Scrapbooking

Chemical characterization of aromatic compounds in extra heavy gas oil by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

Description
Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS)was used for the characterizationof aromatic compounds present inextraheavy gas oil (EHGO) fromBrazil. Individual identification of
Categories
Published
of 9
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
   Journal of Chromatography A, 1218 (2011) 3208–3216 Contents lists available at ScienceDirect  JournalofChromatographyA  journal homepage: www.elsevier.com/locate/chroma Chemical characterization of aromatic compounds in extra heavy gas oil bycomprehensive two-dimensional gas chromatography coupled to time-of-flightmass spectrometry Bárbara M.F. Ávila a , Ricardo Pereira a , Alexandre O. Gomes b , Débora A. Azevedo a , ∗ a Universidade Federal do Rio de Janeiro, Instituto de Química, Ilha do Fundão, Rio de Janeiro, RJ 21941-909, Brazil b Petrobras,CENPES/PDP/TPAP, Ilha do Fundão, Rio de Janeiro, RJ 21941-909, Brazil a r t i c l e i n f o  Article history: Available online 8 October 2010 Keywords: Aromatic hydrocarbonsSulfur compoundsExtra heavy gas oilComprehensive two-dimensional gaschromatographyTime-of-flight mass spectrometry a b s t r a c t Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry(GC × GC-TOFMS)wasusedforthecharacterizationofaromaticcompoundspresentinextraheavygasoil(EHGO)fromBrazil.IndividualidentificationofEHGOcompoundswassuccessfullyachievedinadditiontogroup-typeseparationonthechromatographicplane.Manyaromatichydrocarbons,especiallypolycyclicaromatichydrocarbonsandsulfurcompounds,weredetectedandidentified,suchaschrysenes,phenan-threnes,perylenes,benzonaphthothiophenesandalkylbenzonaphthothiophenes.Inaddition,triaromaticsteroids, methyl-triaromatic steroids, tetrahydrochrysenes and tetraromatic pentacyclic compoundswerepresentintheEHGOaromaticfractions.Consideringtheroof-tileeffectobservedformanyofthesecompoundclassesandthehighnumberofindividualcompoundsidentified,GC × GC-TOFMSisanexcel-lent technique to characterize the molecular composition of the aromatic fraction from EHGO samples.Moreover, data processing allowed the quantification of aromatic compounds, in class and individually,usingexternalstandards.EHGOdatawereobtainedin  gg − 1 ,e.g.,benzo[a]pyrenewereintherange351to 1164  gg − 1 . Thus, GC × GC-TOFMS was successfully applied in EHGO quantitative analysis. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Petrochemical products contain a large and diverse numberof chemical classes, such as paraffins, naphthenes, aromatic andunsaturated hydrocarbons, as well as sulfur, oxygen and nitrogencompounds [1]. There are a great number of individual com- ponents within these classes, making these samples extremelycomplex. For analysis of these mixtures, Blomberg et al. [2]demonstratedtheapplicabilityofcomprehensivetwo-dimensionalgas chromatography (GC × GC) to the characterization of a com-plex petrochemical mixture and several aromatic hydrocarbonsand sulfur compounds were identified in samples. Similarly, inextra heavy gas oil (EHGO) samples, the number of individualcomponents is vast, and no single chromatographic techniqueis able to separate and characterize these complex mixturescompletely. So, comprehensive two-dimensional gas chromatog-raphy (GC × GC) could be particularly useful in solving thisproblem [1,3,4].EHGO samples are obtained by molecular distillation, a proce-dureusuallyusedforthedistillationofthermallyunstablematerial, ∗ Corresponding author. Tel.: +55 21 25627488; fax: +55 21 22603967. E-mail addresses:  debora@iq.ufrj.br, debora quim@hotmail.com (D.A. Azevedo). which is the most economically feasible method of purification[5].Thistechniqueiswidelyappliedinfinechemistry,petrochem-istry,pharmaceuticalchemistryandoilandgreaseanalysis,aswellas in scientific research to concentrate and purify organic chemi-cals of high molecular weight, high boiling point, high viscosity orpoor heat stability [5]. Moreover, since petroleum sources are pro- gressivelydecreasing,thedemandforupgradingheavyfractionsisincreasing.Molecular distillation has been used for heavy petroleum pro-cessing and characterization [6,7]. In this way, GC × GC coupled totime-of-flight mass spectrometry (GC × GC-TOFMS) could be usedfordetailedchemicalcharacterizationofEHGOobtainedbymolec-ulardistillation.Theresultsregardingthechemicalcompositionof EHGO is very important to petrochemical industries, giving infor-mation about the nature, chemical makeup and applicability of these materials.Concerning aromatic compounds, there are few studies report-ing the analysis of such substances in petrochemical samplesby GC × GC. Table 1 shows some of the most important resultsobtained [3,8–13,14–20]. In particular, there is no work regarding EHGO analysis by the mentioned technique. Furthermore, the lit-erature points to only one paper concerning the characterizationof saturated biomarkers in Brazilian EHGO samples using GC × GCcoupled to time-of-flight mass spectrometry [21]. 0021-9673/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2010.09.051  B.M.F. Ávila et al. / J. Chromatogr. A 1218 (2011) 3208–3216 3209  Table 1 Important works regarding aromatic compound analyses in petrochemical samples by GC × GC.Sample Detector used Characterized molecules ReferenceBTEX FID Benzene, toluene, xylenes, alkylbenzenes, naphthalenes, methylnaphthalenes [8]Crude oils FID Naphthalenes, biphenyls, fluorenes, phenanthrenes, chrysenes, dibenzothiophenes,benzonaphthothiophenes, steranes, triterpanes, triaromatic steranes[9] Jet fuel FID Alkylbenzenes [10]Kerosene TOF Monoaromatic compounds and alkylbenzothiophenes [11]Naphtha FID Aromatic compounds [12]Crude oils and FCC products TOF, AED Aromatic thiols, alkylated benzothiophenes, dibenzothiphenes,benzonaphthothiophenes, phenanthrene, pyrene and methylpyrene, chrysene,carbazoles[13]Naphtha FID Mono- and diaromatics [3]Diesel FID Mono-, di- and triaromatics, naphthenic-diaromatics [14]Gasoline FID, TOF Benzene and alkylbenzenes, toluene, naphthalene, styrene, benzothiophenes [15]Gasoline FID Benzene, toluene, ethylbenzene, naphthalene, xylenes [16]Diesel FID Mono- and diaromatics [17]Source rocks FID, SCD Aromatic compounds, benzothiophenes, dibenzothiophenes [18]Downhole fluid FID, TOF Naphthalenes, phenanthrenes, alkylbenzenes [19]Heavy oil TOF Alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) [20] In the present study, the aromatic fractions of EHGO sampleswere analyzed using GC × GC-TOFMS and their molecular compo-sitions characterized, providing a detailed report on the classes of compounds present in these samples. Moreover, the data process-ing allowed for a quantitative analysis of the aromatic extra heavygasoilfractions,anotherobjectiveofthiswork.Becauseofthelim-ited information on the chemical constituents of EHGO, this studyalso enhanced the understanding of these samples and continuedthe study initiated by our group on Brazilian EHGO samples. 2. Experimental  2.1. Sampling and sample preparation Threeextraheavygasoil(EHGO)samplesweresuppliedbyCEN-PES/PDP/TPAP, Petrobras (Brazil), and named RO-59, RO-82 andAL-35. Each of these EHGO samples was obtained by moleculardistillation (10 − 3 mmHg) of the vacuum residue (ASTM D 5236).Molecular distillation is a process used to separate the fractions of differentmolecularweightinthevacuumresidueatthelowestpos-sible temperature to avoid damage. The EHGO samples were thenfractioned into saturated ( n -hexane), aromatic [ n -hexane: CH 2 Cl 2 (8:2)] and polar compounds [CH 2 Cl 2 :MeOH (9:1)] by liquid chro-matography, using activated silica gel (Merck) [22,23].  2.2. GC  × GC-TOFMS The GC × GC-TOFMS system was a Pegasus 4D (Leco, St. Joseph,MI, USA), which is an Agilent Technologies 6890 GC (Palo Alto, CA,USA) equipped with a secondary oven and a non-moving quad- jet dual-stage modulator. Data acquisition and processing wascarried out using ChromaTOF software version 4.0 (LECO Corp.,St. Joseph, MI). The GC column set consisted of a HP-5 ms, 5%-phenyl–95%-methylsiloxane (30m, 0.25mm i.d., 0.25  m d f  ) asthe first dimension ( 1 D) and a BPX-50 (Austin, Texas, USA), 50%-phenyl–50%-methylsiloxane (1.5m, 0.1mm i.d., 0.1  m d f  ) as thesecond dimension ( 2 D). The second column was connected to theTOFMS by an empty deactivated capillary (0.5m × 0.25mm i.d.).The columns and the empty deactivated capillary were connectedby SGE unions using SilTite metal ferrules (Austin, Texas, USA) for0.10–0.25mm i.d. GC columns.GC conditions followed published experimental settings [21].Briefly,theprimaryoventemperatureprogramwas70 ◦ Cfor1min,ramp at 20 ◦ Cmin − 1 to 170 ◦ C, and then ramp at 2 ◦ Cmin − 1 to325 ◦ C. The secondary oven temperature program had a temper-ature 10 ◦ C higher than that of the primary one. Carrier gas flowratewas1.5mLmin − 1 usinghelium.Apreviousanalysiswasmadeusingthesamemodulationperiodforsaturatedhydrocarbons(8s),butseveralwraparoundpeakswereobserved.Therefore,themod-ulation period was altered for 10s with a 2.5s hot pulse durationand a 30 ◦ C modulator temperature offset versus the primary oventemperature.The MS transfer line was held at 280 ◦ C, and the TOFMS wasoperated in the electron ionization mode with a collected massrange of 50-600  m /  z  . The ion source temperature was 230 ◦ C, thedetector was operated at 1650V, the applied electron energy was70eV, and the acquisition rate was 100 spectras − 1 .  2.3. Data processing  GC × GC-TOFMS data acquisition and processing were per-formed by ChromaTOF software version 4.0 (Leco, St. Joseph, MI,USA).Afterdataacquisition,samplesweresubmittedtoadatapro-cessing method where the individual peaks were automaticallydetected on the basis of a 10:1 signal to noise ratio. Individualpeakareaswereautomaticallyacquired,andcompoundidentifica-tionwasperformedbyexaminationandcomparisonwithliteraturemassspectra,retentiontime,authenticstandardsandelutionorder.A standard mixture solution of PAHs (EPA 610) wasacquired from Supelco (Bellefonte, USA). After dilution,the injected solution contained 1.6ng  L  − 1 of anthracene,benzo[a]anthracene, benzo[a]pyrene, benzo[k]fluoranthene,chrysene, indene[1,2,3-cd]pyrene, phenanthrene and pyrene;3.2ng  L  − 1 of benzo[b]fluoranthene, benzo[g,h,i]perylene,dibenzo[a,h]anthracene,fluorantheneandfluorene;and32ng  L  -1 of acenaphthene, acenaphthylene and naphthalene. Thesecompounds were used as external standards for compoundidentification and external quantification, and were analyzedapplying the same analytical conditions used for extra heavy gasoilsamples.Anyresponsefactorwasused,beingthequantificationrelative to the respective external standards.Quantification of identified compounds was achieved from therelation between the sum of peak areas in respect to the PAHstandards and its concentration in the external standard mixture.For example, triaromatic steroid compounds and alkylbenzonaph-thothiophenes were quantified relative to pyrene and chrysenestandards, respectively. Therefore, it was possible to calculate therelative concentrations (ng  L  − 1 ) of each compound identified bythe relationship between its peak area and the peak area of theexternalstandardofknownconcentration.Later,thisconcentrationwas corrected to the initial EHGO mass (  gg − 1 ).  3210  B.M.F. Ávila et al. / J. Chromatogr. A 1218 (2011) 3208–3216  Table 2 Diagnostic ions ( m/z  ) used to identify aromatic compounds in the Brazilian extraheavy gas oils.Compound name or compound classes Diagnostic ions ( m/z  )Alkylbenzenes 105, 119, 120, 134, 148Naphthalene and alkylnaphthalenes 128, 142, 156Phenanthrene and alkylphenanthrenes 178, 192, 206, 220, 234,248, 262, 276Alkylpyrenes 216, 230, 244, 258, 272,286, 300, 314Benzo[a]anthracene and chrysene 228Alkylchrysenes 242, 256, 270, 284, 298Benzo[k]fluoranthene and benzo[a]pyrene 252Alkylbenzo[k]fluoranthenes oralkylbenzo[a]pyrenes266, 280, 394, 308, 322Dibenzo[a,h]anthracene andC1-alkyldibenzo[a,h]anthracenes278, 292, 306, 320Benzo[g,h,i]perylene 276Alkylbenzo[g,h,i]perylenes 290, 304Benzonaphthothiophenes andalkylbenzonaphthothiophenes234, 248, 262, 276Triaromatic steroids 231Methyl-triaromatic steroids 245Tetrahydrochrysenes 259, 273Tetraromatic triterpenoids 281 3. Results and discussion Aromatic compounds in EHGO samples were analyzed onextracted ion chromatograms (EIC) using the diagnostic ions indi-cated in Table 2. The three samples were very similar in regards to their molecular composition. Their aromatic fractions contained alargediversityofalkylbenzenes,polycyclicaromatichydrocarbons(PAHs), benzonaphthothiophenes, alkylbenzonaphthothiophenes,triaromatic steroids, methyl-triaromatic steroids, tetrahydrochry-senes and tetraromatic triterpenoids. The chemical structures aregiven in Appendix A.  3.1. Chromatographic aspects Theresultsobtainedallowedtheidentificationofatleastfifteencompoundclassesinthechromatographicplane,representativeof alkylbenzenes,severalPAHsclasses,aseriesoftriaromaticsteroidsandmethyl-triaromaticsteroids,tetrahydrochrysenesandtetraro-matic terpenoids.Apreviousanalysiswasmadeusingthesamemodulationperiodfor saturated hydrocarbons in EHGO samples (8s), as reported inourpreviouswork[21].However,severalwraparoundpeakswere observed. Therefore, the modulation period was altered to 10s,which enabled the best analytical results. Fig. 1 illustrates theseresults for the AL-35 sample and shows benzo[k]fluoranthene andbenzo[a]pyrene identified in two of the modulation periods used.  3.2. Molecular composition 3.2.1. Alkylbenzenes Several alkylbenzenes were detected by Frysinger et al. [8] by GC × GC in gasoline samples, such as ethylbenzene, xylene, iso-propylbenzene and propylbenzene. In the same way, Mullins etal. [19] detected C5-substituted alkylbenzene isomers in oil sam- ples.Alkylbenzenes,representedbyC3andC4-alkylbenzenes,weredetected in all the samples analyzed (Fig. 2), despite the oil sam- plesbeingsubjectedtothreedistillationprocessesbeforechemicalanalysis.  3.2.2. Polycyclic aromatic hydrocarbons and sulfur compounds Polycyclic aromatic hydrocarbons (PAHs) and sulfur com-pounds have been analyzed in various petrochemical samples,such as crude oils, kerosene, gasoline and source rocks[9,11,13,15,18,19]. These compounds were detected in allaromatic fractions of the EHGO samples, represented by naph-thalene and alkylnaphthalenes (Fig. 2), phenanthrene and Fig. 1.  Mass chromatograms ( m/z   252) showing benzo[k]fluoranthene and benzo[a]pyrene detected with a modulation period of 8s (A) and a modulation period of 10s (B).  B.M.F. Ávila et al. / J. Chromatogr. A 1218 (2011) 3208–3216 3211 Fig. 2.  Alkylbenzenes and naphthalenes detected in the aromatic fraction of the AL-35 EHGO sample. alkylphenanthrenes, alkylpyrenes, benzo[a]anthracene, chry-sene and alkylchrysenes, benzo[k]fluoranthene, benzo[a]pyreneand alkylbenzo[k]fluoranthene or alkylbenzo[a]pyrene,dibenzo[a,h]anthracene and alkyldibenzo[a,h]anthracenes,benzo[g,h,i]perylene and alkylbenzo[g,h,i]perylenes, benzon-aphthothiophenes and alkylbenzonaphthothiophenes.Fig. 3 shows some of the sulfur compounds and phenanthrenesidentified in the RO-82 sample and the roof-tile effect observedfor such compounds. The roof-tile effect was also clearly observedfor the other PAH classes detected, as illustrated in Fig. 4 foralkylpyrenes in the RO-59 sample.  3.2.3. Triaromatic steroids, tetrahydrochrysenes and tetraromatic triterpenoids Studies on the GC × GC analysis of triaromatic steroids in crudeoils have been reported by only a few authors [9]. We undertook ananalysisofthesecompounds,however,andallthesamplespre-sented a series of triaromatic steroids ranging from C19 to C28, Fig. 3.  Benzonaphthothiophenes and phenanthrenes detected in the aromatic fraction of the RO-82 EHGO sample.  3212  B.M.F. Ávila et al. / J. Chromatogr. A 1218 (2011) 3208–3216 Fig. 4.  Roof-tile effect observed for alkypyrenes detected in the aromatic fraction of the RO-59 EHGO sample. as detected by the  m/z   231 ion (Fig. 5). These compounds, usually called biomarkers, are very widespread in crude oil and sedimentsamples [20].Using the  m/z   245 ion, a series of methyl-triaromatic steroidsranging from C20 to C29 were observed in all the samples (Fig. 6),according to fragmentation patterns observed previously [24].Regarding the compounds with the diagnostic  m/  z 259 and  m/  z273 ions, they were associated with methyl-tetrahydrochrysenes,as represented in Fig. 7.Finally, three alkyl tetraromatic triterpenoids, represented bythe structures illustrated in Fig. 8, were also identified in all the samples. Philp reported similar mass spectra with a  m/z   281 diag-nostic ion corresponding to lupane derivatives [25]. However, several geochemical studies have demonstrated the absence of suchacompoundclassinBrazilianoilsamples.Therefore,themassspectra represented in Fig. 8 were interpreted as alkyltetraromatic terpenoidsnotrelatedtothelupaneclass,butfromhopanoidcom-pounds. As evidence, the fragmentation patterns observed clearlyproved the loss of methyl, ethyl and isopropyl groups.Recently, Dutriez et al. performed an important analysis of vacuum gas oil using GC × GC-FID and GC × GC-TOFMS [26,27].Concerning aromatic fractions, the results reported by these Fig. 5.  Triaromatic steroids identified from the  m/z   231 ion detected in the aromatic fraction of the RO-82 EHGO sample.
Search
Similar documents
View more...
Tags
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks