How to prevent catalyst damage

Abstract

To provide a method for restricting damage to a catalyst whereby it is possible to reduce the risk of the catalyst being damaged by the heat generated by a reaction of a propellant.SOLUTION: The present invention discloses a method for restricting damage to a catalyst in the process of reacting a propellant with the catalyst to generate gas. A temperature difference ΔT between a temperature of the catalyst before the propellant reacts and the temperature of the catalyst during the reaction of the propellant is shown in a following formula (1) when a mass of the catalyst is wp, a heat capacity of the catalyst is Cp, a supply amount of the propellant to the catalyst is q, and a surface reaction heat generated on a surface of the catalyst by the reaction of the propellant is ΔHsurface, and the conditions of the catalyst are adjusted based on the formula (1) so that the temperature difference ΔT is equal to or less than a prescribed threshold value.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for inhibiting catalyst damage. [Background technology]

[0002] There are two types of attitude control devices for artificial satellites: monopropellant thrusters and bipropellant thrusters, and the configuration of the former is described in Patent Document 1. In a monopropellant thruster, propellant is reacted with a catalyst to generate high-temperature gas, which generates the thrust required by the artificial satellite. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-46390 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, monopropellant thrusters have a problem in that the catalyst may be damaged due to an increase in temperature caused by heat generated by the propellant reaction.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a method for suppressing damage to a catalyst that can suppress the risk of the catalyst being damaged by heat generated by a propellant reaction. [Means for solving the problem]

[0006] In order to achieve the above object, the present disclosure provides a method for suppressing damage to a catalyst that generates gas by catalytically reacting a propellant, the method comprising: The mass of the catalyst is w p The heat capacity of the catalyst is C p The amount of the propellant supplied to the catalyst is q. The surface reaction heat generated on the surface of the catalyst by the reaction of the propellant is ΔHsurface Then, the temperature difference ΔT between the temperature of the catalyst before the propellant reacts and the temperature of the catalyst when the propellant reacts is expressed by the following equation (1):

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[0007] According to the method of suppressing damage to a catalyst disclosed herein, it is possible to prevent the temperature of the catalyst from exceeding the durability temperature of the catalyst, thereby suppressing the risk of the catalyst being damaged by heat generated by the propellant reaction. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a monopropellant thruster in which the catalyst that is the subject of the method of the present disclosure is used. [Diagram 2] FIG. 2 is a schematic diagram showing the relationship between temperature and reaction rate for the catalytic propellant reaction that is the subject of the method of the present disclosure. [Diagram 3] FIG. 1 is a diagram showing the configuration of an apparatus used in an experiment to determine the relationship between the surface reaction heat and the total reaction heat used in the method of the present disclosure. [Figure 4] 1 is a cross-sectional view of a portion of a catalyst support of a catalyst that is the subject of the method of the present disclosure. [Diagram 5] FIG. 2 is a diagram for explaining a model for simulating the temperature difference between two different positions on a catalyst support when the catalyst that is the subject of the method of the present disclosure is heated. [Figure 6] 4 is a simulation result of the temperature difference within the catalyst support of the catalyst that is the subject of the method of the present disclosure and the change in catalyst temperature over time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a method for suppressing damage to a catalyst according to an embodiment of the present disclosure will be described with reference to the drawings. The embodiment shows one aspect of the present disclosure, and does not limit the present disclosure. The embodiment can be arbitrarily modified within the scope of the technical idea of ​​the present disclosure.

[0010] <Configuration of a monopropellant thruster using the catalyst that is the subject of the method of the present disclosure> The catalyst in which damage has been suppressed by the method described later in this disclosure can be used, for example and without limitation, in a monopropellant thruster 1 as an attitude control device for an artificial satellite, as shown in FIG. 1. The monopropellant thruster 1 includes a propellant tank 2 and a thruster unit 3. The propellant tank 2 contains an arbitrary propellant 7. The thruster unit 3 includes a propellant supply unit 4 and a decomposition gas exhaust port 5. The thruster unit 3 has a shape that widens from the propellant supply unit 4 toward the decomposition gas exhaust port 5. The propellant supply unit 4 is provided on the propellant tank 2 side of the thruster unit 3. A catalyst 6 is provided inside the propellant supply unit 4. The decomposition gas exhaust port 5 is an opening provided on the opposite side of the thruster unit 3 from the propellant supply unit 4.

[0011] <Operation of a monopropellant thruster using the catalyst that is the subject of the method of the present disclosure> A propellant 7 is supplied from a propellant tank 2 to a propellant supply unit 4. The propellant 7 reacts, i.e., is decomposed, by a catalyst 6 provided inside the propellant supply unit 4 to generate high-temperature decomposition gas. This high-temperature decomposition gas is discharged from a decomposition gas outlet 5, thereby providing thrust to an artificial satellite (not shown) equipped with a monopropellant thruster 1.

[0012] <Method of suppressing catalyst damage according to the present disclosure> When the catalyst 6 reacts with the propellant 7, reaction heat is generated, causing a rise in the temperature of the catalyst 6. Depending on the characteristics of the catalyst 6 and the propellant 7, the catalyst 6 may be damaged by the rise in temperature. Below, a method for suppressing the risk of the catalyst 6 being damaged due to such causes will be described.

[0013] There are two possible factors that cause damage to the catalyst 6. The first factor is that the temperature of the catalyst 6 exceeds the endurance temperature of the catalyst 6. The second factor is that the temperature difference between two different positions on the catalyst support of the catalyst 6 becomes large, causing the catalyst support to crack due to thermal stress caused by this temperature difference. Below, methods for dealing with these two factors are explained. Although each countermeasure can be adopted separately and the respective action and effect can be obtained, adopting both countermeasures makes it possible to further suppress damage to the catalyst 6.

[0014] <Responses to the first factor> In the monopropellant thruster 1, when the reaction of the propellant 7 by the catalyst 6 starts, if the reaction rate and reaction heat of the reaction are high, the heat generated on the surface of the catalyst 6 cannot be removed quickly enough, and the heat accumulates in the catalyst 6, causing a rise in the temperature of the catalyst 6. Since the reaction rate increases as the temperature of the catalyst 6 increases, there is a possibility that the temperature rise of the catalyst 6 will become uncontrollable.

[0015] As a result of research, the inventors of the present disclosure have found that, as shown in FIG. 2, when the temperature of the reaction environment of the propellant 7 is low, the reaction rate of the propellant 7 tends to be higher on the surface of the catalyst 6 than the reaction rate in the gas phase, and when the temperature of the reaction environment of the propellant 7 is high, the reaction rate of the propellant 7 tends to be higher in the gas phase than the reaction rate on the surface of the catalyst 6. The temperature at which the magnitude relationship between the two reaction rates is reversed is called T C Then, the temperature of the catalyst 6 is T C However, the temperature rises rapidly to T C At temperatures above this, the reaction rate in the gas phase increases. For this reason, it is believed that the temperature of the catalyst 6 can be prevented from rising uncontrollably if the conditions of the catalyst 6 can be appropriately controlled. Therefore, the following considerations are made.

[0016] The mass of the catalyst 6 provided inside the propellant supply unit 4 is w p The heat capacity of the catalyst 6 is C p The amount of propellant 7 supplied to the catalyst 6 is q. The surface reaction heat generated on the surface of the catalyst 6 by the reaction of the propellant 7 is ΔH surfaceand the temperature difference between the temperature of the catalyst 6 before the propellant 7 reacts and the temperature of the catalyst 6 when the propellant 7 reacts is ΔT, the heat balance is expressed by the following equation (2). w p C p ΔT=qΔH surface (2)

[0017] By transforming equation (2), ΔT is expressed by the following equation (3).

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[0018] Here, the adiabatic flame temperature determined from the composition of the propellant 7 is T D The inlet temperature of the propellant 7 to the catalyst 6, i.e., the temperature of the propellant 7 supplied to the catalyst 6, is T inlet The total reaction heat of propellant 7 is ΔH Total Then, the surface reaction heat ΔH surface is expressed as the following equation (4), and by substituting this equation (4) into equation (3), the surface reaction heat ΔH surface Instead of the easily measurable total heat of reaction, ΔH Total can be used.

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[0019] The maximum temperature inside the catalyst 6 is the temperature T top Therefore, T top is used as the monitoring temperature. The fact that the temperature at the inlet of the catalyst 6 is the highest is based on the research results of the inventors of the present disclosure. This is because the reaction of the propellant 7 by the catalyst 6 in the monopropellant thruster 1 is so fast that the temperature at the inlet of the catalyst 6 becomes the highest. T topIn order to measure the temperature, it is necessary to provide a temperature sensor directly inside the catalyst 6. Regarding this point, according to research by the inventors of the present disclosure, when the temperature of the catalyst 6 at the inlet of the catalyst 6 and the temperature of the outer wall of the propellant supply section 4 corresponding to the inlet position of the catalyst 6 were compared, they were found to be almost the same, and therefore it was found that a temperature sensor can be provided to measure the temperature of the outer wall of the propellant supply section 4 corresponding to the inlet position of the catalyst 6, even if a temperature sensor is not provided to directly measure the temperature of the catalyst 6 at the inlet of the catalyst 6.

[0020] The catalyst 6 includes a catalyst support, such as α-alumina or γ-alumina, and a plurality of catalyst particles, each of which is composed of a catalyst component supported on the catalyst support, such as a metal, such as platinum or iridium, or a compound of such a metal. Damage to the catalyst 6 means that the catalyst support is damaged. For this reason, the threshold value of ΔT in formula (3) is based on the composition of the catalyst support. For example, when α-alumina is used as the catalyst support, the threshold value of ΔT can be 1400°C, and when γ-alumina is used as the catalyst support, the threshold value of ΔT can be 700°C. In addition, the temperature T in formula (4) C is based on the composition of the catalyst component. For example, when platinum is used as the catalyst component, T C = 800 °C, and when iridium is used as the catalyst component, T C = 550°C. ΔT threshold and T C The value of can be obtained in advance by experiments or the like based on the composition of the catalyst carrier and catalyst components of the catalyst 6.

[0021] In order to suppress damage to the catalyst 6, the conditions of the catalyst 6 are adjusted based on the formula (3). Specifically, in the formula (3), the supply amount q of the propellant 7 is arbitrarily determined, and the mass w of the catalyst 6 is adjusted so that ΔT is equal to or less than the threshold value. p In this case, the condition of the catalyst 6 to be adjusted is the mass w p As another example, in formula (3), the mass w of the catalyst 6 p is arbitrarily determined, and the supply amount q of the propellant 7 is determined so that ΔT is equal to or less than the threshold value. In this case, the condition of the catalyst 6 to be adjusted is the mass w pAs another example, the mass of the catalyst 6 is w p The supply amount q of the propellant 7 is arbitrarily determined, and a catalyst is selected such that ΔT is equal to or smaller than a threshold value. The condition of the catalyst 6 to be adjusted is the type (or composition) of the catalyst.

[0022] In this way, the temperature of the catalyst 6 can be prevented from exceeding the endurance temperature of the catalyst, so that the risk of the catalyst 6 being damaged by the heat generated by the reaction of the propellant 7 can be reduced.

[0023] In the explanation so far, the surface reaction heat ΔH surface and the total reaction heat ΔH Total The relationship between is expressed by equation (4), but is not limited to this form. This relationship can be obtained by experiment. For example, as shown in FIG. 3, a catalyst 102 is filled in a reaction vessel 100 configured to be heatable by a heater 101, and a predetermined amount of propellant 103 is supplied in a pulsed manner into the reaction vessel 100. The reaction vessel 100 communicates with a sampling bag 105 via a drain receiver 104, and gas is sampled from the sampling bag 105. The temperature, amount, and composition of the gas are measured, and the temperature rise of the catalyst 102 is obtained from these data, and the surface reaction heat ratio α to the total reaction heat can be estimated. In the experiments conducted by the inventors of the present disclosure, a catalyst 102 containing platinum and iridium as catalyst components was used, and α was 0.1 to 0.15. If α is determined in advance, the surface reaction heat ΔH surface Even if we do not know the total reaction heat ΔH in equation (3), Total can be used. ΔH surface = αΔH Total (5)

[0024] <Measures to address the second factor> Next, the countermeasure against the second factor will be described. Even if the above-mentioned countermeasure against the first factor makes it possible to prevent the temperature of the catalyst 6 from exceeding the endurance temperature of the catalyst, the second factor, that is, as shown in Fig. 4, when the temperature difference between two different positions P1 and P2 on the catalyst carrier 6a of each catalyst particle constituting the catalyst 6 is large, the catalyst carrier 6a may crack due to the thermal stress caused by this temperature difference. It is considered that the second factor can be countered by reducing the temperature difference between the two different positions P1 and P2 on the catalyst carrier 6a.

[0025] As shown in FIG. 5, when propellant 7 is supplied to a catalyst 6 including a catalyst carrier made of alumina with a particle size of 0.8 mm, the inventors of the present disclosure have determined that, for each of catalyst particles 6c and 6d present at positions 2 mm and 4 mm from an inlet 6b of the catalyst 6, the most upstream surface A of the catalyst carrier in the flow direction of the propellant 7 is c ,A d and the temperature of the most downstream surface B c ,B d The change over time in the temperature difference (unit: °C / 0.8 mm) between the inlet and the outlet was calculated by unsteady calculation using a catalytic reaction analysis program that takes into account elementary reactions in a heterogeneous system developed by the inventors of the present disclosure. The results are shown in Figure 6. Figure 6 also shows the change over time in the temperature of the catalyst 6 located at positions 2 mm and 4 mm from the inlet of the catalyst 6.

[0026] According to FIG. 6, the temperature difference becomes maximum about 2 seconds after the start of the supply of the propellant 7, and the maximum value is 100°C / 0.8mm for the catalyst particle 6c located 2mm from the inlet 6b of the catalyst 6, and 50°C / 0.8mm for the catalyst particle 6d located 4mm from the inlet 6b of the catalyst 6. It is known that alumina has thermal shock resistance if the temperature difference between two points is about 200°C. Therefore, based on the maximum temperature difference "100°C / 0.8mm" for the catalyst located 2mm from the inlet 6b of the catalyst 6, if the particle size of the catalyst carrier is set to 1.6mm or less, the temperature difference between two points in the catalyst carrier can be prevented from exceeding 200°C even for the catalyst particle 6c located 2mm from the inlet 6b of the catalyst 6. As a result, damage to the catalyst due to the second factor can be suppressed.

[0027] The inventors of the present disclosure conducted an experiment in which three alumina catalyst carriers, one with a particle size of 2.0 mm, one less than 2.0 mm, and one more than 2.0 mm, were heated to 200°C in about two seconds. As a result, no cracks were observed in the carriers with a particle size of 2.0 mm and one less than 2.0 mm, but damage was observed in the carriers with a particle size of more than 2.0 mm. According to the results of this experiment, it is believed that if alumina with a particle size of 2.0 mm or less is used as the catalyst carrier, damage to the catalyst caused by the second factor can be suppressed.

[0028] The contents described in each of the above embodiments can be understood, for example, as follows.

[0029] [1] A method for suppressing damage to a catalyst according to one embodiment includes the steps of: A method for suppressing damage to a catalyst that generates gas by reacting a propellant (7) with a catalyst (6), comprising the steps of: The mass of the catalyst (6) is w p The heat capacity of the catalyst (6) is C p The amount of the propellant (7) supplied to the catalyst (6) is q, and the surface reaction heat generated on the surface of the catalyst (6) by the reaction of the propellant (7) is ΔH surfaceThen, the temperature difference ΔT between the temperature of the catalyst (6) before the propellant (7) reacts and the temperature of the catalyst (6) when the propellant (7) reacts is expressed by the following formula (3):

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[0030] According to the method of suppressing damage to a catalyst disclosed herein, it is possible to prevent the temperature of the catalyst from exceeding the durability temperature of the catalyst, thereby suppressing the risk of the catalyst being damaged by heat generated by the propellant reaction.

[0031] [2] A method for suppressing damage to a catalyst according to another embodiment is the method for suppressing damage to a catalyst according to [1], The condition of the catalyst (6) is adjusted by adjusting the mass w of the catalyst (6) so that the temperature difference ΔT is equal to or less than a preset threshold value. p This includes adjusting the

[0032] According to this method, by adjusting the mass of the catalyst relative to the amount of propellant supplied, the temperature of the catalyst can be prevented from exceeding the catalyst's durability temperature, thereby reducing the risk of the catalyst being damaged by heat generated by the propellant reaction.

[0033] [3] A method for suppressing damage to a catalyst according to yet another embodiment is the method for suppressing damage to a catalyst according to [1], comprising the steps of: The adjustment of the conditions of the catalyst (6) includes adjusting the supply amount q of the propellant (7) so that the temperature difference ΔT is equal to or smaller than a preset threshold value.

[0034] According to this method, by adjusting the amount of propellant supplied relative to the mass of the catalyst, the temperature of the catalyst can be prevented from exceeding the catalyst's durability temperature, thereby reducing the risk of the catalyst being damaged by heat generated by the propellant reaction.

[0035] [4] A method for suppressing damage to a catalyst according to yet another embodiment is the method for suppressing damage to a catalyst according to [1], comprising the steps of: The conditions of the catalyst (6) are adjusted by adjusting the mass w of the catalyst (6). p and selecting a catalyst (6) such that the temperature difference ΔT is equal to or smaller than a preset threshold value when a supply amount q of the propellant (7) is preset.

[0036] According to this method, by selecting an appropriate catalyst, the temperature of the catalyst can be prevented from exceeding the catalyst's durability temperature, thereby reducing the risk of the catalyst being damaged by heat generated by the propellant reaction.

[0037] [5] A method for suppressing damage to a catalyst according to yet another embodiment is a method for suppressing damage to a catalyst according to any one of [1] to [4], The temperature at which the reaction rate of the propellant (7) in the gas phase is greater than the reaction rate of the propellant (7) on the surface of the catalyst (6) is defined as T C The adiabatic flame temperature determined from the composition of the propellant (7) is T D and the temperature of the propellant (7) supplied to the catalyst (6) is T inlet The total reaction heat of the propellant (7) is ΔH Total Then,

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[0038] According to this method, the temperature of the catalyst can be prevented from exceeding the endurance temperature of the catalyst, thereby reducing the risk of the catalyst being damaged by heat generated by the reaction of the propellant.

[0039] [6] A method for suppressing damage to a catalyst according to yet another embodiment is a method for suppressing damage to a catalyst according to any one of [1] to [4], The total reaction heat ΔH of the propellant (7) Total The surface reaction heat ΔH surfaceThe ratio α is determined in advance by experiment. In the formula (3), ΔH surface = αΔH Total is used.

[0040] According to this method, if α is determined in advance, the surface reaction heat ΔH surface Even if you don't know the total reaction heat ΔH Total By using this, the temperature of the catalyst can be prevented from exceeding the endurance temperature of the catalyst, thereby reducing the risk of the catalyst being damaged by heat generated by the reaction of the propellant.

[0041] [7] A method for suppressing damage to a catalyst according to yet another embodiment is a method for suppressing damage to a catalyst according to any one of [1] to [6], The catalyst (6) comprises an alumina catalyst carrier (6a) and a catalyst component supported on the catalyst carrier (6a), The maximum distance between any two points in the catalyst carrier (6a) is 2 mm or less.

[0042] According to this method, the temperature difference inside the catalyst carrier can be prevented from exceeding 200° C., so that the risk of cracking due to thermal stress can be suppressed.

[0043] [8] A method for suppressing damage to a catalyst according to yet another embodiment is the method for suppressing damage to a catalyst according to [7], The maximum distance between any two points in the catalyst carrier (6a) is 1.6 mm or less.

[0044] According to this method, the temperature difference inside the catalyst carrier can be prevented from exceeding 200° C., so that the risk of cracking due to thermal stress can be suppressed.

[0045] [9] A method for suppressing damage to a catalyst according to yet another embodiment is a method for suppressing damage to a catalyst according to any one of [1] to [8], The catalyst (6) and the propellant (7) are used in a monopropellant thruster (1).

[0046] According to this method, the temperature of the catalyst used in the monopropellant thruster can be prevented from exceeding the catalyst's durability temperature, thereby reducing the risk of the catalyst being damaged by heat generated by the propellant reaction. [Explanation of symbols]

[0047] 1 Monopropellant thruster 6. Catalyst 6a Catalyst carrier 7 Propellant

Claims

1. A method for suppressing damage to a catalyst that generates gas by catalytically reacting a propellant, comprising: The mass of the catalyst is w ｐ and the heat capacity of the catalyst is C ｐ The amount of the propellant supplied to the catalyst is q, and the surface reaction heat generated on the surface of the catalyst by the reaction of the propellant is ΔH ｓｕｒｆａｃｅ Then, the temperature difference ΔT between the temperature of the catalyst before the propellant reacts and the temperature of the catalyst when the propellant reacts is expressed by the following formula (1): [0010] adjusting the conditions of the catalyst based on the formula (1) so that the temperature difference ΔT is equal to or less than a preset threshold value; The catalyst and the propellant are used in a monopropellant thruster, and the method for suppressing damage to the catalyst is provided.

2. The catalyst condition is adjusted by adjusting the mass w of the catalyst so that the temperature difference ΔT is equal to or smaller than a preset threshold value. ｐ 2. The method of claim 1, further comprising adjusting

3. 2. The method for suppressing damage to a catalyst as described in claim 1, wherein adjusting the condition of the catalyst includes adjusting the supply amount q of the propellant so that the temperature difference ΔT is equal to or less than a preset threshold value.

4. The catalyst conditions are adjusted by adjusting the mass w of the catalyst. ｐ and selecting a catalyst such that the temperature difference ΔT is equal to or smaller than a preset threshold value when the amount of propellant supplied, q, is preset.

5. The temperature at which the reaction rate of the gas phase reaction of the propellant becomes higher than the reaction rate of the propellant on the surface of the catalyst is defined as T Ｃ The adiabatic flame temperature determined from the composition of the propellant is T Ｄ and the temperature of the propellant (7) supplied to the catalyst is T ｉｎｌｅｔ The total reaction heat of the propellant is ΔH Ｔｏｔａｌ Then, [0025] and The method for suppressing damage to a catalyst according to any one of claims 1 to 4, wherein the formula (2) is used in the formula (1).

6. The total reaction heat ΔH of the propellant Ｔｏｔａｌ The surface reaction heat ΔH ｓｕｒｆａｃｅ The ratio α is determined in advance by experiment. In the formula (1), DH ｓｕｒｆａｃｅ =αΔH Ｔｏｔａｌ The method for suppressing damage to the catalyst according to any one of claims 1 to 4, comprising the steps of:

7. The catalyst comprises an alumina catalyst carrier and a catalyst component supported on the catalyst carrier, The method for suppressing damage to a catalyst according to any one of claims 1 to 6, wherein the maximum value of the distance between any two points in the catalyst support is 2 mm or less.

8. 8. The method for suppressing damage to a catalyst according to claim 7, wherein the maximum distance between any two points within the catalyst support is 1.6 mm or less.

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