Article

Thermophysical properties of catalysts in dependence temperature

High temperature high pressure
(2008)
Abstract

Abstract Nature and structure of the solvent render essential influence on speed and selectivity liquids geterogen-catalik of processes. The solvent defines laws adsorptions and activation of the substances-participants of reaction, condition of reacting substances in volumetric phases cattails of system, enters into structure of a transitive condition on the active centers of a surface of the catalyst, changes speeds of stages external and internal viss heat and t.s.We carry out a complex of researches directed on finding-out of the reasons of influence of the solvent on law adsorptions and activation of hydrogen and organic connections by a surface of nikel-aluminium catalysts, speed and selectivity by reaction liquids geterogen-catalik of the replaced spirits. The laws adsorptions can be described within the framework of model of a surface with discrete heterogeneity. Irrespective of a nature and structure of the solvent the process adsorptions of organic connections on nikel-aluminium and (Ni+Al, Cu+Al,Ni+Zn,Cu+Zn,Al+Zn) catalysts proceeds on the mechanism of volumetric filling of porous space of the catalyst, and the influence of environment is shown in change basic thermodynamic to thermo physical of the characteristics adsorptions equilibrium. The mechanism of processes adsorptions of organic connections on cattails active metals with the ramified porous structure is offered. The changes adsorptions of ability of reacting substances under action of the solvent render essential influence on speed and selectivity of reactions liquids geterogencatalik. The received data make a basis of methods scientifically - is proved of selection optimum cattails of systems for reaction liquids phase hydrogenate. The method of the integrated equations investigates influence of extreme conditions on structure of researched objects. The structural characteristics of the investigated systems received by the numerical decision of the atom – nuclear integrated equation Ornshten-Sernik with short circuit such as giperprice. The analysis of the received data shows, that the heating at constant high pressure renders significant influence on structure of the volumetric solvent.. In solutions there is a destruction tetrahedral of a grid of hydrogen communications of water, which accompanies by significant reduction of quantity of intermolecular hydrogen communications and increase of number of molecules of the free solvent. The growth of temperature results in essential destruction first hydride of environments kations. With increase of temperature the coordination numbers anion grow. In all systems the heating is accompanied by strong destruction of hydrogen communications between anions and molecules of water in first hydride to sphere. With temperature in solutions the quantity contact is considerably increased and the number hydro division ions of pairs decreases. The research heat capacity of researched system in a wide interval of temperatures and concentration has the important meaning for creation of the theory of the phenomena of carry in the condensed condition of substance regardless to crystal structure and for finding - out of a role structural regulate in formation of a power spectrum of carriers of a charge. We develop experimental methods for research heat capacity and enthalpy of alloys in a wide temperature interval. The installation consists from think-wall of a cylindrical glass made of corrosion-proof steel. On a lateral surface of a glass нарезается the screw deepening, in which is inserted nikhrom a spiral of the certain resistance. The spiral plays a role of a heater allowing to raise temperature of a glass up to 673 K, that is allows to receive a necessary interval of temperatures, in which it is supposed to measure heat - capacity cover. Temperature of a glass and temperature of a sample, taking place in his cavity, concerning ice enters the name by the graph plotter. All device is immersed a heat-shielding casing and is covered by a cover. The general relative error of measurement, heat conductivity, specific heat capacity and temperature conductivity at confidential probability, α=0,95, makes 4 %, 3,0 % and 4,5%. Introduction Thermal conductivity of rocks measured at laboratory is necessary for solving many geophysical problems. However, combination of the experimental study with theoretical methods, allowing one to calculate the thermal conductivity of rocks from their composition, gives new possibilities for using the laboratory data. This enables one to reconstruct the rock’s inner structure, namely, to find the thermal conductivity of mineral skeleton, porosity, and crack shape, i.e., the parameters that mainly control the rock’s thermal conductivity. It is important that porosity and crack geometry govern other physical properties of rocks (electrical-thermal conductivity, permeability, and elastic wave velocities). This fact gives a potentiality to find interrelations between various physical properties based on the structural parameters derived from thermal conductivity data. In order to reconstruct the structural parameters using experimental data, it is necessary to find a theoretical formula relating the parameters with measured thermal conductivity. Solutions to the problem This formula can be obtained, if we use the relation between heat flux passing through the rock, temperature gradient, and thermal conductivity of rock. If rock were a homogeneous body, the relation would be as follows: . Here is the vector of the heat flow density, is the rock thermal conductivity (tensor of second rank), is the temperature gradient vector, and is a point in a rock volume. However, the rock is a microinhomogeneous medium consisting of various mineral grains, pores, and cracks filled with various fluids and gases (so-called, inhomogeneities). The inhomogeneities have different thermal conductivity. In this case, the thermal conductivity becomes a coordinate-dependent tensorial function, and temperature gradient at each point of such a medium depends on the thermal conductivity distribution over the rock volume. If the inhomogeneity size is small compared to the distance at which the temperature field is analyzed, and the medium is statistically homogeneous, the rock can be considered as macrohomogeneous, characterized by so-called effective thermal conductivity relating the heat flow density and temperature gradient averaged over the rock volume: (1) The averaged values of heat flux density and temperature gradient depend on rock inner structure. Consequently, the effective thermal conductivity also involves all structural information. This definition assumes statistical homogeneity of medium, according to which volume average can be replaced by statistical average. Note that the problem of effective thermal conductivity determination is so-called, many-body problem that has no exact solution (Shermergor, 1977). Average-based methods. One way to find the effective thermal conductivity is to apply finite-difference schemes to calculate the distribution of heat flow and temperature gradient fields over the rock volume for various inner structures that can be typical of rocks. However, this way is rather time-consuming and cumbersome. Another way is to use methods of the random function theory, operating with statistical characteristics of microinhomogeneous medium. At first glance, the simplest way to solve this problem is to average the value of thermal conductivity over the rock volume and set (this corresponds to the assumption of constant temperature gradient over the rock volume). One can also average inverse values of , setting (assumption of constant heat flow density in the rock volume). However, the thermal conductivity of inhomogeneities can substantially differ from each other (a few orders of magnitude). In this case, the two methods can produce dramatically different values. For example, for air-saturated sandstone, ( = 0.024 W/(m&#;K) and = 6.6 W/(m&#;K)), we have = 5.33 W/(m&#;K) and = 0.12 W/(m&#;K) for 20-% porosity. These two averages are called, respectively, the upper and lower Weiner bounds. The thermal conductivity is often calculated as average of these two limiting values. Another models similar to Wiener average, among which are the geometric average method (Shermergor, 1977): , Landau method of averaged cubic roots: , and Lichteneker average of logarithms (1931): , are widely used. Note that the Lichteneker formula is the most popular in geothermal study. For a medium containing greatly contrasting components, the aforesaid methods give very different results. Besides, the average-based methods do not take into account the distribution of inhomogeneities over rock volume, shape of mineral grains or cracks (inclusions), and their orientation. These factors may markedly affect the thermal conductivity of rocks containing contrasting components. Therefore, these methods may produce substantial errors when calculating &#;*.. Methods taking into account the inclusion shape. One of the most advantageous approaches allowing one to take into account the effect of rock inner structure, inclusion shape and orientation is the self-consistent scheme. According to this approach, each inclusion (mineral grain or crack) assumed to be of elliptical shape (general ellipsoid) is embedded in a medium having thermal conductivity chosen arbitrarily (but being a constant for all points in rock volume). By analogy with approach of Landau and Lifshits used for electrical filed (1982), in case of stationary temperature field, the temperature gradient in the inclusion can be written via the temperature gradient in the matrix. Using definition of the heat flux (1), we can derive the formula for calculating the effective thermal conductivity, which takes the form (Tertychnyi et al., 2000) (2) Here, I is the 4-th rank unit tensor; F(I) is the depolarization tensor depending on the ellipsoid shape and matrix properties. For ellipsoids of revolution, the tensor can be written in the explicit form. If we set , we have the formulas of self-consistent method in its classical formulation (Willis, 1977; Shermergor, 1977). If inclusions are aligned and similar in shape, in case when is the lowest thermal conductivity value, we have the lower Hashin-Shtrikman bound (Hashin and Shtrikman, 1963). In opposite case, if is the highest conductivity value, we obtain the upper Hashin-Shtrikman bound. These bounds are sufficiently narrower than those of Weiner. For inclusions, differing in shape and orientation, (2) can be written as follows . (3) Here and are the Eulerian angles specifying the rotation of inclusions in space, is volume concentration of the j-th component, is the dis-tribution function over shape and orientation for the j-th component, and N is the number of components. Component is considered to be different, if they have dif-ferent thermal conductivity. It should be mentioned that expression (3) could be reduced to Likhteneker formula for inclusions whose shape is described by the uniform distribution function . Conclusions The effective thermal conductivity of porous rock can be calculated from data on the mineral composition, pore-filling material, catalysts and internal rock structure. The model takes into account an arbitrary number of rock constituents, the diverse shape of pores and mineral grains, the anisotropy of thermal conductivity caused by mineral anisotropy, the grain or crack ordering, and the spatial distribution of fractures. It is possible to construct various modifications of the model, reflecting different aspects of the heat conductance in porous rock. The interpretation of thermal conductivity measured for dry, water-saturated, and ethyleneglycol-saturated limestones in the light of modelling results provides quantitative estimates of parameters related to the pore space geometry and the mineral matrix thermal conductivity. References 1. Bagrintseva, K. I., 1999, Forming conditions and properties of carbonaceous of oil and gas reservoirs, RGGU, Moscow, (in Russian). 2. Bayuk, I. and Chesnokov, E., 1998, Correlation between Elastic and Transport Properties of Porous Cracked Anisotropic Media. Phys. Chem. Earth, 23, 3, 361-366. 3. Hashin, Z. and Shtrikman, H., 1963. A Variational Approach to the Theory of the Elastic Behaviour of Multiphase Materials. J. Mech. Phys. Solids, 11, 2, 127-142. 4. Landau, L.D. and Lifshits, I.M., 1982. Electrodynamics of Continuum. Moscow, Nauka. (in Russian) 5. Lichteneker, K. und Rother, K., 1931. Die Herkeitung des logarithmishen Mischungs-gesetzes ans allgemeinen Prinsipien des stationaren Stroming. Phys. Zeit, 32, 255-260. 6. Popov, Yu., Tertychnyi. V., and Korobkov, D., 2000. Experimental Investigations of Interrelations Between Thermal Conductivity and Other Physical Properties of Rocks. In: Thermo-hydro-mechanical Coupling in Fractured Rock. Physikzentrum, Bad-Honnef, Germany, 52-54. 7. Popov, Yu., Tertychnyi, V., Romushkevich, R., Korobkov, D., and Pohl, J. 2002, Interrelations between thermal conductivity and other physical properties of rocks: Experimental data, PAGEOPH (in print). 8. Shermergor, T.D., 1977. Theory of Elasticity of Microinhomogeneous Media. Moscow, Nauka, (in Russian) 9. Tertychnyi, V., Popov, Yu., and Korobkov, D., 2000. Influence of Internal Structure on Thermal Conductivity of Rocks. In: Thermo-hydro-mechanical Coupling in Fractured Rock. Physikzentrum, Bad-Honnef, Germany, 54-56. 10. Xu, S and White, R.E., 1995. A New Model for Clay-Sand Mixtures. Geoph. Prosp., 43, 91-118.
Keywords

- catalysts,
- heat conductivity,
- temperature,
- density,
- gases,
- geterogen-catalic

Disciplines

Publication Date

Winter December, 2008
Citation Information

Mahmadali Mahmadievich Safarov, Emonidin Sharipovich Таurov, Тahmina Rustamovna Tilloeva and Davlatmurod Ishalievich Bobosherov. "Thermophysical properties of catalysts in dependence temperature" *High temperature high pressure*(2008)

Available at: http://works.bepress.com/mahmadali_mahmadievich_safarov/3/