August, 1926
I N D U S T R I A L AND ENGINEERIMG CHEMISTRY
823
Desulfurizing Effects of Sodium Hypochlorite on Naphtha Solutions of Organic Sulfur Compounds’
mined the effect of sodium hypochlorite on a number HIS paper is a continuation of some previously reof sulfur compounds. Folported work by Wood, Lowy, and Faragher.2 l o w i n g the suggestion of A study has been made of the desulfurizing effects of Kaufmann6 that the decomsodium hypochlorite solutions on naphtha solutions of position of sodium hypoethyl sulfide, n-butyl sulfide, diphenyl sulfide, ethyl dichlorite solutionsis inversely sulfide, n-propyl disulfide, ethyl mercaptan, n-propyl proportional to the concenmercaptan, isoamyl mercaptan, carbon disulfide, hytration of the hydroxyl ions, drogen sulfide, elementary sulfur, and thiophene. The it was found that solutions results indicate that the desulfurizing effects are decontaininglittle excess of pendent on the type and molecular weight of sulfur free alkali (0.22 per cent) ’Odium compound present, on the degree of free alkalinity and were most active in oxidizsulfur ‘OmOn amount of available chlorine present in the hypoing the various sulfur compounds. The chlorite solution, o n the volume ratio of hypochlorite pounds. Solutions of somethod was employed : solution to naphtha solution, and on the time and ind i u m hypochlorite of low tensity of agitation of the hypochlorite and naphtha About 50 cc. of the oil conalkalinity and with chlorine solutions. taining the particular sulfur content of 5 to 8 p e r cent compound were shaken for were shaken with equal volseveral hours with 250 cc. of umes of naphtha solutions a 0.6 N solution of sodium hypochlorite. Oil was then worked several times with a solu- of the sulfur compounds for periods of 15 to 180 minutes. tion of sodium carbonate and with water, and was finally filtered Under these conditions ethyl, propyl, isobutyl, and isoby suction three times through a filter containing bauxite of amyl sulfides were quantitatively converted to the correapproximately 2 cm. thickness. sponding sulfones. In a similar manner ethyl and propyl Under these conditions phenyl mercaptan, ethyl sulfide, disulfides and ethyl mercaptan were quantitatively conphenyl mustard oil, phenyl thiocyanate, and diphenyl sulfox- verted to sodium salts of sulfonic and sulfuric acids. With ide were substantially removed. Diphenyl sulfide, ethyl mer- solutions of higher alkalinity, the oxidation effects were less captan, carbon disulfide, diphenyl sulfone, and ethyl thio- pronounced, the mercaptan being converted in part to the cyanate were completely removed. Only a small portion of disulfide. Elementary sulfur and thiophene were not atthiophene was removed. The degree of alkalinity of the tacked and hydrogen sulfide was converted to elementary hypochlorite solution was not indicated. sulfur along with the simultaneous formation of some sulfuric Wood, Lowy, and Faragher2 determined the effect of a so- acid. dium hypochlorite solution containing 5.25 per cent of availExperimental able chlorine on naphtha solutions of elementary sulfur and several sulfur compounds. These observations were in part The present paper presents a study of the desulfurizing quantitative and in part qualitative. The quantitative ob- effects of sodium hypochlorite solutions on naphtha soluservations were carried out by shaking for one hour 5,10, and tions of ethyl sulfide, n-butyl sulfide, diphenyl sulfide, ethyl 15 cc. of the sodium hypochlorite solution with 50 cc. of naph- disulfide, n-propyl disulfide, ethyl mercaptan, n-propyl tha solutions of isoamyl mercaptan, n-butyl sulfide, ethyl di- mercaptan, isoamyl mercaptan, carbon disulfide, hydrogen sulfide, and thiophene. The qualitative observations were sulfide, thiophene, and elementary sulfur. Hypochlorite made on naphtha solutions of hydrogen sulfide, carbon di- solutions of several strengths of alkalinity and available sulfide, elementary sulfur, diphenyl sulfoxide, and n-butyl chlorine were employed. The volumes of hypochlorite sulfone. The alkalinity of the hypochlorite solution was not solutions used varied from 5 to 50 cc. per 50 cc. of naphtha indicated, but under the cagditipns employed isoamyl mer- solution of sulfur compound. The naphtha used as a solvent for the sulfur compounds 1 Received March 29, 1926. Presented before the Division of Petroieum Chemistry at the 71st Meeting of the American Chemical Society, was a highly refined Pennsylvania distillate withi specific Tulsa, Okla., April 5 to 9, 1926. gravity 0.769, initial boiling point 152’ C. and final boiling
a finished kerosene with 0.06 to 0.10 per cent sulfur; the original distillate contained 0.15 per cent sulfur. The degree Of ratio Of ‘hypochlorite to and Wantity Of bauxite used were not indicated. Waterman and Heima14 d e t e r m i n e d the effect Of
T
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2
THISJOURNAL, 16, Ill6 (1924).
4
J . Inst. PdroZeum Tech., 46, 812 (1924).
* Ibid., 14, 1112 (1922). #
6 6
J . Chem. SOC.(London), 121, 1934 (1925). 2. angew. Chem., 81, 364 (1924).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
824
Vol. 18, No. 8
point 236’ C. The sulfur compounds were used as purchased (Table I). All sulfur determinations were made by the lamp method. The sodium hypochlorite solutions (Table 11) were prepared by passing liquid chlorine into a solution of pure sodium hydroxide.
ening” a distillate, as both sulfides and sulfones are “sweet to the doctor test.” It will be observed that 10 cc. of hypochlorite solution 2, with medium alkalinity and high chlorine content, had a much greater desulfurizing effect on the n-butyl sulfide solution than 10 cc. of hypochlorite solution 1, with low alkalinity and less chlorine. This would indicate Table I-Stock N a p h t h a Solutions that the oxidation of n-butyl sulfide is accelerated by an Sulfur Sulfur Stock solution Per cent Stock solution Percent increase in the amount of available chlorine. The sulfur Ethyl sulfide 0.55 n-Propyl mercaptan content of the n-butyl sulfide solution was not reduced by %Butyl sulfide 0.52 Isoamyl mercaptan Diphenyl sulfide 0.28 Thiophene 0.10 10-cc. and 50-cc. treatments of hypochlorite solution 3. Ethyl disulfide 0.50 Elementary sulfur 0.16 The determination of the available chlorine in the residual n-Propyl disulfide 0.71 Carbon disulfide 0.28 Ethyl mercaptan 0.43 Hydrogen sulfide 0.15 hypochlorite solution from the 10-cc. treatment indicated that any oxidation to the sulfone was negligible. The time Table 11-Hypochlorite Solution factor is also important in the oxidation of the higher molecAlkalinity Available chlorine Solution Per cent Per cent ular weight and correspondingly less reactive sulfur com1 0.29 5.63 pounds. Thus, the n-butyl sulfide solution after a 3-hour 2 0.62 11.03 3 1.68 5.42 treatment with 50 cc. of hypochlorite solution 3 was reduced 4 0.09 0.70 in sulfur content to 0.45 per cent when the 1-hour treatment, Fifty cubic centimeters of naphtha stock solutions of the as indicated, failed to show any reduction. Diphenyl different sulfur compounds were shaken with the indicated sulfide gave results analogous to those of n-butyl sulfide. volumes of solutions 1, 2, and 3 for 1 hour a t room t’emperaUnder the conditions employed, ethyl disulfide was someture. The shaking was effected by placing the solutions in what less readily removed than ethyl sulfide. With hypoa 4-ounce glass-stoppered bottle and attaching the bottle chlorite solutions of low alkalinity and small volume ratio, to a 15-inch wooden wheel which was rotated in a vertical the results were complicated by the acids that developed plane at 40 revolutions per minute. The recovered naphtha since the final wash with the dilute alkaline solution may not solution was washed once with an equal volume of water have removed all the acidic constituents from the naphtha. when the hypochlorite solution remained alkaline or with an The removal of the sulfur was directly proportional to the equal volume of 1per cent sodium hydroxide solution when the decrease in the alkalinity of the hypochlorite solution. hypochlorite solution became acid. The desulfurizing effect I n confirmation of the work of Birch and Norris5 sulfonic was determined from the sulfur content of the naphtha s o h - and sulfuric acids were identified as oxidation products. tion before and after treatment. Tests were made to deter- Hypochlorite solution 3 produced only negligible desulfurizing mine whether the residual hypochlorite solution had re- effects on t,he ethyl and propyl disulfide solutions. mained alkaline or had become. acid during the shaking. The mercaptans were somewhat less readily removed than either the sulfides or disulfides. Hypochlorite solution 3, Results with higher alkalinity, produced comparatively alight deThese results, summarized in Table 111, show elementary sulfurizing effects. Ten cubic centimeters of this solution sulfur and thiophene to be stable in the presence of hypo- did not reduce the sulfur content of the naphtha solution of chlorite solutions of any alkalinity investigated. The alkyl isoamyl mercaptan, indicating that with this volume ratio sulfides show varying degrees of reactivity and desulfuriea- and alkalinity there was no oxidation beyond the analogous tion. Ethyl sulfide was completely removed by the solution disulfide; in fact, the “doctor test” indicated that the merof medium alkalinity and high chlorine content and was captan had not been completely converted to the disulfide. largely removed by the other hypochlorite solutions, since Hypochlorite solutions of lower alkalinity were more reactive, the resulting ethyl sulfone is readily soluble in aqueous solu- carrying the oxidation beyond the disulfide stage and retions. n-Butyl sulfide shows much less reactivity with the moving amounts of sulfur proportionate to the volume hypochlorite solution of higher alkalinity; but with solu- ratio used. Here again some of the results were complicated tions of lower alkalinity formed a copious precipitate of n- because some of the hypochlorite solutions became acid.
Naphtha solution Ethyl sulfide %-Butylsulfide %-Butylsulfide Diphenyl sulfide Ethyl disulfide Ethyl disulfide n-Propyl disulfide Ethyl mercaptan n-Propyl mercaptan Isoamyl mercaptan Isoamyl mercaptan Thiophene Elementary sulfur Carbon disulfide Hydrogen sulfide ’
Sulfur
70
0.55 0.52 0.52 0.28
0.50 0.50 0.71 0.43 0.59 0.46 0.46 0.10 0.16
0.28 0.15
NaOCl Cc. 50 50
10 50
50 10 50 60
50 50 10 50 50 50 50
Table 111 HYPOCHLORITS SOLUTION 1 S in treated naphtha Per cent Residue from NaOCl 0.028 Alkaline, no ppt. 0.18 Alkaline, copious ppt. 0.40 Alkaline, no ppt. 0.26 Alkaline, small ppt. 0.08 Slightly alkaline 0.41 Acidic 0.08 Acidic 0.15 Acidic 0,25 Acidic 0.20 Alkaline 0.43 Alkaline 0.10 Alkaline 0.16 Alkaline 0.20 Acidic 0.06 Alkaline
butyl sulfone which was identified by its melting point. The amount of sulfur in the treated naphtha solution of nbutyl sulfide was not reduced below 0.18 per cent, which is the saturation point for n-butyl sulfone in the naphtha used. Clearly, the amount of n-butyl sulfide that can be removed by treating a petroleum distillate with hypchlorite solution is dependent on the solubility of the sulfone in the distillate. The removal of alkyl sulfides has nothing to do with “sweet-
HYPOCHLORITE SOLUTION 2 S in treated naphtha Per cent Residue from NaOCl 0.00 Alkaline no ppt. 0.186 Alkaline: copious ppt. 0.20 Alkaline, copious ppt. 0.18 Alkaline, medium ppt. 0.05 Alka!ine 0.24 Acidic 0.06 Alka!ine 0.13 Alkaline 0.15 Alkaline 0.17 Alkaline 0.40 Alkaline Alkaline 0.10 0.15 Alkaline 0.16 Alkaline 0.05 Alkaline
HYPOCHLORITE SOLUTION 3 S in treated naphtha Residue from Per cent NaOCl 0,034 Alkaline, no ppt. 0.51 Alkaline, no ppt. 0.51 Alkaline, no ppt. 0.27 Alkaline, no ppt. 0.46 Alkaline 0.49 Alkaline 0.69 Alkaline 0.35 Alkaline 0,045 Alkaline 0.35 Alkaline 0.46 Alkaline 0.10 Alkaline 0.16 Alkaline 0.19 Alkaline 0.08 Alkaline
Carbon disulfide was partially removed by hypochlorite solutions of all strengths investigated. Hydrogen sulfide was converted in part to elementary sulfur, some of which was left in solution in the naphtha. The foregoing results substantially confirm the previously reported results of Birch and Norris,6 when the naphtha solution is treated with an equal volume of hypochlorite solution of low alkalinity and comparatively high chlorine con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1926
tent. They also indicate that the discrepancies between the work of Birch and Norris on the sulfides, disulfides, and mercaptans and the work of Wood, Lowy, and Faragher on the same compounds are due to the fact that Wood, Lowy, and Faragher were using hypochlorite solutions of higher alkalinity in much smaller volume-ratios to the naphtha solution. Industrial Practice
825
drastic than those employed in the present paper and also than those employed by Birch and Norris. Clearly, the desulfurizing, sweetening, and corrosion efficiencies derived from a hypochlorite treatment must be interpreted in terms of the conditions actually employed. The per cent of alkalinity, per cent of available chlorine, volume ratio of hypochlorite used, intensity of agitation, and types of sulfur compounds present are factors affecting the final results. When hydrogen sulfide is absent and mercaptans are present only in traces, the value of the initial caustic wash is questionable. I n the presence of appreciable amounts of mercaptans and hydrogen sulfide, the initial caustic wash is highly beneficia1 as it removes the mercaptans partially and hydrogen sulfide completely, thus preventing the formation of elementary sulfur which is especially corrosive in the copper dish test. It is generally agreed that sodium hypochlorite is a good sweetening agent, but industrial experience concerning its desulfurizing effectiveness seems variable. Dunstan’o has shown that each stage in the complete hypochlorite process has a definite desulfurizing effect. Waterman and Heimal,4 working with a Mexican distillate of gravity 0.83 to 0.85. and a sulfur content of 1.28 per cent observed that the complete hypochlorite process in use removed 68 per cent of t h e total sulfur. Of this amount the hypochlorite treatment in two stages removed 25 per cent. With a Mexican distillate of gravity 0.89 to 0.94 and sulfur content of 2.95 per cent, the complete process removed 40 per cent of the total sulfur, while the hypochlorite treatment in two stages removed only 8 per cent.
The industrial practice with hypochlorite solutions seems to be quite variable. An industrial bulletin on the hypochlorite process’ recommends a chlorine content of 20 to 30 grams per liter for straight-run distillates and 5 to 10 grams per liter for cracked distillates. It is stated that the volume of hypochlorite solution to be used cannot be determined in advance of laboratory tests on the distillate in question. No mention is made of the required alkalinity or of its importance. An initial 3 per cent by volume of caustic wash (8 to 14” Be.) is recommended. This is followed by a water wash, a 30-minute hypochlorite treatment, and a second water and a second caustic-wash similar to the first. The recommended higher chlorine content for straight-run distillates is probably due to the fact that these distillates contain sulfur compounds of the nature of the alkyl sulfides whose oxidation products are not acidic, while the cracked distillates contain hydrogen sulfide, mercaptans, and perhaps disulfides, whose oxidation products are acidic in character. I n the article by Dunstan and Brooks3 the initial caustic and water washes are omitted, the distillate being subjected Experiments with Specially Prepared Naphtha Solutions a t once to a 2-hour hypochlorite treatment (12 grams of available chlorine per liter), followed by a soda wash, a reTwo specially prepared naphtha solutions (Table IV) were distillation, and finally filtration of the resulting residue treated with varying amounts of hypochlorite solutions 1, through an absorbing material. I n this connection it is in- 2 , 3, and 4. teresting to note that the sulfones have a much higher boiling point than the corresponding sulfides; hence a redistillation Table IV-Sulfur Content of Specially Prepared N a p h t h a Solutions Naphtha Naphtha should be of value in reducing the sulfur content of a dissolution 1 solution 2 Per cent S Per cent S Compound tillate that has been thoroughly treated with a hypochlorite Ethyl sulfide 0.01 0.04 solution. It is also interesting to note in this connection that n-Butyl sulfide 0.01 0.05 Diphenyl sulfide 0.00 0.04 the results obtained by Wood, Sheely, and Trusty8 indicate Ethyl disulfide 0.01 0.03 that sulfones and sulfoxides are much more readily removed n-Propyl disulfide 0.01 0.03 Ethyl mercaptan 0.01 0.01 by silica gel, fuller’s earth, etc., than the corresponding suln-Propyl mercaptan 0.01 0.01 Isoamyl mercaptan 0.01 0.01 fides. This probably accounts in part for the desulfurizing Thiophene 0.00 0.01 effects obtained when a distillate thoroughly treated with a Elementary sulfur 0.01 0.03 Carbon disulfide 0 . 0 0 5 0 .01 hypochlorite solution is filtered through fuller’s earth, bauxHydrogen sulfide 0.005 0.00 ite, etc. TOTAL 0.09 0.27 Reide states that some refineries find it necessary to precede sweetening with hypochlorite by a caustic wash, esFifty cubic centimeters of naphtha solutions 1 and 2 were pecially when treating pressure distillates; while others omit the caustic wash successfully on both straight-run and treated for 1 hour with 5 , 10, and 50 cc. of hypochlorite pressure distillates. Concerning the preparation of the solutions 1, 2, 3, and 4. The recovered naphtha was washed hypochlorite solutions, Reid further states that ‘(this solu- with water and the per cent of sulfur determined. Table V indicates that hypochlorite solutions 1, 2 , and 3 tion is generally prepared on a basis of 150 pounds of chlorine are more effective sweetening and desulfurizing agents than to 250 gallons of 13” B B . caustic; and this solution is diluted with 10 parts of water per 1 of 13” BB. solution:” further, hypochlorite solution 4. Hypochlorite solution 4 approxi“that distillates as prepared and derived from :t combina- mates somewhat the type of solution frequently employed in tion of Dubbs and Cross units and Power Specialty pipe still the United States for sweetening cracked distillates. The benzine” may be treated to corrosion and doctor sweet- small volume treatments with this solution did not appreness with 1 per cent by volume treatment instead of the ciably reduce the sulfur content of the naphtha solutions and prescribed 3 per cent by volume treatment. I n this manner produced acid sodium hypochlorite residues. The acid resiit is possible to treat 300,000 gallons of oil with 3000 gallons due was due to the presence of appreciable amounts of diof sodium hypochlorite solution.” The procedure indicated sulfides, mercaptans, carbon disulfide, etc. The recovered by Reid will produce a hypochlorite solution of low alkalinity naphtha was not completely sweetened to the doctor test, containing about 7 grams of available chlorine per liter. because in all probability the mercaptans were present in It is evident that the conditions prescribed by Reid are less excess of those occurring in the usual cracked distillates. The larger volume treatment with hypochlorite solution 4 7 The Mathieson Alkali Works, Inc., New York, 1923. reduced substantially the sulfur content of the naphtha _ .
8 0
THISJOURNAL, 18, 169 (1926). OQ Gas J . , 14, 119 (1925).
10
J . Inst. Petroleum Tech., 10, 61 (1924).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
826
Naphtha NaOCl solution Cc.
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5
10 50 5 10 50
Vol. 18, No. 8
Table V-Results of Experiments on Specially Prepared Naphtha Solutions -HYPOCHLORITE SOLUTION 4c-HYPOCHLORITE 1-HYPOCHLORITE SOLU~IO 2-N -HYPOCHLORITE SOLUTION SOLUTION 3Treated naphths Treated naphtha Treated naphtha Treated naphtha Doctor NaOCl Doctor NaOCl Doctor NaOCl %S Doctor test NaOCl residue %S test residue %s test residue %S test resldue 0.087 Acidic 0.065 Alkaline 0.073 Alkaline 0.072 Alkaline 0.086 Acidic 0.05 Alkaline 0.07 Alkaline 0.07 Alkaline 0.058 Sliahtlv alkaline 0 . 0 4 Alkaline 0.051 Alkaline 0.06 Alkaline 0.27 Acidic0.225 Alkaline 0.20 Alkaline 0.224 Alkaline Acidic 0.26 0.162 Alkaline 0.19 Alkaline 0.216 Alkaline 0.20 Alkaline 0.16 Alkaline 0.17 Alkaline 0.185 Alkaline
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solutions, and produced naphtha solutions sweet to the doctor test without developing acid sodium hypochlorite residues. These results indicate that the type of hypochlorite solution to be used with a petroleum distillate can not be determined in advance of laboratory tests on the distillate in question. If sulfur compounds of the type that produce acids on oxidation are present in very small amounts, it would seem possible to sweeten the distillate satisfactorily with a small volume treatment of a hypochlorite solution of low alkalinity and low chIorine content. On the other hand, if these sulfur compounds are present in larger amounts, the alkalinity, chlorine content, and volume ratio of hypochlorite solution will have to be adjusted accordingly. The naphtha solution of elementary sulfur is very corrosive
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to the copper strip and the copper dish test and is apparently not appreciably affected by treatments with sulfuric acid and sodium hypochlorite solutions; or by filtration through the more common absorbing materials.8 The removal of elementary sulfur from a petroleum distillate may be accomplished by the sodium plumbite treatment as suggested by Wendt and Diggs,ll and by Wood, Lotvy, and Farsgher.2 Acknowledgment
The writers are indebted to W. F. Faragher and Alexander Lowy for their interest in and criticism of this work. Our work with sodium hypochlorite and other petroleum-refining agents was originally outlined by Dr. Faragher. 11
THISJOURNAL, 16, 1113 (1924).
An Improved Laboratory Fractionating Column’ By A. W. T. Loveless RENTCHEMICAL LABORATORY UXIVERSITY OF CHICAGO, CHICAGO, ILL.
I T IS only recently that the knowledge concerning fractional distillation g a i n e d i n industrial practice has b e e n a p p l i e d in the l a b o r a t o r y . It has been known for a number of years that the sharpness of separation of f r a c t i o n s depends principally upon four factors: (1) thermal insulation of the column, (2) ratio of reflux to distillate, (3) intim a c y of contact of vapor and liquid in the column, and (4) length of column. The fractionating columns ordinarily used in laborat o r i e s violate all of these factors with the p o s s i b l e exception of the third. The best column developed to 1 Presented under the title “A Modified Column and Still Head for Accurate Fractional Distillation” before the joint session of the Divisions of Organic Chemistry and Medicinal Products Chemistry at the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926.
date is probably that of Peters and Baker.2 It has been found that with a slight modification this device can be greatly simplified and a high order of precision obtained in the separations. This improved fractionating column resembles an insealed condenser the jacket of which has been silvered and highly evacuated. This method of thermal insulation is quite effective as is known from experience with Dewar flasks. The column is packed with ‘/d-inch lengths of 1/4-inch tubing, as has been suggested by Peters and others. The stillhead may be a simple dephlegmator which controls the reflux ratio or it may be a total reflux condenser to which is sealed a stopcock that diverts a controlled fraction of the condensate. The latter device is much simpler to operate but has been criticized by Peters and Baker. The following results were obtained by distilling a mixture of thionyl chloride and phosphorus oxychloride. This mixture was the result of the action of sulfur dioxide upon phosphorus pentachloride: Column 35 cm. Hempel No. of distillations 7 PCls used, grams 500 SOClz obtained, grams 165 Yield per cent 57.8 76 to 79 Boilidg point range, a C.
50-cm.thermally insulated 2 500 263 92.1 7 6 . 8 to 77.1
Note that there was an increase in yield of nearly 60 per cent and that the product boiled over a range of 0.3’ C. on the second distillation. The distillate gave no test for the presence of phosphorus as phosphoric acid with a molybdic acid reagent. 2
THISJOURNAL, 18, 69 (1926).
Czechoslovak Rayon Industry Depressed-The Czechoslovak rayon industry is undergoing a greater period of depression than any other branch of the textile industry. In recent months the turnover dropped by 25 or 30 per cent from that of last year. Exports are being sent t o South America, where Czechoslovakia has been able to maintain its position.
