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Efficient purification of oily sewage, recycling, and standard discharge have become key issues for the sustainable development of oil fields. In this study, the surface of PPFS was organically modified by a silane coupling agent. Then, covalently bonded cationic block inorganic-organic composite coagulant was prepared by chosen sodium polyacrylate as the template. This unique structure significantly enhances the positive charge and molecular chain length of the coagulant, thus improving its ability to perform charge neutralisation, adsorption bridging, and sweep coagulation. The characteristic functional groups and thermophysical properties of the composite coagulant were analysed by FTIR and thermogravimetric analysis. The transformation of random copolymers to block copolymers was determined by 1 H NMR, thus confirming the successful synthesis of the cationic block structures. The turbidity removal and oil removal properties of oily sewage were investigated by coagulation experiment. The Zeta potential, dynamic and static light scattering, and field emission scanning electron microscopy (SEM) were used to study the effect of composite coagulants on the microscopic morphology and coagulation of flocs. Finally, the coagulation mechanism of the compound coagulant was analyzed with the dynamic change of the particle size of the flocs. The cationic block structure in TP(AM-DAC-PPFS) can effectively neutralise the negative charges on the surface of impurity particles and emulsified oil. The optimal dosage of TP(AM-DAC-PPFS) was 30 mg·L−1, at which the turbidity and oil removal rates can reach 98.3% and 93.8%, respectively. [Display omitted] • The covalently linked composite coagulant TP(AM-DAC-PPFS) was successfully prepared. • The cationic block structure increases the coagulation capacity and avoids polymer agglomeration. • The organic molecular chain destroys the structure of the emulsified oil droplets. • Coagulation mechanism of charge neutralization, adsorption bridging and sweeping is improved synergistically [ABSTRACT FROM AUTHOR]

• PPFS-PAD-RGO compound coagulants were successfully prepared. • The coagulability of PPFS-PAD-RGO has been enhanced. • PPFS-PAD-RGO has certain demulsification ability. • The oil content of oily sludge is reduced. During oil extraction, a substantial volume of oily sewage (water-in-oil emulsion) is generated. The existence of emulsified oil diminishes the effectiveness of conventional coagulants used for purification. Furthermore, coagulants frequently precipitate emulsified oil as impurities, leading to resource wastage. Hence, there is an urgent need to develop multifunctional coagulation/demulsification agents that are environmentally safe. In this study, we synthesized the branched-chain compound coagulant (PPFS-PAD-RGO) and investigated its coagulation and demulsification properties. The results of dynamic and static light scattering and FTIR show that chitosan grafted onto the surface of modified PPFS forms a dendritic flocculation system. In addition, PPFS-PAD is fixed to a reduced graphene oxide carrier with a high specific surface area, which improves the positive charge density and dispersion of the coagulant. The layered structure amplifies the effect of adsorption bridge formation and net aggregation. At a concentration of 80 mg/L, PPFS-PAD-RGO exhibited a turbidity removal rate of 96.15 % and demulsification rate of 74 %. By comparing the structure of PPFS, it was found that the floc volume of PPFS-PAD-RGO is larger. This demulsification ability is mainly attributed to an amine matrix in the chitosan extension chain, which destroys the oil–water interface of the oil-in-water emulsion and induces demulsification. The introduction of RGO increases the local concentration of coagulant molecules. Therefore, the coagulation effect of PPFS-PAD-RGO in oily sewage is attributed to the introduction of demulsifier groups and nanomaterials, which strengthen the synergistic effect of charge neutralization, bridge adsorption and sweeping. [ABSTRACT FROM AUTHOR]

• A method of gravity coagulation was proposed. • The covalently linked coagulant microcapsules was successfully prepared. • The coagulant capsule has able to release its contents slowly upon water impact. • The mechanism of The coagulant capsule was studied. If untreated, oilfield sewage generated during the oil exploitation process can lead to severe environmental pollution. The coagulation/flocculation process plays a pivotal role in the comprehensive treatment of oilfield sewage on a large scale, yet traditional methods exhibit significant limitations. To address the disparity between laboratory experiments and large-scale implementation, this study introduces an innovative coagulant microcapsule. Prepared under gentle conditions, these microcapsules effectively eliminate colloidal particles from water when introduced at the coagulation tank inlet. Featuring a core–shell structure, coagulant microcapsules demonstrate controlled content release upon contact with water. The coagulation process occurs as sewage enters the coagulation tank. The core of the coagulant microcapsule consists of the inorganic polymer coagulant (PASS-C16) with hydrophobic association capabilities. Upon contact with sewage at a specific flow rate, the coagulant is released gradually from the microcapsule. Upon reaching the bottom of the coagulation pool, the coagulant comes into full contact with colloidal particles, influenced by gravity. Ultimately, through integration with Fluent simulation and analysis of floc particle size changes, it was determined that the primary mechanisms of coagulant capsules in aquatic conditions involve charge neutralization and bridging adsorption. The sweeping action is effective only when the test water tends to be static. This technology is viable for application in the coagulation sedimentation tanks of diverse sewage treatment plants. Gravity coagulation demonstrates potential as a replacement for conventional mechanical mixing methods, offering increased efficiency and potential energy savings in various water treatment processes. [ABSTRACT FROM AUTHOR]

• The octopus tentacle-like composite coagulant was prepared. • This special structure can improve performance of the coagulant. • Destabilizing O/W emulsified oil droplets. • The treated sewage meets the reinjection standard. The complexity of oily sewage from oilfields has risen with the advancement of polymer flooding technology, thereby increasing the treatment challenge. In this study, a composite coagulant, PVPAM-PPFS, was proposed, inspired by octopus tentacles, with PVP as the backbone. FTIR, 1H NMR and Rg radius of gyration were used to characterize the functional groups and conformation of PVPAM-PPFS in aqueous environments. The composite coagulant exhibits facile dispersion in water. Upon hydrolysis of PVPAM-PPFS, numerous molecular chains resembling octopus tentacles are formed and confirmed through Atomic Force Microscopy (AFM). When applied to oily sewage in oilfields, PVPAM-PPFS demonstrates enhanced interaction with emulsified oil layers, capturing colloidal particles in water and thereby facilitating efficient separation of oil, water, and flocs. Lastly, the mechanism of PVPAM-PPFS was analyzed through a combination of coagulation experiments and detection of floc morphology. PVPAM-PPFS will better interact with colloidal particles in water through increased charge neutralization, bridging adsorption, and sweeping capabilities. Significantly, an enhanced crude oil recovery rate is observed from the recovered oil droplets following the disruption of the emulsion layer. [ABSTRACT FROM AUTHOR]

• Hydrophobically associated PASSi-C16 was successfully prepared. • PASSi-C16 has a similar structure to the emulsion layer. • PASSi-C16 can better interact with the emulsion layer. • PASSi-C16 composite needs for large-scale applications. 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 1H NMR and 13C 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. [ABSTRACT FROM AUTHOR]

• The hydrophobic association PASS was prepared by a base titration method. • PASS with a small amount of lipophilic group could be improving charge neutralization ability. • The crude water containing polymer was effectively treated. • Floc properties were comparatively investigated. The use of oil recovery technologies has resulted in the weakening of interfacial tension between oil and water in oilfield wastewater due to a large amount of polymer present. This leads to the formation of stable emulsified colloidal systems and increases the difficulty of oilfield wastewater treatment. This study investigated hydrophobically-modified polyaluminium silicate sulphate (PASS-C) as a coagulant for oilfield wastewater treatment. PASS-C was prepared by the condensation polymerisation of Al 2 (SO 4) 3 ·18H 2 O with dialysed and hydrolysed KH570 [3-(trimethoxysilyl)propyl methacrylate] under titration with NaAlO 2 and water glass at low temperature. The zeta potential of PASS-C showed that the introduction of hydrophobic groups increased its charge neutralisation ability. Additionally, compared with conventional PASS, PASS-C showed a satisfactory oil removal rate from simulated polymer flooding oily wastewater. When the hydrophobic group content was 1% and the dosage of PASS-C was 140 mg·L–1, the optimal oil removal rate and turbidity removal rate was 95% and 98%, respectively. The particle size and morphology of the coagulated flocs were characterised by laser particle size analysis and SEM. Compared with PASS, PASS-C formed a larger and more compact floc. These findings indicated that the good flocculability of PASS-C for crude oil wastewater was attributable to the synergistic effects of charge neutralisation, hydrophobic associations and adsorption bridging. [ABSTRACT FROM AUTHOR]

The utilization of a large amount of anionic polyacrylamide (APAM) and sodium alkyl benzene sulfonate can induce the emulsified oil to acquire a stable emulsified colloid system in polymer flooding oily wastewater. However, for the traditional inorganic coagulants, such as polyaluminum, polyiron, etc., a relatively large number of bacteria will breed after oily sewage is treated for a specific period of time. Along these lines, in work, a new type of antibacterial polymeric aluminum silicate sulfate/sepiolite coagulant (PASS-H) was synthesized by using grafting hydrophobic antibacterial monomers in combination with coagulants composed of sepiolite as the base material for improving oily sewage purification. The structure and the surface morphology of the copolymer were systematically characterized, indicating that PASS-H was successfully synthesized. In addition, the coagulation performance of the polyaluminum silicate sulfate (PASS), modified sepiolite, and PASS-H during the treatment of polymer-containing oily wastewater was compared. In the coagulation experiments, PASS-H exhibited excellent turbidity, oil removal, and antibacterial properties. At 60 mg/L, the turbidity, oil removal rate, Zeta potentialand maximum floc size were 98%, 95%, 1.59 mv, and 26 μm, respectively. The mechanism of coagulation was thoroughly investigated based on the order of dosing, the tested water pH, Zeta potential, floc size, and the impact of the floc morphology on the coagulation. The coagulation behavior of the separate addition of the modified sepiolite and PASS was weaker than that induced by the one-time addition of PASS-H. Moreover, the enhanced charge neutralization, bridging adsorption, sweeping, and adsorption played a synergistic role in reducing the total amount of PASS-H and improving the coagulation ability. The introduction of antimicrobial monomers in PASS-H can also effectively inhibit the regeneration of sulfate-reducing bacteria (SRB) in the water. Finally, the residual turbidity and oil removal rate of the different coagulants were statistically analyzed. The extracted results have practical significance for both cost reduction and efficiency increase in large-scale applications. [Display omitted] [ABSTRACT FROM AUTHOR]