Towards process intensification: Remediation of fouling in continuous microscale synthesis of phosphated TiO2

Abstract

The use of continuous flow microreactors offers an interesting approach among the process intensification tools available. Fouling in a microreactor during synthesis of industrially relevant nanoparticles was investigated. In order to achieve this, microscale synthesis of phosphated TiO2 nanoparticles from titanium(IV) isopropoxide (TTIP) and titanium(IV) butoxide (TBUT) was employed. A continuous three step process, consisting of hydrolysis of the respective alkoxide, phosphate modification and precipitation was developed. The resulting catalyst was characterized by means of nitrogen adsorption, dynamic light scattering and SEM/EDX. It was observed that TTIP resulted in massive fouling, while a stable process was possible with TBUT. This was related to the nucleation time of the particles. The particle size directly after the critical hydrolysis step was investigated. The particles formed with TTIP as a precursor (3.4nm) were larger than those obtained from TBUT (2.4nm). Diffusion based reactant concentration gradients within the multilamellar micromixer were calculated, and the corresponding Damköhler numbers for mixing were estimated to be 2.6∙10−3 for TBUT and 3.5∙10−2 for TTIP respectively. These numbers highlight the influence of incomplete mixing on fouling for TTIP as a precursor. Thus, our work demonstrates the necessity to consider the reaction kinetics during process intensification by miniaturization.