Liquid-Liquid Extraction in the Separation of Petroleum Acids EIESVKT G. SCHUTZE, F A L T E R A. QUEBEDE.AUX,
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H. L. LOCHTE, The University of Texas, Austin, Texas
HILE recent developments in the petroleum industry hai-e iiiatle liquid-liquid extraction theory, use., and aiq3aratiii TT ell kiion 11 in that industry, the organic chemist gencrally .till contents himself n-ith simple separatory funnel extraction or v-ith the use of apparatus of the Soxhlet type This is diie, no doubt, in part to the fact that no efficient laboratoiy-4ze extraction apparatus has beconie generally kiion-n.
used a Xair and Schicktanz heavy-solvent type of apparatus, iiiodified to use a rotary column, for some months in the extraction of esters of petroleuni acids nit11 water as solvent. Rotary coluinns of the type developed by Jantzen differ from packed and unpacked coluinns only in the extraction colunin itzelf, the upper and lower sections and accessories heing varied t o meet conditions. Khile a number of types of apparatus nnd schemes haT-e been tried in this work, only two 1nodific:itions will be described. Figure 1 shows column 1 designed like Jantzen's as far as his description permits. Bct\\-er.nthe usual upper and lon-er separating sections is the column proper, conFisting merely of a glass tube within n-hich a ~ n ~ a l l eclosed r tube or rod is rotated at 200 tci ,500 r. p. m. Tlie esact size of rotator, .peed of rotation, and concentration of -olut ions used i n tl;e Peparation rif complex niixture; of acids dcpend m:iinly on t h e eniul-ifying tendency of t l!r mixture. If app:aratui i i operated -0 as to remove the h y d r o c n ~ b o n sand i h t acids fix.-t from a mixture of petroleum acids, the column tend- tn "-lug" o r ceitce countcrcurrent circulation unles the .oliitionc are as dilute as 0.1 .I1 and the rotator is operated at a rehtivel?. lnn. speed, but after the firit cut or t i y o have been renioved t l l i i tendency causes little or no troulile.
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S e p a r a t i o n o f ti-Caproic
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s Jantzen and co-norkers ( 2 ) in the course of a thorough study of the use of liquid-liquid extraction in the separation of coal-tar bases (3, L$ deveioped and tested an effiiient aprsaratus but did not describe i t in detail and their v o r k appears to have escaped general attention. Evans ant1 coworkers ( 1 ) in 1934 described a rotary colunin that proved very effective in the isolat,ion of vitamins. Suinerous packed coluriins have been developed in petroleum laboratories, h i t most' of them require several liters of solution. For use n-it11 s u c l ~volnme;: the packed coluliln appears to lle the nlost conveiiient extractor. The 14-meter columns of N a i r and Fchicktana ( 4 ) are simple in operation and may, of course, be modified for use (made as short as 60 cm.) in an ordinary lal)oratory, prol-ided circulation is continued for a longer period of time, but the authors knox of no way of using simple solvent extraction in the separation of petroleum acids. They h a r e , however:
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4 6 8 N u m b e r o f Fraction
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FIGURE 2 o f n-llexoic from n.,lleptc,ic aci,j .elected a te.t mixture, 15.3 grams of the former and 16.4 gramq of the Litter w r e added t o t h e column, lvhich \vas then fill~dn-it11petroleum ether t o a point just below the upper section. Tenth niolal potassium hydroxide n-as added at the t o p at a rate of about tlvo drops a second, lvhile 0.4 ~ulfuricacid !vas added at the connection near the bottom at a rate ensuring a slight excess of acid as indicated by methyl orange. The interface was held near the bottom of the rotor. The droplets of potassium salt solution descended in very flat spiralq through the
ether-filled column until they reached the sulfuric acid inlet where both of the weak acids !>-ere liberated. A
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INDUSTRIAL AND ENGINEERIXG CHEMISTRr
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small portion of the acids, mostly hexoic at first, dlssolved in the descending acid water spiral while most of the weak acids accumulated and diffused upward where interchange with descending potassium salts took place, hexoic acid replacing heptoic until equilibrium was astablished. I n the run on which the data of Figure 2 are based the column was run until 1 liter of 0.1 M potassium hydroxide had passed through the column, and the accumulated acids of the water layer were extracted with petroleum ether and added to the top of the column. The next liter of water layer collected was extracted for cut 1, the next for cut 2, etc. The per cent of each acid present in each carefully treated cut was calculated from the neutralization equivalent. So/ut,on o f Petroleor Ether
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thus forcing the alkali to pass first through a concentrated solution of the weakest acids. After all the acids had been added in this way the column was rinsed with 100 cc. of pure solvent. The column was then emptied and the 20 per cent cut of weakest acids isolated. The stronger acids were then liberated with sulfuric acid, again taken up in petroleum ether, and passed through the column again and again until the desired number of cuts had been obtained. Cuts 5, 6, and 7 of Figure 4 were obtained after repeated fractionation of the Texas acids through a 180-crn. (6-foot) efficient fractionating column. Density and refractive index were changing only slightly from cut to cut and series to series, so that little more separation would have been obtainable with any reasonable amount of refractionation. After each of the fractions had been cut into five extraction cuts by column 2 they had the density and index of refraction shown for the three series of extracted acids of Figure 4. Since Figure 4 indicates that each of the three sets of five cuts shows analogous changes in constants, additional tests were run by combining cuts 1. 2, l’, and 1 ” ; 3, 2’, 3‘, and 2”; 4, 4’, 3”, and 4 ” ; and 5 , 5’, and 5” and reextracting each combined lot in the same manner. The last cut of each run was combined with the next. These steps were then repeated another time for some and twice more for others to yield the E111 and EIV fractions of Figure 5. Figure 5 shows again the constants of the original distillation cuts along with the final values. The remarkable change in range of constants of a series of acids that were changing only very gradually on redistillation is brought out clearly. KO rotary column so far tested in this laboratory has a throughput of more than 250 ml. of each solution per hour, so that extraction of large volumes by such columns would be tedious. It is hoped that columns now being built will overcome this defect. A t present large volumes are being extracted in 5 to 6 stages without reflux with a modified separatory funnel scheme following a scheme like the one presented by Morton (5, p. 200). The isolation and characterization of individual acids are now under way and will be reported in a future paper, but the great advantage of fractional distribution, based as it i b
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FIGURE 3
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Figure 3 shows column 2 , also designed for batch extraction, but one in which the weaker or less soluble acids were t o be obtained as first cuts instead of the strong ones as in column 1.
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The acids and alkali again pass each other in R very flat spiral but in this case a 0.25 V . solution of potassium hydroxide was continuously added at the top while a 0.1 N Skelly Solve solution of one of three consecutive very closely related distillation fractions of petroleum acids from light burner oil wash, obtained in the refining of Texas petroleum (furnished through the courtesy of the Humble Oil and Refining Company at its Baytown Refiner>-), was added at t’he bottom at such a rate that about 80 per cent of the acids were neutralized by the potassium hydroxide coming down. As the solution of weak acids arrived at the top the petroleum ether was diptilled off,
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€xtraction Cut5
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DECEMBER 15, 1938
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Summary -276‘
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e f r a c t l v a Index
The advantages of fractional extraction following fractionation by distillation in the separation of very complex mixtures of closely r e lated compounds like those found in petroleum acids are stressed. Two rotary columns for countercurrent extraction with or without reflux are described. Results obtained in the separation of caproic and n-heptylic acids and of a complex petroleum acid mixture are presented.
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Literature Cited
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(1) Evans, H. M., et al.,
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IXD. EXG.CHEX, 26, 3 9 i
(1934). (2) Jantaen, Dechema .Monograph, 5’01. 5, “Das
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tionierte Destillieren und das fraktionierte Verteilen als Methoden zur Trennung von Stoffgemischen,” Berlin, Verlag Chemie, 1932. (3) Keyes, IND.EKG.CHEW.., 25, 358 (1933). (4) hlair and Schicktanz, J . Research Xutl. Bur. Stand-
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ards, 17, 912 (1936); 20, 83 (1938).
( 5 ) Morton, “Laboratory Technique in Organic Chemistry,” New York, McGraw-Hill Book Co., 1938.
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RECEIVED July 25, 1938. Presented before the Division
FIGITRE 5
on differences in K. values and in structure as a supplementary method to fractional distillation, is apparent.
of Organic Chemistry at the 95th Meeting of the American Chemical Society, Dallas, Texas, April 18 t o 21, 1938. This paper represents portions of theses presented by W. A . Quebedeaux in partial fulfillment of the requirements for the degree of master of arts, and by H. G . Schutze in partial fulfillment of the requirements for the degree of doctor of philosophy at The University of Texas.
Preparation of Hydriodic Acid Suitable for Alkoxy1 and Friedrich-Kjeldahl Nitrogen Determinations E. P. CL4RK, Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
C
OMMERCIALLY available hydriodic acid has been
used in the many volumetric methoxyl determinations made in this laboratory during the past few years (1). These acids invariably gave high blank values, which were materially reduced by a special purification procedure. However, instead of purifying a commercial acid, i t has been found more economical and as convenient to prepare a n acid for the purpose. The product obtained by the procedure given below is satisfactory, as i t is almost, if not entirely, free from blank and is stable for a long time. The same considerations also apply to hydriodic acid used in the Friedrich-Kjeldahl nitrogen determinations (a), in that the blanks on the specially prepared acids have been found to be from four to eight times lower than those of any commercial acids employed. The preparation of the acid for the purposes under discussion involves the well-known reduction of iodine with hypophosphorous acid and the scrubbing of the resulting constantboiling liquid with carbon dioxide. For this purpose 254 grams of iodine and 185 grams of Tyater were heated to about 50” C. in a 500-cc. flask with a groundjoint condenser, and 66 grams of 50 per cent hypophosphorous acid were added portionwise a t such a rate that the mixture boiled continuously until the iodine was reduced. Heat was then a p plied to the flask and the boiling was continued for 3 hours, during which time a stream of carbon dioxide was passed through t h e
solution. The position of the reflux condenser tvas then changed to allow distillation, and the constant-boiling hydriodic acid was collected. The yield was 447 grams. The preparation was stored in dark bottles and preserved by the addition of a little 50 per cent solution of hypophosphorous acid (about 1 cc. per pound).
A preparation made from one lot of “pure chemicals” of a reputable brand gave a zero alkoxyl blank and a blank of 0.02 cc. of 0.01 N acid for the Friedrich-Kjeldahl nitrogen method. Another preparation made from a different lot of similar chemicals gal-e a n alkoxyl blank of 0.01 cc. of 0.05 N thiosulfate. Hydriodic acid prepared in this manner from commercial hypophosphorous acid or hypophosphites cannot be used in the Zeisel method, as apparently they all contain sulfates. These are reduced with the formation of hydrogen sulfide, which naturally interferes by forming silver sulfide. If, however, sulfur-free hypophosphorous acid or hypophosphites were prepared for the purpose, the product would be satisfactory.
Literature Cited (1) Clark, E. P., J . Assoc. Oj’icial Agr. Chem., 15, 136 (1932) (2) Friedrich, A., Z. Physiol. Chem., 216, 68 (1933).
RECEIVED September 15, 1938.
