617
3 Ionic Liquid for Lignocellulose Conversion
It was 1934 when Graenacher [26] first discovered molten N-alkyl pyridinium chloride for dissolution and cellulose modification. Inspired with the pioneering work of
the Graenacher, in 2002, Swatloski et al. found dialkyl imidazolium-based ionic
liquid (IL) that is capable enough to dissolve cellulose up to 10–25 wt%. In general,
ILs are salts in the liquid state at a temperature below 373 K and exhibit unique
physicochemical properties, including low vapor pressure, high thermal stability,
better solvation capacities, and non-flammabilities. Brønsted acidic ionic liquids
(BAILs) contain free proton (H
+
), which is advantageous to use over the traditional
chemicals owing to its unique performance and tunable properties. Since the breaking of the lignocellulose’s glycosidic linkage is the key step for turning them into
HMF/Fur via monomer formation, the ILs are considered to be useful to disrupt the
H-bonding network even at low concentrations. An enhanced effect of the ionic
liquid-assisted cellulose dissolution was demonstrated under microwave irradiation
[27]. Subsequently, several ILs with acidic hydrogen on anion (e.g., 1-butyl-3methylimidazolium hydrogen sulfate), cation (e.g., N-methyl-2-pyrrolidonium
methyl sulfonate [NMP] + [CH 3 SO 3 ]), and acidic functional groups have been used
for BAIL-mediated/-catalyzed HMF production [28–31]. Tao et al. have demonstrated the catalytic performance of SO 3 H-functionalized BAILs for C 6 and C 5 sugar
conversion [29]. Varying the chain length with different anions (HSO
4−
, CF 3 SO
3−
,
CF 3 COO
−
, and CH 3 COO
−
) of the ILs, the yields of furfural/HMF were found to be
varied due to change in their acidic strengths. But, to perform these challenging and
multistep processes in a single step, several catalytic systems have been studies to
produce HMF from raw biomass. Including agricultural residues such as wheat
straw, paddy straw, reed from Phragmites communis, corn stover, the husk of
Xanthoceras sorbifolium, sugarcane bagasse, weeds, potato tuber, poplar, pinewood, etc. as feedstock (listed in Table 1) [12, 13, 15, 16, 32–35]. Among these
catalysts, Brønsted acidic ionic liquids (ILs), N-methyl-2-pyrrolidonium methyl
sulfonate [NMP] + [CH 3 SO 3 ]- and N,N-dimethylacetamide methyl sulfonate
[DMA] + [CH 3 SO 3 ]-, have been reported as superior catalyst, giving maximum 58
and 52 wt% of HMF. The reaction was reported to be conducted in DMA-LiCl solvent using the one-pot conversion of Foxtail weed biomass under mild reaction
conditions [12]. These acidic IL catalysts were also observed to effectively convert
carbohydrate-rich weed biomass into EMF [12]. This development leads to reduce
the use of ILs in bulk quantity and minimize the use of mineral acids and chlorinated metal salts. The results with acidic ILs have further motivated to explore the
catalytic activity of –SO 3 H-functionalized 1-butylimidazolium ILs with trifluoromethanesulfonate (OTf-) and bis((trifluoromethyl)sulfonyl)amide (NTf2-) counter
ions for the transformation of non-food mushroom biomass into HMF. It is to note
that the yield and selectivity of desired chemicals are directly related to the carbohydrate content in the feedstock used. The higher the sugar content in the biomass,
the greater will be the possibility for high conversion and desired product yield. So,
the selection criteria of biomass for their transformation are (1) presence of high
Catalytic Production of High-Value Chemicals from High Volume Non-food Biomass
3 Ionic Liquid for Lignocellulose Conversion
It was 1934 when Graenacher [26] first discovered molten N-alkyl pyridinium chloride for dissolution and cellulose modification. Inspired with the pioneering work of
the Graenacher, in 2002, Swatloski et al. found dialkyl imidazolium-based ionic
liquid (IL) that is capable enough to dissolve cellulose up to 10–25 wt%. In general,
ILs are salts in the liquid state at a temperature below 373 K and exhibit unique
physicochemical properties, including low vapor pressure, high thermal stability,
better solvation capacities, and non-flammabilities. Brønsted acidic ionic liquids
(BAILs) contain free proton (H
+
), which is advantageous to use over the traditional
chemicals owing to its unique performance and tunable properties. Since the breaking of the lignocellulose’s glycosidic linkage is the key step for turning them into
HMF/Fur via monomer formation, the ILs are considered to be useful to disrupt the
H-bonding network even at low concentrations. An enhanced effect of the ionic
liquid-assisted cellulose dissolution was demonstrated under microwave irradiation
[27]. Subsequently, several ILs with acidic hydrogen on anion (e.g., 1-butyl-3methylimidazolium hydrogen sulfate), cation (e.g., N-methyl-2-pyrrolidonium
methyl sulfonate [NMP] + [CH 3 SO 3 ]), and acidic functional groups have been used
for BAIL-mediated/-catalyzed HMF production [28–31]. Tao et al. have demonstrated the catalytic performance of SO 3 H-functionalized BAILs for C 6 and C 5 sugar
conversion [29]. Varying the chain length with different anions (HSO
4−
, CF 3 SO
3−
,
CF 3 COO
−
, and CH 3 COO
−
) of the ILs, the yields of furfural/HMF were found to be
varied due to change in their acidic strengths. But, to perform these challenging and
multistep processes in a single step, several catalytic systems have been studies to
produce HMF from raw biomass. Including agricultural residues such as wheat
straw, paddy straw, reed from Phragmites communis, corn stover, the husk of
Xanthoceras sorbifolium, sugarcane bagasse, weeds, potato tuber, poplar, pinewood, etc. as feedstock (listed in Table 1) [12, 13, 15, 16, 32–35]. Among these
catalysts, Brønsted acidic ionic liquids (ILs), N-methyl-2-pyrrolidonium methyl
sulfonate [NMP] + [CH 3 SO 3 ]- and N,N-dimethylacetamide methyl sulfonate
[DMA] + [CH 3 SO 3 ]-, have been reported as superior catalyst, giving maximum 58
and 52 wt% of HMF. The reaction was reported to be conducted in DMA-LiCl solvent using the one-pot conversion of Foxtail weed biomass under mild reaction
conditions [12]. These acidic IL catalysts were also observed to effectively convert
carbohydrate-rich weed biomass into EMF [12]. This development leads to reduce
the use of ILs in bulk quantity and minimize the use of mineral acids and chlorinated metal salts. The results with acidic ILs have further motivated to explore the
catalytic activity of –SO 3 H-functionalized 1-butylimidazolium ILs with trifluoromethanesulfonate (OTf-) and bis((trifluoromethyl)sulfonyl)amide (NTf2-) counter
ions for the transformation of non-food mushroom biomass into HMF. It is to note
that the yield and selectivity of desired chemicals are directly related to the carbohydrate content in the feedstock used. The higher the sugar content in the biomass,
the greater will be the possibility for high conversion and desired product yield. So,
the selection criteria of biomass for their transformation are (1) presence of high
Catalytic Production of High-Value Chemicals from High Volume Non-food Biomass