics of ethanol as a fuel Ethanol is an excellent motor fuel. It has a motor octane number of 98 which exceeds that of gasoline (octane number of 80). It also has a lower vapor pressure than gasoline, which results in lower evaporative emissions. Ethanol's flammability in air is also lower than that of gasoline which reduces the number and severity of vehicle fires. Anhydrous ethanol has lower and higher heating Published: 1 May 2008 Biotechnology for Biofuels 2008, 1:6 doi:10.1186/1754-6834-1-6 Received: 12 March 2008 Accepted: 1 May 2008 This article is available from: http://www.biotechnologyforbiofuels.com/content/1/1/6 © 2008 Goldemberg; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Biotechnology for Biofuels 2008, 1:6 http://www.biotechnologyforbiofuels.com/content/1/1/6 Page 2 of 7 (page number not for citation purposes) values of 21.2 and 23.4 MJ/liter, respectively; for gasoline the values are 30.1 and 34.9 MJ/liter (see [2]). On the basis of higher heating value, ethanol has only 67% of the energy content compared with the same volume of gasoline. However, since it has a motor octane number higher than gasoline, it can be used in engines with a higher compression ratio (12-to-1, compared with the 8-to-1 ratio typically found in gasoline-fueled engines). As a result, ethanol-fueled engines are approximately 15% more efficient than motors using gasoline, which compensates to some extent for the lower energy content per unit volume [3]. Typically, one would require approximately 20% more ethanol than gasoline per kilometer driven. In Brazil ethanol was used initially in one of two ways: • blended as an octane enhancer in gasoline; typical blends range from 20% to 25% anhydrous (a mixture called gasohol; anhydrous ethanol is 99.6% ethanol GayLussac (GL) which express the percentage of alcohol in a blend) and 0.4% water; ethanol in fuel by volume, or • on its own, in neat-ethanol engines; used in the form of hydrous ethanol at 95.5 GL. Ethanol's properties (as a fuel) have led to the development of dedicated engines for neat ethanol in Brazil. Initial efforts were conducted by the Centro de Tecnologia Aeronáutica (CTA) in São Paulo state, where most of the tests with engines running with ethanol-gasoline blend and straight ethanol were performed up to 1980 [3]. In the early 1980s, vehicles with neat-ethanol engines that could use hydrous ethanol became highly attractive to consumers, as the government had ensured the pump price of hydrous alcohol would be equivalent to 64.5% of the gasoline price. Sales of neat-ethanol powered vehicles exploded, and the market share occupied by these vehicles increased to more than 90% of all vehicle sales. The total fleet of neat-ethanol fueled vehicles at one point reached 5 million. Most of the service stations were equipped with two reservoirs (one for anhydrous ethanol, and the other for ethanol-gasoline blends at 20% to 25% ethanol). The lack of a guarantee of ethanol production to supply this expanding market became a critical issue, and in the early 1990s a shortage in ethanol production led to a serious crisis and a gradual abandonment of the use of neat-ethanol driven cars. There were other problems associated with neat-ethanol vehicles, including the problem of not being able to use them in neighboring countries or in regions of Brazil which did not have service stations capable of supplying pure ethanol. The introduction of flex-fuel motors in Brazil, in 2003, solved this problem, since they are capable of running with blends from E0 to E100. The technology is based on sensors in the fuel system that automatically recognizes the ethanol level in the fuel. The engine's electronic control unit then self-calibrates for the best possible operation; if ethanol is not present, the engine will self-calibrate to gasoline-only operation. The process is instantaneous and undetectable by the vehicle driver. Present 'status' of the ethanol program in Brazil Presently there are 325 plants in operation crushing 425 million tons of sugarcane per year, approximately onehalf being used for sugar and the other half for ethanol production. Approximately 17.8 billion liters of ethanol were produced in 2006, using 2.9 million hectares of land (Table 1). A typical plant crushes 2 million tons of sugarcane per year and produces 200 million liters of ethanol per year (1 million liters per day over 6 months, April to November) and costs approximately US$150 million. The planted area required to supply the sugarcane is typically 30,000 hectares. Most of the large plants are located in the state of São Paulo, where almost two-thirds of the ethanol is being produced. This state is located at a distance from the Amazonia region, as shown in Figure 1. Ethanol production in Brazil was initiated with a highly subsidized program. The price paid to producers in 1980 was US$700 for 1000 liters; over the intervening years, gains in technology and economies of scale have driven the cost down, reaching as low as US$200 per 1000 liters in 2004 (Figure 2). By 2004, ethanol in Brazil had become economically competitive with gasoline based on international prices Table 1: Ethanol distilleries in Brazil [15] (147 new distilleries are in the planning stages, 86 of which due to be completed up to 2015). Distilleries (units) Cane crushed (millions of tons) Average size (million tons) Brazil (total) 325 425 1.3 São Paulo 148 264 (62% of total) 1.8 Northeast 74 53 0.7 Biotechnology for Biofuels 2008, 1:6 http://www.biotechnologyforbiofuels.com/content/1/1/6 Page 3 of 7 (page number not for citation purposes) for oil (equivalent to US$40 per barrel). At these costs, the production of ethanol from sugarcane is much cheaper that from other crops such as corn, wheat and sugarbeet (Table 2) Characteristics of ethanol as a renewable fuel The impact of alcohol engines on air pollution Presently all gasoline used in Brazil is blended with 25% anhydrous ethanol, a fuel with lower toxicity than fossil fuels [3]. Lead additives to gasoline were reduced through the 1980s as the amount of ethanol blended in the fuel was increased, and these additives were completely eliminated by 1991. The additions of aromatic hydrocarbons (such as benzene), which are particularly toxic, were also eliminated, and the sulfur content was reduced (in vehicles using blended fuel) or eliminated (in neat-ethanol fueled vehicles) [3]. The addition of ethanol instead of lead to gasoline has lowered the total carbon monoxide (CO), hydrocarbons and sulfur emissions significantly. Exhaust emissions associated with ethanol are less toxic than those associated with gasoline, and have lower atmospheric reactivity [4]. The use of ethanol has also reduced CO emissions drastically. Before the Brazilian Alcohol Program started, when gasoline was the only fuel in use, CO emissions were higher than 50 g/km driven; they had been reduced to less than 5.8 g/km in 1995. Lead ambient concentrations in São Paulo Metropolitan Region dropped from 1.4 μg/m3 in 1978 to less than 0.10 μg/m3 in 1991, according to CETESB (the Environmental Company of São Paulo State), which is far below the air quality standard of 1.5 μg/m3 (see [5]). One of the drawbacks of the use of hydrous ethanol in neat-ethanol engines is the inc