Castor Oil

It is reported that there are more than 350 species of oil crop in the world. Among the prominent ones are castor, rapeseed, sunflower, soybean, palm, etc. (Torres et al., 2013). India is the world’s largest exporter of castor oil followed by China and Brazil (Ogunniyi, 2006). Castor oil is known for its high concentration of ricinoleic acid (12-hydroxy-9-octadecenoic acid) that constitutes 89% in the oil. Other fatty acids are present in minor amount that includes linoleic acid (4.2%), oleic acid (3.0%), stearic acid (1%), palmitic acid (1%), dihy-droxystearic acid
(0.7%), linolenic acid (0.3%) and eicosanoic acid (0.3%). The molecule present in ricinoleic acid is known to show three points functionality. These include carboxyl group which

The castor oil possesses a high density. It has been attributed to the presence of ricinoleic acid that contains a hydroxyl group which causes strong intermolecular interactions through hydrogen bonds. This increases the bulk density of the castor oil (Ustra et al., 2013).
Castor oil is hygroscopic and thus it becomes necessary to restrict its exposure to moisture as moisture content in feedstock may cause hindrance to transesterification. Among the non-edible oils, the acid value (2.1 mg KOH g-1
) of castor oil is very less. Mejia et al. (2013) also reported the acid value of castor oil to be low i.e. 1.8±0.1. This is an advantage as a low acid value will
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render an easy single step of transesterification. It is assumed that feed stocks with acid value lower than 4 mg KOH g
-1
could undergo single step transesterification (Dias et al., 2013). The presence of water in the oil causes hydrolysis of the esters produced during the reaction.
Sánchez-Cantú et al. (2013) reported the synthesis of biodiesel from castor oil using hydrocalumite-type compound as heterogeneous catalyst. A high conversion of the castor oil

Kılıç et al.
(2013) reported a high yield of biodiesel (99.81%) obtained from castor oil in a very short reaction time (10 min) at 65 oC using catalyst, CH3OK (1.5% wt of oil) and methanol to oil molar ratio of 7:1. Rodríguez-Guerrero et al. (2013) also studied about the the synthesis of
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biodiesel from castor oil at supercritical temperature (200-350 oC). The advantage with supercritical conditions and the pressure generated due to high temperature was a very less requirement of catalyst (0.1% wt) which was even lesser than that required for neutralization of the castor oil. A high biodiesel yield of 98% has been reported. Thomas et al. (2013) reported esterification of various oils (safflower, cottonseed, castor, used cotton seed) and found that the viscosity reduction among the oils was highest for castor oil even though it was most viscous.
The highest conversion as fatty acid methyl ester has been reported to be observed with castor oil
(93%) followed by safflower (89%), cottonseed (83%) and used cottonseed (80%) oil. Tsoutsos et al. (2013) utilized wastewater for the cultivation of sunflower and castor crop. It was