WO2009025835A1

WO2009025835A1 - Non-thermal plasma synthesis of ammonia

Info

Publication number: WO2009025835A1
Application number: PCT/US2008/009948
Authority: WO
Inventors: Roger Ruan; Shaobo Deng; Zhiping Le; Paul Chen
Original assignee: Regents Of The University Of Minnesota
Priority date: 2007-08-21
Filing date: 2008-08-21
Publication date: 2009-02-26

Abstract

A method for producing ammonia comprises introducing N2 and H2 into a non-thermal plasma in the presence of a catalyst. The catalyst is effective to promote the dissociation of N2 and H2 which is used to form ammonia.

Description

NON-THERMAL PLASMA SYNTHESIS OF AMMONIA

This invention relates to thermal plasma reactors and to the use of non-thermal plasma to dissociate gas molecules to produce reactants, in particular, to use such reactants to produce ammonia.

Adverse environmental impact, rising non-renewable chemical feedstock cost, safety, and costs associated with waste management and equipment are serious concerns of the chemical and energy industries. Many chemical synthesis involve chemical reactions under severe conditions and generate polluting and hazardous wastes. Aimed at reducing or eliminating the use and generation of hazardous substances in chemical synthesis, the concept of "sustainable chemistry" or "green chemistry" gained acceptance about two decades ago.

For most agricultural crops, fertilizers are necessary to optimize yield. The invention of synthetic nitrogen fertilizer is arguably one of the great innovations of the agricultural revolution in the 19th-century. Nitrogen fertilizer is a necessary macronutrient and is applied infrequently and normally prior to or concurrently with seeding. Nitrogen based fertilizers include ammonia, ammonium nitrate and anhydrous urea, all being products based on the production of ammonia.

Ammonia is generated from a process commonly known as the Haber-Bosch Process. The Haber-Bosch Process includes the reaction of nitrogen and hydrogen to produce ammonia. The Haber-Bosch Process has been used since the early 1900s to produce ammonia which in turn has been used to produce anhydrous ammonia, ammonium nitrate and urea for use as fertilizer. The Haber-Bosch Process utilizes nitrogen obtained from air by fractional distillation and hydrogen obtained from methane (natural gas) or naphtha. There is an estimate that the Haber-Bosch Process produces 100 million tons of nitrogen fertilizer per year and consumes 1% of the world's annual energy supply. Nitrogen fertilizer, however, is responsible for sustaining approximately 40% of the earth's population.

SUMMARY OF THE INVENTION

A method for producing ammonia comprises introducing N₂ and H₂ into a non-thermal plasma in the presence of a catalyst. The catalyst is effective to promote the dissociation of N₂ and H₂, which is used to form ammonia.

Another aspect of the disclosure relates to an apparatus. The apparatus includes a gas inlet and a gas outlet, first and second electrodes, and a reaction chamber between the first and second electrodes. The reaction chamber includes a catalyst containing packed bed, which is fluidically coupled to the gas inlet and the gas outlet. At least one dielectric barrier electrically isolates at least one of the first or second electrodes from the reaction chamber. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatical view of one silent discharge NTP reactor of the present disclosure.

Figure 2 is a diagrammatical view of another embodiment of the reactor.

Figure 3 is a diagrammatical view of another embodiment of the reactor.

Figure 4 is a diagrammatical view of yet another embodiment of the reactor.

Figure 5 is a diagrammatical view of yet another embodiment of the reactor. Figure 6 is a diagrammatical view of still another embodiment of the reactor.

Figure 7 is a graphical view of ammonia yield in NTP. Figure 8 is a schematic diagram one catalyst mechanism. Figure 9 is an energy index showing different ionization levels. Figure 10 is a graphical view of ammonia yield versus voltage in a NTP reactor.

Figure 11 is a graphical view of ammonia yield versus reaction temperature in a NTP reactor. Figure 12 is a graphical view showing ammonia yield versus selected levels of N₂ to H₂ in a NTP reactor.

Figure 13 is graphical view showing ammonia yield versus reaction time in a NTP reactor.

Figure 14 is a schematic view of one process of this invention. Figure 15 is a schematic view of another embodiment utilizing the NTP reactor.

DETAILED DESCRIPTION

An aspect of the present disclosure relates to a method in which a non-thermal plasma (NTP) in a silent discharge (dielectric barrier discharge) reactor is used to assist catalyzed reactions. Such reactions when utilizing only a catalyst in conventional thermal chemistry require large amounts of energy in terms of high temperatures and/or high pressures to achieve the desired reaction.

For example Synthetic gas (Syngas) made primarily of carbon monoxide and H₂ may be used to form various synthetic hydrocarbon products. Syngas is made through gasification of a solid carbon based source such as coal or biomass.

One example of use of Syngas as a feedstock is the Fischer-Tropsch process which is a catalyzed reaction wherein carbon monoxide and hydrogen are converted into various liquid hydrocarbons. Typical catalysts used are based on iron, cobalt and ruthenium. Resulting products are synthetic waxes, synthetic fuels and olefins. It has been found that the use of NTP in a silent discharge reactor will assist in driving such a reaction at reduced temperatures and pressures.

One aspect of this disclosure is the production of ammonia from atmospheric hydrogen and nitrogen utilizing non-thermal plasma (NTP) in a silent discharge reactor. Atmospheric nitrogen and hydrogen are reacted under ambient conditions under atmospheric pressure in an NTP silent discharge reactor to produce ammonia. The ammonia is then further processed to produce nitrogen-based fertilizers such as anhydrous ammonia, ammonium nitrate or urea.

By NTP is meant electrically energized matter in a gaseous state which is not in thermodynamic equilibrium, with the energized matter being generated through electric discharge in a gaseous volume. A simple NTP reactor may consist of two electrodes with a space (the discharge volume) and sometimes one or two insulating or dielectric layers in between and connected to a high voltage power supply. By dielectric discharge barrier (DBD) is meant a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. When a high voltage is applied to the electrodes, an electric field is generated across the space between the electrodes, which, if sufficiently high, causes electric discharge. The energy in NTP is thus directed preferentially to the electron-impact dissociation and ionization of the background gas to produce NTP species including electrically neutral gas molecules, charged particles in the form of positive ions, negative ions, free radicals, energetic electrons, and quanta of electromagnetic radiation (photons). These species have an energy level in the range of about 2 to 10 eV at temperature close to ambient condition.

We have found that a packed bed NTP reactor with a strong dielectric barrier discharge extending through the packed bed showed increased yields of ammonia especially when used with a ruthenium catalyst. Suitable packed bed reactors are illustrated in the attached Figures 1 through 6.

One example of a suitable packed bed NTP reactor is generally indicated at 100 in Figure 1. The NTP reactor 100 includes a gas inlet 102, a gas outlet 104, and a packed catalyst bed 106 disposed between gas inlet 102 and gas outlet 104. The reaction occurs within the packed catalyst bed 106 as the gas flows through. The NTP reactor 100 also includes dielectric barriers 112 and 114. In the reactor configuration of Figure 1, the dielectric barriers 112 and 114 are cylindrical in form with dielectric barrier 112 positioned within and spaced from dielectric barrier 114. The packed bed 106 is positioned between the barriers 112 and 114. hi one example, the packed bed 106 is contained between quartz tubes 115, which act as the dielectric barriers 112 and 114. The electrodes 108 and 110 are attached to the respective tubes 115 and are electrically coupled to a power source 116. Power source 116 applies a voltage across electrodes 108 and 110. In this example, each of the electrodes 108 and 110 is physically and electrically isolated from the gas in the flow path 112 by one of the dielectric barriers 112 and 114, respectfully. Dielectric barriers 112 and 114 therefore prevent current from flowing through the packed bed 106 and thereby allow electrodes 108 and 110 to generate an electric field across packed bed 106. Barriers 112 and 114 also physically isolate the gas and packed bed 106 from the electrodes 108 and 110 to help prevent corrosion of the electrodes and contamination of the gas. hi an alternative embodiment, NTP reactor 100 includes only a single dielectric barrier 112 or 114 between electrodes 108 and 110. hi this example, the electrode having no dielectric barrier can be in contact with the packed catalyst bed and/or the gas in the reaction chamber formed between the electrodes. The "exposed" electrode can include a material that can serve as an additional reaction catalyst. For example, the electrode can include silver, copper, aluminum oxide, and/or iron, etc., which, depending on the gas being treated can function as a catalyst.

Another embodiment of the NTP reactor is generally indicated at 150 in Figure 2. The reactor 150 is similar in flow path configuration to the reactor 100 of Figure 1. The reactor 150 includes inner cylindrical dielectric barrier/electrode 158 and outer cylindrical dielectric barrier/electrode 160 with the inner dielectric barrier/electrode 158 (such as an electrode attached to a quartz tube) positioned within and spaced from the outer cylindrical dielectric barrier/electrode 160 (such as another electrode attached to a larger quartz tube). The dielectric barrier/electrode in Figure 2 and in subsequent descriptions of other reactors are referred to as one unit for convenience's sake, but are the same or similar component wise as the dielectric barrier and electrode described with reference to Figure 1, for example. Catalyst is positioned in the space between the barrier/electrodes 158 and 160 to form a packed bed 156. Again, the dielectric barriers electrically and physically isolate the respective electrodes from the gas being treated and the packed catalyst bed. An inlet 152 provides an access point for the gas to flow into the packed bed, exiting the packed bed through outlet 154. Current is supplied to the electrodes of the barrier/electrode elements 158 and 160 from power source 162.

Another embodiment of the NTP reactor is generally indicated at 170 in Figure 3. The reactor 170 includes a cylindrical inner electrode 172 positioned within and spaced from an outer dielectric barrier/electrode 174. In one example, the inner electrode 172 includes a stainless steel tube with no dielectric barrier insulating the electrode from packed bed 178. However, inner electrode 172 can include a dielectric barrier in alternative embodiments. The inner dielectric electrode 172 is held in a spaced-apart position from the outer dielectric barrier/electrode 174 by spacers 175. The inner electrode 172 extends centrally through spacers 175 and the outer dielectric barrier/electrode 174 encompasses the outer periphery of the spacers 175 thereby forming a space for a catalyst packed bed 178 to be positioned between the inner electrode 172 and the outer dielectric barrier/electrode 174 and to provide a means to hold the dielectric barrier/electrodes 172 and 174 in a spaced apart relationship. The inner electrode 172 is hollow and includes an inlet 176 for gas to enter. Gas flows through the dielectric barrier/electrode 172 up to a gas-permeable section 180. For example, gas permeable section 180 can include a section of tube 172 through which a plurality of holes are formed. At gas permeable section 180, the gas enters the catalyst packed bed 178 for the production of ammonia. Ammonia produced in the catalyst packed bed re-enters electrode tube 172 through the same gas permeable section 180 and exits the dielectric barrier/electrode tube 172 through outlet 182. Current is supplied to the dielectric barrier/electrodes 172 and 174 from source 184 to produce the electric field through the packed bed 178. In alternative embodiments, gas permeable section 180 can include any suitable gas permeable material such as a membrane or filter. In one example, gas permeable section 180 includes a porous ceramic material. Another embodiment of the NTP reactor is generally indicated at

190 in Figure 4. The reactor 190 includes an outer cylindrical dielectric barrier/electrode 192 and an inner dielectric barrier/electrode 194 extending centrally through the outer cylindrical dielectric barrier/electrode 192. In this example, inner electrode 194 can include a solid wire or hollow cylinder, for example, with or without a dielectric barrier isolating the electrode from catalyst containing packed bed 196. The catalyst packed bed 196 is disposed within the outer dielectric barrier/electrode 192. Power source 198 provides current to the dielectric barrier/electrodes 192 and 194 to establish an electrical field in the catalyst packed bed 196. In this example, gas enters the catalyst packed bed through inlet 200 located at one end of the dielectric barrier/electrode 192 and exits the catalyst packed bed through outlet 202 positioned at an opposite end of the packed bed 196. Clamping flanges 204 and 206 retain the dielectric barrier/electrodes 192 and 194 in position as described.

Another embodiment of the NTP reactor is generally indicated at 210 in Figure 5. The reactor 210 includes an outer cylindrical dielectric barrier/electrode 212 and an inner hollow cylindrical dielectric barrier/electrode 214 positioned centrally within the dielectric barrier/electrode 212. The inner dielectric barrier/electrode 214 is held in position by end caps 218 and 220. The end cap 218 includes a gas inlet 222 which provides a flow path into the hollow inner dielectric barrier/electrode 214 and end cap 220 includes a gas outlet 224 and provides a flow path for gas to exit the hollow inner dielectric barrier/electrode 214. A catalyst packed bed 226 is positioned between the outer and inner dielectric barrier/electrodes 212 and 214. Gas enters and exits the catalyst packed bed 226 through a gas permeable section 228 in the inner hollow barrier/electrode 214. Current to produce the electric field through the catalyst packed bed is supplied by power source 230.

Another embodiment of the NTP reactor is generally indicated at 240 in Figure 6 in which the dielectric barrier/electrodes are substantially planar. The reactor 240 is made of two outer dielectric barrier/electrode plates which will be referred to for convenience's sake as upper outer plate 242 and lower outer plate 244. It should be understood that the plates may take any type of spatial orientation instead of the horizontal orientation shown in the photo and drawing and still function in the same manner. For example, the plates 242 and 244 may be oriented vertically or in any other angular position between horizontal and vertical. The plates 242 and 244 are spaced from each by spacer 246 which extends continuously around the periphery of the plates 242 and 244 and has an inner section of lesser thickness 243. The plates 242 and 244 each include a dielectric component and an electrode component. The dielectric component physically and electrically isolate the electrode component from the reaction chamber between the electrodes. A catalyst packed bed is positioned between the upper and lower plates 242 and 244 separated by section 243 into two distinct packed bed regions 247 and 249. The upper plate 242 includes a gas inlet 248 and a gas outlet 250 that are positioned on opposite sides of the packed bed to define a gas flow path through the packed bed region 247. Similarly, the lower plate 244 includes a gas inlet 252 and gas outlet 254 that are positioned on opposite sides of the packed bed region 249 to define a gas flow path through the packed bed region 249. Current to produce the electric field through the catalyst packed bed regions 247 and 249 is supplied by power source 258. From the several specific reactor arrangements described herein, it is understood by those skilled in the art that other reactor arrangements may be employed to produce the results of this invention. For example, the reactors may have multiple cylindrical packed catalyst beds or have multiple plate arrangements to increase the number of catalyst packed beds. The multiple packed catalyst beds can be connected in series with one another and/or in parallel with one another, for example, for increasing treatment time or flow capacity, for example.

Dielectric barriers in all the reactor arrangements contemplated herein may be made of a number of materials known for their dielectric properties. The dielectric barriers can include any material having a suitable relative dielectric constant, hi one embodiment, preferred dielectric constants range from 3-300. The higher the relative dielectric constant the better the performance. For example, the dielectric barriers can include plastic, Teflon® (registered trademark of E. I. du Pont de Nemours and Company), glass (such as quartz), ceramic, epoxy resin, and aluminum oxide. An example of a ceramic includes Strontium Titanate (SrTiO₃). Other electrical insulating materials can also be used.

Electrodes are made of conductive materials such as copper and may take various shapes generally following the shape of the dielectric material, for example. The attachment (and/or relative positioning) of the electrode to the dielectric material will depend on the dielectric material used and such attachments (and/or positioning) are well known in the art. What is important is that at least one, of the electrodes 108 and 110 is physically and electrically isolated from the H₂ and N₂ gas in the catalyst packed bed by a dielectric barrier in order to prevent an electrical conduction path through the gas and/or catalyst bed.

The electrodes can have a variety of configurations in alternative embodiments. For example, the electrodes can be formed of thin planar sheets of conductive metal such as a copper foil or of a semiconductor. Other conductive or semi-conductive structures can also be used such a mesh, wire or strip. The combination of electrodes can have a variety of different types, such as plate-to-plate, mesh-to-mesh, plate-to-wire, wire-to-wire, plate-to-mesh, and wire-to-mesh, for example. The plates can be planar or cylindrical, for example. The electrodes can be arranged coaxially with one another, wherein the outer electrode is tubular and the inner electrode is either tubular or a wire.

Power to the electrodes is supplied by any suitable high voltage power supply. In one example, one of the electrodes serves as a ground electrode and the other serves as a high voltage electrode. The power supply can include a pulsed direct-current (DC) or an alternating-current (AC) power supply that is capable of producing a voltage across the electrodes so as to form an electric discharge path across the catalyst packed bed. Since the electrodes have opposite polarity, an electric field is generated across the catalyst packed bed.

The power supply can have any suitable frequency and voltage output for achieving the desired effects. These values can be a function of desired electric field across the packed catalyst bed and the size of the gap, for example. In one illustrative example, the power supply is configured to supply an output having a voltage in the range of HOV to 10OkV, such as 1000 V to 3OkV, and a frequency of 50Hz to 100 kHz. In other examples, the power supply is configured to supply an output voltage outside these ranges. In one specific embodiment, the power supply is configured to supply a standard utility line voltage of 110V at 60 Hz. Other types of power supplies can also be used, and their output voltages can have any suitable waveform, such as sinusoidal, square, or triangular.

Other types plasma reactors can be used in alternative embodiments of the methods described herein. For example, the methods can be implemented with reactors such as, but not limited to, thermal plasma reactors, glow discharge reactors, pulsed electric field reactors, corona discharge reactors, etc.

It has been found that the synthesis of ammonia using the NTP reactor is made more efficient by utilizing a catalyst. In particular, Ruthenium (Ru) has been found to be one suitable catalyst useful for this process when supported on an oxide particle (support) such as Magnesium Oxide (MgO).

It has also been found that the Ru catalyst when used in association with a promoter such as cesium (Cs) develops a synergistic relationship that dramatically increases ammonia synthesis (yield). Figure 7 illustrates ammonia yield under different comparative conditions in a bar graph format. A Cs-promoted Ru catalyst on an MgO support without the use of a NTP at atmospheric pressure is well known to show no ammonia synthesis. The first bar of Figure 7 shows the results of the use of an NTP reactor to promote ammonia synthesis without the use of a catalyst. The yield of some ammonia suggests that the NTP provides energy to dissociate N₂ and H₂ allowing addition-reactions to form NH₃. When the catalyst support, MgO, was packed into the gap between dielectric barriers in the NTP, ammonia yield was greatly improved. Although MgO is not an ammonia synthesis reaction catalyst, the presence of MgO particles promotes intensive surface discharges which favor the dissociation of N₂ and H₂ and promote ammonia formation. The next bar in Figure 7shows that the addition of an Ru catalyst on the MgO support resulted in a marginal increase in ammonia yield. The last bar in Figure 7 shows the addition of the Cs promoter to the Ru catalyst and the MgO support resulted in a dramatic increase in ammonia yield. While not wishing to be bound by theory, it is believed that the mechanism for this reaction requires that an electron be passed onto the anti- bonding orbital of N₂ through the d orbital of Ru in order to weaken the triple bond of dinitrogen. This mechanism is illustrated in Figure 8. The weakened triple bond can then be broken with additional energy, such as the energy provided by the NTP. However, the energy provided by the NTP is only 6 eV, which is insufficient to ionize Ru which has an ionization energy of 7.36 eV as illustrated in Figure 9. When a promoter such as Cs is attached to Ru, a synergistic relationship occurs. Cs with an ionization energy of only 3.89 eV can easily be ionized, producing electrons which are passed on to Ru, and then electrons are passed on to the dinitrogen. Consequently, the synergistic catalysis system of the present invention works efficiently at low temperature and atmospheric pressure due to the energetic characteristics of the NTP.

In addition to the catalysis system, a higher applied voltage to the NTP also favors higher ammonia yield due to the enhanced electrical discharge plasma generated in the NTP as illustrated in Figure 10.

Further, temperature, ratio of N₂ to H₂ and residence time also have an effect on the production of ammonia as illustrated in Figures 11 through 13. Figure 11 shows that ammonia yield peaks at about 24O⁰C utilizing a Cs- Ru/MgO-Tiθ₂ catalyst with a volume ratio of N₂ volume to H_{2 of} approximately 1 :3. The total flow rate through the NTP reactor was 60 ml/minute with a 5,000 v voltage and at a frequency of 10,000 Hz. The effect of temperature utilizing this invention is less significant than the effect of temperature on conventional catalysis. Moreover, a more important observation is the non-equilibrium nature of the NTP assisted catalytic reaction. Using conventional thermal chemistry, the maximum yield of ammonia at 300⁰C is approximately 2.2% at equilibrium. Utilizing the chemistry of this invention, approximately 5.24% yield of ammonia at 300⁰C is achieved.

Furthermore, the optimal N₂ to H₂ ratio is in the range of approximately 1:3 to 1:5 as illustrated in Figure 12, in which a Cs-Ru/MgO- TiO₂ catalyst was used. A 5,000 v voltage at a frequency of 10,000 Hz and an N₂ and H₂ total flow rate of 60 ml/minute was used.

Figure 13 shows that the ammonia yield increased with increasing reaction time (residence time) until it reached its maximum of around approximately 12%. The reaction system maintained the same activity for approximately 4 hours. For this data, a Cs-Ru/MgO-TiO₂ catalyst was used with a volume ratio of N₂:H₂=1 :3, and the N₂ and H₂ total flow rate being 60 ml per minute. A 7,000 v voltage was used at a frequency of 11,000 Hz. The example is intended for illustrative purposes only since numerous modifications and variations can be made to what is described in the example and still be within the scope of this invention.

EXAMPLE

In this example, ammonia was synthesized from H₂ and N₂ using non-thermal plasma with catalysts under atmosphere in a silent discharge type reactor. The results prove that the process of this invention can produce higher concentration ammonia as a synergistic effect of plasma and catalysts.

The measurement OfNH₃ concentrations: The NH₃ concentrations of the vent gases of ammonia synthesis were estimated by bubbling the gases in a known volume of 0.1 N H₂SO₄ solution till the methyl orange indicator changed color from red to yellow.

The concentration of ammonia was calculated according to the following formula:

(The concentration of H₂SO₄ used was 0.1N)

2NH₃ + H₂SO₄ = (NKU)₂SO₄ N₂ + 3H₂ = 2NH₃ 2 mol 1 mol 1 mol 3 mol 2 mol

X mol 0.1/2* W_H2SO4 mol Y mol Z mol X mol

X=O.1 V_H2SO4 mol Y=X/2=0.5 X mol

Z=X*3/2 =1.5 X mol

Wm₃ =X*22.4(L) W_MIX= V^ + VW (Y - Z + X)*22.4 (L)

(V_H2 V_N2; the beginning flow velocity of H₂ and N₂ t: the spending time of methyl orange indicator changed color from red to yellow)

VM/3

NH₃ % = *100%

V MIX

Catalysts preparation:

The catalysts used in this example were oxide supported ruthenium with promoters, such as Ru-CsO/MgO.

The preparation of catalysts was as follows: A selected amount of Ru compounds was weighed and dissolved in water. The Ru compound was impregnated with MgO under room temperature for 6 hours. The result was dried with an infrared lamp and desiccated under 120⁰C for 2 hours. The dried compound was washed with diluted ammonia, and then washed again with water until a neutral pH was reached. The result was a dry, supported Ru catalyst.

Ammonia was produced using the apparatus shown in the flow chart of Figure 14. Schematic diagram of the experimental apparatus: (1) nitrogen;

(2) hydrogen; (3) mass flow controller; (4) dryer; (5) gas purification; (6) temperature control instrument; (7) inner electrode; (8) outer electrode; (9) catalyst bed; (10) plasma reactor; (11) power supply; (12) compressor; and (13) ammonia storage tanks. Using the experimental apparatus described above, an ammonia concentration of 126000 ppm was achieved under the following conditions: (12.6 v/v %) under Ruthenium catalysts (Ru loading 5 wt %), 11000Hz, 7000V, VN₂:VH₂=1:3, N₂ and H₂ total flow rate 60mlΛnin. A comparative test was run with the use of a Ru catalyst and without the use of a Ru catalyst. The results along with process conditions are as follows:

Without catalyst:

The results of ammonia synthesis were as follows:

Effect OfN₂ZH₂ volume rate for ammonia synthesis volume rate (VN₂:VH₂) 1 :1 1 :1. 1 :2.3 1 :3 1 :4 1:5.7 1 :6.7

5 ammonia concentration 5360 935 Ϊ030 Ϊ4Ϊ0 ϊϊlθ 1190 9980 (ppm) 0 0 0 0 0

N₂ and H₂ total flow rate lOOml/min, voltage 5000V, frequency 8000Hz. Effect of N₂+H₂ flow for ammonia synthesis volume flow (ml/min) 60 80 HX) 140 ammonia concentration 16100 15200 13800 11800

(ppm)

VN₂:VH₂=1 :3, voltage 5000V, frequency 8000Hz.

Effect of frequency for ammonia synthesis frequency (Hz) 6000 8000 10000 12000 ammonia concentration 10700 12300 12700 12400

(ppm)

VN₂:VH₂=1 :3, N₂ and H₂ total flow rate 60ml/min, voltage 5000V.

Effect of voltage for ammonia synthesis voltage (V) 5000 6000 ammonia concentration 12300 14700

(ppm)

VN₂=VH₂=I :3, N₂ and H₂ total flow rate 60ml/min, frequency 8000Hz.

With catalysts:

The results of ammonia synthesis were as follows: Effect of catalysts for ammonia synthesis

Catalyst none Ru- Ru/MgO MgO RuJAl₂ Pd/C

Cs/MgO O₃ ammonia 2300 37100 17000 14900 11200 14600 concentration

(ppm)

V_N2:V_H2=1 :3, N₂ and H₂ total flow rate 60ml/min, voltage 5000V, frequency 8000Hz. The results showed that the Ru-Cs/MgO catalyst produced the highest concentration of ammonia. The activities of Ru-Cs/MgO catalyst fall down quickly after ammonia synthesis reaction. After a series of tests we found that using two promoters Cs and K can keep the activities of Ru/MgO catalyst for long time. In our tests the activities of ammonia synthesis can keep above 100000 ppm (10 v/v %) for 3 hours.

Effect of reaction temperature for ammonia synthesis

Temperature 76 79. 82. 8 88 108 109 113 118 125 13

concentration 4 4 7 5 5 5 5 6 7

( v/v %)

Catalyst: Ru-Cs-K/MgO; V_N2:V_H2=1:3, N₂ and H₂ total flow rate 60ml/min, voltage 7000V, frequency HOOOHz.

Effect of voltage and frequency for ammonia synthesis voltage (V) 6000 6400 6400 6000 7000 frequency 9000 9000 9500 10000 11000

(Hz) ammonia 5.23 5.93 6.84 11.1 12.6 concentration

(ppm)

Catalyst: Ru-Cs-K/MgO; V_N2:V_H2=1 :3, N₂ and H₂ total flow rate 60ml/min.

Effect of Effect of N₂/H₂ volume rate for ammonia synthesis

N₂ volume rate ( 15 25 30 40 ml/min) 45 35 30 20 H₂ volume rate ( ml/min) ammonia 5.57 3.19 2.98 2.48 concentration

( v/v %)

Catalyst: Ru-Cs/MgO; voltage 9000V, frequency 9000Hz; N₂ and H₂ total flow rate 60ml/min.

The results of this experiment indicated that higher concentration of ammonia can be produced by using plasma with catalysts under atmosphere.

In thermal catalytic synthesis of ammonia very high pressure such as about 100 atmospheres are needed. The concentration of ammonia must be under equilibration concentration. Using the present invention as the cooperation of plasma with catalysts, the concentration of ammonia is over the equilibration concentration. Such as the maximum ammonia concentration was 31000 ppm

(3.1 v/v %) under catalyst Ru/MgO (Ru loading 5 wt %), 1500Hz, 10000V, reaction temperature 573K, VN₂IVH₂=I :3, N₂ and H₂ total flow rate όOml/min.

In the same reaction condition, the concentration of ammonia is 2.2 V/V %.

The maximum concentration of ammonia was 126000 (12.6 V/V %) under H₂ 45 mL/min, N₂ 15mL/min, Voltage 7000V and frequency 11000 Hz with Ru catalyst.

The results showed that the maximum concentration of ammonia was 1.6% under H₂ 45 mL/min, N₂ 15mL/min, Voltage 8000V and frequency 10000 Hz without catalysts. Suitable Ranges of NTP Parameters for Production of Ammonia in a Silent Discharge Reactor with Catalyst Containing Packed Bed

Electrical field strength: l-30 kV/cm used in test now: 5-12

KV/mm Frequency: lHz-30 kHz used in test: 3 - 2O kHz

Size of catalyst particles: from 15 mesh to 150 mesh, used in test: 30-60 mesh Pressure: 0.01-3 Mpa used in test: 0.1 MPa

Temperature: 1-400 ⁰C used in test: 80~140 °C

Catalyst: Ru 0.01-50 wt % used in test: 5 wt. %

K: Ru (molar ratio) 1000:1- l:1000used in test: 15:1-5:1 Cs:Ru (molar ratio) 1000:1- 1:1000 used in test:

10:1-5:1 Ca:Ru (molar ratio) 1000: 1- 1 : 1000 used in test:

10:1-5:1

Fe:Ru (molar ratio) 1000: 1- 1 : 1 OOOused in test: 10:1-5:1 Co :Ru (molar ratio) 1000:1- 1:1000 used in test:

10:1-5:1 Ni:Ru (molar ratio) 1000:1- l:1000used in test: 10:1-5:1

La:Ru (molar ratio) 1000:1- 1:1000 used in test:

10:1-5:1

Flow rate of N₂ and H₂ through catalyst packed bed (per hours and per gram catalyst):

0.1 - 30000 mL/ h • g used in test: 200-400 mL/h^» g

The production of ammonia utilizing the NTP reactor in another embodiment is part of a system for the production of ammonia, which can be produced from local wind-hydrogen as depicted in the figure below.

The wind-hydrogen can be generated on wind farms, or alternatively the hydrogen may be obtained from biomass degradation. The production of ammonia from such renewable hydrogen sources can reduce air emissions, thermal pollution, water consumption and dependence on petrochemical sources of hydrogen. Acceptable feed stock hydrogen may be obtained through electrolysis of water. Hydrogen obtained from electrolysis can be fed directly to the NTP reactor. In addition, hydrogen may be obtained from biomass conversion from the methane gas being produced. Creation of hydrogen gas from methane is a well known process. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising: a gas inlet and a gas outlet; first and second electrodes; a reaction chamber between the first and second electrodes and comprising a catalyst containing packed bed, which is fluidically coupled to the gas inlet and the gas outlet; and at least one dielectric barrier, which electrically isolates at least one of the first or second electrodes from the reaction chamber.

2. The apparatus of claim 1, wherein the at least one dielectric barrier comprises: a first dielectric barrier, which electrically and physically isolates the first electrode from the reaction chamber and the packed bed; and a second dielectric barrier, which electrically and physically isolates the second electrode from the reaction chamber and the packed bed.

3. The apparatus of claim 1, wherein: the first and second electrodes are cylindrical and coaxial with one another; and the packed bed is positioned in a gap between the first and second electrodes.

4. The apparatus of claim 1, wherein: the first and second electrodes are substantially planar and parallel with another; and the packed bed is positioned in a gap between the first and second electrodes.

5. A method for producing ammonia, the method comprising: introducing N₂ and H₂ into a non-thermal plasma in the presence of a catalyst, the catalyst being effective to promote the dissociation ofN₂ and H₂ which is used to form ammonia.

6. The method of claim 5 wherein the catalyst is an electron donor.

7. The method of claim 6 wherein the catalyst is Ruthenium.

8. The method of claim 5 wherein the catalyst is Ruthenium and an element that is an electron donor having an ionization energy less than Ruthenium.

9. The method of claim 5 wherein the catalyst is provided in a packed bed through which the N₂ and H₂ flows.