Abstract
The catalyst preparation technique plays a significant role in its activity and durability. The present research investigated sodium hydroxide and sodium chloride as the precursor chemicals for impregnation on waste oyster shells that were tested as heterogeneous base catalysts for transesterification of soybean oil. Effects of precursor concentration and calcination temperature on the surface structure and the activity of the catalysts were studied via the one-factor-at-a-time method. The optimal impregnation concentrations of sodium hydroxide and sodium chloride were determined to be 6 mol/L and 2.43 mol/L, respectively. The optimal calcination temperature was determined to be 800 °C for both sodium hydroxide and sodium chloride-impregnated catalysts. Analyses of the catalysts via X-ray Diffraction and X-ray photoelectron spectroscopy indicated that different active species were formed on the surface depending on the calcination temperature. Results obtained from this study could be used to fine-tune the procedure for the synthesis of transesterification catalysts from aquatic animal shells.
Highlights
Solid base catalysts have been extensively studied for their catalytic performance in transesterification reactions [1]
Doped could react with the oxygen present in CaO to produce defect sites on the surface, which served as the enhanced basic sites for transesterification reactions [3,4,5,6,7,8]
Our results indicated that impregnation of NaOH on oyster shell increased the fatty acid methyl esters (FAME) yield from 71% (3 h reaction time) to 87% (1 h reaction time)
Summary
Solid base catalysts have been extensively studied for their catalytic performance in transesterification reactions [1]. CaO is one of such solid base catalysts capable of transesterification of various oils to fatty acid methyl esters (FAME). To increase the catalytic activity of CaO, wet impregnation methods have been employed to modify the surface of CaO to generate more active sites. Doped could react with the oxygen present in CaO to produce defect sites on the surface, which served as the enhanced basic sites for transesterification reactions [3,4,5,6,7,8]. Despite showing a continuous drop in specific surface area (with increasing Li content), all Li-impregnated CaO catalysts that were tested exhibited increased basic strengths when compared to CaO. The transesterification results indicated that the initial reaction rate increased with the increased Li content and reached a maximum when Li content reached 1.23 wt. %
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