Hydrogenation of Typical North American Splint Coals ABNER EISNER, GEORGE C. SPRUNK, LOYAL CLARICE, C. H. FISHER, AND H. H. STORCH Central Experiment Station, U. S. Bureau of Mines, Pittsburgh, Penna.
coals. The liquefaction yields of twelve splint samples were found to be inversely proportional to both the carbon and opaque matter contents. The hydrogenation residues were opaque, which indicates that spores, resins, and other translucent constituents had been liquefied.
Several typical and important North American splint coals were hydrogenated under conditions used previously to liquefy bright coals in excellent yields. The results show that American splint coals are similar to European splint coals i n being less suitable for hydrogenation than bright
KE conclusion drawn from the numerous investigations
0
coal is compared with a bright coal from the same bed and mine, the splint coal generally has the higher ash and total carbon contents and the higher softening temperature of ash; usually the bright coals have the higher moisture, hydrogen, nitrogen, oxygen, and sulfur contents. Volatile matter may vary in either direction and depends upon the exact composition of the bright or splint coals-that is, whether they are spore-rich or resin-rich. I n some instances the relation between the volatile matter and the hydrogen-carbon ratio can be used to distinguish between bright and splint coals (4, 17). The splint coals are easily identified by thin sections under the microscope. They are characterized by a semiopaque to opaque groundmass or attritus, as in Figure 5, whereas the bright coal sections have a groundmass or attritus that is predominantly translucent (Figure 3). The opaque attritus is not homogeneous; it is opaque in medium thin sections, but in extremely thin sections a portion of it becomes semitranslucent or brown. Other fragments can be found in various degrees of translucence and some, even in the thinnest sections, appear to rival fusain in opacity. Some finely divided fusain is also invariably present. It is believed that the opaque material is the result of a high degree of rotting or decomposition in the peat stage. Possibly the moisture conditions in the peat bog favored growth of microorganisms, and the decomposition continued for a longer period than in the case of bright coals. The transformation of tissues into opaque matter might be illustrated by a series of photographs, but only the early and late stages are shown in this paper. Figure 3 is a cross section of a typical bright coal. Figure 4 shows a wood strand (anthraxylon or vitrain) with a well-preserved center and the outer edges partly transformed into opaque matter. I n Figure 5, a typical splint coal, the greater decomposition has resulted in irregular fragmented tissues and high concentration of opaque matter. It is possible that the opaque constituents represent an intermediate stage in the formation of fusain, for in some splints one can detect a greater degree of opacity in the groundmass than in others. In such instances the opaque constituents more closely resemble fusain, and the sections must be ground exceptionally thin before any of the particles become translucent.
of the hydrogenation (19) of European coals is that
bright coals are more suitable for conversion into motor fuel than dull or splint coals (2, 4, 10, 11, 16). South African bright coals (16) also were found preferable to splint coals for hydrogenation purposes. Although it was shown (5, 9, 13) that several American bright coals are amenable to hydrogenation, there have been few data on American splint coals that can be used for purposes of comparison. This paper gives the results obtained on hydrogenating several typical splint coals under conditions used previously (5, 8) to liquefy bright coals and anthraxylon, the characteristic constituent of bright coals.
Properties of Splint Coals I n America four classes of coals are differentiated through their appearance, structure, microscopic composition, and suitability for certain uses (20)-bright coals, splint coals, cannel coals, and boghead coals, The first named is the most common. However, splint coals (durains) are important in West Virginia and Kentucky, particularly in the beds of the Upper Pottsville formation. The splint coals from this region have long been known as excellent steam and domestic fuels. They commonly have a dull luster, grayish black color, and compact structure. They are hard and tough and break with an irregular, rough, sometimes splintery fracture into large lumps and slabs (Figure 1) that stand handling and transportation remarkably well. The beds known as splint coals and sold as such to consumers are seldom more than 75 per cent splint and more often are considerably less. The splint is usually associated with one or more layers of bright or semisplint coal, the latter being intermediate in properties between bright and splint coals. Figure 2 is an example of one of the typical splinty coal beds. In this bed there are two layers of splint, two layers of bright coal, and two layers classed as mixtures; the bed contained 53 per cent splint, 14 per cent semisplint, and 33 per cent bright coal. Because many of the beds are mixtures it is difficult to identify the type of coal from ultimate and proximate analyses of the face or bed sample. However, when a splint 73
INDUSTRIAL AND ENGINEERING CHEMISTRY
74
VOL. 32, NO. 1
TABLEI. ANAlYSEa OF SPLINT LAYERS samde
No.
Stale
County
1
Ky. W. Va.
Sohnaon Boone Harlan Lstcher
2 3 4 5 6 7 8
Ky.
Ky.
W. Va. Mingo w. Va. Renswhs W. Va. Mingo,
w.vs. wyomrng
Bed
Mine
7PTolimsteAs Reoeived MOiavolatile ture Ash matter"
MilleriCresk Consolidstion 156 Coslbuig Silush High Splint Cloversplint Elkhorn No. 204 Upper Cedar Grove Sunioi Dorothy No. 10 Lower Cedar Grove Junior Sewell WYOmi*g
%
%
3.1 2.7 1.5
5.5
2.6
1.4 1.2 1.6 0.6
3.7 5.2
9.3
4.9 15.6
ultima le^
C
N
0
S
. Cslorifio Value
C/H
Ratm
%
%
%
%
%
%
Qmm-ool.
44.4
5.5 5.6
1.6 1.6
1.4
0.7
4.7
7.7 7.9 8.1
3.4
31.9 38.1 39.6 33.1 35.6
81.8 84.2 85.4 85.9 86.2 86.8 87.0
8206 8378 8172
1.4
6.1
0.9
8483
5.8
8439
16.0 17.0
0.5
8467 8556
19.3
43.1
2.2 9.2
, H
20.2
5.4 5.4 5.1
5.2
89.7
4.6
1.5
1.5 1.5 1.1
0.4 0.6
6.6 6.0
0.6
0.3
4.3
8483
14.9 15.0 18.2 15.9 16.7
Dry ash-free basis.
H y d r o g e n a t i o n Procedure Details of the experimental procedure have been given in previous papers (6, 6 ):
L1
..
-. ..~.~. ~
~
.~ ~~
the air was removed by flushing with nitrogen and hydrogen, and hvdroaen was introduced until the pressure at 20" C . \vas 1000
mine), which is chiefly bright coal. liltimate and proximate analyses are given in Table I, where the coals are arranged in order of increasing carbon content. Petrographic analyses are given in Table 11. The proportion of matter in the opaque attritus that i8 inert to hydrogenation is also given in Table 11. These data are subject to inaccuracies, because the content of inert matter was calcnlated on the assumption, only approximately correct, that fusain is completely inert but that anthraxylon @),translucent matter (K), spores (3, 8),and resins (8,5) are completely liquefied by hydrogenation.
(6.8) indicated that these condi6ons are enough to liquefy bright T~Elrli 11.
&bonaceous materr& S p e r h gravities of centrifuged oil8 were determined with a hydrometer; these data. are of questionable Bccuraoy becauso of the presence of traces of wat,er. The centrifuge residues wore wsshcd six times with acetone at room temoerature and then extracted with bcnzene in Souhlet apparatus
I'B:TBoQRAPl%ICCOMPOSITION (FER CENT)
OF SPLINT
-AttritusTrsnsliment Oonaue
Semple AnlhisxyNO. Ion
Fussin
LAYERS
Inert Matter in OpBqUe Attritua'
distillates'deserib~~i in Tables 'VI I and X To procure samples rich in opaque attritiis, the characteristic constitoent of splint coals, layers of coal containing high concentrations of opaque matter x w e selected from several important and typical Korth American splint coals (Tables I and 11). Sample 8 was taken from a splint layer that constituted only 4 per cent of the entire Sexell bed (Wyoming
Liquefaction Yields The splint coals gave comparatively low liquefaction yields
in all instances, which confirmed the prevailing opinion (4, IO, 11) that splint coals are not so suitable for hydrogenation as bright coals. Table 111 shows that the conversion of dry, ash-free splint coals into gases, liquids, and soluble material ranged from 58 to 87 per cent. These yields are considerably lower than those obtained previously under the same conditions a i t h bright coals (5, g), spores (S), resins (S), translucent attritus (S), and anthraxylons (9). The present data and those obtained previously with several samples of opaque attritus (7,5,14)indicate conclusively that TARLE 111. L r e a ~ r ~ DATA c~~o~ Sample No.
IlydroFFnRtiOn
1 2
3s 3Ad
4 5 G
GAd 7
8 *.~. A e
430
430 440 430 430
440 ~.
-PiodueL~--Liileids, solids Gsses Grams Grams 182.8 5.9 187.1 6.5 187.3 7.6 183.6 7.6 18i.Z 6.8 188.8 7.4 189.8 6.7 184.0 8.3 185.6
189.5 IRR
6.5 5.8 7. 8
CcotriLoss Grana 13.6 11.4 7.6 15 9 9.9
8.2 7.6
14.2
12.7 7.7 14 II ~. .
fuged Oil'
% 71
66 49
70
62 65 55
69 64 46
SX .Per cent by weiaht of maleiid oentiifuged. b Dry ash-lree basis. *From wevioun work ( 8 ) . d Cold, initial hydiogen pieamre was 1800 lb. per sq. in. * Cold. ~nzlialhydrogen pressure was 1304 lb. per aq. zn. I
FIGURE 1. Lux? OF TYPICAL SPLINTConi. FROM DOROTHY RED, XANAWIIA COGNTY, W. VA.
Temp. C. 430 430 430 440 430
~~~
~~
convei*ion of Pure Coal& %
86.7 81.8 59.8 78.2 79.7
82.9 74.4 84.6 77.2 57.5 72.4
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
the opaque matter is $,he principal constituent, other than fusain, responsible for the low liquefaction yields obtained with some coals of low and intermediate rank, This has been suggested before (10, d l ) , but previously there have been few s u p porting data. Calculations from data obtained with the eight splint samples of Table I and with four splint samples from a previous paper (8) show that the average liquefaction yield of opaque attritus (at 430°C. for3 hours in the presence of stannous sulfide and with initial hydrogen pressure of 1000 pounds per square inch) is about 60 per cent. For reasons discussed later, however, the liquefaction yields for the individualsamples of opaque attritus range from about 39 to 79 per cent (Table 11). It is possible that other FIGURE2. T Y P E S OF COALIN HIGH samples of opaque SPLINTBED,HARLAN COUNTY, Kr. attritus, depending upon the nature and degree of opacity, will give liquefaction yields outside this rangc. Several attempts were made by earlier.workers (fa,f6,18) to predict hydrogenation yields from the proximate and ultima& analyses of the coal. The results were disappointing,
15
although a rough correlation between carbon content of the coal and liquefaction yield was found. Probably this is partly because the carbon content of splint coals can be used as a rough measure of the content of opaque attritus and partly because both the rank (17) and difficulty of hydrogenation (id) of bright coals increase with increase in carbon content. I n view of the relat,ion between carboii content arid hydrogenation yield observed by previous workers, it is considered interesting to compare the yields of the prescnt work with carbon coirtents of the splint samples hydrogenated. The results (Figure 6) show that the carbon content cannot be used satisfactorily t o predict the liquefaction yields of splint coals. Protiaiily this can be attributed in part t,o tlie presence of low-ca+hon constituents, such as spores and resins, which may obscure the presence of corisiderable amounts of highcarbon opaque attritus. I n Figure 7 residue yields of splint samples of this and a previous paper (8) are plotted against total opaque .matter (fusain plus opaque attritus). Figure 7 seems to show that, although the correlation is far from satisfactory, the residue yield of splint samples can be predicted as me11 from the content of opaque matter as from carbon content. If all types of coals and constituents are included, the residue yield can be predicted more satisfactorily from the petrographic composit,ionthan from the carbon content. For example, fusain @), opaqne attritus (a), and anthraxylon (9), each containing 89 per cent carbon, would give vastly different liquefaction yields, although t.his result would not be predicted from tlie carbon content. The prediction of hydrogenation yields from petrography can undoubtedly be improved when an e&irnate of the nature as well as amount of the different constituents is available. For example, opaque attritiis has been found microscopically to he heterogeneous, containing substances which vary greatly in opacity. Although detailed data are lacking, it is
76
INDUSTRIAL AND ENGINEERING CHEMISTRY
reasonable to assume that the carbon content, carbon-hydrogen ratio, and difficulty of hydrogenation increase roughly with the degree of opacity. This assumption can be used to explain some of the discrepancies in Figure 7. The splint sample from the Chilton bed (No. 3 in Figure 7 and in a previous paper, 8) gave an astonishingly high liquefaction yield on the basis of its high content (80 per cent) of opaque matter. However, microscopic examination showed that an unusually high proportion of the opaque matter was brown or semiopaque. Therefore, this sample could be expected t o hydrogenate 8 more readily than 81 a3 65 87 89 CARBON CONTENT OF SPLINT SAMPLE, PERCENT attritus which is much more FIGURE 6. RELATION BETWEEN CARopaque. Probably BON CONTENT OF SPLINT SAMPLES AND YIELDOF INSOLUBLE CARBONACEOUSit is only a coinRESID- (DRYASH-FREE BASIS) cidence that unusually poor conversions were obtained with the splint samples (Table I) of high ash content. It is interesting that more drastic conditions of hydrogenation give much higher liquefaction yields (Table 111) than standard conditions (430" C. for 3 hours, initial hydrogen pressure of 1000 pounds). It is likely that semiopaque matter is the additional material liquefied by the more drastic treatment. Table IV gives the composition and yields of the gaseous products. As in previous work (6, 8) only traces of carbon monoxide and unsaturated hydrocarbons were found. The chief components of the hydrogenation gases are methane and higher saturated hydrocarbons, the latter occurring in preponderant amounts. The amount of carbon dioxide formed appears to decrease with increase in carbon content of the parent coal. Increasing the pressure and temperature of hydrogenation (from 430' to 440" C.) decreased the yield of
VOL. 32, NO. 1
TABLEIV. COMPOSITION OF HYDROGENATION GASES(IN GRAMS) Sample NO. H 1 2.51
1.99 4.40 4.65 3.00 2.50 2.88 5.17 2.16 3.91 4.73
2 3 3A 4 5 6 6A 7 8 8A
CO
CiHi
CHI
CaHe
COa
0.1 0.2 0.3 0.3 0.2
0.1 0.1 0 0.1 0.1 0.1 0.1 0.2 0.1 0.3 0.2
1.6 2.2 2.7 3.4 2.3 2.3 2.2 2.4 1.9 1.5 2.4
3.3 3.5 3.6 3.2 3.6 4.3 4.1 5.3 4.1 3.5 4.6
0.355 0.427 0.828 0.483 0.416 0.281 0.254 0.044 0.317 0.139 0.011
8.2 0.2 0.1 0.4 0.1
Has 0.461 0.112 0.152 0.111 0.230 0.202 0.061 0.157 0.025 0.005 0.006
NHa
0.001
:...
0 004 0:021 0.021 0,001 0.001 0.004 0,001
TABLEV. HYDROGEN ABSORPTION,MAXIMUM PRESSURE, AND PRESSURE DROP Vnl. "f . __. __ Sample Hydrogen No. Consumed Grams
1 2 3 3A 4 5 6 6A 7 8 8A
Maximum Pressure Lb./sp. in. Ko./sq. cm.
2510 2180 2670 ,4400 2600 2480 2540 4300 2280 2610 3600
3.43 3.95 1.86 6.05 2.94 3.44 3.06 5.53 3.78 2.03 4.07
HydrogenaPressure tion Gaas Drop a t OOC. Kg./sq. cm. Liters
176.4 153.2 187.9 309.2 182.7 174.3 178.5 302.1 160.3 183.4 253.0
30.2 38.7 12.7 41.5 22.5 30.2 27.4 45.7 33.7 20.4 35.8
33.0 28.2 56.6 59.3 41.4 36.4 38.4 66.6 61.2 48.9 69.8
Nature of Products Table VI gives the specific gravities of the centrifuged oils, which are colloidal solutions of the primary liquefaction products in tetrahydronaphthalene. Since the specific gravity of the vehicle is about 0.967 at 25' C., the solute or l i q u e f a c t i o n products must be quite dense to give solutions of the specific gravity shown in Table VI. The con~-siderable variations in 12 specific gravity probably 14 IS 20 I6 are due to differences C&RBON HYDROGEN RATIO OF SPLINT COAL in nature and concentraFIGURE 8. RELATION BETWEEN CARBON-HYDROGEK RATIOSOF tion of the For SPLINTSAMPLES AXD HYDROexample, the presence of GENATION PITCHES considerable amounts of products from spores and resins (7,8) would lower the specific gravity. Although some of the pitches (Table VII) have rather high carbon-hydrogen ratios, the ratios were always lower than those of the antecedent coals. Figure 8, which contains data from this and a previous paper (8), shows that the carbonhydrogen ratios of the hydrogenation pitches are roughly proportional to those of the parent splint coals. GRAVITIES OF CENTRIFUGED OILS TABLEVI. SPECIFIC
OPAQUE MATTER I N SPLINT SAMPLE. PERCENT
FIQURE 7. RELATION BETWEEN OPAQUE MATTER CONTENT OF SPLINT SAMPLES AND YIELDOF INSOLUBLE CARBOXACEOUS RESIDUE
carbon dioxide but increased the yield of saturated hydrocarbons. The coal (sample 1) of highest sulfur content gave the highest yield of hydrogen sulfide. Table V gives the maximum pressures, pressure drop, and hydrogen consumed.
No.
Sp. GI.
Temp.
No,
Sp. Gr.
Temp.
1 2 3A 4 5
1.006 1.022 1,002 1,024 1.013
25.5 25 24 25 24
6 6A 7
1.023 0.999 1.027 1.024
24 24 25.5 25
c.
S
e.
Table VI11 gives the composition and amounts of the dry benzene-insoluble residues. The carbon-hydrogen ratios and composition (calculated from data in Table VIII) of the organic portion of the residues are shown in Table IX. Because
77
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY, 1940
HYDROGENATION RESIDUE FROM FUSAIN,SEARON BED FIQURE 9 ( X 150)
HANDPICKED FUSAIN,SHARON BED
of errors involved in analyzing such residues ( I ) and in correcting to the dry mineral-matter-free basis, the data in Table IX are not absolutely accurate. The ratios of carbon to hydrogen are higher than those of the original coals and lower than those of residues obtained in high yield by hydrogenating fusain (6). All the hydrogenation residues from the splint coals have a similar appearance under the microscope. The individual particles are usually less than 5 microns in diameter, although they may be grouped into larger masses. Fignre 9 shows that they are smaller and more rounded than the sharply angular particles from fusain residues (8). However, both types of residues have little (probably less than one per cent) translucent material other than mineral matter; this indicates that constituents in the splints, such as spores, anttiraxylon, snd residues, were almost completely converted into liquid or soluble products. Analyses of the products obtained by distilling the centrifuged oils to about 215" c. are shown in Table X. It is evident from these data that the largest component of the distillates is the vehicle, tetrahydronaphthalene. The distillates
HYDROGENATION RESIDUE FROM SPLINTCOAL,Doaorav B m
TABLE IX. BENZENE-INSOLUBLE RESIDUES* Sample N"
A
g by Weight--N
TABLE X. COMPOSITION OF DISTILLATES Sample
No.
Distn. 7-Distilate---------. End Sp. XI.. Tar Point Amount 16.fieC. bsses
Phsnols
-
C
N
89.8 89.5
1.4 1.4 1.1 1.2 1.4 1.2 1.2 1.0 1.4 0.9
1
7.3
2
3
7.1 6.4
3A 4 5 6 6A
6.6
7
6.9 6.8 6.8 7.2 6.5
S 8A
6.0 6.4
90.9 91.3 90.1 90.7 90.8 91.1 90.9 92.2 92.3
0.8
0
S
1.3
0.2
1.5 0.8
0.1 0.1 0.2 0.3 0.2 0.2 0.2 0.2 0.2
1.7
1.4 1.0 1.0
0.5 1.0
0.7 0.3
0.3
Calorifio C/H Value Ratio Gram-cor. 9398 8369 9330 9369 9367 9386 9366 9522 9296 9243 9395
6.
0:Qb 0.967 0.965 0.966 0.956 0.965 0.966 0.958
O
i
k
Saturstea % bu d . 0.6 2.2
0.5
1.3
2.2 0.8 0.5 1.D 0.5 0
0.2
conditions. The phenol contents are roughly proportional to the liquefaction yields (Table 111). The neutral oils, consisting largely of aromatic hydrocarbons, contained traces of olefins (soluble in 85 per cent sulfuric acid). The neutral oils also contained small amounts of saturates. Since coal resins, spores, and oil algae have been observed (8) to give comparatively high yields of saturated hydrocarbons boiling below about 215" C., it is believed that the presence of different amounts of these materials in the parent coals may cause some of the variations in saturated hydrocarbon content of the neutral oil.
TABLE VII. PITCEES H
SP.5,.
15.6
0.971
have lower specific gravities and phenol contents but higher saturated-hydrocarbon contents than the corresponding distillates (samples 3, 6 , and 8) obtained under standard
No.
-Neutral
0.967
(samples3A,GA,and8A)fromtheexperimentsmadeat440"C.
Sam&
C/H Ratio
0
12.3 12.6 14.2
13.5 13.1
13.8 13.4 12.7 14.0 15.4 14.4
Acknowledgment TABLE VIII. BENZENE-INSOLUBLE RESIDUES(DRY)
8.mple No. 1 2 3
3A
4 5
6
6A 7
8
SA
Cslcd. from Ash
Found Content
E
C
N
0
S
Grama
Gro-8
%
%
%
%
%
18.6 20.4 45.8 28.5 23.7 21.6 32.6 235 26.9 51.0
19.0 21.1 47.2 32.3 24.9 23.9 34.6 25.0 28.4 65.0 42.2
2.3 3.0 3.1 2.7 3.1 2.7 2.7 2.3 2.9 2.8 2.5
34.7 75.6 70.9
0.9 1.3 1.1 0.9
...
% 9.0
1.1
2.6 3.0 2.6
0.7 0.9 1.7
1.0
4.2 4.0 4.6
1.0 1.2
34.2 15.2 21.6 31.6 18.9 25.9 29.8 41.2 20.8 30.2 39.3
38.1
80.9 72.6 64.2 61.4 50.6
60.6
60.6 52.7
0.9 0.9 0.7
0.7 0.3
3.5
6.0 6.1
4.2
1.5
1.3
1.1
0.6
0.8
Ash
The authors are indebted to H. M. Cooper of the Coat Analysis Section for proximate and ultimate analyses of the coals, residues, and pitches, and to W. A. Selvig of the Miscellaneous Analysis and Cod Constitution Section for his kind interest and criticism of the manuscript. The assistance of Hugh O'Donnell in preparing the samples of splint is gratefully acknowledged. Literature Cited (1) Abernethy, R. F., Cooper, H. M., and Tarpley. W. C., IND. Exo. CI~EM Anal. . , Ed., 10, 389 (1938). (2) Bakes, W. E.. Dept. Sci. Ind. Research (Brit.), Tech. Paper 37 rim).
INDUSTRIAL AND EKGINEERING CHEMISTRY
7%
(3) Erasmus. Paul, “Uber die Bildung und den chemischen Bau der Kohlen”, Stuttgart, Verlag von Ferdinand Enke, 1938. (4) Fisher, C. H., IND.ENG.CHEM.,Anal. Ed., 10, 374-7 (1938). ( 5 ) Fisher, C. H., and Eisner, A., IND.ENG. CREM.,29, 1371 (19371. (6) Fisher, C. H., Sprunk, G. C., Eisner, A., Clarke, L., and Storch, H. H., Ibid., 31, 190 (1939). (7) Ibid., 31, 1155 (1939). (’ ((8) Fisher, C. H., Sprunk, G. C . , Eisner, A,, Clarke, L., and Storch, H. H., Fuel, 18, 132 (1939). (9) Ibid., 18, 196 (1939). (10) Francis, W., J. I n s t . Fuel, 6 , 301-8 (1933). (11) Gordon, K., T r a n s . I n s t . M i n i n g Engrs. (London), 82, P t . 4, 348-63 (1931). (12) Graham, J. G., and Skinner, D. G., J. SOC.Chem. I n d . , 48,129T (1929). (13) Hirst, L. L., et al., IND.ENG.CHEW,31, 869 (1939). ~I
VOL. 32, NO. 1
Horton, L., Williams, F. A,, and King, J. G., Dept. Sci. Ind. Research (Brit.), Fuel Research Tech. Paper 42 (1935). Hovers, T., Koopmans, H., and Pieters, H. A. J., F u e l , 15, 233
\-_-_,.
I1 RR6)
(16) Petrick, A. J., Gaigher, B., and Groenewoud, P., J. Chem. M e t . M i n i n g SOC.S . A f r i c a , 38, 122-4 (1937). (17) Seyler, C . A., Fuel, 17, 177, 200, 235 (1938). (18) Shatwell, H. G., and Graham, J. I., Ibid., 4, 25, 75, 127, 252 (1926). (19) Storch, H. H., I N D .EXG.CHEM.,29,1367 (1937). (20) Thiessen, R., rept. presented before Fuel Engrs. of Appalachian Coals, Jan., 1937. (21) Wright, C. C., and Gauger, A. W.,Am. Mining Congr., Coal Mines Mechanization, Yearbook, pp. 381-3 (1937). PRESENTED before t h e Division of Gas and Fuel Chemistry a t the 97th Meeting of the American Chemical Society, Baltimore, >Id. Published by permission of t h e Director, U. S. Bureau of Mines (not subject t o copyright).
Evaluation of Nitrocellulose Lacquer Solvents A Study of Hydrocarbon Diluents by the ConstantViscosity Procedure V. W. WARE AND W. M. BRUNER E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
HE first paper of this series (9) described in detail the constant viscosity procedure for the evaluation of the solvent strength of nitrocellulose lacquer solvents. By this method a single value may be assigned to the combined viscosity characteristics and hydrocarbon acceptance of a solvent in such a way that a separate study of the two is eliminated, and it may be used, in turn, to relate this combined solvency value to the cost of application. This method of evaluation has been applied to a number of commercially available esters (ethyl acetate, ethyl propionate, isobutyl acetate, wbutyl acetate, isobutyl propionate, and Pentacetate) in their reaction to toluene dilution (IO). I t gives a complete picture of the reaction of nitrocellulose lacquer solvents to hydrocarbon addition throughout the entire range of dilution and affords a means of obtaining an accurate comparison of their solvent action a t the viscosity most applicable to the problem a t hand. The “dilution ratio” of a nitrocellulose solvent has been defined (1) as expressing the limit of tolerance of a solvent for a nonsolvent; but as Gardner (6) points out, the end points are rather indefinite, and considerable experience is necessary to be able to check the results. Doolittle (3) made worthwhile advances in defining the limits and the conditions under which dilution ratios should be determined, but they still remain an unsatisfactory and uninformative type of analytical procedure. Moreover, Stewart (8) reported that the inclusion of resin in the experimental formulation tends to make the end point still more difficult to check than in the case of
T
solutions of nitrocellulose alone. Dilution ratio is used in evaluation of the activity of diluents as well as solvents, and from the above considerations it is obvious why this method is still more unsatisfactory in diluent evaluation than in the evaluation of solvents. This also indicates why the constant viscosity procedure, which eliminates the dilution ratio completely and measures the action of the diluent by means of changes in the viscosity or in the solids which will dissolve a t a given viscosity, offers advantages for this purpose. The viscosity and hydrocarbon tolerance of a solvent are but two of the several important factors which contribute to the value of the material, and it is not the intention of this series of papers to overemphasize that importance. The intent is, rather, to make available to the industry certain pertinent data that give a clearer view of the subject and to point out the more obvious and logical deductions from these data. Stated briefly, the constant viscosity procedure for measuring the power of solvent and solvent-diluent mixtures to dissolve nitrocellulose involves viscosity determinations of nitrocellulose solutions in three or more concentrations in the range of spray viscosity. From these data curves are drawn by plotting viscosity against weight of nitrocellulose per 100 cc. of base lacquer. The exact solids concentration a t any viscosity within the chosen range may be obtained from the curve, and curves may be set up from experimental data in this way for any number of solvent-diluent mixtures. These values for nitrocellulose concentration a t any chosen standard viscosity are in themselves an accurate means of comparing the solvent strengths of two or more solvent mixtures since they combine in one set of values all of the information which previously has required both dilution ratio and viscosity determinations. However, the usefulness of the data may be extended much further; by plotting the solvent-diluent composition against nitrocellulose or solids concentration, as obtained from the first set of curves, a second curve may be obtained (9, IO) from which the ratio of solvent t o diluent which will dissolve a given amount of nitrocellulose a t that viscosity may be read. Then, knowing the apparent value of the diluent and of the solvent in use as standards, the comparative value of the solvent or diluent under test may be established.
