US1160400A - Electrolytic process of detinning. - Google Patents

Description

H. GOLDSCHMIDT.

ELECTROLYTIC PROCESS 0F DETINNING.

APPucATlo FILED ris. 5. |908.

1,160,400, Patented Nov. 16, 1915.

2 SHEETS-SHEET l.

H. GOLDSCHIVHDT. ELEcTRoLYTlc PROCESS 0F DEHNNING.

APPLICATION FILED FEB. 5. 1908.

`Pafrented Nov. 16, 1915.

2 SHEETS-SHEET 2.

'HANS GOLDSCHMIDT, 0F ESSEN-ON-THE-IRUHR, GERMANY; ASSIGNORTO GOLDSCHMIDT DETINNING' COMPANY, OF NEW YORK, N. Y., A CORPORATION 0F NEW JERSEY.

ELEGTROLYTIG POCESS OF DETINNING.

To all whom t may concern Be it known that I, HANS GoLDsoHMID'r, a subject of the King of Prussia, German Emperor, and resident of Essen-on-the- Ruhr, Germany, have invented a certain new and useful Electrolytic Process of Detinning, of which the following is a specifica tion.

This invention relates to an electrolytic process of detinning, and the main object of the invention is to detin scrap by means of an alkaline electrolyte in a more perfect manner than was done with prior processes of the same type.

In the electrolytic alkaline process of detinning, as practised prior to my invention, it'wasy extremely diflicult to effecten even and thorough detinning, chiefly because of the difficulty experienced in .maintaining al proper circulation of the electrolyte through the single electrolytic cell in which it was customary to place the material to be detinned. This diiiiculty in maintaining the proper circulation of an electrolyte of substantially uniform quality, and at a sufiiciently high temperature to produce the best results, made it impossible to circulate the alkaline liquid through a group of electrolytic cells mechanically connected inseries,

or to keep the liquid in the proper condition for good and even detinning. The difficulty of maintaining the propery circulation of an electrolyte of propercondition and quality through a. plurality of electrolyti'c cells mechanically connected in a series is also due in large measure to the fact that the metallic connecting pipes through which it would be necessary to circulate the liquid through the system would quickly become choked up as the result of electro-deposition of tin on the inner Walls of the pipes. this Velectro-deposition being'due to a secondary and undesirable electrolytic action.' For these two reasons chiefly it was extremely difficult to practise the alkaline electrolytic process of detinning with any considerable degree of success prior to the discovery which I made that both of these objectionable features of the process of detinning' of this type could be eliminated by a proper organization of all the elements of the apparatus or system employed in carrying out the process. This organization involved chiefly the provision of means for circulat ing the electrolyte in such a manner that it would pass in a plurality of paths through Specification of Letters Patent. :I ifatelrted NGV, 16, 1915, Application led February 5, 1908. Serial No. 414,439.

all the electrolyt'ic vessels of a series or sys- ,type of plant actually installed and used commercially, through a different one of the vessels of the system. By circulating the electrolyte in this manner a fresh supply of the alkaline liquid was always delivered directly from a source of supply through suitable conducting pipes to each individual electrolytic cell, the cathode vessel of each cell being thus connected in the circulation system in parallel in a manner analogous to the connection in parallel of various electrical devices in purely electric systems. By circulating the electrolyte in this manner I found that it was easy to circulate the electrolyte through a large number of cathode 'and anode vessels of electrolytic cells and through the material contained in the anode vessels of said cells without danger of a stoppage of the flow of the electrolyte through any cell of the system; and I also found that it was easy to maintain the alkaline electrolyte in a perfectly Huid and uniform condition at a sufficiently high temperature to do good detinning. Moreover, I devised means for preventing the electro-deposition of tin on the inner walls of the connecting pipes by secondary electrolytic action, and thereby1 preventing the clogging or choking up of the pipes of the system and consequent reduction of the areas of the openings through which the electrolyte flowed. This I accomplish by specificI means which will he hereinafter de' scribed involving preferably the partial or nearly complete electrical insulation of inlet pipes from thel alkaline bath in the different cathode vessels. This is a very important matter. as tin electrolytically deposited from the bath in the electrolytic alkaline process of detinning is in a spongy state occupying considerable space, and if permitted to deposit on the walls of connecting pipes quickly chokes up the same.

I have found that b v thus organizing the whole system employed in' the alkaline electrolytic detinning process the choking up of the connecting pipes is prevented and the circulation of the electrolyte at a. uniform rate through openings unobstructed, except as they may be intentionally partially obstlucted for the regulation of the flow, may

be readily maintained; ,while the alkaline liquid itself may be readily kept 1n the most perfect condition for detinning, that is, in a perfectly fluid state and at a uniformly high temperature, preferably at a temperature of from C. to 80o C., without difficulty. Vhen the electrolyte 1s in this fluid Acondition and at this temperature it is of substantially uniform composition and is in the best condition for etfecting thorough and even detinning of the niaterial in the anode vessels.

In order to accomplish the best results Il have found'that it is necessary to supply electric current of very high amperage to the different electrolytic cells. The current used in practice for detinning on a large scale is from 800 to 1000 amperes per square foot and current of this density is circulated through each electrolytic cell of the system. An important feature of my ima proved process is therefore the circulation of current of this high density through the system. This electric current need not, however,v traverse the dierent electrolytic cells in parallel, but may pass through electrolytic cells connected in series. In order to obtain the best results, however, it is desirable to divide the anode material of each cell up into small portions which may be connected in parallel'so that the full amperage of the current may pass directly through each portion of the anode material.

Other features of my process which facilitate the circulation of the electrolyte through the various electrolytic vessels and aid in effecting even and thorough detinning of the materials contained in the anode vessels of the electrolytic cells, will be hereinafter described in connection with the accompanying drawings, in which:

Figure 1 is a plan illustrating diagrammatically an electrolytic detinning systemv embodying my invention; Fig. 2 is an end elevation` of the same; Fig. 3 is a detail of parts of two electrolytic vessels illustrating the circuit connections thereof. Fig. 4 is a detail illustrating the supply reservoir and means for heating the` electrolyte therein. Fig. `5 'is a similar view of the return reservoir for the electrolyte and means for heating the electrolyte therein. Fig. 6 is a detail illustrating one of the scrap-containing vessels or baskets supported in place in its cathode vessel.

Similar characters designate like parts in all the figures of the drawings.I

Referring first to Fig. 1, which illustrates one way in which the various elements of a system constructed in accordance with my present invention may be combined, 1 designates a source of supply from which an alkaline electrolyte may be delivered to the various electrolytic vesselsl of the system. This supply reservoir is preferably located above the other elements of the system, 1n

order that the liquidmay flow therefrom while the other pipe 4 in a similar manner supplies the electrolyte to another series of vessels. Two branch supply pipes, such as 5 and 6, lead in this case from the main supply pipe 3 to the electrolytic vessels or vats v of the first series, these vessels being designated by 7, 8,' 9 and 10 respectively. At their ends the branch supply pipes are shown as forked, the forks from the branch supply pipe 5 being designated by 11 and 12, and those from the branch supply pipe 6 by 13 and 1,4. In a similar manner branch supply pipes 15 and 16 leadfrom the main supply pipe 4, and each in turn is forked, these forks being designated by 17 and 18 for the branch pipe l5, and by 19 and 20 for the branch pipe I16. The vessels `or vats of the second series ory roware designated respec` tively by 21, 22, 23 and 24. The forked inlet pipes 11, 12, 13, 14, 17, 18, 19 and 2o are preferably provided with suitable controlling means,such as valves, for governing the flow of the electrolyte into the vessels of the second series. These controlling means or valves for the first series of vessels are designated by 25, and for the second series by 26. It will be noticed thatthe pipes which supply the alkaline liquid to the difi ferent electrolytic vessels decrease in cross section from the supply reservoir 1 as they\ approach said vesesls. This is a matter of great importance in order to control the flow y of the liquid properly and prevent excessive flow while at the same time assuring a suffi` cient flow of the hquid at the` proper temperature and Iin the proper condition. I

'have found in practice that a good ratio for the respective inlet pipes is to provide a main pipe from the main reservoir of from three to four inches in diameter, and to gradually decrease the areas of the intermediate pipes -until the forked pipes are reached, which may have a diameter of about three-fourths of an inch. Moreover,

itis desirable that the inlet ends of the forked inlet sections of the piping be located above the level ofthe liquid of the respective baths, the inlet sections themselves being in the preferred construction made of non-conducting material, such as hard rubber, these hard rubber sections, which are designated by 27, being slipped over the ends of the forked metallic pipes and preferably also being slightly above the level of the bath. When the parts are constructed and combined in the system in this manner stoppage of inlet pipes due to electro-deposition of tin, is avoided, and in addition the 'as 28 within said reservoir.

` proper How of the liquid, which is always under considerable pressure becauseof the Ielevation of the supplyA reservoir, is assured. The supply reservoir will preferably be of large size for ,thei purpose of` keeping n the electrolyte at the proper temperature and in as uniform a condition as possible. In the construction shown the reservoir 1 (with a return reservoir which will be hereinafter specifically described) should be capable of holding from one-third to one-half of the whole amount of alkaline liquid contained in the system. In practice I have used supply and return reservoirs the combined dimensions of which were from about ten to thirty cubic meters.

Inworder. to maintain the electrolyte in the supply reservoir 1 at the proper temperature and in the proper condition, the liquid is preferably heated while in thereservoir, as for example, by means of a heater such This heater may be of the tubular variety, such as shown, and may be supplied with steam throughy suitable inlet and outlet pipes, such asv 29 and 30. It will be noticed that in every instance the electrolyte enters each electrolytic vessel near one end thereof and at the upper side of the bath. In order that as complete a circulation of the liquid through the bath as possible may be obtained, it is preferable to place the outlet from each vessel at the opposite end thereofv and substantially at the bottom of the vessel. This assures a thorough circulation of the alkaline electrolyte from the upper side of the bath at one end thereof to the bottom of the bath at the opposite end of the vessel, from which lpoint it may be permitted to ow out through suitable outlet pipes which in practice may be arranged in a manner analogous to that before described .with reference to the inlet pipes and are preferably about two inches in diameter. Thus, two main outlet pipes, such as 31 and 32, run in this case parallel with and below the two rows or series of electrolytic vesselsy 7 to 10 and 21 to 24. and are connected to the bottoms of the different vessels, there being a. separate branch outlet from each vessel of the two series. This branch outlet from each electrolytic vessel is of diHerent type from the branch connections at the inlet side of the system. These branch outlet pipes are constructed as communicating vertical tubes 33 and 31, open at their upper ends and connected at a point just below their'upper ends by a short cross pipe 35. The pipe 33 connects with the lower end of the electrolytic vessel, while the pipe 34 is connected directly to the main outlet pipe 31 or 32, as the case may be. Each one of the eight electrolytic vessels in the two series has a connection therefrom to its respective main outlet pipe of the character just described. The object of constructing the outlet from each electrolytic vessel in this manner is to prevent the level of the bath rising above a predetermined point, the parts of the system being so constructed and combined that the electrolyte .will overflow from the open upper ends of the pipes 33 and 34; whenever the conditions are such -that the electrolyte rises tod high in the bath.

The lbranch outlet pipes just described lead the slightly cooled electrolyte from -the main outlet pipes 31 and' 32 to a return lar to that before described with reference i to the supply reservoir. The steam inlet and out-let pipes of the return reservoir are designated respectively by 38 and 39.

The connections between the various electrolytic vessels and the return reservoir 36. may be either open or closed conduits or pipes; these being interrupted at intervals by tanks, such as 40, to receive the slime resulting from ythe reaction.

From the return reservoir the circuit through which the electrolyte travels is completed by connections to the lhigh reservoir. These connections preferably include a pump, such as 4l, for pumping'the'electrolyte up into the supply reservoir from the low returnreservoir. This pump is preferably placed at a sightly lower level than the low return reservoir in order that the electrolyte may flow by gravity into the pump. The pump can then readily force it up into the high supply reservoir, this being the more readily accomplished when the electrolyte is brought into a more perfectly fluid condition by heating in the low reservoir in the manner just described.

In order'to keep the electrolyte of the baths in as fluid a condition as possible (and for the further purpose of electrically iso- 11i lating the baths) it is desirable in practice to have each of the electrolytic vessels inclosed by a suitable non-conductor of heat and electricity. Both of these objects are acx complished by boxing the vessels, wooden 12Hv boxes being preferably employed for the purpose, and an. insulating airspace being left between the wooden box and the walls of the iron electrolytic vessels. These boxes are designated respectively by 42.

The electrolytic vessels `7 to 10 and 21 to 24 of the system are usually made of castiron, and constitute the cathodcs of the ap-V paratus. The anodes of the different electrolytic vessels may be of any suitable conthe tin from the scrap. The electrical conneotions ineach cell may be any suitable for the purpose. In this case I have illustrated a `plurality of parallelelectrical connections from a supplyconductor to each anode of a cell. 'Ihe different cells of the two series are, however, in this construction connected in series with one another.

Fromal suitable source of energy 'such as the generator 44, current is fed to sectional supplyconduotors,i such as 45, there being one of them for each electrolytic cell. Preferably these sectional conductors are normally disconnected from one another, but are connected to the .cathodes of adjoining cells. lVhen a scrap-containing vessel 4or anode isin place in a cell 'the circuit is comp leted from the sectional conductor 45 at one side of the cathode vessel to the opposite side thereof through the scrap and its container and the electrolyte, and current can flow through the two elements of such cell. In each instance, however, th'e sectional supply conductor 45 is insulated normally from the cathode, as is the basket 43.

It will be noticed that in the systemshown each gathode vessel contains a plurality. of anode baskets connected in parallel -in the circuit of each electrolytic cell. This permits the total quantity of tin scrap con-v tained in any one cell of the systemy to be divided up into a plurality of smaller portions.

When it is necessary or desirable for any reason to cut out the electric current from any cell of the "system, this may be accomplished by Ineans of a suitable switch, such for example as that shown 'at 46. This switch serves to connect vone end of a sectional supply conductor45 with an adjoining section of the supply conductor, thus short-circuiting the cell of that particular sectional supply conductor and directly connecting said sections of the supply' conductor through the intermediate switch. Each of these Sectional conductors 45 is preferably a copper rod or bar insulated from the wall of the cathode vessel. A strip of wood, such as 47, is usually employed as the insulating support for this conductor, said strip being fastened on the edge of the. vessel. ductor thoughinsulated from its own cath- 65 Each sectional conode vessel is of course electrically connected with-the other cathode vessel. I prefer to usev an angular bond, such as 48, which is soldered or welded to the cathode and has its upper edge in line with that of the sectional 7ov conductor of the cathode vessel to which it is fastened. Whenever two adjoining sectionall supply conductors are connected by their switch 46, the baskets in the short-circuited cell may be readily removed. Moreover, the

controlling valve in the inlet pipe for that cell may be closed, the electrolyte drawn olf from the cathode lvessel, and that vessel itself put out of action without interrupting the detinning process inthe other cells of l the series.

Normally the electric current Hows without interruption through all the cells of the fsystem. The current used, order to vaccomplish the best results, that is, the most 85 economical detinning, will preferably be one of very high amperage, say from 800 to 1,000 amperes per square foot or more. The

use of current of this high density is a matter of much importance and was only deter- ,mined upon after exhaustive experiments which showed that it was the most desirable under all conditions present in a large commercial detinning plant.

The compositlon of the electrolyte for practical detinning on a commercial scale is also a matter of very great importance. I. prefer to use a mixture of stannate of soda and caustic soda with an excess of the caustic soda. The alkaline electrolyte contains also carbonate'of soda, as the alkali takes up and unites with carbonio acid in the air. With an electrolyte of tliis composition the proc-A ess carried on is a continuous one because of the regeneration of the liquid asit circu- ,lates through. the system.

,What I claim is: An improvement in the art of detinning, which consists in immersing ay plurality of lots of scrap tin in each of a plurality of 1104 alkaline baths contained in metal receptacles, supplying electrolyte at a high -tem- `perature to and withdrawing it from the metal receptacles separately and passing an electric current of high amperage through each of said receptacles, its `bath and the tin scrap, said current being distributed at each receptacle in parallel through the several lots of tin scrap.

Signed at New York, in the county of New York, and State of New York, December, lA. D. 1907.

' I-IANS GOLDSCHMIDT.

Witnesses:

GHAS. F. DANE, HUBERT E. Rooms.

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