Effect of H2 and CO as pyrolysis atmosphere on chemical structure of char by XRD and Raman methods
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摘要: 采用XRD和Raman光谱分析方法研究了神木煤在热解主要温度区间（450-750℃）及在三种热解气氛（N2、含H2及含CO）下的化学结构演变规律，并比较了两种方法所获结构参数的相关性。结果表明，原煤在N2气氛下热解制备的半焦，其炭微晶尺寸在横向上不断增长，纵向上层面间距逐渐增大，堆垛高度在650℃左右剧烈转变；Raman参数AD1/AG增加，而AG/Aall降低，表明半焦有序性结构比例降低。热解气氛中的H2促进了炭微晶结构的纵向发展，提高了小分子基团的转化程度，使得半焦有序化程度升高。热解气氛中的CO对炭微晶结构参数影响小于H2气氛，但在700℃以下，CO因析炭作用产生的致密炭颗粒包裹于半焦表面，导致半焦炭有序化程度提高。半焦的Lc与AG/Aall及d002与AD1/AG之间存在一定相关性；La与AD1/AG呈较好的正相关性。Abstract: XRD and Raman spectroscopy were used to study chemical structure evolution of Shenmu coal in the main pyrolysis temperature range (450-750℃) and three pyrolysis atmospheres (N2, H2-containing and CO-containing). Correlation of structural parameters obtained by the two methods was compared. The results show that the char prepared by pyrolysis of raw coal in N2 has a continuous increase in the size of carbon crystallites in the transverse direction, a gradual increase of spacing in the longitudinal direction, and a sharp change of stacking height around 650℃. Raman parameter AD1/AG increases, while AG/Aall decreases, indicating a decrease in proportion of the ordered char structure. The H2-containing atmosphere promotes the longitudinal development of the carbon crystallite structure, increases the conversion of small molecule groups and the ordered degree of char. The influence of CO-containing atmosphere on the carbon crystallite structure parameters is less than that of the H2 atmosphere. But below 700℃, the dense carbon particles produced by CO-containing atmosphere due to carbon deposition are entrapped on the char surface, resulting in an increase in the ordered degree of char carbon. There is a certain correlation between Lc and AG/Aall, and d002 and AD1/AG of char; La has a good positive correlation with AD1/AG.
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Key words:
- low rank coal /
- char /
- pyrolysis atmosphere /
- XRD /
- chemical structure /
- Raman spectroscopy
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图 2 XRD光谱的002峰和100峰的拟合曲线示意图
Figure 2 Schematic of curve-fitted XRD spectrum of 002 and 100 band
图 9 CO的歧化反应特征
Figure 9 Characteristics of CO disproportionation reaction
(a): in the blank experiment, the CO2 release curves were in pure N2, containing CO and containing H2; (b): SEM image of corundum surface after the blank experiment in CO-containing atmosphere
图 10 Raman与XRD谱图之间的关系
Figure 10 A relationship between Raman and XRD parameters
(a): AD1/AG-d002; (b): AG/Aall-Lc; (c): AD1/AG-La
表 1 样品的工业分析和元素分析
Table 1 Proximate and ultimate analyses of sample
Sample Proximate analysis w/% Ultimate analysis wdaf/% Mad Aad Vdaf FCad C H N O* S Raw coal 3.83 7.53 37.06 55.97 71.97 4.38 0.93 22.51 0.20 N2-450 ℃ 0.73 12.30 17.78 69.95 85.18 3.65 0.58 10.43 0.15 N2-550 ℃ 0.82 14.57 12.98 72.54 87.93 2.82 0.59 8.50 0.15 N2-650 ℃ 1.31 10.41 7.86 80.42 90.00 1.97 0.39 7.49 0.14 N2-750 ℃ 1.26 7.86 4.49 86.39 90.88 1.15 0.31 7.50 0.15 H2-450 ℃ 1.07 10.38 14.60 73.95 77.12 2.71 0.49 19.52 0.15 H2-550 ℃ 0.95 14.25 8.83 75.97 82.48 2.27 0.56 14.54 0.14 H2-650 ℃ 1.01 13.96 3.92 81.11 79.86 1.23 0.62 18.13 0.15 H2-750℃ 1.32 7.01 1.79 89.90 86.83 1.07 0.58 11.39 0.12 CO-450 ℃ 0.69 6.36 22.04 70.92 73.45 3.65 0.53 22.20 0.16 CO-550 ℃ 0.70 9.69 13.69 75.86 75.47 2.85 0.44 21.07 0.16 CO-650 ℃ 0.86 9.28 8.26 81.64 88.03 2.01 0.36 9.44 0.15 CO-750 ℃ 0.93 6.45 4.93 87.70 88.81 1.15 0.42 9.46 0.15 *: by difference 
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表 2 半焦的拉曼拟合峰及其振动模式
Table 2 Raman bands and vibration modes of char
Band Raman shift δ/cm-1 Vibration mode D1 1350 disordered graphitic lattice (graphene layer edges, A1g-symmetry) D2 1620 disordered graphitic lattice (surface graphene layers, E2g-symmetry) D3 1530 amorphous carbon D4 1150 disordered graphitic lattice, polyenes, ionic impurities G 1580 ideal graphitic lattice (E2g-symmetry)
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表 3 不同气氛下制备半焦的XRD参数
Table 3 XRD parameters of char prepared under different atmospheres
Temperature t/℃ Atmosphere 2θ(γ)/ (°) β(γ)/min 2θ(002)/ (°) β(002)/min 2θ(100)/ (°) β(100)/min d002/nm Lc/nm La/nm N 450 N2 20.215 1.729 25.050 6.692 42.740 6.803 0.356 1.20 2.56 3.37 H2 20.254 3.127 24.872 6.159 43.509 6.959 0.358 1.31 2.51 3.66 CO 20.354 3.157 24.896 5.677 43.153 6.863 0.357 1.42 2.55 3.98 550 N2 18.908 3.812 24.585 7.129 43.003 6.707 0.362 1.14 2.60 3.44 H2 20.057 3.371 24.695 5.916 43.596 6.784 0.360 1.36 2.58 3.78 CO 20.032 3.007 24.796 6.269 43.558 7.510 0.360 1.23 2.33 3.42 650 N2 18.694 3.354 24.456 7.613 43.371 5.964 0.363 1.06 2.93 2.92 H2 20.250 4.224 24.980 6.338 43.837 5.991 0.356 1.27 2.92 3.57 CO 19.736 3.728 24.485 6.621 43.678 6.189 0.363 1.21 2.83 3.33 750 N2 19.139 3.782 24.434 6.694 43.426 5.431 0.364 1.20 3.22 3.30 H2 20.091 4.090 24.515 6.388 43.886 5.601 0.362 1.26 3.13 3.48 CO 20.175 3.773 24.525 6.658 43.863 5.488 0.363 1.21 3.19 3.33
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表 4 不同气氛下制备半焦的Raman参数
Table 4 Raman parameters of char prepared under different atmospheres
Temp. t/℃ Atmos- phere AD1/ Aall AD2/ Aall AD3/ Aall AD4/ Aall AG/ Aall AD1/ AG AR/ Aall A(D3+D4)/ AG XD1 XD2 XD3 XD4 XG 450 N2 60.92 9.08 8.19 3.99 17.76 3.61 21.26 0.71 1360.53 1613.91 1562.08 1221.82 1589.06 H2 67.04 6.54 8.51 0.95 16.96 4.04 16.00 0.59 1349.84 1601.98 1559.53 1185.44 1572.23 CO 66.35 6.22 5.41 1.35 20.67 3.36 12.98 1.73 1344.38 1603.66 1549.09 1177.94 1574.33 550 N2 62.98 9.59 6.36 5.00 16.06 3.98 20.96 0.73 1359.38 1611.36 1568.79 1209.14 1586.64 H2 68.84 2.89 6.41 0.87 20.99 3.33 10.17 0.37 1345.83 1608.01 1558.71 1178.08 1579.77 CO 66.29 4.70 5.39 0.72 22.90 2.94 10.81 1.74 1347.09 1602.23 1557.40 1180.21 1574.71 650 N2 64.87 9.05 11.32 0.83 13.53 4.81 21.36 0.87 1346.63 1610.04 1534.52 1087.19 1582.18 H2 61.56 8.10 5.80 3.34 22.31 2.78 16.13 0.35 1328.98 1602.11 1496.88 1184.38 1570.88 CO 69.37 5.83 6.49 1.25 16.11 4.31 13.56 0.48 1338.91 1604.01 1551.83 1174.13 1574.31 750 N2 65.22 8.16 11.80 0.63 14.19 4.65 20.59 0.89 1348.30 1612.91 1533.07 1120.00 1584.56 H2 65.99 6.48 7.03 1.46 19.05 3.47 14.96 0.45 1330.42 1601.21 1512.95 1175.59 1572.54 CO 65.88 6.13 7.10 1.46 19.43 3.42 14.69 0.44 1334.44 1602.60 1528.62 1176.30 1572.47 XD1: highest X value of the D1 peak; XD2: highest X value of the D2 peak; XD3: highest X value of the D3 peak; XD4: highest X value of the D4 peak; XG: highest X value of the D1 peak
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