Edition
A nalyt ical Volume 2
Number 4
OCTOBER 15, 1930
Alumina in a New Form as a Laboratory Desiccant’ J. Bryte Barnitt, Ralph B. Derr, and Edward W. Scripture, Jr. ALUmINUM RSSEARCH LABORATORIES,ALUMINUM COXPANY OF
AMERICA, NEw KENSINGTON, PA.
A pure aluminum trihydrate has been produced were graded through 8- and HE absorptive propwhich, by suitable treatment, acquires marked abon 14-mesh screens. These erty of partially desorptive properties and permits the circulation of air U-tubes were connected in a h y d r a t e d aluminum so that it can be rapidly dehydrated. In the dehytrain in the various orders trihydrate has been known for drated form this “activated alumina” can be used as a indicated and air saturated many years, and in the many laboratory desiccant. The efficiency of this alumina with moisture w a s d r a w n investigations (1 to 6) underhas been compared by various methods with other through a t the rate of 3 liters taken to determine the value commercial desiccants, with very favorable results; p e r h o u r . The inside diand efficiency of laboratory moreover it does not have the disadvantagesof the other ameter of the U-tubes was d e s i c c a n t s , a l u m i n a has 1 cm. and the length of usually been employed for materials. column was approximately comparison. A 1t h o u g h it is recognized that the vapor pressure of alumina is very 12 cm., so that at the above flow rate a fairly rapid low, it has not been employed extensively as a desiccant linear flow was obtained. The experiments were performed because heretofore it has not been available in a form in a t room temperature, which was constant for each test but which air or gases could diffuse readily throughout its mass. varied from 22’ to 30” C. in the different tests. Thus the Recently, by a special process, it has been found that total quantity of water absorbed was not exactly the same pure aluminum trihydrate can be produced in the form of in each case, although the same amount of air was drawn hard crystalline lumps which cen be sized and graded varying through the train. I n each test an additional tube confrom a powder to pieces approximately 2 inches in diameter. taining phosphorus pentoxide was placed a t the exit end of This form of alumina, when suitably treated, acquires marked the series to prevent back diffusion and to serve as a check absorptive properties and when graded into sizes varying on the completeness of the removal of moisture. I n no between 4 and 20 mesh permits the circulation of air or gases instance did this safety tube gain in weight. Thus it may be throughout its mass so that they may be rapidly and com- concluded that no moisture passed completely through the pletely dehydrated. Experimental work has shown that train in any case and that there was no diffusion from the this new form of alumina, which is known as “activated exit end. alumina,” compares favorably in desiccating properties with I n Table I the position of the desiccant in the train is phosphorus pentoxide and other commercial desiccants with- indicated for each test, and the gain in weight together out having their disadvantages. with the percentage of water absorbed, based on the total quantity passed, is indicated for each tube. Drying of Air by Passage through Various Desiccants I n the first test alumina absorbed 99.9 per cent of the moisture passed through; calcium chloride actually lost Although determinations of vapor pressure may not be water to the dry air; sulfuric acid did not gain or lose; considered entirely satisfactory for evaluating reagents and the phosphorus pentoxide absorbed the 0.1 per cent so varied in nature as the common desiccants, it will be of moisture passed by the alumina together with the 0.1 interest to know the comparative efficiency of alumina per cent moisture removed from the calcium chloride. In and other desiccants by a method analogous to the dynamic the second test the position of phosphorus pentoxide and vapor-pressure procedure. For this comparison, alumina, alumina in the series was reversed, and in this instance phosphorus pentoxide, sulfuric acid (96 per cent c. P.), the former absorbed 97.8 per cent of the total moisture; calcium chloride, and barium-magnesium perchlorate were both the calcium chloride and concentrated sulfuric acid employed in a train through which air of high humidity absorbed small amounts, while alumina absorbed the residual was drawn under comparable conditions. moisture amounting to 1.8 per cent of the total. I n the Approximately equivalent volumes of each desiccant were three subsequent tests sulfuric acid, calcium chloride, and placed in U-tubes of like dimensions. In the tubes containing barium-magnesium perchlorate occupied the first position sulfuric acid and phosphorus pentoxide, glass pearls were in the series, and in each instance less than 95.2 per cent of added to secure exposed surfaces comparable with those of the total water passed was absorbed in the first tube. Aluthe other desiccants which, being of a crystalline nature, mina preceding the phosphorus pentoxide tube absorbed, within experimental error, the residual moisture. The 1 Received May 28, 1930.
T
ANALYTICALEDITION
356
performance of barium-magnesium perchlorate was checked by several runs. When this material was preceded by either alumina or phosphorus pentoxide, it gave up to the dry air part of the moisture absorbed in the two previous runs. Since the efficiency of absorption of water from a current of gas involves the rate of absorption as well as the vapor pressure of the absorbent, it is apparent in cases such as these, where equilibrium may not have been established, that the amount of residual moisture in the gas will be affected by the rate of flow and by the contact obtained between the gas and the absorbent. These factors account for the fact that phosphorus pentoxide did not give complete drying under the conditions employed, and the results illustrate the difficulty of obtaining high efficiency where satisfactory distribution is not readily secured.
Vol. 2, No. 4
For a short period at the beginning very little moisture is lost to the desiccant and no visible change occurs. A period of rapid dehydration follows; light spots appear on the copper sulfate, and these gradually increase in size and number until the surface is completely covered with pale blue monohydrate. At this point the material reaches a nearly constant weight and the coating decreases the speed of diffusion to a negligible rate. Table I-Drying of Air by Passage t h r o u g h U-Tubes C o n t a i n i n g A l u m i n a Phosphorus Pentoxide Sulfuric Acid C a l c i u m ChlAride, a n d B a r i u m - M a g h e s i u m P e r c h d r a t e Position in series 1st Test: Drying agent Gain in weight, gram Hz0 absorbed of total, percent 2nd Test: Drying agent Gain in weight, gram Hz0 absorbed of total, percent 3rd Test: Drying agent Gain in weight, gram HzO absorbed of total, per cent 4th Test: Drying agent Gain in weight, gram HzO absorbed of total, per cent 5th Test: Drying agent
-41203
+ O . 0778 99.9
PZO, + O , 0764
HZS04 f0.0853
+0.0042
1.8
*o.oooo PI05
0.1 AliOi 4-0.0034
0.0 Pa01 A O ,0000
4.8
0.3
Ba-Mg perchlorate 4-0.0931
Pz05 $0.0054
Alios +0.0042
90.2
5.6
4.2
Ba-Mg perchlorate 4-0.1061 -0.0017
0.2 Ah08 +0.0014
0.3 +O.OOOl CaCL
4.7 HzSOa +0,0002
P201
0.0
4-0. HzSOi 0002
0.1 4120a
95.1
0.0
AlzOa
Gain in weight, gram HzO absorbed of total, per cent 7th Test: Drying agent
99.0
PZOS +0.1110
Gain in weight, gram H?O absorbed of total, percent
Plod +0.0032 2.6
-1.6
Ba-Mg perchlorate 0.0009
-
94.8
Ah03
+0.0070
-0.8
6.0
L ~ E I G H T OF DRYING AGEXTS EMPLOYED
Figure 1-Dehydration of Copper S u l f a t e Pentahydrate over Activated A l u m i n a Sulfuric Acid, C a l c i u m Chloride, a n d BariumMagnesium Peichlorate
Grams
Alumina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.52 Phosphorus pentoxide.. . . . . . . . . . . . . . . . . . . 2 . 5 0 Sulfuric a c i d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.24 Calcium ch1orid.e.. . . . . . . . . . . . . . . . . . . . . 10.27 Barium-magnesium perchlorate . . . . . . . . . 18.55
Dehydration of Copper Sulfate Pentahydrate over Various Desiccants
A more satisfactory method of determining the efficiency of a laboratory desiccant is that of employing the exact conditions obtained in a desiccator. Hydrated manganous nitrate (MnS04.6Hz0) has been employed by Smith (5) for the determination of the efficiency of perchlorates; Marden and Elliott (4) have employed hydrated copper sulfate (CuSO4. 5H20). In the present writers' opinion the latter material is the more suitable for this purpose because of the low melting point and transition temperature of the former. Therefore, in the following experiments equal quantities of copper sulfate crystals were placed in similar weighing bottles over the various drying agents in Scheibler desiccator jars. The samples were weighed periodically until practically constant weight was reached. Then the. copper sulfate was completely dehydrated by heating at 175' C. to determine the residual combined water. In a second test the copper sulfate crystals were ground t o a greater degree of fineness and the determinations of the previous test repeated with the substitution of bariummagnesium perchlorate for phosphorus pentoxide. The results of these experiments are summarized in Table 11, and Figures 1and 2. The dehydration follows a similar course in each instance.
+O.OOOl
95.2
CaClz +0.0698
HzSOi
*o. 0000 +o.oooz
-0.1
CaCh
97.8
Gain in weight, gram HzO absorbed of total, per cent 6th Test: Drying agent
Tune in Days
CaClz -0.0001
Table 11-Dehydration
1
of Copper S u l f a t e Pentahydrate over Various Desiccantsa SECOND TEST
FIRSTTEST 41203
225 grams grams grams grams :rams
I-. UUYi
>
; 9 11 14 16 18 "1 'S
35 a
HzSOd 250
grams
5
%
%
7a
7J
c0
0.3 0.3 l5,6 30.2 40.r 42.1 42.3 42 5 42.6 42 A 42.8
0.2 0.4 2.3 6.5 15.0 30.2 37.6 40.8 41 4 41.3 41.5
0.3 5.0 22.2 34.0 41.0 41.7 41.8 43.0 43 0 43.0 42.0
0.0 0.0 0.2 2.4 15.5 36.5 42.4 42.7 42.7 42.8 43.0
1.1 1.3 21.6 46.3 55.1 55.5 56.0 56.5 57.1 58.2 58.9
0.7 5.9 29.6 53.5 54.7 55.0 55.4 b5.7 55.8 55.9 55.9
CaClr Ba-Mg 225 perchlorate grams 45Ograms %
0.6 0.6 13.1 40.0 52.5 53.1 53.5 53.7 53.7 55.0 55.7
'70 0.3 3.9 12.3 24.0 34.2 40.0 42.2 44.3 44.3 49.4 49.7
IYater removed on basis of total water present.
Dehydration over alumina and sulfuric acid takes place at nearly the same rate. I n the instance of calcium chloride the removal of water from hydrated copper sulfate follows a similar course but is about 5 days slower at the end of any period. On the other hand, phosphorus pentoxide shows less abrupt changes and, although a rapid loss of water starts earlier than over calcium chloride, a constant weight is reached
October 15, 1930
INDUSTRIAL A N D ENGINEERING CHEMISTRY
more slowly. This is explained by the poor diffusion of air through the phosphoric acid formed on the surface. In the comparison of barium-magnesium perchlorate with alumina, sulfuric acid, and calcium chloride the course of dehydration over the last three desiccants was similar to that of the first test except that it was somewhat more rapid and at the point of substantially constant weight the total loss of combined water was increased from 42 to between 55.7 and 58.9 per cent. The rate of dehydration over barium-magnesium perchlorate was slower than over the other desiccants and after 35 days 49.7 per cent of the combined water was absorbed.
357
phosphorus pentoxide, the second over calcium chloride. Owing t o the slight differences in treatment, the groups are not strictly comparable with one another, but the crucibles within any one group were treated similarly and should show variations which are due only to the desiccant. These results are shown in Table 111. T a b l e 111-Changes
in W e i g h t of I g n i t e d A l u m i n a over Various Desiccants Ah08
P20,
HzSO4
Ba-Mg CaClr PBRCALORATS
Gram Gram Gram Gram Gram Group 1: 0.3452 0.3477 0.3728 0.3587 Weight after cooling 0.3441 0.3478 0.3711 0.3588 Weight after 1 day 0.3408 0,3585 0.3444 Weight after 2 days 0.3711 Totalchangein weight -0.0017 -0.0002 -0.0008 -0.0000 Group 2: Weight after cooling 0.3233 , 0.3242 0,3199 0.3298 Weightafterlday 0.3231 , 0.3240 0.3199 0.3302 Weight after 2 days 0.3233 , . 0.3243 0.3199 0.3309 Totalchangein weight * O . O O O O . +O.OOOl *O.OOOO $0,0011
.... .. .
It is assumed that the closest approach to the true weigh6 of ignited alumina is the minimum weight obtainable and, furthermore, if the weight on standing changes from the original, the slowest increase or the fastest decrease is most desirable. In the first group the greatest loss in weight takes place over alumina and the least over phosphorus pentoxide. In the second group alumina, sulfuric acid, and calcium chloride are very similar in their effects, but over barium-magnesium perchlorate the crucible shows a marked increase in weight. Other Advantages of Alumina as a Desiccant
Tioe i n Dpys F i g u r e 2-Dehydration of Co p e r S u l f a t e P e n t a h y d r a t e over Activated A l u m f n a , Sulfuric Acid, C a l c i u m Chloride, a n d P h o s p h o r u s P e n t o x i d e
Changes in Weight of Ignited Alumina over Various Desiccants
A third method of comparing the efficiency of laboratory desiccants and one which is most exacting is that of cooling ignited alumina. Because of the tendency of ignited alumina to absorb moisture, the atmosphere of the desiccator must be maintained at a uniformly low vapor pressure to obtain correct results. In these experiments samples of about 0.5 gram of hydrated alumina were placed in crucibles, ignited 4 hours at 900-1000” C., placed in a desiccator, and allowed to cool for 1 hour. The crucibles were weighed and then each was placed in one of four similar desiccators which were provided with one of the desiccants as shown in Table 111. After 1 day and 2 days they were again weighed. Two groups of four crucibles u-ere treated in this manner; the first group was originally cooled over
From the three series of experiments it is concluded that this new form of alumina is an ideal desiccant in respect to efficiency. Its other advantages, however, as compared with the more common desiccants may be enumerated as follows: Unlike phosphorus pentoxide, it may be easily handled; it is not dangerous, as is sulfuric acid; it does not deliquesce, as do calcium chloride and sodium or potassium hydroxide; the absorption of moisture does not change the volume or physical appearance of the absorbent; it is reasonably neutral, and does not react readily with most gases and vapors; under ordinary desiccating conditions it will absorb 15 to 20 per cent of its weight of water; it may be reactivated in 6 to 8 hours in an oven at 175” C., and this reactivation may be repeated indefinitely, as the alumina does not deteriorate; finally, it is available in any convenient size and is inexpensive. Literature Cited Baxter and Warren, J. A m . Chem. SOC.,88, 340 (1911). Dover and Marden, Ibid., 89, 1009 (1917). Johnson,I b i d . , 84, 911 (1912). Marden and Elliott, J. IND ENG.CHSX., 7, 320 (1915). Smith, Chemist-Analysf,18, No. 2, 18 (1929). ( 0 ) Yoe, Chcm. News, lS0, 340 (1925).
(1) (2) (3) (4) (5)
Russia Plans Sixteen Rayon Plants The Soviet Government proposes to construct 16 rayon plants, costing 3125,000,000, with an annual productive output of 35,000 tons, according to Soviet reports received a t the Department of Commerce. Three rayon mills are already under construction and are expected to commence operation next summer. The productive capacity of the three mills under construction is estimated a t between 4000 and 4500 kilograms per day, according t o Soviet information. Two Soviet trusts have signed 5-year contracts with a German firm for constructing and starting in operation two rayon factories, the German firm to prepare plans for construction, to
give expert opinion, and to turn over to the Soviet trusts licenses for all its patents and processes. The German firm is also t o train Soviet engineers and workmen in its German plants, as well as send German specialists to Russia. The equipment will be ordered partly in Russia and partly from abroad. Only domestic raw materials will be used for rayon production in these factories. The Soviet Government entered into a contract some time ago with Emile Brounert of the “Soieries de Strasburg,” who is also connected with the Union of French Producers of Artificial Silk.
