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摘要: 以半纤维素为添加剂对HZSM-5分子筛进行改性,采用XRD、SEM、N2物理吸附-脱附、NH3-TPD及Py-FTIR手段对其形貌、织构、酸性进行研究。并以丁烯齐聚为探针反应,考察半纤维素改性HZSM-5分子筛对低碳烯烃齐聚的催化能力。结果表明,当半纤维素质量分数为1.6%时,改性分子筛的比表面积、介孔体积最大,酸性最强,催化丁烯齐聚反应表现出了明显的优势,反应140 h转化率仍维持在80%左右,且三聚、四聚产物最多,柴油组分选择性最高。Abstract: The HZSM-5 synthesized with modifying by different contents of hemicellulose.The morphology, texture and acidity were characterized with XRD, SEM, N2 adsorption-desorption, NH3-TPD and Py-FTIR. Butene oligomerization over the modified HZSM-5 was tested. The results indicate that the HZSM-5 with the 1.6% hemicellulose exhibits the best activity and stability on the butene oligomerization reaction, the conversion can maintain about 80% after 140 h on stream, with the highest selectivities of the trimer, tetramer and diesel component in the products. These may be related with its high BET surface and mesoporous volume, and the strongest acidity.
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Key words:
- hemicellulose /
- modified /
- HZSM-5 /
- butene oligomerization
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表 1 不同分子筛的织构性质
Table 1 Textural properties of different zeolites
Catalyst SBET A/(m2·g-1) Pore volume v/(cm3·g-1) vmicro vmeso HZSM-5 364 0.15 0.25 HZSM-5-Hc-1 359 0.13 0.20 HZSM-5-Hc-2 398 0.14 0.32 HZSM-5-Hc-3 582 0.19 0.44 HZSM-5-Hc-4 389 0.14 0.31 note: SBET, BET surface area; vmicro, micropore volume determined by t-plot; vmeso, mesopore volume determined by vtotal-vmico 表 2 不同分子筛的NH3-TPD和Py-FTIR酸性定量计算
Table 2 NH3-TPD and Py-FTIR results for different zeolites
Catalyst Acidity by strengtha/(mmol·g-1) Acidity by typeb/(mmol·g -1) weak medium total brønsted lewis HZSM-5 0.357 0.225 0.600 0.532 0.045 HZSM-5-Hc-1 0.512 0.467 0.979 0.809 0.049 HZSM-5-Hc-2 0.667 0.536 1.203 0.893 0.058 HZSM-5-Hc-3 0.859 0.621 1.480 1.209 0.075 HZSM-5-Hc-4 0.592 0.356 0.948 0.531 0.039 a: density of the acid sites, assorted according to the acidic strength, determined by NH3-TPD. medium, NH3 desorbed at 300-500 ℃; weak, NH3 desorbed at 100-300 ℃;
b: density of the acid sites, assorted according to the acidic type, determined by Py-FTIR表 3 不同分子筛催化丁烯齐聚反应24 h产物分析
Table 3 Catalytic results at 24 h for the butene oligomerization over different catalysts
Catalyst Conversion x/% Selectivity s/% Carbon atom distribution w/% naphtha diesel C8 C12 C16 C20+ HZSM-5 21 29 71 58 36 5 1 HZSM-5-Hc-1 66 25 75 49 41 7 2 HZSM-5-Hc-2 80 18 82 37 49 11 3 HZSM-5-Hc-2 79 26 74 29 38 19 14 HZSM-5-Hc-4 63 24 76 42 40 12 6 -
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