Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl (methyl, ethyl, or propyl) esters. Biodiesel is typically made by chemically reacting lipids (e.g., vegetable oil, soybean oil, animal fat (tallow)) with an alcohol producing fatty acid esters.

Biodiesel is meant to be used in standard diesel engines and is thus distinct from the vegetable and waste oils used to fuel converted diesel engines. Biodiesel can be used alone, or blended with petrodiesel in any proportions. Biodiesel blends can also be used as heating oil.

The National Biodiesel Board (USA) also has a technical definition of “biodiesel” as a mono-alkyl ester.

Biodiesel has promising lubricating properties and cetane ratings compared to low sulfur diesel fuels. Fuels with higher lubricity may increase the usable life of high-pressure fuel injection equipment that relies on the fuel for its lubrication. Depending on the engine, this might include high pressure injection pumps, pump injectors (also called unit injectors) and fuel injectors.

The calorific value of biodiesel is about 37.27 MJ/kg. This is 9% lower than regular Number 2 petrodiesel. Variations in biodiesel energy density is more dependent on the feedstock used than the production process. Still, these variations are less than for petrodiesel. It has been claimed biodiesel gives better lubricity and more complete combustion thus increasing the engine energy output and partially compensating for the higher energy density of petrodiesel.

The color of biodiesel ranges from golden to dark brown, depending on the production method. It is slightly miscible with water, has a high boiling point and low vapor pressure. The flash point of biodiesel exceeds 130 °C (266 °F), significantly higher than that of petroleum diesel which may be as low as 52 °C (126 °F). Biodiesel has a density of ~0.88 g/cm³, higher than petrodiesel (~0.85 g/cm³).

Biodiesel contains virtually no sulfur, and it is often used as an additive to Ultra-Low Sulfur Diesel (ULSD) fuel to aid with lubrication, as the sulfur compounds in petrodiesel provide much of the lubricity.

Compatibility with materials

It is compatible with high density polyethylene. When PVC degrades slowly. Some polymers dissolve them in direct contact.

It affects materials based on copper, it also attacks zinc, tin, lead and cast iron. The materials of stainless steel and aluminum are immune.

Biodiesel breaks down the natural rubber of some old engine components.

When biodiesel cools to a certain point, some molecules aggregate and form crystals. The fuel begins to “cloud” once the crystals become large (a quarter of the wavelength of visible light). This point is called cloud point. The colder the fuel, the bigger the crystals. The lowest temperature at which biodiesel passes through a 45 micron filter is called the cold filter clogging point (CFPP). At lower temperatures the biodiesel becomes gel and then solidifies. Within Europe, there is a lot of difference in this point between countries. The temperature at which pure biodiesel begins to gel depends on the mixture of esters and, consequently, on the raw material used. For example, if it is produced from sebum, it tends to become gel near 16 ° C.

There are many additives that are added to biodiesel to lower this temperature. Another solution is to mix biodiesel with diesel or kerosene. Another is to have a secondary tank of biodiesel accompanying that of diesel oil: the first starts and heats the second, and once the necessary temperature is reached, the feed is changed.

Water pollution
Biodiesel can contain small amounts of water, but they are problematic. Although biodiesel is not miscible with water, it is hygroscopic like ethanol, that is, it absorbs water from atmospheric humidity. One of the reasons why the biodiesel is hygroscopic is the persistence of mono and diglycerides left over from an incomplete reaction. These molecules can act as an emulsifier, allowing the water to mix with the biodiesel. On the other hand, there may be residual water due to the treatment or as a result of condensationof the storage tank. The presence of water is a problem because:

Water reduces the heat of combustion of bulk fuel. This means more smoke, greater difficulties in starting, lower energy efficiency.
Water causes corrosion of the vital components of the fuel system: fuel pumps, injection pumps, fuel lines, etc.
Water and the accompanying microbes clog and spoil paper filters for fuel, which in turn results in premature failure of the fuel pump due to the ingestion of large particles.
The water freezes to form ice crystals near 0 ° C (32 ° F). These crystals provide sites for nucleation and accelerate the gelling of the residual fuel.
Water accelerates the growth of microbial colonies, which can clog the fuel system. There are reports of biodiesel users who have heated the fuel tanks to deal with the problem of microbes.
In addition, water can cause pitting on the pistons of a diesel engine.

Synthesis reactions
The process of transesterification consists of combining the oil (usually vegetable oil) with a light alcohol, usually methanol, and leaving as a residue of added value propanotriol (glycerin) that can be used by the cosmetic industry, among others.

The fats of animals and plants are typically made of triglycerides, which are esters of free fatty acids with glycerol. In the process, alcohol is deprotonated (removed from a hydrogen cation of a molecule) with a base to form a nucleophile (anion with a free pair of electrons) stronger. Ethanol and methanol are commonly used. As seen in the diagram, the reaction has no reactants other than triglyceride and alcohol.

Under normal environmental conditions, the reaction may or may not occur very slowly. Heat is used to accelerate the reaction, in addition to an acid or a base. It is important to note that the acid or base are not consumed during the reaction, that is, they are catalysts. Almost all biodiesel is produced from virgin vegetable oils using a base as a catalyst because it is the most economical method, requiring low temperatures and pressures and obtaining a conversion of 98%. However, there are other methods that use acids likecatalysts that are slower.

During the esterification process, the triglyceride reacts with an alcohol in the presence of a catalyst, generally strong hydroxides (NaOH or KOH). The purpose of doing an acid-base titration is to know how much base is needed to neutralize all the free fatty acids and then complete the reaction.

Transesterification using bases
In this case, the transesterification is carried out through the reaction mechanism known as nucleophilic substitution in the acyl, using a strong base, capable of deprotonating the alcohol, as a catalyst. Commonly, the base is dissolved in alcohol to disperse it in all the oil. The hydroxide must be very dry: any amount of water in the process increases the chances of saponification, and produce soaps consuming the base. Once the mixture of alcohol and base is made, is added to the triglyceride.

The atom of carbon of the carbonyl group of the ester of triglyceride supports a positive charge density and the atom of oxygen of the carbonyl group more electronegative, has a higher charge density, with which the link is polarized . This polarization of the C = O group results in the alkoxide anion (RO-) attacking the positive center of the bond.

Blends of biodiesel and conventional hydrocarbon-based diesel are products most commonly distributed for use in the retail diesel fuel marketplace. Much of the world uses a system known as the “B” factor to state the amount of biodiesel in any fuel mix:

100% biodiesel is referred to as B100
20% biodiesel, 80% petrodiesel is labeled B20
5% biodiesel, 95% petrodiesel is labeled B5
2% biodiesel, 98% petrodiesel is labeled B2

Blends of 20% biodiesel and lower can be used in diesel equipment with no, or only minor modifications, although certain manufacturers do not extend warranty coverage if equipment is damaged by these blends. The B6 to B20 blends are covered by the ASTM D7467 specification. Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. Blending B100 with petroleum diesel may be accomplished by:

Mixing in tanks at manufacturing point prior to delivery to tanker truck
Splash mixing in the tanker truck (adding specific percentages of biodiesel and petroleum diesel)
In-line mixing, two components arrive at tanker truck simultaneously.
Metered pump mixing, petroleum diesel and biodiesel meters are set to X total volume, transfer pump pulls from two points and mix is complete on leaving pump.

Fuel efficiency
The power output of biodiesel depends on its blend, quality, and load conditions under which the fuel is burnt. The thermal efficiency for example of B100 as compared to B20 will vary due to the differing energy content of the various blends. Thermal efficiency of a fuel is based in part on fuel characteristics such as: viscosity, specific density, and flash point; these characteristics will change as the blends as well as the quality of biodiesel varies. The American Society for Testing and Materials has set standards in order to judge the quality of a given fuel sample.

One study found that the brake thermal efficiency of B40 was superior to traditional petroleum counterpart at higher compression ratios (this higher brake thermal efficiency was recorded at compression ratios of 21:1). It was noted that, as the compression ratios increased, the efficiency of all fuel types – as well as blends being tested – increased; though it was found that a blend of B40 was the most economical at a compression ratio of 21:1 over all other blends. The study implied that this increase in efficiency was due to fuel density, viscosity, and heating values of the fuels.

Fuel systems on some modern diesel engines were not designed to accommodate biodiesel, while many heavy duty engines are able to run with biodiesel blends up to B20. Traditional direct injection fuel systems operate at roughly 3,000 psi at the injector tip while the modern common rail fuel system operates upwards of 30,000 PSI at the injector tip. Components are designed to operate at a great temperature range, from below freezing to over 1,000 °F (560 °C). Diesel fuel is expected to burn efficiently and produce as few emissions as possible. As emission standards are being introduced to diesel engines the need to control harmful emissions is being designed into the parameters of diesel engine fuel systems. The traditional inline injection system is more forgiving to poorer quality fuels as opposed to the common rail fuel system. The higher pressures and tighter tolerances of the common rail system allows for greater control over atomization and injection timing. This control of atomization as well as combustion allows for greater efficiency of modern diesel engines as well as greater control over emissions. Components within a diesel fuel system interact with the fuel in a way to ensure efficient operation of the fuel system and so the engine. If an out-of-specification fuel is introduced to a system that has specific parameters of operation, then the integrity of the overall fuel system may be compromised. Some of these parameters such as spray pattern and atomization are directly related to injection timing.

One study found that during atomization, biodiesel and its blends produced droplets were greater in diameter than the droplets produced by traditional petrodiesel. The smaller droplets were attributed to the lower viscosity and surface tension of traditional diesel fuel. It was found that droplets at the periphery of the spray pattern were larger in diameter than the droplets at the center. This was attributed to the faster pressure drop at the edge of the spray pattern; there was a proportional relationship between the droplet size and the distance from the injector tip. It was found that B100 had the greatest spray penetration, this was attributed to the greater density of B100. Having a greater droplet size can lead to inefficiencies in the combustion, increased emissions, and decreased horse power. In another study it was found that there is a short injection delay when injecting biodiesel. This injection delay was attributed to the greater viscosity of Biodiesel. It was noted that the higher viscosity and the greater cetane rating of biodiesel over traditional petrodiesel lead to poor atomization, as well as mixture penetration with air during the ignition delay period. Another study noted that this ignition delay may aid in a decrease of NOx emission.

Emissions are inherent to the combustion of diesel fuels that are regulated by the U.S. Environmental Protection Agency (E.P.A.). As these emissions are a byproduct of the combustion process, in order to ensure E.P.A. compliance a fuel system must be capable of controlling the combustion of fuels as well as the mitigation of emissions. There are a number of new technologies being phased in to control the production of diesel emissions. The exhaust gas recirculation system, E.G.R., and the diesel particulate filter, D.P.F., are both designed to mitigate the production of harmful emissions.

A study performed by the Chonbuk National University concluded that a B30 biodiesel blend reduced carbon monoxide emissions by approximately 83% and particulate matter emissions by roughly 33%. NOx emissions, however, were found to increase without the application of an E.G.R. system. The study also concluded that, with E.G.R, a B20 biodiesel blend considerably reduced the emissions of the engine. Additionally, analysis by the California Air Resources Board found that biodiesel had the lowest carbon emissions of the fuels tested, those being ultra-low-sulfur diesel, gasoline, corn-based ethanol, compressed natural gas, and five types of biodiesel from varying feedstocks. Their conclusions also showed great variance in carbon emissions of biodiesel based on the feedstock used. Of soy, tallow, canola, corn, and used cooking oil, soy showed the highest carbon emissions, while used cooking oil produced the lowest.

While studying the effect of biodiesel on diesel particulate filters, it was found that though the presence of sodium and potassium carbonates aided in the catalytic conversion of ash, as the diesel particulates are catalyzed, they may congregate inside the D.P.F. and so interfere with the clearances of the filter.[clarification needed] This may cause the filter to clog and interfere with the regeneration process. In a study on the impact of E.G.R. rates with blends of jathropa biodiesel it was shown that there was a decrease in fuel efficiency and torque output due to the use of biodiesel on a diesel engine designed with an E.G.R. system. It was found that CO and CO2 emissions increased with an increase in exhaust gas recirculation but NOx levels decreased. The opacity level of the jathropa blends was in an acceptable range, where traditional diesel was out of acceptable standards. It was shown that a decrease in Nox emissions could be obtained with an E.G.R. system. This study showed an advantage over traditional diesel within a certain operating range of the E.G.R. system.

As of 2017, blended biodiesel fuels (especially B5, B8, and B20) are regularly used in many heavy-duty vehicles, especially transit buses in US cities. Characterization of exhaust emissions showed significant emission reductions compared to regular diesel.

Material compatibility
Plastics: High-density polyethylene (HDPE) is compatible but polyvinyl chloride (PVC) is slowly degraded. Polystyrene is dissolved on contact with biodiesel.
Metals: Biodiesel (like methanol) has an effect on copper-based materials (e.g. brass), and it also affects zinc, tin, lead, and cast iron. Stainless steels (316 and 304) and aluminum are unaffected.
Rubber: Biodiesel also affects types of natural rubbers found in some older engine components. Studies have also found that fluorinated elastomers (FKM) cured with peroxide and base-metal oxides can be degraded when biodiesel loses its stability caused by oxidation. Commonly used synthetic rubbers FKM- GBL-S and FKM- GF-S found in modern vehicles were found to handle biodiesel in all conditions.

Technical standards
Biodiesel has a number of standards for its quality including European standard EN 14214, ASTM International D6751, and others.

Low temperature gelling
When biodiesel is cooled below a certain point, some of the molecules aggregate and form crystals. The fuel starts to appear cloudy once the crystals become larger than one quarter of the wavelengths of visible light – this is the cloud point (CP). As the fuel is cooled further these crystals become larger. The lowest temperature at which fuel can pass through a 45 micrometre filter is the cold filter plugging point (CFPP). As biodiesel is cooled further it will gel and then solidify. Within Europe, there are differences in the CFPP requirements between countries. This is reflected in the different national standards of those countries. The temperature at which pure (B100) biodiesel starts to gel varies significantly and depends upon the mix of esters and therefore the feedstock oil used to produce the biodiesel. For example, biodiesel produced from low erucic acid varieties of canola seed (RME) starts to gel at approximately −10 °C (14 °F). Biodiesel produced from beef tallow and palm oil tends to gel at around 16 °C (61 °F) and 13 °C (55 °F) respectively. There are a number of commercially available additives that will significantly lower the pour point and cold filter plugging point of pure biodiesel. Winter operation is also possible by blending biodiesel with other fuel oils including #2 low sulfur diesel fuel and #1 diesel / kerosene.

Another approach to facilitate the use of biodiesel in cold conditions is by employing a second fuel tank for biodiesel in addition to the standard diesel fuel tank. The second fuel tank can be insulated and a heating coil using engine coolant is run through the tank. The fuel tanks can be switched over when the fuel is sufficiently warm. A similar method can be used to operate diesel vehicles using straight vegetable oil.

Contamination by water
Biodiesel may contain small but problematic quantities of water. Although it is only slightly miscible with water it is hygroscopic. One of the reasons biodiesel can absorb water is the persistence of mono and diglycerides left over from an incomplete reaction. These molecules can act as an emulsifier, allowing water to mix with the biodiesel. In addition, there may be water that is residual to processing or resulting from storage tank condensation. The presence of water is a problem because:

Water reduces the heat of fuel combustion, causing smoke, harder starting, and reduced power.
Water causes corrosion of fuel system components (pumps, fuel lines, etc.)
Microbes in water cause the paper-element filters in the system to rot and fail, causing failure of the fuel pump due to ingestion of large particles.
Water freezes to form ice crystals that provide sites for nucleation, accelerating gelling of the fuel.
Water causes pitting in pistons.

Previously, the amount of water contaminating biodiesel has been difficult to measure by taking samples, since water and oil separate. However, it is now possible to measure the water content using water-in-oil sensors.

Water contamination is also a potential problem when using certain chemical catalysts involved in the production process, substantially reducing catalytic efficiency of base (high pH) catalysts such as potassium hydroxide. However, the super-critical methanol production methodology, whereby the transesterification process of oil feedstock and methanol is effectuated under high temperature and pressure, has been shown to be largely unaffected by the presence of water contamination during the production phase.

Biodiesel can be used in pure form (B100) or may be blended with petroleum diesel at any concentration in most injection pump diesel engines. New extreme high-pressure (29,000 psi) common rail engines have strict factory limits of B5 or B20, depending on manufacturer. Biodiesel has different solvent properties from petrodiesel, and will degrade natural rubber gaskets and hoses in vehicles (mostly vehicles manufactured before 1992), although these tend to wear out naturally and most likely will have already been replaced with FKM, which is nonreactive to biodiesel. Biodiesel has been known to break down deposits of residue in the fuel lines where petrodiesel has been used. As a result, fuel filters may become clogged with particulates if a quick transition to pure biodiesel is made. Therefore, it is recommended to change the fuel filters on engines and heaters shortly after first switching to a biodiesel blend.

Since the passage of the Energy Policy Act of 2005, biodiesel use has been increasing in the United States. In the UK, the Renewable Transport Fuel Obligation obliges suppliers to include 5% renewable fuel in all transport fuel sold in the UK by 2010. For road diesel, this effectively means 5% biodiesel (B5).

Vehicular use and manufacturer acceptance
In 2005, Chrysler (then part of DaimlerChrysler) released the Jeep Liberty CRD diesels from the factory into the European market with 5% biodiesel blends, indicating at least partial acceptance of biodiesel as an acceptable diesel fuel additive. In 2007, DaimlerChrysler indicated its intention to increase warranty coverage to 20% biodiesel blends if biofuel quality in the United States can be standardized.

The Volkswagen Group has released a statement indicating that several of its vehicles are compatible with B5 and B100 made from rape seed oil and compatible with the EN 14214 standard. The use of the specified biodiesel type in its cars will not void any warranty.

Mercedes Benz does not allow diesel fuels containing greater than 5% biodiesel (B5) due to concerns about “production shortcomings”. Any damages caused by the use of such non-approved fuels will not be covered by the Mercedes-Benz Limited Warranty.

Starting in 2004, the city of Halifax, Nova Scotia decided to update its bus system to allow the fleet of city buses to run entirely on a fish-oil based biodiesel. This caused the city some initial mechanical issues, but after several years of refining, the entire fleet had successfully been converted.

In 2007, McDonald’s of UK announced it would start producing biodiesel from the waste oil byproduct of its restaurants. This fuel would be used to run its fleet.

The 2014 Chevy Cruze Clean Turbo Diesel, direct from the factory, will be rated for up to B20 (blend of 20% biodiesel / 80% regular diesel) biodiesel compatibility

Railway usage
British train operating company Virgin Trains claimed to have run the UK’s first “biodiesel train”, which was converted to run on 80% petrodiesel and 20% biodiesel.

The British Royal Train on 15 September 2007 completed its first ever journey run on 100% biodiesel fuel supplied by Green Fuels Ltd. Prince Charles and Green Fuels managing director James Hygate were the first passengers on a train fueled entirely by biodiesel fuel. Since 2007, the Royal Train has operated successfully on B100 (100% biodiesel).

Similarly, a state-owned short-line railroad in eastern Washington ran a test of a 25% biodiesel / 75% petrodiesel blend during the summer of 2008, purchasing fuel from a biodiesel producer sited along the railroad tracks. The train will be powered by biodiesel made in part from canola grown in agricultural regions through which the short line runs.

Also in 2007, Disneyland began running the park trains on B98 (98% biodiesel). The program was discontinued in 2008 due to storage issues, but in January 2009, it was announced that the park would then be running all trains on biodiesel manufactured from its own used cooking oils. This is a change from running the trains on soy-based biodiesel.

In 2007, the historic Mt. Washington Cog Railway added the first biodiesel locomotive to its all-steam locomotive fleet. The fleet has climbed up the western slopes of Mount Washington in New Hampshire since 1868 with a peak vertical climb of 37.4 degrees.

On 8 July 2014, the then Indian Railway Minister D.V. Sadananda Gowda announced in Railway Budget that 5% bio-diesel will be used in Indian Railways’ Diesel Engines.

Aircraft use
A test flight has been performed by a Czech jet aircraft completely powered on biodiesel. Other recent jet flights using biofuel, however, have been using other types of renewable fuels.

On November 7, 2011 United Airlines flew the world’s first commercial aviation flight on a microbially derived biofuel using Solajet™, Solazyme’s algae-derived renewable jet fuel. The Eco-skies Boeing 737-800 plane was fueled with 40 percent Solajet and 60 percent petroleum-derived jet fuel. The commercial Eco-skies flight 1403 departed from Houston’s IAH airport at 10:30 and landed at Chicago’s ORD airport at 13:03.

In September 2016, the Dutch flag carrier KLM contracted AltAir Fuels to supply all KLM flights departing Los Angeles International Airport with biofuel. For the next three years, the Paramount, California-based company will pump biofuel directly to the airport from their nearby refinery.

As a heating oil
Biodiesel can also be used as a heating fuel in domestic and commercial boilers, a mix of heating oil and biofuel which is standardized and taxed slightly differently from diesel fuel used for transportation. Bioheat fuel is a proprietary blend of biodiesel and traditional heating oil. Bioheat is a registered trademark of the National Biodiesel Board and the National Oilheat Research Alliance in the U.S., and Columbia Fuels in Canada. Heating biodiesel is available in various blends. ASTM 396 recognizes blends of up to 5 percent biodiesel as equivalent to pure petroleum heating oil. Blends of higher levels of up to 20% biofuel are used by many consumers. Research is underway to determine whether such blends affect performance.

Older furnaces may contain rubber parts that would be affected by biodiesel’s solvent properties, but can otherwise burn biodiesel without any conversion required. Care must be taken, however, given that varnishes left behind by petrodiesel will be released and can clog pipes- fuel filtering and prompt filter replacement is required. Another approach is to start using biodiesel as a blend, and decreasing the petroleum proportion over time can allow the varnishes to come off more gradually and be less likely to clog. Thanks to its strong solvent properties, however, the furnace is cleaned out and generally becomes more efficient. A technical research paper describes laboratory research and field trials project using pure biodiesel and biodiesel blends as a heating fuel in oil-fired boilers. During the Biodiesel Expo 2006 in the UK, Andrew J. Robertson presented his biodiesel heating oil research from his technical paper and suggested B20 biodiesel could reduce UK household CO2 emissions by 1.5 million tons per year.

Cleaning oil spills
With 80–90% of oil spill costs invested in shoreline cleanup, there is a search for more efficient and cost-effective methods to extract oil spills from the shorelines. Biodiesel has displayed its capacity to significantly dissolve crude oil, depending on the source of the fatty acids. In a laboratory setting, oiled sediments that simulated polluted shorelines were sprayed with a single coat of biodiesel and exposed to simulated tides. Biodiesel is an effective solvent to oil due to its methyl ester component, which considerably lowers the viscosity of the crude oil. Additionally, it has a higher buoyancy than crude oil, which later aids in its removal. As a result, 80% of oil was removed from cobble and fine sand, 50% in coarse sand, and 30% in gravel. Once the oil is liberated from the shoreline, the oil-biodiesel mixture is manually removed from the water surface with skimmers. Any remaining mixture is easily broken down due to the high biodegradability of biodiesel, and the increased surface area exposure of the mixture.

Advantages and disadvantages

Biodiesel significantly reduces the main emissions of vehicles, such as carbon monoxide and volatile hydrocarbons, in the case of gasoline engines, and particles, in the case of diesel engines.
The production of biodiesel is an alternative in the use of the soil that avoids the phenomena of erosion and desertification to which may be exposed those agricultural lands that, due to market pressures, are being abandoned by farmers.
Biodiesel represents a saving of between 25% and 80% of the CO2 emissions produced by petroleum fuels, thus constituting an important element to reduce the greenhouse gases produced by transport.
Due to its higher rate of Cetane and lubrication, it reduces the wear on the injection pump and on the nozzles.
It does not have sulfur compounds so it does not eliminate them as combustion gases.
Biodiesel is also used as an oil alternative for two-stroke engines, in several percentages; the most used percentage is 10/1.
Biodiesel can also be used as an additive for gasoline engines (naphtha) for internal cleaning of these.

The exploitation of plantations for oil palms (used to make biodiesel) was responsible for 87% of the deforestation of Malaysia until the year 2000. In Sumatra and Borneo, millions of hectares of forest became the land of these palm trees and in recent years more than double that figure has been achieved, logging and fires continue. They even completely deforested the famous Tanjung Puting National Park in Kalimantan. Orangutans, gibbons, rhinos, tapir tigers, nebula panthers, etc… will be extinguished by the destruction of the habitat. Thousands of indigenous people have been evicted from their lands and 1500 Indonesians were tortured. But governments, whileEurope continues to buy its oil palm to make biodiesel, they will continue to promote the cultivation of these plants for their own benefit.
Due to its better solvent capacity with respect to the petrodiésel, the existing waste is dissolved and sent by the fuel line, being able to clog the filters, case that occurs only when it is used for the first time after having been consumed mineral diesel.
It has a lower energy capacity, approximately 3% less, although this, in practice, is not so noticeable since it is compensated with the higher cetane index, which produces a more complete combustion with less compression.
Certain hypotheses suggest that greater combustion deposits occur and that the cold start of the engines is degraded, but this is not yet documented.
Other problems that it presents relate to the area of storage logistics, since it is a hydrophilic and degradable product, for which an exact planning of its production and shipment is necessary. The product degrades notoriously faster than the petrodiésel.
So far, the shelf life of biodiesel is not clear; some argue that has a very short life time (months), while others claim that their useful life reaches even 10 years or more. But everyone agrees that it depends on their handling and storage.
The average yield for oilseeds such as sunflower, peanut, rice, cotton, soybean or castor beans is around 900 L of biodiesel per hectare harvested. This may make it impractical for countries with little arable land; nevertheless, the great variety of seeds suitable for their production (many of them complementary in their rotation or with by-products usable in other industries) makes it a sustainable project. However, jatropha is beginning to be usedto produce vegetable oil and, subsequently, biodiesel and that can be grown even in desert areas.

Source from Wikipedia