V O L U M E 21, NO. 5, M A Y 1 9 4 9
599
. ...___~
Iron interferes in this method if present in the ferrous state Table TI.
Influence of Certain Cations on Color Intensity of Copper Rubeana te ( I n gresenre of Al, Bi. and Th) RIalonic
c il
A1
MQ.
MQ.
o to!
0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0,102 0.102 0.102
..
Bi
Th
MQ.
MQ.
.. t
..
.. ..
.o
1 .0
10 10 10 10
..
Acid Gram
l’.b 10
10 10 10
.. 10
to
10 10
1.0
.. ..
1. 0 1.0
f.0 1.0
Trnnsrnittanrr
% 24.5 24.5
19 9 19.6 23.0 24.6 19.6 19.8 18.8 22.6 21.4 20.6 24.3 23.7 20.6 20.3
.\lthough aluminum does not produce a color reaction with rubeanic acid, it decidedly affects the color intensity of copper rubeanate. Attempts at complexing aluminum with fluoride, tartrate, and citrate \yere without success. Results for copper in these circumstances were a l ~ a y high. s Malonic acid, however, served to eliminate this error in the presence of as much as 100 mg. of aluminum per aliquot. Employment of a boric acidboras-citrate buffer complex (pH 7 ) appeared to eliminate the aluminum error, but precision and color quality were unacceptable. The manner of niixing color reagent with standard copper solutions caused significant deviation in duplicate standards. Certain other multivalent cations shown in Table IT, although failing to produce a color reaction with rubeanic acid, influence the colloidal properties of copper rubeanate. Thorium and bismuth decrease color intensity. In the absence of malonic acid, copper standards show R lower color intensity.
( 4 ) . Solution of the sample in nitric acid precludes this possibility. The yellow color of ferric citrate is also a source of error. As malonic acid both decolorizes and complexes ferric iron, this factor is conveniently eliminated. The presence of ammonium phosphate, sulfate, perchlorate, and chloride in 1-gram quantities had no effect on the results. The full development of the olive green copper rubeanate is complete within 30 minutes in the range common to magnesium alloys. For refined magnesium in which copper concentrations are extremely low it is advisable t o permit a 60-minute development period before comparison. When the log of the transmittance was plotted against amounts of copper froin 0.010 to 0.002 mg., a straight line was obtained, showing that the results are equally good for these very small amounts of copper. In samples requiring malonic acid (alloys), retardation of color development orcurs if this substance is present in concentrations fully developed colors are stable for ieveral evceeding I %. hours. The application of this method to feiioua and other nontexrous alloys as 4 ell as biological inaterials is being inve5tigated. LlTERATURE CITED
(1) Allport, N. L., arid Skrimshire, G. H., Quart. J . Pharm. Pharmacol., 5, 481 (1932). ( 2 ) Center, J. E., and MacIntoah, R.M.,IND. ESG. CHEM.,Aiv.4~. ED.,17, 239 (1945). (3) Feigl, F., and Kapulitzas, €1. J., Mikrochemie, 8, 239 (1940). (4) Nilsson, G., Analyst, 64, 501 (1939). ( 5 ) RLy, P., and M y , R. M.,Quart. J . Indian Chem. SOC.,3, 118
(1926).
(8) Willard, H. H., and Diehl, H., “Advanced Quantitative -4nalysis,” New York, D. Van Nostrand Co., 1943. (7) Wohler, F., P o g g e n d o r f ’ s A n n d e n , 3, 178 (1825). R E C E I V E .July D 8, 1948.
Metallic Contaminants in Fluid Cracking Catalyst Determination by Emission Spectrograph E. L . GUNN, Humble Oil & ReJining Company, Baytown, Tex. 4 method has been developed for the routine analysis of fluid cracking catalSst for trace metal contaminants bj means of the emission spectrograph, employing the internal standard technique with direct current arc excitation. As applied to typical plant samples, the precision of the method in the respective concentration ranges involved is expressed by a standard deviation of approximatell 8% for iron, 16% for sodium and calcium, 12% for nickel, and 5 % for chromium and vanadium. Results obtained by the spectrographic method are in fair agreement with those obtained by chemical methods. The influence on the method of changes in the alumina content of the catalyst is discussed.
I
X FLUID catalytic cracking operations, quantitative analyses of the catalyst are usually desired a t periodic intervals as an aid in controlling operations and in interpreting results. The analyses required usually are not for the major components, alumina and silica, but for trace contaminants which can accumulate on the catalyst either through metal erosion in the system 01 the deposition of inorganic components imparted to the catalyst from the feed stocks during cracking operations. The tedious and time-consuming nature of chemical methods of analysis makes such methods practically prohibitive for routine control use. The emission spectrograph has been used in this laboratory for the routine determination of catalyst contaminants for about 3 years, and it has pioved capable of providing results of adequate precision and accuracy R hich compare favorably
with those obtainable by the more difficult chemical niet,hods. Furthermore, only 2 to 2.5 hours are required for the complete spectrographic analysis of a catalyst sample for iron, nickel, chromium, vanadium, sodium, and calcium contaminants. Spectrographic methods have been applied (3, 6, 6) to the analysis of various minerals and ores. A method has been described ( 1 ) for the analysis of silica-alumina catalyst for contaminants in which lines of silicon and aluminum are used for reference; empirical factors are introduced to compensate for the differences of film emulsion response of the separate spectral regions of the film. The method of catalyst analysis emplo.yed in this laboratory differs from that described ( 1 ) in several significant respects: (1) the present method uses added internal standards as references against the sought elements; (2) the ex-
ANALYTICAL CHEMISTRY
600 Table I. Element Sought
w a v e Length,
Fe
3407.5 3483.7 4254.3 3184.0 3302.3 3179.3
Ni
Cr V
Ka Ca
tric hot plate a t 450" to 500" C. Although the fluid nature of the catalyst is of considerable aid in mixing, the contents should be stirred initially with a glass rod and occasionally during heating to ensure complete sample homogeneity. Heating is continued for 30 minutes after the water apparently has evaporated. Aworking time of 5 to 7 minutes is normally required to introduce the internal standards for an analysis. Tests with plant-regenerated catalyst samples have shown that the weight of the sample mixture thus prepared for spectrographic analysis is within 0.7% of the weight of the original catalyst sample plus that of the evaporated internal standards before they are mixed. Spectrographic Technique. A portion of the prepared sample is inserted into the sample electrode by forcing the electrode into the catalyst, so that the crater may be fully packed. Three electrodes are prepared in this manner for each spectrogram. The arcing process is carried out immediately under the standard conditions outlined in Table 11. In rare instances the sudden heat of the initial arcing may result in expulsion of the sample from the electrode crater. The operator can detect this occurrence, both by the observed over-all decrease in density compared with other exposures and by the size of the residual fused bead left in the electrode crater, so that this exposure may be rejected and another made. Use of the rotating step sector with four levels of exposure provides for density measurements of the several line pairs in the more favorable regions of the emulsion calibration curve. Film measurements, calculation of intensity ratios, and conversion to percentage of the sought components by reference to the respective analytical calibration curves are carried out in a conventional manner ( 2 ) .
Spectral Line Pairs Used in Analysis of Fluid Cracking Catalyst (4)
A.
Internal Standard
Wave Qength, h
co
3405.1 3474 0 4294.6 3405 1 3405.1 3464.6
co
w
co co Sr
citation source and procedural steps are different; and (3) the group of metal contaminants determined is different in that calcium rather than copper is determined. At the start of the experimental studies in this laboratory it was contemplated that suitable spectral lines of a major catalyst constituent, silicon or aluminum, might be used as references for comparison with appropriate metal contaminant lines. However, the relative paucity of aluminum and silicon lines, as well as their remoteness from lines of the sought elements and unsuitability for density measurements with the source of excitation employed, precluded their use and suggested the addition of internal standards. Three internal standards, cobalt, tungsten, and strontium, are added to the sample prior to analysis. The spectral lines used for measurements are shown in Table I.
Table 11. Equipment and Standard Conditions Used in Analysis of Fluid Cracking Catalyst
REAGENTS AND CALIBRATION STANDARDS
Internal Standard Reagents. Standard Cobalt Solution. Baker's analyzed ,cobaltous nitrate is added to distilled water to prepare a solution containing 1 mg. of cobalt per ml. Standard Tungsten Solution. C.P. Eimer & Amend analyzed para-ammonium tungstate is added to distilled water to prepare a solution containing 20 mg. of tungsten per ml. Standard Strontium Solution. C.P. Baker's analyzed strontium nitrate is added to distilled water to prepare a solution containing 80 mg. of strontium per ml. (Cobalt and strontium reagents may be prepared as one standard solution, but ammonium tungstate must be prepared separately, as it is incompatible with the other two reagents.) Standard Catalyst Blend. A blend for spectrographic calibration is prepared by adding a known amount of the metal contaminant, or contaminants, in solution form to a portion of fresh catalyst. I t is necessary to detect the presence and establish the concentration of each sought element initially present in the fresh catalyst before the blend is made. The contaminants most likely to be found are iron, sodium, and calcium, and account is taken of the amount of each that is present. The fresh catalyst is preignited for 4 hours in a muffle furnace a t 539' C. (lOOOo F.) before the contaminants are added. Sodium is introduced as the chloride or sulfate, vanadium as ammonium vanadate, and iron, nickel, chromium, and calcium as the nitrates. To impregnate the catalyst uniformly with the contaminants, water is cautiously evaporated from the mixture during stirring, and this is followed by ignition in a muffle furnace a t 1000" F. for 8 hours. Internal standards are added and the calibration blends are analyzed in the manner described below.
Spectrograph. A.R.L. grating spectrograph, 1.5-meter, 2460 to 4580 A. region Densitometer. A.R.L. projector-comparator with voltage regulator Source. D.C. full-wave rectifier, 250 volts open circuit, 12.0 * 0.2 ampere excitation current Grating Aperture. Full opening Slit Width. 10 microns Aperture. Rotating sector disk, 18 cm. from slit Lens. 5-inch focal length cylindrical quartz, 31 cm. from slit. Electrodes. Carbon rods 3 inches in length, 0.25 inch in diameter. Lower, positive, having sample crater with depth and diameter of 0.125 inch: upper, negative, with 20' conical trim to 0.125 inch diameter, Analytical Gap. 7.0-mni.. optical axis at center of gap Film. 35-mm., Eastman Spectrum Analysis No. 1 Exposure. For complete arcing time of 30 seconds Development. 3 minutes at 70' F., Eastman Formula D-19. Film Emulsion Calibration. Iron spectrum with rotating sector disk, four steps, factor of 2. Calibrations established fnr 3200 to 3400 and 4200 to 4300 .k. regions
C.P.
V 3184.0
c03105.L
By plotting concentration in per cent against intensity ratio of the selected analytical line pair for each contaminant, a set of calibration curves similar to those of Figure 1 is obtained.
f $
ANALYTICAL PROCEDURE
NI 3483.7 Co 3474.0
Sample Pre aration. A 10-gram portion of the catalyst sampfe is weighed to the nearest hundredth gram into a tared 100-ml. beaker. Exactly 1ml. of cobalt internal standard reagent is added by means of a pipet for the determination of iron, nickel, vanadium, and sodium; 1 ml. of ammonium tungstate reagent is added for the determination of chromium; and 1 ml. of strontium nitrate is added for the determination of calcium. The beaker is covered with a watch glass and heated on an elec-
0
0.1
I
I
I
I I I I I ,
0.001 .O1
I
I
Conce*tr.tlon.
I
l l l l l !
I
I
I
I
I Ill
Wt. percent
Figure 1. Analytical Calibration Curves for Metal Contaminants i n Fluid Cracking Catalyst
V O L U M E 21, NO. 5, M A Y 1 9 4 9 Table 111.
Sample 1
2 3 4
5 6 7 8
601
Determination of Iron in Fluid Cracking Catalyst
Chemical analysis 0.21 0.26 0.27 0.28 0.30 0.32 0.39 0.42
Iron, % Spectrographid analysis 0.18 0.22 0.30 0.24 0.31 0.32 0.42 0.39
Per Cent Deviation Based on Based on sample component -0.03 -14.3
-0.04 +0.03 -0.04 +0.01 0.00 +0.03 -0.03 Av. t 0 . 0 2 6
*
tion is made acid and the chromium determined by photoelectric measurement of the red color produced by the addition of diphenylcarbozide reagent. Vanadium. The phosphotungstovanadic acid complex is developed in a portion of solution from the nickel separation and the vanadium determined by measurement of the yellow color intensity with the photoelectric colorimeter.
-15,4 +11 1
EVALUATION OF METHOD
+ 7 7 - 7.1 9.1
Indications of the reliability of the present spectrographic method as applied to routine plant samples are furnished by the data shown in Tables 111to VI, where the results of chemical and
+- 1 430. ..303
Replicate Spectrographic Determinations Sample 2b Sample l a 0.45 0.20 0.46 0.24 0.41 0.19 0.41 0.24 0.20 0.39 0.24 0.39 0.24 0.42 8 0.43 9 0.45 AV. 0.42 0.22 Standard deviation (based 10.4 on component), T O G 5.9 Range (based on component), 5% 16.6 22.7 0 By average of several chemical determinations, Yo iron = 0.42. b By average of several chemical determinations, 70iron = 0.22.
c
Detn.
c
1 .6
Calculated from standard deviation =
of squares of deviations of each result from their average.
Determination of Calcium in Fluid Cracking Catalyst
Table IV.
Sample 1
2
3
L
Detn. 1
2 3
1
2 3 4 1 2
Calcium, % Chemical Spectrographic analysis analysis 0.04 0.04 0.02 0.02 0.24 0.21 0.19 0.23 0.24 0.53 0.49 0.55
Per Cent D e v i a t i o n Based on Based on sample component 0.00 0.0 0.02 -50.0 0.02 -50.0 0.03 -12.5 0.05 -20.8 0.01 -4.2 0.00 0.0 0.04 -7.5 0.02 3.8 Av. 0 . 0 2 16.5
Iron. Solution of the catalyst is effected by sodium carbonate fusion, followed by the addition of water and hydrochloric acid. The thiocyanate color complex is developed with an aliquot of the solution and the color intensity is measured with a Klett-Summerson photoelectric colorimeter to determine iron. Calcium. Solution of the sample is effected in the same manner as for iron, and after separation of interfering elements calcium is determined as the oxalate. Sodium. The sample is decomposed by sulfuric-hydrofluoric acid treatment, then dissolved in hydrochloric acid. Sodium is precipitated with zinc uranyl acetate reagent for the gravimetric determination. Nickel. The sample is put into solution by the procedure used for iron and calcium. Bv the addition of sodium hvdroxide and sodium peroxide t o a solbtion aliquot, nickel is sepirated as the hydroxide from vanadium and chromium, and these latter are converted to the vanadate and chromate, respectively. Xckel is separated from other insoluble hydroxides, such as iron and titanium, by the use of sodium citrate, ammonium hydroxide, and dimethylglyoxime. The nickelous dimethylglyoxime is extracted with chloroform, then decomposed with hydrochloric acid. Bromine is added to oxidize nickel to the nickelic form, ammonium hydroxide and dimethylglyoxime are added to develop a brown color complex, and the color intensity is measured with the photoelectric colorimeter to determine nickel. Chromium. A portion of the solution from the nickel separa-
I
I
I
20
30
40
%
Alumina
Figure 2. Relation of Iron-Cobalt Intensity Ratio to Alumina Content
Table V.
Determination of Sodium in Fluid Cracking Catalyst Sodium, % Spectrographic analysia 0.16 0.16 0.15 0.22 0.18 Av. 0.17 Standard deviation (based on component), % a 16.5 Range (based on component), % 4 1 . 2 Chemical analysis 0.14 0.16
Detn.
CHEMICAL METHODS
Chemical methods ( 7 , 8) of analysis of fluid cracking catalyst also have been empolyed to obtain data for comparison with results from the spectrographic method. The chemical methods used are briefly as follows:
I ! 10
a
Calculated from standard deviation =
45,
where Z d l = sum of
squares of deviations of each result.
Table VI. Determination of Nickel, Chromium, and Vanadium in Fluid Cracking Catalyst Nickel, To Chromium, % Vanadium, % Sample 1 2 3 4
SpectroSpectroSpectroChemical graphic Chemical graphic Chemical graphic 0.013 0.012 0.004 0,004 0.007 0,011 0.009 0 015 0.003 0.003 0.005 0,005 0.008 0,009 0,004 0.0045 0.002 0,003 0.011 0.011 0,004 0.0037 ... ... Replicate Spectrographic Determinations Nickel. Chromium, Vanadium,
Detn. 1 2 3 4 5 Av. Standard deviation (based on component). %" Range (based on component), yo 0
%
0.012 0.010 0.009 0.009 0.010 0.010
%
0.003 0.003 0.002 0.003 0.003 0.028
12.0
5.3
30.0
33.3
Calculated from standard deviation
=
squares of deviation of each result from their average.
%
0.0039 0.0044 0.0044 0.0042 0.0044 0.0043 5.11 11.6
ANALYTICAL CHEMISTRY
602 Table VII. Sample 1
2 3 4
Spectrographic Analysis of Fluid Cracking Catalyst in Absence and Presence of Strontium Kickel, 7% Chromium, % Vanadium, 70 _ _ _Sodium, _ _ _ _ 70 CalciiiriiL/L No Sr 0.8% Sr No Sr 0.8% Sr S o Sr 0.8% Sr S o Sr 0 85% Sr 0.8“; Sr
Iron, 7% No Sr 0.8% Sr 0.41 0.26 0.73 0.32
0.43 0.26 0.70 0.32
~
0.012 0,0092 0.0075 0.0098
0.013
0,011 0.0070 0.011
0.0037 0.0043 0.0023 0.0025
0.0047 0.0041 0.0023 0.0030
spectrographic analyses of the same samples are compared; sets of replicate spectrographic determinations provide measures of the precision of these determinations. These data indicate for the spectrographic method an approximate precision based on the component of 5% for vanadium and chromium, 8% for iron, 12TC to1 nickel, and 16% for calcium and sodium, whereas the &,viatioris of spectrographic from chrmical results are approvimately 9% for iron, 5% ior chromium, 167’ for calcium and sodium, 22Y0 for nickel, and 30% for vanadium. During development of the preeent spectrographic method thr use of several spectral line pair combinations of the internal standards and sought elements were investigated. Cobalt, foi instance, was found unsatisfactory as an internal standard for calcium because of erratic intensity ratios among the varioui measured lines of these tm-o elements. The addition of strontium provides a satisfactory reference for calcium; but this element was found unsuitable for sodium. I n the development of the method it was considered highly desirable that all contaminants tie cietermined on the same spectrogram; but because the quantity of strontium added (0.8%) is much greater than the amounts of tht other internal standards, its possible interference in the determination of other elements was suspected. To clarify this point, plant samples were analvzed with and without strontium. The results shown in Table VI1 are typical, and reflect no significant influmcc. of strontium on determinations of the other elements. Fluid cracking catalysts supplied by commercial manufacturervary in alumina content from 10 to 20%, according to type. For N given type of catalyst this variation is probably never greater than 1 or 2%. The influence of alumina content on the determination of one element (iron) was investigated by spectrographic analr,i-
0.012 0.0040 0,013 0.0074
0.012
0.003s 0.012 0,0078
....
