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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
for each plant of a research laboratory for t h e solution of t h e problems of t h e specific industry. Such a laboratory will bring t h e chemical department of t h e Institute into most intimate touch with t h e problems of applied chemistry. T h a t the return t o t h e industries will be adequate is promised b y the success not only of the research laboratories in many of our industries b u t of the Research Laboratory of Applied Chemistry a t t h e Institute itself, t h e Director of which, Dr. Wm. H. TTTalker, is t o he in charge of this new
Vol. 8, NO. 9
school. More intimate contact of t h e University with Industry could not possibly be attained, and t h e advantages of t h e reflex action of this contact upon both may surely be anticipated. The Institute and the country a t large owe much t o iifr. Arthur D. Little for this reduction t o practice of the hitherto unworlted theory of cooperation between the Unilyersity and Industry. WARRENK. L E W I S BOSTON, MASSACHDSETTS
ORIGINAL PAPERS LABORATORY INVESTIGATIONS CONCERNING THE REDUCTION OF BARIUM SULFATE TO BARIUM SULFIDE’ By ARTHURE. WELLS Received July 3 , 1916
The necessity of having more exact information t h a n was available in t h e literature on the subject, concerning the reduction of barium sulfate t o sulfide, arose in connection with a critical study of t h e Wet Thiogen Process2 for t h e recovery of elemental sulfur from smelter gases. The study of -this process was undertaken b y the Bureau of Mines in cooperation with the Thiogen Company, forming a part of t h e general program of t h e work carried out in t h e Cooperative IIetallurgical Exhibit Laboratory a t t h e Panama-Pacific International Exposition,3 which dealt with the, general problem of elimination of waste in smelting operations. At t h e close of t h e Exposition this laboratory inrestigation was continued in t h e Bureau of l l i n e s laboratory in the Hearst hlining Building, a t t h e University of California, Berkeley. Stated briefly, the Wet Thiogen ,Process involves t h e recovery of t h e sulfur dioxide from smelter gases b y passing them u p through absorption towers, in which a descending “mother liquor” solution absorbs t h e sulfur dioxide. Barium sulfide is added t o t h e solution of sulfur dioxide and a precipitate, consisting of barium thiosulfate, barium sulfite and sulfur, is thrown out. This precipitate is filtered and t h e elemental sulfur, with one-half of t h e sulfur from the thiosulfate, is distilled: leaving a residue of barium sulfite and some sulfate. This residue is t h e n reduced t o sulfide and the barium sulfide used. again for precipitation, the barium thus being kept in circulation through cycles. I n order t h a t the barium shall be most efficient as a .precipitant during these cycles, it is very necessary t h a t t h e maximum reduction of t h e sulfite or sulfate t o t h e water-soluble sulfide be attained in each cycle. Thus, it was very necessary t o determine the conditions Tinder which the barium sulfite or sulfate was reduced most completely t o t h e sulfide, and considerable experime;tal work has been conducted on t h a t problem. -4s barium sulfate must be used a t the start 1 Published by permission of the Director of the Bureau of Mines and the Thiogen Company. 2 “Metallurgical Smoke,” by Charles H. Fulton, Bureau of Mines, Bull. 84, 74-77, a “The Cooperative Metallurgical Exhibit a t the Panama-Pacific International Exposition,” by G. H. Clevenger and A . E. Wells, M e t . 5 Chcm. Eng., 13 (1915). 743.
in t h e initial reduction, and was present t o a large extent in all precipitates after distillation, and also, as this material could be obtained in quantities much more readily t h a n the sulfite, the greater part of these investigations were concerned with t h e reduction of the sulfate. This is a problem t h a t , aside from its applicability t o t h e Tliiogen Process, is of general interest, and especially t o those who are engaged in the manufacture of barium salts. While i t is true t h a t in these investigations most of t h e reduction tests were conducted with a much purer grade of barium sulfate t h a n is generally used by the manufacturers of barium salts, yet i t is felt t h a t some of the d a t a obtained in these tests are of such general application t h a t a brief presentation of these d a t a may be of possible value a t this time when considerable attention is being devoted t o t h c manufacture of barium salts. In this paper only t h e d a t a concerning t h e first reduction of barium sulfate will be discussed. It: order t o fully understand the d a t a concerning t h e reduction of t h e products from cyclic operations. it would be necessary t o go into a discussion of t h e action of the reduced barium compounds as a precipitant in t h e Thiogen Process cycles, and as such discussion is reserved for another paper, the d a t a concerning the cyclic reductions are also reserved for t h a t paper. I n answer t o several inquiries concerning what was being accomplished a t the present time in t h e reduction of barium sulfate a t various plants where barium salts mere being manufactured from barium sulfate, the information was gained t h a t although 80 or 8 5 per cent of the barium was readily reduced t o acid-soluble compounds, yet current practices rarely reduced more t h a n 60 or 70 per cent of the barium t o water-soluble barium sulfide. The literature verified these statements.l The barium compounds found in the reduced products are classified in this discussion as follows: I Readily Soluble in Hot Water BaS
Bas, BaO
I1 Difficultly Soluble in H o t Water but Soluble in Dilute HC1 BaO BaCOa Bas BaSiOa Traces of BaSOs
111 Insoluble in Acid BaSOd
“.Mineral Industry,” Vol. 19. Schuyler-Frazier, “Calcining Plant for Barium Sulfate.” A. H. Fay, “Roasting Barytes.” Maximilian Toch, “The Barium Industry in the United States since the European War,” M e t . &rChem. Eng., 14 (1916). 4 i . 1
T H E J O U R N A L OF I N D C ' S T R I A L A N D ENGINEERING C H E M I S T R Y
Sept., 1916 I-
W A T E R - S O LU B L E B A R I U M
T h e reduced product, ground t o I O O mesh, was leached in a flask with 2j0 parts water, j u s t below boiling, and filtered into a flask which was tightly stoppered while t h e solution was cooling. -4n aliquot p a r t of t h e solution was t h e n titrated with iodine. a n d in another aliquot p a r t barium a n d sulfur were determined. As a check for t h e iodine value, i . e., t h e barium sulfide content, t h e material was frequently treated directly in a flask with excess iodine for about j min., a n d t h e n t h e excess iodine determined. I n many cases there was barium oxide present in t h e water solution. I n other products there was a slight excess of sulfur over t h a t required for t h e barium t o form sulfide, indicating a polysulfide. I n sereral products of reductions a t high t e m peratures ( ~ o j o t o 1200' C.), where excess carbon was present. t h e presence of t h e carbide was indicated but was not determined quantitatively. 11-BARIUM
COMPOUNDS
SOLUBLE
IN
HOT
SPARINGLY
WATER,
BUT
SOLUBLE
OR
SOLUBLE
IiX
IN-
D I L U T E ACID
I n many products from t h e first reduction, a large portion of t h e oxide present was very sparingly soluble in hot water. b u t was soluble in dilute hydrochloric acid. I n most products of t h e reductions which were effected in a direct fired furnace a t high temperatures a n d where slight sintering h a d taken place, a small amount of the sulfide was found t o be in t h e waterinsoluble portion. I n some products, from 4 t o 6 per cent of t h e total sulfide was found to be sparingly soluble in water. The solubility of this material was incr?ased somewhat by finer grinding. I n a typical average product from t h e first reduction of barium sulfate, 9 ; per cent of t h e sulfide a n d 40 per cent of t h e oxide were readily soluble in hot water, t h e rest being found in t h e acid-soluble portion. I n this water-insoluble, b u t acid-soluble, portion was also found t h e carbonate in varying amounts. T h e products from slow reductions, a t low temperatures, contained more carbonate t h a n did those from rapid reductions a t high temperatures. Very few products contained more t h a n a trace of t h e sulfite or thionates. The reduction tests here discussed will be considered under five series. S E R I E S I-TESTS
TO DETERMINE T H E RELATIVE RATES
O F R E D U C T I O X O F B A R I U M S U L F A T E B Y HYDROGEP-, C A R B O S MONOXIDE, AKD A MIXTURE OF T H E S E
GASES
WITH
OTHER
HYDROCARBONS
AT
D I FF E R E K T T E M P E R A T U R E S
I n these tests precipitated barium sulfate ( 9 9 + per cent BaS04) was placed in a quartz t u b e of about 1 2 mm. (0.47 in.) diameter, a n d heated in a n electrically heated t u b e furnace. The barium sulfate was placed between two asbestos plugs, filling t h e t u b e for a distance of about 30 mm. ( I . 18 in.), b u t was sufficiently loose t o allow t h e passage of gases through t h e material. The gases were passed through t h e
771
tube a t t h e rate of about 2 cc. per min. The d a t a obtained probably did not represent t h e chemical equilibrium a t a n y temperature. The comparative rate of reaction a t different temperatures was obtained, however, as were d a t a concerning the character of t h e gaseous products. REDUCTION W I T H HYDROGES-m'hen hydrogen was reduced as t h e reducing agent, there was practically no reaction a t a n y temperature below j j o ' C. Around 600' C., t h e reaction was extremely slow, less t h a n 5 per cent of t h e hydrogen passing through t h e plug, reacting. T h e gaseous product contained considerable hydrogen sulfide. At 6 joo C., about I j per cent, a n d a t 700' C., about 3 5 per'cent of t h e hydrogen reacted. Between 600 a n d 700' C., t h e amount of hydrogen sulfide formed was a maximum. At 800' C., practically all t h e hydrogen had reacted a n d very little hydrogen sulfide was present in t h e gaseous product. I n general, these d a t a checked those of a previous investigation.' I n t h e products from these reductions with hydrogen, t h e ratio of sulfur t o barium was less t h a n one a t o m of sulfur t o one a t o m of barium. If t h e reductions were effected slowly a t lower temperatures (between 600' a n d 750' C.), t h e loss of sulfur was greater t h a n if t h e reductions were effected more rapidly a t higher temperatures (900 t o 1000' C.). I n one test lasting for a n hour a t 1000' C., 9 4 . 0 per cent of t h e sulfate was reduced t o sulfide a n d 6 . 0 per cent t o oxide. This was t h e maximum reduction obtained using hydrogen. I n some correlated tests, i t was found t h a t , between 700 a n d gooo C., water vapor reacts slowly with barium sulfide, forming sulfur dioxide. hydrogen sulfide a n d barium oxide. For example, through a reduced product of ab'out 2 0 mesh size, containing 89 per cent of t h e barium as sulfide, 7 per cent as oxide a n d carbonate, and 4 per cent as sulfate, was passed, a t 900' C., a mixture of about 16 per cent water vapor a n d 84 per cent nitrogen; about I per cent af t h e water vapor reacted, forming nearly two volumes of sulfur dioxide per volume of hydrogen sulfide. T h e reaction between water vapor a n d barium sulfide at other temperatures was not determined. REDUCTIOX W I T H CARBON M O N O X I D E - w i t h carbon monoxide t h e reduction was very slow below 6jo' C., a n d was fairly rapid a t 750' C., about 70 per cent of t h e carbon monoxide reacting. With temperatures u p t o 900" C., however, there was present in t h e gaseous product some unconsumed carbon monoxide. Above t h a t temperature t h e gaseous product was almost entirely carbon monoxide. I n these reduced products t h e ratio of sulfur t o barium was slightly less t h a n I : I , showing t h a t some sulfur h a d been removed in t h e gaseous products. I n this series as in tests with hydrogen as t h e reducing gas, t h e loss of sulfur was less in t h e cases where reduction was effected rapidly a t higher temperatures (above 900' C . ) , t h a n when effected slowly a t lower temperatures. Thus, t h e products of reduction effected rapidly a t
"Reduction of Sulfate of Alkaline Earths with Various Gases," I,. Marino, R. University of Pisa, Gakz. cham. iial., 43 [ I ] , 416-22. Chem. Abs., 7 (1913), 3202.
T H E JOL-RA'AL O F I i V D U S T R I A L . 4 S D ESGIiYEERIA'G C H E M I S T R Y
772
high temperatures contained the smaller percentages of mater-insoluble barium oxide. R E D U C T I O N S KITIT C I T Y GAS-A series of 2 0 reductions was made, in which an excess of city gas of approximately the following composition was passed a t the rate of z cc. per min. through the charge in the quartz tube: CzHa 6.4
CHa 30.4
CO 13.4
H?
41.4
COa 4.0
h-2 4.2
TOTAL
0 2
0.2
100.0percent
The d a t a obtained are given in Table I . The percentage of barium in the product present in viaterinsoluble, b u t acid-soluble. compounds was less when TABLE I-REDUCTION O F PRECIPITATED BARIUMSULFATE
BY
CITY GAS
IK QU.4RTz T U B E ,EXTERNALLY HEATED PERCEXT O F TOTAL B a I N PRODUCT
PRESENT AS Temperature
c.
650-700 700-750
750-800 800-850 850-900 900-950 950--1000 1000-1050
Time Mi11
fin .. 240 330 60 240 60 240 60
240 60 240 60 I20 240 60 120 240 60 120 240
n'atersoluble BaS and BaO 2.5 58.0 72.5 8.5 75.0 20.6 88.2 50.8 91.5 55.5 91.8 65.2 85.0 92.5 74.7 91.5 93.2 85.2 92.0 93.0
Water-insoluble but Acidsoluble BaO and BaCO3 4.0 15.8 18.2 6.8 13.8 8.4 11.0 7.8 8.3 6.8 8.0 6.2 7.3 7.5 4.8 6.5 6.8 5.0 6.5 i.0
Acidinsoluble Bas04 93.5 26.2 9.3 84.7 11.2 71.0 0.8 41.4 0,: 37.) 0.2 28.6 1 . 6
0.0 20.5 2 0
o n 9.8
1.5 0 0
reductions were effected in a short period of time a t temperatures above goo0 C., t h a n if effected over a longer period of time a t lower temperatures; e . g., compare t h e products obtained when the material was treated for 3 3 0 min. a t 650 t o 700' C.. Kith those obtained in a reduction of 1000 to 1050' C., lasting only 60 min. Any tendency for a reaction between t h e reducing gases a n d the reduced sulfide, resulting in t h e formation of water-insoluble barium compounds. is slight; e. g . , compare the proportion of these compounds in the products of reductions a t 900 t o 10joO C. for 60, 1 2 0 and 240 min. S E R I E S 2--REDUCTIOS
OB B A R I U N S U L % A T E BY C A R B O N
I n these tests, finely pulverized carbon, either coke or charcoal, was intimately mixed with t h e barium sulfate, and heated for x-arying periods of time a t different temperatures, in crucibles or tubes placed in muffle furnaces. The theoretical amount of carbon required for the reduction is 1 0 . 3 per cent of the weight of B a S 0 4 , if t h e carbon is completely oxidized t o COz, or 2 0 . 6 per cent if the carbon is oxidized only t o CO. I n these tests, the carbon added T-aried between I O and 40 per cent of the BaS04. The temperature range was between 7 0 0 and 1250' C. The time allowed for reduction varied betvieen 1 5 and 360 min. In all b u t a few of the tests where the time allowed for reduction mas an hour or more: t h e mixtures! weighing from j o t o I O O g., were placed in I O - or 20-g. fire clay crucibles and heated in a muffle furnace. The muffle had been heated t o the required temperature
Yol. 8, S o . 9
before placing the crucibles in i t , and thus the crucibles and charge mere heated u p quickly. When the time allowed for reduction mas less t h a n I h r . , i; ITas rather difficult t o get satisfactorily concordant d a t a with this size of charge and method of heating. I n order t o reduce the "heating up" period t o a minimum. these reductions were made with much s m d l e r charges ( j t o I O g . ) , in porcelain crucibles. I n Table I 1 most of the temperatures recorded were measured near the crucibles during the period of reduction. Several, however, were measured in the charge itself, after it had come t o the temperature of t h e muffie, but care was taken t o have the heating of the muffie so regulated t h a t t h e temperatures did not 1-ary more t h a n I j or 20' C. either way from t h a t desired; thus, a temperature of 700' C. means between 680 and 7 2 0 ' C . ! sufficiently close for t h e purposes of these investigations. As, in these reductions, it was very important t o keep the air from coming into contact with t h e material as far as possible, the crucibles were covered with a clay cover ground t o fit. I n some tests a charcoal cover about 2 mm. ( 0 . 0 4 in.) thick, was placed on the charge. Even with the tight covering! in some of the tests, there was a slight reversion of the sulfide t o the sulfate, due possibly t o a slight porosity of the crucible malls allowing air t o pass through. Some of the data concerning this reversion will be given later. I n Table I 1 are summarized the results of 76 tests made under conditions which were quite similar, so t h a t the results are comparable. The barium suifate used was the precipitated material. T h e carbon TABLE
11-REDUCTION OF BARIUMSULFATE
BY
CARBON
PERCENTTOTAL BARIUMIN PRODUCT IN FORM OB: Soluble in Dilute HCI Water-soluble Barium Sulfide Min. 700'C. 750 800 850 900 950
15
.. .. ..
48
,.
30 60 12 26 29 35 51 61 58 69 65 85 76 89
90 120 240 360 28 41 65 7 7 55 59 78 . . 63 68 82 . , 78 85 86 . . 87 88 , , . 92 95 . , . .
15
.. .. ..
54
30 21 38 57 65 72
60 37 47 70 78 94 94
..
80
80
89 100
98100
90 40 69 75 87 97 97
., .. ..
720 240 360 54 80 93 73 93 , . 85 98 . . 94 98 , 99 100
,
.
, .
.. ..
., ..
added was 20.6 per cent of t h e weight of t h e barium sulfate; i t was pulverized t o pass a 160-mesh screen and mixed with sulfate until t h e mixture looked homogeneous t o t h e naked eye. T h e variables were the time allowed for reduction and t h e temperatures. Many of the figures given are t h e average of several determinations t h a t in most cases gave concordant results. I n the products of reduction effected a t the lower temperatures over a longer period of time, t h e difference between t h e acid-soluble barium compounds and t h e water-soluble barium sulfide is less in the reductions a t higher temperatures for a short period of time, t h a n in those a t lower temperatures over longer periods. Most o l the products contained excess carbon. Other series of tests were made t o determine t o what extent a decrease in t h e amount of carbon present in the charge affected the reduction. When t h e tests were made in porcelain crucibles fitted with an ordinary porcelain cover, there was al-
Sept., 1916
T H E J O r R N A L O F I N D U S T R I A L A N D E S G I N E E RI N G C H E M I S T R Y
ways sufficient air leaking into t h e crucible either t o burn a small percentage of t h e carbon, or t o reoxidize a small amount of t h e reduced sulfide back to t h e sulfate. As t h e d a t a froin these tests are, therefore, not quite accurate, t h e y are not included in this paper. Similar reductions were repeated in porcelain crucibles, when a light layer of carbon was placed on t o p of t h e charge and other precautions t a k e n t o keep t h e air from coming into contact with t h e charge during cooling, etc. d l t h o u g h t h e carbon cover did have some slight reducing action on t h e charge, i t was decided t h a t t h e d a t a obtained were sufficiently accurate for recording in this paper, a n d t h e y are given in Table 111. TABLE 111-REDUCTION 08 B 4 R I U M SLLFATEA T DIFFERENTTEMPERATURES I N PORCELAIN CRUCIBLES WITH VARIABLE AMOUNTS OF CARBON IN THE MIXTCRES Carbon Per cent Per cent Per,Cent of Total of Total of Bas04 Per Cent Time Carbon Barium in Product Carbon Reduced c. Min. to BaSOa Bas Acid-sol. Insol. Consumed to Bas 42 69 800 60 10.5 50 58 14.5 44 49 56 21.0 20.2 51 800 30 83 14.2 120 10.5 62 70 32 65 20.5 21 . 0 65 66 13.2 850 30 86 60 10.5 70 66 35 65 65 16.8 15.5 60 i0 58 19.8 30 20.5 60 850 15 97 120 i8 85 12.9 10.3 17.0 18 84 76 82 15.5 19.4 74 20 70 20.6 80 900 60 15 100 12.9 85 10.3 80 83 17 87 16.7 15.3 81 76 80 19.4 20 72 20.6 900 120 86 14 100 10.3 80 12.9 16.5 90 10 89 15.5 84 83 13 80 8i 20.6 19.8 950 12.5 30 80 li 100 83 10.3 8i 19.0 i8 84 13 20.6 950 60 79 78 21 59 40.0 94 97 3 100 10.3 12.8 20.6 20.2 96 95 4 93 18 61 30.0 23.4 82 82 I050 30 10.3 82 14 100 86 11.2(a) 2 100 15,,5 96 96 16.1 96 4 89 20.6 95 18.) 1150 20 10.3 90 90 10 100 11.5 99 1 100 15.5 99 15.6 0 90 100 20.6 99 18.2 (a) This carbon consumption factor is probably slightly low due to a slight reduction action of the carbon cover.
Temp.
Later reduction tests, effected in an atmosphere of nitrogen, i. e . , in an atmosphere neither oxidizing or reducing, gave results t h a t checked t h e abovementioned d a t a fairly closely. I n another set of reduction tests t h e barium sulfate was mixed intimately with finely pulverized carbon a n d placed in a porcelain t u b e , in a n electrically heated t u b e furnace. The t u b e was filled with nitrogen gas a t the s t a r t . a n d t h e gases evolved were discharged through a water seal. or into caustic potash solutions. Thus, neither oxygen nor any reducing gases other t h a n t h e carbon monoxide from the carbon came in contact with t h e BaSO?. From t h e d a t a in Table I V it is t o be noted t h a t t h e carbon efficiency was greatest when t h e charge contained t h e smallest percentage of carbon, a n d t h e efficiency decreased with an increase in t h e amount of carbon present. I n general, somewhat higher carbon efficiency was obtained in t h e reductions effected a t t h e higher temperatures t h a n a t t h e lower. Although t h e highest carbon efficiency (about 1 2 . 0 t o 1 2 . j per cent) was obtained when t h e carbon present was about I O per cent of the barium
773
sulfate (the theoretical amount if t h e carbon oxidized completely t o C 0 2 ) , yet with this amount of carbon t h e maximum reduction of t h e barium sulfate a t temperatures u p t o 1000' C. was only about 80 t o 8 j per cent. Between 900 and 1000' C., nearly complete reduction was obtained with a carbon consumption of about 1 4 t o ~j per cent. When t h e carbon was present t o t h e extent of 20 per cent of t h e BaS04, t h e carbon efficiency was much lower, irrespective of whether t h e reduction was a t high or low temperatures, b u t was slightly higher a t t h e high temperatures t h a n a t t h e low. JT7ith a n excess of carbon, t h e reduction seemed t o proceed slightly slower t h a n with t h e lesser amount of carbon present. This is shown especially in t h e series a t 8 j 0 , 900 and 950' C. in Table 111. However, it must be recognized t h a t t h e degree of fineness t o which t h e material is pulverized, t h e intimacy with which t h e sulfate a n d carbon are mixed, and t h e depth of material through which t h e carbon monoxide gas must pass before leaving t h e charge, are factors influencing these figures; e. g., in several tests, straight barium sulfate was placed on t o p of t h e charge containing 20 per cent carbon. This barium sulfate cover was quite largely reduced b y t h e carbon monoxide coming u p from t h e charge proper, t h u s increasing t h e efficiency of t h e carbon when credited with t h e whole amount of barium reduced. Summarized briefly, t h e d a t a from Series z show t h a t when t h e carbon a n d barium sulfate are finely pulverized a n d intimately mixed, a n d t h e reduction is effected in a muffle or crucible type of furnace in absence of outside air or products of combustion of fuel, a n d a t temperatures between 8 j o a n d 1000' C . , a high reduction (go per cent or better) can be obtained when t h e carbon added is about ~j per cent of t h e barium sulfate. While t h e efficiency is greater with t h e addition of less carbon, t h e reduction is not so complete. With more t h a n I j per cent carbon, t h e carbon efficiency decreases, unless provision is made t o utilize t h e carbon monoxide issuing from t h e charge, by passing i t through another charge of barium sulfate. TABLEIV-REDUCTION
OF
BARIUM SULFATE BY CARBON IN TUBEFURNACE, ATMOSPHERE OF NITROGBN
SURROUNDBD BY
Carbon - .. ..~.
Temp. "C 800
900 9 50
Per Cent Carbon to Bas04 in Charge 10 10 20 10 10 10 10 15 14
1000
15 10 15 20
Per Cent of Total Carbon Consumed 80 100 63 95 100 9T 100 90 100 100 100 100 84
Per Cent of Bas04 Reduced to B a s 58 70 84 70 74 75 75 82 96 90 80 90 95
Consumed Per Cent Bas04 Reduced 13.8 14.3 19.8 13.5 13.5 12.9 13.3 16.4 14.2 16. i
12.5 15.6 17.6
Different kinds of barium sulfate gave different results in reductions carried on under t h e same conditions, e . g., t h e materials indicated in Table V, all finer t h a n zoo mesh, were reduced a t t h e same time under t h e same conditions (temperature 900' C.,time 1 2 0 min.), with t h e results given in Table V.
i 74 T A B L E \'-PER
T H E J O L-KNAL OF IXDI'STRI.4L CEhT O F T O T 1 L B A R l U M I N PRODUCT FROM
A N D EiVGIiVEERI_VG CHEiVfISTKY
DIFFERENT
V O ~8. , NO.9
kept filled with briquettes during a test, inore briquettes being added a t the top as the reduced prodMATERIAL uct was withdrawn below. The time the briquettes Pptd. BaSO1.. . . . . , . 9 9 . 6 sa 10 7 Pulverized Y8.0(a! i8 I3 9 were in the furnace varied between I~,'? hrs. and 3 Barytes { : : : : . : . 92.5(b) 72 I8 10 Pptd. Bas03 4- Bas04 . . . . 93 I n ,hrs. During an arerage run of 6 hrs., about 80 kg. ( a ) The impurities were 1 . 4 per cent UaCO; and 0 . 6 per cent FelOt + of these briquettes were reduced. The best average SO?. ( h ) About 3 per cent Fe and 3 ppr cent Si02 \%-erepresent. product obtained from any of the days' runs contained Some comparative tests were made to determine 8 2 . j per cent of the barium as sulfidc, 1 3 . 8 per cent t h e effects of iron on the reduction of barium sulfate. as oxide and carbonate, and 3 . 7 per cent as insoluble Four charges were made u p in 11-hich iron t o t h e ex- sulfate. The best product from any charge during tent of about 6 per cent w a s mired with t h e precipi- this run contained 87 per cent of t h e barium as sulfide: tated barium sulfate. The iron 11-as added t o differ- during this run the maximum furnace temperature ent charges as ferric sulfate, ferrous ammonium was I I j o o C . ; the average carbon monoxide content sulfate, ferrous sulfate, and ferric oxide. Two charges of the gases in the shaft of the furnace was 4 per cent. of the pure precipitated barium sulfate were reduced In this shaft furnace. several runs were also made under the same conditions (temp. 8 5 0 " C.. time 1 2 0 with briquettes of pulverized commercial barytes min.). ( 9 2 . j per cent BaS04), and lampblack carbon. These PER CENT OF TOTAL BARIUMPRESENT I N COMPOUNDS briquettes were zll/? in. ( 6 . 3 6 cm.) long, 2 1 / 2 in. ( 6 . 3 ; (AVERAGE OF 4 T E S T S ) cm.) in diameter and weighed about 0 . 8 1 Ib. ( 3 7 0 g.), Water- Water-insoluble AcidMATERI.4L soluble Acid-soluble insoluble each. With these briquettes, very unsatisfactory Pure BaSOI.. . . , , . 80 I0 10 reductions were obtained, even though the temperaUaSOr with 6 per cent +e' 68 l i 15 ture of t h e furnace 'was raised t o I 100' C . , and broken REOXIDATIOK O F BARICM SULFIDE TO SULFATE I t has been stated t h a t barium sulfide, when a t pieces of coke were charged with t h e hriquettes. red heat, is readily reoxidized t o the sulfate. The The best products contained only about ;o per c e r t d a t a from several of the crucible reduction tests were of the barium as sulfide. Also, unless these large briquettes were broken u p and chilled immediately found t o be of no value since adequate precautions had not been taken t o prevent the oxygen from getting on being removed from t h e furnace, they retained their into t h e crucible. An example of t h e effect of small heat for a long time, and the barium sulfide t o a great air leakages into the crucible is given below. These extent oxidized back t o t h e sulfate. results were obtained when reducing pulverized barytes One charge of reduced briquettes weighing about (98 per cent BaS04) with 2 0 per cent willow charcoal 2 j kg., and containing a t the time of withdrawal a t 1000' C. from the furnace about 7 0 per cent of the barium as PERCENTBARIUM I N P R O D U C T PRESENT I N COMPOUNDS sulfide. was allowed t o stand unbroken in a n iron conWatertainer for about ~j hrs. At t h e end of this time, t h e Waterinsoluble TIME. soluble Acid sol. Insoluble FITOF briquettes in t h e center of the container were still (Bas) Camp. (BaSOA) COVER Ivlin. 60 94 6 .. Tight glowing. The outside cooled briquettes contained 76 3 21 Loose I20 56 4 40 Tight less t h a n 1 5 per cent of the barium as sulfide, t h e rest 3 62 Loose 35 having oxidized back t o sulfate. T h a t t h e reoxidation product is t h e sulfate and not OF BARIUM SULFATE I N T H E t h e oxide, is shown in the above and also in some S E R I E S 4-REDUCTIOS I I E . A R T H R 0 AS T I Pi G F L? R K A C E 1 1 C L T I P L E special tests made t o determine t h e product of oxidation of barium sulfide. I n these tests, material conD E s cR IP TIO s o E P L-R &-A CE-- The m ti 1tipie hearth taining 9 j per cent of the barium as B a s was heated in furnace used for these reduction tests was one designed the air for varying periods of time a t different tempera- b y Mr. Utley TT7edge and loaned t o us for these intures. I n most cases practically all the sulfide was \-estigations (see Figs. I and 11). The furnace reconverted t o the sulfate, and only small amounts n-as 2 4 in. inside diameter and 34 in. high, i. c . , between of oxide were formed. The maxi mum conversion bottom of t h e cast-iron drying hearth t o top of bottom t o oxide was about 7 per cent and was obtained when hearth. Beneath the bottom hearth was a calcine pit, I Z in. deep. -4bove the drying hearth were placed the material was heated t o 800" C. for 2 hrs. t h e driring gears. roller bearings, etc. T h e total S E R I E S ~ - - - - B A R I L - U S U L F A T E , XIXED WITH C A R B O S , height over all was 6 f t . The walls of the furnace .\I.iDE I I i T O BRIQC-ETTES A S D R E D U C E D I K .A were of specialiy moulded fire brick, 8 in. thick, conS H A F T F U R N A C E H E A T E D B Y OIL Precipitated barium sulfate was mixed with lamp- taining openings for gas burners, pyrometer tubes, black carbon from the local oil gas works, and t h e mix- gas sample tubes and mica windows. or peepholes. ture pressed into the form of cupels, I in. ( 2 . j cm.) Outside t h e brick walls of the furnace \vas placed a ' ?thick; this magnesia in diameter, and 1' in. ( 3 . 2 cm.) high. These cupels covering of magnesia board I ~ ~in. covered vrith ,a layer of asbestos cement '/s in. mas were dried and then charged into a small shaft furnace, thick. with fi thin layer of Portland cement on the 1 2 in. ( 3 0 . j cm.) in diameter and 30 in. ( 7 6 . z cm.) high, which was heated t o about 9jo-1100" C . by an outside. T o a revolving center column inside t h e furnace oil flame, t h e products of combustion or excess gases passing through the shaft and maintaining strongly were attached three cast-iron hearths 2 2 in. in diamreducing conditions in the shaft. T h e furnace was eter. Thus? there was an annular space I in. wide Co&wor.sns Per Cent WaterBaSOL soluble
,
Water-insol. Acid-sol.
.kcidinsol.
Sept., 1916
T H E J O U R N A L OF I N D U S T R I A L
hetween these hearths a n d t h e furnace walls. Between these movable hearths a n d helow t h e lowest one were placed three stationary hearths resting o n shelves provided on t h e brick walls. T h e opening at t h e center of these hearths was 6 in. i n diameter, leaving an annular space I in. wide between t h e
F w I ~ M ~ . T W ~II!AITII ~ . E ; Hr,nsTlsc; 1~Ymnca f.onvrd hi. U r . Cllr? I l X x r
stationary hearths and t h e center columns. The total effective hearth area was 1 6 . j sq. i t . Rabbles were attached t o ribs cast on t h e under side of t h e hearths, these rabbles stirring and moving t h e ore across t h e hearths immediately below. The ore on t h e cast-iron drying floor was moved by rabbles revolving with t h e center column. From t h e ' d r y i n g floor t h e ore fell t o t h e center of t h e t o p movable hearth. and was moved by t h e rabbles suspended irom t h e stationary drying hearth, to t h e outside of this revolving hearth, falling on t o t h e second h e a r t h , ii stationary hearth. I t was then moved b y rabbles attached t o t h e first morahle hearth, t o t h e center of t h e stationary hearth. a n d fell on t h e third h e a r t h , a moving hearth. T h e ore was t h u s moved through t h e furnace in a manner similar t o t h a t in a regular, large size, multiple, roasting furnace. T h e cast-iron hearths lasted for many tests when the temperatures were not over 8ooo C . . b u t when temperatures above 900' C. were maintained they warped and cracked and had t o he replaced after eight or nine ~ z - h r .runs. Bristol pyrometers were inserted through t h e walls of t h e furnace for measuring t h e temperature on t h e first, third a n d fifth hearths. Gas samples were also drawn from t h e furnace at these hearth levels. Peepholes were provided at several points for observing t h e charge in t h e furnace. Movable
I
-
8 ...I
9
s I
na
!i %~;
'j
-
776
T H E JOCR.V.IL
OF I N D C S T R I A L A N D E Y G I S E E R I N G C H E M I S T R Y
P~rrcntCarbontollaSOiiiiCh;,ric........ 20 16 20 Rate Charm to Furniirc. K g per hr.. . . . . 8 . 9 5 . 0 3.5 Rate ( h s Consumplion. Cu. I t . pvr mill 5 . 2 5.0 5 . 0 Time 01 Mztrrial in Purnnee. Hrr. (nf,prox.) 2 2.10 2.45 D u r d o n of Test, Total hrs 8 9 I2 A V R W A ~ ~ T B M P ~ Y ~ T (-c.): U R E Tophearth inn 270 300 3rd hearth .m s w 6x1 5 t h ilcrrth 810 860 880 hlnxiinuin'fe.,perrfureof 5th hearth 840 880 8'JO Arcram',; COinFurnarcCase.(inIhearfh) 4 . 5 5 . 0 4.7
.... ............... .... .
25 25 17 18 3.5 3 , 5 2 . 8 3 .O 3 . 7 4 . 6 3.5 3.5 3 1 3.30 3.15 9 9 I O 10 270 420 3in 370 570 760 810 790 89n 895 880 885 895 905 905 910 1 . 6 2.0 0 . 5 0 . 5
15
4.5 3
2.45
12
12.30 3io 760 8:U
460 890
8w 900 2.0
.
S E R I E S j-REDUCTION
OF B.ARIUM SUI.F:\TL:
Q
3 ..5
910 0.5
.. ... ... ...
hlar. ',E Iis.\\'sfer-rolal~leieHo~~rlySninpler13 73 79 67 7 8 82 80 . . . (") Note mlximum rccluction. (1,) I'roduelr fro," all te*Ls rrcepI 7 . nnc1 7 C 0 l l l i l i " C d excess carbon.
per min. T h e main el'forts in these tests x e r e t o obtain t h e maximum rcduction rather t h a n t h e highest efficiency of t h c reducing agent, carbon or gases. I t is 10 he noted from Table 1'1 t h a t with precipitated barium sulfate, t h c highest reductions were obtained when t h e miiteriiil was mixed with carhon. cither 3 s pulverized charcoal or lampblack, a n d when t h e higher temperatures were maintained in t h e furnace. Under thesc conditions t h e percentage of excess-reducing gascs prcscnt in t h e furnace could be reduced t o a vcry low figure. 'l'hc pulvcrized eommercial harytes was more difficult t o reduce t h a n was t h e precipitated hariiim' sulfate. When t h e maximum temperaturc in t h e furnace w a s ahove Xjo' C.. t h e material was slightly sintered into balls about 'is in. in diameter, like cement cinder. These slightly cindcrerl balls formed in the first reductions were casily hrokcn u p , and t h e material was pulverized readily for subsequent use :is ii precipitant in t h e solutions. I t is t o be regretted t h a t reduction tests at higher temperaturcs, i. e . , a b o r e 900' C., could not have been made with this type of furnace. However, we mere not equipped with refractory hearths t o withstand higher temperatures over longer periods of time.
Yol. 8, No.
...
60
68
ill
.. .
:I1
72
t h e hack of t h c furnace. Provision w a s made for t a k i n g samplcs of gas :Lt sex-cral points :*long thc length oi Lhu kiln, and :~lso for measuring the tcnipcwiitiiics :ti these points by thermocouplcs. 'The gaseous products of tlic k i l n werc disrh:irgerl into :L brick stack. Thc dr:ift a t t h e fumacc w a s rrrluccd t o a minimum. so th:it t h c reducing rendition.; in the furnace could lie rontrolled hy t h e air :tnd gas entcring throiigh the hurner pipe. Even with t h e d r a i t reduced t o a minimum, there W:LS consiilcrahlc barium sulfate carried out of t h c f u r n : w liy t h e gnses. In one test, when oil was used and was being discharged through the burner hy :L high air pressure directly along t h e centcr line of the kiln, t h e loss of Inriiiin sulfate was very high. :cliout 30 per cent. \Yhen this oil and air mixture was discharged a t right angles w i t h this center line striking against the sirlcs of t h e kiln. t h e loss w a s greatly reduced.
IS
CEMENT KILN
Through t h e courtesy of t h e Chemistry Department of t h e University of California, we mere given t h e use of a small cement kiln in t h e chemistry building of t h a t university, for further work a t highcr temperatures on t h e reduction of barium sulfate. The cement kiln was 1 2 i t . long, 19 in. outside diameter and I O in. inside diameter. The number of revolutions was I . I j per min.. t h e pitch was I : r 8 (see Fig. 111). In t h e tcsts at this furnacc, city gas or oil fuel was used for heating;. The Ioacr end of t h e kiln was closed by a sheet-iron plate covered with ashestos. Through this plate :I gas burner was inserted. t h e gas being blown in with air under low pressure. A small gate was provided in this sheet-iron plate t o allow drawing out t h e reclued product intermittently. The charge t o t h e furnace was fcd in hy hand :It
F m I I I - C ~ I B N T KILN Chemistry Building, U n i t r r r i l s OJ ColiJur~rio
In these reduction tests. t h c temperature xt thc hottest part of t h e furnace w a s :is high as 1 1 0 0 ' C.. and averaged ~ o j o ' C. For o\-er half oi t h e furnace t h e temperature was :ihovc Sjo' C. The average time t h e charge was in t'hc furnace wiis 2 ' '> hrs.
S e p t . , 1916
T H E JOLRiVAL OF I N D C S T R I A L A N D ENGINEERING C H E M I S T R Y
The average rate of feeding t h e charge t o the furnace was I j kg. per hr., ranging between' I O a n d 2 0 kg. per hr. T h e best reductions were obtained when t h e furnace was kept well filled with t h e charge. T h e material used was finely pulverized barytes (98+ per cent B a S 0 4 ) (material used in paints b y W. P. Fuller C o . ) , as large quantities of t h e precipit a t e d barium sulfate could not be obtained. Six tests were made using city gas a n d one using oil for fuel. T h e main object in these tests was t o obtain a high reduction of t h e barium t o t h e water-soluble sulfide; high efficiency of t h e reducing agent was. a secondary consideration. One test '( 5-7) below, however! was conducted for t h e purpose of obtaining a higher fuel efficiency t h a n t h e others. This test showed t h a t almost as high a reduction could be obtained with much less fuel consumption. Xone of these tests furnished conclusive d a t a for calculating t h e fuel t h a t would be required for effective reduction in a commercial sized kiln. TABLEVII-REDUCTION OF COMMERCIAL PULVERIZRD BARYTES IK CEMENTKILN CAARACTBR OF C USED Pulverized Pulverized Pulv. Coke Charcoal None Coke Coke TESTNo 5-1 5-2 5-3 5-4 5-5 5-6 5-7 Per cent n charge . . . . . . . . . . . . . . . 20 15 20 16 0 18 13 R a t e C h a r g e : K g . p e r h r ... 10 10 15 15.2 12.5 16 18.T Gas Consumption, Cu. ft. 5.4 5.6 6.1 6.3 6.2 oil(a) 3.8
1
hrs . . . . . . . . . . . . . . . . . . 25 10 5 5 4 2 4 Av. Temp. ( " C . ) : Exit Gases . . . . . . . . . . . . . . . . 450 460 420 400 510 ... 370 4 v . Tem Middleof Kiln 850 880 880 860 900 . . . 840 Max. A m p . in Kiln (approx.) . . . . . . . . . . . . . 10.50 1050 1100 1050 llOO+ 1360 1050 4 v . per cent CO in Furnace Gases (middle).. 3.8 4.2 3.1 4.2 6.2 1.5 ANALYSES OF PRODUCT OF TEST: (b) Per cent of Total Ba: , Water-soluble. 89 87 90 89 69 84 82 Acid-soluble . . . . . . . . . . 98 97 98 98 78 96 90 Insoluble (BaSOa). . . . . 2 3 2 2 22 4 10 ( a ) Product of Test 5-5. Clinkered and unreduced Bas04 left in interior of the clinker. ( b ) Rate of oil consumption, 3 gals. per hr.
.
...
........
SUMNARY
I-The d a t a obtained in t h e five series of reduction tests outlined above indicate t h a t t h e maximum reduction of barium sulfate t o sulfide was obtained a t t h e higher temperature, i. e., around 1000' C . , a n d when t h e reductions were effected in a n indirect fired furnace, e . g., in t h e muffle furnace, 1 5 or 16 per cent carbon gave the highest fuel efficiency consistent with completeness of reduction of t h e barium t o t h e sulfide. 11-In reductions effected in a direct fired furnace ( a cement kiln, multiple hearth roasting furnace, or a shaft furnace where hydrogen, hydrocarbons, or where t h e products of combustion of t h e fuel, water a n d carbon dioxide, were brought into contact with t h e sulfate or sulfide) there were formed a larger proportion of barium compounds insoluble in water, t h a n were formed in a furnace indirectly fired. Thus, although t h e barium compounds in t h e best products from a direct fired furnace were 90 t o 95 per cent soluble in acid, yet t h e barium present as t h e watersoluble sulfide was not more t h a n 85 t o 87 per cent of t h e total. 111-By effecting t h e reductions rapidly a t high tempeiatures, i. e . , above 1000' C . , t h e prbportion
777
of these water-insoluble barium oxides a n d carbonates was less t h a n t h a t formed i n reductions a t lower t e m peratures over a longer period of time. IV-Below 750' C. t h e reduction b y carbon or reducing gases was too slow t o be considered commercial. BUREAUOF MINES, WASHINGTON
THE THERMAL DECOMPOSITION OF THE ETHANEPROPANE FRACTION FROM NATURAL GAS CONDENSATE By J.
E. ZANETTIAND E. H. LESLIE Received August 3, 1916
I n a previous paper' one of us presented t h e results obtained b y t h e thermal decomposition of t h e propane-butane fraction from natural gas condensate. As a continuation of t h a t work i t seemed desirable t o s t u d y t h e lower fraction, t h a t containing chiefly ethane a n d propane, which fraction can likewise be found on the market a n d is used mainly for lighting a n d oxygen welding. This fraction comes in cylinders under 500 t o 1000 lbs. pressure, a n d owing t o t h e great difference in boiling points between ethane and butane. -93 a n d + I O , is little contaminated b y butane. At 7 j o lbs. a n d t h e 'temperature of 2;' t h e vapor pressure of butane as calculated from Burrell a n d Robertson's formula2 Log P = -1633/T f 1.7j log T -0.01094 T 7.590 is I j 4 5 m m . , a little above 2 atmospheres. Since t h e pressure in t h e cylinder used was 7 5 0 lbs. above atmospheric, a t 25' t h e amount of butane present in t h e issuing gas would be about 4 per cent. If we consider t h a t t h e vapor pressure of t h e butane must be considerably diminished b y t h e fact t h a t it is dissolved in the liquid ethane a n d propane, t h e amount of impurity in t h e gas from this source becomes small. T h e very high pressure in some of these cylinders would indicate t h a t there is also some dissolved methane in t h e liquid ethane. The critical temperature for ethane is +34' a n d t h e critical pressure j 0 . z atmospheres. As a t 25' t h e pressures are often above t h e critical, t h e only other hydrocarbon present would be methane. This matter is dwelt on a t present as it further bears out t h e observation made b y one of us i n connection with t h e propane-butane fraction t h a t t h e a r o m a t i c h y d r o c a r b o n s obtained f r o m these f r a c t i o n s are built up from a l i p h a t i c c o m p o u n d s of lower carbon content t h a n benzene. There is no possibility of aromatics having been obtained here b y t h e splitting off of t h e benzene ring from phenyl paraffins as no such compound is known t h a t would boil a t t h e temperature of liquid ethane. under atmospheric pressure, or conversely under t h e pressure of liquid ethane a t ordinary temperature. If such compound were present in this gas its vapor pressure would be so small in comparison with t h a t of ethane a n d propane t h a t it would constitute b u t a minimal fraction of t h e issuing gas a n d it could in no way account for t h e yield of t a r obtained in these experiments--2.; cc. of t a r
+
1
2
THISJOURNAL, 8 (1916). 674. J. A m . C h e w SOL.,37, 2190.
