Molecular Structure of Resins and Asphaltenes in Catalytic Natural Bitumen Conversion

Natural bitumens are promising alternative hydrocarbon resources, but their high resin–asphaltene content and strong coke-forming tendency limit their efficient conversion into valuable liquid products. This study elucidates the molecular transformations of resin and asphaltene fractions during thermocatalytic upgrading of natural bitumens from the Beke and Munaily Mola deposits in West Kazakhstan. Cracking experiments were conducted at 450 °C for 60 min using thermal treatment, fly-ash-derived ferrospheres, and di-tert-butyl peroxide (DTBP) as a radical-generating additive. Elemental analysis, average-molecular-weight determination, and nuclear magnetic resonance (NMR) spectroscopy were combined with structural-group analysis to establish changes in the molecular architecture of the heavy fractions. Thermal cracking produced 68–74% liquid products, while DTBP increased the liquid yield to 70% for Beke bitumen and 87% for Munaily Mola bitumen and substantially suppressed coke formation. Cracking promoted extensive degradation of aliphatic and naphthenic fragments, dealkylation, cyclization, dehydrogenation, and aromatization, resulting in increased aromaticity and lower molecular weight of the asphaltenes. The average molecular weight of Beke asphaltenes decreased from approximately 2044 to 1003 amu in the presence of ferrospheres. Although ferrospheres enhanced asphaltene destruction, they increased coke formation under the investigated conditions. These findings demonstrate that radical stabilization is critical for directing heavy-component conversion toward liquid products and provide a molecular basis for optimizing catalytic upgrading of natural bitumen.