Boron-selective membranes by pore-filling and surface functionalization with affinity hydrogel

Boron-selective membranes by pore-filling and surface functionalization with affinity hydrogel

kepng

State-of-the-art reverse osmosis membranes for desalination have limited competence to efficiently remove boron. The boron concentration in seawater is around 5 mg/L while the limit for irrigation is 0.5 mg/L [1]. One promising approach for boron removal is to integrate membrane-based separation with selective adsorption of boron. Two boron removal protocols are proposed: 1) integrate membrane-based separation with selective adsorption of boron; 2) remove the boron via carrier facilitated transport method. Therefore, different membrane modifications are implemented depending on the projected boron removal mechanisms.

For the first target, the pore surface of commercial polyethersulfone micro- and ultrafiltration membranes will be modified with a hydrogel layer in which contains polyol groups for selective boron binding. The modification protocol includes two steps: 1) adsorption of a copolymer which contains tertiary amine groups as co-initiator for free radical generation [2]; 2) surface-initiated grafting of a hydrogel layer by using a monomer solution comprising a polyol monomer, a cross-linker monomer and a redox initiator. The entire modification process is performed with recirculation of the solutions. The influences of flow rate, modification time and composition of the monomer solution are investigated to find optimal modification parameters leading to maximum boron binding capacity at minimized loss of permeability. Boron binding is evaluated by boron adsorption isotherms and kinetics, as well as in break-through experiments.

Pore-filling hydrogel composite membrane is fabricated to achieve second target, which enable a continuous separation process. The boron affinity gel structure and architecture are tailored in order to maximize boron transport selectivity and flux. Overall, the entire boron removal processes in this composite membrane comprises three steps: 1) composite membrane adsorb boron from feed solution under alkaline condition; 2) boron diffusion through the composite membrane; 3) de-complexation in receiver (extraction phase). The influences of hydrogel microstructure, pH value, type of base membrane and kind of extraction phase will be studied to achieve high selectivity while consuming less chemicals and energy.

References

  1. E. Guler, C. Kaya, N. Kabay, M. Arda, Desalination 2015, 356, 85
  2. M. Quilitzsch, R. Osmond, M. Krug, M. Heijnen, M. Ulbricht, J. Membr. Sci. 2016, 518 328

Funding

The work is supported by a Ph.D. scholarship of the Chinese Scholarship Council (CSC).

Contact:
Qirong Ke