Comparative evaluation for catalytic gasification of petroleum coke and asphaltene in subcritical and supercritical water

Abstract

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.