Environ. Scl. Technol. 1983, 17, 305-307
Wu, T. Y. J . Fluid Mech. 1962,13,161-181. Parkinson, G. V.;Jandali, T. J . Fluid Mech. 1970,40, 577-594. Kiya, M.;Arie, M. J . Fluid Mech. 1972,56, 201-219. B i h , J.; Frost, W. Contractor Report NASA CR-2750, The University of Tennessee Space Institute, 1976. Arie, M.; Rouse, H. J . Fluid Mech. 1956,1, 129-141. Bird, R. B.; Stuart, W. E.; Lightfoot, E. N. "Transport Phenomena";Wiley: New York, 1960; pp 149-150. Robertson, J. M. "Hydrodynamics in Theory and Application"; Prentice Hall: Englewood Cliffs, NJ, 1965; pp 263-271.
(18) Bradshaw, P.; Wong, F. Y. F. J . Fluid Mech. 1972,52, 113-135. (19) Chen, F. F. Ph.D. Thesis, University of Illinois at Urbana-Champaign, Urbana, IL, 1982. Received for review June 1,1982,Revised manuscript received December 9,1982. Accepted January 18,1983. We acknolwedge the support of this study by the U.S.Environmental Protection Agency, Industrial Environmental Research Laboratory, Research Triangle Park, NC 27711, under Grant USEPA CR807558,and the American Iron and Steel Institute, Washington, DC, under Grant 78-394.
Development of a Process for PCB Removal from Triaryl Phosphate Hydraulic Fluids by Vacuum Distillation James R. Longanbach* and William H. Mlnk
Battelle Columbus Laboratories, Columbus, Ohio 43201 A method of separating PCBs (Aroclor 1242) from a triaryl phosphate ester based hydraulic fluid that yields a fluid suitable for reuse in an aluminum die casting foundry was identified in a laboratory study. Experiments were done to determine the separation efficiency and product qualities resulting from the use of vacuum, steam, and azeotropic distillation, solvent extraction, foam fractionation, filtration, and adsorption techniques. Vacuum distillation was found to remove over 98% of the PCBs with recoveries of fluid, containing less than 50 ppm PCBs, of 90% at 5 mmHg vacuum, and 85% a t 30 mmHg vacuum. The PCBs (bp 225-365 "C) were distilled from the hydraulic fluid (bp >400 "C). The product met industry standards for acid number and viscosity required for reuse. The data needed to design a 5 gallon/min pilot plant for the vacuum distillation of PCBs from hydraulic fluid in storage at an aluminum die casting foundry were also obtained. Introduction Prior to 1972, polychlorinated biphenyls (PCBs) were frequently used as an additive in hydraulic fluids in foundry die casting machines. When the sale of hydraulic fluids containing PCBs for non-closed-loop applications was stopped in 1972, existing PCB-laden hydraulic fluid stocks were recycled with losses replaced with PCB-free hydraulic fluids. In 1976, when it became illegal to recycle fluids containing more than 50 ppm PCBs, contaminated fluids were removed from foundry operations and stored. However, a problem experienced by many foundries was that PCB residuals tended to remain in die casting machinery and in fluid storage reservoirs even after repeated flushings of the equipment with uncontaminated fluid. The result has been continued leaching of PCBs from equipment and sumps and a rapid accumulation of PCBs in replacement hydraulic fluid stocks to levels in the range 500-3000 ppm. Thus, the amount of PCB-contaminated hydraulic fluid generated by die casting operations has continued to increase long after their ban from industrial markets. A method is needed to reduce the PCB concentrations in stored fluid stocks to below 50 ppm to allow them to be recycled, to reduce storage costs, and to decrease the risk of accidental leakage or spills of PCBs into the environment. The process must be capable of producing high yields of an oil product that meets industry standards for 0013-936X/83/0917-0305$01.50/0
acidity, clarity, viscosity, and ignition resistance. In addition, the process should be applicable to large-scale operation and be relatively simple and inexpensive. In this study, techniques were screened through bench-scale laboratory testing with the goal of identifying one or more methods that might be developed into a large-scale process for removing PCBs from stored hydraulic fluid. The performance characteristics of vacuum distillation were measured to provide data for the design of a 5 gal/min pilot plant. Experimental Details Hydraulic Fluids. The PCB-contaminated hydraulic fluid used in this study was obtained from storage at a die casting foundry. The hydraulic fluid consists of isomers of triisopropylphenyl phosphate blended to obtain a desired viscosity. The stored fluid is a greenish-brown, viscous liquid low in moisture content and free of suspended solids, due in large part to settling that occurred during prolonged storage. The hydraulic fluid sample contained 2300 ppm Aroclor 1242 (Monsanto Industrial Chemicals Co., St. Louis, MO 63166). Other contaminanti+! included phenols, which resulted from thermal decomposition of the phosphate, and mineral oils. PCB Analysis. The procedure described in ASTM D3304-77 was used for measurement of PCB content in the hydraulic fluid samples (1). Analysis for PCBs was accomplished by gas chromatography using a Varian Model 3700 equipped with a W i electron capture detector. A glass column, 6 ft X 4 mm i.d., packed with Silicone XE-60 on Chromosorb WHP was used to separate the PCB isomers. The detection limit for PCBs using this analytical procedure was about 0.001 ppm.
Results and Discussion The candidate techniques included steam distillation, azeotropic distillation, solvent extraction, foam fractionation, filtration, adsorption, and vacuum distillation. No significant PCB removals from hydraulic fluid aliquots were observed with steam distillation as evidenced by negligible PCB levels in the first condensate fractions. Azeotropic distillations were performed by using compounds expected to be good entrainers for PCBs because they contained functional groups similar to those of successful entrainers used with lower boiling dichlorobenzenes, but all had boiling points near the 325-362 OC boiling-point range of Aroclor 1242. The additives tried were 2-
0 1983 American Chemical Society
Environ. Sci. Technol., Vol.
17, No. 5, 1983 305
Table I. Characterization of Hydraulic Oil Samples and Results of Low-Pressure Distillation (0.14-0.35 mmHg) acid init1 PCB neutralization hydraulic oil concn, no., mg of sample no. KOHk PPm 2500 2.1 900 0.1 600 0.3 1200 0.9 1200 0.7 2100 0.5 1500 0.8
solids
pressure, mmHg
trace solids trace solids trace solids large vol of solids moderate solids trace solids trace solids
0.1 5-0.21 0.20-0.24 0.20-0.23 0.21-0.36 0.19-0.35 0.14-0.15 0.25-0.30
aminobiphenyl, 4-phenylphenol, 2-phenylphenol, lauric acid, and 1-tetradecanol. The high distillation temperature required for atmospheric pressure azeotropic distillation (400 "C) resulted in hydraulic fluid decomposition. Thus, the distillations were run under moderate vacuum (14-74 mmHg absolute), which allowed the distillation temperature to remain low enough (139-261 "C) to avoid decomposition of the hydraulic fluid. At temperatures below the boiling-point range of Aroclor 1242 it was possible to remove 29-40% of the PCBs with near quantitative recovery of the hydraulic fluid. However, it was not proven conclusively that azeotropes were formed. If a solvent could be found in which PCBs are soluble and hydraulic fluid is insoluble, a separation method based on solvent extraction might be developed. Acetone, methanol, and ethanol appeared to be promising candidate solvents based on an initial screening of the solubilities of pure hydraulic fluid and Aroclor 1242. However, when an attempt was made to extract PCBs from stored hydraulic fluid with each of the solvents, the mixtures were found to be completely miscible. Two methods were used to produce foams to test foam fractionation. One method involved applying a vacuum and moderate heat to induce foaming. In the second method, air was introduced through a fine sintered-glass gas dispersion tube that was immersed in the hydraulic fluid, resulting in the production of a foam at atmospheric pressure. The second method produced a foam with lower liquid content. With both the vacuum heating method (0.6 psi at 105 "C) and the air bubble method (atmospheric pressure, 25 "C) PCBs were carried out of the bulk fluid with the foam, but no substantial reduction of PCBs in the hydraulic fluid product was achieved. PCBs have been reported in the literature to be attracted to particles such as dirt and carbon (2). Filtration of fluid samples wm carried out with a Millipore (Millipore Corp., Continental Water System Corp., El Paso, TX 79998) apparatus in which two types of cellulose acetate Millipore filters, with pore sizes of 10 X lo* and 0.22 X lo4 m, were tested. The results of these experiments showed no significant removal of PCBs in filtered hydraulic fluid. Adsorption tests were conducted by using two methods: passing hydraulic oil through a column packed with an adsorbent, and long-term exposure of hydraulic fluid slurried with adsorbents. Adsorbents tested in packed columns included washed polyurethane plugs, plugs coated with 0.5% DC200, a gas chromatography packing substrate (3 cm-diameter x 3.5 cm, Analabs, Inc.), and Imbiber Beads (Dow Chemicals, Functional Products and Systems Department). $'our adsorbents were tested in long-term exposure experiments: Teflon, Imbiber beads, PVC (Goodrich Resin 346 powder), and Micro-Cel (Johns306
Environ. Scl. Technol., Vol. 17, No. 5, 1983
PCB concn in hydraulic oil after distillation distillation, ppm temp range, "C 195-2 3 3 220-238 193-232 217-236 234-239 239-243 220-238
17 15 26 35 10 36 27
Mansville, Denver, CO, surface area 95-200 m2/g). PCB removal efficiencies with the washed polyurethane foam plugs ranged from 4% to 15% but were negligible with the other adsorbenta. In the long-term contact trials, which consisted of oil-adsorbent mixtures placed in beakers for 2- and 24-h stirring times, none of the four adsorbents tested achieved significant reductions of PCBs in the hydraulic fluid. Vacuum Distillation. A vacuum distillation was performed on hydraulic fluid during which 12 equal fractions of distillate were taken. Distillation temperatures ranged from 264 to 278 "C at 10-16 mmHg absolute pressure, without reflux at an average distillation rate of 0.7 mL/min. Chlorine determinations by X-ray fluorescence of each fraction indicated that most of the chlorine appeared in the first 10 vol % of the distillate fractions; fraction 1contained 7300 ppm, fraction 2 contained 31OOO ppm, while fraction 8 contained only 5 ppm PCBs. The bench-scale vacuum distillation system achieved PCB reductions of more than 98% with a decontaminated hydraulic fluid yield of more than 90%. A vacuum distillation treatment system should include a filtration step prior to PCB separation. Solids removal is vital in an overall treatment scheme to avoid desorption of PCBs from solids into PCB-free fluid after distillation. A series of tests were conducted to demonstrate applicability of vacuum distillation to a wide variety of stored hydraulic oil stocks, response to varied concentrations of PCBs in the starting oil material, and adaptability for scale-up in lower vacuum operations. The initial PCB concentration, acid neutralization number (mg of KOH required to neutralize 1g of sample), and solids turbidity of each sample are listed in Table I. Concentrations of PCBs in these samples ranged from 600 to 2500 ppm, and the visual turbidity of the samples ranged from only trace amounts of solids to large amounts of visible solids. Each of the samples was filtered by passing it through a large Buchner filter containing Whatman no. 4 paper coated with fullers earth filtering aid after the stored fluids were heated to 80 "C to reduce viscosity. Each of the filtered hydraulic fluid samples was then distilled under low pressure (0.14-0.35 mmHg), keeping the maximum distillation temperature below 244 "C and the average distillation rate at 0.5 mL/min. Distillation was carried out using a 13 in. X 0.5 in. diameter insulated Vigreux column containing approximately three theoretical plates without a reflux head. Sample of hydraulic fluid were taken after distillation of 5%, lo%, and 15% of the initial oil volume. The results of the PCB analyses of the samples taken after distillation of 10% of the fluid are also presented in Table I and show that reductions of PCBs in contaminated fluids to levels below the allowable EPA limit of 50 ppm could be consistently achieved by vacuum distillation for each of the hydraulic fluids tested.
Table 11. Specifications and Properties for Reuse of Hydraulic Oil Distillation Residue@ acid no., color, clarity viscosity SUS at 100 “C mg of KOH/g specifications for new hydraulic oil limits for recycled hydraulic oil sample no. 1 2 3 4 5 6
0.15 i- 0.05 1.0
clear, green clear
215-240 215-300 (see discussions)
water content, % nil nil
clear, brown 29 1 NMC NM NM clear, brown clear, brown 295 NM clear, brown 271 NM clear, brown 299 NM 0.4 clear, brown 315 NM 7 0.3 clear, brown NM NM Ignition resistance was not determined because insufficient material a Residue after distillation of 15 vol % of sample. N M = not measured. However, the water content is expected to be nil after distillation to a was available for the test. final boiling point of about 400 OF. 1.3 0.1 0.2 0.5 0.2
I
the PCB content in the distillation residue was 60 and 32 ppm, respectively. The distillation results are summarized in Figure 1. Comparison of data at various levels of vacuum indicate that more fractionation is required as vacuum is increased. Thus, 40 ppm PCBs could be obtained at 90% yield by using a distillation pressure of 1 mmHg, whereas at 20 mmHg, the oil yield to obtain the same PCB level would be only 85 5%. In addition to reducing PCB concentrations below 50 ppm, several other criteria must be satisfied before the decontaminated fluids can be recycled. Specifications limits have been established for acidity, clarity, and viscosity, which are listed in Table 11. The corresponding properties of the seven hydraulic oil samples obtained after PCB removal by high-vacuum distillation are also listed in Table 11. The data indicate that vacuum distillation was capable of treating contaminated hydraulic fluids to acceptable levels of PCBs while producing a fluid that met the criteria for recycle, with the exception of fire resistance, which was not tested. The laboratory studies provided direction and a data base for the construction of a pilot plant for the vacuum distillation process. Registry No. Aroclor 1242,53469-21-9;trichloro-1,l’-biphenyl, 25323-68-6; tris(isopropylpheny1) phosphate, 26967-76-0.
Literature Cited (1) ASTM D3304-77,“Analysis of Environmental Materials for Polychlorinated Biphenyls”. (2) Hague, R.;Schmedding, D. W.; Freed, U.H. Environ. Sci. Technol. 1974,8,139-142.
Received for review March 8,1982. Revised manuscript received October 4, 1982. Accepted February 7, 1983.
Environ. Sci. Technol., Vol. 17,No. 5, 1983
307
