Assessment of the Industrial Potentials for an Innovative High-tech Separation Method

Abstract

Currently, we are facing a general technological gap for the separation of mixtures containing colloidal particles (metallic nano-particles, macro-molecules, etc.). This project aims to extend the principle of Hollow Fiber Flow Field-Flow Fractionation (HF5) toward continuous size-based separation of colloidal suspensions. HF5 is an analytical technique used for particle fractionation (according to their size) in view of their characterization. The principle of particle separation is based on consecutive focusing of particles of different sizes on different ow streamlines with the aid of a permeate ow applied across the hollow-ber wall and their differential elution by the main ow streamlines at the ber outlet. In this Ph.D., we developed an automated sequential prototype based on the HF5 principles. The accumulation and elution conditions were explored, leading to the prescription of a separation methodology, which applies for stable negatively charged Brownian particles (in order to limit particle aggregation and adsorption on the membrane). A CFD model was developed to guide the initial prototype design and the choice of the operating conditions. The numerical model was extended to include an original description of colloidal dynamics near phase transition and its impact on near-membrane particle accumulation and relaxation processes. We evidenced the existence of a permeate ow-rate (during elution) at which the Brownian diffusion prevails over the drag force, and that allows controlling particle differential elution: this reveals to be a crucial condition for successful separation. The developed prototype allows the processing of higher sample amount than classical HF5, by using the total membrane surface during particle focusing. We performed the separation of latex polystyrene nanoparticles with a size ratio of 5, using 4.74 μg of particles per cm 2 of membrane without compromising the peak resolution (similar to AF4 conguration and superior to HF5). Moreover, the prototype allows running several consecutive separation cycles (up to ve cycles were tested), without increasing membrane fouling. To allow prototype scale-up, further optimization of particle accumulation along the membrane and permeate-ow control during elution are needed. Finally, a system for continuous operation was developed. It is not included in this manuscript for confidentiality reasons.