US2734795A

US2734795A - Uozclz

Info

Publication number: US2734795A
Authority: US
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

Unite PROCESS FOR PREPARATION OF CHLOREES F URANIUM No Drawing. Application October 6, 1944, Serial No. 557,544

7 Claims. (Cl. 23-14.5)

This invention relates to the production of chlorides of uranium by reaction of an oxide of uranium with liquid carbon tetrachloride at an elevated temperature. Prior to the present invention it has been recognized that carbon tetrachloride could be reacted with an oxide of uranium to form a chloride of uranium. Michael and Murphy [American Chemical Journal, vol. 44, page 384, (1910)] described experiments in which small amounts of uranium dioxide (U02) uranium tritaoctaoxide (U308), and uranium tn'oxide (U03) and carbon tetrachloride were placed in glass tubes, and the tubes were then sealed and heated to 250 C. for several hours. The products obtained were said to be uranium tetrachloride or uranium pent'achloride, depending upon the uranium oxide subjected to treatment.

It has recently become desirable to obtain large quantities of various uranium chlorides, substantially free from impurities, such as uranium oxychlorides. As no large scale industrial process for producing these uranium chlorides was heretofore known, it became necessary to develop a process for producing these various uranium chlorides in the quantities desired.

In attempting to produce uranium chlorides by the Michael and Murphy teaching, we conducted an experiment wherein a charge of several hundred grams of uranium trioxide was reacted with liquid carbon tetrachloride-in a closed steel bomb. It was found that pressure within the bomb increased slowly with rising temperature until a temperature of about 120 C. was reached. At this temperature the reaction became very vigorous as indicated by a very rapid rise of pressure and temperature. Within afew minutes the pressure increased to about 500 lbs. per square inch, at which point the safety blow-out patch provided in the steel bomb ruptured States Patent In accordance with the present invention, we have found that the chlorides of uranium, particularly uranium tetrachloride and uranium pentachloride, may be prepared in high yield and of good purity by reacting an oxide of uranium, such as uranium dioxide, uranium tritaoctaoxide, and uranium trioxide, etc. with liquid carbon tetrachloride at an elevated temperature, and under controlled conditions. While the process may be carried out at atmospheric pressure, it is preferable to conduct the process at superatmospheric pressure in order to decrease the time required to Obtain a. complete reaction. The controlled conditions under which the process must be maintained, in order to obtain the desired products, are hereinafter more fully described.

The term controlled conditions as used in the specification and claims is defined to mean the control of temperature and pressure as Well as reaction rate, particularly during that part of the reaction during which heat is so rapidly evolved that temperature and pressure reach such high values as to endanger the yield of material or the security of the reaction vessel unless suitable controls are provided.

The following examples are given for purpose of illustrating various specific embodiments of the invention. It will be understood that these examples are given by way of illustration and not by way of limitation. All parts are given by Weight unless otherwise specified. The pressure value as given in the examples is in pounds per square inch gauge unless otherwise specified.

EXAMPLE 1 Three hundred parts of uranium trioxide, parts of uranium pentachloride, and 2890 parts of dry carbon tetrachloride were charged into a stainless steel autoclave equipped with an agitator. The autoclave was closed, and thereaction mixture heated to a temperature of about C. during a period of approximately two hours. The reaction initiated at about this temperature and during the subsequent period of about forty minutes, the temperature increased to about C. principally as a result of the liberated heat of reaction. Then the reaction mixture was heated to about C. with the aid of external heat over a period of about thirty minutes. Finally, the temperature of the reaction mixture was held in the range of about 155 C. to C. with the aid of external heat for a period of about one hour. During the last twenty minutes of the final period, the pres.

and a substantial portion of the reaction mixture was lost. The'portion which remained in the bomb was a hard, dense cake consisting of unreacted uranium oxide, uranium oxychlorides and uranium chlorides.

Further experiments were conducted whereby a charge of several hundred grams of uranium trioxide was reacted with liquid carbon tetrachloride in a steel bomb. The temperature was raised at a slower rate than in the previous experiment, in order to control the initial stages of the reaction. By so doing, a final temperature of about 160 C. was obtained without building up pressure sufiicient to rupture the safety blow-out patch. The product obtained was examined and found to consist of a minor portion of uranium pentachloride in the form of a layer of crystals, on top of the major portion of a hard, dense cake comprised of uranium oxychlorides, unreacted uranium oxide, and uranium chloride.

It is therefore an object of the present invention to provide an'improved process suitable for producing uranium chlorides in high yield and of good purity on a large industrial scale, particularly uranium tetrachloride (UCl4), and uranium pentachloride (UCls) by the reaction of an oxide of uranium with liquid carbon tetrachloride;

sure in the reaction vessel was substantially constant, indicating the completion ofthe reaction. The reaction mixture was continuously agitated at a rate sufficientto prevent any caking of the components during the re-' action period. By heating in the aforementioned manner, the final temperature of 160 C. was obtained without building up a pressure sufficient to rupture the safety blow-out patch in the autoclave. At .the end of the reaction period, heating was discontinued and the vent valve was opened and carbon tetrachloride vaporized from the reaction mixture. When the reaction mixture cooled to about 80 C. heating was instituted to maintain the reaction mixture at this temperature until sub stantially all of the carbon tetrachloride present in the reaction mixture was vaporized. The last traces of carbon tetrachloride were removed by further heating, after connecting the reactor through a suitable condenser to a vacuum pump and reducing the pressure to the order of a few centimeters of mercury. When the last traces of carbon tetrachloride and any remaining by-product gases were removed, the vacuum was broken by admitting sufficient dry air to the reaction vessel to restore atmospheric pressure. The reactor was then cooled and 462 parts of product was recovered. The product constituted uranium pentachloride of good purity.

Twelve hundred parts of uranium trioxide, 200 parts of uranium pentachloride, and 5580 parts of carbon tetrachloride were charged into a stainless steel autoclave equipped with an agitator. The autoclave was closed, and the reaction mixture heated to a temperature of about 110 C. during a period of approximately two hours. The reaction initiated at about this temperature and during the subsequent one hour, the temperature increased to about 130 C. principally as a result of the liberated heat of reaction. Then the reaction mixture was heated to about 160 C. with the aid of external heat over a period of about one hour. Finally, the temperature of the reaction mixture was held in the range of about 155 C. to 160 C. with the aid of external heat for a period of about one hour. During the final period, the pressure in the reaction vessel was substantially constant, indicating the completion of the reaction. The reaction mixture was continuously agitated at a rate sufiicient to prevent any caking of the components during the reaction period. By heating in the aforementioned manner, the final temperature of 160 C. was obtained without building up a pressure sufficient to rupture the safety blow-up patch in the autoclave. At the end of the reaction period, heating was discontinued and the product recovered according to the method of Example 1. The product was composed of 1579 parts of uranium pentachloride of good purity.

EXAMPLE 3 Two hundred and fifty parts of uranium tritaoctaoxide, 35 parts of uranium pentachloride and 1600 parts of carbon tetrachloride were charged into a stainless steel autoclave equipped with an agitator. The autoclave was closed and the reaction mixture was heated to 110 C. at which temperature the reaction initiated, as is shown in the data in Table I. The temperature rose during the next fifteen minutes to 160 C., partially through evolution of heat of reaction, and partially by application of external heat. The temperature of the reaction mixture was then maintained at 160 C. for fifteen minutes. The reaction mixture was continuously agitated at a rate sufficient to prevent any caking of the components during the reaction period. The product was recovered according to the method of Example 1. This product consisted of 98.8 percent uranium pentachloride and 1.2 percent uranium tetrachloride. The time, temperature and prtelssure relationship are shown in detail in the following ta e:

Table l Temperar m 0 Pressure,

lbs./sq. in. Remarks Pressure rising too rapidly to read.

EXAMPLE 4 Fifteen hundreds parts of uranium trioxide, 200 parts of uranium pentachloride and 6000 parts of carbon tetrachloride were charged into a stainless steel autoclave equipped with an agitator. The autoclave was closed and by means of external heat the temperature of the reaction mixture was rapidly raised to about 120 C. At this temperature the reaction initiated and subsequently the temperature increased very rapidly to about 155 C. 160 C. The temperature of the reaction mixture was maintained in the range of about 155 C. to 165 C. for a period of approximately two hours, and during this period the by-product gases, such as chlorine and'phosgene were purged as produced. Finally, the temperature of the reaction mixture was raised to about 180 C.

and maintained at this temperature by means of external heating for a period of approximately fifteen minutes. Purging was continued during this final period until the vapor evolved was substantially free of by-product gases. The reaction mixture was continuously agitated to prevent any caking of the components during the reaction period. The product was recovered according to the method of Example 1. The product constituted uranium tetrachloride of good purity.

EXAMPLE 5 Two hundred and fifty parts of uranium tritaoctaoxide, 35 parts of uranium pentachloride and 1600 parts of carbon tetrachloride were charged into a stainless steel autoclave equipped with an agitator. The autoclave was closed and the reaction mixture was heated to about C. at which temperature the reaction initiated, as is shown in the data in Table II. The temperature rose during the next ten minutes to 130 C. at which time the presure was lbs. per square inch. A leak developed at about this time and allowed chlorine and phosgene to escape throughout the remainder of the reaction period. The temperature increased to about 155 C. to 160 C. in fifty minutes and was maintained in this range for an additional hour. The reaction mixture was continuously agitated at a rate suflicient to prevent any caking of the components during the reaction period. The product was recovered according to the method of Example 1. The product consisted of 72 percent uranium tetrachloride and 28 percent uranium pentachloride. The time, temperature and pressure relationship are shown in detail in the following table:

Table II lempera- Pressure Tune ture, C. lbs/sq. iri.

100 17 117 38 120 100 leak apparent. 90 Do. 112 160 123 As evidenced by the foregoing examples, in accordance with the present invention we have been able to form a uranium chloride, such as uranium tetrachloride or uranium pentachloride simply and efl'iciently by heating an oxide of uranium with liquid carbon tetrachloride, preferably in amount substantially in excess of the theoretically required amount, under controlled conditions.

The reaction may be conducted in an autoclave or other essentially gas-tight closed vessel capable of withstanding the pressure developed during the operation. This autoclave or reactor may be constructed of stainless steel, glass lined iron or steel, or other suitably resistant material, and should be provided with an agitator, inlets for introduction of the reactants, an outlet in the bottom of the reactor for removal of the reaction products, and an outlet or outlets in an upper portion of the reactor for removing or venting vapors and gases. If desired, a reflux condenser may be connected to the reactor and operated in the system under pressure in such manner as to recover carbon tetrachloride vapor which passes oif from the reactor during purging, venting or flashing, and return the condensate to the reactor. Ordinarily, however, carbon tetrachloride is used in sufficient excess that this recovery operation is not used. The reactor and condenser may be suitably jacketed and provided with the usual means for circulating heat exchange fluid through the jackets. Safety valves, pressure and temperature indicating and/ or recording devices may be provided if desired.'

The process is preferably conducted in the presence of a substantial excess of carbon tetrachloride. Such excess of carbon tetrachloride enables maintenance of closer temperature control and ensures more uniform operation and complete reaction of the uranium oxide undergoing treatment. Thus, in the operation of this process with small amounts of uranium oxide and with the theoretical amount of carbon tetrachloride required, or with but a slight excess thereof, it has been observed that the time required to complete the reaction is unduly long. If the reaction'is not carried to completion by heating for the required length of time, the final product may contain uranium oxychlorides and unreacted uranium oxide. Also when the amount of carbon tetrachloride used is that theoretically required, or a slight excess, it has been observed that the heat evolved in the reaction often causes the temperature and pressure to rise to excessively high levels. This is particularly true of large scale operations.

In contrast, when an excess of 75 percent by weight or more of carbon tetrachloride is used, the time required to obtain a uranium halide of good purity is materially lessened,'and the difiiculty of maintaining suitable temperature control is substantially decreased. The amount of carbon tetrachloride used is sufiicient to maintain the reaction mixture as an essentially liquid or at least fluid slurry throughout the operation. An excess of about 75 to 80 percent by weight of carbon tetrachloride is therefore preferred. For example, if uranium trioxide is subjected to treatment to produce uranium pentachloride, this excess is computed upon the weight of carbon tetrachloride necessary to convert the oxide to uranium pentachloride in accordance with the equation,

When other uranium oxides, such as uranium tritaoctaoxide or uranium dioxide are used as the uranium oxide to be reacted, the excess of carbon tetrachloride is computed in accordance with a' similar equation assuming that one molecule of carbon tetrachloride is required for each atom of oxygen in the oxide.

While the temperatures employed in this process may vary depending upon the nature of the oxide and the amount of excess carbon tetrachloride comprising the charge, it has been found that temperatures within the range of from about 80 C. to about 200 C., and pref erably from about 100 C. to about 180 C. may conveniently be used. Since the reaction is both exothermic and autocatalytic, We have found that by controlling the ratio of excess of carbon tetrachloride in the charge in accordance with the nature of the oxide employed, the process may be carried out rapidly and efficiently to produce the desired uranium chloride.

It will be noted that in the foregoing examples the process was carried out in the presence of a quantity of extraneous uranium pentachloride, which may be ad vantageously used because of the autocatalytic nature of the reaction. However, if desired, the extraneous uranium pentachloride may be omitted from the reaction mixture, but a considerably longer period of reaction is thereby required.

The extraneous uranium pentachloride may be added to the reaction mixture initially or during the reaction, in solid state or as a solution in carbon tetrachloride. Moreover, uranium pentachloride may be generated in situ in the reactor in a prior operation and left in the reactor to aid reaction of future charges.

The amount of uranium pentachlorideused to promote the reaction is capable of some Variation, being determined at least in part by the degree of rapidity of reaction desired. It is quite common to add one-tenth to two or more moles of uranium pentachloride per mole of uranium trioxide in order to ensure a rapid and eflicient reaction. Lesser quantities may be used, however, and occasionally quantities normally regarded as catalytic, for example one percent or more by weight of the uranium oxide used, are found suitable.

The term extraneous uranium pentachloride is intended to mean uranium pentachloride which is present when reactions of a charge of uranium oxide is initiated and/ or which is added to the charge at any time before or during chlorination, and is intended to distinguish from uranium pentachloride which has been produced by the reaction.

It will be noted from the foregoing examples that the reaction mixture was continuously agitated or stirred during the reaction'period. This agitation is essential, for unless caking is prevented, a satisfactory yield of the desired uranium chloride is not obtained. The speed of agitation may vary, but it must be sufficient to keep the solids of the reaction mixture from caking.

If desired the process may be conducted at atmospheric pressure by refluxing the reaction mixture in excess carbon tetrachloride. Generally speaking, however, the process is controlled so that during the period of reaction the pressure within the reactor increases to substantially above atmospheric, for example up to 200 lbs. per sq. in. In large scale production, in the event glass lined equipment, etc. not adapted to withstand pressures of this magnitude, is used, pressures may be prevented from ris ing above the safe limit by bleeding off gases and vapors from the reactor.

The completion of the reaction will be evidenced by the pressure remaining substantially constant when the temperature is held steady. Generally, however, a reaction period of from one-half to four hours within the above specified temperature range is sufficient when the ratio of carbon tetrachloride to uranium oxide, and uranium pentachloride is controlled.

It will be noted from Example 5 that if uranium tetrachloride is the desired end product, this product may be produced in accordance with the present process by purging of the by-product gases, i. e. chlorine and phosgene, after the initiation of the reaction. As illustrated in Example 4, it may be preferred, in order to ensure the production of a high yield of uraniumtetrachloride of good purity, to increase the length of time and temperature of final heating, with continued purging, until the vapor evolved is substantially free of chlorine.

The chlorination is preferably conducted under substantially anhydrous conditions since excessive amounts of water tend to impair the efficiency of the process.

While in the examples a particular method for recovering the product has been disclosed, the invention is not so limited. The uranium chloride may be recovered by other methods, including extraction, and/or classification with filtration, etc.

The process is particularly applicable to the treatment of uranium tritaoctaoxide and uranium trioxide, especially uranium trioxide of low bulk density, such as may be prepared by heating uranium peroxide. Thus, a very reactive oxide may be obtained, for example by precipitating hydrated uranium peroxide (U0421120) from an aqueous uranyl nitrate solution with hydrogen peroxide, and heating the precipitate at a temperature within the range of C. to 400 C., for example 325 C., until uranium trioxide is obtained. Other oxides or oxychlorides including U02, UOaClz, UOCls, UOCl4, and UOClz may likewise be subjected to treatment as herein described. Moreover, other uranium oxide bearing materials, including uranium oxide ores, and mixtures of uranium oxides with other materials may be employed as starting materials.

From our investigation of the reactions involved in the process, it appears that the process is autocatalytic, insomuch as subsequent to the initiation of the reactions the rate of the reactions accelerates greatly. The addition of extraneous uranium pentachloride materially lessens the time required to obtain a desired end product. While it should be understood that we do not wish to be bound by any particular theory which we may set forth herein, our

experiments indicate that the .reactions involved are many, as illustrated .by. the following equations:

Although the present invention has been described with'particular reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the in vention except insofar as included in the accompanying claims.

We claim:

1. A method of preparing a chloride of uranium which comprises heating an oxide of uranium in liquid phase contact with a substantial excess of liquid carbon tetrachloride in the presence of extraneous initially added uranium pentachlon'de, at an elevated temperature in the range from 80 C. to 200 C., and agitating the reaction mixture during the reaction period at a rate sufficient to prevent caking. I

2. A-method of preparing uranium pentachloride which comprises heating an oxide of uranium in liquid phase contact with a substantial excess of liquid carbon tetrachloride -in the presence of extraneous initially added uranium pentachloride, at an elevated temperature in the range from 80 C. to 200 C., and agitating the reaction mixture during the reaction period at a rate sufficient to prevent caking.

3. A method of preparing uranium pentachloride which comprises heating U0 in liquid phase contact with a substantial excess of liquid carbon tetrachloride in the presence of extraneous initially added uranium pentachloride, at an elevated temperature in the range from 80 C. to 200 C., and agitating the reaction mixture during the reaction period at a rate sufiicient to prevent caking.

4. A method of preparing uranium pentachloride which comprises heating UsOs in liquid phasmeontact with a substantial excess-of liquid carbon. tetrachloride' in-the presence of extraneous initially added uraniumpenta; chloride, at an elevatedtemperature in the range from 80 C. to 200 C.,' agitating the reaction mixture-during the reaction period at a rate suflicient to prevent caking, and recovering uranium pentachloride.

5. A method of preparing uranium tetrachloride which comprises heating an oxide of uranium in liquid phase contact with a substantial excess of liquid carbon tetrachloride in the presence ofextraneous initially added uranium pentachloride, atan elevated temperature-in the, range from 80 C. to 200 C., agitating the reaction mixture during the reaction at a rate sufficient to prevent caking, and purging. the evolved by-product gases during the reaction period.

6. A method of preparing uranium tetrachloride which comprises heating U03 in liquid phase contact with a substantial excess of liquid carbon tetrachloride in the presence of extraneous initially added uranium PC1113? chloride, at an elevated temperature in the range from 80 C. to 200 C., agitating the reaction mixture during the reaction at a rate suflicient to prevent caking, and purging the evolvedby-product gases during the reaction period.

7. A method of preparing uranium tetrachloride which comprises heating U308 in liquid phase contact with a substantial excess of liquid carbon tetrachloride in the presence of extraneous initially added uranium pentachloride, at an elevated temperature in the range from 80 C. to 200 C., agitating the reactionmixture during the reaction at a rate sufficient to prevent caking, purging the evolved by-product gases during the reaction period, and recovering uranium tetrachloride.

References Cited in the file of this patent UNITED STATES PATENTS Britton et a]. Nov. 22, 1932 OTHER REFERENCES

Claims

1. A METHOD OF PREPARING A CHLORIDE OF URANIUM WHICH COMPRISES HEATING AN OXIDE OF URANIUM IN LIQUID PHASE CONTACT WITH A SUBSTANTIAL EXCESS OF LIQUID CARBON TETRACHLORIDE IN THE PRESENCE OF EXTRANEOUSD INITIALLY ADDED URANIUM PENTACHLORIDE, AT AN ELEVATED TEMPERATURE IN THE RANGE FROM 80* C. TO 200* C., AND AGITATING THE REACTION MIXTURE DURING THE REACTION PERIOD AT A RATE SUFFICIENT TO PREVENT CAKING.