Use of ultrasound can yield polymer degradation as reflected by a significant reduction in the intrinsic viscosity or the molecular weight. The ultrasonic degradation of two water soluble polymers viz. carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) has been studied in the present work. The effect of different operating parameters such as time of irradiation, immersion depth of horn and solution concentration has been investigated initially using laboratory scale operation followed by intensification studies using different additives such as air, sodium chloride and surfactant. Effect of scale of operation has been investigated with experiments in the available different capacity reactors with an objective of recommending a suitable type of configuration for large scale operation. The experimental results show that the viscosity of polymer solution decreased with an increase in the ultrasonic irradiation time and approached a limiting value. Use of additives such as air, sodium chloride and surfactant helps in increasing the extent of viscosity reduction. At higher frequency operation the viscosity reduction has been found to be negligible possibly attributed to less contribution of the physical effects. The viscosity reduction in the case of ultrasonic horn has been observed to be more as compared to other large capacity reactors. Kinetic analysis of the polymer degradation process has also been performed. The present work has enabled us to understand the role of the different operating parameters in deciding the extent of viscosity reduction in polymer systems and also the controlling effects of low frequency high power ultrasound with experiments on different scales of operation.
The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO2) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5-4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO2 maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH3OH) and n-butanol (C4H9OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO2 (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.
In chemical processing industries, crystallization is one of the most important operations to obtain solid products with desired purity and characteristics. With distinct processing problems for the conventional approaches for crystallization, research into alternate approaches such as ultrasound assisted crystallization has been on the forefront. The present work deals with comparison of the conventional approach and ultrasound assisted approach for crystallization of ammonium sulphate followed by detailed understanding into the effect of important operating parameters (initial concentration, pH, agitation speed, depth of horn, and cooling approach) on the metastable zone width and average crystal size. Ultrasound assisted crystallization has been investigated using both ultrasonic bath and ultrasonic horn to understand the effect of type of irradiation. It has been observed that the maximum reduction in the MSZW was obtained using ultrasonic horn under conditions of optimized initial concentration. The order of average crystal size obtained for ammonium sulphate was conventional cooling crystallization>ultrasonic bath>ultrasonic horn. The average crystal size obtained was in the range of 411-450µm for conventional approach of cooling crystallization, 350-400µm using ultrasonic bath and 200-250µm using ultrasonic horn. The analysis of crystal size distribution and surface characteristics using the SEM analysis was also performed under set of optimized parameters established using the particle size analysis. Overall the work has clearly established that the ultrasound assisted crystallization gave better results as compared to the conventional cooling crystallization in terms of reduced metastable zone width, better crystal characteristics and less agglomeration.
The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36 kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO2 at optimized depth of horn and 27°C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions.
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