Page 110 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: ZBU 2nd Revised Pages
Encyclopedia of Physical Science and Technology EN002G-87 May 19, 2001 20:3

508 Catalyst Characterization

FIGURE 7 Optical photomicrograph of a cross section of a honeycomb catalyst. The thickness of the granular
material, the washcoat, can be measured with a calibrated reticle in the microscope eyepiece.

abatement in aircraft, resistance to vibration as well as by collision with each other or the internal surfaces of
radial strength is important. the reactor. Thus, abrasion resistance is a key catalyst
Measurement for tablets, spheres, extrudates, mono- property.
liths, and so on, is quite simple. A single particle or unit Catalyst material (tablets, extrudates, spheres, or irreg-
representative of the lot is placed between parallel plates ularly shaped catalysts) are charged to a drum, which ro-
of a device capable of exerting compressive stress, and tates for a given set of time, and the “fines” produced are
the force necessary to crush the material is noted. Tablets, measured. The drum usually contains a single baffle, and
extrudates, or monoliths can be placed within the plates its inner surface must be smooth. Powder attrition can be
so as to measure axial or radial crush strength. Naturally, measured using particle size distribution techniques, as
a sufficient number of particles must be tested to obtain described in Section II.B.1. Monolithic catalysts are sub-
proper statistics. The method cannot be reliably used for jected to high gaseous flow rates, and hence erosion of
granular or other materials with irregular shapes. the washcoat from the surface of the monolith is a likely
cause for concern. The most common technique is simply
to subject the washcoated monolith to a jet of gas simu-
2. Attrition and Abrasion
lating the linear velocities anticipated in use and note the
Catalyst particles in fluid-bed reactors such as those used weight change of the catalyst due to erosion. Naturally,
in heavy oil cracking are subjected to potential abrasion one can also collect the attrited particles and correlate