972
Anal. Chem. 1982, 54, 372-375
resin structure, any handling favoring the exposure of new surface area can release appreciable quantites of contaminants such as those shown in Table 111. LITERATURE CITED Crook, E. H.; McDonnel, R. P.; McNulty, J. T. Ind. Eng. Chem. Prod. Res. Dev. 1975, 14, 113. Burnham. A. K.; Calder, G. V.; Fritz, J. S.; Junk, G. A,; Svec, H. J.; Vlck, R. J. Am. Water Works Assoc. 1973, 1 1 , 722. Fritz, J. S. Ind. Eng. Chem. Rod. Res. Dev. 1975, 14,94. Junk, 0. A.; Rlchard, J. J.; Grelser, M. D.; Witlak, P.; Witlak, J. L.; Arouello. M. D.: Vlck. R.: Svec. H. J.:. Fritz.. J. S.: Calder. G. V. J. c6omatcgr. 1474, 9 9 , i45-762. Burnham. A. K.; Calder, G. V.; Fritz, J. S.; Junk, G. A.; Svec, H. J.; Wlllis, R. Anal. Chem. 1972, 44, 139. Ryan. J. P.; Fritz, J. S. J. Chromatcgr. Scl. 1978, 16,488. Vinson, J. A.; Burke, G. A.; Hager, B. L.; Casper, P. R.; Nylander, W. A.; Mlddlemlss, R. J. Envlron. Lett. 1973, 5, 199-207. Suffet, I.H. Envlron. Scl. Techno/. 1978, 12, 1315. Suffet, I.H.; Brenner, L.; Silver, B. Mvlron. Scl. Technol. 1976, 10. 1273. Berkane, K.; Caissle, G. E.; Mallet, V. N. J. Chromatogr. 1977, 130, 386-390. Webb, R. G. EPA Report No. 86014-75-003; Southeast Envlronmental Research Laboratory: Athens, GA, June 1975. Woodrow, J. E.; Sieber, J. N. Anal. Chem. 1978. 50, 1229. Kamlnski, F.; Melcher, R. G. Am. Ind. Hyg. Assoc. J . 1978, 39, 678.
(14) Sydor, R.; Pietrzyk, D. J. Anal. Chem. 1978, 50, 1842. (15) Snyder, A. D.; Hodgson, F. N. EPA Report No. 60012-76-201; Monsanto Research Corp.: Dayton, OH, 1976. (16) Pelllzzari, E.; Bunch, J. E.; Carpenter, B. H.; Sawicki, E. Environ. Scl. Technol. 1975, 9 , 557. (17) Jones, P. W.; Glammar, R. P.; Strup, P. E.; Stanford, T. B. Environ. Scl. Technol. 1978, IO, 807. (18) Russel, J. W. Envlron. Sci. Technol. 1975, 9 , 1175. (19) Pelllzzari, E. D.; Carpenter, 8. H.; Bunch, J. E.; Sawicki, E. Envlron. Sci. Technol. 1975, 9 (13), 553. (20) Fitch, W. L.; Smlth, D. H. Environ. Sci. Technol. 1979, 13, 341. (21) Chang, R. C.; Fritz, J. S. Talanta 1978, 25, 659-663. (22) Amberllte XAD-2, Technical Bulletin; Rohm and Haas Co.: Philadelohia. PA. Nov 1978. (23) hmberllte XAD-4, Technical Bulletin; Rohm and Haas Co.: Philadeiohia. PA. Nov 1978. (24) Strup, P.’E.; Wilkinson, J. E.; Jones, P. W. I n “Carcinogenesis, Vol. 3, Polynuclear Aromatic Hydrocarbons”; Jones, P. W., Freudenthal, R. I., Eds.; Raven Press, New York, 1978. (25) Lentzen, D. E.; Wagoner, D.E.; Ester, E. D.; Gutknecht, W. F. IERLRTP Procedures Manual: Level 1 Environmental Assessment, 2nd ed., EPA Report No. 600/7-78-201, Oct 1978. (28) Arnbersorb Carbonaceous Adsorbents, Rohm and Haas Co.: Phiiadelphla, PA.
RECEIVED for reveiw April 10,1981. Resubmitted September 21,1981. Accepted November 16, 1981.
Separation of Solvent-Refined Coal into Solvent-Derived Fractions M. M. Boduszynskl” and R. J. Hurtubise* Chemistry Department, The Unlverslty of Wyoming, Laramle, Wyoming 8207 I
H. F. Sliver Chemical Engineering Department, The University of Wyoming, Laramie, Wyoming 8207 1
A method for the separatlon of solvent-reflned coal (SRC) and hydrotreated SRC Into n -hexane soluble, “oils”, toluene soiuble-n-hexane insoluble, “asphaltenes”, and pyrldlne soluble-toluene Insoluble, “preasphaltenes”was developed. The separatlon into soivent-derlved fractlons was achleved by eluting a SRC sample which was coated on an inert support material (Fiuoropak) from a llquld chromatographlc column. A sequence of nhexane, toluene, and pyridine solvents were used to elute the SRC fractlons. The unique feature of the method allows for further separation of the soivent-derlved fractions Into major compound classes wlthout the need to evaporate solvents and redlssolve fractlons. Thls can be achleved by Integrating the SRC-coated Fluoropak column wlth llquld chromatographlc columns. Varlous SRC samples were lnvestlgated by using the procedure.
General characterization of coal-derived products has been based on two major separative techniques, namely, solvent extraction and liquid chromatography. Solvent fractionation has long been used as a method of process monitoring despite the fact that it does not produce chemically meaningful fractions (1,2).The most commonly used classification has been pentane solubles (oils), benzene soluble-pentane insoluble (asphaltenes), and pyridine soluble-benzene insoluble 0003-2700/82/0354-0372$01.25/0
(preasphaltenes or asphaltols). Several procedures using various extractive solvents, have been published (3-8). Solvent-derived fractions have been usually obtained over a period of days using time-consuming Soxhlet extractions. The method described by Mima et al. (3) is an example. A less time-consuming but somewhat complex procedure requiring repeated washing, sonication, and centrifugation steps and large volumes of solvents was suggested by Schweighardt and Thames (4). A more rapid method based on sequential elution of a sample after injection onto a liquid chromatography column packed with glass beads was published by Burke et al. (5). Very recently Schultz and Mima (8)published results of a comparison of five different methods currently used. The authors reported that each of the methods produced different results for the same material. A need for a standard method was emphasized. Regardless of the confusion caused by using similar terms (oils, asphaltenes, preasphaltenes) to defiie dissimilar fractions and despite the fact that solvent-derived fractions do not have a unique chemical composition, solvent extraction is still an accepted technique for monitoring coal conversion processes. It is generally recognized, however, that a detailed analysis of solubility fractions is an essential requirement for an indepth study of the chemistry of coal liquefaction. The variety of coal-derived products (e.g., gases, distillates, nondistillable residues, etc.) requires that the separation procedure for in0 1982 Arnerlcan Chemlcal Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982
vestigating their composition be designed for a specific type of sample. The purpose of our work was to develop separation methds specific for solvent-refined coal (SRC) and hydrotreated SRC. The SRC or hydrotreated SRC is defined as a vacuum residue of a solubilized coal prloduct boiling generally above 800 "F (427 "C)which is soluble in pyridine. The hydrotreated SRC samples were subjected to distillation prior to the extractive procedure and thus did not contain low boiling components. The primary objective of our study was to develop methods that would allow an integration of solvent extraction and liquid chromatography techniques so that both the solubility characteristics and the chemical compohiition of SRC or hydrotreated SRC could be obtained. The method developed is unique as it achieves a separation of SRC based on solubility in a sequence of commonly used solvents (n-hexane, toluene, and pyridine) followed by liquid chromatography separation of solvent-derived fractions without the need to evaporate solvents and redissolve fractions for further separation. The liquid chrornatography method which separates the solvent-derived fraction into major compound class fractions ita the subject of a separate paper (9). If only solubility characteristics of SRC simples are required, the method as described here allows for rapid separation of the SRC sample into three solvent-derived fractions by utilizing a liquid chromiitography system equipped with a SRC-coated Fluoropak column. Should more detailed information be needed, the SRC-coated Fluoropak column can be connected to a series of liquid chromatography columns (9). With this arrangement, solvent-derived fractions can be directly introduced into the chromatographic system and separated into major clompound classes. In this paper the separation of SRC into solvent-derived fractions of n-hexane solluble, "oils", toluene solublen-hexane insoluble, "asphaltenesi", and pyridine 13oluble-toluene insoluble, "preasphaltenes", is discussed. EXPERIMENTAL SECTION Materials Studied. Six different untreated and hydrotreated SRC samples were used in this study. These included three "Wyodak SRC" samples that were produced from a subbituminous coal from the Canyon-Anderson seanns in the Amax Coal Co. Belle Ayr Mine in Wyoming. Two Wyodak SRC samples, F-45 low-ash SRC (0.52 w t % ash) and F-46 high-ash SRC (11.7 w t % ash), were supplied from the Southern Company Services, Inc., SRC pilot plant located at Wilsonville, AL,by Catalytic, In@. (10). The F-45 and F-46 SRC samples represent vacuum bottoms boiling above about 800 OF (427 "C) and 650 OF (343 "C), respectively. The third Wyodak SRC sample (F-31) was an upgraded low-ash SRC obtained by severe hydrogenation of F-45 (11). This sample was dicitilled prior to the extractive separation step. The other three samples were "Kentucky SRC" samples produced from a bituminou,~Kentucky 9/14 coal. A low-ash F-51 SRC (0.09 w t %) was obtained from the Pittsburgh and Midway Coal Mining Co., SRC pilot plant near Tacoma, WA. This sample represented a vacuum bottom boiling above 975 OF (524 "C). SRC samples F-36 and F-37 were upgraded low-ash SRC samples obtained from F-51 Kentucky 9/14 SRC by mild and severe hydrogenation, respectively (11). These last two samples were distilled prior to the extractive separation step. Apparatus and Chemicals. The system for a separation of SRC or hydrotreated SRC into n-hexane soluble, toluene soluble-n-hexane insoluble, and pyridine soluble-toluene insoluble fractions is shown in Figure 1. It consisted of a precision bore glass column 9 mm X 50 cm (Altex ScientificInc.) equipped with a solvent delivery pump and pulse dampener (Fluid Metering, Inc.), solvent reservoirs, and fraction receivers. The column bed supports had a 40-60 wm porous Teflon filter set in a Tefzel backing disk. The system was kept under nitrogen gas atmosphere and the column and glsiss graduated cylinders for collecting fractions were covered with black paper.
373
Experimental setup for separation of SRC samples: (1) SRC-coated Fluoropak column, (2) solvent reservoirs, (3) solvent delivery pump, (4) fraction receivers, (5) nitrogen gas. Figure 1.
A nitrogen gas sweep N-Evap evaporator (Organomation Associates) and a vacuum rotary evaporator/Rotavapor R 110 (Buchi) were used to remove solvents from the fractions. An ultrasonic bath Bransonic 12 (Branson Cleaning Equipment Co.) was used to sonicate a mixture of SRC and tetrahydrofuran during the coating procedure. An inert (Teflon) chromatographic support material Fluoropak 80,2040 mesh (The Fluorocarbon Co.), was washed with absolute methanol to remove a static charge and fines. Then it was dried under vacuum with a rotary evaporator at room temperature. Normal hexane 99+ mol % (Phillips Chemical Co.), toluene reagent grade (Mallinckrodt, Inc.), pyridine reagent grade (MCB Manufacturing Chemists, Inc.), and absolute methanol reagent grade (VWR Scientific, Inc.) were distilled prior to use. Tetrahydrofuran, unstabilized HPLC grade (Fisher Scientific Co.), was used as received. Procedures. Coating of Fluoropak with SRC or Hydrotreated SRC Sample. A sample was frozen in dry ice and then ground into a fine powder. This contributes to a rapid dissolving in tetrahydrofuran and efficient coating of Fluoropak support material. A sample of 0.3000 g of SRC or hydrotreated SRC was accurately weighed in a 10-mL vial and 4 mL of tetrahydrofuran was added. The mixture was sonicated for about 5 min. Most of the sample dissolved readily in tetrahydrofuran. Small amounts (up to 10%)of THF insolubles remained suspended in a mixture and were readily transferred together with the solution. The vial content was carefully transferred with a micropipet onto the surface of Fluoropak support material (22 g) contained in a 100-mL round-bottom flask. An additional 1mL of tetrahydrofuran was used to rinse the vial and was also introduced onto the Fluoropak. The solvent was patially removed under nitrogen gas flow at rmm temperature for about 15 min. The SRC-coated Fluoropak was finally dried under vacuum with a rotary evaporator at room temperature for about 15 min. A fresh sample of Fluoropak was used for each run. An Altex glass column was packed with the dry SRC-coated Fluoropak and a small amount of uncoated Fluoropak was added to fill up the column void. The column was then covered with black paper and purged with nitrogen gas to minimize the risk of chemical alteration of the sample due to oxidation and exposure to light. The packed column was connected to the system (Figure 1) and was ready for elution of SRC fractions. Elution of SRC or Hydrotreated SRC Solvent-Derived Fractions. A separation of SRC or hydrotreated SRC into solvent-derived fractions was achieved by pumping a sequence of n-hexane, toluene, and pyridine through a SRC-coated Fluoropak column at a flow rate of 5 mL/min. Fractions of 100 mL volume of each solvent-derived effluent were collected. The amounts of n-hexane solubles, toluene solubles-n-hexane insolubles, and pyridine solubles-toluene insolubles were determined gravimetrically after removing solvents from the fractions. Solvent Removal. Complete removal of solvents from SRC or hydrotreated SRC fractions is essential for obtaining reliable results in gravimetric determinations. It was found that drying with vacuum rotary evaporator for 2 h at 70 OC was necessary to obtain a constant weight of the material eluted with n-hexane and toluene. Removal of pyridine, however, is particularly difficult. It has been our experience that recoveries of the material were over 100% (usually about 105%) even when more severe drying conditions (4 h at 80 "C under vacuum) were applied to a pyridine-soluble fraction. We recommend that the amount of pyridine soluble-toluene insoluble fraction be calculated by
374
'ANALYTICAL CHEMISTRY, VOL. 54, NO. 3, MARCH 1982 "-HEXANE+
2otl/
TOLUENE+
PYRIDINE
w
I
I4
I
I\
0
z
40
2
eo
0
Y
ELUTION
VOLUME
(mu
Flgure 3. Effect of solvent flow rate upon SRC elution pattern.
0 40
20
0 ELUTION
VOLUME (mU
Flgure 2. SRC F-45 elution curves: (1) at 2 mL/min, (2) 4 mL/mln, (3) 8 mL/min, (4) 16 mL/min flow rate. 6
subtracting the sum of the weight percents of n-hexane solubles and toluene solubles-n-hexane insolubles from 100.
RESULTS AND DISCUSSION The SRC-coated Fluoropak column was devised to serve two functions: (1) rapid separation of SRC or hydrotreated SRC into solvent-derived fractions, and (2) sample introdution into a liquid chromatographic system for further separation into major compound class fractions. Obviously a compromise had to be made as there are two contradictory requirements. On one hand, a rapid separation of SRC or hydrotreated SRC into solvent-derived fractions requires high flow rates of solvents. On the other hand, high solvent flow rates are expected to cause broadening of the elution patterns of the fractions which may affect further separation on liquid chromatographic columns. It may also be expected that very high solvent flow rates may cause considerable decrease in the amounts of material eluted by a given solvent as a result of a very short contact time. Considerable attention also had to be given to proper coating of a sample on Fluoropak. The main problem appears to be in obtaining a very thin film of SRC or hydrotreated SRC on the surface of a support material in which all components of the sample are accessible to the eluting solvent. Thus, a careful evaluation of this separation step was required. The effect of solvent flow rate upon amounts of eluted material and also upon the elution pattern of the fractions was of primary interest. Four different flow rates, 2 mL/min, 4 mL/min, 8 mL/min, and 16 mL/min, were used and subfractions of 5 mL were collected to determine elution curves. In Figure 2 elution curves representing weights of recovered material in each 5 mL subfraction as a function of elution volume are shown. The void volume of the SRC-coated Fluoropak column was about 18 mL. Thus, approximately four subfractions of 5 mL each represent the void volume of the column. The results in Figure 2 show that at a flow rate of 2 mL/min, a major portion of each solvent-derived fraction eluted in the f i s t void volume of the column for each solvent. This resulted in three sharp peaks representing n-hexane soluble, toluene solublen-hexane insoluble, and pyridine soluble-toluene insoluble SRC fractions. The small tailing of the peaks was probably caused by nonequilibrium effects. Adsorption of SRC on the Fluoropak surface may be neglected as this is an inert Teflon support material (12). The recovery of the sample was almost complete, and the small uneluted portion that remained on
SOLVENT FLOW RATE
16
12
J
(rnL/minl
Flgure 4. Effect of solvent flow rate upon weight fraction of: (0) n-hexane solubles, (a) toluene solubles-n-hexane lnsolubles, ( 0 ) pyridine solubles-toluene lnsolubles. Fluoropak consisted of mineral matter and unreacted coal. Due to a very slow solvent flow rate at 2 mL/min, the total time required for the elution of SRC was 2.5 h. At a flow rate of 4 mL/min the time required for the separation of SRC into three fractions decreased by half and, as shown in Figure 2, very little effect upon the elution pattern was observed. With an increase in a solvent flow rate to 8 mL/min, the elution was completed in less than 40 min, but slight broadening of the peaks shown in Figure 2 was observed. The total recovery of the material was not affected. The elution of SRC at a flow rate of 16 mL/min resulted in a considerable broadening of the first two peaks represented by n-hexane soluble and toluene soluble-n-hexane insoluble fractions. In this case the elution time was reduced to less than 20 min. There was no effect on totalrecovery of the material but a significant effect on the relative quantity of each fraction eluted by a given solvent was observed. This is illustrated in Figure 3. The amount of n-hexane solubles decreased from 21.3 wt % at 2 mL/min to 14.7 wt % at 16 mL/min flow rate. The amounts of toluene solubles-n-hexane insolubles remained almost constant, 37.3 wt % at 2 mL/min and 38.1 wt % at 16 mL/min. There was an increase in the amounts of pyridine solubletoluene insoluble from 41.5 w t % at 2 mL/min to 47.2 wt % at 16 mL/min. The results imply that the material which did not dissolve in n-hexane at 16 mL/min flow rate probably dissolved in toluene and that which did not dissolve in toluene was finally dissolved in pyridine. Figure 4 shows the effect of a solvent flow rate upon weight fraction of the three solvent-derived fractions determined by the SRC-coated Fluoropak column procedure. The results obtained at flow rates between 2 and 8 mL/min do not appear to be affected significantly by changes in solvent flow rate and remain practically within the error range of the procedure. Higher flow rates than about 8 mL/min can cause considerable differences in the results. A solvent flow rate of 5 mL/min which corresponded to 1 h total elution time was chosen for routine separation of SRC into solvent-derived fractions. The duplicate results obtained for six different SRC samples are shown in Table I. In the case of a high-ash F-46 SRC, a considerable amount of mineral
375
Anal. Chen?. 1982, 54, 375-381
Table I. Results of Duplicate Separations of Various SRC Samples i SRC and in hydrotreated SRC --wt % m toluene pyridine solubles/ solubles/ n-hexane n-hexane toluene sample solubles insolubles insolubles a F-45 20.0 38.3 41.7 19.7 41.1 39.2 F-31 50.6 37.1 12.3 50.6 36.5 12.9 F-51 16.8 38.4 44.8 1K.5 39.6 43.9 F-36 28.6 4i.7 23.7 30.3 45.5 24.2 F-37 47.5 39.6 12.9 49.0 38.5 12.5 F-46 14.0 29.3 45.56 13.8 27.1 44.36 a Calculated by subtracting the sum of the wt % of n-hexane solubles and toluene solubles/iz-hexane insoluDetermined by weighing (high-ash SRC). bles from 100.
matter was retained on the Fluoropak column. According to our experience, an approximate time required for separation of a single SRC sample into three solvent-derived fractions is as follows: sample preparation, 0.5 h; coating
of Fluoropak, 1.0 h; elution of fractions, 1.0 h; solvent removal and weighing, 2.5 h; total, 5.0 h. However, several samples in various stages of analysis can be handled simultaneously. For example, six samples can be separated during one 8-hour working day by using six columns. LITERATURE CITED (1) Pellpetz, M.; Kuhn. E M.; Friedman, S.; Storch, H. H. Ind. Eng. Chem. 1948, 40, 1259-1264. (2) Weller, S.; Pellpetz, M. G.; Friedman, S.; Storch, H. H. Ind. Eng. Chem. 1950, 42, 330-334. (3) Mima, M. J.; Schultz, H.; McKlnstry, W. E. in "Analytlcal Methods for Coal and Coal Products"; Karr, C.. Ed.; Academlc Press: New York, 1978; Vol. I , Chapter 19, pp 557-568. (4) Schwelghardt, F. K.; Thames, 8. M. Anal. Chem. 1978, 50, 1381. (5) Burke, F. P.; Winschel, R. A,; Wooton, D. L. Fue/ 1979, 58, 539. (6) Schwager, I.; Yen, T. F. Fuel 1978, 57. 100. (7) Steffgen, F. W.; Schroeder, K.T.; Bockrath, B. C. Anal. Chem. 1979, 57, 1164. (8) Schukz, H.; Mima, M. J. Prepr. Pap.-Am. Chem. Soc., Dlv. Fuel Chem. 1980, 25, 18, and references thereln. (9) Boduszynskl, M. M.; Hurtubise, R. J.; Sllver, H. F. Anal. Chem. W82, 54, 375. (10) Catalytlc, Inc., Wilsonville, AL, EPRI ProJectRP 1234-2, 1978. (11) Sllver, H. F.; Mlller, R. L.; Corry, R. T.; Hurtubise, R. J., presented at the 182nd Natlonal Meeting of the American Chemlcal Society, New York, Aug 1981. (12) Horvath, C. I n "The Practice of Gas Chromatography"; Ettre, L. S., Zlatkls, A,, Eds.; Wlley-Intersclence: New York, 1967; p 193.
RECEIVED for review June 8, 1981. Accepted November 16, 1981. Financial support was provided by the U. S. Department of Energy, Contract DE-AC22-79ET14874.
Separation of Solvent-Refined Coal into Compound-Class Fractions M. M. Boduszynskl" and R. J. Hurtulbise" Chemistry Department, The University of Wyoming, Laramle, Wyomhg 8207 1
H. F. Silver Chemlcal Engineering Department, The University of Wyoming, Laramle, Wyoming 8207 1
A separatlon method spleclflc for solvent-reflned coal (SRC) was developed. The niethod Is based on the use of SRCcoated Fluoropak-basic alumlna columns and can be applied In two ways. The flrst varlant Involves (a swltchlng column technlque and provldes; solublllty charaoterlstlcs and compound-class composltlon of SRC wlthout the need to evaporate solvents and redlseolve fractions. 'The second varlant permlts a rapld separation of SRC Into compound classes using a dual column system. Model compounds representing various compound classes were used to csvaluate the procedure. I n thls paper a low-ash Wyodak SRC was used to Illustrate the capablllty o f the method. However, the method was successfully used faw separatlon of varlous SRC sampler.
A detailed compound-class composition of coal-derived products is essential foir an indepth studly of the chemistry of coal liquefaction. In recent years, considerable progress has been made in developing methods o r separation and 0003-2700/82/0354-0375$01.25/0
characterization of coal liquids boiling below about 800 O F (427 "C) (1-8), Studies of the composition of solvent-refined coal (SRC), however, are much less advanced. SRC is defined as the pyridine-soluble coal-derived product boiling generally above about 800 O F (427 "C). SRC is particularly difficult to study because of its lack of solubility in solvents commonly used as mobile phases in liquid chromatography. A common approach used to separate SRC is time-consuming solvent extraction of the sample prior to further chromatographic separation. The major problem appears to be the difficulty in redissolving the solvent-derived fractions and the fractions usually contain some insoluble material. T o avoid this problem, chemists have developed separation procedures based on preadsorption of the total sample on top of a chromatographic column followed by a sequential elution of fractions with various solvents (9-11). The preadsorption of a sample on an adsorbent used for the separation can result in low recoveries due to irreversible adsorption of various components. In some cases, recoveries as low as 40% were 0 1982 American Chemical Society
