REACTIVITY of SOLID FUELS *
Ostborg ( 3 ) . Although the selected 40-60 mesh samples may show small differences in other characteristics from the rejected finer sizes, they may be expected to have reproducible specific surfaces and other physical characteristics of the sample bed. The reactivity indices are plotted against volatile content on the dry ash-free basis in Figure 1. It should be noted that the reactivity is highest for the lowest reactivity indices. The anthracites are obviously the least, and the lignites are the most reactive coals. I n the middle-volatile range, however, there is little variation of reactivity with volatile content. The curves in Figure 1 are given by the equations:
Ti, * 8.0’ C. = 229.7 T75 * 11.4’ C. = 272.1
A. A. ORNING Coal Research Laboratory, , Carnegie Institute of Technology, Pittsburgh, Pa.
Reactivity indices are presented for sixty-eight coals and thirty-five cokes. The indices, varying inversely with reactivity, are found to correlate with the volatile content on the dry ash-free basis. They are highest for cokes, decrease rapidly with increasing volatile in the anthracite range, are relatively constant for the medium-volatile bituminous coals, and again fall sharply for the highvolatile coals and lignites. Other factors probably influence the reactivity, but they are not disclosed by the available data. While the precision of the test is high, the details of thermometric procedure are shown to influence the absolute scale of reactivity indices.
- Q.01041 (V - 27.5)3 - 0.01338 (V - 27.5)3
(2)
(3)
The probable errors in these equations are the ranges above and below the empirical curves within which there is an ev& probability of finding the reactivity indices for a given coal. Since a study of duplicate tests has indicated a precision of measurement of about *2’ C., there must be factors other than the volatile content which are responsible for the variation in reactivity index. A study of proximate analysis data has failed to show significant correlations other than that with volatile, although there is a possibility that the reactivity indices increase with ash content. This would be expected, provided the ash did not exert a catalytic influence. INDICES FOR COKES
Reactivity indices are available for thirty-five cokes, but these data must be broken into two groups, on the basis of methods used. for determining their volatile contents. Equations 4 through 9 apply to the first group, containing twenty-one cokes (Figure 2 and Table 11),for which the volatile content on the
ONSIDERABLE interest has been shown, both by producers and consumers of coal, in the Coal Research Laboratory reactivity test since its first publication in 1937 ( 8 ) . The test, originally proposed as a “modified ignition point method” for the measurement of reaction rates of cokes with oxygen, has been extended to all ranks of coals in addition to cokes. Although the test is still undergoing development and the data obtained may be subject to correction of absolute scale, they offer the most comprehensive information on the reactivity of American coals and cokes available at present. The test procedure (3, 3) is, briefly, to heat the sample of coal or coke in air, oxygen, or some known mixture of oxygen and nitrogen, and to determine the sample temperature and its rate of rise at the instant when the furnace and the sample are at the same temperature. At this moment it is supposed that there is no heat flow either to or from the sample. Under these conditions the rate of rise becomes a measure of the reactivity of the sample. By using different rates of power input to the furnace or different oxidizing gases, i t is possible to obtain different rates of rise a t various sample temperatures. These rates may be correlated by the equation:
C
I dT log- - = A P dt
+ B-T
where T = absolute temperature p = partial pressure of oxygen in oxidizing gas From this equation the reactivity indices, TI5 and T,a, are determined as the temperatures at which the rates of rise in pure oxygen would be 15’ and 75’ C. per minute, respectively. INDlCES FOR COALS
Table I gives the proximate analyses and reactivity indices for sixty-eight coals ranging in volatile matter on the dry ashfree basis from 3.5 to 48.2%. The apparatus and procedures for determining the indices, specifically the positioning of thermocouples, are essentially those described by Sherman, Pileher, and
Figure 1. Reactivity Indices, TI^ and TTS,for Coals as a Function of Volatile Matter Contents on Dry Ash-Free Basis
813
INDUSTRIAL AND ENGINEERING CHEMISTRY
814
dry ash-free basis, V , and the ash fusion temperature, F , were determined by the A.S.T.M. procedure:
Tu
* 15.5'
- 29.27 V
T76
f
- 28.51 V
Ti6 Ti6 TIS
f f
f
T76
f
C. = 530.0 17.1' C. 593.1 10.6' C. = 498.9 17.0' C. 562.2 9.2' C. 600,7 11.7' C. = 792.4
- 243.9 log V - 233.6 log V - 240.4 log V - 0.04261 F - 225.6 log V - 0.09604 F
(4) (5) (6) (7) (8) (9)
The dashed curves in Figure 2,are given by Equations 2 and 3 for comparison with the coals; the solid curves are given by Equations 6 and 7. Linear Equations 4 and 5 fit the experimental points almost as well, but they cannot approximate the curvature that wofild be expected in the range of petroleum cokes whose volatile contents lie in the same range as the anthracites, where the empirical curves for the coals show their maximum curvature. The logarithmic functions are capable of forming smooth extensions from the empirical equations given for the coals and yet curve sharply upward, as indicated for the low-volatile fuels. However, the logarithmic equations were fitted to the data on cokes with no attempt to join smoothly with the data on coals. Equations 10 through 15 apply to the second group, containing fourteen cokes (Figure 3 and Table 111),for which the volatile contents were determined by a dry distillation test in which the samples were heated to about 960" C. in a closed tube and the yields of various gases were determined:
Ti6 13.4" C. = 544.5 T?5 * 14.1' C. 582.9 Tis + 13.9' C. = 465.3 T75 * 13.9' C. = 529.8 Tis * 13.2' C. = 294.7 T,i * 13.4' C. = 374.0 f
- 136.1 V - 89.1 V - 58.30 log V - 40.12 log V
- 46.28 log V + 0.0697 F - 29.08 log V + 0.0637 F
(10)
(11) (12) (13) (14) (15)
The quoted volatile contents are the total yields of volatile less the carbon dioxide and water, and are given as percentage of dry ash-free coke. The quoted Volatile contents for these fourteen cokes are all less than those given for the first group of cokes, but "this results only from the differences in analytical procedure and calculation. The cokes of the two groups, of similar reactivity indices, are not fundamentally different. Again for comparison with the coals, the dashed curves in Figure 3 are given by Equations 2 and 3, and the solid curves are given by Equations 12 and 13. The data are represented equally well by linear Equations 10 and 11; but thelogarithmic equations are preferred since, by analogy with the other fuels, a more extended range of volatile content would have demanded a curved rather than a linear dependence upon volatile content. While Equations 8,9,14, and 15, showing the dependence upon ash fusion temperature F,have been included, there is considerable question as to their validity. For each group of cokes the correlation between ash fusion temperature and reactivity indices appeared to be significant, and the equations for the individual reactivity indices are consistent with one another. However, between the two groups of cokes there is an inversion in algebraic sign of the coefficient of ash fusion temperature. This would indicate either: (a) One of the two sets of equations is not valid, the improbable circumstance having occurred that unknown factors had caused the apparent trend in the limited sample; or (b) there is a fundamental difference between the two groups of cokes which is not believed to be true. Since the most plausible reason for any correlation with the fusion temperature arises from the common influence of iron, both on the ash fusion temperature and catalytic effects, a correlation was sought between the reactivity indices and iron, either as a per-
Vol. 36, No. 9
TABLE I. REACTIVITY INDICES Seam Wharton Cooper No. 4 Merrimac Primrose No. 6 Merrimac McAlester Spadra Lsnghorne Pocahontas No. 3
O F CO.4LS
Tis,
Tis,
County V.bLa Ashb B.T.U.: OC.d "C.d Luaerne, Pa. 3 . 5 8 . 7 14,841 405 470 Luzerne Pa. 5 . 8 9 . 8 14,945 312 416 Schuylkhl, Pa. 8.5 7 . 4 15,335 271 333 315 416 Montsomsry, Va. 10.7 18.7 Lewis, Wash. 1 0 . 8 17.9 15:OBO 292 374 Montgomery, Va. 11.8 14.0 Joi!n;on, Ark. 14.4 Montgomery, Va. 15.0 McDowell, W. Va. 1 6 . 3
Po e Ark
. , .,
15.2 10.9 10.7 14.8 5.6
15,742 15,832
259 258 273 255
298 305 317 305
15.769
254
285
Pocahontas No. 4 Pocahontas Np. 3 Upper Kittaning Pocahontas No. 3 Pocahontas No. 4
McDowell, W. McDowell, W. Cambria, Pa. McDowell W McDowell: W:
Va. 16.6 Va. 1 7 . 3 17.7 Va. 18.2 Va. 18.2
5.6 5.3 8.7 6.9 7.1
15,659 15,739 15,873 15,787 15,752
245 239 225 234 238
295 282 269 280 286
Beckley Upper Freeport Lower Kittaning Upper Kittaning Lower Kittaning
hlcDowell W. Va. 18.9 Cambria, Pa. 19.0 Cambria P a 19.7 Carnbria' Pa' 19.7 Cambia: Pa: 21.7
7.4 7.3 7.0 7.4 5.8
15,645 15,740 15,777 15,484 15,530
242 228 235 232 236
292 263 283 272 276
Sewell Sewell . Lower Freeport Carev Carej.
Raleigh W. Va. Wyomiig, W. Va. Cambria, Pa. Buchanan.Va. Buchanan; Va.
22.0 23.2 23.6 25.2 25.6
3.1 6.8 7.2 8.7 9.4
15,748 15,780 15,534 15.701 15;700
228 216 229 230 228
264 248 266 277 267
Sewell Sewell Miller Lower Kittaning Upper Freeport
Fayette W. Va. Fayette( W. Va. Fayette: Pa. Indiana, Pa. Indiana, Pa.
26.0 27.0 28.9 29.5 30.9
5 2 3:7 10.1 8.0 9.0
15573 15:619 15,507 15805 15:567
226 227 225 225 228
264 270 258 262 269
Upper Banner Up er Banner B u t Creek Upper Freeport Lower Fregport
Dickenson Va Dickenson' Val Buchanan,'Va. Indiana Pa Clearfieid, Pa.
31.0 31.0 31.8 32.9 33.3
7.1 5.6 5 9 8.6
15,720 15,710 15610 l6:055 15,558
233 230 225 230 231
271 272 260 266 268
Powellton Eagle Eagle Clintwood Chilton
Logan W . V s . Logan' W. Va. Logan: W. Va. Buchanan Va. Logan, W:Va.
33.4 34.1 34.7 35.0 36.5
3 7 5:2 4.0 5.3 3.9
15 162 15:342 15,469 15,490 15,423
217 226 221 217 217
269 271 263 256 257
Eagle U er Freeport EPdhorn No. 3 Island Creek Pittsburgh
Logan W. Va. ArmsGong Pa. Floyd, Ky: Logan W. Va. Fayetie, Pa.
35.7 36.4 37.0 37.1 37.1
6.0 8.9 3.5 5.9 7.6
15,450 15,296 15,101 15,397 15,353
229 229 209 223 229
265 269 251 265 283
Powellton Fayette, W. Va. Ldwer Island Creek Logan, W. Va. Chilton Logan W Va. Dorothy Boone' W: Va. Island Creek Logan: W. Va.
37.3 37.4 37.5 38.0 38.1
4.3 4.6 3.1
8.1
15,532 15,380 15,342 15,260 15,310
226 210 215 215 223
272 247 258 256 264
Chilton Darby Elkhorn No. 2 High Splint Cedar Grove
Boone W Va. Harlad ky. Floyd, Harlan Mingo,'W. Va.
38.2 38.5 38.5
7.5 4 5 . 74
15,160 14,950
212 200 202
38.8 39.0
3.5 6.5
14,920 15,210
201 216
251 241 239 233 258
Belmont Cedar Grove Harlan Island Creek Illinois No. 6
Kanawha W.Va Kanawha: W, Va: Harlan, Ky. Logan,,W. Va. Franklin, Ill.
39.2 39.5 39.7 39.9 40.3
7.3 6.9 6.1 5.1 9.8
15,080 15,180 14,940 15,213 14,572
210 211 206 214 183
244 246 249 262 205
Ron Air No. 2 Island Creek Illinois No. 5 Illinois No. 6 Illinois No. 6
Fentress, Tenn. Lo an W. Va. G a tatin. 111. Henry Ill. Macodpin, Ill.
40.9 41.3 43.1 44.0 45.0
11.9 4.9 10.0 11.0 11.9
14,950 15,211 14,734 14,386 14,025
211 212 209 167 165
250 265 240 180 178
Noonan Noonan Coteau
Burke N Dak Divid;, N. Dak. Ward, N. Dak.
46.1 47.0 48.2
12.8 11.0 6.1
12,140 12,552 11,850
171 174 178
205 202 207
k8;.
8:1
6.0
Percentage volatile on dry ash-free basis. Percentage on dry basis. B.t.u. per pound of dry ash-free coal. d Differences less than 5' C. are not considered significant. a
b
C
centage in the ash or in the coke, but no significant correlation was found. This agrees with the finding that ferric oxide added to coke had no appreciable effect on its reactivity (1). A catalytic influence of alkali in the ash might be expected, but for the second group of cokes, for which the requisite data were available, no significant correlation was found. The significant difference in the two groups of cokes lies in the methods used for the determination of volatile contents. It is probable that the A.S.T.M. procedure would give the higher values when used on the same cokes. It is also possible, in this procedure, that an increased loss of weight might be due to leak-
4
September, 1944
INDUSTRIAL AND ENGINEERING CHEMISTRY
815
of oxygen, as indicated in Equation 1. As applied to cokes, it is possible with a single oxidizing gas to obtain the rates of rise over a considerable temperature range. This was the basis for the original evidence (9) for the validity of Equation 1 and was used to show that, in the presence of certain added catalysts on cokes, the assumed first-order dependence upon oxygen concentration was not valid (I). The attempt to prove the validity of Equation 1 for a bituminous coal by making a series of determinations in different partial pressures of oxygen (3) is subject to criticism. Although the experimental VOLATILE MATTER, PERCENT VOLATILE MATTER, PERCENT data, plotted according to Equation 1, gave B straight s , Twenty-one Cokes as Function of Volatile Figure 2. Reactivity Indices, TUand T ~ for line, the temperature ranges Matter Contents on Dry Ash-Free Badis, as Determined by A.S.T.M. Procedure for individual oxidizing gases were so limited that it is impossible to s he individual lines were coincident. The fact age of air into the crucible and consequent burning in an amount that the ex ental points fell close to a straight line may correlated with the reactivity of the sample. This would affect be more a characteristic of the apparatus than of the fuel. the correlation with reactivity in the direction found. On the basis of preliminary data in a new type of furnace now ?RECISION OF METHOD being developed, it appears that for lignites the order is more The precision of measurement was somewhat poorer with cokes than with coals, approaching * 10' C . for the highest reactivity indices. As with the coals, it is probable that faotors OF COKESOF GROVP 1 ABLE 11. REACTIVI INDICES other than volatile content might correlate with the reactivity indices; but these cannot be disclosed without more accurate data, particularly on volatile content as well as on reactivity index. The remarkable conclusion is that, for suck widely div e r g e n t 'fuels as cokes, anthracites, bituminous coals, and lignites, a t least to a first-order approximation, the volatile content determines the reactivity index. Other f a c t o r s undoubtedly exist, but they c a n n o t b e determined without further i m p r o v e VOLATILE MATTER, PERCENT ment in the procedure and probably also in the measurement of relevant physical and chemical properties of the fuels themselves. There is, more, over, considerable difficulty in proving the general vaFigure 3. Reactivity Indioes, TI& lidity of the asand T76, for Fourteen Cokes as a s u m e d first-order Function of Volatile Matter Contents on Dry Ash-Free Basis, as dependewe u p o n Determined by SpeOial Tube Test the partial pressure
Volatile,
%"
0.73 0.76 0.82 0.86 0.87 0.87 0.88 0.91 0.96 0.98 0.99 1.01 1.04 1.05 1.07 1.10 1.30 2.12 7.98 8.08 11 .OB
Ash Fusion Temp., O C. 2365 2386 2700 2365 2410 2450 2277 2263 2340 2P71 2265 2700 2263 2287 2700 2270 2340 2417 2000 2700 2700
7 Ash on d r y Basis 3.60 3.65 8.50 3.53 4.33 6.55 3.73 3.65 3.58 3.80 3.75 8.27 4.10 4.45 8.40 4.48 3.83 5.83 0.43 0.33 0.30
TIS C.b 544 557 510 493 493 505 512 516 496 503 504 484 499 502 501 481 481 423 312 248 235
Tis C.b 613 615 554 555 556 556 582 561 567 581 562 542 56'1 573 547 556 551 515 413 301 292
On dry ash-free basis. 10" C. not considered significant.
b Differences less than
INDICES OF COKES OF GROUF 2 TABLZI 111. REACTIVITY
Volatile,
%"
0.033 0.039 0.113 0.170 0.262 0.306 0.365 0.358 0.372 0,398 0.449 0.536 0,540 0.549 a
Ash Fusion
0
Ash on
Temp., C. &y Basis 2669 8.25 2627 9.80 IO.46 2756 2687 10.47 2434 9.50 11.87 2672 2320 9.63 11.29 2657 2332 8.81 2597 9.78 2553 9.87 2545 9.39 8.57 2471 2484 8.39
Fen08 In Ash 12.66 9.55 10.56 10.27 16.06 8.40 9.84 9.70 10.57 9.41 9.99 9.70 9.77 9.26
Tis,
C.b 544 531 551 542 474 506 503 487 480 465 496 499 453 484
Less carbon dioxide and water on dry ash-free basis. loo C. not considered signifioant.
b Differences less than
Ti5
' Cb.
586 572 598 581 534 569 547 518 535 528 559 567 519 549
&
INDUSTRIAL A N D ENGINEERING CHEMISTRY
816
nearly zero and increases toward one with decreasing volatile content. Such a change in the character of the reaction may be due either to the differences in rank of the fuels or to the different temperature levels within which the rates are measurable. I n addition there is a practical difficulty in thermometric procedures. The reactivity indices depend critically upon the determination of that instant at which there is assumed to be no flow of heat to or from the sample. I n a particular case, the assumption that a single thermocouple of the pair used to determine this conditon was in error by 1’ C. resulted in a 10’ difference in a calculated reactivity index. The furnace thermocouple is placed in contact with the outer surface of the tube holding the sample. Since the temperature is rising, there must be a net flow of heat into the wall of the sample tube a t all times. At the instant when the temperatures on the outer surface of the tube and in the middle of the sample are identical, there p u s t be a minimum temperature within the tube wall. This must be true, otherwise the tube wall could not be rising in temperature. Under these conditions a portion of the heat required to heat the sample tube must arise from the heat released from the sample. This is contrary to the original assumption that identity of temperature of sample and furnace thermocouples corresponded to zero heat flow to or from the sample. However, the portion of the heat taken from the sample may be relatively constant. This means that the procedure is in error due to the inclusion of an unknown portion of the heat capacity of the sample tube together with the heat capacity of the sample; the result is an error in absolute scale of reactivity indices. I n spite of these criticisms, the reactivity indices have considerable value. Unlike ignition points which are as much a function of the physical environment as they are of the reactivity
Vol. 36, No. 9
of the sample, the reactivity indices do give a measure of the reactivity of the sample at different sample temperatures. Even for the low-rank coals where there is greatest doubt as to firstorder dependence upon oxygen partial pressure, TISdoes not involve much extrapolation from the experimental points and gives a measure of the reactivity in oxygen. Likewise, T16involves small extrapolations from the experimental points in air, and since the ratio of 75 to 15 is approximately that of the partial pressure;: of oxygen in pure oxygen and air, 2’76 could be interpreted as TI6 measured in air. It is probably for these reasons that such remarkably good correlations are found between the reactivity indices and the volatile contents. The different slopes found for 2’16 and for T76 are indicative of the dependence of the mechanism of reaction upon the rank of the fuel. ACKNOWLEDGMENT
The experimental data presented in this paper were obtained by J. J. S. Sebastian, a member of the staff of the Coal Research Laboratory prior to August, 1942. Grateful acknowledgment is here made to those who supplied the samples and analyses for the work reported in this paper. LITERATURE ClTED
(1) Sebastian, J. J. S.,Div.of Gas and Fuel Chem., A.C.S. meeting,
.
Boston. 1939. .. ~~. (2) Sebastian, J . J . S.,and Mayers, M . 9., IXD. ENG.CHEM.,29, 1118-24 (1937). ( 3 ) Sherman, R . A . , Piloher, J. M ., and Ostborg, H . N . , A m . SOC.
Testing Materials, Bull. 112, 23-34 (1941). in part before the Division of Gas and Fuel Chemistry at the 106th hfeeting of the AMEnICAN CHEXICAL SOCIBTY, Pittsburgh, Pa.
PRESENTED
Solvent Dehydration by Salting Out 0 J
PREDICTION OF MAXIMUM DEGREE OF DEHYDRATION
H. P. MEISSNER AND CHARLES A. STOKES Massachusetts Institute of Technology, Cambridge, Mass.
T
HE problem of removing water from aqueous solutions of
organic solvents is often encountered industrially. Such dehydration is most frequently accomplished by distillation, which may be carried out at, above, or below atmospheric pressure, and with or without the addition of an entraining agent. It is also possible to dehydrate by other methods, such as freezing and filtering out water crystals, reacting the water chemically with materials such as lime, or adsorption of the water on materials such as silica gel. Another dehydration procedure, often mentioned in the literature ( 1 ) and perhaps more frequently used in the laboratory than in industrial plants, is that known as salting out. This involves bringing the wet solvent in contact with some substance, usually an electrolyte, which has the power of withdrawing some of the water present to form a second phase which can then be removed by decantation. The “salting out” of ether by addition of sodium chloride to a solution of water in ether may be cited as an example. The dehydrating substance may be added either as a solid or as a concentrated aqueous solution, this second method being more easily adapted to large-scale continuous countercurrent operations. The addition of such dehydrating substances is advantageous only in those cases
where the possibility of forming a water-rich and a solvent-rich layer exists. Some methods of dehydration may give greater “clean-up” than others. I n industry, that combination of methods is normally chosen which accomplishes the desired result at minimum cost. Dehydration by a salting out process, used either alone or perhaps in combination with a distilling operation, often shows real cost advantages. The object of this paper is to discuss some of the principles of dehydration by salting out and to illustrate them with the system methyl ethyl ketone (MEK), water, and salts. INDUSTRIAL APPLICATION
Dehydration by salting out may be accomplished either in batch or continuous-flow operations. Batch operation might involve agitating the wet solvent either with the dehydrating substance or with an aqueous solution of this substance (hereafter referred to as a “brine”). Similarly, flow operations would involve passing the wet solvent through a bed of the substance (if a solid) or possibly flowing the wet solvent through a tower coun-
