reactions on lithium, beryllium, and 10 boron are generally larger than m.e.v., reaching the value of f26.3 m.e.v. for QBe(3He,-y)W. The results for the carbon monitor raise the interesting possibility of extending the use of the 3He cyclotron to irradiation with high-energy ?-rays, for photoactivation analysis and other purposes.
+
teresting suggestions. The cooperation of the staff of the 5.5-m.e.v. Van de Graaff accelerator is also appreciated. LITERATURE CITED
(1) Cumming, J. B., in “Applications of Computers to X‘uclear and Radiochemistry,” G. D. O’Kelley, ed., Satl.
Acad. Sci.-Natl. Research Council, Xncl. Sei. Ser. NAS-NS 3107 25 (1963\ \-___,.
ACKNOWLEDGMENT
We thank J. E. Strain and F. F. Dyer for their invaluable help in performing the experiments, and for in-
(2) Demildt, A. C., ANAL. CHEM.35, 1228 (1963). (3) Demildt, A. C., Lawrence Radiation Lab.. ReDt. UCRL-10647 (1963). (4) Friedhider, G;,Kennedy, J. W., Miller, J. M., Nuclear and Radio-
chemistry,” 2nd ed., Wiley, New York, 1964. 1 5 ) Heath. R. L.. U.S. At. Enerev Comm.. Rept. IDO-16880(1964). ( 6 ) Hughes, D. J., Schwartz, R. B., Brookhaven Satl. Lab., Rept. BNL-325 (1958). (’i)Lyon, W. S., Jr.:>ed., “Guide to Activation hnalvsis. Tan Nostrand, Princeton, N. J., “1964. (8) Xarkowitz, 8. S., XIahony, J. D., AXAL.CHEM.34, 329 (1962). (9) Montalbetti, R., Katz, L., Goldemberg, J., P h p . Rev. 91,659 (1953). \
Y“
,
RECEIVED for review Janriary 15, 1965. Accepted March 11, 1965. Research s onsored by the Y,S. Atomic Energy 8ommission under contract with the Union Carbide Corp.
Combination Acid Treatment-Adsorption Method for Determination of Saturates in Heavy Petroleum Oils T. A. WASHALL, W. A. MAMENISKIS, and F. W. MELPOLDER The Atlantic Refining Co., Research Division, Glenolden, Pa.
b A combination acid treatment-adsorption (ATA) method was developed for the determination of saturates in heavy petroleum oils. The technique is applicable to the separafion of saturates from olefinic and aromatic stocks in the gas oil and heavier range including residua. Unsaturates in the sample are reacted with a mixture of fuming sulfuric and nitric acids a t ambient temperature. The reacted olefins, aromatics, and any nonhydrocarbons are separated from the saturates by adsorption on a bauxitesilica gel column, and the saturates are recovered from the adsorbent by solvent elution. The per cent saturates is determined gravimetrically while the unsaturates are found by difference. Excellent results were obtained in the analysis of synthetic mixtures of saturates and C2g-Ca5 olefins over a wide concentration range. The saturates fractions recovered from a catalytically cracked gas oil, a lubricating oil, and a bright stock contained less than 3% olefin and were completely free of aromatics. Recovery of the saturates fraction was better than 98% in all cases.
A
of chromatographic techniques for the separation and determination of saturates have been gradually extended to include gas oil, lube oil, and heavier petroleum stocks. Efforts to obtain sharp separations between saturates and unsaturates in the higher molecular weight region have been only partially successful because the adsorbabilities of the saturates, olefins, and monocyclic aromatics PPLICATIONS
748
ANALYTICAL CHEMISTRY
become more similar as the alkyl chains increase in size. Knight and Groennings (4) modified the fluorescent indicator adsorption method ( 1 ) to accommodate gas oil and lube oil samples. Snyder (8) applied the linear elution adsorption technique to the separation of paraffins plus olefins from aromatics in gas oil. Schwartz and Brasseaux (7‘) passed residua through a mixed bed of silica gels and recovered saturate fractions which contained less than 5y0aromatics. Lipkin et al. (6) and Watson (9) also employed silica gel as the adsorbent. Both methods were effective for the determination of saturates in gas oils and lubricating oils but were not applicable to bright stocks. ,Mills (6) found that for an accurate analysis of high molecular weight oils such as bright stocks, clay was a necessary component unless excessive amounts of silica gel were employed. To improve further the chromatographic separation of saturates from heavy petroleum oils, the authors investigated the use of acid treatment to convert the unsaturates into polar derivatives with relatively high adsorbabilities. In contrast to the many chromatographic methods reported for petroleum separations, the literature was virtually void of references to the determination of saturates in heavy oils by acid treatment methods. Kahler et al. (3) studied the effectiveness of increasing strengths of sulfuric acid for the separation of olefins and aromatics from paraffins in a low temperature lignite tar. This study revealed that substantial amounts of both olefins and aromatics remained with the paraf-
fins after the oil was washed with 78% sulfuric acid. A more reactive acid, consisting of a mixture of fuming sulfuric and nitric acids, was employed successfully by Bonetti ( 2 ) for the nitration of aromatics. In view of the high yields obtained in that work, the authors selected this powerful nitrating agent as the reactant for the conversion of olefins and aromatics in heavy oils into highly polar derivatives. Specifically, the object of this investigation was to develop a method for quantitatively separating the saturates from both olefinic and nonolefinic heavy petroleum stocks. EXPERIMENTAL
The following combination acid treatment-adsorption (ATA) method was developed for the determination of saturates in heavy oils including bright stocks. The sample is diluted with a large volume of a low boiling, saturated hydrocarbon and is then contacted with a 2/1 (weight) mixture of fuming sulfuric and nitric acids a t ambient temperature. After settling, the acid phase is discarded and the hydrocarbon phase is percolated through a column containing activated bausite over silica gel. The saturates in the sample are eluted through the column and are recovered after removal of the solvent. Reacted olefins and aromatics are retained by the adsorbent and are not recoverable. Per cent, saturates is determined gravimetrically and per cent unsaturates is found by difference. Scope. The procedure outlined below is applicable to the deterniination of saturates in gas oil and heavier petroleum fractions, including residua containing olefinic and,’or aromatic hydrocarbons over all concentration
ranges. Because of t h e highly exothermic nature of the nitration reaction, this method should not be applied to furnace oil and lower boiling petroleum fractions. Materials. T h e following materials were used: Silica gel, Davison's grade 12, 28- to 200-mesh, activated a t 300" F. for 16 hours; Bauxite, Porocel, 20- to 60-mesh, activated at 300" F. for 16 hours; n-Pentane, or another saturated C + % hydrocarbon purified to have a residue less than 0.2 mg. per 100 ml.: Sulfuric acid, Baker's, 20 to 23% fuming; h'itric acid, Baker's, fuming; Adsorption column, 1-inch i.d. X 12 inches long, having a 500-ml. reservoir a t the top and a 2-mm. Teflon stopcock at the bottom. Procedure. Prepare the mixture of fuming sulfuric and nitric acids in the following manner. (Caution! Extreme care should be exercised in handling the fuming acids.) Because of the evolution of S O z and solvent vapors, all acid treating and mixing should be carried out in a well ventilated hood. Weigh out two parts of fuming sulfuric acid and one part of fuming nitric acid in separate glassstoppered flasks and cool both in a n ice bath. Slowly add small portions of the fuming sulfuric acid to the flask containing the fuming nitric acid. Mix the contents in the fuming nitric acid flask after each addition by gently swirling the flask. Allow time for dissipation of the heat of mixing before making the next addition of fuming sulfuric acid. Keep the flask containing the mixture of fuming nitric and sulfuric acids in the ice bath until all the fuming sulfuric has been added. The mixed fuming acids may be stored a t room temperature in a flask with a glass stopper. Weigh out 5 grams of sample 1 0 . 1 gram into a tared 250-ml. beaker. Dilute the sample with 200 ml. of n-pentane and introduce the mixture into a clean, 1-liter separatory funnel containing 100 ml. of n-pentane. Rinse the beaker twice with 50-ml. portions of n-pentane and add the rinses to the separatory funnel. Slowly add 50 ml. of a 2/1 (weight) mixture of fuming sulfuric-fuming nitric acid to the separatory funnel. Shake vigorously for 3 minutes. Vent separatory funnel occasionally during shaking to release possible pressure. Allow phases to separate and discard the acid layer. Add 100 ml. of distilled water to the separatory funnel and shake. Allow phases to separate and discard the water layer. Insert a plug of glass wool into the bottom of the adsorption column Pack the column with 55 grams of silica gel followed by 60 grams of activated bauxite. Place a clean 1-liter Erlenmeyer flask under the column and prewet the latter with 50 ml. of n-pentane. As the last of the prewetting solvent enters the adsorbent, introduce the pentane phase from the acid treatment. Maintain a percolation rate of 4 to 5
ml. per minute. Rinse the separatory funnel with 50 ml. of n-pentane and add the rinse to the adsorption column as the last of the pentane solution containing sample passes into the adsorbent. Just before the last of the rinse enters the packing, add 400 ml. of n-pentane to the column reservoir. Allow the column to run dry. Evaporate the solvent from the saturates fraction in a tared evaporating dish. Calculate per cent saturates as follows: wt.
yGsaturates
Table 1.
Reactivity of Fuming Acids with c~9-c~~ Olefins
Olefin reacted, Fuming acid 7c 2/1 (wt.) H~SO&INOI 100 32 HNOa 14 HzSOn Charge: 5 grams of cZS-c35 olefin in 400 ml. of isooctane Acid: 25 ml. of 2/1 (wt.) HzS04/ HNOI
=
wt. of saturates fraction wt. of sample
x
100
I n all cases, compounds containing 0, 5 , and S will be calculated as unsaturates. DISCUSStON AND RESULTS
Reactivity of Olefins with Mixed, Fuming Sulfuric and Nitric Acids. Because t h e complete separation of high molecular weight saturates from olefins is difficult and, in some cases, impossible by adsorption, t h e reactivity of fuming sulfuric, fuming nitric, and a mixture of both acids with relatively high molecular weight olefins was investigated. T h e sample employed for this s t u d y was a mixture of cZS-c3S olefins of the R C H = CHR' type. The technique employed in this evaluation was the same as that described in the procedure. Complete reaction of the olefins occurred only when the mixture of fuming sulfuric and nitric acids was employed. The data shown in Table I indicate that with fuming nitric acid alone, 32% of the olefin was reacted, while 14% was reacted when fuming sulfuric alone was employed. When the acid-treating step was eliminated, only 7% of the olefin was retained by the adsorbent, indicating that olefins in this molecular weight range were not strongly adsorbed by the bauxitesilica gel column. An investigation was made also of the reactivity of the mixed fuming acids with other types of olefins. Because a high molecular weight mixture of various olefin types was not available, the study was made using a mixture of CI2 olefins. Five olefin types were present in the mixture including the tetra-substituted ethylene type. The reaction of the olefins with the mixed fuming acids was carried out in npentane solution. After reaction, solvent was evaporated from the pentane phase. The acid phase was diluted with ice water and then extracted with benzene to recover the nitrated products. Qualitative infrared analyses of the solvent-free reaction products found in both the hydrocarbon and acid phases indicated that no unreacted olefin was present. The pentane phase contained predominantly R-KO, and
Table. II. Effect of Mixed Fuming Sulfuric and Nitric Acids on Normal, Iso-, and Cycloparaffins
W Component Before After acid acid treat treat MIXTUREA n-Eicosane 31.9 31.8 2,6,10,14-TetramethyI entadecane 37.2 37 1 1-8yclohexyl tetradecane 30,9 31.1 ~~
100.0 100.0
MIXTUREB o Paraffins Cycloparaffins, 1 ring Cycloparaffins, 2 ring Cycloparaffins, 3 ring Cycloparaffins, 4 ring
64 20 10 4 2
100
65 20 9 4
2
loo
MIXTUREC * Paraffins 23 Mono and/or noncondensed polycycloparaffins 37 Condensed cycloparaffins : Di 20 11 Tri 6 Tetra 2 Penta Hexa
25 37 20 11 6 1
~~
~~
Saturates from a catalytically cracked gas oil fraction; average molecular weight, 310. *Saturates from a lubricating oil fraction; average molecular weight, 492. Analyses: mixture A-gas- chromatography; mixtures B & C-mass spectrometry 5
R-0-NO2 type compounds and small amounts of carbonyl and hydroxyl compounds. Conversely, the acid phase contained predominantly oxygenated compounds and a small amount of R-h'02 and R-0-NO, type compounds. The reaction of the CI2 olefin mixture was much more vigorous than the reaction of the C29-3S olefin mixture indicated above and it was evident that some oxidation occurred. Effect of Mixed Fuming Sulfuric and Nitric Acids on Saturated Hydrocarbons. T h e effect of the mixed fuming acid mixture on saturated hydrocarbons was also investigated. Tests were made on three saturated hydrocarbon mixtures of normal, iso-, VOL. 37, NO. 6, MAY 1965
a
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and cycloparaffins which were obtained as pure hydrocarbons or isolated from petroleum stocks. T h e first mixture, A, contained C19-C20 range saturated, pure hydrocarbons. Mixture B contained Czo-C24saturates from catalytically cracked gas oil, and mixture C contained saturates from a medium lube oil stock. The saturates
Table 111. Application of ATA Method to Analysis of Synthetic, High Molecular Weight Saturate-Olefin Mixtures
Saturates added,
Saturates determined,
7c
7 0
2.5
Mean error -0.4
25.0
-0.5
50.0
+0.6
75.0
-0.3
98.0
-0.8
100.0
-0.8
Average molecular weight: saturates, 492; olefins, 448 (type RCH=CHR').
Table IV.
in mixtures B and C were isolated by adsorption on bauxite and silica gel and only that portion not exhibiting ultraviolet absorption was employed in the test. Mass spectrometric analyses (Table 11) of all three mixtures before and after the acid treatment indicated that high molecular weight saturated hydrocarbons were not reactive when contacted with the mixed fuming acids according to the proposed procedure. Overall recovery of the saturates was better than 98% in all three cases. Application of ATA Method. T h e ATA method was applied to the analysis of six synthetic mixtures in which the concentration of lube oil saturates in a mixture of Cz9-Casolefins ranged from 2.5 to 1 0 0 ~ o .The saturates were isolated and purified by the AT-4 technique and were free of both olefins and aromatics. The data presented in Table 111 indicate that per cent saturates were determined to within 0.4% a t t8he 2.5% level and to within 0.8% a t the 1 0 0 ~ level, o indicating that removal of the olefins was excellent over the entire concentration range tested. In addition, the precision of the method was within 0.2% at all levels and the
Results Obtained from Application of ATA Method to Five Petroleum
Oils Sample Aromatic extract Bright stock Paraffin oil, #l Paraffin oil, 52 Paraffin oil, 53 (1
Saturates determined] yo 18.8, 18.9 60.1, 60.2 65.4, 65.3 88.6, 88.8 98.5, 98.5
Max. U.V. absorptivities" of saturate fractions 220-230 mp 250-260 mp 270-280 mp 0.009
0,006 0.004 0,005 0.005
0.004 0.003
0,003
0.002 0.002
0.002 0.001 0,002
0.003
0.002
Cell, 1 cm.; solvent, isooctane.
Table V.
Comparison of Methods for Determination of Saturates in Heavy Petroleum Fractions Max. U. V. absorptivity0 of Olefinsb in
Method
h
B C D ATA
A B C D ATA A B C D AT A
Saturates recovered saturates determined, yo (260-280 mp) A. Catalytically cracked gas oil (550-757' F.) 49.9 0.002 49.1 0,002 47.7 0.004 49.7 0,001 47.4 0.003 B. Lubricating oil (658-1045" F.) 77.0 0.036 0 001 73.7 0.075 78.3 0.047 78.3 0.003 73.3 C. Bright stock 74 I 0 656 0 015 58 6 72 1 0 400 0 186 70 3 0 004 57 1
recovered saturates, yo ...
4.4
, . . , . .
0.6 ...
5.1 ... , . .
0.9 13 2 2 8
Cell, 1 em.; solvent, isooctane. b Determined by iodine number. A. Watson, A. T . ( 9 ) ; B. Mills, I. W. (6); C. Schwartz, R. D., et al. ( 7 ) ; D. ATA, without acid treatment. Q
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recovery of saturates a t the higher per cent saturates levels was about 99%. The ATA method was then applied to the analysis of five petroleum oils in which the saturates content ranged from 19 to 99%. A11 samples were in the light lube oil to bright stock range. The data shown in Table IV again indicated that the precision of the method was excellent and that the saturate fractions were essentially free of aromatics as evidenced by the low ultraviolet absorptivities in the 220 to 280 mp region. Comparison of ATA Method with Other Published Methods. The AT-4 method was then compared with the published adsorption methods of Watson ( 9 ) , Mills ( 6 ) , and Schwartz and Brasseaux ( 7 ) . The results obtained from the analysis of a conventional catalytically cracked gas oil, a lubricating oil stock, and a bright stock are summarized in Table V. The ultraviolet absorptivities were examined in the 260 to 280 mp region where monoaromatics exhibit their strongest absorption. Generally, the high-molecular weight monoaromatics are difficult to separate from saturates. I n the case of the catalytically cracked gas oil, all five methods appear to be equally effective for the removal of aromatics as evidenced by the low ultraviolet absorptivities of the recovered saturate fractions. However, marked differences occurred between results obtained from the analysis of the lubricating oil. In this case, only the method of Mills (6) and the ATA method produced saturates fractions with a nil aromatic content. Even further discrepancies resulted when the five methods were applied to the determination of saturates in a bright stock. The results show that the saturates fraction recovered from the ATA method had the lowest ultraviolet absorptivity and, consequently, the lowest aromatic content. The saturates fractions obtained from the method of Mills (6) and the ATA method were subsequently analyzed for olefin content by iodine number. The data shown in Table V clearly indicate that the saturates fractions obtained for the three stocks by the Mills (6) method contained from 4.4 to 13.2% olefins while the olefin content of the saturates fractions from the ATA method ranged from 0.6 to 2.8%. Because other published methods (6-9) do not effect a complete separation of unsaturates from the saturates, a subsequent analysis of the recovered saturates fraction by iodine number, bromine number, or infrared is required. In contrast, the saturates fraction obtained by the ATA method is essentially free of unsaturates and does not need further analytical treatment.
CONCLUSION
The results obtained from the investigations described here indicate that the ATd method gives an accurate saturates determination on both olefinic and nonolefinic heavy petroleum fractions, including bright stocks. Unlike most methods reported for the determination of saturates in heavy petroleum fractions, the A T h method is also applicable to mixtures of saturates containing olefins. For example, the AT.4 method is useful for the analysis of baturates in the heavy products from wax cracking. I n addition, the ATA technique is effective for the purification of high molecular
weight saturated hydrocarbons and for the purification of spectrometric grade saturated solvents. ACKNOWLEDGMENT
The authors express their appreciation to Frances J. Galbraith and to Harry Morgan for supplying the mass spectrometer and infrared analyses, respectively, and to Giovanni A. Bonetti for his discussions concerning the use of the nitration mixture for this application. LITERATURE CITED
(1) American Society for Testing Materials, Method D-1319-61T, Phila-
delphia, Pa.
( 2 ) Bonetti, G. A., Paper presented be-
fore Division of Petroleum Chemistry, ACS, Chicago Meeting, September 3-8, 1961. (3) Kahler, J. E., Rowlands, D. C., Brewer, J., Powell, W. H., Ellis, W. C., J. Chem. Eng. Data 5 ( l ) ,94 (1960). (4) Knight, H. S., Groennings, S., A N ~ L . CHEM.28, 1949 (1956). (5) Lipkin, 1LI. R., Hoffecker, W. A., Martin, C. C., Ledley, R. E., Zbzd., 20, 130 (1948). (6) Mills. I. W., Proc. A m . Petrol. Znst., ‘ k’ection’ZII 29M. 50 11949). (7) Schwartz, R. b., Brasseaux, D. J., ANAL.CHEM.30, 1999 (1958). (8) Snyder, L. R., Zbid., 34, 771 (1962). (9) Watson, A. T., Zbw!., 24, 507 (1952). RECEIVED for review November 24, 1964. Accepted March 15, 1965.
Direct Determination of Oxygen in Organophosphorus Compounds by Graphite-Pipe Reduction BEN D. HOLT Chemistry Division, Argonne National laboratory, Argonne, 111.
A novel approach to the carbonreduction method provides for the direct determination of oxygen in organophosphorus compounds with sufficient accuracy to aid in differentiating mixtures of high-molecular-weight organic phosphates, phosphonates, and phosphinates. Phosphorus-bearing decomposition products do not interact with the quartz container. Limitations on the upper operating temperature and on the texture and composition of the reducing carbon, that have characterized the conventional carbonreduction method, are greatly relaxed. The average recovery of oxygen obtained on a group of organophosphorus compounds containing 4 to 30% oxygen was with a relative standard deviation of about &0.5%.
loo.o%,
I
working with highmolecular-weight, organic phosphates, phosphonates, and phosphinates find a need for distinguishing among these compounds by some method other than carbon-hydrogenphosphorus determination and a potentiometric titration. For example, since the difference of one oxygen atom in the chemical compositions of trioctyl phosphate and dioctyl octyl phosphonate accounts for only about 47, of the total molecular weight. it would be informati\ e to measure the total oxygen content of an unknoun substance which might be one or the other of these compounds, or a mixture of the two. If the ineasurement is to be useful in this application, NVESTIGATORS
the relative error should be less than +I%. A fluorination method and a carbonreduction method were tested in this laboratory for the direct determination of oxygen in organophosphorus compounds. By the fluorination method, as reported by Sheft and Katz ( 5 ) ,a sample of the organic material was placed in a nickel vessel containing BrF2SbF6. The vessel was evacuated, disconnected from the vacuum line, and heated on a mechanical shaker for 4 hours at 500’ C. to fluorinate the sample and convert its oxygen to 02. The gas was Toeplerpumped through three cold traps to a calibrated volume for measurement and for subsequent mass spectrometric analysis. S o t only did this tedious procedure involve a rather corrosive reagent a t an elevated temperature, but the production of large quantities of HF caused the development of high pressures within the nickel vessel during the prolonged heating period. Considerable difficulties were experienced with valve leakage and moisture contamination. Cnder optimum operating conditions no more than one sample could be analyzed in one day. S i n e samples of tributyl phosphate were analyzed for oxygen by this method, the average recovery being 91%, with a relative standard deviation of +9%. One possible explanation for the low, erratic reiults was that some of the sample oxygen remained in the form of a volatile oxyfluoride even a t the conclusion of the 4-hour heating period. In 1952 Vnterzaucher (7‘) pointed out that the carbon-reduction method,
which has since been widely used in the direct determination of oxygen in many other organic compounds, was not applicable to the analysis of compounds containing phosphorus or fluorine. When these elements were present, the apparatus suffered damage and the results were unsatisfactory. *illthough during the past decade some improvements have been made in the carbonreduction technique, such as lowering the required temperature of the carbon bed by the addition of a platinum catalyst ( 4 ) and others (1-3)> there remains the need for a procedure by which oxygen can be successfully determined in organophosphorus compounds. A new technique was developed that yielded complete recoveries of oxygen in a series of organophosphorus compounds with a relative error of about +0.5%. It involved the use of a carbon-reduction bed contained in an induction-heated graphite pipe. The SiO, of the quartz reaction chamber as not directly exposed either to the corrosive vapors of the sample or to the hot reducing carbon of the graphite. h c cordingly, considerably more latitude was effected in the operating temperatures of the carbon bed.
APPARATUS
Figure 1 shows a diagram of the reaction chamber in which the sample was pyrolyzed and in which the resulting vapors were carried through hot carbon for the conversion of sample oxygen to carbon monoxide. VOL. 37, NO. 6, MAY 1965
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