JP2007084378A - Method for producing hydrogen and apparatus used in the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the loss of hydrogen by discharging a dehydrogenation product to the outside of a system while maintaining the hydrogen partial pressure of a non-permeation side gas constant for the membrane separation of hydrogen after dehydrogenation of a hydrocarbon. <P>SOLUTION: A preferable method for producing hydrogen includes following steps (I) to (III). The step (I) comprises continuously dehydrogenating the hydrocarbon by a duplex tube and membrane type flow-through dehydrogenation reactor to obtain a mixed gas of hydrogen and the dehydrogenation product, then separating hydrogen from the permeation side being the inner side of a hydrogen separation membrane constituting an inner tube, and obtaining hydrogen and the dehydrogenation product as the non-permeation side gas from the non-permeation side. The step (II) comprises liquefying the dehydrogenation product by cooling the non-permeation side gas. The step (III) comprises separating the non-permeation side gas containing the liquefied component into a gas and a liquid and discharging only the liquefied component substantially containing the dehydrogenation product to the outside of the system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrogen production method for generating hydrogen by a dehydrogenation reaction of a feedstock composed of a hydrocarbon compound, for example, a hydrocarbon having a cyclohexane ring in the field of hydrogen production, and a hydrogen production apparatus used therefor.

  Hydrogen is widely used in various industrial fields including the oil refining and chemical industries. In particular, in recent years, hydrogen energy has attracted attention as a future energy, and research is focused on fuel cells, but hydrogen gas has a large volume per calorie and also requires a large amount of energy for liquefaction. Storage and transport systems are an important issue. In addition, a new infrastructure is required for hydrogen supply (see Non-Patent Document 1). Liquid hydrocarbons, on the other hand, have the advantage of being easy to handle and having a higher energy density than hydrogen gas, and also have the advantage of being able to use existing infrastructure. The method of producing hydrogen from methane is important.

  Production of hydrogen is widely carried out by known techniques such as steam reforming of methane and light paraffin, autothermal reforming, and partial oxidation, but these reactions require high temperatures. Furthermore, when targeting on-site power generation by a fuel cell, particularly a polymer electrolyte fuel cell, a shift reactor and a carbon monoxide remover by CO selective oxidation or methanation are required in the subsequent stage. This is a very complex process. In addition, when an automobile hydrogen station is targeted, high purity hydrogen must be obtained using PSA (pressure swing adsorption). The same applies to the methanol reforming system. In the case of on-site, a carbon monoxide remover is required, and in the case of a hydrogen station, PSA is required.

  On the other hand, in the method of producing hydrogen by dehydrogenating liquid hydrocarbons, the production process is simple because the reaction is simple. Furthermore, since the product is hydrogen, which is a gas, and unsaturated hydrocarbon, which is a liquid at room temperature, the product is relatively easy to separate. In particular, the reaction using a hydrocarbon having a cyclohexane ring as a raw material and dehydrogenating the cyclohexane ring into an aromatic ring proceeds easily in the presence of a dehydrogenation catalyst, and the product hydrogen and aromatic hydrocarbon Is relatively easy, and is suitable for small-scale hydrogen production (see Non-Patent Document 2). However, most of the aromatic hydrocarbons can be liquefied and separated from hydrogen if the temperature of the produced hydrogen and aromatic hydrocarbons is reduced to room temperature under atmospheric pressure, but the amount of aromatics depends on the vapor pressure at room temperature. Hydrocarbons are mixed in hydrogen gas. For example, in the case of toluene, the mixture is about 2.1% at 15 ° C. and atmospheric pressure. Therefore, when it is necessary to increase the purity of hydrogen as in fuel cell applications, a problem arises in the separation of hydrogen and aromatic hydrocarbons.

  As a separation method, there is a method of cooling and separating, but in order to achieve a hydrogen concentration of 99.9% or more, a low temperature of about −30 ° C. at normal pressure is required. Cooling to −30 ° C. using a refrigerator is not a preferable removal method because it causes a decrease in energy efficiency in hydrogen production and the equipment becomes large.

  In addition, there is an adsorptive separation method in which it is adsorbed by an adsorbent and separated. In this method, it is necessary to desorb and recover the aromatic hydrocarbon from the adsorbent after adsorption and to regenerate the adsorbent. Among them, the PSA method (pressure swing adsorption method) in which adsorption and desorption are performed by pressure fluctuation is well known, but the recovery rate and overall efficiency of hydrogen gas are low, and operations such as pressure increase and pressure decrease are performed. Is necessary and has the disadvantage of becoming a large system.

  As a separation method other than the above, there is a membrane separation method. The membrane separation method is characterized by high energy efficiency, and the types of separation membranes are mainly palladium membranes, polymer membranes, ceramic membranes, and carbon membranes. In the purification of hydrogen, a palladium membrane has been put into practical use for the purpose of high-purity hydrogen purification (see Non-Patent Document 3). When the membrane separation method is used, it is necessary to increase the pressure on the non-permeate side. Therefore, it is necessary to increase the pressure of the hydrogen generation reaction (dehydrogenation reaction) or to increase the pressure of the product gas after the reaction. When the pressure of the product gas is increased, energy efficiency is reduced in hydrogen production. Further, in the dehydrogenation reaction, it is necessary to increase the reaction temperature when the reaction pressure is increased from the viewpoint of restrictions on chemical equilibrium.

  However, the dehydrogenation reaction of hydrocarbons mainly having a cyclohexane ring needs to be performed at a lower temperature in order to suppress the decomposition reaction that is a side reaction. For example, in the dehydrogenation reaction of methylcyclohexane, it is necessary to perform the reaction at a temperature of 360 ° C. or lower. Due to equilibrium constraints, it was difficult to lower the temperature of this process. In order to solve this problem, a membrane reactor incorporating a hydrogen separation membrane is used to selectively remove hydrogen generated in the dehydrogenation process from the reaction field, thereby improving the hydrogen yield and lowering the reaction temperature. As a technique, for example, Patent Document 1 discloses a technique in which a porous ceramic membrane that selectively permeates hydrogen is incorporated to perform a dehydrogenation reaction of cyclohexane. Patent Documents 2 and 3 disclose a hydrogen production technique by reaction separation using a palladium membrane. However, any of them uses an inert gas such as argon as a sweep gas, and is not practical in terms of the purity of the produced hydrogen.

Further, in the technology using gas membrane separation, the hydrogen separation driving force is a hydrogen partial pressure difference, so that hydrogen having a partial pressure equal to or higher than the partial pressure of hydrogen on the permeate side always remains on the non-permeate side. There was a problem.
Nori Kobayashi, “Quarterly Energy Comprehensive Engineering”, 2003, Vol. 25, No. 4, p. 73-87 Masaru Ichikawa, “Industrial Materials”, 2003, Vol. 51, No. 4, p. 62-69 Supervised by Masayuki Nakagaki, “Membrane Processing Technology System (Vol. 1)”, Fuji Techno System, 1991, p. 661-662 and p. 922-925 JP-A-4-71638 JP-A-3-217227 JP-A-5-317708

The object of the present invention is to solve problems such as separation, temperature reduction, heat supply, etc. in a hydrogen production method by dehydrogenation of a feedstock consisting of hydrocarbons, for example, hydrocarbons having a cyclohexane ring, and produce hydrogen efficiently. A hydrogen production method and a hydrogen production apparatus therefor are provided.
That is, an object of the present invention is to solve the problem of reducing the hydrogen loss by discharging the dehydrogenated product outside the system while maintaining the hydrogen partial pressure in the non-permeate gas in the membrane separation constant.

  As a result of intensive studies to solve the above problems, the present inventors selectively removed hydrogen from the permeate side of the membrane with a hydrogen membrane separator when generating hydrogen by hydrocarbon dehydrogenation reaction, The product on the non-permeate side of the membrane is extracted from only the liquid phase part obtained by cooling it, so that the hydrogen partial pressure on the non-permeate side can be maintained without removing hydrogen from the non-permeate side. In particular, a method for producing hydrogen is provided.

That is, the first aspect of the present invention relates to a method for producing hydrogen, which comprises the following steps (I) to (IV).
(I) a step of continuously dehydrogenating hydrocarbons to obtain a mixed gas of hydrogen and a dehydrogenated product;
(II) Membrane separation of a mixed gas of hydrogen and a dehydrogenation product is performed with a hydrogen separation membrane to separate hydrogen mainly from the permeate side of the membrane, and hydrogen and dehydrogenation product as a non-permeate side gas from the non-permeate side. Obtaining
(III) cooling the non-permeate side gas to liquefy the dehydrogenated product;
(IV) Gas-liquid separation of the non-permeate side gas containing the liquefied component, and substantially discharging only the liquefied component from the system.
2nd of this invention is related with the manufacturing method of hydrogen characterized by comprising the following process (I) thru | or (III).
(I) Hydrogen is continuously dehydrogenated by a double-pipe membrane-type flow-type dehydrogenation reactor to obtain a mixed gas of hydrogen and a dehydrogenation product, and hydrogen separation constituting the inner pipe Separating hydrogen from the permeate side, which is the inside of the membrane, and obtaining hydrogen and a dehydrogenated product from the non-permeate side as a non-permeate side gas;
(II) cooling the non-permeate side gas to liquefy the dehydrogenation product;
(III) A step of gas-liquid separation of the non-permeate side gas containing the liquefied component and discharging only the liquefied component containing the dehydrogenation product to the outside of the system.
A third aspect of the present invention further includes a step of intermittently discharging a non-liquefied component such as methane out of the system from the gas phase of the gas-liquid separated non-permeate side gas in the first or second aspect of the present invention. The present invention relates to a method for producing hydrogen.
A fourth aspect of the present invention relates to the method for producing hydrogen according to any one of the first to third aspects of the present invention, wherein the hydrogen separation membrane is a ceramic membrane.
A fifth aspect of the present invention relates to the method for producing hydrogen according to any one of the first to third aspects of the present invention, wherein the hydrogen separation membrane is a metal membrane containing 100 to 10 mass% of Pd.
The sixth of the present invention is
Flow-type dehydrogenation reactor,
Hydrogen membrane separator for separating hydrogen,
A cooler to liquefy the dehydrogenation product,
A gas-liquid separator that separates a non-liquefied component and a liquefied dehydrogenated product into a gas-liquid separator, and a liquid level controller that controls the liquid level of the gas-liquid separator;
The present invention relates to a hydrogen production apparatus in which a liquid discharge valve is provided in the gas-liquid separator.
The seventh of the present invention is
Double-pipe membrane-type flow dehydrogenation reactor,
A cooler to liquefy the dehydrogenation product,
A gas-liquid separator that separates a non-liquefied component and a liquefied dehydrogenated product into a gas-liquid separator, and a liquid level controller that controls the liquid level of the gas-liquid separator;
The present invention relates to a hydrogen production apparatus in which a liquid discharge valve is provided in the gas-liquid separator.
An eighth aspect of the present invention relates to the hydrogen production apparatus according to the sixth or seventh aspect of the present invention, wherein the gas-liquid separator is provided with a gas discharge valve.

  According to the present invention, in the production of hydrogen by a dehydrogenation reaction of a hydrocarbon compound, for example, a feedstock mainly composed of a hydrocarbon having a cyclohexane ring, the gas phase portion after cooling the non-permeate side product of the hydrogen separation membrane is By sealing and extracting only the liquid phase part as a product, hydrogen can be efficiently produced without extracting hydrogen from the non-permeate side, maintaining the hydrogen partial pressure on the non-permeate side, suppressing hydrogen loss.

  Hereinafter, preferred embodiments of the present invention will be described.

(material)
The raw material in the present invention is a hydrocarbon, preferably a hydrocarbon having a cyclohexane ring. Specific examples include cyclohexane and cyclohexane alkyl-substituted products, decalin and decalin alkyl-substituted products, and tetralin and tetralin alkyl-substituted products. More preferred are methylcyclohexane, dimethylcyclohexane, decalin, and methyldecalin. These hydrocarbons having a cyclohexane ring may be pure substances, or may be a mixture of a plurality of hydrocarbons. The reactants need not all be hydrocarbons having a cyclohexane ring, and may contain a certain amount of other compounds such as hydrocarbons having no cyclohexane ring.

(Dehydrogenation catalyst)
The catalyst of the present invention is preferably reacted using a solid catalyst having dehydrogenation activity. As this solid catalyst, a catalyst having a catalytically active main component supported on a carrier can be suitably used.

  Since the support has high mechanical strength, is thermally stable and has a large surface area, a metal oxide is formed on the surface of a stable metal oxide or a support having good thermal conductivity (thermally conductive support). Are preferred. Specific examples of the metal oxide include alumina, silica, titania, zirconia, and silica alumina. More preferred are alumina and silica. The thermally conductive support is defined as a support based on a substance having a thermal conductivity at 300 K of 10 W / m · K or more. The base of the thermally conductive support is preferably a metal, and includes a substrate having a film such as an oxide on the surface. Although any metal and alloy that are usually used can be used as the metal of the substrate, aluminum or a metal or alloy having aluminum on the surface is particularly preferable. By using a thermally conductive support, the thermal conductivity of the catalyst is increased, so that heat supply is accelerated and the reaction efficiency is improved. Moreover, there is an effect that the reaction temperature is raised rapidly by energizing directly using the conductivity of the heat conductive support as a metal, and the start-up time of the reactor is remarkably shortened.

  The surface of the heat conductive support is preferably treated so as to have a high surface area so as to have a function as a carrier having a catalytically active main component. As this treatment method, a known method can be adopted. However, as described in, for example, Japanese Patent Application Laid-Open No. 2002-119856, a method having a high surface area based on an anodic oxidation treatment is preferable. The surface of the heat conductive support, for example, the surface of the heat conductive support having a high surface area, preferably forms a stable and high surface area metal oxide layer such as alumina. For this purpose, for example, an alumina hydrate sol can be applied and dried on the surface of the heat conductive support having a high surface, and then fired to form a metal oxide layer.

  The shape of the catalyst carrier including the base of the thermally conductive support is arbitrary, and may be granular, plate-like, tubular, net-like, honeycomb-like, or fin-like installed directly inside the reaction tube. In order to efficiently supply reaction heat, it is preferable that the heat supply source and the catalyst carrier are in direct contact with each other. For this reason, the shape of the catalyst carrier is plate-like, tubular, or an internal fin type. It is preferable that

  The main component of catalytic activity in the catalyst of the present invention is a component having dehydrogenation activity, and can be arbitrarily selected. Yes, specifically iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold. In the present invention, the group numbers in the periodic table are based on the International Pure and Applied Chemistry Union Inorganic Chemistry Nomenclature Commission naming rules 1990 edition. More preferred are nickel, palladium, platinum and rhenium. Two or more of these elements may be combined. The preparation method for supporting these catalytically active main components on a carrier is arbitrary, but an impregnation method is preferred. Specific examples include the Incipient Wetness method and the evaporation to dryness method. The elemental compound used is preferably a water-soluble salt, and is preferably impregnated as an aqueous solution. Preferred examples of the water-soluble compound include chlorides, nitrates and carbonates.

  Additives may coexist in the dehydrogenation catalyst as necessary. Preferable additives include basic substances. The coexistence of the basic substance suppresses side reactions such as decomposition caused by acidity, and suppresses deterioration of the catalyst due to carbonaceous deposition. The type of the basic substance is arbitrary, but compounds of Group 1 elements and Group 2 elements are preferable, and specifically, lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, barium compounds Is preferred. These compounds are preferably water-soluble substances. More preferred are chlorides, sulfates, nitrates and carbonates. The content of the basic substance is preferably in the range of 0.1 to 100 by weight ratio with respect to the catalytically active main component. The preparation method for incorporating these basic substances into the catalyst body is optional, but an impregnation method is preferred. Specific examples include the Incipient Wetness method and the evaporation to dryness method.

(Reaction conditions)
The reaction conditions for dehydrogenation are appropriately selected according to the type of raw material. The reaction pressure is preferably 0.1 MPa or more and 2.0 MPa or less, more preferably 0.1 MPa or more and 1.0 MPa or less. In the present invention, the pressure is expressed as an absolute pressure unless otherwise specified. The reaction temperature is preferably a high temperature in terms of chemical equilibrium, but a low temperature is preferable in terms of energy efficiency. The reaction temperature is preferably 200 ° C. or higher and 400 ° C. or lower, more preferably 270 ° C. or higher and 360 ° C. or lower. Although it is disadvantageous in terms of chemical equilibrium, hydrogen may be added to the raw material for the purpose of preventing the deactivation of the catalyst or for operating the apparatus. When hydrogen is added to the raw material, the molar ratio of hydrogen to the raw material is preferably 0.01 or more and 1 or less. A preferable range of LHSV (liquid hourly space velocity) depends on the activity of the catalyst, but is preferably 0.2 v / v / hr or more and 20 v / v / hr or less.

(Dehydrogenation product)
The products of hydrocarbon dehydrogenation in the present invention are hydrogen and an unsaturated hydrocarbon. In the case of a hydrocarbon having a cyclohexane ring as a raw material hydrocarbon, the unsaturated hydrocarbon is mainly an aromatic hydrocarbon. For example, toluene is obtained as a dehydrogenation product from methylcyclohexane. In addition, lower hydrocarbons such as methane, ethane, propane, ethylene, and propylene may be by-produced and mixed.
The resulting aromatic hydrocarbon can be recovered and hydrogenated again to return it to the starting hydrocarbon. Alternatively, it can also be used as a heat source fuel necessary for the dehydrogenation reaction, if necessary. In addition, since aromatic hydrocarbons generally have a high octane number, substances having a suitable boiling point can also be used as a gasoline base material. It can also be used as other chemical products.

(Hydrogen separation membrane)
As the hydrogen separation membrane, a known hydrogen separation membrane having a function of selectively separating hydrogen from a mixed gas of hydrocarbon and hydrogen can be used, and a metal membrane or a porous inorganic membrane is preferable. The metal membrane is a hydrogen separation membrane in which a metal thin film is formed on the inner surface or outer surface of a tubular porous metal support having pores or a porous ceramic support having tubular pores. A metal film containing 100 to 10 mass% of Pd or a metal film containing 80 to 10 mass% of at least one metal selected from Ag, Cu, V, Nb, and Ta is preferable. Although any method can be selected as the method for forming the metal thin film, specific examples include electroless plating, vapor deposition, and rolling. As the porous inorganic membrane, a hydrogen separation membrane in which a ceramic thin film having a controlled pore size is formed on the inner surface or outer surface of a porous porous ceramic support having pores is preferable. Since the porous inorganic membrane is selectively separated by molecular sieve action, the pore diameter of the thin film portion is preferably 0.3 nm or more and 0.7 nm or less, and more preferably 0.3 nm or more and 0.5 nm or less. A known ceramic material can be used as the material of the ceramic film, but silica, alumina, titania, glass, silicon carbide, and silicon nitride are preferable. As the membrane portion of the membrane reactor described later, an appropriate membrane that can withstand the dehydrogenation reaction pressure and the like can be used.

(Hydrogen separation)
The permeation side pressure of the hydrogen separation membrane is preferably 0.2 MPa or less, more preferably 0.15 MPa or less. Further, an inert gas may be supplied to the permeation side of the hydrogen separation membrane for the purpose of reducing the permeation side hydrogen partial pressure. When supplying the inert gas, the permeation side hydrogen partial pressure is preferably 0.15 MPa or less, more preferably 0.05 MPa or less. The inert gas is preferably steam that can be easily separated by condensation. Moreover, when considering the use of the polymer electrolyte fuel cell, steam is preferable because it can be introduced without removing it.

(Membrane reactor)
Any dehydrogenation reactor can be used. A so-called membrane reactor is preferably used as the reactor used in the flow reaction system. More precisely, the membrane reactor referred to in the present invention is a flow-type reaction tube, and a dehydrogenation catalyst and a hydrogen separation membrane are provided in the reaction tube. Usually, the hydrogen separation membrane forms the inner tube of the double reaction tube, and the catalyst often has a double tube structure in which the catalyst exists in the gap between the outer tube and the inner tube. FIG. 1 shows an example of a membrane reactor having such a double tube structure reaction tube.
Here, in FIG. 1, the reaction tube is a double tube, the outer tube is made of a material having good thermal conductivity, such as metal, and the inner tube is made of a hydrogen separation membrane (hydrogen permeable membrane). Although not shown, an appropriate heating means such as heating with a heat medium is provided on the outside of the double pipe (outside of the outer pipe). The gap between the inner tube and the outer tube is filled with, for example, a catalyst supported on an appropriate granular carrier. The raw material gas is introduced into the gap from one end of the double pipe, and a part of hydrogen and reaction products are discharged from the other end as a non-permeating gas. The dehydrogenation temperature is measured and adjusted by inserting a thermocouple in the gap. Hydrogen selectively separated from the membrane flows into the inner tube as permeate gas and is taken out as high-purity hydrogen.

Production of hydrogen by dehydrogenating hydrocarbons using the membrane reactor having the above structure can be carried out as follows.
That is, using the gap between the double tubes constituting the membrane reactor as a dehydrogenation reaction field, the feed hydrocarbon is supplied from one end of the flow-type reaction tube, and the feed carbonization is performed by the dehydrogenation catalyst existing in the gap. Hydrogen is dehydrogenated to produce hydrogen and dehydrogenation reaction products (including dehydrogenated hydrocarbons such as unsaturated hydrocarbons such as aromatic hydrocarbons, side reaction products and unreacted hydrocarbons).
The produced hydrogen is simultaneously separated in situ by the hydrogen separation membrane constituting the inner pipe of the double pipe. That is, hydrogen is selectively permeated through the membrane, whereby hydrogen is permeated and collected to the innermost side of the double tube, and the hydrogen collected via this is discharged out of the system.
Thus, high purity hydrogen is obtained. The dehydrogenation reaction product is discharged out of the system through the gap between the outer tube and the inner tube of the double tube together with the remaining hydrogen.

  Heat can be easily supplied to the catalyst layer in which the dehydrogenation reaction, which is an endothermic reaction, is performed by providing appropriate heating means from the outside of the tube. As the appropriate heating from the outside of the tube, a known method such as heating with a heating medium can be appropriately employed.

(Hydrogen production equipment)
Taking a membrane reactor as an example, a schematic diagram of the treatment after membrane separation is shown in FIG. In FIG. 2, a cooler for cooling the non-permeate gas after membrane separation and a gas-liquid separator connected to the cooler are provided. The gas-liquid separator includes a valve A for extracting liquid and a valve B for extracting gas. Is arranged. In addition, also when carrying out the membrane separation of hydrogen using a separate membrane separator after dehydrogenation, it can process similarly after membrane separation. Although not shown, the gas-liquid separator is provided with a liquid level controller that is linked to the liquid extraction valve A.
In FIG. 2, the hydrocarbon raw material for the dehydrogenation reaction is introduced into a membrane reactor and converted to hydrogen and unsaturated hydrocarbons such as aromatic hydrocarbons on a dehydrogenation catalyst (not shown).
The produced hydrogen is separated to the innermost side of the double pipe through a membrane (not shown) in the double pipe as a permeation gas for membrane separation, and becomes product hydrogen. At this time, if necessary, steam can be introduced to the hydrogen separation membrane permeation side to lower the hydrogen partial pressure.

The remaining permeated hydrogen and unsaturated hydrocarbons (including unreacted raw materials) such as non-permeated aromatic hydrocarbons are recovered from the gap between the outer tube and the inner tube of the double tube as a non-permeated gas. At this time, since the driving force for membrane separation is a hydrogen differential pressure, hydrogen having a partial pressure equal to or higher than the partial pressure of hydrogen on the permeate side always remains on the non-permeate side.
In the conventional membrane separation operation, the residual hydrogen on the non-permeate side is discharged and discarded out of the system as it is (with hydrocarbon gas and the like). Therefore, in the conventional technology using membrane separation, the hydrogen recovery rate (permeated side hydrogen amount / theoretical generated hydrogen amount of raw material × 100) is the raw material conversion to hydrogen by the loss of hydrogen discharged from the non-permeate side. It is lower than the rate ((permeation side hydrogen amount and non-permeation side hydrogen amount) / theoretical hydrogen generation amount of raw material × 100).
On the other hand, in the present invention, the non-permeate side gas is cooled by an appropriate cooler, and liquefied components such as reaction products and unreacted raw materials contained therein are liquefied, and gas-liquid separation is performed in the gas-liquid separator.
The cooler may be a cooler capable of liquefying dehydrogenated products, for example, aromatic hydrocarbons such as toluene, and also liquefies hydrogen and even lower hydrocarbons such as by-product methane and ethane described later. It is not necessary. Therefore, for example, inexpensive cooling such as water cooling can be used.
Thereafter, the gas phase portion is sealed in the gas-liquid separator, and only the liquid phase portion is taken out of the system as a product. In this way, loss of hydrogen can be eliminated, and the hydrogen recovery rate of the permeate side gas can be made as close as possible to the raw material conversion rate to hydrogen.

In the conventional technique using membrane separation, a part of hydrogen, unsaturated hydrocarbon such as aromatic, and unreacted raw material are recovered as non-permeating gas. Compared with high-purity hydrogen on the permeate side, hydrogen on the non-permeate side, even after cooling, contains aromatic hydrocarbons for saturated vapor pressure and unreacted raw materials for saturated vapor pressure, thus providing a heat source for the reactor. It is common to use fuel.
Since it is inherently inefficient to use hydrogen generated by energy input for combustion, it is preferable to recover it as high purity hydrogen as possible rather than using fuel for heating.
However, since hydrogen having a pressure equal to or higher than the partial pressure of hydrogen on the permeate side always remains on the non-permeate side, the loss of hydrogen discharged from the non-permeate side is not achieved in the conventional technique using membrane separation. The hydrogen recovery rate (permeated hydrogen amount / theoretically generated hydrogen amount of raw material × 100) is the conversion rate of raw material to hydrogen ((permeated and non-permeated hydrogen amount) / theoretical generated hydrogen amount of raw material × 100). Less than.

On the other hand, in the present invention, after the non-permeate side product (aromatic hydrocarbon, unreacted raw material and hydrogen) is cooled, most of the liquefied components of the aromatic hydrocarbon and unreacted raw material are liquefied. The gas phase part composed of unreacted raw material with saturated vapor pressure is closed by closing valve B in FIG. 2, and the liquid phase part is the product. To be taken out of the system. As a result, the processing operation can be performed without losing hydrogen from the non-permeating side, and the hydrogen partial pressure on the non-permeating side of the hydrogen separation membrane is maintained as in the prior art.
Therefore, hydrogen that has been lost from the non-permeate side is recovered as high-purity hydrogen from the permeate side, and the hydrogen recovery rate on the permeate side can be as close to the raw material conversion rate as possible.
Room temperature ₂ such as CO and CO, such as steam reforming, non-liquefied gas at normal pressure is also a reaction separation using a reaction for generating concurrently with the hydrogen was completely sealed gas phase portion after cooling the non-permeate side In this case, since the partial pressure of hydrogen immediately decreases, the hydrogen permeation amount in the hydrogen separation membrane also decreases, and the reaction separation does not function, so this method cannot be applied. The present invention is established for the first time in a system in which only liquefiable hydrocarbons and hydrogen are produced as in the present invention. In this regard, the present invention is a novel method that has not been heretofore.

In order to improve diffusion of unsaturated hydrocarbons such as aromatic hydrocarbons generated during membrane separation, the pipe diameter of the transfer of the reaction product mixture from the membrane separator, preferably from the membrane reactor to the cooler Is preferably as thick as possible.
As for a method for extracting liquid from the gas-liquid separator, a known method can be appropriately used. For example, as shown in FIG. 2, a valve A is provided at a position corresponding to the liquid phase of the gas-liquid separator, and the liquid level of the gas-liquid separator is separately provided with a level sensor or a differential pressure gauge (not shown). By operating the valve A, only the corresponding amount of liquid component is extracted by the amount of the generated unsaturated hydrocarbon such as aromatic hydrocarbon. By doing so, there is no loss of residual hydrogen and the dehydrogenation product can be extracted, and as a result, the hydrogen partial pressure can be maintained.

Regarding the gas phase on the non-permeate side after cooling, when non-trace components such as methane, ethane, ethylene, propane, propylene, etc. that are not liquefied at normal temperature and pressure are by-produced during the reaction, these gases are non-permeate side gases. Which accumulates in, leading to a reduction in hydrogen partial pressure on the non-permeate side.
When the hydrogen partial pressure on the non-permeating side is reduced, the hydrogen permeation amount in the separation membrane is reduced, and the raw material conversion rate to hydrogen and the hydrogen recovery rate are reduced. Since the gas-liquid separator communicates with the separation membrane via the cooler, the partial pressure reduction can be determined by the hydrogen partial pressure in the gas phase in the gas-liquid separator.

  Therefore, as shown in FIG. 2, a valve B is provided at a position corresponding to the gas phase portion of the gas-liquid separator, and is normally closed for sealing. It is possible to always keep the hydrogen partial pressure at the maximum by reducing the accumulation of these gas components. The opening period and opening time of the valve B can be appropriately changed according to the decrease in the hydrogen partial pressure due to accumulation, and can be determined as appropriate so as to keep the hydrogen partial pressure on the non-permeating side to the maximum. That is, since the opening cycle and opening time of the valve B depend on the partial pressure increase on the non-permeate side of the non-liquefied gas at normal temperature and normal pressure, it varies depending on the raw materials and reaction conditions, and the hydrogen partial pressure on the non-permeate side is maximized. It can be decided appropriately to keep. The valve B is opened so that the partial pressure on the non-permeating side of the non-liquefied gas is kept at 0.1 MPa or less at normal temperature and normal pressure. Preferably it is 0.05 MPa or less, More preferably, 0.001 MPa or less is preferable.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the range of these Examples.
In the examples, the following separation membranes and catalysts were used.
[Separation membrane]
After one α-alumina layer is formed on the surface of a porous ceramic tubular support body having an outer diameter of 10 mm, an inner diameter of 8.4 mm, and a length of 300 mm, three γ-alumina layers are formed. Further, one silica layer was formed, and then a silica thin film was formed on the final surface. The hydrogen permeability coefficient was 4.2 × 10 ⁻⁷ mol / m ² / sec / Pa, and the toluene permeability coefficient was 2.8 × 10 ^−. A ceramic membrane having a concentration of ¹⁰ mol / m ² / sec / Pa is referred to as a separation membrane A.
Hydrogen permeation coefficient of 200 cc / cm ^{2 in which} palladium and silver (Pd: Ag = 85: 15) are coated on the outer surface of a porous ceramic tubular support having an outer diameter of 10 mm, an inner diameter of 8.4 mm, and a length of 300 mm by electroless plating. A palladium membrane having a thickness of / min / atm ^1/2 and a thickness of 2.5 μm is referred to as a separation membrane B.

[Dehydrogenation catalyst]
A spherical commercial catalyst having an average diameter of 1.5 mm, in which 0.3 mass% of platinum is supported on a γ-alumina support, is used.
[Membrane reactor]
The cylindrical separation membranes A and B are respectively arranged inside the aluminum tube to form a double tube structure, and the dehydrogenation catalyst is filled in the inner and outer gaps.
Here, as a membrane reactor schematically shown in FIG. 1, 110 ml of catalyst was filled in a gap between a reaction tube having an inner diameter of 24 mm and a length of 300 mm and a hydrogen separation membrane.

Using the hydrogen production apparatus shown in FIG. 2, the non-permeate side gas of the membrane reactor is cooled and supplied to the gas-liquid separator. The liquid level of the gas-liquid separator is a liquid level controller (not shown). Was controlled and adjusted by extracting only the liquid from the liquid discharge valve A.
Here, dehydrogenation was performed using methylcyclohexane as a raw material in a membrane reactor using a separation membrane A as a hydrogen separation membrane. Reaction pressure of membrane reactor 0.2, 0.4, 0.6, 0.8 MPa (absolute pressure), permeate side pressure 0.1 MPa (absolute pressure), reaction temperature (catalyst layer outlet temperature) 300 ° C., 330 The dehydrogenation reaction was performed under the conditions of ° C and LHSV 0.5h- ¹ . Here, LHSV is a flow rate and is represented by (methylcyclohexane liquid volume (cc) / catalyst (cc) / time (h)).
After membrane separation of the reactive organism, the non-permeate side gas composed of toluene vapor and hydrogen is cooled by a cooler and supplied to the gas-liquid separator.

In the gas-liquid separator, gas-liquid separation was performed, and the liquid level was controlled and adjusted by extracting only the liquid from the liquid extraction valve A by the liquid level controller (not shown) as described above.
Further, the valve B in FIG. 2 was closed, and the valve B was opened once every two hours for 2 minutes, and only the internal gas phase component was discharged out of the system. Even when the valve B is released, the pressure on the non-permeate side is not changed by the back pressure valve at the rear stage of the valve B.
Table 1 shows the results after operation for a considerable period.
In Table 1, the hydrogen recovery rate is expressed by (hydrogen recovered from the permeation side of the membrane reactor (mol) / theoretical hydrogen generation amount from the introduced methylcyclohexane (mol) × 100).

  The same experiment as in Example 1 was performed except that the separation membrane B was used as the hydrogen separation membrane. Table 1 shows the results after operation for a considerable period.

(Comparative example)
Methylcyclohexane was dehydrogenated in the same manner as in Example 2 except that the valve B was operated with the valve B always open. The results after operation for a considerable period are also shown in Table 1.
As shown in Table 1, compared with the comparative example, in Examples 1 and 2 in which the valve B was closed, the hydrogen recovery rate on the permeate side could be brought close to the raw material conversion rate to hydrogen.

Schematic diagram of membrane reactor Schematic of treatment after membrane separation according to the present invention

Claims (8)

A method for producing hydrogen, comprising the following steps (I) to (IV):
(I) a step of continuously dehydrogenating hydrocarbons with a flow-type dehydrogenation reactor to obtain a mixed gas of hydrogen and a dehydrogenated product;
(II) Membrane separation of a mixed gas of hydrogen and a dehydrogenation product is performed with a hydrogen separation membrane to separate hydrogen mainly from the permeate side of the membrane, and hydrogen and dehydrogenation product as a non-permeate side gas from the non-permeate side. Obtaining
(III) cooling the non-permeate side gas to liquefy the dehydrogenated product;
(IV) Gas-liquid separation of the non-permeate side gas containing the liquefied component, and substantially discharging only the liquefied component from the system. A method for producing hydrogen, comprising the following steps (I) to (III):
(I) A hydrogen separation membrane constituting an inner pipe by continuously dehydrogenating hydrocarbons with a double-pipe membrane-type flow-type dehydrogenation reactor to obtain a mixed gas of hydrogen and a dehydrogenated product Separating hydrogen mainly from the permeate side of the membrane to obtain hydrogen and a dehydrogenated product as a non-permeate side gas from the non-permeate side;
(II) cooling the non-permeate side gas to liquefy the dehydrogenation product;
(III) A step of gas-liquid separation of the non-permeate side gas containing the liquefied component and discharging only the liquid component containing substantially the dehydrogenated product out of the system.   The hydrogen production according to claim 1 or 2, further comprising a step of intermittently discharging a non-liquefied component such as methane out of the system from a gas phase of the gas-liquid separated non-permeate side gas. Method.   The method for producing hydrogen according to claim 1, wherein the hydrogen separation membrane is a ceramic membrane.   The method for producing hydrogen according to claim 1, wherein the hydrogen separation membrane is a metal membrane containing 100 to 10 mass% of Pd. Flow-type dehydrogenation reactor,
Hydrogen membrane separator for separating hydrogen,
A cooler to liquefy the dehydrogenation product,
A gas-liquid separator that separates a non-liquefied component from a liquefied dehydrogenated product into a gas-liquid separator, and a liquid level controller that controls the liquid level of the gas-liquid separator;
A hydrogen production apparatus in which a liquid discharge valve is provided in the gas-liquid separator. Double-pipe membrane-type flow dehydrogenation reactor,
A cooler to liquefy the dehydrogenation product,
A gas-liquid separator that separates a non-liquefied component from a liquefied dehydrogenated product into a gas-liquid separator, and a liquid level controller that controls the liquid level of the gas-liquid separator;
A hydrogen production apparatus in which a liquid discharge valve is provided in the gas-liquid separator.   The hydrogen production apparatus according to claim 6 or 7, wherein a gas discharge valve is provided in the gas-liquid separator.

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