LAUSR

Abstract Subcritical and supercritical water gasification of petroleum coke and asphaltene was performed at variable temperatures (350–650  °C), feed concentrations (15–30 wt%) and reaction times (15–60 min). Nickel-impregnated activated carbon (Ni/AC) was synthesized as a catalyst for enhancing syngas yields at optimal gasification conditions (650  °C, 15 wt% and 60 min). Structural chemistry of precursors and chars developed at different gasification temperatures was studied using physicochemical and synchrotron-based approaches such as carbon–hydrogen–nitrogen–sulfur (CHNS) analysis, thermogravimetric and differential thermogravimetric analysis (TGA/DTA), scanning electron microscopy (SEM), Fourier-Transform Infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Asphaltene testified to be a better precursor for catalytic hydrothermal gasification leading to 11.97 mmol/g of total gas yield compared to petroleum coke (8.04 mmol/g). In particular, supercritical water gasification using 5 wt% Ni/AC at 650  °C with 15 wt% feed concentration for 60 min resulted in 4.17 and 2.98 mmol/g of H2 from asphaltene and petroleum coke, respectively. Under the same conditions, the respective CH4 yields from catalytic gasification of asphaltene and petroleum coke were 2.54 and 1.07 mmol/g. Nonetheless, asphaltene also seemed to an attractive feedstock for the production of highly aromatic chars through hydrothermal gasification.