Catalysts density measurements

Apparent Bulk Density (ABD) is the density of catalyst as measured, loosely compacted in a specified container. 

However, the intrinsic pseudohomogeneous rate used in Equation (10.39) is not identical to the rate determined from the CSTR measurements since the catalyst density will be different. The correction procedure is... 

In a second series of experiments, similar materials were prepared with I wt % catalyst to investigate the influence of morphology on the toughening. In addition to the two heat treatments to generate solvent-modified and macroporous epoxies as presented before, a third heat treatment was carried out to give a semi-porous morphology. A brief heating above Tg and under vacuum results in partial solvent removal. The differences in the three heat treatments is clearly revealed with density measurements as shown in Fig. 48. 

Apparent bulk density the density of a catalyst as measured usually loosely compacted in a container. 

Density of Steam Deactivated vs. Fresh Catalyst. The results of density measurements on the fresh parent of Catalyst A and on a portion of this catalyst that has been steam deactivated at 815°C for five hours (Table VIII) indicate a direct connection between the loss of crystalline microporous zeolite and increase in catalyst density. The major portion (67%) of the fresh catalyst is found in the density range 2.330 < d < 2.355 g/cc. By contrast, the major portion (87%) of the steam deactivated catalyst is found in the density range 2.372 to 2.394 g/cc. 

Example 10.9 used two different definitions of the catalyst density and at least two more definitions are in common usage. The value pc = 367 refers to the reactor average density. It is quite low in the example because so much of the reactor volume is empty. Normally, the reactor would be packed almost completely, and the reactor average density would approach the bulk density. The bulk density is what would be measured if the catalyst were dumped into a large container and gently shaken. The bulk density is not stated in the example, but it would be about 800 kg/m3 for the catalyst pellets prior to grinding. The catalyst will pack to something less than the bulk density in a small-diameter tube. The pellet density in the example is 1120 kg/m3. It is the mass of a catalyst pellet divided by the external volume of the pellet. The final density is the skeletal density of the pellet. It is the density of the solid support and equals 1120/(1 — 0.505) = 2260 kg/m3 for the example catalyst. The various densities fall in the order... 

Several catalyst densities are used in the literature. True density may be defined as the mass of a powder or particle divided by its volume excluding all pores and voids. In a strict physical sense, this density can be calculated only through X-ray or neutron diffraction analysis of single crystal samples. The term apparent density has been used to refer to the mass divided by the volume including some portion of the pores and voids, and so values are always smaller than the true density. This term should not be used unless a clear description is given of what portion of the pores is included in the volume. So-called helium densities determined by helium expansion are apparent densities and not true densities since the measurement may exclude closed pores. 

In Equation (35), an estimation of the mass transfer with the Weisz-Prater criterion is given. By taking always reasonable estimations or overestimated values, one obtains a good conclusion if mass transfer is present or not. For the characteristic length, 200 pm as particle diameter is used. The reaction order usually has the value of 1 to 4 a value of 4 would therefore be a worst case scenario. The catalyst density can be measured, or the common estimation of 1.3 kg/m3 can be used, which should not be too erroneous for Li-doped MgO. The observed reaction rate re is calculated from the concentration of CH4 at the inlet of the reaction cch4 0 multiplied with the highest observed conversion of 25% (the highest initial value for all tested catalysts), divided by the inverse flow rate, corrected by the reactor temperature. The calculation of re is shown in Equation (33) ... 

In this present work, the objective is to develop a supercritical drying method which prepares aerogel catalysts with tunable physical and chemical properties. For this purpose, catalysts are prepared using supercritical drying and bulk densities of the catalysts are measured and compared with the ones of the xerogels. 

Reaction orders and rate constanB were estimated from periscosity measurements for a bulk catalyst density of 1.2 kg/m. ... 

In some earlier life tests performed by Wilson and co-workers, PEFCs utilizing thin-film platinum catalyst layers typically experienced a gradual performance loss over the first 500 to 1000 h of operation and then stabilized at about 70% of the original performance (here, performance is described in terms of the current density measured at 0.50 V, i.e., close to the maximum power output of the cell). In such life tests. 

The Thiele modulus for the mesoporous structure of the eatalyst, ( ) i, was calculated using the following parameters particle size, Rp = 0.0137 cm mean pore radius, rpore.ave = 20 10 cm catalyst porosity, e = 0.52 catalyst density, pg = 1210 g 1. N2 adsorption-desorption isotherms were used for measurement. The calculated value of effective diffusivity coefficient in the mesoporous structure of the catalyst is Dg = 9.71 10 2 cm min . This value is not affeeted by coke deposition. 

A more accurate procedure is the helium-mercury method. The volume of helium displaced by a sample of catalyst is measured then the helium is removed, and the volume of mercury displaced is measured. Since mercury will not fill the pores of most catalysts at atmospheric pressure, the difference in volumes gives the pore volume of the catalyst sample. The volume of helium displaced is a measure of the volume occupied by the solid material. From this and the weight of the sample, the density of the solid phase, P5, can be obtained. Then the void fraction, or porosity, of the particle, p, may be calculated from the equation... 

Example 11-7 The rate of isomerization of o-butane with a silica-alumina catalyst is measured at 5 atm and 50°C in a laboratory reactor with high turbulence in the gas phase surrounding the catalyst pellets. Turbulence ensures that external-diffusion resistances are negligible, and so Q = Q. Kinetic studies indicate that the rate is first order and reversible. At 50°C the equilibrium conversion is 85%. The effective diffusivity is 0.08 cm /sec at reaction conditions, and the density of the catalyst pellets is 1.0 g/cm, regardless of size. The measured, global rates when pure n-butane surrounds the pellets are as follows ... 

In the petroleum industry, the effective particle density of free-flowing cracking catalysts is measured indirectly by measuring the open pore volume. This consists of adding water or another liquid of low viscosity and volatility, to the powder until the liquid has filled all the open pores and it starts coating the external surfaces of particles the powder cakes-up by surface tension at this point and stops flowing. 

Fig. 32. FCC riser hydrodynamics. The solids concentration near the wall is considerably higher than at the center. Radial catalyst density profile measurements of Schuurmans (1980).

One way it may be possible to increase the frequency factor alone is by inducing the sites to form in patches on the total surface. This would make site density beneficially high within the patches without an increase in the total number of sites per unit of catalyst, as measured by some kind of test, such as adsorption. Theoretical studies of adsorption have considered both uniform and patch-wise site distributions in physical adsorption. The consequences of this dichotomy need to be understood as they relate to catalysis. 

Techniques used to characterize the catalysts were measurements of solid density, ds (Quantachrome Multipycnometer Model MVP-1), bulk density (vibrated graduated cylinder), BET surface area (Quantachrome Quantasorb... 

In a riser reactor, the reaction rate depends on the suspension density, usually expressed in kg/m. Predicting the density is difficult, because there are axial and radial density gradients, which may cover a severalfold range of values. The suspension density is much greater than if the particles acted independently and had a slip velocity equal to the terminal velocity. For example, with 60-/rm FCC catalyst, v, 0.1 m/sec, and if Ug = 15 m/sec, the particle velocity for the ideal case would be 14.9 m/s, almost equal to the gas velocity. However, based on tracer studies and density measurements, FCC risers operate with particle velocities that are much less than the gas velocity. Experimental results are often expressed as a slip factor, f, the ratio of actual gas and particle velocities ... 

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