Hydrogen Generation via Catalytic Pyrolysis of Petroleum Sludge Using Activated Biochar Catalyst Under CO₂

This study offers a practical method for converting petroleum sludge (PS) into H₂-rich gas via CO₂ catalytic pyrolysis using activated biochar (ACB) catalysts. Pre-treatment techniques were applied to prepare phosphoric acid (H₃PO₄; ACB-P), zinc chloride (ZnCl₂; ACB-Z), and potassium hydroxide (KOH; ACB-K), which served as catalysts to boost H₂ production through catalytic pyrolysis of PS. The H₂ selectivity showed a rising trend in the subsequent sequence: noncatalytic (non-C; 6.9 vol%) < raw biochar (7.1 vol%) < ACB-K (9.7 vol%) < ACB-Z (17.8 vol%) < ACB-P (22.9 vol%) at 600°C. These results are attributed to the well-developed porous structure and abundant acid sites of the ACB catalysts, which promote a carbonium-ion mechanism. Using ACB-P yielded higher gas production and H₂ selectivity under CO₂ than under N₂, emphasizing the important role of catalyst acid sites and CO₂ in the pyrolysis of PS. Additionally, ACB-P produced more H₂ than commercial charcoal. Increasing the reaction temperature to 700°C improved gas yield, reaching a maximum of 68.2 wt%. Conversely, H₂ selectivity showed an inverse relationship with temperature, decreasing from 48.4 vol% at 500°C to 16.3 vol% at 700°C.