Isobutane Conversion Research Articles

Kinetic studies on the dimerization of isobutene with Ni/Al2O3 as a catalyst for reactive distillation process

Isooctane is a promising gasoline additive that could be produced by dimerization of isobutene (IB) with subsequent hydrogenation. In this work, the dimerization of IB has been carried out in a batch reactor over a temperature range of 338–383K in the presence of laboratory prepared Ni/Al2O3 as a catalyst and n-pentane as solvent. The influence of various parameters such as temperature, catalyst loading and initial concentration of IB was examined. A Langmuir–Hinshelwood kinetic model of IB dimerization was established and the parameters were estimated on the basis of the measured data. The feasibility of oligomerization of IB based on the reactive distillation was simulated in ASPEN PLUS using the kinetics developed. The simulation results showed that the catalyst of Ni/Al2O3 had higher selectivity to diisobutene (DIB) and slightly lower conversion of IB than ion exchange resin in the absence of polar substances.

Isobutane dehydrogenation over chromia alumina catalysts prepared from MIL-101: Insight into chromium species on activity and selectivity

Various mesoporous chromia alumina catalysts were prepared by five different methods based on a metal-organic framework MIL-101 and their catalytic performances over isobutane dehydrogenation were investigated. The highly dispersed chromium species were produced on catalyst KCrAl-I1 with largest specific surface area of 198 m2·g−1 prepared with aluminium isopropoxide (Al(i-OC3H7)3) by ultrasonic impregnation method. However, the catalyst KCrAl-I2 synthesized by stirring impregnation possessed crystalline α-Cr2O3 phase, which was poorly dispersed. Two types of Cr-rich and Al-rich CrxAl2–xO3 solid solutions, designated as CrAl-I and CrAl-II phase, were formed over the catalysts KCrAl-I3 (prepared by Al(i-OC3H7)3 with nitric acid regulation), KCrAl-C4 (prepared by aluminium chloride hexahydrate) and KCrAl-N5 (prepared by aluminium nitrate nonahydrate). Catalytic evaluation results revealed that KCrAl-I1 exhibited the high isobutane conversion due to its highly dispersed chromium species. However, KCrAl-I3, KCrAl-C4 and KCrAl-N5 showed the higher isobutene selectivity (95.2 %–96.4%) on account of the formation of chromia alumina solid solutions in the catalysts. Moreover, the solid solution over the chromia alumina catalysts could greatly suppress the coke formation.

Simultaneous isobutane dehydrogenation and hydrogen production in a hydrogen-permselective membrane fixed bed reactor

In this study, performance of hydrogen-permselective membrane fixed bed reactors to produce isobutene is studied at steady state condition. The proposed reactors have been modeled heterogeneously based on the mass and energy conservation laws. The considered reaction networks in the model are isobutene dehydrogenation as the main reaction, and hydrogenolysis, propane dehydrogenation as well as coke formation as side reactions that all occur on the catalyst surface. The coke deposition on the catalyst surface results an activity profile along reactors. The reactions occur in the tube side and the hydrogen permeates from the reaction zone to the sweep gas stream. Decreasing the hydrogen concentration over the catalyst pellets improves isobutane conversion and isobutene selectivity. To prove the performance of the proposed configuration, simulation results for membrane process are compared with the conventional process at the same operating condition. In this configuration, the isobutene production rate is enhanced about 10.81% compared to the conventional process at the same catalyst loading.

An Investigation on Isobutane Aromatization Over an H-ZSM-5 Catalyst

The H-ZSM-5(SiO2/Al2O3 = 35) catalyst was synthesized hydrothermally using commercial waterglass as the silica source and it was characterized by XRD, BET, SEM, and NH3-TPD techniques. Isobutane aromatization over the prepared catalyst was studied and the results were compared with those of propane in a fixed-bed reactor. Despite higher conversion of isobutane, the aromatics selectivity was higher for propane with the former exhibited more rapid catalyst deactivation. Furthermore, isobutane aromatization was carried out at 450–550°C. Higher temperature increased aromatics yield as well as deactivation rate.

Insights into the vanadia catalyzed oxidative dehydrogenation of isobutane with CO2

Vanadia-based catalysts were prepared using the sol-gel method and were subjected to the oxidative dehydrogenation of isobutane with CO2. The materials were extensively characterized by using X-ray diffraction, N2 adsorption-desorption, O2-temperature programmed oxidation, temperature programmed surface reaction, and in situ Fourier transform infrared techniques. Catalytic results indicate that a high selectivity toward total C4 olefins over 85% was obtained over all of the catalysts. On the contrary, the highest conversion of isobutane was observed over 12 wt% V2O5/Ce0.6Zr0.4O2(7 wt%)-Al2O3, and a more stable performance was achieved over 6 wt% V2O5-Ce0.6Zr0.4O2(7 wt%)-Al2O3. The catalytic activity for the titled reaction was found to be dependent on the dispersion and crystallinity of the VOx species over the catalyst, and the deposition of the heavier coke over the catalyst was revealed to be the main reason for the catalyst deactivation. Moreover, the benefit of CO2 toward the titled reaction was clearly revealed from TPSR results, and the reaction was confirmed to follow the redox mechanism.

Effect of calcination temperature on isobutane dehydrogenation over Mo/MgAl2O4 catalysts

The catalytic activity of a novel catalyst Mo/MgAl2O4 was studied in isobutane dehydrogenation, and the effect of calcination temperature has been comprehensively investigated. For catalysts with MoO3 loading below monolayer coverage (5Mo/MgAl2O4), isobutane conversion increases with calcination temperature, while the selectivity to isobutene decreases. An opposite trend is observed for catalysts with MoO3 loading above monolayer coverage (30Mo/MgAl2O4). In combination with characterization results, it can be concluded that calcination temperature affects catalyst structure and properties in many aspects including surface area, acidity and reducibility, as well as the interaction between Mo species and support, and thus influences the catalytic behaviors.

Dimerization reactions with iron and cobalt bis(imino)pyridine catalysts: A substrate based approach

Herein, we present a substrate based approach to gain insight into effects on reactivity as well as selectivity of dimerization reactions using bis(imino)pyridine catalysts. Common iron and cobalt systems show several limitations applying sterically demanding alkenes. Systematic substrate alterations reveal that structural properties are able to influence reactivity and dimer selectivity whereas electronic properties have an impact on insertion selectivity. Finally, successful conversion of the simplest vinylidene compound isobutene is achieved by catalyst variation.

Catalytic selective oxidation of isobutane over Csx(NH4)3−xHPMo11VO40mixed salts

A series of mixed Keggin-type heteropolysalts Csx(NH4)3−xHPMo11VO40 with various ammonia/caesium ratios was prepared by the precipitation method and characterized by TGA, N2 adsorption/desorption, XRD, FT-IR, and NH3-TPD techniques. Correlations between the ammonia/caesium ratio and the specific surface area, as well as with the total number of acid sites, were established. Furthermore, the introduction of Cs to the catalytic formulation was beneficial to the stabilization of the Keggin structure and helped limiting the elimination of the V atoms from the primary structure. The as-prepared samples were applied in the catalytic selective oxidation of isobutane at 340 °C under atmospheric pressure. The best results were obtained over Cs1.7(NH4)1.3HPMo11VO40 with an isobutane conversion of 9.6% and a total selectivity to valuable products (methacrylic acid and methacrolein) of 57.1%. This was explained by the well-balanced acidity and specific surface of this catalyst, promoting the C–H bond activation (adequate acid properties) over a large number of accessible active sites (high acid sites density).

Heat integration of isobutane dehydrogenation and hydrogenation of nitrobenzene to aniline in radial flow moving bed reactors: Modelling and operability investigation

In the process intensification subject, heat integration of endothermic and exothermic reactions in a shell and tube reactor is one of the most important approaches to reduce plant size and decreasing operational cost compared to conventional processes. This paper focuses on modelling and simulation of thermally coupled radial flow moving bed reactors to produce isobutene and aniline. A steady state heterogeneous two-dimensional model is developed to predict the performance and operability of the proposed configuration against conventional process. The catalytic nitrobenzene hydrogenation takes place in the exothermic side and supplies a part of necessary heat for isobutane dehydrogenation in the endothermic side. To prove the accuracy of the considered mathematical model and assumptions, the simulation results of the conventional process are compared with the plant data at the same process condition. Isobutane conversion is enhanced about 5.3% in the thermally coupled process compared to the conventional process. In addition, since the nitrobenzene hydrogenation reaction supplies a part of required heat in the isobutane dehydrogenation side, the smaller furnaces can be used in the commercial Oleflex process.

Researching of efficiency of zeolite containing catalysts and their application in industrial synthesis of ethyl tertiary butyl ether in the contemporary context of JSC "Gazprom neftekhim Salavat"

The purpose of this article is researching of chemical process to get an octane–enhancing additive for gasoline by synthesis from ethanol and isobutene using zeolite catalysts. The isobutene are not in the pure state and are contained in the marketable butylene–butadiene fraction produced by JSC Gazprom neftekhim Salavat. This synthesis process proceeds in the presence of heterogeneous catalysts, so for this study authors used a laboratory unit which allows to accurately determine the qualitative performance of zeolite-containing acid catalysts under various parameters of the synthesis process which were as close as possible to industrial conditions. The high degree of process automation and application of precision instruments minimizes the influence of human factors on the accuracy of obtained results. The result of this research is establishment the dependant conversion of isobutene into ETBE from parameters of zeolite catalysts and process parameters of ETBE synthesis, such as pressure and temperature. The most effective zeolite-containing catalyst and conditions for the synthesis of ETBE were determined, which are optimal for this raw material and at the same time ensuring low energy consumption of the synthesis process and high yield of the desired product. For realization of the industrial process for production ETBE using zeolite-containing catalyst, the technological scheme was proposed. This scheme allows to return to the process the ethanol in a cheaper way compared to other existing extraction processes, and also allows to increase the purity of the desired product due to recycle of the ethanol–free hydrocarbons to the rectification zone.

Different Supports-Supported Cr-Based Catalysts for Oxidative Dehydrogenation of Isobutane with CO2

The effect of supports (MSU-1,), gamma-Al2O3, AC (activated carbon), and MgO) on the catalytic activity of Cr-based catalysts was investigated for the dehydrogenation of isobutane with CO2. The catalytic activity was in the order of CrO,IMSU-1 > CrOx/Al2O3 > CrOx/AC > CrOx/MgO. The catalysts were characterized by N-2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). The XRD results indicate that the active species of Cr are dispersed well on the supports. N-2 adsorption-desorption shows that the support MSU-1 has the largest surface area (804.2 m(2)/g), which results in excellent dispersion of Cr and highest activity. The XPS results reveal that Cr6+ is one of the active centers. The results of NH3-TPD indicate that catalyst activity is proportional to the amount of weak acid adsorption sites. As a result, the best support is the MSU-1 zeolite owing to its high specific area and a large amount of weak acid sites. The 59.2% conversion of isobutane and the 39.5% yield of isobutene are achieved on the CrOx/MSU-1 catalyst.

Effect of alumina support on the performance of Pt-Sn-K/γ-Al2O3 catalyst in the dehydrogenation of isobutane

Alumina supports were synthesized by hydrochloric acid reflux and ammonia precipitation methods; after that the Pt-Sn-K/γ-Al2O3 catalysts were prepared by complex impregnation method under vacuum with alumina of different sources as the supports. The catalysts were characterized by N2 physisorption, CO pulse chemisorption, H2 temperature-programmed reduction, NH3 temperature-programmed desorption and thermogravimetric analysis; the effect of the alumina support on the performance of Pt-Sn-K/γ-Al2O3 catalysts in the dehydrogenation of isobutane was investigated. Compared with the catalyst supported on Al2O3 from hydrochloric acid reflux, the catalyst supported on the Al2O3 from ammonia precipitation is provided with smaller platinum particle size and weaker acidic distribution, and then exhibits higher activity and selectivity to isobutene in isobutane dehydrogenation. Moreover, the catalyst with Al2O3 synthesized by ammonia precipitation as the support exhibits better resistance against coke deposition and the coke deposited also has a lower degree of graphitization, which endues the catalyst with better stability. During a long term test of 14 d over the catalyst with Al2O3 synthesized by ammonia precipitation as the support, the conversion of isobutane is initially 56.67% and then decreased to 34.71% after 14 d; meanwhile, the initial selectivity to isobutene is 80% and it remains approximate 94% after 7 d.

Optimal conditions of isobutane dehydrogenation in radial flow moving bed hydrogen-permselective membrane reactors to enhance isobutene and hydrogen production

In the isobutane dehydrogenation process, coupling reaction and separation and optimization of the intensified process can improve the isobutane conversion and selectivity, reduce operational costs and lets to produce pure hydrogen. In this research, the radial flow moving bed reactors in the Olefex technology have been supported by Pd–Ag membrane plate to remove hydrogen from the reaction zone. The reactions occur in the tube side and the hydrogen is permeated from the reaction zone to the sweep gas stream. The proposed configuration has been modeled heterogeneously based on the mass and energy conservation laws considering reaction networks. To prove the accuracy of the considered model, the simulation results of the conventional process have been compared against available plant data. The Genetic algorithm as an effective method in the global optimization has been considered to optimize the operating condition of membrane reactors to enhance isobutene productivity. In this optimal configuration, the isobutene production has been enhanced about 3.7%.

Rate Parameter Distributions for Isobutane Dehydrogenation and Isobutene Dimerization and Desorption over HZSM-5

Deconvolution of the evolved isobutene data obtained from temperature-programmed, low-pressure steady-state conversion of isobutane over HZSM-5 has yielded apparent activation energies for isobutane dehydrogenation, isobutene dimerization and desorption. Intrinsic activation energies and associated isobutane collision frequencies are also estimated. A combination of wavelet shrinkage denoising, followed by time-varying flexible least squares of the evolved mass-spectral abundance data over the temperature range 150 to 450 °C, provides accurate, temperature-dependent, apparent rate parameters. Intrinsic activation energies for isobutane dehydrogenation range from 86 to 235.2 kJ mol−1 (average = 150 ± 42 kJ mol−1) for isobutene dimerization from 48.3 to 267 kJ mol−1 (average = 112 ± 74 kJ mol−1) and for isobutene desorption from 64.4 to 97.8 kJ mol−1 (average = 77 ± 12 kJ mol−1). These wide ranges reflect the heterogeneity and acidity of the zeolite surface and structure. Seven distinct locations and sites, including Lewis and Brønsted acid sites can be identified in the profiles. Isobutane collision frequencies range from 10−0.4 to 1022.2 s−1 and are proportional to the accessibility of active sites, within the HZSM-5 micropores or on the external surface.

Regeneration of a Commercial Catalyst for the Dehydrogenation of Isobutane to Isobutene

AbstractIn the chemical and petrochemical industries, dehydrogenating of hydrocarbons to olefins as raw materials for the manufacture of various chemical products is an important economic issue. So, here, the redispersion and regeneration of a commercial Pt‐Sn/γ‐Al2O3 catalyst utilized for the conversion of isobutane to isobutene was studied. First, in order to regenerate the deactivated commercial catalyst unloaded from a commercial reactor, coke burning under controlled conditions was carried out. Then, to redisperse the platinum on the surface of the catalyst, a HCl solution (injected through a syringe pump) and Cl2 were passed over the catalytic bed at specific flow rates and temperatures. Evaluation tests carried out over the regenerated catalyst prove that the regenerated catalyst has similar conversion, selectivity, and structural characteristics as compared to the fresh one.

Optimal operating conditions of radial flow moving-bed reactors for isobutane dehydrogenation

In this study, radial flow moving bed reactors for isobutane dehydrogenation have been modeled and simulated heterogeneously based on mass and energy conservation laws. The considered reaction networks in the model are isobutene dehydrogenation as main reaction, and hydrogenolysis, propane dehydrogenation as well as coke formation as side reactions that all occur on the catalyst surface. Then, the process condition has been optimized to produce more isobutene under steady state condition. To prove the accuracy of the considered mathematical model and assumptions, simulation results are compared with the plant data. As a powerful method in the global optimization, the genetic algorithm has been used to optimize the considered objective function. The isobutane conversion and isobutene selectivity under optimal conditions are about 40.1% and 91%, respectively.

Steady state modeling and simulation of the Oleflex process for isobutane dehydrogenation considering reaction network

ABSTRACTIn this study, the performance of moving bed radial flow reactors in Olefex technology to produce isobutene from isobutane dehydrogenation is studied at steady state condition. The dehydrogenation reactors have been modeled heterogeneously on the basis of the mass and energy governing laws considering a two‐dimensional model. In this system, isobutane dehydrogenation, hydrogenolysis, propane dehydrogenation, and coke formation reactions occur on the catalyst surface. The coke deposition on the catalyst surface and the catalyst velocity along the axial direction result to an activity profile along reactors that has been calculated from proper correlation. To prove the accuracy of the considered mathematical model and assumptions, simulation results are compared with the plant data at the same process condition. The isobutane conversion and isobutene selectivity have been obtained at about 38.53% and 90.76%, respectively, which have good agreement with the plant data. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Isobutane dehydrogenation over the mesoporous Cr2O3/Al2O3 catalysts synthesized from a metal-organic framework MIL-101

The reactivity of isobutane dehydrogenation over a series of non-ordered mesoporous chromia/alumina (Cr2O3/Al2O3) catalysts with large specific surface area (149.4–381.6m2g−1) and high pore volume (0.77–1.24cm3g−1), synthesized using a metal-organic framework MIL-101 as a molecular host and chromium precursor, aluminium isopropoxide (Al(i-OC3H7)3) as the aluminium precursor, were studied in detail. The chromium species were highly dispersed over the catalyst with chromia loading up to 10wt.%. The specific surface area of the catalyst decreased, whereas the amount of surface Cr3+ species and the mole ratio of Cr3+ and Cr6+ species (Cr3+/Cr6+) increased with the increasing chromia loadings (5–25wt.%) and calcination temperature (500–900°C), respectively. The addition of potassium to the catalyst system greatly promoted isobutene selectivity and catalyst stability. The catalyst with 1.5wt.% K2O and 10wt.% Cr2O3 loadings calcined at 800°C was found to exhibit the highest isobutane conversion 60.1% with the isobutene selectivity up to 93.2% among all the catalysts. The maintainable catalytic reactivity demonstrated the high stability of the catalyst in ten dehydrogenation-regeneration cycles. Moreover, it was proposed that the Cr3+ species was mainly the active site and catalytic selectivity was depended on the surface Cr3+/Cr6+ value over the catalyst. The catalyst presented much more stable dehydrogenation activity compared with the conventional catalyst. Consequently, this study presents a feasible way to facile synthesis of the mesoporous MOF-derived Cr2O3/Al2O3 catalysts with high stability and good catalytic reactivity over isobutane dehydrogenation.

Neural - Wiener Model for Multivariable Methyl Tertiary Butyl Ether (MTBE) Reactive Distillation

MTBE is a chemical that can be used as anti-knock additive to replace lead additive (tetra ethyl lead) which can be efficiently produced using reactive distillation process. It has been established in the literature that MTBE reactive distillation poses a highly nonlinear behavior due to the combination of reaction and separation processes. A reliable model for predicting the behavior is required especially for the control purposes. In this work, a Neural Wiener model which is one of the available types of oriented block model was utilised to develop the MTBE reactive distillation model. The required data for the Neural Wiener model were generated using a validated Aspen dynamics model for the MTBE reactive distillation process. It is found that the Neural Wiener model is capable to predict the MTBE purity and isobutene conversion with accuracy of 98.55% and 96.95%, respectively. Those values are quantitatively better in comparison to the state space model which gives lower values for prediction accuracy of 87.86% and 82.90%, respectively.

Extended activity of zeolite catalysts with CO2 as reaction medium

Isooctane is a typically used vehicle fuel component. However, the synthesis of isooctane is limited due to the coking phenomenon when using zeolite catalysts. In this paper the suitability of CO2 as a solvent for zeolite based acid catalytic reactions was studied in general and isobutene dimerization in particular. The special focus of this study was to clarify whether using CO2 as a solvent reduces coking compared to propane, which was used as a reference solvent in this case. The reaction was carried out in a 50cm3 continuous stirred tank reactor with two solid acid catalysts, ZSM-5 and ZSM-23 zeolites. Besides the desired dimerization reaction, the oligomerization reaction was also considered. The study also includes determination and discussion on phase conditions. Calculations based on thermodynamic methods show that the reaction phase may change during the experiment from a single phase (liquid, gas or supercritical) to a two phase domain (coexistence of vapor and liquid). Experiments with the ZSM-23 catalyst gave initial isobutene conversion of above 80%. The conversion with CO2 was approx. 56% after ∼200h whereas with propane it was approx. 32% after about 120h. These results were similar also over the ZSM-5 catalyst. The reduced coking tendency results in lower carbon dioxide emissions as the need for burning off the coke in catalyst regeneration is decreased. The results show that carbon dioxide is a potential solvent for industrial purposes as it prolongs the catalyst activity due to a reduced coking tendency.