Study on n-butane catalytic cracking for promoting propylene production over nMoOx·HZSM-5
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摘要: 采用等体积浸渍法制备了nMoOx·HZSM-5系列单相复合体，用XRD、NH3-TPD、Py-FTIR、BET、SEM等技术对其物相结构、表面酸性、比表面积进行了表征。在连续固定床微反装置中对nMoOx·HZSM-5单相复合体进行了催化正丁烷裂解性能的评价。结果表明，部分活性组分Mo以MoOx原子簇的形式定位于HZSM-5分子筛的Z形和直形孔道交叉孔处，与分子筛的骨架氧配位形成nMoOx·HZSM-5单相复合体，引起分子筛的骨架收缩，相应的晶胞参数及晶胞体积减小，比表面积下降；随Mo用量的增大，nMoOx·HZSM-5单相复合体的酸量呈先增加后减小趋势；在反应温度625℃，体积空速5600 h-1条件下，Mo用量为0.75%制备的nMoOx·HZSM-5-0.75%单相复合体催化正丁烷裂解反应的转化率为73.83%，略低于HZSM-5分子筛，但丙烯收率却达到了13.13%，较HZSM-5分子筛提高2个百分点以上，表现出较好的增产丙烯效果。Abstract: A series of nMoOx·HZSM-5 single-phase complexes were prepared by incipient wetness impregnation, and characterized by XRD, NH3-TPD, Py-FTIR, BET and SEM techniques. The n-butane catalytic cracking performance over nMoOx·HZSM-5 was investigated by using a continuous flowing micro reactor. The results indicate that active component Mo is located in the cross of Z form channel and straight channel of HZSM-5 in the form of MoOx clusters to generate a nMoOx·HZSM-5 single-phase complex, causing the contraction of HZSM-5 lattice cell and the reduction in the lattice parameters and cell volume of HZSM-5 as well as the decrease in specific surface area of HZSM-5. The acidity of nMoOx·HZSM-5 shows an increases firstly and then a decrease with the increasing dosage of active component Mo. The n-butane catalytic cracking conversion over nMoOx·HZSM-5-0.75% is 73.83% at reaction temperature of 625℃ and gas space velocity of 5600 h-1, slightly lower than that over HZSM-5. However, the propylene yield over nMoOx·HZSM-5-0.75% reaches 13.13%, 2 percent points higher than that over HZSM-5, exhibiting a better performance on the promotion of propylene yield.
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Key words:
- nMoOx·HZSM-5 /
- single-phase complex /
- n-butane /
- propylene /
- conversion /
- yield
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图 1 不同Mo用量的nMoOx·HZSM-5单相复合体的XRD谱图
Figure 1 XRD patterns of nMoOx·HZSM-5 single-phase complex with different dosages of Mo
图 2 HZSM-5分子筛和nMoOx·HZSM-5单相复合体的SEM照片
Figure 2 SEM images of HZSM-5 and nMoOx·HZSM-5 single-phase complex
(a): HZSM-5; (b): nMoOx·HZSM-5-0.5%; (c): nMoOx·HZSM-5-0.75%; (d): nMoOx·HZSM-5-1.0%; (e): nMoOx·HZSM-5-1.5%; (f): nMoOx·HZSM-5-2.0%; (g): nMoOx
图 3 不同Mo用量的nMoOx·HZSM-5单相复合体的NH3-TPD谱图
Figure 3 NH3-TPD profiles of nMoOx·HZSM-5 single-phase complex with different dosages of Mo·HZSM-3.0%; (h): nMoOx·HZSM-5-5.0%
图 4 不同Mo用量的nMoOx·HZSM-5单相复合体吡啶红外光谱谱图
Figure 4 Py- FTIR spectra of nMoOx·HZSM-5 single-phase complex with different dosages of Mo
图 6 不同Mo用量nMoOx·HZSM-5单相复合体的正丁烷裂解转化率
Figure 6 n-butane conversion of nMoOx·HZSM-5 single-phase complex with different dosages of Mo
图 7 不同Mo用量的nMoOx·HZSM-5单相复合体催化正丁烷裂解反应的丙烯收率和甲烷收率
Figure 7 Propylene yield and methane yield of n-butane cracking reaction catalyzed by nMoOx·HZSM-5 single-phase complex with different dosage of Mo
表 1 不同Mo用量的nMoOx·HZSM-5单相复合体的晶胞参数及晶胞体积
Table 1 Lattice parameters(a, b, c) and cell volume(V) of nMoOx·HZSM-5 single-phase complex with different dosages of Mo
Mo w/% a/nm b/nm c/nm V/nm3 0 2.0003 2.0181 1.3459 5.4333 0.5 1.9998 2.0189 1.3453 5.4318 0.75 2.0000 2.0187 1.3455 5.4327 1.0 1.9985 2.0187 1.3461 5.4311 1.5 1.9978 2.0196 1.3457 5.4296 2.0 1.9999 2.0188 1.3446 5.4291 3.0 1.9987 2.0178 1.3445 5.4225 5.0 1.9986 2.0175 1.3454 5.4241 
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表 2 nMoOx·HZSM-5单相复合体的比表面积
Table 2 Specific surface area of nMoOx·HZSM-5 single-phase complex
Mo w/% ABET/(m2·g-1) 0 399 0.5 395 0.75 388 1.0 372 1.5 365 2.0 356 3.0 354 5.0 340
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表 3 nMoOx·HZSM-5单相复合体的酸量
Table 3 Acidic amount of nMoOx·HZSM-5 single-phase complex
Mo w/% Total /(mmol·g-1) Weak acid/% Strong acid/% 0 0.632 54.42 45.58 0.5 0.926 57.79 42.21 0.75 1.035 58.54 41.46 1.0 0.953 58.73 41.27 1.5 0.951 60.04 39.96 2.0 0.793 61.41 38.59 3.0 0.756 62.39 37.61 5.0 0.731 63.44 36.56
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表 4 nMoOx·HZSM-5单相复合体的B酸和L酸酸量
Table 4 Amounts of B acid and L acid sites determined by Py-IR of nMoOx·HZSM-5 single-phase complex
Mo w/% Brønsted/ (mmol·g-1) Lewis/ (mmol·g-1) L/B 0 0.495 0.137 0.277 0.5 0.767 0.159 0.207 0.75 0.831 0.204 0.246 1.0 0.780 0.173 0.222 1.5 0.622 0.328 0.527
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表 5 产物定性分析
Table 5 Identification result of product
Retention time t/min Peak substance Retention time t/min Peak substance 8.122 methane 14.187 propylene 8.948 ethane 16.613 isobutane 9.641 ethylene 17.128 n-butane 11.561 propane
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