COMPARATIVE STUDIES OF BIO-BASED CATALYSTS AND INORGANIC EQUIVALENTS FOR LARGE-SCALE BIODIESEL PRODUCTION
This research focused on optimizing the production of biodiesel via heterogeneous catalysis to lessen the overdependence on fossil fuels. Unlike fossil fuels, biodiesel offers a cleaner alternative by reducing carbon emissions and global warming. With focus on waste to resource, waste cooking oil and ethanol were utilized as the biodiesel feedstock. As well, heterogeneous solid catalysts were sourced from waste biobased resources including eggshell, fish scales and cow bone, thereby providing an alternative to their disposal.
On the individual application of each biobased catalyst in the transesterification reaction, the biodiesel yield determined for each catalyst fell short in performance, thus, necessitating the need to optimize them for a synergistic effect. Optimization techniques employed included physical mixing in varied tri-blend ratios, hot and cold water mixing of tri-blends, and wet-impregnation of potassium promoter (1wt%, 5wt% and 10wt%) on tri-blends. Furthermore, ethanol-to-oil mix ratio was varied. Upon the implementation of these techniques, biodiesel optimum yield of ~75% was obtained when 10wt.% of K was impregnated on a 1:6:3 eggshell, fish scale and cow bone mix ratio.
To better enhance the relatively low yield performance, banana peels which are rich in potassium were explored as a potential bio-based catalyst. Banana peel catalysts were synthesized at calcination temperatures of 600℃, 800℃ and 900℃ to yield BP600, BP800 and BP900 catalysts respectively. BP900 catalyst recorded the highest biodiesel yield of ~96%. However, due to commercialization issues such as low availability and low calcination yield (10%), the synthesis of an inorganic replica of the BP900 catalyst using readily available commercial inorganic precursors became imperative. By considering the elemental compositions in BP900 catalyst, three (3) equivalent inorganic catalysts were synthesized via co-precipitation and co-impregnation methods. The three catalysts showed similar performance with an average biodiesel yield of 84%. The co-precipitated catalyst, BPIn2, was selected and used for further studies.
The parametric analysis of the BPIn 2 catalyst showed that, as the reaction temperature, time, ethanol-to-oil ratio and catalyst weight increased, the biodiesel yields also increased. The obtained optimum process conditions are 70℃, 6 hrs, 21:1 and 2wt% catalyst dosage respectively. Regression analysis on intrinsic kinetic data showed an activation energy need of 39.1 kJ/mol, and reaction orders of 2 and 3 relative to oil and ethanol. A parity plot of the experimental rate and predicted rate revealed an AAD of 22%. Lastly, analysis of the correlation between the catalyst composition and performance revealed that, the biodiesel yield increased significantly as the silicon content increases along with its interaction with potassium.