Environ. Sci. Technol. 1993, 27, 2831-2843

Coal Tar Dissolution in Water-Miscible Solvents: Experimental Evaluation

Catherine A. Peters' and Richard G. Luthy Department of Civil Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 that could be applied either in an in situ injection/recovery Coal tar, a dense nonaqueous phase liquid (NAPL), is a system or in an aboveground treatment operation. The common subsurface contaminant at sites of former man- primary objective of this work was to investigate the extent ufactured gas plants. A proposed remediation technology to which organic water-miscible solvents increase the is water-miscible solvent extraction, which requires un- solubility of coal tar and its constituent compounds. This derstanding of the effect of water-miscible solvents on the work was part of a larger project, presented in Luthy et solubility of coal tar. This study investigated this effect al. (7),aimed at investigating the feasibility of in situ and the extent to which multicomponent coal tar could be solvent extraction for remediation of coal tar contaminated represented as a pseudocomponent in thermodynamic sites. Other aspects of the project included examination modeling. The coal tar used in this study showed a of the mass transfer limitationsto insitu solvent extraction predominance of polycyclic aromatic hydrocarbons with of contaminated soils (8) and large-scale subsurface no single compound accounting for more than 4% (wt). modeling of an in situ solvent extraction process to explore The bulk solubility of coal tar in water was estimated to deployment options and estimate cleanup times (9). be 16 mg/L using composition data and Raoult's law assumption for aqueous solubility. For three solvents, The primary challenge in studying coal tar NAPLs is n-butylamine, acetone, and 2-propanol, equilibrium phase that they are mixtures of hundreds of compounds, pri- compositionsof two-phase coal tar/solvent/water mixtures marily polycyclic aromatic hydrocarbons (PAHs). It would were experimentally determined using radiolabeled ma- be an insurmountable task to completely characterize the terials and are presented as ternary phase diagrams. equilibrium-phase compositions of coal tar/solvent/water Results showed n-butylamine to be a good water-miscible mixtures by measuring and describing the partitioning of solvent for coal tar dissolution. The validity of thermo- every individual compound. The experimental data dynamic modeling of coal tar as a pseudocomponent was required to calibrate models describing phase equilibria explored by examiningthe liquid-liquid solute partitioning for a mixture increases very sharply as the number of of naphthalene, phenanthrene and pyrene and by assessing components in the mixture increases. Even for a ternary the effect of solvent extraction on coal tar phase compo- mixture, the experimental effort required is almost 1order sition. It was found that coal tar partitions as a pseu- of magnitude larger than that needed for a binary mixture docomponent in systems with appreciable solvent, but not (IO). Furthermore, of the many constituent compounds in systems with only coal tar and water. that make up coal tar, only a portion can be identified and quantified through chromatographic methods. The chal- lenge, then, is to adequately describe the dissolution Introduction behavior of a multicomponent mixture such as coal tar, which itself cannot be fully characterized, without the Today there is growing concern about nonaqueous phase burden of enormous data requirements. The approach liquids (NAPLs), a class of subsurface contaminants that used in this investigation involves a simplification, referred are immiscible in water (I). Coal tar is a NAPL that is to here as the pseudocomponent simplification, in which denser than water and often very viscous. Subsurface coal tar is treated as a single component in a system with contamination with coal tar exists today as a result of two other components: solvent and water. Coal tar uncontrolled disposal of process residuals at former solubility was explored by studying the equilibrium phase manufactured gas plant (MGP) sites. The manufactured compositions of two-phase liquid mixtures of coal tar, gas industry ended during the 1950sdue to the widespread solvent, and water for several water-misciblesolvents. The use of natural gas and the exploitation of petroleum. coal tar pseudocomponent simplification allows the com- Groundwater contaminationat MGP sites persists decades position of the two immiscibleliquid phases to be described later because of the slow, continuous dissolution of in terms of volume fractions of only three components. constituent compounds from subsurface coal tar (2-5). This simplification facilitates experimental analysis and There are as many as 1000 MGP sites in the United States data representation using ternary phase diagrams and and likely more (6). Numerous MGP site investigations makes thermodynamic modeling tractable (II), as is have verified the presence of coal tar and subsequent presented in a forthcoming paper (12). groundwater contamination, but cleanup efforts have been only sparsely applied. Conventionalremediation methods, This paper addresses four specific objectives. First, detailed composition analyses of the coal used through- such as direct coal tar pumping or groundwater pump- tar and-treat, have proven to be of limited practical use to out this project are presented. Second, the validity of the achieve low residual concentrations, as is discussed in detail pseudocomponent simplification for semi-empirical ther- elsewhere (5, 7). modynamic modeling is explored using composition anal- yses of coal tar before and after extraction and using The use of water-miscible solvents for the extraction of measurements of the partitioning behavior of three PAH coal tar from contaminated soils is a soil treatment option compounds. Third, an estimate is made of the bulk solubility of coal tar in water, which serves as a baseline * To whom correspondence should be addressed at her present address: Environmental and Water Resources Engineering, De- for comparison with experiments using solvents and partment of Civil and Environmental Engineering, The University indicates the possible extent of groundwater contamination of Michigan, Ann Arbor, Michigan 48109-2125. in terms of all constituent compounds. Finally, phase

0013-936X/93/0927-2831$04.00/0 0 1993 American Chemical Society Environ. Sci. Technol., Voi. 27, No. 13, 1993 2831 equilibria of coal tar/solvent/water systems based on nent. The premise that the composition of the dissolved experimental measurements of water and solvent parti- coal tar is similar to that of the undissolved coal tar, means tioning are presented in the form of ternary phase that diagrams.

Theory

Pseudocomponent Simplification. The character- where the superscripts sw and ct denote the solvent/water ization of phase equilibria of complex mixtures can be and coal tar phases, respectively. Rearranging eq 1gives accomplished in a number of ways. Petroleum products the partition coefficient, Kctlawi,the ratio of the concen- are often characterized using boiling point curves in which tration of i in the coal tar phase to the concentration in the mixture is thought of as a continuum of infinitesimal the solvent/water phase: fractions of pseudocomponents (13). Researchers studying coal tar or other mixture NAPLs have, for the most part, nct Fnct described dissolution in terms of individual compounds for all i (14-19). This approach is necessary when assessing groundwater contamination because cleanup standards Thus, an important implication is that for a given mixture are specified for individual compounds, usually those on the partition coefficients of all coal tar constituent the priority pollutant list. The individual compound compounds must be similar to each other and similar to approach was not useful for this project since the objective the overall partitioning of the coal tar pseudocomponent. was to assess the bulk solubility of coal tar based on the Semi-empirical thermodynamic modeling of ternary coal representation of the entire coal tar mixture as a pseu- tar/solvent/water systems is strictly valid only for systems docomponent. for which eq 2 is true, and the extent to which predictions For most water-miscible solvents and over a large range can be made in composition regions beyond where ex- of compositions, mixtures of coal tar, solvent, and water perimental data were used for calibration is determined will separate into two immiscible liquid phases, which are by the extent to which eq 2 is true for a wide range of referred to here as the “coal tar phase” and the “solvent/ system compositions. water phase”. The coal tar phase consists primarily of This concept was explored experimentally using the undissolved coal tar and small amounts of solvent and solvent n-butylamine, which has been identified as a good water incorporated into this organic phase. The solvent/ water-miscible solvent for coal tar dissolution (7). First, water phase consists of solvent, water, and dissolved coal solute partitioning tests were done for three coal tar tar. The coal tar pseudocomponent comprises all the constituent compounds: naphthalene, phenanthrene, and constituent compounds in coal tar, which can be thought pyrene, which represent compounds with a range of of as everything in the system except the solvent and the aqueous solubilities. Second, the effect of extraction with water. n-butylaminelwater solutions on the composition of the Experimental data are used to determine parameters of coal tar phase was studied using quantitative chromato- a semi-empirical thermodynamic model of ternary liquid- graphic analyses of extracted coal tar samples. liquid equilibrium (LLE) (11,12). Fitted model param- Coal Tar Solubilityin Water. The aqueous solubility eters for the coal tar pseudocomponent can be thought of of constituent compounds from coal tar into water has as describing the equilibrium behavior of a “coal tar been discussed in recent years (14-19) in an effort to molecule”, representing the collective behavior of all the understand groundwater contamination at coal tar sites. constituent PAH compounds. Conceptually, the pseu- It has been found (e.g., ref 15) that predicting aqueous docomponent representation is valid because of the solubilities of coal tar compounds using the Raoult’s law chemical similarity of the PAH compounds in coal tar assumption of ideality and an approximation for pure relative to the two other components of the system. That liquid aqueous solubilities based on heats of fusion offers is, the molecular interactions between two coal tar reasonable agreement with experimental measurements. constituents are much more similar than the molecular This approach was adopted for this work for the purpose interactions between either of these compounds and of estimating the bulk solubility of coal tar as a pseudocom- solvent or water. Strictly speaking, for model parameters ponent. to truly represent the collective thermodynamic properties Equilibrium solute partitioning in liquid-liquid systems of the coal tar pseudocomponent, the coal tar component is characterized by equal fugacities of the compound in in each phase must be identical in composition, Le., each liquid phase (20). If it is assumed that the solute comprised of the same distribution of constituent com- behaves ideally in both the aqueous and coal tar phases, pounds. The extent to which this is true for a given coal the equilibrium relation for solute i becomes (21) tar/solvent/water system depends on the degree of sim- = ct WL ilarity of the partitioning behavior of the individual xp xi xi (3) compounds. Consider the mixing of coal tar with a solvent/ water solution with the subsequent formation of a two- where xp is the mole fraction of solute i in the water phase, phase system in equilibrium. Each coal tar constituent xpt is the mole fraction of i in the coal tar phase, and compound, i, partitions into the solvent/water phase to an xy‘ is the mole fraction equivalent of the aqueous extent described by its concentration, Ctw [mg/Ll. Nor- solubility of pure liquid i. Assuming that the aqueous malizing C;w to the total concentration of dissolved coal phase is sufficiently dilute such that the volume of the tar constituents, CC:”, results in a term that is indicative solution is approximately equal to that of pure water (ZZ), of the abundance of i relative to the total pseudocompo- the aqueous concentration expressed as a mole fraction is

2832 Envlron. Sci. Technol., Vol. 27, No. 13, 1993 proportional to mass concentration. An equation similar and time-consuming for coal tar because of the large to eq 3 can be written number of similar hydrocarbon compounds. 14C-Labeled naphthalene, phenanthrene, and pyrene were obtained cp = "FtS? (4) from Amersham Corp., with specific activities ranging from 30 to 60 pCi/mg and chemical purities of >98%. The 14C- where Cy is the mass concentration of in the water phase i labeled solutes were stored in stock solutions by rinsing [mg/Ll, and S? is the aqueous solubility of pure liquid i the glass ampules with methanol. Stock solution con- [mg/Ll. Coal tar constituent mole fractions were com- centrations ranged from 20 000 to 60 000 dpm/pL (dpm puted by xp = (wt%j/lOO) (MWdMWi), where wt% j is refers to disintegrations per minute in which 2.22 x lo6 the weight percent of i in the coal tar, MWCtis the average dpm = 1pCi). This was sufficiently concentrated so that molecular weight of the coal tar, and MWi is the molecular when used to prepare coal tar radioactive stock solutions, weight of compound i. methanol accounted for less than 1% of the total system For many coal tar compounds, SF is a hypothetical volume. With this small amount, there was little concern quantity since these compounds are solids in the pure for cosslvency effects on constituent solubilities (29). state at ambient temperatures. An expression relating 14C-Labeled solvents, n-butylamine, acetone, and 2-pro- SF to Sy, the pure solid aqueous solubility at the system panol, were purchased from the Sigma Chemical Co. in temperature, is derived from the thermodynamicsof solid- specific activities ranging from 2.8 to 8.2 mCi/mmol with liquid equilibrium where the standard state in the liquid chemical purities of >98%. Stock solutions were pre- phase is defined as the pure subcooled liquid at the pared by diluting the radioactive materials in pure, temperature of the solution (20). Applying this relation unlabeled solvents, resulting in concentrations ranging to eq 4 results in from 90 000 to 200 000 dpm/pL. Tritiated (3H)water was purchased from NEN Research Products of DuPont Co. (5) with a specific activity of 25 mCi/g (5.5 X 1O1o dpm/g). A tritiated water stock solution was prepared by diluting by where the term on the right is the ratio of the pure a factor of 100. component fugacities in the subcooled liquid and the solid Coal Tar Composition Analysis. Composition anal- states. Fugacity ratios are often available in the literature yses that were performed on the Stroudsburg coal tar (e.g., ref 23) or can be approximated by an expression that sample included analysis of volatile aromatic compounds, accounts for the free-energy change between the liquid chromatographic analyses of polycyclic aromatic hydro- and the solid state (20),using a constant entropy of fusion carbons (PAH), and a molecular weight determination. for organic compounds (24). The bulk coal tar dissolved Number-average molecular weight determinations were concentration is the sum of the concentrations of all the done by Galbraith Laboratories, Knoxville, TN, on two dissolved species, i.e., C: = Cin4_1Cy,where m is the total replicate coal tar samples using vapor pressure osmometry. number of compounds in coal tar. Substituting for CT This procedure (30) is based on the relationship between from eq 5 the vapor pressure of a solution relative to that of pure m solvent and the molar concentration of solute in the solution. A Knauer-Dampfdruck osmometer was used with toluene as the solvent. an expression is derived to compute the solubility of bulk Volatile aromatic compounds were extracted with coal tar in terms of individual component properties and methanol according to EPA method 8020. The methanol their relative abundances. extract was analyzed accordingto EPA method 5030, using helium for purging and as the carrier gas in the gas chromatograph (GC). The GC had a 105-m VOCOL Methods capillary column by Supelco Co. The injection temper- Coal Tar, The coal tar used for all laboratory exper- ature was 240 "C, and the carrier gas flow rate was 6 mL/ iments was a sample of the free-flowing liquid tar residing min. The temperature program was 10 min at 45 "C, to in the subsurface at the former manufactured gas plant 200 "C at 4 "C per min, and held for 8 min. Detection was site in Stroudsburg, PA. Several published reports achieved by photoionization, at a temperature of 250 "C. describe the chemical and physical characteristics of this Quantification was done using fluorobenzeneas a surrogate coal tar (25-28). At this site, it is possible to collect liquid standard compound. A five-point calibration was done coal tar by pumping from a NAPL pool in a stratigraphic over the 10-100 ppb range. depression in the confining layer. Coal tar was collected The primary chromatographic analysis of PAH com- (7, 11) from one of several existing wells that had been pounds was done in collaboration with the Coal Science installed for remediation of the site through coal tar Division, Pittsburgh Energy Technology Center (PETC), pumping. This coal tar sample was well-suited for Pittsburgh, PA. A 10-mgsample of coal tar was dissolved laboratory investigations because it is a thin liquid and is in methylene chloride to make a l-mL solution. A sample virtually free of dirt and water bubbles. of this was injected into a 5988A Hewlett-Packard gas Materials. The n-butylamine, acetone, and 2-propanol chromatograph-mass spectrophotometer (GCIMS) with solvents were ACS grade from Fisher Scientific Co. a 35 m X 0.2 mm SB-Phenyl-5 column with 0.3 pm film Deionized water was used for solvent/water solutions. thickness. The injection temperature was 300 "C, the Solute partitioning and coal tar/solvent/water phase helium carrier gas had a linear velocity of 32 cm/s at 30 equilibria were determined using radiolabeled techniques. "C, the ionization potential was 70 eV, and the voltage This provided a means of observing the behavior of was 2551 V. The program was 3 min at 30 "C, to 320 "C individual compounds or system components without the at 4 "C per min, and 5 min at 320 "C. Thirty-five need for chromatographic methods, which are difficult compounds were identified by mass spectra and retention

Environ. Sci. Technol., Vol. 27, No. 13, 1993 2833 indices from the literature. Fourteen compounds were were found to produce erroneously high solute concen- quantitatively determined using individually run calibra- tration measurements in the aqueous phase, possibly due tions. Benzo[blthiophene was added to the coal tar as an to erroneous sampling of either a floating organic film or internal standard to check instrument response. For the a microemulsion of coal tar micelles in the water (11). A remaining 21 identified compounds, an average response more successful experimental method was designed to factor was calculated from the 14 calibrated runs and used eliminate the free-flowing coal tar phase. IMPAQ RG20 to convert peak area into mass injected to estimate the porous silica gel beads with pore diameters of 200 A, weight percents. supplied by the PQ Corp., were used. The beads were Supplementary analysis was done in collaboration with dehydrated by heating at 800 "C for 1 h and then cooled. the Analytical Section of the Research and Development A 1-mL sample of the coal tar radioactive stock solution Division of Texaco, Inc., Beacon, NY. Prior to GC/MS was imbibed into 5 g of beads in a glass vial with a Teflon analysis, the coal tar was fractionated using ASTM method septum and mixed on an orbital rotator for 24 h. This D2007, in which characteristic groups were quantified in amount of coal tar was sufficient to discolor the beads, but weight percent using clay-gel adsorption chromatography. not enough to saturate them. This provided ample This step was done to make a crude separation of the interfacial surface area for mass transfer and eliminated PAH compounds residing in the aromatic fraction from the formation of coal tar phase emulsions. The coal tar the other coal tar compounds, such as heterocyclics, imbibed beads were mixed with water in 50-mL centrifuge oxygenated compounds, and very high molecular weight tubes, with calcium chloride to aid in the settling of any substances. This facilitated the GC/MS analysis, however, particulate matter. Equilibration times ranging from 24 the lack of specificity in the operational definitions h to 1 month were used to test for kinetic hindrances to prescribed by this procedure limits the usefulness of the solute dissolution from bead pore spaces, but no significant analysis, and the crude separation procedure may have differences in aqueous concentrations were observed. In caused some inaccuracies in the quantification step. The all, four replicate experiments were performed for naph- aromatic fraction of the coal tar was diluted 100~in thalene and phenanthrene, and seven were performed for methylene chloride and injected into a GC/MS with a 30 pyrene. The vials were centrifuged. A several milliliter m X 0.25 mm SPB5 capillary column. The program was sample, taken from the top of the vial through the septum 5 min at 100 "C and then up to 300 "C at 5 "C per min. using a syringe, was passed through a 0.2-pm Teflon filter Mass spectral analysis was by positive electron ionization, and, discarding the first milliliter to precondition the filter, between 3 and 250 amu. Approximate weight percentages 1-mLvolumes were expressed into 20-mL scintillation vials were estimated for the groups of compounds identified containing 15 mL of Ultima Gold, Packard Instrument using a single internal standard, assuming identical co. responses and using relative peak areas. The concentration of 14C-labeledsolute in the vial was GUMS analyses of coal tar samples that had been measured using a Beckman 5000 TD liquid scintillation extracted with n-butylaminelwater solutions were also counter. The channel window was set to record events performed by the PETC laboratory. Coal tar samples were with pulse heights from 0 to 670. Quenching was corrected equilibrated with n-butylaminelwater solutions in 500- automatically with the H# method and an internally stored mL separatory funnels using a coal tar-to-solvent/water quench curve generated from 14C standard solutions, solution volume ratio of 1:4. For two of the samples, the obtained from Amersham Corp. Each test vial was counted coal tar was extracted once. The solvent/water solutions twice and for a sufficient time such that the 2a error in used were 20% (vol) n-butylamine/80% water and 40% dpm was less than 1% . Measurements were corrected for (vol) n-butylamine/60% water. For the third sample, the background radiation which averaged 40 dpm in the coal tar was extracted twice sequentially, each time with laboratory. The random coincidence monitoring (RCM) fresh 40 5% n-butylamine/water solution, to observe a trend option was used to indicate samples with high numbers in composition change upon sequential extraction. Over of light-producing events other than radiation, which was a 24-h period, the mixtures were gently agitated inter- problematic especially for coal tar containing samples. To mittently to prevent emulsion formation and then settled reduce the measurement error caused by these added for 24 h to allow phase separation. Samples of the counts, the scintillation vials were stored in the dark for extracted coal tar phases were collected from the bottom at least 24 h, until the RCM %, the percentage of of the separatory funnels. GC/MS analyses were per- nonradiation events relative to total light-producing formed in the manner described above for the PETC events, decreased to less than 1% . analysis of the original coal tar. The amounts of dissolved For each experiment, the radioactivity concentration n-butylamine, estimated using thermodynamic LLE model in the water phase, (dpm/mL)w was measured directly. predictions, were found for all three extracted samples to The radioactivity concentration in the coal tar phase, be approximately 5% of the weight (11). The GC/MS (dpm/mL)Ct,was estimated from knowledge of the total results were corrected to represent weight percent relative radioactivity in the system, dpmT, and the volume of coal to the coal tar portion only, allowing an assessment of the tar, VCt, since the amount of dissolved solute is negligible change in mass distribution of PAH compounds. relative to the undissolved solute. The coal tar/water Solute Partitioning in Coal Tar/Water Systems. partition coefficient, Kctlw,was computed by For each of the three solutes (naphthalene, phenanthrene, and pyrene), coal tar was spiked with several microliters Cct (dpm/mL)ct (dpmT)/VCt of radioactive solute stock solution giving 100 000-900 000 Kct,w = - -N (7) dpm/mL. Common procedures for LLE experiments (dpm/mL)" (dpm/mL)" involve mixing the two liquids in a vial and then agitating, settling, and analyzing each phase. Variations on this The solute's aqueous solubility, Cw, was computed from approach were tried for coal tadwater systems, but these the aqueous concentration of the radiolabeled solute

2834 Environ. Scl. Technol., Vol. 27, No. 13, 1993 relative to the total radioactivity, and an estimate of the The volume fraction of component i in the cy phase, total amount of the solute in the system, mT: vE, is computed by

cw = (dpm/mL)w 1ooomT (8) dpmT where (dpm/mL); is the measured concentration of where CW is in milligrams per liter with mT in milligrams. radioactive i in the cy phase, dpm' is the total radioac- mT was computed from the wt % of the compound in the tivity in the system, and Vi is the total volume of i in the coal tar, the volume of coal tar, and the density of the coal system in milliliters. The subscript i denotes the com- tar. ponent, either water (w) or solvent (s), and the superscript Solute Partitioning in Coal Tar/n-Butylamine/ cy denotes either the solvent/water phase (sw) or the coal Water Systems, In 50-mL centrifuge tubes, coal tar tar phase (ct). The volume fraction of the coal tar spiked with 14C-labeledsolute was added to n-butylamine/ pseudocomponent in each phase is calculated by the water solution. A range of solvent concentrations were difference from unity: used. In all cases, the coal tar-to-solvent/water solution volume ratio was 1:4. For each of the three solutes, at vfct= 1- vfs* - VfW* each solvent concentration, replicate experiments were performed. The mixture was brought to equilibrium at Throughout, when the symbol ct is used as a superscript 25 "C over a period of 24 h. Since vigorous agitation led it refers to the coal tar phase, and when used as a subscript to emulsion formation, the vials were agitated intermit- it refers to the coal tar pseudocomponent. Since both tently (II). After centrifugation, the solvent/water phase phases were sampled, these calculations do not require was sampled with a syringe and expressed through a 0.2- the relative phase volumes, which changed significantly pm Teflon filter, discarding the first milliliter to precon- for high solvent systems. dition the filter. The filtering step removed any suspended Each experimentally determined tie line is the result of coal tar, giving a clear filtrate. Coal tar phases were a single or duplicate measurements of solvent and water sampled by decanting the solvent/water phase from the partitioning. The experiments were designed so that the vial and injecting a syringe into the coal tar. The sampled relative standard deviations (a,/x) from random error coal tar was checked for emulsification by expressing associated with vc and vr*, measurements were less than through a fine needle; emulsions were evidenced by 2% (see ref 11). Because eq 10 is additive, the relative expulsion of intermittent slugs of solvent/water phase. standard deviation for random error in vet is not ap- Observations from such systems were not used. The coal proximated by a constant value; the absolute standard tar phase sample was diluted by a factor of 30-40 in deviation for each vet is approximated by uu2 = (c~,,~+ n-butylamine before adding to the scintillation counting a2 )112, assuming Gaussian distributions for error terms. cocktail to lighten its color and reduce quenching for more UG accurate liquid scintillation counting. Dilution was also For very small values of $2, the random errors likely necessary for solvent/water phase samples that were very have skewed distributions, so this analysis is only an dark due to significant coal tar dissolution. The solute approximation. partition coefficient,Kdlsw, was computed similarly to Kdlw Quantitative tie line data were difficult to obtain near (eq 7), except that for these experiments (dpm/mL)ct was the plait points of the ternary phase diagrams due to measured directly. sampling difficulties which resulted because the two liquid CoalTar/Solvent/Water Phase Equilibria. For the phases were very similar in composition and thus similar three solvents, n-butylamine, acetone, and 2-propanol, in appearance, and often one of the phases was present in LLE of coal tar/solvent/water systems was experimentally a very small quantity. For overall compositions thought determined for a range of compositions that resulted in to be near the plait point, an additional series of exper- two-phase systems. To determine a single tie line of the imental systems was visually examined for heterogeneity ternary phase diagram, an overall composition of coal tar/ to identify compositions that are conclusively within the solvent/water was chosen. Parallel experimental systems two-phase composition region. Heterogeneity was ob- were set up: one using 14C-labeledsolvent and one using served by slight color differencesbetween phases, by light tritiated water. For the solvent partitioning experiments, reflected from the interphase meniscus,and by overturning the solvent/water solution and a spike of 14C-labeled the vial to see a thicker coal tar phase clinging to the solvent stock solution were mixed in a 35- or 50-mL glassware. Tests were continued, moving toward the centrifuge tube such that the total level of radioactive expected direction of the plait point, until a composition solvent, dpm:, was in the range of (5 X 106)-(9 x 107) was found beyond which two phases could not be visually dpm. For the water partitioning experiments, 0.5-1 mL discerned. This point is referred to here as a two-phase of tritiated water stock solution was added to the solvent/ check point. water solution resulting in a total water radioactivity, Water Solubility in Coal Tar. In experiments where dpm:, on the order of 5 X lo8 dpm. Coal tar was added, coal tar is mixed with water containing a spike of tritiated and the vials were equilibrated, centrifuged, and sampled water, the concentration of radioactivity in the coal tar in the manner described above. The solvent/water phase phase can, in principle, be used to compute the volume samples for the vials containing 3H had to be diluted fraction of water using eq 9. While this method was because of the high dpm: needed for these experiments, successfully applied to systems containing solvents, it was For liquid scintillation counting of these samples, the not practically applied to coal tar/water systems since the channel window was set for pulse heights of 0-400. The amount of tritiated water in coal tar was at or below the H#quench curve was generated from 3Hstandard solutions analytical detection limit due to the low solubility and to from NEN Research Products of DuPont Co. the large dilution necessary to count coal tar phase samples.

Environ. Sci. Technol., Vol. 27, No. 13, 1993 2835 Naphthalene 1-Phenylnaphthalene Pyrene 2-Methyl Naphthalene 3-Methylphenathrene Benzo (c) Phenanthrene 1 -Methyl Naphthalene 2-Methylphenanthrene Benzo (a)Anthracene Biphenyl 2-Methylarithracene Chrysene + Triphenylene 2-Ethyl Naphthalene 4 H-Cyclopenta [def] phenanthrene Benzo (j) Fluoranthene 1 -Ethyl Naphthalene 9-Methylphenanthrene + Benzo (b) Fluoranthene 2,6-Dirnethylnaphthalene 1-Methylphenanthrene Benzo (k) Fluoranthene Acenaphthylene 2-Phenylnaphthalene Benzo (e) Pyrene Acenaphthene 9-Ethylphenathrene Benzo (a) Pyrene Dibenzothiophene 2-Ethylphenathrene Perylene Phenanthrene Fluoranthene lndeno (1, 2, 3-04 Pyrene Anthracene Aceanthrylene Picei-te

1

27

IIlll/I/-1 IIIIIIIIIIIIIIIIIIII 12 18 24 30 36 42 48 54 60 66 72 Time (min.) Figure 1. Chromatogram of Stroudsburg coal tar with 35 peaks identified.

Table I. Classification of Stroudsburg Coal Tar into are identified with CS; the others having been estimated Characteristic Groups Using ASTM Method D2007 using average response factors. Summing up the weight percents in Table 11, this composition analysis accounts wt% classification for just under half (46%) of the total coal tar weight, for 34 asphaltenes, the n-pentane insoluble fraction constituent compounds in the molecular weight range from 17 polar compounds, material retained on adsorbent clay after 78 to 278 that produced peak areas sufficiently large and percolation of the samples in an n-pentane eluent distinct. This analysis cannot account for very high 41 aromatics, material that passes through a column of adsor- bent clay in an n-pentane eluent but adsorbs on silica gel molecular weight material not quantifiable by GUMS 8 saturates, material in an n-pentane eluent that is not ad- techniques, for trace compounds such as between peaks sorbed on either the clay or silica gel 9 and 10 in Figure 1, or for compounds that co-elute resulting in peaks that cannot be separated. The amount of tritiated water required for precise The predominance of PAHs is consistent with analyses measurement would have made these experiments ex- of other coal tars (3, 311, the primary group here being pensive and would have involved much higher than normal naphthalenes accounting for 18% of the total weight of radioactivity levels employed for routine laboratory work. this coal tar. It is noteworthy that no single compound It was possible, however, to use information about the accounts for more than 4% of the coal tar weight. The precision of the experimental method to estimate an upper low concentrations of volatile aromatic compounds such bound for the water concentration in the coal tar phase. as benzene, xylene, and toluene (BXT), together account- ing for just under 1wt %. This is consistent with analyses of certain other coal tars (3) where the BXT fraction Results and Discussion accounts for about 1 wt 5% , and is usually closer to 0.5 wt %. Volatile aromatics were indeed produced at MGP Stroudsburg Coal Tar Composition. Results of the facilities, from the volatile fraction of the raw coal and characteristic group analysis of the Stroudsburg coal tar from the aromatic fraction of certain carburettor oils (32- are shown in Table I, giving weight fractions and oper- 34). However, these compounds may not be present in ational definitions. The PAH compounds comprise the significant concentrations in subsurface coal tar because aromatics fraction and are likely also to be present as very light fractions may have been recovered as byproducts at high molecular weight compounds in the asphaltenes MGP facilities and because the relative dissolution and fraction. The results from the PETC chromatographic migration in groundwater of these compounds is higher analysis of the Stroudsburg coal tar are shown in Figure than for other coal tar constituents. The absence of acid- 1. A total of 280 peaks were found, indicating the extractable organics, such as phenols, is consistent with complexity of the mixture. The results of the quantifi- what is expected given the method of production that was cation of compound weight percents from all the chro- used at the Stroudsburg MGP. The process at this plant matographic analyses are shown in Table 11. The com- employed anthracite coal in a carburetted water gas pro- pounds that were quantified using calibration standards cess, which did not produce large quantities of oxygenated

2836 Environ. Scl. Technol., Vol. 27, No. 13, 1993 Table 11. Stroudsburg Coal Tar Composition from GC/MS Table 111. Solubilities in Water-Phase (Experimental and Analyses Raoult’s Law Prediction), Coal Tar/Water Partition Coefficients (Experimental and Raoult’s Law Prediction), molecular and Octanol/Water Partition Coefficients for Three weight wt% Selected Solutes benzene 78 0.050 log toluene 92 0.094 C; (mg/L) 1% (KD) log m-,p-xyleneb 106 0.32 pre- (Kctlw) ye- Wow) o-xylene 106 0.32 exptlo dicted exptP dicted ref 23 o-xylene 106 0.41 naphthalene 3.3f 0.2 3.9 3.81 f 0.03 3.7 3.37 (CS)II naphthalene 128 2.16 phenanthrene 0.68 f 0.06 0.16 4.49 f 0.04 5.1 4.57 2-methylnaphthalene 142 3.75 PFene 0.08f 0.03 0.014 4.8f 0.2 5.6 5.18 1-methylnaphthalene 142 3.80 (CS) acenaphthylene 152 0.68 0 Experimental values are shown with 3u (99 % confidence) random biphenyl 154 0.50 (CS) error estimates. acenaphthalene 154 1.52 (CS) 2-ethylnaphthalene 156 1.84 (CS) 1-ethylnaphthalene 156 0.45 (CS) ferences as well as environmental factors, as is discussed 2,6-dimethylnaphthalene 156 1.99 (CS) elsewhere (3, 11). Nevertheless, the composition of the 9H-fluorene 166 1.4 Stroudsburg coal tar is typical of liquid coal tars because 1H-phenalene 166 0.4 the constituent compounds represented are commonly trialkylated naphthalenes 170 4.3 phenanthrene 178 2.12 (CS) found in all coal tars and because the PAH portion is anthracene 178 0.59 (CS) predominantly composed of naphthalenes. This suggests methyl-9H-fluorenes 180 1.7 that the experimentaland modeling results from this study 4-methyl-l,l’-biphenyl 184 0.2 may be modestly extended for making predictions about dibenzothiophene 184 0.22 (CS) other coal tar sites having pumpable liquid coal tar. 3-methylphenanthrene 192 0.55 2-methylphenanthrene 192 0.43 Coal Tar Solubility in Water. Results of solute 2-methylanthracene 192 0.31 solubility and partitioning in coal tar/water systems are 4H-cyclopenta[deflphenanthrene 192 0.57 shown in Table 111. The experimental values for the and 9-methylphenanthreneb aqueous solubilities are shown with 3a (99% confidence) 1-methylphenanthrene 192 0.33 (CS) methyldibenzothiophene 198 0.3 estimates of the random errors based on repeated mea- fluoranthene 202 0.30 surements, as well as the predicted aqueous solubilities aceanthrylene 202 0.29 based on the Raoult’s law approximation (eq 5). Also pyrene 202 0.50 reported in Table I11 are the measured coal tadwater 1-phenylnaphthalene 204 0.29 2-phenylnaphthalene 204 0.22 partition coefficientswith their estimated 3arandom errors 9-ethylphenanthrene 206 0.17 estimates (log units). Just as the Raoult’s law assumption 2-ethylphenanthrene 206 0.20 was used to derive an expression for Cy, an expression for dimethylphenanthrene 206 2.3 the partition coefficient can be derived (see, e.g., ref 15) methylpyrene 216 3.9 benzo[a]anthracene 228 0.31 (CS) in terms of SF and the molar volume of the organic phase. acepyrene 228 0.4 The Raoult’s law estimate of the partition coefficient KD chrysene and triphenylene b 228 0.27 (CS) was computed for each solute using the average molecular methylchrysenes 242 4.4 weight of 210 and a density of 0.994 g/mL to compute the benzopyrenes 252 1.8 picene 278 0.13 (CS) molar volume of the coal tar phase. These values and, for the sake of comparison, literature values of the octanol/ total 46.46 water partition coefficients are included in Table 111. High a CS, quantification was by individually run calibration standards. correlation between Kcnwand KO,has been demonstrated * Elute together. by others (14, 17, 19) and is to be expected given the correlation between partitioning of solutes in different wastes as was often true with the coal carbonization immiscible organic/water systems as is commonly de- processes with bituminous coal (3). scribed as the linear free-energy relationship (35). The results of average molecular weight determinations Lee et al. (15) found that for several coal tar samples, of two replicate coal tar samples were 209 and 211, giving and for several PAH compounds, experimentalKdw values an average molecular weight for the Stroudsburg coal tar were generally within a factor of 2 of predicted KD’s.In of 210. This is relatively high compared to the compounds logarithmic units, this corresponds to zt0.30. This agree- in Table I1 that have been quantified by GC/MS, indicating ment implies that even though the coal tar phase is a that the majority of the mass that has not been accounted complex mixture it can be modeled as ideal in the Raoult’s for in the GC/MS analysis lies in the high molecular weight law sense which assumes that the molecular interactions range. The average molecular weight of the Stroudsburg are equivalent to those in a pure organic liquid. For this coal tar is low relative to the range of average coal tar investigation, the agreement between experimental and molecular weights of 230-1600 from a study of MGP site Raoult’s law predictions are good for naphthalene, but tar residues (311, but that study was not limited to free- the measured Ciw and Kctlwof phenanthrene and pyrene flowing, liquid coal tars as is present at Stroudsburg. indicate higher aqueous solubilities tha predicted by Additional data that characterize the Stroudsburg coal Raoult’s law. The difference between log KDand log Kctlw tar are a viscosity of 9.93 CP (30 “C), determined by for pyrene corresponds to a Raoult’s law estimate of the capillary viscometry, and a density of 0.994 g/mL (30 “C), partition coefficient five times greater than the measured determined using hydrometers (11). value. The discrepancies for phenanthrene and pyrene Coal tars vary from site to site in terms of composition are not likely due to an inaccurate coal tar molar volume and physical properties, resulting from production dif- estimate since this would have resulted in a constant bias

Environ. Sci. Technol., Vol. 27, No. 13, 1993 2837 Table IV. Calculation of the Bulk Solubility of Coal Tar in Water (25 “C) from Estimates of Constituent Solubilities Using eq 5.

X? S: (mg/L) P/tS)pwe i (mg/L) benzene 1.35 X 103 1780 1 2.4 toleuene 2.15 X 10-9 515 1 1.1 m-xylene 3.17 X 10-9 160 1 0.51 p-xylene 3.17 X 103 215 1 0.68 o-xylene 8.12 f 103 220 1 1.8 naphthalene 3.54 x 10-2 31 3.53 3.9 2-methylnaphthalene 5.55 x 10-2 25 1.24 1.7 1-methylnaphthalene 5.62 X 28 1 1.6 acenap hthylene 9.39 x 103 16.1 4.61 0.70 biphenyl 6.82 X 103 7 2.85 0.14 acenaphthalene 2.07 X 10-2 3.80 5.05 0.40 2-ethylnaphthalene 2.48 X 10-2 8 1 0.20 1-ethylnaphthalene 6.06 X 10-9 10.1 1 0.061 2,6-dimethylnaphthalene 2.68 X 10-2 1.7 6.62 0.30 9H-fluorene 1.77 X 1.9 7.94 0.27 trialkylated naphthalene 5.31 X le2 2.1 2.43 0.27 phenanthrene 2.50 X 10-2 1.10 5.65 0.16 anthracene 6.96 X 103 0.045 11.5 0.024 methyl-9H-fluorenes 1.98 X 1.09 3.92 0.085 4-methyl-l,l’-biphenyl 2.28 X 10-9 4.05 1.59 0.015 2-methylanthracene 3.39 f 103 0.03 66.2 0.0067 1-methylphenanthrene 3.61 X 103 0.27 9.35 0.0091 fluoranthene 3.12 X 10-9 0.26 7.09 0.0058 pyrene 5.20 X 103 0.132 19.8 0.014 benzo[a]anthracene 2.86 X 103 0.011 21.6 0.00068 chrysene 1.24 X 0.002 189 0.00047 triphenylene 1.24 X 10-3 0.043 52.6 0.0028 benzopyrenes 1.50 X 0.004 32.3 0.0019 total 0.42 16.3 Pure compound aqueous solubilities and fugacity ratios are from ref 23.

in log& for all three solutes. The discrepancies are likely such as 1,4,54rimethylnaphthalene. These approxima- due to measurement error resulting from aqueous-phase tions do not contribute significantly to uncertainty in the sampling difficulties in systems which may have an oily estimation of qv The aqueous solubilities of these floating phase and tendencies to form microemulsions. compounds sum to 16.3 mg/L, providing an estimate of K,, is used in this work solely for comparison with KdlSw, CW,. Converting to volume fraction, this corresponds to the solute partition coefficient in coal tar/solvent/water uEt = 1.6 X 10-5. Only a portion of the coal tar has been systems. quantitatively characterized due to analytical limitations; The coal tadwater partition coefficients vary over orders the sum of the mole fractions used in this calculation is of magnitude, which is indicative of the variation of 0.42, and the corresponding sum of the weight fractions aqueous solubilities of the coal tar constituent compounds. is 0.32. However, the majority of the compounds that are Thus, it is immediately obvious that the constituent com- not analyzable by GC/MS methods are high molecular pounds do not equally partition to the aqueous phase, and weight compounds which have very small aqueous solu- eq 2 does not hold for a system with only coal tar and bilities. Their contribution to the sum in eq 6 is negligible. water. This implies that the application of a thermody- For example, pyrene’s aqueous solubility is more than 2 namic model to describe the binary LLE of a coal tar/ orders of magnitude less than that of naphthalene. Also, water system is not strictly valid since the coal tar this calculation is limited by the availability of solubility component of the equilibrated water phase does not have data for constituent compounds. Again, the more soluble the same composition as the coal tar component in the compounds are the ones for which data are available. coal tar phase. A following section discusses the validity When estimating properties of mixtures, the approach of the pseudocomponent simplification for ternary systems of selecting a representative compound is often used. The which include solvent. premise of this method is that there is a single constituent Estimation of the bulk solubility of coal tar in water, compound whose property is representative of the bulk Cz,was accomplished using the predicted aqueous sol- property of the mixture as a whole. While this method is ubilities of constituent compounds based on Raoult’s law tempting because of its simplicity, the above calculation (eq 6). Data for this calculation are shown in Table IV, indicates that it is not immediately obvious how a for compounds which had been quantified (Table 11) and representative compound would be chosen. Since all the for which solubility data and fugacity ratios were available coal tar constituents are present in small quantities, a from the literature (23). For co-eluting compounds, e.g. representative compound cannot be chosen on the basis m- and p-xylene, the weight fractions were taken to be of predominance. Alternatively, the selection of a rep- half of the total for both, effectively using an equally- resentative compound based on a close match with the weighted average aqueous solubilityfor these compounds. number-average molecular weight of coal tar leads to a For quantified groups with limited data available, such as low bias for CW,. The compound with available aqueous trialkylated naphthalenes, solubility and fugacity ratio solubility data, whose molecular weight most closely data for a reported compound in the group were used, matches 210, is 9,lO-dimethylanthracenewith a molecular

2838 Envlron. Scl. Technol., VoI. 27, No. 13, 1993 weight of 206 and subcooled liquid solubility of 2 mg/L at L """"Y 25 "C (23),which is significantly less than 16 mg/L, the A pyrene 0 phenanthrene estimated CW, based on eq 6. For a mixture with relatively 10000 evenly distributed weight, the selection of a representative 0 naphthalene compound based on molecular weight is inherently biased 0 low because there is an approximate logarithmic relation between aqueous solubilities and molecular weight for 8 nonpolar hydrocarbons, and thus the averages do not correspond with each other. For purposes of predicting aqueous solubility, fluorene is more representative of the Stroudsburg coal tar mixture, with a subcooled liquid ! aqueous solubility of 15.1 mg/L and a molecular weight 4 of 166 (23). lo!

Water Solubility in Coal Tar. The solubility of water I in coal tar is of interest because together with coal tar 0 20 40 60 80 0 solubility in water this completelycharacterizes the mutual volume % n-butylamine in initial solubility of these two components. This is useful for solvent/water solution calibration of the binary molecular interaction parameters in a thermodynamic model describing coal tar/solvent/ Flgure 2. Solute partitioning in coal tar/n-butylamlne/water systems with 20% (vol) coal tar overall. water phase equilibria (II,22). An upper bound estimate of 0.001 was obtained for uc (11). Conversion to mole hancement of solubility in a given cosolvent solution. In fraction gives an upper bound estimate for x$ of 0.01, terms of partition coefficients, this corresponds to a more which is comparable to water solubilities in other organic significant decrease in K values with increasing solvent liquids of 0.0030 for water in benzene and 0.0034 in concentration for more hydrophobic compounds. This is, 1-methylnaphthalene (36). in fact, what is shown in Figure 2 for K,t/,,. Thus, for Solvent Selection. A literature survey of organic systems with appreciable n-butylamine (>lo% with compounds used as solvents was conducted to identify an respect to the solvent/water solution), the condition for initial list of 13 water-miscible solvents with suitable similar compositions of dissolved and undissolved coal properties for use in a solvent extraction site remediation tar, i.e., eq 2, is satisfied. Since the validation of the system. As described elsewhere (3,criteria for initial pseudocomponent simplification depends on similarity of selection included the following: suitable chemical prop- K&,,, values, these results may be extended to other coal erties for separation from coal tar and water by distillation, tars with similar constituencies of PAH compounds. Coal relatively low volatility and flammability for industrial tars that contain acidic compounds, such as phenols, and safety and handling, commercial availability, and biode- basic compounds such as anilines may not be suitable for gradability. The 13solvents were evaluated in laboratory this simplification since the solubilities and hydrogen- screening tests to assess their capacity to dissolve coal tar bonding characteristics of these compounds are very and their effect on the physicochemical properties of the different from those of the neutral fraction (17,35). coal tar phase. As a result of this work, three solvents The underlying premise of the pseudocomponent sim- were identified for evaluation for potential use in asolvent plification was further tested by studying the effect of extraction coal tar remediation process: n-butylamine, n-butylaminelwater extractions on the composition of the acetone, and 2-propanol. coal tar phase. The weight percents of 27 compounds were Pseudocomponent Simplification. As discussed ear- quantified for this analysis. The compositions of the coal lier, the validity of thermodynamic modeling of coal tar/ tar phases, corrected for fractions of dissolved n-butyl- solvent/water phase equilibria as ternary LLE depends amine, are presented as weight percent distributions over on the extent to which the composition of the dissolved molecular weight in Figure 3. In Figure 3a, the compo- coal tar component is the same as that of the undissolved sitions of coal tar samples that were singly extracted with coal tar. Experimental solute partitioning observations either 20% or 40% n-butylaminelwater solutions are in coal tarln-butylaminelwater systems are presented in shown relative to the original coal tar composition as Figure 2. The data points shown on the ordinate, for 0% reported in Table 11. In Figure 3b, the compositions of a solvent, are the coal tar/water partition coefficient data coal tar sample that had been sequentially extracted once, (Table 111). With increasing amounts of n-butylamine in then again with a solvent/water solution of 40% (vol) the solvent/water solution, the partition coefficients for n-butylamine are shown relative to the original coal tar. all three solutes approach a comparable value. This The total mass accounted for in each of the extracted coal observation indicates that the effect of n-butylamine on tar samples was approximately 16%. Note that true each compound is different. Specifically, with increasing histograms of the coal tar mass distribution over molecular concentration of solvent the enhancement of the solute weight would likely have long tails extending beyond partitioning to the solvent/water phase is greater for molecular weight 280. compounds such as pyrene than for compounds such as The changes in compound weight percentages from the naphthalene. This is consistent with what has been original coal tar and extracted coal tar samples depicted observed in studies of cosolvents on PAH solubilities in in Figure 3 range from reductions of 15% to 92 % , but the which the cosolvency power, represented by u, the slope majority of the reductions are about 50%. Given that the of the log-linear solubility curve, is theoretically predicted initial weight percentages were already small (<4%),the and experimentally verified (29,37)to be proportional to reductions are not significant in an absolute sense. The the logarithm of the solute's KO,. In other words, the effect of extracting with a 20% n-butylamine solution or more hydrophobic compounds experience a larger en- with a 40% n-butylamine solution is practically the same

Environ. Sci. Technol., Vol. 27, No. 13, I993 2899 Table V. Experimental Measurements of Component Volume Fractions in Solvent/Water and Coal Tar Phases.

Solvent = n-Butylamine 0.048 (0.014) 0.052 (0.001) 0.900 (0.014) 0.959 (0.001) 0.029 (0.001) 0.012 (0.0002) 0.080 (0.013) 0.113 (0.001) 0.807 (0.013) 0.920 (0.001) 0.058 (0.001) 0.022 (0.0004) 0.065 (0.009) 0.165 (0.002) 0.770 (0.009) 0.899 (0.002) 0.073 (0.001) 0.028 (0.0004) 0.106 (0.011) 0.300 (0.005) 0.594 (0.009) 0.910 (0.001) 0.070 (0.001) 0.020 (0.0004) 0.106 (0.008) 0.398 (0.006) 0.496 (0.006) 0.893 (0.002) 0.087 (0.002) 0.020 (0.0003) 0.162 (0.007) 0.456 (0.005) 0.382 (0.004) 0.891 (0.001) 0.090 (0.001) 0.019 (0.0003) 0.196 (0.007) 0.500 (0.006) 0.304 (0.003) 0.887 (0.001) 0.095 (0.001) 0.018 (0.0003) 0.352 (0.008) 0.465 (0.007) 0.183 (0.003) 0.841 (0.003) 0.133 (0.003) 0.026 (0.0005) Solvent. = Acet.nna

Solvent = 2-Propanol 0.001 (0.014) 0.160 (0.002) 0.839 (0.014) 0.928 (0.001i 0.070 (0.001) 0.002 (0.0004) 0.041 (0.008) 0.297 (0.003) 0.662 (0.007) 0.888 (0.002) 0.107 (0.002) 0.005 (0.0007) 0.048 (0.007) 0.485 (0.005) 0.467 (0.005) 0.850 (0.002) 0.144 (0.002) 0.006 (0.0009) 0.041 (0.007) 0.620 (0.006) 0.339 (0.004) 0.814 (0.003) 0.179 (0.003) 0.007 (0.0009) 0.075 (0.010) 0.699 (0.009) 0.226 (0.004) 0.743 (0.005) 0.251 (0.005) 0.006 (0.0011)

L1 10 error estimates are indicated in parentheses

molecular weight

Flgure 4. Experimental coal tarlRbutyhminelwater ternary phase diagram. Error bars on solventlwater phase tie line end points are 30 random error estimates; the errors on the coal tar phase end polnts are insignificant. The shaded circle is the two-phase check point. The primary conclusion to be drawn from this analysis is that there is not a large change in coal tar composition uponextractionwith n-butylaminelwater solutions. These molecular weight studies indicate that theassumptionof coaltar partitioning Flgure 3. Weight percent distributions of coal tar samples that have as a single component in coal tarlsolventlwater systems been extracted with Rbutylaminelwater solutions. is plausible. Coal Tar/Solvent/Water Ternary LLE. For each with regard to weight percent distribution. Furthermore, of the three solvents, experimental results of coal tar/ no significant difference in composition is observed for solvent/water phase equilibria are presented in Table V the coal tar sample that has been extracted once and then as volume fractions of the three components. The data again. Another important observation is that, in the are presented as tie lines on ternary phase diagrams in molecular weight range of 128-278, the effectof extraction Figures 4-6, for n-butylamine, acetone, and 2-propanol, on weight percent does not vary with molecular weight. respectively. Inaternarydiagram, theaxisforaparticular That is, the compounds in this range are being extracted component is a line drawn from the apex (100% of that to the same extent, supporting the solute partitioning component) perpendicular to the opposite triangular face observations shown in Figure 2 for three solutes. The (0% of that component). The triangular space is divided decrease in weight percentages in the 128-278 molecular intotwo regions representingmixturesthat are completely weight range signifies an increase in weight percentages miscible and mixtures that separate into two phases. Tie of compounds beyond this range. The cumulative increase lines within the immiscible region connect points that in the unquantified portion of the coal tar is estimated to indicate the equilibrium compositions of the two immis- be 9% based on a summation of the decreases in mass of cible phases resulting for any overall composition repre- the quantified compounds. Spread over a large number sented by a point on the tie line. of compounds, this represents only a slight increase in The error bars that are shown in Figures 4-6 are 30 relative abundance of each compound. (99 % confidence) random error estimates calculated from

2840 Environ. SCI. Technol.. Vol. 27. NO. 13. 1993 acetone I

eo 60

FlgunS. Experlmntal coaitar/aCB1one/watBrternary phasediagram. Error bars on soiventlwater phase tie line end points are 30 random error estimates: the errors on the coal tar phase end point are insignificant.The shaded circle is the two-phase check point. pro pa no^ fie (b) 80 Figure 7. Three-dimensional error space as determined by error bars for vf, vis. and vf,

precision of ut": diminishes when it is much smaller than uc" or .rew. As a result, relative errors greater than 100% result for very small values of $7. In general, this method provides a means of determining LLE of coal tar/ solvent/water systems with measurements on the order of volume percents. Below ut": estimates of about 0.05, order of magnitude precision can be expected. Even with this level of precision, the data in Table V show that, even with small amounts of solvent, coal tar solubility is Figure 6. Experimental coal tarl2-propanoilwater ternary phase appreciable relative to its bulk solubility in water. diagram. Error bars on soiventlwater phase tie line end points are 3c random enw estimates: the errors on the coal tar phase end points QualitativeTests for Heterogeneity. The plait point are lnsigniflcant. The shaded circle is the two-phase check point. is the point on a ternary phase diagram where the tie line end points converge, and the two phases have identical the standard deviations in Table V. Only the error bars composition. Qualitative tests performed on compositions for the solventlwater end points of each tie line are near the plait point were done to gain additional infor- displayed since the error bars for the coal tar phase end mation about the boundaries of the two-phase regions. points are insignificant. Since the relative errors for The two-phasecheckpoints, shown asgray dots in Figures utwand ucware roughly constant at 1-2 % ,the size of the 4-6, were found to be the same for the acetone and absolute error increases with the magnitude of the ucw or 2-propanolsystems: 10% coal tar, 80% solvent, and 10% water. It is expected that there are compositions slightly measurement value. Three-dimensional error dis- urww above this point that are also heterogeneous, but visual play on a ternary phase diagram must be viewed carefully inspection of these systems were not conclusive because to accurately visualize the size of the error space. The 3u of the small overall volume of coal tar. For n-butylamine, error space can be approximated on the ternary phase the region thought contain the plait point was checked diagram by a hexagon bounded by the ends of the three to for heterogeneity, but determination of the two phases error bars as shown in Figure 7a. For points with large Apoint (shown error bars in two dimensions but with a small error bar in becameimpossiblewithsimplevisualtests. in Figure 4) with 80% n-butylamine in the solvent/water the third dimension, the error space is more like a thick solution, with overall composition of 30% coal tar, 56% bar (Figure 7b). For example, the solvent/water endpoint n-butylamine, and 14% water, was found to be two phases. of the bottom tie line on the n-butylamine ternary phase Although this point is not expected to be near the plait diagram has a small error in the ucw dimension. The point, it provides further information about the upper resulting error space is a horizontal bar roughly parallel boundary of the curve. Note that the uppermost tie line with the tie line. This suggests that the slope of the tie in Figure 4 is not consistent with this observation, since line has been precisely determined, and the uncertainty the solventlwater end point does not extend high enough due to random error lies in the position of the end point to be in line with the two-phase observation. The error along this line. bars calculated based on random experimental error do The representation of coal tar as a single component in not account for this discrepancy, suggesting a systematic a ternary system allowed the bulk dissolution behavior of error likely attributable to errors in solvent/water phase coal tar to be indirectly observed by measuring the sampling, given the difficulty in distinguishing between partitioning behavior of the other two components. Since the two phases. the estimated error in uf": will always be greater than the Plait points exist for ternary systems that have only one larger of the error in utw or .Ew. the measurement partially miscible pair (type I ternary system). In this

Envlron. Sci. Technol.. VoI. 27. NO. 13. 1993 2841 case, the coal tadwater pair is known to be immiscible, all solvents studied, n-butylamine was shown to have the three solvent/water pairs are miscible, and the coal tar/ smallest two-phase region and enhance the solubility of solvent pairs are assumed to be miscible based on visual coal tar to the largest extent. While it is not directly observations that fail to identify two phases. For n-bu- apparent from the ternary phase diagrams, coal tar tylamine, an attempt was made to verify this assumption dissolution in solvent/water solutions containing acetone without reliance on visual observations (11). Coal tar/ or 2-propanol is appreciable in terms of being orders of n-butylamine mixtures were prepared with spikes of magnitude higher than the bulk coal tar solubility in water. radiolabeled solvent. These tests were done in separatory The coal tar/solvent/water phase equilibria provide the funnels to facilitate sampling from the bottom of the vial, necessary equilibrium chemistry for predicting mass which would contain the coal tar phase if indeed two phases transfer limitations in porous media (8) and in solvent were present. The measured concentrations of radiola- extraction process modeling (9). Furthermore, these data beled solvent in samples from the top and the bottom of are used to determine parameters for a semi-empirical the vial and the overall concentration were found to be thermodynamic model describing ternary LLE of highly within experimental error of each other, suggesting single- nonideal liquid mixtures (11,12). phase systems. The conclusion can be drawn that coal tarln-butylamine is a completely miscible pair and that Acknowledgments some water must be present to result in phase separation. Solvent Effectiveness. The information in a ternary Mr. James Villaume of Pennsylvania Power and Light, phase diagram provides a useful metric for assessment of Mr. Curt Kramer of Atlantic Environmental Services, and the effectiveness of a solvent, and it provides necessary Dr. David Nakles and Mr. Robert Weightman of Reme- quantitative data for larger scale process modeling (8,9). diation Technologies Inc. assisted in enabling coal tar The simplest piece of information from the ternary phase sample collection. Dr. Curt White and Ms. Louise Douglas diagram is the vertical height of the two-phase region, of the US. DOE Pittsburgh Energy Technology Center, delineated by the end points of the tie lines. The two- Coal Science Division, and Dr. Edward C. Nelson and Dr. phase region for n-butylamine is smaller than for acetone Ingeborg D. Bossert of Texaco Research Center, Beacon, and 2-propanol, indicating that less solvent is required to NY, arranged for chromatographic analyses. Mr. Zhong- completely dissolve coal tar. For example, on the n-bu- Bao Liu assisted with solute partitioning measurements. tylamine diagram, it is shown that if the overall compo- The authors thank Dr. David Dzombak and Dr. Babu Nott sition of a mixture is 20 % coal tar, 56% solvent, and 24% for their review of this manuscript. The Electric Power Research Institute was the primary sponsor for this water (i.e., 70% solvent-to-water ratio), then the mixture research project through contract RP 3072-2. Dr. Babu is completely miscible. Another indicator of the effec- Nott was the project manager. Additional fellowship tiveness of a solvent is the amount of coal tar dissolved in support was provided by the Patricia Harris Government the solvent/water phase, as indicated by the position of Opportunities Program. the right-side tie line end points, i.e., the solvent/water rich region. The farther the end points from the solvent/ Literature Cited water edge, the greater the amount of coal tar dissolved in this phase. For example, with a mixture of 30% coal Mackay, D. M.; Cherry, J. A. Environ. Sei. Technol. 1989, tar, 40% n-butylamine, and 30% water, the solvent/water 23,630-636. phase will contain just under 20% coal tar. With asimilar Harkins, S. M.; Truesdale, R. S.; Hill, R.; Hoffman, P.; mixture using 2-propanol, the amount of coal tar in the Winters, S. US. Production of Manufactured Gases: solvent/water phase is less than 5%, and with acetone, Assessment of Past Disposal Practices; Research Triangle coal tar dissolution is less than 1% . The ternary phase Institute: Research Triangle Park, NC, 1987. Management of Manufactured Gas Plant Sites; Gas diagram can also be used to quantify the extent of solvent Research Institute: Chicago, IL, 1987; Vol I: Wastes and dissolution into the coal tar phase, as is indicated by the Chemicals of Interest. slopes of the tie lines. A horizontal tie line, such as is Moore, T. EPRI J. 1989, 14, 22-31. approximated by the very lowest tie line in the acetone Luthy, R. G.; Dzombak, D. A.; Peters, C. A.; Roy, S. B.; ternary phase diagram (Figure 5), depicts approximate Nakles, D. V.; Nott, B. Technological Directions for equal partitioning of solvent between coal tar and water. Remediation of Tar Contaminated Soils at MGP Sites. To The case of limited solvent dissolution in coal tar is be submitted for publication. depicted by a tie line steeply sloped down from right to Salvensen, R. H. In Proceedings of the 5th National left, such as is observed for n-butylamine with increasing Conference on Management of Uncontrolled Hazardous solvent content. The amount of solvent in the coal tar Waste Sites; Hazardous Materials Control Research Institute: Silver Spring, MD, 1984; pp 1-15. phase determines the extent to which the physical Luthy, R. G.; Dzombak, D. A,; Peters, C. A.; Ali, M. A.; Roy, properties of this phase are altered, i.e., the change in S. B. Solvent Extraction forRemediationof Manufactured volume, density, viscosity, and surface-wetting properties. Gas Plant Sites; Final report, EPRI TR-101845, Project The amount of solvent that remains in the solvent/water 3072-2; Carnegie Mellon University: Pittsburgh, PA, 1992. phase determines the solvent-to-water ratio in this phase Roy, S. B.; Dzombak, D. A.; Ali, M. A. Assessment of in situ and, thus, affects the extent of coal tar dissolution. solvent extraction for remediation of coal tar sites: Column studies. Submitted to Water Enuiron. Res. Conclusions Ali, M. A.; Dzombak, D. A.; Roy, S.B. Assessment of in situ solvent extraction for remediation of coal tar sites: Process The challenge of characterizing the phase equilibria of modeling. Submitted to Water Environ. Res. a complex mixture was met by representing coal tar as a Orye, R. V.; Prausnitz, J. M. Ind. Eng. Chem. 1965, 57, pseudocomponent. Phase equilibria of coal tar/solvent/ 18-26. water systems were experimentally determined and pre- Peters, C. A. Ph.D. Dissertation, Carnegie Mellon University, sented as tie lines on ternary phase diagrams. Of the three Pittsburgh, PA, 1992.

2842 Environ. Sci. Technol., Vol. 27, No. 13, 1993 (12) Peters, C. A.; Luthy, R. G. Coal tar dissolution in water- (27) Unites, D. F.; Housman, J. J. In Proceedings of the 5th miscible solvents: Semiempiricalthermodynamic modeling. Annual Madison Waste Conference of Applied Research To be submitted for publication. and Practice on Municipal and Industrial Waste; Uni- (13) Edmister, W. C. Applied Hydrocarbon Thermodynamics, versity of Wisconsin: Madison, WI, 1982, pp 344-355. 2nd ed.; Gulf Publishing Co.: Houston, TX, 1988; Vol. 2. (28) Villaume, J. F. Ground Water Monit. Rev. 1985,5,60-74. (14) Lane, W. F.; Loehr, R. C. Environ. Sci. Technol. 1992,26, (29) Fu, J. K.;Luthy, R. G. J. Environ. Eng. 1986,112,328-345. 983-990. (15) Lee, L. S.;Rao, P. S. C.; Okuda, I. Environ. Sci. Technol. (30) Bonnar, R. U.; Dimbat, M.; Stross, F. H. Number-Average 1992,26,2110-2115. Molecular Weights; Interscience Publishers: New York, (16) Mackay, D.; Shiu, W. Y.; Maijanen, A.; Feenstra, S. J. 1958. Contam. Hydrol. 1991,8,23-42. (31) Chemical andphysical CharacteristicsofTar Samples from (17) Picel, K. C.; Stamoudis, V. C.; Simmons, M. S. Water Res. Selected Manufactured Gas Plant (MGP) Sites; Final 1988,22, 1189-1199. report for EPRI Contract RP 2879-12; META Environ- (18) Groher, D. M. Master's Thesis, Department of Civil mental, Inc.: Watertown, MA, 1993. Engineering, Massachusetts Institute of Technology, 1990. (32) Rhodes, E. 0.In Chemistry of Coal Utilization;Lowry, H. (19) Rostad, C. E.;Pereira, W. E.; Hult, M. F. Chemosphere H., Ed.; John Wiley & Sons: New York, 1945; Vol. 11, 1985, 14, 1023-1036. Chapter 31. (20) Prausnitz, J. M.;Lichtenthaler, R. N.; de Azevedo, E. G. (33) Rhodes, E. 0.In Bituminous Materials: Asphalts, Tars, Molecular Thermodynamicsof Fluid-Phase Equilibria,2nd and Pitches; Hoiberg, A. J., Ed.; Kreiger Publishing Co.: ed.; Prentice-Hall, Inc.: Englewood Cliffs, NJ, 1986;Chapter Huntington, NY, 1979; Vol. 111, Chapters 1 and 2. 9. (21) Banerjee, S. Environ. Sci. Technol. 1984, 18, 587-591. (34) Morgan, J. J. In Chemistry of Coal Utilization; Lowry, H. (22) Chiou, C. T.; Schmedding, D. W.; Manes, M. Environ. Sci. H., Ed.; John Wiley & Sons: New York, 1945; Vol. 11, Technol. 1982,16,4-10. Chapter 37. (23) Mackay, D.;Shiu, W. Y.; Ma, K. C. Illustrated Handbook (35) Campbell, J. R.; Luthy, R. G.; Carrondo, M. J. T. Environ. of Physical-Chemical Properties and Environmental Fate Sci. Technol. 1983, 17, 582-590. for Organic Chemicals;LewisPublishers: Boca Raton, FL, (36) Sorensen, J. M.; Arlt, W. Liquid-Liquid Equilibrium Data 1992; Vole. 1 and 2. Collection;DECHEMA: Frankfort, Germany, 1979; Vol. (24) Yalkowsky, S. H. Ind. Eng. Chem. Fundam. 1979,18,108- 5, Part 1. 111. (37) Morris, K. R.; Abramowitz, R.; Pinal, R.; Davis, P.; (25) Ferry, J. P.;Dougherty, P. J.; Moser, J. B.; Schuller, R. M. Yalkowsky, S. H. Chemosphere 1988, 17, 285-298. In Petroleum Hydrocarbons and Organic Chemicals in Ground Water-Prevention, Detection, and Restoration; NWWAIAPI Houston, TX, 1986, pp 722-733. Received for review March 18, 1993. Revised manuscript re- (26) Lafornara, J. P.; Nadeau, R. J.; Allen, H. L. In Proceedings ceived July 23, 1993.Accepted July 28, 1993.' of the 1982 Hazardous Material Spills Conference; Bur. Explo.: Washington, DC, 1982, pp 37-42. @ Abstract published in Advance ACS Abstracts, October 1,1993.

Environ. Sci. Technol., Vol. 27, No. 13, 1993 2843