The influence of functionalized sba-15 on the production of citronellol ester via immobilized candida rugosa lipase
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Date
2016-02-01
Authors
Yasmin Che Ani
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Abstract
Enzymatic esterification using lipase has been proven to be potential in the
ester production. This is due to the diminishing of natural resources used in the ester
production. As an alternative, synthethic ester has been produced as nature-identical
materials. In the present study, citronellyl octanoate ester is being studied as the
model reaction.
Immobilized lipase is very important in an esterification process due to its
reusability, its operational flexibility, and ease of product recovery from the lipase.
Therefore, the pure SBA-15 mesoporous material has been chosen for this study as a
support for immobilized enzyme due to its larger pore size and better thermal and
hydrothermal stability. The non-hydrothermal method that will produce the same
characteristics of SBA-15 has been synthesized in this study. The best conditions
were at a temperature of 40 oC, HCl concentration 2.5 M and 1.79:1 TEOS/TCP
molar ratio which gives the highest BET surface area of 644.14 m2/g, 661.17 m2/g
and 641.35 m2/g respectively. Pure SBA-15 also functionalized with amine
functional groups by post synthesis under reflux conditions at 85 oC for 2 hours. The
best conditions to immobilize pure SBA-15 and APTES-SBA-15 with Candida
rugosa lipase (CRL) were at enzyme activity of 19530 U/mg, initial pH buffer 8.0
and at temperature 35 oC which gives the highest percentage amount enzyme
adsorbed about 95 %. From the results obtained, an adsorption equilibrium study of
CRL on SBA-15 and APTES-SBA-15 was investigated. The adsorption isotherm
study shows that both Freundlich isotherm model and Temkin isotherm model
favoured for CRL-SBA-15 while CRL-APTES-SBA-15 was the best fit with Temkin
isotherm model. The kinetic of immobilized pure SBA-15 and APTES-SBA-15 with
CRL also studied to investigate the mechanism of immobilized CRL on pure SBA-15
and APTES-SBA-15. The pseudo-second order kinetic model fitted for both CRLSBA-
15 and CRL-APTES-SBA-15. The thermodynamic study shows that for both
CRL-SBA-15 and CRL-APTES-SBA-15, this process was exothermic and
favourably spontaneous. In this study, the activation energy for enzyme activity
19530 U/mg was higher at about 163.5 kJ/mol for CRL-SBA-15. While for CRLAPTES-
SBA-15 the activation energy is (-72.2) kJ/mol.
The morphologies of the mesoporous support are known to play an important
role in the performance of the immobilized enzyme. Therefore, the characterization
of immobilized CRL on pure SBA-15 and APTES-SBA-15 mesoporous support has
been investigated using FT-IR, XRD, SEM, TEM, EA and nitrogen adsorptiondesorption
analysis, The enzyme kinetics mechanism for CRL-APTES-SBA-15
follows Ping Pong Bi Bi with noncompetitive inhibition compared to CRL-SBA-15
follows Ordered Bi Bi with uncompetitive inhibition. It shows that CRL-APTESSBA-
15 have higher catalytic efficiency compared to CRL-SBA-15 due to its lower
value of KM.