INDUSTRIAL A N D ENGINEERING CHEMISTRY
610
Vol. 22, No. 6
Effect of Refining Agents and Fused Caustic Alkali on Sulfur Compounds in Naphtha Solution' Merrill A. Youtz and Philip P. Perkins STANDARD OIL COMPANY( I N D I A N A ) ,
PREVIOUS article (1) has described the effect of various refining agents (sulfuric acid, aluminum chloride, silica gel, and hot fuller's earth) on the sulfur content of naphtha containing pure sulfur compounds in solution. A few additional compounds have been treated with sulfuric acid and aluminum chloride and the results here reported. Also a number of compounds in solution have been treated with fused caustic alkali, a mixture of potassium and sodium hydroxides, a t 343' C. (650' F.) and the effect on the sulfur noted.
A
Sulfuric Acid and Aluminum Chloride Treatments
The sulfuric acid treatment was conducted as before-100cc. samples were shaken 3 minutes with 3.3 cc. (25 pounds per barrel) of 93 per cent sulfuric acid and the sludge drawn off. One-half of the treated naphtha was then poured off, washed, dried, and analyzed. To the remaining half were added 3.3 cc. sulfuric acid (50 pounds per barrel) and the procedure repeated.
Figure 1-Apparatus for Caustic Treatment of Naphtha Solutions
For the aluminum chloride treatments, 100-cc. samples were refluxed 3 to 4 hours with one gram of aluminum chloride, then 50 cc. of the solution was poured off, washed, dried, and analyzed. The remaining naphtha was distilled from the refluxing flask through a short bead column,,.practically to dryness. The distillate was washed, dried, and analyzed. The results of these treatments are shown in Table I. Table I-Effect
of Sulfuric Acid and Aluminum Chloride on Sulfur Content -. . .... .. AFTERRE- REFLUXING
ORIGINAL SCLFUR COMPOUNDSOLN. Per cent n-Butylsulfide 0.502
AFTER 25 LBS.
AFTER
75 LBS. %SO4
FLUXING WITH
AND
DIS-
TILLING FROM AlCla
Per cent
AlCla Per cent
0.018 0,022
0,331 0.337
0.173 0.174
0.047 0.053
0.019 0.018
0.167 0.169
0.028 0.026
0.053 0.053
0.021 0.021
0.026 0.021
0.026 0.025
H2S04 Per cent
0.503
0.076 0.077
Isobutylsulfide
0.449 0.447
sec-Butyl sulfide
0.488 0.487
Per cent
These results are in agreement with the conclusions previously reported. Sulfuric acid very thoroughly removes the lower alkyl sulfides. But with aluminum chloride the effects 1
Received March 29,1930.
WHITING, I N D .
differ considerably with change in structure of the sulfides. The normal sulfide is much less completely removed than the secondary and isobutyl sulfides. The isobutyl sulfide is a little more resistant than the normal secondary sulfide. I n the previous work normal primary and normal secondary heptyl sulfides were found to show a similar difference, the normal sulfide being a great deal more stable. Table 11-Effect of Fused Caustic at 650° F. on Sulfur Compounds in Naphtha SULFUR COMPOUND SULFUR Original s o h . Per cent
Distillate Per cent
Ethyl sulfide
0.523 0.526
0.476 0.472
n-Propyl sulfide
0.585 0.585
0.565 0.549
n-Butyl sulfide
0.502 0.503
0,453 0.455
sa-Butyl sulfide
0.488 0.487
0.479 0.483
Isobutyl sulfide
0.449 0.445
0.377 0.373
Isoamyl sulfide
0.471 0.476
0.453 0.448
n-pri-Heptyl sulfide
0.451 0.449
0.069 0.066
n-4-sec-Heptyl sulfide
0.500 0.499
0.109 0.119
Phenyl sulfide
0.506 0,504
0.414
Allyl sulfide
0.527 0.531
0.058 0.052
Ethyl disulfide
0.560 0.563
0.056 0.056
Isoamyl disulfide
0.506 0.506
0.037 0.039
Thiophene
0.549
0.449 0.408
0.521
.....
Caustic Treatment
For the caustic treatment, the minimum melting point mixture of sodium and potassium hydroxides was used. The apparatus (Figure 1) consisted of a dropping funnel, A , with a sealed-in tip, B , for controlling the rate; a flash drum, C, into which the naphtha solutions were dropped and in which they were completely vaporized; a release valve, D, which was opened a t the end of a run to prevent molten caustic being sucked back into the flash drum; a treater, E; and condensers. The flash drum was a section of standard gage 3-inch iron pipe (7.8 cm. i. d.) into which a bottom plate was welded and to the top of which a flange was welded. The top plate was bolted to this with an asbestos gasket between. The top plate contained a thermometer well, a 30-cm. length of '/l-inch pipe (0.91 cm. i. d.) into which the solutions were dropped, and a '/*-inch exit pipe (1.57 cm. i. d.) leading to the treater. The treater was a piece of standard gage 3-inch pipe into which a bottom plate was welded. A top plate was also welded in place and held a 1-inch standard gage pipe coupling with plug, a thermometer well, and a '/*inch riser (1.57 cm. i. d.) leading to an iron, water-cooled condenser. The vaporized naphtha was led beneath the surface of the fused'alkali by a '/*inch pipe welded into the side of the treater and extending to within 1 cm. of the bottom of the vessel.
INDUSTRIAL AiVD ENGINEERING CHEMISTRY
June, 1930
The time of contact of the vaporized naphtha solutions with the caustic was extremely short. The solutions were passed in a t the rate of 150 to 200 cc. per hour, which means that the vapors were in the presence of the caustic not more than 1 or 2 seconds. Yet the effect was very pronounced in some cases. Mercaptans in crude naphthas were removed very completely, so that the doctor test was negative. I n all the pure compounds tested the distillates were also sweet to doctor. The compounds tested and the results are given in Table 11. From the above results it is seen that alkyl sulfides, a t least the lower ones, are very little affected. The small differences are probably not significant except that the two heptyl sulfides are very considerably attacked. It is not clear just why there should be this difference, which apparently is not connected with structure at all but with molecular weight.
611
Aluminum chloride reacts very differently on alkyl sulfides of differing structure, but its effect does not vary with the molecular weight. Phenyl sulfide is not greatly affected, although it is attacked more than the alkyl sulfides. The olefinic allyl sulfide is thoroughly removed. Thiophene is attacked to about the same degree as diphenyl sulfide. Yet the two disulfides are very thoroughly removed, quite as thoroughly as mercaptans. At present this seems to have no practical significance, since disulfides have not been reported in any quantity in naphtha, although they are undoubtedly formed in traces in doctor sweetening, especially if air blowing or free sulfur is used. Literature Cited (1) Youtzand Perkins, IND.ENG.CHEM., 19, 1247 (1927)
Hydration of Calcined Gypsum’ W. C. Hansen EXPERIMHNTAL LABORATORIES, AMERICAN CYANAMID
ALCINED gypsum or plaster of Paris is produced by the following reaction:
C
+ +
CaSOd. 2H20 heat = CaS04.l/2HZ0 l1/zH20
COMPANY, A N D STRUCTURAL
A study has been made to determine why soluble materials when added to calcined gypsum-water pastes either accelerate or retard the setting of the pastes. From a study of time-temperature curves obtained from the hydrations of calcined gypsum in various solutions, it appeared that the controlling factor in the setting was the rate at which precipitation took place from the paste. A study of the rate at which gypsum precipitated from carefully mixed solutions of calcium nitrate and ammonium sulfate to which had been added other salts showed that foreign salts markedly affect the rate at which gypsum precipitates from its supersaturated solution. This effect of foreign materials upon the rate of precipitation of gypsum from its supersaturated solutions appears to explain the ability of foreign materials to accelerate or retard the setting of calcined gypsum pastes.
This calcined gypsum when mixed with water rehydrates and sets into a hard mass. It is well known that almost all materials which are a t all soluble in water will, when mixed with calcined gypsum and water, either accelerate or retard the hydration of the calcined gypsum. Two theories have been offered to exulain the action of foreign haterials upon this reactio-n of hydration. Neither of these theories adequately explains this action. This investigation was undertaken in an effort to find a more complete explanation for this action of foreign materials upon the hydration of calcined gypsum. Theories on Setting of Calcined Gypsum
Lavoisier (4) probably was the first to offer an explanation for the setting of calcined gypsum. His explanation was that gypsum which had been dehydrated by heating took u p water with avidity producing a sudden and irregular crystallization. The small crystals of gypsum which precipitated, becoming confused with one another, formed a very hard mass. Marignac (6) observed that calcined gypsum with water gave solutions far more concentrated than could be obtained from gypsum-that is, the solutions from calcined gypsum were supersaturated with respect to gypsum. Le Chatelier (5) studied the setting of calcined gypsum and ctated the theory which is generally accepted today. He said: On mixing burnt plaster with water each particle soon becomes surrounded by a layer of a solution which is saturated with respect t o the hemihydrate but greatly supersaturated with respect t o the stable gypsum. Crystallization of gypsum soon begins, either spontaneously or more probably from nuclei of
’ Received .4pril 25, 1930
GYPSUMCORPORATION,
LINDEN,
N. J.
gypsum which have persisted unchanged t h r o u g h o u t t h e burning process. Growth of the gypsum crystals t a k i n g place from many neighboring centers, radiating growths are formed, and the interlocking of these is a t least one of the causes of the strength of the mass.
This theory has been modified to include a colloidal stage. Cavazzi ( 1 ) and others (7, 10) claim that calcined gypsum and water first form a colloidal gel or an adsorption complex from which the gypsum crystals form. Combining these two theories. one mav outline the mechanism of the hydration and setting of calcined gypsum into the following stages:
(I) Calcined gypsum plus water forms a gel or an adsorption complex in which only physical or secondary chemical forces are concerned. (2) The adsorption complex dissolves to produce a solution supersaturated with respect to gypsum. (3) Gypsum crystallizes from the supersaturated solution.
This seems to be the mechanism as Xeville sees it. Theories Explaining Accelerating and Retarding Influences of Foreign Materials upon Hydration of Calcined Gypsum
Rohland (8) studied the influence of various materials on the rate of setting of calcined gypsum and concluded that generally those materials which increased the solubility of the hemihydrate in water accelerated the setting, while those which decreased the solubility of the hemihydrate in water retarded the setting. A number of investigators haye found exceptions to Rohland’s theory. Welch (11) has summarized the literature on this subject, so it need not be repeated here. Traube and Neville claim that foreign materials added to calcined gypsum accelerate or retard the formation of the gel or adsorption complex, thus accelerating or retarding the setting. In the case of salts they claim that the action is due
