Four models are presented to describe polymerization i n expanding catalyst particles. The globules are presumed t o be expanding with accumulating polymer, and catalytic reaction sites are dispersed throughout the polymer matrix which i s forming about them. Monomer must diffuse through the polymer t o polymerize a t the catalyst sites.i s a ratio of characteristic diffusion time t o reaction time which i s a measure of the importance of diffusion relative to reaction.Polymerization rates are predicted by the models which are generally dependent on the controlling mechanism. Broad molecular weight distributions are predicted for cases of diffusion control (large IY.) for those models i n which catalyst sites are not equally accessible to monomer.Polymerization rates decline toward an asymptotic final value as the particles expand i n diffusion-controlled cases. Most of the decline which would be readily observable i n a laboratory experiment would have occurred by the time the particle radii had increased to about three times their original value. The Thiele modulus (a), R d m ,Solid polymerization catalysts fluidized in a material that does not dissolve the polymer expand with accumulating polymer during reaction. These particles may grow more than 10,000-fold in volume during polymerization. In fact, since catalysts are generally much more expensive per unit weight than the polymers they produce, a considerable increase in size during polymerization i s usually a prerequisite for the associated process to have commercial value. Otherwise, the catalyst must be recovered. aPresent address,

A model is presented for corrosion of carbon steel in 60-96% weight sulfuric acid with correlations and data to facilitate quantitative use of the model for mechanical and process design. Corrosion is limited by the rate of convective mass transfer of ferrous ion from a ferrous sulfate (corrosion product) film-liquid interface into bulk acid. This interface is saturated with ferrous ion. The model has been verified in both laboratory and plant acids with rotating cylinder and pipeline geometries and with a variety of carbon and low alloy steels. Ferrous ion is an inhibitor for corrosion, and sacrificial corrosion in certain equipment in plants in which acid is recirculated can protect other critical items in the system. Changing liquid levels in storage tanks, acid purges, addition of iron, and lining of vessels can affect corrosion rate in a plant system.Sulfuric acid is an industrial catalyst for numerous organic chemical reactions, such as hydrations and alkylations, to produce many important commodities, such as alcohols, ethers, and gasoline. It is desirable to design plants so that carbon steel can be utilized in preference to more expensive materials as much as possible. Toward this end, quantitative corrosion models valid under chemical and fluid flow conditions anticipated for the plant are most useful. These conditions include presence of various chemical reactants in the acid as well as corrosion products which build up in the system because acid is continuously separated from desired chemical products and recirculated.Much has been written about the corrosion of steel in concentrated sulfuric acid (1). An overview of the corrosion system can be gained by measuring the density of current supplied to a vertical rectangular specimen of AISI !020 steel in stirred 70% weight acid in order to maintain the electrochemical potential of the specimen fixed (see Fig. 1). Two distinct regions appear in the anodic portion of this current potential curve. One is the "sulfation" range (--0.3 to +0.3V with respect to Ag/AgC1 1M CI) where the current is independent of potential. Hines and Williamson found the film formed in this range to be duplex, the inside layer being a thin compact film and the outside layer a thick porous ferrous sulfate film (2). At 50 mV negative to the corrosion potential (here about --0.4V), the anodic rate measured by weight loss is identical to this rate in the sulfation region. The independence of anodic current density on potential near (both positive and negative) the corrosion potential implies that the anodic current, in the sulfation range, is also equal to the free corrosion rate. That is, the anodic process limits the corrosion rate.The second distinct region appearing in the current potential diagram is the passive range, greater than +0.5V, where the steel is apparently covered by a ferric sulfate film over a passive oxide film (3, 4). The sharp peak at about +0.5V in Fig. 1 results from the change in oxidation states of the iron sulfate film already existing on the metal surface....

Guidelines are developed for molding large composite parts via structural reaction injection molding using glass preforms and polyisocyanurate resins. These are based on numerical simulations of the simultaneous heat transfer and reaction kinetics of a commercial system during and after mold filling. Premised requirements are that resin does not gel befxe the mold is filled. yet. reactions are sufficiently vigorous to approach completion. An existing mechanistic kinetic model is used and material parameters found from a chemical kinetics study employing an insulated cup. It is found deslrable to use a high mold temperature and a low preform temperature in molding. Nondimensionalization of the governing equations'reveals the existence of a Nusselt number ( Nu), which describes the relative importance of heat transfer between resin and glass relative to thermal diffusion to the mold wall. With a Nusselt number of about 50 or higher it is possible to use the cooling capacity of the preform to extend gel time. The magnitude of Nu is influenced by part thickness, glass fraction, strand diameter, and flow velocity. Thus, the effect of the preform on extending resin gel time is within control of the molder.

Factors which affect and broaden molecular weight distributions are investigated for polymerizations in catalyst particles which are accumulating polymer, such as Ziegler polymerizations of olefins. Expressions for the Q value, or ratio of weight‐average to number‐average molecular weight, are derived for simple, but important linear models. These expressions are of the form Q = FSX for a kinetic scheme in which polymer chains have an infinite growing lifetime, and Q = 2FGSX for a kinetic scheme in which termination by hydrogen is dominant and each site produces many chains. The factors F, G, S, and X are equal to or greater than unity: F depends on particle geometry and the nature of diffusion and reaction; G depends on environmental history of the particle; S depends on the distribution of site activities; and X depends on the distribution of particle sizes. Effects of reactor type are also studied quantitatively.

Es wird ein Modell zur Vorhersage von Korrosionsgeschwindigkeiten von Kohlenstoffstahl in 60‐96proz. (Gew.‐%) H2SO4 unter industriellen Bedingungen entwickelt, experimentell belegt und sein Gültigkeitsbereich definiert.