July 1953
*
c
INDUSTRIAL AND ENGINEERING CHEMISTRY
gence from the uniform distribution line. After 1 month the solvenbrecovered specimens show an almost identical relative distribution of pentachlorophenol to that found immediately after treatment, indicating that little or no movement had taken place, since very little solvent was present t o cause migration. On the other hand, the impregnated-only specimens after 1 month show a relative distribution that is much more divergent from the uniform distribution line than was the case immediately after treatment. Extrapolation of the upper line in Figure 7, A , indicates that approximately 70% of the pentachlorophenol was present in or near the surface of the wood after 1-month evaporation of solvent. Similar results were obtained with southern pine. This large scale migration of the preservative to the surface of the wood during evaporation of solvent not only is responsible for heavy blooming that is experienced when wood is treated with pentachlorophenol in light solvents and the solvent allowed to evaporate into the air, but also it probably accounts for the fact that test specimens treated with pentachlorophenol in such solvents have failed to give as good service life against wood-destroying organisms as those treated with heavier solvents ( 6 , 18). This has been variously explained; but the data herein reported indicate very strongly that in wood treated with the chemical in light solvents the pentachlorophenol migrates to the surface and is lost quickly by being washed away by rain or displaced from the surface of the wood by shrinkage and swelling stresses and other agencies, leaving the wood virtually untreated in the interior and an easy prey to the wood destroyers. Final proof of this supposition will have to await the outcome of stake decay tests th‘at are already in progress, but will requjre some years to complete. Figure 8 shows a comparison of some of the treated only and solvent-recovered boards from the second series of teats, on which white paint was used. These were photographed 6 months after exposure on the test fence and are included to show the discoloration caused by the surface deposits that were present on the wood that was impregnated only, even when an entire month was allowed for evaporation of solvent before the painting was done. This discoloration is not apparent in Figure 5, because the paint used on those panels was red.
1583
Summary
When wood is pressure treated with pentachlorophenol in volatile solvents, most of the chemical is brought t e the surface of the wood by evaporation of the solvent, leaving objectionable deposits which interfere with paintability. Addition of plasticizing agents to the treating solution prevents formation of the crystalline deposits known as blooming, but does not stop the migration of pentachlorophenol to the surface. By employing a modification of the vapor-drying process, it is possible t o remove and recover most of the solvent vehicle that is normally lost. Usually 6 t o 10 pounds per cubic foot of solution containing 5% pentachlorophenol in the solvent is required for pressure impregnation of wood. The cost of the solvent portion of this solution amounts to from $12 t o $18 per thousand board feet of wood processed, while the value of the pentachlorophenol itself is only about $5.00 to$9.00. The solvent can be recovered by means of t h e vapor process at a cost of about $6.00 t o $8.00 per thousand board feet, which represents a decided economic advantage. I n addition to the saving obtained by removal of this solvent, the vapor process produces a finished product that is free of surface deposits of natural resins and of preservative impregnant t h a t cause discoloration and other defects of paint applied t o the wood. literature Cited (1) American Wood-Preservers’ Association, “Manual of Recommended Practice,” Standard P9-51. (2) Ibid., Standard A6-51. (3) American Wood-Preservers’ Association, Proc. A m . Wood-Preservers’ Assoc., 43, 62 (1947). (4) Carswelland Hatfield, IND. ENG.CHEM.,31,1431 (1939). (5) Chapman Chemical Co., Tech. Newsletter, No. 6 (July 1952). (6) Duncan and Richards, Proc. Am. Wood-Preservers’ Assoc., 46, 131 (1950). (7) Hatfield, Ibid.,40, 47 (1944). (8) Ibid., 45, 84 (1949). (9) Hubert, IND.ENQ.CHEM.,30, 1241 (1938). (IO) Hudson, Forrest Products Research SOC.Proc., 1 , 124 (1947). (11) Hudson, Proc. Am. Wood-Preservers’Assoc., 46, 209 (1950). (12) Hudson, U. S. Patent 2,435,218 (Feb. 3, 1948). (13) Sedziak, J. Forest Products Research SOC., 2 , No. 5 , 2 6 0 (1952). (14) U. S. Forest Products Laboratory, ANC Bull., 21 (1946). (15) Verrall, Southern Lumberman (June 15, 1949). (16) Western Pine Association, BUZZ.6 (July 1951). ACCEPTED February 9 , 1953
RECEIVED for review March 5 , 1951.
Electrolytic Preparation of Beryllium Hydroxide
0 0
0
Aqueous Sodium Beryllium Fluoride as Cathode Liquor RAMAN K. PARIKH AND KARL
KAMMERMEVER
Sfufe University o f lowu, lowa City, lowo
M
UCH work has been done on the electrolysis of molten
beryllium salts ( 2 ) ,and in particular of beryllium chloride (1). Only one reference ( 4 ) seems to exist concerning the electrolysis of aqueous solutions, but no information whatever is available on operating variables. The object of the present work was to investigate the factors involved in the preparation of beryllium oxide by the electrolytic method, using an aqueous solution of sodium beryllium fluoride ( NazBeF4) as a cathode liquor with a graphite rod as a cathode. Beryl, 3Be0.AI2O3.6Si02,is the chief raw material for the manufacture of
beryllium oxide. Ores run from 10 to 12% beryllium oxide. Numerous processes have been developed, studied, and pa& ented for production of beryllium oxide, but very few have actually been successful in industry. The most important two processes now in use in industry are based on (1) fusion of beryl with lime, and (2) fusion of beryl with sodium silicofluoride or sodium ferric fluoride, called the “fluoride process.” The sodium beryllium fluoride solution for electrolysis is obtained in the fluoride process, which is described in detail by Lundin (8).
INDUSTRIAL AND ENGINEERING CHEMISTRY
1584 Table 1.
5% sodium chloride solution were poured into it as the anode liquor. This brought the two liquids to the same level. The anode and cathode were clamped in position, the cathode liquor was stirred by the agitator, the electrical circuit was closed, and the current was adjusted to the required value. The voltage drop across the two electrodes was measured. After the experiment was completed, the circuit was broken, and the mechanical stirrer was removed.
Change in pH of Cathode Liquor during Electrolysis
b
Vol. 45, No. 7
Time, Minutes 0 30 60 90
120 150 180
Amperes = 0 75 Cathode curreqt dessity = 0 0348 ampere/sq. cm. Constant stirring Temperature = 27" to 30' C.
Description of Electrolytic Cell
A diagram of the cell layout is shown in Figure 1. An 800-ml. borosilicate glass beaker served as a container to hold 250 ml. of sodium beryllium fluoride solution. The rectangular diaphragm, D,was placed a t one side of the beaker. The were in the positions shown. anode, A , cathode, C, and stirrer, A small glass tube removed liberated chlorine from the diaphragm space. A thermometer measured the temperature of the bath.
Beryllium hydroxide was produced as a solid suspended in the solution and adhering to the beaker, electrodes, and diaphragm. All the material so obtained was carefully recovered, separated from the solution by filtration, and dissolved in hydrochloric acid. The resulting beryllium chloride solution x a s made up to 250-m1. volume and analyzed for its beryllium content by the 8-quinolinol method. In this method iron and aluminum are separated from beryllium aq insoluble quinolate salts, after which beryllium hydroxide is obtained by treating the solution with ammonia. Experiments were conducted under varying conditions of current density, time of electrolysis, temperature, and mode of stirring. Investigations were also conducted with different anode liquors and with addition of sodium chloride to the cathode liquor. Discussion
The decomposition potential of sodium beryllium fluoride solution with graphite rods as electrodes was measured with a 6-volt dry cell, a voltmeter, and an ammeter. A sudden increase in current occurs a t the decomposition voltage point and the value of this voltage was obtained as 1.70 volts. The results of the electrolysis experiments are presented in Tables I to VII. Table I is a record of the change in pH value of the cathode liquor during the course of electrolysis. The initial pH value of 7.45 changed to a pH of 12.2 after about 1.5 hours. Table I1 shows how the cath?de current density affects the rate and efficiency of electrolysis. The recovery of beryllium oxide rose from 38.74 to 92.6% and then fell to 87% with corrc-
-+VACUUM
__-
-
110 VOLT D C
Figure 1. A. 8. C. D,
Electrolytic
Graphite anode Borosilicate glass beaker Graphite cathode Diaphragm
M.
FRY
Cell
P.
Motor Cathode liquor
S.
Glass stirrer
0. A n o d e liquor
The cathodes used in these investigations were solid graphite rods 30 em. long and 1.4 em. in diameter. The surface submerged in the cathode liquor was 22 sq. em. The anodes were of the same material as the cathodes and had the same dimensions. They were separated from the cathode liquor by a dia hragm. The same surface area (22 sq. em.) was submerged in t i e anode liquor. The diaphragm which separated the cathode and anode liquors consisted of an ordinary unglazed porcelain, rectangular, hollow block closed a t the bottom, 10 em. high, 2.4 em. wide. and 7.6 cm. long, havin.; a wall thickness of 0.2 em. For cathode liquor, an aqueous solution of sodium beryllium fluoride (obtained from The Beryllium Gorp.) was prepared by dissolving the powdered material in cold water, allowing the solution t o settle, and then filtering to obtain a clear solution. About 20 liter8 of solution were wepared, hnalyzed, and marked as siock solution. The pH of the solution was 7.45 and remained constant during the Table II. period of investigation. Experimental Procedure
The electrolytic cell was connected to the 110-volt direct current line in series with a variable resistance, R, a direct current ammeter, A , and a switch key, K . as shown in Figure 2. 'Previously prepakd stock solution of sodium beryllium fluoride (250 ml.) was poured into the glass beaker, the diaphragm was introduced, and 70 ml. of
No. 1
2 3
4
5
6
Figure 2. A. C.
K.
R.
V,
Wiring Diagram
D.c. ammeter
Electrolytic cell Switch key Variable resistance D.c.voltmeter
Effect of Various Current Densities on Electrolysis
Cathode Theoretical Actual Be0 Liberated Be0 Current Current Current Current, Passed in Density Due to Current, Obtained, Efficiency, Amperes Faraday' Amu./Sa. G. G. % . - Cm. 0.25 0.01398 0.0115 0.175 0.172 98.24 0.50 0.02796 0.0230 0.350 0.315 90.10 0.75 1.00 1.25 1.50
0.04194 0.05592 0.06990 0.08388
0.0345 0.0466 0,0578 0.0690
0,525 0.700 0.878 1.050
0.410 0.396 0.390 0,386
Time of electrolysis = 1.5 hours Constant stirring by mechanical stirrer in cathode liquor Quantity of B e 0 present in 250 ml. stock solution = 0.4423 gram
78.10 8 6 , 60 44.50 36.80
Recovery,
7c
38.74 71.03 92.60 89.24 E7.90 E7.00
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1953
Table 111. NO 1 2 3 4 5
Time of Electrolysis, Hours I 05 1 1.25 1 5 2
thick coating of beryllium hydroxide was formed on the cathode; with continuous stirring, this was not the case.
Effect of Time of Electrolysis
Theoretical Be0 Liberated Due to Current, G. 0 1750 0.3550 0 4375 0.5250 0,7000
Actual Current Be0 Efficiency, Obtained, G. % 0.173 98.80 0.340 97.10 0.420 96.00 0.415 79.00 0.402 67.40
%
39.10 76.80 95.00 93.75 90.80
Effect of Temperature on Electrolysis
Temperature of Bath, C. 12 30 50
Voltage Actual B e 0 No. of Bath Obtained, G. 1 14.4 0.4124 11.6 0.4120 2 10.0 0.4160 3 Amperes = 0.75 Cathode current density = 0.0345 amp./sq. om. Constant stirring by mechanical stirrer
Table V.
at
NO.
1 2 3 4
5
Recovery,
%
93 20 93.15 94.10
Effect of Addition of Sodium Chloride to Cathode Liquor Voltage Drop Terminals a t Start 11.6 10.5 9.2 9.0 9.2
Cathode Liquor 250 ml. NazBeFc soln. 250ml. 1% NaCl 250 ml. 2% NaC1 250 ml. 5% NaCl 250 ml. +lo% NaCl
+++
Actual Be0 Obtained, G. 0.4168 0.4100 0.4160 0.4120 0.4080
Recovery on Basis of BeO, % 94.BO 92.70 94.10 93.05 92.20
Amperes = 0.75 Time of electrolysis = 1.26hours Temperature = 27' C. Constant stirring
.
*
Summary
Recovery,
Current = 0.75ampere Cathode current density = 0.0345 amp./sq. om. Constant stirring by mechanical stirrer in cathode liquor
Table IV.
1585
sponding cathode current densities of 0.0115, 0.0345, and 0.069 ampere per sq. cm. The current efficiency was 98.24% a t low current density and then dropped to 36.8% with a current density of 0.069 ampere per sq. cm. At high current densities most of the energv was utilized in heating the electrolyte. Table 111 shows how the time of operation affects the electrolysis. Current efficiency was very high with 0.5 hour of electrolysis, but it decreased for longer times of operation. The percentage recovery of the product increased with the increased time of electrolysis. The highest recovery was obtained after 1.25 hours of operation, a t which time a current efficiency of 96.0% and a 95.0% recovery of beryllium oxide were obtained. With the decrease of concentration of beryllium ions in solution as the electrolysis proceeded, more of the energy supplied to the cell was spent in side reactions. The data in Table IV indicate the effect of temperature on electrolysis. The experimental data presented so far were obtained a t about 30' C. (room temperature). At higher temperatures, the voltage drop across the cell was lower and there was a slight increase in percentage recovery. But the most important observation was the nature of the precipitated beryllium hydroxide. At the higher temperature, precipitates were of sandy and crystalline nature and it was very easy to carry out the filtration. The solutions obtained in the experiments a t 12' C. were cloudy and more time was required for their filtration. I n some experiments sodium chloride was added to the cathode liquor to lower the resistance of the electrolyte and hence t o lower the potential drop through the electrolyte itself for the same current density. The effect of these additions is shown in Table V. The voltage drop across the cell was lowered from 11.6 to 9.2 volts by addition of 2% of sodium chloride to the cathode liquor, but this had a negligible effect on the percentage recovery of the product. Table V I presents information on the effect of various anode liquors: potassium chloride, sodium carbonate, sodium hydroxide, and sodium beryllium fluoride solutions. Sodium carbonate and sodium hydroxide eliminated the liberation of chlorine, but the voltage drop was higher in the case of sodium carbonate. When sodium beryllium fluoride was used as anode liquor the resistance of the cell was high, the diaphragm was attacked, and precipitates were colored reddish. The anode was also attacked and the carbon disintegrated. Results with different degrees of stirring of the cathode liquor are shown in Table VII. Stirring had practically no effect on the per cent recovery of beryllium hydroxide. Without stirring, a
The electrolytic preparation of beryllium hydroxide was investigated using an aqueous solution of sodium beryllium fluoride as cathode liquor and graphite as electrode material. Chlorine gas was liberated when sodium chloride solution was used as anode liquor. Experiments were conducted to establish the effect of the following variables on the recovery of beryllium hydroxide and on the current efficiency: current density, time of electrolysis, temperature, addition of sodium chloride in cathode liquor, different anode liquors, and agitation. Best results were obtained with a solution containing 0.00177 gram per ml., 1.25 hours with continuous stirring, and a cathode current density of 0.0345 ampere per sq. cm. The current efficiency was 96.0% and recovery was 94.6%. These results provide experimental data on which conclusions regarding the economics of the electrolytic process can be based. Such data have not been available before now in the relatively few references found in the literature. I n comparing the operating variables which have been evaluated with results reported by Lundin (3) for the conventional process, it is of importance t o consider that the present work represents an over-all approach from the industrial chemical viewpoint. Consequently, only a limited number of variables were investigated. Although available data show that the electrolytic process requires 9.0 to 19.0 volts, whereas sodium hydroxide can be manufactured a t 3.0 t o 4.5 volts, it is possible that these higher voltages can be reduced appreciably through furt4er research on the process.
Effects of Various Anode Liquors on Electrolysis
Table VI.
Actual B e 0 Anode Liquor Voltage Obtained, G. 70 ml. 5% NaCl 11 6 0.412 70 ml. 5% KC1 12.0 0.414 70ml 57' NazCOa 19.0 0.418 70 ml: 1% NaOH 11.6 0.414 5 70 ml. NazBeF4 18.0 0.420 Amperes 0.75 Cathode current density = 0.0345 amp./sq. cm. Time of electrolvsis = 1.5 hours Constant stirring Temperature = 30° C. No. 1 2 3 4
-
Table VII.
Recovery,
%
93.15 93.56 94,46 93.56 94.91
Effect of Stirring on Formation of B e 0
Actual B e 0 Recovery, Nature of Stirring Obtained, G. % 1 None 0.4114 92.95 2 Every 5 minutes 0.4125 93.22 3 Constant 0.4120 93.15 Amperes = 0.75 Cathode current density = 0.0345 amp./sq. cm. Temperature = 30° C. Quantity of B e 0 present in 250 ml. stock solution = 0.4425 gram
No.
Acknowledgment
The sodium beryllium fluoride required for the investigation was supplied by The Beryllium Corp. and the authors wish t o express their appreciation for this cooperation. literature Cited (1) Cooper, H. S., U. S. P a t e n t s 1,775,589(Sept. 9, 1930); 1,805,567 ( M a y 19,1931). (2) Lebeau, P.,Ann. chim. phys., 39,7744 (1798). (3) L u n d i n , H., Trans. Am. I n s t . Chem. Engrs., 41,671-91 (1945). (4) Seri Holding, S. A.,B r i t . P a t e n t 514,992(Nov. 23, 1939).
R ~ C E I Y Efor D review August 18, 1952. ACCEPTED April 23, 1953. Based on a thesis presented in part fulfillment of the requirements for the M.S.degreein ohemical engineering at the University of Iowa.
