APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
499
points have been corrected to the standard pressure of 760 BOILINGPOINTS OF FLUOROCHLORO HYDROCARBONSmm., using the values of d t / d p calculated from the vapor AT A PRESSURE OF 760 MM. pressure equations and shown in column 4. Other boiling Obsvd. B. P. Calcd. d t / d p at Obsvd. B . P. points which have been reported for these compounds are Compound (This Work)a,b EL P. B. P. (Other Work) also shown in Table V. e. C. C./Mm. c. CHClF? -40.80 -40.80 0.028 -40.8 t o -40.6 (S), -39.8 (9) Literature Cited CHC1.F 8.92 8.92 0.034 8.9 to 9.0 (6).13.5 t o _ ~ .~ ~ _ 15.5 (21, 14.5 ( I f ) (1) Benning, A. F., and McHarness, R. C., ISD.ENG.CHEM.,31, 24 (8),24.9(10) 23.71 0.037 CClsF 23.77 912-16 (1939). 0.039 47 2 5 C (6) 47 3 b (SI, 47.52 47.57 CChF-CClF2 47.4 (12j, 4f.68 (91, ( 2 ) Booth, H. S., and Bixby, E. M., Ibid., 24, 637-41 (1932).
TABLEV.
0
47.7 ~... f7) \ ,
Q
b c
From va or pressure d a t a C o r r e c t e f t o 760 mm. b y &ing the d t / d p ratio given in column 4. Extrapolated t o 760 mm. b y t h e authors.
values and the equations from which they are derived are given, together with the deviation of the observed from the calculated values. The range of each equation is indicated by the magnitude of the deviations. Other vapor pressure measurements which have been made on these compounds and reported in the literature are also shown. Table V gives the calculated and observed boiling point of each compound. Where necessary the observed boiling
(3) Booth, H. S., Mong, W. L., and Burohfield, P. E., Ibid., 24,
328-31 (1932). (4) Booth, H. S., and Swinehart, C. F., J . Am. Chem. SOC.,57, 1337-42 (1935). (5) Henne, A. L., Ibid., 59, 1400-1 (1937). (6) Hovorka, F., and Geiger, F. E., Ibid., 55, 4759-61 (1933). (7) Locke, E. G., Brode, W. R., and Henne, A. L., Ibid., 56, 1726-8 (1934). (8) Midgley, T., Jr., and Henne, A. L., IND..ENO. CHEM.,22, 542-5 (1930). (9) Riedel, L., 2. ges. K d l t e - I d . , 45, 221-5 (1938) (10) Swarts, F., Be?., 26 Ref.,291-2 (1893). (11) Ibid., 26 Ref.,781-2 (1893). (12) Swarts, F., J. chim. phys., 28, 622-50 (1931). ,
I
COBTRIBUTION 3 from Kinetic Chemicals, Inc.
Naphthenic Acids from Gulf Coast Petroleum The naphthenic acids present in the lubricating oil portion of a Gulf Coast petroleum have a molecular weight range of about 220-440, corresponding to 1 4 2 9 carbon atoms per molecule. The hydrogen deficiency below the fatty acid series (C,H2,02) is 6 1 0 atoms per molecule. This is not due to simple unsaturation but to naphthenic rings with possible admixture with aromatic rings. If aromatic acids are absent, at least five naphthene ring closures are indicated in some of these acids. The acids are at least substantially monobasic. HE term "naphthenic acids" describes the cyclic carboxylic acids occurring in and obtained from petroleum. Until recently commercial naphthenic acids have been extracted only from the kerosene and gas oil fractions; therefore their boiling points are within the range of these materials. These acids have an average molecular weight of the order of 200. Only recently have the naphthenic acids extracted from the lubricating oil fractions of petroleum become commercially available. These heavier acids from the higher boiling fractions obviously have higher molecular weights. Although a considerable amount of work has been done on the constitution of naphthenic acids, the experiments have centered mainly about the lighter acids, and comparatively little is known about the acids of high molecular weight.
T
COMPOSITION OF HIGHER BOILING ACIDS ROY W. HARKNESS .4ND JOHANNES H. BRUUN Sun Oil Company, Norwood, Penna. Thus in the early history of the study of these substances the names of Aschan ( 2 ) , Markownikoff (11), Zelinsky (14, 15), and Komppa ( 8 ) appear. The work of these investigators in general indicated that a 5-carbon ring predominated in the nucleus of the low-molecular-weight acids. Within recent years the investigations of von Braun (3, 4) have been outstanding because of their thoroughness. He succeeded in isolating the first homogeneous naphthenic acid from petroleum (6). It was found to be 3,3,4trimethylcyclopentylacetic acid H CH, having a molecular weight of 170 HsC--b--CCH3 I and the accompanying structural formula. The structure was H2-b AH2 established by degradation of the acids to ketones from which a pure \&,H2COOH individual ketone of known comH position was isolated. The existence of homologous acids differing only in the number of methylene groups adjacent to the carboxyl group was proved. With regard to acids of higher molecular weight yon Braun (4)states that they are of two types, monocyclic CnH2, - 201 and bicyclic CnHzn- 402.The monocyclic type comprises in general the acids of 8 to 12 carbon atoms. The bicyclic acids contain from 13 to as high as 23 carbon atoms per molecule.
INDUSTRIAL AND ENGINEERING CHEMISTRY
500
The latter represent the highest molecular weight fraction of acids which he obtained. Muller and von Pilat ( l a ) isolated bicyclic naphthenes with a carbon skeleton of 28 carbon atoms which had been prepared from naphthenic acids of high molecular weight. GULF Cmsr CRUOE PLTROLEUM
DISTllLATlON
T I
TREATMENT OF REDUCED CRUDE W I T H SOOlUM HYOROXIOE AND DISTILLATION
I
I % :::
VOL. 32, NO. 4
nates, were liberated and separated to give a commercial product. Further purification of these naphthenic acids' was accomplishcd (Figure 2 ) by neutralizing the acids with a solution of potassium hydroxide (230 grams per liter) in aqueous ethyl alcohol (1 : 3), using about 10 per cent excess of the theoretical requirements, and extracting the hydrocarbons and similar impurities with liquid butane a t '70-90" C. in a pressure extractor until no more extract was obtained. The hydrocarbon-free naphthenic soaps obtained as an extraction residue were dissolved in dilute sulfuric acid, washed with water until free from mineral acid, and dehydrated. The resulting naphthenic acids were free from hydrocarbon impurities and their saponification and acid numbers were 166.0.
T
r-----!
1 I
LU8RlCATlNO
OIL
f%ACT/ONS
1 1
Fractionation of Purified Acids
1
BOTTOMS CONTAINING ODIUM
#APHTNfNATES
FIGURE 1. ORIGINOF RAW'MATERIAL
Although no pure compounds containing more than two rings to the molecule have actually been isolated from naphthenic acids, there is some evidence that such compounds do exist. Alleman (1) obtained fractions which had 16 to 25 carbon atoms in the molecule, and which showed empirical formulas of CnH2n--402, C,H2,-602, and even CnHz,-802. COMMERCIAL NAPHTHENIC ACID3
Inasmuch as the purified hydrocarbon-free naphthenic acids represented a relatively wide range of different compounds, i t was necessary to subject the material to fractionation into narrowboiling cuts before any reliable information could be obtained regarding their composition or the type of compounds present. I n order to avoid any possibility of decomposing these acids which normally distill up to 350" C. a t pressures of 15 mm. of mercury, the fractionation had to be carried out in a molecular still (13) a t very low pressures. The apparatus used for this purpose was a slight modification of that developed a t the National Bureau of Standards (10) and is shown in Figure 3. The flow of the naphthenic acids from the reservoir a t the top was controlled by means of a magnetic valve in such manner that the feed would enter the top of the column dropwise and then continue in a downward
POTASSIUM
L€CCTROMAGNE T
#A PH THENATES
h'fCL€OD
I
I
HrDUOCAREON
/M PURITIES
I
I
1
I
AlRlflEO NAPHTUCNIC ACIOS (ACJO Na-166)
I
OF NAPHTHESIC ACIDS FIGURE2. PURIFICATION
Since the number of possible isomers increases tremendously with the number of carbon atoms in the molecule, it is evident that the possibility of separating individual acids in a pure condition and accurately determining their structural formulas becomes increasingly smaller as we approach the higher members of the series. The best that one can possibly hope to accomplish under such circumstances is to isolate relatively narrow-boiling fractions and to derive some information regarding their structure and composition from the various physical and chemical properties that can be determined.
Separation and Purification of High-Boiling Acids The naphthenic acids which were the starting point of the present investigation were the heavy acids from Gulf Coast crude oil (Figure 1). After the gasoline and gas oil had been distilled from this crude in the conventional manner, the reduced crude was distilled from sodium hydroxide to obtain the lubricating oil fractions. The corresponding naphthenic acids, retained in the residue from this distillation as naphthe-
FICCRE3. MOLECULAR STILL
1/ACUUM
APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEI, FIRSTFRACTIONATION SERIES
-
736 Grams-Av. temp., yo of c. charge
Serial iYo. of cut
112 130 140 150 160 Residue
A-1 A-2 A-3 -4-4 '4-5 A-6
" Saponification number
TABLE11. Serial S o . of cut
17.4 32. !I 24.2 13 I1 7.3 5.1
c.
Saponification KO. 210
187 167 154 136 110
Serial No. of cut B-1 B-2 B-3 B-4 B-5 B-6
OF PURIFIED lTAPHTHEXIC .ACIDS' 1406 Grams 1415 GramsAv. temp., of Saponifica- Serial No. d v . temp., % of O C. charge tion No. of cut c. charge 100 10.1 21 2 e-1 18.2 93 22.9 112 e-2 19.1 198 101 121 115 c-3 17.7 19.7 179 13.1 14.0 169 121 e-4 128 154 c-5 139 10.8 10.9 133 17.4 26.4 137 C-6 Residue Residue
Saponification So.
Acid So.
LOW-PRESSURE DISTILLATIONS hIol. Weight (Exptl.)
Refractive Index,
nko
Density, dZ0
208 Charge Consisting of Samples 8 - 1 , B-1, C-1; Av. Saponification KO., 72 230 221 219 1.4879 0.9944 D-1 0-2 75 218 215 ,,. 1,4901 0.9964 80 213 210 251 1.4915 0.9954 ,, 1.4936 0.9948 00 -- 43 85 204 202 188 190 323 .... .... D-5 91 164 ... 1.4977 0-6 Residue 164
.
....
Charge Consisting of Samples A-2. B-2, C-2; Av. Saponification KO., 189 E- 1 75 222 214 252 1,4907 0.9958 E-2 77 206 202 1.4925 0.9944 ... 83 201 198 275 1.4937 0.9952 E-3 ... .... .... E-4 88 187 189 .... .... E-5 95 175 176 320 E-6 Residue 157 158 327
....
....
Charge Consisting of Samples A-3, B-3. B-4, C-3; Av. Saponification No.,172 F-1 Xfi 203 199 . . ~~. 268 1.4938 0,9972 ~ 89 189 186 ... .... F-3 95 187 183 291 1.4961 0.9900 P-4 100 180 180 1,4967 0.9886 F-5 1?1 170 169 374 1.4983 F-6 Residue 156 156 .... ....
k-i
.-
Saponification No. 206 183 171 154 147 136
of charge, 166.0.
SECOiiD SERIES O F
Ar. Temp.,
7 -
501
__
111. THIRDSERIES Av. Temp., C.
Serial No. of cut
Saponification No.
O F 1,OW-PRESPURE
Acid No.
hlol. Weight (Exptl.)
DISTILLATIONS
Refractive Index, n?
Density, di0
Charge Consisting of Samples D-5, 0 - 4 , F-2; Av. Saponification KO.,188 I-1 71 208 205 269 1.4932 .... 1.4976 0.9952 195 194 ... 1-2 78 I-3 92 191 190 300 1.4950 0.9909 ... I-4 101 178 177 1.4967 0.9885 I-5 ... ... ... ... .... I-6 ....
...
...
...
...
Charge Consisting of Samples E-6, F-6, G-3, H-1; A v . J-1 116 171 170 329 J-2 122 160 161 ... J-3 131 156 155 382 J-4 139 152 151 ... J-5 150 144 146 406 J-6 Residue 134 132 ...
Saponification No., 157 1.4978 0.9840 1.4995 0.9791 1.5004 0,9752 1.5010 0.9762 1.5024 .... 1.5070 ....
.... ....
...
Charge Consisting of Samples -4-4, B-5, C-4, C-5; Av. Saponification No., No.. 152 G- 1 112 181 181 308 1,4970 0.9877 G-2 0.2 123 166 169 , , , 1.4988 0.9855 _ G-3 134 159 157 364 .... G-4 142 147 147 1.5024 0.9815 G-5 156 136 137 427 1.5048 0.9796 G-6 Residue 123 125 ,. 1.5085 ....
....
~~
.
Charge Consisting of Samples A-5, A-6, B-6, H-1 131 158 158 H-2 138 149 147 H-3 148 144 143 H-4 153 138 137 H-5 167 129 129 H-6 Residue 122 122
TABLE
C-6; Av. Saponification No., 136 350 .... .... ... 1,5023 0.9837 398 1.5029 0.9763 ... 1.5051 0.9814 440 1,5020 0.9756 558
....
....
liquid and resulted in a more uniform operation of the still as well as a better fractionation of the naphthenic acids collected in the top receirers. The starting material used for the distillation con&ed of about 3500 grams of purified naphthenic acids with a saponification and acid number of 166. This material was divided into three portions, and each portion was separately subjected to a distillation in the molecular still. Each portion gave rise to six cuts so that three sets of six cuts each were obtained. The results of these distillations are given in Table I. and a flow diagrain is shown in Figure 4. The second series of distillations of the naplithenic acids consisted of five individual runs (Table 11). The charge for these distillations were obtained by mixing fractions from the first distillations having similar boiling points and saponification numbers, such as A-1, B-1, and C-1. I n the third distillation series (Table 111)fractions from the second distillation having similar constants were mixed and fractionated further. All of these distillations were conducted
direction along the outside of the inner column, the inside of which was packed with jack chain and heated by means of boiling hydrocarbon mixtures, The descending naphthenic acids were thus vaporized and condensed on the relatively cold inside wall of the outside PURIFIED NAPU,THEN& ACIDJ glass column from which they TTere diverted 3500 G. to the various receiving bulbs by means of the ACID N o 166 Av. MOL.Wz 336 collecting cups or ring seals. The lowest boiling compounds were thus collected in the top receivers while the fractions with successively higher boiling points would pass over into the lower bulbs. The undistilled residue accumulated into the bottom receiving bulb. 1-1 I iilthough the original inside columns were made with a plain surface, the column shown in Figure 3 was Drovided with a number of glass rings sealed- horizontally to the outside I/ 1p13i4r.m1 111 t l ~ i 4 1 5 1 sl/ipl3i415161 l I 1 1 2 1 34\345~ 6 1 wall of the inside column a t intervals of 244 263 321 8 mm. This feature (suggested bv B. J. I hlair) eliminated the uneven-distribution previously obtained when the material to be distilled had a tendency to f l o down ~ in narrow streams. The rings kept -practically the entire surface of the inner column covered with FIGURE 4. DISTILLATIOS OF N A P H T H E ~ ACIDS C IS MOLECULAR STILL
I
1 n -
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
502
VOL. 32, NO. 4
TABLE IV. COMPOSITION OF FRACTIONATED CUTSOF PURIFIED NAPHTHENIC ACIDS Serial No. of Cut Saponification No. Acid No. Mol. wt. Exptl. value From saponification No.
0-3
D-1
Carbon yo Hydrog‘en. % Oxygen,,% C/H ratio
J-3
H-5 129
221
191 190
219 244
251 263
300 294
320
321
382 360
440 435
74.69 10.44
76.46 10.81 12.73
76.65 10.74 12.61 7.13
77.95 11.08 10.97 7.05
78.86
11.07
80.19 11.27
0.7
0.8 10.00 1.00 20.8 35.3 2.21
0.4
1.7 7.38
7.07
7.15 0.6
3.0
13.15 0.90
yo
E-5 175 176
213 210
14.87
Bromine NO.^ 0 from saponification No., COOH groups per mol. No. C atoms per mol. No. H atoms per mol. KO.0 atoms per mol.
I-3
230
12.17
10.92 1.02 19.2 32.0 2.36
0.96 16.0 27.0 2.00
13.6 22.7 2.03
156 155
10.07 7.12 8.90 1.06 25.1 42.0 2.40
129
8.54 7.11
1.01 29.4
49.2 2.36
.4v. empirical foruiula
Approx. type formula
Obtained b y the method of Johansen (7).
at pressures between lo-* and 10-3 mm. of mercury, and the liquid temperatures varied between 71’ and 167’ C. The experimental molecular weights given in Tables 11, 111, and IV were determined cryoscopically in benzene and were calculated on the assumption that the acids were 75 per cent associated in the benzene solution. In several cases these values were checked by determining the freezing point lowering in acetic, stearic, and benzoic acids, assuming no association, and also by determining the boiling point elevation in benzene, assuming the degree of association determined by Brocklesby (6).
Discussion of Results Of the fractions obtained from the molecular distillation, six were selected as representing the average composition of the composite higher boiling petroleum acids used in this investigation. These cuts, together with some of their physical and chemical constants, are listed in Table IV. I n Figure 4 they are indicated by blackened squares with the molecular weight stated below each square. TABLEV.
MOLECULAR WEIGHTSOF XAPHTHENIC ACIDS FREEZING POINTMETHOD IN STEARIC ACID^
Acid Naphthenic, No. 1
Saponification No. 183
Mol. Wt. b y Saponification No. 306
Ratio, Concn. G. Acid/1000 G. Solvent 174.5
142.0 103.2 69.0
38.8 0
Naphthenic, No. 2
Naphthenic, No. 3
Benzoic (c. P.)
160
147
...
350
380
122
Oleic (commercial)
Deviation from Theory + 6
2; + 1
- 10 - 8
191.6 156.4 81.6 0
354 354 357 359b
+ 4
1130 2 120.,5 95.1 60.4 0
374
- 6
380 392 401b
- 4 0 f12 +21
122.6
+ 00 .. 06
77.5 64.9
27.1 Undecylic ( E a s t m a n Kodak Co.)
Mo?. Wt. (Exptl.) 312 308 300 307 294 298b
BY
37fi
122.0
0
121.1 121.0b
+ 4 t
7
+ 9
--
0.9 1.0
.. .
186
94.9 73.0 44.5 0
187.2 186.6 186.5 186.0b
4- 1 . 2 4- 0 . 6 f 0.5
...
282
80.1 50.: 32.t 0
2R1.0
-
Determined b y Kurtz and Voelker ( 9 ) . b Extrapolated molecular weight from plot of data.
280.3
280.6
281.Ob
0.0
-
1.0 1.7 1.4
1.0
Although the six cuts can by no means be taken to represent individual compounds, the following generalizations regarding the type and size of the molecules nevertheless seem justified: 1. The specific gravities of the acids present in the Gulf Coast crude were found to decrease in eneral with increasing molecular weight. This corresponds to t i e behavior of Russian naphthenic acids, whereas the specific gravities of naphthenic acids from Rumania show an increase with molecular weight. 2. The higher boiling petroleum acids are of the monobasic type. The number of carboxyl groups per molecule varies between 0.9 and 1.04; for dibasic and tribasic acids this value should be 2.0 and 3.0, respectively. Table V gives some molecular weight data determined cryoscopically in stearic acid for several naphthenic acid samples which were similar in source to those of the present investigation (9). 3. The average empirical formulas indicate that the composition ranges from CnHPn--rlOlup to CnHln-lo03, and the average number of carbon atoms in the molecule varies from 14 to 29. 4. Since the bromine numbers in every case were found to be negligible, it is apparent that the high ratios of carbon to hydrogen are not due to the presence of unsaturated fatty acids. Although von Braun and others found evidence that carbon skeletons of as high as 28 carbon atoms have only one or two rings in the molecule, the carbon to hydrogen ratios of the fractions given in Table I V indicate either that the higher boiling naphthenic acids contain between 2 and 5 carbon rings per molecule or that aromatic acids are present in these fractions. Further work on this subject will be necessary in order to explain with certainty which one of these two possibilities is the predominant reason for the hydrogen deficiency.
Acknowledgment The authors are indebted to F. H. Murphy and W. B. hf. Faulconer, respectively, for the determination of the physical constants and for the organic combustion data included in this paper.
Literature Cited (1) (2) (3) (4)
G., U. S. P a t e n t 1,694,461 (1928). hschan, O., Ber., 25, 3661-70 (1892). B r a u n , J. v o n , Chem.-Ztg., 59, 485-8 (1935). B r a u n , J. v o n , “ S c i e n c e of P e t r o l e u m ” , Vol. 11, pp. 1007-15, Alleman,
N e w Y o r k , O x f o r d U n i v . Press, 1938. (5) B r a u n , J. v o n , M a n n e s , L., a n d R e u t e r , M., Ber., 66B, 14991505 (1933). (6) B r o c k l e s b y , H. N., Can. J . Research, 1 4 B , 222-30 (1936). (7) J o h a n s e n , E. M., IND. EXG.CEEM.,1 4 , 288 (1922). (8) K o m p p a , G., Bel.., 6 2 B , 1562-70 (1929). (9) Kurtz, S. S., Jr., a n d Voelker, H. G., p r i v a t e c o m m u n i c a t i o n . (10) Mair, B. J., S c h i c k t a n s , S.T., a n d R o s e , F. W., Jr., J . Research Nail. Bur. Standards, 15, 566 (1935). (11) M a r k o w n i k o f f , W., Ann.,307, 367-74 (1899). (12) M u l l e r , J., a n d P i l a t , S.y o n , Brennstof-Chem., 17, 461-5 (1936). (13) W a s h b u r n . E. W., B r u u n , J. H., a n d H i c k s , M . M., BUT. Standards J . Research, 2, 477 (1929). (14) Zelinsky, N., Ber., 57, 42-51 (1924). (15) Zelinsky, N., and P o k r o w s k a j a , E., Ibid., 57, 51-8 (1924). PREsENTEn before t h e Division of Petroleum Chemistry a t the 98th hfeeting of the American Chemical Society, Boston, Mass.
