QUANTITATIVE DETERMINATION OF SULFUR COMPOUNDS R. E. BREWER AND J. 14. GHOSM Central E s p s r i m e n t S t a t i o n , U . S . B u r e a u T h e two main objectives of this study were to increase the conversion of coal sulfur to volatile bulfur compounds and to determine the quantitathe distribution of the sulfur in the coke and tar, and as hldrogern sulfide, mercaptans, thiopheneq, carbon disulfide, carbon 0x3 sulfide. and residual sulfur in the gas. The study was undertaken as an answer to the requirement of industry for removing or reducing the undesirable sulfur content of the high-sulfur coals that must be used in the future. The factors which increase the desulfurizing action-a lowering of the sulfur content in the coke produced by carbonizing coal-arc presented and their relative merits are discussed. Quantitative determinations of individual sulfur compounds in the carbonieation gas and of the sulfur in the: coke and in the tar enabled sulfur balances to be made for all tests. Identification of the sulfur compounds and establishment of their relative proportions in the gas afloord valuable guides toward improving niethods of purlf>inggases to be used for chemical purposes. An effectivc program for desulfurizing coal economically- involves initial coal selection, suitable coal preparation to renim e as much sulfur as possible, and a cheap rand simple process for removing o r reducing sulfur during coal utilization, as such, and in its various solid, liquid, and gaseous products.
IVERSE requirements of coal and its products to meet exacting new and wider applications in industry have focused increased attention on development of methods for removing or reducing the undesirable sulfur content of the highsulfur coals that must be used in the future. Results of the present investigation have established that the desulfurizing actionnamely, a lorering of the sulfur content in the coke produced by carbonizing coal-is effected (1)by addition of ammonia, liydrogen, or nitrogen during coal carbonization, (2) by introduction of these gases a t temperatures lower than the final carbonization or reaction teniperaturc, (3) by continued time of treatment of the coal or coke sample a t the reaction temperature with these added gases, and (4)by use of fine-size coke. Carbonization of the coal with added ammonia gas caused a large percentage of the coal sulfur to be converted to volatile sulfur csmpounds; ammonia was markedly superior t o hydrogen, and hydrogen was considerably more effective than nitrogen in desulfurizing the heated coal or coke. Quantitative determinaiions of individual sulfur compounds in the carbonization gas and of the sulfur in the coke and in the tar enabled sulfur balances to be made for all tests. The laboratory investigation suggests that a cheap source of ammonia-such as from ammoniacal liquor-and a simple scrubbing train Wntaining an alkaline solution of suitable coinposition and concentration might be utilized commercially t o effect desulfurization of the solid, liquid, and gaseous products obtained by carbonization, gasification, and combustion of coal. An effective program for desulfurizing coal economically involves initial coal selection, suitable coal preparation to remove as much sulfur as possible, and a cheap, simple process for removing or
of
M i n e s , Pittsburgh, P a .
reducing sulfur during coal utilization, as such, and in its variouc solid, liquid, and gaseous products. Sulfur is an undesirable but economically important constit,iierli of all coals and of their combustion, gasification, and carbonizh,tion products. This coal sulfur amounts to several times tlrc total requirements of the ent,ire United States industry. Fron, the standpoint of addition to the niinernl resources of this country, hon-ever, the commercial recovery and utilization of coal sulfur can be profitable or practical only under certain special cor:ditions. A major intcrePt, tJherefore, is in the development of methods for removing or reducing coal sulfur in order t,hat its injurious effects during the utilization of the coal or of its product,s will be eliminated o i minimized. Interest in the desulfurizat'ion of coal and its products dates back to tlie 1850's and many studies have been made t o reducc, the sulfur content either in the coal before or during its utilisntion, in the gaseous by-products, or in the coke itself. Because the manufacture of coke for inetallurgical purposes is one of the principal uses of coal and because the reserves of low-sulfur coking coals are limited, a primary incentive throughout most of these investigations has been to produce a coke of low-sulfur content. To accomplish this objective, intensive studies have been made of methods that remove or reduce the sulfur content of the coal before coking; conduct the coking process in such manner as t,o cause a greater evolution of the sulfur in the volatile products; and elimiriate some or all of the residual sulfur in the coke by subsequent treatment, made usually while the coke is still hot. Some of these methods have been tested on a pilot plant scale and a few have been tried in commercial-size ovens, but practically all have not been entirely effectivearid none, thus far, ha,,, proved to be economical. PROCESSES FOR REMOVING SULFUR FROM COAL AND COKE
Processes for removing or reducing the sulfur cont,cnt in coa,i and coke may be broadly classified as folloms: Coal-cleaning processes that depend upon: wet-gravityconcentration methods, such as jigs, launders, upward-current classifiers, heavy niediurns (suspensions and solutions of high density), and tables; dry-gravit,y-concentration methods, such as pneumatic table, air jigs, and the air-sand process; and nongravity processes, such as froth flotation. Additions t o tlie coal of inorganic compounds, such as dry or hydrated lime, oxides (calcium, magnesium, ferric iron, or aluminum), carbonates (sodium, calcium. magnesium, or dolomitic), dioxides (manganese or silicon), phosphates (calcium,, iron, or manganese), calcium orthosilicate, portland cement, sodium hydroxide, sodium chloride with. or without oxidizing agents, magnesium chloride, pure iron, iron ore, and metallic: catalyzers (manganese, chromium, copper, calcium, or lead compounds), all of these being follomed by carbonization and leaching. Treatment of the coal during carbonization with gases or vapors, such as direct steam, steam generated within the coking charge, steam and air under controlled pressure, steam-air mix2044
September 1949
yx
ir
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
ture, steam with nitrogen or chlorine, steam and hydrocarbons, steam and amorphous carbon, hydrogen alone (or preceded by oxidation and leaching), carbon dioxide with or without vacuum, nitrogen alone (or passed through water, dilute or concentrated hydrochloric acid, or concentrated ammonium hydroxide), ammonia, carbon monoxide, water gas, water gas and hydrochloric acid, illuminating gas, methane, ethylene, and oxygen. Addition of inorganic compounds before and gases during carbonization-for example, iron oxide and nitrogen or chlorine, iron ore and coke oven gas, iron and hydrogen, calcium oxide and hydrogen, calcium carbonate and chlorine, magnesium oxide and chlorine or coke oven gas, and sodium carbonate and chlorine or coke oven gas. Treatment of coke in oven or after transfer to a special oven with gases and vapors such as steam, air and steam, and carbon dioxide and vacuum. Treatment of the coke after discharge from the oven with gases or vapors such as water vapor and/or steam, hydrocarbon vapors and steam, alternate vacuum and steam, vacuum alone, deam and hydrogen, steam and chlorine, hydrogen, nitrogen, methane, carbon dioxide, carbon monoxide, chlorine, bromine, blast furnace gas, coke oven gas, and air a t atmospheric and a t higher pressures. Treatment of the coke after discharge from the oven with .iolutions such as hydrochloric acid, quenching with water and hydrochloric acid, extraction with dilute hydrochloric acid, alternate water and air during quenching, watering out, water and manganese chloride, sodium carbonate, and dilute nitric acid. I t is beyond the scope of this paper to cite the many literature and patent references that describe these various processes. Most of them have been reviewed by Groves and Thorp (a), Powell and Thompson ( 9 ) , Muhlert (8),Simmersbach and Bchneider ( I S ) , Gluud and Jacobson (5), and Snow (14). Thiessen (16)has summarized the results obtained by use of certain of these methods.
2045
on finely crushed (through 20-mesh) coke. Quantitative determinations were made of the distribution of the coal sulfur in the coke, tar, hydrogen sulfide, mercaptans, thiophenes, carbon disulfide, carbon oxysulfide, and residual sulfur. All test results obtained by treatment of the coal and coke samples with added gas were compared with those found under the same test conditions without addition of gas. For ready comparison of all tests, all test data are referred to the basis of the original 15gram coal samples. DISTRIBUTION OF SULFUR AND ITS DETERMINATION IN PRODUCTS OF COAL CARBONIZATlON
During the carbonization of coal the total sulfur originally present is distributed in the coke, in the tar and liquor, and as hydrogen sulfide, mercaptans, thiophenes, carbon disulfide, carbon oxysulfide, and residual sulfur in the gas. Sulfur in any of these solid, liquid, and gaseous products of coal aarbonization is undesirable. Quantitative determinations of the sulfur concentration in each of these products, therefore, is of interest to both manufacturers and consumers, who require products of low-sulfur content. I n the present investigation the coking process was conducted in such a manner as t o cause an increased evolution of the sulfur in the volatile products with resulting lower sulfur content in the coke.
(*Protective reagent)
PURPOSE AND SCOPE OF INVESTIGATION
Of the processes outlined above, the desulfurization treatment of coal during carbonization with certain added gases or vapors
b
appeared promising for further study. Comparative data by Snow ( 1 4 ) have shown that steam, hydrogen, ammonia, and water gas, all of which contain hydrogen in molecular form, or hydrogen which may be produced in nascent form, have the greatest desulfurizing actions of the 14 gases and vapors that Snow investigated. Himus and Egerton (6) believe that the desulfurizing effect of gases containing hydrogen is evidently twofold: The primary products are diluted, thus reducing the concentration of hydrogen sulfide and diminishing the secondary fixation of sulfur by reaction of carbon with hydrogen sulfide, and the hydrogen reacts with the sulfur compounds to form hydrogen sulfide. The desulfurizing effects of steam and of water gas during the (barbonisation of coal have been studied in detail by a number of workers. A similar study of the desulfurizing effectsof ammonia and of its decomposition gases, hydrogen and nitrogen, will be of interest from the standpoint of their comparative effectiveness and from the viewpoint of the mechanism involved in the case of ammonia. A second important objective in the present investigation was to determine the quantitative distribution of sulfur in the various solid, liquid, and gaseous products of carbonization. To achiere these objectives, the desulfurizing effects of ammonia, hydrogen, and nitrogen when added to sized coal samples and their lump cokes were studied at 700°, SOO", and 875' C. To determine the effect of adding the gas a t lower temperatures, il number of tests were made with ammonia introduced a t 500" C. and with hydrogen introduced at room temperature. One test was made to determine the desulfurizing effect of ammonia
Figure 1. Scheme for Determining Total Sulfur arid Individual Sulfur Compounds in Gas
ANALYTICAL SCHEME.Figure 1 shows the analytical scheme employed in the present work for separating the individual sulfur compounds formed during the carbonization of the coal with or without added gases. The scheme is essentially like that used by Riesz and Wohlberg (IO) and by Hakewill and Rueck (6) at the Institute of Gas Technology for determining various sulfur compounds in synthetic gas mixtures. To remove all of the sulfur in the volatile products, added provisions had t o be introduced in the procedure to condense the tar and liquor, t o absorb the undecomposed added ammonia gas, and t o avoid the appreciable solubility of hydrogen sulfide and mercaptans in the confining liquid in the gas holder by fist removing these constituents by selective absorption (run 1, Figure 1). Minor changes were also introduced with respect to the quantities and concentrations of certain of the reagents as used at the institute t o adapt them to the concentrations of individual sulfur compounds present in the gases produced in the present work. The quantitative determinations of the individual sulfur compounds-hydrogen sulfide, mercaptans, thiophene#, carbon disulfide, carbon oxysulfide, and residual sulfur in the gas-present after removal of tar and liquor from the carbonization gas depend upon results of determinations of total sulfur in the gas by combustion with purified air before and after treatment with selective reagents to remove specific sulfur compounds, and the analysis of certain of the selective reagents for specific sulfur compounds by titration with standard iodine. Three separate
INDUSTRIAL AND ENGINEERING CHEMISTRY
2046
Vol. 41, No. 9
and liquor trap, 10, a guard vessel, 11, and an absorber, 12. containing 100 ml. of normal sulfuric acid which absorbs the (Through 20- on 35-mesh Tyler series sieves, 15-gram sample, 2.11% sulfur) unconsumed ammonia. The A nir carbonization gas, now free rnnnia Sulfur Coke Coal Sulfur of ammonia, passes through Heating Period, Hours con- In ObSulfur in in Volatile two absorbers, 13 and 14, each Products perature, T o reaction A t reaction sumed, Sample, tained Coke Test C. temperature temperature Grams Gram Gram; % Gram Gram % containing 100 ml. of 10% cadmium chloride and 10 MI. 700 1.25 4.775 0 0.3150 10.77 1.60 0.1123 0.1427 45.3 1.41 0.3150 11.01 1.37 0.1508 0.1642 52.1 700 1.25 1.50 of normal sodium carbonate to 700 1 . 2 5 4- 1.50 1.50 f 2.00 3.27 0.3150 10.70 1.29 0,1380 0.1770 56.2 C" remove hydrogen sulfide and 3.25 0 800 1.75 0.3150 10.90 D 1.50 0.1635 0.1515 4 8 . 1 mercaptans? through absorber 800 1.75 1.75 2.36 0.3150 E 10.90 1.30 0.1417 0.1783 55.0 1.75 f 2 . 0 0 5 . 2 5 800 1 . 7 5 3- 1.75 0.3150 10.60 1 . 2 0 0,1260 0.1890 6 0 . 0 15, containing 50 ml. of conFa 800 1.75 1 . 7 5 1.75 f 2.00 5.30 Gagb 0.3150 10.50 1 . 1 3 0.1187 0.1963 6 2 . 3 centrated (1.84specific gravity) 2.50 3.50 875 0 0.3150 H 10.58 1 . 6 1 0.1703 0.1447 45.9 sulfuric acid to absorb thio2.50 1.50 2.10 0.3150 10.60 1.25 0.1325 0.1825 57.9 I 875 2 . 5 0 + 2.50 1 . 5 0 f 2.00 875 4.89 phenes, through absorber 16, 0.3150 10.30 1.17 0.1205 0.1945 61.7 Ja containing 100 ml. of 12% a Coke from Previous test cooled t o room temperature and used a8 test sample; data represent hot,h tests, hased sodium hydroxide to remove on coal sample Coke prodbced under the same conditions as test E was crushed to -20-mesh size and used as sample in test any acid spray, through abG: data %rereferred t3 original coal sampie. sorbers 17 and 18, each containing 50 ml. of 10% potassium hydroxide in 95% ethyl alcohol kept a t 0' C. by an icewater bath, 19, to absorb carbon disulfide and carbon oxysulfide, runs, Figure 1, are necessary to establish the concentrations of and is finally collected in the gas holder, 20, containing a confining the total sulfur, SI,Se, and S3,in the gas reaching the burner solution of 20% sodium sulfate to which is added 5% by volume and determined by combustion. If there are no compounds of sulfuric acid. Gas is removed for combustion through the outother than hydrogen sulfide, mercaptans, thiophenes, carbon let 21, by adjusting the level of the aspirator bottle, 22. $he quantity of ammonia passed into the reaction tube during disulfide, and carbon oxysulfide which are absorbed by the rea test is measured by the previously calibrated flowmeter. The agents used in run 3, then the sulfur in the original gas is divided rate of flow was held constant a t 1.907 liters (X.T.P.) per hour. as follows: A large part of the ammonia is decomposed a t the Carbonization temperature of the coal and aids in its desulfurization. The un= concentration of S as thiophenes SI - S2 = ST used ammonia is neutralized by normal sulfuric acid and is deter= concentration of S as carbon disulfide and carP, - SI = Sno mined by titration with standard alkali. The quantity of ammobon oxysulfide nia consumed during the test is then found by difference between = residual sulfur not absorbed by the reagents $8 = si? the total ammonia passed in and the unused ammonia. Correcused tions are made for the quantity of ammonia formed from the coal and coke samples in tests conducted under comparable conditione The order of reagents in the absorption train must not be except for the addition of ammonia from the cylinder. changed and none omitted in a particular run. By analysis of To avoid disturbing the coal column and for convenience in carrying out the tests, the true temperature of the coal column was certain of the absorption reag6nts after use additional data for f r a t determined from a series of preliminary comparative meascertain sulfur compounds are obtained and when combined with urements made with two thermocouples. One couple was indata from the determination of the sulfur remaining after the serted between the furnace wall and the reaction tube as shown in treatments outlined in runs 1, 2, and 3 give individual values for Figure 2. The second couple wa8 placed with its cold junction at the center of the coal column inside the reaction tube. A rheostat sulfur as hydrogen sulfide, mercaptans, thiophenes, carbon and ammeter in the heating circuit enabled easy control and reprodisulfide, carbon oxysulfide, and residual sulfur. ducibility of any desired heating rate and temperature. ComparSince the data from the three runs are t o be combined, any ative reading8 of the two couples were made by means of a otenvariation in the concentration of the several sulfur compounds in tiometer indicator while the coal was being heated to the Asired reaction temperature (iOO", SOO", or 875" C., in 1.50, 1.75, or 2.50 the gas supplied for runs 1, 2, and 3, respectively, would introduce im erroi. This difficulty is avoided by making the three runs simultaneously, supplying the gas from a manifold. Simultaneous conduction of runs 1, 2, and 3 would require triplicate sets of certain apparatus, and is, therefore, impracticable. Each test recorded in Tables I to VI11 represents a t least three runs. By close adherence to the test conditions described, variation in the concentrations of the several sulfur compounds in the gas supplied for runs 1, 2, and 3 is held to a minimum. Independent checks of individual sulfur compounds in different runs confirmed this conclusion. T.4BLE
1. TEST CONDITIONS
REMOVAL F R O M PITTSBURG€l BED, SH.4NNOPIK MINE, PREHEATED COAL
AND SULFUR
RT22:n
k
+
The apparatus used APPARATU~ AND GENERAL PROCEDURE. for run 3 is shown in Figure 2; that for run 1 is the same with parts 15 to 19 omitted. The apparatus for run 2 differs from that shown in Figure 2 only in that the alcoholic potassium hydroxide absorbers, 17 and 18, and the ice-water bath, 19, are omitted. All cork stoppers and rubber tubing were lorn in or free from sulfur and were treated to protect them from direct contact with the gas. To minimize the areas of contact, connections in the train were made by butting all glass ends together inslde the rubber tubing. For the tests with added ammonia, the ammonia gas from cylinder 1, passes through the capillary-type, glycerol-filled, calibrated flowmeter 2, and silica inlet tube 3, into the bottom part of the silica reaction tube 4, and is thus preheated. The latter tube surrounds the slightly smaller silica tube 5 , which supports the perforated porcelain plate, 6, upon which rests the 10-cm. column of coal, 7, heated by the controlled electric furnace, 8. The temperature of the coal column is measured by a thermocouple, 9, in a manner to be described below. The ammonia gas passes up through the perforated plate and heated coal column, is partly decomposed, and with the carbonization gas goes through a tar
Figure 2. Apparatus for Carbonizing Coal with Added Ammonia Gas and for Collecting Individual Sulfur Compounds in Carbonization Gas Gas cylinder, NHs Flowmeter, glycerol filled "a-inlet tube, 3-mm. bore silica 4. Reaction tube, 24-mm. bore silica 5. Silica-tube support for 6 6. Ferforated porcelain plate 7. Coal column, about 10 om. in length 8. Electric furnace. with rheostat and ammeter 9. Thermocouple, Chromel-Alumrl 10. Tar and liquor trap 11. Guard vessel 12. Absorber containing normal H2SOa 13 and 14. Absorbers contnining 10 70 CdClz and normal YazC08 15. Absorber containing 1.84 sp. gr. HrSOi 16 Tra containing 12 % NaOH Absorbers containing 10% KOH i n CzHsOH I7'and 19. Ice-water bath 20. Gas holder, 18-liter oapacity 21. Gas outlet for combustion sample 22. Bottle, aspirator 1.
2. 3.
lg.
September 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
2047
hours, respectively) and until this reaction temperature reTABLE 11. TESTCONDITIONS AND SULFUR REMOVAL FROM PITTSBURGH BED, SHANNOPIN MINE, RAWCOAL mained constant. The reaction temperatures recorded are (Through 20- on 35-mesh Tyler series sieves, 15-gram sample, 2.41% sulfur) those obtained with the thermoAmCoal Sulfur couple as shown in Figure 2 Sulfur in in Volatile a t readings corresponding to Heating Period, Hours conin Coke Products ature, T o reaction At reaction sumed, Sample, tained, tem eratures at t.he center of Test C. temperature temperature Grams Gram Grams 5% Gram Gram 76 the Eeated coal column. 10.00 2.19 0.2190 0.1425 39.4 0 0.3615 K 800 1.75 4.25 Figure 3 is a schematic diaL 800 1.75 1.50 10.40 1 . 8 9 0,1966 0,1649 45.6 2.02 0.3615 gram of the apparatus asMa 800 1.75 f 1.75 1 . 5 0 f 2.00 10.32 1.38 0.1424 0.2191 6 0 . 6 4.72 0.3615 sembly used for burning the from previous test cooled t o room temperature and used as test sample; data represent both tests based gas. Air for combust.ion is on Coke sample, purified by passage through a train consisting of 95% sulfuric acid t o remove oils and TABLE 111. TESTCONDITIONS AND SULFURREMOVAL FROM ILLINOIS No. 6 BED,No. 6 R ~ I N E , dust, alkaline potassium ferriRAWCOAL cyanide (75 grams potassium (Through 20- on 35-mesh Tyler series sieves, 15-gram sample, 3.55% sulfur) ferricyanide plus 92.5 grams Am: sodium carbonate per liter) Su!fur Coal Sulfur Heating Period, Hours ''?lfur Coke in in Volatile solution t o oxidize and retain in ObCoke Products any sulfur compounds that ature, To reaction At reaction sumed Sample, tained, Test C. temperature temperature Grams' Gram Grams % Gram Gram % ' might be in the air, and actiN 700 1.50 4.50 0 0.5325 9.92 2 . 7 4 0 . 2 7 1 8 0.2607 4 9 . 0 vated wood charcoal t o take 0 700 1.50 1.50 1.84 0.5325 9.95 2 . 6 2 0.2607 0.2718 5 1 . 0 out any chemically inert matePa 700 1.50 f 1.50 1.50 f 2.00 4.08 0.5325 9.70 2 . 4 7 0.2396 0.2929 5 5 . 0 rials and moisture. About 800 1.75 4.25 0 0.5325 10.03 2 . 8 3 0.2838 0.2487 4 6 . 7 150 ml. each of sulfuric acid R 800 1.75 1.50 2.12 0.5325 9.89 2 . 5 2 0.2492 0.2833 53.2 800 1.75 f 1.75 1.50 f 2.00 4.47 0.5326 9.49 1 . 8 4 0,1747 0.3878 6 7 . 2 SO and alkaline potassium ferriTb 800 1.75 1.50 2.48 0.5325 9.70 2 . 4 2 0.2347 0.2978 55.9 cyanide are used to ensure TJa,b 800 1.75 f 1.75 1.50 f 2.00 9.70 1 . 7 7 0,1717 0.3608 6 7 . 8 4.64 0.8325 9.65 2 . 8 6 0,2760 0.2565 4 8 . 2 0 0.5325 3.50 good air-liquid contact. The V 875 2.50 1 . 9 9 0 . 5 3 2 6 9 . 8 8 2 . 6 7 0.2638 0.2687 5 0 . 5 2 . 5 0 1 . 5 0 875 charcoal column is about 4 4.85 0,5325 9.67 1.77 0,1712 0.3613 6 7 . 8 875 2.50 f 2.50 1.50 f 2 . 0 0 inches long and 1.25 inches in a Coke from previous test cooled t o room temperature and used as test sample; data represent both tests, based diameter and is held in place by plugs of cotton a t the onooaisample. b Ammonia gas was started a t 500' C. instead of a t 800' C. ends, The sulfur determination apparatus proper (parts 4 t o 9, Figure 3) is a standard A.S.T.M. apparatus ( 1 ) of PyDETERMINATION O F SULFUR IN COKE AND TAR. Sulfur in coke rex glass provided with standard-taper glass joints for the deis determined gravimetrically by the Eschka method and sulfur termination of sulfur in petroleum oils but with the 26-ml. Erlenin tar by the bomb-washing method (15). meyer flask and cotton wicking removed and the upper end of the DETERMINATION OF SULFUR IN GAS BY COMBUSTION.The burner slightly modified to burn gas. A flame with a well-defined combustion of the gas with purified air as they reach the burner blue inner cone could be easily maintained by proper adjustment (4, Figure 3), after either of the three treatments indicated in of suction with an aspirator water-filter pump (11, Figure 3). Figure I, converts the sulfur compounds remaining in the gas to The flask (10, Figure 3) served to minimize fluctuations in gas sulfur dioxide, which is absorbed in 100 ml. of 10% sodium bicarBow. A somewhat similar adaptation of the A.S.T.M. 'sulfur bonate solution (6 and 8, Figure 3). The resultsingsodium sulfite determination apparatus has been successfully used b y . Wilson in the absorbers is largely oxidized to sodium sulfate by the excess ( 1 7 ) . The total sulfur in the gas reaching the burner (4, F!gure 3) air passing through the solution during the combustion and subin runs 1,2, and 3 is obtained by burning the gas with purified air sequent cooling period. absorbing the combustion products in an excess of 10% sodium The solution in the absorbers when cool is transferred to a 500bicarbonate solution, and gravimetrically determining the sulfur ml. beaker. The absorbers and spray trap are rinsed with several in the absorption solution. small portions of distilled water and the rinsings added t o the contents of the beaker to give a total volume of about 300 ml. The OF SULFUR IN CARBONIZATION ,PRODUCTS alkaline solution is carefully neutralized t o the methyl orange end point with 1 N hydrochloric acid and 1 ml. excess is added, To enThe general procedure for conducting the tests, as outlined in sure complete oxidation of the sodium sulfite to sulfate, 15 ml. of the preceding section, distributes the original sulfur of the coal saturated bromine water is added and the solution is boiled until among the solid, liquid, and gaseous Products of C~rbonizationcolorless. The sulfate in the solution is then determined gravimetrically as barium sulfate and corrected for the blank determination made on the corresponding amounts of reagents, u-ithout combustion of the gas. This combustion method is used also t o determine the sulfur present before and after removal of particular sulfur compounds by scrubbing the gas with specific selective absorbents. From 41. this difference is given the sulfur in the individual sulfur compounds t h a t are removed by these absorbents. DETERMINATION OF HYDROGEN SULFIDEAND MERCAPTANS. The sulfur present as hydrogen sulfide and mercaptans (thiols) is removed by the cadmium chloride-sodium carbonate reagent (absorbers 13 and 14, Figure 2), ~~~~~~
+?
w:-a
O
*
2-a
f
1
HzS Figure 3.
Apparatus Assembly for Sulfur Determination in G a s by Combustion
1. Washer, 9 5 % His04 2. Washer, 10 70alkaline potassium ferricyanide 3. Tower, activated wood charcoal 4. Burner 5. Gas inlet 6 and 7. Absorbers 8. Fritted disk 9. Spray trap 10. Surge flask 11. Gas outlet to aspirator pump
PRSH
kaline + CdClza1acid e CdS + 2HC1
+ CdC1,a1kaline RS-Cd-SR + 2HC1 acid
The analysis of this reagent for the sulfur content in these constituents is based on the principle used by Shaw (11),except that greater scrubbing capacity and more reagent were used because of the high content of hydrogen sulfide and mercaptans in the gas.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2048
Vol. 41, No. 9
TABLEIV. SULFURDISTRIRUTION XN CARBONIZATION PRODUCTS OR PITTSBURGH RED, SHANXOPIN MINE, PREHEATED COAL Sulfur in Products,
Sulfur in Coal,
gas
Gram
Grah
0.0090 0.0003 0.0008 0.0004 0.0006 0.0011 0.0003 0.0002 0.0005
0,3105 0.3131 0.3130 0.2666 0.3226 0.3140 0.3125 0.3116 0.3133
0.3150 0.3150 0,3150 0.3150 0.3150 0,3150 0.3150 0.3150 0.3160
Sulfur Distribution, Gram Test
In coke
In tar
.I5 B
0,1723 0.1508 0.1380 0.1635 0.1417 0.1260 0.1703 0.1325 0,1205
0.0160 0,0194 0.0185
Cb D
E" Faph H
I Jb
0.0186 0,0136 0,0156 0.0170 0,0180
As hydrogen sulfide
As mercaptans
As thio-
0,0940 0.0997 0.1098 0.0913 0.1280 0.1390 0.0984 0.1086 0,1093
0,0115 0.0416 0.0448 0.0111 0,0370 0,0323 0,0272 0.0483 0.0599
0.0048 0.0006 0.0007
phenes
0,0008 0.0009 0,0002 0.0036 0.0038
As carbon disulfide
As carbon oxysulfide
0.0032 -0.0003 0,0008 Nil 0.0003 0,0004 (0,0002) -0.0003 0.0012 -0.0001 0.0012 0.0003 0.0002 0.0007 0.0006 0.0006 0.0007
In residual
Sp,
sc
- Sp, Gram
SC
Sulfur i n Products,
5%
0.0045 0,0019 0.0020 0.0486 -0.0076 0,0010 0,0025 0,0035 0.0019
98.6 99.4 99.4 102:4 99.7 99.2 98.9 99.5
I Xegative values for ea-rbon disulfide and carbon oxysulfide result from solution of simultaneous equations used to calculate test data obtained in determinaeion of t.hese compounds, 5 Coke from previous test cooled t o room temperature and used as test sample; data represent both tests, based on coal sample.
IN CARBOXIZATIoN PRODUCTS TABLE v. SULFUR DISTRIBUTION
-'Test
I n coke
I n tar
As hydrogen sulfide
K
0.2190 0,1966 0.1424
0,0229 0.0114 0 0189
0,1008 0,1309 0.1610
L
Ma
Sulfur Distribution, Gram.
As mercaptans
As thiophenes
0,0211 0,0131 0.0298
0.0002 0.0005 0,0008
As carbon disulfide 0.0002
Nil -0.OOOl
O F PITTSBURGH
In
BED, SHANNOPIX MINE, RAWCOAL
-
As carbon oxysulfide
residual gas
0.0004 0.0010 0.0013
0.0005 0.0003 0.0007
Sulfur in Products, Sp,
Sujfur in Coal,
SC,
SC -
Qp,
Sulfur iu Produch,
Gram
Gram
Gram
%
0 3651 0.3638 0,3548
0.3615 0.3615 0.3615
-0.0036 -0.0023 0.0067
101.0 100 6 98.1
data represent both tests, based on coal sample. Negative value for t Coke from previous test cooled to room temperature and used as test sample; .:arbon disulfide results from solution of simultaneous equations used t o calculate test data obtained in determinations of carbon disulfide and carbon oxysiilnae.
uum into the flask until the liquid retains i t s iodine color. An Each of the specially designed absorbers (13 and 14, Figure 2) additional 5 to 10 ml. of 0.1 N iodine solution is added and the contains 100 ml, of 10% cadmium chloride solution and 10 ml. of contents of the flask are thoroughly shaken. The unused iodine normal sodium carbonate solution. This excess sodium carbonate is backtitrated with 0.1 N sodium thiosulfate solution, using 5 ml. prevents the reverse reactions that would result if the solutions of soluble starch indicator. The hydrogen sulfide sulfur is calcuwere not kept alkaline and ensures complete precipitation of cadlated from the quantity of standard iodine consumed by the hyrriium sulfide and cadmium mercaptides. To determine the total. drogen sulfide released in the acid solution. The sulfur originally sulfur, the absorbers are disconnected from the apparatus and present as mercaptans equals the difference between the total sultheir contents are transferred as completely as possible by drainfur found as hydrogen sulfide and mercaptans and that found as age and by two washings each with distilled water into a liter hydrogen sulfide. flask. This flask is provided with a separatory funnel and a side DETERXINATION OF THIOPHENES. The suitability of concenlube, each of which has a ground-glass stopcock. The flask is evact,rated sulfuric acid (1.84 specific gravity) for complete absorption uated through the side tube by means of a vacuum pump until of thio henes and nonabsorption of carbon disulfide and carbon the contents of the flask 'ust begins to boil due to the reduced preso x y s u l ~ d ehas been established by Hut'chison ( 7 ) and by Riesz sure. The stopcock in the side tube is then closed and the flask is and Wohlberg (IO). Sulfur present' as thiophenes is equivalent to disconnected from the pump. Just the requisite quantity of conthe sulfur determination in the gas after removal of hydrogen sulcentrated hydrochloric acid is now added through the funnel to fide and mercaptans less the sulfur determination after passing dissolve the cadmium sulfide and cadmium mercaptides and bythe gas through cadmium chloride-sodium carbonate reagent and product, cadmium carbonate. The flask and contents are thorand 95% sulfuric acid. It is obtained directly as the difference in oughly shaken, a measured quantity of 0.1 N iodine solution is sulfur between runs 1 and 2-namely, SI - Sz = ST = concenadded, and the flask again shaken vigorously. The walls of the t,ration of sulfur as thiophenes. absorbers are freed of any remaining precipitates by a similar proDETERMINATION O F CARBON DISULFIDE AND CARBON OXYSULcedure using vacuum, concentrated hydrochloric acid, and a FIDE. The carbon disulfide and carbon oxysulfide content of the measured amount of 0.1 N iodine solution and the contents of the gas is equivalent to the sulfur removed by the alcoholic potassium absorbers are transferred, using two washings of distilled water hydroxide solut'ion after the hydrogen sulfide, mercaptans, and for each absorber, t o the main solution in the liter flask. The flask thiophenes have been removed. Fresh alcoholic potassium hyis shaken vigorously to ensure thorough mixing of the contents droxide reagent, kept near 0" C., quantitatively absorbs the carsnd the excess iodine is backtitrated with 0.1 N sodium thiosulbon disulfide and carbon oxysulfide to form the corresponding fate solution, using 5 ml. of soluble starch indicator. Total sulfur xanthates (potassium ethyl dithiocarbonate and potassium ethyl as hydrogen sulfide and mercaptans is then calculated from the monothiocarbonate) according to the reactions: quantity of standard iodine consumed by these compounds when released in acid solution. CS? IlOEt --f KS-CS-OEt (1) Since the iodine re uired per atom of sulfur is twice as great for hydrogen sulfide oxixation as for mercaptan oxidation, the indiCOS KOEt +KS-CO-OEt (2 1 vidual amounts of each of these forms of sulfur must be determined in a second test. Shaw (11)has shown that cadmium merThese xanthates are converted by glacial acetic acid to reactive xanthic acids which are readily oxidized by iodine to give the corcaptides may be separated from cadmium sulfide by solution in 0.3% hydrochloric acid. For the present investigation, 91.7 responding disulfides: ml. of the 10% cadmium chloride, made just acid to methyl orange indicator, and 8.3ml. of 1N hydrochloric 2HS--CS-O>:t + j;tO-CS-S-S.-cS-oEt + 2 ~ 1 (3) acid are placed in each absorber. At this concentration the cadmium mercaptides are kept in solution. At the end of the run, the contents of the absorbers are reIp EtO--CO-S-S -CO-OEt 2HI (4) 2HS-CO-OEt moved and each of the absorbers is washed out with distilled water containing 8.3% of normal hydrochloric acid by To carry out this determination, the solutions are transferred volume. The precipitate is separated from the solution by filterfrom absorbers 17 and 18 (Figure 2 ) to a 20@ml. volumetric ing through a n asbestos filter in a Gooch crucible, washed three flask, using three portions (20 ml. each) of distilled water to wash times with small portions of the acidified distilled water, and each absorber. The total volume is then made up to exactly transferred t o the special liter flask described above. The flask ml. by addition of distilled Water. The contents, after thorough is then partially evacuated so as to prevent loss of hydrogen sulis dissolved mixing, are divided into two equal 100 ml. portions and trans&de when the washed precipitate in a minimum quantity of concentrated hydroohloric acid intraferred t o separate 250-ml. Erlenmeyer flasks. This division is made t o reduce the volume and to provide two aliquot portions duced through the funnel. A measured volume of 0.1 N iodine solution IS added through the funnel and slowly drawn by the vacfor check titrations with standard iodine solution. The solution
-+
+
+
2
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1949
TABLE VI.
SULFUR DISTRIBUTION IN CARBONIZATION PRODUCTS OF ILLINOIS No. 6 BED, No. 6 MINE, RAWCOAL Sulfur Distribution, Gram
As
Test
Ineoke
I n tar
hydrogen sulfide
As mercaptana
As thiophenes
N4
0.2718 0.2607 0.2396 0.2838 0.2492 0.1747 0.2347 0.1717 0.2760 0.2638 0.1712
0.0234 0.0391 0.0254 0.0271 0.0255 0.0359 0.0323 0.0286 0.0235 0.0164 0.0207
0,1789 0.1938 0.2115 0.1872 0.2262 0.2803 0.2381 0.2938 0.2026 0.2205 0.2587
0.0077 0.0106 0.0157 0.0128 0.0067 0.0317 0.0163 Os.0269 0.0163 0.0270 0.0659
0.0010 0.0014 0.0015 0.0005 0.0100 0.0151 0.0024 0,0025 0.0005 0.0052 0.0067
0
Pb
Q"
3 T%'
Ua*h*c
V
3J
2049
As carbon oxysulfide
AS
carbon disulfide -0.0011 0.0020 0.0023 0.0017 0.0020 0.0021 0.0016 0.0016 0;0008 0.0014 0.0015
0.0016 0.0001
Nil
0.0009 0.0002 0.0003
Nil
-0.0003
Nil
In residual gas
0.0001 -0,0002 -0.0002 0.0007 0.0008 0.0008
0.0001 0.0001 0.0003 0.0004 0.0002 0.0001 0.0003
Su)fur In Products, Sp
Sulfur in Coal, Grah
Sp, Gram
-
Sulfur in Products,
Grah 0.4842 0.5079 0.4963 0.5128 0.5197 0,5400 0 5255 0,5253 0.5206 0.5352 0.5258
0.5325 0.5325 0.5325 0 5325 0.5325 0,5325 0.5325 0.5325 0.5325 0.5325 0.5325
0.0483 0.0246 0.0362 0.0197 0.0128 -0.0075 0.0070 0.0072 0.0119 -0,0027 0.0067
90.9 95.4 93.2 96.3 97.6 101.4 98.7 98.6 97.8 100.5 98.7
SC
SC
%
a Negative values for carbon disulfide and carbon oxysulfide result from solution of simultaneous equations used to calculate test data obtained in determinations of these compounds. Coke from previous test cooled to room temperature and used as test sample; data represent both tests, based on coal sample. , Ammonia gas was started at 500' C. instead of a t 800' C.
TABLEVII.
COMPARISON OF DESULFURIZING ACTIONO F AMMONIA, HYDROGEN, AND NITROGEN ON ILLINOIS NO. 6 BED,NO. 6 MINE, RAWCOALAT 800" C. (Through 20- on 35-mesh Tyler series sieves, 15-gram sample, 3.55% sulfur) Heating Period, Hours Sulfur in Coke Sulfur in Coke At reaotion Total Gas Passed, Sample, Obtained, temperature temperature Liters (N.T.P.) Gram Grams % Gram
To reaction
Test
R
1.75 1.75 1.75
RH RN
+ 1.75 1.75 + + 1.75 1.75 1.75 1.75 + 1.75 1.75 + 1.75
S"
1.75 1.75 1.75
SHa Sqa
T THO
U% b
UH%O
1.50 1.50 1.50 2.00 1.50 2.00 1.50 1.50 4- 2.00 1.50 1.50 2.00 1.50 1.50 2.00
+ +
+ +
Ammonia, Hydrogen Ammonia,' Hydrogen,
4.291 12.240 11,442 26.362
0.5325 0.5325 0.5325 0.5323 0.5325 0.5325 0.5325 0.5325 0.5325 0.5325
2.52 3.25 3.30 1.84 2.96 3.41 2.42 2.40 1.77 2.36
9.89 10.16 10.16 9.49 9.22 9.17 9.70 9.81 9.70 9.21
Coal Sulfur in Volatile Products Gram %
0.2492 0,3302 0.3353 0.1747 0.2729 0.3127 0.2347 0,2354 0.1717 0.2174
Cokes from tests R,R H , RN, T, and T H were cooled to room temperature and used as samples in tests 6 , SH,SN, U,and UH, respectively; resent both tests, based on coal sample. Ammonia gas started a t 500' C.: time of passage was 2.25 hours in test T and 5.0 hours in test U. e Hydrogen gas started a t room temperature; time of passage was 3.25 hours in test TH and 7.0 hours in test UH. a
*
in each flask is cooled to approximately 0" C. Two to three drops of phenolphthalein indicator (0.5% by weight in 50% by volume of neutral isopropyl alcohol) are added and the solution is slowly neutralized with glacial acetic acid, added dropwise and followed by three drops in excess after the red color of the indicator disappears. This acidic solution is then titrated with 0.01 N iodine solution a t a tem erature below 5" C. Five ml. of soluble starch solution are usex as indicator; the end point is taken as tho fust appearance of blue color. The mean value of the two titrations (corrected for the reagent blanks) is doubled and used to calculate the weights in grams of sulfur originally present as carbon disulfide and carbon oxysulfide. From Equations 1 and 3 it is seen that 1 mole of carbon disulfide or 2 atoms of sulfur requires 1 atom of iodine and from Equations 2 and 4 that l mole of carbon oxysulfide or l atom of sulfur requires 1 atom of iodine. If the carbon disulfide sulfur is denoted b S D and the carbon oxysulfide sulfur by SO,then the total SD f SO. The combined total sulfur, titratabye sulfur equals as carbon disulfide and carbon oxvsulfide. eauals the difference in sulfur as determined by combus6on in r u i s 2 and 3-namely, Sa Sa,or the difference in wlfur before and after scrubbing the as with alcoholic potassium hydroxide. This total sulfur equals i 2 - Sa = SD SO. The individual values for SDand So are then obtained by solution of these two simultaneous equations. More specifically, S D is equal t o twice the difference between total sulfur and titratable sulfur, whereas So is simply the difference between twice the titratable sulPur and the total sulfur. The method of calculating SD and So will be illustrated by an example (test W, Table VI). The iodimetric titration of the 200ml. total solution of acidic xanthic acids required 4.76 ml. of 0.01 N iodine (corrected for blank reagent). Since 1 ml. of 0.01 N iodine solution is equivalent t o 0.00032 gram of titratable sulfur, the total titratable sulfur is 0.00032 times 4.76 equals 0.00152 gram. The total sulfur, SZ - So (or S D So), determined by combuption in test W was 0.00224 gram. Substituting in the two simultaneous equations,
-
+
av
+
S D f SO = 0.00224 gram and '/a
Then
'/* SD SD
SD
+ So = 0.00152 gram
= 0.00072gram = 0.00144gram
So = 0.0008 gram
data r e p
The sum of the sulfur as carbon disulfide and carbon oxysulfide ma also be obtained by direct gravimetric determination of the sult%r in the oxidized xanthate solution left after the iodimetrio titration. Thus far, this determination has given a lower value than that obtained by the difference, SZ- Sa, between runs 2 and 3, and is considered less reliable. The occasional negative values for carbon disulfide and for carbon oxysulfide found in Tables IV, V, VI, and VI11 require explanation. When one of these constituents is present in amounts comparable t o the algebraic sum of the errors of the two determinations, the solution of the simultaneous equations may lead to a negative value for this constituent. For example, in test A (Table IV), SD = 0.0032 gram and So = -0.0003 gram. The total sulfur, SZ Sa (determined by combustion before and after absorption of carbon disulfide and carbon oxysulfide in alcoholic potassium hydroxide) equals 0.0029 gram, or SD SO.
-
+
EXPERIMENTAL RESULTS
PREPARATION OF COALSAMPLES. Desulfurization tests were conducted on three samples of coal, each prepared in size through 20- and on 35-Tyler mesh sieve series size. The first two samples were from the Pittsburgh bed, Shannopin mine, Greene County, Pa.; the third was from the Illinois No. 6 bed, No. 6 mine, Saline County, 111. The original coal samples from which the sized fractions were prepared were selected for their high-sulfur contents and should not be considered representative of the . average coal mined from these two beds. When the investigation was started, i t was believed that, even with the screened fraction, coking of the coal sample during the tests might interfere with gas passage through it. Therefore, the first sample of Pittsburgh bed coal was preheated in a rotary Fischer retort for 2 hours-the second hour a t 350' to 390" C.-to reduce its coking properties. Later it was found that this preheating was unnecessary. The percentages of sulfate, pyritic, organic, and total sulfur in the three sized samples as tested (16)were: 0.016, 0.869, 1.225, and 2.11 for the preheated Pittsburgh bed coal; 0.177, 1.145, 1.088, and 2.41 for the raw Pittsburgh bed coal; and 0.129, 2.120, 1.301, and 3.55 for the raw Illinois No. 6 bed coal.
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
2050 TABLEVIII.
Testn
Vol. 41, No. 9
COMPARISOS OF SULFUR DISTRIBUTION IN CARBONIZATION PRODCCTS OF ILLINOIS No. 6 BEDCOALAT 800" C. BY TREATMENTS WITH AMMONIA,HYDROGEN, -4ND NITROGEN As
Sulfur Distribution, Gram
-
As
In coke
In tar
hydrogen sulfide
As mercaptans
As thiophenes
carbon disulfide
0.2492 0.3302 0,3353 0.1747 0,2729 0.3127 0,2347 0.2354 0.1717 0.2174
0.0266 0.0171 0.0184 0.0389 0.0210 0.0331 0.0323 0.0482 0,0286 0.0482
0.2262 0,1736 0.1728 0.2803 0,1831 0.1760 0.2381 0.2241 0 2938 0,2362
0.0067 0.0061 0.0016 0.0317 0.0480 0,0020 0.0163 0,0153 0,0269 0.0220
0.0100 0.0011 0.0003 0.0151 0.0017 0.0010 0.0024 0.0030 0,0025 0.0046
0.0020 0.0004 0.0008 0.0021 0.0014 0.0010 0,0016 0,0040 0.0016 0.0041
As carbon oxysulfide Til
0.0025 0.0027 0.0001 0.0028 0 0027 0: 0002 -0.0006d -0.0002d -0.0005d
-
In residual gas 0.0001 0.0001 0.0004 0.0001 0,0002 0,0007 0.0003 0.0008 0.0004 0.0009
Su,lfur in Products, Sp Gram
Sujfur In Coal Gram
Gram
0.5197 0.5310 0.5323 0.5400 0.5311 0.5292 0 , 5255 0.5302 0,5253 0.6319
0.5325 0,5325 0.5326 0.5325 0,5326 0.5325 0.5325 0.5326 0.5325 0.5326
0.0128 0.0015 0.0002 - 0.0075 0.0014 0.0033 0.0070 0.0033 0.0072 0.0006
SO,'
So
- Sp,
Sulfur in Products,
% 97.5 99.7 100.0 101.4 99.7 99.4 98.7 9Q.6 98.6 9Y.9
a Tests R, S, T, and IJ made with ammonia tests R H SH TH, a n d U H with hydrogen a n d tests R N and SN with nitrogen Cokes from tests R , RH, R N , T, and T H k e r e cooleh t o b o r n temperature a n d used as samples in tests 8, SII, SN, U, and 'UH, respectively; data. represent both tests, based on coal sample. Ammonia gas started at 500O C.: time of passage was 2.25 hours in test T a n d 5.0 hours in test U. d Segative value for carbon oxysulfide results from solution of simultaneous equations used t o calculate test d a t a obtained in determinations of carbon disulfide and carbon oxysulfide. e Hydrogen gas started a t room temperature: time of passage was 3.25 hours in test TH and 7.0 hours in test UH.
SULFUR REXOVAL B Y h M i X 0 N I A TREBTIIENT. Tables I, 11, and 111 summarize the carbonization conditions of tests made with and without added ammonia gas and show the distribution of the original coal sulfur into the coke and volatile products from 15-gram samples of Pittsburgh bed preheated coal, Pittsburgh bed raw coal, and Illinois No. 6 bed raw coal, respectively, and from the cokes made from these coal samples. Three series of tests a t 700°, 800°, and 873" C. each were made on the first and third coals, arid one series a t 800" C. on the second coal. In each series, the first test was made on the coal sample without added ammonia, the second on the coal sample with addition of ammonia a t the reaction temperature, and the third on the coke sample froin the second or preceding test vith addition of ammonia a t the reaction temperature. The coke samples in all instances had been cooled to room temperature and were again heated to the reaction temperature before the addition of ammonia. Several special tests were made under modified conditions t o study certain factors. In test G (Table I ) the coke sample, produced under the same condition uced in test E, was crushed t o -20-mesh size before testing with ammonia. I n test T on coal and test C on coke (Table 111) the passage of ammonia was started a t 500" C. instead of 800" C. The percentage of sulfur in the volatile productp (column 11) for all tests is based on the weight of the original 15-gram coal sample. Reference to the data in Tables I, 11, and I11 for each reaction temperature shows that the percentage of sulfur in the volatile products is increased by treating the coal n i t h added ammonia. This desulfurizing effect is augmented by longer treatment of the coke with ammonia and is increased still further if the coke is crushed to a finer size before the ammonia is added. For example, in Table I the sulfur in the volatile products from test D on Pittsburgh bed preheated coal without ammonia is 48.170, that from test E on this coal with ammonia is 55.0%, that from test F on its lump coke Rith ammonia is 60.0%, and that from test G on its finely-crushed coke with ammonia is 62.3%. The percentage of sulfur in the volatile products is also increased if the passage of ammonia is started a t a lower temperature. This increase is illustrated in Table I11 for Illinois bed ram coal samples by tests T and R and for their coke samples by tests U and S. The percentage of sulfur in the volatile products was 55.9 in test T with ammonia started a t 500" C. as compared with 53.2% in test R with ammonia started a t 800 O C. A lower increase was observed from the coke samples used in tests U and 6 , with ammonia added a t 500" and 800" C., respectively, where the corresponding percentages of sulfur in the volatile products were 67.8 and 67.2. The increased desulfurizing effect with increased temperature is particularly marked when the tests are made a t 800 O C., as compared with tests made a t 700' C. .under otherwise similar conditions. Above 800" C. the desul-
furizing effect is not markedly changed; the percentages of sulfur in the volatile products from tests made a t 875' C. are not greatly different from those obtained a t 800" C. In all tests using added ammonia, except test L (Table 11), a greater proportion of the total sulfur of the coal sample appears in the volatile product,s than in the coke. Tables IV, V, and VI show the distribution of the va.rious types of sulfur cornpounds in Ihe carbonization products for the corresponding tests shown in Table I, 11, and 111. The percentages of total sulfur in the products of carbonization given in colunin 13 (Tables IV, V, and VI) are based on the total sulfur originally present in the coal sample. Considering the small amounts present of many of the sulfur compounds and the difficulties of their exact determinat,ions,the deviations from 100% in most instances are small. DEBTILFURIZATION WITH HYDROGEN AND NITROGENGASES. The marked effect of ammonia gas as a desulfurizing agent during the carbonization of coal suggests that ammonia must act in a different manner from that of a simple carrier gas. Conditions during the tests a t 800" C. were favorable for nearly complete decomposition of the ammonia into nascent hydrogen and nascent nitrogen. Nascent hydrogen, particularly, would be expected to react more completely than molecular hydrogen with the sulfur compounds in the coal to form volatile sulfur compounds and would thus reduce the amount of sulfur left in the coke. In order to establish the validity of this hypothesis, tests were made a t 800' C. with molecular hydrogen and with molecular nitrogen under conditions comparable to those used with ammonia gas. The apparatus was the same as illustrated in Figure 2, except that the absorber, 12, was omitted and the glycerol-filled flowmeter, 2, used for ammonia was replaced by a similar type, water-filled flowmeter calibrated for hydrogen or nitrogen. Separate flowmeters were used for these gases. Since two volumes of ammonia, upon complete decomposition, form three volumes of hydrogen and one volume of nitrogen or twice the initial volume, the rate of gas flow chosen for the tests with hydrogen and with nitrogen was practically twice that used in the tests with ammonia gas. In selecting this doubled rate of flow for hydrogen and for nitrogen, a deduct,ion was made for the small amount of total ammonia added that did not decompose in tests a t 800" C.-for example, the rate of passage of ammonia gas in test R a t 800" C. (Table 111) was 1.907 liters (N.T.P.) per hour of which 1.862 liters (N.T.P.) or 97.6% were decomposed into hydrogen and nit,rogen. Doubling this value, 1.862, gives 3.724 liters (S.T.P.) per hour. The rate of gas passage used in the tests with added hydrogen or nitrogen was 3.766 liters (N.T.P.) per hour, whioh checks well with 3.724 liters (S.T.P.) per hour. COMPARISON O F DESULFURIZING ACTIONOF AMMONIA,HYDROGEN, AND NITROGEN.Table VI1 summarizes the results of desul-
September 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
H
m
2051
are found in the tar and gases than do treatments under similar conditions with hydrogen and with nitrogen. As a consequence, the final cokes left after the tests contain less sulfur when ammonia gas is used as the desulfurizing agent. This distribution of cod sulfur is especially desirable when cokes of low-sulfur content are required. From Table VI11 it is observed further t h a t increased I I amounts of sulfur as carbon oxysulfide and of sulfur in the residual gas are formed by treatments with hydrogen (tests RH and SH) and with nitrogen (tests RN and SN) than by treatments with ammonia (tests R and S). Sulfur in these forms is particularly difficult t o remove during gas purification. Figure 4 shows the percentage distribution of the four principal forms of sulfur obtained in tests made a t 700', 800°,and 875" C. These percentages were calculated from the weights of these four forms of sulfur shown for the twenty-three tests summarized in Tables IV, V, and VI. The percentage of sulfur in the tar from test D using ammonia a t 800" C. (Table IV) was not determined. Figure 10 4 also shows the percentages of sulfur in the final coke from test G made on finely crushed coke (Table I ) after ammonia treatment a t 800" C., and in the h a 1 cokes from the Merramanr coal and coke samples (Table VII) after treatment with I I i ?OC 800 875 700 hydrogen a t 800" C. (tests RH and SH) and from the beCARBO1II2INO TEMPiRklTURE .C ginning of the tests a t room temperature (tests TH and Figure 4. Sulfur Distribution in Coke, Hydrogen Sulfide, UH), and after treatment with nitrogen at 800" C. (tests Tar, and Mercaptans R N ' a n d SN). Although the plotted data in Figure 4 show some apparently anomalous results, there are certain definite progressive trends in the proportionate distribution furization tests made by carbonizing Illinois No. 6 bed, No. 6 of the coal sulfur into the four principal forms of sulfur in the mine, raw coal at 800" C. and its lump coke with additions of carbonization products. I n general, increasing the temperature hydrogen and of nitrogen compared with results of similar tests from 700' t o 800" C. causes a marked decrease in the sulfur conmade with the addition of ammonia (tests R, S, T, and U, Table tent of the coke and a pronounced increase in the hydrogen sulfide 111). The gas used in each of the ten tests shown in Table VI1 sulfur in the gas. Beyond 800" C. these changes are less marked was added at a constant rate--1.907 liters (N.T.P.) per hour for and are sometimes reversed. This reversal is explained by the ammonia and 3.766 liters (N.T.P.) per hour each for hydrogen fact that above 800' C. hydrogen sulfide reacts appreciably with and nitrogen. Column 3 in this table shows the respective times hot coke t o fix more sulfur in the coke. Treatment of the coal in hours of passage of the gas used in tests R, RH, RN, S,SH, and and coke samples with ammonia gas usually magnifies the proSN. I n tests T and U the passage of ammonia was begun at 500' C. gressive trends for distribution of the sulfur in the coke and of or a t 1 hour after these tests were started. The total time of hydrogen sulfide in the gas. The desulfurizing effect of ammonia ammonia passage, therefore, in test T was 2.25 hours, or 1 hour gas above 800" C. becomes less effective because the decomposiless than the sum of the times shown in columns 2 and 3, and in tion of ammonia does not increase appreciably above this temtest U was 5.0 hours, or 2 hours less than the sum of these times. perature. Only small changes are observed with increased temIn tests T H and UH the passage of hydrogen was started a t room perature or with ammonia treatment for the sulfur in the tar. temperature when the tests were begun. The total time of hydroThe mercaptan sulfur shows a marked increase above 800" C. gen passage, therefore, was the sum of the times shown in columns and is much higher for the coal and coke samples from. the Pitts2 and 3-that is, 3.25 hours in test TH and 7.0 hours in test UH. burgh bed preheated coal than for those from the Illinois No. 6 The data in Table VI1 for each of the four series of tests show bed raw coal. The tests on Pittsburgh bed raw coal and its coke that treatment of the coal (or of coke from the previous test)with samples give much more sulfur in the coke and much less hydroadded ammonia, hydrogen, or nitrogen under comparable condigen sulfide sulfur in the gas than do the tests on samples from the tions a t 800' C. decrease in that order the proportion of sulfur in other two coals. The percentages of sulfur in the final cokes from the volatile products and increase the proportion of sulfur in the the Illinois No. 6 bed raw coal and its coke samples are decreased coke. I n other words, the desulfurizing action of ammonia is slightly and the percentages of hydrogen sulfide sulfur in the gas greater than that of hydrogen, and that of hydrogen is greater are increased slightly by starting the passage of ammonia gas a t than that of nitBogen. Furthermore, continued treatment of the 500' instead of at 800' C. The percentages of sulfur in the final coke from a previous test with the same gas increases the desulfurcokes from the coal and coke samples of the Illinois No. 6 bed izing action by causing more of the sulfur to appear in the volacoal after treatments with hydrogen and with nitrogen are shown tile products. This observation is illustrated by comparing tests on the vertical line a t the right of Figure 4. Hydrogen, when in.S and R for ammonia, SH and R H for hydrogen, SN and RN for troduced a t room temperature, is more effective than a t 800" C. nitrogen, U and T for ammonia, and U H and TH for hydrogen. in reducing the sulfur contents of the h a 1 cokes. The sulfur conStarting the gas addition a t a lower temperature also increases the tent of the final coke is greater when nitrogen is introduced a t .desulfurizing action, as shown by comparing tests T and R for 800" C. than when no nitrogen is introduced, probably because ammonia, T H and R H for hydrogen, U and S for ammonia, and of its diluting action on the carbonization gases. U H and T H for hydrogen. Figure 5 is a bar diagram showing the percentage distribution Table VI11 shows the distribution of the various forms of sulfur of coal sulfur in the various carbonization products. The data are compounds in the carbonization products for the tests shown in grouped according to test temperatures and show clearly t h e proTable VII. Comparison of these data indicates that treatment gressive changes in sulfur distribution effected by different treat.of the coal and coke samples at 800" C. with ammonia converts ments of the various coal and coke samples. I n addition t o t h e .more of the original coal sulfur t o volatile sulfur compounds that
i2
,
'
Vol. 41, No. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
2052
lid
1 2 3
3
700 i
123
I
123
c 800 c 875 c , 800 c , 700 c. - - 7~
+--
prehea e C a
Figure 5.
12435 123 8orc 875 c.
e:
Pltrburgh
0-1
6 7 8 9 1011 BCZC
eoo'c
Y--1IlI"C 5 IS
,
COII
Sulfur Distribution in Various Carbonization Products
____ + KHs
1 rnni _.
Coal Coke Coal 5. Coke 6. Coal 7. Coal 8. Coke 9. Coke 10. Coal 11. Coke 2. 3. 4.
KHa ++ at 500' C. ++ NHs NIIs at 50Q0 C. I1
+ a t room temperature + Hz Hz + I12 a t room temperature +Nz + N?
principal distributions of coal sulfur into the coko and tar and as hydrogen sulfide and mercaptans in the gas, Figure 5 shows by difference for each test the approxiniate suin of the percentages of sulfur as thiophenes, carbon disulfidc, carbon oxysulfide, and residual sulfur in the gas. The latter data were not plotted for three tests which, without including these four minor forms of sulfur, gave a sulfur balance of more than 100%. -4ctual evperimeiital sulfur baIances, expressed in percentages, for each of the twentynine tests shown in Figure 5 , are given in the last column of Tables IV, V, VI, and VIII.
test and 83 for the 4-hour test as compared with 55.8 for the I .5hour test and 59.2 for the 3.5-hour test in the present work. The quant'ity of coal sulfur originally present appears to be t factor in it's eonversion to volatile sulfur compounds. Test Q (Table 111) on Illinois No. 6 bed raw coal containing 3.55% sulfur and t'est K (Table 11) on Pittsburgh bed raw coal containing 2.41% sulfur, both made a t 800" C. wit.hout added gas, gave percentage conversions t o volatile sulfur compounds of 46.7 and 39.4. respectively. Evans ( 2 ) also found that the higher sulfur coals tend to produce high-sulfur-containing gases and that the rank o! the coal and its pyritic sulfur content both appear to havr L marked effect on the total yield of organic sulfur compounds and on their relative proportions in the gas. The yield of carbon osysulfide, in particular, from mela-lignitious coal (80 to 84% dry, a.sh-free carbon) was higher than from a bituminous coal of equivalent sulfur content. Indian coals of high-sulfur content and having a very high proportion of organic sulfur are under study by the authors to determine the effect of the ratio of organic to inorganic sulfur io the coal on the conversion of the total coal sulfur t o volnt,ilc sulfur compounds in the gas. IPECQMPOSITIOR~O F AM&PONIA GAS BY HOT COKh
Ammonia gas, x-heii brought in contact with hot coke at 700" C or higher, undergoes marked decomposition into nabcent hydrogen and nascent nitrogen. These reactive gases, temporarily in monatomic form, caube a greater proportion of the coal sulfur during t h e carbonization of coal to pass into the volatile product,. than into the coke. This desulfurizing action on heated coal OF coke is appreciably greater than that obtained by the addition of ?. simple carrier gas under similar test conditions.
COMPARISON WITH WORK OF OTHERS
Tests TH and UH (Tables VI1 arid VIII) made with hydrogen gas added throughout the heating period from room temperature to the end of the tests may be compared with two tests conducted by Snow ( 1 4 ) under somewhat similar conditions. Coal samples from the same Illinois KO.6 bed, but from different counties in Illinois, and of like weight (15 giams) and of the same size range (20- t o 35-Tyler mesh) were used in the two investigations. The Saline County, Ill., coal used in the authors' work contained 3.55% of total sulfur (0.13 sulfate, 2.12 pyritic, and 1.30 organic), whereas the Christian County, Ill., coal used by Snow contained 5.34% of total sulfur (0.20 sulfate, 2 51 pyritic, and 2.63 organic). Hydrogen gas was passed in during the 1.75-hour heating-up period from room temperature t o the reaction temperature, 800' C , in each of the four tests. Hydrogen was added at the reaction temperature for 1.5 hours in test TH and for 3.5 hours in test UH, as compared with 1 hour and 4 hours in Snow's tests. The corresponding weight percentages of volatile products produced in the four tests were 34.6, 38.6, 37, and 41. The chief difference in test conditions was that hydrogen passage was a t a rate of 3.766 (N.T.P.) liters per hour in the present work and at 12 liters per hour in Snow's tests. The higher rate of hydrogen passage aided t o some extent by the higher original content of coal sulfur in the coal used by Snow (and possibly by the 0.5 hour longer time of his 4-hour test) increased the percentages of sulfur in the volatile products, a5 compared with corresponding tests in t h e present investigation. Percentages of sulfur in the volatile products a t 800" C. obtained by Snow -were 62.5 for the 1-hour
6 0 L - 1 -
650
700
1_i__ I L, 750
aoo
a50
goo
TEhlP'RATUHE 'C
Figure 6. Decomposition of .&rnmoniaGas by Hot Cokes
Figure 6 shows the percentage clecomposition of ammonia gas. a t 700", 800", and 875" C. when passed through the hot cokes made from Pittsburgh bed preheated coal samples (tests €3, E, and I, Table I ) and the hot cokes made from Illinois No. 6 bed coai samples (tests 0, R, and TI7, Table 111). The curve for Lower Silesian coke, included for comparison in Figure 6, is based on data obtained by Simmersbach ( 1 2 ) . The contact times botween gas and coke in the present work and in Simmersbach's investlgation are comparable at the several temperatures over the r a n g studied. Figure 6 shows that the rate of dccomposit#ionof arnmania above 800" C. does not change appreciably. As pointed out above, the dejulfurizing action of added ammonia gas during the carbonization of coal also does not appreciably change above 800' C., so that this temperature appears to be the practical maximum limit rcquired for most, effective desulfurimtion. ACKNOWLEDGMENTS
The authors arc indebted to 0. T. Barrett, A. L. Bailey, arid F. F. Giese, who sampled the coals a t the mines, and to H. M Cooper and R. F. Abernethy, under whose supervision xere r n m k
September 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
all analyses of the coal, coke, and tar samples in the present investigation. LITERATURE ClTED Am. Soc. Testing Materials, “Tentative Methodof Teet for Sulfur in Petroleum Oils by Lamp Method,” Designation D 90-46T. (2) Evans, C. L., Gus J.,244, 545-7 (1944). (3) Gluud, W., and Jacobson, D. L.,,,“International Handbook of the By-product Coke Industry, Am. ed., pp. 119-27, 429-34, New York, The Chemical Catalog Co., 1932. (4) Groves, C. E., and Thorp, Wm., “Chemical Technology,” Vol. 1, pp. 123-5, London, J. &A. Churchill, Ltd., 1889. ‘5) Hakewill, H., and Rueck, E. M., Am. Gas Asaoc. Proc., 28, 62938 (1946). ( 6 ) Himus, G . W., and Egerton, A. C., Iron & Coal Trades Rev., 138, 663-4 (1939). (7) Hutchison, W . K., Inst. Gus Engra., Commun. No. 175, Appendix I, 323-6 (1937). (8) Muhlert, F., “Der Kohlenschwefel,” pp. 65-72, Halle (Saale), Wilhelm Knapp, 1930. II)
2053
(9) Powell, A. R., and Thompson, J. H., Carnegie Inst. Technol., COOP.BUZZ.7, 1-12 (1923). (10) Riesz, C. H., and Wohlberg, W., Am. Gas Assoc. Proc., 25, 25970 (1943). (11) Shaw, J . A . , IND.,ENO. CHEM.,ANAL.ED., 12,668-71 (1940). (12) Simmersbaoh,O., Stuhl u. Eisen, 34, 1153-9,1209-13 (1914). (13) Simmersbach, O., and Schneider, G., “Grundlagen der Koksohemie,” 3rd ed., pp. 177-86, Berlin, Julius Springer, 1930. (14) Snow, R. D., IND. ENQ.CHEM.,24,903-9 (1932). (15) Stanton, F. M., Fieldner, A. C . , and Selvig, W. A , , U.S. BUT. Mines Tech. Paper 8, 59 pp. (1939). (16) Thiessen, G., “Chemistry of Coal Utilization,” H. H. Lowry, ed., Vol. 1, chap. 12, pp. 425-49, New York, John Wiley & Sons, Inc., 1945. (17) Wilson, C. W., IND.ENQ.CHEM., ANAL.ED.,5, 20-2 (1933). RECEIVED September 30, 1948. Presented before the Division of Gas and Fuel Chemistry at the 114th Meeting of the AMERICAN CHEMIOAL Soarm St. Louis, Mo.
Representation of Viscosity-Temperature Characteristics of Lubricating Oils J. H. RAMSER The Atlantic Refining Company, Philadelphia, P a . o n the basis of a general functional relation between viscosity and temperature, it is shown by mathematical reasoning that the viscosity index and the A.S.T.M. slope are not unique measures of the fractional change of viscosity with temperature because the viscosity enters the derived relations as an independent variable. The properties of the average fractional change of viscosity, computed over comparable sections of the viscositytemperature curve and between constant temperature
limits, respectively, are discussed. Comparable sections are defined on the basis of the mathematical notion of curvature. The point at which the curvature of the viscosity-temperature curve is a maximum was calculated for a wide range of oils. I t was found that the absolute change of viscosity with temperature has a constant value at this point. A measure of viscosity-temperature characteristics, viscosity-temperature rating, is proposed for evaluation of oils under actual operating conditions.
B
The existence of different indexes for what appears t o be one and the same “property” of an oil raises the question, t o what extent do the various proposed indexes actually represent the true variation of viscosity with temperature. Next to viscosity level, the true variation of viscosity with temperature is the most important property of lubricating oils. The existence of different indexes for the same property raises the further question as to the manner in which the various indexes are quantitatively related t o each other. These two problems may be dealt with in a rigorous fashion by starting from a generally valid mathematical relation between viscosity and temperature. By differentiating viscosity with respect to temperature, a relation between the actual change of viscosity with temperature as a function of temperature and other parameters may be obtained. The defining equations for the various measures of viscosity-temperature behavior may then be substituted in this function, with the result t h a t a quantitative rela. tion between the actual change of viscosity with temperature and the various measures of viscosity-temperature behavior is obtained. The result of this method of approach is the proof that the absolute or the fractional change of viscosity with temperature cannot be represented by a single index such as the viscosity index or the A.S.T.M. slope. It will furthermore be shown t h a t the representation of the true variation of viscosity with temperature requires two parameters which must be independent of one another. One of these parameters may be any one of the various
ECAUSE the viscosity-temperature characteristics of lubri-
D
c
cating oils are of considerable practical importance, many attempts have been made to represent them by a single “index,” which may be used as a measure of the viscosity-temperature relation irrespective of the viscosity level of the oil. Some of the proposed indexes seem to satisfy this requirement over a comparatively limited range of viscosity; however, if the viscosity range is suficiently extended t o lower or higher viscosities, i t becomes apparent that none of the indexes used at the present time is strictly independent of viscosity level. This is a n undesirable feature, for the significance of any measure of viscosity-temperature behavior becomes obscured if i t simultaneously depends on viscosity level. A well known example of a measure of viscosity-temperature behavior, which is satisfactory within a certain range of viscosities but inadequate outside this range, is the viscosity index proposed by Dean and Davis (@-4). The shortcomings of the viscosity index were discussed by Larson and Schwaderer (7) and by Hardiman and Nissan (6). The latter authors extended the useful range of the viscosity index by devising a new basis for the viscosity index system. I n addition to the viscosity index, a variety of other indexes for the representation of the viscosity-temperature characteristics of lubricating and hydraulic oils have been proposed. These indude the A.S.T.M. slope ( I ) , the viscosity pole height (II), the viscosity-temperature coefficient (Id), and the viscosity-temperature number (8).
