Alena Brunovská

An analysis of a nonisothermal one-component sorption in a single adsorbent particle

Abstract Heat and mass balances describing the process of a nonisothermal sorption within an adsorbent particle are formulated. Application to gas—solid adsor The governing equations represent a set of coupled strongly nonlinear parabolic equations. A finite-difference method based on explicit—implicit proc The equations are solved for a case of a strong adsorption accompanied with significant heat generation effects for molecular and Knudsen diffusion. It temperature differences may be of the order of magnitude 10–50°C.

Optimal catalyst acitivity profiles in pellets—VIII. General nonisothermal reacting systems with arbitrary kinetics

The theory of optimal catalyst activity profiles is extended to include the most general case, viz. the case of arbitrary number of reactions with arbitrary kinetics occurring in a nonisothermal catalyst pellet with finite external heat and mass transfer resistances. The catalyst performance index can be any one among effectiveness, selectivity or yield. Similar to previous results obtained for simpler situations, it is shown analytically that, in all cases, the optimal catalyst activity distribution is a Dirac delta function, i.e., for optimum performance, all the active catalyst should be deposited at a specific position within the pellet. This position depends, in general, not only on the physicochemical parameters involved but also on the choice of the catalyst performance index selected for optimization. The proof follows an approach which is different from what has been utilized previously, and is illustrated first for a simpler case, before proceeding to the general case.

An analysis of a nonisothermal one-component sorption in a single adsorbent particle—a simplified model

Abstract In this paper on approximation is described making it possible to calculate temporal temperature and adsorbed amount profiles during an adsorption process in a single pellet. The suggested model includes heat transfer in an external film and mass transfer inside a porous structure. The profiles calculated from the approximation and rigorous model are compared and it is shown that for a majority of operating systems the simplified model can be used and approximates very well the results obtained from an exact model.

Estimation of the diffusion coefficient from sorption measurements

Abstract In this paper a procedure for the estimation of the diffusion coefficient for a sorption process from the measurements of the adsorbed amount is proposed. The experiments from which the data have been obtained are described and the numerical results are discussed.

Optimal catalyst pellet activity distributions for deactivating systems

Abstract The optimal activity distribution in catalyst pellets for reacting systems which undergo deactivation is analysed. A general optimality criterion is developed, which allows one to conclude that, under quite general conditions, the optimal activity distribution is of the Dirac-delta type.

Dynamic behaviour of a catalyst pellet with nonuniform activity distribution

Abstract Existence of multiple steady states and sustained oscillations in catalyst pellet with Dirac delta activity distribution and bimolecular reaction with Langmuir-Hinshelwood rate expression is numerically established. In addition it is shown that deactivation may lead to temporary oscillations.

Dynamic behaviour of an isothermal fixed-bed reactor with narrow activity region catalyst

Abstract The dynamic behaviour of an isothermal axial dispersion fixed-bed reactor packed by catalyst pellets with Dirac delta distributed activity in the case of bimolecular Langmuir—Hinshelwood kinetics is studied. The existence of periodic oscillations is numerically established. The influence of the active point location, Thiele modulus and Damkohler number on the dynamic behaviour is discussed.

Oscillatory behaviour of a catalyst pellet with narrow region of activity

Abstract An analysis of the dynamical behaviour of an isothermal continuous stirred tank reactor containing catalyst pellets with a Dirac delta distributed activity is presented. The case of bimolecular Langmuir—Hinshelwood kinetics in studied. The bifurcation diagram in the plane active point location vs parameter X is constructed. Existence of multiple periodic solutions is numerically established. The effects of active point location, Thiele modulus and Damkoehler number are discussed.

Sulphur poisoning of nonuniformly impregnated Pt-alumina catalysts

Abstract An experimental and theoretical investigation of the deactivation of a single narrow activity region catalyst pellet is presented. As the model system the hydrogenation of ethylene on the Pt-alumina catalyst (narrow region of Pt inside the pellet) in the presence of catalyst poison thiophene is considered. The parameters of both deactivation rate expression and energy balance are estimated. It was found that the deactivation mechanism consists of two consecutive steps, reversible catalyst poison precursor adsorption, and irreversible surface reaction, and is described by a nonseparable rate equation. Both steps are proven experimentally. The possibility of a significant increase of the resistance against deactivation using a narrow activity region is illustrated. Optimal activity distribution is estimated for given values of model parameters.

Role of catalyst pellet activity distribution in catalyst poisoning

Abstract The influence of the distribution of catalyst activity on the resistance against poisoning is studied. For a constant amount of catalyst the location and width of the active zone is analyzed experimentally. Several methods for pellet preparation are described. The results demonstrate that for a model experimental system the optimal distribution is a thin active layer inside the pellet. This coincides with our previous theoretical results which are summarized in this paper.