Mass S pe c t rometric An a Iys is of PetroIe urn Samples Boiling in the Kerosine Range
D irec t
Heavy Reformates and Hydrodealkylated Products L. R. SNYDER, H. E. HOWARD, and W. C. FERGUSON Union Research Cenfer, Union Oil Co. of California, Brea, Calif.
b A mass spectrometer method for the analysis of petroleum streams and products boiling between 350" and 550" F. is described. Nine compound types, including eight hydrocarbons and alkyl benzothiophenes, are reported. Additionally, a breakdown of alkyl naphthalenes by carbon number is presented. Olefins, thiophenes, and/or sulfides may be independently determined and the data from these analyses integrated with those obtained by mass spectrometric analysis. The method was developed primarily for the analysis of feed and product streams associated with the production of naphthalene by hydrod ea lkylaf ion. Maximum accuracy ( f 1yo absolute) is obtained with such samples. Slightly lower accuracy is found for other sample types boiling in the kerosine range. The method requires no separation of the sample prior to analysis and is carried out in less than 2 man-hours per sample. spectrometric procedures for the analysis of a wide variety of petroleum fractions have been reported in the literature. They include methods for gasolines (6), heavier distillnles (1, 3, d ) , certain nonhydrocarbons isolated from petroleum (5, 7 , 9 ) , saturates (fO), and paraffin waxes ( 2 ) . Apart from the rather specialized case of waxes, all procedures except those for gasolines require preliminary separation of the sample into two or more fractions. Each fraction must be analyzed individually and the results combined to give values for the total sample. Analytical procedures which require prior separation of the sample have several shortcomings relative to direct mass methods: increased cost and elapsed time, reduced precision and, in some cases, reduced accuracy. I n any separation process, certain material losses are unavoidable. The repeatability of an analysis based on sample separation wiU depend in large measure on the repeatability of the separation process. The accuracy of the analysis will similarly suffer, unless ASS
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ANALYTICAL CHEMISTRY
the errors from the separation step are offset by increased accuracy in the mass analysis of each fraction. At the same time the cost of preseparation and the need for mass analysis of several fractions, rather than a single sample as in direct mass methods, increase the cost of an analysis to the point where full advantage of mass spectrometer techniques may not be taken. A review of the literature emphasizes both the lack of, and the need for, direct mass spectral methods which can analyze samples boiling above the gasoline range with requisite detail and accuracy. Interest in 350" to 550" F. petroleum fractions has been accentuated by the recent advent of commercial hydrodealkylation processes for the production of naphthalene, such as the Unidak process of the Union Oil Co. Research process studies and routine control of commercial units require the ability to analyze streams associated with this process for various molecular types, particularly the alkyl naphthalenes by carbon number. Heavy reformates from the production of gasoline are currently one of the more popular feedstocks for hydrodealkylation. A direct mass procedure has been developed in this laboratory for the compositional analysis of heavy reformates and related hydrodealkylated streams with a high level of accuracy ( f1% absolute). Other sample types in the same boiling range are also analyzed with somewhat lower, but generally satisfactory accuracy. The
Table I.
molecular classes reported include eight hydrocarbon and one d f u r type; naphthalenes are also determined by carbon number. At the same time provision is made in the case of cracked samples and high sulfur samples for integration of data from the independent analysis of three other compound types (IS), thiophenes (II), and -olefins alkyl sulfides (11)-with data obtained from the mass spectrometric method. EXPERIMENTAL
Apparatus. A consolidated Engineering Corp. Model 21-103C mass spectrometer with a Houston Glass Fabricating heated inlet system was used. The magnet current was 0.465 ampere, and the inlet temperature 150" C. The isatrom temperature was about 270" C., giving the following n-hexadecane pattern: m/e + 43 57 71
85
326
Ratio 1.20 1.00 0.55 0.35 0.30
Method Development. Fragment Analysis. The nine compound types listed in Table I are determined by a conventional fragment analysis similar to that followed by previous workers (4). The fragment peak summations of Table I are similar to the normal parent-minus-one sequence, with the exception of the indane-Tetralin and alkyl naphthalene classes. The compounds Tetralin and naphthalene may be present in high concentrations in
Fragment Mass Groupingsa 57 71 85 99 Alkanes Z 69 = 69 S3 97 98 111 112 Noncondensed cycloalkanes 2 67 = G7 4-81 95 4-96 4- 109 121 Condensed cvcloalkanes Z 91 = 91 105 119 133 Alkyl benzeies Z 104 = 104 117 131 145 159 Indanes-Tetralins '/z (128) 141 155 169 183 Alkyl naphthalenes Z 128 153 = 153 167 181 - 0.1 184) - 142 z: 165 = 165 179 193 4- 207 - 162 B 147 = 147 -I-181 f 175 Benzothiophenes 0 All peaks used in these summations are polyisotopic, with the exception of the three alkyl naphthalene parent peaks (156, 170, 184) used in the acenaphthene summation correction. These are monoisotopic. Z 43 = 43
++ ++ + +
+ + ++ ++ + +
++ ++ + ++ + + + + + (156 + 170 +
Table II. Matrix Inverse 43
Alkanes
Noncondensed crcloalkanes Condenecd cycloalkanes Alkyl benzenes
Indnnes-Tetrdins Slkl-l nsphthalenes
-1 4 ~ - I B
