Skeletal Isomerization Of 1-butene Research Articles

Unit cell distortion of ferrierite induced by carbonaceous deposits during skeletal isomerization of 1-butene

In this study, high temperature and ambient X-ray powder diffraction (XRD) are employed to differentiate the impacts of temperature and carbon deposition on the catalytic activity of the zeolite H-ferrierite (H-FER) via changes in the unit cell structure. XRD serves as a straightforward tool to distinguish these influences on the lattice geometry of H-FER, which ultimately affects catalytic activity. Due to its industrial relevance, the isomerization reaction of 1-butene to iso-butene is selected. Pristine H-FER undergoes a thermal contraction when heated from room temperature to 450 °C. However, internal carbonaceous deposits (i.e., deposits inside the micropores of the zeolite) counterbalance this effect, and the unit cell expands anisotropically during the reaction startup phase. Internal carbon deposits act as the driving force for this expansion and counteract external forces. During catalyst deactivation (time on stream >100 h), a slight unit cell contraction (i.e., ΔV = −6 Å3) is observed that stems from external carbon deposit condensation (i.e., deposits on the crystal surface). Characterization of an oxidatively regenerated catalyst supports this finding by proving this structural distortion to be nearly reversible. This study concludes that internal carbon species are primarily responsible for structural distortion and counteract thermal contraction, whereas external coke species are the driving force for catalyst deactivation.

Effect of Acid Amount and Acid Sites Distribution of Ferrierite Zeolite on the Catalytic Behavior in the 1-Butene Skeletal Isomerization

Effect of Acid Amount and Acid Sites Distribution of Ferrierite Zeolite on the Catalytic Behavior in the 1-Butene Skeletal Isomerization

Improved Catalytic Performances of the NaOH-Treated ZSM-22 Zeolite in the 1-Butene Skeletal Isomerization Reaction: Effect of External Acid Sites.

In this paper, a series of alkaline-treated ZSM-22 zeolite samples were prepared by treating the parent ZSM-22 zeolite using NaOH aqueous solution with different concentrations. By investigating the effects of alkaline treatment on the parent ZSM-22 zeolite, we discovered that the alkaline treatment contributed to the reduction of Brønsted acid sites due to the coverage of extra-framework Al on its external surface. In addition, it was found that the alkaline-treated samples were favorable to the improvement of the isobutene yield and selectivity, while these features appeared to be low for the subsequent acid-washed counterparts in the skeletal isomerization reaction of 1-butene. These results indicate that the catalytic performance of ZSM-22 zeolite is related to reduced amounts of Brønsted acid sites in it. To further reveal the reasons for the promoted catalytic performances of the alkaline-treated ZSM-22 series zeolites, we studied the properties of coke deposited on the two series of samples using Raman spectroscopy and thermogravimetric analysis and mass spectrometry (TG/MS-TPO). It was shown that the carbon deposited on the alkaline-treated series samples was mainly distributed at the outer surface, while the coke was distributed to a relatively lesser extent at the exterior surface for the acid-washed series samples. Moreover, by partially passivating outer acid sites of the parent zeolite, the selected alkaline-treated zeolite, and acid-washed zeolite, their isobutene selectivities were all improved with the decrease in outer acid sites. These phenomena confirmed that the improved catalytic performances of the alkaline-treated samples are related to their decreased external Brønsted acid site density, which further demonstrated that the high isobutene yield and selectivity in the skeletal isomerization reaction of 1-butene is realized via the monomolecular reaction pathway of 1-butene.

Engineering the Framework Cobalt and Hierarchical Pores of Aluminophosphates for Enhanced Performance in n‐Butene Skeletal Isomerization

AbstractAn effective method is proposed to synthesize a hierarchical Co‐doped AlPO4 molecular sieve (CoAIP‐CTAB). For the obtained zeolite, both framework and extra framework Co are firstly established and identified by X‐ray absorption fine structure (XAFS). The percentage of framework Co (P–O–Co–O–P) is estimated to be 82%. Due to the hierarchical structure and abundant Co sites in the framework, CoAIP‐CTAB nanocrystals have shown high catalytic activity and stability for the catalytic conversion of n‐butenes to isobutene at mild temperature (350 °C) without gas dilution. This novel synthesis strategy may inspire the design of similar types of industrial zeolite catalysts for selective reactions.

Synthesis and catalytic application of nanorod-like FER-type zeolites

A fluoride-assisted synthesis strategy to obtain nanorod-like FER-type zeolite crystals is successfully developed, which can provide the FER zeolite with high performance in 1-butene skeletal isomerization.

Synthesis of Nano‐Hierarchical Ferrierite with Sole Template and Its Catalytic Application in n‐Butene Skeletal Isomerization

AbstractNano‐hierarchical ferrierite(FER) was successfully synthesized by using pyrrolidine as sole organic structure directing(OSDA) agent under static hydrothermal conditions.SEM images showed that the morphology of the product was a loose three‐stage accumulation structure by nano‐rod crystal grains .The influence of crystallization temperature, gel alkalinity, crystallization time and the amount of OSDA on synthesis of FER was investigated in detail.Moreover,FER catalytic performance in n‐butene skeletal isomerizatio was investigated.The results showed that, compared with the commercial FER, the nano‐hierarchical FER showed better catalytic activity.

Rapid synthesis of ferrierite zeolite through microwave assisted organic template free route

Abstract Ferrierite (FER) zeolite has been successfully synthesized within 2–3 h through microwave assisted crystallization without using organic structure directing agent. Crystallization temperature and seed content were found to be two of the key factors. XRD patterns and SEM images of the samples taken at different periods of time revealed that seeds were only partially dissolved during the crystallization process and silicate (alumino) species in the gel grew upon the surface of the partially dissolved seed. A core-shell zeolite growth model was proposed. Compared with original seed zeolite, as-synthesized FER zeolite had more regular morphology and larger particle size. The FER crystal size could be controlled in the range of 0.4–3.0 μm by adjusting the particle size of the seeds. FER obtained through microwave assisted rapid synthesis showed similar catalytic performance in 1-butene skeletal isomerization with the FER obtained through conventional hydrothermal synthesis.

Formation and Regeneration of Shape-Selective ZSM-35 Catalysts for n-Butene Skeletal Isomerization to Isobutene

Skeletal isomerization of n-butene to isobutene was performed over formed ZSM-35 zeolites in a lab-scale, fixed-bed reactor. The formation conditions to produce isobutene with zeolites were varied to determine the most advantageous binding agent (pseudo-boehmite) amount and steam dealumination conditions. The optimal binding agent amount was 20 wt %. Steam dealumination stabilized the catalysts and enhanced the catalytic performance because of the stable Si/Al framework and suitable acidity. The optimized process conditions involved a reaction temperature of 410 °C, a weight hourly space velocity of 5 h–1, and an n-butene concentration in feedstock of 50%. After being on-stream for 296 h, the catalysts were stable and were able to be regenerated with a comparable catalytic performance. An isobutene yield of 33–43 wt % was achieved, and the selectivity of isobutene was higher than 90% after the reaction was carried out for longer than 15 h. Carbon deposition modified the pore structure to enhance the selectivity of isobutene because of the selective shape effect. This study shows promising results for future industrialization of the skeletal isomerization of n-butene to isobutene in the presence of optimized ZSM-35 catalysts.

Synthesis of FER zeolite with piperidine as structure-directing agent and its catalytic application

The synthesis of ferrierite (FER) zeolite using piperidine as an organic structure-directing agent was investigated. X-ray diffraction, X-ray fluorescence, N2-adsorption, and scanning electron microscopy were used to characterize the crystal phases, textural properties, and particle morphologies of the zeolite samples. The crystallization behavior of the FER zeolite was found to be directly related to crystallization temperature. At 150 °C, pure FER phase was observed throughout crystallization. At 160–170 °C, MWW phase appeared first and gradually transformed into FER phase over time, indicating that the FER phase was thermodynamically favored. In the piperidine-Na2O-H2O synthetic system, alkalinity proved to be the crucial factor determining the size and textural properties of FER zeolite. Furthermore, the obtained FER samples exhibited good catalytic performance in the skeletal isomerization of 1-butene.

Size-controlled synthesis of hierarchical ferrierite zeolite and its catalytic application in 1-butene skeletal isomerization

Nano-ferrierite zeolite aggregates with hierarchical porosity were successfully prepared by using pyrrolidine as sole organic structure-directing agent. SEM and TEM images revealed that nano-sized crystals (40–60 nm) stacked together loosely to form irregular clusters. Influence of crystallization temperature and initial gel compositions (pyrrolidine content, alkalinity, water content) on the synthesis of ferrierite zeolite were investigated in detail. Low crystallization temperature and high alkalinity were beneficial to form nano-ferrierite zeolite aggregates with high hierarchical porosity (total pore volume: 0.461 cm3/g). Compared with commercialized ferrierite zeolite, hierarchical nano-ferrierite aggregates showed better catalytic stability and product selectivity in the 1-butene skeletal isomerization reaction.

Acid site density effects in zeolite-catalyzed 1-butene skeletal isomerization

We have investigated the effect of acid site density on the catalytic performance of high-silica (50⩽Si/Al⩽380) H-HPM-1 zeolite in the 1-butene skeletal isomerization. Changes (⩽0.5) in the number of framework Al atoms, and thus of Brønsted acid sites, per unit cell (60 tetrahedral atoms) led to striking variations in both 1-butene conversion and isobutene selectivity. Combining isobutene yield with catalyst durability, H-HPM-1 with a framework Si/Al ratio of 350 was found to perform better than any of the catalysts studied for this reaction thus far.

Monomolecular Skeletal Isomerization of 1-Butene over Selective Zeolite Catalysts

The mechanism of the 1-butene skeletal isomerization catalyzed by zeolites has remained elusive. We present direct evidence that even the initial isobutene formation over H-ferrierite, the best-known isomerization catalyst, is monomolecular in nature, whereas a bimolecular pathway is significant over the unselective H-ZSM-5. We also report that medium-pore high-silica H-HPM-1 outperforms H-ferrierite in selectively forming isobutene. This new catalyst displays a high activity and selectivity from the onset of the reaction, as well as an excellent resistance to deactivation, thanks to its anomalously weak acidity and low acid site density, together with an ability to effectively isolate reactant molecules from one another.

Skeletal isomerization of 1-butene over micro/mesoporous materials based on FER zeolite

Skeletal isomerization of 1-butene has been studied over composite micro/mesoporous zeolitic catalysts prepared by the recrystallization of ferrierite (FER) in alkaline solutions in the presence of cethyltrimethylammonium bromide and by the desilication of FER in alkaline solutions. Desilication procedure led to the creation of large mesopores in zeolite crystal with broad distribution of size. Recrystallization procedure resulted in two types of mesoporosity: uniform intracrystalline mesopores homogeneously distributed along the crystal and intercrystalline ordered mesoporous layers covering zeolite crystal. Recrystallized materials showed improved catalytic performance in skeletal isomerization of 1-butene with respect to both parent and desilicated ferrierites. The effect is due to the improved accessibility of the acid sites and the creation of new pore mouths, in which the active carbonaceous species responsible for selective pseudo-monomolecular pathway can be formed. The improved stability of catalytic activity with time on stream is due to coating of ferrierite crystals with mesoporous layes, which prevent the deactivation of the catalysts. The best catalytic performance was achieved over composite micro/mesoporous materials with intermediate degree of recrystallyzation due to proper balance between zeolitic and mesoporous phases and the amount and density of the acid sites.

Skeletal Isomerization of Butene in Ferrierite: Assessing the Energetic and Structural Differences between Carbenium and Alkoxide Based Pathways

In this study, the results from a systematic analysis of two different mechanisms for the skeletal isomerization of cis-butene to isobutene in ferrierite (FER) are presented. One involves a conventional mechanism that proceeds via stable alkoxide intermediates and the other is one which proceeds via carbenium ions only. A 27T QM cluster model has been used in this study, which is described using the M06-2X DFT functional. It is found that the alkoxide intermediates formed over the course of the conventional pathway are considerably lower in energy than the carbenium ion formed over the course of the alternate pathway. However, the rate determining step in the latter pathway is predicted to be almost 10 kcal/mol lower in energy. The higher barrier for the latter process is due to the inherent stability of the alkoxide intermediates formed within FER. These results appear to suggest that while these intermediates are formed over the course of the reaction, the skeletal isomerization of linear butenes to form isobutene in FER may occur via a carbenium based mechanism. This proposal is consistent with experimental results that show alkoxide intermediates are experimentally observed species.

ChemInform Abstract: Vibrational Infrared Spectroscopic Studies of 1-Butene Skeleton Isomerization at the Surface of a Silicated Alumina in a Micro Plug Flow Reactor

The skeletal isomerization of 1-butene to obtain 2-methylpropene is catalyzed by the interaction at high temperatures with solids having acidic properties. The nature of the solid-gas interaction is investigated through some vibrational infrared spectroscopic experiments aimed at highlighting the perturbation of the surface molecular groups and the formation of surface complexes on a silicated aluminum under different conditions of pressure and temperature. The spectra recorded during the interactions lead us to propose that the catalytic isomerization occurs through a temperature-dependent proton-transfer equilibrium between an OH surface group and an H-bonded internal olefin.

ChemInform Abstract: Skeletal Isomerization of Hydrocarbons Over Zirconium Oxide Promoted by Platinum and Sulfate Ion.

Abstract The genesis of the high activity of zirconium oxide promoted by platinum and sulfate ion (Pt/SO 4 2− --ZrO 2 ) for skeletal isomerization of butane and pentane in the presence of hydrogen is studied in terms of the interaction of the catalyst with molecular hydrogen. For skeletal isomerization of pentane at 523 K, Pt/SO 4 2− -ZrO 2 showed activity only in the presence of molecular hydrogen, and its activity persisted for a long period. For skeletal isomerization of butane at 523 K, the catalyst showed activity in the absence of hydrogen, but the activity was markedly enhanced in the presence of hydrogen. For pentane and butane skeletal isomerization, the products consisted exclusively of 2-methylbutane and 2-methylpropane, respectively. For a typical acid-catalyzed reaction of cyclopropane ring opening at 373 K, the presence of hydrogen enhanced the activity, but the hydrogen enhancement effect was small. The products consisted exclusively of propene even in the presence of hydrogen: hydrogenation of propene scarcely occurred. Infrared spectroscopic study of adsorbed pyridine showed that by heating the catalyst in the presence of hydrogen in the temperature range 423–623 K, protonic acid sites were formed with concomitant decrease in the number and strength of Lewis acid sites, demonstrating that the protonic acid sites originate from molecular hydrogen. The mechanisms of protonic acid site generation are discussed. It is suggested that molecular hydrogen dissociates on the platinum to hydrogen atoms which undergo spillover on the SO 4 2− -ZrO 2 and convert to an H+ and an e − or H − . The H+ acts as catalytic site for acid-catalyzed reactions.

Alkylate Technology Selection for Fischer−Tropsch Syncrude Refining

Technology selection to produce alkylate from straight run Fischer−Tropsch syncrude has been investigated. Alkylate is a high octane paraffinic motor-gasoline component and can be produced by direct alkylation (olefin addition to isobutane) or indirect alkylation (isobutene dimerization followed by hydrogenation). Neither isobutane nor isobutene is abundant in the light fraction of Fischer−Tropsch syncrude, which is rich in linear alpha-olefins. Direct alkylation (HF and H2SO4) and indirect alkylation (acidic resin and solid phosphoric acid) based flowschemes were evaluated in terms of alkylate yield, octane number, compatibility to Fischer−Tropsch derived feed, and environmental friendliness. It was found that the refining focus determined the selection. Indirect alkylation with solid phosphoric acid was found to be the best in terms of Fischer−Tropsch feed compatibility, environmental friendliness, and least refining complexity. The highest alkylate yield could be obtained by a combination of partial olefin hydrogenation, hydroisomerization, and direct alkylation. Butene skeletal isomerization in combination with indirect alkylation yielded an alkylate with the highest octane number.

Skeletal Isomerization of Butene in Fixed Beds. Part 2. Kinetic and Flow Modeling

Starting from detailed experimental studies of reaction kinetics, catalyst deactivation, and reactor flow conditions, mathematical models describing the dynamic reactor performance in zeolite catal...

Skeletal Isomerization of Butene in Fixed Beds. 1. Experimental Investigation and Structure−Performance Effects

An experimental investigation of structure−performance effects in zeolite catalyzed skeletal isomerization has been carried out. Two structurally different, medium-pore-size zeolites (H-TON and H-FER) with similar acidities were compared in butene skeletal isomerization. While both catalysts proved to be efficient in the test reaction, their deactivation behavior differed substantially. H-FER exhibited significantly higher initial isobutene yields and selectivities, and the catalyst performance was also more stable with time-on-stream. H-TON, on the other hand, needed prolonged operation times in order to achieve product distributions comparable to those of H-FER. The predominant route to isobutene was found to be the monomolecular one, with the bimolecular paths of butene largely responsible for byproduct formation. H-TON was more selective toward disproportionation and, owing to its slightly larger pore dimensions, hydrogen transfer products. H-TON was also observed to be less sensitive to feed reactant...

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.