Isobutene Yield Research Articles

Laboratory evaluation of FCC commercial catalysts: Analysis of products of industrial importance

The results of the conversion of a VGO over six equilibrium commercial FCC catalysts with different formulations in a batch CREC Riser Simulator laboratory reactor at 500 and 550 °C, catalyst to oil ratio 6.1 and reaction times from 3 to 30 s, were analyzed. It was possible to define the main catalyst characteristics in terms of various evaluation items, such as activity, gasoline yield and quality, LPG yield and coke yield, or the yields of particular compounds like, e.g., isobutane. Important differences in activity between catalysts were not observed, but catalyst properties reflected clearly as significant differences in gasoline, LPG or coke selectivities. Particularly, catalyst's hydrogen transfer properties impacted on gasoline composition and isobutane yield. The results showed that the CREC Riser Simulator reactor is an important tool for the evaluation of both commercial catalysts and feedstocks and process conditions.

Linear butene skeletal isomerization over boron-promoted ferrierite

Boron-promoted potassium-ferrierite catalysts were prepared following the wet impregnation technique. Both boron concentration and pH of impregnating solution were changed. Catalytic behavior was measured during the butene skeletal isomerization. H + ion exchange induced by impregnation medium and presence of boron species promote catalytic activity, isobutene yield, and catalyst stability. The catalyst impregnated with 0.01 M solution at pH 0.8 showed the best performance. The effect of temperature, butene partial pressure, and contact time was evaluated. The high stability of this catalyst is an important goal. Large conversion and high isobutene yield were reached in the 400–525 °C range; the largest yield (38%) was obtained at 475 °C. Both linear butene conversion and isobutene yield increased by increasing contact time or by decreasing the butene partial pressure. Isobutene yield remained practically constant during 24 h of reaction. Carbonaceous deposit formed during reaction was characterized by temperature-programmed oxidation and by FTIR. Coke amount at different reaction conditions was lower than 0.7%. Active catalysts displayed the maximum of the combustion peak between 560 and 608 °C, shifting to higher temperature when reaction temperature increases. After 24 h of reaction at 450 °C, the carbonaceous deposit only reaches 0.9%, being it 6.0% after 120 h.

Skeletal Isomerization of Linear Butenes on Boron Promoted Ferrierite: Effect of the Catalyst Preparation Technique

Potassium and acid ferrierites were impregnated with boron species by wet and incipient wetness techniques. All samples display a medium-intensity band at 3,450–3,470 cm−1 associated to Si−OH···O groups corresponding to boron-containing units. The 1,398–1,404 cm−1 band assigned to the B–O stretching in BO3 units does not appear on boron–potassium–ferrierite prepared by wet impregnation. Catalytic performance during the linear butene skeletal isomerization was measured. At 300 °C, boron impregnated by incipient wetness technique on acid ferrierite reduces both linear butene conversion at a short time and isobutene yield in all time range. Boron–potassium–ferrierite prepared by wet impregnation has a suitable acidity to promote isobutene production. At 450 °C, this sample shows the best performance, being the isobutene yield 1.7 times higher than the acid-ferrierite one and reaching the highest isobutene selectivity (92%). This performance is maintained with time. Both isobutene yield and by-product distribution are strongly affected by temperature; dimer intermediates are formed. Finally, both kinds of hydroxyl groups corresponding to 3,466 and 3,635 cm−1 bands influence the isobutene production whereas BO3 sites are inactive for this reaction.

Factors Influencing the Isobutane Yield during the Conversion of Vacuum Gas Oil (VGO) under Fluidized Catalytic Cracking (FCC) Conditions

Fil: Passamonti, Francisco Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Investigaciones en Catalisis y Petroquimica Ing. Jose Miguel Parera. Universidad Nacional del Litoral. Instituto de Investigaciones en Catalisis y Petroquimica Ing. Jose Miguel Parera; Argentina

XPS analysis of several zeolitic and clay-based nanoporous materials for C4 hydrocarbon conversions

The isomerisation of n-butene to iso-butene is a crucial industrial process for the production of high-octane gasoline. The attention of researchers in industry and academia has been oriented toward catalytic process which involve metal added zeolites and mesoporous molecular sieves. The structure, pore size, shape selectivity, acid properties and an derivatisation with metal ions are important parameters influencing the conversion of but-1-ene and the yield of iso-butene. A particularly important function is performed by the metal inserted in the mesoporous material framework and, to date, their role in the catalytic process is not completely clear. Several catalysts (Cu–P, Co–Mo/MCM-36, Mg–HMO, Ni–Ni/AlSA) have been investigated before and after the catalytic process. X-ray Photoelectron Spectroscopy (XPS) has been employed to study the chemical properties of these catalysts. Auger parameter values of some metals, XPS peak-shapes of the metals, binding energy values of the constituent elements have been used to study the effects of the catalytic process on the catalysts. Catalytic investigations have shown that Ni–Ni/AlSA exhibit the highest catalytic activity in comparison with other tested catalysts. When butanes were employed, the dimerisation occurred at T < 450 °C, where cracking is not observed. For Cu–P and Ni–Ni/AlSA there is reduction to Cu + and to Ni 0 as expected. Oxidation states of Co and Mo in Co/Mo-MCM-36 samples and of Mg in Mg–HMO samples were not affected by catalysis. Moreover, an anomalous correlation of the changes in ΔBE (difference of binding energy values of Si 2p and Al 2p) and Si/Al atomic ratio were observed for Ni–Ni/AlSA samples.

Kinetics and mechanism of the oxidative dehydrogenation of isobutane on cobalt, nickel, and manganese molybdates

The kinetics of oxidative dehydrogenation of isobutane in the presence of atmospheric oxygen on manganese molybdate has been studied. The experiments have been carried out in a circulation flow reactor at 470–530°C. The form of kinetic equations and the mechanism of the formation of isobutene, carbon oxides, and cracking products on manganese molybdate are similar to those found previously for the same reaction on cobalt and nickel molybdates. The highest yields of isobutene and propene (isobutane cracking products) are achieved on Co0.95MoO4. The mechanism of the process has been investigated by the unsteady-state response method. Manganese molybdate contains the largest amount of reactive oxygen, whereas nickel molybdate contains the smallest amount of reactive oxygen. The earlier conclusion that molybdate lattice oxygen and chemisorbed oxygen play the main role in the formation of iso-C4H8 and in deep oxidation processes, respectively, is confirmed.

Bimetallic PtSn/C catalysts promoted by ceria: Application in the nonoxidative dehydrogenation of isobutane

A series of bimetallic platinum–tin catalysts supported on CeO 2/C were prepared and tested in the nonoxidative catalytic dehydrogenation of isobutane. Pt–Sn/CeO 2/C catalysts with varying Sn content (Sn/Pt = 0, 0.25, 0.5, and 0.75) were prepared using a co-impregnation method and chlorinated metal precursors. They were characterized by XPS and by CO and ethylene adsorption microcalorimetry at room temperature after in situ reduction treatments. It was found that the presence of cerium in bimetallic catalysts inhibited reduction of tin species, whereas tin facilitated reduction of cerium(IV) to cerium(III). Reduction at 773 K caused a strong decrease in CO saturation coverage for all catalysts studied. For the bimetallic catalysts, a strong interaction between tin and platinum produced significant changes in the initial heat of CO adsorption. The presence of cerium caused a strong decrease in the heat of ethylene adsorption on platinum in catalysts reduced at high temperature. The monometallic Pt catalyst undergoes a fast deactivation with time on stream in the isobutane dehydrogenation reaction. The addition of tin strongly suppresses the deactivation process. It was found that cerium-containing catalysts showed higher isobutene yields compared with their corresponding cerium-free counterparts. The bimetallic catalyst with Sn/Pt = 0.5 showed the best isobutene yield, and it was studied further. This optimized catalyst demonstrated good deactivation behaviour (comparable with the best catalysts reported in the literature). Furthermore, oxidation treatment at a mild temperature (573 K) allowed recovery of nearly all of its catalytic properties.

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

The activity of the vanadium magnesium binary oxides supported on Cact, 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.

Oxidative dehydrogenation of isobutane over activated carbon catalysts

In past work, we reported on the textural and chemical modifications induced by treating an activated carbon under nitrous oxide, oxygen and hydrogen. In this work, we are reporting on the testing of surface modified activated carbons in the oxidative dehydrogenation of isobutane (ODHI). The results show that the different treatments lead to a given catalytic performance associated with the degree of oxidation. At 648 K, isobutene yields are higher in the initial stages for the activated carbons with the highest amounts of carbonyl/quinone groups on the surface, which are considered the active sites for this reaction, and the isobutene yields are lower for the catalysts with lower concentrations of these groups. As the reaction proceeds, the reactant mixture (isobutene–oxygen and argon as carrier gas) is able to introduce active sites onto the carbon surface to the point where they are stabilized for the case of treatment in H 2 and without pretreatment. For the other treatments, N 2O and oxygen, the active sites are rearranged and stabilized after a while. It is observed that there is a tendency towards a similar CO/CO 2 relationship as measured by TPD, corresponding to a yield of about 7% after 5 h of reaction.

Modeling the Dehydration of tert-Butyl Alcohol and Avoidance of the Formation of Oligomers

To model the industrial relevant dehydration process of tert-butyl alcohol in sulfuric acid, a new mechanistic reaction scheme is applied that accounts for a parallel reaction path via di-tert-butyl ether (DTBE). Based on the quasi-steady-state approximation concerning intermediates, a mathematical model is developed that incorporates the acidity of the solvent. Model validation is performed by means of experimental data obtained from stationary continuously stirred tank reactor (CSTR) measurements at different temperatures under reaction conditions that exclude the formation of oligomers. It is shown how numerical simulations, combining this mathematical model with experimental correlations, allow for maximization of isobutene yield in a batch reactor in the regime where the formation of oligomers is avoided.

Selectivity changes during organic photooxidation on TiO 2: Role of O 2 pressure and organic coverage

The selectivity of trimethyl acetate (TMA) photodecomposition on TiO 2(110) as a function of O 2 pressure and TMA coverage was probed at room temperature (RT) using isothermal mass spectrometry (ISOMS) and scanning tunneling microscopy (STM). The selectivity of TMA photodecomposition on TiO 2(110) is sensitive to the initial TMA coverage and O 2 pressure. TMA bridge-bonds to the surface via the carboxylate end of the molecule in a manner consistent with the binding of other carboxylate species (e.g., formate and acetate) on TiO 2 surfaces. Under all conditions, photodecomposition of TMA was initiated via hole reaction with the electron in carboxylate's π system, resulting in opening of the O C O bond angle and formation of CO 2 and a t-butyl radical by cleavage of the C C bond between these groups. The CO 2 product desorbs from the surface at RT, but the t-butyl radical has several options for thermal chemistry. In ultrahigh vacuum (UHV), where the O 2 partial pressure is < 1 × 10 −10 Torr , the TMA photodecomposition results in a near 1:1 yield of isobutene ( i-C 4H 8) and isobutane ( i-C 4H 10) from surface chemistry of the t-butyl radicals. STM results show that the reaction occurs fairly homogeneously across the TiO 2(110) surface. In the presence of O 2, the photodecomposition selectivity switches from initially i-C 4H 8 to a mixture of i-C 4H 8 and i-C 4H 10 and then back to predominately i-C 4H 8. The latter selectivity change occurs at the point at which void regions form and grow in the TMA overlayer. At this point, the photodecomposition rate accelerates and the reaction occurs preferentially at the interface between the TMA-rich and TMA-void regions on the surface. These results illustrate both the changing dynamics of a typical photooxidation reaction on TiO 2 and also how factors such as O 2 pressure and TMA coverage impact the photooxidation reaction selectivity. We also present results that suggest the rate of photodecomposition of monodentate carboxylates is greater than that of bidentate (bridging) carboxylates. This implies that the structural arrangement of Ti cation sites on the surface is an important issue that influences photocatalytic rates on TiO 2.

High-productivity dehydrogenation of light alkanes in a microchannel reactor

Improved heat transfer in an Inconel microchannel reactor leads to higher conversions (up to 40%) of isobutane and higher yields (27–34%) of isobutene in a catalysed dehydrogenation reaction compared with a conventional adiabatic fixed-bed reactor (up to 29% conversion; 19–24% yield), with improved productivity at significantly lower residence times.

The catalytic dehydrogenation of isobutane to isobutene in a palladium /silver composite membrane reactor

Isobutane dehydrogenation to isobutene has been investigated experimentally and by modelling for a membrane reactor and a fixed bed reactor under similar operating conditions using a Pt/alumina catalyst. Reaction kinetics were obtained from experiments in the fixed bed reactor. Comparative tests showed that the membrane reactor achieved much higher yields of isobutene and also gave higher selectivities, with less by-products than the fixed bed system. Using the kinetic data, the simulations gave good agreement with the fixed bed experiments, but over predicted the yields from the membrane reactor. Analysis of these results indicated that in the membrane reactor the hydrogen permeability of the membrane was much greater than its hydrogen transfer requirement and that the reaction rate was the determining factor for isobutene yield.

A highly stable and selective Pt-modified mordenite catalyst for the skeletal isomerization of n-butane

The aim of this work is to investigate the skeletal isomerization of n-butane to isobutane over Pt-modified mordenite zeolite catalysts and proton form mordenite with different SiO 2/Al 2O 3 ratios. The 2-wt% Pt-H-MOR-20 and 2-wt% Pt-H-MOR-12.8 catalysts were synthesized by impregnation method, while H-MOR-12.8 and H-MOR-20 were obtained by calcinations of their ammonium-form counterparts. The influence of reaction temperature, carrier gas and dilution of the feed stream on the conversion of n-butane and yield of isobutane during time-on-stream has been studied. The Pt-modified mordenite catalysts have been characterized using XRD, scanning electron microscopy (SEM), nitrogen adsorption, CO chemisorption and FTIR of adsorbed pyridine. Pt-H-MOR-12.8 exhibited the highest yield and selectivity to isobutane and it was the most stable towards catalyst deactivation. Typically, an excess of propane with respect to pentanes was formed and the selectivity to pentanes remained constant for the different Pt-H-MOR and conditions tested. Selectivity to propane was inversely dependent on the H 2 concentration in the feed and the SiO 2/Al 2O 3 ratio.

Approaching Equilibrium Conversion in the Isomerization of Supercritical n-Butane by Using Sulfated Zirconia Catalysts Promoted with Iron

The application of supercritical temperatures and pressures in the isomerization of n-butane is a means to avoid deactivation of the catalyst by coke and to enhance the throughputs. However, catalysts consisting of unpromoted sulfated zirconia are not sufficiently active to attain equilibrium conversions of n-butane. Through impregnation of iron salts on sulfated zirconium hydroxide, we produced catalysts containing 1 wt % iron with strongly enhanced activity. In pelletized form, these catalysts enabled the processing of n-butane at conversions close to thermodynamic equilibrium. At the preferred reaction temperature of 488 K, the yield of isobutane amounted to 43%. Catalysts manufactured by extrusion were considerably less active.

Oxidative dehydrogenation of isobutane on chromium oxide-based catalyst

Isobutane oxidative dehydrogenation offers a prospect of cheaper and environment friendly route to isobutene. The reaction has been studied at 250 °C, 1 atm and feed flow rate of 75 cm 3/min over supported chromium oxide-based catalysts. Effects of various supports (Al 2O 3, MgO, TiO 2 and SiO 2), catalyst precursors (K 2Cr 2O 7, CaCr 2O 7·H 2O, CrO 3, CrK(SO 4) 2·12H 2O and Cr(NO 3) 3·9H 2O) and binary mixed metal oxide catalysts of the form Cr-M-oxide/γ-Al 2O 3 (where M is V, Ni, Co, Mo, W, Ho, La, Li or Bi) were investigated. The supported catalysts are ranked (based on isobutene yields at 250 °C) as; Cr-Mg-O (3.4%) = Cr-Si-O (3.4%) < Cr-Ti-O (4.5%) < Cr-Al-O (6.0%). The performances of the catalysts showed strong dependence on the precursor used. The 10 wt.% Cr-Al-O prepared using K 2Cr 2O 7 and CrK(SO 4) 2·2H 2O exhibited the lowest isobutene yields of 0.14 and 0.3%, respectively. Partial substitution of chromium ions with nickel or tungsten exhibited minor increase in selectivity to isobutene of about 6% at comparable isobutane conversions. Substitution with other metals show similar or inferior performance compared with the base catalyst. Thus, showing that chromium oxide-based catalysts are active for the reaction and their performance could be improved by appropriate choice of active component precursor, support and additives.

Combinatorial discovery of new catalysts for the selective oxidation of isobutane

By means of high-throughput synthesis and screening techniques a search of new mixed metal oxide catalysts for the selective oxidation of isobutane to methacrolein has been conducted. In a first library design the oxide precursors of nine selected elements (V, Fe, Mo, Cr, Ta, Nb, Mn, Sb and Bi) have been combined by using a sol–gel recipe and the catalysts obtained have been screened for the dehydrogenation and selective/total oxidation properties. Afterwards, the most interesting combinations were studied in more detail by screening the complete triangular composition spreads. Optimal performance towards isobutene and methacrolein yield was found for Mo 10V 10Sb 80O x . Finally, the best catalysts were up-scaled to gram scale and tested in a continuous flow reactor unit equipped with four parallel reactors. The improved performance of the Mo 10V 10Sb 80O x catalyst compared to the other catalyst formulations was consistent with the measurements made in the high-throughput MS-screening setup.

Deactivation Studies During Catalytic Cracking of C8Aliphatic Hydrocarbons over Ultrastable Y-Zeolite. Conversion and Product Yield Profiles with Time Onstream

The deactivation of an ultrastable Y-zeolite during cracking of n-octane, isooctane and 1-octene was studied in a fixed-bed reactor. The relative reactivities of the three reactants in increasing order were n-octane < isooctane < 1-octene. At high residence times, complete conversion was achieved followed by a relatively slow decline that, in fact, presented a falsified deactivation picture. On the other hand, a surprising olefin yield increase with time onstream was observed, i.e., isobutene during isooctane cracking and octene isomers in the case of 1-octene. The isobutene yield increase was assigned to preferential deactivation of strong acid sites that allowed primary products to desorb into the gas phase, increasing their apparent yield rather than undergo secondary reactions. Similarly, 1-octene isomers showed a yield increase with time onstream due to stronger deactivation of cracking reactions than isomerization.

Improvement of catalytic functions of binary V-Sb oxide catalysts for oxidative conversion of isobutane to isobutene

Dehydrogenation of isobutane in the presence of oxygen—industrially prospective process for isobutene production—has been studied over vanadium-antimony oxide catalysts. Their catalytic behaviour was compared with the sample characterisation data by specific surface area (SSA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Substantial improvement of the catalytic performance has been achieved as a result of proper spreading of active V-containing component onto an appropriate support. Optimisation of the composition and loading of the active component, the chemical nature and morphology of support material, as well as the preparation procedure allowed to further improve the yield of isobutene. Microspheric γ-alumina with moderate SSA and large average pore diameter was found to be the best support for the efficient catalyst. The loading of vanadia corresponding to 1–1.5 formal monolayer coverage and doping with antimony (V-to-Sb atomic ratio 8.8) were found to be optimal. The use of “citrate” preparation technique showed an advantage in comparison with ordinary impregnation method, giving the catalyst with well dispersed (amorphous) and homogeneously distributed supported V-Sb-O-component. The optimised catalyst demonstrated improved stability, high activity and olefin selectivity (70% at 36% conversion), producing yields of isobutene (up to 26% per pass) among the best reported in the literature.

Dealumination of ferrierite by ammonium hexafluorosilicate treatment: characterization and testing in the skeletal isomerization of n-butene

Ferrierite zeolite has been treated with ammonium hexafluorosilicate (AHFS). The prepared catalysts were characterized by XRD, atomic absorption spectroscopy, ammonia TPD, FT-IR, SEM, BET/pore size distribution and pyridine chemisorption. Their catalytic activity has been evaluated in the skeletal isomerization of n-butene. Ammonium hexafluorosilicate treatment of ferrierite zeolite leads to a little but progressive framework dealumination, although bulk Si/Al ratio determined by chemical analysis only increases slightly, indicating that most of the extracted aluminum atoms remain in the pores. Higher fluorosilicate amounts decrease crystallinity, micropore area, and volume. Ammonium hexafluorosilicate treatment remove mainly ferrierite external acid sites with a marked improvement in the number of medium strength acid sites. The higher dealumination degree the lower isobutene yield, however, the presence of extraframework aluminum species, medium strength acid sites and lower acid site density reduces the conversion of n-butene through consecutive reactions like n-butene dimerization followed by cracking and hydrogen transfer. These reactions are responsible for the formation of by-products and hence dealuminated catalysts show isobutene selectivity values as high as ferrierite zeolite.