Defoaming of industrial lean methyldiethanolamine solution using ultrasonic waves and their kinetic studies

Amine foaming is a well-known incident in the natural gas sweetening unit. In this study, anionic surfactant sodium dodecylbenzenesulfonate (SDBS) and cationic surfactant hexadecyltrimethylammonium bromide (HTAB) were used as model foam creators in industrial lean methyldiethanolamine (MDEA) solution. The surfactant concentrations of 300, 500, 1000, and 3000 mg/L were prepared in lean MDEA solution and stirred to create foam. The final foam volume was found to increase with the increase in both the surfactant concentration and the stirring speed. However, SDBS showed higher foam volume (35 and 55 mL) than HTAB (20 and 25 mL) at low surfactant concentrations (300 and 500 mg/L). Ultrasonic waves were effective in defoaming all tested solutions. The rate of defoaming increased with temperature rise. At a fixed temperature and stirring, foam formation and defoaming obeyed the exponential function. The differences in physical properties, including density, dynamic viscosity, and surface tension before and after sonication, were insignificant. Interestingly, the content of organic acids, known as primary degraded products, remained almost constant. This work demonstrated the promising potential of ultrasonic waves for defoaming amine solutions in the natural gas industry.