Effect
of Ultrasound on Lignocellulosic Biomass as
a Pretreatment for Biorefinery and Biofuel Applications
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Abstract
The conversion of lignocellulosic
biomass for biofuels and biorefinery
applications is limited due to the cost of pretreatment to separate
or access the biomass’s three main usable components, cellulose,
hemicellulose, and lignin. After pretreatment, each component may
be utilized via chemical conversion, hydrolysis, and/or fermentation.
In this review we aim first, to identify the current status-quo of
knowledge of the parametric effects of ultrasound, second, to evaluate
the potential of ultrasound as a pretreatment and fractionation method
of lignocellulose, and last, to identify the challenges that this
technology faces. Ultrasound produces chemical and physical effects
which were both found to augment the pretreatment of lignocellulose
via delignification and surface erosion. The magnitudes of these effects
are altered when the ultrasonic field is influenced by parameters
such as solvent, ultrasonic frequency, and reactor geometry and type.
Therefore, the implementation of ultrasound for the pretreatment of
lignocellulose must consider the variation of ultrasonic influences
to capitalize on the key effects of ultrasound. Currently the literature
is dominated by low frequency ultrasonic treatment, coupled with alkaline
solutions. High frequency ultrasound, oxidizing solutions, and use
of combined alternative augmentation techniques show promise for the
reduction of energy consumed and synergistic enhancement of ultrasonic
treatment. Furthermore, feedstock characteristics, reactor configuration,
kinetics, and the ultrasonic environment should be considered