2 research outputs found
Separation of Hemicellulose and Cellulose from Wood Pulp by Means of Ionic Liquid/Cosolvent Systems
Pulp of high cellulose content, also
known as dissolving pulp,
is needed for many purposes, including the production of cellulosic
fibers and films. Paper-grade pulp, which is rich in hemicellulose,
could be a cheap source but must be refined. Hitherto, hemicellulose
extraction procedures suffered from a loss of cellulose and the non-recoverability
of unaltered hemicelluloses. Herein, an environmentally benign fractionation
concept is presented, using mixtures of a cosolvent (water, ethanol,
or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium
acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet–Taft
parameters, and appropriate stirring conditions (3 h at 60 °C)
were maintained. This allowed the fractionation of a paper-grade kraft
pulp into a separated cellulose and a regenerated hemicellulose fraction.
Both of these exhibited high levels of purity, without any yield losses
or depolymerization. Thus, this process represents an ecologically
and economically efficient alternative in producing dissolving pulp
of highest purity
Dialkyl Phosphate-Related Ionic Liquids as Selective Solvents for Xylan
Herein we describe a possibility of selective dissolution
of xylan,
the most important type of hemicellulose, from <i>Eucalyptus
globulus</i> kraft pulp using ionic liquids (ILs). On the basis
of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is
well-known to dissolve pulp, the phosphate anion was modified by substituting
one oxygen atom for sulfur and selenium, respectively. This alteration
reduces the hydrogen bond basicity of the IL and therefore prevents
dissolution of cellulose fibers, whereas the less ordered xylan is
still dissolved. <sup>1</sup>H NMR spectra of model solutions and
Kamlet–Taft parameters were used to quantify the solvent polarity
and hydrogen bond acceptor properties of the ILs. These parameters
have been correlated to their ability to dissolve xylan and cellulose,
which was monitored by <sup>13</sup>C NMR spectroscopy. It was found
that the selectivity for xylan dissolution increases to a certain
extent with decreasing hydrogen-bond-accepting ability of anions of
the ILs