THE DETERMINATION OF BINARY GASEOUS DIFFUSIVITIES IN POROUS MATERIALS

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1962

OSTI ID:4784291

Rhodes, R P

A number of processes used in industry today involve the transport of gases within micro-porous solids. Cataliytic reactors, adsorption columns, and gaseous separation barriers are typical places in which these solids are utilized. Rates of transfer in the medium external to the solid have been fairly extensively examined. Relatively littie work however, has been done on the transport of gases within the pores of the solid. A knowledge of the effect of temperature on this transport is even more limited. Previous workers have shown theoretically and experimentally that the efficiency of a heterogeneous catalyst is a function of the reaction rate and the diffusivity in the cataliyst. It has further been shown that the evaluation of catalyst efficiency can be put on a much less empirical basis by use of the rate constant to effective diffusivity ratio. In the past the main difficulty with this method of prediction of catalyst efficiency was the lack of data on rate constants and diffusivities. The area for examination which was chosen in this study is the diffusion of ideal gases through several porous materials. he gases used in this investigation were almost all ideal n the sense of obeying additive volume laws, and of being used at temperatures far removed from their boiling points. The porous solids studied fall into two classes, beds of simple dense granular materials such as glass spheres and beds of high surface area catalyst materials such as alumina and silica gel. In general a statistical model was used in an attempt to present a physical picture of the diffusion process. Earlier work by other authors has indicated the possibility of a discrepancy existing between steady and unsteady state measurements. An attempt was made to resolve this question by making both steady and unsteady state measurements on the same material. The data obtained however, were insufficient to warrant extensive conclusions. In addition a non- volatile oil impregnation technique was developed which qualitatively shows the effect of pore size distribution on the transport through high surface area aluminas. (Dissertation Abstr., 23: No. 3, 1962) The viscosity of molten lithium- 6 and lithium-7 was measured by observing the damping of a freely oscillating sphere filled with molten lithium. The viscosity coefficient was found by treating the damping of a slowly oscillating sphere containing a viscous tluid as a problem in the laminar flow of incompressible fluid. The temperature dependence of the viscosity of lithium-6 was found to be in general agreement with a law stating that the viscosity varies exponentially in the reciprocal of the absolute temperature. This law is also predicted by some existing theories of viscosity. The extrapolated value for the absolute viscosity of lithium8 at the melting point (180.4 deg C) was found to be 4.50 mp. The effect of isotopic mass on viscosity was studied by measuring the viscosity coefficient of lithium-7 at a given temperature and comparing it with that for lithium-6 at the same temperature. The ratio of the viscosity of lithium-7 to that of lithium-8 at 238.8 deg C was found to be (4.186 plus or minus with the theoretical prediction that it is equal to the square root ratio of the atomic mass of lithium-7 to that of lithium6, that is to (7.018/8.017)/1/2 = 1.080. On the assumption that the viscosity coefficient for a mixture of isotopes of an element, consisting predominantly of one component, is a linear function of the number composition, the absolute viscosity of lithium-natural (92.5% lithiurn-7, 7.5% lithium-6) at 236.8 deg C is estimated to be 4.16 mp. This value is 24% lower than the corresponding value obtained by Andrade and Dobbs using lithium-natural. A detailed examination of their paper led to the conclusion that their values are significantly in error. (Dissertation Abstr., 23: No. 3, 1962)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-002132
• OSTI ID: 4784291
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ADSORPTION
ALUMINUM
BOILING
CATALYSIS
COLLOIDS
DIFFUSION
DISTRIBUTION
EFFICIENCY
FABRICATION
GASES
GLASS
HOMOGENEOUS REACTORS
IMPREGNATION
MEASURED VALUES
PHYSICS
POROSITY
QUANTITATIVE ANALYSIS
SOLIDS
SPHERES
STATISTICS
SURFACES
TEMPERATURE
TRANSPORT
VOLUME