Chemistry of inorganic compounds – Nitrogen or compound thereof – Oxygen containing
Reexamination Certificate
2000-11-29
2002-10-22
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Oxygen containing
Reexamination Certificate
active
06468494
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to process for preparing metal nitrates. More particularly, the invention relates to a process for preparing metal nitrates from the corresponding metal wherein the metal is silver, cadmium, bismuth or one of the metals of atomic numbers 24-30.
BACKGROUND OF THE INVENTION
Metal catalysts, such as nickel and cobalt catalysts, are commercially prepared from the corresponding metal nitrate. Aqueous metal nitrate solutions have been prepared in the art by dissolving the metal in nitric acid. When the metal is reacted with nitric acid, considerable amounts of ammonium nitrate are formed as a contaminant as a result of uncontrollable side reactions. When metal nitrate solutions containing significant amounts of ammonium nitrate are utilized to form metal catalysts, the ammonium nitrate must be separated prior to use of the metal nitrate by means of complex and expensive purification processes, or the contaminated metal nitrate is utilized in the catalyst preparation requiring the discharge of large amounts of ammonia in the waste system.
One method for avoiding the formation of ammonium nitrate involves utilization of a metal oxide or metal carbonate as the starting material rather than the metal. Reaction of nitric acid with metal oxides or metal carbonates produces metal nitrate solutions which are free of ammonium nitrate. However, the starting materials, namely, metal oxides and metal carbonates are generally substantially more expensive than the free metal, and also generally of lower purity than a metal obtained for example, by electrolytic deposition or by decomposition of a metal carbonyl.
When nitric acid is reacted with a metal such as nickel, at least five competing reactions can occur:
Ni+4HNO
3
→Ni(NO
3
)
2
+2NO
2
+2H
2
O (1)
3Ni+8HNO
3
→3Ni(NO
3
)
2
+2NO+4H
2
O (2)
4Ni+1OHNO
3
→4Ni(NO
3
)
2
+N
2
O+5H
2
O (3)
4Ni+1OHNO
3
→4Ni(NO
3
)
2
+NH
4
NO
3
+3H
2
O (4)
5Ni+12HNO
3
→5Ni(NO
3
)
2
+N
2
+6H
2
O (5)
As can be seen from the above equations, in addition to the desired nickel nitrate, ammonium nitrate and various nitrogen oxides are formed in the reaction. However, the presence of the nitrogen oxides is not as significant a problem as the presence of ammonium nitrate. Thus, it is desirous to develop a procedure for preparing metal nitrates from the metal and nitric acid which suppresses or significantly reduces the extent of reaction 4.
A process for preparing nickel nitrate from nickel and nitric acid is described in the Russian Journal of Inorganic Chemistry 1959, 11, 1122. The authors recommend adding 30% hydrogen peroxide to the reaction mixture. Based upon the ammonium nitrate, at least stoichiometric amounts of hydrogen peroxide are required, and significant amounts of hydrogen peroxide are consumed under the reaction conditions due to decomposition.
It has also been suggested in Dorofeeva et al, Khim Prom-st. (Moscow) 1974, (8), 603-6, Chem. Abs. 81, 172286 m (1974) that the formation of ammonium nitrate can be suppressed during the reaction of nickel with nitric acid by adding metallic copper to the nickel to be dissolved or by using copper-containing nickel for the reaction with nitric acid. A disadvantage of this process, however, is that the nickel nitrate solution obtained is contaminated with copper nitrate which must be removed using additional purification steps.
In USSR Patent 126,482, Mar. 1, 1960, a procedure for preparing nickel nitrate is described which involves continuously dissolving metallic nickel in nitric acid containing 700 to 1000 g/l of nickel nitrate hexahydrate. It is suggested that this procedure prevents the formation of undesirable ammonium nitrate and the corrosive NO and NO
2
. The process is automatically regulated by the residual concentration of nitric acid in the final solution which must be no more than 1 gram per liter.
A process for the preparation of aqueous metal nitrate solutions by dissolving the metal and nitric acid is described in U.S. Pat. No. 5,039,502 (Horn et al). The formation of ammonium nitrate is reported to be reduced by adding nitrous acid or a substance which forms nitrous acid to the reaction medium. Generally, the reaction is conducted at elevated pressure, and pressures of from 0.1 to 10 MPa are described as being useful, particularly to prevent decomposition of the nitrous acid. This patent describes the preparation of the nitrates of the elements having the atomic numbers 24 to 28 which are iron, chromium, manganese, cobalt and nickel.
U.S. Pat. No. 4,808,393 describes the process for the manufacture of aqueous ferric nitrate solution. The process is reported to overcome the passivation problem associated with the reaction of nitric acid and iron. The process involves continuously gravity-flowing nitric acid through a bed of pieces of metallic iron at a critical reaction temperature less than the ferric nitrate-to-ferric oxide decomposition temperature, and then recycling the effluent through the bed of iron pieces. The effluent is increasingly enriched in ferric nitrate and depleted in unreacted nitric acid by the recycling.
U.S. Pat. No. 2,581,519 also describes the manufacture of metal nitrate by the reaction of nitric acid with a metal such as silver or bismuth. The reaction takes place in an atmosphere of oxygen or a gas consisting mainly of oxygen which replaces the oxygen used in converting the evolved nitrogen oxides directly to nitric acid. Oxygen is introduced into the reaction vessel to expel all of the air from the vessel.
SUMMARY OF THE INVENTION
The invention relates to a process for preparing metal nitrates from the corresponding metal wherein the metal is selected from silver, cadmium, bismuth and the metals of atomic number 24-30. The process comprises
(A) providing a reactor containing
(a) the metal,
(b) nitric acid, and
(c) water
wherein the initial concentration of the nitric acid in the water in the reactor is from about 50% to about 80% by weight, and the reactor is free of
(1) added fuming nitric acid,
(2) added chromium compounds when the metal is iron, and
(3) added oxygen, and
when the metal is nickel, the reactor contains less than 500 g/l of any added nickel nitrate hexahydrate;
(B) maintaining the temperature within the reactor at a temperature to facilitate the formation of the metal nitrate and to maintain the produced metal nitrate in the molten state;
(C) maintaining the pressure within the reactor at between atmospheric pressure up to about 100 psig; and
(D) recovering the metal nitrate from the reactor, provided that when the metal is iron, any recovered iron nitrate is not recycled.
The process of the present Invention results in the formation of metal nitrates and more particularly aqueous solutions of metal nitrates containing reduced amounts of ammonium nitrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The metal nitrates which can be prepared by the process of the present invention include silver nitrate, cadmium nitrate, bismuth nitrate, and the nitrates of the metals of atomic numbers 24-30 which are chromium nitrate, manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, copper nitrate and zinc nitrate. In one embodiment of the present invention, the metal nitrates are nickel nitrate and cobalt nitrate. It is also possible to utilize mixtures of the above-identified metals. However, if it is desired to prepare a mixture of metal nitrate solutions, it is generally easier to dissolve the metal separately in nitric acid and subsequently to mix the finished metal nitrate solutions in the desired ratio. The metal which is to be reacted with the nitric acid can be in various physical forms such as in powder form or in larger pieces such as cathode plates and broken cathode plates. When the metal is too finely divided, there is the disadvantage of the formation of undesired metal dust, and when the reaction is conducted in the vertical reactor, un
Magdics Alex T.
Nappier Thomas E.
Langel Wayne A.
OM Group, Inc.
Renner Otto Boisselle & Sklar
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