ABSTRACT

In this study, waste soya oil was transesterified with methanol in the presence of sodium hydroxide (NaOH) as catalyst among other process conditions to produce biodiesel. Waste soya oil was collected, and characterized to determine its density, refractive index, moisture content, saponification value, viscosity, acid value, peroxide value and iodine value, while those for the biodiesel produced through transesterification were density, cloud and pour points, flash and fire points, anisidine point, API gravity and cetane value. The effects of the process parameters (catalyst concentration, reaction time, reaction temperature, methanol/sample ratio and agitation speed) were studied individually and in matrix form to establish synergistic interactions. Process optimal conditions that gave the maximum yield of 94.70% were: catalyst concentration of 1%, reaction time of 60 minutes, reaction temperature at 70oC, methanol/sample ratio of 6:1, and agitation speed of 300rpm. Other set of conditions that caused the lowest biodiesel yield of 66.20% produced were catalyst concentration of 0.25% at reaction time of 30 minutes, under the reaction temperature of 50oC with methanol to sample ratio of 2:1, and agitation speed of 150rpm. The physiochemical properties of the yield investigated to ascertain their adherence with the ASTM and EN standards for biodiesel production revealed that the developed biodiesel properties conformed within the standard recommendations. NaOH was proven to be efficient as the catalyst for converting the waste used soya oil to biodiesel. From the established results, Cetane index of 74.12, kinematic viscosity of 4.43mm2/s, density of 876.6kg/m3, flash point of 142oC, fire point of 150oC, cloud point of 8.5oC and moistuure content of 0.04% were respectively obtained. All these values fell within the recommended ASTM and EN standards. The use of surface and contour plots for the process parameters explained the synergistic yield during the optimization process. The gas chromatography mass spectrometry (GCMS) analysis carried out to evaluate the quality of the sample with respect to deterioration, gave an ester percentage of 99.8% for the bio-oil which was within the minimum standard range of not less than 96.5% recommended. From the GCMS profiling of the waste bio-oil, it was established that the most prevalent fatty acids identified among other 13 distinct compounds were palmitic, oleic and stearic acids with percentage concentrations of 36.73, 32.39 and 8.84% respectively. Consequently, prominent among other 16 distinct esters found in the biodiesel sample with regards to their percentage concentrations were most prevalently methyl hexadecanoate (22.98%), methyloctadecanoate (16.89%), methyl tridecanoate (16.68%), methyl myristate (9.67%), methyl 15-methylhexadecanoate (5.97%), methyl octanoate (4.49%) and methyl caprylate (3.90%), with exogenous substances identified in the sample to include cyclododecane epoxide, methyl triacontanoate and methyl heptacosanoate.