Transcript Document
Electrodialysis/Reverse Osmosis to Recover Dissolved Organics from Seawater Peter H. Pfromm, Tarl Vetter Department of Chemical Engineering, Kansas State University Manhattan, Kansas E. Michael Perdue, Ellery Ingall, Jean-François Koprivnjak School of Earth and Atmospheric Sciences Georgia Institute of Technology Atlanta, Georgia 1 Index Overview • • Introduction and Motivation Electrodialysis Reverse Osmosis Combined Process Process Characterization Experiments/Results • Conclusions and Outlook • • • • 2 Index Units: Gigatons C, GtC/yr (1 GtC= 109 tons of carbon) 3 •Source: NASA Index •http://earthobservatory.nasa.gov/Library/CarbonCycle Earth scientists would like to know: • • Composition of carbon reservoirs Origin/fate of carbon reservoirs The problem with DOC in the oceans: • • Only 1 gram of carbon in 1000 liters of seawater...... Salt The approach: 4 • Engineers and scientists collaborate • Develop a new separation approach Index What is marine dissolved organic carbon (DOC)? ~30wt% of DOC is “high molecular weight” (HMW) >1000 Da ~70wt% of DOC is “low molecular weight” (LMW) <1000 Da DOC is composed of many types of molecules, examples: Aminosugars Aromatics Polysaccharides Humic Species 5 Index How do you detect marine dissolved organic carbon (DOC)? Not a trivial issue: reasonably accurate part-per-billion level analysis for organic carbon in a high-salt (chloride) matrix. Shimadzu TOC-VCSN high-temperature catalytic oxidation analyzer Sample is acidified to remove inorganic carbon, then combusted over Pt catalyst and CO2 is detected by infrared Many papers, book chapters, and meetings are dedicated to this issue. Perdue at Georgia Tech is one of the well known experts on this. 6 Index The issue: recover pure DOC for scientific analysis. The problem: salt Water Process Solid DOC sample 35 g/L salts 7 ~ 0.001 g/L=1 ppm DOC Salt Index State of the Art Recovery Ultrafiltration Tangential Flow Salt ~30% DOC Adsorption Methods Seawater Porous Non-polar Resin Resin Columns Pore 100-300 μm Water 8 Salt LMW DOC Seawater with remaining DOC Only recovers High Molecular Weight DOC (>1000 Da) Only recovers select species (humic, etc) Salt still present in final sample Must use pH or other method to desorb Index New Approach: RO removes fresh water concentrating salt and DOC Water Reverse Osmosis Process Electrodialysis 35 g/L salts 9 ~ 1 ppm DOC Freeze Dry Solid DOC sample Salt ED removes salt with minimal loss of uncharged species Index RO ED The Processes Electrodialysis 10 Reverse Osmosis Index Electrodialysis Spacers and Membranes 11 Astom AMX/CMX Index Electrodialysis Diluate Return Concentrate Return C A Anode C A Cathode Cl- Na+ Na+ Na+ Na+ ++ C Cl- Na+ Na+ C Cl- Na+ Na+ -- ClCl- Na+ Na+ Na+ Cl- Concentrate Diluate/Feed 12 Index Electrodialysis Characterization Limiting Current (Ilim) 30 25 Limiting 20 Limiting Current Current 15 Density (Amps) 10 (Amps) Reapp = 90 Reapp = 38 5 Re apparent Temperature: 25°C 0 0 10 20 30 40 4 Rh v 50 Conductivity (mS/cm) 13 Index RO ED The Processes Electrodialysis 14 Reverse Osmosis Index Reverse Osmosis Higher Flow Concentration Polyamide Retentate barrier 0.2 μm High Pressure Water ~ Pure Water Salt Water Microporous 40 μm polysulfone Polyester 120 μm fabric Salt Water Discarded Permeate Low Concentration Feed 15 http://www.dow.com/PublishedLiterature/ Index Spiral Wound RO Module 16 http://www.purewaterplanet.com/images/ROMembrane.jpg Index 40 Reverse Osmosis Characterization 35 205 psi 30 40 0.35 180 psi 25 150 psi Retentate Permeate Permeate 35 20 Flowrate (mL/s) 15 90 psi 30 Stage Cut Flowrate (mL/s) 20 0.99 mS/cm 180 psi 60 psi 10 Small25Stage5 0.2 Permeate Cut 0 Large Stage Cut 150 psi 0 2 4 6 120 psi 0.15 CA Qs K s Tm psi 205120psi 0.3 0.25 Retentate Permeate 8 10 12 4.11 mS/cm 14 18 Conductivity (mS/cm) 7.80 mS/cm 0.35 15 90 psi 0.3 12.12 mS/cm 0.1 10 0.99 mS/cm 60 psi 0.25 0.05 4.11 mS/cm 0.2 5 Stage Cut 7.80 mS/cm 0.15 0 0 0 12.12 mS/cm 0.1 0 50 100 2 4 High Feed Flow Rate 0.05 0 6 150 8 10 Low Feed Operating Pressure (psi) 200 12 14 16 18 Conductivity (mS/cm) Flow Rate 0 17 16 50 100 Operating Pressure (psi) 150 200 Index Combined Process Operation RO Unit Electrodialysis Stack 18 Index Overall Drive to site Retrieve seawater sample (200- 400 l) ED/RO 200 l seawater Purge ED/RO systems Freeze ~10 l Freeze dry NMR.... Hope for good weather! 19 Index Experimentation Experiment Date Starting Concentration (ppm) Sample Type Experimental Objective 7/12/2005 0.18 Artificial Seawater 9/28/2005 0.11 Artificial Seawater Determination of operating 10/18/2005 0.05 Artificial Seawater parameters and modes 11/9/2005 0.01 Artificial Seawater 3/6/2006 0.22 Artificial Seawater 4/3/2006 0.06 Artificial Seawater 5/26/2006 1.95 Brackish Water Examine recovery of natural 6/8/2006 2.24 Brackish Water DOC species 7/3/2006 3.30 Brackish Water 7/18/2006 1.20 Seawater (ship board) 7/19/2006 0.93 Seawater (ship board) Recovery of DOC from various 7/20/2006 1.19 Seawater (ship board) locations and depths 7/20, 7/21/2006 1.21 Seawater (ship board) 7/21/2006 0.82 Seawater (ship board) 7/22/2006 1.10 Seawater (ship board) 7/23/2006 0.20 Blank (ship board) Examine DOC leaching 7/24, 7/25/2006 1.22 Seawater (ship board) Adjustment of ED operation 7/25, 7/26/2006 1.10 Seawater (ship board) Attempt total desalination 7/26, 7/27/2006 1.02 Seawater (ship board) Examine high concentration 7/27/2006 5.08 Brackish Water (ship board) Comparison of DOC recovery 8/14/2006 0.96 Seawater Lab reproduction of seawater 8/18/2006 1.08 Seawater Test new membranes 20 Index 100 Salt 75 S % removed 50 Water 25 Examples: ED Start with 200 liter seawater ED 0 0 Three shipboard experiments ED & RO 2 4 6 Time [hrs] 240 200 160 DOC retained 120 [mg] 80 ED ED & RO ED 40 0 0 21 2 4 Time [hrs] 6 Index ED: follow the limiting current density 20 applied current 18 16 14 12 limiting current ED 10 current [A] 8 initial ED only initial seawater sample 201 liters 6 4 RO&ED: water removal balanced by salt removal to maintain conductivity 2 final ED 0 0 22 10 20 30 40 Diluate (seawater) conductivity [mS/cm] 50 Index Summary 100 6 7 103 15 Final DOC ppm 90 3 14 80 6 70 26 21 24 21 15 21 2 17 60 Diluate DOC Recovery (%) 50 40 30 Brackish 20 10 Seawater Lab Lab Lab Lab Lab 0 1 5-26 2 6-8 3 7-3 4 7-18 5 7-19 6 7-21 7 7-20 8 9 7-22 7-21 10 7-25 11 7-24 12 7-26 13 8-14 14 7-27 15 8-18 Date of Experiment 23 Index Conclusions • ED/RO can recover a significant fraction of DOC from seawater (60%-90%) • The process is fast, allowing treatment of large volumes of samples • We are able to reduce salt concentration and water volume to make a sample ready for freeze drying • Preliminary results by NMR: differences from the high MW fraction that was previously available. • Scientists and engineers think differently but can communicate and collaborate successfully 24 Index Outlook • Examine the impact of temperature • Further minimize losses to the ED concentrate, possibly with different membranes • Examine modulation of the ED current to optimize DOC recovery • Applications for recovery of sensitive molecules (proteins, enzymes)? 25 Index Acknowledgements • This work is supported by the National Science Foundation, Grants No. 0425624 and 0425603. (Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF) • Dr. Mary Rezac who initiated the contact between scientists and engineers that made this work possible. • Poulomi Sannigrahi for help at sea and in the laboratory. • We would especially like to thank Captain Raymond Sweatte and the excellent crew of the R/V Savannah for two great and productive cruises. 26 Index