DOI: 10.1002/cssc.201403328
Full Papers
Conversion of Hemicellulose Sugars Catalyzed by Formic
Acid: Kinetics of the Dehydration of d-Xylose, l-Arabinose,
and d-Glucose
Karla Dussan,[a] Buana Girisuta,*[b] Marystela Lopes,[a] James J. Leahy,[a] and
Michael H. B. Hayes[a]
The pre-treatment of lignocellulosic biomass produces a liquid
stream of hemicellulose-based sugars, which can be further
converted to high-value chemicals. Formosolv pulping and the
Milox process use formic acid as the fractionating agent, which
can be used as the catalyst for the valorisation of hemicellu-
lose sugars to platform chemicals. The objective of this study
was to investigate the reaction kinetics of major components
in the hemicelluloses fraction of biomass, that is, d-xylose, l-
arabinose and d-glucose. The kinetics experiments for each
sugar were performed at temperatures between 130 and
1708C in various formic acid concentrations (10–64 wt%). The
implications of these kinetic models on the selectivity of each
sugar to the desired products are discussed. The models were
used to predict the reaction kinetics of solutions that resemble
the liquid stream obtained from the fractionation process of
biomass using formic acid.
Introduction
Furanic compounds, for example, furfural and 5-hydroxyme-
thylfurfural (HMF), as well as organic acids, for example, levu-
linic and formic acids, are important renewable bulk chemicals
derived from lignocellulosic materials, such as agricultural
wastes and energy crops. Approximately 60–62% of the world-
wide production of furfural is used to produce furfuryl alcohol,
an important polymer precursor that is obtained mainly
through the hydrogenation of furfural in the gas phase over
Cu catalysts at mild temperatures.[1] Other furfural derivatives,
such as 2-methylfuran and 2-methyltetrahydrofuran, have been
designated as fuel additives.[2] Lange et al.[2] studied the pro-
duction of ethyl furfuryl ether derived from furfuryl alcohol
and its utilisation as a gasoline additive because of its high
octane number and high energy density (28 MJkgꢀ1). The car-
bonyl and hydroxyl groups of HMF can be transformed
through oxidation and esterification reactions to various bulk
and fine chemicals for a wide range of applications, such as
2,5-furandicarboxylic acid, 2,5-diformylfuran and others. Addi-
tionally, base-catalysed aldol condensation reactions of furfural
and HMF with other aldehydes or ketones at moderate tem-
peratures (50–1208C) are considered as a promising route for
the production of C8–C13 alkanes through a subsequent reduc-
tion of the condensed molecules.[3,4] Levulinic acid (LA) has
been recognised as a versatile building block and highly valua-
ble precursor of biofuels. LA derivatives, such as ethyl and n-
butyl levulinates, have been blended with fossil-based diesel
successfully up to 20%.[5] LA can also be hydrogenated selec-
tively to g-valerolactone, which can be further transformed to
alkane fuel mixtures.[6]
Furfural, HMF and LA can be produced by a complex reac-
tion network of the hemicelluloses fraction of biomass in
acidic aqueous media (Scheme 1). Initially, the glycosidic link-
ages of the hemicellulose are protonated and subsequently hy-
drolysed to release pentoses (i.e., xylose and arabinose) and
hexoses (i.e., glucose, mannose and galactose). The conversion
of d-xylose to furfural is initiated by the protonation of the hy-
droxyl groups of d-xylose in its pyranose form. Some investiga-
tions have suggested that once one molecule of water is elimi-
nated from the d-xylose molecule, an intermediate dehydrofur-
anose is formed, which would dehydrate further to form furfu-
ral.[7,8] The intermediate dehydrofuranose may react with vari-
ous functional groups present in the reaction medium, for
example, the aldehyde group in furfural or the nucleophilic
groups in lignin-derived compounds, to lead to non-valuable
byproducts.[9] Likewise, furfural is known to undergo resinifica-
tion and decomposition reactions through the hydrolytic cleav-
age of its saturated ring. These undesired side reactions are
promoted by acid catalysts and high temperatures[10] and
eventually lead to low selectivity for furfural production in
aqueous acidic media. Although l-arabinose is not especially
abundant in most common crops and agricultural residues
(~15% of total hemicelluloses), its content in bark fractions of
pine wood (Pinus sylvestris, Picea abies) and spruce wood
(Picea abies) can be much higher than in other lignocellulosic
biomass. The studies of Hosia et al. and Eskilsson and Hartler
(cited by Hayes[11]) reported that l-arabinose corresponded to
approximately 50–70% of the total pentoses found in the
stem bark of these wood species. Heartwood from species
[a] Dr. K. Dussan, M. Lopes, Dr. J. J. Leahy, Prof. M. H. B. Hayes
Chemical and Environmental Sciences Department
University of Limerick
Castletroy, Co. Limerick (Ireland)
[b] Dr. B. Girisuta
Institute of Chemical and Engineering Sciences
1 Pesek Road, Jurong Island, 627833 (Singapore)
ChemSusChem 0000, 00, 0 – 0
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