354
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
T'ol. 18, No. 4
Determination of Unsaturated, Aromatic, Naphthene, and Paraffin Hydrocarbons in Motor Fuels and Their Automotive Equivalents' By Gustav Egloff and Jacque C. Morrell UNIVERSAL OIL PRODUCTS Co., CHICAGO, ILL.
N E of the difficult problems in hydrocarbon chemistry The acid-treated oil is washed with water, neutralized is the quantitative determination of the paraffin, with a 10 per cent solution of sodium hydroxide, and then unsaturated, naphthene, and aromatic hydrocarbons redistilled in the same apparatus until the vapor temperature in mixtures. Much study has been given to this problem in the Hempel column reaches 210' C. The volume of in the laboratories of the world, but no systematic procedure the residue of the second fractionation to 210' C. is calculated as a percentage of the first 210' C. fraction, and is has been devised. The primary purpose of this investigation was to relate the percentage of the unsaturatcd hydrocarbons that have the percentage composition of these hydrocarbons to the anti- been polymerized during the acid treatment. This, added to knock DroDerties of certain motor fuels. The analytical pro- the percentage of unsaturated hydrocarbons dissolved by the sulfuric acid, gives the total cedure is accurate enough to percentage of unsaturated give practical information hydrocarbons in the original concerning the antiknock A procedure is described for determining the four 210" C. fraction of t h e qualities of motor fuels and series of hydrocarbons when in presence of each other, motor fuel. is adapted as a standard particularly in motor fuels, and for the calculation of laboratory method of detertheir automotive equivalents. Unsaturated hydroAromatic Hydrocarbons mining the series of hydrocarbons are determined by means of sulfuric acid abInto a graduated separacarbons when in presence sorption and polymerization, aromatic hydrocarbons tory funnel provided with a of each other. by nitration, naphthenes by means of the aniline instopcock and enlarged stem dex, and the paraffins by difference. The efficiency of Analytical Procedure are put 20 cc. of the second the method is shown by an analysis of three synthetic 210" C. fraction obtained Unsaturated Hydrocarbons mixtures. The aromatic hydrocarbon equivalent and during the analysis of the the highest useful compression are calculated by means A 500-cc. charge of the unsaturated hydrocarbons of Ricardo's data for toluene. To confirm the results motor f u e l i s d i s t i l l e d and 50 cc. of nitrating obtained by chemical analysis, motor tests were made to through a Hempel column mixture-nitric acid 25 per determine the antiknock properties of several of the containing glass beads until cent, sulfuric acid 58 per gasolines tested. the t e m p e r a t u r e of the cent, and water 17 per cent vapor at the top of the col-added slowly with stirring umn is 210' C. The residue and cooling. This Darticuis discarded. This temperature is purely arbitrary, and any lar combination of nitrating mixture is important, as itbermits other may be used provided it is used throughout the analysis. nitration of the aromatic hydrocarbons so that the nitration The 210' C. fraction is treated with 80 per cent sulfuric products do not dissolve substantially in the acid sludge but acid, so that the volume ratio of acid to oil is 2:l. The separate as a distinct layer which can be readily determined. mixture is agitated for 15 minutes, allowed to settle, and This operation will require from 15 minutes to an hour, the acid layer separated. The volume of the oil layer is as great care must be taken that the temperature of the measured and the per cent decrease of this volume calculated hydrocarbon mixture does not reach the point where side on the basis of the 210" C. fraction. This calculation gives reactions that might cause explosion may occur. The the percentage of the unsaturated hydrocarbons that have reaction mixture is allowed to stand until no inore gas is dissolved in the acid layer as reaction products. evolved. Usually R three-layer system forms-the acid I n the sulfuric acid absorption one is confronted with layer a t the bottom, an intermediate layer of nitro derivathe overlapping effects of various concentrations of sulfuric tives, and the oil layer on top. By multiplying the number acid upon the unsaturated and aromatic hydrocarbons. of cubic centimeters of nitrated compounds by the factor 4.3 the percentage of aromatic hydrocarbons in the second The acid has two effects on the unsaturated hydrocarbonssolution by reaction and polymerization. Therefore, the 210' C. fraction is obtained. From this the percentage in salient feature of this method is the selection of such a the original 210' C. fraction is calculated. concentration of sulfuric acid as has no effect on the aromatic Naphthenes hydrocarbons but allows determination of the unsaturated hydrocarbons by this twofold effect. Experiments have Naphthene hydrocarbons were determined by the aniline shown that 80 per cent (by weight) sulfuric acid is without method of Tiaard and Marshal1,Z which is based on the lowersubstantial effect on the pure aromatic hydrocarbons and, ing of the temperature of complete miscibility of aniline furthermore, does not react with those of the naphthene and and the paraffins by naphthenes. paraffin series. Pure unsaturated hydrocarbons react with The oil from the nitration treatment is washed with water sulfuric acid of this concentration to form the sulfuric ab- and a 10 per cent solution of sodium hydroxide and then sorption products and polymers. thoroughly dried with calcium chloride. The aniline value 1 Received January 16, 1926. To be presented before the joint session is determined on this dried oil, which is a mixture of parof the Divisions of Petroleum Chemistxy and Industrial and Engineering affin and naphthene hydrocarbons. Ten cubic centimeters Chemistry at the 71st Meeting of the American Chemical Society, Tulsa,
0
Okla., April 5 to Q, 1926.
:J . SOC.Chem. I n d . , 40, 20T (1921).
April, 1926
I N D L'STRIAL A N D ENGINEERING CHEMISTIZY
of freshly distilled aniline and an equal volume of the oil are placed in a test tube that is jacketed by a larger test tube. Into the smaller test tube are placed a thermometer (calibrated in 0.1" C.) and a stirring rod. The mixture is heated until the cloud disappears, when the temperature is read. The heating is continued until the solution is just aboye the cloud point and then allowed to cool until the cloudiness reappears, This cloud point can be read to 0.1" C. The experiments of Tizard and Marshall2 and also of subsequent workers indicate that, under the conditions of the test, the paraffin hydrocarbons are completely miscible u-ith aniline a t 70" C., and that the cloud point is depressed 0.3" C.for each 1per cent of naphthene hydrocarbons present. For example, if the cloud point of a paraffin-naphthene mixture is 55" C., which is 15" C. below the temperature of complete solubility of paraffin hydrocarbon3 in aniline, diriding 15" C. by 0.3" C., Re find that the sample contains 50 per cent of naphthene hydrocarbons. This percentage mubt then he calculated back to the original 210' C.fraction to find the percentage of naphthenes in the original fraction.
355
Table I-Analysis of Synthetic Mixtures (Figures in per cent) I I1 I11
Present Found Unsaturated Aromatic
12 5 12.5
16.0 12 7
HYDROCARBONS Present Found Present Found 16.6 21.2 20.0 18.2 16.6 16.9 20.0 22.r
The results (Table I) show good checks for the aromatic hydrocarbons. The unsaturated hydrocarbons are relatively high in the first two mixtures, but quite good for the third mixture. Application of Method
Cracked gasoline. produced from different charging stocks were analyzed for their contents of unsaturated, aromatic, iiapht hene, and paraffin hydrocarbons, and the aromatic hydrocarbon value. calculated by means of Ricardo's data for toluene.? From these data it was calculated that, so
Parafins The percentage of paraffin hydrocarbons in the original 210" C. is obtained by subtracting the sum of the percentage of Unsaturated, aromatie, and naphthenc hydrocarbons from 100. Criticism of Method As stated previously, the determination of unsaturated hydrocarbons by the sulfuric acid method depends on t v o factors-reaction solution and polymerization. The reaction solution determinatibn is positive, as it depends upon direct measurement of the decrease in volume. The polymerization factor, however, when mixtures such as motor fuels are under consideration, is subject to the criticism that all the polymers formed may not be left in the residue after redistillation of the mixture, but some may be present in the distillate. Comparison of the boiling point curves, before and after acid treatment and also other physical constants such as density and refractive index, will largely take care of this criticism. Furthermore, in such mixtures there may be present ring compounds with unsaturated side chains which may be included in the unsaturated hydrocarbons when determined by the sulfuric acid method. The nitrating mixture used in the determination of the aromatic compounds was seleeted because of its minimum solvent power for the nitro compounds formed. Unsaturated compounds in a mixture of aromatic hydrocarbons will react with this nitrating mixture and increase the volume of the layer of nitro compounds and hence give high results for aromatic hydrocarbons. The writers have found that the volume of aromatic hydrocarbons is about 86 per cent (average of experiments with benzene, toluene, and xylene) of the total volume of the nitro compounds formed by nitration, and this figure may be used to correct for any discrepancies, if applied to aromatic hydrocarbons of higher molecular weight. There is probably some solubility of nitro compounds in the oil layer, which was not taken into consideration. Preliminary experiments show that the critical teniperature for the cloud point varies with different paraffin hydrocarbons, and this point merits further investigation. Analysis of Synthetic Mixtures
Three synthetic mixtures of Pennsylvania gasoline, toluene, amylenes, and octylene were analyzed by the method described. The gasoline, containing only a small amount of aromatic hydrocarbons and a negligible quantity of unsaturated hydrocarbons, was washed first with 98 per cent sulfuric acid and then with sodium hydroxide and water,
TOLUENL V A L U F J P ECRE N T ) Figure 1
far as the antiknock properties in an automotive engine are concerned, 5 per cent of unsaturated hydrocarbons is equivalent to 1 per cent of toluene when both are dissolved in p a r a f i hydrocarbons. Similarly, 4 per cent of naphthenes is equivalent to 1 per cent of toluene. (Of course, the accuracy of this relationship is limited, as Ricardo did no work with pure hydrocarbons.) It is assumed that the toluene values so obtained may be converted directly into aromatic values. To obtain the total aromatic hydrocarbon value or its equivalent, the value calculated from Ricardo's data for the unsaturated and naphthene hydrocarbons is added to that obtained by direct analysis. Table 11-Analyses of Various Cracked (Figures in per cent) Braman, Tonkawa, S o . Kans. K y . Smackover topped fuel heavy HYDROCARBONS crude oil crude Unsaturated 16.1 14.4 14.7 17.8 22.5 27.5 Aromatic i2.s 10.0 21.2 Naphthene Paraffin 03.3 53.1 36.6 24.2 27.9 36.7 Aromatic equivalent Highest useful compression ratio 5.6 5.7 5.9
Gasolines NO.
Texas Lost Soldier, fuel Wyo., oil crude 16.0 11.7 18.6 15.0
11.7
15.4
24.7
57.9 21.2
5.6
5.5
53.7
As a means of further comparison, the highest useful compression ratio, based on Ricardo's toluene value, and the analytical data on the cracked gasolines areshown in Table 11. I n obtaining this compression ratio the aro8 Institute of Petroleum Technology, Report of Empire Motor Fuels Committee, pp. 84, 85, 145.
INDUSTRIAL AND ENGINEERING CHEIMISTR Y
356
matic hydrocarbons found by direct analysis were considered as equivalent to toluene. The highest useful compression ratio of an automotive engine is shown in Figure 1 as a function of the Ricardo toluene values. Figure 2 shows the relation between the boiling points and specific gravities of the series of hydrocarbons under consideration. The percentages of the hydrocarbons of each series in straight-run gasoline derived from the various crude oils and corresponding values for the cracked motor fuels derived from the fuel oil residues by heat and pressure are given in Table 111. The higher useful 9 90
Table V-Distillation Baume gravity Initial boiling point Per cent over
90 95 End point Loss, per cent
Vol. 18, No. 4
Analyses of Known M i x t u r e s Commercial Commercial . gasoline benzol 58.1 29.8 4 3 . 3 ’ C. 80.6’ C.
Temperature
c.
78.9 99.4 113.9 127.2 140.6 152.2 165.6 178.9 i 9 5 .o 207.2 222.8 1
Temperature c. 82.2 82.8 83.3 83.9 84.4 85.6 87.2 90.0 ~... 98.9 111.1 142.8 0.5
088
Analysis by the procedure described in this paper shows that this gasoline contains the following percentages of the various series of hydrocarbons (Table VI).
486 084 082 ~
2
9‘ u $
3
3
080
Table VI-Hydrocarbons
in Commercial Gasoline Per cent Unsaturated 4.5 Aromatic 12.1 Naphthene 17.6 Paraffin 65.8 Aromatic equivalent 17.4
078 07G 074
072 070
Motor tests upon this gasoline and mixtures of this gasoline with benzol give the results shown in Table VII.
068 0 66 0 64
460Z0
Tests upon Commercial Gasoline and Mixtures w i t h Benzol Relative spark advance Commercial gasoline 18.7 Commercial gasoline plus 10% benzol 20.0 Commercial gasoline plus 15%. benzol 23.5 Commercial gasoline plus 207’ benzol 24.2 Commercial gasoline plus 30% benzol 36.5
Table VII-Motor
062
40
60
80
i00
I20
BOILING POINT Figure 2
144
-c
/60
/80
ZOO
220
compression ratio shown by the cracked motor fuels is due f o the higher percentage of unsaturated, naphthene, and :aromatic hydrocarbons present. These three series function a s antiknock constituents in motor fuels, whereas the paraffins knock in high-compression motors. ‘Table 111-Comparison of Hydrocarbons in Straight-Run Gasoline and Cracked Motor Fuels (Figures in per cent) -GUSHING OKLA.- -SOMERSET, KY.HYDROCARBONS Straight-ru; Cracked Straight-run Cracked 12.5 1.6 10.9 3.8 Cnsaturated 14.9 19.8 4.9 5.3 Aromatic 2 0 . 6 1 1.8 2 3 . 7 1 8 . 0 Naphthene 51.3 70.3 69.8 60.8 Paraffin 1 1 . 1 1 1 . 1 2 6 . 5 2 0 .4 Aromatic equivalent 5.6 5.5 5.1 5.2 Ricardo compression ratio
Motor Tests T o confirm the results obtained by chemical analysis, motor tests were made to determine the antiknock properties of several of the gasolines previously tested. The tests were made by the “listening”3 method, using a Hupmobile 4cylind.er motor having a constant compression ratio. The knock of the motor was determined as a function of the spark advance using a standardized knock and checked by two observers. Table IV summarizes the results obtained in these tests. Table IV-Motor
Tests on Cracked Gasolines Relative spark advance Mixture of Tonkawa, Braman, No. Kansas crude 19.5 Smackover crude 32 Kentucky fuel oil 21.7 Cushing, Okla., fuel oil 19.7
I n order to evaluate these data in terms of a known mixture aimilar tests were made upon mixtures of commercial benzol a n d a market gasoline containing cracked gasoline, the distillation analyses of which are shown in Table V. From this table i t is seen that the benzol contains a considerable amount of toluene.
By comparing Tables IV and VI1 it is seen that the various cracked gasolines under test are equivalent to mixtures of the commercial gasoline and benzol. (Table VIII) Analysis of the commercial gasolines shows an aromatic hydrocarbon equivalent of 17.4 per cent (Table VI). Gasolines E uivalent to Varying Percentages of Benzol Added to a ‘Eommercial Gasoline
Table VIII-Cracked
Benzol Tonkawa. Braman. No. Kansas crude ’ Smackover crude Kentucky fuel oil Cushing, Okla., fuel oil
10 28 12.5 10
Aromatic hydrocarbons in blends of benzol and gasoline
Gasoline 90 72 87.5 90
27 40.5 27.7 25.7
Comparative values of the motor fuel from actual motor tests and chemical analysis are given in Table IX. Table IX-Aromatlc Hydrocarbon Equivalents of Cracked Gasolines-Comparative Values Tonkawa, Braman, SmackKy. Cushing, Okla., No. Kansas over fuel fuel oil oil crude crude Motor test 25.7 40.5 27.7 25.7 Chemical analysis 24.2 36.6 29.0 26.5
The conversion of the percentages of unsaturated, aromatic, and naphthene hydrocarbons into an aromatic hydrocarbon number or toluene value gives good checks, as is shown by actual automotive engine performance when working upon synthetic blends of commercial benzol and gasoline.
Soluble Silicates-Correction In the article by J. D. Carter under this title, THIS JOURNAL, 18, 248 (1926), the firsr sentence under Figure 2 should read: In Figure 6 the cheesecloth on the left was treated with silicate and hypochlorite, the one on the right with the hypochlorite solution only.
