Abstract:
A process of producing metal powders by feeding a metal oxide and a reducing agent into a rotary reactor to form a mechanical fluid bed. The fluid bed is rotated with a rotation speed of about 100 rpm. The fluid bed is then heated to a reaction temperature of up to 1200° C. The pressure is then set within the rotary reactor to a pressure in a range of 0.001 bars to 2.0 bars, as a result reducing the reaction temperature to a temperature in a range of 600° C. to 1200° C. Finally, the pressure and the rotation are maintained, wherein a high value metal powder is formed without the requirement for post-grinding process steps. A product resulting from specific settings of the process include a high value molybdenum powder capable of being used as a chemical catalyst and other specialty applications specific to the metal, eliminating costly production methods.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The instant application claims benefit of provisional application Ser. No. 61/735,094, filed Dec. 10, 2012, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a pressure controlled system and method of producing metal powders and other metal compound forms including but not limited to molybdenum powder and vanadium power starting from their respective oxides. 
         [0004]    2. Description of the Related Art 
         [0005]    Starting from the higher degree of oxidation it is possible to produce metals or metal oxides with various degrees of oxidation for a variety of applications, for instance as metallurgical powders or alloy formation. Making iron powders from their oxides by using only one reactor set with specific operating conditions is shown by U.S. Pat. No. 8,333,821 to Di Luca. 
         [0006]    Operating conditions dictate purity levels of useful metal powders. For instance, the reduction of molybdenum oxide (MoO 3 ) is exothermic so the partial pressure of hydrogen must be controlled to prevent overheating of the powder. As a result particularly low temperatures and partial pressures must be achieved. Other metals, such as vanadium cannot be reduced in the same range and with the same reductant, and in some cases other compound results such as the corresponding carbide. The process known today for the reduction of vanadium pentoxide (V 2 O 5 ) requires the use of a strong reductant, such as aluminum, which in an exothermic reaction will convert to alumina (Al 2 O 3 ) thereby reducing the V 2 O 5 , and usually when blended with iron will produce a ferroalloy. Converting the alumina to slag will remove the alumina formed, which will float in the liquid alloy of iron and vanadium. 
         [0007]    As known then, in order to produce a metal powder with desirable characteristics the high temperature and thermodynamics of the process control the rate of the reaction, e.g. the nature of the reactants, the product of the reaction (solids, gases), and the change in the number of mols of the reaction which will produce a change in the rate of the reaction itself. There is a need, then, for a more efficient and flexible method for obtaining metal powder which accounts for pressure as the state variable for defining the system in a way that can be used for the production of specialty products at a lower cost, reducing the use of energy and the process steps required to deliver the final product. The advantages of the instant method result in an environmentally friendly process and, in addition, produces a higher quality product, as follows. 
       SUMMARY OF THE INVENTION 
       [0008]    It is the objective of the present invention to produce metal powder or metallic compounds using as a raw material natural or synthetic metal oxides. 
         [0009]    It is a further objective of the present invention to reduce the processing cost of obtaining metal powder, or other metal oxides by using a mechanical fluid bed process and a variety of reacting agents singularly or in combination, such as coal, ammonia, hydrogen, and natural gas, changing the reducing agent and/or the pressure to obtain the desired results. 
         [0010]    It is a further objective of the present invention to reduce the metal oxide, in a single stage step, by heating the powder at a suitable temperature estimated between 600° C. and 1200° C. under pressure/vacuum, in a mechanical fluid bed that will prevent sintering or agglomeration of the powder, eliminating the need for milling in an inert atmosphere. 
         [0011]    It is a further objective of the present invention to prevent agglomeration of the powder by rotating the mechanical fluid bed at high rotating speed which, when combined with internal blades (mixing fins), optimizes the fluidization of the load and prevents sintering, as well as improves the contact between the reducing gases and the powder. Therefore the size and number of particles throughout the process remain approximately the same within the desired range to eliminate unusable waste particles. 
         [0012]    It is a further objective of the present invention to operate the stabilized mechanical fluid bed at various degrees of vacuum and/or pressure to control the degree of reaction of the metal oxides as well as reduce the reaction temperature as much as possible to eliminate the possibility of sintering or agglomeration of the powder. 
         [0013]    It is a further objective of the present invention to inject a process gas such as ammonia to generate nitrogen and hydrogen which will be used to produce an inert or slightly reducing atmosphere to prevent a change in the oxidation state of the same during the cooling stage of the product. 
         [0014]    It is a further objective of the present invention to prevent re-oxidation of the reduced powder by cooling the same under an inert or slightly reducing gas blanket generated by the process gas by-products. 
         [0015]    It is a further objective of the present invention to reduce the use of energy in the production of these products by reducing the reaction temperature and eliminating milling of the product, leading to an environmentally friendly method when compared to existing processes. 
         [0016]    Accordingly, the instant invention comprehends a process of producing metal powders by feeding a metal oxide and a reducing agent into a rotary reactor to form a mechanical fluid bed. The fluid bed is rotated with a rotation speed of about 100 rpm. The fluid bed is then heated to a reaction temperature of up to 1200° C. Critically, the pressure is then set within the rotary reactor to a pressure in a range of 0.001 bars to 2.0 bars, as a result reducing the reaction temperature to a temperature in a range of 600° C. to 1200° C. Finally, the pressure and the rotation are maintained, wherein a high value metal powder is formed without the requirement for post-grinding process steps, such post-processing steps increasing production costs and increasing the amount of unusable particles and waste. 
         [0017]    A product resulting from specific settings of the process include a high value molybdenum powder capable of being used as a chemical catalyst and other specialty applications specific to the metal, eliminating costly production methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a diagram showing the overall process. 
           [0019]      FIG. 2  is a condensed scale graph of the thermodynamic analysis of the production of molybdenum using the instant methodology. 
           [0020]      FIG. 3  is a full scale graph of the thermodynamic analysis. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The invention will now be described in detail in relation to a preferred embodiment and implementation thereof which is exemplary in nature and descriptively specific as disclosed. As is customary, it will be understood that no limitation of the scope of the invention is thereby intended. The invention encompasses such alterations and further modifications and applications as would normally occur to persons skilled in the art to which the invention relates. This detailed description of this invention is not meant to limit the invention, but is meant to provide a detailed disclosure of the best mode of practicing the invention. 
         [0022]    Referencing then  FIGS. 1-3 , for the instant system and method, the raw material used for manufacturing metallic powders are intermediate forms of metal oxides. The metal oxide powder can be natural or synthetic. The metal oxide material is typically obtained as fines in the production of metal ore or as a byproduct of chemical processes. The purity of the final product will depend on the purity of the raw material used for its production. 
         [0023]    Even though this process and apparatus can be used for a variety of final products, focused herein as an example is the production of fine molybdenum powders for use as a catalyst or in the powder metallurgy industry or other special applications. By a change in operating conditions and by using the particular starting oxide, other powders can be produced such as vanadium. The example using molybdenum is an example only of the preferred embodiment. 
         [0024]    In the preferred embodiment of the instant system and method the raw material then is a fine from the processing of Molybdenum ore. This is typically stored in a storage silo  1 . From this silo  1 , the oxide powder is discharged to a grinding mill, which preferably is a jet mill  2  operating with air or a similar device. As a result a consistent particle size of the metal powder can be obtained. 
         [0025]    After milling, the metal oxide powder is stored in the receiving bin  3 , while a reducing agent such as coal powder is stored in the coal silo  4 . The reducing agent can be coal, hydrogen, natural gas, ammonia, carbon powder, synthetic gas or any combination thereof. The reducing agent will reduce the metal oxide when combined therewith to form a mechanical fluid bed  9 . 
         [0026]    Thus, the metal oxide from the receiving bin  3  and the coal (or reducing agent) from the coal silo  4  are fed to a rotary reactor, namely the reactor feed chute  7 , by way of rotary feeders  5  and  6  in the ratio required by the process (at the rate defined by the production capacity of the unit) to form a mechanical fluid bed  9 . The components are fed directly into the rotary reactor through the feed chute  7  and the block and bleed system  7   b.  Critical is that a rotary reactor be used which includes rotating, internal fins. It has been determined through significant experimentation that the rotary reactor&#39;s internal fins or blades set at a rotation speed between 6 and 100 rpm, will produce the appropriate fluidization of the mechanical fluid bed  9 . 
         [0027]    The mechanical fluid bed  9  within reactor is heated to the reaction temperature by an external means such as an electric heater, natural gas burners or similar device. The reaction temperature could reach up to 1200° C. However, an internal pressure change is applied to the mechanical fluid bed  9 , by implementing a vacuum pump  15 . Thus, subsequently to the reaction temperature being reached or simultaneously during the temperature rise, the pressure with the rotary reactor is set to a pressure in the range of 0.001 bars to 2.0 bars (depending on the application), which reduces the reaction temperature within the mechanical fluid bed  9  to a temperature in the range of 600° C. to 1200° C. The above mentioned factor of applying pressure is critical to allow a substantially complete reaction of the powder at such a low temperature, and critically, an identical product can be produced at the same or similar low temperature even by varying the amount of reactants as long as the operating pressure is changed, this, also achieved within one reactor. 
         [0028]    A process gas, including blends thereof with or without nitrogen, such as ammonia, ammonia doped with oxygen, hydrogen, or natural gas, may be injected in some applications through the feed rotary joint  12 , and released through the discharge of the vacuum pump  15  to the off-gas system  16 . The reacted gases will be mainly N 2 , CO 2 , H 2 , and traces of CO and H 2 O. The off-gas is processed through the trap bed  25  that operates with a caustic reactant which retains the CO 2  and H 2 O, leaving in the stream only N 2 , a small amount of H 2 , and traces of CO. If required the off gas can also be processed through a thermal oxidizer (not shown) before passing the same through the trap bed  25 . This gas is used to provide a blanket of the metal powder or the oxide powder that is cooling down in the cooling chamber  18 . The gas blanket resides or can be separately injected into the mechanical fluid bed  9  to prevent re-oxidation of the high-purity metal powder. 
         [0029]    As indicated above, the material is fed continuously to the mechanical fluid bed  9  through the feed rotary joint  12  and it is discharged from the mechanical fluid bed  9  through discharge rotary joint  13  and dropped into the cooling chamber  18  through a block and bleed system  17 . Once the metal reaches a temperature below 60° C., it is dropped from the cooling chamber  18  through a block and bleed system  19  to a conveying system  20  and subsequently delivered to a classifier  21 , which will sort the material (according to particle size) in three or more bins, for example according to the arrangement shown in  FIG. 1 . 
         [0030]    As above, the low process temperature that results from the vacuum applied to the mechanical fluid bed  9  combined with the fluidization of the powder using a fin-implemented reactor with optimized rotation speed prevents re-agglomeration of the powder and eliminates the need for post-grinding of the material, i.e. post-production steps inherently required by previous, high-temperature processes. Depending on the desired characteristics, as exemplified below, what results is a metal with a purity related to the concentration of residuals in the raw material. Basically more than 99% of the metallic content of the raw material will be converted to metal powder. Furthermore, as a result of the elimination of the post-grinding step, each particle that has reacted with the reactants individually during the process will maintain this individuality, i.e. it will not agglomerate or sinter. Therefore the size and number of particles throughout the process remain approximately the same within the desired the range to eliminate unusable waste particles. Critical then is that the instant process reduces the metal oxide powder while simultaneously maintaining particle size distribution even as the individual chemistry of each particle is changing. 
       EXAMPLE 1 
       [0031]    As an example, described is the production of molybdenum powder which can be used as a chemical catalyst, among other specialty applications. 
         [0032]    Molybdenum Oxide (MoO 3 ) is the raw material which can be obtained as fines from the ores of molybdenum, or which can be produced synthetically. The selection of the raw material will be defined by the desired purity of the molybdenum powder. The metal oxide is fluidized in the reactor by flowing a blend of H 2  and N 2  as the reducing agent. The particle size distribution of the metal oxide may vary. Typically, as produced by this process the end product powder will have a particle size which approximates the particle size of the oxide. 
         [0033]    The above material is loaded in the mechanical fluid bed in the following proportion: for every 1000 kg of MoO 3 , required will be 316 Nm 3  of H 2  and 790 Nm 3  of N 2 . The mechanical fluid bed  9  reaction zone is set at a temperature optimally in the range of 620° C.-640° C. and the pressure is set at up to 1 bar. Milled molybdenum oxide is fed through the reactor feed chute, while the blend of H 2 /N 2  is flown through the rotary joint  13  at a rate of 18.4 Nm 3 /hour per 1000 kg of MoO 3 . 
         [0034]    To prevent agglomeration in the interior of the mechanical fluid bed  9  the rotation speed of the same is set at about 100 rpm thereby creating a fluid bed within the rotary reactor. “About” as it relates to rotation speed means the rotation speed is adjusted according to the actual flow rate of the gas and temperature of the reaction zone to achieve the stabilization of the fluid bed. Since the reaction is strongly exothermic the operator monitors the temperature of the bed and typically is required to make necessary small corrections. 
         [0035]    The residence time of the molybdenum oxide is set at thirty (30) minutes by controlling the feed rate. 
         [0036]    The molybdenum powder formed will then pass through the block and bleed system  17  and the cooling chamber  18  in which is injected nitrogen as a blanket to prevent re-oxidation of the molybdenum powder. The blanket is maintained until the temperature of the iron powder reaches 60° C. At this temperature, or lower, the molybdenum powder is removed through the block and bleed system  19 . 
         [0037]    The molybdenum powder produced by this method can then be used as a catalyst for the chemical industry (“utilization”), as well as other high end applications that require high purity and small particle size such as the metallurgical powder industry. If required the molybdenum powder is processed through a classifier  21  and sorted to the proper bins  22 ,  23 ,  24  for bagging and shipping.