JP2005213087A - Method for producing high purity hydrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing high purity hydrogen, e.g. of ≥99.99% purity, conveniently and efficiently, suitable for a small scale production, and a system for producing hydrogen. <P>SOLUTION: This method for producing high purity hydrogen comprises conducting a dehydrogenation reaction of a raw material oil containing a hydrocarbon in the presence of a catalyst to produce a mixture of hydrogen and a dehydrogenated oil containing an unsaturated hydrocarbon, cooling and separating/removing most part of the dehydrogenated oil from the mixture utilizing a cooling and separating means, and further separating/removing the dehydrogenated oil as an impermeable gas and taking out hydrogen as a permeable gas utilizing a membrane separation means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing hydrogen, and particularly in the field of hydrogen production, hydrogen is generated by a dehydrogenation reaction using a feedstock mainly composed of hydrocarbons having a cyclohexane ring, and the hydrocarbons contained in the hydrogen are cooled. The present invention relates to a method and system for producing hydrogen, characterized by being removed using membrane separation after separation.

  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, for example).

Liquid hydrocarbons, on the other hand, have an energy density that is easier to handle than hydrogen gas, and also have the advantage of being able to use existing infrastructure, so hydrocarbons can be stored and transported and used as needed. The method of producing hydrogen from methane is important.
Methods for producing hydrogen from hydrocarbons are 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. To do. Furthermore, in the case of on-site power generation using a fuel cell, particularly a polymer electrolyte fuel cell, carbon monoxide removal using a shift reactor and CO selective oxidation or methanation is performed after the hydrogen production by these methods. Equipment is required, which is a very complex process. In addition, when a hydrogen station for automobiles is targeted, carbon monoxide must be removed using a purification method by pressure swing adsorption (PSA). The same applies to the reforming system of methanol. In the case of on-site, a shift reactor and a carbon monoxide remover by CO selective oxidation or methanation are required. In the case of a hydrogen station, carbon monoxide by PSA is used. Need to be removed.

  On the other hand, among the methods for producing hydrogen from hydrocarbons, the method for producing hydrogen by dehydrogenating hydrocarbons, preferably liquid hydrocarbons, has a simple reaction because the reaction is simple. Furthermore, since the product is mainly composed of gaseous hydrogen and unsaturated hydrocarbon which is liquid at room temperature, the product has a feature that it is relatively easy to separate them. 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, for example, Non-Patent Document 2).

  In general, high purity hydrogen is often required for the chemical reaction raw material hydrogen. However, in the method for producing hydrogen by dehydrogenation of the hydrocarbon described above, the obtained hydrogen is unsaturated hydrocarbon, For example, since aromatic hydrocarbons are inevitably mixed, it is necessary to remove and purify the aromatic hydrocarbons.

Here, apart from a large-scale industrial hydrogen purification method, there is not yet a sufficient proposal as a small-scale and simple hydrogen production apparatus as described above. Particularly suitable for small-scale production that produces high-purity hydrogen by selectively separating and removing unsaturated hydrocarbons as a small proportion of impurities contained in hydrogen, for example, aromatic hydrocarbons as targets. There has been little proposed method.
That is, when it is necessary to increase the purity of hydrogen, for example, when it is increased to 99.99% or more, a problem arises in the separation of hydrogen and aromatic hydrocarbons. Most aromatic hydrocarbons can be liquefied and separated from hydrogen by reducing the temperature of the generated hydrogen and aromatic hydrocarbons to normal temperature under atmospheric pressure, but the amount of aromatic hydrocarbons depends on the vapor pressure at normal temperature. Must be mixed in hydrogen gas. For example, in the case of toluene, it becomes about 2.1% contamination at 15 ° C. and atmospheric pressure. As a countermeasure, a cooling / separation method can be employed.

  However, in order to achieve a hydrogen concentration of 99.99% or higher even if cooled and separated, it is necessary to cool to a low temperature of about −50 ° C. at normal pressure as calculated from the vapor pressure of the hydrocarbon. Although cooling separation is basically a simple method, cooling to −50 ° C. using a refrigerator is not a preferable removal method because energy efficiency is low and facilities are large.

  As another separation method, there is an adsorption 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 pressure swing adsorption method (PSA method) in which adsorption and desorption are performed by pressure fluctuation is known because it is easy to regenerate the adsorbent, but the hydrogen gas recycle ratio and overall efficiency are known. However, there is a disadvantage that the system is large because operations such as step-up and step-down are necessary.

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 used in the membrane separation method mainly include palladium membranes, polymer membranes, ceramic membranes, and carbon membranes.
The membrane separation method is also a simple and preferable method.
Several membrane separation techniques have been introduced. For example, Patent Document 1 discloses a method for separating hydrogen sulfide and hydrogen by using a porous ceramic membrane made of silica, alumina, and silicon nitride as a diaphragm. Is disclosed. In Non-Patent Document 3, an Si ₃ N ₄ film obtained by pyrolyzing polysilazane on a porous support obtained by sintering Si ₃ N ₄ powder for separation of helium and nitrogen and carbon dioxide and nitrogen is used. ing. Further, in Patent Document 2, in order to remove carbon monoxide from hydrogen obtained by steam reforming alcohol and lower hydrocarbon, the separation layer formed on the porous ceramic membrane supporting the metal catalyst is used to remove the carbon monoxide. There is a disclosure of a technique for removing carbon oxides. The metal catalyst is for the oxidation of carbon monoxide, the substrate of the porous ceramic membrane is α-alumina, silica, titania, zirconia, etc., and the separation layer membrane is silica, silica-alumina, silica-zirconia, It consists of silica and titania. We propose to separate and oxidize and remove carbon monoxide in hydrogen from steam reforming.

  However, for example, when focusing on aromatics as a target for separation / removal and membrane separation from hydrogen, a reaction gas having a composition of hydrogen / benzene = 3/1 (volume ratio) is converted to a hydrogen / benzene permeability coefficient ratio. Even if 1,500 membranes (for example, ceramic membranes and carbon membranes) are used and separation is performed at a recycling ratio of 20%, the hydrogen concentration is actually improved only to about 99.954%. If more rigorous operating methods are used, purity may improve to some extent, but of course not practical.

As described above, there is still a method for producing hydrogen that is small-scale and simple and that focuses on separation and removal of unsaturated hydrocarbons, particularly aromatic hydrocarbons, for example, high-purity hydrogen having a purity of 99.99% or more. Not fully proposed.
Kobayashi N, Seasonal Energy Engineering, Vol. 25, No. 4, pp. 73-87 (2003) Masaru Ichikawa, Industrial Materials, Vol. 51, No. 4, 62-69 (2003) H. Mori. et.al., J.A. Membrane Science 147 (1998) 23-33 JP-A-53-99078 JP 2003-71287 A

  An object of the present invention is to provide a hydrogen production method and a hydrogen production system which are suitable for small-scale production, and which produce high-purity hydrogen having a purity of 99.99% or more simply and efficiently.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have developed a hydrogen generator that generates hydrogen by a reaction for dehydrogenating hydrocarbons, a cooling separator for hydrocarbons contained in the generated hydrogen, and The present inventors have found a method for efficiently producing high-purity hydrogen by combining a membrane separator to be performed after cooling separation.

  That is, in the first aspect of the present invention, dehydrogenated oil is separated from a mixture of hydrogen produced by dehydrogenating a feedstock containing hydrocarbons in the presence of a catalyst and dehydrogenated oil containing unsaturated hydrocarbons to obtain high purity. In the method for producing hydrogen, a cooling separation means is used as the separation means to separate and remove most of the dehydrogenated oil from the mixture, and then the dehydrogenated oil is further separated and removed as a non-permeated gas by the membrane separation means. Hydrogen is a method for producing high-purity hydrogen, wherein hydrogen is produced by taking it out as a permeate gas.

  According to a second aspect of the present invention, in the first aspect of the present invention, a mixture of hydrogen produced by dehydrogenating a feedstock containing hydrocarbons having a cyclohexane ring and dehydrogenated oil containing aromatic hydrocarbons is used. A method for producing high-purity hydrogen, characterized in that dehydrogenated oil containing an aromatic hydrocarbon is separated and removed.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a dehydrogenated oil containing toluene from a mixture of hydrogen produced by dehydrogenating a feedstock containing methylcyclohexane and dehydrogenated oil containing toluene. Is a method for producing high-purity hydrogen, characterized by separating and removing hydrogen.

  A fourth aspect of the present invention is the method for producing high purity hydrogen according to any one of the first to third aspects of the present invention, wherein the membrane used for the membrane separation means is a ceramic membrane.

  A fifth aspect of the present invention is the method for producing high purity hydrogen according to any one of the first to third aspects of the present invention, wherein the membrane used for the membrane separation means is a polymer membrane.

  A sixth aspect of the present invention is a method for producing high purity hydrogen according to any one of the first to third aspects of the present invention, wherein the membrane used for the membrane separation means is a carbon membrane.

  A seventh aspect of the present invention is the method for producing high purity hydrogen according to any one of the first to sixth aspects of the present invention, wherein the non-permeated gas after membrane separation is recycled to the front stage of the cooling separation step.

The eighth of the present invention is
A dehydrogenation reactor that dehydrogenates the feedstock oil into a dehydrogenated mixture of dehydrogenated oil and hydrogen;
A cooling separator in which the dehydrogenated oil is selectively separated by cooling the dehydrogenated mixture, and the separated dehydrogenated oil is discharged from the cooling separator and removed from the system;
A membrane separator that further removes the dehydrogenated oil from the dehydrogenated mixture from which most of the dehydrogenated oil has been removed in the cooling separator to remove dehydrogenated oil in the non-permeate gas and hydrogen in the permeate gas; and
Recycling means for returning non-permeate gas discharged from the membrane separator to the cooling separator,
A high-purity hydrogen production system comprising:

  The ninth of the present invention is a hydrogen station using the eighth high-purity hydrogen production system of the present invention.

According to the method of the present invention, hydrogen is generated mainly from a hydrocarbon having a cyclohexane ring by dehydrogenation, and the hydrocarbon contained in the hydrogen is cooled and separated, and then removed by membrane separation. In addition, while being a method suitable for small-scale production, high-purity hydrogen having a purity of 99.99% or more can be efficiently produced.
If a hydrocarbon containing a cyclohexane ring is used as a dehydrogenation raw material, most of the raw material reacts, and the reacted hydrocarbon is converted into an aromatic hydrocarbon, so that the hydrocarbon in the resulting dehydrogenation product is substantially free. It becomes an aromatic hydrocarbon and becomes a method particularly suitable for the present invention.
By using a ceramic membrane or a carbon (carbon) membrane for membrane separation, it is possible to operate advantageously when an aromatic hydrocarbon is contained in the dehydrogenated oil.
By recycling the non-permeating gas that does not permeate the membrane in the membrane separation to the cooling separation step, the purity of hydrogen can be further improved easily.
Hereinafter, the present invention will be described in detail.

  In the method for producing hydrogen in the present invention, a feedstock containing hydrocarbons, preferably alicyclic hydrocarbons, more preferably hydrocarbons containing cyclohexane rings, is dehydrogenated to unsaturated hydrocarbons, preferably dehydrogenated oils containing aromatics. Thus, hydrogen is generated and the dehydrogenated oil is separated.

A catalyst is usually used for the dehydrogenation reaction of the present invention. Although any catalyst having dehydrogenation activity can be used as the catalyst, it is preferable to use a solid catalyst as the catalyst and perform the dehydrogenation reaction in a fixed bed flow type reaction mode. The solid catalyst comprises a carrier and a catalytically active main component, and a metal oxide that is usually stable and has a large surface area can be suitably used for the carrier.
The catalytically active main component is an active component containing a metal having dehydrogenation activity and can be arbitrarily selected, but is preferably a Group 8 element, a Group 9 element, or a Group 10 element, specifically Are iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. More preferably, they are nickel, palladium, and platinum. Two or more of these elements may be combined. In the present specification, the group numbers in the periodic table are based on the International Pure and Applied Chemistry Union Inorganic Chemistry Nomenclature Nomenclature 1990 Edition.

The preparation method for incorporating this catalytically active main component into the formed catalyst in combination with the support is arbitrary, and a known method can be used, but an impregnation method for impregnating this catalytically active main component into the support is preferred, and specific examples Specific examples include the Incipient Wetness method and the evaporation to dryness method. The elemental compound used in the impregnation method is preferably a water-soluble salt, and is preferably impregnated as an aqueous solution. Preferred examples of the water-soluble salt include chlorides, nitrates and carbonates.
The carrier to be impregnated is preferably a stable metal oxide because it has high mechanical strength, is thermally stable and has a large surface area, and specifically includes alumina, silica, titania, zirconia, silica / alumina, and the like. More preferred is alumina, silica or a mixture thereof.

  The catalyst for dehydrogenation of the present invention may contain an additive if necessary, and a preferable substance is a basic substance. 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 kind of the basic substance is arbitrary, but any element of Group 1 element and Group 2 element in the periodic table or a compound containing the element is preferable. Specifically, lithium, sodium, potassium, Compounds of rubidium, cesium, beryllium, magnesium, calcium, strontium and barium are preferred. More preferred are compounds of Group 1 elements, specifically, lithium, sodium, potassium, rubidium, and cesium compounds. As the additive, a water-soluble substance is preferable. As water-soluble salts, chlorides, sulfates, nitrates, and carbonates are more preferable. The content of the additive is preferably in the range of 0.1 to 100 by weight ratio with respect to the catalytically active main component. A preparation method for adding the additive to the catalyst body is arbitrary, but an impregnation method is preferable. Specific examples include the Incipient Wetness method and the evaporation to dryness method. It is prepared by impregnating the carrier with the catalytically active principal component together with or separately from the catalytically active principal component.

  The feedstock oil in the present invention contains hydrocarbons, preferably hydrocarbons that are easily dehydrogenated to produce unsaturated hydrocarbons, such hydrocarbons contain aliphatic cyclic hydrocarbons in the molecule, and are dehydrogenated. More easily unsaturated hydrocarbons, preferably hydrocarbons that convert to or produce aromatic hydrocarbons. Such a hydrocarbon is preferably a hydrocarbon containing a cyclohexane ring. Preferably, it is a hydrocarbon that becomes a liquid by appropriate heating even at room temperature or solid at room temperature. The cyclohexane ring contained in the preferred hydrocarbon can be condensed or non-condensed, and specific hydrocarbons include cyclohexane and cyclohexane alkyl substituents, decalin and decalin alkyl substituents, tetralin and tetralin alkyl substituents. More preferred are cyclohexane, methylcyclohexane, dimethylcyclohexanes, decalin, and methyldecalins, with cyclohexane and methylcyclohexane being preferred. These can also be mixtures.

The feedstock used for dehydrogenation can contain other substances, for example, organic compounds other than hydrocarbons, as long as the object of the present invention is not impaired. Usually the content of such substances is less than 50% by weight.
The products of the dehydrogenation reaction in the present invention are hydrogen and dehydrogenated oil, the dehydrogenated oil contains unsaturated hydrocarbons, and the unsaturated hydrocarbons are preferably mainly aromatic hydrocarbons, and hydrocarbons in the feedstock oil When is a cyclohexane, it is benzene, and when it is methylcyclohexane, it is toluene. The dehydrogenated oil may contain unreacted hydrocarbons. In the dehydrogenation of the present invention, most raw materials are subjected to a dehydrogenation action and converted to unsaturated hydrocarbons. Particularly preferably, in the hydrocarbon containing a cyclohexane ring, most of the raw material hydrocarbons react and all of them are converted to aromatic hydrocarbons. Unreacted hydrocarbons are substantially not included. As a result, the hydrogen obtained from the dehydrogenation reaction of hydrocarbons stepping on the cyclohexane ring is essentially composed of aromatic hydrocarbons as the contained hydrocarbons.

  The dehydrogenated oil can be reused as a raw material oil by collecting it and hydrogenating it again. Furthermore, the dehydrogenated oil can be used as a fuel for a heat source 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. Alternatively, it can be used as a chemical product.

The dehydrogenation reaction conditions of the present invention are carried out by adjusting the reaction pressure, reaction temperature, etc., but will be appropriately selected according to the type of feedstock, the type of catalyst, and the like. The dehydrogenation reaction from the cyclohexane ring to the aromatic ring is a reversible reaction, and high temperature, low pressure, or both conditions are preferred for the dehydrogenation reaction to proceed from the viewpoint of chemical equilibrium.
Specifically, the reaction pressure of the dehydrogenation reaction of the present invention is preferably 0.1 MPa or more and 1.0 MPa or less, more preferably 0.1 MPa or more and 0.5 MPa or less. In the present specification, unless otherwise specified, the pressure is an absolute pressure.
The reaction temperature of the dehydrogenation reaction of the present invention is preferably a high temperature in terms of chemical equilibrium, but is suitably a low temperature in terms of energy efficiency. Therefore, preferable reaction temperature is 200 degreeC or more and 450 degrees C or less, More preferably, it is 250 degreeC or more and 380 degrees C or less.
In the dehydrogenation reaction of the present invention, 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 feedstock, the molar ratio of hydrogen to feedstock is preferably 0.01 or more and 1 or less. A preferable range of LHSV (liquid space velocity) for the dehydrogenation reaction is preferably 0.2 v / v / hr or more and 20 v / v / hr or less, although it depends on the activity of the catalyst.

By the above-described dehydrogenation reaction, a mixture of hydrogen and dehydrogenated oil (sometimes referred to as a dehydrogenated mixture) is obtained. Dehydrogenated oil contains unsaturated hydrocarbons and unreacted hydrocarbons. As described above, preferred unsaturated hydrocarbons are aromatic hydrocarbons, and hydrocarbons containing a cyclohexane ring, which is preferred as a raw material, are mostly converted into aromatic hydrocarbons and substantially free of unreacted hydrocarbons. I can't.
If the dehydrogenation reaction is a gas phase reaction, the dehydrogenation mixture takes the form of a mixed gas.

Next, dehydrogenated oil is separated and removed from the above mixture to produce high-purity hydrogen.
As a method for separating hydrogen and dehydrogenated oil from the dehydrogenation mixture in the present invention, cooling separation is used, and then membrane separation is further used.
A cooling separator can be used as the cooling separation means in the present invention. Rather than simply cooling, it is preferable to employ a method of gas-liquid separation of the liquefied component by compressing the gas and cooling it under high pressure. Specifically, the cooling separator usually comprises a compressor, a cooler (heat exchanger), and a gas-liquid separator. The dehydrogenated mixture obtained in the dehydrogenation reactor is compressed and cooled to separate the dehydrogenated oil.・ To be removed. The removed dehydrogenated oil is discharged out of the system and, for example, hydrogenated as described above can be used as a raw material oil.

The compression condition and temperature condition of the cooling separation can be appropriately selected depending on the target hydrogen concentration after the cooling separator. The compression pressure is not required to be high, and is preferably 0.1 MPa or more and 80.0 MPa or less, more preferably 0.1 MPa or more and 30.0 MPa or less. The cooling temperature is preferably higher than −50 ° C. and 30 ° C. or lower, more preferably −20 ° C. or higher and 20 ° C. or lower.
In the cooling and separating step, after compression and cooling (heat exchange), the dehydrogenated oil is liquefied, and the liquefied dehydrogenated oil is separated and recovered from the gas-liquid mixture by the gas-liquid separator. A cooler (heat exchanger) can be provided in front of the compressor as appropriate.

After cooling separation of the liquefied dehydrogenated oil, the dehydrogenated mixture can preferably contain up to 0.5% dehydrogenated oil, and more preferably, the dehydrogenated mixture containing up to 0.1% is transferred to the next membrane separation step. . In other words, the conditions and the like of the cooling separation operation may be selected so that the cooling separation is preferably 0.5% or less, more preferably 0.1% or less. Separation / removal of dehydrogenated oil to such a concentration can be easily achieved by the cooling separation of the present invention without requiring a special cooling machine or the like.
From the cooling separator of the invention, a gaseous dehydrogenation mixture containing preferably up to 0.5% dehydrogenated oil flows out as described above. From this, by using a membrane separation means, high-purity hydrogen is produced by separating and removing the dehydrogenated oil.

A membrane separator can be used as the means for membrane separation of the present invention, and the membrane separator comprises a separation membrane and a support. In the membrane separation, the dehydrogenated oil is further removed by the separation membrane from the hydrogen containing the dehydrogenated oil after the cooling separation. The support of the membrane separator is formed in a tubular shape, and a separation membrane is formed on the outer periphery thereof to be integrated to form a tubular membrane separator. A dehydrogenation mixture is introduced from one outer end of the tubular membrane separator, and a non-permeate gas is removed from the other end. On the other hand, the permeate gas can pass into the inside of the tube and take out high purity hydrogen.
As the separation membrane of the present invention, any membrane that can selectively separate hydrogen can be used without any particular limitation.

Here, in the purification of hydrogen, a palladium membrane has been industrially put into practical use for the purpose of high-purity hydrogen purification (supervised by Masayuki Nakagaki, membrane treatment technology system (first volume), Fuji Techno System, pages 661 to 662 and 922- 925 (1991)) (however, hydrogen is not from hydrocarbon dehydrogenation, but mainly from steam reforming of hydrocarbons or electrolysis of water). However, since palladium is very expensive, it is not economical and has limited resources, so the applicable range is limited to special purposes. Furthermore, since the membrane separation process in this case involves a process of dissociating and bonding hydrogen to protons and electrons, a certain operating temperature is required and it does not function near room temperature. However, even when heated, peeling between the palladium membrane and the support becomes a problem due to expansion due to hydrogen absorption at 250 ° C. or lower.
Therefore, preferably, in the present invention, a porous membrane type separation membrane, particularly a membrane that performs selective gas separation by molecular sieve action is employed. The pore diameter of such a porous membrane is preferably 0.3 nm or more and 0.7 nm or less, and the upper limit is more preferably 0.5 nm or less.
Specifically, such a film is preferably a ceramic film, a polymer film, or a carbon film.

  Any material can be used as the material of the polymer film as long as it is a porous film made of a polymer material, but polyimide, tetrafluoroethylene, cellulose acetate, and polysulfone films are preferable, and a polyimide film is more preferable.

By the way, the polymer film has low resistance to liquid hydrocarbons, particularly aromatic hydrocarbons, and is preferably used at a low concentration. In the cooling separation process of the present invention, for example, the gas from the gas / liquid separator may contain a small amount of liquid components, but the liquid may be condensed during the membrane separation process. If the concentration is low, it can be used while paying attention to resistance.
On the other hand, among various membrane materials, ceramic membranes and carbon membranes have high chemical resistance, and can be preferably used for separation of aromatic hydrocarbons. For example, it is possible to use ceramic membranes and carbon membranes used for separation of aromatic hydrocarbons as introduced in the magazine “Membrane”, Soichiro, Vol. 19, No. 3, pages 146-154 (1994). it can.

As the material of the ceramic film as a preferable film material, known ceramic materials can be used in addition to the above, but silica, alumina, titania, glass, silicon carbide, and silicon nitride (for example, Si ₃ N ₄ ) are preferable. This ceramic film is usually formed on a support that mechanically holds the film. The support is preferably a porous ceramic support, more preferably porous alumina, silica, or silicon nitride.

  Any carbon film can be used as long as it is a porous carbon (carbon) film as described above. Usually, a carbon film prepared by carbonizing polyimide is used. The carbonization temperature of polyimide is preferably 700 ° C. or higher and 1300 ° C. or lower. More preferably, it is 900 degreeC or more and 1100 degrees C or less.

In the membrane separation, the mixed gas from the cooling separation process is brought into contact with the membrane under pressure to selectively permeate hydrogen to obtain high-purity hydrogen as a permeate gas, and the dehydrogenated oil gas permeates the membrane as a non-permeate gas. It remains without.
The separation conditions for membrane separation vary depending on the type of dehydrogenated oil, the performance of the separation membrane, the required hydrogen purity, and the size (length, etc.) of the separation membrane. The following ranges can be applied.
The introduction pressure for membrane separation is usually preferably 0.2 MPa or more and 80 MPa or less, and the upper limit is more preferably 30 MPa or less. The differential pressure of the separation membrane is preferably from 0.01 MPa to 2 MPa, more preferably from 0.1 MPa to 1 MPa.
The membrane separation temperature is preferably such that the dehydrogenated oil does not condense on the non-permeate side of the membrane, and is usually from −10 ° C. to 80 ° C., preferably from 10 ° C. to 50 ° C. It can be heated appropriately for this purpose. In addition, when a high purity is required for the hydrogen concentration, it is possible to appropriately perform a multistage separation operation of two or more stages in which the hydrogen of the permeated gas is further separated by a separate membrane separation process.

In membrane separation, hydrogen selectively permeates through the membrane, hydrogen with less dehydrogenated oil content and higher purity is recovered as product hydrogen, and the remaining non-permeate gas that does not permeate the membrane is appropriately discharged out of the system. can do.
For example, when obtaining higher-purity hydrogen, preferably, the non-permeate gas is supplied to the preceding stage of the above-described cooling separation step, mixed with the dehydrogenated mixture before the compressor, and recycled to the cooling separation step.

  Here, the removal rate of dehydrogenated oil in the cooling separation is uniquely determined by the pressure and temperature. That is, it is determined as a vapor pressure that is uniquely determined under the temperature and pressure. Therefore, dehydration of the dehydrogenated mixture after removing the dehydrogenated oil by cooling separation under constant pressure and temperature conditions, regardless of changing the recycle rate of the nonpermeate gas, that is, regardless of the amount of nonpermeable gas to be recycled. The raw oil concentration does not change. Therefore, if the non-permeating gas in the membrane separation is recycled to the cooling separation step, the product hydrogen concentration as the permeating gas after the membrane separator can be controlled by this recycling ratio. In other words, if higher purity hydrogen is required, the recycle ratio can be increased and a larger amount of non-permeate gas can be recycled. It is one of the features of the present invention that the product hydrogen concentration can be easily controlled. Although this recycle ratio can be determined as appropriate, it can be set to a value in the range of 1 to 99%, for example.

The recycle ratio (%) can be defined as the following value.
Recycle ratio = flow rate of hydrogen in non-permeate gas (per unit time) / flow rate of hydrogen introduced into membrane separation (per unit time) × 100
= (1-high-purity hydrogen flow rate (per unit time) / hydrogen flow rate introduced into membrane separation (per unit time)) × 100
By the method of the present invention, the hydrogen concentration of product hydrogen can be made 99.99% or more easily and easily. Preferably, the hydrogen concentration can be 99.999% or more, more preferably 99.9999% or more.

A conceptual diagram of a hydrogen production system according to the present invention is shown in FIG.
In the figure, the feedstock is introduced into the dehydrogenation reactor 1 to produce a dehydrogenation mixture comprising dehydrogenation oil containing hydrogen and preferably aromatic hydrocarbons. The resulting dehydrogenated mixture is pressurized in the compressor 2 and then cooled in the heat exchanger 3, and most of the dehydrogenated oil, preferably aromatic hydrocarbons, is removed by gas-liquid separation in the gas-liquid separator 4, followed by dehydration. The elementary mixture is gaseous and is introduced into the next membrane separator 5.

The permeate gas that permeates the membrane in the membrane separator is product hydrogen with increased purity, and the non-permeate gas that does not permeate the membrane is discharged out of the system through an appropriate pipe (not shown). In a preferred embodiment, the non-permeate gas that does not permeate the membrane is recycled at an appropriate recycle ratio before the compressor 2 and is mixed with the dehydrogenated mixture to be supplied to the cooling separation process again.
By using the hydrogen production system of the present invention as described above, a hydrogen station can be simply and effectively constructed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to the range of these Examples.

[Separation membrane]
The separation membranes A, B, and C used in the following examples and comparative examples are as follows. All were used as tubular membrane separators.

Separation membrane A
The inner surface of a tubular support made of porous alumina is coated with a silica membrane, and has a hydrogen permeability coefficient of 4.2 × 10 ⁻⁷ mol / m ² / sec / Pa, a toluene permeability coefficient of 2.8 x a ^{10 -10 mol / m 2 / sec} / Pa, ceramic membrane membrane area 0.0013M ² a, the separation membrane a.

Separation membrane B
Hydrogen permeability coefficient ^{5.0 x 10 -6 mol / m 2} / sec / Pa, and toluene permeability coefficient ^{3.4 x 10 -10 mol / m 2} / sec / Pa, the polyimide film of the membrane area 0.0002 m ² This is separation membrane B.

Separation membrane C
Hydrogen permeability coefficient obtained by carbonizing polyimide at 900 ° C. for 20 minutes under high purity argon, 1.6 × 10 ⁻¹⁰ mol / m ² / sec / Pa, toluene permeability coefficient 2.7 × 10 ⁻¹³ mol / m ² / sec / Pa, the carbon film of membrane area 0.0126m ^2, the separation membrane C.

(Comparative Example 1)
40 cc of a commercially available spherical catalyst having an average diameter of 1.5 mm, in which 0.3 mass% of platinum is supported on a γ-alumina carrier, is charged into a fixed bed flow reactor, and methylcyclohexane is introduced as a raw material at 0.305 g / min. The dehydrogenation reaction was performed under conditions of 340 ° C. and 0.1 MPa. The product gas containing the obtained dehydrogenation mixture was separated at 15 ° C. and 3.0 MPa in a cooling separator to produce hydrogen.
The hydrogen concentration after separation is determined and shown in Table 1.

(Comparative Example 2)
Hydrogen was produced in the same manner as in Comparative Example 1 except that separation was performed at −10 ° C. in a cooling separator. The hydrogen concentration after separation is determined and shown in Table 1.

(Comparative Example 3)
40 cc of a spherical commercial catalyst with an average diameter of 1.5 mm, in which 0.3 mass% of platinum is supported on a γ-alumina support, is charged into a fixed bed flow type reactor, and methylcyclohexane is introduced as a raw material at 0.070 g / min. The dehydrogenation reaction was performed at 380 ° C. and 0.3 MPa. The product gas containing the obtained dehydrogenation mixture is separated by a membrane separator using the separation membrane A under conditions of an inlet pressure of 0.3 MPa, a permeate pressure of 0.1 MPa, a recycle ratio of 80%, and 170 ° C., Hydrogen was produced. Since the temperature in the membrane separation was considerably high, the product gas from the dehydrogenation reactor was introduced into the membrane separator to such an extent that it was slightly cooled.
The hydrogen concentration after separation is determined and shown in Table 1.

40 cc of a spherical commercial catalyst with an average diameter of 1.5 mm carrying 0.3 mass% platinum on a γ-alumina support was charged into a fixed bed flow reactor, and methylcyclohexane was introduced as a raw material at 0.305 g / min. The dehydrogenation reaction was performed under conditions of 340 ° C. and 0.1 MPa. The product gas containing the obtained dehydrogenation mixture is separated at 15 ° C. and 3.0 MPa in a cooling separator, and then the inlet pressure is 3.0 MPa and the permeation side pressure is 2. by the membrane separator using the separation membrane A. Separation was performed under conditions of 7 MPa, a recycle ratio of 80%, and 70 ° C. to produce hydrogen.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen was produced in the same manner as in Example 1 except that methylcyclohexane was introduced as a raw material at 0.510 g / min, and separation was performed in a membrane separator under conditions of a permeate pressure of 2.5 MPa and a recycle ratio of 90%.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen was produced in the same manner as in Example 1 except that methylcyclohexane was introduced as a raw material at 1.03 g / min and separation was performed in a membrane separator under conditions of a permeate pressure of 2.0 MPa and a recycle ratio of 90%.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen was produced in the same manner as in Example 1 except that methylcyclohexane was introduced as a raw material at 0.308 g / min and separation was performed at −10 ° C. in a cooling separator.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen was produced in the same manner as in Example 4 except that methylcyclohexane was introduced as a raw material at 0.514 g / min and separation was performed in a membrane separator under conditions of a permeate pressure of 2.5 MPa and a recycle ratio of 90%.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen was produced in the same manner as in Example 4 except that methylcyclohexane was introduced as a raw material at 1.030 g / min and separation was performed in a membrane separator under conditions of a permeation pressure of 2.0 MPa and a recycle ratio of 90%.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen as in Example 1 except that methylcyclohexane was introduced as a raw material at 0.343 g / min, separation membrane B was used as a membrane separator, and separation was performed under conditions of a permeation pressure of 2.5 MPa and a recycle ratio of 64%. Manufactured.
The hydrogen concentration after separation is determined and shown in Table 1.

Hydrogen as in Example 4 except that methylcyclohexane was introduced as a raw material at 0.345 g / min, separation membrane B was used as a membrane separator, and separation was performed under conditions of a permeate pressure of 2.5 MPa and a recycle ratio of 92%. Manufactured.
The hydrogen concentration after separation is determined and shown in Table 1.

As in Example 1 except that methylcyclohexane was introduced as a raw material at 0.004 g / min, separation membrane C was used as a membrane separator, and separation was performed under conditions of a permeation pressure of 2.0 MPa and a recycle ratio of 90%. Hydrogen was produced.
The hydrogen concentration after separation is determined and shown in Table 1.

  As in Example 4 except that methylcyclohexane was introduced as a raw material at 0.004 g / min, separation membrane C was used as a membrane separator, and separation was performed under conditions of a permeate pressure of 2.0 MPa and a recycle ratio of 90%. Hydrogen was produced.

The results are shown in Table 1.

As Comparative Examples 1 to 3 in Table 1 show, it is not easy to make the hydrogen concentration 99.99% or more with only the cooling separator and only the membrane separator.
On the other hand, in the Example which performed the separation by various separation membranes from A to C after the cooling separation, the hydrogen concentration of 99.999% can be easily achieved under each condition. Thus, it is possible to achieve even a hydrogen concentration of 99.9999%.
Here, in order to achieve a hydrogen concentration of 99.999% or higher only by cooling separation, the conditions of −45 ° C. and 3.0 MPa are necessary, and in order to achieve a hydrogen concentration of 99.9999% or higher, The conditions of −65 ° C. and 3.0 MPa are required. On the other hand, in the present invention in which membrane separation is performed after cooling separation at about −10 ° C., it is clear that the present invention has an advantage in that energy consumption is much less.

  In the present invention, as a preferred embodiment, the non-permeate gas of the membrane separator is recycled before the cooling separation step. Since the hydrocarbon removal rate in the cooling separation is uniquely determined by the pressure and temperature, the hydrogen concentration after the cooling separation does not depend on the recycling amount. Therefore, the final hydrogen concentration after the membrane separator can be easily controlled by the recycle ratio.

  According to the present invention, high-purity hydrogen can be produced easily and easily on a small scale, and the present invention can be used as, for example, a so-called hydrogen station.

It is a conceptual diagram of the hydrogen production system by this invention.

Explanation of symbols

1: Dehydrogenation reactor 2: Compressor 3: Heat exchanger 4: Gas-liquid separator 5: Membrane separator

Claims (9)

  In a method for producing high-purity hydrogen by separating dehydrogenated oil from a mixture of hydrogen produced by dehydrogenating a feedstock containing hydrocarbon in the presence of a catalyst and dehydrogenated oil containing unsaturated hydrocarbon, the separation As a means, most of the dehydrogenated oil is separated / removed from the mixture by the cooling separation means, and then the hydrogenated hydrogen is separated and removed as a non-permeate gas by the membrane separation means, and hydrogen is taken out as a permeate gas to produce hydrogen. A method for producing high-purity hydrogen characterized by the above.   Separating and removing dehydrogenated oil containing aromatic hydrocarbons from a mixture of hydrogen produced by dehydrogenating a feedstock containing hydrocarbons having a cyclohexane ring and dehydrogenated oil containing aromatic hydrocarbons; The method for producing high-purity hydrogen according to claim 1, wherein   3. The high dehydrogenation oil according to claim 1, wherein the dehydrogenation oil containing toluene is separated and removed from a mixture of hydrogen produced by dehydrogenation of the raw material oil containing methylcyclohexane and dehydrogenation oil containing toluene. A method for producing pure hydrogen.   The method for producing high-purity hydrogen according to any one of claims 1 to 3, wherein the membrane used for the membrane separation means is a ceramic membrane.   The method for producing high-purity hydrogen according to any one of claims 1 to 3, wherein the membrane used for the membrane separation means is a polymer membrane.   The method for producing high-purity hydrogen according to any one of claims 1 to 3, wherein the membrane used for the membrane separation means is a carbon membrane.   The method for producing high-purity hydrogen according to any one of claims 1 to 6, wherein the non-permeate gas after membrane separation is recycled to the front stage of the cooling separation step. A dehydrogenation reactor that dehydrogenates the feedstock oil into a dehydrogenated mixture of dehydrogenated oil and hydrogen;
A cooling separator in which the dehydrogenated oil is selectively separated by cooling the dehydrogenated mixture, and the separated dehydrogenated oil is discharged from the cooling separator and removed from the system;
A membrane separator that further removes the dehydrogenated oil from the dehydrogenated mixture from which most of the dehydrogenated oil has been removed in the cooling separator to remove dehydrogenated oil in the non-permeate gas and hydrogen in the permeate gas; and
Recycling means for returning non-permeate gas discharged from the membrane separator to the cooling separator,
A high purity hydrogen production system comprising:   A hydrogen station using the high-purity hydrogen production system according to claim 8.

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