Transalkylation and disproportionation of toluene and C9 aromatics over zeolite beta

Transalkylation and disproportionation (TADP) of toluene and C₉ aromatics from a commercial stream have been studied over a zeolite possessing a three-dimensional, 12-membered ring pore system. The study encompassed the effect of C₉ aromatics content in feed on TADP. Formation of xylenes was maximum with a feed containing 50 50 toluene and C₉ aromatics. In order to understand the role of different C₉ aromatics in TADP, experiments using individual C₉ aromatics with and without toluene mixture as feed were carried out. An interesting observation of these experiments was that ethyltoluenes produced xylenes through disproportionation of toluene generated from their deethylation. The total yield of xylenes was much less than that obtained from trimethyl benzenes. A reaction scheme accounting all the reactions taking place during TADP is proposed.     

Synthesis and characterization of massive molybdenum carbides and supported carbide-containing catalysts Mo2C/C prepared through mechanical activation

Procedures for the synthesis of massive molybdenum carbide by the mechanical activation of a mixture of MoO₃, commercial carbon, and Zn in air and the synthesis of the supported carbide-containing catalyst Mo₂C/C by the mechanical activation of commercial carbon impregnated with a 16% aqueous solution of ammonium paramolybdate in an inert atmosphere were developed for the first time. With the use of a set of physicochemical methods, the metal contents, particle sizes, specific surface areas, and phase compositions of the mechanically activated composites were determined. The structure of the carbide-containing supported catalyst was studied by electron microscopy, and its acidic properties were studied by the temperature-programmed desorption of ammonia; catalytic tests in the model reactions of dibenzothiophene (DBT) and alkane aromatization were performed. It was found that the Mo₂C/C catalyst exhibited high activity in these reactions: the conversion of DBT at a contact time of 3–6 h was 80–85%. The conversion of n-heptane at a contact time of 2 h was 31.2%, and 100% toluene was the reaction product. An increase in the contact time to 6 h led to a decrease in the conversion of n-heptane to 1.3%, and to 47% C₆-C₇ cycloalkanes were present in the reaction products. The results of this work are indicative of the high catalytic activity of the Mo₂C/C catalyst obtained by mechanical activation.     

Partial oxidation of methane to synthesis gas on a Rh/TiO2 catalyst in a fast flow porous membrane reactor

The partial oxidation of methane to synthesis gas has been studied over a 3% Rh/TiO₂ catalyst in a fixed bed and a novel membrane reactor under autothermal conditions using O₂ as oxidant. The membrane reactor allows the partial oxidation reaction to be performed without premixing the reactants reducing the risk of explosion even at low methane/oxygen ratios. The membrane reactor can operate autothermally and at millisecond residence time. Methane conversions of up to 65% with CO and H₂ selectivities of 90 and 82% respectively have been achieved. The low methane oxygen ratio and the high flow rates are the key factors to attain autothermal behavior. The most sensitive factor to attain high conversion and selectivities appears to be short contact time but high temperature. A kinetic model was used to interpret the experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on kinetics of catalytic isomerization of methyl linoleate

Kinetics of isomerization of methyl linoleate are studied on ruthenium (5%) on carbon in the temperature range 200–270 C with different solvents. Some equilibrium experiments also are carried out with rhodium and ruthenium catalysts. The reactions taking place are isomerization, hydrogenation and polymerization. The activities and the selectivities are dependent on the nature of the solvent used. Highly protic solvents like methanol or isopropyl alcohol exhibited very high activity and selectivity for hydrogenation, whereas aprotic solvents like hexane or cyclohexane showed very high selectivities for isomerization reaction. The reaction kinetics were found to be further complicated by polymer formation at low solvent concentrations. The effects of temperature, solvent concentration, catalyst quantity and time of reaction also were investigated.     

Partial oxidation of CH4 and C2H6 over noble metalcoated monoliths

The direct partial oxidation of hydrocarbons offers promising alternatives to chemical synthesis. By replacing endothermic processes such as steam reforming and steam cracking, fast and exothermic oxidation reactions should require much smaller and simpler reactors. However, direct oxidation reactions are much more difficult to manage because of potential heat release in total oxidation and hazardous because of the possibility of homogeneous reactions which are nonselective and can produce flames and explosions. We describe experiments in which monolith catalysts are used for partial oxidation of CH₄ and C₂H₆ to produce synthesis gas or alkenes by direct oxidation at or above atmospheric pressure in pure O₂ in nearly adiabatic reactors operating at 1000°C with very high flowrates (space velocities of 10⁶h⁻¹ and residence times of 10⁻³ s). With methane oxidation we obtain over 90% selectivities to synthesis gas (a 2:1 H₂:CO mixture) with> 90% conversion of the methane and complete conversion of O₂ on Rh coated ceramic monoliths with contact times of 10⁻³ s. With Pt catalysts under the same conditions, the H₂ selectivity drops to 70%; while with Pd, the catalyst rapidly forms carbon. This process appears to be primarily a surface reaction in which CH4 pyrolyzes on the hot Rh surface and the H atoms dimerize and the carbon is oxidized to CO. A model has been constructed which accurately predicts the conversions and selectivities and the variations between Rh and Pt. With higher alkanes, synthesis gas is produced on Rh with comparable selectivities and conversions on metal-coated monoliths. However, with Pt we observe up to 70% selectivity to alkenes with 80% conversion of alkanes at adiabatic temperatures near 1000°C with approximately 5 ms contact times. These results can be explained as occurring by predominantly surface reactions in which the alkane adsorbs to form the alkyl by H abstraction with adsorbed O atoms. Then the adsorbed alkyls undergo primarily β-elimination reactions on Pt to produce alkenes. These products are therefore far from thermodynamic equilibrium at these very short contact times, even though the temperatures are very high. The use of very short contact times and high temperatures promises to provide new routes to production of partial oxidation products with very small adiabatic reactors and thus opens up new types of reactions and reactors for chemical synthesis.     

An Improved Process for Selective Liquid-Phase Air Oxidation of Toluene

An improved process for the oxidation of toluene to obtain benzaldehyde and benzyl alcohol with high selectivities using a Co/Mn/Br^– composite catalytic system in liquid phase is described. A protocol for recovery and reuse of the composite catalyst is developed. The use of low concentrations of composite catalytic systems aimed at minimizing corrosion of the reaction, and higher concentrations of toluene affording higher productivity and recyclability of the catalyst giving high turnover number, are the remarkable achievements of the present methodology. Investigation into the recycle, aging and spectroscopic studies of the catalytic system improves the understanding of the process, chemistry and mechanism of the reaction. As the market demand for each product fluctuates, the dynamic system developed here to meet changing demands is very important to obtain one of the products in excess quantities with a change of the ratio of Br^–/Cl^–.     

Hetero-homogeneous processes involved in oxidative conversion of methane, ethane and hydrocarbon mixtures over basic oxides

The conversion, selectivities and yields of methane-oxygen and ethane- oxygen mixtures over Li/MgO catalysts have been compared. The differences which are observed are likely to be due to the much shorter life time of ethyl radicals which are rapidly transformed into ethylene, thus preventing subsequent heterogeneous deep oxidation. Data on the oxidative dehydrogenation of ethane over rare earth oxides are also reported. The insensibility of this reaction to the chemical nature of these solids contrasts with what is observed for the oxidative coupling of methane. This is also accounted for by the short life time of ethyl radicals. When mixing methane with another hydrocarbon, cross coupling occurs only if the hydrocarbon C---H bond strength is relatively small (propene, toluene) suggesting that radicals are involved. ¹³CH₄ experiments have shown that for the case of toluene, the reaction proceeds via the addition of a Cl block from CH₄. The selectivity of cross coupling compared to homo-coupling is also explained in terms of life time of radicals.     

Millisecond catalytic reforming of monoaromatics over noble metals

The millisecond autothermal reforming of benzene, toluene, ethylbenzene, cumene, and styrene were independently studied over five noble metal‐based catalysts: Pt, Rh, Rh/γ‐Al₂O₃, Rh–Ce, and Rh–Ce/γ‐Al₂O₃, as a function of carbon‐to‐oxygen feed ratio. The Rh–Ce/γ‐Al₂O₃ catalyst exhibited the highest feedstock conversion as well as selectivities to both synthesis gas and hydrocarbon products (lowest selectivities to H₂O and CO₂). Experimental results demonstrate a high stability of aromatic rings within the reactor system. Benzene and toluene seem to react primarily heterogeneously, producing only syngas and combustion products. Ethylbenzene and cumene behaved similarly, with higher conversions than benzene and toluene, and high product selectivity to styrene, likely due to homogeneous reactions involving their alkyl groups. Styrene exhibited low conversions over Rh–Ce/γ‐Al₂O₃, emphasizing the stability of styrene in the reactor system. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Noncatalytic and catalytic pyrolysis of toluene

Noncatalytic and catalytic pyrolysis of toluene has been studied at atmospheric pressure in the temperature range of 1043 to 1153 K using steam or nitrogen as the diluent. The catalyst used was potassium carbonate impregnated calcium aluminate. Compared to noncatalytic pyrolysis, the conversions were significantly higher in the presence of the catalyst although the product selectivities were not affected. With nitrogen as the diluent the main products were hydrogen, methane, benzene, bibenzyl and higher hydrocarbons. When steam was used as the diluent, in addition to the above products appreciable amounts of carbon monoxide and carbon dioxide were also produced. The overall reaction of toluene could be represented by two parallel paths; one for toluene decomposition and the other for the toluene-steam reaction. The kinetic constants of these two reactions for catalytic as well as noncatalytic pyrolysis were determined by nonlinear optimization. In the presence of the catalyst, the activation energy for toluene decompostion was significantly reduced, whereas there was only a marginal reduction in the activation energy of the toluene-steam reaction.     

Oxidative dehydrogenation of propane over monoliths at short contact times

A specially designed tubular microreactor with independent control of feed preheat as well as catalyst temperature and allowing to rapidly quench reaction products was used to test performance of supported Pt-based monolithic catalysts in the reaction of propane oxidative dehydrogenation at short contact times. To minimize the impact of undesired homogeneous reactions capable of decreasing propylene selectivity, proprietary straight-channel thin-wall high cell density corundum micromonoliths were chosen as supports. Catalytic properties of supported platinum were modified by using promoters known as dehydrogenation catalysts (tin, zinc aluminate spinel, transition metal pyrophosphates) as well as by tuning reaction mixture composition (propane/oxygen ratio, water and hydrogen content). In the operation temperature range up to 900°C with contact times 0.03–0.1 s, ethylene/propylene selectivities were found to strongly depend upon the chemical composition of the active component and type of feed. The results thus obtained demonstrate that for Pt-based catalysts, propylene yield can be substantially improved by suppressing secondary reactions of deep oxidation and cracking.     

甲苯液相均相选择性催化氧化研究进展

将甲苯液相均相选择性催化氧化反应的催化剂分为：过渡金属盐、杂多化合物、过渡金属配合物、非金属化合物、复合催化剂等,对反应条件、结果和机理进行了总结。杂多化合物或金属卟啉参与反应时,反应条件较温和,对苯甲醛和苯甲醇的选择性高。复合催化剂通常表现出更好的催化性能,而且,当催化剂由非金属催化剂和金属催化剂组成时,对产物的选择性主要取决于金属催化剂部分。此外,以甲苯侧链的氧化为重点阐述了反应机理,指出开发更高效的复合催化剂和粗甲苯的氧化工艺是今后的发展重要方向。     

Production of p‐toluenesulfonic acid by sulfonating toluene with gaseous sulfur trioxide

Toluene was sulfonated by gaseous sulfur trioxide to prepare p‐toluenesulfonic acid. The effects of reaction temperature and toluene conversion on the isomer selectivities and the dynamic viscosity of the reaction mixture in a well‐stirred tubular glass reactor of 4 cm diameter and 16 cm height were investigated. Lower selectivity to the m‐isomer was obtained at lower reaction temperature and lower conversion of toluene, whereas the selectivity to the p‐isomer seemed to be less affected by these parameters. With the increase in toluene conversion a sharp increase in viscosity of the reaction mixture was observed, which was attributed to the saturation of the toluenesulfonic acids dissolved in toluene. A pilot‐scale stainless steel jet loop reactor (JLR) of 0.3 m diameter and 4 m height with an external cooler was constructed and used for the continuous sulfonation of toluene. It was found that the JLR was very effective for the fast removal of the large amount of reaction heat, and selectivities to the p‐isomer around 85% and to the m‐isomer below 1.2% were obtained. © 2001 Society of Chemical Industry     

基于PX选择性强化的短流程甲苯甲醇甲基化PX生产新工艺

基于改性的高硅铝ZSM-5催化剂反应动力学模型,本文探讨了甲苯甲醇甲基化反应中影响对二甲苯（PX）选择性的因素,提出了基于选择性强化的短流程甲苯甲醇甲基化PX生产工艺,并从原料利用率、能耗以及经济指标等角度,与已有工艺进行了对比分析。结果表明,在短停留时间、高甲苯/甲醇进料比、高稀释剂/甲醇进料比、较低反应温度和压力条件下,可以促使PX在二甲苯异构体中的选择性达到99.7 %以上。短流程PX生产工艺规避了二甲苯异构体的分离,具有原料利用率高、能耗低、工艺简单的特点,具有良好的经济性。当前工艺研究进一步提升了甲苯甲醇甲基化PX生产工艺的技术竞争力,利用非石油基的甲醇,有助于形成煤化工和石油化工技术互补、协调发展的新格局。     

Optimization by response surface methodology (RSM) for toluene adsorption onto prepared acid activated clay

Adsorption of toluene onto acid activated clay was carried out. Modified clay was prepared by acid attack (H₂SO₄) on raw material. Response surface methodology based on a 2‐level, 4‐variables central composite orthogonal design was used to evaluate the effects of important parameters on the adsorption of toluene on to activated clay. Temperature (53.8–96.2°C), contact time (0.57–6.93 h), mass ratio of liquid/solid (3.38–7.62) and strength of acid (7.75–57.24%) were chosen as process variables for the optimization. Of these parameters, temperature reaction and time had greater impact on toluene adsorption than did the other parameters. Analysis of variance (ANOVA) shows a good agreement between theoretical analysis and experimental data. The validity of model is verified by an experiment at the optimum conditions. The optimum conditions for the maximum adsorption of toluene onto activated clay are: temperature of 96.2°C, a contact time of 6.93 h, a liquid/solid ratio of 5.98 and strength of acid of 32.94%. Since the predicted values and the actual experimental value obtained for the maximum adsorption of toluene are within 95% confidence intervals, the final model is considered valid and has satisfactory predictive ability.     

Catalytic combustion of natural gas as the role of on-site heat supply in rapid catalytic CO2---H2O reforming of methane

Development in highly active catalysts for the reforming of methane with H₂O, CO₂, and H₂O+CO₂, and partial oxidation of methane was conducted to produce hydrogen with high reaction rates. A Ni-based three-component catalyst such as Ni---La₂O₃---Ru or Ni---Ce₂O₃---Pt supported on alumina wash-coated ceramic fiber in a plate shape was very suitable for both reactions. The catalyst composition was set at 10 wt.-% Ni, 5.6 wt.-% La₂0₃, and 0.57 wt.-% Ru for example, or molar ratios of these components were 1:0.2:0.03. Even with such a low concentration, the precious metal enhanced the reaction rate markedly, and this synergistic effect was ascribed to the hydrogen spillover effect through the part of precious metal and it resulted in a more reduced surface of the main catalyst component. In particular, a marked enhancement in the reaction rate of CO₂-reforming of methane was observed by the modification of a low concentration Rh to the Ni---Ce₂0₃---Pt catalyst. Very high space-time yields of H₂ (i.e., 8300 mol/1 h in partial oxidation of methane at 600°C with a methane conversion of 37.5%, and 3585 mol/1 h in CO₂reforming of methane at 600°C with a methane conversion of 58%) were realized in those reactions. By combining the catalytic combustion reaction, methane conversion to syngas was markedly enhanced, and even with a very short contact time (10 ms) the conversion of methane increased more than that at 50 ms. The space-time yield of hydrogen amounted to 2,780 mol/1 h with a methane conversion of 90% at 700°C. Furthermore, in a reaction of CH₄---CO₂---H₂O---O₂ on the four components catalyst, an extraordinarily high space-time yield of hydrogen, 12 190 mol/1 h, could be realized under the conditions of very high space velocity (5 ms).     

Cationic polymerization of isobutylene by AlCl3 in n-hexane and toluene at mild temperatures

This study aims to find more efficient ways to manufacture highly reactive polyisobutylene (HRPIB) and modified conventional PIB materials (MCPIB) industrially with high vinyl exo-group contents through cationic polymerization at mild temperatures. The study performed polymerizations using aluminum trichloride (AlCl3) as a catalyst with different nonpolar solvents (hexane and toluene), reaction temperatures (10 and 30°C), and co-catalysts (water and dibutyl ether [DBE]). At 30°C, toluene can provide vinyl contents above 30 mol%. Particularly, an important synergetic effect was observed between toluene and ether, as corroborated by statistical analyses, resulting in vinyl contents above 50 mol%, while reactions performed in n-hexane provided maximum vinyl content of 20 mol%. In all cases, number average molar masses ranged from 200 to 1000 Da, which are typical of CPIB and MCPIB materials. Moreover, addition of excess of ether indicated the likely inhibition of reaction rates in presence of high ether concentrations (≥1.18 × 10 ⁻¹ mol/L). The obtained results indicated that AlCl3 can be used successfully to manufacture MCPIB products with terminal vinyl contents above 50 mol% at mild temperatures in common nonpolar solvents (n-hexane and toluene) and in presence of common co-catalysts (water and DBE) with high rates of reactions.     

Mono (V, Nb) or bimetallic (V–Ti, Nb–Ti) ions modified MCM-41 catalysts: synthesis, characterization and catalysis in oxidation of hydrocarbons (aromatics and alcohols)

Mesoporous MCM-41 molecular sieves modified by single (V and Nb) or bimetal (Nb–Ti and V–Ti) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis with two different silica sources (sodium silicate and TEOS) and characterized (as-synthesized samples and those used after reaction) by XRD, N₂ adsorption–desorption, TEM, SEM and FTIR techniques. Niobium and titanium were stabilized in the autoclavized gel by complexation with a ligand (acetylacetone and oxalic acid, respectively). V modified MCM-41 catalysts gave a very high activity in hydroxylation reaction of benzene and toluene and a low conversion in oxidation of styrene while Nb-modified MCM-41 samples showed very high conversion in oxidation of styrene but low oxidation conversion of benzene and toluene. Further introduction of titanium in V- and Nb-modified MCM-41 materials conducted to the less well-ordered hexagonal arrangement and gave very different effect on activity in oxidation of aromatics. Introduction of Ti into V-MCM-41 solids led to an increase in activity in oxidation of styrene and benzene but a decrease in conversion in oxidation of toluene. While the addition of Ti in Nb-MCM-41 resulted in a slight increase in conversion of styrene oxidation but a significant decrease in activity of benzene and toluene oxidation. It reveals that the introduction mode of oxidant in the reactors can also influence the activity and selectivity of reaction. An increase in reaction rate of oxidation, in the first 20 h, was obtained by introduction of H₂O₂ step by step during the reaction. The present paper evidenced that the side chain oxidation is main reaction of styrene oxidation while the hydroxylation is main reaction of benzene and toluene. That is why these two reactions need different catalytic centers as revealed by this paper. The oxidation of alcohols using V-modified MCM-41 as catalysts has also been explored and these catalysts showed a very low catalytic activity which increases in the order: hexanol相似文献   

Mixed nickel-aluminium oxides catalysts for the nitroxidation of toluene by no into benzonitrile

This paper describes the catalytic properties (activities, selectivities and stabilities with time on stream) of nickel oxide-alumina aerogels and xerogels, towards the transformation of toluene by NO into benzonitrile at 440°C in a differential flow reactor. The stability of the catalysts depends upon the NiO content. When the ratio Ni/Al increases to unity, the catalysts (aerogel as well as xerogel) are very stable with time on stream and are active and selective like pure nickel oxide. The latter is indeed initially active and selective, but very unstable with time on stream. A redox model is proposed to explain the reaction mechanism.     

Characterization of bimetallic rhodium-germanium catalysts prepared by surface redox reaction

The preparation of bimetallic rhodium-germanium/silica and rhodium-germanium/alumina catalysts was investigated by controlled surface reaction. Their catalytic performances were measured for two gas phase reactions (toluene hydrogenation at 323 K and cyclohexane dehydrogenation at 543 K) and for a liquid phase reaction (citral hydrogenation at 343 K).

Elemental analysis of bimetallic catalysts showed that germanium can be deposited by redox reaction between hydrogen activated on a parent monometallic rhodium catalyst and germanium tetrachloride dissolved in water (catalytic reduction method). EDX microanalysis of rhodium-germanium/silica catalysts indicated that rhodium and germanium were deposited in close contact on the silica support. However, on alumina-supported catalysts, germanium deposition occurred also separately on the support. For the different test reactions, the catalytic properties of rhodium were strongly altered by the addition of germanium. On alumina-supported catalysts, interesting catalytic effects were observed in citral hydrogenation when not only close contact exists between both metals but when, in addition, the second metal was deposited on the support in the close vicinity of rhodium.     

Cyclodimerisation and Cyclotrimerisation During the Ring-Opening Reactions of Ethylene Sulfide (Thiirane) over Acidic Molecular Sieves and Alumina

Liquid phase benzylation (by benzyl chloride) and acylation (by benzoyl chloride) of benzene and toluene over a Ga–Mg hydrotalcite (which is a basic anionic clay) with or without HCl gas pretreatment and also over the hydrotalcite used earlier in the toluene benzylation (at 110°C) have been investigated. The fresh, used and HCl-gas-pretreated hydrotalcite catalysts were characterized for their surface area, basicity, crystalline structure and phases and also for their surface composition. The fresh hydrotalcite showed no catalytic activity for both the benzylation and benzoylation reactions for a long period. However, after a long induction period (2.7 h), the catalyst showed a very high activity in the toluene benzylation (at 110°C). Whereas, the catalyst after its use in the toluene benzylation or after its HCl gas pretreatment showed very high activity for both the reactions with a much shorter induction period. The hydrotalcite-derived catalyst consists essentially highly dispersed gallium and magnesium chlorides on MgO. The presence of moisture in the reaction mixture has beneficial effects on the acylation reactions over the used catalyst.