Thermal Cracking of Paraffinic and Middle East Atmospheric Residues and Hydrotreatment of Distillate Products

摘要

Thermal cracking of paraffinic atmospheric residue (AR) was performed in a continuous-flow reactor under the reaction conditions of 440-520 ℃ and N2 0.2-0.8 MPa, and the effects of the reaction temperature and pressure on the product distribution were examined. The vacuum residue fraction gradually decreased up to 480 ℃ and almost disappeared at higher temperatures. Accordingly, the yields of total distillate and coke increased and became nearly constant over 480 ℃. As the heavy distillate yield increased over 480 ℃, the yield of lighter distillates was the highest at 480 ℃ and decreased at higher temperature. When the reaction pressure was increased, the heavy distillate yield decreased with increasing yields of lighter distillates and coke. Two paraffinic and two Middle East ARs were thermally cracked under the conditions of 480 ℃, N2 0.4 MPa and 0.5 h, and the product composition and properties were compared. The yield of distillates (C4-500 ℃) was around 90 % for paraffinic ARs, and 70-80 % for Middle East ARs. The sulfur contents of the distillate products from paraffinic ARs were much lower than those of Middle East ARs, but the difference in the nitrogen contents was not significant. Pyrolyzed middle and heavy distillates were hydrotreated to investigate their hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactivities. The HDS rates of the distillates obtained from paraffinic ARs were 4-6 times higher than those of Middle East ARs. The HDN rates were comparable for the middle distillates, but the HDN rates of the heavy distillates from paraffinic ARs were lower than those from Middle East ARs.