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Equations are derived for predicting the effective thermal conductivity of beds of unconsolidated particles containing stagnant fluid. The effective thermal conductivity a t these conditions, called the stagnant conductivity, is a function of the thermal conductivities of the solid and fluid phases, the void fraction, and, if radiation is important, the emissivity, meanWith these concepts the following expression can be derived for q : 1-cos 8 . ) ] (11)

Continuous kinetics of thermal degradation of poly (styrene-ally1 alcohol) (PSA)

A new method for determining adsorption equilibrium constants, rate constants, and intraparticle diffusivities is described and applied for the adsorption of ethane, propane, and n-butane on silica gel. The method rests upon recently developed theory for relating the moments of the effluent concentration wave from a bed of adsorbent particles to the rate constants associated with the various steps i n the overall adsorption process. It is necessary to operate at concentrations of adsorbable gas such that the adsorption isotherm is linear. However, it is possible to take into account effects of longitudinal dispersion and diffusion to the particle surface as well as the intraparticle processes of diffusion and adsorption on the pore surface.The method gave reasonable values for intraparticle diffusivities and adsorption rate constants. Intraparticle diffusion was a major resistance for all particle sizes studied and for the largest size (R = 0.50 mm.) this step controlled the overall rate.From the consrants determined chromatographically it i s possible to predict breakthrough curves for the adsorption of these hydrocarbons on silica gel. The predicted curves agree well with experimentally established breakthrough curves.The importance of separating gases by fluid-solid operations has created a need for predicting the performance of adsorption equipment. The design of fixed-bed adsorbers particularly involves the prediction of the concentration-time relationship, or breakthrough curve, of the effluent stream. Apart from the influence of axial dispersion, a mathematical model of adsorption from the gas stream should take into account: (a) diffusion of the component from the main body of the gas phase to the external surface of the adsorbent particle (external diffusion), ( b ) diffusion through the porous network of the particle (internal diffusion), and (c) the adsorption process itself. Quantitative treatment of rates of adsorption using this model requires values of the diffusion and adsorption rate constants that describe the three steps. The purpose of this study is to show that such constants, as well as axial diffusivities, can be evaluated from relatively simple chromatographic measurements. The overall validity of the methods can be ascertained by comparing breakthrough curves measured experimentally with those predicted from the rate constants. THEORYThe concentration, c(z, t ) , of the adsorbing gas as a function of time and axial position in the bed can be obtained by solving the following system of equations: mass balance of the adsorbable component in the gas phase:

Liquid holdup and mass transfer rates were measured in a 2.58‐cm I.D. tube, packed with glass beads and granular CuO · ZnO catalyst or β‐naphthol particles, and operated as a trickle bed. Gas‐to‐liquid (water) transport coefficients were determined from absorption and desorption experiments with oxygen at 25°C and 1 atm. Liquid‐to‐particle mass transfer was studied using β‐naphthol particles. Holdup and both mass transfer coefficients were unaffected by gas flow rate but increased with liquid rate. The data were correlated with equations that could be used for predicting mass transfer coefficients at high temperatures and pressures for use in the reaction studies reported in Part II.

T h i s work was undertaken because recent heat transfer results and preliminary data o n velocity had suggested t h a t , contrary t o common supposition, t h e velocity across t h e diameter of a packed bed m i g h t n o t be uniform. Data obtained in pipe sizes f r o m 2 t o 4 inches showed t h a t a peak velocity occurred approximately one pellet diameter away f r o m t h e pipe wall. For D l / D p less t h a n 30 this peak velocity ranged f r o m 30 t o 100% greater t h a n t h e velocity a t t h e center of t h e tube. T h e results indicate t h a t unless Dt/Dp i s greater t h a n about 30, important velocity variations exist across a packed bed. Such variations

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