DESIGN OF CONTINUOUS-FLOW PHOTOREACTION SYSTEM

Abstract

Continuous flow systems are extensively employed in chemical engineering due to their efficiency and reliable output. These systems operate with a continuous stream of inputs, allowing for uninterrupted chemical reactions. One major advantage of continuous flow systems is their ability to maintain steady-state conditions, which improve product quality and increase overall productivity. Unlike batch processing, where materials are added in discrete amounts and each batch must be processed before adding new material, continuous flow systems provide a constant and uniform flow of material throughout the process. Continuous flow systems are employed in many chemical reactions. In this thesis, we interested in inorganic material synthesis (chapter 3) and photochemical reaction (chapter 4 and 5)

In chapter 3, we developed a simple continuous flow system made of a PFA tube to purify silver nanoparticles (AgNPs) which were synthesized from chemical reduction. The continuous-flow extraction is a promising technique to remove impurities from the solution. This novel method is non-destructive to the nanoparticles as the extraction maintains their morphology as well as physical properties such as light absorption. We demonstrated that this method could remove the ligands in the solution in a significant level (~56.7% extraction, in the experiment with a volumetric ratio of 1:3 for the unpurified sample to the solvent). Further removal of ligands is achieved through higher extraction solvent usage or cascading of extraction. This method was also demonstrated as an in-line purification after the flow synthesis of AgNPs. About 73.3% removal of ligands was obtained during continuous production of AgNPs. Therefore, this continuous-flow purification can potentially replace the conventional methods that are time-consuming and laborious.

In chapter 4, we built a photoreactor based on PFA tubing. we demonstrated the use of PDA and PEI for immobilizing TiO2–P25 (P25) onto the wall of the PFA tubing. The FTIR spectra confirmed the presence of the deposited PDA and PEI, while the SEM/EDX verified the immobilization of P25. A higher density of P25 was achieved through a layer-by-layer assembly of PEI–P25, with the highest loading being 0.107 ± 0.009 mg/cm2 for the five bilayers, which also gave the highest activity of 37.07% of dye decolorization at a residence time of 10 min. This simple fabrication from a commercially available tubing opens up considerable opportunities for continuous-flow photocatalytic applications.

In chapter 5, we explored a new type of photoreactor, a continuous flow flat-plate reactor to perform a photocatalytic benzene hydroxylation to phenol. A continuous flow flat-plate reactor emerges a promising option, as it allows for a large irradiation window and a short photon penetration depth. In this work, TiO2 (Degussa P25) was applied as a photocatalyst. Use of smectite clays and a 3D-printed casting template were keys to the uniform immobilization of photocatalysts over the glass window surface. Acetonitrile was selected to be a carrier solvent for benzene since the fluid dynamics exhibited an efficient mixing with the aqueous H2O2 flow solution. Response surface methodology was employed to examine the effects of residence time, temperature, and light power. Our flat-plate reactor exhibited a photocatalytic space-time yield of 1.2 × 10-11 mol/W s, which is about 1-2 orders of magnitude higher than the reported batch counterparts. The transport phenomena equation was also formulated to elucidate the kinetics of the photocatalytic reaction, giving the adsorption constant and the intrinsic kinetic constant to be 0.0535 m3/mol and 8.21 × 10-6 mol/ (m2.s), respectively.

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