April, 1929
IND VSTRIAL AND ENGINEERING CHEMISTRY
46.046/23,3791° = 2.0304 grams (or 2.805- cc. a t -23.67" C.). The 2.036- grams is equivalent to 2.063 grams per liter a t 0' C. and 760 mm., to 2.1155 for LO(when 1 X = 1.0254) and a mol weight of 46.17, compared, respectively, to 2.0576, 2.1098, and 46.046 as given in the International Critical Tables. The agreement is better than 3 parts in 1000, which represents approximately the accuracy of the apparatus and procedure, and it completes the identification of the material as dimethyl ether. Notwithstanding the fact that the data of Table 11, which are intended for identification purpose only, have not the accuracy of precision measurements, the writers have employed them to give the approximate specific gravities of dimethyl ether between -80" and -20' C. These have been found useful in converting directly the volumes of liquid ether collected into grams. They were calculated from the extrapolated gravity of 0.7240 a t -23.65' C. and the t#emperaturevolume relationship represented in Figure 3 in which these approximate specific gravities are likewise graphed.
+
IQ Values from International Critical Tables, Vol. 111, 1,. 4, a n d represent weight of 1 cc. or t h e molecular weight divided b y true gram-molecular volume of methyl ether.
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Extent of Ether Production in M e t h a n o l Synthesis
The data on the dimethyl ether produced between 300" and 400" C. as a by-product of the methanol synthesis (with normal zinc chromate as the catalyst) are given in Table I. This production of ether calculated as carbon monoxide converted to ether is shown graphically by the lower curve in Figure 1. The extent to which this ether formation affects the values for percentage conversions of carbon monoxide to methanol in Table I is not very great. Under the experimental conditions employed, the formation of ether is slow compared with the methanol reaction, and if the carbon monoxide converted ultimately to ether is subtracted from the carbon monoxide which enters the catalyst chamber, the correction is about 3.0.6 per cent for the conversions in runs F and H and negligible in the others. The influence of time of contact is evident from the data of Table I for 350' C. At space velocities of 3000 and 7500 the ether found was, respectively, 1.42 and 0.71 grams per pass. Similarly, a t 375' C. the production was 3.16 and 1.47 grams for the same respective space velocities.
Petroleum Wash-Oil Thickening in the Scrubbing of Coke-Oven Gas' H. M. Ullmann, D. S. Chamberlin, C. W. S i m m o n s , a n d M . A. T h o r p e LEHICHL-NIVERSITY, BETHLEHEM, PA.
A
HIGH-BOILING petroleum oil is used in the countercurrent absorption of light oils from coke-oven gas in . scrubbing towers. With continued use the wash oil increases in gravity from 0.834 to 0.90 and contains a suspension which, when settled out, does not materially affect the gravity of the oil. This process is called thickening. With thickening, a wash oil reduces in absorption capacity and the accumulation of the suspended material presents mechanical difficulties throughout the entire system. It is the object of this investigation t o determine the primary cause of such thickening. C a u s e of Thickening
Kiemstedt* in 192.5 summarized the suggested causes of thickening as follows: (1) The oxygen content of the gases and its influence on the wash oil, especially on the phenols of the wash oils. (2) The oxidation of hydrogen sulfide to sulfur and its asphalt-forming property. (3) The capacity of oils for inorganic materials, especially compounds of iron and their catalytic influence on the process. (4) The moisture content of the oils. ( 5 ) Cracking. (6) The prevailing pressure on the system.
I n 1926 Hilgenstock3 pointed out that "even a t this late date no satisfactory explanation has been given for thickening." Offe,4 and K a t t ~ i n k e l ,although ~ disagreeing as to the mechanism of thickening, point to hydrogen sulfide as the primary cause. Offe states that the thickening is caused by Received M a y 28, 1928. Revised manuscript received November 7, 1928. * Kiemstedt, Brennsloff-Chem., 6, 185, 201 (1925). 8 Hilgenstock, Ibid., 7, 123 (1926). 4 Offe, GQS Wnsserfacir, 66, 67 (1923); 68, 136 (1925). 6 Kattwinkel, I b i d , 67, 406, 474 (1924); 68, 323 (19251; BrennstofChem., 7, 123 (1926).
the reaction of hydrogen sulfide with the unsaturated conipounds present in the wash oil and their subsequent polymerization by heat with the regeneration of hydrogen sulfide. Kattwinkel, however, views the thickening as due to polymerization of the wash oil by sulfuric and sulfo acids formed from the oxidation of the hydrogen sulfide present. Since hydrogen sulfide is present in the coke-oven gas to the extent of 500 grains per 100 cubic feet, such reasons seem quite logical. I n addition, the wash oil on thickening increases in sulfur content from 0.182 to 0.967 per cent. All attempts to thicken a new wash oil with hydrogen sulfide were unsuccessful. No thickening resulted when hydrogen sulfide was bubbled through cold or hot oil for 3 weeks, or when a saturated solution of the gas in the oil was subjected to a treatment similar to that given in the stripping stills and heat exchangers. Even when steel wool was used as a catalyst and the above processes duplicated, there was no thickening. I n some cases, however, there was a slight and insignificant increase in the sulfur content of the wash oil after treatment. Another suggested mechanism is that thickening may be the result of sulfur as such, being produced in the system by the reduction of hydrogen sulfide. If was found, however, that flowers of sulfur, although dissolving in hot oil, would precipitate on cooling and produce no thickening. It has been suggested that thickening may be produced by cracking of the wash oil in the stripping process. Experiments with new wash oil, benzolized wash oil, and wash oil saturated with hydrogen sulfide and flowers of sulfur, all produce no thickening when heated to a cracking temperature. In every case a black, carbonaceous residue is precipitated and the light fractions formed volatilize, but the residual oil does not increase in gravity. According to Bergbau and Lothingen6 the thickening may be due to oxygen or carbon dioxide, or both, since their method 8
Bergbau and Lothringen, German Patent 432,378 (January 3, 1924).
I N D U S T R I A L A N D ENGINEERING CHE;MISTRY
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of preventing thickening is the elimination of these constituents from the steam used in the stripping stills. The influence of finely divided tarry matter on the thickening of wash oils has been discussed by Gerhard,’ Stumpf,5 and T h a ~ . Brooks’O ~ points out that petroleum ether when added to certain oxidized hydrocarbons will cause a solid substance to precipitate. This method applied to spent wash oil gave a light brown flocculent precipitate containing 78.30 per cent carbon, 6.28 per cent hydrogen, 9.25 per cent sulfur, and by difference6.17 per cent oxygen. This indicates that a complex sulfur compound is formed in the wash oil. The fact that it could not be produced by subjecting the oil to treatments with sulfur in various combinations led to the conclusion that it entered the system as such in the raw cokeoven gas. When spent wash oil is allowed to settle a t low temperatures, a black plastic mass separates. This materia1 has all the physical appearances of ordinary coal tar. I n addition, a t valves and other connections along the raw gas line where small leaks are possible, this same tarry material accumulates in stalactitic form. When this material is dissolved in benzene, added to wash oil, and stripped of the benzene, a pronounced thickening in the oil is produced. Similarly, ordinary coal tar from tar sumps under the same conditions produces thickening in new wash oil. The fact that this method had artificially produced thickening pointed to a tar in suspension in the raw gas as the primary cause of thickening. When raw coke-oven gas was passed through an experimental absorption tower unit with glass-bead packing and new wash oil, it was found that, after careful stripping, the oil had increased in specific gravity from 0.834 to 0.845. This inerease in the specific gravity, and hence the relative thickening, appears small. However, a critical study points to their actual significance. At this rate, in a plant treating 50,000,000 cubic feet of gas a day with 60,000 gallons of wash oil, the oil would become uniit for further use in the absorption system in 3.7 months. Executives at such a plant state that the life of an oil is about 3 months and therefore the experimental thickening closely approximates operating plant results. Quantity and Character of Suspended Material To determine the quantity and character of the suspended material in the gas, a quantitative experimental Cottrell precipitator similar to that described by Drinker and Thomson‘l was used. An applied voltage of 20,000 at 3 amperes was used in a tube 11inches (28 cm.) long and 1inch (2.5 cm.) inside diameter containing a removable celluloid foil upon which the material collected. A dark brown, sticky and tarry material with a rather characteristic obnoxious odor was formed on the foil. It was found that the gas contains 3.17 grams of this material per 100 cubic feet (2.8 cubic meters). It was further found that no thickening was produced by a gas from which this material had been removed with a Cottrell precipitator. Determinations on the amount of suspended material before and after passing through the experimental wash-oil absorption unit showed that approximately 90 per cent of this material remained in the gas, although thickening at plant rate was obtained. As an extreme test, a Cottrell precipitator showed the existence of this material in appreciable quantities in the gas delivered to the domestic consumer. The fact that the gas after light-oil stripping passes through a Koppers hydrogen sulfide absorption tower, two gas holders, Gerhard, Gas Wasserfach, 66, 189 (1923). Stumpf, Ibid.. 67, 615 (1924). 9 Thau, Ilrzd., 67, 163 (1924). I D Brooks, “Non-Benzenoid Hydrocarbons,” p. 53 (1922). 11 Drinker and Thomson, J . I n d . H y g . . 7, 261 (1926). 7
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Vol. 21, No. 4
and several miles of distributing mains points to the extreme fineness of the suspension. The tarry material precipitated from the gas by the Cottrell was found to contain 12.50 per cent sulfur as compared with 4.54 per cent sulfur in the tarry material settling from spent wash oil and 0.97 per cent sulfur in ordinary coal tar. Thus the raw gas contains 0.0038 gram of sulfur per cubic foot (0.028 cubic meter) exclusive of hydrogen sulfide. The increase in sulfur in the wash oil on thickening, which has been attributed to sulfur in various forms, can be accounted for by the high sulfur content of the suspended material, which in itself produces thickening. It would appear that the tarry material in suspension contains a large proportion of a highsulfur constituent of coal tar. The analysis and physical properties of the material settling from spent wash oil indicate that it contains a higher proportion of ordinary coal tar than the suspension. Considering as before, an operating condition where 60,000 gallons of wash oil are used in the treatment of 50,000,000 cubic feet of gas per day, the above sulfur figures have interesting application. Under these conditions where wash oil on thickening increases in sulfur content from 0.182 per cent (sp. gr. 0.834) to 0.967 per cent (sp. gr. 0.900), the tarry material would account for the entire thickening and produce a spent wash oil in 8.6 days. However, it has been shown that only one-tenth of the tarry material is absorbed so that complete thickening would be produced in 86 days. This length of time is again in close agreement with the commercial approximation of 3 months. Conclusions The thickening in petroleum wash oil is shown to be the direct result of a tar or a tar constituent in a finely divided form suspended in the gas, which still persists in measurable quantities when the gas has reached the domestic consumer. It would appear then that thickening results from the direct bafAing of this material in the absorption system and from its solution in the light oils with subsequent precipitation on stripping. This is perhaps the reason for the opinion sometimes expressed that thickening is produced by polymerization in the stripping stills. Experimental work using a Cottrell precipitator indicates that the removal of these high-sulfur tar constituents from the raw gas before entrance into the scrubber system will eliminate the thickening of wash oil in the countercurrent scrubbing of coke-oven gas. The elimination of the thickening constituents of raw gas on a commercial scale is now being investigated. Acknowledgment This investigation was carried out under a Henry hlarison Byllesby Memorial Research FeIlowship in Engineering. Grateful acknowledgment is also expressed to C. E. Underwood and his staff, of the Coke Works of the Bethlehem Steel Company, and J. W. Fehnel, of the Department of Industrial Hygiene of the Metropolitan Life Insurance Company *
Consolidation in the Czechoslovak Dye Industry The Czechoslovak Government has given its approval to the organization of the Czechoslovak Consolidated Dye Co., a joint stock company which will be formed by a merger of the Czechoslovak dye factories a t Aussig, Braunau, Roechlitz, and Liberec, with the Joint Dye Works of Vienna. The shares of the Austrian company are now owned by the Dyeing and Printing Joint Stock Co., Chur, Switzerland, with which are affiliated the Hungarian Textile Dyeing Co., Budapest, the Budapest Wool Manufacturing Co., and the Textile Printing Co., of Naefels, Switzerland. The headquarters of the new company will be in Liberec.
