Acetylene Hydrogenation Reaction Research Articles

Identification at the Single Molecule Level of C2Hx Moieties Derived from Acetylene on the Pt(111) Surface

A low-temperature scanning tunneling microscope operated at 4.7 K was used to observe individual molecules produced from the thermal decomposition and hydrogenation reactions of acetylene on the Pt(111) surface. Acetylene molecules observed on the surface following adsorption at 50 K are seen to persist up to room temperature at the same time as two other moieties are observed to form. One moiety greatly increases in amount when the acetylene is coadsorbed with hydrogen and is attributed to the vinyl species, HCCH2, in agreement with a recent study using reflection absorption infrared spectroscopy. A third species observed at room temperature is identified as vinylidene, CCH2. The identification of these species is aided by using voltage pulses from the STM to further decompose them into species containing fewer atoms. Ethylidyne, CCH3, is identified after heating the surface to 400 K and was confirmed by comparison to results obtained following ethylene adsorption. Exposure of the surface held at 800 K to acetylene produced C2 molecules on the surface, which could be subsequently hydrogenated to ethylidyne. The hydrogenation of residual surface carbon also leads to the formation of ethylidyne, suggesting that the residual carbon was in the form of C2 molecules rather than carbon atoms.

A novel configuration for Pd/Ag/α-Al2O3 catalyst regeneration in the acetylene hydrogenation reactor of a multi feed cracker

Acetylene is one of the byproducts of olefin plants with the potential to poison the catalysts in polymerization plants, which can be avoided by reducing the acetylene concentration to less than 1ppm. Catalytic hydrogenation in tail-end systems is the method most commonly used in the industry to eliminate the acetylene. The Pd/Ag/α-Al2O3 catalysts used in this process undergo moderate deactivation due to coke and green oil formation, necessitating their regeneration after certain runtimes. The domestic petrochemical plant which has been investigated in this research is an olefin plant. Close monitoring of the two regeneration cycles in this plant, have revealed complications that caused a dramatic reduction in catalyst lifetime and also disrupted the temperature profile in the reactor overtime. In the present study, a new configuration of regeneration process is suggested based on inspecting the conventional protocol and a comparative analysis to other plants. The results emphasize the need to reconfigure the reactors and pipelines in order to achieve complete regeneration throughout the reactors.

The effect of palladium clusters (Pdn, n = 2–8) on mechanisms of acetylene hydrogenation: A DFT study

The mechanisms of acetylene hydrogenation on palladium clusters (Pdn, n=2–8) are researched by using the B3PW91/GENECP method of density functional theory. The calculation results indicate that there are two possible pathways for the hydrogenation reaction on Pdn cluster from the reactant acetylene to the product ethane. One of the pathways undergoes through two intermediates, the vinyl (Pdn(H)⋯CHCH2) and ethene (Pdn⋯CH2CH2) to form the ethane, and the other goes along vinylidene (Pdn(2H)⋯CCH2), ethylidyne Pdn(2H)⋯CCH3) and ethylidene (Pdn(2H)⋯CHCH3) to ethane. Those intermediates in the two pathways can convert into each other which make the reaction profile complicated. The value of n in Pdn cluster can directly affect the reaction pathway: when n≤4, the acetylene hydrogenation reaction will proceed via the pathway of Pdn(2H)⋯CHCH→Pdn(H)⋯CHCH2→Pdn⋯CH2CH2→Pdn(2H)⋯CH2CH2 to form ethane. However, when n>4, the reaction choose the following pathway: Pdn(2H)⋯CHCH→Pdn(H)⋯CHCH2→Pdn⋯CHCH3→Pdn(2H)⋯CHCH3. In addition, the value of their turnover frequency (TOF) for the ethylene formation catalyzed by Pdn cluster is larger than that for ethane, which indicates that the catalytic cycles in the formation of ethylene is efficient.

Density functional theory study of the effect of subsurface H, C, and Ag on C 2H 2 hydrogenation on Pd(1 1 1)

The selective hydrogenation of acetylene in the presence of ethylene over Pd catalysts (generally modified with silver) is of critical importance to prevent deactivation of polyethylene polymerization catalysts. In this study, density functional theory has been used to investigate the diffusion of carbon and hydrogen into the subsurface region of Pd(1 1 1), and subsequently, to explore the effects of these subsurface species on the selective acetylene hydrogenation reaction on Pd(1 1 1). In addition, the influence of subsurface Ag on the thermodynamics and kinetics of C 2H 2 hydrogenation has been examined. We find that the presence of subsurface H lowers the barriers for each C 2H X hydrogenation step, and could increase the overall activity of the hydrogenation reaction with a corresponding decrease in the selectivity towards ethylene. In contrast, modification with subsurface C or Ag appears to lead to heightened barriers for ethylene hydrogenation, and may increase the selectivity of the Pd(1 1 1) catalyst.

Predicting Kinetic Parameters of Acetylene Hydrogenation Reaction Via Optimization Techniques

In this study simulation and optimization of an industrial acetylene hydrogenation reactor was studied. Three well known kinetic models were used for a nearly similar catalyst to predict the industrial data. Due to the complexity of the reactions, none of the offered kinetic models could be considered as an exact kinetic model and it is necessary to determine the kinetic parameters. One of the best methods to determine the kinetic of a process is to simulate the process and then minimize the deviations between industrial data and calculated ones. Thus the hydrogenation reactor was simulated at the industrial operating conditions which were taken from an operational petrochemical plant and the optimum kinetic parameters were determined using optimization technique. Since such problem has many local optima, the genetic algorithm (GA) and simulated annealing (SA) methods were used to optimize the kinetic parameters of the three models. Due to the strong dependency of the GA performance on the GA condition, it was tried to investigate the effect of GA parameters on overall GA performance in detail. For this purpose, different GA parameters were used to solve the problem and results were discussed.

Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylene: Part II: Surface characterization and catalytic performance

The structurally well-defined intermetallic compounds PdGa and Pd 3Ga 7 constitute suitable catalysts for the selective hydrogenation of acetylene. The surface properties of PdGa and Pd 3Ga 7 were characterized by X-ray photoelectron spectroscopy, ion scattering spectroscopy and CO chemisorption. Catalytic activity, selectivity and long-term stability of PdGa and Pd 3Ga 7 were investigated under different acetylene hydrogenation reaction conditions, in absence and in excess of ethylene, in temperature-programmed and isothermal long-term experiments. Chemical treatment with ammonia solution—performed to remove the gallium oxide layer introduced during the milling procedure from the surface of the intermetallic compounds—yielded a significant increase in activity. Compared to Pd/Al 2O 3 and Pd 20Ag 80 reference catalysts, PdGa and Pd 3Ga 7 exhibited a similar activity per surface area, but higher selectivity and stability. The superior catalytic properties are attributed to the isolation of active Pd sites in the crystallographic structure of PdGa and Pd 3Ga 7 according to the active-site isolation concept.

Selective acetylene hydrogenation over core–shell magnetic Pd‐supported catalysts in a magnetically stabilized bed

AbstractA novel magnetic microspherical catalyst support with enough mechanical strength was prepared through coating Al2O3 on a magnetic core of NiFe2O4 spinel ferrite using the oil drop method to synthesize magnetic Pd‐supported catalyst for acetylene hydrogenation reaction. The synthesized core–shell composite Pd/Al2O3 catalyst shows high surface area and pore volume as well as sufficient saturated magnetization property, characterized by powder X‐ray diffraction, low‐temperature N2 adsorption–desorption analysis, and magnetic measurements. Catalytic performance of this magnetic Pd/Al2O3 catalyst was measured for acetylene hydrogenation reaction in a magnetically stabilized bed (MSB) reactor under different operation conditions. Under the optimal conditions of 353 K, 1.5 MPa and a gas hourly space velocity of 12,000 h−1, C2H2 conversion and C2H4 selectivity approximated 100% and 84%, respectively, over this magnetic Pd/Al2O3 catalyst in the MSB reactor, as a control over the commercial catalyst for hydrogenation reaction C2H2 conversion and C2H4 selectivity was near 37 and 64% under the similar conditions. Significant improvement of acetylene hydrogenation processes over this novel magnetic catalyst enlightens us a promising route to explore process intensification techniques through MSB. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Preparation, Characterization and Catalytic Performance of Carbon Nanotubes Promoted Ni‐B Amorphous Alloy

AbstractNi‐B and Ni‐B/CNTs amorphous alloy catalysts were prepared by chemical reduction and impregnation‐chemical reduction methods, respectively, and characterized by TEM, ICP, XPS, XRD, BET and CO chemisorption techniques. Their catalytic activities were evaluated in acetylene selective hydrogenation reaction. Based on characterizations, the effects of carbon nanotubes on Ni‐B amorphous alloy were attributed to both its structure effect, dispersing Ni‐B particles, leading to bigger surface area of active nickel and enhancing the thermal stability, and the electronic effect, resulting in electron‐rich nickel centers. Therefore, the superior thermal stability and acetylene selective hydrogenation activities of Ni‐B/CNTs to Ni‐B amorphous catalyst were obtained in the present study.

Ethylene selectivity variation in acetylene hydrogenation reactor with the hydrogen/acetylene ratio at the reactor inlet

Variation in the selectivity of ethylene produced by acetylene hydrogenation in an integral reactor was analyzed as a function of the hydrogen/acetylene ratio in the reaction stream at the reactor inlet. The analyses were made for two sample catalysts, which showed different dependence of the ethylene selectivity on the reactant composition. Even a small mismatch between the hydrogen/acetylene ratio at the reactor inlet and the ratio for converted reactants caused a large change in the ethylene selectivity along the reactor position, particularly when the conversion was high. The results of this study indicate two important factors to be considered in the design and operation of acetylene hydrogenation process: the hydrogen/acetylene ratio in the reactor inlet should be controlled close to the ratio for converted reactants; and catalysts showing high ethylene selectivity over a wide range of the hydrogen/ acetylene ratio are required for the design of a highly selective hydrogenation process.

The kinetic model of hydrogenation of acetylene–ethylene mixtures over palladium surface covered by carbonaceous deposits

The kinetics of hydrogenation reactions of acetylene–ethylene mixtures over a Pd/α-Al 2O 3 commercial catalyst was studied. Reaction rates were measured by using a gradientless reactor. The kinetic expressions derived, based upon a mechanism involving two types of active sites produced on the palladium surface by carbonaceous deposits, were used for the interpretation of experimental results. The kinetic parameters in these equations and in recently published kinetic expressions were estimated by using multiresponse technique. Statistical analysis of regression showed that the proposed kinetic model describes the process more adequately than do the competitive models.

Control policies for an industrial acetylene hydrogenation reactor

AbstractThis paper addresses the problem of finding optimal operational policies for an acetylene reactor for day to day operation. A lumped parameter model based on four main reactions is developed and used to examine the effects of the reactor manipulated variables on key reaction parameters. An optimal and a sub‐optimal operational policy which minimize the ethylene loss over time are formulated and the solution techniques are presented. The results indicate that the reactor model is in good agreement with industrial plant data. The performance of the optimal control policy is very similar to the performance of the sub‐optimal control policy. However, the sub‐optimal formulation, while retaining the dominant features of the optimal response, reduces the computational requirements. Finally, some issues concerning the real‐time implementation of an advanced acetylene reactor control scheme are presented. These include the estimation of the optimum regeneration cycle, a recursive model update algorithm, the process optimizer and their overall coordination. A preliminary analysis of the benefits associated with the advanced control scheme suggests a considerable reduction in the yearly ethylene loss.

Theoretical study on the catalytic activity of palladium for the hydrogenation of acetylene

The catalytic activity of palladium for the hydrogenation reaction of acetylene is studied by the ab initio quantum chemical method with the use of the cluster model. Based on our previous theoretical result that the hydrogen molecule is easily adsorbed dissociatively on the Pd2 fragment, we investigate the reactivity of this absorbed hydrogen for acetylene in two modes of the reaction, namely the Eley-Rideal (ER) mode and the Langmuir-Hinshelwood (LH) mode. Full catalytic reaction cycles are studied for both modes. From the study of the ER mode, it is shown that these hydrogens are almost as reactive as free atomic hydrogens in spite of the existence of the Pd-H bonds binding these hydrogens on the surface. The barrier of the reaction is calculated to be 32 kcal/mol. The electronic origin of the catalytic activity of palladium is shown to be the electron correlation and the participation of the dangling bond of the palladium surface. The nature of the reaction is clarified by analyzing the force and electron density along the reaction process. From the study of the LH mode, which is more realistic as a model of the catalytic reaction than the ER mode, it is shown that the two-step mechanism involving vinyl radical as a surface reaction intermediate is more preferable than the one-step simultaneous mechanism. The barriers of these catalytic cycles of the reactions are calculated to be 7 and 28 kcal/mol, respectively. The mechanism of the catalytic selectivity that acetylene is selectively converted to ethylene (not to ethane) in the ethylene-acetylene mixture is clarified.

Hydrogen sorption by a supersaturated solution of carbon in palladium

The phase transitions occurring during the acetylene hydrogenation reaction of a palladium catalyst containing up to 13% C have been studied by X-ray diffraction. The hydrogen desorption isotherms for PdC and Pd have been obtained using volumetric apparatus. A solid solution of composition PdC0.13 had no tendency to form the β-hydride phase, unlike pure Pd. Solutions with lower carbon content showed decreasing tendency to form the β-hydride phase, as shown by the shorter plateau section of the isotherm and the decrease in the hysteresis of the PdH system.

Infrared spectra of hydrocarbons chemisorbed on silica-supported metals: I. Experimental and interpretational methods; acetylene on nickel and platinum

A description is given of the experimental methods and spectroscopic interpretational procedures used in a series of studies of the infrared spectra of hydrocarbons chemisorbed on silica (pressed CabOSil disc) supported metals. Infrared spectra have been obtained from the surface species formed by initial adsorption, and subsequent hydrogenation, of acetylene on silica-supported nickel and platinum. On nickel, absorption bands from CH, CH 2, and CH 3 groups are obtained on initial adsorption. The former probably correspond to MCHCHM surface species (M = metal), and the latter to surface alkyl groups formed by self-hydrogenation and polymerization processes. After hydrogenation the spectra indicate the presence of surface attached n-butyl groups, M(CH 2) n CH 3, ( n = 3.) On platinum a weak initial spectrum is obtained and a large intensity increase occurs on hydrogenation. This indicates that the dissociation of acetylene to form a surface carbide together with MH bonds is greater on platinum than on nickel. The surface species after hydrogenation are alkyl groups with an average value of n ≥ 4. i.e. the degree of surface polymerization is somewhat greater on platinum. The published spectra from acetylene on palladium and copper are similar to those on platinum except that the initially adsorbed species have a higher proportion of olefinic CH bonds. It is suggested that the relatively smaller activity of nickel as compared with platinum for the acetylene hydrogenation reaction is related to a higher proportion of hydrocarbon surface residues (and a smaller proportion of MH bonds) formed by adsorption on nickel.

Elucidation of the role of different adsorption centers in the hydrogenation of acetylene over nickel Communication 2. Investigation of the kinetics of the hydrogenation and activated adsorption of acetylene at a nickel catalyst

1. Adsorption centers differing in their heats of adsorption and activation energies differ also in their catalytic properties. The hydrogenation and methane-forming reactions of acetylene occur at different groups of active centers, differing in their heats of adsorption and activation energies. 2. A mechanism has been proposed for hydrogenation in which the first stage is the reversible chemical adsorption of acetylene. 3. Methane formation occurs by two processes, one of which proceeds at a higher temperature via the reduction of a nickel carbide, and the other proceeds by the splitting of a partially hydrogenated adsorbed acetylene molecule at the carbon-carbon linkage, followed by addition of a hydrogen molecule. The first process occurs at active centers having very high heats of adsorption, and the second occurs at active centers having lower heats of adsorption.

Some Catalytic Exchange and Hydrogenation Reactions of Acetylene and Ethylene1,2

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSome Catalytic Exchange and Hydrogenation Reactions of Acetylene and Ethylene1,2John E. Douglas and B. S. RabinovitchCite this: J. Am. Chem. Soc. 1952, 74, 10, 2486–2489Publication Date (Print):May 1, 1952Publication History Published online1 May 2002Published inissue 1 May 1952https://doi.org/10.1021/ja01130a011RIGHTS & PERMISSIONSArticle Views117Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (522 KB) Get e-Alerts Get e-Alerts

On the Hydrogenation and Polymerisation Reaction of Acetylene. IV. Kinetics of Polymerisation by Use of Thermal Separation Column. II

Abstract (1) A method for calculating both reaction velocity and activation energy in the case when the reaction has been carried out in the thermal separation column of Clusius and Dickel has been described. (2) The method has been applied to the polymerisation reaction of acetylene previously investigated by the present authors. (3) It has been found that the calculated heat of activation is slightly smaller than our preliminary value, but larger than the directly observed value by Taylor and van Hook, and that the calculated velocity constants are several times larger than those hitherto have been observed.

Hydrogenation and Polymerisation Reactions of Acetylene. III. Kinetics of Polymerisation by Use of the Thermal Separation Column. I

Abstract (1) In order to investigate the kinetics of the polymerisation reaction of acetylene, a thermal separation column has been used as reaction vessel, and the superiority of this device has been stressed, both theoretically and experimentally. (2) The results of experiment have shown that the reaction is of second order, and that the apparent activation energy is 44.8 kcal.

Hydrogenation and Polymerisation Reactions of Acetylene. I. The Reaction in Liquid Phase and the Effect of High Tension Discharge

Abstract (1) Some theoretical considerations with regard to the hydrogenation and polymerisation of acetylene have been made. (2) The reaction has been studied in liquid phase with such catalysts as nickel, cobalt, palladium, and copper. (3) The effect of high tension discharge has been studied with and without catalyst. (4) It has been found that high tension discharge not only accelerates the reaction, but also changes the nature of the reaction.