Mass-spectrometric method for quantitative determination of isoprenoid paraffins in petroleums

MASS..SPECTROMETRiC METHOD FOR QUANTITATIVE DETERMINATION OF ISOPRENOID PARAFFINS IN PETROLEUMS* F. G. U~OE~, I. B. USHAKOVA, L. M. I~OZENBERG, A. A. POLYAKOVA

and P. I. SA~I~ Bashkir Scientific Research Institute fbr Processing of Oil, Uf~ A. V. Topchiev Institute of Petrochemical Sy~lthesis, U.S.S.R. Ac~xlemy of' Sciences

(Received 15 July 19tiP) STUDIES have been published since 1962 discussing the presence in oils of a considerable amount of isoprenoids--paraffins, containing methyl substituents in each three carbon chain units of the molecule [1, 4]. Mass spectra of 2,6,10-trimethylundecane, 2,6,10-trimethyltridecane and 2,6,10-trimethyltetradecane and isomeric n-paraffin hydrocarbons obtained under the same conditions were examined in a previous report [5]. Using the mass-spectra of these compounds a system was proposed for the identification of normal and branched paraffin hydrocarbons. This paper describes the mass-spectra of isoprenoids, fl'om C14 to C~0 in composition and compares them with the spectra of other hydrocarbons of the C,~H2~+2group; a method is developed for their quantitative determination in petroleum fractions. Mass-spectra of isoprenoids were obtained in a MKh-1303 mass-spectrometer with a loop oscillograph as a recorder [6] and a rhenium wire cathode and a device measuring the value proportional to the complete ion current, which was recorded by one of the galvanometers of the loop oscillograph, loaded with amplifier VI-2 with a feedback resistance of 1 ohm. The input stage of the amplifier was joined to a plate on which part of the ions retained after emerging from the aperture slit of the source (Fig. 1). The value proportional to the entire ionic current I n is related to the total of all intensities ~ I of lines of any mass spectrum b y coefficient _K; K × I n = ~ I . The K value was maintained for all spectra with an accuracy of 4-1.5% in spite of the fact that I n related to unit weight of material, varied within 4-6% for toluene in a week. The electron current was 1.5 mA, accelerating voltage for ions--2 kV and for electrons--50 kV. The temperature of the ionization chamber and the inlet system was 300 ° ~nd the spectra were re* Neftekhimiy~ 10, No. 3, 444-450, 1970. 132

Quantitative determination of isoprenoid paraffins in petroleums

133

producible with an accuracy of ± 1.5%. All samples were weighed in VLA-200M type analytical scales. The weight of any sample was below 0.0022 g, which corresponded to approximately 2 ~1 of a liquid sample. Mass-spectra of iso1 2\

Fro. 1. A p p a r a t u s for measuring the value proportional to the entire gas current: 1 aperture lens of the ionic source; 2 - - p l a t e on which p a r t of the ion b e a m is retained; 3--insulators; 4 - - b o l t with disc; 5 - - H - 7 0 0 loop oscillograph with a galvanometer recording the value proportional to the complete gas current; 6 - - Y I - 2 amplifier; 7--electrometer stage of the amplifier.

(%kEI) 22

•~ 18

.!,o g

i i. •

i

!

2 I

8

I

I

5

7 9 II 13 Numbep of C a~oms ~nfhe ion

~5

FIe. 2. Dependence of the probability of formation of C~H~.+I ions on the n u m b e r of carbon atoms for various C1~ isomeric paraffinic hydrocarbons. Scales on the right and left refer to the right and left h a n d side parts of the Figure. 1--n-Paraffin; 2 - - 2 - m e t h y l paraffin; 3--isoprenoid.

134

F. (;. 17NOER, et al.

T A B L E ]. MASS-SPECTRA OF ISOPRENOIDS :FOR E N E R G I E S OF IONIZING ELECTRONS OF 5 0 (

M =molecular peak P r o b a b i l i t i e s o f t h e f o r m a t i o n o f ions, °/o r e l a t e d to t o t a l gas c u r r e n t role

~ 2,6,102ALlt)2,6,10t ritritrimethylmethylmethyl+undeeane] d o d e c a n e t r i d e e a n e

2,6,10lrimettDq_ tetra(leeane

2,6,10trimethylpentadocane

2,6.10,14-i 2,6,10. tetra- i tetramethylmethylpenta- j hexadeeane [ deeane !

(7,.0

26 27 28 29 30

0.12 0.63 0.22 1.35 0.06

0.12 0-41 0-35 1.28 0.05

0.1 ] 0.41 0.37 0.98 0.04

0.09 0.39 0.61 1.02

0.09 0.28 0.36 0.82 0.02

0.1() 0.28 0.43 0.73 0.05

C3

39 40 41 42 43

0.49 0.14 4.03 1.19 10.29

0.43 0.17 3.49 <).83 7.34

0.38 0.11 3.03 0.90 9.82

0.34 0.12 3.06 0.82 10.17

0.31 0-12 2.73 0.59 5.55

0.3<) 0.12 0.25 0-66 7. l 0

0.26 0.11 2.37 0.58 5.92

0.23 0.16 2.85 4.16 22.16 1.07

0.05 0.03 0.23 0.15 2'75 3-30 19.27 0.83

0.07

C4

51 52 53 54 55 56 57 58

(1.23 0.16 3.15 2.87 16.79 0.74

0.22 0.15 3.06 3.16 16.33 0.73

(I.04 0.04 0.21 0.17 3-64 3.28 16.38 0.74

0.17 0.16 2.74 3-14 18.25 0.81

0.04 0.15 .... 0.] l 2.96 2.74 16.29 <).81

C5

63 64 65 66 67 68 69 70 71 72

0.05 0.05 0.05 0.28 0.24 2.37 1.98 21.37 1.23

1' 65 2.52 18.36 1.01

0.05 0.06 0.05 0.3 I 0.26 2.25 3.60 17.20 0.94

0.05 • 0.04 0.05 0.04 0.32 0-26 2.35 1.99 13.78 0.79

0.05 0.05 0.06 0.05 0.55 0.47 4.46 2.64 10.92 O.59

0.06 0.05 0.05 0.26 0.27 2-43 1.93 18.25 1.01

0.05 0.04 0.28 0.27 2.29 2.52 16.51 0.96

C6

81 82 83 84 85 86

0-14 0.09 0.63 1.66 3.17 0.24

0.14 0.09 0.69 0.96 8.49 0.56

o.21 0.14 O.98 2.13 9.13 0.66

0.24 0.17 1.00 3.06 10.72 0.70

0.53 0.35 2.37 1.18 5.55 0.43

0.18 0.17 0.91 1.22 7-30 0'52

0.25 0.19 1.26 1.11 10.36 0.74

C7

95 96 97 98 99 100

0.12 0.08 0.84 0.19 0-87 (1.15

(1.09 0.35 1.42 0.52 1-56 0.18

0.16 0.37 1.56 0.58 2.87 0.26

0.02 0.31 1.25 0.71 3.37 0.32

0.61 0.61 2.82 2.28 2.73 0.25

0" 15 0.32 1"25 0'51 3"19 0.30

0.22 0.50 1.96 0'59 3-44 0.30

(1.05 0'06 0.06 0.05 0.25

;

i

0.1o 0.22 ~ 0.31 0.81 0.04

- -

135

Q u a n t i t a t i v e d e t e r m i n a t i o n o f i s o p r e n o i d p a r a f f m s in p e t r o l e u m s TABLE 1

(cont.)

P r o b a b i l i t i e s of t h e f o r m a t i o n of ions, % r e l a t e d t o t o t a l g a s c u r r e n t

2,6,10tri-, methylundecane

m/e

Cs

C9

Clo

2,6,10trimethyltetradeeane

2,6,10trimethylpentadecane

2,6,10,14tetramethylpentadeeane

2,6,10tetramethylhexadecane

0.12 0.07 0.25 4.12 5.54 0.41

0.06 0.05 0.24 1.56 2.62 0.25

0.12 0.11 0.08 1.64 2.87 0.27

0.13 0.12 0.66 1.74 3.27 0.31

0"46 0"36 2"73 2"28 2"84 0"27

0.08 0.12 0"63 2"58 4"87 0.41

0"13 0"13 0"81 1"52 3"74 0"36

123 124 125 126 127 128 129

0.08 0.05 0.09 0.23 0.51 0.06 0.06

0.05 0.04 0.10 1.01 2.00 0.29 0.04

0.08 0.04 0.29 0.45 1.15 0.15 0.02

0.08 0.04 0.30 0.67 1.43 0.17

0"27 0"15 1"46 1"46 1"46 0"15 0"03

0"05 0"05 0"20 1"01 2"33 0"25 0.05

0"07 0"09 0"59 1"33 3"55 0"37 0.04

137 138 139 140 141 142

0.02 0.02 0.04 0.09 0.20 0.02

0.03 0.05 0.08 0.46 0-07

0.024 0.03 0.25 0.74 2.29 0.26

0.10 0.13 0.69 0.08

0"09 0"08 0.18 0-36 0"68 0.09

0.02 0.15 0.32 0.06

0.06 0.11 0.27 0.07

0.02 0.05 0.25 0.50 0.07

0.04 0.13 0.61 1.89 0.27

0.05 0.14 0.17 0"37 0"05

0.06 0.27 0.65 0.09

0.07 0.19 0.88 0.12

0.04 0.05 0.07 0.15 0.05

0.11 0.68 0.42 1.18 0.18

0.05 0-06 0.28 O.06

0.02 0.10 0.15 0"59 0.09

0.81 2-03 3.04

0.07 0.44 1-96 0.20

0.09 0.20 0.12

0.39 1.10 0.17

Cn

Clz

166 167 168 169 170

0.14 0.19 0.04

179 180 181 182 183 184

0"14 0.04 0"04 0"08 0"32 0.06

196 197 198

0"06 0.03 0"02 M

C14

2,6,10trimethyl trideeane

109 ll0 ill 112 113 114

152 153 154 155 156

Cls

2,6,10trimethyldodecane

0.02 0.03 0.09

0.10 0.23

0.22 0.70 0.11

0"07 0"02 0"04 0"29 0"98 0"16

0'05 0"03 0"06 0"33 1"02 0"15

0"17 0"08 0"27 0"54 0"91 0"14

0.05 0.25

0"09 0"15

0"08 0"15

0"22 0"13

0.04 0"08 0"14 1"01 0-14

0.18 0.40 1.55 0.20

q

136

IF. G. UNCIEI¢et, al. TABLE I (cont.) Probabilities of the fomnation of ions, °/o relat.ed to total gas current 2.6.102.6.102.6.10tritrttrimethyl- methyl- methylundecano dodoeane tridecano

(Jl5

C~

(~7

C ts

C,~ C2o

211 212 223 224 225 226 237 238 239 240 252 253 254 267 268 269 270 282

2.6.10~rimethyl[,et, P a -

2,6,10tri. methylpent+a-

2,6,10,14tetramethylpenta-

2,6,10tetramethylhexa-

(|ocf~no

deea,Ilo

(] C Cql,I 1(~

(le(~lt, I] ('

0-09

0.0s

0.26

Ib~)3

,~*06

0.15 0.O3

0.13 0.05 M

0.06 0.05 O.24 0.06

0.08 0.05 M

0.07 i

0.09 0.14 0.17 0.06 0.20 0.05 0.48 0.11M

0.]4 0.04

0.09

! O.04 ! 0.07

0.07 0.09

O.O2 0.05

0.05 0.15 O.03

0.09 0.17 0.04

O.04 0.0l M

0-04

0.06

0.16 0.04 O.O2 M

prenoids are shown in T a b l e 1. P e a k intensities are e x p r e s s e d as t h e p e r c e n t a g e of t o t a l intensities o f all s p e c t r u m lines. H i g h e s t m o l e c u l a r p e a k s give 0 . 0 5 % 2 , 6 , 1 0 - t r i m e t h y l t r i d e c a n e , 0.05~'o 2 , 6 , 1 0 - t r i m e t h y l t e t r a d e c a n e a n d 0.1 1 ~o 2 , 6 , 1 0 - t r i m e t h y l p e n t a d e c a n e . Molecular s t a b i l i t y to electron i m p a c t , a p p a r e n t l y , increases w i t h a n increase in u n b r a n c h e d chain length of c a r b o n a t o m s . This is also verified b y the lower intensities of m o l e c u l a r ions of tlm o t h e r isoprenoids e x a m i n e d . Molecular ions m a i n l y b r e a k d o w n w i t h f o r m a t i o n of C4H9, + CsH ~ n+ ions a n d as the n u m b e r of c a r b o n a t o m s increases in t h e ion, t h e i r p e a k intensities m a r k e d l y decreases. On c o m p a r i n g t h e p e a k intensities o f f r a g m e n t e d ions in t h e m a s s - s p e c t r a o f isoprenoids a n d o t h e r isomers a n increase is o b s e r v e d in t h e n u m b e r o f m a x i m a on t h e d i s t r i b u t i o n curve as t h e n u m b e r of m e t h y l s u b s t i t u e n t s increases (Fig. 2). T h e long chain of t h e n-paraffin molecule h a s one m a x i m u m in t h e r a n g e + of ions 43 +, 57 + or 71 + a n d t h e p e a k i n t e n s i t y o f CnH2,+I ions t h e n decreases e v e n l y u p to t h e m o l e c u l a r p e a k , which is fairly high [7]. T h e s p e c t r a o f m o n o m e t h y l - s u b s t i t u t e d paraffins h a v e a second m a x i m u m in t h e r a n g e of ions

Quantitative determination of isoprenoid paraffins in petroleums

137

with 3 or 4 carbon atoms, according to the 2nd, or 3rd position of the methyl substituent and a very low molecular peak [8]. The breakdown of isoprenoid hydrocarbons can be shown as: 2,6,10-Trimethylpentadecane CH~CH--

CH~CH~CH~CH--

I

CH2CH2CH~CH--

CH2CH~CH~CH2--CH3

i

CH3

CHs

43 +

113+

183+

2,6,10,14-Tetramethylhexadecane CH3CH--

I

CH2CH2CH~CH--

CH2CH~CH2CH--

i

CHs

CHs

43 +

113+

CH~CI-IICH~CH-- CH2CHa

I

CHs 183+

253+

Ionic peaks in this system form maxima in the spectra according to the number of tertiary units in the molecule. The regular repetition of methyl branches after 3 carbon atoms explains the alternation of relatively high peak intensities after each 5 CH~ groups in the "spectrum of isoprenoids. Since during the breakdown of the molecule at the C--C bond the charge is normally localized on a fragment of smaller size, the ion with mass 113 + is typical of the molecule containing methyl radicals in position 2,6. The ion with mass 183 +, of which the peak has a somewhat lower intensity, characterizes the skeletal group with substituents in position 2,6,10 and the ion with mass 253 +, the skeletal groups with substituents in position 2,6,10,14. Therefore, ions with masses 113 +, 183 +, 253 + are characteristic in the mass-spectra of isoprenoids and can be used for analysis. For all the isoprenoids studied ionization sections were found in relation to toluene b y determining the value proportional to the entire gas current and related to unit material passed into the inlet volume. Toluene was used as standard (Table 2). I t follows from the foregoing that for isoprenoids containing 14 to 20 C atoms in the molecule a linear dependence of the section on molecular weight exists. Isomeric C15 hydrocarbons have similar ionization sections. A comparison of results obtained with information published in the literature [7, 8] proves that sections have similar values for isomeric hydrocarbons containing 14 to 20 C atoms in the molecule. When developing the method of determining isoprenoids in petroleum fractions the presence in the spectra of other paraffin ions (M--CsHs) +, (M--CdHx)+, (M--CH~) +, M + was taken into account, the overall number of

138

F. (~'. UNC,Ea et al.

which almost 20 times exceeds the value of corresponding peaks for isoprenoids. This m a d e it possible to derive the linear equation syst,em

(i)

111a, "X'.+Il13iXi=Iila ]"

where ~ I ~ , and I~i are the total peak intensities (M--CsHz) ~, (M--C4H~)and (M--CHx)+, Ii13~,, Ii13i are the relative intensities of p e a k 113 + in t h e massspectra of s t a n d a r d paraffin and isoprenoid h y d r o c a r b o n s , respectively, related to the complete g~s current, %; X,, and Xi are the relative concentrations; ~I~, I'ns is the total of peak intensities in the mass-spectra of fractions analysed and the i n t e n s i t y of peak 1 13 ~. T A B L E 2. I O N I Z A T I O N S E C T I O N S OF I S O P R E N O I D S I N R E L A T I O N TO TOLUENE

Hydrocarbon

Sections 1.56 1.63 1.58 1.60 1.77

2,6,10-Trimethylundecane 2,6,10-Trimethyldodecane n-Pentadecane 2-Mothyltetradecane 2,6, I 0 .Trimethyltridecane 2,6,10 -Trimethyltetradeeane 2,6,10-Trimethylpenta~lecane 2,6,10,14-Tetramethylpentadecane 2,6,10,14-Tetramethylhexadecane

1.86 1.95 2-04 2.14

A generalization o f mass-spectra of individual paraffin a n d n a p h t h e n i c h y d r o c a r b o n s [7, 9], t h e boiling points of which are in the 220-400 ° range, m a d e it possible to depict s y s t e m (1) as

12.18Xn ÷ 0.52X~----~I~ t 1.64X n + 3.62X~-~ I~ 18)"

(2)

The ~ I ' c value is f o r m e d from t h e intensities of t h e ions listed below, in accordance with t h e boiling range of the m i x t u r e to be analysed: Range, °C 220-240 240-260 260-280 280-300 300-320 320-360 360-400

Ranges of peaks to be summarized 120+ 143+ 157 + 171 ~ 185 + 199 + 213 ~

156 + 170 + 184 ~ 198~ 2124. 226 + 240 +

Quantitative determination of isoprenoid paraffins in petroleums

139

Only peaks 163 +, 165 +, 175 +, 179 +, 189 +, 191+, 203 +, 205 +, 219 +, 233 + and 217 + relating to naphthenic hydrocarbons are excluded from the totals described. As a result of solving system (2) the relative content of isoprenoids and other paraffin hydrocarbon isomers in the mixture is determined. Their absolute concentration can be found from the overall amount of paraffinic hydrocarbons determined [4, 10, 11]. The reproducibility of these methods is ± 2 % , the error for synthetic mixtures being less than ± 6 % , sensitivity 5-60/o (for isoprenoids with naphthenic hydrocarbons). Table 3 shows results of the quantitative determination of isoprenoid content in some fractions of Irkutsk and Romashkin crudes. TABLE 3. I S O P R E N O I D CONTENT IN PETROLEUMS, 0j0 WT. Hydrocarbon

Romashkin

Irkutsk

0.2 0.5 0.3 0.7

0.6 0.6 0.6 0.9

2,6,10-Trimethyltridecane 2,6,10-Trimethylpentadecane 2,6,10,14-Tetramethylpentadecane 2,6,10,14-Tetramethylhcxadecane

The methods help to determine isoprenoid fragments only, i.e. parts of hydrocarbon molecules, containing substituents in position 2, 6. The other part of the molecule m a y huve both isoprenoid and irregular structure. SUMMARY

1. A study was made of the mass spectra of seven C14-C~0 isoprenoids. 2. Molecular stability to electron impact increases with an increase in the unbranched chain of carbon atoms. 3. According to the regular arrangement of methyl substituents, the ions in which the number of carbon atoms differs by 5 and which have weights of 113 +, 183 +, etc., are the most typical in the mass-spectra. 4. Relative ionization sections of isoprenoid and some isomeric paraffins were determined. The sections are a linear function of the molecular weight of isoprenoid hydrocarbons and differ little for normal isomers and monomethyl-substituted paraffins. 5. A mass-spectrometric method was developed for determining the overall amount of isoprenoid paraffins in the narrow fractions boiling in the 200-400 ° range. The sensitivity of the method is 5-6% and the error is not more than ±6~o rel. REFERENCES 1. J. G. BENDORAITIS, B. I. BROWN and L. S. HEPNER, Analyt. Chem. 34, 49, 1962 2. J. G. BENDORAITIS, B. L. BROWN and L. S. HEPNER, 6th World Petrol. Congress

Proc. Sect. V, Pap. 15, Frankfurt, Germany 3. I. B. USHAKOVA, L. M. ROZENBERG, I. S. GENEKi~ and P. I. SANIN, Neftekhimiya 8, No. 5, 651, 1968

] 40

F. (~. UN(i~,m et al.

4. L. M. ROZENBERG, I. B. USHAKOVA, I. S. GENEKH, F. G. UNGER, L. A. SOSULINA, B. A. SMIRNOV, T. A. ZABOTNOVA, A. A. POLYAKOVA and P. I. SANIN, Neftekhimiya 9, :No. 3, 331, 1969 5. L. A. flOSULINA, A. A. POLYAKOVA, L. M. ROZENBERG, I. B. USHAKOVA and F. G. UNGER, Zh. organ, khimii 5, :No. 11, 1897, 1969 6. Ye. L. MATVEYEV, A. A. POLYAKOVA, R. A. KHMELNITSKII and F. A. MEDVEDEV, Pribory i tekhn, cksperim., No. 5, 172, 1965 7. N. D. COGGESHALL, J. Chem. Phys. 33, 1247, 1960 8. A. HERLAN, Brennstoff-Chemic 8, 45, 1964 9. American Petroleum Institute Research Projec~ 44, Mass Spectral Data, New York, 1952 10. A. A. POLYAKOVA, R. A. KHMEL'NITSKII and F. A. MEDVEDEV, K h i m i y a i tekhnol. ~opliv i mascl 6, 56, 1965 11. A. HOOD and M. O'NEIL, Uspekhi mass-spektrometrii (Progress in Mass.Spectrometry). Izd. inostr, lit., Moscow, 1963