Unveiling mechanisms of heavy oil component separation and conversion via Peroxymonosulfate activation by nitrogen-doped biochar

The efficient conversion of heavy components (asphaltenes and resins) are pivotal for crude oil viscosity reduction. This study presents a novel oxidative fraction conversion strategy using a nitrogen-doped biochar (N-BC) to activate peroxymonosulfate (PMS) for the selective cracking and conversion of heavy oil into lighter fractions, thereby achieving component fraction conversion and viscosity reduction. The process and mechanism were deciphered through advanced characterizations (SARA, FTIR, 1 H NMR, GC–MS) and radical quenching experiments. Under optimized conditions (90 °C, 8 h, 2 g/L N-BC, 2 g/L PMS, oil/water 7:3, 3 wt% tetralin), a 70 % viscosity reduction was achieved, originating from a remarkable 12.5 % decrease in asphaltene content due to polyaromatic ring-opening and aggregate degradation. Concurrently, a 4.0 % reduction in resins, accompanied by side-chain cleavage and a 44.9 % decrease in branching index, facilitated their conversion into saturates, which increased by 4.0 % and were enriched with medium-chain alkanes (C₂₀–C₃₀). Electron paramagnetic resonance (EPR) analysis identified surface-bound SO₄• − as the dominant reactive species, generated at the N-BC's nitrogen sites, which enables superior performance even in high-salinity environments. This work provides a mechanistic foundation for a sustainable and efficient chemical separation technology, highlighting its potential for heavy oil upgrading and the treatment of complex oily wastes. • A novel oxidative separation system achieves 70 % viscosity reduction via heavy to-light component conversion at 90 °C. • N-doping creates efficient active sites on biochar for targeted peroxymonosulfate activation. • Surface-bound SO₄• − is identified as the key species for selective asphaltene network degradation.