Spectrographic Analyses of Cracking Catalysts Determination of Magnesium and Zirconium LEON W. GA3IBLE Esso Laboratories, Esso Standard Oil Co., Baton Rouge, La. 10.0% magnesia, while the zirconium method is useful in the range of 0.01 to 5 % zirconium oxide. The results obtained by the spectrographic methods are in fair agreement with those obtained by the use of chemical methods. The effect of large amounts of alumina on the determination of zirconium is discussed. Both methods are applicable to the analysis of clays.
The need for rapid methods for determining magnesium and zirconium in connection with catalyst development problems led to the study of spectrographic procedures. Internal standards, copper for determination of magnesium and cobalt for determination of zirconium, were employed with direct current excitation. The method for magnesium has been applied to samples containing from 0.2 to
A
LTIIOUGH the emission spectrograph has been employed for a number of years in metallurgical laboratories ( l a ) ,its use in the petroleum industry has been limited. From 1920 to 1945 only four articles (IS)described application of the emission spectrograph to problems of the petroleum industry. Since then, however, twelve publications (1-S, 6, 7 , 10, 11, 13; 16, i7, 19, 10) have appeared, and in the majority of cases the methods described mere applied either to the analysis of oil for additives or to cracking catalysts for contaminants introduced during their preparation or in subsequent use. The Committee on Analytical Research of the American Petroleum Institute has established a subcommittee for studying these methods. These cracking catalysts were of the silica-alumina synthetic or the natural clay type. Another type, silica-magnesia, which i8 especially adapted for the production of motor gasoline, was recently tested on a commercial scale (4 16).
0.2
0.4 0.6 0.8 1.0
2.0 3.0 4.0 6.08.010.0
20.0
W T To McO
Figure 1. Analytical Working Curve for Determination of Magnesium in Cracking Catalyst DETERMIKATION OF MAGNESIUM
The conventional chemical method of magnesium deterniination-i.e., precipitation as the phosphate-is very lengthy, particularly if the separation from calcium is carried out; therefore, it was desirable to develop a more rapid method for control purposes. The spectrographic method presented in this paper covers a fairly wide range of magnesia, 0.2 to 12% magnesium oxide and is much more rapid, 2.5 hours' elapsed time for one analysis compared with approximately 16 hours by the conventional chemical method, This procedure is applicable to the analysis of clay as uell as synthetic catalysts such as silica-magnesia, silica-alumina, or mixtures of the two.
Apparatus and Materials. Grating Spectrograph. The 1.5-meter instrument is equipped with a 24,000 line per inch concave grating with 5 cm. (2 inches) of ruled surface. The linear dispersion is 7.4 per mm. in the first order. A cylindrical quartz lens of 5-inch focal length was used to form an image of the arc at the grating. A rotating st,ep sector (4 steps, factor of 2; was mounted a t the secondary focus of the grating. hIult,isource unit, 5 kv.-aInp. Comparator-densitometer, nonrecording type with voltage regulator. Automatic rocking filni development equipment. Infrared dryer. All the above listed equipment, was manufact,ured by Applied Research Laboratories. Film, 35-nim. Eastman Spectrum Analysis So. 1. Copper oxide, Baker's C . P . Graphite SP-2, 17ationsl Carbon Co., Xiagara Falls, S . Y.. or regular grade spectroscopic electrodes gruund in a pencil sharpener. Magnesium nitrate, 5%, prepared by dissolution of 10 grams of C . P . magnesium ribbon in 1 to 1 nitric acid, and dilution to 200 nil. Specpure silica, Johnson, Matthey Co., Ltd. Experimental. PREPARATIOS OF STANDARDS. To weighed amounts of ignited catalyst various quantities of the magnesium nitrat.e solution were added. When necessary, more water was added to form a thick slurry, and the mixture was stirred frequently while being heated on a hot plate. After the mixture was dry, it was calcined a t 1600" F. for 3 hours. FILYEMCLSIOX CALIBRATIOS ~ V R V E Swere obt.ained using an iron arc and a step sector (8, 14). Homologous lines between 3200 and 3300 A. suggested by Dieke ( 5 ) mere employed in constructing the curve. ANALYTICAL KORXING CL-RYE. The standard samples were prepared and arced as described in the procedure. By plot,ting intensit,y ratio 'Ig 2779'8 against per cent magnesia, a wcrking Cu 2768.9 curve similar tmoFigure 1 is obtained. ASALYTICAL PROCEDURE. Approximately 5 t o 10 grams of catalyst are ground in an agate mortar, subsequently ignited for 30 minutes at 1600" F., and cooled in a desiccator. A motordriven mortar and pestle has been effective iri reducing sample preparation time and in producing a uniform sample. Thirty minutes' grinding will normally pulverize a sample so that 90% will pass 325 mesh. Then 0.1 gram is weighed into an agat,e mortar and mixed with 1.9 graiiis cf copper oxide. Approximately one half of the copper oxide and the sample is mixed by grinding and the remaining portion of the copper oxide is gradually added with continued stirring until the two substances are thoroughly mixed. Then with continuous mixing 4.0 grams of graphite are added. A portion of the prepared mixture is transferred to the graphite elect'rcde (0.25 X 3 inch electrode; 0.0625inch crater n-ith a center post) by forcing the electrode into the catalyst mixture repeatedly until the crater is fully packed. Xormally, three electrodes charged in the foregoing manner are arced for one analysis. By utilizing the step sector, measurements may be made a t the respective intensity levels to provide from one to three intensity ratios per spect,rum; hence, from t'hree Ppectra, three t'o twelve intensity ratios thus become
1817
a
1818
ANALYTICAL CHEMISTRY
Table I. Procedure for Spectrochemical Determination of Magnesium in catalysts Spectrograph Gratin aperture Slit wi2th. microns Sector aperture Electrodes, regular spectroscopic grade Upper, inch Lower, inch Depth of crater, inch Electrode gap, mm. Power Type unit Volts Amperes Inductance, microhenries Resistance, ohms Capacitance. microfarade Phase switch Rotar gap pointer Rectizer tube switch Exposure time. seconds Film Type Development Developer Time, min. Fixing time, min. Drying time, infrared dryer, min. Analytical lines Magnesium, A. Copper (Internal standard), A.
Full opening 10 4
0.125 0.25 0.0625 cut with center post
7
Multisource
300
10
400 23 60 n 96 1 60
Spectrum anal. No. 1
B
C
A B
C D
E
Table 111. Application of Spectrographic Method to Analysis of Bureau of Standards Samples for Magnesia % Jf€!O
76
Sample Designation Burnt refractory
97
Flint clay
KBS
No.
NBS certified value 0.58
3 2 2
Deviation Based on experiBased on NBS certified mental average value
~
By analysis 0.43 0.55 0.54
D-19
-0.08 +0.04 fO.03
-0.15 -0.03 -0.04
+0.02
-0.01 -0.04 +0.07
0.51 0.26
0.25 0.22 0.33
2779.8 2768.9
available, by means of m hich a single analysis for magnesium is made. The details for excitation and film development are outlined in Table I. Results and Discussion. CHOICEOF INTERNAL STAKDARD. On the basis of boiling point and excitation potential, molybdenum and copper were investigated as to suitability for use as internal standards in the determination of cracking catalysts. Initial experiments were made by arcing- a .portion of a 5-gram sample to which 10 mg. of molybdenum (as ammonium molybdate) had been added as an internal standard. The data are presented in Table II and Figure curve A . The dotted lines drawn parallel to the worlhng curve show the variation range of the intensity ratios. Employing copper as the internal standard and the method of preparation previously desrribed, a number of spectra on each of five svnthetic catalvst s a m ~ l e swere obtained. Reference to Table I1 and Figure 1, curve B, will show that the reproducibility of intensity ratios is considerabl~ improved, 6.0% us. approxiniately 33% average deviation. ANALYSISOF SYNTHETIC AND BUREAU OF STANDARDS S~RIPLES. As a further test of the reliability of the method, two Bureau of Standards samples were analyzed by this technique (Table HI).
Samp!e
I n most cases, agreement between the Bureau of Standards value and the determined value is very good. At higher concentration levels, typical data in Table IV illustrate that the method is applicable to magnesia ranges up to 12%. The samples were prepared by mixing silica-magnesia catalyst, the magnesia content of which had been established chemically, and silica-alumina catalyst.
-0.05 t0.06
0.27
Table 1V. Application of Spectrographic Method to Analysis of Synthetic Catalysts for Magnesia 70 LlgO Sample
Theoretical
Determined
1 2
6 3 12 5
6 3 11 9
DETERMINATION OF ZIRCONIUM
I n some catalytic cracking catalysts, zirconium oxide is employed in addition to silica-alumina (18). .4t these laboratories it has been desirable t o study catalysts containing zirronia in the range of 0.01 to approximately 5.0%. To cover the entire concentration range, it Fas necessav to employ t m zirconium lines, 3392 A. far the 0.01 to 0 3% zirconiumoxide and 2371.4 A. for 0.1 t o 5% zirconium oxide.
Experimental, lNTERNAL S T A N D ~ RBLESD. D Eight grams of graphite (SP-2) and 2 grams of cobalt oxide are ground together in a motor-driven mortar and pestle for approximately 1 hour. PREPARATION OF STASDARDS. In the low concentration range (0.01 to 0.3% zirconium oxide) Bureau of Standard samples were employed. The used, together xith certified zirconium oxide analyses, are given in Table V. In the high concentration range several types of standards were em~loved-catalvsts analyzed ch&n&ally by ;re+ Table 11. Reproducibility of Intensity Ratios cipitation as cupferron; diluKO,of N o . of IntenIntensity Ratio t i o n s of t h e catalyst with RIgO Spectra sity Ratios Dev. from % dev. from Concpntration Film Specpure silica; Bureau of Level No. Measured Averaged Average average, average, =t Standards samples; and synMagnesium zs, Molybdenum thetic samples of zirconium I J l g 2871 oxide impregnated on silicaI M o 2781 a l u m i n a c a t a l y s t s . These 0 31 29 2 0.83 1 3 10 106 samples were prepared in the 2 56 0 0 75 0 12 3 9 following manner: 0 31 33 7 3 11 0 92 3 Zirconyl nitrate which had 0.18 20.9 1.66 1 3 10 0.86 0.24 15.6 been previously analyzed 2 3 12 1.54 0.55 40.4 3 11 1.36 3 chemically was dissolved in a 4 37.7 1.30 0.49 3 7 mixture of nitric and hydroAv. 3 3 . 4 chloric acids and diluted to Magnesium ua. Copper I Mg 2871 volume in a volumetric flask. I Cu 2769 The catalyst, previously dried 0.41 1 3 3 0.23 0.0 0.0 at 1600" F., was impregnated 0.83 1 2 4 0.41 0.02 5.0 with various aliquots of the 2 0.34 0.01 2.8 3 6 zirconyl nitrate solution to1.67 1 0.62 0.02 3.2 3 10 gether with sufficient water to 3.32 1 3 11 1.05 0.10 9.5 form a pasty mass. After the 3 12 0.98 0.05 5.1 m i x t u r e w a s m a d e slightly 4.1 1 3 12 1.19 0.10 8.4 alkaline with ammonium hyAv. 6.0 droxide, it was carefully dried with frequent stirring on an
*
V O L U M E 23, NO. 12, D E C E M B E R 1 9 5 1 Table V.
1819
Standards Employed in Spectroscopic Calibration for Zirconia (0.01 t o 0 . 3 % ZrOn)
NBS 91 76 97 98 98
+ SiOP (1 : 1) 97 + Si020 (1:l)
a
% ZrOz Certified 0.01 0.07 0.25 0.04 0.02
Sample Designation Opal glass Bauxite Flint clay Plastic clay
KO.
... ...
0.125
Specpure silica from Johnson, h l a t t h e y & Co., Ltd.
the pulverized sample is calcined approximately 30 minutes a t 1600" F. After cooling in a desiccator, 0.5 gram of sample and 0.5 gram of the internalfstandardmixture are weighed and mixed in an agate mortar or an electric motor shaker (9). A portion of the sample is transferred to the electrode as described above and arced according to conditions outlined in Table VI, Film development details are also presented in this tabulation.
Results and Discussion. ACCURACYAND REPRODUCIBILITY. To test the accuracy and reproducibility in the low concentration range, two Bureau of Standards samples were analyzed as unknowns (Table VII). I n the higher concentration range, several samples have been analyzed chemically as well as spectrographic all^ , Typical data are compared in Table VIII.
electric hot plate. After the mixture xas thoroughly dry, it was further calcined for 2 hours a t 1600" F. ANALYTICAL WORKING CURVES similar t o Figures 2 and 3 are prepared from standard samples according to steps outlined in the analytical procedure. The points plotted are the averages of a number of exposures; the vertical lines represent the range of the data. ANALYTICAL PROCEDURE. Five to 10 grams of sample are pulverized with a motor-driven agate mortar and pestle, and IU (L
z
I
I
I
0.2
0.1
l l l l l l l 0.4 0.6 0.8 1.0 W T . 7'0 Z R 0 2
I
I l l 2.0
1
1
3.0 4.0 6.0
Figure 3. Analytical Working Curve for Determination of Zirconium in Cracking Catalyst 0.25 to 5 % Z r 0 1
$ s,
I , , 0.01
0.02
I , , 1 1 1 1 0.04 0.06
0.10
I
I
,I
0.2 0.3
WT.% Z R O ~
Figure 2. Analytical Working Curve for Determination of Zirconium in Cracking Catalyst 0.02 to 0.25% ZrOz
Table VI. Procedure for Spectrochemical Determination of Zirconium in Silica-Alumina Catalysts Spectrograph Grating aperture Slit width. microns Sector aperture Electrodes, regular spectroscopic grade Gpper. inch Lower, inch Depth of crater, inch Electrode gap, mm. Power Type unit Volts Amperes Inductance, microhenries Resistance, ohms Capacitance, microfarads Type of excitation Exposure time, seconds Film Type Development Developer Time, min. Drying time, infrared dryer, min. Analytical lines 0.01 t o 0,30% ZrOr Zirconium, A. Cobalt, A. 0 . 1 to 5 . , 0 % ZrOz zirconium, A. Cobalt, A.
Table VII. Replicate Spectrographic Analyses of Bureau of Standards Samples for Zirconia % ZrOz NBS No. 98
Sample Designation Plastic clay
NBS certified 0.040
97
Flint clay
AY. 0.25
Full opening 10 4 0.125 0.28 0 . 0 6 2 5 c u t with centerpost 7
Av.
By analyeis 0.035 0.034 0.040 0.042 0.040 0.038 0.19 0.25 0.24 0.24 0.26 0.24
Deviation Based on Based on average NBS -0.003 -0,005 -0,004 - 0 OOA 1-0.002 0.000 +0.004 +0.002 i o I002 0.000 10.003 +0.002 -0.05 -0.06 +o. 01 0.00 0.00 -0.01 0.00 -0.01 +0.02 +c.o1 hO.01 *0.02
Table VIII. Comparison of Chemical and Spectrographic Zirconia Analyses
3Iultisource 340 10 400 21 60 Full wave d.c. 90
Sample No. Method Spectrographic Chemical separation Cupferron Phosphate
1
Weight % ZrOz 2 3
4
3.3
3.3
5.3
2.8
3.0 2.9
3.8
5,5 5.4
3.0 2.9
...
Spectrum anal. No. 1 D-19 3 2 3392.0 3398.8 2571.4 2587.2
Table IX. NBS Sample No. 69 78 77
Effect of Alumina on Spectrographic Determination of Zirconia
Sample Designation Bauxite B u r n t refractory B u r n t refractory
AlrOa NBS Certified, % 55.1 70.0 59.4
ZrOl, Weight yo BY certified analysia 0.08 0.043 0.12 0.05 0.09 0.031 NBS
1820
ANALYTICAL CHEMISTRY
INTERFERENCES. In the analysis of other Bureau of Standards samples it was found that high concentrations of alumina (above 40% A1203) suppressed the zirconium line and thereby caused low results, as illustrated by Table IX. In samples containing iron abo\e lY0,it is possible that for the low concentration zirconium oxide range the iron line at 3399.3 A. may interfere with the cobalt internal standard line at 3398.8 A. LITERATURE CITED
Helz, A. IV.,and Scribner, B. F., J . Research Nutl. Bur. Stand-
ards, 38, 439 (1947). Hughes, H. K., A4nderson,J. W., Murphy, R. W., and Rather, J. B., Jr., Proc. Am. PetroleitmInet., 29 M (3),89 (1949). hlarling, J. B., -19.1~.CHEM., 20, 299 (1948). Meggers, IF7. F., and Scribner, B. F., “Index to the Literature on Spectrochemical Analysis,” Part I (1920-1939), 2nd ed., Part I1 (1940-1945), Am. SOC.Testing Slaterisls, Philadelphia, Pa. Murray, .\I. J., and Plagge. H. :I., Proc. Am. Petroleum Inst., 29 M 13). . , , 84-8 (1949). Pierce, W.C., and Nachtrieb, S . H.. IND.EXG.CHEM.,ANAL. ED.,13, 774-81 (1941). Richardson, R. JT., Johnson, F. R.,and Robbins, L. V.. I d . Eng. Chem., 41, 1729-33 (1949). Russell, R. G., ASAL. CHEM.,20, 206 (1948). Ibid., 22, 904 (1950). Thomas, C. L., and Lee, E. C. (to Cniwrsal 011Products Co.), U. S. Patent 2,347,648 (May 2 , 1944). Veaaer, J. R., and Brattain, R. R., ASAL. CHEM.,21, 1038 (1949). Weber, G., Oil &. Gus J., 49, 110 (1950) .
(1) Burdett, R. A., and Jones, L. C., AXAL.CHERT., 19, 23841
(1947). (2) Calkins, L. E., and White, h l . M., iVatl. Petroleum News, 38,
S o . 27, 519 (1946).
( 3 ) Carlson, hl. T., and Gunn, E. L., BSAL.C m x , 22, 1118 (1950).
Conn, 9.L., >leehan, IT. F., and Shankland, R. V., Chem. Eng. Progress, 4 6 , 176-86 (1950). Dieke, G. H., “Progress Report on Study of Standard Methods of rlnalysis,” Office of Scientific Research and Development, OSRD, Seriul W-54(1943). Gassmann, A. G., and O’Xeill, V. R., Proc. Am. Petroleum Inst., 29 M(3), 79 (1949). Gunn, E. L., A s a ~CHEY., . 21, 599 (1949). Harvey, C. E.. “Spectrochemical Procedures,” pp. 71-81, Pasadena, Calif., Applied Research Laboratories, 1950.
(4)
(5) (G)
(7) (8)
I
RECEIVED March 26, 1951. Presented before the Sixth Southwest Regional Meeting, AMERICANCHENICALSOCIETY San Antonio, TFX.,December 7 t o 9, 1950.
Spectrographic Determination of lubricating Oli Additives J. P. PAGLIASSOTTI AND F. W. PORSCHE Research Department, Standard Oil Co. (Indiana), Whiting, Znd.
A spectrographicmethod has been developed for the direct and rapid determination of phosphorus, barium, calcium, and zinc in lubricating oils and additive concentrates for phosphorus. Important features of the method include the iise of the magnesium salt of 2-ethylhexoic acid as a spectrochemical buffer and of nickel as an internal standard. The presence of each additive element being determined has no effect on the determination of the others. Nine metalscontaining additives, seven different base oils, and twenty-two elemental compositions of oils and additives have been investigated without finding a combination for which the method failed. The viscosity of the oils likewise has no effect on the analysis. The procedure, which is fast, simple, and accurate, has been used as an effective plant-control procedure for one year.
T
HE characteristics of lubricating oils have been improved in
recent years by the incorporation of addition agents, one or more of which are today a part of most premium-grade motor oils, These additives may be classified as pour point depressants, viscosity-index improvers, detergents, oxidation inhibitors, corrosion inhibitors, antifoam agents, and color improvers. Such addition agents may contain one or more of the following elements: phosphorus, potassium, barium, calcium, and zinc. -4s chemical methods for the determination of these elements in oil and additive concentrates are time-consuming and tedious, a rapid and accurate analytical procedure is needed to ensure the proper control of plant-blending operations. Emission spectrographic techniques for the analysis of oils have been studied by several investigators. Calkins and White ( 2 ) impregnated their electrodes with the oil to be analyzed. Gassmann and O’Neill(5) introduced the sample into the spark through a porous graphite cup used as the upper electrode ( 3 ) . The present authors (8)introduced the oil into the spark by means of a rotating graphite electrode partially immersed in the oil sample. The method presented here retains this sample-handling technique but improves on the earlier method by incorporating nickel as the internal standard and magnesium as a spectrochemical buffer. These changes make possible accurate determinations of barium, calcium, and zinc in addition to phosphorus. The presence of each additive element, alone or in combination, is shown to be without effect on the determination of the others.
The geographical source of the base oil used in compounding the oil as well as the viscosity of the oil sample is likewise shown to be without effect on the analysis. The method is proposed for the analysis of experimental oils as well as plant-blending control samples. EXPERIMENTAL
The spectrographic equipment used and the preparation of phosphorus calibration standards have been described (8). The chemical analyses of the barium and calcium calibration standards follorved the procedures recommended by the American Society for Testing Materials ( 1 ) . The zinc was determined by the procedure outlined by Kolthoff and Sandell (7).
A number of test oils were prepared by blending several additive concentrates and base oils to study various phases of the problem. These blends included nine additive compounds, seven base stocks derived from four distinctly different crude oils, and twenty-two elemental compositions of oils and metal-containing additives. In addition, a highly chlorinated phosphorus-containing additive was used. The additive Concentrates studied included a phosphorus and a phosphorus-potassium additive. Two internal-standard solutions, one for oils and the other for additive concentrates, were prepared, each containing the magnesium buffer. The solution used for lubricating oils contained 1.0% nickel, 0.75% magnesium, and 25% methyl ethyl ketone in a petroleum fraction known as mineral seal oil boiling between 500” and 700” F. The internal standard solution used for addi-
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