Hydrogen-rich gas production via supercritical water gasification (SCWG) of oily sludge over waste tire-derived activated carbon impregnated with Ni: Characterization and optimization of activated carbon production

In this study, the production of activated carbon (AC) through the chemical activation of waste tire (WT) using H3PO4 and KOH for H2 production by SCWG of oily sludge (OS) donated by Persian Gulf Star Oil Company was investigated. H3PO4 was the best activating agent based on some pretests results, and then the synthesis of AC was optimized using Response Surface Methodology. Based on BET surface area of synthesized ACs, thirty combinations of the four variables namely; activation temperature (350–550 °C); activation time (1–4 h); H3PO4 to WT ratio (1–3 w.w−1); and H3PO4 concentration (20–40 wt%) were optimized. CHNS, TGA, FE-SEM, and EDS-mapping analyses were used to characterize the AC and catalyst synthesized in optimum condition (activation temperature: 450 °C; activation time: 2.5 h; H3PO4 to WT ratio: 2 w.w−1; and H3PO4 concentration: 40 wt%), which presented a surface area of 170 m2 g−1. Finally, Ni was impregnated on the optimized AC with different loadings (5–15 wt%) to evaluate its performance in H2 production by SCWG of OS. Although H2 yield in catalytic experiments was higher than that observed in non-catalytic experiment, results showed that the maximum H2 selectivity was 66% in SCWG of OS using AC impregnated with 10 wt% Ni.