Biodiesel
Biodiesel is non-flammable and non-explosive (flash point 150°C for biodiesel and 64°C for petrodiesel). It is biodegradable and non-toxic.
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2 Fuel quality, standards and properties 3 Production 4 Availability 5 Oil preparation 6 Biodiesel recipe 7 See also 8 External links |
Transesterification of a vegetable oil was conducted as early as
1853, by scientists E. Duffy and J. Patrick, many years before the first diesel engine became functional.
Rudolf Diesel's prime model, a single 10 ft (3 m) iron cylinder with a flywheel at its base, ran on its own power for the first time in Augsburg, Germany on August 10, 1893. In remembrance of this event, August 10 has been declared International Biodiesel Day. Diesel later demonstrated his engine at the World Fair in Paris, France in 1898. This engine stood as an example of Diesel's vision because it was powered by peanut oil—a biofuel. He believed that the utilization of a biomass fuel was the real future of his engine.
In a 1912 speech, Rudolf Diesel said, "the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the coal-tar products of the present time."
During the 1920s, diesel engine manufacturers created a major challenge for the biofuel industry. Diesel engines were altered to utilize the lower viscosity of the fossil fuel (petrodiesel) rather than a biomass fuel (vegetable oil). The petroleum industries were growing and establishing themselves during this period.
Some see a conspiracy here and argue that the business tactics and the wealth that many of these "oil tycoons" already possessed greatly influenced the development of all engines and machinery. The alteration was the first step in the elimination of the production infrastructure for biomass fuels. Some see this as the first step in forcing the concept of biomass as a potential fuel base into obscurity, erasing the possibilities from the public awareness.
However, others have pointed out that fossil diesel is simply cheaper than vegetable oil, and that no conspiracy is necessary to explain the move toward fossil fuels.
In the 1990s, France launched the production of biodiesel fuel (known locally as diester) obtained by the transesterification of rapeseed oil. It is mixed to the proportion of 5% into regular diesel fuel, and to the proportion of 30% into the diesel fuel used by some captive fleets (public transportation). Renault, Peugeot and other manufacturers have certified truck engines for use with up to 30% biodiesel. Experiments with 50% biodiesel are underway.
Biodiesel is a clear amber-yellow liquid with a viscosity similar to petrodiesel (the industry term for diesel produced from petroleum). Much of the world uses a system known as the "BD factor" to state the amount of biodiesel in any fuel mix, in contrast to the "BA" system used for bioalcohol mixes. For example, 20% biodiesel is labeled BD20. Pure biodiesel, 100%, is referred to as BD100. In the United States, a similar system is used, but the "D" is dropped (B100, B20, B5, etc.).
The international standard for biodiesel is ISO 14214. In Germany, the requirements for biodiesels are fixed in a DIN standard. There are three different sorts of biodiesel, which is made of different oils:
In a study at a U.S. military base, a biodiesel blend was used as a replacement for heating oil at housing on the base. Due to the solvent power of biodiesel, residues that had been present in fuel tanks for decades were dissolved. The particulate component of the residues caused repeated clogging of fuel strainers, requiring repeated replacement, cleaning, and in some cases installation of higher capacity filters. Due to the relatively smaller surface area and service life of fuel tanks in motor vehicles and mobile equipment, filter clogging is less prevalent but still a factor to be considered.
Properties necessary for biodiesel to ensure trouble-free operation in diesel engines are:
History
Fuel quality, standards and properties
Biodiesel can be mixed with petroleum diesel at any concentration in most modern engines, although it has the disadvantage of degrading rubber gaskets and hoses in older vehicles (prior to 1992). Biodiesel is a better solvent than petrodiesel and has been known to break down deposits of residue in fuel lines of vehicles that usually run on petroleum. Fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made, but the biodiesel cleans the engine in the process.
The basic industrial tests includes gas chromatography that verifies only the really more important variables (glycerides,...). More complete testings cost more.
Pure biodiesel (BD100 or B100) can be used in any petroleum diesel engine, though it is more commonly used in lower concentrations. Some areas that have mandated ultra-low sulfur diesel (ULSD) petroleum, which changes the natural viscosity of the fuel because certain materials have been removed. Additives are required to make it properly flow in engines, and biodiesel is one popular alternative. Ranges as low as 2% (BD2 or B2) have been shown to restore lubricity. Also, many municipalities have started using 5% biodiesel (BD5 or B5) in snow-removal equipment and other systems.
Biodiesel can be produced from biolipids. These include:
Production
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. A 1998 joint study by the U.S. Department of Energy (DOE) and the U.S. Department of Agriculture (USDA) traced many of the various costs involved in the production of biodiesel and found that overall, it yields 3.2 units of fuel product energy for every unit of fossil fuel energy consumed.
Some nations and regions that have pondered transitioning fully to biofuels have found that doing so would require immense tracts of land. It is likely that the United States, which uses more energy per capita than any other country, does not have enough arable land to fuel all of the nation's vehicles. Other developed and developing nations are in better situations, although many regions cannot afford to divert land away from food production.
For third world countries, biodiesel sources that use marginal land could make more sense, e.g. honge nuts grown along roads. Biodiesel can use waste vegetable oil, but alternative uses for WVO compete with its use as biodiesel, making large scale conversion of WVO to biodiesel more expensive than petrodiesel.
The direct source of the energy content of biodiesel is solar energy captured by plants during photosynthesis. The website biodiesel.co.uk discusses the positive energy balance of biodiesel:
- When straw was left in the field, biodiesel production was strongly energy positive, yielding 1 GJ biodiesel for every 0.561 GJ of energy input (a yield/cost ratio of 1.78).
- When straw was burned as fuel and oilseed rapemeal was used as a fertilizer, the yield/cost ratio for biodiesel production was even better (3.71). In other words, for every unit of energy input to produce biodiesel, the output was 3.71 units (the difference of 2.71 units would be from solar energy).
Biodiesel is becoming of interest to companies interested in commercial scale production as well as the more usual home brew biodiesel user and the user of straight vegetable oil or waste vegetable oil in diesel engines. Homemade biodiesel processors are many and varied.
Biodiesel is commercially available in most oilseed-producing states in the U.S. At this time, it is considerably more expensive than fossil diesel, though it is still commonly produced in relatively small quantities (in comparison to petroleum products and ethanol). 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. Similarly, some agribusinesses and others with ties to oilseed farming use biodiesel for public relations reasons. In 2003 some tax credits are available in the U.S. for using biodiesel. In 2002 almost 3.5 million gallons (13,000 m³) of commercially produced biodiesel were sold in the U.S., up from less than 0.1 million gallons (380 m³) in 1998. Due to increasing pollution control requirements and tax relief, the U.S. market is expected to grow to 1 or 2 billion gallons by 2010. The price of biodiesel has come down from an average $3.50/gallon ($0.92/L) in 1997 to $1.85 ($0.49/L) a gallon in 2002. However this is still higher than petrodiesel which averaged about $0.85 ($0.22/L) a gallon in 2002 before road tax is added.
Biodiesel processor machines, need the vegetable oil to have some specific properties:
Like a recipe for making a cake, a biodiesel recipe specifies quantity of every ingredient required, and the steps for combining and processing them to make biodiesel fuel.
The most common recipe uses waste vegetable oil (WVO), alcohol (methanol or ethanol) and sodium hydroxide (caustic soda), to produce biodiesel and glycerol. To produce 1 t of biodiesel:
Transestrification is crucial for producing biodiesel from biolipids. The transesterification process is the reaction of a triglyceride (fat/oil) with an bioalcohol to form esters and glycerol.
The reaction may be shown
CH2COOR1
Since we are dealing with nature, the alkyl group on the triglycerides are probably different, so it would actually be more like
CH2OC=OR1
During the esterification process, the triglyceride is reacted with alcohol in the presence of a catalyst, usually a strong alkaline (NaOH, KOH or sodium silicate). The main reason for doing a titration to produce biodiesel, is to find out how much alkaline is needed to insure a complete transesterfication. 6.25 g / l NaOH produces a very usable fuel. One uses about 6g NaOH when the WVO is light in colour and about 7g NaOH when it is dark in colour.
The alcohol reacts with the fatty acids to form the mono-alkyl ester (or biodiesel) and crude glycerol. The reaction between the biolipid (fat or oil) and the alcohol is a reversible reaction so the alcohol must be added in excess to drive the reaction towards the right and ensure complete conversion.
You want to mix the base (KOH,NaOH) with the alcohol to make a reactive anion
KOH + ROH -> RO- + H2O
KOH and NaOH are strong bases, so the reaction equilibrium is far to the right.
The ROH needs to be very dry. Any water in the alcohol will reduce the amount of RO- that gets formed.
The RO- is a reactive guy, so you must be very careful with this stuff. Often in chemistry alcohols are mixed with KOH to make a "base bath" for cleaning glass. It actually dissolves the surface of the glass, so be really careful with this stuff.
Once the RO- group is formed, it is added to the triglyceride. The Sn2 reaction that follows replaces the alkyl group on the tricglyceride in a series of reactions.
The carbon on the ester of the triglyceride has a slight positive charge, and the oxygens have a slight negative charge, most of which is located on the oxygen in the double bond. This charge is what attracts the RO- to the reaction site
This yields a transition state that has a pair of electrons from the C=O bond now located on the oxygen that was in the C=O bond.
These electrons then fall back to the carbon and push off the glycol forming the ester.
Then 2 more RO's react via this mechanism at the other 2 C=O groups. This type of reaction has several limiting factors. RO- has to fit in the space where there is a slight positive charge on the C=O. So MeO- works well because it is small. As the R on RO- gets bigger, reaction rates decrease. This effect is called steric hinderance. That is why methanol and ethanol are typically used.
There are several competing reactions, so care must be taken to ensure the desired reaction pathway occurs. Most methods do this by using an excess of RO-.
The acid catalysed method is a slight variance, but is also affected by steric hinderance.
Availability
Oil preparation
Biodiesel recipe
The most common steps are:
There are three basic routes to biodiesel production from biolipids (biological oils and fats):
Almost all biodiesel is produced using base catalyzed transesterification as it is the most economical process requiring only low temperatures and pressures and producing a 98% conversion yield. For this reason only this process will be described bellow.Reaction
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CHCOOR1 + 3 CH3OH ↔ (CH2OH)2CH-OH + 3 CH3COO-R1
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CH2COOR1
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CHOC=OR2 + 3 CH3OH ↔
(CH2OH)2CH-OH + CH3COO-R1 + CH3COO-R2 + CH3OC=O-R1
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CH2COOR3
R1, R2, R3 : Alkyl group.Base catalysed Mechanism
R1
backside attack |
RO- -----------------> C=O
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O-CH2-CH-CH2-O-C=O
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O-C=O R3
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R2
R1
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RO-C-O- (pair of electrons)
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O-CH2-CH-CH2-O-C=O
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O-C=O R3
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R2
R1
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RO-C=O
+
-O-CH2-CH-CH2-O-C=O
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O-C=O R3
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R2
Process
The reaction mix is kept just above the boiling point of the alcohol (around 70 ÃÂðC) to speed up the reaction and the reaction takes place. Recommended reaction time varies from 1 to 8 hours, and some systems recommend the reaction take place at room temperature. Excess alcohol is normally used to ensure total conversion of the fat or oil to its esters.See also
External links