Butane Conversion Research Articles

Influence of the fluorine loading level on the skeletal isomerization of 1-butene over fluorine-modified alumina

γ-alumina catalysts modified with different weight loadings of fluorine have been used for skeletal isomerization of 1-butene in order to investigate the effects of the fluorine loading level on the conversion of 1-butene and the selectivity to isobutene formation. Increasing the actual loading of fluorine up to 0.012 wt% led to an increase in conversion of 1-butene over fluorine-modified γ-alumina catalysts, while the high selectivity to isobutene remains almost unchanged. On the other hand, a clear trend of increasing 1-butene conversion with a decreasing selectivity to isobutene is observed for the γ-alumina catalysts with higher loadings of fluorine. An analysis of the results from the thermal analysis, NH3 temperature-programmed desorption, infrared and the 1-butene sorption measurments clearly indicates that the number of strong acid sites in the modified γ-alumina catalysts is greatly enhanced at fluorine loadings higher than 0.012 wt%, leading to the acceleration of 1-butene oligomerization followed by cracking to light hydrocarbons. Therefore, the 1-butene isomerization selectivity from fluorine-modified γ-alumina catalysts can be understood in terms of a competition between the monomolecular and bimolecular reaction pathways, which highly depend on the concentration of strong acid sites.

Direct Conversion of Butane into Isobutene over Various Zeolite-like Materials Loaded with Platinum or Gallium(III) Oxide.

The direct conversion of butane into isobutene was investigated with various zeolite-like materials loaded with platinum or gallium(III) oxide at a comparatively high temperature of 823 K. MFI-type ferrisilicate loaded with platinum produced isobutene from butane in the highest yield (15.1% at 6 h on stream) among all the catalysts investigated in this work.

Skeletal isomerization of 1-butene into isobutene over Mg-ZSM-22 modified by the deposition of silicon alkoxide

Mg-ZSM-22, modified by the deposition of silicon ethoxide, was prepared and investigated as a catalyst for the skeletal isomerization of 1-butene to isobutene in a fixed-bed flow reactor. The prepared catalysts were characterized by XRD, TPD, SEM-EDX, ICP and FT-IR. The deposition of silicon alkoxide on Mg-ZSM-22 led to a decrease in the amount of strong acid sites, confirmed by TPD experiments with ammonia and γ-collidine. The treatment also affected the size of pore opening, as evidenced by constraint index measurement and chemisorption experiment using \(n\)-hexane. As the deposition time increased, the conversion of 1-butene decreased as the result of reduced acidity, while selectivity to isobutene increased. The deposition of silicon alkoxide resulted in the suppression of side reactions and coke deposition, thus enhancing the skeletal isomerization. The modification of Mg-ZSM-22 by deposition of silicon alkoxide was very effective in terms of catalytic stability and coke removal.

Isobutane/2-butene alkylation on fresh and regenerated La-EMT-51 compared with H-EMT. The catalysts selectivity changes at high butene conversion in a slurry reactor

Isobutane/2-butene alkylation was carried out in a semibatch slurry reactor using the hydrogen and lanthanum exchanged form of hexagonal faujasite (EMT, Si Al bulk ratio of 3.5) as catalysts. 51% La exchange in the EMT sample (La-EMT-51) gave a very slight enhanced alkylate activity and yield compared to the parent H-EMT catalyst. The improved activity correlated with a higher relative concentration of strong acid sites as measured by IR. The alkylation experiments were performed with a rather high dilution of butene to be able to investigate the product selectivity for a longer period at high butene conversion. Important changes in the distribution of the trimethylpentanes (TMP) could be observed with time of reaction and were separated into four regions based on catalyst activity. These were the regions of initial activity, high activity, rapid deactivation and complete deactivation. In the high activity period, the fraction of the more spacious and thermodynamically favoured 2,2,4-and 2,2,3-TMP actually increased unlike experiments with fast decay, mainly attributed to kinetic effects such as diffusional limitation in the zeolite pores. The La-EMT-51 was regenerated by burning off coke in air and reused in alkylation under similar conditions as the fresh sample. The catalyst proved to be regenerable with only a slight loss in alkylation activity. Thorough investigations showed that the alkylate selectivity, in particular towards the 2,2,4-TMP among the isooctanes, was improved.

The effects of steam on n-butane oxidation over VPO as studied in a riser reactor

The effects of steam, fed to the riser section of a laboratory recirculating solids reactor, on butane oxidation over a vanadyl pyrophosphate catalyst are reported. Gas red to the riser was either butane in inert or butane co-red with oxygen in inert. The catalyst regenerator-vessel was fluidized with air in all cases. It was observed that steam added to the riser competes for sites required for gas-phase oxygen activation, while catalyst lattice oxygen utilization is not affected. The competition for sites with oxygen causes a decrease in butane conversion and a corresponding increase in selectivity to maleic anhydride. The improvement in selectivity is more pronounced under anaerobic conditions, and an explanation for this result is offered. This study demonstrates the opportunity offered by a recirculating solids reactor to study various aspects of selective oxidation catalysis independent of the complicating effects of simultaneous catalyst reduction and oxidation reactions.

Solid acid catalysts from clays: Acid leached metakaolin as isopropanol dehydration and 1-butene isomerization catalyst

Some samples of acid leached kaolin were prepared by calcination of the natural clay at 873 K to obtain metakaolin followed by treatment at 353 K for 4 h with HCl or H 2SO 4 solutions of various concentrations. Some samples were washed with distilled water after the treatment. The modified clays were studied by chemical analysis, differential thermal analysis (DTA), and X-ray diffraction. The nature and strength of the acid sites was evaluated by FT-IR spectroscopy of adsorbed pyridine. All samples were tested as catalyst for the 1-butene isomerization and isopropanol dehydration. The sulfuric acid treated and washed MKH 2SO 4 1 Mw sample resulted in a very active isopropanol dehydration catalyst. The MKH 2SO 4 1 Mw sample and the two unwashed HCl treated samples MKHCl 2 M and MKHCl 6 M were found very active in the conversion of 1-butene to iso-products, which requires strong Brønsted acid sites. The well known K10 catalyst is less active in both reactions and the MKH 2SO 4 1 Mw catalyst could be proposed as its suitable substitute.

Vanadium-Phosphorus Catalysts Modified with Magnesium, Calcium and Barium

Vanadium-phosphorus catalysts specially modified with promotors can ensure an efficient and selective oxidation of C4 hydrocarbons, even also that of butane to maleic anhydride. The catalysts with incorporated Mg, Ca or Ba ions provide a higher conversion of butane, yield of maleic anhydride, and selectivity for the latter compound than the unmodified catalyst. The conversion of butane and yield of maleic anhydride decrease with increasing basicity of the incorporated modifiers in the order: Mg, Ca, Ba, however, the selectivity of formation of maleic anhydride increases in the opposite order, which is interpreted by the idea that on the modified V-P catalysts the conversion of butane decreases faster than the yield of the anhydride with the natural basicity of the above-mentioned modifiers.

Catalytic Conversion of Butane into Isobutene over .GAMMA.-Alumina-supported Gallium(III) Oxides.

The catalytic conversion of butane into isobutene was investigated using various kinds of metal oxides supported on γ-alumina. Gallium(III) oxide catalyst alone converted butane into isobutene with low selectivity. The activity of gallium(III) oxide catalyst was affected by reduction with hydrogen and by doping with various kinds of metal oxides, but the selectivity was little affected. The XRD patterns and XPS spectra indicated that doping effect was caused by the variation in the oxidation state of gallium(III) oxide due to the formation of a solid solution. Gallium(III)-copper(II) oxide supported on γ-alumina was found to exhibit the highest isobutene yield, as high as 2.3%.

On the role of gallium for the aromatization of lower paraffins with Ga-promoted ZSM-5 catalysts

Aromatization of butane or propane was conducted with a series of ZSM-5 catalysts. A small amount of oxygen in the feed promoted butane conversion to aromatic hydrocarbons on H-ZSM-5. It suggests that if hydrogen atoms on the zeolite surface are removed effectively, H-ZSM-5 exhibits a high selectivity for aromatic hydrocarbons. A hybrid catalyst composed of the physical mixture of Ga/SiO 2 and H-ZSM-5 showed comparable activity and aromatic selectivity to those of the Ga-supported ZSM-5 zeolite, whereas the Ga/SiO 2 itself exhibited little catalytic activity for the paraffin conversion and olefin aromatization. The excellent promotional effect of Ga/SiO 2for aromatics formation was observed only when it was intimately contacted with H-ZSM-5. These results suggest that the supported Ga promotes the zeolite-catalyzed aromatization of lower paraffins by promoting hydrogen desorption via the ‘reverse spillover’ effects.

PRODUCTION OF ETHYLENE AND PROPYLENE FROM ETHANE, PROPANE, AND N-BUTANE MIXED WITH STEAM IN A MICROWAVE-IRRADIATED SILICON-CARBIDE LOADED REACTOR

ABSTRACT We studied the production of ethylene (C2) and propylene (C3) by the decomposition of pure ethane, propane, and n-butane, mixed with steam, in a microwave-irradiated fixed bed reactor packed with silicon carbide. We found that ethylene production was maximized using ethane as the feed, with per pass yields as high as 63% at an ethane conversion level of 74%. With propane and n-butane feeds, more ethylene than propylene was produced, but the propylene amounts were significant. Combined per pass yields of C2 and C3 were 56% at a butane conversion of 99%, and 50% at a propane conversion of 93%. This microwave process appears to be a viable way of producing ethylene and propylene.

Effect of Promoters on the Selective Oxidation ofn-Butane with Vanadium-Phosphorus Oxide Catalysts

The effect of additives on the catalytic performance of vanadium phosphate catalysts is described and discussed in detail for materials prepared using HCl as the reducing agent for V2O5in water or isobutanol solvents. Performance data are compared on the basis of a simplified kinetic model forn-butane oxidation involving a series-consecutive reaction scheme of pseudo first-order reactions (where C4H2O3signifies maleic anhydride):[formula]Using this simplified kinetic scheme it is possible to calculate three factors: (a) the rate constant for butane conversion corrected for surface area (k1+k2)/sa which is a measure of the specific activity; (b) the primary selectivityS0(selectivity extrapolated to zero conversion); and (c) the relative rates of oxidation ofn-butane and maleic anhydridek3/(k1+k2), the latter two factors being a measure of the selectivity of the catalyst. It is proposed that these can be used to determine the relative catalytic performance of promoted catalysts. Hence an improved catalyst would require high specific activity (i.e., a high value of (k1+k2)/sa) together with high maleic anhydride selectivity (i.e., a high value ofS0and a low value ofk3/[k1+k2]). For catalysts prepared by the isobutanol/HCl method the addition of Co is found to promote the specific activity while Mo is found to promote both the specific activity and the selectivity to maleic anhydride at high conversion (>90%). However, for most additives no effect on the specific activity is observed although certain additives are found to act as poisons (Ag, Cs) while others promote the oxidation of maleic anhydride (Cs, Pd, Ru, Zn). The specific activity of catalysts prepared using water/HCl with an additional water-washing step was found to be promoted by the addition of a range of transition metal additives and the effect is described in detail with Co promoted catalysts. The mechanism of the promotion is discussed in terms of structural and electronic effects.

Conversion of various hydrocarbons over supported Pd during simulated cold-start conditions

This paper reports measured oxidation rates of synthetic automotive exhausts over an aged palladium (Pd) catalyst during simulated cold-start conditions. Surface reaction rates and species concentration profiles at points along a catalyst of Pd on Al 2O 3 with ceria are reported for A/F ratios from 10 to 16. The synthetic exhaust streams contain levels of carbon monoxide and hydrocarbons like those in auto exhausts during a cold-start, and include representative amounts of CO, CO 2, O 2, H 2, NO, SO 2 and H 2O in N 2. The hydrocarbon compounds are represented by 1-butene as a surrogate for the most reactive hydrocarbons, and propane and methane as surrogates for species with intermediate and very low reactivities, respectively. The data reveal important features of multicomponent oxidation under fuel-rich conditions. First, as expected, hydrogen is the most reactive species, reaching diffusion-limited oxidation at the inlet of the reactor for a temperature of 320°C, even for exhaust streams with 500 ppm NO. Second, the oxidation of carbon monoxide and 1-butene over an aged palladium catalyst follows similar conversion histories for excessively fuel rich and near-stoichiometric conditions. Third, the hydrocarbons oxidize simultaneously, but at rates that follow the ranking of reactivities seen in tests with individual fuel species. Whereas the magnitude of the 1-butene conversion rate is much lower than carbon monoxide's because of its much lower inlet level, this hydrocarbon is eliminated on nearly the same time scale as carbon monoxide. But propane and methane are converted on much longer time scales. Fourth, the oxidation of all the fuel species is inhibited by the presence of nitric oxide in the feedstream, especially propane.

Modification of the ZSM-5 zeolite using Ga and Zn impregnated silica fibre for the conversion ofn-butane into aromatic hydrocarbons

The modification of ZSM-5 by metals is generally performed by methods such as ion-exchange, impregnation, chemical vapour deposition and physical mixing. In this work a silica fibre pre-impregnated with Ga and Zn has been used during the synthesis by which Ga-ZSM-5 and Zn-ZSM-5 zeolite catalysts were prepared. The synthesised zeolite catalysts were characterised by an X-ray powder diffractometer, a scanning electron microscope, an X-ray fluorescence spectrometer, a solid state NMR, an energy dispersive X-ray analyser and a sorptomatic 1900. The acidity of the catalysts was determined by temperature programmed desorption of ammonia. The reaction ofn-butane to aromatic hydrocarbons was carried out over the H-ZSM-5, Ga-ZSM-5 and Zn-ZSM-5 catalysts and it was observed that these catalysts exhibited high catalytic activity in the conversion ofn-butane and formation of aromatic hydrocarbons. The effect of temperature on the conversion ofn-butane and formation of aromatic hydrocarbons was studied at 713, 743, 773 and 803 K with a space velocity (WHSV) of 2.5 h−1. The effect of time on stream on then- butane conversion and formation of aromatic hydrocarbons over the synthesised catalysts was investigated at 803 K for 4.5 h.

Kinetic Study and Modelization of n-Butenes Oligomerization over H-Mordenite

n-Butenes have been oligomerized at temperatures lower than 450 K in the liquid phase over H-mordenite in a continuously stirred tank reactor. The composition and molecular weight of the products are very dependent on reaction temperature. Products are essentially dimers, trimers, and tetramers. The complex reactions were modeled by taking into account only the type of carbonium ion; the initial rates showed that the oligomerization reactions followed a Rideal mechanism. The dimerization rate constants of butenes and oligomers decrease with increasing number of carbon atoms of the olefins, while the adsorption constants increase with the hydrocarbon chain length. A model for the conversion of butenes to liquid products over H-mordenite is proposed. This model fits the experimental data rather well, although some simplifying approximations were made to describe these complex reactions.

Isomerization of 1-butene on supported and unsupported metal-oxygen cluster compounds (heteropoly oxometalates)

On 12-tungstophosphoric acid (HPW) supported on silica, 1-butene is isomerized to cis- and trans-2-butene at 100°C and higher while a temperature of 150°C is required to form isobutene. While the conversion remains at 80–90% regardless of the loading of HPW on the support and the reaction temperature, the selectivity to isobutene reaches a maximum of 33% at a loading of 23% HPW/SiO2 and 300–350°C. Small quantities of Cn (n = 3,..., 8) species are also formed. These results together with those from ammonia poisoning, temperature-programmed desorption of ammonia,1H MAS NMR and infrared spectroscopy show that HPW/SiO2 possesses sites of strength as high as or higher than those on HZSM-5, that such sites are required for the skeletal isomerization process and that both mono- and bimolecular processes are occurring on the catalyst. The absence of dependence of conversion of 1-butene and selectivities to cis- and trans-2-butene on loading and reaction temperature can best be rationalized on the basis of a rapid attainment of an equilibrium between the aforementioned three species and sec-butyl carbenium ions from which pool the energy barrier to the primary butyl carbenium and hence to isobutene is surmounted, given appropriate conditions.

A Comparison Between the Structural and Catalytic Properties of Supported W2C, WC and WC1−x

ABSTRACTA series of γ-Al2O3 and SiO2 supported tungsten carbides was synthesized by the temperature programmed reaction of supported tungstates with CH4/H2 mixtures. The three known phases, W2C, WC and WC1−x, were evaluated as butane dehydrogenation catalysts. The microstructure and composition of the supported carbides depended on the loading and final synthesis temperature. The low and medium loaded materials were x-ray amorphous suggesting highly dispersed carbide domains on the support. The high loaded materials possessed small crystallites of W2C, WC or WC1-x. The supported carbides were as active as a commercial dehydrogenation catalyst with comparable selectivities in several cases. The butane conversion activity decreased in the following order: W2C > WC > WC1-x. The dehydrogenation selectivity decreased as the activity increased. The results suggest that there were two different types of sites, those catalyzing the selective dehydrogenation of butane and those capable of butane hydrogenolysis. The activity of these latter sites declined significantly with time on stream. We believe the hydrogenolysis activity was due to acid sites on the supported carbides.

Selective oxidation of carbon monoxide in the presence of butane and maleic anhydride

The selective oxidation of carbon monoxide in the presence of butane and maleic anhydride has been studied over platinum- and palladium-containing zeolites as well as palladium-on-silica (Pd/SiO 2 catalysts. The results show that although a zeolite support is needed in many systems to effect a kinetic control to improve selectivity, thermodynamic control using Pd(∼2–4ppm) SiO 2 is sufficient to give the desired selectivities in this system. In addition, a palladium-containing vanadium-phosphate catalyst was prepared that showed complete oxidation of carbon monoxide, conversion of butane to maleic anhydride, and no observable decomposition of the maleic anhydride.

Conversion of 1-butene over WO 3-TiO 2 Catalysts

The conversion of pure 1-butene over WO 3-TiO 2 Catalysts has been studied in a flow microreactor at 693 K and at 723 K. For comparison, experiments have also been carried out on the bare TiO 2 support. Significant activity in the skeletal isomerization has been found, together with double bond migration, cis-trans isomerization, hydrogenation and cracking. By increasing time-on-stream the conversion of 1-butene is increasingly limited due to the formation of carbon residues on the Catalyst surfaces. Working with τ = 6.44 h at 723 K (9.33% WO 3 by weight), the selectivity to products different from n-butenes decreases from nearly 75% after 15 min time-on-stream to less than 6% after 3 h. Initial selectivity to isobutene also decreases from nearly 14% to less than 2% after 3 h. A Fourier transform infrared study suggests that Catalyst deactivation is due to the oligomerization of butenes on the surface Bronsted acid sites. Carbon residues formed are largely constituted of aromatized butene polymers anchored to the surface through car☐ylate and alcoholate groups. Burning of the carbon residue occurs at 623–723 K and restores Catalytic activity. The activity and the deactivation of the bare commercial TiO 2 support is attributed to the weaker Brønsted acidity arising from silica impurities observed on the surface.

Selective oxidation of butane on phosphorus-modified silica supported vanadia catalysts

Triethylphosphate impregnation of 2.8 wt% V/SiO2 and subsequent controlled calcination produced phosphorus-modified supported vanadium catalysts. Phosphorus modification enhanced the yield of maleic anhydride in the partial oxidation of butane. Varying the phosphorus to vanadium atomic ratio from 0 to 2.8 increased the selectivity to maleic anhydride from 0 to approximately 48%. The selectivity was nearly constant up to 20% butane conversion and for different O2/C4H10 ratios. The Raman spectra of the phosphorus-modified samples had bands at 1040 and 930 cm−1, and broad unresolved bands between 580 and 540 cm−1. It was concluded that the active phases in these samples were α-VOPO4.

Catalytic skeletal isomerization of linear butenes to isobutene

The increased demand for isobutene, used for the production of the octane-enhancer methyl tert-butyl ether, has generated tremendous interest in the catalytic conversion of the linear butenes to isobutene. In this review we survey the progress made since the late 1970s in implementing the catalytic skeletal isomerization reaction of these linear alkenes. Halogenated catalysts, especially those based on alumina, and prepared using a variety of compounds of fluorine, chlorine or bromine, have been shown to exhibit both high conversions and selectivities for the reaction, resulting in high yields of isobutene, when water is added to the feed stream. Elution of the halogen from the catalyst leads to the loss of catalytic activity and necessitates the continuous or discontinuous addition of the halogen compound. As a consequence, environmental and other considerations are most likely to weigh against the industrial usage of these catalysts. Another class of catalysts exhibiting high activities and selectivities, again in the presence of water, are the silicated aluminas. No information is, however, available on their long-term stability. Even alumina on its own displays high activity and selectivity, provided water is co-fed with the hydrocarbon stream. More recent results obtained over other types of catalysts such as zeolites and molecular sieves are also presented. Most promising are the results obtained with the zeolite ferrierite which gives high yields of the branched isomer in the absence of any other additive or diluent. The catalyst also appears to be fairly stable showing no decrease in the yield of isobutene after 14 days on-stream. The high yields of isobutene can be ascribed to the small channel diameters which prevent the extensive dimerization or oligomerization of the linear butenes or of the product isobutene. Plans for the first large-scale demonstration plant to produce isobutene from n-butenes using ferrierite as catalyst have already been announced in the United States.