392
G. Qu et al. / Carbohydrate Polymers 148 (2016) 390–396
d
1566
2968
3342
1429
1255
2902
902
1028
c
1568
2970
2889
3346
1434
1259
899
1033
b
a
2896
1431
3329
3346
893
1028
Fig. 1. Experimental flow chart. (1) Nitrogen bottle; (2) mass flow meter; (3) heating
device; (4) reactor; (5) condenser tube; (6) liquid bottle; (7) aluminum foil sample.
1431
2891
898
1029
(1) The synthesis of [bmim]Cl: Molar ratio of N-methyl imidazole
to chlorobutane 1:1 were mixed in a dry 250 ml flask with
condensing facility, then heated with stirring for 48 h under
70 ◦C. After reaction, reactants were washed for three times
using ethyl acetate, and then streamed to remove ethyl acetate
at 80 ◦C. Finally, the pale yellow viscous liquid [bmim]Cl was
obtained.
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber(cm -1)
Fig. 2. Infrared spectra of cellulose. (a) Cellulose raw materials; (b) pyrolized cellu-
lose under 180 ◦C; (c) pyrolized cellulose under 240 ◦C; (d) pyrolized cellulose under
340 ◦C.
(2) The synthesis of [bmim]OTf: Molar ratio of potassium tri-
fluoromethanesulfonate to [bmim]Cl 1:1 were mixed, using
dichloromethane as solvent, reflux condensation for 48 h under
60 ◦C. After removing the dichloromethane by reduced pres-
sure distillation at 40 ◦C, the milky viscous liquid [bmim]OTf is
obtained finally.
umn is 40 ◦C, then was increased to 220 ◦C as a rate of 5 ◦C/min, then
was kept for 5 min. The interface temperature of GC–MS is 280 ◦C
with the source of EI (70 ev), EM voltage 1106 V, solvent delay 3 min.
GC(Gas chromatograph, GC9790) was used to analyze the gas
phase: Chromatographic column: GDX-104; Column temperature:
40 ◦C; Bridge: 100 mA; Detector: TCD thermal conductivity detec-
tor; Injection port: 100 ◦C; The carrier gas: nitrogen; Column
pressure before I: 0.28 MPa, Column pressure before II pressure:
0.20 MPa, the total pressure: 0.3 MPa; Sample quantity: 1 ml.
2.3. The pyrolysis of microcrystalline cellulose in [bmim]OTf
Flow chart of the experiment is shown in Fig. 1. Nitrogen was
used as carrier gas. Gas produced from the reactor was purged
with nitrogen into aluminum foil bag. Nitrogen flow was con-
trolled at 5 ml/min by mass flow controller. Used a glass sand at the
bottom of the reactor to ensure nitrogen take away gas phase prod-
ucts. 1.000 g microcrystalline cellulose and 10,000 g [bmim]OTf
were added into reactor. Nitrogen was kept aerating until the
reactor contained no more air but only nitrogen. The reactor is con-
nected to the aluminum foil bags, and then using magnetic stirring
for 2 h under the condition of 180 ◦C, 240 ◦C and 340 ◦C, respec-
tively. When pyrolysis reaction finished, close the heating device
and aerate moderate amount of nitrogen. The gas phase products
are collected under the nitrogen purging aluminum foil sample
bag while volatile liquid products are collected in a liquid bot-
tle after the condensation. Deionized water and dichloromethane
were added while the reactor was cooled to room temperature, and
then the cracking solid products were collected and dried by suction
filtration. Liquid products was added into the separatory funnel,
after stratification, the lower liquid was evaporated to remove the
methylene chloride in order to obtain difficult volatile liquid prod-
ucts.
3. Results and discussion
3.1. The analysis of solid phase products of cellulose pyrolysis
3.1.1. FTIR analysis
Fourier transform infrared spectrum was used for the analysis of
cellulose raw materials and cellulose cracked under 180 ◦C, 240 ◦C,
340 ◦C in ionic liquid [bmim]OTf. The results are shown in Fig. 2.
The infrared absorption peak position of cellulose cracked under
180 ◦C is same as the raw materials, however, cellulose cracked
under 240 ◦C and 340 ◦C produced a new infrared absorption peak.
The intramolecular hydroxyl OH stretching vibration appears
at the 3500–3300 cm−1. There is a CH stretching vibration peak
near 2900 cm−1, and the bending vibration of cellulose CH2 is
1431 cm−1, the 1000–1100 cm−1 is a sugar COH stretching peak,
and the 898 cm−1 is a -(1,4)-glycosidic bond vibration peak. Com-
pared with the cellulose raw materials, a new infrared adsorption
peak of the cellulose cracked under 240 ◦C and 340 ◦C appeared
at 2968 cm−1, 1566 cm−1 and 1259 cm−1. And the 2968 cm−1 is
attributed to the symmetric stretching of CH2, which means cel-
lulose structure has changed and molecular chain ruptured and
generated Substance of olefin structure. 1566 cm−1 is correspond-
ing with carboxyl group(−COOH) antisymmetric expansion which
means that carboxylic acid was generated during the cracking pro-
cess; absorption peak at 1259 cm−1 is the cyclic anhydride COC
antisymmetric expansion which shows that the annular carboxylic
acid was generated.
2.4. Product analysis methods
FTIR(Fourier transform infrared spectrum, brooke in German,
tensor27), XRD (X-ray diffraction, Dandong diffraction instru-
ment factory, TD2500 type) and SEM (electronic scanning electron
microscopy, the German Zeiss EVO 10) were used to analyze the
solid products.
GC–MS (gas chromatography–mass spectrometry instrument,
GCMSD5975, Agilent) was used to analyze the liquid products.
A
chromatographic column HP-INNOWax (30 m, diameter of
3.1.2. XRD analysis
0.25 mm) was chosen: thickness of 0.25 lm, flow rate of 1 ml/min,
diversion ratio: 20:1. Initial temperature of chromatographic col-
The X-ray diffraction diagram of cellulose cracked in the ionic
liquid [bmim]OTf under 180 ◦C, 240 ◦C, 340 ◦C and cellulose raw