ISDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1931
ment in relation to the quality of carbon black being made. Most of these factors can be determined only through largescale experimentation. The prime importance of channel height and rate of gas flow may be deduced from the experimental data already given. Finally there is the question of proper draft control which, as well as being of prime importance, is also most delicate and elusive. Many attempts have been made to regulate the draft by means of continuous analysis of the flue gases which escape through the top of the house. This method is found more cumbersome, as well as less sensitive, than the method of drafting based upon what is called the ‘[smoke blanket” of a burning house. This is a pall or cloud of smoke consisting, not of carbon black, but of sooty material which hangs a t about the general level of the channels and which rises or falls in a remarkably sensitive manner as the influx of air is varied. In addition to the ‘‘smoke blanket” the degree of luminosity of the flames (described as the “lightness” or “darkness” of the house) serves as an additional optical guide to the state of drafting. With any given set of conditions as to house construction, arrangement of flames, and channels, and with continuous
181
control of the quality of black produced, the operative in charge of the plant is able to determine by the hourly output of carbon black the exact drafting conditions that will yield the best results. Proper adjustments are necessary as between winter and summer and as between night and day. Thus there rests a heavy load of responsibility on “Those Slaves of Fire who, morn and even,” and in a climate already semi-tropical, tend the ten million flames which yield the carbon black of commerce. Acknowledgment
It is desired gratefully to acknowledge the important assistance rendered by J. W. Snyder and H. A. Braendle. Literature Cited (1) Bone and Townend, “Flame and Combustion in Gases,” Chapts. 28 to 32. (2) Chamberlin and Thrun, IND. ENG.CHEM.,19, 764 (1927). (3) Luckiesh, “Artificial Light,” Chapt. V I . (4) Payman, Fuel Science Practice, 3, 403-6 (1924). (5) Smithells, J . Chem. Soc., 61, 217 (1892). (6) Smithells, Thorpe’s Dictionary of Applied Chemistry, p. 212 (1922). (7) Smithells and Ingle, J . Chem. SOC.,61, 204 (1892). (8) Thomson, “Conduction of Electricity through Gases,” Chapt. X.
Action of Alkali Hydroxides on Elementary Sulfur and Mercaptans Dissolved in Naphtha’ V. Vesselovsky2 and V. Kalichevskya
T
HIS investigation represents a qualitative and quantitative study of the effect of potassium and sodium hydroxides in various solvents on solutions of elementary sulfur and mercaptans in naphtha. The study of these reactions was undertaken with the purpose of determining the possibility of their utilization for sweetening and corrosion treatment of light petroleum distillates. Previous investigators working along similar lines reported that anhydrous potassium hydroxide reacts with elementary sulfur and mercaptans in gasoline (8). Potassium carbonate in alcoholic solution likewise reacts with sulfur, while in water the same reaction proceeds a t a much slower rate (3,4 ) . Partial removal of mercaptans by aqueous alkali hydroxides has been also investigated ( 2 ) . These publications present interesting possibilities for studying similar reactions in a variety of solvents and stimulated the present research. Materials
Sulfur purified by recrystallization from benzene. Ethyl, n-butyl, and n-heptyl mercaptans (Eastman Kodak Company reagents). Solvent naphtha of the following characteristics: Color. . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Acidity, . . . . . . . . . . . . . . . . . . . . . . . . . .... Sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . .... Specific gravity . . . . . . . . . . . . . . . . . .. . . . Engler distillation: Initial boiling point. . . . . . . . . . . . . . . . . 55 per cent off a t . , . . . . . . . . . . . . . . . . . End point.. .................... .... Sayholt thermal viscositg . . . . . . . . . . . . . . Copper strip test at 122 F. (50° C.) . . . . Doctor t e s t . . .....................
....
Anhydrous potassium and sodium hydroxides (c. P.). Absolute ether, absolute ethyl and isopropyl alcohols.
* Received October 13, 1930.
* Senior student in Chemical
Engineering, New York University, New York, N. Y. * 616 Livingston Road, Elizabeth, N . J.
Commercial 91 and 98 per cent isopropyl alcohols containing some butyl and amyl alcohols. Analytical Methods
DETERMINATION OF SuLFuR-Lamp method (check determinations agreed within 0.005 per cent). Though the lamp method for determining elementary sulfur in the oil usually gives low results, for purely comparative purposes observations made by this method should prove wholly satisfactory. For this reason the lamp method was used in favor of a more tedious analytical procedure. QUALITATIVE TEST FOR ELEMENTARY SULFUR-fiVe cubic centimeters of the sample were shaken with 1 cc. of 1 per cent naphtha solution of ethyl mercaptan in the presence of 5 cc. of doctor solution. Discoloration indicated the presence of elementary sulfur. The method permits detection of less than 0.0025 mg. of sulfur per cubic centimeter of naphtha solution, while the standard copper-strip corrosion test a t 122’ F, (50” C.) fails to discover less than 0.005 mg. of sulfur per 1 cc. QUALITATIVETEST FOR hbRCAPTANs-Standard doctor test. Reactions of Elementary Sulfur
On mixing a t room temperature a 0.227-0.315 per cent solution of elementary sulfur in naphtha with varying quantities of potassium and sodium hydroxide solutions or suspensions in various solvents, the following observations were made: On addition of the reagents to the naphtha solutions the oil develops an orange-yellow color and becomes turbid owing to separation of some minute particles of a white substance. A golden-yellow precipitate collects a t the bottom of the reaction vessel, but the oil remains turbid. On further standing the precipitate acquires a dark yellow-brown coloration and the white substance which is responsible for the turbidity of the oil precipitates out. On washing with
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water the naphtha regains its original color and the turbidity disappears while the water acquires a yellow coloration. When potassium hydroxide solutions in absolute ethyl and isopropyl alcohols, absolute ether, and 91-98 per cent commercial isopropyl alcohol are used, the reaction proceeds almost instantaneously. The use of absolute alcohols as solvents for the potassium hydroxide results in the formation of solid, partially crystalline, red-brown precipitates, while the use of impure alcohols yields a heavy, dark-red liquid. The absolute-ether solution gives a very characteristic flocculent deep yellow precipitate. The saturated solution of potassium hydroxide in water also reacts with sulfur but a t an extremely slow rate, and after several days of contact a considerable quantity of sulfur is still left in the naphtha. Solutions of sodium hydroxide in the same solvents react similarly but a t a slower rate. r,
c F 30
I
I
I
Vol. 23, s o . 2
show that the removal of sulfur from the naphtha solution proceeds in steps. The reaction goes a t a very rapid rate until the mol ratio of sulfur removed to potassium hydroxide present reaches approximately 1.3, which corresponds to the formation of potassium trisulfide. The presence of fairly large quantities of this substance a t this stage of the reaction is further substantiated by the golden-yellow color of the precipitate formed. Potassium trisulfide is, however, not the primary product of the reaction. The experimental data show that after the first 2 minutes the mol ratio of sulfur removed to potassium hydroxide present corresponds to the formation of potassium disulfide according t o the equation: 6KOH 4- 6 s
+ 2K2S2 + 3H20
K~S203
Previous investigations on formation of polysulfides of alkali metals in the presence of an excess of free sulfur show that formation of polysulfides is always preceded by the formation of a monosulfide of the metal ( 7 ) . For these reasons the primary products of the reaction under investigation must be potassium thiosulfate, potassium monosulfide, and water, the higher polysulfides being formed by the secondary reactions of straight addition of sulfur to the lower polysulfides. Table I-Effect of T i m e in Treating a Solution of Elementary Sulfur in Naphtha with a De6cient Quantity of P o t a s s i u m Hydroxide Dissolved in Absolute Ethyl Alcohol
0
5
50
500
J-000
R M C T / O N T/N€ (M/NUT€S).
Small quantities of potassium hydroxide in the alcoholic or ether solutions are sufficient for the complete removal of sulfur, as shown by the following experiments: On adding 6 cc. of a 21.82 per cent solution of potassium hydroxide in ethyl alcohol to 200 cc. of a 0.227 per cent solution of elementary sulfur in naphtha, the sulfur was completely removed. This fact was ascertained by the negative copper-strip corrosion and ethyl mercaptan tests. However, on adding 4 cc. of the same potassium hydroxide solution to 200 cc. of the above sulfur solution, a very small quantity of sulfur remained in the oil, as indicated by the positive ethyl mercaptan test but negative copper-strip corrosion test. The mechanism af the reaction was investigated with the solution of potassium hydroxide in absolute ethyl alcohol. The naphtha solution of elementary sulfur was treated with deficient quantities of alcoholic potassium hydroxide solution in order to effect only a partial removal of sulfur. Samples of treated oil were withdrawn from the main body 01 the reacting mixture a t various intervals, thoroughly washed with water, filtered, and analyzed for their sulfur content. Two sets of experiments were made which differed only by the degree of agitating the oil with the reagent. The experimental data are presented in Table I, and shown graphically in the accompanying diagram. The water washings were collected and evaporated to dryness. Potassium thiosulfate was identified in the residue by qualitative tests with hydrochloric acid, ferric chloride, and silver nitrate. The solid precipitate deposited in the reaction vessel showed the presence of polysulfides of potassium, as on acidifying its mater solution hydrogen sulfide was evolved and free sulfur precipitated out. On the basis of these tests the reaction was assumed to proceed according to the following general equation: 6KOH nS = K&03 2K2Sn 3HzO -
+
+
2
This equation, however, does not express the intermediate stages of the reaction. The curves portrayed in the diagram
MOL-RATIO OF S U L F U R
KOH IN S U L F U R IN TIME OF SIJLFYR IN REMOVED TO NAPHTHA NAPHTHA CONTACT SOLUTIONKOH ADDED Grams/lifer Gvams/liler Minutes % One-minute agitation a t beginning of t r e a t followed b y moderate occasional shaking of reacting mixture 0 0.251 1.779 1.240 0.145 i:is 5 0.133 10 1.32 0 . 1 3 2 1.33 15 0.130 1.35 30 0 . 1 1 2 1.55 60 0.062 2 11 120 1.91 1440 0.080 0.138 1.26 2880 One-minute agitation a t beginning of treat only 1.532 1.975 0 0.339 2 0.199 1:oo ? n 176 1.17 5 0.161 1.29 10 0.161 1.29 1.24 15 0.166 1.23 30 0.167 1.25 60 0.165 1.24 129 0.166 1.30 930 0.157 1.25 2880 0.165 1.14 5900 0.179
The experimental data further shoiT that as soon as potassium trisulfide is formed the mol ratio of sulfur removed to potassium hydroxide present remains constant for a certain length of time and, if the mixture is not agitated, no higher polysulfides of potassium are obtained. These results are also in agreement with the chemical properties of potassium trisulfide, which is known to be a stable compound ( 5 ) . On shaking, however, potassium trisulfide is kept in suspension in naphtha and absorbs additional quantities of sulfur to form still higher polysulfides, with the ultimate formation of potassium pentasulfide and possibly also of potassium hexasulfide. Formation of potassium pentasulfide is substantiated, not only by the increase in the ratio of sulfur removed t o potassium hydroxide present, but also by the change in the color of the precipitate from golden-yellow to dark yellowbrown and by the hygroscopic properties of this precipitate, which easily deposits well-defined crystals of elementary sulfur on exposure t o the air. The experiments further show that after the removal of sulfur reaches its maximum the sulfur content of the naphtha begins to increase. This is distinctly demonstrated in both
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February, 1931
sets of the experimental data, but is more pronounced when the reacting mixture is agitated. The solutions which showed such an increase were shaken with metallic mercury to remove all the elementary sulfur and then analyzed for their sulfur content. All the sulfur was found t o be removed, thus indicating that sulfur is thrown back in the naphtha in its elementary form. Experiments were made with the purpose of investigating this phenomenon in greater detail. Potassium hydroxide solutions in absolute ether, absolute isopropyl, and 91 per cent isopropyl alcohol were added to the solution of elementary sulfur in naphtha. The amount of potassium hydroxide used was sufficient to effect a complete removal of sulfur, and the ratio of potassium hydroxide added to the sulfur present was the same in all samples. These samples were examined at regular intervals by the ethyl mercaptan test to detect when the elementary sulfur reappeared in naphtha. It was found that the sulfur first reappeared in the sample treated with the solution of potassium hydroxide in absolute ether and then in the sample treated with the solution of potassium hydroxide in absolute isopropyl alcohol. The sample treated with the potassium hydroxide solution in 91 per cent isopropyl alcohol remained free of elementary sulfur for a very considerable length of time. As absolute ether is a good oxygen carrier and as the experiments jvere made in the presence of air, it was assumed that the observed phenomenon was due to the oxidation of the reaction products. Potassium polysulfides are known to liberate sulfur according t o the typical equation (6): 2K2Ss
+ 302
2KzS208
+ 6s
Potassium thiosulfate is also liberating sulfur on oxidation: 2KzS203
+
0 2
=
2K2S04
+ 2s
If these reactions actually take place in treating solutions of elementary sulfur in naphtha with potassium hydroxide dissolved in various solvents, the observed phenomenon should not occur in the absence of air. Experiments were therefore made in a neutral atmosphere by displacing the air vithin the reaction vessel by nitrogen. It was found that under these conditions sulfur was not liberated. These observations showed conclusively that oxidation of the reaction products with the oxygen of the air is responsible for the reappearance of the elementary sulfur in naphtha and that the presence of an oxygen carrier such as alcohol or especially ether greatly promotes the oxidation process. Reaction of Mercaptans On adding potassium or sodium hydroxide solutions in absolute alcohols2 to naphtha solutions of ethyl, 12-butyl, and n-heptyl mercaptans, a heavy, dark brown liquid separated a t the bottom of the reaction vessel. After this treatment the naphtha solution of the mercaptans was sweet t o the doctor test. The t h e required for the reaction to go to completion varied with the nature of the reagent used. Sodium hydroxide solutions sweetened the oil almost instantaneously, whereas potassium hydroxide solutions required a certain length of time before the same results are accomplished. Similar tests showed that anhydrous sodium hydroxide also removes the mercaptans quantitatively, while anhydrous potassium hydroxide is considerably less active. 2 T h e presence of 1 t o 2 per cent of water in alcohols is permissible as this small q u a n t i t y of water is insufficient t o hydrolyze t h e mercaptides t o mercaptans t o t h e extent rrhich can be detected b y t h e doctor o r ethyl mercaptan te4ts.
I83
The mechanism of the reaction was investigated by adding to the naphtha solution of n-butyl mercaptan deficient quantities of alcoholic sodium hydroxide in order to effect only a partial removal of mercaptan. The experimental data are presented in Table 11. Table 11-Removal of n-Butyl Mercaptan from Its Solution i n Naphtha b y Sodium Hydroxide Dissolved i n Absolute Ethyl Alcohol S a O H ADDEDT O 50 CC. O F
MOLRATIOOF
MERCAPTAX SOLXa
SCLFGR IY SOLN.
cc.
70
0 3 6
1 580 0 906
a
MERCAPTAP: REMOVED To
NaOH ADDED
0.21s
0.1128 gram
0'98 0.99
N a O H per 1 cc. of solution.
These results show that the mol ratio of mercaptan removed to sodium hydroxide added is, within the limits of the experimental error, very close to unity. It was therefore assumed that the product of the reaction is sodium mercaptide, which is formed according to the general equation: RSH
+ XaOH = RSNa + Ha0
This assumption was tested for its validity by acidifying the sludge formed in the reaction with dilute hydrochloric acid. The separated oil was sour, thus indicating the reappearance of the mercaptan and the correctness of the assumed mechanism of the reaction. In the course of the investigation it was observed that on leaving the treated solution in contact with the sludge the sulfur content of the naphtha shows a gradual increase and the sweetened oil again becomes positive t o the doctor test. A sample of the solution of n-butyl mercaptan in naphtha with an initial sulfur content of 0.435 per cent was treated with a deficient amount of alcoholic sodium hydroxide and showed 0.255 per cent sulfur after 5 days' standing. On the eleventh day, however, the sulfur content of the same oil increased to 0.308 per cent. Another sample of the mercaptan solution was completely sweetened with the alcoholic sodium hydroxide, but after 4 days' standing it was positive to the doctor test. On adding water to the sweetened oil in the presence of the sludge, a similar effect was observed, but only in a much shorter time. These tests show that the increase in the sulfur content of the oil is undoubtedly due to a t least a partial hydrolysis of the sodium mercaptide originally formed. Conclusions
1-Potassium and sodium hydroxides in the anhydrous state or in solutions or suspensions in various organic solvents remove quantitatively sulfur and mercaptans from petroleum oil. Sodium hydroxide is particularly well adapted for the removal of mercaptans. and potassium hydrouide for the removal of elementary sulfur. 2-The products of the reaction between potassium hydroxide in alcoholic solution and elementary sulfur dissolved in naphtha are potassium thiosulfate, potassium monoor polysulfides, and water. Higher polysulfides are formed by direct addition of sulfur to the lower sulfides. Potassium trisulfide is the highest polysulfide formed if the reacting mixture is not agitated. If, however, the reagent is kept in intimate contact with the sulfur solution potassium, pentaand possibly hexasulfides are found among the final products of the reaction. On keeping the precipitated substances in contact with naphtha for a considerable length of time, some of the sulfur is returned to the oil in its elementary form. This is shown to be due t o the effect of the dissolved air.
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which oxidizes the Dolvsulfides and the thiosulfate with the liberation of free sulrur: 3-The products Of the between hydroxide in alcoholic solution and mercaptans dissolved in naphtha are sodium mercaptide and water. On keeping the pimipitate in contactwith naphtha some of the mercaptansare returned to the oil owing to partial hydrolysis of the sodium mercaptide.
Vol. 23, KO.2
Literature Cited (1) A. S. T.M.Tentative Standard, 1929, D90-29T, p. 409. (2) Borgstrom, Dietz, and Reid, IND. END.CHEM,, 22, 245 (1930). (3) Bovle, “SceDtical Chemist.” Oxford. 1680. (4) Davis and Hill, J. A m . Ckem. Soc., 49 3114 (1927). (5) Mellor, “Inorganic and Theoretical Chemistry,” Vol. 11, p. 630 (1922). (6) Mellor, I b i d . , p. 639. ),( Pomeranz, z. Farbe* Chem., 392 (1905). (8) Wilson, Canadian Patent 278,381 (March 6, 1928).
Effect of Mild Heat Treatments on the Chemical Composition of Wood’ L. F. Hawley and Jan Wiertelak2 FORESTPRODUCTS LABORATORY, MADISON,WIS.
HE many studies of the decomposition of wood by heat have been concerned almost entirely with the exothe,rmic r e a c t i o n occurring at about 275” C. during which the main chemical copstituents of the wood are completely decomposed. It has been noted that much lower temperatures affect the color and strength of wood and that thefse p h y s i c a l changes were p r o b a b l y acc o m p a n i e d by chemic a1 changes, but at the time the analyses reported here were undertaken there were no q u a n t i t a t i v e data on the subject.*
T
Analyses are recorded of white ash and Sitka spruce wood before and after heat treatments in a closed iron tube at 138” C. for 2,4, and 8 days. In both woods the losses are largely in the carbohydrate constituents and there are also gains in the lignin and the alcoholbenzene soluble. In both woods the methoxyl content remains practically constant. In the ash wood the carbohydrates lost are entirely pentosans, but in the spruce wood they are largely hexosans and even the stable (not readily hydrolyzed) cellulose is decomposed. In the ash wood the acetic acid by hydrolysis is rapidly decreased to a minimum at the fourth day. The changes in composition are discussed in the light of the empirical analytical methods used in determining the changes in composition. The indications of a change from carbohydrates to a lignin-like substance are so important that a special investigation of the change has been started.
Experimental Procedure
Samples of white ash and Sitka spruce that had been subjected to different temperatures for various periods of time were available together with well-matched specimens of unheated wood for comparison. For the present work those samples were selected that had been heated to 138” C. for 2, 4, and 8 days. The details of the heat treatments can be found in the articles describing the effect of the treatment on various physical properties of the wood (4, 5 ) . The wood was heated in sealed iron tubes contained in a small steam retort, the temperature being regulated by the steam pressure. The wood was previously dried to about 10 per cent moisture content so that it was not in contact with a large amount of water during the heating period. The samples were analyzed according to the methods in use a t the Forest Products Laboratory. These methods as described by Bray (1) were modified only in that alcoholbenzene was used instead of ether for the extractions previous to the lignin determination. Additional determinations were made of the methoxyl content of the isolated lignin and of the hydrolysis number (3)of the isolated cellulose. The complete analytical results are shown in Table I, 1 Received November 4, 1930. Presented before the Division of Cellulose Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 t o 11, 1930. 2 Research Fellow from Poland. 8 Campbell and Booth have recently published an article bearing upon this subject (2).
together with the losses in weight observed during the heat treatments. General Changes Common to Hardwood and Softwood
The solubility of the wood in cold water, alcohol-benzene, and 1 per cent caustic soda after different periods of h e a t i n g v a r i e d in the same manner. The solubilities were increased at first and later decreased, in some instances becoming a little less than those of the original wood. I n both the hardwood and the softwood the general effects of the h e a t i n g are a decrease in the carbohydrate components and an increase in lignin. The increase in lignin may be only a p parent, since the Forest Products Laboratory method for determining lignin is based on its insolubility in 72 per cent H&Oc and in other characteristics the “lignin” formed by heating may be different from the lignin present in the unheated wood. The isolated lignins from the heated and unheated samples were analyzed for methoxyl content as shown in Table I. There was always a lower percentage of methoxyl in the isolated lignin from the heated samples than from the corresponding unheated samples, indicating that, in this characteristic a t least, there is a difference. In another (qualitative) characteristic, however, the isolated lignins were similar. It was found that they could all be put into solution by the treatment used in the analytical method for isolating cellulose-namely, chlorination followed by treatment with sulfites. Although it is not maintained that by this heat treatment carbohydrates have been transformed into lignin, yet certain carbohydrates have lost some of their carbohydrate characteristics and have been transformed into a material that possesses some of the characteristics of lignin. These indications of the transformation of carbohydrate to lignin by long-continued low-temperature heating are, however, so important in the field of the relationships between the carbohydrates and lignin in wood that further experiments are now under way in the similar heat treatments of pure wood carbohydrates. The variations in the figures for methoxyl in Table I are
