Abstract: This research based on catalytic cracking pilot plants unit, the use of inferior straight-run gas oil as raw material, through change different conversion rate ,we can get the transfer coefficient of polycyclic aromatic hydrocarbons, test result may illustrate conversion rule of polycyclic aromatic hydrocarbons: under the condition of conversion rate below 48.22%, the transformation of polycyclic aromatic hydrocarbons, the main reaction as the branched chain rupture; when Conversion rate ranged from 48.22% to 62.71%, the three ring and the four ring aromatic hydrocarbons transfer coefficient changed little in the catalytic heavy oil, aromatic nucleus is relatively stable, polycyclic aromatic hydrocarbons transfer coefficient is about 0.3~0.4. the conversion rate is suitable for high selective catalytic cracking. When the conversion rate is higher than 62.71%, the polycyclic aromatic hydrocarbons will condensate rapidly, enhance the contributions to coke increases.

Key words: polycyclic aromatics, coke, aromatics, transfer coefficient