Experimental investigation on the degradation of polymer-containing oily sludge in sub-/supercritical water

Polymer-containing oily sludge (PCOS) has caused tremendous hazards with the broad application of polymer flooding technology. Traditional methods cannot meet the treatment demand due to the high-water content of PCOS. In this work, the degradation of PCOS in sub-/supercritical water is studied to explore an appropriate treatment method. The influence of residence time (15-90 min), temperature (340-700 degrees C), catalysts (sulfates, carbonates, and alkalis), and co-solvents (methanol-water and ethanol-water) on the distribution of end products is studied in details. Results show that PCOS is hardly gasified under the subcritical conditions and the increase in residence time and temperature has positive effects on the phase conversion. The conversion rate reaches 81.77% at 60 min, 340 degrees C, compared to 67.09% at 15 min. Supercritical water shows a great solubility for PCOS, and no solid residues are detected at supercritical conditions (400-700 degrees C, 23 MPa). Organic matter in liquid phase is classified into nine types, and the increase in temperature greatly changes its composition. The relative proportion of ketones reaches more than 50% of the organic matter in liquid at 400 degrees C. Ketones are proven to be the main source of CO2 and disappear at above 500 degrees C. Moreover, the migration of elements (carbon and nitrogen) is comprehensively studied.