Naphthenic Acids in Crude Oils Characterized by Mass

8/12/2019 Naphthenic Acids in Crude Oils Characterized by Mass

http://slidepdf.com/reader/full/naphthenic-acids-in-crude-oils-characterized-by-mass 1/7

Naphthenic Acids in Crude Oils Characterized by MassSpectrometry

C h a n g S . H s u , *,† G . J . D echert, † W. K . R obbins,† a n d E . K . F u k u d a ‡

Exxon Research & En gineeri ng Co., Annand ale, New J ersey 08801, and Ru tgers U ni versit y,

New Brunswick, New Jersey 08901

Receiv ed Au gust 9, 1999. Revised M anu scr ip t R eceiv ed October 17, 1999

The presence of naphthenic acids in crude oils is of concern in the petroleum industry due totheir corrosivity t o refinery units. I t is desirable to determine the ring type a nd car bon num berdistributions because the corrosivity of napht henic acids is dependent on t he sizes and structures.The chara cterizat ion of naphth enic acids is a lso of interest to geochemical studies, part icularlymigrat ion a nd biodegrada tion, and to refinery w ast ewa ter trea tment for environmenta l compli-ance. We have evaluated chemical ionization, liquid secondary ion mass spectrometry (fast ionbombardment), atmospheric pressure chemical ionization (APCI), and electrospray ionization inboth posit ive and negative ion modes for the determination of molecular distribution of acidswit hout derivat izat ion. Negat ive-ion APCI using a cetonitrile as a mobile phase yields the cleanestspectra with good sensit ivity am ong the ionizat ion techniques evaluated. The select ivity of

negative-ion APC I for na phthenic acids ha s a lso been demonstrated by comparing results for awhole crude oil with those for the isolated acid fract ion. APCI also holds a great potential foron-line liquid chromat ography -ma ss spectrometr ic (LC/MS) to separa te a cids by high-performa nceliquid chroma tography (HP LC) followed by ma ss spectrometric char acterizat ion of a cids.

Introduction

Naphth enic acids, originally identified a s carboxylica c ids in c ru de o i ls wi t h s in g le o r mu lt ip le s a t u ra t e drings, is the phrase loosely used to include all acidiccomponents in crude oils that may even contain aro-matic functionality. Their presence in crude oils is ofconcern due to their corrosivity to refinery units.1-3 I t

is highly desirable to determine the ring-type distribu-tion and the carbon number distribution of each ringt y p e be ca u s e t h e corros ivi t y of n a p h t h e n ic a c ids isdependent on the sizes and structures.4 The char a cter-izat ion of na phthenic acids is a lso of interest to geochem-ical st udies, particularly migra tion and biodegrada tion,5-7

and to refinery wastewater treatment for environmentalcompliance.8

Mass spectrometry is well suited for characterizingacidic components at the molecular level. Due to theirpolarit y, a cids a re commonly deriva tized t o correspond-

ing esters for deta iled gas chroma togra phy/ma ss spec-trometric (GC /MS) an alysis.9,10 However, direct acidana lysis is more desirable because it can provide ra pidanalysis without the concern of losing material throughderivat izat ion. S evera l m ethods ha ve previously beendeveloped for such purposes, including fluoride-ionchemical ionization 11 and negative-ion fast-atom bom-ba rdme n t .12 We ha ve evaluated a lternative soft ioniza-

t ion techniques, including chemical ionizat ion (CI),liquid secondary-ion mass spectrometry (LSIMS), at-mospheric pressure chemical ionizat ion (AP CI), a ndelectrospray ionization (ESI), that would yield molecularor pseudo-molecular ions for the determination of mo-lecular distribution of na phthenic acids.

Experimental Section

For CI experiments a Finnigan TSQ-46B tandem quadru-pol e m ass spec t r om e t er t hat w a s ope r at e d a t a s i ngl e-st ag emode was u sed. Only th e most commonly used reagent ga ses,m e t hane , i sob ut ane , a nd a m m onia, w e r e use d for t he e val u-at i on. I n i sob ut ane C I , for e xam pl e, a n e xc ess a m ount of

isobuta ne wa s introduced into a CI source unti l the forepumppr essur e r ead i ng w as at 0.4 Tor r and t he i on g aug e r e ad i ngw a s 2 × 10-5 Torr. At this pressure, isobutane generates tert -b u t yl i on s (5 7 D a ) p r e dom in a n t l y t o r ea c t w i t h s a m p lemolecules. A sma ll amount (less tha n 1 mg) of the sa mple wa sdeposited into a capil lary quartz tube that was then inserted

* C orrespondi ng a uthor: Fax: (9 08 ) 73 0-3314. E-mail: [email protected].

†

Exxon Research & Engineering C o.‡ Rutg e rs U ni ve rsity .(1) Derun gs, W. A. Corrosion 1956, 12 , 617t -622t.(2) Gut zeit, J . Mat er. Perform. 1977, 16 , 24-35.(3) Piehl, R. L. NACE Conference, Corrosion/ 87 , 1987, Pape r No.

196.(4) Slavcheva, E.; Shone, B.; Turnbull, A. NACE Conference Cor-

rosion/ 98 , 1998, Paper No. 579.(5) Ahsan, A.; Kalsen, D. A.; Patience, R. L. M ar . Pet. Geol . 1997,

14 , 55-64.(6) J affe, R .; Albrecht, P .; Oudin, J . L. Geochi m Cosmochim . Acta

1988, 52 , 2599-2607.(7) Koike, L.; Reboucas, L. M. C.; Reis, F. De A. M.; Marsaioli , A.

J .; Richnow, H . H.; Micha elis, W. Or g. Geochem . 1992, 18 , 851-860.(8) Lai, J . W. S.; Pint o, L. J .; Kiehlmann, E.; B endell-Young, L. I .;

Moore, M. M. Environ. Toxicol. Chem . 1996, 15 , 1482-1491.

(9) Schmitter, J . M.; Arpino, P.; Gu iochon, G . J. Chromatogr . 1978,167 , 149-158.

(10) Green, J . B .; St ierwa lt, B . K.; Thomson, J . S.; Treese, C. A. An a l .Chem . 1985, 57 , 2207-2211.

(11) Dzidic, I.; Somerville, A. C.; Raia , J . C.; Ha rt, H . V. An al. Chem .1988, 60 , 1318-1323.

(12) Fan , T.-P . Anal. Chem. 1991, 65 , 371-375.

217E n er g y & Fu el s 2000, 14 , 2 17-223

10.1021/ef9901746 CC C: $19.00 © 2000 American C hemical SocietyP ubl ish ed on Web 12/04/1999



Figure 1. Positive-ion isobutane chemical ionization mass spectrum of the TCI Acid.

Figure 2. Negative-ion fa st iodide anion bombardment mass spectrum of the TCI Acid.

218 E n er gy & F u el s, V ol . 14, N o. 1, 2000 H su et al .

http://dontstartme.literatumonline.com/action/showImage?doi=10.1021/ef9901746&iName=master.img-001.png&w=502&h=348




into the cavity of a probe. The probe was then inserted intothe ion source of the mass spectrometer through a vacuumlock. The sa mple was heat ed ball istically from a mbient tem-perature to 400 °C via a heating coil around the cavity of theprobe. In the CI experiments, both positive -ion and negative-i on m ass spe c t r a of t he sam pl e w e r e ac q ui r e d . A Fi nni g anI NC O S d at a sy st e m w as use d for i nst r um e nt al c ont r ol anddata acquisit ion.

For LS IMS experiments a VG-ZAB reverse-geometry double-focusing mass spectrometer was used. A cesium iodide pelletis heated to produce Cs + a n d I - ions with an emission currentreading at 2 A. For naphthenic acids the negative-ion modewas found to be more effective than the positive-ion mode. Inthe negat ive-ion mode, the sa mple was mixed w ith t riethano-l am i ne (T E A) and b om b ar d e d b y fast i od i d e ani ons w i t h akinetic energy of 25 keV. The sa mple ions genera ted from fa stiodide anion bombardment (FIAB) were extra cted and acceler-at e d out of t he i on sour ce at 8 kV. A VG S I O S d at a sy st e mwas used for the instrument control and data acquisit ion.

The APCI and ESI experiments were carried out at Rutgers

University using Micromass Platform II mass spectrometer(an instrument for liquid chroma tography -ma ss spectrometry)equipped with a DECpc computer running on a Version 2.2 ofthe Ma sslynxNTsoftwa re. The single quadrupole instrumentcan be opera ted in either th e APCI or ESI mode. The sa mplewas dissolved in acetonitri le and introduced through a loopinjector onto the t ip of a h eated APC I nebulizer probe wheret he m obi le phase c ont ai ni ng t he sam pl e w a s pneum at i c al lyconve r t ed i nt o a n ae r osol and r api d ly he at e d t o 450 ° C i nt ovapor phase a t t he probe t ip. A corona discharge pin a t 3 kVwas used to ionize the vapor from the nebulizer. The sourcet e mp er a t u r e w a s m a i n t a in e d a t 1 50 ° C . Th e s a m p le a n dreagent ions passed th rough a count er electrode prior to beingexpan ded through a sample cone an d skimmer assembly intothe ma ss spectrometer.

Multiple-scan carbon-13 nuclear magn etic resonance (13CNMR) spectra were acquired with a Varian Unity + 500 MHzNMR spectrometer. Samples are diluted in deuterated chlo-roform (CDCl3) to 30%solution cont ain ing 25 mg of chromiumacetoacetonate (CrAcAc) as a relaxation agent per mill i l i terof the solution.

The commercial samples of naphthenic acids for MS evalu-at i on w e r e pur c hase d fr om K od ak, Fl uka, P fal t z & B aue r(P&B), and TCI America. For the APCI selectivity studies,

napht he ni c ac i d s w e r e i sol at e d fr om an ac i d i c C al i for ni ancrude oil with TAN (total acid number) of 4.06 mg KOH/gsample by solid-phase extraction w ith aminopropyl si l ica. 13

Results and Discussions

CI (low-pressure CI or conventional CI) has evolvedinto a routine ma ss spectrometric opera t ion.14,15 Com-monly used reagent ga ses are metha ne, isobuta ne, andammonia, although other gases can also be used. For

(13) Morrison, B.; DeAngelis, D.; Bonnette, L.; Wood, S. PittCon/92, New Orleans, M ar ch, 1992.

(14) Harr ison, A. G . Chemical I onization M ass Spectrometry , 2nde d.; C RC P re ss: Boc a Rat on, FL , 19 92 .

(15) Munson, B. An a l . C h em . 1977, 49 , 772A-778A.

Figure 3. Negative-ion atmospheric pressure chemical ionization (APCI) mass spectrum of the TCI Acid.

Table 1. Conversion of Nominal z * Series toCorresponding O2 z -Series

z * z (O 2)

-10 0-

12 -

2-14 -4

-2 -6-4 -8-6 -10-8 -12

N aph t h en i c A ci d s i n Cr u d e Oi l s E n er gy & F u el s, V ol . 14, N o. 1, 2000 219




naphth enic acids, the use of F -, C l-, or OH - would beexpected t o yield useful nega tive-ion CI (NIC I) spectra ,bu t t h e s e re a g e n t g a s es a re n ot con v en ien t ly u s edwithout sa fety a nd opera t ional concerns. In our evalu-at ion, both posit ive- and negative-ion modes were ap-plied using common reagent gases individually. Whenmethane and isobutane are used for NICI, near-zero-energy thermal electrons are generated, result ing inresona nce electron capture or dissociat ive electron

captur e. In th e ca se of alicyclic naphth enic acids electroncapture is n ot a n efficient process. In ad dition, electronca p t u re ca n be v ery e ff icien t f or ce rt a in p oly cy cl icaromatic hydrocarbons that are not naphthenic acids.Wh en a m m on ia i s u s e d f or N I C I , v e r y b a s ic N H2

-

reacta nt ions a re generated. The NH 2- ions can abst ra ct

not only a proton from an acid but also a proton fromthe benzylic position of aralkyl compounds. Thus, am-monia NICI is not suitable for select ive ionizat ion ofnaphth enic acids in crude oils either.

In the posit ive-ion mode, metha ne CI yields excessa mo u n t s o f f ra g men t ion s . A mmon ia CI y ields bo t hprotonated and ammonium-adduct molecular ions withov era l l lowe r s en s i t iv i t y . Th e bes t CI s pe ct ra we re

obt a in e d w it h p os i t iv e-ion CI u s in g is obu t a n e a s areagent gas in which naphthenic acids yield primarilyprotonated molecular ions with minimal fragmentation.

FIAB is a specific type of mass spectrometric tech-n iq u e g e n e ra l ly k n o wn a s L SI M S.16-18 I n L S I M S , acesium iodide pellet is heated to produce Cs + a n d I -

ions. Depending on the polarity of the sample ions tobe analyzed, either Cs+ or I - ions a re a ccelera ted by apotential drop of 25 kV to bombard the target containing

the sam ple in a liquid mat rix. For the chara cterizat ionof acids, the negative-ion mode was found to be moreeffect ive t han the posit ive-ion mode because it gavecleaner spectra with very good sensitivity. In the nega-t ive-ion mode, the sa mple wa s mixed w ith t riethanola-min e (TE A) t h a t is u s e d a s a l iq u id ma t r ix a n d bom-ba rde d by f a s t iodide a n ion s . Th is wo u ld p rodu cedeprotona ted molecula r a nions of the sa mple by protontransfer from the sample to TEA. Although the sample

wa s bombarded by iodide ion w ith high kinetic energies(25 keV), the internal energies of the deprotona tedmolecu la r a n ion s a re low, re su lt in g in min ima l f ra g -mentat ion.

APCI and ESI are commonly used in liquid chroma-togra phy/ma ss spectrometr ic (LC /MS) experiment s. 19,20

We have found that ESI is an order of magnitude lesssensitive than APCI using relatively nonpolar solventsthat are normally used for hydrocarbon mixtures (unlesswe an alyze wa ter samples containing small am ounts of

(16) Bar ber, M.; B ordoli, R. S .; Elliott, G . J .; Sedgwick, R. D .; Tyler,A. N. Anal. Chem . 1982, 54 , 645A-657A.

(1 7) Pac huta , S . ; C ooks, R. G. Anal. Chem . 1987, 87 , 647-669.(18) Benninghoven, A. I n t . J . M a ss Sp ec t r om . I on Ph y s . 1983, 46 ,

459-462.

(19) Bru ins, A. P . (a) M ass Spectrom . Rev . 1991, 10 , 53-78. (b) Trend Anal. Chem . 1994, 13 , 37-43.

(20) Gar cia, D . M.; Huan g, S. K.; Sta nsbury, W. F. J . Am. Soc. M ass

Spectrom . 1996, 7 , 59-65.

Figure 4. Ca rbon number distribution of individual ring t ype in the TCI Acid.

Figure 5. Typical na phthenic acids.






oils. In that case, we can a dd a ba se to deprotona te the

a c ids f or e n h a n ce d ion iza t ion ). F o r e xa mp le, u s inga c e t o n it r i le a s a mo bile p h a s e t h e a c id wil l be in an e ut ra l f orm t h a t wo u ld y ie ld w e a k s ig n a ls in E SI . I naddition, ESI is more susceptible to signal suppressionby matrix materials. In APCI, the sample is dissolvedin a solvent and injected onto a liquid chromatographor a loop injector t o tra nsfer the sample molecules tothe tip of a heated nebulizer. The mixture of solvent andsample vapor is then ionized by corona discharge at 3-5kV. For na phthenic acids, a cetonitrile has been foundto be a good solvent and reagent gas. Acetonitrile isdeprotonat ed to form the a cetonitrile anion, CH 2C N -,under the APCI conditions. The acid molecules are thenionized by proton t ran sfer to CH 2C N -, yielding depro-

tonated molecular ions with minimum fragmentat ionand high sensit ivity.

Four commercial samples of naphthenic acids fromKodak, Fluka, Pfa ltz &B auer (P&B), and TCI were usedfor the evalua tion. These acid mixtures represent a cidsisolated from petroleum fract ions (typically gas oils)from different sources. Although several MS techniquess h ow s imila r re s ult s f o r e a c h a c id s a mp le, t h e a ciddistribut ions among th ese commercial sam ples differ.21

The acid sample from TCI (i.e. , “TCI Acid”) are used

below to illustrate the char acterist ics of i C 4-CI, FIAB,and APCI. Figures 1-3 exhibit the positive-ion i C 4-CI,negative-ion FIAB, and negative-ion APCI mass spectra,respectively, of the TCI Acid. Note t ha t positive-ion i C 4-CI yields protonated molecular cation, (M + H )+, whilenegative-ion F IAB and APC I yields deprotonat ed mo-lecular anion, (M - H )-. The molecular ion profiles int h e ma s s s p ect ra a re s imila r . H owe v er , i C 4-CI givesslightly lower carbon number distributions t han FIABa nd APCI MS du e to low volat ility of higher-molecula r-weight species. Since i C 4-CI requires va porizat ion of thes a mp le by direct h e a t in g , de ca rbo xy la t ion (t h e rma ldecomposition) of a cids is a lso possible. The low-ma ss

(21) Hsu, C . S.; D echert, G . J .; Robbins, W. K.; Fukud a, E .; Roussis,S . G . Prepr. Pap.-Am. Chem. Soc., Div. Petrol. Chem . 1998, 4 3 , 127-

130.

Figure 6. 13C Nuclear magn etic resona nce spectrum of t he TCI Acid.

Figure 7. Ring-type distribution of the TCI Acid.






ions (<150 D a) observed in i C 4-CI are believed to bef ra g me n t ion s p rodu ce d in t h e ch e mica l ion iza t ionprocesses. FIAB an d APCI yield a lmost identical ma ss

spectra. However, FIAB also yields acid dimer clusters(>350 Da ) due to ionizat ion in a liquid mat rix neededf or a n a l y s is . H e n ce , A P C I g iv es t h e cl ea n e st m a s s

Figure 8. Comparison of APC I ma ss spectra of the isolat ed acidic fraction (top tra ce) and t he wh ole Ca li fornian crude oil fromwhich th e a cids a re isolat ed (bottom tra ce).





spectra among the techniques evaluated, it does notyield fra gment a nd dimer cluster ions.

The molar ma sses of a cid components can be easilyobtained from the dalton values of the protonated ordeprotonat ed molecular ions. From the m olar ma sses,t h e r i ng -t y pe d is t r ib u t ion of a c id s a n d t h e ca r b onn u mbe r dis t r ibu t io n in e a c h r in g t y p e c a n be de t e r-mined. For exam ple, the deprotonat ed molecular ion of237 D a s h own in F ig ure 3 corre s pon ds t o a n a c idic

s pe cies of mola r ma s s of 238. U s in g t h e a p p roa c hsuggested by H su et a l . , the nominal m ass series, z *, oft h e 238 D a a c id ca n be de t ermin ed t o be -14 by t h eremainder of the nominal ma ss divided by 14, i .e., themodulu s of (nomina l ma ss/14) - 14.22 The nominal massseries can then be converted into corresponding z -seriesin the genera l formula of Cn H 2n +z O2 for acids, accordingto the Table 1.

The 239 Da acid is in the z ) -4(O2) series that isbelonged t o 2-ring na phth enic acid (see below). Once thez -valu e is determined, th e ca rbon number of th is specificacidic species can be easily determined to be 15.

As for hydrocarbons, the distribution of acids deter-mined by mass spectrometric analysis can be conve-

niently expressed by z -series where z represents hydro-gen deficiency in the molecular formula of C n H 2n +z O2.For example, acyclic (0-ring) aliphat ic a cids have ageneral formula of C n H 2n O2. The whole series can beexpressed as z ) 0 (O2) series. One-ring naphthenicacids have a formula of Cn H 2n -2O2. Hence, they can beexpressed as a z ) -2(O2) series. Figure 4 shows thecarbon number distribution of seven acid series in theTCI Acid.

Figure 5 shows typical 1- to 4-ring naphthenic acidswit h z -values of -2 (O2) t o -8 (O2), respectively. Notethat 4-ring naphthenes share identical molecular for-mula as benzenes. Hence, the z ) -8 (O2) series can beeither 4-ring na phthenic acids or a n a cid series conta in-

ing one phenyl group in their hydrocarbon backbones.A s s u min g t h a t a l l o f t h e n a p h t h e n ic r in g s a re f iv e -membered, the m inimum number of car bon a toms for4-ring naphthenic acids would be 14. However, the z )

-8 (O2) acids sta rt a t carbon number of 12 as shown inF i gu r e 4. Th i s s u gg es t s t h a t t h es e a r e n ot 4-r i ngn a p h t he ni c a c id s , b u t r a t h e r a r o ma t i c a ci ds w i t h aphenyl group in the hydrocarbon backbones. Similarly,t h e a c i d s w i t h z ) -10(O2) a n d -12(O2) s t a r t w i t hcarbon numbers much less tha n the sma llest na phthenicacids with 5- and/or six-membered rings, suggestingthat they are aromatic acids as well. The presence ofaromatic acids in the TCI Acid was confirmed by 13CNMR a na lysis, shown in Figure 7. The chemical shifts

in t h e 120-150 ppm region indicate the presence ofaroma tic carbons.

F ro m t h e ca rbo n n u mbe r dis t r ibu t ion s s h own inFigure 4, the carbonyl carbons a re calculat ed to be 6.8mol %that agrees quite well with 6.5%determined by13C NMR. However, the aromatic carbon est imated byMS is 3.1%, compa red t o 5.4%determ ined by 13C NMR.

The higher a romatic number by 13C NMR is probablydue to the presence of nonacidic aroma tic hydrocarbonstha t a re not detected by the selective negat ive ion FI ABand APCI techniques. Figure 7 exhibits the ring-typedistribut ion of the TCI Acid, wh ich shows t ha t t he mosta bu n da n t n a p h t h e n ic a c ids h a v e t wo s a t u ra t e d r in g s .As discussed above, the 4-, 5-, and 6-ring “naphthenicacids” are actually acids containing aromatic rings. Thetotal am ount of aroma tic acids is less tha n 10%.

To evalua te th e selectivity of AP CI to the w hole ra ngeof acidic components in a crude oil, we ha ve isolat ed a nacid fra ction from a C a lifornia n crude oil with high a cidcontent. The whole crude oil and its acid fraction weresepar at ely introduced into the LC/MS through a loopinjector without chromatographic separat ions. Figure8 comp a re s t h e n e g a t ive -ion AP C I s pe ct ru m of t h eisolated acid fraction (top spectrum) with that of wholecrude oil (bottom spectrum). The similarity of these twospectra indicates th a t only the a cidic components in t hecru de oi ls y ield n e ga t iv e AP C I ion s , lea v in g ot h e rcomponents lar gely un-ionized. The TAN (tota l a cidnumber, i.e., mg KOH /g oil for neutr a lizat ion23) of thecrude oil is 4.06, which is equivalent to 0.0725 mmol

a c id/g oi l. Wit h a n a v e ra g e mola r ma s s a ro u n d 500shown in Figure 8 the acids would account for about3.6% of t h e cru de o i l by ma s s , con s ist e n t wit h t h ea mount of acids a ctually isola ted (3.9 ma ss %). Hence,t h e s elect iv it y of t h e A P CI t e ch n iq u e t o t h e a cids incrude oils is demonstrated.

Conclusions

For the char acterization of naphthenic acids, we foundthat NICI does not give any advantages over posit ive-ion CI , re g a rdles s o f t h e re a g e n t g a s u s ed (me t h a n e ,isobutane, and ammonia). In addit ion, the interferingbackground ions in NICI ar e diff icult to elimina te. Forpositive-ion CI, isobuta ne wa s found to yield the cleanest

s pe ct ra wit h g ood s en s i t iv i t y o v er me t h a n e a n d a m-m on i a . F or F I AB a n d AP C I , on t h e o t h er h a n d , t h enegative-ion mode was more selective and sensitive tothe acids than the positive-ion mode.

Negat ive-ion APCI using a cetonitrile as a solvent a ndmobile p h a s e a p pe a rs t o y ield t h e clea n e s t s pe ct raam ong the ma ss spectrometric techniques evalua ted forthe chara cterization of acids, without t he discriminat ionof h ea v i er i on s a n d t h e f o rm a t i on of f r a g me nt a n dclu st e r ion s . A P CI a ls o h o lds a g re a t p ot e n t ia l f o rfurther development of on-line liquid chromatography -

ma ss spectrometric (LC/MS) methods t o sepa ra te a cidsby high-performance liquid chromatography followed bymass spectrometric characterization for the determina-

tion of acid structures.

Acknowledgment. The authors acknowledge the13C NMR spectrum of the TCI Acid provided by SteveRucker and A. R. Garcia of Exxon Research & Engi-neering Co.

EF9901746

(22) Hsu, C. S.; Qian, K.; Chen, Y. C. An a l . C h i m . Ac t a 1992, 26 4 ,79-89.

(23) 1 99 8 An n u a l Bo ok o f AST M St a n d a r d s ; American Society forTesting a nd Mat erials: West C onshohocken, P A.; Vol. 05.01, ASTMD 664/IP 177.


Documents

Naphthenic Acids in Crude Oils Characterized by Mass