Characterization of emulsified water in petroleum sludge

Abstract

Increasing depletion of conventional oil resources has driven interest in recovery of oil resources from petroleum sludge. To improve the quality of recovered oil, it is essential to maximize the removal of emulsified water, dissolved salts, and other impurities. Therefore, this study was conducted to characterize the emulsified water droplets and salt in petroleum sludge through differential scanning calorimetry (DSC). To accomplish this, samples of three different types were evaluated before and after centrifugation. The results indicated that with DSC water content and eutectic of salt hydrates could be identified during controlled heating from −60°C to room temperature. Moreover, a new equation to retrieve water droplets size distribution according to the cooling phase of the DSC thermogram from 50°C to −60°C is proposed. Samples collected from a mixed petroleum sludge storage tank and a tank cleaning wastewater reservoir were found to contain emulsified water droplets with a broadened size distribution, and the freezing peaks shifted from −44°C to −20°C as the diameter of water droplets increased. Additionally, water droplets in the sample collected from the crude oil storage tank were very strongly emulsified and were relatively uniform, with a diameter of 2.7–3.3μm. Following centrifugation, small droplets were found in the upper oily layer, suggesting that de-emulsification pre-treatment prior to water/oil/solid phase separation is essential to obtain high-purity oil resources. This is the first time DSC is employed to characterize emulsified water and deduce water droplets size distribution in petroleum sludge. These results are essential and useful for optimization of petroleum sludge treatment.