Abstract:
A method is provided for extracting hydrogen from lithium hydride. The method includes (a) heating lithium hydride to form liquid-phase lithium hydride; (b) extracting hydrogen from the liquid-phase lithium hydride, leaving residual liquid-phase lithium metal; (c) hydriding the residual liquid-phase lithium metal to form refined lithium hydride; and repeating steps (a) and (b) on the refined lithium hydride.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of co-pending U.S. patent application Ser. No. 13/222,002, filed Aug. 31, 2011, entitled “Hydrogen, Lithium, and Lithium Hydride Production,” the entire contents of which are incorporated by reference herein. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    The U.S. Government has rights to this invention pursuant to contract number DE-AC05-00OR22800 between the U.S. Department of Energy and Babcock &amp; Wilcox Technical Services Y-12, LLC. 
     
    
     FIELD 
       [0003]    This disclosure relates to the field of material processing. More particularly, this disclosure relates to hydrogen, lithium and lithium hydride production. 
       BACKGROUND 
       [0004]    Lithium hydride (LiH) is a useful material. It reacts with water to produce hydrogen gas and lithium hydroxide. Although this is a violent reaction, it was used in World War II to provide a lightweight source of hydrogen to inflate signaling balloons. In addition to various applications that require the production of hydrogen, there are many applications that require high purity lithium and many applications that require the production of high purity lithium hydride. Standard methods for production of high purity lithium and high purity lithium hydride are generally expensive. What are needed therefore are safer and more economical means for using lithium hydride to produce hydrogen, and better means for producing high purity lithium and high purity lithium hydride. 
       SUMMARY 
       [0005]    The present disclosure provides various embodiments of hydrogen, lithium, and lithium hydride processing apparatuses. Typically these apparatuses have a hot zone to heat solid-phase lithium hydride to form liquid-phase lithium hydride. A vacuum source is typically provided to extract hydrogen and gaseous-phase lithium metal from the liquid-phase lithium hydride. Embodiments of the apparatuses also typically have a cold zone to condense the gaseous-phase lithium metal as purified solid-phase lithium metal. A heater is typically provided to melt the purified lithium metal in the cold zone and form refined liquid-phase lithium in the hot zone. A moderate zone may be provided and is typically disposed between the hot zone and the cold zone to capture a lithium condensate portion of the gaseous-phase lithium and to return the lithium condensate portion to the hot zone as liquid-phase lithium condensate. 
         [0006]    The present disclosure further provides methods of producing hydrogen. The methods typically employ a step “a” of heating lithium hydride to form liquid-phase lithium hydride, a step “b” of extracting hydrogen from the liquid-phase lithium hydride, leaving residual liquid-phase lithium metal, and a step “c” of hydriding the liquid-phase lithium metal. The methods typically involve repeating steps “a” and “b” at least once. 
         [0007]    The present disclosure also provides methods of processing hydrogen and lithium material. Methods typically include steps of heating a lithium hydride source material that includes lithium hydride to form liquid-phase lithium hydride. The methods generally also involve reducing an ambient pressure over the liquid-phase lithium hydride. Typically, a further step involves extracting hydrogen and gaseous-phase lithium metal from the liquid-phase lithium hydride. Generally the methods also involve condensing the gaseous-phase lithium metal as solid-phase lithium metal. Then the solid-phase lithium metal may be melted to form refined liquid-phase lithium metal. Some methods may include hydriding the refined liquid-phase lithium metal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Various advantages are apparent by reference to the detailed description in conjunction with the figures, wherein elements are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
           [0009]      FIG. 1  is a somewhat schematic cross-sectional view of an apparatus for processing hydrogen and lithium materials; 
           [0010]      FIG. 2  is a vapor pressure curve for hydrogen in lithium hydride as a function of temperature; 
           [0011]      FIG. 3  is a vapor pressure curve for lithium metal as a function of temperature; and 
           [0012]      FIG. 4  is an exemplary temperature profile for extracting hydrogen from lithium hydride and purifying the resultant lithium. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In the following detailed description of the preferred and other embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration the practice of specific embodiments of hydrogen and lithium material processing apparatuses and embodiments of methods of processing hydrogen and lithium material. It is to be understood that other embodiments may be utilized, and that structural changes may be made and processes may vary in other embodiments. 
         [0014]    Lithium hydride is a very space-efficient material for the storage of hydrogen. The hydrogen density in lithium hydride is greater than the density of metallic (solid) hydrogen. In other words there is more hydrogen stored in a cubic unit measure of lithium hydride than in the same cubic unit measure of pure metallic hydrogen. This phenomenon provides a potential for the use of lithium hydride as a means of compact storage of hydrogen for use in hydrogen-powered vehicles and other applications where a source of hydrogen on demand is needed. 
         [0015]    At atmospheric pressure lithium hydride melts at about 692° C. By reducing the ambient pressure to near vacuum conditions, lithium hydride may be melted at about 680° C. At atmospheric pressure liquid lithium hydride decomposes into lithium metal and hydrogen gas at about 850° C. The temperature at which the decomposition occurs may be lowered to about 750° C. by reducing the ambient pressure over the liquid lithium hydride to near vacuum conditions. These characteristics may be used in thermal processes to generate hydrogen from lithium hydride with relative safety compared with a chemical reaction of water with lithium hydride. Such thermal processes have a further advantage of producing lithium metal instead of the lithium hydroxide that results from the chemical reaction of water with lithium hydride. Typically, many impurities in the lithium hydride are removed during these thermal processes such that a refined lithium metal is produced. In addition, such thermal processes may be extended to economically produce high purity lithium hydride by re-hydriding the refined lithium metal. 
         [0016]      FIG. 1  illustrates an apparatus  10  that may be used to generate hydrogen and lithium metal, as well as to produce high purity lithium and high purity lithium hydride. The apparatus  10  may also be used to store hydrogen and release the stored hydrogen for subsequent use. The apparatus  10  provides a hot zone  14 , a moderate zone  18 , a cold zone  22 , and an extraction zone  26 . The apparatus  10  also includes a vacuum system  38  that is connected by an extraction line  34  to the top of the extraction zone  26  through a manifold  30 . Typically the vacuum system  38  is an oil-free vacuum pump. A valve  42  is typically provided in the extraction line  34  to permit sealing off the vacuum system  38  from the extraction zone  26 . 
         [0017]    In the embodiment of the apparatus  10  depicted in  FIG. 1  the hot zone  14  includes a shim pot  46  that is disposed within a process vessel  50 . A “shim pot” is a double-walled vessel with a space between the walls for containing materials. In the embodiment of  FIG. 1 , a lithium hydride source material  58  is disposed between the walls of the shim pot  46 . In the embodiment of apparatus  10  depicted in  FIG. 1 , a center can  54  is disposed within the open space formed by the inner wall of the shim pot  46 . The shim pot  46  and the center can  54  are preferably constructed from a material such as iron that is compatible with lithium. In some embodiments the shim pot  46  is not used and the lithium hydride source material  58  is disposed between the process vessel  50  and the center can  54 . In such embodiments the process vessel  50  is preferably constructed from a material such as iron that is compatible with lithium. In embodiments where a shim pot is used (such as shim pot  46 ) the process vessel  50  may be constructed from stainless steel, which could be susceptible to erosion if contacted with hot lithium were it not for the protection against such erosion that is provided by the shim pot  46 . Typically the shim pot  46 , the process vessel  50  and the center can  54  are concentric circular annular shapes. 
         [0018]    The lithium hydride source material  58  is substantially lithium hydride, but the lithium hydride source material  58  may include up to ten percent impurities. That is, the lithium hydride content may be in a range from about ninety to one hundred percent of the lithium hydride source material  58 . 
         [0019]    Typically the operation of the apparatus  10  begins with establishing a flow of purge gas such as argon  62  from a tank  64  through the manifold  30 . Then the vacuum system  38  is activated with the valve  42  open. The purge flow tends to reduce the flow of dust from the lithium hydride source material  58  into the vacuum system  38 . The process vessel  50  and the shim pot  46  (if used) and the center can  54  are then heated with an appropriate energy source (e.g., electric resistance, induction, natural gas). The hot zone  14  is kept under dynamic vacuum by the vacuum system  38  as the temperature is increased. The term “dynamic vacuum” means that the hot zone  14  is being actively pumped by the vacuum system  38  (i.e., it is not just pumped to vacuum and then valved off, leaving a trapped vacuum condition). This active pumping removes the argon  62  and any off-gasses from the lithium hydride source material  58 . Heating continues until the lithium hydride source material reaches at least 680° C., which is a melting temperature of lithium hydride at reduced atmosphere. Radiation baffles  66  are provided in the embodiment of  FIG. 1  to reduce the heat loss through the top of the hot zone  14 . Even so, when the bottom of the hot zone  14  is at 680° C. the top of the hot zone  14  may only reach 400° C. This is acceptable. Once the lithium hydride source material  58  is melted the flow of purge gas (e.g., argon  62  through the manifold  30 ) may be discontinued. 
         [0020]    As this process proceeds, a barrier crust may form above the liquid-phase lithium hydride in the shim pot  46  (or in the process vessel  50  if the shim pot  46  is not used). The barrier crust is a slag-like material that may be formed from impurities in the lithium hydride, and from lithium hydroxide formed from lithium hydride reacting with trace amounts of water vapor in the apparatus  10 , and/or from other contaminants. The barrier crust slows down the evolution of hydrogen from the liquid-phase lithium hydride. To overcome this,  FIG. 1  illustrates that the apparatus  10  may include an agitator  70  for retarding the formation of the barrier crust. In some embodiments the agitator  70  may comprise an inert gas sparge, such as a gas sparge using a flow of the argon  62  that was discontinued as a purge gas when the lithium hydride source material  58  melted. Such a sparge flow substantially retards the formation of the barrier crust above the molten phase. In some embodiments the agitator  70  may comprise an energy source having a periodic waveform (such as ultrasonic vibration) that is applied to the bottom of the shim pot  46  to retard the development of a barrier crust. In embodiments that do not employ the shim pot  46 , the agitator  70  is applied at the bottom of the process vessel  50  between the process vessel  50  and the center can  54 . 
         [0021]    After the lithium hydride source material  58  melts, the process vessel  50  and the shim pot  46  (if used) and the center can  54  are further heated such that the lithium hydride source material  58  reaches a temperature of at least 750° C. At that temperature, under near vacuum conditions, the molten lithium hydride decomposes into lithium metal and hydrogen.  FIGS. 2 and 3  illustrate the comparative vapor pressures of hydrogen in molten lithium hydride ( FIG. 1 ) versus the vapor pressure of lithium metal. At any temperature in the range of 700° C. to 1000° C. the vapor pressure of hydrogen from lithium hydride is ten to thirty times higher than the vapor pressure of lithium vapor from lithium metal. Lithium hydride decomposes when the vapor pressure of the hydrogen content is above about 30 torr. This occurs at about 750° C., and at that temperature the vapor pressure of Li from lithium metal is about 1 torr. Consequently, at 750° C., hydrogen is preferentially (almost exclusively) generated, with very little lithium vapor generated. Typically at 750° C., hydrogen generation occurs as fast as it can be pumped until all of the lithium hydride in the lithium hydride source material  58  has decomposed to lithium metal and hydrogen. 
         [0022]    As the lithium hydride decomposes into hydrogen and lithium metal, the vacuum system  38  pulls the hydrogen along paths  74  through the moderate zone  18 . In embodiments where an inert gas sparge is employed, the vacuum system  38  also pulls the inert sparge gas through the moderate zone  18  and the cold zone  22 . 
         [0023]    The hydrogen (and inert sparge gas, if present) flows out of the vacuum system  38  into an accumulator  94 . Certain impurities may also be pulled into the accumulator  94 . A hydrogen membrane filter  98  (such as a side stream palladium filter) may be used to extract hydrogen  102  (which is substantially pure after filtration) and store it in a hydrogen storage compartment  114 . The hydrogen  102  may be piped out of the hydrogen storage compartment  114  for use in a fuel cell process or for use in other devices or chemical processes. If an inert gas sparge (such as the argon  62 ) is used, recovered inert gas  106  may be temporarily stored in an inert gas storage compartment  110 . The recovered inert gas  106  may then be returned to the tank  64  and reused. 
         [0024]    The just-concluded description of extraction of hydrogen from the lithium hydride source material completes the process application steps needed for some embodiments. In such embodiments the apparatus  10  may be reused for multiple repetitive operations by re-hydriding the lithium that remains in the hot zone  14 . To do this, the hot zone  14  with the refined lithium metal in the process vessel  50  is heated to a temperature of about 800° C. (if it is not already at that temperature). Then hydrogen (at approximately 16 psia) is introduced into the hot zone  14  from a source of hydrogen  170 , and the lithium metal is converted to lithium hydride. With this approach the apparatus  10  provides a reusable, high density hydrogen storage device. In such embodiments the apparatus  10  may be simplified by eliminating the shim pot  46  and eliminating elements described and discussed later herein such as the inclined deflector  78 , the elements in the moderate zone  18 , and the elements of the cold zone  22 . 
         [0025]    In some embodiments it is desirable to purify the liquid-phase lithium metal that remains in the process vessel  50  after extraction of the hydrogen from the lithium hydride. To do this, the process vessel  50  and the shim pot  46  (if used) and the center can  54  are further heated to about 900° C. At that temperature the vacuum system  38  is able to extract gaseous-phase lithium metal from the liquid-phase lithium in the hot zone  14 . An inclined deflector  78  may be provided to keep molten gaseous-phase lithium metal from weeping to the sides of the radiation baffles  66 , and falling back into the space between the shim pot  46  and the center can  54 . The deflector  78  is typically inclined at an angle  82  that is at least 12 degrees. In embodiments where the shim pot  46 , the process vessel  50 , and the center can  54  are annular, the deflector  78  is generally conical-shaped. The use of the sparge gas (e.g., the argon  62 ) encourages the formation of lithium vapor, and because the lithium vapor is relatively heavy the sparge gas helps to float the lithium vapor up to the top and out of the liquid lithium where it is pulled by the vacuum system  38  into the cold zone  22 . 
         [0026]    The cold zone  22  typically includes a chiller  122 , such as a counter flow gas to gas heat exchanger. The gaseous-phase lithium metal pulled into the cold zone  22  solidifies as solid-phase lithium metal in the cold zone  22 . Some of the gaseous-phase lithium metal vapors passing through the moderate zone  18  may condense back to liquid-phase lithium metal in the moderate zone  18  before reaching the cold zone  22 . This condensed liquid-phase lithium metal (lithium metal condensate) flows by gravity back down through the funnel-shaped portion  130  of the moderate zone  18  to the center can  54  in the hot zone  14 . Upon its return to the process vessel  50  the condensed liquid-phase lithium metal is again converted to gaseous-phase lithium metal. Eventually all gaseous-phase lithium metal vapors pass through the moderate zone  18  and condense in the cold zone  22  where the lithium metal is trapped in the solid phase. 
         [0027]      FIG. 3  presents a summary of an exemplary temperature profile that may be used to extract hydrogen and lithium metal from the lithium hydride source material  58 . The process starts at point “A” where the process vessel  50  is heated and argon  62  is introduced as a purge gas through the valve  42 . When the lithium hydride source material  58  reaches a temperature of about 680° C. (at point “B”) and is molten, the flow of argon  62  is switched to a sparge gas through the agitator  70 . During the time interval “C” the lithium hydride becomes molten. The temperature of the molten lithium hydride is then increased to about 750° C. and during time interval “D” the lithium hydride decomposes to lithium and hydrogen, and the hydrogen is pumped away. When the lithium hydride decomposition is complete (at time “E”) the molten lithium is further heated to about 900° C. where, during time interval “F,” the lithium metal vaporizes and is frozen in the cold zone  22 . 
         [0028]    Upon completion of the thermal decomposition of lithium hydride and the deposit of the solid-phase lithium metal in the cold zone  22 , the gas pressure in the device approaches full vacuum (provided that the inert gas sparge, if used, is turned off). At that point, the valve  42  to the vacuum system  38  may be closed and the apparatus  10  may be cooled, typically by simply turning off power to the apparatus  10 . 
         [0029]    The highly purified lithium metal that has condensed in the cold zone  22  may be extracted by using heaters  146  to heat the cold zone  22  to a temperature above 180° C., the melting temperature of lithium metal. Supplemental heaters  150  may be applied to the moderate zone  18 . The purified liquid-phase lithium metal runs down into the center can  54  of the hot zone  14  (which is now cold) through a cylinder  158 , thereby providing refined lithium metal. The cylinder  158  has an end  162 , and it beneficial to have the end  162  of the cylinder  158  terminate at an elevation that is below the top of the center can  54 . 
         [0030]    As previously noted, the apparatus  10  may be recharged for repetitive operations by re-hydriding the refined lithium in the hot zone  14  such that the refined lithium metal is converted to refined lithium hydride. Alternately, the vapor distilled, ultra-high purity refined lithium metal may be removed from the process vessel  50  under inert conditions for other uses. In some embodiments the apparatus  10  is used as a reiterating lithium or lithium hydride refining device, and in such embodiments the source of hydrogen  170  may include hydrogen  102  extracted from a prior decomposition of lithium hydride. 
         [0031]    In addition to various embodiments of apparatuses, the present disclosure provides methods of processing hydrogen and lithium material. The methods typically involve heating a lithium hydride source material that includes lithium hydride to form liquid-phase lithium hydride. The lithium hydride source material is heated to a temperature that is typically in the range of 750° C. to 800° C. to form a liquid-phase lithium hydride. A reduced ambient pressure over the liquid-phase lithium hydride (such as provided by a vacuum pump) extracts hydrogen and gaseous-phase lithium metal from the liquid-phase lithium hydride as the lithium hydride decomposes. The reduced ambient pressure also has a benefit of reducing the decomposition temperature of the lithium hydride. Typically the gaseous-phase lithium metal is condensed as solid-phase lithium metal. Sometimes a lithium condensate portion of the gaseous-phase lithium may be captured and returned to the lithium hydride source material as liquid-phase lithium condensate. The solid-phase lithium metal may be extracted from the cold zone by melting to form refined lithium metal, and the refined lithium metal may be hydrided using hydrogen gas to form a re-charged lithium hydride. The previously-described process steps for decomposing lithium hydride may then be repeated one or more times using recharged lithium hydride as the lithium material. 
         [0032]    Some processes may involve retarding the formation of a barrier crust that may form adjacent the liquid-phase lithium hydride. This retarding step may involve sparging the liquid-phase lithium hydride with an inert gas such as argon, and/or it may involve agitating the liquid-phase lithium hydride with an energy having a periodic waveform, such as ultrasonic energy. 
         [0033]    In summary, embodiments disclosed herein provide a hydrogen and lithium material processing apparatus and methods of processing hydrogen and lithium materials. The foregoing descriptions of embodiments have been presented for purposes of illustration and exposition. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of principles and practical applications, and to thereby enable one of ordinary skill in the art to utilize the various embodiments as described and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.