Deactivation of ferrierite during the skeletal isomerization of linear butenes

Deactivation of ferrierite during the skeletal isomerization of 1-butene at atmospheric pressure and 0.15 atm 1-butene partial pressure was studied. At 300°C, the carbon content shows a sharp increase during the first 30 min-on-stream, with a slower growth thereafter. Temperature-programmed oxidation profiles corresponding to different times-on-stream are similar, showing two well-defined combustion peaks centered at about 325 and 640°C, respectively. When starting the 1-butene feed with the catalytic bed at 100 or 200°C and then increasing the temperature up to 300°C, no significant difference is observed, neither in carbon content nor in oxidation profiles. Important differences in the profiles are observed by comparing at the same time at each temperature. The lower the temperature, the higher the reactivity toward oxidation at low temperature. The carbonaceous deposit formed at 100°C shows the main combustion peak at the lowest temperature (135°C) and a more olefinic character; it could be related to a strong adsorption of reactant molecules. At 200°C, the proportion of saturated species associated to oligomers increases; while at 300°C, coke shows both aromatic and olefinic species.     

Isomerization of n-butene over ferrierite zeolite modified by silicon tetrachloride treatment

Ferrierite zeolite modified by the deposition of SiCl₄, was prepared and investigated as a catalyst for the skeletal isomerization of 1-butene. The prepared catalysts were characterized by XRD, atomic absorption spectroscopy, ammonia TPD, FT-IR, BET/pore size distribution and pyridine chemisorption. The deposition of SiCl₄ preserved zeolite crystallinity although XRD and FT-IR analysis suggested a little framework de-alumination not evidenced by chemical analysis. This treatment narrowed pore size and diminished the strong/weak and Brönsted/Lewis acid sites ratio. As the SiCl₄ amount increased, the conversion of 1-butene decreased and selectivity to isobutene increased. This may be attributed to the higher spatial constraints inside the pores which restrict undesired reactions, such as 1-butene dimerization followed by cracking.

Abstract

The effect of temperature, weight hour space velocity and partial pressure of 1-butene was studied over modified and parent catalyst, indicating that a unimolecular mechanism prevails on modified samples while bimolecular processes are present on fresh ferrierite specially at short times on stream.     

Migration of butene isomers onto the acidic OH groups in small micropores of ferrierite

Kinetics on the adsorption of n-butene onto the acidic OH groups existing in the small pores of ferrierite (FER) were studied between 233 and 253 K by IR spectroscopy. The activation energies for the adsorption of 1-butene and cis-2-butene were estimated as 23.3 and 28.4 kJ mol⁻¹, while that of trans-2-butene was not obtained due to its rapid adsorption. The activation energy for adsorption was considered to have resulted from the diffusion of n-butene molecules into the small micropores of FER.     

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.     

The skeletal isomerization of C4-C7 1-olefins over ferrierite and ZSM-5 zeolite catalysts

The skeletal isomerization of C₄-C₇ 1-olefins was studied on ferrierite (FER) and ZSM-5 (MFI) zeolites to elucidate the effect of the molecular distribution in zeolite pores on the selectivity foriso-olefin formation. Regardless of the difference in molecular length of 1-olefins, the FER zeolite showed high selectivity foriso-olefins, while the selectivity became slightly low at the skeletal isomerization of long olefin molecules. The drastic decrease in the selectivity of MFI zeolites by increasing the conversion is concurrently observed in the skeletal isomerization of C₄-C₇ 1-olefins. The high selectivity of FER zeolites is explained by their sparse distributions of olefin molecules in pores, which induces a high preference for monomolecular skeletal isomerization.     

Co- and Ni-exchanged ferrierite: The contribution of synchrotron X-ray diffraction data to siting of TMIs

High-silica zeolites exchanged with transition metal ions (TMIs) are the subject of great interest for their unusual catalytic activity and selectivity. Structural information like coordination and accessibility of TMIs in zeolites are important factors for understanding their catalytic activity. Siting of TMIs in zeolites is typically obtained by spectroscopic (EXAFS, EPR, UV–vis and IR) and computational methods, as in the case of Co-ferrierite. However, some controversy exists in the literature concerning the model for incorporation of bare Co ions in ferrierite. We show here that the results of our synchrotron X-ray powder diffraction studies on Co- and Ni-exchanged ferrierite (Si/Al = 8.5) are in a good agreement with the model of Co siting based on an indirect spectroscopic approach and help to validate this model. By direct structural evidences, a possible explanation for the larger catalytic activity of Co sites in the main channels of ferrierite can be inferred. A combination of data from in situ XRD continuous monitoring of the Co ion migration during calcination and crystal-chemical considerations allows to device a strategy for the design of optimised co-cations containing Co-ferrierite catalysts.     

The role of carbonaceous deposits in the skeletal isomerization of 1-butene over ferrierite zeolites

The inner pores of ferrierite (FER) with a Si/Al ratio of 21 have been modified by plasma-polymerized propylene loading and subsequent thermal treatment under a flow of He at 550°C in order to identify the exact role of carbonaceous deposits (coke) in the skeletal isomerization of 1-butene. It was found that even a small weight loading (0.8 wt%) of carbonaceous deposits within the inner pores of FER zeolite was sufficient to modify the pore structure of the zeolite, leading to a noticeable enhancement of the selectivity to isobutene. This may be attributed to the increased spatial constraints inside the pores which restrict undesired side reactions, such as 1-butene dimerization followed by cracking to light hydrocarbons.     

Trimerization of isobutene over zeolite catalysts: Remarkable performance over a ferrierite zeolite

Oligomerization of isobutene has been investigated using several zeolites in order to produce triisobutenes that are useful chemical feedstocks for heavy alkylates and neo-acids. Stable isobutene conversion and high selectivity for trimers are obtained over a ferrierite zeolite at high temperature and low space velocity. Trimers selectivity increases with increasing isobutene conversion. Isobutene is quantitatively oligomerized over a ferrierite catalyst with selectivity for trimers higher than 60% up to 50 h at high isobutene WHSV of 10 h⁻¹. Moreover, a deactivated catalyst can be regenerated easily by calcining in flowing air. The ferrierite zeolite is one of the potential catalysts for the isobutene trimerization showing high stability, quantitative conversion, high selectivity and easy regeneration.     

An integrated dynamic model for reaction kinetics and catalyst deactivation in fixed bed reactors: skeletal isomerization of 1-pentene over ferrierite

Catalyst deactivation in fixed beds is a critical issue in many industrial processes. A general dynamic model for fixed bed reactors involving catalyst deactivation was presented and simplified. The simplifications were based on the pseudo-steady state hypothesis for the fluid phase. Catalyst deactivation was treated by a linear model with respect to surface intermediates. A semi-analytical solution was obtained for the surface intermediates. The approach was applied to skeletal isomerization of 1-pentene over ferrierite. The comparison of experimental results and model predictions revealed that the model is able to describe the essential features of catalyst deactivation in skeletal isomerization and it can be useful for process scale-up.     

Mechanism and side reactions of the anionic condensation of styrene with alkyl halides

The reactions occurring in the system styrene + butyl bromide + lithium in tetrahydrofuran are studied as a model for olefine/dihalide reactions pioneered by Richards and co-workers for the purpose of synthesising highly regular copolymers. Computer fittings of a kinetic scheme and of gel permeation chromatographs of the products leads to the conclusion that homopolymerisation of styrene tends to be a serious side reaction to the desired condensation between the styrene dianion and two moles of butyl bromide. As expected from previous work, this is found to be much less serious in the analogous system with alpha methyl styrene in place of styrene.     

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites: influence of zeolite acidity

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO₂Al₂O₃ ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH₃ temperature-programmed desorption results from FER and MFI catalysts with the same SiO₂/Al₂O₃ ratio reveal that the pore structure of FER zeolite rather than its acidity may play an important role in achieving high selectivity for the skeletal isomerization of 1-butene to isobutene.     

Comparative study of the catalytic properties of ferrierite zeolite exchanged with alkaline earth metals in the skeletal isomerization of n-butene

Ferrierite zeolites ion exchanged with alkaline earth cations (Mg²⁺, Sr²⁺, Ba²⁺) were prepared and examined as catalysts for the skeletal isomerization of 1-butene. The samples were characterized by XRD, atomic absorption spectroscopy, ammonia TPD, FT-IR, BET/pore size distribution and pyridine chemisorption. The acidity studies indicated that acid strength increases in the order H⁺>Mg²⁺>Sr²⁺>Ba²⁺, therefore, the number of weak acid sites follows the opposite trend. At the same time, Brønsted acid sites associated with protons disappear and the number of Lewis acid sites increases with metal content. The presence of bulky cations like Mg²⁺, Sr²⁺, Ba²⁺ leads to a slight reduction of surface area and pore size. Ferrierites containing magnesium exhibit the highest isobutene yield. Lewis acid sites are responsible for improvement in catalyst stability as well as suppression of coke formation.     

Synthesis of DME from syngas on the bifunctional Cu–ZnO–Al2O3/Zr-modified ferrierite: Effect of Zr content

The catalytic activity on the coprecipitated Cu–ZnO–Al₂O₃/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5 wt.% was investigated for the direct synthesis of dimethylether (DME) from H₂-deficient and biomass-derived model syngas (H₂/CO molar ratio = 0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3 wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH₃-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N₂O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH₃-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength.     

Hydroisomerisation of n-alkanes over partially reduced MoO3: Promotion by CoAlPO-11 and relations to reaction mechanism and rate-determining step

The reaction mechanism and the rate-determining step (RDS) of the isomerisation of n-alkanes (C₄–C₆) over partially reduced MoO₃ catalysts were studied through the effects of the addition of an alkene isomerisation catalyst (i.e. CoAlPO-11). When an acidic CoAlPO-11 sample was mechanically mixed with the MoO₃, a decrease of the induction period and an increase of the steady-state conversion of n-butane to isobutane were observed. These data support previous assumptions that a bifunctional mechanism occurred over the partially reduced MoO₃ (a complex nanoscale mixture of oxide-based phases) during n-butane isomerisation and that the RDS was the skeletal isomerisation of the linear butene intermediates. The only promotional effect of CoAlPO-11 on the activity of partially reduced MoO₃ for C₅–C₆ alkane hydroisomerisation was a reduction of the induction period, as the RDS at steady-state conditions appeared to be dehydrogenation of the alkane in this case. However, lower yields of branched isomers were observed in this case, the reason of which is yet unclear.     

CH4-SCR of NO over Co and Pd ferrierite catalysts: Effect of preparation on catalytic performance

Selective catalytic reduction of NO with methane (CH₄-SCR) in the presence of oxygen excess and water vapour was studied over two bimetallic cobalt/palladium-based FER catalysts, which differ on the order of introduction of metal ions. H₂-TPR and UV–vis analysis showed that the simple change in the order of addition of metals to catalyst, gives rise to totally diverse species (Co²⁺ ions, Co oxides, Co-oxo cations and Pd species) both in type and quantity but also in location within zeolite framework. Experiments of TPD and TPSR of NO and NO₂ provided important information to establish a relation between the various active sites formed on both catalysts and their function in the reaction mechanism. The importance of NO₂ in the mechanism of NO reaction with CH₄ and O₂ was explored and the catalyst with a higher capacity to retain adsorbed NO₂ is the less active for deNO_x. The preparation of a bimetallic catalyst active for NO reduction must provide the proximity between Co and Pd species, and the presence of Co-oxo cations together with palladium species seem to be essential. Furthermore, a suitable amount of cobalt oxides must exist in order to originate NO₂ that is the main reaction intermediate. Nevertheless, an excessive amount of these Co species can lead to an increase of adsorbed NO₂, which reduces the rate of the reaction of some of the mechanism steps.     

The role of zeolite type on the lean NOx reduction by methane over Pd loaded pentasil zeolites

The lean selective catalytic reduction of NO_x by methane over protonic palladium loaded ZSM-5, FER and MOR, as well as, on bimetallic Pd–Pt-HMOR was examined. Special emphasis was paid on the combined effects of water and SO₂ in the feed stream. Under dry conditions and in the absence of SO₂, the degree of NO_x conversion at 450°C decreases as follows: Pd-HZSM-5>Pd-HMOR>Pd-HFER. Sulfur dioxide alone has no apparent effect on the activity for NO_x reduction, but the coexistence of water and SO₂ inhibits both NO_x and methane conversions. The extent of inhibition by water and SO₂ on NO_x reduction is Pd-HFER>Pd-HZSM-5>Pd-HMOR. Acid mordenite doped with low levels of Pt and Pd leads to an active catalyst that is more tolerant to the presence of either water or SO₂ than the corresponding monometallic Pt- and Pd-HMOR. Nevertheless, NO_x reduction is also inhibited at temperatures below 450°C when SO₂ and water are both present. TPD experiments of water over calcined samples of protonic Pd supported pentasil zeolites, Pd/γ-Al₂O₃ and Pt–Pd-HMOR with and without pretreatment in SO₂+O₂ indicate that sulfation of the surface increases water chemisorption by the support. Therefore, the observed decrease of NO_x reduction on Pd-loaded zeolite catalysts when SO₂ and H₂O coexist in the feed stream may be due to enhanced water inhibition and presumably active site poisoning.     

Towards molecular sieve inorganic catalysts that are akin to enzymes: studies of a selective cyclo-dimerization over ferrierite at ambient temperature

The solid-acid (Brønsted)-catalyzed cyclo-dimerization of 3-hydroxy-3-methylbutan-2-one (HMB) over a synthetic ferrierite molecular sieve is reported. HMB is a stable liquid at ambient temperatures but in acidic solutions it readily undergoes reaction to generate a variety of products. However, in the acidic molecular sieve catalyst studied here, only one product – the cyclic dimer (proven by in situ solid state ¹³C NMR and other evidence) – is observed, together with some unreacted HMB. A plausible, proton-catalyzed mechanism is proposed, and prompts comparison between the cyclo-dimerization of HMB within ferrierite and the mode of action of certain enzymes.     

Degradative side reactions in the syntheses of exactly alternating silarylene-siloxane polymers

Summary Four principal synthetic methods for preparation of exactly alternating silarylene-siloxane polymers: the chlorosilane, the acetoxysilane, the aminosilane and the ureidosilane polymerization reactions, were compared under equivalent experimental conditions. As indicated earlier, polymers with considerably different molecular weights were obtained. The highest molecular weight polymer resulted from the ureidosilane reaction, while the lowest ones were obtained from the chlorosilane and the acetoxysilane routes. Because thorough precautions were taken to ensure equally favorable conditions in all preparations, these results seem to support a hypothesis that the latter two reactions are limited by the occurrence of degradative desilytation side reactions which are inherent to the nature of these polymerization systems.Dedicated to Professor Dragutin Fle on the occasion of his 70th birthday     

丁烯异构化催化剂镁碱沸石的合成研究进展

在丁烯异构化反应催化剂中,镁碱沸石分子筛由于具有十元环和八元环交错的独特的二维孔道结构、良好的水热稳定性和化学稳定性、较高的选择性等诸多优点受到广泛关注;但由于有机模板剂的影响,在环境友好方面有所欠缺。本文综述了镁碱沸石（FER）的合成方法：有机模板剂合成法、非模板剂合成法、层状前体合成法、乳化剂控制合成法,归纳比较了各种合成方法的优缺点,阐述了FER的合成后处理方式,指出采用无毒无害的原材料替代有机合成模板剂,从而提高镁碱沸石分子筛的催化性能,对环境友好大大改善,是未来研究镁碱沸石分子筛催化剂的发展方向之一。     

Parametric optimization with uncertainty on the left hand side of linear programs

Although parametric optimization with uncertainties on the objective function (OF) or on the so-called “right-hand-side” (RHS) of the constraints has been addressed successfully in recent papers, very little work exists on the same with uncertainties on the left-hand-side (LHS) of the constraints or in the coefficients of the constraint matrix. The goal of this work has been to develop a systematic method to solve such parametric optimization problems. This is a very complex problem and we have begun with the simplest of optimization problems, namely the linear programming problem with a single parameter on the LHS. This study reviews the available work on parametric optimization, describes the challenges and issues specific to LHS parametric linear programming (LHS-pLP), and presents a solution algorithm using some classic results from matrix algebra.