Preparation of polymeric ferric sulfate–quaternary ammonium cationic modified starch composite flocculant and its application in oily sludge treatment

Inorganic-organic compound flocculant of PFS-quaternary ammonium cation-modified starch composite flocculant was prepared by etherification and compounding method, with corn starch, sodium hydroxide (NaOH), cationic etherifying agent 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTMA), polymeric ferric sulfate (PFS) as raw materials. The best preparation conditions were the rate of PFS and quaternary ammonium cation-modified starch mass 4:1, pH of the solution 2, temperature 60 ℃, and the reaction time of 4 h. The factors were ranked according to the influence degree as follows: mass ratio > reaction time > pH > temperature. The flocculant prepared under optimal preparation conditions was applied to the treatment of oily sludge in the oil field. When pH of the oily sludge–flocculant mixture was 7 and the dosage at 110 mg/dm3, the deoiling rate of the oily sludge reached 82.25%, which was an effective conditioning flocculant for oily sludge. SEM analysis showed that the mechanisms of flocculant were mainly net catching and adsorption bridging action. Thermo-gravimetry (TG) and energy dispersive spectroscopy (EDS) analyses showed that crude oil and bound water were removed by the composite flocculant.