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摘要: 通过对比不同孔结构分子筛的甲苯甲醇烷基化催化性能，发现分子筛孔道尺寸与目标芳烃分子动力学尺寸的有效匹配以及孔道空间限制效应对反应路径的约束管理，对实现高性能烷基化至关重要。并结合XRD、BET、NH3-TPD和SEM表征分析，通过先后负载La2O3和P2O5对硅铝比为60的ZSM-5进行复合改性修饰，提升其骨架水热稳定性的同时，选择性地消除内外表面大部分强酸中心，保留弱+中强酸作为烷基化催化活性位，所得MAT-HZSM-5催化该反应表现出很高的甲醇烷基化效率和良好的反应稳定性，在氮气反应气氛下，连续运行500 h无明显失活迹象，甲苯转化率维持在35%-38%，二甲苯选择性60%-77%，甲醇烷基化效率大于90%。Abstract: By comparing the catalytic performance of toluene methanol alkylation over zeolites with different pore structure, it was found that the effective matching of the zeolite pore size with the molecular dynamics size of the target aromatic compounds and the constrained management of the reaction path by pore confinement effect are essential for achieving high performance of alkylation. Combined with XRD, BET, NH3-TPD and SEM characterization, it has been confirmed that ZSM-5 with Si/Al ratio of 60 modified by successively loading La2O3 and P2O5 had better hydrothermal stability of the frameworks and most of the strong acidic sites on its internal and external surface were selectively eliminated while the weak and medium strong acidic sites were remained as the active sites of alkylation. The obtained MAT-HZSM-5 exhibited high methanol alkylation efficiency and good stability under nitrogen reaction atmosphere. There was no obvious deactivation during 500 h reaction. The conversion of toluene was maintained at 35%-38%, the selectivity of xylene was 60%-77%, and the methanol alkylation efficiency was higher than 90%.
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Key words:
- toluene /
- methanol /
- alkylation /
- ZSM-5 /
- xylene
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图 1 HSAPO-34、HZSM-5(60)、HBeta和HMOR对甲醇甲苯烷基化反应的催化性能
Figure 1 Catalytic performance of HSAPO-34, HZSM-5(60), HBeta and HMOR for alkylation of methanol and toluene
图 3 HZSM-5分子筛的SEM照片(a)、催化剂样品XRD谱图(b)和NH3-TPD谱图(c)
Figure 3 SEM image of the HZSM-5 zeolite (a), XRD spectra of the catalyst samples (b) and NH3-TPD profiles (c)
A: HZSM-5(60); B: La-HZSM-5; C: P-HZSM-5; D: MAT-HZSM-5
图 4 MAT-HZSM-5催化甲醇甲苯甲基化反应评价结果(a); HZSM-5(60)、La-HZSM-5和P-HZSM-5催化甲醇甲苯烷基化反应稳定性对比(b)
Figure 4 Catalytic performance of MAT-HZSM-5(a); stability comparison of methanol-toluene alkylation catalyzed by HZSM-5(60), La-HZSM-5 and P-HZSM-5 (b)
表 1 不同孔道结构分子筛催化剂的比表面积及孔容
Table 1 Specific surface area and pore volume of zeolite catalysts with different pore structures
Catalyst Specific surface area A/(m2·g-1) Pore volume v/(mL·g-1) total specific surface area (BET) external specific surface area internal specific surface area mesopore micropore HSAPO-34 385.9 114.2 271.7 0.104 0.129 HZSM-5(60) 328.7 145.9 182.8 0.138 0.081 HBeta 464.2 279.6 184.6 0.195 0.115 HMOR 458.5 138.1 320.4 0.179 0.126 γ-alumina 303.5 303.3 0.2 0.312 0.000 HZSM-5(30) 343.2 151.8 191.4 0.134 0.094 HZSM-5(200) 347.5 136.2 211.3 0.168 0.096 HZSM-5(500) 365.3 159.8 205.5 0.173 0.089 
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表 2 不同硅铝比HZSM-5分子筛催化剂的酸量
Table 2 Acidity of the HZSM-5 zeolite catalysts with different Si/Al ratios
Catalyst (Si/Al ratio) Acidity /(mmol·g-1) (Weak acid+ moderate strong acid)/strong acid total acidity weak acid+ moderate strong acid strong acid HZSM-5(30) 1.29 0.79 0.50 1.58 HZSM-5(60) 0.99 0.61 0.38 1.61 HZSM-5(200) 0.51 0.36 0.15 2.40 HZSM-5(500) 0.06 0.054 0.006 9.00 weak acid+moderate strong acid: ammonia desorption occurred at 623 K and below;
strong acid: ammonia desorption occured above 623 K
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表 3 不同硅铝比HZSM-5分子筛催化甲醇甲苯烷基化反应(0.33 h)
Table 3 Alkylation of toluene with methanol catalyzed by HZSM-5 zeolites with different Si/Al ratios (0.33 h)
Catalyst (Si/Al ratio) Toluene conversion x/% Selectivity s/% Other aromatic hydrocarbons /% Yield of p-xylene w/% Alkylation efficiency of methanol/% para-xylene xylene benzene ZSM-5(30) 50.1 22.4 51.1 39.9 9.0 5.73 28.9 ZSM-5(60) 47.5 24.1 54.0 37.8 8.2 6.18 30.7 ZSM-5(200) 28.4 23.6 78.0 2.0 20.0 5.23 65.7 ZSM-5(500) 20.5 23.1 80.4 1.7 17.9 3.81 46.8
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表 4 HZSM-5(60)和改性催化剂的比表面积和孔容
Table 4 Specific surface area and pore volume of the HZSM-5(60) and MAT-HZSM-5 modified catalysts
Catalyst Specific surface area A/(m2·g-1) Pore volume v/(mL·g-1) total specific surface area (BET) external specific surface area internal specific surface area mesoporous microporous HZSM-5(60) 328.7 145.9 182.8 0.138 0.081 La-HZSM-5 317.8 141.1 176.7 0.134 0.078 P-HZSM-5 314.8 140.2 174.6 0.131 0.076 MAT-HZSM-5 302.4 135.3 167.1 0.125 0.072
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表 5 不同助剂改性所制得ZSM-5催化剂的酸量
Table 5 Acidity of the ZSM-5 catalyst modified by different promoters
Catalyst Acidity /(mmol·g-1) (Weak acid+moderate strong acid)/ strong acid total acidity weak acid+moderate strong acid strong acid HZSM-5(60) 0.99 0.61 0.38 1.61 La-HZSM-5 0.84 0.55 0.29 1.90 P-HZSM-5 0.97 0.66 0.31 2.13 MAT-HZSM-5 0.81 0.60 0.21 2.86 weak acid+moderate strong acid: ammonia desorption occurred at 623 K and below; strong acid: ammonia desorption occured above 623 K
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表 6 不同助剂改性制备的HZSM-5催化剂反应稳定期性能对比
Table 6 Performance comparison of the HZSM-5 catalyst modified with different promoters in the stable period of reaction
Catalyst Toluene conversion x/% Selectivity s/% Other aromatic hydrocarbons s/% Yield of p-xylene w/% Alkylation efficiency of methanol/% para-xylene xylene benzene ZSM-5(60) 47.7a 24.0 52.0 36.8 11.2 5.96 35.6 La-ZSM-5 42.0b 23.7 56.9 29.6 13.5 5.66 45.4 P-ZSM-5 45.8c 23.9 61.6 21.6 16.8 6.74 67.1 MAT-ZSM-5 39.0d 24.1 61.3 3.3 35.4 5.76 98.6 a: reaction results at the third hour; b: reaction results at the tenth hour; c: reaction results at the tenth hour; d: reaction results at the Fortieth hour
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