Catalytic stability of catalyst performance parameters(2)

Anti-toxic stability: The ability of catalyst to resist deactivation of adsorbed active poisons is called anti-toxic stability, these poisons refer to compounds containing sulfur, phosphorus, halogens and arsenic, which may be impurities in raw materials, or by-products or intermediate compounds produced in the reaction; various catalysts have different anti-toxic resistance to various harmful impurities, and the same catalyst has different anti-toxic resistance to the same impurity under different reaction conditions. 

The same catalyst has different resistance to the same impurity under different reaction conditions. The following criteria are used to measure the stability of catalysts against toxicity: add a certain amount of the toxic substance to the reaction gas to poison the catalyst, and then test it with pure feed gas to observe the degree of activity and selectivity retention; add the toxic substance to the reaction gas until the activity and selectivity are maintained at a given level. 

And observe the maximum allowable concentration of the toxic substance; regenerate the poisoned catalyst to see if the activity and selectivity can be restored, and if they can be restored. The catalysts were regenerated to see if the activity and selectivity could be restored and the degree of restoration.

Mechanical stability: The ability of catalysts to resist friction, impact and gravity is called mechanical stability, which determines the breakage and wear of catalysts during use. Catalysts with high mechanical stability can withstand friction between particles, between particles and fluids, and between particles and walls.

During the use of catalysts, the efficiency decreases gradually and affects the catalytic process. For example, decreasing catalytic activity or selectivity, as well as increasing bed pressure drop due to catalyst crushing, etc., all lead to lower economic efficiency of the production process and even prevent normal operation.

There are many reasons for the decay of catalyst efficiency and shortening of catalyst life, mainly: the toxic effect of impurities in the raw material; the thermal effect at high temperature increases the grain size of the active component in the catalyst, which leads to the reduction of specific surface area or causes the catalyst to deteriorate. 

The dust in the reaction material or the carbon deposit generated during the reaction covers the catalyst surface; the active component in the catalyst is lost during the reaction; the strong thermal shock or pressure fluctuation breaks the catalyst particles; the flushing of the reactant fluid makes the catalyst pulverized and blown away, etc.

During the catalytic reaction, the activity and selectivity of the catalyst can be reduced due to various reasons described above, but if appropriate measures are taken, the stability of the catalyst can be maintained so that it has a long enough life. For example, adding certain additives to the catalyst can improve the stability of the active structure and the thermal conductivity of the catalyst; purifying the reaction material to avoid catalyst poisoning; improving the mechanical strength of the catalyst to reduce the wear and tear of the catalyst, breaking and reasonable regeneration measures.