Coke formation on activated carbon during catalytic upgrading of coal pyrolysis volatiles
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摘要: 中低温热解煤焦油存在重质组分含量高、焦油品质差等问题,通过引入催化剂原位调控热解挥发分的反应,可有效改善焦油品质,但催化剂易积炭失活,影响其持续使用时间。利用下行床连续热解反应器,研究了挥发分在活性炭催化剂上的积炭行为,通过改变进煤时间(30、60和100 min),考察了挥发分的反应及其在活性炭上形成积炭的过程机制。结果表明,挥发分反应在活性炭上形成了大量积炭,随着进料时间的延长,活性炭上积炭的绝对量增加,但积炭形成的速率降低,因此,对于干基煤积炭的产率减小。随着活性炭上积炭量增加,活性炭的比表面积显著减小,催化裂解活性降低,焦油产率以及其中的沥青产率均有增大。焦油的组成分析表明,随着进料时间的延长,含氧化合物的相对含量增加,C−O弱键的断裂被抑制,这也使得积炭形成速率有所降低。Abstract: The content of heavy pitch in tar generated from coal pyrolysis is high. To improve the quality of tar, catalysts are applied for adjusting the reaction of volatiles during coal pyrolysis. However, catalysts are easy to deactivate due to coke deposition. In this study, coke amount on activated carbon catalysts during catalytic upgrading of coal pyrolysis volatiles was investigated in the downer-bed reactor. The process of coke formation was studied at different feed time (30, 60 and 100 min) of coal. Results show that a great amount of coke is generated on the activated carbons. With the increase of feed time, the amount of coke on activated carbon increases, while the rate of coke formation decreases, thus decreasing the coke yield based on dry coal. The specific surface area and catalytic cracking activity of the activated carbon decrease with the increase of coke amount. Hence, the yields of tar and pitch increase with the increase of feed time. The relative content of oxygen-containing compounds in the tar increases with the increase of feed time, which indicates that the cleavage of weak chemical bond C−O is suppressed. That may result in a decrease in the rate of coke formation.
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Key words:
- coal pyrolysis /
- volatiles /
- activated carbon catalyst /
- coke /
- tar
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图 1 下行床煤热解反应装置示意图
Figure 1 Schematic diagram of the experimental apparatus
1-feeder; 2-quartz reactor; 3-furnace; 4-gas flowmeter; 5-preheating furnace; 6-condenser pipe; 7-condenser; 8-collection bottle; 9-U glass tube; 10-absorption bottle; 11-absorbent cotton filter; 12-wet gas flowmeter; 13-polymeter filter; 14-desiccant; 15-Raman laser gas analyzer
表 1 NMH煤的工业分析、元素分析和格金干馏焦油产率
Table 1 Proximate analysis, ultimate analysis and tar yield by Gray-King assay of NMH coal
Proximate analysis w/% Ultimate analysis wdaf/% Gray-King assay Mad Ad Vdaf C H N St O* tar yield wd/% 19.50 5.80 50.12 74.35 5.13 0.72 0.31 19.49 15.4 note: ad: air dried basis; d: dried basis; daf: dried and ash-free basis; St: total sulfur; *: by difference 表 2 反应前后活性炭的氮气吸附孔结构特征参数
Table 2 Characteristic parameters of pore structure for fresh and used activated carbon by nitrogen adsorption characterization
Sample SBET/(m2·g−1) Smic/(m2·g−1) Sext/(m2·g−1) vtot/(cm3·g−1) vmic/(cm3·g−1) vmes/(cm3·g−1) dave/nm AC-1-Fresh 1221.24 469.38 751.86 0.58 0.19 0.38 2.13 AC-1-Spent 699.05 367.46 331.59 0.34 0.15 0.18 2.32 AC-2-Fresh 953.34 836.00 117.35 0.39 0.33 0.07 1.99 AC-2-Spent 725.42 639.62 85.81 0.30 0.25 0.05 1.88 note: SBET: BET surface area, Smic: micropore area, Sext: external surface, vtot: total pore volume, vmic: micropore volume, vmes: mesopore volume, dave: average pore diameter 表 3 不同进料时间反应后活性炭的氮气吸附孔结构特征参数
Table 3 Characteristic parameters of pore structure for spent activated carbons at different times by nitrogen adsorption characterization
Sample SBET/(m2·g−1) Smic/(m2·g−1) Sext/(m2·g−1) vtot/(cm3·g−1) vmic/(cm3·g−1) vmes/(cm3·g−1) dave/nm AC-1-30 min 1125.44 368.80 756.64 0.47 0.15 0.32 1.93 AC-1-60 min 777.51 315.57 461.94 0.33 0.13 0.20 1.97 AC-1-100 min 699.05 367.46 331.59 0.34 0.15 0.18 2.32 -
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