Flocculation of Waste Waters from Petroleum Refineries

Abstract

Abstract Waste waters from petroleum refineries can be considered as a ternary-like system, the components of which have been characterized. They are: the alkaline liquor, the hydrocarbon rich oil in suspension and the silica rich solid also in suspension. The parameters controlling the destabilization and the flocculation of these suspensions have been studied by light transmittance and electrophoretic mobility. Rate of flocculation, critical coagulation concentration (CCC) , critical restabilization concentration and optimum flocculation conditions have been determined for different combinations of added polyelectrolytes and/or simple electrolytes. Among eleven different polyelectrolytes, four of the cationic type were selected for their property to flocculate the suspension. It has been shown that an excess of polyelectrolyte brings about the restabilization of the particules. No flocculation has been observed for any of the anionic polymers tested. Simple electrolytes are found to obey the Schulze-Hardy rule in their flocculation capacity. Various combinations of a polyelectrolyte with a simple salt lead to a lower CCC together with a broader concentration range between destabilization and restabilization. It is concluded that this binary suspension behaved essentially like a classical lyophobic sol.