4474 | New J. Chem., 2018, 42, 4474--4484 This journal is
©
The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
Cite this: New J. Chem., 2018,
42, 4474
Hydrothermal alkaline sulfite pretreatment in the
delivery of fermentable sugars from sugarcane
bagasse†
Joa
˜
o Tavares, *
ab
Rafał M. Łukasik,
b
Teresa de Paiva
a
and Fla
´
vio da Silva
a
This work aims to demonstrate the importance of hydrothermal alkaline sulfite pretreatment of
sugarcane bagasse in the delivery of fermentable sugars. The pretreatment conditions, namely sodium
sulfite loads (5.0–10.0 wt%), temperatures (140–160 1C) and reaction times (30–60 min), were tested
according to the full factorial design of experiments. The employed pretreatment was characterized by
high lignin removal (43–77 wt%) and partial extraction of xylans (up to 25.0 wt%), mainly by cleavage of
acetyl and arabinosyl groups. After 72 h of enzymatic hydrolysis with 10 FPU (filter paper unit) cellulase
and 10 CBU (cellobiose unit) b-glucosidase per g of pretreated bagasse, the conversion of the
carbohydrate-enriched substrates was in the range of 51 to 80 mol% for cellulose and 45 to 71 mol% for
xylans. The best hydrothermal alkaline sulfite pretreatment conditions (10.0 wt% sulfite load, 150 1C and
45 min) were found to be highly efficient for the delivery of fermentable sugars with a yield as high as
40.4 1.9 g for 100 g native bagasse.
1. Introduction
Due to the negative environmental impact, fossil resources are
considered as unsustainable.
1
Thus, in the last few decades a
growing demand for alternative and renewable energy sources
has been observed.
2
Among the several types of renewable
energy resources available, biomass, especially lignocellulosic
biomass, is one of the most relevant natural carbon feedstock.
Lignocellulosic biomass is an abundant and generally low cost
raw material and once it is non-food and non-feed competitive,
it is an important feedstock for production of biofuels and
value-added commodities.
3
Agro-industrial wastes and residues
can be excellent examples of such biomass, because nowadays
they are mostly used as a solid fuel. Therefore, smarter and
more valuable valorization of such residues would bring some
advantages from the societal, environmental and economic
points of view.
Sugarcane bagasse is one of the relevant agro-industrial
residues, as it is the leftover of sugar and ethanol industries
used chiefly for energy purposes. Sugarcane bagasse is also
one of the most abundant lignocellulosic feedstocks of high
potential, which can be used for bioenergy and bioproducts.
4
Sugarcane bagasse, as other lignocellulosi c feedstocks, is consti-
tuted by the biopolymers of cellulose, hemicellulose and lignin,
which are interlinked and form a resistant and recalcitrant
structure against microbiological and chemical agents. Therefore,
to provide an effective fractionation of this complex matrix and
to deliver upgradable saccharides, an appropriate biomass
preprocessing step, called pretreatment, is required.
5
In recent
years, various pretreatment methods have been developed and
have been examined extensively. Among them are those including
non-catalytic pretreatments, e.g. steam or hot water, and biological
(e.g . fungi), or chemical pretreatment s with acids, alkalis, organic
solvents or ionic liquids.
5–11
Although there is a significant
advance in the development of more efficient, environmentally
acceptable and economically feasible processes, there is still a
strong need for effective pretreatment technologies that could
enhance the economics of biomass valorization. One of the
promising proce sses is the use of sulfur-containing compounds,
and some recent reports
12
showed encouraging results for pre-
treatment of hardwoods,
13
softwoods,
14
corn stalk,
15
switchgrass
16
and other feedstocks. The pretreated feedstocks generally are
characterized by high hydrolysis potential, as the enzymatic
conversion rate can be as high as 90%. One of the reasons for
this might be the fact that during the acid sulfite pretreatment,
most of hemicellulose is hydrolyzed together with a vast part
of lignin. In addition, the reduction of cellulose crystallinity
is observed. However, to minimize losses of hemicellulose and
cellulose, and to prevent the formation of fermentation inhibitors,
a
University of Sa
˜
o Paulo, Engineering School of Lorena, Estrada Municipal do
Campinho s/n
o
, Campinho, Lorena-SP, 12602-810, Brazil
b
National Laboratory for Energy and Geology (LNEG, I. P.), Unit of Bioenergy,
Estrada do Paço do Lumiar 22, 1649-038 Lisbon, Portugal.
E-mail: joao.tavares@lneg.pt; Tel: +35 1964898069
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7nj04975g
Received 15th December 2017,
Accepted 5th February 2018
DOI: 10.1039/c7nj04975g
rsc.li/njc
NJC
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