Sulfur removal from coal by analytical-scale supercritical fluid extraction (SFE) under pyrolysis conditions

Sulfur removal from coal by analytical-scale supercritical fluid extraction (SFE) under pyrolysis conditions Peter K. K. Louie, Ronald and David J. Miller

C. Timpe,

Steven

Energy and Environmental Research Center, University Grand Forks, ND 58202-9018, USA (Received 15 May 1993; revised 2 1 June 1993)

B. Hawthorne of North Dakota, PO Box 9018,

Sulfur removal methods were developed using analytical-scale supercritical fluid extraction (SFE) under pyrolysis (450°C) conditions on a bituminous coal sample (IBC-101) obtained from the Illinois Basin Coal Sample Program (IBCSP) and on physically cleaned Indiana No. 3 coal samples from AMAX Research and Development Center. Approximately one-half of the total sulfur was removed from IBC-101 using supercritical CO, (40.53 MPa) under pyrolysis-SFE conditions. Using on-line SFE gas chromatographymass spectrometry (SFE-g.c.-m.s.), the major organic sulfur forms removed by pyrolysis-SFE were identified as alkyl-thiophenes (C&2,). When phosphoric acid was added to the coal prior to pyrolysis-SFE, about 80% of the total sulfur was removed from both coals regardless of whether the sulfatic sulfur, or both the sulfatic and pyritic sulfur, were removed (by HCl and HNO, extraction, respectively) prior to pyrolysis-SFE. These results demonstrate that the major fraction of sulfatic, pyritic and organic sulfur were extracted in the presence of phosphoric acid. In contrast, pyrolysis&FE with CO,-methanol appears to preferentially extract organic sulfur species, since only about 60% of the total sulfur was removed from the raw coal by pyrolysis-SFE using CO, modified with 10% methanol, while about 80% of the total sulfur was extracted if the sulfatic and pyritic sulfur were removed prior to extraction. (Keywords:

sulfur removal; pyrolysis; supercritical fluid extraction)

INTRODUCTION A major industry

problem that still plagues the coal utilization is the lack of cost effective methods for sulfur

removal from coal’. To develop an effective sulfur removal method, reliable identification and quantitation of the forms of sulfur in coal are important. Numerous attempts at characterizing sulfur species in coal have been made using classical methods such as Soxhlet extraction with perchloroethylene, and more sophisticated methods such as X-ray absorption near edge structure (XANES)*x3, X-ray photoelectron spectroscopy (XPS)4 and temperature-programmed reduction (TPR)‘,“. However, no present technique is suitable to routinely yield reliable quantitative determinations of sulfur forms in coal. Analytical-scale SFE has recently become a popular alternative to solvent extraction, because supercritical fluids have superior mass transfer capabilities and diffusivities compared to liquid solvents, and SFE produces less solvent waste7. A rapid method to extract and quantitate elemental sulfur from coal using SFE with CO,-10% methanol at 40.53 MPa and 110°C has been previously reported*. However, for the removal of sulfur species other than elemental sulfur from the coal matrix, more severe conditions such as higher temperature and the use of reactive reagents may be required. Treating coal with strong bases’,“, phosphoric acid”, or peroxyacetic acid’ 2, and extraction with supercritical ethanol 0016-2361/94/07/i 173-06 i: 1994 Butter~orth-~einemann

Ltd

and methanolI or acetone-water mixturesI have been reported to yield reductions in total sulfur content by 31-61%; but the use of such high severity conditions to directly determine sulfur forms in coal has been limited. In addition, the majority of these extractions were performed under batch (rather than flowing) conditions, which may allow retrograde reactions to reincorporate extracted sulfur species into the coal matrix. In the present paper, the use of dynamic (constant flow) SFE conditions, including pyrolysis at 450°C and the addition of chemical reactants, is investigated to determine the potential for removing inorganic and organic sulfur species for the direct determination of sulfur forms in coal. Raw coal and elemental sulfur-free coal (prepared by SFE with 10% methanol-modified C028, were treated by batch HCl and HNO, extraction to obtain sulfatefree, and sulfate- and pyrite-free coal, respectively. SFE at temperatures up to 450°C (pyrolysis-SFE) with methanol-modified CO,, and with the addition of phosphoric acid, was then used to extract sulfur species from the raw coal, sulfate-free, and sulfate- and pyritefree coal samples. On-line pyrolysis-SFE-sulfur chemiluminescence detection (pyrolysis-SFE-SCD) and on-line pyrolysis&FE-gas chromatography-mass spectrometry (pyrolysis-SFE-g.c.-m.s.) were used to obtain extraction time information for the pyrolysis-SFE experiments and to identify extracted sulfur species, respectively.

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EXPERIMENTAL Coal samples A bituminous coal, IBC-101, obtained from the Illinois Basin Coal Sample Program (IBCSP) and a physically cleaned Indiana No. 3 coal sample from AMAX Research and Development Center (AMAX) were used for this investigation. The Indiana No. 3 coal sample was initially washed at the mine to remove the fines and ash, followed by physical cleaning by magnetic separation to remove a portion of the inorganic sulfur species from the coal mass. All of the coal samples used in this work were ground under a stream of argon to - 75 pm and stored under argon in plastic containers before use. Preparation of elemental sulfur-free coal A Suprex Prepmaster pump (Suprex Corp, Pittsburgh, PA) was used to prepare elemental sulfur-free coal samples under mild SFE conditions (CO,-10% methanol, 40.53 MPa, 110°C) as previously reported’. Typically, a 5 g raw coal sample was loaded in a 10.4 ml Keystone SFE extraction cell (Keystone Scientific, Bellefonte, PA) and extracted with premixed CO,-10% methanol (Scott Specialty Gases, Inc., Troy, MI), at 40.53 MPa and 110°C for lOOmin. A 1Ocm long crimped stainless steel tube (l/16” o.d. x 0.020” i.d.) was attached at the outlet of the extraction cell to regulate the fluid flow (typically 1.5 ml min-’ as pressurized fluid measured at the pump), and the extracted effluent was collected by depressurizing into a sample vial containing 3 ml of toluene (Optima grade, Fisher Scientific, Pittsburgh, PA). The analysis of the extract was performed at regular intervals by gas chromatography with atomic emission detection (g.c.AED, Hewlett-Packard Company, Avondale, PA). Since no elemental sulfur was detected from extracts obtained during the final 15 min, quantitative removal of the elemental sulfur was assumed’. Preparation of sulfate-free coal Sulfate sulfur-free coal was prepared by using the HCl batch extraction method in accordance with ASTM guidelines (D-2492)i5. Coal samples (2g) were extracted with boiling 4.8N HCl, washed with water, filtered and dried in an oven at 100°C for 2 h. The sample was then stored under argon in plastic containers until used. Similarly, coal samples that were free of elemental and sulfate sulfur were obtained by performing HCl batch extraction on elemental sulfur-free coal samples. Preparation of pyrite and sulfate sulfur-free coal Pyritic and sulfate sulfur-free coal samples were obtained by performing HNO, batch extractions on both raw and elemental sulfur-free coal samples in accordance with ASTM method D-2492”. Coal samples (2g) were extracted with boiling 2N HNO,, washed with water, filtered, and dried in an oven at 100°C for 2 h. The sample was then stored under argon in plastic containers until used. Pyrolysis-SFE As depicted in Figure 1, the supercritical fluids (pure CO, or CO,-10% methanol, Scott Specialty Gases) were introduced into the extraction cell via a Suprex Prepmaster pump or an ISCO Model 1OOD syringe pump (ISCO, Lincoln, NE) and a 2m long (1/16”o.d. x 0.020” i.d.) stainless steel preheating coil. Keystone high

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Figure 1 A schematic diagram of the pyrolysis-SFE extraction system. Either a Suprex Prepmaster or an ISCO pump, filled with CO, or CO,-10% methanol, was used to deliver the supercritical fluids. The methanol-modified fluid was transported via a 0.020” i.d. stainless steel tubing and preheating coil (2 m long) before entering the extraction cell placed in a g.c. oven

pressure liquid chromatography (h.p.1.c.) columns (30 mm long, 4.6mm id. x 6.35mm o.d., 0.5ml volume, Keystone Scientific Inc., Bellefonte, PA) were used for the pyrolysisSFE experiments, because of the high pressure and temperature (54.72 MPa and 482°C respectively) capability of these cells (note that the SFE cells sold by the same supplier are not suitable because of the failure of the polyimide seals at 450°C). The preheating coil and the extraction cell were placed inside a g.c. oven (HewlettPackard 5890 Series II gas chromatograph, Avondale, PA) to control the extraction temperature. A fluid flow rate of about 1.6 ml min- ’ (measured as liquid CO, at the pump) was achieved using a crimped 1Ocm long (l/16” o.d. x 0.020” i.d.) stainless steel restrictor attached at the outlet of the extraction cell. The effluent from the cell was vented into a hood. Pyrolysis-SFE experiments were performed on 50 mg coal samples that were mixed with 50mg of clean sand (sea sand, Fisher Scientific) to avoid the formation of a hard plug during the extraction. A premixed cylinder of 10% (v/v) methanol in CO, (Scott Specialty Gases) was used to supply the methanol-modified CO, for the 30min extractions. Pyrolysis-SFE experiments involving the addition of other additives to coal samples prior to extractions were performed using pure CO, as an extraction fluid. Approximately 200 ~1 of phosphoric acid (85% reagent grade, J. T. Baker Chemical Co., Phillipsburg, NJ), ethanol (dehydrated, US Industrial Chemical Co. New York, NY) or acetic acid (h.p.1.c. grade, Fisher Scientific) were introduced by spiking on to the coal samples prior to pyrolysis-SFE. After assembling the extraction apparatus, the extraction cell was pressurized to 40.53 MPa and held under static conditions (no flow out of the cell) while the oven was heated rapidly at about 32”Cmin’ to 450°C (requiring about 13 min). The dynamic extraction (constant fluid flow) was then begun and was continued for 30min at 40.53 MPa and 450°C. After each extraction was completed, the oven was cooled to ambient temperature before the extraction cell was detached from the extraction line. The entire content of the extraction cell was collected and analysed for total sulfur using a LECO titrimetric analyser (LECO Corp., Bellefonte, PA) in accordance with ASTM guidelines. The extent of sulfur species removal from either untreated or treated coal feeds (expressed in percentage of sulfur removed) was determined by comparing the total sulfur content in the SFE-extracted residues (in mg of sulfur) with that in the untreated raw coal (in mg of sulfur).

Supercritical On-line pyrolysis-SFE-SCD Applications of on-line SFE (in which the extraction cell is interfaced directly to an analytical instrument) for direct analysis of SFE extracts from complex matrixes have been describedt6. In the present study, on-line pyrolysis&FE-SCD was used to obtain real-time information about total sulfur species removed by pyrolysisSFE while minimizing any potential analyte losses (e.g. volatile sulfur-containing species) that would likely occur during off-line SFE collection. The on-line technique is similar to pyrolysissSFE except that the extracted sulfur species are detected in real time in the SFE extract during the extraction by a sulfur chemiluminescence detector (SCD Model A, Sievers Research Inc., Boulder, CO). For pyrolysis&FE-SCD, the extraction cell was mounted in the same g.c. oven that contained the flame ionization detector (FID) needed for the SCD detector. SFE extracts were directly transferred to the FID (and thus the SCD detector) by attaching the outlet restrictor of the SFE cell to the FID in a manner similar to that which would normally be used to install a capillary gas chromatographic column. Since the sensitivity of the SCD for sulfur is too high to allow all of the extract to be transferred to the detector, the SFE effluent was split prior to entering the detector by attaching a 33 pm i.d. 7 cm fused silica capillary tube (for a vent line) and a 15 pm i.d. 1Ocm silica capillary tube (connected to the FID) to a 1.6mm stainless steel ‘tee’. This arrangement allowed reproducible introduction of about one-tenth of the SFE effluent into the detector as previously described”. On-line SFE-g.c.-ms. On-line pyrolysis-SFE-gc-m.s. was performed similarly to pyrolysis-SFE except that a g.c.-ms. was used to analyse the SFE extracts, and the extraction cell was maintained at a constant temperature with a tube heater. Typically, about 1 mg of coal was mixed with sand and placed in the extraction cell before the cell was sealed and placed in the tube heater. The extracted analytes were directed by a 1Ocm long x 30pm i.d. fused silica restrictor connected to the extraction cell and threaded through a septumless injector (SGE Incorporated, Austin, TX) into the split-splitless injection port of an HP5985 g.c.-m.s. equipped with a 25 m x 0.32mm i.d. thin film (0.17 pm film thickness) DB-5 column as previously described for SFE-g.c. I6 . The extraction cell was preheated from ambient temperature to 450°C for 15 min, followed by a 30min extraction with 40.53 MPa CO, at 450°C. The extracted analytes were trapped cryogenically (- 50°C) at the inlet of the g.c. column. After the SFE step, the trapped analytes were analysed by rapidly heating (50°C min- ‘) the g.c. oven to 35°C followed by a temperature ramp at 8°C min-’ to 320°C.

RESULTS

fluid extraction

Table 1 Proximate and Indiana No. 3

of sulfur: P. K. K. Louie

and total sulfur analysis

of coal samples

et al. IBC-101

Coal sample

Moisture (wt %)

Volatile matter (wt %)

Fixed carbon (wt %)

Residue (wt %)

Total sulfur (wt %, db)

IBC-101” Indiana No. 3b

9.0 4.8

35.8 41.7

44.6 46.8

10.5 11.5

4.3 4.2

“Analysis performed by Energy and Environmental University of North Dakota, Grand Forks, ND b Analysis data provided by AMAX

Research

Center,

the physically cleaned Indiana No. 3 have relatively high organic sulfur (73 and 70% total sulfur, respectively) based on the difference measurement used by the ASTM technique. The elemental sulfur values of both IBC-lOl* and Indiana No. 3 coal samples are similar, and are relatively low compared with the total sulfur values, i.e. 0.11 and 0.17 wt % of the coal, respectively. Establishing

pyrolysis-SFE

conditions

By performing pyrolysissSFE under dynamic conditions, the possibility of secondary reactions involving the extracted sulfur species and the coal matrix may be reduced since solvated species are rapidly removed from the coal. Preliminary extractions with CO,, performed with the extraction cell in a muffle furnace, demonstrated that a substantial amount of the total sulfur (about 50%) was removed under pyrolysis-SFE conditions at temperatures up to about 500°C. However, this system did not allow accurate temperature control, and could not be used to determine the important temperature ranges for sulfur removal. Therefore, on-line pyrolysis-SFE-SCD was performed using temperature programming in a g.c. oven to observe the extent of sulfur removal as a function of extraction temperature and time. The sulfur response versus temperature and time for on-line pyrolysis-SFESCD from 45 to 450°C with 40.53 MPa CO, is given in Figure 2. The initial peak at about 300°C may be attributed to non-thiophenic sulfur species5*‘8,‘9. As the temperature increased from 300 to 450°C a larger peak was detected which may be attributed to thiophenic sulfur species5,‘8,‘9. It appeared that most of the extractable sulfur species were removed under the pyrolysis-SFE conditions employed, since after the extraction temperature reached 450°C no significant amount of sulfur species was extracted. Therefore, all the subsequent

AND DISCUSSION

Characterization

of samples

Proximate and total sulfur analyses of the two coal samples used in this study, IBC-101 and the physically cleaned, non-magnetic fraction of Indiana No. 3, are given in Table 1. Sulfur form analyses of coal samples IBC-101 and Indiana No. 3, based on the ASTM guidelines15 and the SFE method for quantitating elemental sulfur*, are given in Table 2. IBC-101 and the Indiana No. 3 have similar total sulfur values. In addition, both IBC-101 and

0”

I

10

20

30

40

50

60

Time (min) I 45

I 45

I 100

I 200

300

400

I 450

I 450

Temperature (OC)

Figure 2 Sulfur response versus temperature for on-line analysis of extracted sulfur using pyrolysis-SFE-SCD carried out over the temperature range 45450°C with 40.53 MPa CO,

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Sulfur form analyses of coal samples IBC-101 and Indiana No. 3 ASTM-defined ‘organic’ sulfur

Coal sample

Sulfatic sulfur (wt % sulfur)

Pyritic sulfur (wt % sulfur)

Organic sulfur (wt % sulfur)

Elemental sulfur (wt % sulfur)

IBC-10lb Indiana No. 3

16 19

11 11

70 66

2.5 4.0

‘Values determined using the method in reference 8 *Average values of sulfur form analyses performed by MVTL and Huffman Laboratories, Inc. ‘Average values of sulfur form analyses performed by MVTL, Huffman Laboratories, Inc. and AMAX

pyrolysis-SFE 40.53 MPa.

expe~ments were performed at 450°C and

Sul_fiirremoval using pyrolysis-SFE with and without additives The amounts of total sulfur extracted from coal with different supercritical fluids and chemical reagents (expressed in percentage of sulfur removed) are given in Table 3. Pyrolysis-SFE with pure CO, removed about one-half of the total sulfur content from IBC-101, but the addition of 200~1 aliquots of either acetic acid or ethanol yielded no increase in extraction efficiencies. (The failure to increase the sulfur removal with acetic acid or ethanol may possibly be because these additives were likely removed rapidly from the coal sample once the dynamic SFE extraction was begun. However, the coal samples were exposed to these reagents at 40.53 MPa CO, during the 13min required to heat the g.c. oven from ambient to 450°C.) When the premixed 10% methanol in CO, was used as the extraction fluid, the sulfur removal increased to about 60% for both coal samples. However, the highest sulfur removal (about 80% from both coals) was achieved using the 200~1 addition of phosphoric acid with pure CO, as the extraction fluid (Table 3). Based on the high percentage of sulfur removal, pyrolysis-SFE with CO,-10% methanol, and COz with phosphoric acid spiked on the coal samples, were chosen for further evaluation using the elemental sulfur-free, sulfate-free, and pyrite-free coals. Percentages of total sulfur removal from both raw and partially desulfurized coal samples of IBC-101 and Indiana No. 3 by pyrolysisSFE using CO,-10% methanol and CO,-phosphoric acid are given in Table 4 on a raw coal basis. The total amount of sulfur extracted using C02-10% methanol depended heavily on whether the inorganic forms had previously been extracted. For example, about

Table 3 Percentage of sulfur removal from elemental-free IBC-101 and Indiana No. 3 with different supercritical fluids -Percentage of total sulfur removed” SF fluids-reagents

IBC-101

Indiana No. 3

COZ CO,-MeOH CO,-acetic acid CO,-ethanol CO,-H,PO,

4911 62+3 43&2 48kl 82_+3

ND” 6Oi7 ND” NDb 78+9

“Standard deviations are based on triplicate, 30min extractions bND, not determined

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Table 4 Pyrolysis-SFE sulfur removal from IBC-101 and Indiana No. 3 using supercritical CO,-10% MeOH and CO,-phosphoric acid % sulfur removal on total sulfur basis*

CO,-MeOH IBC-101

Indiana No. 3

IBC-101

Indiana No. 3

62+3 70&l 68-t-l 78kl 81&2

60&7 72kl 68+2 74*3 72&4

82,3 83+13 81,12 78&13 80&11

78k9 85&23 84+7 81 k 12 74+10

Coal samples Raw Sulfate-free S,- and sulfate-free Sulfate- and pyrite-free S,-, sulfate- and pyrite-free

CO,-phosphoric acid

’ Standard deviations are based on triplicate. 30 mm extractions

60% of the total sulfur (coal basis) was extracted from

the raw coal samples IBC-101 and Indiana No. 3. When the sulfate-free coal was extracted the total sulfur removal was about 70%, and when the sulfate- and pyrite-free coals were extracted the total sulfur removal increased to about 80%. The removal of elemental sulfur prior to pyrolysis-SFE had little effect on the total sulfur removal, as would be expected since elemental sulfur only accounted for 34% of the total sulfur (Table 2). Since the total sulfur removal achieved using pyrolysisSFE with CO,-10% methanol depended on the prior removal of the inorganic forms, it is reasonable to expect that pyrolysis&FE primarily extracts organic sulfur species. In contrast to the COz-10% methanol extractions, the total amount of sulfur extracted from both coals using pyrolysis-SFE performed with the addition of phosphoric acid showed no dependence on prior removal of the sulfate and pyrite (Table 4). Approximately 80% of the total sulfur was removed regardless of any pretreatment, and the same removal was achieved with raw coal with a single step extraction in the presence of phosphoric acid. These results demonstrate that pyrolysis&FE with phosphoric acid removes all major sulfur forms in both coal samples including sulfate, pyrite and a large proportion of the organic sulfur. (As was the case for the CO,-10% methanol extractions, the prior extraction of the elemental sulfur had no significant effect on the results since the concentration of elemental sulfur in both coals was very low.) Interestingly, the maximum sulfur removal achieved using pyrolysis-SFE with CO,-10% methanol (after removal of the inorganic forms) and using CO2 with phosphoric acid (regardless of whether the sulfate

Supercritical

of sulfur: P. K. K. Louie et al.

fluid extraction

CO, removals were only about 10% lower than those achieved using CO,-10% methanol as shown in Tables 3 and 4.) As shown in Figure 3, pyrolysis-SFE-g.c.-m.s. demonstrated that the sulfur-containing organics were primarily C-C, alkyl-thiophenes, benzothiophene and dibenzothiophene. These species are thought to correspond to the second peak obtained with pyrolysisSFE-SCD (Figure 2). Since trapping efficiencies are poor for very volatile species, some volatile sulfides may not be detected during on-line pyrolysis-SFE-g.c.-m.s.. A strong sulfide smell was noticed at about 300°C in off-line pyrolysissSFE, which indicates their presence and may correspond to the first peak obtained during pyrolysisSFE-SCD (Figure 2). Since previous investigations using SFE under lower temperature conditions (e.g. 40.53 MPa CO,-10% methanol, 1lO“C) showed only elemental sulfur in coal extracts’, the presence of high concentrations of thiophenic organics indicates that pyrolytic bond breaking is necessary for the organic forms of sulfur to be extracted.

and pyrite were removed) were essentially the same for both coal samples (Table 4). Estimation of organic sulfur removed

The results shown in Table 4 using the raw, sulfate-free, and sulfate- and pyrite-free coals demonstrate that both pyrolysis&FE conditions remove a substantial portion of the true organic sulfur. Assuming that the HCl extraction quantitatively removes sulfate, and that the HNO, extraction quantitatively removes sulfate and pyrite, the percentage of organic sulfur removed by CO,-10% methanol and by the addition of phosphoric acid followed by pyrolysis-SFE can be estimated. For example, if 70% of the sulfur in IBC-101 is organic, and if CO,-10% methanol combined with HNO, extraction removed 78% of the total sulfur (Table 4), then the minimum fraction of true organic sulfur extracted by pyrolysis&FE with CO,-10% methanol would be 73% (78% total sulfur removed minus 27% inorganic removed by HNO,, equals 51% of total sulfur extracted by SFE; which is equivalent to 73 % of the organic sulfur removed by SFE). Similarly, pyrolysis-SFE with CO,-methanol extracts a minimum of 70% of the true organic sulfur from the Illinois No. 3 coal. The results shown in Table 4 also demonstrate that the addition of phosphoric acid causes the extraction of both sulfate and pyrite as well as a substantial portion of the organic sulfur. Again, assuming that the HNO, quantitatively extracts the sulfate and pyrite, the minimum fraction of organic sulfur extracted by pyrolysis-SFE with the addition of phosphoric acid would be 69 and 73% for IBC-101 and Illinois No. 3, respectively.

CONCLUSIONS Pyrolysis&FE, at 450°C with CO, and phosphoric acid, extracts about 80% of the total sulfur from bituminous coals in 30min. Since the total sulfur extracted does not change when sulfate and pyrite are removed by HCl and HNO, extraction prior to SFE, pyrolysis-SFE with phosphoric acid results in the removal of sulfatic, pyritic and organic sulfur. In contrast, pyrolysis-SFE with CO,-10% methanol selectively removes organic sulfur, since pre-extraction with HNO, to remove sulfatic and pyritic sulfur was required to obtain a total sulfur removal of about 80%. Assuming that HNO, extraction quantitatively removes sulfatic and pyritic sulfur, the use of either pyrolysissSFE with added phosphoric acid, or pyrolysis&FE with CO,-10% methanol, extracts a minimum of about 70% of the true organic sulfur. On-line pyrolysis-SFE-gc-m.s. demonstrated that the major organic forms of sulfur removed were thiophenic.

Pyrolysis-SFE-g.c.-m.s.

Since it is clear from the results in Table 4 that a substantial amount of organic sulfur species were extracted by pyrolysis-SFE, attempts to identify the organic sulfur species removed were made using on-line pyrolysisSFE-g.c.-m.s. (40.53 MPa, 450°C) using pure CO,. (On-line pyrolysis-SFE-g.c.-m.s. could not be performed with the additives because of the negative effects of the additives on the chromatographic system. However, the results obtained using pyrolysissSFE with pure CO, should be representative of the organic sulfur species removed with methanol or phosphoric acid since pure

ACKNOWLEDGEMENTS The authors acknowledge the US Department of Energy (Morgantown Energy Technology Center) for their

C5 Thiophene

C3 Thiophene

i

! Dibenzothiophene

i

_.~_

0.0

5.0

10.0

15.0

20.0

25.0

.~

30.0

- -/$oo

35.0

Time (min.) Figure3

Total ion chromatogram

ofextract

obtained

by pyrolysis-SFE-g.c.-m.s.

on-line extraction

and detection

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support of this project. Gratitude is also extended to ISCO corporation (Lincoln, NE), Suprex Corporation (Pittsburgh, PA) and Sievers Research Inc. (Boulder, CO) for instrument support.

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REFERENCES

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Dorland, D., Stiller, A. H., Mintz, E. A. Fuel Process. Technol. 1992,30, 195 Jagtoyen, M., McEnaney, B., Stencel, J., Thwaites, M. and Derbyshire, F. Am. Chem. Sot. Div. Fuel Chem.. Prepr. 1992, 37(2), 505 Palmer, S. R., Hippo, E. J., Kruge, M. A. and Crelling, J. C. Coal Prep. 1992, 10, 93 Chen, J. W., Muchmore, C. B., Kent, A. C. and Chang, Y. C. Am. Chem. Sot. Div. Fuel Chem., Prepr. 1985,30(3), 173 Azzam, F. O., Fullerton, K. L., Kesavan, S. and Lee, S. Fuel Sci. Technol. Int. 1992, 10(3),347 American Society for Testing and Materials, ‘Annual book of ASTM standards’, Vol. 05.05, ‘Gaseous Fuels: Coal and Coke’, ASTM, Philadelphia, 1991 Hawthorne, S. B., Miller, D. J. and Langenfeld, J. J. J. Chromatogr. Sci. 1990, 28, 2 Timpe, R. C., Louie, P. K. K., Miller, D. J. and Hawthorne, S. B. in ‘Proceedings of the Eighth Annual International Pittsburgh Coal Conference’, Pittsburgh Coal Conference, Greensburg, PA, 1991, p. 63 Attar, A. in ‘Analytical Methods for Coal and Coal Products’, Vol. III, Academic Press, New York, 1979, Ch. 56 Majchrowicz, B. B., France, D. V., Yperman, J., Reggers, G., Gelen, J., Martens, J., Mullens, J. and van Poucke, L. C. Fuel 1991,70,434