Modeling And Optimization Of Isoamyl Acetate Production In Enzyme Catalyzed Esterification
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Date
2011-06
Authors
Hashim, Nur Hamizah Abdul Ghani @
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Abstract
Isoamyl acetate is an important substance which is used in various industries
including flavour and fragrance industry. The production of this compound using
enzymes had attracted many attentions due to its advantages of moderate operating
parameters, limited side reactions and easy product recovery. In enzyme catalyzed
esterification, acetic acid and isoamyl alcohol are used as substrates to the Candida
antarctica immobilized lipase to produce isoamyl acetate. In direct esterification
reaction, the ester synthesis is affected by excess water which can change the
thermodynamic balance of reaction towards hydrolysis. On the other hand, during the
initial stage of the reaction, water activates the enzymes and increases enzyme
activity thus increases the reaction rates. Therefore, the amount of water content has
been a critical parameter in enzyme catalyzed esterification. Beside this, few
parameters considered to affect the process were temperature, enzyme loading,
concentration of substrates and reaction time. In order to understand the process and
the relationship of these selected parameters, process optimization and model
development are essential. The processes optimizations were done via “one-factor-ata-
time” and response surface methodology (RSM). The optimum conditions obtained
from “one-factor-at-a-time” were compared with RSM and the results were in range.
The coefficient of determination, R2 of the RSM model was 0.9448. Then, the error
obtained from model validation was less than 5% which is acceptable. RSM was
considered advantageous due to less number of experiments and the model obtained
was replicable. Therefore, the water content was optimized using RSM. The models obtained from additional response were reliable with R2 of 0.9925 and 0.9779. The
maximum product yield was 94% at optimized conditions; temperature at 36.5oC,
alcohol/acid molar ratio 0.94, enzyme/substrate ratio of 0.75 g/l within 6 hours.
Based on enzyme kinetic study, two mathematical models were proposed. The first
model shows the relationship between ester yield and substrates molar ratio,
meanwhile the second model shows relationship between reaction rate and
temperature. The R2 for enzyme kinetic and temperature dependence model were
0.906 and 0.992 respectively. These developed models showed percentage error up to
17%.
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Keywords
Acetates