Energy &Fuels 1995,9, 308-313
308
Biogeneration of Iron-Based Catalyst Precursors by Acidianus brierleyi on High- and Low-Pyrite Coals for Direct Liquefaction M. V. S. Murty,? F. E. Huggins,$ M. I. H. Aleem,$ R. I. Kermode,+ and D. Bhattacharyya"?? Department of Chemical Engineering, The Consortium for Fossil Fuel Liquefaction Science, and School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506 Received August 3, 1994@
Treatment of high-pyrite, high-sulfur Illinois (IBC) coals and pyrite-free Blind Canyon (DECS) coal with added pyrite in the presence ofAcidianus brierleyi showed formation of iron oxyhydroxide (FeOOH) particles and subsequent sulfiding caused enhancement in liquefaction and oil yield. IBC No. 101 and 105, and DECS No. 17 containing different amounts of pyrite were treated with A. brierleyi to evaluate its effect on FeOOH formation. Chemical analysis of the liquid phase and Mossbauer analysis of the coals revealed that all the biotreated coals showed significant reduction in pyrite after 21 days (or less with pH alteration in the middle of IBC No. 105 coal run) of incubation. Further data on bioprocessed coals obtained from Mossbauer spectroscopy verified the formation of an FeOOH phase, which acts as a catalyst precursor for direct coal liquefaction (DCL). The direct liquefaction conversion and oil yield of the biotreated DECS No. 17 coal with added pyrite increased by 14 and 5%, respectively, over the control which did not contain A. brierleyi.
Introduction
to physical and chemical methods because the biological process not only desulfurize^^,^ but may also convert As the demand for energy continues to increase, and pyrite to active Fe-based catalyst precursors,11 which depletion of domestic petroleum resources accelerates, have also been synthesized chemically.12 The mechait is apparent that there is a need to develop alternate nism of biological and nonbiological oxidation of pyrite energy resources such as coal more efficiently. Although has already been postulated.13J4 abundant coal is readily cost-competitive In our laboratory, extensive work has been carried technology for conversion to clean liquid fuels is still out on the biological desulfurization of Kentucky coals lacking. In addition, combustion of coal is associated using Acidianus brierleyi2J1and Thiobacillus ferrooxiwith the emission of SO2 into the atmosphere. Initial dans.li It was observed that over a 30 days period iron efforts to solve the problem of sulfur removal relied from pyrite was oxidatively dissolved (as Fe2+ and/or mainly on physical and chemical m e t h ~ d s . ~ More Fe3+)in the aqueous phase and was reprecipitated onto recently, the removal of sulfur from coal prior to comthe surface of coal particles in the presence ofA. brierleyi bustion by microbiological methods has been s t ~ d i e d . ~ , ~ - l ~at pH 2.5. This whole process might be occurring in Bioprocessing appears to be an attractive alternative two steps. The first step is dissolution and oxidation of pyrite by A. brierleyi. The second step appears to be * To whom correspondence should be addressed. Address: Dr. D. the reprecipitation of an iron oxyhydroxide on coal Bhattacharyya, Alumni Professor, Department of Chemical Engineerparticles. The reprecipitated particles were identified ing, University of Kentucky, Lexington, KY 40506-0046. Phone (606) 257-2794. FAX (606) 257-7251. E-mail:
[email protected]. by room temperature and low temperature (77 and 12 + Department of Chemical Engineering. K) Mossbauer spectroscopy as an iron oxyhydroxide (aThe Consortium for Fossil Fuel Liquefaction Science. 8 School of Biological Sciences. FeOOH or goethite) phase and jarosite.ll Formation of Abstract published in Advance ACS Abstracts, February 15,1995. jarosite in the presence of T. ferrooxidans at a pH 12.1 (1)Nowacki, P. Coal Liquefaction Processes; Noyas Data Corp.: New has been previously reported.15J6 Potassium jarosite Jersey, 1979. (2) Murty, M. V. S.; Bhattacharyya, D.; Aleem, M. I. H. In Biological was precipitated at a pH as low as 1.3-1.5.16 In these Degradation and Bioremediation of Toxic Chemicals, Chaudhry, G. R., literature studies pyrite oxidation was carried out in a Ed.; Dioscorides Press, Portland, OR, 1994; Chapter 22, pp 470-492. biological growth medium containing various compo(3) Wheelock, R. D. Coal Desulfurization: Chemical and Physical Methods; ACS Symposium Series 64; American Chemical Society: nents such as sulfate, phosphate, potassium, and ni@
Washington, DC, 1977. (4) Runnion, K.; Combie, J. D. FEMS Microbiol. Rev. 1993,11,139144. ( 5 ) Dugan, P. R. Biotechnol. Bioeng. Symp. 1986, 16, 185-203. (6) Dugan, P. R.; Wey, J. E.; Stoner, D. L.; Quigley, D. R. Resour., Conseru. Recycl. 1990,3, 161-167. (7) Khalid, A. M.; Bhattacharyya, D.; Aleem, M. I. H. Deu. Ind. Microbiol. 1990, 31, 115-126. (8) ElSawy, A. FueZ 1991, 70, 591-594. (9) Olsson, G.; Larsson, L.; Holst, 0.;Karlsson, H. T. Fuel Process. Technol. 1993, 33, 83-93. (10)Orsi, N.; Rossi, G.; Trois, P.; Valenti, P. D.; Zecchin, A. Resour., Conseru. RecycZ. 1991, 5 , 211-230.
(11)Bhattacharyya, D.; Hsieh, M.; Francis, H.; Kermode, R. I.; Khalid, A. M.; Aleem, M. I. H. Resour., Conseru. Recycl. 1990,3, 8196. (12) Zhao, J.;Feng, Z.; Huggins, F. E.; Huffman, G. P. Energy Fuels 1994,8, 38-43. (13) Olsson, G.; Larsson, L.; Holst, 0.;Karlsson, H. T. Chem. Eng. Technol. 1993, 16, 180-185. (14) Rossi, G. Fuel 1993, 72, 1581-1592. (15) Smith, J. R.; Luthy, R. G.; Middleton, A. C. J. Water Pollut. Control Fed. 1988, 60, 518-530. (16) Grishin, S. I.; Bigham, J. M.; Tuovinen, 0. H. Appl. Enuiron. Microbiol. 1988, 54,3101-3106.
1995 American Chemical Society
Energy & Fuels, Vol. 9, No. 2, 1995 309
Biogeneration of Liquefaction Catalyst Precursors
trogen. The composition of the growth medium influenced the pyrite oxidation and composition of the products formed.15-17 However, many of the elements such as K, P, S, and N are generally present in the coal itself in significant quantities. Therefore, pH, composition of the coaypyrite mixture, and availability of the pyrite, are some of the important parameters responsible for controlling the formation of FeOOH and other phases of iron. Synthesis of other fine-grained iron crystals (e.g., magnetite) by sulfate-utilizing bacteria is well documented in the literature.ls Several studies have shown that Fe19 and/or S,19320 F ~ S ZMoos, , ~ ~ Fe2O3, and A l 2 0 3 2 0 can act as coal liquefaction catalyst precursors. At a liquefaction temperature of approximately 400 "C and high pressure, pyrite is rapidly converted to H2S and iron sulfide (pyrrhotite). Thus pyrite may act as a catalyst precursor.22However, Fe203(S0d2-showed a higher activity for hydrogenation of bituminous coal than It has been reported that sulfided iron oxyhydroxide (FeOOH) acts as a catalyst during coal hydroliquefact i ~ n This . ~ ~led to the investigation of the formation of FeOOH in the presence of A. brierleyi and its effect on direct liquefaction of coal. Direct coal liquefaction (DCL) is a chemical process involving coal reacting with hydrogen (in the presence of a hydrogen donor solvent) a t elevated temperatures and pressures t o increase the WC ratio in the coal, thus producing coal 1iquids.l An iron-based catalyst, (such as sulfided FeOOH) could be used to reduce the operating temperature or the residence time required for direct liquefaction. The main objective of this research was to oxidatively dissolve the iron present in high-pyrite Illinois Basin coals (IBC No. 101 and No. 1051, and from pyrite added to a low-sulfur Blind Canyon coal (DECS No. 17) and then reprecipitate the dissolved iron onto the coal as FeOOH using A. brierleyi. The focus of the present study is on different sources (coals and FeS2) and the amount of pyrite, and the role of pH. These factors may influence the formation of FeOOH and other phases of iron, which may in turn influence the direct liquefaction and oil yield due to the formation of active catalysts from FeOOH.
Materials Chemicals. All chemicals were of reagent grade and obtained from Sigma or Fisher (USA). Iron pyrite (FeSz, mesh size 50) was obtained from Sargent-Welch Scientific Co. (IL). Coals. Different Illinois basin coal samples (IBC No. 101 and No. 105) and Blind Canyon (DECS No. 1 7 from Utah) coal were used in this study. IBC No. 101 is a Herrin (Illinois No. 6) coal obtained from a commercial preparation plant in west central Illinois. I t has the highest organic sulfur content of any coal in the program but one of the lowest pyritic sulfur values for a conventionally washed coal. IBC No. 105 is a Herrin channel lot collected from the same site and at the same (17)Hoffmann, M. R.; Faust, B. C.; Panda, F. A.; Koo, H. H.; Tsuchiya, H. M. Appl. Enuiron. Microbiol. 1981, 42, 259-271.
(18) Sakaguchi, T; Burgess, J. G.; Matsunaga, T. Nature, 1993,365, 47-49. (19) Wu, W. R. K.; Storch, H. H. In US Bureau ofMines Bull. 1968, 633-635. (20) Bacaud, R.; Besson, M.; Charcosset, H.; Oberson, M.; Huu, T. V.; Varloud, J. Fuel Process. Technol. 1986, 14, 213-220. (21) Mukerjee, D. K.; Chowdhury, P. B. Fuel 1976,55, 4-8. (22) Baldwin, R. M.; Vinciguerra, S. Fuel 1983, 62,498-501. (23) Yokoyama, S.; Yamamoto, M.; Yoshida, R,Maekawa, Y Kotanigawa, T. Fuel 1991. 70, 163-168. (24) Andres, M.; Charcosset, H.; Chiche, P.; Davignon, L.; Mariadassou, G. D.; Joly, J. P.; Pregermain, S. Fuel 1983, 62, 69-72.
Table 1. Illinois Basin Coal (IBC No. 101 and 10S)aand Blind Canyon (DECS No. 17IbCoal Analyses (%, moisture-freebasis) element IBC No. 101 IBC No. 105 DECS No. 17 76.2 carbon 69.1 63.5 5.8 4.5 hydrogen 5.1 1.3 1.2 nitrogen 1.3 9.7 7.6 9.5 oxygen 0.1 0.1 total C1 0.44 4.4 total sulfur 4.5 0.1 0.01 sulfatic 0.0 1.2 2.4 0.02 pyritic 3.1 0.41 2.1 organic aData was obtained from Illinois State Geological Survey. Data was obtained from Penn State Coal Sample Bank.
m
Lzzl
Lry A. brierleyi
7 AIR
c
IBC OR DECS COAL
5%
SHAKE-FLASK
TEMP. CONTROI.
c
MEDIUM
pH 2.5
68°C
P E O U S PYASE ANALYSIS
MbSSBAUER
.LIQUEFACTION
.Fe
.PROTEIN
Figure 1. Schematic representation of experimental prowdure for catalyst precursors formation with A. brierleyi. time that the Argonne National Laboratory (ANL) obtained its No. 3 lot in the Argonne Premium Coal Sample Program. It was blanketed with argon at the mine and processed at ANL in a controlled humidity environment under nitrogen. The DECS No. 1 7 coal has low pyrite and low organic sulfur. The elemental analysis of these coals is given in Table 1. Microorganism. Acidianus brierleyi [Deutche Sammlung Von Mikroorganismen, Germany (DSM No. 165111, a thermoacidophilic, facultative autotroph was grown a t 65 "C and pH 2.0 using elemental sulfur as the sole energy source. Methods for growth and cell preparation for A. brierleyi have been described previous1y.l' The cells were obtained by centrifugation a t 10 OOOg for 30 min and washed three times with distilled water acidified with 0.1 N HC1 (pH 2.8). The protein content of the cells was determined in duplicate by the Goa methodz5using Bovine Serum Albumin (BSA) as the protein standard. The minimum detection limit for this method was 20 pg/mL. All absorption measurements were carried out using a Beckman DU 50 spectrophotometer or Hewlett Packard 8452 spectrophotometer with appropriate blanks. Oxygen uptake by A. brierleyi cells was measured polarographically using a Clark-type 0 2 electrode (Yellow Springs Instruments, OH) t o check the cellular activky.
Experimental Section A general schematic representation of the experimental procedure for the catalyst precursor formation with A. brierleyi is given in Figure 1. The coals generally contain a significant quantity of various minor elements such as Al, K, Na, P, S, and N. Most of these elements have been widely used in microbial growth medium. The present experimental growth (25)Goa, J. Scan. J. Clin. Lab. Inuest. 1953, 5 , 218-222.
310 Energy & Fuels, Vol. 9, No. 2, 1995
Murty et al.
medium contained water (except the addition of 0.1 N HzS04 or 0.5 M NaZC03 for maintaining the pH) and coal, since other elements can be derived from the coal. Duplicate experiments were performed with 5% (&VI coal (average mesh size, 80) slurries in 500 mL Erlenmeyer flasks, which were agitated in an Incubator Shaker (New Brunswick Scientific C o . ) at 68 "C. The inoculum size and agitation were maintained at 300 mg of p r o t e i f i and 100 rpm, respectively. The pH was adjusted periodically by manual addition of sodium carbonate (0.5 MI. But in one case with IBC No. 105 coal medium, 0.2 M NaOH was used in the middle of the run to adjust pH from 2.4t o 2.8. Pyrite (2500 ppm = 1160 mg Fe/L and 1300 mg S/L)) was added to the pyrite-free DECS No. 17 coal (Table 1). Microbial cells were added to half of the flasks (biotreated) and the remaining flasks were used as control samples. Samples were collected and filtered through a 50 pm Millipore filter to separate the coal from the slurry and were thoroughly washed --C- Test (with A. brlerleyl) with distilled water. The filtered coal samples were dried at 100 "C for an hour and stored in different air-tight containers until further analysis. Iron concentration in the filtrate was estimated by atomic absorption spectrophotometer (Varian, AA-575 Series). Sulfate present in the filtrate was determined by a gravimetric method.26 Estimation of known quantity of sulfate, which was added t o the filtered sample, showed that the quantification was accurate to f5%. 10 20 0 MiSssbauer Spectroscopy. Determination of the reactions of pyrite and its transformations in the treated and untreated Time, days coals was undertaken using 57FeMossbauer s p e c t r o s c ~ p y . ~ ~ ~ ~ ~ Figure 2. Variation of protein content in the liquid phase Mossbauer spectroscopy was used t o identify and determine containing IBC No. 105 when incubated with A. brierleyi at the relative amount of iron compounds in biotreated coals. 68 "C and pH 2.5 (initial). Mossbauer absorption spectra were obtained at room temperature using a constant acceleration Mossbauer spectrometer. of f l %in the total conversion. The coals treated with A. Isomer shifts (IS) were measured with respect to metallic Fe brierleyi and raw coals were subjected to direct liquefaction at room temperature. The different phases of iron were in two separate runs. The average values are reported. identified from the values of quadrupole splitting (QS)and IS exhibited in the spectra. All the spectra in the treated coals were fitted with at least two quadrupole doublets. Results and Discussion Direct Coal Liquefaction. ARer treatment, both biotreatCoal Treatment with A. brierleyi. Three types of ed and control coal samples were subjected t o direct liquefaccoals (IBC No. 101 and 105 and DECS No. 17 with tion. The liquefaction experiments were conducted in a 50 mL added pyrite) were treated with and without A. brierleyi stainless steel microautoclave reactor containing 5 g of coal, 7 in a coal-water slurry under aerobic conditions. These g of tetralin, and about 0.8 g of dimethyl disulfide which was used for sulfiding the catalyst precursor. The reaction was coals contain different amounts of pyritic sulfur and iron carried out under Hz pressure (cold) of 800 psi which rose t o (Table 1). IBC No. 101 contains 600 and 520 mg/L of 2000 at the liquefaction temperature of 385 "C. After 15 min, pyritic S and Fe, respectively (calculated from Table 1). heating was stopped and reactor was cooled to room temperIBC No. 105 and DECS No. 17 coals with added pyrite ature. The pressure was reduced by transferring gas to a contain about twice the amounts of pyritic sulfur and small bomb where it could be analyzed. The liquid products iron than IBC No. 101. IBC No. 105 contains 1200 and and the unreacted coal were transferred into a thimble in a 1050 and DECS No. 17 contains 1300 and 1160 mg/L Soxhlet funnel for extraction with benzene. Following extracof pyritic S and Fe, respectively (calculated from Table tion, the benzene-insoluble material was dried under vacuum 1). These variations may actually affect the metabolic and reextracted with pyridine. The thimble was again vacuumactivity of A. brierleyi. At the expense of the pyrite dried to remove traces of pyridine from pyridine insolubles. The benzene containing benzene-soluble materials was rotary oxidation and reduction of the atmospheric carbon evaporated leaving behind the oil and asphaltenes fraction. dioxide,A. brierleyi can release iron and sulfate into the The oil fraction was dissolved in pentane t o separate the aqueous phase and build up its cell protein. Therefore, asphaltenes by filtration. The total conversion of the reacted the parameters such as protein, pH, sulfate, and total mass was estimated as follows: iron content of the liquid phase were monitored to assess
conversion = gas
+ oil + asphaltenes + preasphaltenes
The experimental procedure for liquefaction was also described elsewhere.29 Duplicate samples produced a variation ~~
(26) Sulfate Estimation. In 1989 Standard Methods for the Examanation of Water and Waste Water 17th ed.; Clesceri, L. S., Greenberg, A. E., Trussel, R. H., Eds.; h e n c a n Public Health Association (APHA), American Water Works Association (AWWA), Water Pollution Control Federation (WPCF): Washington, DC, 1989; pp 4-204-4-207. (27) Huffman, G.P.; Huggins, F. E. Fuel 1978,57, 592-604. (28) Huggms, F.E.; Hufhan, G. P. In Analytical Methods for Coal and CoaZProducts, Karr,Jr. C., Ed., Academic Press: New York, 1979; Vol. 111, Chapter 50, pp 371-423.
the extent of pyrite oxidation by A. brierleyi. The increase in protein content (Figure 21, sulfate (Figure 3), and iron (Figure 4) released into the aqueous medium, in the presence of IBC No. 105, shows that the organism was able to grow by oxidizing the pyrite present in the coal. Total iron concentration in the aqueous phase initially increased and after about 9 days started to drop. The decreases in protein and liquidphase iron contents occurred at the same time (Figures 2 and 4). The simultaneous decrease of both iron and protein could be due to the attachment of microbial cells (29) Murty, M. V.S.;Aleem, M. I. H.; Kermode, R. I.; Bhattacharyya, D.J. Chem. TechnoZ. Biotechnol. 1994, 60, 359-367.
Energy & Fuels, Vol. 9, No. 2, 1995 311
Biogeneration of Liquefaction Catalyst Precursors 600
300-Arrow 0 Biotreated 0 Control
500
i
'
Coal IBC t105 Temp., 68 "C pH, 2.5
s
-
E" 400
-
lndlcates pH adlurted from 2.4 to 2.8 0 Treated by A. brlerleyl Control (no cells)
250. '
Temp. 68°C Coal IBC t105 (5%)
6 (P
'c
a 300
Q v) (P
c n
.-Ua
200
w
5
100
-0lW1 0
Available pyrltlc S 1200 mg/L
20
30
Time, days
Figure 3. Sulfate released from IBC No. 105 (5%coal) when incubated with A. brierleyi at 68 "C and pH 2.5 (initial). Maximum available pyrltlc Fe 1050 mglL
1
0 Blotreated '
0 Control Coal IBC t105
e
.-2
;100 .-AU
I 0
10 20 Time, days
30
Figure 4. Variation of liquid-phase iron released from IBC No. 105 (5%coal) when incubated with A. brierleyi at 68 "C and pH 2.5 (initial).
to the iron particles. This adherence of cells to the iron precipitate may help in controlling the ultrafine size of the catalyst precursor. The mechanisms of microbial adherence to solid surfaces has been studied in depth by several r e ~ e a r c h e r s . ~ O - ~ ~ (30) Marshall,K. C.; Stout, R.; Mitchell, R. J.Gen. Microbiol. 1971, 68, 337-348. (31)Marshall, K. C. In Bacterial Adhesion: Mechanisms and Physiological Significance; Savage, D. C., Fletcher, M., Eds.; Plenum Press: New York, 1985; Chapter 6, pp 133-156. (32)Wicken, A. J. In Bacterial Adhesion: Mechanisms and Physiological Significance, Savage, D. c., Fletcher, M., Eds., Plenum Press: New York,1985; Chapter 2, pp 45-67. (33)Costerton,J. W.;Irvin, R. T.; Cheng, K.J.Annu. Rev. Microbiol. 1981,35,299-324. (34) Bagdigian, R. M.; Myerson, A. S. Biotechnol. Bweng. 1986,28, 467.
0
5 10 Time (Days)
15
Figure 5. Rapid precipitation of liquid-phase iron on the coal IBC No. 105 when treated with A. brierleyi.
The time required for precipitation of the liquid-phase iron was approximately 9 days in the case of biotreated IBC No. 105 coal a t pH 2.5 (Figure 4). However, the precipitation time was dramatically reduced to 1 day when the pH of the medium of a similar run with IBC No. 105 coal was adjusted from 2.4 to 2.8 (Figure 5). Mijssbauer Analysis. Mossbauer spectroscopy was used to identify and determine the relative amounts of iron compounds in the coals after the treatments with and without microbial cells. Room temperature Mossbauer spectra for the control and biotreated DECS No. 17 coal with added pyrite are shown in Figure 6. The results of the Mossbauer analysis are summarized in Table 2. Jarosite is present in all spectra; it is readily recognizable because of the large quadrupole splitting (1.1-1.25 m d s ) exhibited by the outer quadrupole doublet. Identification of the inner doublet with the smaller quadrupole splitting is based on the value of the isomer shift (IS): an IS between 0.30 and 0.33 m d s was taken to indicate pyrite, whereas a value between 0.35 and 0.38 m d s was taken to indicate FeOOH. The IS values vary with temperature as indicated in our previous work.ll IS values between 0.33 and 0.36 m d s would be indicative of mixtures of pyrite and FeOOH. The IS values vary with temperature as indicated in our previous work.ll However, in the samples investigated (at room temperature) in this study, the values of the IS were always consistent with pyrite for the three control samples, whereas they were always consistent with an FeOOH for the three biotreated samples. The jarosite content decreased and an iron oxyhydroxide (FeOOH) increased in biotreated coals. The IS (0.34) and QS (0.5-0.6) values of the control sample show that the pyritic content is greater in the control samples. This shows that pyrite is consumed in the biotreatment and that the iron-bearing oxidation products Cjarosite and FeOOH) are precipitated in all these coals with jarosite being the major product. It is possible t o infer some compositional information about the jarosite phase in these samples from the value for
312 Energy & Fuels, Vol. 9, No. 2, 1995 101
Murty et al. ~~
T
Jarosite
C
-
~
~~
~ ~~
~
~~
Coal was treated with A. brierleyi Coal wa% treated without A. brierleyi
Q,
b
C (convcrsion) T (conversion) c (Oil) T (oil)
s i 99
.-0
-
!
.-
v)
E d
98
-
97
-
1. IBC #lo1
Carbonate?
c Control DECS-17 (with added pyrite)
96!
-8
. -6. . -4. . -2. . 0. . 2. . 4. . 6. . 8. Velocity, mmkec
102 > 101
0
100 99 8 98 .- 97 v) ." 96
s E
$
2 3 Coal Figure 7. Direct liquefaction conversion and oil content of IBC and DECS coals (5%) incubated with A. brierleyi at 68 "C,pH 2.5 (initial) and agitated for 21 days.
95 94
93 92 91 90
II
-
1
!
-8
. -6. . -4. . -2. . 0. . 2. . 4. . 6. . 8. Velocity, mmlsec
Figure 6. Mossbauer spectra of the processed DECS No. 17 coal with added pyrite in the presence (biotreated)and absence (control) of A. brierleyi at 68 "C and pH 2.5. Table 2. Composition and Phases of Iron Determined by MCTssbauer Analyses of IBC and DECS Coals (5%) Incubated with and without A. brierleyi at 68 *C, pH 2.5 (Initial), and Agitated for 21 days coal type IBC No. 101F IBC No. 10ICc IBC No. 105T IBC No. 105Ce DECSNo. 17TbvC DECS NO.17CbeC
pyrite
9 Fe FeOOH"
jarosite
nd 11 nd 12 nd 80
36 nd 22 nd 12 nd
64 89 78 85 88 14
others -C
0 3
-
5
*
The IS value for FeOOH is 0.37 f 0.02 "/s. Pynte (2500 ppm) was added to the DECS coal. T = test, coal was treated with A. brierleyi. 'C = control or coal was treated without A. brierleyi. - below detection limit.
the quadrapole splitting parameter, based on the previous work.35 A value of 1.13 mm/s obtained from DECS No. 17 control sample is consistent with a potassiumrich iron jarosite. However, most of the other samples exhibited a value of 1.20 m d s ; such values are likely to arise from aluminum substituting for the iron in the jarosite structure. This would indicate that the conditions used for the biotreatment not only affect the pyrite but also the clay minerals, which are the source of aluminum in coal. Based solely on room temperature Mossbauer spectra, it is not possible to identify the specific mineralogical form of FeOOH. However, previous work on the oxidation of pyrite in coal indicates that goethite (a-FeOOH) is the most likely FeOOH polymorph to be formed at (35)Leclerc, A. Phys. Chem. Miner. 1980,6,327-334.
temperatures around 25-50 0C.36*37 Assuming the FeOOH phase to be goethite, its totally paramagnetic appearance in these spectra indicates a maximum particle size of no more than 120 A.38 Further confirmation of the formation of FeOOH could be made by examining low-temperature Mossbauer spectra. In fact, in earlier work, low-temperature Mossbauer spectra of the biotreated Kentucky coal (No. 91 182) established that ultrafine a-FeOOH was formed on the coal, whereas room temperature Mossbauer analysis showed broad spectra.*' An interesting metabolic activity of some of the microbes is that they can control crystal size by adhering to its surface. The phenomenon of microbial adherence occurs due to the production of extracellular polymeric adhesive materials such as acid polysaccharides, glycoproteins, and other biopolymer^.^^-^^ The biofilm formation can prevent further growth of such iron crystals. Direct Liquefaction Conversion. The results of the direct liquefaction (at 385 "C for 15 min) of the bioprocessed coals treated with or without A. brierleyi are summarized in Figures 7 and 8. The purpose of conducting the direct liquefaction was to determine the effect of catalyst precursor formation on coals and to compare the liquefaction conversion of test samples with that of the control (without A. brierzeyi) samples. DECS No. 17 coal with added pyrite (1160 mg FeL) showed a significant increase ( 14%) in liquefaction conversion (Figure 7). The increase in conversion occurs when the coal contains FeOOH (in the presence of sulfiding agent). However, upon comparing the test and control sample liquefaction experiments on the different IBC (36)Huggins, F. E.; Huffman, G. P.; Lin, M. C. Int. J. Coal Geol. 1983,3,157-182. (37)Huggins, F. E.; Huffman, G. P. In Coal Science and Technology, Vol. 14: The Chemistry of Coal Weathering; Nelson, C. R., Ed.; Elsevier: Amsterdam, 1989; Chapter 2, pp 33-60. (38)Ganguly, B.; Huggins, F. E.; Rao, K. R. P. M.; Huffman, G. P. J. Catal. 1993,142, 552-560.
Biogeneration of Liquefaction Catalyst Precursors
'" I EZ 60 -
Control
I Biotreated Coal, IBC # l o 5 Q,
d
50 -
c .? 40-
2 0
> 0
.
3020 10 -
08
11
15
(pH, 2.4)
(PH, 2.8)
(pH, 2.8)
Time, days
Figure 8. Time course of direct liquefaction of the coal (5%) treated with A. brierleyi a t 68 "C.
coals, we find that the test run of the bioprocessed coal (IBC No. 105, contains 1050 mg of FeL) showed a 5% increase in liquefaction, whereas IBC No. 101(with 520 mg of FeL) showed negligible conversion over the control. In our previous work, biotreated high sulfur (total S 3.2%; pyritic Fe 433 mgL) Western Kentucky coal No. 11 (or 91182) generated under the same conditions (pH 2.5, 5% coal, 30 days incubation and formation of FeOOH) showed a 10% increase in conversion (at 385 0C).39 The higher yield with Kentucky coal could be due to smaller particle size (200 mesh), although the amount of pyritic iron was less than that of IBC coals whose average particle size is bigger (80 mesh). It is reported that the physical and chemical nature of pyrite differs from one source to another.40 This could also influence the variation in oxidation products. Raw IBC coals with no catalyst precursor showed low conversion (4596, total). Experiments were repeated to establish experimental reliability. From the repeated experiments, it was found that all the liquefaction conversion values were within f l % . Oil formed during the process of direct liquefaction of the treated coals was also estimated. The amount of oil formed in the bioprocessed DECS No. 17 coal increased by 555, whereas IBC coals showed a small enhancement of oil formation (3%, No. 105) and a negligible enhancement in No. 101(Figure 7). The short reaction time (15 min) for the liquefaction is the likely reason for obtaining relatively low oil yields. Short reaction time was selected to show the variation between treated and untreated coals. Although we did not analyze organic sulfur content in the bioprocessed coals or the liquefaction products of the present study, (39)Neem, M. I. H.; Bhattacharyya, D.; Huffman, G. P.; Kermode, R. I.; Murty, M. V. S.; Venkatachalam, H.; Ashraf, M. Prepr. Pap.-Am. Chem. Sac., Diu. Fuel Chem. 1991,36,53-57. (40) Olson, G.J.; Kelly, R. M. Z-ksour., Conseru. Recycl. 1991,5,183193.
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we can expect that the oil formed from low-sulfur (0.4%) DECS coal will contain negligible organic sulfur content when compared to IBC coals (2.1-3.1% S, Table 2). Lowsulfur oil is a more valuable source of energy because of environmental considerations. Coal samples collected at different times of the treatment (with the pH changed from 2.4 to 2.8) were also subjected to DCL to determine the effectiveness of catalyst precursor formation (Figure 8). A maximum increase in total conversion of 12% was observed from the sample obtained at the end of the 1l t h day, one day after the adjustment of pH from 2.4 to 2.8. The sample obtained at the end of the 15th day did not show any substantial increase in total conversion from that of the 11th day sample. This result clearly showed that maximum effect of catalyst precursor was found when maximum iron precipitation took place. Moreover, the total conversion was increased from 5% (constant pH 2.5, Figure 7) to 12% when the pH of the IBC No. 105 coal medium was adjusted from 2.4 to 2.8 (Figure 8). For a greater increase in direct conversion, the biotreated coal requires more availability of oxidizable pyrite and an efficient in-situ catalyst precursor formation.
Conclusions Pyrite was oxidized and iron was reprecipitated on coal when coal was treated with A brierleyi a t low pH of 2.5 and at the high temperature of 68 "C. The iron phases that precipitated were jarosite and an iron oxyhydroxide (FeOOH). Different coals, with different amounts and availability of pyrite, showed variations in the precipitation of iron phases as well as in liquefaction yield. Formation of a more active phase of the catalyst was observed only in the case of DECS No. 17 coal, which contained the highest amount (starting 1160 mg of FeL) of supplemental pyrite. This was assumed to be more available as it was not embedded inside the coal particles. As a result, a significant increase in liquefaction (14%) and oil (5%) yield was measured for the biotreated DECS No. 17 coal. The pH adjustment from 2.4 to 2.8 in the middle of the run with IBC No. 105 coal helped in reducing the total time required for the precipitation of soluble iron as well as in increasing the total conversion. Although the different coals showed variation in precipitation of iron phases, liquefaction, and oil yield, the source of pyrite influencing the catalyst precursor precipitate needs to be further investigated. Acknowledgment. This research is supported by the U.S. Department of Energy under contract No. DEFC22-90PC90029, as a part of the research program of the Consortium for Fossil Fuel Liquefaction Science. The authors thank Dr. G. P. Huffman for his support. We are thankful to Dr. Chusak Chaven of Illinois State Geological Survey, IL, and Dr. David Glick of Energy and Fuels Research Center, The Pennsylvania State University, PA, for supplying the IBC and the DECS coals (and analysis), respectively. Thanks to Dr. Mehdi Taghiei for conducting some liquefaction runs a t the Center for Applied Energy Research, University of Kentucky. EF9401583
