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Plant Seed Oils and Their Potential for Biofuel Production in India

L. C. Meher1,2 and S. N. Naik1*

1 Centre for Rural Development and Technology, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi, India

2 Defence Institute of Bio-Energy Research, DRDO, Haldwani, Nainital, Uttarakhand, India

Abstract

Many tree-borne oilseed plants are grown in India which produce non-food grade oil. Some of these have the potential to produce feedstock for biodiesel. Plants such as Pongamia and Jatropha are found throughout the country, whereas Mahua, Rubber, and Nahor are found in specific regions. The oilseeds are collected to a lesser extent by the local population for traditional uses as medicine, to fuel lamps, etc. and for the preparation of soap in industries. The National Mission on Biofuel has focused to grow Jatropha, whereas the existing tree born oilseeds are also potential sources for biodiesel feedstock. Non-edible oils with their potential as biodiesel feedstock in the country is discussed in this chapter. The oilseed plants less explored for biodiesel have also been discussed.

Keywords: Biodiesel, vegetable oil, non-edible oil, transesterification, methyl esters, jatropha, pongamia

1.1 Introduction

Presently, petroleum fractions are the preferred fuels for internal composition engines used for transport, as well as in the industrial and agricultural sectors. The global consumption of fossil based liquid fuels was above 100 million barrels per day during 2019 and forecasted to continue at the same rate during 2021 [1]. The contribution of CO2 to the atmosphere is about 3.1-3.2 times the consumption of fossil fuel. The exhaust emissions as a result of widespread use of fossil fuel are a global concern for the present time. The level of unburnt hydrocarbon and oxides of nitrogen, along with CO2, are gradually increasing in the atmosphere. The research and development activities have been focused for the last few decades in search of alternative fuel from renewable sources for the nations to be self-reliant for energy sources and much effort is being done by countries with no oil reserves.

Biodiesel is the fatty acid methyl esters derived from renewable lipid feedstocks, such as vegetable oils, as an alternative to diesel fuel. The invention of diesel engines and compression ignition engines dates back to the 19th century and the vegetable oils were used as fuel. The high viscosity and poor volatilities of vegetable oils, as well as the availability of middle distillate, i.e., diesel fuel, did not attract much interest for vegetable oil based fuel during those days.

The research and development activities on vegetable oil based biodiesel were initiated at the beginning of this century. The transesterification of vegetable oil reduces the viscosity by one-tenth, lower molecular weight of the triglyceride molecule by one-third, and improves the volatility along with the physical properties of the biodiesel. Worldwide biodiesel industries are set up and biodiesel blended diesel fuel is technically suitable for use in existing diesel engines with slight or no engine modifications. There is a scarcity of biodiesel feedstock for countries like India where the domestic demand of edible oil is met by import. The present article describes the potential non-food grade vegetable oil sources as feedstock for biodiesel in Indian context.

1.2 Background

India ranks third in terms of consumption of fossil fuels after China and the USA. Consumption grew by 2.3% in 2019 with a global share of 5.8%. Petroleum based fuel is the second largest energy source (239.1 million tons oil equivalent) after coal (452.2 million tons oil equivalent). The transportation fuel in India is mainly petroleum based diesel and the consumption is recorded at 83.5 million tons during 2018-19 [2].

The recent BS-VI in India, effective from 2020, is a stringent emission norm for diesel engines. The new pollution norm involves the reduction of NOx by 68% and particulate matter by 82-93% [3]. The fuel for diesel engines should burn clearly, which can be achieved by the inclusion of oxygenated fuel, i.e., biodiesel in petroleum based diesel fuel.

In the global context, the surplus of edible oils such as Rapeseed in Europe, Canola in Canada, Soybean in the USA, and Palm oil in Malaysia and Indonesia are the available feedstocks for biodiesel. In the Indian scenario, the requirement of edible oil is met by import. India imports Palm oil from Malaysia and Indonesia, and Soybean from Argentina and Brazil, and Sunflower from Ukraine and Russia. The import of vegetable oil was 150.02 lakh tons during 2017-18, which increased to 155.49 lakh tons during 2018-19 [4]. The import of edible oils for the last five years is shown in Table 1.1 [5]. The non-food vegetable oils may be a potential source of biodiesel feedstock.

There are over 300 different species of oilseed plants grown in India. Various tree borne oilseed derived oils are not suitable for human consumption due to the presence of toxic components, for example karanjin and pongamol in Pongamia oil, azadirachtin in neem oil, ricin in Castor oil, and phorbol esters in Jatropha oil. These tree-borne oilseeds require agricultural inputs in the initial period and rarely require any expense associated with its maintenance once fully grown. It can also be a cost-effective way to produce oilseed. The production for tree borne oilseed is about 3.0-3.5 million metric tons whereas 0.5-0.6 million tons of seed are collected [6]. The potential non-edible oilseed plants are Jatropha (Jatropha curcas), Karanja (Pongamia pinnata), Mahua (Madhuca indica), Nahor (Mesua ferrea), Rubber (Hevea brasiliensis), Castor (Castor communis), Neem (Azadirachta indica), Sal (Shorea robusta), Undi (Calophyllum inophyllum), Simarouba (Simarouba glauca), etc. Oil derived from tree born oilseed plants such as Neem, Castor, and Sal find specific applications. Neem oil containing azadirachtin is a natural pesticide and emulsifier in the agricultural sectors. The Castor oil with ricinoleic acid in the triglyceride has high viscosity and finds commercial application as a precursor for polyurethane, lubricant, binder, etc. Fat derived from the Sal tree is used as cocoa butter substitute for manufacturing of chocolates. With these exceptions, the rest of the oilseeds may be feedstock for biodiesel.

Table 1.1 Import of major edible oil by India (in Lakh Tons) [s].

Various missions at national and state levels were made to promote the cultivation of oilseed crops. Pongamia and Jatropha were selected as suitable oilseed plants for plantation in the waste and degraded lands, avenue plantations, and perimeter fencing. Massive plantation of Jatropha has been carried out in the Chhattisgarh state and similarly, Pongamia in the Karnataka state of India. These are in addition to the existing potential of oilseed in the country.

1.3 Non-Edible Oil as Feedstock for Biodiesel

The biodiesel derived from vegetable oil should have properties as per EN 14214:2012 A1:2014 or IS 15607:2016 specifications. Properties such as iodine value, linolenic acid methyl ester, and oxidation stability are dependent upon the qualities of the feedstock. The physico-chemical properties of oils are listed in Table 1.2 [7, 8] and their fatty acid compositions in Table 1.3 [7, 9-12]. The saponification value (SV) and the iodine value (IV) are indicative of structures such as chain length of fatty acid and degree of unsaturation of fatty acids in the triglyceride. The cetane index (CI) is related to the saponification value and iodine value as per Equation (1.1) and the cetane number (CN) is related to the cetane index as per Equation (1.2) [9]. The MWoil (weight average molecular weight of the oil) is calculated from the saponification value as per Equation (1.3) and the requirement of methanol for transesterification is calculated based on the MW oil.

Table 1.2 Physico-chemical characterisation of potential non-edible oils for biodiesel feedstock.