Environmental Engineering Reference
In-Depth Information
Fig. 5.10
Ionic liquid, 1-butyl-3-methylimidazolium chloride that is referred to as [bmim][Cl].
The
cation
is organic and the
anion
is inorganic. The melting point of [bmim][Cl] is about 69 °C.
The chloride anion plays a key role in the ability of the ionic liquid to dissolve biomass
Fig. 5.11
Basic steps for processing biomass with ionic liquids. The feed can be any type of
lignocellulosic biomass in practical studies or simple carbohydrates in research studies. The dis-
solution step and the reaction step (
dashed box
) are sometimes combined. Reaction products can
be separated as a precipitate by adding water or an organic solvent
In solvothermal methods that use ionic liquids as solvent, solutions are heated
under mild conditions (80-120 °C) to dissolve the biomass, after which there are
many possibilities in its processing. In this section, ionic liquids will be introduced
as the solvent of interest.
Ionic liquids (ILs) are organic salts that have melting points close to room tem-
perature. Ionic liquids became popular as solvents to study in 2002, when it was
discovered that some ionic liquids can dissolve cellulose (Swatloski et al.
2002
) and
biomass (Fort et al.
2007
). An ionic liquid that dissolves both cellulose and biomass
is shown in Fig.
5.10
.
The basic steps for processing biomass with an ionic liquid are shown in Fig.
5.11
.
In the dissolution step (1), conditions can be chosen such that the ionic liquid is
non-derivatizing or derivatizing. Non-derivatizing conditions are important when
it necessary to maintain the polymeric structures of the compounds of the biomass,
whereas derivatizing conditions are used when depolymerization is required. In the
reaction step (2), homogeneous (liquid) or heterogeneous (solid) catalysts are used
to promote formation of the desired products (Guo et al.
2012
); these can be car-
bohydrates such as glucose or commodity chemicals such as biofuels (Fang et al.
