What is the impact of the nitrogen content in the feedstock of hydrocracking units on the activity and stability of hydrocracking catalysts?

Therefore, it is necessary to strictly control the content of organic nitrogen compounds in the feedstock entering the cracking reactor, with a requirement generally of less than 10 ppm. (A. Nitrides are classified into two main categories: basic nitrides and non-basic nitrides, depending on whether the nitrogen atom in the molecule possesses lone pairs of electrons. Since basic nitrides contain free lone pairs on their nitrogen atoms – including certain amines, dihydroindoles, and six-membered heterocyclic nitrogen compounds – they can easily adsorb onto the acidic active sites of catalysts, thereby exerting a significant toxic effect on those catalysts. Catalysts containing molecular sieves are more sensitive to basic nitrides than amorphous catalysts, as the adsorption of organic basic nitrides on the catalyst is related to the acidity or basicity of the catalyst. Molecular sieves have greater acidity than amorphous materials, and desorption is dependent on temperature; consequently, catalysts based on molecular sieves operate at relatively lower temperatures, resulting in slower desorption. Nitrides not only affect the stability of catalysts but also have a significant impact on catalyst fouling. Studies show that the nitrogen content in the carbon deposition on the catalyst is much higher than that of the nitrogen-containing compounds in the oil. Some scholars believe that small and medium-sized nitrogen-containing compounds are precursors to the formation of coke and carbon. Aromatic compounds and nitrogen compounds are strongly adsorbed by the catalyst, remaining concentrated at the center of B-acid molecules for an extended period; this leads to polycondensation reactions that result in the formation of carbon deposits covering the active surface, thereby reducing the activity of the cracking catalyst. Laboratory data also show that for Ni-Mo series catalysts, under the same conversion rate, the difference in reaction temperature between feedstocks with a nitrogen content of 2000 ppm and 0 ppm can reach 85°C; this effect is even greater for precious metal catalysts, where the difference reaches 110°C. When the nitrogen content increased from 500 ppm to 1300 ppm, the catalyst deactivation rate increased by nearly 3 times. Therefore, the primary focus among all the indicators is the nitrogen content in the raw materials. Compared with many foreign crude oils, Chinese crude oils are characterized by low sulfur content and high nitrogen content; therefore, when processing domestic onshore crude oils, special attention should be paid to the nitrogen content in them. 1 R. w- {: a- T/ p4

Nitrogen molecules are large; they first adsorb on the acidic sites of the catalyst, thereby inhibiting the cracking reaction. To achieve a greater degree of reaction, it is necessary to increase the cracking temperature. Shortens the catalyst's service life. . . .

One is the formation of amines that adsorb on the active centers of the catalyst, making other reactions difficult to occur; another issue is the easy accumulation of carbon on the catalyst surface