Surfactant Selection and Bench-Scale Testing

Transcription

1 ESTCP Surfactant Selection and Bench-Scale Testing Center for Petroleum and Geosystems Engineering The University of Texas at Austin CPGE SEAR Workshop

2 What is SEAR? SEAR stands for Surfactant Enhanced Aquifer Remediation SEAR involves the injection of surfactants to recover NAPL-contaminants by either enhanced solubilization or mobilization due to interfacial tension reduction. SEAR Surfactant Selection and Bench-Scale Testing 2

3 Surfactant Ionic Type Classification Surfactants Anionics Nonionics Cationics Soaps Sulfates Sulfonates Phosphates Sulfosuccinates Ethoxylated alcohol Ethoxylated sorbitan fatty ester Sulfoxides Amine oxides Amine salts Quaternary ammonium SEAR Surfactant Selection and Bench-Scale Testing 3 SEAR Amphoterics Imidazoline Betaines Sulfobetaines Amino acid Lecithins

4 Types of Alcohol Ether Sulfate Surfactants C14 EO3-sulfate (linear alcohol) C14 EO3-sulfate (C4 branch at the #2 carbon) C14 PO3-sulfate (C4 branch at the #2 carbon; propylene oxide instead of ethylene oxide) SEAR Surfactant Selection and Bench-Scale Testing 4

5 Examples of Nonionic Structures Alcohol Ethoxylates C14 EO3 HLB = 7.7 C14 EO7 HLB = 11.9 C14 EO14 HLB = 14.9 SEAR Surfactant Selection and Bench-Scale Testing 5

6 Sodium Dihexyl Sulfosuccinate (Di-1,3-Dimethyl Butyl Sulfosuccinate, Sodium Salt) Trade Name: Aerosol MA Surfactants are surface active agents. They are molecules composed of two differing parts: a lyophobic tail and a lyophilic head. This structure leads to the molecule's interesting behavior. CH 2 CH O C C O O CH 3 CH CH O CH 3 (SO 3 ) - (Na) + CH 2 CH 2 CH 3 CH CH CH 3 CH 3 CH 3 SEAR Surfactant Selection and Bench-Scale Testing 6

7 Custom Designed Surfactant Hydrophobic Tail Hydrophilic Head CH 3 (CH 2 ) m O CHCH 2 O CH 2 CH O S O - Na + CH 3 O CH 3 (CH 2 ) n x Where m+n = SEAR Surfactant Selection and Bench-Scale Testing 7

8 How Surfactants Work: Solubilization Surfactants can enhance contaminant solubilization Contaminant Solubilization (mg/l 1,000, , , , ,000 - Volumetric GC Solubilization 8 wt.% Sodium Dihexyl Sulfosuccinate, 4 wt.% IPA Calcium Chloride Concentration (wt.%) SEAR Surfactant Selection and Bench-Scale Testing 8

9 How Surfactants Work: Mobilization Surfactants reduce interfacial tensions thereby allowing NAPL to be recovered by mobilization Interfacial Tension at 23 C, dynes/cm Hill AFB DNAPL-water ~ 9 MCB Camp Lejeune DNAPL-water ~ 10 4% MA, 8% IPA, 9,350 mg/l NaCl, TCE % MA in Hill AFB Source Water, Hill AFB DNAPL 0.2 4% MA, 4% IPA, mg/l NaCl, Hill AFB DNAPL % MA, 25,000 mg/l NaCl, PCE 0.14 SEAR Surfactant Selection and Bench-Scale Testing 9

10 Salinity Scan Solubilization Ratio Composition: 4% (active) sodium dihexyl sulfosuccinate 0% isopropanol sodium chloride trichloroethylene Trichloroethylene Water 0 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Salinity (mg/l NaCl) SEAR Surfactant Selection and Bench-Scale Testing 10

11 Comparison of Chun Huh Predicted and Measured Interfacial Tensions Interfacial tension, dyne/cm PCE exp. data (Jin, 1995) Decane exp. data (Delshad, 1986) Chun Huh correlation Solubilization Parameter SEAR Surfactant Selection and Bench-Scale Testing 11

12 DNAPL Mobilization Norm. Residual DNAPL Saturation SEAR Surfactant Selection and Bench-Scale Testing 12 SEAR Calculated Dwarakanath, 1997 Pennell et al., Trapping Number

13 Critical SEAR Remediation Variables Microemulsion phase behavior Interfacial tension Surfactant adsorption Viscosities Densities Mass transfer and diffusion Surfactant biodegradation Polymer compatibility and properties Cost and availability of chemicals SEAR Surfactant Selection and Bench-Scale Testing 13

14 Surfactant Selection Criteria Phase behavior Solubilization potential Environmental acceptability Viscosity of surfactant solutions Coalescence behavior Transport characteristics in permeable media Sorption characteristics SEAR Surfactant Selection and Bench-Scale Testing 14

15 Myths and Misconceptions Mass transfer effects limit contaminant solubilization by surfactant Surfactants reduce aquifer permeability Performance affected by surfactant sorption Cannot reduce saturation to less than 2 3% Lowering IFT will induce downward DNAPL mobilization Can avoid mass transfer limitations by adding cosolvent SEAR Surfactant Selection and Bench-Scale Testing 15 SEAR

16 Myths and Misconceptions (cont.) Can avoid reduction in aquifer permeability by using surfactants that do not form gels/emulsions and liquid crystals Can minimize surfactant sorption by using anionic surfactants Achieved 0.035% during the 1996 AFCEE demonstration Achieved 0.03% during the 1996 AATDF demonstration Can use neutral buoyancy SEAR to minimize downward mobilization SEAR Surfactant Selection and Bench-Scale Testing 16

17 Review of Surfactant Behavior Description of Microemulsions Thermodynamically stable and swollen micellar solutions should not be confused with macroemulsions Forming stable microemulsions rapidly is cornerstone of application of surfactants for NAPL recovery SEAR Surfactant Selection and Bench-Scale Testing 17

18 Surfactant Phase Behavior Winsor Type I Behavior Oil-in-water microemulsion Can solubilize significant volume of contaminant TCE Usually associated with solubilization type remediation regimes SEAR Surfactant Selection and Bench-Scale Testing 18

19 Surfactant Phase Behavior (cont.) Winsor Type II Behavior Water-in-oil microemulsion Surfactant lost to the NAPL Should be avoided in EOR and SEAR operations Water SEAR Surfactant Selection and Bench-Scale Testing 19

20 Phase Behavior Experiments Phase behavior experiments Measure contaminant solubilization Measure coalescence/equilibration time Determine microemulsion viscosities Specific surfactants can be tailored for specific NAPLs, such as in MCB Camp Lejeune and Naval Station Pearl Harbor SEAR Surfactant Selection and Bench-Scale Testing 20

21 Surfactant Phase Behavior (cont.) Aqueous Phase Nonaqueous Phase Microemulsion Phase Type I Type III Type II To effect a transition from Type I-III-II Increase electrolyte Add heavy alcohols Reduce temperature Increase surfactant tail length SEAR Surfactant Selection and Bench-Scale Testing 21

22 Volume Fraction Diagram % 4% Sodium Sodium dihexyl dihexyl sulfosuccinate, sulfosuccinate, 8% 8% 2-Propanol, 2-Propanol, ppm ppm xanthan xanthan gum, gum, Sodium Sodium Chloride, Chloride, Hill Hill AFB AFB Field Field DNAPL DNAPL Oleic Phase Volume Fraction Microemulsion Phase Aqueous Phase SEAR Surfactant Selection and Bench-Scale Testing 22 SEAR ,000 4,000 6,000 8,000 10,000 12,000 14,000 NaCl Concentration (mg/l)

23 Sodium Dihexyl Sulfosuccinate with TCE Surfactant Concentration, vol./vol. SEAR Surfactant Selection and Bench-Scale Testing 23 SEAR ,000 mg/l NaCl at 23 C Overall Composition Microemulsion Composition Binodal Curve Trichloroethylene Concentration, vol./vol.

24 Microemulsion Viscosities % IPA NaCl, wt% Solubilization, mg/l Viscosity, cp , , , , , , , , SEAR Surfactant Selection and Bench-Scale Testing 24

25 Microemulsion Density SEAR Surfactant Selection and Bench-Scale Testing 25 SEAR Microemulsion Density, g/cc % Surfactant 0% TCE, 0.6% NaCl 8% Surfactant 3% PCE, 3% NaCl 8% Surfactant 0% PCE, 3% NaCl 4% Surfactant 4% TCE, 0.6% NaCl Isopropanol Concentration, wt%

26 Ternary Diagram Ternary Diagram Phase behavior of Alfoterra 123-4POSO 4 Na with Chevron LNAPL (P-I2-45) at 500 ppm Ca++ Surfactant Concentration (wt.%) SEAR Surfactant Selection and Bench-Scale Testing 26 SEAR LNAPL Concentration(vol. %)

27 Microemulsion Viscosity Microemulsion Viscosity, cp SEAR Surfactant Selection and Bench-Scale Testing 27 SEAR % Alfoterra 145(PO) 4 sodium ether sulfate, 16% IPA, 0.2% CaCl 2 UTCHEM Model Measurement DNAPL Concentration in Microemulsion Phase

28 Volume Fraction Diagram 4% by Weight Alfoterra PO Sulfate, 16% by Weight IPA, PCE, and Calcium Chloride at 25 C DNAPL Volume Fraction Winsor Type I Winsor Type III Microemulsion Phase Winsor Type II Aqueous Calcium Chloride (wt.%) SEAR Surfactant Selection and Bench-Scale Testing 28 SEAR

29 Comparison of GC Measured and Volumetric Estimates of Contaminant Solubilization Hill Contaminant Solubilization (mg/l) 1,000, , , , ,000 8 wt.% Sodium Dihexyl Sulfosuccinate, 4 wt.% IPA Volumetric GC Solubilization CaCl 2 Concentration (wt%) SEAR Surfactant Selection and Bench-Scale Testing 29 SEAR

30 Volume Fraction Diagrams at Different Temperatures Volume Fraction 8 wt.% Sodium Dihexyl Sulfosuccinate, 4 wt.% IPA, Hill AFB DNAPL ºC 21ºC 15ºC 12ºC 23C 21C 15C 12C DNAPL Winsor Type I Microemulsion Winsor Type III Winsor Type II Aqueous Phase Normalized Electrolyte Concentration SEAR Surfactant Selection and Bench-Scale Testing 30

31 Effect of Surfactant Hydrophobe Length on Optimal Salinity and Optimum Solubilization Parameter Optimum Salinity, wt.% NaCl Optimum Salinity, TCE 6.5 Optimum Salinity, Hill AFB DNAPL Optimum Solubilization Parameter, TCE Optimum Solubilization Parameter, Hill AFB DNAPL Optimum Solubilization Parameter 100 wt.% Sodium Diamyl Sulfosuccinate Fraction of Sodium Dihexyl Sulfosuccinate 100 wt.% Sodium Dihexyl Sulfosuccinate SEAR Surfactant Selection and Bench-Scale Testing 31

32 Contaminant Solubilization at Different Temperatures 8 wt.% Sodium Dihexyl Sulfosuccinate, 4 wt.% IPA, Electrolyte, Hill AFB DNAPL Contaminant Solubilization, mg/l 1,000, , , , ,000 23C 23ºC 21C 21ºC 15C 15ºC 12C 12ºC Normalized Electrolyte Concentration SEAR Surfactant Selection and Bench-Scale Testing 32

33 Equivalent Alkane Carbon Number vs. Optimal Salinity Equivalent Alkane Carbon Number Optimum Salinity, wt% SEAR Surfactant Selection and Bench-Scale Testing 33 SEAR ,2-C 2 H 4 Cl 3 CH 2 Cl 2 & CHCl 3 Toluene Hill AFB DNAPL 1,1,2,2-C 2 H 2 Cl 4 DCB TCE Decane Octane PCE CCl 4 Hexane P-Xylene Chlorocarbons Hydrocarbons Calculated

34 Equilibrium Behavior of Microemulsions The most important and widely neglected selection criterion for surfactant solutions is rapid coalescence to a classical microemulsion when mixed with NAPL Liquid crystals, gels, and emulsions are common with surfactants and very undesirable because they can cause slow equilibration, high viscosity, plugging, and high retention in the soil SEAR Surfactant Selection and Bench-Scale Testing 34

35 Equilibrium Behavior of Microemulsions (cont.) Co-solvents can be used very effectively and inexpensively to eliminate this problem with a good surfactant with a branched hydrophobe The phase behavior must be carefully and accurately observed as a function of all pertinent variables, such as temperature and electrolyte content When classical phase behavior criteria are met, sorption is so low that it is negligible, and mass transfer is so rapid that local equilibrium on a field scale can be achieved SEAR Surfactant Selection and Bench-Scale Testing 35 SEAR

36 Non-Equilibrium Processes and Implication Batch Tests: Effects of Surfactant Type on Kb Ln(Cs-C) Ln(C s -C) = Ln(C s ) - k b t 1.6% MA80 1.6% SDS 1.6% Tween 1.6% Mixture Time, min SEAR Surfactant Selection and Bench-Scale Testing 36

37 Soil Column Results Final NAPL Saturation Experiment NAPL Mass Balance Tracers DW#2 PCE DW#3 PCE DW#4 TCE DK1 TCE DW#5 JP JP4#2 JP DK4 TCE POLYTCE#1 TCE POLYTCE#2 TCE POLYTCE#3 TCE HILLOU2#7 DNAPL HILLOU2#8 DNAPL SEAR Surfactant Selection and Bench-Scale Testing 37

38 Soil Column Results (cont.) Experiment NAPL Initial K Darcy Final K Darcy DW#2** PCE DW#3 PCE DW#4 TCE DK1 TCE DW#5** JP JP4#2 JP DK4 TCE POLYTCE#1 TCE POLYTCE#2 TCE POLYTCE#3 TCE HILLOU2#7 DNAPL HILLOU2#8 DNAPL SEAR Surfactant Selection and Bench-Scale Testing 38

39 Viscosity Measurements: Mobility Control Using Polymer Increases viscosity of surfactant formulation Improved sweep efficiency Reduce remediation time and amount of surfactant needed for chemical flood Flow without polymer Flow Flow with polymer Flow Non-Uniform Fluid Front Porous Media Uniform Fluid Front Porous Media SEAR Surfactant Selection and Bench-Scale Testing 39

40 Effect of Polymer on Phase Behavior 1.0 4% Sodium Dihexyl Sulfosuccinate, 8% IPA, Trichloroethylene Volume Fraction mg/l 500 mg/l SEAR Surfactant Selection and Bench-Scale Testing 40 SEAR NaCl Concentration, %wt

41 Comparison of Solubilization and Mobilization Remediation Regimes 1,000,000 Contaminant Solubilization (mg/l) 100,000 10,000 1, Solubilization Mobilization Pore Volumes SEAR Surfactant Selection and Bench-Scale Testing 41 SEAR

42 Normalized Tritium and 14C Concentrations for HILLOU2#8 Normalized Concentration SEAR Surfactant Selection and Bench-Scale Testing 42 SEAR Normalized Tritium Normalized 14C Cumulative Volume Produced, cc

43 Commercial Availability of SEAR Surfactants One size does not fit all Commercial production of surfactants for specific SEAR applications requires certain considerations Availability of hydrophobes & intermediates TSCA inventory (PMN s, R&D exemptions) Economics Environmental & safety regulatory questions Alfoterra? CONDEA s product line for SEAR Branched alcohol propoxylate sulfates Tailored for contaminant and site conditions MCB Camp Lejeune, Naval Station Pearl Harbor, future use at other sites SEAR SEAR Surfactant Selection and Bench-Scale Testing 43

44 Effects of Surfactant Structure on Biodegradation The concept of biochemical infallibility (what Nature synthesizes, Nature also degrades): ability to degrade surfactants is related to their structures/chemical groups being analogous to natural substances Branching of hydrophobe decreases biodegradation rates Propoxylation decreases biodegradation rates compared to equivalent degrees of ethoxylation Sulfonates (carbon to sulfur bond) are more difficult to break than sulfates (carbon to oxygen to sulfur bond) Ester linkages between hydrophobe and hydrophilic groups are easily broken SEAR Surfactant Selection and Bench-Scale Testing 44

45 Effects of Surfactant Structure on Biodegradation Biodegradation requiring oxidative attack (e.g., oxygenase activity) will not occur readily in anoxic subsurface environments (e.g., LAS, Dowfax?) Desirable that biodegradation intermediates exhibit less microbial toxicity than the parent compound (alkyl phenol ethoxylates are examples of this problem) Purposeful design of a SEAR surfactant to maximize biodegradation may result in a poor performer: Balance between performance and biodegradation is important SEAR Surfactant Selection and Bench-Scale Testing 45

46 Treatability Above-Ground To recycle or not to recycle...? Above-ground surfactant treatment technologies that directly or indirectly relate to surfactant structure Micellular enhanced ultrafiltration (MEUF): CMC is important Biological treatment Surfactant precipitation Chemical destruction: hydrolysis, oxidation (requirement for labile groups) Phase separation SEAR Surfactant Selection and Bench-Scale Testing 46

47 Conclusions on Structure vs. Performance Use of anionics (do not sorb as much to sediments) Soluble at concentrations & temperature of SEAR (nature of hydrophile is important) Matching hydrophobe with NAPL contaminant (e.g., HLB) Surfactants that disrupt structure are best for microemulsions of NAPL (e.g., branching, PO) Ability to tailor surfactants is useful It is essential that optimization of surfactant for performance does not create another environmental problem. SEAR Surfactant Selection and Bench-Scale Testing 47

48 Summary and Conclusions SEAR is a very viable technology in remediating NAPL-contaminated soils If the proper screening techniques for surfactant selection are used residual NAPL saturations as low as 0.03% can be achieved in both lab and field tests New advances have allowed us to custom-design surfactant molecules for specific contaminants SEAR Surfactant Selection and Bench-Scale Testing 48

49 Any Questions? SEAR Surfactant Selection and Bench-Scale Testing 49