Variants of the organization of a controlled-temperature-profile catalyst bed in a tubular reactor for the single-step water gas shift reaction

The possibility of bringing the actual temperature profile along the catalyst bed to the profile maximizing the CO conversion in the water gas shift (WGS) reaction in a tubular reactor is considered for new, highly efficient catalysts as heat-conducting composite plates (HCCPs). It is demonstrated by the example of a controlled-temperature-profile (CTP) tubular reactor integrated into an experimental model of a fuel cell of a 5-kW power plant that the efficiency of the WGS process can be raised by using the catalyst as HCCPs. Use of these catalysts in CTP apparatuses can markedly increase the efficiency of the WGS stage of natural gas reforming for ammonia synthesis, hydrogen production, and the production of fuel gas for fuel cells.     

Esterification of decanoic acid with methanol using Amberlyst 15: Reaction kinetics

Methyl decanoate is used as a surrogate fuel. The surrogate fuels are structurally similar to actual biodiesel. We synthesized methyl decanoate in a small batch reactor by esterification reaction using decanoic acid and methanol on solid acid catalyst Amberlyst 15 used in dry state. The outcome of different reaction parameters including catalyst loading, temperature, molar ratio, stirrer speed, water concentration effect, and adsorption on catalyst pellets were studied for optimization of rate of conversion. The effect of external and internal diffusion limitations on catalyst granules was calculated theoretically from the reaction kinetics data. An analysis of the reaction kinetics revealed that the esterification reaction was rate controlled by adsorption of methanol on the solid acid catalyst and the reaction can be modeled as Eley–Rideal model. Activation energy of the esterification reaction was 39.4?KJ/mol. Reaction enthalpy and entropy were found to be 29.81?kJ/mol and 87.38?J/mol. K, respectively.     

Preparation of zeolite-coated pervaporation membranes for the integration of reaction and separation

Pervaporation is a promising option to enhance conversion of reversible condensation reactions, generating water as a by-product. In this work, composite catalytic membranes for pervaporation-assisted esterification processes are prepared. Catalytic zeolite H-USY layers have been deposited on silica membranes by dip-coating using TEOS and Ludox AS-40 as binder material. Membrane pre-treatment and the addition of binder to the dip-coat suspension appear to be crucial in the process. Tuning of catalytic layer thickness is possible by varying the number of dip-coat steps. This procedure avoids failure of the coating due to the high stresses, which can occur in thicker coatings during firing. In the pervaporation-assisted esterification reaction the H-USY coated catalytic pervaporation membrane was able to couple catalytic activity and water removal. The catalytic activity is comparable to the activity of the bulk zeolite catalyst. The collected permeate consists mainly of water and the loss of acid, alcohol and ester through the membrane is negligible. The performance of the membrane reactor is mainly limited by reaction kinetics and can be improved by using a more active catalyst.     

Design and elaboration of new solid acids for the synthesis of butylacetate

New and efficient solid-acid catalysts were designed and prepared by the coprecipitation-impregnation method, for the esterification of acetic acid and butanol synthesizing the butylacetate ester in fine chemical industry, in which the conventional catalyst was sulfuric acid. This work resulted in a cleaner process for acid-catalyzed reaction. The preparation parameters in the precipitation step and in the calcination were improved for a better performance. With the optimized new solid-acid catalyst, a good ester yield of 93.3% was achieved with the selectivity of 96.0%. The samples were characterized by XRD, N₂-adsorption and TGA measurements, the SO₄²⁻ anion was essential in the active structure.     

Novel Esterification of Glycerol Catalysed by Tin Chloride (II): A Recyclable and Less Corrosive Process for Production of Bio-Additives

Abstract  

In this work, a novel process based on use of a SnCl₂·2H₂O catalyst which is less corrosive, inexpensive, and a water tolerant Lewis acid was employed for synthesis of fuel bio-additives from glycerol. High yields and selectivities were achieved for glycerol esterification with acetic acid under mild reaction conditions. The SnCl₂ catalyst showed to be as active as p-toluene sulfonic and sulfuric acid, catalysts commonly used in acid-catalysed esterification reactions. However, its use has significant advantages in comparison to these Br?nsted acid catalysts, including lower reactor corrosion and unnecessary neutralization at the end reaction. The SnCl₂ catalyst can also be recovered and reused without loss of catalytic activity. Additionally, effects of reaction temperature, HOAc:glycerol molar ratio and catalyst concentration on both selectivity and yield of glycerol acetates were also investigated. The lower corrosiveness, facilitated handling, as well as potential for reuse without activity loss after simple recycle protocols are positive aspects of SnCl₂ catalysts.     

Esterification in a structured catalytic reactor with counter-current water removal

In this research the liquid phase esterification of hexanoic acid and 1-octanol was studied. Very high activities were obtained for zeolite BEA and Nafion/silica composite with 13% of Nafion. The advantage of water removal in this system was demonstrated. In a closed system an equilibrium conversion of 35% was reached, while in a system with water removal all the reactants were converted in a shorter period. The initial reaction rate decreases when increasing the initial water concentration, following a Langmuir–Hinshelwood type of rate expression. An active zeolite coated structured monolithic reactor configuration was prepared. Enhancement by the counter-current water stripping of the performance of the structured catalysts was demonstrated.     

Liquid-phase esterification of acetic acid with isobutanol catalyzed by ion-exchange resins

Esterification of carboxylic acids with alcohols represents well-known liquid-phase reactions of considerable industrial interest due to the importance of organic ester products. These ester products include environmentally friendly solvents, flavors, pharmaceuticals, plasticizers, and cosmetics.In this study, the esterification kinetics of acetic acid with isobutanol in 1,4-dioxan as a solvent without adding a catalyst and catalyzed by ion-exchange resins are carried out using a batch reactor. The effect of catalyst type, stirrer speed, the effects of reaction temperature and catalyst loading on the initial reaction rate, the effect of speed of agitation and the conversion of acetic acid versus time were investigated. The kinetics of heterogeneous catalyzed esterification of acetic acid with isobutanol was correlated by a kinetic model based on pseudo-homogeneous catalysis. The strong acidic cation exchange resins were used as solid catalysts, Dowex 50 Wx2, Amberlite IR-120, respectively. As a result, it was found that the weight-based activity of the heterogeneous catalysts increases in the following order: Dowex 50 Wx2 > Amberlite IR-120 and these catalysts were effectively for the synthesis of isobutyl acetate under these experimental conditions.     

Towards an efficient process for small-scale, decentralized conversion of methane to synthesis gas: combined reactor engineering and catalyst synthesis

Anthropogenic methane emissions not only pose an increasing global problem but can also be seen as an untapped renewable resource for hydrogen or liquid fuel production. Utilization of this resource requires the development of efficient processes for small-scale, decentralized methane conversion. We see catalytic partial oxidation of methane to synthesis gas as an ideal candidate for such a process. In the present study, we investigate the effect of heat-integration, flow rate and catalyst stability on syngas yields over alumina-supported Pt and Rh catalysts in a reverse-flow reactor configuration. We furthermore demonstrate that novel high-temperature stable nanocomposite catalysts can dramatically lower the noble metal requirement for this reaction, improve catalyst stability and further increase synthesis gas yields. Finally, we demonstrate that the combination of the reverse-flow reactor with these nanocomposite catalysts exploits the efficiency of this reaction route very effectively while maintaining a simple and compact reactor design.     

氧化酯化反应催化剂的研究进展

本工作综述了近年来醛或醇氧化酯化催化剂的研究进展,介绍了均相催化剂和非均相催化剂的研究情况,其中均相反应体系,催化剂不易分离且能耗较大,价格普遍偏高,适用于氧化酯化的均相反应体系难以工业化。非均相反应体系在工业化方面具有很大优势,催化剂分离简单易还原、可回收再利用等,但同样存在稳定性较差及收率较低的问题。分析了贵金属催化剂和非贵金属催化剂的合成、结构及催化醛氧化酯化性能,总结了部分催化剂催化醛氧化酯化的反应机理。通过各种制备方法调控催化剂的结构、形貌、比表面积,进而暴露大面积活性面及延长催化剂的使用寿命来提高催化剂的经济效益。展望了氧化酯化反应催化剂的研究方向,贵金属催化剂由于成本限制,非贵金属催化剂将是未来醛氧化酯化领域重点研究的方向。     

Modeling of a metal monolith catalytic reactor for methane steam reforming-combustion coupling

A novel metal monolith reactor for coupling methane steam reforming with catalytic combustion is proposed in this work, the metal monolith is used as a co-current heat exchanger and the catalysts are deposited on channel walls of the monolith. The transport and reaction performances of the reactor are numerically studied utilizing heterogeneous model based on the whole reactor. The influence of the operating conditions like feed gas velocity, temperature and composition are predicted to be significant and they must be carefully adjusted in order to avoid hot spots or insufficient methane conversion. To improve reactor performance, several different channel arrangements and catalyst distribution modes in the monolith are designed and simulated. It is demonstrated that reasonable reactor configuration, structure parameters and catalyst distribution can considerably enhance heat transfer and increase the methane conversion, resulting in a compact and intensified unit.     

Using vanadium catalysts for the oxidation of hydrogen chloride with molecular oxygen

Regeneration of chlorine by oxidation of hydrogen chloride is an important problem in the production of chloroorganic products. The known catalysts for this reaction are insufficiently active and typically not stable enough, while data on the use of V catalysts for this process are absent. Here we report on our study of the stability and catalytic activity of the industrial sulfuric acid production sulfate-promoted vanadium catalyst IK-1-6 in the process of oxidation of hydrogen chloride with molecular oxygen. Under conditions of low conversion (less than 15%) with the reaction in the external diffusion region, the catalyst activity attained 660 g/(kg cat h) at 400°C, and the mass loss rate of the catalyst was (due to the formation of volatile vanadyl chloride) 4.6 % per hour, based on vanadium. Under high conversion conditions (over 60%), the vanadyl chloride formed in the top layer of the catalyst was hydrolyzed and precipitated on subsequent layers as the conversion of the reaction mixture increased, leading to a redistribution of vanadium over the catalyst bed height and hindering its removal form the reactor. The stable operation of the catalyst can be ensured by intermittently changing the flow direction of the reactant gas in the catalytic reactor or using an array of several reactors connected in series, intermittently changing their places in the inlet-outlet chain. Our results show that the industrial sulfate-promoted vanadium catalysts for the oxidation of sulfur dioxide are more active and stable than all known catalysts of the Deacon process (except for ruthenium catalysts) and could be used for catalytic oxidation of hydrogen chloride.     

合成乙酸异龙脑酯催化剂的研究

研究分子筛催化剂HYI在合成乙酸异龙脑酯反应中的性能,考察焙烧温度、反应温度及颗粒度对催化剂反应性能的影响,在优化反应条件下考察催化剂稳定性。结果表明,在焙烧温度500 ℃制备的催化剂具有较高的活性、选择性和稳定性,催化剂直径小于2 mm条件下,可以消除内扩散对催化剂的影响。在反应温度75 ℃、常压和莰烯空速0.6 h^-1条件下,莰烯转化率74%,乙酸异龙脑酯选择性94%,成型催化剂在固定床反应器上连续稳定反应2 500 h以上。利用N₂吸附-脱附、NH₃-TPD和TG-DSC对HYI催化剂进行表征,分析催化剂的失活原因,结果表明,催化剂失活主要与反应过程中积炭导致的比表面积和孔容下降有关,催化剂活性可以通过烧焦再生恢复,具有良好的工业应用前景。     

Selective catalytic reduction of nitrogen oxide by hydrocarbons over mordenite-type zeolite catalysts

The reduction of NO by hydrocarbons such as C₂H₄, C₂H₆, C₃H₆, and C₃H₈ has been investigated over mordenite-type zeolite catalysts including HM, CuHM, NZA (natural zeolite), and CuNZA prepared by an ion-exchange method in a continuous flow fixed-bed reactor. NO conversion over CuNZA catalyst reaches about 94% with 2000 ppm of C₃H₆ at 500°C. As reductants, alkenes seem to exhibit a higher performance for NO conversion than alkanes regardless of the catalysts. No deterioration of the catalytic activity due to carbonaceous deposits for CuNZA was observed above 400°C even after 30 h of on-stream time, but SO₂ in the feed gas stream causes a severe poisoning of the CuNZA catalyst. The effect of H₂O on NO conversion was significant regardless of the catalysts and the reductants employed in this study. However, CuNZA catalyst shows a unique water tolerance with C₃H₆. The reaction path of NO to N₂ is the most important factor for high performance of this catalytic system. NO is directly reduced by a reaction intermediate, C_n′H_m′(O) formed from hydrocarbon and O₂, N₂O is another reaction intermediate which can be easily removed by C_n′H_m′(O).     

Kinetics of catalytic esterification of propan-1-ol with propanoic acid using cation-exchange resin

The kinetics of liquid phase esterification of propan-1-ol with propanoic acid catalysed by Dowex-50W cation-exchange resin in the H⁺ form have been studied in a batch reactor. The effects of catalyst concentrations, mol ratios and temperatures on the conversion were studied. An empirical correlation relating the specific reaction rate constant in terms of these variables has been developed, and a mechanism proposed on the lines of the Langmuir-Hinshelwood model. The effect of different catalysts on the conversion is compared.     

非酸性催化剂催化合成均苯四酸四辛酯研究

以均苯四甲酸二酐（或酸）与2-乙基己醇在非酸性催化剂存在下进行酯化反应,合成了均苯四酸四（2-乙基己）酯增塑剂（统称均苯四酸四辛酯增塑剂）。研究了催化剂用量、投料配比、反应温度及时间对均酐（酸）转化率的影响,确定了最佳工艺条件,转化率可达99．8％。对酯化动力学进行了初步研究,并建立了300吨／年生产装置。采用非酸性催化剂进行酯化反应,取消了中和、水洗工序,降低了原料消耗,减少了废水,回收醇的质量也得到改善。     

Mesoporous materials as host for an entrapped enzyme

Three mesoporous materials, silica, alumina and titania, were used as host for a lipase and the enzyme-loaded particles were employed as catalyst for esterification of caprylic acid using a mixture of glycerol and water as reaction medium. The reaction proceeded well with all three oxides but alumina gave considerably higher conversion than the other two. Hydrophobized silica gave an even higher degree of esterification. The degree of esterification obtained is believed to depend on the microenvironment of the enzyme. When alumina, which is positively charged under the conditions used, and hydrophobized silica are used as host material, the negatively charged lipase can be assumed to be adsorbed at the walls of the pores. The water activity is believed to be lower at the solid surface than in the middle of the pores, where the enzyme is situated when silica and alumina are used as host material. It is shown that the lipase is not irreversibly entrapped in the pores of the mesoporous materials. When the particles are removed by filtration after completed reaction and subsequently washed with an aqueous buffer, the enzyme is leached out. The lipase can be immobilized in the pores, however, by cross-linking in situ inside the pores using glutaraldehyde as cross-linking agent. Mesoporous materials loaded with cross-linked lipase can be reused several times with only marginal loss of activity.     

Pervaporation membrane reactor study for the esterification of acetic acid and isobutanol using polydimethylsiloxane membrane

In this study, isobutyl acetate, a valuable solvent in cosmetics, aroma and paint industries, is produced by pervaporation–esterification equilibrium reaction in a batch pervaporation membrane reactor (PVMR) using homogeneous (sulphuric acid) and heterogeneous (Dowex 50W-X8) catalysts. The effects of catalyst loading, catalyst type, reaction time, membrane thickness, temperature and initial molar ratio of reactants were investigated. A cross-linked polydimethylsiloxane (PDMS) membrane selective to esters was prepared and used in PVMR. Batch reactions were carried out also in a simple batch reactor (SBR) without pervaporation under the same conditions to compare the conversions for the reactions with and without pervaporation. In conclusion, PVMR experiments showed that the PDMS membrane can be used to remove the isobutyl acetate formed selectively with acceptable conversions and pervaporation fluxes.     

Preparation and characterization of zeolite catalysts for etherification reaction

Catalytic etherification of 2-naphthol with ethanol has been carried out over a series of solid-acid catalysts such as H-Beta, H-MOR and H-ZSM-5 using a flow-type reactor. H-Beta zeolite shows higher conversion and catalytic stability than other catalysts for the production of 2-naphthyl ethyl ether, which may be correlated to the amount and strength of acid sites. H-Beta zeolites with different Si/Al ratios show that conversion decreases with increasing Si/Al ratios. The NH₃-TPD profiles indicate that the weak acidity decreases more sharply with increase in Si/Al ratios, compared with the strong acidity. The influences of ethanol/2-naphthol molar ratios, reaction temperature, and space velocity with respect to catalytic activities are investigated for H-Beta zeolite in the present work.     

Kinetic modeling of benzoic acid esterification using functionalized silica gel

In our study, we synthesized two types of solid acid catalysts. Silica gel with a particle size of 0.063–0.2?mm was silanized first at reflux (S1) and second at room temperature (S3) using (3-mecaptopropyl)trimethoxysilane in toluene, and further oxidized with H₂O₂, and methanesulfonic acid. Characterization of the synthesized catalysts was performed using adsorption/desorption of nitrogen (BET), Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Both catalysts were used in esterification reactions of benzoic acid with methanol. All reactions were performed in a batch reactor at temperatures, ??=?55, 60, and 64.5°C, stirrer speed, f_s?=?400?min^?1, and catalyst loading, m?=?5, 10, and 15?g. The concentration of produced methylbenzoate was determined by HPLC. The study was supplemented with a kinetic study of the reaction. First-order kinetics was confirmed for this esterification reaction. Using catalyst S1, higher conversion was reached, while catalyst S3 is much more suitable for reuse.     

AlMCM-41介孔分子筛催化合成苯甲酸甲酯的研究

本文以介孔分子筛AlMCM-41为催化剂,采用碳酸二甲酯(DMC)作为酯化试剂与苯甲酸(BA)反应制备苯甲酸甲酯(BA)。反应结果表明,碳酸二甲酯是一种很好的酯化试剂,介孔分子筛AlMCM-41对此酯化反应是高效的催化剂。并且还发现苯甲酸的转化率和苯甲酸甲酯的选择性与催化剂上的Lewis酸位有很大联系。另外本文还讨论了此反应的机理。