Characteristic and composition of several non-edible oils compared to diesel.
Biodiesel derived from plant species has been a major renewable source of energy and has received global interest mainly due to climate change issue. It has increasingly received worldwide attention as a promising alternative fuel. Growing interest in biodiesel production from edible oil brings scarcity in food supply. To overcome this problem, utilization of non-edible oils could be explored. Non-edible oil as biodiesel feedstock impressed in many factors such as energy sustainability and independence in certain areas, especially in rural community, creating job opportunities, elevating environmental merits, and avoiding monoculture of fuel resources. The present chapter reviews several such potentials, including fatty acid methyl ester (FAME) or biodiesel production process of non-edible oil resources as biodiesel feedstock in South-East Asian geographical region. The South-East Asian countries fall in the tropical region of the world and have many species as non-edible oil, viz., jatropha, karanja, polanga, neem, rubber, and mahua. The oils derived from these species have shown considerable potential as biodiesel feedstock.
- oil properties
- renewable energy
- potential crop
Biodiesel has energy sustainability benefit for most of the countries in Asia, aiming to reduce nations’ dependence on fossil fuels, who still import the oil and other petroleum product [1, 2]. It is also considered as the final strategy for clean development mechanism (CDM). Utilization of edible oil as feedstock for biodiesel production has increased its price and created demand in the world market . More than 60% of the world’s population resides in Asia leading to a higher demand for food and energy. Utilizing non-edible oils as a biodiesel feedstock assists the sustainability of biodiesel production and minimizes the impact directly on food supply .
2. Non-edible oil merits as biodiesel feedstock
Deforestation and destruction of ecosystem due to urbanization and plantation expansion is a big issue in utilizing edible oil as biodiesel feedstock. Furthermore, the boundary line between food and fuel is blurred since both the fields are competing for the same resources. Debating over food versus fuel is still a dilemma. There are large surplus of food crops in developed countries. However, millions of people in developing countries still face the scarcity of food. Conversion of food crops such as palm oil, coconut oil, corn, soybean, and sugarcane to biodiesel could lead to serious food shortage. Countries in South-East Asia fall in the tropical belt and have many species of crops both edible as well as non-edible ones. Developing biodiesel production based on non-edible oil is one of the scenarios for fuel security without interfering with the food supply. This is especially true for palm oil which makes up about one-third of vegetable oil as biodiesel feedstock and has become the hottest environmental topic in South-East Asia.
High price of high quality refined edible oil makes them not feasible as tent to uneconomic for developing countries like India due to high production cost of methyl or ethyl ester from the edible oil. The cost is about four times higher compared to the cost of diesel . Valuable nutrient elements in edible oil such as essential amino acids, β-carotene, α-carotene, vitamin-E, lycopene, tocotrienols, and carotenoids will be neglected, if this oil is converted to fuel.
Non-edible crops can grow in waste and unproductive land which may be helpful for reclaiming the land [1, 5, 6]. Furthermore, non-edible oils may contain toxic substances such as triterpenoids and strong odor in neem oil, and furanoflavones, furanoflavonols, chromenoflavones, flavones, and furanodiketones in karanja oil . Rubber seed oil contains cyanogenic glucoside that yields poisonous prussic acid (HCN) due to enzymatic reaction . Jatropha oil contains toxic phorbol esters (0.03–3.4%)  or curcain , depending on the variety. Hence, it is better to exploit these non-edible oils as feedstocks for biodiesel production.
2.1. Non-edible oil crops in South-East Asia
2.1.1. Jatropha (
2.1.2. Karanja (
2.1.3. Polanga (
2.1.4. Neem (
2.1.5. Rubber (
The rubber tree is a perennial plantation crop, indigenous to South America and cultivated as an industrial crop since its introduction to South-East Asia around 1876. Rubber tree can grow in hot and moist regions. Its productivity starts from eighth year onwards. The yield of the seeds is about 300–500 kg/ha/year . Rubber seed kernels (50–60% of seed) contain 40–50% of pale yellow oil [25, 26, 27]. Rubber seed oil does not contain any unusual fatty acids, but is rich in polyunsaturated fatty acids C18:2 and C18:3 that make up 52% of its total fatty acid composition . Rubber seed oil contains 18.90% saturated fatty acid (10.20% palmitic acid, 8.70% stearic acid) and 80.50% unsaturated fatty acid (24.60% oleic acid, 39.605 linoleic acid, 16.30% linolenic acid) .
2.1.6. Mahua (
3. Characteristic of non-edible oils
Characteristics of vegetable fats and oils depend on the length and degree of un-saturation of the fatty alkyl chains. Thus, the fatty acid plays an important role in determining biodiesel characteristics. Amount of each fatty acid, chain length, and number of double bond present in the hydrocarbon chain influences the biodiesel properties . The stability of biodiesel also depends on the feedstock properties used for biodiesel production. The most abundant fatty acids in the oil samples were oleic, linoleic, linolenic, palmitic, and stearic fatty acid. Oleic acid comprises of a major portion of the total fatty acid irrespective of non-edible oil summarized in Table 1 . All oils have high unsaturated fatty acids (up to 80%) which mean they have good low temperature properties and are suitable as biodiesel feedstocks ( Figure 3 ). Higher concentrations of saturated fatty acids can increase cloud point (CP) and cold filter plugging points (CFPP), which makes them undesirable as liquid fuel [31, 32]. On the other hand, unsaturated fatty acids helps to maintain oil in liquid form, but if the concentration of polyunsaturated fatty acids exceeds certain limit they can form polymers under heat which can block the fuel system of a vehicle . The oils with larger proportion of saturated fatty acids will be more stable than those having larger portion of unsaturated fatty acids. But again, higher proportion of saturated fatty acids lowers the temperature for becoming solid even in the room temperature. The presence of double bond in the fatty acid brings diesel on poor stability. This decomposition occurs very fast at an exponential rate.
|Oilseed content, %w||55||33||65||40–50||50||44.5||—|
|Viscosity 40°C (mm2/s)||18.2||27.8||72.0||76.4||24.6||—||7.50|
|Calorific value (Mj/kg)||38.2||34.0||39.3||37.5||36||—||42.25|
The amount and type of free fatty acid (FFA) in the biodiesel determines the viscosity, one of the most important characteristics of biodiesel. Due to the presence of higher amount of long chain FFA, polanga (72.0 mm2/s) and rubber (76.4 mm2/s) seed oils may have a slightly higher viscosity compared to others. Karanja and mahua oil has similar viscosity, due to the presence of same FFA. Iodine value represents the degree of unsaturation and relatively high iodine value is reported in range 69.3 in neem to 135 in rubber seed oil ( Table 1 and Figure 1 ). These properties are relatively applicable in cold climates. From calorific value, non-edible oils have potential to be biodiesel feedstocks.
Cetane number (CN) is widely used as diesel fuel quality parameter related to the ignition delay time and combustion quality [14, 32]. Higher cetane numbers in all vegetable oils listed in Table 1 , will give better ignition properties. Cetane number increases with the increase of saturated fatty acid, and increases linearly with the chain length, decrease with number of double bonds and carbonyl groups move toward the center of the chain. High level of saturated fatty acid (C14:0, C16:0, C18:0) raise cloud point, cetane number, NOx, and improve stability, while more polyunsaturated (C18:2, C18:3) reduce cloud point, cetane number, stability, and raise NOx.
4. Barrier of transesterification process for non-edible oils
Generally, non-edible oil has high free fatty acid content of 2.53–22% in weight basis. Alkaline transesterification is not feasible for oil containing high free fatty acid for producing biodiesel [33, 34]. It generates soap, consumes more catalyst and reduces the effectiveness of catalyst. Subsequently, soap causes the solution to be more viscous, and leads to the formation of gel and foam that inhibits purification of biodiesel from glycerol . To overcome this dilemma, biodiesel production from non-edible oils that has high free fatty acid was conducted by several methods; two/three stages reaction, acid-catalyzed esterification and alkaline-catalyzed transesterification; enzymatic process; and supercritical methanol [36, 37]. In enzymatic process, water content in the raw material does not interfere to the reaction conducted in low temperature. Lipase reaction occurs at the interface between the aqueous and oil phase  which generates alkyl ester with high purity and easy separation . Due to deactivation of catalyst and time cut in a few minutes, supercritical transesterification in high temperature and pressure can tolerate presence of high percentage of water in the feedstock [40, 41, 42].
5. Biodiesel production from non-edible oil
Several studies have shown that there exists an immense potential for the production of plant-based oil to produce biodiesel. Azam et al.  studied the prospects of fatty acid methyl esters (FAME) of some 26 non-traditional plant seed oils as potential biodiesel feedstocks. Among them,
Most of the researchers [20, 36, 43, 44] used two stage (acid catalyzed and alkaline catalyzed) esterification for biodiesel production from
Two-stage process was conducted in producing biodiesel (up to 20% FFA) from
Crude polanga oil generally has 22% free fatty acid. Hence, it must be carried out in three-stage process for producing appropriate biodiesel [6, 20, 47]. Three-stage transesterification process was zero catalyzed transesterification, acid catalyzed transesterification, and alkaline catalyzed transesterification. The oil was purified from organic matter and other impurities by mixing 0.5%v toluene and 35%v methanol as reagent. The reaction was carried out at 65°C for 2 h. Acid catalyzed esterification was conducted by 0.65% v H2SO4, molar ratio of alcohol to oil of 6:1 for 4 h. This process reduced FFA less than 2%. Sahoo and Das  added 0.5%v ortho-phosphoric acid as a reagent that reduced FFA from 14.5 to 1.62%. Alkaline catalyzed transesterification process was conducted by using 1.25% w KOH, molar ratio of methanol to oil of 8:1, 60°C for 2 h. Biodiesel from polanga still gets unsatisfactory yield below 90%. Further research needs to be done to get better yield in order for polanga to be more acceptable in the biodiesel production.
Neem seed contains 20–30% and kernel contains 30–52% oil . The oil of neem seed has several uses from making soap, pesticides, and pharmaceuticals to biodiesel. The seed oil contains 29.30% saturated fatty acid (14.90% palmitic acid, 14.40% stearic acid) and 69.40% unsaturated fatty acid (61.90% oleic acid, 7.50% linoleic acid) . Biodiesel production from neem seed oil is quite the same with other non-edible oil resources in order to get appropriate product.
Several researchers produced biodiesel from rubber seed oil [25, 29, 48]. Ikwuagwu et al.  produced biodiesel from fresh rubber seed oil, where the FFA in crude oil was 2% and in refined oil 0.5%. The reaction carried out under condition of molar ratio of methanol to oil was 6:1 and 1% NaOH as catalyst, ester yield from crude seed oil was just 76.64% compared to refined oil (84.46%). Ramadhas et al.  produced biodiesel from rubber seed oil with high free fatty acid by two stages reaction. Acid esterification reduced FFA of oil from 17% to less than 2% when reaction with 0.5% v H2SO4, methanol to oil molar ratio of 6:1, temperature at 50°C for 20–30 min. Final stage was alkaline transesterification, where the oil mixture with methanol to oil molar ratio of 9:1 and 0.5%w of NaOH at temperature 40–50°C during 30 min for achieving conversion efficiency almost 100%. Result from Ramadhas et al.  showed rubber seed oil is appropriate as biodiesel feedstock. The viscosity of biodiesel obtained is close to diesel, although yield that Ikwuagwu et al.  achieved was considered uneconomical. However, further research is needed for fostering the biodiesel quality as well as more acceptability.
Ghadge and Raherman [35, 49] studied the process optimization for biodiesel production from
6. Characteristic of biodiesel from non-edible oils
Table 2 represents the fuel properties of methyl esters (biodiesel) from various plant-based oils. Specific gravity of biodiesel methyl esters of six non-edible oils meet the standard biodiesel ranging from 0.86 to 0.89.
|EN 14214||ASTM 6751–09|
|Calorific value (MJ/kg)||42.7||42.1||41.4||37.0||40.1||36.5||42.5||—||—|
|Viscosity (mm2/s) at 40°C||4.2||4.4||4.0||4.0||8.8||5.8||3.8||3.5–5.0||1.9–6.0|
|Flash point (°C)||148||163||140||208||—||130||45||≥120||≥130|
|Cloud point (°C)||10.2||14.6||13.2||—||—||4.0||−1.0||—||—|
|Pour point (°C)||4.2||5.1||4.3||6.0||—||−8.0||−16.0||—||—|
|Cetane number||60.7–63.3||59.7–60.9||52.5||—||—||—||—||—||47 min|
Viscosities of all non-edible oils were ranging from 3.8 to 8.8, which comply with the standard biodiesel of EN 14214 and ASTM 6791–09, except neem methyl ester ( Table 2 ). The neem oil was the most viscous one among the six oils. Consequently, the viscosity of neem methyl ester was the highest in their respective series. Biodiesel derived from jatropha, karanja, polanga, rubber, mahua, and neem were found to comply with the industrial standards.
7. Status of biodiesel production in South-East Asia
Recently, biodiesel production from non-edible oil has risen. In South-East Asia, countries such as Indonesia, Malaysia, Philippines, and Thailand have taken initiatives to develop biodiesel from non-edible oil generally using
Malaysia started with breeding high quality
Production of biodiesel from edible oil such as palm, coconut, soybean, corn, rape seed oils, or other food crops like sugarcane will lead to severe shortage in food and its security. High price of edible oil makes them not feasible for the production biodiesel. In this situation, use of oils from non-edible sources may increase fuel security without interfering with the food security. South-East Asian countries fall in the tropical region and have many species of crops of non-edible oil. The non-edible crops can grow in waste as well as in marginal lands which may be helpful for reclaiming the unproductive areas. It is better to exploit these non-edible oils as feedstocks for biodiesel production. Major non-edible plants in this region are jatropha, karanja, polanga, neem, rubber, and mahua have shown significant potential as biodiesel feedstock. Biodiesel properties and fatty acid composition has in-direct correlation because transesterification cannot change the fatty acid composition. Fatty acid compositions give paradoxal properties among cetane number, low temperature properties, and stability of the products. Optimal characteristics could not be achieved within this current time. At present the end usage production is low and utilization of these oils are limited. Exploitation and utilization of these non-edible oils as biodiesel feedstock can save foreign currency, fossil fuel dependency, and equally improve the rural economy as well as future job opportunities.