Ryszard Pohorecki

Kinetics of reaction between carbon dioxide and hydroxyl ions in aqueous electrolyte solutions

Abstract The measurements of the rate of absorption of CO 2 into aqueous solutions of KOH, NaOH and LiOH containing neutral electrolytes (carbonates, chlorides, bromides, nitrates and sulphates) have been performed using the laminar-jet technique. The dependence of the reaction rate constant on the temperature and ionic strength has been presented for the reaction of CO 2 with hydroxyl ions in aqueous electrolyte solutions.

Mixing-precipitation model with application to double feed semibatch precipitation

Abstract A general mixing-precipitation model describing interactions between mixing of various scales (macro-, meso- and micromixing) coupled with the population balance for crystallization is presented. Macro-, meso- and micromixing were interpreted as a circulation through the zones of different rate of energy dissipation, inertial-convective disintegration of large eddies and an engulfment of fluid from the environment, respectively. The model was verified experimentally for double feed semibatch BaSO 4 precipitation. Experiments were carried out in a Rushton type stirred tank reactor. The effects of feed tube positions, addition feed rate, intensity of mixing, initial reagent concentration and volume ratio on particle size distribution and particle morphology were investigated. The model enables prediction of supersaturation profiles in the system and resulting CSD; the predicted history of supersaturation structure explains the influence of operating conditions on crystal morphology.

Turbulent micromixing in chemical reactors - a review *

Abstract The idea of micromixing, its definition and measures are outlined. The concepts of mixing environments and mixing earliness are presented. The paper concentrates on the effects of turbulent mixing of incompressible fluids in single-phase systems on the course of chemical reactions. The processes of turbulent micromixing are discussed in detail: the fluid mechanical interpretation of turbulent micromixing (effect of fluid element deformation on the acceleration of molecular diffusion, engulfing of environment, inertial—convective disintegration of large eddies and local intermittency) is presented. It is concluded that stretching of material elements and vortices, accompanied by molecular diffusion results in the growth of the mixing zones. The groth of the zone mixed on the molecular scale is a characteristic feature of micromixing and should be included in micromixing modelling. The characteristic time constants for the consecutive stages of mixing are presented and compared with the characteristic time for chemical reaction — the numerical criteria are outlined. The two approaches, i.e. eulerian and lagrangian, are described; it is shown that each requires different methods of description and generates specific problems (closure problem, problem of environment). The applications of the micromixing theory to the most important fields of industrial practice, such as complex reactions, precipitations and polymerizations, are outlined.

The use of a new model of micromixing for determination of crystal size in precipitation

Abstract The course of the precipitation process and the size distribution of the solid particles obtained depend significantly on the intensity of mixing in the crystallizer. The authors have used a new model of micromixing, based on the spectral interpretation of mixing in the isotropic, homogeneous turbulent field to evaluate the influence of the intensity of mixing on the rate of precipitation and on the particle size of the product obtained in a stirred vessel with ideal macromixing The results obtained from the model are in good agreement with the experimental results obtained for the precipitation of BaSO 4 .

Modelling of the coalescence/redispersion processes in bubble columns

Abstract In order to determine physically formed relations between bubble characteristics and physicochemical properties of the liquid employed, bubble size distributions and average bubble diameters were calculated using a simplified version of the theoretical model developed by Prince and Blanch (A.I.Ch.E. Journal, 36 (10) (1990) 1485–1499). The results of calculations were compared with experimental data, obtained using two different columns: a laboratory column and a pilot plant column. Good agreement was found between calculated and experimental values.

THE EFFECTS OF MICROMIXING AND THE MANNER OF REACTOR FEEDING ON PRECIPITATION IN STIRRED TANK REACTORS

The effect of micromixing on the course of a precipitation process involving instantaneous irreversible chemical reaction (of the type: A + B → C) between two ionic solutions snd subsequent crystallization of the product is considered. It is demonstrated that the micromixing intensity and the manner of reactor feeding (batch or continuous, premixed or unpremixed feed system) are major factors affecting the precipitation process and the resulting size distribution of precipitated particles. The method of prediction of these effects is based on a micromixing model, which is related to the theory of turbulent mixing in an isotropic, homogeneous turbulent field.

Kinetic model of cyclohexane oxidation

A model of the process of the catalytic cyclohexane oxidation in the liquid phase, including both reaction kinetics and mass transfer, is presented. As catalysts cobalt napthenate and chromium napthenate were used. The reaction rate constants as well as the activation energies were determined on the basis of the experimental results obtained in a laboratory reactor. A mathematical model of an industrial reactor for the cyclohexane oxidation is also presented. The results of the cyclohexane oxidation simulations are compared with the data from different industrial reactors (CYCLOPOL process).

Desorption with chemical reaction in the system CO2-aqueous solution of potassium carbonate

Abstract The rate of desorption of CO2 from aqueous potassium carbonate solutions in a glass wetted-wall column has been measured and the kinetic and equili The values of the kinetic coefficient KR and the equilibrium coefficient Kp necessary for calculations of the mass transfer rates in th

Liquid-phase oxidation of cyclohexane : modeling and industrial scale process simulation

Abstract New models of the process of cyclohexane oxidation in the liquid phase, including both reaction kinetics and mass transfer, are presented. The models have been used for the simulation of the industrial process in order to determine the influence of the hydrodynamic factors on the conversion and selectivity. The results of simulation are compared with the industrial data (CYCLOPOL process). Good agreement with experimental data was obtained using kinetic models comprising the free radical formation stages.

A new absorbent for carbon dioxide and hydrogen sulphide absorption process

Abstract The results of investigations on the process of CO 2 and H 2 S absorption in a new absorbent, propylene carbonate (PC) modified by triethanoloamine (TEA), are presented. The data on CO 2 and H 2 S solubility, as well as the results of measurements of the absorption rate of these gases in the TEA–propylene carbonate solution are reported. The measurements were carried out in the range of parameters most interesting in terms of the commercial application of the process.The data on CO 2 and H 2 S solubility in the TEA–propylene carbonate solution are presented in the form of correlation equations as functions of gas partial pressure, temperature and TEA concentration. CO 2 and H 2 S diffusion coefficients obtained in kinetic investigations are correlated with temperature and TEA concentration. The mechanism of CO 2 and H 2 S absorption in the TEA–propylene carbonate solutions is explained. Application of the propylene carbonate with TEA as an additive in the CO 2 absorption process has been tested in a pilot plant and will be offered as a commercial process.