The permeability of a number of thin organic films toward oxygen and nitrogen has been measured. For an ethyl cellulose film the studies were extended to include CO2, A, He, and H2. The enrichment of a binary gas mixture in a single stage of permeation has been calculated for the extreme cases of perfect mixing and no mixing. Application of these results indicates that the use of a fractional permeation process may be of practical importance in effecting the separation of oxygen from air, helium from natural gas, and hydrogen from coke-oven gas, as examples.

No abstract

A study has been made of the thermal decomposition of MgC03 . 3H20 (nesquehonite) and MgC03 . (NH&C03 . 4H20 using a variety of experimental techniques, including thermogravinietric analysis, differential thermal analysis and optical microscopy. The solids remaining at various stages during decomposition were characterized by measurement of their X-ray powder diagrams, surface areas, and particle densities. Nesquehonite decomposes first to crystalline MgC03. HzO, then to an amorphous magnesium carbonate of essentially zero surface area and finally to high area " active ¶ ¶ magnesia (-250 m2/g). Magnesium ammonium carbonate loses (NH&CO3 and most of its water below 100°C to give a second amorphous magnesium carbonate differing from that derived from nesquehonite in having a high surface area (-400 m2/g) and smaller COz content. Both of the amorphous carbonates have the pseudomorphic form of the parent crystal, and both recrystallize abruptly to magnesite on heating to 510°C in an atmosphere of C02.

The Bergius process for the hydroliquefaction of coal has an 80-year history. This selective review attempts to trace the role of catalysis, and especially of catalyst dispersion, in this process. The metals commonly used in liquefaction catalysts, iron, molybdenum, and tin, were discovered and utilized in large-scale plants in Germany and England well before World War 11. The usefulness of achieving high dispersion, and therefore high interfacial contact of catalyst with coal, coal-derived liquids, and hydrogen, was demonstrated in autoclave and pilot plant experiments during the early 1950s. Research since then has followed several themes. Although impregnation of catalyst on coal was recognized early as one method of achieving high dispersion, the cost of impregnation led to studies of other methods. Use of oil-soluble catalyst precursors (typically organometallics) without impregnation, and methods for generating particulate catalysts of high surface area, have been pursued with success, at least on a research scale. Although iron remains the catalyst metal of choice because of cost and availability, the effectiveness of well-dispersed molybdenum at low concentrations has led to much research on precursors based on that metal, and on possible recovery and recycle of the catalyst. Interest also remains in determining the chemical fate of precursors, and on using catalysis as a tool in further understanding the complex mechanism of liquefaction.

No abstract

The chemical engineer frequently has to correlate kinetic data for heterogeneous reactions simply and accurately in order to make useful predictions of reaction rates over a range of conditions. The Langmuir-Hinshelwood approach, which is frequently used for this purpose, does not have the theoretical validity commonly attributed to it, and its use leads to unnecessary mathematical complexity. A simpler method of analysis is suggested which is based on power dependencies of the rate on concentrations, the powers being restricted to integral or half-integral values. The data for several-reactions are shown to be adequately correlated by the suggested procedure, which is simple and convenient.During the last decade it has become increasingly popular for chemical engineers to analyze the kinetic data for complicated solid-catalyzed gas reactions in terms of the extended LangmuirHinshelwood theory (8, 21). This approach may be illustrated by a sample case :The gas reaction A + B .--f C is catalyzed by a solid, and the reaction is not limited by mass or heat transfer. If it is assumed that a bimolecular surface reaction of A and B is rate controlling and that A , B, and C are adsorbed on the catalyst without dissociation, then the reaction rate is written the K's being (unknown) adsorption coefficients characteristic of the individual gas. Other assumed mechanisms result in different equations, and the occurrence of a better fit of the data to one equation than to another is frequently employed as a sufficient criterion of the reaction mechanism.

No abstract

No abstract