Exploring Trends in Scale Control with Homologous, Structurally Expanded, Phosphonate Functionalized Linear Amino Acids as Environmentally Acceptable Scale Inhibitors

A homologous series of amino methylenephosphonate-based nonalpha aliphatic linear amino acids (LAAs) were developed. These new phosphonated linear amino acids, known as PLAAs (HOOC-(CH2)n-N-(PO3H2)2), include phosphonated derivatives of glycine (PLAA-C2,n= 1), β-alanine (PLAA-C3,n= 2), γ-aminobutyric acid (PLAA-C4,n= 3), 5-aminovaleric acid (PLAA-C5,n= 4), and ε-aminocaproic acid (PLAA-C6,n= 5). The performance of these PLAAs as scale inhibitors was evaluated against calcium sulfate, calcium carbonate, and barium sulfate under oilfield dynamic conditions (approximately 80 bar and 100 °C) and compared with the commercial inhibitor Hydrodis-SI. The study also investigated their thermal stability and calcium compatibility. Notably, PLAAs with shorter chains between the carboxylic acid group and aminomethylenephosphonate moiety, such as PLAA-C2, PLAA-C3, and PLAA-C4, showed the highest inhibition efficiency for calcite scale. Furthermore, the PLAAs demonstrated superior thermal stability compared to Hydrodis-SI, particularly at 130 °C for 7 days, with no loss in inhibition performance. However, all tested inhibitors, exhibited poor performance against barium sulfate (Barite) due to an insufficient number of phosphonate groups in their backbone. PLAAs also showed good calcium compatibility, with PLAA-C4 and PLAA-C5 standing out for their exceptional compatibility across various saturations and Ca2+ concentrations.