US 4,996,246 enhancing colourstabiuty to sterilizing radiation of polymer compositions

Abstract

The detoxification of water has been performed at a pilot scale under solar irradiation at the Plataforma Solar de Almeria (Spain). The photoreactor consisted of a tank (247 l) connected to compound parabolic collectors (CPCs) (147 l), through which the aqueous suspension of titania (0.2 g/l of TiO2 Degussa P-25) was circulated at a flow-rate of 3.5 m3/h. Two model molecules have been chosen: 2,4-D (2,4-dichlorophenoxyaceticacid), a common herbicide and benzofuran (BZF). Both pollutants disappeared following a first-order kinetics and were completely mineralized according to the total organic carbon (TOC) analysis within a residence time <1 h. The main intermediate product of 2,4-D photodegradation was 2,4-dichlorophenol and that of BZF was salicylaldehyde. The degradation pathways were found to be identical to those previously determined in the laboratory. The absence of detection of other intermediate products, such as chlorohydroquinone or 2-coumaranone for 2,4-D and BZF, respectively, was ascribed to the design and the working conditions of the photoreactor. A high conversion was obtained at the end of one pass and the recycling of the thus purified suspension to the tank prevented the detection of intermediate products, while favoring the disappearance of the pollutant (decrease of competitive adsorption). The temperature changes during the day in the reaction mixture were <6°C and did not influence the kinetics of the reaction. Reaction rates for pollutant and TOC removal were found to be proportional to the global radiant flux including both direct and diffuse UV light. The presence of clouds in the sky suppressed direct UV light but the CPC could maintain the absorption of diffuse UV light. The zero kinetic order of TOC disappearance enables one to envisage an easy way of controlling the overall rate of photocatalytic detoxification of large quantities of water containing a mixture of pesticides.