.
238
ANALYTICAL CHEMISTRY
Accuracy. When various amounts of standard cobalt solution were added to numerous types of stainless steel, etc. (cf. Table I), results had a maximum deviation of *0.04% cobalt from the total amount present. On high-cobalt steels (20 to 6OyG), the sensitivity and accuracy necessary are decreased somewhat, since smaller samples and aliquote must be used. Precision. If the method is carefully applied, the difference readings should not vary more than one scale division. As a check on the reproducibility of the procedure, one 60 co-30 Cr6 &Io-3 Xi alloy was chosen for pxperimentation. Five individually weighed 0.1000-gram samples, when separately analyzed by an analyst familiar with the procedure, gave identical readings throughout. As a further check on the precision, three analysts who had no previous experience with the method obtained the following rwilts on four “unknown” samples: Cobalt Found Analyst
Cobalt Found Gravimetrically
Analyst A
%
%
B %
2.99 2.95 8.45 8.40 12.2 12.1 20.4 20.4
3.03 2.99 8.46 8.30 12.2 12.2 20.4 20.3
3.00 8.43 12.25 20.31
4PPLICATION
The method as written is applicable to any known type of stainless steel, ingot iron, mild steels, numerous ferrous alloys, and probably many nonferrous alloys and other materials not yet investigated. The procedure has been used successfully on stainless steels containing from 0.008 to as high as 60.0% cobalt. Experiments have proved that there are few, if any, interfering elements. Alloys investigated contained large amounts of iron, chromium, nickel, manganese, copper, titanium, carbon, aluminum, silicon, molybdenum, vanadium, tungsten, columbium, selenium, and numerous residual elements (cf. Table 11). ACKNOWLEDGMENT
The authors are deeply indebted to the Rristless Iron and Steel Division of The American Rolling Mill Company, Raltimore, hld., for permission t o publish this paper. LITERATURE CITED
Analyst, C
% 3.03 2.86 8.44 8.42 12.3 12.0 20.3 20.6
(1) Ditz, H., Chem.-Ztg., 46, 121-2 (1922). (2) Dorrington, B. J. F., and Ward, A. M., Analyst, 54,327-32 (1929). (3) Feigl, F., and Stern, Rosa, 2. anal. Chem., 60, 1-43 (1921). (4) Heymans, J. IT., Satuurzc. Ti?dschr.,11, 151-3 (1929). ( 5 ) Hoffman, 3. I., Bur. Standards J . Research, 7 , 883-92 (1931). (6) Kolthoff, I. M., Mikrochemie (N.S.) 2, 176-81 (1930). (7) Tomula, E. S., Acta Chem. Fennica, 2,72-80 (1929). ( 8 ) Vorontzov, R. V.,J . Applied Chem. (U.S.S.R.), 8 , 555 (1935). (9) Young, R. S., and Hall, A . J., I n d . Eng. Chem., 18, 262-6 (1946).
Analysis of Silica-Alumina Cracking Catalysts Spectrographic Determination of Contaminants R. A . BURDETT AND L. C. JONES,
JR., Wood
River Research Laboratories, Shell Oil Co., Znc., Wood River, I l l .
A spectrographic method for the determination of iron, sodium, vanadium, nickel, chromium, and copper in silica-alumina cracking catalysts incorporating a novel photometric technique is described. The procedure is very rapid and correlates well with the conventional chemical analyses.
T
HE use in the petroleum industry of silica-alumina type
cracking catalysts has become common in recent years. Inevitably it has been necessary to analyze these catalysts for contaminants introduced in their manufacture and in subsequent use in the cracking process. Nost of the available analytical methods are very time-consuming and in many cases are of inadequate sensitivity. Others involve analytical techniques of such complexity that the results obtained by any but highly skilled technicians are subject to large errors. However, it has been found in this laboratory that the application of the spect,rograghic method to the analysis of these products yields a rapid procedure of adequate accuracy which is easily mastered by semiskilled personnel. Iron, sodium, vanadium, chromium, nickel, and copper are determined simultaneously by this method. The spectrographic analysis of catalysts presents several difficulties which are not met in the analysis of steels or other slloys, notably the lack of certified standard samples. The selection of suitable internal standard lines also leads to certain difficulties. Table I shows typical silica and alumina contents of Four commercial cracking catalysts produced by four different manufacturers. It will be noted that silicon is the natural choice for the internal standard element when the products of different manufacturers are compared, since the extreme variation is only 4 . 6 S on a total silicon basis. Aluminum on the other hand
shows a spread of 33:;. Unfortunately silicon has a very limited number of spectral lines of suitable jntensity and all these are grouped in the region 2460 to 2540 A., so that it is not possible t o use internal standard and analysis lines of very nearly the same wave length, as is the usual practice. This difficulty has been overcome, however, by a novel photometric technique which is described below. In the comparison of catalysts of substantially the same alumina content it is possible to use aluminum lines as internal standards. In the determination of sodium the application of the dilution factor principle (7)permits the use of an aluminum internal standard for samples with a wide range of aluminum concentrations. However, this technique does not work for certain other contaminants, notably nickel and iron. The high streaming velocity electrode system of H a s h and
Table I.
Silica and Alumina Contents of Commercial Cracking Catalysts
Catalyst 1 2 3 4
8 1 ~ 0 8 ,%
13.5 14.4 10.5 10.4
54 86.4 85.5 89 4 89 5
Y102,
V O L U M E 19, NO. 4, A P R I L 1 9 4 7
239
Table 11. Line Pairs for Determination of Contaminants
Contaminant Iron Iron Sodium Sodium Vanadium Vanadium Kickel Chromium Copper 0
Wave Length of Contaminant Line,
A.
2723.6 2723.6 3302.3 3302.3 3184.0 3184.0 3414.8 4254.3 3274.0
Internal Standard Aluminum Siljcon Silicon Aluminum Aluminum Silicon Silicon Silicon Silicon
Wave Length of Stcft,rd
A. 2568.0 2532.4 2532.4 3066.2 2568.0 2532.4 2532,4 2532.4 2532.4
Range of Concentration, 5% Weight 0.04-0.7 0.04-0.7 0.12-1.0 0.04-0,12 0.01-0.07 0.01-0.07 0.001-0.01 0 001-0.01 0.0002-0.01
Discharge" Type
A
A A B A A A
.I A
Refer t o Table 111
Harvey ( 2 ) was adopted, since it combines high sensitivity with good precision. A rotating step sector was used to reduce the intensities of the stronger spectral lines. The sector also permitted the use of a single spectral line over a broad range of concentration. The line pairs for the determination of various contaminants are listed in Table 11.
duces a film transmission of 5y0, this transmission-being selected arbitrarily. This is justified only by the fact that it leads to a consistent and precise set of intensity ratios. Having the calibration curves cross a t a different transmission would lead to a11 equally consistent set of intensity ratios differing only by a constant factor. The 2500 to 3200 B. curve was used for the determination of copper, nickel, and sodium, although it does not hold exactly at the slightly longer wave lengths used for these elements. Other factors seemed t o limit the accuracy obtained for these elements. X o correction for continuous background was necessary except in the case of the Na 3302.3 line obtained under discharge conditions B of Table 111. In thisohstance the highest transmission in the region 3301 to 3302 A. was used as a measure of the background intensity, the correction being made in the manner of Pierce (6).
Table 111. Multisource Settings for Catalyst Analysib A , General Capacitance, microfarads Inductance, microhenries Resistance. ~~. - , ohms ~. Output voltage, volts Output current, ampe:es Charge us. dischaige, Initiator voltage, volts Initiator a t Discharge timer, seconds Pre-exposure discharge timer, seconds Polarity of upper electrode ~~
EQUIPMENT
The spectrograph used in this work wab the Applied Research Laboratories-H. W. Dietert grating spectrograph ( 4 ) fitted with a 24,000 line per inch concave grating with 5 cm. (2 inches) of ruled surface and 1.5-meter radius of curvature. The instrument has a linear dispersion of 7 A. per millimeter in the fir$ order and is adjusted to photograph the region 2130 to 4330 A. on a single film. A cylindrical quartz lens of &inch focal length was used to form an image of the arc a t the grating. h rotating step sector (4 steps, factor of 2) was mounted a t the secondary focus of the grating. The ARL-Dietert Multisource unit (1, 3) was used to excite the spectra. The input voltage to this unit was held a t 230 * 4 volts bv a General Electric AIRS tvoe constant-voltage transformer. "This regulator also furnished a controlled "1 15-volt input to the ARL-Dietert densitometer-projection-comparator used in densitometry. The films (Eastman Spectrum Analysis NO. 1) were processed in the Dietert film-developing machine which is equipped with a thermostat to hold the developing trays a t 65" * 1" F.
~
~
B,Na
60 560
m n .-. 940 2.75 0 3000 Continuous 15 5 Segative
< O.lc$
60 400
15 _.
940 13.5 0 3000 Continuout 15 5 Segative
I
z
0 v)
5
wz
d IO I-
% W 0
a
0 w
PHOTOMETRY
The film calibration curves (Figure 1) were obtained by the method of Pierce and Nachtrieb (6), using an iron arc and the step sector. Synchronization of the sector wheel with the regular cyclic fluctuations of the arc was avoided by observation of the sector under fluorescent light of the same frequency. Tw: calibrations were obtained, one for the region 2500 to 3200 A., a second for the region 4250 to 4265 A. The curves were plotted so as to intersect a t 5y0 transmission. Intensity ratios were calculated in the conventional manner when both lines lay in the short wave length region. However, it will be noted in Table I1 that in the determination of chromium it is necessary to calculate the intensity of Cr 4254 relative to Si 2532. Both curves are used in this calculation, the intensity of the silicon line being read from the short wave length curve, that of the chromium from the long wave length calibration. The sample computation herewith illustrates the method of calculation: Sample Calculation of Intensity Ratio by Dual Curve Method from 4-Step Spectrogram Spectral Line
Step of Spectrum
Si 2532 Cr 4254
1 3
Relative Intensity of Step
5%
Transmission
1 10.0 4 32.0 Intensity C r 4254 4.5 X 1 o'20 Intensity Si 2532 =4-5
Relative Intensity from Figure 1 5.6 4.5
This method is based:n a tacit assumption that lines of wave lengths 2532 and 4254 A. are of equal intensity when each pro-
100 01
I RELATIVE INTENSITY
Figure 1.
IO
Film Calibmtion Curves A . 2500 to 3200 A. B . 4250 to 4265 A.
All films were developed for 3 minutes in Eastman Formula D-19 a t 65" * 1' F., emersed in a 3% acetic acid ShOrt-Stop bath for 5 seconds, and fixed in Easgman x-ray fixing bath for 30 seconds. Gammas of 1.7 at 3000 A. and 3.4 a t 4254 A. wvrr obtained under these conditions. STANDARD SAMPLES
The working curves were based upon the spectrograms of frrch and used catalysts which had been analyzed chemically for sodium and iron and polarographically for vanadium. The iron was determined colorimetrically with o-phenanth! oline (8) after sodium carbonate fusion of the catalyst and solution of the melt in dilute sulfuric acid. Sodium was determined gravimetrically as sodium zinc uranyl acetate after removal of the silicon as the tetrafluoride. The vanadium was determined polarographically by an adaptation of the method of Page and Robinson (6) after removal of the interfering ions. The nickel, chromium, and copper contents of the standards were determined by an indirect spectrographic method: Synthetic catalyst standards containing known amounts of nickel, chromium, and copper were prepared by absorbing solutions of salts of these metals on ignited (at 1OOO" C. for 4
ANALYTICAL CHEMISTRY
240 hours), fresh patalyst known to be spectroscopically free from these metals. The stock copper solution consisted of 0.0996 gram of copper metal (Baker's preci itated powder) dissolved in dilute nitric acid and diluted to 1 h e r to give 0.0996 mg. of copper per ml. Aliquots of this solution were diluted to give concentrations of 0.0498, 0.0249, 0.0124, and 0.0062 mg. of copper per ml. A 0.502 mg. per ml. solution of nickel was obtained by dissolving 0.0502 gram of the metal (Mallinckrodt Analytical Reagent grade) in dilute nitric acid and diluting to 100 ml. Other nickel solutions containing 0.251, 0.125, 0.0625, 0..0313, and 0.0156 mg. of nickel per ml. were prepared by dilution. The chromium stock solution (1mg. of chromium per ml.) was obtained by dissolving 0.2829 gram of potassium dichromate (Mallinckrodt Analytical Reagent) in 100 ml. of distilled water. Aliquots of the stock solution were diluted to give 0.250, 0.125, 0.0625, 0.0313, and 0.0156 mg. of chromium per ml. B single example will illustrate the method of preparing the aynthetic standards. It had been determined that 1 gram of the ignited catalyst would completely absorb 1 ml. of water. Accordingly, 10 ml. of the stock copper solution were pipetted onto 10.00 * 0.01 g r a m of the fresh catalyst in a 100-ml. beaker. The mixture was stirred thoroughly while moist, then dried in an oven at 110' C. for 4 hours. The dried catalyst, which contained 0.01% copper, was then ground in a mortar to ensure homogeneity. I n this manner other standards were prepared from the above solutions which contained 0.0050, 0.0025, 0.00125, and 0.00062~0 copper; 0.050, 0.025, 0.0125, 0.0063, 0.0031, and 0.0016% nickel; and 0.025, 0.0125, 0.0063, 0.0031, and 0.0016~0chromium. One part of each of these synthetic standards was then mixed with 5.0 parts of anhydrous Analytical Reagent grade sodium carbonate and fused in a platinum crucible. The fusion was ground thoroughly in a mortar and 0.100 giam of the ground material burned in a graphite electrode with 3 X 3 mm. crater for LO minutes. A direct current arc of 2.5 amperes at 940 volts was used.
0.011 00001
Figure 3.
0 001
I
I 0 901
0 01
I 01
% METAL
Figure 2.
Preliminary Working Curves for Nickel, Copper, and Chromium
llnder these conditions excellent working curves were obtained when the ratio of the intensity of the nickel, chromium, or copper h e to that of the adjacent background was plotted on log-log paperlas a function of the concentration of the contaminant. Theselpreliminary working curves aFe shown in Figure 2. The standard catalyst samples were then treated in the same inanner and analyzed for nickel, chromium, and copper by means of these working curves. The synthetic standards do not give the same working curve as the regular standards for the streaming +lectrode technique. iNALYSIS OF CATALYSTS BY STREAMING ELECTRODE METHOD
.
Determination of Iron, Vanadium, Nickel, Chromium, Copper, and Sodium (Na > 0.12). About 0.2 ml. of the catalyst was measured with a special cup-shaped spatula and mixed with ttn equal volume of ammonium chloride (Analytical Reagent grade used as received), and the mixture was transferred to an all-graphite center post electrode and arced against a 2-mm. graphite upper electrode according to section A of Table 111. The rotating step sector was'used in all cases. After the film
01
1
Working Curves for Catalyst Analysis, General Procedure
Figure 4.
01' 0 0001
001 PERCENT M E T L
Working Curve for Sodium, L o w Range
was processed the densities of the lines listed in Table I1 were determined, the measurement for each line being made on a step of the spectrum with a transmission of between 5 and 50%. The required intensity ratios were obtained by the methods outlined in the section on photometry. Each standard was run in this manner to obtain the working curves of Figure 3. All standards and samples were run in duplicate and the average intensity ratio was used. Determination of Sodium in Samples of 0.04 to 0.12% Sodium. The procedure was similar to that above except that discharge conditions, B, of Table I11 were used, and that the rotating step sector was not needed for this analysis. The working curve for sodium in this range was based on the intensity ratio Na 3302.3/
Table IV. Catalyst Sample
Comparison of Chemical and Spectrographic Analyses for Iron Chemical 0.40 0.38 0.11 0.16 0.17 0.12 0.18
Per Cent Iron Spectro-
graphic 0.39 0.39 0.11 0.14 0.17 0.12 0.18
%
Deviation 0.01 0.01
Deviation 2.5 2.5
0.00
0.0 12.5 0.0 0.0 0.0
0.02 0.00 0.00 0.00 Av. 0.006
*2.9
V O L U M E 19, NO. 4, A P R I L 1 9 4 7 Table V. 3ample Yo.
1 2 3 4
5 6
7 8
9 10
241
Comparison of Chemical and Spectrographic Analyses for Sodium Chemical
0.150 0.185 0.185 0.205 0.260 0.290 0.300 0.340 0.390 0.415
Per Cent Sodium SpectroaraDhic -High Range
0.145 0.175 0.185 0.205 0.250 0.260 0.305 0.330 0.395 0.415
Deviation
0.005 0.010 0.000
3.3 5.4 0.0 0.0 3.9 10.3 1.7 2.9 1.3 0.0 ~2.9
0.000 0.010
0.030 0.005 0,010 0.005 0.000 Av. * 0 . 0 0 8
0.044 0.110 0.110 0.059 0.052 0.066
Low Range 0.044 0.108 0.112 0.055-
0.056 0,064 Av.
c.;.
Deviation
0.000 0.002 0.002 0.004 0.004 0.002 +=0.0023
0.0 1.8 1.8 7.3 7.1 3.1 *3.5
Table VI. Polarographic and Spectrographic Analyses for Vanadium Catalyst Per Cent Vanadium s a m p l e Polarographio Spectrographic 1 0.021 0.021 2 0.026 0.026
3 4 5
0.035 0.046 0.066
0.036 0.048 0.066
Av.
07 /G
Deviation
0.000 0.000 0.001 0.002 0.000 *0.0006,
Deviation
0.0 0.0
2.9 4.2 0.0 ~ 1 . 4
A1 3066.2, corrected for background intensity and the aluminum content of the sample or standard in question. The latter correction was made by multiplying the intensity ratio by %Al/5.73, 6.73% being the %A1 in most of the standards. This method was found t o give reliable results for catalysts of alumina contents varying over the range shown in Table I. The working curve is presented in Figure 4. DISCUSSION OF RESULTS
Comparisons of chemical and spectrographic determinations of the iron and sodium contents of a number of catalysts are given in Tables IV and V.
Table VII. Duplicate Spectrographic Analyses for Chromium, Nickel, and Copper Catalyst Sample 1
Chromium, % 0.0057,O. 0065
2
0.0019,0.0021
3 4
0.0058,O. 0062 0.0048,O. 0052 0.0074,O. 0069
5
Nickel, % 0.0053,O. 0060 0.0041,0.0040 0.0035,0.0038 0.0017,O. 0018 0.0070,O. 0071
Copper. %
0.0032,O. 0030 0.0010,0.0008 0.0012,O. 0012 0.0020,O. 0021 0.0010,0.0012
A similar comparison of polarographic and spectrographic results for vanadium is shown in Table VI. The analyses shown are for catalysts of similar aluminum content, the A1 2568 line being used as internal standard. Use of the silica internal standard gave similar values but poorer precision. Since suitable chemical methods for the determination of nickel, chromium, and copper in the concentrations and matrices in which they occur in catalysts were not in use in these laboratories, comparative analyses cannot be given for these metals. However, Table VI1 indicates the precision obtainable. About 30 minutes are required for the complete analysis when the sodium content of the catalyst is greater than 0.1%. Another 15 minutes may be added for catalysts of low sodium content because of the additional arcing necessary in such cases. ACKNOWLEDGMENT
The authors wish to express their indebtedness to B. E. Gordon who performed the polarographic analyses and t o Mrs. K. B. Woods who performed many of the spectrographic analyses. LITERATURE CITED (1) Hasler, M. F., and Dietert, H. W., J . Optical Soc. Am., 33, 218-28 (1943). (2) Hasler, M.F., and Harvey, C. E., IND. ENCI. CHEM.,ANAL.ED., 13, 540-4 (1941). (3) Hasler. 31. F., and Kemp, J. W., J . Optical SOC.Am., 34, 21-32 (1944). (4) Hasler, 51. F., and Lindhurst, R. W., Metal PTogress, 30, 50-63 (1938) (5) Page, J. E., and Robinson, F. A., Anakist, 68, 269 (1943).
(6) Pierce, JV C., and Nachtrieb, N. H., IND. ENCI.CKEiv.,
*~NAL.
ED., 13 774-81 (1941). (7) Post, C. B , Schoffstall. D. G., and Hurley. G., Ibid., 17, 412-16 (1945). (8) Saywell, L G . ,and Cunningham, B. B., Ibid., 9, 67 (1937).
Determination of Water in Phenol LOUIS R. POLL4CK, Industrial Laboratory, Mare Island .Vasal Shipyard, Vallejo, Calif.
Water in phenol is determined cryoscopically. The freezing point is determined before and after dehydration by boiling, and the percentage of w-ateris calculated as a linear function of the freezing point lowering. Satisfactory accuracy is ohtained up to 29'0 water, even in the presence of 1.1% rresol.
I
N T H E examination of phenol samples a t this laboratory, it was considered advantageous to determine the water content. A desirable method should be rapid and simple, even when determinations are made infrequently. The literature revealed no adequate method urhich met these requirements. Fischer ( 1 ) proposed a specific volumetric method which has been thoroughly studied (6) and used by many investigators. However, infrequency of determinations would necessitate a restandardization against freshly prepared standards each time the reagent was used. This disadvantage appeared great enough to eliminate the method from further consideration.
Standard methods, such aa vacuum drying, heating a t 105O C., or drying over sulfuric acid or phosphorus pentoxide, yield erroneous results because of the volatility of phenol. Jones, Prahl, and Taylor ( 4 ) discussed the possibility of determining water in impure resorcinol by the difference in crystallizing points before and after drying. They were unable to dry their samples without changing the composition and so failed in their attempt, although they obtained a straight line when plotting crystallizing point against added water. The ease with which phenol may be dried by boiling makes a cryoscopic method entirely feasible, especially in view of the low
