May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY DISCUSSION
*
The structure of compounds is apparently correlated with their antioxidant activities. The presence of a tertiary alkyl group in the 2,5 positions on hydroquinone results in increased activity. The benzyl group also serves to give comparable stabilization. With p-phenylenediamines either a secondary butyl or a phenyl group serves to give high antioxidant activity. Insufficient data are available on the 1,2-dihydroquinolinesJ but additional work ivith these three groups and others might provide a basis for predictions of antioxidant activity from their chemical structure. Solubility and consequent penetration of the antioxidant into the site of carotene occurrence may be of extreme importance, especially since the water-soluble compounds such as catechol and pyrogallol are relatively ineffective. Why complete stabilization of carotene with increasing amounts of antioxidant is not achieved is not apparent. The occurrence of carotene in two forms as shown by Weier (IS) in carrots, one of which is more readily stabilized, would explain the anomaly to some extent.
*
CONCLUSIONS
AXTIOXIDLVTS. 2,5-Disubstituted hydroquinones, p-substituted phenylenediamines, and derivatives of 2,2,4trimethyI-1,2dihydroquinoline were the most active compounds tested for stabilizing carotene in alfalfa. SOLVENTS.Vegetable oils plus acetone were superior to alcohols, Cellosolve, or kerosene as carriers for 2,5-di-tert-butylhydroquinone. The addition and subsequent removal of a large amount of volatile solvent were not particularly beneficial.
925
SYNERGISTIC COMBINATIONS. Combinations of antioxidants were synergistic to some extent. The addition of metal deactivators METALDEACTIVATORS. failed to give increased stability. ACKNOWLEDGMENT
The author gratefully acknowledges the analytical assistance of E. M. Bickoff and I. V. Ford. LlTERATURE CITED
G. F., A t k i n s , M. E., a n d Biokoff, E. M., IND.ENQ. CHEM.,41,2033 (1949). Bailey, L, F., a n d M c H a r g u e , J . S., Plant Physiol., 20, 79 (1945). Bickoff, E. M., and Williams, K. T., Oil & Soap, 23,65 (1946). Calkins, V.P., J . Am. Chem. SOC.,69,384 (1947). Clausen, D. F., L u n d b e r g , W . 0.. and Burr, G. O., J . Am. Oil Chem4ts' Soc., 24, 403 (1947). K e p h a r t , J. C. (to N a t i o n a l Alfalfa D e h y d r a t i n g a n d Milling Co.), U. 8. P a t e n t 2,474,182 (June 21, 1949). Mills, R. C., and H a r t , E. B., J . Dairy Sci., 28, 1 (1945). R a o , S. D a t t a t r e y a , Indian J . Med. Research, 33, 63 (1945). S h e r m a n , W. C., E l v e h j e m , C. A,, a n d H a r t , E. B., J . Riol. Chem., 107, 383 (1934). Sieffert, L., 2.Vitaminforsch., 17, 52 (1946). Silker, R. E., Sohrenk, W. G., and King, H. H., INDENQ. CHEM.,36,831 (1944). Bailey,
Tennessee E a s t m a n Corp., communication. Weier, T. E., Am. J . Rot., 29,35 (1942).
RECEIVED January 20, 1950. Report of a study made under the Research and Marketing Act of 1946 a t the Western Regional Research Laboratory, Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.
.
Desulfurization of Heptane Solutions of Organic Sulfur tornpounds J. R . MEADOW
AND T. A. WHITE' C'niversity of Kentucky, Lexington, Ky.
Quantitative data have been presented to show *e desulfurizing action, at room temperature, of 95qo sulfuric acid, concentrated sulfuric acid saturated with nitrogen dioxide, anhydrous aluminum chloride and bromide, anhydrous hydrogen fluoride, and aqueous solutions of hydrofluoric acid on various organic sulfur compounds dissolved in n-heptane. The results show that for the amounts of the reagents used concentrated sulfuric acid, nitrogen dioxide dissolved in 95% sulfuric acid, and anhydrous hydrogen fluoride were generally the most effective desulfurizing agents studied. The latter agent would have certain economic advantages in recovery and re-use. The sulfuric acid-nitrogen dioxide mixture was quite effective in removing alkyl disulfides which were relatively unaffected by the other desulfurizing agents,
The present study has extended the observations of some of these investigators to include higher molecular weight organic sulfur compounds, and also furnishes quantitative data on the removal of these compounds by desulfurizing agents about which more information seems desirable. In order to study the effect of a desulfurizing agent on a particular organic sulfur compound, solutions were made in which a known amount of the pure sulfur compound was dissolved in n-heptane, an inert hydrocarbon diluent of known specifications and purity. MATERIALS AND REAGENTS
The following desulfurizing agents were used in this rork: Concd. Has04 (95 5 % ) sp. gr. 1.84 Concd. H1SO4. sp.' gr. i.84,saturated with KO2 a t 20° C. AlCla C.P anhydrous AIBri, c.;; anhydrous HF, acid (52%) HF, anhydrous
.
P
REVIOUS work by Wood and co-workers (27,288)showedthe effect of petroleum refining agents on certain organic sulfur compounds dissolved in naphtha. Reduction in sulfur content of naphtha solutions by treatment with silica gel, bauxite, copper oxide, zinc oxide, and fuller's earth a t elevated temperatures has been reported by various authors (8, IS, 86-89), 1
Present address. Esso Standard Oil Company, Baltimore, Md.
Normal heptane, A.S.T.M. reference fuel, was selected as the solvent for the sulfur compounds listed in Table I. Some of its physical properties are given below: Purity mole 0 Refrao'tive i n g x a t 20' C. Freezing point, O C. Sulfur content, %
99.5 1.3878 -90.68 Less than , 0 . 0 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
926
Vol. 42. No. 5
treating agent used, and also on the molecular weight of the sulfur compound removed. Slight mechanical losses were unavoidable. The total sulfur content for each heptane solution before and after treatment was determined by the lamp method and calculations were made according to the method reported by the Bureau of Mines ( 8 ) . The above procedure was used for all desulfurizing agent,s except aqueous and anhydrous fluoride where plastic containers and copper vessels mere substituted for glass apparatus. The contact time, however, remained the same. The quantity of desulfurizing agent selected for a given treatment was determined largely by the availability and cost of the compound, and its possible re-use in industrial work. The lat,ter would apply especially to hydrogen fluoride.
'""I
DESULFURI%ATIO\ RESULTS
Concentrated Sulfuric Acid. MERCAPTANSThe effectiveness of sulfuric acid as a desulfurizing agent in quantities arbitrarily
0
2 4 6 8 IO VOLUME PERCENT OF TREATING AGENT
Figure 1. Desulfurizing Effect of Concentrated Sulfuric Acid 1. 2. 3. 4. 5. 6.
n-Butyl mercaptan Isobutyl mercaptan n-Butyl sulfide Isobutyl sulfide n-Butyl disulfide Benzyl mercaptan
7. Thiophene
8. 9. 10. 11. 12.
Tetrahydrothiophene tert-Dodmyl mercaptan n-Dodecyl mercaptan n-Dodecyl sulfide n-Dodecyl disulfide
The organic sulfur compounds included in this study are listed in Table I and in subsequent tables. Compounds No. 1, 2, 3, 4, 6, 7 , and 9 were received in the purest form obtainable. S o . 7 (thiophene) was at least 99% pure. No. 9 (tert-dodecyl mercaptan) was a mixture of isomers representing a mercaptan (thiol) purity of 96.8% (21). Some of the higher molecular weight sulfur compounds were not readily available and were synthesized by conventional methods; these include Sos. 5 , 8, 10, 11, and 12 in Table I. n-Dodecyl disulfide (KO. 12) was prepared by the method of Noller and Gordon (18). STOCKSOLUTIONS.Solutions of the twelve sulfur compounds were made by dissolving each of them in n-heptane as solvent, and the total sulfur content was determined by the lamp method (1). The concentration of sulfur in each solution approached an arbitrarily chosen figure of about 0.5%. Table I lists the heptane solutions of each of the compounds used together with the original sulfur content of each solution in weight per cent. These have been repeated in the other tables for the sake of clarity and ease of comparing values. DESULFURIZATION PROCEDURE
Desulfurization was carried out in a 100-ml. narrow-mouthed glass bottle placed in a water bath at approximately 25" C. Fiftyml. portions of each n-heptane solution were mixed batchwise with various amounts of treating agent (exact amounts indicated in tables); a fresh 50-ml. portion of stock solution was used in each treatment. With the liquid treating agents, volumes of 2 ml., 4 ml., and 6 ml., representing 3.85, 7.4, and 10.7 volume %, respectively, were generally used. The contact time with the reagent in all experiments was limited to 10 minutes with vigorous mechanical stirring. After standing a few minutes, a separation of the two layers was effected; the top layer, which was the treated portion or "raffinate," after being washed and dried represented in general a recovery of about 92 t o 96% of the volume of the original solution. In each case, the loss to the extract, or bottom layer, depended largely on the efficiency of the
selected for use in this work is summarized in Table I and in Figure 1. With mercaptans the use of a 2-ml. and 4-ml. sulfuric acid treatment. equivalent to 25.8 and 51.6 pounds of acid, respectively, per barrel of naphtha solution, showed relatively little reduction in sulfur content. -46-ml. treatment with acid, equivalent to 77.4 pounds of acid per barrel, resulted in only a 20 to 35% reduction of the original sulfur with the use of primary mercaptans. tert-Dodecyl mercaptan was more easily removed than the primary mercaptans. Investigation of the extracts indicated that at least some of the primary mercaptans were changed by the acid to disulfides. This is in agreement with the observations of Wood and others ( 6 , d Y ) . SULFIDES.Alkyl sulfides proved to be readily soluble in sulfuric acid when as little as 2 ml. of acid (3.85 volume yo)were used. Larger quantities of acid effected a more complete removal of the sulfides, usually 90% or better. The solubility improved slightly with a decrease in molecular weight and unchanged sulfides appeared in the acid extracts. DISIJLFIDES. The disulfides tested were much less soluble in sulfuric acid than the sulfides containing corresponding alkyl groups. Sulfur reduction was more noticeable with the lower molecular weight disulfide. With n-butyl disulfide a slight decrease in sulfur content with added amount of acid was noted. An increase in the amount of acid used was ineffective in removing more of the higher molecular veight disulfide, n-dodecyl disulfide
TABLEI. DESULFURIZATIOK EFFECTS WITH SULFURICACID AND NITROGEN DIOXIDEIN SULFURIC ACID
1.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
gr after Constituent % 9 before H&OaoTreatmenta in n-Heptane Treatment 2 ml. 4 ml. 6 ml. n-Butyl mercaptan 0.48 Isobutyl mercaptan 0.41 n-Butyl sulfide 0.49 Isobutyl sulfide 0.47 n-Butyl disulfide 0.50 Benzil mercaptan 0.47 ThioDhene 0.47 Tetrahydrothiophene 0.80 tert-Dodecyl niercaptan 0 . 4 8 0.43 n-Dodecyl mercaptan n-Dodecyl sulfide 0.46 n-Dodecyl disulfide 0.44
2&2%9
Treatmento 2 ml. 4 mi 0 . 4 4 0 07 0 . 3 3 0.03 0.04 0 . 0 2 0.07 0.02 0.36
0.03 0.01 0.22 0.04
0.34 0 .36 0.17
0 . 30 79
0.17 0.04
0.03
0.03 0.08 0.02
Volumes of 2 ml., 4 ml., and 6 ml. of treating aEent are equivalent t o 3.86, 7.4, and 10.7 volume %, respectively.
As might be expected, two successive 3-ml. treatments with fresh sulfuric acid on the same 50-ml. sample of n-butyl disulfide solution proved to be slightly more effective than a single 6-ml. treatment. THIOPHEKE. Pure thiophene mas effectively removed by sulfuric acid, and in this respect it resemblgd the lower molecular weight alkyl sulfides and tetrahgdrothiophene. In dilute solutions of thiophene in benzene Meyer ( 1 7 )has reported that sulfonation of the former takes place with sulfuric acid.
May 1950
I
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Sulfuric Acid-Nitrogen Dioxide Mixture. Ninety-five yo sulfuric acid, specific gravity 1.84, saturated with dry nitrogen dioxide gas at 20' C., proved to be an effective desulfurizing agent. Negative tests for nitrogen in a typical raffinate (No. 11 in Figure 2) were obtained when diphenylamine in sulfuric acid was used as an absorbent for the effluent gases from a regular combustion furnace. Positive tests were obtained under the same conditions with known samples containing only 0.004 mg. of nitrogen. MERCAPTANS.Comparing Figures 1and 2, and the data given in Table I, it is evident that all mercaptans, with the exception of tert-dodecyl mercaptan, were more completely removed with 4 ml. of the sulfuric acid-nitrogen dioxide mixture than with 6 ml. of sulfuric acid alone. In general, the results suggest that the presence of nitrogen dioxide in the sulfuric acid may have increased the conversion of the mercaptan to an oxidation product which was readily remeved. SULFIDES. Both concentrated sulfuric acid and the sulfuric acid-nitrogen dioxide mixture showed a marked solvent action on all alkyl sulfides and the cyclic sulfide, tetrahydrothiophene. DISULFIDES.Both alkyl disulfides, n-butyl disulfide, and n-dodecyl disulfide, were nearly completely extracted by the use of as little a+s 2 ml. of the sulfuric acid-nitrogen dioxide mixture. This was in sharp contrast to the action of other desulfurizing agents used in this work. This compound was more completely removed THIOPHENE. from the heptane solution by the sulfuric acid-nitrogen dioxide mixture than by the use of sulfuric acid alone. Identification of the tarry mass from the acid extract was not attempted. Anhydrous Aluminum Halides. Wood and others (27),working with aluminum chloride to remove low molecular weight sulfur compounds from naphtha solutions, used from 2 t o 8 moles of aluminum chloride per mole of sulfur compound for 1 hour at room temperature. Youtz and Perkins (29) used about 1 mole or less of aluminum chloride per mole of sulfur compound, chiefly sulfides, and refluxed the solution 3 t o 4 hours at 99' to 100" C. The desulfurization results obtained at 20" C. with approximately 0.3, 0.6, and 1.2 moles of aluminum chloride per mole of sulfur compound (as n-butyl mercaptan) in n-heptane solution are shown in Table 11. Results with aluminum bromide are also Included in this table. The time of contact was limited to 10 minutes as in other experiments. Although previous results (27) Suggested better removal of some sulfur compounds with the use of more aluminum chloride, it was thought advisable to employ only those conditions and amounts of the aluminum halide reagent which would be economical and practical to use in industry. However, such quantities of aluminum chloride which seemed practical touse from an industrial viewpoint-Le., 1.2 to 1.0molar
TABLE 11. DESULFURIZATION EFFECTS WITH ANHYDROUS ALUMINUMHALIDES SS
% S after AlCla
$ ~ ~
Constituent % S before lhatment' 0.4 G. in n-Heptane Treatment 0.2 g. 0.4 g. 0.8 g . b AlBrsC 0.48 n-Butyl'mercaptan 0.43 0.38 0.32 0.44 1. 0.41 0.38 0.31 0.4i 0.40 2. Isobutyl mercaptan 0.49 0.48 0.44 0.41 0.45 a. n-Butyl sulfide 0.47 0.49 0.40 0.37 0.45 4. Isobutyl sulfide 0.41 0.41 0.35 0.50 0.48 6. n-Butyl disulfide 0.47 0.45 0.30 0.47 0.44 6. Bensyl mercaptan 0.47 0.48 0.45 0.42 0.42 7. Thiophene 0.50 0.50 0.50 0.43 0.45 8. Tetrahydrothiophene 0.48 0.36 0.34 0.39 8. teYt-Dodecy1 mercapta.n 0.48 0.43 0.42 0.41 0.43 0.43 10. n-Dodecyl mercaptan 0.45 0.46 0.41 0.42 0.44 11. n-Dodecyl sulfide 0.44 0.44 0.41 0.38 0.41 12. n-Dodecyl disulfide 4 Wpiehtn refer to amount of aluminum halide used for each 50 ml. of . n-heptane solution. b 0.2 g., 0.4 g., and 0.8 g. are equivalent, respectivejy, to 0.29 mole, 0.58 mole and 1.16 moles of AlCls per mole of n-butyl mercaptan. 0 Equivalent to 0.29 mole of AlBra per mole of n-butyl mercaptan.
0
927
2 4 6 VOLUME PERCENT OF TREATING AGENT
Figure 2. Desulfurizing Effect of Concentrated Sulfuric Acid S a t u r a t e d w i t h Nitrogen Dioxide 1. 2. 3. 4. 5. 6.
n-Butyl nlercaptan Isobutyl mercaptan n-Butyl sulfide Isobutyl sulfide n-Butyl disulfide Benzyl mercaptan
7. Thiophene 8. Tetrahydrothiophene 9. tert-Dodecyl mercaptan 10. n-Dodecyl mercaptan 11. n-Dodeoyl sulfide 12. n-Dodecyl disulfide
TABLE 111. EFFECTOF ALUMINUMCHLORIDE AT TEMPERATURE (98" C.)
AN
ELEVATED
% S after AlCh Treatment Constituent in n-Heptane n-Butyl mercaptan n-But 1 sulfide Thiopxene
7 S before Aeatment
0.48 0.49 0.47
0.4 g. a t 200 c. 0.38 0.44 0.45
0.4g. at 980 c. 0.37 0.43 0.29
ratio of halide to sulfur compound-did not show any pronounced desulfurizing action on the sulfur compounds studied. The cost involved in employing larger quantities of this treating agent would seem to make its use unattractive. Anhydrous aluminum bromide, on a molar basis, seemed to offer no advantage over aluminum chloride a.s a desulfurizing agent. Neither compound ww very effective in removing sulfur compounds with the use of such low mo!,ar ratios. It has been suggested (26, 87) that aluminum chloride forms addition compounds with organic sulfur compounds at fairly low temperatures; ~ is ~probably ~ also ~ true ~ with ; anhydrous f this aluminum bromide. Raising the temperature from 20' to 98 O C. for the same contact time caused no significant change in the sulfur content of the n-butyl mercaptan and n-butyl sulfide raffinates; however, a slightly greater reduction was noted with thiophene at the elevated temperature. The results are shown in Table 111. Anhydrous Hydrogen Fluoride. The use of hydrogen fluoride m an alkylating agent and condensing agent for organic reactions is well known (6, i', 9,11, 18, 88, 84). Hofmann and Stegemann (14) suggested the use of hydrogen fluoride for refining coal tar oils in a German patent in 1927. Frey (10) has patented the use of hydrogen fluoride in improving the quality of lubricating oil stocks. Burk (4)has recommended the use of a mixture of boron trifluoride in hydrogen fluoride
8
928
INDUSTRIAL AND ENGINEERING CHEMISTRY
zo 4
60.
1; 3
0 w n
+z- 40 w
u
4 a 20
2 / 12
0
2 4 VOLUME PERCENT
4
10 a OF TREATING AGENT
6
Figure 3. Desulfurizing Effect of Anhydrous Hydrogen Fluoride 1. n-Butyl mercaptan 2. Isobutyl mercaptan 3. n-Butyl sulfide Isobutyl sulfide %-Butyl disulfide 6. Benzyl mercaptan
Thiophene Tetrahydrothiophene tert-Dodecyl mercaptan n-Dodecyl mercaptan 11. n-Dodecyl sulfide 12. n-Dodecyl disulfide 7. 8
9. 10.
i:
over a wide range of temperatures and pressures for the removal of aromatic compounds, aliphatic unsaturates, and sulfur compounds from crude petroleum and its fractions. Other articles (3, 8, 19, 20) which have appeared recently indicate an increased interest in the use of hydrogen fluoride in the petroleum field. Aside from its hazardous nature, a consideration of the physical properties of hydrogen fluoride ( 2 2 , d S )reveals a number of important technical advantages of this reagent which would make its use as a desulfurizing agent for oils seem attractive; these include high density, oil insolubility, convenient boiling point, low freezing point, and ease of recovery and re-use. According to Simons (32),hydrogen fluoride is a polar solvent with a dielectric constant close to that of water. Fredenhagen, Cadenbach, and Klatt ( 0 ) made a study of the solubility and conductivity of various organic compounds in anhydrous hydrogen fluoride. They found hydrogen fluoride to be a better solvent than water and that it produced more highly conducting solutions. Simons (23) has stated that the chemical properties which probably govern the action of
TABLEIV. DESULFURIZING RESULTSWITH ANHYDROUS HYDROGEN FLUORIDE ASD WITH 52% HYDROFLUORIC ACID Constituent in n-Heptane 1. n-Butyl mercaptan 2. Isobutyl mercaptan 3. %-Butyl sulfide 4. Isobutyl sulfide 5. %-Butyl disulfide 6. Benzyl mercaptan 7. Thiophene S. Tetrahvdrothioohene 9. tert-Do&ecyI mehaptan 10. n-Dodecyl mercaptan 11. n-Dodecyl sulfide 12. n-Dodecyl disulfide a
70 S before Treatment 0.48 0.41 0.49 0.47 0.50 0,47 0.47 0.50 0.48 0.43 0.45 0.44
% S after % S after Treating with Treating with 10.7 Vol. % 10.7 1'01. % Anhydrous HF ilqueous HFQ 0.34 0.38 0.04
0.02
0.43 0.32 0.22 0.01 0.25 0.33 0.06 0.44
0.46 0.40 0.49 0.46 0.50 0.46 0.44 0.46 0.48 0.44 0.45 0.45
The aqueous hydrofluoric acid contained 52% by weight of HF.
Vol. 42, No. 5
anhydrous hydrogen fluoride in organic reactions are its strong solvent property, its high acidity, its great dehydrating powei, and its unusual tendency to combine with itself and other substances to form molecular complexes. The present authors' results with the use of anhydious hydrogen fluoride as a desulfurizing agent with pure sulfur compounds are summarized in Table IV and in Figure 3. Data from this work point to the strong selective solvent action of hydrogen fluoride for certain types of organic sulfur compounds diesolved in an aliphatic-type hydrocarbon solvent. Due to the difficulty of handling anhydrous hydrogen fluoride, only one set of experiments was run in which 10.7 volume % ' of the desulfurizing agent was used with each sulfur compound. This quantity of hydrogen fluoride was selected because it affords some comparison with a similar volume of concentrated sulfuric acid used in previous experiments. It also offered a reasonably high molar ratio of hydrogen fluoride to sulfur compound (about 50 to 1 with n-butpl mercaptan, for example). A recent article by Lien, RIcCaulay, and Evering (15) reports the use of a larger quantity of hydrogen fluoride (20 volume %) in studying the extraction of sulfur compounds by hydrogen fluoride at a contact period of 1 hour. Although the conditions employed by these authors were somewhat different from those used here, the results in each case follow a similar general pattern. MERCAPTASS. A comparison of hydrogen fluoride l\ith concentrated sulfuric acid indicates that a 10.7 volume % treatment with each of these desulfurizing agents had somewhat the same effect on mercaptans, the former exercising chiefly a solvent action, followed by rearrangements in some cases, and the latter presumably some oxidizing effect. Primary mercaptans were not effectively removed by treatment with hydrogen fluoride; a ith teit-dodecyl mercaptan, however, a reduction in sulfur content of about 48y0 occurred and evolution, of some hydrogen sulfide was observed. This result is in accord with a previous ohservation by Meadow (16) in which it was shown that lert-butyl sulfide, higher molecular weight sulfides, and hydrogen sulfide were present in the reaction mixture when tert-butyl mercaptan was treated with a Friedel-Crafts type catalyst such as hydrogen fluoride. The ease with which such sulfides dissolve in hydrogen fluoride offers a reasonable explanation for the higher desulfurization result with tert-dodecyl mercaptan. SULFIDES. As indicated in Table IV, the alkyl sulfides weie nearly completely removed from the heptane solution by the action of anhydrous hydrogen fluoride; in some instances thev were recovered unchanged from the hydrogen fluoride extracts by diluting the latter with a large amount of water. I n this respect hydrogen fluoride resembled concentrated sulfuric acid. DISLLFIDES.The disulfides possessed a very limited solubility in anhydrous hydrogen fluoride. %-Butyl disulfide 11 a i slightly more soluble in hydrogen fluoride than the higher molecular weight compound, n-dodecyl disulfide, which appeared to be insoluble in this quantity of hydrogen fluoride. A low solubility of these two disulfides in concentrated sulfuric acid nas also observed (see Figure 1). About half of the sulfur in the original thiophene THIOPHENE. solution was removed from the heptane solution by the quantity of hydrogen fluoride used; some of the compound was changed b y action of the anhydrous hydrogen fluoride into a dark brown solid, insoluble in organic solvents, and melting over a range from 80' to 100" C. Fredenhagen and co-workers ( 9 )have suggested that thiophene is polymerized in the presence of hydrogen fluoride. Aqueous Hydrofluoric Acid. The desulfurizing action of aqueous hydrofluoric acid (52y0,)was compared with that of anhydrous hydrogen fluoride, and the former was found to be ineffective in removing any of the sulfur compounds studied. The results with 52% hydrofluoric acid are included in Table IV. A feM7 experimerts were carried out with other concentrations of aqueous hydrofluoric acid on a specific sulfide, such as tetrahydrothiophene. Fifty-milliliter samples of the heptane solution
+
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May 1950
TABLE \-. EXTRACTION O F TETRAHYDROTHIOPHENE BY AQCEOUS HYDROFLUORIC ACID Concn. of HF in
Treating Agent, % None(untreated sample) 52 80 90
Anhydrous grade (Harshaw (Harshaw Chemical Co.)
Wt. % s in Raffinate 0.50 0 .50
De-
sulzrization
..
0.46 0.01 0.02
8 98 96
0.01
98
of this sulfide, containing 0.50 weight % sulfur, were treated with 6 ml. (10.7 vol. %) of aqueous hydrofluoric acid of different concentrations. The results are shown in Table V. These data would indicate that the presence of water in hydrofluoric acid, at least up to about 20%, would have little effect on the extraction of tetrahydrothiophene, and possibly other sulfides which are readily soluble in hydrofluoric acid. SUMMARY
Mercaptans and disulfides were not as com letely removed from n-heptane solutions as thiophene and sulfi&s by the action of concentrated sulfuric acid. Nitrogen dioxide added to 95% sulfuric acid wm much more effective than the acid alone. Disulfides, especially, were very soluble in this mixture. Anhydrous hydrogen fluoride, well-known catalyst and condensing agent in organic reactions, has been used as a desulfurizing agent and found to be somewhat similar in effect to that of sulfuric acid under the conditions studied. Aqueous hydrofluoric acid (52%) was not satisfactory as a treating agent. Anhydrous aluminum chloride and aluminum bromide were not very effective as desulfurizing agents with the quantities used and a t the temperatures employed. ACKNOWLEDGMENT
The authors wish to acknowledge the valuable suggestions and assistance of Arlie A. O’Kelly and A. N. Sachanen, and to thank the Socony-Vacuum Oil Company for some of the materials used in this work. LITERATURE CITED (1) American Society for Testing Materials, Designation D 90-347, Standards, Pt. 111, 1939, pp. 626-9. (2) Ball, J. S., U . S.Bur. Mines, Rept. Invest., R.I. 3591, 7-5 (December 1941).
929
(3) Barieau, R. E., and Barusch, M. R., “Action of Hydrofluoric Acid on Hydrocarbon Solutions of Sulfur Compounds,” Petroleum Division preprints for the 115th Meeting of the AM. CHEM.SOC., San Francisco, Calif., March 1949. (4) Burk, R.E. (to Standard Oil Co. of Ohio), U. S. Patent 2,343,841 (March 7, 1944). (5) Calcott, W. S., Tinger, J. M.,and Weinmayr, V., J . A m . Chem. Soc., 61, 949 (1939). (6) Erlenmeyer, E., Jahresber. Fortschritte Chem., 1861, 590. (7) Fieser, L. F., and Johnson, W. S.,J . A m . Chem. Soc., 61, 1647 (1939). (8) Foster, A. L., Oil Gas. J., 45, 96 (June 15, 1946). (9) Fredenhagen, K., Cadenbach, G., and Klatt, W., 2. physilc. Chem., A164,176 (1933). (10) Frey, F. E. (to Phillips Petroleum Co.), U. S.Patent 2,378,762 (June 19,1945), ( 1 1 ) Grosse, A. V. (to Universal Oil Products Co.), Ibid., 2,216,274 iOrt. 1.194nL \ - - -
- 1 - - - - , .
(12) Grosse, A. V., and Linn, C. B. (to Universal Oil Products Co.), Ibid., 2,267,730 (Dee. 30, 1941). (13) Hale, J. H., Simmons. M. C., and Whisenhunt, F. P.. IXD. ENG. CHEM.,41,2702 (1949). (14) Hofmann, F., and Stegemann, W., Ger. Patent 501,725 (June 26, 1927). (15) Lien,-A. P., McCaulay, D. A., and Evering, B. L., IXD.ENQ. CHEM.,41,2698 (1949). (16) Meadow, J. R., U. 8. Patent 2,366,453 (Jan. 2, 1945). (17) Meyer, V., Ber., 17, 2641 (1884). (18) Noller, C., and Gordon, J., J . Am. Chem. Soc., 55, 1090 (1933). (19) Scafe, E. T., Petroleum Refiner, 25, 413 (1946). (20) Schneider, K. W., and Gottschall, H., Erdol u. Kohle, 1, 74 (1948). ENG.CHEM., (21) Schulze, W. A., Lyon, J. P., and Short, G. H., IND. 40,2308 (1948). (22) Simons, J. H., Chem. Reus., 8, 218 (1931). (23) Simons, J. H., IND. ENG.CHEM.,32, 137 (1940). (24) Simons, J. H., and Archer, S., J . Am. Chem. Soc., 60, 986 (1938). (25) Thomas, C. A., “Anhydrous Aluminum Chloride in Organic Chemistry,” A.C.S. Monograph 87, p. 830, New York. Reinhold Publishing Corp., 1941. (26) Waterman, H. I., and Perquin, J. N. J., Brennstof-Chem., 6, 255 (1925). (27) Wood, A. E., Lowry, A., and Faragher, W.F., IND.ENG.CHEM. 16, 1116 (1924). (28) Wood, A. E., Sheely, C., and Trusty, A. W., Ihid., 18, 169 (1926). (29) Youtz, M. A., and Perkins, P. P., Ihid,, 19, 1247 (1927). RECEIVED July 20, 1949.
CORRESPONDENCE Minimum Reflux Ratio for Multicomponent Distillation SIR: After publication of the paper on “Minimum Reflux Ratio for Multicomponent Distillation” [IND. ENG.CHEM.,41, 2775 (1949)l an observation was made which enabled the dea,b,c/ velopment of simple equations for solving the case , d,e,f . when q = 1or q = 0, thus eliminating the need for graphical assistance for such cases. An example calculation and indicated development of these equations follow,
..
..
The minimum reflux ratio for the complete separation of the mixture . . abc/dej . is determined by resolving the original mixture into (abc)’/d, (abc)”/e, (abc)”’/f . . . such that ( L / D ) m= (L‘/D’)m = (L“/D”)m = (L“‘/D“‘)m and (abc)’ (abc)” (abc)”’ . . = abc. The solution for (L‘/D’)mis, of course, obtained by rpsolving (abc)’/dinto c‘/d‘, b’ld‘‘, a’/d”‘ with similar solutions being obtained for the other resolute mixtures. At the condition of minimum reflux it has been observed that d ’ / d = e ‘ / e = f’/f, which fact reduces the problem to a ronsideration of the primary
.
+.
resolute mixtures with c‘ and d‘ as the only unknowns. The solution thus amounts to solving two simultaneous equations by successive approximation. Equating ( L / D ) m for each resolute mixture, for bubble point feed
(&),
..
+
e(arsc”
= e’(a
+ e’)
+ b + c ) ” ( f ~-~1)~ - I =
+
Substituting d/d’ for e/e’ and,f/f’ and noting that c’ cTl
=
(a (a
+ b + c)’ + b + c)”
and
(a
~
c”’
(a
+ b + c)’
+b+
c)”’
the following relationship can be derived for bubble point feed:
