US3251756A - Electrolytic process for making phosphine - Google Patents

Description

May 17, 1966 G. T. MILLER Filed March 4, 1963 4 Sheets-Sheet l May 17, 1966 G. T. MILLER ELECTROLYTIC PROCESS FOR MAKING PHOSPHINE 4 Sheets-Sheet 2 Filed March 4, 1963 NQQQQQQQh 3 NQQQQQQQM May 17, 1966 G. T. MILLER ELECTROLYTIC PROCESS FOR MAKING PHOSPHINE 4 Sheets-Sheet 5 Filed March 4, 1963 May 17, 1966 e. T. MILLER ELECTROLYTIC PROCESS FOR MAKING PHOSPHINE 4 Sheets-Sheet 4 Filed March 4, 1963 United States Patent M 3,251,756 ELECTROLYTIC PROCESS FOR MAKING PHOSPI-IINE George T. Miller, Lewiston, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed Mar. 4, 1963, Ser. No. 262,497 4 Claims. (Cl. 204101) This invention relates to an electrolytic cell and a 'process whereby a reactive material in such a cell reacts more efliciently at an electrode, with a product produced there electrolytically, to yield a desired end product.

Electrolytic cells have been utilized to produce phosphine. In such cells, employing phophorus as a reactive material, phosphine is recovered in the catholyte gas. However, after operation for a period of time, the yield of phosphine in the catholyte gas gradually diminishes, due to spongy deposits that form on the surface of the cathode as the reactions in the cell progress. The concentration of phosphine in the catholyte gas decreases as the size of and area covered by these spongy coatings or deposits increase. The spongy coatings appear to be formed by deposits of metallic ions, from either the electrolyte or the phosphorus, usually at or near the cathode.

Although the description of the apparatus of the invention is directed to its preferred embodiment, that of an electrolytic cell which produces phosphine, it is to be understood that the apparatus may also be utilized when a reactive material is to be reacted with a product of electrolysis to produce a desired end product.

In accordance with the invention it has been found that a spongy mass is hindered from forming on the electrode in an electrolytic cell comprising an electrode having a plurality of sharp edges by which the reactive material is caused to wick up the electrode, and an electrolyte from which a product of electrolysis is generated at the electrode, the reactive material being so located as to react with the product of electrolysis in the vicinity of the electrode, a second electrode in operative relationship with the electrode, the electrolyte in operative relationship with the electrode, and second electrode and means for causing an electrical current to flow between the electrode and second electrode through the electrolyte to electrolyze it and produce a material with which the reactive material reacts. Preferably there is also present a diaphragm in between the electrode and second electrode to separate the gases evolved.

The invention and modifications thereof are shown by the accompanying drawings, in which:

FIGURE 1 is a central sectional view in elevation of an electrolytic cell taken along plane 11 of FIGUR-E.2.

FIGURE 2 is a horizontal sectional view taken along plane 22 of FIGURE 1.

FIGURE 3 is an isometric .view of a preferred contact electrode of the invention, with the grooves being exaggerated for clear illustration.

FIGURES 4-12 are isometric views illustrating corresponding modifications in the contact electrode of the invention.

The terms wicking and wicking up are used throughout the description to describe the phenomenon in which molten reactive material, e.g., phosphorus, in contact with the lower portion of a vertical electrode surface rises above the level of the molten pool thereof to form a thin layer on the surface of the electrode.

A description of the drawings is as follows:

Referring to FIGURE 1, there is shown a cell vessel having an anode compartment 12, containing an anode 14, and a cathode compartment 16, containing a contact electrode (cathode) 18 having a plurality of edges 46 and Patented May 17, 1966 grooves 48, as seen in FIGURE 2. A porous diaphragm 20, separates the anode compartment 12 and the cathode compartment 16 and separates the electrolyte into anolyte 17 and catholyte 19 sections. In the cathode compart-ment 16 is reactive material 24, e.g., phophorus, in a liquid state. Diaphragm 20 is covered, coated or protected in such a manner that the side thereof facing the reactive material, where it may otherwise contact that material is coated with a coating, cover or sheath 22 against which the reactive material then does not adhere or wet. This action is evidenced by convex meniscus 21. Ports 2 6 and 28 permit the addition and removal of anolyte 17 from the anode section 12. Ports 30 and 32 permit the'addition and removal of catholyte 19 from the cathode section 16. Port 34 permits the addition and removal of molten phosphorus from cathode section 16'. Suflicient molten yellow phosphorus 24 is added to the cathode compartment 16, to contact the lower edge of the contact electrode 18, thereby permitting wicking up of the molten phosphorus onto the outer surface of the cathode. Anolyte gas discharge port 36 is provided in' the top of the anode section to remove anolyte gas from the electrolytic cell. Catholyte discharge port 38 is provided in the top of cathode section 14 to remove catholyte gas. The level of the anolyte and catholyte in the electrolytic cell is indicated as interface 15.

Anode electrolytical wire connector 40 and cathode electrolytical wire connector 42 are connected to the anode and cathode and to the positive and negative poles, through plugs 41' and 43, respectively, of a source of direct current 44. If desired, a heating source such as a constant temperature hath (not shown in the drawing), may be employed to maintain the catholyte and anolyte at a desired temperature.

Cell vessel 10 may be constructed of material capable of resisting corrosion by the electrolyte and other materials employed in the cell. Typical examples of suitable materials of construction for cell vessel 10 include glass,

glazed ceramics, tantalum, titanium, hard rubber, polyethylene, rigid materials coated with phenol-formaldehyde resin, and the like.

Diaphragm 20 which separates the anode section 12 I from cathode section 16, may be a porous or semipermeable material resistant to the cell contents and capable of maintaining anode and cathode gases separate. Typical examples of suitable materials for use as a diaphragm include porous alundnm, porous porcelain, sintered glass, glass fabric, resin impregnated W001, W001 felt, and diaphragms normally employed in lead storage batteries.

Any solid material having a hydrogen over voltage, as normally measured in the absence of the reactive material, e.g., phosphorus, or any material exceeding the hydrogen over voltage of smooth platinum may be employed as a cathode. Typical cathodic materials include lead, lead mercury, amalgam, cadmium, tin, aluminum, nickel, alloys of nickel, such as Mumetal (an alloy containing 77.2 percent nickel, 4.8 percent copper, 1.5 percent chromium and 14.9 percent iron), Monel, copper, silver, bismuth, and alloys thereof. For examp-ile, lead-tin, lead-bismuth, and tin-bismuth alloys may be employed.

It has been found that when a cathode in a phosphine producing cell is made a contact electrode, in accordance with the invention, the reactive material contacts the cathode more efliciently forming reservoirs of phosphorus disclosed herein and allow a phosphine cell to remain in operation for longer periods of time than previously realized.

FIGURES 4-12 illustrate various modified contact electrodes which may be employed in the practice of the invention. FIGURE 3 illustrates the preferred contact electrode of the invention. The edges 46 and grooves 48 of these electrodes may be formed by machining, pressing, bending, rolling, soldering sheets or rods together, or casting the contact electrode to a desired shape.

FIGURES 3-7 illustrate contact electrodes which have been machine pressed, machined, or cast. FIGURE 8 illustrates a fiat sheet of metal which has been bent into the desired shape to provide sharp edges. FIGURE 9 illustrates a plurality of bars soldered together while FIG- URE 10 illustrates a group of octagonal rods in close proximity to one another held together by known means. FIGURE 11 illustrates a grouping of short cylindrical discs soldered to a base plate. FIGURE 12 illustrates circular orifices in a base plate which provides sharp edges 46. Suitable results may be achieved with a contact electrode having between about 2 and 55 inches of sharp edges per square inch. It is preferred that the contact electrode have between about 4 and 42 inches of sharp edges per square inch, but the cell has been found to operate in an efficient manner when the cathode contains between about 10 and inches of sharp edges per square inch. The spacings between the edges 46 or the width of the base of each groove 48 may be between about A of an inch and A,; of an inch with a preferred width being between about of an inch and A; of an inch, however, optimum results are achieved utilizing between about of an inch and of an inch. Thus the number of grooves per inch on the electrode should be between about eight and thirty-two, with between about ten and twenty grooves per inch. being preferred, but optimum results being obtained utilizing between about fourteen and.

eighteen grooves per inch.

The depth of the groove may vary depending upon the modification utilized. A depth greater than of an inch yields suitable results. When rods or bars are utilized to provide edges, it is the width between each bar that provides reservoirs for phosphorus as seen in FIGURES 9 and 10. However, the preferred range for the depth of the groove, is between about of an inch and 1 inch, with optimum results being obtained when the depth of the groove is between about of an inch and /8 of an inch.

Suitable anode materials include lead, platinum, lead.

peroxide, graphite, and other materials of construction capable of conducting a current and resisting corrosion under the conditions of electrolysis employed, An electrolyte which is non-reactive with molten phosphorus or the reactive material and which is capable of forming hydrogen ions during electrolysis may be employed as a catholyte and anolyte. Typical examples of suitable compounds in aqueous solution, whichmay be employed as electrolyte include hydrochloric acid, sodium chloride, lithium chloride, potassium chloride, sodium sulfate, potassium sulfate, monosodium phosphate, disodium phosphate, acetic acid, ammonium hydroxide, phosphoric acid, sulfuric acid, and mixtures thereof. The concentration of the electrolyte may vary between about five and about 90 percent with a concentration of between about 10 and 75 percent being preferred, and a concentration of between about 5 and about 50 percent yielding optimum results.

Improved results have been obtained when metallic ions are present in the electrolyte in small proportions. For example, ions of metals such as antimony, bismuth, lead, tin, cadmium, mercury, silver, zinc, cobalt, calcium, barium, and mixtures thereof may be employed. The metal ions may be placed in the electrolyte by employing a consumable anode of the desired metal or metalssuch as a lead anode, whereby metal ions are formed in the electrolyte and transferred to the area adjacent to the cathode. Sal-ts or other compounds of the metals such as chloride, phosphates, acetates and the like may be dissolved in the electrolyte if desired. In another embodiment finely divided metal in elemental form is dissolved in the electrolyte. Suflicient metal ion may be added to the electrolyte to provide a metal ion concentration of between about 0.01 and 3.0 percent by weight of the electrolyte, with between about 0.02 percentand 0.5 percent by weight of electrolyte being the preferred range, but between about 0.01 and .5 percent also being a suitable range.

During electrolysis the temperature of the catholyte and anoly-te should be maintained above the melting point of phosphorus (about 44 centigrade), and below the boiling point of the electrolyte. Temperatures between about 60 centigrade and 110. centigrade are satisfactory but optimum yields of phosphine are obtained at temperatures between about 70 centigrade and about centigrade I When an electric current is passed through the cell, molten phosphorus on the surface of the cathode is consumed in the formation of the catholyte gas in the cathode section. The catholyte gas is predominately phosphine but contains some hydrogen. The anolyte gas depends on the over voltages of the anions and the anolyte with reference to the anode material. Thus, for example, the anolyte gas predominates in oxygen if sulfuric acid or phosphoric acid is used with a platinum anode, whereas for the same anode, chlorine predominatesif hydrochloric acid is used as the anolyte. Thus, the co-productionof anionic oxidation products may be carried out in the anode compartment of the cell of this invention without departing from the spirit of the invention.

As phosphorus is consumed on the surface of the cathode to yield phosphine, additional phosphorus passes from the molten pool of reactive material, phosphorus, to the vertical cathodic surface. The current density on the cathode may be controlled so that the grooves between the edges act, as a reservoir for phosphorus. phosphorus is consumed at the part of the reservoir in contact with the electrolyte, it is readily replaced from the extra supply in the reservoir. The consumed phosphorus then being replenished on vthe cathode surface continuously from the molten pool of phosphorus or other reactive material. The cathodic current density may be 'set by the operator and is dependent on which density gives the best results, the celldesign and the construction of the cathode.

The phosphine containing gas produced at the cathode has a relatively high concentration of phosphine, usually more than sixty percent, and it may be as high as ninety percent phosphine by volumeor higher. The catholyte gas is substantially free from other phosphorus hydrides.

In one embodiment of the invention, a lead plate containing machined grooves and a graphite rod are employed as the cathode and anode, respectively. Under these conditions it is found that the wicking effect of the cathode is markedly improved. In carrying out the process of the invention, it was observed that a wicking action occurred at the cathode prior to energizing the cell, that is, the thin layer of molten phosphorus formed on the outer surface of the vertical cathode. above the level of the molten pool of phosphorus before any current was impressed upon this system. As soon as the current was caused to flow, the wicking action became rapid, occurring substantially over the entire surface of the cathode. The thin layer of phosphorus contacting the cathode was maintained continuous over a period of six months without any formation of spongy masses. The rate of the wicking action was faster with some metals than with others, and the thickness of the phosphorus layer on the metal surfaces was thicker on some metals than on others. Although in the-description of the invention a plate-like cathode is illustrated, it is to be understood that grooved Thus, as

rods or cylindrical shape cathodes are also within the scope of the invention.

Suitable reactive materials which may be utilized in the practice of this invention are sulfur; the alkali metals, e.g., potassium, sodium, lithium, rubidium, and cesium; the alkaline earth metals, e.g., beryllium, calcium, strontium, barium, as well as magnesium, and germanium; and lead.

The diaphragm may or may not be coated as illustrated in FIGURE 1. However, in the preferred embodiment of the invention, whereas phosphorus is the reactive material, a coating of glass fabric gives beneficial results.

The following examples are presented to further define the invention without any intent of being limited thereby. All parts are by weight and all temperatures are in degrees centigrade unless otherm'se specified.

Example 1 A lead cathode was placed in an electrolytic cell. This lead plate had protrusions covering its surface which measured x of an inch across its top and was A; of an inch deep. The distance between each protrusion was of an inch. These protrusions were on only one surface of the lead plate and were formed by amultiplicity of longitudinal and horizontal grooves as illustrated in FIGURE 4. A- graphite anode surrounded by a porcelain diaphragm was also placed in the cell. An electrolyte of six percent hydrochloric acid plus 0.05 percent lead was utilized as the anolyte and the catholyte electrolyte. This electrolyte mixture was maintained at 85 centigrade. Molten yellow phosphorus was admitted to the cell so that the bottom of the contact electrode (cathode) was in contact with the phosphorus. It was observed that the 'phosphorus climbed up the cathode and completely cov- Example 2 A porous lead plate having smooth surfaces on both sides was'utilized as the cathode in the electrolytic cell. In all other respects the apparatus was similar to that of Example 1, except five percent hydrochloric acid containing 1.5 grams per liter of lead chloride was utilized as the electrolyte. A cathodic current density of 24 amperes per square foot was maintained for a period of 17 days. The cell was shut down when the spongy deposits, which appeared on the surface of the cathode, began to decrease the efiiciency of the cell. During the operation of this cell the cathode gas was found to contain between about 85 to 86 percent phosphine.

Example 3 The apparatus of Example 1 was again utilized, except that the contact electrode (cathode) contained protrusions on both sides A of an inch square x /s of an inch deep arranged so as to form grooves ,4 of an inch wide and an electrolyte comprisingten percent hydrochloric acid and 0.04 percent lead was utilized. The current density was maintained at 32 amperes per square foot. After sixty-six days of continuous operation the cell was shut down and the cathode examined.

The cathode showed no evidence of a spongy mass or failure of the phosphorus layer. During the operation of the cell from 82 to 86 percent phosphine was found in the phosphine gas.

Example 4 The electrolytic cell of Example 1 was again utilized.

' inch deep throughout its length. The grooves were of an inch wide. A current density of 30 amperes per square foot was applied to the cathode for a period of 21 days. After this period of time no failure of the phosphorus film was experienced. On a visual inspection of the cathode no spongy masses were found. During the operation of the cell between and 92 percent of the cathode gas was phosphine.

It will be recognized by those skilled in the art that various modifications within the invention are possible, some of which are referred to above. Therefore, the above description should not be limiting, except as defined by the appended claims.

What is claimed is:

1. process for preparing phosphine which comprises contactin phosphorus with a cathode containing a plurality of sharp-edged longitudinal grooves on its surface, whereby the phosphorus climbs up and substantially contacts the entire surface of the cathode, and maintaining an electrical current through said cathode in the'presence of an anode, a diaphragm and an electrolyte so that phosphine is produced, and recovering phosphine from the catholyte gas evolved.

2. A process in accordance with claim 1 wherein the cathode contains between about eight and thirty-two grooves per inch of cathode surface.

3. A process in accordance with claim 1 wherein the cathode contains a series of protrusions.

4. A process in accordance with claim 1 wherein the cathode contains a series of horizontal and vertical grooves.

References Cited by the Examiner UNITED STATES PATENTS 1,771,091 7/ 1930 Lawaczeck 204283 2,025,674 12/1935 Schweitzer 204289 3,085,967 4/1963 Motock 204284 3,109,788 11/1963 Miller et al. 204-101 3,109,791 11/1963 Gordon 204101 JOHN H. MACK, Primary Examiner. MURRAY A. TILLMAN, Examiner.

L. G. WISE, H. M. FLOURNOY, Assistant Examiners.

Claims (1)

1. A PROCESS FOR PREPARING PHOSPHINE WHICH COMPRISES CONTACTING PHOSPHORUS WITH A CATHODE CONTAINING A PLURALITY OF SHARP-EDGED LONGITUDINAL GROOVES ON ITS SURFACE, WHEREBY THE PHOSPHORUS CLIMBS UP AND SUBSTANTIALLY CONTACTS THE ENTIRE SURFACE OF THE CATHODE, AND MAINTAINING AN ELECTRICAL CURRENT THROUGH SAID CATHODE IN THE PRESENCE OF AN ANODE, A DIAPHRAGM AND AN ELECTROLYTE SO THAT PHOSPHINE IS PRODUCED, AND RECOVERING PHOSPHINE FROM THE CATHOLYTE GAS EVOLVED.

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