JP2016188154A - Method for purifying ammonia - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying ammonia, in which high-purity ammonia can be obtained by using a minimum number of impurity removal means while suppressing an equipment cost or a running cost.SOLUTION: The method for purifying ammonia comprises: a liquid sampling step of sampling crude ammonia as liquid ammonia; a first oil content removing step of introducing the sampled liquid ammonia into a liquid-phase filter to remove the oil content thereof; a vaporizing step of vaporizing the liquid ammonia, the oil content of which is removed at the first oil content removing step, in a vaporizer; a pressure adjusting step of adjusting the pressure of the vaporized ammonia gas to a preset pressure; a second oil content removing step of removing the oil content, which is not removed at the first oil content removing step and remains in the vaporized ammonia gas, by using a gas-phase filter; and a water content removing step of removing the water content in the ammonia gas by using an adsorbent.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for purifying ammonia, and in particular, a method for purifying ammonia to obtain high-purity ammonia suitable for using anhydrous ammonia or industrial ammonia as a raw material for producing semiconductor elements such as gallium nitride films. About.

  Manganese oxide and other specific metal oxides can be used to purify crude ammonia such as anhydrous ammonia and industrial ammonia containing various impurities to remove impurities and obtain high-purity ammonia that can be used as a raw material for manufacturing semiconductor devices. Various purification methods have been proposed, such as a method using a mixture of the first metal oxide and a mixture of a specific first metal oxide and a second metal oxide dispersed on a porous support. (For example, refer to Patent Documents 1 and 2.)

JP 2004-142987 A JP 2005-169392 A

  However, although the conventional purification methods can purify ammonia to a certain high purity, they all have a problem of high equipment costs and running costs.

  Accordingly, an object of the present invention is to provide a method for purifying ammonia that can obtain high-purity ammonia while minimizing facility costs and running costs with minimal impurity removal means.

  In order to achieve the above-mentioned object, the ammonia purification method of the present invention is a liquid sampling method in which the crude ammonia is collected as liquid ammonia in the ammonia purification method for obtaining high purity ammonia by removing impurities in the raw crude ammonia. A first oil component removing step for removing the oil component by introducing the collected liquid ammonia into the liquid phase filter, a vaporizing step for vaporizing the liquid ammonia after the first oil component removing step with an evaporator, A pressure adjusting step for adjusting the pressure to a preset pressure, a second oil removing step for removing oil remaining in the ammonia gas that has not been removed in the first oil removing step by a gas phase filter, and an adsorption And a moisture removal step of removing moisture in the ammonia gas by the agent.

  Further, in the ammonia purification method of the present invention, the adsorbent is MS3A, MS4A or MS5A of synthetic zeolite filled in a plurality of adsorption cylinders operated by switching between an adsorption step and a regeneration operation, The regeneration operation for regenerating the adsorbed adsorbent includes a first purge stage in which purge gas is circulated in the adsorption cylinder while purging moisture while heating the adsorbent while maintaining the operating pressure of the water removal step, After the purge stage is finished, the high purity ammonia gas is introduced into the adsorption cylinder, the second purge stage in which the high purity ammonia is circulated in the cylinder, and the heating is stopped while continuing the circulation of the high purity ammonia after the completion of the second purge stage. And a cooling step for cooling the adsorption cylinder in a state in which the pressure is maintained at the operating pressure after the cooling step is completed.

  In addition, the oil removal management in the first oil removal step is performed with the amount of oil stored in the drain trap provided in the liquid phase filter, and the oil removal management in the second oil removal step is performed on the gas inflow side and the gas of the gas phase filter. It is characterized by the fact that it is performed with a differential pressure from the outflow side.

  Furthermore, a final purification step for removing water, oxygen, carbon monoxide, and carbon dioxide by a catalyst and an adsorbent is performed after the water removal step, and the adsorbent in the final purification step is used as a reducing gas. It is characterized by playing in.

  According to the method for purifying ammonia of the present invention, high purity ammonia can be obtained by purifying crude ammonia with a simple equipment configuration.

It is explanatory drawing which shows an example of the ammonia purification apparatus which can implement the purification method of ammonia of this invention. It is a figure which shows the difference in the water concentration by the presence or absence of an activated carbon filter. It is a figure which shows the change of the moisture concentration in the exit gas at the time of regeneration operation. It is explanatory drawing of the ammonia purification apparatus incorporating the final purification process.

  First, in developing the present invention, impurities in various generally available ammonia containers and ammonia gas being supplied were investigated. Table 1 shows the results of measuring impurity components contained in the gas phase and liquid phase in a 50 kg ammonia container obtained from three companies, Company A, Company B, and Company C, and products of high-purity ammonia that are commercially available. The standard value is shown.

  As a result, the main impurities are hydrogen, methane, carbon dioxide, carbon monoxide, oxygen and moisture, and each of these impurities varies depending on the storage state in the container, but hydrogen, methane, carbon dioxide, Since carbon monoxide and oxygen are components having a lower boiling point than ammonia, they are easily concentrated on the gas phase side. For this reason, when the gas phase in the container is collected, the impurity concentration changes greatly and the concentration also increases in conjunction with the change in the storage liquid temperature accompanying the flow rate fluctuation. On the other hand, when the liquid phase in the container is collected, these impurities in the supply gas are extremely small and are below the required impurity concentration. It will be good.

  On the other hand, in the ammonia production process, there is a possibility that lubricating oil for preventing wear of sliding parts such as compressors for compressing raw materials and compressors for refrigerators used for cooling may be mixed into the product ammonia gas. is there. For this reason, when refining ammonia, it is necessary to remove the oil contained in the ammonia, and for each of the impurities, since the liquid phase in the container is collected, the amount other than moisture is extremely small. It is only necessary to remove moisture.

  FIG. 1 shows an example of an ammonia purification apparatus that can carry out the ammonia purification method of the present invention. This ammonia refining apparatus is for performing a storage tank or container 11 storing anhydrous ammonia or industrial ammonia as raw raw crude ammonia, and a liquid sampling process for collecting liquid phase ammonia as liquid ammonia from the storage tank or container 11. A liquid sampling tube 12, a liquid phase filter 13 for performing a first oil component removal step for removing oil in the liquid ammonia collected by the liquid sampling tube 12, and a vaporization step for vaporizing the liquid ammonia after the first oil component removal step are performed. Vaporized without being removed in the evaporator 14, the pressure regulator 15 that performs a pressure adjustment step of adjusting the pressure of the vaporized ammonia gas to a preset pressure, and the first oil component removal step in the liquid phase filter 13. A gas phase filter 16 for performing a second oil removal step for removing oil remaining in the ammonia gas, and in the ammonia gas after oil removal Moisture and a moisture adsorbing column 17 for water removal step of removing the adsorbent.

  That is, the oil contained in the liquid ammonia taken out from the container 11 is removed by the liquid phase filter 13 and then introduced into the evaporator 14 to be gasified. After adjusting the supply pressure with the pressure regulator 15, the gasified ammonia gas is introduced into the gas-phase filter 16 to remove fine particles and oil mist in the gas, and finally filled with an adsorbent for moisture removal. The gas is supplied to each process using high-purity ammonia after passing through the moisture adsorption cylinder 17.

  As described above, the liquid phase filter 13 is for removing oil such as lubricating oil mixed in ammonia in the ammonia production process. When liquid ammonia is used as a raw material as in the present invention, an evaporator for gasifying ammonia is required before being supplied to the user. However, if oil is mixed in liquid ammonia, Oil, which is not compatible with liquid ammonia, is heavier than liquid ammonia and hard to vaporize, so it stays at the bottom of the evaporator, causing heat exchange efficiency and causing contamination, and also has a negative effect on downstream impurity removal performance Will be affected. For this reason, long-term continuous operation of the apparatus becomes possible by removing most of the oil component in the liquid ammonia in the previous stage of the evaporator 14 that performs the vaporization step.

  As the liquid phase filter 13, a coalescer type used for liquid-liquid separation such as oil-water separation is suitable. In this coalescer method, minute droplets are coarsened and separated by using a coarse filter such as media having relatively large pores for minute target components in the mixed solution. In combination with a filter having a shielding effect, a highly efficient oil collecting rate can be obtained. The oil removal management in the liquid phase filter 13 can be performed by the amount of oil stored in the drain trap 13 a provided in the lower part of the liquid phase filter 13.

  On the other hand, although it is conceivable to use activated carbon that adsorbs oil as a filter, activated carbon adsorbs and desorbs moisture, and thus is not suitable as the liquid phase filter 13. FIG. 2 shows an example of measuring changes in the amount of water when supplying a cylinder filled with activated carbon as a filter for collecting oil and when not using a filter when supplying industrial ammonia. .

  As shown in FIG. 2A, when the supply is resumed after the supply of ammonia is temporarily stopped, the moisture adsorbed on the activated carbon during the previous stage of ammonia supply is desorbed from the activated carbon and resumed in the supply gas. Along with this, ammonia containing a high concentration of water is supplied. On the other hand, as shown in FIG. 2 (B), when the activated carbon filter is not used, the water concentration only slightly increases at the same time when the supply is resumed. Since this shows the same tendency when the flow rate of ammonia changes, it can be said that it is not preferable to use activated carbon when supplying high-purity ammonia.

  The evaporator 14 can be of any structure as long as it can vaporize liquid ammonia, but a shell and coil type in which a coil 14b through which ammonia flows is disposed in a shell 14a into which a heating medium is introduced is preferable. The coil-type evaporator has a simple structure and a storage capacity of the heating medium in the shell 14a, so that the heat capacity can be increased and the temperature change of the load fluctuation due to the fluctuation of the ammonia gas supply amount is prevented. Has the advantage of being able to. However, when the oil removal by the liquid phase filter 13 is insufficient, there is a possibility that the oil will stay inside the coil 14b. Therefore, it is preferable to provide drainage.

  The pressure regulator 15 adjusts the pressure according to the required pressure at the place where the ammonia gas is used. If the pressure regulator 15 can be adjusted to a predetermined pressure, a commercially available pressure regulator, expansion valve or secondary side pressure can be adjusted. Arbitrary types can be used, such as those that are detected and controlled by a control valve. The pressure regulator 15 can be provided at the rear stage of the adsorption cylinder 17 or the like. However, since the gas temperature is lowered by adiabatic expansion, in consideration of prevention of reliquefaction and restrictions on equipment, the outlet of the evaporator 14 is provided. It is preferable to adjust the pressure to the required pressure. Moreover, since there exists a possibility that the oil component and water | moisture content contained in ammonia gas may accumulate, it is preferable to arrange | position the several pressure regulator 15 in parallel, and to be able to switch.

  The gas phase filter 16 is used to prevent the moisture adsorption cylinder 17 in the final process from being contaminated by removing a small amount of oil remaining in the ammonia gas without being removed by the liquid phase filter 13. In addition, it is possible to use a fine particle removal filter in gas having a collection mechanism using diffusion collision and Brownian motion for oil mist, solids, and the like in the gas phase. Also in the gas phase filter 16, a filter using an adsorbent such as activated carbon cannot be used for the same reason as described above. The gas phase filter 16 also functions when the ammonia gas is accompanied by oil due to a malfunction of the liquid phase filter 13. The oil removal management in the gas phase filter 16 can be performed by the differential pressure between the gas inflow side and the gas outflow side of the gas phase filter 16.

The moisture adsorbing cylinder 17 removes moisture by circulating ammonia gas in a cylinder filled with an adsorbent having moisture adsorbing ability, and synthetic zeolite such as MS3A, MS4A, MS5A is used as the adsorbent. it can. It is preferable that the moisture adsorption cylinder 17 includes a plurality of moisture adsorption cylinders 17 so that moisture can be continuously removed by alternately repeating the adsorption operation and the regeneration operation. In addition, ammonia (NH ₃ ) is close to the effective molecular diameter of moisture (H ₂ O), and also has the polar effect of zeolite, so that ammonia itself is also adsorbed. Regeneration operation is performed so as not to cause problems in the performance and equipment of the purification system.

  In the optimum regeneration operation, first, the inlet valve 17a and the outlet valve 17b of the moisture adsorption cylinder 17 that has passed through the moisture adsorption amount are closed, and the moisture adsorption cylinder 17 is temporarily stopped in the operating pressure state. A purge gas made of an inert gas, usually nitrogen gas, is circulated at a predetermined flow rate from the purge gas introduction path (not shown) into the moisture adsorption cylinder 17 and the heater 17c is activated to heat the adsorbent. . The adsorbent is heated to a preset regeneration temperature, and the operating pressure and the heating state are continued until the moisture concentration in the outlet gas (nitrogen gas) led out from the moisture adsorption cylinder 17 to the purge gas lead-out path becomes a predetermined value or less. While continuing the first purge stage.

  After the water concentration has decreased to a predetermined value, the purge gas is switched to ammonia while continuing the heating state, and the process proceeds to the second purge stage. Then, when the moisture concentration in the outlet gas (ammonia gas) becomes equal to or lower than the predetermined value, the heating is stopped, the purge gas is continuously circulated for a predetermined time, and the cooling step is performed to cool the water to the predetermined temperature. The regeneration operation is completed by performing a sealing step in which the adsorption cylinder 17 is sealed to stop introduction / extraction of the purge gas.

  FIG. 3 shows the change in the moisture concentration in the outlet gas when this regeneration operation was performed at a heating temperature of 200 ° C., nitrogen gas circulation for 10 hours, ammonia gas circulation heating for 10 hours, and ammonia gas circulation cooling for 4 hours. . In addition, the adsorbent can be sufficiently regenerated by setting the heating temperature in the regenerating operation to 200 ° C. or less, preferably 200 ° C. On the other hand, when the temperature is set higher than 200 ° C., for example, at 250 ° C., the adsorption capacity is reduced to about half compared to 200 ° C., and at 300 ° C., the adsorption capacity tends to further decrease.

  As described above, in the regeneration operation of the moisture adsorption cylinder 17, an inert gas such as nitrogen gas is used in the first stage while heating to a predetermined temperature, preferably 200 ° C., while maintaining the operating pressure, for example, 0.3 MPa. After purging and desorbing moisture in the absence of ammonia in the atmosphere, purging with the purified ammonia (high purity ammonia gas) and gas replacement in the cylinder in the second stage, the moisture adsorption cylinder 17 The filled synthetic zeolite such as MS3A, MS4A, and MS5A can be sufficiently regenerated, and sufficient water removing ability can be exhibited in the next adsorption operation.

  FIG. 4 shows an example in which a final purification cylinder 18 for performing a final purification step for removing moisture, oxygen, carbon monoxide and carbon dioxide is incorporated in the subsequent stage of the moisture adsorption cylinder 17 of the ammonia purification apparatus. In the following description, the same components as those of the ammonia purifying apparatus shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The final purification cylinder 18 is filled with a catalyst 18a containing nickel and nickel oxide on the upstream side in the in-cylinder gas flow direction, and with an adsorbent 18b made of MS3A on the downstream side. As a final purification step, the impurity concentration in the high-purity ammonia gas can be further reduced, and impurities due to leakage in the middle of the piping can be removed. The regeneration operation of the final purification cylinder 18 is preferably performed using a reducing gas, and it is desirable to use high-purity ammonia gas particularly in the final stage of the regeneration operation.

DESCRIPTION OF SYMBOLS 11 ... Container, 12 ... Liquid collection tube, 13 ... Liquid phase filter, 13a ... Drain trap, 14 ... Evaporator, 14a ... Shell, 14b ... Coil, 15 ... Pressure regulator, 16 ... Gas phase filter, 17 ... Water adsorption Tube, 17a ... Inlet valve, 17b ... Outlet valve, 17c ... Heater, 18 ... Final refined tube, 18a ... Catalyst, 18b ... Adsorbent

Claims (5)

  In a method for purifying ammonia, which removes impurities in crude ammonia as a raw material to obtain high purity ammonia, a liquid collection step for collecting the crude ammonia as liquid ammonia, and introducing the collected liquid ammonia into a liquid phase filter for oil content A first oil removing step for removing water, a vaporizing step for vaporizing the liquid ammonia after the first oil removing step with an evaporator, a pressure adjusting step for adjusting the pressure of the vaporized ammonia gas to a preset pressure, A second oil removing step for removing oil remaining in the vaporized ammonia gas without being removed in the first oil removing step by a gas phase filter; and a moisture removing step for removing moisture in the ammonia gas by the adsorbent. A method for purifying ammonia.   The adsorbent is a synthetic zeolite MS3A, MS4A or MS5A filled in a plurality of adsorption cylinders operated by switching between an adsorption step and a regeneration operation, and the regeneration operation for regenerating the adsorbent adsorbing moisture is: A first purge stage for purging moisture by circulating a purge gas through the adsorption cylinder while heating the adsorbent while maintaining the operating pressure in the moisture removal step, and a high purity ammonia gas adsorbing cylinder after completion of the first purge stage A second purge stage for introducing high-purity ammonia into the cylinder after introduction into the cylinder, a cooling stage for stopping heating and cooling while continuing the circulation of the high-purity ammonia after completion of the second purge stage, and after completion of the cooling stage The method for purifying ammonia according to claim 1, further comprising a sealing step of sealing the adsorption cylinder while maintaining a pressure at the operating pressure.   Oil removal management in the first oil removal step is performed with the amount of oil stored in the drain trap provided in the liquid phase filter, and oil removal management in the second oil removal step is performed on the gas inflow side and gas outflow side of the gas phase filter. The method for purifying ammonia according to claim 1 or 2, wherein the method is carried out at a pressure difference between   The ammonia according to any one of claims 1 to 3, wherein a final purification step of removing water, oxygen, carbon monoxide, and carbon dioxide by a catalyst and an adsorbent is performed after the water removal step. Purification method.   The method for purifying ammonia according to claim 4, wherein the adsorbent in the final purification step is regenerated with a reducing gas.

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