Acid-base bifunctionalized hydrotalcite catalyst for biodiesel production from waste cooking oil using ultrasound-assisted reactor system
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Date
2016-09-01
Authors
Mohd.Razealy Anuar
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Abstract
This research work is focused on the development of an advanced catalytic fatty acid methyl ester (FAME) production from waste cooking oil using an ultrasound-assisted system. Hydrotalcite (HT) catalyst prepared using combustion method was employed with some structural modification in order to develop acid-base bifunctionalized HT. The acid-base bifunctionalized HT was meant to be beneficial in conducting simultaneous transesterification and esterification reaction. The use of ultrasound-assisted system could overcome the emulsification and mass transfer limitations due to immiscibility of oil and alcohol. Hence, reaction time could be significantly shortened. Two important parameters to synthesize MgAl based HT i.e. calcination temperature (550 oC–850 oC) and fuel type (saccharose, glucose and fructose) were particularly investigated. Alteration on MgAl based HT structure was done by introducing second divalent metals (nickel, copper and zinc). The amphoteric properties of these transition metals successfully resulted in bifunctional acid-base properties of HT. The structural, crystallinity, surface morphology, thermal decomposition, bonding characteristics and acid strength of the synthesized HT were elucidated by several characterization techniques. The dependence of HT’s characteristics on the synthesis parameters and correlations with their catalytic performance under ultrasound condition were successfully studied. The MgAl based HT catalyst prepared using saccharose and calcined at 650 oC showed high biodiesel yield (about 76.45 %) in just 60 minutes in the presence of low ultrasound amplitude (~11 kHz). Meanwhile, HT introduced with 10 % nickel demonstrated the highest FAME yield of about 86.84 % in just 60 minutes. The simultaneous transesterification and esterification reactions were evidently demonstrated by carrying out the FFA test reaction. The FAME yield was found to increase due to the esterification of FFA to FAME. The HT catalyst synthesized was highly stable which was capable to perform several cycles of reaction with significantly low total FAME reduction (4.52 %) and with no significant leaching of active component. The optimization study successfully demonstrated effects of 4 independent reaction variables i.e. reaction time (30-90 min), methanol to oil ratio (7:1-23:1), amplitude (40-60 %) and catalyst amount (0.06-0.08 g catalyst/ g oil). A quadratic model is generated with 95.84 % of confidence level. The most reasonable optimum parameters with the smallest error (1.15 %) are identified. The quality of the obtained FAME was evaluated which conform to the ASTM D6751 and EN 14214 specifications. Lastly, kinetic study was also investigated and the apparent activation energy for the simultaneous transesterification and esterification reactions (73.11 kJ/mol) is lower than that of transesterification reaction (81.16 kJ/mol) which indicates an accelerated reaction.