Multi-Layer Filters: Adsorption and Filtration Mechanisms for Improved Separation.

Aysu Onur,Aaron Ng,Warren Batchelor,Gil Garnier

doi:10.3389/fchem.2018.00417

Abstract

Filters made of cellulose fiber and perlite particles were prepared using a wet laying papermaking technique. Polyamide-amine-epichlorohydrin (PAE) was added to provide wet strength. Filters were prepared at two different total basis weights of 200 and 400 grams per square meter (gsm). Single and multi-layered filters were structured for each total basis weights. The effect of total basis weights and multi-layered structure on methylene blue adsorption and silicon dioxide (SiO2) particle filtration was investigated. Methylene blue adsorption was performed in two modes: constant pressure and constant flow rate. In both operation modes, the adsorption capacity of multi-layered filters was significantly higher (16–100%) than for single-layer filters at the same overall weight. The effect of layer separation was also characterized using polypropylene separators and tested under constant flow rate operation. Separators provided more effective methylene blue adsorption by generating a well-distributed flow. Filtration performance was quantified with 0.5 μm silicon dioxide particles under constant pressure conditions; this is to mimic bacteria rejection. Filtration capability of SiO2 particles was reduced slightly (12%) with decreasing individual filter layer thickness regardless of the multi-layered structure. Filtering polyethylene glycol (PEG) molecules with two different molecular weights was performed; however, no rejection was recorded. The filter internal pore structure was visualized by 3D-X ray computed tomography and the void fraction was quantified. 400 gsm single layer presented areas of low fiber density forming pores, while the pore volume decreased for thinner filter layers.

Highlights

Depth filters (Sutherland, 2011) are porous filtering mediums composed of cellulose fibers and inorganic absorbents
Cellulose fibers used for the composites are unrefined northern softwood NIST RM 8495 bleached Kraft pulp and bleached radiata pine softwood Kraft pulp refined to 400 Canadian standard freeness (CSF) in a disk refiner
Filtration of 0.1 wt.% polyethylene glycol (PEG) molecules of molecular weight of 600 and 5,000 kDa was performed under constant pressure (1.5 bar) mode for each filter configuration

Summary

Introduction

Depth filters (Sutherland, 2011) are porous filtering mediums composed of cellulose fibers and inorganic absorbents. Unlike surface filtration, they can retain contaminants through the thickness as well as on the surface during liquid filtration. They can retain contaminants through the thickness as well as on the surface during liquid filtration These composite structures combine two different separation principles and technologies in a single medium. Separation can further be improved by combining other additives, such as charged polyelectrolytes in the network (Dizge et al, 2011). The medium can be modified with a cationic polymer adsorbing the common negatively charged dissolved contaminants significantly smaller than the average pore size.

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Conclusion