JPS6141841B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-purity hydrogen gas from liquid ammonia, and more specifically, decomposes liquid ammonia to produce a decomposed gas consisting of nitrogen and hydrogen, and separates nitrogen from gas and liquid at an extremely low temperature from the decomposed gas,
The present invention relates to a method for purifying the obtained hydrogen gas by adsorption. Hydrogen gas used in semiconductor manufacturing, etc. is filled in cylinders under high pressure of 150 to 210 kg/cm ² G and transported by transportation means such as trucks. For example, cylinders that can hold 7 m ³ of hydrogen The weight of is about 60
kg, and the weight of the hydrogen charged is 0.63 kg. In other words, approximately 1% of the transported weight is the desired hydrogen gas, and 99% is unnecessary heavy cargo.Transporting large amounts of hydrogen gas in cylinders requires a large capacity of the cylinder. Therefore, not only is transportation cost high and uneconomical, but also transporting large amounts of high-pressure flammable gas is extremely dangerous. Conventionally, the technology to cool hydrogen gas itself to around -250℃, liquefy it, and transport it has already been established, but this method requires extremely insulated containers,
It requires expensive hydrogen liquefaction equipment and also requires a huge amount of energy for liquefaction. Furthermore, during transport, a considerable amount of hydrogen gas is released through natural evaporation while being transported on roads, and especially in countries like Japan, where the population is high, power lines and other objects on roads can become ignition sources. From the point of view of risk prevention, it is undesirable to transport the products to a place where they are stored. In places where hydrogen gas is required, there are methods to obtain hydrogen gas by thermally decomposing substances other than ammonia, such as butane and methanol, but these methods contain large amounts of hydrocarbons as raw materials, so The gas contains large amounts of water, carbon dioxide, carbon monoxide, etc. It is technically difficult to remove even trace amounts of carbon monoxide from hydrogen gas.
On the other hand, since carbon monoxide is an extremely harmful substance in the production of semiconductors, it is not preferable to produce hydrogen gas by decomposing such hydrocarbon-containing substances. In the production of hydrogen using ammonia as a raw material, the main components of the decomposed gas obtained by thermally decomposing ammonia are hydrogen and nitrogen, and it only contains impurities such as undecomposed ammonia and a trace amount of water, so its purification is difficult. It's relatively easy. Furthermore, since semiconductor manufacturing requires a large amount of nitrogen as well as hydrogen, the ammonia decomposition gas can effectively utilize both hydrogen and nitrogen. Methods for removing impurities from a mixed gas containing hydrogen include the PSA method (pressure adsorption, vacuum desorption method) and the palladium permeable membrane method, but the hydrogen recovery rate is 80%.
It is technically and economically difficult to increase the value beyond this level. Further, even if nitrogen is separated and removed from ammonia decomposition gas by these methods, the separated nitrogen gas is contaminated with a large amount of hydrogen and cannot be used as nitrogen gas. In addition, in the PSA method, the valve is opened and closed once every 2 to 5 minutes, so the life of the valve is short.On the other hand, in the palladium permeable membrane method, a thin palladium permeable membrane with a thickness of 5 to 10 μm is
Since the palladium is permeated at a high temperature of 450°C and with a pressure difference of about 5 to 10 kg/cm ² , there is a drawback that there are many failures due to damage to the palladium permeable membrane. The present invention aims to solve the above-mentioned drawbacks of the conventional method, transport liquid ammonia to a site where hydrogen is required, and obtain high-purity hydrogen gas from the liquid ammonia as a raw material at the required site. In other words, if hydrogen gas and nitrogen gas are combined, liquefied, and transported as liquid ammonia, heavy pressure-resistant cylinders are not required.
If liquid ammonia can be safely transported in a normal container and decomposed at a place where hydrogen is needed, 1 kg of liquid ammonia can be decomposed to produce approximately 2 m ³ of hydrogen.
^0.67m3 of nitrogen gas can be obtained. The present inventor has already published Japanese Patent Application No. 51-21158 (Japanese Unexamined Patent Publication No. 51-119382) titled "Gas Low Temperature Adsorption Purification Column" and Japanese Patent Application No. 52-108775 (Unexamined Japanese Patent Application No. 54-42370) titled "Gas Low Temperature Adsorption Purification Column". ``Cryogenic purification equipment for gas'', Japanese Patent Application No. 111637 (Sho 52-111637) (Japanese Patent Application No. 54-45680) and ``Cryogenic adsorption purification equipment for gas'', Japanese Patent Application No. 53-5808 (Japanese Patent Application No. 54-99778). ``Gas cryogenic adsorption purification tube'' in Japanese Patent Application No. 53-11534 (Japanese Unexamined Patent Publication No. 54-104485), ``Gas purification device'', and Japanese Patent Application No. 53-24551 (Japanese Patent Application No. 54-117391) "Cryogenic adsorption purification equipment for helium or hydrogen gas"
We have applied for a series of gas purification technologies such as, and by combining these methods with an ammonia decomposition device and compressor, we can safely and economically produce extremely high-purity hydrogen gas from liquid ammonia. found that it is possible. That is, the present invention vaporizes liquid ammonia,
It is decomposed in a cracking furnace to produce a cracked gas consisting of nitrogen and hydrogen. After adsorbing and removing undecomposed ammonia and moisture from the cracked gas, the pressure is increased in a compressor, and then in a gas-liquid separator at an extremely low temperature, the nitrogen in the gas is removed. In a method for producing high-purity hydrogen gas, the gas-liquid separator separates hydrogen from liquid nitrogen and passes the resulting separated hydrogen gas through an adsorption purification column at extremely low temperatures to adsorb and remove residual nitrogen. It consists of a heat exchange section that pre-cools the introduced cracked gas by heat exchange with the vaporized gas and separated hydrogen gas, and a rectification tube that is externally cooled with liquid nitrogen and filled with rectifying filler. This is a method for producing high-purity hydrogen gas, characterized in that it separates gas and liquid by rectification. Hereinafter, the present invention will be explained in detail with reference to FIG. 1 showing a flow. Liquid ammonia is introduced from a tank 1 into a vaporizer 2 and vaporized, and the pressure is adjusted with a pressure reducing valve 3. Next, the ammonia is introduced into a decomposition furnace 5 filled with a nickel catalyst, etc., and the temperature inside the furnace is maintained at 900 to 950°C, whereby the ammonia is decomposed into hydrogen and nitrogen, but since this decomposition reaction is reversible, the decomposition reaction does not occur. Depending on the pressure and temperature, 5 to 500 ppm of undecomposed ammonia still exists in the decomposed gas. In addition, a small amount (5 to 1000 ppm) of water contained in the raw material ammonia remains. This mixed gas is passed through an adsorption cylinder 6 filled with an adsorbent such as synthetic zeolite to remove undecomposed ammonia and water to the lowest possible concentration.
The almost complete mixed gas of hydrogen and nitrogen is pressurized by the compressor 7 to 10 kg/cm ² G or more, preferably 15 kg/cm ² G. Next, it is introduced into a gas-liquid separator 9 and cooled to -180°C or lower, preferably -196°C using a cryogen such as liquid nitrogen, to liquefy and separate nitrogen from the hydrogen-nitrogen mixed gas. The gas-liquid separator 9 used in the present invention is
-11534 (Japanese Unexamined Patent Publication No. 54-104485), in which heat transfer tubes through which liquefied gas and purified gas pass are arranged in parallel, and after exchanging heat with the gas to be purified, liquid nitrogen A gas purification device is used in which the gas is rectified using an externally cooled rectification tube. The rectifying tube is filled with a rectifying filler such as a Ratschig ring,
By further providing an adsorbent layer on the top of the rectification tube, it can also be used for the next adsorption purification process.
Even when an adsorption purification step is provided, the load can be reduced and the degree of purification can be improved. Examples of such gas-liquid separators are shown in FIGS. 2 and 3. In FIG. 2, the interior of a body 21 whose outside is covered with a heat insulating layer 21 is functionally divided into upper and lower parts, and a heat exchange device in the upper part and a rectification apparatus in the lower part are incorporated. One of the external heat insulating layers 21 may use vacuum heat insulation. The upper heat exchange device has one of the outer tube sheets 22 on the upper part.
1 of the inner tube sheet 23 and 2 of the inner tube sheet 23 at the bottom.
Four tube sheets 1 and 2 of the outer tube sheet 22 are arranged, and a heat transfer tube 24 through which the rectified and separated hydrogen gas passes through 1 and 2 of the outer tube sheet 22 is also provided. Heat transfer tubes 25 are fixedly installed through plates 23 1 and 23 2 through which vaporized gas of liquid nitrogen passes, and a plurality of baffle plates are provided in the space between inner tube plates 23 1 and 23 2. 26 is installed. In the lower rectifying device, a rectifying tube 28 is fixedly installed through the upper tube sheet 27 1 and the lower tube sheet 27 2 . The inside of the rectifying tube 28 is filled with a rectifying packing 30 such as a Luschig ring, but preferably an adsorbent 29 such as activated carbon or molecular sieve is placed in the upper part of the rectifying tube instead of the rectifying packing. is filled. Liquid nitrogen 31 is injected into about the lower half of the outer space of the rectification tube 28, and a liquid reservoir 32 having an outlet 32 at the bottom of the tip where the liquefied components of the decomposed gas stay is protruded from the bottom of the body. There is. At the top of the body 21 is a rectified separation gas discharge pipe 3.
3. A discharge pipe 3 for vaporized liquid nitrogen gas is provided on the body wall between 1 of the upper outer tube plate 22 and 1 of the inner tube plate 23.
4. An injection pipe 35 for introducing mixed gas is installed on the body wall between 1 of the upper inner tube plate 23 and the first baffle plate, and an injection pipe 35 is installed on the body wall between the last baffle plate and 2 of the lower inner tube plate 23. An exhaust port 36 for the mixed gas cooled by heat exchange, and an inlet 37 for vaporized liquid nitrogen gas are provided in the body wall between the lower inner tube sheet 23 2 and the lower outer tube sheet 22 2. . The body wall between the upper tube plate 27 1 and the lower tube plate 2 2 of the rectifier has an exhaust port 38 for vaporized gas of liquid nitrogen in the upper part, and an inlet 39 for liquid nitrogen in the center thereof. Yes, lower tube plate 27-2
An inlet 40 for a mixed gas cooled by heat exchange is opened in the body wall of the gas retention chamber between the liquid reservoir 32 and the liquid reservoir 32 . The discharge port 36 and the injection port 40 are connected by a connecting pipe 41 disposed inside the heat insulating layer 21, and the discharge port 38
and the injection port 37 are connected to each other by a connecting pipe 42 disposed within one of the heat insulating layers 21 . A liquid nitrogen pipe 24 from the outside is connected to the inlet 19 via a valve 23 within the heat insulating layer 21 , and further connected to the outlet 32 of the liquid reservoir 32 via a valve 25 and a connecting pipe 46 .
It is connected to 1 of FIG. 3 shows a modification of the embodiment in which an adsorption layer is provided in the upper part of the rectification tube, and the gas exiting the plurality of rectification tubes is purified by passing through a single adsorption layer 39 provided in the center of the body. . In the above gas-liquid separator, the mixed gas introduced from the injection pipe 35 flows along the baffle plate 26 as a body-side fluid of the heat exchange device, and the heat exchanger tube 25 through which the vaporized gas of liquid nitrogen 31 flows and the rectifier It is cooled by exchanging heat with the heat transfer tube 24 through which gas flows. The cooled mixed gas enters the lower part of the cylinder from the inlet 40 through the connecting pipe 41 and flows into the rectification pipe 28 . Since the rectifying tube 28 is cooled with liquid nitrogen 31 from the outside of the tube, nitrogen and other impurities in the mixed gas are liquefied and rectified, and the liquefied product falls and stays in the liquid reservoir 32. This retained liquid passes through the connecting pipe 46 to the inlet 1
9 is added to liquid nitrogen 31 and used as a refrigerant. The rectified gas undergoes heat exchange through the heat exchanger tube 24 and is then obtained from the exhaust port 13 as highly pure hydrogen gas. When the upper part of the rectifying tube 28 is filled with an adsorbent, the purity of the obtained hydrogen gas is greatly improved. The hydrogen gas separated in this way contains 0.48 to 0.68 nitrogen when not filled with an adsorbent.
Approximately % remains. Note that liquefied nitrogen does not contain detectable hydrogen. The hydrogen gas containing a small amount of nitrogen thus obtained is introduced into the cryogenic adsorption purification column 10, which is filled with an adsorbent such as activated carbon or synthetic zeolite cooled by a cryogen such as liquid nitrogen. By passing it through, residual nitrogen is adsorbed and removed, reducing nitrogen to approximately 0.2ppm.
High purity hydrogen gas free of other impurities can be obtained as follows. In addition, as a method of low-temperature adsorption, the patent application
21158 (Japanese Unexamined Patent Publication No. 119382/1982), the raw material gas is subjected to first-stage heat exchange with liquid nitrogen vaporized gas cooled in an adsorption tube, second-stage heat exchange with purified gas, and adsorption. Although it is possible to use a cryogenic adsorption purification tube that purifies gas by adsorption through a tube, this is further improved by Japanese Patent Application No. 53-5808 (Japanese Unexamined Patent Publication No. 54-99778).
The gas cryogenic adsorption purification cylinder described in No.) may also be used. FIG. 4 is a vertical sectional view of an example of the latter improved gas cryogenic adsorption purification column used in the embodiment of the present invention, which is shown as the cryogenic adsorption purification column 10 in FIG. 1. As can be seen from FIG. 4, this adsorption purification cylinder basically has a structure similar to that of the gas-liquid separator shown in FIG. and a suction chamber B at the bottom. The hydrogen gas exiting the gas-liquid separator 9 is introduced into the cylinder from the injection port 52 in FIG. 4, and is cooled in the heat exchange chamber A by heat exchange with the refrigerant from the adsorption chamber and purified hydrogen gas. Adsorption chamber B via connecting pipe 53
The adsorption tube 54 in the adsorption chamber B is filled with an adsorbent such as activated carbon or molecular sieve, and the outside thereof is cooled by a refrigerant 55. As the refrigerant, any refrigerant may be used as long as it exhibits the adsorption ability of the adsorbent, but it is preferable to use liquid nitrogen, which is the same as that used in the gas-liquid separation column 9. The hydrogen gas adsorbed and purified in the adsorption chamber is sent to the heat exchange chamber A through the connecting pipe 56.
After exchanging heat with the introduced hydrogen gas, it is taken out from the outlet 57 as high-purity hydrogen gas. According to the method of the present invention, when liquid ammonia is used as a raw material and nitrogen is liquefied and separated from the cracked gas obtained, a gas-liquid separator that performs a rectification operation is used, so the purity and yield of the obtained hydrogen are improved. It is possible to produce highly pure hydrogen gas with an extremely high nitrogen concentration of 0.2 ppm. In order to implement the method of the present invention at a site where hydrogen gas is used, a considerable amount of capital investment is initially required for production equipment, but compared to the conventional method of filling and transporting hydrogen gas in cylinders, transportation costs are lower It is extremely inexpensive and has excellent safety. Furthermore, since nitrogen gas produced as a by-product can be used, it is believed that this will greatly contribute to the semiconductor manufacturing industry. Examples The following examples were carried out according to the flow sheet shown in FIG. 1, and the specifications of the equipment used were as follows. (1) Ammonia tank 4 A commercially available 500Kg ammonia cylinder (2) Vaporizer 2 A commercially available air-type evaporator with a capacity of 20Kg/hr (3) Pressure reducing valve 3 Stainless steel, diameter 15A, primary pressure 0.7Kg/cm ²
G, with a secondary pressure of 0.2 to 0.5 Kg/cm ² was adjusted to 0.2 Kg/cm ² G and used. (4) Heat exchanger 4 Shell and tube type heat exchanger, the material is
SUS304, tube outer diameter 6.35mm, inner diameter 4.35
mm, 19 pipes with a length of 800 mm, the outer diameter of the shell
A piece with a diameter of 76.3 mm, an inner diameter of 66.3 mm, and a length of 800 mm was used. (5) Ammonia decomposition furnace 5 Decomposition cylinder 5-1: Material Hastelloy X, outer diameter 128 mm, inner diameter 120 mm,
Two pieces of 800mm length were lined up vertically and the bottoms were connected with a pipe. N-134 catalyst manufactured by JGC Chemical Co., Ltd. (outer diameter 16 mm, inner diameter 6 mm, length 116 mm)
18 cylindrical catalysts) were used. Electric furnace 5-2: Use an electric furnace with a capacity of 18KW/hr and a temperature of 950℃.
heated to. Cooler 5-3: The material used was SUS304 and the cooling capacity was 2500 kcal/hr. (6) Adsorption cylinder 6 Material: SUS304, outer diameter 165.2mm, inner diameter 158.4mm,
Synthetic zeolite 5A is filled into a tube with a length of 900 mm.Height
Filled to 800mm. The filling amount was 11Kg. (7) Compressor 7 Nishi Seisakusho vertical type 3-stage water-required oil-free electric motor
Use one with 7.5KW, pressure 15Kg/cm ² G
The pressure was increased to (8) Aftercooler 8 Included with the compressor. (9) Gas-liquid separator 9 A heat exchange device in which a heat exchanger tube through which vaporized gas of refrigerant liquid nitrogen passes and a heat exchanger tube through which purified gas passes are arranged in parallel to exchange heat with the gas to be purified. Rectification is carried out through a rectification adsorption tube whose upper part is filled with granular activated carbon as an adsorbent.
The apparatus of FIG. (10) Cryogenic purification column 10 After exchanging heat in a heat exchange chamber in which a heat transfer tube through which vaporized gas of refrigerant liquid nitrogen passes and a heat transfer tube through which purified gas passes are arranged in parallel, activated carbon cooled with liquid nitrogen is used. The apparatus shown in FIG. 4 performs adsorption purification. According to the flow shown in Fig. 1, 7.6 kg of ammonia per hour is introduced from the ammonia tank 1 through pipe a into the vaporizer 2 and vaporized, and then the pressure reducing valve 3
The pressure was reduced to 0.2 Kg/cm ² G, heated to 860° C. with a heat exchanger 4, and introduced into an ammonia decomposition furnace 5. The mixed gas obtained by being decomposed into hydrogen and nitrogen at 950°C in decomposition column 5-1 was cooled to 22°C in cooler 5-3. When this mixed gas was analyzed, 125 ppm of undecomposed ammonia and 33 ppm of moisture were detected. This mixed gas was introduced into the adsorption cylinder 6, and undecomposed ammonia and moisture were adsorbed and removed at a temperature of 22°C. Analysis of the mixed gas at the outlet of the adsorption column detected 0.8 ppm of undecomposed ammonia and 2.3 ppm of moisture. This mixed gas was pressurized to 15 kg/cm ² G by a compressor 7, cooled to 22° C. by an aftercooler 8, and introduced into a gas-liquid separator 9. Hydrogen gas exiting the gas-liquid separator 9 is purified by adsorption in a cryogenic adsorption purification column 10. The nitrogen concentration in the obtained hydrogen gas was extremely small, 0.2 ppm, and the hydrogen gas was extremely pure. Nineteen hours after the start of purification, the nitrogen concentration at the outlet side of the gas-liquid separator 9 began to rise rapidly, reaching about 7000 ppm in 19 hours and 40 minutes. This is because the adsorption capacity of the activated carbon contained in the gas-liquid separator 9 has reached its limit. However, when purification was continued, the nitrogen concentration at the outlet of the cryogenic adsorption purification column 10 was 0.2 ppm until 32 hours had passed since the start of purification.
It was hot. After 32 hours, an increase in nitrogen concentration was observed, reaching almost 7000 ppm in 33 hours. During this time,
High purity hydrogen gas obtained from pipe b is total
It was ^486Nm3 . In the hydrogen production of the present invention, two cryogenic adsorption purification columns 10 are provided and operated alternately to continuously produce high-purity hydrogen.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an embodiment of the method of the present invention. 2 and 3 are longitudinal cross-sectional views of a gas-liquid separator used in the present invention, and FIG. 4 is a vertical cross-sectional view of a cryogenic adsorption purification column used in the present invention.
The correspondence between the main parts illustrated and the symbols is as follows. 1... Liquid ammonia tank, 2... Vaporizer,
3... pressure reducing valve, 4... heat exchanger, 5... decomposition furnace,
7...Compressor, 8...Aftercooler, 9...
Gas-liquid separator, 10...cryogenic adsorption purification column.

Claims (1)

[Claims] 1 Liquid ammonia is vaporized and decomposed in a cracking furnace to produce a cracked gas consisting of nitrogen and hydrogen. After adsorbing and removing undecomposed ammonia and water from the cracked gas, the pressure is increased in a compressor, and then the gas is decomposed in a gas-liquid separator. In a method for producing high-purity hydrogen gas, in which nitrogen in the gas is liquefied at low temperatures and separated from hydrogen in gas and liquid, the resulting separated hydrogen gas is passed through an adsorption purification column at extremely low temperatures to adsorb and remove residual nitrogen. The gas-liquid separator has a heat exchange section that pre-cools the introduced cracked gas by heat exchange with vaporized liquid nitrogen gas and separated hydrogen gas, and a rectification tube that is externally cooled with liquid nitrogen and filled with rectification filler. A method for producing high-purity hydrogen gas, characterized in that nitrogen is separated into gas and liquid from introduced cracked gas by rectification.