New Breakthroughs in Water Purification

Transcription

1 Fiber Nanofiber d 300nm Functionalized soft matter: Using plastics, instead of expensive ceramic materials Nanofiber Technology & Molecular Engineering for Environment: Application to Water Purification New Breakthroughs in Water Purification Benjamin Chu 1-3, Benjamin S. Hsiao 1,3 Departments of Chemistry 1, Materials Science & Engineering 2, Biomedical Engineering 3 Colleges of Arts & Sciences, Engineering, Medicine Stony Brook University Key point: Opportunities offered by combining Biology, Chemistry, Engineering, and Physics to solve An important global problem How to purify water cheaply Christian Burger Xuming Chen u Chu Dufei Fang Hsiao Kyunghwan Yoon, Xuefen Wang Ultra-filtration: Kwanghwan Yoon, Dr. Xuefen Wang, Dr. Xuming Chen Electro-spinning Technology: Dr. Dufei Fang Other participants

2 Outline on New Breakthroughs 1. Human Population & Water Resources 2. Concept on 3-Tier Approach 3. New Breakthroughs: a. Nanofiber support with interconnected pores, high mechanical strength, and high porosity b. Top barrier layer with high flux capability 4. Impacts to society Projected World Population Growth 9 billion Population in billions billion before the end of the 21 st century (2010) Close to 7 billion (1990) 5 billion North America Europe Latin America Africa W-Asia Asia Oceania billion 9 billion by lectures/human_pop/human_pop.html

3 Global Water Distribution & Available Fresh Water Precipitation = 2 x 10 5 km x 10 9 Km 3 Lots of water Greenland Antarctica Rivers 1-2 parts Fresh Water per million of Total Water Water distribution uneven, often not matched with population location Population increase Global climate change Physics Today, 56, 40 (2003)

4 33-meter-high lime deposits on formerly submerged walls Receding water levels in Lake Powell, Utah, with less than 50% of its capacity in 1999 Lake Mead, Nevada & Arizona, water Level has fallen (see white rock), and is only half full. Exposing climate change New Breakthroughs: High-Flux Low-Fouling Membranes SWP High-Flux New Breakthroughs: Water Filtration High Membranes New Format Thin layer of smooth hydrophilic coating Breakthrough 2 Three-Tier Approach Support New Format ~150 nm diameter nanofibrous scaffold support Breakthrough 1 2 µm Mid-layer 1 µm Fractured Additional layer Increased edge filtration Speed; Less plug up of membrane, Known as fouling Coating 10-μm diameter non-woven support Increased filtration speed

5 1. Composite membranes with conventional and E-spun E support Conventional composite membranes Top coating layer (next slides) Flow rate/area is increased Due to higher surface pore density 1. Mid-layer Support 1. Conventional mid-layer support 2. Nano-fibrous mid-layer support 2 µm Three-Tier Approach Mid-layer Support 12 μm µm Fractured layer edge Higher pore volume Much higher surface pore density Coating Payoff: up to 5 times increase in filtration efficiency 2. Top coating layer of composite membranes Conventional composite membranes 2. Top coating layer Conventional Top coating layer Nano-composite Top coating layer support 2 µm Three-Tier Approach Mid-layer Support 12 μm µm Fractured layer edge Based on same thickness & chemical composition, New nano-composite top layer Is stronger mechanically with nanofibers Can increase flow efficiency Coating Payoff: Combined overall increase in Filtration Efficiency > 100 times

6 First demonstration of a higher efficiency membrane A: Feed C: Pure water B & C have the same clarity Commercial Membrane B: After filtration E-Spun Composite Membrane (PVA coated PAN E-Spun Membrane) What are nanofibers? Fiber NANOFIBERS (Definition) Nanofiber D 300 nm from a single polymer molecule, to small textile fibers, 0.5 nm 5000 nm Typically nanofibers are ranged from nm 1 nm = one billionth of a meter = cm

7 What a small diameter fiber can mean Earth The distance from earth to moon is 380,400 km. How many grams of polymer are needed to electrospin a fiber of 100 nm diameter that can reach the moon from earth? Solution: Grams of polymer = V ρ = (πr 2 L) ρ = π(50 nm) 2 (380,400 km) (1 g/cm 3 ) 3 g 380,400 km Moon Stonybrook Technology and Applied Research How big is a spider silk? Argiope spider Typically 2-20 μm! Bundles 1 μm = one millionth of a meter = cm

8 Electrospinning Technology Polymeric Fluid Droplet under Electric Field Forces on the polymeric solution 1. Gravity/extrusion forces 2. Surface tension U 0 > 0 r r Electrode R 0 3. Applied electric field strength E Spin-draw ratio millions Ground Stonybrook Technology and Applied Research Photographs of the pendent droplet and jet 0 millisecond 20 millisecond 26 millisecond Jet stream 28 millisecond 34 millisecond 50 millisecond Courtesy of Dr. Darrell Reneker, U. Akron

9 Visualization of Electrospinning Low speed camera High speed camera Courtesy of T. A. Kowalewski, S. Błoński, Polish Academy of Sci. A. L. Yarin of Technion Unique esjets technology for mass production Control of fiber diameters (down to 10 nm dia.) Control of membrane porosity Control of chemical composition of fibers Pattern formation Multi-layer formation Remote controller display Syringe pump module Multiple spinnerets module Collection conveyer system Precision rail system Apparatus and Methods for Electrospinning Polymeric Fibers and Membranes, inventors: Benjamin Chu, Benjamin S. Hsiao and Dufei Fang, issued March 30, 2004, Patent #6,713,011; PCT Int. Appl. WO Stonybrook Technology and Applied Research

10 SEM SEM Images of of PAN/Chitosan Composite Membrane Surfaces 20 μm Nonwoven Polyester Substrate 1 µm PAN 10 & 4 wt % E-spun Membrane Mid-layer Support 1 µm Chitosan-coated E-spun Top- layer Membrane Asymmetric features of E-spun E nanofiber mid-layer K. Yoon, KS Kim, XF Wang, DF Fang, B. Hsiao, and B. Chu, Polymer, (2006), 47(7), Nano-Trusses have Mechanical Stability & High Porosity Inter-connected continuous free space Soldering-like like attachments Nano-Trusses Chu/Hsiao SBU Volume of empty space 80% High surface pore density Payoff: faster purification speed: up to 5 times faster

11 PAN E-Spun E Fiber Density and Diameter Control 4 wt% 6wt% 8wt% 10 wt% d :124 nm 2 μm d :280 nm 2 μm d :682 nm 2 μm d :720 nm 2 μm d = average fiber diameter Electric field strength : 1.0 ~ 2.5 kv/cm Syringe pump rate : 10 ~ 40 µl/min. Distance between spinneret and collector drum : cm PAN Diameters can be controlled by about a factor of 6 PAN E-Spun Fiber Sizes & Porosities PAN E-Spun Fiber Sizes & Porosities PAN 6% PAN 8% PAN 12% 10µm 10µm 10µm Porosity (%) PAN 12 PAN 8 PAN 6 Average Fiber Diameter (nm) Porosity Change (3%) << Fiber Diameter Change by a factor of >8

12 Hydraulic Resistance of of PAN PAN E-Spun Membranes 14% flux decrease 10 X Commercial PAN UF membranes 5 times thickness increase Low hydraulic resistance : 14% flux decrease 5 X thickness increase Emulsified Oily Oily Water Filtration :: PVA-PAN for for hours hours 99.6 % Rejection E-spun membrane 98.7 % Rejection 12 X 99.4 % Rejection Test conditions : Cross-flow mode, Inlet pressure 90 psi, C Feed - Soybean oil (1350 ppm) + DC 193 fluid (150 ppm)

13 PVA PVA Coating Layer Layer Dependence on on Pure Pure Water Flux Flux Behavior PAN e-spun e membrane (5~6 x 10 3 l/m 2 h) Chu/Hsiao PVA coated PAN e-spun membranes Sample selected PVA coating solution concentrations : 2 ~ 8% 2.5 Test Conditions : Dead end 18 psi Commercial PAN UF membranes (Sepro) PAN 10 : MWCO PEG 20k 95 % PAN 400 : MWCO PEG 20k 75 % PVA coating solution : PVA (Mw : 177k) 2 ~ 8 wt%, Molar ratio of Glutaraldehyde / [-OH] in PVA = 0.25 with HCl ( ph ~ 2 ) PAN e-spun membranes : 40 µm thickness Water flux is highly dependent on the coating layer thickness Nanocomposite coating to enhance flux E-spun membrane coated with PVA and 10 wt% oxidized MWNT 10 µm ~ 2μm hydrophobic hydrophilic Environmental Science and Technology, 2005, 39, 7684

14 Emulsified Oily Oily Water Filtration :: PVA/MWNT-PAN for for hours hours Chu/Hsiao PVA (Mw : 78k) coating thickness : ~ 3 µm 4X If thinner (say from 3 µm to 0.5 µm, we may gain another factor of 2.5, yielding 12 x 4 x 2.5 = 120! PAN (Mw : 150k) e-spun layer : ~ 100 µm Rejection (%) : > 99% for all cases Test conditions : Cross-flow mode, Inlet pressure 100 psi, C Feed - Soybean oil (1350 ppm) + DC 193 fluid (150 ppm) Advantages of high-flux low-fouling filters What a substantial increase in efficiency will do Cost effective Low pressure systems with plastic fittings Manual operation within reach system flexibility Flexible designs to meet specific targets Incorporation of active surface sites for metal removal medical applications Broad range of applications, including desalination, energy generation