Chemical Degradation of HPAM by Oxidization in Produced Water: Experimental Study

Hydrolyzed polyacrylamide (HPAM) degradation is a critical technical and environmental concern in oilfields, where HPAM is extensively used in drilling or chemical enhanced oil recovery process, especially polymer flooding. However, how to treat the residual HPAM in produced water has become an urgent issue. In this work, the HPAM chemical degradation characteristics were investigated through series of laboratory experiments. The oxidative, ionic and thermal degradation of HPAM were studied, and the feasibility of HPAM degradation by oxidization was examined. The results will help the oil industry to find a practical and optimal HPAM treatment method. In the experiments, the oxidization effects of photo-catalysis and strong oxidants at different temperatures, as well as the presence of typical ions with different concentrations on HPAM degradation process were studied. In addition to this, the related reaction mechanism during the degradation process was investigated.

The experimental results show that the natural sunlight has little effect to excite the HPAM degradation, while the light generated by a high-pressure mercury lamp with a wave length λ < 385 nm can stimulate the catalytic function of TiO₂, which consequently accelerates the HPAM degradation reaction. Also, the strong oxidant such as Na₂S₂O₈ and H₂O₂ can greatly improve the HPAM degradation, especially at higher temperature with a degradation degree η less than 0.15. In the HPAM-Na₂S₂O₈ system, free radical reaction is the main mechanism accounting for the chain scission of HPAM, while the strong reduction-oxidation of hydroquinone (HQ) and generation of H₂O₂ are the dominant reason for HPAM degradation in HPAM-hydroquinone system, which makes the HQ a stronger reagent for HPAM degradation compared with Na₂S₂O₈. The degradation degree of HPAM is significantly affected by the ion type in produced water, decreasing in an order of Al³⁺ > Mg²⁺ > Ca²⁺ > Na⁺ under the same ion concentration. This study not only probed into the HPAM viscosity loss problem caused by polymer chemical degradation, but also provided the necessary guide for the residual HPAM removal in produced water, which will boost the application of polymer flooding process.