Studies on catalytic pyrolysis of heavy oils: Reaction behaviors and mechanistic pathways

Catalytic pyrolysis of heavy oils on various catalysts was investigated in a confined fluidized bed reactor. As for catalytic pyrolysis of Chinese Daqing atmospheric residue (Daqing AR) on catalyst CEP-1, reaction temperature, residence time, weight ratios of catalyst-to-oil, steam-to-oil and feed properties have significant influence on product yields and product distribution. The optimal laboratory operating conditions are as follows: reaction temperature is within 650-680 °C, residence time within 2.0-4.0 s and catalyst-to-oil weight ratio within 13-18. The catalytic pyrolysis ability becomes better and the yields of light olefins become higher with the larger H/C mol ratio and the lower aromatic carbon content of feedstocks. After the cracking mechanisms of hydrocarbons are analyzed and the thermal pyrolysis of Daqing AR is investigated, a mechanism parameter RM is proposed to study the mechanistic pathways of heavy oil catalytic pyrolysis. As for the processes of Daqing AR catalytic pyrolysis on catalysts LCM-5 and CEP-1, the relative acting percentage of the free radical mechanism and that of the carbonium ion mechanism are obtained.