Characteristics of products of thermal and catalytic cracking of heavy oil asphaltenes under supercritical water conditions

Abstract

This work deals with the reactivity and structural changes of asphaltenes during cracking in supercritical water using water-soluble salts Co and Ni. Cracking of the asphaltenes was carried out in an autoclave with a volume of 12 cm3 at a temperature of 450 °C, the process time was 80 min and the pressure was ≈ 29–30,8 MPa. The reactivity and structural changes of the asphaltenes were evaluated based on the yield and composition of the products (gas, maltenes, and coke) and the characteristics of the residual asphaltenes obtained by the method of structural group analysis based on elemental analysis, the values of molecular weight and 1H nuclear magnetic resonance (1H NMR), and XRD. Under supercritical water conditions, coke formation reactions are slowed down, with increasing diameter of the carbon stack structure. It is found out that the cobalt-containing catalyst promotes the formation of additional amounts of lower molecular weight components, i.e. maltenes and gas. In this case, the structure of secondary asphaltenes refers to the "island", and the number of packs and the total height in the asphaltene cluster increase.