JP6667381B2 - Hydrogen gas production method and hydrogen gas production device - Google Patents

Description

  The present invention relates to a hydrogen gas production method and a hydrogen gas production device.

  Hydrogen stations for filling fuel cell vehicles with hydrogen include on-site hydrogen stations that produce hydrogen from fossil fuels such as natural gas locally, and hydrogen produced elsewhere in the form of compressed hydrogen. There is an off-site hydrogen station that is transported and used locally. At an off-site hydrogen station, a method for transporting hydrogen as an organic hydride such as methylcyclohexane has been studied as a means for transporting the produced hydrogen.

  The organic hydride used for transport in the off-site hydrogen station is an organic compound that reversibly absorbs and releases hydrogen through a catalytic reaction, and recovers hydrogen by releasing hydrogen to an aromatic compound. be able to. The dehydration reaction of the organic hydride is performed at a high temperature by a catalytic reaction, but the hydrogen produced after the reaction has an organic compound generated after the dehydrogenation reaction remaining by the vapor pressure. For example, when methylcyclohexane is used as the organic hydride, when dehydrogenating, toluene corresponding to the vapor pressure remains in the hydrogen gas. Since the aromatic compound is mixed in the hydrogen gas produced by the dehydrogenation reaction, in order to use the hydrogen gas in a fuel cell vehicle or the like, a hydrogen-rich gas mixed with the aromatic compound is purified, It needs to be highly purified.

  As a method for removing the aromatic compound remaining in the hydrogen-rich gas, an adsorption removal technique using an adsorbent employing a PSA (Pressure Swing Adsorption) method capable of downsizing the apparatus has been disclosed (JP-A-2012-87012). Reference).

  However, the PSA type adsorption tower has a relatively low recovery rate of high-purity hydrogen gas obtained by purification, and therefore, it is desired to improve the recovery amount of hydrogen gas in the entire apparatus.

JP 2012-87012 A

  The present invention has been made on the basis of the above-described circumstances, and in a hydrogen gas production in which a hydrogen-rich gas obtained by a dehydrogenation reaction of an organic hydride is purified by a PSA-type adsorption tower, a hydrogen gas capable of improving the hydrogen recovery amount It is intended to provide a production method and a hydrogen production apparatus.

  The present invention has been made to solve the above problems, a step of performing a dehydrogenation reaction of an organic hydride by heating in the presence of a catalyst, and a step of purifying a hydrogen-rich gas obtained in the dehydrogenation reaction step with a PSA-type adsorption tower. A method for producing a hydrogen gas, comprising: a step of gas-liquid separating an aromatic compound from an off-gas discharged from the PSA type adsorption tower by cooling; and a step of purifying the off-gas after the gas-liquid separation step by the PSA type adsorption tower. It is.

  According to the method for producing hydrogen gas, in a PSA-type adsorption tower for purifying a hydrogen-rich gas obtained from an organic hydride, an offgas obtained by separating an aromatic compound from an offgas generated at the time of regeneration of the adsorption tower is purified by the adsorption tower. Hydrogen contained in off-gas can be recovered as product gas without reducing the regeneration efficiency of the tower. As a result, the hydrogen gas production method can improve the amount of recovered hydrogen.

  The method may further include a step of recovering the aromatic compound separated from the off-gas in the gas-liquid separation step. By recovering the aromatic compound in this manner, the aromatic compound can be reused as a raw material of an organic hydride or the like, so that the production cost of hydrogen gas can be reduced.

  The method may further include a step of gas-liquid separation of the aromatic compound by cooling from the hydrogen-rich gas before the purification step, and the gas-liquid separation of the hydrogen-rich gas and the gas-liquid separation of the off-gas may be performed by the same separator. By performing the gas-liquid separation of the hydrogen-rich gas in this manner, the amount of the aromatic compound adsorbed in the adsorption tower can be reduced, so that the cost for regeneration or replacement of the adsorbent can be reduced. Furthermore, the hydrogen-rich gas and the off-gas are separated into gas and liquid by the same separator, so that the entire hydrogen gas producing apparatus can be downsized.

  Another invention made to solve the above-mentioned problem is a reactor for performing a dehydrogenation reaction of an organic hydride by heating in the presence of a catalyst, and a PSA-type adsorption tower for purifying a hydrogen-rich gas discharged from the reactor. A separator for gas-liquid separation of aromatic compounds from the off-gas discharged from the PSA-type adsorption tower by cooling, and a line for supplying the PSA-type adsorption tower with the off-gas obtained by gas-liquid separation of the aromatic compounds by the separator. And a hydrogen gas producing apparatus comprising:

  According to the hydrogen gas producing apparatus, in a PSA-type adsorption tower for purifying hydrogen-rich gas obtained from organic hydride, an off-gas obtained by separating an aromatic compound from off-gas generated at the time of regeneration of the adsorption tower is purified by the adsorption tower. Hydrogen contained in off-gas can be recovered as product gas without reducing the regeneration efficiency of the tower. As a result, the hydrogen gas production device can improve the amount of hydrogen recovered.

  As described above, according to the hydrogen gas production method and the hydrogen production apparatus of the present invention, in the hydrogen gas production in which the hydrogen-rich gas obtained by the dehydrogenation reaction of the organic hydride is purified by the PSA-type adsorption tower, the hydrogen recovery amount is improved. it can.

It is a schematic diagram showing the hydrogen gas production device of one embodiment of the present invention. It is a graph which shows the relationship between the value of R 'and (alpha), and the value of R. It is a graph which shows the relationship between the value of R 'and (alpha), and the value of _CCH4,2 .

  Hereinafter, embodiments of a hydrogen production apparatus and a hydrogen gas production method of the present invention will be described in detail with reference to the drawings as appropriate.

[Hydrogen gas production equipment]
The hydrogen gas producing apparatus shown in FIG. 1 includes a reactor 1 for performing a dehydrogenation reaction of an organic hydride A by heating in the presence of a catalyst, and an aromatic compound by cooling from a mixed gas of an aromatic compound and hydrogen discharged from the reactor 1. A first separator 2 for gas-liquid separation of the compound, a PSA-type adsorption tower 3 for purifying the mixed gas (hydrogen-rich gas B) separated by the first separator 2, and an off-gas F discharged from the PSA-type adsorption tower 3 A second separator 4 for gas-liquid separation of the aromatic compound by cooling, and an off-gas supply line for supplying an off-gas (off-gas G after separation) obtained by gas-liquid separation of the aromatic compound by the second separator 4 to the PSA type adsorption tower 3 100 is mainly provided. Further, the hydrogen gas producing apparatus includes a hydrogen-rich gas buffer tank 5 mainly storing the hydrogen-rich gas B discharged from the first separator 2 and a product gas storing the product gas E discharged from the PSA type adsorption tower 3. It further includes a buffer tank 6 and an off-gas buffer tank 7 for storing off-gas F discharged during regeneration of the PSA-type adsorption tower 3.

  Examples of the organic hydride A used in the hydrogen gas production device include hydrogenated aromatic compounds such as methylcyclohexane (hereinafter also referred to as MCH), cyclohexane, dimethylcyclohexane, ethylcyclohexane, decalin, methyldecalin, dimethyldecalin, and ethyldecalin. Can be For example, when MCH is used as the organic hydride A, it is converted to toluene as an aromatic compound by a dehydrogenation reaction.

  The hydrogen gas production apparatus is used for supplying hydrogen to vehicles using hydrogen as fuel, such as hydrogen vehicles and fuel cell vehicles, and for medium- to large-scale power generation using fuel cells.

<Reactor>
The reactor 1 is a dehydrogenation reactor that performs a dehydrogenation reaction of the organic hydride A by heating in the presence of a catalyst. Specifically, the reactor 1 has a dehydrogenation catalyst for accelerating the dehydrogenation reaction of the organic hydride A, and heats the organic hydride A and brings the organic hydride A into contact with the dehydrogenation reaction catalyst, so that hydrogen is converted from the organic hydride A to hydrogen. An oxidation reaction that separates Thereby, a mixed gas of the aromatic compound and hydrogen is generated. When MCH is used as the organic hydride A, the mixed gas may contain unreacted MCH and by-products such as methane and benzene.

  As the dehydrogenation catalyst used in the reactor 1, for example, sulfur, selenium, alumina carrying fine platinum particles, and the like are known.

  The lower limit of the heating temperature of the organic hydride A in the reactor 1 is preferably 150 ° C, more preferably 200 ° C. On the other hand, the upper limit of the heating temperature of the organic hydride A is preferably 400 ° C., and more preferably 350 ° C. If the heating temperature of the organic hydride A is less than the above lower limit, the reaction rate of the organic hydride A and the yield of hydrogen gas may be insufficient. Conversely, if the heating temperature of the organic hydride A exceeds the above upper limit, the energy cost required for heating may unnecessarily increase.

<First separator>
The first separator 2 gas-liquid separates the mixed gas of the aromatic compound and the hydrogen discharged from the reactor 1 into a mixed gas of the aromatic compound and the hydrogen by cooling to obtain a hydrogen-rich gas B. The first separator 2 has a cooling mechanism for cooling the gas flowing inside. By cooling the gas inside the first separator 2, aromatic compounds such as MCH having a relatively high boiling point can be easily separated from the mixed gas, and aromatic compounds containing toluene and the like in the separated gas can be obtained. The concentration is reduced. The aromatic compound separated as a liquid is discharged from the first separator 2 as drain D.

  The lower limit of the temperature of the mixed gas at the outlet of the first separator 2 is preferably −40 ° C., and more preferably −35 ° C. On the other hand, the upper limit of the temperature of the mixed gas at the outlet of the first separator 2 is preferably −10 ° C., and more preferably −15 ° C. If the temperature of the mixed gas at the outlet of the first separator 2 falls below the lower limit, the energy required for cooling the mixed gas may be excessive. Conversely, when the temperature of the mixed gas at the outlet of the first separator 2 exceeds the above upper limit, the concentration of the aromatic compound in the mixed gas after separation is not sufficiently reduced, and the adsorption load in the subsequent adsorption tower is large. Therefore, the life of the adsorbent may be reduced, and the recovery rate of hydrogen gas may be reduced.

  The lower limit of the concentration of the aromatic compound in the mixed gas after separation in the first separator 2 is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the concentration of the aromatic compound in the mixed gas is preferably 800 ppm, more preferably 600 ppm. If the concentration of the aromatic compound in the mixed gas is less than the lower limit, the cooling cost in the first separator 2 may be significantly increased. Conversely, when the concentration of the aromatic compound in the mixed gas exceeds the upper limit, the adsorption load in the subsequent adsorption tower increases, and the life of the adsorbent may decrease and the recovery rate of hydrogen gas may decrease. is there. The “concentration” in this specification is a ratio on a volume basis.

<Hydrogen-rich gas buffer tank>
The hydrogen-rich gas buffer tank 5 primarily stores the hydrogen-rich gas B discharged from the first separator 2 to absorb fluctuations in the flow rate and supply the hydrogen-rich gas B to the PSA-type adsorption tower 3 in a stable manner. 101 is provided. Specifically, the hydrogen-rich gas B discharged from the first separator 2 is compressed by a compressor (not shown) and stored in the hydrogen-rich gas buffer tank 5. The hydrogen-rich gas buffer tank 5 also stores an off-gas G after separation, which will be described later.

  The lower limit of the pressure in the hydrogen-rich gas buffer tank 5 is preferably 5 atm in absolute pressure, more preferably 8 atm. On the other hand, the upper limit of the pressure in the hydrogen-rich gas buffer tank 5 is preferably 20 atm, more preferably 10 atm. If the pressure is lower than the lower limit, supply of the hydrogen-rich gas B or the like to the PSA-type adsorption tower 3 may not be easy. Conversely, if the pressure exceeds the upper limit, the equipment and operating costs may be excessive.

<PSA type adsorption tower>
The PSA type adsorption tower 3 purifies the hydrogen-rich gas B and the separated off-gas G separated by the first separator 2 to obtain a high-purity hydrogen gas having a higher purity than the hydrogen-rich gas B as a product gas E. Specifically, the PSA-type adsorption tower 3 is filled with an adsorbent that can be regenerated by the PSA method, and is used to separate hydrogen-rich gas B such as hydrocarbon gas as a by-product generated in the dehydrogenation reaction from organic hydride. Thereafter, impurities contained in the off-gas G are removed by adsorption, and the product gas E is discharged.

  Specifically, the hydrogen gas producing apparatus includes a plurality of (4 in the figure) PSA-type adsorption towers 3a, 3b, 3c, and 3d, and a hydrogen gas communicating with the plurality of PSA-type adsorption towers 3a, 3b, 3c, and 3d. The apparatus includes a rich gas supply line 101, a product gas discharge line 102, and an off gas discharge line 103. The number of PSA type adsorption towers 3 is arbitrary.

  The hydrogen-rich gas B and the separated off-gas G are supplied to a plurality of PSA-type adsorption towers 3a, 3b, 3c, 3d through a hydrogen-rich gas supply line 101.

  The PSA type adsorption tower 3 is filled with an adsorbent for adsorbing the above impurities in the hydrogen-rich gas B and the separated off-gas G, and discharges a high-purity product gas E from the product gas discharge line 102. These PSA type adsorption towers 3 are operated by sequentially switching a series of steps of adsorption, decompression, washing and equalization, pressure increase, and adsorption. Specifically, after the end of the adsorption step, the adsorbed impurities are removed and the adsorbent is regenerated by a step of reducing the pressure in the adsorption tower and a step of purging with a hydrogen gas as the product gas E. . Thereafter, the pressure of the adsorption tower in which the adsorbent has been regenerated is increased again, and the pressure is again applied to hydrogen purification. During the operation of the hydrogen gas producing apparatus, the timing of the series of steps is shifted in each adsorption tower so that at least one adsorption tower is an adsorption step, so that adsorption and regeneration are simultaneously performed in different adsorption towers. And the product gas E can be continuously produced.

  The PSA type adsorption tower 3 is filled with an adsorbent capable of adsorbing MCH, toluene, methane, moisture and the like, which are main impurities in the hydrogen-rich gas B and the separated off-gas G. The adsorbent is not particularly limited as long as it can adsorb each impurity and can be regenerated by the PSA method. As such an adsorbent, X-type or A-type zeolite, activated carbon, porous silica, porous alumina, and a metal organic structure can be particularly preferably used.

  In the case of removing a plurality of types of impurities, it is possible to respond by filling the corresponding adsorbents in order. Specifically, it is preferable to fill the aromatic compound adsorbent and the lower hydrocarbon adsorbent sequentially from the introduction direction (inlet side) of the hydrogen-rich gas B.

  The hydrogen-rich gas supply line 101 is a line for introducing the hydrogen-rich gas B and the separated off-gas G into the PSA-type adsorption tower 3. The hydrogen-rich gas supply line 101 and the PSA type adsorption tower 3 are connected via hydrogen-rich gas supply valves V1a, V1b, V1c, and V1d, respectively.

  The product gas discharge line 102 is a recovery line for the product gas E, which is a high-purity hydrogen gas obtained by removing impurities of the hydrogen-rich gas B and the off-gas G after separation in the PSA-type adsorption tower 3, and includes a plurality of PSA-type adsorption towers 3a. , 3b, 3c, 3d are connected via product gas discharge valves V2a, V2b, V2c, V2d, respectively. The recovered product gas E is temporarily stored in the product gas buffer tank 6 and supplied as appropriate. This product gas E is also used as a purge gas (cleaning gas) for the PSA type adsorption tower 3.

  Further, on the discharge side of the PSA type adsorption tower 3, a pressure equalizing line 104 and a washing line 105 are connected in addition to the product gas discharge line 102, respectively. The pressure equalizing line 104 is connected to the PSA type adsorption towers 3a, 3b, 3c, 3d via pressure equalizing valves V4a, V4b, V4c, V4d, respectively, and the washing line 105 is connected to the PSA type adsorption towers 3a, 3b, 3c, 3d. Are connected via cleaning valves V5a, V5b, V5c and V5d, respectively. The product gas discharge line 102, the pressure equalizing line 104, and the washing line 105 collect the product gas E from at least one PSA type adsorption tower 3, and collect the product gas buffer tank 6 with respect to another PSA type adsorption tower 3. Alternatively, the product gas E is supplied from the remaining PSA-type adsorption tower 3, and the pressure increasing and washing steps can be performed.

Specifically, by performing the following steps cyclically as shown in Table 1, the above steps can be performed in each PSA type adsorption tower 3.
(1) By supplying the hydrogen-rich gas B and the separated off-gas G to one of the four PSA-type adsorption towers 3 (PSA-type adsorption tower 3a), impurities are adsorbed and removed to produce high-purity hydrogen gas. Adsorption step (2) A part of the gas remaining in the PSA type adsorption tower 3a which has completed the adsorption step is transferred to the PSA type adsorption tower 3c which has been subjected to a second equalization step described later, and the PSA type adsorption tower 3a and the PSA First pressure equalizing step for equalizing the internal pressure with the type adsorption tower 3c (3) Holding step for maintaining the pressure equalized state in the first equalizing step (4) In the PSA type adsorption tower 3a after the holding step is completed. Part of the remaining gas is transferred to the PSA-type adsorption tower 3d, and a second equalization step (5) for equalizing the internal pressure of the PSA-type adsorption tower 3a and the PSA-type adsorption tower 3d is performed. In the completed PSA type adsorption tower 3a The existing gas is transferred to the off-gas buffer tank 7 and the internal pressure is reduced to the atmospheric pressure. (6) The PSA type adsorption tower 3a, which has been reduced to the atmospheric pressure in the first pressure reducing step, is further subjected to the atmospheric pressure using the vacuum pump P1. (7) The high-purity hydrogen gas is supplied from the product gas buffer tank 6 or another PSA-type adsorption tower 3 in a state where the PSA-type adsorption tower 3a is depressurized to below the atmospheric pressure in the second pressure-reducing step. An adsorbent regeneration step for supplying and desorbing impurities adsorbed on the adsorbent of the PSA type adsorption tower 3a (8) The holding step for the PSA type adsorption tower 3a for which the regeneration of the adsorbent has been completed in the adsorbent regeneration step has been completed. A second equalization step (9) in which a part of the gas remaining in the PSA type adsorption tower 3b is transferred and the internal pressure of the PSA type adsorption tower 3a and the PSA type adsorption tower 3b is equalized. First pressure equalization step (10) PSA in which a part of the gas remaining in the PSA type adsorption tower 3c whose transfer is completed is transferred to equalize the internal pressures of the PSA type adsorption tower 3a and the PSA type adsorption tower 3c. Pressure step of introducing high-purity hydrogen gas into the adsorption tower 3a and increasing the pressure in the PSA adsorption tower 3a to the pressure at which the adsorption step is performed.

When there are three PSA-type adsorption towers 3, the above steps can be performed in each PSA-type adsorption tower 3 by performing the following steps cyclically as shown in Table 2.
(1) By supplying the hydrogen-rich gas B and the separated off-gas G to one of the three PSA-type adsorption towers 3 (PSA-type adsorption tower 3a), impurities are adsorbed and removed to produce high-purity hydrogen gas. Adsorption step (2) A part of the gas remaining in the PSA type adsorption tower 3a after the adsorption step is transferred to the PSA type adsorption tower 3c after the regeneration step described later, and the PSA type adsorption tower 3a and the PSA type adsorption tower (3) Transfer the gas remaining in the PSA type adsorption tower 3a after the pressure equalization step to the off-gas buffer tank 7 and reduce the internal pressure to the atmospheric pressure. Step (4) A second pressure reducing step in which the PSA type adsorption tower 3a, which has been reduced to the atmospheric pressure in the first pressure reducing step, is further reduced to a pressure lower than the atmospheric pressure by using the vacuum pump P1. While the A-type adsorption tower 3a was depressurized to a pressure lower than the atmospheric pressure, high-purity hydrogen gas was supplied from the product gas buffer tank 6 or another PSA-type adsorption tower 3 to be adsorbed by the adsorbent of the PSA-type adsorption tower 3a. Adsorbent regeneration step for desorbing impurities (6) A part of the gas remaining in the PSA type adsorption tower 3b after the adsorption step is transferred to the PSA type adsorption tower 3a where the adsorption step has been completed in the adsorbent regeneration step. Pressure equalizing step for equalizing the internal pressure between the PSA type adsorption tower 3a and the PSA type adsorption tower 3b (7) High-purity hydrogen gas is introduced into the PSA type adsorption tower 3a, and the pressure in the PSA type adsorption tower 3a is reduced. Step-up step to increase the pressure to perform the adsorption step

  The off-gas discharge line 103 is a line used to reduce the pressure inside the adsorption tower during the regeneration of the PSA adsorption tower 3 and discharge off-gas. The off-gas discharge line 103 is connected to the PSA type adsorption towers 3a, 3b, 3c, 3d via off-gas discharge valves V3a, V3b, V3c, V3d, respectively. The suction side of a vacuum pump P1 for reducing the pressure to below the atmospheric pressure during regeneration of the PSA type adsorption tower 3 is connected to the off-gas discharge line 103. The off gas buffer tank 7 is connected to the off gas discharge line 103.

<Off-gas buffer tank>
The off-gas buffer tank 7 temporarily stores the off-gas discharged during regeneration of the PSA-type adsorption tower 3 and supplies the off-gas to the second separator 4. Further, when the hydrogen gas producing apparatus is started up, a part of the off-gas stored in the off-gas buffer tank 7 is separately processed without being supplied to the second separator 4.

<Second separator>
The second separator 4 performs gas-liquid separation of aromatic compounds from the off-gas F discharged from the PSA type adsorption tower 3 by cooling. The configuration of the second separator 4 can be the same as that of the first separator 2. By cooling the off-gas inside the second separator 4, the aromatic compound T is separated as a liquid. By recovering the aromatic compound T, it can be reused as a raw material for an organic hydride.

  The temperature of the off-gas at the outlet of the second separator 4 can be similar to the temperature of the mixed gas at the outlet of the first separator 2. In addition, the concentration of the aromatic compound concentration in the off-gas separated by the second separator 4 can be similar to the concentration of the aromatic compound concentration in the mixed gas separated by the first separator 2.

<Off-gas supply line>
The off-gas supply line 100 supplies the PSA-type adsorption tower 3 with the separated off-gas G after gas-liquid separation of the aromatic compound T by the second separator 4. Specifically, the off-gas supply line 100 connects the outlet of the separated off-gas G of the second separator 4 and the inlet of the hydrogen-rich gas B of the hydrogen-rich gas buffer tank 5. The separated off-gas G is mixed with the hydrogen-rich gas B by the off-gas supply line 100 and purified in the PSA type adsorption tower 3.

[Hydrogen gas production method]
Next, the hydrogen gas producing method will be described using the hydrogen gas producing apparatus of FIG.

  In the hydrogen gas production method, high-purity hydrogen gas is produced from a hydrogen-rich gas containing hydrogen gas and an impurity gas other than hydrogen by a PSA-type adsorption tower. The method for producing hydrogen gas includes a step of performing a dehydrogenation reaction of organic hydride A by heating in the presence of a catalyst (dehydrogenation reaction step), and a step of cooling from a mixed gas of an aromatic compound and hydrogen discharged in the dehydrogenation reaction step. (First gas-liquid separation step) and a step of purifying the hydrogen-rich gas B obtained in the first gas-liquid separation step with the PSA-type adsorption tower 3 (hydrogen-rich gas purification step) A step of gas-liquid separation of the aromatic compound T from the off-gas discharged from the PSA type adsorption tower 3 by cooling (second gas-liquid separation step); and a step of separating the off-gas after the second gas-liquid separation step from the PSA type adsorption tower. (Off-gas purification step). The hydrogen gas production may further include a step of recovering the aromatic compound T separated from the off-gas in the second gas-liquid separation step (aromatic compound recovery step).

<Dehydrogenation reaction step>
In the dehydrogenation reaction step, the organic hydride A is dehydrogenated by heating in the presence of a catalyst using the reactor 1.

<First gas-liquid separation step>
In the first gas-liquid separation step, the first separator 2 is used to perform gas-liquid separation of the mixed gas of the aromatic compound and hydrogen discharged from the reactor 1 into a mixed gas containing the aromatic compound and hydrogen. A rich gas B is obtained. This gas-liquid separation is performed while cooling the gas flowing inside the first separator 2 with a refrigerant. As described above, by cooling the gas flowing inside the first separator 2 in the first gas-liquid separation step, the aromatic compound and the hydrogen are easily separated, and the concentration of the aromatic compound in the gas after the separation is reduced. Reduced.

<Hydrogen-rich gas purification process>
In the hydrogen-rich gas purification step, the PSA-type adsorption tower 3 is used to purify the hydrogen-rich gas B to obtain high-purity hydrogen gas. In the hydrogen-rich gas purification step, the hydrogen gas may be purified while cooling the gas flowing through the PSA-type adsorption tower 3 with a refrigerant. By cooling the gas flowing inside the PSA type adsorption tower 3 at the time of adsorption, the effective amount of impurities adsorbed by the adsorbent is increased, the required amount of the adsorbent is reduced, and the apparatus can be downsized.

  In the adsorption tower, the impurities in the hydrogen-rich gas B are adsorbed by the adsorbent, and the saturated adsorption portion of the adsorbent increases. Therefore, in order to prevent impurities from being mixed into the product gas E, it is necessary to stop the adsorption operation in a state where the unadsorbed portion of the adsorbent remains.

<PSA type adsorption tower regeneration process>
In the PSA type adsorption tower regeneration step, the PSA type adsorption tower 3 is regenerated using the above-described pressure equalizing line 104, washing line 105, and off-gas discharge line 103, and high-purity hydrogen gas as a purge gas to discharge off-gas F. I do. The hydrogen gas used as the purge gas may be obtained by the hydrogen gas producing method or may be a previously prepared hydrogen gas.

  Specifically, in the regeneration of the adsorption tower, the gas in the adsorption tower is discharged from the off-gas discharge line 103, and the pressure is reduced to normal pressure. At this time, by providing a void on the product gas outlet side of the adsorption tower, hydrogen existing in the void is used for purging the adsorbent, and contributes to desorption of impurities such as aromatic hydrocarbons.

  After the pressure is reduced to normal pressure, the gas in the adsorption tower is sucked through the off-gas discharge line 103 by the vacuum pump P1, and the pressure in the adsorption tower is reduced to a negative pressure. Thereafter, the vacuum pump P1 is further operated, and the adsorbent is further regenerated by introducing a purge gas into the adsorption tower through the washing line 105 while maintaining the inside of the adsorption tower at a negative pressure. By suctioning with the vacuum pump P1, some of the impurities in the gas existing in the gap between the adsorbents are removed, and the partial pressure is reduced, so that the adsorption equilibrium shifts to the attachment / detachment side. It becomes easier to regenerate the agent. In addition, in this reduced pressure suction operation, the hydrogen gas present in the gap between the adsorbents and the hydrogen present in the voids move to the exhaust side to act as a purge gas, contributing to the progress of the attachment and detachment of impurities. After the regeneration of the adsorbent, the pressure equalizing operation is performed, and then the product gas E is introduced into the adsorption tower to repressurize the adsorbent, and then the adsorption operation is performed again.

  At the end of the purge, the adsorbent has not been completely regenerated and some of the adsorbed impurities remain, but the unsaturated adsorbent of the adsorbent has increased compared to the end of the adsorption. Even if the process shifts to the adsorption step again, a sufficient adsorption capacity can be recovered. In addition, for the decrease in the adsorption capacity of the adsorbent due to repeated adsorption, depressurization, depressurization, and purging, the adsorption time is set to a shorter value in response to the decrease in the adsorption capacity, thereby improving the purity of the product gas during adsorption. Can be secured. Also, instead of setting the adsorption time short, the purity of the product gas can be ensured by a method of reducing the amount of hydrogen-rich gas introduced into the adsorption tower and lowering the linear velocity LV of the gas in the adsorption tower. is there.

  Note that the hydrogen-rich gas purification step and the PSA-type adsorption tower regeneration step are alternately performed in the plurality of PSA-type adsorption towers 3a, 3b, 3c, 3d while shifting their periods.

<Second gas-liquid separation step>
In the second gas-liquid separation step, the aromatic compound T is gas-liquid separated from the off-gas discharged in the PSA-type adsorption tower regeneration step using the second separator 4, and the separated off-gas G is obtained. Specifically, the off-gas F discharged from the PSA type adsorption tower 3 is stored in the off-gas buffer tank 7, and the off-gas F is supplied to the second separator 4 from the off-gas buffer tank 7 to perform gas-liquid separation. This gas-liquid separation is performed while cooling the off-gas flowing inside the second separator 4 with a refrigerant. As described above, by cooling the gas flowing inside the second separator 4 in the second gas-liquid separation step, the aromatic compound and the hydrogen are easily separated, and the concentration of the aromatic compound in the gas after the separation is reduced. Reduced. For example, in the case of toluene, the concentration decreases until the saturated vapor pressure is reached.

  The off-gas F discharged from the PSA-type adsorption tower 3 contains hydrogen, aromatic compounds such as toluene, methane, and the like. However, the above-described gas-liquid separation removes aromatic compounds that are difficult to desorb from the adsorbent. Since it can be removed, a decrease in the regeneration efficiency of the PSA type adsorption tower 3 is prevented.

  The lower limit of the ratio of the amount of off-gas supplied to the second separator 4 and thus the PSA-type adsorption tower 3 to the total amount of off-gas discharged from the PSA-type adsorption tower 3 (recycling rate) is preferably 0.3, and 0.1%. 4 is more preferred. On the other hand, the upper limit of the recycling rate is preferably 0.7, and more preferably 0.6. If the recycle rate is smaller than the lower limit, the effect of increasing the amount of hydrogen recovered by off-gas recycling may be insufficient. Conversely, if the recycle rate is higher than the upper limit, the cost of the auxiliary equipment such as a compressor may increase, and the concentration of impurities in the system may increase.

<Off-gas purification process>
In the off-gas purification step, the off-gas after the second gas-liquid separation step is purified by the PSA type adsorption tower 3. Specifically, the separated off-gas G discharged from the second separator 4 is mixed with the hydrogen-rich gas B discharged from the first separator 2, and the raw material gas obtained by mixing the separated off-gas G with the hydrogen-rich gas B is separated from the raw gas. Purification is performed in the PSA type adsorption tower 3. The procedure for purifying the separated off-gas G in the PSA-type adsorption tower 3 is the same as the hydrogen-rich gas purification step. That is, the off-gas purification step is performed simultaneously with the hydrogen-rich gas purification step.

<Aromatic compound recovery process>
In the aromatic compound recovery step, the aromatic compound T separated from the off-gas F in the second gas-liquid separation step is recovered. For example, when methylcyclohexane is used as an organic hydride, toluene is mainly separated as an aromatic compound T in the second gas-liquid separation step. By recovering this toluene, the toluene is recovered and used as a raw material for organic hydride and other uses. Available. When methylcyclohexane is used as the organic hydride, a small amount of MCH is also contained in the aromatic compound T to be separated. Therefore, the hydrogen gas production method may further include a step of separating MCH from toluene.

<Advantages>
According to the hydrogen gas production method and the hydrogen gas production apparatus, in a PSA-type adsorption tower for purifying hydrogen-rich gas obtained from organic hydride, an off-gas obtained by separating an aromatic compound from off-gas generated during adsorption tower regeneration is purified by the adsorption tower. By doing so, hydrogen contained in the off-gas can be recovered as a product gas without reducing the regeneration efficiency of the adsorption tower. As a result, the hydrogen gas production method and the hydrogen gas production method can improve the hydrogen recovery amount.

[Other Embodiments]
The hydrogen gas production method and the hydrogen gas production apparatus of the present invention are not limited to the above embodiment.

  In the above embodiment, the gas mixture after the dehydrogenation reaction is separated into gas and liquid. However, this gas and liquid separation is not essential and can be omitted. That is, the mixed gas discharged by the dehydrogenation reaction may be supplied as it is to the PSA type adsorption tower as a hydrogen-rich gas.

  Further, in the above embodiment, the first separator and the second separator are used, but the gas-liquid separation of the hydrogen-rich gas and the gas-liquid separation of the off-gas may be performed by the same separator. That is, the off-gas discharged from the PSA-type adsorption tower may be supplied to the first separator for performing gas-liquid separation of hydrogen gas. Thereby, the whole hydrogen gas production apparatus can be downsized.

  Further, when the first separator and the second separator are used, the off-gas separated by the second separator may be directly supplied to the hydrogen-rich gas buffer tank, or may be supplied downstream of the hydrogen-rich gas buffer tank.

  Further, the hydrogen-rich gas buffer tank and the off-gas buffer tank in the above embodiment are not essential components, and can be omitted. Further, a vacuum pump is an optional component.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not to be construed as being limited based on the description of the examples.

In the hydrogen gas production apparatus shown in FIG. 1, methylcyclohexane was used as the organic hydride, and the hydrogen recovery R under various conditions was calculated. First, the hydrogen amount of the hydrogen-rich gas B is F _H2,1 [Nm ³ / h], the hydrogen amount of the raw material gas obtained by mixing the hydrogen-rich gas B and the separated off-gas G is F _H2,2 [Nm ³ / h], and the off-gas If the recycling rate of α is α and the apparent hydrogen recovery rate in the raw material gas obtained by mixing the hydrogen-rich gas B and the separated off-gas G is R ′, the following equation (1) holds. Here, the “off-gas recycle rate” is a flow rate ratio of the separated off-gas G mixed with the hydrogen-rich gas B by the off-gas supply line 100 among the off-gas F discharged from the PSA-type adsorption tower 3.
F _H2,2 = F _H2,1 / {1-α (1-R ′)} (1)

From the above equation (1), the relationship of the following equation (2) holds.
R = R′F _H2,2 / F _H2,1 = R ′ / {1-α (1-R ′)} (2)

  FIG. 2 shows the relationship between the values of R ′ and α and the value of R obtained by using the above equation (2). As shown in FIG. 2, it can be seen that increasing the recycling rate α increases the hydrogen recovery rate R.

The hydrogen-rich gas methane concentration _{C CH4,2} of B as a raw material gas obtained by mixing after separation off-gas G and [vol%], the methane concentration _{C CH4,1} [vol%] in the hydrogen-rich gas B, after mixing Since the concentration of methane and toluene in the raw material gas is smaller than the concentration of hydrogen, it is expressed by the following equation (3). Here, F _CH4,2 [Nm ³ / h] is the methane amount of the raw material gas obtained by mixing the hydrogen-rich gas B and the separated off-gas G.
C _CH4,2 = F _CH4,2 / F _H2,2 = {1-α (1-R ′)} / (1-α) · C _CH4,1 (3)

FIG. 3 shows the relationship between the values of R ′ and α and the values of _CCH4,2 obtained using the above equation (3). As shown in FIG. 3, when the recycling rate α is increased, the methane concentration of the source gas is increased. However, when the methane concentration is 1000 ppm or less, even if the methane concentration is doubled, the size of the adsorption tower only needs to be 1.1 times, and the reduction in the hydrogen recovery rate accompanying this is less than 1%. Therefore, by increasing the recycling rate α, the amount of hydrogen recovered can be improved.

  Since the concentration of toluene is reduced by gas-liquid separation until it reaches a saturated vapor pressure, the concentration of the raw material gas does not change due to the recycling rate.

  As described above, the hydrogen gas production method and the hydrogen gas production apparatus can improve the amount of hydrogen recovered in hydrogen gas production in which a hydrogen-rich gas obtained by dehydrogenation of an organic hydride is purified by a PSA-type adsorption tower. It is suitably used for supplying high-purity hydrogen.

Reference Signs List 1 reactor 2 first separator 3, 3a, 3b, 3c, 3d PSA type adsorption tower 4 second separator 5 hydrogen-rich gas buffer tank 6 product gas buffer tank 7 off-gas buffer tank 100 off-gas supply line 101 hydrogen-rich gas supply line 102 Product gas discharge line 103 Off gas discharge line 104 Equalizing line 105 Cleaning line A Organic hydride B Hydrogen rich gas D Drain E Product gas F Off gas G Separated off gas T Aromatic compounds V1a, V1b, V1c, V1d Hydrogen rich gas supply valves V2a, V2b , V2c, V2d Product gas discharge valve V3a, V3b, V3c, V3d Off gas discharge valve V4a, V4b, V4c, V4d Equalizing valve V5a, V5b, V5c, V5d Cleaning valve P1 Vacuum pump

Claims (3)

Performing a dehydrogenation reaction of the organic hydride by heating in the presence of a catalyst,
A step of subjecting the mixed gas of the aromatic compound and hydrogen obtained in the dehydrogenation reaction to gas-liquid separation in a first separator,
A step of purifying the hydrogen-rich gas obtained by the gas-liquid separation by the first separator in a PSA-type adsorption tower,
Storing the off-gas discharged from the PSA-type adsorption tower in an off-gas buffer tank;
Supplying the stored off-gas to the second separator,
A step of gas-liquid separation of the aromatic compound by cooling from the off-gas in the second separator,
Supplying the offgas after gas-liquid separation by the second separator to the PSA type adsorption tower via a hydrogen-rich gas buffer tank;
Purifying the supplied off-gas after gas-liquid separation in the PSA type adsorption tower ,
Above the total amount of PSA type off-gas discharged from the adsorption tower, the PSA type The ratio is 0.3 or more and 0.7 der Ru hydrogen gas production process following the off-gas supplied to the adsorption tower. The method for producing hydrogen gas according to claim 1, further comprising a step of recovering the aromatic compound separated from the off-gas in the gas-liquid separation step. A reactor for performing a dehydrogenation reaction of an organic hydride by heating in the presence of a catalyst,
A first separator for discharging a hydrogen-rich gas by gas-liquid separation of a mixed gas of an aromatic compound and hydrogen discharged from the reactor,
A PSA-type adsorption tower for purifying the hydrogen-rich gas,
An offgas buffer tank for storing offgas discharged from the PSA type adsorption tower;
A second separator that discharges the off-gas after separation by gas-liquid separation of the aromatic compound by cooling from the off-gas supplied from the off-gas buffer tank,
A hydrogen-rich gas buffer tank that stores the hydrogen-rich gas discharged from the first separator and the separated off-gas discharged from the second separator and supplies the gas to the PSA-type adsorption tower ;
The PSA-type relative to the total amount of off-gas discharged from the adsorption tower, the PSA-type ratio of the amount of off-gas supplied to the adsorption tower Ru der 0.3 to 0.7 hydrogen gas production apparatus.

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