Effect of pre-treatment on solvents extraction and physico-chemical properties of castor seed oil

Abstract

Extraction of castor oil from castor seed was carried out by Soxhlet method using polar and non-polar commercial solvents at the optimum conditions obtained from the preliminary oil extraction study. The solvents used were hexane, pentane, petroleum ether, cyclohexane, ethylacetate, methanol, and isopropanol. The effect of different process parameters such as temperature, solute to solvent ratio, and extraction time were studied to optimize and compare the extraction efficiency of different solvents. The higher oil yields of 56.07% and 55.22% were obtained by using polar solvents, i.e., ethyl acetate and methanol, respectively. The physico-chemical properties of the castor oil extracted using different solvents were also estimated to determine its quality potential using ASTM methods. Similarly, the performance of seed pre-treatment on the oil yield and the suitability of methanol as a possible extracting and reactive solvent for biodiesel production was also investigated. The pre-treatment of castor seed has slightly increased the oil yield and decreased the values of acid value (3.92 to 0.925 mg KOH/g) and pour point (−15 to −21 °C) significantly. Apart from that, thermal and oxidative stability analysis was performed using thermo gravimetric analysis and differential scanning calorimetry under nitrogen and air atmosphere, respectively. The fatty acid profile of castor oil was determined by using gas chromatography. The 1H nuclear magnetic resonance spectroscopy was employed for two castor oil samples (extracted after and before heat-treatment of seeds) to compare and identify the different protons in present the oil. The obtained physico-chemical properties indicate that oil meets the prescribed biodiesel feedstock quality standards and further justifying that methanol can be a capable solvent for simultaneous extraction and transesterification.