data from this work are given in Table VI. I n each case a nickel concentration of 1.18 p.p.m. was used and an approximately 25 fold excess of the foreign ion was introduced. The recommended procedure was followed. At the concentration level studied only cobalt, copper, silver. and manganese appear to interfere seriously with the determination of nickel. Cobalt forms a complex which has an absorbance maximum a t 475 mp and this curve overlaps the nickel curve sufficiently to cause serious interferences when the recommended procedure is followed and when the cobalt and nickel concentrations are approximately equal. It is possible that by measuring the absorbance a t both 520 and 475 mp, nickel could be satisfactorily determined in the presence of cobalt. As indicated in Table VI, citrate ion does not seriously interfere with the color reaction and this should be useful for complexing many of the heavy metal
ions which would otherwise interfere by forming precipitates under the conditions used. I n none of the experiments with cations reported in Table VI was this precaution necessary. No hydrous oxide precipitates were observed, perhaps because of the slow rate of formation of these in the dilute solutions used. Further work is necessary to evaluate fully the applicability of quinoxaline2,a-dithiol to the determination of small quantities of nickel in the presence of other ions. However. it would appear to be a potentially useful reagent. I n acidic solutions, nickelous ion formed a green precipitate with quinoxaline-2,3-dithiol which was readily soluble in organic solvents, giving intensely green solutions. Furthermore, it was possible to extract nickel from aqueous acidic solutions with solutions of the reagent in organic solvents. The green color so formed u-as sufficiently intense for direct colorimetric
analysis; alternatively the nickel could be transferred back to an aqueous solution by extraction of the organic layer nith concentrated ammonia. The resulting solution had the intense red color described herein. These obserT ations suggest the possibility of transferring nickel back and forth between aqueous and organic solvents, which may appreciably enhance the specificity of the reagent. Further work on these properties of the reagent is now in progress. LITERATURE CITED
[l) Mitchell, A. M., hlellon, hi. G., IND. ENG.C H E ~ I .ANSL. , ED. 17, 380 11945). (2) Morrison, 11. C., Furst, A , , J . Org. Chem. 21, 470 (1956).
(3) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed.. D. 470. Interscience. New Tork,
1956 RECEIVED for review .4ugust 5 1957. rlccepted h-ovember 11, 1957.
Wet Ash Spectrochemical Method for Determination of Trace Metals in Petroleum Fractions JOHN HANSEN
and C.
R. HODGKINS
Esso Research and Engineering Co., Products Research Division, linden, N. 1.
b Catalyst degradation due to metallic poisons introduced b y catalytic cracking feed stocks reduces the yield of useful products. The development of processes to produce feed stocks containing a minimum of metallic contaminants is dependent on a suitable method of analysis. This method employs copper metal powder as a carrier on which the trace metal contaminants of petroleum fractions are deposited when the sample is decomposed by a sulfuric acid wet-ash method. The determination of as little as 0.05 p.p.m. of nickel and vanadium in a 10-gram sample is possible. This method has been found particularly useful in the analysis of fractions obtained from bench-scale or small pilot plant studies. Variations in the technique to employ either photographic or direct reading instruments are described.
C
cracking operations suffer rather severe debits due to catalyst degradation. To a large extent, this degradation can be attributed to poisons introduced into the units with the feed stocks. Even very minute traces of nickel, vanadium, and iron in ATALYTIC
368
ANALYTICAL CHEMISTRY
feed stocks can cause catalyst degradation of economic significance. The successful development of procedures to reduce or eliminate the catalyst poisons in feed stocks is predicated on the precision and accuracy of the analytical methods employed in the determination of the elements of interest. The low concentration of the metals in many fractions, as well as the limited quantity of sample available from bench-scalc or small pilot plant studies, makes it necessary to employ sensitive methods of analysis. Some workers have questioned the reliability of the results obtained when ignition ashing is used to destroy the organic material because of the possibility of a loss of vanadium and nickel as “fly ash” during the combustion of the sample. Greater credence is placed in the sulfuric acid wet ash decomposition of the sample to destroy the organic material and produce the inorganic residue for analysis. The spectrochemical analysis of the wet ash residues has an advantage over colorimetric methods because of grpater sensitivity, simultaneous determination of several elements, and elimination of a calculated reagent blank correction. I n the spectrochemical analysis of or-
ganic samples for small traces of metals. it is necessary to utilize some suitable material to serve as a matrix and t o provide bulk on which the trace metals can be deposited. By such a technique the metals of the sample become, in effect, impurities in the matriv material. The elements in the matrix should not be present in the sample to be analyzed. The matrix should be available in a relatively pure state. or a t least it should not contain any of the elements of interest. It must be in a stable chemical state when the sample preparation is completed, and it should not have an eytensive spectrum, or a t least it should not have spectral lines which mask the principal lines of the elements of interest. Various materials have been succ6ssfully employed as common matrices. A number of authors ( 2 , 5 , 6, 16) have reported the use of lithium carbonate alone or niived with graphite for the analysis of powder samples. Some workers ( I , 13) have described a method using silica as an “ash aid” in the analgsis of petroleum fractions. Tliv addition of magnesium nitrate to organic samples prior to the decomposition step has been reported by sevpral authors (4,14, 15). Jaycos 18-11) and othrrs
( 7 ) h a r e described the quantitative and semiquantitative determinvtion of a numbw of elenients in a n-ide variety of niatcrials by use of coppcr oxide matrix. Methods in n-hich alumina or silica-aluniina catalyst are added to the sample prior to decomposition of the organic material have been described (12, 17). Fitze and Murray ( 3 ) have reported the use of a hariuni nitrate-ammonium chloride mixture. This laboratory has, for a nunibcr of years. successfully used copper mc+l ponclcr as a carrier-matriy for the determination of the vanadium and nickel content of the ignition ash residues of potroleuni fractions. The addition of spectroscopically pure graphite poir der to the copprr residue mixture reducts the sputtering during excitation and results in more reproducible spectrograms. Variations in techniques in order to en:ploy either a spectrograph or QZuantoniPt u :ire discussed.
Y of i\Ietal per 40 M g . of Copper 0.5 5.0 50.0
Figure 1 . Electrode
f
DRILL,
Il
(PITH1V03). LIetalhc organic compounds, available from Sational Spectrographic, Laboratories, Inc., Cleveland Ohio. Graphite powler. spectroscopically pure. Calibration Standards. Sri.ciRoT h i t e oil blends ot nictalloorganic compounds of vanadium, nickel, and iron IT ere prepared to contain k n o n n concentrations of these metals. Analytical curves for t h e spectrographic procedure are based GRAPH.
2 20
..
..
40
One milliliter of solution A is equivalent to 50 y of each metal; 1 ml. of solution B is equivalent to 250 y of each metal.
EXPERIMENTAL
Equipment a n d Apparatus. The folloiving spectrographic equipment is manufactured by t h e Applied Research Laboratories, Glendale, Calif. Spectrograph S o . 2060, 1.5 meter. Alternating current arc Unit S o . 2040. Projection comparator densitometer s o . 2250. Temperature controlled rocking dewloping machine. Industrial Research Quantometer. High precision source unit Model C4700. Beakers, Vycor, Griffin type; 260 ml. Chromolov hot plate or equivalent, fitted with stainless steel cover plate. Electrodes, high purity spectroscopic graphite. Sample electrode, 2 inches x '4 inch (see Figures 1 and 2 ) . Counter Electrode. Spectrograph, 2 inches X inch. Spectrometer, 2 inches X inch, 120" included angle cone. Reagents. Copper metal. precipitated ponder. Sulfuric acid, highest purity attainable (batches selected by a test for blank). Glycerol, reagent grade, free of iron and nickel (otherwise purified by taking heart cut of vacuum distillation). K h i t e oil (check for metal blank). Ferric nitrate, C.P. [Fe(?JO& 9H20]. Sickel nitrate, C.P. [Ki(SOa)26H20]. Ammonium metavanadate, C.P.
MI. of Composite Soh. Reqd. to Treat 8.0 Grams of Copper Soln. A Soln. B
FLAT+
Figure 2. Electrode cutter on t h e use of varying knom-n quantities of these blends t o cover a range from 0.3 to 100 y of the metals. The standards are digested in the same nianner, using the same quantity of reagents as in the preparation of the saniples. I n this way the effect of any reagent blank is nullified. QUASTOJIETER. Thrre calibration standards for use n ith the eniission spectronieter are prepared by imprcgnating copper metal powder n ith knov n quantities of vanadium. nickel. and iron, using aqueous or slightly acid solutions of the metals. The metal concentrations of the aqueous solutions and the volunic used to prepare 8.0 granis of each standard are summarized as follone :
P R C P A R a T I O N O F STAKDrlRD. Place 8 grams of copper meta,l in a casserole and form into a slurry with distilled water before adding the desired volume of the composite solution. Heat on a steam bath with frequmt stirring until most of the water has evaporated, then stir constantly until dry. Place in a muffle furnace a t 1000" F. for a half hour to convert the copper metal to the oxide. Remove from muffle and allow to cool. Remove the copper oxide cake and grind using a mullite mortar and pestle. Remuffle for a half hour, grind, and bottle. Digestion of Standards. The three calibration standards. which are digested n i t h each batch of samples, are prepared in t h e following manner: Place 100 mg. of each of t h e copper civide standards in 400-nil. T'ycor beakers. T o each beaker add 4 grams of glycerol, 4 grams of white oil, and b nil. of concentrated sulfuric acid (same acid as used in preparing samples). Digest and muffle in the same manner as in the analysis of samples. After ignition, add 80 mg. of graphitc powder, mix, and grind using a mullite mortar and pestle. Check the reagents used in the preparation of samples and standards for purity, because excessive amounts of Inrtal contaminants cannot be tolerated.
Sample Electrode. T h e dimensions and shape of t h e sample electrode are shown in Figure 1. T h e feather edge of the sample crater reduces t h e wandering of t h e arc away from the sample. The electrode crater can be readily filled by placing t h e samplematrix-graphite mixture on a watch glass and pressing electrodes into t h e mixture, removing a n y excess by rolling the tapered edge on t h e watch glass. T h e cutter used in shaping the electrode is shown in Figure 2. Sample Preparation Study. To establish the optimum quanbity of copper. metal powder t o use as the matrix, a quaiitit3 of a blended oil standard to yield 1 y of the metals \vas at1tIt.d to varying quantities of copper powdu and then wet-ashed using 2 nil. of sulfuric acid. A quantity of graphite po~\-derequivalent to the weight of copper was added to each of the resitlues. inspection of the spectrograms of each of the residues indicated that 40 nig. of copper and 40 mg. of graphite nxuld be the most suitable. In some inst,ances: particularly n-hen a VOL. 30, NO. 3, M A R C H 1958
e
369
'
small quantity of sample was employed, there was a marked difference in the appearance of the residue after decomposition and ashing. The absence of sufficient organic material caused the formation of copper sulfate. In an attempt t o overcome this difficulty, sucrose, mannitol, and glycerol were investigated a s sources of readily carbonizable organic material. A relatively high concentration of iron and nickel ruled out the use of these materials unless purified. T h e heart cut obtained by vacuum distillation of USP glycerol was satisfactory. I n addition to preventing the formation of copper sulfate, the rapid formation of carbonaceous particles aided in the decomposition step by reducing the tendency to foam. During the decomposition, the copper powder is suspended in the mass and the final residue, after ignition a t 1000" F. in the muffle furnace, appears as a filigree which can easily be brushed out of the Vycor beaker. Normal cleaning procedures, such as a soap-and-scouringpowder wash and distilled-water rinse of the Vycor beakers, were inadequate and contamination of succeeding analyses could occur. The practice of soaking the washed beakers in warm aqua regia for a half hour proved effective.
Type of Excitation, Alternating Arc Voltage, kv. Current, amperes Slit width, microns Excitation time, seconds
Sample Analysis. Weigh 40 mg. of copper metal precipitated powder, and transfer into a 250-mI. Vycor beaker. Weigh a quantity of sample or standard blend (amount depending on the estimated concentration of the contaminant metals) into the beaker, using either a torsion or analytical balance. Add 2 grams of rectified glycerol and 4 ml. of concentrated sulfuric acid in the order mentioned. Place the beaker on a hot plate maintained a t 700" t o 800" F. and agitate by a swirling motion until the sample is charred and any foaming has subsided. Allow sample to remain on the hot plate until the evolution of sulfur trioxide fumes ceases, then increase the heat to the highest heat of the hot plate (1000" F.). Burn off the final traces of carbon by placing the beaker in a muffle furnace at 1000" F. The heating element of the muffle should be enclosed in the refractory; if not, a refractory sleeve should be used to prevent any metal particles which flake off the heating elements from contaminating the sample. When the carbon has been burned off, remove the beaker from the muffle and cool. Add 40 mg. of graphite powder. Mix the graphite and n-et-ash residue. Brush the mixture into a mullite mortar and grind thoroughly. Pack the cavities of two sample electrodes with the samplematrix mixture. Analysis by Spectrograph. Place the sample electrode in the lower electrode holder of the arc spark stand and adjust the counter electrode t o a 6-mm. gap, with the optical axis a t the mid-point of the gap. The excitation parameters shown below produced suitable spectrograms and yielded reproducible results.
Sample Sample wt., grams
370
ANALYTICAL CHEMISTRY
Current 5 2 50 50
Table 1. Determination of Nickel in Gas Oils by Spectrograph
G
Sample Sample wt., grams
H
10
K
5
3
Nickel, P.P.M. Chemical, colorimet0.442 2.51
ric
Spectrographic, run No.
10 11
Av. Std. dev. Coeff. of variation,
70
~
1.20
0.56 0.52 0.56 0.56 0.47 0.50 0.44 0.49 0.46 0.47 0.49 0.502 0.043
2.8
3.1 3.3 3.5 3.3 3.0 3.0 3.1 2.9 2.8 3.4 3.11 0.24
1.3 1.4 1.7 1.4 1.4 1.2 1.4 1.5 1.3 1.3 1.3 1.38 0.13
8.6
7.7
9.4
~
~~
II.
Determination of Vanadium in Gas Oils by Spectrograph
Table
H
G 10
K
5
3
Vanadium, P.P.M. Chemical, colorimetric
I., ANAL. CHEY.24, 742 (1952). Hartmann, W.,Prescott, B. E., J . Opt. SOC.Am. 38, 539 (1948). Jawox, E. K., ANAL.CHEM. 22, 1115 (1950). (9) Jaycox, E. K., SOC.Appl. Spectroscopy Bull. 3, No. 3, l(1948). (10) Japcox, E. K., J . Opt. SOC.Am. 35, 175 (1945). (11) Ibid., 37, 162 (1947). (12) bIcEvoy, J. E., Rlilliken, T. H., Juliard, -4. L., A N A L . CHEM.27, 1869 (1955). (13) RInrrav; h1. J., Plagge, H. -4., Proc. Am.' Petrol. Insf. 111 29M, 84 (1948). (141 O'Connor, R. T., Heinzelman, D. C., A4XAId, CHEhf. 24, 1667 (1952). (15) O'Connor, R. T., Heinzelman, D. C., Jefferson, 11.E., J . Opt. SOC.Am. 24, 185 (1947); 25, 408 (1948). (16) Weaver, J. R., Brattain, R. R., ASAL. CHEM.21, 1038 (1949). (17) Vork, P. L., Juliard, A. Id.,Ibid., 28, 1261 (1956). RECEIVED for review June 10, 1957. Accepted November 16, 1957. Division of Refining, 22nd Meeting, American Petroleum Institute, Philadelphia, Pa., 11ay 1957.
Bromine Number of Propylene and Butylene Polymers J. C. S. WOOD' Sun Oil Co., Marcus Hook, Pa. Bromine numbers of propylene and butylene polymers of low molecular weight (C, to CJ as determined by ASTM methods, are 10 to 30% higher than theoretical. Investigation of the composition of such polymers shows that they consist substantially of aliphatic mono-olefins. Elimination of the mercuric chloride catalyst in the titration solvent of the ASTM electrometric method gives results that agree with theoretical values. Additional data, though limited, indicate that the modified method is also more accurate for the types of olefins normally occurring in cracked gasolines.
372
ANALYTICAL CHEMISTRY
B
NUMBER methods have been in use for the past 30 years to determine the presence and estimate the concentration of olefins in gasolines (6-8, 10, 11). Data on pure compounds ( 2 , 14) by two ASTN test methods (2, 7 , 8) show the methods are generally applicable t o straight-chain and many branched-chain olefins. However, certain highly branched olefins exhibit bromine numbers much higher than theoretical. Some aromatics (mesitylene, isodurene, and many polycyclic aromatics) have significant bromine numbers by ASTM method D 1159
ROMINE
(3) even though they do not have an olefinic bond (12). The -4STlI methods give high values when applied to olefin polymer gasolines and distillate fractions from these gasolines. Bromine numbers of propylene trimer (C,) and tetramer (C12) are 10 to 307, higher than values calculated for the corresponding monoolefins. Strictly interpreted, these high ralues would indicate the presence of substantial quantities of diolefins
1 Present address, Sun Oil Co., 1608 Walnut St., Philadelphia 3, Pa.
