JP6403135B2 - Method for producing ammonia-decomposing hydrogen from ammonia nitrogen-containing waste - Google Patents

Description

  The present invention relates to a method for producing ammonia-decomposing hydrogen from ammonia nitrogen-containing waste.

Examples of waste containing ammonia nitrogen include methane fermentation digestive fluid, domestic wastewater, and industrial wastewater. When the content of ammonia nitrogen contained in the methane fermentation digestive liquid is 3,000 ppm or more, methane fermentation stops. As a countermeasure, a method of diluting the methane fermentation digestive solution is employed, but there is a problem that the fermenter volume is increased by adding diluted water. In addition, there is a method in which ammonia nitrogen is taken out as ammonia gas using a stripping tower, and ammonia gas is recovered as ammonium sulfide using a sulfuric acid solution and used as fertilizer. However, in Japan where excessive nitrogen is a problem, Currently, there is no technology development other than the use of. In addition, domestic wastewater and industrial wastewater are treated by the activated sludge method, but this method requires an aeration tank and a denitrification tank, and it is necessary to put fuel such as hydrocarbons necessary for the activities of denitrification bacteria into the denitrification tank There is. Thus, in the conventional method, the fermenter size and excessive nitrogen in the soil become problems, and the input of energy in denitrification also becomes a problem.
In recent years, if the market for fuel cell vehicles has risen and the number of shipments will increase rapidly in the future, demand for hydrogen fuel is expected to increase in proportion to the number of vehicles owned. Unlike petroleum fuel, the hydrogen production market is expected to develop in the future.
Ammonia contains hydrogen in its molecular structure and can be used as a hydrogen source. For example, it has been proposed to take out hydrogen energy by decomposing pure ammonia gas (Patent Document 1).

JP 2005-279442 A

  This invention makes it a subject to provide the method of taking out hydrogen energy from ammonia water effectively using the waste containing ammonia nitrogen.

So far, when water vapor is mixed with ammonia, the catalyst metal is generally deactivated by steam oxidation or metal surface coating with -OH groups, so it is impossible to decompose ammonia water into hydrogen and oxygen to extract hydrogen energy It was thought to be. As a result of intensive studies, the present inventors separated ammonia from waste containing ammonia nitrogen, sprayed the concentrated ammonia water directly onto the catalyst layer composed of specific catalyst particles, and converted the ammonia water into hydrogen and nitrogen. It was conceived that hydrogen could be produced by decomposition.

That is, the present invention is as follows.
[1] A method for producing hydrogen by decomposing ammonia,
A separation process for separating ammonia from waste containing ammonia nitrogen,
A concentration step of concentrating the ammonia separated in the separation step to obtain aqueous ammonia;
An ammonia decomposition step of spraying the ammonia water on the catalyst layer to decompose it into hydrogen and nitrogen;
A process for producing ammonia-decomposing hydrogen.
[2] The ammonia decomposing hydrogen production according to [1], wherein the ammonia decomposing step is carried out in a catalytic reactor in which porous ceramic particles or a carbon material having a high specific surface area is provided with catalyst particles supporting metal nanoparticles. Method.
[3] The ammonia decomposing hydrogen production method according to [2], wherein the porous ceramic particles include at least one selected from the group consisting of alumina, silica, zeolite, titanium oxide, zirconia, lanthanum oxide, and ceria.
[4] The ammonia-decomposing hydrogen production method according to [3], wherein the porous ceramic particles are alumina and / or silica.
[5] The ammonia-decomposing hydrogen production method according to any one of [2] to [4], wherein the metal nanoparticles include at least one selected from the group consisting of ruthenium, iron, and nickel.
[6] The ammonia-decomposing hydrogen production method according to [5], wherein the metal nanoparticles are nickel and / or ruthenium.
[7] The ammonia-decomposing hydrogen production method according to any one of [1] to [6], wherein the ammonia water is 10 wt% or more of ammonia water.
[8] The ammonia-decomposing hydrogen production method according to any one of [1] to [7], wherein the temperature in the catalytic reactor in the ammonia decomposition step is 250 ° C to 700 ° C.
[9] The ammonia-decomposing hydrogen production method according to any one of [1] to [8], wherein the waste containing ammonia nitrogen is a methane fermentation digestive juice.

  The present invention provides a waste treatment technique capable of obtaining hydrogen energy from waste containing ammonia nitrogen.

It is a figure which shows the outline | summary of the ammonia water decomposition hydrogen manufacturing method of this invention. It is a graph which shows the thermodynamic equilibrium calculation result of decomposition | disassembly of the ammonia water by NASA-CEA. It is a graph showing the ammonia conversion in the decomposition reaction using a Ni / SiO ₂ catalyst of the pure ammonia or ammonia water. Aqueous ammonia decomposition hydrogen production method of the present invention, in the decomposition reaction using a Ni / SiO ₂ catalyst, the reaction temperature, the flow rate is a graph showing the effect on the ammonia conversion. It is a graph which shows the influence which the reaction temperature and flow volume have on the ammonia conversion rate in the decomposition reaction using the Ru / Al ₂ O ₃ catalyst in the ammonia water decomposition hydrogen production method of the present invention. It is a graph which shows the relationship between the flow volume and the ammonia conversion rate of the ammonia water decomposition hydrogen manufacturing method of this invention. By Ni / SiO ₂ catalyst fixed bed with or fluidized bed reactor, it is a graph showing the ammonia conversion in the decomposition reaction at the reaction temperature 873 K. By Ni / SiO ₂ catalyst fixed bed with or fluidized bed reactor, it is a graph showing the ammonia conversion in the decomposition reaction at the reaction temperature 923 K. By Ni / SiO ₂ catalyst fixed bed with or fluidized bed reactor, it is a graph showing the ammonia conversion in the decomposition reaction at the reaction temperature 973 K.

  Hereinafter, the present invention will be described in detail according to embodiments. However, the present invention is not limited to the embodiments explicitly or implicitly described in this specification.

  The present invention includes a separation step of separating ammonia from waste containing ammonia nitrogen, a concentration step of concentrating the ammonia separated in the separation step to obtain aqueous ammonia, spraying the aqueous ammonia onto a catalyst layer, hydrogen and It includes an ammonia decomposition process that decomposes into nitrogen. The outline of the ammonia water decomposition hydrogen production method of the present invention is shown in FIG.

  The waste containing ammonia nitrogen of the present invention is preferably a digested liquid fermented in a methane fermentation tank from the viewpoint of using renewable energy and supplying reaction heat to the catalyst layer. Examples of the wastewater fermented in the methane fermenter include sewage sludge, human waste, livestock manure, and food waste. Biomass having a high water content is fermented in a methane fermenter, and digestive liquid (aqueous waste) is produced in almost the same amount as the raw material together with methane gas. This aqueous waste contains ammonia nitrogen. In the present invention, the wastewater fermented in the methane fermenter is preferably livestock waste from the viewpoint of suppressing the fermenter volume.

  In the separation step of the present invention, for example, an aqueous waste containing ammonia nitrogen is introduced from a methane fermentation tank into a stripping tower, mixed with compressed air in the stripping tower, and the ammonia content in the aqueous waste is separated in the stripping tower. Ammonia is separated from the aqueous waste by being diffused and sent to an ammonia washing tower as ammonia-containing air. The aqueous waste after removing ammonia is returned to the methane fermenter. In addition, since separation in the stripping tower is possible as long as it is liquid, solid waste containing ammonia nitrogen can be liquefied and used for the separation step.

  In the concentration step of the present invention, the ammonia-containing air separated in the separation step and sent to the ammonia washing tower is washed in the ammonia washing tower to produce ammonia concentrated water (hereinafter referred to as ammonia water). It is separated into air from which air has been removed.

  In the ammonia decomposition step of the present invention, the ammonia water generated in the concentration step is sent from the ammonia washing tower through a conduit to the catalyst reactor provided with the catalyst layer, and the ammonia water sent into the catalyst reactor is the catalyst layer. Sprayed directly on. And ammonia water is decomposed | disassembled and hydrogen-nitrogen mixed steam gas is obtained.

With respect to the ammonia decomposition reaction in the ammonia decomposition step of the ammonia water decomposition hydrogen production method of the present invention, the equilibrium composition was calculated by thermodynamic equilibrium calculation from the initial conditions of NH ₃ : 20 mol% and H ₂ O: 80 mol%. For thermodynamic equilibrium calculations, S. Gordon and B.M. J. et al. McBride, “Computer Program for Caluc
Using the NASA-CEA described in ulation of Complex Chemical Equilibrium Compositions and Applications, “NASA Reference Publication 1311 (1996). ^the ammonia decomposition process of hydrogen production _{method, * H, HNO, HNO 2} , HO 2, H 2 O 2, * N, * NH, NH 2, NH 2 OH, * NO, NO 2, NO 3, N 2 H ₂ , NH ₂ NO ₂ , N ₂ H ₄ , N ₂ O, N ₂ O ₃ , N ₂ O ₄ , N ₂ O ₅ , N ₃ , N ₃ H, ^* O, ^* OH, ^* O ₂ , O ₃ H ₂ O (cr) was found not to be thermodynamically generated.

As the catalytic reactor used in the ammonia decomposition step of the present invention, a tubular reactor (continuous) or a continuous tank reactor can be used. The catalyst layer may be a flow-through fixed bed or a fluidized bed (reactor). Examples of the material for the catalytic reactor include stainless steel, and SUS316 is preferable. Moreover, it is preferable to control the reaction temperature by heating by heat exchange of the combustion gas generated when the methane gas generated in the methane fermentation process is partially combusted. When using a fluidized bed reactor, a high ammonia conversion can be achieved even if the ammonia flow rate is increased.
The reaction temperature in the reactor can be measured with a CHINO K thermocouple provided in the catalyst layer. The reaction temperature is preferably 250 ° C. or higher, more preferably 500 ° C. or higher, from the viewpoint of ammonia conversion. Moreover, 700 degrees C or less is preferable and 650 degrees C or less is more preferable.
The pressure in the reactor is more advantageous as the pressure becomes lower from the viewpoint of the equilibrium of ammonia decomposition. On the other hand, power is required to reduce the pressure. Therefore, in this embodiment, the pressure in the reactor is preferably about atmospheric pressure.
In general, it is said that the performance of the fluidized bed reactor is lower than that of the fixed bed reactor.
In the present invention, even if a fluidized bed reactor is used, a high ammonia conversion rate can be achieved at a low processing temperature. Although the details of the mechanism are not clear, the fluidized bed reactor is efficiently supplied from the heater to the entire reaction vessel because the powder catalyst is agitated to promote the heat supply from the heater. It is presumed that heat can be diffused and the residence time of ammonia in the reaction vessel contributes. When the apparatus is enlarged, it is expected that a high ammonia conversion rate can be achieved at a lower temperature by employing a fluidized bed reactor.

The catalyst layer of the present invention comprises a layer of catalyst particles, and can be provided at the center of the catalyst reactor. In this invention, ammonia is decomposed | disassembled into hydrogen and nitrogen by spraying the ammonia water introduce | transduced through the conduit | pipe from the ammonia washing tower in which the said concentration process was performed directly to a catalyst layer. As a spraying method of the ammonia water, it is sufficient that it can be sprayed directly onto the catalyst, and examples thereof include a method of spraying onto the catalyst layer as micrometer-order droplets using a nebulizer or a two-fluid nozzle.
In the present invention, the ammonia water is preferably ammonia water having an ammonia concentration of 10 wt% or more, more preferably 20 wt% or more, and particularly preferably saturated ammonia water from the viewpoint of catalytic activity and processing efficiency.
In the present invention, the ammonia water is decomposed by directly spraying the ammonia water onto the catalyst layer to obtain a hydrogen / nitrogen mixed steam gas. When a saturated aqueous solution of ammonia is directly sprayed, the water vapor concentration becomes 80 wt% at 373K.
In the present invention, when the water vapor concentration is high, the activity of the catalyst tends to decrease. However, when the water vapor concentration is 25 wt% to 80 wt%, the activity decreasing rate is constant, and a constant ammonia conversion rate is achieved. Found that is possible. This is because the catalyst particles are deactivated by steam oxidation or competitive adsorption, while the catalytic reduction reaction by hydrogen derived from the ammonia decomposition reaction also occurs at the same time, so that the oxidation-reduction reaction of both is maintained in a balanced state. It is presumed to be due to what is being done.
In the catalyst reactor, an inert Ar gas or the like may be flowed as a carrier gas. The gas flow rate is preferably 100 ml / (min · g _cat ) or more, more preferably 250 ml / (min · g _cat ) or more from the viewpoint of reaction efficiency. Moreover, 500 ml / (min * _gcat ) or less is preferable and 300 ml / (min * _gcat ) or less is more preferable. The gas supply amount is a unit representing the gas flow rate in normal notation, and represents the gas flow rate at 0 ° C. and 1 atm (atmospheric pressure) (reference state).

  The catalyst particles constituting the catalyst layer of the present invention are not particularly limited as long as ammonia water can be decomposed. However, catalyst particles carrying metal nanoparticles on porous ceramic particles or a carbon material having a high specific surface area are provided. preferable. Since the catalyst activity is higher as the particle size of the catalyst metal particle is smaller, it is preferably 50 nm or less, more preferably 10 nm or less from the viewpoint of the ammonia decomposition reaction rate. The lower limit of the particle size of the catalyst metal particles is not particularly limited, but is usually 5 nm or more. Further, the size of the catalyst particles on which the metal is supported is on the order of μm, and the particle diameter can be measured using a sieve. Although the metal to carry | support is not specifically limited, 2 wt% or more of the whole catalyst particle is preferable, 5 wt% or more is more preferable, and 10 wt% or more is especially preferable. Moreover, 50 wt% or less of the whole catalyst particle is preferable, and 40 wt% or less is more preferable.

  Although it does not specifically limit as a porous ceramic particle, It is preferable to contain at least 1 sort (s) chosen from the group which consists of an alumina, a silica, a zeolite, a titanium oxide, a zirconia, a lanthanum oxide, and a ceria, and an alumina and / or a silica are more preferable. As the porous ceramic particles, for example, they can be prepared and used by a sol-gel method, or commercially available activated alumina manufactured by Wako Pure Chemical Industries, Ltd. can be used.

The carbon material having a high specific surface area is so-called activated carbon or carbon nanotube, and is not particularly limited as long as it has a high specific surface area. The specific surface area can be measured by the BET method, and is 100 m ² / g or more. Is preferably 300 m ² / g or more. Commercially available carbon materials can be used, and examples thereof include multi-walled carbon nanotubes manufactured by Wako Pure Chemical Industries.

The metal nanoparticles are not particularly limited as long as ammonia can be decomposed into hydrogen and oxygen, but preferably contain at least one selected from the group consisting of ruthenium, iron and nickel from the viewpoint of ammonia decomposition reaction activity. Nickel and / or ruthenium are more preferred. The above elements may be used alone or in combination of two or more. When the porous ceramic particles as the support are alumina and ruthenium is supported as the metal nanoparticles, a particularly high catalytic activity is exhibited, which is preferable. In addition, when the porous ceramic particles as the support are silica and nickel is supported as the metal nanoparticles, the activity before and after the introduction of water vapor hardly decreases. Further, when the porous ceramic particles as the support are alumina and nickel is supported as the metal nanoparticles, a higher ammonia conversion rate can be obtained in the fluidized bed reactor.
The particle size of the metal nanoparticles is preferably 50 nm or less, and more preferably 10 nm or less. The particle size of the supported metal nanoparticles can be calculated by the Scherrer equation using X-ray diffraction.

The catalyst particles of the present invention can be produced using a usual method, and are not particularly limited, and examples thereof include a wet impregnation method and a coprecipitation method.
Hereinafter, described a process for the preparation of Ni / _Al 2 _{O 3} catalyst by wet impregnation method. First, nickel nitrate hexahydrate (Ni (NO ₃ ) · 6H ₂ O) is used as a precursor so that 10 wt% of Ni is supported. Next, the mixture of the catalyst metal and the carrier is calcined at 700 ° C. for 2 hours under an Ar gas flow, and then subjected to a reduction treatment at 700 ° C. for 1 hour under an H ₂ gas flow, whereby Ni / Al ₂ O ₃ A catalyst is obtained.
The surface structure of the catalyst can be analyzed by X-ray diffraction (XRD).

  The catalyst particles can be used after being formed into a certain shape. Examples of the shape of the molded body include granules, pellets, rings, and honeycombs. Further, the surface of the structure formed into a monolith such as a honeycomb, a ring shape, or a spherical shape may be used in a state where the catalyst particles are coated.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded.

<Effect of water vapor on catalyst activity>
The reaction temperature was 873 K, the flow rate (indicated as F in FIG. 3) was fixed at 750 ml / (min · g _cat ), and the ammonia conversion rates of the five catalysts were examined. Pure ammonia was introduced for 30 minutes into a catalyst reactor (fixed bed reactor) provided with a catalyst layer, and the ammonia conversion rate was measured. Subsequently, in order to simulate hydrogen production from a saturated aqueous ammonia solution instead of pure ammonia, 20 wt% ammonia and 80 wt% steam were introduced, ammonia decomposition was performed, and the conversion rate was measured. The catalyst includes catalyst particles (Ni / LaO ₃ ) in which nickel is supported on lanthanum oxide, catalyst particles (Ni / Al ₂ O ₃ ) in which nickel is supported on γ-alumina, and catalyst particles (Ni / SiO ₂ ) in which nickel is supported on silica. ₂ ), catalyst particles in which nickel is supported on titanium oxide (rutile), and catalyst particles (Ni / ZrO ₂ ) in which nickel is supported on zirconia were used. The results are shown in FIG.
FIG. 3 shows that the decomposition of pure ammonia showed high activity with a solid base carrier such as alumina and lanthanum oxide, but the neutral carrier such as silica showed high activity when decomposed from aqueous ammonia. In particular, it can be seen that the Ni / SiO ₂ catalyst has almost no decrease in activity before and after the introduction of water vapor, and can achieve a high ammonia conversion rate comparable to the decomposition of pure ammonia from aqueous ammonia.

<Effects of reaction temperature and flow rate on ammonia conversion>
The effect on the decomposition of ammonia (hereinafter referred to as ammonia conversion rate) was examined by changing the reaction temperature and flow rate.
(1) Nickel / silica catalyst In order to simulate hydrogen production from a saturated aqueous ammonia solution, 20 wt% ammonia and 80 wt% water vapor are introduced into a catalyst reactor (fixed bed reactor) provided with a catalyst layer to decompose ammonia. went. As the catalyst, catalyst particles (Ni / SiO ₂ ) in which 10 wt% nickel was supported on silica were used.
Reaction temperature is 873 K (600 ° C.), 923 K (650 ° C.), 973 K (700 ° C.), and a flow rate (denoted as F in FIG. 4) is 150 to 1500 ml / (min · g _cat ). Under the conditions, the ammonia conversion was measured. For reference, ammonia conversion from pure ammonia at 873 K (600 ° C.) and 923 K (650 ° C.) was also measured. The results are shown in FIG.
FIG. 4 shows that the Ni / SiO ₂ catalyst shows a higher ammonia conversion rate at a lower flow rate than at a higher flow rate. Moreover, it turns out that the high temperature shows the high ammonia conversion rate. It can be seen that the Ni / SiO ₂ catalyst can completely decompose ammonia water at a low flow rate and at 923 K or higher. It can be seen that at 973K, the completely resolvable flow rate is wider than that of 923K.
(2) Ruthenium / alumina catalyst In order to simulate hydrogen production from a saturated aqueous ammonia solution, 20 wt% ammonia and 80 wt% water vapor are introduced into a catalyst reactor (fixed bed reactor) provided with a catalyst layer to decompose ammonia. went. As the catalyst, catalyst particles (Ru / Al ₂ O ₃ ) in which 1 wt% ruthenium was supported on γ-Al ₂ O ₃ were used.
Measurement of ammonia conversion rate at reaction temperatures of 773 K (500 ° C.), 873 K (600 ° C.), 973 K (700 ° C.), and at a flow rate of 750 to 1500 ml / (min · g _cat ). did. The results are shown in FIG.
As shown in FIG. 5, the ammonia conversion rate was highest when the reaction temperature was 873 K (600 ° C.). Moreover, when the ammonia flow rate was increased, the ammonia conversion rate tended to decrease. This is presumed to be due to deactivation due to steam oxidation or competitive adsorption in the catalyst particles.

<Relationship between flow rate and ammonia conversion>
The reaction temperature was fixed at 873 K (600 ° C.), the ammonia flow rate was changed, and the ammonia conversion rate was examined. In order to simulate hydrogen production from a saturated aqueous ammonia solution, 20 wt% ammonia and 80 wt% steam were introduced into a catalyst reactor (fixed bed reactor) provided with a catalyst layer, and ammonia decomposition was performed. As the catalyst, catalyst particles in which 1 wt% ruthenium was supported on γ-Al ₂ O ₃ were used. The results are shown in FIG.
FIG. 6 shows that at 600 ° C., the smaller the ammonia flow rate supplied per catalyst layer weight, the higher the ammonia conversion rate. Further, it has been found that by using alumina catalyst particles carrying ruthenium, ammonia can be completely decomposed at a reaction temperature lower than that of the Ni / SiO ₂ catalyst.
From these experimental results, it was shown that by controlling the flow rate and reaction temperature, the ammonia-decomposing hydrogen production method of the present invention can be completely decomposed into hydrogen and nitrogen.
As described above, according to the ammonia decomposing hydrogen production method of the present invention, ammonia decomposition and hydrogen production can be performed from waste containing ammonia nitrogen, that is, waste treatment and hydrogen energy can be extracted from ammonia water. .

<Reference example>
Using a fixed bed reactor and a fluidized bed reactor, the ammonia conversion rate was examined by changing the ammonia flow rate under the conditions of reaction temperatures of 873 K (600 ° C.), 923 K (650 ° C.), and 973 K (700 ° C.). As the catalyst, catalyst particles (Ni / SiO ₂ ) in which 10 wt% nickel was supported on silica were used. The results are shown in FIGS.
As shown in FIG. 7, in order to completely decompose ammonia at an ammonia flow rate of 700 ml / (min · g _cat ) or higher, it is necessary to set the temperature to 650 ° C. or higher in a fixed bed reactor. It has been found that by using the reactor, ammonia can be completely decomposed at a low temperature of 600 ° C. even with the same Ni / SiO ₂ catalyst. 8 and 9, it can be seen that 973K shows the same ammonia conversion rate, but in 923K, the ammonia conversion rate of the fixed bed was almost inversely proportional to the increase in flow rate, whereas in the fluidized bed reactor, it was almost 100%. It turns out that it was constant.

  The hydrogen production method of the present invention provides a method by which hydrogen can be easily obtained from ammonia water obtained from wastes containing ammonia nitrogen such as livestock wastewater (eg human waste), industrial wastewater, and fermentation digestive juice. In particular, it is very useful industrially as an energy conversion process from biomass.

Claims (2)

A method for decomposing ammonia to produce hydrogen,
A separation process for separating ammonia from waste containing ammonia nitrogen,
A concentration step of concentrating the ammonia separated in the separation step to obtain aqueous ammonia;
An ammonia decomposition step of spraying the ammonia water on the catalyst layer to decompose it into hydrogen and nitrogen;
Only including,
In the ammonia decomposition step,
The catalyst particles used in the catalyst layer are nickel particles or ruthenium particles of 50 nm or less supported on lanthanum oxide, alumina, silica, titanium oxide, or zirconia,
The reaction temperature is 250-700 ° C.
The ammonia concentration of the ammonia water is 10 wt% or more,
After spraying the ammonia water directly on the catalyst layer, the resulting water vapor concentration is 25 wt% to 80 wt%,
The method for producing ammonia-decomposing hydrogen, wherein the catalyst layer is a fluidized bed . The ammonia-decomposing hydrogen production method according to claim 1 , wherein the waste containing ammonia nitrogen is a methane fermentation digestive juice.