Especiaciòn de Azufre en Crudo

8/11/2019 Especiacin de Azufre en Crudo

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(4) Dutton, H. J., Mounts, T. L., J .Cata lys i s 3, K O . , 363 (1964).

, 5 ) Faryuhar, J . W. , Insull, W., Rosen,P., Stoffel, TI ., Ahrens, E. H., S u t r .A b a t ~ . ev. 17, No. , Part 11, 1 (1959).

( 6 ) Hall, W . K., NacIver, 1). S., Weber,H. P., lad . Eng. Chem. 5 2 421 (1960).

( 7 ) Hoelscher, H. E., Poyner, W . G.,Weger, E., Chem. Revs. 54, 575 (1953).

( 8 ) Homing, E. C. , Ahrens, E. H., Jr. ,Lipsky, S R., Rlattson, F. H., Mead,J . F. , Turner, D . A., Goldwater, U'. H.,J . Lipid Research 5, 20 (1964).

( 9 ) Humk o Products, Sterick Bldg., Mem-phis, Tenn., Humko Tech. Bull., 1963.

(10) James, A. T., Wheatley, 5 . R.,

(11) Klenk, E. , Eberhagen, D. . Hovve-Biochem. J . 63, 269 (1956).

Seylers Z . Physiol . Cheh . 328, K O .3-6,180 (1962).

112) Kokes. R . J.. Tobin. H.. Jr. . Emmett .P . H. , . A m . Chem. S O C . ~ ~ , 860(1955).

(13) Korn, E. D., J . B iol . Chem. 238,3584 (1963).

(14) Lindeman, L. P., Chem. Eng. .Vetus40 N o . 38, 61 (1962).

(15) Luddy, F. E., Barford, 11. A.,Riemanschneider, R . W., . .4m. OilChemists SOC. 7, 447 (1960).

(16) Woodford, F. P., \.anGent, C . R l

RECEIVED or review September 21, 1964.Accepted Rlarch 4, 1965. PittsburghConference on Analytical Chemistry andApplied Spectroscopy, Pittsburgh, Pa.,March 2 to 6, 1964. Article not copy-righted. The Northern Laboratory ispart of the Korthern Utilization Researchand Development Division, AgriculturalResearch Service, U. S. Department ofAgric ulture. hle ntio n of firm namesortrade products does not imply that they

are endorsed or recommended by theDepartment over comparable productsofother manufacturers.

J . L ipid Res. 1, 188 (1960).

Determination of Sulfur-Compound Distributions

in Petroleum Samples by Gas Chromatographywith a Coulometric Detector

RONALD L. MARTIN and JOHN A. GRANT

Research and Development Department, American Oil Co., Whiting, Ind.

The distributions of sulfur compoundsin a va riety of petroleum' sampleswere determined by a combination ofgas chromatography and microcoulo-metric sulfur detection. The detect ionsystem responds to sulfur compoundsbut not to hydrocarbons. Under op -timum operat ing conditions, i t quan-titatively determines individual sulfurcompounds at sulfur levels down toabout 5 p.p.m. Gas chromatographicseparations are made on a silicone-rubber column, from which sulfurcompounds are eluted nearly in orderof boil ing point. Sulfur-compound dis-tributions b y boili ng point are shownfor gasoline, coke-still naphtha, lightcatal ytic cycle oil, vi rgi n naphtha,kerosene, and gas-oil, On ly in thelower-boiling samples can individualsulfur compounds be determined. Fora crude oil, gas chromatography-inconjunction with other ana lyt ica l tech-niques-has been used to determinethe distribution of the five principalsulfur-compound types as a functionof carbon number to C20 These dataillustrate a typical sulfur distributionfor virgin petroleums.

KCRISASEI) KNOWLEDGE of the typesI and d istribution s of sulf ur com-1)ounds is needed in many phases of~ ~ e t r o l e u mrocessing. As a ineans foracquiring such knowledge, gas chro-niatogt,aIihj. with selective niicrocoulo-metric sulfur detection was investigated.'I'he coulometric detector reslmnds tocomllounds containing sulfu r but not tohj .di .oc~arbonh, nd t he i~ fo re an deter-minp tracc amounts of sulfur com-1)ounds.even if hydrocarbons are elutedwith t hcni.

hficrocoulometric sulfur detectors forgas chromatography were developedindependently by Coulson andCavanagh 7 ) , and Klaas (IS). T h edetector of Coulson and Cavanagh,which followed the design of an earlierhalide detector 6), has been usedexten sively in the ana lysis of pesticides

4 , 5 , 7 ) nd was suggested for petroleumanalysis 7 ) . Klaas I S ) developed asimilar detector and successfullyapplied it to petroleum samples; selec-t ive gas chromatography columns wereused in clever fashion to determinesulfur-compound types- in .naphthas.Fredericks and Harlow (9) also used acoulometric detector for sulfur com-poun ds; the y modified the halidedetector (6) to accurately and select ivelydetermine thiols in natural gas. Thistype of detector was not used in ourstudy because it does not respond toother types of sulfur compounds.

In this work, microcoulometr ic sulfurdetect ion was tested for quant i ta t iveperformance, interferences, and ap-plicability to all types of petroleumsamples. Sulfur distributio ns by boilingpoint for seven types of petroleum

samples were determined by thecombination of gas chromatographyand coulometr ic detect ion. The gaschromatographic separations were ob-tained with conventional nonselectivecolumns. Analyses for sulfur-com-pound types were obtained by othertechniques to supplement t he gas chro-matographic data . For a Middle-Eastcrude, resul ts f rom gas chromatography,mass spectrometry, and liquid-solidchromatography were combined toob tain distributio ns of t he five principalsulfur types as a function of carb onnumber to Cz0.

MICROCOULOMETRIC SULFUR DETECTOR

The microcoulometr ic detect ionsystem is manufactured by DohrmannInstrument Co. (Model C-100) ac-cording to the design of Coulson andCavanagh (6, 7 ) . It has two maincomponents-combustion tu be andt i t rat ion cel l. The combust ion tub e islocated between the column and t i t ra-tion cell, and serves to osidize thecolumn eff luent ; sulfur compounds formsulfur dioxide, which subsequently ist i t ra ted automatical ly with coulo-metr ical ly generated iodine. Hydro-carbons are converted to carbon dioxideand water and general ly do not affectthe t i t ra t ion. The current used foriodine generation is recorded to give anordinary different ial chromatogram forsulfur compounds. The combustiontube, which is maint,a ined at750 C., is10 inches by 5 / 1 6 inch and packed withquartz chips. Xitrogen sweep andoxyg en flows of 150 ml. per minute eachare brought in at the head of th e tubealong with the column effluent.

The detector is sensitive as well asselective; the minimum detectable

amo unt is abou t gram of sulfur(between t 'hat for thermal-conduct ivi tyand f lame-ionizat ion detecto rs) , andsamples with sulfur contents in the parts-per-million range can be analyze d. Th edetector t ime constant is larger thanthat of conventional detectors because ofthe time needed for combustion andtitration; this limits the effectivenessfor closely-spaced 1)eaks eluted in th efirst several minutes, but otherwisecauses no problems. Th e detector iseasy to opera te and main ta in .

Quantitative Performance of D e -tector. F o r q u a n t i t a t i v e a n a l y s e s ,

644 ANALYTICAL CHEMISTRY


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sulfur dioxide product ion from al ltypes of su l fu r compou nds mus t bereproduc ib le and d i rec t ly p ropor t iona lt o s u l f ur c o n t e n t . S u l f u r c o m p o u n d sare conver ted main ly to su l fu r d iox ide,bu t convers ion never r eaches 1 0 0 ~ on ddepends on operat ion of the combust iontube. For example, the conversion tosulfur dioxide at several combust ion-tube tem perature s is shown in Tab leIfor thiophene.

Th e conversion to sulfur dioxide wascalculated from the numb er of coulombsused for iodine generation. I t isat amaximum in the 650-7500 C. range,and d rops ra the r sha rp lyas t empera tu reis increased to 950'. The drop in con-version probab ly is due ei ther to greaterprod uctio n of sulfur trioxide (which iskinetically possible even though op-posite to the direction of equilibrium),or to less-complete decom position of thesulfur compound because of a decreasein catalyt ic act ivi ty.

Th e age of t ,he qu art z packing alsoaffects sulfur dioxide production.

Freshly packed tubes produced lesssulfur dioxide, especially in th e 500 -700' C. range, than did ones used for amonth o r more .

When alumina or 10% plat inum onasbestos was used instead of quartzchips, sulfur dioxide production wasonly a few per cent of theory at allt empera tu res .

T he flow rate of oxygen, sweep, andcolumn-eluting gases have little effecton sulfur-dioxide product ion. Forexample, with quartz chips a t 750 ' C. ,varying oxygen from 20 t o 300 a n dnitrogen sweep from 0 to 300 ml. perminute had essent ia l ly no effect , nordid th e use of helium ins tead of nitrogenas elut ing and sweep gases .

Even though conversion to sulfurdioxide is not complete , quant i ta t iveanalyses are possible with the coulo-metr ic detect ion system. This isindicated by the analysis of a syn the t i cmix ture (Tab le11), or which chromato-graphic peak areas were assumed pro-port ional to sulfur content and werenormalized to th e value for total sulfu r ;combustion was performed at 750' C.The difference between added andfound values averaged only 3%, whichis qui te acceptable . Th e per cent con-

version to sulfur dioxide is nearly th esame, apparent ly, for compoundsof alltypes and boiling points.

Linearity of response for the coulo-metr ic detect ion system extends fromthe minimum detectable amount(abou t 10-8 gra m of sulfur) upwar d forabout three orders of magni tude.Larger amo unts were not tes ted becausethe 1)eaks became bro ad and flat-topliedas a result of insufficient speed of iodinegeneration.

De tec to r In te r fe rences . In te r fe r-ence has been encoun te red f rom la rgesamples of hyd rocarbons , and f rom

c o m p o u n d s t h a t p r o d u c e s t r o n g ox-id iz ing agen t s dur ing combus t ion-e . g . , c o m p o u n d s c o n t a i n i n g b r o m i n e ,ch lo r ine , o r n i t rogen .

Interference from hydrocarbons varieswith the size and composition of thesamples . I t i s not not iceable in theusual-sized sam ple (0.1 to 5 p1, of anindividual hydrocarbon or up to about100 p l . of a mixtu re of aide boi l ingrange) . However, larger samples of tengive an interfer ing response thatgenerally is positive, but is sometimesnegat ive or a l ternately both posi t iveand negat ive. Th e interference fromhydrocarbons ap parent ly ar ises becauselarge samples are incompletely oxidized,and some of the interm ediate productsare either oxidized by iodine or reducedby iodide in the titration cell.

Hydrocarbon response tends to di-minish, but is not e l iminated, as theoxygen and particularly the sweep flowrates are increased. However, detectornoise also increases with flow rate, andbecomes excessive when th e flows exceed

a b o u t 300 ml. per minu te . Limit ingthe sample size has been the onlysuccessful means of eliminating hyd ro-carbon response. Thi s usual ly l imitsthe min imum de tec tab le amou nt fo rindividual sulfur compounds to about5p .p .m.

Compounds containing chlorine, bro-mine, or nitrogen interfere because theircombust ion produces s t rong oxidizingagen ts, which in tur n oxidize iodide ionin the t i t ra t ion cel l to give a negat iveresponse. Bromine comp ounds inter-fere seriously even in trace amounts.Interference from chlor ine compoundsis less severe, and it can be reduced andsometimes el iminated if the oxygen isbubbled through water before combus-tion Y), n which case the combustionproduct is mostly hydrochloric acidrath er th an chlorine. Kitrogen com-pounds interfere less severely than thehalogens, and their concentrations inpetroleum samples general ly are toolow to be troublesome.

GAS CHROMATOGRAPHIC SEPARATIONS

Th e gas chromatographic separat ionswere made wi th a stainless steel column,

20 feet by inch i.d., packed wit h15% by weight of silicone rubber(General Electr ic SE-30) on acid andcaustic washed 30-60 mesh Chromosorb-W . Column temperature was pro-g r a m m e d a t 4 per minute f rom 60 C.to as high as 400 . The flow of elutinggas was maintained at 100 ml. perminu te .

The silicone column was chosenbecause i t e lutes sulfur compounds,regardless of type, nearly in order ofboil ing point . In the naph tha andkerosene ranges, boiling points could bepredicted from elution time within5' C.;

Tab le 1 Conversion to Sulfur Dioxideat Different Temperatures

Combustion-tube Conversiontemp erature, C. to sulfur dioxide

550enn650700750850950

70809193897463

Tab le II. Determination of Sulfur Com-pounds in Synthetic Mixture

Sulfur, ToAdded Found

Thiophene 0 0081 0 0085Methylpropylsulfide 0 0052 0 00503-Methylthiophene 0 0059 0 00581-Pen tanethio l 0 0092 0 00902,5-l>imethylthiophene 0 0057 0 0060

1-Hep anethiol 0 0068 0 0066n-Butylsulfide 0 0035 0 0037Benzolblthiophene 0 0145 0 01442-Methvlhenzo Iblthio-

Ethyldis ulfide 0 0101 0 0095

i

phen i 0 0232 0 0236n-Am yldisulfide 0 0058 0 0057Dibenzothiophene 0 0107 0 0109

errors in the gas-oil range would besomewhat higher. I n this work, it wasimportant that e lut ion t ime could berelated to boiling point, because in-dividual compounds generally could notbe identified, and identification byboiling point had to suffice.

T he silicone column occasionally wasused to 400' C.; column bleed beginsear l ier (a t about 300 C.) but does notlead to significant response from thecoulometric detector. Th e relativelyhigh percentage of silicone rubber(150j0) is used to avoid adsorption ofthiols on the Chromosorb-W support .After several months operat ion, thioladsorpt ion increases , and the columnmu st be replaced.

APPLICATIONS

Character is tic sulfur dis t r ibut ions areillustrated by determinations on gaso-line, coke-still naphtha, catalytic cycleoi l , whole crude, and the hea vy nap htha ,kerosene, and gas oil fractions from thecrude (Figures 1 th rough 7) . T h efigures are plots of sulfur concentrationu s boiling point of th e sulfur com-pounds, where boiling point has beenestimated from the elution times of purecompounds with known boiling points.I3ecause all su l fu r t y lm of ten a re p res-ent in virgin samldes, identification ofindividual mpmbers is difficult, anddistributions by boiling 1)oint oftenmu st suffice. In the refined samp les,however, sulfur distributions usuallyare less complex, and some individual

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D I S U L F I D E S 2S U L F I D E S I IT H I O L S IT H I O P H E N E S 61B E N Z O T H I O P H E N E S 5

100

c g 'BrThs

1 2 5 0 3 5 0 4 50 5

BO ILIN G POlN T,O F

Figure 1 Sulfur compounds by boiling point in gasoline

I - R I N G T H I OP H E N ES I

2 - R I N G T H I O P H E N E S 7 9

3 - R I N G T H I O P H E N E S 14

CIO

BzThs' C I I

2MTh

IISH

HYDROGEN SULFIDE 5T H I O L S 15D I S U L F I D E S 3S U L F I D E S 20T H I O P H E N E S 5 2BENZOTHIOPHENES

II

I00 200 300 400 500 I

BOILING POINT, O F

Figure 2. Sulfur compounds by boiling point in coke-sti l l naphtha

comp onents or group s of com pone ntscan be determined orat least estimated.

Gasoline. Th e dis tr ibu t ion of sul-f u r compou nds in gaso line is r e la t ive lysimple, as shown in F igure 1 for a reg-u la r-g rade sample con ta in ing0.090%su l fu r. Mos t of t h e c o m p o u n d s a r ethiophenes, a few of which-thio-phene, 2- and 3-methyl thiophenej benzo-[bl thiophene, and 2- and S-methyl-benzothiophene-were identified byemergence times and are labeled on th echromatogram. The others are ident i-fied only by carbon number becauseindividual reference compounds werenot avai lable .

The b reakdown of su l fu r types in thegasoline, as determined by specific tests(S, 10, 11 1 4 , 15, I T ) , i s shown a t theupper lef t of the chromatogram. Th esulfides, thiols, and disulfides are dis-t r ibuted throughout the boi l ing range.

About one third of t he sulfur is incom1)ounds boiling above the normalgasoli ne end 1)oint of a bo ut 415' F.,most of which are benzothiophenes.This I)rol)or t ionis higher than might besuspected, but is character is t icof mostgasolines.

About 20 gasolines and catalyticallycracked naphthas (which provide thebulk of sulfur in most gasolines) havebeen surveyed by gas chromatography.Interestingly, similar sulfur profileswere obtained in each case, even thoughthe samples were produced by differentcompanies from different crudes andwith different catalytic cracking proc-esses.

Coke-Still Naphtha. In coke-st i l ln a p h t h a , w h i c h is formed from re-s i d u u m b y t h e r m a l c r a c k i n g , t h ed i s t r ibu t ion of su l fu r compounds i smore complex , a s shown in F igure2for a typ ica l sample con ta in ing0.7201,sulfur. Thiop henes still predo minate,but significant am oun ts of hydrogensulfide, thiols, an d sulfides also ar epresent .

Mo st of the thiols could be identified.

They are concentrated in the lower-boiling pa rt of th e sample and decreasein concentrat ion from ethyl to amyl.Most of them are straight chain ed;isopropyl is the main exception.

Two peaks ( thiacyclopentane andmethyl thiacyclopentane) were tenta-tively identified as sulfides by emergencetimes. Mo st of the other sulfides forma background under the thiophenes;they are probably cyclic, because theunidentified pea ks, like those in gasoline,do not match the retent ion t imes ofchain sulfides. Chain sulfides probablyare not suff icient ly s table to survive thecracking reactions.

I n l i gh tcatalyt ic cycle oi l , which come5 fromca ta ly t i c c rack ing of gas oi l , thed i s t r i b u t i o n of su l fu r compounds a l soi s re la t ive ly uncompl ica ted , a s shownin F igure 3 for a typ ica l sample con-ta in ing 1 ,42y0 su l fu r. Al though th i schromatogram has many unresolvedpeaks, the sulfur distribution is lesscomplicated than those of virgin stocksof the same boiling range.

M o s t of the sulfur is thiophenic;the analyses for sulfur types 14) ,which are included on the chromato-gram, show that two- and three-r ingthiophenes account for 79% a n d 14 ,respectively, of the total sulfur.

Only a few individual compoundscould be identified with certainty-benzothiophene, 2- and 3-methylbenzo-thiophene (In the peak labeled C SBaThs) , and dibenzothiophene. How-ever, ma ny of th e peak groupings weretentatively identified by carbon number.Such identifications were achieved bycomparing mass spectrometr ic and gas

Light Catalytic Cycle Oil.

0



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BOIL ING POINT,OF

Figure 4. Sulfur compounds by boi l ing p oint in crude oi l

chromatographic data on two- andthree-r ing aromatic concentrates ob-tained by liquid-solid chromatography.Wi th gas chrom atography, compoundswere found, as a first approximation,to

group toge ther by ca rbon number.An analysis by carbon number forbenzothiophenes and dibenzothio-phenes, as calculated from th e Figure3chrom atogra m, is given in Table 111.These values were obtained by inte-grat ing the area s of peaks at t r ib uted toeach carbon number, and normalizingthe areas to the value for total sulfurless that determined as nonthiophenicsulfur ( 1 4 ) . Although such analyses areonly qualitatively valid, they have beenvery useful in following the progress an dpatterns of desulfurization reactions.

Crude Oil. F i g u r e 4 s h o w s t h ed i s t r ibu t ion of su l fu r compo unds bo i l -ing to 1000 F. i n t h e M i d d l e - E a s twhole c rude (con ta in ing 2 72y0 sul-f u r ) , a n d i l l u s t r a t e s t h e c o m p l e x i t yof su l fu r d i s t r ibu t ions in -v i rg ins a m p l e s . O n l y a few componentscan be ident if ied with much certainty,and essentially none can be determined.Quali ta t ive information, however, canbe deduced. Sulfur in the nap hth arange is low. Th e big rise begin s in t'hekerosene range with the two-r ingthiophenes, most of which are benzo-thiophenes and are vis ible over thebackground of other peaks. A secondand steeper rise start 's in the light gas-

oil range wit,h the three-ring thiophen es,which are most ly dibenzothiophenesand naphthothiophenes. The sulfurcompounds boi ling throug h1000 F., asdetermined by the chart area and alsoby analyzing distillation fractions, ac-count for 40 of the total sulfur.

.i b e t t e r l o o k a tt h e n a p h t h a - r a n g e s u l f u r c o m p o u n d sis p r o v i d e d b y F i g u r e 5 which showsthe heavy nap h tha (con ta in ing0.090~osulfur) from the Middle-East crude be-fore and a fter removal of thiols an ddisulfides (after reduction) with silverni t rate .

Virgin Naphtha.

The lower-boiling portion of the totalnaphtha contains mainly thiols, most ofwhich are identified in Figure5 . Un-like the thiols in coke-still naphtha,these are mainly branched, which is

consistent with the findings of o the rs onvirgin naphthas 3 ) . Some of thesethiols were not originally present in thecrude oil, but rather were formed duringdistillation.

The sulfur compounds in the thiol-free naphtha are mainly sulfides, sincethe thiophene analysis ( 1 4 ) representedonly 1 of the total sulfur. A few ofthe major peaks ar e definitely identif iedas straight-cha in sulfides. Mo st of the

Tab le 111. Thiophenic Compounds byCarbon Number in Light Cata ly t ic

Cyc le O i l

Sulfur, c LB E N Z O T H I O P H E N E S

C* 0 014C9 0 15ClO 0 27cu 0 25c12 0 18e 3 0 12Ci4 and higher 0 14

ClZ 0 017Cl? 0 08

D I B E N Z O T H I O P H E N E S ~

e;;Clb nd higher

0 .070 05

One-ring thiophenes and non-thiophenic sulfur* 0 .10__

1 . 4 2

a Includes naphthothiophenes.Determined by catalytic-decomposi-

tion method 14) .

peaks between the s t raight-chainmembers probably are branched-chainsulfides. Cyclic sulfides app aren tly arepresent in smaller amounts than chainsulfides, which is reverse to the usuals i tua t ion ( 1 , 2 , 1 8 ) . Cycloparaffins inthis naphtha also are present only insmall amounts , which suggests thatpro por tion s of cyclic and chain sulfidesin crude oils may follow the proportionsof cyclic an d ch ain paraffins.

I I I I I I 1

HIOL-FREE N A P H T H A

II

T O TA L N A P H T H AD I S U L F I D E S 6S U L F I D E S 5 7

IH I O P H E N E S1 0 0

100 2 0 0 3 0 0 4 0 5 00

B O I L I N G P O I N T , O F

Figure 5 . Sulfur compounds by boi l ing point in heavy naphtha

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T H I O L S 6D I S U L F l D E S 3S U L F I D E S 4 2 EzThsI - R I N G T H I O P H E N E S 22 - R I N G T H I O P H E N E S 453 - R I N G T H I O P H E N E S

CI O C I I

I I I I I I I I1 350 450 5 5 0 650 i

cI38T hs

1H I O L SS U L F I D E S 2 2I - R I NG T H I O P H E N E S I

B O I L I N G P O I N T , OF

Figure 6. Sulfur compounds by boil ing p oint in kerosene

DiBzThs

A nearly complete resolution ofnaphtha-range sulfur compounds mightbe obtained with selective liquid phases,such as those suggested by Karchmer

l a ) and Klaas ( I S ) . Long, wide-borecapillary columns might be particularlyeffective for such work.

Kerosene. Th e dis tr ibu t ion of sul-fu r compounds in the ke rosene (con-ta in ing 0 .50% sul fu r ) f rom the Mid-d le -Eas t c rude i s shown in F igure 6 .The major peaks extending above thebackground represent chiefly the 9-,lo-, 1 - , and 12-carbon benzothiophenes;benzothiophene itself is too small to bepositively identified. Th e higher-boilingportion contains some dibenzothio-phenes, and dibenzothiophene itself isidentified. Th e background consistsmostly of sulfides, which account forabout 42Q/ ,of the total sulfur. Again,one-ring thiophenes are present only insmall amou nts . Thiols account foronly 6% of the total sulfur, which is alower percentage than in the naphtharange, but a similar absolute amount.

Quant i t a t ive use of this chromato-gram is limited to determining sulfurdistribution by boiling point. In-dividual compounds or compounds bycarbon number cannot be determinedwith certa inty . An estim ate of the pro-portion of thiophenic su lfur can , how-ever, be made.

Gas Oil. Th e d i s t r ibu t ion of su l fu rc o m p o u n d s i n t h e l i g h t v a c u u mvirgin gas oi l (containing 2.60%sul fu r ) f rom the Midd le -Eas t c rude i sshown in Figure 7 . Again, thiophenic

compounds extend above the back-ground of other peaks. Th e first seriesof peaks (between 450 and 600 F.)consists mostly of benzothiophenes.Th e second series (from abo ut 630' to750 F.) consists mostly of dibenzoth io-phenes, nhich project above an intense

ound that includes benzothio-lthenes as well as sulfides. In contrastto cycle oil, two- and three-ring thio-phenes cannot be determined, becausethe background of other sulfur com-pounds is too gre at. Th e distribution ofthio1)henic types must be obtained byanother m ethod 14) .

2 - R I N G T H I O P H E NE S 353 - R I N G T H I O P H E NE S 37 D i B z T h

4 - R I N G T H I O P H E N E S 4

SULFUR TYPES BY CARBON NUMBERIN CRUDEOIL

I0 0

Gas Chromatography can be moreeffective when used in combination withother analyt ical techniques than by i t -self. Th e effectiveness of combininggas chromatography, mass spectrom-etr y, liquid-solid chrom atograph y, andspecific tests is illustrated by Figure8,which shows distributions by carbon

numb er of th e five principal sulfur type sin the Middle-East crude oil. Data forthiophenic types came from analysis ofliquid-solid chromatographic fractionsby gas chromatography and/or low-voltage mass spectrometry, and analysisof distillation fractions by the catalyticdecomposition method ( 1 4 ) . Sulfideand thiol values came from specific testson distillation fractions 8, 10, I Y ) , andwere verified by values for nonthio-

phenic sulfur obtained by catalytic de-composition ( 1 4 , 1 5 ) ; carbon numberswere estimated from the boiling rangesof th e fraction s. One-ring thioph enesare not included in Figure S becausetheir levels are insignificantly low.Disulfides are not included becausethey mere not found in freshly distilledfractions. Because some assumptio nshad to be made to prepare the plots ,the data should be considered only assemiquanti ta tive. The data for four-ring thiophenes probably are the leastaccurate.

Two- and three-ring thiophenes are

the pr incipal compound types in thecrude oil. Ma ss spectrometric analysisof chromatographic fractions indicates

B O I L I N G P O l N T p F

Figure 7. Sulfur compounds b y boili ng point in gas oil

. 0 6

o s

01

:

Figure 8. Sulfurtypes by Carbon 03Number in Middle- gEast crude

.02

01

I I I I I I I I I

I\

\2 - R I N G \ /

. . . - . . - -

I / \

THIOPHENE^

d B 16 20 1 4

C A R B O N N U M B E R



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t h a t 80 to 90% of these thiophenes aretul ly arom atic . Two-r ing thiophenesa r e a t a m a u im u m a t CI1( three carbonsabove the first member of the series),and then decrease gradual ly with in-creasing carbon num ber. Three-r ingth iophenes a re a t a max imum a t CI4( two carbon numbers above the f i rs tmem ber of th e series) and t hen decreaserather sharply with increasing carbonnum ber. Benzothiophene itself is pres-ent in very small proportion (0 .0002~o)dibenzothiophene, however, is about0.009%.

Sulf ides increase in amount to aboutCQ0 nd then level off ; they are thepr inc ipa l type in the heavy naph tha(C,-C,) range. Thiols are a t a maxi-m u m a t a b o u t Cs; they then decreaseand are negligible in the gas-oil r ange.

The sulfur compounds through Cz0plotted in Figure 8 account for 0.67%sulfur, which is only 25y of th e totalsulfur in the crude. Hydrocarbonsthrough C?, account for 607, of thetotal crude.

Figure 8 illubtrates a typical distribu-

tion of sulfur compounds in petroleum.Crude oils contain different absoluteamounts of sulfur and slightly differentproportion s of th e various sulfur types

f4), ut their dis t r ibut ions by carbonnumber, in our euperience, usual ly aresimilar. Two - and three-ring thio-phenes, for example, generally possessthe same maxima and s imilar ra tes of

decline as those shown in Figure 8.This c rude has a slightly smaller pro-portion of sulfides than most crudes

f4), ut the sulfides show the char-acter is t ic s teady r ise in amounts intothe gas-oil range. Th e crude also showsa fairly typical distribution of thiols; ofal l the compound types, thiols probablyare th e most var iable among crude oi ls .

CONCLUSION

Ga s chrom atography with coulo-metr ic detect ion has proved to be aneffective m eans for chara cterizing sulfurdis t r ibut ions, even though individualcompounds general ly cannot be deter-mined. In futu re work, gas chroniatog-raphy should be used more in combina-tion with other analytical techniques.Two excellent techniques would belinear elution adsorption chromatog-raphy I C ) , and mass spec t romet ry ;fract ions separated by l inear chromatog-raphy would be analyzed by bo th gaschromatography and mass spectrom-e t ry. Such a combination should

yield much more information than thetechniques could produce individually,and should be amenable to rout ineapplication.

LITERATURE CITED

( 1 ) Birch, 8. F., Cullum, T. V., Dean,R . A , , Ilenyer, R. L., I n d . Eng Chem.47, 240 1955 ).

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.,Res idue Rev. 5, 57 1 964 ).

5 ) Coulson, D. M., n Gas Chroma-tography, L. Fowler, ed., p. 213,Academic Press, New York, 1963.

6 ) Coulson, I>. Al., Cavanagh, L. A , ,A I VA L .H E M .2, 1245 1960).

( 7 ) Coulson, D. A I . Cavanagh, L. A.,Mcrocorilometric D etection in GasChro matog raphy, Pittsbur: h Confer-ence on Analytical Chemistry andApplied Spectroscopy, JIarch1961.

8 ) Ilrushel, H. \. \[iller. J. F.. A N A L .C H E M .7. 495 i 955).

9 ) Fredericks, E. A I . Harlow, G . A.,

10) Hastingr, S. H., Ib id . , 25,420 1953).( 1 1 ) Hubbard, R . L., Haines, W. E.,

12) Karchmer, J . H., Ib id . , 31, 1377

13) Klaaq, P. J. , bid . , 33, 1851 1961 ).14) Mart in, R . L., Grant , J. A., Ib id . ,

15) l I cCoy, R. N. , Weiss , F. T. , Ib id . ,

16) Snyder, L. R., Ib id . , 33, 1527, 1538

Ib id . , 35, 263 1 964) .

Ball, J . S., bid . , 30, 91 1958).

1959).

37, 649 1965 ).

26, 1928 1954).

1961).

RuFeau of M i n e s Rept. Inves t . 62521963).

RECEIVEDor review December 14, 1964.Accepted January 28, 1965. Division ofPetroleum Chemistry, 149th LIeeting,ACS, Detroit, N ich. , April1965.

Determination of Thiophenic Compounds byTypes in petroleum SamplesRONALD L M A RT I N a n d J O H N A. GRANT

Research and Development Department Am erican Oil Co., Whiting Ind.

A m ethod for determining thiophenic-compound types in pet ro leum samplesof a l l types and boi l ing ranges hasbee n devel op ed. Nonthiophenic sul-fur compounds are decomposed overa lumina a t 500 C. t o fo rm hydrogensulfide and arom atic thiols which ar ecol lec ted and t i t ra ted to determineto tal nonthiophenic sulfur. Thiopheniccompounds extens ively dealkyla tedin the decomposi t ion react ion aresepa ra t ed by gas ch roma tog raphyaccording to number of r ings anddetected by microcoulometric t i tration;thiophenic types with one two threefour and f ive or more rings aredetermined. Accuracy of the methodi s good as judged by analyses on testsamples and by compar ison wi th o theranaly tical techniques. Disti l lation frac-tions and residua from seven crudeoi ls were analyzed to provide sul fur-

type characterizations heretofore un-attain able. Differences among crudesin the distribution of sulfur-compoundtypes usually are not la rg e . Thiopheniccompounds typically account for 50 to7 7 f the sulfur; excep t in residuamost of these compounds have eithertwo or three rings.

r THE R E F I N I N G f high-sulfur crudeI oils, the dete rm inat ion of sulfur-compound types of ten is important .T he need for such analyses is partic-ularly great in the gas oil and residuumranges, where avai lable methods haveno t been completely satisfactory. Oneparticular use is to follow the Iirogressof desu lfuri zatio n processes, which pro-ceed a t different rate s for each of thesulfur types.

In the f i rs t re la t ively completedelineation of the sulfur types in gas

o il s, Lum pkin and Johnson 1 3) showedthat compounds containing condensedthiophene and aromatic r ings accountedfor iiiost of the sulfur. Th eir workprovided the basis for the f i rs t methodfor thiophe nic types-the mass -sl)ectro-metr ic method of H ast ings, John son,and Lumpkin (10)-which gives semi-quantitative determinations of benzo-,dibenzo- , and naphthobenzothiophenes.Although th is method ha s been veryvaluable in following composition tren dsand react ion behavior, i ts accuracy andalq)licability leave someth ing to bedesired. In our experience, values forthiophenic sulfur frequently are high,paiticularly for samples with limitedboiling ranges. Ma ss sl)ectronietryalso has been used t o determine on e-r ing thiophenes 9) , but on ly in naph tha -range samples.

Liquid-solid chromatography on

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