Optimization Of Various Pretreatments In The Enzymatic Hydrolysis Of Kapok, Oil Palm Empty Fruit Bunch And Kenaf Core Fibres For The Production Of Cellulosic Alcohol
Loading...
Date
2014-06
Authors
Tye, Ying Ying
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
The original kapok (Ceiba pentandra), oil palm (Elaeis guineensis) empty fruit bunch (EFB) and
kenaf (Hibiscus cannabinus) core fibres were hardly to be hydrolyzed by enzyme without any
pretreatments, which yielded only 0.8%, 2.6% and 0.4% of reducing sugar (glucose), respectively. Various
pretreatments, namely water, acid and alkaline pretreatments prior to enzymatic hydrolysis of the three
fibres for sugar production were optimized in this study. Response Surface Methodology (Expert Design®)
was applied to statistically analyze and optimize pretreatments conditions based on total glucose yield as
response variable. Moreover, the effects of chemical composition and physical structure of the fibre on the
total glucose yield were discussed comprehensively. Based on the statistical analysis of RSM, the
response surface models built for each pretreatment of all the three raw materials were polynomial
equations. Besides, the optimum pretreatment condition for kapok fibre was the alkaline pretreatment with
condition of 120 ºC for 60 min in 2.0% NaOH solution. While the optimum pretreatment conditions for EFB
and kenaf core fibres were the same, which was the water pretreatment with condition of 170 ºC for 45 min.
Among the fibres, alkaline pretreated kapok fibre achieved the highest total glucose yield (glucose yield
calculated baed on the untreated fibre) (39.6%), followed by the water pretreated EFB fibre (38.1%) and
kenaf core fibre (25.5%). Alkaline pretreated kapok fibre exhibited the highest total glucose yield, mainly
due to its high tendency on lignin elimination and the most severe structural destructive effect. On the other
hand, water pretreatment was the most effective method in enhancing the enzymatic hydrolysability of EFB
and kenaf core fibres due to the removal of hemicellulose in a large amount (>77%). However, unlike EFB
fibre, kenaf core fibre did not show better enzymatic hydrolysability after the pretreatment, which resulted in
a low structural alteration and high lignin retained in the fibre. Moreover, it was believed that the increased
of crystallinity index and decreased of crystallite size of all pretreated fibres might be parts of the reasons
that improved the enzymatic hydrolysability of fibre. Fermentation of sugar hydrolyzate by yeast without
supplement of nutrient had yielded 19.1%, 18.5% and 12.7% of total ethanol for kapok, EFB and kenaf
core fibres, respectively. Based on the results obtained, it was found that fibres with different physical
properties required different pretreatment process to have a better enzymatic hydrolysability. Moreover, the
removal of the entire recalcitrant polymers (lignin and hemicellulose) from biomass by pretreatment was
not necessary to maximize the conversion of cellulose into reducing sugar by enzymatic hydrolysis.
Description
Keywords
Optimization of various pretreatments , in the enzymatic hydrolysis