Parametric optimization of calcined and Zn-doped waste egg-shell catalyzed biodiesel synthesis from Hevea brasiliensis oil
Wasi Ur Rahman, Abu Mustafa Khan, Abdul Hakeem Anwer, Umar Hasan, Bisheswar Karmakar, Gopinath Halder
Abstract
The utilization of waste sources for energy development is increasingly gaining popularity because of its two-fold benefit to the environment. The present study discusses the synthesis of biodiesel from commercially available rubber seed oil using two catalysts: CaO derived from calcined waste egg-shells and Zn-CaO prepared by doping ZnSO4 onto the calcined egg-shells through wet impregnation. An L9 Taguchi matrix was used to optimize the process, and can accomodate 4 parameters at 3 levels each. Data obtaind was used for a comparative evaluation of their catalytic performance. During catalyst characterization studies, morphological analyses showed the effectiveness of calcination in development of a porous structure that was capable of adsorbing Zn in high quantities, which was further verified through spectral analyses. Using CaO the optimal biodiesel yield noted was 80.2%, while Zn-CaO enabled a biodiesel yield of 94.12%. The optimal conditions were a reaction temperature of 55°C, methanol to oil molar ratio of 12:1, catalyst concentration of 5% w/w for both catalysts within a reaction duration of 1.5 h (for CaO) and 2 h (for Zn-CaO). Fuel characterization tests through ASTM prescribed procedures showed that the obtained product has acceptable physico-chemical properties and is thus suitable for use as biodiesel. Reusability studies (tested up to 4th reuse) indicated that CaO loses its catalytic efficiency much faster compared to Zn-CaO, primarily due to the vacant active sites in CaO being blocked by increased adsorption of organic molecules during the transesterification phase compared to Zn-CaO.