Phosphonomethylated chitosan oligomers: synthesis, characterization, and performance as green inorganic scale inhibitors

Abstract

One of the main operational challenges in the oil industry is the formation of inorganic scales, which can lead to significant economic losses. Synthetic chemical additives are already used to control scale formation, and their efficiency is related to their chemical structure and molar mass. However, there is a growing demand for efficient and environmentally friendly scale inhibitors. This work aimed to modify and characterize chitosan, as well as evaluate its performance as an inorganic scale inhibitor. For this purpose, chitosan was oxidatively degraded using sodium nitrite to obtain samples with different molar masses and subsequently modified by phosphonomethylation. The samples were characterized using spectroscopic, thermal, and viscometric techniques. Solubility tests were conducted as a function of pH (1−10). Static performance tests using carbonate and sulfate containing brines were carried out at two temperature conditions to evaluate inhibitory efficiency. Scanning electron microscopy analyses were performed on the precipitates generated during the static tests. A significant reduction in chitosan molar mass was achieved without altering its backbone structure. The characterization analyses provided evidence for the possible occurrence of phosphonomethylation, resulting in increased solubility over a broad pH range. The modified chitosan samples exhibited inhibitory efficiency, with the best performance at 90 °C observed for the oxidatively degraded sample treated with approximately 5.4 v/v% sodium nitrite for 3 h and subsequently phosphonomethylated. Morphological analyses indicated modification of the crystal surface and possible inhibition of nucleation sites. The combination of oxidative degradation and phosphonomethylation proved to be a promising strategy for developing efficient and environmentally friendly inorganic scale inhibitors.