Catalytic oxidation of polymer used in oilfield by supported Co(II) complex within a high pH range

Abstract

In this study, a clean oxidation process for the treatment of wastewater containing hydroxypropyl guar gum (HPGG) and other polymers under a high pH range was designed. For that, 5-sulfosalicylic acid (L)-Co(II) complex supported on bentonite (B) (B@Co(II)L) was prepared for treatment of wastewater by hydrogen peroxide ($\mathrm{H}_{2}\mathrm{O}_{2}$). The morphology and pore structure of B@Co(II)L was first characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier infrared spectrometer (FT-IR), and $\mathrm{N}_{2}$ adsorption–desorption isotherms, after which the catalytic performance was investigated for the treatment of polymer wastewater. Results show that B@Co(II)L performed high catalytic performance in a wide range of 7.0 to 13.0. The viscosity of the HPGG can be decreased effectively from 22 to 2.5 mm$^{2}$/s under the optimal conditions of 45 °C, pH 10.0, 10% $\mathrm{H}_{2}\mathrm{O}_{2}$ (mass ratio to HPGG), and 10% B@Co(II)L (mass ratio to $\mathrm{H}_{2}\mathrm{O}_{2}$), and the removal rate for chemical oxygen demand (COD) of HPGG, CMC, and PAM reached to 95.9%, 94.8%, and 93.7%, respectively, within 240 min. Most of all, by applying the catalyst in the oilfield, it was found that the catalyst has high performance and the removal rate for COD of oilfield wastewater, fracturing fluids, and drilling fluid can be achieved by 92.1%, 94.2%, and 90.7%, respectively.

Keywords

• Bentonite supported complex
• Catalytic oxidation
• Oilfield wastewater
• Hydroxypropyl guar gum
• Fenton like process