Biodiesel: Origin, Properties and Blends

The term ‘biodiesel’ refers to the diesel fuel produced from natural oils and fats of plant or animal origin. Biodiesel is suitable for or designed for use in diesel engines, replacing the diesel fuel obtained from petroleum sources. Another commonly used term is ‘biofuel’, which is a general term indicating ‘fuel produced from “bio” or natural sources’. Biofuel is a general term and biodiesel may be considered as a type of biofuel with specific properties and applications.

Specifically, biodiesel is produced by converting the triglycerides of vegetable oils and animal fats into mostly methyl esters. The resulting mixture of methyl esters of long-chain fatty acids in the oils and fats has been standardized so that they can be used to run diesel engines of automobiles or for power generation. 

Thus, biodiesel is a renewable, biodegradable and clean-burning fuel manufactured from vegetable oils, animal fats, or recycled or used (waste) cooking oils (or greases) from restaurants. It produces less toxic pollutants and greenhouse gases than petroleum diesel. Biodiesel meeting the specified standards is also called as ‘green diesel’. Pure or unblended biodiesel is also referred to as B100 or neat biodiesel, i.e., it contains 100% biodiesel. Like the petroleum-based diesel, this biodiesel is used to run the compression-ignition engines. It can be used in pure form (B100), or it can be blended with petroleum-based diesel in different proportions. Biodiesel is less toxic and also has reduced exhaust emissions compared to petroleum-based diesel. Biodiesel is a major eco-friendly alternative source of energy.

Biodiesel has helped many countries in the world in reducing their dependence on imported crude oil and diesel fuels, as it is produced domestically and can be used in any diesel engine with little or no modification of the engine or the fuel system.

The present series of blog articles offer an overview of technical and commercial aspects of biodiesel. The historical developments, properties, manufacturing technologies, grades and their specifications, applications and also the production and international trade of biodiesel are covered in these articles. 

ORIGIN

Although petroleum-based diesel fuel was in widespread use for automobiles during the early 20^th century in European countries, there was significant interest in vegetable oils themselves as a replacement for diesel fuel in many countries across the world. Several vegetable oils were tested in diesel engines but were not successful due to high viscosity of the vegetable oils. Blends of vegetable oils with petroleum-based diesel, ethyl alcohol, etc., were also tried at that time.

Fuel products similar to the present-day biodiesel were first described in the Belgian Patent 422877 granted on 31 August 1937. It described the process of transesterification or alcoholysis of vegetable oils to replace glycerol by ethyl alcohol (i.e., ethanol) (or by methyl alcohol or methanol), thus transforming the triglycerides into ethyl esters of long-chain fatty acids. The resulting mixture of fatty acid ethyl esters was the first ‘biodiesel’. In 1977, Brazilian scientist patented the first industrial process for the production of biodiesel. This process has been classified as ‘biodiesel process’ by international norms, conferring a ‘standardized identity and quality’ to the biodiesel product. This biodiesel has been validated by the automobile industry. 

Biodiesel produced from sunflower oil by transesterification and subsequent refining was developed and standardized in South Africa in the early 1980s. Engine testing of this fuel-grade biodiesel was completed in 1983. This technology was licensed by an Austrian company, Gaskoks. The company constructed the first biodiesel pilot plant in November 1987. The industrial-scale biodiesel plant based on the same technology was commissioned in April 1989 to biodiesel from 30000 TPA of rapeseed (mustard) oil per year. 

During the 1990s decade, many European countries started producing biodiesel from rapeseed oil. It was called as ‘diester’. This biodiesel was mixed with the petroleum-based diesel at the level of 5% and even up to the level of 30%. By the year 1998, about 21 countries in the world had started producing biodiesel. Many different vegetable oils and other starting materials are used today to produce biodiesel.

PROPERTIES

Most of the physical properties of biodiesel are similar to those of petroleum-based diesel, but they differ in many aspects as well. 

Depending on the starting raw material and manufacturing process, the colour of biodiesel varies from golden to dark brown. It is slightly miscible with water. As explained earlier, biodiesel is a mixture of methyl or ethyl esters of long-carbon-chain fatty acids. Petroleum-based diesel consists of hydrocarbons only. Flashpoint of biodiesel exceeds 130 deg. C, which is significantly higher than that of petroleum diesel (as low as 52 deg. C). The density of biodiesel is about 0.88 g/cc, which is higher than petroleum diesel (about 0.85 g/cc). Biodiesel does not contain any sulfur as compared to petroleum diesel.

Biodiesel has a calorific value of about 37 MJ/kg, which is about 9% lower than that of regular no. 2 petroleum diesel. The feedstock used for producing biodiesel decides the energy density of biodiesel. Lubricity of biodiesel is reported to be better than that of petroleum diesel. Biodiesel undergoes complete combustion resulting in increasing the engine energy output and partially compensating for the higher energy density of petroleum diesel. Biodiesel with higher lubricity may increase the usable life of high-pressure fuel injection equipment of the engines. 

Typical physical properties of biodiesel are listed in the following table. The specific values may vary slightly depending on the feedstock used for production of biodiesel.

TABLE: TYPICAL PHYSICAL PROPERTIES OF BIODIESEL

BLENDS

Biodiesel is blended with petroleum-based diesel in different ratios, and these blends are used in different types of vehicles having diesel engines. Although 100% pure biodiesel is available commercially, these blends are commonly used by vehicle owners and are available at the retail fuel outlets. A labelling system known as the “B” factor is used throughout the world to indicate the amount of biodiesel in any fuel blend. 

The most common and commercially available biodiesel blends with petroleum diesel and their contents of biodiesel are listed in the following table. 

TABLE: STANDARD BLENDS OF BIODIESEL AND THEIR COMPOSITION

Biodiesel blends from B6 to B20 are covered by the international standard ASTM D7467.

Biodiesel blends containing 20% or lower biodiesel can be used in diesel engines with no or only minor modifications. Pure biodiesel (B100) can be used to run diesel engines but may require certain modifications to avoid maintenance and performance problems.

Blends of biodiesel and petroleum diesel are prepared generally prepared by mixing the 100% biodiesel (i.e., B100) with the petroleum-based diesel using different methods. The most common methods are listed below.

1. Mixing in storage tanks at the biodiesel manufacturing plants prior to delivery to tanker trucks
2. Splash mixing in the tanker trucks by adding specific percentages of biodiesel and petroleum diesel
3. Biodiesel and petroleum diesel may be mixed in the pipeline itself while delivering the mixture to the tanker trucks (In-line mixing)
4. Biodiesel and petroleum diesel are mixed using metered pumps to obtain specified total volume of the blend

These biodiesel blends are transported in tanker trucks to the retail fuel outlets for distributing to consumers. 

Production and distribution of biodiesel blends are regulated by the respective government bodies in different countries. The respective government policies govern which blends are to be produced and used in different vehicles.

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