4. Barrier of transesterification process for non-edible oils

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 [11]. 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.

Figure 3. Distribution of fatty acid and its influence on the characteristics of biodiesel in different non-edible oils.

Sources: Azam et al. [11], Ghadge and Raheman [35], Karmee and Chadha [42], Puhan et al. [30], Ramadhas et al. [5, 29],

Properties Jatropha Karanja Polanga Rubber Mahua Neem Diesel

Flash point 174 205 221 198 232 — 50 Calorific value (Mj/kg) 38.2 34.0 39.3 37.5 36 — 42.25 Iodine value 93.0 80.9 93.8 135.3 74.2 69.3 38.3

Table 1. Characteristic and composition of several non-edible oils compared to diesel.

/s) 18.2 27.8 72.0 76.4 24.6 — 7.50

Viscosity 40C (mm<sup>2</sup>

206 Advances in Biofuels and Bioenergy

Tiwari et al. [16], Sahoo and Das [20], Islam et al. [53].

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 [35]. 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 [38] which generates alkyl ester with high purity and easy separation [39]. 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 [40–42].
