Polymer assisted forward osmosis for desalination and water reuse

Transcription

1 Polymer assisted forward osmosis for desalination and water reuse Xinying Wang Illinois Sustainable Technology Center

2 Earth s water percentage 71% Earth surface is covered by water Only 0.3% of the fresh water or 0.007% earth water can be readily accessed.

3 Clean water crisis By middle of this century The world population is estimated to reach 10 billion 47% of population will be living in areas suffering clean water stress

4 71% Earth surface is covered by water, but we are facing > salt water problem. Isn t it ironic?

5 Desalination

6 Desalination technologies Electric Thermal CO2 RO 4-8 kwh/m 3 0 kwh/m 3 MSF kwh/m kwh/m 3 >1.7 Kg/m 3 >9.4 Kg/m 3 MED kwh/m kwh/m 3 >7.0 Kg/m 3 T.Mezher et al. Desalination

7 What is forward osmosis? Forward Osmosis Reverse Osmosis ΔP Δπ Salty water Salty water Δπ Draw solution Feed J w = A(Δπ-ΔP)

8 FO process advantages Reverse Osmosis Forward Osmosis Energy Source High grade Low grade Membrane Fouling High Low Operation pressure High Low

9 Forward osmosis desalination Brine in Draw solution out Fresh Water Brine out Membrane Draw solution in Draw solution concentration process

10 Where is the challenge? Conc DS Diluted DS Conc DS Water Take diluted draw solution as final product Select appropriate draw solute, i.e. NH4HCO3, modified magnetic particles

11 Ammonia-CO2 draw solution NH4HCO3 heat NH3 + CO2

12 Magnetic particles draw solution

13 Our Solution-Aquapod Use polymer to extract water from diluted solution Aqueous two phase extraction Top phase: polymer, water, and tiny amount of draw solute Bottom phase: concentrated draw solution and tiny amount of polymer

14 Our Solution-Aquapod Polymer used: Poly ethylene glycol-poly propylene glycol (UCON TM ) Cost: $2.2/lbs Cloudy point: 60/140 ⁰C/⁰F Non-toxic Draw solution: MgSO4

15 Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product

16 Forward osmosis process Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product

17 Forward osmosis Membrane: TFC (lab-made) and HTI (commercial) Draw solution: 20wt% MgSO4 Lab-scale forward osmosis system FO system HTI TFC

18 Forward osmosis TFC-PA membrane Flux(LMH) Time(min) 25.0 DI feed 2000 ppm NaCL feed 10000ppm NaCL feed 20000ppm NaCl feed 30000ppm NaCl feed HTI membrane 20.0 Flux(LMH) Time (min) DI 2000ppm NaCl 10000ppm NaCl 20000ppm NaCl 30000ppm NaCl

19 Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product

20 A polymer extraction example Stock solution: MgSO4 20wt%, polymer 10wt%, and water 70wt% Top phase or polymer phase : MgSO4 0.02wt%, polymer 59.4wt%, and water 40.6wt% Bottom phase or salt phase: MgSO4 23.5wt%, polymer 0.018wt%, and water 76.5wt% UCON Water MgSO4

21 Gravity separation (time) Centrifuge-assisted (energy) Centrifuge speed (G force/rpm) Water extraction Centrifuge time (min) MgSO4 Concentration UCON concentration 151/ / / /4000 Polymer-rich phase (g/l) Salt-rich phase (g/l) Polymer-rich phase (g/l) Salt-rich phase (g/l)

22 Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Water product

23 Water polymer separation by heat Heat can lead polymer chain reconfiguration Above cloudy point, the polymer becomes hydrophobic and precipitates out from the homogenous solution. Above cloudy point Below cloudy point

24 Water polymer separation by heat 0 min 0.25 min 1 min 3 min 5 min

25 Water polymer separation by heat Temperature Top phase (water) Bottom phase (polymer) UCON660(g/L) MgSO4 (g/l) UCON660 (g/l) MgSO4(g/L) 70⁰C ND 80⁰C ND 90⁰C ND

26 Our Solution-Aquapod Polymer Diluted Draw Solution FO Concentrated Draw Solution Water Extraction Polymer Polymer Heart exchanger Polymer solution Water polishing Raw water Water-polymer Separation Polished water

27 Water polishing Water sample from polymer-water separation unit process has ~1wt% polymer ~0.5wt% MgSO4 A Nanofiltration process was evaluated for the polishing

28 Water polishing Flux (LMH) NF Permeate recovery rate (%) Membrane: NF Pressure: 70psi Water product: Polymer ~7ppm Flux(LMH) NF Permeate Recovery (%) Membrane: NF Pressure: 70psi Water product: Polymer ~110ppm

29 Process integration

30 Summary A novel polymer-assisted FO desalination process is proposed A suitable draw solution-polymer pair is identified Four sub-processes are evaluated individually

31 Acknowledgement Dr Kishore Rajagopalan John Scott Vinod Patel And all other people at ISTC who helped me on this project

32 Thank you!