INDUSTRIAL AND ENGINEERING CHEMISTRY
716
Vol. 22, No. 7
Production of Oxygen from Lime and Chlorine' 0. R. Sweeney, J. W. Hussey, and Wheeler Ralston DEPARTMENTS OF CHEMICAL ENGINEERING A N D CHEMISTRY, IOWASTAT*COLLEGE, AMES, IOWA Table I-Relative
D
U R I S G the World War considerable quantities of oxygen were formed from the bleaching powder in the chloropicrin plant at Edgewood Arsenal. It was assumed that this oxygen was evolved from the bleaching powder by the reaction Ca(OC1)t
+CaClt +
0 2
the iron of the bleach tanks or the iron and manganese occurring as impurities acting as catalysts. This reaction has been
C
n
I
Q
Efficiencies of Various Catalysts COXCENTRATIONEVOLUTION CATALYST OF CATALYST O F OXYGEN Gram per 100 cc. Cc per mrn.a 0 029 14 18 cO(N0a)z 6HzO Ni(NOd2 6Hz0 0 029 14 02 MnOz (black) 0 OS7 1 20 MnOz (brown) 0 087 1 42 FeSOa 7Hz0 0 278 4 25 CuS04 5H20 0 250 0 013 crz03 0 152 0 013 No catalyst 0 000 0 013 Chlorine 25 cc per minute
C'
The effect of the rate of chlorine flow upon the rate of oxygen generation was studied using the same apparatus. T h e o x y g e n p r o d u c e d was found to be almost directly proportional to the amount of chlorine, as shown in Figure 3. The effect of varying the concentration of the catalyst was studied by holding other factors constant and varying the amount of nickel nitrate used as a catalyst. The results are shown in Figure 4.
n
I
U I
I
Large-Scale Apparatus
A larger apparatus of Pyrex glass was designed Figure 1-Apparatus for S t u d y of O p t i m u m Conditions for Reaction to duplicate more closely probable commercial studied by various investigators in the Chemical Engineering conditions. (Figure 5 ) Chlorine entered the apparatus a t Laboratories a t Iowa State College. It has been shown in A and s t e a m a t B. A suspension of lime in-a 0.001 M preliminary experiments that a yield of 88 per cent of the nickel hydroxide suspension was run from the mixing tank, theoretical yield of oxygen could be secured by heating dry H , into the reaction tower through G. As the lime solubleaching powder. A yield of 99 per cent was secured by tion trickled down over the perforated plates of the tower, passing chlorine into a hot milk-of-lime suspension using co- it reacted with the chlorine forming calcium chloride and balt nitrate as a catalyst. By passing chlorine over lime a t oxygen. The oxygen was drawn off a t E. The calcium 850" C. oxygen was also evolved giving anhydrous calcium chloride solution containing nickel hydroxide in suspension chloride as a by-product. It was shown that cobalt and nickel oxides and nitrates gave very good results as catalysts. Ferrous salts acted as catalysts, but less efficiently. A
Y
Optimum Conditions for Reaction
A study of the optimum conditions of the reaction was made. To determine the optimum temperature, the apparatus in Figure 1 was set up. The chlorine gas was bubbled through sulfuric acid in the wash bottle, A , and measured in the flowmeter, B. The tubes C and C' contained a swpension of lime into which the chlorine was passed, liberating oxygen which was bubbled through a 50 per cent potassium hydroxide solution in wash bottle D. The oxygen was measured in the graduated cylinder, F. The temperature of the mixture of chlorine and lime in tubes C and C' was regulated by placing the tubes in a thermostat. Ten grams of lime in 200 cc. of 0.001 M cobalt nitrate solution were used for each run. The relationship between temperature and yield of oxygen is shown graphically in Figure 2 . The optimum temperature was found to be 94" c. The effect of various catalysts on the rate of reaction was studied, using the same apparatus and the same quantities of lime as before. Each run was made a t 94" C. The following catalysts in order of efficiency were used: cobalt nitrate, nickel nitrate, manganese dioxide, ferrous sulfate, copper sulfate, and chromium oxide. Presented before the meeting of the Ameri1 Received M a y 3, 1930 can Institute of Chemical Engineers, Detroit, Mich., June 4 to 6, 1930.
TEMPUPITU(T-
CCYTIC~~OC
Figure 2-Relation between Temperat u r e a n d Yield of Oxygen
was drawn off a t B. The nickel hydroxide was filtered out and re-used. This apparatus could be regulated so as to convert all the lime to the chloride and oxygen -without losing any chlorine in the oxygen.
INDUSTRIAL AND ENGINEERISG CHEMISTRY
July, 1930
Design of Commercial Plant
(89)
A design for a commercial plant was worked out, as shown in Figure 6. A susDension of lime in a 0.001 M solution of nicke7 sulfate (NiSi)4.7H20) is mixed in a mixing tank equipped with an agitator. About 10 pounds of lime to 24 gallons (3.2 cubic fret) of solution are used. The nickel sulfate will be in proportion of 0.234 pound per 100 gallons of solution. I t hvdrolvzes to the hvdroxide which is oxidized t o the nickelic h y h o x i i e (Xi (OH);).
717
(k5) (k8)
):(
= 334.3 pounds
The amount of catalyst for 1000 cubic feet of oxygen is 0 234 (m) (i)(334.3) = 1.87 pounds
The m o u n t of catalyst used up "ith 90 per cent recovery is (1 87) (0 10) = 0 187pound
The amount of chlorine used is
(F)(334.3)
(0.98)
=
414 pounds
The amount of calcium chloride produced is
(z)
(89)
=
617 pounds
The cost of materials for making 1000 cubic feet of oxygen using average prices for the past year is shown below. Lime-335 pounds at $8.50 a t o n . . . . . . . . . . . . . . . . $ 1 . 4 3 0.02 Xickel salt-4.188 pounds at 10 cents per pound, . .
R47-E
OF
FLOW
OF
CXLOP/NE
of Kate of Chlorine Flow u p o n R a t e of Oxygen G e n e r a t i o n
Figure 3-Effect
The suspension of lime and nickel hydroxide will be pumped to the top of the reaction tower where it flows to the bottom. The tower is kept partially filled with solution. The exact level of solution in the tower for most efficient commercial operation must be determined by experiment. Chlorine and steam are blown in as shown. The chlorine first reacts with the suspension of Ca(OH)n to form CaOC12. As the solution becomes heated to 95" C. by the steam, oxygen is liberated and calcium chloride is formed. The oxygen passes out of the top of the tower. The calcium chloride solution passes to a settling tank where most of the nickelic hydroxide settles out as a sludge which goes to the mixing tank to be mixed with the new lime suspension. The calcium chloride solution is drawn off the top of the settling tank ready for use in solution or to be evaporated to the solid form.
B
: w
l6
I
$
95
IO
0
t
8
a 5
B b G
ti i i i i i i i i i i C
005
i i i i i i i
010
OJ5
I
I
020
C C N C E N T P ~ I T I OcNf NIINo,),. 6 H, 0 - G Pce 100 c c
Figure 4-Effect
of C o n c e n t r a t i o n o f C a t a l y s t on K a t e of Oxygen Generation
Costs of Production
The cost of producing oxygen by this method is calculated from the reaction: 2Ca(OH)2
-+ 2C12 +2CaCl2 + 2H20 + 02
The lime required for 1000 cubic feet (89 pounds) of oxygen using a chemical lime of 98 per cent calcium oxide and operating a t an efficiency of 95 per cent in the process is:
Chlorine-414 pounds at 4 cents a pound.. . . . . . . . . or 414 pounds at 2 cents a pound.. . . . . . . . . . . . . Total with chlorine at 4 cents Der Dound.. . . . . . . . . Toial with chlorine at 2 cents per p o u n d . . . . . . . . . . Value of calcium chloride, 617 pounds at $20 per ton Net cost with chlorine at 4 cents per pound.. . . . . . Piet cost with chlorine at 2 cents per pound
16. .56
8 28 18.01 9.73 6.17 11.84 3.56
I n these calculations the chlorine price of 4 cents a pound represents the average cost, during the past year, of chlorine in tanks. Chlorine can be produced as cheaply as 2 cents a pound under favorable conditions. I n the electro1y:ic production of caustic soda the disposal of the chlorine is-usually the limiting factor. I n order to compete with the soda ash and lime process, the chlorine must be disposed of. There are plants in which chlorine is produced as a waste product where it would be valued a t less than the figure of 2 cents per pound. The actual cost of chlorine will in these cases vary between nothing and 2 cents per pound, making the net cost of materials after selling t h e c a l c i u m chloride vary between a negative $4.62 and a positive $3.56. The cost of processing has not been calculated in detail, but is estimated at $12 per 1000 cubic feet. This would make the oxygen cost between $7.38 and $15.56 per 1000 cubic feet. The usual price of oxygen in cylinders is from $10 to $25 per 1000 cubic feet. u
Economic Value of Process
This process would not in general compete successfully A with air-reduction m e t h o d s F for the production of oxyFigure 5-Large-Scale Labogene There a r e , h o w e v f r , ratory Apparatus f o r Oxygen several industries moducing Generation slaked lime as a l;-aste byproduct which must be disposed of. This process would enable this waste lime to be utilized. I n 1,he case of acetylene generation from calcium carbide the waste lime
71s
INDUSTRIAL A N D EI1'GIATEERISGCHEMISTRY
Vol. 22, N o . 7
contains enough iron compounds to act as catalysts. If no value were placed on the lime, t h e cost of the oxygen would vary from $5.93 to $14.11. Where a mixture of oxygen and carbon dioxide could be used, a suspension of precipitated calcium carbonate can satisfactorily be substituted for the suspension of lime. Precipitated calcium carbonate in suspension is a common bv-product of no value. This method of oxygen manufacture is particularly well adapted to small-scale production of oxygen, since the process is simple in operation and the equipment needed is relatively low in cost. I n localities where there is a local overproduction of chlorine and a demand for oxygen, the process should take care of the overproduction as it occurs. It is, of course, of particular value where chlorine is being produced as a by-product and is practically a waste product. In many localities it might be possible to dispose of the calcium chloride in solution as it comes from the settling tanks for local uses such as application to roads. The smaller laboratory apparatus may be used advantageously in laboratories where oxygen is ordinarily purchased in small cylinders for experimental use. Frequently in laboratories where oxygen is used only occasionally or in limited amounts daily, the rental charge on cylinders costs more than the oxygen used. Where the oxygen is made by this method, the rental charge on the cylinders is eliminated. If chlorine is purchased in cylinders for the exclusive purpose of producing oxygen, there would be no great advantage. The cylinder rental would be reduced because a cylinder of chlorine at the usual pressure of 120 pounds per square would be equivalent to 1.6 cylinders of oxygen of the same size a t the usual pressure of 2000 pounds per square inch. This comparison is based on a yield of oxygen of 95 per cent. However, both chlorine and oxygen are ordinarily used in the laboratory. With chlorine a t 12 cents a pound and lime a t 1 cent a pound, oxygen can be produced for 5 cents a cubic foot. This is approximately the cost in cylinders exclusive of the usual rental charge. KO credit for the calcium chloride has been allowed in making this estimate. The prices for chlorine and lime are those actually paid for these materials in small quantit ies.
_ _
I
:j
9 d. 4
Figure 6-Design
of Commercial Plant for Production of Oxygen
Tower-Absorption Coefficients 111-Absorption of Benzene by Mineral Oil' C. W. Simmons and J. D. Long LEHICHUNIVERSITY, BETHLEHEM, PA.
HE rate of solution in a n absorbing liquid of a soluble gas from an inert carrier has been studied in cases where the solute obeys Henry's law and where the solute is very soluble in the extractor ( 2 ) . Here the rate of solution is expressed by the equation
T
sorbing liquid and where equilibrium conditions are expressed by the equation n = f(m). V h e n the solute obeys Henry's law, the rate of solution may be expressed in the form dm/dt = -K2(km - n)
where k is Henry's coefficient. dm/dt = - K f ( m ) Cantelo ( 1 ) considered a small element of volume of a where m is the concentration of the gas in the carrier, expressed packed tom-er between the heights z and z dx from the boteither in terms of volume concentration or of partial pressures, tom of the tower and assumed a continuous process in which the velocities of the carrier and extractor were uniform. He and K Pis the dissolution coefficient. I n considering the form of f ( m ) ,Donnan and Masson (3), pointed out the functional relationships between the dissoluLewis (J), and Whitman and Keats ( 5 ) have expressed this tion coefficient and velocities of the liquid and the gas, the function of the concentration in terms of either concentrations temperature of the system, and the concentration of the solute or partial pressures in the solvent and the inert carrier. Thus in the inert carrier. For the purposes of experiment Cantelo Donnan and Masson give as a general form f ( m ) - n, where transformed the equation d m l d t = -K?(km - n) n is the concentration of the soluble component in the abinto one involving d n l d x , which upon integration between ' Received April 5 , 1930
+
