Effect of polyaluminium silicate sulphate with different alkyl chain lengths on oily sewage in oil fields

When the amount of anionic polyacrylamide (APAM) and petroleum sulphonate in polymer-flooding oily sewage increases, a stable emulsification system forms. This makes the treatment of oily sewage increasingly difficult. To better develop high-efficiency coagulants from scratch, this study first determined the structure and carbon number of petroleum sulphonate using H-1 NMR and C-13 NMR spectroscopy. Then, hydrophobic monomers with different chain lengths were copolymerised with aluminium salts to prepare inorganic polymer coagulants with different hydrophobic association abilities. Three novel coagulants were successfully prepared, as verified by FTIR and hydrodynamic radius detection, and their coagulation mechanism and performance in oily sewage were investigated and compared with (polyaluminium silicate sulphate) PASSi. The particle size and morphology of flocs after the addition of coagulant were detected by laser particle size analysis and scanning electron microscopy. The structure-activity relationship between emulsifiers and coagulants with different chain lengths was studied via the second virial coefficient A(2). Polyaluminium silicate sulphate-hexadecyltrimethoxy (PASSi-C16) was determined to have the best coagulation effect by turbidity, oil removal rate and Zeta potential detection. This may have been due to PASSi-C16 containing a similar lipophilic group to the carbon chain structure of petroleum sulphonate, which could easily destroy the emulsion layer. These results provide insights into methods to improve the hydrophobic association capacity and for the targeted use of associative coagulants in large-scale applications.