Patented Mar. 12, 1946 2,396.465 PATENT OFFICE

PREPARATION OF SODUMARSENTE Erroll Hay Karr, Tacoma, Wash, assignor to The Pennsylvania Manufacturing Company, Philadelphia, Pa, a corporation of Pennsyl vania No Drawing. Application October 12, 1943, Serial No. 506,00 3 Claims. (C. 23-53) This invention relates to the production of from hydroxide and high arsenic content water soluble, alkali metal without the necessity of using arsenites, and more particularly, it relates to an the alkali metal hydroxide in powder form. improved method of causing a controlled reac Another object of the invention is to provide tion between an alkali metal hydroxide and a cheap and easily performed process for the arsenic trioxide to obtain a granular product in preparation of alkali metal arsenites from con a one-step operation. centrated solutions of caustic alkali and pow It is known that can be dered arsenic trioxide in standard mixing equip prepared by mixing together powdered Solid ment. caustic soda and arsenic in a heap and O An additional object of the invention is to pro initiating the reaction by adding a small quan vide a process for obtaining alkali metal arsenites tity of water. Ullmann's Encyclopedia der Techn. in granular form from concentrated solutions of Chemie., volume I, page 588. This method will caustic alkali and powdered arsenic trioxide. yield a solid material but it is attended by sev A further object of the invention is to provide eral disadvantages. 5 a process for the preparation of granular alkali . Preparing solid sub-divided caustic alkali re metal arsenites, e.g. Sodium arsenite, by the inter quires special pulverizing equipment since such action of concentrated Solutions of caustic alkei alkalies as sodium or potassium hydroxides read and powdered arsenic trioxide with substantial ily absorb moisture from the atmosphere and in elimination of dust formation through avoiding dust form are extremely irritating. Mixing of 20 dry mixing of ingredients and in addition, safe solid sub-divided caustic alkali with powdered guarding against insufficient or over-violent re arsenic trioxide causes loss of material as an actions by bringing the ingredients together un irritating and poisonous dust. A dry mixture of der specified conditions. this kind can be caused to react in either two A still further object of the invention is to pro ways-by applying heat or water. To apply 25 vide a process which will yield a dry, water heat to the dry mixture of arsenic trioxide and soluble, granular alkali metal arsenite product sub-divided alkali causes a violent and Sudden containing a high percentage of trivalent arsenic reaction which in the case of producing high and having a low water content. arsenic content alkali metal arsenites leaves some Another object of the invention is to provide unreacted arsenic trioxide. Lack of control in 30 a process wherein prolonged digestion of arsenic causing the vigorous reaction to spread intimate trioxide in dilute alkali metal hydroxides is ly through the dry mass is a drawback and dur avoided with a resultant saving of considerable ing such violent eruption some of the dry mix heat ordinarily required to form the alkali metal ture is forced off as a fine dust. To cause a re arsenite and to evaporate the excess water pres action between the alkali and arsenic trioxide 35 ent to form a dry solid. in a heap by the addition of water yields a prod Other objects and advantages will be apparent uct which is not uniform throughout its mass from a study of this specification and claims. and which will either contain too much or too This invention is based upon the concept that little water, yielding anywhere from a thick the reaction between caustic alkali and arsenic syrupy or semi-solid substance to a hard cement 40 trioxide should take place in the shortest possible like mass on cooling. time in the presence of a quantity of Water So The product, of the prior art, is obtained in a limited that the reaction heat accumulated will variety of forms, depending upon the quantity drive of sufficient water to enable the formation of water added to the dry mixture of alkali and of a completely-reacted, granular material, in arsenic trioxide to initiate the reaction, the size 45 the mixer, in a one-step operation. . of the mixture heap, the temperature of the Sur Since the alkali metal arsenite which is most rounding atmosphere, etc. Since additional commonly employed is sodium arsenite, the in water is formed during the reaction, any Solid vention will be described in connection with its mass obtained will usually contain Sufficient preparation. Water to render it sticky and difficult to handle. 50 According to the invention a weighed amount Even if this material is first heated, it is still of arsenic trioxide is uniformly distributed in necessary to crush it to produce a granular the bottom of a mixer equipped with a Suitable product. agitator. A corresponding amount of a hot con An object of the invention . is to provide a centrated solution of is then method of preparing high arsenic content alkali SS introduced into the mixer on top of the arsenic 2 2,896,465 trioxide. The hot sodium hydroxide solution will agitator (shaft turns 4 R. P. M.) was started lie quietly on the arsenic trioxide if undisturbed. and a vigorous reaction followed which sub To cause the reaction, the agitator blades are Set sided in about 20 seconds. A damp, granular into motion when a vigorous reaction Occurs. mass, containing about 10% of water, was ob The heat of the reaction expels a Substantial tained. part of the total water present, including water The damp, granular substance was dried by formed by the reaction. The vigorous reaction passing a current of hot gases from an oil burner takes about 15 to 30 seconds to subside, and after into the mixer for a of 60 minutes, with about 5 to 10 minutes of continued agitation, a the agitators in Operation. The temperature of granular product is obtained. O the hot gases at the injection point varied be The fact that the hot sodium hydroxide solu tween 200 C. and 250 C. The dried substance tion will lie quietly, on the arsenic trioxide, until obtained contained 2%-3% of water and on grind all of it has been added and the layers disturbed, ing in a suitable mill, produced a white powder. is an important feature of the invention since it Iaboratory tests showed that the powdered allows the reaction to be started Suddenly after 15 product contained not less than 80 percent of all the necessary quantities of the reactants have AS2O3 as arsenite in water-soluble form. been brought together, resulting in Simultaneous Eacample 2 reaction throughout the entire mass with liber ation of Sufficient heat to expel a quantity of The same procedure, as described in Example water such that a granular material will be 20 l, was employed to cause the reaction between formed. 200 pounds of white arsenic trioxide and 65 The quantity of Water present during the re pounds of Sodium hydroxide in 25 pounds of action is an important factor. Sufficient water water. should be present to bring about a controllable, The dry powdered product obtained contained vigorous reaction. With low quantities of water, 25 not less than 76% of As2O3 as arsenite in the approaching anhydrous molten caustic Soda, the water-soluble form. This product was quickly reaction is difficult to control and a uniform re Soluble in water and gave clear, amber solu action throughout the mass is difficult to obtain. tions, free from any noticeable amount of in At the same time, the quantity of water em solubles. ployed is So limited that the heat of reaction 30 The essence of the invention is that the quan will expel sufficient Water vapor to yield a gran tity of water is so limited and the reactants are ular product. So brought into presence of each other that a Control of the quantity of water added will de Sudden evolution of heat is caused to occur; thus termine the degree of rapidity and extent of re yielding a Solid, granular product in a one-step action at various temperatures and, therefore, 35 Operation, avoiding cumbersome, lengthy, and the quantity of heat liberated. The Sodium hy expensive evaporation with the subsequent neces droxide solutions employed will contain not more Sary crushing and handling operations. than about 40% of water and usually not more I claim: than about 30% of water will be present, in the i. A process for the preparation of a granular, sodium hydroxide solution employed, when a dry 40 Sodium arsenite product by the interaction of granular product is desired. As stated, as an Sodium hydroxide and arsenic trioxide which hydrous molten Sodium hydroxide is approached, comprises placing arsenic trioxide into a mixing the violence of the reaction and the difficulty of Vessel; then adding a preheated concentrated controlling it increases, and for this reason, it solution of Sodium hydroxide to said arsenic tri is preferred to employ solutions having a con oxide, in Said mixer, in a proportion such that centration within the range of about 60% to the molecular ratio of Na2O to As2O3 of the about 80% NaOH. final mixture will be from 0.8:1 to 1:2; then The temperature of the sodium hydroxide em Setting said mixer into motion and continuing ployed will be about 175° C. although somewhat the mixing of the mixer contents to produce a higher temperatures may be employed. The 50 Solid material in granular form. violence of the reaction will increase With in 2. The process of claim 1 wherein the con crease in temperature. A temperature in the Centration of the Sodium hydroxide Solution lies range of about 165° C. to about 195° C. is pre- . in the range of from about 60% to about 80% ferred, but a slightly higher temperature, say up by weight; and wherein the sodium hydroxide to about 230 C., can be employed. 5 5 Solution is preheated to a temperature within In general, the concentration and temperature the range of from 165° C. to 230° C. of the Sodium hydroxide Solution added will be 3. A process for the preparation of a high selected so that the quantity of water added will arsenic containing water soluble, granular sodium not exceed the quantity that can be expelled by arsenite product by the interaction of sodium hy the heat of reaction. 60 droxide and arsenic trioxide, which comprises The invention is particularly adapted to the placing arsenic trioxide into a mixing vessel; then preparation of Sodium arsenites having a molec adding a preheated approximately 70% sodium ular ratio of Na2O to AS2O3 of from about 0.8:1 hydroxide Solution to said arsenic trioxide in said to about 1:2. mixer in a proportion such that the molecular 65 ratio of Na2O to As2O3 in the final mixture will The following examples will serve to more fully be from 0.8:1 to 1:2; the temperature of the illustrate the invention: sodium hydroxide solution being within the range Eacample 1 of 175 C-195 C.; and then setting said mixer 300 pounds of white arsenic trioxide (99%) into motion and continuing the mixing of the were placed in the bottom of a mixer (of the 70 mixer contents to produce a solid material in type used for mixing mortar, equipped with a granular form. ventilating hood). A hot solution, consisting of ERROL HAY. KARR. 80 pounds of Sodium hydroxide and 34 pounds of Water, Was quickly added to the mixer. The