US2396664A - Method of dehydrating caustic solutions - Google Patents

Description

March 19, 1946. LADD 2,396fifi4 METHOD OF DEHYDRATING CAUSTIC SOLUTIONS Filed April 10, 1942 2 SheetsSh.eet l v 1 it??? %1NvEN1-?J( ATTORNEY D D A L E METHOD OF DEHYDRATING CAUSTIG SOLUTIONS Filed April 10, 1942 2 Sheets-Shae"v 2 INVENTO ATTORNEYS Patented Mar. 19,1946

UNITED STATES PATENT, OFFICE METHOD OF DEHYDRATING CAUSTIC SOLUTIONS Edward Thorndike Ladd, Lewiston Heights, N. Y. Application April 10, 1942, Serial No. 438,443

11 Claims.

This invention relates to methods of dehydratlng caustic'solutions, and more particularly to methods of this kind which may be carried on without adding impurities to the caustic liquids.

It has always been a serious problem to produce solid caustic potash and caustic soda or fairly concentrated solutions thereof free from contamination from the equipment in which this material has been concentrated or dehydrated, since these caustic solution have a tendency to attack nearly all materials which are ordinarily available for use in the building of such equipment. For many purposes, caustic potash or soda free from metallic impurities and carbonates is essential, and it is also desirable to have these pure caustics available in solid form. In my Patent No. 2,270,376, dated January 20, 1942, I have disclosed a process by means of which metallic impurities, such as compounds of iron, aluminum, and other metals, can be removed'from caustic solutions. If, however, such pure solutions are then dehydrated in the ordinary manner now commonly used, which involves heating the solutions in a large iron container, then during the dehydration, the solution pick up iron to such an extent as to greatly reduce their commercial value and to render them unsuitable for certain uses.

One of the objects of this invention is to provide a process whereby a caustic solution can be dehydrated without the addition thereto of impurities. Another object is to provide a process of this kind by means of which a caustic solution free from metallic impurities can be dehydrated without adding such impurities thereto. It is also an object of this invention to provide an eflicient and reliable process of. making solid caustic potash or soda in which no metallic impurities are added to this material during the dehydration thereof. A further object is to provide a continuous process for dehydrating caustic solutions without adding impurities thereto.

Other objects of this invention will appear from the following description and claims.

I have found that under certain conditions, caustic solutions can be dehydrated without contamination while in contact only with carbon surfaces. The use of carbon for lining containers for the caustic solutions during dehydration has heretofore not been considered practical for the reason that the temperatures employed for dehydration are so high as to cause fairly rapidoxidation of the carbon, and furthermore, carbonates would be formed as impurities in the caustic solutions. I have found, however, that oxidation of carbon and the formation of carbonates of potassium or sodium can be prevented by the exclusion of an oxidizing atmosphere, such as air, from contact with the carbon surfaces which are subjected to the action of the caustic solutions. Under these conditions, it is also possible to expose the carbon to temperatures materially higher than those to which carbon can ordinarily be subjected, without oxidizing the carbon.

While any form of carbon may be employed on the surfaces contacting with the caustic liquids,

, I have found that graphitic carbon, particularly when in dense or compacted form is preferable and capab.e of withstanding higher temperatures than other forms of carbon. Ordinarily in the com mercial production of solid caustics, the pots or containers in which water is evaporated from the .caustic solutions are of large size, sufficient to contain at least several ton of caustic solution, and heat is applied to the outer wall of the pot by means of oil burners, coal fires or the like. No pots or containers of this size-could at present be made of carbon and the heat could, of course, not be applied to the exterior surfaces of such pots, since this would destroy them. Consequently, it is desirable for large production to provide an apparatus having a heating chamber through which a relatively smallstream of caustic solution passes, and in which the heat necessary for dehydration is applied to the interior of the apparatus. In the accompanying drawings, I have, consequently, shown a preferred form of apparatus of the latter type, it being understood, however, that it is not intended to limit this invention to use in connection with the particular apparatus disclosed, since obviously my process may be carried on in any type of evaporating apparatus having a chamber so constructed that caustic liquid contacts therein with carbon surfaces only, and in which heat is applied directly within the chamber, and in which air is to a large extent excluded from the interior of that part of the chamber in which the caustic liquid is contained.

In the accompanying drawings:

Fig. 1 is a central sectional elevation of one form of dehydratin apparatus, by means of which my improved process may be carried out, the secthereof, showing in section some of the trays for the liquid which is being dehydrated.

In the apparatus shown in the drawings, there isprovided a heating chamber or tower through shown in Fig.2, which have which liquid to be dehydrated passes from the top to the bottom in contact with carbon surfaces only, and means are provided for introducing heat into the chamber, for example, by admitting a heated non-oxidizing gas or vapor-near the bottom oi the tower, from which heat is transferred to the liquid to cause water to be evaporated ther'efrom- For example, superheated 1 steam may be employed'ior removing water from the solution, and preferably a pressure slightly in excess of atmospheric is maintained within the chamber so that air is excluded.

The apparatusshown in the drawings includes an upright column or tower ll, the walls of which are made of stoves or blocks ll of carbon or graphite, the staves shown being of greater length than width and having their side faces providedwith longitudinally extending recesses in which suitable caulking material I! may be inserted so as to produce a liquid tight joint between adjacent staves I I. Since, the tower i II is higher than the staves, two or more seriesof these staves H are preferably employed, one on top of the other, and the joints between the two tiers of staves are preferably of the stepped or overlapping type as shown at l3, so that liquid would have to-now upwardly in order to pass out of the tower at these joints.

The staves H ofthe tower may be held in correct relation to each other in any suitable manner, for example, by means of bands or hoops l4, those shown being made of two halves connected by means of bolts I5 passing through suitable brackets "secured near adjacent ends of the half hoops. Springs ll acting on the bolts tend to contract the hoops to clamp the staves II together. The bolts may have suitable nuts, by

' means of which thetension oi the springs may. be varied as desired.

The hoops or bands 44 may engage the blocks or staves ll directly, or if desired, channel bars I! may be provided, as their flanges engage portions 01 adiacent'blocks. The hoops, conseformed in the block it and terminating in the hollow middle portion thereof. In the construction shown, the gaseous heating medium is conducted to the radially extending pipes by means of a manifold pipe 33 which connects by means of a pipe 34 with a suitable heating coil arranged within a heater 36. A supply of the gaseous heating medium passes into the coils .of the heater through an inlet pipe 3! controlled by a valve 38.

Any suitable or desired heating medium may, ofcourse, be used in the column In. The heating medium may be any non-oxidizing gas or vapor which does not react with the caustic solutions' or the carbon material, of which the column is constructed, and preferably I employ superheated steam. Steam or other vapor or gas passes into the heater 35 from the pipe 31 and is raised therein to a high temperature by means of any suitable source of heat. For example, an oil burner indicated diagrammatically at 38 may be used. Inorder to provide for eiiicient operasteamor other medium to a fairly high temperature, and this temperature should be high enough to maintain anhydrous caustic in molten or liquid condition, so that it can readily be discharged through the pipe 24. For example, temperatures approximating from 500 to 800 F. are preferably employed.

Liquid to bedehydrated is conducted into the tower or chamber I 0 in any suitable or desired manner, an inlet pipe or duct .40 being shown more or less diagrammatically in Fig. 1, and a suitable valve 4| is preferably employed for controlling the flow of liquid to the apparatus. 1

Any suitable-means may be provided for causing the liquid to now slowly through the apparatus so that ample opportunity is provided for removal of moisture therefrom. Any suitable or desired checker work of carbon or graphite may be employed for this purpose, and by way of ex- I ample, I have illustrated in the drawings a series quently, engage the channels I l and press them toward the center of -the tower and into engagement with adjacent staves. Any other means for constructing the towermay, oi course, be em:-

. ployed, if desired.

The lowest tier of staves ll rests upon a base block is suitably supported on: a steel plate II, which in turn is suitabl mounted by means of frame members 20 on upright columns or pillars 2|. The base block II has a central recess in which the liquid will collect after passing down through the interior of jrecess terminates in a pan-shaped lower block the tower in, and this 22, which has a discharge opening 23 therein which mayconnect with a discharge pipe 24 through which the liquid end product may be discharged from the apparatus. The block may be supported froma plate 26 suitably suspended from the plate l9, and a smaller block 25 having an aperture in registration with the aperture and to which the pipe connection 24 is secured, may be supported in correct relation to the block 22 by meansof a plate 29 suspended from the plate 25. Any other means for withdrawing the flnished material from the apparatus may be provided, it desired.

The block ll preferably is also provided with a series of inlet passages for the heating medium, and in the construction shown, four pipes 30 extend into downwardly inclined apertures 3| other gaseous heating medium of pans 44 and 45 which are alternately arranged sothat the liquid to be acted upon cascades from one pan to another until it reaches the bottom of the tower. The pans are also made oi carbon and may be supported in any suitable or desired manner, this being preferably done by means of rows orders of blocks 48, four such rows being shown in the construction illustrated, see Fig. 2. The pam; 44 are annular in shape and of larger outside diameter than the pans 45 and preferably have inner flanges 41 and outer flanges 48, and if desired, the outer flanges may be slightly great.

er in height so that liquid will tend to overflow the inner flanges 41 of the pans 44 and thus discharge into the next lower pans 45, having outer flanges 49. By means of the blocks 48 as shown, the pans are so supported that when a pan 45 overflows, the liquid will drop upon the next lower annular pan 44, It will also be noted that the arrangement of these pans is such that the circular pans 45 prevent the passage of steam or directly upwardLv through the middle portion of the tower, and the annular pans 44 of larger diameter approach so closely to the inner wall of the column l0 as to permit only a small part of the heating medium to flow between these annular pans and the inner back through the central opening or thenext or other oxidizing medium is substantially exhigher annular pan, In this way, a greater poreluded. It is well known that a temperature of tion of the heating medium will be forced to flow about 800 F., carbon oxidizes rapidly and the crosswise of the cascading liquid and also most oxidation of carbon in contact with caustic soluof the heating medium will contact with all of 5 tions would, consequently, result in the producthe pans so as to impart a high degree of heat to tion ofcarbonates of potassium or sodium. If the same. air is entirely excluded from the process, both the The apparatus is arranged on the counterfiow oxidation and deterioration-of the carbon at the principle so that the hottest heating medium or high temperatures is prevented, as well as the superheated steam acts on the most concentrated production of carbonates in the caustic material. solution near the bottom of the tower, while the One of the advantages of my process is that by gaseous heating medium at the top of the tower means of the same, caustic solutions can be deacts on the relatively cool liquid which has just hydrated without the introduction into the same entered the tower. For most efiicient operation of any metallic impurities, and this can be done of the apparatus, it is, of course, desirable to supwithout increased cost in producing the dehyply liquid to the apparatus through the pipe 40 drated materials. While it is preferable to opat a rate just enough to enable the desired erate my process with air entirely excluded from amount of water to be removed from the caustic the chamber, yet the presence of small quantities liquid while passing through the tower. If an of air will, of course, have only a very slight anhydrous caustic is desired, this can readily be deteriorating effect upon the material of which obtained bythe proper regulation of the flow of the column is constructed and the amount of liquid and gaseous heating medium passing to .carbonates thus produced in the product will be the tower. Any degree of concentration of the practically negligible. However, even this'slight caustic liquid can, of course, be obtained b the degree of contamination of the caustic and oxidaproper regulation of the quantity of caustic liquid tion of carbon canreadily be avoided by mainand heating fluid admitted to the apparatus. taining a slight pressure of steam or heating The top of the tower l0 may be closed in any medium in the tower I 0. The process also has I suitable or desired manner. In the construction the advantage that once it" is started, it requires shown for this purpose, I provide a dome or 'top very little attention, except ;to maintain an adeincluding an annular outer wall 50 and a top wall q t p y of ca s c so ut -a d fam or or lid 5|. A discharge passage 52101 the spent other heating'medium. I v heating medium and steam resulting from dehy- I claim as my invention: I a 'f' dration of the caustic solution is provided in the 1. A pro s f P in caustic l tions of annular wall 50, and an annular bafiie wall 53 is high concentration and substantially free. from proferably provided within the dome and which metallic impurities,,. yvhich process includes passrests upon a supporting wall 54. The baille well ing a stream of thesolution to be evaporated 53 has an opening through which steam from the and which is substantially free from metallic top of the tower may enter the annular space impuritiesthro gh a sub t n i y closed @011- between the walls 50 and 53 and finally pass out tainer from which air is substantially excluded through the pipe 52. and in contact only with carbon surfaces, supply- I, In order to exclude air or" other oxidizing mein h t t d c ntc p ate m ure dium from the dehydrating chamber or tower In, therefrom andto maintain said solution in liquid a discharge valve 56 may be provided in the disform, and withdrawing, the remaining solution charge passage 52 and the opening in the disfrom said container while the same is in liquid charge valve may be readily adjusted so as to form. maintain a slight pressure within the chamber In. A p s f dehydrating caust s uti ns. Preferabl the tower is also insulated to retard Wi h t in m l pur th r which the escape of heat from the same, and conseincludes admitting a caustic solution to be dequently, the tower may be surrounded by any hydrated into one end of a chamber into contact suitable insulating wall 68, which is arranged so only with graphitize'd carbon surfaces, admitting about the column id in spaced relation thereto, to said chamber a non-cxidizinggaseous heating 60 represents an annular member or band of medium elevated to a temperature in excess of carbon which extends about the block l 8 and the fusing point of the dehydrated caustic and which has its upper end shaped to form a trough into contact with said-caustic solution to remove 6i in which any caustic liquid may be collected 55 moisture therefrom by evaporation, and diswhich has seeped through the wall of the tower charging jthevheating medium together with or chamber 10. From this trough, which may vaporized water from said chamber near that obviously be formed as a part of the block l8, end thereof at which said solution is admitted.

liquid may flow back into the tower through the 3. -A process of dehydrating caustic solutions, lap joint which connects the block i 8 with the ,60 without addinginetallic impurities thereto, which lowest set of staves I I, processincludes passing a stream of'said solution The finished material withdrawn from the disinto a substantially closed-chamber into contact charge pipe may, of course,'be led into suitable only with graphitized carbon surfaces, passing containers in which it may cool and crystallize. through said chamber in contact with said solu- In operating in accordance with my process, tion a current of a gaseous, non-oxidizing heatany type of carbon surface may be employed with ing medium raised to a temperature of "approxiwhich the caustic liquid may contact. In order mately from 500 F. to 800F., and excluding air to provide for the most eflicient operation and for from said chamber. utilizing the highest possible temperatures, it "is 4. A process of dehydrating caustic solutions, preferable to employ graphiteblocks of a com- 79 without adding metallic impurities thereto, which pact and dense nature and relatively impervious "process includes passing a stream of said solution to caustic solution. In using such graphite into the one end of a substantially closed cham-' blocks, temperatures as high as 800 F. and even her into contact only with graphitized carbon somewhat higher maybe employed in connection surfaces, admitting to the other end of said with m dehydration process, providing that air chamber into contact with said solution steam superheated to temperatures from approximately 500 F. to 800 F., and discharging steam from the first mentioned end of said chamber.

5. A process of dehydrating caustic solutions, without adding metallic impurities thereto, which includes continuously passing a stream of caustic solution to be dehydrated into the upper portion of a closed chamber lined with graphitized carbon, cascading the solution through said chamber and while in contact only with graphitized carbon surfaces and non-oxidizing gas, heating'the solution in said chamber above the Iusing point of the caustic solutions to vaporize water therefrom and to maintain said solution liquid, 'and discharging vapor-from said chamber.

6. A continuous process of dehydrating caustic solutions, without adding metallic impurities thereto, which includes "continuously passing a stream of caustic solution to be dehydrated into the upper portion of a closed chamber lined with graphitized carbon, cascading the solution through said chamber and while in contact only with'graphitized carbon surfaces, excluding air from said chamber, heating the liquid to a temperature above the boiling point of water while passing throughsaid chamber to vaporize water contained in said solution, and discharging the vaporized water from one end of said chamber and dehydrated caustic in molten form from the other end'thereof.

'7. A process of dehydrating caustic solutions, without adding metallic impurities thereto, which aseaoec includes continuously passing a stream of caustic solution to be dehydrated into the upper portion of a closed chamber lined with graphitized carbon, cascading the solution through said chamber and while in contact only with graphitized carbon surfaces and non-oxidizing gas, heating the liquid in said chamber to a temperature above the boiling point of water to vaporize water therefrom, maintaining in said chamber a non-oxidiz ing gas at a pressure in excess of that of the atmosphere to exclude air from said chamber, discharging water vapor from the upper end of said chamber, and withdrawing dehydrated caustic in liquid form from the lower endof said chamber.

8. A process of dehydrating caustic solutions without adding metallic impurities thereto, which includes passing a stream of caustic solution to be dehydrated into a closed chamber into contact only with carbon surfaces, and bringing a current of heated non-oxidizing gas which is inert with reference to carbon and said caustic solution into contact with said solution to evaporate water therefrom.

9. A process according to claim 8 and including the step of excluding air from said chamber.

10. A process according to claim 8 and including the step of maintaining said gas under pres-

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