Development of technology for the production of microspherical alumina support for the alkane dehydrogenation catalyst: II. The influence of hydrothermal treatment conditions on the operational characteristics of microspherical alumina support and chromium oxide/alumina catalyst for the dehydrogenation of iso-butane

For the purpose of improving the mechanical strength and reducing the abrasive activity of micro-spherical chromium oxide/alumina catalysts for the processes of alkane dehydrogenation in fluidized bed, we have developed technology for the production of new highly durable boehmite support with the use of technical aluminum trihydrate as an initial raw material. The technology includes two consecutive stages: the dehydration of aluminum trihydrate and the subsequent hydrothermal treatment of dehydration product into boehmite. Part II covers the results on the influence of conditions for the hydrothermal treatment of aluminum trihydrate dehydration products in an industrial autoclave of special construction on the phase composition, physicomechanical and structural characteristics of boehmite support, the acidic properties of its respective oxide form and chromium oxide/alumina catalyst based on this support and also on the catalytic properties of this catalyst in the reaction of iso-butane dehydrogenation into iso-butylene. It has been shown that differently sized boehmite crystallites and also gibbsite are formed in the volume of microgranule under hydrothermal conditions of χ-Al₂O₃ dehydration depending on a chosen regime (temperature, time). For the production of iso-butane dehydrogenation selective chromium oxide/alumina catalyst with the minimal content of strong acidic sites, catalyzing the cracking reactions, it is necessary to provide such hydration conditions, under which large (43–47 nm) boehmite crystals are formed. The appearance of strong acidic sites is caused by small boehmite crystals and the presence of nonhydrated χ-Al₂O₃ phase. In the absence of the impurity gibbsite phase, the highly durable microgranules of boehmite support and catalyst are formed. The conditions, providing the complete χ-Al₂O₃ hydration into macrocrystalline boehmite, have been defined. The application of the developed two-stage technology gives the iso-butylene yield of 45–49%, the selectivity of 88–90%, and the abrasivity of 0.10 g/(m² h). The given technology for the production of catalyst is realized in an industrial unit with the capacity of 100 t per month at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk). Industrial catalyst lots are currently under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftekhim.     

新型直链烷烃脱氢催化剂载体的研制

介绍了新型脱氢催化剂载体研制过程和物化性质的表征,并在工业装置将载体制备成催化剂,在接近工业应用的反应条件下进行了脱氢反应性能评价,结果表明,自制载体制备的催化剂初活性与工业参比剂基本相当,稳定性略好一些.     

Development of technology for the production of microspherical alumina support for the alkane dehydrogenation catalyst: III. The effect of the phase composition of microspherical supports on their thermal stability

This publication continues a series of our reports on the optimization of preparation conditions for obtaining a thermally stable support for the alkane dehydrogenation catalyst. The phase composition effect on the stability, particle size distribution, structure, texture, and mechanical properties of supports heated to 1100°C is reported. Microspherical alumina supports obtained by successive thermal and hydrothermal treatments of gibbsite are compared to commercial supports obtained by the thermochemical activation (TCA) of gibbsite. The dimensions of the support granules decrease upon heating because of shrinkage, which is governed by the phase composition of the granules and by the packing of their constituent boehmite and alumina crystallites. Three temperature intervals can be distinguished in the shrinkage of the granules. In region I (<600°C), there is intensive shrinkage via the diffusion glide of crystallites, the mechanical strength of the granules remaining invariable. In region II (600–900°C), the polymorphic transformations of alumina accompanied by sintering via surface diffusion do not affect the dimensions and strength of the granules. In region III (>900–1000°C), shrinkage takes place via coalescent sintering. For commercial manufacturing of microspherical alkane dehydrogenation catalysts and for ensuring their stability at 550–900°C, it is recommended to use alumina supports containing the minimum possible amount of χ-Al₂O₃. As the single-phase boehmite support obtained by our technology is heated to 1100°C, its granules shrink by no more than 14.4% and show an attrition resistance of 89% or above. The support based on the gibbsite TCA products, which contains 14–23 wt % χ-Al₂O₃, is characterized by 3–5% greater granule shrinkage and 6–12% lower mechanical strength.     

Isobutane/butene alkylation over supported heteropoly acid catalysts: I. Influence of the structure of silica

Catalysts consisting of heteropoly acids (HPAs) supported on different silica and mesoporous molecular sieves have been prepared by impregnation and the sol–gel method, respectively, and their catalytic behavior in fixed‐bed alkylation of isobutane with butene has been investigated. The activity, selectivity and stability of the supported‐HPA catalysts could be correlated with the surface acidity of the catalysts, the structure of supports as well as the time on stream (TOS). In the fixed‐bed reactor, the acidity of the heteropoly acid is favorable to the formation of dimerization products (C ₈ ⁼ ); especially, the pore size of supports was seen to have an important effect on activity and product distribution of the catalysts. Contrary to the traditional solid‐acid catalysts, the supported‐HPA catalysts own an excellent stability for alkylation, which makes it possible for these supported catalysts to replace the liquid‐acid catalysts used in industry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pilot tests of a new domestic ZhKD catalyst for the dehydrogenation of isoamilenes into isoprene

At the Synthetic Rubber Plant of OAO Nizhnekamskneftekhim, the dehydrogenation of isoamilenes into isoprene is currently performed on KDOM-08 catalysts with an insufficiently high yield of isoprene throughout the period of its industrial operation. More stable and highly active catalysts must be used to make the process more efficient. Under Russian Federation Government Decree No. 218, ZhKD-1 and ZhKD-2 iron-potassium catalysts have been developed by improving their formulas and optimizing their phase composition through selecting the proper ratio of initial compounds. To evaluate the possibility of transitioning to the new domestically-produced iron-potassium catalysts, we have performed pilot tests of the ZhKD-1 and ZhKD-2 catalysts in the dehydrogenation of methylbutenes into isoprene in adiabatic flow fixed-bed reactors at the Synthetic Rubber Plant of OAO Nizhnekamskneftekhim. The KDOM-08 catalyst used in the amount of 25 t in reactor 1 of the first system is taken as a base for comparison. The ZhKD-1 and ZhKD-2 catalysts are loaded into parallel reactors 7 and 8 of the fourth system. The KDOM-08 catalyst is shown to operate more efficiently under industrial conditions at loads of 1.0–2.0 t/h for 1000–3000 h, after which its performance characteristics deteriorate due to its gradual deactivation. The ZhKD-1 and ZhKD-2 catalysts are substantially superior to their industrial analogues in isoprene yield. It has been found that the ZhKD-2 catalysts operate more efficiently at even longer runs (4000–5000 h) and feedstock flow rates of 1.0–2.0 t/h, and the ZhKD-1 catalysts exhibits better activity (30–33 %) and selectivity (87–92 %) at higher loads of 2.3–3.0 t/h for up to 5000 h. From our analysis of the catalysts’ operation over the last 1000 h, it follows that at the same process temperatures (619°C) and feedstock loads (2.5 t/h), the ZhKD-1 and ZhKD-2 catalysts operate at a lower steam dilution coefficient (6.1 t/t) than the KDOM-08 catalyst (6.8 t/t). The rebuilding of reactors 7 and 8 allows the loaded catalyst mass to be reduced from 25 to 17 t, thereby almost doubling the daily output of isoprene per ton of catalyst. It is obvious that higher activity and selectivity along with smaller loads makes the use of the ZhKD-1 and ZhKD-2 catalysts economically profitable.     

Selecting the conditions of molding iron oxide catalysts for dehydrogenation

The effect of the conditions for molding iron oxide catalysts for dehydrogenation of iso-amylenes to isoprene on their operation characteristics was studied. The investigation of laboratory samples allowed us to determine the optimum molding pressure (200–250 MPa) under which high mechanical strength (strength factor K _G = 33.4–37.3 N/mm), the stability of the kinetic characteristics in the dehydrogenation reaction, and the formation of 15–50 nm pores, ensuring the occurrence of the process in the kinetic region, were attained. we propose using the extrudate density as an indirect criterion for estimating the molding pressure under industrial conditions of extrusion. It was shown that in order to develop high strength properties (K _G ∼ 29.1 N/mm) of the catalysts upon their production under industrial conditions and to ensure the occurrence of the reaction in the kinetic region, the extrudate density must be 2.40–2.46 g/cm³. The obtained results were verified via paste molding on various industrial extruders, thereby enabling us to recommend the type of molding extrusion equipment.     

Development of technology for the production of microspherical aluminum oxide supporter for the paraffin dehydrogenation catalyst

For the purpose of improving the mechanical strength and to reduce the abrasive activity of microspherical chromoalumina catalyst for the paraffin dehydrogenation in fluidized bed, technology, using technical aluminum trihydrate as an initial raw material and including consecutive stages of Al(OH)₃ dehydration and hydrothermal processing of its product into boehmite, has been developed for the production of highly durable boehmite supporter. As applied to the iso-butane dehydrogenation into iso-butylene, microspherical chromoalumina catalysts, which are synthesized with the use of boehmite supporter, exceed their known industrial analogous in activity, selectivity and physicomechanical properties. The technology of supporter and iso-butane dehydrogenation catalyst is realized at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk) for the production with the capacity of 100 t per month. Industrial catalyst lots are under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftechim. The given article consists of two parts. In the first one, investigation results are presented for the changes in technical properties of Al(OH)₃ during its dehydration in an industrial continuous baking drum-type furnace. The changes in physicomechanical characteristics of granules at the dehydration stage are caused by phase transformations of gibbsite and boehmite, by crystalline structure rearrangements in the volume of microgranules and do not depend on mechanical loads in a baking furnace and on porous structure changes. The conditions of gibbsite complete phase change into the two-phase boehmite-χ-Al₂O₃ mixture with minimal reduction in the microgranules strength have been determined: T _av = 435−475°C, ν_THA = 170 kg/h, and τ_av = 0.8 h.     

On the intrinsic activity of vanadium centres in the oxidative dehydrogenation of propane over V–Ca–O and V–Mg–O catalysts

The performance of V–Ca–O catalysts for the oxidative dehydrogenation of propane has been studied for the first time, being compared with that of similar V–Mg–O catalysts, and their differences are interpreted in terms of their physico-chemical properties. The VCaO catalyst showed the same initial selectivity to propene as the most selective VMgO composition, but it decreased faster with increasing propane conversion. Vanadium species present in the catalyst surface were different for the two supports: isolated V⁵⁺ tetrahedra on CaO and magnesium orthovanadate and pyrovanadate on MgO. The intrinsic activity of isolated vanadium centres in the surface of the V–Ca–O catalyst was more than one order of magnitude higher than that of dimeric or polymeric tetahedral species in the magnesium-containing catalysts. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface organometallic chemistry on metals. Application to chemicals and fine chemicals

Some applications of surface organometallic chemistry on metals to catalysis are presented, showing the great importance of the modification of a metallic surface by organometallic compounds on its catalytic properties. The selective hydrogenation of α–β unsaturated aldehydes such as citral (Z and E) can be achieved on rhodium–tin catalysts. While rhodium alone is relatively unselective, geraniol (and nerol) can be obtained selectively (> 98%) without a significant loss of activity by use of a rhodium–tin catalyst showing a typical ligand effect of the organotin fragment on the surface. Similarly, in the isomerization of (+) 3-carene into (+) 2-carene or the dehydrogenation of butan–2–ol into methyl ethyl ketone, the selectivity into the desired product is increased by introduction of small amounts of tin which will form adatoms poisoning unselective sites. An alloying effect of tin is also presented in the dehydrogenation reaction of isobutane in isobutene. This revised version was published online in June 2006 with corrections to the Cover Date.     

空心微球氧化铝负载Pt-In催化异丁烷脱氢研究

针对异丁烷脱氢催化剂存在容易烧结与积碳的问题,开发了采用水热法制备的2种不同形貌的Al₂O₃载体,将其负载Pt-In获得的催化剂用于异丁烷脱氢反应中,研究其对异丁烷脱氢催化行为的影响。借助XRD、SEM、TEM、NH₃-TPD、XPS、TG-DTA及低温N₂吸-脱附法对催化剂进行物化性能研究。结果表明:由纳米片构建的多孔空心微球氧化铝负载Pt-In催化剂具有较小的Pt纳米粒子、低的比表面积、强的Pt-In相互作用、高的In³⁺/In⁰比例且缺少强酸位,从而获得优异的异丁烷脱氢性能,其异丁烯选择性和产率高达93.5%和40.3%,同时异丁烷转化率可稳定在43.0%,反应后的金属颗粒无聚集烧结现象,表现出优异的抗烧结和积碳性能。     

Chromia-alumina catalysts for the dehydrogenation of propane prepared by a modified method of codeposition

A method for preparing chromia-alumina catalysts for the dehydrogenation of propane, enabling us to increase the activity and thermal stability of a catalyst relative to currently known catalysts, is proposed. Chromia-alumina catalysts were prepared for the first time using a modified method of codeposition, in which a suspension of chromium and aluminum hydroxides was subjected to a high-temperature treatment (550°C). The proposed method is simple and allows us to reduce the number of stages in the preparation of the catalyst. The phase composition and texture of the catalyst, and the formation and properties of surface-active forms in dependence on the conditions of catalyst preparation, were studied using a set of physicochemical methods. The selected conditions of catalyst preparation ensured high specific surface area and a stable bond between the surface forms of chromium and the support, hindering the formation of the catalytically low-activity form α-Cr₂O₃ during calcination. In this work, we synthesized and studied laboratory samples of a chromia-alumina catalyst with different contents of chromium (2.8–11.3 wt %). With respect to the main parameters (conversion of propane, selectivity to propylene, and resistance to coke formation), the catalyst was as good as more active samples known from the literature and exhibited high activity at low chromium contents (2.8–5.5 wt %). This method of catalyst preparation is protected by a patent of the Russian Federation and recommended for improving industrial technology.     

Developing a method for increasing the service life of a higher paraffin dehydrogenation catalyst,based on the nonstationary kinetic model of a reactor

The service life of an industrial catalyst can be prolonged by improving the technological conditions of its operation. This allows us to maximally eliminate the catalyst deactivation factors. A specific feature of the catalytic dehydrogenation of hydrocarbons is its nonstationarity produced by the deactivation of catalysts. The results of modeling the industrial catalytic process of C₉-C₁₄ paraffin dehydrogenation—the key stage in the production of linear alkylbenzenes—is discussed in this paper. We consider (1) thermodynamic analysis of reactions by means of quantum chemistry, (2) estimation of the kinetic model’s parameters by solving the inverse kinetic problem, (3) selection of an equation that describes the coke deactivation of a catalyst, and (4) development of a method for increasing the service life of a dehydrogenation catalyst using a nonstationary model based on the quantitative consideration of the water added to a reactor within a temperature range of 470–490°C. The higher alkane dehydrogenation flowsheet proposed on the basis of these models allows us to predict the operation of a reactor in different water supply regimes. It is shown that the service life of a catalyst grows by 20–30% on the average, if water is fed by increasing portions.     

异丁烷催化脱氢反应机理与失活动力学研究进展

异丁烯是化工行业重要的基础原料,国内外对异丁烯的需求量逐年递增。仅靠石油催化裂解已无法满足对异丁烯的需求,开展异丁烷脱氢制异丁烯工艺的研究备受关注。综述Cr系异丁烷脱氢催化剂的研究进展,探讨Cr系催化剂的活性中心以及发生在活性中心上的多种反应机理和相应的动力学模型,详述催化剂的失活机理,总结积炭的形成过程,指出Cr系异丁烷催化脱氢反应和失活机理以及相关动力学方面研究的不足,并对未来研究前景进行展望。     

Activity of vanadium magnesium oxide supported catalysts in the dehydrogenation of isobutane

The activity of the vanadium magnesium binary oxides supported on C_act, SiO₂, γ-Al₂O₃ and ZnO in the dehydrogenation of isobutane to isobutene under the carbon dioxide or inert gas atmosphere was investigated. The highest isobutene yield (34.8%) was obtained over active carbon supported catalyst. The role of carbon dioxide in the dehydrogenation process was determined on the basis of additional tests: the RWGS reaction, gasification of coke and regeneration of partially reduced catalysts. The temperature-programmed techniques (TPR-H₂, TPD-NH₃ and TPD-CO₂) were used to characterize the catalysts.     

Evaluation of the rheological properties of sulfonic acids and sodium sulfonates

Sulfonic acids of linear alkylbenzene (LAB) are converted into the corresponding sodium salts to produce the most widely used anionic surfactant worldwide, linear alkylbenzene sulfonate (LAS). Used in many industrial applications and consumer products, the physical and mechanical properties of the sulfonates are strongly dependent on the LAB manufacturing process. Until recently, commercial alkylation of benzene has employed aluminum chloride or hydrogen fluoride catalysts, but a new fixed-bed alkylation process (DETAL) has been developed with improved 2-phenyl isomer selectivity and low tetralin concentration. In order to better understand the rheology of LAS in aqueous media, a comprehensive comparative evaluation of sulfonic acids and sodium sulfonates of the three LAB process derivatives has been done using dynamic mechanical rheometry, steady shear viscometry, and X-ray diffraction for phase identification. LAB sulfonic acids are Newtonian fluids in the temperature range of 20–60°C. The neat AlCl₃, HF, and DETAL sulfonic acids are Newtonian fluids within the temperature range of 20–60°C. At 30 wt%, all three sulfonates are Newtonian at 20–60°C, and the 40 wt% AlCl₃ sodium sulfonate remains in the Newtonian regime within this temperature range. Lamellar liquid crystalline phases have been identified for the sulfonates in the concentration range of 40–60 wt% in water at 20–60°C, and a hexagonal lattice phase also has been identified for DETAL sodium alkylbenzene sulfonate at 40 wt%, 60°C. The presence of anisotropic phases results in non-Newtonian pseudoplastic behavior with time-dependent viscosity functions.     

Synthesis of high surface area γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as an efficient catalyst support for dehydrogenation of n-dodecane

In this work mesoporous nanocrystalline γ-Al₂O₃ has been synthesized by a three step (hydrolysis, condensation and hydrothermal treatment) sol–gel procedure in nitric acid medium with cationic surfactant (hexadecyltrimethyl ammonium bromide) as template. The prepared sample was employed as a carrier for the n-dodecane dehydrogenation catalyst. The synthesized samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TG) and temperature programmed reduction (TPR) techniques. The nitrogen adsorption analysis showed that the samples possessed mesoporous structure with high specific surface areas larger than 370 m² g⁻¹ and pore volumes larger than 1.5 cm³ g⁻¹. The prepared samples also showed a high thermal stability up to 750 °C which is important for carrier of heterogeneous catalysts. The results of catalyst testing in the dehydrogenation reaction of n-dodecane confirmed that the synthesized support has a good potential to function as a carrier for n-dodecane dehydrogenation catalysts.     

异丁烷脱氢Pt系催化剂研究进展

介绍异丁烷脱氢制备异丁烯Pt系催化剂的研究进展,表明催化剂的活性中心、载体和助剂对异丁烷脱氢反应性能影响较大。催化剂活性中心的积炭覆盖和烧结是催化剂失活的直接原因;载体的酸性有助于调变积炭的形成速率,而活性中心与助剂的交互作用可促使积炭的表面迁移;活性中心与载体的交互作用有利于减少活性中心的烧结。     

Catalytic dehydrogenation of isobutane over ordered mesoporous Cr2O3–Al2O3 composite oxides

A series of ordered mesoporous Cr₂O₃–Al₂O₃ composite oxides synthesized via improved one-pot evaporation induced self-assembly strategy were investigated as the catalysts for catalytic dehydrogenation of isobutane. These mesoporous catalysts with good structural properties and thermal stability performed excellent catalytic properties. Besides, the effect of the ordered mesopore structure on improving catalytic properties was also studied. Compared with non-mesoporous catalyst, the current mesoporous catalyst could accommodate the gaseous reactant with more “accessible” active sites. Therefore, the present materials were considered as promising catalyst candidates for catalytic dehydrogenation of isobutane.     

Silica-Supported Au–Ni Catalysts for the Dehydrogenation of Propane

Abstract  

Inspired by previous studies on model systems, a series of silica-supported Au–Ni catalysts were prepared and tested for the conversion of propane in the presence of hydrogen. The Au–Ni/SiO₂ catalysts were prepared by successive impregnation, i.e. Ni was deposited first followed by Au. TEM/EDX results confirmed the presence of bimetallic Au–Ni nanoparticles. The dehydrogenation of propane to propylene was observed on the Au–Ni bimetallic catalysts, whereas only hydrogenolysis products were observed on the monometallic Ni catalyst. The selectivity to propylene was found to increase monotonically with the Au loading. The results are in good agreement with the results on model catalysts.     

In situ characterization of carbonaceous deposits formed on chromia/zirconia during isobutane dehydrogenation

The formation of carbonaceous species during isobutane dehydrogenation on chromia/zirconia was studied by in situ diffuse reflectance Fourier transform infrared spectroscopy combined with mass spectrometry for on-line product gas analysis. The reactions of the hydroxyl groups of zirconia support with the hydrocarbons and the reduction of the chromates resulted in the formation of adsorbed acetone, formate and acetate. However, they were suspected not be involved in the dehydrogenation. The reduced chromia/zirconia catalysts were active in the dehydrogenation of isobutane but deactivated due to formation of coke. These unsaturated/aromatic hydrocarbon species were suggested to form through the adsorbed dehydrogenation intermediates or products.