Catalytic performance of SAPO-11/HZSM-5 composite supported Cr2O3 in the transformation of LPG to light olefins
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摘要: SAPO-11晶化液中预置HZSM-5合成了HZSM-5（核）/SAPO-11（壳）复合分子筛。以复合分子筛为载体负载10% Cr2O3，研究了其孔分布、酸性质及其对液化石油气（LPG）转化制乙烯和丙烯反应的催化性能。结果表明，复合分子筛由HZSM-5表面包覆不同厚度的SAPO-11微晶组成，随着晶化时间延长，复合分子筛壳层厚度增加。复合分子筛负载Cr2O3催化剂的介孔率先增加后降低；弱酸量先增加后降低，强酸强度增加，强酸量先降低后增加，强酸密度减小。复合分子筛载体在LPG选择转化反应中催化性能优于单个分子筛和机械混合分子筛，其中，晶化12 h合成样品负载Cr2O3用于LPG转化反应对原料总转化率和乙烯+丙烯选择性最高，分别为42.63%和65.89%，CH4和C5+选择性分别为6.32%和15.48%。通过控制晶化时间可调变壳层厚度、复合分子筛介孔率以及酸性质，改善产物分布。Abstract: HZSM-5(core)/SAPO-11(shell) composite molecular sieves were hydrothermally synthesized by crystallization of SAPO-11 outside HZSM-5 surface. After loading 10% Cr2O3, the pore distribution, acidity, and catalytic activity of the composite supported Cr2O3 in the transformation of liquefied petroleum gas (LPG) to ethene and propene were investigated. The results showed the HZSM-5 surface was coated with SAPO-11 microcrystalline of different thicknesses. With the increase of crystallization time, the shell thickness of the composite molecular sieves is increased; the mesoporosity and acidity can then be regulated by controlling the shell thickness. The composite supported Cr2O3 exhibits superior activity in the transformation of LPG to olefins than the single molecular sieves or mechanically mixed ones. The Cr2O3 catalyst supported on the composite by crystallization for 12 h gives the highest activity and selectivity to the target products; the feed conversion and the selectivity to ethene and propene are 42.63% and 65.89%, respectively, while the selectivities to CH4 and C5+ are 6.32% and 15.48%, respectively.
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Key words:
- composite zeolite /
- chromium oxide /
- LPG /
- selective conversion /
- ethene and propene
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图 1 分子筛样品的XRD谱图
Figure 1 XRD patterns of the molecular sieve samples
(a): single molecular sieve supporting; (b): composite molecular sieve supporting
图 3 合成分子筛样品的SEM和TEM照片
Figure 3 SEM and TEM images of various synthesized molecular sieves
SEM: (a): HZSM-5; (b): SAPO-11; (c): Z+S; (d): Z/S-12; TEM: (e): Z/S-12; (f): Z/S-24
图 4 分子筛负载Cr2O3样品的NH3-TPD谱图
Figure 4 NH3-TPD profiles of the molecular sieve supported Cr2O3
图 7 不同样品上LPG转化反应的产物分布
Figure 7 Product distribution for the LPG transformation over different catalysts
图 8 C2=+C3=选择性随反应时间的变化
Figure 8 Selectivity to C2=+C3= with time on stream over various catalysts
表 1 分子筛负载Cr2O3样品的孔参数
Table 1 Pore parameters of the molecular sieve supported Cr2O3
Supporter Ratio ABET/(m2·g-1) vpore /(cm3·g-1) dpore/nm Mesoporosity /% vmicro vmeso vtotal dmicro dmeso HZSM-5 - 334 0.146 0.081 0.227 0.556 2.204 35.7 SAPO-11 - 225 0.102 0.075 0.177 0.566 5.194 42.4 Z+S 1：3.0 215 0.092 0.078 0.170 0.568 2.124 45.9 Z/S-6 1：1.8 208 0.089 0.087 0.176 0.542 2.151 49.4 Z/S-12 1：2.0 167 0.071 0.085 0.156 0.526 2.138 54.5 Z/S-24 1：2.3 167 0.072 0.085 0.157 0.525 2.151 54.1 mesoporosity: vmeso / vtotal 
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表 2 分子筛负载Cr2O3样品的NH3-TPD酸量
Table 2 NH3-TPD acid amounts of the molecular sieve supported Cr2O3
Sample Temperature t/℃ Acid amount /(mmol·g-1) Strong acid density/(mmol·m-2)×105 weak acid strong acid weak acid strong acid total HZSM-5 210 413 0.127 0.066 0.193 19.76 SAPO-11 200 398 0.250 0.005 0.255 2.22 Z+S 204 406 0.258 0.028 0.286 13.02 Z/S-6 208 472 0.315 0.016 0.331 7.69 Z/S-12 200 464 0.400 0.009 0.409 5.39 Z/S-24 209 475 0.389 0.012 0.401 7.19
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