Reactive extraction of castor seeds and storage stability characteristics of produced biodiesel

• Reactive extraction of castor seeds was investigated using NaOH catalyst.
• Highest biodiesel conversion of 92.43% was obtained with NaOH compared to KOH (72.3%).
• Storage stability study suggested that biodiesel stored in a dark condition is stable.

In the present study, oil was extracted from a single castor seed by eppendorf vial method, and the oil yield was compared with the yield obtained from Soxhlet method. The oil yield from both methods was about 55% and comparable. Free Fatty Acid (FFA) content of extracted castor oil was found to be lower (<1 mg KOH/g oil). Therefore, single step transesterification (reactive extraction) was carried out to study the effect of various reaction variables on the conversion of castor oil biodiesel. The optimum biodiesel conversion of ∼93% was achieved under following conditions: 4 h, 1:250 oil to MeOH molar ratio, 1 wt.% NaOH, 40 °C, 0.75 mm particle size, 20 g seed, 600 rpm and 10 (vol.%) co-solvent. The estimated fuel properties of biodiesel obtained with NaOH, KOH and NaOH (with co-solvent) were found to be similar and within the limits of ASTM standards. Similarly, storage stability of prepared biodiesel was evaluated over a six-month storage period (180 days) under three different storage conditions. The results showed a sharp decrease in fuel stability over time in terms of increase in density from 0.878 to 0.984 g/cm3, kinematic viscosity (10.59–16.18 cSt), acid value (0.52–5.15 mg KOH/g) respectively. While, iodine value significantly decreased from 82.5 to 54.57 g I2/100 g oil over time. Biodiesel sample stored in the open air degraded faster than samples stored in other storage conditions.