JP2000247632A - Production of ammonia using metal hydride as hydrogen source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To synthesize ammonia under mild conditions by supplying hydrogen in the form of atoms of high activity to a reaction chamber side from a gaseous hydrogen atmosphere and reacting the same with the active nitrogen dissociatively adsorbed on a catalyst deposited on a reaction chamber side diaphragm surface by using a metal hydride as a hydrogen permeable membrane. SOLUTION: The hydrogen in the form of atom of high activity on the reaction chamber side is stationarily supplied from the gaseous hydrogen atmosphere (1.5 atm) on the one side of the diaphragm by using the metal hydride as the hydrogen permeable membrane (diaphragm). The Ru/MnO2 catalyst 2 is deposited on the reaction chamber side diaphragm surface. The active nitrogen subjected to the dissociation adsorption by passing the gaseous nitrogen of ordinary pressure on this Ru/MnO2 catalyst 2 and the hydrogen in the form of atom supplied from the diaphragm are reacted to synthesize the ammonia. The ammonia synthesis is possible even if the reaction temperature is low temperature near room temperature. The ammonia may be synthesized under the reaction conditions milder than the method of around 500 deg.C and about 200 atm in pressure which is heretofore industrially practiced. There is no need for a specific apparatus for high pressure resistance and high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the synthesis of ammonia, and more particularly to the use of a metal hydride as a hydrogen permeable membrane (separation membrane) to provide an active hydrogen supply source, or the use of a metal hydride itself. As a source of active atomic hydrogen, the reaction between the supplied active hydrogen and the active nitrogen dissociated and adsorbed on the catalyst supported on one side of the hydrogen permeable membrane or on the surface of the metal hydride powder, The present invention relates to a method for producing ammonia under much milder reaction conditions than the method.

[0002]

2. Description of the Related Art Conventionally, ammonia synthesis has been carried out on a large scale on an industrial level by the Harvard method. This method synthesizes ammonia from nitrogen and hydrogen, and is operated under a high temperature and a high pressure of about 500 ° C. and a pressure of about 200 atm using an iron-based ternary catalyst. Further, as an improvement of the above method, there are the Fauser method, the Uhde method, the Tokyo Industrial Laboratory method, and the like, which are slightly different from the Harbor method.

[0003]

In the current ammonia synthesis at a plant level, severe reaction conditions of high temperature and high pressure are required even if an iron-based ternary catalyst is used due to inert nitrogen molecules, and a great deal of reaction is required. Energy is consumed. Furthermore, expensive equipment that can withstand these harsh reaction conditions is required.

[0004]

In order to solve the above-mentioned problems, there is a method of activating hydrogen molecules in addition to the use of a catalyst for promoting the dissociative adsorption of nitrogen and hydrogen molecules.
In the present invention, by using the hydrogen permeable diaphragm of metal hydride as a constant source of atomic hydrogen, or by using the metal hydride itself as an atomic hydrogen source, these released active hydrogen and the reaction chamber The reaction with the active nitrogen dissociated and adsorbed on the catalyst layer supported on the surface of the membrane or the surface of the metal hydride makes it possible to greatly reduce the reaction conditions compared to the conventional method using only the catalyst.

[0005]

According to the present invention, conventional ammonia production requires high-temperature, high-pressure reaction conditions, whereas ammonia can be produced under mild reaction conditions, and special equipment for high-pressure resistance, high temperature is required. And not.

According to the present invention, a hydrogen permeation membrane or metal hydride powder is used as a source of atomic hydrogen, and a catalyst having a dissociative adsorption activity of nitrogen molecules carried on the reaction chamber side surface of the membrane or the metal hydride powder surface. By reacting with the above active nitrogen, ammonia can be produced under mild conditions.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of the ammonia reactor of the present invention.

Using the apparatus shown in FIG. 1, nitrogen gas is passed at a hydrogen pressure of 1.5 atm inside the diaphragm and at normal pressure outside the diaphragm,
The reaction temperature was in the range of 50 ° C to 250 ° C. The loading of the nitrogen dissociation adsorption catalyst on the surface of the diaphragm was performed by an impregnation method. The amount of produced ammonia was determined by collecting the produced ammonia with a dilute aqueous sulfuric acid solution and determining the pH change before and after the reaction. Further, the amount of produced ammonia was also determined by a spectrophotometric method using a Nessler reagent.

[0009]

[Table 1]

Table 1 shows the ammonia generation rate at each reaction temperature using the hydrogen permeable diaphragm of the present invention. It was confirmed that ammonia synthesis was possible under normal pressure even at a low reaction temperature of 50 ° C. close to room temperature.

FIG. 2 shows the results of an Arrhenius plot of the ammonia production rate with respect to each temperature. Activation energy obtained from the slope of the plot is 5.9 kcal / m
ole, which is much lower than the value of the catalyst alone supported on the hydrogen permeable diaphragm alone of 15 kcal / mole. It became clear.

[0012]

According to the present invention, atomic hydrogen having high reaction activity is constantly supplied to the reaction chamber side by using a metal hydride, and furthermore, a diaphragm on the reaction chamber side or the metal hydride powder itself is used. By reacting atomic nitrogen dissociated and adsorbed on the catalyst supported on the surface of the metal with active hydrogen released from the metal hydride, ammonia can be produced under extremely mild conditions.

[Brief description of the drawings]

FIG. 1 schematically shows an ammonia reactor of the present invention.

FIG. 2 shows the production of ammonia by a reaction with active nitrogen dissociated and adsorbed on a catalyst using a metal hydride itself as a hydrogen supply source.

FIG. 3 shows the results of an Arrhenius plot of the ammonia production rate at each temperature, for a reaction using a hydrogen permeable diaphragm and without using a hydrogen permeable diaphragm.

Claims (2)

[Claims] 1. A method of using a metal hydride as a hydrogen permeable membrane (diaphragm) to constantly supply highly active atomic hydrogen from a hydrogen gas atmosphere on one side of a membrane to a reaction chamber side, and to supply the active atomic hydrogen to the reaction chamber side. A technology for synthesizing ammonia under milder conditions by reacting with active nitrogen dissociated and adsorbed on a catalyst supported on a catalyst. 2. A catalyst layer which is active for dissociation and adsorption of nitrogen molecules is provided on the surface of the metal hydride powder, and the atomic nitrogen generated on the surface reacts with the atomic hydrogen supplied from the metal hydride. Technology for producing ammonia under mild conditions.