-Workshop on Challenges in Crude Evaluationwith Changing Crude Scenario.

APPLICATION OF CHROMATOGRAPHYIN PETROLEUM FIELD

S.D. BhagatIndian}nstitute of Petroleum, Dehradun-248 005

ABSTRACT

Modern chromatography by virtue offantastic capabilities for separation, qharacteriza-tion, quantitation and fractionation has emerged as a potential analytical technique forhydrocarbon industry. Presently the gas chromatography alongwith high performanceliquid chromatography coverwide range ofapplications in diversified areas including Basicand applied research. Availability of large number of stationary phases, specific detectors,newer analytical procedures, improved instrumentation alongwith hyphenated techniqueshave made chromatography an indispensable and versatile tool.

This paper deals with the recent trends in chromatography for the analysis of variouspetroleum fractions, right from light gases to higher boiling fractions using gas chromatog-raphy (GC),high performance liquid chromatography (Hplc)and supercritical fluid chroma-tography (SFC).

INTRODUCTION

In recent years chromatography has emerged as one of the most efficient andconvenient technique for separation, detection, characterization and quantificationof components in a complex mixture. Presently on account of substantial develop-ment on chromatographic instruments, availability oflarge number of stationaryphases (columns) along with newer analytical procedures, chromatography hasbecome an indispensable tooi for analytical scientists.

CQmbination ofhighly efficient and selective separation techniques alongwithspecific detectors has widened the scope to varieties of applications includingstructural elucidation. Hyphenated chromatographic techniques like GC-MS, LC-MS, GC-IR, GC-UV,LC-UV, GC-IR-MSD etc. where components after separation

60

are directly transferred into the ion source of mass spectrometer, to infrareddetector or to ultravoilet spectrometer etc. has provided additional capabilities forpositive identification of large number of components in a complex mixture. Thesuccess of modem chromatography is due to very high separation efficiency,sensitivity, precision and accuracy of analytical data.

APPLICATIONS OF GAS CHROMATOGRAPHY (GC)

Gas chromatography has proved to be one of the most important analyticaltool in the area of petroleum hydrocarbons. With the invent of multidimensionalcolumn switching system and hyphenated techniques GC hasfurther proved to bean indispensable technique for the industry in process control, process develop-ment, monitoring the product quality and formulating specifications as well aswaste and pollutant analysis. In petroleum industry GC finds wide application toestimate the potential of crude oil for lighter hydrocarbons, naphthas, higherfractions and specific products.

Lighter Hydrocarbon Analysis

Analysis of gaseous hydrocarbon is required in various refinery streams,petrochemical industry, gas and oil condensate in fields, exhaust and, mine gasesetc. Natural gas analysis is one of the important analysis in Petroleum industry.Estimation -of C1-C5hydrocarbon in gasoline was one of the first gas liquidchromatographic application in petroleum industry for monitoring gasoline volatil-ity.

Gaseous hydrocarbons generated during conversion process can also beanalysed using porous layer open tubular (PLOT) column coated with AI2O/KCI.Fig.1 shows the resolution of C1 to C5 hydrocarbons alongwith C4-C5isomersseparation.

Analysis of individual HC Upto Cs

One ofthe most difficult and time consuming analysis confronting petroleumand petrochemical laboratories is the determination of individual HC in gasolinefraction upto 180°C.More than 200 compounds ofwide chemical nature, consistingof normal and branched paraffins, mono and bicyclo paraffins and mononucleararomatics exist normally in straight run naphtha.

61

Most of the components in naphtha can be charactenzed and quantifiedeasily using HRGC under temperature programming. Johansen et all have identi-fied around 200 hydrocarbons in petroleum naphtha using wall coated open tubular(WCOT) column of methyl silicone (OV-IOl) with flame ionisation detector (Fig.2).

Separation of Mono-Aromatics

Petroleum streams are seamingly an endless source of aromatic hydrocar-bons for a number of industries, hence their qualitative and quantitative estima-tions in straight run, reformed and cracked naphtha, gasoline are desirable.Monoaromatics in gasoline can be analysed using a polyethylene glycol capillarycolumn with operating conditions as given in figure-3.

Analysis of n-Paraffins in Kerosine

The determination of normal alkanes distribution in hydrocarbonm~ture is ofconsiderable importance in petroleum industry. Normal alkanes fr

tm petroleum

sources are important feedstocks for petrochemical industries, t e long chainalkanes can be converted to lubricant and fuel additives, plastici2;ers, industrialsurfactants etc. Such wide applications have generated a new ~nterest in therefinery processes for recovering long chain alkanes from petroleum. The distribu-tion ofnCll-nCl4 alkanes obtained from kerosene fraction has immense potential inthe manufacture of biodegradable detergents. A capillary GC method has beendeveloped2at LLP. for estimation ofnormal-alkanes in kerosene using capillary GCalongWith substractive chromatography as shown in Fig.4.

DEDICATED GAS CHROMATOGRAPHS FOR PETROLEUM INDUSTRY

Hydrocarbon Type Analyzer (Piona)

The determination of hydrocarbon group type components in petroleumnaphtha and gasoline blending stocks is extremely important in the petroleumrefining industry. PlaNA analyzer automatically characterizes isoparaffins, n-paraffins, iso-olefines, n-olefines, saturated naphthenes, olefinic naphthenes andaromatics in a single injection in petroleum distillates boiling upto 200°C. PlaNAseparation scheme of cracked naphtha is shown in Fig.5.

62

Natural GaslRefinery Gas Analyzers

Natural gas is an important-energy source and is available in abundant. Thegas composition must be accurately determined in order to establish a fair marketprice based on calorific heating value. N~tural gas analyzers are configured for fullyautomated analysis offixed gases and light hydrocarbon. Standard reports includ-ing sample components, spe<f~ficgravity, heating value, and gallons of liquid per1000.cm.ft 3 gas (gpm) can be obtained with these analyzers. Refinery gas analyzersare configured to analyze various refinery gases, liquified petroleum gases, crackedefiluents and petrochemical down streams. Refinery gas analyser3 are most effec-tive by using multi column switching techniques as shown in Fig. 6.

Oxygenates Analyzers

Lead additives in gasoline are being phased out because of the toxicity.Oxygenated compounds are now preferred as gasoline octane boosters. In order toprovide consistent product quality, the concentration of these additives must bedetermined. Oxygenates analyzers are specially designed for automated analysisC1-C4alcohols and MTBE in gasoline according to ASTM D-4815. The multidimen-sional combination results in complete separation without interference from hydro-carbons in gasoline. Fig.7 shows the separation of various oxygenates analysed ingasoline.

SIM DIS Analyzers

GCtechniques have been found to be suitable for the determination ofboilingrange distribution. of petroleum products. Based upon a fused silica AI-Cladcapillary column, this turnkey analyzer for crude oil and petroleum fractionsprovide solution for specific analytical problems which cannot be solved by othermethods. SimDis analyzer are highly suitable for crude oil analyses, barrel bottomanalysis, high vacuum oils and residual analysis upto 750°Cboiling point determi-nation. They reduce the total operators time involved and increase the overallproductivity. Sim Dis analysis compares very well with TBP distillation data andcovers extended range Fig.8.

PROCESS GAS CHROMATOGRAPHS

The advantage of Process GC is to obtain data with high speed of response

63

which is comparable to process change. The analytical datum is utilized quickly fortaking corrective measures in the process control. A distinguishing character ofprocess GCis that the sample is quickly transferred from process sampling point tothe chromatographic column untouched by human hands. The overall design ofprocess GCin petroleum industry is influenced by several important factors viz. thepurpose, location, reliability, automatic operation, maintainability and use ofdata.Block diagram of process GC is shown in Fig.9.

APPLICATION OF HIGH PERFORMANCELIQUID CHROMATOGRAPHY (HPLC)

HPLC is idealy suited for separation of macromolecules, ionic species, labileproducts and variety of other high molecular weight or less stable compounds.Characterization of petroleum products has grown increasingly important becauseof the need to optimise feed stock use and for evaluating products performance asa function of chemical composition. .

HPLC has four basic separation modes ego Absorption, Partition, Ion-exchange and Size exclusion.

Further more the greater variety of stationary phases widen the scope ofLCusefulness. The scope of HPLC application widens further by incorporating recy-cling, pre or post column derivatization, solvent and gradient programming, columnswitching devices, specific detectors and by using ancillary (tandem) techniques.

Light Distillates

Two rapid HPLC techniques for separating light and heavy gasoline distil-lates into saturated, olefinic, and aromatic compounds are described5. The first oneinvolves adsorption chromatography using silica column. The second method isbased on charged transfer chromatography with silver coated or bonded to silica geland n-C5 as mobile phase. Suatoni et al6 achieved separation of saturates, olefinsand aromatics in gasoline range material (60-215°C)by employing a low polarityperfluorocarbon mobile phase and a small particle silica column (proposed as analternative for the FIA method, ASTM D-1319). Fig.l0 presents the hydrocarbongroup type analysis of gasoline.

64

Middle distillate analysis (Kerosene and Diesel Fuels)

The importance of hydrocarbon type analyses in diesel fuel is well known.The detennination of olefins is necessary for monitoring and predicting the stabilityof diesel fuels. The measurements of aromatics is of interest for the correlation ofstructural characteristics with combustion properties. A dielectric constant detec-tor with olefin selective column for hydrocarbon group type analyses (saturates,olefins and aromatics) with distillate end point upto 400°C has been reported 7usingFreon 123 as a mobile phase. A HPLC method is described8 for quantification of thecompound class composition (saturates, one ring, two rings, polynuclear aromaticsand polars) of olefin free kerosene and diesel fuels.

Aviation Turbine Fuels

HPLC separates the components of aviation fuels into saturates, olefins andaromatics. Mter emergence of saturates and olefins from the column, back flushinggives a single peak of total aromatics (RI detector). Naphthaleneis estimated usingUV detectors at 285nm. Separation is achieved through two 4x250mm silicacolumns with hexaI).e mobile phase.

Lubricating Oils

Hydrocarbon types in lubricating oil base stocks by preparative HPLC coversthe separation and determination of saturates and aromatics boiling above 270°C.All compounds more polar than saturates including those containing S, N or 0 aredetennined as polars. Separation is achieved through two 7x500 mm column ofsilica gel with hexane solvent and RI detector. Hydrocarbon types are determinedgravimetrically (lP designation 368/84). Hydrocarbon group-type characterizationis shown in Fig. 11 of virgin and used oil.

Hydrocarbon Group Type Analysis

A rapid hydrocarbon group-type analysis of petroleum fractions (b.p.I90-360OC)is reported9 for separation ofsaturates, mono-olefins, di-olefins and aromat-ics using two silica columns with hexane as mobile phase. Suatoni et altOdescribedprocedure to analytically determine hydrocarbon group types, saturates, aromatics,polars and n-hexane insolubles. This basic method is applicable to total crude 'oiJs,

65

. /

gasolines, kerosene, middle distillates fuel oils, residues, lubricating oils andsynthetic crudes derived from coal liquids, shale oils and tar sands. Data arepresented which includes both calibration factors and 8:Ilalysisof these materials.

CrudeOils, Bitumens and Related Materials

HPLC involves class fractionation into four major hydrocarbon groupsasphaltenes, saturates, aromatics and polars. Arapid automated HPLC system hasbeen developed11forsemipreparative separation ofcrudeoils,bitumens and relatedmaterials into either compound class group type fractions or aromatic ring numberfractions. The quantitative data oil crude and process oils varied upto 2% for anycompound class fractions analysed on amino column. The heavy oil residues andpitches from petroleum and coal processing often contain many polycyclic aromatichydrocarbons, saturated hydrocarbons, polar substances etc. HPLC proceduregives aromatic ring distribution (ARD)to meet the requirement for further utiliza-tion of these heavy oil produ;cts from thermally cracked residues, ethylene tarresidues, coal tar pitches, decant oils, residual oils etc. Crude oil as such can beseparated into hydrocarbon groups (Fig. 12).

Molelcular Weight Distribution by OPC

A gel permeation chromatographic technique12is used for the determinationof the molar mass of petroleum distillation residues. UV and IR detectors are usedto indentify aromatics and paraffinic compounds respectively and a system ofthreegel columns allows the wide range of component molar masses from 100 to 10,000glmol to be identified. The determination of the molecular weight distribution(MWD) of pitches and resids is important for industrial utilization of heav.yresidues. A method for determining MWD ofres ids, heavy oils, and pitches etc hasbeen established by high performance GPC and VPO. .

Ion-Chromatography in the Oil industry

Ion chromatography determines inorganic and short carbon chain organicanions and cations in aqueous solution at ppm and lower levIes. Some ofthe anionsreported when petrol is combusted in an engine (petro analysis 87). These ions cancause corrosion and can be detrimental to lubricating oils (Fig. 13).

66

Polars in Petroleum

Mckay et al14have reported the analysis of acids in high boiling petroleumdistillates. The major acidic compound types were identified as carboxylic acids,phenols, carbazoles and amides. GPC, LSC, and TLC were used, for compound typeseparation and structural studies conducted using mass, X-ray fluorescence andNMR.

HYPHENATED(TANDEM)TECHNIQUES

The technique of on line coupled high performance liquid chromatography/capillary gas chromatography is applied15to the analysis of kerosene and dieselfuels. Normal phase microbore HPLC is used to obtai!).a group type separation andthe capillary GC for detailed analysis ofindividual components in the fuel. On linefractionation and identification ofdiesel fuel polycyclicaromatic compounds by twodimensional microbore HPLC/capillary GC to the aromatic ring-size is described.These compounds are thought to contribute towards diesel exhaust polycyclicaromatic compounds (PCA) and are listed as priority pollutants. The potential of acoal or shale derived liquid fuel precursor to be upgraded to a fuel product can beassessed, if the composition ofthe precursor is known. HPLC and GC-MSprovidedcompositional data to allow one to estimate fuel upgrading potential.

ANALYTICAL METHODOLOGY FOR CRACKED PRODUCTS

Modem petroleum refining has several conversion processes in its arsenal forupgrading heavy ends to light fuel products and petrochemical bulding blocks. Theknowledge ofproduct distribution is helpful in optimising the reaction-parametersfor maximisation of desired productsl5.

Such information is useful not only from the view point of understanding thereaction chemistry, but also for evaluation product yields and quality for exampleproduct stability dependence on olefinsl6.

Products obtained during conversion process are complex mixture andcontain compounds ofall classes of hydrocarbon (paraffins, naphthenes, olefins &aromatics), often present as hybrid structures. To investigate such complex mix-ture, number of analytical techniques to be employed for example gaseous products

67

byGC, liquid products byHRGC, GC-MS, HPLC andFT-IR, while yields ofdifferentboiling fractions were estimated by simulated distillation. GC-MS is best suited fordetailed characterization of the product constituents as shown in Fig. 14 whileHPLC gives hydrocarbon group type information.

SuperCritical Fluid Chromatography(SFC)

Anew approach in chromatography has emerged through the introduction ofsupercritical fluid chromatography which combines the selectivity of HPLC sepa-rations with the power of GC detectors. With SFC one can analyse a full polarit:rrange of analytes-offering potential for screening complex samples mainly asaresearch tool for analyses that are challanging to GC and HPLC. In petroleumindustry SFC extends analytical range ofhydrocarbons that can be analyzed by GC.The SFC excels at hydrocarbons class separations, having selective and sensitivedetection necessary for analyzing complex mixture of hydrocarbon and additives.High boiling and complex mixtures can be quickly analysed using flame ionisationdetector at lower temperature, than are used in GC. Further more SFC performsASTM m,ethod D-5186 for determining aromatic content in diesel fuel with theadded benefits of UV detector of aromatic fractions. SFC separations of largemolecules with molecular weight upto 5000 Dalton using CO2as mobile phase canbe executed at temperature of 100°C and below. Class type and carbon no wiseanalysis is shown in Fig. 15.

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

N.G.Johansen, L.S.Ettre and R.L.Miller, J.Chromatog. Sc.256, 393, (1983)

S.C.Vishnoi, V.B.Kapoor, S.K.Chopra, S.D.Bhagat & R.Krishna. Analyst112,49(1987).

Hewlett Packard Technical bulletin, 1993.

Gas Chromatography by G.Schomburyp-183.

P.Gareil et. alj.,Chromatogr., 357, 381 (1986).

J.C.Suatoni, H.R.Garber and RE. Devis, J.Chromatogr. Sci. 13,367 (1975).

P.C.Hayes and S.D.Anderson, Anal. Chem., 58, 2384 (1986).

D.J.Cookson, C.J.Rix, I.M. Shaw and RE.Smith, J.Chromatogr., 312,237(1984).

68

15.

16.

J.C.Suatoni and H.R.Garber,J.Chromatogr. Sci., 14, 546 (1976).

J.C.Suatoni and R.E.Swab. J.Chromatogr. Sci., 13,361 (1975).

P,L.Grizzle and D.M.Sablotny, AnaL Chem., 58, 2389 (1986)

P. Guieze and J.M.Williams, J.Chromatogr., 312, 261 (1984)

J.F.Mckay, et.al. Fuel, 54, 50 (1975).

I.L.Davies, K.D. Bartle, G.E.Andrews and P.T.Williams, J.Chromatogr. Sci..26, 125 (1988).

Y.V.Kissan, J.Catal.,132, 409 (1991).

RP.Badoni, S.D.Bhagat & G.C.Joshi, Fuel 71, 483, (1992).

9.

10.

11.

12.

13.

14.

69

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51.63610

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Fig 2 Chromatogram ofindiyjdual HC in naphtha fraction run on 100mx0.32mm squalane capillarycolumnat ambient temperature.

70

~ Bz.ToL'-~'.

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Fig 3 Separation ofJD()OOoaromaticson 30m x O.22mm OV-275 capllarycolumn at 65OC.

1.1 n-e,. n-C'3 n.c'2 n-e" n-C,o

n.e.~

Ibl

(a) without molecular'sieve and (b) with mofecular sie've

Fig 4 Analysis OrB-paraffinsin kerosene on sOm x O.32mmOV-IOIcapillaJy column operated under temperature program.

71

OV27$

PIONA SEPARATION SCHEME

OLEFINTRAP

131

uparilion of

INJ.

non.

aromilles

by

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I) Pl(h)ONA ANALYSIS OF NAPHTHA (FCC)I)

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poly.N>200'C

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Fig 5 PlONA Analyzer.

72

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i-par n.par naph !-par n.par naph

3 .00 .00 .00 .00- .00 .00 .00 .004 .31 .58 .00 .32 2.65 .00 .00 3.BE5 4.51 1.03 .14 4.14 4.99 .49 .00 15.306 4.13 .74 1.44 4.93 3.38 1.90 .53 17.07 3.26. .46 3.26 3.84 .97 2.05 2.49 17.8 2.43 .39 2.49 2.64 1.17 1.30 4.99 15.409 1.85 .33 1.49 2.13 .77 .74 7.29 14.5910 1.31 .20 -87 2.16 .52 .66 4.28 10.0011 .99 .11 .49 1.15 .30 .64 .00 3.69

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2. Ethanol3.MTBE4.ETBE5. Ethlene glycoldimethylether6. Benzenel1-meth~ cyclopentane7.T~8. Heavy hydrocarbons

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Fig 7 Analysisofoxygenatesin ~lir30m x O.S3mmx 2.6Smm HP.

7~rSU,

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28nL-"': '."'" l.-50 55 80 85 7~~L15.80 82 84 88 88 90

YIELD, 'HIWT.Use of SM DIS Nth TBP in crude ass8Y lysls

'V SM DIS OF SHORT PATHSTill DISTI.LATE

0 SM DISAS WT%0 TBFERATURE OF TBP

FRACTIONS

Elution curves of . mixture of Five DirterentPetroleum Fractions (20~ eac:h)

Tlme(min.) ..0 20 080 80

nC 120 100 80 80..0 20

Fia 8 SIM DIS analysesof petroleum fiactions.

73

,

Fig. 9 Process Control Gc.Light Gc:soline

SaturatesMono-Olellns

Benzene

~ -.--- ~~

Fig. 10 Hydrocarbon Group-Type Separation of Gasolineby HPLc.

.....0en.

VIrgin motor oil Used Motor oil

Saturates 73.7Aromatics 25.4Polan 0.9AsphaJtenes Nil

....0CI)

RI

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Fig. 11 HPLC characterization of Lube Oils.

74

C~blnda IA"9oll}

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1oV' .Fig. 12 HPLC Sepantion of Crude oil into

Hydrocarbon Groups.

Fig. 13 Anionsfrom Comb~of Petrol.

L80.

Expanded Mass Chromatogram.

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Fig. 14 Mass Chromatogram of Cncked Product of n-bnadecane.

75

COL~

Class-Typt Seplntion of Petroleum products.

...,.

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GASOUNE

A

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Separation of Silicone Fluid.

SFC sepenlllon of polyllloune add (500-750)"0lIl . S8mpIt SIIcen8 811d....-Cobnn 1Om.5Oum.1.0.. ~ DB-S, Medallea, 11mthlclcntn 0.2 urn.MobIlephase supercrillcalCO2.temperatures Linear program tom 100 to 150~Pressures Isymtotlc dIMIty program. Detector FIDInstrument Cn E\1)1SFC 3000

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Fig. 15: Applications of SFC.

76

Q.

Ans.

Q.

Ans.

DISCUSSION

B.R.TyagiIOC, R&DFaridabad

S.D.BhagatlIP, Dehradun

N.S.RamanIOC R&DFaridabadS.D.Bhagat

Can simulated distillationpredict the quality of wide cut?

With the help of simulateddistillation, we can predictdistribution of <4ITbonnumbersand percentage distribution ofdistillate cuts viz, naphtha,Kerosene, diesel etc, on thebasis of boiling rangedistribution for wide cuts aswell as crude oils.

What reference samples are youusing for simulated distillation?

We are using reference samples ofnormal paraffins having carbonranges [C3-C18][CS-C18][Cs-C4Jand [C3-C4J

77