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CRUSH Series - ASTM D4179, ASTM D6175, ASTM D7084 Application note

The ASTM procedure
CRUSH-BK and CRUSH-SP are dynamometers of general use for compression measurements. As far as catalysts are concerned, the ASTM standard methods ASTM D4179 and ASTM D6175 are recommended. ASTM D4179 refers to tableted pellets,  which can be measured in either axial or radial way. As the axial crush strength is much higher, it is not representative of the catalyst behavior in the reactor, therefore the radial crush strength must be measured for industrial purposes (the type of crush strength  measured must always be specified).

ASTM D6175 procedure refers to extrudates (the radial measurement can be only performed in this case).  The radial crush strength is usually expressed in kg/mm or Newton/mm.


Bulk crush strength measurements are performed by standard method ASTM D7084. A faster and simplified procedure developed by Ma.Tec. is available to our customers.

The official text of the two methods can be found at www.astm.org

Catalyst pretreatment
The crush strength of a catalyst is not appreciably dependent on reactor loading, but mainly on reactor operation.

When the catalyst does not require activation, the crush test should be conducted on fresh dried samples.

When the catalyst has to be activated in the reactor, only measurements on activated samples are significant.

Problems arising from low crush strength of catalysts
a)     Pressure drop increase in axial reactors.
b)     Bypass formation in radial reactors.

Crush strength specifications for some industrial catalysts
Single-pellet radial or, for irregularly shaped particles, bulk crush strength must be measured for any catalyst used in fixed-bed and trickle-bed reactors. A minimum value of the force required to break the pellets is usually specified for single-pellet crush strength (such value should not refer to axial measurements).

For bulk crush strength, either the minimum pressure giving 1% fines (ASTM D7084), or the maximum percentage of fines formed under the pressure of 23 bar (Ma.Tec. procedure) are specified.

Examples of currently used crush strength specifications of some industrial catalysts:

Single-pellet radial
       Alumina spheres                      
       LTS pellets*                            
       HTS pellets*                            
       Methanol pellets*                     
       Formaldehyde rings                  
       Hydrotreating extrudates         
       Styrene extrudates   
       Alumina spheres                       
       Hydrotreating extrudates           
       Alumina extrudates                  
       Active carbon granules              
       Ammonia (prereduced) granule   
7 kg min
5 kg min
10 kg min
8 kg min
2 kg min
3 kg/mm min
2 kg/mm min

10% max
5% max
15% max
20% max
1% max

*activated catalysts
**Ma.Tec. procedure

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