THE STRUCTURE OF ACTIVE SITE AND THE ROLE OF BIVALENT CATION IN FERRITE-FERRIC OXIDE CATALYSTS FOR OXIDATIVE DEHYDROGENATION OF BUTENES

The relations between catalytic activities and compositions of the systems Mg_xZn_(1-x)Fe_2O_4, Co_xZn_(1-x)Fe_2O_4, Co_xMg_(1-x)Fe_2O_4, Cd_xZn_(1-x)Fe_2O_4 and Mg_xZn_(1-x)Fe_2O_4·0.17Fe_2O_3 have been studied by flow differential reactor, XRD, and derivative IR techniques. It has been found that the appropriate normal-inverse spinel combination substantially increases the activity for the title raction. The structure of the active site and the role of the bivalent cation in the title catalyst have been inferred.

Numerical simulation of diffusion process for oxidative dehydrogenation of butene to butadiene

A comprehensive single particle model which includes the mesoscale and microscale models was developed to study the influence of particle diameter on mass and heat transfer occurring within a ferrite catalyst during the oxidative dehydrogenation of butene to butadiene process. The verified model can be used to investigate the influence of catalyst diameter on the flow distribution inside the particle. The simulation results demonstrate that the mass fraction gradients of all species, temperature gradient and pressure gradient increase with the increase of the particle diameter. It means that there is a high intraparticle transfer resistance and strong diffusion when applying the large catalysts. The external particle mass transfer resistance is nearly constant under different particle diameters so that the effect of particle diameter at external diffusion can be ignored. A large particle diameter can lead to a high surface temperature, which indicates the external heat transfer resistance. Moreover, the selectivity of reaction may be changed with a variety of particle diameters so that choosing appropriate particle size can enhance the production of butadiene and optimize the reaction process.

Dehydrogenation of n-butane over vanadia catalysts supported on silica gel

VOx/SiO2 catalysts prepared by impregnation method were used for catalytic dehydrogenation of n-butane to butenes and characterized by X-ray diffraction, FT-IR, UV-vis, Raman, and BET measurements. The effects of VOx loading and the reaction temperature on the VOx/SiO2 catalysts and their catalytic performances for the dehydrogenation of n-butane were studied. When the VOx loading was 12% g/gcat and reaction temperature was between 590 ℃ and 600℃, n-butane conversion and butenes yields reached the highest value under H2 flux of 10 ml/min and n-butane flux of 10 ml/min. Product distribution, such as the ratio of 2-butene to 1-butene and the ratio of cis-2-butene to trans-2-butene, was mainly influenced by the reaction temperature.

Self-metathesis of 1-butene to ethene and hexene over molybdenum-based heterogeneous catalysts

A novel route involving self‐metathesis of1‐butene under mild conditions that gave high yields ofethene and hexene was proposed.The results of thermodynamic analysis revealed that the Gibbsenergy of the target Metathesis I reaction(1‐butene?ethene+3‐hexene)was much higher thanthat of the main side Metathesis II(1‐butene+2‐butene?propene+2‐pentene).Suppression of1‐butene double‐bond isomerization was the key step to increase the selectivity for the target olefinin the reaction network.The relationship between the catalytic performance and support nature was investigated in detail.On basis of H2‐TPR,UV‐Vis spectra and HRTEM results,an alumina(Al2O3)support with large surface area was beneficial for the dispersion of molybdenum(Mo)species.Both suitable acidity and sufficient Mo dispersion were important to selectively promote the self‐metathesis reaction of1‐butene.On the optimal6Mo/Al2O3catalyst,1‐butene conversion reached47%and ethene selectivity was as high as42%on the premise of good catalytic stability(80°C,1.0MPa,3h?1).?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Partial amination of cationic exchange resins and its application in the hydration of butene

In this work, the amination of sulfonated polystyrene resin with alkyl secondary amine is investigated. The catalytic activities of the modified resins are determined through the hydration of l-butene. The optimum chain length and the best range of amination rate are determined. It is found that the single-pass conversion of 1 -butene was raised 2% on average, and the relative activity was increased over 30% after modification. A hypothesis about the enhancement of catalytic activities by the inclusion of alkyl chain to wrap up the butene molecule is proposed.

Modeling of Isobutane/Butene Alkylation Using Solid Acid Catalysts in a Fixed Bed Reactor

A dynamic mass transfer model of isobutane/butene alkylation over solid acid catalysts in a fixed bed reactor was established. In the model, a modified equation for the relationship between point activity and effective diffusion coefficient was proposed. It is found that the simulation results fit the experimental data well and the breakthrough time of the bed layer is predicted accurately. By modeling the alkylation process, the time-space distribution of butene and point activity profiles of catalysts can be obtained. Furthermore, the reasons for the deactivation of solid acid catalysts were investigated. It indicates that the main reason for the deactivation of catalysts is the site coverage near the inlet of the reactor, while it is ascribed to the steric effect in the region far away from the inlet.

Alkylation of Isobutane and Butene on BrФnsted-Lewis Conjugated Solid Superacids

A BrOnsted-Lewis (B-L) conjugated solid superacid HPW-SbF_5/SiO_2 wassynthesized by a two-step method. This B-L acid shows high acid strength, high activity, goodselectivity and moderate stability in alkylation of isobutane/butene due to strong interactionbetween the BrOnsted acid and the Lewis acid, as confirmed by the results of IR, NMR and XPS. Undera mild reaction condition (30℃, 15-35xl0~5 Pa), the conversion of butene was maintained at 100% for110 hours on stream and the main products were C_8 and TMP. The results of alkylation conductedunder various operating conditions indicated that the activity was improved by increasing theloading content of HPW and SbF_5. The selectivity of TMP in the products was enhanced when theisobutane/butene ratio in the feedstock was increased. The existence of some intermediates was alsoreported.

Metathesis of 1-butene and 2-butene to propene over Re_2O_7 supported on macro-mesoporous γ-alumina prepared via a dual template method

Macro-mesoporous γ-alumina support（MMA） was prepared by a sol-gel route in aqueous medium using pseudo-boehmite as aluminum source and polystyrene microspheres and Pluronic P123 as hard and soft dual templates,respectively.MMA had a BET specific surface area of about 259 m2 g-1,total pore volume of about 1.61 cm3 g-1,macropore diameter of about 102 nm,and mesopore diameter of about 14 nm.Re2O7/MMA and conventional Re2O7/Al2O3 were prepared by a incipient-wetness impregnation method,and their catalytic performances in the metathesis of 1-butene and 2-butene were tested in a fixed-bed tubular reactor.The result showed that Re2O7/MMA possessed higher activity and far longer working life-span than conventional Re2O7/Al2O3.

Co-feeding with DME:An effective way to enhance gasoline production via low temperature aromatization of LPG

The aromatization of light alkenes in liquefied petroleum gas (LPG) with and without dimethyl ether (DME) addition in the feed was investigated on a modified ZSM-5 catalyst.The results showed that under the given reaction conditions the selectivity of alkenes to high-octane gasoline blending components was markedly enhanced and the formation of propane and butanes was greatly suppressed with the addition of DME.It was also found that the distribution of C5+ components was changed a lot with DME addition into the LPG feed.The formation of branched hydrocarbons (mainly C6 C8 i-paraffin) and multi-methyl substituted aromatics,which are high octane number gasoline blending components,was promoted significantly,while the content of n-paraffins and olefins in C5+ components was decreased obviously,indicating that in addition to the oligomerization,cracking,hydrogen-transfer and dehydrogenation-cyclization of alkenes,the methylation of the formed aromatics and olefins intermediates also plays an important role in determining the product distribution due to the high reactivity of surface methoxy groups formed by DME.And this process,in combination with the syngas-to-methanol/DME technology,provides an alternative way to the production of high-octane gasoline from coal,natural gas or renewable raw materials.

Preparation of mesoporous alumina with large pore size and their supported rhenium oxide catalysts in metathesis of 1-butene and 2-butene to propene

Mesoporous γ-aluminas with large pore size （up to 19 nm, denoted as MAI9） are prepared from dispersed pseudo-boehmite using pluronic P123 as template. It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size （5 nm）. At 60 ℃ and atmospheric pressure with WHSV = 1 h^-1, the similar stable conversions of butene （ca. 55%） for all the 13 wt% Re207/alumina catalysts were obtained near the chemical equilibrium, and the stable working life-spans of Re2OT/MA19 were far longer than that of Re2O7/A1203, being about 70 h and 20 h, respectively.

Modulated hydrocarbon distribution of gasoline deriving from butene conversion in the presence of syngas

With the expansion of butene production capacity,clean and efficient conversion of mixed butene attracts increasing attention.Herein we report direct co-conversion of butene and syngas to highquality gasoline enabled by a bifunctional OXZEO catalyst comprising ZnCrO_(x) oxide and ZSM-5 zeolite.A gasoline selectivity of 71.6% at 98.1% butene conversion and 26.2% CO conversion have been obtained under the reaction conditions of 360℃,3 MPa and 3000 mL g^(-1) h^(-1).The space time yield of gasoline of0.25 g·g^(-1) h^(-1) is achieved.Interestingly,the presence of syngas can effectively facilitate iso-paraffin production while hindering the formation of aromatics.This is attributed to the prohibited hydrogen transfer aromatization process of butene on ZSM-5 in the presence of H2.Fu rthermore,the formation of isomers of gasoline range hydrocarbons is favored because the active intermediates generated from CO/H_(2) activation over ZnCrO_(x) oxide could react with butene over ZSM-5 zeolite.Thus,the product distribution among gasoline range hydrocarbons is modulated with reduced heavy aromatics and improved iso-paraffins,which is desirable for application as fuels.This provides an alternative environmentally friendly technology to utilize still increasing mixed butene.

Ethene and butene oligomerization over isostructural H-SAPO-5 and H-SSZ-24: Kinetics and mechanism

BrФnsted-acidic zeolite and zeotype materials are potential catalysts for the conversion of ethene to higher alkenes. In this study, two materials with AFI structure but different acid strength, H-SAPO-5 and H-SSZ-24, were subject to studies of ethene, cis-2-butene and ethene-butene mixture conversion under conditions where C3-C5 alkene formation is thermodynamically favoured over higher hydrocarbons(673-823 K, 1 atm). Ethene and cis-2-butene partial pressures were varied in the range 9-60 and 0.9-8.1 kPa, respectively, and contact times were varied in the range 3.78-756 and 0.573-76.4 s.μmol H+/cm^3 over H-SAPO-5 and H-SSZ-24, respectively. Less than 1% conversion of ethene and less than 10% conversion of butene was obtained in the range of conditions used for elucidation of rate parameters. The ethene conversion rates were more than an order of magnitude higher over the more acidic H-SSZ-24 than over H-SAPO-5(6.5 vs. 0.3 mmol/mol H+.s at 748 K, Pethene = 33 kP a), with corresponding lower reaction order in ethene(1.5 vs. 2.0 at 673 K) and lower apparent activation energy(52 vs. 80 kJ/mol at 698-823 K). Propene selectivity was substantially higher over H-SSZ-24 than over H-SAPO-5(68% vs. 36% at 0.5% ethene conversion). A similar difference in apparent reaction rates was observed for cis-2-butene conversion over the two catalysts, and for co-feeds of ethene and cis-2-butene. However, the cis-2-butene conversion to C3-C5 alkenes was found to be severely influenced by thermodynamic limitations, impeding a detailed kinetic analysis, and leading predominantly to isobutene formation at the highest temperatures.

DFT Studies on the Isomerization of Butene Double Bond Catalyzed by 1-Butyl-3-methyl-imidazolium in Ionic Liquid

The geometries of reactant, product and transition state of the title reaction have been optimized by using density functional theory (DFT) at the B3LYP/6-31G(d,p) and B3LYP/6- 311++G(d,p) levels. The variations of the bond parameters in the course of reaction were analyzed. The zero point energy corrections were performed by vibrational analysis. The equilibrium states and the transition state were verified according to the number of virtue frequency of geometry. The intrinsic reaction coordinates (IRC) were calculated from the transition state. The calculated results show that the double bond rearrangement of butene catalyzed by 1-butyl-3-methyl-imidazolium cation is a one-step reaction. The forward energy barrier of isomerization from 1-butene to 2- butene is about 193 kJ·mol-1 and the reverse energy barrier about 209 kJ·mol-1 at the B3LYP/6- 31G(d,p) level, which means that the reaction is easy to proceed at or above room temperature.

Catalytic Dehydrogenation of n-Butane over V/SiO_2 Catalyst: A Comparison with Cr/SiO_2 Catalyst

V/SiO2 catalysts compared to Cr/SiO2 catalysts were studied for dehydrogenation of n-butane to butenes. Several methods for characterization of catalysts such as FT-IR, UV-vis and Raman spectroscopies were used. Some differences between two catalysts were showed, including the performances of catalysts, distribution of products and mechanism of reactions. The results showed that prepared catalysts with 12m% of active component loading all demonstrated best conversion of n-butane to butene at a reaction temperature of around 590 ℃. Two different reaction mechanisms were mentioned to well explain why iso-butene was produced on V/SiO2 catalysts but not on Cr/SiO2 catalysts.

A synergistic effect of zinc oxide nanoparticles and polyethylene butene improving the rheology of waxy crude oil

This research examined the use of 75 nm zinc oxide nanoparticles(nano ZnO)and polyethylene butene(PEB)to decrease the viscosity of Nigerian waxy crude oil.The rheology of the crude oil was assessed by measuring the viscosity and shear stress of samples containing PEB at 500,1000,2000,3000,4000 or 5000 ppm and nano ZnO at 1,2,3 or 4 wt% between 10 and 35℃ at shear rates from 1.7 to 1020 s^(-1).Rheological modeling indicated that a power law pseudoplastic model was the best fit for the experimental data,giving a regression coefficient of 0.99.The addition of these inhibitors induced Newtonian fluid behavior in the crude samples such that the shear stress-shear rate relationship plots were linear at all temperatures.The optimum concentrations of the inhibitors in this study were 2000 ppm PEB(providing a 33% viscosity reduction)and 1 wt% nano ZnO(providing a 26% viscosity reduction).A combination of these additives at these concentrations provided a synergistic effect and gave a greater viscosity reduction of 41%.This work demonstrates that a blend of ZnO nanoparticles and PEB can improve the flowability of waxy crude.

Coke precursor as an intermediate during the alkylation of isobutane/butene over a solid superacid

Alkylation of isobutane/butene was conducted on a Br?nsted-Lewis conjugated solid superacid. It is found that some hydrocarbons accumulated on the catalyst surface. These hydrocarbons, as called coke precursor, played an intermediate role at the initial stage of the alkylation before they lead the catalyst to lose its activity. The presence of the intermediate is beneficial to the alkylation between isobutane and butene, while increase the TMP content and TMP/DMH ratio in the products

Kinetic Analysis on Pyrolysis Characteristics of Butene Isomer Fuels with CO_(2) Additions

This article compared the pyrolysis characteristics of butene isomer fuels(n-butene,trans-2-butene,isobutene)under CO_(2) atmosphere.The focus of the study was on the impacts of fuels isomerization and CO_(2) chemistry on the formation of important pyrolysis intermediate products under two temperature conditions(at 1273 K and 1573 K).The results demonstrated that at 1273 K,the concentrations of all products in isobutene pyrolysis were significantly lower than those of the corresponding products formed by the pyrolysis of n-butene and trans-2-butene in the process of fuels pyrolysis.The generation or consumption rate of each species was arranged from high to low as n-butene>trans-2-butene>isobutene.At 1573 K,the chemical effect of CO_(2) could inhibit the consumption of ethylene(C_(2)H_(4)),promote the formation of diacetylene(C_(4)H_(2)),and inhibit the formation of acetylene(C_(2)H_(2))and benzene(A_(1)).During the pyrolysis of n-butene at 1573 K,the chemical effect of CO_(2) was mainly reflected in changes of the consumption paths of C_(2)H_(2) and benzyl(A_(1)CH_(2)).For trans-2-butene pyrolysis at 1573 K,CO_(2) addition could change the main consumption paths of methyl(CH_(3)),which then inhibited C_(2)H_(2) formation.In addition,CO_(2) chemical action significantly changed the consumption paths of C_(4)H_(2) and A_(1) in trans-2-butene pyrolysis at 1573 K.As for isobutene pyrolysis at 1573 K,the chemical effect of CO_(2) significantly inhibited the production of A_(1) by changing the main consumption paths of C_(2)H_(2) and propargyl(C_(3)H_(3)).