US3721619A

US3721619A - Electrolytic cell

Info

Publication number: US3721619A
Application number: US00075317A
Authority: US
Inventors: F Ruehlen
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1970-09-25
Filing date: 1970-09-25
Publication date: 1973-03-20
Anticipated expiration: 1990-03-20

Abstract

An electrolytic cell having a heat exchanging shell disposed therein and dividing the cell container into an upper and lower electrolyte chamber. Electrode tube means extend through said shell and are in communication with said electrolyte chamber. Electrode means are disposed in said electrode tube means in a manner to preserve said communication. Downcomer tube means, interspersed among said electrode tube means, also extend through the shell into communication with said electrolyte chamber. An auxiliary electrode is disposed in said electrode tube means between the wall thereof and said electrode, with guide vanes disposed on the auxiliary electrode to direct gases formed at the auxiliary electrode toward the inner surface of the electrode tube means.

Description

United States Patent 1191 Ruehlen 1March 20, 1973 ELECTROLYTIC CELL [75] inventor: Forrest N. Ruehlen, Bartlesville,

Okla.

[73] Assignee: Phillips Petroleum Company, Bartlesville, Okla.

[22] Filed: Sept. 25, 1970 21 Appl. No.: 75,317

FOREIGN PATENTS OR APPLlCATlONS 719,838 12/1954 Great Britain "204/284 l,l98,332 6/1963 Germany ..204/284 Primary Examiner-John R. Mack Assistant Examiner-W. 1. Solomon Attorney-Young and Quigg [57 ABSTRACT An electrolytic cell having a heat exchanging shell disposed therein and dividing the cell container into an upper and lower electrolyte chamber. Electrode tube means extend through said shell and are in communication with said electrolyte chamber. Electrode means are disposed in said electrode tube means in a manner to preserve said communication. Downcomer tube means, interspersed among said electrode tube means, also extend through the shell into communication with said electrolyte chamber. An auxiliary electrode is disposed in said electrode tube means between the wall thereof and said electrode, with guide vanes disposed on the auxiliary electrode to direct gases formed at the auxiliary electrode toward the inner surface of the electrode tube means.

10 Claims, 12 Drawing Figures PATEHTEUHAR 2 01973 SHEET 10F 2 INVEN R.

F. N. RUE N X 0 0 Q Q Q QQ 0000 Q G CG A TTORNEVS @QQQQ /Q R.

PATEHTEDHARZOISYB 3,721,519

SHEET 2 0? 2 O O O O O O O O O O O O INVENTOR. F. N. RUEHLEN ATTORNEYS ELECTROLYTIC CELL 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. No. 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 to the 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.

ln electrolytic cells of this type, difficultiesare encountered from overcooling of the walls of the cathodic tubes. Overcooling the wall of a cathodic tube can cause the formation of a film of overcooled 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. Furthermore, since electrolytic cells are normally operated at low voltages, any increase in voltage drop is a serious matter because itrapidly decreases the cell efficiency. 1 n 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. It is desirable that the walls of the cathodic tubes be operated as warm as possible, consistent with the requirements for cooling the electrolyte. Increasing the temperature of the entering coolant medium does not provide an adequate solution because this results in a marked decrease in cooling efficiency due to the decrease in the temperature differential between the coolant and the electrolyte being cooled.

The present invention provides a solution for the above-described problems. The present invention provides an improved electrolytic cell of the type described, wherein an auxiliary cathode is provided in the cathodic tube means between the wall thereof and the anode disposed in said cathodic tube means. This provides a number of advantages. Said auxiliary cathode, which can conveniently comprise a foraminous member such as a metal screen, can be operated at higher temperatures than the wall of the cathodic tube means. This will reduce cell voltage requirements. Said auxiliary cathode can be placed closer to the anode, and thus further reduce cell voltage requirements because of the smaller space between the anode and the auxiliary cathode. As will be evident from the further description given hereinafter, said auxiliary cathode can be more economically and easily replaced than the wall of the cathodic tube. For example, when employing carbon anodes in the cathodic tube means, a piece of carbon can break away from the anode, lodge against the cathodic tube wall, and cause a hole to be burned in said tube wall. When employing the auxiliary cathodes of the invention, it will be the cheaper and more easily replaced auxiliary cathode which will be damaged instead of the tube wall.

Thus, according to the invention, there is provided an electrolytic cell comprising, in combination: an electrode tube means comprising a heat exchange element, the wall of said tube means also serving as an electrode in said cell; and a foraminous auxiliary electrode connected to the inner surface of said wall and spaced apart therefrom.

The invention is applicable to and can be employed in cells 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 point relatively close to the desired cell operating temperatures. The essentially anhydrous liquid hydrogen fluoride electrolytes containing a conductivity additive, such as potassium fluoride, are examples of such electrolytes. These electrolytes are used in processes for the electrochemical fluorination 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 1:4.5 to 1:1 and having freezing points within the range of about 50 to about 200 C. A presently preferred group of saidelectrolytes 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 7 about 60 to about 75 C. Since the preferred cell to operate the wall of the cathodic tube at the desired FIG. 2 is a diagrammatic plan view of the cell illustrated in FIG. 1.

FIG. 3 is a diagrammatic plan view of another cell structure in accordance with the invention.

FIGS. 4 and'5 are diagrammatic illustrations of various embodiments of a heat exchanging shell which can be employed in the cell of FIG. 1.

FIGS. 6, 7, 8, 9 and 10 are diagrammatic illustrations 7 of various embodiments of the auxiliary cathode of the invention.

FIG. 11 is a cross section of one type of anode which can be employed in the cells of the invention.

FIG. 12 is a diagrammatic plan view of a downcomer tubemeans in the heat exchanging shell of the cell of FIG. 1 showing the inclusion of fins on the walls of said downcomer tube means. 7

Referring now to the drawings, wherein like reference numerals have been employed to denote like elements, the invention will be more fully explained. In FIGS. 1, 2, and 3, there is illustrated an electrolytic cell, designated generally by the reference number 10, which comprises a container 12 having a heat exchang ing shell 14 mounted therein. Said container and heat exchanging shell can be fabricated integrally, but preferably are fabricated separately and the heat exchanging shell then mounted in said container 12, as shown. Any convenient means can be employed for mounting and/or supporting the heat exchanging shell in the cell container. For example, lugs 15 can be employed. Said heat exchanging shell 14 divides said container 12 into an upper electrolyte chamber 16 and a lower electrolyte chamber 18. A coolant inlet means comprises a header conduit 20, and a plurality of inlet conduits 22 (only one is shown) connected to a wall of said container and in communication with a passageway 24 formed in said heat exchanging shell. A coolant outlet means comprises a header conduit 26', and a plurality of outlet conduitsv 28 (only one is shown) connected to a wall of said container and in communication with another passageway 30 formed therein. Preferably, said coolant inlet means'and said coolant outlet means are connected to opposite walls of said heat exchanging shell, and also spaced apart vertically, as illustrated in the drawing. However, it is within the scope of the invention for said coolant outlet means and said coolant inlet means to be connected to the same wall of the heat exchanging shell, as illustrated in FIGS. 4 and 5. In such instances, it is usually preferred that said coolant inlet means and said coolant outlet means be connected to said same wall, one above the other, i.e., spaced apart vertically. The relative vertical positions of said coolant inlet means and said coolant outlet means can be reversed from that shown, depending upon the service of the cell. Said container 12 and heat exchanging shell 14 can be constructed of any suitable metal, such as steel, stainless steel, or the like. It is preferred that the heat exchanging shell 14 be constructed of a metal or other material having a high heat conductivity.

Preferably, at least one baffle means 32 extends generally horizontally across said heat exchange shell from a wall thereof, to a point adjacent an opposite wall thereof, and between said coolant inlet means and said coolant outlet means so as to form said

passageways

24 and 30 and provide multiple pass flow of coolant within said shell between said coolant inlet means and said coolant outlet means. Depending upon the size of the cell and the heat exchanging shell mounted therein, it is usually preferred to employ a plurality of said baffle means 32 so as to provide more flow. passageways through said heat exchange shell. When said heat exchange shell 14 and said container 12 are fabricated integrally, the wall(s) of container 12 become walls of said heat exchange shell, and said bafflemeans32 are connected thereto. FIG. 4 illustrates diagrammatically a heat exchange shell wherein only one baffle means is employed and the coolant inlet means and coolant outlet means are connected to the same wall of said shell. FIG. 5 illustrates diagrammatically a heat exchange shell wherein a plurality of baffle means 32 are employed and again said coolant inlet and said coolant outlet means are connected to the same wall of the shell 14.

As here illustrated, a plurality of cathodic tube means 34 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 36 is disposed in each of said cathodic tubes 34 in a manner to provide an annular space 38 surrounding said anode means so as to preserve said communication between the upper and lower electrolyte chambers.

A plurality of downcomer tube means 40 extend in a generally vertical direction through said heat exchanging shell 14 and also are in communication with said upper electrolyte chamber 16 and said lower electrolyte chamber 18. Said downcomer tubes 40 are open tubes and do not contain any electrode structure. If desired, the inner wall of said downcomer tubes 40 can be provided with internally extending fin 42. See FIG. 12. Preferably, said cathodic tube means 34 and said downcomer tube means 40 are arranged in alternate rows, with respect to each other, which rows extend across said shell and thus across said container. Still more preferably, the centers of said downcomer tubes 40 in a row thereof are positioned between the centers of said cathodic tubes 34 in an adjacent row thereof. See FIG. 2. In the presently most preferred arrangement, each one of said downcomer tubes 40 is disposed generally at the center of a cluster of a plurality of said cathodic tubes 34. See FIG. 2 whereina said cluster of cathodic tubes 34 comprises four tubes arranged in a generally rectangular pattern with a downcomer tube '40 at the general center of the rectangle. While in FIGS. 1, 2, and 3, the cells of the invention have been illustrated as containing a plurality of said cathodic tubes 34 and a plurality of said downcomer tubes 40, it is within the scope of the invention to provide the cell with only one cathodic tube 34 and only one downcomer tube 40. The cells of the invention have been illustrated as having a plurality of cathodic tubes 34 and a plurality of downcomer tubes 40 because this is the usually preferred arrangement in commercial installation, and is the arrangement in which the invention finds its greatest and most valuable application.

In accordance with the invention, a foraminous auxiliary cathode 35 is disposed in ,annular space 38 between the wall of cathodic tube means 34 and anode 36. Said auxiliary cathode is connected to the wall of cathodic tube means 34 at one or more points by any suitable means such as welding, etc. As illustrated in FIG. 1, said auxiliary cathode comprises a metal screen. Said screen can be formed of any suitable electrically conducting material, such as steel, stainless steel, etc., which is compatible with the remainder of the system ln one sometimes preferred embodiment, said screen can be provided with vertically spaced apart guide vanes 37 extending in a generally vertical direction for directing gases, e.g., hydrogen, formed at said auxiliary cathode through said'screen and toward the inner surface of cathodic tube means 34. Said gases will exert a shearing force on said inner surface, will tend to inhibit formation of electrolyte film thereon, and will improve the cooling efficiency of said surface. One modification of this embodiment of the invention is illustrated in FIG. 6. If desired, said guide vanes can be mounted on one side of the screen and tilted or inclined in a manner to direct said gases through the screen. If desired, said screen, with or without said guide vanes, can be provided with spaced apart reinforcing rods 39 extendingvertically and/or horizontally as illustrated in FIG. 7.

In another embodiment of the invention, said foraminous auxiliary cathode can comprise a perforated plate, sheet, or foil of a suitable metal such as steel, stainless steel, etc., as illustrated in FIG. 8. Preferably, said perforations will be inclined as illustrated in FIG. 9, and provided with guide vanes 37' on one or both sides for directing said gases toward the inner wall of cathodic tube 34. However, it is within the scope of the invention for said perforations not to be inclined, and provided with guide vanes on one or both sides, as illustrated in FIG. 10.

Said anode means 36 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 36 is shown in FIG. 11. As illustrated in FIGS. 1 and 11, said anode structure is a composite carbon anode structure comprising a first or outer section of porous carbon 44 which is generally cylindrical in shape and is hollow. A second or core section of less porous carbon, or essentially impervious carbon, 46 has the general'shape of a generally cylindrical rod and is disposed within said first section of carbon 44 and secured therein by any suitable means, such as a friction fit. A current collector 48, here shown to be aihollow metal conduit, such as copper, extends into said second section of carbon 46. Said current collector can be disposed in a hole drilled to fit and accommodate the metal conduit, or said current collector can be threaded into said second section of carbon. Said first section of carbon 44 extends at the lower end thereof beyond the lower end of said second section of carbon 46. The bottom surface of said second section of carbon 46, together with the inner surfaces of said .extended portion of said first section of carbon 44, define a cavity 50 in the lower portion of the anode. A vaporous feedstock can be introduced from feedstock header 52 by means of the header arrangement shown and passed through said current-collector48to cavity 50 for introduction into porous carbon section 44 of the anode 36. Each of the current collectors 48 isconnected by meansof asuitablelead 54 to the anode bus 56. The heat exchanging shell means 14 can be rendered cathodic by means-of any suitable connection thereto which is also connected to "the cathode bus of the electric currentsource. If desired, the entire cell container 12 can be rendered cathodic by suitableconnections thereto. In such instances the heat exchanging shell 14 would be connected to container 12 bysuitable means.

It will be noted that each of the anodes 36 is individually suspendedby means of suspension-means60 in a cathodic tube 34 and is individually connected to feedstock header 52, and the anode bus 56. Said suspension means 60 can comprise any suitable suspen- Electrolyte temperature sion means. As here illustrated, said suspension means comprises a flange member which covers an opening 62 in the top of container 12. Said opening is large enough to permit the ready removal of the anode 36 from the container. Said suspension means or closure members '60 can be made of any suitable metal, properly insulated from the container shell, or can be made of any suitable insulating material such as Teflon or other suitable plastic material.

Referring now to FIG. 3, there is illustrated a cell structure generally similar to that illustrated in FIGS. 1 and 2 except that the container 12' is generally circular in shape. The 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 40 and a plurality of cathodic tube means 34 are arranged as described above in connection with said FIGS. 1 and 2. While not shown in FIG. 3, it will be understood that the cell of FIG. 3 can be provided with suitable baffle means 32 and inlet conduit means and outlet conduit means arranged as described above in connection with FIGS. 1, 4, and 5 so as to provide multipass flow of coolant through the cell.

In the operation of the cell structure illustrated in the drawings, for example, in the fluorination of a fluorinatable feedstock such as ethylene dichloride, an essentially anhydrous KF' 2HF electrolyte is introduced into the cell. The level of said electrolyte 64 is preferably maintained slightly above the tops of the anode structures 36. The ethylene dichloride feedstock in vapor form is passed via conduit 52 through hollow current collector 48 and introduced into cavity 50. Said feedstock then enters the porous carbon section 44 of anode 36, travels upwardly therethrough, and within the pores of said anode is at least partially fluorinated. Products of the reaction and unreacted feedstock exit from the top of the porous section of the anode and are withdrawn from the cell via conduit 66 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 36 creates a thermal siphon in the cathodic tube 34, causing electrolyte to circulate from lower electrolyte chamber 18 up through annular space 38, around auxiliary cathode 35, and into upperelectrolyte chamber 16, as shown by the arrows in the drawing. Hydrogen liberated at auxiliary cathode 35 aid this circulation by a gas lift effect. Said circulating electrolyte in passing through annular space 38cools anodes 36. The circulating electrolyte then flows downwardly through downcomer conduits 40 wherein the heat collected by the electrolyte is dissipated through thewalls of the'downcomer tubes and removed from the system by means of coolantintroduced through coolant inlet means 20 and removed via conduit outlet means 26.

The following calculated example will serve to furtherillustrate the invention.

EXAMPLE Employing an auxiliary cathode in accordance with the invention can result in power savings of up to at least about :1 8 percent, calculated as'follows:

Electrolyte composition (l-IF-KF) 4l wt. HF

2.07 ohm inches 1.39 amps/in. 2.9 volts Specific resistance of electrolyte Current density through electrolyte Voltage drop through the one inch annular space Normal cell voltage at the above current density and one inch space Placing the auxiliary cathode in the center of said one inch space decreases the space to a inch and reduces the voltage drop to 1.45/8 X 100 18 percent saving in power cost 8 volts 1 .45 volts liberated at the cathode, the above designated cathodic 20 tubes are designated as anodic tubes and contain a cathode. In such instances, auxiliary cathode 35 would become an auxiliary anode. Thus, generically speaking, cathodic tube means 34 can be referred to as an electrode means, and anode means 36 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 process described above, electrochemical cyanation, and cathodic conversions such as the reduction of alcohol to hydrocarbons or the reduction of acid to alcohols.

Further details of an electrochemical fluorination process in which the cells of the invention can be employed can be found in U.S. Pat. No. 3,511,760, issued May 12, 1970, to H. M. Fox and F. N. Ruehlen. See also U.S. Pat. Nos. 3,461,049 and 3,461,050, issued Aug. 12, 1969, to W. V. Childs.

The electrolytic cells of the invention can be of any suitable dimensions, depending upon the process to be carried out therein, and the desired throughput for said process. By way of example, and not by way of limitation, in one embodiment of the invention the heat exchanger shell 14 was designed to have an overall length of approximately 90 inches and overall width of approximately 75 inches, with cathodic tubes 34 having an outside diameter of approximately 9% inches, and downcomer tubes 40 having an outside diameter of approximately 6% inches. The overall height of said heat exchanger shell 14 was approximately inches. Anode 36 had an overall length, including fittings on the top, of approximately 36 inches. Said anode had an overall outside diameter in the carbon portion of approximately 795 inches. The remainder of the elements of the cell were generally proportional in size.

While certain embodiments of the invention have been described for illustrative purposes, the invention is not limited thereto. Various other modifications or embodiments of the invention will be apparent to those skilled in the art in view of this disclosure. Such modifications or embodiments are within the spirit and scope of the disclosure.

I claim: 1. An electrolytic cell comprising, in combination: a first electrode means; an electrode tube means comprising a heat exchange elem nt, the wall of said tube means surrounding said irst electrode means and also serving as a second electrode in said cell;

a foraminous auxiliary electrode connected to the inner surface of said wall and spaced apart therefrom; and

vertically spaced apart guide vanes provided on said foraminous auxiliary electrode, extending outwardly from the surface thereof, and inclined in a generally vertical direction toward said inner surface of said electrode tube means for directing gases formed at said auxiliary electrode toward said inner surface for exerting a shearing force on said inner surface.

2. An electrolytic cell according to claim ,1 wherein said cell comprises, in further combination:

a container;

a heat exchanging shell mounted in said container and dividing said container into an upper and a lower electrolyte chamber; and wherein at least one of said electrode tube means extends in a generally vertical direction through said heat exchanging shell and in communication with said upper and lower electrolyte chambers.

3. An electrolytic cell according to claim 2 wherein:

the wall of said electrode tube means serves as a cathode;

said first electrode means is an anode and is disposed in said electrode tube means with an annular space surrounding said anode so as to preserve said communication; and

said auxiliary electrode is an auxiliary cathode and is positioned in said annular space around said anode.

4. An electrolytic cell according to claim 3 wherein said auxiliary cathode comprises a metal screen.

5. An electrolytic cell according to claim 4 wherein said metal screen is provided with spaced apart rein forcing rods.

6. An electrolytic cell according to claim 4 wherein said inclined guide vanes extend through said screen.

7. An electrolytic cell according to claim 3 wherein said auxiliary cathode comprises a perforated plate.

8. An electrolytic cell according to claim 7 wherein the perforations in said plate extend therethrough in a generally horizontal direction, and said inclined guide vanes are provided on each side of said plate im-.

mediately above said perforations.

9. An electrolytic cell according to claim 7 wherein said perforations are inclined in a generally vertical direction.

10. An electrolytic cell according to claim 9 wherein said guide vanes are provided on each side of said plate immediately above said inclined perforations and are inclined at substantially the same angle as said perforations.

Claims

2. An electrolytic cell according to claim 1 wherein said cell comprises, in further combination: a container; a heat exchanging shell mounted in said container and dividing said container into an upper and a lower electrolyte chamber; and wherein at least one of said electrode tube means extends in a generally vertical direction through said heat exchanging shell and in communication with said upper and lower electrolyte chambers.
3. An electrolytic cell according to claim 2 wherein: the wall of said electrode tube means serves as a cathode; said first electrode means is an anode and is disposed in said electrode tube means with an annular space surrounding said anode so as to preserve said communication; and said auxiliary electrode is an auxiliary cathode and is positioned in said annular space around said anode.
4. An electrolytic cell according to claim 3 wherein said auxiliary cathode comprises a metal screen.
5. An electrolytic cell according to claim 4 wherein said metal screen is provided with spaced apart reinforcing rods.
6. An electrolytic cell according to claim 4 wherein said inclined guide vanes extend through said screen.
7. An electrolytic cell according to claim 3 wherein said auxiliary cathode comprises a perforated plate.
8. An electrolytic cell according to claim 7 wherein the perforations in said plate extend therethrough in a generally horizontal direction, and said inclined guide vanes are provided on each side of said plate immediately above said perforations.
9. An electrolytic cell according to claim 7 wherein said perforations are inclined in a generally vertical direction.
10. An electrolytic cell according to claim 9 wherein said guide vanes are provided on each side of said plate immediately above said inclined perforations and are inclined at substantially the same angle as said perforations.