Transesterification of Waste Cooking Oil in Presence of Crushed Seashell as a Support for Solid Heterogeneous Catalyst

摘要

Developing relatively cheap and widely available resources for heterogeneous solid catalyst synthesis is a promising approach for biodiesel fuel industry. Seashell which is essentially calcium carbonate can be used as a basic support for transesterification heterogeneous catalysts. In the present investigation, the alcoholysis of waste frying oil has been carried out using seashell-supported K_3PO_4 as solid catalyst. The rationale for this derives from the fact that waste frying oil contains both long-chain free fatty acids (FFA) and triglycerides (TG) which are catalysed on acid and basic sites respectively. Thus, the K_3PO_4 /seashell catalyst may serve the dual role of promoting both esterification and transesterification reactions. The catalyst was synthesized following a dipping impregnation of pre-crushed and calcined seashell in an aqueous solution of K_3PO_4. Samples with different percentage loadings of K_3PO_4 (5 to 25 wt%) were prepared. The catalyst samples were characterised (textural and acid-base properties) and biodiesel production activity was evaluated in a slurry reactor. The liquid phase composition in the reactor was determined using gas chromatography-mass spectrometry (GC-MS) analysis. The effects of different process variables; ethanol: oil ratio (3:1-15:1), catalyst concentration (10-50gL~(-1) of mixture oilðanol) on the percentage yield of ethyl ester were assessed. Reaction data revealed that K_3PO_4 /seashell solid supported heterogeneous catalyst displayed a quite un-common behaviour during the transesterification reaction of waste oils. Although the catalyst showed the occupation of two different active sties namely acid and base, its catalytic activity was found to highly associated to the strength of its basic sites. Catalyst BET surface area as well as the ratio of basic to acidic site density (BASD) were found to increase with elevating the amount of K_3PO_4 being loaded on calcined shells. Optimal ethyl ester yield was achieved with a catalyst with W=0.10 which was found to be quite beneficial achievement in terms of biodiesel economy.