3. Results and discussion
3.1. Approach for extractive removal of lignin from biomass using
room temperature ionic liquid
The widespread utilization of lignocellulosic biomass as a raw
material for the production of biofuels, chemicals and materials
and its inherent compositional variability makes the rapid assessment
of its composition of critical importance, particularly as we
move toward renewable resources [17]. A major impediment in
assessing the composition and in utilizing lignocellulosic biomass
is the intractable properties of lignin, which is extremely difficult
to extract [18–20]. Until now most laboratories assess lignin content
of biomass in multistep processes involving lignin extraction
and closure of mass balance [24]. More recently, FTIR spectroscopy
[25] has been used to estimate lignin content as well as solutionstate
13C NMR spectroscopy but these methods require finding solvents to dissolve biomass samples [26]. Until now, the application
of 13C CP MAS ssNMR spectroscopy has only been used for the
qualitative assessment of lignin in biomass samples presumably
because of the lack of available pristine, unmodified, lignin standard.
The most widely available lignin is lignosulfonate, a side
product of the pulp and papermaking industry, has distinctive
NMR spectral characteristics making it unsuitable as a standard.
Thus, we first undertook to explore methods to directly extract
pristine lignin from lignocellulosic biomass using room temperature
ionic liquids (RTILs) [27]. Unfortunately, 1-ethyl-3-methylimidazolium
acetate RTIL [27] afforded lignin containing large
amounts of cellulosics based on 13C CP MAS ssNMR (Supporting
Information Fig. S2).