JP4509055B2 - Water vapor detection membrane - Google Patents

Description

  The present invention relates to a water vapor detection film for detecting water vapor in a mixed gas.

  Unlike fossil fuels such as oil, coal, and natural gas, hydrogen is attracting attention as an environmentally friendly energy source because it does not generate carbon dioxide that causes global warming even when it is burned. It is expected to be used as a fuel for fuel or as a raw material for fuel cells. Known methods for producing hydrogen include decomposition of water using a solar cell or a photocatalyst, a steam reforming method of hydrocarbons, a partial oxidation reaction of hydrocarbons, a carbon dioxide gas reforming method of hydrocarbons, and the like. When producing hydrogen from hydrocarbons, it is effective to use methane having the largest hydrogen content per unit weight.

  Steam reforming is a method of obtaining hydrogen and carbon monoxide by reacting hydrocarbons with high-temperature steam in the presence of a catalyst, and is currently the most common method for industrialized hydrogen production. By using a hydrogen separation membrane, only hydrogen can be separated from the mixed gas of hydrogen, carbon monoxide and steam obtained by steam reforming. Obtainable. The separation of hydrogen by a hydrogen separation membrane utilizes the difference in the diameter of gas molecules contained in the mixed gas. By using a ceramic membrane having micropores, the diameter of the gas molecules is reduced from the mixed gas containing hydrogen. Only the smallest hydrogen can be separated.

As a hydrogen separation membrane used when only hydrogen is separated from a mixed gas, a porous siloxane polymer membrane is known. However, it is known that a porous siloxane-based polymer film undergoes a change in microstructure when reacted with high-temperature water vapor, resulting in a decrease in hydrogen permeation performance. For this reason, in the steam reforming method for producing a mixed gas containing a large amount of water vapor, there is a problem that the hydrogen permeation performance of the porous siloxane-based polymer membrane is reduced by the water vapor in the mixed gas. In addition, in the hydrogen production method using other methods, water vapor may be accidentally mixed into the reaction system. In such a case, the same problem of the porous siloxane polymer film occurs. Yes. In order to improve such characteristics of porous siloxane-based polymer membranes, the reactivity with high-temperature steam is reduced by using siloxane-based polymer membranes with a small amount of elements added as raw materials for hydrogen permeable membranes. A porous siloxane polymer film is disclosed (see Patent Document 1).
JP 2005-270887 A

  However, the degradation of the hydrogen separation membrane induced by high-temperature steam is an irreversible reaction, and when the hydrogen separation membrane is degraded by contact between the high-temperature steam and the hydrogen separation membrane, it can no longer be used. The hydrogen separation membrane had to be replaced. For this reason, in order not to contact the hydrogen separation membrane with the high-temperature steam, an attempt is made to remove the high-temperature steam from the mixed gas by using a water vapor removing means, etc. It was. On the other hand, even when the water vapor removing means or the like is used, high temperature water vapor may be accidentally mixed in the hydrogen separating means, and it is necessary to prevent deterioration of the hydrogen separation membrane even in such a case.

  The present invention provides a hydrogen production apparatus having a water vapor removing means, wherein even if water vapor is accidentally mixed in a hydrogen separation unit having a hydrogen separation membrane, the water vapor and the hydrogen separation membrane do not come into contact with each other. A hydrogen production apparatus that can be safely implemented is provided.

  In the hydrogen production apparatus provided with the water vapor removing means, the present inventors accidentally mixed water vapor into the mixed gas due to an abnormality of the water vapor removing means when the water vapor detecting film is disposed downstream of the water vapor removing means. Even in this case, it has been found that contact between water vapor and the hydrogen separation membrane can be prevented, and the present invention has been completed.

  (1) A water vapor detection film disposed downstream of a water vapor removal unit that removes the water vapor from a mixed gas containing water vapor, wherein the water vapor detection film is in the mixed gas after passing through the water vapor removal unit. The water vapor detection film | membrane which is a film | membrane with which the gas permeability of the said water vapor detection film | membrane becomes small according to a raise of water vapor | steam density | concentration.

  According to the invention of (1), when water vapor is not contained in the mixed gas, the gas permeability of the water vapor detection membrane does not decrease, so the mixed gas can permeate the water vapor detection membrane. . On the other hand, if water vapor is accidentally mixed into the gas mixture due to an abnormality in the water vapor removing means, the water vapor detection membrane has a reduced gas permeability due to the water vapor in the gas mixture. Cannot pass through. Therefore, it is possible to detect water vapor with a change in gas permeability.

  (2) The water vapor detection film is made of a porous film, and the average pore diameter of the porous film is reduced according to an increase in the water vapor concentration in the mixed gas after passing through the water vapor removing means. Water vapor detection membrane.

  According to the invention of (2), when water vapor is not contained in the mixed gas, the average pore diameter of the water vapor detection membrane that is a porous membrane does not decrease, so the mixed gas permeates the water vapor detection membrane. can do. On the other hand, if water vapor is accidentally mixed into the gas mixture due to an abnormality in the water vapor removal means, the water vapor in the gas mixture reduces the average pore size of the water vapor detection film, which is a porous film. Cannot pass through the water vapor detection membrane.

  (3) The water vapor detection film according to (1) or (2), wherein the water vapor detection film is a siloxane polymer film.

  According to the invention of (3), since an inexpensive siloxane polymer film is used as the water vapor detection film, the cost of the water vapor detection film can be kept low.

  (4) Water vapor removing means for removing the water vapor from the mixed gas containing water vapor, the water vapor detection film according to any one of (1) to (3) disposed downstream thereof, and the gas after permeating the water vapor detection film A water vapor removal system comprising: detection means for detecting the pressure and / or flow rate of the gas; and flow rate control means for controlling the flow rate of the gas after passing through the water vapor detection film in accordance with a detection value of the detection means.

  According to the invention of (4), when the water vapor removing means functions normally and water vapor is completely removed from the mixed gas, the water vapor does not come into contact with the water vapor detection film. The gas permeability does not decrease, and the mixed gas can permeate the water vapor detection membrane. On the other hand, if the water vapor removal means has some abnormality and the water vapor cannot be completely removed from the mixed gas, the water vapor contacts the water vapor detection film and the gas permeability of the water vapor detection film is reduced. The gas cannot pass through the water vapor detection film, and the pressure and / or flow rate of the gas after passing through the water vapor detection film changes. For this reason, a change occurs in the detection value of the detection means, and the flow rate of the gas after passing through the water vapor detection film is controlled by the flow rate control means according to this change. Therefore, the flow rate of the gas discharged from the water vapor removal system can be controlled depending on whether or not the water vapor removal means is functioning normally.

  (5) After obtaining a mixed gas containing hydrogen by reforming hydrocarbons, water vapor is removed from the mixed gas, and then hydrogen is separated from the mixed gas using a hydrogen separation membrane. The water vapor removing system according to (4), which is used for removing water vapor.

  According to the invention of (5), the water vapor mixed in the mixed gas as the hydrocarbon is reformed can be removed by the water vapor removing means. If the water vapor removing means does not function normally, the water vapor detection membrane and the flow rate control means can prevent the water vapor from being mixed into the apparatus including the hydrogen separation membrane, so that the water vapor contacts the hydrogen separation membrane. It is possible to prevent deterioration of the hydrogen separation membrane.

  According to the water vapor detection film of the present invention, it is possible to prevent water vapor from being mixed into the mixed gas even when the water vapor removing means is not functioning normally. Therefore, by using the water vapor removal system according to the present invention in an apparatus having a hydrogen separation membrane that deteriorates due to water vapor, such as a hydrogen production apparatus that produces and separates hydrogen by reforming hydrocarbons, hydrogen separation is achieved. Contact between the membrane and water vapor can be prevented, and therefore deterioration of the hydrogen separation membrane can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Overall configuration>
FIG. 1 is a diagram showing an outline of a hydrogen production apparatus 1 in the present embodiment. In the hydrogen production apparatus 1 according to the present embodiment, the hydrogen production apparatus 1 is located in the uppermost stream of the hydrogen production apparatus 1 and is located downstream of the hydrogen generation means 10 and the hydrogen generation means 10 that generates hydrogen from a raw material such as natural gas by a chemical reaction. The water vapor removing system 20 that removes water vapor from the mixed gas generated in the hydrogen generating means 10 and the hydrogen separation that is located downstream of the water vapor removing system 20 and separates only hydrogen from the mixed gas from which water vapor has been removed by the water vapor removing system 20 Unit 30.

[Hydrogen generation means]
Examples of the hydrogen generating means 10 include a steam reforming reaction unit using a steam reforming reaction of natural gas. The steam reforming reaction unit comprises a reaction chamber for reacting steam and natural gas, a steam generator for heating pure water to generate high-temperature steam, and a steam that connects the steam generator to the most upstream part of the reaction chamber. A supply path, a natural gas supply path connecting a natural gas tank existing outside the steam reforming reaction unit to the most upstream part of the reaction chamber, and a mixed gas discharge path connecting the most downstream part of the reaction chamber and the steam removing means 22 It consists of.

  In the present embodiment, a steam reforming reaction unit has been described as the hydrogen generation means 10, but is not limited thereto. In other words, the hydrogen generating means 10 of the present invention may utilize a natural gas carbon dioxide reforming reaction or a natural gas partial oxidation reaction. Further, the hydrogen generating means 10 may not be one using natural gas, and may be water electrolysis using a solar cell or a photocatalyst, for example.

  Furthermore, in this embodiment, natural gas is used as the hydrocarbon used in the steam reforming reaction unit, but the present invention is not limited to this. That is, the gas used in the steam reforming reaction unit may be industrially produced methane, ethane, propane or the like, or a mixture of these gases. Of these, methane is preferred in terms of the highest hydrogen content per unit weight, but from the viewpoint of convenience, natural gas is preferably used as it is.

[Water vapor removal system]
The water vapor removal system 20 is disposed downstream of the water vapor removal means 22 and the water vapor removal means 22 for removing only the water vapor from the mixed gas using the physicochemical characteristics of the gas, and increases the water vapor concentration in the mixed gas. The water vapor detection film 24 having a gas permeability that decreases in response, a detection unit that is provided downstream of the water vapor detection film 24 and detects the pressure and / or flow rate of the mixed gas after passing through the water vapor detection film 24, and And flow rate control means for controlling the flow rate of the gas after passing through the water vapor detection film 24 in accordance with the detected value.

(Water vapor removing means)
Examples of the water vapor removing unit 22 include a water vapor adsorption unit that utilizes the property that a hygroscopic chemical substance adsorbs water vapor. The water vapor adsorption unit is an adsorption tank filled with zeolite or silica gel, and a mixed gas discharge path of the steam reforming reaction unit. The mixed gas supply path leading to the most upstream part of the adsorption tank, the most downstream part of the absorption layer, and water vapor And a dry mixed gas discharge passage connecting the separation unit.

  In the present embodiment, a water vapor adsorption unit is used as the water vapor removing unit 22, but the present invention is not limited to this. That is, the water vapor removing means 22 may be a method using a decrease in saturated water vapor pressure due to cooling or a method of passing a mixed gas through a water-absorbing liquid such as triethylene glycol, and selectively using only water vapor from the mixed gas. Any method that can be removed may be used.

(Water vapor detection membrane)
As the water vapor detection film 24, a film whose gas permeability decreases as the water vapor concentration in the mixed gas increases is used. As such a membrane, for example, a porous membrane in which the average pore diameter of the pores of the porous membrane decreases as the water vapor concentration in the mixed gas increases. As the water vapor detection film 24, it is desirable to use a porous film whose gas permeability is likely to be rapidly lowered in the presence of high temperature water vapor. Specifically, a siloxane polymer film or the like to which no metal is added can be used. The water vapor detection film 24 has a hydrogen permeability coefficient of the order of 10 ⁻⁶ (m ³ (STD) / m ² / s / kPa) to 10 ⁻⁴ (m ³ (STD) / m ² / s / kPa). Use.

(Method for producing water vapor detection film)
The water vapor detection film 24 is produced by a sol-gel method. Table 1 shows the starting composition of the colloidal sol used for forming the water vapor detection film 24 and the average particle size (measured by the dynamic light scattering method) of the colloidal sol. According to Table 1, the starting materials are mixed, stirred for 10 minutes to 1 hour, 10 g of nitric acid is added, and water is added to make the total volume 500 ml. The mixture is stirred while being heated, and the mixture is boiled and stirred for about 20 to 40 hours while keeping the solution concentration constant while adding water.

  The obtained colloidal sol solution is coated on an alumina plate coated with α-alumina fine particles and baked at 400 to 800 ° C. Coating and baking are performed in several steps from a colloidal sol having a large particle size to a colloidal sol having a small particle size.

  The material of the water vapor detection film 24 according to the present invention is not limited to the siloxane polymer film, and any material can be used as long as the gas permeability is reduced in the presence of high temperature water vapor such as an alumina film. Also good.

(Detection means)
The detection means may be anything as long as it can detect the pressure and / or flow rate of the gas. As such a detection means, a commercially available pressure sensor or flow rate sensor can be used. For example, “KP-50” (manufactured by KEYENCE Corporation), “PA-800” (manufactured by MC Systems), “mass flow”. A meter "(manufactured by HORIBASEC) can be used.

(Flow control means)
The flow rate control means may be anything as long as it can control the flow rate of the gas after passing through the water vapor detection film 24 in accordance with the detection value obtained from the detection means. As such a flow rate control unit, for example, a detection value input unit to which a detection value from the detection unit is input and a valve 26 positioned downstream of the water vapor detection film 24 according to the input detection value are opened. A signal conversion unit that transmits a signal indicating whether the valve is closed or left, an operation unit that opens and closes the valve 26 in response to a signal from the signal conversion unit, and a valve located downstream of the water vapor detection film 24 26, and a flow rate control means.

[Hydrogen separation unit]
The hydrogen separation unit 30 is a cylindrical hydrogen separation chamber provided with a hydrogen separation membrane, a dry mixed gas discharge path of a water vapor adsorption unit, a dry mixed gas supply path leading to the uppermost stream of the hydrogen separation chamber, and a cylindrical hydrogen A separation membrane, a hydrogen discharge passage that communicates with a space outside the hydrogen separation membrane at the most downstream side of the hydrogen separation chamber, and a hydrogen separation mixed gas discharge passage that communicates with the lumen of the hydrogen separation membrane at the most downstream side of the hydrogen separation chamber; Consists of.

(Hydrogen separation membrane)
As the hydrogen separation membrane, for example, a siloxane polymer membrane to which metal is added is used. As the hydrogen separation membrane, one having a hydrogen permeability coefficient of the order of 10 ⁻⁶ (m ³ (STD) / m ² / s / kPa) to 10 ⁻⁴ (m ³ (STD) / m ² / s / kPa) is used. . Since the shape of the hydrogen separation membrane is cylindrical, it is possible to increase the hydrogen permeation amount per installation area as compared with other shapes of hydrogen separation membranes.

(Method for producing hydrogen separation membrane)
The hydrogen separation membrane is produced by a sol-gel method. Table 2 shows the starting composition of the colloidal sol used for forming the hydrogen separation membrane and the average particle size (measured by the dynamic light scattering method) of the colloidal sol. According to Table 1, starting materials are mixed, and metal addition (Zr, Ti, Mn, Pt, Ru, K, Fe, etc.) is performed as necessary. Stir for 10 minutes to 1 hour, add 11 g of hydrochloric acid and add water to bring the total volume to 500 ml. The mixture is stirred while heating, and the mixture is boiled and stirred for about 20 to 40 hours while keeping the solution concentration constant while adding water.

  The obtained colloidal sol solution is coated on an alumina tube coated with α-alumina fine particles, and is fired at 400 to 800 ° C. Prior to firing, firing in water vapor at 400 ° C. to 800 ° C. is performed as necessary (pre-firing in water vapor). Coating and baking are performed in several steps from a colloidal sol having a large particle size to a colloidal sol having a small particle size. After film formation, if necessary, the film is left in air at 40 ° C. to 80 ° C. having a humidity close to saturation humidity for 10 hours to 40 hours and then fired at 400 ° C. to 800 ° C. (high humidity pretreatment). .

  As the hydrogen separation membrane according to the present embodiment, a cylindrical shape is used, but is not limited thereto. In other words, the hydrogen separation membrane may be planar, or may be a cylinder having a column filled with a siloxane polymer resin. In addition, the material of the hydrogen separation membrane according to the present invention is not limited to the siloxane polymer membrane, and any material that can selectively separate only hydrogen, such as an alumina membrane, a SiC membrane, or a Pd membrane, can be used. There may be.

<Operation of hydrogen production equipment>
(Operation of hydrogen generation means)
In the steam reforming reaction unit, first, pure water is heated in a steam generator to generate high-temperature steam, and compressed as necessary using a gas pump, and steam is fed into the reaction chamber through a steam supply path. At the same time, natural gas is sent from the natural gas tank to the reaction chamber through the natural gas supply path, and the high temperature steam and the natural gas are reacted. Along with the reaction, almost all hydrocarbons contained in natural gas are decomposed into carbon monoxide or carbon dioxide and hydrogen. The mixed gas generated by the reaction is sent to the water vapor removing means 22 through the discharge path.

  This reaction is performed in the presence of an excess amount of water vapor in order to react all hydrocarbons.

(Operation of water vapor removal system)
The mixed gas generated in the hydrogen generating means 10 first reaches the water vapor removing means 22 and then reaches the adsorption tank from the mixed gas supply path. In the adsorption tank, zeolite and silica gel are adsorbed while the water vapor contained in the mixed gas remains at a high temperature, and the dried dry mixed gas containing no water vapor is discharged from the dry mixed gas discharge passage. When the zeolite or silica gel is saturated with water, the water vapor can be removed by heating or reducing the pressure and used for re-adsorption.

  According to the water vapor adsorption unit, it is possible to remove water vapor while the mixed gas remains at a high temperature, so that the cost required for cooling the mixed gas can be reduced. In addition, when hydrogen produced by the hydrogen production apparatus 1 is used as a fuel for thermal power generation, thermal energy contained in high-temperature hydrogen gas can be used as an energy source as it is, which is preferable in terms of power generation efficiency.

  When the water vapor removing unit 22 is operating normally, the dry mixed gas does not contain water vapor. Therefore, even if the dry mixed gas and the water vapor detecting film 24 come into contact with each other, the gas permeation of the water vapor detecting film 24 is achieved. Therefore, the pressure and flow rate of the mixed gas after passing through the water vapor detection film 24 do not change. Therefore, since the detection value detected by the detection means does not change, the signal conversion unit that has received the detection value from the detection value input unit transmits a signal indicating that the open state of the valve 26 remains unchanged, and the operation unit is the valve. 26 is not opened and closed, and the mixed gas is sent to the hydrogen separation unit as it is.

  On the other hand, when the water vapor removing means 22 is not operating normally, water vapor is mixed in the dry mixed gas, so that the water vapor detection membrane 24 has gas permeability due to contact between the water vapor and the water vapor detection membrane 24. descend. For this reason, the permeation | transmission amount which the dry mixed gas containing water vapor permeate | transmits the water vapor | steam detection film | membrane 24 reduces. In addition, since the pressure and flow rate of the mixed gas after passing through the water vapor detection film 24 decrease and the detection value detected by the detection means changes, the signal conversion unit that receives the detection value from the detection value input unit uses the valve 26. A signal to close is transmitted, and the operation unit closes the valve 26. For this reason, the dry mixed gas mixed with water vapor does not reach the hydrogen separation unit 30.

(Operation of hydrogen separation unit)
The dry mixed gas that has passed through the water vapor adsorption unit reaches the hydrogen separation chamber through the dry mixed gas supply path. The dry mixed gas that has reached the hydrogen separation chamber reaches the lumen of the hydrogen separation membrane, and passes through the lumen of the hydrogen separation membrane under a pressure of not less than atmospheric pressure and not more than 100 atmospheres. The outside of the hydrogen separation membrane has a lower air pressure than the lumen of the hydrogen separation membrane, and the surface of the hydrogen separation membrane is provided with holes with a diameter that allows only hydrogen to pass through. Can be transmitted. The hydrogen that has permeated through the hydrogen separation membrane is discharged and recovered from the discharge path. The mixed gas that has not permeated the hydrogen separation membrane is discharged from the hydrogen separation mixed gas discharge passage.

<Effect>
According to the hydrogen production apparatus 1 according to the present invention, hydrogen can be generated from natural gas or the like, and separated and recovered. When separating hydrogen from the dry mixed gas, a hydrogen separation membrane is used. Even if water vapor is accidentally mixed into the dry mixed gas by providing a water vapor removal system 20 upstream of the hydrogen separation membrane, hydrogen separation is performed. Deterioration of the film can be prevented.

  In the present invention, the water vapor removal system 20 is described as being used in the hydrogen production apparatus 1, but is not limited thereto. That is, the water vapor removal system 20 according to the present invention can be used for apparatuses other than the hydrogen production apparatus 1.

It is drawing which showed the outline of the hydrogen production apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrogen production apparatus 10 Hydrogen generating means 20 Steam removal system 22 Steam removal means 24 Steam detection membrane 26 Valve 30 Hydrogen separation unit

Claims (5)

A water vapor detection film disposed downstream of a water vapor removing means for removing the water vapor from a mixed gas containing water vapor,
The water vapor detection film is a water vapor detection film that is a film in which the gas permeability of the water vapor detection film decreases as the water vapor concentration in the mixed gas increases after passing through the water vapor removal means.   The water vapor detection film according to claim 1, wherein the water vapor detection film is made of a porous film, and the average pore diameter of the porous film is reduced in accordance with an increase in the water vapor concentration in the mixed gas after passing through the water vapor removal means. film.   The water vapor detection film according to claim 1, wherein the water vapor detection film is a siloxane polymer film. Water vapor removing means for removing the water vapor from the mixed gas containing water vapor, and the water vapor detection film according to any one of claims 1 to 3 disposed downstream thereof,
Detection means for detecting the pressure and / or flow rate of the gas after passing through the water vapor sensing membrane;
A water vapor removal system comprising: a flow rate control unit that controls a flow rate of the gas after passing through the water vapor detection film according to a detection value of the detection unit.   After removing the water vapor from the mixed gas after reforming the hydrocarbon to obtain a mixed gas containing hydrogen, and then separating the hydrogen from the mixed gas using a hydrogen separation membrane, the removal of the water vapor The water vapor removal system according to claim 4, which is used in the above.

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