Energy & Fuels 1992,6, 804-808
804
Biodesulfurization of Some Turkish Lignites by Sulfolobus solfataricus T. Durusoy, T. &bag, A. Tanyolac, and Y. Yuriim'~+ Department of Chemistry and Department of Chemical Engineering, Hacettepe University, Beytepe, 06532 Ankara, Turkey Received May 20, 1992. Revised Manuscript Received September 9, 1992
Experiments have been carried out to determine the effects of biodesulfurization time on the removal of sulfur constituents of six Turkish lignites by Sulfolobus solfataricus. The changes in sulfur content of Tuncbilek, Karliova, Beypazari, Can, Elbistan, and Mengen lignites are shown as functions of time. A decrease in all sulfur forms with increasing time was observed for each coal. The highest total and organic sulfur reductions were observed with Beypazari lignite as 57.1 and 47.895,respectively. The influence of analyses of the original samples on total and organic sulfur reductions has been investigated through multiple linear regression analysis. The resulting determination coefficients are compared to obtain the best fitting parameter set. For the six lignites the experimental values of total and organic sulfur reductions appeared to agree with the values calculated for the models.
Introduction The major processes developed for the removal of sulfur from coal may be classified into two categories: (1) precombustion desulfurization and (2) postcombustion desulfurization of coal. Precombustion coal desulfurization processes can employ physical or chemical methods. Physical methods are only effective for the removal of pyritic sulfur and, in general, more cost effective than chemical methods. The chemical precombustion desulfurization methods operate at high temperatures and a t high pressures and are energy intensive.lV2 Desulfurization after combustion of coal requires large volumes of processing water and causes equipment wear and corrosion problems under moderate pressure. Microbial coal desulfurization, namely biodesulfurization, before combustion may have notable advantages over physical and chemical methods. Biodesulfurization usually requires lower capital and operating costs compared to the high costs of chemical processes and physical operations. Finely distributed sulfur compounds can be removed by microbial catalysis, without causing any significant energy loss or coal refuse, as biodesulfurization operates at relatively low temperatures (25-75 O C ) and low pressures and, therefore, is less energy intensive than chemical processes. There are many bacteria, mold, and mixed cultures held responsible for the desulfurization of coal, and research is still carried on new generations to increase both the reaction rate and removal ~ercentage.~-~ The most
* Author to whom correspondence should be addressed.
Department of Chemistry. (1)Wheelock, R. A. Coal Desulphurization: Chemical and Physical Methods; ACS Symposium Series 64; American Chemical Society: Washington, DC, 1977;pp IX-XI, 101-120. (2)Meyers, R. A. Coal Desulphurization: Marcel Dekker Inc.: New York, 1977;pp 26-40,61-83,187-191. (3)Kargi, F., Enzyme Microb. Technol. 1982,4, 13-19. (4)Monticello, D. J.; Finnerty, W. R. Annu. Rev. Microbiol. 1985,39, 371-389. ( 5 ) Bos, P.; Kuenen, J. G. Microbial Corrosion; Mercer, A. D., Tiller, A. K., Wilson, R. W., Eds.; The Metal Society: London, 1983;pp 18-27. +
commonly considered and used microorganisms are Thiobacillus ferrooxidam and Thiobacillus thiooxidam. These bacteria have been shown to be effective for the removal of pyritic sulfur from coal.l0 The reported removal rates until now, however, have been too low to make the biodesulfurization process economically attractive. Another bacterium, Sulfolobus acidocaldarius, is a chemoautotrophic and thermophilic microorganism isolated from acidic hot springs. It can also remove some of the organic sulfur as well as inorganic pyrite. Sulfolobus brierleyi and Sulfolobus solfataricus are also very active. Sulfolobus species are used especially for the removal of organic sulfur integrated in the structure of ~ o a l . ~ ~ J ~ Our preliminary investigations showed that Sulfolobus solfataricus yields comparatively faster desulfurization rates and higher conversion percentage for organic sulfur contents of some Turkish lignites.13 The primary objective of this study was to determine the effects of biodesulfurization time of six Turkish lignites on the total, sulfate, pyritic, and organic sulfur forms of the samples. The second objective was to investigate the effects of lignite types on various sulfur reduction values for desulfurization by Sulfolobus solfataricus.
Experimental Section Microorganism and Culture Medium. A pure culture of DSM (Deutache
Sulfolobus solfataricus was obtained from
(6)Olson, G. J.; Brinckman, F. E. Fuel 1986,65, 1638-1646. (7)Detz, C. M.; Barvichak, G.Mining Congr. J . 1979,65 (6),75-82. (8)Brock, T. D.; Brock,K. M.;Belly,R. T.; Weiss, R. C.Arch. Microbiol. 1972,84, 54-68. (9)Hoffmann, M. R.; Faust, B. C.; Panda, F. A.; Koo, H. H.; Tsuchiya, H. M. Appl. Enuiron. Microbiol. 1981,42(2),259-271. (10)Kargi, F.; Robinson, J. M. Appl. Enuiron. Microbiol. 1982,44(4), 878-883. (11)Brierly, C. L.; Brierly, J. A. Can. J. Microbiol. 1973,19 (2)183188. (12)Ollson, G.; Larsson, L.; Holst,O.; Karlsson, H. Fuel 1989,68,12701274. (13)Gullu, G.; Durusoy, T.; &bas, T.; Tanyolac, A.; Ytirtim, Y. Biodesulphurization of Coal; YClriim, Y.,Ed.; Clean Utilization of Coal, Coal Structure and Reactivity, Cleaning and Environmental Aspects: NATO AS1 Series C, Vol 370;Kluwer Academic Publishers: London, 1992;pp 185-205.
0887-0624/92/2506-0804$03.00/00 1992 American Chemical Society
Energy & Fuels, Vol. 6, No. 6,1992 808
Biodesulfurization of Some Turkish Lignites Table I. Analyses of Lignite Samples Tungbilek Karliova Beypazari proximate analysis (mf %) volatile matter fixed carbon ash ultimate analysis (dmmf %) carbon hydrogen sulfur nitrogen oxygen analysis of sulfur forms (mf % ) total
sulfate pyritic organic petrographic analysis (vol %) huminite liptinite inertinite mineral pyrite (external) pyrite (internal) rational analysis ( 5% ) bituminous humic acids ligneous matter contents cellulose matter contents analysis of ash composition ( % ) Si02 A1203
Fez03 CaO MgO
others
can
Elbistan
Mengen
34.0 31.1 34.9
38.0 21.2 40.8
35.4 27.2 37.4
54.0 31.4 14.6
57.6 17.6 24.8
50.5 30.9 18.6
68.8 5.7 1.8 2.5 21.2
37.0 4.4 8.3 1.5 48.8
62.5 5.0 6.5 1.9 24.1
54.2 4.8 2.8 1.6 36.6
55.3 6.0 3.7 1.5 33.5
70.3 5.3 11.8 1.2 11.4
1.15 0.68 0.19 0.28
4.93 1.35 0.67 2.91
4.08 1.31 0.70 2.07
2.44 1.06 0.43 0.95
2.77 0.10 0.25 2.42
9.58 2.38 1.21 5.99
85.0 6.0 0.4 7.9 0.7 0.0
80.3 15.0 1.5 3.2 0.0 0.0
79.8 9.2 0.7 2.6 3.4 4.3
80.1 4.4 0.5 13.9 0.3 0.8
80.6 9.0 0.8 8.0 1.0 0.6
44.2 1.8 1.6 50.6 1.8 0.0
4.4 7.2 86.9 1.5
8.9 69.1 21.2 0.8
4.0 14.0 82.0 0.0
5.2 15.5 74.2 5.1
5.7 57.2 35.1 2.0
4.6 70.6 23.4 1.4
46.5 21.7 13.8 5.4 7.7 4.9
42.3 25.0 10.1 13.6 0.6 8.4
52.2 18.8 13.4 6.7 2.8 6.1
51.2 26.4 10.5 5.5 2.0 4.4
18.0 10.4 6.5 47.5 2.7 14.9
11.6 25.8 9.0 21.8 2.5 29.3
Sammlung von Mikroorganismen and Zellkulturen GmbH) with strain no 1616. The inoculum culture used in experiments was grown in a medium with the following composition (g/L): Yeast extract, 1.0;KH2PO4, 3.1; (NH4)2SOd, 2.5; MgSO4.7H20, 0.2; CaClz,H20,0.25; MnClz.4Hz0,1.8 X Na2B40,.10H~O, 4.5 X lo-? ZnSO4m7HzO, 0.22 X lo+; CuC12.2H20, 0.05 X W; Na2VOSO4.Hz0, 0.03 X le3; CoSO4.7H20, M004-2Hz0,0.03 X 0.01 X 10-3. The initial medium pH was adjusted to 4.0-4.2 with 10 N HzSO4, and the medium was autoclaved at 121 OC for 15 min. A 24-h-grown culture was used for inoculation. Method of Assay. Tungbilek, Karliova, Beypazari, Can, Elbistan, and Mengen lignites were selected for their high sulfur contents for biodesulfurization by Sulfolobussolfataricus in this study. The coal samples were not washed before subjecting them to the microbial desulfurization. Original lignites, dried at 106 f 2 "C, were used in biodesulfurization experiments. The lignite samples were ground in a ball mill and sized to -200 pm and were analyzed for proximate, ultimate, petrographic, rational, sulfur forms, and ash composition. The results are presented in Table I. Carbon and hydrogen contents were determined by Heraus Combustion Apparatus, Type Standard for Microanalytical Determination and nitrogen by Kjeldahl instrument. Total sulfur and inorganicand pyritic sulfur forms of lignites were determined by Eschka Method accordingto ASTM D3177 and ASTM D2492 respectively, and organic sulfur content was calculated from the difference. A Leitz MPV 2 Orthoplan Microscopefotometer microscope was used for the petrographic analysis of the lignite samples. Rational analysis was carried out in order to determine the bituminous, humic acid, ligneous matter, and cellulose matter contents of the lignite samples. Coal samples were extracted with benzene-alcohol (1:l) solution, and the bituminous fraction was calculated from the weight of the extract. Humic acid fraction was found by NaOH extraction, followed by ether extraction to obtain the ligneous matter coi@tnt. Cellulose matter eontent was found by difference."
The Box-Wilson experimental design was used for the determination of the growth kinetics of S. solfataricus.13 Optimum growth conditions were found at the temperature of 70 OC, initial pH of 3.0, shaking rate of 40 rpm, initial glucose concentration of 10g/L, initial ammonium sulfate concentration of 3.2 g/L, and inoculum percent of 6.5% (v/v), with the other medium constituents at the fixed concentrations given above. Biodesulfurization experimentswere carried out at these optimum conditions by using a 24-30-h-grown inoculum and 4% (w/v) of dry lignite in 250-mL Erlenmeyer flasks in a water bath shaker. The growth of the culture was not followed during the biodesulfurization period. Although the concentration of the microorganism can be determined in the growth medium by using a spectrophotometer, the growth of the S. solfataricus cannot be satisfactorily followed in the coal slurry medium. In the latter case, some of the microorganisms adhere to the coal particles and cause a reduction in the concentration of microorganism in the slurry. Moreover, the culture does not have a rigid cell wall and shows its activity like bulk enzyme solution. Hence, it is impossible to determine the growth as found in the biodesulfurization runs of the lignite samples. Since all of the operational parameters were kept constant during the biodesulfurization experiments, the difference observed in the results had to be due to only the difference of the coal samples. A set of initial experiments were carried out in order to determine the optimum growth conditions of the S. solfataricus in the absence of the coal samples. Desulfurization experiments were done along with blanks under determined near-optimum conditions. The blank runs which contained no culture did not show any significant change in sulfur contents. Furthermore, the experiments have been systematically repeated by using Beypazan lignites. Sulfur forms analyses and biodesulfurization results were the same within the *5% error margin of the employed experimental methods. (14) Kreulen,J. W. Sechs Abhandlungen-LIberBraunkohlenlLignite; Freiberger Forschungsheft Nr. A/244, Academie-Verlag: Berlin, 1962; Vol. 6, pp 12-78.
806 Energy I%Fuels, Vol. 6, No. 6,1992
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Durusoy et al. Total Sulphate
2
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10
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0
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15
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day
5
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-
Results and Discussion Experiments have been carried out to determine the effects of biodesulfurizationperiod on the removal of sulfur contents of six Turkish lignites. The changes in total sulfur, sulfate sulfur, pyritic sulfur, and organic sulfur contents of Tungbilek, Karhova, Beypazari, Can, Elbistan, and Mengen lignites are shown as a function of time in Figure la-f, respectively. A decrease in all sulfur forms with increasing time was observed for all lignite samples. The results given in Figure 2a-d, show that S.solfataricus can effectively remove all sulfur forms in the lignites studied. The values of total sulfur content reduction as functions of time for the lignite samples are given in Figure 2a. The highest decrease in the total sulfur content (57.1 7%) was obtained with Beypazari lignite on the 14th day of biodesulfurization. This was followed by Tungbilek and Can lignites, and the lowest total sulfur reduction (15.9 % ) was obtained with Elbistan lignite.
15
10 t.
day
day
4'
3 4
Figure 2b represents the change in sulfate sulfur reduction values with time for the samples. Beypazari and Can lignites yielded maximum reductions on the 14th day of sulfur removal. Although S.solfataricusremoved almost all of the pyritic sulfur (approximately 95 % ) contents of the Tungbilek, Karhova, and Elbistan lignites, pyritic sulfur reduction for Can lignite was 23.3% at the end of the biodesulfurization runs (Figure 2c). Organic sulfur content reduction values for the lignites are given as functions of time in Figure 2d. Data revealed maxima for Tungbilek and Beypazari samples, but minima for Karliova and Elbistan lignites. It was concluded from the total sulfur reduction results (Figure 2a) that the lignite samples can be classified into three groups during biodesulfurization: Tungbilek and Mengen lignites, Karliova and Beypazari lignites, and Can and Elbistan lignites. Similar trends were also observed for organic sulfur reduction values (Figure 2d). Since the metabolic pathways of the S. solfataricus are not known
Energy & Fuels, Vol. 6,No. 6, 1992 807
Biodesulfurization of Some Turkish Lignites
Table 11. Equations and Determination Coefficients Obtained by Multiple Linear Regression Analysis for Total and Organic Sulfur Reductions
m
.-
50
ia
no.
m
Q v,
3c
30 20 10 n
v
Tunqbilek Karliova B e y p m
Can
Elbistan Mengen
Lignite Sample
Tunqbilek Karliova Beypazari
@I
Elbistan Mengen
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
equation
r2
1.OOO 1.OOO 0.280 0.529 1.OOO LOO0 0.956 0.916 0.422 0.999 0.997 1.OOO 0.999 0.604 0.928 0.912 0.984 0.982 1.OOO 0.907 0.904 0.710 0.774 0.800
Lignite Sample
Tunqbilek Karliova Beypazan @I Lignite Sample cn
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ae .-$ d
Elbistan Mengen
.
4 0
0
30 20
'I
8
10 n Tunqbilek Karliova Beypazari Can Lignite Sample
Elbistan Mengen
Figure 2. (a, top) Changes in total sulfur reduction values of lignite samples with biodesulfurization times: 1.2,4,and 14 days. (b, upper middle) Changes in sulfate sulfur reduction values of lignite sampleswith biodesulfurization times: 1.2,4,and 14days. (c, lower middle) Changes in pyritic sulfur reduction values of lignite samples with biodesulfurization times: 1.2,4,14days. (d, bottom) Changes in organic sulfur reduction values of lignite samples with biodesulfurization times: 1.2, 4, 14 days.
for varioussubstrates as well as coaltypes, the classification can be identified only by the analyses of the lignites (Table I). As an initial step to generalize the desulfurization behavior of lignites, the sulfur reduction values were correlated through a multiple linear regression analysis'5 after 14 days of the biodesulfurization of all of the coal samples.
The fitted equations and determination coefficients obtained by multiple linear regression analyses using transformed data are shown in Table 11. Total and organicsulfur reduction valueswere correlated to carbon, nitrogen, mineral matter, humic acid, and organic sulfur forms of the lignite samples and determination coefficients (r2)obtained for these combinations were 1.OOO (eqs 1 and 2 in Table 11). In the absence of humic acid percentage in the combination, the values of the coefficient dropped to 0.280 and 0.529 (eqs 3 and 4), respectively. These results show that humic acid content of the lignites studied was an important parameter for biodesulfurization by S. solfutaricus. Total and organic sulfur reduction values were also correlated to only ultimate analyses of lignites and determination coefficients were obtained as 1.OOO (eqs 5 and 6). For these combinations, omission of each element of the ultimate analyses of coals resulted eqs 7-16, respectively. It can be concluded that the carbon, hydrogen, sulfur, nitrogen, and oxygen contents of the coal samples are also effective parameters for the total and organic sulfur reductions during the bioprocess. Total and organic sulfur reduction values were also correlated to all sulfur forms of lignites (eqs 17 and 18). The determination coefficients for total and organic sulfur reductions were calculated as 0.984 and 0.982, respectively. Total sulfur reductions were also correlated to huminite, mineral matter, humic acid, ligneous matter, and organic sulfur contents of the lignites (eq 19) with r2 = 1.OOO. Equations 20-24 were also obtained for the total sulfur reductions via the absence of each parameter in the same equation. The results showed that all of the correlation parameters considered in eq 19 were effective for total sulfur removal. Experimental and theoretical values of the total and organic sulfur reductions are shown in Figure 3a for eqs 5 and 17, and in Figure 3b for eqs 6 and 18, respectively. The calculated values of reductions in total sulfur and (15) Vandergraft, J. S . Computer Science and Applied Mathematics; Introduction to Numerical Computations: Academic Press Inc., La.: New York, 1978;p 156.
Durusoy et al.
808 Energy & Fuels, Vol. 6, No. 6, 1992
forms of lignites and time (eqs 5 and 6). The determination coefficientswere obtained as 0.945and 0.696,respectively. Equations 7 and 8 show the correlations between the relative total and organic sulfur removal rates and huminite, mineral matter, humic acid, ligneous matter, and organic sulfur contents of the lignites and time with r2 = 0.981 and 0.882,respectively. It can be concluded from the time-dependent correlations that the relative total and organic sulfur reduction rates are inverselyproportionalto the same powers of time. These powers are 1.489 and 1.189 for the relative total sulfur removal rate (eqs 1, 3, 5, and 7) and the relative organic sulfur removal rate (eqs 2,4,6,and 81, respectively. The results showed that the biodesulfurization mechanism of the six lignite samples proceeds on the same timedependent reaction kinetics for S. solfataricus.
Experimental Values
Conclusion S. solfataricus can remove all sulfur forms of lignites at 70 O C and a shaking rate of 40 rpm during biodesulfurization. The highest total and organic sulfur reductions 0' were observed for Beypazarl lignite as 57.1 and 47.8%, 0 10 20 30 40 50 respectively. Experimental Values The influence of analyses of the originallignites on total Figure 3. (a,top) Comparisonof experimental and model values (calculated from eq 5 and eq 17) of total sulfur reductions of and organic sulfur reductions has been investigated. For lignite samples. (b, bottom) Comparison of experimental and this purpose, multiple linear regression analysis has been model values (calculated from eq 6 and eq 18) of organic sulfur applied to the experimental data. The resulting deterreductions of lignite samples. mination Coefficients are compared to obtain the best Table 111. Relative Total and Organic Sulfur Removal fitting parameter set. For the six lignites in this study the Rate Equations Obtained by Multiple Linear Regression experimental and model values for total and organicsulfur Analysis and Determination Coefficients reductions (Figure 3a,b) appear to agree well. no. equation r2 The behavior and properties of the coals are known to 1 rSt,nl e-m.416(~)-l.489(C)2.l38(N)6.38((M)1.172(Ha)2.307(So)~.0,981 9ffi 2 rso,ml = e-8.238(t)-l.l89(C)~'.s22(N)5~1.751(Ha)1.~(S0)~.595 130(M) 0,882 differ sharply. Therefore, the validity of the results would 3 rStnl= e75.215( ~)-i.~S(C)-l3.5S3(N)-Z.~(H)B.253(St)-3.Ol6(~)-7.2~ 0.981 be limited and could not be generalized. The subject 4 rSo,nl = e93.325(t)-l.lsS(C)-l5.~(N)-6.0M)(H)3.452(St)-3.7ffi(0)-8.276 0.882 microorganism is another parameter in biodesulfurization 5 r%ml= e-28.408( t)-1.489(St)25.317(S~)-2.904(S )-8.322(S0)-12.679 0.945 6 rso,nl = e-".234(t)-l.189(St)21.BBO(Sll)-0.758(S )-9.73S(SO)-8.452 0.696 kinetics. Then, the results would be specific to the 7 = ~33.7~3(t)-1.~9(Hum)-2l.~2(M)-2.2~(Ha)9.~(L)8.778(So)-8.7ffi 0.981 thermophilicbacterium, S.solfataricus, and the six lignites 8 rs0,., = e8.33o(t)-l.l89(Hum)-6,~3(M)O,3o3(Ha)3.566(L)1.7ffi(So0.882 )-2.77* of this study. On the other hand, the fact that a model has been organic sulfur forms of lignites are in good agreement with successfully developed using results of ultimate, sulfur the experimental data. type, rational, and petrographic analyses seems to be very Total and organic sulfur reduction rates were calculated interesting. In conclusion, it could be suggested that at various times of biodesulfurizationfor each coal sample. systematic analysissuch as this may graduallylead to more The sulfur removal rates were normalized relative to initial complete and general theory of biodesulfurization mechsulfur reduction rates. Relative total sulfur reduction anism. (r&,J and relative organic sulfur reduction (rsa,rc,) rates were correlated to various parameters and time (Table Notation 111). Equations 1 and 2 in Table I11 show the correlations L ligneous matter content of lignites (%) mineral matter content of lignites (vol % ) M between the relative total and organic sulfur removal rates humic acids (% ) Ha and carbon, nitrogen, mineral matter, humic acid, and huminite (volume % ) Hum organic sulfur forms of coal samples and time with the relative total sulfur reduction rate determination coefficientsas 0.981and 0.882,respectively. relative organic sulfur reduction rate The relative sulfur reduction rates were also correlated organic sulfur (mf 5% ) pyritic sulfur (mf %) to only ultimate analyses of lignites and time, and values sulfate sulfur (mf %) of determination coefficientsforeqs 3 and 4were calculated total sulfur (mf %) as 0.981 and 0.882,respectively. organic sulfur reduction (% ) The total and organic sulfur removal rates relative to total sulfur reduction (%) biodesulfurization time (day) initial sulfur reduction rates were correlated to all sulfur "
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