However, heating the bath formulation to 100" C. made a difference. No color developed a t 0.4 but a blue color appeared at the point of origin on the paper. This spot a t the origin also gave the molybdenum blue color before the paper was placed in the ammonia fumes. This suggests that in the APOT H P C formulations used for treating cotton the T H P C is converted into an insoluble polymer only when heated but remains in the bath formulation as THPC. In regard to the yellow color with ,4PO, the addition of APO to an ammonium molybdate solution forms a yellow precipitate. The reaction is highly exothermic and the addition of concentrated solutions of APO to ammonium molybdate should be avoided. The APO molybdate was filtered and titrated with sodium hydroxide according to the usual procedure for a phosphorus determination. Each mole of APO took 5.5 to 5.9 moles of sodium hydroxide. The infrared spectra of the precipitate differ from those of the molybdate formed b y sodium phosphate, in that an intense absorption at
7.25 microns in the spectra of the latter is absent in the APO molybdate spectra. On standing, the color of the precipitate changes from yellow to green, which is the same type of color change produced by mixing a reducing agent with ammonium phosphomolybdate. The infrared spectrum of the molybdate that forms from the acid-extracted APO-THPC-treated fabric is the same as for ammonium phosphomolybdate. The completely polymerized APO, a white water-insoluble solid, does not form a molybdate and does not migrate during the chromatographic test described. However, when the polymerized APO is boiled in 1% hydrochloric acid, it dissolves and the solution will form a yellow ring at Rr 0.8 in the test. Other phosphorus-containing flameresistant cotton fabrics were extracted with 1% hydrochloric acid and chromatograms were run. These included phosphorylated cotton and cotton treated with diallylcyanoethane phosphonate, the bromoform adduct of triallyl phosphate in combination with T H P C , and chloroethylene (vinyl chlo-
ride)-antimony oxide in combination with THPC. Of these, only phosphorylated cotton gives the same yellow ring at R, 0.8. However, phosphorylated (urea phosphate) cotton can be distinguished from APO-treated fabric by the following test (4): A small piece of fabric from which any wax finish has been removed by solvent extraction is spotted with ammonium molybdate solution. Phosphorylated cotton will immediately turn yellow; APO-THPCtreated cotton does not. LITERATURE CITED
(1) Bestian, H., :4nn. Chem. Liebigs 566,
210 (1950). (2) Drake, G. L., Jr., Cuthrie, J . D., Textile Research J . 29, 155-64 (1959). ( 3 ) Hoffman, A., J . Am. Chew SOC. 52, 2995 (1930). ( 4 ) Nuessle, A . C., Ford, F. M., Hall, WT.P., Lippert, .4.I.., Yertiie Research J . 2 6 , 32-9 (1956). (5) Reeves, W. A,, Drake, G. L., Chance, L. H.. Guthrie. J. D.. Ibid.. 27. 260-8 RECEIVEDfor review June 22, 1959. Accepted September 8, 1959.
Determination of Arsenic in Petroleum Stocks and Catalysts by Evolution as Arsine DAVID LIEDERMAN, J. E. BOWEN, and 0.1. MILNER Research Department,
P oulsboro Laboratory,
,An improved method has been deveioped to determine arsenic in reforming charge stocks and catalysts. The range of the method for charge stocks is from zero to several hundred parts per billion, and for catalysts from zero to several thousand parts per million. The arsenic is extracted from the naphtha and separated as arsine which is measured spectrophotometrically after reaction with silver diethyldithiocarbamate in pyridine. Catalysts are fused before the arsine separation and spectrophotometric determination. The method has been applied to a wide variety of reforming samples.
A
contained i r reforming charge stocks poisons platinumbearing petroleum reforming catalysts. To study this poisoning process and to find ways to minimize it, a sensitive, rapid, and precise method was needed to determine from 1 to 100 p.p.b. of arsenic in charge stocks. A method was also needed for determining 1 to RSENIC
2052
rn
ANALYTICAL CHEMISTRY
Socony Mobil Oil Co., Inc., Paulsboro,
5000 p.p.m. of arsenic in reforming and pretreating catalysts, generally cobalt oxide-molybdena-alumina. Previous chemical methods for the determination of traces of arsenic in petroleum and catalysts have been based on the separation of arsenic by arsine evolution and final determination by a modification of the Gutzeit method (3, 6),or distillation as the trichloride and formation of the arsenic-molybdeniim blue complex ( 4 ) . A method using neutron activation has been presented (8). The authors' previous method (d), although sensitive and precise, was lengthy. T o develop a more rapid method, a colorimetric procedure introduced by Vasak and Sedivek (9) was adapted. The method involves the reaction of arsine with a pyridine solution of silver diethyldithiocarbamate (AgDDC). After the work included in this paper was completed, other studies based on the use of AgDDC were reported ( I , 6). However, these mrthods are applicable only to liquid petroleum products. In t,he present method as applied to
N. 1. liquid stocks, the arsenic is extracted and simultaneously oxidized by a mixture of sulfuric acid and hydrogen peroxide. Catalysts are solubilized by a sodium peroxide fusion. If platinum is present in the catalyst, it is largely removed by a basic filtration; last traces are removed by extraction as the platinum-stannous chloridr complex. The arsenic is then determined by a modification of the Vasak and Sedivek procedure. Quantities of arsenic d o w i to 0.03 y can be detected. APPARATUS
Evolution apparhtus (Figure 1). Separatory funnels. Although ordinary separatory funnels can be used, the specially designed one shown in Figure 2 is much more convenient. Spectrophotometer cells, special 70mm. ( 4 ) . REAGENTS
The water was treated by passing it through a mixed-bed ion exchange
column. T h e sulfuric acid was redistilled over potassium permanganate. STANDARD ARSENICSOLUTIONS, 0.1, 1, and 100 y per ml. Dissolve arsenious oxide in dilute sodium hydroxide, acidify with dilute sulfuric acid, and dilute to volume. ZINCMETAL,reagent grade, granular 20-mesh. The arsenic content of this reagent varies widely. A low-arsenic lot, as determined by blank runs, should CALIBRATED be reserved for this determination. AT 3.10 ML.SILVER DIETHYLDITHIOCARRAMATE (AgDDC). Prepare two solutions, one containing 1.7 grams of silver nitrate in 100 ml. of water and the other containing 2.3 grams of sodium diethyldithio- ' O D i carbamate in 100 ml. of water. Cool below 20" C. and mix slowly with stirring. Filter off the lemon yellow precipitate of AgDDC and wash thoroughly with distilled water. Dry in a vacuum desiccator Figure 1 kept below 30" C. The dry salt is stable a t room temperature for at least six months. SILVER DIETHYLDITHIOCARRAhlATE SOLUTION. Dissolve 1.0 gram of the salt in 200 ml. of pyridine. This reagent is stable for a t least several months. LEADACETATE-COATED GLAS WOOL. Soak glass wool in 10% lead acetate solution, drain well, and dry. Store in a capped jar. STANNOUS CHLORIDE SOLUTIOE;. Dissolve 20 grams of reagent in 100 ml. of concentrated hydrochloric acid.
HYDROGEN
~
-__-__ EVOLUTION FLASK
l
W
M
E
I
E
R FLASK
Arsine evolution apparatus
n
\CM$
2 0 MM
TO CENTER OF CONSTRICTION
METHODS
Procedure for Chromia-AluminaMolybdena Catalysts. Proceed as above t o the adjustment of the volume t o 48 nil. Then add dropwise, with swirling, 3Yc hydrogen peroxide until one drop no longer gives t h e bluish purple tinge of perchromic acid. Complete as described above.
Procedure for Platinum-Bearing Catalysts. Acidify t h e solution in the
Arsenic in Liquid Stocks.
Add 15 ml. of concentrated sulfuric acid and 20 nil. of 30YG hydrogen peroxide t o a 500-ml. Kjeldahl flask containing one or two boiling stones, and cool t o 0 t o 5" C . Add u p t o 100 ml. of sample containing 0 t o 1 y of arsenic to t h e flask. Some samples, especially those high in olefins, react vigorously with t h e acid-peroxide mixture. Therefore, shake t h e mixture gently at first. If a vigorous reaction is apparent or if t h e bottom of t h e flask heats u p quickly, plunge t h e flask into ice water until the reaction subsides. If t h e mixture darkens a t any time, add more hydrogen peroxide. Shake the mixture vigorously for 1 minute, then reflux t h e sample for 0.5 hour with occasional shaking. Cool the mixture, transfer it to a separatory funnel, and drain the acid layer back into the Kjeldahl flask, washing the hydrocarbon layer once with 10 ml. of water. With samples that do not char easily and with samples of 10 ml. or less, the separation may be eliminated and the organic layer merely boiled away. Heat the solution to sulfuric acid fumes, adding hydrogen peroxide when necessary to prevent excessive charring. Cool the solution, wash it into an evolution flask, and adjust the total volume to 50 f 5 ml. Cool the solution again, and add 1 ml. of 15% potassium iodide solution and, with swirling, 5 or 6 drops of stannous chloride solution. Add 1.0 ml. of isopropyl alcohol to the flask to slow down the subsequent evolution rate. Add 5.0 =k 0.1 grams of zinc
dena-Alumina Catalysts. Transfer a n aliquot of 25 ml. or less of t h e above solution, containing no more than 10 7 of arsenic, t o a n evolution flask. Adjust t h e volume t o 25 ml. with water. Acidify with 1 t o 1 sulfuric acid until t h e precipitate of aluminum hydroxide formed just redissolves, then a d d 12.0 ml. more. Adjust t h e volume to 48 ml. a n d add 2.0 ml. of 15y0potassium iodide solution and 5 or 6 drops of stannous chloride solution. Add 3.8 ml. of A g D D C solution t o t h e absorber. Add 5.0 i. 0.1 grams of zinc t o t h e evolution flask and immediately attach the hydrogen sulfide scrubber and absorber. Allow t h e arsine t o evolve for 45 minutes, then remove t h e absorber and carefully dilute t o 3.80 ml. with pyridine. (Some pyridine has been lost by evaporation.) Pass a gentle air stream through t h e absorber t o mix t h e solution, then drain into a 1-cm. spectrophotometer cell. Measure t h e absorbance at 540 mp against A g D D C as a reference. Relate t h e absorbance t o a standard curve obtained by evolving known amounts of arsenic under t h e same conditions.
Figure 2. Special extraction funnel
metal and immediately attach the hydrogen sulfide scrubber and the absorber containing 3.8 ml. of AgDDC solution. Allow the evolution to proceed for 45 to 50 minutes, then detach the absorber and dilute the solution to exactly 3.80 ml. with pyridine. Pass a gentle air stream through the absorber t o mix the solution. Measure the absorbance a t 540 mp in the 70-mm. cell; use AgDDC solution as a reference. Arsenic in Catalysts. For samples estimated t o contain less t h a n 0.05Q/, of arsenic, weigh 0.6 gram of finely ground catalyst into a 30-ml. nickel crucible; for those estimated t o contain over O.O5Q/,, weigh 0.3 gram. Add 3.0 + 0.2 grams of sodium peroxide t o t h e crucible and mix well. Cover t h e sample with a n additional 1 h 0.2 gram of sodium peroxide. Fuse in a furnace a t 525 i 25' C. for 0.5 hour. Leach t h e salts in 50 ml. of water and gently boil the alkaline solution for 10 minutes t o coagulate t h e precipitate and decompose t h e excess peroxide. Cool and filter into a 100-ml. volumetric flask and dilute to volume with water. I n t h e case of catalysts containing platinum, filter into a separatory funnel. Complete according t o one of t h e following procedures.
Procedure for Cobalt Oxide-Molyb-
separatory funnel with 1 t o 1 sulfuric acid until the aluminum hydioxide just redissolves. Add 8 ml. of concentrated hydrochloric acid and cool. Add 1 ml. of stannous chloride solution and dilute to about 90 ml. Extract with three 15-ml. portions of n-butyl acetate, drawing off the butyl acetate layer each time. Finally, drain the aqueous layer into a 100-ml. volumetric flask and dilute to volume with water. Transfer an aliquot of 15 ml. or less (containing less than 10 y of arsenic) to an evolution flask containing 12.0 ml. of 1 to 1 sulfuric acid. Adjust the volume t o 48 ml. and continue the analysis as above, starting with the addition of 2.0 ml. of potassium iodide solution. DISCUSSION
STANDARDIZATIONS. Calibration curves are prepared by evolving arsine from known amounts of arsenic added as arsenious oxide. For petroleum fractions, 0.1 to 1.0 y is taken; for catalysts, 1 t o 10 y are taken. A 3.80ml. volume of AgDDC solution is used. The concentrations of sulfuric acid and the other reagents are the same as for the respective types of samples. SPECTROPHOTOMETRIC CURVE. Vasak and Sedivek found 560 mp to be the wave length at which the arsenicAgDDC reaction product has maximum absorbance. However, curves traced with several instruments showed maximum absorbance to be 540 mlr. I n VOL. 31, NO. 12, DECEMBER 1959
2053
any case, thc wave length should be adjusted on any particular instrument to give maximum absorbance per unit of arsenic content. IIEAGEKT ELAXKS.I t is important to choose reagents as low as possihlo ir
arsenic content, especially in the analysis of. petroleum fractions, where the total amount of arsenic dealt with is usually 0.1 to 1 y. A large portion of the total reagent blank is contributed hy the arsenic in the zinc. A grade which contains 0.3 y or less of arsenic per 5 grams of zinc should be used. To keep the blank constant, both the amount of zinc added and the amount dissolved must be kept uniform. Under the specified evolution conditions, practically all of the zinc is dissolved each time; this ensures that the same amount of arsenic is contrihuted for each evolution. A new blank should be determined each time a new lot of a reagent is used or \\hen the quhntity is altere& for example, in handling olefinic stocks,
Table I. Recovery of Arsenic Added as Triphenylarsine to a Typical Reformate ~ _ _ _ Arsenic, _ _ _ _ P.P.B. _ _ _
Added
Found
2
0, 2 6. 5 8 ; 10
5 10
30,27
28 53
50,54 85,80
79
Table II.
Determination of Arsenic in Petroleum Products
Arsenic TrichlorideMolybdenum Blue, P.P.B.
Sample Reformer charge 4 Reformate Heavy naphtha Reformer ch irge B Light thermal naphtha Straight-run naphtha Heavy straight-run naphtha
Table Ill.
COO-MOO3A1203
0
1.00 3.00 5.00
13 20,21 23, 25 47, 49 82, 89, 86, 85, 84
20
Arsenic, added Found 5.00 5 .O b 5.00 5.14 5.00 5.05 5.00 4.90,4.94 0.00 0.00
Arsenic, y Added Present Found 0 2.00 5.00 7.00
2
47, 43, 50 81, 83, 86
Table IV. Recovery of Arsenic Added to Typical Pretreating Catalysts
Material Cr&L1003A1403
3
1
2 14 19, 18
Effect of Chromium(V1) on Arsenic Recovery
Cr(V1) ildded, Gram 0.00 0.09 0.18 0.35 0.00
Arsine EvolutionAgDDC, P.P.B.
...
0.38 2.39
2.38 5.38 7.38
5.36
...
0.48 1.48
7.25
1.48 3.48 5.48
nhere larger quantities of hydrogen peroxide are needed. Avoidance of Contamination. Reagents should be reserved for these methods only. All glassn are must be made scrupulously clean by boiling with nitiic acid before use. Because of the great difference in arsenic levels, separate sets of apparatus should be used for catalysts and for naphthas t o avoid contamination. EVOLUTIOK COKDITIOKS. A convenient concentration of sulfuric acid and total volume were chosen so that the evolution proceeded at a moderate rate. The time necessary to obtain complete recovery was then determined. Results showed that 99% of the arsenic is recovered after 30 minutes. T o eliminate errors from small variations in evolution rate, 45 to 50 minutes were used.
3.56 5.50
RESULTS
Recovery of Arsenic from Petroleum
Table V.
Determination of Arsenic in CL*+alysts
hrsenic, 70 Sample Neutron activation COO-J~OG~-AI~O~ ... ... ... ...
Pt-AI2Oa
0.0011,0.0012 ...
0.037”’ 0.100
2054
ANALYTICAL CHEMISTRY
AsC13
0.0026,O. 0023 0.009,0.011,0.012 0,089,O.087,O.088
0.181
0.0012,0.0011,1.0010 0.008
0.016 0.033,0.033 0.109
ASH3 0 0020,0,0020
0.013
0,090 0 195
0.0010,0.0009 0 007,0.007 0.016,0.016
0,034,O.031
0.099,o. 101
With the special Iongpath, small-volume cell, as little as 0.03 y of arsenic can he detected. This corresponds t o about 0.4 p.p.b. on a 100-ml. sample. To test the recovery of arsenic, samples oi a typical reformate containing added amounts of triphenylaisin? mere :inalyzed. T h e results in Table I shon good recoveries. Results for typical petroleum fractions analyzed by this method and by the arsenic trichloride d:stillationmolybdenum blue method (4)are given in Table 11. Interferences. Metals 01 salts of metals Such as cobalt, mercury. nickel, platinum, silvei, palladium, and large amounts of copper, chromium, and molybdenum have been reported to interfere n ith the evolution of arsine (2, 7 ) . Among these, cobalt, nickel, platinum, chromium, and molybdenum are likely to he encountered in catalysts used in the petroleum industry. Cobalt, nickel, and most of the platinum are eliminated hy filtering the leachate after the peroxide fusion. Po+ sible interferences from the other metal salts likely to be present and from small amounts of platinum were studied. Fractions.
* O t
20
i
\
0
10 IO0 PLATINUM ADDED,
Figure 3.
IO00
f
Platinum interference
CHROhllUM AND AIOLYBDLNUM. Chromium(V1) interferes mainly by making difficult the reduction of arsenic(V) to arsenic(lI1) prior to arsine evolutiop and by increasing the rate of hydrogen evolution (2, ‘7). T o eliminate chromium(VI), dilute hydrogen peroxide mas added to oxidize it to perchroniic acid, IT hich spontaneously decomposes to chromium(II1). Known amounts of chromium(V1) added to standard arsenic solutions were treated in this manner, then arsine was evolved. The results in Table IT1 show no appreciable interference. Analyses were also made of typical chromia-aluminamolybdena catalysts to which known amounts of arsenic were added. These results, given in the first half of Table IV indicate that molybdenum also does not interfere. COBALT AXD MOLYRDEKJI. To prove that any cobalt left after the basic
filtration would not interfere. various amounts of arsenic wcrp added to acidif i c d portions of the filtrate and the arm c n a p then generated. The results in the second half of Tahle I V show no interference 1)y any residual cobalt or, again, by the molybdenum. Results for cobalt-alumina-molybdena catalysts bv this method were also compared with those obtained by the arsenic trichloride diitillation method (6) (Table V). PLATIXX. I n processing catalysts containing from 0 A to l.OYc platinum, up to 500 y of platinum had been found in the filtrate after the initial basic filtration. T o measure the extent of interference from this amount of platinum. arsine was generated from solutions containing chloroplatinic acid. Severe interference $\-as observed (Fig-
ure 3). Therefore, the extraction of the last traces of platinum as the stannous chloride-platinum complex n as incorporated into the procedure. R e u l t s on typical platinum-bearing cata1,vsts are given in Table V. i l s ~ 1 a r o ~ ; r The . only likely interference in the color development is from stibine, which forms a red color with maximum ahsorbance near 510 mp. The sensitivity for antimony a t 540 mp is only about 8’3 that of arsenic. Thus far, interfering amounts of antimony in petroleum stocks or catalysts have not been detected. LITERATURE CITED
(1) Albert, D. K., Granatelli, L., ASAL. CHEK31, 1593 (1959).
( 2 ) Harkins, W. D., J . Am. Chem. Soc’
32.518(19101. , (3) Jay, R. R:, Dickson, L. R., Petrol. Processing 9 , 371 (1954). (4) Liederman, D., Bowen, J. E., hIilner, 0. I., ANAL.CHELI. 30, 1543 (1958). (5) Maranowski, S . C., Snyder,_R. E., Clark, R. O., Ibid., 29, 353 ( 1 9 0 , ) . (6) Powers, G. K., Jr., Martin, R. L., Piehl, F. J., Griffin, J. AI., Ibid., 31, 1589 (1959). ( i ) Sandell, E. B., “Colorimetric Drtermination of Traces of Metals,!’ 2nd ed., Interscience, New York, 1950. (8) ShiDman. G . F.. Afilner. 0. I.. ANAL. CHEX 30, 210 (1958). (9) Vasak, V., Sedivek, V., Chem. itsty 46, 341 (195%). -
\
~
RECEIVEDfor review May 27, 1959. Accepted September 16, 1959. Division of Petroleum Chemistry, 136th Meeting, ACS, Atlantic City, K. J., September 1959.
Determination of Hydroxyl Value of Alcohols by Near-Infrared Spectroscopy R. 0.CRISLER and A.
M. BURRILL
Miami Valley laboratories, The Procter & Gamble Co., Cincinnati 31, Ohio
b A method is described for the determination of hydroxyl value of aliphatic primary alcohols which uses the hydroxyl-stretching overtone band at 1.4 microns in the near-infrared region. Samples are analyzed as dilute solutions in carbon tetrachloride or tetrachloroethylene. Using a calibration curve, results on a number of fatty alcohol samples are compared with values obtained by the acetic anhydride-pyridine method. The standard deviation is 0.27 in the range 85 to 115 mg. of hydroxyl per gram of sample. Some differentiation between types of hydroxyls can b e made using the overtone region. Extension of this method to other alcohols, particularly tertiary and others difficult to acetylate, is suggested.
T
problem of determining the hydroxyl (OH) value of fatty alcohols using the OH stretching overtone a t 1.4 microns was undertaken as part of a n investigation of the usefulness of near-infrared spectroscopy. K i t h the availability of commercial near-infrared recording spectrophotometers of high accuracy and resolution, such a method might have material advantage in both time and applicability over the several n e t chemical methods currently in use. I n particular, HE
the applicability to tertiary and other alcohols that can be acet,vlated only with difficulty makes such a method attractive , The overtone band has been used in studies of hydrogm bonding ( 1 . 2, 6) and for specific analyses, such as the determination of hydroxyalkyl aniline in alkyl anilines (8)and the unncetylated hj-drouvl content of cellulose acetate (6). Hoaevcr, no stud>- of its usefulness for the determination of hydroxyl value has been presented. Ka! e. in his comprehensive review (4) suggests usr of the overtone region for the determination of alcohols in hydrocarbons and acids. I n the presrnt xork, near-infrared spcctra of a numbrr of fatty alcohols werr obtained a t several concentrations arid calibration curves prepared. H>droxyl values determined b y the near-infrared method on a number of commercial alcohols were compared with hydroxyl values determined by the acetic anhydride-pyridine method (3,Y). I n the fats and oils field, hydroxyl value is defined as the milligrams of potassiuni hydroxide equivalent to the OH content of 1 gram of sample. As this definition has little meaning in the near-infrared method, results have been calculated and reported as milligrams of OH per gram of sample.
APPARATUS A N D MATERIALS
Spectrophotometer. -4 Cary Model 14 spectrophotometer equipped with a n absorbance slide-wire v a s used. Quantitative d a t a were obtained a t a scanning speed of 10 A. per second, and a t a slit-control setting of 15. T h e slit, width a t the analytical n a v e length was 0.1 mm., corresponding t o a 3.5-A. spectral slit width. T h e instrunient was swept a i t h dry nitrogen to reduce absorption by a t mospheric water vapor. T h e cells used were 10 cni. in lengt’h with sealed Corex end w i n d o w . Solvents. Baker analyzed carhon tetrachloride and Natheson Coleman and Bell tetrachloroethylene, industrial grade, were used as solvents. Both were purified by the addition of 0.5 pound of anhydrous silica gel per liter of solvent, shaking and filtering before use. Alcohols. T h e fatty alcohol standards used for calibration were middle cuts taken from t h e distillation of commercial alcohols. Their puritirs were established by gas-liquid partition chromatography and their hydroxyl values from replicate analyses using the acetic anhydride-pyridine method. Other hydroxyl compounds were commercial samples. For most of these, no purification was attempted; however. purities were estimated from gas-liquid partition chromatographic data. All VOL. 3 1 , NO. 1 2 , DECEMBER 1 9 5 9
2055
