Nickel-aluminum Particle With Improved Grindability

Abstract

A water shattered Raney alloy characterized by a readily crushable mechanical structure comprising for the most part loosely agregated lamenae, convoluted and folded to irregularly shaped masses.

Description

The present invention is concerned with Raney metal and, more particularly, with Raney nickel alloy.

It is known that nickel alloys containing nickel in the range of about 25 percent to about 70 percent by weight with the balance being essentially aluminum or other alkali soluble metal can be leached with caustic solutions, e.g., aqueous solutions of sodium hydroxide to provide masses of highly catalytically reactive nickelferrous material. Other catalytically active metals can be produced by essentially the same process. For example, aluminum-rich binary alloys of silver, iron, cobalt, copper as well as more complex alloys, e.g., aluminum-iron-nickel or aluminum-cobalt nickel rich in aluminum can be leached with caustic to give catalytically active metal masses. For purposes of this specification and claims all such alloys will be called "Raney alloys" and the present invention is pertinent to all of them even though particular reference will be with respect to "Raney nickel alloy." The residue after caustic leaching will be identified as "Raney metal" e.g., "Raney nickel."

In industrial use, Raney metal is often required to be in a form of a coating on small particles of Raney metal alloy so that it can be used as a catalyst in either a fixed or a fluid bed. Heretofore Raney nickel has been cast in massive form and has been broken up and ground to a desired particle size. This prior process has two disadvantages. The metals of the Raney alloy can segregate during casting and thus give non-uniformity in the casting. Secondly, substantial power is required to break up and grind the cast alloy.

It is an object of the present invention to provide Raney metal alloy in a form which can immediately be leached to provide a useful catalyst product and which if necessary, can be ground to any required fineness.

Other objects and advantages will become apparent from the following description taken in conjunction with the drawing which depicts the product of the present invention.

Generally speaking the present invention contemplates water-shattered Raney metal alloy having a mechanical structure comprising for the most part loosely agregated laminae (layers) less than about 0.2 centimeters (cm) thick, folded and convoluted to irregularly shaped masses having a high proportion of internal voids in communication with the exterior surfaces and having, in a fraction screened to pass through a 2 cm mesh and to be retained on a 0.3 cm mesh, a tapped bulk density of about 0.3 to about 1.2 grams per cubic centimeter (g/cc). This product is characterized by extreme ease of fragmentation (i.e., it is extremely friable) and by good catalytic activity when leached with aqueous caustics.

In manufacturing the product of the present invention the Raney metal alloy is melted and is poured at a superheat of at least about 50.degree. in centigrade units in a molten stream through an essentially horizontally flowing stream of water. It is essential that the water be flowing at a minimum velocity to shatter the Raney metal alloy because mere quenching from the liquid state is reported to result in a product which is very hard and difficult to break up. Assuming a metal pouring rate of about 1.5 kg/second in a thin stream and a roughly rectangular stream 1.6 cm thick by 6.35 cm wide a minimum water flow rate of 350 liters per minute is necessary to provide the shattered, fragmented structure of the present invention.

Raney metal alloy suitable for use in providing the structure of the present invention advantageously, contains about 25 percent to about 65 percent by weight of catalytic metal from the group of nickel, cobalt, iron, copper, silver and mixtures thereof with the balance apart from impurities, incidental elements and promotors and promotor precursors being aluminum. Normally, it is advantageous to use about equal parts by weight of catalytic metal and aluminum with impurities, incidental elements and promoting ingredients, if any, being limited in total to, at most, about 5 percent by weight of the composition. Table I contains melting point and pouring temperature data as to examples of Raney metal alloy amenable to being produced as the product of the present invention.

TABLE I ______________________________________ Alkali Pouring Example Catalytic % by Sol. % by MP Temp. No. Metal Wt. Met. Wt. (.degree.C) (.degree.C) ______________________________________ 1 Ni 42 Al 58 1080 1200 2 Fe 55 Al 45 1230 1350 3 Co 50 Al 50 1400 1500 4 Ag 35 Al 65 620 750 5 Ni 50 Al 50 1310 1480 6 Ni 60 Al 40 1570 1650 7 Co 40 Si 60 1140 1300 8 Ni 50 Zn* 40 -- 1300 9 Cu 55 Al 45 600 800 ______________________________________ *Alloy includes 10% aluminum

Any of the exemplifying alloys of Table I can be modified by inclusion of catalyst promoters or modifiers. For example, small amounts of alkaline earth metals, e.g., calcium, barium or the like, thorium vanadium, chromium, molybdenum or similar elements known in the metallic or oxidic forms to promote particular catalytic activity can be included in the Raney metal alloys useful as the product of the present invention. Likewise, small amounts of inert metal, e.g., copper in nickel catalysts or nickel in silver catalysts can be used either alone or in combination with promoters to appropriately modify the Raney catalyst produced by leaching the product of the present invention.

In manufacturing the product of the present invention the catalytic metal, e.g., nickel, is melted and the alkali soluble metal, e.g., aluminum is added, due care being taken in view of exothermic reaction of the metals. Alternatively, the alkali soluble metal is melted and the catalytic metal is added and dissolved in the melt. Any modifying ingredient can then be added. The molten alloy is then poured in a thin stream into a flowing stream of water. Using the rectangular, essentially horizontally flowing water stream described hereinbefore and a flow of molten metal of about 1.5 kg/sec a water flow rate of about 850 liters per minute produces excellent product. Slower flow of water is not desirable because under those conditions water is likely to be entrapped in bubble-like particles rendering drying difficult. At water flow rates below about 350 liters per minute effective metal shattering is not readily achieved. The water temperature is not critical, no effect being noticed because of water temperature variation in the range of about 27.degree.C. to about 65.degree.C.

In order to give those skilled in the art a better understanding of the invention the following specific description is given. A 24 kilogram heat of the alloy of Example 5 was made by melting nickel, pouring the molten nickel into a ladle and adding aluminum. The molten alloy was then poured into a preheated tundish which directed the metal stream into a horizontally flowing water stream about 1.6 cm thick by about 6.4 cm wide flowing at a rate of about 750 to about 950 liters per minute. The metal passed through the tundish nozzle at a rate of about 1.5 kilogram/second. Metal temperature was approximately 1,480.degree.C. and the water temperature was about 40.degree.C. The product produced is depicted in the drawing which shows a water fragmented, highly friable alloy of high surface area of low bulk density. The individual particles of the alloy are composed essentially of laminae convoluted and folded to provide a high specific surface area. Upon leaching with aqueous alkali, the Raney metal produced from the Raney metal alloy product of the present invention exhibits high catalytic activity for hydrogenation and other reactions. The product is also readily ground to whatever size is required.

Five samples of the water-shattered Raney metal alloy of the present invention screened to pass through a 3/4 inch (about 1.9 cm) mesh screen with about 30 percent to 80 percent of the material passing through a 1/4 inch (about 0.635 cm) mesh screen exhibited tapped bulk densities of about 0.7 to 1.0 g/cc. A relatively coarse fraction passing through a 3/4 inch mesh screen and retained on a 1/2 inch (about 1.27 cm) mesh screen exhibited a tapped bulk density of about 0.6 g/cc whereas a fraction passing through a 1/4 inch mesh screen gave a tapped bulk density of 1.0 Raney catalyst made by leaching Raney metal alloy of the present invention with caustic was tested for activity in the hydrogenation of 2, 4-dinitrotoluene and was found to have commercially satisfactory activity.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

Claims

I claim:

1. A Raney metal alloy product comprising water shattered particles each consisting essentially of thin, convoluted and folded laminae having internal voids in communication with the particle surface said particles being characterized by a tapped bulk density of about 0.3 to about 1.2 grams per cubic centimeter "and consisting of about 25 percent to about 65 percent by weight of a catalytic metal from the group consisting of iron, nickel, cobalt copper, silver and mixtures thereof with the balance, apart from impurities, incidental elements and promoting ingredients, being an alkali-soluble metal selected from the group consisting of aluminum, zinc, silicon and mixtures thereof".

2. A Raney metal alloy product as in claim 1 wherein the alkali-soluble metal is aluminum.

3. A Raney metal alloy product as in claim 1 wherein the catalytic metal is nickel.

4. A Raney metal alloy product as in claim 1 wherein the alloy contains about 50 percent by weight of nickel and about 50 percent by weight of aluminum.