JP2010006653A - Method for producing hydrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing hydrogen where the recovering rate of hydrogen can be significantly enhanced comparing with a conventional technique by increasing the separating efficiency of hydrogen while attaining high inversion rate of a dehydrogenation reaction under a low pressure condition. <P>SOLUTION: The method for producing hydrogen where the dehydrogenation reaction of the hydride of an aromatic hydrocarbon is performed in a dehydrogenation reactor 2 with a catalyst layer and where hydrogen is separated from a product by the dehydrogenation reaction in a hydrogen separating device 3 with a hydrogen separating membrane is characterized by that the temperature of the hydrogen separating membrane in the hydrogen separating device 3 is higher than the average temperature of the catalyst layer in the dehydrogenation reactor 2 by 10-100°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrogen production method, and more particularly, to a hydrogen production method with an improved hydrogen recovery rate than in the past.

  In recent years, hydrogen has been considered promising as a new energy source due to environmental problems and energy problems. For example, development of hydrogen automobiles using hydrogen directly as fuel or fuel cells using hydrogen has been promoted. Although the fuel cell is small, it has high power generation efficiency. In addition, the fuel cell does not generate noise and vibration, and has excellent advantages such as the ability to use waste heat.

  On the other hand, in using hydrogen as an energy source, it is essential to supply hydrogen as a fuel safely and stably. In contrast, a method of supplying hydrogen directly as compressed hydrogen or liquid hydrogen, a method of storing and supplying hydrogen using hydrogen storage materials such as hydrogen storage alloys and carbon nanotubes, and steam reforming methanol and hydrocarbons to generate hydrogen. Various methods such as a supplying method have been proposed.

  As a hydrogen supply method similar to these, in recent years, the hydrogen storage rate is high, and it is possible to reuse by repeatedly storing and supplying hydrogen. A method for supplying hydrogen has attracted attention.

  In such a method for producing hydrogen by a dehydrogenation reaction using a hydride of an aromatic hydrocarbon, the reaction mixture after the dehydrogenation reaction usually contains unreacted aromatic hydrocarbons in addition to hydrogen gas. This includes hydrides, aromatic hydrocarbons produced by dehydrogenation, and by-products. Therefore, after separating hydrogen gas from the reaction mixture after the dehydrogenation reaction by gas-liquid separation, a method of purifying the hydrogen gas using pressure swing adsorption (PSA) has been proposed in order to further increase the purity of hydrogen. Yes. However, when PSA is used, there is a problem that the hydrogen recovery rate is as low as about 70 to 85%. In order to achieve a high hydrogen recovery rate, various methods for recovering hydrogen from the reaction mixture after the dehydrogenation reaction using a hydrogen separation membrane have been proposed.

  For example, Japanese Patent Laid-Open No. 2006-232607 (Patent Document 1) discloses that a gas phase immediately after a dehydrogenation reaction is made high-purity hydrogen by means of hydrogen purification using a hydrogen separation membrane, and a part of the high-purity hydrogen. A method for producing high-purity hydrogen with a high hydrogen recovery rate by recycling to a dehydrogenation reactor is disclosed.

  Japanese Patent Laid-Open No. 2007-099528 (Patent Document 2) describes that a hydrogen separation membrane is operated at a first temperature of 150 ° C. or higher and lower than 350 ° C., and when the hydrogen separation membrane is stopped, the hydrogen separation membrane is set to 300 ° C. The operation of the hydrogen separation membrane is stopped after the heating treatment to a second temperature higher than the first temperature, or the hydrogen separation membrane is operated at a first temperature of 150 ° C. or higher and lower than 350 ° C. When the hydrogen recovery rate in the hydrogen separation membrane decreases, the temperature of the hydrogen separation membrane is raised to a second temperature that is 300 ° C. or higher and higher than the first temperature, and then the temperature of the hydrogen separation membrane A method for producing high-purity hydrogen continuously or intermittently while maintaining a high hydrogen recovery rate by lowering the temperature to a first temperature of 150 ° C. or higher and lower than 350 ° C. and continuing the operation is disclosed.

  Furthermore, Japanese Patent Application Laid-Open No. 2005-035842 (Patent Document 3) discloses a hydrogen generation reactor in which a hydrocarbon having a cyclohexane ring is used as a raw material, and hydrogen is generated by a reaction in which the cyclohexane ring is dehydrogenated to an aromatic ring. And a hydrogen membrane separator for removing hydrocarbons contained in hydrogen by membrane separation using a ceramic membrane, and a hydrogen production system capable of producing high-purity hydrogen with high energy efficiency is disclosed. Yes.

JP 2006-232607 A JP 2007-099528 A Japanese Patent Laid-Open No. 2005-035842

  However, in the above prior art, the method of separating and recovering hydrogen with a hydrogen separation membrane by utilizing the heat capacity of the product gas from the dehydrogenation reactor is adopted, so the temperature of the dehydrogenation reactor is inevitably set to the hydrogen separation temperature. It was higher than the temperature of the film. Here, a noble metal catalyst is generally used for the dehydrogenation reaction, and when it is operated for a long time at a high temperature, the catalytic activity is deteriorated due to aggregation of the noble metal.

  On the other hand, generally, measures such as keeping the temperature of the dehydrogenation reactor low are taken in order to suppress the deterioration of the catalyst. However, in the conventional hydrogen production method, since the temperature of the dehydrogenation reactor is higher than the temperature of the hydrogen separation membrane, it is necessary to operate a hydrogen separation membrane that is inherently high temperature and excellent in separation efficiency at a low temperature. There was a drawback that the hydrogen recovery rate was lowered by the separation.

  In addition, in order to improve the reduced separation efficiency, a method of operating at an increased pressure has been tried. However, when the pressure is increased, the conversion rate of the dehydrogenation reaction decreases, and the amount of hydrogen generation decreases. there were.

  Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, achieve a high dehydrogenation conversion rate under low pressure conditions, improve the hydrogen separation efficiency, and increase the hydrogen recovery rate compared to the prior art. An object of the present invention is to provide a hydrogen production method that can be greatly improved.

  As a result of intensive investigations to achieve the above object, the present inventor conducted a dehydrogenation reaction of a hydride of an aromatic hydrocarbon in a dehydrogenation reactor having a catalyst layer, and a hydrogen separation having a hydrogen separation membrane. In the hydrogen production method in which hydrogen is separated from the dehydrogenation reaction product by the apparatus, the temperature of the hydrogen separation membrane in the hydrogen separation apparatus is made 10 to 100 ° C. higher than the average temperature of the catalyst layer in the dehydrogenation reactor. Thus, the inventors have found that the hydrogen recovery rate is improved, and have completed the present invention.

That is, the hydrogen production method of the present invention performs a dehydrogenation reaction of an aromatic hydrocarbon hydride in a dehydrogenation reactor including a catalyst layer, and generates the dehydrogenation reaction by a hydrogen separation device including a hydrogen separation membrane. In a hydrogen production method for separating hydrogen from a product,
The temperature of the hydrogen separation membrane in the hydrogen separator is 10 to 100 ° C. higher than the average temperature of the catalyst layer in the dehydrogenation reactor.

  In the present invention, the average temperature of the catalyst layer means an average temperature obtained by dividing the catalyst layer into three equal parts in the flow direction of the aromatic hydrocarbon hydride and measuring the temperature at the center of each part.

  In a preferred embodiment of the hydrogen production method of the present invention, a heat medium for heating the dehydrogenation reactor and the hydrogen separation device is passed through the dehydrogenation reactor after passing through the hydrogen separation device. Here, it is further preferable that the heat medium discharged from the dehydrogenation reactor is reheated and supplied to the hydrogen separator.

  According to the present invention, while the temperature of the hydrogen separation membrane in the hydrogen separator is 10 to 100 ° C. higher than the average temperature of the catalyst layer in the dehydrogenation reactor, a high dehydrogenation conversion rate is achieved. The hydrogen separation efficiency is improved, and as a result, the hydrogen recovery rate can be improved.

  A preferred embodiment of the present invention will be specifically described below with reference to FIG. However, the present invention is not limited to the form shown in FIG.

  In the hydrogen production method of the present invention, for example, the aromatic hydrocarbon hydride is pumped from a tank 1 for storing the aromatic hydrocarbon hydride as a raw material with a pump or the like, preheated, and then supplied to the dehydrogenation reactor 2. , Dehydrogenation reaction is performed. Here, the preheating of the aromatic hydrocarbon hydride is preferably performed by a heat exchanger (not shown), and the heat source uses heat generated by burning the fuel with a heating means such as a burner. be able to.

  Examples of hydrides of aromatic hydrocarbons used in the present invention include cyclohexanes and decalins, but those having substituents from the viewpoint of safety and ease of handling of aromatic hydrocarbons produced after dehydrogenation reaction. It is preferable to use alkylcyclohexane such as methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, diethylcyclohexane and trimethylcyclohexane, alkyldecalin such as methyldecalin, ethyldecalin, dimethyldecalin and diethyldecalin, and mixtures thereof.

  The dehydrogenation reactor 2 used in the present invention is filled with a catalyst, and an aromatic hydrocarbon hydride is supplied to cause a dehydrogenation reaction. Here, as a supply method to the dehydrogenation reactor 2, either a method of supplying an aromatic hydrocarbon hydride as a liquid or a method of supplying it as a preheated gas can be used. It is preferable to supply the gas to the bed reactor.

  In addition, as a dehydrogenation reaction catalyst charged in the dehydrogenation reactor 2, at least one metal selected from the group consisting of platinum, ruthenium, palladium, rhodium, tin, rhenium, and germanium is supported on a porous carrier. The average pore diameter is preferably selected as appropriate depending on the type of the aromatic hydrocarbon hydride supplied to the dehydrogenation reactor 2. That is, a catalyst having an average pore diameter of 40 to 80 mm is particularly preferred when using one-ring cyclohexanes, and a catalyst having an average pore diameter of 65 to 130 mm is particularly preferred when using two-ring decalins. It is preferable to select them, and it is preferable that the volume of pores having a preferable pore diameter is 50% or more of the total pore volume.

In order to control the average pore diameter and pore volume ratio of the dehydrogenation reaction catalyst, it is preferable to use Al ₂ O ₃ or SiO ₂ as the catalyst support, and each may be used alone or at an appropriate ratio. You may use combining both. When the aromatic hydrocarbon hydride is a mixture of one ring and two rings, a catalyst having a preferable average pore diameter may be mixed and used depending on the composition.

  Further, the metal loading in the dehydrogenation reaction catalyst is preferably in the range of 0.001 to 10% by mass, and more preferably in the range of 0.01 to 5% by mass. If the metal loading is less than 0.001% by mass, the dehydrogenation reaction cannot be sufficiently progressed. On the other hand, even if the metal is loaded exceeding 10% by mass, an effect commensurate with the increase in the amount of metal cannot be obtained. .

In the dehydrogenation reaction carried out in the present invention, for example, in the presence of the catalyst for dehydrogenation reaction, LHSV is 0.5 to 4 hr ⁻¹ , reaction temperature is 100 to 450 ° C., preferably 250 ° C. to 450 ° C., reaction pressure is It is carried out by circulating hydrogen at normal pressure to 2 MPaG, preferably normal pressure to 0.4 MPaG. In the hydrogen production method of the present invention, the reaction temperature of the dehydrogenation reaction, that is, the average temperature of the dehydrogenation catalyst layer is appropriately selected according to the temperature of the hydrogen separation membrane described later. The hydrogen flow rate is preferably in the range of 0.01 to 10 in terms of a hydrogen / aromatic hydrocarbon hydride molar ratio. When hydrogen is circulated and the dehydrogenation reaction is performed, side reactions can be suppressed compared to when hydrogen is not circulated, and not only hydrogen can be produced efficiently, but also the oil recovered after the dehydrogenation reaction is hydrogenated again. Thus, impurities contained in the reuse as an aromatic hydrocarbon hydride can be reduced. Furthermore, in order to produce hydrogen efficiently, it is preferable to select reaction conditions so that the conversion rate is 85% or more.

  The gas produced by the dehydrogenation reaction is mainly composed of hydrogen, but in addition to this, unreacted aromatic hydrocarbon hydride, aromatic hydrocarbons produced by the dehydrogenation reaction, methane, ethane produced by side reactions, etc. It may contain lower hydrocarbons, alkylcyclopentane produced by side reactions, and the like. However, carbon monoxide contained in the reaction product gas when hydrogen is produced by a reforming reaction of city gas, kerosene, naphtha, etc. is not included in the dehydrogenation reaction product gas of the aromatic hydrocarbon hydride. .

  In the hydrogen production method of the present invention, the dehydrogenation reaction product is supplied to a hydrogen separation device 3 having a hydrogen separation membrane, and high-purity hydrogen is obtained using the hydrogen separation membrane. Here, it is preferable to purify the reaction product immediately after the dehydrogenation reaction using a hydrogen separation membrane without gas-liquid separation. In this case, cooling and reheating of the dehydrogenation reaction product gas have been required. Compared to technology, energy efficiency can be improved.

  The hydrogen separator 3 used in the present invention is not particularly limited as long as it includes a hydrogen separation membrane. Examples of the hydrogen separation membrane used in the hydrogen separation device 3 include metal membranes, zeolite membranes, ceramic membranes, polymer membranes, etc., which operate from the components contained in the temperature, pressure, and fluid of the dehydrogenation reactor 2. It is preferable to use a Pd alloy film as possible. Examples of the Pd alloy film include a Pd—Ag film and a Pd—Cu film, and a Pd—Cu film that can be thinned as a rolled film and has little hydrogen embrittlement is particularly preferable. The Pd—Cu film can be produced, for example, by the method described in US Pat. No. 3,439,474.

  Here, in the hydrogen production method of the present invention, the temperature of the hydrogen separation membrane in the hydrogen separation device 3 is dehydrated in order to obtain high-purity hydrogen from the gas produced by the dehydrogenation reaction through the hydrogen separation membrane with a high hydrogen recovery rate. The average temperature of the catalyst layer in the elementary reactor 2 needs to be 10 to 100 ° C. higher, preferably 20 to 50 ° C. higher. While the hydrogen permeation rate through the hydrogen separation membrane increases as the temperature rises, the dehydrogenation reaction catalyst tends to aggregate active metals at higher temperatures. Therefore, by increasing the temperature of the hydrogen separation membrane above the average temperature of the catalyst layer, Deterioration of the dehydrogenation reaction catalyst can be prevented while improving the permeation rate. And by making the temperature of a hydrogen separation membrane 10 degreeC or more higher than the average temperature of a catalyst layer, the permeation | transmission rate of hydrogen with respect to a hydrogen separation membrane further improves, and a hydrogen recovery rate improves. When the temperature of the hydrogen separation membrane is higher than the average temperature of the catalyst layer by more than 100 ° C., setting the average temperature of the catalyst layer so that the dehydrogenation reaction proceeds sufficiently will increase the temperature of the hydrogen separation membrane. If the temperature of the hydrogen separation membrane is set so that hydrogen permeates sufficiently, the average temperature of the catalyst layer becomes too low. The reaction rate of the dehydrogenation reaction decreases.

  The temperature of the hydrogen separation membrane in the hydrogen separation device 3 is preferably in the range of 300 to 400 ° C. When the temperature of the hydrogen separation membrane is less than 300 ° C., the hydrogen permeation rate is lowered and the hydrogen recovery rate is lowered. On the other hand, when the temperature of the hydrogen separation membrane exceeds 400 ° C., the crystal form of the hydrogen separation membrane is changed. As a result, the hydrogen permeation rate decreases, and the hydrogen recovery rate decreases.

  In the hydrogen production method of the present invention, the reaction pressure of the dehydrogenation reaction and the pressure of the hydrogen separation membrane are preferably 0.4 MPaG or less. In this case, the conversion rate of the dehydrogenation reaction is improved, and the amount of hydrogen produced can be improved. In order to efficiently produce hydrogen, it is necessary to control the differential pressure and temperature so that the hydrogen recovered through the hydrogen separation membrane is 85% or more of the hydrogen in the dehydrogenation reaction product gas. preferable.

  In the hydrogen production method of the present invention, in order to make the temperature of the hydrogen separation membrane in the hydrogen separator 3 10 to 100 ° C. higher than the average temperature of the catalyst layer in the dehydrogenation reactor 2, for example, as shown in FIG. Furthermore, it is preferable that the heat medium heated by the heating means 4 is passed through the dehydrogenation reactor 2 after passing through the hydrogen separator 3. Here, examples of the heating unit 4 include a burner. For example, hot air generated by burning fuel with a heating unit such as a burner passes through the hydrogen separator 3 and then passes through the dehydrogenation reactor 2. Can be made. From the viewpoint of improving energy efficiency, it is preferable to reheat the heat medium discharged from the dehydrogenation reactor 2 by the heating means 4 and supply it to the hydrogen separator 3 as shown in FIG.

  The high-purity hydrogen produced through the hydrogen separation membrane according to the present invention can be used as a fuel for fuel cells such as fuel cell vehicles or stationary fuel cells. Further, a part of the high-purity hydrogen may be recycled to the dehydrogenation reactor 2 and used as circulating hydrogen necessary for the dehydrogenation reaction. The circulating hydrogen used for the dehydrogenation reaction includes hydrogen introduced from the outside, hydrogen contained in the unpurified gas of the reaction product gas exiting from the dehydrogenation reactor 2, and hydrogen contained in the gas that did not permeate the hydrogen separation membrane. However, if the hydrogen purity is low, the concentration of gases other than hydrogen will increase during recycling, and the advantage of performing the dehydrogenation reaction under hydrogen flow will not be sufficiently obtained. The high-purity hydrogen obtained by permeating the hydrogen separation membrane is preferably recycled to the dehydrogenation reactor 2.

  In the present invention, the gas recovered from the dehydrogenation reaction product gas without passing through the hydrogen separation membrane is introduced into, for example, the gas-liquid separation device 5, and is generated by an unreacted aromatic hydrocarbon hydride and dehydrogenation reaction. It is preferable to separate into liquid components such as aromatic hydrocarbons and alkylcyclopentane generated by side reactions, and hydrogen and other gases. Other gases in the gas component include lower hydrocarbons generated by side reactions and liquid vapor that could not be separated. Here, hydrogen and other gases are used as a heat source raw material, for example, by being burned by a heating means 4 such as a burner together with other fuel for heating the hydrogen separator 3 and the dehydrogenation reactor 2. be able to. On the other hand, a liquid containing unreacted aromatic hydrocarbon hydride, aromatic hydrocarbon generated by dehydrogenation reaction, alkylcyclopentane generated by side reaction, etc. is recovered in the recovered oil tank 6 and hydrogenated again. It can be reused as an aromatic hydrocarbon hydride.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
As shown in FIG. 1, hot air (heat medium) was passed through the hydrogen separator 3 and then passed through the dehydrogenation reactor 2 to perform dehydrogenation reaction and hydrogen separation. A fixed bed flow reactor is used as the dehydrogenation reactor 2, and a 0.5% Pt / Al ₂ O ₃ catalyst (average pore diameter is 72.9 kg, 40-80 kg of the total pore volume is used as the dehydrogenation catalyst. The catalyst was charged into a fixed bed flow reactor using a pore volume ratio of 60%). Here, the volume of the catalyst layer was 10 cm ³ . Methylcyclohexane (MCH) is used as the aromatic hydrocarbon hydride, the reaction pressure is 0.5 MPaG, the liquid space velocity (LHSV) is 2.0 hr ⁻¹ , and the hydrogen / oil ratio (H ₂ / Oil) is 1.0 mol / mol. The dehydrogenation reaction was performed under the conditions described above, and the outlet gas from the dehydrogenation reactor 2 was passed through a hydrogen separation device 3 having a hydrogen separation membrane to selectively permeate hydrogen. In addition, the inlet gauge pressure of the hydrogen separator 3 is 0.5 MPaG which is the same as the reaction pressure of the dehydrogenation reaction, while the outlet gauge pressure is 0.0 MPaG. In addition, a Pd—Cu membrane was used as the hydrogen separation membrane. When hot air of 450 ° C. was passed through the hydrogen separator 3 and then passed through the dehydrogenation reactor 2, the temperature of the hydrogen separation membrane in the hydrogen separator 3 was 350 ° C. The average temperature of the catalyst layer was 327.6 ° C. The flow rate of the permeate gas of the hydrogen separation membrane, the hydrogen concentration of the permeate gas, the flow rate of the gas after the non-permeate gas of the hydrogen separation membrane is gas-liquid separated by the gas-liquid separation device 5 (non-permeate gas flow rate), and the gas content Table 1 shows the hydrogen concentration and hydrogen recovery rate.

(Examples 2 to 4)
A dehydrogenation reaction and hydrogen separation were performed in the same manner as in Example 1 except that the reaction pressure of the dehydrogenation reaction and the inlet gauge pressure of the hydrogen separator 3 were changed to the pressures shown in Table 1. The results are shown in Table 1.

(Comparative Example 1)
As shown in FIG. 2, the hot air (heat medium) is passed through the dehydrogenation reactor 2 and then passed through the hydrogen separator 3 to perform the dehydrogenation reaction and hydrogen separation, as in Example 1. Then, dehydrogenation reaction and hydrogen separation were performed. The results are shown in Table 1.

(Comparative Examples 2 to 4)
A dehydrogenation reaction and hydrogen separation were performed in the same manner as in Comparative Example 1 except that the reaction pressure of the dehydrogenation reaction and the inlet gauge pressure of the hydrogen separation apparatus were changed to the pressures shown in Table 1. The results are shown in Table 1.

  From Table 1, it can be seen that the hydrogen recovery rate is improved by raising the temperature of the hydrogen separation membrane by 10 to 100 ° C., preferably 20 to 50 ° C., higher than the average temperature of the catalyst layer in the dehydrogenation reactor. On the other hand, it can be seen from the results of the comparative example that when the temperature of the hydrogen separation membrane is lower than the average temperature of the catalyst layer in the dehydrogenation reactor, the hydrogen recovery rate is significantly reduced compared to the example of the same pressure. .

It is a schematic diagram which shows one aspect | mode of the hydrogen manufacturing method of this invention. It is a schematic diagram which shows the hydrogen manufacturing method of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aromatic hydrocarbon hydride tank 2 Dehydrogenation reactor 3 Hydrogen separator 4 Heating means 5 Gas-liquid separator 6 Recovery oil tank

Claims (3)

In a hydrogen production method in which a dehydrogenation reaction of an aromatic hydrocarbon hydride is carried out in a dehydrogenation reactor comprising a catalyst layer, and hydrogen is separated from the dehydrogenation reaction product by a hydrogen separation device comprising a hydrogen separation membrane. ,
The method for producing hydrogen, wherein the temperature of the hydrogen separation membrane in the hydrogen separator is higher by 10 to 100 ° C than the average temperature of the catalyst layer in the dehydrogenation reactor.   2. The hydrogen production method according to claim 1, wherein a heat medium for heating the dehydrogenation reactor and the hydrogen separation device is passed through the dehydrogenation reactor after passing through the hydrogen separation device. .   Furthermore, the heating medium discharged | emitted from the said dehydrogenation reactor is reheated, and it supplies to the said hydrogen separator, The hydrogen production method of Claim 2 characterized by the above-mentioned.

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