I
MURRAY RElCHl and HARRY KAPENEKAS2 University of Akron, Government laboratories, Akron, Ohio
Nitrogen Purification A sodium dithionite scrubbing solution containing phosphate buffers and zinc sulfate purifies commercial nitrogen to less than 0.03% oxygen
0
XYCEN is detrimental to the reaction rate of emulsion polymerizations at low temperatures. Feldon and Gyenge (74) showed that added air retarded reactions prepared by sugar-free and tetraethylenepentamine-diisopropylbenzene monohydroperoxide formulas at 41' F. and lowered slightly the rate of those conducted by the Mutual formula a t 122' F. The air (0 to 42 ml. per 50 grams of monomer) was added either before initiation or at about 25% conversion, To evaluate variations in polymerization formula properly, essentially oxygen-free nitrogen is utilized to purge the reactors. Nitrogen containing approximately o.03y0 or less oxygen is desirable for purging operations in the pilot plant, but the cost of high purity nitrogen makes its use impractical. Contamination of gases, liquids, and water by oxygen is a constant problem in the chemical industry and innumerable methods have been developed for its removal from the medium. Purification processes can be classified as combustion and chemisorption. Combustion. Gas containing a little oxygen passed over finely divided copper at high temperatures forms copper oxide (7, 77, 32). At GOO' C. the gas does not contain oxygen, and at 230' C. it has 0.001770 (28). The copper oxide can be reduced to copper at moderate temperatures (30) with hydrogen gas, or a small quantity of hydrogen can be circulated with the gas so that water is formed. Cobalt(I1) oxide (32) prepared from cobalt(I1) carbonate a t 340' C. and very high vacuum has been reported for purification of nitrogen. At 650' C. 5% palladized asbestos catalyzes flameless combustion of oxygen and hydrogen at 90% efficiency; at room temperature efficiency is 70 to 75% (37). Reaction of phosphorus and oxygen to form phosphorus pentoxide was utilized by Wallace (49), Hamon (76), and others (37) to purify gaseous mixtures containing oxygen Hamon removed gaseous products by passing the effluent gas through mercuric chloride. Sodium hydride (22) or hydrides of calcium or
Present address, Food Machinery and Chemical Corp., Princeton, N. J. a Present address, Kapenekas Laboratory Services, Akron, Ohio.
lithium (24), heated to 250' C., pick up oxygen and water continuously from gases. Highly reactive carbon (36) was heated to 600' C. and brought into contact with the gas mixture to combine with substantially all the oxygen to form compounds other than carbon monoxide. Scott (43) employed low-carbon steel disks a t 800' C. to fix impurities, as oxides. Oxygen can be removed from olefins (70) by passage, at not less than 20 atm., through vessels containing copper, nickel, silver, platinum, or palladium. Alkali metal nitrides mixed with heated tantalum powder pick u p traces of oxygen and steam (46). Gas in contact with a reactive alloy containing 5 to 5Oy0 of magnesium and 95 to 50% of lead ( 2 ) removes oxygen. I n general, these combustion methods require high temperatures and/or pressures, the equipment is tedious to construct, gaseous products result in some methods, and the catalyst must be regenerated by hydrogen a t high temperatures. Chemisorption. These processes usually involve passage of the gas through liquid and necessitate a packed column for maximum efficiency; the solvent must be regenerated or replaced. Hartshorne and Spencer (77) employed chromium(I1) chloride in the presence of amalgamated zinc as the absorbent for the removal of oxygen from carbon dioxide, whereas Rust and Vaughan (40) used a dilute solution of chromium(I1) sulfate to remove oxygen from commercial nitrogen. The acidified chromium(I1) solution must stand many hours prior to use and maintenance is an annoyance (29). Ammoniacal solutions of copper(1) chloride or carbonate have been used (8, 9 ) to remove oxygen from ammonia. Pyrogallol (42) removes oxygen in the microestimation of blood gases. Nitrogen (50), mixed in a steel bomb for 3 hours with a solution of saturated ammonium carbonate, concentrated ammonium hydroxide, water, and ammonium chloride, with excess copper and a small quantity oftin, had an oxygen content of 0.0001%. Meites (29) employed two solutions of 0.1M vanadyl sulfate in contact with excess amalgamated zinc, in series with water to wash out vanadium, to remove oxygen completely from commercial nitrogen. One drawback is the prohibitive cost of vanadium sulfate. Oxygen
has been removed from "low line" refinery gases by absorption in naphtha (72). Nitrogen forced through a porous membrane immersed in sodium dithionite contained less than 0.0007% oxvgen (23). Zikeev (;52) used 20 parts of sodium dithionite, 10 of potassium hydroxide, and 70 of water to remove oxygen. Fieser (75) recommended a solution of 16 grams of sodium dithionite, 6.6 grams of sodium hydroxide, and 2 grams of sodium anthraquinone 0sulfonate in 100 ml. of water in a bubbling type of absorption pipet or the Friedrichs gas-washing pipet for removal and determination of oxygen in gas. Others (79,34,47,47) used sodium anthraquinone p-sulfonate to catalyze the absorption of oxygen by a solution of dithionite in potassium hydroxide. Stevens and coworkers (48) tested different reagents with a solution of 28% sodium dithionite in 10% potassium hydroxide ; they recommended replacement of the quinone with indigo carmine. With ferric chloride, a black precipitate was noted on the surface near the meniscus. However, solutions of sodium dithionite are unstable (78). COSteanu ( 5 ) reports that solutions of sodium dithionite which reduce copper, lead, mercury, and silver salts in the cold, after 3 days lose the power to reduce lead, whereas copper and mercury salts are reduced only on heating, and silver is still reduced in the cold. Sodium dithionite solutions recommended for absorption of oxygen in gas analysis decompose after a few days even if air is excluded and are not satisfactory for further use (35). Burford (3) employed Fieser's dithionite solutions to remove oxygen from ethylene (for use over nickel catalysts). Jellinek (27) mentioned that in electrolytic manufacture of sodium dithionite it is necessary to cool the liquid in the cathode compartment, to stir rapidly, and to pass relatively large amounts of current through the solution. To minimize oxidation of dithionite by air during preparation of the solutions employed for gas analysis, Wesson (57) devised a special tube and procedure. T o increase the stability of dithionite solution, Chappell (4) used the double zinc salt instead of the sodium salt; he and Eustis (73) emVOL. 49,
NO. 5
*
M A Y 1957
869
-c Z 5
1-1 Monometer-
I l l Ill From m L Linde High Purity ). Nitrogen Cylinder Cylrnder if o r Reference Purposes
I
,
1
,
1
Surge
Rotometet-
I l l Column 3 4 X 72 0
Cm
n 250-MI
Graduated
1'
I
Solution
I
I
I
Vessel
Nitrogen G a s Out
P-J
83-Gallon Holding
I
51-Gallon
V e s L
Holding Vessel
c
' 8
Weinmdn, 15 GPM, I
Water Trap
Exhausf
Figure 1. Laboratory system for removal of oxygc?n from nitrogen
ployed the product of formaldehyde and dithionite (sodium formaldehyde sulfoxylate), and Rodman (39) suggested alkali metal bicarbonate for the salt. Anhydrous sodium dithionite was considered to be more stable (20) when mixed with alkali metal hydroxides, carbonates, phosphates, or silicates in amounts of at least 2 moles for each mole of reducing agent. Seyewetz (45) has stated that the best stabilizers (in grams per liter) for sodium dithionite in the presence of air are in the order: trisodium phosphate (loo), sirupy sodium silicate (loo), pyrogallic acid (IO), and ammonium thiocyanate (10) ; potassium thiocyanate is not a stabilizer. Scribner (44) has reported that sodium dithionite solutions are stable (2970 loss in 168 hours) when the alkalinity is sufficient to control tendency of solution to become acid and the temperature is maintained at one point and means are provided to remove the heat of reactions that may be evolved. Pate1 and Rao (33) claim that the maximum yields of sodium dithionite from the electrolytic reduction of bisulfite at the mercury cathode are obtained at concentrations of 30y0 sodium bisulfite, 3y0 sodium bicarbonate, and 1% Nekal BX (General Aniline and Film Gorp.). The sodium dithionite method appeared to be the most promising. High temperatures were considered somewhat hazardous for pilot-plant operation. A packed column, 8 inches in diameter and 15 feet high, was available for adaptation to this method of oxygen removal. Initial experiments by Lang (27) were performed on a laboratory scale to determine the extent to which commercial nitrogen could be purified by the sodium dithionite method and to ascertain whether the existing plant equipment could be utilized for the absorption process. Purification Procedures
Laboratory. The flow sheet for the gas-scrubbing process and the equip-
870
I - S t a g e Pump
Figure 2. Pilot plant equipment for removal o f oxygen from commercial nitrogen
ment employed for the laboratory runs are shown in Figure 1. The trisodium phosphate was added in the solid state to the 250-ml. flask, which was then stoppered. Water was added to the system through the addition funnel, and the water was circulated through the system until all of the phosphate was dissolved; this required 10 to 15 minutes. During this period, nitrogen was bubbled through the column to displace as much of the air in the system as possible. The 250-ml. flask was then unstoppered, and part o€ the water was removed to permit addition of dry sodium dithionite to the system; the flask was immediately refilled with the water that had been removed, and then restoppered. The solution was again circulated until all of the dithionite was dissolved ( a p proximately 10 minutes). The gas and liquid flow rates and the column pressure were then adjusted and maintained constant until the system came to equilibrium, after which time the oxygen content of the effluent gas was determined. Pilot Plant. The flow sheet for gas scrubbing (oxygen removal) process and the equipment employed are shown in Figure 2. The column-type scrubber consists of a 15-foot section of 8-inch diameter stainless steel pipe packed with 1-inch Raschig rings. The entire system was operated at a pressure of 100 to 120 pounds per square inch. Commercial nitrogen from a bulk unit, containing 72 cylinders, was delivered through a gas meter into the column at a point approximately 2 feet above the bottom. The gas passed upward through the solution in the column where the oxygen reacted with the sodium dithionite. A surge tank (converted reflux condenser) located at the top of the tower prevented liquor from leaving with the gas during surges. After leaving the column, the nitrogen passed through an orifice-type differential controller which prevented surge and excessive gas flow through the column. The nitrogen passed through a trap for the removal of water before it was piped to various parts
INDUSTRIAL AND ENGINEERING CHEMISTRY
of the plant. Procedure. The following procedure was developed for charging the sodium dithionite solution to either of two iron holding vessels Dissolve the trisodium phosphate dodecahydrate in water at 130' F. (0.2 pound of trisodium phosphate per pound of water) and transfer to the solution holding tank. Dissolve in a 55-gallon vessel 65% of the tripotassium phosphate in water (Solution A) a t 80" F. (0.63 pound of tripotassium phosphate per pound of water). Dissolve in another vessel the remainder of the tripotassium phosphate in water (Solution B) a t 80" F. (0.72 pound of tripotassium phosphate per pound of water). Dissolve completely zinc sulfate in water at 80' F., using a minimum amount of agitation (0.077 pound of zinc sulfate per pound of water). Add the zinc sulfate to Solution B with a minimum of agitation, and then add the composite to Solution A. Add sodium dithionite slowly to the zinc sulfate-tripotassium phosphate solution while maintaining a blanket of nitrogen over the solution. When the sodium dithionite has been dissolved, transfer the solution to the holding tank without allowing the solution to come into contact with air.
8 0.040 t-
z W c 2
00
0.030
1
I I
4-
I
OD00 0
I APPROXIMATE TIME, HOURS
2
Figure 3. Depletion curve for sodium hyposulfite after point o f initial failure in packed 40-cm. column Nitrogen flow of 8.20 cc. per second; oxygen
0.1 24%
NITROGEN PURlFlCATlON To clean, fill the tank with a water solution at 200' F. containing 1% Daxad (Dewey and Almy Chemical Go.) and 0.5% Versene (Versenes, Inc.) After 1 hour drain the solution and rinse with water. The sodium dithionite solution was pumped into the top of the column by a Weiman, Type G, Size 1 centrifugal pump. Recycle flow was indicated by a rotameter and was hand-controlled at approximately 4 gallons per minute. The solution was returned to the holding vessel from the bottom of the column. The unit was operated at a variable flow rate which was determined by the nitrogen requirement of the plant. The maximum use of nitrogen occurs during a purge of the reactor a t a rate of about 430 cubic feet per hour. The life and/or efficiency of the scrubbing solution, as given in Tables I and 11, varied because of the nonuniform flow of nitrogen as well as for additional reasons noted. The oxygen content of the gas was usually determined once daily by polarographic analysis (6, 26) which involved the use of a dropping mercury electrode; the method was also adapted for continuous analyses of the effluent nitrogen (7). Every fourth hour, the effluent gas was tested for volatile sulfide with silver nitrate solution and for colloidal sulfur with concentrated sodium hydroxide. The amount of sodium dithionite in the solution was determined volumetrically by a method developed especially for the phosphate-buffered solutions of dithionite, and it utilized suitably complexed copper sulfate (38). Another method consisted of measuring the pressure drop resulting from exposure of a known volume of air with a definite amount of solution (25). The solution was discarded when hydrogen sulfide was noted in the effluent gas, the oxygen content of the effluent nitrogen was greater than 0.030j0, or the amount of sodium dithionite was low
Table I. Oxygen Removal from Commercial Nitrogen" in Unpacked Column
(less than about 0.50 ml. of complexed copper sulfate required to react with 1 ml. of scrubbing solution). Scrubbing solutions containing small quantities of sodium dithionite were not capable of removing oxygen at high flow rates of nitrogen, although, at small flow rates, the oxygen content was under 0.03yG (7). Results and Discussion Laboratory Work. Data for experiments with an unpacked column are shown in Table I. Aqueous solutions containing 10% each of sodium dithionite and of tripotassium phosphate were very viscous and tended to foam when nitrogen was circulated through the system. At concentrations of 5% of sodium dithionite and 2% of trisodium phosphate the foaming was eliminated. The absorptive capacity of the more dilute solution with the unpacked column of 20 and 30 cm. decreased with increasing nitrogen recycle rates, possibly because of'bypassing. At the higher reflux flows the bubble size apparently increased, reducing the surface area of contact. A longer column of 40 cm. seemed to improve the efficiency. The data for the packed columns, 20 and 40 cm. high, are shown in Table 11. Effluent nitrogen from the packed column of 20 cm. contained less oxygen than that obtained from the unpacked column of 20 or 30 cm. even at much higher reflux rates. Varying the recycle rate from 0.03 to 0.07 gallon per minute did not seem to affect the oxygen content to any marked extent. The solution effectively decreased the oxygen content of commercial nitrogen, although Figure 3 shows that the oxygen content of the effluent nitrogen increased with time, and the solution became ineffective. The laboratory tests verified previous work that oxygen can be removed from commercial nitrogen by a sodium dithionite solution and that a packed column
Table II.
8.1 8.1
0.44 0.66 0.66
0.032 0.046 0.013
Cc./Sec. 8.20 3.56
8.20
8.20
a
*
Recycle Flow, Gal./Min.
Oxygen Content of Effluent, %
Remarks
Column Height of 20 Cm. 0.030 0.028 0.030 0.007
Column practically dry
0.033
Column practically dry
0.004 0.003 0.040 0.004 0.006 0.043 0.070 0.006 0.098 0.013 Column Height of 40 Cm. 0.030 0.025 0.043 0.010 0.055 0.007 0.070 0.009
0.038
30 30 40
8.1 Oxygen content 0.124y0. Solutio. foamed a great deal; addition of amyl alcohol decreased foam somewhat.
Oxygen Removal from Commercial Nitrogen" in Column Packed with 6-Mm. Raschig Ringsb
Gas Flow,
Recycle Oxygen Column Flow, Content of Height, Cc./Sec. Gal./Min. Effluent, 3 ' % Cm. Recycle Solution 10% NazS~04.2HaO; 10% Na3P04. 12H20b 60 2.0 0.22 0.005 3.6 0.22 0.004 60 Recycle Solution 5% NaA04.2HzO; 2% NuPO4.12Hz0, pH of 10.8 8.1 0.22 0.026 20 8.1 0.44 0.036 20 8.1 0.66 0.044 20 0.033 30 8.1 0.22
Gas Flow,
would sufficiently increase the gas-liquid contact to make the method practical on a pilot-plant scale. Calculations showed that a plant column containing 1-inch Raschig rings would increase the contact time, assuming a 75% packing factor, from 0.48 to 1.11 minutes. The packed absorption column of Type 316 stainless steel with Type 304 piping located in the pilot plant was employed for the gas scrubbing operation. Pilot Plant Operation. Data for the runs made in the pilot plant are shown in Tables I11 and IV. The initial experiments in the pilot plant demonstrated that a 2 to 1 ratio of trisodium phosphate dodecahydrate to sodium dithionite measurably improved the life and efficiency (defined as the number of cubic feet of nitrogen purified per pound of sodium dithionite) of the absorbing solution when compared to the ratios used in the laboratory. However, hydrogen sulfide periodically was detected in the effluent gas and the solution was discarded, even though it contained active dithionite, to prevent contamination of reactions in the pilot plant; hydrogen sulfide is a shortstop for free radical polymerizations. Variations in the charging procedure or in the equipment to alleviate this condition, without success, included: painting the internal surfaces of the holding vessels with Ebonal (a creosote asphalt paint) to prevent corrosion; manual cleaning of the Raschig rings in the gas scrubbing column to improve liquid-gas contact a t interface; varying the ratio of buffer to dithionite; and use of sodium sulfite. The sodium dithionite solutions USUally contained a precipitate of ferrous sulfide which apparently formed when soluble sulfide in solution reacted with the iron surfaces of the charge vessel. The corrosion was not immediately harmful, but it indicated that the vessels would eventually fail. Exposure of the dithi-
a
b
Column flooded
No foam in column Insuf. recycling to wet column Foam in bottom of column Column uniformly wetted
0.098 0.015 Oxygen content of 0.124%. Recycle solution. 5% Na2Sz04 2Hz0; 2% NasPOc.12H20.
VOL. 49, NO. 5
M A Y 1957
871
Table 111.
Run No. l b
2b 3b 4b 5b 66 7 8 9 10 11 12 13-15 16 17 18-19 20 21 22 23 25 27 29 31 33 35 37 39 41 43 45 47 5 le 53" 55 57 59.' 61 63
Charge and Purification Data for Nitrogen Scrubbing Column Using Trisodium Phosphate-Sodium Dithionite Dihydrate Solution Lb./100 Lb. HzO Na2SnO4 aHTo TSPe 2.5 2.5 2.5 2.5 2.5 2.5 4.99 7.48 7.48 9.97 11.80 9.97 9.97 9.97 9.97 9.97 9.97 9.97 9.97 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 9.25 7.22 7.22 12.28 12.28
4.99 4.99 4.99 4.99 4.99 4.99 4.99 4.99 4.99 4.99 5.90 4.99 4.99 4.99 4.99 4.99 4.99 4.99 4.99 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 3.18 4.63 4.34 2.89 3.61 3.61
Nitrogen Purified,
Cu. Ft. Total Per lb. NazSzOa
...
...
Nil 9,320 2,430 11,440 7,340 13,820 13,960 8,040 16,750 24,400 10,130 15,190 11,160 9,500 14,980 15,720 6,910 7,710 24,580 24,310 23,620 14,560 17,220 26,350 22,190 24,840 24,980 33,100 33,890 10,240 6,620 2,040 6,340 12,670 9,100 18,900 23,580 23,040
Nil 466 110 520 333 629 634 3 65 761 938 461 691 507 432 680 716 3 14 351 1,118 1,105 1,072 66 1 783 1,198 1,008 1,130 1,132 1,504 1,540 465 305 93 288 396 303 948 943 922
a Trisodium phosphate dodecahydrate. b 0.453lb. of sodium hydroxide was added to solution. c Unit was stopped to clean prior to week-end shutdown. d Potentiometer was faulty and solution was discarded after e
Inlet nitrogen Contained 0.4% oxygen. 0.145 lb. of sodium sulfite added t o solution.
onite solution to air decreased the pH and resulted in the concomitant evolution of hydrogen sulfide. The evolution of hydrogen sulfide from a highly alkaline solution as indicated by its pres-
Table IV.
Scrubbing Solution Days in Reason for discarding use
...
None 3 3 1 2 4 5 5 8 6 4 6 3 4
6 3 3 2
6 5 5 4 2 8 6 8 10 7 10 3 2 1 2 6 3 6 7 5
HzS Hz S HIS = 0.07% = 0.03%
0 2
= 0,0770
HzS HzS H2S Os = 0.0470
HzS HzS 02 = 0.06% Week-end shutdownc HzS HzS 0 %= 0.04% 0 2 = 0.05% 0 2 = 0.0470 HzS HzS 0 2 = 0.03% d
d
0 2 = 0.03%
0 2 = 0.0470 02 = 0.04% Week-end shutdownC 02 0.06% Week-end shutdownC 0 2 = 0.09% HzS HzS HzS HzS
HpS
normal period of operation.
ence in the effluent gas was believed to be caused by the accumulation of soluble sulfide and a decrease in pH at the liquid gas interface. Sequestering agents such as Versene
Charge and Purification Data for Nitrogen Column Using Phosphate-Buffered Dithioniie Solution Lb./100 Lb. HzO
TPPb Versene R u n KO. TSPa 0.145 65 12.28 0.434 67 12.28 0.434 12.28 69 0.145 12.28 71 0.145 73 12.28 9.53 0.157 75d 7.80 0.157 9.53 77 7.80 0.157 9.53 79 7.80 9.53 0.157 81 7.80 14.73 16.48 83 16.33 13.58 85 16.33 13.58 87 14.6 12.2 133 14.6 12.2 135 a Trisodium phosphate dodecahydrate. b Tripotassium phosphate.
... ...
... ... ...
... ... ... ... ...
872
Os
0 2
effectively suppressed the formation of ferrous sulfide but increased the rate of corrosion of the iron surfaces which were exposed to the solution and did not prevent the formation of hydrogen sulfide. Laboratory tests indicated that inclusion of a sufficient quantity of zinc ions in phosphate-buffered solutions of sodium dithionite prevented the formation of sulfide even in the presence of iron. The amount of phosphate in solution was increased by substituting tripotassium phosphate for part of the trisodium phosphate and zinc sulfate was included in the sodium dithionite charge solution. These changes increased the life of the solution, decreased the efficiency, and did not prevent the formation of sulfide in the solution (data not shown). Increasing the amount of zinc sulfate in the solution and adding it to some of the tripotassium phosphate markedly reduced the formation of sulfide and resulted in a sodium dithionite solution whose nitrogen scrubbing performance in the pilot plant correlated with that of similar solution in the laboratory. The final scrubbing solution contained 7.2 pounds of sodium dithionite per 100 pounds of water as the oxygen absorbant, 12.2 and 14.6 pounds of trisodium and tripotassium phosphate, respectively, as the pH buffer agents, and 0.77 pound of zinc sulfate to retard the formation of soluble sulfide in the scrubbing solution and to prevent the occurrence of hydrogen sulfide in the effluent gas. Typical data for the operation of the column using this solution are given under runs 333 and 135, Table I V ; about 40,000 cubic feet of commercial nitrogen were purified to an oxygen content of less than 0.03y0, and the solution endured for 12 days before the sodium dithionite was depleted. The gas-scrubbing system, in operation a year, using the same type of solution as for run 135 (Table IV), has brought about considerable savings over single Linde prepurified cylinders. The cost analysis is shown in Table V.
INDUSTRIAL AND ENGINEERING CHEMISTRY
ZllSOI
... ... ... ... ... a . .
0.0217 0.0217 0.0217 0.0806 0.0806 0.824 0.77 0.77
NaZS201. 2Hz0 3.51 3.51 3.51 3.51 3.51 3.83 3.83 3.83 3.83 7.95 7.95 7.95 7.2 7.2
Nitrogen Purified, Cu. Ft. Per lb. NazSzOa.
Scrubbing Solution Reason for discarding Days in use 9 Na~S204depletion 38,450 1,538 3 System flooded 618 15,450 3 Week-end shutdownc 1,526 16,650 7 High sulfide 30,460 1,211 804 20,150 HzS 7 10 0 2 = 0-06% 1,545 40,900 NalSzOa depletion 1,422 7 40,810 9 NazSz04 depletion 1,454 38,560 NaaSzOa depletion 8 1,420 37,630 15 Na2SzOddepletion 62,850 1,141 11 NazSzO4 depletion 670 36,840 12 NazS204 depletion 47,210 850 NanSzOn depletion 7 33,250 1,179 12 Na2Sz0a depletion 1,055 49,360 c Unit stopped prior t o week-end shutdown. d 0.038 lb. of iron(I1) sulfate heptahydrate added t o system.
Total
2Hz0
NITROGEN PURIFICATION Table V. Ingredient
(21) Jellinek, Karl, Z . Elektrochem. 17, 245-61 (1909). (22) Jost, Friedrich, U. S. Patent 1,681,702 (Aug. 21, 1928). (23) Kautskv. H.. Thiele. H.. Z. anore. U. a&km. &em. 152, 342-6 (i926j. (24) Klema, E. D., U. S. Patent 2,547,874 (April 3, 1951). (25) Kniel, I. A., Fuller, R., B. F.
Cost of Materials for Gas Scrubbing Operation Total Cost Weight, Lb. Cost/Lb.
\
For Large Pot Trisodium phosphate Tripotassium phosphate Zinc sulfate Sodium dithionite
80 95.5 4.85 46.8
$0.0565 0.165 0.08 0.25
$ 4.52 15.76 .37 11.70 $32.35
$0.0565 0.165 0.08 0.25
$ 2.73 9.52 0.23 7.05 $19.53
Goodrich Co., Institute, W. Va., private communication. (26) Laitinen, H. A., Higuchi, T., Czuha, M., Jr., J . Am. Chem. Soc. 70, 561
For Small Pot Trisodium phosphate Tripotassium phosphate Zinc sulfate Sodium dithionite
48.3 57.7 2.92 28.2
(1948). (27) Lang, W. C., “Preparation of Oxygen-
Free Nitrogen,” Government Laboratories, AU-827 (June 2, 1950). (28) Liebhafskv, H. A , , Winslow, E. H., J . A m . Chem. Soc. 68,2734-5 (1946). (29) Meites, Louis, Meites, Thelma, IND. ENG.CHEM.,ANAL. ED., 20, 984-5
Materials for Cleaning Solution For Large Pot Daxad 11 Versene
7 3
$0.23 0.70
$ 1.61 2.10 $ 3.71
$0.23
$ 0.99 1.26
(1 9481. .-*. \ - -
(30) Moore, W. C., U. S. Patent 2,496,353 (Feb. 7,1950). (31) Owen, L. W., J . Sac. Chem. Tnd. (London) 69, 272-5 (1950). (32) Parel. H. A,. Frank. E. D.. J . A m . ’ ??hem Soc. 63.146819 (1941). (33) Paiel, C. c., kao, M.‘ R. A., Proc. Natl. Inst. Sei. India 15, 126 (1948). (34) Peters, J. P., Van Slyke, D. D.,
For Small Pot Daxad 11 Versene
4.3 1.8
0.70
Cost of Solution Assuming 3 solutions per month, average material monthly cost = $86.76 Average time to charge and clean unit = 352 minutes Average monthly time = 17.6 hours = 35.48 Cost = 17.6 X 2.016 min hr. = 25.59 Testing of solution = 45 60 min. day X 20 days X $1.706/hr. X $147.83 Total cost of solution Average use of nitrogen = 82,660 cu. ft./month Co$t of individual cylinders = $834.87 Cost of Linde high purity (0.01% 02) = 300.00 Cost of shipment = 90d/cylinder = 187.50 Labor for cylinders = 50$/cylinder = $1322.37 Total cost of cylinders Total cost of bulk unit = $619.95 Cost of unit = 147.83 Cost of solution = $767.78 Total cost of bulk unit Savings = $554.59 Advantages of bulk unit Less labor involved. No empty cylinders to increase cost Disadvantages of bulk unit. Difficult to determine when leaks are present
Literature Cited (1) Almquist, J. A., Crittenden, E. D., IND.ENG.CHEM.18, 886-7 (1926). ( 2 ) Ashcroft, E. A., Can. Patent 196,490 (Jan. 27,1920). (3) Burford, W. B., 111, Frazer, J. C. W., J . A m . Chem. Soc. 67, 341-2 (1945). (4) Chappell, N. J., J . Sac. Dyers Coloutists 37,206 (1 921 ). (5) Costeanu, R. N., Bull. f a c . Stiinte Cernauti 11,269-70 (1937). ( 6 ) Czuha, M., “Determination of Oxygen in Gases by Means of a
Dropping Mercury Electrode,” Government Laboratories, AU-P216, SP-T-465, CD-2625 (Nov. 20, 1951 ). ~ .
-
~
( 7 ) Czuha,
M., “Determination of Oxygen in Fluids by Means of a Dropping Mercury Electrode,” Government Laboratories, AU1181 (Aug. 12,1953). ( 8 ) Dely, J. G., Refrig. Eng. 59, 113-19, 158-60 ( 1 945). (9) Directie vande Staatsmijnen, Limburg, Dutch Patent 66,295 (Aug. 15,1950).
(10) Du Pont de Nemours & Co., E. I.,
(to Imperial Chemical Industries),
Brit.
Patent 565,991
“Quantitative Clinical Chemistr: Methods.” “Vol. 2. Methods, Williams’ & Wilkins, Baltimore,
1932. (35) Quig&, Dorothy, IND.ENG.CHEM., ANAL.ED. 8, 363 (1936). (36) Ray, A. B., U. S. Patent 2,019,632 (Nov. 5,1936). Ger. (37) Regina-Elektrizitats-Gesellschaft, Patent 236.966 (Julv 21. 1909). (38) Reich, M., Kapenekas, H., “Use of
Sodium Dithionite Solution for Removal of Oxygen from Commercial Nitrogen,” Government Laboratories, AU-1185 (Nov. 2, 1953).
Rodman, C. J., Maude, A. H., U. S. Patent 1,736,464 (Nov. 19, 1930’1. Rust, J. F., Vaughan, W. E., J . Org. Chem. 5 , 449 (1940).
Scholander, P. F., J . Biol. Chem. 146,159 (1942).
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7
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RECEIVED for review June 29, 1956 ACCEPTED November 14, 1956 Work performed as part of a research project sponsored by the National Science Foundation, VOL.49, NO. 5
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