The Proximate Analysis of Gasoline 4
CHARLES L. THOMAS, HERMAN S. BLOCH,
AND
JAMES HOEKSTRA, Universal Oil Products Company, Chicago, Ill.
ANY methods have been devised for determining the chemical group composition of gasolines. Excellent reviews of these methods have been published by Faragher, Morrell, and Levine (S), Schildwiichter and Martin (I.$), Manning and Shepherd (Y),Kester and Pohle (6),and others ( I ) . Both the early methods reviewed in these papers and the more recent procedures, including those of Minter ( I O ) , Carriere and Lautie (2), Marder (8), Vlugter (16), and Kurtz and Headington (6), have the general disadvantage of being too cumbersome for the rapid routine analysis of the small amounts of gasoline most conveniently obtained from small-scale laboratory operations. In addition, many of the methods are of doubtful accuracy. It has been desirable for the authors' work to develop a method which combined rapidity, simplicity, and reasonable accuracy with an adaptability to the analysis of relatively small samples (100 to 300 cc.). The method finally adopted involves the separation of the gasoline into fractions in which the hydrocarbons of each chemical group contain approximately the same number of carbon atoms; the determination of the olefins in each fraction by the bromate-bromide method; the determination of total olefins and aromatics in each fraction by a single extraction a t 0" C. with fuming sulfuric acid containing 25 per cent of sulfur trioxide; and the estimation of the naphthene content of the residue from the acid extraction by its refractive index.
tionating efficiency equivalent to 5 t o 10 theoretical plates. The column illustrated in Figure 1 has been found especially useful for this purpose. When the gasoline contains Ct hydrocarbons, the dry ice condenser is used and Cc can be refluxed so that a clean separation between Cq and CS is made. The column is a combination of the head described by Marshall (9) and the type of body described by Podbielniak (IS). The gasoline is separated into fractions as follow8: Fraction
1 2
(CdO
3
(C7)
Boiling Point
(Cs)
Constituents
c.
10- 40 40- 70
C6 paraffins, olefins C6, Ca naphthenes
Ca paraffins, olefins Ca naphthenes. aromatics C i paraffins, olefins 4 (CS) 100-125 C i naphthenes, aromatics Ca paraffins, olefins, naphthenea 5 (Co) 125-150 Ca naphthenes, aromatios COparaffins, ole6ns, naphthenes 6 (Cis) 150-175 CParomatics , -C;, paraffins, olefins, naphthenes 7 (CII) 175-195 CLO aromatics CII paraffins. olefins, naphthenes a Because only paraffins and olefins are present in this fraction, the olefin deterniination alone IS necessary, the paraffins being obtained by difference. 70-100
This fractionation separates the mixture into fractions in which the constituents of each chemical group have about the same molecular weight. Because of the overlapping of the boiling points of some of the isomers and imperfect fractionation, however, each fraction will usually contain some hydrocarbons which belong to the next lower and next higher boiling fractions. Before each cut is made the column is run under total reflux for 5 to 10 minutes to be sure that the cut temperature
Fractionation The fractionation may be carried out with any small labora-
tory fractionating column having a low holdip and a frac-
BLP
FIGURE 1.
F R A C T I O S A T I N G COLCBIN, W A T E R CONDENSER, AND
1.53
DRY ICECONDESSER
INDUSTRIAL AKD ENGINEERING CHEMISTRY
154
VOL. 10, NO. 3
has been reached. If the temperature drops under total reflux, more dist'illate is removed until the cut temperature is again reached. Alternation between total reflux and a slow distillation is continued until the temperature does not fall with the column running a t total reflux.
Olefin Determination The olefins are determined by a modification of the methods of Francis (4) and Mulliken and Wakeman (11). REAGENTS.c. P. carbon tetrachloride, 10 per cent sulfuric
acid, a solution containing 15 per cent of c. P. potassium iodide,
a 1 per cent solution of "soluble starch" containing 0.1 per cent of zinc chloride as a preservative, a solution containing 13.92
grams of potassium bromate (c. P.) and 50 grams of potassium bromide (c. P.) per liter (this solution is 0.5 N), and a 0.2 N solution of sodium thiosulfate.
Procedure Mix 10 cc. of carbon tetrachloride and 10 cc. of 10 per cent sulfuric acid in a 250-cc. glass-stoppered Erlenmeyer flask and chill thoroughly in ice. Add to this mixture 1 cc. of the hydrocarbon measured at a known temperature. The most volatile fractions must be precooled before pipetting. Mix the sample in the carbon tetrachloride by shaking and cool again in ice. From a buret add 1 cc. of 0.5 N bromate-bromide solution. Shake vigorously and quickly immerse in ice. Continue periodic shaking and immersion until the yellow bromine color disappears. Continue to add 1-cc. portions of the bromate-bromide solutions in this manner until a permanent yellow color is observed in the carbon tetrachloride. (The bromate-bromide solution may be added in 2- to 5-cc. portions when it is known that the sample is quite unsaturated.) For each 10 cc. of bromate-bromide solution used add 5 cc. of 10 per cent sulfuric acid. When the yellow color no longer disappears] add 5 cc. of 15 per cent potassium iodide and titrate with 0.2 N sodium thiosulfate. Add the starch indicator when the color of the iodine in the carbon tetrachloride has almost disappeared. Until the potassium iodide is added it is imperative to keep the mixture as near to 0" C. as possible, in order to minimize substitution reactions and prevent loss of bromine vapor. The bromine number, B , is calculated from the formula 8
B ;I(NiVi - NzV2) N , = normality of bromate-bromide solution VI = cc. of bromate-bromide solution used NI = normality of thiosulfate solution V z = cc. of thiosulfate solution wed d = density of hydrocarbon sample at temperature used The weight per cent, W , of olefins may be calculated from the equation W=- M 160 W = weight per cent olefins B = bromine number M = molecular weight of olefins in fraction (70 for Ca, 84 for Ca,etc.)
Determination of Aromatics Pipet 10 cc. of the sample into a modified BahPROCEDCRE. cock bottle, and chill thoroughly in ice water. Gradually add, little by littIe, three volumes of fuming sulfuric acid (25 per cent sulfur trioxide), shaking the bottle vigorously after each addition, but keeping it immersed in ice water. After all the acid has been added, and a smooth emulsion achieved, centrifuge the mixture at 1000 r. p. m. for 2 or 3 minutes or allow it to stand until a clean separation into two layers is effected. The unabsorbed volume is read at the same temperature (either o" or room temperature) as was used in measuring the sample. The volume of aromatics is the difference between the total amount absorbed and the volume of olefins present. DETERMINATIOX OF KAPHTHEKES AND PARAFFINS.Kaeh the residue from the sulfuric acid absorption in a small separator)funnel, tn?ce with water and once with a 10 per cent sodium carbonate wlution. Dry it xvith anhydrouq potassium carbonate
u
/.360,00
u
80 60 40 20 MOL PEAC€/VT PARAFF/NS 0 20 40 60 80 MOL P€RC€NT NAPNTNENES
0
/OO
FIGURE 2. REFRACTIVEINDEX-COMPOSITIOW CURVESFOR PARAFFIN-NAPHTHENE MIXTURES or sodium sulfate, and determine the refractive index, ny. The Droportion of naphthenes present in the mixture is determined from the appropriate curve of Figure 2.
Errors and Calculations Mulliken and Wakeman (11) have shown that the bromatebromide method gives accurate results with a large number of aliphatic and cyclic olefins ranging from hexene and cyclohexene to hexadecene and cyclohexylheptene. Check runs made by the authors' procedure (which differs in only minor features from that of Mulliken and Wakeman) on several olefins are summarized in Table I. TABLE I. BROMINE NvMBERDETERMINATIONS Substance
B , Calculated
B , Found
20% diisobutylene in isoactane Cyclohexene n-Octenes 2-Ethyl-liexene-l Pentene-1
29.6
28 2 188 141 139 93,"
195
143
143 228
Some error is undoubtedly introduced by the presence of diolefins in some cracked gasoline. It is not believed that this error, in general, will be large. If the presence of conjugated diolefins in significant amounts is suspected] they may be removed by the procedure of Kurtz and Headington (6) before the distillation of the gasoline. Absorptions carried out on mixtures of paraffins, naphthenes, olefins, and aromatics of known composition with sulfuric acid of various concentrations showed that the amount of absorption was dependent on both acid concentration and temperature. To eliminate the latter variable, 0" C. was chosen as the most conveniently attainable constant temperature; this low temperature has the further advantage of making less violent the absorption n-ith highly olefinic fractions. At 0' C., with the experimental procedure employed, no acid concentration less than fuming sulfuric containing 20
MARCH 15, 1938
ANALYTICAL EDITION
155
It is believed that, especially for the lower fractions, the error involved in the estimation of naphthenes and paraffins from Figure 2 does not exceed the experimental error inherent in the other group determinations. The curves were drawn from the average of values reported in the literature TABLE11. ABSORPTION OF BEXZEKE FROIf BEKZEKE-n-HEP- for the known hydrocarbons occurring in each fraction. Only those naphthenes likely to occur in petroleum products TANE MIXTUREBY SCLFURIC ACID were considered, however; derivatives of cyclopropane and Acid TemperaAromatics E\-pt. Concentration ture Present Found An?' cyclobutane were excluded. I n the higher-boiling naph7i c. % % thene fractions, considerable uncertainty is involved in 1 95.6 0 50 5 ,..... estimating an average refractive index because of the neces2 95.6 Room 50 21 ...... 3 95.66 Room 50 46 ...... sity for including isopropylcyclohexane, the menthanes, and 4 9s 0 50 11 ..... 5 98 Room 50 50 -0 0062 decalin with naphthenes of much lower refractivity. Since the amount of these higher fractions is relatively small in 50 48 .... 6 99 Room 50 29 7 100 0 the average gasoline, relatively large errors may be tolerated 50 50 -o:oo4n 8 100 Room 5n 50 -n.o032 in the analysis of these fractions without greatly changing 9 Fuming, 5 So3 o 5n 50 0039 10 Fuming, 10 So3 o the analysis for the entire gasoline. When the CY, and CH 0 50 50 -0.0012 I1 Fuming, 15 So3 fractions are the main constituents of a high-boiling naphtha 0 50 53 t o .no02 12 Fuming, 20 So3 the authors cannot recommend this method of analysis. 0 50 52 +o. 0002 13 Fuming, 25 SOa 52 14 Fuming, 2 6 . 5 So3 --I 50 Theoretically, the results should all be expressed in con0 50 53 +o:ooo2 15 Fuming, 2 6 . 5 So3 sistent units-i. e., either weight per cent or volume per cent. in0 16 I n practice, however, i t has been found more convenient to 100 170 100 18d express the per cent of olefins as the weight per cent experi"in? observed index of residue minus index of n-heptane (1.3878). mentally determined; the per cent of aromatics as the dif6 Kattwinkel reagent (30 grams of PzOa per 100 cc. of acid). ference between the latter quantity and the volume per cent Sample waa residue of 16. d Sample was residue of 17. of aromatics plus olefins; and the per cent of naphthenes and paraffins as the mole per cent of the residue left from the Lowering of the temperature to -7" C. did not cut down sulfuric acid absorption, the amount of residue being exthis additional absorption. Three successive absorptions with pressed in volume per cent. 100 per cent sulfuric acid at 0" C. (experiments 16 to 18) also TABLE Iv. CALCULATED RESULTS gave extra absorption, so that this procedure has no advanWeight Olefins Paraffins Naphthenes Aromatira tage over a single extraction with stronger acids. Fiaction of Total A B A B A B A B The results given in Table I11 show that., although 100 per % % % % % % 7 c % 7 c cent sulfuric acid at room temperature and fuming acid R u n B6 4 containing 5 t o 10 per cent of sulfur trioxide produced the 2') 15 1 51 51 6 7 5 4 38 38 L E J Cr 28.2 18 18 52 49 8 8 22 25 correct absorption from a paraffin-naphthene-olefin-aromatic Ca 29.0 9 9 56 53 4 3 31 38 mixture, no acid weaker than 25 per cent sulfur trioxide 21.5 3 3 61 56 8 8 28 33 c 9 1 1 64 64 Residue 6.5 30 30 5 5 fuming sulfuric left a residue of the correct refractive index. per cent of sulfur trioxide removed benzene completely from a benzene-heptane mixture, as shown in Table 11. At the same time, this and more concentrated acids showed absorption of 2 to 3 per cent above the aromatic content.
P
0
Total gasoline
TABLE 111. ABSORFTIONO F AROMATICS MIXTURE^ Expt.
Sulfuric .4cid Concentration
19 20 21 22 23
95.6 98 98 99 100
%
24 25 26 27 28
+ PzOaC
100 Fuming, 5 603 Fuming, 10 SOs Fuming, 15 So8 Fuming, 20 SOa
Temperature
AND
OLEFINS FROM
+
c.
%
%
40 40 40 40 40
38 24 34 36
Room
40 40 40 40 40
40 40 40 43 41
0 0
36
CS
c8 c7
Aromatics Olefins Present Found
Room 0 Room Room 0 0 0
A
Anyb , . , . . .
......
....., , . . . . .
...... +O +O
+o +O +o
0081 0040 on32 0019 0015
29 Fuming, 25 SOs 0 40 44 0. oono 44 ..... 30 Fuming 2 6 . 5 SOs -7 40 31 Fuming: 2 6 . 5 SOs 0 40 45 -0,0002 a hfixture contained 40 per cent n-heptane, 19.5 per cent benzene. 20 per cent cyclohexane, 10.5 per cent octenes, and 10 per cent cyclohexene {by volume). b any = observed index of residue minus index of 2: 1 n-heptane: cyclohexane mixture. c Kattwinkel reagent.
I n spite of the fact that the latter reagent absorbed 4 per cent more than the total olefin-aromatic content, i t was chosen as the best all-round absorbent a t 0" C. Methods involving the use of weaker acids and distillation to remove polymers were considered undesirable because of the small samples available; furthermore, the results on the benzene%-heptane mixture (Table 11), in which polymerization is improbable, make i t doubtful whether the 98 per cent sulfuric acid used by Faragher, Xiorrell, and Levine (S), by Ormondy and Craven ( l a ) ,and by others completely absorbs all aromatics.
C8
c9
ClO
Residue Total gasoline
0 6 30 21 15 4 22
18
3 1 0 3 2 5 6
100 78 16 I1 40 71 52 33
18
45
R u n B6D 100 0 78 4 16 10 11 9 40 1 71 0 52 0 33 5
42
6
0
31
34
0 4 9
0 10
7 1 0 0
0 0
0 h 8 7 1 0 0
5
5
5
0 10 64 72 58 29 48 57
0 10 67 75 5s 29 48 57
8
8 1
The error introduced by mixing units (weight per cent, volume per cent, and mole per cent) becomes smaller the more closely the density of the olefinic portion of each fraction a p proaches the density of the fraction as a whole, and the percentages approach volume per cents. T h a t this error is well within the experimental error was shown by calculating in two ways the results for two cracked gasolines of widely different composition. The first method of calculation, A , was the convenient one just outlined. The second method, B, expresses all the results as weight per cents, and involves the estimation of average densities for the paraffins and naphthenes of each fraction, conversion of the volume per cent of the paraffin-naphthene mixture to weight per cent, and then finding the weight per cent of aromatics by difference, the olefins being determined as weight per cent experimentally. The results are shown in Table IV. It should be noted that the deeply cracked gasoline (B6D) shows a jump in olefin content in the fractions boiling above 125" C. (Cg, C10, and residue). The olefins present may be aromatic olefins (styrene and its homologs) since these fractions show unusually high densities and refractive indices. These olefins may therefore be considered either as such or as aromatics, depending upon the purpose of the analysis.
INDUSTKIAL AND ENGINEERING CHEMISTRY
156
To test the consistency of the entire method, two mixtures were prepared from analyzed cracked gasolines, and the compositions of the mixtures were determined by experiment and found by calculation. A comparison of the results is given in Table V.
Paraffins
Per Cent Saphthenes .Iromatics
can be used with other procedures, do much to recommend it as a routine method, especially for comparative purposes. As such, it should prove valuable until more exact methods are available.
Literature Cited
TABLE v. COhfPARATIVE RESULTS aaiiiiilc
VOL. 10, NO. 3
Olefins
In no case do the differences exceed 5 per cent; in most cases they are much lower. It is believed that this value represents also the limit of precision of the method.
Conclusion
It is clear that the analytical method herein outlined is not rigorously accurate. Nevertheless, in the absence of a simple exact method, the rapidity and simplicity of the operations involved in the procedure, the fact that the errors for different samples tend in the same direction, and the adaptability of the method to the analysis of smaller amounts than
(1) Anon., Petroleum Z . , 32 (23,1 and (9), 1 (1936). (2) Carriere and Lautie, Chiniie & industrie, Spec. KO. 3. 337-9 (1931). (3) Furasher, Morrell, and Levine, ISD. ESG. CHEZI.,Anal. Ed., 2, 18 (1930). (4) Francis, ISD. ESG. CHERI., 18, 821 (1926). (5) Kester and Pohle, I b i d . , Anal. Ed., 3 , 294 (1931). ( 6 ) Kurtz and Headington, I b i d , 9, 21 ,1937).
( 7 ) LIanning and Shepherd, Dept. of Sei. Ind. Research (Brit.), Fuel Research Tech. Paper 2 8 (1930). (81 hlarder et al.. Oel. Koide. Erdoel. Teer 11. 1. 41. 182 222 119351. (9) Marshall, IBD. EBG.C H E M , 20, 1379 (1928). (10) Minter, Nutl. Petroleum /Yews, 25, KO.8, 25, 27 (1933). (11) hlulliken and Wakeman, ISD. ENG.CHEW,Anal. Ed., 7, 59 (1935). (12) (13) (14) (15)
Ormondy and Craven, J . I n s t . Petroleum Tech., 13, 311 (1927). Podbielniak, IND. EKG.Cmnf., Anal. Ed., 3, 177 (1931). Schildwachter and Martin, BTennstofl-Chem., 16, 301 (1935). Wugter, J. I n s t . Petroleum Tech., 21, 36 (1935).
RECEIVEDJanuary 6, 1938. Presented before t h e Division of Petroleum Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. Y.,September 6 t o 10, 1937.
Chemical and X-Ray Diffraction Studies of Calcium Phosphates HAROLD C. HODGE, MARIAN L. LEFEVRE, AND WILLIAM F. BALE University of Rochester School of Medicine and Dentistry, Rochester, N. Y.
The constancy and punty of composition
of various commercial primary, secondary, and tertiary calcium phosphates are estimated. Secondary calcium phosphates are of least variability; primary and tertiary of marked variability. Evidence of three crystalline forms each of unignited primary and secondary cal-
D
ESPITE the profusion of papers on the chemistry of the
calcium phosphates, there are many fundamental points still obscure. As Drakunov (11) points out, t h e study of these important substances involves great experimental difficulties. Larson (20)reported the preparation and properties of primary, secondary, and tertiary calcium phosphates "in pure crystalline form." However, a number of recent investigations offer contradictory evidence especially on the nature of the tertiary calcium phosphates. The work reported herewith proposes to examine the commercially prepared primary, secondary, and tertiary calcium phosphates chemically and by x-ray diffraction studies in order (a) to estimate the constancy and purity of composition of the commercial products, and (b) to interpret the analyses in the light of recent findings on the nature of these compounds. I n the interpretations, no attempt will be made to review exhaustively even the recent literature, but only such experiments or hypotheses as seem pertinent will be included. The commercially prepared calcium phosphates used in this investigation have been obtained from eight different
cium phosphates is found from x-ray studies, The commercial tertiary calcium phosphates are probably hydroxylapatite with more or less adsorbed phosphate ions resulting in empirical formulas approaching the theoretical value for Ca3Pz08. Secondary calcium phosphate may be admixed. companies-five in this country, two in Germany, and one in England. Two samples each (of different lot numbers) of the tertiary phosphates and one each of the secondary and primary phosphates were used.
Analytical Procedure In each case, samples were taken from the top and bottom of the bottle; inssmuch as no difference was found, these two values served as duplicate determinations on each product. The samples were dried at 105' C., cooled in a desiccator, and analyzed for calcium and phosphorus according to the gravimetric methods (accuracy: Ca, 0.3 per cent; P, 1.0 per cent) of Washburn and Shear (28). For ignition, a third sample was similarly dried, cooled, weighed into a platinum crucible, heated for 1 hour at 900" C . , cooled, and weighed, and samples were taken for analy-
sis as before.
X-Ray Diffraction Procedure For x-ray powder diffraction photographs, an apparatus was used similar in design to the General Electric diffractive apparatus Type YWC, Form D, described by Davey (8). In order to
obtain intensity measurements of diffraction maxima, a series of standard densities was obtained by a graduated, accurately
