One of the reasons: "cation" poisoning
1. Composition of cations: metal ions and basic nitrides, ammonia and organic amines in C4 raw materials.
2. Source of cation:
① Sodium and calcium ions caused by incomplete water washing of upstream raw materials;
② Soluble iron and chromium ions produced by equipment pipes or valves;
③ Trace aluminum and silicon ions in FCC molecular sieve;
④ Ammonia, methylamine and other basic compounds in C4 also belong to the category of cations.
3. Poisoning principle and form: these cations and so3oh in the catalyst produce ion exchange and make the catalyst "poisoned". The reaction formula is as follows: so3oh + m + (Na +, Ca2 +, Fe3 +, Cr4 +, AL4 +, NH4 +, CH3NH2 + )
Poisoning form: "one layer at a time", i.e. those who first contact with materials are poisoned first, and then contact materials are temporarily out of service

Cause 2: poisoning of hydrolyzable nitriles and amides
1. Source:
① in FCC, C4 and C5 feedstocks usually contain acetonitrile and propiononitrile.
② in C4 feedstock of steam cracking, DMF for extraction of butadiene upstream is occasionally present
2. Poisoning principle: for example, acetonitrile: ch3ch2cn + h2och3ch2c-nh2 product amine will poison the catalyst.
3. Poisoning form: diffusion type. This kind of substance makes the form of catalyst different from the above, spreading the poisoning scope to all corners of the catalyst.
The third reason is that the catalyst channel is blocked, which makes the catalyst inactive
1. Polymer plugging pore: polymer comes from butadiene and self polymerizes at high temperature.
2. Control content index of butadiene: general requirement is less than 0.2%.
Reason 4: catalyst group falls off and deactivates the catalyst
The maximum temperature resistance of the catalyst is 120 ℃, but when the catalyst is operated at this temperature for a long time, the sulfonated group of the catalyst will fall off the structural framework and flow into the liquid phase, which will cause the deactivation of the catalyst