Method for producing magnesium oxide

Abstract

This invention provides a method for stably mixing two or more types of magnesium oxide with different levels of reactivity in a method for producing magnesium oxide. [Solution] The method for producing magnesium oxide comprises an input step, a mixing step, and a storage step. In the input step, magnesium oxides with different levels of activity are introduced from a raw material tank 11, in which each of the magnesium oxides is stored, into a corresponding storage tank 12. In the mixing step, each of the magnesium oxides introduced into the storage tank 12 is mixed in a mixer 40. In the storage step, the mixed magnesium oxide mixed in the mixer 40 is stored in a product tank 13. All of the input step, mixing step, and storage step are carried out in a closed system.

Description

[Technical Field]

[0001] This invention relates to a method for producing magnesium oxide. [Background technology]

[0002] Magnesium oxide is known to be used in a variety of applications. For example, Patent Document 1 discloses magnesium oxide for annealing separation agents containing boron, characterized in that the ratio of three-coordinate boron in the boron contained in the magnesium oxide is 55 to 70%. Patent Document 2 discloses magnesium oxide with a BET specific surface area of ​​7 to 50 m². 2 Magnesium oxide granules for pharmaceutical or food additive use are disclosed, having a concentration of / g and a CAA80 / CAA40 ratio of 2 to 7. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-176144 [Patent Document 2] International Publication No. 2015 / 128940 [Overview of the project] [Problems that the invention aims to solve]

[0004] Patent Document 1 states that magnesium oxide for annealing separation agents is obtained by mixing two or more types of magnesium oxide. However, Patent Document 1 does not describe a specific mixing method. Patent Document 2 states that magnesium oxide granules are obtained by mixing medium-activity magnesium oxide and low-activity magnesium oxide in a weight ratio of 10:90 to 80:20. However, Patent Document 2 does not describe a specific mixing method.

[0005] When mixing two or more types of magnesium oxide with different levels of activity to produce new magnesium oxide, there is a concern that the desired properties of magnesium oxide may not be produced depending on the mixing method.

[0006] An object of the present invention is to provide a method for stably mixing two or more types of magnesium oxides having different activities in a method for producing magnesium oxide.

Means for Solving the Problems

[0007] The present invention includes the following respective disclosures.

[0008] ​​​​​​​​​​​​​​​​​​​​3 / cm 2 It is made of a material whose material content is less than or equal to min.

[0011] (Fourth Disclosure) In the fourth disclosure, in the second or third disclosure, the ratio A / B of the cross-sectional area A of the inlet of the chute to the cross-sectional area B of the outlet of the chute is between 1.0 and 2.5.

[0012] (Fifth Disclosure) In the fifth disclosure, in any of the first to fourth disclosures, at least one of the transport of the magnesium oxide from the raw material tank to the storage tank in the input process, and the transport of the magnesium oxide from the mixer to the product tank in the storage process, is by pressurized transport.

[0013] (Disclosure 6) In the sixth disclosure, in the fifth disclosure, the mixing ratio of air and magnesium oxide in the above-mentioned pressurized transport is defined by the following formula: Mixing ratio = Mass of magnesium oxide (kg) / Mass of air (kg). At that time, when the CAA 40% of the magnesium oxide is 40 seconds or more and less than 100 seconds, the mixing ratio shall be 15 or less. When the CAA 40% of the magnesium oxide is 100 seconds or more and less than 3000 seconds, the mixing ratio shall be 10 or less.

[0014] (Disclosure No. 7) In the seventh disclosure, as in the sixth disclosure, the air described above has a relative humidity of 0-60% and a temperature of 0-35°C.

[0015] (Disclosure No. 8) In the eighth disclosure, in any of the first to seventh disclosures, the supply rate of the magnesium oxide conveyed to the mixer in the mixing step is as follows: When the CAA 40% of the magnesium oxide is 40 seconds or more but less than 100 seconds, the supply rate is 1.8 to 2.4 kg / min. When the CAA 40% of the magnesium oxide is 100 seconds or more but less than 3000 seconds, the supply rate is 0.1 to 0.8 kg / min. [Effects of the Invention]

[0016] According to the present invention, a method for stably mixing two or more types of magnesium oxide with different levels of reactivity can be provided in a method for producing magnesium oxide. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing an example of the configuration of an apparatus used in the method for producing magnesium oxide according to the first embodiment. [Figure 2] This is a schematic diagram showing an example of the configuration of an apparatus used in the method for producing magnesium oxide according to the second embodiment. [Figure 3] This is a photograph showing the magnesium oxide adhering to the inside of the conveying screw 22-1 after the production of mixed magnesium oxide in Comparative Example 1. [Figure 4] Figure 3 is a photograph showing the inside of the transport screw 22-1 after the removal of the attached magnesium oxide. [Modes for carrying out the invention]

[0018] (First Embodiment) The method for producing magnesium oxide according to the first embodiment will be described below.

[0019] [Method for producing magnesium oxide] The magnesium oxide production method according to this embodiment is a method for producing new magnesium oxide by mixing two or more types of magnesium oxide with different levels of activity. The production method comprises an input step, a mixing step, and a storage step. Each step will be described below.

[0020] (1) Feeding process The input process is a process of inputting magnesium oxides with different activities from the raw material tanks in which each of the magnesium oxides is stored into the corresponding storage tanks. That is, in this process, the magnesium oxide serving as the raw material is conveyed from the raw material tank to the predetermined storage tank corresponding to the magnesium oxide and input into the storage tank.

[0021] As the magnesium oxide serving as the raw material, a plurality of types of magnesium oxides are used. The plurality of types of magnesium oxides have different activities. The plurality of types of magnesium oxides are stored in separate raw material tanks for each type. That is, one raw material tank stores magnesium oxide of one type of activity. Therefore, at least the same number of raw material tanks as the number of types of magnesium oxides are provided corresponding to the plurality of types of magnesium oxides. Note that two or more raw material tanks may store the same type of magnesium oxide. In that case, the number of raw material tanks is more than the number of types of magnesium oxides.

[0022] The raw material tank is a tank for receiving magnesium oxide used as the raw material stored in a container such as a flexible container. The raw material tank is formed of a material that does not allow outside air to pass through. As the material, the air permeability is 1500 cm 3 / cm 2 ·min or less, preferably 1000 cm 3 / cm 2 ·min or less, and there is no particular limitation as long as it does not react with magnesium oxide. Examples of the material include metals and synthetic resins. Examples of the metal include alloy steels such as carbon steel and stainless steel, steels such as cast iron, nickel alloys, and non-ferrous metals such as aluminum. Examples of the synthetic resin include polyolefin-based resins such as polyethylene and polypropylene, polyvinyl chloride, polyester-based resins such as polyethylene terephthalate, and silicone-based resins. However, the method for measuring the air permeability will be described later.

[0023] Furthermore, the raw material tank may be waterproofed or water-repellent on its inner and / or outer surfaces. This can further suppress the absorption of moisture by magnesium oxide.

[0024] The activity of magnesium oxide, that is, the reactivity of magnesium oxide with other substances, is not particularly limited. Examples of such activity include citric acid activity (CAA), specific surface area measurement based on nitrogen gas adsorption, and iodine adsorption. Here, we will use CAA. In this case, a difference in activity means a difference in CAA. CAA is expressed as the time required for a predetermined amount of magnesium oxide added to citric acid to react. For example, CAA 40% indicates the time required for 40 mol% of the total amount of magnesium oxide added to citric acid to react. The measurement method will be described later.

[0025] Magnesium oxide stored in raw material tanks is transferred from the raw material tanks to corresponding storage tanks. Here, the corresponding storage tanks are storage tanks designated as the input destinations for each of the multiple types of magnesium oxide or each of the multiple raw material tanks. Therefore, the magnesium oxide stored in each of the multiple types of magnesium oxide or each of the multiple raw material tanks is transferred to the corresponding storage tank. However, there may be one or more corresponding storage tanks. In other words, the magnesium oxide stored in each of the multiple types of magnesium oxide or each of the multiple raw material tanks is transferred to one or more corresponding storage tanks. In this case, the number of storage tanks may be greater or less than the number of types of magnesium oxide. Furthermore, magnesium oxide from separate raw material tanks may be transferred and stored in a single storage tank. However, in this case, the type of magnesium oxide transferred to the single storage tank must be the same. That is, one type of magnesium oxide with the same activity level is transferred to each storage tank.

[0026] The correspondence between "multiple raw material tanks" and "multiple storage tanks" can be "1:1", "multiple:1", or "1:multiple". However, in "1:1", one storage tank corresponds to one raw material tank. In "multiple:1", one storage tank corresponds to two or more raw material tanks that store the same type of magnesium oxide. In "1:multiple", two or more storage tanks into which the same type of magnesium oxide is supplied correspond to one raw material tank.

[0027] A storage tank is a tank for storing magnesium oxide before the mixing process. The materials used to form the storage tank and the processing that can be applied to it are the same as those for the raw material tank. In the storage tank, for example, equipment for measuring the discharged magnesium oxide may be installed to allow for the extraction of a specific amount of magnesium oxide.

[0028] (2)Mixing process The mixing process involves mixing each of the magnesium oxides introduced into the storage tanks using a mixer. In other words, this process involves transporting magnesium oxides with different levels of activity from multiple storage tanks to a mixer and mixing them within the mixer.

[0029] In multiple storage tanks, the magnesium oxide stored in one tank will have different levels of reactivity. Magnesium oxide with different levels of reactivity from these different storage tanks is transported to a mixer and mixed in the mixer. However, as mentioned above, the magnesium oxide stored in one storage tank may have the same level of reactivity, so some magnesium oxide with the same level of reactivity may be transported to the mixer and mixed in the mixer.

[0030] The mixer mixes several types of magnesium oxide transported from multiple storage tanks. The mixer is not particularly limited, and known mixers can be used. Examples of mixers include screw mixers, ribbon mixers, paddle mixers, Henschel mixers, Nauter mixers, drum mixers, and V-type mixers. The mixer has a structure that prevents outside air from entering and is covered with an airtight material. For example, at least the housing of the mixer is made of an airtight material. The airtight materials and possible processing are as previously described.

[0031] (3) Storage process The storage process involves storing the mixed magnesium oxide, which was mixed in the above-mentioned mixer, in a product tank. In other words, this process involves transporting the new magnesium oxide, i.e., the mixed magnesium oxide, formed by mixing magnesium oxides of different activity levels, from the mixer to the product tank and storing it in that product tank.

[0032] Mixed magnesium oxide, formed by mixing magnesium oxides of different activity levels and stored in product tanks, is, for example, shipped as a product.

[0033] A product tank is a tank for storing mixed magnesium oxide. The materials used to form the product tank and the processing that can be applied to it are the same as those used for a raw material tank.

[0034] In this method, the input step (1), the mixing step (2), and the storage step (3) are all carried out in a closed system. However, a closed system means that each tank and piece of equipment involved in this method has a structure that is closed to the outside and does not allow outside air to enter. In a closed system, for example, each tank and piece of equipment is equipped with a housing made of an airtight material and is connected to each other with an airtight material. Here, the airtight material has an air permeability of 1500 cm. 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2The material is less than min, and the specific material and possible processing are as described above. The tanks and equipment involved in this method, i.e., the tanks and equipment of the manufacturing facility, include multiple raw material tanks, multiple storage tanks, product tanks, a mixer, and equipment that handles the transfer of multiple magnesium oxides between these devices.

[0035] However, in this specification, air permeability refers to the air permeability determined by Method A (Fragile method) as defined in JIS L 1096 "Air permeability".

[0036] As described above, new magnesium oxide can be produced by mixing two or more types of magnesium oxide with different levels of activity.

[0037] In this manufacturing method, all processes—the input process, the mixing process, and the storage process—are conducted in a closed system. Therefore, the inflow of moisture-laden outside air into all processes can be suppressed. Consequently, the adhesion and clogging of magnesium oxide due to moisture absorption in the tanks and equipment of the manufacturing facility can be suppressed. As a result, two or more types of magnesium oxide with different reactivity levels can be stably mixed.

[0038] The magnesium oxide used as a raw material is not particularly limited, as long as the content of other substances, such as impurities, is less than 10% by mass. The content of other substances is more preferably less than 5% by mass, and more preferably less than 3% by mass. There are no particular restrictions on the method for producing such magnesium oxide as a raw material, and known methods can be used. One example of such a method is to synthesize magnesium hydroxide by reacting a magnesium raw material with an alkali raw material, and then calcining the magnesium hydroxide to obtain magnesium oxide. Examples of magnesium raw materials include water-soluble magnesium salts or their hydrates. Magnesium chloride hexahydrate, magnesium chloride dihydrate, and anhydrous magnesium chloride are preferred as magnesium raw materials. Other magnesium raw materials that may be used include seawater, brine, and bittern. When calcining magnesium hydroxide, the calcination atmosphere can be, for example, air or nitrogen. Examples of alkali raw materials include calcium hydroxide, sodium hydroxide, and potassium hydroxide. Another example of a production method is to use magnesium oxide obtained by calcining the mineral magnesite. The manufacturing method involves hydrating magnesium oxide obtained from the mineral magnesite to obtain magnesium hydroxide, and then calcining the magnesium hydroxide to obtain magnesium oxide.

[0039] Next, the method for producing magnesium oxide in this embodiment will be specifically described with reference to the drawings.

[0040] Figure 1 is a schematic diagram showing an example of the configuration of an apparatus used in the magnesium oxide production method according to the first embodiment. Apparatus 1 comprises a plurality of raw material tanks 11, a plurality of conveying screws 21, a plurality of chutes 31, a plurality of storage tanks 12, a plurality of conveying screws 22, a plurality of chutes 32, a mixer 40, a chute 33, and a product tank 13.

[0041] Each of the multiple raw material tanks 11 stores magnesium oxide, which is the raw material. In this example in Figure 1, two raw material tanks, 11-1 and 11-2, are provided. Raw material tanks 11-1 and 11-2 store magnesium oxide with different levels of reactivity. In other words, the magnesium oxide stored in raw material tank 11-1 and the magnesium oxide stored in raw material tank 11-2 have different levels of reactivity.

[0042] Each of the multiple conveying screws 21 conveys magnesium oxide from the raw material tank 11 to the chute 31. Each conveying screw 21 has its inlet connected to the raw material tank 11 and its outlet connected to the chute 31. In this example in Figure 1, conveying screw 21-1, provided for raw material tank 11-1, has its inlet connected to raw material tank 11-1 and its outlet connected to chute 31-1. Conveying screw 21-2, provided for raw material tank 11-2, has its inlet connected to raw material tank 11-2 and its outlet connected to chute 31-2.

[0043] Each of the multiple chutes 31 delivers magnesium oxide, transported by the transport screw 21, into the storage tank 12. Each chute 31 has its inlet connected to the transport screw 21 and its outlet connected to the storage tank 12. In this example in Figure 1, chute 31-1, provided for transport screw 21-1, has its inlet connected to transport screw 21-1 and its outlet connected to storage tank 12-1. Chute 31-2, provided for transport screw 21-2, has its inlet connected to transport screw 21-2 and its outlet connected to storage tank 12-2.

[0044] Each conveying screw 21 and each chute 31 is a conveying device that transports magnesium oxide from the raw material tank 11 to the storage tank 12. This conveying device is a closed-system device as described above. However, this conveying device is not limited to this example; any known closed-system conveying device can be used.

[0045] The materials forming the housing of the conveying screw 21 and each chute 31, including the conveying screw 22 and chutes 32 and 33 described later, are made of materials that do not allow outside air to pass through. The materials that do not allow outside air to pass through and the processing that can be applied are as previously described. For the chutes, soft materials, such as polyester resin or silicone resin, are particularly preferred. Using soft materials makes it easier to connect the tank and the conveying screw and allows for a certain degree of misalignment. Furthermore, any problems such as scale buildup or clogging are easier to detect, making repair and maintenance easier. In that case, the chutes may be waterproofed or water-repellent.

[0046] Each of the multiple storage tanks 12 stores the transported magnesium oxide. In the example shown in Figure 1, two storage tanks, storage tank 12-1 and storage tank 12-2, are provided. Therefore, in the example shown in Figure 1, raw material tank 11-1 and storage tank 12-1 correspond 1:1 to magnesium oxide of a predetermined activity level, and raw material tank 11-2 and storage tank 12-2 correspond 1:1 to magnesium oxide of a different activity level.

[0047] For example, the magnesium oxide from the raw material tank 11-2 may be added not only to the storage tank 12-2 but also to another storage tank 12 (not shown). Alternatively, for example, the storage tank 12-2 may contain not only the magnesium oxide from the raw material tank 11-2 but also magnesium oxide of the same activity level from another raw material tank 11 (not shown).

[0048] Each of the multiple transport screws 22 transports magnesium oxide from the storage tank 12 to the chute 32. Each transport screw 22 has its inlet connected to the storage tank 12 and its outlet connected to the chute 32. In this example in Figure 1, the transport screw 22-1 provided for storage tank 12-1 has its inlet connected to storage tank 12-1 and its outlet connected to chute 32-1. The transport screw 22-2 provided for storage tank 12-2 has its inlet connected to storage tank 12-2 and its outlet connected to chute 32-2.

[0049] Each of the multiple chutes 32 feeds the magnesium oxide transported by the conveyor screw 22 into the mixer 40. Each chute 32 has its inlet connected to the conveyor screw 22 and its outlet connected to the mixer 40. In this example in Figure 1, chute 32-1, provided for conveyor screw 22-1, has its inlet connected to conveyor screw 22-1 and its outlet connected to the mixer 40. Chute 32-2, provided for conveyor screw 22-2, has its inlet connected to conveyor screw 22-2 and its outlet connected to the mixer 40.

[0050] Each conveying screw 22 and each chute 32 is a conveying device that transports magnesium oxide from the storage tank 12 to the mixer 40. This conveying device is a closed-system device as described above. However, this conveying device is not limited to this example; any known closed-system conveying device can be used.

[0051] The mixer 40 mixes multiple magnesium oxides transported from multiple storage tanks 12. In this embodiment, the mixed magnesium oxide is also called mixed magnesium oxide. In the example in Figure 1, magnesium oxide of a predetermined activity level transported from storage tank 12-1 and magnesium oxide of a different activity level transported from storage tank 12-2 are mixed in the mixer 40.

[0052] For example, not only the magnesium oxide from the raw material tank 11-2 that was stored in storage tank 12-2, but also the magnesium oxide from the raw material tank 11-2 that was further added to another storage tank 12 (not shown) may be added to the mixer 40.

[0053] Chute 33 delivers the mixed magnesium oxide, which has been mixed in mixer 40, to product tank 13. Chute 33 has its inlet connected to mixer 40 and its outlet connected to product tank 13.

[0054] Product tank 13 stores mixed magnesium oxide. The mixed magnesium oxide can be used as magnesium oxide for the product.

[0055] The conveying screws 21 and 22 are screw conveyors that transport magnesium oxide. The chutes 31, 32, and 33 are devices that slide and receive the magnesium oxide discharged from the conveying screws 21 and 22 and the mixer 40. The conveying screws 21 and 22 and the chutes 31, 32, and 33 are the closed-system devices described above.

[0056] In the example shown in Figure 1, the method for producing magnesium oxide according to this embodiment is as follows.

[0057] First, in the input process, magnesium oxide of a predetermined activity level is introduced from the raw material tank 11-1 to the storage tank 12-1 corresponding to the magnesium oxide in the raw material tank 11-1, via the conveying screw 21-1 and chute 31-1. Similarly, magnesium oxide of other activity levels is introduced from the raw material tank 11-2 to the storage tank 12-2 corresponding to the magnesium oxide in the raw material tank 11-2, via the conveying screw 21-2 and chute 31-2.

[0058] Next, in the mixing process, the magnesium oxide introduced into storage tank 12-1 is introduced into the mixer 40 via the conveying screw 22-1 and chute 32-1. Similarly, the magnesium oxide introduced into storage tank 12-2 is introduced into the mixer 40 via the conveying screw 22-2 and chute 32-2. The magnesium oxide from storage tank 12-1 and the magnesium oxide from storage tank 12-2 are then mixed in the mixer 40.

[0059] Next, in the storage process, the mixed magnesium oxide mixed in the mixer 40 is fed into the product tank 13 via the chute 33. The fed mixed magnesium oxide is then stored in the product tank 13.

[0060] As described above, new magnesium oxide can be produced by mixing two or more types of magnesium oxide with different levels of activity.

[0061] In one embodiment of this model, the mixing step may include a conveying step and a moving step. The conveying step involves using a conveyor to transport the magnesium oxide from the storage tank to each of the first chutes of the storage tank, at a rate of supplying highly active magnesium oxide faster than the supply rate of less active magnesium oxide. The moving step involves moving the magnesium oxide transported by the conveyor to the mixer via the first chutes. In this case, each of the first chutes has an air permeability of 1500 cm². 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is made of a material whose material content is less than or equal to min.

[0062] In the example shown in Figure 1, if the magnesium oxide stored in raw material tank 11-1 has high reactivity and the magnesium oxide stored in raw material tank 11-2 has low reactivity, the conveying and moving processes of the mixing process described above will be as follows.

[0063] In the conveying process, highly active magnesium oxide is conveyed from storage tank 12-1 to chute 32-1, which is the first chute of storage tank 12-1, at a relatively fast supply rate using a conveying screw 22-1, which is a conveying machine. On the other hand, less active magnesium oxide is conveyed from storage tank 12-2 to chute 32-2, which is the first chute of storage tank 12-2, at a relatively slow supply rate using a conveying screw 22-2, which is a conveying machine.

[0064] The transfer process involves moving highly active magnesium oxide, transported by the conveyor screw 22-1, to the mixer 40 via the first chute 32-1, and moving less active magnesium oxide, transported by the conveyor screw 22-2, to the mixer 40 via the first chute 32-2. In this case, each of the first chutes, chute 32-1 and chute 32-2, has an air permeability of 1500 cm. 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is formed from a material with a material density of min or less. In this case, it is preferable that the conveying screws 22-1 and 22-2, which are the conveying devices, are closed-system equipment that does not allow outside air to pass through.

[0065] Thus, in this manufacturing method, the supply rate of highly active and easily hygroscopic magnesium oxide is made relatively fast, making it difficult for highly active magnesium oxide to absorb moisture. Furthermore, in this manufacturing method, the air permeability of the first chute that moves the magnesium oxide to the mixer is 1500 cm². 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is made of a material with a material content of min or less. This further suppresses the adhesion and clogging of magnesium oxide due to moisture absorption in the first chute and mixer, and also suppresses changes in the activity of magnesium oxide due to moisture absorption.

[0066] In one embodiment of this model, the storage step may include other transfer steps. The other transfer step is to transfer the magnesium oxide mixed in the mixer to a product tank via a second chute. In this case, the second chute has an aeration of 1500 cm². 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is made of a material whose material content is less than or equal to min.

[0067] In the example shown in Figure 1, the other transfer steps described above are as follows: The other transfer step is to transfer the magnesium oxide mixed in the mixer 40 to the product tank 13 via a second chute, which is a chute 33. In this case, the second chute, which is a chute 33, has an air permeability of 1500 cm 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is made of a material whose material content is less than or equal to min.

[0068] Thus, in this manufacturing method, the second chute that moves the mixed magnesium oxide to the product tank has an air permeability of 1500 cm². 3 / cm 2 Less than min, preferably 1000 cm 3 / cm 2 It is made of a material with a material content of less than min. This further suppresses the adhesion and clogging of magnesium oxide due to moisture absorption in the second chute and product tank, and also suppresses changes in the activity of magnesium oxide due to moisture absorption.

[0069] In one embodiment of this design, the ratio A / B of the cross-sectional area A of the chute inlet to the cross-sectional area B of the chute outlet may be 1.0 to 2.5. In this case, the chute is the first chute and / or the second chute described above. In the example in Figure 1, the chutes are chute 31 (31-1, 31-2), chute 32 (32-1, 32-2), and / or chute 33. There may be multiple outlets. In this case, the cross-sectional area B of the outlets is the sum of the cross-sectional areas of each of the multiple outlets. It is preferable that the inlet and outlets overlap when viewed from the vertical direction. This suppresses the adhesion of magnesium oxide inside the chute and allows the chute to be used effectively for transport.

[0070] Thus, in this manufacturing method, the ratio A / B of the cross-sectional area A of the chute inlet to the cross-sectional area B of the discharge port is 2.5 or less, preferably 2.0 or less. This suppresses the adhesion of magnesium oxide inside the chute. On the other hand, if the ratio A / B of the cross-sectional area A of the inlet to the cross-sectional area B of the discharge port is 1.0 or more, the chute can be effectively used for conveying.

[0071] The cross-sectional area A of the chute opening can be, for example, 100 to 3000 cm². 2 These include, 200-2000cm 2 Preferably, 300-1600cm 2 100cm is preferable. 2 With the above, the chute can be effectively used for transport, 3000cm 2 The following conditions can prevent an oversupply of magnesium oxide to the discharge point. The cross-sectional area B of the chute outlet can be, for example, 100 to 2400 cm². 2 These include, 150-1800cm 2 Preferably, 200-1400cm 2 100cm is preferable. 2 With the above, the chute can be effectively used for transport, 2400cm 2 The following conditions can suppress the adhesion of magnesium oxide within the chute.

[0072] In one embodiment of this product, the supply rate of magnesium oxide conveyed to the mixer in the mixing process may be set as follows, based on the CAA 40% of the magnesium oxide: When the CAA 40% of the magnesium oxide is 40 seconds or more and less than 100 seconds, the rate shall be 1.8 to 2.4 kg / min, preferably 1.9 to 2.2 kg / min. When the CAA 40% of the magnesium oxide is 100 seconds or more and less than 3000 seconds, the rate shall be 0.1 to 0.8 kg / min, preferably 0.1 to 0.6 kg / min. This suppresses the phenomenon in which shear force is applied to the magnesium oxide during conveyance, causing localized heat generation and partial deterioration of the magnesium oxide, which can lead to adhesion and scaling.

[0073] Thus, in this manufacturing method, when magnesium oxide has a high citric acid activity (CAA 40%) (40 seconds or more, but less than 100 seconds), the supply rate to the mixer is increased. On the other hand, when magnesium oxide has a low citric acid activity (CAA 40%) (100 seconds or more, but less than 3000 seconds), the supply rate to the mixer is decreased. This suppresses the phenomenon where shear force is applied to the magnesium oxide during transport, causing localized heat generation and partial deterioration of the magnesium oxide, which can lead to adhesion and scaling.

[0074] In particular, when conveying magnesium oxide powder using a conveyor screw, it is necessary to consider the effect of the screw's shear force on the magnesium oxide. That is, there is an appropriate screw rotation speed (= magnesium oxide supply speed) according to the activity of the magnesium oxide. Below the lower limit of the supply speed, productivity deteriorates, and above the upper limit, agglomeration and adhesion occur, and furthermore, deterioration of the magnesium oxide may occur due to localized heat generation, etc.

[0075] (Second Embodiment) Next, a method for producing magnesium oxide according to the second embodiment will be described. In this embodiment, the differences from the first embodiment will be mainly explained.

[0076] This embodiment differs from the first embodiment in that at least one of the transport of magnesium oxide from the raw material tank to the storage tank in the input process, and the transport of magnesium oxide from the mixer to the product tank in the storage process, is carried out by pressure. However, pressure transport is a method of transporting powder to the discharge point by blowing a transport gas at the transport source. A quantitative feeder or rotary valve for quantitatively introducing powder into the transport pipeline may be provided at the transport source, and a cyclone (classifier) ​​or filter may be provided at the discharge point. In this way, the gas and powder can be separated and transported continuously to the discharge point. In this embodiment, the transport source is, for example, a raw material tank or a mixer, and the discharge point is, for example, a storage tank or a product tank. The powder is, for example, magnesium oxide. Examples of gases include air and nitrogen.

[0077] The transport pipeline is formed from a material that does not allow outside air to pass through. The materials that do not allow outside air to pass through and the processing that can be applied to them have been described above, but furthermore, a material that does not allow air to pass through, has excellent mechanical strength and does not wear down during pressurized transport, such as ethylene propylene diene rubber (EPDM), is preferable. This is because it reduces the amount of magnesium oxide mixed into the material.

[0078] In this case, the transport pipeline, as well as the connections between the transport pipeline and the raw material tank and storage tank, are closed-system equipment and structures.

[0079] Thus, in this manufacturing method, a pressurized transport system is used to transport magnesium oxide in at least one of the input and storage processes. By adopting a pressurized transport system, that is, by not using gravity-only transport such as a chute, the ceiling of the manufacturing building can be kept low. This makes the manufacturing building more compact and makes it easier to control the atmosphere inside the manufacturing building. Furthermore, it is possible to suppress the adhesion and clogging of magnesium oxide due to moisture absorption in each piece of equipment in the manufacturing facility.

[0080] In one aspect of this embodiment, in the above-described pressurized transport, the mixing ratio of air, which is the transport gas, and magnesium oxide, which is the powder, is given by the following formula: Mixing ratio = Mass of magnesium oxide (kg) / Mass of air (kg). At that time, when the CAA 40% of magnesium oxide is 40 seconds or more and less than 100 seconds, the mixing ratio may be 15 or less. When the CAA 40% of magnesium oxide is 100 seconds or more and less than 3000 seconds, the mixing ratio may be 10 or less.

[0081] Thus, in this manufacturing method, when magnesium oxide has a high citric acid activity (CAA 40%) (40 seconds or more, but less than 100 seconds), the mixing ratio is increased, and less air is mixed in. On the other hand, when magnesium oxide has a low citric acid activity (CAA 40%) (100 seconds or more, but less than 3000 seconds), the mixing ratio is decreased, and more air is mixed in. This suppresses the decrease in activity due to moisture absorption from the air during pumping when the activity is high. On the other hand, it suppresses the decrease in transport efficiency during pumping when the activity is low.

[0082] In one aspect of this embodiment, in the above-described pressurized transport method, the air used as the transport gas may have a relative humidity of 0 to 60% and a temperature of 0 to 35°C.

[0083] Thus, in this manufacturing method, the air used for pressurized transport has a relative humidity of 0-60% and a temperature of 0-35°C. This further suppresses the adhesion and clogging of magnesium oxide due to moisture absorption in each piece of equipment in the manufacturing facility.

[0084] Next, the method for producing magnesium oxide in this embodiment will be specifically described with reference to the drawings.

[0085] Figure 2 is a schematic diagram showing an example of the configuration of an apparatus used in the magnesium oxide manufacturing method according to the second embodiment. Apparatus 1a differs from apparatus 1 in Figure 1 of the first embodiment in that the transport of magnesium oxide between the raw material tank 11 and the storage tank 12, and the transport of magnesium oxide between the mixer 40 and the product tank 13 are carried out by pressure transport using transport pipelines 51 and 53, respectively.

[0086] In the input process, magnesium oxide is transported from raw material tank 11-1 to storage tank 12-1 by pressurized transport using transport pipeline 51-1. Magnesium oxide is transported from raw material tank 11-2 to storage tank 12-2 by pressurized transport using transport pipeline 51-2. In the storage process, magnesium oxide is transported from mixer 40 to product tank 13 by pressurized transport using chute 33 and transport pipeline 53. [Examples]

[0087] The present invention will be further described below with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples and Comparative Examples.

[0088] (1) Raw materials Highly active magnesium oxide and lowly active magnesium oxide as raw materials were prepared. Their physical property values are as shown in Table 1 below.

[0089] (2) Example 1 and Comparative Example 1 Example 1: Using the apparatus 1a in FIG. 2, highly active magnesium oxide and lowly active magnesium oxide were mixed at a ratio of 85:15 to produce the mixed magnesium oxide of Example 1. The supply rate of the highly active magnesium oxide was 2.1 kg / min, and the supply rate of the lowly active magnesium oxide was 0.38 kg / min, and they were conveyed to the mixer 40. In the chutes 32-1, 32-2, and 33, the air permeability was 600 cm 3 / cm 2 ·min, the cross-sectional area of the inlet was 482 cm 2 , and the cross-sectional area of the outlet was 256 cm 2 . Also, the mixing ratio of air as the conveying gas and magnesium oxide as the powder was 2.3. Comparative Example 1: In the apparatus 1a in FIG. 2, the mixed magnesium oxide of Comparative Example 1 was produced in the same manner as in Example 1, except that the conveying screws 22-1 and 22-2 were modified so that outside air was taken in.

[0090] (3) Evaluation As evaluations of magnesium oxide and the mixed magnesium oxide, CAA40% (seconds), moisture content (mass %), BET specific surface area (m 2 / g), D10, D50, and D90 (μm) of the particle size distribution were determined. However, the measurement methods for each evaluation value are as follows.

[0091] <Measurement method of CAA40%> The measurement method of CAA40% is as follows. 1 × 10 of a 0.4N citric acid solution -4 m3 and an appropriate amount (2×10 -6 m 3 ) of 1% phenolphthalein solution was added to a beaker of 2×10 -4 m 3 . The solution temperature was adjusted to 30°C. While stirring the citric acid solution at 700 rpm using a magnetic stirrer, magnesium oxide of 40 mol% of the final reaction equivalent was added to the citric acid solution. Then, the time from the addition to the final reaction, that is, the time (seconds) until the citric acid was consumed and neutralized, was measured and designated as CAA40%.

[0092] <Method for Measuring Moisture Content by Ignition Loss Method> A sample of a predetermined mass is heated to a high temperature, and the change in the mass of the sample after burning or volatilizing a part of its components is measured. The change in mass, that is, the decrease, is divided by the initial predetermined mass to obtain the percentage value (mass%), and this value is taken as the moisture content.

[0093] <Method for Measuring BET Specific Surface Area> Approximately 0.26 g of the sample was weighed into the cell, vacuum degassed as a pretreatment, and heated at 105°C for 1五分钟. Then, for the cell after the pretreatment, the specific surface area by nitrogen adsorption was measured using a pore size distribution measuring device BELSORP MR6 (manufactured by Microtrac·BEL Corporation). The specific surface area (m 2 / g) was analyzed by the BET one-point method.

[0094] <Method for Measuring Particle Size Distribution (D10, D50, D90) of Magnesium Oxide> The particle size distribution (volume basis) was measured using a particle size distribution measuring device MT3300EXII (manufactured by Microtrac·BEL Corporation). First, the inside of the particle size distribution measuring device was filled with ion-exchanged water and the ion-exchanged water was circulated. Next, an appropriate amount of the sample was added thereto, and after confirming that it was within the appropriate range, it was circulated for 3 minutes and then measured. The measurement time was set to 30 seconds. The measurement was performed twice, and the average value was obtained for each of D10, D50, and D90.

[0095] (4) Results In the magnesium oxide production of Example 1, although not shown in the diagram, no magnesium oxide deposits or scale were observed on the transport screws 22-1 and 22-2 or the chutes 32-1 and 32-2. On the other hand, in the production of magnesium oxide in Comparative Example 1, magnesium oxide deposits and scale were observed on the conveyor screws 22-1 and 22-2 and the chutes 32-1 and 32-2. Figures 3 and 4 show the condition of conveyor screw 22-1. Figure 3 is a photograph showing the magnesium oxide deposits inside conveyor screw 22-1 after the production of mixed magnesium oxide in Comparative Example 1. Figure 4 is a photograph showing the condition inside conveyor screw 22-1 after the removal of the deposited magnesium oxide. From a comparison of Figures 3 and 4, it was found that in Comparative Example 1, magnesium oxide was deposited throughout the inside of conveyor screw 22-1. In particular, magnesium oxide deposits were observed on the screw shaft and the inner wall of the tube covering the screw. Aggregates of magnesium oxide were also observed. Therefore, compared to Comparative Example 1, Example 1 was able to suppress the deposit and clogging of magnesium oxide due to moisture absorption, etc.

[0096] The measurement results for each of the evaluation values ​​mentioned above are shown in Table 1 below. From the "CAA40%" result shown in Table 1, Comparative Example 1 had a higher CAA40% compared to Example 1. Therefore, it is considered that Comparative Example 1 absorbed moisture from the outside air, resulting in a decrease in activity.

[0097] As shown in Table 1, the moisture content of Example 1 was similar to that of the highly active magnesium oxide used as a raw material. However, the moisture content of Comparative Example 1 was significantly higher, about twice that of Example 1. Therefore, it is considered that in Comparative Example 1, hydration progressed due to the absorption of moisture from the ambient air.

[0098] Furthermore, as shown in Table 1, the BET specific surface area of ​​Comparative Example 1 was smaller than that of Example 1. Therefore, it is considered that aggregation occurred in Comparative Example 1 due to the absorption of moisture from the outside air.

[0099] Furthermore, from the results of "D10" to "D90" shown in Table 1, the value of "D10" is larger in Comparative Example 1 compared to Example 1, indicating that the fine particles have grown larger due to aggregation. Therefore, it is considered that aggregation occurred in Comparative Example 1 due to the absorption of moisture from the outside air.

[0100] [Table 1]

[0101] Furthermore, the results obtained using apparatus 1 in Figure 1 were generally the same as those shown in Table 1.

[0102] As can be seen from the above results, the method for producing magnesium oxide can suppress adhesion and clogging of magnesium oxide due to moisture absorption, and thereby it was possible to stably mix two or more types of magnesium oxide with different levels of activity.

[0103] The manufacturing method disclosed herein is applicable when mixing magnesium oxides with different levels of reactivity. It is particularly effective for mixing magnesium oxides where strict control of reactivity is required, specifically for the production of magnesium oxide for pharmaceutical and food additives and magnesium oxide for annealing separation agents.

[0104] The magnesium oxide production method of the present invention is not limited to the embodiments described above, and can be appropriately combined or modified without departing from the purpose and spirit of the present invention. [Explanation of Symbols]

[0105] 11, 11-1, 11-2 Raw material tanks 12, 12-1, 12-2 storage tanks 13 product tanks 21, 21-1, 21-2, 22, 22-1, 22-2 Conveyor screws 31, 32, 33 Shots 40 Mixer 51, 53 Transport pipeline

Claims

1. A method for producing magnesium oxide, A feeding step involves feeding magnesium oxides with different levels of reactivity from the raw material tanks in which each of the magnesium oxides is stored into the corresponding storage tanks. A mixing step in which each of the magnesium oxides introduced into the storage tank is mixed in a mixer, A storage process involves storing the mixed magnesium oxide, which has been mixed in the aforementioned mixer, in a product tank. Equipped with, The input step, the mixing step, and the storage step are all carried out in a closed system. Manufacturing method.

2. The aforementioned mixing step is A conveying process in which, using a conveyor, magnesium oxide with higher activity is supplied at a faster rate than magnesium oxide with lower activity is supplied from the storage tank to each of the first chutes of the storage tank, A transfer step of moving the magnesium oxide conveyed by the conveyor to the mixer via the first chute, Includes, Each of the first chutes has an air permeability of 1500 cm ３ / cm ２ - Made of a material whose material is less than or equal to min. The manufacturing method according to claim 1.

3. The aforementioned storage process is, The process includes another transfer step of moving the magnesium oxide mixed in the mixer to the product tank via a second chute, The second chute has a ventilation degree of 1500 cm ３ / cm ２ - Made of a material whose material is less than or equal to min. The manufacturing method according to claim 1.

4. The ratio A / B of the cross-sectional area A of the chute's inlet to the cross-sectional area B of the chute's outlet is 1.0 to 2.

5. The manufacturing method according to claim 2 or 3.

5. At least one of the transport of magnesium oxide from the raw material tank to the storage tank in the input process, and the transport of magnesium oxide from the mixer to the product tank in the storage process, is by pressurized transport. The manufacturing method according to claim 1.

6. In the aforementioned pressurized transport, if the mixing ratio of air and magnesium oxide is given by the following formula, The mixing ratio = Mass of magnesium oxide (kg) / Mass of air (kg) When the CAA 40% of the magnesium oxide is present for 40 seconds or more and less than 100 seconds, the mixing ratio is set to 15 or less. When the CAA content of the magnesium oxide is 40% for 100 seconds or more and less than 3000 seconds, the mixing ratio shall be 10 or less. The manufacturing method according to claim 5.

7. The aforementioned air has a relative humidity of 0-60% and a temperature of 0-35°C. The manufacturing method according to claim 6.

8. In the mixing process, the supply rate of the magnesium oxide conveyed to the mixer is: When the CAA content of the magnesium oxide is 40% or more but less than 100 seconds, the concentration should be 1.8 to 2.4 kg / min. When the CAA content of the magnesium oxide is 40% for 100 seconds or more and less than 3000 seconds, the rate is 0.1 to 0.8 kg / min. The manufacturing method according to claim 1.

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