In situ reactive coating of porous filtration membranes with functional polymer layers to integrate boron adsorber property

The state-of-the-art reverse osmosis membranes for seawater desalination have limited competence to efficiently remove boron. One promising approach for boron removal is to integrate membrane-based separation with selective adsorption of boron in pre- or posttreatment of seawater desalination; the porous support layer of established filtration membranes, constituting the largest part of total membrane volume shall be utilized for this function. Therefore, this study focuses on performing in situ modification of commercial polyethersulfone (PES) microfiltration membranes toward reactive coating the pore surface with a boron affinity polymer-based hydrogel. Modification is carried out in two steps: 1) adsorption of an amphiphilic copolymer which contains tertiary amine groups as co-initiator for surface-selective free radical generation; 2) grafting of a hydrogel layer by using a monomer solution comprising polyol-containing monomer as boron ligand, a cross-linker monomer, and the redox initiator ammonium persulfate (APS). The entire modification process is performed under flow-through conditions. Membranes with different pore sizes were modified; modification parameters, such as molar mass of macromolecular co-initiator as well as composition of reactive monomer solution, were systematically varied. It was found that using an integrated initiation system with low molecular weight co-initiator N,N,N',N'-tetraethyl ethylenediamine (TEMED) added to the reactive solution, yielded significantly higher degree of grafting and therefore superior adsorber properties. Boron binding capacity of modified membranes was evaluated in terms of boron adsorption isotherms, adsorption kinetics, break-through behavior under filtration conditions and regeneration of the adsorber. The trade-off between permeance and boron binding capacity of modified membrane was studied in order to identify promising materials with competitive overall separation performance, i.e. high permeance at a specific filter cut-off in combination with high boron binding capacity.

Automated summary

This study focuses on the in situ modification of commercial polyethersulfone (PES) microfiltration membranes to efficiently remove boron in seawater desalination. By coating the pore surface with a boron affinity polymer-based hydrogel, the modified membranes showed superior adsorber properties. The trade-off between permeance and boron binding capacity was studied to identify promising materials for competitive overall separation performance.