NAPHTHENIC ACIDS ARUBA ACID J. R. M. KLOTZ AND EDWIN R. LITTMANN Stanco Incorporated, Elizabeth, N. J.
T
HE commerical uses of naphthenic acids are derived from their acidic properties. In some cases the acidity of any particular sample of acid is the only requisite for its use; in others, such as in driers, acidity alone is not the only factor to be considered. The present investigation was undertaken as part of a series of studies on the compositions of commercial naphthenic acids and the possible effects of some of the nonacid components, which include phenols, bases, etc., on the chemical properties of the acids. Aruba naphthenic acid is extracted from Colombian gas oil with dilute sodium hydroxide and recovered from its alkaline solution by acidification with sulfuric acid. After washing with water to remove mineral acid, a naphthenic acid is obtained which has the following typical analysis : Sp. gr.-(' A. P. I.)
behavior of the product is obtained by using the acid number of the residual acid. Under such conditions the average molecular weight of the acids in the 10 per cent fraction is about 175 and of those in the 80 per cent fraction is about 278. The known action of phenols as oxidation inhibitors suggested the possibility that the phenolic bodies in the naphthenic acid fractions would show this effect. When benzaldehyde was blown with air under standard conditions in the presence of the several fractions, a definite inhibitory action was evident in some cases; in others a neutral or slight catalytic effect was observed. Table I and Figure 1 show that there is a rough correlation between the phenol content of each fraction and its inhibitory action on the oxidation of benzaldehyde. In view of the inhibitory action of several of the acid fractions on the oxidation of benzaldehyde, it became of immediate interest to determine whether this effect was carried through in the presence of an oxidation catalyst. When carried out in the presence of both the naphthenic acid fractions and 0.05 per cent manganese as manganese naphthenate, the oxidation of benzaldehyde showed that the inhibitory action of the various fractions had not only disappeared but had been changed to a catalytic action. Table I1 and Figure 1 also show that in every case the combination of manganese naphthenate with naphthenic acid was a better oxidation catalyst than the manganese salt alone.
1 5 . 7 ((
The presence of phenols in naphthenic acids has been demonstrated by several investigators, although only one record (2) has been found relative to the quantities of phenolic bodies present or their distribution in fractions obtained by the distillation of the commercial acids. I n the present work a sample of Aruba naphthenic acid was distilled under reduced pressure into eight 10 per cent fractions and a 20 per cent residue. The phenol content of each of these fractions was determined as well as the effect of these fractions on the air oxidation of benzaldehyde in the presence and absence of a manganese naphthenate catalyst. In addition some characteristics of the acids in each of the fractions were determined. It has been shown that the phenols are distributed mainly in the low- and high-boiling ends of Aruba acid and that the intermediate fractions contain only relatively small quantities of phenolic bodies. The results of these experiments are shown in Table I.
TABLE11. EFFECT OF MANGANESE NAPHTHENATE ON OXIDATION INHIBITION OF ARUBANAPHTHENIC ACID FRACTIONS WITH BENZALDEHYDE
a
b c
Acid No.'
Total Aoid, %
T.A. P. No.
0-10 10-20
2000+ 250
Oxidation Equivalent' 0.05% Mn
No catalyst 1.3
20-30 25 30-40 25 40-50 37 50 50-60 125 60-70 1000 70-80 Blank Cc. of 0.5 N sodium hydroxide required t o formed.
..
TABLE I. PHENOL CONTENTOF ARUBANAPHTHENIC ACID FRACTIONS Fraction, %
Fraction, %
Acid No. of Residual Acidb T . A. P. No.C
7.5 9.1
10.0 14.6 7.5 6.7 9.8 11.2
42.8 44.1
42.2 44.9 46.3 49.0 46.4 44.9
33.3 neutralize the benzoic acid
It is doubtful whether the differences between the oxidation equivalents in the last column of Table I1 are significant since a fugitive end point was obtained because of the rapid oxidation of the benzaldehyde on shaking in the presence of air during the titration. Despite a possible error of about 10 per cent, it is significant that the lowest value for oxidation equivalent is 26.5 per cent higher than the blank which was run and titrated under exactly the same conditions. The method of analysis for the determination of acid number, total acid, and acid number of the residual acid is the subject of a separate communication (5) and consists essentially in extracting the unsaponifiable matter from a solution of sodium naphthenate which is neutral to phenolphthalein, recovering, weighing, and titrating the purified acids. From the initial and final titrations made during the process, it is possible to obtain the acid number of the original sample and the purified (residual) acids as well as the total acid content.
Of the fraction a8 a whole. Of the acids freed from unsaponifiable material.
M g . of phenol per 100-cc. sample calculated as tert-amylphenol.
It is evident that the acid number of any particular fraction is meaningless unless the total acid content and the acid number of the residual acid are taken into consideration. On the basis of the acid number alone, the calculated average molecular weight of the 10 per cent fraction would be about 412 while that of the 80 per cent fraction would be about 284. Since the acid itself is the important constituent of any fraction or sample of naphthenic acid, a truer picture of thepossible 590
APRIL. 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
T-\ I500
1
\
P H E N O L CONTENT V S . FRACTIONS
OXIDATION EQUIVALENTS
0.05% M N
BLANK
BLANK
ci 0
0 10
40 50 FRACTION ( X I
30
20
60
70
80
FIQURE1 The phenol determination was made by comparing the colors formed when a toluene solution of naphthenic acid was treated with nitrous acid, followed by alcoholic potassium hydroxide, with standards prepared from tert-amylphenol when treated under the same conditions.
Experimental Procedure DISTILLATION AND PURIFICATIOX O F FRACTIONS. Three liters of Aruba acid were distilled from a &liter flask, which was heated in an oil bath, through a 14-inch (35.6-cm.) Hempel column containing 10 inches (25.4 cm.) of cut-glass tubing. Fractions were cut a t each 10 per cent (300 cc.). The results of the distillation are given in the following table: Fraction, % 10 20 30 40 50 60 70 80
B. P.,
O
C.
T o 165 165-180 180-186 186-196 195-205 195-200 200-210 190-210
Preaaure, Mm. 28-30 28-30 28-30 25-30 20-25 10-15 10-15 5-8
Refractive Index, n2,0 1.4657 1.4686 1.4731 1,4780 1,4812 1.4857 1.4887 1.4928
Each of the above fractions was dissolved in a 20 per cent excess of a 10 per cent sodium hydroxide solution, diluted with equal volumes of alcohol and water, and extracted three times with petroleum ether. The naphthenic acid was then recovered by acidification with concentrated sulfuric acid, taken up in petroleum ether, and washed with water. After being filtered through a dry filter, the petroleum ether was evaporated on the steam bath and finally by heating the acids to 120” C. in an open beaker. ANALYSIS. The analyses for acid number, total acid, and acid number of the residual acid were made by a method described in detail in another paper ( 3 ) . The analyses for phenols were made according to a modification of the method devised by Buc ( 1 ) : Into a 2-ounce
591
bottle place a solution composed of 1 cc. of naphthenic acid and 9 cc. of toluene. To this add 3 cc. each of 3 per cent sulfuric acid and sodium nitrite solution containing 1 gram per 175 cc. of water and shake for 2 minutes. Then agitate while filling the bottle slowly with a saturated solution of potassium hydroxide in methanol. After shaking thoroughly, filter through a dry paper and compare the color of the filtrate with standards prepared from tert-amylphenol. For the present work, standards containing 5, 10, 20, 30, 40, 50, 100, and 200 mg. per 100 cc. of toluene were found to be satisfactory. In the event that the colors formed by the sample under examination are too dark, dilutions of 1:20 to 1:lOO may be used. It is not advisable, however, to use dilutions lower than 1:5 since in such a case some undesirable color bodies may be retained by the methanol solution. It is obvious that the method as used is not strictly quantitative. However, it does serve for purposes of comparison and to show the presence or absence of phenols. OXIDATION OF BENZALDEHYDE. To 10 cc. of benzaldehyde was added 0.5 cc. (0.45 gram) of the naphthenic acid. After mixing, air was bubbled through the solution a t an unknown but constant and reproducible rate. At the end of 2 hours the solution was diluted with 25 cc. of alcohol and titrated with 0.5 N sodium hydroxide solution, using phenolphthalein as indicator. Corrections were made for the acidity of the benzaldehyde and for the free naphthenic acid. For comparison a blank run on benzaldehyde alone was made. In the experiments in which manganese naphthenate was used as catalyst, 0.18 cc. of solution containing 6 per cent manganese was added to the reaction mixture. The following table shows the details of the oxidation experiments: Fraction,
%
0-10 10-20 20-30 3040 40-50 50-60 60-70 70-80 Blank
Titration (0.562 N NaOH) No 0.05% catalyst Mn 8.1 45.0 13.5 46.0 44.0 14.5 15.0 46.0 19.0 47.2 12.3 49.2 11.4 46.7 14.0 45.2 12.4 32
Titration Correction No 0.0570 catalyst Mu 6.9 6.9 6.8 6.8 6.4 6.4 6.1 6.1 6.0 6.0 5.6 5.6 5.4 5.4 5.3 5.3 2.4 2.4
Oxidation Equivalent No 0 05% catalyst Mu 38.1 1.2 39.2 6.7 37.6 8.1 8.9 39.9 13.0 41.2 6.7 43.6 6.0 41.3 39.9 8.7 10.0 29.6
Although sufficient information is not yet available from which to draw a final conclusion, it appears that the general use of the acid number as a criterion for the purchase or evaluation of naphthenic acid does not give sufficiently detailed information to be of much use to the consumer.
Acknowledgment The authors wish to express their thanks to t8heChemical Division, Esso Laboratories of the Standard Oil Development Company for valuable assistance in the preparation of this paper.
Literature Cited (1) Buc, H. E., private communication. (2) Gurwitsch, “Wissenschaftliche Grundlagen der Brdolverarbeitung”, p. 99 (1924). (3) Klotz a n d L i t t m a n n , ISD. EXQ.CHEM.,-4nal. E d . , 12, 76 (1940). PRESENTED before the Division of Petroleum Chemistry a t the 98th Meeting of the American Chemical Society, Boston, Mass.
