US3659001A - Electrolytic cell - Google Patents

Abstract

An electrolyte cell having a heat exchanging shell disposed therein and dividing the cell into an upper and a lower electrolyte chamber. Cathodic tube means, segregated in one region of the shell, extend through said shell and are in communication with said electrolyte chambers. Anode means are disposed in said cathode tubes in a manner to preserve said communication. Down-comer tube means, segregated in another region of said shell, also extend through the shell into communication with said electrolyte chambers.

Description

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April 25, 1972 MILLS 3,659,001

ELECTROLYTIC CELL Filed Feb. 26, 1970 2 Sheets-Sheet 2 INVENTOR.

K. L. MILLS A 7' TORNEVS United States Patent 3,659,001 ELECTROLYTIC CELL, King L. Mills, Bartlesville, 0kla., assignor to Phillips Petroleum Company Filed Feb. 26, 1970, Ser. No. 14,293 Int. Cl. B01k 3/00 US. Cl. 204-274 8 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell having a heat exchanging shell disposed therein and dividing the cell into an upper and a lower electrolyte chamber, Cathodic tube means, segregated in one region of the shell, extend through said shell and are in communication with said electrolyte chambers. Anode means are disposed in said cathodic tubes in a manner to preserve said communication. Downcomer tube means, segregated in another region of said shell, also extend through the shell into communication with said electrolyte chambers.

This invention relates to improved electrolytic cells. Electrolytic cells comprising a heat exchanging shell disposed in the cell container are 'known in the art. For

example, US. Pat. 3,404,083, issued Oct. 1, 1968, in the name of M. S. Kircher, relates to an electrolytic cell of this type. In the cells described in said patent, cylindrical cathodic tubes extend vertically through the heat exchanging shell and are in communication with an upper and a lower electrolyte chamber which contains a liquid electrolyte. An anode is suspended in each of said cathodic tubes in a manner to leave an annulus between the Wall of the cathodic tube and the outer wall of the anode. Interspersed among said cathodic tubes are other open tanks, generally like said cathodic tubes, but which do not contain an anode and are referred to as downcomer tubes. A coolant inlet is connected to one side of said shell for the introduction of a' coolant medium, A coolant outlet means is connected to an opposite side of said shell to provide an outlet for said coolant medium. In operation, heat is liberated at the anode and creates a thermal siphon and electrolyte circulates upwardly from the lower tothe upper electrolyte chamber and cools the anode. Heat is dissipated through the walls of the cathodic tubes into the coolant flowing through the heat exchanging shell.

In electrolytic cells of this type, difficulties are encountered from overcooling of the walls of the cathodic tubes. In these instances, the cold coolant entering the heat exchanging shell and directly impinging the wall of a cathodic tube causes the formation of a film of cool electrolyte on said wall. Since the conductivity of the electrolyte decreases with decreasing temperature, the resistivity of the cell will be increased and a higher voltage will be required to maintain the desired constant current -flow. This will result in increased power costs. In some cases, such as where the electrolyte has a freezing point close to the cell operating temperature, crystallization of the electrolyte on the wall of the cathodic tube can occur. In aggravated cases this can lead to blockage of the annular space between the wall of the anode and the wall of the cathodic tube. Since electrolytic cells are normally operated at low voltages, any increase in voltage drop is a serious matter which rapidly decreases or reduces the cell efliciency. Increasing the temperature of the entering coolant medium does not provide an adequate solution because this results is a marked decrease in cooling efficiency due to the decrease in the temperature differential between the coolant and the electrolyte being cooled.

3,659,001 Patented Apr. 25, 1972 The present invention provides a solution for the abovedescri'bed problems. I have now found that by segregating the downcomer tubes in a downcomer region adjacent the coolant inlet, and segregating the anode-containing cathodic tubes in a cathodic tube region adjacent the coolant outlet, efficient cooling can be obtained without the formation of an overcooled film of electrolyte on the walls of the cathodic tube.

An object of this invention is to provide an improved electrolytic cell. Another object of this invention is to provide an electrolytic cell having improved electrolyte cooling means. Another object of this invention is to provide an electrolytic cell having a heat exchanging shell mounted therein, said shell being provided with downcomer tube(s) segregated in a downcomer (tube(s) region and cathodic tube(s) segregated in a cathodic tube(s) region. Another object of this invention is to provide an improved electrolytic cell adapted for operation of a plurality of electrodes, either anodes or cathodes, and wherein said electrodes can be easily and conveniently removed and replaced individually without interruption of cell. operation. Other aspects, objects, and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention, there is provided an electrolytic cell comprising: a container; a heat exchanging shell mounted in said container and dividing said container into an upper electrolyte chamber and a lower electrolyte chamber; a coolant inlet means connected to one side of said heat exchanging shell; a coolant outlet means connected to an opposite side of said heat exchanging shell; at least one electrode tube means extending in a generally vertical direction through said shell in an electrode tube region of said shell adjacent said coolant outlet means, and in communications with said upper and lower electrolyte chambers; an electrode disposed in said electrode tube means with an annular space surrounding said electrode so as to preserve said communication; and at least one downcomer tube means extending in a generally vertical direction throughsaid heat exchanging shell in a downcomer tube region of said shell adjacent said inlet means.

A number of advantages are obtained or realized in the practice of the invention. Segregation of the downcomer tubes in one downcomer tube region located adjacent the coolant inlet, and introduction of the cold coolant directly into said downcomer tube region where the cooling load is greatest, not only avoids the formation of an overcooled film of electrolyte on the walls of the cathodic tubes which causes increased power requirements, but also makes it possible to maintain a greater temperature differential between the temperature of the coolant and the temperature of the electrolyte tobe cooled. This provides for maximum efficiency in the cooling of the electrolyte. Said coolant is preheated in the downcomer region before introduction into' the cathodic tube region. This eliminates essentially all danger I makes it possible to employ a larger temperature differential in the downcomer region to obtain maximum cooling efficiency. Obtaining maximum cooling efficiency in the cooling of the electrolyte in the downcomer tube region makes it possible to reduce the number of downcomer tubes and increase the number of cathodic tubes.

Thus, overall cell efficiency is increased because "cell' throughput is increased. I

Still another advantage of the invent on is that the flexibility. of the cell is increased. The number of different electrolytes which can be used in any given cell arrangement is greater because the danger or risk of forming an overcooled film of electrolyte, or of freezing of any particular electrolyte on the walls of the cathodic tubes can be eliminated. The difference in cooling loads in the segregated cathodic tubes and in the segregated downcomer tubes can be more'readily controlled and/or adjusted than is possible when said tubes are not segregated.

The invention is applicable to and can be employed in .cells used for carrying out a wide variety of electrochemical conversion processes using a wide variety of electrolytes. The invention is particularly applicable to cells wherein the electrolyte being used has a freezing pomt relatively close to the desired cell operating temperatures.

The essentially anhydrous liquid hydrogen fluoride electro lytes containing a conductivity additive, such as potassium fluoride, are examples of such electrolytes. These electrolytes are used in processes for the electrochemical ifluorination of fluorinatable compounds. Said conductivity additives can be present in the electrolyte in any suitable molar ratio of additive to hydrogen fluoride ranging from about 124.5 to 1:1 and having freezing points within the range of about 50 to about 209 C. A presently preferred group of said electrolytes includes those having a conductivity additive to hydrogen fluoride ratio within the range of about 1:4' to about 1:2 and .having freezing points within the range of about 60 to about 75 C. Since the preferred cell operating temperature in fluorination processes employing those electrolytes .is usually within the range of about 60 to about 105 C., commonly about 80 to about 100 (2., it is important that the wall of the cathodic tube not be overcooled so as to avoid the formation of an overcooled film, or crystal- .lization or freezing of said electrolytes, on the walls of said cathodic tube.

FIG. 1 is a diagrammatic illustration, partly in cross section of a cell structure in accordance with the inventhe invention will be more fully explained. In F168. 1 and 2, there is illustrated an electrolytic cell, designated generally by the reference numeral 10, which comprises a container 12 having a heat exchanging shell 14 mounted therein. Said container and heat exchanging shell can be fabricated integrally as illustrated or, if desired, said heat exchanging shell can be fabricated separately and then mounted in said container 12 in any suitable manner.

Said heat exchanging shell 14 divides the container 12 into an upper electrolyte chamber 16 and a lower elecstructed of a metal or other material having a high heat conductivity.

As here illustrated, a plurality of cathodic tube means 24 extend in a generally vertical direction through said heat exchanging shell 14 and are in communication with said upper electrolyte chamber 16 and said lower electrolyte chamber 18. An anode means 26 is disposed in each of said cathodic tubes 24 in a manner to provide an annular-like space 28 surrounding said anode means so as to preserve said communication between the upper and lower electrolyte chambers. It will be noted that said cathodic tubes 24 are segregated in a cathodic tube region which is located in one end of the cell adjacent said coolant outlet means 22.

A plurality of downcomer tube means 30 extends in a generally vertical direction through said heat exchanging shell means 14 and also are in communication with said upper electrolyte chamber 16 and said lower electrolyte chamber 18. Said downcomer tubes 30 are open tubes and do not contain any electrode structure. If desired, the inner wall of said downcomer tubes 30 can be provided with internally extending fins. It will be noted that said downcomer tubes 30 are segregated in a downcomer tube region which is located in the other end of the container 12 and adjacent said coolantinlet means 20. While in FIGS. 1 and 2 the cells of the invention have been illustrated as containing a plurality of said cathodic tubes 24 and a plurality of said downcomer tubes 30, it is within the scope of the invention to provide the cell with only one cathodic tube 24 and only one downcomer tube 30. The

Icell has been illustrated as having a plurality of cathodic tubes 24 and a plurality of said downcomer tubes 30 because this is the usually preferred arrangement in commercial installations.

If desired, a plurality of baflle means 32 can be provided to extend inwardly from the wall of heat exchanging means 14 into the downcomer tube region so as to direct the flow of coolant into said region and prevent its fiow along the outer walls of the heat exchange shell. Said baffles serve to insure that essentially all of said coolant is preheated before it enters the cathodic tube region.

Said anode means 26 can comprise any suitable type of anode structure, depending upon the requirements of the electrolytic conversion process to be carried out in the cell 10. An enlarged cross-sectional view of said anode 26 is shown in FIG. 4. As illustrated in FIGS. 1 and 4,

said anode structure is a composite carbon anode structure comprising a first section of porous carbon 34 which is generally cylindrical in shape and is hollow. A second section of less porous carbon, or essentially impervious carbon, 36 has the general shape of a generally cylindrical rod and is disposed within said first section of carbon 34 and secured therein by a friction fit. A current collector 38, here, shown to be a hollow metal conduit, such as copper, extends into said second section of carbon 36. Said current collector can be disposed in a hole drilled to fit and accommodate the metal conduit, or said current trolyte chamber 18. When container 12 andheat exchanger 14 are fabricated integrally as illustrated, they have common outer walls in the region between said electrolyte chambers 16 and 18. A coolant inlet means 20 is connected to one side of'said heat exchanging shell.

A coolant outlet means 22 is connected to an opposite spaced apart side of said heat exchanging shell. Said container 12 and heat exchanging means 14 can be constructed of anysuitable metal, such as stainless steel, or

the like. If desired, the container 12 can be constructed collector can be threaded into said second section of carbon. First section of carbon 34 extends at one end beyond one end of said second section of carbon 36. The bottom surface of said second section of carbon 36, together with the Inner surfaces of said extended portion of said first section of carbon 34, define a cavity 40 in the lower portion of the anode. A vaporous feedstock can be introduced from feedstock header 42 into hollow current collector 36 by means of the header arrangement shown. and passed through said current collector 36 to cavity 40 for introduction into porous carbon section 34 of the anode 26. If desired; said current collector 36 can be a solid metal rod. In such instances, the feedstock can be introduced into said cavity 40 from a suitable header arrangement 44 which extends into the cell 10. Each of said current collectors 36 is connected by means of a suitable lead wire 46 to the anode bus. As here illustrated, the heat exchanging shell means 14 is constructed integrally with cell container 12 and the entire structure is rendered cathodic by means of a suitable lead wire 48 which is connected to the cathode bus of the electric current source. 8

It will be noted that each of the anodes 26 is individually suspended by means of suspension means 50 in a cathodic tube 24 and is individually connected to feedstock header 42 and the anode bus. Suspension means 50, as here illustrated, comprises a closure member which fits into an opening into the top of container 12 which is large enough to permit the ready removal of the anode 26 from the container. Said suspension means or closure member 50 can be made of any suitable insulating material, such as Tefion or other suitable plastic material. 1

Referring now to FIG. 3, there is illustrated a cell structure generally similarto that illustratedin FIGS. 1 and 2. except that the container 12' is generally circular in shape. Said heat exchanging means 14' conforms in shape to the shape of said container 12'. As in FIGS. 1 and 2, a plurality of downcomer tubes 30 are segregated in a downcomer tube region which is defined by a segment of said generally circular heat exchanging means and which is located on one side of the heat exchanging means adjacent coolant inlet 20. Said segment of the heat exchanging means is in turn defined by an are on one side of the generally circular heat exchanging means, a first baflle means 52 which extends from the wall of said heat exchanging means at one end of said are to one of the downcomer tube means 30 adjacent thereto, and a second baffle means 54 which extends from the wall of said circular heat exchanging means at the other end of said are to another of said downcomer tubes 30 which is adjacent thereto. If desired, suitably sized flow regulating orifices 56 can be provided in said baffies 52 and 54 to permit a small flow of coolant medium from the downcomer tube region into the cathodic tube region and thus eliminate quiescent areas behind said bafiies 52 and 54.

In the operation of the cell structures illustrated in the drawings, for example in the fluorination of a fluorinatable feedstock such as ethylene dichloride, an essentially anhydrous KF-ZHF electrolyte is introduced into the cell. The level of said electrolyte 58 is preferably maintained slightly above the tops of the anode structures 26. The ethylene dichloride feedstock in vapor form is passed via conduit 42 through hollow current collector 38 and introduced into cavity 40. Said feedstock then enters the porous carbon section 34 of anode 26, travels upwardly therethrough, and within the pores of said anode contacts the electrolyte and is at least partially fluorinated. Products of the reaction and unreacted feedstock exit from the top of the anode and are withdrawn from the cell via conduit 60 and passed to any suitable separation means for the recovery of the products. If desired, the unconverted feedstock can be recycled to the cell by means of a recycle line not shown. During the cell operation, the heat liberated at anodes 26 creates a thermal siphon in in the cathodic chambers 24, causing electrolyte to circulate from lower electrolyte chamber 18 up through annular space 28 and into upper electrolyte chamber 16, as shown by the arrows in the drawing. Hydrogen liberated on the walls of cathodic tubes 24 aids this circulation by a gas lift effect. Said circulating electrolyte in passing through annular space 28 cools anode 26. The circulating electrolyte then flows downwardly through downcomer conduits 30 wherein the heat collected by the electrolyte is dissipated through the walls of the cathodic tubes and removed from the system by means of the coolant intro duced through coolant inlet means and removed via conduit outlet means 22.

The electrolytic cells of the invention are applicable to a wide variety of electrochemical conversion processes. The cells of the invention are applicable to any electrochemical conversion process wherein it is desired to remove heat of reaction from the system. Said electrolytic cells can be employed in systems where heat is liberated at the anode or in systems where heat is liberated at the cathode. Where the principal reaction is occurring at the cathode and heat is liberated at the cathode, the above designated cathodic tubes are designated as anodic tubes and contain a cathode. Thus, generically speaking, cathodic tube means 24 can be referred to as an electrode tube means, and anode means 26 can be referred to as an electrode means. Some examples of processes wherein the cells of the invention can be employed are electrochemical halogenation such as the fluorination described above, electrochemical cyanation, and cathodic conversions such as the reduction of alcohols to hydrocarbons or the reduction of acids to alcohols.

As a further example of an electrochemical fluorination process, in the conversion of ethylene dichloride to dichlorotetrafluoroethane (Freon 114) and other fluorinated materials using an essentially anhydrous KF- 2HF electrolyte, typical operating conditions are as follows:

Cell temperature93 C.

Ethylene dichloride conversion-41% Feed rate1.43 moles/hr. Faradays/hr.2.22

Moles products/hr.-0.592 Faradays/mole1-.55

- Current densityl78 ma./cm.

By-products l 3 8 1 Products other than Freon 114 or convertible to Freon 114 on recycle.

EXAMPLE In this illustrative embodiment a single anode cell embodying the essential features of the cell illustrated in FIG. 1 was employed. Said anode was a commercial size anode having an outside diameter of 7.5 inches and a length of about 24 inches. Said anode was suspended in a centrally disposed cathode tube having an inside diameter of 8.75 inches. Four downcomer tubes each having an ins de diameter of about 2.3 inches were uniformly spaced around said cathode tube. Boiling methanol was used as the coolant. Temperature control on the methanol coolant was effected by using nitrogen partial pressure and lncreasing or decreasing said nitrogen partial pressure to increase or decrease the boiling point of the methanol. The bulk electrolyte temperature was maintained at C. by heat exchange with said coolant. The cell was operated at 750 amperes current input. Measurements of cell voltage necessary to maintain said current input at varying methanol coolant temperatures were as follows:

Methanol coolant Cell temp. F.: voltage 190 8.60 181 8.76 175 8.94 9.20

limited*thereto.Various other modifications or embodiments of the invention will be apparent to thoseskilled in the art in view of this disclosure. Such modifications or embodiments arev within the spirit and scope of the disclosure,

I claim: I I

1. An electrolytic cell comprising: a container; a heat exchanging shell mounted in said container and dividing sand container into an upper electrolyte chamber and a lower electrolyte chamber; a coolant inlet means connected toone side of said heat exchanging shell; a coolant outlet means connected to an opposite side of said heat exchanging shell; at least one electrode tube means extending in a generally vertical direction through said shell in an electrode tube region of said shell adjacent 'said coolant outlet means, and in communication with said upper and lower electrolyte chambers; and electrode disposedv in said electrode tube means with an annular space surrounding .said electrode so as to preserve said communication; and at least one downcomer tube means extending in a generally vertical direction through said heat exchanging shell in a downcorner tube region of said shell adjacent said inlet means.

2. An electrolytic cell in accordance with claim 1 wherein: a plurality of said electrode tube means are provided in said electrode tube region; an a plurality of said downcomer tube means are provided in said downcomer tube region.

3. An electrolytic cell in accordance with claim 2 wherein: said container is generally rectangular in shape, said heat exchanging'shell conforms in shape to the shape of said. container; said electrode tube means region is located in one end of said shell adjacent said coolant outlet means; and said downcomer tube region is located in the opposite end of said shell adjacent said coolant inlet means. t 4. An electrolytic cell in accordance with claim 3 wherein baflle means extend inwardly from the wall of said heat exchanging shell into said downcorner tube means region.

5. An electrolytic cell in accordance with claim 2 wherein: saidicontainer is generally circular in shape;

said heat exchanging shell conforms in shape to the shape of said container; said downcorner tube means region is defined by a segment of said generally circular heat exchanging shell located on one side thereof; said electrode tube means region comprises the remainder of said generally circular heat exchange shell; and said coolant outlet means is located diametrically oposite said coolant inlet means.

6. An electrolytic cell in accordance with claim 5 wherein said downcomer tube means region is defined by: an are on one side of said generally circular heat can changing shell; a first bafile means extending from the Wall of said heat exchanging shell at one end of said are to one of said downcomer tubes adjacent thereto; and a second baffle means extending from the Wall of said heat exchanging shell at the other end of said are to another of said downcomer tubes adjacent thereto.

7 An electrolytic cell in accordance with claim 2 wherein said electrode tube means is a cathodic tube and said electrode is an anode.

8. An electrolytic cell in accordance with claim 7 wherein: each of said anodes comprises a first section of porous carbon which isgenerally cylindrical in shape and is hollow, a second section of substantially impermeable carbon having the general shape of a generally cyclindrical rod and which is disposed within said first section of carbon to a point adjacent the bottom thereof and secured therein by a friction fit, and a metal current collector mounted in said second section of carbon; each of said conduit current collectors is individually connected to a feedstock headercondluit; and each of said anodes is individually suspended in one of said cathodic tube means;

US. Cl. X.R.

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