US3884780A - Absorption of gaseous cell product in cell liquor - Google Patents

Abstract

The efficiency of electrolytic cells in which a gaseous cell product reacts with a component of the cell liquor or a reagent added to the electrolytic cell, may be substantially improved by the insertion of gas dispersing means above the electrodes of the electrolytic cell and below the surface of the cell liquors. The dispersing means serves to mechanically diffuse the gaseous cell product into the cell liquor containing the reactant to provide intimate mixing and increased contact of reactants. The gas dispersing means may be any inert conventional absorption packing or distillation column packing such as, Berl saddles, Raschig rings, bubble trays, glassbeads, and the like.

Description

United States Patent Cook, Jr. et al.

[451 May 20, 1975 [54] ABSORPTION OF GASEOUS CELL 3,640,804 2/1972 Westerlund 204/95 PRODUCT IN CELL LIQUOR [75] Inventors: Edward H. Cook, Jr.; Morris P. Pr'mary EXamlner F:' Edmundson Gmtheer both of Lewiston N Y Attorney, Agent, or Firm-Peter F. Casella; Donald C.

Studley [73] Assignee: Hooker Chemicals & Plastics Corporation, Niagara Falls, NY.

[57] ABSTRACT [22] Filed: Oct. 21, 1971 The efficiency of electrolytic cells m which a gaseous PP 191,533 cell product reacts with a component of the cell liquor Related Application Data or a reagent added to the electrolytic cell, may be sub- I stantially improved by the insertion of gas dispersing [62] 3 1968 means above the electrodes of the electrolytic cell and below the surface of the cell liquors. The dispersing [52] U 5 Cl 204/95. 423/472. 261/94 means serves to mechanically diffuse the gaseous cell [51] Colb Bolk 3/00 product into the cell liquor containing the reactant to 58] Fie'ld 2O4/95 278 provide intimate mixing and increased contact of reactants. The gas dispersing means may be any inert conltional absorption packing or distillation column [56] References Cited packing such as, Berl saddles, Raschig rlngs, bubble UNITED STATES PATENTS trays, glassbeads, and the like. 2,204,506 6/l940 MacDougall 204/95 X 2,981,667 4/ 1961 Foreman et al 204/8] 2 Claims, 1 Drawing Figure e -'-"'9' 1-- lq 0'l- "-5 0 'o O 28 26 24 .6

Q T: :T:: I: '1 v o i a, e

ABSORPTION OF GASEOUS CELL PRODUCT IN CELL LIQUOR This is a division, of application Ser. No. 755,845,

filed Aug. 28, 1968, now U.S. Pat. No. 3,616,443.

Diaphragm-less electrolytic cells for the production of alkali metal chlorates are effectively equipped with gas dispersing means to remove residual chlorine values from the hydrogen gas evolved at the cathode. The packing serves to disperse and break up gas bubbles which contain small amounts of chlorine. This dispersion results in intimate mixing with the near neutral cell BACKGROUND FOR THE INVENTION Chemical reactions are frequently conducted within the confines of electrolytic cells. Generally a component product of electrolysis is caused to react with another reagent chemically within the electrolytic cell. Such reactions may be broadly grouped into electro -lyt1c oxidations and addition type reaction. The reactant which is caused to undergo chemical reaction with the product of the electrolytic cell may in itself be part .of the electrolyte within the cell or may be an added foreign reagent, such as, an olefin, acetylenic com- P an aliphatic hydrocarbon or halogenated hydrocarbon. For example, in a cell producing chlorine at an anode, chlorination reaction can occur within the electrolytic cell. Such reactions include-chlorination of olefin, acetylene, aliphatic hydrocarbon; a partially chlori- Hated ydrocarbon or any chemical compound normally considered to undergo chlorine substitution or chlorine addition. In addition, oxidation reaction where the sole function of the chlorine is to act as an oxidant.

Various methods have been used in the past to optimize the reaction between an electrolytic cell product and another reactant. Conventionally, the cell product a emoved from the cell and caused to react in a spef y deslgned eactor where the conditions for reacy be closely controlled. It is generally considered to be advantageous to avoid the necessity for complex costly chemical apparatus and to perform the reactlons of electrolytic ll products, especially the gas- Products, as soon as possible so as to initiate the reaction while the gaseous reaction is still in a nascent or near nascent state.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the instant invention, there is P vrded an electrolytic cell wherein a compound is p duced by chemical interaction between a gaseous electrolytic product and a reactant which is dissolved in the electrolyte of said cell or introduced into a reaction zone within the electrolyte. The electrolytic cell of the instant invention comprises a cell top, a cell bottom and sidewalls, electrodes comprising an anode and a cathode, means for conducting current to said cell,

electrolyte feed means and withdrawal means, in which there is disposed above the cell electrodes but at least partially immersed beneath the top of the cell liquor a dispersing means which serves to break up and diffuse,

large gas bubbles within the liquid phase of the cell contents. g

The gas dispersion means may be completely submerged below the upper level of the cell liquors, in

which case it serves as packing to completely mix a gaseous cell product with the cell liquor or foreign reacas an antimisting shield. An additional advantage at-. .tributable to the electrolytic cell packing of the instant invention resides in an overall increase in the yield of the desired product within the cell itself. By increasing the in-cell production, the necessity for special retention tanks or external reaction vessels is diminished as is the additional reaction time normally lost in completing reactions in extra-cell reactors.

The dispersing means disposed within the electrolytic cell may consist of packing material conventionally employed in absorption towers or distillation columns. For example, a packing of Berl saddles, Raschic rings, glass bead bubble trays or any known device for dispersing gases and liquids by mechanical diffusion which is inert toward the contents of the electrolytic cell, may constitute the dispersing means of the instant invention.

Electrolytic cells, either of the diaphragm or diaphragm-less type may be provided with internal dispersing means in accordance with this invention. The electrolytic cells may be of the monopolar or bipolar type.

DETAILED DESCRIPTION OF THE INVENTION For a complete understanding of the present invention, reference may be made to the accompany drawing in which:

The FIGURE represents a side elevation p y in section of the electrolytic cell of this invention.

The electrolytic cell depicted, in the FIGURE repr sents the conventional monopolar cell provided with a cell top 10 cell bottom 12 and internally a disposed anodes 14 cathodes 16. Cell feed inlet 22 provides for the introduction of electrolyte while gas vent 20 allows for thedischarge of the gaseous electrolysis products and overflow outlet 28 provides liquid removal means. Th dispersing means or absorption packing 18 which represents one aspect of this invention is disposed withi the cell top 10 on tray 30. The normal operating liquid and suspended gas level 24 exemplifies operation with absorption packing 18 completely submerged in the electrolyte. The gas disengaging region within the electrolytic cell is shown 26.

cell, enters the region of the dispersing means or ab-v sorption packing 18 at which point large gas bubbles are finely dispersed and intimately mixed with a reactant within the cell, either foreign or inherent to the electrolyte, to product a desired product. The product is withdrawn from the cell by overflow withdrawal means 28.. Non-reactive gases continue to rise in the liquid electrolyte and form a relatively less dense liquidfilled with suspended gas at 24, within cell top 10. The

non-reactive gas disengages itself from liquid 24 filling space 26 and exiting cell top through gas vent 20.

When employing gas dispersion means in a conventional diaphragm type electrolytic cell, where the chlorinegenerated at the anode is to react with an added reactant such as ethylene, propylene or butylene, the cell packing is placed above the anodes in the anolyte. Theolefin may be introduced into the cell via the cell feed iniet 22 or by way of a manifold injection system which, inserts the gaseous olefin at a point below the packingin the cell. The gaseous olefin reacts with hypochlorous acid to form the corresponding halohydrin which in gaseous form exits the cell via vent 20. The haloliydrin may be recovered from the other gaseous cell products by procedures known to the art.

'T'he'following examples are directed toward exemplijfication of the instant invention through illustration of cation of a decomposition voltage, between the anode and cathode across the electrolyte, results in the production of chlorine at the anode and hydrogen plus hydroxy ions at the cathode. Chlorine within the aqueous electrolyte reacts with water to form hypochlorous acid and the chloride ion. Hypochlorous acid is in equilibrium with hypochlorite ions in the substantially neutral electrolyte. The hypochlorous acid will-react with a hypochlorite ion to produce chlorate ions and chloride ions. The hydrogen gas evolved at the cathode intermingles with some of the gaseous anode product within the electrolyte and serves to entrain chlorine, which is carried with the hydrogen and vented from the conventional chlorate cell. By means of the instant invention, this conventionally lost chlorine value is recovered directly within the cell through reaction with water in the cell to produce more hypochlorous acid. This recovery occursas a result of the disposition of absorption packing or gas dispersing means above the electrodes of the cell. Example 1 An electrolytic cell capable of operating on approximately 55,000 amperes, equipped with graphite anodes and sheet steel cathodes was operated under conventional sodium chlorate producing conditions. The cell top was modified to provide a perforated shelf extend- "ing entirely over the surface area of the electrolyte One quarter inch Berl saddles (3 inches deep) were placed on top of the perforated shelf to serve as gas dispersing means. Under otherwise equivalent conditions except for the perforated shelf and Berl saddles inside the cell top, the cell was operated to determine the relative amount of chlorine recovered in the gas dispersing region of the cell. The results of this operation are presented in Table 1.

TABLE I CURRENT DENSITY C1, 1N VENT GAS Without With Saddles Saddles 0.6Am res r uare inch 4.10 0.75 I pe pe sq 5.10 0.34 3.36 0.60 2.92 1.04 3.36 1.00 4.03 1.84 4.11 3.49 2.49 3.12 3.29

Average 3.58 0.93

0.8 Amperes per square inch 1 5.85 3193 Average 5.85 3.24 0.9Am res r uareinch t 11.2 2.56 pe Pe sq 7.7 2.47

Average 8.08 2.51.

The height of the absorption packing or dispersing means within the electrolytic cell serves to increase the efficiency of chlorine absorption within the cell. Examples l-6 An electrolytic cell comparable to that describedin Example 1 containing no diaphragm, equipped with graphite anodes and sheet steel cathodes, was employed in the production of sodium chlorate. The solution containing approximately 260 grams per liter sodium chloride, grams per liter sodium chlorate and 2 grams per liter sodium dichromate was continuously electrolyzed in each of the following examples until the desired amount of sodium chlorate was produced. Sodium chloride brine was added as makeup during the course of the electrolysis. The cell operating temperature was between 40 centigrade and 45 centigrade. The results of these experiments are tabulated in TABLE II. The current efficiencies shown in the Table are based on chemical assay over the life of the experiment.

TABLE [1 Current. Tempcraturc Flow Final Final Hypo- Batch Density range, rate, NaOl, NaClOa, chlorite, assay Experiper degrees liters A cell grams grams grams content ment; square Volume centipH per head, per per per efiieiency, number Amperes inch ratio grade range minute inches liter liter liter percent Remarks 1 260 0.6 3.25 41-45 7. 7.2 11.5 20 101 483 3.3 79.0 No packing. 2... 360 0. 6 4. 25 42-50 6. 8-7. 2 1. 4 25 107 503 1. 2-3. 7 86. 4 Three inches packing above A cell.

"Three inches of packing. 390 0. 9 4. 81 X 340 8 4. 25 40-48 6.8-/. l 4 25 128 434 2. 1-2. 9 84. r

4. 340 0.8 4. 25 40-41 6.8-7.0 4 25 160 340 1.5-2.7 90.2 Ten inches packing- 340 0. 8 4. 25 4H7 6. 6-7. 0 1.4 25 106 498 1. 7-2. 2 83. 7 second part of run insufficient because flow through cell stopped on one weeken 340 0. 8 4. 25 47-52 6. 7-7. 0 1. 2-1. 4 25 87 520 2.1-2.0 89. 4 Ten inches packing.

6.. 340 0. 8 16. 0 43-49 6.7-7.1 1. 11.6 25 92 520 1. 9-3.7 89. 3 Ten inches packinglowered cell on head.

Although chlorine losses during operation of the chlorate cells involved in the preceding experiments could be substantially eliminated by maintaining the electrolyte pH between 7 and 7.5, in this pH range more oxygen is produced at the anode and the overall current efficiency is only 79% (Experiment 1). Therefore, for efficient operation of this chlorate cell a lower pH range must be maintained in the electrolyte to avoid oxygen production at the anode.

In comparison with Experiment 1, operating the electrolytic cell with a 3 inch layer of :4 inch Berl saddles placed in the electrolyte above the electrodes it was possible to operate the cell at a lower pH range (6.8 to 7.2) with lower chlorine losses than if absorption packing is absent. The height of the electrolyte was inches while operating the cell with gas dispersing means. The combination of lower pH and the 3 inch packing above the electrodes resulted in increased current efficiency from 79% to between 85 and 87% (Experiments 2 and 3). Increasing the absorption packing height to 10 inches further increased the current efficiency to 90% over most of Experiment 4. However, during the last days of Experiment 4 the flow of brine to the cell was interrupted, causing a stagnant situation to develop. One nights operation at very low efficiency caused the overall batch efficiency to drop to 84%. Approximately 94% of the sodium chlorate produced in Experiments 2 through 4 was produced inside the cell, as opposed to lower in cell production followed by production in a conventional retention tank. Continuing with a 10 inch level of absorption packing, the current concentration of 340 amperes (0.8 amperes per square inch) was raised from 4.25 amperes per liter to 8.5 amperes per liter by decreasing the size of the retention tank. This resulted in an overall current efficiency of 89.4% (Experiment 5) from electrolysis of the solution low in sodium chloride (87 grams per liter) with a high sodium chlorate (559 grams per liter) concentration.

In Experiment 6, the current volume ratio was further increased to 16.2 amperes per liter at the same current density. An overall efficiency of 89.3% was observed at a final sodium chloride concentration of 92 grams per liter and a final sodium chlorate concentration of 520 grams per liter.

With a 3 inch layer of packing, increasing current density from 0.6 to 0.8 amperes per square inch increased chlorine losses in the vent gases by about 1%. However, these losses were eliminated by increasing the absorption packing height to 10 inches. In the absence of the packing, chlorine losses varied from 1 to 12%. With 3 inches of packing, chlorine losses varied from 0.7 to 4%; and with 10 inches of packing the chlorine losses were below 2% at chlorate concentrations below 400 grams per liter. Higher chlorine losses were usually observed at chlorate concentrations above 400 grams per liter.

Example 7 An electrolytic cell capable of operation on approximately 55,000 amperes and equipped with graphite anodes'and steel cathode separated by an asbestos diaphragm was provided with six inches of packing in the cell top above the anodes in the anode compartment. The packing was below the surface of the anolyte within the anode compartment.

The cell was operated under normal conditions for the electrolysis of sodium chloride brine. Sodium chloride brine containing 300 grams per liter NaCl was introduced into the anode compartment and a decomposition voltage was applied between the electrodes. Ethylene was continuously introduced into the anolyte below the lower level of the packing in stoichiometric excess.

The gaseous product recovered contained predominately ethylene chlorohydrin and small amounts of unreached ethylene and ethylene dichloride.

What is claimed is:

1. In the process for the production of an oxyhalogen acid selected from hypochlorous acid and hypobromous acid, by the electrolysis of a halide containing brine in electrolytic cell, said halide being selected from chloride and bromide, wherein said brine is electrolyzed between anode and cathode members in said cell to form a halogen anode product corresponding to the halide of said brine, a cell liquor containing water and the said oxy-halogen acid and a hydrogenous gaseous cathode product, which cathode product has entrained therein a portion of the halogen anode product, the improvement which comprises passing said gaseous cathode product containing the entrained halogen upwardly in the cell through a layer of inert, absorptive packing material, which layer is pervious to said gaseous cathode product and is disposed completely above the anode and cathode members of the cell but at least partially below the upper surface of the cell liquor in the cell, maintaining the upper surface of the cell liquor above the anode and cathode members but below the top of the cell so as to form a gas disengaging zone between the top of the cell and the upper surface of the cell liquor in which separation of the gases from the cell liquor is effected, dispersing said gaseous cathode product in said cell liquor so as to effect intimate mixing of the cell liquor and the gaseous cathode product as it passes through said packing material, and, thereby, reacting the halogen in said gaseous cathode product with the water in the cell liquor to form additional oxyhalogen acid.

2. The process as claimed in claim 1 in which the brine is a sodium chloride brine, the anode product is chlorine, the gaseous cathode product is hydrogen and the cell liquor contains water and hypochlorous acid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,884,780

DATED May 20, 1975 INVENTOR(S) Edward H Cook, Jr. et al It is certified that error appears in the ab0veidentitied patent and that said Letters Patent are hereby corrected as shown below:

Columns 5 and 6, lines 1-20, Table II Experiment 1, change "7.0-7.2" to ---7.07.5---. Experiment 2, change "360" to --340--; "6.6" to ---0.8---; "1.4" to ---1---; and a "above delta celll' to ---above cell.- Experiment 5', change "4. 25" to ---8.5--; "47-52" to ---42-52---; "1.2-1.4" to --1.4-2.1---; and "520" to ---559--. Experiment 6, change "25" to ---21---. Column headings change "delta cell head, inches" to ---cell head,

inches--; "Density" to --density---; and omit the horizontal line between "Current" and "density".

Signcd and Scaled this {SEAL} seventh r mb-ar1975 Allesf.

Claims (2)

1. IN THE PROCESS FOR THE PRODUCTION OF AN OXY-HALOGEN ACID SELECTED FROM HYPOCHLOROUS ACID AND HYPOHROMOUS ACID, BY THE ELECTROLYSIS OF A HALIDE CONTAINING BRINE IN ELECTROLYTE CELL, SAID HALIDE BEING SELECTED FROM CHLORIDE AND BROMIDE, WHEREIN SAID BRINE IS ELECTROLYZED BETWEEN ANODE AND CATHODE MEMBERS IN SAID CELL TO FORM A HALOGEN ANODE PRODUCT CORRESPONDINT TO THE HALIDE OF SAID BRINE, A CELL LIQUOR CONTAINING WATER AND THE SAID OXY-HALOGEN ACID AN A HYDROGENOUS GASEOUS CATHODE PRODUCT, WHICH CATHODE PRODUCT HAS ENTRAINED THEREIN A PORTION OF THE HALOGEN ANODE PRODUCT, THE IMPROVEMENT WHICH COMPRISES PASSING SAID GASEOUS CATHODE PRODUCT CONTAINING THE ENTRAINED HALOGEN UPWARDLY IN THE CELL THEOUGH A LAYER OF INERT, ABSORPTIVE PACING MATERIAL, WHICH LAYER IS PERVIOUS TO SAID GASEOUS CATHODE PRODUCT AND IS DISPOSED COMPLETELY ABOVE THE ANODE AND CATHODE MEMBERS OF THE CELL BUT AT LEAST PARTIALLY BELOW THE UPPER SURFCE OF THE CELL LIQUOR IN THE CELL, MAINTAINING THE UPPER SURFACE OF THE CELL LIQUOR ABOVE THE THE ANODE AND CATHODE MEMBERS BUT BELOW THE TOP OF THE CELL SO AS TO FORM A GAS DISENGAGING ZONE BETWEEN THE TOP OF THE CELL AND THE UPPER SURFACE OF THE CELL LIQUOR IN WHICH SEPARATION OF THE GASES FROM THE CELL LIQUOR IS EFFECTED, DISPERS ING SAID GASEOUS CATHODE PRODUCT IN SAID CELL LIQUOR SO AS TO EFFECT INTIMATE MIXING OF THE CELL LIQUOR AND THE GASEOUS CATHODE PRODUCT AS IT PASSES THROUGH SAID PACKING MATERIAL, AND, THEREBY, REACTING THE HALOGEN IN SAID GASEOUS CATHODE PRODUCT WITH THE WATER IN THE CELL LIQUOR TO FORM ADDITIONAL OXYHALOGEN ACID.

2. The process as claimed in claim 1 in which the brine is a sodium chloride brine, the anode product is chlorine, the gaseous cathode product is hydrogen and the cell liquor contains water and hypochlorous acid.

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