ANALYTICAL CHEMISTRY
1014
tion under field conditions, the methods appear to be sufficiently general to provide a basis for the design of a variety of instruments for many chemical metering, analysis, and control uses Continuous titration by competitive rates of addition of the titrating agent can be achieved in several ways, but the electrolytic method of introduction has much to recommend its use. It iq not difficult to devise ways in which electrolysis can enter into many analytical titrations (12) in either static or continuous flov systems. The instrument described in this report can be used for the continuous determination of gases such as hydrogen sulfide, sulfur dioxide, and acrolein in the range above 0.1 p.p.m. By slight modification of the apparatus, the halogens and carbon monoxide may be determined. ACKNOWLEDGMENT
The authors R ish to acknou ledge the assistance and eiicouragenient of their colleagues C. IT. Gould, Jr., \V. H . Eberhardt, J. IT-.Sease, G. Holzman, W. Schlinger, and R. Mills. They are indebted to C. G. Siemann and E. H. Su-ift, official investigators, for their sponsorship and consultation throughout the period of development of the instrument. They were assisted by H. Y. H Aircraft Assemblies, Glendale, Calif., in the construction of thts titrimetcr illustrated. LITERATURE CITED
(1) Briglio, A., Jr., Brockman, J. A., Jr., Schlinger, W., and Shaffet,
P. h.,Jr., U. S.Dept. Coninierce Offive of Publication Board. OSRD R e p t . 6047, PB 5925,1945. (2) Briglio, A, Jr., Brockman, J. -4., Jr., and Shaffer, P. A,. .TI , Ibid., OSRD Rept. 6183, PB 5940, 1945. (3) Epstein, J., Sober, H. A., and Silver, S. D., .4x.4~.CHEY..19, 675-7 (19471. (4) Gould, C., Re’denian, C., Shaffer, P. A,, Jr., Brocknia~i.J. -1..
Jr., Holzman, G., and Lee, T. S.,U. S.Dept. Commerce. Office of Publication Board, OSRD Rept. 4627, PB 5939, 1945. (5) Liston, M. D., Quinn, C. E., Sargeant, W. E., and Scott, 0 . G., Rev. Sci. I n s t r u m e n t s , 17, 194-8 (1946). (6) JIacColl, L. A, “Fundamental Theory of Servomechanisms,” New York, D. Van Nostrand Co., 1945. Discussion of feed-
back in automatic control systems. S.Dept. Commerce, OSRD R e p t . 401, 1942.
(7) Northrop, J. H., U.
(8) Ibid., 1444, 1943. (9) Palevsky, H., Swank, R. K., and Grenchik, R., Rev. S c t . Insti i i m e n t s , 18,298-314 (1947). CHEM.,19, (10) Sease, J. W., Niemann, C., and Swift, E. H., A N ~ L 197-200 (1947). (11) Shaffer,P. A,, Jr., Farrington, P. S.,and Niemann, C., I h i d , 19, 492-4 (1947). (12) Szebelledy, L.; and Somogyi, Z., Z. anal. Chem., 112, 313. 323, 332,385,391,395,400 (1938). and Fitt, T.C., ANAL.CHEM..18, (13) Thomas, M. D., Ivie, J. 383-7 (1946), and references given there.
o.,
RECEIVED,\:arch 1. 1948. T h e instruments and experimental results described in this paper are the result of work carried out a t the California Institute of Technology on behalf of the Office of Scientific Research and Development under Contract O E X s r 323. Contribution 1180 froin the Gates and Crellin Laboratories of Chemistry, California Institute of T w h nology.
Automatic Distillation Apparatus for A.S.T.M. Method D-86 F. B. KOLFSON, C. J. PEKTHEK, AND D. J. POMPEO Shell Development C o m p a n y , Emeryzille, Culif. A n apparatus is described which automatically plots a complete distillation curve in accordance w-ith the standard il.S.T.41. D-86 procedure. The operator need only fill the distillation flask with liquid, insert the chart paper, and set the initial heat; the apparatus performs the distillation, recording all required data, such as correction temperature, initial boiling point, end point, and distillation rate. When the distillation is completed the apparatus automaticall? resets itself for the next test.
B
ECAUSE labor expended in checking refinery products and
unit streams for control purposes represents a sizable part of total refinery labor costs, means are constantly being sought to simplify test procedures and release laboratory and operating personnel for other work. One such development is this automatic distillation apparatus. The standard method of test for the distillation of gasoline, naphtha, kerosene, and similar petroleum products as crtahlished by the American Society for Testing Xaterialr provides for manual operation of a simple laboratory still. The procedure is tedious and demands constant attention from the operator if all provisions of the method are strictly followed. Too fast distillations result in temperature readings being misset! and then estimated, errors may be made in reading and recording temperatures, techniques vary from one operator to another, and the number of samples that an operator can handle is limited. h c cordingly, the development of this automatic apparatus was undertaken so that the difficulties encountered in manual operation would be avoided. Suggestions from refinery laboratory staffs as to how an automatic device was to operate were carefully considered and most of them were successfully incorporated in the apparatus described.
This apparatus was tested both in the development laboratory and a t a refinery control laboratory on a variety of materials including cracked and aviation gaqolines, kerosenes, insecticidr bases, special solvents, and benzene. In general, the distillation curves obtained by the automatic apparatus checked, well withiir the A.S.T.M. tolerancrb, those obtained manually. Initiallv some discrepancies were found betxveen initial boiling point and end point obtained by the recorder and manually, although check runs made with the recorder on the same material were practicallxexact duplicates of each other. Subsequent work on the thermocouple mounting eliminated even these discrepancies. The equipment should find wide use, not only in refinery control laboratories, but also in still control houses where the operatoi can save considerable time by running a distillation to check thc performance of a column. Ill addition, although the present apparatus was specifically designed to perform only B.S.T.11 I)-86 distillations, slight modifications such as variable distillation rate control and substitution of warmer fluid in the condenser bath in place of ice, can easily adapt it to a variety of specification distillations encountered in the refinery. It is expected that its ultimate capabilities can be determined only by extended usc in laboratories and refineries.
V O L U M E 2 0 . N O . 11, N O V E M B E R 1 9 4 8
1015
8. A u t o m a t i d y determining the 5-nL residue point and maintaining constant heat thereafter. 9. Determining the final boiling point (E.P.) from the maximbm temperature reached on the curve and aut.omatical1y returning all mechanisms to starting conditions. APPARATUS
The recording and electronic components of the automatic distillation apparatus were designed t o fit the available space within the outline dimensions of a standard Precision Type 4730 Front view distillation apparatus (made by Precision Scientific Company, 3737 West Cortland St., Chicago 47, 111. Arrangements have been made with this firm for the manufacture of the automatic distillation apparat,us for general sale) as shown in Figure 1.
rouna eommeroiai sppi~cauur~ UL
O.LE
uuilitiu nliailji).
A.S.T.M. REQUIREMENTS
The American Society for Testing Materials standard method of test for distillation of pasaline, nwhtha, kerosene, and similar . petroleum products, A.S.T.M. Designation D-86-45, sets up standards of apparatus, preparation of apparatus, and proeadurr: such that, quotingfromparagraph 5 : With proper care and strict attention to details, duplicate results obtained far initial boiling paint and end point, respectively, should not. differ from each other by more than 6 " F. (3.3" C.). Duplicate readings of the volume of distillate collected in the cylinder when each of the prescribed temperature points is roached should not differ from each other by more than 2 ml. In ease observations are made on the basis of prescribed percentagc points, the difference in temperature readings shodld not. exceed the amount,s &valent to 2 ml. of distillate a t each point i n question. Allrequirements of the method are followed in detail; the most. essential have been met by the following:
1. A specially designed heater to permit rapid changes in temnerature required by automatic heat control. 2: A thermocouple mounting designed to duplicate the thermal c:haracteristios of standard A.S.T.M. mercury-in-glass thermc,meters. 3. Air cooline of the distillate receiver housing to maintain the rec 4. to brir 1"s.
Recording, by means of an inked dot on the chart the "correction temperature" 2 minutes after starting. 6. Recording the first drop temperature (I.B.P.) as the start of the distillation curve and thereupon placing the distillatc e contact with the SDOut of the condenser tube. gradur~ t in 7. Tracing a complete c u k e of vapor temperature against distillrite volume, maintaining automatically the correct distillat,ian nLte, and marking the curve with distinctive timing marks for evc'ry minute and 10-minuteinterval.
The flask, condenser, and ice water h i t h are all as originally provided in the precision apparatus. The air-cooled distillationveeeiver and recorder compartment is closed o f fwith a glass-faced door which permits observation of the equipment and of the curve being traced during operation. The motors for the pen carriage and recorder drum, and the tubes relays, and other electronic parts for the recorder are mounted'in the assembly shown in Figure 2. The top view of the apparatus (Figure 3) shows t,he upper deck of t,his xssemhly as well as the heater control and pyrometer sections which have been removed from the case. In this photograph the position of the flask, thermocoup!e, condenser, and sir-cooling ooil can also he seen. The functional block diagrmn,(Figure 4) shows all Lhe components required for the automatic distillation. The operator placcs paper on the chart, drum, charges t h e flask, sets the initial heat, and presses the start button. Thxs applles power to the hoater and starts the time marks motor. During the interval between 5 and 10 minutes the first drop comes over and partidly intercepts a light, beam focused on a phototube mounted near the top of the graduate. The associated amplifier then energiecs a solenoid which simultaneously places the graduate in cantitot wit.h thc condenser discharge tip and places the pen on tho paper. It also supphes power to the volume "follow-up" motor. As subsequent drops come aver, they increase the height of the meniscus in the graduate whiclr intercepts a second light beam focused on another phototuhc. This phototube and a pen are mounted on a carriage which is moved upward hy a vertical screw rotated by a reversihln motor. Thc srnsitivitv of the phihotuhc-
1016
ANALYTICAL CHEMISTRY
Figure 3. Top View of Automatic Distillation Apparatus Relay deck end -ling oompmmsnt c o v e s rsmosed end hsat control and remder section withdrawn fmm cabinet
r
amplifier system is such that changes in level of the order of a few thousandths of an inch are followed, resulting in a smooth curve with no discernible steps. Upper and lower limit switches &re actuated by the pen carriage, &s is the switch which turns off the heat-rate tiFing motor a t the 95% point. The requirement of Method D-86 for heat regulation based on distillate per unit time is solved by making heater power a funetion of the voltage between the sliding contacts of two parallelconnected potentiometers, one of which is driven a t a constant rate by a synchronous motor while the other, attached to the volume fOhN-Up and pen osrriage, changes directly with the distillate level (volume). This differential voltage varies the output of a pair of thyratrons controlling a saturable reactor which in turn controls the heater current. The slider of the potentiometer driven by the timing motor is adjustable from the control panel, so that the initial hest can be set. When the "start" push button is operated, the heater is turned on at the Bet value, where i t stays until the first drop comes over and starts operation of the timing potentiometer and volume follow-up system. If the volume potentiometer rate is correct there is no increase in hestcontrolling output voltage. If, however, the distillate is coming over too slowly, the volume potentiometer lags behind the timing potentiometer and the differential voltage increases so as to increme the heat; conversely, if the distillation rate is too high, the volume potentiometer advances in position relative to the timing potentiometer, decreasing the differential voltage, which in turn lowers the heat until the distillation rate is again correct. When the distillate level reaches the 95% point, the switchactuating rod operates the timing motor disconnect switch and the slide on the volume potentiometer contacts a sleeve over the resistance coil which prevents any further change in potential. The heat is thus held constant a t the value attained at the 95% point &s specified. The temperature-recording mechanism consists of a potentiometer slide wire mounted directly on the recording drum, with the usual standard cell and bridge and cold junotion compensating resistors and a Brown Electronik amplifier for converting the thermocouple direct voltage to a n alternating current voltage of proper phase and magnitude to drive the drum motor. A friction clutch on the drive shaft allows unlimited angular motion in the direction of increasing temperature, but operates the "end-point" switch, shutting down the equipment and returning the volume
1
Figure 4. Functional Block Diagram
1017
V O L U M E 20, N O . 11, N O V E M B E R 1 9 4 8 follow-up system to the starting point, a short time after the chart drum has reversed its direction, which it does after passing the maximum end-point temperature. Another synchronous motor with cams and microsn-itches provides a connection which momentarily drops the pen on the paper 2 minutes afte starting to record the correction temperature.
i
3 0 GAUGE IRON-CONSTANTAN GLASS-COVERED THERMOCOUPLE WIRE APPROX. 36" LONG
?-
and liquid combination, which it should in order to have the carriage start off readily from true zero; ( 2 ) for small volumes (heights) reflections from the bottom cause the carriage to overshoot the meniscus level. Both difficulties have been overcome in the special graduates, shown in Figure 6, which are constructed by sealing in as a bottom, a flat glass disk with polished edges and with surfaces ground to reduce reflection. Black lacquer is applied t o the under side to reduce reflection further. Since, with the direct pen connection used, the height of the graduated portion of the receiver must be the same as the volume axis of the distillation chart, i t is necessary to use precision-bore tubing stock for the graduates. The exact height of the graduates was dictated by the available stock size of such tubing. This tubing has an inside diameter of 1.0391 * 0.0002 inch corresponding to a height of 7.20 inches for 100 ml., which falls within the limits of 7 to 8 inches (17.5 to 20 cm.) as mecified bv A.S.T.M. standards. Therefore, the charts were made upon fhe scale of 7.2 inches for 100 ml. Heater. The requirement of rapid response to power input for
Q
6-7mm O.D,3mm I D y705-2 PYREX CAPILLARY TUBING
SMOOTH GLASS SEAL TO KOVAR
K O W TIP SEE OETAfL -COPPER
BRAZE, WITH BOFAX FLUX THERMOCOUPLE WIRES TO KOVAR TIP FINISH SMOOTH
Figure 5. Kovar-Tipped Thermocouple
GLO-TECK PRECIS10 N BORE TUBING
~
Connections are also provided for supplying to the pyrometer circuit every minute a small unbalance voltage which momentarily unbalances it, producing small pips or time marks on the curve. Slightly larger unbalances are produced every 10 minutes to identify the 10-minute marks. SPECIAL CO\IPONE>TS
Thermocouple. To duplicate the thermal characteristics of a mercury-in-glass thermometer, it is necessary that the thermocouple mounting resemble the glass thermometer not only in physical size and shape but also in heat capacity and thermal conductivity. The thermocouple mounting shown in Figure 5 matches the performance of a glass thermometer in all respects.
'0
11 1
~
I
110'TH'K. GLASS BOTTOM, ROUGH GROUND SURFACES W I T H POLLSHED EDGES CAREFULLY R I N Q SEALED TO T U B E TO E L I M I N A T E O P T I C A L DISTORTION.
1 i I
C E M E N T GLASS TO BASE WITH L I T H A R G E AND GLYCERINE CEMENT.
-
1 - 3 / 0 * 0 D X I - 77/32' / 3 2 ' I . '9.0. O.
-
5/16*DIA
HOL+-E/'-
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____ .?-$A' D l 4
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-1 J1
- 1 THIS D I M E N S I O N HELD BY ASSEMBLY JIG
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The Kovar tip is bored out to have the same heat capacity as a thermometer bulb (heat conductivity here is not important); the glass stem (glass must be used here to obtain the desired characteristics) has the same capacity and conductivity as a standard thermometer. A brass bulb and stainless steel stem have also been tried and found to give incorrect temperature for some boiling ranges. Because the A.S.T.M. standards recognize a low range thermometer (30" to 580" F.) and a high range thermometer (30" to 760' F.),these two ranges are provided. The temperatures reported on A.S.T.L\I. distillations are in error by the amount of emergent stem error, and in addition, the high and low range thermometers have different emergent stem errors. A standard thermocouple e.m.f. chart is therefore not applicable, and the emergent stem errors and thermocouple e.m.f. values appearing in Table I were used in making the recorder charts, which are distorted correspondingly. Special Graduate. As might be expected, difficulty is encountered a t the zero volume level when an ordinary graduate is used. The two maindifficulties are: (1)thebottomof the graduate does not intensify the light beam in the same manner as the tube
Figure 6. Graduate
Table I . Calibration l h t a for Airtonintic Distillation Equipment Distorted to Provide Emergent Stem Error Distillation Range
Low
Indicated Temperature, F.
32
50 100
200
300
400 500 580
High
E M.F., Millivolts
0
0.52 1.96 4.97 8.10 11.34 14.65 17.32
Emergent Error, Stem F
0 0 0
1.6
5.2 10.7 18.1 25.4
ANALYTICAL CHEMISTRY
1018 ____
-
I
-~_____-
-
I
I
tical for this type of apparatus, a5 it requires no manipulation or attention on the part of the operator
HOLE FOR BOTTOM OF FLASS
-JL/4'
I
DISCUSSIO\ OF RESULTS
This equipment was tested at a refiner) corltrol laboratory and three of the charts obtained at that time are shown in Figures 8, 9, and 10. These curves were run using the stainless bteel thermocouple which was later found to be unsatisfactory. Manually obtained result> are L 4 STUPAKOFF CYLINDRICAL supelimposed (dots). CERAMIC INSULATORS 4 5 m m DO. 1 WITH 2 1 2 5 m m HOLES X 2.5 INCH Figures 11 and 12 were run a t the development LONG SUPPORTED O N A ALUMINUM CHROMEL WIRE GRID. laboratory, using the Kovar and glais thermoHEAT SHIELD couple mounting. The plotted pointq (shown by dots) were obtained from duplicate runs, employing manual obbervation, with a carefully calibrated il S.T.M. thermometer using the autoFigure i.Flask Heater matic heat control of the apparatus. These curves -. shon tsuxllent agreement between automatic and manual temperature recording a t all points on the chart. C'urvei traced from repeated run$ on the same sample are practically identical. Figure 13 shows the same sample as Figure 12, but the same -tainles,i steel thernlocouple mounting was used as at the refinery. This particular sample magnifies the end point error due t o the steepness of tht, curve a t that point, an error which had not hec~i detectr~li n pit'vious runs a t either laboratory.
TERMINALS
A
0
on
8 H 2 8
i
,MODIFICATIONS
5: IO
PO
40
30
60
x)
m
80
90
00
Volume Recovered ( m l )
Figure 8. Aviation Gasoline I.B.P. I Automatic Manual
Control laboratory perdonnel have suggested that additional ordinates on the chart, particularly for the last 10 nil., would increase the accuracy of reading the recovered voluniv.
F.B.P. 2790 2720
108' 108'
J
1
IO
20
30
40
50
60
70
80
90
100
Volume Recovered [mr)
Figure 9. €'etroleiim I Automatic
Manual
Solbent
I.B.P. 3696 362
F.B.P. 430' 423'
the heater was solved by the cunstruction shown in Figure 7, as designed by ITr. B. Milligan of this laboratory. Cooling System. The A.S.T.M. standards require that the graduate or receiver be maintained at a temperature between 55 'and 65 F.
In the present apparatus this is accomplished by a small blower recirculating air from the enclosed receiver compartment through a cooling tube located in the ice chest. This system delivers 15 cubic feet per minute of air to the compartment and removes heat a t the rate of about 50 watts. I t is controlled at 60" F. by a small thermost.atlocated at the inlet to the blower. This thermostat is shunted by a resist'or which operates the blower a t reduced speed, maintaining reduced air circulation when the contacts of t,he thermostat have opened. Yse of a series resistor possesses the further advantage of grratly rcducing sparking at thci contacts. It would be possible to place the receiver in a transparent water bath maintained at the required temperature, as described in the A.S.T.M. standards. The phototubes will respond through the transparent bath in the same manner &s in the present apparatus. J Io\vcver, the cold air circulation method is considered more prac-
10
20
I Automatic SIanual
30
40
M
60
m
80
I.B.P.
F.B.P.
90; 91
404' 400'
90
(00
V O L U M E 20, NO, 11, N O V E M B E R 1 9 4 8 -------
1019 A /L
’
-.I
-
I
c--- I I
I
10
20
33
40
50
60
70
80
90
100
Volume Recovered ( m l )
Figure 12. Aviation Gasoline
scribed by Method D-86. Installation of such a control would have the possible disadvantage of one more knob for the operator to set, although a record of the actual distillation rate is always printed on the chart. I t has been demonstrated that the distillation rate for certain gasoline samples tested could be increased to 12 or 15 ml. per minute without seriously affecting the curve produced. Further investigation would be reqHired to determine the desirability of using this increased distillation rate for variouq ,amples. Although every effort has been expended on the present apparatus to duplicate the readings of the mercury-in-glass thermometer in order to duplicate manual operation, other uses for this type of equipment may arise wherein the inherent advantage3 possessed by the thermocouple of small heat capacity and no emergent stem error may be a great advantage. One example i. the special solvents distillation used for narrow boiling rang(’ products, for which the present apparatus could be equipped with multiple temperature ranges of 20’ C. span, and suitable thermocouple p d charts. Such an apparatus should solve the probleni of thermometer lag encountered in observation of the initial boiling point when a mercury thermometer iq used. CONCLUSION
.. n
.
1 I
10
20
40
S
!Idurn*
Figure 13.
50
60
70
80
90100
Reeoveitd l m l )
Aviation Gasoline
General ease of operation combined with good accuracy an(l reproducibility when used to run standard AI.S.T.M.Method D-86 distillations recommends this apparatus as a plant control instrument which can be operated at the still by the operator, a replacement for manually operated equipment in the contrnl laboratory, or a “referee” instrument which can be used to settli. disputes arising from varying laboratory and/or operator terhniques. 4CKiYOWLEDGMENT
\Then distilling low boiling materials a boiling chip is required in the flask to prevent superheating, a condition resulting in a relatively large quantity of distillate coming over as the first drop, and causing the automatic heat control to decrease the heat to n point v, here distillation may cease entirely. Although on some samples it has been possible to interpret the curve to show a dry point, there are not yet sufficient data available nith the new thermocouple to state positively that this can alm-a>-sbe done. AiB j C O alarm and light could be easily installed to warn the operator, so that he could observe the dry point and so mark the chart. Another possible modification is the addition of a control to produce, automatically, any desired rate of diqtillation. rit prcsent, o n 1 ~one rate i q provided, the 4.5 ml. per minute prc-
The authors \vi41 to extend their thanks to J. A. Wood for his mechanical ingenuity in construction of the recorder components, and to IT. B. Jlilligan for his suggestion of the special “low-lag” heater. LITERATURE CITED
(1) Josten, G. W., U.
S.Patent 1,953,716 (April 3, 1934). Apparatus
for automatically recording volumetric and temperature distillation data. (2) Leeds & Korthrup Co., private communication. (3) U. S. Technical Oil Mission, Reel 6, Bag 2747, Item 2; German Patent application 14,527 (1943). Continuous measurement, and recording of boiling point and gravity during distillation at constant heat input (pneumatic-hydraulic with photoelectric drive). R E C E I V EJDa n u a r y 19, 1948.
Determination of Nitrogen in Organic Materials Application of the Mass Spectrometer S. G. HINDIN’ AND A. \-.GROSSEa, Houdry Process Corporation, Marcus Hook, Pa.
W
I T H the usual methods of chemical analysis, one must quantitatively convert the element sought to some specific compound having characteristic and desired properties, isolate this compound in pure form, and then quantitatively measure the total amount of the compound formed. The procedure suggested herein is analogous to t,he “int,ernal standard” method o f emission 1 Present address, American Sugar Refining Co.. Re,!earch and De\-eIopment Division, Philadelphia 48, Pa. 2 Precrnt address, Temple Research I n - t i t i i t ? , P h i l n r i ~ l g h i n ,P a .
spectroscopy. In such analysis, the ehmcnt sought is determined relative to some major constituent of the sample, or to somc element not present originally but added in known amount. This paper describes a similar internal standard method of analysis for nonmetals in organic materials, in which the mass spectrometer is used as a measuring tool. Basically, the procedure entails these steps: known weight of sample, containing the element to he determined, is taken.
