that 80 to 90% of these thiophenes are tully aromatic. Two-ring thiophenes are a t a mauimum a t CI1 (three carbons above the first member of the series), and then decrease gradually with increasing carbon number. Three-ring thiophenes are a t a maximum a t CI4 (two carbon numbers above the first member of the series) and then decrease rather sharply with increasing carbon number. Benzothiophene itself is present in very small proportion (0.0002~o) ; dibenzothiophene, however, is about 0.009%. Sulfides increase in amount to about CQ0and then level off; they are the principal type in the heavy naphtha (C,-C,) range. Thiols are a t a maximum a t about Cs; they then decrease and are negligible in the gas-oil range. The sulfur compounds through Cz0 plotted in Figure 8 account for 0.67% sulfur, which is only 25y0 of the total sulfur in the crude. Hydrocarbons through C?, account for 607, of the total crude. Figure 8 illubtrates a typical distribution of sulfur compounds in petroleum. Crude oils contain different absolute amounts of sulfur and slightly different proportions of the various sulfur types (f4), but their distributions by carbon number, in our euperience, usually are similar. Two- and three-ring thiophenes, for example, generally possess the same maxima and similar rates of
decline as those shown in Figure 8. This crude has a slightly smaller proportion of sulfides than most crudes (f4),but the sulfides show the characteristic steady rise in amounts into the gas-oil range. The crude also shows a fairly typical distribution of thiols; of all the compound types, thiols probably are the most variable among crude oils.
( 2 ) Brown, R., Meyerson, S., Ibzd., 44, 2620 (1952). ( 3 ) Coleman, H. J., Thompson, C. J., Hopkins, R. L., Rall, H. T., J . Chem. Eng. Data 10, 80 (1965). ( 4 ) Challacombe, J. A,, AIcNulty, J. A., Residue Rev. 5, 57 (1964). ( 5 ) Coulson, D. M.,in “Gas Chromatography,” L. Fowler, ed., p. 213, Academic Press, New York, 1963. ( 6 ) Coulson, I>. Al., Cavanagh, L. A,, AIVAL. CHEM.32, 1245 (1960). ( 7 ) Coulson, D. AI., Cavanagh, L. A.,
CONCLUSION
“Mcrocorilometric Detection in Gas Chromatography,” Pittsbur: h Conference on Analytical Chemistry and Applied Spectroscopy, JIarch 1961. ( 8 ) Ilrushel, H. \’., \[iller. J. F.. ANAL. CHEM.27. 495 i1955). ( 9 ) Fredericks, E. AI., Harlow, G. A.,
Gas chromatography with coulometric detection has proved to be a n effective means for characterizing sulfur distributions, even though individual compounds generally cannot be determined. I n future work, gas chroniatography should be used more in combination with other analytical techniques. Two excellent techniques would be linear elution adsorption chromatography ( I C ) , and mass spectrometry; fractions separated by linear chromatography would be analyzed by both gas chromatography and mass spectrometry. Such a combination should yield much more information than the techniques could produce individually, and should be amenable to routine application. LITERATURE CITED
( 1 ) Birch, 8. F., Cullum, T. V., Dean,
R. A , , Ilenyer, R. L., I n d . Eng. Chem.
47, 240 (1955).
Ibid., 35, 263 (1964). (10) Hastingr, S. H., Ibid., 25,420 (1953). ( 1 1 ) Hubbard, R. L., Haines, W. E., Ball, J. S.,Ibid., 30, 91 (1958). (12) Karchmer, J. H., Ibid., 31, 1377 (1959). (13) Klaaq, P. J., Ibid., 33, 1851 (1961). (14) Martin, R. L., Grant, J. A., Ibid., 37, 649 (1965). (15) lIcCoy, R. N., Weiss, F. T., Ibid., 26, 1928 (1954). (16) Snyder, L. R., Ibid., 33, 1527, 1538 f 1961).
RuFeau ’of M i n e s Rept. Invest. 6252 (1963).
RECEIVED for review December 14, 1964. Accepted January 28, 1965. Division of Petroleum Chemistry, 149th LIeeting, ACS, Detroit, Nich., April 1965.
Determination of Thiophenic Compounds by Types in petroleum Samples RONALD L. MARTIN and JOHN A. GRANT Research and Development Department, American Oil
A method for determining thiopheniccompound types in petroleum samples of all types and boiling ranges has been developed. Nonthiophenic sulfur compounds are decomposed over alumina a t 500” C. to form hydrogen sulfide and aromatic thiols, which are collected and titrated to determine total nonthiophenic sulfur. Thiophenic compounds, extensively dealkylated in the decomposition reaction, are separated b y gas chromatography according to number of rings and detected by microcoulometric titration; thiophenic types with one, two, three, four, and five or more rings are determined. Accuracy of the method is good as judged by analyses on test samples and by comparison with other analytical techniques. Distillation fractions and residua from seven crude oils were analyzed to provide sulfur-
Co., Whiting,
Ind.
type characterizations heretofore unattainable. Differences among crudes in the distribution of sulfur-compound types usually are not large. Thiophenic compounds typically account for 50 to 7070 of the sulfur; except in residua, most of these compounds have either two or three rings.
I
ri THE REFINING of
high-sulfur crude oils, the determination of sulfurcompound types often is important. T h e need for such analyses is particularly great in the gas oil and residuum ranges, where available methods have not been completely satisfactory. One particular use is to follow the Iirogress of desulfurization processes, which proceed a t different rates for each of the sulfur types. I n the first relatively complete delineation of the sulfur types in gas
oils, Lumpkin and Johnson (13) showed that compounds containing condensed thiophene and aromatic rings accounted for iiiost of the sulfur. Their work provided the basis for the first method for thiophenic types-the mass-sl)ectrometric method of Hastings, Johnson, and Lumpkin (10)-which gives semiquantitative determinations of benzo-, dibenzo-, and naphthobenzothiophenes. Although this method has been very valuable in following composition trends and reaction behavior, its accuracy and alq)licability leave something to be desired. In our experience, values for thiophenic sulfur frequently are high, paiticularly for samples with limited boiling ranges. Mass sl)ectronietry also has been used to determine onering thiophenes ( 9 ) ,but only in naphtharange samples. Liquid-solid chromatography on VOL. 37, NO. 6 , M A Y 1965
649
hydrated alumina (18, 19) can be used to separate thiophenic compounds along with hydrocarbons according to number of aromatic rings. These procedures, however, are lengthy and usually are not amenable to routine use; they are subject to errors arising from overlap between types and from handling and analysis of the fractions. A procedure using linear elution adsorption chromatography has been developed for onering thiophenes (2 7 ) . Linear procedures, in general, are faster and more amenable to routine use than the others, but have not been extended to the higher thiophenes. The new method described here is applicable to petroleum samples of all types and boiling ranges. It determines thiophenic types having one, two, three, four, and five or more rings, as well as total nonthiophenic sulfur. T h e nonthiophenic compounds are removed by catalytic decomposition over alumina (26) a t 500" C. to form hydrogen sulfide and aromatic thiols, which are collected and titrated. Thiophenic compounds are extensively dealkylated by this treatment and subsequently are separated according to number of rings using gas chromatography with selective microcoulonietric detection (3, 12, 1 4 ) . T h e method has been applied to distillation and residuum fractions from seven crude oils. These heretofore unattainable data show how the distributions of thiophenic compounds vary with boiling range among crude oils. EXPERIMENTAL
The catalytic decomposition apparatus is shown in Figure 1. T h e reaction tube is made of quartz and is 16 inches long and 'Iz inch in internal diameter. The front tip of t,he tube reduces to a diameter of 'I4 inch, and is fitted with a rubber serum bottle cap, through which the sample can be added by syringe. The bed of alumina catalyst, is about 11 inches long, and is supported a t the ends by glass wool. T h e catalyst is maintained at 500" 10" C. with a tubular electric furnace, which extends a n inch or more beyond each end of the catalyst bed. The entrance and exit arms to the reaction tube are maintained a t about 500' C. by nichrome-wire resistance heating. Absorbers I and I1 are made from graduated cylinders of 25- and 100-ml. sizes; connections are made with glass tubing and ball joints. The nitrogen carrier gas is passed through copper filings a t 325" C. to remove traces of oxygen. Procedure. Fill the reaction tube with crushed alumina (Harshaw 01041') of 10-16 mesh size. (Change t h e alumina about every 5 runs or when it becomes very dark from coke deposits.) Charge absorber I with 20 ml. of a hydrocarbon mixture of wide boiling range that contains no more than 5 p.p.m. of sulfur-e.g., catalytic
650
ANALYTICAL CHEMISTRY
/-
Cu FILINGS AT 3 2 5 O C .
STOPCOCK?
SIDEARM AT 5 0 0 ° C S E R U M B O 1'1LE C A P
NEEDLEVALVE
H 2 0 BUBBLER u I1 u EXIT AT 500°C.
ABSORBER1 HYDROCARBON SOLVENT
ABSORBER .U 4% AQUEOUS NaOH
a Figure 1.
Apparatus for catalytic decomposition
reformate-and immerse the absorber in a hot water bath (SO" C.). Fill absorber I1 with 90 ml. of aqueous 401, sodium hydroxide solution, and protect the surface of the solution with a blanket of nitrogen. Connect the absorbers and flush with a nitrogen flow of 3-6 bubbles per second (observed in absorber 11) for 15 minutes. Decrease the flow of nitrogen as much as possible (to about one bubble every 2 seconds) while still maintaining a steady bubbling rate, and replace the hot water bath wit'h an ice bath. With a hypodermic syringe equipped with a needle long enough to extend into the catalyst bed, charge an amount of sample containing from 0.2 to 10 mg. (preferably more than 2 mg.) of nonthiophenic sulfur. (From the volume and density of the sample, determine the weight charged for later use in the calculation of nonthiophenic sulfur.) Add the sample slowly so the pressure buildup does not stop the nitrogen flow through the apparat'us, as observed in the water bubbler; take 6 to 8 minutes for sample of 1 ml. or smaller, about 12 minutes for 2 ml., and about 20 minutes for 5 ml. (Xormally, the sample is limited to about 5 ml., but more can be added in special situations; if more than 2 ml. is needed and the sample is of low volatility, remove dissolved oxygen by bubbling with nitrogen.) After samlde introduction, increase the nitrogen flow to 3 to 6 bubbles per second for 10 minutes. Close the stopcock, and inject two 2.5-ml. portions of oxygen-free water with a 2-minute interval between injections. Open the stopcock and continue the rapid flow of nitrogen for 5 minutes. Close the stopcock and inject 4 ml. of fresh absorbant I (oxygen free) to wash out any sample left in the exit arm. After one-half minute, open the stopcock and continue the flow of nitrogen for 2 minutes. Transfer the sodium hydroxide solution to a titration beaker, add l ml.
of ammonium hydroxide, and immediately titrate sulfide ion potentiometrically (20) with 0.1 or 0.01.V silver nitrate. Retain a few drops of absorbant I for gas chromatographic analysis; transfer the remainder to a titration beaker containing 100 ml. of 0.1N alcoholic sodium acetate solution, and immediately titrate thiols and hydrogen sulfide with 0.01N silver nitrate (20). Calculate nonthiophenic sulfur as the sum of sulfur found as hydrogen SUIfide and thiols by both titrations. Calculate thioyhenic sulfur as the difference between total sulfur ( I , 22) and nonthiophenic sulfur. Determine the proportions of thiophenic types in the retained absorbant I by gas chromatography with coulometric detection (14). Cse an 8-foot by '/*-inch i.d. column packed with 3% diethyleneglycol sebacate polyester (LAC-737) on Chromosorb-W and a nitrogen flow rate of about 140 ml. per minute. Charge from 1 to 100 pl. of sample (depending on the thiophenic sulfur content), and program the column temperature from 50" to 280' C. a t 2' per minute. Planimeter the chart areas for one-, two-, three-, and four-ring thiophenes (see top half of Figure 2), and apportion the thiophenic sulfur accordingly. If the sample is suspected to contain sulfur compounds with more than four rings-Le., its end point is above about 500" C.-calculate the amount of thiophenic sulfur in compounds with four or less rings from the recorder chart areas; do this by comparing the chart area for thiophenic types with that of a standard sample of known sulfur concentration. The % thiophenic sulfur in rings of four or less is equal to:
(% S in stn'd) x (area from abs. I per p l . ) (ml. abs. I after run) (area from std. per pl.) (ml. s a m p F charged)
(Since this determination is not extremely accurate, it should not be uqed except when sulfur compounds of more than four rings are expected.) Calculate the amount of thiophenic sulfur in compoundr of five or more rings as the difference between total thiophenic sulfur and that for thiophenic compounds of four or less rings. Short-Cut Procedure. hbsorber I is present mainly t o separate aromatic thiols from hydrogen sulfide so both can be titrated. I t can be eliminated when analyzing virgin distillates, because then thiols produced are a negligible proportion ( I to 27,) of the nonthiophenic sulfur. The short-cut procedure is essentially the same as the regular procedure except that it uses only one abiorber, which contains 10 ml. of absorliant I and 90 ml. of 4% sodium hydroxide. After catalytic decomposition, the supernatant absorbant I, which contains the thiophenic sulfur, is drawn off with a n eyedropper and saved for gas chromatographic analysis. Only the hydroxide solution is titrated for nonthiophenic sulfur. The ieparate absor tier I must be used for catalytically cracked samples, becauie up to 30yG of the nonthiophenic sulfur may appear as aromatic thiols. It also should be used for residuum samples, becaube this analysis depends on recovering all thiophenic sulfur, which is accomplished more efficiently with the two absorbers. DISCUSSION OF METHOD
Catalytic Decomposition. T h e procedure for decomposing a n d determining nonthiophenic sulfur compounds is essentially the same as t h a t used by McCoy and Weiss (16), who showed t h a t most nonthiophenic sulfur compounds decompose over alumina a t 450" or 500" C., while thiophenic conipounds do not. Hydrogen sulfide is Iiroduced from most, nonthiophenic com1)ounds; however, compounds containing a sulfur atom attached to a n aromatic ring decompose part'ly to aromatic thiols and partly to hydrogen sulfide. Total nonthiophenic sulfur is determined, therefore, by titrating both hydrogen sulfide and thiols. Two changes were made from the McCoy-IYeiss procedure (1 6). One was the use ol 500" C,. as reaction teinperature rathcr than 450" C., which is not inconsistent with the findings of McCoy a t 500' C., we obt'ain more cotnl)lete decomposition of nonthiophonic, compounds and, more iml)ortantly, greatrr dealkylation of thioIihenic compounds (necessary for gas c h r o r n a t o ~ r a ~ ~ h iseparations). c The data in Talde I and also those of McCoy and Kciss (16) show that both thio1)henic and nonthiophenic compounds yield more hydrogen sulfide a t 500" than a t 450'. At the higher temperature, the conversion of nonthiophenic rompounds is improved several per cent to 957c or better, wherens.that from
thiophenic compounds is still only 1 to 2%. The second change in procedure is the injection of water into the reaction tube after the decomposition has been completed; the water helps to dislodge hydrogen sulfide from the alumina and improves the yield by several per cent. Adsorption of hydrogen sulfide on alumina can be very strong, which is probably why Hamniar (7) was unsuccessful in using hydrogen sulfide production as a measure of nonthiophenic sulfur. Recovery of hydrogen sulfide will be incomplete if any hydrogen sulfide is oxidized by traces of oxygen remaining in the system, or if any nonthiophenic molecules pass through the alumina without decomposing. To avoid loss by oxidation, oxygen must be completely eliminated from the carrier gas, the absorber solutions, and the injected water. Incomplete decomposition is minimized by keeping the reaction tube a t 500" C. and by passing the sample through the alumina at very low space velocities. Of the possible side reactions during catalytic decomposition, two were eliminated as sources for error. Aromatic rings are not lost from thiophenes, and thiophenes are not produced in significant amounts frotn nonthiophenic compounds. Small amounts of thiophenes are produced from certain compounds-e.g., thiophene frotn thiacyclopentane-but in no case did they account for more than O . l % of the original compound. Another possible side reaction is the cracking or rearrangement of saturated rings on thiophenic compounds. Although the amounts of thiophenes with saturated rings undoubtedly are small, their presence along with the fully aromatic members has been confirmed by mass spectrometry. 1,2,3,4-Tetrahydrodibenzothiophene, which was provided by W.E. Haines of API Project 48, was the only compound of this type t h a t could be obtained. I t decomposed catalytically to give the following: Sulfur,
7c
Tetrah drodibenxothiophene (unczanged) Dibenzothiophene Alkylbenxothiophenes Hydrogen sulfide
70 22 5 3
Two typical catalytic-cracking reactions occurred-dehydrogenation to form dibenzothiophene. and opening of the saturated ring to form alkylbenzothiophenes. However, 707, of the starting material was unchanged. From the behavior of 1,2,3,4-tetrahydrodibenzothiophene, it appear? t h a t thiophenes containing saturated rings can be determined in the same manner as aromatic thiophenes-i.e., tetra-
Table
I.
Decomposition of Sulfur Compounds over Alumina
Recovery as hydrogen sulfide, '70 of sulfur added. 450' C. 500" C. Thiophene 0 9 1 7 3-llethylthiophene 1 7 2,5-Dimethylthiophene 2 2 Benzothiophenes b from catnlytic cycle oil 1 2 1 7 Benzothiophenesb from gas oil 2.2 Dibenzothiophene 0.9 Dibenzothiophenes from catdlytic cycle oil 0 9 1 3 Naphtho benzothiophenes from catalytic cycle oil 1 0 1-Heptanethiol 92 95 n-Butylsulfide 94 98 Thiacyclopentane 95 99 n-Propyldisulfide 96 Synthetic mixture of 15 nonthiophenic sulfur compounds 96 1 ml. of sample added containing about 0.5% sulfur in an aromatic solvent. b Obtained by liquid-solid chromatography. 5
Table
II.
Recovery of Sulfur Compounds from Alumina Sulfur,
%
R e 7 Added covered. Thiophene 0.0081 0 .ooso 3-Methylthiophene 0,0059 0.0060 2,5Dimethylthiophene 0.0057 0.0056 Benzo[b]thiophene 0.0145 0 0145b 2-Methylbenzo [b]thiophene 0 0232 0.0234 Dibenzothiophene 0.0107 0.0108 Naphthobenzothiophenesc 0.0065 0.0064 a Determined by gas chromatography with coulometric detection ( 1 4 ) . * Value assumed to be 0.0145%; other components then determined by comparison of their peak areas to that of benzothiophene. c Obtained from a heavy catalytic cycle oil by liquid-solid chromatography.
hydrodibenzothiophene yields 92y0 of three-ring products and therefore is designated as a three-ring thiophene in our characterizations. T h e yield of products from other compounds of this type undoubtedly will vary, but it seems reasonable to assume that most of the products will contain the same number of rings as the starting material. Recovery of Thiophenes from Alumina. T h e water injected to remove t h e laSt traces of hydrogen sulfide also serves to quantitatively desorb thiophenic compounds. Although most of the lower-boiling thiophenes are eluted with nitrogen, the higher boiling ones-dibenzothiophenes and naphthobenzothiophenes-are eluted quantitatively only by displacement with water. The loss of volatile one-ring thiophenes from the hydrocarbon solvent in VOL. 37, NO. 6 , M A Y 1965
651
COL.: 8 ' X 1/8", 3% LAC-737 O N CH-W
2-RING
TEMP.: 50" - 280"C, 2"/MIN. N2 FLOW : 140 ML/MIN.
w
v)
z
0
4-RING
a v)
w
E
-
E
0 t-
o
Cot : 20' X 1/8", 15% SE 30 O N CH
tw n
TEMP : 50" -38OoC, 3"/MIN.
W
b'
N2FLOW: 100 ML,/MIN.
fi
1
1
0
40
1
1
I
80
I
120
___ L
16
MINUTES Figure 2.
Thiophenic compounds in a reacted residuum by gas chromatography
absorber I is eliminated by chilling the absorber with ice. The effectiveness of the thiophenerecovery process is indicated by the data in Table I1 for a synthetic mixture of sulfur compounds. Since there is no bias for high- or low-boiling compounds, evidently all of the compounds are removed completely from the alumina, and none are volatilized from the absorber. The fate of compounds higher boiling than naphthobenzothiophenes is uncertain; even if removed from the alumina, they are too high boiling to be determined by the gas chromatographic procedure. G a s Chromatographic Determination of Thiophenic Types. T h e determination of thiophenic types depends on separation by gas chromatography and detection by selective microcoulometric titration (3, 12, 14). The quantitative ability of the detector, which responds to sulfur compounds but not to hydrocarbons, has been established (14). For the separation by number of rings, two requirements must be met. First, there must be considerable dealkylation of chains from the rings. Second, the gas chromatographic column must selectively retain compounds with two rings longer than those u i t h one ring, and those with three longer than those with two, etc. Dealkylation during catalytic decomposition at 500" C. narrows the boiling range of each compound type just enough so a selective column can make these separations. Columns of diethyleneglycol sebacate polyester have the selectivity needed 652
rn
ANALYTICAL CHEMISTRY
for separating the partially dealkylated thiophenes. This is illustrated by Figure 2, which shows chromatograms of a catalytically decomposed residuum from the polyester column and a silicone rubber column. With the silicone column, the thiophenic compounds are eluted approximately in order of boiling point, and are not grouped by types. With the polyester column, however, thiophenic compounds are eluted in four distinct groups containing, respectively, one, two, three, and four rings. The groups were identified by comparing their retention times to those for concentrates of one-, two-, three-, and four-ring thiophenes isolated by liquid-solid chromatography. Although there is some overlap-e.g., some two-ring compounds with relatively long alkyl chains are eluted at the beginning of the three-ring range-a semiquantitative analysis by number of rings can be made. Dibenzothiophene is eluted at about the same time as the octylbenzothiophenes. Thus, if alkyl chains on benzothiophenes are kept to a maximum of about seven carbons, all benzothiophenes will be eluted before the dibenzothiophenes. The chart areas are directly proportional to the amount of sulfur contained in each ring type; where there is overlap, the contribution from each type must be estimated. For samples lower boiling than residuum, overlap is generally less than is shown in Figure 2. Other polar liquid phases evaluated for separating thiophenic types were either less selective, more volatile, or had decomposition products that made the coulometric detector inoperable. For
example, ethylene oxide polymer (Union Carbide Polyox WSR-301) was not sufficiently selective; nitrile silicone gum (General Electric XE-30), although normally temperature stable t o about 280" C., gave products at 180" C. that produced an intense negative response in the detector. Diethyleneglycol sebacate polyester (L.iC-737) was chosen over t'he other LAC polyesters because it is the least volatile. Although column bleed from the sebacate polyester occurs a t temperatures above 210" C., it was possible to use columns to 280' or even higher, because the volatile products produced no response in the coulometric detector. Application of Method to Residua. T h e new method was applied to residua-i.e., samples heavier t h a n gas oil-in the same manner as with lower-boiling samples. However, for most residua, it was necessary to dilute with white oil to permit syringe injection. The thiophene reaction products of one to four rings were separable by gas chromatography, as shown in Figure 2 ; compounds of five or more rings were determined by difference between total thiophenic sulfur and thiophenic sulfur in compounds of four or Iess rings. Unfortunat'ely, there is no satisfactory way of assessing the accuracy of these result's. They probably are a t least qualitatively correct, even though there are several pot,ential sources for error. For example, thiophenic compounds of one through four rings that are not dealkylated, at least partially, during catalytic decomposition would not be determined ; they would be included as
~
Table IV.
Table Ill. Analysis of Synthetic Mixture by New Method
Sulfur, 70 Added Foundo 0.70 Nonthiophenicsulfur* 0 . 7 1 0.074 One-ring thiophenesc 0 070 0,41 Two-ring thiophenesc 0 , 4 0 0.51 Three-ring thiophenes 0 49 0.35 Four-ring thiophenes 0.37 a Average of triplicate results; individual values have average deviations from mean of about 4y0. h AIixture of 10 different compounds in nearly equal mounts. Obtained from heavy catalytic cycle oil by liquid-solid chromatography.
~
~~~~~~~
Comparison with Other Methods
Heavy catalytic cycle oil LiquidNew solid methodn chr0rnat.e
Heavy gas oil Kerosene LiquidLiquidSew solid hIass New solid method" chromat. specc methoda chr0mat.d Nonthiophenic sulfur One-ring thiophenes Two-ring thiophenes Three-ring thiophenes Four-ring thiophenes
0 76
0 64j
0 044
0 04
0 83
0 89
0 99 0 25
0 64'
0 25
0 26j
0 090
0 OS/
0 010
0 011
0 0016
0 0012
0 9Q
0 23
0 23
0 28
0 28
1 04
1 68
0 009
1 22
1 25
0 26
0 58
0 14
0 12
Average of triplicate results; individual values have average deviations of about 47,. procedure of Snyder (19); run was monitored with low-voltage mass spectrometry. Four-ring thiophenes determined by difference between total sulfur and that found for the other types. c According to procedure in reference (10). d One-ring thiophenes determined by procedure of Snyder ( 1 7 ) ; two-ring thiophenes determined by difference between total sulfur and nonthiophenic sulfur plus one-ring thiophenes. e Sample chromatographed on a %)-foot by I-inch column of alumina into 186 cuts; run monitored by low-voltage maqs spectrometry on the cuts. Analyses for thiophenic types calculated from values of total sulfur determined on the cuts. f Sum of sulfides determined colorimetrically (4, 8) and thiols and disulfides by titration a
* Run on 3 columns according to
thiophenic compounds of five or more rings. Another source of error might be molecules containing two or more thiophenic ring systems separated by alkyl or heteroalkyl chains. If the chains were cracked during .catalytic decomposition, the products would be counted as separate thiophenic compounds by gas chromatography. Accuracy of Method. T h e accuracy of t h e method was tested on synthetic mixtures and on samples analyzed previously by liquid-solid chromatography and mass spectrometry. Analysis of a synthetic mixture is shown in Table 111. The added and found values all agree within 5%. This is considered good agreement, especially since the thiophene concentrates used t o prepare the mixture contained some impurities. Table IV compares analyses on three samples by the new method with those obtained by liquid-solid chromatograllhy, b y mass spectrometry, and by methods specific for sulfides, thiols, and
Table VI.
Fraction number Boiling range, C. Weight 70 of crude O
1
Only completely aromatic structures included ; % sulfur calculated assuming molecular weight of thiophenic compounds averages 320. Table V.
Sulfur, yo Total of sulfides, Sulfides thiols, and colorimetrically disulfides (4,8) 0.115 0.053
Nonthiophenic by catalytic decomposition 0.111 0 41
0 42
0 36
0io
0 53 0 60 0 60 0.62
0 52 0 61 0 73
0.78
0.58
Thiols plus disulfides by titration (11,ZO)
0.062 0 06 0 03
0 59
0 02 0 01
0.61
0.01
Sulfur Compounds b y Types in Middle-East Crude Oil
98-204 18.0 0,090 '
Determination of Nonthiophenic Sulfur in Distillation Fractions from Wasson Crude
Distillatip cut points, C. 50"-119" 118°-2260 2260-2630 263"-319' 319"-380" 380"-436'
2
50-98 4.1
Total sulfur 0.02 Nonthiophenic sulfur a Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring &Ring and larger
(11,2 0 ) .
0.083
0.007
0.006 0.001
3 204-269 10.2
4 269-327 9.8
5
327-376 8.5
6 376-424 7.1
WEIGHT9;SULFUR I N FRACTIOSS 1.69 2.77 2.93 0.44 0.55 0.64 1.25 2.22 2.29 0.015 0.022 0.032 0.011 0.79 0.41 0.89 0.74 0.34 1.46 0.95 0.52 0.69 0.27 0.42
Residuum 42439.9 4.87 1.42 3.45 0.06 0.84 0 50
0.28 1.77
WEIGHT70SULFUR IN WHOLECRUDE
Total sulfur Sonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring %Ring and larger
0.0008 a
0.016 0.015 0.0013 0.0011 0.0002
0.070 0.027 0.043 0.0011 0.042
0.166 0.043 0.123 0.0015 0.088
0.033
0.236 0.047 0.189 0,0019 0.063 0.124
0.208 0,046 n. 162 0.0023 0.056 0.067 0.037
1 94
Totals of fractions 2 64
0 57
0 75
0 11 0 71
0 0 0 0 0
1 37 0 023 0 33 0 20
1 89 03 58
42
15 71
Sample not available for analysis.
VOL. 37, NO. 6 , M A Y 1965
e
653
Table VII.
Fraction number Boiling range, C. Weight % of crude Total sulfur Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger
1
50-1 11 7.8 0.110 0.11 0.00
Sulfur Compounds by Types in Hendricks Crude Oil
2 111-209 19.4
3 209-267 11.4
0.230 0.222 0.008 0.007 0.001
0.48 0.28 0.20 0.005 0.19
4 267-332 13.0
5
332-393 10.5
6 393-451 8.3
WEIGHTyo SULFUR IN FRACTIOKS 1.07 1.85 1.70 0.37 0.46 0.53 0.70 1.39 1.17 0.006 0.012 0.022 0.45 0.38 0.35 0.24 1.00 0.56 0.24
Residuum 45127.6 2.35 0.70 1.65 0.044 0.32 0.34 0.21 0.74
WEIGHTyoSULFUR IN WHOLECRUDE
Total sulfur Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger
0.0086 0,0086 0,000
0.046 0.044 0.0016 0.0014 0.0002
disulfides. Of the three sets of d a t a obtained for the heavy gas oil, the first two agree reasonably well, although nonthiophenic sulfur by the new method is higher than that measured for sulfides, thiols, and disulfides. The values for thiophenic types by the new method and by liquid-solid chromatography agree reasonably well; the values by mass spectrometry are higher than those with the other two methods, which is typical of our experience. Actually, thiophenic values by mass spectrometry should be lower than those by the new method, because thiophenes with saturated rings and those with more than one sulfur atom per molecule are not included as thiophenes by mass spectrometry.
Table
Fraction numb:r Boiling range, C. Weight % of crude Total sulfur Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring CRing 5-Ring and larger
1 50-114 6.0 D
a . l
0.055 0.032 0.023 0.0006 0.022
0.139 0.048 0.091 0.0008 0,059 0.031
0.194 0.048 0.146 0.0013 0.040 0.105
The two analyses of the kerosene agree well; in this case, nonthiophenic sulfur determined by the new method is slightly lower than the total measured for sulfides, thiols, and disulfides. The agreement between the two analyses of heavy catalytic cycle oil is very good for all compound types. The lack of agreement with the heavy gas oil between nonthiophenic sulfur determined by catalytic decomposition and t h a t as the total of sulfide, thiol, and disulfide prompted further checking. Table V contains values for nonthiophenic sulfur by both procedures for six distillation fractions from Wasson crude oil. Good agreement is shown for the four lower-boiling fractions; values in
0.141 0,044 0.097 0,0018 0,029 0.046 0.020
0.65 0.19 0.46 0.012 0.09 0.10 0.06 0.20
Totals of fractions 1.23 0.41 0.82 0.018 0.24 0.28 0.08 0.20
the first three fractions are actually slightly lower by catalytic decomposition. However, the two highest-boiling fractions, which are in the gas-oil range, give considerably higher values by catalytic decomposition. One possible explanation is that the colorimetric method for sulfides (4, 8) gives low results in the heavy gas-oil range; perhaps some of the sulfur atoms in these large molecules are sterically hindered from complexing with iodine. We see no particular reason why catalytic decomposition should give high values only in the heavy gas-oil range. All checks on the new method in the naphtha, kerosene, and light gas-oil ranges have indicated good or excellent
VIII. Sulfur Compounds b y Types in Kawkawlin Crude Oil 2 114-204 16.7 0.037 0.036
0.0005 0.0005
3 4 5 6 204-260 260-310 310-364 364-416 10.7 11.2 8.7 7.5 WEIGHTyo SULFUR I N FRACTIONS 0.074 0.124 0.330 0.451 0.050 0,052 0.109 0.148 0.024 0.072 0.221 0,303 0.0007 0.0008 , 0.0020 0.0028 0.023 0.051 0.066 0.081 0.020 0.153 0 135 0.084
Residuum 41636.4 0.61 0.20 0.41 0.0030 0,074 0.076 0.037 0.22
WEIGHT% SULFUR I N WHOLECRUDE
Total sillfur Ir;ont,hiophenicsrilfur Thioohenic sulfur 1-Ring 2-Ring 3-Ring 4-Jling 5-Ring and larger a Sample not available for analysis.
654
ANALYTICAL CHEMISTRY
0,0062 0.0061 0,00008
0.00008
0.0079 0.0053 0.0026 0.00007 0.0025
0.0139 0, 0.0081 0.00009 0,0057 0.0023
ooas
0.0287 0,0094 0.0193 0.00017 0.0058 0.0133
0.0338 0.0111 0.0227 0.00021 0.0061 0.0101 0,0063
0.222 0.073 0.149 0.0011 0.027 0,028 0.013 0.08
Totals of fractions 0.313 0.111 0.202 0.002 0.047 0.054 0.019 0.08
Sulfur Compounds b y Types in North Smyer Crude Oil
Table IX.
Fraction number Boiling range, ' C. Weight yo of crude Total sulfur Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger
1 50-92 10.0
3 202-257 12.5
2
92-202 25.2
0.0006 0.0006
5 314-357 8.5
6
3571412 6.8
WEIGHTyo SULFURIS FRACTIOW 0.152 0.291 0.342 0,026 0.054 0.074 0.121
0.0077 0.0072 0.0005 0.0005
0,000
4 257-314 12.6
0 033
o o
0.007 0 0004 0 0066
098
ooi3 0 081 0.016
n
217 0 0023 0 085
0.130
n
221
0 00s
0 092
0.103 0.020
Residuum 41218.0 0.456 0.134 0.322 0.008
0.078 0.066 0.067 0.103
WEIGHTyo SULFUR IN WHOLECRUDE Totals of fractions
Total sulfur Nonthiophenic sulfur ThioDhenic sulfur 1-Ring 2-Rinz 3-Ring 4-Ring 5-Ring and larger
0.00006 0.00006 0,0000
0.00194 0.00181 0.00013 0.00013
accuracy. With heavy gas-oil and residuum samples, accuracy probably is good b u t is difficult to assess. Some caution should be exercised in interpreting values for thiophenic kypes in heavy samples. Compounds determined as four-ring thiophenes, for example, could be of several types; in addition to the most likely members, naphthobenzothiophenes and phenanthrothiophenes, there could be compounds containing two thiophene rings and those containing one or more saturated rings. Gas chromatography would not distinguish among these. Values for one-ring thiophenes also should be viewed with some caution, especially in the higher-boiling virgin
Total sulfur
Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring %Ring and larger
1 50-100 1.5 0
a
0.0192 0.0068 0.0124 0.00016 0,0102 0.0020
0.0248 0.0063 0.0185 0.00020 0,0072 0.0111
samples. Satisfactory answers normally should be obtained. However, as mentioned previously, a few per cent of the thiophenic compounds containing a condensed saturated ring will lose the saturated ring during catalytic decomposition; some one-ring thiophenes could be formed by this means. Because the concentration of the latter is low, a small contribution from another source could cause a significant error. For two-, three-, and four-ring thiophenes, the error should be insignificant because any additional amount should be only a small proportion of that already present. With catalytically cracked samples, this source of error should be nil, even for one-ring
Table X.
Fraction number Boiling range, a C. Weight 70 of crude
0.0041 0.0033 0.0008 0.00005 0.00075
0.0233 0.0082 0.0151 0.0004 0.0063 0.0070 0.0014
100-2 12 7.6 0,009 0.005
0.004 0.004
3 2 12-271 17.5 0,034 0.018 0.016 0.0021 0.014
4 271-326 19.2
5 326-372 12.7
0.058
0.0014 0.014 0.012 0.012 0.019
0.155 0.050 0.105 0.0023 0.039 0.032 0.013 0.019
thiophenes, because thiophenic compounds have already lost unstable nonaromatic rings. APPLICATION TO PETROLEUM DISTILLATION FRACTIONS
Thiophenic types and total nonthiophenic sulfur were determined in six distillation fractions and the residua from seven. crude oils. One crude is from the Middle East (Table VI), and six are from the United StatesHendricks (Texas) , Kawkawlin (Michigan), North Smyer (Texas), South Houston (Texas), Wasson (Texas), and Wilmington (California)-Tables VI1 through XII. Wasson and Wilmington crude oils are being used by
Sulfur Compounds by Types in South Houston Crude
2
0.082 0.024
Oil
6 372-413 8.0
WEIGHTyo SULFUR I N FRACTIOXS 0.104 0.227 0.230 0.040 0,066 0.107 0.064 0.161 0.123 0.0023 0.0040 0,0082 0.036 0.024 0.033 0.026 0.133 0.061 0,021
Residuum 41332.0 0.390 0.165 0.225 0.012 0.041 0.044 0.038 0.090 ~
~~
WEIGHTYo SULFURI N WHOLECRUDE Total sulfur Sonthiophenic sillfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger * Sample not available for analysis.
0.0007
0.0004 0.0003 0.0003
0.0060 0,0032 0.0028 0.0004 0.0024
0.0200 0.0077 0.0123 0.0004 0.0069 0,0050
0.0289 0.0084 0.0205 0.0005
0.0031 0.0169
0.0184 0.0086 0,0098 0.0006 0.0026 0,0049 0.0017
0.125 0,053 0,072 0,004 0.013 0.014
0.012 0.029
Totals of fractions 0.199 0.081 0.118 0.006 0.028 0.041 0.014 0.029
VOL. 37, NO. 6, MAY 1965
655
Sulfur Compounds b y Types in Wasson Crude Oil
Table XI.
Fraction number Boiling range, C. Weight yo of crude O
Total sulfur
Nonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring &Ring and larger
50-119 8.8
2 119-226 21.6
3 226-263 7.2
0.112 0.111 0.001 0,001
0.44 0.41 0.03 0.019 0.011
0.90 0.52 0.38 0.023 0.36
1
4 263-319 11.9
5
319-380 10.1
6 380-436 8.0
WEIGHT70SULFURI N FRACTIONS 1.97 2.15 1.51 0.73 0.78 0.61 1.24 1.37 0.90 0.039 0.031 0.038 0.70 0.51 0.47 0.17 0.69 0.59 0.27
Residuum 43630.0 3.36 1.24 2.12 0.07 0.44 0.32 0.23 1.06
WEIGHT% SULFURI N WHOLECRUDE
Total sulfur Xonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger
0.0099 0.0098 0,0001 0.0001
of sulfur compounds in petroleum (2, 21). Four of the others have been described previously ( 2 5 ) , as has the distillation procedure used to obtain the fractions (15). These crude oils represent wide ranges of hydrocarbon distributions (15), and therefore might also represent wide ranges of sulfurcompound distributions. The analyses for sulfur-compound types are reported both as per cent sulfur in the fractions, and as per cent sulfur in whole crude. The cut-point temperatures of the fractions, given acroqs the tops of the tables, were determined by gas chromatography (5, 8 ) . K i t h respect to the distributions of the sulfur-compound types, gross differences among crudes were not found-
Table XII.
Total sulfur Sonthiophenic sulfur Thiophenic sulfur 1-Ring 2-Ring 3-Ring 4-Ring 5-Ring and larger
0.172 0.062 0 110 0 003 0 038 0 047 0.022
1.01 0.37 0 64 0 02 0 13 0 10 0.07 0.32
Similarities among the seven crudes in distributions of sulfur compounds are evident. All show relatively low sulfur levels in the naphtha range (fractions 1 and 2) and sharp rises in the kerosene (fraction 3) and light gas oil (fractions 4 and 5) ranges. The residuum fraction (portion boiling over about 440' C.) always contains a higher percentage of sulfur than any of the lower boiling fractions, and always accounts for more than 50% of the total sulfur in the crude. All the crudes show a predominance of nonthiophenic sulfur in fractions 1 and 2, and except for U'ilniington, all show a predominance of thiophenic sulfur in fractions 4, 5 , 6, and residuum. A11 the crudes show relatively small proportions of one-ring thiophenes (0.5 to 6% of the total sulfur) in fractions 3, 4, 5, 6, and
Sulfur Compounds by Types in Wilmington Crude Oil
50-116 2.4
2 116-212 9.5
3 2 12-274 9.3
0,007 0,003 0.004 0.004
0.157 0.124 0.033 0.032 0,001
0.56 0.37 0.19 0.023 0.167
1
0.199 0.074 0 125 0 004 0 051 0 070
e.g., nonthiophenic sulfur compounds are not present to the virtual exclusion of thiophenic compounds, or vice versa. The distributions of the sulfur types among crudes are more alike than different. The absence of gross differences parallels what has been found for hydrocarbon types. For example, the proportions of thiophenic sulfur in the seven crudes vary a little less than twofold (from 47 to 747, of the sulfur in fractions 1 through 6), which is similar to the variation for aromatic hydrocarbons (19 t o 327, of total hydrocarbons) in the same fractions of four of the crudes (15). Further, the proportions of individual thiophenic types vary among crudes only to about the same degree as do the proportions of individual aromatic types (15).
API Research Project 48 in its study
Fraction niimb:r Boiling range, C. Weight % of crude
0.180 0.073 0 107 0 004 0 083 0 020
0.065 0.037 0 028 0 002 0 026
0.095 0.089 0.006 0.004 0.002
Totals of fractions 1.73 0.71 1 02 0 04 0 33 0 24 0.09 0.32
4 274-332 10.0
5 332-390 10.5
6 390-445 10.9
WEIGHT7cSULFURIN FRACTIONS 1.16 1.56 1.49 0.58 0.72 0.81 0.58 0.84 0.68 0.06 0.09 0.09 0.46 0.42 0.27 0.06 0.33 0.23 0.09
Residuum 44545.8 2.13 1.18 0.95 0.12 0.23 0.10 0.026 0.47
WEIGHT7cSI-LFURI N WHOLECRUDE Total siilfur Sonthiophenic sulfur Thiophenic srilfur 1-Ring 2-Ring 3-Ring 4-Ring &Ring and larger
656
0,0002 0.0001 0.0001 0.0001
ANALYTICAL CHEMISTRY
0.0149 0.0118 0.0031 0.0030 0,0001
0.052 0,034 0.018 0.0022 0,0158
0.116 0,058 0.058 0.006 0.046 0.006
0.164 0.076 0.088 0.009 0.044 0,035
0.162 0,0X8
0.074 0.010 0.029 0.025 0.010
0.98 0.54 0.44 0.06 0.11 0.05 0.012 0.21
Totals of fractions 1.49 0.81 0.68 0.09 0.24 0.12 0.022 0.21
residuum. All show small absolute amounts of one-ring thiophenes in fractions 1 and 2 , but with South Houston and Wilniington crudes, these constitute a significant proportion of the total sulfur in the fraction. I n all the crudes, two- and three-ring thiophenes aceount for a much higher proportion of the thiophenic sulfur t h a n do one- and four-ring compounds; compounds with five or more rings, however, dominate in the residuum fractions. There are small differences among crudes in t h e relative proportions of two- and three-ring thiophenes. For example, some crudes (Wasson) have more two-ring compounds, while others (South Houston) have more three-ring compounds; however, ratios of the two types usually do not vary among crudes by more than 2 to 1. Wlmington crude shows the most atypical distribution of sulfur types. For example, one-ring thiophenes account for about 6% of its total sulfur, as compared to only 1 to 374 for the other crudes, and nonthiophenic sulfur accounts for 54% of the sulfur, as compared to only 28 to 4 l y G for t h e others. These differences probably are real; however, the high proportions of oxygen (0.44%) and nitrogen (0.65%) in
Kilmington possibly could cause errors. For example, saturated rings containing oxygen or nitrogen could open during catalytic decomposition, and some onering thiophenes would be produced. Also, aromatic rings containing sulfur along with oxygen or nitrogen might be more susceptible to opening than rings containing sulfur only. This problem would not exist with the other crudes, because they contain much smaller proportions of oxygen and nitrogen. LITERATURE C I T E D
(1) Am. Soc. Testing Materials, “ASThI
Standards, 1964,” )\lethod D-129-62, part 17, p. 63. (2) Ball, J. S., Rall, H. T., Proc. Am. Petrol. Inst. 42 (111).128 11962). (3) Coulson, D. M.,’ Cavanagh, L. A., “llicrocoulometric Detection in Gas Chromatography,” Pittsburgh Conference on Analytical Chemistry and A4ppliedSpectroscopy, March 1961. (4) Drushel, H. J’., AIiller, J. F., ANAL. CHEM.27. 495 11955). ( 5 ) Eggertsen, F. T.; Groennings, S., Holst, J. J., Ibid., 32, 904 (1960). (6) preen, L. E., Schmauch, L. J., Worman, J. C., Zbid., 36, 1512 (1964). ( 7 ) Hammar, C. G., Svensk Kem. T i d s k r . 63, 135 (1951). (8) Hastings, S. H., ANAL.CHEM. 25, 420 (1953). (9) Hastings, S. H., “Percolation-Mass
Spectrometric Method for Determining Thiophenes,” 10th Southwest Regional ACS Meeting, Fort Worth, Texas, December 1954. (10) Hastings, Y. H., Johnson, B. H., Lumpkin, H. E., ANAL.CHEM.2 8 , 1243 (1956). (11) Hubbard, R. L., Haines, W. E., Ball, J. S., I b i d . , 30, 91 (1958). (12) Klaas, P. J., Ibid., 33, 1851 (1961) (13) Lumpkin, H. E., Johnson, B. H.. Zbid., 26, i7i9 (1954);. (14) Martin, R. L., Grant, J. A , , Zbid., 37, 644 (1965). (15) Martin, R. L., Winters, J. C., Williams, J. A,, “Composition of Crude Oils by Gas Chromatography,” Proceedings Sixth World Petroleum Congress, Section \., p. 231, 1963. (16) l\IcCoy, 11. N., Weiss, F. T., ANAL. CHEM.26, 1928 (1954). (17) Snyder, L. R., Ibid., 33, 1538 (1961). (18) Snyder, L. R.,J . Chromatog. 6, 22 (1961). (19) Snyder, L. R., Union Oil Co. of Calif., Union Research Center, Brea, Calif., private communication. (20) Tamele, 11. W., Ryland, L. B., hIcCoy, R. N., AXAL.CHEM.32, 1007 (1960j. (21) Thompson, C. J., Coleman, H. J., Hookins. It. L.. J . Chem. Eno. Data 9. 293. (1964). (22) Yao, T. C., Porsche, F. W., ANAL. CHEM.31, 2010 (1959). RECEIVED for review December 14, 1964. Accepted February 4, 1965. Division of Petroleum Chemistry, 149th Meeting, ACS, Detroit, Mich., April 1965.
Thermal Peaks Accompanying Solute Peaks in Preparative Scale Gas Chromatography JAMES PETERS and C. B. EUSTON’
F & M Scientific Corp., Avondale, Pa. Temperature variations have been measured radially across a 1-inch diameter preparative column, and it is suggested that these variations contribute to the decrease in efficiency observed as column diameter is increased. The high sample loadings frequently used in preparative scale gas chromatography increase these temperature differences and further reduce column efficiency. Programmed temperature preparative columns were considered, and the gradients existing were recorded. Gradients frequently reach several degrees centigrade and are related directly to program rate. Similar measurements on temperatureprogrammed columns show that the temperature at the column center lags the wall by about 1 minute for a 1 -inch diameter column. The temperature difference thus is proportional to heating rate, and may reach several degrees a t high programming rates.
P
of large samples through preparative scale columns may create a significant local disturbance in column temperature because of the evolution and absorption of the heat of solution of the sample. These temperature disturbances will alter the velocity of the solute zone and, of particular importance, this change in velocity will not be equal over the cross-section of the column. The creation of such a distorted velocity profile will seriously affect column performance. With this consideration in mind, the radial variations in column temperature were measured in 1-inch columns as component peaks passed through. The sample size was varied over a 50-fold range. Because of the considerable interest shown recently in the combination of programmed temperature and preparative scale gas chromatography, several temperature measurements were also made in 1-inch programmed columns. ASSAGE
An earlier paper by Scott (a)discussed the temperature changes associated with solute passage in analytical columns, but because of the small diameter of the columns, the radial variations so important in preparative scale work were not measured. EXPERIMENTAL
Apparatus.
T h e columns used for this study were 1-inch copper tube, 3 feet long, a n d contained 20% SE-30 on 60- to 80-mesh Chromosorb P. They were split a t their mid-sections t o allow accurate placement of three 5000-ohm thermistor beads radially across, t h e column a t distances of a n d 1 / 2 inch from t h e column wall. The column was then assembled and filled in the usual manner. Electrical connections to each bead kvere made via two thin magnet wire lead$ enclosed in l/l+j-inch stainless steel Present address, F&M Scientific Europa N.T’., Basisweg (Sloterdijk), Amsterdam, The Netherlands. VOL. 37, NO. 6, MAY 1965
657
