Water removal by reactive stripping for a solid-acid catalyzed esterification in a monolithic reactor

Solid-acid catalysts are attractive replacements for processes using conventional homogeneous catalysts. In the esterification of an alcohol with a carboxylic acid, however, the side product water strongly inhibits the activity of a solid-acid catalyst. Since an esterification is an equilibrium limited reaction, full conversion is not possible unless one of the products is removed. A novel reactor type, utilizing a solid-acid catalyst coated monolith, is presented in which water can be removed from the liquid reaction mixture by means of reactive stripping. In this manner the inhibition is eliminated and complete conversion can be reached. The advantages of this reactor concept are demonstrated by both experiments and reactor modeling.     

非酸催化酯化合成对苯二甲酸二异辛酯的反应动力学

由对苯二甲酸与异辛醇在ＳｎＣｌ_２非酸催化剂作用下酯化合成了对苯二甲酸二异辛酯。研究了酯化反应的动力学行为，提出酯化反应的速率方程（－ｄＣ_Ａ）／（ｄｔ）＝ｋＣ_Ａ，反应表观活化能Ｅ＝４０．ｋＪ／ｍｏｌ，反应速率常数ｋ＝３．８２×１０~４ｅｘｐ（－４８３７／Ｔ）。     

A structured test reactor for the evaporation of methanol on the basis of a catalytic combustion

The kinetics of the catalytic deep oxidation of methanol was studied in stacked segments of a turbulence insert (SSTIs) coated with Pt/γ-Al₂O₃ and Pt/zeolite catalysts. These geometries, which are termed a structured test reactor in the heading, are intended to replace plane expanded metal discs (PEMDs) used in the so-called catalytic burner at Research Centre Jülich, up to the present. The catalytic burner performs the low-pollution combustion inter alia of the anode exhaust gases of the fuel cell. SSTIs coated with Pt/γ-Al₂O₃ showed different kinetics for differential conversions as a function of temperature. At low reaction temperatures (100–130°C) ignition kinetics with a very high activation energy of 60.3 kJ/mol was found. In the further course of the reaction, the kinetically controlled reaction with an activation energy of 48.5 kJ/mol was observed. In the range of non-differential conversions, the activation energy decreased significantly, which suggests a limitation of the reaction process by mass transport phenomena. Compared to the PEMDs, clearly higher reaction rates were observed, which enable a reduction of the catalyst mass. This as well as the spatial structure of the SSTIs make it possible to achieve a reduction in volume and weight and thus improved dynamics in constructing a novel catalytic burner. The SSTIs coated with Pt/zeolite showed perceptibly lower reaction rates than the Pt/γ-Al₂O₃ substrates and could thus not compete with the PEMDs.     

A structured catalytic bubble column reactor: hydrodynamics and mixing studies

This paper reports the results of a comprehensive experimental study of the hydrodynamics and mixing in two bubble column reactors of 0.1 and 0.24 m in diameter with KATAPAK-S^® as packing material. Total gas hold up and axial dispersion coefficients were measured in the structured bubble columns and the values were compared with experimental results obtained in the same work with empty bubble columns. The results reveal that the gas hold up in structured bubble columns is practically the same as in empty bubble columns when compared at the same superficial gas velocity based on open area available for gas–liquid dispersion. The presence of the structured elements in the bubble column reactor reduces the liquid phase backmixing by one order of magnitude.     

Simultaneous methanol removal and destruction from wastewater in a trickle-bed reactor

The stripping of methanol from wastewater was studied in a trickle-bed reactor packed with a mixture of hydrophobic catalyst and hydrophilic support. The process involves air stripping of methanol followed by a gas phase oxidation of methanol into CO₂ and H₂ O over a platinum catalyst. At temperatures between 25 and 70°C, the overall rate was found to be controlled by the stripping step. Since the oxidation results in a lower concentration of methanol in the gas phase, the increased driving force for interfacial mass transfer leads to higher overall methanol removal efficiency.     

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.     

Esterification of acetic acid with ethanol: Reaction kinetics and operation in a packed bed reactive distillation column

The reaction kinetics of the esterification of acetic acid with ethanol, catalyzed both homogeneously by the acetic acid, and heterogeneously by Amberlyst 15, have been investigated. The reactions were carried out at several temperatures between 303.15 and 353.15 K and at various starting reactant compositions. Homogeneous and heterogeneous reactions have been described using the models proposed by Pöpken et al. [T. Pöpken, L. Götze, J. Gmehling, Reaction kinetics and chemical equilibrium of homogenously and heterogeneously catalyzed acetic acid esterification with methanol and methyl acetate hydrolysis, Ind. Eng. Chem. Res. 39 (2000) 2601–2611]. These models use activities instead of mole fractions. Activity coefficients have been calculated using ASOG [K. Kojima, K. Tochigi, Prediction of Vapor–liquid Equilibria by the ASOG Method, Elsevier, Tokyo, 1979] and UNIFAC (Aa. Fredenslund, J. Gmehling, P. Rasmussen, Vapor–liquid Equilibria Using UNIFAC. A Group Contribution Method, Elsevier, Amsterdam, 1977] methods.

A packed bed reactive distillation column filled with Amberlyst 15 has been employed to obtain ethyl acetate. The influence of feed composition and reflux ratio have been analyzed.     

Modeling of vanillin production in a structured bubble column reactor

Vanillin is an important flavour. Semi-synthetic vanillin can be produced by the oxidation of lignin. Experimental studies leading to vanillin production in a batch reactor and a structured bubble column reactor (SBCR) lead us to the conclusion that the SBCR could have non-idealities such as dispersion. The radial and axial liquid-phase dispersion within the packed criss-crossing sandwich structures of Mellapak-750Y had been studied. A 2D model accounting for axial and radial velocities and dispersion was formulated and solved. The model predictions were compared with that of an experimental residence time distribution curve. The axial dispersion coefficient of the liquid phase is of the same order of magnitude as the radial dispersion coefficient. The reaction kinetics available in literature is adopted for the present study. Model for the SBCR was formulated and simulated using commercial modeling software. Simulation experiments were conducted in a SBCR. The effect of the following parameters on the yield of vanillin is studied: lignin concentration, lignin molecular weight, oxygen partial pressure and reaction temperature. It can be said that lignin molecular weight is a crucial parameter in vanillin production.     

Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed (RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient (k_LS) have been investigated. The correlation for predicting k_LS was proposed, and the deviation between the experimental and predicted values was within ± 12%. The liquid–solid volumetric mass transfer coefficient (k_LSa_LS) ranged from 0.04–0.14 1⁻¹, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.     

Conceptual design and CFD simulation of a novel metal-based monolith reactor with enhanced mass transfer

This paper introduces a novel structured metallic catalyst that improves mass transfer performance of a monolith reactor for highly exothermic gas–solid reactions. The monolith channels are designed to have metallic substrates that consist of two layers with one of the layers being the metallic support and another layer being a foam metal annular that is tightly deposited onto the support surface by some means. Parametrical studies based on a 2D monolith reactor model showed that the present design yields an enhanced mass transfer between the bulk fluid and the catalyst layer due to a decrease in external film resistance, and an enhanced mass transfer within the solid phase mainly due to the viscous flow effect within the porous catalyst layer.     

Kinetic study of the catalytic cracking of polypropylene in a semibatch stirred reactor

A lumped kinetic model including both thermal and catalytic cracking and catalyst decay has been developed for the cracking of polypropylene in a semibatch stirred reactor. Two decay equations in where the catalyst decay is either a function of time on stream or function of coke on catalyst have been tested. The kinetic model fits very well the experimental results and is able to simulate the process in a wide range of operating conditions.     

Heterogeneous catalytic reactor design with optimum temperature profile II: application of non-uniform catalyst

A new methodology has been developed to design non-isothermal, non-adiabatic heterogeneous catalytic fixed bed and tubular reactors with optimal temperature profiles inside a reactor. Catalyst characteristics such as pellet diameter, shape and activity distributions inside a pellet are considered simultaneously for reactor design. Various types of non-uniform activity distributions inside a pellet are modelled and optimised for the maximisation of an objective such as yield or selectivity. Dirac-δ, layered and general non-uniform distribution profiles such as egg-shell, egg-yolk and middle peak distributions are applied for the reactor design. The research demonstrates that different catalyst distribution profiles can approach the optimum performance. Whilst it is known that the Dirac-δ profile (and its step-function equivalent) always gives the best performance for clean catalyst, other profiles can approach this performance and might offer advantages in catalyst manufacture and under degraded conditions. A profile-based synthesis approach is applied to generate various shapes of activity profiles for multiple sections along the reactor during the optimisation of non-uniform catalyst pellets. A case study with the ethylene oxidation process illustrates that the catalyst characteristics, such as activity distribution profiles inside a pellet, sizes and shapes can be manipulated to control the temperature through the reactor very effectively, leading to significant improvements in selectivity or yield. The non-uniform catalyst pellet is further applied to various reactor configurations such as inert mixing and side stream distributions. This work is the first to consider all of these effects simultaneously.     

Micro-engineered catalyst systems: ABB’s advancement in structured catalytic packings

ABB has advanced catalysis with micro-engineered catalyst (MEC) systems by providing a uniquely small particle size on a formable catalyst support through the integration of catalysis and reaction engineering. A mechanically strong catalytic web of micro-fibers has been engineered and shaped utilizing both computational fluid dynamics (CFD) and cold flow experiments to optimize flow characteristics. This article discusses techniques used for the development of novel catalytic structured packings for catalytic distillation applications. CFD models (verified through experiments performed on small-sized structures) were shown to be of great utility in screening new structure ideas. Results will illustrate achievement of both high gas–liquid contacting and bulk mixing at low pressure drop with the potential to provide enhanced catalyst utilization by taking advantage of the intrinsic MEC properties, particularly its high porosity and exposed geometric fiber and catalyst surface area. This was shown by the successful testing of one of these catalyzed structures in the selective hydrogenation of C4 acetylenes.     

Modelling of reactive stripping in monolith reactors

In this work, (reactive) stripping carried out in film flow monolith reactors developed for counter-current operation is investigated. Usually mass transfer in reactive separation has to be determined experimentally due to the complex flow patterns. However, monoliths have a simple geometry; only laminar flow is present throughout the column. This allows the calculation of the thickness of the liquid layer directly using Navier–Stokes equations. With this thickness known, the mass transfer can be calculated based on the convection in axial direction, diffusion in radial direction and vapour–liquid equilibrium. A model has been developed and implemented in Fortran^® based on the concept of a direct solution of convective diffusion equations, using the Thomas algorithm for solving the counter-current operation mode. Experimental data from literature have been used to validate the model for a binary and a multi-component system. The stripping of oxygen from saturated water by nitrogen was modelled assuming Fickian diffusion and vapour–liquid transfer based on the Henry constants. In a second step, multi-component diffusion and complex mass transfer at the interface were taken into account to describe the stripping of water by nitrogen from a mixture of hexyl-octanoate and cumene (solvent) under reactive stripping conditions.     

Kinetics of the solvent-free hydrogenation of 2-methyl-3-butyn-2-ol over a structured Pd-based catalyst

The solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) was studied over a Pd/ZnO structured catalyst and compared to its behavior in water-assisted conditions. The catalytic behavior was correlated with the surface properties of the catalysts which were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The catalyst showed high selectivity and stability with the performance being superior to that of the industrial Lindlar catalyst (50%). The addition of a sulphur-containing modifier in the reaction mixture was found to affect the activity and to hinder the over-hydrogenation reaction. The MBE yield of 97% was attained at MBY conversion >99%. The reuse of the catalyst showed that it deactivated by a 38% and that its selectivity slightly increased (0.5%) over 10 runs. The reaction kinetics was modeled using a Langmuir–Hinshelwood mechanism considering competitive adsorption for the organic species and dissociative adsorption for hydrogen. The kinetic experiments were planned and the results analyzed following a design of experiments (DOE) methodology. This approach led not only to a robust model that predicts the reaction rate in a wide range of reaction conditions but also to the determination of its kinetic parameters.     

催化还原法去除饮用水中硝酸盐氮研究进展

综述了催化还原法去除饮用水中硝酸盐氮的研究进展,介绍了反应机理,总结了促进组分、载体、制备方法对催化剂催化性能的影响以及还原剂的新发展,阐明了溶液pH值、水质因素和传质条件对硝酸盐去除效果的制约。     

Performance of a catalytic membrane reactor for the Fischer–Tropsch synthesis

The study of permeable composite monolith (PCM) membranes for the Fischer–Tropsch synthesis is continued. On the scale of membranes with outer diameter of 42 mm, it is proved that PCM can combine high productivity of hydrocarbons (>55 kg_C5+ ( h)⁻¹ at 0.6 MPa, 484 K), high selectivity towards heavy hydrocarbons (_ASF > 0.85, C₅₊ upto 0.9) as well as high heat-conductivity and high mechanical strength.     

Evolution of spatiotemporal temperature patterns in monolithic catalytic reactor

Experimental data on dynamic evolution of spatiotemporal temperature patterns and temporal conversion patterns for CO and hydrocarbon oxidation and NO reduction in a monolithic catalytic reactor reflecting variations of inlet conditions are presented. Possibility of increasing conversion of NO_x reduction by periodic variation of inlet conditions is experimentally documented.     

Kinetic study of catalytic esterification of acrylic acid with butanol catalyzed by different ion exchange resins

The esterification of acrylic acid and n-butanol catalyzed by three different ion exchange resins, Amberlyst 15, Amberlyst 131 and Dowex 50Wx-400 was studied. Amberlyst 131 was found to be more efficient catalyst giving the maximum conversion of acrylic acid. The effects of temperature, molar ratio of alcohol to acid, stirrer speed and catalyst loading on the reaction rate were investigated. The chemical equilibrium constants were obtained experimentally and theoretically from thermodynamic properties. The experimental data were tested with four different reaction mechanisms according to adsorption status of reactants. The activity coefficients were calculated using UNIQUAC method to account for the non-ideal thermodynamic behavior. The activation energy was found to be 57.4 kJ/mol according to the LHHW model which correlates the experimental data with minimum error.     

Conversion of hydrocarbon fuels to syngas in a short contact time catalytic reactor

Some results of the theoretical and experimental research on the oxidative production of syngas from hydrocarbon fuels in catalytic reactors which operate at high temperatures and short contact times are presented. Pilot scale tests of the partial oxidation of methane, isooctane and gasoline have been carried out in nearly adiabatic conditions on structured catalysts developed at the Boreskov Institute of Catalysis and characterized by a low (≤0.5 wt./wt.%) content of noble metals. High yield of syngas and stable performance of the catalysts were revealed in the experiments. The details of interaction between chemical and physical processes inside adiabatic monolith reactor have been elucidated by mathematical modeling of the partial oxidation reaction on the base of catalyst detailed chemistry. The problems that emerged from the short contact time reactor operating on a pilot scale are also discussed.