1、API PUBL*K4531 91 O732290 0101401 2 = Chemical Fate and Impact of Oxygenates in Groundwater: Solubility of BTEX from Gasoline-Oxygenate Mixtures HEALTH AND ENVIRONMENTAL SCIENCES API PUBLICATION NUMBER 4531 AUGUST 1991 American Petroleum Institute 1220 L Street. Northwest 11 Washington, D.CL 20005 A
2、PI PUBL*4531 91 I 0732290 0101402 4 Chemical Fate and Impact of Oxygenates in Groundwater: Solubility of BTEX from Gasoline-Oxygenate Compounds Health and Environmental Sciences Department PUBLICATION NUMBER 4531 AUGUST 1991 PREPARED UNDER CONTRACT BY: J.F. BARKER, R.W. GILLHAM, L. LEMON, C.I. MAYFI
3、ELD, M. POULSEN, AND E.A. SUDICKY INSTITUTE FOR GROUNDWATER RESEARCH DEPARTMENT OF EARTH SCIENCES UNIVERSITY OF WATERLOO WATERLOO, ONTARIO, CANADA American Petroleum Institute FOREWORD API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL,
4、 STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND TIONS UNDER LOCAL, STATE, OR FEDERAL LAWS. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED AS FACTURE, SALE
5、, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COVERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED BILITY FOR INFRINGEMENT OF LElTERS PATENT. API IS NOT UNDERTAKING TO MEETTHE DUTIES OF EMPLOYERS, MANU- SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGA- GRANTING ANY RIGHT, BY IMPLIC
6、ATION OR OTHERWISE, FOR THE MANU- IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIA- Copyright O 1991 American Petrolem Instimte API PUBL*453L 91 W O732290 OLOL404 8 ACKNOWLEDGMENTS The following people are recognized for their contributions of time and expertise in the preparation of t
7、his report: 7- API Staff Contacts Roger Claff, HESD Bruce Bauman, HESD Members of the SoiVGroundwater Technical Task Force Oxygenates Impact on Groundwater Contamination Proiect Team AI Liguori, Exxon Research and Engineering Dorothy Keech, Chevron Oil Field Research Eugene Mancini, ARCO Victor Krem
8、esec, Amoco Research William Rixey, Shell Development Funding for this study was provided by the American Petroleum Institute (API) and by the Ontario University Research Incentive Fund (URIF). The laboratory experiments and analyses were performed by Shirley Chatten. Ed Sudicky provided the groundw
9、ater transport model and assisted with the modelling exercise. The authors would like to thank Don Mackay and Stan Feenstra for discussions and review of an earlier draft of the manuscript. API PUBL*453L 91 0732290 OLOL405 T H TABLE OF CONTENTS INTRODUCTION . 1-1 HYDROCARBON SOLUBILITY AND THE EFFEC
10、TS OF OXYGENATE COSOLVENTS . PREVIOUS RESEARCH AND THE APPROACH SELECTED 1-2 LABORATORY EXPERIMENTS . 2-1 EXPERIMENTAL METHODS 2-1 TIME-TO-EQUILIBRIUM EXPERIMENTS . 2-2 EFFECT OF VARYING AQUE0US:GASOLINE PHASE RATIOS 2-4 AQUEOUS BTEX CONCENTRATIONS FROM OXYGENATE-GASOLINE MIXTURES 2-6 COSOLUBILITY E
11、FFECTS OF HIGH METHANOL CONTENTS . 2-7 VOLUME PROPORTIONS OF BTEX . 2-10 PREDICTING AQUEOUS CONCENTRATIONS OF BTEX FROM PS-6 GASOLINE . 3-. PARTITIONINGTHEORY 3-1 EFFECT OF AQUE0US:GASOLINE PHASE RATIO ON BTEX SOLUBILITY . 3-3 PREDICTING AQUEOUS BTEX CONCENTRATIONS FROM GASOLINE EFFECT OF A HYDROPHI
12、LIC OXYGENATE ON THE AQUEOUS EFFECT OF A HYDROPHOBIC OXYGENATE ON THE AQUEOUS CONTAINING OXYGENATE ADDITIVES . 4-1 CONCENTRATIONS OF BTEX . 4-2 CONCENTRATIONS OF BTEX . 4-6 ENHANCED SOLUBILITY OF BTEX BY HYDROPHILIC SOLVENTS . 4-8 Cosolvencv Theory 4-8 -. Effect of Methanol on Benzene Solubilitv . 4
13、-11 -. Effect of Methanol on BTEX Solubilitv From Gasoline 4-14 Summary Of Cosolvencv Effects 4-21 DISSOLVED BTEX PLUMES RESULTING FROM SPILLS OF METHANOL-GASOLINE MIXTURES 4-21 API PUBL*453L 91 0732290 OLOL4Ob L I Effect of Aqueous:Gacoline Phase Ratios at Hiaher Methanol Contents 4-19 Methanol Par
14、titioninq 4-21 Successive Batches 4-22 BTEX Plumes . 4-24 CONCLUSIONS 5-1 REFERENCES . 6-1 APPENDIX A . SPECIFICATIONS AND COMPOSITION OF PS-6 GASOLINE . A-1 APPENDIX B . ANALYTICAL METHODS/QUALITY CONTROL RESULTS B-1 APPENDIX C . PARAMETER VALUES USED IN CALCULATIONS C-1 APPENDIX D . RELATIONSHIP B
15、ETWEEN NORMALIZED AND UNNORMALIZED DATA D-1 APPENDIX E . SUCCESSIVE BATCH SIMULATIONS E-1 API PUBL*4531 91 O732290 01OLL)OIz 3 m Table 2-la. Table 2-1 b. Table 2-2. Table 2-3. Table 2-4. Table 2-5. Table 2-6. Table 3-1. Table 4-1. Table 4-2. Table 4-3. Table 4-4. Table 4-5. Table 4-6. Table 4-7. Tab
16、le 4-8. Table 4-9. LIST OF TABLES Average aqueous BTEX concentrations for various water:gasoline volume ratios. 2-5 Average dissolved benzene concentrations for various water:benzene volume ratios. . 2-5 Average experimental aqueous oxygenate and BTEX concentrations for various gasoline-oxygenate mi
17、xtures 2-7 Average aqueous BTEX concentrations with varying methanol content of the aqueous phase (v/v) at equilibrium . 2-8 Average aqueous benzene concentration with varying methanol content of the aqueous phase at equilibration . 2-9 Effect of initial aqueous methano1:gasoline ratio on aqueous BT
18、EX concentrations . 2-10 BTEX composition of PS-6 gasoline (volume percent). 2-1 1 aqueous:gasoline phase ratios. . 3-4 Calculated dissolved BTEX concentrations for varying Calculated aqueous methanol and BTEX concentrations for gasoline with varying methanol content. . 4-4 Calculated aqueous BTEX c
19、oncentrations for gasoline with varying MTBEcontent 4-6 Calculated aqueous benzene concentration in water-methanol mixtures contacting pure benzene. 4-12 Calculated aqueous BTEX concentrations in water-methanol Calculated aqueous BTEX concentrations in water-methanol mixtures contacting gasoline (lo
20、w methanol content). . 4-1 7 mixtures contacting gasoline (high methanol content). 4-18 Effect of aqueous:gasoline phase ratio on aqueous BTEX concentrations for gasoline contacted with 50% aqueous methanol by volume. . , . 4-19 Aqueous benzene concentrations (mg/L) in successive batches of water ex
21、posed to gasoline pools with varying methanol content 4-23 Aqueous benzene concentrations (mg/L) in successive batches of water exposed to M-85 fuel pools of varying size. . 4-24 Transport parameters for groundwater flow modelling. 4-25 API PUBL*453L 91 I 0732290 OLOL408 5 I Figure 1-1. Figure 2-1.
22、Figure 4-1. Figure 4-2. Figure 4-3. Figure 4-4. Figure 4-5. Figure 4-6. Figure 4-7. Figure 4-8. Figure 4-9. LIST OF FIGURES Ternary phase diagram for gasoline-water-methanol at 20C 1-3 Results of time-to-equilibrium experiments for dissolved BTEX from gasoline. 2-3 Effect of methanol content on aque
23、ous benzene concentration . 4-4 Effect of initial methanol content in gasoline on aqueous BTEX concentrations 4-5 Effect of MTBE content on aqueous BTEX concentrations 4-7 Cosolvency effect of methanol on aqueous benzene concentration (linear scale) at an aqueous methanokbenzene phase volume ratio O
24、f10 . 4-13 Cosolvency effect of methanol on aqueous benzene concentration (logarithmic scale) at aqueous methanokbenzene phase volume ratios of 10 and 1 4-13 Cosolvency effect of methanol on aqueous BTEX concentrations (linear scale) 4-15 Cosolvency effect of methanol on aqueous BTEX concentrations
25、(logarithmic scale) 4-16 as a function of KO, . 4-18 Effect of aqueous:gasoline phase ratio (VJVJon BTEX concentration for gasoline contacted with 50% aqueous methanol (v/v) 4-20 Figure 4-10. Examples of dissolved benzene plumes arising from spills of Figure 4-1 1. Examples of dissolved benzene plum
26、es arising from spills of Figure 4-12. Examples of dissolved benzene plumes arising from spills of Figure 4-13. Examples of dissolved methanol plumes arising from spills of Figure 4-14. Examples of dissolved methanol plumes arising from spills of gasoline with no methanol. 4-27 gasoline with 50% met
27、hanol. 4-28 gasoline with 85% methanol. 4-29 gasoline with 50% methanol. 4-30 4-31 gasoline with 85% methanol. Figure 4-15. Examples of dissolved benzene plumes arising from spills of gasoline with 85% methanol content for initial water:gasoline volume ratio (VJV,) = 0.1. 4-32 Figure 4-16. Examples
28、of dissolved benzene plumes arising from spills of gasoline with 85% methanol content for initial water:gasoline volume ratio (VJV,) = 1.0. 4-33 Figure 4-17. Examples of dissolved benzene plumes arising from spills of gasoline with 85% methanol content for initial water:gasoline volume ratio (VJV,)
29、= 10. 4-34 API PUBLM4531 91 0732290 0101410 3 = EXECUTIVE SUMMARY Oxygenate compounds such as ethers and alcohols have been increasingly added to gasoline to improve octane ratings and/or reduce vehicle emissions of pollutants such as carbon monoxide. The increased use of oxygenate additives has rai
30、sed questions as to the effects of these additives on the water solubility of gasoline constituents such as benzene, toluene, ethylbenzene, and xylenes (collectively referred to as BTEX). In the event of a spill of an oxygenate fuel to groundwater the oxygenate may act as a cosolvent, dissolving hig
31、her concentrations of BTEX in the groundwater than would be dissolved from neat gasoline. This laboratory study was conducted to investigate the cosolubility effect of oxygenates. Oxygenates studied include methanol, methyl tertiary-butyl ether (MTBE), ethanol, tertiary-amyl methyl ether (TAME), and
32、 isopropyl ether. This study was conducted as a component of a large-scale research effort to evaluate the fate and impact of oxygenates in groundwater. Other components of the research effort include laboratory experiments on the sorptive properties and biodegradation kinetics of oxygenates and BTE
33、X in gasoline, and natural gradient tracer studies conducted in a shallow sand aquifer at Canada Forces Base Borden, Ontario, Canada. The results of these studies will be published separately. STUDY OBJECTIVES The specific objectives of this study were to: o evaluate through a series of laboratory e
34、xperiments the effects of waterfuel ratio and oxygenate addition on the aqueous solubility of BTEX; predict i ng aqueous BTEX conce nt rations contacti ng oxygenate fuels ; and o apply this model in a hydrogeological context to characterize dissolved BTEX and oxygenate plumes that could result from
35、fuel spills. o develop from cosolvency theory a calibrated model capable of ES-1 API PUBL*4531 91 W 0732290 OLOL4LL 5 E These objectives, and study findings relative to these objectives, are summarized below. EFFECTS OF WATER:FUEL RATIO AND OXYGENATE ADDITION ON THE AQUEOUS SOLUBILITY OF BTEX The aq
36、ueous solubilities of gasoline constituents such as benzene, toluene, ethylbenzene, and xylene depend on the proportions of gasoline, water, and oxygenate brought into contact (Le., the mixed composition). For a fuel of fixed composition, such as an oxygenate-free gasoline or a gasoline with fixed o
37、xygenate content, aqueous BTEX solubility (at fixed temperature and pressure) depends only on the proportions of water and fuel brought into contact, conveniently expressed as a water:fuel ratio. * Determination of Equilibration Time The term aqueous solubility implies aqueous solubility at equilibr
38、ium. Equilibrium solubilities are static and do not change with time. Through a series of batch experiments, an equilibration time of four hours was found to be sufficient to ensure attainment of compositional equilibrium between aqueous and fuel phases. A four hour equilibration time was employed i
39、n all subsequent laboratory experiments. - Effect of Water:fuel Ratio on Aqueous BTEX Solubility from Oxvaenate-free Gasoline The first experiments investigated the effect on aqueous BTEX solubility of varying the volume ratio of water brought into contact with an oxygenate-free gasoline. These expe
40、riments found that BTEX solubility varied only insignificantly with water:fuel ratio, * This water:fuel ratio is the volume ratio of water to fuel prior to mixing. Following mixing and equilibration, the mixture will separate into gasoline and aqueous phases, at a unique phase volume ratio. For oxyg
41、enate-free gasoline, the water and fuel are mutually insoluble, and the water:fuel ratio and equilibrium phase ratio can be considered equal. For oxygenate gasoline, however, a substantial proportion of the oxygenate is transferred to the water phase upon equilibration. The water:fuel ratio and equi
42、lbrium phase ratio are consequently considerably different. ES-2 API PUBL*4531 91 I 0732290 0101li12 7 I for ratios less than 20:l (by volume, v/v). The total BTEX concentration remained nearly constant at about 11 8 mg/L at these ratios. At higher ratios aqueous BTEX solubility was observed to decr
43、ease with increasing ratio. - Effect of Oxvgenate Addition on Aqueous BTEX Solubility Subsequent experiments evaluated the effect of oxygenate additives on aqueous BTEX solubility. Oxygenate addition reduces by dilution the proportion of BTEX in gasoline. Consequently for oxygenate fuels, a lower pr
44、oportion of BTEX is available for dissolution in the aqueous phase. All other physical considerations aside, the presence of oxygenates should tend to reduce the aqueous solubility of BTEX. Most oxygenates, however, have very high solubilities or are completely miscible in water. At reasonably low e
45、quilibrium phase ratios, an aqueous phase in equilibrium with an oxygenate fuel will have a high oxygenate concentration. Gasoline organics such as BTEX are more soluble in concentrated aqueous oxygenate than in water alone. This preferential solubility, referred to in this study as the cosolubility
46、 effect, tends to increase the aqueous phase solubility of BTEX from oxygenate fuels. The presence of oxygenates in gasoline thus tends to decrease BTEX solubility by dilution and increase BTEX solubility by the cosolubility effect. The relative significance of these two offsetting tendencies were i
47、nvestigated in the oxygenate experiments. Methanol and MTBE were selected as the oxygenates for these studies, in part because of their differing solubilities from gasoline. Methanol is hydrophilic and partitions preferentially into the aqueous phase, whereas MTBE is hydrophobic and partitions prefe
48、rentially into the gasoline phase. The findings of the laboratory experiments on the effect of oxygenate addition were as follows: ES-3 API PUBL*453L 91 0732290 OLOL4L3 9 W a For an initial (prior to mixing) waterfuel ratio of 10:l (vh), the aqueous phase BTEX concentration at equilibrium was found
49、to decrease linearly with increasing initial MTBE content of the gasoline. No cosolubility effect of MTBE was observed. For an initial MTBE content of 15% (v/v) in gasoline, contacted with water at an initial water:fuel ratio of 1O:l (v/v), the aqueous BTEX solubility was found to be 121.5 mg/L. a For an initial water:fueI ratio of 1O:l (v/v), the aqueous phase BTEX concentration at equilibrium was found to remain relatively constant with increasing initial methanol content of the gasoline. The observed BTEX solubility was found to be about 120 mg/L, regardless of the initial methan
