Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7–1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620 °C, WHSV 3.5 h⁻¹, 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N₂ addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620 °C.     

Synergistic effects of tungsten and phosphorus on catalytic cracking of butene to propene over HZSM-5

Synergistic catalysis effects among tungsten, phosphorus and HZSM-5 on 1-butene cracking to propene and ethene have been demonstrated by catalytic tests. The tungsten–phosphorus-modified HZSM-5 (W–P/HZSM-5) catalyst, with very low density of acid sites, offers a fairly high conversion rate of butene and selectivity to propene. The status of doped tungsten is characterized by using techniques of D₂/OH exchange, NH₃ adsorption microcalorimetry, FT-IR spectroscopy, Raman spectroscopy, N₂ adsorption and X-ray photoelectron spectroscopy. The tungsten would be monotungstate that interacted with phosphorus before steam treatment and partly congregated to polytungstate species during steaming process at high temperature. The enhanced performance of the catalyst for 1-butene cracking to propene and ethene can be correlated to the synergistic effect between the doped tungsten and phosphorous on the reaction network of the cracking process. The W–P/HZSM-5 is a promising catalyst for the 1-butene cracking to propene and ethene.     

硅源对ZSM-5分子筛合成和催化性能的影响

为了考察硅源对ZSM-5分子筛合成和催化性能的影响,分别采用白炭黑、硅胶、硅溶胶和单分散SiO₂为硅源合成ZSM-5分子筛,对合成的ZSM-5分子筛进行XRD、SEM、BET和NH₃-TPD表征,并以C₄烯烃为原料评价合成的ZSM-5分子筛的催化裂解性能。结果表明,以硅溶胶为硅源合成的ZSM-5分子筛具有较好的结晶度和催化活性。水热处理使分子筛酸量减少,孔容缩小,改善了分子筛的乙烯丙烯选择性。经600 ℃水热处理4 h的ZSM-5分子筛在常压、580 ℃和空速9 h^-1反应条件下,丁烯催化裂解为乙烯和丙烯平均转化率为90.2%,乙烯和丙烯总收率达61.1%。     

Catalytic transfer hydrogenation on a hydrogen-absorbing alloy (CaNi5) using hydriding–dehydriding properties

By using the characteristics of a hydrogen-absorbing alloy, the hydrogen produced by catalytic dehydrogenation of saturated compounds can be absorbed to form metal hydrides, and, vice versa, the resulting metal hydrides are able to hydrogenate efficiently unsaturated compounds upon dehydriding. Gas-phase reactions between 2-butene and 2-propanol on a hydrogen-absorbing alloy CaNi₅ have been studied in the temperature range of 393–473 K. CaNi₅ showed interesting characteristics as an active catalyst for the catalytic transfer hydrogenation of butene from propanol as a hydrogen donor. 2-propanol was effectively dehydrogenated at 423 K to yield acetone in which the dissociated hydrogen was completely absorbed by CaNi₅ to form the metal hydride. When the alloy was hydrided to some extent, butene was hydrogenated by the absorbed hydrogen in the metal hydride to produce butane. The overall reaction on CaNi₅ was expressed as catalytic transfer hydrogenation of 2-butene from 2-propanol through intermediate formation of metal hydrides, rather than the direct reaction between butene and propanol on the alloy. Thus, CaNi₅ effectively repeated hydriding–dehydriding cycles: hydriding of CaNi₅ by 2-propanol dehydrogenation with subsequent dehydriding for the hydrogenation of 2-butene. The use of hydrogen-absorbing CaNi₅ provides a novel reaction system for the catalytic transfer hydrogenation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Carbon dioxide reforming of methane under periodic operation

The carbon dioxide reforming of methane under periodic operation over a commercial Ni/SiO₂·MgO catalyst was investigated at two different temperatures, 923 and 1,023 K. According to this operation, pure methane and carbon dioxide were alternately fed to the catalyst bed where methane cracking and the reverse Boudouard reaction took place, respectively. Therefore, hydrogen and carbon monoxide products appeared separately in different product streams. The performance of this operation was compared to that of the steady state operation with simultaneous feed of both carbon dioxide and methane. At 1,023 K, the methane conversion and hydrogen yield from the periodic operation initially decreased with time on stream and eventually leveled off at values about half of those obtained in the steady state operation with co-feed of both reactants. The decreased catalytic activity was due to the accumulation of carbonaceous deposit and loss of metal active sites. However, a different trend was observed at 923 K. The methane conversion and hydrogen yield were almost constant over the time on stream, although more carbonaceous deposit was progressively accumulated on the catalyst bed during the reaction course. At this temperature, the periodic operation offered the equivalent hydrogen yield to the steady state operation. The observed behavior could be due to the different mechanisms of carbon formation over the catalyst. Finally, it was found that cycle period and cycle split did not influence the reaction performance within the ranges of this study.     

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C₈ fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores.     

1-丁烯催化裂解制丙烯和乙烯反应性能的研究

以MCM-49分子筛为催化剂,纯1-丁烯为原料,考察了反应压力和空速对烯烃催化裂解制丙烯,乙烯反应性能的影响.选择适宜的反应压力和空速条件能够有效地抑制副反应,从而提高丙烯,乙烯的总产率。     

Decomposition of sec-butyl acetate on charcoal

The decomposition of sec-butyl acetate on de-ashed 20-to 30-mesh coconut-shell charcoal (1500 m²/g) was studied in a fixed bed reactor in the temperature range 300–375°C, and at partial pressures of 1 atm. and 0.29 atm. The ester decomposed principally to n-butene and acetic acid, and only small amounts of other products were found. The ratio of 1-butene to 2-butene was about 1:1, very close to that observed for thermal decomposition of the ester but far removed from the equilibrium butene ratio. The butene selectivity was independent of conversion. The rate of reaction followed the rate equation r = kA P_E/1 + AP_E This expression corresponds to surface reaction on one site being rate controlling. The activation energy of rate constant k was 32.7 kcal/mole, compared to 46.6 kcal/mole for the gas-phase reaction. The temperature dependence of adsorption constant A showed a heat adsorption of 12 kcal/mole. Gas chromatographic measurements confirmed this value and also showed that ester is the principal adsor-bate on the charcoal.     

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.     

Selective isomerization of n-butenes into isobutene over aged H-ferrierite catalyst: nature of the active species

The nature of the active species responsible for butene isomerization over aged HFER samples is reexamined in the light of the change in the product yields at very short time-on-stream and of the reversible and irreversible increases in weight of the zeolite during the reaction. At very short time-on-stream, the selectivity of butene isomerization is that expected from a dimerization-cracking process, in particular simultaneous formation of isobutene, propene and pentenes. A rapid decrease of all the yields is observed with time-on-stream; however, for isobutene but not for the other products, the initial decrease is followed (after 10 minutes-on-stream) by an increase. The decrease in the yield can be related to the formation of carbonaceous compounds (``coke') which block the access to the pores, while the increase in isobutene yield can be explained by the development of a new isomerization mode which is very selective to isobutene. This new mode could be catalyzed by carbonaceous compounds and/or by reaction products which are shown to be retained inside the pores during the reaction. It is proposed that at short time-on-stream the increase in isobutene yield is due to an autocatalytic reaction, n-butene isomerization occurring on t-butyl carbenium ions formed by adsorption of isobutene molecules (which are slowly desorbed from the pores) on the protonic sites of the zeolite. At long time-on-stream, the active species would be benzylic carbocations formed from carbonaceous compounds trapped in the pores near the outer surface of the crystallites. This revised version was published online in July 2006 with corrections to the Cover Date.     

正戊醛的合成工艺研究

以1-丁烯和合成气为原料,对氢甲酰化制备戊醛的工艺进行了研究。在热力学计算的基础上,主要考察了均相催化体系下膦铑比（摩尔比）、催化剂浓度、丁烯用量、反应温度、时间、压力、搅拌速度等条件对1-丁烯氢甲酰化反应的影响。在保持1-丁烯较高转化率和戊醛较高选择性的条件下,给出了适宜的工艺条件：反应温度为100℃左右,反应压力2．2MPa,搅拌速率250rpm,反应时间30min,催化剂浓度300—350ppm,膦铑比为400～500。     

Coke formation through the reaction of ethene over hydrogen mordenite: III. IR and 13C-NMR studies

IR and high-resolution solid-state^l3C-NMR studies provided evidence for successive steps in coke formation upon reaction of ethene over the zeolite hydrogen mordenite. Adsorbed at room temperature, ethene polymerizes to branched and possibly also linear alkanes. Upon heating up to 500 K, the alkanes isomerize and crack. Meanwhile, the¹³C-NMR spectra show the formation of carbocations of alkylic, allylic and aromatic nature. Above 500 K, high-temperature coke develops under formation of alkylaromatics and subsequently small polyaromatic and/or polyphenylene molecules. Over dealuminated hydrogen mordenites, ethene also forms paraffinic deposits at low temperatures. Above 500 K, however, a substantial amount of C₁C₄ alkanes are formed together with unsaturated species.     

A Comparison of Catalytic Oxidative Dehydrogenation of Ethane Over Mixed V-Mg Oxides and Over Those Prepared via a Mesoporous V-Mg-O Pathway

The catalytic oxidative dehydrogenation of ethane was investigated in a fixed-bed tubular microreactor at 500, 550 and 600 °C and a space velocity of 35 027ml g^-1h^-1. Two kinds of V-Mg oxides catalysts containing various V/Mg atomic ratios were employed. One group of catalysts was prepared by the solid reaction between fine powders of vanadium pentoxide and magnesium nitrate and the other ones were obtained from mesostructured V-Mg-Os. For the former catalysts, it was found that the selectivity to ethene increased and the conversion of ethane passed through a maximum with increasing V/Mg atomic ratio. For the catalysts obtained from the mesoporous materials, an optimum V/Mg atomic ratio was found, for which the conversion of ethane and the selectivity to ethene were maxima. Compared with the mixed-oxide catalysts, those obtained from the mesoporous materials exhibited much higher yields to ethene. Several new phases, such as pyro-Mg₂V₂O₇, ortho-Mg₃(VO₄)₂ and meta-MgV₂O₆, formed between magnesia and vanadia, were identified by XRD in the mixed V-Mg oxide catalysts; they may be responsible for the catalytic activity. In the catalysts prepared from mesoporous V-Mg-O, a V₂O₃ phase, which may contain highly dispersed magnesium, was identified and suggested to be responsible for the higher catalytic performance.     

Low methane selectivity using Co/MnO catalysts for the Fischer-Tropsch reaction: Effect of increasing pressure and Co-feeding ethene

CO hydrogenation using cobalt/ manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C₃ hydrocarbons at moderate reaction conditions (GHSV < 500 h^–1, < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1–2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO₂ conversion > 8 mol/1-catalyst h can be observed. Co-feeding ethene during CO hydrogenation is investigated by the reaction of¹³C0-¹²C₂H₄-H₂ mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C, species that can react further to form methane and higher hydrocarbons.     

The catalytic performance and characterization of a durable perovskite-type chloro-oxide SrFeO3–δClσ catalyst selective for the oxidative dehydrogenation of ethane

The catalytic performances and properties of SrFeO_3-0.190 and SrFeO_3-0.382Cl_0.443 catalysts have been investigated for the oxidative dehydrogenation of ethane (ODE). XRD results showed that both catalysts exhibited oxygen-deficient perovskite-type structures. The inclusion of chloride ions in the SrFeO_3-δlattice matrix can significantly enhance ethene selectivity and ethane conversion. The SrFeO_3-0.382Cl_0.443 catalyst showed an ethane conversion of ca. 90%, an ethene selectivity of ca. 70%, and an ethene yield of ca. 63% under the reaction conditions: C₂H₆:O₂:N₂ = 2:1:3.7, temperature 680°C, and space velocity 6000 ml h^-1 g^-1. With the increase of space velocity, ethane conversion decreased, whereas ethene selectivity increased over SrFeO_3-0.382Cl_0.443. Lifetime studies showed that the perovskite-type chloro-oxide catalyst was durable. The results of O₂-TPD and TPR experiments illustrated that the implanted chloride ions caused the oxygen nature of SrFeO_3-δ to change. By regulating the concentration of oxygen vacancies and the Fe⁴⁺/Fe ratio in this perovskite-type chloro-oxide catalyst, one can generate a durable chloro-oxide catalyst for the ODE reaction with excellent performance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydrogenation of Carbon Dioxide on Rh, Au and Au–Rh Bimetallic Clusters Supported on Titanate Nanotubes, Nanowires and TiO2

Supported gold, rhodium and bimetallic rhodium-core?Cgold-shell catalysts were prepared. The supports were TiO₂ as well as titanate nanotube and nanowire formed in the hydrothermal conversion of titania. The catalytic properties were tested in the CO₂ hydrogenation at 493?K. The amount and the reactivity of the surface carbonaceous deposit were determined by temperature-programmed reduction. The surfaces of the materials were characterized by X-ray photoelectron and low-energy ion scattering spectroscopy (LEIS). The surface forms during the catalytic reaction were identified by DRIFT spectroscopy. On the XP spectra of bimetallic catalysts the existence of highly dispersed gold particles could be observed besides the metallic form on all supports. Small Rh particles could also be identified on the titanate supports. LEIS spectra demonstrated that Rh-core?CAu-shell particles formed, since no scattering from Rh was detected. The main product of CO₂ hydrogenation was CH₄ on all catalysts. IR spectra revealed the existence of CO and formate species on the surface. In addition, a new band was observed around 1,770?cm^?1 which was assigned as tilted CO. It is bonded to Rh and interacts with a nearby the oxygen vacancy of the support. Agglomeration of highly dispersed Rh was observed on bimetallic samples induced by reaction or reactant.     

Catalytic cracking of 1-butene to propene and ethene on MCM-22 zeolite

Catalytic cracking of butene to propene and ethene was investigated over HMCM-22 zeolite. The performance of HMCM-22 zeolite was markedly influenced by time-on-stream (TOS) and reaction conditions. A rapid deactivation during the first 1 h reaction, followed by a quasi-plateau in activity, was observed in the process along with significant changes in product distributions, which can be attributed to the fast coking process occurring in the large supercages of MCM-22.

Properly selected reaction conditions can suppress the secondary reactions and enhance the production of propene and ethene. According to the product distribution under different butene conversion, we propose a simple reaction pathway for forming the propene, ethene and by-products from butene cracking.

HMCM-22 exhibited similar product distribution with the mostly used high silica ZSM-5 zeolite under the same conversion levels. High selectivities of propene and ethene were obtained, indicating that the 10-member ring of MCM-22 zeolite played the dominant role after 1 h of TOS. However, MCM-22 exhibited lower activity and stability than that on high silica ZSM-5 zeolite with longer time-on-stream.     

A periodic separating reactor for propene metathesis

Periodic product separation and regeneration of sorbent were accomplished in a novel reactor application through pressurisation, adsorption, blowdown and purge steps. The switching from sorption to reaction to regeneration was accomplished in a two-bed sorption/reaction apparatus. Models developed for the mass and momentum transfer in the catalyst bed and sorber were solved using orthogonal collocation within the method of lines. The effects of operating conditions and cycle configurations on performance were assessed. The results from dynamic experiments with propene metathesis to produce ethene and 2-butene in a fixed-bed catalytic reactor were in agreement with model predictions, demonstrating that conversion and product quality can be enhanced by periodic cycling reactors. Further, the separation of the products help reduce the downstream processing costs of exit mixtures, enabling utilisation of reactant through recycling and improved product handling at subsequent stages. The efficacy of the periodic separating reactor in terms of product purity, conversion, recovery, yield and productivity were demonstrated for obtaining ethene by propene metathesis.     

Single- and double-stage catalytic preferential CO oxidation in H2-rich stream over an α-Fe2O3-promoted CuO–CeO2 catalyst

Single- and double-stage catalytic preferential CO oxidation (CO-PrOx) over-Fe₂O₃-promoted CuO–CeO₂ in a H₂-rich stream has been investigated in this work. The catalyst was prepared by the urea-nitrate combustion method and was characterized by X-ray diffractometer (XRD), X-ray fluorescence (XRF), Brunauer–Emmet–Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM). The catalytic activity tests were carried out in the temperature range of 50–225 °C under atmospheric pressure. The results of the single-stage reaction indicated that complete CO oxidation was obtained when operating at a O₂/CO ratio of 1.5, W/F ratio of 0.36 g s/cm³, and at a reaction temperature of 175 °C. At these conditions, H₂ consumption in the oxidation was estimated at 58.4%. Applying the same conditions to the double-stage reaction, complete CO oxidation was found and H₂ consumption in the oxidation was reduced about 4.9%. When decreasing the double-stage reaction temperature to 150 °C, the results elucidated that CO could be converted to CO₂ completely while H₂ consumption in the oxidation was further reduced to 33.5%. A temperature blocking 2² factorial design has been used to describe the importance of the factors influencing the catalytic activity. The factorial design was according to the experimental results. When adding CO₂ and H₂O in feed, reduction of CO conversion for single- and double-stage reaction is obtained due to a blocking of CO₂ and H₂O at a catalytic active site. Comparing CO conversion obtained when operating with/without CO₂ and H₂O in feed for single- and double-stage reaction, less reduction is achieved when operating in double-stage reaction.     

Heterogeneous reactive extraction for secondary butyl alcohol liquid phase synthesis: Microkinetics and equilibria

The reaction kinetics for the liquid phase synthesis of a racemic mixture of the secondary butyl alcohols (SBA) from linear butene isomers (1-butene (1B); cis-2-butene (c2B); trans-2-butene (t2B)) and water (W) using a macroporous sulfonic acid ion exchange resin as catalyst were determined experimentally in a multiphase CSTR in the temperature range 39–433 K at 6–8 MPa. This range of pressures is necessary to dissolve butenes in the aqueous phase and to ensure a liquid state of all components. For temperatures higher than 423 K the reaction kinetics for the used catalyst size are influenced by mass transfer resistances within the catalyst matrix. The reaction takes place in the water swollen gel phase of the catalysts microspheres. Due to the large excess of water in the gel phase the compositions in the gel phase, in the macropore fluid, and in the catalyst surrounding aqueous phase are assumed to be identical. According to the literature the reaction is rather catalyzed by hydrated acid protons (specific catalysis) than by polymer-bonded-SO₃H groups (general catalysis). The experimental results can therefore be described sufficiently by a pseudo-homogeneous 3-parameter rate expression in aqueous phase activities. The forward reaction is first-order in butene. The reverse reaction is first-order in secondary butyl alcohol. The activation energy was determined to be 108 kJ/mol. Practically no pressure dependence could be observed for pressures exceeding 6 MPa. The ever-present isomerization of the linear butenes on acid catalysts was found to be remarkably faster than the hydration of butenes to SBA. Therefore, the isomerization is considered to be always in equilibrium during the olefin hydration. The formation of the possible by-product di-sec-butyl ether (DSBE) was never observed to a measurable extent. Simultaneous chemical and phase equilibria were investigated theoretically using the volume translated Peng–Robinson equation of state (VTPR-EoS) in combination with a g^E-mixing rule. Parameters of the used g^E-model were adjusted to experimental ternary liquid–liquid equilibrium (LLE) data.