Steam Catalvsis in Calcinations of Dolomite and Limestone Fines J
W. H. MACINTIRE The University of Tennessee Agricultural Experiment Station, Knoxwille, Tenn.
T. B. STANSELI The American Zinc, Lead and Smelting Co., Mascot, Tenn.
T
HE initial objective of work reported was the conversion of
slightly soluble dolomite into an activated carbonate-oxide concentrate, incorporations of which would expedite development of “available” magnesium in fertilizers (64)and in soils. T h e second objective was the expeditious calcination of high-calcic limestone a t a temperature well below the one recognized as critical for the conversion of calcium carbonate to lime ( 2 7 ) . ACTIYATION O F DOLOMITE FINES
The use of dolomite to supply magnesium to “standard” superphosphate and its mixtures has been detailed by Sweet ( 5 1 ) . I n 1920, only 1000 tons of dolomite fines were used in making mixed fertilizers in the United States, but a t the end of 1950 7,750,000 tons (39) of dolomite had been so used. The physical improvement and chemical effects that follow the inclusion of dolomite fines in standard superphosphate were reported a t The University of Tennessee (60,26, 29-31, 34, 36-38). Recently, however, the admissible input of dolomite has not been sufficient to supply desired percentages of readily available nutrient magnesium in high-analysis fertilizers, toward which there is a decided trend (54). Because of the teaching that additive magnesium is tovic to vegetation (16), the utility of dolomite as a liming material was questioned. Acceptancewas rapidafter the favorable crop responses reported by Lipman et al. (21) and because of the decided responses to dolomited fertilizers (16, p. 231). A large increase in the use of raw dolomite followed the revelation by Garner et al. (11) that “sand drown” in tobacco in the Coastal Plain is caused by a paucity of exchangeable magnesium in soils. I n the past 30 years more than 12,000,000 tons of by-product dolomite fines were shipped from one flotation operation near Knoxville. The requirements that the raw dolomite be fine and that protracted intervals ensue between incorporation and seeding (33,35) were stressed by representatives of 25 agricultural experiment stations in a 3-day conference a t Knoxville in 1922 (20). The findings from the lysimeter experiments a t the Tennessee Station prompted the proposal to use an activated dolomite concentrate to overcome the low solubility of dolomite fines and provide “available” magnesium t o phosphatic fertilizers ( 2 4 ) without causing percentage decrease in content of available phosphorus pentoxide. Definition of Dolomite. The generic term “limestone” embraces mineral deposits that are comprised of the carbonates of calcium and magnesium, but it is important to distinguish among magnesian limestone, dolomitic limestone, and dolomite. Van Tuyl(52) and Clarke ( 7 , 8 )reviewed the geochemical theories for the formation of dolomite. Clarke ( 7 ) observed that “the term ‘dolomite’ is sometimes used by geologists as equivalent to magnesian limestone. Properly, the word should be restricted to the definite double carbonate,” and Knibbs (16) concluded likewise. The Association of Official Agricultural Chemists ( 1 ) defines dolomite as “a mineral composed chiefly of carbonates of calcium and 1
Deoeaeed.
magnesium in substantially unimolal proportion.” Dolomite is rhombohedral and identifiable through its resistance to dilute solutions of acids and by the logwood test ( 6 ) . Knibbs noted that “there has been much speculation and research on the nature of dolomite” and concluded that “dolomite may conceivably be a mixture, a solid solution, or a compound” (16, p. 81). According to Azbe (3, p. 3 7 ) , “the two carbonates do not appear to be in either a physical mixture or in a chemical combination,” but MacIntire and S h a a ( 3 2 ) proved that true dolomite is the double carbonate, as is also the dolomite fraction of a dolomitic limestone, and substantiated the findings reported by Leather and Sen (18). Calcination of Dolomite. Although inclusions of a calcium carbonate-magnesium oxide calcine in phosphatic fertilizers mere found to develop readily dissoluble dimagnesium and dicalcium phosphates (24, SO), the calcine did not come into commercial production; one reason for this was the contention that the component carbonates of dolomite undergo decomposition simultaneously during calcination (3,dO). Mitchell (40)concluded t h a t
K)
DEGREES C . Figure 1. Progression in Thermal D e c o m position of Dolomite in Steam and in Air (17)
the dissociation of calciuin and magnesium carbonates was a onestep process, the dolomites occurred as carbonate mixtures, the component carbonates “did not split up before dissociation,” and (‘the calcium carbonate molecule dissociated as a whole.” Upon the basis of such findings, Knibbs ( 1 6 ) also concluded that “dolomites are not mixtures, do not split up before dissociation, and t h e CaCOs.MgCOa molecule dissociates as a whole.” I n contrast,
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INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1953
Kallauner (14) believed that dolomite undergoes disruption into its component Carbonates at about 500" C. and Scherer (45)contended that the magnesium carbonate content of dolomite dissociate8 a t 500" to 600' C., without a concomitant decomposition of the companion carbonate of calcium.
0
'
.o
s
6 0
I
52
3
45
HOURS Figure 2. Fallacy of Use of Losses of Weight to Measure Selective Calcinations of Dolomite Fines into Calcium Carbonate and Magnesium Oxide without Determinations of Percentage of Free Lime in Calcine A. 650° C. imposed A'. As in A , but rabbled B. 670" C. imposed- free CaO in calcine, 5.87% B'. As i n E , but radbled; free CaO in calcine, 9 8 0 % C. 700" C. imposed Control, 600' C. imposed in steam
=
I n 1922, Shaw and Bole (47) obtained a product comprised of 70% of calcium carbonate and 25.5% of magnesium oxide from calcinations of dolomite at 725" C. They concluded that ( a ) there are three types of dolomite; ( 6 ) these behave differently under calcination; (e) o n e k i n d undergoes a separation of the component carbonates, t h e separated magnesium carbonate then undergoing decomposition within a stipulated range of temperature; ( d ) another kind of d o 1o m i t e undergoes dissociation of its calcium and magnesium carbonates simultaneously; and a third kind ( e ) behaves as though it were a mixture of kinds (c) and ( d ) . I n 1933, Lathe ( 1 7 ) reported that dolomite decomposed in two stages; the first stage occurs a t about 725" C. and consists in the separation of the molecule of magnesium carbonate, and its immediate decomposition. A s e l e c t i v e calcine (55.18y0 calcium carbonate and 21.7% magnesium
1549
oxide) was produced commercially in Canada through the direct heating of definitely sized dolomite at 725" C. in a kiln "used for the production of dead-burned clinkers." "The use of powdered coal as fuel a t such a low temperature made necessary an external combustion chamber in order to ensure proper ignition, but by its use the temperature could be maintained at any desired point" ( 1 7 ) . After tests on eighteen dolomitic stones and seven special dolomites, Murray, Fischer, and Shade ( 4 1 ) reported the characteristic temperatures of magnesium carbonate in dolomite to be 745" C., in the range between 720' and 770" C . Fallacy of Using Weight Losses in Selective Calcinations. Lathe (17)used loss in weight to measure temperature critical for the disruption of the dolomitic bond and for the subsequent d e composition of the separated magnesium carbonate in air (Figure 1). Appropriate allocation of the dispelled carbon dioxide re quires determination of the free lime content of the calcines and the losses then can be proportioned precisely t o the magnesium and calcium carbonate components. The results given for free lime (Tables I and 11)and for the six calcinations in Figure 2 were obtained by the sucrose procedure (60) and show the importance of the foregoing observation. Calcination of -100-mesh dolomite for 1 hour a t 600" C. in steam caused a weight loss of 22.5%, yet the calcine obtained only 0.74% of free lime, whereas the 2-hour calcination of a like charge a t 700" C. in air caused a weight loss of 19.570 and a free lime content of 9.26%. The values graphed in Figure 2 for the other four calcinations a t temperatures between 650" and 670' C. are in like order and demonstrate the accentuation resultant from the {'rabbling" of the dolomite charges. Experimental Findings. Dolomites from Ohio, Pennsylvania, Tennessee, North Carolina, and West Virginia were calcined under variations as to atmosphere, temperature, duration, par-
TABLEI. CATALYTIC EFFECTO F ATMOSPHERE O F STEAM I N SELECTIVE CALCINATION OF NORTHCAROLINA DOLOMITE IN ELECTRIC FURNACE AT 550" TO 650' C.
Dolomite, Particle Size
Conditions Imposed during Calcination of 25-GramQ Charges of Dolomite O C. Hours Atm.
Loss of coz G. %
From Dolomite Charges of 25 Grams" Calcine Assay, % CaCOs Equivalent Gain FreeCaO Found Total As CaO As MgO
0 5-1 inch 0 5-1
600 600
2 5 2 5
Air Steam
0 30 2 88
11 25
1.18
0 17 0 80
104 42 115 26
1 17 12.01
0 30 143
0 87 10 58
0 25-0 5 0 25-0 6
600 600
2 5 2 5
Air Steam
0 25 3 31
0 97 13 07
0 15
0 68
105 01 118 76
1 70 15 51
0 26 1 21
1 50 14 30
600 600 650
2.5 2.5 2.5
Air Steam Steam
0.88 0.22 4 . 7 1 18.84 6 . 0 8 24.32
0.16 0.76 2.56
104.17 128.23 135.43
0.92 24.98 32.18
0.28 1.36 4.57
0.64 23.62 27.66
850 ... 650
2.5 2.5
Air Steam
0.85 3.40 6 . 4 8 26.92
* 0.26
4.57
108.33 137.14
5.96 34.77
0.61 8.08
5.35 26.69
1.5 2.5 2.5 2:5 2.5 2.5
Nitrogen NHs: 8"
Helium Air Steam
3.00 0.75 3.24 0.81 2.88 0.72 1.00 4.00 1.68 0.42 5.30 21.20
0.44 0.24 0.48 0.46 0.23 0.76
108.01 107.60 108.08 108.96 104.12 130.78
5.67 5.23 5.71 6.59 1.75 28.41
0.77 0.43 0.86 0.82 0.41 1.34
4.90 4.80 4.85 5.77 1.34 27.07
1 2.5 3 4
Steam Steam Steam Steam
4.17 16.68 5 . 3 0 21.20 5.60 22.40 5.60 22.40
0.68 0.76 1.04 1.13
124.40 130.78 132.15 131.99
22.03 28.41 29.78 29.62
1.20 1.34 1.84 2.00
20.83 27.07 27.94 27.62
1 1.5 2 2.5
Steam Steam Steam Steam
6 . 2 0 24.89 6.29 25.16 6.49 25.90
0.61 1.75 2.61
137.69 138.64 135.79
35.32 36.27 33.42
1.09 3.14 4.66
34.23 33.13 28.76
'/s-O. '/s-O. '/s-O.
26 25 25
- 100-mesh material
600 600 600 600
1.88 31.39 1.05 135.64 33.27 Steam 6.23 24.99 3 1.38 33.14 136.89 34.52 0.77 5.95 23.80 Steam 2.5 33.17 1.25 31.92 0.70 '135.54 Steam 5 . 8 1 23.24 2 133.54 31.1 1.57 29.60 0.88 5 . 4 8 21.92 1 . 5 Steam Analytical charges for 0.5- to I-inch and 0.25- to 0.5-inch separates in first column were, reading downward, 25.30, 25.42,25.65, and25.31 grams. b Anhydrous NHs CaCOs equivalence of raw North 0 Derived from aspiration through aqueous solution that contained 26% NHa. Carolina dolomite was 103.25% for l/s-inch and coarser material, and 102.37% for 100-mesh material.
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IN D U S T R I A L A N D E N G IN E E R IN G C H .EM I S T R Y
Vol. 45, No. 7
of steam in calcinations (13). Bailey ( 4 ) introduced steam in three proportions and noted that “the inrrease in carbon dioxide produced by the use of steam is an indication of its value as a catalytic agent in lime burning,” but he then expressed the opposite conclusion “that any gas, for example, air, would give the same results as revealed by the use of steam.” Knibbs (16, p. 102) observed that water appears to act catalytically in the combination of oxide and carbon dioxide, and w-e would expert it to have a similar effect in the reverse direction-the dissociation of the carbonates-yet he stated also that “there is, however, no direct evidence that it has any effect whatever on disA B . sociation.” In rejecting Bailey’s ( 4 ) conFigure 3. Electric Furnace elusion that water exerts a catalvtic effect Dolomite calcined selectively at 550-60O0 C. in steam t o obtain calcine comprised of calcium upon the liberation of carbon dioxide in carbonate and magnesium oxide, and limestone caloined completely i n steam at 700’ C. the calcination of dolomite, Knibbs (16, A . Front-end motor drive and steam generator B . Rear end for input of charge and delivery of calcine p. 102) stated that Bailey’s findings “actually proved nothing,” although admitticle size, and weight of the charge in four types of furnace, three ting that “it is impossible to say that the presence of water vapor does not hasten dissociation” and “the only conclusion that can be of which were electrically heated laboratory units. The ultimate tubular calciner was a 3 X 20 foot oil-fired “drier,” modified to alarrived a t is that if steam is effective in assisting the calcination low input of steam into six horizontal 6-inch tubes. The cited of limestone, it i s difficult to explain its action” (16, p. 104). Azbe ( 3 ) conducted calcinations of dolomite in air, in atmosfinding that 725’ C. is critical for the selective calcination of pheres of 33 and 100% carbon dioxide, and in atmospheres of dolomite in air (5, i 7 , 47) was substantiated through 3-hour exploratory calcinations of 500-gram charges of 100-mesh Ohio steam containing 33% carbon dioxide. In a paper entitled “Contrary to General Belief, Steam Does Kot Help Calcination dolomite in a conventional electric furnace (Figure 4). Hence, --Actually Hinders Process,’’ Azbe contended that steam the primary objective of the succeeding experimental calcinations does not accelerate calcination of dolomite and does not lessen dewas to effect the selective calcination of dolomite below 725” C. composition temperature ( 2 ) . The approach was: Frear (10) suggested that the “soft” type of burnt lime ob1. Charges of dolomite (25 grams) of various particle size tained by Pennsylvania farmers might result from the relatively were calcined in the range of 550” to 650” C. in atmospheres of large release of steam from the wood used by them in the home air, nitrogen, helium, ammonia, and steam in tubular electric furburning of limestone. naces. 2. Charges of 100-mesh dolomite (500 grams) in motion were In general, the conclusions cited were for calcinations of lumps, calcined in steam a t 600‘ C. in the electrically heated rotating where steam effect would be primarily a limited surface action, chamber furnace (Figure 3). whereas the present studies were restricted to calcinations of fines 3. Batch charges of dolomite fines (500 pounds) were calcined in an atmosphere of steam maintained below 725 O C. in steam at 600” C. in six 6-inch tubes that were embodied in the 3 x 20 foot externally heated rotating Traylor dryer. ELECTRIC FURNACE. Laboratory Calcinations. IN TUBULAR 4. Continuously fed fines of different dolomites were calcined The conclusion that any inert gas would have had the same effect in steam a t 6OO0C.,as in 3, toproduce 2.5 tons of selective calcines as water vapor (16, p. 102) was tested through laboratory calcinaper day in three-shift operations. tions of dolomite fines in atmospheres of inert gases and in steam within the range of 550” to 650” C., and for durations of 1.5 to 3 Catalytic Function of Steam in Selective Calcination. Several hours (Tables I and 11). The air was displaced through gentle considerations prompted the hope that steam might function inflow of steam without injection into the charges, which were catalytically to lower critical temperature and shorten duration contained unstirred in a platinum boat. for the selective calcination of dolomitic fines. Ostwald (49) deHeated 3 hours a t 600” C. in atmospheres of nitrogen, helium, fined a catalyst as “any substance which alters the velocity of a ammonia, or air, as in Table I, the dolomite charges suffered only chemical reaction without appearing in the end products,” and Schwab, Taylor, and Spence ( 4 6 ) observed that “an ideal catalyst must accelerate the reTABLE11. CATALYTIC EFFECTO F ATMOSPHERE O F STEAM I N SELECTIVE CALCINATION O F action in the same ratio in each TENNESSEE ICzrox DOLOMITE AT 600’ C. IN ELECTRIC FURI~ACE direction.” As moisture is esFrom Dolomite Charges of 25 Grams sential to reaction between calConditions Imposed Calcine Assay, % during Calcination of cium oxide and carbon dioxide CaCOa Equivalent 25-Gram Charges of Dolomite, Gain (25, 40), the present authors Dolomite Loss of cot Particle Size Total As CaO A s M g O G 7 Free CaO Found a C. Hours Atm. assumed that an atmosphere Runofpileasb 600 3 .4ir 0.38 1.52 0.21 94.73 1.24 0.38 0.86 of steam might function oppositely to catalyze the disruption of the dolomitic bond and then induce decomposition of the released magnesium carbonate. Conflicting opinions have been expressed as to the effect
Runofpileatb -100-meshc -100-meshc
-1OO-meshC -100-meshc a
b
600 600 600 650 630
3 3 3 3 3
Steam Air Steam Air Steam
4.40 0.35
17.60 1.40
4.60
18.40
0.65 0.21 0.75
1.25 6.00 6.40 25.60
0.69 6.51
All through 20-mesh. 65% was through 100-mesh. CaCOa equivalence $3.49%. CaCOa equivalence 94.48%.
113.62 97.20 116.74 100.42 127.85
20.13 2.72 22.26 6.93 34.36
1.16 0.38 1.34 1.23 11.63
18.99 2.34 20.92 5.70 22.73
July 1953
*
R .
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INDUSTRIAL AND ENGINEERING CHEMISTRY
meager decompositions. In contrast, calcination in steam a t 550" C. caused dolomites to undergo substantial disruption and, upon further imposition of that temperature, the separated magnesium carbonate underwent complete conversion to magnesium oxide. The imposed temperature is 175" C. below the one established as critical for the selective calcination of dolomite in air (417, $6, 47). The factors of particle size and duration of the calcinations in air and in steam are considered in Table I. The finer the dolomite the greater was the development of magnesium oxide per unit of time in the steam atmosphere. The temperature deemed ideal for selective calcinations in steam is 600" C., but because of the findings given in Table I, the choice between 600 O and 550' C. and between shorter or longer durations would be governed by response from a particular dolomite and the economy of the desired conversion. Imposition of 650" C. in steam is inadmissible because resultant calcines contain undue percentages of free lime. Although the steam induced a lowering of 175' C. in the selective calcination of the unstirred charges of 100-mesh dolomites, the conversion was not expedited to the extent desired. The 1hour heating of 100-mesh unstirred charges from cold to 600" C. was not long enough to induce complete conversion of the contained magnesium carbonate to magnesium oxide. Extensions of calcinations beyond 2.5 hours at 600" C. proved unnecessary and conducive to higher percentages of free calcium oxide in the calcines. Obviously, the 0.25- to 0.50-inch screenings were not sufficiently fine because, even after 2.5-hour calcination a t 600' C. in Bteam, their calcines had acquired only half transitions of magnesium carbonate to magnesium oxide. Even so, the half calcinations of the large particles in steam exceeded greatly the - 1% decompositions of those screenings after the longer heatings at 600" C. in air. The run of mine (20-mesh screenings) of the Knox dolomite suffered only slight decomposition a t 600" C. in air, yet yielded a good calcine at 600" C. in steam. Again, 3-hour imposition of 650' C. was not admissible, because of the high percentage of engendered calcium oxide. The low percentage of free calcium oxide in the steam-induced calcines of the Knox dolomite is noted because of the relative stability of the 9 to 10% content of calcite that occurs in the interstices between the distinctive dolomite crystals of that rock. Through substitutions of five gases in multiple calcinations of dolomite in the stationary quartz tube furnaces, it was established that dolomite can be calcined into calcium carbonate-magnesium oxide selectively a t 550" C. in an atmosphere of steam and steam functions catalytically in the lowering of dissociation temperature. IN SPECIALELECTRIC FURNACE. Although the imposed atmosphere expedited selective calcination, greater rapidity was sought by means of a specially designed revolving furnace, in which 500-gram charges of dolomite were kept in continuous motion (Figure 3) by means of shallow horizontally placed lifts in the cylindrical chamber, which was rotated continuously by means of a sprocket chain. The charges were kept in sliding motion from side to bottom, and vice versa; but the lifts did not provide rabbling or agitation, and steam was not injected into the charge. After the air of the furnace had been displaced, input of steam was continuous and slow and was not a sweeping action to effect rapid diminution in carbon dioxide pressure. Hence in the furnace chamber atmospheres soon were preponderantly steam and were diluted only through the relatively slow evolution of carbon dioxide a t a temperature that precluded carbonatation. The 500-gram charges of Tennessee and North Carolina dolomite fines calcined in steam atmosphere in this furnace yielded calcines similar to those obtained from the 25-gram charges in the tubular electric furnace. The calcines from four samples of New Jersey dolomite a t 98.5% purity (Table 111) are representative of the products ob-
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%°0'
"f
4
I
I
I
I
I
2
3
4 DAYS
5
6
Figure 4. Speed of Hydration, at Room Temperature, of Magnesium Oxide Contents of Four Dolomite Calcines A.
B.
C. D.
1.25-hour calcination a t 600' C. i n steam, free CaO content 1.05% I-hour calcination a t 650' C. in steam, free CaO content 1.98% 3-hour calcination at 550' C. i n steam, free CaO content 0.79% 3-hour calcination at 725O C. i n air, free CaO content 0.70%
tained from 500-gram charges by means of the mechanically rotated furnace (Figure 3). Again the steam functioned as a catalyst to effect a substantial lowering of calcination temperature; but the desired brevity of calcination was not attained and rapidity in selective calcination was the chief objective of the subsequent large scale operations.
TABLE 111. SELECTIVE CALCINATIONS O F 600-GRAM CHARGES OF WEST VIRGINIADOLOMITE^ INTO CALCIUM CARBONATE AND MAGNESIUM OXIDEIN ATMOSPHERE OF STEAMAT 600" C.
IN AN
ELECTRIC FURNACE^
Selective Calcine, CaCOs Equiv., % 140 0 139 6 140 0 141 8 a b
COz LOSS,
%
24 24 24 24
08 09 06 09
cscos res., Yo 52 52 52 52
09 07 13 07
Composition of Calcine, % CaO Magnesium as CaCOs CaCOa Free equiv. equiv. MgO 0 79 1 41 87 91 42 02 0 80 1 43 87 53 87 42 00 41 84 0 77 1 37 0 80 1 43 89 73 42 89
100-mesh 98.52% purity. Duration: 3 hours; continuous motion of charge in furnace, Figure 3.
Reactivity of Selectively Engendered Magnesium Oxide. One hoped-for result was that calcination of dolomite a t the lower temperature would yield a reactive form of magnesium oxide. Therefore, the specific reactivities of the oxide components of the four calcines of Table IV were measured through 7-day progression in uptake of water in humidified atmosphere at room temperature. The ultimate hydration of calcine A from the 1.25hour heating in steam a t 600" C. was 4% greater than the ultimate hydration of calcine B (1 hour a t 650" C . ) , which had a
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INDUSTRIAL AND ENGINEERING CHEMISTRY
higher percentage of the more readily hydrated oxide of calcium. However, the 3-hour calcines in steam a t 550" C. and those in air a t 725" C. registered comparably in thr rapidity and percentages of water uptake.
TABLE IV. INFLUEKCE O B PARTICLE SIZEA K D AGITATION^ CAI1CIK.4TION
O F APPALACHIAK
fi'1ARBI.E
IN
ON
ATRIOSPHERC O F
STEAMAT 700" C. Particle Size of Marble Charges, Inch -1, +0.5 ' --0.,5 +o.zii 0 : 2 5 , ' +S-mesh -ZO-mesh, f100-mesh Through 100-mesh Through 100-meshb Through 100-meshc . -%mesh +20-meshu -&mesh: +ZO-mesh e
-
Agitateda No pi0 K O
Yes Y es Yes Yes Yes Yes
Charge, coz Grams Grams % 25.11 4.5 17.9 25.4 5.03 19.8 25 5 . 7 1 22.84 25 10.61 42.44 25 11.1 44.4 10.62 42.48: 25 25 5 . 9 3 23.72 25 0.4 1.6 26 10.6 42.4
Calcine Assay, 70 Free CaO COZ 26.25 ... ... 30.10 ... 36.75 1.45 ... . . 0.70 2.40 ... ,.. 26 24 1.75 ... 1,07 ..
Calcinations of Fines in Steam in 20-Foot Externally Heated Tubular Furnace. I n all of the foregoing steam-induced calcinations the charges of dolomite were merely exposed to steam, and in no case was i t injected into or atomized into the dolomite. Whether such injection would expedite calcination was a particular objective in the succeeding large scale calcinations that were made in an oil-fired 3 X 20 foot Traylor cast iron 6-tube dryer, which was housed in a 40 X 60 foot building. The dryer was modified to allow the influx of steam into the si.; horizontal tubes in the segments above the combustion chamber. The input of steam was through a concentrically placed 1-inch pipe that was provided with a Rlorand joint, and thence into a battery of 0.5-inch pipes that extended 8 feet into the six tubes in which calcinations took place. These tubes were 6 inches in diameter and were made of 3/16-inch tubing. The smaller pipes were provided with multiple spindles that were welded to the pipes a t right angles. I n exploratory batch calcinations of 500pound charges of Knox dolomite the termini of the spindles were about 1.5 inches from the walls of the 6-inch tubes; but it was found necessary to decrease that space. I n 48 daily calcinations of the 95 conducted, the 500-pound charges of dolomite were preheated during slow progress from the "coo1 end" of the six tubes of the furnace to the 6-foot zone above the fire box t h a t maintained the operative temperature of 600" C. in the delivery end of the six tubes. T o assure imposition of that temperature into the dolomite a t the inside wall of the 6-inch cast iron tubes of 925' C., the flame was located at the bottom of the firebox to meet the 925' C. requirement forthe outside of the cast iron tubes. The temperature readings were registered by thermocouples and also by means of an optical pyrometer. Calcine delivery was through its discharge into a closed housing, which was provided with a counterweight gate. The compositions of the calcines from the exploratory batch runs on stirred fines in steam atmosphere, and durations of calcination, were similar to the results obtained by means of the electric furnaces in the laboratory. Later, however, selective calcines resulted from injections of steam into the moving dolomite 1.75 hours after its introduction as cold fines. Immediately after the deep injection of steam into the preheated agitated dolomite a t 600" C. the outgoing gases registered a n increase of 200' C. for 1 hour, and indicated the period in which an ideal carbonate-oxide calcine was being attained. The superheating of the steam before its injection in the Traylor unit did not expedite the conversion of dolomite into the selective calcine. The basic structure of the loaned Traylor cast iron dryer was not modified appreciably through the adjunct equipment for the introduction of dolomite charge, for input of steam, or for calcine delivery. Variations in the location of the burners in the combustion chamber and in furnace operation were pointed to the expediting of selective calcination. A condition that proved imperative to effect speedy calcination a t 600" C. was that the steam delivery spindles should terminate close to the walls of the externally heated tubes. The atomized jets of steam passed into the
Vol. 45, No. 7
dolomite fines under 25-pound pressure and helped t o stir them a t critical temperature as they "waved" against the wall of the tubes. Jointly, the atomized input of steam and the concomitant ebullition of liberated carbon dioxide caused the dolomite charge to undergo vigorous "boiling," much like that caused by release of combined mater from gypsum during its calcination into its semihydrate. This "boiling" of the preheated and:steamimpregnated charge ensued, however, upon arrival of the dolomite into the 6-foot zone, where the temperature of 600" C. was maintained while steam was being atomized into the agitated charge. When the essentials were met, the influxed fines were converted into carbonate-oxide calcines within 15 to 20 minutes. Similar findings were obtained in tests conducted recently in an industrial investigation. The finer the charge, the more rapid was the production of an ideal selective calcine. Calcinations of fines of moist Ilnox dolomite were more expeditious than calcinations of kiln-dried material, and an appreciable increase in duration was necessary to obtain an ideal calcine of that fraction of the 35-mesh dolornit? that was coarser than 100-mesh. After multiple selective calcinations of batches of Knox dolomite had established ideal conditions, the Traylor dryer v, as used in continuous operations in three %hour labor shifts to obtain daily outputs of 2.5 tons of selective calcines from fines of Knox and North Carolina dolomites. The calcines from the Knox and North Carolina dolomites had calcium carbonate-equivalent values of 118 and 132%, respectively. The emergent gas from the calcinations in the Traylor dryer was comprised of steam and carbon dioxide, with only nugatory incidence of hydrogen sulfide from the small occurrences of sphalerite in the dolomite. When the vented gases reached the "dew point" of steam, the hydrogen sulfide passed into the condensate, and the eventual effluent was virtually carbon dioxide, utilizable for the production of dry ice. Although ideal calcinations should not b~ expected from the modified cast iron equipment that had been intended as a dryer, and not as a furnace, the 6-month use of the second-hand dryei demonstrated that selective calcinations of dolomite could be made in steam a t 600" C. without using special metal for the 6inch tubes that were exposed to that temperature, although the immediate observation might not hold for extended periods. Other types of calciners will prove applicable and effective, as indicated by Hall and Jolley (12). Laboratory findings confirmed earlier conclusions that a product comprised of calcium carbonate and magnesium oxide can be produced through prolonged calcination of particulate dolomite in air a t 725" C. Heated t o 600 C. in nitrogen. helium, ammonia, or air, dolomite fines proved virtually stable, whereas calcines comprised of calcium carbonate and magnesium oxide were obtained through corresponding calcinations in steam. Obviously, the dolomitic combination was disrupted a t 550" C. in steam, because extended heating a t that temperature resulted in ideal selective calcines. Such calcines were obtained when 500gram charges of dolomites from Tennessee, North Carolina, and West Virginia were calcined in steam in a rotary electric furnace (Table 111, Figure 3) and also through calcinations of 0.25-ton inputs of fines of Knox and North Carolina dolomites a t 600" C. in steam in the oil-fired Traylor dryer. The deep injection of steam into the preheated moving charges of doloniite fines in the 3.75-foot zone of the dryer a t 600" C. caused the effluent gas t o show a rise of 200" C. for an hour and resulted in an ideal selective calcine. Daily productions of 2.5 tons of selective calcines were obtained from calcinations of dolomite fines in steam a t 600' C. in three-shift-per-day operations of the oil-fired Traylor unit. In those operations the selective decompositions occurred within 15- t o 20-minute passage through the outgo zone a t 600" C. and the finer the dolomite, the more rapid were the calcinations. Upon the basis of records for all consumption, generation of steam, and output of dolomitic calcine per day-and disregarding economic conservation of carbon dioxide-the costs of continu-
July 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1553
ous calcination of dolomite t o calcium carbonate-magnesium oxide in steam in an indirectly k e d tubular dryer were computed by engineer personnel of two reputable manufacturing agencies. Both engineers reported that the proved calcinations of dolomite fines a t 600' C. in steam can be utilized for the economic production of a calcine comprised of calcium carbonate and magnesium oxide. Besides the utility of the selective calcine in imparting available magnesium in fertilizers and in soils, the product can be utilized in economic procedures, such as the extraction of magnesia by means of hydrogen sulfide ($6)and the production of magnesium thiosulfate (88). CALCINATION O F HIGH-CALCIC LIMESTONE FINES AT 700' C. I N STEAM
"
1
The major difficulties encountered in the manufacture of high grade burnt lime are the incomplete conversion of the limestone into caustic lime, or "underburning," and the opposite effect, the deactivatibn of the calcine through "overburning." Limestone of high purity is apt to yield an inferior grade of burnt lime when calcination at admissible temperature is prolonged unduly, or when an excessive temperature is imposed over a shorter period. Such inferiority of burnt lime from high-grade rock is due to collapse in the structural arrangement of the skeleton of the crystals of the starting rock (b), with resultant formation of a dense and relatively impervious calcine, as distinguished from one of ideal porosity. The probability of detrimental effect from excessive temperature and unnecessary duration in the calcinations of lumps of limestone in a shaft kiln is increased when imposed temperature exceeds 910" C. Although that temperature is "critical" for the disruption of calcium carbonate, the temperature in the shaft kiln must be much higher t o assure rapid and adequate penetration of heat into the lumps. The fundamentals of lime burning were discussed comprehensively by Cunningham (9). It seemed logical that the expedited calcination of limestone at a low-ered temperature should result in a more reactive lime, with attendant savings in fuel and less rejection of calcines. Therefore, after the catalytic function of steam had been demonstrated through the selective calcination of dolomite, a like effect of steam was tested in experimental calcinations of high-calcic limestones. Experimental. Limestone separates were calcined in an atmosphere of steam in the laboratory furnace (Figure 3) at various temperatures downward from the 910" C. critical. The exploratory calcinations established 700 O C. as the temperature at which the catalytic steam induced complete conversion of limestone to lime ( 2 7 ) , whereas parallel heatings of the limestone at 700 C. in air caused a carbon dioxide loss of only 1.6%. The effect of a temperature differential of 50" C. in the calcinations of steam is registered through the substantial difference between the 2.401, residue of carbon dioxide after 2.5-hour calcination a t 700" C. and the 26.24% residue after the 3-hour calcination at 650" C. Conversely, the loss in weight from the 3-hour calcination a t 650 O C. was only 53% of the loss induced by the 2.5hour calcination a t 700" C. I n contrast to the 26.24% of carbon dioxide in the residue from the 3-hour calcination a t 650" C. (Table IV), the calcine from the 3-hour calcination at 700' C.an elevation of 50 a C.-contained only 0.70% carbon dioxide. As in the selective calcinations of dolomite, the several factorsatmosphere, particle siae, agitation, and duration-were considered, singly and jointly. The data of Table 111 register h d i n g s for calcinations of coarse particles and 100-mesh limestone in an atmosphere of steam, without its injection into the charges and without agitation. Even so, near absolute calcines were obtained from 2.5-hour calcinations of -20 100-mesh and 100-mesh screenings a t 700" C. in steam. Apparently, 8-mesh limestone could be calcined satisfactorily in similar operations in rotary kilns. Moreover, the migration. or r'flow,'' of limestone fines
+
1
2
3
4
5
6 7 6 MINUTES
9
1011 I 2 1 3 I C
Figure 5. Hydration Reactivities of CommeroiaR Caustic Limes and Limes Calcined at 700" C. in Steam Atmosphere Measured by rise in tempcrature in wetting of CaO calcines k Commercial shaft kiln product from Appalachian marble A-1. Product from 700' C. rotary kiln calcination of Appalachian marble fincs i n steam atmosphere B. Commercial abaft kiln product from Williams marble B-1. Product from 700° C. rotary kiln calcination of Williams marble fines i n steam atmosphere
that contained some particles coarser than 100-mesh was more uniform than that of a charge of exceeding fineness. These findings, and those obtained in the dolomite calcinations, were used as controls in subsequent calcinations t o obtain some 20 tons of lime b y means of the Traylor dryer. Again, it was established that the finer the particles of limestone the more expeditious was the conversion and t h a t deep injection of steam into the limestone in motion was essential to expedite complete calcination. While the conversions of limestone fines a t 700' c. in steam represented a decrease of 210 ' C. from the recognized critical for the calcination of calcium carbonate in air, that decrease does not register the larger difference between 700°C. and the temperature imposed for calcinations of limestone lumps in shaft kilns. Properties of Lime Obtained through Calcinations in Steam. After 700' C. had been established as critical for calcination in steam, two Tennessee limestones of 98.5y0 purity were converted into calcines A-1 and B-1 of Table V, through calcinations at 700' C. in steam for comparisons with the corresponding commercial limes, A and B.
TABLE V. SOLUBILITYVALUBSOF T w o COMMERCIAL Lmas AND
LABORATORY CALCINESOBTAINEDAT 700' C.
STEAM"
Carbon Dioxide,
96 0 97.5 95.1 92.9
1.4 0.1 2.2 1.6
%
Commercial lime A Experimental calcine A-1 Commercial lime B Experimental caloine B-1 5 From Tennessee marble.
IN
Water-Soluble Lime,
%
Calcine A-1 was from a - 1/8-inch t o 1-mm. screening, and calcine B-l was from a 10-mesh screening, 52% of which was 100mesh. Commercial lime A was hot when drawn from a shaft kiln of the Knoxville Lime Manufacturing Co. ; lime B was a bagged ground product from the Williams Lime Co., of Knoxville. The samples of the two commercial limes were passed through a 100mesh screen and preserved in air-tight containers.
-
The rise in temperature that occurs when lime is immersed and the persistence of a suspension of the resultant hydroxide are
INDUSTRIAL AND ENGINEERING CHEMISTRY
1554
Vol. 45, No. 7
determined upon each of the 100-mesh samples of the four limesA, 8-1, B, and B-1-that had been evaluated according to watersoluble calcium oxide content.
A 7.5-gram charge was placed in a tall insulated glass cylinder and its temperature and t h a t of the freshly boiled distilled water were recorded. Twenty milliliters of t h a t water was added to the lime charge and the mixture was stirred constantly by means of a thermometer. Readings were made a t intervals of either 15 or 30 seconds until rise in temperature was maximal and noticeable quantities of moisture were being dispelled, particularly from calcines A-l and B-l, both of which induced a temperature reading of 98” C. a t a laboratory altitude of 1000 feet. The elevations in temperature readings, graphed in Figure 5, show that calcines A-1 and B-1 were decidedly more reactive than the commercial limes A and B. Calcines -4-1 and B-1 induced temperature of 98” C. in 15 seconds against a rise to 75” C. for lime B in 7 minutes, and to 60’ C. for lime A in 8 minutes. Settling Rates of Hydrated Limes from Steam-Induced Calcines. One factor in the evaluation of burnt lime for certain uses is the persistence of its hydrate as a dispersoid in an aqueous system. That behavior is measured through its reciprocal, or the settling of the hydrate of the burnt lime from a suspension that was uniform initially.
901
4 Ib i
210
2‘s i o is 40‘ 45‘
50 ‘
HOURS
I
24
MINUTES
F i g u r e 6. S e t t l i n g R a t e s of F r e s h l y H y d r a t e d L i m e s from C o m m e r c i a l C a l c i n e s a n d L i m e s M a d e at 700” C. in S t e a m A t m o s p h e r e A.
A-1.
B. B-1. C.
D.
Hydrate of commercial shaft kiln product from Appalachian marble Hydrate of product from 7W0 C. rotary kiln calcination of Appalachian marble fines i n steam atmosphere Hydrate of shaft kiln product from Williams marble Hydrate of product from 700‘ C. rotary kiln calcination of Appalachian marble fines in steam atmosphere Hydrate of commercial rotary kiln ‘&mildburn” product from dense stone (53) Hydrate of commercial shaft kiln “hard burn” product from dense stone (53)
used in the evaluation of burnt lime. Findings for the values indicated by the data of Table V and the graphs of Figure 5 were obtained in conformity to observations and statements by Washburn (65) and others, as given in an American Society for Testing Materials Symposium on Lime, Columbus, Ohio, in 1939. WATER-SOLUBLE CaLcImi OXIDE COSTEKT. High-calcic limes are evaluated upon the basis of their “water-solubility” and high-calcium quicklime usually contains from 88 t o 90% water-soluble calcium oxide ( 5 3 ) . The value cited does not mean t h a t such percentage of free lime is dissolved from a burnt lime through a single aqueous extraction. The term “water-soluble” is a misnomer, because a saturated solution of lime is one of low concentration, and a single saturated extraction from an analytical charge of lime could dissolve only a fraction of the charge, which then would have been converted into calcium hydroxide. Nevertheless, the calcium oxide content of an analytical charge of a burnt lime could be extracted cumulatively through successive aqueous extractions. Therefore, the designation “potential water-soluble calcium oxide” would be more exact than the expression “water-soluble.” The percentages of free calcium oxide in limes A, A-1, B, and B1 were determined by means of the sucrose procedure (50), and are given in Table T’. All solubility values were above the 90% value that was cited as requisite for a calcine t o be classified a superior lime. Rise in Temperature from Wetting of Burnt Lime. Rise in the temperature of a paste formed upon the addition of a definite quantity of distilled water t o a definite weight of caustic lime is an accepted criterion for chemical ILreactivity.” That value was
Ten milliliters of the boiled distilled water was added to a 7.5gram charge of 100-mesh burnt lime in a beaker, and the mixture was stirred immediately to a thick putty of hydroxide by means of a glass rod. In 30 seconds calcines A-1 and B-1 were converted into smooth hydroxide pastes, whereas 10 minuteswererequiredto bring the commercial limes into similar pastes. The beaker t h a t contained the watered paste then was placed under a bell jar, along with a guard of soda-lime, and was kept there 1 hour to assure complete hydration of the oxide. Then 75 ml. of boiled distilled water was poured into the beaker, and its contents were stirred into a homogeneous suspension which was poured into a 100-ml. graduated cylinder immediately and made to volume through washings from the beaker, and then agitated thoroughly. The depth of the clear supernatant and depth of its reciprocal suspension of calcium hydroxide then were read a t ten successive 5-minute intervals, and finally, after 24 hours. The graphs in Figure 6 show the settling rates for commercial limes A and B, experimental calcines 8-1and B-1, and two commercial limes that had been evaluated by Washburn (55). The two limes from the calcinations a t 700’ C. in steam were exceedingly pulverous, as registered by their decidedly greater tendencies to remain in suspension. The configurations show substantial disparities between the settling rates registered by commercial limes and those registered by the two calcines. The corresponding differences in the depths of settled hydrates were still substantial after 24 hours, when the maximal difference between the largest and smallest final volumes of the hydroxide solids was 47.5%. The superiority of calcine A-1 over lime A from the shaft kiln was evidenced by the marked disparity in the configurations between the settling rates, and also through the differencebetween the volumes of their solids after 2-2 hours. The foregoing values are accentuated in relation to the differences between the properties reported by Washburn ( 5 3 )for limes from “mild” and “hard” burnings of a Pennsylvania limestone, as reflected by the decided differences in the settling rates of the commercial products, C and D, and by their final volumes (63). Summary for Calcinations of Limestone Fines a t 700” C. in Steam. After electric furnace calcinations of limestone fines a t 700” C. in steam had demonstrated complete conversions of calcium carbonate to calcium oxide, ten &ton lots of high-calcic limestone fines were calcined completely and expeditiously in an oil-fired 3 X 20 foot 6-tube rotary dryer. The prescribed operation brings the fullest exposure of limestone fines t o a catalytic atmosphere and into a “boiling” that is induced jointly by the atomized influx of steam and the evolving carbon dioxide. I n comparisons as to “solubility,” conversion to pastes and rapidity of slaking, and settling rate, the limes produced from
e
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1953
two Tennessee limestones a t 700” C. in steam proved superior to corresponding limes from industrial kilns. The gaseous effluent from the prescribed calcination in steam at 700 O C. was readily freed of solid matter, and a t the dew point of steam the effluent gas becomes high-purity carbon dioxide that is available for liquefication and for conversion into dry ice. The foregoing findings ($7) represent the initial record of jointly implemented catalysis and mechanics of fluidization to effect a markedly expedited calcination of limestone fines a t a substantially lowered temperature. ACKNOWLEDGMENT ”x
w
The laboratory findings and their implementation into large scale operations on both dolomite and limestone were the immediate responsibility of the late junior author. Material assistance in the limestone calcinations was rendered by Jack Thompson, now of Oak Ridge, Tenn. REFERENCES (1) Assoc. Offic. Agr. Chemists, J . Assoc. Ofic. Agr. Chemists, 21, 58 (1938). (2) Azbe, V. J., Rock Products, 51, 86-9 (September 1948). (3) Azbe, V. J., “Theory and Practice of Lime Manufacture,” pp. 36-9 (as of 1926). (4) Bailey, Rock Products, 25, 19 (Oct. 7 , 1922). (5) Bole, G. A., and Shaw, J. B., J . Am. Ceram. SOC., 5,817 (1922). (6) Clarke, F. W., U. S.Geol. Survey, Bull., 330 (1908). (7) Ibid., 616 (1916). ( 8 ) lbid., 770, 566 (1924). (9) Cunningham. W. A.. IND. ENG.CHEM..43. 635 (1951). (10j Frear, Wm., Pa. State College Expt. Sta., Annual Report, Part 2, 48 (1899). (11) Garner, W. W., McMurtrey, J. E., Bacon, C. W., and Moss, E. G., J . Agr. Research, 23, 27-40 (1923). (12) Hall, C. C.. and Jolley, L. J., Petroleum, 13, 217-23 (September 1950). (13) Herzfeld, Festschrift zur Eroffnung des Instituts ftir Zukerindustrie, p. 469, cited by Knibbs (16, p. 102). (14) Kallauner, O., Chem.-Ztg., 37, 1317 (1913). (15) Kite, R. P., and Roberts, E. J., Eng. Mining J., 148, 146-50 (November 1947); Chem. Eng., 54, 112-15 (December 1947). (16) Knibbs, N. B. S.,“Lime and Magnesia,” London, Ernest Benn, 1924. (17) Lathe, F. E., Proceedings of Engineering Institute of Canada, Montreal. Quebec. Feb. 8-9. 1934. (18) Leather, J. W., and Sen, J. N., Mem. Dept. Agr. India, Chem. Ser., 3, No. 8, 204-34 (1914). (19) Lenhart, W. B., and Rockwood, N. C., Rock Products, 11, 3-116 (January 1948). (20) Lime Conference Proceedings, Knoxville, Tenn. 1
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1555
Lipman, J. G., Blair, A. W., McLean, H. C., and Prince, A. L., S o i l S ~ i .15, , 307-28 (1923). MacIntire, W. H., J . Assoc. Ofic. Agr. Chemists, 16, 589-98 (1933).
MacIntire, W. H., Soil Sci., 7, 325-453 (1919). MacIntire, W. H. (to University of Tennessee), U. S. Patent 1,953,419 (1934).
MacIntire, W. H. (to American Zinc, Lead & Smelting Co.), Ibid., 2,118,353 (1938). Ibid., 2,155,139 (1939). Ibid.., -,-2.212.446 . - ~(1940). Ibid., 2,403,940 (195lj. MacIntire, W. H., Hardin, L. J., and Oldham, F. D., IND. ENG.CHEM.,28, 711-17 (1936). Ibid., 30, 651-9 (1938). MacIntire, W. H., and Shaw, W. M., Ibid., 24, 1401-9 (1932). MacIntire, W. H., and Shaw, W. PI., J . Am. SOC.Agron., 22, 14-27 (1930). Ibid., pp. 272-6. Ibid., 26, 656-61 (1934). MacIntire, W. H., and Shaw, W. M., Soil Sci., 20, 403-12 (1925). MacIntire, W. H., Shaw, W. M., Hardin, L. J., and Winterberg, S.H., Ibid., 65, 27-34 (1948). MacIntire, W. H., and Shuey, G. A., IND.ENQ. CHEM.,24, 933-41 (1932). MacIntire, W. H., Winterberg, S.H., Sterges, A. J., and Clements, L. B.. Soil Sci.. 67, 289-97 (1949). Mehring, A. L., Research Administration, U. S. Dept. Agr.,. letter, Dec. 4, 1951. Mitchell, A. E., J . Chem. SOC.Trans., 123, 1055 (1923). Murray, J. A., Fischer, H. C., and Shade, R. W., Proceedings. p. 32, Annual Convention of National Lime Assoc., hIay 11-13, 1950. Myatt, D. O., Chem. Eng. News, 29, 686 (1951). Ostwald, W., Physik. Z., 3, 313 (1902). Rex, C. R., U. S.Patent, 2,193,842 (1940). Scherer, Robert, “Der Magnesit,” Vienna, Hartleben, 1908. Schwab, G.-M., Taylor, J. S.,and Spence, R., “Catalysis, from the Standpoint of Chemical Kinetics,” p. 16, New York, D. Van Nostrand Co., 1937. Shaw, J. B., and Bole, G. A., J . Am. Ceram. SOC.,5 , 3 1 1 (1922). Shaw, W. M., J . Assoc. Ofic. Agr. Chemists, 24, 244-9 (1941). Shaw, W. M., MacIntire, W. H., and Hill, J. J., Univ. Tenn. Agr. Expt. Sta., Bull. 212 (July 1949). Shaw, W. M., MacIntire, W. H., and Underwood, J. E., IND. ENG.CHEM.,20,312 (1928). Sweet, F., Comm. Fertilizer, 76, 14-21, 42-3 (April 1948). Van Tuyl, F. M., Iowa Geol. Survey, 25, 251-422 (1914). Washburn, D. E., A.S.T.M. Symposium on Lime, Columbus Regional Meeting, March 1939. Whitaker, C. W., Rader, L. F., Jr., and Zahn, K. V., Am. Fertilizer, 91, 5-8, 24 (Dec. 9, 1939). RECEIVED for review September 18, 1952. ACCEPTED March 18, 1953. Presented before the Division of Fertilizer Chemistry at the 122nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J.
Some Reactions of Polychlorotri-
fluoroethylene J
MATTHEW T. GLADSTONE1 General Electric Research Laboratory, Schenectady, N . Y .
P
OLYCHLOROTRIFLUOROETHYLENE [Poly F-1113, Kel F (M. W. Kellogg Co.), Fluorothene (Carbide & Car-
bon Chemicals Corp.)] is reported to be thermally stable and chemically inert (4,8,9). Chemical tests on the polymer have generally been run below 100” C., and Frey et a2. ( 2 ) report that under these conditions only chlorine caused a color change in the test sample. Thermally, Watson et al. ( I f ) have shown that poly1
Present address, Behr-Manning Corp., Troy, N. Y.
monochlorotrifluoroethylene does not show any significant decomposition as evidenced by loss of weight or evolution of gas a t 250” C. or below when heated for 3 hours a t temperature in a stream of moist air. However, as this polymer is considered for higher temperature use (4), the effect of various chemicals a t elevated temperatpres is of interest. Therefore the reactions of some organic substances t h a t may be used as dispersion or solvent media and metals t h a t may be used as substrate for films have been studied.
