Castor oil, owing to its chemical structure has the potential to be used as a bio-fuel in place of petrol-based fuels. In the last few years, there has been a growing debate on whether castor oil can be an effective biofuel (biodiesel) stock.

Interested to know if castor oil can be an efficient bio-fuel and bio-diesel?

Analyze the following:

•  Characteristics of oils or fats affecting their suitability for use as fuel
•  Characteristics of efficient bio-fuels and bio-diesels
•   How does the bio-diesel derived from castor oil rate on the above aspects
•  Based on the above three aspects, preliminary inference for “Can Castor Oil  Make a Good Biodiesel?”

Characteristics of Oils Affecting their Suitability for Use as Fuel

The following aspects need to be considered while evaluating a plant oil feedstock for biofuel.

·         Melt Point or Pour Point

·         Cloud Point

·         Flash Point (FP)

·         Iodine Value (IV)

·         Viscosity

·         Aniline Point/Cetane Number (CN)

·         Density

·         Ash Percentage

·         Sulfur Percentage

·         Potassium Percentage

 Characteristics of Efficient Bio-fuels and Bio-diesel

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% of 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).

Engine Manufacturers Association (EMA) Recommended Guideline on Diesel Fuel 

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

·     Iodine Value   : The transesterified castor oil has an iodine value of about 85. This is quite an acceptable value for biodiesel. The lower the iodine value, the better the fuel will be as a biodiesel. 

·         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 (cetane number of petro diesel is about 45, while for most biodiesel, the cetane number falls in the range 45-65), and the cetane number of castor oil biodiesel is in acceptable range for diesel engines.

·         Melting Point : 5ºC. This is acceptable for diesel engines.

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

·        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. (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 very high.

·        Flash Point: 260oC. It compares favourably with other vegetable oils.

·        Cloud Point: < -7oC; within acceptable range.

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

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

·        Sulfur %: is less than 0.04%

More analysis on the above in terms of various aspects can be found from the Comprehensive Castor Oil Report

 Evaluation Table for Castor Oil as Biodiesel Candidate

 A comparison on various parameters is made for castor oil properties with those suggested for suitable diesel fuel as well for biodiesel. Refer to the above section for more details of comparison

 Following are some of the initiatives that are being taken in order to explore the viability of castor oil as a biodiesel feedstock.

More insights, facts and data on the Castor Biodiesel is available from the Comprehensive Castor Oil Report