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Analysis of Cautions for Catalyst Use or Poisoning (Inactivation)

Jun 08, 2020

One of the reasons: "cationic" poisoning

1. Composition of cations: metal ions and basic nitrides, ammonia gas and organic amines in C4 raw materials.

2. Source of cation:

①Sodium ions and calcium ions brought by incomplete washing of upstream raw materials;

②Soluble iron ions and chromium ions produced by equipment pipes or valves;

③ Trace aluminum ions and silicon ions in FCC molecular sieve;

④The basic compounds such as ammonia and methylamine in C4 also belong to the category of cations.

3. The principle and form of poisoning: these cations and the SO3OH in the catalyst produce ion exchange, which makes the catalyst "poisoned". The reaction formula is as follows: SO3OH+M+ (Na+, Ca2+, Fe3+, Cr4+, Al4+, NH4+, CH3NH2+...)

Poisoning form: poisoning "layer by layer", that is: poisoning the material first, then not poisoning the material.

The second reason: poisoning of hydrolyzable nitriles and amides

1. Its source:

① In catalytic cracking, C4 and C5 raw materials usually contain acetonitrile and propionitrile.

②In the steam cracking C4 feed, occasionally there is DMF for the extraction of upstream butadiene.

2. Poisoning principle: such as acetonitrile: CH3CH2CN+H2OCH3CH2C-NH2 product amine will poison the catalyst.

3. Poisoning form: diffusion type. Such substances make the form of the catalyst different from the above, and spread the poisoning range to all corners of the whole catalyst  .

The third reason: the pores of the catalyst are blocked and the catalyst is deactivated

1. The polymer blocks the pores: the polymer is derived from butadiene and self-polymerizes at high temperature.

2. Control the content index of butadiene: general requirements <0.2%.

The fourth reason: the catalytic group falls off, deactivating the catalyst

The maximum temperature of the catalyst is 120℃, but when it is operated at this temperature for a long time, the sulfonated groups of the catalyst will fall off from the structural skeleton and flow into the liquid phase, thus causing the catalyst to be deactivated.