WO2012132559A1 - Method for purifying ammonia and ammonia purification system - Google Patents

Abstract

The present invention is a method for purifying ammonia and an ammonia purification system whereby impurities in crude ammonia can be efficiently adsorbed and removed and whereby ammonia can be purified by a simplified method. In an ammonia purification system (100), a first adsorption tower (21) and a second adsorption tower (22) adsorb and remove impurities in crude ammonia, using an adsorption agent having the ability to adsorb moisture and hydrocarbons only. A first condenser (31) partially condenses the ammonia from which the impurities have been adsorbed and removed, to thereby separate out and remove highly volatile impurities as gas phase components.

Description

Ammonia purification method and ammonia purification system

The present invention relates to a purification method and an ammonia purification system for purifying crude ammonia.

In a semiconductor manufacturing process and a liquid crystal manufacturing process, high-purity ammonia is used as a processing agent used for producing a nitride film. Such high-purity ammonia can be obtained by purifying crude ammonia to remove impurities.

The crude ammonia contains hydrogen, nitrogen, oxygen, argon, nitrogen monoxide, carbon dioxide and other low-boiling gases, hydrocarbons, moisture and the like as impurities. The purity of generally available crude ammonia is about 98 to 99% by weight.

Generally, hydrocarbons contained in crude ammonia are mainly those having 1 to 4 carbon atoms. However, when producing hydrogen gas used as a raw material for ammonia synthesis, the oil content in the cracking gas is insufficiently separated. Or, when the oil is contaminated with pump oil from pumps during production, hydrocarbons having a high boiling point and a large molecular weight may be mixed. Moreover, if ammonia contains a large amount of moisture, the function of a semiconductor or the like manufactured using this ammonia may be greatly reduced, and the moisture in ammonia needs to be reduced as much as possible.

Depending on the type of process in which ammonia is used in the semiconductor manufacturing process and the liquid crystal manufacturing process, the manner in which the impurities in ammonia vary. The purity of ammonia is required to be 99.9999% by weight or more (each impurity concentration of 100 ppb or less), more preferably about 99.99999% by weight. In recent years, a moisture concentration of less than 30 ppb has been demanded for the production of a light emitter such as gallium nitride.

As a method for removing impurities contained in crude ammonia, a method for adsorbing and removing impurities using an adsorbent such as silica gel, synthetic zeolite, activated carbon, and a method for removing impurities by distillation are known.

For example, Patent Document 1 discloses a first distillation column that removes low-volatile impurities from liquid crude ammonia, and impurities (mainly moisture) contained in gaseous ammonia derived from the first distillation column. An ammonia purification system is disclosed that includes an adsorption tower that adsorbs and removes with an adsorbent, and a second distillation tower that removes highly volatile impurities from gaseous ammonia derived from the adsorption tower. Patent Document 2 discloses a method of purifying ammonia by distilling and removing moisture contained in gaseous crude ammonia with an adsorbent composed of barium oxide.

JP 2006-206410 A JP 2003-183021 A

As an adsorbent that adsorbs and removes impurities contained in crude ammonia, it is common to distinguish between adsorbents that have a high adsorption capacity for moisture and adsorbents that have a high adsorption capacity for hydrocarbons. In the technology for purifying ammonia disclosed in Patent Document 1, moisture is adsorbed and removed by an adsorbent composed of synthetic zeolite 3A, and in the technology for purifying ammonia disclosed in Patent Document 2, adsorption composed of barium oxide is performed. Moisture is absorbed and removed by the agent.

In order to adsorb and remove moisture and hydrocarbon impurities contained in crude ammonia, an adsorption tower packed with an adsorbent having a high adsorption capacity for moisture and an adsorbent having a high adsorption capacity for hydrocarbons It is necessary to make it the structure provided with a plurality of adsorption towers with the adsorption tower filled with or a structure where a plurality of adsorbents are stacked and packed in one adsorption tower.

When a plurality of adsorbents are stacked in one adsorption tower, when the amount ratio of moisture and hydrocarbons contained as impurities in the crude ammonia varies, even if one adsorbent has not reached adsorption saturation The other adsorbent reaches adsorption saturation and breaks through. For this reason, it is not possible to efficiently absorb and remove moisture and hydrocarbons contained in the crude ammonia by making maximum use of the adsorption capacity of the adsorbent, and the management of adsorbent breakthrough becomes complicated. End up.

Further, in the technology for purifying ammonia disclosed in Patent Documents 1 and 2, impurities contained in the crude ammonia are adsorbed and removed by an adsorption tower, and further, the ammonia is purified by distillation by distillation using a distillation tower. The derived gaseous ammonia after purification is cooled and recovered as liquid ammonia. That is, in the technology for purifying ammonia disclosed in Patent Documents 1 and 2, impurities contained in the crude ammonia are adsorbed and distilled off, and further cooled to obtain purified liquid ammonia. It cannot be said to be simplified.

Accordingly, an object of the present invention is to efficiently remove moisture and hydrocarbons contained as impurities in crude ammonia by making maximum use of the adsorption capacity of the adsorbent and to remove ammonia by a simplified method. To provide a method for purifying ammonia and an ammonia purification system that can be purified.

The present invention is a method for purifying crude ammonia containing impurities,
An adsorption removal step of adsorbing and removing impurities contained in the crude ammonia by an adsorbent having an adsorption ability for moisture and hydrocarbons alone;
Ammonia from which impurities have been adsorbed and removed in the adsorption removal step is fractionated and separated into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and carbon number 1 And a fractionation step of separating and removing hydrocarbons of ˜8 as a gas phase component to obtain liquid ammonia as a liquid phase component.

In the method for purifying ammonia according to the present invention, the liquid ammonia obtained in the fractionation step is vaporized, and the vaporized ammonia is fractionated and separated into a gas phase component and a liquid phase component, thereby removing impurities. It is preferable to further include a re-denaturation step of separating and removing as a gas phase component to obtain liquid ammonia as a liquid phase component.

In the ammonia purification method of the present invention, it is preferable that the adsorbent used in the adsorption removal step is porous synthetic zeolite.

In the ammonia purification method of the present invention, the synthetic zeolite is preferably a synthetic zeolite having a pore diameter of 5 to 9 mm.

In the ammonia purification method of the present invention, in the partial reduction step, 70 to 99% by volume of ammonia from which impurities have been adsorbed and removed in the adsorption removal step is condensed and separated into a gas phase component and a liquid phase component. Is preferred.

In the ammonia purification method of the present invention, in the partial reduction step, the ammonia from which impurities have been adsorbed and removed in the adsorption removal step is condensed at a temperature of −77 to 50 ° C. to obtain a gas phase component and a liquid phase component. It is preferable to separate them.

The present invention is also an ammonia purification system for purifying crude ammonia containing impurities,
An adsorbing part that adsorbs and removes impurities contained in the crude ammonia by an adsorbent having an adsorption ability for water and hydrocarbons alone;
The ammonia from which the impurities are adsorbed and removed by the adsorbing part is fractionated and separated into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and carbon number of 1 to And a fractionation unit that separates and removes 8 hydrocarbons as a gas phase component to obtain liquid ammonia as a liquid phase component.

According to the present invention, the ammonia purification method is a method for purifying crude ammonia containing impurities, and includes an adsorption removal step and a partial condensation step. In the adsorption removal process, impurities contained in the gaseous crude ammonia are adsorbed and removed by an adsorbent having adsorption ability for moisture and hydrocarbons alone. In the partial condensation process, gaseous ammonia from which the impurities have been adsorbed and removed in the adsorption removal process is fractionated and separated into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, Carbon dioxide and hydrocarbons having 1 to 8 carbon atoms are separated and removed as gas phase components to obtain purified liquid ammonia as liquid phase components.

In the ammonia purification method of the present invention, the adsorption removal step uses an adsorbent having an adsorption ability for water and hydrocarbons alone, so that the adsorbent having an adsorption ability for moisture and the hydrocarbon are adsorbed as in the prior art. There is no need to use a plurality of adsorbents with adsorbents having adsorbability. As a result, moisture and hydrocarbons contained as impurities in the gaseous crude ammonia can be efficiently adsorbed and removed by making full use of the adsorption capacity of the adsorbent, and management of adsorbent breakthrough is simplified. can do. Further, in the ammonia purification method of the present invention, in the partial condensation step, a part of the gaseous ammonia after adsorption removal is condensed and separated into a gas phase component and a liquid phase component. Liquid ammonia purified as a liquid phase component can be obtained by separating and removing dissolved low boiling point gas such as hydrocarbon, hydrogen, nitrogen, oxygen, argon, carbon monoxide and carbon dioxide as a gas phase component. Therefore, ammonia can be purified by a simplified method without passing through a distillation step as in the prior art.

According to the present invention, the method for purifying ammonia further includes a re-denaturation step. In this re-fractionation process, liquid ammonia obtained in the fractionation process is vaporized, and the vaporized ammonia is fractionated and separated into a gas phase component and a liquid phase component, so that impurities become gas phase components. Separation and removal are performed to obtain liquid ammonia as a liquid phase component. In the re-differentiation step, a part of the ammonia vaporized from the liquid ammonia obtained in the partial reduction step is condensed and separated into a gas phase component and a liquid phase component, so that highly volatile impurities are removed from the gas phase component. As a result, it is possible to obtain more purified liquid ammonia.

Further, according to the present invention, the adsorbent used in the adsorption removing step is a porous synthetic zeolite. As a result, moisture and hydrocarbons contained as impurities in the crude ammonia can be efficiently adsorbed and removed.

According to the present invention, the synthetic zeolite used as the adsorbent has a pore diameter of 5 to 9 mm. As a result, moisture and hydrocarbons (particularly higher-order hydrocarbons such as butane, pentane, and hexane) contained as impurities in the crude ammonia can be efficiently adsorbed and removed.

According to the present invention, in the partial reduction process, 70 to 99% by volume of gaseous ammonia from which impurities are adsorbed and removed in the adsorption removal process is condensed and separated into a gas phase component and a liquid phase component. As a result, it is possible to separate and remove highly volatile impurities contained in the gaseous ammonia after adsorption removal as a gas phase component, and to obtain liquid ammonia purified as a liquid phase component with a high yield.

Further, according to the present invention, in the partial reduction process, gaseous ammonia from which impurities have been adsorbed and removed in the adsorption removal process is condensed at a temperature of −77 to 50 ° C. to separate into a gas phase component and a liquid phase component. To do. Thereby, gaseous ammonia after adsorption removal can be efficiently condensed to obtain liquid ammonia, and the purity of the liquid ammonia can be increased.

Further, according to the present invention, the ammonia purification system is a system for purifying crude ammonia containing impurities, and includes an adsorption part and a partial condensation part. The adsorbing part adsorbs and removes impurities contained in the gaseous crude ammonia by an adsorbent having an adsorption ability for moisture and hydrocarbons alone. The partial reduction part separates gaseous ammonia from which impurities have been adsorbed and removed by the adsorption part and separates it into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide Carbon and hydrocarbons having 1 to 8 carbon atoms are separated and removed as gas phase components to obtain purified liquid ammonia as liquid phase components.

In the ammonia purification system of the present invention, the adsorbing part adsorbs and removes impurities contained in the gaseous crude ammonia by an adsorbent having adsorption ability for moisture and hydrocarbons alone, so that the adsorption capacity of the adsorbent is maximized. Can be efficiently adsorbed and removed. Further, in the ammonia purification system of the present invention, the partial condensation part condenses part of the gaseous ammonia after the adsorption removal and separates it into a gas phase component and a liquid phase component. The dissolved low boiling point gas such as hydrogen, hydrogen, nitrogen, oxygen, argon, carbon monoxide and carbon dioxide can be separated and removed as a gas phase component to obtain purified liquid ammonia as a liquid phase component. Therefore, ammonia can be purified with a simplified system without providing a distillation section as in the prior art.

Objects, features, and advantages of the present invention will become more apparent from the following detailed description and drawings.
It is a figure which shows the structure of the ammonia purification system 100 which concerns on 1st Embodiment of this invention. It is a figure which shows the structure of the ammonia purification system 200 which concerns on 2nd Embodiment of this invention.

FIG. 1 is a diagram showing a configuration of an ammonia purification system 100 according to the first embodiment of the present invention. The ammonia purification system 100 of the present embodiment is a system that purifies crude ammonia containing impurities.

The ammonia purification system 100 includes a raw material storage container 1, a first adsorption tower 21 and a second adsorption tower 22 that are a plurality of adsorption towers as the adsorption unit 2, and a first capacitor 31 and a second capacitor 32 as the partial condensation unit 3. The recovery tank 4 and the product tank 7 are included. Further, the ammonia purification system 100 realizes the ammonia purification method according to the present invention, the first adsorption tower 21 and the second adsorption tower 22 execute the adsorption removal step, and the first capacitor 31 and the second capacitor 32 are separated. Perform the shrinking process.

The raw material storage container 1 stores crude ammonia. In the present embodiment, the crude ammonia stored in the raw material storage container 1 has a purity of 99% by weight or more, preferably a purity of 99.9 to 99.99% by weight. Examples of such crude ammonia include industrial grade ammonia (manufactured by Ube Industries, Ltd.) having a purity of 99.9% by weight, industrial grade ammonia having a purity of 99.9% by weight (manufactured by Mitsui Chemicals, Inc.), etc. Is mentioned.

The raw material storage container 1 is not particularly limited as long as it is a heat insulating container having pressure resistance and corrosion resistance. The raw material storage container 1 stores crude ammonia as liquid ammonia and is controlled so that the temperature and pressure are constant. A gas phase is formed in the upper part of the raw material storage container 1 in a state where liquid ammonia is stored. When the crude ammonia is derived from the raw material storage container 1 to the first adsorption tower 21 or the second adsorption tower 22, it may be derived as liquid ammonia, but in this embodiment, the crude ammonia is extracted from the gas phase. Derived as gaseous ammonia. A first pipe 71 is connected between the raw material storage container 1 and the first adsorption tower 21 and the second adsorption tower 22, and crude ammonia derived from the raw material storage container 1 passes through the first pipe 71. It is supplied to the first adsorption tower 21 or the second adsorption tower 22 through.

The first pipe 71 is provided with a flow rate regulator 5 for adjusting the flow rate of gaseous crude ammonia flowing from the raw material storage container 1 to the first adsorption tower 21 or the second adsorption tower 22. Further, the first pipe 71 is provided with a first valve 81 and a second valve 82 that open or close a flow path in the first pipe 71. In the first pipe 71, the first valve 81 is arranged upstream of the flow rate regulator 5 in the flow direction of the crude ammonia (that is, the raw material storage container 1 side), and the second valve 82 is placed from the flow rate regulator 5. Is also arranged downstream of the flow direction of the crude ammonia (that is, the first adsorption tower 21 and the second adsorption tower 22 side). When supplying crude ammonia to the first adsorption tower 21 or the second adsorption tower 22, the first valve 81 and the second valve 82 are opened, and the flow rate is adjusted by the flow rate regulator 5, so that Gaseous crude ammonia flows in the first pipe 71 toward the adsorption tower 21 or the second adsorption tower 22.

The first adsorption tower 21 and the second adsorption tower 22 adsorb and remove impurities contained in the gaseous crude ammonia derived from the raw material storage container 1 with an adsorbent. In the present embodiment, since the two adsorption towers of the first adsorption tower 21 and the second adsorption tower 22 are connected in parallel, for example, impurities contained in the crude ammonia are removed from the first adsorption tower which is one of the adsorption towers. The second adsorption tower 22 which is another used adsorption tower so that the adsorption removal operation can be performed again by the second adsorption tower 22 which is another used adsorption tower while the tower 21 is performing adsorption removal. Can be reprocessed. In this case, the opening / closing valve 82a and the opening / closing valve 83a of the second adsorption tower 22 are opened, and the second valve 82 and the third valve 83 of the second adsorption tower 22 are closed.

The adsorbent filled in each of the first adsorption tower 21 and the second adsorption tower 22 has an adsorption ability for moisture and hydrocarbons alone. Examples of such an adsorbent include porous synthetic zeolite. Among the synthetic zeolites, synthetic zeolites having a pore diameter of 5 to 9 mm are preferable. Examples of the synthetic zeolite having a pore diameter of 5 mm include MS-5A, and examples of the synthetic zeolite having a pore diameter of 9 mm include MS-13X. Among these, it is particularly preferable to use MS-13X, which is a synthetic zeolite having a pore size of 9 mm, as an adsorbent. The adsorbent used in the present embodiment can be regenerated by desorbing the adsorbed impurities (water and hydrocarbons) by any one of heating, decompression, heating and decompression. For example, when desorbing impurities adsorbed on the adsorbent by heat treatment, heating may be performed at a temperature of 200 to 350 ° C.

In the ammonia purification system 100 of the present embodiment, the first adsorption tower 21 and the second adsorption tower 22 adsorb and remove impurities contained in the gaseous crude ammonia using an adsorbent that has adsorption ability for moisture and hydrocarbons alone. Therefore, unlike the prior art, it is not necessary to use a plurality of adsorbents, that is, an adsorbent having an adsorption ability for moisture and an adsorbent having an adsorption ability for hydrocarbons. Therefore, moisture and hydrocarbons contained as impurities in the gaseous crude ammonia can be efficiently adsorbed and removed by utilizing the adsorption capacity of the adsorbent to the maximum. Furthermore, the crude ammonia supplied to the first adsorption tower 21 or the second adsorption tower 22 by adsorbing and removing impurities contained in the gaseous crude ammonia with an adsorbent having adsorption ability for moisture and hydrocarbons alone. Even if the quantity ratio between the moisture and the hydrocarbon contained in the fluctuates, the first adsorption tower is based on the analysis result of the amount of ammonia impurities derived from the first adsorption tower 21 or the second adsorption tower 22. Management of breakthrough of 21 and the second adsorption tower 22 can be easily performed.

Further, since the synthetic zeolite used as the adsorbent has a pore diameter of 5 to 9 mm, particularly MS-13X having a pore diameter of 9 mm, moisture and hydrocarbons (especially higher-order hydrocarbons) contained in the crude ammonia as impurities. ) Can be efficiently adsorbed and removed.

In addition, in the 1st adsorption tower 21 and the 2nd adsorption tower 22, it can use combining the adsorption agent which has the adsorption ability with respect to a water | moisture content and hydrocarbon independently, and another adsorption agent, However, With respect to a water | moisture content and a hydrocarbon, It is preferable to use only an adsorbent having adsorbability alone. Examples of other adsorbents include MS-3A (pore diameter 3 mm), MS-4A (pore diameter 4 mm) and the like, which are synthetic zeolites excellent in moisture adsorption ability.

In the ammonia purification system 100 of the present embodiment, the temperature of the first adsorption tower 21 and the second adsorption tower 22 is controlled to 0 to 60 ° C., and the absolute pressure (hereinafter sometimes simply referred to as “pressure”) is set. The pressure is controlled to 0.1 to 1.0 MPa. When the temperature of the first adsorption tower 21 and the second adsorption tower 22 is less than 0 ° C., cooling to remove adsorption heat generated during adsorption removal of impurities is necessary, and energy efficiency may be lowered. When the temperature of the 1st adsorption tower 21 and the 2nd adsorption tower 22 exceeds 60 degreeC, there exists a possibility that the adsorption capacity of the impurity by adsorbent may fall. Moreover, when the pressure of the 1st adsorption tower 21 and the 2nd adsorption tower 22 is less than 0.1 Mpa, there exists a possibility that the adsorption capacity of the impurity by adsorption agent may fall. When the pressure in the first adsorption tower 21 and the second adsorption tower 22 exceeds 1.0 MPa, a large amount of energy is required to maintain a constant pressure, and the energy efficiency may be reduced.

The linear velocity in the first adsorption tower 21 and the second adsorption tower 22 is the amount of crude ammonia supplied to the first adsorption tower 21 and the second adsorption tower 22 per unit time. Preferably, the range of values obtained by dividing by the empty cross-sectional areas of the first adsorption tower 21 and the second adsorption tower 22 is 0.1 to 5.0 m / sec. If the linear velocity is less than 0.1 m / sec, it takes a long time to remove impurities, which is not preferable. If the linear velocity exceeds 5.0 m / sec, the impurity adsorption band length increases. There is a possibility that the adsorbing ability of impurities in the first adsorption tower 21 and the second adsorption tower 22 is lowered.

A gaseous state derived from the first adsorption tower 21 or the second adsorption tower 22 filled with an adsorbent having an adsorption capacity for moisture and hydrocarbons alone (especially MS-13X which is a synthetic zeolite having a pore size of 9 mm). Ammonia flows through the ninth pipe 79 branched from the second pipe 72 connected between the first adsorption tower 21 and the second adsorption tower 22 and the first condenser 31, and passes through the ninth valve 89. It is introduced into the analysis unit 61. The analysis unit 61 includes a gas chromatograph analyzer (GC-4000, manufactured by GL Science Co., Ltd.) and a cavity ring-down spectroscopic analyzer (MTO-LP-H ₂ O, manufactured by Tiger Optics).

About gaseous ammonia derived | led-out from the 1st adsorption tower 21 or the 2nd adsorption tower 22, hydrocarbon concentration, hydrogen, nitrogen, oxygen, and monoxide with a gas chromatograph analyzer (GC-4000, GL Sciences Inc.) When the carbon concentration was analyzed and the moisture concentration was analyzed with a cavity ring-down spectroscopic analyzer (MTO-LP-H ₂ O, manufactured by Tiger Optics), the results shown in Table 1 below were obtained.

Table 1 shows a cylindrical tube (length) filled with synthetic zeolite MS-13X having an adsorption capacity for moisture and hydrocarbons, using 99.9 wt% industrial grade ammonia manufactured by Ube Industries, Ltd. as crude ammonia. The analysis results when gaseous crude ammonia is passed through the first adsorption tower 21 or the second adsorption tower 22 having a diameter of 50 cm and an inner diameter of 2 cm under conditions of a temperature of 25 ° C. and a pressure of 0.4 MPa are shown.

Also, at the time when breakthrough of the first adsorption tower 21 or the second adsorption tower 22 starts, methane having the smallest molecular size among the hydrocarbons is detected, and then ethane is detected. From the above, the impurities contained in the gaseous ammonia derived from the first adsorption tower 21 and the second adsorption tower 22 are low boiling point gases such as hydrogen, nitrogen, oxygen, carbon monoxide, and the first adsorption. It turns out that it is a highly volatile impurity, such as low-order hydrocarbons, such as methane and ethane, depending on the operating conditions of the tower 21 and the second adsorption tower 22. Gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22 is supplied to the first condenser 31.

In the ammonia purification system 100 of the present embodiment, a second pipe 72 is connected between the first adsorption tower 21 and the second adsorption tower 22 and the first condenser 31, and the first adsorption tower 21 or the second adsorption tower 21. Gaseous ammonia derived from the adsorption tower 22 flows through the second pipe 72 and is supplied to the first capacitor 31. The second pipe 72 is provided with a pressure gauge 6 for measuring the pressure of gaseous ammonia flowing from the first adsorption tower 21 or the second adsorption tower 22 to the first condenser 31. The second pipe 72 is provided with a third valve 83 and a fourth valve 84 that open or close the flow path in the second pipe 72. In the second pipe 72, the third valve 83 is disposed upstream of the pressure gauge 6 in the ammonia flow direction (that is, the first adsorption tower 21 and the second adsorption tower 22 side), and the fourth valve 84 is It is arranged downstream of the pressure gauge 6 in the flow direction of ammonia (that is, on the first capacitor 31 side). When supplying gaseous ammonia to the first condenser 31, the third valve 83 and the fourth valve 84 are opened, the pressure is measured by the pressure gauge 6, and the first adsorption tower 21 or the second adsorption tower 22 performs the second measurement. Gaseous ammonia flows in the second pipe 72 toward the condenser 31.

Here, the partial contraction of gaseous ammonia by the first condenser 31 as the partial contraction unit 3 in the ammonia purification system 100 of the present embodiment will be described. The first capacitor 31 separates and removes highly volatile impurities contained in the ammonia as a gas phase component by partial condensation of gaseous ammonia and separating it into a gas phase component and a liquid phase component.

Impurities contained in industrially produced ammonia (crude ammonia) are broadly classified into dissolved low boiling point gases such as hydrogen, nitrogen, oxygen, argon, carbon monoxide and carbon dioxide. , Hydrocarbons, moisture and the like. As the hydrocarbons contained in the crude ammonia, methane is the most abundant, but ethane, propane, ethylene and propylene are the next most abundant. In terms of carbon number, hydrocarbons having 1 to 3 carbon atoms constitute the main component of hydrocarbons.

However, crude ammonia contains hydrocarbons having 4 or more carbon atoms, and in many cases hydrocarbons having 4 to 6 carbon atoms, although the content thereof is small. In addition, when liquefying industrially produced ammonia gas, an oil pump or the like is used for compression. In such a case, hydrocarbons having a large molecular weight such as oil components derived from pump oil mixed from an oil pump or the like are contained in the crude ammonia.

It is indispensable to produce ammonia for the electronics industry, which is an ammonia purification system capable of removing hydrocarbons having a wide range of carbon atoms, which constitute these impurities.

The present inventors have found that a method using partial condensation is excellent as a method for removing impurities in crude ammonia in place of rectification.

For example, when hydrocarbons are separated by rectification, it is generally necessary to provide a rectification column having 5 to 20 stages and perform distillation at a reflux ratio of 10 to 20. In this distillation (rectification), hydrocarbons mainly having 1 to 8 carbon atoms contained in ammonia are removed from the top of the distillation column as highly volatile components. When high-purity ammonia is obtained by this rectification operation, the desired high-purity ammonia can be obtained by what proportion of ammonia containing highly volatile impurities discarded from the top of the distillation column. It becomes a problem whether it can be done. Even when crude ammonia having a relatively low impurity content is used as a raw material, the proportion discarded from the top of the distillation column must be as large as about 10% of the crude ammonia supplied to the distillation column. is there.

Table 2 shows the boiling points of ammonia and saturated n-hydrocarbons having 1 to 8 carbon atoms, but hydrocarbons having 4 to 8 carbon atoms have a boiling point higher than that of ammonia when the hydrocarbon is present as a pure substance. However, in the rectification operation, it is discharged from the top of the distillation column as a highly volatile compound.

The reason for this is not clear, but the present inventors presume as this reason as follows. That is, the boiling point of hydrocarbons having 1 to 8 carbon atoms is, for example, the boiling point of propane having 3 carbon atoms. When propane is put into a container and the temperature is changed, the pressure in the container is reduced. This is the temperature at 1 atm (0.1013 MPa). The state of propane at this time is a state in which adjacent propane molecules are attracted to each other by van der Waals force or the like, and if the pulling force is strong, the boiling point appears high. However, in the situation where the concentration of propane present in ammonia is very low, which is now a problem, there is no propane molecule or other hydrocarbon molecule that can be attracted next to the propane molecule. There is just one propane molecule floating in the sea of liquid ammonia.

Generally, a large intermolecular force is generated between those having similar properties such as hydrocarbon molecules and ammonia molecules. However, this intermolecular force generated between molecules with very different properties such as propane molecules and ammonia molecules is small. Thus, in the situation where a very small amount of hydrocarbon impurities are present in ammonia, the conventional distillation concept is no longer meaningful. In liquid ammonia, the ammonia molecules exert a pulling force on each other. On the other hand, even if the pure substance is a hydrocarbon having 4 to 8 carbon atoms having a boiling point higher than that of ammonia, they are The interaction is small. For this reason, in liquid ammonia, it is no wonder that hydrocarbons having 4 to 8 carbon atoms having a boiling point higher than that of ammonia behave as compounds having a boiling point lower than that of ammonia. In fact, the result of rectification shows that hydrocarbons having 1 to 8 carbon atoms behave as highly volatile compounds having a boiling point lower than that of ammonia.

The concentration of hydrocarbons with 1 to 8 carbon atoms contained in trace amounts in ammonia shows the concentration distribution in the gas phase and liquid phase of liquefied ammonia by changing the temperature in various ways in ammonia. Table 3 shows the results of the measurement when the concentration at 1 reached the vapor-liquid equilibrium state. The distribution ratio was measured after adjusting the initial concentration of each saturated n-hydrocarbon concentration in liquid ammonia to 5000 ppm, and then standing at a predetermined temperature for 2 days.

The gas-liquid distribution coefficient shown in Table 3 serves as an index of how much impurities can be separated by partial contraction, and is defined as follows.
Distribution coefficient (Kd) = A ₁ / A ₂ (1)
Wherein, A ₁ represents an impurity concentration of gaseous ammonia after the gas-liquid equilibrium, A ₂ represents an impurity concentration in liquid ammonia after gas-liquid equilibrium. ]

However, the impurity concentrations A ₁ and A ₂ in the above formula (1) have mol-ppm as the unit, and are defined by the following formula (2).
Impurity concentration (A ₁ , A ₂ ) =
Impurity (mol) / (ammonia (mol) + impurity (mol)) × 10 ⁶
... (2)

According to this definition, an impurity having a larger gas-liquid partition coefficient is contained more in uncondensed gaseous ammonia that has not been condensed by partial condensation. A hydrocarbon having a smaller carbon number has a higher ratio in the gas phase than in the liquid phase, and a hydrocarbon having a carbon number of up to 8 exists in a higher concentration in the gas phase. Furthermore, the lower the temperature, the higher the concentration of hydrocarbons in the ammonia gas phase.

Furthermore, the time to reach the equilibrium shown in Table 3 becomes longer as the concentration of hydrocarbons contained in ammonia decreases, and at the concentration shown in the ppm order, it takes several times to reach the equilibrium. It turns out that it takes days. This means that in the operation of removing impurities in ammonia by rectification, the mass transfer of hydrocarbons as impurities is not sufficiently performed in the short gas-liquid contact time that occurs in each distillation stage of the rectification column. Show. From this result, it is considered that the method of using rectification for purification of ammonia is less effective industrially. Table 3 shows data on saturated straight-chain hydrocarbons. In the case of 4 or more carbon atoms, the corresponding various isomers, and in the case of hydrocarbons of 2 or more carbon atoms, unsaturated bonds are included in the molecule. There is also a tendency shown in Table 3.

As described above, the present inventors have confirmed that the behavior of hydrocarbons having 1 to 8 carbon atoms, which are dilute impurities in crude ammonia, is significantly different from the state considered conventionally. Taking this a step further, we thought that the difference in properties of this hydrocarbon having 1 to 8 carbon atoms in ammonia could be used for the purification of ammonia. Accordingly, 95% of the gaseous crude ammonia containing methane, ethane and propane at about 5000 ppm, about 500 ppm and about 500 ppm, respectively, the ammonia gas temperature is kept at −20 ° C., and the wall temperature in the first capacitor 31 is −30 When liquefied by condensation at a temperature of ° C., it was found that these hydrocarbons were not detected in the obtained liquid ammonia, and most of the impurities remained in the gaseous ammonia that was not condensed. According to the distribution ratio in Table 3, it is calculated that methane, ethane, and propane are present at 54 ppm, 24 ppm, and 56 ppm, respectively, in the liquid ammonia condensed at −20 ° C. by the partial reduction operation. The partial reduction in the first capacitor 31 has a much smaller value, which indicates that the crude ammonia can be purified to a very high purity within a short time.

When the impurities contained in the crude ammonia are separated and removed by rectification, since distillation is performed while refluxing, liquid ammonia is heated and evaporated in a distillation tower to form gaseous ammonia, while the condenser at the top of the distillation tower Thus, the operation of condensing gaseous ammonia from the rectification column to form liquid ammonia is repeated. Therefore, large energy is input to the rectification operation.

On the other hand, when the impurities contained in the crude ammonia are separated and removed by the partial condensation in the first capacitor 31, only the gaseous ammonia is condensed once, so that less energy is required. Thus, compared with the purification method of ammonia by rectification, the purification method by partial condensation in the first condenser 31 not only provides high-purity ammonia in a short time but also has a great energy advantage. I understand that.

Further, the present inventors have liquefied gaseous crude ammonia to about 90 to 99.5% by the first capacitor 31 when the impurities contained in the crude ammonia are hydrocarbons having 1 to 8 carbon atoms. When the partial condensation operation is performed, the concentration of impurities contained in the liquid ammonia obtained as the liquid phase component is greatly reduced compared to the concentration of impurities contained in the first gaseous crude ammonia. I found the fact that.

In the purification method in which the impurities contained in the crude ammonia are separated and removed by the partial condensation in the first capacitor 31, the liquid ammonia obtained as a liquid phase component by the partial condensation is expected from the gas-liquid distribution ratio as described above. Beyond that value, the concentration of impurity hydrocarbons is much lower. The reason for this is not clear, but it is presumed that in the partial reduction, the equilibrium relationship is lost and dynamic impurity separation occurs, and most of the impurity hydrocarbons remain in the vapor phase components that are not condensed. The correctness of this inference is that liquid ammonia obtained as a liquid phase component by partial contraction in the first capacitor 31 does not immediately take out from the first capacitor 31 and stays in the first capacitor 31 in the state of liquid ammonia. This is supported by the fact that the concentration of impurity hydrocarbons in liquid ammonia gradually increases over time.

This inference and result is that liquid ammonia obtained as a liquid phase component by partial contraction in the first capacitor 31 is quickly derived from the first capacitor 31, and only the uncondensed gas phase component is present inside the first capacitor 31. This indicates that the operation of the first capacitor 31 is necessary to obtain high-purity ammonia.

Note that, in order to increase the purification efficiency of ammonia, it is only a guide, but a larger gas-liquid partition coefficient is considered preferable. As described above, this gas-liquid distribution coefficient is affected by temperature, and a larger gas-liquid distribution coefficient can be obtained as the partial contraction temperature is lower. This is because when the set temperature of the partial condensation operation in the first capacitor 31 is high, for example, when the temperature at which the partial condensation of ammonia is 50 ° C., the pressure of ammonia supplied to the first capacitor 31 is 1.81 MPa. This means that ammonia can be partially condensed, but it means that the separation efficiency of the hydrocarbon impurities may be reduced as compared with the case where the set temperature of the partial operation is low.

The first capacitor 31 condenses gaseous ammonia from which impurities have been adsorbed and removed by the first adsorption tower 21 or the second adsorption tower 22 and separates it into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, Oxygen, argon, carbon monoxide, carbon dioxide, and hydrocarbons having 1 to 8 carbon atoms are separated and removed as gas phase components to obtain liquid ammonia purified as liquid phase components. Specifically, the first capacitor 31 converts ammonia into gaseous phase derived from the first adsorption tower 21 or the second adsorption tower 22 by cooling treatment, and a part thereof becomes a gas phase component. And condensed into a gas phase component and a liquid phase component. Examples of the first capacitor 31 include a multi-tube capacitor and a plate heat exchanger.

In the present embodiment, the first capacitor 31 condenses 70 to 99% by volume of gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22 and separates it into a gas phase component and a liquid phase component. To do. In this case, 1 to 30% by volume, which is part of gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22, is condensed so as to become a gas phase component, It separates into a liquid phase component. As a result, it is possible to separate and remove highly volatile impurities contained in the gaseous ammonia after adsorption removal as a gas phase component, and to obtain liquid ammonia purified as a liquid phase component with a high yield.

Further, the condensation conditions in the first condenser 31 are not limited as long as a part of the gaseous ammonia led out from the first adsorption tower 21 or the second adsorption tower 22 becomes a liquid. The temperature, pressure and time may be set as appropriate. In the present embodiment, the first condenser 31 condenses gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22 at a temperature of −77 to 50 ° C. to condense the gas phase component and the liquid phase. It is preferably configured to separate into components. As a result, it is possible to obtain purified liquid ammonia by efficiently condensing gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22, and to increase the purity of the liquid ammonia. . When the temperature at the time of condensation with respect to gaseous ammonia in the first condenser 31 is less than −77 ° C., it is not preferable because much energy is required for cooling. Since the concentration of impurities contained in the liquid ammonia obtained by condensing the part becomes high, it is not preferable.

The first capacitor 31 condenses gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22 under a pressure of 0.007 to 2.0 MPa to condense a gas phase component and a liquid phase component. It is preferable that it is comprised so that it may isolate | separate. When the pressure at the time of condensation with respect to gaseous ammonia in the first capacitor 31 is less than 0.007 MPa, the temperature for condensing ammonia is lowered, so that a lot of energy is required for cooling, which is not preferable. If the pressure exceeds 2.0 MPa, the temperature at which ammonia is condensed becomes high, which is not preferable because the concentration of impurities contained in liquid ammonia obtained by condensing a part of ammonia is increased.

In the ammonia purification system 100 of the present embodiment, the first condenser 31 condenses a part of gaseous ammonia after adsorption removal by the first adsorption tower 21 or the second adsorption tower 22 to vapor phase component and liquid phase component. Therefore, highly volatile impurities can be separated and removed as a gas phase component to obtain liquid ammonia purified as a liquid phase component. Therefore, ammonia can be purified with a simplified system without providing a distillation section as in the prior art.

The first capacitor 31 is connected to a third pipe 73 and a fourth pipe 74 provided with a fifth valve 85. The third pipe 73 is connected between the first capacitor 31 and the recovery tank 4.

In the first capacitor 31, highly volatile impurities separated and removed from ammonia as a gas phase component are discharged to the outside of the system through the fourth pipe 74 with the fifth valve 85 being opened. In the first capacitor 31, the liquid ammonia obtained as the liquid phase component is supplied to the recovery tank 4 through the third pipe 73.

The recovery tank 4 stores the condensed liquid ammonia obtained as a liquid phase component by the first condenser 31. The recovery tank 4 is preferably controlled at a constant temperature and pressure so that the condensed ammonia can be stored as liquid ammonia.

In the upper part of the recovery tank 4, a gas phase is formed in a state where liquid ammonia is stored, and a fifth pipe 75 provided with a sixth valve 86 is connected to the gas phase portion. The fifth pipe 75 is also connected to the second capacitor 32. That is, the fifth pipe 75 is connected between the collection tank 4 and the second capacitor 32. The liquid ammonia derived from the first capacitor 31 and stored in the recovery tank 4 may contain a very small amount of highly volatile impurities. By leaving the liquid ammonia in the recovery tank 4 for a predetermined time (5 to 10 hours), a very small amount of highly volatile impurities contained in the liquid ammonia can be concentrated in the gas phase above the recovery tank 4. The purity of liquid ammonia can be further increased.

Gaseous ammonia containing highly volatile impurities concentrated in the gas phase above the recovery tank 4 is supplied to the second condenser 32 through the fifth pipe 75 with the sixth valve 86 opened. The

The second capacitor 32 degenerates gaseous ammonia derived from the gas phase in the upper part of the recovery tank 4 and separates it into a gas phase component and a liquid phase component, thereby removing highly volatile impurities in the gas phase component. To obtain liquid ammonia purified as a liquid phase component. Specifically, the second condenser 32 condenses ammonia by gaseous cooling to gaseous ammonia derived from the gas phase at the top of the recovery tank 4 so that a part thereof becomes a gas phase component. Thus, the gas phase component and the liquid phase component are separated.

In the present embodiment, the second capacitor 32 condenses 70 to 99% by volume of gaseous ammonia derived from the gas phase at the top of the recovery tank 4 and separates it into a gas phase component and a liquid phase component. In this case, 1 to 30% by volume of gaseous ammonia derived from the gas phase at the upper part of the recovery tank 4 is condensed so as to become a gas phase component, and the gas phase component and the liquid phase component are condensed. And will be separated. The condensation conditions such as temperature, pressure, and time in the second capacitor 32 may be the same as those for the first capacitor 31.

The second condenser 32 is connected to a sixth pipe 76 and a seventh pipe 77 provided with a seventh valve 87. The sixth pipe 76 is connected between the second capacitor 32 and the collection tank 4.

In the second capacitor 32, highly volatile impurities separated and removed from ammonia as a gas phase component are discharged to the outside of the system through the seventh pipe 77 with the seventh valve 87 opened. In the second capacitor 32, the liquid ammonia obtained as the liquid phase component is supplied to the recovery tank 4 through the sixth pipe 76.

In the lower part of the recovery tank 4, a liquid phase is formed in a state where liquid ammonia is stored, and an eighth pipe 78 provided with an eighth valve 88 is connected to the liquid phase portion. The eighth pipe 78 is also connected to the product tank 7. That is, the eighth pipe 78 is connected between the recovery tank 4 and the product tank 7. The liquid ammonia stored in the recovery tank 4 is supplied to the product tank 7 through the eighth pipe 78 with the eighth valve 88 opened.

The product tank 7 stores liquid ammonia supplied from the recovery tank 4 as product ammonia. The temperature and pressure of the product tank 7 are controlled under constant conditions so that ammonia can be stored as liquid liquid ammonia.

In the ammonia purification system 100 configured as described above, a highly volatile impurity contained in gaseous ammonia derived from the first adsorption tower 21 or the second adsorption tower 22 is removed from the gas phase component by the first condenser 31. Further, a highly volatile impurity contained in gaseous ammonia derived from the gas phase of the recovery tank 4 is separated and removed as a gas phase component by the second capacitor 32. As described above, in the ammonia purification system 100 of the present embodiment, highly volatile impurities can be removed without performing distillation accompanied by reflux, so that energy is suppressed and ammonia is efficiently purified. be able to.

In addition, the ammonia purification system 100 of the present embodiment is liquid ammonia obtained as a liquid phase component by being divided by the first capacitor 31 and the second capacitor 32 and separated into a gas phase component and a liquid phase component. Then, the liquid ammonia stored in the recovery tank 4 may be vaporized, and a re-division process for re-division of the vaporized ammonia may be performed.

Specifically, a circulation pipe for connecting the gas phase portion of the recovery tank 4 and the second pipe 72 is provided, and ammonia vaporized in the recovery tank 4 is allowed to flow through the circulation pipe, and further, What is necessary is just to make it flow into 2 piping 72, and to supply to the 1st capacitor | condenser 31 and the 2nd capacitor | condenser 32. In addition, the re-denaturation process of ammonia vaporized in the recovery tank 4 may be repeatedly performed a plurality of times.

In the ammonia purification system 100 configured as described above, the ammonia vaporized in the recovery tank 4 is divided by the first capacitor 31 and the second capacitor 32 to be separated into a gas phase component and a liquid phase component. , Highly volatile impurities are separated and removed as a gas phase component to obtain liquid ammonia as a liquid phase component. Thereby, more purified liquid ammonia can be obtained.

FIG. 2 is a diagram showing a configuration of an ammonia purification system 200 according to the second embodiment of the present invention. The ammonia purification system 200 of the present embodiment is similar to the ammonia purification system 100 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In the ammonia purification system 200, the configuration of the partial reduction unit 207 is different from the partial reduction unit 3 of the ammonia purification system 100 described above. The above-described partial reduction unit 3 includes the first capacitor 31 and the second capacitor 32, whereas the partial reduction unit 207 includes only the first capacitor 31.

In addition, the ammonia purification system 200 is configured to derive crude ammonia as liquid ammonia when the crude ammonia is derived from the raw material storage container 1 to the first adsorption tower 21 or the second adsorption tower 22. In this embodiment, the vaporizer 203 is provided between the raw material storage container 1 and the flow rate regulator 5, and when the crude ammonia is led out from the raw material storage container 1 to the vaporizer 203, the raw material storage container 1 Derived from the liquid phase as liquid crude ammonia.

A tenth pipe 201 is connected between the raw material storage container 1 and the vaporizer 203, and liquid crude ammonia led out from the raw material storage container 1 is supplied to the vaporizer 203 through the tenth pipe 201. Is done.

The tenth pipe 201 is provided with a tenth valve 202 that opens or closes the flow path in the tenth pipe 201. When supplying the liquid crude ammonia to the vaporizer 203, the tenth valve 202 is opened, and the liquid crude ammonia flows in the tenth pipe 201 from the raw material storage container 1 toward the vaporizer 203.

The vaporizer 203 vaporizes a part of the liquid crude ammonia led out from the raw material storage container 1, that is, the liquid crude ammonia is heated and vaporized at a predetermined vaporization rate, so that the vapor phase component and the liquid phase are vaporized. Separated into components, gaseous ammonia is derived. Since the vaporizer 203 vaporizes a part of the liquid crude ammonia, low-volatile impurities (for example, moisture, hydrocarbons having 9 or more carbon atoms, etc.) contained in the crude ammonia remain in the liquid phase, Gaseous ammonia in which impurities with low volatility are reduced can be derived.

In this embodiment, the vaporizer 203 vaporizes the liquid ammonia derived from the raw material storage container 1 at a vaporization rate of 90 to 95% by volume and separates it into a gas phase component and a liquid phase component. In this case, 90 to 95% by volume of liquid ammonia derived from the raw material storage container 1 is a gas phase component, and 5 to 10% by volume is a liquid phase component.

An eleventh pipe 204 provided with an eleventh valve 205 and a twelfth pipe 206 are connected to the vaporizer 203. The twelfth pipe 206 is connected between the vaporizer 203 and the flow rate regulator 5.

In the vaporizer 203, low-volatile impurities separated and removed from ammonia as a liquid phase component are discharged to the outside of the system through the eleventh pipe 204 with the eleventh valve 205 opened. Further, gaseous ammonia obtained as a gas phase component in the vaporizer 203 flows through the twelfth pipe 206 and is supplied to the first adsorption tower 21 or the second adsorption tower 22 via the flow rate regulator 5. The

The impurities contained in the gaseous ammonia supplied to the first adsorption tower 21 or the second adsorption tower 22 in this way are used for the moisture and hydrocarbons filled in the first adsorption tower 21 or the second adsorption tower 22. It is adsorbed and removed by an adsorbent having adsorbability alone. Gaseous ammonia after adsorption removal derived from the first adsorption tower 21 or the second adsorption tower 22 is supplied to the first capacitor 31. The first capacitor 31 condenses a part of the gaseous ammonia after the adsorption removal and separates it into a gas phase component and a liquid phase component, and separates and removes a highly volatile impurity as a gas phase component. Here, the partial reduction condition of the first capacitor 31 in the ammonia purification system 200 is the same as that of the first capacitor 31 in the ammonia purification system 100 described above. The ammonia purification system 200 of the present embodiment can obtain purified liquid ammonia as described above.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the examples.

<Rough ammonia>
As the crude ammonia A, industrial grade ammonia having a purity of 99.9% by weight manufactured by Ube Industries, Ltd. was used. Further, crude ammonia B having a purity different from that of the crude ammonia A was prepared. Table 4 shows the concentration of impurities contained in the crude ammonia A and the crude ammonia B.

As for the impurity concentration, the hydrocarbon concentration, hydrogen, nitrogen, oxygen, and carbon monoxide concentration are analyzed by a gas chromatograph analyzer (GC-4000, manufactured by GL Sciences Inc.), and the moisture concentration is determined by cavity ring. The analysis was performed using a down-spectroscopic analyzer (MTO-LP-H ₂ O, manufactured by Tiger Optics).

Example 1
As an adsorbent, a gaseous adsorbent was placed in a cylindrical adsorption tower (length: 50 cm, inner diameter: 2 cm) packed with synthetic zeolite MS-13X (F-9, manufactured by Tosoh Corporation) having adsorption ability for moisture and hydrocarbons alone. Crude ammonia A was passed under conditions of a temperature of 25 ° C. and a pressure of 0.4 MPa.

Gaseous ammonia derived from the adsorption tower is supplied to a SUS multi-tube condenser (first condenser) under the conditions of a temperature of −10 ° C. and a pressure of 0.4 MPa, and 95% by volume of the supplied ammonia is supplied. It condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated by highly volatile impurities) corresponding to 5% by volume of ammonia supplied to the multitubular capacitor (first capacitor) is removed from the upper portion of the multitubular capacitor (first capacitor). Drained and removed.

Next, liquid ammonia obtained as a liquid phase component in the multi-tube condenser (first condenser) was supplied to the recovery tank. Then, the liquid ammonia stored in the recovery tank is allowed to stand for 5 hours or longer, and the gas phase component (2% by volume of liquid ammonia) in the recovery tank is supplied to the multi-tube condenser (second condenser). 95% by volume of the ammonia was condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated by highly volatile impurities) corresponding to 5% by volume of ammonia supplied to the multitubular capacitor (second capacitor) is removed from the upper portion of the multitubular capacitor (second capacitor). Drained and removed.

(Example 2)
As an adsorbent, gaseous crude ammonia A was placed at a temperature of 40 ° C. in a cylindrical tubular adsorption tower (length: 50 cm, inner diameter: 2 cm) packed with synthetic zeolite MS-5A having adsorption ability for moisture and hydrocarbons alone. It was passed under the condition of pressure 0.6 MPa.

Gaseous ammonia derived from the adsorption tower is supplied to a SUS multi-tubular condenser (first condenser) under the conditions of a temperature of −5 ° C. and a pressure of 0.4 MPa. The volume% was condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated with highly volatile impurities) corresponding to 10% by volume of ammonia supplied to the multitubular capacitor (first capacitor) is removed from the upper portion of the multitubular capacitor (first capacitor). Drained and removed.

Next, liquid ammonia obtained as a liquid phase component in the multi-tube condenser (first condenser) was supplied to the recovery tank. Then, the liquid ammonia stored in the recovery tank is allowed to stand for 5 hours or longer, and the gas phase component (2% by volume of liquid ammonia) in the recovery tank is supplied to the multi-tube condenser (second condenser). 90% by volume of ammonia was condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated with highly volatile impurities) corresponding to 10% by volume of ammonia supplied to the multitubular capacitor (second capacitor) is removed from the upper portion of the multitubular capacitor (second capacitor). Drained and removed.

(Example 3)
As an adsorbent, a gaseous crude ammonia B was placed at a temperature of 25 ° C. in a cylindrical tubular adsorption tower (length: 50 cm, inner diameter: 2 cm) filled with synthetic zeolite MS-13X having adsorption ability for water and hydrocarbons alone. It was passed under the condition of pressure 0.4 MPa.

Gaseous ammonia derived from the adsorption tower is supplied to a SUS multi-tube condenser (first condenser) under the conditions of a temperature of −10 ° C. and a pressure of 0.4 MPa, and 95% by volume of the supplied ammonia is supplied. It condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated by highly volatile impurities) corresponding to 5% by volume of ammonia supplied to the multitubular capacitor (first capacitor) is removed from the upper portion of the multitubular capacitor (first capacitor). Drained and removed.

Next, liquid ammonia obtained as a liquid phase component in the multi-tube condenser (first condenser) was supplied to the recovery tank. Further, the liquid ammonia stored in the recovery tank was re-denaturated. Specifically, the liquid ammonia stored in the recovery tank is allowed to stand for 5 hours or more, and the gas phase component (2% by volume of liquid ammonia) in the recovery tank is supplied to the multi-tube condenser (second condenser). , 95% by volume of the supplied ammonia was condensed and separated into a gas phase component and a liquid phase component. A gas phase component (concentrated by highly volatile impurities) corresponding to 5% by volume of ammonia supplied to the multitubular capacitor (second capacitor) is removed from the upper portion of the multitubular capacitor (second capacitor). Drained and removed.

(Comparative Example 1)
A cylindrical tube filled with the same volume of synthetic zeolite MS-3A (A-3, manufactured by Tosoh Corporation) having an adsorption capacity for moisture and activated carbon (Kuraray GG, manufactured by Kuraray Chemical Co., Ltd.) having an adsorption capacity for hydrocarbons. Gaseous crude ammonia A was passed through an adsorption tower (length 50 cm, inner diameter 2 cm) under conditions of a temperature of 25 ° C. and a pressure of 0.4 MPa.

Gaseous ammonia derived from the adsorption tower was supplied to a SUS jacketed distillation tower under a pressure of 0.4 MPa. The distillation column was temperature-controlled with a refrigerant having a temperature of −10 ° C., and the reflux ratio was set to 20. From the top of the distillation column, 7% by volume of ammonia with respect to the supplied ammonia was discharged, and from the bottom of the distillation column, 93% by volume of liquid ammonia with respect to the supplied ammonia was led out. And the liquid ammonia led out from the tower bottom of the distillation tower was stored in the collection tank.

(Comparative Example 2)
A cylindrical crude adsorption tower (length: 50 cm, inner diameter: 2 cm) filled with activated carbon (Kuraray GG, manufactured by Kuraray Chemical Co., Ltd.) having an adsorption capacity for hydrocarbons as an adsorbent is mixed with gaseous crude ammonia A at a temperature of 25 It was passed under the conditions of ° C and pressure 0.4 MPa.

Gaseous ammonia derived from the adsorption tower is supplied to a SUS multi-tube condenser under the conditions of a temperature of −10 ° C. and a pressure of 0.4 MPa, and 95% by volume of the supplied ammonia is condensed to the gas phase. Separated into component and liquid phase component. A gas phase component corresponding to 5% by volume of ammonia supplied to the multitubular capacitor was discharged from the upper portion of the multitubular capacitor and removed.

Next, liquid ammonia obtained as a liquid phase component in the multi-tube condenser was supplied to the recovery tank. Then, the liquid ammonia stored in the recovery tank was allowed to stand for 5 hours or more, and the gas phase component in the recovery tank (2% by volume of liquid ammonia) was discharged from the upper part of the recovery tank and removed.

<Analytical results of impurity concentration in ammonia>
In Examples 1 to 3 and Comparative Examples 1 and 2, the impurity concentration of liquid ammonia stored in the recovery tank was analyzed. The analysis results are shown in Table 5.

As is apparent from the results in Table 5, the liquid ammonia obtained by the ammonia purification method of Examples 1 and 2 was the liquid ammonia obtained by the ammonia purification method of Comparative Example 1 including a distillation removal step using a distillation column. It is equivalent in purity.

Further, the liquid ammonia obtained by the ammonia purification method of Comparative Example 2 contains a large amount of moisture. This is because, as the adsorbent packed in the adsorption tower, activated carbon that does not have the ability to adsorb moisture and only has the ability to adsorb hydrocarbons was used. It is because it concentrated in the liquid ammonia isolate | separated as a phase component.

From the above results, the method for purifying ammonia in Examples 1 and 2 can obtain high-purity liquid ammonia even though it does not include a distillation removal step by a distillation column. It can be seen that ammonia can be efficiently purified while suppressing energy consumption.

Further, in Example 3, although crude ammonia B having low purity (high impurity concentration) was used, finally (after re-denaturation treatment: second condensation), Examples 1, 2 and High purity liquid ammonia equivalent to or higher than that of Comparative Example 1 can be obtained. From this result, it can be seen that the ammonia purification method of Example 3 performs re-denaturation treatment of the ammonia vaporized in the recovery tank, so that more purified liquid ammonia can be obtained.

The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all points, and the scope of the present invention is shown in the scope of claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the claims are within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Raw material storage container 2 Adsorption part 3,207 Partial reduction part 4 Collection | recovery tank 5 Flow regulator 6 Pressure gauge 7 Product tank 21 1st adsorption tower 22 2nd adsorption tower 31 1st capacitor 32 2nd capacitor 61 Analysis part 71 1st Piping 72 2nd piping 73 3rd piping 74 4th piping 75 5th piping 76 6th piping 77 7th piping 78 8th piping 79 9th piping 81 1st valve 82 2nd valve 83 3rd valve 84 4th valve 85 5th valve 86 6th valve 87 7th valve 88 8th valve 89 9th valve 100,200 Ammonia purification system 201 10th piping 202 10th valve 203 Vaporizer 204 11th piping 205 11th valve 206 12th piping

Claims (7)

1. A method for purifying crude ammonia containing impurities,
   An adsorption removal step of adsorbing and removing impurities contained in the crude ammonia by an adsorbent having an adsorption ability for moisture and hydrocarbons alone;
   Ammonia from which impurities have been adsorbed and removed in the adsorption removal step is fractionated and separated into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and carbon number 1 And a fractionation step of separating and removing hydrocarbons of 8 to 8 as a gas phase component to obtain liquid ammonia as a liquid phase component.
2. The liquid ammonia obtained in the partial condensation step is vaporized, and the vaporized ammonia is separated and separated into a gas phase component and a liquid phase component, whereby impurities are separated and removed as a gas phase component, and a liquid phase The method for purifying ammonia according to claim 1, further comprising a re-denaturation step of obtaining liquid ammonia as a component.
3. The method for purifying ammonia according to claim 1 or 2, wherein the adsorbent used in the adsorption removal step is a porous synthetic zeolite.
4. The method for purifying ammonia according to claim 3, wherein the synthetic zeolite is a synthetic zeolite having a pore diameter of 5 to 9 mm.
5. 5. The partial reduction process according to claim 1, wherein 70 to 99% by volume of ammonia from which impurities have been adsorbed and removed in the adsorption removal process is condensed and separated into a gas phase component and a liquid phase component. The method for purifying ammonia according to any one of the above.
6. The ammonia in which impurities have been adsorbed and removed in the adsorption removal step is condensed in the partial condensation step at a temperature of −77 to 50 ° C. to be separated into a gas phase component and a liquid phase component. 6. The method for purifying ammonia according to any one of 1 to 5.
7. An ammonia purification system for purifying crude ammonia containing impurities,
   An adsorbing part that adsorbs and removes impurities contained in the crude ammonia by an adsorbent having an adsorption ability for water and hydrocarbons alone;
   The ammonia from which the impurities are adsorbed and removed by the adsorbing part is fractionated and separated into a gas phase component and a liquid phase component, so that hydrogen, nitrogen, oxygen, argon, carbon monoxide, carbon dioxide, and carbon number of 1 to And a fractionation unit for separating and removing 8 hydrocarbons as a gas phase component to obtain liquid ammonia as a liquid phase component.

Images