ALKYLATION OF BENZENE USING BATCH AND CONTINUOUS FIXED-BED REACTORS

Alkylation reactions of benzene with propylene using heterogeneous catalysts H⁺-β zeolite, MCM-22, and ZSM-5 were studied for their affinity for cumene production. This work focused on the gas-phase reaction using different crystalline catalysts at several temperatures and amounts of reactants using both batch and continuous fixed-bed reactors. The properties of baseline commercial H⁺-β catalysts versus versions modified with Ga, La, and Pt were studied. Quantitative analysis of product mixture was performed by gas chromatography. For the batch reactor, β-zeolite produced the highest cumene yield and selectivity of 72% and 92%, respectively, at 225°C. At this temperature, a benzene:propylene dilution of 7:1 molar ratio was the optimum. For the continuous system, cumene production is favored at lower space velocities, higher benzene-to-propylene ratio, and temperatures close to 225°C. Ga modification of the H⁺-β zeolite significantly enhanced cumene yield in the continuous fixed-bed reactor at 225°C, from 27% of the unmodified β-zeolite to 36% for the Ga-modified one. The life span of modified β-catalysts was studied in the fixed-bed reactor for the first eight hours of reaction.     

Study on a catalytic distillation column with a novel internal

A novel internal for holding a catalyst in a catalytic distillation column was studied and its feasibility was verified by a model reaction, which is the alkylation of benzene with propylene over Hβ zeolite catalyst. The novel internal enlarges the void of the catalyst bed and provides the gas and liquid flow channels. It was proved that the catalytic distillation column with the novel internal has such advantages as simple structure, low operating cost, convenience for loading and unloading catalyst, and large catalyst loading fraction. It was found that the operational capability of the column with the novel internal whose volume fraction is about 30% is similar to that of a column filled with catalysts mixed with Cannon rings whose volume fraction is about 80%. It was also found that compared with the fixed-bed bubble reactor, the selectivity of cumene and the conversion of benzene are significantly improved in the CD (Catalytic Distillation) column with the internal.     

Friedel–Crafts type benzylation and benzoylation of aromatic compounds over Hβ zeolite modified by oxides or chlorides of gallium and indium

Liquid phase benzylation (by benzyl chloride) and benzoylation (by benzoyl chloride) of benzene and other aromatic compounds over different Ga- and In-modified Hβ zeolite catalysts at 80 °C have been investigated. An impregnation of the zeolite by oxides or chlorides of Ga and In makes the zeolite highly active in the benzylation process but it results in a decrease in the acidity, particularly the strong acid sites (measured in terms of the ammonia chemisorbed at 250 °C) of the zeolite. Both the redox function, created due to the modification of the Hβ zeolite by Ga or In, and the zeolitic acidity seem to play important role in the benzylation or benzoylation process. Among the different Ga- and In-modified Hβ zeolite catalysts, the In₂O₃/Hβ showed highest activity for the benzene benzylation. This catalyst also showed high activity for both the benzylation and benzoylation of other aromatic compounds, even in the presence of moisture in the reaction mixture; in case of the benzoylation, the moisture has beneficial effect. The In₂O₃/Hβ catalyst can be reused in the benzylation for several times. Kinetics of benzene benzylation (using excess of benzene) over the different Ga- and In-modified Hβ zeolite catalysts has also been investigated. A plausible mechanism for the activation of both the reactants (aromatic substrate and benzyl or benzoyl chloride, forming corresponding carbocation) over the catalyst and also for the reaction between the carbocation and the activated and/or non-activated aromatic substrate is proposed.     

醋酸胶溶剂对Hβ分子筛催化剂性能的影响

实验考察了醋酸胶溶剂对Hp分子筛催化剂成型强度的影响,并以丙烯和苯合成异丙苯为模型反应,分别以气-液半连续和液-液连续操作两种方式,实验评价催化剂的性能。结果表明：催化剂强度随成型过程中醋酸用量的增加呈现先增大后减小的趋势,最高催化剂强度对应的醋酸用量为6％。随着醋酸用量增加,催化剂活性略有增加,对异丙苯选择性影响不大,但催化剂稳定性却降低。     

异丙苯合成工艺进展

综述了分子筛催化异丙苯工艺的最新进展,指出分子筛催化工艺必将取代传统的固体酸工 艺,高活性、高选择性、长寿命、低苯烯比的新型分子筛催化剂的开发是异丙苯催化剂开发的方向。     

Effects of Zeolite Structures, Exchanged Cations, and Bimetallic Formulations on the Selective Hydrogenation of Acetylene Over Zeolite-Supported Catalysts

Supported PdAg bimetallic catalysts were evaluated for the selective hydrogenation of acetylene in the presence of ethylene. The effects of different zeolite structures and cations were investigated using flow reactor studies, with K⁺-β-zeolite supported PdAg showing the lowest activity but highest selectivity comparing to the γ-Al₂O₃ support and other alkaline metal exchanged β-zeolite supports. The K⁺ promoter effect on γ-Al₂O₃ was also tested, which showed that adding K⁺ to γ-Al₂O₃ increased activity and selectivity. Bimetallic catalysts consisting of Pd and a Group IB metal were also compared. It was found that the PdAg bimetallic catalyst had similar activity but better selectivity comparing to PdCu, while the PdAu catalyst showed the highest activity but lowest selectivity.     

Alkylation of 1-Dodecene with Benzene over H3PW12O40 Supported on Mesoporous Silica SBA-15

The SBA-15 supported 12-phosphotungstic acid catalysts were prepared and measured in the alkylation of benzene with 1-dodecene at the atmospheric batch reactor. It is found that the catalysts exhibit much higher catalytic activity, selectivity and stability than HY zeolite in this reaction at the reaction temperature of 80 °C, with the 1-dodecene conversion of nearly 90%, 2-phenyldodecane selectivity of nearly 40%, and monoalkylbenzene selectivity of 100%.     

VPT法制备MCM-22分子筛催化剂颗粒及其烷基化性能

采用汽相法（VPT）制备了以成型干胶颗粒为基体的MCM-22分子筛催化剂.利用XRD、SEM和BET测试技术对所制备催化剂进行了物相表征、形貌观察和织构分析,并以苯和丙烯烷基化合成异丙苯为模型反应,在液-固固定床反应器上对所制备催化剂的性能进行了评价.结果表明：汽相法制备的MCM-22分子筛催化剂不仅具有较好的结晶度和较高的微孔表面积,而且具有更好的晶体生长取向性和更加致密的结构;在烷基化反应中也具有很好的活性、选择性和稳定性,特别是对目的产物异丙苯的选择性明显高于水热法（HTS）合成的催化剂,在异丙苯合成上具有很好的应用前景.     

STUDY ON A CATALYTIC DISTILLATION COLUMN WITH A NOVEL INTERNAL

A novel internal for holding a catalyst in a catalytic distillation column was studied and its feasibility was verified by a model reaction, which is the alkylation of benzene with propylene over Hβ zeolite catalyst. The novel internal enlarges the void of the catalyst bed and provides the gas and liquid flow channels. It was proved that the catalytic distillation column with the novel internal has such advantages as simple structure, low operating cost, convenience for loading and unloading catalyst, and large catalyst loading fraction. It was found that the operational capability of the column with the novel internal whose volume fraction is about 30% is similar to that of a column filled with catalysts mixed with Cannon rings whose volume fraction is about 80%. It was also found that compared with the fixed-bed bubble reactor, the selectivity of cumene and the conversion of benzene are significantly improved in the CD (Catalytic Distillation) column with the internal.     

Liquid‐Phase Alkylation of Benzene with Propylene Catalysed by HY Zeolites

Benzene alkylation with propylene over a Ca modified HY zeolite to obtain cumene has been studied. Time on stream behavior of the catalyst was quite steady without any sign of deactivation and the results were reproducible. The external mass transfer does not influence the cumene reaction. The pore diffusion has a substantial influence on the cumene reaction only in the final region of the reactor, where the olefin concentration is very low. A simple power law kinetic model fits the experimental data significantly better than other models. A general time and space dependent model was developed to analyze the performance of a two‐phase downflow fixed bed reactor used for alkylation of benzene with zeolite catalyst. The model could be instructive in exploratory simulations evaluating the conditions for benzene alkylation in liquid phase.     

In situ MAS NMR investigations of molecular sieves and zeolite-catalyzed reactions

Solid-state MAS NMR is a powerful technique to study heterogeneous catalysts and the way by which they operate. In situ MAS NMR has been demonstrated to be a powerful method to understand reaction mechanisms, to study the nature, dynamics and reactivity of surface intermediates and active sites, and to characterize structural modifications in the catalyst itself, in particular when using ¹³C strategically labelled substrates. In this paper, three examples selected from our own work are used to illustrate the potential of in situ MAS NMR. They are the formation of cumene and its isomerization to n-propylbenzene on zeolite H-ZSM-11, the activation of propane at low temperature and the alkylation of benzene with propane on zeolite H-ZSM-5, and the characterization of the aluminophosphate molecular sieve VPI-5 structure with temperature. Studies of the alkylation of benzene with propene confirmed that cumene was the primary reaction product. The undesired n-propylbenzene by-product results from the intermolecular reaction between cumene and benzene, enhanced by molecular shape-selective effects in medium pore size zeolites (e.g., H-ZSM-11). It explains why large pore zeolites, e.g., zeolite Beta, are used commercially today for this process. Propane can be activated at low temperature (ca. 573 K) on bifunctional medium pore size zeolites possessing intimately related acidic Brønsted sites and a dehydrogenation function provided by Ga or Zn species. In Ga/H-ZSM-5 catalysts, at 573 K, the activation of propane was shown to occur via a protonated pseudocyclopropane (PPCP) intermediate (or transition state). The latter evolves in a manner that can be formally described by the formation of CH ₃ ⁺ , C₂H ₂ ⁺ , and C₃H ₇ ⁺ carbenium ion intermediates. These species can react with olefins, alkanes, or other electron-rich molecules such as benzene. The primary reaction products of the reaction of propane with benzene are n-propylbenzene (in small amount), ethylbenzene and toluene. Their subsequent reactions lead eventually to toluene and xylenes as the final products. In the structural characterization of VPI-5, ²⁷Al, ³¹P, and ²⁷Al nutation MAS NMR spectra show that, at 294 K, fully hydrated VPI-5 contains three equally populated Al and P crystallographic sites and that one-third of Al is 6-coordinate. The VPI-5 structure then belongs to the P6₃ space group. Above 353 K, VPI-5, fully or partially hydrated, undergoes a structural transformation to a higher framework symmetry, i.e., the P6₃cm space group. The transformation occurs at nearly the same temperature in both cases, indicating that the breakdown of the hydrogen-bonded helical water structure inside the VPI-5 pores is not a factor in the process.     

Kinetics of the vapour-phase hydrogenation of benzene over a supported nickel catalyst in a stirred-vessel reactor

The catalytic hydrogenation of benzene was investigated over a supported nickel catalyst in a continuous stirred-vessel reactor between 260° and 450°F at atmospheric pressure. The effects of temperature, ratio of hydrogen to benzene and total feed rate (or contact time) on the conversion of benzene and yield of cyclohexane were determined. The use of the stirred reactor helped to eliminate mass transfer limitations. The investigation was carried out using surface-coated catalysts in order to eliminate pore diffusion which might otherwise mask the actual kinetics. Studies of the mixing characteristics of the reactor were carried out under both reacting and non-reacting conditions, by following conversion as a function of stirrer speed and by a tracer (pulse) technique, respectively. The kinetic data were analysed to determine the most probable model to represent the reaction. The Houghen–Watson type analysis was carried out using non-linear least squares instead of the usual linear one. The model that satisfactorily correlated the data over the entire temperature range describes the rate-controlling step as the surface reaction between adsorbed hydrogen and adsorbed benzene, the hydrogen addition being simultaneous. The following Hougen–Watson type equation was proposed: r = k_e K_H ³K_B P_H ³P_B/(1+K_HP_H+K_BP_B+K_CP_C)⁴. The constants in this rate equation were expressed as a function of temperature.     

Diffusion Transfer in the Course of Benzene Alkylation with Propylene over a β-Zeolite Catalyst

By simulating benzene alkylation with propylene over -zeolite in a fixed-bed bubble reactor, suitable external mass-transfer correlation equations were chosen from the literature to calculate the coefficients and the external mass-transfer resistance. The internal mass-transfer resistance was derived from the experimental efficiency factor of catalyst pellets. When the catalyst pellet is 3 mm in diameter and consists of 0.2-m zeolite crystals, the mass-transfer resistance in the alkylation process decreases in the following order: gas–liquid film > liquid–solid film > macropore diffusion > intrinsic kinetics > intracrystalline diffusion.     

Methylation of benzene with methanol over zeolite catalysts in a low pressure flow reactor

Previous studies in this laboratory have shown oxygen to be a crucial requirement for the reaction of methane with benzene over zeolite catalysts at 400°C in a high pressure batch reactor. Thus, a two-step mechanism involving the intermediate formation of methanol by partial oxidation of methane followed by the methylation of benzene with methanol in the second step, was postulated. This paper now shows clearly that there is excellent correlation between the performance of the zeolite catalysts used for the methylation of benzene with methanol in a low pressure flow reactor and the methylation of benzene with methane in the presence of oxygen in a high pressure batch reactor. This finding therefore gives further support to the two-step mechanism for the oxidative methylation reaction at 400°C.     

The nature of the active sites in the reactions of cumene on HY and LaY catalysts

The secondary reactions which accompany cumene cracking have been studied at 360°, 430°, 500°C, over an HY zeolite catalyst using a tubular packed bed reactor. The concept of “Optimum Performance Envelope” was used in order to identify which of the observed reaction products are primary and which are secondary. In this way, benzene, ethylbenzene, n-propylbenzene, cymene, m- and p-diisopropylbenzene, as well as propylene, i-butene, and butene have been found to be primary products, while methane, ethylene, ethane, toluene, ethyl toluene, and i- and n-butane are identified as secondary products. The initial selectivities for the primary products have been calculated, and from these, the initial kinetic rate constants. These values, as well as the activation energies of primary product formation, are compared with those obtained using a LaY zeolite catalyst. The observed differences are discussed in terms of the nature and number of the active sites on the catalyst and lead us to conclude tthat LaY and HY have identical active sites but differ in site concentration.     

水热处理条件对Hβ沸石醚化活性的影响

采用水热处理的方法对Hβ沸石改性,制备出改性Hβ沸石醚化催化剂.在温度70℃、压力0.8 MPa、醇烯摩尔比1.05、空速 1.0 h^-1的反应条件下对改性催化剂进行醚化活性评价.系统考察了水热处理条件对Hβ沸石催化剂醚化活性的影响.结果表明,随着处理苛刻度的增大,催化剂的醚化活性呈现先升后降的趋势.水热处理温度对催化剂活性的影响最大.在300℃、1h、氮气与水蒸气分压比1.0、水空速0.4 h-1的条件下,水热处理提高了Hβ沸石的催化活性,叔碳烯烃的转化率为57.48 ％.水热处理Hβ沸石经酸洗后醚化活性进一步提高,叔碳烯烃的转化率达59.17％.对经过水热处理后的Hβ沸石进行金属Mo改性,叔碳烯烃转化率达到60.81%.     

AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.     

Study on alkylation of benzene with propylene over MCM-22 zeolite catalyst by in situ IR

For the alkylation reaction of benzene with propylene over MCM-22 zeolite catalyst, two completely different results can be obtained for two different operating procedures. If the benzene is pumped into a reactor then followed by propylene (operation 1), the alkylation reaction proceeds normally, while the reaction can not occur if the propylene is introduced first followed by benzene (operation 2). In situ IR technology was used to investigate two modes designed to simulate the above operating processes. The mechanisms of the two operations are as follows: in operation 1, benzene molecules first fully were adsorbed on the acidic sites of MCM-22 zeolite, when propylene was introduced, propylene molecules seized the acidic sites by repelling benzene, at the same times propylene molecules were polarized and reacted with absorbed benzene molecules. This is synchronous reaction mechanism; in operation 2, propylene introduced was molecularly absorbed on acidic sites strongly resulting in producing carbonium ions of CH₃–C⁺H–CH₃, then the carbonium ions reacts with other propylene molecules further to form polymeric species. The polymers blocked the pores and covered the acidic sites so that the alkylation reaction with benzene can not take place. This process is carbonium ions reaction mechanism of propylene itself.     

催化精馏合成异丙苯过程催化剂装填结构研究

为考察不同催化剂装填结构对催化精馏合成异丙苯过程的影响 ,在热态反应器中进行苯烃化催化精馏合成异丙苯的研究。反应器直径为 3 0mm ,高 2 0 0 0mm ,所用催化剂为 β改性沸石分子筛。操作压力0 .7MPa ,温度 43 0— 480K ,苯质量空速 4— 6h- 1 ,苯烯摩尔比 1.1— 2 .2 ,回流比 9— 2 0。催化剂装填结构由不锈钢填料与催化剂颗粒组成 ,三种装填结构的空隙率分别为 85 .1% ,81.6%和 79.4%。结果表明 ,对于异丙苯合成体系 ,装填结构对催化精馏的总体效果起决定性影响。在催化剂装填总量不变的前提下 ,异丙苯的选择性与丙烯的转化率均随催化剂装填结构空隙率的提高而提高。在优化条件下 ,异丙苯的选择性达97% ,丙烯转化率接近 10 0 %。催化剂装填结构对异丙苯选择性的影响比对丙烯转化率的影响更显著     

AF-5分子筛催化剂上苯气相乙基化反应的失活动力学研究——(Ⅰ)实验研究

在绝热固定床实验反应器中对苯和乙烯在 AF-5分子筛催化剂上进行的烷基化反应的失活动力学作了研究。初步考察表明乙烯和苯都会引起失活,但乙烯引起的失活是主要的。在和工业反应器类似的操作条件下系统测定了由催化剂失活引起的乙烯转化率随操作时间的变化。所得数据将用于建立失活动力学模型。