Deactivation of ICI low temperature methanol catalyst in an industrial reactor

The deactivation behavior of one of the ICI low temperature methanol catalysts (ICI-51-Z) in a typical ICI multibed quench reactor has been studied in relation to methanol production with respect to time of operation, using some representative sets of plant data collected over two years time span. A pseudo-homogeneous first order model of the methanol synthesis reactor was formulated for this purpose. The best set of catalyst deactivation parameters for different beds was found using a nonlinear parametric estimation technique. Catalyst in the entering bed was found to deactivate most with the time of operation, while subsequent beds deactivate progressively less quickly.     

柴油加氢反应器不同位置精制剂的失活分析

针对某炼油厂柴油加氢裂化装置停工换剂时发现加氢精制反应器床层顶部的精制剂表面覆盖垢物的现象,对不同位置的精制剂进行取样分析。对所取精制剂进行甲苯抽提、再生后采用比表面积及孔径分析仪、碳-硫分析仪（C-S）和扫描电子显微镜（SEM）等手段进行检测。结果表明：不同位置的失活精制剂上积炭量均较低,而比表面积等孔结构参数均显著降低,尤以装填位置靠上的精制剂更为明显,失活精制剂的再生效果均不理想;再生精制剂上出现磷酸铝特征衍射峰,精制剂表面沉积含磷、硅、铁和少量砷元素的无机物,或少量进入精制剂孔道,其是导致精制剂失活的主要原因,而且沿着物流自上而下的流向精制剂上杂质的沉积量逐渐减少,催化剂的失活程度减弱。     

陶瓷膜反应器中环己酮氨肟化的催化剂失活机制与再生

基于陶瓷膜反应器开发出无有机溶剂的环己酮氨肟化新工艺,探讨TS-1催化剂失活机制。采用XRD及Rietveld全谱拟合、FT-IR、N₂吸附-脱附、TGA/DSC、GC-MS等手段对TS-1分子筛的骨架结构、晶胞参数、比表面积和有机物种类进行了表征分析。结果表明,无有机溶剂的环己酮氨肟化反应过程中,存在硅流失的现象,但TS-1骨架完整,晶胞参数未明显变化;环己酮、环己酮肟及反应副产物等吸附在TS-1催化剂的表面及孔道内,使比表面积下降52.6%、孔体积减少了41.6%,是造成TS-1失活的主要原因,空气氛围中于600℃煅烧3 h,可以恢复催化剂的活性。     

Simulation of temperature peak attenuation by catalyst dilution in a tubular packed-bed reactor

Temperature peak attenuation is an important problem for safe process control. Simulations of the axial temperature and product progression in stationary ammonia synthesis with different axial catalyst dilutions have been carried out. It is demonstrated that the requirement of temperature peak attenuation together with a maximum product yield can be met by an optimal catalyst dilution profile at the entrance of the bed.     

Deactivation of alkane oxidative dehydrogenation catalyst by deep reduction in periodic flow reactor

The activity loss of β‐NiMoO₄ catalyst has been studied in the oxidative dehydrogenation of propane with an operating periodic flow reactor. Under severe operating conditions (i.e., high temperature and long periods of the pulses), the lattice oxygen depletion is faster than the reoxidation one. After an induction period, carbon whiskers on the catalyst surface were detected together with noticeable amounts of cracking products in the gas phase as CH₄, C₂ hydrocarbons and H₂. Deep reduction dramatically changes the reaction path and irreversibly modifies the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Multiplicity of solutions in the optimization of a bifunctional catalyst blend in a tubular reactor

The reaction scheme for the isomerization and hydrogenation of methylcyclopentane using bifunctional catalyst is considered in a tubular reactor. The aim is to maximize the concentration of benzene at the outlet of the reactor by choosing the optimal blend of the catalyst along the reactor. When the problem was attempted by nonlinear programming employing sequential quadratic programming, twenty-five local optima were obtained from 100 random starting conditions. By using iterative dynamic programming in addition to the best two local optima obtained by nonlinear programming, the global optimum was also obtained.     

Deactivation of a vinyl acetate catalyst

Kinetic studies as well as morphological and physico-chemical surface studies have been carried out on the deactivation of a palladium carrier catalyst for vinyl acetate synthesis in the ethylene gas phase process. The experiments cover concentration and temperature ranges of technical interest at a total pressure of 900 kPa. The deactivation rate depends on the temperature and the oxygen and acetic acid concentrations. The decline in activity is best described by a rate law of second order relative to the activity number. This behaviour is attributed to the observed aggregation of finely dispersed palladium. It can be concluded that palladium(II) acetate acts as a transport species in a chemically assisted sintering mechanism. At temperatures T ≤ 438 K the more advantageous final texture of the catalyst will only be formed on reaction.     

Optimal operation of a catalytic tubular reactor with fouling catalyst by coke deposition

The dehydrogenation of isopentane over chromia-alumina catalyst has been carried out at three isothermal levels. The catalyst fouling and the deposited coke profiles were observed in a catalytic tubular reactor. A kinetic model is proposed and the kinetic parameters have been estimated by non linear regression methods.For the dehydrogenation with catalyst fouling, the problem of finding the isothermal optimal control was formulated by a distributed maximum principle and a computational algorithm using a quasi-steady state assumption was presented. The dehydrogenation of isopentane was carried out experimentally at the evaluated isothermal optimal temperature. The observed conversion, yields and coke content profiles agreed with the evaluated ones fairly well, which suggests that the kinetic model may be useful for optimal controls.     

Emulsion copolymerization in a tubular reactor

A study was conducted on the emulsion copolymerization of vinyl acetate and butyl acrylate in a tubular reactor. It was performed at a constant temperature of 60°C and at different fluid velocities and feed compositions. Conversion, particle size distribution, and copolymer composition were measured, respectively, with gravimetric method, laser light scattering, and nuclear magnetic resonance. Maximum conversions were found for each of the monomer compositions; this maximum conversion varied, however, with the recipe used. The amount of butyl acrylate has a direct effect on the number of particles and on the final conversion. In lower levels of butyl acrylate particle size distribution is wide and bimodal. High levels of butyl acrylate leads to narrow and monomodal particle size distribution. Therefore the level of butyl acrylate and the velocity of fluid flowing inside the tube have strong effects on the shape (monomodal‐bimodal) and the width of particle size distributions. This effect may vary at different levels of butyl acrylate and flow rate. The results obtained from copolymer composition show that an alternating block copolymer is made during the reaction. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 833–842, 2000     

催化剂颗粒形状对甲烷水蒸气重整反应的影响及工业反应器模拟

甲烷水蒸气重整工艺是现阶段最主要的工业制氢技术,催化剂颗粒形状和反应器操作条件是影响重整反应器性能和产物组成的重要因素。首先从颗粒尺度研究催化剂形状对甲烷水蒸气重整反应的影响,在不同的反应温度和压力下,计算并比较了球形、柱形和环形催化剂的效率因子,其大小顺序为:柱形 < 球形 < 环形。其次,将反应器床层的质量、热量和动量传递与环形催化剂颗粒的扩散-反应方程相结合,建立了用于描述甲烷水蒸气重整工业反应器的一维轴向数学模型。计算并分析了反应器进口温度和压力对反应器床层的温度和压力分布、催化剂效率因子以及甲烷转化率和各组分浓度分布的影响,确定了适宜的工业反应器进口温度和压力,分别为773 K和3 MPa。     

Steam reforming of methane in a membrane reactor

Methane reforming in a Pd/Ag membrane reactor was carried out. The operational limits for the steam-to-methane ratio are discussed. To avoid carbon formation, this ratio has to be higher in a Pd/Ag membrane reactor than in a conventional steam reforming tubular reactor.     

Calcination of limestone in a tubular reactor

Theoretical expressions were developed for the design of a tubular reactor for the calcination of limestone, pneumatically conveyed by flue gas. The total residence time and the length of the reactor are affected in particular by the particle size, the excess thermal capacity of the gas and the heat transfer coefficient. High throughput can be achieved in relatively small reactors. An experimental investigation verified a theoretical prediction, that a considerable part of the decomposition takes place in the first few centimeters of the reactor length. The rate of heat transfer in this section was high, with Nusselt numbers of 9.9 to 31.7.     

Experimental, kinetic and 2-D reactor modeling for simulation of the production of hydrogen by the catalytic reforming of concentrated crude ethanol (CRCCE) over a Ni-based commercial catalyst in a packed-bed tubular reactor

Mechanistic kinetic models were formulated based on Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal approaches to describe the kinetics of hydrogen production by the catalytic reforming of concentrated crude ethanol over a Ni-based commercial catalyst at atmospheric pressure, temperature range of 673-863 K, ratio of weight of catalyst to the molar rate of crude ethanol 3472-34722 kg cat s/kmol crude in a stainless steel packed bed tubular microreactor. One of the models yielded an excellent degree of correlation, and was selected for the simulation of the reforming process which used a pseudo-homogeneous numerical model consisting of coupled material and energy balance equations with reaction. The model was solved using finite elements method without neglecting the axial dispersion term. The crude ethanol conversion predicted by the model was in good agreement with the experimental data (AAD%=4.28). Also, the predicted concentration and temperature profiles for the process in the radial direction indicate that the assumption of plug flow isothermal behavior is justified within certain reactor configurations. However, the axial dispersion term still contributed to the results, and thus, cannot be neglected.     

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.     

Comparison of the performance of a direct-contact bubble reactor and an indirectly heated tubular reactor for solar-aided methane dry reforming employing molten salt

A theoretical approach is presented for the comparison of two different atmospheric pressure reactors—a direct-contact bubble reactor (DCBR) and an indirectly heated tubular reactor (IHTR)—to evaluate the reactor performance in terms of heat transfer and available catalytic active surface area. The model considers the catalytic endothermic reactions of methane dry reforming that proceeds in both reactors by employing molten salts at elevated temperatures (700–900 °C) in the absence of catalyst deactivation effects. The methane conversion process is simulated for a single reactor using both a reaction kinetics model and a heat transfer model. A well-tested reaction kinetics model, which showed an acceptable agreement with the empirical observations, was implemented to describe the methane dry reforming. In DCBR, the heat is internally transferred by direct contact with the three phases of the system: the reactant gas bubbles, the heat carrier molten salts and the solid catalyst (Ni-Al₂O₃). In contrast, the supplied heat in the conventional shell-and-tube heat exchanger of the IHTR is transferred across an intervening wall. The results suggest a combination system of DCBR and IHTR would be a suitable configuration for process intensification associated with higher thermal efficiency and cost reduction.     

加氢裂化催化剂的失活与激活

针对中石油吉林化学股份公司炼油厂加氢裂化装置在生产中遇到的加氢裂化催化剂失活问题， 分析其失活原因， 并介绍了在生产过程中 “激活” 催化剂的措施， 使中毒催化剂的活性逐渐得以恢复。     

加氢裂化催化剂失活与再生

利用XRD、XPS、TPR、ICP、IR、TEM 等技术, 测试和表征几种不同类型新鲜的、失活的和再生后工业用非贵金属加氢裂化催化剂的性能, 找出该催化剂失活的主要原因。经研究发现,加氢裂化预精制催化剂主要失活原因是积炭和金属聚集; 加氢裂化催化剂主要失活原因是积碳、所含沸石倒塌、金属聚集、孔结构堵塞及倒塌, 对于单段加氢裂化催化剂失活原因, 还包括酸中心中毒等。本文还探讨了器内与器外再生方式利弊及今后发展趋势。     

Variants of the organization of a controlled-temperature-profile catalyst bed in a tubular reactor for the single-step water gas shift reaction

The possibility of bringing the actual temperature profile along the catalyst bed to the profile maximizing the CO conversion in the water gas shift (WGS) reaction in a tubular reactor is considered for new, highly efficient catalysts as heat-conducting composite plates (HCCPs). It is demonstrated by the example of a controlled-temperature-profile (CTP) tubular reactor integrated into an experimental model of a fuel cell of a 5-kW power plant that the efficiency of the WGS process can be raised by using the catalyst as HCCPs. Use of these catalysts in CTP apparatuses can markedly increase the efficiency of the WGS stage of natural gas reforming for ammonia synthesis, hydrogen production, and the production of fuel gas for fuel cells.     

Numerical simulation of a tubular polymerization reactor

A mathematical model for a tubular emulsion polymerization reactor is developed. The partial differential equations describing the mass balances on initiator, monomer, and number of polymer particles are numerically solved using an implicit–explicit scheme based on the Crank–Nicholson method. The model adequately simulates experimental results reported by Rollin and co-workers and sufficiently explains the unusual behavior of the reactor when operating at relatively low emulsifier concentrations.