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Castor Oil as Biodiesel & Biofuel

CastorOil.in provides you links & resources related to castor, castor oil, castor derivatives & castor oil producers. We hope to make this a one-stop resource for all info about castor and castor products, and hope that you find this site to be of use.

 This section of Castoroil.in provides details about the use of castor oil as fuel and as bio-diesel.

 Castor Oil as Biodiesel & Biofuel


This section provides resources for the topic “Castor Oil as Bio-diesel & Bio-fuel”. While the topic of bio-fuels is indeed a hot one, the plants whose oils are popularly considered for bio-fuel are soybeans, sunflower, safflower, rapeseed, jatropha and palm.

 This section explores whether the oil produced from the castor plant can be used as an efficient bio-fuel and as bio-diesel. This is an area of on-going research and we expect more info on this topic in the months and years to come. We will keep this section updated with those findings.

 The purpose of this section is not to prove or disprove castor oil’s claim to mainstream bio-fuel/biodiesel. Rather, it is to explore the idea, present various findings from around the world and provide a resource that can be used by those who are seeking objective inputs in this area.

The following are the topics under this section

  1. What is castor oil?
  1. Can castor oil become an efficient bio-fuel and bio-diesel?
  1. How is castor oil converted into bio-diesel?
  1. Castor oil as bio-diesel – facts and nuggets
  1. Fantasy – If Castor Oil were to completely replace biodiesel!
  2. Data & Stats
  3. Biodiesel Reference

1. What is castor oil?

 Castor oil is the oil derived from castor beans.

 Castor oil is one of hard oils, where the oil content in the seed is relatively high. In the case of castor seed, the oil content is close to 50% of the total by weight - the castor bean contains 50-55% oil. The oil itself contains a number of fatty acids similar to those in cooking oils, such as oleic acid, linoleic acid, stearic acid and palmitic acid. However, among vegetable oils, castor oil is distinguished by its high content (over 85%) of ricinoleic acid. No other vegetable oil contains so high a proportion of fatty hydroxyacids. Castor oils unsaturated bond, high molecular weight (298), low melting point (5ΊC) and very low solidification point (-12ΊC to -18ΊC) make it industrially useful, most of all for the highest and most stable viscosity of any vegetable oil

 Castor oil is unique among all fats and oils. It has an unusual chemical composition of a triglyceride of fatty acids. It is the only source of an 18-carbon hydroxylated fatty acid with one double bond. The product uniformity and consistency of castor oil are significantly high for a naturally occurring material.

 The chemical composition of castor oil is:


  • Ricinoleic Acid – 89.5%
  • Linoleic Acid – 4.2%
  • Oleic Acid – 3%
  • Stearic Acic – 1%
  • Palmitic Acid – 1%
  • Dihydroxystearic Acid – 0.7%
  • Linolenic Acid – 0.3%
  • Eicosanoic Acid – 0.3%

More info on Castor Oil from CastorOil.in – The Home of Castor Oil on the Internet

2. Can castor oil become an efficient bio-fuel and bio-diesel?

 In order to answer the question, the following needs to be discussed:


  1. What is a bio-fuel and bio-diesel?
  2. What are the characteristics that make an oil an efficient bio-fuel and bio-diesel?
  3. How does castor oil compare of these characteristics?


 What is a biofuel?

 Biofuel is any fuel that derives from biomass — recently living organisms or their metabolic byproducts. Thus it could be oils from plants, manure from cows, wood from trees and so on. It is a renewable energy source, unlike other natural resources such as petroleum, coal and nuclear fuels.

 Agricultural products specifically grown for use as biofuels include corn and soybeans, primarily in the United States, and flaxseed and rapeseed, primarily in Europe. Waste from industry, agriculture, forestry, and households can also be used to produce bioenergy; examples include straw, lumber, manure, sewage, garbage and food leftovers. Most biofuel is burned to release its stored chemical energy, though research is active into more efficient methods of converting biofuels and other fuels into electricity utilizing fuel cells.

 The production of biofuels to replace petroleum-based oil and natural gas is in active development. The carbon in biofuels was recently extracted from atmospheric carbon dioxide by growing plants, so burning it does not result in a net increase of carbon dioxide in the Earth's atmosphere. As a result, biofuels are seen by many as a way to reduce the amount of carbon dioxide released into the atmosphere by using them to replace non-renewable sources of energy.

  What is bio-diesel?

 Biodiesel refers to any diesel-equivalent biofuel made from renewable biological materials such as vegetable oils or animal fats. While there are numerous interpretations being applied to the term biodiesel, the term biodiesel usually refers to an ester, or an oxygenate, made from the oil and methanol (in other words, the name ‘‘biodiesel’’ can be applied to any transesterified vegetable oil that makes it suitable for use as a diesel fuel).

Technically, as mentioned earlier, biodiesel is vegetable oil methyl ester, or in general one could say that biodiesel consists what are called mono alkyl-esters. It is usually produced by a transesterification and esterification reaction of vegetable or waste oil respectively with a low molecular weight alcohol, such as ethanol and methanol. During this process, the triglyceride molecule from vegetable oil is removed in the form of glycerin (soap). Once the glycerin is removed from the oil, the remaining molecules are, to a diesel engine, somewhat similar to those of petroleum diesel fuel. There are some notable differences though. While the petroleum and other fossil fuels contain sulfur, ring moluecules & aromatics, the biodiesel molecules are very simple hydrocarbon chains, containing no sulfur, ring molecules or aromatics. Biodiesel is thus essentially free of sulfur and aromatics. Biodiesel is made up of almost 10% oxygen, making it a naturally "oxygenated" fuel.

The concept of using vegetable oil as a fuel dates back to 1895 when Dr. Rudolf Diesel developed the first diesel engine to run on vegetable oil. Diesel demonstrated his engine at the World Exhibition in Paris in 1900 using peanut oil as fuel.


Bio-diesel can be used in diesel engines either as a standalone or blended with petro diesel. Much of the world uses a system known as the "B" factor to state the amount of biodiesel in any fuel mix. For example, fuel containing 20 % biodiesel is labeled B20. Pure biodiesel is referred to as B100.

 Characteristics of Efficient Bio-fuels and Bio-diesels

Biodiesel is noteworthy for its similarity to petroleum-derived diesel fuel, while at the same time having negligible sulfur and ash content. Bioethanol has only about 70% the heating value of petroleum distillates such as gasoline, but its sulfur and ash contents are also very low. Both of these liquid fuels have lower vapor pressure and flammability than their petroleum-based competitors – an advantage in some cases (e.g. use in confined spaces such as mines) but a disadvantage in others (e.g. engine starting at cold temperatures).

Despite their wide range of possible sources, biomass feedstocks are remarkably uniform in many of their fuel properties, compared with feedstocks such as coal or petroleum. For example, there are many kinds of coals whose gross heating value ranges from 20 to 30 GJ/T (gigajoules per metric tonne). However, nearly all kinds of biomass feedstocks destined for combustion fall in the range 15-19 GJ/T. For most agricultural residues, the heating values are even more uniform – about 15-17 GJ/tonne (6450-7300 Btu/lb); the values for most woody materials are 18-19 GJ/tonne (7750-8200 Btu/lb).

However, in contrast to their fairly uniform physical properties, biomass fuels are rather heterogeneous with respect to their chemical elemental composition.

Most biomass materials are more reactive than coal, with higher ignition stability. This characteristic also makes them easier to process thermochemically into higher-value fuels such as methanol or hydrogen.

Characteristics of Oils or Fats Affecting their Suitability for Use as Fuel

Calorific Value, Heat of Combustion – Heating Value or Heat of Combustion, is the amount of heating energy released by the combustion of a unit value of fuels.


One of the most important determinants of heating value is moisture content. Air-dried biomass typically has about 15-20% moisture, whereas the moisture content for oven-dried biomass is negligible. Moisture content in coals vary in the range 2-30%. However, the bulk density (and hence energy density) of most biomass feedstocks is generally low, even after densification – between about 10 and 40% of the bulk density of most fossil fuels. Liquid biofuels however have bulk densities comparable to those for fossil fuels.

Melt Point or Pour Point - Melt or pour point refers to the temperature at which the oil in solid form starts to melt or pour. In cases where the temperatures fall below the melt point, the entire fuel system including all fuel lines and fuel tank will need to be heated.

Cloud Point - The temperature at which an oil starts to solidify is known as the cloud point. While operating an engine at temperatures below an oil’s cloud point, heating will be necessary in order to avoid waxing of the fuel.

Flash Point (FP) - The flash point temperature of diesel fuel is the minimum temperature at which the fuel will ignite (flash) on application of an ignition source. Flash point varies inversely with the fuel’s volatility. Minimum flash point temperatures are required for proper safety and handling of diesel fuel.

Iodine Value (IV) - Iodine Value (IV) is a value of the amount of iodine, measured in grams, absorbed by 100 grams of a given oil.

Iodine value (or Iodine number) is commonly used as a measure of the chemical stability properties of different biodiesel fuels against such oxidation as described above. The Iodine value is determined by measuring the number of double bonds in the mixture of fatty acid chains in the fuel by introducing iodine into 100 grams of the sample under test and measuring how many grams of that iodine are absorbed. Iodine absorption occurs at double bond positions - thus a higher IV number indicates a higher quantity of double bonds in the sample, greater potential to polymerise and hence lesser stability.

Iodine Numbers for some plant oils (before conversion into biodiesel):

Coconut oil: 10

Rapeseed oil: 94-120

Soybean oil: 117-143

Sardine oil: 185

Iodine Numbers after conversion to biodiesel through transesterification (approximate values):

Rapeseed Methyl Ester (Rapeseed Biodiesel): 97

Rapeseed Ethyl Ester (Another variety of Rapessed biodiesel): 100

Soy Ethyl Ester (Soy biodiesel variety 1): 123

Soy Methyl Ester (Soy biodiesel variety 2): 133

One can hence see that the process of transesterification (conversion of plant oil int6o biodiesel) reduces the iodine value to a small extent.

Viscosity – Viscosity refers to the thickness of the oil, and is determined by measuring the amount of time taken for a given measure of oil to pass through an orifice of a specified size. Viscosity affects injector lubrication and fuel atomization. Fuels with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in leakage or increased wear. Fuel atomization is also affected by fuel viscosity. Diesel fuels with high viscosity tend to form larger droplets on injection which can cause poor combustion, increased exhaust smoke and emissions.

Aniline Point/Cetane Number (CN) - Is a relative measure of the interval between the beginning of injection and autoignition of the fuel.  The higher the cetane number, the shorter the delay interval and the greater its combustibility.  Fuels with low Cetane Numbers will result in difficult starting, noise and exhaust smoke. In general, diesel engines will operate better on fuels with cetane numbers above 50.


Cetane tests provide information on the ignition quality of a diesel fuel. Research using cetane tests will provide information on potential tailoring of vegetable oil-derived compounds and additives to enhance their fuel properties. References – Cetane Number Testing of Bio-diesel – from Biodiesel.org (PDF).

Density – Is the weight per unit volume.  Oils that are denser contain more energy.  For example, petrol and diesel fuels give comparable energy by weight, but diesel is denser and hence gives more energy per litre.

The aspects listed above are the key aspects that determine the efficiency of a fuel for diesel engines. There are other aspects/characteristics which do not have a direct bearing on the performance, but are important for reasons such as environmental impact etc. These are:

Ash Percentage - Ash is a measure of the amount of metals contained in the fuel. High concentrations of these materials can cause injector tip plugging, combustion deposits and injection system wear.

Ash content for bio-fuels is typically lower than for most coals, and sulphur content is much lower than for many fossil fuels. Unlike coal ash, which may contain toxic metals and other trace contaminants, biomass ash may be used as a soil amendment to help replenish nutrients removed by harvest.

Sulfur Percentage - The percentage by weight, of sulfur in the fuel Sulfur content is limited by law to very small percentages for diesel fuel used in on-road applications.

Potassium Percentage - The percentage by weight, of potassium in the fuel

Engine Manufactures Association (EMA) Recommended Guideline on Diesel Fuel






#1 DF(1)



#2 DF(1)

Flash Point, °C min.

D 93



Water, ppm max




Sediment, ppm max

D2276 or D5452



Distillation % Vol. Recovery, °C

D 86



90%, max.




95%, max.




Kinematic Viscosity, 40 °C

D 445

1.3 - 2.4

1.9 - 4.1

Ash, % max.

D 482



Sulfur, % max.

D 2622



Copper Corrosion, max.

D 130



Cetane Number, min.

D 613



Cetane Index, min.

D 4737



Rams Carbon, 10% residue max.

D 524



API Gravity, max.

D 287



Lubricity, g. min.




Accelerated Stability, mg/L max.

D 2274



Detergency - L10 Injector

CRC Rating



Depositing Test

% Flow Loss



Low Temperature Flow, °C

D2500 or D4539



Microbial Growth





Source: Engine Manufacturers Association 

 How does the bio-diesel derived from castor oil rate on the above aspects?


  1. Ash content: Castor oil has an ash content of about 0.02%


  1. Sulfur %: is less than 0.04%


  1. Potassium: Negligible


  1. Heating value: 39.5 GJ/T. At this number, it compares favourably with most vegetable oils. Petro-based diesel & gasoline have heating values of approximately 45 GJ/T. Hence, one could say that most biodiesel, including that from castor, have heating values that are about 10% lower than that for gasoline or petro diesel.


  1. Viscosity: Castor oil in its raw form is one of the most viscous of oils (9.5 – 10.0 dPa.s @ 20 degress C – about 990 cP). The other plant oils, in themselves, have viscosities much higher than those for gasoline and petro-diesel. Castor oil has a viscosity of over 100 times that of petro-diesel!

One can hence see that viscosity could be a major bottleneck in castor oil becoming a biodiesel. However, this high viscosity can be considerably reduced by subjecting the vegetable oils to the process of transesterification. Transesterification is the process most commonly used for converting a plant oil into biodiesel.


We currently do not have data for the kinematic viscosity of transesterified castor oil. Should this be much than what is acceptable in diesel engines, then this could prove to be a bottleneck for castor oil to be a biodiesel. However, from the news articles and information gathered from around the world (and especially from Brazil), it does appear that the viscosity of biodiesel prepared from castor oil is within acceptable limits for use in diesel engines.


More information on transesterification is available from our Biodiesel Encyclopedia section.


  1. Iodine Value: The transesterified castor oil has an iodine value of about 80. This is quite an acceptable value for biodiesel. The lower the iodine value, the better the fuel will be as a biodiesel. While most countries do not have mandatory upper limits for iodine value, in some countries of Europe the upper limits have been stipulated at around 120. One can hence see that castor oil biodiesel easily passes this test (while soy biodiesel, whose iodine value is about 120, perhaps does not).


  1. Cetane Number: The higher the cetane number, the better is the fuel as a diesel. The Cetane Number of most biodiesel fuels are higher than petro-diesel, and the cetane number of castor oil biodiesel is in acceptable range for diesel engines. In fact, castor oil has one of the highest cetane numbers amongst vegetable oils, and all the other biodiesel contenders have cetane numbers slightly lower than that for castor oil (The cetane number of petro diesel is about 45, while for most biodiesel, the cetane number falls in the range 45-65) (See Biodiesels from Vegetable Oils – PDF)


  1. Melting Point: 5ΊC. This is acceptable for diesel engines.


  1. Solidification Point – Castor oil has a very low solidification point (-12ΊC to -18ΊC). This is a positive characteristic for colder climates, since it implies that the biodiesel solidifies fewer times than those biodiesels with higher solidification points.


  1. Density: Castor oil, before transesterification has a density of 0.956-0.963 g/ml (@ 20 degrees C. The conversion into alkyl esters decreases the density by a small extent, hence one can expect the castor oil based biodiesel to have a density of about 0.9 g/ml – this number needs to be confirmed though. (Comparative values are approx 0.74 g/ml for gasoline and 0.85  g/ml for diesel). While the castor oil biodiesel has a density somewhat higher than petro-diesel, this is unlikely to be a bottleneck as the difference is not significant.


  1. Flash Point: 260 degrees C. It compares favourably with other vegetable oils, though of course it is much higher than for petroleum-based diesel (about 50 degrees C). With a much higher flash point than it is for petro-diesel, biodiesel is classified as a non-flammable liquid by the Occupational Safety and Health Administration. This property makes a vehicle fueled by pure biodiesel far safer in an accident than one powered by petroleum diesel or the explosively combustible gasoline.


  1. Cloud Point: Within acceptable range.


  1. Pour Point: At a pour point of about -32 degrees C, it compares well with other plant oils, and is acceptable in diesel engines.



Cost of Castor Oil


The final, and possibly one of the most important, aspects to be considered is the cost. If one were to take the current prices of the various plant oils as a measure of the input cost, the following is what emerges as data:


The following were the spot prices for the various oils in India on March 10, 2006 in Indian rupees/Kg ( One US $ equals 45 Indian rupees, approximately)


  • Castor Oil – 32.3
  • Groundnut Oil/Peanut Oil – 43.6
  • Mustard Oil – 36.4
  • Palm Oil (RBD) – 38.1, Palm Oil Crude – 36.4
  • Refined Soy Oil – 36.7

While the above list does not provide data for all the vegetable oils that are biodiesel candidates, from the list it can be seen that castor oil is one of the lowest priced oils, if not the oil with the lowest price.

Preliminary Inference for “Can Castor Oil Make a Good Biodiesel?”

The only important piece of input that affects castor oil’s ability to be a biodiesel that we do not currently have is the kinematic viscosity of castor oil biodiesel.


From the news articles and information gathered from around the world (and especially from Brazil), it does appear that the viscosity of biodiesel prepared from castor oil is within acceptable limits for use in diesel engines. However, we do not currently have the viscosity data with us @ CastorOil.in. Assuming transesterified castor oil biodiesel can have an acceptable kinematic viscosity, based on the above facts and analysis, it does appear that castor oil can be a candidate to be a bio-diesel.

It is however important to note than viscosity plays an important role in a diesel, and hence the viscosity data for castor oil biodiesel needs to be determined before even a preliminary conclusion can be drawn.


Data to be determined: Kinematic viscosity of transesterified castor oil biodiesel.

3. How is Castor Oil converted into bio-diesel?


The most common process of converting castor oil into a product that can be used as diesel, is the same as what is used in the case of converting other similar vegetable oils into diesel. The process is called transesterification.


Transesterification refers to a reaction between an ester of one alcohol and a second alcohol to form an ester of the second alcohol and an alcohol from the original ester, as that of methyl acetate and ethyl alcohol to form ethyl acetate and methyl alcohol; interesterification.


Transesterification largely eliminates the tendency of the plant oils and fats to undergo polymerisation and auto-oxidation, and also reduces the viscosity of the oil to about the same as petroleum diesel.


More details and resources for the transesterification process are provided in a later section.


Please see the Biodiesel Encyclopedia section for more details and links for transesterification.

4. Castor Oil as Biofuels – Facts & Nuggets


  • Crude castor oil is refined and biodiesel is produced through the process of esterification and transesterification
  • According to one school of thought, castor oil is the best substance for producing biodiesel because it is the only one that is soluble in alcohol, and does not require heat and the consequent energy requirement of other vegetable oils in transforming them into fuel
  • Japan has recently shown interest in importing castor oil to produce biodiesel (a mixture of the oil with diesel derived from petroleum), which will start to be used in Brazil this year. (Feb 2005)
  • Brazil, the world's second largest producer of soybean, has passed a Bill (in 2004?) making it compulsory to produce a 2% bio-diesel fuel blend, made from castor oil and soyaoil.
  • The Myanmar government plans to implement a project to grow castor bean plants on 50,000 acres in each of Myanmar’s nine military divisions for use as biofuel. (Jan 2006)
  • China is exploring major investments in Brazil to produce both ethanol and castor oil or biodiesel for shipment to China
  • Castor beans contain about 54% oil by weight!

5. Fantasy: If Castor Oil were to completely replace diesel!

Just playing with numbers to see what comes up:

Worldwide Castor Oil Production: Approximately 0.5 million tonnes per annum (2006 estimates)

Total consumption of gasoline and diesel per day, worldwide – approximately 10 million tonnes per day

Thus, a back-of-the-envelope calculation shows that if castor oil were to completely replace diesel, the world needs to produce about 7000 times the amount of castor oil that is being produced today! Put another way, the entire production of castor oil today is just 0.014 % of the total petro-diesel & gasoline requirements.

Extending this train of thought to all oilseeds, the total production of vegetable oils is about 120 million T per annum worldwide. Even if a 1:1 ratio of substitution between petrodiesel/gasoline with vegetable oils is assumed (some estimates say that for every 1 Kg of petro-diesel, we would require about 1.l Kg of Biodiesel for equivalent energy), the total world production of vegetable oils can only provide about 10 days’ worth of transportation fuels! While admittedly this calculation is not rigorous, it shows just how early we are in the evolution of biofuels.

6. Data & Stats

Typical Extractions of Oil from Oilseeds

(Kg of oil from 100 Kg of oilseed)

Oilseed           Extraction

Castor            36
Palm               36

Rapeseed       37

Soybean         14

Sunflower       32

Yield Comparison of Castor Oil with other Plant Oil Biodiesel Candidates

Crop             Oil in Liters per hectare

Castor            1413

Sunflower       952

Safflower        779

Palm               5950   

Soy                446

Coconut          2689

One more ref:

Oil - Producing Crops (Plant - Lb Oil/Acre)
1. Oil Palm – 4585; 2. Macauba Palm – 3462; 3. Pequi – 2881; 4. Buriti Palm – 2515; 5. Oiticia – 2311; 6. Coconut – 2072; 7. Avocado – 2033; 8. Brazil Nut – 1843; 9. Macadamia Nut – 1730; 10. Jatropha – 1458; 11. Babassu Palm – 1413; 12. Jojoba – 1401; 13. Pecan – 1380; 14. Bacuri – 1098; 15. Castor Bean – 1089; 16. Gopher Plant – 1026; 17. Piassava – 1020; 18. Olive Tree – 934; 19. Rapeseed – 917; 20. Opium Poppy – 897; 21. Peanut – 816; 22. Cocoa – 791; 23. Sunflower – 734; 24. Tung Oil Tree – 724; 25. Rice – 638; 26. Buffalo Gourd – 610; 27. Safflower – 601; 28. Crambe – 540; 29. Sesame – 536; 30. Camelina – 449; 31. Mustard – 441; 32. Coriander – 413; 33. Pumpkin Seed – 412; 34. Euphorbia – 403; 35. Hazelnut – 371; 36. Linseed – 369; 37. Coffee – 354; 38. Soybean - 344; 39. Hemp - 280; 40. Cotton – 250; 41. Calendula – 235; 42. Kenaf – 211; 43. Rubber Seed – 199; 44. Lupine – 179; 45. Palm – 173; 46. Oat – 168; 47. Cashew Nut – 136; 48. Corn – 133

Some Gasoline/Petrol & Diesel Facts:


Sulfur Content: 0.05 percent maximum allowed for diesel


Density : 7.076 lb/gal (diesel)  6.15 lb/gal (gasoline)


Heating Values

Diesel: 19300 Btu/lb (136,567 Btu/gal)

Gasoline: 20300 Btu/lb (124,845 Btu/gal)

Approximately 45-47 GJ/T


American standard testing methods (ASTM) tests and limits for Diesel fuels


Test ASTM                                Test No.                  ASTM limits for no. 2 Diesel fuel

Carbon residue (wt.%)               D 524                      0.35 % max.

Cetane no.                                 D 613                       40 min.

Distillation range (K)                  D 86                         555–611

Flash point (K)                           D 93                        325 min.

Higher heating value (MJ kg_1)  D 2015                     45.2 min.

Viscosity (mm2 s_1)                  D 445                       1.9–4.1


Kinematic Viscosity Specs & Standards


Specifications: (viscosities in mm2/s)


Europe Petrodiesel: 2.0–4.5

Europe Biodiesel : 3.5–5.0

US specification of viscosity for low-sulfur No.2 diesel fuel: 1.9-4.1 mm2/s  (this is the fuel that is biodiesel is most often compared to)

US Specification for No. 1 diesel fuel is 1.3–2.4 mm2/s.

Most alkyl esters of vegetable oils have kinematic viscosities less than 5.0 mm2/s.



7. Bio-diesel Reference – Pl see the Biodiesel Encyclopedia section