Hydrolysis and thermal stability of partially hydrolyzed polyacrylamide in high-salinity environments

Partially hydrolyzed polyacrylamide (HPAM) is the water-soluble polymer most often used in flooding applications in the petroleum industry. However, in aqueous solutions at high temperatures, HPAM undergoes hydrolysis of the lateral amide groups, and the presence of salts in the solution can lead to precipitation of this polymer. Therefore, a method was developed to monitor the thermal stability of HPAM solutions in different saline environments and varying temperatures. The proposed test method involved measurements of intrinsic viscosity as a function of time and determination of the degree of hydrolysis of the HPAM by elemental analysis. The results obtained indicated that the presence of divalent cations (Ca+2 and Mg+2) negatively influenced the intrinsic viscosity of the solutions and in some systems led to precocious precipitation of the polymer in environments with higher concentrations of these cations. The hydrolysis reaction of the amide groups to the acrylate groups of the HPAM chain was significantly affected by rising temperature: at 50 degrees C, hydrolysis occurred, but not as significantly as at 70, 85, 90, and 95 degrees C. Hydrolysis up to 84% was observed for solutions processed at 90 degrees C. The results also indicated limits of hardness for the brine at some temperatures: 1353 ppm for 95 degrees C and 2867 ppm for 70 degrees C. For brine containing 13,610 ppm or more of divalent cations, hydrolysis and precipitation of the polymer were not observed at 50 degrees C. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47793.