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Advantages and Disadvantages of Biodiesel

Updated on March 21, 2011

Biodiesel is a biofuel, that is a fuel made from renewable sources such as vegetable oils and animal fats, similar to petroleum-derived diesel

Contrary to popular belief, biodiesel is a simple and pure vegetable oil such as canola oil, but the result of a chemical process (transesterification with methanol) from these or other biological components.


Fuel quality, specifications and properties


Biodiesel is a biofuel, liquid, transparent and amber colored, made entirely from vegetable oil (rapeseed, sunflower or other), with a viscosity similar to diesel fuel obtained by fractional distillation of crude oil. For the identification of mixtures will be used in scoring BD (similar to BA for mixtures containing bio-alcohol). Pure biodiesel is assigned the symbol BD100, mixtures a number corresponding to the percentage of biodiesel (eg, diesel BD20 for a cut of 20% biodiesel). In the U.S., scoring is similar, but without the D (B100, B20, B50, etc.).


The international standard specifications for biodiesel are set out in ISO 14214. The United States also refer to the ASTM D 6751. Germany to a special DIN specification identifies three types of biodiesel:


                RME (rapeseed oil methyl ester - DIN E 51606)


               PME (vegetable oil methyl ester alone - DIN E 51606)


               FME (methyl esters of vegetable and animal fats - DIN V 51606)


The specifications set some important points in the process of biodiesel production:


        completeness of the reaction

        removal of glycerol

        removal of the catalyst

       removal of the alcohol

       absence of free fatty acids

Compliance with these characteristics is generally verified by gas chromatography.


The fuel obtained according to these quality levels is very low toxicity, the lethal dose LD50 is greater than 50 ml / kg, ten times higher than that of common salt.


Biodiesel can be blended with diesel in any proportion and used in modern diesel engines, although some older vehicles manufacturing are subject to a degradation of rubber tubes and joints due to the greater solvent power than petroleum diesel, in this case The rubber can then be dissolved by biodiesel or deposits clog the supply lines of the vehicle. The adoption of more resistant tires on vehicles of recent manufacture (since 1992) should have solved this problem, in addition the greater solvent power of biodiesel helps keep the engine clean by dissolving residues may be present.


Since biodiesel is more often used mixed with diesel oil, there is less information and formal studies on the effects of pure biodiesel on engines and non-modified vehicles currently in use, but we do not expect major problems in the use of biodiesel pure with the current engines, at least until all the engine parts are compatible with its greater solvent power.


In any diesel engine can use biodiesel (or B100 BD100), although more commonly used diesel fuel with lower concentrations of biodiesel. Used as an additive to diesel fuel, improves lubricity. In some areas it is required to use ultra-low sulfur diesel, which reduces the natural viscosity of the fuel and lubricating oils have been removed as sulfur and certain other substances. To make it flow properly in the engines of additives are required, and biodiesel is a popular alternative. Concentrations up to 2% (BD2 or B2) have been shown capable of restoring lubrication. Also, many municipalities have started using the biodiesel to 5% (BD5 or B5) in the media for the removal of snow and other systems.


The melting point of biodiesel is affected by the nature and amount of foreign contains. However, most biodiesel products - including that obtained from soya oil - have a melting point higher than that of diesel fuel that requires, especially in areas with winter climates, the heating of storage tanks.


Biodiesel has a cetane number higher than that of diesel fuel caught fire so easily when it is injected into the engine. Compared to diesel is not explosive, with a flash point placed at 150 ° C to 64 ° C biodiesel compared with diesel. Unlike diesel, is biodegradable and nontoxic, and significantly reduces toxic emissions when burned as fuel.


Environmental impact


From an environmental perspective, biodiesel has some differences compared to diesel:


Compared with diesel, reduces net emissions of carbon monoxide (CO) by approximately 50% and 78.45% of carbon dioxide because the carbon released during its combustion is the one that was already present in the atmosphere and the plant has established during its growth and not, as in case of diesel, carbon that was trapped in ancient times the earth's crust. Here should be considered in energy consumption during cultivation of the raw material, processing and transport.


Practically does not contain aromatic hydrocarbons, emissions of aromatic condensed ring (eg benzopyrenes) are reduced by up to 71%.


It has no emissions of sulfur dioxide (SO2), since it does not contain sulfur.


Reduces the emission of particulate matter up to 65%.


Produces more emissions of nitrogen oxides (NOx), diesel fuel, which can be inconvenient content redesigning the diesel exhaust and equipping of special catalysts.




The biofuel industry continues to record double-digit growth rates and is increasingly the focus of international geopolitical agreements. In parallel, however, also raise other issues. The impact of the spread of agrofuel monocultures on biodiversity and in relation to other food crops. The coordinator for the energy of the FAO, Gustavo Best notes that, in case of uncontrolled growth of the sector, the high profits of the new chain could cause a mass exodus of players and a resulting shortfall in local food production. A particularly high risk in developing countries in the third and fourth world.


Many economists believe that the production of biofuels is causing poverty and world hunger, because it deprives poor countries, which base their economy on the primary sector, sonstanziose amount of food necessary for the survival of the less affluent social classes. In the world there is a sufficient supply of agricultural land (0.11 hectares per capita, source FAO) to produce food for 6 billion people and a significant amount of biofuels for cars (see the various releases of the FAO which is said to concern about the 'impact of biofuels on food availability).


Crops in semi-arid and desert land with the technologies that we have in the future can support a growing of plants which produce biofuels, especially where governments are committed to applying innovative solutions for sustainable development. Meanwhile, the FAO index of prices of basic food items has reached its historical peak (2010) and also why in 2011 in North Africa broke numerous revolts.




The transesterification of vegetable oil was conducted as early as 1853, by scientists E. Duffy and J. Patrick, many years before the first diesel engine became functional. The first model of Rudolf Diesel, a single iron cylinder with a 3-meter fly at the base, worked for the first time in Augsburg (Germany) August 10, 1893. In commemoration of this event, August 10 was declared International Biodiesel Day. Diesel then presented his engine at the World Exhibition in Paris in 1898. This engine stood as an example of Diesel's vision because it was powered by peanut oil - a biofuel, though not strictly biodiesel, since it was trans. Diesel believed that the use of a fuel from biomass to be the real future of his engine. In a speech in 1912 said "the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, over time, as important as petroleum and coal of our day."


During the twenties, the diesel engine manufacturers altered their engines to take advantage of the lower viscosity of the fossil fuel (petrodiesel) to the detriment of the vegetable oil. The petroleum industries were able to make inroads in fuel markets because their product was cheaper to produce than the alternatives derived from biomass. The result was, for many years, the almost complete elimination of the infrastructure of production of biomass fuel. Only recently, concerns about the environmental impact and decrease the cost differential made biomass fuels as a viable alternative.


In the nineties, France launched the local production of biodiesel (known locally as diester) obtained by transesterification of rapeseed oil. Is mixed in proportion of 5% in regular diesel fuel, and the proportion of 30% in diesel fuel by means of some fleets (public transportation). Renault, Peugeot and other manufacturers have certified truck engines for use with this partial biodiesel., Experiments are underway to employ a 50% biodiesel.


From 1978 to 1996, the National Renewable Energy Laboratory (NREL) U.S. pioneered the use of algae as source of biodiesel, in dell'Aquatic Species Program. The experiments of NREL, which lasted 16 years, are now completed as the research program has not been subsequently rolled.



Chemically, biodiesel is a fuel composed of a mixture of alkyl esters of long chain fatty acids. A lipid transesterification process is used to convert the base oil in the summer and wanted to remove free fatty acids. After this procedure, as opposed to simple vegetable oil, biodiesel has combustion properties and viscosity similar to diesel derived from petroleum and can replace most of its uses.

The most common production process uses methanol to produce methyl esters, but can also be used as ethanol, thus obtaining a mixture of ethyl esters biodiesel. As a byproduct, the process of transesterification is obtained by glycerol.

Base Oils


A variety of biolipidi can be used to produce biodiesel. These include:


Virgin vegetable oils, rapeseed oil or soya bean is the most commonly used, although other crops such as mustard, palm oil and algae are promising;


Waste vegetable oil;


Animal fats.


Many advocates suggest that the waste vegetable oil is the best source of oil for biodiesel production. However, the available supplies are significantly less than the amount of petroleum fuel that is burned for transportation and home heating throughout the world. According to the Environmental Protection Agency (EPA) U.S. restaurants produce about 13.6 million U.S. gallons (3 million gallons) of waste cooking oil per year, while for example in Italy we consume annually 39 billion liters of diesel and gasoline.


Even if it is economically advantageous to use waste vegetable oils to produce biodiesel, is even more profitable use to convert them into products such as soap. Therefore, most vegetable oils, waste is not thrown into landfill, but used for other purposes. Animal fats have similar limitations in the availability, would not be effective and raise animals only for their fat. However, producing biodiesel with animal fat that would otherwise be discarded could replace a small percentage of petroleum diesel.


To have a truly renewable source of oil, crops should be considered appropriate. Plants use photosynthesis to convert the energy of the sun into chemical energy. Part of this chemical energy is stored in the biodiesel and released when burned. The result is that plants could provide a sustainable source for biodiesel production. Here is an estimate of the average production of some plants (in cubic meters per square kilometer)


Soy: 40 to 50


Mustard: 130


Rapeseed: 100 to 140


Palm Oil: 610


Algae: from 1.000 to 2.000


The cultivation of unicellular algae to extract oil for biodiesel has not yet been undertaken commercially, but studies to evaluate its effectiveness have come to Italy to give yields of 10-20 tons per year of pure vegetable oil and then biodiesel per hectare . Specially selected varieties of mustard can produce reasonably high amount of oil, and have the added value of being able to use some of the waste production as a biodegradable pesticide.


The soy beans are not an efficient source for the production of biodiesel, but because the United States there is widespread availability of soybean, which is used for human consumption even after the extraction of oil, soya has become the primary source of biodiesel.


There are areas of research to find crops with a higher yield of oil, but with current technology, vast areas of land should be put into production to get enough oil to replace the current use of fossil fuels, competing with food crops or otherwise exposing additional areas of soil erosion and the risk of desertification.


Domestic production


With seed oil


The seed oil has a viscosity of 70-80 cSt, instead of 2 / 6 cSt fuel oil. Prolonged use of seed oil in diesel engines designed or modified constituting a serious damage of the injection (pump and injectors, which are left on the carbon deposits, sludge, or gums). However, if you use a mixture of vegetable oil in a small percentage compared to diesel pumps and injectors for the risks are greatly reduced and the engine can run for many tens of thousands of kilometers without any problems.


The only way to bring the vegetable oil density values comparable to diesel is a transesterification reaction (ie conversion of an ester into another ester) that break the molecules of triglyceride oil components in smaller chains and then more fluid: the basic molecule of the original triglyceride, consisting of one molecule of glycerol and three fatty acid molecules is converted by transesterification (a triglyceride molecule "oil" + three methanol molecules) in 3 + 1 molecules methyl glycerol molecule. This process is used industrially for the production of biodiesel, whose technical name is EMV (vegetable methyl ester).


The procedure involves the use of absolute methyl alcohol (ie methanol) as reagent and sodium hydroxide as a catalyst that facilitates the reaction. The reaction stoichiometry is never real and tends to an equilibrium that forces you to use excess reagents to obtain a complete reaction.


The recipe with methanol plans to follow the pattern:


x liters of fresh oil


0.2 ° x liters of methanol


3.5 ° x grams of sodium hydroxide (NaOH, the proportions are about 0.2 liters of methanol and 3.5 g of sodium hydroxide (NaOH) per liter of fresh oil).


The use of methanol in the domestic production requires much more, both because it usually has no biological origin, and because it is much more toxic than ethanol. With ethanol instead must use more catalyst (7g/litro oil against 3.5 g / liter methanol) and we also need a greater amount of alcohol (27.5% versus 20% of the oil with methanol ).


The rules provide that the first process to mix alcohol with the catalyst. Then combine the mixture and oil, at a temperature between 35 and 60 ° C (optimum at 45-50 ° C) shaking for about an hour.


With cooking oil


If you are using as fuel oil from the fried food is good to submit it to the same procedure. With oil not too used to the total dose of NaOH is approximately 6.25 g / l. It should, however, a surplus of soda to remove residues of food and water vapor. This rate of soda can be calculated with the titration.


At the end of the reaction the biodiesel is washed with water to remove residual hazardous to the health of the engine: free fatty acids, mono-and di-glycerides, soaps, methanol and caustic soda, etc..


Efficiency and economy


Currently, the costs of biodiesel production sometimes make them competitive on price than diesel, but the current world production of animal fats and vegetable oils needed to produce it is not sufficient to replace fossil fuels, if not in small part. Some environmental groups fear a massive increase in pesticide use and an uncontrolled use of land to meet increased demand for vegetable oils to be used in the production of biodiesel.


Thermodynamic efficiency


In addition to evaluating the energy balance for the entire product life cycle, from sowing to combustion, it is important to note that the theoretical and actual thermodynamic efficiency of biofuels is lower than that of the conventional petrol and diesel as well. In other words, a liter of biofuel is far from 15-20 km / liter, which is possible with the normal diesel. Always using a diesel engine, the same then, and percentage of heat loss in transmitted power to the wheels, the power supplied by the combustion of one liter of biofuel is less than that produced elsewhere. The calorific value of bio-fuel is lower. If emissions are lower per liter, it is true that to have the same speed and performance, serve a larger amount of biofuel.


Methane has a lower cost and a much higher energy efficiency (it is used for gas turbine and combined), while emissions are comparable.




To assess whether the energy expenditure to produce a liter of biodiesel makes sense (that is, whether it is consumed less than one liter of fuel to produce one liter of biodiesel), it is necessary to refer to concepts such as EROEI (ratio of energy produced (obtained) and energy expended (invested)).


Is commonly regarded as energy efficiency (EROEI) of biodiesel a value of about 3 which means that the pure point of view of energy with the energy of a liter of biodiesel are obtained after a year of growing three liters of biodiesel. Just does not pass a year to get three gallons of biodiesel from a liter but passes a number of years equal to the Energy Pay Back ratio of biodiesel.


Nell'EROEI are not counted but the economic costs are counted only the energies, then the salaries of the farmers are not considered. A value of energy yield of 3 is a value much lower dell'EROEI a wind farm (20-30) or the oil (10-100) but is acceptable for agricultural cultivation.


According to a study prepared by Drs. Van Dyne and Raymer for the Tennessee Valley Authority, the average American consumes fuel for farmers to an extent of 82 liters per hectare (8.75 U.S. gallons per acre) of land for the production of a crop. But the oil needed for crops is not limited to the one used by tractors, that is why we use the concept of EROEI to include the energy to manufacture chemical fertilizer, pesticides, herbicides, to produce tractors, etc., etc..


The same study estimated a harvest American standard of rapeseed oil to produce an average of 1,029 l / ha (110 U.S. gal / acre), while a crop of the same high-yield seeds produces about 1,356 L / ha (145.0 U.S. gal / acre). In Italy, the average production of biodiesel from rapeseed and sunflower equal to 966 liters per hectare (850 kg / ha).


The cultivation of oil plants are obtained many important and useful products (protein, biomass for heating, etc.) that make it useful biodiesel production over the value of his hero.


Biodiesel from palm oil may have HEROES best while that of micro algae can not be determined because there are no facilities for the calculation dell'EROEI. Please note that the EROEI vine calculated on existing plants.


The return was determined by comparison with the energy equal to 3 at other plants in the case of biodiesel.


The article by David and Tad, however, neglects the production of materials from recycled vegetable oils such as vegetable waste, agricultural waste processing, and so on. In this case, the advantage is that the disposal produces a raw material, and destroyed or stored only represent a cost, then any gain, although small, is better than nothing.


Efficiency of the algae


Studies on a kind of seaweed with an oil content of up to 50% have concluded that it may be enough just 28,000 km ² of the U.S. (corresponding to 0.3% of total) needed to produce biodiesel to replace all the fuel in transport which is currently used in the country. Other studies have shown that to replace the entire U.S. oil imports (about 12 million barrels per day) takes about 36 million acres (360,000 km ², 4% of U.S. territory) whereas the best yields for microalgae (20,000 liters of biodiesel per hectare). Further encouragement comes from the fact that the land most suited to the growth of algae have characteristics like high desert sunshine, and with low economic value for any other use, and you could use agricultural waste and excess CO2 produced industries to speed the growth of the algae themselves.


A recent paper by Michael Briggs of the University of New Hampshire Biodiesel Group, offers estimates for the replacement of all fuel for vehicles with biobiesel, using algae have an oil content above 50%.


Critics say there is no large-scale testing on algae, there are no known diseases that afflict when you have a monoculture extended, you do not have the cost of the plant to produce biodiesel from algae. In the area of intensive agricultural production is no longer used the manure and had to dip into a costly research, chemical pest control and fertilizing. Critics wonder whether there will be similar to algae or new requirements for high yields.


In a document of the National Renewable Energy Laboratory, "American publish some disadvantages of micro algae as the fuel cost double the hypothesis of production whereas" aggressive ", the need to make CO2 bubbling in the tanks, the problem of heating the pools of culture in the desert at night and other problems. However, the production of oil and then biodiesel is excellent and it comes with a quantity 30 times greater than that grow oil on soil


This ratio is the sum of the results achieved and it was done because the DOE (Department of Energy) decided to cut U.S. funding for projects relating to the biodiesel from algae after 16 years of studies to devote its funds to assumptions most promising


A Spanish company based in Britain said they were ready for 2007 to produce a continuous oil phytoplankton to be processed into biodiesel, said that after three years of research is ready for production in quantity. There are no known prices of the raw material produced.


The direct source of the energy content of biodiesel is solar energy captured by plants through photosynthesis. The efficiency of fotosistesi of higher plants is around 1 percent against such an efficiency of 12% and 50% of the experimental solar panels, while the yield observed in the experiments with the unicellular algae has been around 6%, and theoretically it is believed, however, can not exceed 11%.


This means that with the best biodiesel (that obtained from seaweed), it takes more than extensions of land (double, triple or quadruple) the photovoltaic panels that necessary to achieve the same amount of energy. Unlike photovoltaic But biodiesel has the advantage of not producing waste (the panels are made with polluting materials), require a more sustainable technology and is a constant source (solar panels because they wear out with age, losing efficiency) .




Biodiesel is attracting the interest of companies oriented to production for trade on a large scale, as has happened in general for those using biodiesel, home made directly or vegetable oil (pure or waste) in diesel engines . There are many types, having various characteristics of bio-refineries craft.

Of interest for the production of biodiesel is the BTL (biomass to liquid), ie the transformation of bio-based materials into liquid fuel. For many it is now called second-generation biodiesel SunDiesel or, as he called the German company that developed the new technology (Choren Industries).

The production of biodiesel in Italy, was a quota for 2005 to 200,000 tons, because the manufacturing cost is higher than that of diesel is tax-free and to make it competitive.


A growing number of service stations are making biodiesel available to consumers and a growing number of large transport companies use a percentage of biodiesel in their fuel.

In Italy biodiesel is not available at service stations, but can be mixed with diesel in the refinery (up to 7%) to improve the lubricity.

In the U.S. the price of gasoline without taxes (20%) was in August 2005 amounted to $ 84 a barrel [8] ($ 0.66 / l), and biodiesel from agriculture was subsidized by the very American, has a price in 2001 ranged between 55 excluding taxes and $ 63 per barrel (0.34 to 0.40 USD / l).

According to a source in 2004 the Australian government, non-subsidized biodiesel at a cost of $ 97 per barrel (0.80 AUSD / gal). Since August 2005, oil was $ 58 per barrel can be calculated roughly that an oil price of around 67USD/bar lead for the Americans in the break-even price of biodiesel and non-subsidized fuel oil. This type of speech is valid if the biodiesel does not hold its price on the oil market, that is if the two prices are independent, something that experts doubt.

Biodiesel is commercially available in most vegetable oils producing states of the United States. It is currently significantly more expensive than fossil fuel, but it is still generally produced in relatively small quantities (in comparison with the products of petroleum and ethanol). Many farmers producing oilseeds used in principle a mixture of biodiesel for tractors and machinery, to help stimulate the production of biodiesel and public opinion. It is generally easier to find biodiesel in rural areas than in cities. Similarly, some farmers and people generally associated with the production of biodiesel using oilseed for reasons related to public relations.For 2003, the United States have been granted tax breaks for the use of biodiesel. In 2002, nearly 3.5 million U.S. gallons (13,000 m³) of commercially produced biodiesel were sold in the United States, a significant increase compared to the total of 0.1 million U.S. gallons (380 m³) in 1998. Because raising the requirements of pollution control and tax benefits, it is expected that the use of biodiesel in the United States will increase to 1 to 2 billion U.S. gallons (4 million to 8 million cubic meters) by 2010. The price of biodiesel has dropped from an average of $ 3.50 per U.S. gallon ($ 0.92 / l) in 1997 to $ 1.85 per U.S. gallon ($ 0.49 / l) in 2002, but is usually more expensive than petrodiesel in oil-producing countries (in 2002, the United States, before the introduction of the "road tax", the average price of diesel was about $ 0.85 per U.S. gallon, $ 0.22 per liter).

Financial aspects


The price per quintal of wheat, flour and cereals, in Europe and the USA, are fixed by a competent authority decides that a political price, otherwise the raw material for biofuels, obtains a market price. Barclays Bank was working on a project to open a futures market for biofuels, which would be in addition to similar existing markets for grain and cereals. A market of this type could play both speculative effects of price stabilization. Biofuels are standardized products, low unit value and become a large consumer goods: in these respects is comparable to a "commodity", which enjoys a large market and maybe in the future of a stable price. The unknown factor is the supply of the product, and for the commodity in general exceeds the requirements.



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