Photometric Determination of Nickel in Petroleum Cracking Catalyst A. T. BLACKWELL, ARCHIE M. DANIEL, and JESSIE D. MILLER Davison Chemical Co., Division o f
W. R. Grace & Co., Baltimore 3, Md. evaporate to dryness. Add 5 ml. of sulfuric acid and fume strongly for 15 minutes to expel excess fluoride. Cool, transfer the sample to a 250-ml. volumetric flask, and boil for 5 minutes. Cool, dilute to volume with water, and mix. Filter through a dry Whatman KO.40 paper and transfer an aliquot containing up to 300 y of nickel to a 100-ml. beaker. Proceed exactly as described for preparation of the standard curve, omitting only the addition of the sulfuric acid.
A rapid method was required for detecting nickel contamination in petroleum cracking catalyst. None of the proposed procedures using dimethylglyoxime was satisfactory for this particular purpose, mainly because the proper conditions of pH and the control of interferences were not described. The proposed method gives excellent reproducibility, is simple, and compares favorably with the lengthy gravimetric procedure. The color is stable and no precipitation of nickel occurs in the range up to 300 y of nickel per gram of sample.
EXPERIMENTAL
In the initial work on the procedure, erratic results were obtained Frequently no color development took place and a t times the colors which developed ranged from brown to red with a stability that ranged from seconds to days. Precipitation often took place even in very low concentrations of nickel. Tests vi-ere made a t many pH ranges and with various quantities of bromine, ammonia, sodium hydroxide, and dimethylglyoxime. I t was found that no difficulty was encountered with the proposed procedure, which gives a stable color for days and no precipitation within the range specified.
T
HE determination of nickel in petroleum cracking catalyst is signiiicant because the nickel is a catalyst poison and also a very likely contaminant in oil feed stocks. Dimethylglyosime has long been used as the specific reagent for gravimet,ric determinations, and procedures have been proposed for its use in the phot’ometric determination of nickel. I n this laboratory none of these procedures was successfully applied to petroleum cracking catalysts. Therefore, a procedure was developed for the photometric determination of nickel by dimethylglyoxime, with improvements to give more stable color in a wider range. Control of interfering substances is achieved by the use of tartaric acid and phosphoric acid ( 3 ) to complex iron and alumina ( 2 ) : and by measurement a t a wave length of 530 mp. -4st,able color is obtained and losses due to decomposition are controlled by using bromine ( 1 ) as an oxidation agent and by adding the dimethylglj-oxime under the proper conditions of pH and t,emperature. The procedure is applicable in the range from 10 to 300 y of nickel and the colors are stable for more than 24 hours ( 2 ) . The absorbance of the colored complex nickel compound ( 5 ) may be read in a Beckman DU spectrophotometer a t 530 mp or by use of No. 525 filter in a Fisher Electrophotometer or nephelometw. Interference from cobalt and iron is of little consequence a t this wave length ( 2 ) . PROCEDURE
Reagents. The following reagents, all analytical reagent grade chemicals, are required: hydrofluoric acid, sulfuric acid, nitric acid, phosphoric acid, tartaric acid, ammonium hydroxide, sodium hydroxide, a saturated water solution of bromine, and a 1% alcoholic solution of dimethylglyoxime. Standard nickel solution. Dissolve 0.1002 gram of pure metallic nickel in nitric acid with boiling. Add 2 ml. of sulfuric acid, evaporate until fumes of sulfur trioxide are evolved, and dilute to volume in a 1-liter volumetric flask. Transfer 50 ml. of this solution to a 500-ml. volumetric flask and dilute to volume. One milliliter of the final solution should contain 10 y of nickel. Preparation of Standard C w e . Prepare a series of solutions in 100-ml. beakers to contain 0, 10, 20,30,50, 100, 200, and 300 y of nickel. To each add 5 ml. of a 20’30 solution of tartaric acid, 2 ml. of 1 to 4 phosphoric acid, and 2 ml. of 1 to 1 sulfuric acid. Dilute to 50 ml. with water and add 5 ml. of a saturated water solution of bromine. Mix and allow to stand for a t least 1 minute. Add 1 to 1 ammonium hydroxide dropwise, meanwhile stirring until excess bromine is destroyed as shown by clearing of the color of the solution. Add a 2-ml. excess of 1 to 1 ammonium hydroxide and cool in a water bath below 20” C. Raise the pH of each solution to 11.5 i= 0.5 by the addition of 6-V sodium hydroxide, and immediately add 2 ml. of 1% dimethylglyoxime solution. Transfer the solutions to 100-ml. volumetric flasks, dilute to volume, mix, and, after 15 minutes, read the absorbance a t 530 mp. Plot readings on linear graph paper against micrograms of nickel. Preparation of Samples. Transfer from 2 to 5 grams of sample to a 100-ml. platinum dish and wet with water. Add hydrofluoric acid in small increments to decompose the silica, and finally
Table I.
Comparison of Gravimetric and Photometric Procedures for Nickel
Nickel Found, % Gravimetric Photometric 0.096 0.093 0.092 0.086 0,082 0,079 0.073 0.061 0.017 0.015 0.013 0,011 0,009 0,008 0,005
0.097 0.096 0.092 0.081 0.086 0.085 0.072 0.054 0.015 0.011 0.011 0.010 0.007 0.009 0.005
Diff., %
+o,
001 +0.003
-0:005 +0.004 fO.006 -0.001 -0.007 -0,002 -0,004 -0.002 -0.001 -0.002 +0.001
RESULTS AND DISCUSSION
Fifteen different samples of regenerated petroleum cracking catalysts were tested by both the gravimetric and photometric procedures. The results are shown in Table I. The chief advantages of this method are its simplicity and rapidity. S o separations are necessary and, thus, few error8 are introduced. With proper planning and some experience, a test may be run in 2 hours; the procedure is also adaptable to the simultaneous determination of several samples. While little exploratory work has been done, the authors believe the method can be used on a wide variety of materials ACKNOWLEDGMENT
The authors wish to acknowledge the help and information found in E. B. Sandell’s book ( 4 ) . LITERATURE CITED
(1) Feigl, F.. Ber. 57, 758 (1924).
(2) Makepeace, G. R . , Craft, C. H., IND.ENQ.CHEM.,~ N A L ED. . 16, 375 (1944). (3) Mitchell, A. M., Mellon, M. G., Ibid., 17, 380 (1945). (4) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., Interscience, New York, 1950. ( 5 ) Wulff, P., Lundberg, Z., Ver. deut. Chemiker, Beih. No. 48, 76 (1944). R E C E I ~ Efor D review November 1, 1955. Accepted April 16, 1956. Presented a t meeting of Maryland Section, ACS, John Hopkins University, Baltimore, Md., November 1955.
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