Determination of Total Paraffins, Monochloroparaffins, and Polychloroparaffins by the Fluorescent Indicator Adsorption Method Thomas A. Washall A R C 0 Chemical Co., Research Division, Philadelphia, Pa. THETOTAL MONWHLOROPARAFFIN CONTENT of products from paraffin chlorination can be determined readily by chloride analysis when di- and polychloroparaffins are absent. However, because the latter are almost always present to some extent, other techniques which differentiate monochlorinated products from polychlorinated products must be employed. For example, products from chlorination of multicarbon number range n-paraffins have been analyzed by gas chromatography. In this case, total n-paraffins, most of the individual monochloroparaffin isomers, and total polychloroparaffins were determined. However, the analysis was not simple in spite of the tremendous resolving power of this analytical tool. In many cases, there was significant overlap between higher molecular weight monochloroparaffins and lower molecular weight dichloroparaffins. The work reported in this paper describes the results obtained from application of the Fluorescent Indicator Adsorption (FIA) Method ( I ) to the determination of total paraffins, monochloroparaffins, and polychloroparaffins in products from paraffin chlorination and in fractions from further separation of chlorination products. Previously, the FIA technique outlined in ASTM Method D1319-66-T (I) had been employed almost exclusively for the determination of hydrocarbon types in petroleum fractions. Essentially, this technique employs silica gel adsorption to differentiate saturates, olefins, and aromatics. It has been found recently that olefins and monochloroparaffins of about the same molecular weight have similar adsorbabilities on silica gel. Consequently, the yellow fluorescent dye employed in the FIA method to mark the boundary between the separated paraffin and olefin zones of a hydrocarbon mixture can also serve to mark the paraffin-monochloroparaffin boundary in paraffin chlorination products. In addition, it has been observed that di- and polychloroparaffins have adsorbabilities similar to aromatics on silica gel. As a result, separated diand polychloroparaffins can be visualized by the same blue fluorescent dye normally employed to mark the aromatic zone of a separated hydrocarbon mixture. EXPERIMENTAL
Apparatus. The apparatus employed was essentially the same as that detailed in ASTM Method D1319-66-T (I). Reagents. Except for the specially prepared dyed gel enriched in the blue component, the reagents employed in the analysis of paraffinxhloroparaffin mixtures were the same as those described in ASTM Method D1319-66-T (I). Dyed gel enriched in blue component was prepared by fractionation of the Standard Dyed Gel employed in the FIA method. Approximately 60 grams of Davison Code 923 silica gel were packed into a 24 inch- X inch-diameter adsorption column followed by eight grams of Standard Dyed Gel. After a preliminary elution with cyclohexane, the yellow component was separated by elution with hexene-1 and the blue component was recovered by elution with benzene. The (1) ASTM Method D1319-66-T, ASTM Standards, Petroleum Products, Part 17, Jan. 1968, Philadelphia, Pa.
benzene effluent was evaporated to near dryness under a stream of nitrogen at 40-50 “C. The residue was diluted with diethyl ether and the resulting mixture was slurried with four grams of Davison’s Code 923 silica gel under a stream of nitrogen. After the gel became partially dry, the mixture was transferred to a round bottom flask attached to a rotary evaporator. Final traces of ether were removed under vacuum at 40-50 “C. The resulting dyed gel enriched in blue component was placed in a small bottle and stored in the refrigerator. The Standard Dyed Gel mixture was employed for all samples except those in which the ratio dichloroparaffins/monochloroparaffins was high. In the latter cases, a mixture containing 90 wt dyed gel enriched in blue comStandard Dyed Gel was employed. ponent and 10 wt Procedure. The procedure employed in the analysis of paraffin-chloroparaffin -mixtures was essentially the same as that described in ASTM Method D1319-66-T (I). The following minor changes in procedure were made in the application of the FIA method for the analysis of paraffinchloroparaffin mixtures: 1. The plug of dyed gel was placed at the bottom of the charger section and in the capillary connecting the charger and separator sections rather than in the center of the separator section. 2. The hypodermic syringe used to charge the sample to the silica gel column was not chilled below room temperature. 3. A 50 vol mixture of isopropyl and isoamyl alcohols was used as the desorbent in all cases. 4. Two pounds air pressure were applied to the top of the silica gel column after introduction of the desorbent and maintained until the red, alcohol-sample boundary passed through the capillary connecting the charger and separator sections. At that time, the air pressure was increased to 5-7 lbs. and maintained at that level to the end of the determination. Calculations on a weight per cent basis can be obtained using the densities of the three component types. Densities for normal paraffins and some chloroparaffins are available in the literature (2, 3). If appropriate values for monochloroparaffins and polychloroparaffins are not available, they can be separated readily by silica gel adsorption on a larger scale and the densities of the recovered fractions can be determined experimentally. In the present investigation, density values of 0.742, 0.867, and 0.972 were determined experimentally on paraffin, monochloroparaffin, and polychloroparaffin concentrates separated from a C,,-C13 mixture having an average carbon number of about 11.2. Scope. The procedure outlined above is applicable to the determination of total paraffins, monochloroparaffins, and polychloroparaffins in the C & I ~ range.
z
z
z
RESULTS AND DISCUSSION
Analysis of Synthetic Mixtures Containing Paraffins, Monochloroparaffins, and Polychloroparaffins. Initially, the FIA technique outlined above was applied to a series of synthetic mixtures containing n-hexane, I-chlorohexane, and (2) “Selected Values of Physical and Thermodynamic Properties of Hydrocarbons and Related Compounds,” API Project 44, Carnegie Press, Carnegie Institute of Technology, Pittsburgh, Pa. 1953. (3) E. H. Huntress, “Organic Chlorine Compounds,” John H., Wiley and Sons, Inc., New York, N. Y.,1948. VOL. 41, NO. 7 , JUNE 1969
971
~
~~
Table I. Analysis of Synthetic Mixtures of CIO-CI~ Paraffin, Moaochloroparaffin, and Polychloroparaffin by the FIA Method
Component Mixture #1
Mixture #2
Mixture 63
Mixture #4
Mixture #5
P
c
DCPC
=
P"
85.0
MCP
10.9
DPCP
4.1
Wt % component Determined
Mean error +0.4
-0.4 0
P
84.3
-0.1
MCP
13.3
-0.5
DPCP
2.4
$0.6
P
84.8
-0.1
MCP
14.1
-0.5
DPCP
1.1
$0.6
P
50.2
$0.4
MCP
38.2
-0.6
DPCP
11.6
$0.2
9.8
-0.1
MCP
58.3
-1.1
DPCP
31.9
$1.2
MCP
27.6
+1.2
DPCP
72.4
-1.2
P
Mixture #6
a
Known
paraffins.
* MCP = monochloroparaffins. =
di- and polychloroparaffins.
Table 11. Analysis of Synthetic Mixtures of Mono- and Polychloroparaffios Using the Total FIA Dye and the Modified FIA Dye Mixture
Mixture #1
Mixture #2
Mixture #3
Mixture #4
a
Component
Known
MCP
27.8
DPCP
72.2
MCP
19.7
DPCP
80.3
MCP
10.6
DPCP
89.4
MCP
5.0
DPCP
95.0
90 wt % prepared blue component dye, 10 wt % conventional FIA dyed gel.
* MCP = Clo-Cls monochloroparaffins. DPCP
972
=
ClrClr di- and polychloroparaffins.
ANALYTICAL CHEMISTRY
Wt % component Total dye
Modified dye"
82.9
cannot be analyzed cannot be analyzed cannot be analyzed cannot be analyzed
8.1
91.8
1,6-dichlorohexane. Results from the initial evaluation indicated excellent agreement between known and determined values for all three component types. However, the ultimate objective of this investigation was to develop a technique for the analysis of products from chlorination of heavier paraffins having a 4-5 carbon atom spread. In addition, it was desirable to apply the same technique to the analysis of fractions from subsequent separation of the chlorinated products. Consequently, a series of synthetic mixtures containing various concentrations of C10-C13 paraffins, monochloroparaffins, and di-plus polychloroparaffins were analyzed by the FIA technique. Pure paraffins, monochloroparaffins, and di-plus polychloroparaffins were separated from chlorination product by silica gel adsorption. a C1~-C13 Purity of the fractions was checked by gas chromatography and chloride analysis. Results from chloride analysis of the polychloroparaffin fraction indicated that it contained almost exclusively dichloroparaffin. The data shown in Table I indicate that there was excellent agreement between known and determined values for all three component types over wide concentration ranges. It was found subsequently that zone boundary differentiation was extremely difficult or impossible in the analysis of paraffin free mixtures containing more than about 85% dichloroparaffins. Because of the high intensity of the yellow dye fluorescence and the relatively low intensity of the blue dye fluorescence, the monochloroparaffindichloroparaffin zone could not be differentiated. In order to overcome this difficulty, the blue component was recovered from the dyed gel mixture by elution chromatography and re-adsorbed on Davison Grade 923, 100-200 mesh silica gel. In order to increase the intensity of the blue fluorescence, the isolated blue component was re-adsorbed from ether solution on only one half the weight of silica gel that was used in the isolation procedure. A mixture containing 90% of the blue component gel and 10% standard FIA dyed gel was prepared and compared with the standard FIA dye mixture for the analysis of samples that contained 70-95% dichloroparaffin. The data shown in Table I1 indicate that almost identical results were obtained with the standard FIA dye and the prepared dye mixture in the analysis of mixtures containing 70-80Q/, dichloroparaffin. However, at the %95% dichloroparaffin levels, the samples could not be analyzed with the conventional FIA dye while samples of this type were analyzed successfully with the modified dye mixture. Application of the FIA Method to the Analysis of Products from Paraffln Chlorination. Subsequently, the FIA technique was employed for the analysis of a variety of laboratory chlorinated products and fractions from subsequent separation of chlorinated products. A comparison of FIA and gas chromatographic results from the analysis of four samples is shown in Table 111. Examination of the data indicates that there was excellent agreement between the FIA and gas chromatographic analyses. In general, the data from this investigation indicate that the FIA method, previously employed exclusively for hydrocarbon analysis, can be applied to the analysis of mixtures containing
Table 111. Analysis of Chloroparaffin Products by the FIA Method and Gas Chromatography Wt component Component FIA GC Sample 10 pa 88'3] 88.3 88.1 88.3 MCPC 10.6 DPCPd 1.5 1.3 1.6 Sample 20 P ... ... MCP 96.5 96.2 96.5 DPCP 3.8 3.5
'"'"}
Sample 3"
...
P
MCP
... 97.6
DPCP Sample 40
0.7
P
70.9 71'2] 71.1
MCP
70.6 29.0
DPCP
0.9 0.8
a
b
0.4
Claproduct. P = paraffin.
MCP = monochloroparaffin. DPCP = di- and polychloroparaffin. e CloClsproduct. c
d
paraffins, monochloroparaffins, and polychloroparaffins. In addition, mixtures having broad carbon number ranges and wide variations in the distribution of paraffins, monochloroparaffins, and polychloroparaffins can be analyzed successfully by the FIA technique. The apparatus is inexpensive and the manipulation and interpretation is uncomplicated. Because olefins exhibit an adsorbability on silica gel similar to monochloroparaffins and polychloroparaffins are similar t o aromatics, it is obvious that the presence of these two hydrocarbon types will interfere. However, because chloroparaffins are relatively inert, it should be possible to remove these unsaturated hydrocarbons by acid treating or other chemical treatments prior to FIA analysis. In addition, it has been found that the FIA technique as applied to paraffin-chloroparaffin mixtures is also applicable to other paraffin-haloparaffin mixtures. For example, paraffin-bromoparaffin and paraffin-iodoparaffin mixtures have been analyzed successfully by the FIA technique. ACKNOWLEDGMENT
The author thanks D. J. Skahan and N. P. Kilargis for the gas chromatographic analyses of the paraffin chlorination products. RECEIVED for review February 18, 1969. Accepted April 1, 1969.
VOL. 41, NO. 7, JUNE 1969
973
