Abstract :
[en] Pretreatment is still the most expensive step in lignocellulosic biorefinery processes.
It must be made cost-effective by minimizing chemical requirements as well as power
and heat consumption and by using environment-friendly solvents. Deep eutectic
solvents (DESs) are key, green, and low-cost solvents in sustainable biorefineries.
They are transparent mixtures characterized by low freezing points resulting from at
least one hydrogen bond donor and one hydrogen bond acceptor. Although DESs
are promising solvents, it is necessary to combine them with an economic heating
technology, such as microwave irradiation, for competitive profitability. Microwave
irradiation is a promising strategy to shorten the heating time and boost fractionation
because it can rapidly attain the appropriate temperature. The aim of this study was to
develop a one-step, rapid method for biomass fractionation and lignin extraction using
a low-cost and biodegradable solvent.
In this study, a microwave-assisted DES pretreatment was conducted for 60 s at
800 W, using three kinds of DESs. The DES mixtures were facilely prepared from
choline chloride (ChCl) and three hydrogen-bond donors (HBDs): a monocarboxylic
acid (lactic acid), a dicarboxylic acid (oxalic acid), and urea. This pretreatment was
used for biomass fractionation and lignin recovery from marine residues (Posidonia
leaves and aegagropile), agri-food byproducts (almond shells and olive pomace),
forest residues (pinecones), and perennial lignocellulosic grasses (Stipa tenacissima).
Further analyses were conducted to determine the yield, purity, and molecular weight
distribution of the recovered lignin. In addition, the effect of DESs on the chemical
functional groups in the extracted lignin was determined by Fourier-transform infrared
(FTIR) spectroscopy. The results indicate that the ChCl-oxalic acid mixture affords the
highest lignin purity and the lowest yield. The present study demonstrates that the
DES-microwave process is an ultrafast, efficient, and cost-competitive technology for
lignocellulosic biomass fractionation.
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