Nanocomposite Polymeric Membranes for Thermally Driven Desalina8on Processes. Ming Li and Jonathan Brant, P.E., Ph.D. University of Wyoming

Transcription

1 Nanocomposite Polymeric Membranes for Thermally Driven Desalina8on Processes Ming Li and Jonathan Brant, P.E., Ph.D. University of Wyoming

2 Presentation Outline Background and motivation Thermally-driven processes and membrane requirements Nanocomposite membrane properties and development Experimental approach Properties and synthesis of imogolite nanotubes Membrane characterization Preliminary results and discussion Summary and future work AWWA/AMTA 2

3 Thermally-Driven Processes Membrane Distillation (MD) Water transports across a hydrophobic, microporous membrane, down a vapor pressure gradient Pervaporation (PV) Water transports across a hydrophilic, non-porous membrane via solution diffusion Feed Air + Water Air Condensing Stream Air + Water Condensing Stream Reject Feed Reject Air AWWA/AMTA 3

4 Thermally-Driven Processes Challenges Improvement Opportunities Pore flooding loss of flux Need for waste energy/heat Latent heat transfer/temp. polarization more severe for ceramics > precipitation at higher temperatures (inverse solubility) Use non-porous membranes to eliminate need for poreliquid interface (PV) Reduce temperature requirements / increase specific flux Polymer-ceramic composites having desirable properties of each constituent AWWA/AMTA 4

5 Nanocomposite Membranes Nanocomposite membranes nanomaterials used to enhance thin-film properties Nanomaterials selected to tailor mechanical and chemical properties of thin-film Zeolite and silica Metal oxides Nanotubes Mechanical properties Enhanced robustness Low-fouling surfaces Increased hydrophilicity Catalytic reactions / ROS production Flux improvements Increased hydrophilicity High-speed water pathways AWWA/AMTA 5

6 Nanotubes in Membranes Structure/Performance Increased water flux Brominated polyphenylene oxide Flux 197 to 487 LMH w/ 5 wt.% SWCNT Polysulfone Flux 300 to 370 LMH w/ 5 wt.% SWNTs Mechanisms: Reduced active layer thickness Affinity for water Application Challenges Weak interaction with polymer = low loading Poor dispersion = clumping/structural imperfections Nanotube alignment CNT: closed end AWWA/AMTA 6

7 Imogolite Nanotubes Imogolite - mineral (aluminum silicate) that forms nanotubes Rigid / straight structures as opposed to spaghetti structures formed by CNTs Simple synthesis techniques relative to CNTs Modifiable physical and surface properties Interior and exterior surface chemistry modified by grafting Precursor (Si, Ge) determines opening diameter Length controlled by pressure and temperature conditions Credit: Creton et al. (2008). AWWA/AMTA 7

8 Research Objective Overall Objective: develop nanocomposite membranes having enhanced mechanical and performance characteristics in thermally-driven separation processes Research tasks covered in this presentation: Physical characterization of imogolite nanotubes and the manipulation of their properties through modification of solution chemistry Physical and surface-chemical properties of thin-films containing imogolite nanotubes Separation and water flux properties of imogolite containing thinfilms in pressure and thermally-driven systems AWWA/AMTA 8

9 Synthesis of Imogolite Nanotubes Precursors Slow Hydrolysis Autoclave Tetraethyl orthosilicate and aluminum perchlorate Germanium ethoxide and aluminum perchlorate l = 100~1000 nm d = 1 nm l = 100~200 nm d = 3 nm in l = Several µm d = 1 nm l = 1000 nm, d = 3 nm Al perchlorate 0.1 mol/l Tetraethyl orthosilicate (TEOS) 0.05 mol/l Al/Si=2 Mixing in 25 ml ultra pure water ph 7 Titration by NaOH (0.1 mol/l, 50 ml, 1 ml/min, vigorously stir) Stir (1 hour) Heating (95 C, 1 week) Dialysis (ultra pure water, 5 days) AWWA/AMTA 9

10 Nanocomposite Synthesis poly (vinyl alcohol) PVA Polyvinyl alcohol (PVA) used for initial testing Hydrophilic High density of reactive chemical functionalities for crosslinking (-OH) Synthesis procedure Imogolite & glutaraldehyde mixed in 5% PVA solution Mixture applied to polyacrylonitrile substrate via spin coater Dried in vacuum oven at 50 C for 1 hr PAN substrate imogolite-pva 150 rpm 30 s glutaraldehyde 300 rpm 60 s Credit: Chollet et al. (2018). AWWA/AMTA 10

11 Membrane Performance Membrane Imogolite-PVA/PAN membrane Active Layer Material Water Contact Angle Imogolite-PVA 55.6±3.2 Flow Meter FI Crossflow Concentrated Water Sweeping Gas Air Drying Column Pure PVA/PAN membrane PVA 54.8±5.3 DOW FILMTECH RO membrane HTI TFC membrane Polyamide 36.1±4.0 Cellulose Triacetate 46.3±4.8 Heater Feed Tank and Warm Bath Feed Pump Pressure Gauge Membrane Cell Pressure Meter P Permeate Parameters measured: Specific water flux Salt (NaCl) rejection Flux decline due to concentration polarization Air Permeate Water Collector Condenser Pervaporation Test System AWWA/AMTA 11

12 Imogolite Nanotube Structure ph 7 Single imogolite nanotube Length: ~1 µm Diameter: 1 nm ph 4 Physical Dimension: 1. Length = 1 to 1.5 µm 2. Diameter = 1 nm Nanotube Dispersion 1. Increased more basic ph 2. High aspect ration favoring aggregation AWWA/AMTA 12

13 Imogolite Surface Charge Charge & ph relationship Strongly charged > ph 9 Zeta potential decreases with an increase of ph Fixed charge structure imperfection Zeta Potential, mv ph 10 mmol NaCl; T = 22±1 C Isoelectric Point at ph 10 AWWA/AMTA 13

14 Membrane Characterization Water flux for nanocomposite membrane compared favorably to low-pressure RO membrane Flux, L/(m 2 *h) Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane DOW RO Membrane Water flux increased with addition of imogolite nanotubes to PVA Imogolite-PVA/PAN > PVA/PAN Difference in flux b/n pure PVA and nanocomposite disappeared as ΔP approached 300 psi J= P π/μ R tot = P π/μ( R m + R f ) Feed Pressure, psi Ultra Pure Water; T = 22±1 C; Stirring Speed = 50 rpm Flux, L/(m 2 *h) Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane DOW RO Membrane Time, s Ultra Pure Water; ΔP = 100 psi; T = 22±1 C AWWA/AMTA 14

15 Membrane Characterization Flux decline for LPRO and pure PVA membranes attributed to concentration polarization System operated in dead-end mode CP results in reduced P net (increased Δπ) Lack of flux decline for imogolite nanocomposite membrane implies reduced salt rejection Nanotubes may enhance salt passage Flux, L/(m 2 *h) Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane DOW RO Membrane Time, min 10,000 mg/l NaCl; ΔP = 100 psi; T = 22±1 C; Stirring Speed = 50 rpm AWWA/AMTA 15

16 Membrane Characterization Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane HTI TFC Membrane 1E+07 Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane HTI TFC Membrane Flux, L/(m 2 *h) Membrane Resistance, m 2 *h/(l*s) 1E+07 1E+07 9E+06 8E+06 7E+06 6E+06 5E+06 4E+06 3E Temperature, o C Ultra Pure Water; Cross Flow Rate = 2,500 ml/min; Sweeping gas = Dry Air; Gas Flow Rate = 12 scfh Water flux: imogolite-pva/pan membrane > pure PVA/PAN membrane 35.66% enhancement under 30 C; 46.48% enhancement under 50 C; 72.47% enhancement under 70 C Membrane Resistance, m 2 h/(sl) 3.5E E E E E Temperature, o C Imogolite-PVA/PAN Membrane PVA/PAN Membrane Dow RO Membrane 1.0E Pressure (psi) AWWA/AMTA 16

17 Membrane Characterization Water flux evaluated in thermally-driven configuration Water flux was comparable for the nanocomposite and TFC membrane (an FO membrane) Water flux was almost double that for the pure PVA Flux decline was comparable for the TFC and nanocomposite membranes Reason is unclear as system was operated in a closed-loop configuration and NaCl is not scale forming Temperature (50±1 C) may be affecting membrane properties (10,000 mg/l NaCl) Flux, L/(m 2 *h) Imogolite-PVA/PAN Membrane Pure PVA/PAN Membrane HTI TFC Membrane Time, hr 10,000 mg/l NaCl; T = 50±1 C; Cross Flow Rate = 2,500 ml/min; Sweeping gas = Dry Air; Gas Flow Rate = 12 scfh AWWA/AMTA 17

18 Summary The imogolite nanotubes dispersed better in lower ph condition The addition of imogolite nanotubes effectively enhance permeate water flux 13.28% enhancement under 100 psi,18.36% enhancement under 150 psi, 5.65% enhancement under 200 psi 35.66% enhancement under 30 C, 46.48% enhancement under 50 C, 72.47% enhancement under 70 C Imogolite-PVA/PAN membrane has better mechanical strength compared to PVA/PAN membrane AWWA/AMTA 18

19 Acknowledgements This work is supported by funds provided by the following agencies: KC Harvey & Associates, Bozeman, MT Center of Excellence in Produced Water Management (CEPWM), Laramie, WY Gratefully acknowledge the assistance of Dr. Lavard in nanotube synthesis and characterization AWWA/AMTA 19

20 Questions? Jonathan Brant University of Wyoming Dept. Civil & Architectural Engr E. University Avenue Laramie, WY Phone: (307) AWWA/AMTA 20