Optimization Of Enzymatic Synthesis Of Ethyl Valerate In Stirred Tank Reactor

• Main Author: Wan Amir Faisal
• Language: English
• Published: Universiti Sains Islam Malaysia 2018
• Online Access: http://ddms.usim.edu.my:80/jspui/handle/123456789/16001

Enzymatic synthesis of ethyl valerate, a flavour ester was successfully carried out by Lipase catalyzed esterification reaction between valeric acid and ethanol. In this study, commercial immobilized lipase from Candida Antartica (Novozym 435) was used as biocatalyst. The study was divided into four parts which is the optimization of reaction synthesis at small scales using conventional method, optimization using Response Surface Methodology (RSM) in Stirred Tank Reactor (STR), kinetic study and reactor study. Finally was verification of the product of the reaction. Preliminary synthesis of ethyl valerate was carried out in a small scale reaction with a total volume of 3.5 mL using screw-capped vials. Optimization reaction study via conventional method of varying one parameter at-a-time approach was carried out. A high percentage conversion yield of >70% was achieved at optimum reaction time of 45 min, reaction temperature of 37°C and amount of enzyme of 10% w/w at fixed agitation speed of 150 rpm. The reaction synthesis was further optimised by Response surface method (RSM) based on five-level, three-variable central composite rotatable design (CCRD) to evaluate the interactive effects of important parameters in larger scale processing which are reaction time (20-60 min), reaction temperature (40-60°C) and amount of enzyme (5-15% w/w). Generally, simultaneously increasing amount of enzyme, reaction temperature and amount of enzyme would improve the yields. The reaction was scaled-up to 40x with a total volume of 340 ml. A high percentage conversion of 69.41% was achieved under the optimum condition, which compared well with the maximum predicted value of 70.88%. Kinetic study of the reaction was also carried out, whereby the rates of reactions at different concentrations of substrate were studied. Result shown that the reactions follows Ping-pong Bi-bi mechanism which means the reaction obeyed Michaelis- Menten kinetics for single substrate as observed from the relationship between initial rate and varying alcohol concentrations. In order to evaluate reactor as a mixing device, the effect of four types of impeller mixing were used to study the reactor performance. The impellers are concave Rushton turbine, anchor, propeller and hydrofoil. The result shows there are no -* . significant different of the conversion yield of ethyl valerate. Finally, FTIR was used to verify the presence of ethyl valerate after esterification reaction. The peaks observed around 1200 cm-' corresponding to C-0 stretch of the ester group. While wavelength around 1680 cm-' corresponding to the C=O stretch of the ester group and around 3000 cm-' corresponding to aliphatic C-H stretch.