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.