Nine copolymers of acrylic acid and sodium methallyl sulfonate were tested as scale inhibitors in thermal desalination. The nine antiscalants covered molar masses between 2000 and 9500 g.mol-1 and concentrations of sulfonated monomer ranging between 10 and 30 mole percent. A pressure measurement and control (P-MAC) unit and a high-temperature pressurized vessel were used to measure the effectiveness of the scale inhibitors in seawater, concentrated seawater, and model solutions at 125 °C. The effectiveness of the novel copolymers was comparable to commercial antiscalant at times up to 15 min and improved at longer times. Molar mass was a more important determinant of effectiveness than degree of sulfonation, with the greatest mitigation of calcium sulfate precipitation observed for antiscalants of molar mass 2000 to 2500 g.mol-1 regardless of sulfonate content. Antiscalants of molar mass 4500 to 5000 g.mol-1 showed a higher threshold effect than antiscalants of molar mass 7000 to 9500 g.mol-1, with a 30% sulfonated polymer of molar mass 4500 g.mol-1 performing appreciably better than other polymers of a similar molar mass.
Keywords: calcium sulfate; scale inhibitor; seawater desalination; thermal desalination.