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Ambient Temperature Vapor Pressure and Adsorption Capacity for (Perfluorooctyl) Ethylene, 3‑(Perfluorobutyl)propanol, Perfluorohexanoic Acid, Ethyl Perfluorooctanoate, and Perfluoro-3,6dioxaheptanoic Acid Bryan J. Schindler,*,† James H. Buchanan,‡ John J. Mahle,‡ Gregory W. Peterson,‡ and T. Grant Glover† †

SAIC, P.O. Box 68, Gunpowder, Maryland 21010, United States Edgewood Chemical Biological Center, 5183 Blackhawk Road, Aberdeen Proving Ground, Maryland 21010-5424, United States

‡

ABSTRACT: With increased use of highly fluorinated compounds has come an increased need for knowledge of the fundamental properties of these chemicals, such as vapor pressure, to determine how they will behave in the environment and how to remove them. A modified vapor saturation method was used to measure the ambient temperature vapor pressure of 3(perfluorobutyl)propanol, (perfluorooctyl)ethylene, perfluorohexanoic acid, ethyl perfluorooctanoate, and perfluoro-3,6-dioxaheptanoic acid between (254.15 and 309.15) K. The freezing point for perfluorohexanoic acid was determined to be between (291.15 and 293.15) K. The vapor pressures, which ranged from (0.87 to 978) Pa, were used to generate saturated vapor streams of the compound so that adsorption capacities on BPL activated carbon could be determined. Adsorption equilibrium data for three of the chemicals, measured at a feed concentration of 139 μL·L−1 at high and low relative humidity, are presented and discussed.

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INTRODUCTION The use of highly fluorinated chemicals has expanded greatly over the last half century. Perfluorooctanoic acid has found widespread use as a surfactant in polytetrafluoroethylene (PTFE) cookware, carpet treatments, textile treatments, floor wax, fire-fighting foams, sealants, and food contact paper.1 Other perfluorocarbons, such as perflubron and perfluorodecalin, have been investigated as breathing alternatives for trauma patients and in deep diving.2 The increased use of these compounds is related to the unique chemical characteristics associated with the extreme electronegativity of the fluorine atom, which enhances the carbon−fluorine bonds’ resistance to hydrolysis, photolysis, and microbial degradation. Exposure to these chemicals has been shown to have physiological impact. This class of compounds is persistent in the environment3−5 and bioaccumulative,6,7 can increase the risk of cardiovascular disease, 8 and exhibits signs of toxicity.7,9−15 Its inclusion in cookware16,17 has led to actions by regulatory agencies. These effects are most pronounced for certain subclasses such as perfluorocarboxylic acids (PFCA), fluorotelomer alcohols (FTOH), and perfluoroalkyl sulfonates (PFOS). The increased use of these compounds has not led to an increased reporting of the fundamental physical properties, especially at ambient conditions. Theoretical18 and empirical studies on partitioning behavior at the air−water interface19−21 and the air/particle interface22 have been documented. Kaiser et al. 23 measured the vapor pressure of a series of © 2013 American Chemical Society

perfluorocarboxylic acids from (332.4 to 520.5) K and reported normal boiling points.24 The vapor pressure of solid perfluorooctanoic acid was studied from (298 to 318) K.25 Melting and boiling points of fluorinated ethers and perfluoroalkanes including 3-(perfluorobutyl)propanol were reported by Szabo et al.,26 and a few of the fluorinated telomer alcohols have had boiling points27 and vapor pressures4,28−31 measured. Predicted vapor pressure values have also been published,32−34 and physical properties were reviewed by Rayne and Forest.18 Ambient temperature vapor pressure data is required to accurately model the fate of volatile chemicals in the environment. Limited vapor pressure data of some fluorinated species have been reported. In this work we report the measured vapor pressure of 5 perfluorinated compounds from (254 to 309) K. These vapor pressure experiments were conducted because measured ambient temperature data do not exist for these compounds and only estimated or extrapolated values were available.24,27,32,34 The conventional method for vapor capture is by adsorption. For vapors with boiling points above ambient temperature, activated carbon is favored due to low cost, high porosity, and low coadsorption of water. Here the adsorption capacity of three perfluorinated chemicals is reported on a commercially Received: March 1, 2013 Accepted: May 14, 2013 Published: May 24, 2013 1806

dx.doi.org/10.1021/je400205g | J. Chem. Eng. Data 2013, 58, 1806−1812

Journal of Chemical & Engineering Data

Article

Table 1. Purity Analysis chemical

CAS no.

PFBPc PFOEd PFHxAe EPFOf PDHAg

83310-97-8 21652-58-4 307-24-4 3108-24-5 151772-58-6

source Oakwoods Oakwoods Oakwoods Oakwoods Oakwoods

Products, Products, Products, Products, Products,

Inc. Inc. Inc. Inc. Inc.

purification method

mol fraction

analysis method

none none none none none

97.5 99.0 >98.0 99.7 99.6

GCa GCa NMRb GCa GCa

a

Gas chromatography. bNuclear magnetic resonance spectroscopy. c3-(Perfluorobutyl) propanol. d(Perfluorooctyl)ethylene. ePerfluorohexanoic acid. fEthyl perfluorooctanoate. gPerfluoro-3,6-dioxaheptanoic acid.

pressure of the lab was measured throughout the experiments using a PRINCO Nova model mercury barometer, with corrections according to the manufacturer’s directions to ± 13.3 Pa. The saturator was allowed to equilibrate at the experimental temperature for (0.41 to 1.0) h before the carrier gas flow was attached to the inlet of the saturator; longer times were allowed for lower temperatures. The outlet arm of the saturator was wrapped with heat tape to keep the temperature near 343.15 K for experiments performed above ambient temperatures to prevent condensation in the outlet arm. For solid PFHxA, the saturator was submerged in the EGW bath set at 253.15 K for 6.0 h to ensure that the chemical was solid. The water bath was then raised to the experiment temperature and held for 1.0 h before the test was started. The saturated vapor stream was generated by passing a dry nitrogen carrier gas at (3.87·10−7 ± 1.5·10−9) m3·s−1 or (7.74·10−7 ± 1.5·10−9) m3·s−1 through a saturator containing the chemical. Higher flow rates were used for lower vapor pressure points to ensure sufficient mass loss was achieved during the experiment. One data point was run at both flow rates to verify that the chemical was saturated. The minimum mass loss in the current work was 50 mg. The vapor pressure values were calculated from the mass losses by eq 1:

available, coal-derived adsorbent using a microbreakthrough method reported earlier.35,36 The effect of water on the adsorption capacity was determined by measuring capacity at both high and low relative humidity (RH). Gas phase concentrations of the perfluorinated compounds were held constant at 139 μL·L−1.

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EXPERIMENTAL SECTION Materials. 3-(Perfluorobutyl)propanol (CAS 83310-97-8; purity 97.5 %; PFBP), (perfluorooctyl)ethylene (CAS 2165258-4; purity 99.0 %; PFOE), perfluorohexanoic acid (CAS 30724-4; purity >98.0 %; PFHxA), ethyl perfluorooctanoate (CAS 3108-24-5; purity 99.7 %; EPFO), and perfluoro-3,6dioxaheptanoic acid (CAS 151772-58-6; purity 99.6 %; PDHA) were obtained from Oakwoods Products, Inc., (West Columbia, SC) and were used without further purification. BPL activated carbon was obtained from Calgon Carbon Corp. (Pittsburgh, PA). Vapor Pressure. A modified version of the ASTM E 119437 vapor saturation method was used for this work. The custom glass saturators have been described previously and were used to measure the ambient temperature vapor pressure of solids and liquids.38−40 In the current experiments, gravimetric mass loss was used to infer the vapor pressures as before.39 Four chemicals were analyzed for purity before and after the vapor pressure experiments using a Hewett-Packard 6850 GC, equipped with a thermal conductivity detector (TCD). For PFHxA, 19F NMR spectra were obtained using a Varian 300 NMR spectrometer with spectra referenced to external aqueous α,α,α-trifluorotoluene (−63.72 ppm, 19F). The purity analysis for all chemicals showed no change in the liquid purity before and after the gravimetric vapor pressure experiments; purities are listed in Table 1. A Mettler-Toledo model XS-204 calibrated balance with a capacity of (220 ± 0.0001) g was used in this work. The new saturator was purged overnight with dry nitrogen at (3.87·10−7 ± 1.5·10−9) m3·s−1 at room temperature, capped, and the tare mass was determined. To minimize weighing errors, the exterior of the saturator was triple rinsed with (400 to 500) mL of distilled water after each run, hand dried with Kimwipes, and air-dried (22.2 ± 0.5) °C for 1 h, 0.5 h on each side, longer for low temperatures, to allow the samples to thermally equilibrate. The average of three measurements was used to determine the mass of the saturator before and after each experiment. The mass measurements were performed at least 300 s apart and the difference between the individual measurements was less than 5 % of the mass loss. The saturator was submerged in a NESLAB RTE 740 bath to control the temperature. The bath was filled with a 50 % ethylene glycol-water (EGW) solution. The temperatures were measured using a series of NIST traceable mercury thermometers, accurate to within ± 0.1 K. The ambient

P o = Pambientnchem(nchem + ncarrier)−1

(1)

where Po is the vapor pressure of the chemical from measured data, Pambient is the ambient atmospheric pressure, nchem is the number of moles of the chemical measured by mass loss, and ncarrier is the number of moles of the nitrogen carrier gas. Microbreakthrough. Microbreakthrough experiments were conducted using an apparatus that has been described previously35,36 and shown in Figure 1. A capacity to saturation was calculated using the method outlined by Glover et al.36 The saturator cell was submerged in a temperature controlled EGW bath to generate a saturated chemical stream. This stream was mixed with a saturated water vapor stream downstream of the

Figure 1. Schematic of microbreakthrough system. 1807



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Table 2. Adsorption Equilibrium Experimental Conditions and Concentrations at 139 μL·L−1a Chemical Temperature Tc, Chemical Flow Rate vc, Water Temperature Tw, Water Flow Rate vw, Diluent Flow Rate vd, Concentration C, and Relative Humidity RH Tc chemical PFOE PFOE EPFO EPFO PFBP PFBP

K 273.85 273.85 291.85 291.85 296.45 296.45

vc

Tw

3 −1

m ·s

−8

6.19·10 6.19·10−8 6.19·10−8 6.19·10−8 6.19·10−8 6.19·10−8

vw

vd

3 −1

3 −1

m ·s

K

m ·s

−8

298.15 298.15 298.15 298.15 298.15 298.15

C −7

4.64·10 2.48·10−7 4.64·10−8 2.48·10−7 4.64·10−8 2.48·10−7

2.01·10 0.00 2.01·10−7 0.00 2.01·10−7 0.00

mg·m−3

RH

2735 2735 2711 2711 1705 1705

15 80 15 80 15 80

a The standard uncertainties for the temperatures u(Tc) = 0.1 K and u(Tw)= 0.1 K and the relative expanded uncertainty for the concentration U(C) = 0.0034 with 0.95 level of confidence.

saturator and diluted with clean air to achieve a predetermined concentration of 139 μL·L−1 and humidity at a flow rate of (3.09·10−7 ± 1.5·10−9) m3·s−1 at (293.15 ± 0.5) K and ambient pressure. The stream was then passed through the sorbent bed. The sorbent bed was filled with BPL carbon to a height of ∼4 mm in a tube with an internal diameter of 4 mm. All of the samples were dried for 1.0 h at 333 K in dry nitrogen and then pre-equilibrated at the RH of the test for 2.0 h. The relevant conditions used for each microbreakthrough test and resulting concentrations are listed in Table 2. The exiting stream was analyzed using an FTIR, Nicolet 380 with DTGS detector equipped with a 2.0·10−5 m3 gas cell (Axiom, Inc., LFT 205). The challenge concentration was established prior to the bed exposure by bypassing the bed using a 4-way valve. The FTIR was calibrated by mixing saturated vapor and clean carrier. Flows were measured using a bubble meter and controlled using mass flow controllers. The air carrier was purified using a Balston Mfg. Co., Inc., Purge Gas Generator model 76−52. A calibration equation was derived for each analyte using classical least-squares algorithm supplied with the FTIR control software. Quantification ranges were between (5 and 200) μL·L−1 and were chosen such that water does not interfere with the signal. The adsorption capacity tests were run at both (15 or 80) % RH at 293.15 K, and the feed concentration was chosen to be 139 μL·L−1. The adsorption capacities of PFBP, PFOE, and EPFO were evaluated using the microbreakthrough method. PFHxA and PDHA were not evaluated because of concerns that as acids, they could potentially damage the experimental instrumentation.

Figure 2. Vapor pressure data of blue diamonds, PFOE; red squares, EPFO; purple triangles, PDHA; green circles, PFBP; brown diamonds, PFHxA. Solid lines are fits to liquid data, and the dashed line is the fit to solid PFHxA data.

Table 3. Experimental Vapor Pressure for PFBP Pexp, Calculated Vapor Pressure Pcalc, Percent Difference Δ, Volatility V, and Heat of Vaporization ΔHvapa Pexp

Pcalc

V

ΔHvap

Pa

Pa

Δ

mg·m−3

kJ·mol−1

255.65 273.15 282.45 293.15 309.15

0.87 7.65 21.21 57.17 216.95

0.87 7.75 20.82 57.62 216.70

0.22 −1.23 1.86 −0.79 0.12

114 949 2466 6576 23449

75.77 69.58 66.87 64.13 60.66

a

The standard uncertainties for the temperature u(T) = 0.1 K. The relative expanded uncertainty for the vapor pressure Ur(P) is 0.0052 with a 0.95 level of confidence.

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RESULTS AND DISCUSSION Vapor Pressure. Figure 2 shows the measured vapor pressure data and the Antoine equation41 correlations for 4 of the 5 compounds and the Clausius−Clapeyron fits for PFHxA. Tables 3 − 7 summarize the measured vapor pressure data, and calculated values for vapor pressure. Equation 2 was used to correlate vapor pressure. Equation 3 was used to calculate volatility. Equation 4 was used to calculate enthalpy of vaporization at the temperatures used to measure vapor pressure data for each compound except for the solid PFHxA which gives the heat of fusion. The percent difference between the measured and calculated vapor pressure was determined using eq 5 ln(P) = a − b(c + T )−1

T K

Table 4. Experimental Vapor Pressure for PFOE Pexp, Calculated Vapor Pressure Pcalc, Percent Difference Δ, Volatility V, and Heat of Vaporization ΔHvapa T

Pexp

Pcalc

K

Pa

Pa

Δ

254.15 272.45 290.75 309.15

12.69 68.23 284.32 977.96

12.70 68.22 284.56 978.01

−0.04 0.02 −0.09 0.00

V

ΔHvap

mg·m−3

kJ·mol−1

2 13 52 169

680 435 516 748

53.71 52.09 50.73 49.56

a


(2) 1808



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Table 5. Experimental Vapor Pressure for PFHxA Pexp, Calculated Vapor Pressure Pcalc, Percent Difference Δ, Volatility V, and Heat of Vaporization ΔHvapa T

Pexp

Pcalc

K

Pa

Pa

263.15 270.15 278.15 283.15 285.15 290.15

1.26 2.94 7.91 13.40 17.26 35.51

1.16 2.94 7.99 14.51 18.32 32.33

ΔHvap

V Δ

mg·m

Table 8. Antoine Equation Coefficients

−3

kJ·mol−1

Solid 8.24 0.09 −1.01 −7.67 −5.78 9.84

167 411 1 085 1 936 2 427 4209

78.15 78.15 78.15 78.15 78.15 78.15

44.00 84.34 165.58

44.25 83.48 166.45

−0.57 1.03 −0.52

5 702 10 506 20 404

66.33 66.33 66.33


a

Table 6. Experimental Vapor Pressure for EPFO Pexp, Calculated Vapor Pressure Pcalc, Percent Difference Δ, Volatility V, and Heat of Vaporization ΔHvapa T

Pexp

Pcalc

Pa

Pa

Δ

263.15 278.15 293.15 308.15

5.16 23.13 89.88 264.94

5.13 23.76 87.42 268.14

0.66 −2.63 2.81 −1.19

V

ΔHvap

mg·m−3

kJ·mol−1

1 4 15 46

036 542 858 273

64.06 60.41 57.40 54.86


Table 7. Experimental Vapor Pressure for PDHA Pexp, Calculated Vapor Pressure Pcalc, Percent Difference Δ, Volatility V, and Heat of Vaporization ΔHvapa Pexp

Pcalc

ΔHvap

V

K

Pa

Pa

Δ

263.15 278.15 293.15 308.15

4.51 22.38 92.88 316.80

4.50 22.56 92.13 317.99

0.17 −0.81 0.81 −0.37

mg·m

−3

609 2888 11 191 36 744

kJ·mol−1 66.36 64.43 62.76 61.30

a


where a, b, and c are empirical coefficients and T temperature (K). V = PM(RT )−1

(3)

where M is molecular mass and R is the gas constant. ΔH vap = bRT 2(c + T )−2

(4)

Δ = 100·(Pmeas − Pcalc) ·Pcalc−1

(5)

231.3 265.6 978.4 400.0 200.0 894.8

C −103.42 −47.641

−93.565 −57.083

Tba

chemical

Pa

K

PFBP PFOE PFHxA EPFO PDHA

89.23 477.84 69.85 129.36 141.64

441.5 413.1 409.6 450.0 413.5

Extrapolated.

models18,32−34 have been used to predict the saturated vapor pressure of PFHxA at ambient temperature with the results ranging from (51 to 457) Pa. Using eq 2 and the PFHxA liquid correlation coefficients reported in Table 8, the interpolated vapor pressure at 298.15 K was 70 Pa. Wang et al.32 used a COSMOtherm model to predict the ambient temperature vapor pressure of PFOE to be 170 Pa. Using eq 2 and the PFOE constants in Table 8, the interpolated vapor pressure at 298.15 K was 478 Pa. Oberg and Lui33 used a QSPR model to predict the ambient temperature vapor pressure for EPFO to be 55 Pa. Using eq 2 and the EPFO constants in Table 8, the interpolated vapor pressure at 298.15 K was 129 Pa. PFHxA passes through a phase change from solid to liquid between (291.15 and 293.15) K. The freezing point was determined by visual inspection. The sample was stored overnight at 253.15 K in the EGW bath. The temperature of the EGW bath was then set at 285.15 K and allowed to equilibrate for 1.0 h. The sample was removed and inspected then placed back in the temperature bath. The temperature was increased by one degree and allowed to equilibrate for 0.5 h. At 291.15 K the chemical was a solid and at 293.15 K the chemical was a liquid. Due to the limited range of temperatures caused by the freezing point transition, the PFHxA solid data was correlated using the Clausius−Clapeyron equation, by setting c in eq 2 to zero. The same procedure was used to fit the PFHxA liquid data. To quantify the uncertainty in the measurements, a simple sensitivity analysis was performed. In these experiments, there are four different areas where the uncertainty can enter: (1) the temperature of the water bath Tbath, (2) the weighing of the saturator cell which is related to the moles of chemical, nchem, (3) the uncertainty in the mass flow rate ncarrier, and (4) the ambient pressure Pambient. The thermometer used has a stated accuracy of ± 0.1 K. As discussed by Williams et al.42 the uncertainty is difficult to directly determine because of the logarithmic function of temperature. However, we will estimate in the same way by calculating the differences in the vapor pressure computed from Antoine coefficients by a change of 0.1 K at a central temperature. This (0.1/250) gives an error of UT = 0.04 %. The mass balance has an accuracy of ±0.1 mg, which gives a maximum uncertainty of Um = 0.2 %, (0.1/50) since the

a

T

B 3 4 7 9 3 4

P

a

K

A 21.085 23.197 31.006 35.873 20.504 25.258

Table 9. Calculated Vapor Pressure at T = 298.15 K and Extrapolated Normal Boiling Point Tb

Liquid 293.15 300.15 308.15

chemical PFBP PFOE PFHxA liquid PFHxA solid EPFO PDHA

The Antoine coefficients are included in Table 8. The vapor pressure at 298.15 K and the extrapolated normal boiling point are calculated in Table 9. The normal boiling point for PFOE was measured to be 420.15 K27 and PFHxA had a boiling point of 430.15 K at 98 925 Pa (742 mmHg).24 Eight different 1809



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minimum mass loss used in the work was 50 mg. The mass flow controller uncertainty is estimated to be Uvc = 0.02 % (0.01/ 50). The uncertainty of the ambient pressure is estimated to be UP = 0.01 %, based on manufacturer’s documentation (13.3/ 101325). The relative expanded uncertainty, based on eq 6 is Up = (UT + Um + Uvc + UP)1/2

Table 10. Adsorption Capacity (mol/kg) of PFOE, PFBP, and EPFO at 139 μL·L−1 Feed Concentration PFOE 15 % RH 80 % RH

(6) 15 % RH 80 % RH

estimated to be 0.52 %. The uncertainty of the measurements is similar to previous work.39,42 Adsorption Capacity. Figure 3 presents the microbreakthrough profiles measured for EPFO, PFOE, and PFBP

PFBP

1.66 4.53 1.60 3.66 Percent Purged NA 30 10 16

EPFO 1.95 1.71 7 6

For low RH the adsorption capacity followed a trend with PFBP > EPFO > PFOE, which is consistent with order of the vapor pressures. At low RH PFOE elutes early through the bed, possibly due to poorly packed beds; however, since the experiment is run to steady state, this observation does not affect the adsorption capacity calculation. EPFO and PFBP begin breaking through the packed bed at approximately 2.5 and 2.92 h, respectively. In the purge step, the concentration was monitored as humidified air continues to flow through the BPL. EPFO exhibits very little desorption while 30 % of PFBP is desorbed. At high RH the adsorption capacities follow a trend similar to low RH, PFBP > EPFO > PFOE. EPFO starts eluting through the bed at around 1.25 h into the experiment, as did PFOE, with PFBP breaking at around 2.5 h. It may appear if Figure 4 that PFOE should have a higher loading than EPFO but due to the differences in the molecular weight of the two chemicals EPFO has a lower feed concentration. PFOE and EPFO both show minimal desorption while desorption for PFBP is significant. No desorption was recorded for PFOE at low RH on BPL. EPFO can form ethanol and perfluorooctanoic acid via hydrolysis. To determine if this reaction was occurring, prehumidified samples of BPL, at both low and high RH, were spiked with a loading of 0.7 mol/kg. Two sets of samples were prepared, one set was stored at 50 °C and the second sample was stored at 25 °C. Chloroform was used to extract the ethanol and the samples were analyzed with GC/MS. The samples stored at 50 °C contained ethanol while the samples stored at 25 °C did not. This demonstrates that in the microbreakthrough system EPFO was not reacting via the hydrolysis route. Both PFOE and EPFO show a slight decrease in loading going from low RH to high RH; however, PFBP had almost a 1 mol/kg difference between low and high RH. Water vapor adsorbs due to capillary condensation in large pores in activated carbon and negligibly in small pores. The higher adsorption capacity of PFBP indicates that it occupies a larger pore volume and larger pores than PFOE and EPFO. In these larger pores water coadsorption can compete to a greater extent with PFBP than the other two compounds. Similarly the fraction of PFBP in larger pores of BPL is likely less well bound and thus more easily desorbed resulting in a larger desorption fraction for the less volatile PFBP. There are many factors that affect the adsorption capacities of these chemicals; such as reduced pressure, degree of fluorination, molecular weight, density, and humidity. The high electronegativity of the carbon−fluorine bond causes low intermolecular forces, which result in lower loadings of PFOE and EPFO. The difference in reduced pressure does not translate into a large difference in capacity for these highly fluorinated compounds, granted the range of reduced pressure is not large. On the other hand PFBP has a significantly higher

Figure 3. Effluent concentration vs time: red line PFOE, blue line EPFO, and green line PFBP on BPL at 20 °C and 15 % RH. Chemical concentration 139 μL·L−1.

Figure 4. Effluent concentration vs time: red line PFOE, blue line EPFO, and green line PFBP on BPL at 20 °C and 80 % RH. Chemical concentration 139 μL·L−1.

on BPL carbon at low RH; Figure 4 presents similar data at high RH. In each case, breakthrough curves conform to a sigmoidal shape commonly observed for favorably adsorbed vapors. A saturation condition is reached when the effluent concentration reaches the feed concentration. Table 10 lists the mols adsorbed per mass of BPL for each chemical at either humidity. 1810



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loading with essentially the same incremental change in reduced pressure due to the lower fluorine fraction.

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CONCLUSIONS This work presents ambient temperature vapor pressure data for five highly fluorinated chemicals, measured using a modified gas saturation technique. The measured data, Antoine coefficients, and calculated vapor pressures at 25 °C are provided, as well as calculated values for the heats of vaporization and volatility. PFHxA was shown to melt between (291.15 and 293.15) K. The normal boiling points were extrapolated from the ambient temperature data. The adsorption capacities on BPL activated carbon of three of these chemicals at 139 μL·L−1 at low and high RH were measured. We show that PFBP has a larger adsorption capacity at both relative humidities. The humidity does not have a large effect on the adsorption capacities of EPFO and PFOE, but does affect PFBP. EPFO does not undergo hydrolysis on BPL at 25 °C, but does at elevated temperatures. We have demonstrated that BPL activated carbon has a large adsorption capacity for the three compounds tested and can effectively remove the chemicals from humid air at high concentrations.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +1 (410) 436-1996. Fax: +1 (410) 436-5513. E-mail: [email protected]. Funding

This work was conducted under funding from the Joint Science and Technology Office for Chemical and Biological Defense. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank George W. Wagner for NMR purity analysis, Kenneth B. Sumpter for GC/TCD purity analyses, Tara Sewell for running the GC/MS, and David E. Tevault for conversations relating to quantifying experimental error.

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Ambient Temperature Vapor Pressure and ... - ACS Publications

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