Determination
OF
LEON DO"
Basic Nitrogen in Hydrocarbon Feed AND
HARRY LEVIN, The Texas Company, Beacon, N. Y .
Treatment of a sample in naphtha solution involved diluting a liquefied snmplc with naphtha, from which basic compounds n-ere extmcted by dilute sulfuric acid using ordinary separatory iunnelG. Good result's were obtained on C, hydrocarbon samples hut when appreciable quantities of CS or lower boiling hydrocarbons weTe presrnt the manipulations were hazardous and impracticalbecauseof the pressuresinvolved. The procedure which proved satisfactory involves condensation of the hydrocarbon sample into a substantially nonaqueous standard solution of sulfuric acid in acetone, evaporation of the hydrocarbon, and titration of the excess acid to methyl red indicator. The condensation is effected by a dry ice-acetone bath (at about -60" C.); constituents not retained a t this temperature are measured on emergence from the condensation flask. Though the lower boiling hydrocarbons are not completely condensed, their basic constituents are quantitatively retained in the nonaqueous acid through which they pass. Sample size is determined from the sum of the condensed and uncondensed portions Of the sample, the former by weighing, the latter by gas metering and gravity determination. The time required to complete a determination on a 400-gram sample is not more than 4 hours.
Ammonia is not retained when very dilute gaseous concentrations are bubbled through dilute sulfuric acid. Storage of such dilute gaseous mixtures in iron cylinders results in loss of appreciable basic nitrogen content. Ammonia and amines in concentrations between 0.000015 and 0.008% calculated as ammonia have been s,uccessfully determined in normally gaseous hydrocarbon feed stocks b y a new method that involves passage of a cooled (about -60" C.) hydrocarbon sample into a substantially nonaqueous standard solution of sulfuric acid, evaporation of the hydrocarbon, and titration of the excess acid with standard alkali. A b o u t 4 hours are required for a 400-gram sample.
T
IthCE impurities in hydrocarbon gases have a serious and harmful effect, upon certain catalytic processes. The elimination of such impurities and control of their concentration are deptmdent upon suitable analytical methods. blf.tllods for determining minute quantities of R-ater ( 1 ) and oxygcn ( 2 ) in such gases have been described and the present puper describes a suitable method for ammonia or other basic nitrogen compounds. 111 the investigation of methods for determining basic nitrogen, two general types of procedure were considered for transferring the basic compounds from the hydrocarbon t o the aqueous media in which they subsequently could be determined by conventional methods. Both methods involved aqueous acid ex: traction; in one the sample was treated in the gaseous phase and in the other, in naphtha solution. Where the sample was treated in the gaseous phase, frittedglass scrubbers containing dilute sulfuric acid failed t o retain small concentrations of ammonia. I n a run on 70 grams of hydrocarbon ssmple, in which six such sc-rubbers in series rvere use,l, the first shelved o ~ 0 0 0 0 5of~ ammonia the sixth 0 . 0 0 0 0 4 ~ . I n almost every test t h e second scrubber collectd pr:ictir:iIly as much b 5 the) f i ~ iin thfb writs.
DETAILS OF METHOD
hydroxide, aqueous, 0.02 N . REAGENTS.'Odium by diluting clarified 5070 sodium hydroxide solution with carbon dioxide-free waterand protecting from carbon dioxide with a soda-lime tube. Sulfuric acid, 0.02 N . Prepare by diluting aqueous 4 N sulacid with acetone' Methyl red indicator, a saturated solution of the free acid in 0.1N aqueous sodium hydroxide, PROCEDURE. Half fill the condensing bath with acetone and in it carefully immerse a perforated can containing small pieces of dry ice. Acetone will enter the can through its perforated bottom and rapidly dissipate the dry ice. Remove the empty can, refill v i t h dry ice, and again immerse in the acetone bath, repeating the operations until the effervescence, which is violent a t first, practically ceases. Then add several pieces of dry ice directly t o the bath t o maintain its temperature a t about -60" C. Pipet 20 ml. of 0.02 N solution of sulfuric acid in acetone into the dry condensing flask and a like portion into a 250-ml. Erlenmeyer flask containing 50 ml. of water; the latter serving as blank is reserved until the sample is titrated, when it also is titrated. Stopper the condensing flask with the onehole glass plug and carefully dip i t into the cold acetone bath until all the coils of the flask areimmersed. Remove the flask from the bath, quickly wipe the bottom, set upon a cork ring on a pan balance, weigh rapidly Rithin 1 gram, and record as tare weight. Reimmerse the flask in the cold bath and assemble the apparatus as shown in Figure 1. The assembly may be mounted on a suitable rack for convenience in carrying to and from sampling points. Completely fill the gas-sampling pipet with water, as well as the loGrer arm of the tee t o which i t is attached. This may be conveniently accomplished by upward flow. Close stopcock Sc and leave stopcock S6open t o the water reservoir. Introduce the sample through the Ascarite scrubber, and by manipulating stopcock S, bypass the condensing flask for a few moments to flush the tubing through stopcockS3. A rate of
GAS METER
Figure 1.
Sample Collection Unit
593
594
Vol. 18, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
passage as high as 170 liters (6 cubic feet) per hour as indicated by the gas meter has been found t o yield good results. Open and record the initial reading of the meter, its temperavent SI, ture, and the barometric pressure. Readjust stopcock S2, close SI, and start introduction of the sample into the flask. iidd pieces of dry ice as required to the condensing bath t o maintain its temperature a t about -60" C. If the sample is completely retained in the condensing flask, the meter will, of course, indicate no gas passage. If uncondensed gases are present, take a sample for gravity determination after about 0.2 cu. foot (5663 cc.) have by-passed the sampling pipet and assured purging of air, etc. For a truly representative sample, small portions should be drawn over the entire collecting period after purging, but for most purposes the sample may all be collected a t one time. Regulate stopcocks SB and Sa, so that substantially atmospheric pressure is indicated on the manometer with which the gas meter is equipped. When approximately 1 liter of gas has been collected, detach sampling pipet and determine the specific gravity of the gas against air. When sufficient sample has been taken, stop its flow, detach the condensing flask, and weigh rapidly as before. I n most cases a 400-gram sample is adequate, but when extremely low concentrations are involved, the sample should be increased. Record the new weight and meter reading.
GLASS BRACE-
GLASS ROD PACKING
f LITER FLASK
8MM 9/42 J
Figure'%
P = barometric pressure, mm. of mercury 28.32 = liters per cubic foot 1.223 = weight in grams of 1 liter of air a t 15.6" C. and 760 mm. of mercury This may be simplified to: Noncondensed gas (grams) =
yo basic nitrogen (calcd. as S H 8 ) = ( A - B ) X N X 1.7 grams of sample
where A = ml. of sodium hydroxide required t o titrate the blank B = ml. of sodium hydroxide required t o titrate t h e sample N = normality of sodium hydroxide Grams of sample = grams of noncondensed gas plus grams of condensed gas DISCUSSION
The accuracy of this method is indicated by the typical values shown in Table I. Concentrations of ammonia or amine as low as 0.00001570 and as high as O.OOSyc, calculated as ammonia, have been successfully determined. It is apparent that as the concentration decreases to a minimum, a small titration error will contribute t o a large percentage error. Ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, isopropylamine, and methylethylamine, ranging in boiling points from -33" t o $39" C., xere all used t o prepare known samples for analysis. The quality of the results was unaffected by the nature of the base employed. I n preparing the samples, ammonia and methylamine were measured gasometrically in small sample pipets under controlled conditions of temperature and pressure, and then flushed dut of the measuring pipets Kith the hydrocarbon gas concerned. Samples containing the other nitrogen bases were prepared by adding standard alcoholic or pentane solutions of the base t o liquefied hydrocarbons. Acetone is used to dilute the aqueous 4 N sulfuric acid. The imtial dilution is made with water because it is expected that
Table
where V
cubic feet measured a t meter G = specific gravity of noncondensed gas (specific gravity of air = 1.0000) T = average meter temperature, degrees absolute
I.
Typical Data Obtainled with This Method
E E F
E
G
G a
Composition of blending gases shown in Table 11.
Table Methane
B
c
D
E
=
F
G
Base Calculated as Ammonia, % Taken Found 0.00123 0.00123 0.00022 0.00022 0.00127 0.00129 0.00125 0.00127 O.OQ097 0.00097 0.00147 0.00147 0.000016 0.000024 0.00120 0.00120 0.000137 0.000137 0.00073 0.00074 0 00004 0.00004 0 00003 0.00004 0.00223 0.00227
Base Taken Ammonia Ammonia Ammonia Ammonia Methylamine Methylamine Methylamine Methylamine Ethylamine Ammonia Ammonia Ammonia Ammonia
Blending Gasa A B B C C D E
A
Koncondensed gas (grams) = V X 28.32 X G X 1.223 X 288.6 X P T X 760
T
Per Cent Basic Nitrogen.
Glass Condensing Flask-Evaporation Trap
Gently swirl the flask and set it on a cork ring in a. good hood for evaporation of its hydrocarbons. Remove the one-hole plug from its neck. Pour water through the evaporation trap shown in Figure 2, drain a few moments, and insert in the neck of the flask. Close the inlet tube of :he condensing flask with a short piece of rubber tubing fitted with a glass plug t o prevent ejecting liquid during the subsequent evaporation step. To hasten evaporation carefully immerse the flask in a bath of water a t about 60" C. Less than 45 minutes are required to evaporate the hydrocarbons. Upon evaporation of the sample, add 50 ml. of water to the flask through the trap. Remove the trap a s well as the rubber tubing and plug from the inlet tube. Rinse down the coil or inlet tube of the flask with water, add methyl red indicator t o the flask, and titrate with standard 0.02 N sodium hydroxide. Titrate the blank in a like manner. CALCULATIONS. Noncondensed Gas. (The calculation for noncondensed ga8 is generally sufficient. However, t o be strictly correct, the volume of noncondensed gas V , and it? specific gravity, G, should be calculated t o a dry bisis.)
13.15 X V X G X P
... ... ... ...
12.4
Ethylene 1.6
...
II. Composition of Blending Gases
Ethane
... 37.1 8.4 14.6
...
Propylene 3.3
..,
Iso-
Propane butane Per cent by nolume
100 49.0 44.5 41.0
...
... ...
0.5 1.9
...
n-Butane
...
... 1.5 45.8 12.5
...
0.8
... ...
100
1-Butylene n160IsoISOButane butane butylene pentane 69.7 22.9 2.5 ... 53.5 ... ... . I .
Heavier
1.3Buts liene
,..
46.5
October, 1946
ANALYTICAL EDITION
neutralization reactions will proceed with greatest ease in the presence of water. iZcctone i q wed, because it is a solvent for both liquefied hydrocarbons and water, apparently has no effect upon the standard acid, and lowers the freezing point of the solution to below -60" C. The titer of 0.02 N sulfuric acid In acetone dropped less than 1% in 144 hours. Other solvents, ketones and alcohols, were not so satisfactory for one or more reasons involving high freezing point, poor miscibility, or instability of the titer of the standard acid prepared with them. I t was found t h a t samples cannot be kept or weighed in iron containers, though free of brass valves and fittings, since reaction or adsorption occurs, reducing the base content of the hydrocarbon. Solutions of ammonia in n-butane, kept in iron cylinders, changed from an initially determined value of 0.00081% t o loner and lower values until after 16 hours' storage only 0.0001 R remained. Solutions of methylamine in n-butane, similarly stored, changed from 0.00149 to 0.00103% in 16 hours. Similir iolutions
59s
prepared with these bases, as well as with bases up to and including isopropylamine, but in pressure glass tubing, retained their initial concentrations after storage, demonstrating that loss of base was not due to reaction between it and the hydrocarbon solvent. The Florence flask, equipped with condensing coil, eliminates the need for metal sample containers. ACKNOWLEDGMENT
The authors express their sincere appreciation to S.11.Garrison for her valuable assistance in the preparation of the manuscript. LITERATURE CITED (1) Levin, Uhrig, and Roberts, IND. EXG.CHEM.,ANAL.ED.,17, 212 (1945). (2) Uhrig, Roberts, and Levin, Ibid., 17, 31 (1945). PREBENTED before the Division of Petroleum Chemistry at the 108th MeetN. Y .
ing of the AMERICAN CHEMICAL SOCIETY, New York,
Use of High-Frequency Oscillators in Titrations and Analyses FRED W. JENSEN
AND
A. L. PARRACK
Agricultural and Mechanical College of Texas, College Station, Texas Energy absorption from high-frequency fields forms the basis for a new method of conductometric analyses. Distinct advantages are that this method eliminates the use of electrodes, and that. values may be read directly on a meter. It is very flexible and highly sensitive. A n y changes in ionic or dipole content in ionized or un-ionized solutions may be followed. The electrical circuit i s described and a variety of types of titrations are presented.
/
E
LECTItICAL methods for titrations and analyses are generally limited in their scope and application by the necessity of using electrodes of various types. Galvanic methods usually are restricted to ionized solutions and ordinarily are not usable in organic liquids, particularly if the organic liquid is a very poor ionizing medium. Conductometric methods have a wide field of application but frequent' readjustments are usually required. By using the field of a high-frequency oscillator it is possible to produce ionic or dipole motion without the introduction of electrodes. The energy required to produce this motion causes a change in the oscillator current which is easily measured. Thus when an oscillator is loaded by the introduction of a liquid or a solution into its tank circuit, its characteristics are altered. Chiefly three factors govern the magnitude of the loading: the type and circuit constants of the oscillator, the volume of the solution and its location viithin the tank circuit, and the conductance of the solution due to its ionic or dipole concentration. The changes in conductance during a reaction cause variations in loading, whereby the course of the reaction can be followed. Oscillators differ widely in the manner in which they load. I n Figure 1are shown types of loading curves which can be obtained from various oscillators or even from the same oscillator by changing its frequency or its circuit constants. Conditions which produce linear curves of steep slope are desirabie, since oscillators producing such curves show high and uniform sensitivity throughout their loading range. However, oscillators with such high sensitivity also load out of oscillation readily. Therefore provision for restoring oscillation is highly essential. A study of the characteristics of various types of oscillators ( 5 ) indicated that the tuned-plate tuned-grid oscillator was the most adaptable to analytical work, since it could be made highly sen-
/
LOA31 PJ G Figure 1.
Typical Loading Curves
sitive and yet maintain reasonable stability, and could be readily brought back into oscillation when necessary. ELECTRICAL CIRCUIT
I n Figure 2 is shown the electrical circuit of a tuned-plate tuned-grid oscillator with a sensitive metering system in the positive power-supply lead. A regulated power source furnishes high voltage. Oscillations occur when the two tank circuits, LICI and L z C ~are , resonant a t approximately the same frequency. The condenser, C1,is the primary factor in determining the frequency of oscillation, while condenser C ) controls the excitation to the grid of tube A . Any triode vacuum tube having good oscjllating characteristics may be used. Current flowing through resistance R1 produces the grid-bias voltage. The trimmer condenser, Cs,by-passes high-frequency energy around RI and is adjusted to give maximum sensitivity t o loading in the plate tank circuit. Introduction of the glass tube, T,containing the solution into coil L1 accomplishes the loading. Condensers C, to Cs, inclusive, and choke coil La reduce stray high-frequency
.
