United States Patent Office Patented Mar
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2,784,061 United States Patent Office Patented Mar. 5, 1957 2 the preparation of the oxides of sodium. The first, direct oxidation of the metal in air or oxygen produces both the 2,784,061 oxide and peroxide, but production of the superoxide PROCESS FOR PRE PARNG ALKAL METAL requires prolonged oxidation by means of gaseous oxygen OXDES AND PEROXDES at high temperatures and pressures. The objection to such procedures is the requirement of metallic sodium George L. Cuaningham, Cleveland Heights, Ohio, assignor which must be produced by an expensive electrolysis. A to Horizons incorporated second proposed method, the dehydration of sodium hy No Drawing. Application December 6, 1954, droxide has not been found to be feasible. A third sug Serial No. 475,843 10 gested method which is disclosed in U. S. Patent 1,961,160, is based on the distillation of dilute sodium amalgams to 3 Claims. (CI. 23-184) produce pure sodium which is then oxidized by means of pure oxygen. it has been found virtually impossible to ob This invention relates to a new and useful process for 5 tain pure sodium by this process because of several opera the preparation of metallic oxides. More particularly it tional obstacles inherent in the patented process. The relates to a process whereby metallic oxides, peroxides method involves the distillation of relatively large amounts and superoxides may be inexpensively prepared in the of metallic mercury per unit of sodium produced. The form of pure compounds. separation is rendered difficult because the vapor pressure Many processes have been suggested for the prepara 20 of mercury decreases in a very marked fashion with rela tion of oxides of the various metals. Generally speaking, tively slight increase in the concentration of the sodium. one common approach involves the direct oxidation of the Thus, in very concentrated amalgams, the vapor pressure metal. An obvious disadvantage of methods based on of mercury is very low and when the temperature is direct oxidation of the metal is that to be commercially raised the vapor pressure of the Sodium approaches that attractive, the metal itself must be available at a reason 25 of the mercury which renders the removal of me ury able price. Another suggested approach is the decompo alone difficult and almost impossible. Accordingly, sition of oxygen containing compounds such as carbonates, sodium and the other alkali metals made in this fashion nitrates, Sulphates, phosphates, oxalates, tartrates and the are contaminated with considerable amounts of mercury, like, either with or without the presence of reducing agents and the method has not found a wide acceptance. such as carbon. Such methods are of limited application, 30 Since the aforementioned patented process discloses and have not been found suitable for the direct prepara that when an amalgam is distilled, two liquid layers are tion of the oxides of most metals. Still another approach obtained, and the published phase diagrams for the alkali involves electrolytic production of the metals followed by metal-mercury systems show no regions of concentrations oxidation of the metal. Still another procedure which has or temperatures where two liquid layers would exist, the 35 inability of the process to produce pure alkali metal is beenamalgams. suggested is the oxidation of relatively dilute apparently inherent therein. One object of my invention is to produce the oxides, I have found a method whereby most oxidic derivatives peroxides or superoxides of various metals by a simple of the alkali metals can be prepared at relatively low process not Subject to the disadvantages present in the temperatures in a relatively simple manner. According prior art. to the method I have invented, a pool of alkali metal 40 amalgam is formed in any convenient manner, in which A more specific object of my invention is to produce the the alkali metal concentration is chosen after consulting oxides, peroxides and Superoxides of some of the alkali the alkali metal-mercury system diagram, so as to be metals by a process which does not employ the alkali higher than the concentration at which a high melting metal, in the form of a pure metal, perse. solid product exists. in the case of sodium, for example, These and other objects are accomplished by a process 45 the Na-Hg system published in Mellor's Treatise on In in which an amalgam is prepared containing the metal organic and Theoretical Chemistry indicates that at about whose oxidic derivative is to be produced and the amal 5% sodium, a compound melting at about 353 C. exists, gam is then oxidized under carefully controlled conditions corresponding to NaHg2. The phase diagrams for the . by direct contact with oxygen or an oxygen containing gas. other alkali metals exhibit a similar configuration, the in a preferred embodiment of my invention a relatively 50 maximum-dystectic-point being shown at about 50 atomic dilute amalgam is obtained by electrolysis of a compound percent for lithium (LiHg), 25 atomic percent for potas of the metal whose oxidic derivative is sought and this sium (KHg3), 33 atomic percent for cesium (CSHg2) and dilute amalgam is added to a reservoir of a more concen 14 atomic percent for rubidium (RbHg6). The pool of trated amalgam which is then oxidized and from which amalgam of the desired concentration is prepared in any the oxide derivative is readily removable. 55 convenient manner. One convenient method is to plunge While the method of my invention is applicable gen pieces of alkali metal, held in an inverted cup, under the erally to the formation of most, although not all, of the surface of a body of mercury, in which the pieces will oxidic derivatives of the metals, it has been found to be readily dissolve. Another method by which the pool of particularly useful for the preparation of oxidic com amalgam may be prepared is by the carefully controlled pounds of the alkali metals. Since the preparation of 60 distillation of dilute amalgams. Whatever the manner sodium oxide, sodium peroxide and sodium superoxide in which it is formed, in accordance with my invention, may be taken to be representative of the practice of my there is fed into the prepared pool of amalgam, either invention, the process will be hereinafter specifically de continuously or intermittently, dilute amalgam formed in scribed with reference to these three compounds, it being a manner well known in the art, and the pool is subjected understood that except for incidental variations in the 65 to a controlled oxidation to effect the formation of the specific process conditions (e. g., higher temperatures, desired alkali metal oxidic product, the rate of oxidation different concentrations, etc.), this description applies with . being controlled so that the amount of alkali metal re equal force and effect to the preparation of oxides, perox acted is approximately equal to the amount of alkali metal ides and superoxides of the other alkali metals generally furnished to the pool in the form of a dilute amalgam. insofar as they are amenable to the described treatments. 70 Sodium amalgam can be produced by any suitable At least three distinct methods have been proposed for method. For example, sodium amalgam is presently 2,784,061 usra 4. made commercially by the electrolysis of a substantially still, by any suitable type of heat exchanger. In this way. saturated solution of sodium chloride at about 90 C., the heat of vaporization of the mercury may be largely using a graphite or platinum ancde and a mercury cathode. recovered. Chlorine and sodium amalgam formed at the anode and The still in which the pool of combined amalgams is cathode respectively, are recovered. In accordance with being distilled also serves as the vessel in which the sodium present practice such a ceil operated at about 4 volts (in or other alkalimetal is oxidized. The oxidation is effected comparison with about 7 volts in a fused sodium chloride by means of a suitable oxidizing agent, preferably air or cell) will have a current efficiency of about 95%. Cor oxygen, which must be carefully added to avoid the oxi rosion of the apparatus is negligible. The cell operates dation of the mercury. Mercury can be distilled at tem with brines which may be relatively impure, and over 95% peratures of about 350° C. in the presence of air without of the sodium chloride in the brine can be converted into any appreciable oxidation of the mercury. In the pres chlorine and Sodium amalgam. Other cells, e. g. a cell ence of even trace amounts of sodium or other alkali employing aqueous sodium hydroxide could be electro metals, mercury under otherwise similar conditions is lyzed whereby oxygen as well as the desired amalgam rapidly oxidized. could be obtained. 5 I have found that in spite of the aforesaid difficulties, The sodium amalgam produced in such cells usialiy the alkali metal in the amalgam may be controllably oxi contains about 0.1% sodium (by weight). At slightly dized to form the oxide, peroxide or, in the case of potas lower efficiencies, amalgams with up to about 0.5% (by sium, cesium or rubidium, the superoxide, by carefully weight) of sodium can be produced. The production of controlling the factors influencing the reaction, particu amalgams with more than 1% sodium is not generally 20 larly the temperature, oxygen partial pressure and alkali practiced because the efficiency of the cell is materially metal concentration. By proper control of these vari reduced. Furthermore, the formation of a product which ables, oxidation of the mercury may be prevented or any is solid at the cell temperature places an upper limit on mercury which may be oxidized, may be decomposed the amount of sodium which the amalgam can contain, as as rapidly as it forms.