Color of Distilled Naphthenic Acids EDWIN R. LITTMANN' AND J. R. M.KLOTZ Stanco Distributors, Inc., New York 1 1 , N . Y .
A preliminary investigation on the sources of color of commercial naphthenic acid was made. Efficient fractionation does not completely remove either the organic source of color or the oil associated with naturally occurring naphthenic acids. Evidence is presented to indicate that the color of purified naphthenic acids is either closely associated with the structure o f the acid or inseparable from it by distillation.
T
HE persistent demand in the paint trade for light colored naphthenic acids arises from their use in the manufacture of very pale driers such as zinc and lead naphthenates. Because distillation is the method most conlmonly used to obtain color improvement, the present investigation was undertaken to determine the practical ultimate in color reduction. The materials contributing t o the dark color of crude naphthenic acids are generally considered to be iron salts, volatile color bodies, such as are found in gas oils, and oxidation products of phenols and unsaturated materials. Although iron salts are readily removed by distillation, some question exists as to the fate of the organic coloring materials also present. The degree to which products resulting from the cracking of naphthenic acids during distillation affect the quality of the distillate has also been the subject of some speculation. Associated with the problem of color improvement is the reduction in oil content of the acid.
I
0
600
500
400
WAVLLLHGTH I N M l L L l M l C R O H S
Figure 1. Typical Absorption Curves of Unpurified Naphthenic Acid Cuts
EXPERIMENTAL
reflux ratio of 5 to 1 was used. The temperatures and pressurea a t the top of the column were recorded and the temperatures were then corrected to atmospheric pressure. Eighteen 5% cuts and a 10% bottoms were collected. The over-head fractions were analyzed for acid number and unsa onifiable material by the method of Klotz and Littmann ( 1 ) . gectrophotometric analyses were made on the standard Coleman spectrophotometer, model 11, using a PC 4 filter.
Commercial naphthenic acids derived from mixed Venezuelan gas oils were used in the present experiments. Samples of crude naphthenic acids were washed with water in a separatory funnel to remove dissolved or suspended salts. The dried sample was then distilled in glass at 5-mm. pressure through a glass column packed with metal helices and having 20 equivalent plates. A 1
Present address, Enjay Company, Ino., New York 19. N. Y.
TABLEI. Cut No. Initial C. at 760 mm. Final a C. at 760 mm. Color Robinson Lovibond Color disk Color Neutralization No., mg. K O W g . Unsaponifiable matter, %
Transmission readings W a v e length, mp 360 375 400 425 450 475
1 160.0 173.9
2 173.9 226.7
23
2 1a/4
R
Y
22
R
Y
4 285.0 307.2
3 226.7 286.0
10.5 1 . 5 44.2 72.2
11.0 1.6
28 19 44 57 06 73 80 83 87 78 88 86 86
24 24 37 55 65 78 77 87 86 92 86 89 85
197.0 41.6
Y
23
R 17.0 2 . 4 272.0 18.2
Y
R
9.0 1 1
288.0 11.6
5 307.2 312.8
IXSPECTIONS OF
6 312.3 337.8
231/4
22 8/4
Y R 9.5 1.2 289 7.4
Y R 9.5 1 . 2 286.0 5.8
7 337.8 348.9 22
21
R
Y
1 2 . 0 1.6
272.0 4.6
26 24 39 57 67 80 83 87 87 87 88 85 85
1462
FR.4CTIONS
20
Y I 1 Y R 1 3 . 0 1.6 15.0 1 . 6 270.0 262.0 3.9 3.8
% ' Transmission at Specified Wave Length Using a Coleman Spectrophotometer 23 22 33 50 63 71 78 81 84 87 87 86 94
5%
(Crude naphthenio acid8 8 9 348.9 348.9 348.0 348.9
20 16 26 45 68 76 78 83 87 83 90 88 88
July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
Alternate cuts of the naphthenic acid distillate were freed of oil by the following procedure: one hundred grams of material were dissolved in 50% isopropyl alcohol and neutralized with a small but definite excess of sodium hydroxide. This solution was then extracted three times with petroleum ether. The naphthenic acids were recovered by first removing the alcohol from the sodium naphthenate solution on the steam bath and acidifying the alcohol-free solution with sulfuric acid. After taking up in petroleum ether and washing free of sulfuric acid with aqueous sodium sulfate solution, the ether was removed on the steam bat.h and the purified acids were heated to constant weight. Bromine numbers were determined by the usual method of dissolving the s a m d e in an alcoholic solution of hyd;ochloric acid and potassium bromide and titrating with a standardized potassium bromate solution. The effect of heat and/or air was determined by heating samples in glass a t 148.9' C. for 1 hour with constant agitation and free access of air. After cooling, the samples were analyzed spectrophotometrically.
1463
TABLE11. SPECTROPHOTOMETRIC ANALYSIS OF NAPHTHENIC ACIDFRACTIONS BEFORE AND AFTER HEATING" cut NO. 1
3
56 7b 9b 11b
12 b 13b 14b 15b 17
Conditions and Sample 425 Naphthenic acid 1 Heated 24 Oil Heated 3 Naphthenic acid 26 3 Heated 3 Oil 0 Heated 42 Naphthenic acid 4 Heated Naphthenic acid 46 16 Heated Nauhthenic acid 41 21 Heated Naphthenic acid 48 7 Heated Naphthenic acid 37 25 Heated Naphthenic acid 21 Heated 6 17 Nauhthenic acid 6 Heated 22 Naphthenic acid 5 Heated 3 Na hthenic acid 0 fieated Oil 0
% Transmission Reading, Wave Length in M s 450 1
475 2
500 3
32 35 5 5 0 54 5 56 24 51 32 59 12 50 37 31 11 28 9 35
44 8 48 9 10 1 63 8 65 34 61 43 68 21 60 48 43 18 40 16 47 17 10
54 12 58 14 17 1 70 15 72 43 67 53 75 30 67 58 53 27 51 23 57 25 17 0 0
10
6 0 0
0
0
525 530 555 7 8 17 Insufficient sample 63 65 71 68 17 70 18 24 75 21 26 1 75 24 77 53 75 62
80
42 75 66 63 36 61 32 65 33 26 1 0
23 28 1 76 26 79 55 78 64 82 44 76 68 64 38 63 35 67 35 28 1 1
31 34 2 81 36 82 62 83 71 85 54 79 74 71 49 71 44 73 45 37 2 2
580 27
605 38
630 46
650
76 28 80 41 41 5 84 45 85 68 85 76 87 62 81 78 75 56 75 52 77 52 46 5 3
78 33 84
80 37 86 55 55 13 89 63 87 75 88 82 89 70 84 84 80 68 80 64 83 65
81 41 85 60 58 19 90 66 88 77 89 83 89 72 85
8
15 13
86
88 72
89 77
60
49 9 87 55 87 72 87 79 88 67 83 82 78 63 78 59
81
59 54 10
11
82 72 81 66
84 69 64 19
60
19
Naphthenio acid +O.J%
PX
441 66 44 55 73 78 35 44 53 Heated 17 25 13 Naphthenic acid +0.1% PX 44 1 19 29 41 52 61 Heated 10 16 25 34 43 a Wave lengths below 425 and above 650 ml.r beyond range of b Insufficient oil sample. Commercial oxidation inhibitor.
The results of the experimental work are presented in the tables. The ei hteen 5% cuts and a 10% bottoms w h c h were collected were analyzed for acid number and oil content and were also subjected to spectrophotometric analysis in the range of visible color with a Coleman spectrophotometer (Table I). In order to determine the effect of the unsaponifiable material upon both the original color of the distillate and the color .stability of the acids themselves, the oil was removed from alternate samples and the analyses were repeated on the purified materials (Table 11).
An examination of Table I shows that even efficient fractionation does not completely separate the oil from any of the fractions. Because of the wide boiling ranges of both the naphthenic acids and the oil, it is not possible to determine if a true constant boiling mixture exists, though the relatively constant oil content of the middle fractions would tend to that belief. A further examination of the data in Table I indicates that appreciable cracking took
79 55
83 64
68
....
89 78
64 71 75 79 81 45 54 60 65 68 instrument and available filters.
83 70
place during the distillation, as there was an increased oil content in the higher boiling fractions. This phenomenon is emphasized further by the rapid increase in color in these fractions and by Table 111,which shows the average molecular weights of the several cuts calculated from the acid numbers converted to an oil-free basis. The decrease in molecular weight of the two highest boiling fractions is probably the result of cracking. I n an attempt to locate the origin of the color of the distilled naphthenic acids, typical absorption curves on both the unpurified and purified distillates were prepared and studied (Figures 1 and 2). Within the wave length range used there seems to be no significant difference between the several cuts of the unpurified
FROM DISTILLATION AT 5-MM. PRESSURE from Aruba) ..~ 10 11 12 13 14 15 16 17 18 C u t No. Initial C. a t 760 mm. 348.9 376.7 421.1 429.4 , 435.0 443.3 471.1 Final C. a t 760 mm. 376.7 421.1 429.4 435.0 443.3 471.1 485.0 Color Robinson 198/4 20'/4 191/2 20 1g8/4 17 17I/z 17 48/4 Lovibond Y R Y R Y R Y R Y R Y R Y R Y R Y R Color disk 10.5 1 . 4 11.0 1.4 14.0 1 . 5 11.0 1.1 14.0 1 . 0 21.0 1.2 8 3 . 0 22.0 102.0 29 Toodark Color Neutralization No., mg. KOH/g. 250.0 247.0 240.0 231.0 224.0 206.0 190.0 156.0 101 Unsaponifiable matter, % 3.5 3.1 3.0 2.8 2.9 6.2 9.8 21.6b 56.3 Transmission readings % Transmission a t Specified Wave Length Using a Coleman Spectrophotometer Wave length, mfi 360 18 18 16 16 18 13 14 12 2 376 14 13 11 11 11 8 8 7 1 400 22 20 18 17 14 8 6 4 1 425 41 41 36 37 33 17 10 6 1 450 59 59 54 56 53 37 26 17 1 69 70 67 64 72 58 49 40 1 475 500 76 75 78 76 78 71 65 60 3 525 79 85 79 84 86 79 73 71 7 550 85 84 80 84 87 79 78 77 10 575 83 83 80 85 83 81 79 80 13 600 84 83 81 89 85 86 79 81 17 625 84 85 86 84 86 83 80 79 21 650 82 85 82 81 84 82 81 82 26 Commercial naphthenic acid from Wecker still. b High unsaponifiable number attributed t o cracking during distillation.
-
85
Insufficient sample
EXPERIMENTAL RESULTS
....
53
....
.. ..
....
11'/2
Y
R
245:o
..
10 5 4 6 14 26 39 48 55 59 67 68 30
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
1464
Vol. 41, No. 7
WAVELE\GTH IN M I L L I M I C R O N S
Figure 3.
WACLENGTH I N MILLIUICRONS
F i g u r e 2.
Typical Absorption Curves of Purified N a p h t h e n i c Acid C u t s
Effect of Heat on Purified N a p h t h e n i c Acid Distillates
distillates were heated in glass for 1 hour at 148.9" C. with agitation and free access to air. These conditions are cornparable to those encountered in the conversion of the acids to the lead and zinc salts. The heated samples were then analyzed spectrophotometrically (Tables I1 and V- and Figure 3). All samples tested deteriorated to a marked extent, This effect can be ascribed only to a partial modification of the structure by either oxidation or cracking and is probably associated with the acid itself. The fact that the oil separated also underwent the same phenomenon does not of itself change the picture, for the same structures may exist in the oil as in the acid. The effect of an antioxidant was tested by conducting the thermal stability
acids, though a review of Table I as well as the chart shows a possible peak in transmission at about 625 mp. This peak does not appear in the data shown in Table I1 or in the curve for the purified distillates. This phenomenon may, therefore, be attributed to the oil content of the distillates. A comparison of the transhission spectra of the differedt cuts in the yellow region (625 to 630 mp) as shown in Table IV indicates that with the exception of cuts 1 and 17 no appreciable change in transmission was obtained by the removal of the oil. This information couDled with the similarity of the absorption curves with regard to form and intensity of absorption leads to the conclusion that, for cuts 1 and 17, the oil content does not seriously DATAO F FRACTIONAL DISTILLATION STUDY (-4RUBA TABLE 111. AKALYTICAL affect the color of the distillate. It SAPHTHEXIC ACIDS) appears that cuts 1 and 17 and probBromine ably 18 are abnormal in behavior. XO. Calcun - t . 7c Neut. No. NaphCalculated Whether the basic cause of this abnorlated MolecNeut. No., Wt. % Saphyo Naphthenic thenic mality is cracking is as yet unknown, cut hIg. Unsap. thenic Total dcid, 31s. Acid, Acid ular No. KOH/G. Matter Acid Recovery KOH/G. G./100 G. No. Weight though i t seems unlikely that prod67.0 la 11.3 ... ... 44.0 55.7 ucts of cracking would be present during 115.4 317 73.2 2b ... 42.2 206.1 99.2 323.7 82.8 1.3 3 272.0 16.4 the early part of the distillation. I n any 316 100.1 4 90.4 ... 293.0 9.7 event, the acids in the first and last two 312.6 100.1 0.6 92.8 5 284.2 7.3 6 ... ... ... cuts add measurably to the color of the 99.4 283:o 1.0 7 5.0 274:0 94.4 ... ... 8 ... whole distillate. 2 6 6 :9 93.0 1.3 97.0 9 259:7 4.0 T o determine further possible sources ... 10 ... ... iOi:4 250: 1 1.6 11 249:o 98.0 3.4 of color, the purified samples of naph100.3 243.6 1.8 97.1 12 239.0 3.2 232.6 101.2 1.8 98.0 13 215.8C 3.2 thenic acid distillates were analyzed for 227.5 101.6 2.7 98.2 14 224.0 3.4 unsaturation by determining their bro215.9 103.0 98.8 2.8 15 209.1 4.2 ... 16 ... mine numbers (Table 111). The negli3:i 103:4 19i:o 156:5 22.0 81.4 17 ... ... 18 ... ... gible quantities of bromine absorbed indicated little if any unsaturation. As a Analyses questionable: oil and acid too volatile for handling on steam bath. b Values questionable. only small quantities of material having Value questionable. aromatic nuclei are generally present in naphthenic acids, it is doubtful that any unsaturation or complex aromatic comAT 625 TO 630 N p TABLE ITr. PERCENTTRAKSMISSION pounds present contribute appreciably to c u t No. 1 2 3 4 5 6 7 8 Q 10 11 12 13 14 15 16 17 18 the color of the product. Unpurified distillate 86 89 86 85 88 89 87 88 87 84 85 86 84 86 83 ' 80 79 21 I n order to determine the effect of 89 84 80 80 83 . 60 .. Purified distillate 48 , . 86 . . 89 . . 87 , . 88 heat, samples of purified naphthenic acid . I .
C
..
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949
TABLE v. EFFECTO F HEAT ON C u t No. Wave length, rn#
% Transmission, purified distillates
yo Transmission, heated
3 450 630 35
450
purified distillates
5
Loss in transmiasion
85.7
60 30.2
630
630
90.8
87 24
63 57.2 29.2
450
450 630
32 75 13.8
630 69
88
50
89 12
82 37.2
6.8
test in the presence of a commercial oxidation inhibitor. The results of two such tests are shown in Table 11,from which it may be seen that no great benefit resulted. The absence of more extensive data precludes any further interpretation of this observation. Although many of the data accumulated fail to locate specifically the source of color and the cause of color deterioration by heat as regards the responsible structures, the evidence indicates that the naphthenic acids themselves probably contain the factors responsible for this behavior. I t appears from the work presented that the naphthenic acid molecule is degraded by heat and/or oxidation t o yield products of greater color than the original material and that the darkening of commercial acids under manufacturing conditions is a phenomenon related to the acids themselves as well as the accompanying oil. Because of the importance of the formation of color during manufaeburing operations involving naphthenic acids, this presen-
79.7
NAPHTHENIC ACID DISTILLATES 12 450 630
11
51
56 89
5
9
450
54 86
TRANSMISSION O F PURIFIED
7
5
84
37
13 14 450 450 630 630
31
26.0
28
80
0
15.0
630 35
83
10
9 68
64.5
15 450
80
11
84
70 21.4
1465
64 67.9
6
60
0 65
71.5 20.0
17 450 630
15 100
21.7
75.0
tation should be considered as preliminary to a more detailed investigation directed to the establishment of the cause of color formation in naphthenic acids. ACKNOWLEDGMENT
The authors express their sincere appreciation to Louis S. Tregre, Jack W. Burt, Kenneth M. Purdy, and C. E. Starr, Jr., of the Esso Laboratories, Louisiana Division, Standard Oil Company of New Jersey, and t o E. W. Carlson and C. F. W. Gebelein of the Chemical Products Laboratory, Stanco Distributors, Inc., for their efforts in connection with this work. LITERATURE CITED
(1) Klotz, J. R. M., itndLLittmann, E.R.,IND. ENQ.CHEM.,ANAL.
ED., 12,76 (1940). RECEIVED September 19, 1947
Concentrates of Fat-soluble Constituents of Leaf Meal Extracts PREPARATION BY MOLECULAR DISTILLATION MONROE E. WALL Eastern Regional Research Laboratory, Philadelphia 18, Pa. Fat-soluble constituents of vegetable leaf extracts may be concentrated and partially separated by molecular distillation. Prior to distillation, it is necessary to remove phospholipides by saponification or acetone precipitation, and to dissolve the residual material in a suitable carrier oil. By distilling at 80" to 220' C. and 1 to 10 microns pressure, a series of concentrates containing phytol, tocopherol, sterols, carotene, and xanthophyll is obtained.
P
REVIOUS publications from this laboratory have shown that properly prepared vegetable leaf meals (2)are excellent sources of carotene ( I B ) , xanthophyll ( 16), chlorophyll (16), tocopherol ( I S ) , and sterols (14). I n addition, vitamin K (3) and many other less well known compounds may be present. The conventional methods for isolating or concentrating any individual compound from leaves are usually so specific that many of the other products are destroyed or ignored (3, 4, 10, 15). For more complete utilization of vegetable leaves, a method suitable for concentrating or partially separating a number of leaf lipides is desirable. A literature survey showed that the process known as shortpath or molecular distillation had been successfully applied to the concentration of heat-sensitive substances such as vitamins A and D from marine oils (6,6) and tocopherols from vegetable oils (8). This method has been brought to a high theoretical and technological stage in this country largely through the research of Hickman and co-workers. The purpose of this paper
is to present the methods developed in this laboratory for the preparation of leaf extracts suitable for molecular distillation and to discuss some of the distillation products. The leaf meals were prepared from broccoli, Lima bean, rhubarb, snd spinach leaf wastes. They were dried to approximately 570 residual moisture and freed of stems by a process developed a t this laboratory (2). The dry meal was then ground in a cutter over a l/le-inch screen. Commercially dehydrated alfalfa Ieaf m e d was used for comparison. Twenty to twenty-five poupd batches of leaf meal were extracted with acetone or hexane in a large Soxhlet apparatus ( 1 6 ) for 12 hours. The extracts thus obtained constituted the crude leaf lipide extract. The components of this mixture which were quantitatively studied and the references to the analytical methods used are as follows: carotene (II), xanthophyll (16), tocopherol ( I S ) , and sterol ( I d ) . In addition, chlorophyll, phytol (derived from chlorophyll), and phospholipides were investigated to a limited extent. A cyclic, falling-film type of molecular still with a capacity of one liter was secured from Distillation Products, Inc. Similar models have been described in considerable detail by Hickman (6,n Two distinct processes were involved in the preparation of fatsoluble concentrates: ( a ) the preparation of a crude extract in a form suitable for molecular distillation in the falling-film still and ( b ) the subsequent distillation of the extract. Figure 1 is a flow sheet of the various processes.
