Hollow fiber nanofiltration

Patent filing no.: 742/KOL/2014

Technology title: Novel hollow fiber nanofiltration membrane using ZnCl₂ incorporated polysulfone Polysulfone (PSF)/Polyethyleneglycol (PEG) blend

1. Brief description

            In this work, organic (polyethylene glycol, PEG-200)  as  well  as inorganic  (ZnCl₂)  are simultaneously used as additives  (both  are  well  known  pore  constrictors) to polysulfone (PSF)/ dimethyl formamide (DMF) system  in order  to get hollow fiber NF membrane. Synergistic effects of pore constriction by zinc chloride and polyethylene glycol (PEG) are exploited to get nanofiltration grade fibers. The composition of the membrane was 16 to 18 wt% PSF, 2 wt% PEG-200, ZnCl₂ 1 to 2 wt% and rest dimethyl formamide (DMF). The molecular weight cut off of this membrane was 250 to 900 Da. This membrane is used for rejection of multivalent salts and organic dye. 30 to 45 % NaCl salt are rejected through this membrane at pH 2 to 11 range. 55 to 60% Na₂SO₄ salt are rejected at pH 11 through this membrane.   

2. Commercial aspects of the technology & Industries benefiting from it

            Commercial NF hollow fiber membrane is prepared using a spinneret which is costly. Therefore, the commercial hollow fiber cartridges are expensive. In this invention, nanofiltration hollow fibers were spun using an indigenously designed low cost process. Synergistic effects of pore constriction by zinc chloride i.e. inorganic additive and polyethylene glycol (PEG) i.e. organic additive are exploited to get nanofiltration grade fibers.

Some applications of hollow fiber NF are listed below. 

 (i) Removal of dyes (or colored component) from water by physical separation without any chemical treatment.

(ii) Concentration of fruit juices without any thermal treatment.

(iii) Removal of humic acid, bacteria and other pathogenic organisms from waste water.

 (iv) Textile industry effluent water treatment (reduction in COD content) without any chemical treatment.

(v) Desalination of salt water.

(vi) Removal of heavy metals from industrial pollutant.

3. Advantages of this technology

·         Unique formulation of membrane to obtain NF hollow fiber in one step.

·         No additional step for surface modification.

·         Solutes with molecular weight 250 to 900 are completely removed from solution.

4. Summary of the technical details

            Polymer (PSF) was heated to 70 to 80^oC for 2-3 h so that the moisture in the polymer was evaporated. Fixed amount (2%) of PEG (molecular weight 200 Da) and ZnCl₂ 1.0 to 2.0 % was added to a premixed 16 to 18% PSF in DMF dissolved at 60 to 80°C. The polymer was dissolved in DMF and the mixture was kept for 6 to 8 hours at 60 to 80^oC temperature under mild stirring. This solution was used for spinning the hollow fibers.

5.    Future prospects of the technology:

Uses as waste water treatment in textile and pharmaceutical industries, desalination. The technology is off the shelf and can easily be scaled up for industrial purposes.