Karel Klusáček

Dynamics of non-isobaric diffusion in porous catalysts

Abstract A measuring cell was constructed for determining the time development of total pressure changes inside porous pellets, caused by composition step-change of the gas flowing along one flat face of pellets. Using this cell and swopping of gases in binary systems H2-N2, H2-Ar, He-N2, He-Ar, experimental pressure response curves were obtained for porous α-alumina pellets with mono- and bidisperse pore structures. Utilizing description of the combined gas transport according to the mean transport-pore model and dusty gas model the pressure responses were simulated numerically. Transport parameters of pellets obtained by fitting experimental responses were compared with parameters determined independently by steady-state methods.

Stationary catalytic kinetics via surface concentrations from transient data: Methanol dehydration

Abstract A novel approach to the analysis of the transient data from CSTR is illustrated on the catalytic dehydration of methanol. The method allows to determine adsorbed amounts of reaction components under reaction conditions and it is applicable in cases where at least one reaction component is not (or slighty) adsorbed. Because new types of data can be obtained in this way a deeper discrimination between rival kinetic models is possible. The method permits also determination of total concentration of active sites on the catalyst surface. Comparison of transient data analysis with the steady-state results is presented.

Multicomponent diffusion of gases in a model porous catalyst during methanol dehydration

Abstract The effect of internal diffusion on dehydration of methanol on model pellets of porous catalyst (sulfonated styrene-divinylbenzene ion exchange resin) was studied experimentally. The results proved that bulk diffusion of a multicomponent reaction mixture in a porous catalyst can be satisfactorily described by Stefan-Maxwell equations. The kinetics of methanol dehydration on catalyst particles, used for preparation of model pellets, was studied independently.

Effect of size and shape of catalyst microparticles on pellet pore structure and effectiveness

Abstract Catalyst pellets with bidisperse pore structure were simulated by packed bed of microporous ion exchange resin (sulfonated styrene-divinylbenzene copolymer) and inert glass particles. Inert particles of different size and shape were used to modify the shape and volume of transport macropores (voids between the particles). Tortuosities of pellets were obtained from the experimentally measured effect of internal diffusion on the rate of catalytic methanol dehydration. Analysis of results shows that in the region of strong internal diffusion influence the highest pellet effectiveness is achieved for equal-size spherical microparticles. To ensure optimum macropore structure even in the transition region between the kinetic region and the region of strong diffusion influence, volume of transport macropores has to be reduced by combination of appropriately-sized spherical catalyst microparticles.

Dynamics of water-gas shift reaction system

Abstract The water-gas shift reaction on a commercial CuO/ZnO/A12O3 catalyst was investigated using transient experimental technique. Reaction mechanism was derived on the basis of experimental results. It has been found that catalyst surface contains active (reaction) and inactive (storage) sites. The oxidation level of active sites is strongly dependent on the composition of gaseous phase. The catalyst contains a remarkable amount of water which is slowly transported to the active sites during system transients. A dynamic quatitative models have been derived for the dynamic system behavior and the comparison of measured and simulated results has been made.

Temperature-programmed reduction of a cobalt-molybdenum catalyst activated by hydrogen and hydrogen sulphide under different temperature regimes

Abstract The rate of temperature increase of a CoMo/Al2O3 hydrorefining catalyst during its activation with a H2SH2N2 mixture affected its reducibility and activity. The reducibility has been evaluated by a temperature-programmed reduction (TPR) method and the activity by hydrogenation of ethylene. The rapid temperature increase caused a decrease in the amount of hydrogen sulphide evolved during TPR, an increase in the initial temperature of H2S evolution and a decrease in the ethylene hydrogenation activity. The rate of reduction of Co and Mo sulphides was described by a model based on a heterogeneous catal surface. The model parameters, the pre-exponential factor and the activation energy for the reduction decreased with increasing rate of temperature rise during activation. As the activity of the hydrorefining catalyst decreased at higher rates of temperature increase during activation, these catalysts should first be activated at low temperature, followed by a slow increase in temperature.

HDS catalyst regeneration: Coke burning-off by air in a shallow bed

Abstract Regeneration of coked HDS catalyst by air in a thin layer was studied experimentally and simulated using a simple model of the reactivation reactor. Using kinetic data on deposited coke oxidation obtained separately, the time course of the catalyst pellet temperature was correctly predicted. Conditions under which safe regeneration takes place were determined and verified experimentally as well as conditions under which coke ignites spontaneously. Under ignition conditions the degree of regeneration can not be controlled, which might result in irreversible catalyst deactivation.