| The composition of polymer-flooding wastewater was complicate and stable.The contents of oil and suspended substance were high, and hydrolyzed polyacrylamide (HPAM) present in wastewater made it hard to treat. In order to improve wastewater treatment, firstly the fractions of polymer-flooding wastewater must be separated and analyzed to find emulsion-activity fractions and subfrations, and then the relation between the composition and property of subfraction and the stability of emulsion was studied. In addition, the external factors that influence the emulsion stability were investigated. Some significant results have been obtained.Two fractions were obtained from oily wastewater by an extraction produce using solvents of increasing polarity. Then, the two fractions were divided into six subfractions based on polarity using the methods of solvent deposition and extraction. The composition and structures of these subfractions were characterized and the interfacial tensions of dilute solutions of these subfractions in heptane-benzene/water (pH=7.5) were determined. The emulsifying activity of subfactions was studied and the relations between constitutes,structures and characters of fractions and emulsifying activity was studied. It was found that the method of separating oil fractions was effective. The analysis results revealed significant differences in composition, structure, interfacial tension and emulsification among these subfractions. The total heteroelements content and acid numbers in subfractions were two critical factors for emulsifying activity. The total heteroelements content in subfractions SF41 and SF42 was higher than other subfractions. These two subfractions, which were the heaviest and the most polar subfractions, had strong interfacial activity in a low concentration. Subfractions SF31 and SF1 had higher acid values, lower interfacial tension and stronger emulsifying activity than subfractions SF2. Subfractions SF31 and SF1 contribute to the stability of polymer-flooding wastewater in GuDao2#. In a limited concentration range, subfraction SF2 which had a weaker emulsion-activity restrained emulsion-activity of subfractions, such as SF41, SF42, SF31, With the settling time increasing, the relative contents of SF1, SF31 and SF42 increased obviously, while the others decreased.HPAM in polymer-flooding oily wastewater was isolated and purified. Impure and purified HPAM samples were characterized using element and IR analysis. It was found that the method of isolating and purifying HPAM was effective. The element and IR analysis results revealed the structure of purified HPAM was similar to the structure of the commercial sample. In order to find the external cause of the higher content of oil in wastewater, the factors that influence the stability of wastewater emulsion, such as HPAM content, salinity and pH were investigated. The results showed that the HPAM content and the pH of the aqueous phase were two main factors affecting the emulsion stable. When the HPAM concentration surpasses 200 mg·L-1and pH≥7, the emulsion is extremely stable.
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