Peter R. Rony

Diffusion kinetics within supported liquid-phase catalysts

Abstract The homogeneous hydroformylation of propylene by butyl benzyl phthalate solutions of (Ph3P)2Rh(CO)Cl was successfully used as a model reaction system to demonstrate the existence of an optimum liquid loading in supported liquid-phase catalysts (SLPC). The experimental results were consistent with a theoretical treatment of supported liquid-phase catalyst systems.

Supported liquid-phase catalysts

Abstract A generalized treatment is formulated for a catalyst pellet consisting of a porous solid within which a homogeneous liquid-phase catalyst is dispersed. The theoretical relations governing diffusion and reaction kinetics in such a catalyst are derived. The rate of reaction depends not only upon the characteristics of the catalyst solution and reactants, but also upon the liquid loading within the solid and the pore size distribution. The resulting equations are similar to those derived by Thiele[1] and other investigators for the heterogeneous catalyst without a liquid phase. The derivation is also extended to a broader class of catalysts — multiphase catalysts — in which catalytically active species are also present on the surface of the solid phase.

Supported metal complex catalysts

Abstract Metal complexes supported on porous solids have been found to be active catalysts for hydrocarbon conversion reactions, both in the presence and absence of a solubilizing liquid phase. Four of the metal complexes were more active when dissolved in a liquid phase: an isomerization catalyst, RhCl3; three hydroformylation catalysts, (Pφ3)2RhCOCl, (Asφ3)2RhCOCl and Co2(CO)6 (PBu3)2. For the hydrogenation catalyst (Pφ3)3 RhCl, however, the supported solid catalyst was appreciably more active than its supported liquid-phase counterpart. An active supported liquid-phase catalyst can be made from almost any type of non-volatile catalyst solution, provided that the reactants and products are gases at reaction conditions.

The Extent of Separation: A Universal Separation Index

Abstract A universal separation index, the extent of separation, is proposed and mathematically described. This index is easily calculated, normalized, invariant to a permutation in indices, and conceptually similar to the De Donder extent of reaction. It applies to any type of separation system, any initial or final level of component purity, any concentration profile (if one exists), any initial amount of components, multicomponent systems, and both separation and mixing processes. The index is employed to characterize one of the simplest of all separation systems—the single equilibrium stage.

MULTIPHASE CATALYSIS: CONCEPTS AND POTENTIAL APPLICATIONS

When chemical engineers speak of a multiphase system, they usually refer to a chemical system in which molecules are transported between two or more phases or interfaces. Such systems are quite common to the field of chemical engineering, and their experimental and theoretical characterization has received considerable attention. Practical examples of multiphase systems include the unit operations of distillation, gas absorption, humidification, drying, extraction, leaching, crystallization, and heterogeneous catalysis. In any multiphase system, the necessity for mass transfer between the phases imposes restrictions both on the length of the diffusion paths and on the amount of interfacial area. In general, engineers try to minimize the former quantity and maximize the latter. The field of chromatography provides excellent examples of multiphase separation processes that are conducted on such a basis. For example, Martin and Synge’s discovery of liquid-liquid elution chromatography owes its success to such principles. A similar conclusion can be drawn for each of the other types of chromatography (column 3, TABLE 1) . Recent work by Horvath and Lipsky,’ Kirkland,2 and others on “pellicular,” “controlled surface porosity,” or “surface textured” supports continues the trend toward shorter diffusion path lengths. In the area of multiphase catalysis, a field that is at least as old as chromatography, an appreciation for sound chemical engineering principles has been evident for three decades.* The classic example of a multiphase catalystthe heterogeneous catalyst, a porous solid pellet containing a dispersed metal or metal oxide-has been employed both in gas-solid and solid-liquid catalytic reactors (column 4, TABLE 1) . The analogy between such reactors and the corresponding multiphase separation coIumns-gas-solid and solid-liquid chromatography, respectively-is readily apparent. There are, however, at least two types of multiphase catalytic techniques that have never had extensive laboratory or commercial application: gas-liquid and liquid-liquid catalysis (column 4, TABLE 1 ) . The catalyst employed-called a supported liquid-phase catalyst 5 7 c ~ n ~ i ~ t ~ of a porous solid containing a dispersed liquid-phase catalyst. These techniques operate in a manner similar to gas-liquid or liquid-liquid chromatography, with the additional feature that a chemical reaction occurs within the stationary liquid phase. A further distinction is that steady-state catalysis is easy to achieve and is generally a preferred mode of operation. Two additional types of multiphase catalytic techniques that show promise both on a laboratory and commercial scale are gas-solid-liquid and liquid-solid-

The chemistry of palladium complexes: VI. Studies on the palladium(II)-catalyzed decomposition of vinyl acetate☆

Abstract The kinetics and mechanism of the palladium(II)-catalyzed decomposition of vinyl acetate to give acetaldehyde and acetic anhydride were studied. The experiments were performed in acetic acid in the presence and absence of excess chloride, nitrile, and water, which served either as promoters or inhibitors for the decomposition reaction. Rate constants are plotted and tabulated for a variety of reaction conditions and a mechanism that is supported by deuterium studies is proposed.

The Extent of Separation: Applications to Elution Chromatography

Abstract The fundamental equations for calculating the extent of separation in binary elution chromatographic systems are derived. At a specific instant of time, the elution curve in such systems is characterized by two quantities: the optimum cut-point location and the optimum extent of separation. Equations relating the optimum extent of separation to the resolution and to the extent of separation for a single equilibrium stage are given. A number of figures obtained from computer examples illustrate the use of the theoretical results, A new type of component detector—a mobile detector—is proposed.

A Theory of Chemical Separations: The Fundamental Equation for Ideal Partitioning Separation Systems

Abstract The fundamental conservation-of-mass equation is derived for linear one-dimensional chemical systems in which no lateral diffusion or rate control exists. The theoretical results are applied to (a) a comparison of the fields of chemical separations, thermodynamics, and kinetics; (b) the derivation of a general equation for gradient elution and programmed temperature chromatography; and (c) the description of three new carrier chromato-graphic techniques, carrier magnetochromatography, solid phase carrier electrochromatography, and inverse carrier electrochromatography. The role of chemical equilibria in chromatographic systems is briefly discussed.

The Extent of Separation: Close Separations

Abstract Under the condition of close separations, the equations for the extent of separation have been calculated for twelve different separation techniques, including elution chromatography, multicontact distribution, multistage distribution, and cataphoresis. A method for comparing all separation techniques on an equivalent basis is proposed. It is suggested that the concept of a theoretical plate in chromatographic systems be abandoned.

The Extent of Separation: Applications to Multistage Systems

Abstract The fundamental equations for calculating the extent of separation are given for countercurrent multistage systems operated at either zero reflux, partial reflux, or total reflux. With the component distribution coefficients assumed constant, simple expressions for the maximum extent of separation are derived. The calculations clearly show how multistaging and reflux influence component separation.