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Comparison of anthracene and phenanthrene in coal liquefaction
Comparison of anthracene in coal liquefaction Kyung
and phenanthrene
C. Kwon
Chemical Engineering Department, School of Engineering institute, AL 36088, USA (Received 27 January 7984; revised 30 May 7984)
and Architecture,
Tuskegee
A comparison of anthracene and phenanthrene as solvents was undertaken by liquefying either Wyodak or Kentucky 9/14 coal in the presence of hydrogen or nitrogen. Phenanthrene was found to be a better physical solvent than anthracene for liquefying both coals. Anthracene and its derivatives are better hydrogenshuttling solvents than phenanthrene and its derivatives. Hydrogenation of anthracene to tetrahydroanthracene was observed with both coals. Dihydroanthracene is a better hydrogen-shuttling solvent than dihydrophenanthrane in the liquefaction of Kentucky 9/14 coal. Anthracene is a better solvent than phenanthrene in the presence of l-methylnaphthalene in liquefying both Wyodak coal under hydrogen and Kentucky 9/14 coal under nitrogen. The minerals in Kentucky 9/14 coal appear to be better hydrogenation catalysts than those in Wyodak coal. Labile hydrogen from coal appears to escape readily before reacting with hydrogen-shuttling solvents under the atmospheric environment. (Keywords: coal; liquefacaction;anthracene; phenanthrene)
Solid coal is dissolved with the aid of molecular hydrogen, donative hydrogen from hydroaromatic compounds, labile hydrogen from coal itself and physical solvents in the coal liquefaction process. Solid minerals or commercial catalysts may assist in coal dissolution. Various experiments have been carried out to try to understand the interactions between: coal and donative hydrogen from hydroaromatic compounds; coal and molecular hydrogen; and coal and the solvent. The effects of solvent quality and transfer of labile hydrogen from coal to aromatic compounds have also been investigated. BACKGROUND Neavel’ and Vernon’ found that molecular hydrogen stabilizes free radicals and rehydrogenates the hydrogen donor solvent, and also initiates a hydrocracking reaction during coal liquefaction. High pressure hydrogen can increase the hydrocracking of some carbon-carbon bonds in the coal structure. However, hydrogen may also assist in ring opening of hydroaromatic molecules and accelerate the dealkylation of alkyl aromatic compounds. These two reactions are undesirable in the coal liquefaction process as the former causes donor solvent degradation and the latter leads to high gas yields and high hydrogen consumption. Appel13 investigated the effect of solvent composition on product distribution in coal liquefaction, using Wyodak coal and Kentucky 9/14 high volatile bituminous coal, and solvents such as SRC-11 heavy distillate and lmethylnaphthalene. Padrick and co-workers4 studied the dffect on the dissolution of Wyodak coal, using solvents such as quinoline, tetrahydroquinoline and hydrogenated creosote oil. Their results indicated a strong dependence on a hydrogen donor solvent for conversion of Wyodak aoal. Derbyshire and Whitehurst’ discussed the disso-
lution of coals principal model
in polyaromatics using pyrenes compound. Utz et aL6 attempted
as the
to rank a series of hydrogen donor solvents using the short contact time liquefaction (SCTL) process and to determine the effect of molecular hydrogen on the SCTL process. Guin and co-workers’ suggested that some hydrogen, either molecular or donor, must be present to prevent retrogressive reactions of coal fragments during the early reaction stage. Direct hydrogenation of the coal using molecular hydrogen at high reaction temperatures is an important mechanism of liquefaction. Rottendorfand Wilson’ reported that the major role of the nickel-molybdenum catalyst during coal liquefaction is to rehydrogenate the donor vehicle after its dehydrogenation by coal. Mochida et aL9 examined the solvolytic liquefaction of various coals with a variety of solvents at 370-390°C under nitrogen to elucidate the role of solvents in coal liquefaction and to find the solvents which gave the highest liquefaction yields. Pyrene and solvent refined coal (SRC) were shown to be excellent solvents. Curtis and co-workers” ranked various hydroaromatic compounds according to their ability to convert coal into THF solubles, using Western Kentucky No. 9/14 coal. Several investigators used indigeneous coal minerals as catalysts in coal liquefaction. Garg and Givens” mentioned that both coal conversion and oil yield increased on addition of pyrite to the feed slurry, using Elkhom No. 3 and Kentucky No. 9 coals. Curtis and co-workers” used various indigeneous coal minerals, such as pyrite, kaolinite, montmorillonite, alumina oxide, titanium oxide and silicon dioxide in the hydrogenation of cyclohexene. Jackson’ 3 showed that the addition of iron as haematite led to an increase in coal conversion. Gangwar14 used minerals such as pyrites, limonites, diapore and magnetites as hydrogenation catalysts in coal liquefaction and
0016-2361/85/060747~07$3.00
80 1985 Butterworth & Co. (Publishers) Ltd.
FUEL,
1985,
Vol 64, June
747
Anthracene
and phenanthrene
in coal liquefaction:
K. C. Kwon
found that the catalytic activities of these minerals are reduced upon annealing them. Lytle” used metal chlorides such as SnCl,, ZnCl,, and FeCl, as catalysts in short residence time coal liquefaction. EXPERIMENTAL Materials The coals used were: Wyodak coal, 11.9 wt% ash and particle size - 100 mesh (0.147 mm); and Kentucky 9/14 coal, 10.1 wt% ash and particle size -200 mesh (0.074 mm), see Table I. The coals were dried in a vacuum oven and stored in a desiccator. Anthracene and phenanthrene were used as the aromatic compounds; 9,10-dihydroanthracene and dihydrophenanthrene were used as the hydroaromatic compounds; and 1-methylnaphthalene (1 -MN) was used as a physical solvent (although a small amount of interaction is known to occur), Nitrogen was used in the reaction systems when hydrogen was absent. l-Methylnaphthalene only was used in those runs where tricyclic aromatics were absent. Procedure A series of reactions, to liquefy either Wyodak coal or Kentucky 9/14 coal under the various operating conditions, were conducted in a 25 cm3, 316 stainless steel microreactor, see Table 2. Another series of reactions were performed in a 50cm3 flask at atmospheric pressure to each coal with either neat aromatic compounds such as anthracene and phenanthrene, or mixtures of aromatics and their dihydroaromatics. The microreactor consisted of a 316 stainless steel swagelock tee, a pressure transducer, a thermocouple and a quick-connect valve to introduce either hydrogen or nitrogen into the microreactor. This microreactor with the desired reactants is attached to a mechanical wristaction shaker, which swings in a 16” arc, and is then submerged in a fluidized sandbath. Following a reaction, the reactor is quenched in water and the gas products are released. The liquid and solid reaction products are removed completely from the reactor by dissolving with tetrahydrofuran (THF). The Table 1
Typical
analysis
of Kentucky
9/14 and Wyodak
Ky 9/14
Wyodak
Type of coal
wt%
wt%
Ultimate analysis Carbon Hydrogen Nitrogen Sulphur Ash Oxygen (by diff.)
71.5 4.8 1.5 3.3 10.1 8.8
65.2 4.8 1.0 1.2 11.9 15.9
coals
__--
Table 2
Reaction
conditions
Reaction temperature: Reaction duration: Reactor charge Hydrogen: Coal: Aromatic compound: Solvent :
748
for a microreactor
operation
350°C or 425°C 540 min 3.45 MPa hydrogen or 7.58 MPa hydrogen at the room temperature 1 g of Wyodak coal or 1 g of Ky 9/14 coal 1 g of anthracene or 1 g of phenanthrene 4 g of I-methylnaphthalene
FUEL, 1985, Vol 64, June
Table 3 Reaction conditions for the liquefaction of coal in the presence of aromatic compounds and in the absence of I-methylnaphthalene under 1 atm air pressure Reaction temperatures: Pressure: Reaction duration: Reactor charge Coal: Aromatic compound:
329”C34O”C 1 atm air 60 min 1 g of Wyodak coal or 1 g of Ky 9/14 coal 10 g of anthracene, or 10 g of phenanthrene, or 8 g of anthracene plus 2 g of 9.10-didydroanthracene, or 8 g of phenanthrene plus 2 g of dihydrophenanthrene
reaction product is separated into a THF-soluble fraction, an ethyl-acetate-insoluble fraction and a and cyclohexane-insoluble fraction to obtain the following product distribution: preasphaltenes, asphaltenes, and oil plus water plus gas. The THF solubles are filtered, using a pressure filtration procedure” and the THF-insoluble fraction is calculated from the amount of vacuum oven dried filter cake and the filtrate containing THF is introduced into a rotary evaporator to remove THF. The THF-free extract is added to excess ethyl acetate to precipitate the preasphaltenes which are isolated by pressure filtration. The filtrate is processed in the rotary evaporator to remove ethyl acetate. This filtrate is mixed with an excess of cyclohexane, so that the asphaltenes are precipitated. The cyclohexaneinsoluble or asphaltene fraction is obtained from the amount of the dry filter cake. The filtrate is introduced into the rotary evaporator to remove cycle-hexane. This filtrate, free of THF, ethyl acetate and cyclohexane, and containing the oil-plus-water fraction, aromatics and their hydroaromatic derivatives, is diluted with THF. The oil-plus-water fraction is calculated by substracting the preasphaltene and asphaltene fraction from the THFsoluble fraction. The THF-diluted oil fraction is injected into a gas chromatograph equipped with a flame ionization detector and a 0.318 cm (6 in) dia., 182.9 cm (6 ft) long lo”/,-SP2100-packed column, to analyse conversions of aromatics into their hydroaromatics. Coal conversions are calculated on a dry, ash-free basis. DISCUSSION Effect of elapsed reaction time on coal dissolution A series of experiments were conducted in the presence of either anthracene or phenanthrene by increasing reaction duration from 5 to 60 min at 425°C see Table 3. A 25 cm3 microreactor was loaded with 1 g of either Wyodak or Kentucky 9/14 coal; 1 g of either anthracene or phenanthrene, 4 g of 1-methylnaphthalene and 7.58 MI% hydrogen (initial pressure). Conversions of both coals into a THF-soluble fraction increase in the presence of either anthracene or phenanthrene, as reaction duration increases. Wyodak coal appears to be less reactive than Kentucky 9/14 coal in terms of THF solubles, see Table 4. However, Wyodak coal yields a larger oil-water-gas fraction, and a smaller preasphalteneplus-asphaltene fraction than does Kentucky 9/14 coal. Both anthracene and phenanthrene have a higher conversion to their hydro derivatives in the presence of Ky 9/14 coal than in the presence of Wyodak coal. This suggests that minerals in Ky 9/14 coal have a stronger
Anthracene catalytic effect than minerals in Wyodak coal on hydrogenating aromatics such as anthracene and phenanthrene in the presence of molecular hydrogen. Wyodak coal yields a higher oil-water-gas fraction in the presence of anthracene than in the presence of phenanthrene. It does, however, produce the same amount of preasphaltenes-plus-asphaltenes in the presence of either anthracene or phenanthrene. Therefore, anthracene and its derivatives are in some respects better solvents than phenanthrene and its derivatives in the liquefaction of Wyodak coal. Conversion of Ky 9/14 coal into THF-solubles is almost the same in the presence of either anthracene or phenanthrene, whereas its conversion into preasphaltenes-plus-asphaltenes is a little higher in the presence of anthracene and its derivatives than in the presence of phenanthrene and its derivatives. For Ky 9/14 Table 4
Effects of reaction
durations
on coal conversion
and phenanthrene
in coal liquefaction:
K. C. Kwon
coal liquefaction the preasphaltene-plus-asphaltene fraction is much larger than the oil-water-gas fraction but the reverse is true for Wyodak coal. These data show that both the coal and the solvent have an effect on the product distribution. Efft(cts of initial hydrogen pressure on coal conversion The conversion of both Wyodak and Ky 9/14 coal increases as the initial hydrogen pressure increases in the presence of both anthracene and phenanthrene, as shown in Table.5. I-Methylnaphthalene,a relatively inert solvent, is present in excess in these and most of the following experiments. The conversion of Ky 9/14 coal is influenced more by hydrogen pressure than that of Wyodak coal in the presence of either solvent. This suggests that molecular hydrogen may play a more dominant role than solvent
at 7.58 MPa initial hydrogen
pressure
and 425°C
_
Run No.
13
3
14
15
4
16
17
6
18
20
7
21
I g Aromatics plus 4 g I-MN Anthracene Phenanthrene
+ -
+ -
+ _
+
_
-
+
+
+ -
+ _
-
+
+
_ +
+ -
+ _
+ -
+ _
+ _
+ -
_ +
_ +
-
+
-
+
5
15
60
5
15
60
5
15
60
:
15
6’0
45.5
57.7
79.1
44.3 _
47.9
76.8 _
75.4 28.6 26.1
83.8 26.9 33.6
88.9 21.7 24.8
76.6 29.5 25.6
84.7 27.6 30.0
88.5 19.7 26.9
Type of coal Wyodak Ky 9114 Reaction duration Coal conversion THF-soluble Preasphaltene Asphaltene Preasphalteneplus-asphaltene Oil-water-gas
(min) (wt”;)
Conversion of aromatics Conversion to dihydroaromatic Unconverted aromatics Conversion to tetrahydroaromatic
Table 5
+
12.6 45. I
26.6 52.6
12.4 31.9
10.6 31.3
26.8 50.1
54.1 20.7
60.5 23.2
46.5 42.4
55.1 21.6
57.6 27.0
46.6 41.9
7.0 93.0
16.9 77.2
20.7 52.3
0 100
0 100
1.8 98.2
22.6 72.3
28.4 50.7
22.3 26.5
1.6 98.4
3.8 95.3
10.5 87.8
5.9
27.0
0
0
5.0
21.0
51.1
0
0
0
pressure
Run No. Hydrogen charge at room temperature (MPa)
on coal conversions
Coal conversion (wt:‘,) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
0
-
0
_
for 15 min at 425°C 6
38
10
7
3.45
7.58
0
3.45
7.58
+ -
+ _
+ _
_ +
+
+
+ -
+
_ +
+
+
_ +
+
47.9
42.4 11.0 18.1 29.1 13.2
72.4 26.3 26.5 52.7 19.7
83.8 26.9 33.6 60.5 23.2
37.7 13.4 14.9 28.3 9.5
75.3 21.0 25.1 46.2 29.1
84.7 27.6 30.0 57.6 27.0
4.4 95.6
17.6 71.7
28.4 50.7
0 100
0 100
3.8 95.3
45 -
1
3
2
4
37
0
3.45
7.58
3.45
7.58
0
-
+ -
+ -
+
+
+
+ -
+ -
+ -
36.1
44.3 _
57.7 _
8.0 28.2
14.0 30.3
12.6 45.1
40.3 _ _ 11.6 28.7
NA NA
6.4 93.6
16.9 77.2
0
0
100
100
1-MN
Type of coal Wyodak Ky 9114
Conversion of aromatics Conversion to dihydroaromatics Unconverted aromatic
11.9 33.6 (wt%)
Effects of hydrogen
1 g Aromatics plus 4 g Anthracene Phenanthrene
_
_ _
_ 10.6 37.3
(wt%)
-
FUEL, 1985, Vol 64, June
749
Anthracene
and phenanthrene
in coal liquefaction:
K. C. Kwon
structure in the liquefaction of Ky 9/14 coal or that the minerals in Ky 9/14 coal are actively hydrogenating the aromatic solvent. Analysis of the oil fraction suggests the latter. The conversion of anthracene to dihydroanthracene increases as the initial hydrogen pressure increases. With anthracene, the conversion of Wyodak coal increases from 44 to 58% and the hydrogenation of anthracene increases from 6 to 17% by increasing the initial hydrogen pressure from 3.45 to 7.58 MPa. Hydrogenation of phenanthrene is not observed although the conversion of Wyodak coal increases from 40 to 48% upon increasing the hydrogen pressure. With Ky 9/14 coal, hydrogenation of phenanthrene is not observed at 3.45 MPa initial hydrogen pressure but does occur at 7.48 MPa initial hydrogen pressure. Coal solubilization, however, increases sharply with pressure. These observations show that anthracene is more readily hydrogenated than phenanthrene and may be a better hydrogen shuttler or donor precursor than phenanthrene in the liquefaction of some coals. The conversion of Ky 9/14 coal is 42.4% and the hydrogenation of anthracene is 4.4% under nitrogen pressure, in the absence of hydrogen (Table 6). When the anrhracene is replaced by phenanthrene, the conversion of Ky 9/14 coal decreases to 38% and no hydrogenation of phenanthrene is observed. This shows that anthracene is more active than phenanthrene in the liquefaction of Ky 9/14 coal in the absence of hydrogen, by extracting hydrogen from coal to be converted into dihydroanthracene and then breaking down the coal structure. Hydrogen can thus transfer from coal to anthracene to produce dihydroanthracene. The data in Table 7 show that less dihydroanthracene is formed from Wyodak coal and thus suggests that slightly more labile hydrogen is available in Ky 9/14 coal than in Wyodak coal. In essence, these tests verify that anthracene is a better hydrogenshuttling agent than phenanthrene. The conversions of Ky 9/14 coal and anthracene to hydroanthracenes are 72.4 and 17.6x, respectively, in the presence of 3.45 MPa initial hydrogen pressure, while the conversions of Ky 9114 coal and phenanthrene are 75.3 and Oy’, respectively, in the presence of 3.45 MPa initial hydrogen pressure, despite the fact that more hydrogen donor is available in the former case (Table 5). The preasphaltene-plus-asphaltene fraction is 53 and 46”/; in the presence of anthracene and phenanthrene, respectively at 3.45 MPa initial hydrogen pressure. This may indicate that either solubility of Ky 9/14 coal in phenanthrene and its derivatives is inherently better than in anthracene and its derivatives, or that dihydroanthracene (or the radical formed by loss of one hydrogen atom) may be undergoing extensive retrogressive reaction with coal or itself, producing more preasphaltene-plus-asphaltene fraction in the presence of anthracene than in the presence of phenanthrene. It may also suggest that the transfer rate of labile hydrogen from coal to anthracene is much faster than that of molecular hydrogen from the gaseous phase to liquid anthracene during the very early reaction state due to low hydrogen pressure. The product distribution of Ky 9/14 coal with anthracene approaches that obtained with phenanthrene upon increasing the initial hydrogen pressure from 3.45 to 7.58 MPa. This indicates that the role of molecular hydrogen becomes dominant in liquefying Ky 9/14 coal, as the initial hydrogen pressure increases.
750
FUEL, 1985, Vol64,
June
Effeects of solvent quality on coal conversion A series of experiments were performed in the absence of hydrogen to investigate the effectiveness of the base line solvent 1-methylnaphthalene (l-MN), a mixture of anthracene and l-MN, and a mixture of phenanthrene and lMN in liquefying Ky 9/14 coal. In the absence of the more reactive polynuclear aromatic compounds, 5 g of l-MN, neat, is introduced into a microreactor to obtain the extent of conversion in a, relatively, chemically inert but good physical solvent. Conversion of coal in the presence of l-MN is slightly higher than that in the presence of phenanthrene and lMN mixture, in terms of THF insolubles, as shown in run 46, and run 38 in Table 6. The pre-asphaltene-plusasphaltene fraction in the presence of l-MN is lower than that in the presence of either anthracene and l-MN or phenanthrene and l-MN mixture, probably because of significantly less adduction of the l-MN than the more chemically-reactive tricyclics. Another series of runs were carried out in the presence of hydrogen to evaluate the effect of solvent plus hydrogen on conversion of coal. Conversions of coal in the presence of hydrogen are almost the same for three different solvents in terms of THF solubles, as shown in run 6, run 7, and run 42 in Table6, whereas product distributions are quite different among three different solvents. These data may indicate that product distributions depend on solvent quality both in the presence and absence of hydrogen in Kentucky 9/14 coal liquefaction. High preasphaltene and low oil-water-gas fractions suggest adduct formation. A series of experiments was carried out to try to understand the effect of solvent quality on conversion of Wyodak coal in the presence of hydrogen, as shown in run 3, run 4 and run 44, Table 7. Conversion of coal in the presence of anthracene and its derivative is considerably higher than that in the presence of either phenanthrene or l-MN, where the conversion of anthracene to its hydrogen donors totals 22.2x, run 3. This indicates that formation of a good hydrogen donor solvent plays a dominant role in Wyodak coal liquefaction. Another series of runs was conducted to determine the Table 6 Effects of solvent quality on conversion of Ky 9/14 coal for 15 min at 425°C ~_.__ Run No. 46 31 38 42 6 7 Hydrogen charge at the room temperature (7.58 MPa) Nitrogen charge at the room temperature (7.58 MPa) I g Aromatics plus (Ant.) 4 g l-MN (Phen.) Coal conversion THF-soluble Preasphaltene Asohaltene Preasphalteneolus-asohaltene bil-gas-water
_
_
_
+
+
+
+ -
+ + -
+ +
-
+ -
+
39.8 7.6 16.4
42.4 11.0 18.1
37.7 13.4 14.9
84.5 21.3 31.2
83.8 26.9 33.6
84.7 27.6 30.0
23.9 15.9
29.1 13.2
28.3 9.5
52.4 32.1
60.5 23.2
51.6 27.0
NA NA
4.4 95.7
0 100
NA NA
28.4 50.7
3.8 95.3
(wt:d)
Conversion of aromatic (wt”/,) Conversion to dihydroaromatic Unconverted aromatic
Anthracene effect of solvent quality on the liquefaction of Wyodak coal in the presence of nitrogen, run 45, run 48 and run 49, Table 7. Conversion of Wyodak coal is higher in the presence of phenanthrene than anthracene in the absence of hydrogen. This may indicate that phenanthrene is a better physical solvent than anthracene in the absence of hydrogen for Wyodak coal, suggesting that it is the ease of hydrogenation of anthracene and the excellent H-donor behaviour of its hydroderivatives that makes anthracene such a good solvent in the presence of hydrogen or conditions where labile hydrogen cannot escape readily. Effects of temperature on conrersion of Kentucky 9114 coal in the presence of nitrogen A series of experiments was carried out at 7.58 MPa initial nitrogen pressure to determine effects of solvent on conversion of Ky 9114 coal at 350 and 425°C Table 8. Conversion of coal in the presence of either anthracene or phenanthrene was higher with reaction temperature, as expected. Table 7 Effects of solvent 15 min at 425°C
quality
on conversion
Run No.
45
48
Hydrogen charge at the room temperature (7.58 MPa) Nitrogen charge at the room temperature (7.58 MPa)
49
of Wyodak
coal for
44
3
4
+
+
+
+
+
+
-
-
-
1 g Aromatics plus 4g l-MN _ Anthracene Phenanthrene
+ _
+
-
+ -
+
36.1
37.1
39.5
51.2
57.7
47.9
8.0 28.2
8.6 28.5
9.1 30.4
14.1 37.1
12.6 45.1
10.6 37.3
NA NA
3.3 96.8
0 100
NA NA
16.9 77.8
0 100
Coal conversion (wt”;) THF-soluble Preasphaltene-plusasphaltene Oil-water-gas Conversion of aromatics (wt%) Conversion to Dihydroaromatics Unconverted aromatics
Table 8 Effects of reaction temperatures on conversions of Ky 9/14 coal in the presence of aromatics for 15 min at 7.58 MPa initial nitrogen pressure Run No.
40
37
41
38
1 g Aromatic plus 4 g I-MN Anthracene Phenanthrene Reaction temperature (“C)
+ -
-
-
350
+ 425
$0
4+25
Coal conversion (wty;) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
30.1 11.6 13.7 25.3 4.9
42.4 11.0 18.1 29.1 13.2
27.9 15.7 12.6 27.9 -o-
37.7 13.4 14.9 28.3 9.5
Conversion of aromatic (wt%) Conversion to dihydroaromatic Unconverted aromatic
2.6 97.4
4.4 95.6
0 100
0 100
and phenanthrene
in coal liquefaction:
K. C. Kwon
Coal conversion in the presence of anthracene is higher than in phenanthrene at both reaction temperatures. Phenanthrene is not hydrogenated at 350 or 425°C but the extent of hydrogenation of anthracene is 2.6% at 350°C and 4.4% at 425°C. The difference in coal conversion between anthracene and phenanthrene is less significant at lower reaction temperature. This suggests that less labile hydrogen is transferred from coal to anthracene at the lower temperature and the inherent solvent power of the vehicle used is important. Solvent quality untler atmospheric absence of I-methylnaphthalene
pressure
and in the
A series of experiments was carried out by reacting 1 g of coal with 10 g of tricyclic aromatic compounds such as 10 g of anthracene, 10 g of phenanthrene, 8 g of anthracene plus 2 g of dihydroanthracene, and 8 g of phenanthrene plus 2 g of dihydrophenanthrene in the absence of 1-methylnaphthalene at their boiling points under 1 atm air pressure (see Table 9). Conversion of Wyodak coal in the presence of phenanthrene is higher than in anthracene, where no hydrogenation of either anthracene or phenanthrene was observed. This shows that the solubility of Wyodak coal in phenanthrene is higher than in anthracene under 1 atm air pressure and in the absence of other solvents. Conversion of Wyodak coal in the presence of a mixture of anthracene and dihydroanthracene is higher than in the presence of a mixture of phenanthrene and dihydrophenanthrene. Dihydroanthracene is, therefore, a better hydrogen donor solvent than dihydrophenanthrene. The hydrogen donor solvent plays a more dominant role than physical solubility in the liquefaction of Wyodak coal at low pressure and in the absence of other solvents. The conversion of Ky 9/14 coal is higher in the presence of phenanthrene than in the presence of anthracene, where no hydrogenation of either phenanthrene or anthracene was observed, run 19 and 22, Table 9. On the other hand, the conversion of Ky 9/14 coal in the presence of phenanthrene is lower than in anthracene at 350°C under 13.79 MPa nitrogen pressure, run 40 and 41, Table8. This suggests that either labile hydrogen does not react with anthracene or escapes into the atmosphere before reacting with anthracene at low pressure, whereas labile hydrogen reacts with anthracene under pressure. The conversion of Ky 9/14 coal in the presence of a mixture of phenanthrene and dihydrophenanthrene is higher than in the presence of a mixture of anthracene and dihydroanthracene, and the conversion of dihydrophenanthrene is higher than that of dihydroanthracene, see run 23 and 24, Table 9. However, the effect of dihydroanthracene on the increment of coal conversion, run 19 and 23, Table 9, is higher than the effect of dihydrophenanthrene on the increment of coal conversion, run 22 and 24, Table 9. This, again, shows that dihydroanthracene is a better hydrogen donor solvent than dihydrophenanthrene. Neat anthracene is a poorer solvent than neat phenanthrene (by ~333%) for both Wyodak and Ky 9/14 coal at 330°C. But when 20% of the dihydrocompound is present, the anthracene compound mixture is a better solvent than the phenanthrene mixture. With Ky 9/14 coal, the phenanthrene is the best solvent, both neat and in the presence of the dihydrocompound. The disappearance of the dihydrocompounds is in agreement with the liquefaction of coal. In the presence of
FUEL, 1985, Vol 64, June
751
Anthracene Table 9 pressure
and phenanthrene
Effects of aromatic
compounds
in coal liquefaction:
K. C. Kwon
and their dihydroaromatic
compounds
on coal conversion
in the absence of I-methylnaphthalene
under air
Run No.
5
8
11
12
19
22
23
24
Type of coal (1 g) Wyodak Ky 9114
+
+ -
+ -
+
+
+
+
+
-
-
+
+
-
Aromatics 10 g Anthracene 10 g Phenanthrene 8 g Anthracene-plus dihydroanthracene 8 g Phenanthrene-plus dihydrophenanthrene Temperature (“C)
+ 2 g
2
g
2
g
2g
Coal conversion (wt%) THF-soluble Preasphaltene Oil-water-gas and asphaltene Conversion of dihydroaromatic
(wt%)
-
+ -
+
+
-
-
-
-
-
+
339
335
340
336
334
333
329
6.5 2.2 4.3 0
18.3 1.0 17.3 0
51.8 2.3 49.5 36.3
9.8 6.2 3.6 0
32.6 7.2 25.4 0
37.3 19.4 17.9 14.8
45.8 15.8 30.0 26.0
21.6 1.4 20.2 18.9 -___
Table 10 Effects of neat aromatic absence of 1-methylnaphthalenefor pressure and 425°C Run No.
compounds on coal conversion in the 15 min at 7.58 MPa initial nitrogen
50
51
Type of coal (1 g) Wyodak Ky 9J14
+
+
5 g Aromatics Anthracene Phenanthrene
+
_
Coal conversion (wt%) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas Conversion of aromatic (wt%) Conversion to dihydroaromatic Unconverted aromatic
32.4
10.8 8.8 19.6 12.8 0 100
-
52
+ -
+
+ _
+
51.3 11.1 14.0 25.1 26.1
33.1 10.8 6.7 17.5 15.7 2.7 97.3
42.6 0.5 14. I 14.5 28.1
Effects of neat aromatic compounds and inert gas on coal conversion A series of runs were performed in the presence of both 5 g of neat aromatic compound and 7.58 MPa initial nitrogen pressure and in the absence of l-MN for the reaction time of 15 min at 425°C see Table 10. The conversions of Ky 9/14 and Wyodak coal are 32% and 33% in the presence of anthracene and 51% and 43% in the presence of phenanthrene, respectively. These data show that neat phenanthrene is a better physical solvent than neat anthracene in liquefying both coals in the absence of hydrogen and emphasize the importance of l-MN which appears to improve the behaviour of anthracene as a hydrogen shuttling agent. Another series of runs, with Ky 9/14 coal, was carried out in the absence of hydrogen but under nitrogen pressure, see Table 1 I. The conversions of Ky 9/14 coal are 42% in terms of the THF-soluble fraction and 29% in terms of the preasphaltene-plus-asphaltene fraction at 7.58 MPa initial nitrogen pressure, whereas the con-
FUEL, 1985, Vol64,
June
on conversions
of Ky 9/14
Run No.
37
38
47
Nitrogen charge at the room temperature (MPa)
7.58
7.58
0.08
I g Aromatic plus 4 g l-MN Anthracene Phenanthrene
+ _
+
+ _
Coal conversion (wt%) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
42.4 11.0 18.1 29.1 13.2
37.7 13.4 14.9 28.3 9.5
39.5 10.0 13.9 23.9 15.6
Conversions of aromatics (wt%) Conversion to dihydroaromatics Unconverted aromatics
4.4 95.6
100
0
4.5 95.5
0 100
Wyodak coal, dihydroanthracene is lost most rapidly, whereas in the presence of Ky 9/14 coal, the dihydrophenanthrene is lost most rapidly.
752
pressures
53
+ -
0 100
Table 11 Effects of initial nitrogen coal for 15 min at 425°C
versions of Ky 9/14 coal are 39% and 24% respectively at 0.08 MPa initial nitrogen pressure. The similarity of the values for dihydroanthracene formed suggests that the conversion of coal and the product distribution would also be similar. The only firm conclusions are that pressure helps total liquefaction and anthracene is a better solvent than phenanthrene in the presence of excess lMN. CONCLUSIONS The relative behaviour of phenanthrene and anthracene in the liquefaction of coal depends on the coal, on the gaseous environment and on whether the solvents are compared neat or in the presence of other solvents. When anthracene is the better solvent, conditions appear to favour the formation of dihydroanthracene which is an excellent hydrogen donor. When phenanthrene is the better solvent, the inherently better solvent power of phenanthrene itself for the coal appears to be the dominant factor. The minerals in the coal, and possibly the coal itself, are also important in determining the preferred solvent. Anthracene is a better solvent than phenanthrene in the presence of 1-methylnaphthalene in Wyodak coal liquefaction under hydrogen pressure, whereas phenanth-
Anthracene
rene is a better solvent than anthracene for the other liquefaction conditions of Wyodak coal. Anthracene is a better solvent than phenanthrene in the presence of lmethylnaphthalene in Ky 9/14 coal liquefaction under nitrogen pressure. On the other hand, neat phenanthrene is about three times better than neat anthracene in Ky 9/14 coal liquefaction under air, but neat phenanthrene is about twice as effective as neat anthracene in the liquefaction of Ky 9/14 coal under nitrogen pressure. The minerals in Ky 9/14 coal appear to be better hydrogenation catalysts than those in Wyodak coal. Labile hydrogen from coal escapes readily before reacting with hydrogen shuttling solvents under the atmospheric environment. ACKNOWLEDGEMENTS The author gratefully acknowledges Dr Herbert R. Appell for his guidance and suggestions during this research work at the Pittsburgh Energy Technology Center. The author also acknowledges the US Department of Energy and The Oak Ridge Associated Universities for support of this research through The Summer Faculty Research Participation Program. REFERENCES 1
Neavel,
R. C. Phil. Trans. Roy. Sot., Land. 1981, A300, 141
and phenanthrene 2 3
4
5
6
7 8 9 10
11 12 13 14 15 16
in coal liquefaction:
K. C. Kwon
Vernon, L. W. Fuel 1980,59, 102 Appell, H. R. ‘The Effect of Solvent Composition on Product Distribution’, Pittsburgh Energy Technology Center, unpublished report Padrick, T. D., Lynch, A. W. and Stephens, H. P. ‘Effect of Solvent on the Dissolution of Wyodak Coal’, ‘Proceedings of the Department of Energy Integrated Two-Stage Liquefaction Meetings’, Albuquerque, New Mexico, USA, October 1982, pp. 6-2 Derbyshire, F. J. and Whitehurst, D. D. ‘The Influence of Polyaromatic Solvent Components on Coal Liquefaction’, ‘Proceedings on the Fifth Annual EPRI Contractor’s Conference on Coal Liquefaction’, USA, 1980, pp. 9-l Utz, B. R., Appell, H. R. and Blaustein, B. D. ‘Vehicle Studies in Short Contact Time Liquefaction’, ‘Proceedings of the Department of Energy Integrated Two-Stage Liquefaction Meetings’, Albuquerque, New Mexico, USA, October 1982, pp. 7-l Guin, J. A., Curtis,C. W. and Kwon, K. C. Fuel 1983,62, 1412 Rottendorf, H. and Wilson, M. A. Fuel 1980,59, 175 Mochida, I., Takarabe, A. and Takeshita, K. Fuel 1979, 58, 17 Curtis, C. W., Guin, J. A. and Kwon, K. C. ‘Coal and Solvolysis in a Series of Model Compound System’, AIChE Annual Meeting, November 1982, Los Angeles Garg, D. and Givens, E. N. lnd. Eng. Chem. Process. Des. Dev. 1982,21, 113 Curtis, C. W., Guin, J. A., Kwon, K. C. and Smith, N. L. Fuel 1983,62, 1341 Jackson, W. R., Larkins, F. P., Marshall, M., Rash, D. and White, N. Fuel 1979,58, 281 Gangwar, T. E. and Prasad, H. Fuel 1979,58, 577 Lytle, J. M., Wood, R. E. and Wiser, W. H. Fuel 1980, 59, 471 Utz, B. R., Narain, N. K., Appell, H. R. and Blaustein, B. D. ‘Solvent Analysis of Coal Derived Products, Using Pressure Filtration’, Am. Chem. Sot. Symp. Ser. Washington, DC., 1982
FUEL,
1985,
Vol64,
June
753
and phenanthrene
C. Kwon
Chemical Engineering Department, School of Engineering institute, AL 36088, USA (Received 27 January 7984; revised 30 May 7984)
and Architecture,
Tuskegee
A comparison of anthracene and phenanthrene as solvents was undertaken by liquefying either Wyodak or Kentucky 9/14 coal in the presence of hydrogen or nitrogen. Phenanthrene was found to be a better physical solvent than anthracene for liquefying both coals. Anthracene and its derivatives are better hydrogenshuttling solvents than phenanthrene and its derivatives. Hydrogenation of anthracene to tetrahydroanthracene was observed with both coals. Dihydroanthracene is a better hydrogen-shuttling solvent than dihydrophenanthrane in the liquefaction of Kentucky 9/14 coal. Anthracene is a better solvent than phenanthrene in the presence of l-methylnaphthalene in liquefying both Wyodak coal under hydrogen and Kentucky 9/14 coal under nitrogen. The minerals in Kentucky 9/14 coal appear to be better hydrogenation catalysts than those in Wyodak coal. Labile hydrogen from coal appears to escape readily before reacting with hydrogen-shuttling solvents under the atmospheric environment. (Keywords: coal; liquefacaction;anthracene; phenanthrene)
Solid coal is dissolved with the aid of molecular hydrogen, donative hydrogen from hydroaromatic compounds, labile hydrogen from coal itself and physical solvents in the coal liquefaction process. Solid minerals or commercial catalysts may assist in coal dissolution. Various experiments have been carried out to try to understand the interactions between: coal and donative hydrogen from hydroaromatic compounds; coal and molecular hydrogen; and coal and the solvent. The effects of solvent quality and transfer of labile hydrogen from coal to aromatic compounds have also been investigated. BACKGROUND Neavel’ and Vernon’ found that molecular hydrogen stabilizes free radicals and rehydrogenates the hydrogen donor solvent, and also initiates a hydrocracking reaction during coal liquefaction. High pressure hydrogen can increase the hydrocracking of some carbon-carbon bonds in the coal structure. However, hydrogen may also assist in ring opening of hydroaromatic molecules and accelerate the dealkylation of alkyl aromatic compounds. These two reactions are undesirable in the coal liquefaction process as the former causes donor solvent degradation and the latter leads to high gas yields and high hydrogen consumption. Appel13 investigated the effect of solvent composition on product distribution in coal liquefaction, using Wyodak coal and Kentucky 9/14 high volatile bituminous coal, and solvents such as SRC-11 heavy distillate and lmethylnaphthalene. Padrick and co-workers4 studied the dffect on the dissolution of Wyodak coal, using solvents such as quinoline, tetrahydroquinoline and hydrogenated creosote oil. Their results indicated a strong dependence on a hydrogen donor solvent for conversion of Wyodak aoal. Derbyshire and Whitehurst’ discussed the disso-
lution of coals principal model
in polyaromatics using pyrenes compound. Utz et aL6 attempted
as the
to rank a series of hydrogen donor solvents using the short contact time liquefaction (SCTL) process and to determine the effect of molecular hydrogen on the SCTL process. Guin and co-workers’ suggested that some hydrogen, either molecular or donor, must be present to prevent retrogressive reactions of coal fragments during the early reaction stage. Direct hydrogenation of the coal using molecular hydrogen at high reaction temperatures is an important mechanism of liquefaction. Rottendorfand Wilson’ reported that the major role of the nickel-molybdenum catalyst during coal liquefaction is to rehydrogenate the donor vehicle after its dehydrogenation by coal. Mochida et aL9 examined the solvolytic liquefaction of various coals with a variety of solvents at 370-390°C under nitrogen to elucidate the role of solvents in coal liquefaction and to find the solvents which gave the highest liquefaction yields. Pyrene and solvent refined coal (SRC) were shown to be excellent solvents. Curtis and co-workers” ranked various hydroaromatic compounds according to their ability to convert coal into THF solubles, using Western Kentucky No. 9/14 coal. Several investigators used indigeneous coal minerals as catalysts in coal liquefaction. Garg and Givens” mentioned that both coal conversion and oil yield increased on addition of pyrite to the feed slurry, using Elkhom No. 3 and Kentucky No. 9 coals. Curtis and co-workers” used various indigeneous coal minerals, such as pyrite, kaolinite, montmorillonite, alumina oxide, titanium oxide and silicon dioxide in the hydrogenation of cyclohexene. Jackson’ 3 showed that the addition of iron as haematite led to an increase in coal conversion. Gangwar14 used minerals such as pyrites, limonites, diapore and magnetites as hydrogenation catalysts in coal liquefaction and
0016-2361/85/060747~07$3.00
80 1985 Butterworth & Co. (Publishers) Ltd.
FUEL,
1985,
Vol 64, June
747
Anthracene
and phenanthrene
in coal liquefaction:
K. C. Kwon
found that the catalytic activities of these minerals are reduced upon annealing them. Lytle” used metal chlorides such as SnCl,, ZnCl,, and FeCl, as catalysts in short residence time coal liquefaction. EXPERIMENTAL Materials The coals used were: Wyodak coal, 11.9 wt% ash and particle size - 100 mesh (0.147 mm); and Kentucky 9/14 coal, 10.1 wt% ash and particle size -200 mesh (0.074 mm), see Table I. The coals were dried in a vacuum oven and stored in a desiccator. Anthracene and phenanthrene were used as the aromatic compounds; 9,10-dihydroanthracene and dihydrophenanthrene were used as the hydroaromatic compounds; and 1-methylnaphthalene (1 -MN) was used as a physical solvent (although a small amount of interaction is known to occur), Nitrogen was used in the reaction systems when hydrogen was absent. l-Methylnaphthalene only was used in those runs where tricyclic aromatics were absent. Procedure A series of reactions, to liquefy either Wyodak coal or Kentucky 9/14 coal under the various operating conditions, were conducted in a 25 cm3, 316 stainless steel microreactor, see Table 2. Another series of reactions were performed in a 50cm3 flask at atmospheric pressure to each coal with either neat aromatic compounds such as anthracene and phenanthrene, or mixtures of aromatics and their dihydroaromatics. The microreactor consisted of a 316 stainless steel swagelock tee, a pressure transducer, a thermocouple and a quick-connect valve to introduce either hydrogen or nitrogen into the microreactor. This microreactor with the desired reactants is attached to a mechanical wristaction shaker, which swings in a 16” arc, and is then submerged in a fluidized sandbath. Following a reaction, the reactor is quenched in water and the gas products are released. The liquid and solid reaction products are removed completely from the reactor by dissolving with tetrahydrofuran (THF). The Table 1
Typical
analysis
of Kentucky
9/14 and Wyodak
Ky 9/14
Wyodak
Type of coal
wt%
wt%
Ultimate analysis Carbon Hydrogen Nitrogen Sulphur Ash Oxygen (by diff.)
71.5 4.8 1.5 3.3 10.1 8.8
65.2 4.8 1.0 1.2 11.9 15.9
coals
__--
Table 2
Reaction
conditions
Reaction temperature: Reaction duration: Reactor charge Hydrogen: Coal: Aromatic compound: Solvent :
748
for a microreactor
operation
350°C or 425°C 540 min 3.45 MPa hydrogen or 7.58 MPa hydrogen at the room temperature 1 g of Wyodak coal or 1 g of Ky 9/14 coal 1 g of anthracene or 1 g of phenanthrene 4 g of I-methylnaphthalene
FUEL, 1985, Vol 64, June
Table 3 Reaction conditions for the liquefaction of coal in the presence of aromatic compounds and in the absence of I-methylnaphthalene under 1 atm air pressure Reaction temperatures: Pressure: Reaction duration: Reactor charge Coal: Aromatic compound:
329”C34O”C 1 atm air 60 min 1 g of Wyodak coal or 1 g of Ky 9/14 coal 10 g of anthracene, or 10 g of phenanthrene, or 8 g of anthracene plus 2 g of 9.10-didydroanthracene, or 8 g of phenanthrene plus 2 g of dihydrophenanthrene
reaction product is separated into a THF-soluble fraction, an ethyl-acetate-insoluble fraction and a and cyclohexane-insoluble fraction to obtain the following product distribution: preasphaltenes, asphaltenes, and oil plus water plus gas. The THF solubles are filtered, using a pressure filtration procedure” and the THF-insoluble fraction is calculated from the amount of vacuum oven dried filter cake and the filtrate containing THF is introduced into a rotary evaporator to remove THF. The THF-free extract is added to excess ethyl acetate to precipitate the preasphaltenes which are isolated by pressure filtration. The filtrate is processed in the rotary evaporator to remove ethyl acetate. This filtrate is mixed with an excess of cyclohexane, so that the asphaltenes are precipitated. The cyclohexaneinsoluble or asphaltene fraction is obtained from the amount of the dry filter cake. The filtrate is introduced into the rotary evaporator to remove cycle-hexane. This filtrate, free of THF, ethyl acetate and cyclohexane, and containing the oil-plus-water fraction, aromatics and their hydroaromatic derivatives, is diluted with THF. The oil-plus-water fraction is calculated by substracting the preasphaltene and asphaltene fraction from the THFsoluble fraction. The THF-diluted oil fraction is injected into a gas chromatograph equipped with a flame ionization detector and a 0.318 cm (6 in) dia., 182.9 cm (6 ft) long lo”/,-SP2100-packed column, to analyse conversions of aromatics into their hydroaromatics. Coal conversions are calculated on a dry, ash-free basis. DISCUSSION Effect of elapsed reaction time on coal dissolution A series of experiments were conducted in the presence of either anthracene or phenanthrene by increasing reaction duration from 5 to 60 min at 425°C see Table 3. A 25 cm3 microreactor was loaded with 1 g of either Wyodak or Kentucky 9/14 coal; 1 g of either anthracene or phenanthrene, 4 g of 1-methylnaphthalene and 7.58 MI% hydrogen (initial pressure). Conversions of both coals into a THF-soluble fraction increase in the presence of either anthracene or phenanthrene, as reaction duration increases. Wyodak coal appears to be less reactive than Kentucky 9/14 coal in terms of THF solubles, see Table 4. However, Wyodak coal yields a larger oil-water-gas fraction, and a smaller preasphalteneplus-asphaltene fraction than does Kentucky 9/14 coal. Both anthracene and phenanthrene have a higher conversion to their hydro derivatives in the presence of Ky 9/14 coal than in the presence of Wyodak coal. This suggests that minerals in Ky 9/14 coal have a stronger
Anthracene catalytic effect than minerals in Wyodak coal on hydrogenating aromatics such as anthracene and phenanthrene in the presence of molecular hydrogen. Wyodak coal yields a higher oil-water-gas fraction in the presence of anthracene than in the presence of phenanthrene. It does, however, produce the same amount of preasphaltenes-plus-asphaltenes in the presence of either anthracene or phenanthrene. Therefore, anthracene and its derivatives are in some respects better solvents than phenanthrene and its derivatives in the liquefaction of Wyodak coal. Conversion of Ky 9/14 coal into THF-solubles is almost the same in the presence of either anthracene or phenanthrene, whereas its conversion into preasphaltenes-plus-asphaltenes is a little higher in the presence of anthracene and its derivatives than in the presence of phenanthrene and its derivatives. For Ky 9/14 Table 4
Effects of reaction
durations
on coal conversion
and phenanthrene
in coal liquefaction:
K. C. Kwon
coal liquefaction the preasphaltene-plus-asphaltene fraction is much larger than the oil-water-gas fraction but the reverse is true for Wyodak coal. These data show that both the coal and the solvent have an effect on the product distribution. Efft(cts of initial hydrogen pressure on coal conversion The conversion of both Wyodak and Ky 9/14 coal increases as the initial hydrogen pressure increases in the presence of both anthracene and phenanthrene, as shown in Table.5. I-Methylnaphthalene,a relatively inert solvent, is present in excess in these and most of the following experiments. The conversion of Ky 9/14 coal is influenced more by hydrogen pressure than that of Wyodak coal in the presence of either solvent. This suggests that molecular hydrogen may play a more dominant role than solvent
at 7.58 MPa initial hydrogen
pressure
and 425°C
_
Run No.
13
3
14
15
4
16
17
6
18
20
7
21
I g Aromatics plus 4 g I-MN Anthracene Phenanthrene
+ -
+ -
+ _
+
_
-
+
+
+ -
+ _
-
+
+
_ +
+ -
+ _
+ -
+ _
+ _
+ -
_ +
_ +
-
+
-
+
5
15
60
5
15
60
5
15
60
:
15
6’0
45.5
57.7
79.1
44.3 _
47.9
76.8 _
75.4 28.6 26.1
83.8 26.9 33.6
88.9 21.7 24.8
76.6 29.5 25.6
84.7 27.6 30.0
88.5 19.7 26.9
Type of coal Wyodak Ky 9114 Reaction duration Coal conversion THF-soluble Preasphaltene Asphaltene Preasphalteneplus-asphaltene Oil-water-gas
(min) (wt”;)
Conversion of aromatics Conversion to dihydroaromatic Unconverted aromatics Conversion to tetrahydroaromatic
Table 5
+
12.6 45. I
26.6 52.6
12.4 31.9
10.6 31.3
26.8 50.1
54.1 20.7
60.5 23.2
46.5 42.4
55.1 21.6
57.6 27.0
46.6 41.9
7.0 93.0
16.9 77.2
20.7 52.3
0 100
0 100
1.8 98.2
22.6 72.3
28.4 50.7
22.3 26.5
1.6 98.4
3.8 95.3
10.5 87.8
5.9
27.0
0
0
5.0
21.0
51.1
0
0
0
pressure
Run No. Hydrogen charge at room temperature (MPa)
on coal conversions
Coal conversion (wt:‘,) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
0
-
0
_
for 15 min at 425°C 6
38
10
7
3.45
7.58
0
3.45
7.58
+ -
+ _
+ _
_ +
+
+
+ -
+
_ +
+
+
_ +
+
47.9
42.4 11.0 18.1 29.1 13.2
72.4 26.3 26.5 52.7 19.7
83.8 26.9 33.6 60.5 23.2
37.7 13.4 14.9 28.3 9.5
75.3 21.0 25.1 46.2 29.1
84.7 27.6 30.0 57.6 27.0
4.4 95.6
17.6 71.7
28.4 50.7
0 100
0 100
3.8 95.3
45 -
1
3
2
4
37
0
3.45
7.58
3.45
7.58
0
-
+ -
+ -
+
+
+
+ -
+ -
+ -
36.1
44.3 _
57.7 _
8.0 28.2
14.0 30.3
12.6 45.1
40.3 _ _ 11.6 28.7
NA NA
6.4 93.6
16.9 77.2
0
0
100
100
1-MN
Type of coal Wyodak Ky 9114
Conversion of aromatics Conversion to dihydroaromatics Unconverted aromatic
11.9 33.6 (wt%)
Effects of hydrogen
1 g Aromatics plus 4 g Anthracene Phenanthrene
_
_ _
_ 10.6 37.3
(wt%)
-
FUEL, 1985, Vol 64, June
749
Anthracene
and phenanthrene
in coal liquefaction:
K. C. Kwon
structure in the liquefaction of Ky 9/14 coal or that the minerals in Ky 9/14 coal are actively hydrogenating the aromatic solvent. Analysis of the oil fraction suggests the latter. The conversion of anthracene to dihydroanthracene increases as the initial hydrogen pressure increases. With anthracene, the conversion of Wyodak coal increases from 44 to 58% and the hydrogenation of anthracene increases from 6 to 17% by increasing the initial hydrogen pressure from 3.45 to 7.58 MPa. Hydrogenation of phenanthrene is not observed although the conversion of Wyodak coal increases from 40 to 48% upon increasing the hydrogen pressure. With Ky 9/14 coal, hydrogenation of phenanthrene is not observed at 3.45 MPa initial hydrogen pressure but does occur at 7.48 MPa initial hydrogen pressure. Coal solubilization, however, increases sharply with pressure. These observations show that anthracene is more readily hydrogenated than phenanthrene and may be a better hydrogen shuttler or donor precursor than phenanthrene in the liquefaction of some coals. The conversion of Ky 9/14 coal is 42.4% and the hydrogenation of anthracene is 4.4% under nitrogen pressure, in the absence of hydrogen (Table 6). When the anrhracene is replaced by phenanthrene, the conversion of Ky 9/14 coal decreases to 38% and no hydrogenation of phenanthrene is observed. This shows that anthracene is more active than phenanthrene in the liquefaction of Ky 9/14 coal in the absence of hydrogen, by extracting hydrogen from coal to be converted into dihydroanthracene and then breaking down the coal structure. Hydrogen can thus transfer from coal to anthracene to produce dihydroanthracene. The data in Table 7 show that less dihydroanthracene is formed from Wyodak coal and thus suggests that slightly more labile hydrogen is available in Ky 9/14 coal than in Wyodak coal. In essence, these tests verify that anthracene is a better hydrogenshuttling agent than phenanthrene. The conversions of Ky 9/14 coal and anthracene to hydroanthracenes are 72.4 and 17.6x, respectively, in the presence of 3.45 MPa initial hydrogen pressure, while the conversions of Ky 9114 coal and phenanthrene are 75.3 and Oy’, respectively, in the presence of 3.45 MPa initial hydrogen pressure, despite the fact that more hydrogen donor is available in the former case (Table 5). The preasphaltene-plus-asphaltene fraction is 53 and 46”/; in the presence of anthracene and phenanthrene, respectively at 3.45 MPa initial hydrogen pressure. This may indicate that either solubility of Ky 9/14 coal in phenanthrene and its derivatives is inherently better than in anthracene and its derivatives, or that dihydroanthracene (or the radical formed by loss of one hydrogen atom) may be undergoing extensive retrogressive reaction with coal or itself, producing more preasphaltene-plus-asphaltene fraction in the presence of anthracene than in the presence of phenanthrene. It may also suggest that the transfer rate of labile hydrogen from coal to anthracene is much faster than that of molecular hydrogen from the gaseous phase to liquid anthracene during the very early reaction state due to low hydrogen pressure. The product distribution of Ky 9/14 coal with anthracene approaches that obtained with phenanthrene upon increasing the initial hydrogen pressure from 3.45 to 7.58 MPa. This indicates that the role of molecular hydrogen becomes dominant in liquefying Ky 9/14 coal, as the initial hydrogen pressure increases.
750
FUEL, 1985, Vol64,
June
Effeects of solvent quality on coal conversion A series of experiments were performed in the absence of hydrogen to investigate the effectiveness of the base line solvent 1-methylnaphthalene (l-MN), a mixture of anthracene and l-MN, and a mixture of phenanthrene and lMN in liquefying Ky 9/14 coal. In the absence of the more reactive polynuclear aromatic compounds, 5 g of l-MN, neat, is introduced into a microreactor to obtain the extent of conversion in a, relatively, chemically inert but good physical solvent. Conversion of coal in the presence of l-MN is slightly higher than that in the presence of phenanthrene and lMN mixture, in terms of THF insolubles, as shown in run 46, and run 38 in Table 6. The pre-asphaltene-plusasphaltene fraction in the presence of l-MN is lower than that in the presence of either anthracene and l-MN or phenanthrene and l-MN mixture, probably because of significantly less adduction of the l-MN than the more chemically-reactive tricyclics. Another series of runs were carried out in the presence of hydrogen to evaluate the effect of solvent plus hydrogen on conversion of coal. Conversions of coal in the presence of hydrogen are almost the same for three different solvents in terms of THF solubles, as shown in run 6, run 7, and run 42 in Table6, whereas product distributions are quite different among three different solvents. These data may indicate that product distributions depend on solvent quality both in the presence and absence of hydrogen in Kentucky 9/14 coal liquefaction. High preasphaltene and low oil-water-gas fractions suggest adduct formation. A series of experiments was carried out to try to understand the effect of solvent quality on conversion of Wyodak coal in the presence of hydrogen, as shown in run 3, run 4 and run 44, Table 7. Conversion of coal in the presence of anthracene and its derivative is considerably higher than that in the presence of either phenanthrene or l-MN, where the conversion of anthracene to its hydrogen donors totals 22.2x, run 3. This indicates that formation of a good hydrogen donor solvent plays a dominant role in Wyodak coal liquefaction. Another series of runs was conducted to determine the Table 6 Effects of solvent quality on conversion of Ky 9/14 coal for 15 min at 425°C ~_.__ Run No. 46 31 38 42 6 7 Hydrogen charge at the room temperature (7.58 MPa) Nitrogen charge at the room temperature (7.58 MPa) I g Aromatics plus (Ant.) 4 g l-MN (Phen.) Coal conversion THF-soluble Preasphaltene Asohaltene Preasphalteneolus-asohaltene bil-gas-water
_
_
_
+
+
+
+ -
+ + -
+ +
-
+ -
+
39.8 7.6 16.4
42.4 11.0 18.1
37.7 13.4 14.9
84.5 21.3 31.2
83.8 26.9 33.6
84.7 27.6 30.0
23.9 15.9
29.1 13.2
28.3 9.5
52.4 32.1
60.5 23.2
51.6 27.0
NA NA
4.4 95.7
0 100
NA NA
28.4 50.7
3.8 95.3
(wt:d)
Conversion of aromatic (wt”/,) Conversion to dihydroaromatic Unconverted aromatic
Anthracene effect of solvent quality on the liquefaction of Wyodak coal in the presence of nitrogen, run 45, run 48 and run 49, Table 7. Conversion of Wyodak coal is higher in the presence of phenanthrene than anthracene in the absence of hydrogen. This may indicate that phenanthrene is a better physical solvent than anthracene in the absence of hydrogen for Wyodak coal, suggesting that it is the ease of hydrogenation of anthracene and the excellent H-donor behaviour of its hydroderivatives that makes anthracene such a good solvent in the presence of hydrogen or conditions where labile hydrogen cannot escape readily. Effects of temperature on conrersion of Kentucky 9114 coal in the presence of nitrogen A series of experiments was carried out at 7.58 MPa initial nitrogen pressure to determine effects of solvent on conversion of Ky 9114 coal at 350 and 425°C Table 8. Conversion of coal in the presence of either anthracene or phenanthrene was higher with reaction temperature, as expected. Table 7 Effects of solvent 15 min at 425°C
quality
on conversion
Run No.
45
48
Hydrogen charge at the room temperature (7.58 MPa) Nitrogen charge at the room temperature (7.58 MPa)
49
of Wyodak
coal for
44
3
4
+
+
+
+
+
+
-
-
-
1 g Aromatics plus 4g l-MN _ Anthracene Phenanthrene
+ _
+
-
+ -
+
36.1
37.1
39.5
51.2
57.7
47.9
8.0 28.2
8.6 28.5
9.1 30.4
14.1 37.1
12.6 45.1
10.6 37.3
NA NA
3.3 96.8
0 100
NA NA
16.9 77.8
0 100
Coal conversion (wt”;) THF-soluble Preasphaltene-plusasphaltene Oil-water-gas Conversion of aromatics (wt%) Conversion to Dihydroaromatics Unconverted aromatics
Table 8 Effects of reaction temperatures on conversions of Ky 9/14 coal in the presence of aromatics for 15 min at 7.58 MPa initial nitrogen pressure Run No.
40
37
41
38
1 g Aromatic plus 4 g I-MN Anthracene Phenanthrene Reaction temperature (“C)
+ -
-
-
350
+ 425
$0
4+25
Coal conversion (wty;) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
30.1 11.6 13.7 25.3 4.9
42.4 11.0 18.1 29.1 13.2
27.9 15.7 12.6 27.9 -o-
37.7 13.4 14.9 28.3 9.5
Conversion of aromatic (wt%) Conversion to dihydroaromatic Unconverted aromatic
2.6 97.4
4.4 95.6
0 100
0 100
and phenanthrene
in coal liquefaction:
K. C. Kwon
Coal conversion in the presence of anthracene is higher than in phenanthrene at both reaction temperatures. Phenanthrene is not hydrogenated at 350 or 425°C but the extent of hydrogenation of anthracene is 2.6% at 350°C and 4.4% at 425°C. The difference in coal conversion between anthracene and phenanthrene is less significant at lower reaction temperature. This suggests that less labile hydrogen is transferred from coal to anthracene at the lower temperature and the inherent solvent power of the vehicle used is important. Solvent quality untler atmospheric absence of I-methylnaphthalene
pressure
and in the
A series of experiments was carried out by reacting 1 g of coal with 10 g of tricyclic aromatic compounds such as 10 g of anthracene, 10 g of phenanthrene, 8 g of anthracene plus 2 g of dihydroanthracene, and 8 g of phenanthrene plus 2 g of dihydrophenanthrene in the absence of 1-methylnaphthalene at their boiling points under 1 atm air pressure (see Table 9). Conversion of Wyodak coal in the presence of phenanthrene is higher than in anthracene, where no hydrogenation of either anthracene or phenanthrene was observed. This shows that the solubility of Wyodak coal in phenanthrene is higher than in anthracene under 1 atm air pressure and in the absence of other solvents. Conversion of Wyodak coal in the presence of a mixture of anthracene and dihydroanthracene is higher than in the presence of a mixture of phenanthrene and dihydrophenanthrene. Dihydroanthracene is, therefore, a better hydrogen donor solvent than dihydrophenanthrene. The hydrogen donor solvent plays a more dominant role than physical solubility in the liquefaction of Wyodak coal at low pressure and in the absence of other solvents. The conversion of Ky 9/14 coal is higher in the presence of phenanthrene than in the presence of anthracene, where no hydrogenation of either phenanthrene or anthracene was observed, run 19 and 22, Table 9. On the other hand, the conversion of Ky 9/14 coal in the presence of phenanthrene is lower than in anthracene at 350°C under 13.79 MPa nitrogen pressure, run 40 and 41, Table8. This suggests that either labile hydrogen does not react with anthracene or escapes into the atmosphere before reacting with anthracene at low pressure, whereas labile hydrogen reacts with anthracene under pressure. The conversion of Ky 9/14 coal in the presence of a mixture of phenanthrene and dihydrophenanthrene is higher than in the presence of a mixture of anthracene and dihydroanthracene, and the conversion of dihydrophenanthrene is higher than that of dihydroanthracene, see run 23 and 24, Table 9. However, the effect of dihydroanthracene on the increment of coal conversion, run 19 and 23, Table 9, is higher than the effect of dihydrophenanthrene on the increment of coal conversion, run 22 and 24, Table 9. This, again, shows that dihydroanthracene is a better hydrogen donor solvent than dihydrophenanthrene. Neat anthracene is a poorer solvent than neat phenanthrene (by ~333%) for both Wyodak and Ky 9/14 coal at 330°C. But when 20% of the dihydrocompound is present, the anthracene compound mixture is a better solvent than the phenanthrene mixture. With Ky 9/14 coal, the phenanthrene is the best solvent, both neat and in the presence of the dihydrocompound. The disappearance of the dihydrocompounds is in agreement with the liquefaction of coal. In the presence of
FUEL, 1985, Vol 64, June
751
Anthracene Table 9 pressure
and phenanthrene
Effects of aromatic
compounds
in coal liquefaction:
K. C. Kwon
and their dihydroaromatic
compounds
on coal conversion
in the absence of I-methylnaphthalene
under air
Run No.
5
8
11
12
19
22
23
24
Type of coal (1 g) Wyodak Ky 9114
+
+ -
+ -
+
+
+
+
+
-
-
+
+
-
Aromatics 10 g Anthracene 10 g Phenanthrene 8 g Anthracene-plus dihydroanthracene 8 g Phenanthrene-plus dihydrophenanthrene Temperature (“C)
+ 2 g
2
g
2
g
2g
Coal conversion (wt%) THF-soluble Preasphaltene Oil-water-gas and asphaltene Conversion of dihydroaromatic
(wt%)
-
+ -
+
+
-
-
-
-
-
+
339
335
340
336
334
333
329
6.5 2.2 4.3 0
18.3 1.0 17.3 0
51.8 2.3 49.5 36.3
9.8 6.2 3.6 0
32.6 7.2 25.4 0
37.3 19.4 17.9 14.8
45.8 15.8 30.0 26.0
21.6 1.4 20.2 18.9 -___
Table 10 Effects of neat aromatic absence of 1-methylnaphthalenefor pressure and 425°C Run No.
compounds on coal conversion in the 15 min at 7.58 MPa initial nitrogen
50
51
Type of coal (1 g) Wyodak Ky 9J14
+
+
5 g Aromatics Anthracene Phenanthrene
+
_
Coal conversion (wt%) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas Conversion of aromatic (wt%) Conversion to dihydroaromatic Unconverted aromatic
32.4
10.8 8.8 19.6 12.8 0 100
-
52
+ -
+
+ _
+
51.3 11.1 14.0 25.1 26.1
33.1 10.8 6.7 17.5 15.7 2.7 97.3
42.6 0.5 14. I 14.5 28.1
Effects of neat aromatic compounds and inert gas on coal conversion A series of runs were performed in the presence of both 5 g of neat aromatic compound and 7.58 MPa initial nitrogen pressure and in the absence of l-MN for the reaction time of 15 min at 425°C see Table 10. The conversions of Ky 9/14 and Wyodak coal are 32% and 33% in the presence of anthracene and 51% and 43% in the presence of phenanthrene, respectively. These data show that neat phenanthrene is a better physical solvent than neat anthracene in liquefying both coals in the absence of hydrogen and emphasize the importance of l-MN which appears to improve the behaviour of anthracene as a hydrogen shuttling agent. Another series of runs, with Ky 9/14 coal, was carried out in the absence of hydrogen but under nitrogen pressure, see Table 1 I. The conversions of Ky 9/14 coal are 42% in terms of the THF-soluble fraction and 29% in terms of the preasphaltene-plus-asphaltene fraction at 7.58 MPa initial nitrogen pressure, whereas the con-
FUEL, 1985, Vol64,
June
on conversions
of Ky 9/14
Run No.
37
38
47
Nitrogen charge at the room temperature (MPa)
7.58
7.58
0.08
I g Aromatic plus 4 g l-MN Anthracene Phenanthrene
+ _
+
+ _
Coal conversion (wt%) THF-soluble Preasphaltene Asphaltene Preasphaltene-plus-asphaltene Oil-water-gas
42.4 11.0 18.1 29.1 13.2
37.7 13.4 14.9 28.3 9.5
39.5 10.0 13.9 23.9 15.6
Conversions of aromatics (wt%) Conversion to dihydroaromatics Unconverted aromatics
4.4 95.6
100
0
4.5 95.5
0 100
Wyodak coal, dihydroanthracene is lost most rapidly, whereas in the presence of Ky 9/14 coal, the dihydrophenanthrene is lost most rapidly.
752
pressures
53
+ -
0 100
Table 11 Effects of initial nitrogen coal for 15 min at 425°C
versions of Ky 9/14 coal are 39% and 24% respectively at 0.08 MPa initial nitrogen pressure. The similarity of the values for dihydroanthracene formed suggests that the conversion of coal and the product distribution would also be similar. The only firm conclusions are that pressure helps total liquefaction and anthracene is a better solvent than phenanthrene in the presence of excess lMN. CONCLUSIONS The relative behaviour of phenanthrene and anthracene in the liquefaction of coal depends on the coal, on the gaseous environment and on whether the solvents are compared neat or in the presence of other solvents. When anthracene is the better solvent, conditions appear to favour the formation of dihydroanthracene which is an excellent hydrogen donor. When phenanthrene is the better solvent, the inherently better solvent power of phenanthrene itself for the coal appears to be the dominant factor. The minerals in the coal, and possibly the coal itself, are also important in determining the preferred solvent. Anthracene is a better solvent than phenanthrene in the presence of 1-methylnaphthalene in Wyodak coal liquefaction under hydrogen pressure, whereas phenanth-
Anthracene
rene is a better solvent than anthracene for the other liquefaction conditions of Wyodak coal. Anthracene is a better solvent than phenanthrene in the presence of lmethylnaphthalene in Ky 9/14 coal liquefaction under nitrogen pressure. On the other hand, neat phenanthrene is about three times better than neat anthracene in Ky 9/14 coal liquefaction under air, but neat phenanthrene is about twice as effective as neat anthracene in the liquefaction of Ky 9/14 coal under nitrogen pressure. The minerals in Ky 9/14 coal appear to be better hydrogenation catalysts than those in Wyodak coal. Labile hydrogen from coal escapes readily before reacting with hydrogen shuttling solvents under the atmospheric environment. ACKNOWLEDGEMENTS The author gratefully acknowledges Dr Herbert R. Appell for his guidance and suggestions during this research work at the Pittsburgh Energy Technology Center. The author also acknowledges the US Department of Energy and The Oak Ridge Associated Universities for support of this research through The Summer Faculty Research Participation Program. REFERENCES 1
Neavel,
R. C. Phil. Trans. Roy. Sot., Land. 1981, A300, 141
and phenanthrene 2 3
4
5
6
7 8 9 10
11 12 13 14 15 16
in coal liquefaction:
K. C. Kwon
Vernon, L. W. Fuel 1980,59, 102 Appell, H. R. ‘The Effect of Solvent Composition on Product Distribution’, Pittsburgh Energy Technology Center, unpublished report Padrick, T. D., Lynch, A. W. and Stephens, H. P. ‘Effect of Solvent on the Dissolution of Wyodak Coal’, ‘Proceedings of the Department of Energy Integrated Two-Stage Liquefaction Meetings’, Albuquerque, New Mexico, USA, October 1982, pp. 6-2 Derbyshire, F. J. and Whitehurst, D. D. ‘The Influence of Polyaromatic Solvent Components on Coal Liquefaction’, ‘Proceedings on the Fifth Annual EPRI Contractor’s Conference on Coal Liquefaction’, USA, 1980, pp. 9-l Utz, B. R., Appell, H. R. and Blaustein, B. D. ‘Vehicle Studies in Short Contact Time Liquefaction’, ‘Proceedings of the Department of Energy Integrated Two-Stage Liquefaction Meetings’, Albuquerque, New Mexico, USA, October 1982, pp. 7-l Guin, J. A., Curtis,C. W. and Kwon, K. C. Fuel 1983,62, 1412 Rottendorf, H. and Wilson, M. A. Fuel 1980,59, 175 Mochida, I., Takarabe, A. and Takeshita, K. Fuel 1979, 58, 17 Curtis, C. W., Guin, J. A. and Kwon, K. C. ‘Coal and Solvolysis in a Series of Model Compound System’, AIChE Annual Meeting, November 1982, Los Angeles Garg, D. and Givens, E. N. lnd. Eng. Chem. Process. Des. Dev. 1982,21, 113 Curtis, C. W., Guin, J. A., Kwon, K. C. and Smith, N. L. Fuel 1983,62, 1341 Jackson, W. R., Larkins, F. P., Marshall, M., Rash, D. and White, N. Fuel 1979,58, 281 Gangwar, T. E. and Prasad, H. Fuel 1979,58, 577 Lytle, J. M., Wood, R. E. and Wiser, W. H. Fuel 1980, 59, 471 Utz, B. R., Narain, N. K., Appell, H. R. and Blaustein, B. D. ‘Solvent Analysis of Coal Derived Products, Using Pressure Filtration’, Am. Chem. Sot. Symp. Ser. Washington, DC., 1982
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1985,
Vol64,
June
753