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3.9 P article Analysis 231

0.0040
0.0035
0.0030

0.0025
0.0020 mesopores
dV/dD
0.0015
macropores
0.0010
0.0005
0.0000
0 20 40 60 80 100 120
pore diameter D (nm)
Figure 3.66 v e catalyst. Pore size distribution of an automoti

Rigid adsorbents, like charcoal or silica gel, swell by only a small percent, but nonrigid
adsorbents, lik e agar–agar,veral times the original size. Provided the adsorp- may swell to se
tion occurs slowly, the rigid solid may accommodate the stresses, but if suddenly e xposed
to high vapor pressure the material may shatter.

3.9.5 Mechanical strength

The mechanical strength of a catalyst is really important in its commercial applications, since
broken pieces and losses can lead to a decrease in catalytic activity and a significant expense,
especially when precious metals are used as the catalytic agents. Mechanical strength is
equally important in adsorption and ion exchange, especially in fixed-bed operations.
Crush strength is defined as the resistance of a formed particle to compressie forces. v
Measurements of crush strength provide an indication of the ability of the particle to main-
tain its physical integrity during handling and use. When crush strength is measured for
”
single pieces, it is called “piece crush strength, and when it is measured for a bulk sam-
ple it is called “bulk crush strength. Other terms that hae been used for piece crush
”
v
strength but which are not recommended are static crush strength and single-pellet crush
strength. The loss of solid during handling or use is called “attrition. Abrasion, grinding,
”
or rubbing of the particles with each other or with container walls can lead to attrition.

3.9.6 Density

In this section, definitions of terms used in relation to particle density are presented. As
will be sho these issues exhibit many alternatie approaches. For instance, density is
wn,
v