Study On The Application Of Acid Additives To Catalytic Cracking Of Heavy Oil Containing Nitrogen Compounds

In order to improve the catalytic cracking performance of heavy oil with nitrogen compounds, ten kinds of acid additives or acid additive precursors, which include acetic acid,methanol,n-butyl bromide,additive A and so on were applied into the model compound system comprised by some nitrogen compounds and hexadecane or the model heavy oil system made up of Kalamay vacuum gas oil(VGO) and pyridine or Kalamay coker gas oil(CGO) system in a simulated fix-bed catalytic cracking micro-reactor. Then their improvement was investigated in the two model systems and the CGO system. Besides the investigation of the external acid additives, the upgraded CGO FCC preceded by simple tentative pre-oxidizing, which could generate the internal acid function groups like–COOH and–OH in the CGO system, was evaluated and studied. The main conclusions can be drawn as follows:Both base nitrogen compounds including pyridine and quinoline and non-base ones (i.e. indole) could lower hydrocarbon conversions by poisoning the acid FCC catalysts. The acid additives in the model compound system allevated nitrogen compounds poisoning so that a conversion jump and a good product distribution could be achieved. Among the external acid additives, their upgrading effects were with the order : n-butyl bromide>methanol>acetic acid>additive A. The reason might relate to the Friedel-Crafts reaction and hydrogen donation. However, methanol and additive A showed better properties, while acetic acid and n-butyl bromide less effects in the model heavy oil system containing pyridine. Alcohol series including ethanol, glycol and glycerol gave the similar performance to methanol. As to the additive A, a substantial improvement on product distribution including the increase of gasoline and the decrease of the dry gas and coke on the same total conversion could occur with a 200-500 g?g-1 dosage. In the CGO FCC system, both methanol and the additive A were favorable to catalytic cracking with 1%the maximal increase of conversion and 1-2m% the light oil recovery.Pre-oxidization of CGO with potassium permanganate(KMnO4) and ter-butyl hydrogen peroxide(C(CH3)3OOH) not only generated the internal acid function groups like–COOH and–OH and"neutralized"base nitrogen compounds in the CGO, but also resulted in the decrease of molecular weight of CGO. After pre-oxidization treatment of CGO, nitrogen compounds poisoning in the CGO FCC could considerably be alleviated, and CGO conversion be increased and a good product distribution could be achieved. The jump of gasoline yield and the total conversion could be up to 10% and 4m% while the yields of dry gas and coke were clearly lowered. Between the two oxidants, KMnO4 showed better effect than C(CH3)3OOH.