Rapid Chemical Determination of Iron, Nickel, and Vanadium in Petroleum Oils J. S. FORRESTER and J. L. JONES Esso Research Laboratories, Esso Standard, Division of Humble Oil & Refining Co., Baton Rouge, La.
b A rapid chemical procedure has been developed for the determination of trace metals in petroleum oils. The method has an elapsed time of less than 2 hours; one operator can analyze 15 oil samples per day for iron, nickel, and vanadium. This short analysis time i s made possible by a combination of rapid perchlorate ashing and direct colorimetric finishing. A spectrophotometric study was made of a number of color reactions so that sufficiently sensitive procedures could be used. Results show a-furil dioxime and 3,3 -dimethylnaphthidine to be excellent reagents for nickel and vanadium, respectively. Bathophenanthroline, 4,7-diphenyl-l,1 O-phenanthroline, i s applied to the iron determination. 8
UIZING the
past years, coiisiderable research in petroleum laboratories has been directed ton-ard replacing chemical analyses with instrumental techniques. Particularly, optical and x-ray emission spectrography have been applied to the determination of iron, nickel, and vanadium in pc+roleum hydrocarbons and in cracking catalysts. This laboratory initiated a n effort to develop improved chemical methods for trace metals in oils. Rapid decomposition procedures were combined with sensitive and selective reagents to reduce analysis times to a fraction of that demanded by current methods. The result is a chemical method of high precision and accuracy., with analysis tinies competitive with those of instrumental methods.
dred hydrocarbon samples have been safely decomposed. The mixed acid procedure depends on the fact that hot concentrated perchloric acid does not effect any oxidation below 203’ C. By use of high nitric-to-perchloric acid ratios, the destruction of all reactive hydrocarbons is assured a t lower temperatures; the perchloric acid only serves t o oxidize the more refractive carbonaceous materials. Since vanadium itself is a catalyst for perchlorate oxidations ( I ) , decomposition rates are a direct function of vanadium concentrations. This helps to regulate the oxidation rates, speeding up the oxidation of heavy inaterials high in vanadiuni and, for the lighter oils, retarding thc reaction to a safe speed. The devdopnicnt of witable colorimetric procedure. follon-mg perchlorate decompo-ition iiecrssarily requires satisfactory color development in perchlorate media. An ad1 aiitage is derived from the 11:itule of such media to minimize complrxation, thereby supporting the formation of stable color systems. EVALUATION OF
COULOMETRIC METHODS
Table I suniniarizeg the colorimetric reagents considered for this application. The following discussion is confined to the colorimetric systems ultimately selected for the oil analysis. DETERMINATION OF NICKEL WITH a-FURIL DlOXlME
The use of cy-furil dioxime
RAPID DECOMPOSITION PROCEDURE
The major portion of analysis tinir is s p m t on decomposition of the hydrocarbon. A substantial improvement map be made by the use of the “liquid fire reaction” (IO). This technique prescribes the use of mixed nitric and perchloric acids to oxidize the hydrocarbons rapidly and safdy and leave the trace metals as soluhlt. pcrchlorates; use of a muffle furnace and subsequent need for resolubilizing metal oxides are eliminated. Under the conditions prescribed in the section on procedure, several hun-
HO-3
S-OH
for thv deterinination of nickel has been reported. Sickel reacts with the reagent to give a red color, which may then be estractcd into chloroform. The spectral curve of the chloroform solution is shonn in Figure 1. Gahler et al. (5) recoiiiniended a n optimum pH range of 7 . 5 to 8.3, nhich Sandell subsequently recognized as “surprisingly narrow” (8). Taylor reports ( 2 1 ) using the reageiit in aninioniacal solution. The use of a-furil dioxime offers a n
incentive due to its high sensit’ivity ( 2 = 19,000). I n addition, nickelfuril dioxime may be extracted into chloroform, offering further concentration and additional selectivity. Effect of pH. Since pH selectivity was the primary objection t o the use of the reagent, a study was made of this variable. The results are summarized in Figure 2 . T h e following conclusions may be drawn: Chloride solutions of nickel will not w t r a c t when neutralized wit,h sodium hydroxide; conversion of the chloride solutions t o perchlorate, prior t o neutralization with sodium hydroside, results in the narron- pH dependence previously reported ( 5 ) . St,rong color developnicnt as w l l as extraction over a widc pH range occurs after prior addition of ammonium hydroxide; and with perchlorate solutions, the single use of ammonium hydroxide is prevented because of the buffering action a t pH 8.5 froin slightly soluble ammonium pwchlorate. Color formation possibly takes place through the nickel amine ion. The final procedure calls for the addition of a fevi drops of ammonium hydroxitlc, followed by the addition of sodiuin hydroxide to a phenolphthalein end point. The need for any critical neutralization is eliminated by the \Tide p H latitude of the system. Khile the over-all trace metal analysis is designed for use with perchloric acid, the final a-furil dioxime procedure gave quantitative results from hydrochloric, sulfuric, or nitric acid. Adaptation t o existing analysis schemes is, therefore, readily possible. Color Stability. Maximum color development occurred in 5 minutes and no variation in color intensity was observed over a period of 17 hours. N o test,s were made after t h a t time. Extraction Efficiency. Under t h e proper experimental conditions. a single extraction removes more than 997, of t h e total nickel color. An additional experiment was made t o determine the minimum amount of extraction t h a t could be conveniently used in a n analysis-the smallest volunie necessary for proper contacting. Two extractions, with 10 ml. each of chloroform, resulted in a quantitative transfer; this is a convenient volume since 25 ml. is the minimum VOL. 32, NO. 11, OCTOBER 1960
1443
amount of solvent necessary to fill a 5-cm. spectrophotometer cell. Although xylene was an equally efficient extractant, density considerations made chloroform the preferred solvent. Interferences. Tests were made t o determine interferences resulting from the possible presence of iron, vanadium, copper, or chromium. The presence of u p to 0.5% of iron or vanadium showed no effects. B y washing the chloroform extract twice with 10% ammonium hydroxide, a n y copper interference is easily eliminated. Chromium can be tolerated u p to 0.1%; however, larger amounts are readily volatilized during the decomposition step.
Oxidation of Ni-Furil
Dioxime.
B y analogy to the Wi-dimethylglyoxime system, an oxidation of Wifuril dioxime was attempted in the hope of obtaining increased sensitivity; iodine was used as an oxidant under two different conditions. The results in each case Tvere unsatisfactory.
-
0.0 3 50
375
400
425 NAVE
LENGTH,
4 50
475
500
5 5
"r*
Figure , Spectral curve of Ni-furil extract
dioxime chloroform
Ni concn., 2.00 p g , per ml. Cell length, 1 .O cm.
Table I. Rapid Chemical Determination of Fe, Ni, and V in Oils Metal V
Heagent Phosphotungstic acid Phosphotungstic acid
Extracted with .
I
.
...
Phosphotungstic acid
...
Phosphotungstic acid
Butyl alcohol
8-Quinolinol Diphenylbenzidine
Amyl alcohol ,..
3,3'-Dimethylnaphthidinea Benxohydroxamic acid
Si
Hexyl alcohol
...
Formaldoxime 2,3-Quinoxalinedithiol Cyclohexanedione dioxime Furil dioxime. Fwil dioxime Dithizone Dimethylglyoxime
Chloroform Chloroform
+ oxidant
4-Isopropyl-1,2-cyclohexane-
dione dioxime Diethyldithiocarbamate
Fe
1,2-Cycloheptanedione dioxime 4-Methylcyclohexane 1,2-Dione dioxime 1,lO-o-Phenanthroline Bathophenanthrolinea
, Reagents discussed in text.
1444
ANALYTICAL CHEMISTRY
... Chloroform Toluene IsoaA&' alcohol
Sensitivity, Wave Gram-Atm. --I Length, Coninients Cm.--I M p 2800 Complete separation from iron is necessary. 375 1750-1900 Sensitivity dependent on types of oxidant used for 400 vanadium. Perchlorate solutions frequently gave tungstate precipitation. Interference from Fe, Cu, Cr: 1280 Poor sensitivity. Poor precision of finishing pro436 cedure. Butyl alcohol too soluble, amyl alcohol satisfactory, 2100 400 but perchlorate solutions frequently precipitated. Extraction also gives good separation from Cr, Cu, and Fe. 5100 475 Xot sufficiently specific. Color unstahle, pH sensitive, temperature aensi23,800 5i5 tive . 17,800 550 Color stable for -1 hour. Good reproducibility; not pH nor temperature sensitive. 450 ... Iron interferes. Procedure recommends separation by electrolysis. Reacts with V(1V) in basic solution. Fe, \In, Co, 6200 400' and Ni interfere. Only recently reported in literature. Cu, Co, and 19,000 520 Ag interfere. ... . . . Does not appear to offer any advantage over other vic-dioximes. This procedure is very satisfactory; cf. discussion. 19,000 535 15,400 535 ... * . . Very low specificity. 4940 540 Only persulfate oxidation results in stable color. 6400 400 Insufficient sensitivitv: 4400 383 " , Fe, , Co, , and Cu interference. ... Fe, Cu, and Pb interfere; with slight modification, 37,000 this could be another excellent reagent. ... 4660 3340
365
Insufficient sensitivity.
11,000 22,400
520 533
Perchlorate interferes. Procedure satisfactory in perchlorates. Reagent concentration must be kept high to prevent Ni interference. Cr, Cu, and V do not interfere.
Figure 2. Effect of pH on extraction of Ni-furil dioxirne
0
NiCI:! in HCI neutralized with NHIOH
A Ni(C1O4)2in HClO, neutralized with N a O H 0 NiClz in HClOl neutralized with N a O H 0 Ni(C10& in HClOa neutralized wlth NHjOHf NaOH DETERMINATION OF VANADIUM WITH 3,3'-DIMETHYLNAPHTHlDlNE
3,3'-Dimethylnaphthidine(DMK) as a reagent for detecting vanadium was first reported by Belcher and coworkers (1). Milner and Kall (7) subsequently developed a procedure for determining vanadium in alloys. Results were satisfactory, provided a dilute reagent solution was used to reduce difficulties from high blanks. I n a later study, Scholes (9) concluded that the reagent was not suitable for developing a precise method. The spectral curve for vanadium with 3,3'-dimethylnaphthidine is shown in Figure 3. Acid Concentration. Some preliminary experiments with vanttdium and D M N showed that strong acid solutions iTere favorable to color development. The single use of perchloric acid showed slow color development; maximum color stability occurred in 1 S solutions. This is shown in Figure 4. The speed of color development was substantially improved in mixtures of perchloric and phosphoric acid. Figure 5 s h o w that equal concentrations of 10% volumes of perchloric and phosphoric acids provide suitable analysis conditions.
After 15 minutes of color development, the intensity remains unchanged over a period of approximately 1 hour. Small variations in perchloric acid concentration did not affect the color stability under these conditions. Reagent Concentration. A study was made of the optimum reagent concentration (Figure 6) which showed the need to operate a t a higher strength than previously recommended (7). Although solutions were made from reagents obtained from two different sources, the high blanks reported by Milner and Nall (7) were not observed. Reagent Stability. Vanadium determinations were made over a 1week period to check the storage stability of the reagent. While a gradual increase was noted in the reagent blank, the analytical results remained constant.
ilyL
lid Figure 5. Color stability of HCIOI/ H3P04-DMN solution
as an extractant to overcome "previously observed perchlorate interference." Simultaneously, they reported increased sensitivity which we found to be less than 5%; experimental difficulties in obtaining clean extractions with nitrobenzene made use of this solvent unattractive. It is important that the reagent concentration be kept sufficiently high to prevent any nickel interference. Failure to do so leads to the preferential formation of a nickel-bathophenanthroline species, which absorbs below 370 mp a n d causes low iron results. Chromium, copper, and vanadium do not interfere.
0 2% vol. HCIO, (72% wt.) vol. HCI04 (72% wt.) VOI. HC104 (72% wt.)
Scholes (9) claims failure of the reagent to give reproducible calibration curves. Our experience is that reagents, even from different sources, give absolutely reproducible Calibration curves. Interferences. Tests viere made to determine interferences resulting from the presence of any iion, nickel, copper, or chromium. Up to0.570 iron,nickel, or copper failed to have any effects. Since the violet D l I Y color results from oxidation of the reagent, chromium interferes seIiously. All traces of chromium can be removed by volatilization as chiomyl chloride during sample decomposition.
PROCEDURE
Apparatus and Reagents. Spectrophotometer, Beckman DU or equivalent, with matched 0.50-, 1.00-, and 5.00-cm. Corex cells. Flasks, Erlenmeyer, Vyco~',250 ml. with drip caps. Dispensers, automatic, assorted sizes, California Laboratory Equipment CO., 98 Rincon Road, Berkeley 7, Calif. Bathophenanthroline Test Kit, Cat. S o . 108, G. F. Smith Chemical CO., 867 McKinley Ave., Box 5906, Columbus 23, Ohio. This kit consists of specially purified reagents including : Ferrous iron, standard solution, 1.00 pg. of Fe per milliliter. Hydroxylammonium chloride, 10% solution. Sodium acetate, 10% solution. Bathophenanthroline, 0.001M in 50% ethyl alcohol. Isoamyl alcohol. a-Furil dioxime, Eastman S o . 3308,
DETERMINATION OF IRON WITH BATHOPHENANTHROUNE (6)
I
42,
I
I 100
$SO **"I LCUGTH
I
,
610
6,O
Figure 3. Spectral curve of vanadium with dirnethylnaphthidine V concn., 2.0 pg. per mi. Cell path, 1 .OO cm.
t
"'JL I
Figure 4. Color stability of HC104DMN solution
X 10% A 20%
O s
The high absorptivity of this reagent (2 = 22,400) made it especially attractive for the determination of iron. The color is generally developed in a buffered solution and extracted into isoamyl alcohol. Interferences. While the perchlorate anion reacts with o-phenanthroline, no such interference was observed for bathophenanthroline. This apparently is contrary t o the observations of Collins and Diehl, who reported (3) the use of nitrobenzene
I
I
['I ,
b-
1
I i
l RilOrri
Figure 6. tration
X-
I -x
/
,
l
,
*1 ,511 I L
Effect of reagent concen-
Reagent, 3,3'-dimethylnaphthidine, 0.1
VOL. 32, N O . 1 1 , OCTOBER 1960
70
1445
Table II. Rapid Chemical Determination of Fe, Ni, and V in Oils
Sample Vacuum distillation residuum
Metal Fe
Xi
v Heavy crude oil
Fe Ni V
Precision Data5 Over-all Analysis No. Av. 2u detns. 6.5 25.6 85.4 10.3 52.4 402
0.11 0.43 2.6 1.1
0.79 3.8
5 6 6 5 6 6
Finishing Step Only NO.
Av.
2u
detns.
6.9 25 8 86.1 11.2 53.7
0.28 0.24 1.3 0.80 0.41 2.2
6 6 6 6 6 6
401
(A 10% volume perchloric acid concentration is necessary at this step in the method. Any modification of the procedure must make allowance for this requirement.) Add 2.5 ml. of phosphoric and 2.5 ml. of 3,3’-dimethylnaphthidine; dilute to volume. After 15 minutes, read at 550 mp against reagent blank, choosing cell path t o bring absorbance reading into optimum spectrophotometric range. STATISTICAL EVALUATION OF PROCEDURE
Precision. An integrated procedure was developed using the three reagents described above. Two representative samples were analyzed using this method. F o r each metal, six nium chloride and 8 ml. of sodium Table 111. Determination of Vanadium separate determinations were made acetate. Adjust p H to between 3 and 4 Accuracy Data on each oil; one of these samples was with 20% sodium hydroxide and add 4 Yew RIethod, taken through six identical color ml. of bathophenanthroline. Extract ASThLa P.P.M. P .P.M. with 6 ml. of isoamyl alcohol as above developments. This experimental deSO. KO. and read final color against a reagent, sign served t o differentiate t h e preSample Av. detns. Av. detns. blank. Choose proper cell path to cision of t h e finishing step from t h e 15.7 7 17.3 4 1 bring reading within optimum spectroprecision of the over-all procedure. 76 7 71.2 4 2B photometric range. 3c 123 7 126 4 Determination of Nickel. CALIBRA- The results are shown in Table 11. 4D 218 7 210 4 Accuracy of Vanadium Procedure. TION. Prepare a series of 60-ml. a Average values from 2 laboratories The accuracy of the vanadium pro0 to 60 separatory funnels containing using 2 different methods. cedure was checked by analyzing a pg. of nickel. Add 5 ml. of 10% aeries of ASTM samples previously sodium citrate, 5 drops of phenolphthalein, and 3 drops of concentrated characterized by two independent 1% in 50% ethyl alcohol. 3,3‘-Diammonium hydroxide. Add 20% soprocedures and two different laboramethylnaphthidine, 0.1% in glacial dium hydroxide to phenolphthalein end tories. I n t h e absence of results for acetic acid, Eastman No. 7333. point and a 3-drop excess. Add 3 ml. of nickel and iron, no similar comparisons Decomposition of Sample. The a-furil dioxime. Extract twice with could be made for these metals. subsequent decomposition must be 10 ml. of chloroform, transferring ilccuracy data for vanadium are carried out using facilities suitable for extracts to a 25-nil, volumetric flask. shown in Table 111. use with perchloric acid. A specially Dilute to volume with chloroform and constructed hood or a glass fume add I gram of sodium sulfate. Read ACKNOWLEDGMENT eradicator should be used. Loss of final colors in 1-em. cells at’ 435 mp volatile porphyrins can be prevented by against a reagent blank. Plot calibraThe authors are indebted to L. AI. use of a Bethge digestion apparatus tion curve. Addison for advice and encouragement, DETERJIIXATIOS. Transfer 10 nil. of (3,4): and to Esso Standard, Division of Weigh 0.2 to 2.0 grams of oil into a the decomposed sample to a 60-ml. Humble Oil & Refining Co., for persuitable digestion flask. Add 2 ml. of separatory funnel. Proceed as above. mission to publish these results.’ saturated sodium chloiide, 20 ml. of Read color a t 435 mp against a reagent nitric acid, 15 ml. of perchloric acid, blank, using correct cell path to bring LITERATURE CITED and several glass boiling beads. Slowly izbsorbance reading into optimum spec(1) Belcher, R., Xutten, A. J., Stephen, raise the temperature and hold just high trophotometric range. (Note: A R. I., Analyst 76, 430 (1951). enough so that sample bubbles in the brownish color indicates the presence of (2) Bethge, P. O., Anal. Chim. Acta 10, liquid phase. When boiling rate incobalt. Prepare a new sample. Omit 317 (1954). creases due to exothermic oxidation of the addition of sodium citrate. After (3) Collins, P., Diehl, H., iix.4~.CHEM. perchloric acid, shut off heat. After adjusting the pH, add 5 ml. of 20% 31, 1692 (1959). bubbling decreases, again heat and fume sodium thiosulfate. Remove any pre(4) Forrester, J. S.,Senn, R.L., Jones, until perchloric acid has been reduced cipitate by centrifugat’ion and proceed J L., unpublished research. (51 Gahler, A. R., Mitchell, A. hI., to approximately 6 ml. Cool. add 10 as before.) Mellon, 31. G., ANAL. CHEW 23, 500 ml. of water, and continue to boil for 1 Determination of Vanadium. CALI(1951). minute to expel any chlorine. Transfer BRATION. Weiah 0.3338 a r a m of (6) McCurdy, W. H., Jr., Diehl, H., to a 25-ml. volumetric flask and dilute to ammonium va&date into 250-ml. Analyst77,418 (1952). volume. beaker. Add 10 ml. of perchloric acid (7) Milner. G. W.C.. Kall, W. R., Anal. Determination of Iron. CALIBRA- and heat to strong fumes. Cool, a d d ‘ Chim.Acta 6 , 420 (1952). TIOX. Prepare a series of calibration 100 ml. of water, and boil. Cool (8) Sandell, E. B., ‘Colorimetric Metal standards by transferring 0, 10, 25, and transfer t o a 1-liter volumetric Anal>-sis,” p. 674, Interscience, Kew York, 3.Y., 1959. 40, a n d 60 ml. of t h e standard iron flask. Dilute t o volume. Dilute 100 (9) Scholes, P. H., Analy,st 82, 525 (1957) solution into 60-ml. separatory flasks. ml. of this solution t o 1 liter. This (10) Smith, G. Frederlck, “The \Yet To each add 2 m;. of hydroxylfinal solution contains 10 fig. of vanaAshing of Organic hfatter Employing ammonium chloride, 8 ml. of sodium dium per milliliter. Prepare a series of Hot Concentrated Perchloric Acidacetate, 4 ml. of bathophenanthroline, 26-m1. volumetric flasks containing from The Liquid Fire Reaction,” The G. F. and 6 ml. of isoamyl alcohol. Shake. 0 to 60 fig. of vanadium. Add 2.5 ml. Smith Chemical Co., 867 McKinley After 5 minutes, drain alcohol into of perchloric acid, 2.5 ml. of phosphoric Ave., P. 0. Box 1611, Columbus, Ohio, 25-ml. volumetric flask. Dilute t o acid, and 2.5 mi. of 3,3’-dimethylnaph1954. (11) Taylor, C. G., Analyst 8 1 , 369 thidine. Dilute to volume. After 15 volume with ethyl alcohol. Read (1959). minutes, read absorbances a t 550 mp absorbances against a reagent blank at 533 mp in 1.0-cm. cells and plot in 1-em. cells. The color is stable for RECEIVEDfor review March 7 , 1960. results. 1 hour. Plot calibration curve. Accepted July 19, 1960. Pittsburgh ConDETERMIXATION. Transfer 5 ml. of DETERMIXATION. Transfer the reference on Analytical Chemistry and decomposed sample into a separatory maining 10 ml. of the decomposed Applied Spectroscopy, February and funnel. Add 2 ml. of hydroxylammosample to a 25-ml. volumetric flask. March 1960. @
All values expressed as p.p.m.
a
1446
0
ANALYTICAL CHEMISTRY
