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Dependence of coal liquefaction behaviour on coal characteristics. 6. Product distributions from coals treated in a continuous-flow reactor
Dependence of coal liquefaction behaviour coal characteristics. 6. Product distributions from coals treated a continuous-flow reactor* Peter H. Given
orl in
and Ajay Soodt
Department of Materials Science University Park, Pa. 76802, USA tGulf Research and Development USA
and Engineering, Company,
Pennsylvania
PO Drawer
2038,
State
University,
Pittsburgh,
Pa. 15230,
Further experimentation with coals in a continuous-flow reactor system at 440 and 455°C confirms the significance of the previous classification of a set of coals by cluster analysis. The greatest yields of distillable products tend to be given by coals of high sulphur content in the middle of the range of the high-volatile bituminous rank classes. Yet the lowest yields of preasphaltene (tolueneinsoluble material) tend to be given by coals of high rank and medium sulphur content. 1 he group of low sulphur, low-rank coals (mostly Rocky Mountain province), in a solvent different from that used for the other groups, showed poor conversion and poor distillate yield at the higher temperature. It is concluded that this coal/solvent combination is particularly prone to retrogressive reactions, including coking. (Keywords: coal liquefaction;
coal rank; sulphur
content)
In an earlier Paper of this series,’ it was shown by the statistical procedure known as ‘cluster analysis’ that a group of 104 coals of the high-volatile bituminous rank classes, selected from three geological provinces of the US, should be partitioned into three relatively homogeneous subsets. Conversion to liquids plus gases (in tetralin at 4OO”C, no HZ) was one of 15 characteristics used in the analysis. However, ‘discriminant analysis’ showed that contents of carbon and sulphur alone could correctly assign a coal to its cluster (subset) in 102 cases out of 104. Thus, the levels of these contents, and of the conversion values, were the most obviously differing characteristics of the subsets; it was not primarily occurrence in one or other of the provinces that determined to which subset a coal belonged. ‘Factor analysis’ of the full set of variables for the coals showed that the systematic relations between properties differed markedly for each subset. It appeared that a new classification of a reasonably large set of coals had been achieved, which was related to geochemical processes and relevant to liquefaction. These liquefaction studies were carried out in the batch mode in small tubing bomb reactors. They have been augmented by experiments on some of the same coals in a continuous-flow reactor, with a throughput of 1 kg h-l, to approach more realistic conditions. In work already published,’ some of the results obtained with two of the subsets defined by cluster analysis were described. Here, some further data are presented.for coals of these subsets * Presented Liquefaction’,
at International Lorne, Victoria,
Workshpp on the ‘Science Australia, 24-28 May, 1982
001&2361/82/100968-04S3.00 @ 1982 Butterworth & Co (Publishers)
968
Ltd.
FUEL, 1982, Vol 61, October
of Coal
(medium sulphur content, relatively high rank, mostly Appalachian province; high sulphur, medium rank, partly Interior and partly Appalachian); and also similar data for coals of the third subset (low sulphur, low to medium rank, mostly of the Rocky Mountain province). More complete presentations of data, with statistical analyses, will be published later. EXPERIMENTAL Coals used
The coals of the original set of 104 samples were identified in the earlier Paper.’ The coals from the first two subsets selected for study in the continuous-flow reactor were indicated also in a previous Paper.’ For convenience here, brief identifications of coals from all three subsets are shown in Table I; for further detail the interested reader should refer to the Papers cited,‘s2 or write to one of the authors (P.H.G.). Apparatus
and methods
As described previously,2 the experiments were carried out in a 500 cm3 well-stirred reactor, pressurized with hydrogen at 20.7 MPa (3000 psi) and maintained at 440 or 455°C. A 2:l slurry of coal in partly hydrogenated anthracene oil3 was used for all of the coals of the first two subsets and a few from the third, whereas all of the third subset were slurried in a recycle solvent from the P-99 SRC-II pilot plant operated by Gulf Research and Development Company at its Pittsburgh Center.3 The solvents are compared in Table 2, the P-99 solvent has appreciably more N, S, 0, and tends to be higher boiling.
Dependence Table 1 Brief identifications
of coal liquefaction
of coals used in continuous-flow
C (wt%, dmmf)
Seam, State
219 265 270 271 281 300 302 320 328 330 337 354 359 363 371 501 592 734
Kentucky No. 4 Jawbone, Va. American, Ala. Mary Lee, Ala. Indiana No. 7, Ind. Pee Wee, Tenn. Lower Banner, Va. Pittsburgh, Pa. U. Freeport, Pa. M. Kittanning, Pa. L. Kittanning, Pa. L. Kittanning, Pa. L. Elkhorn, Ky. Hazard No. 5A, Ky. Imboden, Ky. U. Sunnyside, Utah Illinois No. 5, Ill. U.Kittanning,W. Va.
Tab/e 2
Characteristics
82.1 86.7 85.2 86.5 83.6 84.4 88.2 90.4 85.4 83.5 86.1 84.7 84.1 83.9 87.0 83.4 82.7 86.4
Seam, State
C (wt%, dmmf)
252 276 277 278 279 284 285 286 290 305 308 341 353 399 401 553 580 585 593 594 596 598 607 751 767
Illinois No. 5, III. Ohio No. 8, Ohio Ohio No. 9, Ohio Ohio No. 9, Ohio Indiana No. 3, Ind. L. Dekoven, Ill. Davis, Ill. Tebo, Missouri III. No. 4, Ill. Ohio No. 11, Ohio Ohio No. 5, Ohio Clarion, Pa. U. Clarion, Pa. Fort Scott, Okla. Mineral, Okla. (Unnamed), Iowa Illinois No. 5, Ill. Indiana No. 5, Ind. Illinois No. 5, Ill. Illinois No. 5. Ill. Indiana No. 7, Ind. Indiana No. 7, Ind. Opdyke, III. Ohio No. 6, Ohio (Unnamed), Okla.
82.3 83.5 81.5 80.5 80.1 83.7 84.5 85.1 81.3 82.3 80.2 86.0 84.9 82.6 82.6 80.1 81.2 81.4 79.9 80.7 81.3 81.6 79.9 81.5 82.1
of donor solvents used
C H N S 0
HAOa
P-99b
90.0
88.2 8.27 1 .Ol 0.35 2.03
8.36 0.53 0.05 1.08
(w-t %I
composition
~
Temp. (“C) 40-193 193-288 288-482
Subset 3 (low S, low rank)
Sample No. PSOC
Boiling point distribution Elemental
P. H. Given and A. Sood
reactor
Subset 2 (high S, med. rank)
Subset 1 (med. S, high rank) Sample No. PSOC
on coal characteristics:
range HAOa
P-996
3 33 64
2 29 67
a HAO, hydrogenated anthracene oil b Recycle solvent generated in P-99 pilot plant from coal of Pittsburgh seam, Powhatan No. 5 mine
An aliquot of the product slurry was mixed with an excess of ethyl acetate and filtered. Conversions were calculated from the weight of dried filter cake and the weight of coal fed during a 3-4 h period after the system had reached a steady state (5-7 h). An aliquot of the filtrate, after evaporation of the ethyl acetate, was distilled at 400 Pa (3 mm Hg) pressure to a pot temperature of 4OO”C, and the loss in weight of the contents of the still, less the weight of solvent, is reported as ‘distillate’. Another aliquot of the filtrate was subjected to ‘SARA’ analysis which separates oils, asphaltenes and preasphaltenes (toluene-insoluble materials) by conventional methods and also determines alkanes, aromatics and ‘resins’ (polar substances) by h.p.1.c. procedures.4
RESULTS The mean values of the conversion to liquids plus gases are shown for each of the three subsets in Table 3 (the Gu!f
Sample No. PSOC
Seam, State
c (wt%, dmmf)
223 232 233 235 237 249 309 310 311 312 313 314 315 316 435 440 453 495 548
Kentucky No. 6, Ky. Colorado C. Colo. Wadge, Colo. Colorado 82, Cola. Rock Canyon, Utah Rock Canyon, Utah New Mex. No.8, New Mex. New Mex. No.7, New Mex. New Mex. No.6, New Mex. Red, Arizona Hiawatha, Utah Blind Canyon, Utah Wadge, Colo. Fish Creek, Cola. Utah B, Utah Utah B, Utah Blind Canyon, Utah Hiawatha, Utah Wolf Creek, Colo.
81.9 77.4 78.3 81.0 81.9 81.3 78.8 77.9 78.9 78.0 80.2 81.5 76.6 78.3 76.2 79.9 81.2 81.3 79.1
data for Subsets 1 and 2 are repeated, for comparison, from Given et aL2). As stated previously, the continuousflow reactor results for Subset 3 were obtained with a solvent different from (and inferior to) that used for Subsets 1 and 2. Four coals were used in both solvents, and the results suggested that the figures for conversion of Subset 3 could be put on an approximately comparable basis with the data for Subsets 1 and 2 by multiplying them by 1.2, and this has been done, with results shown in parentheses, in Table 3. The figures in the Table show that the coals of the three groups are even more distinct in their conversion levels under the conditions of the continuous-flow reactor than they were in the PSU batch reactor tests. Thus, the general significance of the classification of coals brought about by cluster analysis is confirmed. The ratio of conversions at 440 and 455”C, included in Table 3, shows that the temperature coefficient is much smaller for Subset 3 than for the other subsets, judging from the ratio of mean conversions at the two temperatures. In fact, conversion at 455°C was often 1eSs than at 440°C; the reasons for this are discussed later. In a previous Paper,2 reasonably good linear regressions were found when the individual conversion values for the same coals in the two reactor systems were plotted against one another. The variance (R2) explained by the regressions was 88 and 86.5x, respectively, for the two temperatures. This is surprising in view of the considerable differences in conditions. However, similar regressions for the coals of Subset 3 show essentially no correlation (R2 = 1.1 and 11% for 440 and 455”C, respectively). One possible reason for the difference is that the donor solvent dominates coal behaviour; the hydrogenated anthracene oil may be similar in behaviour to tetralin, in being largely hydroaromatic, whereas the recycle solvent is different, presumably containing some
FUEL, 1982, Vol 61, October
969
Dependence
of coal liquefaction
on coal characteristics:
phenols and bases, as well as hydroaromatics and highermolecular-weight hydrocarbons. Mean values for proximate analyses of liquids and gases are shown in Table 4 (no attempt has been made here to correct the Subset 3 data for the difference in solvent). Solids removal by filtration of product slurry has proved very difficult in liquefaction pilot plants, and so both the SRC-II and the Exxon Donor Solvent processes rely on vacuum distillation as a means of removing solids and obtaining a saleable product. For this reason, the yields of distillable material shown in Table 4 are of particular interest. Presumably the distillate yields for Subset 3 would have been higher if the hydrogenated anthracene oil had been used; such comparative data as are available are given in Table 5. Thus, it seems very likely that even if all of the coals of Subset 3 had been used in the same solvent as Subsets 1 and 2, Subset 2 would still tend to show the highest yields of distillable material. This subset also shows the highest total conversion; in fact, distillate as a fraction of total conversion varies little for any subset, except for the Subset 3 at 455°C. The low yield ofdistillate from Subset 3 coals at 455°C when the P-99 solvent is used (see both Tables 3 and 4) should be noted. The yields of distillate for the coals of Subsets 1 and 2 have been plotted previously* against their carbon contents to show, in an easily visualized form, the wide range of values found for distillate yield. However, the points were in bands showing a tendency for distillate to decrease with increasing rank. Similar plots for Subset 3 coals in the P-99 solvent show essentially no correlation with the carbon content of the coal; the points are to be
Tab/e 3 Mean values for conversion of coals in different I+ standard deviation)
Gulf results, 440” c No. of samples Gulf results, 455” c No. of samples Ratio of mean values
subsets
Subset 1
Subset 2
Subset 3a
57.5 f 8.8 17
79.5 ? 9.7 25
57.6 ? 7.5f69.2 19
f 9.0)
65.1
87.4
60.0
+ 11.5)
+ 8.6 16
k 8.4 21
1 .lO
1 .I3
+ 9.6f71.6 19
52.9 t 7.37 30
64.0 f- 4.3 38
70.6 + 6.5 36
Mean values of some product
comparable
compositional
with
parameters
Subset
Temp. CC)
Distillate fwt %,dmmf
f%)
No. of coal samples
Temp. (“Cl
Hydrogenated anthracene oil
P-99
4 3
440 455
26.7 32.5
24.7 19.5
(Gulf continuous-flow
Mean ratio, dist./conv. No. of samples
solvents
Mean yield of distillate
1.03
a The figures in parentheses are approximately those for Subsets 1 and 2; see text Table.4
contained within a circle rather than an ellipse of high axial ratio. The range is 9.5-53.8 at 440°C and 9.8-32 at 455°C. Product analysis is particularly difficult when a continuous-flow reactor is used in a non-recycle mode, each experiment being made with a standard solvent not generated in the system. The solvent, or materials derived from it, must be subtracted from the measured yields to be able to determine how much product is derived from the coal. To make the subtraction, it is assumed that the solvent is unchanged in solubility and boiling range. Thus, the figures in Table 4 for yields of the components of the SARA analysis cannot be very accurate, and in fact were not closely reproducible.3 Nevertheless, the lower mean yields of ‘preasphaltenes’ from Subset 1 coals, particularly at 440°C are probably real. The high mean yield of asphaltenes from Subset 3 coals at 455°C may be associated with the low yield of distillables at the same temperature. The variability of yields of asphaltenes and preasphaltenes, and the ratio of them, was particularly wide for coals of Subset 3. Figures for gas yields do not suffer from these problems. Differences in mean yields of hydrocarbon gases are small. Elimination of oxygen-containing functional groups as CO and CO, is expected to be greater for lower-rank coals, and the yield of these gases + H,S is indeed greater for Subset 3 than for Subset 1. The fact that coals of Subset 2 give the highest mean yields of CO +CO, + H,S is no doubt due to a combination of relatively low rank and high pyrite contents. The sum of the yields of the two kinds of gases is by no means enough to account for the differences in total conversion at 440 and 455°C for coals of Subsets 1 and 2. However, if the mean total yield for Subset 3 is subtracted from the mean conversions in Table 3, it appears that the mean yield of liquids at 440°C was 50.8% (P-99 solvent), and at 455°C was 49.6%, suggesting that production of liquids actually might tend to be less at the higher temperature. It seems significant that experiments with two coals of Subset 3 in the P-99 solvent had to be rejected because of
Tab/e 5 Yields of distillate for different
PSU results, 400°c No. of samples
P. H. Given and A. Sood
Asphaltene
reactor)
Preasphaltene
coal)
Resinsa
Cl--C4
co.
gases
“2s
fwt %, dmmf coal)
1
18 16
440 455
24.6 27.0
0.43 0.41
19.3 19.5
12.7 18.4
19(5) 18(4)
4.9 8.0
1 .6 2.2
2
32 21
440 455
33.8 38.5
0.43 0.44
19.5 18.6
24.9 23.6
13(8) 16(3)
5.0 7.0
5.0 5.0
3
196 196
440 455
24.7 19.4
0.43 0.33
15.9 24.1
24.9 23.6
-
3.9 6.3
2.9 4.1
a Data available only for the number of samples shown in parentheses b All samples used with P-99 solvent
970
FUEL, 1982, Vol 61, October
co2.
Dependence of coal liquefaction on coal characteristics: P. H. Given and A. Sood coking in the reactor (PSOC-310 and 311; but no coals from the other Subsets). In fact the behaviour of coals of Subset 3 (in the P-99 solvent) differs from that of the other coals in a number of important respects: the lowtemperature coefficient of total conversion, the apparent decrease in production of total liquids and of distillable products at the higher temperature, the high mean asphaltene yield at 455°C and the wide, apparently adventitious, variability of the asphaltene/preasphaltene ratios and of the distillate yield for individual coals. All of these observations are consistent with the suggestion that the combination of Subset 3 with the P-99 solvent are specially prone to retrogressive reactions, including coke formation. In addition, this combination is set apart from the other subsets and solvent by the largely random relation between Gulf and PSU conversions, and between distillate yield and carbon content. This scatter could also be due to an adventitious incidence of retrogressive reactions. Whether this incidence of retrogressive reactions arises from the characteristics of the coals of Subset 3 or of the P99 solvent, cannot, at this time, be established. This solvent no doubt corresponds more closely than hydrogenated anthracene oil to what is likely to be
available commercially. It is noteworthy, therefore, that coals of Subset 3 do not perform particularly well in the P99 solvent, and that ideally they need a more effective donor solvent if they are to be used effectively.
ACKNOWLEDGEMENTS This work was carried out under Contract No. DE-AC2276-ET-10587 from the US Department of Energy.
REFERENCES Yarzab, R. F., Given, P. H., Spackman, W. and Davis, A. Fuel 1980, 59, 81 Given, P. H., Schleppy, R. and Sood, A. Ftlel 1980, 59, 747 Given, P. H., Spackman, W., Davis, A., Walker, P. L., Lovell, H. L., Coleman, M. M. and Painter, P. C. ‘The Relation of Coal Characteristics to Liquefaction Behaviour’ (Parts I and II), Final Technical Report, July 1976-Feb. 1981, from Pennsylvania State University to US Di,partment of Energy, Report Nos. FE-2494-FR-1 and FE-2494-FR-2 Given, P. H., Spackman, W., Davis, A., Walker, P. L., Lovell, H. L., Coleman, M. M. and Painter, P. C. ‘The Relation of Coal Characteristics to Liquefaction Behaviour’, Quarterly Technical Progress Reports, Jan.-June 1978, from Pennsylvania State University to US Department of Energy, Report Nos. FE-2494TR718
FUEL, 1982, Vol 61, October
971
orl in
and Ajay Soodt
Department of Materials Science University Park, Pa. 76802, USA tGulf Research and Development USA
and Engineering, Company,
Pennsylvania
PO Drawer
2038,
State
University,
Pittsburgh,
Pa. 15230,
Further experimentation with coals in a continuous-flow reactor system at 440 and 455°C confirms the significance of the previous classification of a set of coals by cluster analysis. The greatest yields of distillable products tend to be given by coals of high sulphur content in the middle of the range of the high-volatile bituminous rank classes. Yet the lowest yields of preasphaltene (tolueneinsoluble material) tend to be given by coals of high rank and medium sulphur content. 1 he group of low sulphur, low-rank coals (mostly Rocky Mountain province), in a solvent different from that used for the other groups, showed poor conversion and poor distillate yield at the higher temperature. It is concluded that this coal/solvent combination is particularly prone to retrogressive reactions, including coking. (Keywords: coal liquefaction;
coal rank; sulphur
content)
In an earlier Paper of this series,’ it was shown by the statistical procedure known as ‘cluster analysis’ that a group of 104 coals of the high-volatile bituminous rank classes, selected from three geological provinces of the US, should be partitioned into three relatively homogeneous subsets. Conversion to liquids plus gases (in tetralin at 4OO”C, no HZ) was one of 15 characteristics used in the analysis. However, ‘discriminant analysis’ showed that contents of carbon and sulphur alone could correctly assign a coal to its cluster (subset) in 102 cases out of 104. Thus, the levels of these contents, and of the conversion values, were the most obviously differing characteristics of the subsets; it was not primarily occurrence in one or other of the provinces that determined to which subset a coal belonged. ‘Factor analysis’ of the full set of variables for the coals showed that the systematic relations between properties differed markedly for each subset. It appeared that a new classification of a reasonably large set of coals had been achieved, which was related to geochemical processes and relevant to liquefaction. These liquefaction studies were carried out in the batch mode in small tubing bomb reactors. They have been augmented by experiments on some of the same coals in a continuous-flow reactor, with a throughput of 1 kg h-l, to approach more realistic conditions. In work already published,’ some of the results obtained with two of the subsets defined by cluster analysis were described. Here, some further data are presented.for coals of these subsets * Presented Liquefaction’,
at International Lorne, Victoria,
Workshpp on the ‘Science Australia, 24-28 May, 1982
001&2361/82/100968-04S3.00 @ 1982 Butterworth & Co (Publishers)
968
Ltd.
FUEL, 1982, Vol 61, October
of Coal
(medium sulphur content, relatively high rank, mostly Appalachian province; high sulphur, medium rank, partly Interior and partly Appalachian); and also similar data for coals of the third subset (low sulphur, low to medium rank, mostly of the Rocky Mountain province). More complete presentations of data, with statistical analyses, will be published later. EXPERIMENTAL Coals used
The coals of the original set of 104 samples were identified in the earlier Paper.’ The coals from the first two subsets selected for study in the continuous-flow reactor were indicated also in a previous Paper.’ For convenience here, brief identifications of coals from all three subsets are shown in Table I; for further detail the interested reader should refer to the Papers cited,‘s2 or write to one of the authors (P.H.G.). Apparatus
and methods
As described previously,2 the experiments were carried out in a 500 cm3 well-stirred reactor, pressurized with hydrogen at 20.7 MPa (3000 psi) and maintained at 440 or 455°C. A 2:l slurry of coal in partly hydrogenated anthracene oil3 was used for all of the coals of the first two subsets and a few from the third, whereas all of the third subset were slurried in a recycle solvent from the P-99 SRC-II pilot plant operated by Gulf Research and Development Company at its Pittsburgh Center.3 The solvents are compared in Table 2, the P-99 solvent has appreciably more N, S, 0, and tends to be higher boiling.
Dependence Table 1 Brief identifications
of coal liquefaction
of coals used in continuous-flow
C (wt%, dmmf)
Seam, State
219 265 270 271 281 300 302 320 328 330 337 354 359 363 371 501 592 734
Kentucky No. 4 Jawbone, Va. American, Ala. Mary Lee, Ala. Indiana No. 7, Ind. Pee Wee, Tenn. Lower Banner, Va. Pittsburgh, Pa. U. Freeport, Pa. M. Kittanning, Pa. L. Kittanning, Pa. L. Kittanning, Pa. L. Elkhorn, Ky. Hazard No. 5A, Ky. Imboden, Ky. U. Sunnyside, Utah Illinois No. 5, Ill. U.Kittanning,W. Va.
Tab/e 2
Characteristics
82.1 86.7 85.2 86.5 83.6 84.4 88.2 90.4 85.4 83.5 86.1 84.7 84.1 83.9 87.0 83.4 82.7 86.4
Seam, State
C (wt%, dmmf)
252 276 277 278 279 284 285 286 290 305 308 341 353 399 401 553 580 585 593 594 596 598 607 751 767
Illinois No. 5, III. Ohio No. 8, Ohio Ohio No. 9, Ohio Ohio No. 9, Ohio Indiana No. 3, Ind. L. Dekoven, Ill. Davis, Ill. Tebo, Missouri III. No. 4, Ill. Ohio No. 11, Ohio Ohio No. 5, Ohio Clarion, Pa. U. Clarion, Pa. Fort Scott, Okla. Mineral, Okla. (Unnamed), Iowa Illinois No. 5, Ill. Indiana No. 5, Ind. Illinois No. 5, Ill. Illinois No. 5. Ill. Indiana No. 7, Ind. Indiana No. 7, Ind. Opdyke, III. Ohio No. 6, Ohio (Unnamed), Okla.
82.3 83.5 81.5 80.5 80.1 83.7 84.5 85.1 81.3 82.3 80.2 86.0 84.9 82.6 82.6 80.1 81.2 81.4 79.9 80.7 81.3 81.6 79.9 81.5 82.1
of donor solvents used
C H N S 0
HAOa
P-99b
90.0
88.2 8.27 1 .Ol 0.35 2.03
8.36 0.53 0.05 1.08
(w-t %I
composition
~
Temp. (“C) 40-193 193-288 288-482
Subset 3 (low S, low rank)
Sample No. PSOC
Boiling point distribution Elemental
P. H. Given and A. Sood
reactor
Subset 2 (high S, med. rank)
Subset 1 (med. S, high rank) Sample No. PSOC
on coal characteristics:
range HAOa
P-996
3 33 64
2 29 67
a HAO, hydrogenated anthracene oil b Recycle solvent generated in P-99 pilot plant from coal of Pittsburgh seam, Powhatan No. 5 mine
An aliquot of the product slurry was mixed with an excess of ethyl acetate and filtered. Conversions were calculated from the weight of dried filter cake and the weight of coal fed during a 3-4 h period after the system had reached a steady state (5-7 h). An aliquot of the filtrate, after evaporation of the ethyl acetate, was distilled at 400 Pa (3 mm Hg) pressure to a pot temperature of 4OO”C, and the loss in weight of the contents of the still, less the weight of solvent, is reported as ‘distillate’. Another aliquot of the filtrate was subjected to ‘SARA’ analysis which separates oils, asphaltenes and preasphaltenes (toluene-insoluble materials) by conventional methods and also determines alkanes, aromatics and ‘resins’ (polar substances) by h.p.1.c. procedures.4
RESULTS The mean values of the conversion to liquids plus gases are shown for each of the three subsets in Table 3 (the Gu!f
Sample No. PSOC
Seam, State
c (wt%, dmmf)
223 232 233 235 237 249 309 310 311 312 313 314 315 316 435 440 453 495 548
Kentucky No. 6, Ky. Colorado C. Colo. Wadge, Colo. Colorado 82, Cola. Rock Canyon, Utah Rock Canyon, Utah New Mex. No.8, New Mex. New Mex. No.7, New Mex. New Mex. No.6, New Mex. Red, Arizona Hiawatha, Utah Blind Canyon, Utah Wadge, Colo. Fish Creek, Cola. Utah B, Utah Utah B, Utah Blind Canyon, Utah Hiawatha, Utah Wolf Creek, Colo.
81.9 77.4 78.3 81.0 81.9 81.3 78.8 77.9 78.9 78.0 80.2 81.5 76.6 78.3 76.2 79.9 81.2 81.3 79.1
data for Subsets 1 and 2 are repeated, for comparison, from Given et aL2). As stated previously, the continuousflow reactor results for Subset 3 were obtained with a solvent different from (and inferior to) that used for Subsets 1 and 2. Four coals were used in both solvents, and the results suggested that the figures for conversion of Subset 3 could be put on an approximately comparable basis with the data for Subsets 1 and 2 by multiplying them by 1.2, and this has been done, with results shown in parentheses, in Table 3. The figures in the Table show that the coals of the three groups are even more distinct in their conversion levels under the conditions of the continuous-flow reactor than they were in the PSU batch reactor tests. Thus, the general significance of the classification of coals brought about by cluster analysis is confirmed. The ratio of conversions at 440 and 455”C, included in Table 3, shows that the temperature coefficient is much smaller for Subset 3 than for the other subsets, judging from the ratio of mean conversions at the two temperatures. In fact, conversion at 455°C was often 1eSs than at 440°C; the reasons for this are discussed later. In a previous Paper,2 reasonably good linear regressions were found when the individual conversion values for the same coals in the two reactor systems were plotted against one another. The variance (R2) explained by the regressions was 88 and 86.5x, respectively, for the two temperatures. This is surprising in view of the considerable differences in conditions. However, similar regressions for the coals of Subset 3 show essentially no correlation (R2 = 1.1 and 11% for 440 and 455”C, respectively). One possible reason for the difference is that the donor solvent dominates coal behaviour; the hydrogenated anthracene oil may be similar in behaviour to tetralin, in being largely hydroaromatic, whereas the recycle solvent is different, presumably containing some
FUEL, 1982, Vol 61, October
969
Dependence
of coal liquefaction
on coal characteristics:
phenols and bases, as well as hydroaromatics and highermolecular-weight hydrocarbons. Mean values for proximate analyses of liquids and gases are shown in Table 4 (no attempt has been made here to correct the Subset 3 data for the difference in solvent). Solids removal by filtration of product slurry has proved very difficult in liquefaction pilot plants, and so both the SRC-II and the Exxon Donor Solvent processes rely on vacuum distillation as a means of removing solids and obtaining a saleable product. For this reason, the yields of distillable material shown in Table 4 are of particular interest. Presumably the distillate yields for Subset 3 would have been higher if the hydrogenated anthracene oil had been used; such comparative data as are available are given in Table 5. Thus, it seems very likely that even if all of the coals of Subset 3 had been used in the same solvent as Subsets 1 and 2, Subset 2 would still tend to show the highest yields of distillable material. This subset also shows the highest total conversion; in fact, distillate as a fraction of total conversion varies little for any subset, except for the Subset 3 at 455°C. The low yield ofdistillate from Subset 3 coals at 455°C when the P-99 solvent is used (see both Tables 3 and 4) should be noted. The yields of distillate for the coals of Subsets 1 and 2 have been plotted previously* against their carbon contents to show, in an easily visualized form, the wide range of values found for distillate yield. However, the points were in bands showing a tendency for distillate to decrease with increasing rank. Similar plots for Subset 3 coals in the P-99 solvent show essentially no correlation with the carbon content of the coal; the points are to be
Tab/e 3 Mean values for conversion of coals in different I+ standard deviation)
Gulf results, 440” c No. of samples Gulf results, 455” c No. of samples Ratio of mean values
subsets
Subset 1
Subset 2
Subset 3a
57.5 f 8.8 17
79.5 ? 9.7 25
57.6 ? 7.5f69.2 19
f 9.0)
65.1
87.4
60.0
+ 11.5)
+ 8.6 16
k 8.4 21
1 .lO
1 .I3
+ 9.6f71.6 19
52.9 t 7.37 30
64.0 f- 4.3 38
70.6 + 6.5 36
Mean values of some product
comparable
compositional
with
parameters
Subset
Temp. CC)
Distillate fwt %,dmmf
f%)
No. of coal samples
Temp. (“Cl
Hydrogenated anthracene oil
P-99
4 3
440 455
26.7 32.5
24.7 19.5
(Gulf continuous-flow
Mean ratio, dist./conv. No. of samples
solvents
Mean yield of distillate
1.03
a The figures in parentheses are approximately those for Subsets 1 and 2; see text Table.4
contained within a circle rather than an ellipse of high axial ratio. The range is 9.5-53.8 at 440°C and 9.8-32 at 455°C. Product analysis is particularly difficult when a continuous-flow reactor is used in a non-recycle mode, each experiment being made with a standard solvent not generated in the system. The solvent, or materials derived from it, must be subtracted from the measured yields to be able to determine how much product is derived from the coal. To make the subtraction, it is assumed that the solvent is unchanged in solubility and boiling range. Thus, the figures in Table 4 for yields of the components of the SARA analysis cannot be very accurate, and in fact were not closely reproducible.3 Nevertheless, the lower mean yields of ‘preasphaltenes’ from Subset 1 coals, particularly at 440°C are probably real. The high mean yield of asphaltenes from Subset 3 coals at 455°C may be associated with the low yield of distillables at the same temperature. The variability of yields of asphaltenes and preasphaltenes, and the ratio of them, was particularly wide for coals of Subset 3. Figures for gas yields do not suffer from these problems. Differences in mean yields of hydrocarbon gases are small. Elimination of oxygen-containing functional groups as CO and CO, is expected to be greater for lower-rank coals, and the yield of these gases + H,S is indeed greater for Subset 3 than for Subset 1. The fact that coals of Subset 2 give the highest mean yields of CO +CO, + H,S is no doubt due to a combination of relatively low rank and high pyrite contents. The sum of the yields of the two kinds of gases is by no means enough to account for the differences in total conversion at 440 and 455°C for coals of Subsets 1 and 2. However, if the mean total yield for Subset 3 is subtracted from the mean conversions in Table 3, it appears that the mean yield of liquids at 440°C was 50.8% (P-99 solvent), and at 455°C was 49.6%, suggesting that production of liquids actually might tend to be less at the higher temperature. It seems significant that experiments with two coals of Subset 3 in the P-99 solvent had to be rejected because of
Tab/e 5 Yields of distillate for different
PSU results, 400°c No. of samples
P. H. Given and A. Sood
Asphaltene
reactor)
Preasphaltene
coal)
Resinsa
Cl--C4
co.
gases
“2s
fwt %, dmmf coal)
1
18 16
440 455
24.6 27.0
0.43 0.41
19.3 19.5
12.7 18.4
19(5) 18(4)
4.9 8.0
1 .6 2.2
2
32 21
440 455
33.8 38.5
0.43 0.44
19.5 18.6
24.9 23.6
13(8) 16(3)
5.0 7.0
5.0 5.0
3
196 196
440 455
24.7 19.4
0.43 0.33
15.9 24.1
24.9 23.6
-
3.9 6.3
2.9 4.1
a Data available only for the number of samples shown in parentheses b All samples used with P-99 solvent
970
FUEL, 1982, Vol 61, October
co2.
Dependence of coal liquefaction on coal characteristics: P. H. Given and A. Sood coking in the reactor (PSOC-310 and 311; but no coals from the other Subsets). In fact the behaviour of coals of Subset 3 (in the P-99 solvent) differs from that of the other coals in a number of important respects: the lowtemperature coefficient of total conversion, the apparent decrease in production of total liquids and of distillable products at the higher temperature, the high mean asphaltene yield at 455°C and the wide, apparently adventitious, variability of the asphaltene/preasphaltene ratios and of the distillate yield for individual coals. All of these observations are consistent with the suggestion that the combination of Subset 3 with the P-99 solvent are specially prone to retrogressive reactions, including coke formation. In addition, this combination is set apart from the other subsets and solvent by the largely random relation between Gulf and PSU conversions, and between distillate yield and carbon content. This scatter could also be due to an adventitious incidence of retrogressive reactions. Whether this incidence of retrogressive reactions arises from the characteristics of the coals of Subset 3 or of the P99 solvent, cannot, at this time, be established. This solvent no doubt corresponds more closely than hydrogenated anthracene oil to what is likely to be
available commercially. It is noteworthy, therefore, that coals of Subset 3 do not perform particularly well in the P99 solvent, and that ideally they need a more effective donor solvent if they are to be used effectively.
ACKNOWLEDGEMENTS This work was carried out under Contract No. DE-AC2276-ET-10587 from the US Department of Energy.
REFERENCES Yarzab, R. F., Given, P. H., Spackman, W. and Davis, A. Fuel 1980, 59, 81 Given, P. H., Schleppy, R. and Sood, A. Ftlel 1980, 59, 747 Given, P. H., Spackman, W., Davis, A., Walker, P. L., Lovell, H. L., Coleman, M. M. and Painter, P. C. ‘The Relation of Coal Characteristics to Liquefaction Behaviour’ (Parts I and II), Final Technical Report, July 1976-Feb. 1981, from Pennsylvania State University to US Di,partment of Energy, Report Nos. FE-2494-FR-1 and FE-2494-FR-2 Given, P. H., Spackman, W., Davis, A., Walker, P. L., Lovell, H. L., Coleman, M. M. and Painter, P. C. ‘The Relation of Coal Characteristics to Liquefaction Behaviour’, Quarterly Technical Progress Reports, Jan.-June 1978, from Pennsylvania State University to US Department of Energy, Report Nos. FE-2494TR718
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