HRP-12催化剂上苯与直链烯烃的烷基化反应 Ⅱ. 失活动力学研究

采用连续操作的釜式反应器，利用悬浮态的负载杂多酸催化剂HRP-12上的烷基化反应的实验数据进行参数估值，确定了失活反应速率常数、失活反应活化能、活性保留函数的失活反应级数和烯烃摩尔浓度的失活反应级数，建立了苯与直链烯烃烷基化反应的失活动力学模型。模型表明：该失活反应对于活性保留函数是一级失活反应，对于烯烃摩尔浓度是二级失活反应。统计检验表明：所得失活动力学方程在显著性水平α=0.005下有较高的实验数据拟合精度和模型可信度。     

Green process of fuel production under porous γ-Al2O3 catalyst: Study of activation and deactivation kinetic for MTD process

One of the methods of industrial dimethyl ether production is the catalytic dehydration of methanol. In this research work, methanol dehydration reactor has been modeled using continuous model and its results have been compared with experimental works and Voronoi pore network model. A 1D heterogeneous dispersed plug flow model was utilized to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. The mass and heat transfer equations are numerically solved for the reactor. The concentration of the reactant and products and also the temperature varies along the reactor, therefore the effectiveness factor would also change in the reactor. We used the the effectiveness factor that was simulated according to the diffusion and reaction in the catalyst pellet as a Voronoi pore network model. Sensitivity analysis was performed to determine the influence of T, P and weight hourly space velocity on performance of the chemical reactor. Acceptable agreement was reached between the measured and the model data. The results showed that the maximum reaction conversion was obtained about 90 % at WHSV = 10 h^?1 and T = 560 K, while the inlet temperature (T_inlet) had a greater effect on methanol conversion. In addition, the effect of water in the feed on methanol conversion was quantitatively studied. Also, the deactivation kinetics of γ-Al₂O₃ heterogeneous-acidic catalyst in methanol to dimethyl ether dehydration process was studied using integral analysis method. Based on independent deactivation kinetics, a second order was found that accurately fitted the experimental conversion time data. The main reaction activation energies and catalyst deactivation energies were 143.1 and ?102.1 kJ/mol, respectively.     

Modeling of a radial-flow moving-bed reactor for dehydrogenation of isobutane

A mathematical model for the performance of a radial-flow moving-bed reactor for dehydrogenation of light paraffins was developed. Assuming relevant kinetic expressions for the main reaction and catalyst deactivation, the kinetic parameters were obtained through lab-scale fixed-bed reactor testing using the integral method of analysis. The conversion was found to be a function of a dimensionless decay time, i.e., the ratio of a “catalyst deactivation time constant” to the residence time of the catalyst within the reactor. For a large dimensionless decay time (negligible catalyst decay), the performance equation approached that of a simple packed-bed reactor. The predictions of the model were compared with those of a commercial unit, and fair agreements were observed.     

裂化催化剂水热失活动力学及装置平衡活性模型

根据裂化催化剂水热失活过程伴随着超稳化过程的特点，确定了对应不同自抑制函数的催化剂水热失活动力学模型方程。利用裂化催化剂水热失活实验数据进行参数估值，建立了裂化催化剂水热失活动力学模型。统计检验结果表明，二级自抑制的一级水热失活模型能很好地模拟实验数据，是较理想的水热失活动力学模型。考虑工业装置中裂化催化剂呈全混流，建立了裂化催化剂平衡活性模型方程，并且装置平衡催化剂微反活性的模型计算值与实测值相当吻合。该模型的预测结果表明，随着再生器温度或催化剂藏量的提高，平衡剂的微反活性逐步降低；平衡剂微反活性随催化剂单耗的提高先快速提高，然后缓慢提高。     

The kinetic effects of decreasing catalytic activity on a simple rate expression

When kinetics are studied for a catalyzed reaction, the active catalyst surface available affects the results. This article illustrates the effect of a progressively decreasing available surface on the heterogeneous kinetics of a gas‐phase reaction in a closed system. The present contribution focuses on the effect of simple mth order surface deactivation on a simple nth order kinetic expression. The basic analysis and general results are unchanged if more complex equations are used. It is shown that there are certain common anomalous characteristics of kinetic expressions involving deactivation. In particular, the apparent rate constant and the apparent order are usually dependent on both the actual and initial pressures of the reactant, and the reaction may not go to completion. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 7–16, 2000     

Formation of sulfur surface species on a commercial NO<Subscript>x</Subscript>-storage reduction catalyst

The influence of SO₂ exposure under lean (oxidizing) and rich (reducing) reaction conditions on the storage and oxidation/reduction function of a commercial NO_x storage-reduction catalyst was investigated by temperature-programmed uptake experiments and high temperature XRD. Both the storage capacity and the oxidation/reduction function of the catalyst were deactivated by SO₂ exposure under lean and rich reaction conditions. The deactivation of the storage component, i.e. the loss of the NO_x storage capacity, resulted mainly from the formation of Ba-sulfates accumulating in the bulk phase, which have a high thermal stability (>800°C) and, therefore, cannot be removed under the typical operation conditions of a NSR catalyst. For the oxidation function only a temporarily deactivation during lean reaction conditions was observed. Besides the formation of SO^2- ₄ species on the storage component at the beginning of the SO₂ exposure under rich conditions, an adsorption of SO₂ on the noble metal component was observed resulting in the formation of sulfur deposits. The oxidation of these sulfur species with a subsequent spillover of SO^2- ₄ species to the storage component during lean conditions could accelerate the deactivation of the storage capacity.     

Synergistic effect between Sn and K promoters on supported platinum catalyst for isobutane dehydrogenation

Catalytic dehydrogenation of isobutane has recently received considerable attention because of the increasing demand for isobutene.In this study,the synergistic effect between Sn and K on PtSnK/γ-Al2O3 catalysts has been investigated by changing the content of Sn.It was found that with the presence of potassium,suitable addition of Sn could not only increase the metal dispersion,but also reduce the catalyst acidity.In these cases,the synergistic effect could also strengthen the interactions between the metal and support,which resulted in an increase in both catalytic activity and stability.In our experiments,Pt-0.6SnK/Al catalyst exhibited the lowest deactivation rate (12.4%) and showed a selectivity to isobutene higher than 94% at the isobutane conversion of about 45.3% after running the reaction for 6 h.However,with the excessive loading of Sn,surface property of active sites and the interactions between metal and support were changed.As a result,the initial optimal ratio between the metallic function and acid function would be destroyed,which was disadvantageous to the reaction.     

Polymerization kinetics of octene-1 catalyzed by metallocene methylaluminoxane investigated with attenuated total reflectance fourier transform infrared (ATR-FT-IR) spectroscopy

The kinetic parameters have been measured for octene-1 solution polymerization at 120°C catalyzed by zirconocene with the cocatalyst methylaluminoxane. The polymerizations were performed in an attenuated total reflectance (ATR) reaction cell. The progress of the reactions were followed by observing the disappearance of octene-1 using the 910 cm^?1 band measured by FT-IR spectroscopy. The dependence of the reaction rate, R_p, on catalyst concentration and cocatalyst/catalyst ratio was examined. The catalyst deactivation mechanism was studied by fitting the experimental data to mathematical models involving second-order propagation and either first or second order catalyst deactivation. Second-order catalyst deactivation provided a much better fit. The calculated deactivation rate constant, k_d, is 21 (Ms)^?1. This model is used to determine the propagation rate constant for Al/Zr = 4 × 10³ as k_p = 19.9 (M s)^?1. A decrease in Al/Zr = 3 × 10² lowered the propagation rate constant, k_p, to 9.6 (M s)^?1 indicating that less than 50% of the initial Zr is active at this Al/Zr ratio.     

Mechanism of oxygen poisoning of ammonia synthesis catalyst

The effect of oxygen adsorbed on the surface of a commercial catalyst from a mixture of hydrogen with water vapor on the steady-state and nonsteady-state ammonia synthesis kinetics is studied under gradientless conditions at the pressures of the stoichiometric nitrogen-hydrogen mixture below the atmospheric pressure and at the temperatures of 285 and 240°C. The results obtained are discussed on the basis of the concepts of the ammonia synthesis theory of Temkin. The poisoning effect of oxygen on the reaction rate is explained by an increase in the activation energy of the rate constant k ₊ in the Temkin-Pyzhev equation, i.e., an increase in the activation energy of the rate constant of nitrogen adsorption at the fixed nitrogen adsorption heat. This conclusion agrees with the concepts of Ertl et al., according to which the activation energy of nitrogen adsorption on iron changes in symbasis with the variation of the electronic work function. Oxygen adsorption on the catalyst surface increases the electronic work function. Thus, the mechanism of the catalyst poisoning by oxygen (at its low surface coverage) consists in an increase in the electronic work function. Assumptions are stated as to the role of chemical promoters of iron catalysts.     

Kinetics of the initial stage of catalytic radical chain oxidation of cumene with catalyst deactivation

We have developed a method for estimating the rate constant for the reaction of catalyst deactivation in a radical chain process in the presence of catalysts with low stability. Its applicability is demonstrated in the reaction of oxidation of cumene in the presence of alkylammonium halides.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 2, pp. 69–74, March–April, 1994.     

A kinetic study on the reaction between glycidyl vinyl ether and carbon dioxide with quaternary ammonium salts as catalyst

The kinetics of the reaction between glycidyl vinyl ether (GVE) and carbon dioxide has been studied by using quaternary ammonium salts as catalyst. The catalysts having larger cations and more nucleophilic counter-anions showed higher activity. In a semi-batch reactor where CO₂ is continuously supplied, the reaction is first order with respect to the concentration of GVE. In a high pressure batch reactor, the reaction is first order with respect to both GVE and CO₂ and second order overall. In the latter case, a simple method to evaluate the rate constant and Henry's constant is also proposed.     

Kinetics of oxidative dehydrogenation of isobutyraldehyde over Cs2HPMo12O40 catalyst

The kinetics of oxidative gas-phase dehydrogenation of isobutyraldehyde over Cs₂HPMo₁₂O₄₀ catalyst has been studied in a flow-through integral reactor at 523 K at atmospheric pressure. The catalytic reaction has been found to be accompanied by oxidation of isobutyraldehyde outside the catalyst bed. The rate of formation of methacrolein is satisfactorily described by the rate equation derived on presumption of change in the mean activation energy. The rate of the reaction in the homogeneous phase was described by empirical pseudo-first order equation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effective conversion of cellobiose and glucose to sorbitol using non-noble bimetallic NiCo/HZSM-5 catalyst

The tandem hydrolysis and hydrogenation of saccharides into sorbitol is an especially attractive reaction in the conversion of biomass. Here, an economical and efficient bimetallic catalyst for the transformation of glucose and cellobiose into sorbitol is reported. Non-precious metal based catalysts such as NiCo, Ni, and Co, were prepared via modified impregnation method, and NiCo/HZSM-5 showed superior performance for the synthesis of sorbitol (86.9% from cellobiose, 98.6% from D-glucose). Various characterizations, such as Brunner-Emmet-Teler (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), confirmed that NiCo alloy formed and highly dispersed in NiCo/HZSM-5 catalyst. The high performance of fabricated catalyst would be attributed to the formation of nickel-cobalt alloy over HZSM-5 zeolite surface. High temperature and H₂ pressure were favorable for the tandem hydrolysis and hydrogenation reaction. Besides, the reaction pathway was also proposed based on the kinetics study. Cellobitol was detected as the intermediate in the reaction mixture. Furthermore, in the catalytic stability study, it was found that active metal species of NiCo/HZSM-5 were stable. The deactivation of catalyst would be due to the covering of acidic sites over NiCo/HZSM-5.     

Laws of selective CO oxidation over a Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the surface ignition regime: II. Transition states

The kinetics of selective CO oxidation (or individual CO or H₂ oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 g_Cat⁻¹ h⁻¹ and reagent percentages of ∼1 vol % CO, ∼1 vol % O₂, ∼60 vol % H₂, and N₂ to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H₂ oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.     

乙炔氢氯化反应铜系催化剂的反应机理

以电石乙炔法制备氯乙烯的非汞催化反应体系为研究对象,用量子化学密度泛函理论(DFT)研究了以Cu基催化剂为代表的非汞催化剂的反应机理.模拟了以石墨烯为载体的乙炔氢氯化反应在Cu基催化剂作用下的两条反应路径及其过渡态.将该反应机理应用到不同金属氯化物催化剂中,通过计算相应的活化自由能和反应速率常数讨论了不同金属氯化物的活性顺序,与实验结果相比较印证了反应机理的合理性.讨论了Cu基催化剂的失活原因以及在载体中掺杂氮原子或磷原子对反应活性的影响.为非贵金属无汞催化剂的研究提供了一定的理论指导.     

镍基催化剂用于合成气甲烷化的实验研究

实验基于工业用镍基甲烷化催化剂,分别考察了操作温度、原料气CO浓度、操作压力、空速等对合成气(CO浓度5%~25%)甲烷化反应的影响,并分析了造成催化剂失活的因素。结果表明,在300~500 ℃ CH₄的生成速率随着温度的升高、压力的增大、CO浓度的增加而增大。但CO的浓度不能过高,当H₂/CO≤3时催化剂的催化活性会逐步下降。通过XRD、EDS等分析结果得知,催化剂表面存在积炭,催化剂的失活跟积炭有关,通过进一步的对照实验和BET分析表明,积炭的速率与反应温度有关,温度越高积炭速率越快。     

Kinetics and Thermodynamics of Synthesis of Hybrid Oligomer‐Acrylated Cycloaliphatic Epoxy in the Presence of Triphenylphosphine and Triethylamine Catalysts

The kinetics for the esterification of cycloaliphatic epoxy resin with acrylic acid was investigated in the presence of two different catalysts, namely triethylamine (TEA) and triphenylphosphine (TPP). The reactions were carried out at four different temperatures in the range of 80–110°C and 60–90°C for TPP and TEA catalysts, respectively. The power law kinetics model was adopted for analyzing experimental data to determine reaction equations. Both differential and integral methods were applied to determine the reaction orders and reaction constants. The overall reaction order for the reaction systems was found to be 2 using both differential and integral methods. According to the differential method, the reaction orders with respect to epoxide and carboxylic acid groups were calculated to be 1.2 and 0.8, respectively. The reactions could be considered as first‐order reactions with respect to each group based on integral method analysis. The activation energies and frequency factors of these esterification reactions were found to be 77.2 kJ·mol⁻¹ and 1.72E+10 L·mol⁻¹_·min⁻¹ in the presence of TPP and 65.3 kJ·mol⁻¹ and 1.44E+7 L·mol⁻¹·min⁻¹ in the presence of TEA. The thermodynamic parameters of reaction in the presence of TPP and TEA were calculated. The results confirmed that both reactions were spontaneous and irreversible. It was found that the reaction in the presence of TEA produced a highly ordered activated complex.     

Gas phase polymerization of ethylene with a silica-supported metallocene catalyst: influence of temperature on deactivation

Ethylene was polymerized at 5 bar in a stirred powder bed reactor with silica supported rac-Me₂Si[Ind]₂ZrCl₂/methylaluminoxane (MAO) at temperatures between 40°C and 80°C using NaCl as support bed and triethylaluminium (TEA) as a scavenger for impurities. For this fixed recipe and a given charge of catalyst. the average catalyst activity is reproducible within 10% for low temperatures. The polymerization rate and the rate of deactivation increase with increasing temperature. The deactivation could be modeled using a first order dependence with respect to the polymerization rate.     

烷基化催化剂表面酸性及催化性能的动力学研究

在确定关联升温速率、脱附峰温和脱附峰覆盖率的程序升温脱附动力学模型的基础上，通过TPD实验和模型参数估值，建立了表征催化剂酸密度、酸强度及强度分布情况的方法。研究表明，随着活化温度的提高，固体酸催化剂表面酸中心强度分布先变宽后趋于均匀，350?℃活化催化剂的强度分布最宽；催化剂表面酸强度和酸密度随活化温度提高均呈先增大后降低、分别在350 ℃和250 ℃活化温度达到极大值的变化规律。催化剂酸性与催化性能关联的结果表明，随着活化温度的提高，烷基化反应速率常数与总脱附量的变化趋势相同，而催化剂失活速率常数与脱附活化能变化趋势相同；催化剂活性稳定性随其酸强度的增大而变差，催化剂活性与催化剂酸量和酸强度有关。     

甲醇制烯烃催化剂失活模型

在固定床反应器中,研究了甲醇制烯烃反应中当SAPO-34分子筛处于失活期时催化剂活性的变化情况,主要考察催化剂活性随反应温度、空速和运行时间的变化,通过对实验数据的分析拟合,得到了催化剂活性与失活时间、反应温度、空速的经验关联式(失活模型),对失活模型的检验表明,该模型与实验数据较为吻合,表明了该式的准确性。 通过对失活模型的分析,获得了当失活速率达到最大时的失活时间与反应时间、空速的关联式,失活过程应服从不均匀表面失活机理,并且当催化剂处于失活区时,失活时间对活性的影响要大于空速和温度。