Determination of the concentrations of polyacrylamide-type polymers by a modified nitrogen digestion method

Abstract

This paper presents a laboratory study on the effectiveness of the nitrogen digestion method to determine the polymer concentrations for 3 different kinds of polyacrylamide–type polymers including partially hydrolyzed polyacrylamides, sulfonated polyacrylamides, and cationic polyacrylamides. Different from the classic nitrogen-bromination method for determination of polymer concentrations, the nitrogen digestion method is based on the digestion of amide groups in the polymers as free nitrate ions. The experimental results show good correlations between the nitrogen content and polymer concentration for individual polymers in aqueous solution with pH range from 5 to 8. It turns out the error of the correlations ranging from ±2.0% to ±8.6%. Sodium and calcium ions do not impact the nitrogen content measurement, providing the reliability of the measurement in high salinity environment. The influence of anionic surfactant is negligible, however, quaternary ammonium cationic surfactant and betaine-type surfactants have strong impact on the polymer concentration measurement because of the presence of nitrogen in the surfactant molecular structures. In order to improve correct the accuracy of polymer concentration results caused by the hydrolysis reaction of acrylamide groups that happen in the long time polymer flooding process especially at high temperature, infrared (IR) spectroscopy analysis was introduced to identify the hydrolysis degree based on the absorption peaks at 1568 cm−1 and 1671 cm−1, representing acrylamide group and acrylic acid group, respectively. The absorbance ratio (Ra) of the peak intensities was correlated with the hydrolysis degree (HD) as Ra = 1.35–0.590*HD. Consequently, a normalized correlation was set up based on the polymer concentration, nitrogen content and hydrolysis degree to improve the accuracy of polymer concentration measurement.