No abstract

In the present study, nonedible seed oils from underutilized Nigerian NIG800 clonal rubber seeds were extracted using a solvent method to obtain a yield of 43 wt % after extraction for 1 h using a 0.5 mm kernel particle size. The oil was characterized by GC-MS, FT-IR, and NMR analyses, and found to possess several potential industrial applications. The physicochemical properties determined agreed with reported values in the literature. The low ash content (0.001 wt %) indicates the absence of trace metals that catalyze oxidation reactions. The low moisture (1.73 wt %) and carbon residue (0.4 wt %) contents, high volatile matter (97.869 wt %), and low freezing point (−18 °C) properties of the oil indicate a better source material for biodiesel synthesis for use in cold regions compared to other vegetable oils. The higher heating value of 39.37 kJ/kg for the oil is within the range of values reported by researchers for other nonedible vegetable oils. The high content of saturated fatty acids (30.67 wt %) and moderately low monounsaturated fatty acids (69.33 wt %) confer a good shelf life compared to other oils. A closer examination of results of the NMR and GC-MS show a satisfactory agreement that these genetically modified rubber seeds have an insignificant proportion of polyunsaturated fatty acids (linoleic, linolenic, etc.). This insignificant presence of polyunsaturated fatty acids supports higher thermal stability, and slower rate of oxidation of the oil compared to other vegetable oils. The kinetics of thermal oxidative degradation follows a first-order reaction. The activation energy of 13.07 kJ/mol was obtained within the temperature range 100–250 °C.

In the present study, waste rubber seed shell (RSS) obtained from our previous study was investigated as a plausible solid base catalyst for the transesterification of esterified rubber seed oil (RSO) to biodiesel. TGA, XRF, XRD, SEM, and N 2 adsorption/desorption analysis (BET) were used to characterize the catalyst. Central composite design (CCD) was employed to design the experiments conducted to study the influence of the process variables (reaction time, methanol/oil ratio, and catalyst loading) on biodiesel yield. Response surface methodology (RSM) technique, was used to optimize the process, and the quadratic model developed was statistically significant with F-value of 12.38 and p-value (<0.05). The optimum conditions obtained from RSM are as follows: reaction time (60 min), methanol/oil ratio (0.20 vol/vol), and catalyst loading (2.2 g) with a maximum biodiesel yield of 83.11% which was validated experimentally as 83.06 ± 0.013%. Reusability test of the catalyst at optimum conditions shows that the biodiesel yield was over 80% after fourth cycle of usage and the leached Ca 2+ ion content of biodiesel was 3.26 mg/kg (ppm). The ester content determined by a precalibrated gas chromatography and the oxidation stability of the biodiesel are 96.7% and 7.8 h, respectively. The characterized biodiesel complied with ASTM D 6751 and EN 14214 biodiesel standards.