The Study Of Persulfate Based Advanced Oxidation Processes For Viscosity Degradation Of HPAM

In order to improve the oil recovery rate,polyacrylamide（HPAM）is widely used in the tertiary recovery stage as a polymer for oil displacement,resulting in a great increase in the viscosity of the recovered water and makes the wastewater treatment more difficult.Aimed at the problem that the treatment efficiency of sedimentation filter device in the sewage treatment system is reduced and the effluent quality is difficult to meet standard of reinjection stably,this paper first compares the effects and process of different advanced oxidation methods and optimizes that persulfate（PS）is the best way to degrade high concentration HPAM.Further,the thermal activation and Fe²⁺activation persulfate systems were used to investigate the influence process and mechanism of different factors on the viscosity reduction rate of HPAM.The specific research contents are as follows:（1）Comparing with the treatment process and effect of Fenton method,potassium perferrate method,Na Cl O method and persulfate method on HPAM.The results showed that persulfate was at least 4 mmol/L in the best treatment results.It showed good viscosity reduction performance in a short time and the viscosity reduction rate of reaction 10 min could reach 69.0%.Compared with other three oxidation methods,persulfate had the characteristics of the lowest required experimental conditions,long stability time and wide application range,which was the best method to degrade HPAM.（2）A thermally activated persulfate degradation system for HPAM was established,and the effects of temperature,PS concentration and initial p H on the viscosity reduction efficiency were analyzed.Under optimal conditions,when the HPAM content was 1000 mg/L,PS dosage was 4 mmol/L,the temperature was 45°C,and the initial p H was 7,the viscosity decreased95.1%after the reaction reached 60 min.The optimization model with the viscosity reduction rate of HPAM as the response value was established by Box-Behnken design（BBD）.It showed that the viscosity reduction effect of HPAM increased with the increase of temperature and PS concentration,and with the decrease of p H,which was most affected by temperature.For four different commercial HPAM,the degradation rate could reach more than 97.8%under the optimal experimental conditions.The thermal activated PS system had no significant effect on the degradation of high temperature salt-tolerant polyacrylamide.EPR spectrometry experiments have proved that the existence of sulfate radicals and hydroxyl radicals in the system.Free radical quenching experiments demonstrated that the main free radical in the system was SO₄·^-at p H 7 and·OH at p H 10.（3）A Fe²⁺activated persulfate degradation system for HPAM was established,and the effects of PS concentration,Fe²⁺concentration and initial p H on the viscosity reduction efficiency were analyzed.The optimal degradation conditions obtained by the BBD simulation:3.71 mmol/L PS,p H=4.06,and 0.05 mmol/L Fe²⁺,the predicted degradation efficiency of about94.6%,which is similar to the viscosity reduction effect of the thermally activated PS system alone under the optimal process conditions.The viscosity reduction rate of HPAM oxidized by Fe²⁺activated persulfate was most affected by p H,which decreased with the increase of p H and increased with the increase of PS and Fe²⁺concentration.The existence of SO₄·^-and·OH in the system was confirmed by EPR detection;The degradation process of COD showed that HPAM was mainly degraded in the form of reducing molecular weight through chain scission,but a small was completely mineralized into CO₂ and H₂O.The FT-IR showed that PS oxidizes the amide group of HPAM side chain to carboxyl group.The UV-VIS of HPAM before and after oxidation indicated that the long-chain structure was changed by PS,which was broke into shorter chains,and a small was oxidized into smaller organic molecules.Through the comparison of SEM images,it showed that the HPAM molecule after sulfate oxidation is seriously damaged,and the long chain was broken into small fragments.The above two activated persulfate methods can achieve the oxidation and viscosity reduction of HPAM quickly and effectively.Considering the actual industrial wastewater treatment conditions,Fe²⁺activation method has the advantages of lower temperature and more energy saving.Through comprehensive comparison,the Fe²⁺activated persulfate system is more suitable for the degradation of polymer-contained wastewater in actual oil fields.