mixtures were easily resolved; however, the mixtures ben-
zene-l,l-dimethylcyclopentane, 3-methylpentane-l-trans-3dirnethylcyclopentane, and 2,3,3-trimethylpentane-l-trans-3cis-3-trimethylcyclopentane were unresolved. All of the above-mentioned unresolved mixtures were easily resolved by using squalane Kel-Flo as the substrate. To illustrate further the capability of the substrate, Figures 2, 3, and 4 are chromatograms in which the n-paraffin peaks have been labeled in a long range naphtha, a raffinate and a
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heavy isocrackate. Gasolines isomaxates, and various distillates have also been analyzed by using squalane Kel-Fro Kel-F4, coated columns have as substrate. Two squalane been used to 120 OC for over six months and another to 140 "C for several months without any apparent loss of resolution.
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RECEIVED for review March 20, 1968. Accepted August 16, 1968. The author thanks the Dow Chemical Co. for permission to publish this article.
eparation by Carbon Number and etermination of aphthene and ontent of Saturate Petroleum J. V. Brunnock and L. A. Luke The British Petroleum Company Limited, BP Research Centre, Chertsey Road, Sunbury-on-Thames,Middlesex, England A novel technique employing a high temperature gassolid chromatographic process using Type 13X molecular sieve has been discovered which permits a uantitative separation of the saturate hydrocarbons c! feedstocks boiling up to 185 "C by carbon number or by bulk hydrocarbon type within each carbon number. Factors influencing performance and the conditions necessary to achieve the separations have been assessed and the probable order of elution within the naphthene and paraffin types has been established with the use of auxiliary analytical procedures. In this way it is possible to obtain concentrates of particular series of isomers, for example 16 Cgand 43 Cl0bicyclo compounds have been successfully classified. Examples of capillary column chromatographic analyses of the segregated carbon number fractions and their individual naphthene and paraffin contents are also given. The apparatus is simple, easy to operate, and suitable for analytical determinations. The times for the analysis of distillates of 150 "6: and 185" C end point can be reduced if required to 20 minutes and 40 minutes, respectively, without serious loss of resolution. This paper describes the technique and its application to the analysis of different naphthas. THECAPACITY TO RESOLVE saturate hydrocarbons into naphthenes and paraffins and to estimate the concentration of these types is of great practical importance within the petroleum industry. Previously some success has attended the use of liquidmodified Pelletex (1) to separate CB-C7hydrocarbons by carbon number, but, until now there has been no practical means of quantitatively segregating naphthenes from paraffins. The relative concentration of naphthenes and paraffins however can be determined in a number of ways. In the lower boiling range, such estimations are obtained by capillary gas chromatography, but the accuracy of the determination deteriorates with the rise in the number of multicomponent peaks that occurs with increase in boiling range. Because of this, effective routine measurement is confined to distillates boiling up to about 130 "C. Hydrocarbon type analyses of higher boiling saturates consequently are usually performed by (1) F. T. Eggertsen and S. Groennings, ANAL.CHEM., 30,20 (1958).
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ANALYTICAL CHEMISTRY
mass spectrometry or the results are derived by the use of correlations based upon physical property data. These methods all suffer from limitations consequent upon the use of average data. A new approach has now become available following the discovery of a novel property possessed by Type 13X molecular sieve (2)which can be adapted either to measure the naphthene and paraffin content of a saturate petroleum distillate at each carbon number, up to and including GO, or to obtain fractions of segregated naphthenes and paraffins for further examination. EXPERIMENTAL
Type 13X pelleted molecular sieves (Union Carbide and Carbon Corp.) were ground and screened to 40-60 mesh. The performance of this size of material was found to be superior to that of finer mesh; it also presents no difficulty in ensuring uniform packing of the relatively small bore columns employed. For the analytical determination of the carbon number and naphthene/paraffin separations glass columns 12-inch X l/s-inch i.d. and 36-inch X i.d., respectively, were used. Both columns were packed with sieve in such a way that the sieve packing terminated 21/2 inches from the inlet and 1 inch from the outlet of the column. This arrangement tends to prevent any hold-up of high molecular weight material in the samples arising from cold spots at the end of the heater block. The inlet end was packed with 11/2 inches of 60-100 mesh Embacel (May and Baker Ltd) to assist in the even vaporization of the sample and to cut down dead space in the column; the exit end was left unpacked. The analysis required the columns to be operated up to about 450 "C and a heater block (3) was used for this purpose. The columns were either maintained isothermally or temperature programmed from 180 "C at various rates up to about 450 "C with the flame ionization detector maintained at 200 "C. It is essential to eliminate all traces of oil from the (2) J. V. Brunnock and L. A. Luke, British Patent Application
08401/68. (3) 5. V. Mortimer, and L. A. Luke, Anal. Chim. Acta, 38, 119 (1967).
ASBESTOS LAGGING
/
THERMOCOUPLE
I
SAMPLE INJECTION UU T H R O W SEPTUM PAD
lBl'
I
A
la
-
IA*
I- I n
&ASS
CAPILLARY
4
I
HELIUM
6 0 - 8 0 MESH EMBACEL
' 4 0 - 8 0 MESH TYPE I 3 X
MOLECULAR SIEVE
BOROSILICATE GLASS TUBE 1/4i~.ODX5/32inID TO FOD
Figure 1. Schematic diagram of gas solid chromatographic apparatus
helium gas stream; otherwise, partial oxidation of the sample on the sieve will commence at temperatures in excess of 300 "C. Helium was used as the carrier gas at a constant mass flow of 80 ml/min. A schematic diagram of the apparatus is given in Figure 1. For the carbon number analysis of a saturate petroleum distillate boiling up to 185 "C, the 12-inch X l/s-inch i.d. column was maintained isothermally at 400 "C when at this temperature the Clo hydrocarbons were eluted within 20 minutes. The naphthene/paraffin analyses were obtained on the 36-inch x 1/8-inchi.d. column held at an initial temperature of 180 "C and temperature programmed at 2 "C per minute up to a final temperature of 400 "C. If the programming rate is increased up to about 20-25 "C per minute, more rapid analyses without too serious a loss of resolution may be obtained. For separations where the fractions were required for further examination, glass columns 22-inch x 5/a2-in~h i.d. and i.d. were used for the carbon number and 36-inch x 5/32-in~h naphthaleneiparaffin separations, respectively. Both columns were packed with sieve in a similar manner to that employed for the analytical columns, and the fractions collected at the exit to the detector by means of capillary tubes chilled with cardice. The 22-inch x 5/32-in~h i.d. column was found to be capable of handling sample sizes of up to 50 p1 and when maintained isothermally at 400 "C and monitored with thermoconductivity detection, the individual carbon number eluates including Clowere collected easily in under 30 minutes. For the naphthene/paraffin separations, the column employed was operated either isothermally or temperature programmed. The optimum sample sizes for the 36-inch X 6/32-in~h i.d. column ranged from 8 pl at Gs to
