CARBIDES AND NITRIDES OF TRANSITION ELEMENTS APPLIED ON THE CATALYTIC DECOMPOSITION OF HYDRAZINE

Abstract: The present invention relates to the use of carbides and nitrides of transition elements in devices such as catalytic engines or continuous reactors for the catalytic decomposition of hydrazine. The use of these materials to substitute the commercial catalysts will lead to smaller costs and simpler manufacturing techniques for a performance similar to the best materials now available in the market. Besides, the carbides and nitrides of transition elements, being more stable during the decomposition process, exhibit great simplicity in their deployment.

Description: CARBIDES AND NITRIDES OF TRANSITION ELEMENTS APPLIED ON THE CATALYTIC DECOMPOSITIONOFHYDRAZINE The present invention relates to the use of carbides and nitrides of transition elements in devices such as catalytic engines or continuous reactors used to generate and use gases obtained from the catalytic decomposition of hydrazine. The catalytic system shown in Figure 1 comprises a fixed bed (1) made with grains of carbides or nitrides of tungsten, molibdenum, niobium or other transition metals, placed inside a chamber (2) , which is an integral part of an engine or a continuous reactor. The hydrazine, in its liquid phase and kept in a pressurized vessel (3) is admitted into the chamber through injectors (4) . The hydrazine is then vaporized and decomposed by the catalytic bed, generating the gases nitrogen, hydrogen and ammonia (5) . These gases may be then employed, for instance, in artificial sattelites propulsion or in submarines emergency ballast sytems. The start up of this system can be performed cold or through proper heating (to temperatures up to 200°C) . Commercially used similar systems are different because they use an iridium catalyst_supported on alumina with a high metal content (US Patent 4,124,538) , a much more expensive device whose deployment leads to a more stringent homologation routine which among other things implies into a pre-estabilization procedure of the catalyst submitted to a strong deactivation process. The present patent of invention is different from the existing techniques in the change of the catalytic bed, usually made with extremely expensive items such as iridium supported on alumina and submitted to a strong deactivation process, by a highly inexpensive material, which requires the use of less complex manufacturing techniques, and which possesses better thermal and mechanical properties while keeping a similar_ performance, such as carbides and nitrides of tungsten, molibdenum and niobium. The main mean characteristics of the nitrides and carbides of tungsten, molibdenum and niobium are the following: Porous Specific Volume: 0 to 1.2 cm 3 /g; Specific Area: 2 to 230 m 2 /g; Crystalline Phase: compact hexagonal, face-centered cubic; Residual Oxigen Content: 0 to 30%. Materials with a residual oxigen content above zero may also be referred as oxinitrides and oxicarbides. The prepared compounds may have the shape of irregular plates, spheroidal-cylinders (bastonets) or spherical particles and powders with characteristic dimensions varying from ten to tens of mm. The material can also be deposited on screens or on an inert support such as alumina . TYPICAL EXAMPLE It is shown next the performance of a 2N engine (Figure 2) using tungsten oxicarbide with the following characteristics: Specific Area: 50 m 2 /g; Porous Specific Volume: 0.15 cm /g; Oxigen Content: 1%; Shape: Extruded cylinder:1.6 mm diameter and 2.8 mm long; Crystaline Phase: Hexagonal . The engine was operated inside a vacuum chamber (10 "3 torr, ambient temperature) , hydrazine injection pressure of 5 to 15 bar, initial bed temperature of 373 K, operating time of 200 s with pulses of 200 ms (electro valve opening time) and 1 Hz frequency. Figure 3 shows the first ten pulses obtained with this material (where 1- hydrazine injection pressure, 0 to 10 bar scale; 2- chamber stagnation pressure, 0 to 10 bar scale; 3- engine temperature, 0 to 600°C scale; 4- thrust, 0 to 4 N scale) . For comparison purposes the performance of the commercial catalyst SHELL 405 operating in the same engine and under the same experimental conditions is shown in Figure 4 (1- hydrazine injection pressure, 0 to 10 bar scale; 2- chamber stagnation pressure, 0 to 10 bar scale; 3- engine temperature, 0 to 600°C scale; 4- thrust, 0 to 4 N scale) . Figures 5 and 6 (where 1- chamber stagnation pressure, 0 to 10 bar scale, in both figures) show the performances of the tungsten oxicarbide and of the catalyst SHELL 405, respectively, under 5 s continuous operation regime.

Claims: CLAIMS 1 - Carbides and nitrides of transition elements characterized by their use in devices such as catalytic engines or continuous reactors in the hydrazine catalytic decomposition reaction. 2 - Carbides and nitrides of transition elements as in claim 1, characterized by their application in engines with catalytic bed used in artificial sattelites propulsion devices. 3 - Carbides and nitrides of transition elements as in claim 1, characterized by their application in continuous reactors with catalytic bed used in submarines emergency ballast systems. 4 - Carbides and nitrides of transition elements as in claim 1, characterized by their application in continuous reactors with catalytic bed used in the generation of gases such as hydrogen and nitrogen.

Inventors: DJEGA-MARIADASSOU GERALD, HINCKEL JOSE NIVALDO, MARQUES CRUZ GILBERTO, RODRIGUES JOSE AUGUSTO JORGE, DJEGA-MARIADASSOU, GERALD, HINCKEL, JOSE, NIVALDO, MARQUES CRUZ, GILBERTO, RODRIGUES, JOSE, AUGUSTO, JORGE
Applicants: DJEGA MARIADASSOU GERALD, HINCKEL JOSE NIVALDO, INST NACIONAL DE PESQUISAS ESP, MARQUES CRUZ GILBERTO, RODRIGUES JOSE AUGUSTO JORGE, DJEGA-MARIADASSOU, GERALD, HINCKEL, JOSE, NIVALDO, INSTITUTO NACIONAL DE PESQUISAS ESPACIAIS, MARQUES CRUZ, GILBERTO, RODRIGUES, JOSE, AUGUSTO, JORGE
Application year: 1996
Main classification: B01J27
IPC codes: B01J7, B01J27, B63G8, B64G1, F02K9