Liquid Biofuels

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Biofuels are liquid fuels produced from biomass feedstock through different chemical or biological processes. Today, biomass is the only available renewable source for producing high-value liquid biofuels such as ethanol or biodiesel. These fuels can offer renewable alternatives to transportation fuels that presently are obtained almost exclusively from oil. Ethanol, the most common biofuel, is produced by fermentation of annually grown crops (sugar cane, corn, grapes, etc.). In this process, starch or carbohydrates (sugars) are decomposed by microorganisms to produce ethanol. Ethanol can be produced from a wide variety of sugar or starch crops, including sugar beet and sugar cane and their byproducts, potatoes and corn surplus. In Russia after the Bolshevik revolution, Lenin proposed the use of agricultural alcohol to produce industrial fuels and products. This diversion amounted to the use of Russian people's beloved source of vodka, however, the plan was soon abandoned. During World War II in Europe, blends of ethanol with gasoline were used, but only anhydrous ethanol is miscible, with gasoline phase separation otherwise causing stalling of the engines. Ethanol has been promoted and used more recently extensively in Brazil and the United States as a response to the OPEC oil embargoes and rising gasoline prices (but also to subsidize farmers). Beginning in that period, Brazil - one of the largest sugar cane producers in the world - gave farmers financial incentives to switch from sugar to ethanol production. This plan was implemented, and by the mid-1990s about 4.5 million vehicles were running on pure ethanol, and the remainder of the fleet on a blend of gasoline containing up to 24% ethanol by volume. With falling oil prices and the end of price subsidies for ethanol at the end of the 1990s however, the sales of pure ethanol cars fell almost to zero [60, 61] (Fig. 8.12). Increasing oil prices, experienced in the recent past, have now revived interest in ethanol. The production of ethanol from sugar cane in Brazil reached some 15 million m3 per year in 2004 [62]. The extraordinarily high productivity of

Brazil Automobile Production Total
Figure 8.12 Percentage of ethanol-powered Source: Associa^ao Nacional dos Fabricantes automobile produced in Brazil compared to de Veículos Automotores ANFAVEA, Brazilian the country's total automobile production. Automotive Industry Yearbook 2005.

sugar cane (up to 80 t cane per hectare, compared to 10-20 t for most plants cultivated under temperate climates), associated with low wages, has contributed to a great extent to the competitiveness of ethanol in Brazil. So-called flexible fuel vehicles (FFV), able to run on any mixture of gasoline and ethanol, have also been introduced recently. However, it must be pointed out that the amount of ethanol produced annually in Brazil represents only the equivalent of some 7-8 million tonnes of petroleum oil, less than the quantity consumed by the world in a single day. Besides alcohol, sugar cane byproducts - principally bagasse (sugarcane husk) - are burned to supply Brazil's grid with about 600 MW of electricity [63]. This again, is less than the output of a single large-scale fossil fuel or atomic power plant.

In the United States, ethanol produced from corn is used in gasohol, a blend of 10% ethanol and 90% gasoline, as well as an oxygenated additive in gasoline since the early 1980s (Fig. 8.13). However, ethanol is only economically competitive because of a significant tax subsidy (currently $0.54 per gallon). Growing corn for ethanol production is also very energy-intensive because of the need and cost of fertilizing, harvesting, and transporting the corn, as well as subsequent fermentation and distillation which requires large amounts of energy that are generally provided from oil and natural gas. It should be emphasized that, in fact, ethanol produced from corn produces at most only 25 -35% more energy than was consumed in its production [64, 65]. Indeed, some claims state that the process is a net energy user [66-68]. In any case, corn used for ethanol production is far from an ideal feedstock, though dedicated energy crops and new genetically engineered crops could increase the energy efficiency. Utilization of the cellulose content of plants, which is resistant to fermentation, to produce ethanol has in the past only been possible by prior hydrolysis with sulfuric acid. Currently, the

Figure 8.13 Historic production of ethanol Sao Paulo Sugarcane Agroindustry Union in the United States and Brazil. Based on data (UNICA). from Renewable Fuel Association and

development of new strains of microorganisms capable of digesting cellulose directly is being explored, and this may allow the use of other types of vegetation with lower production costs to be processed to ethanol, making the overall process cheaper and more efficient.

Biodiesel, processed from seed crops such as rape, sunflower and soy, are currently mainly produced in Europe and the United States on a limited scale (Fig. 8.14). Market penetration is small and the production costs relatively high, although interest is growing. In 2004, biodiesel represented less than 1% of the 270 Mt fuel (gasoline and diesel fuel) consumed by road transport in Europe [69, 70]. The direct use of plant oils in diesel engines is not recommended as it will considerably reduce the engine's lifetime. This drawback has been mitigated by reacting these oils with methanol or ethanol in a so-called transesterification process to yield commercial biodiesel. Biodiesel can be blended without major problems with regular diesel oil in any proportion. The production of biodiesel is also less energy-intensive than ethanol from corn because no fermentation and distillation is necessary. However, biodiesel from oil seed crops requires up to five times more land per unit of energy produced than ethanol.

Methanol was once produced from wood, and is therefore sometimes still referred to as wood alcohol. This process (called pyrolysis) was still being used at the beginning of the 20th century, and involves the heating of wood in the absence of air to yield a mixture of solid, liquid, and gaseous products from which methanol could be extracted in low yields. Today, methanol is predomi-

Figure 8.14 Production of biodiesel in Europe. Source: European Biodiesel Board and Eurobserver.

nantly produced by steam reforming of methane (natural gas) and subsequent reaction of the produced syn-gas to methanol. However, any source of carbonaceous material could be converted to syn-gas and thus methanol. This includes also biomass which could therefore become a source of methanol in the future.

Biomass as an energy source has many advantages. It is renewable, provides a convenient way of storing energy (e.g., in the form of wood), which is not the case for wind or solar energy, and it can be found in different forms all over the world. It can reduce the energy-dependence on foreign countries. Biomass is also versatile as it includes solid fuels such as wood or crop residues, liquid biofuels such as ethanol, and biodiesel, as well as gaseous fuels in the form of biogas or syn-gas. From an environmental point of view, biomass can help mitigate climate change, as the CO2 released by use of bioenergy is captured from the atmosphere by the growing plants and should therefore induce no net CO2 emissions (it is carbon neutral). On the other hand, the conversion of solar energy to biomass is only achieved at an efficiency of around 1%, which is very low even compared to the inefficient conversion of solar energy to electricity with solar cells (in excess of 10%). In order to generate bioenergy on a large scale, vast areas of land are necessary. Also, great care must be taken in choosing crops for energy production, as these should have a high photosynthetic efficiency, grow rapidly, use minimal amounts of fertilizers, herbicides and insecticides, and have limited water needs to minimize energy input into their cultivation. These "energy crops" should also preferably be grown on land not dedicated to food crops in order to avoid competition with food production. The vast expanses of the seas can also be used to grow algae, which can be utilized to produce bioenergy, and experimental facilities in the United States and Japan have explored this possibility. With the present technology, a large part of the world's agricultural land would have to be devoted to energy crops if they were to supply a substantial amount of our energy needs. Even if the use of bioenergy could be cost-effective in certain cases for the production of heat and electricity, it has generally higher costs than conventional energy sources. An economical and sustainable large-scale use of this resource will therefore require technological advances or breakthroughs, especially in the bioengineering field to design suitable high-yield energy crops. In the transportation sector, the production of cellulose-based ethanol and other liquid fuels, particularly methanol through biomass gasification, will allow a higher yield per unit of land [71]. Algae grown in the sea might also eventually extend the scope of bioenergy.

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Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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