THERMIDOR: A new model for combined simulation of operations and optimization of catalysts in residues hydroprocessing units

Atmospheric or vacuum residues can be upgraded under high hydrogen pressure into valuable distillates and low sulfur fuel oils using several types of hydroprocessing units. Starting from such highly asphaltenic feeds, with the goal to achieve current very low sulfur targets (<0.3%) in fuels for export or subsequent upgrading by catalytic cracking technologies, fixed bed technologies like the HYVAHL process are still the most efficient. This paper discusses some recent developments of HYVAHL, aiming at improved desulfurization levels and operating times. These improvements were helped by the predictions of a newly developed mathematical model called THERmal Monitoring for Isoperformance Desulfurization of Oil Residues (THERMIDOR). This model simulates the HYVAHL process operation along time on stream, taking into account the complex associations of guard bed materials and catalysts including particle size, activity, pore size and shape grading effects. A crucial non trivial achievement in THERMIDOR is the realistic representation of the two main catalyst deactivation mechanisms in residues hydroprocessing: coke and metals deposition. The model shows clearly the synergy between dedicated HDM (“chesnut bur” type, larger mesopores, and macropores) and HDS (higher surface area and activity) catalysts. A very well defined optimum partition of the two catalysts is predicted and found in excellent agreement with the typical optimum determined from pilot plant experiments, and further implemented in commercial plants. The simulation results are successfully compared with representative operational data from a typical HYVAHL plant and reveal new insights on the complex catalyst deactivation phenomena involved in residue hydroprocessing.     

Study of accelerated deactivation of hydrotreating catalysts by vanadium impregnation method

The main causes of catalysts deactivation for hydrotreating are coking and metals deposition. In this present work, accelerated deactivation of hydrotreating catalysts was studied. In this respect, vanadium which is deposited with nickel during hydrotreating reaction was impregnated into the fresh hydrotreating catalyst. Different percentage of vanadium was impregnated and their hydrodemetalization (HDM) and hydrodesulfurization (HDS) activities were studied in bench-scale reactor of heavy crude oil. Accelerated deactivations for both HDM and HDS were observed on vanadium impregnated catalysts. The rate of HDS deactivation was faster than that of HDM reaction. The rapid deactivation of HDS may be due to the coverage of active sites by impregnated vanadium atom. The deactivation is slower when the V loading is low; but above 10 wt% loading a rapid deactivation is observed. A comparison of deactivation is made in between normal deactivation and the deactivation by vanadium impregnation. It was found that deactivation by vanadium impregnation is lower than that of normal deactivation. It suggests that at initial stage the formation of coke causes deactivation of the catalyst whereas at later stage when metals sulfides deposition is quite high, these sulfides take part in deactivation.     

Deactivation patterns of Mo/Al2O3, Ni–Mo/Al2O3 and Ni–MoP/Al2O3 catalysts in atmospheric residue hydrodesulphurization

In the present work, a comparative study on the deactivation behavior of three types of industrial hydrotreating catalysts, namely, Mo/Al₂O₃, Ni–Mo/Al₂O₃ and Ni–MoP/Al₂O₃, that are used to promote primarily hydrodemetallization (HDM), hydrodesulphurization (HDS) and hydrodesulphurization + hydrodenitrogenation (HDS/HDN) reactions, respectively, in the first, second and third reactor of commercial atmospheric residue desulfurization (ARDS) units was carried out. The main objective of the study was to contribute to a better understanding of the relationship between catalyst type and catalyst deactivation patterns. The used catalysts from these experiments were fully characterized to determine the extent and the cause of deactivation. Special emphasis was paid to understanding the nature of the coke and metal deposition on the used catalysts by applying chemical analysis and various advanced analytical techniques, such as solid-state carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR), temperature-programmed oxidation (TPO), electron probe micro-analysis (EPMA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results are discussed scientifically based on the physico–chemical properties of the three catalysts.     

酯化反应用阳离子交换树脂催化剂的失活机理研究

针对醋酸异丙酯催化合成过程存在的催化剂失活现象,采用“催速失活”方法考察了Fe³⁺对催化剂活性的影响,并对失活前后的阳离子交换树脂催化剂进行了扫描电镜观察、元素定碳分析、元素能谱鉴定、X射线荧光组成分析和X射线光电子能谱等表征。结果表明,反应介质中存在的Fe³⁺吸附到催化剂上,取代了磺酸基团中的H⁺,部分导致催化剂活性下降,磺酸基团的流失也是失活原因。     

Deactivation handling in a high-throughput kinetic study of o-xylene hydrogenation

The objective of the study is to develop an HT methodology to enable kinetic modeling of diverse catalysts. The reaction of o-xylene hydrogenation is selected as a probe reaction to evaluate the “metallic” features of a library of about 80 diverse bimetallic catalysts. A major issue to overcome is deactivation phenomena which are catalyst dependent and which cannot a priori be predicted. A prerequisite is therefore to handle correctly deactivation processes for accessing intrinsic kinetic parameters. For this purpose, an adapted screening strategy is developed, using a proprietary 16 channels multi-tubular reactor which enables to test catalysts at the same time-on-stream. Original data treatment procedures are implemented in order to correct observed data from deactivation phenomena for the calculation of kinetic parameters. Effects of metal nature, dopants and supports on deactivation rate are analyzed using a statistical approach, and a tentative classification of deactivation processes based on coke analyses performed on aged materials is provided.     

Studies on recycling and utilization of spent catalysts: Preparation of active hydrodemetallization catalyst compositions from spent residue hydroprocessing catalysts

Spent catalysts form a major source of solid wastes in the petroleum refining industries. Due to environmental concerns, increasing emphasis has been placed on the development of recycling processes for the waste catalyst materials as much as possible. In the present study the potential reuse of spent catalysts in the preparation of active new catalysts for residual oil hydrotreating was examined. A series of catalysts were prepared by mixing and extruding spent residue hydroprocessing catalysts that contained C, V, Mo, Ni and Al₂O₃ with boehmite in different proportions. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, pore size and crushing strength measurements. The hydrodesulfurization (HDS) and hydrodemetallization (HDM) activities of the catalysts were evaluated by testing in a high pressure fixed-bed microreactor unit using Kuwait atmospheric residue as feed. A commercial HDM catalyst was also tested under similar operating conditions and their HDS and HDM activities were compared with that of the prepared catalysts. The results revealed that catalyst prepared with addition of up to 40 wt% spent catalyst to boehmite had fairly high surface area and pore volume together with large pores. The catalyst prepared by mixing and extruding about 40 wt% spent catalyst with boehmite was relatively more active for promoting HDM and HDS reactions than a reference commercial HDM catalyst. The formation of some kind of new active sites from the metals (V, Mo and Ni) present in the spent catalyst is suggested to be responsible for the high HDM activity of the prepared catalyst.     

Alumina-silica binary mixed oxide used as support of catalysts for hydrotreating of Maya heavy crude

Alumina-silica binary mixed oxide support is used to prepare catalysts for hydrotreating of Maya heavy crude. Support is prepared by urea hydrolysis. Sequential incipient wetness and co-impregnation techniques are employed for preparation of catalysts. Ammonium heptamolybdenum is used as precursor of MoO₃. Catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and the pore size distribution. Hydrodemetallation (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and asphaltene conversion (HDAsp) reactions are studied on these catalysts. One reference catalyst is also taken for comparison. Coke and metals depositions on spent catalysts are measured. The catalyst deactivation rate is also studied. The X-ray diffraction (XRD) results reveal that molybdenum atoms are well dispersed into CoMo catalyst, whereas MoO₃ crystalline phases are found in PCoMo and PNiMo catalysts. TPR reduction profiles are different for different catalysts. The laboratory made catalyst is reduced at one temperature, whereas the reference catalyst shows two reduction profiles. The reference catalyst shows the highest activities among four catalysts. The highest HDM and HDAsp activities of the reference catalyst may be due to its bigger pore diameter. The presence of TiO₂ in the reference catalyst enhances HDS and HDN activities. The CoMo catalyst shows higher activities than those of PCoMo and PNiMo catalysts. The presence of crystalline MoO₃ causes for lower activities of catalysts PCoMo and PNiMo.     

Review on the deactivation of FCC catalysts by cyclic propylene steaming

The deactivation of FCC catalysts in small-scale units in the presence of contaminant metals has been the industry workhorse for a number of years due to the robustness and simplicity of such methods.

A major advance in the deactivation of metallated catalysts on a small-scale that better simulated the performance of commercial FCC catalyst, was the introduction of the cyclic propylene steaming (CPS) method. In the CPS protocol, FCC catalyst is impregnated with vanadium and nickel prior to deactivation in reduction–oxidation cycles and the latter provides significant advantages over traditional methods such as the Mitchell approach. In certain situations, however, the contribution of vanadium to catalyst deactivation is over-emphasized in the CPS method, and therefore this method has been developed further.

This paper describes a number of modifications that have been made to the CPS method to further attenuate the destructive effects of vanadium on the FCC catalyst during deactivation. This includes exposing the metallated catalyst to pre-stabilisation steps with reduction-oxidation cycles and changing the ratio of the time the catalyst spends in reducing and oxidising environments during the CPS cycles. The comparison of activity and selectivity data obtained from FCC catalysts having age distribution with those obtained from CPS showed that both scenarios gave the same catalyst ranking.

These investigations have also shown that the use of reduction–oxidation cycles better simulates the deactivation of FCC catalysts in the absence of contaminant metals. These investigations have also shown that the use of reduction–oxidation cycles better simulates the deactivation of FCC catalysts in the absence of contaminant metals “the part” than traditional deactivations in a 100% steam atmosphere.     

Desaktivierung von technischen Silber-Trägerkatalysatoren für die Herstellung von Ethylenoxid

Deactivation of industrial supported silver catalysts for ethylene oxide production. In view of the model character of the reaction and the unique nature of the catalyst system, it is of interest to study the deactivation behaviour of technical supported silver catalysts for the production of ethylene oxide. In the present study the influence of the catalyst components support, silver, promoter and inhibitor upon the deactivation behaviour is described. The results of chemical, physical and technical investigations of various catalysts and catalyst components are presented. The investigations show that a decrease in the surface area of the exposed silver and increased deposition of chloride are responsible for catalyst deactivation. The possible influence of alkali promoters is discussed and modifications to the catalyst which have been described in the literature as influencing the deactivation are also evaluated.     

多孔催化剂颗粒的内扩散效应对伴有失活的二级反应动力学的影响

采用正交配置等数学方法,研究在均匀独立失活的催化反应系统中,内扩散效应对等温球形催化剂失活速率的影响,建立适用于任何内扩散区域的二级反应、m级失活系统的失活有效因子和失活西勒模数的定量关系,对n级反应、m级失活系统也作了相应地推广.运用加压微反-色谱-数据处理机联合装置,通过分析在原颗粒丝光沸石催化剂上进行的临氢甲苯歧化反应的失活数据,研究了内扩散对二级反应失活动力学的影响规律.同时,在实验范围内,建立了一套内扩散存在下的甲苯歧化失活动力学模型.     

An integrated dynamic model for reaction kinetics and catalyst deactivation in fixed bed reactors: skeletal isomerization of 1-pentene over ferrierite

Catalyst deactivation in fixed beds is a critical issue in many industrial processes. A general dynamic model for fixed bed reactors involving catalyst deactivation was presented and simplified. The simplifications were based on the pseudo-steady state hypothesis for the fluid phase. Catalyst deactivation was treated by a linear model with respect to surface intermediates. A semi-analytical solution was obtained for the surface intermediates. The approach was applied to skeletal isomerization of 1-pentene over ferrierite. The comparison of experimental results and model predictions revealed that the model is able to describe the essential features of catalyst deactivation in skeletal isomerization and it can be useful for process scale-up.     

The thermal conductivity of porous catalyst compacts

Thermal conductivities of pellets made from porous catalyst supports and supported nickel catalysts have been measured by a steady state method. Results are presented in the form of plots of thermal conductivity against macropore voidage and the experimental data are compared with the predictions of two models.     

A comparative study for heavy oil hydroprocessing catalysts at micro-flow and bench-scale reactors

CoMo and NiMo catalysts were prepared and the catalytic activities were evaluated in fixed bed micro-flow and bench-scale reactors with different feed composition. Experiments were conducted at conditions close to those that exist in the industrial practice. Due to the different nature of the feeds, the conditions were varied with respect to both evaluation scales. The fresh and spent catalysts were characterized. Spent catalyst textural properties indicated that catalysts were deactivated and the surface area and pore volume dropped by 20–60%. The adsorption–desorption hysteresis of spent catalysts indicated that cylindrical pores are deactivated at the pore mouth and played an important role in modification by either closing one end of the pore or forming a narrow neck pore, which is indicative of the formation of “ink-bottle” type pores. Thus, the deposition of metal and carbon takes place preferentially at the pore entrance, which causes pore mouth plugging. These results are also supported by the SEM–EDAX analysis, where metal and carbon depositions are evident and taking place at the superficial region of a catalyst particle. The increase in absolute area of hysteresis is based on the catalyst's average pore diameter: the higher the average pore diameter, the lower the area of the spent catalyst. The activity and deactivation of the catalyst are discussed on the basis of catalyst porosity and deposited metal characterization. The composition of catalysts varies, considering two applications in a multi-reactor system: a CoMo catalyst for the first reactor, and a NiMo in the second reactor; the former is supported on γ-Al₂O₃ and the latter on TiO₂/Al₂O₃. As a comparison, the CoMo catalyst exhibited better hydrogenolysis while the NiMo catalyst showed better hydrogenation activity in both micro-flow and bench-scale reactors. It appears that there is a moderate effect of TiO₂ content in support on Ni and V hydrodemetallization (HDM) while hydrodeasphaltenization (HDAs) and hydrodesulfurization (HDS) activities were slightly improved when a partially hydrotreated feed, which contains more refractory compounds than virgin feedstock, was employed.     

大孔结构重油加氢脱金属催化剂的制备、表征及重油在催化剂中有效扩散系数的求解

以大孔拟薄水铝石为原料，沥青残渣为造孔剂，经超临界干燥和焙烧得到催化剂载体，通过浸渍活性组分得到重油加氢脱金属催化剂并进行扩散实验。结果表明，制备条件对重油加氢脱金属催化剂的物性影响较大，通过对各种制备因素进行优化并对催化剂进行表征和扩散实验，进一步表明制备的催化剂具有较大的比表面积、孔容、适宜的孔分布及大孔结构，适合加工金属含量较高的原油，重油分子在添加造孔剂催化剂中的有效扩散系数变大。     

An integrated criterion of efficiency for Pt catalysts in the dehydrogenation of higher <Emphasis Type="Italic">n</Emphasis>-paraffins

The deactivation of catalysts by coke-forming structures in the dehydrogenation of higher n-paraffins is discussed. The patterns of coke formation on a catalyst subject to process conditions are presented. A mathematical model of the process is described to show its adequacy. A calculation algorithm for the optimum mode of operation of a dehydrogenation catalyst is constructed, and the calculation results are given. Dehydrogenation catalysts of different brands are compared with respect to several parameters (coke formation on catalysts, the yield of the reaction by-product, and the dynamics of temperature rise in the reactor). The model can be used to estimate the efficiencies of catalysts in a cycle and to compare them.     

Coking behavior and catalyst deactivation for catalytic pyrolysis of heavy oil

For the catalytic pyrolysis of heavy oil on catalyst CEP-1, coking behavior was investigated in a confined fluidized bed reactor. Coke content on the spent catalyst decreases with the increase of H/C mol ratio of feeds and catalyst-to-oil weight ratio, while it increases with the enhancement of reaction temperature. An empirical model is proposed to predict the coke content based on feed properties and operating conditions. The predicted coke content is close to the experimental data. The relationship between micro-activity index of catalysts and coke content is studied. A coking deactivation model for pyrolyzing catalysts is established, and then model parameters are determined by the least square regression analysis. According to the deactivation model, the variations of relative activity of catalysts with both residence time of catalysts and catalyst-to-oil weight ratio are predicted.     

Dry Reforming of Methane with a Ni/Al2O3‐YSZ Catalyst: The Role of the Catalyst Preparation Protocol

Many studies of Ni based ceramic supporting reforming catalysts are found in the literature. A synthesis of the reported results shows that their efficiency and durability are significantly affected by their fabrication protocol. This research has been aimed at evaluating how the conditions of 1) the ceramic support preparation and 2) the Ni deposition, through an impregnation‐drying‐calcination‐reduction protocol, affect the catalytic activity and the catalyst deactivation over time during methane dry reforming. The catalyst support used in this study was obtained by the mixing and pressing of alumina and YSZ (Yttria Stabilized Zirconia) powders, then calcining the mixtures at high temperature to form pellets of limited porosity (specific surface of 1.5‐10 m²/g), without inducing change to the crystalline phases. The results show that the surface density of the nickel particles, the catalyst activity, and its life span are highly dependent upon the catalyst preparation protocol. The initial nitrate solution concentration, the duration of the impregnation and the specific surface of the ceramic support have, all of them, a considerable influence on the size range of the deposited nickel particles. The surface density, the amount and the size of the latter highly affect the catalytic activity. It has been also shown that an increase in the ratio CH₄/CO₂ is detrimental to the catalytic activity of the tested formulations; a small excess of methane is enough to initiate the deactivation process of the catalyst very quickly for all of the composition tested in this study. A phenomenological deactivation kinetics model has been built and optimized. Although there are differences in deactivation rates among the different formulations tested, the model shows that the deactivation rate is highly dependent upon the reaction rate constant and that zero‐ and first‐order kinetics give statistically the same prediction error; the latter is always lower or equal to the experimental error.     

COMPUTER SIMULATION OF HYDRODEMETALLATION IN FIXED-BED REACTORS

An isothermal model for hydrodemetallation (HDM) of crude oils in catalytic fixed-bed reactors is proposed. This model involves a consecutive reaction mechanism, which is capable of accounting for particle deposit profiles with interior maxima. Consistent with the fact that HDM catalysts are conglomerates formed by precipitation, the porous catalyst itself is modeled as randomly overlapping spheres of equal size. The metal is deposited as growing metal sulfide crystallites on the inner surface of the catalyst. These crystallites originate from a certain number of randomly scattered nuclei and increase in size as the deposition proceeds. The random sphere model for the catalyst and the deposit provides the changes in the catalyst pore structure—local porosity and surface area.

The mass transport within the domain of the particle is due to restricted liquid diffusion, since the diameter of the metal bearing compound (porphyrin) and the intermediate are comparable to the pore size. The diffusion restrictions taken into account are the enhanced drag imposed on a molecule by adjacent pore walls and steric partitioning.

Since the deposition process is much slower than diffusion and reaction, the pseudo-steady-state assumption can be justified. The equations of conservation for mass are solved by orthogonal collocation on finite elements. Based on this solution technique a computer simulation program of HDM is designed that allows two modes of operation: constant temperature and constant conversion. The simulation program “SIMULA” is highly flexible with regard to reaction kinetics, catalyst structure, reactor design, and operating conditions. In comparison to a base case with uniform activity, the effect of intraparticle (radial) and bed (axial) activity profiles on the conversion rate is discussed. For the case investigated, a radial distribution of activity higher at the center of the particle than at the edge can increase catalyst life by 25%, but axial distribution was less successful.     

镍基乙醇水汽重整催化剂:机理、失活与构效关系

为了应对潜在的氢能利用需求,乙醇水汽重整反应受到了越来越多的关注。镍基催化剂因其高活性、高选择性以及成本优势而极具应用前景,同时在提高催化剂稳定性、降低反应温度、提高氢气收率等方面仍然有进一步发展的空间。更深入认识反应机理、失活机制和催化剂的构效关系是开发高效催化剂的关键。本文对近年来镍基乙醇重整催化剂的研究进展进行了整理总结,首先介绍了通过原位光谱、动力学以及理论计算等手段取得对反应中间物种与反应机理的新认识,分析了催化剂失活的主要原因,并且讨论了镍基催化剂的活性相、尺寸效应、助剂效应,双金属效应等问题,最后简单介绍了得益于基础研究进展的催化剂合成方面的成果,并提出对镍基乙醇水蒸气重整（ESR）剂未来发展的看法：在线/原位表征技术和理论计算将有助于真正理解镍基ESR催化剂的构效关系和反应机理,而新材料,如碳化钼的应用可能在提高催化剂反应性能方面起到作用。