Conversion of Coal Sulfur to Volatile Sulfur Compounds during


Conversion of Coal Sulfur to Volatile Sulfur Compounds during Carbonization in Streams of Gases. Robert D. Snow. Ind. Eng. Chem. , 1932, 24 (8), pp 90...
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August, 1932

I N D U S T R I A L AN D E N G I N E E R I N G C H E M I S T R Y

There is a noticeable decline in the pyrethrin content of the 1929 and 1930 crops as the age of the whole flowers increases. This investigation is being continued, using freshly harvested flowers for the storage experiments. The effect of different methods of drying and storing the green flowers on the pyrethrin content will also be determined. SUMI1ZSRY Freshly ground pyrethrum flowers stored in various types of containers lost from 30 to 43.6 per cent of their pyrethrin content in one year. The toxicity of the flowers to flies also decreased in approximately the ratio to be expected Analysis I

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of ground and powdered pyrethrum showed that the loss of pyrethrins continues after storage for more than 2 years in tin containers, Examination of a large number of shipments of whole Japanese flowers indicated that the pyrethrin content decreases as the age of the flowers increases. LITERATURECITED (1) Gnadinger, C. B., and Corl, C. S., J . A m . Chem. Soc., 51, 3054 (1929). (2) Gnadinger, C. B., and Cod, C. S., Ibid., 52, 3306 (1930). (3) Peet, C. H., and Grady, A., J . Econ. Entomol., 21, 612 (1928). RECEIVED March 8, 1932.

Conversion of Coal Sulfur to Volatile Sulfur Compounds d-uring Carbonization in Streams of Gases ROBERTD. Sxow, Engineering Experiment Station, University of Illinois, Urbana, 111. scale carbonization?. The early H E study of methods of The object of this study u a s io increase the views ( I , 7 , 9) of the behavior eliminating sulfur from conrersion of coal sulfur to simple nolatile comof the various sulfur compounds coal prior to combustion pounds. Fiffeen-gram samples of 20-40 mesh during carbonization were widely was undertaken as a part of the coal were heated 4 hours at various temperatures divergent, !)robably because of general program for the prevenin streams qf various gases. The gases and solid differences in coals used and lack tion of c o r r o s i o n and atmosof f u n d a m e n t a1 information. pheric pollution resulting from residues were analyzed ,for sulfur. Percentage Powell (11, 13) made the first the sulfur oxides in the combussulfur eliminafions obtained at 1000" C. were: systematic laboratory study of tion products. T h e s u l f u r is nitrogen, carbon dioxide, carbon monoxide, the reactions of the various forms present in the raw coal mainly methane, and ethylene, 50 to 60; water gas, of sulfur during carbonization. as pyrites and o r g a n i c s u l f u r 76; anhydrous ammonia, 82; and hydrogen, 87. He concluded as a r e s u l t of compounds of unknown composideterminations of t h e s u 1f u r tion. Of the sulfur present in Steam gare 84 per cent, and water gas with distribution during carbonizathese forms, only the c o a r s e r hydrochloric acid gaze 72.5 per cent sulfur tion of &gram s a m p l e s of particles of pyrite, corresponding elimination at 800" C . Partial removal of various coals in an inert gas to about 20-25 per cent of the pyrite by oxidation and leaching, followed by that the primary reactions were: total sulfur in the coal studied, carbonization in hydrogen, gane a sulfur elimina(1) the c o m p l e t e decomposican be economically reinoved by tion of the iron pyrites to ferrous mechanical means. The elimition of 93 per cent. Instantaneous carbonizasulfide, pyrrhotite, and hydronation of the organic sulfur and lion in hydrogen removed 59 per cent of the coal gen sulfide below 600" C. and the sulfur in the finer particles of sulfur. principally in the range 400pyrite will undoubtedly require 500" C . ; ( 2 ) the reduction of other methods of t r e a t m e n t . Thermal decomposition of the coal for the conversion of im- the sulfates to sulfides below 500" C.; and (3) the decomposiportant quantities of sulfur to hydrogen sulfide, wliich can be tion of the organic sulfur compounds below 500" C., with the removed from the gases and converted to free sulfur, suggested liberation of one-fourth to one-third of the sulfur as hydrogen itself as one method of attack. The present study O F the sulfur sulfide, and a pronounced chemical change in the organic distribution during carbonization under various conditions of sulfur remaining in the solid. A comparatively small amount temperature and atmosphere was undertaken with the object of the organic sulfur appears as volatile organic compounds in of developing methods of increasing the proportion of sulfur the gas and tar. Secondary reactions observed by Powell passing into the gas. Such conversion of the coal sulfur to were: (1) the disappearance, about 500" C., of a part of the simple volatile compounds would greatly facilitate the ultimate ferrous sulfide and pyrrhotite, the sulfur apparently being elimination. transferred to a carbon complex; (2) the action of the hydrogen in the coal gas in removing sulfur from the coke as hydrogen sulfide at high temperatures; and (3) the reaction of PREVIOUS WORK hydrogen sulfide with incandescent coke to form carbon It has long been known t h a t 40 to 50 per cent of the coal disulfide. The results of Wibaut and Stoffel (31), published sulfur is volatilized, principally as hydrogen sulfide, during a short time previously, agree quite well with those of Powell. ordinary by-product coking (2,2 1 ) . About 30 to 35 per cent Those authors found that in laboratory carbonization of of the total sulfur is evolved during low-temperature carboniza- several coals, 50 t o 60 per cent of the total coal sulfur was retion (3, 10). Laboratory-scale carbonization experiments tained by the coke, partly as metallic sulfides and the re( 2 , 3 ) show about the same distribution of the sulfur of mainder as a carbon-sulfur complex or "organic" sulfur bituminous coals between the gas and the coke as do plant- compound. They supposed that this organic sulfur com-

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sulfur is retained by the carbon and anpound was formed by the s e c o n d a r y other part is converted to carbon disulreaction of h y d r o g e n sulfide and hot fide. They studied the hydrogen sulfidecarbon. carbon-carbon disulfide e q u i l i b r i u m a t Views somewhat different from those 815" C. Wibaut and co-workers (28, 27, of Powell were expressed by Foerster and 30, 32) investigated the so-called organic Geissler (3). They carbonized a bitumisulfur compounds in coke and similar nous coal a t 500" and a t 1000" C. They products prepared by h e a t i n g varioui concluded that the pyrite and sulfates forms of amorphous carbon with sulfur were only a b o u t half d e c o m p o s e d a t vapor. They found that sulfurous car500" C., that the greater part of the sulfur bons containing as much as 14 to 19 per volatilized came from the inorganic comcent sulfur could be prepared, and that pounds, and t h a t the organic sulfur conthis sulfur could not be extracted by ortent remainpd practically c o n s t a n t in dinary solvents for sulfur. The sulfur amount. On the contrary, their results content could be reduced to 2 t o 4 per cent obtained by carbonization of brown coals by continued heating a t 800-1000" C. high in organic sulfur show the evolution under high vacuum. Kibaut (2.9) hai of 70 per cent of the total coal sulfur as recently concluded that the sulfur reh y d r o g e n sulfide, most of which must movable by vacuum treatmeiit a t high have come from the organic sulfur in the F G H temperatures is held by the carbon in coal. T h e y b e l i e v e d t h a t s u l f u r is F~~~~~ 1. APPARATUSFOR cARBORIZITIOU I N STREAM OF GAS some physical manner such a. by adnot transferred directly from pyrite or sorption or by solid solution, but that ferrous sulfide t o carbon, but Indirectly through the action of the water of decomposition and the the residual sulfur] in the carbon after the vacuum treathydrogen in converting the sulfur to hydrogen sulfide which ment is combined chemically with the carbon. Effort3 subsequently reacts with carbon. However, they found that t o isolate such chemical compounds or to obtain direct evisuperheated steam had no noticeable effect upon the sulfur dence of their existence have been unsuccessful. Poivell (14) made a careful phase-rule study of the sulfur in cokes distribution u p to 500" C. Ditz and Wildner ( 2 ) carbonized Arsa coal containing 8 to and sulfurous carbons made by heating sugar charcoal with 9 per cent sulfur (96 per cent of which was organic) and found sulfur vapor. He concluded that: (1) the sulfurous carbon>, that only about one-half of the sulfur was retained in the coke. prepared by heating sugar charcoal with sulfur vapors, conThese results and those of Wibaut and Stoffel support Powell's tain sulfur in the elementary form, partly adsorbed on the statement t h a t a considerable portion of the sulfur present in surface of the carbon and partly held in solid solution by it; the coal as organic compounds is liberated as hydrogen sulfide. (2) coke, prepared by rapid heating in the laboratory, conHoltz and Huff ( 5 ) have shown that hydrogen sulfide reacts tains ferrous sulfide and free sulfur in solid solution with and with incandescent carbon in such a manner that a part of the adsorbed on the carbon; and (3) in metallurgical coke the

'w LL

OF SULFURFROM SOLIDFUEL FIGURE 2. ELIMINATION DURING CARBOIVIZATION IN INERTGASES

NITROGEN PASSED THROUGH 0 WATER

FIGURE3. EFFECTOF SMALLCONCENTRATIONS OF WATER V A P O R , HYDROGEN CHLORIDE, AND AMXOTKA 14 NITROGEN

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INDUSTRIAL AND ENGINEERING CHEMISTRY

FIGURE4. CARBOKIZATION IN HYDROGEN WITH SLOWA N D RAPIDHEATING RATES sulfur is present principally in the solid solution form with small amounts combined as calcium sulfide and magnesium sulfide. Powell's data would indicate that the form of sulfur in coke commonly spoken of as organic sulfur is mainly free sulfur held physically by the carbon. Although the studies of Powell and Wibaut have shown that ash-free carbon can retain considerable quantities of sulfur, the inorganic irnpurities in coal undoubtedly have some effect upon the amount of sulfur retained in the solid residues. Ditz and Wildner ( 2 ) claimed that the calcium oxide content of d r s a coal was mainly responsible for the large amount of sulfur retained by the coke from that coal. Similar action of such substances as calcium carbonate, dolomite, and magnesium carbonate have been observed by Trifonov (23), Foerster and Geissler (J), and Priestley and Cobb ( 1 7 ) . The last-named authors found that addition of 5 per cent iron oxide noticeably decreased the hydrogen sulfide evolution in a n inert gas such as nitrogen but had little effect upon the hydrogen sulfide evolution in hydrogen above 800" C . Lisaner (6) stated that addition of 5 to 10 per cent iron improved the desulfurization by hydrogen. On the other hand, the experiments of Powell and of R i b a u t with pure sugar charcoal indicate t h a t considerable sulfur can be retained by carbon in the absence of mineral matter so that the mineral constituents alone are not the determining factors. Sumerous studies of the desulfurization of metallurgical coke and carbonized residues have been made. Powell (12, 16) has studied the desulfurization by means of hydrogen and by-product gas a t temperatures in the range i00-1000" C. He has shown that there exists between the sulfur in the coke and the hydrogen sulfide in the gas an equilibrium n-hich can be approached from either side; that is, the carbon will absorb sulfur from a gaseous atmosphere containing more than the equilibrium concentration of hydrogen sulfide. I n inetallurgical coke the sulfur is less accessible and the equilibrium i q reached a t a very low partial pressure of hydrogen

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FIGURE5. CARBONIZATION IX STEAM, ANHYDROUS A~WMONIA, AND CARBOY MONOXIDE sulfide. I n the case of small coke samples prepared by rapid heating in the laboratory, desulfurization becomes appreciable a t lower temperatures and is much more rapid than is the case with metallurgical coke. The reason given for this is that coke prepared by short rapid heating contains a greater part of the sulfur in the absorbed state and less in the solid solution state. Similar studies of the desulfurization of coke in nitrogen and in hydrogen have been made by Monkhouse and Cobb (8). Wibaut (26, 28, 30) has shown that the wlfurous carbons can be quantitatively desulfurized by hydrogen, the reaction beginning a t about 500" and being nearly complete a t 700-800" C. Powell and Thompson (16) and Foerster and Geissler (3) have studied the desulfurization of coke by steam. They have found, as have previous investigators, that desulfurization by steam takes place only in the temperature range a t n-hich the water gas reaction becomes active and is accompanied by considerable gasification of the coke. Grunert (6)has recently studied the fundamental reactions involved in the desulfurization by steam. He has found that when steam and nitrogen are passed over pure pyrite, the latter is decomposed slonly a t 500" C. and rapidly, but not completely, a t 600" C. I n the presence of amorphous carbon, only about one-half of the sulfur is evolved as hydrogen sulfide, the rest remaining as ferrous sulfide and adsorbed sulfur. He concluded that considerably better desulfurization can be obtained if the coking is done with steam instead of dry distillation. I n the latter case, important proportions of the pyritic sulfur are adsorbed by the carbon, probably because the equilibrium in the reaction between hydrogen and sulfur is attained much more slo~vly than is the equilibrium of the hydrolysis of sulfur. Simmersbach and Wolff (19) have shown t h a t carbon monoxide is more effective than hydrogen up to 600" C., and gives a good desulfurizing action a t 800" C. From the foregoing considerations it would seem t h a t conditions occurring in the by-product coke ovenq would be

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favorable for the retention of sulfur. d large share of the primary decomposition products from the coking zone pass through a layer of incandescent coke on their way out. Furthermore, the outer portions of the charge are heated for

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C O A L SrZhIPLE

The coal used v-as a number 6 coal from Christian County, Ill., having about the following analysis (dry basis): 70 .ish

I

590. LL -1' 3

080

I 0

/

WATER GAS AND HCL WATER GAS-DRY I

l

l

i

l

l

l

Carbon Hydrogen

17.65 61.75 5.14

% Sulfur Oxygen Nitrogen

5.11 9.35 1.00

It was ground to pass entirely a 20-mesh sieve, and the portion retained by a 40-mesh sieve was used in the experiments. The working sample was thoroughly mixed and was dried by heating for 4 hours at 110" C. in a vacuum drying oven. The oven was filled with nitrogen before opening. The coal sample was immediately transferred to a desiccator and Tvas alloTYed to cool in a vacuum. Analysis of the sample for sulfur forms by the method of Powell and Parr (15) gave the following values (dry basis): %

Pyritic sulfur Organic sulfur Sulfate sulfur

2.51 2.63 0.20 5.34

XPPARAT~S AXD PROCEDURE The apparatus in Figure 1 is designed t o obtain somewhat better contact between the coal and the gas than is possible when the coal sample is allowed t o rest on the bottom of a horizontal combustion tube and the gas stream is passed over it in the usual manner.

FIGURE 6 . CARBONIZATION IN \TATER Gas a long time a t very high temperatures, Tr-hich would be expected to favor the conversion of the sulfur retained to the less accessible solid solution or the chemically combined state. On the other hand, the conditions favoring sulfur elimination would seem t o be: (1) immediate dilution of the primary decomposition products with a sulfur-free gas and removal of the mixture from the hot solid in order to minimize secondary fixation of sulfur; ( 2 ) the use of a reactive gas such as hydrogen or steam for further conversion of sulfur to hydrogen sulfide; and (3) the avoidance of the extended heating of portions of the charge a t high temperature. Unfortunately, the literature contains little information obtained under such conditions. Powell (12) has reported the carbonization of three coals a t 500" and 1000" C. in streams of hydrogen and lean coke-oven gas containing 50 per cent hydrogen. With hydrogen he obtained degrees of desulfurization a t 1000" C. varying from 67 t o 92 per cent. Wheeler and Jolly (24) found that desulfurization of bituminous coal could be increased from 30 per cent by carbonization of the coal in a stream of nitrogen, to 48 per cent by carbonization in nitrogen of a mixture of two parts of that coal with one part of anthracite. The increased desulfurization in the latter case is a result of the nascent hydrogen evolved by the anthracite during thermal decomposition. Foerster and Geissler (3) carbonized coal a t 500" C. in superheated steam, but found no noticeable increase of desulfurization due to the steam a t that temperature. The present paper presents the results of a study of a single coal carbonized in various gaseous atmospheres throughout the temperature range 350' to

1000" c.

The sample container, -4,is a fused silica tube, 1b,'16 inch in outside diameter, and having a porous sintered plate 41/2inches from the top end. Below the plate the tube is reduced to about inch. The sample tube is supported by means of a rubber stopper within the 1 X 24 inch silica combustion tube, B. A silica protection tube for the thermocouple, J, extends from the top of the combustion tube to about the center of the coal sample. Heating is done by means of an ordinar combustion furnace, I . C is a tar trap containing a plug of g&ss wool and immersed in hot water. The gases are finally scrubbea for the removal of sulfur in the two Drechsel bottles, D and E , each containing 30 cc. water, 20 cc. of 30 per cent hydrogen peroxide, and 20 cc. concentrated ammonium hydroxide. Bottles F , G , and H contain reagents for purifying and drying the gases used. A 15-gram sample of the dry 20-40 mesh coal was placed in sample container A , and the apparatus was assembled as shown in Figure 1. The stream of gas was started and was regulated to approximately 200 cc. per minute. After about 20 minutes, during which time sufficient gas had passed to displace the air from the sample, the heating vias started. The same rate of heating Tas used in all experiments, except those designated as rapid heating in hydrogen. The rate of temperature rise is shown approximately by the data in Table I. TABLEI. RATE OF RISE OF TEMPERATURE TIME TEMP.OF ELAPSED COALSAMPLE Minutes c. 20 40 60

250 500 650

TIME ELAPSED Minutes 80 120 160

TEMP.OF COALSAMPLE

c.

725 860 1000

This rate of heating \\-as sufficiently slow so that practically no fusion occurred in the coal used. Shortly before the temperature of the test was reached, the heating current was adjusted t o maintain that temperature. The sample was maintained at the test temperature for 4 hours. At the end of that period the heating current was turned off and combustion tube B was lowered to a position such that the sample tube was below the furnace in order to hasten the cooling. The sample vias allowed t o cool to room temperature in a stream of dry gas, usually nitrogen. The sample was then removed, Tveighed, and carefully analyzed for total sulfur by the Parr peroxide fusion method. The total elimination of sulfur from the solid was calculated from these data. The scrubber solutions in bottles D and E were combined and diluted to 500 cc., and 100-cc. portions were gravimetrically analyzed for sulfur. The procedure was modified somewhat in the rapid heating experiments using hydrogen. The air in the combustion tube

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INDUSTRIAL AND ENGINEERING

was displaced with hydrogen and the tube mas heated to the test temperature without the sample container in place. lieanwhile the sample was placed within the sample container and a stream of hydrogen was passed through it to displace the air. Then the sample tube was quickly inserted into the heated combustion tube and the passage of hydrogen was continued. In these experiments the sample n-as held a t the test temperature for only cine hour. The hydrogen and nitrogen were scrubbed with alkaline pyrogallate solution and dried with concentrated sulfuric acid and anhydrone. The carbon dioxide, anhydrous ammonia methane, and ethylene were commercial products used without further purification. The carbon monoxide and water gas were prepared by reaction of carbon dioxide and steam, respectively, with activated charcoal a t high temperatures. These gases were purified and dried by caustic solution, ascarite, and anhydrone. C:ARBONIZATIOS IN I N E R T

GASES

Preliminary experiments showed that the first traces of hydrogen sulfide appeared in the exit gases below 200" C. This sulfur may have been present as adsorbed hydrogen sulfide in the coal, since noticeable decompositioii of this coal begins above 270" C. The sulfur eliminated up to 270" C. is about 0.1 per cent of the total coal sulfur and that eliminated up to 360" C. is 10 per cent of the total. The data obtained

O V '

300

1

1

I

1

1

I

I

1

800 900 1000 TEMPERATURE - CENTIGRADE

400

500

600

700

FIGURE 7. Loss OF WEIGHTOF COALSAMPLE.: DURISG CARBONIZATION I N VARIOUS GASES in the 4-hour tests with nitrogen, carbon dioxide, methane, and ethylene are plotted in Figure 2 as the percentage elimination of the total coal sulfur calculated from the sulfur remaining in the carbonized residues. The best desulfurization is about 50 per cent in all cases and is practically reached a t 600" C. There is no noticeable increase in the sulfur elimination with carbon dioxide a t 800" C. where the combustion loss became appreciable. Seither is there any evidence of desulfurization by the nascent hydrogen liberated by the cracking of methane or ethylene a t 800-1000" C. The detrimental masking effect of the carbon deposited on the coal residue as a result of thermal decomposition of these hydrocarbons apparently offsets the beneficial action exerted by the nascent hydrogen. For the purpose of comparison, a series of similar carbonization tests was made without the passage of a stream of gas. Purified nitrogen was first passed through the coal sample for 20 minutes to displace air. Then the flow of nitrogen was

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stopped, and the coal mas heated to the test temperature a t the usual rate and was kept a t that temperature 4 hours. It was then cooled to room temperature with the passage of a slow stream of pure nitrogen after the temperature had fallen below 200" C. The data thus obtained are given in Table 11. TABLE

11.

CARBOSI2.4TIOS

WITHOUT P A S S A G E O F sTRE.4M

OF

Gas

c. 400 600 800 1000

16.1 29.33 35.41 37.12

19.5 4718 49.0

4.69 3.77 3.49 3.59

24.7 47.9 55.9 55.9

The values for total sulfur elimination are limited by the sodium peroxide fusion method of sulfur determination to an accuracy of * 2 per cent of total coal sulfur. Duplicate experiments have usually checked much closer than that however. A comparison of the values in the last column of Table I1 with those plotted in Figure 2 , show that, under the conditions of the experiments (i. e., a small charge of coal a t a nearly uniform temperature), the passage of a stream of inert gas produces no appreciable increase in the sulfur elimination. I n the case of a large coking charge, however, it should increase the sulfur elimination by decreasing the time of contact of the primary decomposition products with the hot coke.

EFFECTOF SMALLCOXCENTRATIONS OF WATER, HYDROGES CHLORIDE, AXD AMMONIA It might be expected from the theory of Foerster and Geissler with regard to the desulfurization by the water of decomposition that small amounts of added water would further increase sulfur elimination. Hydrogen chloride also should assist in the decomposition of ferrous sulfide, thus preventing the transfer of sulfur so combined to the carbon. In carrying out these experiments, purified nitrogen was bubbled through water, the hydrochloric acid, or the animonium hydroxide a t room temperature, before passing into the carbonization tube. Concentrated ammonium hydroxide, 38 per cent hydrochloric acid, and 19 per cent hydrochloric acid were used. The data obtained are plotted in Figure 3. Hydrogen chloride may assist slightly in the desulfurization, but none of these addition agents shows a marked effect in the desulfuriLation by nitrogen. The sulfur elimination is again 50 to 60 per cent, and little further desulfurization occurs above 600" C. In all of the experiments it was found that the sulfur elimination was most rapid during the first hour after the heating was started, but that the rate decreased rapidly thereafter. With inert gases the evolution of hydrogen sulfide had practically ceased after 15 minutes a t the test temperature. I n the subsequent experiments with reactive gases such as hydrogen, desulfurization continued a t a decreasing rate over a long period of time, but was extremely slow after the first two or three hours a t the test temperature. For all practical purposes then it may be assumed that the values given by the 4-hour tests represent the equilibrium conditions. REACTIVEGASES Figure 4 shows the data for hydrogen. The higher curve represents the experiments made with slow heating, and the lower curve represents those involving rapid heating. The duration of heating a t the test temperature was 4 hours in the former case, and only one hour in the latter. The desulfur-

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FIGURE 9. OXIDATION BY FERRIC SULFATE, L E ~ C H I NAGN,D C.4RBONIZATION IN HYDROGEN FIGURE8. RATIOOF PERCENTAGE SULFURELIMINATION TO TOTALM.4TERIAL VOL4TILIZED izing action of hydrogen is evident even a t 400" C. At 500" C. an apparent maximumis reached in the upper curve with a desulfurization of 65 to 70 per cent. A further desulfurization appears to begin above 700" C., with the result that 8; per cent of the sulfur was eliminated a t 1000" C. I n the rapid heating experiments the coal fused quite extensively, and a hard coke was formed a t and above 800" C. This would materially reduce the contact of the solid with the gas. That factor, together with the shorter duration of the hydrogen treatment, explains the lower results obtained. I n Figure 5 are plotted the data for carbon monoxide, steam, and anhydrous ammonia. Carbon monoxide is noticeably more effective than nitrogen below 500" C., but above that temperature it is no more effective than is nitrogen. Steam is no more effective than nitrogen below 500" C., but above t h a t temperature it produces a marked desulfurization. At 800" C. the water gas reaction becomes active and the curve becomes very steep, but at this temperature the additional desulfurization is obtained a t the expense of a high combustion loss (Figure 7 ) . However, a t TOO" C., 70 per cent sulfur elimination is obtained with no greater loss of weight than with nitrogen. Anhydrous ammonia becomes an effective desulfurizing agent above 600" C., probably owing to the liberation of hydrogen. With this reagent, 81.3 per cent of the coal sulfur is eliminated a t 1000" C. As previously stated, the elimination of sulfur by steam is active only in the temperature range a t which the water gas reaction takes place; consequently rather large quantities of the carbon also are gasified, and the solid residue is high in ash content. Since both carbon monoxide and hydrogen are effective a t lower temperatures, it would seem that these difficulties could be avoided by the use of previously generated water gas. However, so far as can be found in literature, no

one has studied the desulfurizing effect of water gas below 800" C. I n Figure 6 are shown the results obtained with water gas alone and water gas bubbled through concentrated hydrochloric acid. I n each case the full line represents the total elimination calculated from the sulfur content of the carbonized residue, and the broken line represents the sulfur passing out in the gas. The difference between the two values, usually amounting to 5 to 8 per cent of the coal sulfur, is principally the sulfur in the tar. This relation is in good agreement with the observations of Powell ( 1 2 ) . Similar relative distributions of the sulfur between the gas and the tar were generally obtained with the other gases tested. The curves in Figure 6 show that water gas is somewhat less effective than pure hydrogen, but that its desulfurizing action is improved by small concentrations of hydrochloric acid. In Figure 7 is plotted the percentage loss of weight of the coal by volatilization in various gases. K i t h hydrogen the loss of weight is slightly greater than with nitrogen. Methane and ethylene give a smaller loss of weight owing to the deposition of carbon. With steam and carbon dioxide the loss of weight increases rapidly above 700" C. The curves in Figure 8 were plotted as a rough comparison of the various gases with respect t o their selective action upon the coal sulfur. Hydrogen was the most effective of the gases, especially a t the lower temperatures. Steam is quite efficient in the range 500-700" C., but above that temperature the combustion loss increases much more rapidly than the sulfur elimination. Water gas lies between hydrogen and carbon monoxide, as might be expected. The addition of hydrogen chloride to the water gas produces a marked increase in the efficiency, probably by desulfurization of ferrous sulfide. The noticeable effect of carbon monoxide below 600" C. is well illustrated by the curve. Carbon dioxide and nitrogen are noticeably inefficient because they increase the

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I SIT R Y I ND U S T R I A L A N D E N G I N E E R I N G C H E &

volatilization of carbonization products without increasing the desulfurization. OXIDATIOK BY F E R R I C SULFATE FOLLOWED BY C.4RBOSIZATIOS I N HYDROGEN

Stokes (22) has shown that pyrite can be oxidized to ferrous sulfate and sulfuric acid by heating u-ith an acid solution of ferric sulfate. Since the ferric sulfate could be regenerated by air oxidation in the presence of sulfur dioxide (18), it seemed desirable to test its application to the removal of pyrite from coal. One hundred grams of 20-40 mesh coal were boiled 24 hours with a solution containing 400 grams ferric ammonium sulfate and 80 cc. concentrated sulfuric acid in 2000 cc. of water. The coal was then filtered, washed free from soluble sulfates, and dried in vacuo a t 100" C. The sulfur analysis was 4.27 per cent, corresponding to an eliniination of 20 per cent of the original coal sulfur. Samples of this treated coal mere then carbonized during 4 hours a t various temperatures in a stream of hydrogen. The total elimination of sulfur by the combined oxidation, leaching, and carbonization process is plotted in Figure 9. The sulfur elimination is approximately the same as that obtained with the untreated coal in hydrogen a t 400" C., but is noticeably greater at the higher temperatures. This may be a result of the removal, during the leaching process, of some of the mineral constituents, especially iron. By this combined treatment a carbonized product containing 0.64 per cent sulfur was prepared from c7oal containing 5.34 per cent sulfur. This corresponds to an elimination of 93.1 per cent of the coal sulfur. IVSTBNTANEOUS

ClRBOSIZATION

O F c09L 11's 1?,E 4CTIJ-E

(;A SE S

The above-mentioned three conditions favoring elimination of sulfur from coal during carbonization would seem to be exceptionally well supplied by the instantaneous carbonization of finely ground coal in a manner similar to the methods of Sinnatt (20) and White (AT'), but with the added feature of a countercurrent stream of a reactive gas such as hydrogen, steam, carbon monoxide, ammonia, water gas, or purified coal gas. Such a process would lend itself well to heat regeneration, sulfur recovery, and recirculation of the gas used. TABLE111. EXPERIMESTS WITH IXSTANTASEOUS CARBONIZATION SULFUR CONTEXT SLLFUR TEMP.OF FLOWO F RATEOF L o s s o ~ OF ELIYINARETORT HYDROGEX COALFEEDWEIGHT RESIDUE T I O N C. Cu. ft./mzn. Grarns/hour % % 70 1000 0 0137 130 41.1 3 99 56 , 1000 0 0183 130 39 9 3.64 59

The laboratory experiments were carried out by slowly feeding, by means of a spiral feeder, 20-40 mesh coal into the top of a silica tube 1.5 inches inside diameter by 5 feet long, the

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middle 4 feet being heated to 1000" C. The coal was quickly carbonized in a countercurrent stream of hydrogen while falling through the heated portion of the tube. The residue dropped into a receiver where it was rapidly cooled to room temperature. The data for two experiments are shown in Table 111. The product is light and has a large specific surface. Further desulfurization can be accomplished by insulating the receiver to retain the heat and by passing the desulfurizing gas through the hot residue. AkCB1ZOJVLEDG31EST

The author wishes to express his appreciation for the valuable suggestions and criticisms given by D. B. Iceyes, under whose direction this study was made, and to H. F. Johnst'one and the late S. W.Parr who suggested the st'udy of coal treatment as a research project. This investigation was conducted in cooperation with the Utilities Research Commission, Inc., of Chicago, to whom the author is indebted for financial support and direction. LITERATURE CITED (1) Campbell, Bull. Am. Inst. M i n i n g Eng., 1916,177. (2) Ditz and Vildner, Brennstof-Cheip., 5, 149 (1924).

(3) Foerster and Geissler, Z. angew. Chem., 35, 193 (1922). (4) Grunert, J . prakt. Chem., 122,1 (1929). (5) Holtz with Huff, Johns Hopkins Univ., Dissertation, 1930. (G) Lissner, Brennstof-Chem., 4, 3 0 5 4 (1923). (7) McCallum, Chem. Eng., 11, 1, 27 (1910). ( 8 ) Monkhouse and Cobb, Gas J . , 156,234-40 (1921). (9) Parr, Bull. Am. Inst. Met. M i n i n g Eng., 1919, 1807. (10) P a r r and Layng, Mining and M e t . , 1920,No. 158, Sec. 4. (11) Powell, J. I N D .EXG.CHEM.,12,1069 (1920). (12) Powell, Ibid., 12, 1077 (1920). (13) Powell, Ibid., 13,33 (1921). (14) Powell, J . Am. Chem. Soc., 45,1 (1923). (15) Powell and Parr, Univ. Illinois, Eng. Expt. Sta., Bull. 111 (1919). (18) Powell and Thompson, Carnegie Inst. Tech., Bull. 7 (1923). (17) Priestley and Cobb, Gas J . , 182,951-4 (1928). (18) Ralston and Maier, Bur. Mines, Bull. 260 (1927). (19) Simmersbach and Tl'olff, GliickaJ, 41,906 (1905). (20) Sinnatt, Proc. 2nd Intern. Conf. Bituminous Coal, 1928, I, 560. (21) Sperr, Ibid., 1928, 11, 37. (22) Stokes, Am. J . Sei., 12,414 (1901). (23) Trifonov, Brennstof-Chem., 11, 165-9 (1930). (24) Wheeler and Jolly, Colliery Guardian, 127, 1120 (1921). (26) White, Gas Age-Record, 58,833 (1926). (28) Wibaut, Rec. trav. chim., 38,159 (1919). ( 2 i ) TT'ibaut, Ibid., 41, 153 (1922). (28) Wibaut, Brennstof-Chem., 3, 2i3-S (1922). (29) Wibaut, Proc. Srd Intern. Conj. Bituminous Coal, 1931. (30) Wibaut and LaBastide, Rec. trav. chim., 43,731 (1924). (31) Wibaut and Stoffel, Ibid., 38, 132 (1919). (32) Wibaut and VanderKam, Ibid., 49,121 (1930). RECEIVED March 10, 1932. Presented before the Division of Industrial and Engineering Chemistry at the 83rd Meeting of t h e American Chemical Society, New Orleans, La., Narch 28 to April l, 1932. Published by permiasion of the director of the Engineering Experiment Station, University of Illinois. The author's present address is 609 Delaware St., Bartlesville, Okla.

German Potash Sales Total sales of German potash in the first five months of 1932 mere about 16 and 34 per cent, respectively, under the corresponding periods of 1931 and 1930, and amounted to 480,619 metric tons of potassium oxide. This compared with 570,953 tons in 1931, and 733,149 in 1930. It is estimated that total German deliveries of potash for 1932 will amount to between 800,000 and 850,000 tons of potassium oxide, compared with 964,000 tons for 1931, which year showed a decrease of 29 per cent from total sales of 1,357,000 tons of potassium oxide for 1930. The contraction of almost 16 per cent in volume of total

German potash sales this year is due t o bmaller domestic sales and especiallv to a marked drop in exports. Total exports of raw salts in"the first four months of this year amounted to 153,519 tons compared with 193,315 and 327,913 tons in the same period of 1931 and 1930, respectively; exports of potash compounds fell to 61,056 tons, from 112,907 and 163,690 tons, respectively. The heavy decline in expork is due not only to decreased consumption, but also to rising production in other countries coupled with increasing restrictions placed upon imports by many important consuming countries.