JPH0243681B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing liquid hydrogen using methanol as a raw material, which is easy to handle and has excellent storage properties. Conventionally, high-purity hydrogen gas for liquid hydrogen production has been produced using the following gases as raw materials. a Off-gas from petroleum refineries, etc. b Off-gas from salt electrolyzers (caustic soda production, etc.) c Synthetic gas obtained by distillation reforming of natural gas, petroleum, etc. d Synthesis gas obtained by partial oxidation of natural gas, petroleum, etc. The general flow of producing high-purity hydrogen gas for liquid hydrogen production using these gases as raw materials will be explained. The above off-gas (a) contains hydrogen, carbon monoxide, and light hydrocarbons as main components, and its composition varies depending on the equipment configuration of the petroleum refinery and the like. To produce the above-mentioned high-purity hydrogen gas from this off-gas,
Basically, it is produced by the same process as the production process from synthesis gas (described later) in c or d above. Since the hydrogen purity of the above-mentioned off-gas (b) is usually about 99.8 mol%, it is used as is for producing liquid hydrogen. The process for producing the above-mentioned high-purity hydrogen gas from the synthesis gas in c above, including the step of synthesizing the synthesis gas in c, is as follows. The raw material (in this case, natural gas) desulfurized in the desulfurization equipment is mixed with superheated steam and fed into a reaction tube filled with a catalyst placed in a reformer, where the pressure is 7 to 7.
Heated by combustion of fuel under 30 atmospheres (approximately 900℃)
The gas is then converted into crude synthesis gas, whose main components are CO and _H2 . This crude synthesis gas is heat-recovered using water in a heat recovery device, and then undergoes a CO conversion process and a decarboxylation process to become purified hydrogen gas with a hydrogen purity of approximately 98 mol%.
Remaining CO ₂ , CH ₄ , and CO are removed by a low-temperature purification process, resulting in a purified gas with a hydrogen purity of 99.99 mol% or more, which is sent to the liquefaction process. The process for producing the above-mentioned high-purity hydrogen gas from the synthesis gas in d above, including the process of synthesizing the synthesis gas in d, is as follows. The raw material (heavy oil in this case) is mixed with water vapor and injected into the reactor through a burner together with oxygen obtained, for example, by cryogenic separation of air, and a partial oxidation reaction mainly produces CO and _H2 . It is converted into crude synthesis gas. The reaction temperature at this time is 1200~
The temperature is 1500℃ and the pressure is 20-150 atm. After this crude synthesis gas is heat-recovered using water in a heat recovery device, it is further cooled with water in a cooling/dedusting device to remove carbon and at the same time replenish the water necessary for CO conversion. The gas is then fed to a CO conversion process, where the CO in the gas is converted into CO ₂ and H ₂ . After that, acidic gases such as H ₂ S and CO ₂ are absorbed and removed by an alkaline solution, etc., and the gas becomes purified hydrogen gas with a hydrogen purity of about 98 mol%.The remaining CO ₂ , CH ₄ , and CO are removed during the low-temperature purification process. Hydrogen purity removed by approximately 99.99
It becomes a purified gas of mol% or more and is sent to the liquefaction process. Note that the acidic gases such as H ₂ S and CO 2 removed by the above-mentioned alkaline solution etc. are converted into S ₂ , CO _{2 etc.} in a sulfur plant. The above conventional method has the following drawbacks. In the case of methods a and b above, in which off-gas is used as a raw material, (1) high-purity hydrogen gas production equipment and liquefaction equipment are attached to oil refineries, caustic soda plants, etc., so there are controls at the installation location; (2) off-gas There is a difference in the pattern of the amount of hydrogen generated and the amount of liquid hydrogen produced, and there are cases where it is necessary to store and use off-gas, but there are disadvantages such as off-gas has poor storability and is inconvenient to handle. In addition, in the case of methods c and d above that use synthesis gas as a raw material, (1) a special high-temperature heat-resistant alloy is required in terms of equipment materials, and depending on the process, pure oxygen production equipment is required, which requires large-scale equipment. (2) Since both are high-temperature processes of over 1000℃, it takes a considerable amount of time to start up and shut down the operation, and the blunt can be started and stopped at any time or even on a daily basis. (3) The ability to follow load transformation and the range of variation are insufficient. The present invention has been made with the object of eliminating the above-mentioned drawbacks and providing a simple and economical method for producing liquid hydrogen using methanol, which is liquid at room temperature and pressure, as a raw material. That is, the present invention has the following features: (1) Methanol is decomposed at a pressure of 30 atmospheres or less and a temperature of 250 to 500°C, and the crude synthesis gas obtained by decomposition is converted to hydrogen by a pressure swing method using an adsorbent. While obtaining hydrogen gas with a purity of 99.99 mol% or more, the combustible gas produced as a by-product is used as a heat source for the improvement reaction, and when high-purity hydrogen gas is liquefied in the liquefaction process, the gas's own pressure is used to expand it. A method for producing liquid hydrogen, characterized by driving a turbine and using it as power for a liquefaction process. (2) The method for producing liquid hydrogen according to item 1 above, which includes the step of pressurizing the crude synthesis gas after methanol decomposition to about 10 to 30 atmospheres. It is related to. The new ideas of the present invention are listed below. (1) Use methanol as the liquid hydrogen raw material. (2) Use the following methanol decomposition reaction for the purpose of producing liquid hydrogen. CH ₃ OH endothermic reaction ---→ CO + 2H ₂ This reaction temperature is low at 250 to 500℃ and does not involve high-temperature operation above 1000℃, so special heat-resistant materials are not required for the equipment, and it is easy to start up and shut down the plant. can be done easily and in a short time. Moreover, for the amount of heat required for the reaction, a low-temperature heat source of about 400 to 600°C can be used. By separating the generated carbon monoxide gas from hydrogen and using it as a heat source for the main decomposition reaction heat, a highly economical process can be constructed. Steam reforming of methanol (CH ₃ OH + H ₂ O → CO _{2 +}
3H ₂ ) requires make-up water or steam, as well as a steam generator, whereas this decomposition reaction does not require makeup water or steam. (3) The raw material is methanol, which is liquid at room temperature and pressure, so it is easy to store the raw material. (4) A method for producing liquid hydrogen from methanol that combines methanol decomposition, separation and purification of hydrogen gas from crude synthesis gas using an adsorbent, and cryogenic liquefaction of hydrogen gas using an expansion turbine. From the above (1) to (4), it can be seen that the present invention has the following advantages. (1) Since there are no particular restrictions on the installation location of a plant that implements the method of the present invention, the method can be easily implemented even in remote areas such as remote islands and non-industrial areas. (2) Since the operating temperature is low, a simple and inexpensive heat supply system and a simple and inexpensive reaction apparatus can be used. (3) Since the plant can be easily started and stopped, intermittent operation can be performed on a daily or weekly basis depending on the demand for liquid hydrogen. (4) No water or steam is required for the process;
This process is particularly effective in areas where fresh water is difficult to obtain. In addition to general liquid hydrogen production, the method of the present invention also
It can also be applied to the production of hydrogen for fuel cells, hydrogen for hydrogenation for the oil and fat and food industries, and hydrogen for reduction for the metal refining and semiconductor industries. Hereinafter, the method of the present invention will be explained in detail with reference to the accompanying drawings and the like. FIG. 1 is a diagram showing the basic flow of the method of the present invention. In Fig. 1, liquid methanol 4 pressurized to about 30 atmospheres is heated to 300 to 500°C to become gaseous, and in the decomposition step 1, it is passed through a catalyst layer to produce a crude compound consisting mainly of H ₂ and CO. It is converted to gas 5. The above catalyst is NiO (60~80wt
%)-CuO (20~40wt%), 90~ of the NiO-CuO
NiO- _CuO -ZnO (containing equal amounts of NiO, _CuO , and ZnO, 90-95wt of NiO-CuO-ZnO)
% supported by 5 to 10 wt% of γ-Al ₂ O ₃ ,
NiO−CuO−Cr ₂ O ₃ (containing equal amounts of NiO, CuO, and Cr ₂ O ₃ ), 90 to 95 wt% of the NiO−CuO−Cr ₂ O ₃
A material in which 5 to 10 wt% of γ-Al ₂ O ₃ is supported is used. The main reaction in decomposition step 1 is represented by the following formula. CH ₃ OH endothermic reaction ---→ CO+2H ₂ ...(1) Next, the crude synthesis gas 5 is cooled and supplied to the separation/purification step 2. Separation/purification step 2 involves impurities other than hydrogen.
The purpose is to remove CO, CH ₄ , CO ₂ , etc.
There are various removal methods, but when the purpose is to produce liquid hydrogen, it is particularly preferable to remove all impurities by the PSA (pressure swing adsorption) method from the economic point of view. Note that synthetic zeolite or the like is used as an adsorbent in the PSA method. The off-gas 8 released from the separation/purification process 2 is
It contains CO ₂ , CH ₄ , CO, H _{2 ,} etc., and has value as a fuel, so it is used as a heat source in the decomposition step 1. The purified gas 6 from the separation/purification step 2 is at approximately room temperature,
Below about 30 atmospheres, with a hydrogen purity of about 99.99 mol% or above,
It is supplied to the liquefaction process 3. By setting the hydrogen purity of the purified gas 6 to about 99.99 mol% or more, low-temperature purification in the liquefaction step 3 is basically unnecessary. Note that methanol decomposition may be operated at normal pressure of about 10 atmospheres or less, and in this case, it is necessary to increase the pressure of purified gas 6 to a pressure of about 10 atmospheres or more, which allows gas separation and purification by the PSA method. be. In the liquefaction process 3, the self-pressure of the purified gas 6 is used to drive an expansion turbine, and this is used as compression power for liquefaction to achieve self-cooling (heat exchange with hydrogen gas at the same temperature level as liquid hydrogen). )
The liquid hydrogen 7 is produced by cooling indirectly using a refrigerant such as nitrogen or helium, or by a combination thereof. According to the method of the present invention described in detail above, the following effects can be achieved. (1) Temperature control is limited to approximately 500°C or less, and equipment
It simplifies materials and operation, makes it easy to start and stop the plant, and enables flexible movement that matches the demand for liquid hydrogen. (2) The off-gas 8 from the separation/purification process 2 can be used as a heat source for the decomposition process 1, and the natural pressure of the synthesis gas (approximately 10 to 30 atmospheres) can be used to reduce the power in the liquefaction process 3, making it efficient and It is an economical process. (3) Compared to the method of producing synthesis gas by alcohol reformation, process water and steam are not required, and basically all that is needed is methanol, which is easy to handle, and the plant can be located in non-industrial areas and remote islands. On-site (local manufacturing) for remote areas such as
Particularly useful on plants. FIG. 2 is a diagram showing a specific embodiment of the method of the present invention. In FIG. 2, methanol 14 is a crude synthesis gas 15 (approximately 350°C) coming out of a decomposition reactor 134.
and heat exchangers 131, 132, by combustion gas 114 used as a heat source for heat supply for the decomposition reaction.
133 , it is sequentially indirectly heated and supplied to a decomposition reactor 134 . In the decomposition reactor 134, methanol is decomposed under conditions of approximately 350° C. and approximately 0.9 atm, and converted to crude synthesis gas 15 containing hydrogen and carbon monoxide as main components. The heat required for this reaction is about 500℃ of combustion gas 1
14. This combustion gas 114 is produced by combustion of the fuel 12 and the off-gas 18 from the PSA device 139 with the air 113 in the hot air generating furnace 135 . This decomposition reactor 134 is a shell and tube type heat exchanger, and inside the tube is NiO-CuO- _{Cr2O3 .}
It is filled with a catalyst (containing equal amounts of NiO, CuO, and Cr ₂ O ₃ ), into which methanol gas is supplied. As a heating method for the decomposition reactor 134, the heat of reaction can also be provided by using a heat carrier with high thermal stability, such as heat carrier oil or molten salt, instead of the combustion gas 114. The crude synthesis gas 15 is cooled in a heat exchanger 136,
Enters compressor 137. Here, the crude synthesis gas 15 at about 0.8 atmospheres is pressurized to about 15 atmospheres, and the crude synthesis gas whose temperature has increased as a result is cooled in a heat exchanger 138.
The hydrogen is supplied to a PSA device 139, where it is separated and purified to a purity of approximately 99.99 mol% or higher. If this purified gas 16 contains impurities such as CO, CH ₄ and CO ₂ of approximately 0.01 mol% or more, this will freeze during the liquefaction process and adhere to the equipment, causing trouble such as blockage. If impurities are not removed using the PSA device 139 or the like, low-temperature purification is required, but this is not necessary by employing the PSA device. An example of the PSA device 139 is schematically shown in FIG. Figure 3 shows four adsorption towers 1 filled with adsorbent.
56 are used. In FIG. 3, while crude synthesis gas 151 having a hydrogen purity of about 67 mol % at about room temperature and about 15 atmospheres passes through an adsorption tower 156, components other than hydrogen are adsorbed by an adsorbent. Before the adsorbent is saturated with impurities, the supply of synthesis gas 151 is stopped and the pressure is reduced, and then purified gas 16 is added.
A part of the adsorbent is poured into the adsorbent to remove impurities adsorbed on the adsorbent and regenerate the adsorbent. The purified gas 16 required for this regeneration is stored as an off-gas 18 in an off-gas tank 158, and is used as a fuel for a heat source for decomposition. Note that FIG. 3 shows a state in which three towers are refining the synthesis gas 151 and one tower is regenerating the adsorbent using a part of the purified gas 18. In this way, by sequentially and cyclically carrying out the operations of adsorption, depressurization, and regeneration in each column, purified gas 16 having a hydrogen purity of about 99.99 mol % or more is obtained. The hydrogen recovery rate in this case is about 75%. The purified gas 16 exiting the PSA device 139 enters the liquefaction process at about 40° C. and about 14 atmospheric pressure. In the liquefaction process, it first enters the expansion turbine 140, where the pressure is reduced to approximately normal pressure, and then the cold box 1
43, 144, where it is indirectly heat exchanged with deep-chilled helium to become approximately 20㎓ of liquid hydrogen, which is stored in a liquid hydrogen tank 146 and used as product liquid hydrogen 17 at any time. The above-mentioned refrigerant, helium 115, has a pressure of about 1.2 atm at the outlet of the expansion turbine 142, which is about 15㎓, and the cold box (aluminum plate heat exchanger) 1
After indirectly liquefying the entire amount of hydrogen in step 44, it is branched into two streams: one helium stream precools the hydrogen gas in a cold box (heat exchanger) 143, and the other helium stream flows through a cold box (heat exchanger) 143. 1
45 pre-cools the helium gas from the compressor 141 at a pressure of about 300㎓ and about 15 atm. These branched helium gases are combined again and sent to the compressor 141. Helium thus forms a completely closed cycle. Note that the expansion turbines 140 and 142 are recovered as power for the compressor 141 in the liquefaction process, and the insufficient power is supplemented by the electric motor 148. Table 1 shows an overview of the logistics in the main lines mentioned above. 【table】

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic flow of the method of the present invention, FIG. 2 is a diagram showing an example of an embodiment of the method of the present invention, and FIG.
The figure shows a specific example of the PSA device 139 used in FIG. 2.

Claims (1)

[Claims] 1 Methanol is decomposed at a pressure of 30 atmospheres or less and a temperature of 250 to 500°C, and the crude synthesis gas obtained by decomposition is purified to hydrogen purity by a pressure swing method using an adsorbent. At the same time as obtaining hydrogen gas of 99.99 mol% or more, the combustible gas produced as a by-product is used as a heat source for the improvement reaction, and when high-purity hydrogen gas is liquefied in the liquefaction process, the natural pressure of the gas is used to generate an expansion turbine. A method for producing liquid hydrogen, characterized in that the hydrogen is driven and used as power for a liquefaction process. 2. The method for producing liquid hydrogen according to claim 1, which includes the step of pressurizing the crude synthesis gas after methanol decomposition to about 10 to 30 atmospheres.