Intensification of depolymerization of polyacrylic acid solution using different approaches based on ultrasound and solar irradiation with intensification studies

• Application of combined treatment based on solar and ultrasound for the first time.
• Comparison of different approaches based on ultrasound and additives.
• Process intensification of depolymerization using ozone and hydrogen peroxide.
• Ultrasound in combination with solar and H2O2 is the best treatment approach.

Depolymerization of polyacrylic acid (PAA) as sodium salt has been investigated using ultrasonic and solar irradiations with process intensification studies based on combination with hydrogen peroxide (H2O2) and ozone (O3). Effect of solar intensity, ozone flow and ultrasonic power dissipation on the extent of viscosity reduction has been investigated for individual treatment approaches. The combined approaches such as US + solar, solar + O3, solar + H2O2, US + H2O2 and US + O3 have been subsequently investigated under optimum conditions and established to be more efficient as compared to individual approaches. Approach based on US (60 W) + solar + H2O2 (0.01%) resulted in the maximum extent of viscosity reduction as 98.97% in 35 min whereas operation of solar + H2O2 (0.01%), US (60 W), H2O2 (0.3%) and solar irradiation resulted in about 98.08%, 90.13%, 8.91% and 90.77% intrinsic viscosity reduction in 60 min respectively. Approach of US (60 W) + solar + ozone (400 mg/h flow rate) resulted in extent of viscosity reduction as 99.47% in 35 min whereas only ozone (400 mg/h flow rate), ozone (400 mg/h flow rate) + US (60 W) and ozone (400 mg/h flow rate) + solar resulted in 69.04%, 98.97% and 98.51% reduction in 60 min, 55 min and 55 min respectively. The chemical identity of the treated polymer using combined approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant structural changes were obtained during the treatment. Overall, it can be said that the combination technique based on US and solar irradiations in the presence of hydrogen peroxide is the best approach for the depolymerization of PAA solution.