212
INDUSTRIAL AND ENGINEERING CHEMISTRY DISCUSSION
The samples for analysis were not all analytically pure. Since there was insufficient time for their purification, it was decided to determine their nitrogen content by some accepted analytical method. Friedrich’s method for nitrogen determinations can be applied to a wide diversity of substances and for this reason was used as the standard by which results by the potassium iodide method could be compared. Results by both methods agree very closely. Even though some of the samples tested are volatile and one might egpect losses from the relatively high temperatures employed in open flasks, such is not the case. Compounds that have a nitro group in addition to the nitrile group yield all their nitrogen. Further work will be undertaken to determine whether the method can be applied to nitro compounds in general. Other types of nitrogen compounds which require special treatment before Kjeldahl digestion were also analyzed by the potassium iodide method, but sometimes with unsuccessful results. -111 the nitrogen in an azo dye, naphthalene-8-azo-p dimethylaniline, was recovered, whereas only part of the nitrogen of rn-xylene-azo-,&naphthol was so obtained. It seems that the position of substituent groups in these azo compounds may hinder attack by these reagents. Unsuccessful results were also obtained with hydrazine, pyridine, and inorganic nitrates. The presence of a few milliliters of water does not interfere with the analysis, but large dilution has a deleterious effect. Subsequent to the development of the above method it was de-
Vol. 17, No. 4
cided to determine the nitrogen due to nitrates in a mixture of nitrates and nitriles, using the standard salicylic acid-thiosulfate method ( 1 ) . It was found that the nitrile nitrogen was quantitatively recovered. Four nitriles were then analyzed by this salicylic acid method with results that compare well with the potassium iodide and Friedrich’s methods (see Table I). SUMMARY
Nitrogen has been determined in nitrile compounds by reduction with potassium iodide and sulfuric acid preliminary to digestion by the Kjeldahl method. No special technique or apparatus is required. Results by the new method compare well with those by the Friedrich method and can be obtained in much less time. The nitrogen in nitro groups substituted on aromatic compounds interferes by being reduced by the potassium iodide. The nitrogen of pyridine, hydrazine, nitrates, and certain azo dyes is also partly reduced. LITERATURE CITED
(1) Assoc. Official AQ. Chem., Official and Tentative Methods of
Analysis, 5th ed., p. 26 (1940). (2) Drushel, W. A., and Brandegee, M. M.,Am. J. Sei. (4), 39,398 (1915). (3) Dumas, J. B., Ann. Aim. phys.. 2 , 198 (1831).
(4) Fleury, P., and Levdtier, H., Bull. SOC. chim., 37, 330-5 (1925). ( 5 ) Friedrich, A., Kuhaas, E., and Schurch, R., Z. physiol. Chem., 216,68-76 (1933). (6) Guillemard, H., BUZZ. SOC.chim. (4), 1, 196-200 (1907).
Determination of W a t e r in Hydrocarbon Gases HARRY LEVIN, KARL UHRIG, AND
F. M. ROBERTS, The Texas Company,
A method is described for determining water in normally gaseous hydrocarbons. I t i s based on the observation that when a gas containing moisture is contacted with cold dehydrated acetone, the water is retained b y the acetone, in which it can b e determined b y reaction with acetyl chloride, titrating the liberated acid. Olefins and diolefins d o not interfere and provision is made for correcting for interference b y acidic or basic constituents of sample.
A
STUDY of plant operations to determine factors affecting catalyst life made it important to have a method for determining the water content of normally gaseous hydrocarbon charge stocks. The requirement that it be independent of the variable composition of the test gas eliminated from consideration most of the methods proposed in the literature.
A dew-point method, involving wet- and dry-bulb thermometers or thermocouples, was proposed by Deaton and Frost ( 2 ) . Presence of high-boiling hydrocarbons interferes with such a method. Perry (8) condensed the hydrocarbon in a cooled weighed trap, evaporated the gas, and considered the increase in weight to be water, but stated the method is unsatisfactory if the samples contain heavy ends. Evans and Davenport ( 3 ) described a manometric method for water in gases removed from oils by evacuation, brtsed on reduction in the pressure of the gas upon exposure to a film of lithium chloride monohydrate. The manometer measurements are apparently applied to gas containing rather high concentrations of water and is unsuitable for the low concentrations with which we are concerned-namely, &s little as 0.001%. Todd and Gauger (f3) recommended determination of water vapor by near infrared absorption spectra, which requires rather elaborate apparatus. Silica gel and other activated drying agents are sometimes recommended. However, such absorbents are restricted to the determination of water in nonhydrocarbon gases, since they also absorb hydrocarbons (11).
Chemical methods are preferred by some investigators because they are specific for water. Henle (6) described an involved
Beacon,
N. Y.
procedure employing aluminum ethylate. Calcium carbide has long been used because of the ease with which it produces acetylene on exposure to water, the latter being estimated dy measuring the acetylene gasometrically (9), colorimetrically as cuprous acetylide (5), or gravimetrically as copper oxide (f4)‘ Such methods are unsuitable for the present purpose because of the nature of the samples and the small amounts of water involved. Bell (1) described a method utilizing the hydrolysis of a-naphthoxydichlorophosphine and Ross (10) used benzoic anhydride. Both methods are tedious. h test based on the change in color of cobalt bromide on hydration was proposed by the Natural Gasoline Association of America ( 7 ) , but the color changes are deceptive and uncertain. Fischer (4) used a methyl alcohol solution of iodine, sulfur dioxide, and pyridine, with which water reacts to form acid 2HzO
+ SO2 + Iz = His04 + 2HI
the water in the sample being estimated from the iodine consumed in a direct titration employing the iodine color as indicator. Roth and Schulz (11) use magnesium nitride to determine moisture in gas from the ammonia liberated.
MaN2
+ 6 H z 0 = 3Mg(OH), + 2SH,
Smith and Bryant (12) utilize the fact that acetyl chloride in the presence of pyridine reacts quantitatively with water to produce 2 moles of acid and with absolute alcohol t o produce 1,
+ HOH + o
x
COCHi \Cl / +ROH+
CHaCOOH
+ CHsCOOR
the increase in acidity of the sample over the blank with alcohol bPing equivalent to water in the sample. This formed the basis
April, 1945
ANALYTICAL EDITION
of the following method which has been adopted for determining water in normally gaseous hydrocarbons. The chemistry is the same as that of the previously mentioned authors, what novelty there is being in the apparatus and technique employed in the preliminary operation of collecting the water. REAGENTS
Pyridine, c.P., containing as high as 1 mg. of water per ml. is satisfactory; C.P. acetyl chloride 0.75 molar in toluene (approximately 60 ml. of acetyl chloride per liter of dry C.P. toluene) ; absolute ethyl alcohol; 0.10 N sodium hydroxide in water; 1% phenolphthalein in alcohol; Drierite (anhydrous calcium sulfate) ; solid carbon dioxide; C.P. acetone containing 0.5 mg. maximum of Ivater per ml. Since water present in the acetone as well as in the sample reacts with acetyl chloride, high blanks may be obtained which reduce the accuracy of the method. The C.P. grade of acetone dried with calcium chloride still contains too much water and must be specially dehydrated. This is efficiently done by allowing the acetone to stand on calcium chloride for several days to remove the bulk of the water and thus save reagents used in the final dehydration. The acetone is then filtered into a dry bottle where it is shaken for 10 minutes with an excess of acetyl chloride in the presence of pyridine, to bind the acids formed. The unconsumed acetyl chloride is esterified by adding amyl alcohol to the bottle and shaking for 10 minutes to form an ester of a higher boiling point than acetone, the latter being then recovered by fractional distillation, with precautions to prevent access of moisture. For each gram of water in the acetone approximately 30 ml. of pyridine, 10 ml. of acetyl chloride, and 20 ml. of amyl alcohol are used, these representing a sufficient excess t o ensure quantitative reactions. I n this manner acetone has been dehydrated to contain as little as 0.05 mg. of water per ml., although as much as 0.5 mg. can be tolerated. The dry acetone is very hygroscopic and must not needlessly be left, exposed to the atmosphere. PROCEDURE
The apparatus is assembled as shown in Figure 1, and the pipet
(D closed) and flask are evacuated to 1 mm. of mercury pressure through the third leg of A for 10 to 15 minutes to remove moisture. Stopcock C is then placed in “neutral” (closed to all three legs), and stopcock A turned to cut off the vacuum pump. Air is admitted through the drying tube until the pressure has returned to atmospheric by opening stopcock B to Its three legs simultaneously. With the p1pet still evacuated and stopcock C closed, the Erlenmeyer flask is lowered o u t of place (done best by keeping the pipet clamped in a fixed position) and dehydrated acetone drawn up into the pipet to the 5-ml. mark. The flask is promptly returned to its former position and the weighed sample container is attached t o the open leg of C. The entire system to the valve on the sample container (but not the pipet) is then reevacuated a t -4 for 5 minutes to remove moisture from the tubing and the acetone remaining in the tube below C. Air is again admitted through the drying tube till the manometer indicates atmospheric pressure. Five milliliters of pyridine and 25 nil. of dehydrated’ acetone are quickly introduced into the momentarily lowered flask, which is quickly replaced and then cooled to - 5 7 O to -62’ c. (-70” to -80” F.) with solid carbon dioxide and acetone. After 10 minutes the whole system, excluding the pipet, is evacuated and the pump cut off by turning stopcock A .
213
The entire sample is introduced rather rapidly, by permitting it to expaad and flow through the lower cylinder valve into the acetone. This requires 1 or 2 minutes or less. The sample (maximum 50 ml.) should not be so large as to reach the tip of the delivery tube; otherwise difficulties will be experienced with the subsequent evaporation of the gases. The water which usually freezes in the delivery tube below C must be washed into the acetone before evaporating the gases and this is accomplished by permitting the acetone from the pipet to be drawn into the flask. The cooling bath is now removed and the contents of the flask are agitated for about a minute, without removing the flask from the pipet assembly, to ensure extraction of the water from the condensed gases which usually are not soluble in the acetone a t the temperature of the cooling bath unless they are rich in olefins. The cooling bath is replaced, and after 5 minutes, evaporation of the gases may be started. The controlled evaporation requires some care. Kith the flask in the cold bath, it is subjected to vacuum applied a t A and when the manometer indicates subatmospheric pressure the cold bath is lowered out of place and pumping is continued until most of the gas is evaporated, tvhich is noted in the flask or by behavior of the manometer. It is necessary to start evacuating the flask while it is in the cold bath to prevent too active boiling and niechanical loss of water. During the pumping of the gases the manometer indicates a pressure corresponding roughly to the vapor pressure of the acetone-gas mixture a t the temperature of pumping. This pressure is considerahly higher than the absolute pressure of 1 mm., to which the system had originally been evacuated, and varies with the nature of the sample but will remain fairly constant until about 90% of the gas has evaporated and then the manometer will indicate increasing vacuum. .4t thispoint the vacuum pump is cut off by turning stopcock A , a positive pressure of about 20 mm. of mercury is permitted to build up in the flask, and the residual gases are gradually eliminated through the drying tube, the positive pressure being maintained a t all times by careful manipulation of stopcock B. The flask, which mill have come t o room temperature, is removed from the system and quickly closed with a glass stopper. If removed while it is below room temperature, moisture from the air will condense in it and ruin the determination. The sample container is now disconnected and 5 mi. of dehydrated acetone are drawn in and shaken for a few seconds and the cylinder washings are added to the contents of the flask through the tube by which the sample was introduced into the reaction flask. This is necessary because noncondensed hydrocarbons can contain more moisture than liquefied gaies can hold in solution a t the same temperature; thc excess separating and
Figure 1.
Diagram of Apparatus
INDUSTRIAL AND ENGINEERING CHEMISTRY
214 1.
Table
Run No.
Determination of Water i n Gases Containing 0.9% of A c i d i c or Baric Material Acidic Material
Gas
HC1 HC1 HC1 HIS HnS HIS HzS CHsSH CHaSH CHISH
1 2 3 4 5
6
k
9 10
Water Present Found
MQ.
MQ.
16.4 12.7 23.2 11.0 27.4 11.5 10.0 10.1 8.4 17.4
16.9 13.1 23.5 11.2
27.5 11.4 10.2 9.8 8.5 17.1
Alkaline Material
:4nlo LHio
Nk
NI
-~ Table
II. Effect of Rate of Parmge of Gas on Recovery of Water
Iiun No
Gas Tested
Rate
Present
L./hr.
lug.
Water
Found MQ.
adhering to the walls of the cylinder may otherwise be lost from the water determination. Sample size is obtained by weighing the container. Ten milliliters of 0.78 molar acetyl chloride in toluene solution are added to the Erlenmeyer flask, the contents of the stoppered flask are shaken and allowed to stand 3 minutes, and the excess of acetyl chloride .is decomposed by adding 1 ml. of absolute ethyl alcohol and agtatlng. After standing 5 minutes, 25 ml. of absolute ethyl alcohol are added, to produce a homogeneous solution, and the mass is titrated with 0.1 S sodium hy&oxide to phenolphthalein. A blank is run in the manner of the determination on all the reagents. The increase in acidity of the test over the blank is a measure of the water in the sample. If the water content of the sample is known to be low, less acetyl chloride may be taken to avoid high blanks. Four milliliters of the reagent will permit determining up to 0.05% water with one 50-ml. buret filling. If the sample consists of hydrocarbons which do not condense a t the temperature of the cooling oath the following modifications are necessary: I n charging the sample a,pressure of a p proximately 20 mm. above atmospheric is permitted to build in the system,.stopcock A being adjusted t o pass the gas a t the rate of 30 liters maximum per hour, maintaining this pressure. The gas is measured (cu. ft.) with a wet gas meter which is attached to stopcock A and the gravity of the gas is determined. The gas inlet tube is washed down wlth 8 cc. of dehydrated acetone from the pipet by applying a gentle suction, as previously described. The contents of the Erlenmeyer are allowed to come to room temperature and further treated as above. The blank in this case is run on 30 ml. of acetone. 4 determination in duplicate requires about 2 hours. Typical results by this method are given in Table 111. If a sample contains acidic material correction must be made. A weighed amount of sample is condensed on 35 ml. of dehydrated acetone and 5 ml. of pyridine, as already described, and the gas allowed to evaporate takmg the precautions previously given. Tiventy-six milliliters of absolute ethyl alcoho! are added and the mixture is titrated with 0.1 N sodium hydroxide using phenolphthalein. It would be ideal if one could take portions of equal mass for the determination of acidity and for water, but this being impractical the volume of sodium hydroxide used in the acidity titration is corrected to what it would be for the quantity of sample used in the mater determination and this is added to the blank. I n the course of the present work no plant sample was found to contain acid nor alkali; therefore a number of blends were pre-
Vol. 17, No. 4
pared to contain approximately 0.2% by volume of acidic or basic materials that could conceivably be present in such gases. Determinations of water in these blends yielded satisfactory results (Table I). PRECAUTIONS
To prevent bumping and mechanical carry-over of water the gas should be thoroughly cooled before pumping is started and the cold bath should not be removed until the flask has been evacuated. Sometimes bumping occurs after the solution has warmed, particularly if particles of stopcock grease or rust from the sample container have been carried into the flask, but this may be overcome by replacing the bath until the mixture is again cool. Bir must be completely excluded from the system while it is evacuated and cold. After condensed gases have been removed, the system should be kept closed until a positive pressure builds up in the flask and then it may be opened, when necessary, through the drying tube. . Pipets must be uniformly dry; this is ensured by drawing laboratory air through them for 5 minutes before using. Noncondensable gases should not be charged faster than 30 liters per hour (Table 11). The large difference between the solubility of water in a liquefied hydrocarbon and the quantity of water possible in the vapor in equilibrium with the liquid phase makes it imperative that portions of liquefied samples should not be taken from the vapor side of a container. It is safest to use the entire sample and include the acetone washings of the container. CALCULATIONS. 1 ml. of 0.1 N NaOH 0.0018 gram of HzO Water in Samples Which Condense Completely a t the Temperature of the Cooling Bath.
a = ml. of 0.1 W NaOH for titration of sample b = ml. of 0.1 N NaOH for blank c = ml. of 0.1 N NaOH required for acid in sample Water in Samples Which Do Not Condense at the Temperature of the Cooling Bath. Weight % H20 =
+
0.18 X [a - ( b f c)] X (273 t ) X 760 V X 28.32 X G X 1.293 X 273 X P
a = ml. of 0.10 N NaOH for titration of sample b = ml. of 0.10 N S a O H for blank c = ml. of 0.10 N S a O H required for acid in sample
Table Run No. 1 3 3 4 5 6
Ill. Determination of Water in Knowns and Unknowns Sample Cornniercial butane
11 12
Butadiene-1.3
13 14
Mixture of n- isobutane isopentane
+ +
Present
Water
Found
.ug.
NO.
19 13 14 I9 8
20 6
19.2 13 8 13 9 18 9 8 3 20.7
29.2 26.7
29.4 26.8
31.0 20.2
31.0 20.1
2 9 0 2 3
% by wt. Unknown
0.0060-0.0065 0.001~0.0012 0.0041-0.0044 0.0086-0.0090 0.0021-0.0020
ANALYTICAL EDITION
April, 1945 Table
IV.
Effect
of Water Content of Acetone on Recovery of Water from Methane
Water Preaent in Water Added to Dried Methane Acetone Mg. Mg./ml. 2.60 23.7 2.20 19.9 1.56 22.4 0.92 37.6 0.66 22.3 0.62 26.9 0.22 18.3 0.16 32.4 a Corrected for water present in acetone.
215
The amount of water vapor employed was determined from the difference in weight of the humidifier before and after passage of the gas. The entire known was used in each determination.
Wdter Founda
ACKNOWLEDGMENT
Mg. 19.1 10.5 13.8 25.0 12.4 27.4 17.7 31.8
V = volume of sample in cu. ft. G = gravity of sample P = barometric pressure average meter pressure - vapor pressure of water tt t , all expressed as mm. of mercury t = meter temperature, C.
+
The reason for requiring dehydrated acetone in the proposed method is unexplained at this writing. However, numerous experiments have demonstrated the fact that ordinary C.P. acetone is unsatisfactory and that reliable results are obtained if the acetone does not contain more than 0.5 mg. of water per ml. This fact is borne out by Table IV. Knowns were prepared by passing carefully dried gas through
The authors express their appreciation to B. R. Stanerson fer valuable assistance in the initial work. LITERATURE CITED
(1) Bell, R. P., J . Chem. Soc., 1932, 2903. (2) Deaton, W. M., and Frost, E. M., Bur. Mines Rept. Investigat i a s 3399 (May, 1938). (3) Evans, R. N., and Davenport, J. E., IND.ENG.CHEN.,ANAL. ED., 14, 732 (1942). (4) Fischer, K., Angew. Chem., 48, 394 (1935). (5) Hartley, H., and Raikes, H. R., J. Chem. Soc., 127, 524 (1925). (6) Henle, F., Ber., 53, 719 (1920). (7) Natural Gasoline Assoc., Natl. Petroleum News, 24, 38 (April 6, 1932). (8) Perry, c. P.,IND.ENQ.CHEM.,ANAL.ED.,10, 513 (1938). (9) Roberts, R. W., and Fraser, A,, J . SOC. Chem. Ind., 29, 197 (1910). (10) Ross, J., Ibid., 51, 121T (1932). (11) Roth, F., and Schulz, A., Brennstoff-Chem., 20, 317 (1939). (12) Smith, D. M . , and Bryant, W. M. D., J . Am. Chem. Soc., 57, 841 (1935). (13) Todd, F. C., and Gauger, 8. W., Proc. A m . SOC.Testing MateriaZs, 41, 1134 (1941). (14) Vtorova, E. I.,'Sintet. Kauchuk, 4, 29 (1936).
a small bubble counter, which in some experiments was warmed,
cont,aining a small amount of water. The water vapor was carried by the gas and passed with it to the dehydrated acetone.
Assay
OF
PREBENTED before the Division of Petroleum Chemistry at the 105th lleeting of the AMERICAN C H E M I C a L SOCIETY, Detroit, Mich.
Lead and Sodium A z i d e by Cerate Oxidimetry J. W. ARNOLDI, Inspection Board of the United Kingdom and Canada
L
EAD azide is a salt of hydrazoic acid, HN, (aziomide). It is a very sensitive and powerful explosive and is used in percussion detonators and in detonators which are ignited by a flash. Various methods for determining the azide value of lead azide have been proposed and used. At least two procedures based on solution of the sample and reprecipitation of the azide as insoluble silver azide with standard silver nitrate solution have been described. Another more widely used procedure is by determination of the nitrogen, based on the reaction of ammonium hexanitratocerate and lead azide according to the following equation: Pb(N3)Z
+ 2(NHdz.Ce(NOde Pb(NOJ2
-
+ 4NH&Os + 2Ce(N03)a + 3S2
The evolved nitrogen is measured in a water-jacketed nitrometer over water (4). This report is concerned nith describing a procedure based on the reaction of ammonium hexanitratocerate and lead azide, the cerate being added to excess and the excess titrated with ferrous sulfate employing o-phenanthroline ferrous complex as the indicator. REAGENTS
Ammonium hexanitratocerate, (yH4)2Ce(N03)j,molecular weight 548.25, 0.1 N in 1 N nitric acid. Dissolve 04.8 grams of ammonium hexanitratocerate in 60 cc. of concentrated nitric acid (70% specific gravity 1.42) and 40 cc. of water. Stir well. Add 4 cc. of nitric acid plus 96 cc. of water and stir well. Dilute slowly t o 1 liter with water, stirring continuously. Protect solution from light ( 2 ) . Ferrous sulfate, 0.1 N in 6 N sulfuric acid. Store solution under hydrogen. 1
Present address, 59 Emerald Crescent, New Toronto, Ontario, Canada.
o-Phenanthroline ferrous complex, indicator solution. T o 1000 ml. of ferrous sulfate, 0.025 molar solution, add 14.85 grams of o-phenanthroline monohydrate, C ~ Z H.-H20 ~ N ~(3). Sodium oxalate (primary standard grade), supply dried a t 100" C. for 2 hours. Potassium dichromate, 0.1 Y solution, prepared from accurate weight of dried reagent. STANDARDIZATION OF AMMONIUM HEXANITRATOCERATE SOLUTION
DIRECThfETHOD WITH SODIUM OXAL.4TE ( 2 ) . Weigh accurately 0.3000 gram of primary grade sodium oxalate, previously dried for 2 hours a t 100" C., and place in a 250-ml. Erlenmeyer flask. Moisten with 10 ml. of distilled water, add 75 ml. of 1.0 molar sulfuric acid, and run in 50 ml. of ammonium hexanitratocerate from a buret. Heat to 50" and allow to cool to room temperature. Add one drop of the indicator and titrate the excess ammonium hexanitratocerate with approximately 0.1 N ferrous sulfate solution prepared as above. Titrate 50 ml. of the cerate solution with the ferrous sulfate solution, following the above procedure.
Calculations.
Where a = ml. ferrous sulfate required to reduce 50 ml. of cerate solution b = ml. ferrous sulfate solution required to reduce excess cerate solution w = weight of sodium oxalate Equivalent weigiit of Xa2C20c= 67.01 w x 1000 Cerate normality = 6 7 . 0 1 X (50 ISDIRECT METHODWITH 0.1 N SOLUTIONOF POTASSIUM DICHROMATE ( 2 ) . Measure out 50 ml. of the dichromate from a calibrated buret or pipet into a 250-ml. Erlenmeyer flask, and dilute to 100 cc. with distilled water. Add 2 drops of the indicator and carry out titration with ferrous sulfate solution, 0.1 N in 6 N sulfuric acid. Having obtained the relationship between the ferrous sulfate solution and the standard dichromate solution,
q)
