Industrial Catalysis

Catalyst packing characteristics

It is important to achieve uniform loading of the tube with catalyst since this will ensure uniform gas pressure drop through the tube and uniform temperature with no hot spots. Catalysts in the form of long cylinders with holes in them tend to give good uniform packing, but thin cylinders with holes through the centre can stack resulting in poor gas distribution down the reformer tube.

Catalyst break up

All catalysts suffer some break up during use. The main mechanism is through the start up - shut down cycle. At start up the heated tube expands and the catalyst settles a little. At shut down the tube contracts and the catalyst breaks a little. Since such breakdown can lead to a gas pressure drop through the tube of up to 10% a year, the catalyst shape is designed to resist break up. The problem is that increased strength can lead to reduced activity and so a compromise may be required.

Catalyst poisons

Many poisons affect reforming catalysts including sulphur, metals, halides and phosphates.
Sulphur is a particular problem because:

  • nickel is a very good sulphur adsorbent
  • only a small amount of sulphur can cause problems
  • sulphur can totally deactivate a reforming catalyst

The good news is that sulphur poisoning is reversible. Steam can be used to slowly strip off the sulphur over a period of 24 hours. The less good news is that the catalyst may lose some of its activity permanently. The effective answer is to remove sulphur from the feedstock gases before they enter the reformer tube.

   
 
Packing of cog shapes. The void will lead to an uneven pressure drop and therefore uneven heating of the contents of the tube.
  Only a small amount of sulphur can poison a catalyst. It is adsorbed into the surface of the nickel catalyst and stops the methane and steam attaching themselves.