Coke formation of heavy oil during thermal cracking: New insights into the effect of olefinic-bond-containing aromatics

Abstract

The distributions of olefinic-bond-containing aromatic hydrocarbon (OAH) and the effect of OAH on coke formation during heavy oil thermal cracking have been rarely studied in the past. Here, the information of olefins in thermally cracked products derived from vacuum residue (VR) was investigated first, and then the effect of OAH on coke formation was elaborated by revealing the evolution characteristics of self/co-addition systems participated by representative OAH model compounds. The results found that OAHs were generated during VR thermal cracking, and they could participate in further reactions to promote coke formation. During thermal reaction, OAHs were more reactive for addition reactions than alkenes, and the reactivity of OAH increased roughly with the number of aromatic rings. Meanwhile, the higher concentration of OAH or the longer thermal reaction time or the higher thermal reaction temperature, the higher conversion of addition products, and the greater condensation degree of reaction products. OAHs participating in the larger structure molecule formation involves free radical addition reactions, which could occur between different OAHs as well as between OAHs and conventional aromatic molecules. More importantly, OAHs could form larger structure molecules by direct addition reaction of unsaturated double bond via non-free radical addition reaction, thus promoting fast coke formation.