The use of photocatalytic based materials for mineralization of organic compounds is a technique that has recently been receiving a lot of attention in the water treatment community for removal of organic contaminants from water. The photocatalytic process is such that when these catalyst absorb the appropriate amount of energy from photons (give by their respective band gap) an electron-hole pair forms and allows reduction and oxidation reactions to occur. This photocatalytic material has been employed in a wide variety of reacting systems from coated walls reactor to packed bed reactors, however, implementation of these catalysts in the various systems demands the functionality be such to accommodate the requirements of that given reactor. For example the catalyst particles chosen for a packed bed reactor need to be able to adsorb organic compounds as well as be photoactive. On the other hand the catalyst chosen for a slurry reactor needs to be highly photoactive and the adsorption properties are not a concern due to continuous mixing. The main properties of interest are physical properties such as adsorption, mechanical stability, light absorption, and photocatalytic activity. More often then not one photocatalytic material will not have all of the desired properties (whether it is adsorption, density, or simply particle size) and consequently these catalysts are composite material with a given catalyst support, adsorbent/zelolite, and photocatalyst. These catalyst particles need to be carefully screened for each different applications and many trials need to be performed to determine the optimal composite and the volume of each material rendering this process very costly and time consuming.

Recently the use of a novel water treatment process that utilizes draft tube transport and advanced oxidation has been posed to the community. This process is designed around the characteristics of a draft tube spouted moving bed reactor (DTSMB) in which the reactor consists of an annular moving packed bed (water purification region) and an internal draft tube for hydraulic transport of catalyst for regeneration. This system was studied for overall optimal design and operation of based on a utility cost objective function, however no investigation was placed on the design of the catalyst particle.

In this paper we would like to present a systematic approach used to study the effects of the bulk properties of the catalyst particles and in particular investigate the optimal selection of bulk properties to be used in the DTSMB system. We develop and present a theoretical model that captures the steady state design and operation of the DTSMB reacting system. We then define a problem statement and formulate it into a nonlinear mathematical program and outline a method to determine globally optimal catalyst properties. A case study is performed using water contaminated with reactive red (RR) to demonstrate the strength of the proposed methodology and discuss the selected catalyst properties. This catalyst selection process will give insight as to what photocatalyst, adsorbent, and support should be considered and the optimal loading of each when selecting catalysts.