Oily wastewater generated from oilfield exploitation features a highly stable emulsified system, which cannot be effectively treated by conventional processes. Polyacrylamide (PAM) has become the dominant treatment agent due to its low cost and outstanding oil-water separation efficiency. Polyacrylamides with different charge types deliver vastly varied flocculation performance in practical applications, and molecular simulation technology can visually reveal the microscopic interaction rules between the agent and oil contaminants to provide theoretical support for on-site process optimization.
Cationic polyacrylamide (CPAM) boasts the optimal overall flocculation performance. Its cationic groups on molecular chains generate powerful electrostatic adsorption to rapidly capture dispersed oil droplets and aggregate them into dense, large flocs. Simulation calculations confirm the optimal oil removal efficiency is achieved at a dosage of 35 mg/L, ambient temperature of 40 °C and water pH of 6.6. Excessive dosing triggers self-aggregation of PAM molecules and impairs its oil adsorption capacity. Anionic and nonionic polyacrylamides exhibit weaker adsorption capacity; nonionic PAM only binds oil droplets via faint intermolecular forces and fails to treat oily water with complex compositions.
Surfactants in water directly alter the flocculation efficiency of polyacrylamides. Certain surfactants compete for adsorption sites with PAM and block the binding between agents and oil droplets, while benzene-ring structured surfactants facilitate the aggregation of oil molecules and improve separation efficiency. Electronic-scale analysis indicates cationic polyacrylamide possesses superior electron transfer activity, with amide and cationic groups serving as core active sites for oil adsorption. The removal difficulty of oil components rises in the order of light oil, wax, resin and asphaltene. These microscopic findings can be directly applied to the molecular modification of novel polyacrylamide agents and working condition regulation for oilfield oily wastewater treatment.