Research On The Type And Distribution Of Nitrogen Compounds In FCC Process

With the quality of crude oil becoming heavier and poorer, the content of nitrogen compounds in FCC feedstock tends to rise. Nitrogen compounds impact on environment, refining process and fuel quality negatively, so the research on the conversion rules of nitrogen compounds means an important significance to the development of processing technology and catalyst for high nitrogen content feedstock.The research on the influence of nitrogen compounds on FCC reaction showed that: Non-basic nitrogen compounds represented by indole had a certain impact on FCC reaction of Daqing VGO. The addition of indole would reduce the reaction conversion and yield of LPG and gasoline, and the coke yield fell slightly. Basic nitrogen compounds represented by quinoline and 7,8-benzoquinoline had a relatively great impact on the reaction of Daqing VGO. Its impacts mainly resulted in the decrease of reaction conversion and yield of LPG and gasoline, and the increase of the dry gas yield. The higher the indole and quinoline content in feedstock was, the greater the influence of nitrogen compounds was.The research on the conversion of nitrogen compounds in FCC processing showed that: Indole and quinoline mainly converted into diesel fraction and coke after FCC reaction, which accounted for about 43%～67% and 20%～43%, respectively. And about 10%～18% of nitrogen compounds was converted into gasoline fraction. The rest distributed in gas and heavy oil.7,8-benzoquinoline was mainly converted into diesel fraction, which accounted for about 80%. The proportions in heavy oil and coke were approximately the same, which were about 10%. Trace content of nitrogen compounds was found in gas and gasoline.Nitrogen-containing heterocyclic rings in indole and quinoline molecule could be saturated by hydrogen transfer reaction, and then cracked to aniline or aliphatic amine. Benzene rings in indole and quinoline molecule could be saturated also by hydrogen transfer reaction, and then cracked to pyrrole or pyridine. But these reactions were more difficult than ring-opening cracking reaction of Nitrogen-containing heterocyclic rings. Indole and quinoline could be converted to alkyl-indole or alkyl-quinoline by transalkylation reaction. 7,8-benzoquinoline could be converted into aliphatic amine or ammonia by ring-opening cracking reaction after the nitrogen-containing heterocyclic ring and the middle benzene ring were saturated by hydrogen transfer reaction, but aniline couldn’t be generated by this reaction. Ammonia could be generated by cracking reaction of aniline. Ammonia reacted with olefin to form aniline, pyrrole, pyridine, and further into indole, quinoline and some other nitrogen compounds by cyclization and condensation reactions.The research on the influence factors of conversion of nitrogen compounds in FCC processing showed that:Increasing reaction temperature could obviously improve the conversion of nitrogen-containing feedstock, especially for improving the reaction conversion and gasoline yield of feedstock with basic nitrogen compounds represented by quinoline. Increasing C/O ratio or reducing space velocity could promote the conversion of nitrogen-containing feedstock and improve product distribution. Improving reaction severity could promote the coversion of nitrogen compounds from liquid product to gas or coke.Catalyst with higher acid content and specific surface area, larger pore volume, and lower silica alumina ratio could improve the reaction conversion of nitrogen-containing feedstock, and promote LPG and gasoline yield. Meanwhile, these catalysts contributed to the conversion of nitrogen compound from liquid product into coke and gas, and promoted the generation of alkyl-indole, alkyl-quinoline and aniline.