Electrically enhanced Haber-Bosch (EEHB) anhydrous ammonia synthesis

Abstract

The present invention is directed to a method and system for enhancing the production of ammonia from gaseous hydrogen and nitrogen. Advantageously, the method and system does not emit carbon gases during production. The method and system enhances the production of ammonia compared to traditional Haber-Bosch reactions.

Claims

1. A reactor for producing ammonia from nitrogen and hydrogen gas with a supported catalyst, comprising: a reactor body comprising an elongated tube having a first terminal end and a second terminal end opposite the first terminal end; an inlet in fluid communication with the first terminal end of the elongated tube for providing the nitrogen and hydrogen gas to the reactor; an electrical port extending into the elongated tube from the first terminal end; an interchangeable container positioned at and removably secured to the second terminal end of the elongated tube and in fluid communication with the second terminal end of the elongated tube, wherein the interchangeable container is a separate and distinct structure from the reactor body such that the interchangeable container removably secured to the second terminal end of the elongated tube can be changed; one or more electrodes disposed within the interchangeable container; an electride-supported metal-containing catalyst disposed within the interchangeable container; and an outlet for receiving product gases; wherein the electride-supported metal-containing catalyst is disposed exclusively within the interchangeable container; and wherein the electrical port is configured to transmit an electrical current from a power source to one or more electrodes disposed within the interchangeable container.

2. The reactor of claim 1, further comprising a condenser for condensing an ammonia gas in the product gases to ammonia liquid.

3. The reactor of claim 1, wherein the metal of the electride- supported metal-containing catalyst comprises ruthenium.

4. The reactor of claim 1, wherein a support material of the electride-supported metal-containing catalyst is selected from the group consisting of Pentacalcium trialuminate (C5A3), Monocalcium aluminate (CA), Tricalcium aluminate (C3A) and Calcium oxide (CaO).

5. The reactor of claim 1, wherein a weight percent of a catalyst on the electride-supported metal-containing catalyst is between about 0.5 wt. % and about 20 wt. %.

6. The reactor of claim 1, wherein a catalyst dispersion of the electride-supported metal-containing catalyst is between 0.1% and about 90%.

7. The reactor of claim 1, wherein a surface area of the electride-supported metal-containing catalyst is between about 1 and 100 m.sup.2/g.

8. The reactor of claim 1, wherein the electrical port provides an electrical current selected from the group consisting of DC, pulsed DC, Nonfaradaic Electrochemical Modification of Catalyst Activity (NEMCA)-mode electrical bias, an electrical field enhancement or AC electrical current.

9. The reactor of claim 1, wherein at least one of the one or more electrodes is an annular electrode disposed within the interchangeable container.

10. The reactor of claim 1, wherein the reactor comprises at least two electrodes disposed within the interchangeable container, and at least two of the at least two electrodes are concentrically aligned annular electrodes disposed within the interchangeable container.

11. The reactor of claim 9, wherein the interchangeable container comprises a first end abutting the second terminal end of the elongated tube of the reactor body and a second end opposite the first end, and the reactor further comprises: a porous support located proximate the second end of the interchangeable container; wherein the electride-supported metal-containing catalyst is disposed on the porous support.

12. The reactor of claim 11, wherein the porous support comprises a ceramic fiber, and wherein the porous support is configured to hold the electride-supported metal-containing catalyst in place within the interchangeable container while allowing product gas to pass through the porous support.

13. The reactor of claim 10, wherein the electride supported metal-containing catalyst is located at least between adjacent concentrically aligned annular electrodes.

14. The reactor of claim 9, wherein the electrical port is connected to the at least one annular electrode.

15. The reactor of claim 14, wherein the interchangeable container comprises a cup sidewall, and wherein the electrical port is further connected to the cup sidewall such that the cup sidewall acts as an additional electrode.

16. The reactor of claim 9, wherein the interchangeable container comprises a central axis, and the reactor further comprises: a central electrode rod aligned with the central axis of the interchangeable container; wherein the at least one annular electrode is concentrically aligned with the central electrode rod.

17. The reactor of claim 1, wherein the interchangeable container comprises a first end and a second end opposite the first end, and the first end of the container abuts the second terminal end of the elongated tube.

18. The reactor of claim 17, wherein the second end of the interchangeable container is porous.

19. The reactor of claim 1, wherein: the interchangeable container comprises a flange at a first end of the interchangeable container; the elongated tube comprises a flange at the second terminal end of the elongated tube; and the flange at the first end of the interchangeable container is removably secured to the flange at the second terminal end of the elongated to tube to thereby removably secure the interchangeable container to the elongated tube.

20. The reactor of claim 19, wherein the flange at the first end of the interchangeable container is removably secured to the flange at the second terminal end of the elongated tube using bolts or adhesive.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) FIG. 1 illustrates NH.sub.3 formation on electride-supported catalyst (from Kitano);

(3) FIG. 2 illustrates the NH.sub.3 synthesis rate on commercial iron oxide based catalyst without bias and with −1 V NEMCA bias (from Yiokari);

(4) FIG. 3 illustrates the increase in CO oxidation as a function of frequency for a 22,000 V cm.sup.−1 electric field (data from Lee);

(5) FIG. 4 illustrates the increase in conversion of benzene to cyclohexane for different electric field strengths and frequencies (data from Lee);

(6) FIG. 5 illustrates a schematic diagram of the EEHB lab-scale test reactor;

(7) FIG. 6 illustrates a version of the replaceable catalyst cup that can be used for unbiased, NEMCA-mode electrically enhanced, and field-mode electrically enhanced NH.sub.3 synthesis measurements;

(8) FIG. 7 illustrates the performance of Ru-decorated C12A7:e− in the lab-scale test reactor;

(9) FIG. 8 illustrates stabilized NH.sub.3 synthesis rate as a function of total reactor flow rate.

(10) FIG. 9 illustrates the x-ray diffraction patterns of C.sub.3A before and after being annealed in CO;

(11) FIG. 10 illustrates the x-ray diffraction patterns of C5A3 before and after being annealed in CO;

(12) FIG. 11 illustrates the x-ray diffraction patterns of C12A7 before and after being annealed in CO;

(13) FIG. 12 illustrates the x-ray diffraction patterns of CA before and after being annealed in CO; and

(14) FIG. 13 illustrates the x-ray diffraction patterns of CaO before and after being annealed in CO.

DETAILED DESCRIPTION

(15) The present invention is directed to a method to produce NH.sub.3 using EEHB, and the materials and apparatus used therein. More specifically, and as provided in greater detail below, this can be accomplished using an electride supported catalyst in the reactor. In some embodiments, an electrical current can be provided to the electride supported catalyst. Methods for making the electride support and electride supported catalyst are also provided.

Catalyst Support Materials and Synthesis

(16) The common method for making C12A7:e− powder involves making an off-stoichiometry powder, adding Ca metal to it, and annealing in vacuum. During the process, the white, insulating, off-stoichiometry powder becomes a dark, electrically conductive, C12A7:e− electride. It is recognized in the catalyst industry that this method of C12A7:e− cannot be readily scaled up for mass production. The prior art method for making single crystal C12A7:e− are generally taught by placing a single crystal of C12A7:O (C12A7 with oxygen anions in its cages, rather than electrons) at ambient atmosphere in a closed carbon crucible and annealing it in a tube furnace purged with inert gas at around 1200 C for 10-15 h. The anneal caused the single crystal to change from clear to green and develop a charge carrier concentration around 10.sup.19 cm.sup.−3.

(17) The present invention is directed to a scalable method for producing C12A7:e− powder. It was found that annealing C12A7:e− powder in controlled CO atmospheres at 900 C for 15 h caused it to darken and become conductive while retaining the C12A7 crystal structure. Annealing at 100% CO for 15 h at 900 C caused complete conversion to C12A7:e−, producing material with the theoretical maximum charge concentration for this material. Annealing at CO concentrations less than 25% caused the C12A7 powder to darken progressively less and not become measurably conductive. Although it was not measured, it is likely that CO concentrations between 25% and 100% cause intermediate charge carrier concentrations.

(18) Furthermore, and in one aspect of the invention, it was found that annealing other calcium aluminates in an environment of about 5 vol. % to about 100 vol. % CO, in some embodiments about 100 vol. % CO (which reduces the required annealing time) at between about 600° C. and about 1100° C., in some embodiments about 900° C. (which quickly results in a conductivity change while minimizing or eliminating the chance of calcium aluminate phase change) for about 0.1 to about 30 hours in some embodiments between about 1-15 hours (which maximizes the high carrier concentration while minimizing or eliminating the chance of causing unwanted calcium aluminate phase changes) also causes them to change from white, electrically insulating powders to dark, electrically conductive powders while retaining their original crystal structure. In addition to C12A7, this behavior has been observed in CA, C5A3, and C3A (known as celite) calcium aluminates. The rate of conversion of the C12A7 powder to an electride is dependent upon the parameters such as the concentration of a reducing agent (in this example, CO can be used as a reducing agent, though other reducing agents can also be utilized without deviating from the invention), the temperature of the reaction and the time of the reaction. The lower any of these parameters are, then the longer the conversion reaction will take. Other calcium aluminate powders can also be used, including CA, C3A, and C5A3, and combinations thereof.

(19) Annealing CaO (calcium oxide, C in cement chemistry notation) in about 5 vol. % to about 100 vol. % CO, in some embodiments about 100 vol. % (which reduces the required annealing time) at between about 600° C. and about 1100° C., in some embodiments about 900° C. (which results in a quick quickest conductivity change while minimizing the chance of phase change) for about 0.1 to about 30 hours, in some embodiments about 1-15 hours (which maximizes the high carrier concentration while minimizing the chance of causing unwanted phase changes) converts it from a white, insulating powder to a dark, electrically conducting powder while retaining its original crystal structure. This material is mentioned separately from CA, C3A, C5A3, and C12A7 because it is not, strictly speaking, a calcium aluminate. However, it responds to the CO anneal in a similar manner as the calcium aluminates.

(20) In the case of C12A7, annealing in hydrogen does not cause C12A7:O to fully convert to C12A7:e− like annealing in CO does. A reducing agent with similar Gibbs free energy as a function of temperature as CO should also cause conversion of calcium aluminates and CaO from electrically insulating to electrically conductive materials.

(21) FIGS. 9, 10, 11, 12, and 13 illustrate x-ray diffraction patterns of C3A, 82 wt. % C5A3, C12A7, CA, and CaO, respectively, before and after annealing in about 100 vol. % CO for about 15 hours at about 900° C. In each case, the x-ray diffraction pattern illustrates no significant change even though the material converted from a white, electrically insulating powder to a dark, electrically conductive powder. These patterns indicate that the material underwent an electronic change like electride conversion or semiconductor doping, rather than a change in chemical stoichiometry or crystal structure.

(22) Conversely, calcium aluminates C3A (also known as celite) and CA change from white, electrically insulating powders to off-white, electrically insulating powders after being annealed in about 10-100 vol. % CO, in some embodiments about 100 vol. % CO to reduce annealing time) at about 1100-1300° C., in some embodiments about 1200° C., for about 0.1-30 hours, in some embodiments about 6 hours. This suggests an upper temperature limit for the conversion process.

(23) It is generally known that annealing C12A7 in a dry anoxic environment causes it to decompose to C5A3. The present invention relates in one embodiment to annealing C12A7 in a CO atmosphere for about 6 hours at about 1200° C. results in a dark, electrically conductive powder with a large mass fraction (over about 80 wt. %) of C5A3. FIG. 9 illustrates x-ray diffraction patterns for the resulting darkened and conductive C5A3 electride powder. There are some peaks associated with CA and C12A7 in the pattern, but most of the peaks and peak area are associated with C5A3. This suggests that the C12A7 mixture is being converted to a C5A3 electride in a manner similar to the C12A7 to C12A7:e− conversion. Increasing the temperature to greater than about 1300° C. begins to sinter or melt the powder, producing a fused mass.

(24) C5A3 can also be made conductive by first converting C12A7 to C5A3 and then making the C5A3 conductive. The C12A7 was converted to C5A3 by annealing it in vacuum at about 1000-1200° C. (preferably 1100° C.) for about 1-12 hours (preferably 6 hours). This converts the C12A7 to about 80 wt. % C5A3 and 20 wt. % other calcium aluminates. Attempts were made to make phase pure C5A3 by annealing a mixture of C12A7 and Al.sub.2O.sub.3 with C5A3 stoichiometry (about 0.015 g Al.sub.2O.sub.3 for each 1.000 g C12A7) under the same conditions, but the product was still about 80 wt. % C5A3. In both cases, the white, electrically insulating C5A3 could be converted to a dark, electrically conductive C5A3 by annealing in about 100 vol. % CO for about 15 hours at about 900° C. This suggests that the C5A3 is being converted to a C5A3 electride in a manner similar to the C12A7 to C12A7:e− conversion.

(25) The compounds CA, C5A3, C3A, and CaO can be electrides or have some other conductivity mechanism at work (for example, oxygen vacancies). While not wishing to be bound by theory, the electrically conducting forms of C5A3, C3A, CA, and CaO can enhance NH.sub.3 synthesis in the same manner that C12A7:e− does, but does not require an electrical bias. An electrical bias can be used. It is believed that the electrically conductive C5A3, C3A, CA, and CaO can also have low work function and the ability to incorporate hydrogen atoms as H.sup.− hydride ions like C12A7:e− does. It has recently been reported that calcium nitride enhances NH.sub.3 synthesis, and it does not have a cage structure like C12A7 does. However, it does have the ability to form hydride ions and its calcium cations can enhance catalysis by creating local regions with low work function. This lends credence to the speculation that electride forms of C5A3, C3A, and CA can also enhance NH.sub.3 synthesis.

(26) The specific surface areas (surface area per unit mass) of C12A7, C5A3, C3A, CA, and CaO have all been increased by planetary ball milling with a nonaqueous solvent. Support materials can be made with specific surface areas. In some embodiments, the surface area of the support material can range from about 1 to 100 m.sup.2/g, in some embodiments about 20 m.sup.2/g to 80 m.sup.2/g. In general, a higher specific surface area can be preferable as it allows more catalyst to be supported by a given mass of support. However, if the high surface area is achieved by material with pore spaces that have very slow transport times (a tortuous path so the reactants and products take a long time to/from the catalytic sites), then the increased surface area may not result in a better catalyst decorated support. Thus, there is a balance between the surface area and the porosity of the support material.

Decoration of Support Material

(27) An aspect of the present invention is a method to decorate a support material, and the resulting decorated support. The present invention utilizes incipient wetness techniques and a ball milling technique to decorate the support materials with a metal material, such as Ru. Incipient wetness is a common decoration method in which a metal compound is dissolved in a solvent to form a solution, the support powder is wet with that solution, the solvent is allowed to evaporate from the support powder, and then the remaining dispersed metal compound is converted to metal by an appropriate anneal known by those skilled in the art. For example, Ru carbonyl can be converted to Ru or Ru oxide by annealing in steps up to about 250 ° C. in either an inert or oxygen-containing atmosphere. RuCl.sub.3 hydrate can be converted to Ru oxide or Ru metal in a similar way by annealing at 450° C.

(28) The solvent used with the method to decorate the support material will depend upon the material being dissolved in the solvent. Thus, a comprehensive list of solvents is not possible. However, the material to be dissolved will be highly soluble in the solvent, and the solvent will evaporate quickly under the process conditions. Furthermore, the temperature and the atmosphere can be varied to achieve the desired results. In some embodiments, the decoration process can be performed at room temperature and the solvent can be a non-aqueous solvent (since some of the materials will hydrate or change phase when an aqueous solution is used). In general, non-aqueous solvents can typically be used with metal-organic compounds, while salts of the desired metal that have high solubility in water can typically utilize aqueous solvents. In either case, however, the solvent must also be compatible with the support material.

(29) The calcium aluminate and CaO support powders are all cement-formers, and thus are altered by water. Thus, a non-aqueous solvent must be used for incipient wetness Ru decoration. Ru carbonyl and RuCl.sub.3 are not strongly soluble in organic solvents, which increases the amount of solvent that must be used and evaporated.

(30) The catalyst dispersion is the percentage of the catalyst atoms that are at a free surface and thus able to interact with the reactants. The catalyst dispersion can range from about 0.1% to about 90%, in some embodiments about 0.1% to about 50%. Catalyst dispersion of between about 40-60% dispersion, in some embodiments about 50%, dispersion, corresponds to catalyst islands just a few nanometers in diameter.

(31) Catalyst decorated supports ranging from about 0.5 wt. % to about 20 wt. % metal, in some embodiments Ru, can be used. In some embodiments, the catalyst decorated supports can range from 0.05 wt. % of the metal to about 5 wt. % of the metal. In general, the metal dispersion decreases after a critical wt. % of the metal is exceeded because the metal starts to make larger islands instead of making more small ones, which is more desirable. Furthermore, the amount of catalyst supported can depend upon the support material. For example, calcium amide can support a higher weight of a metal than some other support materials while maintaining a high dispersion. Furthermore, although catalyst loading is normally given in wt. %, that amount can be misleading when comparing different support materials or different catalysts because each material has a different molecular mass. For example, iron (molecular weight about 55.85) is much lighter than ruthenium (molecular weight about 101.1), so a support with 1 wt. % Fe would have many more catalyst atoms than one with 1 wt. % Ru. In the end, optimal catalyst loading is determined empirically. For example, if going from 1 wt. % Ru to 2 wt. % Ru only increases the activity by 25%, it may be more economical to use 25% more 1 wt.% Ru decorated support in the reactor.

(32) Another aspect of the invention is directed to an alternative method of decorating the support powders with a metal, such as Ru. Either Ru carbonyl or RuCl.sub.3 hydrate powders are added to the support powder along with enough organic solvent, nonlimiting examples include acetone or heptane, to make a loose paste. This paste is milled in a ball mill, nonlimiting examples include a planetary ball mill, for between about 5 minutes to about 1 hour, in some embodiments about 30 minutes, and at a speed between 100 rpm to about 1000 rpm, in some embodiments about 400 rpm. The speed of the ball mill can depend upon the model of the ball mill used in the process. This method breaks up the Ru compound and disperses it on the support powder without requiring it to be fully dissolved in the solvent. The milled Ru+support paste can be baked or annealed using methods and parameters known to those skilled in the art for a particular metal compound to convert the Ru compound to Ru metal or Ru oxide. RuCl.sub.3 hydrate is the preferred Ru compound because it is much cheaper than Ru carbonyl.

(33) Although this method can produce highly dispersed Ru, in some embodiments a dispersion up to about 90%, it also causes the conductive support powder to become non-conductive, likely due to surface damage on the powder particles. Exposing the electrically conductive support powders to the Ru compound and solvent without milling does not remove its conductivity, and milling the conductive support powders without the Ru compound does remove its conductivity. The powder still retains its dark color, and therefore is still an electrically conductive core surrounded by a more insulating shell, which can be suitable to the NH.sub.3 synthesis enhancement.

(34) The insulating shell can be beneficial to electrical enhancement because it will allow the CO-annealed powder to be used in an electric field mode as the insulating powder would not short circuit the capacitor plates. If the insulating shell still allows hydride ion transport and/or retains features that foster N.sub.2 activation, it can be beneficial.

Differential Reactor for Catalyst Activity Testing

(35) The catalyst-decorated electride's ability to catalyze NH.sub.3 can be tested at the lab scale in a small differential reactor. One skilled in the art would understand that a laboratory model can be scaled up.

(36) A schematic diagram of an embodiment of a reactor is illustrated in FIG. 5. The reactor 100 used in the design of the invention was a “tube in a tube” design in which the outer tube 102 is a pressure vessel and the inner tube 104 directs gas flow through an interchangeable cup 106 that contains the catalyst. Hydrogen and nitrogen gas are admitted to the reactor by mass flow controllers connected to the inlet flange 108 of the reactor. The nitrogen and hydrogen flow rates can maintain a desired gas mixture, NH.sub.3 production rate, NH.sub.3 concentration, space velocity, or linear gas velocity in the reactor. A thermocouple 110 that measures the catalyst temperature and electrical connections that provide bias 112 to the catalyst also enter the reactor 100 through feedthroughs in the inlet flange 108. The central portion of the reactor 100 is heated with heaters. The heaters can be insulated resistive heaters 120 that can heat the reactor 100 from room temperature to about 650° C. In some embodiments, the temperature in the reactor can be between about 300° C. and about 600° C. In some embodiments, the temperature in the reactor can be between about 450° C. and about 480° C. The product gases exit the reactor 100 through the outlet flange 114. The pressure in the reactor 100 is monitored downstream of the outlet flange with a pressure sensor 116. The reactor pressure can be controlled by a backpressure regulator 118 located downstream of the pressure sensor 116 that can raise the reactor pressure to about 150 psig. This pressure was chosen to ensure that at high temperature operation softening of the reactor's outer wall would not cause it to rupture. If the reactor components are sufficiently strong, higher pressures can be used. A practical upper limit to the reactor pressure is the pressure at which the NH.sub.3 condenses to a liquid. NH.sub.3 condensation can cause inaccurate NH.sub.3 production measurements or compromise the operation of the reactor. The specific total pressure at which NH.sub.3 condensation will occur depends on the NH.sub.3 concentration in the reactor and the reactor temperature. In some embodiments, the pressure can be between about 0 and about 140 psig. Higher pressures can result in higher synthesis rates. Product gases exiting the backpressure regulator 118 are at ambient atmospheric pressure. The product gas NH.sub.3 concentration is measured by a device downstream of the backpressure regulator 118. The product gases can be flared (i.e. ignited) to convert the NH.sub.3 and any unreacted N.sub.2 and H.sub.2 reactants to nitrogen and water so they can be safely exhausted to atmosphere for disposal.

(37) The inner tube 104 of the reactor 100 extends from the bottom side of the inlet flange 108 to near the center of the reactor 100, where it terminates in a flange. An interchangeable cup 106 containing the catalyst-decorated electride support is attached (e.g. bolted, adhered, etc.) to that flange. The cup 106 can be easily changed to allow changes to its size, shape, and electrode configuration. While FIG. 5 illustrates the cup near the center of the reactor, this position is not required. Rather, the cup simply needs to be in a region with uniform temperature. The cup diameter can be adjusted so that the gas flow rates produce a linear gas velocity that removes stagnation layers from the catalyst-decorated support particles. The length of the cup can also be adjusted for a given diameter so that the cup contains enough catalyst to produce a measured concentration of NH.sub.3. In some embodiments, between about 0.1 grams and about 50 grams of the catalyst can be used in the cup. The bottom of the cup 106 can be porous to allow gas to flow through it. In operation, the reactant gases flow through the inner tube 104, through the catalyst-decorated electride support in the cup 106, and out the outlet flange 114 of the reactor 100. The inner tube 104 and cup 106 can be electrically isolated from the rest of the reactor 100 by using an electrically insulating gasket and ceramic bolt sleeves at the inner tube's attachment to the inlet flange 108.

(38) Suitable materials for the insulation can include Kevlar fiber reinforced BUNA rubber gasket materials, or other suitable materials. Any suitable material can be used for the reactor flanges, tubing, walls, and catalyst cup. In some embodiments, the material can be stainless steak or a non-stainless steel alloy. Some or all of the reactor can be coated for corrosion protection. In general, materials selected for the reactor are compatible with NH.sub.3. Steel is a cheap option, as are most ceramics and BUNA elastomer seals. Specific incompatible materials are copper alloys, aluminum alloys, and viton elastomer seals.

(39) FIG. 6 illustrates a configuration of the catalyst cup featuring concentric cylindrical electrodes in an embodiment of the invention. The top and bottom of the electrodes 614 (e.g. A-D) rest in circular grooves in ceramic disks 610 at the top and bottom of the cup, which fix the electrode separation. The electrodes can be supported by ceramic disks 610. The ceramic disks 610 can maintain electrode separation and support the electrodes and fiber materials that keep the catalyst-decorated electride support from falling through the gas flow openings in the ceramic discs. Support tabs 612 can be used to support the ceramic disks 610. The minimum separation will be limited by the ability to put catalyst powder between the electrodes and the ability to keep the electrodes from touching each other if they warp when heated. In some embodiments, the spacing can be a minimum of about 1 mm. The maximum spacing can be limited when the reactor is in field enhancement mode as this mode requires electrodes capable of applying a sufficient electric field given power supply voltage limitations.

(40) The electrode spacing can be adjusted to allow easy loading of catalyst-decorated electride support between the electrodes and generation of the desired electric field strength (V/cm) for the available voltage. For example, if the desired field strength is about 20,000 V/cm peak to peak and the available power supply outputs about 2000 V peak to peak, then the electrode separation needs to be about 0.1 cm. A center threaded electrode rod 602 can be used to clamp the ceramic disks rigidly to the cylindrical electrodes and secured with a nut or fastener end 604. The ceramic disks have holes in the regions between the electrodes 608 to allow gas to flow through the catalyst-decorated electride support. Wires extend from the electrodes through the upper ceramic disk to allow electrical bias to be applied to them. A dopant is not required to increase the conductivity of the system. Rather, the wires can be attached to the electrode, for example by welding, soldering, or contact with fasteners. The cup flange 620 connects the cup 106 to the inner flange illustrated in FIG. 5. The cup wall 616 provides an exterior surface of the cup 106 and can act as an electrode using electrode connection A. The ceramic fiber 618 is porous enough to allow gases to flow through it, but dense enough to prevent the catalyst-decorated electride support from falling through the gas flow openings in the ceramic disks 610.

(41) The catalyst cup implementation illustrated in FIG. 6 allows the catalyst to be tested (a) without any bias, (b) in a non-current-passing NEMCA-mode electrically enhanced configuration if an electrically conductive catalyst is used and the cup and its electrodes (A, B, C, D, E) are all connected to a voltage source that applies a voltage relative to the grounded reactor body, (c) a current-passing NEMCA-mode electrically enhanced configuration if an electrically conductive catalyst is used and the electrodes are alternately connected to the positive and negative outputs of a power supply (for example electrodes A, C, and E connected to the positive potential and electrodes B and D connected to the negative potential), and (d) a field-mode electrically enhanced configuration if an electrically non-conductive catalyst is used and the electrodes are alternately connected to the positive and negative outputs of a power supply (for example electrodes A, C, and E connected to the positive potential and electrodes B and D connected to the negative potential).

(42) The catalyst cup implementation illustrated in FIG. 6 can be modified by replacing electrodes B and D with electrical insulators (for example, ceramic cylinders). In this arrangement, electrodes A and E can be connected to the positive output of a power supply and electrode C can be connected to its negative output (or vice versa). One skilled in the art would understand that other configurations can accomplish the end result without deviating from the invention. An electrically conductive catalyst-decorated support can be placed between each of the cylinders. When an electrical bias is applied, charge can be moved from the catalyst-decorated support in spaces A-B and C-D to that in spaces B-C and D-E. A NEMCA-mode electrical enhancement can be achieved by applying an AC, pulsed DC, or arbitrary waveform between the power supply terminals. This waveform can alternately enhance H.sub.2 activation, N.sub.2 activation, or intermediate species formation, causing the overall NH.sub.3 synthesis rate to be increased. In effect, the catalyst-decorated electrically conductive support in each space can alternately act as a counter electrode or working electrode as the applied potential changes in time.

(43) The C12A7:e− electride can act as a support for any NH.sub.3 catalyst. A catalyst can decorate the support (i.e. applied to the surface of the support). The catalyst can include, but is not limited to, a metal oxide, a metal nitride (cobalt molybdenum nitride, for example), a metal (including promoted iron), an alkali promoted iron catalyst, and combinations thereof. In some embodiments, the catalyst can be a metal oxide, such as an iron oxide. In some embodiments, the catalyst can contain a metal, for example any Group VIII metal, such as ruthenium, iron, osmium, nickel, palladium, platinum or combinations thereof. In some embodiments, the catalyst can be an alkali promoted metal oxide catalyst, for example an iron oxide potassium oxide catalyst. In some embodiments, the catalyst can be an alkali promoted metal catalyst, for example Cs promoted Ru metal. A “promoted” catalyst refers to an added material to the catalyst that results in the catalyst having a higher activity. In the case of NH.sub.3 catalysts, alkali metals (Cs, K, Na, etc.) are often added to the metal, for example Ru or Fe, to increase the Ru or Fe activity. Typically, the alkali metals do not do not catalyze NH.sub.3 synthesis on their own, rather these metals help Fe and Ru work better.

(44) The amount of catalyst-decorated electride support used can depend on the reactor and the desired production rate. By way of non-limiting example only, in some embodiments, between about 0.01-2 kg of catalyst can be used.

(45) Lab testing of the catalyst-decorated electride support can examine reagent flows, N.sub.2:H.sub.2 ratios, total pressures, temperatures, and electrical enhancement parameters such as applied voltage, applied electric field strength, and the frequency and form of time-varying applied voltages and electric fields. The test parameters can be chosen to ensure high reaction site availability and thus accurate measurement of the reaction rate. For example, the reagent flow rate should be high enough that further increases in flow rate do not cause increased NH.sub.3 synthesis rate. Under that condition, the reaction rate is only limited by the catalytic activity, rather than diffusion through a gas stagnation layer around the catalyst-decorated support particles. Experiments suggest that optimal H.sub.2:N.sub.2 ratios can range from about 3:1 to about 1:1. The total pressure can be adjusted in combination with H.sub.2:N.sub.2 ratios to create different reagent partial pressures to elucidate the partial pressure dependence of the rate law. Temperature can range from room temperature to about 650° C., although experiments suggest a preferred range of about 350-500° C. This configuration is chosen because it is much more difficult to elucidate reaction kinetics using integrated rate laws, and accurate reaction rate information is essential to larger reactor modeling. The rate parameters can be determined by regression of the experimental data.

(46) Reaction kinetics can initially be measured without electrical bias. Catalysts with good performance without electrical bias can then be tested with NEMCA-mode or field-mode electrical enhancement. In some embodiments, when NEMCA is used, the process can begin with a DC “no current” configuration, which would apply a potential to the catalyst relative to ground. In some embodiments, a current-flowing configuration, which is between adjacent plates, can be used. Once a flow has been established, then the current can be steady or pulsed.

(47) When an optimum DC bias for NEMCA-mode electrical enhancement is found, the effect of applying pulsed DC bias at that potential using different pulse frequencies and duty cycles can be examined. While not wanting to be bound by theory, it is believed that a pulsed DC potential can have a larger NEMCA effect than a DC potential because it can temporally organize the intermediate reactions. For example, one potential may be optimal for removing H atoms from the Ru islands by converting them to trapped H.sub.−, another may be optimal for injecting electrons from the Ru into the N.sub.2 to weaken its triple bond, and a third might be optimal for fostering reactions between trapped H.sub.− and excited N.sub.2 to form NH.sub.3. By pulsing between these potentials, the net reaction rate can be increased by first maximizing N.sub.2 adsorption on the Ru, then maximizing electron injection to the adsorbed N.sub.2, and then maximizing excited-state N.sub.2 conversion to NH.sub.3.

(48) When an optimum sinusoidally varying AC frequency is used for field-mode electrical enhancement, further optimization can be achieved by altering other wavefunctions such as triangle waves, square waves, stepped waves, and arbitrary wavefunctions. While not wanting to be bound by theory, it is believed that an arbitrary wavefunction can have a larger electric-field-enhancement effect than a sinusoidal one because it can provide different field strengths and durations to temporally organize the specific intermediate reactions for NH.sub.3 formation. It is likely that the optimal peak-to-peak amplitude and frequency will depend on the specific wavefunction.

Production Reactor for NH.SUB.3 .Synthesis

(49) Other reactors can be used in practice, including reactors that harvest the NH.sub.3 and recirculate the unreacted N.sub.2 and H.sub.2 through the reactor or pass it to a subsequent reactor for use. NH.sub.3 can be harvested by condensing it from a product gas or absorbing it into a material or filtering it from a product gas. In some embodiments, the material can absorb the NH.sub.3, which can be for example, MgCl.sub.2. Such reactors can also add nitrogen and hydrogen gas via the inlet to maintain the reactor pressure.

(50) Reactors intended for production of NH.sub.3, rather than catalyst testing, can be operated at higher pressures to both increase the NH.sub.3 synthesis rate and increase the temperature at which the NH.sub.3 can be liquefied, adsorbed, or absorbed for extraction from the product stream. Such reactors can use internal heating of the catalyst to allow the reactor walls to operate at a lower temperature by being either actively or passively cooled. This can help maintain their structural strength and ability to contain higher operating pressure.

EXAMPLES

Example 1

(51) The lab-scale differential test reactor described above has been used to test the non-electrically enhanced NH.sub.3 synthesis capability of Ru-decorated C12A7:e−. The catalyst support was a −45 mesh powder with a surface area of 6.2 m.sup.2 g.sup.−1 as measured by nitrogen BET analysis. Its surface was decorated with 1 wt. % Ru with 26% dispersion as measured by pulsed CO chemisorption.

(52) The catalyst cup used for the measurement was that shown in FIG. 6, but with the electrode assembly removed. The bottom of the cup was fit with a stainless steel screen. A 6 mm layer of ceramic fiber insulation was placed on top of the screen to support the catalyst powder. The cup was loaded with 5.081 g of catalyst, which created a catalyst bed approximately 1.5 cm deep.

(53) The reactor was run at a total pressure of 140 psig and a total flow of 4 sLm. The H.sub.2:N.sub.2 ratio was successively maintained at nominal values of 3:1, 2:1, 1.5:1, and 1:1. At each gas ratio, the reactor's internal temperature was ramped from approximately 400° C. to 500° C. at a rate of 50° C. h.sup.−1 while the rate of NH.sub.3 formation was monitored by a non-dispersive infrared sensing method (Bacharach model AGMSZ detector). The data from the measurements is illustrated in FIG. 7. The NH.sub.3 synthesis rate peaked at approximately 9.54 mmol g.sup.−1 h.sup.−1 at approximately 497° C. using the 1.5:1 H.sub.2:N.sub.2 ratio. H.sub.2:N.sub.2 ratios with more nitrogen than hydrogen have been tested, but they lead to much lower NH.sub.3 synthesis rates.

(54) Although the data illustrated in FIG. 7 did not use an electrically enhanced Haber-Bosch process, it demonstrations that the test reactor is capable of synthesizing NH.sub.3 with a Ru-decorated C12A7:e− electride catalyst. The catalyst's activity with no electrical enhancement peaked at a 1.5:1 to 2:1 H.sub.2:N.sub.2 ratio, whereas the promoted iron catalyst used in prior NEMCA-related research (data shown in FIG. 2) peaked at a 1:1 ratio with no NEMCA bias and at a hydrogen lean ratio near 0.7:1 H.sub.2:N.sub.2 when it was under −1 V NEMCA bias. The ability to perform well at higher H.sub.2:N.sub.2 ratios suggests that this catalyst is less prone to hydrogen poisoning and better able to activate N.sub.2 for reaction with H.sub.2.

(55) The data in FIG. 7 suggest that examinations of electrical enhancement of NH.sub.3 synthesis on Ru-decorated C12A7:e− electride should focus on temperatures ranging from between about 400-500° C. and H.sub.2:N.sub.2 ratios containing no less than 1 part hydrogen to nitrogen.

Example 2

(56) The lab-scale differential test reactor described above was used to test the total flow rate dependence of non-electrically enhanced NH.sub.3 synthesis on Ru-decorated C3A support. The C3A support was a −45 mesh powder with a surface area of 3.6 m.sup.2 g.sup.−1 as measured by nitrogen BET analysis. Its surface was decorated with 5 wt. % Ru with 1% dispersion as measured by pulsed CO chemisorption.

(57) The catalyst cup used for the measurement was that illustrated in FIG. 6, but with the electrode assembly removed. The bottom of the cup was fit with a stainless steel screen. A 6 mm layer of ceramic fiber insulation was placed on top of the screen to support the Ru-decorated C3A support powder. The cup was loaded with 5.040 g of catalyst, which created a catalyst bed approximately 1.5 cm deep in the 2.7 cm internal diameter cup.

(58) The reactor was run at 470° C., 140 psig total pressure, and a 2:1 H.sub.2:N.sub.2 ratio. The stabilized NH.sub.3 synthesis rate and product gas NH.sub.3 concentration was measured at a series of total gas flows. The data from the measurements is illustrated in FIG. 8. The NH.sub.3 synthesis rate increased monotonically with flow rate, and was approximately 13.2 mmol g.sup.−1 h.sup.−1 at 10 sLm total flow. The NH.sub.3 concentration at that flow was approximately 2.8 ppt, well below the equilibrium value of approximately 5% (50 ppt). This data suggests that the NH.sub.3 synthesis rate was being limited by diffusion across a stagnation layer surrounding the catalyst-decorated support particles. Removal of that stagnation layer will require flow rates higher than 10 sLm if the 27 mm internal diameter catalyst cup is used.

(59) The 2.7 cm internal diameter catalyst cup has a linear gas velocity of 29.1 cm/s at 10 sLm. An alternative to increasing the flow rate to increase the linear velocity is to decrease the catalyst cup's cross-sectional area. For example, if the cross sectional area is reduced by a factor of 3 (diameter reduced by a factor of 3.sup.1/2), the gas linear velocity will be increased by a factor of 3 at the same total flow.

(60) When the NH.sub.3 synthesis rate is no longer increased by increasing the gas linear velocity, the stagnation layer has been removed from the catalyst-decorated support particles. This provides a minimum gas flow velocity to achieve maximum NH.sub.3 synthesis rate in a production reactor. Although the data illustrated in FIG. 8 did not use an electrically enhanced Haber-Bosch process, the approach described above is valid for electrically enhanced processes.

Example 3

(61) NH.sub.3 synthesis rates have been measured on Ru-decorated CO-annealed supports where the supports consisted of CA, C5A3, C3A, C12A7, and CaO (calcium oxide, C in cement chemistry notation). Table 2 shows the conditions for each support that have produced the highest NH.sub.3 synthesis rates at 4 sLm total flow.

(62) TABLE-US-00002 Area, Ru Tem- Rate, m.sup.2 Ru, disp., perature, mmol g.sup.−1 Support g.sup.−1 wt. % % H2:N2 ° C. h.sup.−1 C12A7 6.2 1 26 1.5:1 497 9.54 C5A3 3.5 2 2 1.5:1 495 5.82 CA 4.0 2 11 1.5:1 499 4.33 C3A 4.4 2 12 1.5:1 455 11.49 CaO 9.1 1 36 1.5:1 447 11.43

(63) Ranges have been discussed and used within the forgoing description. One skilled in the art would understand that any sub-range within the stated range would be suitable, as would any number within the broad range, without deviating from the invention.

(64) The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.