Solvent Action of Liquid Propane On the Pentane-Soluble Fraction of a High-Temperature Bituminous Coal Tar C. S. KUHN, J R . , ' Carnegie Institute of Technology, Pittsburgh, Penna.
liquid-liquid system formed with liquid propane and the pentane-soluble fraction of a high-temperature bituminous coal tar.
The use of selective solvent action in the separation of complex mixtures has assumed considerable technical importance in recent years. A study has been made of the liquid phases formed by the action of liquid propane on the pentane-soluble fraction of a high-temperature bituminous coal tar. As the ratio of propane to tar is increased there is a n increase in average density, refractive index, and molecular weight, and a decrease in hydrogen-carbon ratio of the extract, and corresponding changes i n the residue. The separation is largely on the basis of molecular weight, but a t high tar-propane ratios there is some evidence that alkylated cyclic structures have been preferentially extracted. In general, there is a tendency for oxygen, nitrogen, and sulfur compounds to concentrate in the residue.
Experiment a1 The coal tar was obtained from the Clairton plant of the Carnegie-Illinois Steel Corporation, where it was made by high-temperature carbonization of a blend of bituminous coals in the Koppers type by-product coke ovens and subsequent,ly topped to 170" C. to remove light oil and moisture. I n order to obtain a material sufficiently fluid for batchext'raction with liquid propane, and to eliminate the precipitation of pitch in the liquid-phase pressure extractor, the coal tar was first treated in the following manner: The tar, after tTeighing, was dissolved in two thirds its volume of c. P. thiophene-free benzene, and the solution sprayed under 2.8 kg. per sq. cm. (40 pounds per square inch) pressure through a Sprayco turbine nozzle into an excess ( 5 to 1) of pentane (commercial petroleum product, boiling point 34-40 C.),while the pentane was subjected to vigorous mechanical agitation. A considerable quantity of pitch ("primary precipitate") was precipitated by this treatment. The extracted material was then treated with five times its volume of pentane to precipitate an additional quantity of pitch ("secondary precipitate"), giving an extract which was called "pentane-soluble coal tar" and which was used later in the experiments with liquid propane. In three such runs 34 kg. of the original coal tar were extracted with a yield of 38.2 per cent of pentane-soluble material. The properties of the original tar and its solvent extraction products are shown in Table I, and data from the fractional distillation of the original tar, t'he pentane-soluble portion, and a propane extract in Table 11. The fractional distillations were made using a 30-em. Hempel column attached to a 100-cc. round-bottomed flask. The average molecular weights gii.en in Table I were determined cryoscopically in diphenyl (9). Prior to extraction of the pentane-soluble tar with liquid propane, yolumetric estimat'ions of the phase point and the per cent extracted \?-ere obtained from measurements a t room temperature in a series of eight sealed tubes containing yarious ratios of the two materials. The results of this work defined the limiting conditions in the two-phase system and shoJyed that it was physically adaptable to a phase analysis in the customary manner. Extractions of the pentane-soluble tar a t 30", GO", SO", and 90" C. were conducted in a specially designed liquid-phase pressure extractor illustrated in Figure 1. O
F
RACTIONATIOS of complex mixtures with selective solvents has long been a valuable analytical procedure, and has assumed considerable technical importance in recent years, notably in the petroleum industry. Since such a procedure avoids high temperatures it appeared that it might be of special value in the fractionation of coal tar. Previous workers have investigated the action of many of the common organic solvents on coal tar, and have shown that the lon-er paraffin hydrocarbons are particularly effective as pitch precipitants (2-4, 6, 8). It has also been claimed ( 5 ) that by use of solvents a separation can be effected of hydrocarbon structures from those containing other elements, such as oxygen, nitrogen, or sulfur. This work and the successful use of liquid propane for deasphaltizing petroleum (1, 11) have directed attention to the possibilities of this particular paraffin hydrocarbon for fractionating coal tar. The following report is concerned primarily n ith the experimental details and results obtained in a study of the 1
Present address, Magnolia Petroleum Company. Dallas, Texas.
O F BY-PRODUCT COALTARAKD ITSSOLVENT-EXTRACTION PRODUCTS TABLEI. PROPERTIES u - t . 7"of
Designation 1 By-product coal tar
2
Primary precipitateb
3
Secondary precipitatec
4
Pentane-soluble t a d
5
Propane-soluble tar
6 Precipitate from propane
Source Clairton Plant of Carnegie-Illinois Steel Corp. From treatment of benzene solution of (1) with excess pentane From treatment of benzene- pentane-soluble material with pure pentane From treatment of benzene- pentane-soluble material with pure pentane From extraction of (4) with excess propane (Expt. 5 , Table 111) From extraction of (4) with excess propane (Expt. 5 Table 111)
86
0ri:lnal Tar
1101. Wt.
C
100
...
26.2
, ,
0
Density at 25' C.
%
H %
%
%
70
89.30
5.45
1.02
0.66
3.57
1.166
.
88.41
5.16
1.16
0.02
4.65
1.20 1.176
S
S
(Did.)
5.6
...
87.74
5.28
1.20
0 59
5.19
38.2
192
90.45
6.45
0.63
0.63
1.84
1.084
27.5
180
90 88
6.57
0.43
0.58
1.50
1 057
10 7
250
90 06
5.70
0 85
0.82
2.Si
1.150
FEBRUARY 15,1940
ANALYTICAL EDITION
The extractor, which consisted of a chrome-molybdenum steel pressure bomb of 3.4 liters capacity having a high-pressure Pyrex sight glass mounted above the head to permit observance of the liquid interface during discharge operations, was suspended by trunnions on roller bearings in an electrically heated constanttemperature oven. One trunnion was connected with the drive of a 0.25-horsepower electric motor equipped with speed-reduction gears for revolvin the extractor a t 32 r. p. m.; the other trunnion was drilled, t o carry thermocouple leads from the extractor to a commutator, thus permitting temperature readings while the extractor was in motion, The oven was built in two sections, the upper half being hinged and counterbalanced to allow complete access to the extractor. It was insulated with 7.5 cm. (3 inches) of Sil-0-Cel between an outside wall of sheet iron and an inside wall of Transite, and was equipped with socket wrenches for remote control of the extractor valves, a small circular door in the base through which discharge lines could be connected to valves A and B, and a double glass window through which the sight glass was visible when illuminated by an ordinary 60-watt light and reflector. The oven contained two 1000-watt circular heaters, an electric fan, and a de Khotinsky thermoregulator for maintaining a constant temperature in the air bath. The liquid propane, which was a commercial grade and reported to contain less than 1.5 per cent of ethane and no butane, boiling point -44.5" C., was measured into the extractor from a calibrated steel buret fitted with a gage glass and top and bottom needle valves. Connections of the buret to the extractor or to a commercial cylinder of propane were made through a valve block, using heavy-walled copper tubing. Both the buret and the valve block were mounted on vertical supports by means of adjustable clamps.
87
liquid phases. The bomb WBS then allowed to remain in an inverted position for 5 hours to permit drainage and division of the two layers prior to discharging the contents through brass lines, attached to valves A and B, into glass flasks. The flasks, in turn,
4
B
2
-
I
S
I
D L
Extractions with liquid propane were carried out as follows:
- 1 .
LA-
Weighed samples (100 to 300 grams) of the pentane-soluble tar were placed in the extractor, and the buret was connected from its top and bottom valves to extractor valve, A , and threaded inlet, U,respectively. The extractor and lines were then partially evacuated on a water pump, and after equalization of pressure in the apparatus by escape of propane vapor from the buret, the desired quantity of liquid was run into the bomb; the valves were closed and transfer lines disconnected, and the extractor was brought to the proper temperature. Agitation, by revolving the bomb, was continued for at least 16 hours at constant temperature to ensure equilibrium of the two
L I Q U I D-P H A S E PRESSURE EXTRACTOR
FIGURE 1. LIQVID-PHASE PRESSURE EXTRACTOR
TABLE 11. DISTILLATION DATA OX BY-PRODUCT C O A L TARAND PENTANE A N D PROPASE EXTRACTS Boiling Range, C. By-product coal t a r , grams Pentane-soluble coal tar, grams Propane e'ttract, Expt. 5 , grams yo of fraction Soluble in pentane Soluble in propane
To 170'
170;
36 36
9; 87
235; 235 270 1.1 10.8 7.3 0 4 10.3 4.4 0.4 9.4 3.7 60 50
TABLE111. DATAFOR Expt. NO.
6 4
3 1
2 5
To 350' 30.5 25.2 20.8
89 64
82
THE
68
Aboye
350 69.5 13.0 6.7 18
9
Liquid Propanc Grams cc.
307.2 209.4 202.3 214.0 205.7 99.9
ll0.E 112.9 147.6 241.4 523.8 712.3
227 231 303 495 1073 1460
Liquid Propane Weight Ratio)
-
Upper Phase-
Propane Qrams 30' Isothermal
2.7; 1.85 1.37 0.89 0.392 0,140
36.2 73.5 116.2 215.l 510.8 710.n
60" Isothermal . ~ ~
12
E
7
10 11
304.0 202.6 207.8 197.3 105.6
288 192 197 187
281.1 263.5 200.1 202.1 101.9
270 252 192 194 97
310.4 309 9 205.5 138.8
300 299 198 134
100
112.0
258 252
2.72
557
0.86 0.485 0.175
147.6 242.9 458.6 628.3
317 386 636 1201 1645
2.32 1.78
124.6 201.2 254 5 792.0
366 592 745 2320
109.5 241.7 406.1 603,3
936 1390
.M,N . Thermocouple wells
P. Propane inlet tlibe Q. Washers R. Filter ring S. Protecting screens .'2 Pyrex sight glass U. Threaded propane inlet W. Dr.illed hole for thermocouple leade X . Roller bearings Y . Commutator 2. Trunnion
SYSTEM:PENTANE-SOLUBLE COALTAR-LIQUIDPROPANE Tar -__
Pentane-Soluble Coal T a r Grama Cc.
284 194 188 198 190 93
270; 350 11.3 10.1 7.3
A , E . Hoke valves c. Control valve D. Propane inlet valve E. Inner pressure head F. Outer cap G. Body H. Thrust ring J. Thrust bolts K. Support and valve block for sight glase L. Packing nuts
1.85
% of
Tar Grams
total tar
18.7 35.9 49 0 71.4 104.5 72.0
6.1 17.1 24.2 33.3
---
Louer Phase-
% of
Tar Grams
total tar
74.6 39.4 30.8 25.7 13.0 1.8
250.2 173.4 154.4 141.4 98.4 24.7
94.5 82.8 76.3 66.1 47.8 24.7
5.5 18.8 37.0 50.4
86.6 42.5 26.4 14.5 2.6
286.9 163.5 129.3 94.0 28.0
94,4 80.8 62.3 47.6 26.5
72.9
19.2 22.7 39.9 50.0 72.1
63.5 53.5 23.1 16.1
227.6 201.5 115.8 97.0 27.2
81.0 76.6 57.9 47.9 26.9
16.1 60.6 77.8 91.0
5.2 22.5 37.11 65.5
103.5 65.1 25.5 5.9
294.3 236.4 122.3 46.5
94.8 76.4 59.5 33.5
50.8
72.1
Propane GTams
~ ~ ~ . .
25.4 67.0 215.3 391.6 600.7
16.7 38.2 76.9 99.6 74.0
70.1
80' Isothermal
li 15
13 14 16
22 21
20 23
121.1
0.826
57.6 94.1 219.8 442.5 625.5
0.441 0.161 90' Iaothermal 2.49 21.5 1.53 133.9 0.809 228.5 0.175 786.1
54.1 59.8 79.9
101.1
2.8
INDUSTRIAL *43D ENGINEERING CHERIISTRY
88
TABLE IV.
VOL. 12, NO. 2
PROPERTIES OF EXTRACTS A K D RESIDUES Extracts
Temp.
c.
Eupt.
Residues--
Molecular wight
D?5
0.868 0.038 0.022
1G5 180 170 16:
Le29
0.880
155
1.638
0.845 0.001 0.850
H/C
KO.
Tar/Progane
D?b
6 5 12 11
2 77 0 , 140 2.72 0.175
1,033 1 . 057 1.054 1,064
102,;
0 . !I01
1 G32
17
2.32
1.049
16
0.161
1.061
22 23
2.490.lIJ
1.051 1,065
11%
l.G3!I
1.639
1.630 1.635
7
nlolecular
g
H/C
1.084 1 . 1.50 1.086 1 141
1.6.52 1.670
1.651 1 .ti6
0.810 0.760 0.847 0.77"
190 230 18.5 22.5 230
li0 10:
1 092
1 .f j j 8
0 821
163 173 175
1 . 132 1 083 1 13G
1.66 1 ,ti.51 1.66
0.74; 0.883 0.787
1so 225 2;: I !IO
I1
weight
"40
the Yolunie of the bomb, 3400 cc., and the volumc of the tar. Having thus obtained a value for -11at room tpmper:bture, it was possible to calculate the value of 2' for the temperature at n-llich the run was mnde.
At go", near the critical temperature of propalie, the valueb for 21, calculated in this n-ay, were fouii(l to he greatly in error, probalily because of mpitl vapor pres.ure cliangei a d comequeiit clianges in vapor density. -1number of tiirect tleterininations of the volume of liyuitl propane as.sociatet1 with tlie phases,at various tar-propane ratios am1 a t 30°,600, a 1 ~8O"C;., 1 gave rallies in reasonaide agreeinelit with t h e calculated hy tlie abo\-c equation. The fraction of the tar i i i the upper pliase is plotted as a fuiictioii of tar-propane ratio for 30°, tiOD, 80") and 00" C. in Figure 2 . The solubility of the tar i i i liqiiitl propane is shstantially independent of temperature over the range covered 11y this investigation. TAR/ LIQUID PROPANE
FIGURE2.
FRICTIONOF TARIN CPPER PHISC1s P I'rrvcrrov OF TAR-PROPA\E R~TIO
were coiinected n-it11 glass U-traps and a standard n-et-test gas meter for measuring the propane. Careful regulation of valves il and C or B and C permitted an exact separation of the tlyo liquid phases. The portions of the pentane-soluble tar entering the upper and lower phases were collected, weighed, and identified by physical properties.
Results and Discussion Data for the two-phase system formed with pentane-soluble coal tar and liquid propane are shown in Table 111. The amount of liquid propane present in tlie runs a t 30", 60", and 80" C. was determined indirectly by a method TThich is described below. I n the measurements a t 90" the amount of liquid propane associated with the lower phase was determined direct,ly,by passage, after gasification, through a standard wet-test meter. The total liquid propane 17-as determined in a similar maimer and that associated with the upper phase obtained b y difference. The gas volumes read from the standard wet-test meter were converted to cubic feet of dry gas at normal temperature and pressure and then conrerted to liters and grams using the constants 28.32 (liters per cubic foot) and 2.020 (density of propane in grams per liter a t 0" C. and 760 mm. of mercury). Values of dGand d L in grams per cc. were obtained by conversion of the densities, in cubic feet per pound, determined by Sage et al. ( 7 ) . The indirect method of determining liquid propane i n i s as follows : The volume, u, of liquid propalie passed into the bomb, which had been evacuated and filled w t h propane vapor in approximate equilibrium with liquid propane at room temperature, was measured in the liquid propane buret. The total mass, M, of propane in the bomb at this temperature, liquid plus gaseous, was computed from the relation d a ( V - 0 ) f dLz' = k?,where d~ and dL are the densities of gaseous and liquid propane, respectively, and vis the volume of the space above the tar, the difference between
FIGURE3. DISTILL- TIO OX CURVES FOR EXTR.4CT FROM EXPERIMENT 2
ASD
RESIDUE
Density, refractive index, hytlrogen-carbon ratios, and molecular weights n-ere determined on the extracts and residues for various tar-propane ratios a t 30", BO", 80", and 90" C. The results are summarized in Table IT. These data are in accord with the view that coal tar consists of cyclic structures of varying molecular xeight, but of similar molecular type. As the amount of propane added to the tar is increased, there is an increase in average density, refractive index, and molecular weight, and a decrease in hydrogen-carbon ratio of the extract, and corresponding changes in the residue. The extract, compared with the residue, is in all cases of lower density, lower refractive index, lower molecular weight, and higher hydrogen-carbon ratio, indicating the concentration of the lower molecular weight and lese highly condensed bodies in the upper phase, the extract. The separation is largely on the basis of molecular weight, as indicated in Figure 3, where distillation curves for extract and residue from experiment 2 are shown. However, a t high tar-propane ratios tlie hydrogen-carbon ratios of the extracts indicate that there has been some selective solvent action and that alkylated cyclic structures have been preferentially extracted. The data of Table I indicate that there is a tendency for oxy-
FEBRUARY 15, 1940
ANALY'TIC.4L EDITION
gen, nitrogen, and sulfur compounds to concentrate in the residue.
89
(4) M o r g a n , G. T., J . Yoc. Chem. I d , 47, 1 3 1 T ( 1 9 2 8 ) ; 48, 2 9 T (1929). ( 5 ) P a i k h u r s t . G. L.. U . 9. P a t e n t 1.RRIl.679 - (19:?41. ( t i ) Rr~n-r. 1;. 51...I. SOC.C'hem. I M . ,45, 9 9 T (1926'. ( 7 ) Sage. B. H.. S c h a a f s m a , J. G., a n d L a c e y , I!l. i., IND.EXG. CHEM..26, 1218-24 (1931). ('I ' i n r l a t t ~ F.'., 4, 263 (19"). (9) Smith. R.C.. a n d H o w a r d . H . C., J . Am. Chcm. Soc., 57, 512 I~
Acknowledgmeii t The author wishes to express his gratitude to R. S.Ashury, Leo Kasehagen, and J. A. Thompson for valuable advice on the design and construction of the extraction equipment, and to J. hl. Lan-rence for independent determination of the liquid propane associated with the phases.
\ - - - -
(1935).
Literature Cited
(10) Spilker, A , "Tiokerei und T e e r D r o d u k t e d e r St
