Rob J. Berger

The six-flow reactor technology. A review on fast catalyst screening and kinetic studies

Catalyst testing in laboratory reactors requires careful experimentation and data interpretation. Current methods of catalyst development tend to be slow, laborious, and incapable of addressing most of the complex challenges, of multi-component chemical systems. In order to speed up this process in an efficient way, the six-flow parallel reactor technology is proposed. This enables parallel catalyst testing, which enhances the number of catalysts tested significantly and reduces the time for kinetic studies. Thus, operation costs are lowered and the success rate for important breakthroughs is increased. The six-flow set-up allows a proper catalyst testing, under more realistic and accurate conditions than in conventional combinatorial techniques, especially when the catalyst development stage is advanced and quantitative data are required. The application of this assessed technology is reviewed and combined with criteria for ideal behavior in reactor models and transport phenomena, crucial in order to achieve intrinsic catalyst performance data.

Design of adiabatic fixed-bed reactors for the partial oxidation of methane to synthesis gas. Application to production of methanol and hydrogen-for-fuel-cells

Abstract Adiabatic fixed-bed reactors for the catalytic partial oxidation (CPO) of methane to synthesis gas were designed at conditions suitable for the production of methanol and hydrogen-for-fuel-cells. A steady-state, one-dimensional heterogeneous reactor model was applied in the simulations. Intra-particle concentration gradients were taken into account explicitly, by solving the continuity equations in the catalyst pellet at each position along the fixed-bed reactor co-ordinate. The reactor designs are based on supported Ni catalysts, which catalyse the indirect formation of synthesis gas via total oxidation followed by steam reforming and water–gas shift. In both cases water was added as a reactant. Atmospheric, air-based fixed-bed CPO reactors for fuel-cell applications are feasible due to low catalyst temperatures. At high-pressure methanol conditions, however, catalyst deactivation will be very important as a result of the calculated high catalyst temperatures. The influence of the steam-reforming rate was investigated separately by performing simulations with the kinetic reforming models proposed by Numaguchi and Kikuchi (Chem. Eng. Sci. 43 (1988) 2295) and Xu and Froment (AIChEJ. 35 (1989) 88). The influence of the oxidation kinetics was studied as well. Application of different reforming models leads to significantly different maximum catalyst temperatures. Also, the possible occurrence of gas-phase reactions was investigated: homogeneous reactions will be very important at conditions suitable for methanol production.

Eurokin. Chemical Reaction Kinetics in Practice

The chemical reactions taking place in the chemical reactor form the heart of any chemical process. Reaction kinetics are the translation of our understanding of the chemical processes into a mathematical rate expression that can be used in reactor design and rating. Because of the importance of correct and safe design of chemical reactors, chemical reaction kinetics is a key aspect of research and development in chemical industries, in research institutes, and academic centers, as well as in industrial laboratories. There is, and there will always be, a strong need for knowledge and a skill base concerning the determination of reaction kinetics and their application in the form of a kinetic model. This paper is a result of cooperation within Eurokin, a consortium of over 10 European companies and 4 universities. An industrial questionnaire in 1995 highlighted that industry is not only a little conservative in the methods it uses to determine kinetics, but also that there was a wide awareness of the scope for improvement. Eurokin was thus founded in 1998 to try and establish the best practices and to facilitate development work in kinetics and associated areas. The paper briefly explains some underlying theory of heterogeneously catalyzed chemical reactions and their kinetics. It deals specifically with the acquisition of kinetic data, and gives recommendations for the selection of the experimental reactor and conditions. A primary aim of this paper is discuss kinetic experimentation and modeling through a series of case studies, attempting to illustrate good practice, methods in kinetic modeling, pitfalls, and recommendations. The paper closes with some recommendations and a perspective on the future needs of industrial reaction kinetics.

Catalyst performance testing: bed dilution revisited

Abstract A study was performed to investigate the systematic (negative) deviation of the conversion caused by dilution of the catalyst bed with inert particles in gas–solid systems for an irreversible first order reaction. Dilution may significantly reduce the conversion due to local bypass effects. Bed dilution does not yield a homogeneous activity decrease, but gives rise to a discrete local activity in an inert surrounding. In particular at high dilution, i.e. when using more diluent than catalyst, the effect may become significant. This phenomenon was studied both experimentally with catalytic N 2 O decomposition over Co–La–Al mixed oxide, and using a random particle distribution model. The experimental and model results agree well although there is some uncertainty due to the value of the average particle size to be used. The best description of the experimental data was obtained using an apparent particle size of 0.30 instead of the 0.18 mm , which may be ascribed to agglomeration. For practical application, the relative deviation in conversion Δ can be well estimated from observable parameters, i.e. the observed conversion x i ,dil , the volume fraction of bed dilution b , the bed height h bed and the particle diameter d p . In particular the combination high dilution and high conversion should be avoided in kinetic studies.

Catalyst performance testing: the influence of catalyst bed dilution on the conversion observed

Abstract A study was performed to investigate the influence of inert dilution on the conversion in a gas–solid laboratory micro-reactor for an irreversible reaction, viz. the catalyzed N2O decomposition over two different catalysts: FeZSM-5 and Co-La, Al mixed oxide (denoted as Co-La Al-ox). Vertically and horizontally segregated beds, as well as mixed beds with different degrees of dilution were considered. The results showed that catalyst dilution should be applied with caution since it may significantly influence the conversion and lead to an erroneous interpretation of data from catalyst activity measurements and kinetic studies. If the catalyst and the diluting particles are not well-mixed, the conversion reduces significantly due to bypassing and axial dispersion. Also apparent activation energies are reduced. The effects are stronger at high conversion levels (>0.4). Also over beds in which the catalyst and the diluent are perfectly mixed the conversion may be negatively affected by the dilution. It was found that the relative deviation in conversion caused by the dilution can be well estimated from observable parameters, i.e. the observed conversion, the volume fraction of bed dilution, the bed height, and the particle diameter. The relative deviation is approximately proportional to the reaction order. The combination of a high degree of dilution and high conversion should be avoided in catalyst activity measurements.

Mass transfer and kinetics of the three-phase hydrogenation of a dinitrile over a Raney-type nickel catalyst

The hydrogenation kinetics of a dinitrile over a Raney-type nickel catalyst was evaluated from experiments performed in a fed-batch operating autoclave at 320–355K and 2–7MPa hydrogen pressure. This complex catalytic reaction consists of two main parts: almost 100% selective hydrogenation of the dinitrile to the corresponding aminonitrile and consecutive hydrogenation to either the desired primary diamine or to pyrrolidine via ring formation. An extensive study has been made on the effects of mass transfer in the applied slurry-type reactor for this reaction. The gas–liquid mass transfer is enhanced by the presence of catalyst particles, and at typical hydrogenation conditions, kLa values up to 1.0s−1 can be reached. A Sherwood correlation for the three-phase reactor showed that important parameters in the gas–liquid mass transfer are stirrer speed and the density and viscosity of the solvent. The kinetic experiments were performed in absence of mass and heat transfer limitations. The kinetic data were modeled using two rate models based on Langmuir–Hinshelwood kinetics, assuming the reaction of dissociatively adsorbed hydrogen and nitrile compound as rate-limiting step. The first model involved competitive adsorption between hydrogen and organic compound and the second model was based on non-competitive adsorption. Both models successfully described both reaction parts. The reaction of dinitrile to aminonitrile is nearly 100% selective due to the relatively strong adsorption of the dinitriles as compared to the aminonitriles. By increasing the hydrogen partial pressure, higher yields of primary amine can be obtained. The models predict that operating in the mass-transfer regime at relatively high temperatures reduces the formation of the primary diamine.

High-throughput experimentation in catalyst testing and in kinetic studies for heterogeneous catalysis

Abstract Quantitative data in high-throughput experimentation are extremely important in the secondary development stage, comprising catalyst testing, kinetic studies, diagnostics, catalyst characterization (temperature programmed techniques), and stability tests. Even for systems that require long analysis times parallellization is worth application. The information from catalyst testing should be scalable. The reactor should be designed properly and the relevant criteria should be adhered to. The test reactor is not per se a scaled down version of the associated commercial reactor but in specific cases, e.g. riser technology the so-called Dinky Toy approach is appropriate. For structured reactors the scaled down version really simulates the commercial unit. Here, the Dinky Toy approach could well be the best. This is in particular attractive for the pharmaceutical industry. Parallellization is the logical approach in catalyst testing, but single units will survive, however, where the reactor operation is too complex or when one of the aims is to produce semi-commercial amounts of products. Analysis is crucial in design of parallel testing units. GC is the benchmark in quantitative studies, but other techniques should also be taken into consideration. This holds in particular for optical techniques, that offer the potential of fast and in situ analysis. In catalyst testing in a packed bed it is usually advisable to dilute the catalyst bed. It is crucial to carry out the dilution such that a well-mixed bed is created. Even for a homogeneously mixed bed dilution should not be exaggerated and for gas systems the proposed criterion should be adhered to. This bed dilution case study shows the advantage of parallellization for situations where a highly quantitative comparison between different samples is required.

Sorbitol dehydration in a ZnCl2 molten salt hydrate medium: molecular modeling

A molecular modelling study, using standard DFT B3LYP/6-31G*, was carried out to develop a better understanding of sorbitol dehydration into isosorbide in ZnCl2 molten salt hydrate medium. Catalysis of sorbitol dehydration by ZnCl2 most likely starts with complexation of the sugar alcohol functions to Zn, followed by an internal SN2 mechanism of a secondary alcohol function attacking a primary alcohol function with the Zn-complex acting as a favourable leaving group. The dehydration reactions to 1,4- and 3,6-anhydrosorbitol show a very similar activation barrier in good accordance with experimental results. The same holds for the formation of isosorbide from 1,4- and 3,6-anhydrosorbitol, albeit with a slightly higher activation barrier. The relative level of the activation barriers reflects the increased strain in the sorbitol skeleton in the corresponding transition states. ZnCl2 turns the dehydration reaction from an endothermic one to an exothermic one by forming a strong complex with the released water. Finally, the ZnCl2–H2O system has been compared with HCl–H2O, which could have been an alternative; it, however, turned out not to be the case.

Software Functionality Assessment for Kinetic Reaction Model Development, Model Discrimination, Parameter Estimation and Design of Experiments

An inventory was carried out on the capabilities and user-friendliness of commercially available modeling packages aimed at estimation of (kinetic) parameters and capable to describe two or more dimensional reactor models. Four case studies were developed in order to evaluate these packages in more detail. It appeared that all the packages need improvement in order to become really good and user friendly. Especially the quality of the statistics, the number of useful statistical tools and several user-friendliness aspects need significant improvement. However, discussion of these issues with the software vendors already initiated the developers of the packages to improve the software functionality. This paper is a result of co-operation within Eurokin, a consortium of over 10 European companies and 4 universities.