Different options to upgrade engine oils by gasification with steam and supercritical water

This work reports for the first time a treatment to manage engine oils in an environmentally friendly manner which, besides, upgrades them into valuable gases: gasification with steam and supercritical water (SCW). Pressure, temperature and wt% ranges from 50 to 500 bar, 500–800 °C and 0.42–2.0%, respectively, were investigated. The process can be faced in two different ways regarding the temperature. A low-temperature gasification at 550 °C to transform up to 60% of oil into carbon-containing gases such as CH4 and ethane in less than 2 min; and a high-temperature gasification at 750 °C that produces H2, CH4 and CO2 as main gaseous products. Namely, SCW gasification at 250 bar, 750 °C and 0.83 wt% for 1.9 min transformed more than 85% of the oil into a gaseous mixture containing 37% H2 and 29% CH4, two valuable green fuels. The treatment is herein used to upgrade fresh engine oils but it is potentially applicable to the upgrading of such an abundant and polluting residue as waste engine oils.