ANALYTICAL EDITION
January, 1945 LITERATURE CITED
Am. SOC. Testing Materials, Method D155-39T. I b i d . , Method D157-36. Ibid.,Method D445-42T. Ibid., Method D663-42T. A m . SOC.Testing Materials Proc., 43, 275 (1943). Am. SOC.Testing Materials, "Standards on Petroleum Products", 1940. Borgmann, C. W., and Mears, R. B., "Principles of Corrosion
Testing", A.S.T.M. Symposium on Corrosion Testing Procedure, 1937. Brown, R. H., and Mears, R. B., Trans. Electrochem. SOC.,81, 465-83 (1942).
Dix, E. H., Jr., and Mears, R. B . , S . A . E . J o u r d , 4 6 , 2 1 5(1940).
5
(10) Hunter, B. F., Ambrose. H. .I..and Powers. K. P..Poiuer. 83. 97-9 (1939). (11) Mardles, E. W. J., Proc. World Petroleum Congress. 2,59 (1933). (12) Mears, R. B., Belt Lab. Record, 11, 141 (1933). (13) Mears. R. B., and Brown, R. H., Trans. Electrochem. Soc., 74, 519 (1938). (14) Mears, R. B . , and Fahrney, H. J.. Trans. A m . Inst. C h m . Engra., 37, 911 (1941). (15) Story, L. G., Provine, R. W., and Bennett, H. T., IND. ENG. CHEM.,21, 1079 (1929). PREBEATED before the Division of Petroleum Chemistry, Sympoaium on Bench Scale Techniques, a t the 108th Meeting of the A U ~ R I C ACNE I ~ M I C A L SOCIETY.New York, N. Y.
Ternary Mixtures of' Three Isomeric Heptanes
A
Quantitative M e t h o d of Analysis
VERLE A. MILLER, Research Laboratories Division, This paper describes a method based on a refinement of the solution temperpture of the hydrocarbon mixture in diethyl phthalate and nitrobenzene, b y which the composition of a mixture containing P,4- and P,%dimethylpentane with 4,4,3-trimethyIbutane may be determined quantitatively, the first two components within 396 and The entire analysis requires the last component within 0.3%. approximately one hour.
F
RrlCTIONAI, distillation, supplemented with curves for other pertinent physical data, is entirely suitable for the analysis of paraffin mixtures up to and including the hexanes, but these methods alone are not adequate for the analysis of certain mixtures of the heptanes (see Table I). Attempts have been made by a great many workers, in several fields of research, to develop adequate methods of hydrocarbon analysis. These include ultraviolet and infrared abeorption spectra (3, 19, 2.2, 24, 15) and Raman spectra (9, 14, 15, $8, sa), and more recently the mass spectrograph has been applied to the solution of i;hi3 problem. Rosenbaum, Grosse, and Jacobson (26) in their work on the Raman spectra of the nine isomeric heptanes, report that analysis of close to 50-50 binary mixtures gave results within 5%. However, an attempted analysis of t b ternary mixture of 2,4- and 2,2-dimethylpent,ane with 2,2,3triwt:thyibutne (the heptane mixture which boils a t about 80" C,;,?even in approximately equal proportions, gave results whirh varied as much as 120/,. This paper describes a method, based on a refinement of the solutios temperature of the hydrocarbon mixture in diethyl phthalate and nitrobenzene, by which the composition of a mixture containing 2,4- and 2,2-dimethylpentane with 2,2,3trimethylbutane may be determined quantitatively, the first two components within 3% and the last component within 0.37,. IC order to analyze such a ternary mixture quantitatively, it is only necessary to determine the solution temperature of the unknown sample in diethyl phthalate and nitrobenzene with en accuracy of ==O.0loC. These temperatures are then used with a series of calibration curves, which were prepared with mixtures of known composition, to determine graphically the percentage of each of the three constituents present in the unknown mixture. The entire analysis requires approximately one hour. HETORY OF APPLICATION OF CRITICAL SOLUTION TEMPERATURE MEASUREMENTS TO HYDROCARBON ANALYSlS
Chavanne and Simon (6) first observed that the presence of aromatic hydrocarbons decreased the critical solution tempera-
General Motors Corporation, Detroit, Mich.
ture of a hydrocarbon mixture in aniline and that the lowering was directly proportional to the weight of aromatics present. Tizard and Marshall (31) introduced the more simple determination of "aniline points", which numerous workers (2, 4, 13, 17, 18, 21, 23) have shown to be of the greatest utility for the determination of the quantity of the various classes of compounds present in gasoline and kerosene distillates. I t has been common practice to employ pure, dry aniline that will give an aniline point of 70" * 0.1" C. for n-heptane and a reproducibility of about 0.1" C. is usually claimed. As compared with freshly distilled aniline, water-saturated aniline may cause a rise of as much as 20" C. in the observed aniline point. Tilitsheyew and Dumskaya (29) studied the method for mixtures of pure aromatic hydrocarbons and mixtures of pure aromatic hydrocarbons with light petroleum distillates. .4ubree (1) used a second solvent, benzyl alcohol, and thus obtained two equations with two unknowns which he could solve for the aromatic content without removal of these hydrocarbons by chemical means. Erskine (12) first used nitrobenzene instead of aniline for the determination of aromatics and'reported that this critical solution temperature decreased with rise in molecular weight instead ot increasing as with aniline. Considerable work on the critical solution temperature of various pure hydrocarbons in one or more of the three solvents, aniline, benzyl alcohol, or nitrobenzene has been done by Chavanne and Simon ( 6 ) , Garner (13), Maman (,El),Edgar and Calingaert (fO),and Wibaut, Hoog, and Smittenberg (33). As far as the author has been able to determine there is no mention in the literature of any attempt to use this valuable and easily determined constant for the quantitative determination of individual paraffin compounds which are present in a mixture, SEARCH FOR OTHER CRITICAL SOLUTION TEMPERATURE SOLVENTS
A preliminary study showed that the spread between the aniline points of pure 2,4- and 2;2-dimethylpentane is only 0.35' C. This agrees well with the value (0.4') obtained by Wibaut, Hoog, and Smittenberg (33) but not with that (1.1") obtained by Edgar and Calingaert (10) (see Table I). In all, 97 compounds were investigated in an attempt to find solvents which would give a wider spread of solution temperetures for these two hydrocarbons. The criteria for such a solvent are: It must be obtainable in a pure state; it should be fairly stable; it must give a solution temperature within a reasonable working range; and it mi=- give a satisfactory end point with B
6
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 17, No. 1
t o permit handling of tlic tube which extended to within 4.8 em. of the bottom of the air Boiling Point, jacket . Hydrocarbon c. Refractive Index, ny Aniline Point, O C. The reaction tube contents 2,2-Dimethylpentane 7 9 . l a 1 . 3 8 2 3 (10. 1 6 ) ; 1 . 3 3 2 2 (27, SS) 7 7 . 7 ( 1 0 ) ; 7 8 . 3 (33) were illuminated by piping in 2.4-Dimethylpentane 80.8 1.3814 (6,SO); 1.3820 038) ; 1.3832 (SS) : the light from an automobile 1.38233 ( 1 0 ) 7 8 . 8 (io);7 8 . 7 (3s) 2,2,3-Trimethylbutane 80.83 1.3894 ( 1 0 ) ; 1.3896 (35); 1 3899 (t8) 7 2 . 4 (10);7 2 . 2 (33) headlight bulb by means of a bent Lucite rod. The bulb and 3,3-Dimethylpentone 86 0 1 3911 7 1 . 0 (IO); 6 9 . 7 (SS) the top of the Lucite rod were 2,3-Dimethylpentane 89.7 1.3920 6 8 . 1 (10, 1 3 . PS); 6 0 . 0 (3.9) enclosed in a water-cooled metal 2-Methylhexane 90.0 1.3851 7 4 . 1 ( 1 0 ) ; 7 3 . 6 (33); 7 2 . 8 ( 6 , 13) jacket. This arrangement elimi3-Methylhexane 91.8 1.3887 1 0 . 5 (10, 13) nated the troublesome light 3-Ethylpentane 93.3 1.3837 6 6 . 3 (10) reflections from the various n-Heptane 98.38 1.38774 7 0 . 0 (6,1 0 ) ; 7 0 . 1 (39):7 1 . 0 ( 1 5 ) curved glass surfaces and per* Data given without literature reference taAeii froni (11) mitted the concentration of the light at the desired observation pcint without introducing any heat into the bath. THERMOMETER A N D STIRRER.The temperature measurements paraffin hydrocarbon. When these conditions were eatisfied were made with a Leeds & Northrup platinum resistance theronly 12 solvents remained to be studied. mometer Xo.8163-A,which had beenstandardized bythe National Bureau of Standards, used with a Type G-2 llueller bridge The solution tem erature of each of 6 isomeric heptanes in S o . 8069 and a Type R galvanometer Xo. 2500-a in a modified equal volume with t i e various solvents was determined with an Julius suspension. With this bridge readings can be made accuracy of about 0.1" C., using an iron-constantan thermodirectly to 0.0001 ohm which corresponds to 0.001" C. For couple and a Leeds & Northrup Type K potentiometer. The this work readings were made to the nearest 0.001 ohm or 0.01a C. hydrocarbon samples were distilled (first 10 to 20% rejected) The top of a 24/25 J ground-glass joint which fits into the top into dry glass-stoppered bottles and were stored in a desiccator of the reaction tube waa blown out into a bulb and to this wm over phosphorus pentoxide. Each solvent was distilled just sealed a glass tube 19.7 cm. long of a diameter that would just before it was used. These data (tabulated in Table 11) indicated permit the glass-sheathed resistance thermometer to pass throu h that only acetyl diethylamine and diethyl phthalate gave a large ( B , Figure 2). To this same bulb was sealed another tufe enough spread between the solution temperature values for 2,4(sealed a t the top) in which was placed an iron core resting on a and 2,sdimethylpentane (1.8' and 1.3", respectively) to make bronze coil spring. To this core was soldered a wire which exit at all possible to use them for analytical purposes. The end tended doxn through the ground-glass joint into the reaction point obtained with diethyl phthalate was much the sharper of tube where it was soldered onto a 4-ring basket-type stirrer. the two, so it was chosen to be used for this study. The thermometer passed down through the rings of this stirrer, which was made to guide on the walls of the reaction tube and was APPARATUS not permitted to touch the thermometer. An electromagnetic coil was placed around this second glass tube to control the BATH. The solution temperature measurements wcre determovement of the iron core and consequently the movement of mined in a small, closed glass tube which was mounted in another the stirrer. The current entering this coil was passed through a gla.Qstube (which served as an air bath) which in turn was suprelaxation oscillator which was so constructed that both the ported in a large, well-stirred, vacuum-jacketed liquid bath. powcr, and consequently the length of stroke, and the frequency This arrangement pcrniitted a careful control of the rate of could be varied. The thermometer \vas inserted in the first g!as. heating and cooling of the sample. tube and the opening was sealed by a piece of rubber tubing which An unsilvered, wide-mouthed, vacuum-jacketed vessel with a fitted over the end of the glass tube and around the thermompter. capacity of 4300 ml. and a n inside diameter of 15.2 cm. held the The height of the thermometer \vas adjusted, so that it just did liquid bath which is composed of a 507, solution of ethylene glycol not touch the bottom of the reaction tube but that the bottom in distilled water. (It is necessary to use distilled water to prering of the stirrer rested on the flat bottom of this tube. In vent a clouding of the solution due to deposition of salts as the this manner none of the solvent layer could be trapped under water slowly evaporates and is replaced from time to time.) the stirrer and thus cause the observed end point to vary because This bath liquid level should always be adjusted to the same of variations in concentration. inark before proceeding with any determination. An electrically ALL-GLASSSOLVEKT DISPENSER.The required dry solvent driven, pump-type stirrer thoroughly agitated this bath, in which can be obtained by distilling it just before use and discarding the was supported a mercury thermometer graduated in 0.1" C. first wet portion of the distillate. ?'his is not dcsirahle from a The bath temperature was raised with a 125-watt knife-type time standpoint and is especially to be avoided in this case, since immersion heater and lowered by allowing carbon dioxide to one of the solL'ents must be distilled under high vacuum to expand from a siphon-type cylinder through copper tubing which prevent decomposition. was supported in the bath so that it did not touch the walls of An apparatus (see Figure 1) was designed and constructed in the vessel or the air bath. A coil of the copper tubing was which the solvent could be kept dry and from which it, could be placed near the bottom of the bath and this was connected by means of a straight tube near the back of the vessel to another coil near the top of the bath with an open space beTable I I . Comparison of Solution Temperatures of S i x Isomeric Heptanes with Various Solvents tween, 60 that the tubc in which (Hydrocarbon content, 50% b y volume. Accuracy of determination, 0.1' C.) the determinatioiis were made Solution Temderature could be seen. Difference, C.,betweenFor the air !Jath a glass tube 2,4->1er 2,2-Me1 2,4-hIe! 3.5 cm. in diameter and 23 cm. pentane pentane pentane Solution Temperature, ' C. and and and long was supported i n the liquid 2,2-Mer 2,4-Mer 2,2,3->1e: 2.3-1fe2 2-Me n2,2,3-S1er 2,2,3->Ie: 2.2-XIel bath, so that it did not touch Solvent pentane pentane butane pentane hexane heptane butane butane pentane the cooling coils or tlie knife .4niiine 78 05 78.4 72.0 67.95 7 3 . 5 70.0 6.4 6 05 0.35 heater. This tube \vas conBenzyl alcohol 64.7 64 9 53.5 46.4 57 25 50.7 11.4 11.2 0.2 stricted near tlie top to form a Dieths-1 hthalate 31.1 32.4 16.9 18.85 30.05 2 8 . 2 15.5 14 2 1.3 8-PhenyPethyIalcohol 4 6 . 6 47.05 34.45 28.2 39.1 20.7 12 6 12.15 0.45 seat which would support the 6 65 0 .2 o-Toluidine 2 8 . 2 2 8 . 4 2 1 . 5 5 1 7 . 7 2 3 . 6 19 7 6 . 8 5 tube holding the mixture under m-Toluidine 27.65 28 0 20.7 16.25 23.25 18.85 7 3 6.95 0.35 examination. Phenyl acetate 11.55 11.7 5.65 4.05 8.9 7.45 6.15 6.0 0.15 Acetyl diethylamine 1.1 2.95 - 11.95 , , ., 6 25 14.90 13 05 1.85 The reaction tube was made Nitrobenaene 26.8 26.55 20 9 1 6 . 0 5 22:35 18 15 5 65 5 e - 0 . w hy sealing a glass tube 1.6 cm. Beneonitrile 13.2 13.05 7.35 3.0 8.45 . , .. 5.70 5.85 -0.15 in diameter and 14 cm. long o-Bromophenol 3.85 3.15 - 3 . 8 0 .... ... .., . 6 95 7.65 -0.70 Benzyl benzoate 12.35 12.1 2.55 -3.65 4.45 -2.06 9.55 9 8 -0.25 to a 24/25 T ground-glass joint, so that the top of this Negative reading for temperature differences indicates reveraal in order of hydrocarbon which gives higher solution temperature, joint extended just far enough above the top of the air bath Table
I.
Physical Data
January, 1945
ANALYTICAL EDITION
Freezing Point and Critical Solution Temperature Apparatus
Stopcocks K I , K I , and K s (see Figure 2) are closed. T h e thermometer, T,and basket-stirrer, S,are rinsed with a stream of C.P. acetone from a wash bottle to remove all the material from the preeoding determination. The drops of acetone at the tip of the thermometer are touched OK with a clean cloth which is used only for that purpase. The apparatus, B, which holds the thermometer is then placed in Rask A by uniting the ground-glass joint, G. A is evacuated by opening K,. This removes the acetone and traces of hydrocarbon left in the upper arms of B ffil. ?Get which is' i r a d & e d in-O.l-ml. i&vals (0.1 ml. = ~ a p from the preceding determination. K S is opened and clased proxirmtely 1 om.). The hydrocrcrbon is measured out with a several times, allowing a stream of dry nitrogen to pass over T. 3.00-m;. delivery pipet which has been calibrated by the National Finally Kr is closed but K I is left open while the r a t of the Bnresu of Standards. apparatus is prepared. The cork, C, which fits into the top of the reaction tubs has PROEEDURE two holes bored in it. The one permanently contains the bent glass tube, J . The other is for glass tube H and to pass the Since a reproducibility of *O.0lo C. is aholutely essential, pipet through 89 doscribed belaw. The rubber connection, V!, in order that this method may be applicable t o the quantitative is attached to J a t F. Tube H is placed in C, BO thnt the rubber snalysis of this particular hydrocarbon mixture, every precaution collar, D, fits tightly in the hole. Rubber tube V , is then stmust he taken to see that this procedure for the preparation of tached to H a t E. K , ia opened and the Bow of dry nitrogen is regulated with a reducing valve until the concentrated sulfuric the apparatus, rrPking up of the ssmple,.and the act,ual determiaoid in the Rowmeter stands a t M,. Then the reaction tube, nation of the solution temperature is followed exactly. Otherwith a stream of nitrogen passing throu h it, is heated with a wise enough deviation in results occurs to make the method hare E r n e until it is hot. Rubher tube is attached to pipet useless. P a t N and the reaction tube 18 allowed to cool with the a t r e v of nitrogen assing through i t and out throu h the pipet Thrs PREPARATION OF REACTIONTUBEAND SOLUTION TEMPERA- effectively d%es both the reaction tube and t%e pipet. f n order to save time, a second reaction tube is dried while the rest of the TURE SAMPLE. The apparatus which holds the thermometer and stirrer must be cleansed of all material from the precedin determination is being made. determination, hy riasing with acetone, followed by repeate! When the reaction tube has reached room temperature Ks is closed while the vacuum in A is released bv closine K , and allowevacuations and Rushing with dry nitro en The reaction tube inn nitroeen to Row in throueh K , until tbe m e r c k level in the is washed with acetone and heated wit% bare E r n e w6ile a rna?ome& stands at hqs. 'l'lren K , is r1ost.d and K , is owned stream of nitrogen is p m i n through i t and out through the .V and If, i i removed from qrnn. I'iw pilwi is d s r o n n r c r d hydrocarbon pipet. This ejeectively dries both the reaction tubs and the pipet. The top of the dried reaction tube is flushed J a i F. Tube V , is diwonor-tpd from H at E and ia a l t s c h d 10 J st P. 'Tirbe II is removed from the reaction tuhr slowlv. BO with a stream of nitrogen during the time required to measure the hydrocarbon and solvent into it. that the nitrngen coming in hrough J will replace the volume of
%,
Vol. 17, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
8
H and not allow air from the room to enter the resction tube. During the rest of the time required to make up the sample the top of the reaction tube is flushed by the stream of nitro en 898ing in through a n l o u t through the hole in C which formerly held H . The hydrocarbon is then transferred from P to the reaction tube through the hole in 0; the tip of P is kept close to the bottom of the reaction tube to prevent splashing and consequent loss by evaporation. The last drop of hydrocarbon is touched off on the side of the tube. The solvent is measured into the reaction tube from the solvent dispenser through the hole in C and again the last drop is touched off against the side of the tube. Cork C is removed from the reaction tube and B is rapidly removed from A and placed in the reaction tube, so that the groundlass joint fits tightly. he ground-glass stopper, B,, is placed in A to prevent air and moisture from entering this flask. K J is closed.
a.co ~ - c O T T O ~ Y RUG
f
5
DETERMINATIO O FN SOLUTIONTEMPERATURE.
Figure 1
The reaction tube containing the sample and fitted with the resistance thermometer is placed in the air-bath tube in the liquid bath. The temperature of the liquid bath is adjusted until it is 0.5' to 1.0" C. a h v e the expected solution temperature. The electrom netic stirrer is started. Stirrin ring R1is always above the liquslevel and the power of the osciflator is adjusted so that Rn comes just to the top of the liquid (at the top of the stroke) but does not break the surface. This prevents splashing onto the walls of the tube and consequent concentration changes. The stirrer frequency is adjusted so as to give the optimum end point. The solution temperature measurement is made with the temperature rising and then the bath temperature is dro ped about 0.5' below the observed solution temperature whic! is again determined with the temperature fallin . This may be repeated if necessary. Some practice and skij are required repeatedly to take the same place as the end point, but once this was learned no trouble a t all was encountered in reproducing this within 0.01' if the temperature of the solution was not permitted to paw through the end point too rapidly. The end int, a sudden clouding or final clearing of the solution, is slightgshsrper with the temperature falling rather than rising. EXPERIMENTAL
P~EPARATXON OF HYDROCARBONS. The hydrocarbons required for this analytical problem were synthesized with extreme care and all possible precautions were taken to emure that each intermediate was in turn puriiied, so that the final products would be as pure as posaible. In the usual manner, 2,2-dimethyl-3-pentanol and 2,pdimethyl-% ntanol were prepared from tert-butyl m chloride p k propionaldehyde and isobutyl magnesium%:% lus acetone. Pinacolone (2,2-dimethyl-3-butanone), obtained reducin acetone with m esium activated b mercuric kloride and the conversion of% unieolated pinacoKto pinacolone according t o the improved method of Cramer (7),waa reacted with methyl m y e a i w n iodide to give the hydrate of 2 2 &tri4,4Dmethyl-%pentene wa8 obtained b' the methyl-3-butano thermal decomposition of the acetate (8) of 'the iirat. car&nol and the other two carbinols were dehydrated +th iodme. The olefins were dlstilled from d u m and then fractionated through a 100-plate column and thoee portions which had a constant
.
All-Glass Solvent Dispenser
refractive index were collected and h drogenated over Raney nickel. The araffins were purified clemically and then were fractionated &rough a 100-plate column and again only those ortions were collected which had a constant refractive index, hese values checked well with the mmt reliable refractive index
F
ny 2,l-Dimethylpentane 2,2-Dimethylpentane 2,2,3-Trimethylbutane
1.3818
1.3823 1 ,3897
Freerin Point,
E.
-119.3 -123.7 2b.l
-
data from the literature, which are given in Table I. Freezing point data obtained with these hydrocarbons indicated that 11 had a purity of 99.8% or higher. SOLVENTS. Diethyl phthalate from Commercial Solvents Corporation was distilled under 1.5-mm. pressure in a dry nitrogen atmas here. The middle ortion of the distillate waa collected and p h e d in an all-glass 8spenser under dry nitrogen. ny = 1.5022. Eastman Kodak Company C.P. nitrobenzene was distilled from an all- lass apparatus (so that the water from the first wet portion of the %istillate could be removed from the apparatus by flashing with a free flame) and the dry distillate was placed in a dispenser.
GRAPHICALMETHOD FOR TERNARY MIXTTJRE ANALYSIS. Since the composition us. solution temperature c w e s for synthetic binary mixtures of 2,2-dimethylpentsne plus 2,2,3-trimethylbutane, 2,4-dimethylpentane plus 2,2,5tnmethylbutane, and 2,2- plus 2,4-dimethylpentane are not straight-line functions, the percentage of each component present can be determined graphically more easily than mathematically. These diethyl phthalate point calibration c w e a are all that are required for the quantitative analysis of m i x t m that are known to contain only two of these hydrocarbons, but a second determination must be made in order to analyze a ternary mixture. The composition-diethyl phthalate point data for these three b;narv mixturea were plotted on the edges of a Lvge triangular graph end straight linea wem drawn through the h l u t i o n tempenrtwe pointe on two eidea of the triangle to form a aeries
9
ANALYTICAL EDITION
January, 1945
M,
- M,-
1
&
/I
TO
N,
TANK
TO VACUUM LINE
MANOMETER
Figure 9 .
Reaction Tube, Thermometer, and Stirrei
of iso-solution temperature lines These were proved to be straight lines, and not curves. by locating points on the triangular graph according to the known composition of synthetic ternary mixtures of these hydrocarbons. I n all cases the straight line drawn between the points, on two sides of the triangle, which represent the experimentally determined diethyl phthalate point of that particular ternary mixture, came within 1% of the point which represented the sctual cornposition of the ternary mixture in question. In a similar manner the iso-refractive index lines were proved to be straight lines. However, the refractive index could not be used as the second sebof data needed for this analysis, since the iso-diethyl phthalate point lines and the iso-refractive index lines both slope in the same direction and have only slightly different angles of slope (see Figure 3). Thus a variation of O.OOO1 in refractive index (author's experimental limit) can cause a great difference as to where the two lines intersect which would result in large errors in the per cent of 2,2- and 2,4-dimethylpentane found. The time required to make a solution temperature determination on an unknown sample can be considerably shortened if the approximate temperature a t which to set the bath is known. This desired bath temperature setting can be obtained from a small-scale triangular plot of the iso-refractive index and isosolution temperature lines. The refractive index of the unknown samplc is located on this chart and the approximate bath temperature can be read directly from the chart (see Figures 3 and 4). . Reference to Table I1 showed that, with all the solvents tested, the solution temperature of 2,2,3-trimethylbutane is lower than that for either 2,4- or 2,2-dimethylpentane. For most of the iolvents tested the solution temperature of 2,4- was higher than that of 2,2-dirnethylpentane, but with some few solvents the
Figure 3.
Graph for Ternary Mixture Analysis
solution temperature of 2,2- was observed to be higher than that of 2,+dimethylpentane. These few solvents will have iso-solution temperature lines with a negative slope with respect to the isodiethyl phthalate point lines. This would make possible a sharper intersection of lines and give a corraspondingly more accurate answer. Nitrobenzene was the second solvent chosen to be used.
10
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 17, No. 1
due to vaporization in the apparatus would bring the concentration toward the flat part of the curve instead of away from it. The reaction tube was constructed so that 4.5 ml. of liquid came slightly above the top of the sensitive portion of the thermometer. All subsequent analytical samples were prepared from 3.00 ml. of hydrocarbon plus 1.50 ml. of solvent. The value of dD/dt for diethyl phthdate was determined experimentally and that for nitrobenzene was obtained from International Critical Tables. From the data in Table I11 and thesc density values it was calculated that the change in the amount of solvent delivered caused by a room temperature change of as much as 15" C. would cause a variation in the solution temperature obtained of only about 0.01' C. Diethyl phthalate: dD/dr dao** Nitrobensene: dD/dt
_ - - - 1.1810 .?.2+UfCNlhK
2.+C2
mryc
Figure 4. Graph for Ternary Mixture Analysis
The procedure for determining the composition of ternary mixture 29 (see Table V) is illustrated in Figure 5. The nitrobenzene data chart in this figure shows that the per cent of 2,2,3-trimethyllutsne in 2,S-dimethylpentane corresponding to a nitrobenzene point of 26.52" is 28.4, which is represented by point A , and the per cent of 2,2,3-trimethylbutane in 2,2-dimethylpentane corresponding to this same nitrobenzene point is 31.2, which is represented by point B . On the triangular graph straight line A B is an iao-nitrobenzene point line which represents all the different compositions of these three hydrocarbons which can give this nitrobenzene point of 26.52". In a similar manner, the diethyl phthalate point data chart shows that the per cent of 2,2,3-trimethylbutane in 2,Cdimethylpentane corresponding to a diethyi phthalate point of 28.03 is 34.8 which is represented by point D, and the per cent of 2,2,3trimethylbutane in 2,2-dimethylpentane corresponding to this same dieth 1 phthalate point is 27.0 which is represented by point C. 8 n the triangular chart straight line CD is an isodiethyl phthalate point line which represents, all the different compositions of these three hydrocarbons whch can give this diethyl phthalate point of 28.03'. The point where A B and CD intersect represents the percentage composition of the unknown ternary mixture.
ELIMINATION OF VAFUABLES. Reproducible results could not be obtained when equal volumes of hydrocarbon and nitrobenzene were used. The critical solution temperature curve for 2,2,34rirnethylbutane with nitrobenzene was determined with a mercury thermometer graduatd in 0.1'. From 60 to 66.7% hydrocarbon concentration (instead of 50% as obtained with aniline) the curve goes through a maximum of only 0.05". [These data agree with tho% of Woodburn, Smith, and Tetewsky ( 3 4 ) . The experimental work of this paper was completed in March, 1941, and way the subject of a mearch report a t that time, but the press of later war work prevented earlier publication of the data obtained.] A similar curve w m obtained fur diethyl phthalate with 2,2,3-trimethylbutane, except that this was not as steep a t the 50% concentration as was the nitrobenzene curve. The critical solution temperature curves for 2,2- and 2,4dimethylpentane with nitrobenzene were carefully determined over a limited range with the platinum resistance thermometer (see Table 111). Through most of the flat part of the critical solution temperature curve the end point with nitrobenzene is poor, owing to an opalescence which appears some time before the true end point. However, a t a hydrocarbon concentration of 66.770 a beautifully sharp end point is obtained again. This is slightly past the peak but is still on a comparatively iiat portion of the critical solution temperature curve and any slight loss of hydrocarbon
---
0.0009/" C. d"*' 1.1074 O.OOlO/" C.
-
1.1182; d'a.8
-
1.1124:
Since it will be difficult to obtain perfectly dry eamples from small distillation cuts of the hydrocarbon unknowns, it was thought to be best to standardiae the procedure by using hydrocarbons saturated with water a t a definite temperaturc. (Variations in solution temperature of a t least 0.12' were obtained with hydrocarbons of various degrees of wetness.) The solvent? must be kept dry,for when the two water-saturated solutions are mixed a water layer separates and a poor end point is obtained. Oxidation products materially lower the solution temperature which is obtained. Thus, 8 sample of 2,2,3-trimethyIbutane which had been distilled October 23, 1939, and which had a refractive index a t that time of 1.3897 was examined March 14, 1941. At that time it had a refractive index of 1.3900 and gave a diethyl phthalate point of 14.84'. After purification it again had a refractive index of 1.3897 and gave a diethyl phthalate point of 17.44', a rise of 2.6". The same type of change, but to a smaller degree, was observed with 2,4-dimethylpentane. No change in solution temperature with time was observed with 2,2-dimethylpentane.
111.
Nitrobenzene Solution Temperature-Concentration D a b (3.00 ml. of hydrocarbon saturated with water at 30' C.) Nitrobenzene Solution Temperature NitroHydro2,2-hfer 2,4-Mer benrene carbon pentane pentane
Table
MI.
%
1.90 1.70 1 00 1.50 I 40
81.2 88.8 85.2 66.7 88.1
0
c.
28.26 28.27 28.26 28.33 28.15
c.
27.97 27.97 27.96 27.92 27.84
Poor end point Poor end point Intermediate Sharp end point Sharp end point
PREPARATION OF CALIBRATION CHARTS. Binary mixturea of freshly distilled 2,4-dimethyIpentane plus 2,2,3-trimethylbutane, 2,2-dimethylpentane plus 2,2,3-trimethylbutane, and 2,4- plus 2,>dimethylpentane were prepared by pi petting various proportions of the two hydrocarbons into lass-stoppered weighing bottles (80 X 15 mm.), so that tho t o t 8 volume of liquid ww 10 ml. The actual amount of each hydrocarbon present was determined by weight. The refractive index of each sample was measured at 20" C. A few drops of water were added to each of these solutions, which were thcn thoroughly shaken and placed in the thermostat at 30' * 0.1" C. They were taken from the thermostat a t intervals, shaken several times, and then left in the thermostat overnight, after which the solution temperature of each in nitroben:,ene and diethyl phthalate w w determined (see Table IV). In order that the accuracy of plotting and reading on the calibration charts would be equal to the accuracy of determining the solution temperature, these data obtained with the binary mixtures wcre plotted on a large scale (2.5 cm., 1. inch, on the ordinate axis represents a change of 0.20"in the solution temperature and 1 inch on the abscissa axis represents a change of 5.0% in the concentration of 2,2,3trimethylbutane). I n the analysis of an unknown the values read from these large charts were plotted on a standard 22.5cm. (9-inch) triangular graph paper according to the method described earlier.
11
ANALYTICAL EDITION
January, 1945
ACCUR.ACY OF METHOD.After all the calibration charts had been constructed from these experimental data from the binary mixtures, seven ternary mixtures of these pure hydrocarbons, in widely varying proportions by weight, were prepared. The nitrobenzene and diethyl phthalate points of each sample were determined and from these data the percentage composition of each sample was determined graphically. When the per cent of each of the three components found E-as compared with the per cent of each actually present, it was seen that the percentage of 2.1- and 2,2-dimethylpentane found and present agreed, usually withiu 1%, and with a maximum daerence of 3%> and the percentage of 2,2,3-trimethylbutane found and present had a maximum difference of 0.27%. These data are given in Table V. CALIBRATION OF SOLVENTS. In actual practice it was found necessary to calibrate the solvents occasionally in order to correct the solution tcmperature obtained for the change caused by the small amount of water which is slowly absorbed by the solvent in the dispenser, and thus make the results comparable with those obtained when the calibration charts were prepared. Purified n-heptane was used as the standard against which this change in the solvents could be checked. The difference between the n-heptane solution temperature a t the time the calibration charts were prepared and a t the time the unknown sample was being analyzed i s added algebraically to the observed solution temperature of the unknown and then the calibration charts are used as previously described. Kitrobenzene which had been in the dispenser from July 9, 1940, to November 25, 1941, was found by analysis with Karl
Fischer reagent to contain 0.030 to 0.035% of watei while a sample of freshly distilled nitrobenzene contained 0.0038 to 0.0046~0of water. No water could be detected in the diethyl phthalate with this reagent. Some idea of the quantity of water which would cause the results obtained by this method of analysis to vary was obtained by determining the solution temperature of isooctane (2,2,4trimethylpentane saturated with water a t 30') with these two samples of nitrobenzene: Isooctane Solution Te rnpera ture
Nitrobenzene, H10 Content
c.
% 0.035
29.51
0.004
29.38 0 13
Difference
..-
For the author's work a comparatively hirtight room waa built with a light grade of Masonlte and the humidity and temperature in this room were controlled by circulating the sir from
I
P E R C E N T 2,2,3-TRl M E T H Y L B U T A N E
Figure 5.
Ma. 0.63 0.07 0.68
Thus, a change of only 0.04 mg. of water in 1.5 ml. of nitrobenzene caused the solution temperature to vary 0.01"C. EFFECTOF HIGH HUMIDITY.This intrpduces one other limitation to this method of analysis. Since a reproducibility of =tO.0lo must be obtained, some means of controlling the humidity in the room is necessary if this method is to be used during the hot, humid summer months. The calibration data given in Table I V were determined when the humidity was 3.5 t o 7.6 mm. of mercury, but results were perfectly reproducible as long as the absolute humidity was kept belov 12 mm.
DIETHYL P H T H P L A T E P O I N T D A T 4
___
Weight of HaO/1.11
MI of Nitrobenrene
PERCENT 2,2,3-TRI E T H Y L BUT ANE
Composition of Ternary Mixture 99
INDUSTRIAL AND ENGINEERING CHEMISTRY
12
Table IV. Solution Temperature and Refractive Index Data of Heptane Binary Mixtures (3.00 ml. of hydrocarbon 1.50 rnl. of solvent. Hydrocarbon saturated with HrO a t 30° C. Solvent calibrations:
+
nitrobenzene-n-heptane 19.35' C. Diethyl phthalate-n-heptane 28.29' Diethq I Phthalate Point, ' C Nitrobenzene Point, C. % by Weight Bample 2,4-Mez 2,Z-Mez CalcuDifferCalcuDifferlatedo Observed ence No. pentane pentane lated" Observed ence 100 32.85 .... 27.99 . .. . 1 80.01 i9:w 32:57 32.56 - 0 . 0 1 28:04 28.02 -0.02 -0.01 28.08 28.06 -0.02 2 32.29 32.28 59.96 40.04 -0.01 28.13 28.11 -0.02 32.01 32.00 40.06 59.94 3 20.02 79.98 31.73 31.72 -0.01 28.17 28.16 -0.01 4 . . . . 100 .., 31.46 . . 28.23
.. .
5
6 7 8 9 10 11 12 13
14 16 16 17 18 19 20 21 22
2,4-hIer 2,2,3-Me~ pentane butane . . . . 100 0.67 90.33 19.68 80.32 29.48 70.62 39.57 60.43 49.48 50.52 59.39 40.61 69.64 30.36 79.64 20.36 89.96 10.04 100
....
2.2-Me: 2,2,3-Mea pentane butane .... 100 9.69 90.31 19.69 80.31 29.46 70.54 60.44 39.66 50.53 49.47 40.57 59.43 30.31 69.69 20.36 79.64 10.01 89.99 100 ....
1i:92 20.46 21.98 23.53 25.06 26 59 28.17 29.71 31.30
17,43 19.15 20.91 22,53 24.15 25.70 27.19 28.68 30.09 31.49 32.85
1B:iO 20.20 21.67 22.99 24.38 26.77 27.21 28.61 30.00
17,44 18.95 20.47 21.93 23.41 24.81 26,20 27,58 28 01 30.21 31.40
...
...
. . ..
..
C.) Refractive Index, n ? ? Calculated" Observed . . .. , 1.3817 1 . 3 8 1 1 ~ 1.3818 1.38198 1.3819-20 1.38212 1.3821-2 1.38226 1.3822-3 1.3824
.....
40:23
+o
55 .+0.62 f0.64 fO.60 4-0.51 +0.38 +O. 19
.... ....
....
23:00 23.68 24.15 24.74 25.31 25.89 26.48 27,06 27.66
22.44 23.04 23.65 24.25 24.85 25.43
26,OO 26.57 27.12 27.68 28.24
$0.04 +0.07 + o . 10 +O.ll
+0.12 +0.11 +0.09 +0.06 +0.02
....
.....
1.38899 1.38826 1,38755 1,38681 1 ,38009 1.38530 1.38461 1.38389 1.38313
.....
Calculated values Ere based on assumption t h a t d a t a would be a straight-line function. how observed d a t a vary from such a straight-line function.
Table
1.3897 1.3889 1.3882-3 1,3876-7 1,3809 1.3861-2 1.3854 1 3847 1.3840 1.3832 1 3824
Differences show
V. Analysis of Heptane Ternary Mixtures
+
preparation of the apparatus, and his many helpful suggestions during the course of this investigation. LITERATURE CITED
(1) Aubert, M . , and Aubree, E., Compt. rend., 182, 577 (1926); Chimie & Indusfrie, Special No., 336 (Sept., 1926). (2) Brame, J. S. S., and Hunter, T. J., J . Inst. Petroleum Tech., 13, 794 (1927). (3) Brattain, R., Rasmussen,
R., and Cravath, A., J .
4-0.46
+0.15 +0.27 +0.36 4-0.42 +0.43 +0.43 f0.37 f0.30 f0.15
Vol. 17, No. 1
(3.00 mi. of hydrocarbon 1.50 ml. of solvent. Hydrocarbon saturated with Hz0 a t 30° C.) sam.Solution Temperature 2,4-Dimethylpentane 2,2-Dimethylpentane 2,2,3-Trirnethylbutane Diethyl NitrcDifferDifferDifferphthalata benrene Present Found enoe Present Found ence Present Found ence
Applied Phys., 14, 418 (1943). (4) Carpenter, J. A , , J . Znsf. Petroleum Tech., 12, 518 (1926); 14, 446 (1928). (5) Chavanne, G., and deGraef, H., Bull. S O C . chim. Bdg., 33, 366 (1924). (6) Chavanne, G., and Simon, L. J., Compt. rend., 168, 1111, 1324 (1919); 169, 185, 285 (1919). (7) Cramer, P. L., unpublished
work.
(8) Cramer. P. L., and Miller, V. A . , J . A m . Chem. SOC., 62,'1452 (1940). (9) Crigler, E. A., I b i d . , 54, 4207 (1932). (10) Edgar, G., and Calingaert, G., Zbid.,51,1540 (1929). (11) Egloff, Gustav, "Physical
Constantg ,of the Hydrocarbons , New York, Reinho:d Publishing Co.,
1940. (12) Erskine, A. M., IND. &NO. CHEM.,18, 694 (1926). oc. 'C. % % % % % % % % % (13) Garner, F. H., J . Inst. Pe 23 24.98 25.40 9.72 11.2 +1.48 39.64 38.3 -1.34 50.64 50.5 -0.14 troleum Tech., 14, 695 25.60 25.34 39.59 40.6 4-1.01 9.71 8.8 -0.91 50.70 5 0 . 6 -0.10 24 49.93 60.0 4-0.07 40.03 39.8 -0.23 10.04 10 2 +0.16 25 30.91 27 55 (1928). 80.06 8 0 . 4 +0.34 9.86 9.4 -0.46 10.08 1 0 . 2 f0.12 26 31.35 27.48 (14) Gorbeau, J., 2. anul. Chem., +O.ll 10.05 10.1 +0.05 27 30.33 27.65 9.86 9.7 -0.16 80.09 80.2 105, 161 (1936). 28 20.63 23.62 9.73 9.8 4-0.07 9.70 9.7 .... 80.57 80.5 -0.07 29 28.03 26.52 29.74 27.0 -2.74 39.89 42.9 4-3.01 30.37 30.1 -0.27 (15) Gorbeau, J., and Schneider, V. von, Angew. Chem:, 53, 531 (1940). (16) Graef, H. de, Bull. S O C . chim, Belg., 34, 427 (1925). the room over a cooling coil to remove the moisture and then (17) Howes, D. A., J . Inst. Petroleum Tech., 12, 68 (1926). (18) Ibid., 16, 54 (1930). ovef a steam coil to warm it up to about.21.1' C. (70' F . ) (19) Liddel, U., and Kaaper, C., Bur. Standards J . Research. 11, 599 a a n . This arrangement kept the humidity from exceeding a%out 7 or 8 mm. of mercury, which was well on the safe side (1933). ae long as the precautions given in the procedure were strictly (20) Maman, A., Pub. sci. tech. ministBre air (France), 66, 55 (1935); Compt. rend., 198, 1323 (1934); 205, 319 (1937). followed. After this room had been built the hydrocarbons were satu(21) Minchin, S. T., and Nixon, G . R., J . Inst. Petroleum Tech., 14, 477 (1928). rated with water a t a room temperature of about 70" F. instead of in the thermostat a t 30' C. (86' F.). This caused a lowering sci. U.R.S.S.,Ser. phys., 4,98 '1940). (22) Neumin, H . G., Bull. d . of 0.02" in the observed nitrobenzene point and 0.03" in the (23) Ormandy, W . R., and Craven, E. C., J . Inst. Petroleum Tech,, diethyl phthalate point and this correction had to be made 12, 68 (1926). before using the calibration charts. According to the data (24) Randall, H. M . , Barker, E. F., and Sleator, W.W., Physics, 4, 2, 39 (1933). obtained with isooctane and nitrobenzene containing various amounts of water, this change in solution temperature indicates (25) Rose, F. W.,Jr., Bur. Standards J . Reaearch, 19, 143 (1937); that samples of hydrocarbons saturated with water a t 70' F. 20, 129 (1938). contain about 0.004% less water than those saturated a t 86" F. (26) .Rosenbaum, E. J., Grosse, A. V., and Jacobson, H. F., J . A m . Chem. SOC.,61, 689 (1939); IND. ENQ.CEEM.,12, 191 (1940). (27) Schurman, I., and Boord, C. E., J . A m . Chem. Soc., 55, 4930 ACKNOWLEDGMENT (1933). (28) Smittenberg, J., Hoog, H.. and Henkes, R. A,, Ibid., 60, 17 (1938). The author wishes to thank the following co-workers for their (29) Tilitsheyew, M. D., and Dumskaya, A. I., J. Inst. Petroleum help in the study of this problem: Tech., 15, 465 (1929). (30) Timmermans, J., Bull. POC. dim. Belg., 36, 502 (1927). W. G. Love11 for the suggestion of the problem and his aid (31) Tisard, H. T., and Marshall, A. G . , J . SOC.Chem. Ind., 40, 20T throu hout the investigation. (1921). V. Smith for his help in the preparation of the apparatus. (32) Volkenahtei.n, M. V., Shorygin, P. P., and Shomova, N. N., C. R. Begeman for the distillation connected with the prepaZauodakuya Lab., 9, 860 (1940). ration of the h drocarbons. (33) Wibaut, J., Hoog, H., Smittanberg, J., et al., Re. trow. chim., L. K. Cosd &r the hydrocarbon freezing point determinations. 58, 329 (1939). P. K. Winter for the Karl Fischer reagent water analyses. (34) Woodburn, Smith, and Tetewsky, IND ENO. CHEM.,36. 588 P. L. Cramer for the original suggestion of the method of ( 1944)* r t t m k of the problem, the g l m blowing in connection with the
.&!
8.
