Energy & Fuels 1989, 3, 236-242
236
Table VIII. Sulfur Concentration vs Time for 0.01% Sulfur DoDant from ThioDhenol Hydrocracked Hydrofined Shale-I1 JP-5 Jet A Jet A stock Jet A stock week mg of S week mgof S week mg of S week mgof S 0 0.21 0 0.20 0 0.21 0 0.20 1 2 3 4 5 6 7 8
0.03 0.02 0.00 0.00 0.00 0.00 0.00 0.00
1 2 3 4 5 6
7 8
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1
2 3 4 5 6
7 8
0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00
1
2 3 4 5 6
7 8
0.09 0.12 0.05 0.07 0.06 0.04 0.03 0.05
0.01% added sulfur, peroxide inhibition stops in the fifth week of stress when the added thiophenol concentration was reduced to zero as measured by the sulfur detector. The comparison of sulfur concentration to peroxidation indicated that control or inhibition of peroxidation was lost a t approximately 0.2 f 0.1 mg of added sulfur in all fuel samples.
Conclusions The effect of adding sulfur in the form of an aromatic thiol, thiophenol, was significant to peroxide formation.
Thiophenol has been found to act as an inhibitor or controller of peroxide formation in Jet A, Shale-11-derived JP-5, and petroleum-derived Jet A blending stocks. Hydrotreated jet fuels exhibited higher peroxide formation and concentration than other fuels. Hydrotreatment reduces the sulfur content of the fuel, which removes those naturally occurring sulfur compounds that possibly act as inhibitors to peroxide formation. There appeared to be a minimum concentration of sulfur as thiophenol above which peroxide formation was inhibited. If this concentration was decreased or consumed, peroxidation began. In a mixture as complex as a fuel, when a sulfur dopant is present a t a concentration of 0.10% or less, the sulfur compound reaction products are not possible to detect. Sulfur compound MS and hydrocarbon MS are quite similar, and the sulfur compounds are buried in the GC of the fuel. We suggest that since aromatic thiols are quite reactive in the presence of peroxide species, the thiophenol most likely undergoes oxidation by the peroxide.16 In model systems, in dodecane solvent, we found in our preliminary studies with hydroperoxides and sulfur model compounds that both aryl disulfides and oxidized sulfur species such as sulfoxides and sulfones were formed from thiophenol. Registry No. Thiophenol, 108-98-5.
Effect of Coal Properties, Temperature, and Mineral Matter upon a Hydrogen-Donor Solvent during Coal Liquefaction B. Chawla,* R. Keogh,* and B. H. Davis* Center for Applied Energy Research, 3572 Iron Works Pike, Lexington, Kentucky 40511 Received February 18, 1988. Revised Manuscript Received December 12, 1988
The tetrahydrofuran-soluble fraction of coal liquids, containing tetralin (T) and naphthalene (N), was analyzed by using a high-performance liquid-chromatographic technique. The amount of H2 consumption (calculated from experimental T / N ratios) during coal liquefaction showed a direct relationship with the carbon content of the coals. While the T / N ratios obtained for residence times of 5-65 min defined similar trends, the value of the ratio did depend on the carbon content of the coals.
Introduction Coal liquefaction processes have been studied' in the presence of hydrogen-donor as well as non-hydrogen-donor
solvents for many years.'-15 Two generally accepted p a t h w a y ~ ~ ~ ~for J ~ JH~ transfer -'~ from a donor solvent ~~~
(1) Pott, A.; Broche, H.; Schmitz, H.; Scheer, W. Gluckauf 1933, 69, 903. (2) Bergius, F. Nobel Lectures-Chemistry, 1922-1941; Elsevier: Amsterdam, 1966; p 244. (3) Orchin, M.; Storch, H. H. I n d . Eng. Chem. 1948,40, 1259. (4) Curran, G. P.; Struck, R. T.; Gorin, E. Ind. Eng. Chem. Process Des. Dev. 1967, 6, 166. (5) Wiser, W. H. Fuel 1968,47, 475. (6) Neavel, R. C. Fuel 1976, 55, 237 and references cited therein. (7) Tsai, M. C.; Weller, S. W. Fuel Process Technol. 1979, 2, 313. (8)Solvent Activity Studies; Catalytic Inc.: Wilsonville, AL, 1983; DOE/PC/50041-18, DE83, 015870. (9) Whitehurst, D. D.; et al. Coal Liquefaction-The Chemistry & Technology of Thermal Processes Academic Press: New York, 1980.
0887-0624/89/2503-0236$01.50/0
(10) (a) Derbyshire, F. J.; Whitehurst, D. D. Presented at the EPRI Contractor's Meeting, Palo Alto, CA, May 1980. (b) Derbyshire, F. J.; Odoerfer, G. A.; Rudnick, L. R.; Varghese, P.; Whitehurst, D. D. EPRI Report, AP-2117, Vol. 1, Project 1655-1; EPRI: Palo Alto, CA, 1981. (11) Ohe, J.; Itoh, H.; Makaba, M.; Ouchi, K. Fuel 1985, 64, 902. (12) Skowronski, R. P.; Ratto, J. J.; Goldberg, I. B.; Heredy, A. Fuel 1984, 63, 440. (13) Besson, M.; Bacaud, R.; Charcosset, H.; Cebolla-Burillo, V.; Oberson, M. Fuel Process. Technol. 1986, 12, 91. (14) Storch, H. H. Chemistry of Coal Utilization. Lowry, H. H., Ed.; John Wiley and Sons: New York, 1945; Vol. 11. (15) Heredy, L. A,; Fugasi, P. Phenanthrene Extractions of Bituminous Coal. In Coal Science; Given, P. H., Ed.; Advances in Chemistry Series 55; American Chemical Society: Washington, DC, 1966; p 448. (16) Whitehurst, D. D.; Farcasiu, M.; Mitchell, T. 0. The Nature and Origin of Asphaltenes in Processed Coals. EPRI-AF-252, 1st Annual Report; EPRI: Palo Alto, CA, 1977. 0 1989 American Chemical Society
H-Donor Solvent in Coal Liquefaction
Energy & Fuels, Vol. 3, No. 2, 1989 237
(tetralin) to coal during coal liquefaction are shown in eq 1-6.
1 .o
0.9
-
pathway I T h e w " Cleavage
R . (Coal Radical Species1
Coal - ,
(1) (2)
pathway I1
H, Rich Portion
L.
H
H
1
iition
'
Following a mechanism of H atom transfer to ipso positions of coal structures for coal pyrolysis processes,2o McMillen, et a1.21have proposed an alternate model for coal liquefaction (pathway 111). Their mechanism involves pathway I11
0
1
2
3
4
5
6
7
8
4
TETRALIN / NAPHTHALENE I%)
F i g u r e 1. Plot of ratios of LC peak areas of tetralin and naphthalene (Taea/Naea) versus T / N (%) ratios.
naphthalene (N). In order to determine the effect of temperature, coal properties, and mineral matter upon a donor solvent, tetralin, T / N ratios were obtained for the liquefaction of several coal samples of different carbon contents using three temperatures, 385,427, and 445 OC, with reaction times ranging from 5 to 65 min.
Experimental Section The liquefaction experiments were conducted in a microauthe transfer of H atoms through solvent-derived radicals toclave reactor of 50-mL capacity. The microautoclave was (produced by the reactions of coal radicals and solvent charged with 5 g of coal (-100 mesh; dried overnight under vacuum molecules) and scission of strongly bonded coal structures of approximately 25 in. of Hg a t 80-90 "C), 7.5 g of tetralin, and in donor solvent systems. a steel ball (1/4 in. dia.) for mixing. The system was pressurized Higher coal conversions in the presence of donor solvents with 800 psi of H, a t ambient temperature (ca. 2000 psi at 445 have dictated that no matter which pathway dominates, OC) and immersed in a heated sand bath for the desired reaction time. Typically, it required less than 2 min to reach the desired the solvent hydrogen-donor ability plays an important role reaction temperature. To ensure thorough mixing of ingredients, in the process of coal liquefaction. However, only a small the shaker speed (vertical) was set a t 400 cpm. At the end of the fraction of the research efforts that are presently being experiment, the reactor was inserted in a cold sand bath. Once made toward coal liquefaction processes is being devoted the reactor had attained nearly ambient temperature (within 2 to understanding the fate of the H-donor solvent. min), the unreacted H, and other gases were slowly released into Tetralin, a donor solvent, involvement during coal lia gas-sampling apparatus. The products were removed from the quefaction processes is indeed highly c ~ m p l e x ~ ~ ~and * ' ~ J ~ *reactor '~ with tetrahydrofuran (THF) and were Soxhlet extracted may produce various compounds such as naphthalene, to obtain the coal conversions. The extraction was continued for 1-methylnaphthalene, 1-methylindan, indan, indene, buabout 24 h or more until the liquid extract in the thimble was clear. tylbenzene, dimers and C0-Cl1 hydrocarbons, etc. HowThe THF-soluble reactor products were analyzed by a highever, the major product of tetralin (T) conversion is performance liquid chromatographic (HPLC) technique. The technique requires only the stirring of the reactor products ov(17)Pina, B.B.Hydroliquefaction Performance of Two Kentucy Coals ernight with an excess of THF. The T H F filtrate is then injected in Solvents of Various Hydrogen-Donor Strengths. M.S. Thesis, 1984, into the HPLC system. The ratio of peak areas (number of counts) University of Louisville, Louisville, KY, and references cited therein. of tetralin (T) and naphthalene (N) can be used to obtain the T / N (18)Ratto, J. J.; Heredy, L. A.; Skowronski,R. P. In Coal Liquefaction ratio directly (without knowing solution concentration) from a Fundamentals; Whitehurst, D. D., Ed., ACS Symposium Series 139 linear calibration plot of T,,,/N,,, versus T / N (see Figure 1). American Chemical Society: Washington, DC, 1980;p 347. (19)Stevens, H. P. In Proceedings of the I983 International ConferThis technique was developed by optimizing the conditions for ence on Coal Science; Center for Conference Management: Pittsburgh, the analysis of the THF-soluble reactor products: column, SuPA, 1983;p 105. pelcosil, LC-PAH (25 cm X 4.6 mm); mobile phase, THF-H20, (20)Gavalas, G. R.;Cheong, P. H.; Jain, R. Ind. Eng. Chem. Fundam. 4060; flow, 0.9 mL/min; detector, UV, 254 nm. The performance 1981,20, 113. of the HPLC system was checked against a standard mixture of (21)(a) McMillen, D.F.; Malhotra, R. International Conference on Coal Science 1987; Elsevier: Amsterdam, 1987;p 193. (b) McMillen, D. uracil, acetophenone, benzene, and toluene with CH30H:HzO = F.; Malhotra, R.; Chang, S.-J.; Ogier, W. C.; Nigenda, S. E.; Fleming, R. 6040 as a mobile phase with a typical flow rate of 1 mL/min. H. Fuel 1987,66, 1611. (c) McMillen, D.F.; Malhotra, R.; Hum, G. P.; The precision and reproducibility of the data were established Chang, S.-J.Energy Fuels 1987,1,193. (d) McMillen, D.F.; Malhotra, by making repeated measurements for completely independent R.; Chang, S.-J.; Nigenda, S. E. P r e p . Pap.-Am. Chem. Soc., Diu. Fuel experiments performed on different days. The precision of the Chem. 1985,30(4),297. (e) McMillen, D.F.; Malhotra, R.; Nigenda, S. E. P r e p . Pap-Am. Chem. Soc., Diu. Fuel Chem. 1987,32(3), 180. T / N data was found to be better than 1%.The accuracy of the
238 Energy & Fuels, Vol. 3, No. 2, 1989
Chawla et al.
T / N
R 10
I
* Ic
, : < A 04 68
I
70
~
72
I 74
I
76
I
78
I
80
I
82
I
84
86
WT X CARBON ( d a f )
Figure 2. Variation of the T/N ratios with the carbon contents of the coals: (+) 385 "C; (A)427 "C; (W) 445 "C.
results was verified by comparing the T/N ratios obtained by GC and HPLC. The maximum uncertainty in the T/N ratios was determined t o be less than 5%. The mineral matter was obtained by extracting 22 g of a nondistillate portion of SRC received from the Wilsonville,AL, pilot plant (K-125,Sample No. 59279, S/lO/SO) with THF. About 6 g of nonextractable mineral matter remained, and this was used in studies where ash was added. The chemical analyses of the coals used in this work are presented in Table I. The Western Kentucky samples (W. Ky. No. 9, No. 11,Breckinridge)were obtained from the working face of the mine. The samples were ground to -100 mesh and stored under Ar. The Illinois No. 6 and Wyodak samples were obtained from washed stockpilesat the mine site. These samples were also ground to -100 mesh and stored under Ar. The samples from the Penn State Sample Data Bank were used as received. Prior to the liquefaction experiments, the coals were dried overnight in vacuo. The HPLC grade THF and water and the commercially available tetralin were used as supplied.
Results and Discussion I. Effect of Temperature and Coal Properties on the T/N Ratios. Liquefaction runs using eight of the coals were made by using three reaction temperatures (385, 427, and 445 "C),an H2atmosphere (800 psig, ambient) and a 15-min residence time to determine the extent of conversion of tetralin to naphthalene. The tetralin/ naphthalene ratios (T/N) obtained from the THF soluble products are presented in Table 11. The overall variation in the T / N values (1.80-18.7) is significant for the range of the coal properties. The data presented in Table I1 indicate that the T / N ratios decrease with increasing reaction temperature for each of the coals studied. The decrease in the T / N ratios is accompanied by an increase in coal conversions with an increase in reaction temperature. However, the relationship between coal conversions and T / N ratios shows considerable scatter, particularly at the highest reaction temperature. This is most likely due to secondary reactions, i.e., asphaltene and/or preasphaltene conversions to produce oils and gases, becoming dominant at the higher reaction temperature. A standard correlation matrix was constructed by using the coal property, liquefaction, and T / N data presented in Tables I and 11. The correlation coefficients indicated that a relationship existed between the carbon (rank) and pyritic sulfur contents of the coals with the experimental T / N ratios obtained by using the three reaction temperatures. The T / N ratio increases (less tetralin conversion to naphthalene) with an increase in the carbon and pyritic sulfur contents of the coals (Figures 2 and 3 respectively).
Energy & Fuels, Vol. 3, No. 2, 1989 239
H-Donor Solvent in Coal Liquefaction
Table 11. Conversions and T/N Ratios at Three Temperatures and a 15-min Reaction Time % conversion T / N ratio coal sample 445 "C 427 "C 385 O C 445 O C 427 "C 385 "C 94.6 90.4 66.3 4.03 f 0.21 6.63 f 0.62 17.40 f 1.0 71154 (W. Ky. No. 9) 37.8 3.51 f 0.27 5.96 f 0.18 18.7 Breckinridge 90.6 72.3 57.8 2.78 f 0.12 4.30 f 0.15 10.3 f 0.5 71072 (W. Ky. No. 9) 87.0 73.3 64.8 2.62 f 0.06 3.70 f 0.11 9.14 f 0.05 71064 (W. Ky. No. 11) 95.7 94.7 55.6 2.37 f 0.25 3.99 f 0.13 11.13 f 0.22 71081 (W. Ky. No. 11) 93.6 90.6 1.86 f 0.06 PSOC 866 77.2 91648 (Wyodak) 89.5 85.6 58.0 2.07 f 0.06 2.60 k 0.04 5.73 f 0.20 PSOC 833 84.0 77.8 35.6 1.80 f 0.05 2.86 f 0.05 6.30 f 0.10
.
I
.....,I I,.',
04 0.0 0.2 0.4
0.6
0.8 1.0
1.2
1.4
&'.I
0
,
"c;
385 OC
T N = 0.133(C) - 7.61
R2 = 0.77 (7)
427 "C
T N = 0.237(C) - 14.03
R2 = 0.79 (8)
445 "C
T N = 0.755(C) - 47.14
R2 = 0.71 (9)
where TN is the experimental T / N ratio and C is the dry, ash-free (daf) carbon content of the coals. The equations obtained by using pyritic sulfur in the linear regression are
R2 = 0.87 ( 10)
427 "C
T N = 2.573(Pyr S)
+ 2.373
R2 = 0.80 (11)
445 OC
T N = 8.478(Pyr S)
+ 4.921
I
6
:
8
I
:
I
:
I
10 12 14 16 18
Figure 4. Parity plot of T / N ratios using carbon and pyritic sulfur as predictive variables: (e)385 "C;(A)427 "C;(W) 445
OC.
A linear regression was performed on the data obtained by using the three reaction temperatures to evaluate the relationship between the T / N ratios and the carbon and the pyritic sulfur contents of the coal. For the variable carbon, the following equations resulted:
T N = 1.367(Pyr S) + 1.728
:
4
EXPERIMENTAL T / N
WT X P Y R I T I C SULFUR ( d a f )
Figure 3. Variation of the T/N ratios with the pyritic sulfur (W) 445 "C. contents of the coals: (e)385 "C;(A)427
385 OC
2
.
R2 = 0.77 (12)
where T N is the T / N ratio and Pyr S is the pyritic sulfur content (daf) of the coals. The results of the linear regression analyses indicate that the relationships between the carbon and pyritic sulfur contents of the coals may not be linear. The data presented in Figures 2 and 3 show that although a general trend exists between the T / N ratios and the carbon and pyritic sulfur contents, the relationships apparently are not linear for the three reaction temperatures studied. A multiple linear regression was performed by using the carbon and pyritic sulfur values and the T / N ratios obtained for each reaction temperature studied. As can be seen in Figure 4, this linear combination of coal properties can predict the experimental T / N ratios obtained from the liquefaction for the majority of the coals.
The following equations resulted from the multiple regression analysis:
+ 0.2284(C) - 11.0652
385 OC
T N = 6.230(Pyr S)
427 OC
R2 = 0.78 (13) T N = 1.432(Pyr S) + 0.1159(C) - 5.7413 R2 = 0.83 (14)
445 "C
T N = 0.989(Pyr S)
+ O.O446(C) - 1.4601 R2 = 0.89 (15)
The relationship does, however, show some scatter of the data representing the lowest reaction temperature. Two coals, a Western Kentucky No. 11 (71064) and the Breckinridge coal, do not fall on the parity line shown in Figure 4. These coals are responsible for the lower R2value of the data at this temperature. It has been suggested that coals can be more effective hydrogen donors than tetralin and that the liptinite maceral groups can donate hydrogen22*23 under liquefaction conditions. These factors may account for the deviation from the parity line in Figure 4 of the Breckinridge and the Western Kentucky No. 11 coals. The Breckinridge sample, a cannel coal (H/C = 1.27) with a 40.0 vol 5'% liptinite content, may donate hydrogen internally during coal dissolution. This could possibly lower the hydrogen demand from the solvent tetralin; hence, the higher T / N ratio than would be expected from the carbon content of the coal. The atomic H/C ratios of the coals were included as a third dependent variable in the regression analysis. The resulting parity plots of the experimental and predicted (22) Collins, C. J.; Benjamin, B. M.; Raaen, V. F.; Maupin, P. H.; Roark, W. H., P r e p . Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1977,22, 98. (23) Choi, C.; Stock, L. M. In Chemistry and Characterization of Coal Macerals Winans, R. E.; Crelling, J. C., Eds.; ACS Symposium Series 252; American Chemical Society; Washington, DC, 1984; p 157.
Chawla et al. 2 0 ' I
I
I
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,
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,'
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.
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2.2
10 12 14 16 18 20 1 .8
Coa1:Tetralin
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EXPERIMENTAL T / N
Figure 5. Parity plot of the T/N ratios using carbon, pyritic sulfur and H/C ratios as predictive variables: (+) 385 "C; (A) 427 O C ; (H) 445
"c.
T / N ratios obtained by using the carbon, pyritic sulfur, and H/C data are shown in Figure 5. The following equations resulted from the multiple regression analysis: 385 "C T N = 1.461(Pyr S) 0.542(C) + R2 = 0.89 (16) 12.950(H/C) -43.694
+
+
427 "C
T N = 0.752(Pyr S) 0.161(C) + 1.846(H/C) - 10.392 R2 = 0.85 (17)
445 "C
T N = 0.854(Pyr S) + O.O53(C) + R2 = 0.90 (18) 0.540(H/C) - 2.484
where H/C is the atomic H/C ratio of the coals. The results indicate a substantial improvement in the predicted T / N ratio obtained for the liquefaction of the Breckinridge and Western Kentucy No. 11 coal. The addition of the H/C ratios to the regression analysis did not substantially improve the predicted T / N ratios of the eight coals for the 427 and 445 "C reaction temperatures. In fact, the addition of the H/C ratios slightly increased the residuals between the predicted and experimentally determined T / N ratios a t these temperatures. From the data obtained, it appears that a relationship exists between the coal properties, carbon and pyritic sulfur, and the conversion of tetralin to naphthalene as measured by the T / N ratios. It appears from the data that the T / N ratio increases (less tetralin conversion) with increasing carbon and pyritic suIfur contents of the coal. For two of the coals studied, it appears that internal hydrogen donation may be important in determining the T / N ratio for a low reaction temperature. By use af the H/C ratios as an approximate measure of this property, the predicted and experimental T / N ratios show better agreement for these two coals. 11. Effect of Residence Time on T/N Ratios. To determine the effect of residence time (kinetic versus equilibrium tetralin conversions), experiments were performed in which the tetralin to coal ratios and the presence of H2 or Ar atmospheres were varied by using a reaction temperature of 445 "C and residence times of 5-65 minutes. Two coals of different rank, a subbituminous Wyodak coal and a high-volatile bituminous Western Kentucky No. 9 (71072) coal, were used in the experiments. In addition to the coal experiments, a series of blank runs using tetralin in the presence of 2 g of a catalyst (Ni/Mo-alumina) and an Hz atmosphere was completed for the same range of residence times. The data from these experiments are presented in Figure 6. As shown in Figure 6, the T / N value, regardless of the conditions used, decreases sharply with an increase in
CoakTetralin
1.o 0.6
1
0.21 0
CoabTetralin 1:1.5 Ky #9 IArl
'
8
I
'
16
24
'
32
'
40
'
48
'
56
'
64
Time (minl
Figure 6. Trends of T/N values for experimentsperformed under a differentprocess conditions at 445 "C versus the reaction time: (+) catalyst (2 g) + tetralin (7.5 g) and PH*(ambient) = 800 psig; (0) W. Ky. coal No. 9 (71072) (5 g) + tetralin (10 g) and PHp (ambient)= 800 psig; (0) W. Ky. coal No. 9 (71072) (5 g) tetralin (7.5 g) and P H(ambient) ~ = 800 psig; (A)W. Ky. coal No. 9 (71072) (5 g) + tetralin (7.5 g) and PA,(ambient) = 800 psig; (H) Wyodak-Wyoming coal (5 g) + tetralin (7.5 g) and PH1(ambient) = 800 psig.
+
reaction time until it reaches some pseudoequilibrium value for either the coal or the blank experiments. Since the pseudoequilibrium values are different for the two coals, the pseudoequilibrium T / N value also appears to be coal rank dependent. The relatively low and different pseudoequilibrium T / N values for the two coals (1.3 and 1.9) as compared to that of the catalyzed (Ni/Mo) tetralin conversion reaction (4.0) clearly suggest that the conversion of tetralin to naphthalene is primarily due to the extent of the hydrogen demand by the coal during liquefaction. This is further supported by the fact that there were significant differences between the pseudoequilibrium T / N values obtained for a Western Kentucky coal No. 9 (71072) when liquefied either under Ar or Hz pressure in the presence of tetralin (Figure 6, A and 0). The parallel behavior of T / N ratios of two coals of different ranks over the entire range of reaction times (Figure 6) suggests that the solvent involvement follows a similar course in the initial as well as the later processes of liquefaction of the two coals. This phenomen is partially supported by the fact that the conversions for the two coals are similar for both 15 and 45-min residence time experiment~.~~~~~ To understand the solvent involvement during the initial and the "steady-state" stages of the liquefaction processes, additional experiments using a 45-min residence time and a 445 "C reactor temperature were performed with the eight coals. The T / N ratios obtained by using the longer residence time and the 15-min residence time exhibit a linear relationship with a slope of nearly unity (1.2). That is, the trend in the T / N ratios observed a t the longer residence times is the same as that observed at the shorter residence times even though the set of reactions causing (24) Our unpublished results.
H-Donor Solvent in Coal Liquefaction
Energy & Fuels, Vol. 3, No. 2, 1989 241
the hydrogen demand should be different. Since coal conversion (ca. 90%), was complete in 15 min, the hydrogen consumption a t longer times must be due to hydrogen consumption by secondary reactions. Consistent with this, the preasphaltene content decreases from 20-25 wt % for 15 min to only 3-4 wt % at 45 min; at the same time, oil and gas yields increase. 111. Effect of Mineral Matter on Tetralin Conversion. In order to use T / N ratios for calculating accurate hydrogen consumptions by several coals of different carbon content, it was important to determine the amount of tetralin conversion, if any, through the reactions of tetralin with the inorganic constituents of coals. This was investigated by heating the tetralin with a residence time of 45 min in the presence of gaseous H2at 385,427, and 445 "C with or without ash derived by low temperature ashing or with mineral matter obtained from the liquefaction of a Kentucky Coal in the Wilsonville pilot plant (K-125 sample; see Experimental Section). The insignificant (less than 3 % ) conversion of tetralin to naphthalene in these experiments confirmed that the conversion of tetralin, under the reaction conditions described in this study, was primarily due to the hydrogen demand by the organic component of the coal sample rather than dehydrogenation reactions catalyzed by the mineral matter. This was further supported by the results from heating a mixture of tetralin and phenanthrene (1.5:l weight ratio) for 15 min at 385 OC in the presence of H2and mineral matter. The analysis of the products indicate that there were no significant products obtained from the H transfer from tetralin to phenanthrene. Therefore, these results indicate that the mineral matter had minimal effects on the conversion of tetralin to naphthalene. IV. Calculation of Hz Consumption from the T/N Ratios. Since, as discussed in section 111,the conversion of tetralin during liquefaction is primarily due to the hydrogen demand by the organic component of the coals, calculations to determine the actual amount of hydrogen transferred from tetralin to coal for a 445 "C reaction temperature and a 45-min residence time in the presence of H2were made. From these experiments, the total tetralin plus naphthalene recovery is 95.6%, i.e., T + N = 95.6. Defining R = T / N and substituting in the equation results in defining the tetralin (T) present a t the end of the experiment as Tunreackd = (95.6 - T/R). Rearranging the equation results in the following: Tunreacted
= 95*6R/(1 + R)
From blank runs using only tetralin, hydrogen, a reaction temperature of 445 "C, and a 45-min residence time, it was experimentally determined that 92.4% of the tetralin remains. Therefore it follows that (Tconsumed is due to the demand from coal): Tconsumed
Tconsumed H2 consumed
(%) = g2a4
(g) = (T (%)
- Tunreacted
X Tinitid
(g))/100
(g) = ((4.03Tc0n~ume~)100)/132.2 X coal (daf) (g)
Four liquefaction experiments were performed (445 "C, a 45-min residence time, and an argon atmosphere (800 psig, ambient)) in which the amount of Ky. No. 9 coal (71072) was varied from 1 to 7.5 g with a fixed amount of tetralin (7.5 8). The T / N values obtained from these experiments were used to calculate the amount of H2 consumed in each experiment (Figure 7). A linear relationship with zero intercept between the amount of H2 consumed versus the amount of dry ash-free coal further
0.16
0.12 \
9 z
0.08
8 N
I
0.04
0.00 0
2
4
6
8
10
COAL (maf,g)
Figure 7. Relationship between the total amount of H2consumed at 445 "C and 45-min reaction time and the amount of coal charged t o the reactor. Table 111. Hydrogen Transfer to Coal Samples at 445 "C, 45-min Residence Time, PAror Pga(cold) = 800 psig H transfer, g of H2/100 g of coal through through molecular tetralin hydrogen coal Ar HI (difference) 71154 (W. Ky. No. 9) 2.37 1.39 0.98 71153 (W. Ky. No. 9) 2.37 1.37 1.00 71092 (W. Ky. No. 9) 2.42 1.45 0.97 71072 (W. Ky. No. 9) 2.54 1.50 1.04 91648 (Wyodak) 2.84 1.90 0.94
supports the view that the T / N ratios are a measure of hydrogen consumption by the coals during coal liquefaction. A similar conclusion was reached by Tsai and Wellere when they compared their results from blank experiments using tetralin and either cobalt-molybdate-alumina, Co/Mo/Alz03, or stannous chloride catalyst at 400 "C with those of coal liquefaction runs. V. Competition between Molecular Hydrogen and Hydrogen-Donor Solvent during H-Transfer Processes. Independent of the coals studied, the T / N values obtained for experiments performed under the H2atmosphere are always higher than those obtained under the Ar atmosphere for the same initial pressures. The only difference between the two systems is that one of the systems has two H donors (H2 gas and tetralin) whereas the other has only one (tetralin). Therefore, in the absence of any other catalytic reactions discussed above, the different T / N values for these systems are evidence of molecular hydrogen involvement during coal liquefaction. The T / N values were used to determine the amount of hydrogen transfer from tetralin during the liquefaction of five coal samples under those two sets of conditions (445 "C with 45-min residence time; Table 111). These data show that the amount of molecular hydrogen consumed is about 1.0 wt % daf coal, about 25-30 wt % of the total H transfer (depending upon the coal) under our experimental conditions. Furthermore, the amount of H transfer from molecular hydrogen appears to be independent of the coal studied. This suggests that there are two independent pathways for H transfer to coal, one from molecular hydrogen and one from tetralin (solvent). This observation contrasts to the findings of, for example, Ouchi et al.,= who
242 Energy
(e
Chawla et al.
Frcels, Vol. 3, No. 2, 1989
Table IV. H2Consumption by Coals at 445 "C, 45-min Residence Time
P
HZ
70 C (daf)
(wt % )
consumption, g of H2/100 g of coal
84.99 84.15 83.21 82.45 81.21 80.66 80.37 79.19 78.80 78.39 78.28 75.25 74.91 73.49 71.02 68.64
30.58 6.96 9.07 11.07 6.78 6.43 4.10 10.00 10.03 10.40 4.80 11.30 13.59 15.87 7.59 12.00
2.37 2.38 2.44 2.37 2.42 2.11 2.57 2.54 2.52 2.68 2.64 2.72 2.85 2.92 2.84 2.94
dry ash,
coal sample 71154 (W. Ky. No. 9) 71155 (W. Ky. No. 9) 71157 (W. Ky. No. 9) 71153 (W. Ky. No. 9) 71092 (W. Ky. No. 9) Breckinridge 71185 (W. Ky. No. 11) 71072 (W. Ky. No. 9) 71064 (W. Ky. No. 11) Illinois No. 6 71081 (W. Ky. No. 11)
PSOC 866 71059 (W. Ky. No. 11)
:
71058 (W. Ky. No. 11) 91648 (Wyodak) PSOC 833
:
2.02
R 2 = 0.909 2
8
2.50
N
I
g (1
5
2.50
2.10 2.26
OBSERVED H 2 CONSUMPTION
Figure 9. Parity plot of H2consumption (g of H2/100 g of coal) using carbon and pyritic sulfur content and H/C ratios of 16 coals as predictive variables (445 "C and 45-min residence time).
quefaction (Figure 8). The one sample that shows a large deviation from this relationship is the Breckinridge cannel coal. As discussed in section I, the low H2 consumption is most likely due to the amount of internal hydrogen donation from the coal itself. A multilinear regression was performed by using H2 consumption calculated from the T / N ratios and the carbon and pyritic sulfur contents and atomic H/C ratio to determine if a similar relationship exists for the 16 coals. The following equation predicts the H2consumption under these experimental conditions quite well, as shown in Figure 9 (R2 = 0.946): H2 CONS = - 0.427(C) + 0.0422(Pyr S) - 0.9111(H/C) 6.766 (19) where H2 CONS is the hydrogen consumption (g of H2/100 g of maf coal), C is the carbon content, Pyr S is the pyritic sulfur content, and H/C is the atomic H/C ratio of the coals.
+
2.42 2.34
6 N
1
2.10 68
. I' Breckinridge
70
I
L
72
74
76
78
ao
02
04
06
WEIGHT % CARBON (mafl
Figure 8. Relationship of the amounts of H2consumed during coal liquefaction versus the carbon content (rank) of coals.
suggested the H transfer from solvent to coal, in the presence of a catalyst, is initiated by transfer of molecular hydrogen to the solvent. molecular Hz solvent coal
-
-
Sixteen coal samples of different carbon contents have been liquefied in the presence of tetralin at 445 "C and a residence time of 45 min. The experimental T / N values were used to calculate H2 consumption. These results (Table IV), together with carbon and ash contents, show some systematic relationships. It appears the higher the carbon content, the lower the Hz consumption during li(25) Ohe,
s.;
Itoh, H.; Makabe, M.; Ouchi, K. Fuel 1986, 64, 1108.
Conclusions The conclusions derived from this work are as follows: (1)an increase in reactor temperature and/or residence time increases the conversion of tetralin to naphthalene; (2) the higher the carbon content, the lower is the overall consumption of H2 during coal conversion in tetralin; (3) T / N ratios follow a parallel course over the entire range of residence time of 5-65 min in the processes of coal conversions; (4) mineral matter does not have a significant effect on conversion of tetralin to naphthalene on the time scale used in this study. Acknowledgment. This work was supported by the Commonwealth of Kentucky, Kentucky Energy Cabinet, and DOE Contract No. DEFC22-85PC80009 as part of the Consortium for Fossil Fuel Liquefaction Science (administered by the University of Kentucky). Registry No. Tetralin, 119-64-2; naphthalene, 91-20-3; pyrite, 1309-36-0.
