Environ. Sci. Technol. 1985, 19, 919-924
Interactions of Aqueous Metal Ions with Organic Compounds Found in Coal Gasification: Model Systems Andrew
D. Jorgensent
University of Southern Indiana, Evansville, Indiana 477 12
Joseph R. Stetter" and Vassllis C. Stamoudls Energy and Environmental Systems Division, Argonne National Laboratory, Argonne, Illinois 60439
The interaction of metal ions with organic compounds indigenous to coal gasification materials was studied in a model system. Aqueous solutions of Fe3+,Cu2+,and Ni2+ in contact with mixtures of selected organic compounds were examined by using chromatographic and spectroscopic techniques. Aqueous Fe3+ ions and, to a lesser extent, Cu2+ ions extract organic compounds from the nonaqueous layer and associate with these organic molecules in aqueous solution. Quantitative aspects of the extraction process were measured by gas chromatographic methods, while spectroscopic measurements were used to characterize the association between metal ions and organic molecules. The interaction of the metal ion solutions was compared to that of buffers of similar pH. The behavior of both the iron and copper ion solutions differed from that of the buffers. Introduction Coal gasification byproduct condensates are very complex mixtures. Specific organic and inorganic compounds present in such condensates have been identified (1-10). Although condensible organics will be recycled in future commercial gasification plants, the potential will remain for accidental release of a broad range of chemicals into the environment. Aquatic toxicity and the transport of toxic chemicals within the ecosystem depend on the specific chemical species present. Organometallic compounds play a substantial role in biological systems through their effect on enzyme activity and their pharmacologic and toxicologic properties. Equally important in ecological and environmental studies are trace metal species ( I I ) , whose speciation is a consideration in developing geochemical models (11-13). Clearly, an understanding of the chemical interactions of synfuel materials with the environment is needed to assess and model the potential health and environmental effects of coal conversion. Most chemical characterizations of coal conversion products have dealt with the speciation of organic and inorganic compounds as distinct issues (1-10). Previous studies typically report the composition of the organic materials and the composition of the inorganic materials separately (14). Although evidence for organometallic associations in coal and coal products has been reported, the presence and precise nature of these associations are only speculative (15,16).Metal ion release and interaction with naturally occurring organics (e.g., humic materials) have been studied (17). However, no study of the direct interaction of metal ions with coal gasification organics has been reported. In a closely related study (18), 10 compounds representative of chemicals present in coal gasification process streams were placed in an organic solvent and exposed to aqueous metal ions. In this experiment, which simulated t Present address: Allegheny College, Meadville, PA 16335.
0013-936X/85/09 19-0919$01.50/0
Table I. Constituents of Model Solutions in Toluene solution compound I isooctaneb 2,4-dimethylaniline (DMA) naphthaleneb (N) quinoline (4) 3-phenylpyridine (3PP) 4-aminobiphenyl (4AB) I1 p-nitroaniline (NA) diphenylamine (DPA) 4-azafluorene (4AF) dibenzylamine (DBA)
retention time, mina 0.9 3.6 6.3 6.7 8.6 13.1 9.4 10.5 11.6 12.5
M* 114.23 121.18 128.19 129.16 155.20 169.23 138.13 169.23 167.22 197.28
Chromatographic conditions are described in the text. Internal standards mesent in both solutions I and 11.
the release of coal conversion organics into a real environment, strong interactions were observed between these process chemicals and aqueous Fe3+ions. This research suggested that studying the interactions of metal ions with the complex matrix of an actual coal conversion condensate would yield specific information about the chemical species involved and the mobility of coal conversion constituents if released to the environment. The results of a study of the interactions of aqueous metal ions with organic compounds found in coal gasification materials are presented in two papers. This paper deals with the model system that elucidates interactions between specific metal ions and organic chemicals, and a subsequent paper (19) discusses experiments to quantify the effects of exposing authentic coal gasification condensates to aqueous iron ions. Experimental Section Model Solutions. Several nitrogen-containing organic compounds were chosen for this model study based on known liquid synthetic fuel compositions. Particular attention was given to aromatic amines and azaarenes, because these compounds are known to interact with aqueous metal ions (18) and are recognized as health hazards (1, 4). For the chromatography experiments, two solutions were prepared in a toluene solvent, each containing four compounds with concentrations of 200 ppm by weight and two internal standards (isooctane and naphthalene) at 400 ppm by weight (Table I). These concentrations were chosen because, in a typical coal gasification oil/tar matrix, the basic constituents are present in concentrations of several hundered parts per million by weight (19). The chemicals were all of reagent-grade purity, with the exception of quinoline, which was a practical grade with a minimum purity of 85%. Aqueous solutions of iron(II1) chloride hexahydrate, nickel(I1) chloride hexahydrate, or anhydrous copper(I1) chloride were prepared in distilled water a t metal ion concentrations of 200 ppm by weight. Solutions of lower
@ 1985 American Chemical Society
Environ. Sci. Technol., Voi. 19, No. 10, 1985
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concentration (i.e., 20 and 2 ppm) were obtained by dilution. These choices of ions and concentrations were made after considering that a concentration of 3 ppm of Fe3+ion in a coal gasification process stream aqueous/oil emulsion had been reported (18) and that natural streams may contain up to 10 times this amount. The maximum concentration used in this study (200 ppm) would approximately yield a 1:l ratio between metal ions and the total number of organic amine molecules. Also, buffer solutions with pH values of 2-7 were prepared by using appropriate concentrations of acetic acid and sodium acetate in distilled water. Gas Chromatography. All solutions were analyzed on a Varian 3740 gas chromatograph (GC) with a flame ionization detector connected to a Hewlett-Packard 3390A integrator. A 6-ft column of l/s-in. i.d. stainless steel, packed with 80/100 mesh WAW and with a liquid phase of 10% Apiezon L and 2% KOH (Alltech Associates, Arlington Heights, IL), was used. The column temperature was set initially a t 90 "C; after a 1-min hold, it was increased a t a rate of 18 "C/min until the maximum temperature of 210 "C was reached. Injection volumes were approximately 1.5 pL for both aqueous and organic samples. Area counts from the integrator were corrected for variations in injection volume and detector efficiency by comparison with the internal standards. The precision of all measurements was within 5 % ; inaccuracies could have been approximately twice this value. It was assumed that the internal standards were not affected by these experiments, except for a slight (-2%) solubility of isooctane in water. After correction for this factor, the consistency between the results for each of the standards gave weight to this assumption. In a typical experiment, a small volume of one of the toluene solutions (e.g., 300 pL) was mixed with a like volume of an aqueous metal ion solution. The solutions were mixed by shaking and repeated syringe injection of one phase into the other. Samples were removed periodically from the bulk of the organic and aqueous phases and analyzed by GC to determine the concentration of the organic chemicals listed in Table I. This procedure was repeated until an apparent equilibrium value was achieved. In this set of experiments, the aqueous phases, as well as the organic phases, were analyzed over time. Equilibration generally occurred in less than 100 h, but several solutions were studied for 200 h to ensure that chemical equilibrium had been achieved. Spectroscopy. To determine the partitioning and speciation of any compound between the aqueous and organic layers, similarly prepared solutions were examined by using ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. Hydrochloric acid with a pH of 2.88 was studied spectroscopicallyand compared to the 40-ppm Fe3+ solution, which had the same pH. Stock solutions were made of 2,6-dimethylquinoline (DMQ), quinoline (Q), or 3-phenylpyridine (3PP) in methylene chloride (dichloromethane) or toluene, and dilutions of these stock solutions were prepared as required. Since methylene chloride is slightly soluble in water and exhibits spectral absorption near 310 nm, all data were taken with water in the reference cell, saturated with methylene chloride. A Cary Model 14 spectrophotometer was used to obtain absorption spectra for all original solutions and for the phases separated after mixing. Fluorescence spectra were measured on a Perkin-Elmer MPF-2A fluorescence spectrometer. The excitation wavelength was fixed, and emission wavelengths were scanned. An excitation wave920
Environ. Sci. Technoi., Vol. 19, No. 10, 1985
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40
60
80
100
120
140
160
160
200
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Flgure 1. Effect of aqueous Fe3+ on model solution component concentrations.
length was chosen such that the separate stock solutions exhibited essentially no fluorescence,but the aqueous layer was fluorescent after it had been in contact with one of the organic solutions. In a typical spectroscopy experiment, 3 mL of an aqueous solution and 1.5-3 mL of an organic solution were thoroughly mixed by shaking and repeated syringe injection of one phase into the other. Spectroscopic measurements were made before and after the solutions had been mixed.
Results Chromatography. When a toluene solution containing the Table I compounds was contacted with an aqueous Ni2+or Cu2+(200 ppm) solution, no decrease in concentration of any compound other than dibenzylamine (DBA) was detected by GC analysis. Because DBA is rather soluble in water, it would be expected to migrate. However, contact with the aqueous Fe3+solution caused considerable transport of several species from the toluene to the aqueous layer. The equilibrium percentage of 2,4-dimethylaniline (DMA), Q, 3PP, or 4-azafluorene (4AF) transported from the organic phase when in contact with aqueous Fe3+was found to depend on the concentration of Fe3+(Figure 1). Concentrations of p-nitroaniline (NA), 4-aminobiphenyl (4AB), and diphenylamine (DPA) in the toluene solution were not significantly changed after contact with the aqueous Fe3+solutions. In all cases, DBA was completely extracted by the aqueous Fe3+solutions. Chromatographic analysis of the aqueous solutions accounted for 100% of the DBA, but for only 30% of the extracted Q, DMA, 3PP, and 4AF. To isolate the classical acid/base extraction behavior of the organic chemical from true metal ion/organic interactions, a series of buffer solutions was used to extract toluene solutions containing the target compounds. The equilibrium percentages extracted from the toluene phase are summarized in Table 11, and the results for 3PP, Q, and DMA are compared in Figure 2. The buffer with a pH of 2.55 has the same pH as the 200-ppm Fe3+ salt solution. The amount of compound extracted increases with the increasing basic strength of the compounds. Chromatographic analysis of the aqueous phase buffer for the organic compounds accounted for 100% of the DBA extracted from the water, but for only about 30% of the extracted DMA or 3PP. When metal ions are present, organic compounds are extracted much more slowly (over several hours) than with acid alone. A comparison of pH extraction (Table I1 and Figure 2) with the results for Fe3+ solutions (Figure 1) shows that in most cases the Fe3+ solution extracted
Table 11. Concentration Changes for the Organic Solution Components after Contact with Aqueous Buffers organic compound
PKC
2.0
2.55
2,4-dimethylaniline quinoline 3-phenylpyridine 4-aminobiphenyl p-nitroaniline diphenylamine 4-azafluorene dibenzylamine
4.89 4.81 4.80 4.22 1.00 0.77
-89 -90 -5 1
-70
-18
-65 -17 +5 -6 +6 -14 -100
concentration change, %, by pH of buffer 4.0 3.0 3.5 -44 -43 -5 +1 -3
-26 -24
-13
-12 +2
-1 -2
+5 -4
-6 +4 -2
-100
-100
+10 -4 +6
5.0
7.0
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+1 +1 +27
+4 0 -64.5
-1
-100
+5 -1 -1 -1
-5
pK. of the conjugate acid (20).
3-phenylpyridine 2,4-dimethylaniline and quinoline
330
320
310
300
Wavelength (nm)
Figure 3. Absorption spectra of aqueous 40-ppm Fe3+solution after contact with 30 ppm of 2,6-dimethylquinoline in CHPCI,. Reference beam is aqueous 40-ppm Fe3+ solution saturated with CH,CI,.
increase in absorbance did not exceed 0.04. An aqueous HC1 solution (pH 2.88) was placed in contact with the 30-ppm DMQ solution. A single peak a t 316 nm with an absorbance of 0.815 was observed after about 1min. This absorbance increased to 0.90 after about 90 min. The two major differences between the effects of the HCl solution and the Fe3+solution on the DMQ solution were the speed a t which the absorbance developed and the number of maxima. The organic layer containing the DMQ exhibited a decrease in absorbance when in contact with the aqueous Fe3+. The absorbance of the peak a t 321 nm decreased from 1.13to 0.63 after 45 h, indicating that approximately half of the DMQ left the organic phase. This finding is consistent with an confirmed by previous experiments (18). A series of experiments parallel to those just described was performed with an aqueous Cu2+solution. A 20-ppm aqueous Cu2+solution exhibited an absorption maximum a t 210 nm with an absorbance of 0.38. This absorbance Environ. Sci. Technol., Vol. 19, No. 10, 1985 921
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Flgure 5. Molar ratlo method plot. Ordinate is 300-nm absorbance of aqueous 2-ppm Fe3+solution (buffered, at pH 3.0) after contact with quinoline in CH2C12solutions. Abscissa is ratio of molar concentrations in water (L = quinoline; M = Fe3+).
0 230
220
210
Wavelength (nm)
Flgure 4. Absorption spectra of aqueous 20-ppm Cu2+ solution after contact with 30 ppm of 2,64imethylquinoiine in CH2C12. Reference beam is water saturated with CH2C12.
increased to 0.55 and shifted to a maxima at 214 nm after 160 min of contact with the 30-ppm DMQ solution. This effect is illustrated in Figure 4 (note that DMQ does not absorb a t 214 nm). The copper solution had negligible absorbance in the spectral region where DMQ absorbs (320 nm). The absorbance of the aqueous layer at 320 nm also increased in 160 min, suggesting that a measurable amount of DMQ entered the aqueous phase. The stoichiometric ratio in this case was 1.6 times more copper than DMQ. If Fe3+ or Cu2+does in fact form a complex with extracted organics, absorption spectroscopy using the molar ratio method can be used to indicate the number of ligands around the metal ion (21). For this experiment, solutions of various concentrations of Q in toluene were prepared and placed in contact with an aqueous Fe3+solution. (The Fe3+solution was diluted to a concentration of 2 ppm of Fe3+ and buffered to a pH of 3 with a mixture of acetic acid and sodium acetate.) The Q concentrations were varied from 1to 20 times the molar concentration of the aqueous Fe3+. However, because only 40% of the Q entered the aqueous phase, the concentration of Q was corrected by this amount in the molar ratio plot calculations. Figure 5 is a plot of absorption a t 300 nm vs. the molar ratio of ligand to metal ion. The intersection of the linear portions occurs at a ratio of approximately 4. The change in slope for this plot is from 0.21 to 0.14. Fluorescence Spectroscopy. The aqueous 40-ppm Fe3+solution and the 30-ppm DMQ solution in methylene chloride described above were studied a t an excitation wavelength of 323 nm. When excited with radiation of this energy, DMQ in methylene chloride exhibited fluorescence at 340-450 nm of about 1% of full scale (FS). Neither aqueous Fe3+nor the organic solvent fluorescence under these conditions. However, when the organic phase was in contact with aqueous Fe3+or HC1, a strong fluorescence was observed in the aqueous solution. In the case of Fe3+,the wavelength of maximum emission was 430 nm, with a relative intensity of 6% FS after about 2 min. This intensity increased to 922
Environ. Sci. Technol., Vol. 19, No. IO, 1985
47% FS after 2 h. As in the absorption spectroscopy results, the HC1 solution produced a more rapid and more pronounced response than did the Fe3+solutions. Within 1min, an intensity of 95% FS was seen at a wavelength of 415 nm. Similar fluorescence experiments were performed with an aqueous Cu2+solution (20 and 200 ppm) by using an excitation wavelength of 323 nm, where no emission by aqueous Cu2+is observed. When the organic DMQ solution was in contact with the aqueous phase containing the 200-ppm Cu2+ solution, an emission of 36% FS with a maximum at 415 nm was observed after 1 h of contact. The pH of this Cu2+solution was 5.3. An experiment was also performed with a buffer a t the same pH. The broad emission around 415 nm was observed, but the intensity was only 5-10% FS. Discussion In the previous work (18),several possible mechanisms, including simple protonations and complex formation, were proposed for the observed transport of organic molecules in aqueous/organic systems. However, no evidence to support a specific process was available. In the experiments reported here, several techniques-including chromatography, ultraviolet-visible spectroscopy, and fluorescence spectroscopy-were used to examine the same solutions and to observe specific interactions. The transport of basic nitrogen-containing organic compounds between organic and aqueous phases is dominated by pH effects. All three measurement techniques (chromatography and absorption and emission spectroscopy) show that these compounds are rapidly extracted from the organic phase when exposed to acidic waters. The amount extracted depends on the base strength, or pK,, of the compound and the acidity of the water (see Table 11). However, complete extraction is not approached until the pH is well below those studied here (C2.5). In addition, however, both chromatographic and spectroscopic measurements support the conclusion that formation of organic/metal ion complexes is simultaneous with pH extraction. Since chromatographic analysis of the solutions could not account for all of the extracted compound, some of the organic chemicals might have been altered to a nonchro-
matographable form, been changed to degradation products not analyzed here, or concentrated a t the interface. The comparative absorption spectroscopic studies of Fe3+ solutions (Figure 3) and H+ solutions indicate that when the metal ion is present, slightly more DMQ is extracted than with acid, but the extraction proceeds more slowly. In addition, the absorbance characteristics of the aqueous phase differ in that Fe3+causes a double maxima spectrum, whereas the acid yields a single maximum. Absorption spectroscopic studies of Cu2+solutions (Figure 4) clearly show that DMQ exerts a ligand field effect, modifying the energy level of the light absorption a t 214 nm. In this case, the DMQ enters the aqueous phase and clearly associates with the metal ion. The different fluorescence maxima (415 vs. 430 nm) for the acid solution and for a Fe3+solution a t the same pH (3.0) indicate differences between protonated DMQ and DMQ associated with Fe3+. The effects of the protonated species were reduced for the Cu2+fluorescence studies because the pH was 5.3. In this case, where pH effects are substantially reduced, the effect of the metal ion is clearly observed, and Cu2+ caused a substantially increased fluorescence over the simple buffer. This result is the reverse of our observations of Fe3+fluorescence at low pH (3.0), where pH effects are dominant. The specific interaction of Q and Fe3+is elucidated by the molar ratio plot (Figure 5). Here the organic compound is clearly extracted by the aqueous phase, and the Q is associated with the Fe3+. To postulate an octahedral or tetrahedral complex with four ligands around a central Fe3+ is entirely reasonable.
Conclusions The interaction of aqueous solutions and organic compounds environmentally significant to synfuel industries is an important and complex topic. Our prior work suggested several possible mechanisms for transport of chemicals from an organic phase to an aqueous phase and the potential effects of ubiquitous aqueous metal ions such as Fe3+ (18). The work reported here extends our understanding of these phenomena and helps to clarify some aspects of this complex problem. The particular species of metal ion is extremely important, as is shown by the very strong interaction of DMQ with Fe3+,the lesser effects observed for Cu2+,and the absence of an effect with Ni2+ ions. Our major findings and conclusions are as follows: (1) Simple protonations cause substantial and rapid transport of nitrogen species from organic to aqueous phases. (2) Some metal ions, especially Fe3+,can significantly enhance organic compound partitioning from organic to aqueous streams, and these effects may predominate a t higher pH. The kinetics of this process is slower than for protonations, and effects may require several days to reach chemical equilibrium. (3) Aqueous Fe3+ is in equilibrium with a four-ligand quinoline complex a t low concentrations. (4)Ecological models must take into account chemical speciation when transport of organic or inorganic substances in the environment is considered. (5) In the case of synthetic fuel multiphase systems (such as a wastewater/oil/tar) recovered for treatment or analysis, the phases cannot be viewed independently because components in one phase can greatly affect the concentrations and types of chemical species present in the other phases. It was difficult in these experiments to quantitatively account for all of an organic species after its contact with
the aqueous layer. For example, Fe3+caused 80% of the DMA and Q to migrate from the organic layer, but only about 30% of these compounds was found (by chromatographic analysis) in the aqueous layer. The missing DMA and Q could be ionized, complexed, or adsorbed a t the interface of the aqueous and organic phases. We have not yet studied the interfacial aspects of this problem; such work remains to be performed.
Acknowledgments We much appreciate the data collection efforts of Harold Tenbarge a t the University of Southern Indiana. Registry No. DMA, 95-68-1; N, 91-20-3; Q, 91-22-5; 3PP, 1008-88-4; 4AB, 92-67-1; NA, 100-01-6; DPA, 122-39-4; 4AF, 244-99-5; DBA, 103-49-1;Fe3+,20074-52-6; Cu2+,15158-11-9;Ni, 22541-64-6; isooctane, 540-84-1.
Literature Cited (1) Stamoudis, V. C.; Bourne, S.; Haugen, D. A.; Peak, M. J.; Reilly, C. A., Jr.; Stetter, J. R.; Wilzbach, K. In “Coal Conversion and the Environment: Chemical, Biological, and Ecological Considerations”; Mahlum, D. D.; Gray, R. H.; Felix, W. D., Eds.; U S . Department of Energy: 1981; CONF-80-1039, NTIS (DE82000105),pp 67-95. (2) Luthy, R. G.; Stamoudis, V. C.; Campbell, J. R.; Harrison, W. J . Water Pollut. Control Fed. 1983, 55, 196-207. (3) Willey, C.; Iwao, M.; Castle, R. N.; Lee, M. L. Anal. Chem. 1981,53,400-407. (4) Wilzbach, K. E.; Stetter, J. R.; Reilly, C. A., Jr.; Willson, W. G. “EnvironmentalResearch Program for Slagging Fixed Bed Coal Gasification”; Argonne National Laboratory: Argonne, IL, 1981; ANL/SER-1. (5) Davidson, C. I.; Sanathanan, S.; Stetter, J. R.; Flotard, R. D.; Gebert, E. Environ. Monit. Assess. 1982, 1, 313-335. (6) Epler, J. L.; Young, J. A.; Hardigree, A. A.; Rao, T. K.; Guerin, M. R.; Rubin, I. B.; Ho, C. H.; Clark, B. R. Mutat. Res. 1978, 57, 265-276. (7) Schweighardt, F. K.; White, C. M.; Friedman, S.; Shultz, J. L. In “Organic Chemistry of Coal”;American Chemical Society: Washington, DC, 1978; ACS Symp. Ser. No. 71, pp 240-257. (8) Klein, D. H.; Andren, A. W.; Carter, J. A.; Emery, J. F.; Feldman, C.; Fulkerson,W.; Lyon, W. S.; Ogle, J. C.; Talmi, Y.; Van Hook, R. I.; Bolton, N. Environ. Sci. Technol. 1975, 9,973-979. (9) Sanathanan, L. P.; Reilly, C. A.; Marshall, S. A,; Wilzbach, K. E. “Health Effects of Synfuels Technology-A Review”; Argonne National Laboratory: Argonne, IL, 1981; ANL/ ES-111. (10) Felix, W. D.; Mahlum, D. D.; Weimer, W. C.; Pelroy, R. A.; Wilson, B. W. “Chemical/Biological Characterization of SRC-I1 Product and By-Products”; Pacific Northwest Laboratory: Richland, WA, 1980; PNL-SA-8813. (11) Jenne, E. A. In “Environmental Speciation and Monitoring Needs for Trace Metal-Containing Substances from Energy-Related Processes”;Brinckman, F. E.; Fish, R. H., Eds.; National Bureau of Standards: Washington, DC, 1981;NBS Spec. Publ. No. 618, pp 39-53. (12) Jenne, E. A.; Luoma, S. N. In “Biological Implications of Metals in the Environment”; National Technical Information Service: Springfield, VA, 1975; CONF-750929, pp 110-143. (13) Thayer, J. S. J. Organomet. Chem. 1974, 76, 265-295. (14) “EnvironmentalSpeciation and Monitoring Needs for Trace Metal-Containing Substances from Energy-Related Processes”; Brinckman, F. E.; Fish, R. H., Eds.; National Bureau of Standards: Washington, DC, 1981; NBS Spec. Publ. No. 618. (15) Taylor, L. T.; Hausler, D. W.; Aquires, A. M. Science (Washington, DC.) 1981, 213, 644-646. (16) Filby, R. H.; Sandstrom, D. R.; Lytle, R. W.; Greegor, R. B.; Khalil, S. R.; Ekambaram, V.; Weiss, C. S.; Grimm, C. A. In “Environmental Speciation and Monitoring Needs for Trace Metal-Containing Substances from Energy-ReEnvlron. Sci. Technol., Vol. 19,
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lated Processes"; Brinckman, F. E.; Fish, R. H., Eds.; National Bureau of Standards: Washington, DC, 1981; NBS Spec. Publ. No. 618, pp 21-38. Saar, R. A,; Weber, J. H. Environ. Sci. Technol. 1982,16,
Aqueous Solution";International Union of Pure and Applied Chemistry, Butterworth: London, 1965. (21) Yoe, Y. H.; Jones, A. L. Ind. Eng. Chem. Analy. Ed. 1944, 16, 111-115.
510A-516A.
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Stetter, J. R.; Stamoudis, V. C.; Jorgensen, A. D. Environ. Sci. Technol., following paper in this issue. Perrin, D. D. "Dissociation Constants of Organic Bases in
Received for review September 27, 1983. Revised manuscript received January 1,1985. Accepted April 17,1985. This work was supported by the US.Department of Energy under Contract W-31-109-Eng-38.
Interactions of Aqueous Metal Ions with Organic Compounds Found in Coal Gasification: Process Condensates Joseph R. Stetter" and Vassiiis C. Stamoudls Energy and Environmental Systems Dlvision, Argonne National Laboratory, Argonne, Illinois 60439
Andrew D. Jorgensent University of Southern Indiana, Evansville, Indiana 477 12
The acidic, basic, and neutral fractions of a coal gasification tar were analyzed by capillary column gas chromatography and gas chromatography/mass spectroscopy. Studies were performed to characterize the interactions between basic and neutral fraction components of the tar and aqueous solutions containing Fe3+. Basic organic constituents, especially pyridines and anilines, were affected by the presence of aqueous iron ions, while the neutral constituents were not.
Introduction In the preceding paper (I),a model system was used to elucidate the chemical interactions between aqueous metal ions and certain organic chemicals that are present in coal gasification condensates. However, no measurements have been made that would indicate the effect of exposing an authentic coal conversion material to the environment. In this paper, results are reported of a detailed analysis of (1) the basic and neutral components of a tar obtained from a condensate of a high-Btu coal gasification pilot plant and (2) the interactions of aqueous iron ions with the complex basic and neutral fractions of these samples. Because the basic and neutral fractions of coal gasification tars are known to contain a wide variety of chemicals, including several potent mutagens (2-14))the analysis, fate, and toxicology of these compounds are of great concern. Environmental and health consequences depend on the particular species present and the extent to which trace aqueous metal ions can influence the partitioning of real materials between aqueous and organic solutions.
Experimental Section Sample Description. The tar sample was taken from the HYGAS coal gasification pilot plant in Chicago. Operated by the Institute of Gas Technology, the plant is designed to produce 1.5 million ft3 of substitute natural gas equivalent per day from approximately 80 tons of coal. The plant was operating with a feed of bituminous coal (Kentucky no. 9 and no. 11)during run 84 when the ma+Present address: Allegheny College, Meadville, PA 16335. 924
Environ. Sci. Technol., Vol. 19, No. 10, 1985
terials studied in this investigation were collected. The HYGAS plant uses a three-stage fluidized-bed hydrogasification system; details of the facility and its operation have been published (25). The feed coal is pulverized, pretreated, and mixed with a recycling oil (initially toluene) to create a slurry. The coal slurry, which is fed into the top of the gasifier, is subsequently stripped of light oil and gasified in three stages at progressively higher temperatures. A sample was taken from the upper part of the gasifier, called the low-temperature reactor (LTR),where the first stage of gasification takes place. The LTR sample is representative of the chemicals formed during the gasification process and, in principle, provides information on the less-volatile materials formed (2). The basic and neutral fractions used in this study were obtained from the LTR condensate. Phase Separation and Distillation. The original LTR sample consisted of an aqueous layer and an oil layer. These layers were separated, and the oil was concentrated by rotary evaporation to a nonvolatile organic residue (NVO). The NVO residue (tar) was held a t 50 "C and 1 mmHg for 2 h after the solvents were removed. Acid-Base-Neutral pH Fractionation. The NVO sample was partitioned between 1.0 N HC1 and methylene chloride (dichloromethane) to give an aqueous layer containing the alkaline chemicals as salts and a methylene chloride layer containing the acidic and neutral chemicals. The latter were then partitioned between methylene chloride and 1.0 N NaOH to give an aqueous layer containing the acids as salts and a methylene chloride layer containing the neutral chemicals. The aqueous layers were each neutralized and back-extracted with methylene chloride to obtain separate methylene chloride extracts of the acidic, basic, and neutral chemicals. Analysis of Basic and Neutral Fractions. The organic compounds in the basic and neutral fractions were analyzed by capillary column gas chromatography (GC) to quantify individual compounds and by gas chromatography/mass spectrometry (GC/MS) to identify compounds. A Hewlett-Packard (HP) Model 5880A equipped with H P level 4 computer control and reporting capability was used for gas chromatographic analyses. Flexible, fused
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0 1985 American Chemical Society
