2.2. Ionic liquids and treatment
In order to determine the effect of various ILs in fractionation of
lignocellulosic compounds of RS, four ILs, 1-butyl-3-methylimidazolium
chloride ([Bmim]Cl), 1-ethyl-3-methylimidazolium chloride
([Emim]Cl), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) and
1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim]Su), were
purchased from Sigma–Aldrich (St. Louis, MO, USA). [Emim]Ac
and [Emim]Su are highly viscous liquids at room temperature,
while two others exist in liquid form at higher temperatures
80–90 C.
The pretreatment of RS with ILs was carried out as follows. First,
1 g of RS was mixed with 20 mL of individual IL and incubated in
an oven at 130 C for 24 h. After dissolution, 20 mL of ethanol used
as an antisolvent was added into the rice straw solution to precipitate
and regenerate the rice straw-cellulose under vigorously stirring
condition. The precipitated bulky material was then filtered
through filtering paper (Whatman #2) using a Buchner funnel
under a reduced pressure and washed with 20 ml of ethanol. The
filtered liquid containing IL and ethanol was obtained to recover
ILs for subsequent reutilizations using a rotary evaporator (BUCHI
Rotavapor R-200, Switzerland) to remove the antisolvent. The precipitated
bulky material was continuously washed thoroughly with
distilled water and then dried at 105 C for 24 h prior to the carbohydrate
analysis and subsequent enzymatic treatment.
2