Abstract:
A microreactor ( 10 ) for investigation of material reactions and properties includes a core body ( 12 ) defining a chamber ( 22 ) adapted to contain one or more sample materials and having a fluid passageway ( 52 ) from the chamber to the exterior of the core body. The chamber is in fluid communication with an external manifold ( 50 ) whereby gases, liquids or fluids can be injected and their activities can be controlled externally from ambient conditions to 400 degrees Celsius and 4,500 psi. Transparent windows ( 30   a   , 30   b ) in the core body permit continuous visual access to the chamber, allow direct probe beam interaction with sample during a reaction or observation, and external detection of the probe beam to investigate in situ reaction processes.

Description:
RELATED APPLICATION DATA  
       [0001]     This application is based on and claims the benefit of U.S. Provisional Patent Application No. 60/398,689 filed on Jul. 26, 2002, which is incorporated herein by this reference. 
     
    
     STATEMENT OF GOVERNMENT FUNDING  
       [0002]     The United States Government provided financial assistance for this project through the Department of Energy under Grant No. IF-01262. Therefore, the United States Government may own certain rights to this invention. 
     
    
     BACKGROUND  
       [0003]     The present invention relates to reaction cells for observation of in situ reactions and/or material properties. More specifically, it relates to a miniature reaction cell for the study of in situ solid-fluid and fluid-fluid reaction, as well individual solid-fluid and fluid-fluid reactions/interactions in multi component systems, wherein the pressure and temperature can be fully controlled during reaction.  
         [0004]     A wide range of high-pressure and temperature studies of materials have been successfully carried out using diamond-anvil-cells (DACs) and hydrothermal DACs. One such study of ultrahigh pressure transitions in solid hydrogen using a DAC is described by Mao, H. K. and Hemley, R. J., 66  Rev. Mod. Phys.  671 (1994), which is incorporated herein by this reference. Such studies, however, are often limited to very small reaction volumes due to the scarcity and high cost of suitable diamonds. See, for example, Mao and Hemley, supra, and Xu, Ji-an Mao, Ho-kwang 290  Science  783 (2000), which is incorporated herein by this reference. This limits the control of critical reaction process parameters, including reactant activity, over pressure and temperature ranges of interest, such as for pressures ranging from 0 to 4,500 psi and temperatures from 20 to 400° C. Larger batch style diamond cells of about 6 μl have been developed to study solid-fluid reactions, as described by Fulton, J. L., Darab, J. G. and Hoffman, M. M., 72  Rev. Sci. Instrum.  2117 (2001), which discusses X-ray absorption spectroscopy and imaging of heterogeneous hydrothermal mixtures using a diamond microreactor cell. Such cells, however, do not offer external reactant activity control. External activity control is available in diamond flow cells designed to probe fluid phases (e.g., aqueous solution) under controlled temperatures and pressures, as disclosed by Hoffman, M. M., Addleman, R. S. and Fulton, J. L. 71  Rev. Sci. Instrum.  1552 (2000). These cells, however, are not well suited for the study of solid-fluid or multicomponent solid-fluid and fluid-fluid properties and reactions.  
         [0005]     Although internal pressure control has previously been used in previous designs, it has been found to be difficult to incorporate, and inaccurate at best, for the pressure and temperature range of interest herein (ambient temperature and pressure to 400° C. and 4,500 PSI). In prior designs, reactant pressure/activity inherently decreases as a reaction progresses and the reactant gas/fluid is consumed. This effect is particularly limiting, as reaction conditions cannot be well controlled during observation.  
         [0006]     There is a need, therefore, for an apparatus that provides better control of pressure and temperature during in situ material investigations, including solid-fluid and fluid-fluid reaction investigations as well individual solid-fluid and fluid-fluid reactions and interactions in multi-component systems. It is an object of the present invention to provide such an apparatus.  
         [0007]     Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by the instrumentalities and combinations pointed out herein.  
       SUMMARY  
       [0008]     To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described in this document, there is provided a microreactor for investigation of material reactions and properties. The microreactor includes a novel chamber design for in situ investigations of commercially and fundamentally important reaction processes with full external temperature and pressure control from ambient conditions to 400° C. and 4,500 psi. The sample chamber is in fluid communication with an external manifold, whereby gases, liquids or fluids can be injected and their activities can be controlled externally. Because pressurizing fluid (which can be supercritical or subcritical fluid, gas or liquid) can be externally supplied, the microreactor allows the activity of the pressure medium, as well as the pressure itself, to be fully controlled as the medium is consumed during reaction or observation. Such external pressure and activity control has not been available for solid-fluid or combined solid-fluid and fluid-fluid investigations in the past. The system thus enables the investigation of a variety of materials under controlled temperature, pressure, and activity conditions.  
         [0009]     The microreactor includes transparent windows that allow direct probe beam (light, X-rays, etc.) interaction with a sample during a reaction or observation, as well as external detection of the probe beam to investigate in situ reaction processes. The windows permit sequential or simultaneous microscopic observation of the sample (e.g., before, during and after reaction) and continuous visual access to the chamber.  
         [0010]     The invention has the inherent advantages of (i) precise control of the pressure and activity of the gas or fluid of interest (ii) allowing investigations to be observed under constant reactant gas or fluid activity (e.g., pressure); and (iii) allowing the study of equations of state of systems in the absence of reactions (e.g., phase transitions in fluids).  
         [0011]     Potential commercial applications of the novel microreactor of the invention are broad in scope. The microreactor can be used for the in situ investigation of a variety of important chemical and materials processing applications involving supercritical or near supercritical, as well as subcritical fluids. These include organic and organometallic reactions, pharmaceutical materials processing, organic waste decomposition, geochemical and mineralogical reactions, and solvothermal materials synthesis reactions. For example, ammonolysis and hydrogenation reactions in supercritical fluids provide a useful alternative to standard synthesis methods. In addition, organic synthetic reactions using supercritical (CO 2 ) fluids can eliminate the organic waste solvents that are used in traditional methods. Similar applications extend to commercially important solvent extraction processes, such as the decaffeination of coffee. There are important advantages in the preparation of drug delivery systems using supercritical fluids rather than standard organic solvents (e.g., polymer encapsulation of drugs and production of monodispersed micron-sized proteins and other compounds). Decomposition oxidation reactions of fluorocarbons and other organic waste materials are efficiently achieved using supercritical aqueous solvents. Moreover, there is a growing use of solvothermal methods in the production and processing of inorganic materials to which the microreactor can be applied. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments and methods of the invention. Together with the general description given above and the detailed description of the preferred embodiments and methods given below, they serve to explain the principles of the invention.  
         [0013]      FIG. 1  is an exploded view of an exemplary embodiment of a microreactor according to the present invention.  
         [0014]      FIG. 2  is a cross-sectional view of the assembled microreactor of  FIG. 1  also showing in schematic form the connection of the core chamber to an external source of a gas or fluid of interest for providing external pressure and activity control.  
         [0015]      FIG. 3  is a perspective view of the core of the microreactor of  FIG. 1  showing the core construction in more detail  
         [0016]      FIG. 4  is a cross-sectional plan view of the microreactor core of  FIG. 3  showing the fluid passageway and the thermocouple well.  
         [0017]      FIG. 5  is a cross-sectional plan view of the microreactor core of  FIG. 3 .  
         [0018]      FIG. 6  shows one embodiment of a heater assembly for heating the microreactor chamber according to the invention.  
         [0019]      FIG. 7  is an example of an optional sample holder for use with the microreactor to hold a solid sample for observation.  
         [0020]      FIG. 8  is a cross-sectional view of the assembled microreactor of  FIG. 1  showing an exemplary sample holder in the chamber and showing the chamber containing gas and liquid-rich reaction media. 
     
    
     DESCRIPTION  
       [0021]     Referring to  FIGS. 1 through 5 , an exemplary embodiment of a microreactor according to the present invention is shown. The microreactor  10  includes a core  12  having a generally cylindrical body  14  and a neck  16 . The microreactor core  12  is made of a corrosion resistant material, such as metal. The core body  14  has two generally flat opposing faces  18   a ,  18   b . A bore  22  extends through the core body  14  to form openings  24   a ,  24   b  in the core faces  18   a ,  18   b . Each of the openings  24   a ,  24   b  is countersunk to form a shoulder  26   a ,  26   b  within the bore  22  near each opening  24   a ,  24   b . The core body  14  is made to accommodate optically and probe transparent windows  30   a ,  30   b  at both ends of the bore  22 . The window materials allow for visual and spectroscopic access to the chamber  37  for the various analysis techniques to be employed. Suitable materials for the windows  30   a ,  30   b  may include, for example, moissanite or sapphire. Each of the windows  30   a ,  30   b  is positioned within each of the openings  24   a ,  24   b  and is seated against a flat sealing gasket  32   a ,  32   b , which rests against the shoulder  26   a ,  26   b  of the opening  24   a ,  24   b . The sealing gaskets  32  should be corrosion resistant and must be sufficiently deformable to provide a tight seal. Suitable materials for the sealing gaskets  32  may include elastomers, metals (e.g., Kalrez or gold) or graphite material (e.g., graflex). Other sealing materials (e.g., o-rings) may also be used. The core  12 , sealing gaskets  32   a ,  32   b  and windows  30   a ,  30   b  are held together within a clamping frame comprising a frame backing plate  34  and an opposing frame pressure plate  36 . The backing plate  34  and pressure plate  36  are made from a material having sufficient rigidity and durability to hold the assembly of the core  12 , sealing gaskets  32   a ,  32   b  and windows  30   a ,  30   b  in place over the temperature and pressure ranges of interest. If necessary, the thermal stability of the sealing gaskets  32   a ,  32   b  at higher temperatures may be improved by matching the thermal expansivity of the frame plates  34 ,  36  and the associated frame assembly to that of the microreactor assembly. It is also preferable to use flexible gaskets as stress relief gaskets  33   a ,  33   b  between the clamping frame and the windows  30   a ,  30   b  to minimize the stress on the windows  30   a ,  30   b.    
         [0022]     When assembled in this configuration, the bore  22  and windows  30   a ,  30   b  form a chamber  37  that provides a relatively large volume (e.g., 0.1 ml) pressure vessel for controlled materials and reaction observation. Advantageously, the vessel volume can be increased to accommodate larger volume investigations simply by using a core of larger size. The windows  30   a ,  30   b  allow observation of the chamber, as described in more detail below. The windows  30   a ,  30   b  are of a material that allows for the transmission of a probe beam through the windows  30   a ,  30   b  used for investigation of materials and reactions in the chamber  37 . Observation openings  39 ,  41  extend through the plates  34 ,  36  to expose the windows  30   a ,  30   b . The observations openings  39 ,  41  are tapered at an angle to allow for detection of a diffracted probe beam transmitted through the windows  30   a ,  30   b , such as X-ray diffraction. The investigative methods which can be utilized with the microreactor include, but are not limited to, X-ray, Raman, infrared, and neutron spectroscopy and/or diffraction. Nuclear magnetic resonance (NMR) studies are also possible when the core  12  is constructed with a non-ferrous material, such as Be-doped copper, and electrical feed-throughs are added. The windows  30   a ,  30   b  also preferably are transparent to permit visual inspection of the chamber  37  and the materials in the chamber.  
         [0023]     The backing plate  34  includes a plurality of guide rods  38  extending perpendicularly from the backing plate  34 . The guide rods  38  are positioned and sized to be received in and extend through corresponding alignment holes  40  in the pressure plate  36  when the microreactor  10  is assembled. When assembled, the guide rods  38  rest in alignment notches  39  located in the periphery of the core body  14 , thereby providing for precise alignment of the core  12  between the plates  34 ,  36 . The pressure plate  36  is removably secured to the backing plate  34  using cap screws  42  that extend through holes  44  in the pressure plate  36  and are screwed into threaded screw holes  46  in the backing plate  34 . When the cap screws  42  are tightened, the backing plate  34  and pressure plate  36  press the windows  30   a ,  30   b  tightly against the sealing gaskets  32   a ,  32   b  to form a seal that prevents gases or fluids in the chamber  22  from leaking out and prevents ambient air from entering the chamber  22 . Further thermal stability of the assembly an be achieved by the use of spring-type washers  48  with the cap screws  42 .  
         [0024]     Within the core neck  16  is a fluid passageway  52  that terminates at one end in an input port  54  in the wall of bore  22  and terminates at the other end in a threaded opening  56  for receiving an external high-pressure fluid supply line  58 , as shown in  FIG. 2 . The fluid supply line  58  has a high-pressure threaded fitting  60  on one end that is inserted into the threaded opening  56 . The fitting  60  preferably is a small fitting that has minimal impact on the overall volume of the core chamber  37  and that can tolerate the pressures and temperatures to which the microreactor will be subjected (e.g., a high-pressure liquid chromatography fitting). The other end of the fluid supply line  58  is coupled to a manifold  50 . The manifold  50  includes one or more valves  51 , which can be used to couple one or more sources of gases, liquids or fluids to the supply line  58  and chamber  37 . In this configuration one or more gases, liquids or fluids can be injected into the chamber  37  and their activities controlled externally during the reaction or observation of interest. Preferably, the manifold  50  includes a connection to a vacuum line, which can be used to evacuate the chamber  37  and supply line  58  to remove unwanted gases and fluids. For example, the vacuum line can be used to remove air from the chamber  37  and supply line  58  before injecting a fluid into the chamber  37  to load it for observation. The external connectivity of the chamber  37  to the supply line  58 , manifold  50  and external gas/fluid sources allows for accurate control and measurement of the pressure and activity of external gas or fluid to be input into microreactor chamber  37 . The configuration of the manifold connections shown in  FIG. 2  is but one example of connectivity for loading fluid(s). It will be understood by those skilled in the art that other connection configurations are readily achievable. After the microreactor is loaded, any of the external connections shown can be used to connect the gas/fluid of interest to the reaction chamber and provide external pressure and activity control.  
         [0025]     Referring to  FIG. 4 , a thermocouple well  62  extends from the exterior of the core body  14  to a point within the core body very near the reaction chamber  37  (e.g., within a millimeter of it) but without penetrating into the chamber  37 . The thermocouple well  14  is sized to receive a thermocouple (not shown) for measuring the temperature of the core body  14  adjacent the chamber. In this configuration, no seals are needed for the thermocouple, yet it provides an accurate reading of the internal sample and microreactor temperature.  
         [0026]     The microreactor chamber  37  can be heated or cooled by any means known in the art. In one advantageous embodiment, the microreactor chamber  37  is heated using a heater like that shown in  FIG. 6 . The heater  70  comprises a heat-conducting body  72  with a well  74  for closely holding the assembled microreactor  10  so that the frame of the assembled microreactor is in thermal contact with the heater body  72 . In a presently preferred embodiment, the heater body  72  is made of brass. Heating elements known in the art (not shown) are disposed within heating element cavities  73  the body  72 . The heater  70  includes an opening  76  for inserting the microreactor  10  into the heater well  74 . The heater opening  76  and an opposing opening  77  expose the observation openings  39 ,  41  and windows  30   a ,  30   b  of the microreactor assembly  10  to allow for transmission of a probe beam through the chamber  37 . The heater body  72  also includes thermocouple passageways  78  located to align with the thermocouple well  62  of the microreactor assembly  10  to allow for insertion of a thermocouple into the microreactor core  12  when the microreactor assembly  10  is resting in the heater well  74 . The thermocouple passageways  78  are symetrically located so that this insertion can be achieved regardliss of which orientation the microreactor assembly  10  is placed into the heater well  74 .  
         [0027]     By disassembling the backing plate  34  and the pressure plate  36  and removing the windows  30   a  and  30   b , a solid sample can be loaded into or removed from the microreactor chamber  37 . Referring to  FIGS. 7 and 8 , an example is shown of a sample holder  80  that can be used to hold a solid sample in a fixed position within the chamber  37  for observation for horizontal microreactor applications, i.e. applications where the probe beam is and windows  30   a ,  30   b  are aligned generally horizontally. The sample holder  80  comprises an optically and probe transparent half-disk  82  having a slit  84  formed therein for holding the solid sample. A corrosion resistant retainer spring  86  holds the half-disk  82  firmly in place against the exit window  30   b . For vertical applications, the sample can, for example, simply rest on the interior surface of the bottom window  30   b . In the example of  FIG. 8 , the sample holder  80  is shown to the left side of the interior of the chamber  37 , with the probe beam entering from the right and exiting and being detected to the left. It will be understood, however, that beam access can be from either side, with the sample holder  80  positioned accordingly and it will be apparent to those of skill in the art that the microreactor of the present invention can be used with many different sample positioning options. In the exemplary reaction setup of  FIG. 8 , a two-phase mixture consisting of a liquid-rich phase and a gas-rich fluid are shown, with the liquid-rich phase in contact with a solid sample that can be loaded in the sample holder  80 . This allows in situ observations of the reaction of the solid with the liquid-rich phase, as well as simultaneous observations of the interactions between the liquid-rich phase and the gas-rich fluid. Supercritical, as well as gas- and liquid-rich fluids can be investigated in combination with fluid-solid reactions.  
         [0028]     An embodiment of a microreactor according to our invention has been manufactured and successfully used up to 400° C. and 4,500 psi, with independent temperature and pressure control. The microreactor core  12  is made of Hastelloy C-276 and has a chamber volume of about 0.1 ml. The windows  30   a ,  30   b  are made of moissanite. The sealing gaskets  32   a ,  32   b  are made of graflex. The frame plates  34 ,  36  are made of stainless steel. The microreactor has been found to be leak tight for periods of up to a month. The microreactor has been successfully used for X-ray synchrotron work and Raman spectroscopy, and it can be easily adapted to utilize FTIR spectroscopy, neutron scattering, NMR spectroscopy as well as other techniques for in situ investigations of materials and reaction processes under controlled pressure and temperature.  
         [0029]     The microreactor according to our invention can be used to study any combination of compatible solids and fluids (supercritical fluids, gases and liquids), and can be used to study materials in vacuum and in elevated pressures and in sub-ambient temperatures as well as in elevated temperatures.  
         [0030]     The above-described invention possesses numerous advantages as described herein. The invention in its broader aspects is not limited to the specific details, representative devices, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the general inventive concept.