Conversion of 4-ethylphenol to light aromatics on the Cr2O3/Al2O3 modified by phosphoric acid
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摘要: 以烷基酚转化为轻质芳烃(苯和甲苯)为目标,制备了Cr2O3/Al2O3催化剂,并以4-乙基酚为模型化合物研究了其加氢反应性能。体积空速、氢油比、反应压力和温度升高时,脱烷基率、芳烃总选择性、轻质芳烃选择性呈先增大后减小的趋势,反应温度对转化率影响较大。以不同浓度磷酸对Cr2O3/Al2O3进行改性,随着磷酸用量的增大,催化剂酸量总体增大,主要是弱酸和中强酸,酸强度先增加后降低,磷酸用量较高时,弱酸增加幅度较大。与未改性相比,质量分数8%磷酸改性Cr2O3/Al2O3上4-乙基酚转化率99.5%,脱烷基率提升9.4%,达74.4%,轻质芳烃选择性提高4.0%,达到57.0%,以较高选择性实现了转化制轻质芳烃,同时,芳烃总选择性高达80.4%,较高程度保持了芳环不被破坏。提出了Cr2O3/Al2O3上4-乙基酚加氢反应的路径并对反应机理进行了研究。Abstract: With the goal of conversion of alkylphenols to light aromatics (benzene and toluene), Cr2O3/Al2O3 catalysts were prepared and their hydrogenation performance was investigated using 4-ethylphenol as a model compound. With the increase of LHSV, H2/oil, reaction pressure and temperature, the dealkylation rate, the total selectivity of aromatics, and the selectivity of light aromatics first rose and then dropped. The conversion of 4-ethylphenol was obviously influenced by the reaction temperature. Cr2O3/Al2O3 was modified with different concentrations of phosphoric acid. As the increase of the amount of phosphoric acid, the general amount of weak and medium acids on the catalyst increased, and the strength of acid was first enhanced and then weakened. The amount of weak acid increased significantly under a high value of the amount of phosphoric acid. Compared with the unmodified catalyst, the conversion of 4-ethylphenol on the catalysts modified by 8% phosphoric acid is higher than 99.5%, while the dealkylation rate of 4-ethylphenol increased by 9.4%, reaching to 74.4%, and the selectivity to light aromatics (benzene and toluene) increased by 4.0%, reaching to 57.0%. Conversion of 4-ethylphenol to light aromatics was achieved in high selectivity. Furthermore, the total selectivity of aromatics was as high as 80.4%, which meant that most of the aromatic rings was not broken. The path of hydrogenation reaction of 4-ethylphenol on Cr2O3/Al2O3 was proposed and the reaction mechanism was discussed.
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Key words:
- coal tar /
- 4-ethylphenol /
- phosphoric acid /
- alumina /
- chromium oxide
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图 7 不同含量磷酸改性对Cr2O3/Al2O3催化4-乙基酚加氢反应性能的影响
Figure 7 Effect of modification with various content of phosphoric acid on the performance of the Cr2O3/Al2O3 catalysts for the hydrogenation of 4-ethylphenol
reaction conditions: LHSV=6 h-1, H2/oil=500 :1, p=3.5 MPa, t=450 ℃ P-0: 0 H3PO4; P-1: 4%H3PO4; P-2: 6%H3PO4; P-3: 8%H3PO4; P-4: 10%H3PO4; P-5: 12%H3PO4
图 8 不同含量磷酸改性Cr2O3/Al2O3催化剂反应前后的XRD谱图
Figure 8 XRD patterns of the Cr2O3/Al2O3 catalysts modified with various content of phosphoric acid before and after reaction
reaction conditions: LHSV=6 h-1, H2/oil=500 :1, p=3.5 MPa, t=450 ℃; AF: after P-0: 0 H3PO4; P-1: 4%H3PO4; P-2: 6%H3PO4; P-3: 8%H3PO4; P-4: 10%H3PO4; P-5: 12%H3PO4
表 1 不同含量磷酸改性Cr2O3/Al2O3催化剂的孔结构参数表
Table 1 Pore structure parameters of the Cr2O3/Al2O3 catalysts modified by various content of phosphoric acid
Catalyst Specific surface area
A/(m2·g-1)Pore volume
v/(cm3·g-1)Average pore size
d/nmP-1 140.6 0.44 12.5 P-2 148.8 0.47 12.5 P-3 146.7 0.47 12.7 P-4 134.5 0.41 12.1 P-5 131.9 0.40 10.4 reaction conditions:LHSV=6 h-1,H2/oil=500 :1,
p=3.5 MPa,t=450 ℃
P-1: 4%H3PO4;P-2: 6%H3PO4;P-3: 8%H3PO4;P-4: 10%H3PO4;P-5: 12%H3PO4表 2 不同含量磷酸改性Cr2O3/Al2O3催化剂表面元素相对百分含量
Table 2 Relative percentage content of surface elements of the Cr2O3/Al2O3 catalysts modified with different phosphoric acid content
Catalyst Content w/% P O Cr P-0 0.00 96.06 3.94 P-1 1.61 94.54 3.85 P-2 2.09 94.21 3.70 P-3 2.32 93.78 3.90 P-4 2.65 93.34 4.01 P-5 3.59 92.55 3.86 AFP-3 2.20 93.78 4.02 reaction conditions:LHSV=6 h-1,H2/oil=500 :1,p=3.5 MPa,t=450 ℃
P-0: 0 H3PO4;P-1: 4%H3PO4;P-2: 6%H3PO4;P-3: 8%H3PO4;P-4: 10%H3PO4;P-5: 12%H3PO4 -
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