US3179583A - Fluid treatment - Google Patents

Description

April 1965 WILLIAM Kwo-wE CHEN ETAL. 3,179,583

April 1965 WlLLIAM Kwo-wE` CHEN ETAL 3,l79,583

FLUID TREATMENT u 3 Sheets-Sheet 3 Filed July 26, 1960 INVENTOR. WILLlAM KWO-WEI CHEN MILTON SHELDON MlNTZ ATTORN EY United States Patent Ofiice 3,179,583 Pa'zented Apr. 20, 1965 3,179,583 FLUID TREATMENT William Kwo-Wei Chen and Milton Sheldon Mintz, Stamford, Conn., assignors to The American Machine and Foundry Company, a corperation of New Jersey Filed July 26, 1960, Ser. No. 45,415 1 Claim. (Cl. 204-301) This invention relates in general to the treatment of fluids in electrode chambers, and, more particularly, to the acidification of electrodialysis stacks.

In the treatment of natural brines and other solutions by electrodialysis, the base produced at the cathode and at polarized interfaces between the surface of a membrane and the solution causes troublesome precipitation if some means is not provided to counteract it. Methods have been proposed which utilize the acid produced at the anode to counteract the formation of a base elsewhere in the stack. Since the quantity of acid produced electrolytically at the anode can never eXceed the quantity of the base produced within the stack, these procedures provide no Safety factor and slight changes in the brine or solution characteristics of the fluid being treated may readily upset the delicate electrochemical balance. For this reason, it has been a more common ractice to add acid from an external source to the electrodialysis stack. The major objection to this latter procedure is the relatively high cost of the equipment required for introducing acid at the proper rate and pressure.

It is, therefore, an Object of this invention to provide a less costly method for the introduction of acid into an electrodialysis stack.

Another Object of this invention is to provide an electrodialysis stack which can be operated for longer periods of time without requiring service due to precipitation within the stack.

An additional Object of this invention is to provide an inexpensive apparatus which will circulate fluid from an external source through an electrode chamber.

Yet another Object of this invention is to provide a simple apparatus which will add acid from an external source to the cathode chamber of an electrodialysis stack.

Many other objects, advantages and features of invention reside in the particular construction, combination and arrangement of parts involved in the embodiment of the invention and its practice as will be understood from the following description and accompanying drawing wheren:

FIG. 1 is a perspective view of an electrodialysis stack with attached acid feeding apparatus;

FIG. 2 is a side view of an electrodialysis stack with a central portion broken away, with a small additional portion broken away in section to show internal construction and with an attached acid feeding apparatus;

FIG. 3 is an exploded perspective view of the elements forming the electrodialysis stack;

FIG. 4 is a Vertical longtudinal enlarged section through a fragment of one end of the electrodialysis stack and the attached acid feeding apparatus; and

FIG. 5 is a perspective view of a fragment of one end of a gasket and an adjacent membrane.

Referrng to the drawing in detail, FIGS. 1, 2 and 4 show an assembled electrodialysis stack generally designated by the nurneral 29. The stack 29 is clamped between two end plates 30 and 31, which may be steel or other rigid material, by tightening the bolts 32 and drawing the end plates together. Heavicr blocks of electrical insulating material 33 and 34 may be placed inside the end plates 30 and 31 so that the bolts 32 are disposed beyond the center of the stack 29 and electrically insulated from it. The end plate 30 and the block 33 have the cathode chamber intake and exhaust pipes 36 and 35 fixed into them. The end plate 30 also receives the product stream pipe 39 and the concentrate stream pipe 40. In a like manner, the end plate 31 receives two intake stream pipes 41 and 42 and the anode chamber intake and eXhaust pipes 37 and 38. Referring now to FIG. 3, the pipes 35, 36, 37, 38, 39, 40, 41 and 42 lead to fluid flow apertures 64, 63, 73, 74, 61, 62, 70 and 71 respectively, which are formed in the elements compris ing the stack 29. These fluid fiow apertures in the stack elements form manifold passages within the stack 29.

Referring now to FIG. 5, a gasket 50 is an elongated rectangle in its external shape with a central rectangular cutout portion 52. Pars of fluid flow apertures 45 and 46 at each end of the gasket 50 form manifold passages. Communicating from one of these fluid flow apertures 45 or 46 to the cutout chamber 52 are the small passages 47. Thus each end of the gasket 50 contains small passages 47 communicating with oppositely disposed fluid flow apertures to form hydraulic Connections. A membrane 48 lies next to each side of each gasket 50. The membranes 48 contain manifold apertures corresponding to those formed in the gaskets 50.

FIGS. 3 and 4 show the arranged elements of an electrodialysis stack. A steel plate 31 or other reinforcement member, a plastic block 34 and an insulating sheet contain the two fluid intake apertures 61 and 62 and also the anode chamber intake and exhaust apertures 73 and 74. Below the insulating sheet 65 lies the gasket 66 having a central opening 77 which provides the anode chamber. This chamber may be from about 0.1 to about 2.0 cm. thick. There are no internal passages formed within the gasket 66 communicating with the manifold apertures 61 and 62 which it has formed in one end. The anode chamber 77 contains the anode 67 which may be of platinum foil or other suitable material. An electrical connection 68 extends from this anode to be connected to a suitable current source. The connection 68 may also be seen in FIGS. 1 and 2.

After the gasket 66, there is placed a sheet 69 of a porous non-woven material which is sufliciently porous to allow either anions or cations to pass while it resists the passage and attack of chlorine or other degradation agents generated at an electrode. This sheet 69 may be made of any porous, relatively inert material. Following the sheet 69 there are placed a number of layers each consisting of an anion permeable membrane 48A, a gasket 50A, a cation permeable membrane 48K, and another gasket StlB. It is to be noted that the gaskets 50A and 50B are identical except that the gasket 50B is the same as gasket 50A in the inverted position. Thus fluid may flow from the intake manifolds formed by the aligned fluid flow apertures 61 and 62 into alternate chambers 52C or 521). In a like manner, fluid flows from these alternate chambers designated 52C or 52D into either a manifold formed by the fluid flow apertures 70 or a manifold formed by the fluid flow apertures 71.

As long a series of cells may be built up in this man ner as desred by stacking up the alternate layers of gaskets 50A and 50B with the interspersed membranes 48A and 4331. At the other end of the stack, the lower end as seen in FIG. 3, there follows in reverse order another porous sheet 69 and another gasket 66 from about 0.1 to about 2.0 cm. thick which contains a cathode 72. Another insulating sheet 65, another plastic block 33 and another plate 30 follow; each containing the fluid flow apertures 70 and 71 and also the cathode chamber intake and eXhaust apertures 63 and 64. When the electrodes 67 and 72 are connected to a direct current source so that the electrode 67 is an anode and the electrode 72 is a cathode, the cut out portions 52D in the gaskets 50A will form diluting cells and the cut out portions SZC in the gaskets SGB will form concentrating cells. Thus a solution entering the stack through the intake pipes 41 and 42 will emerge as a dilute and a concentrate Stream.

Referring now to FIG. 4, a reservoir is connected to the electrode chamber 77 containing the cathode 72 by means of the pipes 35 and 36. EXtending upward from the reservoir 10 is the standpipe 11 which vents the reservoir 10 to the atmosphere through filter material 12.' The pipe 36 communicates between the lower portion* of the reservoir 10 and the lower portion of the electrode compartment'77. The pipe 35 extends from the top of the electrode chamber '77 upwards at an angle until it enters the reservoir 10. The reservoir 10 is filled with a suitable solution 14 to a level which is higher than the top of the electrode compartment '77. Since a liquid will reach a State of equilibrium by seeking its own level, the solution 14 will fill the electrode compartment 77. This solution 14 may be any suitable acid, or it may be water in which is placed a premolded cake 25 of a suitable acid salt such as sodium bisulfate to form a saturated solution. If a solid cake of an acid salt, or if acid salt in a loose form, is packed in the reservoir 10, the top cover 15 of the reservoir 10 may be made removable so that the reservoir may be more easily charged. If a liquid acid solution is used, it may be easily poured into the reservoir 10 through the standpipe 11.

When the electrodialysis stack is in operation, bubbles 26 will be liberated at the cathode 72. These bubbles will rise within the solution in the electrode compartment and they will continue to move upward through the pipe 35. Since the density of the Combined fiuid and bubble mxture in the electrode compartment '77 and the pipe 35 will be less than that of the solution alone, the relatively more dense fiuid 14 within the reservoir 10 will force some of the fiuid 14 and the rising bubbles within the electrode chamber 77 and the pipe 35 to percolate. out of the pipe 35 and back into the reservoir 10.

The gasses which are liberated at the cathode 72 pass upward through pipe 35 into the reservoir 16 in the bubbles 20 and then escape from the reservoir 10 through the standpipe 11. In this manner a recirculation of fiuid between the reservoir 10 and the cathode chamber 77 is mainta'ned as long as the electrodialysis stack is operating. This is a vapour lift device which depends on the passage of gas through liquid in a confined channel.

The top of pipe 35 need not be placed above the level of the solution 14 in the container 10 as shown in FIG. 4. If pipe 35 terminates below the level of the solution 14, the rate of circulation will increase as the bubbles 20 will not have to raise the fluid to a given head before circulation starts, but the bubbles will only have to overcome the hydraulic resistance of the recirculation path. In any case, the pipe '35 leading from the top of the electrode compartment to the reservoir 10 must extend generally upward or a vapour lock may result. A pocket of the released gas in bubble form which was trapped by a downward extension of pipe 35 could interrupt the recirculation flow. This apparatus requires little attention and will automatically operate simultaneously with the electrodialysis stack without requiring the manipulation of any valves or other controls. The reservoir 10 may be made of suicient capacity so that an electrodialysis stack may operate for a very long period of time before the acid or acid salt solution is used up in treating bases formed at the cathode. Further, if an anion permeable membrane 48A is placed adjacent to the cathode '72, water transferred by electroendosmosis will be directed out of the cathode conpartment. However, an equilibrium water content will be mantained as normal osmotic water transfer takes place back into the cathode compartment by virtue of its high acid or Salt concentration.

If the electrodialysis stack operates in the manner that has been described, the anode may be washed by means of water directed into pipe 37 which will then ex-haust through pipe 33. However, if it is desired to reverse the stack periodically electrically (for example, every quarter hour or perhaps every two or three hours), the pipes 37 and 38 may also be connected to the reservoir 10 in the same manner as are the pipes 35 and 36. In this case, either anion permeable membranes tA or cation permeable membranes 48K would be placed adjacent to both electrode compartments so that water transfer out of one electrode compartment by electroendosmosis would tend to be balanccd by water transferred into the other electrode compartment by means of electroendosmosis. Water transferred into an electrode compartment by electroendosmosis would be carried upwards by bubbles into container 10 While water transferred out of an electrode compartment by electroendosmosis would tend to balance such an accumula tion of water. This feature of the invention would allow electrical reversal to be made at longer intervals as the fluid level would not be changing in the reservoir 10.

If a separate reservoir were connected to each electrode chamber of an electrodialysis stack which was periodically electrically reversed, the capacity of each reservoir would have to be sufiicient to contain water added by electroendosmosis to one of the two chambers before electrical reversal. To extend the period of operation before electrical reversal became necessary, an overfiow could be provided in each reservoir to drain off excess fiuid.

While one particular electrodialysis stack structure has been shown having parallel flow through it, this :invention rnay be used in eleotrodialysis apparatus regardless of its construction or flow pattern. This invention may also be used in .other applications wherein it is desired to circulate fiuid from a reservoir through an electrode containing compartment. r

What is claimed is;

in electrodialysis apparatus having ion selec tive permeable membranes defining alternating concentrating and diluting cells, between a pair of end electrode chambers, a cathode :in one electrode chamber and an anode in the other electrode chamber, a direct current source connected to said elcctrodes, and means for fiowing a concentrate stream and a di-luting Stream through said concentrating and diluting cells, the improvernent comprising a vented reservoir for an acid to be circulated continuously through the cathode electrode chamber, a first conduit extending upwardly from the topof the cathode electrode chamber to said reservoir, and a second conduit extending from said .reservoir to the lower end of said cathode electrode chamber, whereby bubbles of gas liberated at the cathode during operation of the apparatus create a vapor lift to induce circulation of acid continuously between the reservoir and the cathode electrode chamber.

Refercnces Cited by the Examiner UNITED STATES PATENTS 1,986,920 1/35 Cross 204-301 2,180,663 11/39 Delavenna 204-234 2,204,506 6/ 40 MacDouga-ll 204-272 2,796,395 6/57 Roberts 2G4-237 2,848,403 8/58 Rosenberg 204- 2,863,813 12/58 Juda 204-30l 3,003,940 10/61 Mason 204-18Q IOHN H. MACK, Primary Examner.

MURRAY TILLMAN, Exam'ner.

Images