MASS S P E C T R O M E T R I C A N A L Y S I S OF KEROSINE F R A C T I O N S brDC 543.51 : 665.521.3

R. M. P a r a m o n o v , Yu. A. S a f i n , A. S. G a i s i n , and R. V. D z h a g a t s p a n y a n

The molecular weight distribution of hydrocarbons in kerosine determines the average molecular weight of the finished product. Higher contents of n-paraffins in kerosine are associated with final products with a higher degree of biodegradability in comparison with products derived from naphthenic and isoparaffinic hydrocarbons. Lowmolecular-weight aromatic hydrocarbons in kerosine decrease the molecular weight of the alkylbenzenesulfonates and thereby reduce their detergency. Mass spectrometric analysis, which is widely used ip petroleum research in the USSR and elsewhere, can provide an answer to questions involving these characteristics of kerosine (group composition, molecular weight distribution of hydrocarbons, and isomer composition). The information provided by mass spectrometry is most valuable and complete. It may be supplemented by information obtained by optical spectroscopy [1], chromatographic adsorption [2], selective extraction, etc. Here we are describing a mass spectrometric method for determining the group and isomer composition of paraffins in kerosine fractions boiling between 190 and 250"C, and also for determining the average molecular weight

[3 -51. This work was carried out with an MKh 1303 mass spectrometer with the following operating conditions: accelerating voltage 2 kV, cathode emission current 1.5 mA, ionizing voltage 50 V, ionization-chamber temperature 250~ temperature of intake chamber 250~ temperature of inner intake tube 250~ A system preheated to 250400~ was used for direct introduction of the sample into the intake chamber, this system having a metal seal [6]. Hydrocarbon

Group Composition

As characteristics of the ions for use in calculating the group composition, we selected ions with the following values of m/e: 71, 85, 99, 113 ... (271) for the paraffinic hydrocarbons; 69, 83, 97, 111 ... (Z69) for the naphthenic hydrocarbons; and 77, 78, 91, 92, 105, 106, 119, 120 ... (Z77) for the aromatic hydrocarbons. TABLE 1. Inverse Matrices for Determining Group Composition of Kerosine m/e

271 Z69 E77

2;71 E69 Z77 Z71 Z69 Z 77 Z71 2]69 Z77 Z71 E69 Z77

A

1,0012 --0,0476 --0,0011 1,0021 --0,0650 --0,0011 1,0024 --0,0631 --0,0016 1,0031 --0,0761 --0,0017 1,0064 --0,1405 --0,0020

B

--0,0137 0,5562 --0,0020 ---0,0185 0,6041 --0,0025 0,0237 0,6387 --0,0045 --0,0289 0,7015 --0,0050 --0,0337 9,7514 --0,0057

C

--0,002l --0,0001 0,2563 --0,0036 0,0007 0,3031 ---0,0064 ---0,0021 0,4851 --0,0031 --0,0056 0,4951 --0,0170 --0,0438 0,5080

n

10 11 12 13 14

Translated from Khimiya i Tekhnol_ogiya Topliv i Masel, No. 6, pp. 50-53, June, 1975. 9 1976 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part o f this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15.00.

481

TABLE 2. Results from Mass Spectrometric Analysis of Kerosine Used in Manufacture of Alkylbenzenesulfonates Hydrocarbon content, mole % Product

CnHzn+2-

Original Salavat kerosine (200-250"C fraction) 1 2*

CnH2n_n

normal

branched

12,4 11,5

43,4 45,0

37,9 38,2 34-- 36

6,3 5,2 5,5--8

12 12,1 12,2 ~t

14,5 15,1

44,5 46,2

28,1 24,3

12,9 14,3

I1,7 12,1

12,1

50,3

38,6

15,3

51,6

32,1

3~f Original Karaevsk kerosine (190-250"C fraction) 1 2* Dearomatized Salavat kerosine (200-250"C fraction) Deatomatized Karaevsk kerosine (200-250"C fraction)

CnH9n

Carbon number in average gao~ecule ~nt~2+n ,

12,5 1,0

12,0

* Data from plant analyses with MKh 1303 mass spectrometer. SData from analyses by aniline point method. Measured by cryoscopic method.

70

xe

FO

5O

{/

!,~

3O

{,0bY

20

12

1#

Carbon number Fig. 1

1F

10

8

J

10

J

I

72 74, Carbon number

I

7F

Fig. 2

Fig. 1. Moiecular weight distribution of paraffinic hydrocarbons in ffactions of Salavat kerosine: 1) 205-220"C, nay = 12.0; b) 220-250"C fraction, nay = 18.0; 3) 250-275"C fraction, nav-- 14.2. Fig. 2. r71/I M as a function of molecular weight for n-paraffins. No account was taken of the presence of polycyclic naphthenes, in view of the low intensity of their ions. For example, the intensity of the characteristic ions of bicyclic naphthenic hydrocarbons (L109) in the mass spectra of a dearomatized Salavat kerosine amounted to 5-8% of the intensities of characteristic ions of rnonocyclic naphthenic hydrocarbons (Z69) after deducting the intensities introduced by the paraffinic and monocyclic naphthenic hydrocarbons [6J. The content of aromatic hydrocarbons was estimated on the basis of the characteristic ions of alkylbenzenes (L77), as these were the predominant class of compounds in the aromatic part of the kerosine fractions that were studied. For example, the intensity of characteristic ions of indans and tetralins (Zl17), which are the next type of aromatic compounds in rank of abundance after the alkylbenzenes, was 10-11% of the intensity of characteristic ions for the alkylbenzenes after deducting a correction for superposition. This corresponds to a 0.6-0.8~ content of indans and tetralins in this kerosine. Calculation of average superposition coefficients of the characteristic ions was carried out for hydrocarbons with an average carbon n u m b e r n = I0-14, on the basis of the mass spectra of individual substances [3, 4].

482

The relative sensitivity coefficients of the characteristic ions for the paraffins and naphthenes were found by c a l c u l a t i o n and were checked e x p e r i m e n t a l l y on a kerosine for which the composition had been determined by an aniline point method. The relative sensitivity coefficients for the aromatic hydrocarbons (n= 12-13) were d e t e r mined by taking mass spectra of artificial mixtures prepared from a d e a r o m a t i z e d kerosine and the corresponding aromatic part. These aromatic hydrocarbons had been removed by a chromatographic separation [7] in columns (d-- 10-14 ram) packed with KSM silica gel with a grain size of 0.2-0.5 ram. The residual content of paraffinic and naphthenic hydrocarbons in the aromatic part was monitored by mass spectrometry on the basis of ions with m / e = 85 and 83, the intensities of which were 0.04 and 0.05 (respectively) relative to the intensity of the ion with m / e = 91; in the original kerosine, these respective values were 13.3 and 12.3. For e a c h of the five values of average m o l e c u l a r weight of the kerosine, a system of linear equations was set up. Solutions of the systems in the form of inverse matrices, convenient for c a l c u l a t i n g group composition, are shown in T a b l e 1, where A, B, and C are the total intensities of characteristic ions of paraffinic, naphthenic, and a r o m a t i c hydrocarbons as calculated from the mass spectra, and ~71, 269, and 277 represent the same intensities without any superposition due to other hydrocarbons. The group composition of the kerosine is determined by norrealization of these values. In determining the average m o l e c u l a r weight of the kerosine, we can l i m i t ourselves to finding n for the paraffinic hydrocarbons, since in kerosine and g a s - o i l fractions the values of n coincide for paraffinic and naphthenic h y drocarbons [8]. The m o l e c u l a r weight distribution of paraffinic hydrocarbons was calculated on the basis of the monoisotopic intensities of their m o l e c u l a r ions, with allowance for the relative sensitivity coefficients of these ions [6]. In order to avoid unduly high values for the fluxes of ions with m / e = 114, 128, and 142 due to naphthalene derivatives which are always present in kerosine [9], the determination of average m o l e c u l a r weight was performed by taking the mass spectra of the kerosine after d e a r o m a t i z a t i o n . The molecular weight distribution of paraffins in the fractions of the Salavat kerosine is shown in Fig. 1. Determination

of Isomer

Composition

of Paraffinic

Hydrocarbons Together with chromatographic adsorption [10, 11] and differential gas chromatography [12], mass s p e c t r o m etry can be used to d e t e r m i n e the isomer composition of paraffins. Mass spectrometric analyses have beendescribed for n o r m a l and branched paraffinic hydrocarbons in paraffin mixtures [13], in naphthas [14J, including o l e f i n - f r e e naphthas [15], and in heavy petroleum fractions [6, 16]. The determination of the quantity of n-paraffins as a part of the total paraffinic hydrocarbons is based on the difference in their dissociative ionization under the influence of electron i m p a c t [17J. The a n a l y t i c a l p a r a m e t e r for the relative content of n-paraffins is the ratio of the sum of their characteristic ions to the total characteristic sum. In order to find this ratio, we must know the values for the ratios of the characteristic ion sums for the n - p a r a f fins to the intensities of their m o l e c u l a r ions (Z71/IM). As was shown in [6], the use of mass spectra catalog d a t a [3] in this type of calculation leads to a large r e l a tive error, so that i t is necessary to resort to e x p e r i m e n t a l d e t e r m i n a t i o n of 271/IM. The measured values of this ratio for n-paraffins n-13 and higher were used in c a l c u l a t i n g the content of these hydrocarbons in the h i g h - m o l e c u l a r - w e i g h t fractions of petroleum [6J. The calculations of ~'71/IM for the n-paraffins present in kerosine (n= 8-16) were based on mass spectra taken in an MI
483

The r e l a t i v e quantity of n - p a r a f f i n s was c a l c u l a t e d from the formula i = n m a x 'Y,71 " -IM C = t~nmln

.K, E71

where C is the relative concentration of n-paraffins; IMi is the monoisotopic intensity of the molecular ion of the individual n-paraffinic hydrocarbon in arbitrary units; L71 is the sum of intensities of characteristic ions of paraffinic hydrocarbons, in arbitrary units, as calculated from the inverse matrix (see Table 1); and K is a correction factor, which was found to be 0.457 for the kerosine fractions. By maintaining the temperature of the ionization chamber at a stable level within ~ 1"C (the measurements were made in a PSR type instrument), reproducibility of the results was improved. Mass spectrometric analyses of the group composition of kerosines and the isomeric composition of paraffins have been conducted under both laboratory and plant conditions. The accuracy in determining the isomer composition of the paraffins was 10-12%, and the accuracy in determining group composition of the kerosine was 5-7%. In Table 2 we have listed the results from analysis of kerosine fractions being used in the manufacture of alkylbenzenesulfonates. For the Salavat kerosine, we have also listed analytical data obtained by an aniline point method. LITERATURE CITED 1. 2. 13. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

484

M.M. Kusakov, M. V. Shishkina, A. N. Kislinskii, et al., Neftekhimiya, 82 3 (1968). A.V. Kiselev and E. A. Mikhailova, in: Composition and Properties of Crude Oils and Gasoline-Kerosine Fractt ms [in Russian], Izd. Akad. Nauk SSSR, Moscow (1957), pp. 35-60. American Petroleum Institute, Research Project 44, Mass Spectral Data, New York (1952). E. Stenhagen (editor), Atlas of Mass Spectral Data, New York (1969). R. /k. 13rown, Anal. Chem., 23, 430 (1951). A.A. Polyakova and R. A. Kh"-'mel'nitskii, Introduction to Mass Spectrometry of Organic Compounds [in Russian], Khimiya, Moscow (1966). B.V. Aivazov, Practical Manual on Chromatography [in Russian], Izd. Vysshaya Shkola, Moscow (1968), p. 47. N.E.Htzegerald, V. A. Cirillo, and F. J. Galbraith, Anal. Chem., 34, 1276 (1962). A.V. Topchiev et al., in: Composition and Properties of Crude Oils and Gasoline-KerosL,le Fractions [in Russian], Izd. Akad. Nauk SSSR, Moscow (1957), p. 465. 13. Whitam, Nature, 182, 391 (1958). H.S. Knight, Anal. chem., 39, 1452 (1967). O.F. Folmer, Anal. Chem. Acta, 60, 37 (1972). J. Franke, Erdoel Kohle, 14, 816 (1961). R.A. Khmel'nitskii, K. I. Zimina, and A. A. Polyakova, Khim. i Tekhnol. Topliv i Mase]~ No. 6, 55 (1961). W.C. Ferguison and H. E. Howard, Ana~. Chem., 30, 314 (1958). A . A . Polyakova, R. A. Khmel'nitskii, and F. A. Medvedev, Neftekhimiya, 5, 153 (1965). H. Sobcov, Anal. Chem., 24, 1908 (1952). F. Cramer, Einschlussverbin-~eungen (Inclusion Compounds), Springer-Verlag, Berlin (1954).