JP5426201B2 - Ammonia decomposition apparatus and ammonia decomposition method using the apparatus - Google Patents

Description

  The present invention relates to an ammonia decomposing apparatus for decomposing ammonia in a gas containing ammonia and oxygen and an ammonia decomposing method using the apparatus.

  In recent years, there has been a demand for technology that emits less carbon dioxide for the purpose of preventing global warming. When hydrogen is used as a fuel, it does not emit carbon dioxide and has attracted attention as a fuel. As means for obtaining hydrogen, there are means such as hydrogen by-produced in a chemical reaction and hydrogen by-produced during steelmaking. However, these techniques use by-produced hydrogen, and it is difficult to stably obtain hydrogen.

As a means for obtaining hydrogen, there is a decomposition reaction of ammonia, and the reaction is NH ₃ → 0.5N ₂ + 1.5H ₂ . This reaction is a large endothermic reaction of 10.9 kcal / mol, and supply of reaction heat becomes a problem. As a method for supplying the reaction heat, there is an autothermal reformer (ATR) that partially burns ammonia or hydrogen generated by decomposition and uses the heat of combustion (Patent Document 1, Non-Patent Document 1), and the combustion reaction is NH ₃ +. 0.75O ₂ → 0.5N ₂ + 1.5H ₂ O, H ₂ + 0.5O ₂ → H ₂ O. As a catalyst used for ATR, there are a catalyst in which Ru is supported on alumina (Patent Document 1) and a catalyst in which Pt and Rh are supported on alumina (Non-Patent Document 1).

  However, when these catalysts are used in the reaction, it may be difficult to control depending on the catalyst composition, and it may not be easy to obtain a constant concentration of hydrogen. In addition, the temperature of the catalyst layer may change, causing damage to the ammonia reformer and deterioration of the catalyst. On the other hand, when the reforming of ammonia is not sufficient, a poor quality fuel is provided when hydrogen is used as the fuel.

International Patent Publication WO 01/87770 A1

Muroi Takagi, "Industrial Precious Metal Catalysts" Koshobo, May 26, 2003, p297

  The present invention provides an apparatus for controlling temperature rise of a catalyst layer to prevent damage to the apparatus and catalyst deterioration in an ammonia autothermal reformer (ATR) apparatus, and an ammonia decomposition method using the apparatus.

  As a result of intensive studies, the inventors of the present invention have proposed a reformer filled with a catalyst for decomposing ammonia in a gas containing ammonia and oxygen into hydrogen as a method for solving the above-described problem, and introducing a plurality of oxygen-containing gases. It has been found that introduction through the mouth can suppress an excessive increase in the temperature of the catalyst layer and prevent damage to the reformer and deterioration of the catalyst, thus completing the invention.

  In the case of a catalyst having a good balance between the ammonia decomposition activity and the ammonia combustion activity, the heat generated by the combustion and the endotherm by the decomposition reaction are well balanced, and the rise in the catalyst layer temperature can be suppressed. However, such a catalyst is, for example, a noble metal catalyst such as Rh, Ru, or Ir, and is expensive and has a small amount of resources. Therefore, it is conceivable to use non-noble metal-based decomposition catalysts such as transition metals such as Fe, Co and Ni, and nitrides and carbides such as Mo and Co as the decomposition catalyst, but ammonia combustion activity is low and ignition is performed at a low temperature. Often difficult to do. Further, when oxygen is present, the catalyst performance may be deteriorated due to oxidation. Therefore, when using a non-noble metal-based decomposition catalyst, it may be used in combination with a catalyst having high ammonia combustion activity, but there is a problem that the temperature of the catalyst layer is too high in the ammonia combustion catalyst layer. As a result of diligent studies to solve this problem, the present inventors have found that an increase in the temperature of the catalyst layer can be suppressed by providing a plurality of inlets for supplying oxygen-containing gas to be supplied.

  According to the present invention, in an ammonia autothermal reformer (ATR) device, the temperature rise of the catalyst layer can be controlled to prevent damage to the device and deterioration of the catalyst.

FIG. 1 is a schematic diagram showing a state of filling a reactor and a catalyst in Example 1. FIG. FIG. 2 shows the temperature change from the gas inlet side (0 mm) of the catalyst to the gas outlet side (100 mm) of the catalyst during the reforming reaction in Example 1. FIG. 3 shows the temperature change from the gas inlet side (0 mm) of the catalyst to the gas outlet side (100 mm) of the catalyst during the reforming reaction in Comparative Example 1.

  As a result of intensive studies to solve the above problems, the inventors have found the following technique and completed the invention. The present invention will be described in detail below, but is not limited to the following contents as long as the effects of the present invention can be obtained.

  The reaction according to the present invention is to decompose ammonia in a gas containing ammonia and oxygen into hydrogen. The ratio of the total amount of oxygen to the raw material ammonia (oxygen / ammonia) is 0.05 to 0.4 (molar ratio), preferably 0.1 to 0.2 (molar ratio). Others that can be included are the product hydrogen, a gas inert to the reaction, such as nitrogen. Nitrogen is often supplied along with oxygen as air, and it is not particularly necessary to add it excessively. The amount of nitrogen to be added is 0 to 10 (molar ratio) with respect to oxygen.

  Oxygen can be introduced alone, but can also be diluted with an inert gas and supplied. Usually, it is preferable in terms of cost to supply air.

  The gas used in the present invention may be any gas containing ammonia and oxygen (hereinafter also referred to as “reaction gas”), preferably the ammonia partial pressure is 10 to 1000 kPa, more preferably 20 to 500 kPa, preferably ammonia. The molar ratio of the total amount of oxygen added from each inlet to 1 is 0.05 to 0.4, more preferably 0.1 to 0.2. The reaction gas can contain hydrogen and nitrogen. A gas containing oxygen is introduced from a plurality of inlets. However, if there are too many inlets, the apparatus becomes complicated, so the number of inlets is preferably two. The amount of oxygen added to the inlet 1 (apparatus inlet) is preferably 20 mol% to 80 mol%, more preferably 30 mol% to 70 mol% of the total amount of oxygen added. The oxygen-containing gas is preferably air from a practical viewpoint.

The reaction gas has a space velocity with respect to the catalyst of 1000 to 100,000 h ⁻¹ , preferably 2000 to 50,000 h ⁻¹ .

  Subsequently, the amount of oxygen supplied in a divided manner can be changed and used depending on the number of times of divided charging, the catalyst activity and amount, and the temperature of the catalyst layer. It is also effective to measure the activity of the catalyst used in advance and determine the amount and frequency of oxygen to be dividedly supplied.

The catalyst layer maximum temperature, 550 to 900 ° C., preferably from 600 to 750 ° C., the reaction temperature is designed to measure the catalyst layer, it is possible to prevent the catalyst Ru exposed to excessive temperatures. The temperature at which oxygen is introduced is 0 to 400 ° C, preferably 100 to 300 ° C.

  The catalyst according to the present invention uses a catalyst having two kinds of actions, one is an ammonia combustion catalyst having an action for ammonia combustion, and the other is ammonia having an action for decomposing ammonia decomposition. It is a decomposition catalyst. A catalyst having both functions can also be used. The catalyst is used by filling the reaction gas flow with an ammonia decomposition catalyst after the ammonia combustion catalyst.

  The amount of the catalyst used is 1 to 100% by volume, preferably 2 to 50% by volume, of the ammonia decomposition catalyst with respect to the ammonia combustion catalyst.

(Ammonia combustion catalyst)
The ammonia combustion catalyst that can be used in combination with the ammonia decomposition catalyst according to the present invention may be any catalyst as long as it can burn ammonia to form N ₂ and H ₂ O. For example, vanadium oxide, tungsten oxide Molybdenum oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, perovskite oxide, Pd, Pt, and the like can be used. Precious metals such as Pd and Pt can be used by being supported on a carrier having a high specific surface area such as alumina, silica, zirconia, and titania.

(Ammonia decomposition catalyst)
As the composition of the ammonia decomposition catalyst, a transition metal system of Fe, Co, Ni, and Mo and a rare earth system of La, Ce, and Nd can be used. Transition metal systems can be used as alloys, nitrides, carbides, oxides, composite oxides, rare earth systems can be used as oxides, and both transition metal systems and rare earth systems are alumina, silica, zirconia, titania, etc. It can be used by being supported on a carrier having a high specific surface area.

  As a catalyst preparation example, a general preparation method can be used, for example, a method in which a water-soluble catalyst component precursor is dissolved in water, precipitated as a hydroxide with ammonia or the like, dried and calcined to obtain a catalyst. (Precipitation method), a method of using an oxide of an element used for a catalyst component alone or by mixing a plurality of types of oxides (mixing method), a method of supporting a catalyst component precursor as an aqueous liquid on a high specific surface area carrier ( Can be used.

  The catalyst may be in the form of granular pellets or may be supported on a cordierite or stainless steel honeycomb.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples unless it is contrary to the gist of the present invention.

Example 1
A catalyst precursor having Pt supported on alumina as an ammonia combustion catalyst was subjected to hydrogen reduction treatment to obtain a catalyst. This is referred to as catalyst A. As an ammonia decomposition catalyst, a catalyst precursor comprising Co, Ce, and Zr elements was subjected to hydrogen reduction treatment to obtain a catalyst. Two reaction tubes made of quartz having a diameter of 10 mm and a length of 50 mm and a diameter of 10 mm and a length of 100 mm are prepared as reaction tubes having this as catalyst B. The first reaction tube has catalyst A with a layer length of 3 mm and catalyst B with a layer length. Filled 17 mm. The second reaction tube was filled with catalyst A with a layer length of 3 mm and catalyst B with a layer length of 77 mm. An oxygen-containing gas inlet was provided between the first reaction tube and the second reaction tube, and the two reaction tubes were connected in series. A reaction gas containing 74 mol% ammonia, 5 mol% oxygen, and 21 mol% nitrogen was heated to 200 ° C. with a preheater and introduced into the reaction tube 1 at a flow rate of 916 ml / min at normal pressure. Air was introduced from the intermediate oxygen inlet at 242 ml / min, mixed with the reaction tube 1 outlet gas, introduced into the reaction tube 2 and reacted. The reactor was kept warm and insulated. The reactor outlet gas consumed oxygen, ammonia, and consisted of hydrogen, nitrogen, and water. The results are shown in FIG.

  The maximum temperature of the catalyst layer could be suppressed to about 700 ° C.

(Comparative Example 1)
The same catalyst as in Example 1 was used as an ammonia combustion catalyst / ammonia decomposition catalyst, and a reaction tube made of quartz having a diameter of 10 mm and a length of 150 mm was filled with catalyst A with a layer length of 5 mm and catalyst B with a layer length of 95 mm. A reaction gas containing 58 mol% ammonia, 8.7 mol% oxygen, and 33 mol% nitrogen was heated to 200 ° C. with a preheater and reacted at a normal pressure and a flow rate of 1152 ml / min. The reactor was kept warm and insulated. The reactor outlet gas consumed oxygen, ammonia, and consisted of hydrogen, nitrogen, and water. The results are shown in FIG.

  The maximum temperature of the catalyst layer has risen to 950 ° C. or higher.

  The present invention can suppress the temperature rise of the reactor / catalyst and can use the catalyst for a long time. Hydrogen can be obtained from the ammonia-containing gas.

Claims (3)

  A method for producing hydrogen using a catalyst that decomposes ammonia in a gas containing ammonia, oxygen, and hydrogen into hydrogen, wherein the reactor is provided with a plurality of oxygen-containing gas inlets, and oxygen is dividedly supplied, and The partial pressure of ammonia in the gas is 10 to 1000 kPa, the molar ratio of the total amount of oxygen added from each inlet to ammonia 1 is 0.05 to 0.4, and the amount of oxygen added to the inlet of the reactor is A method for decomposing ammonia, characterized by being 20 to 80 mol% of the total amount of added oxygen.   The ammonia decomposition method according to claim 1, wherein the catalyst is a combination of an ammonia combustion catalyst and an ammonia decomposition catalyst.   The ammonia decomposition method according to claim 1 or 2, wherein the oxygen-containing gas is air.

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