乙炔选择性加氢催化剂研究进展

乙烯是石化工业中最重要的工业原料之一,然而乙烯产品中少量乙炔杂质的存在会直接影响乙烯的下一步应用。乙炔选择性催化加氢被认为是脱除乙炔杂质最有效的方法之一。本文综述了乙炔选择性加氢催化剂近年来的研究进展,介绍了乙炔选择加氢的反应机理,归纳总结了活性组分、助剂、载体以及结构对乙炔加氢催化剂性能的影响。鉴于Pd基催化剂仍然是工业应用的主流催化剂,文中综述了Pd基催化剂的研究现状和目前存在的一些挑战,同时提出了催化性能优化的建议。最后,就如何进一步提高乙炔选择性加氢催化剂性能的发展趋势进行了归纳,主要从单原子合金催化剂、催化剂微观调控以及电化学炔烃加氢方面进行论述,为未来提高乙炔加氢催化剂的性能提供了指导方向。     

Experimental and modelling investigations of steady-state and dynamic characteristics of ethylene hydrogenation on Pt/Al2O3

A robust strategy based on fluid-phase measurements is described for the testing and development of kinetic models for heterogeneous catalytic reactions. Steady-state, step-response, feedback-induced Hopf bifurcation and forced concentration cycling experiments were applied to ethylene hydrogenation over 0.05% Pt/Al₂O₃ in a CSTR at 80°C. Two versions of a reaction mechanism that differ in the order for hydrogen adsorption describe the experimental steady-state data. However, only one of these models adequately describes the system responses to step changes in the feed composition. Step-response experiments were used to identify a time scale of 5000 s which is associated with chemisorbed hydrogen. Conversely, feedback-induced Hopf bifurcation data indicate this time scale to be of the order of 1 s in magnitude. In the overall strategy of dynamic modelling, the two techniques are complementary since each inherently focuses on an opposite region in the spectrum of time scales for the reactor system. A detailed method for analysing feedback-induced Hopf bifurcation with a time delay is presented. The dynamic model based upon steady-state, step-response and bifurcation data was found to be inadequate for describing the results from cycled-feedstream experiments. Cycling the feedstream composition resulted in an improvement of the time-average reaction rate for the ethylene hydrogenation reaction compared to steady-state reactor operation. Rate improvement was observed for the entire range of ethylene feed concentrations that were tested, including conditions which give rise to a maximum in the steady-state reaction rate surface.     

A DFT Study of Ethylene Hydrogenation Reaction Mechanisms on Ni13 Nanocluster

Metal nanoclusters can potentially exhibit high catalytic activity and selectivity due to not only a high number of exposed surface atoms but also active sites with different coordination numbers as compared to bulk catalyst surface. In this study ethylene hydrogenation was used as a model reaction in an effort to elaborate reactivity of small Ni nanoclusters and the ethylene hydrogenation reaction mechanism. Two mechanistic pathways; representing Eley–Rideal and Horiuti–Polanyi type of mechanism for ethylene hydrogenation reaction are studied. It has been concluded that Horiuti–Polanyi type is more favorable when compared to Eley–Rideal type.     

Catalysis of semihydrogenation of acetylene to ethylene: current trends,challenges, and outlook

Ethylene is an important feedstock for various industrial processes, particularly in the polymer industry. Unfortunately, during naphtha cracking to produce ethylene, there are instances of acetylene presence in the product stream, which poisons the Ziegler–Natta polymerization catalysts. Thus, appropriate process modification, optimization, and in particular, catalyst design are essential to ensure the production of highly pure ethylene that is suitable as a feedstock in polymerization reactions. Accordingly, carefully selected process parameters and the application of various catalyst systems have been optimized for this purpose. This review provides a holistic view of the recent reports on the selective hydrogenation of acetylene. Previously published reviews were limited to Pd catalysts. However, effective new metal and non-metal catalysts have been explored for selective acetylene hydrogenation. Updates on this recent progress and more comprehensive computational studies that are now available for the reaction are described herein. In addition to the favored Pd catalysts, other catalyst systems including mono, bimetallic, trimetallic, and ionic catalysts are presented. The specific role(s) that each process parameter plays to achieve high acetylene conversion and ethylene selectivity is discussed. Attempts have been made to elucidate the possible catalyst deactivation mechanisms involved in the reaction. Extensive reports suggest that acetylene adsorption occurs through an active single-site mechanism rather than via dual active sites. An increase in the reaction temperature affords high acetylene conversion and ethylene selectivity to obtain reactant streams free of ethylene. Conflicting findings to this trend have reported the presence of ethylene in the feed stream. This review will serve as a useful resource of condensed information for researchers in the field of acetylene-selective hydrogenation.     

Numerical modelling of the electrochemical behaviour of 316L stainless steel based upon static and dynamic experimental microcapillary-based techniques

Microcapillary-based techniques allow the selection and interrogation of single metallurgical sites and are therefore becoming increasingly popular to investigate the electrochemical behaviour of metallic phases and non-metallic heterogeneities in alloys. This study has been carried out to assess the differences between current measurements made using a ‘closed’ microcapillary system (the electrochemical microcell technique) with current measurements derived from a flowing ‘open’ microcapillary droplet cell (the scanning droplet cell). The experimental results were compared with calculations derived from a model system adopting a finite element approach. The corrosion system consists of four parallel electrochemical reactions: three cathodic reactions (the oxygen reduction reaction, the hydrogen evolution reaction and water dissociation) and one anodic reaction (metal dissolution reaction). Comparative experimental results have shown there is a large discrepancy between the magnitudes of the cathodic current obtained by the two techniques. The results of this study allow an assessment of the parameters responsible for the mass transport and distribution of species in the closed and open systems. Critical parameters (for example, microcell crevice geometry, specimen surface-capillary gap distance, etc.) which lead to significant modifications of the curves were then identified using the numerical simulation.     

Kinetics and mechanism of the hydrogenation process – the state of the art

It is just over a century ago that the first industrial hydrogenation plant for edible oils was commissioned. Although at that time several fatty acids had been identified, the analytical characterization of these oils was mainly by physical properties like melting point, density and refractive index and chemical properties like saponification value and iodine value. Some of these properties were used to follow a hydrogenation reaction. Early kinetic studies of the hydrogenation reaction focused on triglycerides but with the advent of GC, fatty acid compositions became so readily available, that kinetic studies switched to the ‘common fatty acid pool’ concept. According to this concept, the rate of reaction of an unsaturated fatty acid in a triglyceride molecule does not depend on the chemical nature of the other fatty acid moieties in this molecule. The concept greatly simplified the understanding of what happens during a hydrogenation reaction and thereby stimulated research. It took more than 50 years before this concept was shown to be an incorrect assumption. Kinetic studies of the hydrogenation process have also been hampered by the lack of an instrument that can measure the hydrogen concentration in oil. That may well be the reason why this concentration has received rather little attention and that its effect on the relative rates of the various, simultaneously proceeding reactions has only fairly recently become clear. Accordingly, the present review will describe the mechanism of the various reactions that occur during the hydrogenation process and highlight the effect of the hydrogen concentration and the triglyceride composition rather than that of the fatty acid composition. It will discuss industrial process conditions rather than laboratory conditions and therefore limit itself to nickel catalysts. It will also paint the most simple picture that is consistent with generally accepted observations.     

Electrochemical stability of Cu-10Al-5Ni alloy in chloride-sulfate electrolytes

The electrochemical behavior of the Cu-10Al-5Ni alloy in simulated electrolytes like those used in the industrial processes under normal working conditions was investigated. Conventional electrochemical techniques including open circuit potential measurements, polarization techniques, and electrochemical impedance spectroscopy were used. The alloy was found to be more stable against corrosion when the chloride-sulfate solution had a pH of 7-9. A sulfate concentration of ≅0.1 M in the chloride-sulfate electrolyte leads to the passivation of the alloy surface. The activation energy of the corrosion process was found to be 8 kJ mol⁻¹ assigning a diffusion controlled reaction. The impedance measurements and impedance data fitting to equivalent circuit models have shown that the passive film posses a duplex nature.     

Copper catalysts in the selective hydrogenation of soybean and rapeseed oils: I. The activity of the copper chromite catalyst

In the hydrogenation of soybean and rapeseed oils with fresh copper chromite catalyst, the rate of reaction −d(IV)/dt varies extensively with time. These variations are ascribable to changes in phase composition of the catalyst during its reduction. This reduction is not restricted to an initial period but proceeds in two steps during the major part of a normal hydrogenation for the reduction of the linolenate content of the oil. Variations of the catalyst activity followed by experimental measurements have been related to the changes of the catalyst composition.     

Possible mechanisms in thermal polymerization of vegetable oils. II. Polymer formation

Summary From molecular distillation data, and information obtained by hydrogenation in dilute solution, extents of reaction have been calculated for the polymerization of linseed, safflower, tung, and oiticica oils. The hydrogenation data indicate that more than one double bond per molecule can be consumed during polymerization. The kinetic order of the polymerization of nonconjugated oils increases from an initial value of unity to approach a value of two. With conjugated oils, second-order characteristics were maintained during the course of the bodying. An explanation of this difference in reaction order based on monomer disappearance is presented. Rate constants and overall energies of activation were calculated and compared with those obtained from viscosity measurements. Agreement between the two sets of values was obtained. Oiticica oil, which gives curved viscosity plots that cannot be resolved, has been treated successfully in this manner. Intraglyceride reactions have been studied, and differences in behavior between nonconjugated and conjugated oils at high and low polymerization temperatures have been observed. Contribution from the Division of Applied Biology, National Research Laboratories, Ottawa, Canada. Issued as N.R.C. No. 4434. Presented at the 29th Fall Meeting, American Oil Chemists' Society, Philadelphia, October, 1955.     

Low-<Emphasis Type="Italic">trans</Emphasis> Shortening and Spread Fats Produced by Electrochemical Hydrogenation

Partially hydrogenated soybean oils (90–110 IV) were prepared by electrochemical hydrogenation at a palladium/cobalt or palladium/iron cathode, moderate temperature (70–90 °C) and atmospheric pressure. The trans fatty acid (TFA) contents of 90–110 IV products ranged from 6.4 to13.8% and the amounts of stearic acid ranged from 8.8 to 15.4% (the higher stearic acid contents indicated that some reaction selectivity had been lost). The solid fat values and melting point data indicated that electrochemical hydrogenation provides a route to low-trans spreads and baking shortenings. Shortenings produced by conventional hydrogenation contain 12–25% trans fatty acids and up to 37% saturates, whereas shortening fats produced electrochemically had reduced TFA and saturate content. Electrochemical hydrogenation is also a promising route to low-trans spread and liquid margarine oils. Compared to commercial margarine/spread oils containing 8–12% TFA, the use of electrochemical hydrogenation results in about 4% TFA. Names are necessary to report factually an available data: the USDA neither guarantees nor warrants the standard of the product, and the use of the name USDA implies no approval of the product to the exclusion of others that may also be suitable.     

STUDY ON THE ACETYLENE HYDROGENATION PROCESS FOR ETHYLENE PRODUCTION: SIMULATION,MODIFICATION, AND OPTIMIZATION

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen flow rate, and H-1/H-2 ratio were regulated as adjustable parameters for the process optimization. The simulation shows that ethylene selectivity increases by 12%, while acetylene concentration and hydrogenation reactor temperature remains within acceptable ranges. Such selectivity could be achieved at the hydrogen flow rate of 50 kg/h with H-1/H-2 ratio of 0.1/0.9.     

乙烯装置碳二前加氢工艺技术及运行稳定性研究

本文介绍了乙烯装置中使用的碳二前加氢工艺技术,并针对前脱丙烷前加氢工艺技术的特点,分析了影响碳二前加氢反应器运行稳定性的因素,提出了工业生产中避免反应器波动的操作方法。     

FRIPP低碳烃加氢制备乙烯裂解料技术开发与工业应用

随着炼油工业的发展,炼厂气的深加工越来越受到人们的重视。以C_2~C_5馏分加氢作乙烯原料是解决乙烯原料不足问题的有效方法。近年来抚顺石油化工研究院(FRIPP)开发出系列低碳烃加氢制备乙烯裂解料技术,包括低碳烃加氢专用催化剂LH-10系列及其配套的工艺技术;这些技术已经全部完成了工业化,总计新建成五套工业生产装置,为企业带来了良好的经济效益和社会效益。     

A simulation study of industrial vegetable oil hydrogenation reactors

A mathematical model has been developed to predict the course of industrial vegetable oil hydrogenation reactors. The model assumes that the reaction is mass-transfer-controlled. Suitable empirical equations have been used to describe rate of hydrogenation in preference over a mechanistic approach. The agreement between theoretical predictions from the model and plant data is generally satisfactory. Temperature, pressure and agitation intensity have strong effect on the kinetics of the reaction and on selectivity ratio under conditions of industrial reactors. The product quality is determined by overall selectivity which is governed by operating conditions, as well as the catalyst selectivity. D.N. Saraf, Currently on leave at the Petroleum Recovery Institute, Calgary, Alberta, Canada.     

Monte Carlo simulation of kinetic discontinuities in hydrocarbon hydrogenation reactions

Recent experimental studies of alkene and alkyne hydrogenation reactions have shown the presence of a transition between a reactive regime at low hydrocarbon surface coverage and a less reactive regime in which the catalyst surface is saturated with the hydrocarbon. This transition is discontinuous but reversible. Langmuir-Hinshelwood rate expressions cannot account for this discontinuity between the two regimes, indicating that the origin of the transition is related to the non-random distribution of reactants on the catalyst surface. Time-dependent Monte Carlo simulations of ethylene hydrogenation have been used to predict the presence of this transition and investigate the complex dynamics of the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Promotion of the electrochemical hydrogenation of nitrobenzene at hydrogen storage alloys studied using a solid electrolyte method

The electrocatalytic properties of an AB₅-type hydrogen storage alloy towards the electrochemical hydrogenation of unsaturated organic compounds have been studied by a solid electrolyte method using electrochemical hydrogenation of nitrobenzene as a model reaction. Voltammetric studies reveal that the kinetics of the nitrobenzene electro-reduction on the hydrogen storage alloy electrode is similar to that on a Ni electrode. Aniline and p-aminophenol are produced as the reaction products. Compared to the Ni electrode, the production of aniline is considerably promoted on the hydrogen storage alloy electrode. Modifying the alloy surface with a thin layer of Cu enhances the reaction selectivity and current efficiency for aniline formation. Compared to a Cu electrode, the electrochemical hydrogenation of nitrobenzene to aniline is promoted on the Cu-modified alloy electrode. The hydrogenation promotion effect is attributed to the chemical reaction between nitrobenzene and metal hydrides that are electrochemically generated in situ. Hydrogen storage alloys therefore make it possible to intensify the electrochemical hydrogenation process of unsaturated organic compounds.     

Computation of nickel catalyst activity in the hydrogenation of triacylglycerol oils

The development of a new method for a faster and more accurate computation of the nickel catalyst activity was studied. This catalyst is used in partial catalytic hydrogenation of vegetable oils for production of edible fats. In order to index the activity, a computer program, CATACT, was developed using FORTRAN language. This program uses 3 easily determined experimental values as input data (refractive index at 60 C, catalyst concentration and hydrogenation time). Output data are catalyst activity indexes either in word or numerical form. The hydrogenation data were gathered from a laboratory reactor under laboratory conditions. Using these data, we computed the activity of Ni catalysts which have been reused in oil hydrogenation under industrial conditions. The classical method of determining such activity by evaluating the melting point is, in view of the very low activity of such catalysts, inadequate to provide sufficient information for easy interpretation.     

Effect of nickel content on the electrochemical behavior of Cu-Al-Ni alloys in chloride free neutral solutions

The electrochemical behavior of Cu-Al-Ni alloys in chloride free neutral solutions was investigated. The effect of Ni content on the corrosion resistance of the alloys was examined and evaluated. Conventional electrochemical techniques and electrochemical impedance spectroscopy, EIS, have been used. Potentiodynamic measurements revealed that the increase in the Ni content decreases the stability of the Cu-Al-Ni alloys. The polarization measurements were confirmed by EIS experiments. The morphology of the alloy surface was investigated by scanning electron microscopy, SEM, and surface analysis was made by energy dispersive X-ray technique. The experimental impedance data were fitted to theoretical data according to a proposed equivalent circuit model representing the electrode/electrolyte interface. The results of these experiments are discussed in reference to the potential-pH (Pourbaix) diagrams of the alloying elements.     

Dynamic modeling and validation studies of a tubular solid oxide fuel cell

Solid oxide fuel cell (SOFC) is a key component in the new vision of distributed power generation. However, for connecting SOFC reliably to a load-varying grid, its transient behavior needs to be studied in detail with a thoroughly validated dynamic model. Dynamic models are also important for synthesizing efficient controllers. In this paper, a detailed dynamic model of a tubular SOFC is validated using experimental data from an industrial cell operating over a broad operating range. Steps in voltages and flows are used to study the system response. In the process of validation, phenomena that affect the transient response of the cell significantly are identified. The effects of Knudsen diffusion along with that of the increased active area for the electrochemical reactions are considered in this model observing the deviations of the simulation results from the experimental data. A dynamic model that includes these effects provides a very good match with the experimental data. Characteristics of the transient responses and various nonlinearities in the fuel cell dynamics are also studied in detail.     

Simulation of an Industrial Pyrolysis Gasoline Hydrogenation Unit

A model is developed based on a two‐stage hydrogenation of pyrolysis gasoline to obtain a C₆–C₈ cut suitable for extraction of aromatics. In order to model the hydrogenation reactors, suitable hydrodynamic and reaction submodels should be solved simultaneously. The first stage hydrogenation takes place in a trickle bed reactor. The reaction rates of different di‐olefines as well as hydrodynamic parameters of the trickle bed (i.e., catalyst wetting efficiency, pressure drop, mass transfer coefficient and liquid hold‐up) have been combined to derive the equations to model this reactor. The second stage hydrogenation takes place in a two compartment fixed bed reactor. Hydrogenation of olefines takes place in the first compartment while sulfur is eliminated from the flow in the second compartment. These reactions occur at relatively higher temperature and pressure compared to the first stage. The key component in this stage is considered to be cyclohexene, of which the hydrogenation was found to be the most difficult of the olefines present in the feed. The Langmuir‐Hinshelwood kinetic expression was adopted for the hydrogenation of cyclohexene and its kinetic parameters were determined experimentally in a micro‐reactor in the presence of the industrial catalyst. The model was solved for the whole process of hydrogenation, including hydro‐desulfurization. The predictions of the model were compared with actual plant data from an industrial scale pyrolysis gasoline hydrogenation unit and satisfactory agreement was found between the model and plant data.