mal sample aim and one substantially larger than normal. If the same results are obtained for each sample size, nonlinearity is unlikely t o occur for the analysis when using the normal sample size. Table I shows comparative analyses for naphthalenes in a series of representative gasolines, using both the normal (0.050 ml.) sample size, and a double charge (0,100 ml.), ACKNOWLEDGMENT
The author acknowledges the experimental assistance of F. 0. Wood
and A. E. Youngman, both of whom contributed substantially to the design of the routine equipment and procedure, as well as helpful discussions with J. K. Fogo. LITERATURE CITED
(1) Field, F. H., Hastings, S. H., ANAL. CHEM.28, 1248 (1956).
(2) Gordon, R. J., Moore, R. J., Muller, C. E.. Ibid.. 30. 1221 (1958). (3) Kearns, G. L., Maranowski, N. C., Crable, G. F., Ibid., 31, 1646 (1959). (4) Kenyon, W. C., McCarley, J. E., Boucher, E. G., Robinson, A. E., Wiebe, A. E., Ibid., 27, 1888 (1955).
((5) 5 ) Lumpkin, Lumokin. H. E., E.. Johnson, Johnson. B. 9., 9.. Ibid., 26, 1719 (1954). (6) Shore, L. B , Ockert, K. F., S.A.E. Trans. 66,285 (1958). (7) . . Snyder, L. R.. ANAL. CEIEM.33, 1527
(mi).
(8) Snyder, L. R., J. Chromatog. 5 , 468
(1961). (9j I b G , 6, 22 (1961). (10) American Society for Testing Materials, ASTM Standards on Petroleum Products and Lubricants, “Proposed Method of Test for Naphthalene Hydrocarbons in Jet Fuel by Ultraviolet Spectrophotometry,” 1135, 1959. RECEIVEDfor review March 6, 1961. Accepted August 7, 1961.
Applications of Linear Elution Adsorption Chromatography to the Separation and Analysis of Petroleu m 111.
Routine Determination of Certain Sulfur Types
LLOYD R. SNYDER Union Research Center, Union Oil Co. o f California, Brea, Calif.
b linear elution adsorption chromatographic methods have been developed for the routine determination in heavy (400”F. plus) petroleum samples of sulfur present in each of three compound types. Per cent sulfur as (I) alkyl thiophenes, (11) alkyl monosulfides, (including saturated cyclic monosulfides) and (111) nonvicinal aromatic sulfides plus nonvicinal polysulfides is reported. Routine methods for these sulfur types have not been previously described. The Hastings method for aliphatic sulfide sulfur (I1 plus 111) gives high results for some sample types, due to interference from basic nitrogen compounds.
T
first detailed and relatively complete description of the sulfur types occurring in a petroleum heavy distillate WW reported by Lumpkin and Johnson (6). This study provided the basis for the subsequent routine mass spectral procedure of Hastings, Johnson, and Lumpkin (4) for the determination of condensed thiophenes in similar petroleum stocks. This method in conjunction with the iodinecomplex method of Hastings (2, 3) for determining aliphatic sulfides permits the routine breakdown of sulfur compounds in heavy samples into four classes. The mass spectral method determines b e n zo t h i o p h e n es, dibenzot h io p h e n es , a n d naphthobenzothioHE
1538
ANALYTICAL CHEMISTRY
phenes. The iodine-complex method reports aliphatic sulfide sulfur, which comprises acyclic monosulfides; saturated cyclic monosulfides; nonvicinal aromatic sulfides
where /
R-S-R,
the sulfur is not joined to an aromatic nuclei; and nonvicinal polysulfides, R-S-R-S-R. Vicinal aromatic sulfides,
@S-R,
where the sulfur is / joined to an aromatic nucleus and are not vicinal polysulfides, R-SxR, included in this aliphatic sulfide determination. The combination of the above two routine methods for the determination of sulfur type offers one of the most detailed and complete analyses of its kind. The only major sulfur type not represented are the alkyl thiophenes; their nonroutine detection by ultraviolet spectroscopy in narrow chromatographic fractions has been reported ( 4 ) . Further breakdown of the various sulfide types has not been previously accomplished. As will be discussed in a following section, we have recently found that the Hastings sulfide determination is subject to interference from petroleum basic nitrogen compounds. For most sample types the method possesses a t least semiquantitative accuracy, but in some c u c s the re-
ported sulfide sulfur value is as much as a n order of magnitude high. Routine methods for determining alkyl thiophene sulfur and sulfur present in two or more individual sulfide types, without interference from basic nitrogen, appear desirable. Combined with methods such as that of Hastings et al. for the determination of condensed thiophene sulfur types, these procedures would increase the completeness, detail, and accuracy possible in the routine determination of sulfur type in gas oil samples. EXPERIMENTAL
Determination of Alkyl Thiophene Sulfur by Nonlinear Separation Plus Elemental Analysis. T o a d r y 4 foot
by 3/4 inch column containing about 150 rams of Alcoa F-20 activated alumina calcined at 400’ C.) are charged approximately 2 grams of sample. Elution is begun with n-pentane and IO-ml. fractions collected. The ultraviolet absorbance of the fractions at 270 mp is measured. Absorbance first rises and then falls aa the monoaromatics are eluted. When the absorbance falls to one tenth of the maximum value, or when i t reaches a minimum and begins to rise B second time, elution is discontinued and the fractions collected to that point combined as fraction A. A second B fraction is obtained by stripping the column with methanol-benzene. These two fractions are freed from solvent and weighed to obtsin a weight
4
per cent yield of A fraction. The sulfur content of the A fraction is obtained by the hydrogenative desulfurization method ( 7 ) . Normally a small amount of alkyl sulfides is included in this fraction, since sulfides begin to elute shortly before the diaromatics (8). The sulfide sulfur content of the ii fraction is obtained by the Hastings method (3) and subtracted from the total sulfur to give alkyl thiophene sulfur. Multiplication of this value by the weight fraction of the A cut gives the thiophene sulfur content of the total sample. Determination of Alkyl Thiophene Sulfur by Linear Elution Adsorption Chromatography (LEAC). The LEAC separation of sample alkyl thiophenes from polyaromatics is accomplished using a general technique previously described (9). Ten to 100 pl. of sample (Table I) are charged to a 400 X 8 mm. column containing 10 grams of 0.47. H20-A1203 [chromatographically tested Alcoa F-20 ( I O ) ] , and a 75-ml. initial fraction A eluted with n-pentane (prepurified over silica). This fraction contains all of the sample saturates, alkyl benzenes, and alkyl thiophenes, but none of the higher aromatics or condensed thiophenes. The corrected absorbances of the fraction, AZ45 and respectively, are obtained a t 245 and 270 mp in 1O-cm. cells. Sample thiophene content in weight per cent, S t , is calculated Sr
=
(2.25 A245 - 0.576 A z ; o ) / ~ d (1)
where v is the volume of sample charged in microliters, and d is sample density. LEAC Sulfide Sulfur Determination. A 400 X 8 mm. colunin containing 10 grams of 3.77* HZ0-Al203 is assembled in the usual manner and 10 to 100 pl. of sample are charged (Table I). Iso-octane (purified over silica gel) is passed through the column and 40 ml. (4 ml. of eluent per gram of gel) collected in a 50-ml. flask to which 10 ml. of iso-octane have previously been added. This fraction contains the alkyl monosulfide sulfur. Elution is now continued with 50% CC14iso-octane, and a 50-ml. fraction is collected; this contains all of the aromatic and polysulfide sulfur. Two blends are made with each fraction, one containing an equal volume of isooctane to use as a blank sample solution, the other with an equal volume of an iodine-iso-octane solution (4.6 grams per liter) to provide the iodine-sulfide complex solution. The absorbances, AI and Az (corrected), are now obtained a t 308 mp for the sample solution (us. iso-octane as standard) and the sampleiodine solution (us. a 50-50 blend of the original 4.6 grams per liter iodine solution and iso-octane or 50% CCl4iso-octane as standard), respectively. The alkyl monosulfide sulfur content (first fraction) or nonvicinal aromatic plus nonvicinal polysulfide sulfur content (second fraction) is calculated by Equation 2.
Determination of Alkyl Thiophene Sulfur. The petroleum separations of Lumpkin and Johnson (6) as well as pure compound studies carried out in these laboratories (8) have established that in the elution chromatographic separation of petroleum samples from alumina by saturated eluents, alkyl thiophenes and benzenes emerge as a single fraction, reasonably well separated from the saturates which precede them, and the diaromatics, including alkyl sulfides and benzothiophenes, which follow them. Sulfur in the form of alkyl thiophenes may thus be determined by separation of a saturate monoaromatic alkyl thiophene -\cut and determination of its sulfur content. A reasonably large sample must be charged to permit recovery of sufficient A cut for a sulfur determination, and this is most conveniently accomplished by a nonlinear procedure [contrast linear separation (8, IO)] such as is described in the experimental section. Thirtyone widely different light and heavy gas oil range samples (including straight run, cracked, hydrotreated, etc.) were analyzed in this fashion for alkyl thiophene sulfur. Since about four man-hours per sample are required for a single determination, routine application is unattractive. S k y 1 benzenes show strong ultraviolet absorption at 270 mp and weak absorption a t 245 nip] while the reverse situation exists for the alkyl thiophenes. The ultraviolet analysis for thiophenes (moles per liter) or sulfur present as thiophenes (grams per liter) in solutions with benzenes and the nonabsorbing saturates is, therefore, in principle possible. The routine LEAC procedure described in the experimental section was developed to permit the separation of milligram quantities of sample, a resulting A cut being recovered in pentane solution. Weight per cent sample thiophene sulfur S t should theoretically be given as St = ( a Azrj
- b A z ~ ) l vd
(3)
Here, a and b are constants, -4245 and A210 are the absorbances a t 245 and 270 mp of a constant volume of eluent containing the sample thiophenes, benzenes, and saturates; v is the volume of sample charged to the separation; and d is sample density. Each of the preceding 31 samples, for which St was known, was separated in this fashion, and values of .4245and A?ia measured. Insertion of the independently measured value of Si and the experimental values of Azds, A4zio, v, and d into Equation 3 for each sample then permitted the calculation of best values of the coefficients a and b according to the principle of least squares. a was 2.25 + 0.36, and 6 was 0.576 0.06. The standard deviation of the LEAC thio-
.*
Table l. Sample Charge for Routine LEAC Thiophene and Sulfide Tests
Estimated Total Sulfur in Sample, To
Sample Charge,
0.2%. Two of the preceding samples were submitted to multiple LEAC thiophene sulfur determinations to test linearity and measure reproducibility. The results are shown in Table 11. The experimental values appear essentially independent of sample charge for these two samples, thus confirming linearity for a normal sample charge. Reproducibility appears to be about &lo% relative for samples with more than 0.017. wt. alkyl thiophene sulfur. Alkyl thiophene sulfur normally accounts for about 10% of the total sulfur of straight run light gas oils. This figure is lower (1 to 3%) for catalytically cracked gas oils and higher (15 to 250/*) for solvent-extracted gas oil raffinates. The relative fraction of total sample sulfur as alkyl thiophenes declines with increasing sample boiling point. Hydrodesulfurization removes alkyl thiophene sulfur a t the same approximate rate as total sample sulfur. Determination of Two Sulfide Sulfur Types in Petroleum. The LEAC separability of a number of pure sulfide types has been investigated. Table 111 summarizes some data in the form of equivalent retention volumes R" (milliliter per gram) for n-pentane elution from 3.77* wt. Hz0-L41203. The R" values of different sulfides may begrouped according to sulfide type. The alkyl (including cycloalkyl) monosulfides have retention volumes falling between 1 and 3 while the nonvicinal aromatic and polysul-
-
Table II. Multiple LEAC Thiophene Sulfur Determinations on Two Samples
Sample A
Volume Charged, PI. 25 25
Alkyl Thiophene Sulfur, Wt. yc
50 5
0.0091 0.105 0.113 0.115 0.113
25
B
10
25 25
25
0.0096
0.0086
0.0100
0.117
VOL. 33, NO. 1 1 , OCTOBER 1961
1539
E"
fides show values of greater than 3 and less than 20. The vicinal aromatic sulfides possess retention volumes which overlap those of both the alkyl and nonvicinal sulfides, but their negligible iodine complex absorption makes this unimportant in the determination of the former two sulfide types. The retention volumes of basic nitrogen compounds in this' chromatographic system are all considerably greater than 20; for example, 2,6-lutidine, one of the least strongly adsorbed basic nitrogen compounds (IO), has a retention volume of 50. I n view of the preceding considerations, it should be possible to separate chromatographically alkyl monosulfides from nonvicinal sulfides, and both from basic nitrogen compounds, following which each of these two sulfide types can be determined accurately in their respective fractionq. The linear elution of sulfur-containing petroleum samples gives two types of sulfide elution curves. For low sulfur light gas oil samples, where nonvicinal sulfides would not be expected to contribute significantly to total sulfide sulfur because of statistical considerations, the simple elution curve of Figure 1 is typical. The single maximum and the logarithmic decline of sulfide con-
Table 111.
W
k
a
3 _I
W
z a 3 IL
-I 3
cn W
P
LL
_I
3
cn
IL
0 2
0 c
a
LT k
z W
0
z 0 0
w
1 k
a
J W
a
I 0
I
I
I
I
I 2 3 4 5 E L U A T E VOLUME, m l p e r g g e l
Figure 1.
Elution of sulfide sulfur in
low sulfur light gas oil from H20-Al203 by n-pentane
3.7y0
Sample charged to dry column
Separability and Detection Properties of Individual Sulfides
Absorptivity" Iodine Complex a308
Retention Sulfide Sulfur Recovery,c Volume,* R' - Cut A 72 Cut B Ml./Gram
Alkyl Monosulfides 2-Thiabutane 1.2 4-Thiaheptane 1.2 3-Methyl-2-thiabutane 1.2 Cycloalkyl Monosulfides Thiacyclobutane 380 1.2 Thiacyclopentane 1.8 99 n 630 Endo 4,7-ethano-cis-2-thiahindrane 570 cis-3-Thia( 3,3,0)bicyclo-octane 480 frans-3-Thia( 3,3,0)bicyclo-octane 590 cis-Z-Thia(3,3,0)bicyclo-octane 340 Thiaadamantane 340 Vicinal Aromatic Sulfides 1-Phenyl-1-thiaethane 60 1.6 97 17 1-Thiaindane 20 100 0 1-Thiatetralin 20 3.8 91 0 Konvicinal Aromatic Sulfides CeHs-CH2-S-R 410 3.5 56 39 CeHs-( CHz)z-S-Rd 550 5.1 0 98 C.5Hs-( CHz)3-S-Rd 550 5.1 5 8i 2-Thiatetralin 280 0 84 Z-C~OHS-CHZ-S-C~H~ 500 0 87 Nonvicinal Polysulfidesd R-S-CH2-S-R 150 5.0 26 58 R-S-( CHz)z-S-R 310 9.2 0 93 R-S-( CHz),-S-R 400 11.8 0 100 R-S-( CHz),-S-R 570 16.8 2 85 a rlbsorptivity of iodine complex in 2.3 g./L iodine-iso-octane expressed as cm.Z/g. * Equivalent retention volume, pentane elution from 3.7yGHzO-A1203. LEAC sulfide procedure given in experimental section. Cut A contains alkyl and cyrlic monosulfides; cut B contains nonvicinal sulfides. R equals variously ethyl, n-propyl, and/or n-amyl, and values reported are averages
1540
ANALYTICAL CHEMISTRY
centration in the eluate past the maximum are characteristic of the elution of chromatographically homogeneous classes such as saturates, monoaromatics, and diaromatics. For samples of this type, elution of sulfide sulfur is complete for an eluate volume of 4 ml. per gram of adsorbent, with sample charged to a dry column. For high sulfur gas oils, and for all heavy gas oils, a more complex clution curve results, as shown by the representative separation of Figure 2. Past an eluate volume of 3 ml. per gram of adsorbent, the beginning of elution of a second sulfur type is evident. The middle of the elution curves (R" values) of various pure sulfide t G e s are shown in Figure 2, and it is apparent that the second elution band arises from various nonvicinal sulfide t,ypes. If, following the elution of alkyl monosulfides by 4 ml. per gram of pentane as in Figures 1 and 2 to give an A cut, elution is continued with 507, v. iso-octane-carbon tetrachloride to yield a B fraction, nonvicinal sulfide types can be removed quantitatively from the column with a reasonably small eluate volume. This is s h o m in Figure 3 for the elution of both a light and a, heavy high sulfur straight run gas oil. This change in cluent from pentane to carbon tetrachloride both rrduces separation time and increases the sensitivity of detection of nonvicinal sulfides in fraction B. The nonvicinal sulfide fraction (B), col1ectt.d as in Figure 3, shows the characteristic sulfide-iodine complex ultraviolet spectrum (net), thus substantiating the identity of the species giving rise to the net complex absorption a t 308 mp, The Hastings procedure (3) provides for blending the sample with iodine in iso-octane to give a final iodine concent'ration of 0.9 gram per liter. The absorptivity of the iodine sulfide complex in such solutions is assumed equal t'o 372 sq. em. per gram. The rout.ine LE-IC sulfide procedure described in t'he experimrntal section and the absorptivity data of Table I11 use an iodine concentration of 2.3 grams per liter of iodine. This higher iodine concentration has the theoretical advantage of decreasing the dependence of complex absorptivity on temperature and sulfide concentration. For the strongpr iodine solutions, the assumption of a complex absorptivity of 490 gives answers in agreement with the Hast'ings procedure, which is in turn based on average absorptivities for a number of pure alkyl and cycloalkyl sulfidrs The iodine complex absorptivities of the various nonvicinal sulfides and alkyl sulfides of Table I11 range from 150 to 600, but cluster around a value of 490, and this valup is assumcd fo? both sulfide types in Equat'ion 2 AF ali additional chrck on t h e a"
c
I
R-S-R
-'', R-S-Cz-S-R
-
R-S- C 3 - S - R R - S- C 5 - S - R
t
I
I
I
0
2
4
6
I
t
0
I
I
IO 12 ELUATE VOLUME, m l p e r g gel
8
Figure 3. Elution of nonvicinal sulfides v. CCId-iso-octane after by 50% elution of alkyl sulfides b y n-pentane
Figure 2. Elution of sulfide sulfur in high sulfur light gas oil from 3.7% HzO-AIz03 by n-pentane
3.7% HzO-Al203
Sample charged to dry column
sunied absorptivity value of 490, a straight run California light gas oil of 3.670 sulfur content was separated into several fractions by nonlinear pentane elution from alumina. X mass spectral procedure was used to calculate the relative concentrations in each fraction of aromatic hydrocarbons anti related thiophene types, while the Hastings analysis of each fraction gal-e the sulfide ,sulfur content. This information was combined with the molecular weight of each fraction to calculate total sulfur content in each fraction. Table IV summarizes these data, as well as total sulfur determinations on each fraction, for the varigus aromatic fractions, with the exception of those cont'aining more bhan 0.1% nitrogen. The calculated sulfur contents of each fraction are in good agreement with experimental values. From this we may infer that all major sulfur types in each fraction are accounted for and that the sulfide-iodine complex absorptivity assumed for bot'h sulfide types is correct. (Fractions 2 and 3 of Table IS' constitute a further check on the validity of the alkyl thiophene sulfur determinations previously described in that total fraction sulfur less sulfide sulfur agrees well with mass spectral alkyl thiophene sulfur content.) The preceding discussion furnishes the basis for the routine LEAC procedure described in the experimental section for the determination of sulfur present both as alkyl and nonvicinal sulfides. Two aspects of this procedure deserve further comment. First, isooctane is substituted for pentane as eluent for experimental convenience.
Heavy straight run gas oil H tight straight run gas oil
The two eluents are essentially equivalent in eluting poner. Srcond, the pure compound retention volume data of Table I11 suggest a cut point between the t x o sulfide types of 3 to 3.5 ml. per gram, rather than the value chosen, 4 ml. per gram, This overlooks the fact that there is some overlap of the two sulfide elution curves, and that the nonvicinal sulfides are normally lower in concentration than the alkyl sulfides. 'Cnder these circumstances, the relative accuracy of each sulfide type determination is increased if essentially all of the alkyl sulfides are collected in the alkyl sulfide fraction.
IV.
Yield, Weight 7c
2 3
5.1 9.9 3.4 3.5
.i
The reproducibility and linearity of the LEAC sulfide sulfur procedure was examined by making 13 repeat determinations on a heavy straight run gas oil. The average results, 0.33 + 0.01% alkyl monosulfide sulfur and 0.18 =t 0.025!& nonvicinal sulfide sulfur, indicated a repeatability of =!=lo% relative or better. Varying sample charge from 10 to 100 pl. resulted in no consistent variation in the final results, thus demonstrating that linearity normally exists for column loadings in this range.
Sulfur Content of Chromatographic Fractions from California Straight Run Light Gas Oil
Fraction Number 4
1 2 3 4 5 ELUATE VOLUME, mi p e r g g e l
fi
19 _. .4
7 8 9 S-4, 5, 6'
0.8 2.5
~
1.7 11 .o
Total Sulfide S,a
Total Thiophene
0.0 0.21 9.41 4.2f T.6f 2,3f,h 4.6h 6.7h 11.3f
3.3e 1.e 1.1g 4.40
%
S,*70
1.99 4.7' 4.0i
1.8i 0.0
Total Fraction Calculatedc 3 3
io
0.5 8.6 9.5 7.0 8.6
8.5 1.3
s, 7 0
Experimentald 2.9 1.8
10.6
8.1 9.4 7.5
9.1 9.1
11.3
By Hastings procedure. By mass spectral method of appendix. c Summation of sulfide and thiophene sulfur. d By hydrogenation desulfurization ( 7 ) . Predominantly thiophenes. Predominantly alkyl monosulfides. Predominantly benzothiophenes. h Predominantly nonvicinal sulfides. i Predominantly dibenzothiophenes. f Alkyl suhide concentrate from alumina fractions by chromatography over silica. a b
VOL. 33,
NO. 1 1 , OCTOBER 1961
1541
On applying the routine LEAC: sulfide separation procedure to pure compounds, the sulfide recovery in fractions -4and B could be determined as shown in the last two columns of Table 111. Total sulfide recoveries are neax quantitative in all cases, and the only nonvicinal types analyzing partially as alkyl monosulfides are the 1,3disulfides and the benzyl alkyl sulfides. Since the purity of the various nonvicinal sulfides was 85 to 957& the failure to obtain recoveries of exactly 1 0 0 ~is o not considered significant. The first and second columns of Table V show the results of the separation and determination of these two sulfide types in a number of gas oil range samples derived from California crudes. These data show, as expected from statistical considerations, that the ratio of alkyl mono- to nonvicinal sulfide sulfur decreases with increasing total sample sulfur and decreases with increasing sample boiling point (compare samples No. 1 through 3). Thus, as total sulfide sulfur increases, the probability of two sulfide groups occurring in one molecule to form a nonvicinal disulfide increases. Similarly, as sample molecular weight increases, the probability for two or more sulfide groups occurring in one molecule increases even if total sulfide sulfur content is held constant. Furthermore, the fraction of the total sample consisting of aromatics normally increases with increasing boiling point, and this will lead to an increasing probability of sulfide groups being present in aromatic molecules to form nonvicinal aromatic sulfides. The ratio of alkyl mono- to nonvicinal sulfide sulfur is decreased in solvent extract raffinates, all other things held constant (see samples No. 4 through 7). This is also rea-
Table V.
1 2
3 .
4 5 6 7 8
9
10 11
12 13
sonable, since extraction preferentially removes both alkyl sulfides and aromatics. Nonvicinal sulfides contain not one extractable functional group but two, and hence would be expected to be even more readily extracted than simple alkyl monosulfides. The fraction of tot'al sample sulfur present as sulfides is much lower in catalytically cracked gas oil samples than in other sample types. Sulfides appear to crack more readily than other sample sulfur compounds to give products out of the gas oil range. Comparison of LEAC Sulfide Sulfur Determination with that of Hastings. Alkyl monosulfides and nonvicinal sulfides all show R. well defined maximum a t 308 mp, the wave length used for the measurement of sulfide-iodine complex absorption. As previously noted, vicinal sulfide types do not give appreciable iodine complex absorption a t this wave length. Interference from other sample components such as aromatics, oxygen compounds, or nitrogen compounds has been assumed to be negligible ( I ) . With aromatics, the absorption with iodine a t 308 r n M is too weak to affect significantly the measured sulfide value, except possibly a t very low sulfide concentrations. The normally low concentration of oxygen and nitrogen compounds in petroleum samples is the basis for assuming that interference of these components to the Hastings determination is unimportant. The reliability of the Hastings analysis for gas oil range samples has been tested (I, 4, 6) by comparison of total sulfur contents with the sum of sample sulfide sulfur and sulfur present in thiophene ring systems. The observed agreement between these two quantities has been taken as a measure of the accuracy of the Hastings determination
Sulfide Sulfur Distribution in Various Petroleum Samples
HastLEAC Sulfide S, % ings Nitrogen Total samNonSulfide Content, 70 ple S, Sample Alkyl vicinal Total s, % Total Basic 9% ,Light SR gas oil 0.42 0.023 0.44 0.51 0.07 0.03 " 0 . 9 1 ' Light SR gas oil 2.11 0.25 2.36 2.59 0 14 0 058 3.60 Heavy SR gas oil which cor- 0.33 0.18 0.51 0.93 0.37 0.11 1.44 responds to sample KO. 1 Lubricating gas oil 0.069 0.000 0.069 0,074 0.003 a 0.11 Low viscosity lubricating oil 0.074 0.000 0,074 0.082 0 003 a 0.12 Medium viscosity lubricating 0,099 0.000 0,099 0.109 0.005 0.17 oil 0.08 Bright stock lubricating oil 0,174 0.019 0.193 0.263 a 0.33 Coker distillate light gas oil 0.73 0.063 0 , 7 9 1.06 0.31 0.153 2.39 Hydrodesulfurized product 0,015 0.000 0.015 0.066 0 13 0.053 0.088 from samule No. 8 Fractions fr'om FCC gas oil 0 055 0 000 0 055 0 144 0 08 0 054 1 1 b 360-460" F. cut 540-570" F c u t 0 029 0 007 0 016 0 123 0 16 0 056 640-670" F. cut 0 007 0 000 0 007 0 182 0 27 0 054 670-710" F. cut 0 009 0 004 0 013 0 237 0 46 0 052 Not measured. For 360-710" F. FFC gas oil which gave distillation cuts 10-13.
1542
ANALYTICAL CHEMISTRY
and of the methods for determining thiophenic sulfur. Since these coniparisons have been restricted to gas oils or chromatographic fractions whose oxygen and nitrogen contents arc> low, the lack of interference from these latter constituents has not b r m established. I n addit'ion to L E I C alkyl iiioiiosulfide and nonvicinal sulfide sulfur values: Table Ti includes the total CJf these two in the third coluniii m i l the sample aliphatic sulfide content by the Hastings procedure in the fourth column. The values by the Hastings procedure are invariably higher than the sum obtained by the LEXC procedure, and the disagreement is frequently serious. The difference bctween the Hastings and LEAC total sulfide sulfur values roughly parallels the nitrogen content of the sample, which is shown in the fifth column. Gas oils derived from many California and other crudes shoiv nitrogen contents in excess of 0.1 weight %. IF'hen applying the Hastings methods to chromatographic fractions isolated from such samples, an appreciable interference is evident in the most strongly adsorbed fractions where oxygen and nitrogen concent'rate. Such fractions frequently show sulfide-sulfur contents by the Hastings procedure which exceed the total sulfur content of the fraction. Furthermore, the iodine complexes of such fractions do not show absorption maxima a t 308 mp, but absorption in the ultraviolet continues to increase with decreasing wave length from 340 to 260 mp. I n Table VI, the relative iodine complex absorption a t 308 mp of several oxygen and nitrogen compounds is shown, expressed as apparent per cent sulfide sulfur per per cent of oxygen or nitrogen. Appreciable interference to sulfide sulfur determinations occurs only with basic nitrogen compounds. As a critical test both of the importance of this compound type in interfering with the Hastings determination and of the validity of the present LEAC sulfide sulfur determination, sample No. 11 of Table V, a 540' to 570" F. cut from an FCC gas oil, was passed over a n acid ion exchange resin so as to remove only basic nitrogen compounds from the sample. Basic nitrogen content was decreased from 560 to 4 p.p.m. The Hastings analysis of the treated material gave a n average of 0.033 k 0.004% sulfide sulfur, in contrast with a value of o.123y0 for the untreated sample and in excellent agreement with the LEXC total sulfide sulfur value of 0.036Y0 for untreated sample. The last column of Table V shows basic nitrogen values for most of the samples to demonstrate that the interference of basic nitrogen in the Hastings determination varies with sample type.
ACKNOWLEDGMENT
It doen not appear possible to correct a Hastings sulfide sulfur value even when the basic nitrogen content is known. It cannot be emphasized too strongly that while the Hastings determination appears satisfactory for many straight run samples, and all nitrogen-free samples, i t can be in error by a n order of magnitude in such sample types aa catalytically cracked gas oils, hydrodesulfurized gas oils derived from feeds possessing appreciable basic nitrogen contents, and special fractions from virtually any sample where a concentration of nitrogen compounds has been effected. The Hastings method has not been a p p l i e d p r e v i o u s l y t o asphalts, primarily because of their large absorbance a t 308 mp. The large nitrogen contents of such samples undoubtedly preclude their accurate sulfide determination by the Hastings method, even where the relative absorbance of a sample appears to permit such a determination. The present LEAC procedure permits the determination of each sulfide type in asphalts providing t h a t the sample is first diluted with CCL.
Table VI. Interference of Pure Compounds Containing Oxygen or Nitrogen for Hastings Sulfide Sulfur Determination
Apparent Sulfide Sulfur,a
Compound 70 Oxygen Compounds Anisole 0.00 Methyl benzoate 0.00 Phenyl acetic acid 0.00 1,4-Naphthoquinone 0.00 Benzyl alcohol 0.00 Nonbasic Nitrogen Compounds Indole 0.00 Carbazole 0.00 Basic Nitrogen Compounds 2-Ethylpyridine 0.08 4-Ethylpyridine 0.09 Quinoline 0.40 Quinaldine 0.25 7-Methylquinoline 0.53 8-Methylquinoline 0.02 0.07 Acridine Phenanthridine 0.47 I-Azapyrene 0.12 a Apparent per cent sulfide sulfur per 1yooxygen or nitrogen in sample.
The author acknowledges the advice and assistance of G. R. Lake and E. C. Copelin of these laboratories, as well as helpful discussions with S. H. Hastings of the Humble Oil Co., and M . J O’Neal and G. P. Hinds of the Shell Oil Co., Houston. Several of the pure sulfides of Table I11 were the gift of the American Petroleum Institute Project 48 group a t Laramie, Wyo. LITERATURE CITED
(1) Drushel, H. V., Miller,
J. F., ANAL. CHEY.27,495 (1955). (2) Hastings, S. H., Zbid., 25, 420 (1953). (3) Hastinns. S H.. Johnson. B. H.. Zbid.. 27,564 (i955). ’ 14) \ , Hastinzs. S. H.. Johnson. B. H.. Lumpkin: H. E., Zdid., 2 8 , 1243 (1956). ( 5 ) Lumpkin, H. E., Ibid., 30,321 (1958) (6) Lumpkin, H. E., Johnson, B. H., Zbid., 26,1719 (1954). ( 7 ) Schluter, E. C., Jr., Parry, E. P. Matsuyama, G., Zbid., 32,413 (1960). ( 8 ) Snyder, L. R., Zbid., 33,1527(1961). (9) Ihid., p. 1535. (10) Snyder, L. R., J. Chromatog. 6 , 22 (1961). RECEIVEDfor review March 6, 1961. Accepted August 7, 1961. ~I
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A Total Analysis Digital System for Chromatographs F. W. KARASEK, M. C. BURK, and 6. 0. AYERS Research and Development Department, Phillips Petroleum Co., Bartlesville, Okla.
b A total analysis digital system (TADS), developed for use with gas chromatographs, types out normalized sample compositions in digital form. The TADS includes a card programmer to control chromatograph functions and signal gates, and to select the proper bridge attenuation to compensate for differences in detector response factors. Integration of chromatographic peaks by a voltage to frequency converter provides linear response over a wide dynamic range. TADS has been applied to a 14-component analysis. The stability and precision of the system is shown b y a deviation of kO.013 weight % at a 1.5% level for 13 hours of operation with a sample of fixed composition. Analytical accuracy i s within *1,5%, The combination of several chromatographs with a single TADS permits the accumulation o f compositional data throughout a plant for use in process control and accounting. In control laboratories, routine analyses can be programmed on a number of chromatographs tied into a central TADS unit. With the complete program for each chromatograph contained on the programmer card, only a single card change i s required for each analysis.
W
the state of advancement of the analytical and instrumental phase of chromatography has progressed rapidly, the data handling and presentation aspects appear to have advanced little beyond elementary stages. Laboratory analyses are obtained largely by hand operation of individual chromatographs followed by hand measurement of the chromatogram peaks and calculation of sample composition. Some aids made calculation easier by providing peak integration (2, 3, 6). I n HILE
TOTAL COUNTER
STORAGE
D IG ITAL DIVIOER
M L T A G E TO FREQUENCY DECIMAL REAWUT
the process field, the information provided to plant operators is usually a multicomponent repetitive bar graph. Devices which store peak values or integrated values and present a continuous output suitable for control of one or more components have been described (1,4). However, these are aimed at closed-loop process control more than a t the general problem of data handling and presentation. One step in advancing the techniques of data handling is described here The system controls the opcration of a chromatograph, accepts the voltagetime curve represented by the chromatogram, integrates each component peak, and prints a normalized total analysis in digital form. It possesses a flexibility permitting use in either a laboratorj situation or in process instrumentation where both monitoring and control functions are desired. A unit which performs these functions provides one with a total analysis digital system (TADS).
, BINARY
DESCRIPTION OF SYSTEM PROCESS COUPUTLR
Figure 1.
TADS block diagram
A block diagram of the system is shown in Figure 1. The millivolt signal from the Chromatograph is VOL. 33, NO. 1 1 , OCTOBER 1961
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