Jan.‘ 14, OXIDATION R ROF’MILLER ALKALI METALS Filed Sept. 15, 1942 24 A/ 2/ 2 // ‘ l3f4A1'.L /ME7/A/. ROMAN RMILLER m WWW/J WW Patented Jan. 14, 1947 2,dli,lld 2,414,116 GXIBATIGN 0F ALKALI METALS Roman R. Miller, Washington, D. ‘C. Application September 15, 1942, Serial No. 458,439 5 Claims. (Cl. 252-184) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 This invention relates to the oxidation of alkali metals, and it is particularly directed to a method of preparing potassium tetrcxide and mixed higher oxides of sodium and potassium. It has long been known that various alkali metal higher oxides are capable of giving up oxy— gen to the air, under certain conditions, and also of absorbing carbon dioxide to V9. greater or less extent. Therefore, these materials are used in breathing equipment designed either to protect the user from toxic gases or to purify or regen crate a limited supply of air. Of the various higher oxides the most eilicient from the stand point of ava- e oxygen per weight of the oxide is potassium tetroxide. 2 with oxygen, and in practice it is most con venient to bring the metal vapor into contact with an excess of air (which may be further di luted or enriched with oxygen) so that all of the vapor will be oxidized to the highest oxide. Al though the oxidation may be carried out at re duced or increased pressure there is no advantage in doing so, and the temperature of the metal vapor (before burning) is most conveniently reg ulated by employing different concentrations of an inert gas, such as nitrogen, to carry the vapor into the burning chamber, if operation at the boiling point of the metal is not desired. How ever, in the preferred form of the invention the Sodium peroxide yields 15 metal or mixture of metals (particularly a mix less oxygen but it generally reacts more quickly, ture of sodium and potassium) is vaporized at the in the beginning of the reaction, with moisture in boiling point. the air, possibly due to the formation of hydrates. In order that the invention may be more clear Accordingly it is common practice to use a mix ly understood a typical operation for the oxidation ture of potassium tetrox" "o (K204) and sodium of potassium is described, with reference to the peroxide (NazGz) eoui~ out for air regenera accompanying drawing. tion although the pure potassium tetroxide can In the drawing, potassium metal is melted in a be used alone to yield a greater quantity of oxy heated reservoir Ill and the liquid metal ?ows through a conduit ll, controlled by a valve l2, It has heretofore been difficult to prepare po tassium tetroxide, sodium peroxide and mixtures '' into a furnace iii. The furnace l3 consists of an iron chamber l4 electrically heated by a coil l5 thereof pure form on a commercially practi and covered with heat insulation l6. In the cable sea . Various methods which have been furnace 53 the potassium is vaporized and the include dissolving the alkali metal in vapor removed by passing nitrogen into the cham liquid ammonia and bubbling oxygen through the 30 ber ill through a conduit IT. The nitrogen is presolution, and of course burning the metals and heated in the conduit ll, by means of a heating their alloys in either liquid or solid form in air coil is, in order to prevent condensation of potas or pure oxygen. The former method yields a sium vapor as it is removed for burning. The mixture of nitrogen and potassium vapor passes through an exit tube l9 which is also heated by a coil Ell to prevent condensation of potassium. From the exit tube It the nitrogen and potassium vapor pass into a burning chamber 2| into which the former, but it- is virtually impossible to obtain air is introduced through a conduit 22. As the a pure product. At best a mixture of higher and 40 air and potassium vapor meet the latter imme lower oxides is produced, often including tiny diately ignites and burns to the tetroxide which particles of the unburned metal in the oxide ash. appears as an extremely ?ne, ?u?y powder, most This invention provides a method of preparing of which settles slowly as the nitrogen and un the alkali metal higher oxides substantially free used air pass out of the burning chamber 2|. from lower oxides and metal, simply and eco 45 Some of the tetroxide is so ?nely divided that it nomically, Without the attendant hazards of remains as a smoke, and it is removed as the exit the prior known processes of preparing the pure gases leave the chamber 2| and pass through a material. the higher oxides (e. g. K204 and conventional Cottrell precipitator 23. By scrap fairly pure product but it is very expensive, re quLes rigid control andvpresents an explosion haz" rd in the unavoidable gaseous mixture of am monia and oxygen. The latter method, on the other hand, avoids the hazards and costliness of N .09 may be obtained in pure form or in ad _ ire with one another. ing the sides of the precipitator 23 periodically The method of this 50 the tetroxide particles are caused to fall into a inv ltion is particularly useful for the prepara collecting vessel Ell. The unused air and nitrogen tion of potassium tetroxide. pass out of the system through a vent 25. Other The process of this invention comprises the di collecting means than a Cottrell precipitator may rect oxidation of the alkali metal in vapor form be employed to collect the oxide. A series of col by bringing the metal vapor directly into contact 55 lecting drums or entrainment traps have been 2,414,116 3 successfully used, especially in large scale op eration. It is desirable, although not essential, that the nitrogen used to carry the potassium vapor from the chamber Ill be free from oxygen, for if even small amounts of oxygen are present there is a 4 as the vapors may be led directly from the reac tion zone to the burning chamber. Many other variations will be apparent to those skilled in the art and the invention should not be limited other than as de?ned by the ap pended claims. The invention described herein may be manu~ tendency for potassium tetroxide to build up in factured and used by or for the Government of the exit tube l9 and eventually plug it up. It is the United States of America for governmental essential that both the nitrogen and the air used for burning the potassium be as free as possible 10 purposes without the payment of any royalties thereon or therefor. of moisture, as otherwise the tetroxide will be I claim: contaminated with lower oxides and sometimes 1. Process for making alkali metal higher potassium hydroxide. Similarly these gases oxides which comprises vaporizing the alkali should be free of carbon dioxide if the presence of carbonates in the product is to be avoided. 15 metal, carrying the vapor away from unvaporized metal by means of an inert gas, bringing the Other inert gases may be employed instead of vapor into contact with oxygen and collecting nitrogen, such as helium, but nitrogen is most the alkali metal oxide thus formed. practically obtainable. If desired the nitrogen 2. Process for making alkali metal higher may be dispensed with and pure potassium vapor brought into contact with the air in the burning 20 oxides which comprises vaporizing the alkali metal, carrying the vapor away from unvaporized chamber. . metal by means of a stream of nitrogen, bringing Above about 500° C. the vapor pressures of the the mixture of nitrogen and alkali metal vapor alkali oxides increase fairly rapidly with tem into contact with dry air and collecting the alkali perature and in the case of potassium it reaches 760 millimeters (the boiling point) at 760° C. 25 metal oxide thus formed. 3. Process for making mixed sodium and Therefore it is most practicable to operate the potassium higher oxides which comprises vapor~ furnace l3 at some temperature above about 500° izing a mixture 01" sodium and potassium metals, C., and for large scale operation the most satis factory operating temperature is the boiling point of the alkali metal or mixtures of alkali metals. This is particularly true for mixtures of sodium and potassium. However, the precise operating temperature which is most ei?cient for a given installation depends on a number of engi neering factors, such as furnace size, cost of fuel 35 for heating, etc.,‘ and it is easily determined by carrying the vapor mixture away from un vaporized metal by means of a stream of nitrogen, bringing the vapor mixture and nitrogen into contact with dry air and collecting the mixed oxide thus formed. 4. Process for making potassium tetroxide which comprises vaporizing potassium metal, carrying the vapor away from unvaporized metal by means of a stream of nitrogen, bringing the those skilled in the art. mixture of vapor and nitrogen into contact with Similarly sodium metal may be substituted for dry air and collecting the oxide thus formed. the potassium referred to in the above operation, 5, Process for making sodium peroxide which. and, as already indicated, mixtures or alloys of 40 comprises vaporizing sodium metal, carrying the sodium and potassium may be employed, the vapor away from unvaporized metal by means of composition of which depends on the proportion a stream of nitrogen, bringing the mixture of of potassium and sodium oxides desired in the vapor and nitrogen into contact with dry air and product; The process is particularly adapted for the oxidation of the sodium-potassium vapor 45 collecting the oxide thus formed. mixtures obtained by the decomposition of molten potassium salts by contact with sodium metal, ROMAN R. MILLER.