Step by step modeling for thermal reactivities and chemical compositions of vacuum residues and their SFEF asphalts

Abstract

In this paper, thermal conversions of 40 samples, including eight vacuum residues (six Chinese vacuum residues from Daqing, Dagang, Gudao, Shengli, Huabei and Liaohe crudes, two from Oman and Saudi Arabia Light crudes) and their deoiled asphalts with different yields obtained by supercritical fluid extraction fractionation (SFEF) technique were carried out in a 100-ml autoclave at 410°C and 1 h. The elemental composition (C, H, S and N), SARA (saturates, aromatics, resins and asphaltenes) composition and average molecular weight (MW) of the feedstocks were determined, and their average structural parameters were elucidated. It is found that the cracking and condensation conversion of the samples were correlated with their H/C ratio, contents of sulfur (S%) and nitrogen (N%), MW, and SARA composition (weight percentages of saturates (Sat), aromatics (Ar), resins (Re) and asphaltenes (Asp)). The results obtained by a non-linear regression fit method indicated that the characterization factors K r or K r′ for thermal cracking defined by following two equations: K r =( H/C) 0.257( S%) 0.158( N%) 0.184( MW) −0.151 or: K r ′=( Sat) 0.026( Ar) 0.008( Re) 0.380( S%) 0.170( MW) −0.230 can characterize well the thermal cracking reactivity of the eight vacuum residues and their SFEF asphalts at the 410°C and 1 h. Moreover, the characterization factors K c or K c′ for thermal condensation defined by the following two equations: K c =( H/C) −3.80( MW) 0.40 or: K c ′=( H/C) −3.80( Re+Asp) 0.30( MW) 0.24 can characterize well the thermal condensation reactivity of most samples at the same reaction conditions. It is also found that the yields of toluene insolubles of the feedstocks were correlated linearly with the concentration ratio of asphaltenes to resins plus aromatics of the cracked residues. This indicates that the formation of coke was the result of not only the condensation reaction of asphaltenes but also the phase separation of the colloidal system of residues.