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INDUSTRIAL A N D ENGINEERING CHEMISTRY
yields, Those determined, the technic of the catalytic chemist must be called in to find the catalysts most suitable for the two reactions. This achieved, the engineer is required to adapt the process to technical operation and the
Vol. 18, No. 9
economic expert to decide whether the process so adapted has commercial possibilities. I n such ways there are added to the growing list of catalytic processes new examples and a wider range of further consequent possibilities.
Effect of Time and Temperature of Burning on the Properties of Lime' By R. T. Haslam and E. C. Hermann CHEMICAL ENCINBRRINC DEPARTMENT, MASSA CHUSBTTS INSTITUTE
OF
TECHNOLOGY. CAMBRIDGD, MASS.
The effect of time and temperature of burning on the LTHOUGH lime burnof 30 minutes was required to propertfes of lime have been studied. Two limestones ing is one of the oldbring the furnace and its were used, one a n Eastern stone not usually considered est chemical i n d u s contents back to the desired to be capable of producing a plastic hydrate, and the tries, little definite informatemperature. other an Ohio stone that does give a plastic hydrate. tion regarding it is availNumerous preliminary runs It has been found that there is an optimum temperaable. For example, i t is a were made to determine the ture and time of burning for the production of the most commonly accepted fact that best size of stone and shortplastic lime and that these optimum conditions proest time necessary for comwood-burned lime is better duce a very plastic hydrate from each limestone. Rate than that burned with coal. plete calcination a t the lowest of interaction of the lime hydrates with acid, the rate temperature used, 1800" F. The reasons given for this of settling, and volume of putty all vary with the plasThis was found to be 3 / 4 to superiority are legion, the ticity. The indication is that fineness of the hydrate 1 inch stone and a time of 3 most frequent ones being the particles is an important factor in producing a plastic hours. Time was reckoned effect of the large amount of hydratefrom the moment the limewater present in the wood and the lack of sulfur. The moisstone was placed in the furture in the wood was believed by the authors to be a n im- nace until the power was shut off and the cooling had portant factor; however not of itself, but because it lowered begun. At the end of the 3 hours the power was shut the temperature of the flame. The present investigation off, the top of the furnace removed, and the lime allowed was based on this belief-namely, that the most important to cool to room temperature. After cooling it was removed factor in lime burning is the temperature a t which the lime and ground to pass through a 10-mesh screen and then is burned. As the investigation proceeded the effect of time put into tightly covered tin cans to prevent air slaking. of burning was studied beca,use the temperature effect did The other runs with varying times and temperatures were made in the same manner. Temperatures were measured not offer a complete explanation. by means of an optical pyrometer. Limestones Investigated HYDRATION OF LIME-A weighed amount of the lime was The two limestones studied in this investigation were placed in a tin can set into a basin of running cold water. (1) a n Eastern stone that usually gives a nonfinishing hydrate On the assumption that the composition of the lime was when burned commercially, and (2) an Ohio stone that is 90 per cent CaO, enough water was measured out to hydrate used to produce a plastic finishing hydrate. The analyses the lime, with 50 per cent excess to take care of evaporation. of these two limestones are as follows: The water was added slowly and the mass was vigorously stirred to prevent the formation of lumps and local overEastern limestone Ohio limestone Per cent Per cent heating. The hydrate formed was set aside in glass containCaO 34.35 30,63 ers for one day to age, after which it was ready for analysis 14.45 20.60 2.63 0.26 and testing. This procedure produced a dry hydrate. 0.81 0.30 FezOa SiOa 3.43 0.28 DETERMINATION OF PLASTICITY-This was carried Out Loss in ignition 44.50 47.96 according to the method outlined by the American Society Procedure for Testing Materials.2 Briefly the method was as follows: Three hundred grams of lime were hydrated as above, but PREPARATION OF S-mmLE-The limestone was received in large lumps and these were crushed down t o an average size instead of aging were immediately formed into a putty by of from 3 / 4 to 1 inch in a Dodge crusher, the fines being dis- adding a sufficient quantity of water. This putty was allowed to soak in a beaker covered with a damp cloth for not carded. CALCINATION-The limestone was calcined in the electric less than 16 nor more than 24 hours. It was then molded resistor furnace shown in Figure 1. It was possible to hold the in a rubber ring such as is used with a Vicat needle, resting the temperature constant to within 25" F. without any trouble, specimen on a glass plate. The needle used was a modified form of the Vicat needle, and with care this could be regulated to within 10" F., by made of a piece of aluminum tubing 12.5 mm. in diameter changing the pressure on the electrodes or throwing the power and filled with shot to weigh 30 grams. The lower end was switch on and off. After t h e desired temperature was reached and the furnace closed without shoulders or curvature. It was mounted in had had time to heat evenly, 5 pounds of the prepared lime- the Vicat needle stand. The initial reading was taken with stone were dumped into the clay-graphite, porcelain-lined the bottom of the needle in contact with the surface of the crucible. This cooled down the furnace, and a maximum specimen; the final reading was taken 30 seconds after the
A
2%
I Presented a t the 8th Annual Convention of the National Lime Association, French Lick, Ind., June 10, 1926.
2 Standard Specifications for Hydrated Lime for Structural Purposes, Serial C-6-24,p. 715 (1924).
INDUSTRIAL A N D Rh'GINEERING CHEMISTRY
September, 1926
plunger was released. A penetration of 20 mm. was considered standard with a permissible variation of 5 mm. on either side. If the penetration was less than standard, the sample was removed from the mold, mixed with more water, and retested. If the penetration was more than standard, the sample was discarded and a new one prepared.
1
7
1
961
base plate and paste were placed in the instrument and the carriage turned up by hand until the surface of the paste was in contact with the disk and the distance between the disk and the top of the base plate was ll/q inches. The carriage was then thrown into gear and the motor started exactly 120 seconds after the first portion of the paste has been put into the mold. The time when the first portion of the paste was put into the mold was recorded as zero time. Care was taken to protect the specimen from drafts during the test. The scale r e a d i n g w a s recorded every min0.70 Ute until the test was completed. 0.60 T h e t e s t was c o n s i d e r e d comO.M p l e t e when (a) the scale reading r e a c h e d 100, ( b ) a n y reading was 040 less than the one before, or (c) the z 0.30 scale reading rem a i n e d constant o.20 for three consecutive readings ( 2 minutes) and the o,lo specimen had visibly r u p t u r e d o r broken loose from 0 20 40 60 BO 100 % SAMPLE D(550CVED the base plate. The t i m e a n d Figure 4 scale reading at the end of the experiment were noted. The plasticity figure was calculated from the formula
2
3
z
P
LONGITUDINAL SECTION Figure 1-Electric
Furnace
The sample was then ready for testing for plasticity. This was conducted on an improved form of the Emley plasticimeter, the constants of which were as follows:
I 200 -
r
VI 200
The rubber ring previously mentioned was lubricated with a thin film of water placed on a porcelain base plate filled with the paste and struck off level. The mold was removed by raising it vertically without distorting the paste. The
=
1/F?
+ (10T)Z
in which P is the plasticity figure, F is the scale reading a t the end of the experiment, and T is the time in minutes from when the first portion of the paste was put into the mold to the end of the test.
required to reach it were noted. V o L u M E OF PUTTY-One hundred
RATEOF SEmuNQ-This was done by the Holmes, Fink, and Mathers method,3 where 10 grams of the hydrate were placed in a lw-cc. graduate (2.58 cm. internal diameter), Chem. Met. Eng., 47, 1212 (1922).
ILVDVSTRIAL ASD ESGIhTEERIiYGCHE-VllSTRY
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filled to the 100-cc. mark, and allowed to settle, readings being taken every 5 minutes. RATE OF REACTION-This was done by the Whitman and Davis method,4 which consists in measuring the rate of interaction between the lime and hydrochloric acid.
Vol. 18, s o . 9
I n almost every case, for a given limestone, the greater the plasticity of the resultant hydrate, the faster is the rate of reaction with hydrochloric acid, the slower. the rate of settling, and the greater the volume of putty. These facts
Results
Table I shows the effect of the temperature of burning on the plasticity, rate of slaking (“quickness”), and volume of putty from both varieties of limestone. Table I1 shows the effect of time of burning these limestones on the plasticity of the hydrate produced from the resultant quicklime, the temperature of burning being maintained a t 2000’ F. Table I-Effect
Lemp.
n.
F.
Run
Time Hours
of Temperature of Burning Eastern Limestone
Plasticity p = dF2+(10T)2 195 410 342 398 454 198 217
RATE OF S L A K I X C Max. Minutes T’olume of temp. t o reach putty a. F. max. temp. Cc./IOO g .
...
0.73 0.25 0.25 13.0
I92 1i o 240 220 180
ai’
5.0
100
3.00 0.30 2.50
170 250 165
2400
12 13 14
1800 2000 2200
3 3 3
...
171 160 171 175 98.5
0.50
...
Okio Limestone 24 1 128 493 183 206 72
Table 11-Effect of Time of Burning Temp. F. Eastern Limestone 2000 2000 2000 2000 Ohia Limestone 2000 2000 2000
Run 9 8 and 9 (av.) 10 11 15
16 17
Time Hours
Plasticity
2 3 4 6
243 426 550 270
2 4 6
450 395
371
On account of the importance of plasticity and to afford a better coni p a r i B o n, the effect of temperature of burning the two limestones on the plasticity of the resultant hydrates is shown in Figure 2 while the effect of time of burning is shown in Figure 3. Other data are given in Figures 4 to ’7.
0.70
0.60
0.50
p 0.40 $ z 0 30
Y
F
0.20
Discussion of Results
0.10
I
I
I/Vl
V I
I
I
It w a s somewhat pur p r i s i n g Figure 5 to find the limestone (Ohio) that commercially produces a finishing hydrate just as susceptible to temperature of burning as the one that does not (Eastern). The runs dealing with the effect of time of burning indicate that, while each limestone is sensitive to temperature, the one that commercially produces a plastic hydrate is not susceptible to a variation in the time of burning. This fact may explain the relative ease of producing plastic hydrates from some limestones. 0
20
40 60 0 6 SAMPLE M S O L V L D
(THIS JOURNAL, 18, 118 (1926).
80
lOa
TIME IN MINUTES Figure 6
indicate that the fineness of the hydrate particles is a controlling factor in the plasticity of lime-the finer the particles the more plastic the hydrate. For factory control it should be practicable to use the rate of settling, a very quick test, as a check on the plasticity of the hydrate produced from a given limestone. It is also interesting to note that from a given limestone the lime xith the fastest rate of slaking-i. e., the quickest lime-produces the most plastic hydrate. This is not necessarily contrary to opinion prevailing in the industry, because this statement refers only to any given limestone.
0
IO
20
30
40
50
60
TIME IN MINUTES
Figure 7
Conclusions
I-The temperature at which a limestone is burned has an important bearing upon the properties of the resultant hydrates. In the laboratory a very plastic lime was made from limestone usually considered to be incapable of producing a plastic finishing hydrate. 2-Time of burning is of equal or greater importancei. e., the properties of the resultant quicklime are greatly influenced by the time of burning. 3-For the limestones studied. 2000” F. gives hydrates having the maximum plasticity and volume of putty and the slowest rate of settling.
Sept'ember, 1926
INDUSTRIAL A X D ENGINEERISG CHEMISTRY
4-The Ohio limestone, producing commercially a plastic finishing hydrate, does not seem to be sensitive to time of burning, whereas the Eastern limestone, not usually considwed as producing a plastic hydrate, is quite sensitive. &For a given limestone the plasticity of the hydrate seems
963
to increase with increasing volume of putty, increasing rate of interaction with acid, and decreasing rate of settlingall of which indicates that fineness of the hydrate particles is an important factor in producing plasticity.
Antioxidants and Their Retarding Action in the Deterioration of Rubber' By L. E. Weber2 729 BOYLSTON ST.,BOSTON, h1IASS.
HE physical properties of crude rubber, which determine its value as a useful commodity, are overshadowed by the physical properties of vulcanized rubber, with one striking exception; and it is a n irony of chemical fate that the only property of crude rubber which is actually impaired by vulcanization should be its stability. The higher grades of crude rubber are exceedingly stable provided the rubber is stored a t normal temperatures in the absence of direct sunlight; in fact, the rate of deterioration is so slow that no significant changes are observable over a period of many years. Devries, for instance, found that crude rubber which had been stored for four years showed no appreciable impairment in its quality. During the abnormally low rubber market, when crude rubber was held in storage for a long time, considerable apprehension mas felt that the stored rubber would shorn evidence of deterioration. S o n e was observable, however. Vulcanized rubber does not show this very pronounced stability. A rubber-sulfur mixture, normally vulcanized, will usually begin to show evidence of deterioration some time between the first and second year subsequent to vulcanization, and the deterioration will proceed more rapidly ii the mixture in question has been either under- or overvulcanized.
T
spread upon it. I n order to appreciate how extremely sensitive is this catalytic action of the copper, it should be realized that this percentage of copper is distributed throughout the cloth as a whole and only a very small fraction of the copper is in actual contact with the rubber. Inconsistencies in Oxidation Theory
There is, then, a large amount of evidence to indicate that the deterioration of vulcanized rubber is due to oxidation. The action of the oxygen is generally regarded as a n additive reaction involving the double bonds present in the rubber molecule, and the extent of the deterioration as proportional to the amount of oxygen absorbed. There are, however, certain inconsistencies. Chief of these is the fact that vulcanized rubber is considerably more susceptible to deterioration than crude rubber. It is difficult to reconcile this increased susceptibility to deterioration of vulcanized rubber with a theory of additive oxidation-that is, with a reaction involving merely the addition or absorption of oxygen by the molecule. An additive reaction involves one or more of the double bonds, and one would therefore expect crude rubber to be more sensitive than vulcanized rubber to an additive reaction with oxygen, since the degree of unsaturation of the crude rubber is higher. Therefore, crude rubTheory of Deterioration ber should be more susceptible to deterioration than vulThe deterioration, or perishing, of crude rubber is generally canized rubber, which we have found is not the case. In regarded as a process of oxidation. This theory was hinted other words, if we accept the additive oxygen theory of dea t some sixty years ago and evidence has been accumulating terioration, we are faced with the inconsistency that a subcrude steadily in substantiation. Briefly, the outstanding facts stance on a higher degree of unsaturation-namely, in support of the oxidation theory are the following: If rubber-is less susceptible to deterioration than vulcanized vulcanized rubber is exposed to sunlight in atmospheres, rubber, a closely related substance on a lower degree of respectively, of hydrogen, carbon dioxide, air, oxygen, and unsaturation. This inconsistency, furthermore, is in acalso in z'ucuo, only the samples in air and oxygen suffer any cordance with the experimental results of Peachey and deterioration within a period of several months; the samples Leon,3 who found that vulcanized rubber actually did comin the other gases are unaffected. The deteriorated rubber is bine with oxygen less rapidly than crude rubber, a finding found, upon a n elementary analysis, to contain oxygen; and which is in accordance with the chemistry involved in reacfurthermore, i t has been possible to recognize in such de- tions of additive oxidation, but which is contrary to our teriorated rubber the presence of levulinic aldehyde, the experience on the relative deterioration of crude and vullatter having been identified by the pyrrole reaction, and also canized rubber. There is a further inconsistency in the additive oxidation by actual isolation of its pyridazine derivative. Further corroboration of the oxidation theory of the de- theory of deterioration. It is well known that rubber that terioration of rubber is the fact that certain substances, is either under- or overvulcanized deteriorates with increased which are known to function as oxygen carriers, have a n rapidity. I t is very difficult to explain this on the basis of unusually severe action upon both crude and vulcanized a n increase in the addition of oxygen. I n attempting to rubber. Notable in this respect are the salts of copper and explain the deterioration of incorrectly vulcanized rubber, manganese, the former especially being very active in ex- we are, of course, still confronted with the inconsistency distreme dilution. Thus, a sample of cloth containing a n ex- cussed above, but in addition we have to explain why an cess of 0.005 per cent copper (introduced as copper sulfate irregularity in the time-temperature-sulfur relationship for mordanting) will bring about in a very few months the necessary for vulcanization aggravates the deterioration. deterioration of a vulcanized-rubber coating that has been A mere additive oxidation theory is not convincing. On the other hand, we are not justified in rejecting broadly Received July 8 , 1926. 2
Died on July 17, 1926.
* J. SOC.Chem. Ind , 37,
56T (1918).
