Synthesis and hydroisomerization performance of n-C12 over ZSM-48 molecular sieve with low silicon-aluminum ratio
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摘要: 通过静态水热合成法,溴化六甲二铵作为结构导向剂合成出系列低硅铝比的ZSM-48沸石分子筛(Si/Al < 100),所合成样品中最低硅铝比为38.6(ICP-AES),这将拓宽ZSM-48高硅沸石分子筛的应用范围。制备Pt负载双功能催化剂,用于正构十二烷临氢异构催化反应。结果表明,硅铝比的改变可以影响催化剂的活性,投料硅铝比为70的双功能催化剂具有最优的催化性能,但硅铝比改变对异构产物的分布没有明显的影响,其异构产物以支链在中间位的异构体为主。Abstract: A series of ZSM-48 zeolites with low Si/Al ratios (Si/Al < 100) were synthesized by hydrothermal synthesis method using hexamethydiammonium bromide as the structure directing agent. ICP-AES results showed that the Si/Al ratio of the synthesized sample was as low as 38.6, indicating the zeolite could be widely used. Pt supported on ZSM-48 with different Si/Al ratios were used for n-paraffin hydroisomerization. The catalytic reaction results showed that Pt/HZSM-48 with Si/Al ratio of 70 exhibited the best catalytic performance. However, the distribution of isomers had not been affected by Si/Al ratio of the ZSM-48, and the central-branched isomers were the main hydroisomerization products.
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Key words:
- ZSM-48 zeolite /
- low Si/Al ratio /
- n-dodecane /
- hydroisomerization /
- bifunctional catalyst
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表 1 样品元素含量
Table 1 Elemental content of the samples
Sample Si/(mg·L-1) Al/(mg·L-1) Si/Al ZSM-48-50 19.62 0.49 38.6 ZSM-48-70 15.14 0.32 45.6 ZSM-48-90 18.86 0.31 58.7 表 2 样品的酸含量
Table 2 Acid content of the samples
Sample Peak
temperature
t /℃NH3
uptake/
(μmol·g-1)Total
NH3 uptake/
(μmol·g-1)HZSM-48-50 236 217 471 436 254 HZSM-48-70 235 222 422 435 200 HZSM-48-90 234 183 369 426 186 表 3 样品的EDS分析数据
Table 3 EDS analysis data of the samples
Sample watom/% Si/Al Si Kα Al Kα ZSM-48-50 97.3 2.7 36.3 ZSM-48-70 97.8 2.2 44.2 ZSM-48-90 98.2 1.8 54.8 表 4 样品的孔结构参数
Table 4 Pore structure parameter of the samples
Sample ABET/
(m2·g-1)Amic/
(m2·g-1)Ames/
(m2·g-1)vtotal/
(cm3·g-1)vmic/
(cm3·g-1)vmes/
(cm3·g-1)Relative
crystallinityHZSM-48-50 208 118 90 0.24 0.05 0.19 69.5 HZSM-48-70 269 163 106 0.33 0.07 0.26 73.3 HZSM-48-90 215 123 92 0.20 0.05 0.15 86.5 表 5 不同催化剂的正十二烷异构产物分布
Table 5 Results of n-dodecane isomerization over the catalysts
Catalyst Pt/HZSM-48-50 Pt/HZSM-48-70 Pt/HZSM-48-90 Pt/HZSM-48-200 Temperature t/℃ 320 320 340 360 Conversion x/% 52.16 46.38 55.59 51.3 sT/% 78.56 92.65 77.97 82.61 sMB/% 53.40 70.82 54.89 57.96 sDB/% 25.16 21.83 23.06 24.65 sMB/sDB 2.12 3.24 2.38 2.35 s/% 2-methylundecane 10.71 15.05 11.26 11.68 3-methylundecane 12.13 15.87 12.27 13.06 4-methylundecane 10.53 13.80 10.76 11.47 5-methylundecane 18.55 24.65 19.40 20.59 6-methylundecane 1.48 1.45 1.20 1.16 2, 4-dimethyldecane 0.57 0.43 0.53 0.51 2, 5-dimethyldecane 1.63 1.37 1.65 1.77 2, 6-dimethyldecane 5.93 5.13 5.81 6.52 2, 7-dimethyldecane 3.31 2.72 3.08 3.45 2, 8-dimethyldecane 2.03 1.89 2.11 2.46 2, 9-dimethyldecane 2.84 2.55 2.66 2.94 3, 3-dimethyldecane 0.72 0.59 0.74 0.78 3, 7-dimethyldecane 0.00 0.60 0.00 0.35 3, 8-dimethyldecane 0.87 0.00 0.79 1.03 Methylethylnonane 4.36 4.96 3.57 3.12 Other isomer 2.89 1.59 2.14 1.74 -
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