Study On The Functionalized Preparation Of Cationic Flocculants And Its Performance

The oil processing and utilization industry produces large amount of oily wastewater every year,and the use of oil recovery technology leads to the presence of a large number of polymers in oilfield wastewater,which weakens the interfacial tension between oil and water,making it more difficult to treat oilfield wastewater.Oily wastewater has been recognized as a common global pollutant with strong toxicity,organic volatility and high carcinogenicity,which will undoubtedly pose a serious threat to aquatic ecosystems and human health if discharged directly into receiving waters without proper treatment.Therefore,it is important to find a simple and efficient treatment method.Flocculation technology is widely used to treat oily wastewater because of its easy operation,good treatment effect and relatively low cost,and the key to flocculation is the selection of a suitable flocculant.Traditional cationic polyacrylamide flocculants have many shortcomings when used alone and are difficult to adapt to the current wastewater treatment requirements.To address the problem of oil-bearing wastewater treatment in oil and gas fields,this paper researches and prepares functionalized cationic flocculants instead of traditional cationic polyacrylamide flocculants,applies them to oil-bearing wastewater treatment,and evaluates their flocculation performance.The main work of the thesis is divided into two parts:1.PADO functionalized cationic flocculants were prepared by aqueous free-radical micellar polymerization using acrylamide（AM）,dimethyldiallyl ammonium chloride（DMDAAC）and octadecyl acrylate（OA）as raw materials and a redox system consisting of K₂S₂O_8-Na₂SO₃ as initiator,and their structures were characterized by infrared spectroscopy（FT-IR）,nuclear magnetic resonance hydrogen spectroscopy（¹HNMR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）and thermogravimetric（TGA）analysis.The polymer synthesis conditions were explored and studied by single-factor experiments to determine the optimal synthesis conditions.The prepared PADO flocculants were used for the treatment of simulated oily wastewater,and the effects of PADO flocculant dosage,initial solution p H,solution temperature,stirring speed,stirring time and settling time on the oil removal rate and turbidity removal rate of simulated oily wastewater were systematically evaluated.By introducing hydrophobic groups into the cationic polyacrylamide polymer can improve affinity to oil substances in water,the hydrophobic associative flocculants show better flocculation performance in the treatment of oil-containing wastewater.The results showed that the best performance of the PADO flocculant was synthesized at the total monomer mass fraction of 30%,the monomer ratio n（AM）:n（DMDAAC）of 2:1,hydrophobic monomer content of 2%,initiator content of 0.4%,reaction temperature of 70°C,reaction time of 6 h and reaction system p H of 4.Under the conditions of solution temperature of 40℃,initial solution p H of 7,stirring speed of 400 r/min,stirring time of 20 min and static settling time of15 min,the oil removal rate and turbidity removal rate could reach 98.06%and 98.53%,respectively,when PADO polymer was dosed at 40 mg/L.The possible mechanism of flocculation and oil removal was investigated by combining the zeta potential results,in which the synergistic effects of hydrophobic association,adsorption bridging and electrical neutralization played essential roles.2.On the basis of the successful preparation of PADO hydrophobic-conjugated flocculants,graphene oxide（GO）,carbon-based material,was introduced to obtain PADO-GO composite flocculants,and their structures were characterized and analyzed by FT-IR,XRD,SEM and TGA.The optimal synthesis conditions were determined by exploring the influencing factors such as synthesis time,synthesis temperature,PADO mass fraction,GO mass fraction.Finally,it was applied to treat oily wastewater,and the effects of PADO-GO flocculant dosing,initial solution p H,stirring speed,stirring time and settling time on the flocculation effect were systematically evaluated.The results showed that the best performance of the PADO-GO flocculant synthesized by the reaction was achieved at GO mass fraction of 0.8%,reaction temperature of 60°C and reaction time of 6 h.At room temperature,when the PADO-GO flocculant was added at 40 mg/L,the initial solution p H of 7,the stirring speed was 400 r/min,the stirring time was 20 min,and the settling time was 10 min,the PADO-GO flocculant could achieve the best flocculation and oil removal effect,and the oil removal rate and turbidity removal rate were 98.25%and 99.67%.PADO-GO reduced the settling time from 15 min to10 min by 1/3 compared to PADO,and formed larger and denser flocs,which further improved the flocculant oil removal rate.