Subcritical hydrothermal purification from oily sludge recovered from petroleum oily sludge by adding sodium hydroxide, sodium bicarbonate, and formic acid

Subcritical water upgrading has received a great deal of attention because of its high efficiency and environmental protection technology features, but its high temperature and high-pressure reaction conditions have limited its further development. This article investigates the hydrothermal upgrading recovered oil from oily sludge at 350 & DEG;C and for a residence time of 60 min recovered oil. The effects of the type and concentration of various additives sodium hydroxide (NaOH), sodium bicarbonate (NaHCO3) and formic acid (CH3COOH) on the yield and quality of recovered oil were analyzed and discussed. The addition of 2 wt % NaOH increases the recovered oil yield to 78.6%, due to the demulsification effect of alkaline additives. Meanwhile, the CH3COOH effectively increased the H/C ratio of the recovered oil to 1.69, which can be attributed to the hydrogenation of large molecules in the sludge with hydrogen generated from the added CH3COOH. The effect characteristics and mechanisms of adding additives on the increase in the recovered oil yield and quality of oil-bearing sludge in a sub-critical hydrothermal environment were revealed. Subcritical water upgrading technology provides a new technological route for resource recovery of oily sludge with mild reaction conditions and high efficiency and simplicity.