Citation
Zulkefli, Syarilaida
(2015)
Pretreatment of lignocellulosic materials by deep eutectic solvents for enhanced enzymatic hydrolysis.
Masters thesis, Universiti Putra Malaysia.
Abstract
The potential of deep eutectic solvent (DES) for the process of oil palm biomass and
cellulose conversion into glucose was investigated. DES has been studied extensively
in various fields such as organic synthesis, biocatalysis, dissolution, electrochemistry
and extraction process. Owing to its cheap and ‘green’ properties, we are interested in
exploring the potential of DES for biomass processing. In order to achieve optimized
glucose conversion via enzymatic hydrolysis, biomass must undergo pretreatment in
order to break down the structure and this can enhance the access of cellulase to
cellulose matrix which usually preferred amorphous or unorganized cellulose structure.
Herein, choline chloride:glycerol (ChCl:Gly), choline chloride:ethylene glycol
(ChCl:EG), ethylammonium chloride:glycerol (EAC:Gly), ethylammonium
chloride:ethylene glycol (EAC:EG) and choline chloride:urea (ChCl:U) with 1:2 molar
ratio for all DESs were used as solvent for pretreatment of oil palm biomass and
cellulose. The dissolution process was done by heating and stirring 5% (w/w) oil palm
biomasses which were trunk (OPT), frond (OPF) and empty fruit bunch (EFB) in
ChCl:Gly, ChCl:EG, EAC:Gly, EAC:EG and ChCl:U at 100 °C for 48 h and cellulose
for 24 h at the same temperature. The chemical composition for pretreated oil palm
biomass was investigated and it was found that EAC:EG gave major removal of
hemicellulose in OPT, while significant lignin reduction was shown in all DESs for
OPT. The highest percentage of dissolution for oil palm biomass was recorded by OPT
pretreated in EAC:EG with 55.6% while the lowest dissolution recorded by OPF
pretreated in ChCl:Gly with only 20%. The highest percentage of dissolution for
cellulose was also recorded when pretreated in EAC:EG with 22.9% while ChCl:EG
gives the lowest dissolution with only 7.6%. The regenerated or pretreated oil palm
biomass was recovered by adding distilled water/ethanol to the pretreated sample.
Recovered pretreated samples were analysed by optical microscopy for physical
structure study. The result shows that EAC:EG provides better media for dissolution
process as the solvent produced more small fragments which indicates that dissolution
occurred for oil palm biomass and cellulose. From FTIR analysis, EAC:EG was
recorded to be the best solvent for disruption of hydroxyl group in the biomass material
while ChCl:U recorded the best solvent in removing lignin for OPT.The screening of parameter study was carried out for enzymatic hydrolysis in order to
determine the optimum conversion for the substrate pretreated in DES. Study of few
crucial factors affecting the reaction rate such as hydrolysis media, enzyme loading and
substrate concentration was conducted. The highest glucose release among pretreated
oil palm biomass was when hydrolysing OPT pretreated in EAC:EG with 60%
conversion. Cellulose hydrolysis recorded high amount of glucose release within range
of 77-95% conversion. The optimisation study was carried out by using OPT pretreated
in EAC:EG, not the cellulose because it considered to already achieved high
conversion rate. The optimum condition was obtained by using 15 mg/ml as substrate
concentration, 50 FPU/g and 100 CBU/mL as enzyme loading for Celluclast 1.5 L and
Novozyme 188 respectively at 50 °C for 24 h with 73.5% glucose conversion.
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