After the extraction of oil from the oil palm plant, the remaining plant
matter (above) can be converted into useful chemicals, including xylose.
The waste plant materials remaining from palm oil extraction processes
can now be converted into a useful sugar
Palm oil extraction annually
produces approximately 13 million tons of waste plant matter. Some of this
by-product, known as empty fruit bunch (EFB), is currently incinerated to
produce heat and electricity to run palm oil mills, but it is now on the path
to a sweeter use. By adapting and optimizing an established technique to
convert sugarcane bagasse and corn stover to the useful sugar xylose, a
research team in Singapore, led by Jin Chuan Wu from the A*STAR Institute of
Chemical and Engineering Sciences, has
experimentally extracted high yields of xylose from EFB1.
EFB contains xylan, which is a
carbohydrate made up of units of xylose. Xylan is very susceptible to being
broken down to these individual sugar molecules in the presence of mild acid.
Known as hydrolysis, this process is not widely applied to EFB — despite its
well-established use for converting sugarcane bagasse and corn stover — because
of difficulties in making it cost effective. The key to Wu and his team’s
success was the combination of acids they selected for hydrolyzing EFB: sulfuric
(H2SO4) and phosphoric acid (H3PO4). “The combined use of H2SO4 and H3PO4 has a
synergistic effect in improving sugar yields,” explains Wu.
Since the elements sulfur and
phosphorus are essential for the fermentation of xylose using microbes, the
researchers’ combination of acids will play a fundamental role in the further
conversion of xylose into other useful chemicals, such as the sugar substitute
xylitol, lactic acid and ethanol. After hydrolysis and neutralization, these
acid components can be used directly in a microbial fermentation. Hydrolysis
requires the levels of these elements to be low, with higher levels being
detrimental. In previous EFB hydrolysis techniques, higher concentrations of
acids were used, but the levels of sulfur and phosphorous were too high for the
microbial fermentation stage.
After discerning the right
combination of mild acids, Wu and his team used computer modeling followed by
supporting experiments to find the optimal conditions for hydrolysis. They
obtained xylose yields of 80–90%. The conditions they optimized included the
concentrations of the two acids, the reaction temperature, the dilution of the
solution and the size of the EFB particles.
"Next, we will convert the
sugars into lactic acids by microbial fermentation using lactic acid bacteria,”
explains Wu. This lactic acid will be used for producing polylactic acid: a
renewable and completely biodegradable biopolymer, that he says is stable at
high temperatures and has broad applications.
The A*STAR-affiliated researchers
contributing to this research are from the Institute of Chemical and Engineering
Sciences
References
- Zhang, D., Ong, Y. L., Li, Z. & Wu, J. C.
Optimization of dilute acid-catalyzed hydrolysis of oil palm empty fruit
bunch for high yield production of xylose. Chemical Engineering
Journal 181–182, 636–642 (2012). | article
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