Chemistry of organophosphonate scale growth inhibitors: 3. Physicochemical aspects of 2-phosphonobutane-1,2,4-tricarboxylate (PBTC) and its effect on CaCO3 crystal growth

Abstract

Industrial water systems often suffer from undesirable inorganic deposits, such as calcium carbonate,calcium phosphates, calcium sulfate, magnesium silicate, and others. Synthetic water additives, such asphosphonates and phosphonocarboxylates, are the most important and widely utilized scale inhibitors in a plethora of industrial applications including cooling water, geothermal drilling, desalination, etc. The designof efficient and cost-effective inhibitors, as well as the study of their structure and function at the molecularlevel are important areas of research. This study reports various physicochemical aspects of the chemistry ofPBTC (PBTC = 2-phosphonobutane-1,2,4-tricarboxylic acid), one of the most widely used scale inhibitors inthe cooling water treatment industry. These aspects include its CaCO3 crystal growth inhibition andmodification properties under severe conditions of high CaCO3 supersaturation, stability towards oxidizingmicrobiocides and tolerance towards precipitation with Ca2+. Results show that 15 ppm of PBTC can inhibitthe formation of by ∼35 %, 30 ppm by ∼40 %, and 60 ppm by ∼44 %. PBTC is virtually stable to the effectsof a variety of oxidizing microbiocides, including chlorine, bromine and others. PBTC shows excellenttolerance towards precipitation as its Ca salt. Precipitation in a 1000 ppm Ca2+ (as CaCO3) occurs after 185ppm PBTC are present.