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Fate of chlorine in rice straw under different pyrolysis temperatures Bingxian Peng, Xinrui Li, Jing Luo, and Xing Yu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b02097 • Publication Date (Web): 21 Aug 2019 Downloaded from pubs.acs.org on August 29, 2019
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Fate of chlorine in rice straw under different pyrolysis temperatures
2
Bingxian Peng*,
3
College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, P. R. China
Xinrui Li, Jing Luo, Xing Yu
4 5
ABSTRACT: The fate of Cl in rice straw after pyrolysis in 200-1000 oC was investigated through
6
heating of tubular furnace, sequential extraction, and determination using pyrohydrolysis
7
combined with ion chromatography (PIC) for total Cl, ion chromatography (IC) for inorganic Cl
8
and gas chromatography-mass spectrometer (GC-MS) for CH3Cl. The rice straw and (or) its chars
9
after pyrolysis were characterized with TGA (thermogravimetric analysis), SEM (scanning
10
electron microscope), XRD (X-ray diffraction) and XRF (X-ray fluorescence spectrum). The
11
results showed that, from 200 to 400 oC, the water soluble Cl in rice straw char decreased from
12
60.31% to 40.13%; the released Cl was dominated by Cl-CH3Cl (Cl as CH3Cl) and Cl-HCl (Cl as
13
HCl), with release rate from 10.41 to 16.81% and from 28.76 to 35.34%, respectively. At 400 oC,
14
5.84% of Cl in tar (tar-Cl) was found. In the pyrolysis from 400 to 700 oC, in chars, the water
15
soluble Cl changed a little and organic bound Cl increased from 1.25% to 7.50%; the released
16
Cl-CH3Cl and Cl-HCl respectively decreased from 13.41% to 2.42% and from 29.19% to 12.84%,
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and the tar-Cl increased from 9.19% to 18.14%. At 700 oC, the Cl as KCl (Cl-KCl) started to
18
release. For the pyrolysis from 700 oC to 1000 oC, the release rate decreased from 40.20% to
19
4.48% for the water soluble Cl and from 7.50% to 0.34% for organic bound Cl, a small amount of
20
residual Cl was found in chars; the released tar-Cl and Cl-KCl increased from 18.74% to 26.01%
21
and from 17.40% to 64.64%, respectively; Cl-HCl decreased from 12.80% to 2.16%. Cl-CH3Cl
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disappeared above 800 oC. These results may be caused by the following reasons: the
23
evaporation of water and volatile matter, decomposition and carbonization of organic matter,
24
changes of composition in tar and char, and the reactions of the various Cl forms. During the
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whole pyrolysis stage at 200-1000 oC, the released Cl from rice straw can pose a certain of
26
environmental risks. In order to reduce the release of harmful Cl in rice straw, the measures such
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as fully evaporating water before the pyrolysis, pyrolysis temperature above 700 oC and passing
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the exhaust gas into NaOH and acetone solution in turn, can be taken.
29 30
1. INTRODUCTION
31
It is an inevitable trend with the social development that non-renewable fossil fuels are
32
replaced by renewable energy sources.1 Biomass is an important and abundant renewable energy
33
source, which contains low N and S compared with fossil fuel, and with net CO2 emission.2 The
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pollution for biomass is far less than that of fossil fuel during combustion. But biomass contains a
35
lower carbon content which leads to less heat generation. Therefore, biomass usually need to be
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pyrolyzed to translate into char for replacing coal in combustion, which can increase energy
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utilization of biomass and generate tar and gas.
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Biomass often contains a larger amount of Cl (100-70000 mg/kg),3,4 which is easily released
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and transferred into gas phase during thermal reaction.5,6 The released Cl can be deposited on the
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downstream equipment, causing corrosion, fouling and slag.7 The chlorine in biomass is mainly
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released as HCl, KCl, CH3Cl and enter tar through pyrolysis.8-10 HCl is the most important
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atmospheric pollutant except SO2 and NOx. CH3Cl is a carcinogen, with greenhouse effects.9,11,12
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Tar-Cl is toxic and act as environmental hazards.13 For bomass pyrolysis, some studies8-10
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proposed, that the major form of released Cl was HCl in 250-500 oC; some studies 9,11 showed that
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volatilization of Cl-CH3Cl occurred below 350 oC; Wang et al 12 found the released HCl can be
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reacted with char and formed organic Cl; the organic Cl can enter tar at the temperature higher
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than 300 oC. KCl started to sublime at 700-800 oC.14 Above 800 oC, the released Cl mainly stemed
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from KCl sublimation.6,14,15 These studies indicated that Cl released through biomass pyrolysis
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have significant impacts on the environment.
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The transport and transformation of Cl during biomass pyrolysis have attracted considerable
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attention. The release behavior of Cl varies greatly for different biomass at different pyrolysis
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temperatures. For the pyrolysis of sugarcane trash, switch grass, lucerne and straw rape, the
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release rates of Cl were less than 10% at 200 oC, 30-60% Cl was still present in chars at 900 oC,
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and the released Cl at low temperature might be caused by the reaction of alkali metal Cl with
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organics.16 During corn straw pyrolysis for 20 min in 500-1150 oC, the chlorine release rate was
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approximately 50% at 500 oC, and then decreased slightly from 500 oC to 700 oC; after that, it
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gradually increased, and complete release for Cl was at 1150 oC.14 As for wheat straw, rice husk
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and sawdust in the process of fixed bed pyrolysis, the chlorine release of was mainly concentrated
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on 200-600 oC, and increased slightly in 600-1000 oC.15 The chlorine release rate of mallee bark in
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pyrolysis was close to 100% when the temperature was higher than 500 oC, and that in gas phase
61
was about 23%, in tar was about 77%.10 These studies indicated that the release behavior of Cl
62
varied largely during different biomass pyrolysis at different temperatures.
63
Rice straw is an important biomass in agriculture, accounting for more than half of total crops
64
in China. The transport and transformation of Cl during rice straw pyrolysis has been concerned
65
by many researchers. Jensen et al17 found that Cl was mainly released in two temperature ranges
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during rice straw pyrolysis, about 60% of Cl released within 200-400 oC, the remainder Cl was
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almost released in 700-900 oC, and the Cl release rate was low in the range of 400-700 oC. The
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chlorine release during pyrolysis at high temperature (1000-1200 oC) can be inhibited by
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torrefaction pretreatment at 250 and 300 oC.18 The literature8 showed that the released Cl
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increased with the rise of temperature and retention time; particle size was one of important
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factors, the Cl release rate of rice straw with 74-124 µm sizes was 60.78% and 27.25% higher than
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that of 250-420 µm sizes at 350 oC. These works indicated that temperature, pretreatment,
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retention time and grain size affect the Cl release during rice straw pyrolysis, and in which
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temperature was the most important influence factor.
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It can be seen from above that after biomass pyrolysis, the chlorine would undergo
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significant migration and transformation, most of Cl enters gas and tar, and a small part of Cl
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remained in char. The distribution and form of Cl in the products are different under different
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conditions. Biomass pyrolysis may generate environmentally risky Cl such as CH3Cl, HCl and
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tar-Cl during pyrolysis. However, little research has simultaneously focused on the migration,
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distribution and change of various forms of Cl from rice straw and its environmental effect during
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pyrolysis at different temperatures.
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In this study, the rice straw samples were treated at different pyrolysis temperatures
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(200-1000 oC) to procuce char for burning. TGA, XRD, XRF and SEM were used to characterize
84
the matrix composition and physicochemical properties before and after pyrolysis of rice straw;
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the total Cl, water souble Cl and organic bound Cl in rice straw and its chars, and the released
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Cl-HCl, Cl-KCl, Cl-CH3Cl and tar-Cl at different temperatures were respectively measured. By
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this way, the fate of Cl in rice straw during pyrolysis and its possible release and transformation
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mechanism were explored, and the environmental risk of Cl in rice straw during pyrolysis at
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different temperatures would be evaluated. The corresponding measures to reduce the release of
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harmful Cl were put forward.
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2. EXPERIMENT
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2.1. Sample collection and preparation
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The experimental samples were rice straw near the Poyang lake in Jiangxi province. The rice
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straw was smashed with a grinder, and the particles with size of 98-125 µm were screened out.
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The particles were air dried at room temperature. The proximate and ultimate analysis of rice
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straw was given in Table 1. From Table 1, it can be seen the rice straw contained more volatile
97
matter, and less fixed carbon, N and S, with 0.65% Cl.
98 99
Table 1 Proximate and ultimate analysis of rice straw. Proximate analysis (w/%, air-dried basis)
100
Ultimate analysis (w/%, air-dried basis)
Moisture
volatiles
Fixed carbon
Ash
C
H
N
O1
S
Cl
4.41
72.22
7.52
15.85
37.09
6.12
0.64
35.89
-2
0.65
1
By difference; 2 Not detected.
101 102
2.2. Rice straw pyrolysis
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The rice straw pyrolysis apparatus was shown as Figure 1. Before the experiment, a 2.0 g
104
straw powder was put into a porcelain boat which surface was covered with 2.0 g quartz sand
105
(20-50 meshes) to prevent the sample from taking away by N2, then it was placed in water-cooled
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chamber at the inlet of the silica tube. N2 was injected into the silica tube to exhaust the air, and
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then adjusted to 100 mL/min. Two 50 ml volumetric flasks were respectively put in a solution of
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30 mL 0.1 M NaOH, and then placed in an ice basin (99.999%)
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was used as a carrier gas with a flow rate of 100 mL/min. The mass-loss curve (TG) and its
183
derivative (DTG) were recorded as a function of sample temperature. After the experiment, N2
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flow was kept for 30 min to get rid of the volatile components in gas cell.
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2.5. Chemical and mineralogical analysis
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Major and minor element analysis (chemical composition) of rice straw was conducted using
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XRF (S4 PIONEER). The test condition was Rh target, 4 kW, 60 kV, 140 mA, Be-U of detection
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range and 250 µm of minimum analysis of micro zone.
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The mineral compositions of rice straw and its chars at different pyrolysis temperatures were
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analyzed using a D8 ADVANCE X-ray diffractometer (XRD) with Cu K-alpha radiation. The
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pattern was recorded over a 2 h interval of 10-70o, with a step increment of 0.01o.
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The images of the samples to further insight into the morphology changes of the chars from
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rice straw were determined by SEM (S-3400N).
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3. RESULTS AND DISCUSSION
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3.1. Thermal degradation properties of rice straw in N2 atmosphere
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The effects of heating temperature on pyrolysis of rice straw at a heating rate of 10 °C/min were
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shown in Figure 2. The TG and DTG curves suggested that the pyrolysis process can be divided into
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three stages. The first stage was from room temperature to 200 °C. Because of the removal of moisture
199
and volatile components, the sample weight loss rate was 11.41%. The second stage occurred between
200
200 and 400 °C, the intense decomposition of hemicellulose, cellulose, and lignin in rice straw was
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observed in the stage.23 With the heating temperature increase from 200 oC to 400 oC, the weight of rice
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straw lost a lot, with a loss rate of 45.40%. The third stage corresponds to the carbonization process
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above 400 °C. Residues in this stage from rice straw were mainly ash and fixed carbon, the weight loss
204
rate was 22.21% from 400 to 1000 °C.
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5000
300
4500
250
TG DTG
4000
200
TG (g)
3500 3000
150
2500 100 2000
DTG (g/min)
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1500 1000
0
500 -100
0
100
200
300
400
500
600
700
800
900 1000 1100
o
T ( C)
205 206
Figure 2. The TG and DTG curves of rice straw in N2.
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208
3.2. Change of physicochemical property of rice straw after pyrolysis
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3.2.1. The composition of rice straw ash. The chemical constituents of rice straw ash were
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analyzed by XRF, which results were shown in Table 3. It can be viewed, in decreasing order of
211
significance, the main chemical components of rice straw ash were SiO2, K2O, Na2O, CaO, MgO,
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P2O5, Al2O3, MnO and Fe2O3. The content of SiO2 and K2O was respectively 68.72% and 10.32%,
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indicating a large amount of Si and K in rice straw.
214 215
Table 3. Properties of rice straw ash wd/%. Constituent
SiO2
Al2O3
CaO
Fe2O3
P2O5
K2O
TiO2
MgO
Na2O
MnO
Content (%)
68.72
0.46
1.82
0.26
1.30
10.32
0.05
1.72
1.28
0.37
216
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3.2.2. XRD analysis of rice straw and its chars.
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The XRD analysis of the rice straw and its pyrolysis chars in 200-1000 ℃ for 20 min was shown
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as Figure 3. It can be seen KCl crystal started to appear in char at 300 oC. With the increase of
220
temperature, the amount of precipitated KCl crystal gradually increased, and achieved the
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maximum value at 700 oC in the experimental temperatures. To 800 oC, the diffraction peak of
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KCl decreased, indicating that KCl sublimed to the gas phase. As to 900 oC, only a small amount
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of KCl crystal existed in char. For 1000 oC, the diffraction peak of KCl crystal disappeared and
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the stable KAlSi2O6 diffraction peak appeared.
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226 227
Figure 3.
XRD patterns of rice straw and its pyrolysis chars. a, KCl; b, KAlSi2O6.
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3.2.3. SEM analysis of rice straw and its chars. SEM images of raw rice straw and its pyrolysis
230
chars at different temperatures revealed the change of char morphology. Figure 4 and Figure 5
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respectively showed the structural changes of the epidermis and ground tissue of rice straw and its
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chars from 200 to 1000 oC of pyrolysis temperature.
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From Figure 4 and studies,24,25 it could be seen that the epidermis of the raw rice straw was
234
highly silicified, with obvious siliceous papillae. The papillaes were arranged in an orderly way,
235
which contained a large amount of amorphous silica (SiO2.nH2O).26,27 At 200 oC, there was no
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noticeable change on the epidermis; silica mastoids were obviously broken at 300 oC, and
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completely broken above 400 oC, and the amorphous silica (SiO2·nH2O) was turned into SiO2
238
particles;21 to 800
239
aluminosilicates,19,30 began to appear on the surface of the epidermis, and there were considerable
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vitreous bodies formed at 900-1000 oC.
oC,
vitreous bodies, which consisted of stable silicates28,29 and
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In Figure 5, the small coadjacent chambers, which showed rectangular, were come from the
242
plant cells. The sheets forming the chambers were derived from cell walls in the ground tissue.21,31
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Depending on Figure 5, the chambers did not change significantly in 200-300 oC, began to
244
collapse at 400 oC and was obviously broken at 800 oC. To 1000 oC, larger holes appeared in
245
ground tissue.
246
Combined with Figure 2, Figure 4 and Figure 5, it was known during the pyrolysis of rice
247
straw, the epidermal tissue changed markedly at 300 oC, and the ground tissue broke down
248
obviously at 400 oC, which was caused by the decomposition of cellulose, hemicellulose and
249
lignin. After 400 oC, the changes of epidermal and ground tissue were caused by the secondary
250
reactions of char.
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252 253
Figure 4. SEM photos of epidermis from rice straw and its pyrolytic chars at temperatures from 200 oC to 1000 oC.
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REP and EP denote raw epidermis and epidermis of char, respectively.
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256
257 258
Figure 5. SEM photos of internal surface with ground tissue from rice straw and its pyrolytic chars at temperatures
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from 200 oC to 1000 oC. RGT and GT denote raw ground tissue and ground tissue of char, respectively.
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3.3. Fate of chlorine in rice straw at different pyrolysis temperatures
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According to the methods in Table 2, total Cl, water soluble Cl and organic bound Cl in rice
263
straw and its chars at different pyrolysis temperatures were respectively measured. It can be
264
known from the results calculated by Eq. (I), the form of Cl in rice straw was mainly water soluble
265
Cl which accounted for 97.14% of total Cl, and the total Cl and various forms of Cl in raw rice
266
straw and its pyrolysis char were shown in Figure 6.
267 268
On the basis of the results calculated by Eq. (II), (III), (IV) and (V), the changes of Ri with the pyrolysis temperature were shown in Figure 7.
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270 271
Figure 6. Change of Cl in char after rice straw pyrolysis at different temperatures.
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273 274
Figure 7. Chlorine release after rice straw pyrolysis.
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Compared Figure 6 with Figure 7, the fate of Cl in rice straw and its possible mechanism
276
were illustrated by the following three pyrolysis temperature stages.
277
3.3.1. Pyrolysis in 200-400 oC. It can be seen from Figure 6, there was 60.31% Cl (water soluble
278
Cl) in rice straw char at 200 oC, which indicated that nearly 40% Cl may release with water vapor
279
and volatile components before 200 oC. According to Figure 2, the loss rate of water and volatile
280
matter in this stage was 11.14%, which indicated that water and volatile matter had a stronger
281
capacity for carrying Cl. The Cl in char mainly occurred as water soluble Cl which declined with
282
the rise of temperature, and this form Cl was 40.13% at 400 oC. As shown in Figure 2 and the
283
research,32 the organic matter such as cellulose, hemicellulose and lignin was mainly decomposed
284
during pyrolysis at 200-400 oC, with weight loss rate of 45.40% and Cl release rate of 18.83%,
285
indicating a weaker release of Cl caused by the decomposition of organic matter in rice straw.
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Figure 7 showed the total Cl release rate of rice straw increased from 39.16% to 57.99% with
287
temperature rise from 200 oC to 400 oC. The tar-Cl began to appear, with a content of 5.84% at
288
400 oC. In this stage, the Cl were mainly released as HCl and CH3Cl. As can be seen from the
289
work,32 tar was generated when biomass was pyrolyzed above 200 oC, which indicated the tar was
290
formed earlier than tar-Cl and both were simultaneously taken out with the decomposition of
291
organic matter in rice straw. At 200 oC, 300 oC and 400 oC, the release rates were 28.76%, 35.34%
292
and 33.81% for Cl-HCl, and 10.41%, 16.81% and 15.58% for Cl-CH3Cl, respectively. There was
293
no KCl released at this stage.
294 295 296
It can be deduced from above, in the pyrolysis temperature of 200-400 oC, most of water soluble Cl in rice straw was released as HCl and CH3Cl, less Cl entered tar. Czégény et al33 thought that during pyrolysis, KCl in biomass can reacted with lignin and
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formed CH3Cl, which showed as Reaction (1). A large amount of lignin in rice straw may be the
298
reason for the generation of CH3Cl during rice straw pyrolysis. Said et al34 thought the one reason
299
of mass loss of rice straw during pyrolysis at 300 oC was the decomposition of lignin. Moreover,
300
the thermogravimetric analysis in Figure 2 showed that the decomposition of rice straw at 300 oC
301
was the fastest, which indicated that the reaction (1) at this stage was strong and the released
302
CH3Cl was more. Du et al15 believed that at the lower pyrolysis temperature, the biomass would
303
also take place Reaction (2) and formed HCl. It can be seen from Table 3 and SEM
304
characterization in Figure 4, the rice straw contains a large amount of SiO2, which may be the
305
reason for the generation of more HCl in this stage.
306 307
2KCl+ nSiO2+ H2O = K2O·(SiO2)n + 2HCl
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3.3.2. Pyrolysis in 400-700 oC. This was the carbonization stage of rice straw at middle
309
temperature, with the weight loss rate 14.04% (according to Figure 2). From Figure 6, it can be
310
seen the Cl in char mainly comprised of water soluble Cl and organic bound Cl at this stage. From
311
400 oC to 700 oC, the water soluble Cl changed a little, the organic bound Cl increased from
312
1.25% to 7.50%.
313
(2)
On the basis of Figure 7, the total Cl release rate of rice straw decreased slightly, with
314
57.99% at 400 oC and 51.01% at 700 oC. From 500 oC, 600 oC to 700 oC, the release rate of tar-Cl
315
increased from 9.19%, 14.29% to 18.74%; in gas phase, the release rate of Cl-CH3Cl and Cl-HCl
316
decreased from 13.41%, 8.79% to 2.42% and from 29.19%, 27.31 to 12.81%, respectively; KCl
317
began to sublime at 700 oC, with the Cl-KCl release rate of 17.41%.
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It was generally believed that the most tar was generated during biomass pyrolysis at 500
319
oC.32
320
stage. It may be mainly caused by the following two reasons: HCl and CH3Cl in quartz tube
321
increased with the rise of temperature, which led to the occurrence of reaction (3) 10 and the
322
increase of organo-Cl; in addition, the composition of tar changed with increasing temperature,32
323
which increased the capture of Cl. The reaction (3) also resulted in the decrease of CH3Cl and
324
HCl.
325
CH3Cl/HCl+OrganicOrganic-Cl
326
3.3.3. Pyrolysis in 700-1000 oC. According to Figure 6, the Cl in rice straw char occurred as water
327
soluble Cl and a small amount of organic bound Cl at this stage. From 700 oC to 1000 oC, water
328
soluble Cl and organic bound Cl decreased sharply from 40.20% to 4.48% and from 7.50% to
329
0.34%, respectively. In addition, the char contained a certain of residual Cl at 900 oC and 1000 oC
330
by the mass balance closure.
331
However, in this study, the tar-Cl and ClCO increased with the increase of temperature at this
(3)
Based on Figure 7, from 700 oC to 1000 oC, the total release rate of Cl from rice straw
332
increased from 50.14% to 92.89%. At this stage, the tar-Cl increased slightly, with release rate
333
from 18.74 to 26.01%; more KCl and less HCl were released, with release rate from 17.40% to
334
64.64% for Cl-KCl and from 12.80% to 2.16% for Cl-HCl. CH3Cl nearly stopped releasing above
335
800 oC.
336
This process was a carbonization stage of rice straw at high temperature, with the weight loss
337
rate of 8.16% (according to Figure 2). The direct sublimation of KCl in char may be the main
338
reason for the release of Cl in rice straw during pyrolysis, which can be inferred by decrease of
339
KCl crystal peak gradually above 700 oC from Figure 3. Based on mass balance closure, part of
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Cl-KCl in char was converted to tar-Cl and Cl-HCl. Reactions (3) and (4)11,17 may be the main
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reasons for the decrease of Cl-HCl and Cl-CH3Cl. Similar to the pyrolysis of 400-700 oC stage, the
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increase release of organic bound Cl in char and the change of composition in tar (the main
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components of tar was PAH after 800 oC32)
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of tar-Cl. In addition, the inclusion of Cl by the vitreous body incluing stable silicate and
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aluminosilicate generated during the pyrolysis of 900 oC and 1000 oC may be the main reason for
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the formation of residual Cl in char.7
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CH3Cl/HCl+Organic-KOrganic+KCl
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3.4. Environmental effect and prevention of chlorine release during pyrolysis of rice straw
may be the main reason for the continuous increase
(4)
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From Figure 7, it can be seen that in the pyrolysis of 200-400 oC, relativly larger amounts of
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Cl-CH3Cl (10.41-16.81%) and Cl-HCl (28.76-35.34%) were released, and the tar-Cl generated at
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400 oC was 5.84%. Thus, the Cl released by pyrolysis at this stage caused larger pollution to the
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atmosphere. At 500-700 oC, the released Cl-CH3Cl, tar-Cl and Cl-HCl were respectively
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2.41-13.41%, 9.19-18.74% and 12.81-29.19%, which indicated the released Cl in this stage had
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certain impacts on the atmosphere and the surrounding environment. In the pyrolysis of 800-1000
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oC,
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without any CH3Cl release, which indicated more pollution to the surrounding environment. From
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what had been discussed above, the Cl released during the whole stage of rice straw pyrolysis at
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200-1000 oC can cause a certain of risks to the environment.
the release rates of tar-Cl and Cl-HCl were respectively 16.81-26.01% and 10.24-2.16%,
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According to the release of Cl in rice straw at different pyrolysis temperatures, the following
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measures can be taken to reduce the harmful Cl entering the environment. (1) Before pyrolysis of
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rice straw, fully evaporating water can reduce the release of Cl during pyrolysis at low
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temperature. (2) The pyrolysis temperature was increased to above 700 oC, so that the Cl in the
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straw was mainly released as harmless KCl. (3) The emission of HCl, tar-Cl and CH3Cl which are
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harmful to the environment can be effectively reduced by passing the exhaust gas into NaOH and
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acetone solution in turn.
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4. CONCLUSION
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(1) At 200-400 oC stage of rice straw pyrolysis, the Cl in char mainly occurred as water soluble Cl;
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the release rate of Cl in rice straw increased with the rise of temperature. The released Cl-HCl and
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Cl-CH3Cl were higher. At 400 oC, more than half of the total Cl released, the tar-Cl began to be
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formed. The fate of Cl in rice straw at this stage may be caused by the following reasons:
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volatilization of water and volatile matter, decomposition of organic matter, reactions between
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lignin and KCl and between SiO2 and KCl, H2O.
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(2) During pyrolysis of rice straw in 400-700 oC, in char, the water soluble Cl changed a little, and
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the organic bound Cl increased largely. The total Cl release rate decreased slightly; there was not
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any significant change for tar-Cl; KCl began to sublime at 700 oC; the release rates of Cl-HCl and
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Cl-CH3Cl decreased obviously. The reasons for Cl fate at this stage were the change of tar
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composition and the secondary reactions between Cl and char.
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(3) In the rice straw pyrolysis of 700-1000 oC, the water soluble Cl and organic bound Cl were
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significantly reduced, a small amount of residual Cl appeared in char. The total Cl release rate
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increased significantly; the released KCl increased sharply and the release of HCl decreased
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gradually; the tar-Cl was higher. The principal seasons of Cl fate were the change of composition
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in tar, the direct sublimation of KCl and the inclusion of Cl by the vitreous body formed by
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silicate and aluminosilicate.
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(4) During all the pyrolysis process in 200-1000 oC, a certain amount of the released tar-Cl,
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Cl-CH3Cl and Cl-HCl indicated the environmental risks caused by Cl in rice straw cannot be
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ignored. The measures, such as fully evaporating water before the pyrolysis, pyrolysis temperature
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above 700 oC and passing the exhaust gas into NaOH and acetone solution in turn, can be taken to
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reduce the release of harmful Cl.
389 390
■ AUTHOR INFORMATION
391
Corresponding Author
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*E-mail:
[email protected] (B.P.).
393
ORCID
394
Bingxian Peng: 0000-0002-8921-726X
395
Notes
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The authors declare no competing financial interest
397
398
■ ACKNOWLEDGEMENTS
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This work was sponsored by National Natural Science Foundation of China (Grant No.
400
21966014) and Science and Technology Research Project from educational department of Jiangxi
401
Province in China (GJJ170173) .
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403 404
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