T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y AN INVESTIGATION OF THE WET THIOGEN PROCESS’ By A. E. WELLS Received July 31, 1917
I n the last several years, t h e Bureau of Mines has devoted considerable s t u d y t o various proposed methods for eliminating or recovering sulfur dioxide from smelter smoke. Among these has been included a critical s t u d y of t h e Wet Thiogen Process. The results of t h e investigations on this process are given in U. S. Bureau of Mines Bulletin 133, “The Wet Thiogen Process for Recovering Sulfur from Sulfur Dioxide in Smelter Gases,” by A. E. Wells. The Wet Thiogen Process is based on the fact t h a t when barium sulfide, either in finely divided water suspension or in solution, is added t o a solution of sulfur dioxide, t h e following reaction takes place:
+ +
+ +
aBa5 3 S 0 2 = 2BaS03 3s nBaS 3 S 0 2 = ?Bas203 S. I n carrying out t h e process, t h e gases are first cooled a n d cleared of all dust a n d fumes, then passed through a n absorption tower i n which t h e sulfur dioxide is absorbed in water or mother liquor. T o t h e solution of sulfur dioxide is added powdered barium sulfide, when t h e reactions given above take place. T h e precipitate containing t h e sulfite, thiosulfate, and sulfur is settled, a n d t h e mother liquor is returned t o t h e absorption tower. The settled precipitate is then filtered a n d dried. The elemental sulfur a n d onehalf t h e sulfur from t h e thiosulfate is distilled and t h e sulfur vapors are condensed. The residue, consisting of barium sulfite or sulfate is then reduced t o t h e sulfide, which is returned t o t h e operation as a precipitant. I n t h e investigations of t h e Bureau, all t h e operations involved in t h e process were studied, both on a laboratory scale, and on a scale t h a t may be considered semi-commercial, a n d t h e technical possibilities of t h e process were determined. I n t h e experiments concerning t h e absorption of sulfur dioxide in water or mother liquor, t h e gases, cooled t o about 2 5 0 C. a n d containing from 3.5 t o I O per cent sulfur dioxide, were caused t o ascend a t a velocity of about 2 f t . per second, through a tower containing for 4o f t , of i t s height a checkerwork of wooden blocks. This checkerwork caused t h e descending stream of t h e solvent t o be broken u p into thin sheets or drops a n d allowed intimate contact of t h e gases with t h e solvent. It was demonstrated in these experiments t h a t with water as t h e absorbing agent, i t is possible t o obtain a high extraction of t h e sulfur dioxide, and a t t h e Same time obtain solutions which will contain within I O per cent of t h e amount of sulfur dioxide t h a t , theoretically, t h e solution could contain in equilibrium with t h e gas concentration, i. e., t h e concentrations may be within I O per cent of t h e theoretical saturation values. These theoretical saturation values are obtained b y calculation, applying the Law of Partial Pressures t o t h e values obtained with a pure gas a n d given in Landolt-Bornstein’s “Physikalisch Chemische Tabellen,” 4th ed., page 597. or,
1
Author’s abstract of Bureau of Mines Technical Paper. 183.
Vol. 9 , No. q
With the mother liquor as a n absorbing medium, i t is possible t o obtain solutions containing 30 per cent more SO2 t h a n is theoretically possible in water, and a t t h e same time retain t h e greater portion of t h e sulfur dioxide. The concentrations obtained in these tests were within I O per cent of those obtained in a small glass absorption tower by t h e engineers of t h e Thiogen Company in earlier tests. From these absorption tests, it was evident t h a t for a commercial operation, t h e percentage of SO2 in t h e gases should be a t least 5 per cent, and the absorbing liquor should be cool, i. e., less t h a n 2 5 ” C.; otherwise the volume of solution to be handled for a given amount of sulfur dioxide absorbed would be very large. Furthermore, a fairly constant concentration of t h e sulfur dioxide in t h e gases is necessary if saturated solutions and a high absorption of t h e sulfur dioxide are t o be obtained at t h e same time. On adding barium sulfide t o t h e sulfur dioxide solution, either in dry pulverized condition, in water Suspension or in solutions, in amounts equivalent t o effect t h e reactions given above, t h e reactions were found t o take Place immediately. The principal barium product was t h e thiosulfate rather t h a n t h e sulfite. Thus t h e main reaction was: 3 S 0 2 = 2BaS203 S. 2BaS If sufficient barium sulfide had been added t o combine with most of t h e so,, there were very few barium salts left in solution, a n d t h e specific gravity of t h e solution did not go above 1.03. With a large excess of so2 in solution after t h e B a s had reacted, there was a re-solution of some of t h e barium as thiosulfite. The best practical method for incorporating t h e barium sulfite was found t o be by making a n emulsion of t h e B a s in a portion of t h e sulfur dioxide solution and stirring this emulsion into t h e bulk of t h e solution in a n agitator tank. The precipitate settled readily, if t h e mother liquor contained a slight excess of so2 after precipitation. If this solution after precipitation contained a n excess of B a s [Or Ba(SH)2 f Ba(OH)31, t h e Precipitate was Slimy a n d settled rather Slowly. I n t h e larger scale tests, a settling capacity equivalent t o t h e volume of solution being precipitated in 2 0 minutes was ample for satisfactory settling. T h e overflow of supernatant liquor contained Some light flakes of sulfur which did not increase in t h e cycles nor interfere in t h e pumps or absorption towers. The settled precipitate did not contain more t h a n j o per cent water. This precipitate was dewatered still further on a canvas filter using vacuum. I n large scale operations no difficulty would be experienced in reducing t h e moisture in t h e precipitate t o about 2 j per cent, in a standard filtering apparatus, using moderate suction or pressure. The ease and efficiency with which t h e settling, decantation and filtering operations are carried out are dependent largely on t h e condition under which t h e precipitation takes place. Thus, i t is necessary t h a t t h e sulfur dioxide content of t h e solution coming from t h e tower shall be fairly constant, or t h e attention of a n
+
+
Sept., 1917
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
attendant will be necessary t o see t h a t t h e solution is not t o o acid or too alkaline after precipitation. The further drying of t h e precipitates preliminary to the distillation of t h e sulfur must be effected b y steam coils or b y a special type of drying furnace in which there would be no danger of overheating, with attendant loss of sulfur. I n t h e distillation operations, it was found t h a t t h e sulfur began t o distil rapidly a t 180’ C. and from t h a t temperature u p t o 4joo C., t h e boiling point of sulfur, t h e r a t e of distillation would depend upon t h e rapidity with which t h e vapors were removed from t h e retort as well as t h e temperature. I n all cases, whether t h e precipitate consisted of zBaSz03 S or whether a considerable proportion of t h e precipitate zBaS03 3s was also present, t h e sulfur was completely distilled a t 450’ C. The distilled and condensed sulfur was practically pure. The residual product from t h e distillation was barium sulfite a n d sulfate. I n t h e reduction of t h e barium sulfite or sulfate, b y mixing t h e residue with carbon, coke or coal a n d heating t o a temperature between 7 5 0 a n d 1200’ C., there was some tendency for t h e formation of small amounts of t h e oxides a n d carbonates of barium. When t h e reduced material was used as a precipitate these reacted very slowly with t h e SOz in t h e dilute solutions from t h e absorption towers. Therefore, they became “inert” substance, diluting t h e active B a s , a n d increasing in amount in each cycle of operations. If t h e reduction was effected in a direct fired furnace where t h e products of combustion passed over t h e material, t h e proportion of these inert compounds was greater t h a n if t h e reduction was brought about by carbon of high purity, quickly, a t a high temperature, a n d in a furnace externally heated. The use of a coal containing a high percentage of ash also adds “inert” substances t o t h e reduced material in each cycle, a n d therefore as pure carbon as possible is desirable as reducing agent. The oxide or carbonate can be connected t o t h e sulfite by agitation with a strong sulfur dioxide solution, or t o t h e sulfate by treatment with sulfuric acid. When reductions are effected in a direct fired furnace, probably I O per cent of t h e material would have t o be treated with strong sulfur dioxide solution or sulfuric
+
+
acid in each cycle t o keep t h e barium as sulfite in sulfate t o be reduced again t o t h e sulfide. If coal, high in ash, is used as reducing agent, and t h e amount of insoluble matter increases t o a certain amount, i t will be necessary t o leach t h e entire amount of reduced material, getting t h e B a s into reduction and discarding t h e insoluble material. With t h e addition of these supplementary operations, i t is believed t h a t t h e technical operation of t h e process can be carried out successfully for t h e recovery of sulfur from sulfur dioxide in waste smelter gases. The indications are t h a t , at least in some localities, the process can be applied on a commercial scale which will allow t h e production of sulfur a t a cost of about $ 1 2 per ton. WEIGHING BURETTE FOR LIQUIDS By W. ED. BURKHARD Received July 9, 1917
The weighing burette illustrated below has been found very valuable. The capacity which determines t h e diameter of t h e burette is governed b y t h e material t o be analyzed.
AI/ j’oinfs Connections
lo be yround
The cup A is used t o prevent fuming while weighing, etc. B is made preferably for oleum or other material t h a t would c a m e spattering. I n case of “oleum over 2 0 per cent” t h e water into which t h e acid is t o be run has a layer of neutral fine Glauber’s salt crystals. By keeping t h e tip of B in t h e crystals all spattering is avoided. The attachment is left in t h e solution while titrating. GEXERAL CHEMICAL COMPANY BAVONNSWORKS,BAYONNE, N. J
ADDRESSES THE VAPOR PRESSURE AND VOLATILITY OF SEVERAL HIGH-BOILING METALS-A REVIEW’ By JOHN JOHNSIOS Received July 19, 1917
The question as to the vapor pressure of a metal a t a given temperature-or its boiling point a t a particular pressure-often arises, as a knowledge of this property is valuable in connection with a number of problems. But the somewhat scanty data to be found in the literature refer, for any one metal, to a small I Presented a t the Symposium on the Chemistry and Metallurgy of Zinc, 54th Meeting American Chemical Society, Kansas City, April 10 to 14, 1917.
873
1
number of pressures, and in many cases, to a single vapor pressure only-that of one atmosphere; therefore in order to ascertain the vapor pressure a t any particular temperature one must in general plot the curve and extrapolate. This procedure takes time and trouble and is moreover not feasible when only one point on the curve has been determined by experiment; more can be learned, as we shall see, by plotting a t one time the available data for all the metals hitherto investigated, for by so doing we can set up equations which enable us to calculate the vapor pressure a t any temperature with as much certainty as is inherent in the experimental results. On account of the greatly increased availability and usefulness of the data as
