Citation
Sulaiman, Safwan
(2018)
Covalent immobilization of α-CGTase on cellulose nanofiber derived from kenaf bast for enzymatic membrane reactor.
Doctoral thesis, Universiti Putra Malaysia.
Abstract
Nanobiocatalyst is a new frontier of emerging nano-sized material support in
enzyme immobilization application. This approach provides an innovative
strategy between enzyme technology and utilization of natural nano-cellulose
support in nanobiotechnology. This research work was focused on the covalent
immobilization of α-cyclodextrin glucanotranferase (α-CGTase) on the cellulose
nanofiber (CNF) support from kenaf bast fiber. The obtained immobilized α-
CGTase-CNF was applied in stirred-cell ultrafiltration (UF) membrane system
as enzymatic membrane reactor (EMR). Chemical-physical treatment (e.g.
delignification, 3-stage of bleaching and high-intensity ultrasonication) were
firstly performed to isolate the CNF from kenaf bast fiber. The combination of
this treatment contributes to the efficiency of hemicellulose and lignin removal,
and reduce its size from micro to nano-order. SEM and TEM analysis show the
size distribution of fiber in a range of nano-order scale (<100 nm), which higher
ultrasonication output power resulted in smaller size of CNF. Chemical
composition analysis reveals the cellulose content increased up to 90% after the
treatment. FTIR analysis reveals the changes in the surface functional group of
CNF, contributes successful in removal of lignin and hemicellulose in the fiber.
FTIR analysis also confirms successful immobilization of α-CGTase on CNF
through ligand–spacer arm interaction (α-CGTase–GA–1,12-diaminododecane–
CNF), where there is no significant damages on the dimensional structural of
fiber after went through these treatments process. The efficiency of immobilized
α-CGTase shows more than 62% of binding yield and more than 45% of its
residual activity were obtained. The membrane fouling of α-CGTase-CNF layer
using UF membrane indicated to the higher permeate flux declined when
applying higher pneumatic pressure to the system, but it decreased in production yield of α-CD. Reusability profile of fouled α-CGTase-CNF layer is
able to retain up to 50-60% of α-CGTase activity at 10th cycle and α-CD
productivity that represent for each operation cycle was slightly decreased from
its initial cycle. Substrate concentration and pneumatic pressure contribute to
the major effect of fouled α-CGTase-CNF layer toward the performance of
membrane operation and enzymatic production yield. Permeate flux profiles
indicate the lowest substrate concentration with high pneumatic pressure
showed the best performance of membrane operation with lowest permeate flux
declined. Meanwhile, enzymatic production of α-CD profiles indicate that
higher substrate concentration with lowest pneumatic pressure contributed to
the highest value of α-CD production. Mass transfer and reaction kinetic of
fouled α-CGTase-CNF layer were evaluated using gPROMS software. This
software was used to study the mechanism and behavior of fouled α-CGTase-
CNF layer toward the effect of substrate concentration and pneumatic pressure
for the performance of membrane operation and its effectiveness during
enzymatic reaction. The application of enzymatic membrane reactor (EMR)
module system with accuracy of mathematical modelling is beneficial for further
development of continuous membrane operation system with excellent
enzymatic performance and it is able to be reused for multiple times.
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