Changes in char properties after catalytic reforming volatiles from pyrolysis of brown coal
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摘要: 为降低焦油产率，提高褐煤气化效率，采用胜利褐煤热解所得的半焦作为催化剂，在二阶石英反应器中对煤热解的焦油进行原位催化重整，分析和讨论了反应前后半焦催化剂的性质变化。结果表明，反应后半焦质量较反应前普遍有所下降，半焦是一种消耗性催化剂；反应后半焦的比表面积由422 m2/g降到231.8 m2/g；Raman分析结果表明，反应后半焦含氧官能团、小环（3-5个缩合芳环）与大环（大于5个缩合芳环）体系之比均有所降低。在半焦-挥发分作用过程中，快速热解制得半焦主要将挥发分裂解为小分子气体，慢速热解制得的半焦则主要使挥发分缩聚结焦脱除。Abstract: To decrease tar yield and thus improving gasification efficiency, tar from pyrolysis of Shengli brown coal was catalytically reformed in situ in a two-stage quartz reactor using char (as catalyst) prepared from the pyrolysis of same coal. The properties of char catalysts before and after reactions were analyzed and compared. The results show that the mass of char generally decreases after the reforming reactions, which means that char is a kind of consumptive catalyst. The maximum reduction in specific surface area after reactions is from 422 to 231.8 m2/g. Results from Raman spectroscopy show that the O-containing functional groups, as well as the ratio of small aromatic rings (3-5 aromatic rings) to big aromatic rings (more than 5 aromatic rings) in char, decrease after the reactions. Besides, it appears that during the interaction between char and volatile, char from fast-heating pyrolysis mainly cracks the volatiles into small-molecule gases, while char from slow-heating pyrolysis removes the volatiles by coking on its surface.
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Key words:
- brown coal /
- pyrolysis /
- char /
- volatile /
- catalytic reforming
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图 1 半焦催化剂制备及焦油催化重整反应装置示意图
1.electrical furnace; 2.thermocouple; 3.coal sample injection; 4.char (catalyst) injection; 5.fluidising gas (argon); 6.distilled water; 7.pump; 8.the absorption apparatus of tar[8]
Figure 1 A schematic diagram of experimental rig for char catalysts preparation and tar reforming
图 3 半焦反应前后的质量变化
(a): slow-heating pyrolysis char; (b): fast-heating pyrolysis char
Figure 3 Changes of char weight after the reforming reaction
图 4 反应前后慢速热解半焦的比表面积变化
Figure 4 Changes in specific surface area of slow-heating char after the reforming reaction
图 5 反应前后快速热解半焦的比表面积变化
Figure 5 Changes in specific surface area of fast-heating char after the reforming reaction
图 6 反应前后半焦的拉曼总峰变化
(a): slow-heating char; (b): fast-heating char
Figure 6 Total Raman peak area of fast-heating char before/after the reforming reaction
图 7 反应前后快速热解半焦的IGr/ID和I(Gr+ Vl+ Vr)/ ID比值
(a): slow-heating char; (b): fast-heating char
Figure 7 IGr/ID and I(Gr+ Vl+ Vr)/ ID ratios of fast-heating char before/after the reforming reaction
图 8 不同升温速率下半焦反应前后的反应性能
SI-char: slow-heating and inactivated char；SA-char: slow-heating and activated char；FI-char: fast-heating and inactivated char；FA-char: fast-heating and activated char (a): fresh char; (b): spent char-700 ℃; (c): spent char-800 ℃; (d): spent char-900 ℃
Figure 8 Changes in the reactivity of char with different heating rates after the reforming reaction
图 9 不同活化时间半焦空气反应性能
Figure 9 Changes in the reactivity of char with different activation time
图 10 半焦炭对挥发分催化重整可能反应路径示意图
Figure 10 Proposed catalytic reforming pathways for volatile by char catalysts derived from fast/slow pyrolysis
表 1 胜利褐煤的元素分析和工业分析
Table 1 Proximate and ultimate analyses of Shengli brown coal
表 2 800 ℃经半焦催化后焦油的转化率
Table 2 Conversion of tar after catalytic reforming by chars at 800 ℃
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