Titanium dioxide catalytic hydrothermal liquefaction to treat oily sludge: As hydrogen production catalyst

•TiO2 shows high catalytic performance for oily sludge in HTL with high temperature and dark environment.•TiO2 undergoes electronic transitions to generate H2 and O2 with subcritical water in HTL.•Petroleum was cracked and converted into small molecular organic hydrocarbons through hydrocracking and oxidative cracking. Oily sludge is a pollutant associated with the petrochemical industry, and its harmfulness and resource disposal are urgent problems to be solved. Nano-TiO2 was used to catalyze HTL to treat oily sludge and showed excellent technical advantages in this study. When T = 230°C and w = 1.5%, the total oil removal efficiency reaches 82.69%, of which 77.68% can be extracted and utilized. Compared with the blank group without TiO2, the oil removal efficiency is increased by nearly 35%, and the oil extraction efficiency is increased by more than 55%. The result imply that TiO2 might can be excited by HTL to generate h+ and e−, which will react with subcritical water produced by HTL to produce O2 and H2. H2 can promote the degradation and lightening of organic matter through hydrocracking, O2 can promote the oxidative cracking of organic hydrocarbons. TiO2 catalysis obviously changes the distribution trend of oil in HTL. Without TiO2 catalysis, the removed oil is mostly oxidized or coked to form coke. The H2 produced by TiO2 can inhibit the coking reaction and form liquid petroleum hydrocarbons that can be extracted and utilized. Due to gas release and coke reduction, which can create pathways to promote the release of oil and water. Nano-titanium dioxide hydrogen production catalysts can obviously improve the treatment efficiency of oily sludge and have broad application prospects in the harmless and resourceful treatment of organic solid wastes. [Display omitted]