Precautions for Catalyst Use or Poisoning (Analysis of Deactivation Causes)

One cause: "Cation" poisoning

1. Composition of cations: Metal ions and basic nitrogen compounds, ammonia, and organic amines in C4 raw materials.

2. Sources of cations:

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

② Soluble iron and chromium ions from equipment, pipelines, or valves;

③ Trace amounts of aluminum and silicon ions in FCC molecular sieves;

④ Basic compounds such as ammonia and methylamine in C4 also fall under the category of cations.

3. Principle and form of poisoning: These cations undergo ion exchange with SO3OH in the catalyst, causing the catalyst to be "poisoned." The reaction formula is as follows: SO3OH + M+ (Na+, Ca2+, Fe3+, Cr4+, Al4+, NH4+, CH3NH2+...)

Form of poisoning: Poisoning occurs "layer by layer," meaning that materials that come into contact with the material first are poisoned first, while materials that come into contact with the material later are not poisoned immediately. Reason Two: Poisoning by Hydrolyzable Nitriles and Amides

1. Sources:

① In catalytic cracking, C4 and C5 feedstocks typically contain acetonitrile and propionitrile.

② Occasionally, C4 feedstocks from steam cracking may contain DMF used for butadiene extraction from upstream sources.

2. Poisoning Mechanism: For example, the amine product of acetonitrile (CH3CH2CN + H2O → CH3CH2C - NH2) poisons the catalyst.

3. Poisoning Form: Diffusion type. These substances cause the catalyst to behave differently than those mentioned above, spreading the poisoning to every part of the catalyst.

Reason Three: Catalyst Pore Blockage, Leading to Catalyst Deactivation

1. Polymer Pore Blockage: The polymer originates from butadiene and undergoes self-polymerization at high temperatures.

2. Butadiene Content Control: Generally required to be <0.2%.

Reason Four: Catalyst Group Deactivation.

The catalyst can withstand temperatures up to 120°C, but if it operates at this temperature for a long time, the sulfonated groups of the catalyst will detach from the structural framework and flow into the liquid phase, thereby causing catalyst deactivation.