Effects of inherent minerals on oily sludge pyrolysis: Kinetics, products, and secondary pollutants

Abstract

Considerable inherent minerals in oily sludge (OS) caused intricate effects on OS pyrolysis behaviors. This work investigated the effects of individual mineral on pyrolytic products and secondary pollutants by pyrolysis of artificial OS, which was prepared by assembling pure mineral chemicals (SiO2, CaO, MgO, Fe2O3, and Al2O3) with petroleum oil. Results showed that the effects of inherent minerals on OS pyrolysis tightly depended on pyrolysis temperature, where the thermal cracking and secondary reactions of heavy hydrocarbons were promoted at high temperature. Their effects also varied with inherent mineral species. The existence of SiO2 in OS had negligible influences on OS pyrolysis. CaO and MgO were favored for almost invariant quality of liquid product and the lowest total petroleum hydrocarbons (TPHs) content in solid residues. Because CaO and MgO weakened the stabilities of hydrogen bonds and hydroxyls groups and thus accelerating devolatilization of TPHs from OS. Fe2O3 and Al2O3 helped in the lower TPHs content in solid residues as well. Moreover, they were favored for more pyrolytic gases and long chain liquid product though the yield of liquid product decreased. It may attribute to the enhanced deoxidation and polymerization of Fe2O3 and Al2O3. Along with OS pyrolysis, inherent minerals tended to inhibit N/S/Cl-containing pollutants at the stage of dehydration and devolatilization (<358 °C), but promote their releasing at the stage of thermal cracking and secondary reactions (>358 °C). This work might provide inspiration for getting insight into the OS pyrolysis behaviors and proposing clean fuel production strategies.