Shale-Oil Naphthas Analysis of Small Samples by the Silica Gel Adsorption Method G. c'. DISNEEN, C. W. BAILEY, J. H. SMITH, AND JOHN S. H i L L Petroleum and Oil-Shale Experiment Station, Bureau of .Mine.s. Lnramie. Wyoming
Amethod for theanalysis of small samples of shale-oil naphthas is based upon the selective adsorption of the various classes of compounds by silica gel. Data are presented on adsorbability of various classes of hydrocarbons, sulfur compounds. and nitrogen compounds. For best results, the tar acids and haws should be removed before analysis by this method.
T
HE synthet,ic liquid fuels program of t'he Bureau of h h e s , as established by Public Law 290, 78th Congress, has as one
of its object,ives ( 7 ) the development of analytical methods suitable for the analysis of shale oil and its products. Naphtha from shale oil contains, in addition to paraffins, naphthenes and aromatics which are found in straight-run petroleum napht'has, large quant,ities of unsaturated hydrocarbons. Appreciable quantities of sulfur, nitrogen, and oxygen compounds are also present. It was necessary in certain analytical studies to be able m t o determine the hydrocarbon groups in naphthas and fractions therefrom. The nature of shale oil limits the use of GAS certain tests that are common in the petroleum industry. Bromine-number determinations for use in estimating the olefin content of shale oil are unreliable because of interfering substances. Specific dispersion or refractive-index determinations are made difficult by the color of the material, and methods for determining aromatics using these properties are subject to interference by olefin content. As limited quantities of the samples were available, a method was developed that utilized only 10 ml. of sample. This method was based upon the selective adsorption of the various classes of compounds by silica gel and was similar in principle to methods developed by the Bureau of Standards Treatment of shale-oil naphtha Rith sodium hydroxide solution (20% by weight) removes the so-called tar acids, which are largely phenolic in character. In different naphthas obtained from shale oils retorted by conventional methods from Colorado shales the quantity of this material ranges from 1.5 to 2 5 . The tar bases, which are removed by sulfuric acid (2070 by weight), contain the major portion of the nitrogen compounds and generally comprise 5 to 7% of the naphtha, although in certain instances this figure has been as high as 15%. Removal of both tar acids and tar bases has little effect upon the sulfur content, which generally i.j slightly higher in the remaining oil than in the original naphtha, corresponding approui-
* PRINCIPLE OF THE METHOD
The sample to be analyzed is passed into a column of d i v a yt' vhich selectively adsorbs the various groups of compound.vthe equation: and make the proper corrections for these compounds it is necessary to know their effect on the adsorption analysis (3, 15). .4 correction for sulfur compounds proposed by Mair (8) is based
i
2
-
V O L U M E 19, NO. 12
996 where V8is the volume per cent of sulfur compounds, P , is the weight percent of sulfur, M is the average molecular weight of the sulfur compounds in the boiling range of the fraction being analyzed, Df is the density of the fraction at 20" C., 32 is the atomic weight of sulfur, and D,is the average density of the sulfur compounds a t 20 O C. The sulfur content is determined on a separate portion of the fraction. The percentage of sulfur compounds calculated by. this equation is subtracted from the total percentage of aromatics obtained from the silica gel adsorption curve. This equation assumes 1 atom of sulfur to the molecule. An approximation for this correction, which is usually sufficiently accurate, may be made by omitting the densities in the above equation. Occasionally a check on the correction may be obtained when the curve shows a separate plateau attributable to sulfur compounds a t the end of the aromatic group. Synthetic samples containing representative compounds froni several classes of nitrogen compounds, such as pyrroles, pyridines, and piperidines, Rere analyzed to determine the relative adsorbability of the nitrogen compounds. Pyrroles are more strongly adsorbed than any of the sulfur compounds used, but their adsorbability is enough less than that of the desorbing liquid to permit them to be recovered (Figure 6,$). The pyrrole used in this analysis was not purified, which may account for the large loss. The pyridines and piperidines are so strongly adsorbed that they do not appear in the filtrate, even though a number of fractions are taken after essentially pure desorbing liquid has been obtained (Figure 6,B). They do, of course, mow down the column
chrornatographic theory and would eventually issue from the tip. However, they are shown as a loss by this method of analysis. The more basic compounds (tar bases), which are usually removed by an acid wash, are the ones most strongly adsorbed. Consequently, in a sample that has been so treated only the less qtrongly adsorbed compounds, such as pyrroles, are likrly to 1x1 iit*curdariw with
A
I.56Dt
t
I
I
I
I
n-HEPTANE I-DODECENE TOLUENE
I I I PERCENT PERCENT ADDED RECOVERED 40 37 30 32 30 31
-4
l.520b
J l
~ 1 . 5 00
TOLUENE
n
z
-
-1.480
W
2
$1.460-
e
z1.440 -
-
- I-DODECENE
I 420 -
I*
1.400
I
I
I
I
1
1 PERCENT ADDED 25 25
n-OCTANE 1.5401 I-0CTE N E 2-ETHYLTHIOPHENE 25 1.520 PYRROLE 25 2-ETHYLTHIOPHENE
!-
-n-HEPTANE
I
__PERCENT RECOVERED 24 25 24 18
1
!I 21.480
'
I
I
I
n-HEPTANE I-DODECENE tert.-BUTYLBENZENE
1'540k
7
1.500
B
1560
1
I
PERCENT ADDED 40 30 30
I
I
I
I
PERCENT RECOVERED
1
4 I
I
41
i
30 29
I
PYRROLE-
I'-i + ! lert.-BUTYLBENZENE-
!-
SI 4 6 0
1
1.420 I 420
-1-OCTENE I400
-I-DODECENE
-n-OCTANE 14001 Ib
I3'Ob
1555
t
1535 I515
B
I
20
d.0
I
I
4!0
1
n-HEPTANE DI ISOBUTYLENE TOLUENE PYRIDINE
2.0
I
PERCENT ADDED 25 25 25 25
,b
60 I
810
1
1
I
do'
PERCENT RECOVERED 26 25 24 0 -PYRIDINE
1 3 4
I
1.560
I
l
210
310
410
510
$0
710
810
910
1
I
1
I
I
I
I
I
I
520k1
n-HEPTANE I-DODECENE lerl.-AMYLBENZENE
I 540
1
C
ZI 4 7 5
I
-lJ-DISO-
"I5,
BUTYLENE
w
-n-HEPTANE 1
Figure 6 .
PERCENT RECOVERED 41 30 29
I
,1500
1ert.-AMYLBENZENE-
11,4801
21.460
1 3 7 5 ~ 1'0
PERCENT ADDED 40 30 30
Id0
,
i1
r-i-ToLUENE
n
I395
-n-HEPTANE
lb
20
a
I
W U
41.440
-I-DODECENE
I,
\-c
1
30 40 20 610 70 VOLUME OF FILTRATE I N M L
m J I il
20
90
Analyses of RIixtures Containing Nitrogen Compounds
Id0
1
1.400t
i -n-HEPTC,NE 4 13806
Ib
210
7b
310 40 5b 60 VOLUME OF FILTRATE IN ML
Figure 7 .
do
Effect of Viscosity
90
997
DECEMBER 1947 tu present, and the correctioii can btJ 11iatic:in the same manner Its for sulfur compounds. Effect of Boiling Range and Viscosity. The presence of con-tituents with low boiling points (below approximately 60° C.) vaused marked fluctuations in the refractive indices of the paraffin-naphthene plateau. Since these compounds are paraffins of low molecular weight, they tend to appear a t the end of this portion of the curve immediately before the olefin break and may c'ause difficulty in interpretation. The elimination of these compounds by distillation considerably simplifies the analysis. Gooding and Hopkins (6) have shown that for silica gel adwrption u ork on higher-boiling petroleum distillates the viscosity of the desorbent must be higher than that of the material being drsorbcd. Experiments described in this papcr havr shown that viscosity is a factor not only for the desorbent but also for the groups that muit be deaorbed successively within a sample. Khcn the aromatic group has a lower viscosity than either the paraffin-naphthene or olefin groups, difficulty is experienced in the analysis, as shown in Figure 7 where toluene does not desorb 1-dodecene quantitatively. However, tert-butylbenzene improves the analysis and tert-amylbenzcne gives a satisfactory analysis. The difficulty due to vibcosity may be auspected when a very gradual break is obtained between groups of compounds. It has been found that when a sample contains a paraffin-naphthene group having a higher viscosity than other groups dilution with n-heptane permits a satisfactory analysis.
determined on a separate portion of the fraction by the nitrogen tetroxide method ( 8 ) to make certain that the lowest plateau of the curve did not represent aliphatic olefin. The result checked well with the olefin content for fraction A given in Figure 9. Fraction B contains only a small quantity of naphthenes. The olefin portions of the curves for both fractions show a mixture of aliphatic and cyclic olefins; fraction A has a higher relative proportion of cyclics. The aromatic portions of both curves indicate the presence of sulfur compounds of high refractive index. Although the quantity of sulfur compounds in ea:h fraction is roughly the same, the concentration relative to the aromatics is more than twice as great in fraction A as in fraction B, so that the separation between the two classes in the former instance is relatively poor and the refractive index of the n-hole aromatic plateau is raised. In fraction B the separation is fairly good, and the refractive index of the major portion of the aromatic plateau corresponds to that, of the xylenes. From these silica gel adsorption curves, boiling-point data, ultraviolet absorption curves for distinguishing individual a r e matics, and independent analyses for sulfur and nitrogen, BD 1.520 I
t*
1.520
z
-
-1.460
W
2
Hydrogenation. The method ha6 been used to follov the raourse of hydrogenation of shale-oil naphtha. In order to obtain complete hydrogenation a t relatively low temperatures ( J f the olefins in shale-oil naphtha, a series of runs was required. As the hydrogenations were carried out in small-scale batch c,quipment, it was desirable to withdraw a minimum amount of sample for analysis after each run of a series. The adsorption method was used, since the bromine number has not been applied wccessfully as a measure of the olefin content of shale-oil naphtha. The method has the advantage of giving additional information on the progress of hydrogenation, such as the cxtent of attack on the compounds forming the aromatic group. The original naphtha (Figure 8 , A ) used as a charge for these experiments was from shale oil obtained by retorting Colorado shale in a Parry retort. The extent of reaction on this naphtha a t different stages of hydrogenation is shown in Figure 8, B and C. The reduction in the aromatic group as hydrogenation proceeds is apparently caused largely by the removal of sulfur. The method has been incorporated in an analysis scheme used to differentiate between crude shale oils obtained from different conditions of retorting. It has been used to evaluate results of cracking experiments, continuous hydrogenation experimeni s, and treating experiments. Fractionation. Analyses of two fractions from a distillation of >hale-oil naphtha are shoiTn in Figure 9, which also includes for rtJference a plot of boiling point versus refractive index for a' number of compounds occurring in the appropriate boiling range. Iqterpretation of thew analyses is based upon the results on synthetic mixtures, trends indicated in the analyses of the series of fractions from which these two were selected, and other analytical data obtained on the fractions. The curves shown were selected because they represent two typcs of adsorptogram frequently encountered and illustrate the practical application of several points mentioned in the discussion. The paraffin-naphthene group of fraction A s h o w the downward trend in refractive index characteristic of a sample containing a high concentration of naphthenes relative to paraffins (approximately 7 to I). Before this phase of the curve was investigated by using synthetic mixtures, the olefin content was
-
51.440
I
I
I
I
I
I
I
l
l
ORIGINAL SHALE-OIL NAPHTHA
~ 1 . 4 8 0-
n
EXAMPLES OF ANALYSES APPLIED TO SHALE-OIL NAPHTHA
I
PARAFFINS AND NAPHTHENES
34 %
OLEFINS
40 Y.
AROMATICS
18 %
E LL
$ 1 420
I
I3800I l l l l l l l l l j 1.0 2.0 3.0 4.0 51) 61) 70 8.0 9.0 10.0 1.400
1.520 I 1.520 x 1.480
-
t"
I
'
W >
1.460
I
I
l
l
I
I
I
1
AFTER SECOND HYOROGENATION
-
PARAFFINS AND NAPHTHENES
56 %
-
OLEFINS
28 %
AROMATICS
16 %
W
0
I
F
2 1.440 -
E 1.420
t I520 1520
-
x I480
-
0 W
'1460
W
E21440-
\1 c
I
1
1
I
I
I
1
OLEFINS
1
-
AFTER SIXTH HYDROGENATION PARAFFINS AN0 NAPHTHENES
I
87 x
-
0%
-
13%
AROMATICS
-
,E 21420%
-
1400-
I
I
I
I
I
998
0. 1 2 I525
1.505
1.485
I
-
I
L
1
I
I
I
I
-
-
z
-1.465
w
- 1.505 ETHYL%ENZENL
- -
-
i.525
I
I
.2,5mHE rHILThlW1HENf I-EThYLTI11OPHENE
- -
FRACTION FROM A DISTILLATION ANALYSISOF SHALE-OIL NAPHTHA BOILING RANGE 134.8-135.4%
W X
n
I
I
O>XYkNE
-I 4 8 5
- -
- 1.465
2
.I.2-DIMET~YUYCCOYEXE~-l
I-ET~YLCYCLOHEXENE-I
- -
- 1.445
w .I,I,3-TRlMETH-YfXANE
1,405-
-
4 0 %
PARAFFINS AN0 NAPHTHENES OLEFINS AROMATICS S U L F U R COMPOUNDS NITROGEN COMPOUNOS
34 21
% %
-
-I425 .2,6-DIHETHYLHEPTfNE-, *3-METHYLOCTENE-I
- -
40 % 0 I 7,
- 1.405
.2,5-OIMETHYLMEPTANE Z,6-OIML?HYLII~PTANE
'3850
I!O
1525
5 1.505
'
20
3!b
ob
2.0
2.0
7.10
8!0
a0
I
I
I
I
I
I
I
I
10.0
% !I
147
Ik
1391.385
I
I
I
I
I525
2,4-OIMhHYLTHIOP*EN:13.D1MtT~LT"oR1ENf
-
FRACTION FROM A DlSTlLLATlON
f - -
-
ANALYSIS OF SHALE-OIL NAPHTHA BOILING RANGE 137.5 1378OC
- 1505 p!YLEN;m-XnENE
- -
1485-
-
Y X Q
.
li5
-I 485
- -
5 1.465-
- I465
W
1 : I
2l,44&-
i
E W
- -
+J
a
19
PARAFFINS A N 0 NAPHTHEUES OLEFINS AROMATICS
1425-
I
1.385
0
IO
I
2.0
I
3.0
I
I
5.0
40
-
% 1: 43% 00 X
S U L F U R COMPOUNDS NITROGEN COMPOUNDS
1.405-
%
32 45
I 6.0
I
70
I
8.0
-
.2,4,4-TRiMETnYLCYCLol(EXE~i I445 3.5p.TRltETnYLCYUOnEXENE-I , I-METHYL-I-lSOPROPYLCYCLOPENTENE-1
- -
.I,3,5-TRIMETHYUVCL~EXANE
.4-ETHYLHEPTANE .I-METHYLOCTENE-l .3,3-DlMETHYLHEPTANE 04,4~OIMETHYLMEPTANF
- L-
I
9.0
'
100
I
137
I
138
I
139
I
140
- I425 -1405
1385 141
LITERATURE CITED
AIII. SOC.Testing
Fraction H
Fraction A
,,,
,
Diiuethylheptanes 1,1,3-Trimethylcyclohex:1 iw Cs-Aliphatic olefins Cs-Cyclohexenes Ethylbenzene p-Xylene '.' Thiophene derivative8
Uiiilathyiheptanea L,3,5-Trimethylcyclohexanr Cs-Aliphatic olefins CeCyclic olefins p-Xylene m-Xylene Thiophene derivatives
16 3
I6 Ifi
5 10 4
ACCURACY AND PRECISION
The method is more accurate when the concentrittiouv ot t h t various groups of compounds are approximately equal. Based on the determinations made on the known mixtures, the method is probably reliable for estimating certain components of shale oil with a possible error of 1 to 3Vo. 4CKNOWLEDGMENT
This work was done under a cooperative agreement between the University of Wyoming and the Bureau of Mines. The writers acknovledge the encouragement and suggestions of H. hl. Thorne, engineer-in-charge, oil-shale research and develop ment.
Materials, Report of Committee D-2 or1 Pe troleum Products and Lubricants, 1946 Preprint 73, pp. 22-30 Bond, G. R., Jr., IND. END.CHEW,ANAL.ED., 18, 692 (1946) Borgstrom, P., and MoIntire, 3. C., Ind. Eng. Chem., 23, 321 (1931). Cassidy, H. G., J . Am. Chem. SOC.,62, 3073 (1940); 62, 307h (1940); 83, 2628 (1941). Claesson, S., Arkiv. Kemi, Mineral. GeoT., 23A, No. l(1946). Gooding, R. M., and Hopkins, R. L., Paper 11, Division of Petroleum Chemistry, 110th Meeting of AMERICAN CHEMICAI SOCIETY, Chicago, Ill., 1946. Kraemer, A. J., and Buchan, F. E., Chem. Eng. News, 23, 1526 (1945). Mair, B. J., J . Research Xatl. Bur. Standards, 34, 435 (194.5) iMair, B. J., and Forziati, 9.F.,Ibid., 32, 151, IC5 (1944). Mair, B. J., Schicktanz, S. J., and Rose, F. TV., Jr., Ibid.. 15 557 (1935). Mair, B. J., and White, J. D., Ibid., 15, 51 (1935). Rosini, F. D., Mair, B. J., Forsiati, A. F., Glasgow, A. R., J r . . and &rilhgham, C. B., Oil Gas J . . 41, No. 27, 106 (1942). Willingham, C. B., J. Regearch .Vatatl. Bur. Standards, 22, 321 (1939). Wilson, J. N., J . Am. Chem. SOC.,62, 1583 (1940). Youtz, M. A , , and Perkins. P. P.. Ind. Eng. Chem., 19, 1247 (1927). RECEIVEDM a y 13, 1947. Presented before t h e Division of Petroleum CHEMICAL SOCIETY,AtChemistry a t t h e 111th RIeeting of the AMERICAN l a n k City, N . J. Published by permission of t h e director, Bureau of Mines. U . S. Department of t h e Interior
