Skeletal Isomerization Of 1-butene Research Articles

Skeletal isomerization of 1-butene: A thorough kinetic study over ZSM-22

Zeolites and mesoporous materials are important catalysts not only for oil-refining processes, but nowadays even for the production of fine and specialty chemicals. Few thorough studies on the important factors in chemical reaction engineering: kinetics, deactivation, mass and heat transfer and flow modeling have been carried out. In the present work, a comprehensive analysis of 1-butene skeletal isomerization over ZSM-22 was conducted. Kinetics of the main product formation, i.e. isobutene, as well as side-products, i.e. propene and pentene, was modeled using Langmuir–Hinshelwood approach. The axial-dispersion model was used for describing the reactor. The behavior of the main products and byproducts was successfully explained. Uniform coking was applied to describe the deactivation behavior of the reaction and the formation of byproducts.

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.

Comparison of butene skeletal isomerization selectivity over a pair of commercial H-ferrierites

The conversion of butenes to isobutene was compared at atmospheric pressure and 250–350 °C over two commercial H-ferrierite catalysts having different chemical compositions, crystal morphologies, and diffusional resistance (DR). The Si/Al ratio affects the number of Brönsted acidic (BA) sites but not their intrinsic acid strength. These equally strong BA sites are thought to be active sites for the skeletal isomerization. Catalyst selectivity seems mainly depend on the diffusional resistance of micropores and the reaction conditions. The DR is affected by the presence of extra-framework species in the 10MR channels of the zeolite which might include charge compensating cations, Al-containing species, and coke. To see their effect on the selectivity for i-butene versus oligomerization products we tested zeolites with basic exchanged cations and removed Al-containing debris from the transport channels with EDTA solutions. A proper balance of the extra-framework species and the reaction conditions allowed nearly 100% isobutene selectivity at relatively high branched butene yield.

Comparative catalytic studies on the conversion of 1-butene and n-butane to isobutene over MCM-22 and ITQ-2 zeolites

The catalytic properties of H-MCM-22 and Pt-MCM-22 for the skeletal isomerization of 1-butene and the dehydroisomerization of n-butane were compared with those obtained from their delaminated derivatives, H-ITQ-2 and Pt-ITQ-2. The overall results of our study strongly suggests that the desired 1-butene and n-butane conversions to isobutene in steady state occur mainly near the pore mouth inlets of the sinusoidal 10-ring channels retained in both of MCM-22 and ITQ-2 and inside this intralayer void space, respectively, which may be attributed to the unique geometric constraints imposed by the two-dimensionality of the pore system with a suitable degree of ellipticity of 10-ring channels. Whereas coke formation on the sinusoidal channels during the 1-butene skeletal isomerization can occur in such a way as to make most of the intrachannel Brønsted acid sites less available for nonselective dimerization-cracking reactions, it appears that the presence of H 2 in the n-butane dehydroisomerization stream would prevent extensive coke buildup, thereby allowing pore diffusion of reactants and products even in steady state.

Mechanism of butane skeletal isomerization on sulfated zirconia

A kinetic model of the skeletal isomerization of n-butane and isobutane on sulfated zirconia in the absence of Pt is presented. The skeletal isomerization of butane on sulfated zirconia has been shown to be initiated by oxidative dehydrogenation of the alkane. This is followed by the formation of alkoxy groups/carbenium ions at the surface, induced by strong Brønsted acid sites. The isomerization of the sec-butyl carbenium ion occurs mono-molecularly, as suggested by the 100% selectivity for isomerization extrapolated to zero conversion. With increasing conversion, the selectivity decreased linearly, leading to propane and pentanes up to 40% of conversion. The lower selectivity for isomerization is qualitatively explained by reactions of isobutene present in small concentrations in the reactor at higher conversions. Transient experiments show conclusively that the isomerization of the carbenium ion and not the hydride transfer from the alkane to the carbenium ion is the rate-determining step.

Physico-chemical and catalytic properties of Zr- and Cu–Zr ion-exchanged H-MCM-41

H-MCM-41 catalyst ion-exchanged by Zr and/or Cu-cations were synthesized and characterized by XPS, 27Al- and 29Si-MAS-NMR, FTIR of pyridine adsorption, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and direct current plasma atomic emission spectrometry. The catalysts were evaluated towards 1-butene skeletal isomerization after pre-treatment with hydrogen or synthetic air. The dispersion of metals after ion-exchange was reasonably good, as revealed by LA-ICP-MS. Binding energies observed by XPS indicated that after reduction or oxidation pre-treatments copper is mainly present as Cu2+, except in case of reduced Cu-H-MCM-41. Pre-treatment had no influence on the oxidation state of Zr4+ species. Zr ion-exchange decreased the concentrations of Bronsted and Lewis acid sites. As a result, the initial conversion of 1-butene was decreased, but the selectivity and stability of the catalyst were increased. As reported before, the copper introduction decreased the Bronsted acid site density, but increased the conversion. The enhancement in the catalytic activity has been connected to the presence of copper with oxidation state +1, which is formed under reaction conditions due to the hydrogen formation. This led to a peculiar effect over oxidized bimetallic Cu–Zr-H-MCM-41 at a low temperature and high weight hourly space velocity (523 K and 15 h−1, respectively): The initial conversion of 1-butene was almost zero but increased during the time-on-stream reaching the value of about 13 mol%. These observations are related to the reduction of Cu2+ species to Cu+ during the reaction. The catalyst evaluation and characterization results led to a conclusion that the presence of Zr stabilizes copper’s oxidation state of Cu+2 under reductive conditions in the bimetallic Cu–Zr-H-MCM-41 catalyst.

Isomerization of 1-butene over SAPO-11 catalysts synthesized by varying synthesis time and silica sources

A series of SAPO-11 catalyst samples were synthesized by varying source of silica and synthesis time. Products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption and FTIR spectroscopy of pyridine adsorption as well as evaluated towards 1-butene skeletal isomerization. By using waterglass as a source of silica, tridymite phase instead of SAPO-11 was obtained. The combination of colloidal silica and aluminum oxide as sources of silica and alumina resulted in SAPO-11 phase but small amounts of other phases, such as tridymite, were obtained. The number of the acid sites was observed to increase if synthesis time was prolonged indicating more silicon incorporation into the framework. Acidity and phase distribution had an influence on the conversion of 1-butene and selectivity to isobutene. The selectivity to isobutene was higher with catalysts, which contained more SAPO-11 phase.

Regeneration of WO x/Al 2O 3 and MoO x/Al 2O 3 catalyst used during skeletal isomerization of 1-butene

The regeneration of W and Mo supported on γ and α–θAl 2O 3 catalysts used during 1-butene skeletal isomerization, was studied. The regenerated catalysts were characterized by several techniques and the results compared with those of the fresh catalysts. It was found that it is necessary a 15 h at 465 °C treatment to completely eliminate coke on W/γA and Mo/γA, both catalysts recovering the initial activity and selectivity. Using this procedure, the properties of the catalysts were not modified. The same treatment did not allow the activity recovery in W/α–θA, due to differences in the nature of coke, that is aromatic or pregraphitic, and could not be totally removed.

Characterization of WO x/Al 2O 3 and MoO x/Al 2O 3 catalysts and their activity and deactivation during skeletal isomerization of 1-butene

A comparative study of the activity and deactivation of alumina supported tungsten and molybdenum oxides was performed. The catalysts were prepared by impregnation on γ- and α-θAl 2O 3 and their activity, selectivity and deactivation during skeletal isomerization of 1-butene (380 °C, atmospheric pressure) was assessed. The catalysts were further characterized by means of temperature programmed reduction (TPR), X-ray diffraction (XRD), sortometry and laser Raman spectroscopy. The amount and nature of coke deposits produced during the reaction were determined by temperature programmed oxidation (TPO) and laser Raman spectroscopy. Best activity and selectivity values for both catalysts were obtained at intermediate W and Mo loadings which seemingly corresponded to an optimum concentration of surface tetrahedrally coordinated species. Tungsten supported catalysts performed better than molybdenum ones. When the support was α-θAl 2O 3 the amount of coke was low but high calcination temperatures were needed to burn it off, because of its aromatic or pregraphitic nature.

Active copper species in 1-butene skeletal isomerization: comparison between copper-modified MCM-41 and beta catalysts

The role of copper was studied in the skeletal isomerization of 1-butene over copper-modified mesoporous MCM-41 molecular sieve and Beta zeolite. The Cu–H-MCM-41 and Cu–H-Beta catalysts were synthesized in our laboratory and characterized by XRD, nitrogen adsorption, X-ray fluorescence, FTIR of adsorbed pyridine and direct current plasma atomic emission spectrometry. The oxidation state of copper after oxidation and reduction in Cu–H-MCM-41 was evaluated by FTIR with probe molecules. Copper ion-exchanged and the proton forms of MCM-41 and Beta catalysts were tested towards 1-butene skeletal isomerization by varying the weight hourly space velocity and temperature. Quantum chemical calculations at the B3LYP/6-31 + G ** level were performed in order to understand the role of copper at the molecular level. Copper in Cu–H-MCM-41 pretreated in synthetic air was mostly in the form of Cu 2+ but reduced during the catalytic experiment to the metallic form Cu 0 via Cu +. Even if the copper exchange decreased the amount of Brønsted acid sites, Cu–H-MCM-41 pretreated in synthetic air was more active than H-MCM-41 towards 1-butene skeletal isomerization. The enhanced catalytic activity is due to copper Cu +, which was formed during the reaction. Introduction of copper into H-Beta, however, did not have any effect at all on the performance of the catalyst. The probable reason for this is the high initial activity of copper-modified H-Beta causing a very fast reduction of copper to the inactive metallic form Cu 0.

Influence of Carbon−Chlorine Surface Complexes on the Properties of Tungsten Oxide Supported on Activated Carbons. 2. Surface Acidity and Skeletal Isomerization of 1-Butene

Chlorinated activated carbons and the respective tungsten oxide catalysts supported on them were tested as catalysts in the decomposition reaction of 2-propanol and characterized by measurement of their pHPZC. Supported catalysts were also used in the skeletal isomerization of 1-butene. Results found show that an increase in the chlorine content of the support increases the total surface acidity, as measured by the pHPZC, of both the support and the supported catalysts. However, there is also a decrease in their Bronsted type acidity, as determined from the results obtained from the dehydration reaction of 2-propanol. Thus, it seems that the effect of chlorine is to increase Lewis type acidity in both the support and the supported catalyst. In addition, during the dehydration of 2-propanol there was a partial reduction of W(VI) to W(V) in most of the catalysts, which brought about a restructuring of the metal oxide particles. Isomerization of 1-butene gives only isobutene and trans-2-butene. Selectivity t...

Skeletal isomerization of linear butenes on tungsten promoted ferrierite

Samples of ammonium, protonic and potassium ferrierites were impregnated with tungsten species. The catalytic behavior of samples with and without tungsten during the linear butene isomerization reaction was studied. Tungsten loadings between 0.5 and 1.0% on ammonium ferrierite produce a synergetic effect both on activity and isobutene yield, while tungsten addition on the protonic form worsens the catalytic behavior of the unpromoted ferrierite. The presence of tungsten species on potassium ferrierite promotes the linear butene skeletal isomerization, with an optimum in the performance when the tungsten loading is between 3.5 and 4.0%. Tungsten species show a weak interaction with the potassium ferrierite surface. On the other hand, on protonic ferrierite the interaction is slightly stronger than on ammonium ferrierite, and the reduction of tungsten occurs practically in one step. The effect of both pretreatment and operational conditions over catalytic performance and deactivation of materials was also addressed. The higher the calcination temperature of ammonium ferrierite, the lower the linear butene conversion and the isobutene yield. Protonic ferrierite, tungsten promoted ammonium ferrierite, and tungsten promoted protonic ferrierite show similar qualitatively behaviors. After 5 min of reaction at any operational conditions, a high activity with low isobutene selectivity is observed. This behavior is related to the presence of strong acid sites. At long time-on-stream (TOS), the linear butene conversion at 450 °C is significantly higher than the one reached at 300 °C, while the isobutene yield remains between 12 and 18% for both reaction temperatures. Tungsten promoted potassium ferrierite samples display a different behavior. At 5 min the high activity is not reached, and both linear butene conversion and isobutene yield appear more stable with TOS; what is associated with the absence of strong acid sites. When reaction takes place at 450 °C, the isobutene yield significantly increases, approaching the yield obtained with the other samples. For all samples, the presence of hydrogen previously and during the reaction does not significantly modify the catalytic behavior, showing a small effect over the by-product distribution. By-products are formed from oligomers, which are among the products even at long TOS. The level of the carbonaceous deposit formed during reaction on protonic ferrierite, tungsten promoted ammonium ferrierite, and tungsten promoted protonic ferrierite was usually 6.0–7.8 wt.%. The oxidation profiles displayed two combustion peaks when the reaction took place at 300 °C, and only a high-temperature combustion peak when the reaction was carried out at 450 °C. On tungsten promoted potassium ferrierite, the deposit was considerably smaller (0.3–0.7 wt.%); coke formed at 300 °C showed a well-defined combustion peak at moderate temperature, while only a high-temperature combustion peak appeared when the deposit was formed at 450 °C. The amount of carbonaceous deposit is associated to the strength of acid sites while its nature is more strongly influenced by the reaction temperature.

Synthesis of thermally stable tetragonal zirconia with large surface area and its catalytic activity in the skeletal isomerization of 1-butene

Thermally stable zirconia with a large BET surface area was prepared by using zirconium atrane derivatives and commercial alkyltrimethylammonium bromide. The zirconia samples were characterized by wide-angle X-ray diffraction, thermal analysis and N2 adsorption/desorption analysis. The results showed that the present zirconia existed as a thermally stable tetragonal crystallite and consisted of mesoporous material with microporous contribution. The BET surface area was found larger than 240 m2/g even after calcination at 600 °C. The present zirconia after sulfation was applied to the skeletal isomerization of 1-butene, and its catalytic activity was found superior to that of the conventional sulfated zirconia.

Skeletal Isomerization of Butene on Si, Zr-substituted Aluminum Phosphate Zeolites

Si,Zr-substituted aluminumphosphate zeolites were synthesized by hyd rothermal method.XRD data indicated that they bear the same AEL structure with A PO-11 zeolite.Of interest is that the crystal shape of SAPO-11 and APO-11 all are sphere-like,while ZAPO-11 exists as bar-like.Simultaneously,the introduc tion of heteroatoms in APO-11 skeleton could lead to the positive modification of acidity and micropore features.SAPO-11 showed higher acidity and ZAPO-11 po ssessed less micropore volume.Of special is that SAPO-11 with Si/Al =0.15 is th e optimum shape-selective catalyst of skeletal isomerization of butene.The isom erization effect factors,such as butene partial pressure,temperature,were also e xtensively investigated.Of special is that the inconsistency in concentration ch anges between product isobutene and by-product,C3 and C5,was continually occurr ed while the reaction parameters were accordingly changed.It indicated that isob utene is shape-selectively formed via mono-imolecule mechanism,while the by-p roducts C3 and C5 are mainly formed via bimolecular mechanism.

Dispersion measurement of heteropoly acid supported on KIT-1 mesoporous material

Heteropoly acid (HPA) catalysts supported on KIT-1 mesoporous material were prepared with different loadings and characterized using XRD, UV–VIS and N 2 adsorption. Supported HPA was dispersed mainly on the inner surface of pores, resulting in the disappearance of XRD peaks. The diffraction peaks of HPA from the KIT-1 mesoporous material loaded with HPA of 41 wt% was very weak compared to those of physical mixtures of HPA and mesoporous material. The remaining adsorption amount of 1-butene on the supported HPA catalysts revealed the exposed amount of HPA molecules, which is useful in determining the HPA dispersion. HPA dispersion of supported HPA catalysts was useful to interpret their catalytic activity in the skeletal isomerization of 1-butene.

Effects of Metal Cation on the Skeletal Isomerization of 1-Butene over Clinoptilolite

Skeletal isomerization of 1-butene to isobutene has been investigated over various metal-cation-exchanged natural clinoptilolite zeolites. The effects of metal cation exchange were examined by XRD, NH 3-TPD, FT-IR, and solid-state NMR to elucidate the controlling factors affecting the selectivity to isobutene. Cobalt-cation-exchanged natural clinoptilolite zeolite (Co–HNZ) showed a higher selectivity to isobutene compared with that of HNZ at the same conversion of n-butenes under the same reaction conditions, while barium-cation-exchanged zeolite (Ba–HNZ) exhibited a higher activity but a very low selectivity to isobutene. It could be suggested that the high selectivity over the Co–HNZ catalyst was induced by selective removal of strong acid sites that were responsible for the side reactions of dimerization cracking as well as by imposing an effective constraint on zeolite channels. On the other hand, the high density and easy accessibility of acid sites mainly on the external surface in Ba–HNZ could increase the extent of the bimolecular reaction pathway, leading to high yields of by-products. Thus, a selective catalyst for skeletal isomerization of 1-butene should satisfy multiple requirements regarding its acid site, namely, strength, type, concentration, and accessibility.

Effects of Metal Cation on the Skeletal Isomerization of 1-Butene over Clinoptilolite

Effects of Metal Cation on the Skeletal Isomerization of 1-Butene over Clinoptilolite

Butene skeletal isomerization over H-ferrierite: a TEOM and in situ IR study on the role of carbonaceous deposits and the location of Brønsted acid sites

Butene skeletal isomerization over H-ferrierite (H-FER) is monitored in a catalysis set-up including a tapered element oscillating microbalance (TEOM) and using in situ infrared (IR) spectroscopy. For the first time the location and number of vacant Brønsted acid groups sited in the 10, 8, 6, and 5 membered rings (MRs) of the H-ferrierite framework are established as a function of time-on-stream (TOS). By deconvolution of the acid site-band, it is determined that with proceeding reaction the 8 MR channels are blocked and the available micropore volume and Brønsted acidity on the aged H-ferrierite will be primarily located inside the 10 MR channels. When a maximum amount of hydrocarbons is deposited on the catalyst, vacant Brønsted acid sites are still present. Additionally, IR spectroscopy shows that with TOS carbonaceous deposits are slowly converted from hydrogen-rich alkyl-aromatics into hydrogen-poor cyclopenta-fused-alkyl-aromatics, reducing by-product formation and therefore enhancing isobutene selectivity.

The skeletal isomerization of n-butene over ferrierite catalysts

Abstract The catalytic properties of H-ferrierite zeolites, prepared by hydrothermal and dry-state synthesis, were compared in the skeletal isomerization of 1-butene. The activity was found to be strongly influenced by the presence of extra-framework Al (EFAl) species in the zeolite micropores and by the carbonaceous deposit formed during the reaction. The dynamics of mass transport in the zeolite crystallites were studied by the frequency-response (FR) method using acetylene, propane, n - and i -butane as probe molecules. The selectivity of n -butene conversion showed correlation with the dynamics of the n -butane sorption process. Either the diffusion or the sorption was the rate-controlling slowest step of n -butane mass transport, depending on the amount and the distribution of the EFAl species in the sample. In the catalyst sample, free of EFAl, the transport was found to be controlled by the rate of sorption. At an EFAl content of about 0.5–1.0 EFAl/unit cell the diffusion resistance of the micropores governed the n -butane transport rate.

Tungsten-Ferrierite Catalysts Prepared by Impregnation and Ion-Exchange: Characterization and Activity During the Skeletal Isomerization of Linear Butenes

Tungsten-ferrierite catalysts were prepared by impregnation and ion-exchange. Potassium (KF), ammonium (AF), and protonic (HF) ferrierites were used as starting materials. Characterization of impregnated catalysts shows reduction peaks characteristic of tungsten species, whereas the absence of a peak in the corresponding profiles of the exchanged material indicates such species were incorporated into the framework. For impregnated materials, the tungsten species-surface interaction is not strong. Catalytic performance during the linear butene skeletal isomerization at 300 °C and at atmospheric pressure was measured. Exchanged materials reach both conversion and isobutene yield larger than the impregnated ones. Samples prepared from AF and HF practically display the same catalytic behavior at 5 min, being associated with the presence of strong acid sites. Tungsten-impregnated KF does not reach a high activity at a short time-on-stream (TOS), showing a particular by-product distribution related to the absence of strong acid sites. Even though exchanged samples starting from KF show the HF characteristic behavior, differences at 5 min appear. By-product distributions allow us to consider their formation from dimers and/or oligomers. At 5 min, the C5+ fraction is the main one, following propene, propane, and butane in similar proportions. Over the “clean” surface, propene could be involved in other reactions considering its high reactivity. At a long TOS, both the C5+ fraction and propane decrease, whereas propene increases, verifying the bimolecular mechanism.