(11) Hudson, J. L. "Sulfur Dioxide Oxidation in Scrubber Systems"; EPA Circular 600/7-80/083, 1980. 1121 Matteson. M. J.: Stober. W.: Luther. H. Ind. Ene. , Chem. Fundam 1979,8,677 (13) Bassett. H.: Parker. W. G. J Chem S O C 1951.1.1540 (14) Schroeter, L. C. "Sulfur Dioxide: Application in Foods, Beverages, and Pharmaceuticals"; Pergamon Press: Oxford, 1966; p 56. (15) Backstrom, H. L. J . Am. Chem. SOC.1927,49,1460. (161 Barrie, L. A.; Georgii, H. W. Atmos. Enuiron. 1976,10, 743. (17) Fuller, E. C.; Crist, R. H. J . Am. Chem. SOC.1941,63,1644. (18) Brimblecombe, P.; Spending, D. J. Atmos. Enuiron. 1974, 8 , 937.
(19) Coughanowr, D. R.; Krause, F. E. Ind. Eng. Chem. Fundam. 1965,4,61. (20) Karraker, D. G . J . Phys. Chem. 1963,67,871. (21) Dasgupta, P. K., University of California, Davis, CA, private communication. 1980.
Receiued for reuiew December 19,1980. Accepted August 28,1981. This work was funded by the Biomedical and Environmental Research Division of the U.S. Department of Energy under contract no. W-7405-ENG-48 and the Morgantown Energy Technology Center, U.S. Department of Energy, under contract no. 80MC14002.
Dimethyl Sulfate in Particulate Matter from Coal- and Oil-Fired Power Plants Delbert J. Eatough," Milton L. Lee, Douglas W. Later, Bruce E. Richter, Norman L. Eatough, and Lee D. Hansen Department of Chemistry and Thermochemical Institute, Brigham Young University, Provo, Utah 84602
Dimethyl sulfate cannot be determined in alcoholic extracts of acidic particulate matter because of artifact formation of alkylated sulfates. Dimethyl sulfate can be directly determined in methanolic extracts of acidic samples after neutralization of the sample with trimethylamine. Alternatively, the reaction of dimethyl sulfate in the sample with gaseous ammonia or a primary amine converts the dimethyl sulfate to monomethyl sulfate and the ammonia or amine to methyl- or methylalkylamine, respectively. These reaction products can be determined in aqueous extracts of the sample. By each of these analytical procedures, both monomethyl sulfate and dimethyl sulfate are shown to be present in an acidic coal fly ash sample collected at 110 "C. Only monomethyl sulfate is detected in particulate matter from the flue lines of two large coal- and oil-fired power plants with flue-line temperatures near 150 "C. Both dimethyl sulfate and monomethyl sulfate are present in plume particulate matter from these sources. Introduction We have reported dimethyl sulfate ((CH30)2SOz) and its hydrolysis product, monomethyl sulfate (CH30S03-), to be present in coal fly ash and in airborne particulate matter associated with emissions form coal-fired boilers ( I ). The identification of dimethyl sulfate is important because of the known mutagenic and carcinogenic properties of this compound ( 2 ) . In the previously reported study ( I ) neutral or basic fly ash samples from two coal-fired boilers and neutral or basic atmospheric particulate samples of emissions from a small coal-fired boiler were analyzed for dimethyl and monomethyl sulfates. Samples were first extracted with dichloromethane to remove nonpolar organics from the samples. The samples were then extracted with methanol, and the methanol extracts analyzed for dimethyl sulfate by capillary column gas chromatography with a sulfur-selective flame photometric detector (FPD) and also by gas chromatography-mass spectroscopy (GC-MS). Dimethyl sulfate was also determined in water extracts of the sample by analysis by gas chromatography for methanol produced by hydrolysis of the dimethyl sulfate (eq 1). 0
0
I1
CH,OSOCH,
II
+
H,O
=
1I 1I
CH,OSOH
+
CH,OH
(1)
0 0 Monomethyl sulfate was determined by ion chromatography 1502
Environmental Science & Technology
(IC) in aqueous extracts or in methanolic extracts after the methanol was evaporated and the residue dissolved in water. The hydrolysis of dimethyl sulfate in water extracts was also followed by measuring the increase in the concentration of monomethyl sulfate with time according to reaction 1. The results presented in the earlier report (1)were all based on the analysis of basic particulate matter. In those' analyses, dimethyl sulfate concentrations determined directly by GC-MS analysis of methanol extracts agreed with concentrations determined from the increase in methanol and monomethyl sulfate in aqueous extracts. Monomethyl and/or dimethyl sulfate is formed from sulfate during methanol extraction of acidic samples according to eq 2 and 3. H2S04 + 2CH30H = (CH30)2S02 H2S04
+ 2H20
+ CH30H = CHsOSO3H + HzO
(2)
(3)
While reactions 2 and 3 are endothermic by 22 and 15 kcal/ mol, respectively ( 3 , 4 ) ,the reactions proceed as written because of the high activity of the alcohol solvent. Studies were thus initiated to find a suitable method for determination of dimethyl and monomethyl sulfates in acidic samples. The results of these studies are reported in this paper. These techniques were then used to determine the concentrations of dimethyl and monomethyl sulfates in particulate matter from the flue lines and the plumes of coal- and oil-fired power plants. The results conclusively prove the presence of monomethyl and dimethyl sulfates in emissions from these plants. Experimental Section To provide a homogeneous sample for comparison of analytical techniques, we collected several hundred grams of particulate matter from the flue line (gas temperature 110 "C) of a modern chain-grate, stoker-type, coal-fired heating plant which burns -20 000 ton of coal/yr. The coal was lowsulfur (0.5%),high-ash (14%) coal from southern Utdh. Since the particulate acidity increases as the particle size decreases ( 5 ) , a fly ash sample was collected from the flue line in a nonisokinetic sampler designed to collect only very small particles. The flow velocity of gases in the flue line is 4 m/s. A 2.2-mm diameter sampling nozzle was pointed downstream in the line, and air drawn through the nozzle onto an acidwashed quartz filter at a sampling rate of -60 L/min. The fly ash so obtained was characterized by light microscopy to be reasonably homogeneous in nature, largely free of large glassy spheres, and highly carbonaceous. The fly ash appeared to 0013-936X/81/0915-1502$01.25/0
@ 1981 American Chemical Society
consist of 2-5-pm aggregates of smaller particles. Every 24 h the filter was changed and the collected material removed by shaking. Collected fly ash was stored in a glass bottle a t -80 "C. When several hundred grams of total sample had been obtained, the sample was mixed well and stored at -80 OC. In order to characterize this test sample, water-extractable anions and cations were determined by extraction of either cg. 5 mg of ash/(mL of H2O) or 200 mg of ash/(mL of H2O) for 20 min in an ultrasonic bath followed by IC analysis of the extracted material using a Dionex Model 10 ion chromatograph. Anions were determined by using either a 250-mm anion separator column with 2.4 mM NazC03-3.0 mM NaHC03 eluant a t a 40% pump rate or a 1000-mm anion separator column with 1.2 mM NazC03-1.5 mM NaHC03 eluant at a 20% pump rate. The latter eluant and column were specifically designed to separate CI-, NOz-, and CH30S03( I ) . Extracts were rontinely spiked with NO2- and/or CH30S03- to verify chromatogram peak identification. Cations were determined by using a 250-mm cation separator column with 5.0 mM H N 0 3 as eluant at a 40% pump rate. Estimates of acidity in the sample were obtained from pH measurements of aqueous extracts, from pH measurements of aqueous soluble material resulting from alcoholic extracts of the sample followed by vaporization of the alcohol, and from measurements of NH4+ increase in the sample following exposure to NH3(g). The unextracted ash sample was also analyzed at Argonne National Laboratory by infrared spectroscopy (IR) to determine the acidic sulfate content of the sample (6) and by time-dependent leaching experiments to estimate total strong mineral acidity (7). To test for completeness of extraction and artifact formation in various solvents, we determined dimethyl sulfate in extracts of 1.0-g aliquots of ash with 50 mL of methanol, ethanol, 1-propanol, acetonitrile, nitromethane, and dichloromethane. The sample was extracted for 20 min in an ultrasonic bath. The resulting solution was concentrated to 0.1 mL by using either a Rotovac (40 "C) or a N2 stream (25 "C), and the extracted organics were determined by GC-MS (I). Monomethyl sulfate was determined in these extracts by evaporating the remaining solvent with a Nz stream (25 "C), dissolving the residue in 2.0 mL of HzO, and analyzing the resulting solution by IC ( 1 ) .In all cases the IC determination was carried out immediately following the dissolution in water. To determine which types of acidic sulfates would result in artifact methylated sulfates, we measured the formation of methylated sulfates in methanol from sulfuric acid (reagent grade, 97%) and reagent-grade sulfate salts (NaHS04.Hz0, KHSO4, Na2S04, and F ~ ~ ( S O ~ ) ~ - XEither H ~ O )2.5 . H.L of H2SOdmL of CH3OH) or 1-2 mg of the salts/(mL of CH30H) was equilibrated for 20 min in an ultrasonic bath at room temperature. The resulting methanol solutions were then analyzed for dimethyl and monomethyl sulfates as described above. Two procedures for the determination of methylated sulfates in acidic samples were deveIoped. The first procedure involved neutralization of any strong mineral acidity followed by extraction with methanol. The sample was extracted with a 2 wt % solution of trimethylamine in dichloromethane for 20 min, washed with dichloromethane, and extracted with methanol. Determinations of dimethyl and monomethyl sulfates in the methanol extract were done as described above. In addition to the analysis of the fly ash sample, experiments were also conducted with H2S04 and KHS04 to show that neutralization with trimethylamine would prevent the formation of methyiated sulfates during dissolution of these sulfate species in methanol. In the second pTocedure developed for determipation of dimethyl sulfate in acidic samples, the fly ash was reacted with
a compound which could be methylated and the products of the methylation reaction were determined. Our earlier work ( I ) showed that measurement of the products of reaction 1, in which water is methylated, could be used to determine the amount of dimethyl sulfate originally present. However, the reaction is slow and the GC determination of methanol is tedious and insensitive. In addition, our earlier work indicated that, in some samples, hydrolysis of monomethyl sulfate could apparently be catalyzed by some coextracted material so that the increase in monomethyl sulfate due to reaction 1was not always a reliable indicator of dimethyl sulfate in aqueous extracts. The reaction shown in eq 4
can be conveniently carried out by exposure of the sample to NH,(g). Experiments with reagent dimethyl sulfate showed that exposure of the compound to NHdg) resulted in the quantitative conversion of dimethyl sulfate to monomethyl sulfate with no sulfate being formed. Therefore, the fly ash sample was analyzed by exposing 1-g portions to NH3(g), removing the unreacted NH3(g)by sweeping the container with Ar(g),extracting the fly ash with H20 for 20 rnin in an ultrasonic bath, and immediately analyzing the resulting solution for monomethyl sulfate and methylamines by IC as described above. The retention times of CH3NH3+ and K+ are too similar for these ions to be resolved with a 5 mM HN03 eluant; therefore, the K+ concentration was established from experiments in which the fly ash was not exposed to ammonia. This value was then used to correct for the K+ contribution to the chromatographic peak containing both K+ and CH$NH3+ ions. The experiments indicated that traces of dimethyl- and trimethylamines were also formed by exposure of the fly ash to ammonia. In all cases, these cations accounted for less than 5% of the methylation reaction. The dimethyl- and trimethylammonium cations elute after K+ and CH3NH3+ with the aqueous 5 mM HN03 eluant. We found that CH3NH3+ could be separated from all other cations present by using a 500-mm cation separator with a 2-propano1/2.5 mM H N 0 3 (1:4by volume) eluant a t a 40% pump rate. This procedure was also used to determine CH3NH3+ in the fly ash after exposure to NH3(g) and to determine the concentration of CH3NH3+ in the fly ash prior to reaction with NH3(g). The developed experimental techniques were used to determine the concentrations of methylated sulfates in particles produced by combustion of coal or oil. Samples were obtained from the flue lines and near downwind plumes of a coal-fired power plant and an oil-fired power plant and analyzed by the developed procedures. Determination of CH30S03- in the presence of large amounts of C1- in the ambient samples was improved by addition of AgNOa(aq) to remove the C1-. The CH30S03- peak was unaffected by this addition, as verified by standard addition of CH30S03- to the samples. The coal-fired power plant studied is an 800-MW plant located a t the mouth of a large canyon in the Colorado River basin. Particulate samples were obtained from the flue line after the electrostatic precipitator. Size-fractionated particulate samples were obtained 3 km from the stack by sampling from a plateau in the canyon wall which is impacted by the plume when wind flow directs the plume up the canyon. Details of the sampling location and procedures have been published (8). The oil-fired power plant studied is located on the Pacific Ocean coastline in central California. The plant has four generating boilers with a maximum output capacity of 1030 MW. The boilers may be fired with either natural gas or lowsulfur (0.5% by weight) fuel oil. Flue gases exit directly from the boilers into 140-m high stacks. Flue-line samples were obtained near the stack breeching when the plant was burning oil. Particulate samples were obtained by isokinetic sampling. Volume 15, Number 12, December 1981
1503
Particles were collected onto acid-washed, quartz-fiber filters (8) at 160 OC. The S03(g)in the airstream after the filter was collected by the controlled condensation technique (9),and SOz(g) was collected in two 0.1 M NaOH-HZOz bubblers after the controlled condensation coil. Sulfate concentrations in the collected particles, the condensation coil, and the bubblers were determined by ion-chromatography procedures as detailed above. Offshore breezes during the daytime cause the plume from the oil-fired power plant to travel up a 6-10-km wide valley. Several large volcanic cones are located in the valley floor, and the tops of these cones are impacted by the transported plume. Plume samples were obtained from a 290-m high cone located 12 km from the stacks. The sampling procedures used were the same as those described for the large coal-fired plant (8).
Results The results of the experiments on the formation of methylated sulfates from pure sulfate compounds are given in Table I. The data show that the major product is dimethyl sulfate, with lesser quantities of monomethyl sulfate being formed. Methylated sulfates result from extraction of acidic sulfate compounds, but not from neutral sulfate salts. The formation of traces of CH3OSO3H in methanol solutions of Fez(S04)s.xHzO is not unexpected as Fe(II1) hydrolysis will result in an acidic solution. Furthermore, exposure of the acid to trimethylamine in dichloromethane effectively prevents formation of the methylated sulfates during subsequent methanol extraction. The water-extractable cations and anions (other than H + and CH30S03-) determined in the fly ash sample from the small heating plant are given in Table 11. The results of the various experiments to determine dimethyl and monomethyl sulfates and strong mineral acidity in the sample are given in Table 111. The estimates of total sample acidity from the IR, NH~(g)-uptake, and leaching experiments are in reasonable agreement. All three methods verify the presence of strong mineral acidity in this sample. The IR data also indicate that the acidity is present as bisulfate salts. The concentrations of methylated sulfate species in this fly ash sample as determined by various methods are given in Table IV. Table 1. Formation of Methylated Sulfates from Dissolution of Pure Compounds in Methanol % of sulfate converted l o (CH30)2Soz CH30S03H
60 25 33
