Central Composite Design of Biodiesel Production from Waste Cooking Oil using Tympanotonus fuscatus (Periwinkle) Shells as Catalyst

Abstract

Biodiesel has been generally accepted as an environmentally – safer alternative to fossil based fuels. However, concerns of the cost of production, use of acid catalysts leading to corrosion, and recovery of homogenous catalyst remain. This study therefore seeks to optimize the transesterification process parameters in the conversion of waste cooking oil (WCO) using waste Tympanotonus fuscatus shell (WTFS). The catalysts were characterized using XRD, FTIR, and XRF. Temperatures ranging from 30°C to 90°C, catalyst loading from 1 to 10% by weight, and reaction durations from 30 to 180 minutes were examined for the transesterification technique. The physiochemical properties of the waste cooking oil revealed a high acid value (10.02mgKOH/g), kinematic viscosity of 13.30 mm2/s, pour point, 156oC, flash point of 104oC, Calorific value of 34.78 MJ/kg, carbon content of 2.65% m/m, among other parameters while the GCMS analysis indicated the presence of C16 to C21. The biodiesel however showed an acid value of 0.416 mgKOH/g, viscosity of 4.638 mm2/s, pour point of 0.3oC, flash point of 104oC, calorific value of 40.17 MJ/kg, and carbon content of 0.019% m/m which were in agreement with the EU and American standards. The elemental composition and crystalline structure of the catalyst revealed a considerable concentration of CaO, MgO, Al2O3, SiO2, and other metal oxides. The CCD approach used to design the experiments was significant (p <0.0001) and the biodiesel synthesis which resulted in a maximum yield of 91.70% was obtained with 5.5% WFTS, 105 minutes of reaction time, 65 oC, and a 1:7 oil–Methanol ratio. The operating parameters of temperature (p <0.0001), catalyst load (p = 0.00713), and time (p = 0.0288) all had significant effects on biodiesel yield; however, temperature had a stronger influence than the other process variables. The ANOVA results showed that the factors were extremely significant while Fit statistics and model comparison revealed a coefficient of determination of 97.66%, with the predicted value of 84.68% and the adjusted value of 95.00%. The biodiesel produced met the biodiesel standards.