Research ArticleENGINEERING

Hydrophobic nanostructured wood membrane for thermally efficient distillation

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Science Advances  02 Aug 2019:
Vol. 5, no. 8, eaaw3203
DOI: 10.1126/sciadv.aaw3203
  • Fig. 1 The process schematic of nanowood membranes for MD.

    (A) Schematic of MD using the wood membrane. (B) Digital photograph of the nanowood and the corresponding beneficial properties for MD applications. (C) Schematic of the water (vapor) and heat transfer in the wood membrane during MD. Photo credit: T. Li, University of Maryland.

  • Fig. 2 Structural characterization of the nanowood membrane.

    (A) Photo of the hydrophobic nanowood membrane. (B) Photo that shows hydrophobicity after silane treatment. (C) Water contact angle of the nanowood membrane. (D) SEM images of the nanowood surface that exhibit aligned texture, xylem vessels, and lumina (channels). (E) SEM images that exhibit mesopores [(G) cross section and (H) pits] growing on the walls of the xylem vessels and lumina. (F) SEM images that exhibit microsized pores amid the cellulose fibers. (I) PSD of the hydrophobic natural wood and nanowood membranes. Photo credit: D. Hou, University of Colorado.

  • Fig. 3 Thermal conductivity characterization of the wood membranes.

    (A) Photo of the hydrophobic nanowood membrane. (B) Photo of the hydrophobic natural wood membrane. (C) Schematic representation of contact heat source measurement. IR thermographs of (D) the wood membranes. (E) Measured thermal conductivity of the wood membranes from 40° to 60°C. (F) Comparison of the thermal conductivity of the woods at 60°C before and after hydrophobic silane treatment. Error bars represent the SDs based on three independent experiments. Photo credit: D. Hou, University of Colorado.

  • Fig. 4 MD performance of the wood and commercial membranes.

    (A) Water flux and (B) experimental thermal conductivities for the hydrophobic wood membranes with feed temperature continuously varying between 40° and 60°C and distillate temperature of 20°C. (C) Intrinsic permeability of the membranes. (D) Thermal efficiency versus water flux of the wood membranes and commercial membranes. Error bars represent the SDs based on three independent experiments.

  • Table 1 Characteristic comparisons of the new wood membranes and commercial polymeric membranes.

    LEP, liquid entry pressure; ECTFE, ethylene chlorotrifluoroethylene.

    MembraneManufacturerActive
    layer
    Support
    material
    Pore size
    (μm)
    Thickness
    (μm)
    Porosity
    (%)
    Contact
    angle (°)
    LEP
    (kPa)
    Intrinsic
    permeability
    (×10−10 kg m−1
    s−1 Pa−1)
    Thermal
    conductivity
    (W m−1 K−1)*
    Thermal
    efficiency
    (%)
    Reference
    ECTFE3MECTFE0.4346671180.39~0.034~60(22)
    0.45PP3MPP0.79110851300.950.048~58(22)
    QM902ClarcorePTFE0.4570-85~51(22)
    2400CelgardPP0.04325411380.020.111<3(22)
    0.22PPTischPP1.79 ± 0.10§196 ± 1872 ± 311942.7 ± 0.30.64 ± 0.020.06644 ± 1This study
    0.45PPTischPP2.65 ± 0.24§175 ± 472 ± 112538.6 ± 0.50.68 ± 0.040.06639 ± 3This study
    0.22PTFETischPTFEPP0.33 ± 0.00§188 ± 575 ± 4121126 ± 21.21 ± 0.220.08253 ± 0This study
    0.45 PTFETischPTFEPP0.36 ± 0.00§156 ± 1178 ± 2117133 ± 51.15 ± 0.210.07559 ± 2This study
    Natural
    wood
    Cellulose0.18 ± 0.02§540 ± 1521 ± 314298.5 ± 0.80.20 ± 0.040.21012 ± 2This study
    NanowoodCellulose0.28 ± 0.03§502 ± 3589 ± 314474.7 ± 0.51.44 ± 0.090.040ǁ71 ± 2This study

    *The theoretical values were based on the assumption of isotropic thermal property (in this table and section S12) (39, 47, 59). However, the real nanowood is anisotropic with a measured, while the anisotropic thermal conductivity in x (fiber growth direction), y, and z (transverse direction) directions was 0.060, 0.030, and 0.030 W m−1 K−1, respectively.

    †The experimental feed temperature and distillate temperature were 60° and 20°C, respectively.

    ‡Nominal pore size.

    §Averaged pore size.

    ǁTheoretical thermal conductivity at room temperature.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/8/eaaw3203/DC1

      Section S1. The hydrophobic silane treatment mechanism

      Section S2. The nanowood membrane before and after hydrophobic treatment

      Section S3. The natural wood membranes

      Section S4. Comparison of the wood membranes and common papers

      Section S5. Anisotropic thermal insulation property of the nanowood membrane and the potential benefits

      Section S6. Commercial hydrophobic membranes

      Section S7. Pore size distribution of the commercial membranes

      Section S8. Morphology and pore structure of the commercial membranes

      Section S9. Surface hydrophobicity/hydrophilicity

      Section S10. DCMD reactors and configurations

      Section S11. Water flux of commercial membranes

      Section S12. Theoretical thermal conductivity estimation

      Section S13. Thermal insulation of commercial membranes

      Section S14. Experimental thermal conductivity and membrane permeability

      Section S15. Theoretical permeability coefficient and intrinsic permeability

      Section S16. Wood membrane durability

      Section S17. Wood membrane application and fouling

      Fig. S1. Schematics of hydrophobic treatment of wood membranes using silane coupling agent (50).

      Fig. S2. Surface morphologies and pore size distribution of the nanowood membrane before and after hydrophobic treatment.

      Fig. S3. Visual images of the hydrophobic natural wood membrane after silane treatment.

      Fig. S4. Temperature plots of isotropic and anisotropic thermal insulators from a point heat source.

      Fig. S5. Visual images of the commercial hydrophobic membranes purchased from Tisch Scientific (North Bend, Ohio).

      Fig. S6. PSD of the commercial membranes.

      Fig. S7. SEM images of the surface and cross-section of the commercial membranes.

      Fig. S8. Water contact angles of the commercial and hydrophobic natural wood membranes.

      Fig. S9. Schematics, images, and control interface of the apparatus for direct contact membrane distillation (DCMD).

      Fig. S10. Water flux of the commercial polymeric membranes in DCMD with feed [NaCl (1 g liter−1)] temperature continuously varying between 40° and 60°C and distillate (DI water) temperature of 20°C.

      Fig. S11. IR thermographs of the commercial membranes with the heat source temperature of 60°C.

      Fig. S12. Temperature plots of anisotropic nanowood and isotropic commercial membranes from a point heat source.

      Fig. S13. Comparison of experimentally measured intrinsic (thickness-normalized) membrane permeability of the wood and commercial membranes.

      Fig. S14. Water flux of the hydrophobic wood membranes in DCMD with feed [NaCl (1 g liter−1)] and distillate (DI water) temperatures controlled at 60° and 20°C, respectively.

      Fig. S15. Water flux of the hydrophobic nanowood membrane in DCMD with [NaCl (35 g liter−1) and synthetic wastewater] and distillate (DI water) temperatures controlled at 60° and 20°C, respectively.

      Table S1. Comparison between nanowood and common paper.

    • Supplementary Materials

      This PDF file includes:

      • Section S1. The hydrophobic silane treatment mechanism
      • Section S2. The nanowood membrane before and after hydrophobic treatment
      • Section S3. The natural wood membranes
      • Section S4. Comparison of the wood membranes and common papers
      • Section S5. Anisotropic thermal insulation property of the nanowood membrane and the potential benefits
      • Section S6. Commercial hydrophobic membranes
      • Section S7. Pore size distribution of the commercial membranes
      • Section S8. Morphology and pore structure of the commercial membranes
      • Section S9. Surface hydrophobicity/hydrophilicity
      • Section S10. DCMD reactors and configurations
      • Section S11. Water flux of commercial membranes
      • Section S12. Theoretical thermal conductivity estimation
      • Section S13. Thermal insulation of commercial membranes
      • Section S14. Experimental thermal conductivity and membrane permeability
      • Section S15. Theoretical permeability coefficient and intrinsic permeability
      • Section S16. Wood membrane durability
      • Section S17. Wood membrane application and fouling
      • Fig. S1. Schematics of hydrophobic treatment of wood membranes using silane coupling agent (50).
      • Fig. S2. Surface morphologies and pore size distribution of the nanowood membrane before and after hydrophobic treatment.
      • Fig. S3. Visual images of the hydrophobic natural wood membrane after silane treatment.
      • Fig. S4. Temperature plots of isotropic and anisotropic thermal insulators from a point heat source.
      • Fig. S5. Visual images of the commercial hydrophobic membranes purchased from Tisch Scientific (North Bend, Ohio).
      • Fig. S6. PSD of the commercial membranes.
      • Fig. S7. SEM images of the surface and cross-section of the commercial membranes.
      • Fig. S8. Water contact angles of the commercial and hydrophobic natural wood membranes.
      • Fig. S9. Schematics, images, and control interface of the apparatus for direct contact membrane distillation (DCMD).
      • Fig. S10. Water flux of the commercial polymeric membranes in DCMD with feed NaCl (1 g liter−1) temperature continuously varying between 40° and 60°C and distillate (DI water) temperature of 20°C.
      • Fig. S11. IR thermographs of the commercial membranes with the heat source temperature of 60°C.
      • Fig. S12. Temperature plots of anisotropic nanowood and isotropic commercial membranes from a point heat source.
      • Fig. S13. Comparison of experimentally measured intrinsic (thickness-normalized) membrane permeability of the wood and commercial membranes.
      • Fig. S14. Water flux of the hydrophobic wood membranes in DCMD with feed NaCl (1 g liter−1) and distillate (DI water) temperatures controlled at 60° and 20°C, respectively.
      • Fig. S15. Water flux of the hydrophobic nanowood membrane in DCMD with NaCl (35 g liter−1) and synthetic wastewater and distillate (DI water) temperatures controlled at 60° and 20°C, respectively.
      • Table S1. Comparison between nanowood and common paper.

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