US2747972A - Charge boat for volatilization - Google Patents

Description

May 29, 1956 Filed Sept. 9, 1944 R. KROHN 2,747,972

CHARGE BOAT FOR VOLATILIZATION 2 Sheets-Sheet l 2 Sheets-Sheet 2 May 29, 1956 .R. KROHN CHARGE BOAT FOR VOLATILIZATION Filed Sept. 9, 1944 INVENTOR. Roy )frohn CHARGE BOAT FQR VOLATILIZATIQN Roy Krohn, Berkeley, Calif., assignor to the United Statesof America as represented by the United States Atomic Energy Commission This invention relates to improvements in sublimation apparatus and processes for the volatilization of chemicaI materials. More particularly this invention concerns improvements in charge boats and procedure for volatilizing chemical materials in sublimation processes, especially uranium compounds, exemplified by certain. halogen derivatives of uranium. The invention constitutes an improvement over the inventions disclosed in U. S. Patent applications, Serial No. 552,556, filed September 2, 1944, now Patent No. 2,574,842, and Serial No. 552,557, filed September 2, 1944.

In companion application Ser. No. 553,446 filed September 9, 1944, in which I am a joint inventor, it is indicated that a number of sublimation processes and apparatus have been described in the prior art. Said companion application concerns a novel sublimation apparatus and process having advantages over the prior art.

In the present application there are described certain improvement features which may be employed in sublimation apparatusconstructions of the type described in the companion application aforementioned as well as novel features ofconstruction which may be utilized in sublimation apparatus generally or in related fields.

I have found that there are improvements which may be made inthe devices or units used for holding the chemical materials to be volatilized and in related parts whereby volatilization is quicker, separation better and other advantages obtained. In further detail I have provided an improved construction of the charge holding means, referred to herein as a charge boat, which construction is particularly useful in the volatilization of certainuraniurn halides for obtaining better charge distribution and accelerated volatilization.

This invention has for one object to provide improvements in sublimation apparatus and processes.

Another object is to provide an improved construction for the charge holding and volatilizing device referred to herein as a charge boat.

I Still another object is to provide a charge boat construction in which there may be obtained better charge distribution and accelerated volatilization.

Another object is to provide a charge boat construction that: is particularly useful in methods of processing uranium materials.

- Stilbanother object is to provide a boat construction that facilitates thevolatilization and separation of mixed halide. compounds.

Another" object is to provide a process for the rapid volatilization of chemical materials.

- Another object is to provide a method of volatilization applicablextothe processing of uranium halide materials to;UCl'e and UCl4.

. Atstillfurther object is to provide a process in which theremay be simultaneous separation and crystallizing stepsiappliedtto.uranium halides.

Qthervobj'ects: will appear hereinafter.

I have found that improved operation in sublimation V .processesfmay be obtained bymeans of employing a 2,747,972 Fatented May 29, 1956 charge volatilizing device comprising an elongated boat construction having a number of trays or shelves therein.

For a further understanding of my invention, reference is made to the attached drawing forming a part of the present application.

Fig. 1 is a semi-diagrammatic side elevation view of a sublimation apparatus in which certain parts have been shown broken away and other parts shown in section. In this figure the general relationship and positioning of my improved charge boat in a sublimation apparatus is indicated;

Fig. 2 is a sectional view taken on the line AA of Fig. 1 showing certain of the related parts in a sublimation unit of a type in which it has been found advantageous to use my charge boat.

Fig. 3 is a sectional view on enlarged scale, taken on the line BB of-Fig. 1, showing the positioning of my charge boat within the supporting member therefor.

Fig. 4 isla detailed view of the inner shelf or tray portion of the charge boat construction of the present invention.

Fig. 5 is a detailed view, on enlarged scale, showing the outer portion of the charge boat construction.

In order to provide a better understanding of the environment and conditions under which the improved charge boat of the present invention may be used, there is briefly described ahorizontal sublimation apparatus of a type in combination with which theuse of the novel charge boat of the present invention has been found particularly satisfactory. Following the general description of the sublimation equipment, details concerning the improved charge boat of the present invention are set forth.

Referring now to Fig. 1 concerning a sublimation apparatus, reference numeral 2 represents a movable electric furnace. The furnace may be of conventional construction'including heating elements 3, insulation 4, and various other usual parts for the construction and operation of electric furnaces. Wheels 6 which move on track- 7 may be provided for permitting the movement of the furnace into and out of heating position. That is, the furnace may be moved out of position for cooling, repair, and other similar action as respects the apparatus.

As-may be seen in the drawing, the furnace is adapted to-move onto and inclose an elongated hollow member 8 which member houses the charge boat 9 of the present invention, the latter being better shown in Figs. 3, 4 and 5. Member 8 is connected to, and projects horizontally outwardly from, a condenser structure 11, better shown in Fig; 2, such that the interior of the hollow member 8 communicates with the interior of condenser 11.

The condenser 11 is connected by means of conduit 12 to a vacuum system (not shown). The particular vacuum system employed for reducing the pressure on the condenser and charge boat, and for removing air which might cause oxidation, is not a limitation on the present invention. In general, means for obtaining reduced pressure less than 50 millimeters of mercury would be employed in conducting the sublimation process.

Referring now to Fig. 2, the condenser includes an inner liner 21 disconnected from the outer shell 22. After removing the condenser closure 24 (see Fig. l), the entire'liner 21 maybe pulled out of the apparatus. The outside of the condenser is provided with a number of cooling coils 23 of conventional design which may be connected. to water. lines or other cooling medium by means of detachable connections.

Within the liner 21 but attached thereto is the convolute' or: spiral metallic member 26. This member functions to cause the. vapors from the volatilization in: the charge boat construction of the present invention tomove in an elongated spiral path. Also the metal member 26 functions as a condenser surface as will be further described under the operation of the equipment.

The liner 2.1 fits within the apparatus against boat 9 in a substantially vapor tight manner by means of the interposed sealing ring 7. This ring 27 is similar to an automotive piston ring and by expanding against the interior surface of member 8 gives a vapor tight seal. This prevents vapors evolved in the charge boat from penetrating between liner 21 and the condenser wall 22. The liner 21 has a removable head 28 attached thereto by bolts indicated at 2?.

As stated above, the sublimation apparatus assembly which has been described constitutes one type of arrangement in which my improved charge boat may be employed. However, the details of construction of the sublimation apparatus in general are not a limitation on the use of the charge boat as there are other sublimation apparatus constructions or other devices for similar purposes in which my charge boat may also be used. For

example, reference is made to the sublimation apparatus described in companion Hecker application, Ser. No. 552,557 filed September 2, 1944.

Considering now in detail the construction of the charge boat with which the present invention is primarily concerned, as indicated the charge boat and its position in a sublimation apparatus has been shown in Fig. 1, the boat being indicated by reference numeral 9. The outer portion of the boat is better shown in Fig. and is in effect a cylindrical metal tank with a portion cut away as indicated at It). The boat and related parts, as the trays or shelves, are preferably constructed from a corrosive and heat resistant alloy. For example, the commercially obtainable alloy Hastelloy" may be employed. It has been found that alloys containing a high content of nickel and chromium, together with smaller contents of elements such as cobalt, tungsten, molybdenum, manganese and iron constitute satisfactory materials of construction. Since these various alloys may be obtained commercially, further description is unnecessary.

Referring to Fig. 3 showing the boat construction in section, it will be noted that the boat 9 is supported within and by means of hollow member 8. The boat 9 contains the shelf or tray carrying member 31 that supports the trays upon which the chemical material to be sublimed is distributed. That is, a plurality of trays or shelves 35, 36, and 37 are provided which are hinged to member 31 by means of the hinge and rod constructions 32, 33 and 34.

The details of the shelf or tray construction may be further observed by reference to Fig. 4 wherein it will be noted that the shelves or trays 35, 36, and 37 may be folded up for the purpose of permitting the insertion of the tray carrying member 31 into the cutaway portion of boat 9. Suitable cross members 38 may be provided for supporting the shelves or trays when they are opened out into a position for carrying the material to be volatilized. While the cross member 38 is described only in connection with the upper shelf, it may be used for supporting other of the shelves, if desired. The lower shelves, as 36 and 37, may be notched as indicated at 39 and 4:) to permit the shelves being folded up without interference from member 38.

It will be noted that the overall length of the trays and associated parts is less than the length of boat 9. Therefore, when the trays are positioned within boat 9, there is a space 44 (see Fig. 1) into which the vapors from the trays may escape.

In the operation of the apparatus the member 31 is inserted into boat 9 by folding up the shelf members 35, 36, and 3'7. After insertion, the shelf members may be successively opened out, and the materials to be volatilized spread on the surface of the shelves or trays in layers of the desired thickness depending upon the par ticular material to be processed, the size of the apparatus and related factors. As apparent, the lower shelf, shelf 37, would first have charge distributed thereon before unfolding shelf 35. In general the weight of the charge contained in boat 9 may be between to 250 pounds, but this would, of course, depend on the size of the apparatus.

The sublimation apparatus in which my charge boat is to be used, such as the apparatus shown in Fig. l, is opened. That is, the condenser head 24 is removed and the liner and other parts within the apparatus taken out. The boat 9, filled with the charge distributed on the trays 35, 36, and 37, is then slid into the hollow member 8 to the back thereof. The sealing ring 27 is inserted through the front of the apparatus and pushed back into member 8 so that the ring 27 abuts the end of boat 9. The liner 21 is next pushed into place through the front of the apparatus so that it abuts the above-mentioned sealing ring. In this manner, inasmuch as the ring expands against the member 3, a vapor tight fit to prevent vapors from penetrating between liner 21 and wall 22 is obtained. The liner closure head 23 and condenser head 24 and other parts are bolted into place, couplings made to the cooling fluid connections, and other action taken to complete the readiness of the apparatus for operation.

As already mentioned, the charge boat of the present invention is useful for processing uranium halides. For example, in converting or separating uranium halides into UClc and UClr the shelves 35, 36, and 37 would have spread thereover the charge of uranium halides to be sublimed. After the charge has been distributed in the charge boat as described and the apparatus otherwise assembled, the pressure is slowly reduced to prevent any carryover of charge particles through conduit 12. The furnace is rolled into place as shown in Pig. 1 and heat applied to cause volatilization of the charge. The furnace temperatures employed may vary from about C. or C. up to several hundred degrees centigrade. The degree of reduced pressure on the system, as indicated above is generally below 50 millimeters of mercury and suflicient at the particular temperature and other conditions involved to cause sublimation to take place without the formation of a liquid phase. In other words, when processing uranium halides as referred to above, it is not desired that liquid uranium halides form in the system because of their corrosive action.

After heating under reduced pressure has been accomplished for a sufficient period for eliminating entrapped air and the like, the temperature of heating may be increased to a sufficiently high point that the solid charge on the trays is volatilized, vapor passing from the trays into space 44, out or" the charge boat through opening 10 into the interior of the metal spiral 26 and then around the metal spiral. This metal spiral 26 causes the vapors to pass in an elongated path before they can reach the exit conduit 12. During their passage they become condensed on the metal spiral 26. This condensation may be obtained by applying suitable cooling to the exterior of the condenser, as for example, a Dry Ice acetone mixture, or part 26 may be cooled directly by running suitable cooling conduits thereto. Also, the condensing temperature may be controlled to some extent by the positioning of this metal spiral or bafiie 26 at a predetermined distance from the outer, cooled condenser surface. Since the interior of the apparatus is under reduced pressure, the temperature change by conduction is limited. Consequently, the spiral is cooled principally by radiation. However, by the application of a cooling medium such as Dry Ice and acetone or comparable materials, satisfactory condensing temperatures may be obtained. By interposing this metal spiral or convolute 26, practically all of the sublimed product is condensed out so that none passes out of the system through conduit 12.

After the process has continued for a sufiicient period so that substantially all of the sublimable materialin boat 9 under the temperature and pressure conditions involved, has been volatilized; the furnace-2 may be rolled olf, and the apparatus permittedto cool; Coolingmay be expedited by introducing, by any-conventionalmeans, a dry, inert gas as nitrogen'within the condenser chamber thereby-providing a medium through which the heat may be transferred by conduction; After the equipment has cooled down suificiently, the condenser head 24 is removed. The liner 2]. may be pulled out, capped and taken to a dry box where thesublimate may be chipped out and'placed' in suitable containers. Inasmuch as the purified sublimed-product is hygroscopic, it is desirable that the material: be maintained in a dry atmosphere. Thereafter the apparatus may be cleanedtas by washing, dried, and another filled charge boat, ring, and liner inserted, and the process repeated on another batch of crude material.

I have found that the charge boat and method of volatilization in accordance with the present invention is particularly. useful in the treatment of certainuranium halide materials for obtaining. a sublimate ofuranium hexachloride. The source of, the materials which'may. be treated, for example, is exemplified by the reaction product. of uranium oxide with a: clilorinatingmedium such as carbon tetrachloride. The exactchemicalnature of the uranium chloride obtained. isnot a limitation on the present invention. Such uraniumi chloride materials may comprise, for example, amixtureof uranium hexachloride and uranium tetrachloride. .The materials may comprise uranium pentachloride. or materials inwhich the ratio of uranium to chlorine therein approximates this compound. Or the uranium materials may include various amounts of all of the aforementioned uranium derivatives, namely, the uranium pentachloride, hexachloride and tetrachloride. Therefore, the charge materials are generically referred to herein as uranium chloride materials.

It has been found that such uranium chloride materials may be advantageously processed by sublimation to obtain uranium hexachloride therefrom. By means of the excellent charge distribution obtainable on the tray construction of the present invention, the uranium hexachloride may be rapidly volatilized even though one-third to two-thirds of the charged materials may remain on the trays as residue, as for example, a substantial residual content of uranium tetrachloride. The uranium hexachloride is relatively more volatile than uranium tetrachloride and may be sublimed at furnace temperatures between 100 C.200 C. The degree of reduced pressure utilized during the sublimation is less than 50 millimeters of mercury and during the sublimation, a reduced pressure of the order of 2 l0 may be employed. The use of reduced pressure removes oxygen, moisture and otherwise eliminates gaseous components which might contaminate or exert a destructive influence on the uraniumhexachloride. Also the reduced pressure facilitates the sublimation and prevents formation of the liquid phase.

When such a charge is treated in the apparatus, UCla is driven off in vapor form and UCl4 remains as a residue. The UCls is condensed in crystalline form on the spiral 26. Therefore, there is obtained substantially simultaneous conversion or separation and crystallization. By means of the boat construction and charge supporting shelves of the present invention the speed of volatilization and acceleration of the conversion or separation of UCls to UCls and UC14 are facilitated.

In a similar manner other materials susceptible of sublimation may be rapidly volatilized and processed by utilizing apparatus constructed such as described above. Although the charge boat has been shown as heated by an electric furnace, it may be heated by gas heat or other suitable means. Other changes will be apparent.

It-is to be understood that all matter contained in the above description and examples are to be interpreted asillustrative and'not limitative of the scope of this invention, and it is intended to claim the presentinvention as broadly as possible in view of the prior art.

I claim:

1. A sublimation apparatus comprising a chamber having an elongated heating portion and a condensing portion communicating with said heating portion, an elongated removable substantially closed container positioned within said heating portion, said container having a relatively narrow opening at its top extending along theentire length thereof, and an elongated tray structure removably positioned within said container, saidtray stmcture having a plurality of normally substantially horizontal shelves for supporting portions of a charge to be sublimed in layers in said heating portion, said tray structure including means for pivotally supporting said shelves for rotation about respective axes which parallelthe longitudinal axis of said container, whereby said shelves may be rotated to substantially a vertical position and the tray structure may thereafter be removed through the opening in the top of said container.

2; In asublimation apparatus, an elongated substantially closed container having a relatively narrow opening extending along its entire length at the top thereof, and an elongated tray structure removably positioned within said container, said tray structure having a plurality of normally substantially horizontal shelves for supportingindividual layers of a charge to be sublimed, said tray structure including means for pivotally supporting said shelves for rotation about respective axes which are-parallel to-thelongitudinal axis of said container, whereby said shelves may be collapsed to a vertical position and the tray structure thereafter removed through the opening in the top of said container.

3. In combination, a substantially closed horizontally disposed cylindrical container, said container having an opening extending along its top and parallel to its axis, and an elongated tray structure removably positioned within said container, said tray structure comprising a vertically disposed support frame, a plurality of normally substantially horizontal shelves, and means for pivotally supporting said shelves from said frame for rotation about respective axes which are parallel to the axis of said cylindrical container, each of said shelves having a width which corresponds to the transverse width of said container at the particular location of each shelf.

4. A sublimation apparatus comprising a chamber having an elongated heating portion, an elongated removable substantially closed container positioned within said heating portion, said container having a relatively narrow opening at its top extending along the entire length thereof, and an elongated tray structure removably positioned within said container, said tray structure having a plurality of normally substantially horizontal shelves for supporting individual layers of a charge to be sublimed, said tray structure also including means for pivotally supporting said shelves for rotation about respective axes which are parallel to the longitudinal axis of said container, whereby said shelves may be rotated to a vertical position and the tray structure thereafter removed through the top opening of said container.

5. A sublimation apparatus comprising a chamber having a heating portion and a condensing portion communicating with said heating portion, an elongated removable substantially closed container positioned within said heating portion, said container having a relatively narrow opening extending lengthwise of said container at the top thereof, and an elongated tray structure removably positioned within said container, said tray structure having a plurality of material supporting shelves, said tray structure including means for pivotally supporting said shelves for rotation about respective axes which parallel the longitudinal axis of said container,

whereby said shelves may assume either a substantially horizontal material supporting position or a substantially vertical collapsed position, said tray structure being spaced from that end of said container which is nearest the condenser portion of said chamber.

6. In a sublimation apparatus having a heating chamber, a substantially closed horizontally disposed cylindrical container removably positioned within said chamber, and an elongated tray structure removably positioned within said container, said tray structure comprising a vertically disposed support frame, a plurality of verticaiiy spaced shelves, and hinge means at the inner edges of said shelves for pivotally supporting said shelves from said frame for rotation about respective axes which parallel the axis of said cylindrical container, at least some of said shelves being of suflicient width that their outer edges engage the inner surface of said cylindrical container when said shelves assume a substantially horizontal position.

7. In a sublimation apparatus, in combination, an elongated horizontally disposed substantially closed container, said container having an opening extending lengthwise thereof at its top, and an elongated removable tray structure disposed within said container, said tray structure comprising vertically disposed end members spaced along the length of said container, a plurality of horizontally extending vertically spaced shafts for retaining said end members in spaced relation, a plurality of material supporting shelves, means for pivotally mounting the inner edges of said shelves on said shafts for rotation thereabout, and at least one horizontally disposed transverse supporting member attached to at least one of said end members for engaging the under surface of at least a pair of said shelves for supporting said pair in a substantially horizontal position.

8. In combination, a substantially closed horizontally disposed cylindrical container, said container having an opening extending along its top and parallel to its axis, and an elongated tray structure removably positioned within said container, said tray structure comprising a vertically disposed support frame, a plurality of normally substantially horizontal shelves, and means for pivotally supporting said shelves from said frame for rotation about respective axes which parallel the axis of said cylindrlcal container, whereby said shelves may be rotated to a substantially vertical position so as to etfectively collapse said entire tray structure, said tray structure in said collapsed condition having over-all dimensions smaller than said opening so that it may be removed from said container through said opening.

References Cited in the file of this patent UNlTED STATES PATENTS 870,835 Loew Nov. 12, 1907 964,871 Johnson July 19, 1910 1,304,572 Kluchansky May 27, 1919 1,662,070 Lyford Mar. 13, 1928 1,888,996 McInerny et al Nov. 29, 1932 1,955,272 Carl et al Apr. 17, 1934 2,035,453 Betterton Mar. 31, 1936 2,113,230 Ceccon Apr. 5, 1938 2,258,374 Amati Oct. 7, 1941- 2,289,328 Pechukas July 7, 1942 2,304,463 Maier Dec. 8, 1942

Claims (1)

1. A SUBLIMATION APPARATUS COMPRISING A CHAMBER HAVING AN ELONGATED HEATING PORTION AND A CONDENSING PORTION COMMUNICATING WITH SAID HEATING PORTION, AN ELONGATED REMOVABLE SUBSTANTIALLY CLOSED CONTAINER POSITIONED WITHIN SAID HEATING PORTION, SAID CONTAINER HAVING A RELATIVELY NARROW OPENING AT ITS TOP EXTENDING ALONG THE ENTIRE LENGTH THEREOF, AND AN ELONGATED TRAY STRUCTURE REMOVABLY POSITIONED WITHIN SAID CONTAINER, SAID TRAY STRUCTURE HAVING A PLURALITY OF NORMALLY SUBSTANTIALLY HORIZONTAL SHELVES FOR SUPPORTING PORTIONS OF A CHARGE TO BE SUBLIMED IN LAYERS IN SAID HEATING PORTION, SAID TRAY STRUCTURE INCLUDING MEANS FOR PIVOTALLY SUPPORTING SAID SHELVES FOR ROTATION ABOUT RESPECTIVE AXES WHICH PARALLEL THE LONGITUDINAL AXIS OF SAID CONTAINER, WHEREBY SAID SHELVES MAY BE ROTATED TO SUBSTANTIALLY A VERTICAL POSITION AND THE TRAY STRUCTURE MAY THEREAFTER BE REMOVED THROUGH THE OPENING IN THE TOP OF SAID CONTAINER.

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