Kinetic modelling and a novel packed bed photocatalytic reactor

Abstract

A superior parameter estimation approach, based on the Box-Draper method of non-linear estimation using all the experimental data, is described and compared to the method of initial rates. It is shown that this approach results in better and more objective parameter estimates in the Langmuir-Hinshelwood kinetic models typically applicable to photocatalytic reactions.

The photocatalytic degradation of tetrahydrofuran, 1.4-dioxane, and their mixture is achieved in near-UV illuminated aqueous titanium dioxide slurries.

Two different commercial photocatalysts, Degussa P25 and HombiKat UV 100, are used to degrade 1.4-dioxane photocatalytically in an annular slurry photoreactor. The optimum photocatalyst loading for Degussa P25 is found to be 1.5 gL^-1 while for Hombikat UV 100, it is between 3.0-4.0 gL^-1. The photoactivity of Degussa P25 is higher than Hombikat at lower concentrations whereas it is lower at higher concentrations. The photoactivity of UV 100 titanium dioxide is found to be twice that of Degussa P25 at optimum concentrations. Degussa P25 titanium dioxide with the optimum concentration of 1.5 gL^-1 is used in the kinetic studies of tetrahydrofuran 1.4-dioxane, and their mixture.

Using both gas chromatography/mass spectrometry (GC/MS) and ion chromatography (IC) methods, possible intermediates for the photocatalytic degradation of tetrahydrofuran and 1.4-dioxane are identified. 2(3H)-Furan-one, dihydro- (y-butryolacetone), succinic acid, acetic acid, formic acid, B-hydroxybutyric acid, and glycolic acid are identified as tetrahydrofuran intermediates during its photocatalytic reaction. Similarly, 1,2-ethanedoil, diformate, acetic acid, formic acid, 3-hydroxybutyric acid, and glycolic acid are identified as intermediates of the photocatalytic degradation of 1.4-dioxane.

Based on the proposed intermediates, reaction mechanism pathways and kinetic models for the photocatalytic degradation of tetrahydrofuran, 1.4-dioxane, and their mixture are developed. It is shown that the photocatalytic degradation of tetrahydrofuran and the binary system follows a modified Langmuir-Hinshelwood rate form whereas 1.4-dioxane follows a simple Langmuir-Hinshelwood model.

Finally, a novel tellerette packed bed photoreactor (TPBP) is introduced. Stainless steel is used to make the tellerette packings. The experiments reveal that mass transfer limitations in this packed bed photoreactor are insignificant, such that the reaction appears to be kinetically controlled. Also, it is shown that the ratio of the surface area of the photocatalyst to the photoreactor volume is adequate and sufficient UV light penetrates throughout the system.