JP4873894B2 - Method for producing high purity purified phosphoric acid - Google Patents

Description

  The present invention relates to a method for producing high-purity purified phosphoric acid, and more particularly to a method for producing high-purity purified phosphoric acid by purifying raw phosphoric acid derived from wet phosphoric acid by a simple operation.

  High-purity purified phosphoric acid (hereinafter also simply referred to as “high-purity phosphoric acid”) has a very low impurity content, so it is used for electronic materials used in semiconductor manufacturing processes, for surface treatment of semiconductor elements and liquid crystal display panels, It is useful for surface treatment of metals such as metallic aluminum and alumina, glass etching, phosphate glass raw materials and the like.

  Conventionally, as a method for producing purified phosphoric acid, a method of treating wet phosphoric acid and a method of purifying dry phosphoric acid are known.

  As a method for treating wet phosphoric acid, in general, wet phosphoric acid is activated carbon and / or oxidized to remove contained organic impurities, and this is further treated with a medium such as isopropyl alcohol, butyl alcohol, and phosphate ester. In this method, the amount of metal impurities such as Fe, Mg, and Al is reduced by solvent extraction. However, since impurities in wet phosphoric acid are originally quite high, it is necessary to make this highly pure. is there.

  On the other hand, as a method for purifying dry phosphoric acid, a crystallization tube in which a refrigerant is circulated is immersed in a raw material phosphoric acid solution, and a semi-water crystal of primary purified phosphoric acid is formed on the surface of the crystallization tube. There is known a method of precipitating and subjecting the primary purified precipitated crystal to a sweating operation to secondarily purify impurities inside the crystal (see Patent Document 1). Here, the perspiration operation is an operation of melting 10 to 40% by mass of the phosphoric acid crystal and purifying the molten liquid with impurities taken into the crystal. In this method, it is preferable to perform substitution cleaning with ultrapure water or the like as necessary.

  However, this method is essentially a method for dry phosphoric acid, and requires not only a crystallization operation but also a sweating operation (and further replacement cleaning), which is quite complicated in process. Is the method. Not only that, the amount of impurities in the dry phosphoric acid is originally relatively low, whereas the purified phosphoric acid derived from wet phosphoric acid has a much higher impurity content. For example, in purified phosphoric acid derived from dry phosphoric acid marketed as an example, the Fe concentration is 0.18 ppm, whereas in purified phosphoric acid derived from wet phosphoric acid, the Fe concentration is about 0.7 ppm. Therefore, even if this method is directly applied to purified phosphoric acid derived from wet phosphoric acid, it is considered difficult to achieve the desired effect.

Japanese Patent No. 3382561 ([0017] to [0028], [0029] [Example]))

  An object of the present invention is a method for producing high-purity purified phosphoric acid in which raw phosphoric acid derived from wet phosphoric acid is greatly reduced by a simple crystallization operation and without further recrystallization or sweating operation. Is to provide.

According to the present invention, the following method for producing purified phosphoric acid with high purity is provided.
[1]
(1) (a) A cylindrical, tubular, or columnar container that contains the raw phosphoric acid aqueous solution; and (b) a cooling temperature gradient is formed along the axis from the bottom surface of the container toward the surface of the phosphoric acid aqueous solution. In a crystallization apparatus equipped with a cooling temperature gradient forming means capable of containing and cooling the raw phosphoric acid aqueous solution, a phosphoric acid crystal layer is formed,
(2) forming a cooling temperature gradient in the aqueous solution so that the interface of the formed phosphoric acid crystal layer gradually advances in the raw phosphoric acid aqueous solution in the axial direction;
(3) A method for producing high-purity purified phosphoric acid, comprising separating the precipitated phosphoric acid crystal layer thus grown to a desired thickness from the raw phosphoric acid aqueous solution.

[2]
A method for purifying phosphoric acid to obtain high purity purified phosphoric acid,
(1) Prepare an aqueous solution of 70-90% by mass of raw material phosphoric acid,
(2) Cooling the bottom of the vessel containing the raw phosphoric acid aqueous solution to crystallize phosphoric acid crystals into a thin layer on the bottom,
(3) The vicinity of the crystal interface is cooled so that the interface of the formed phosphoric acid crystal layer gradually advances in the raw phosphoric acid aqueous solution,
(4) The method for producing high purity purified phosphoric acid according to [1], comprising separating the precipitated phosphoric acid crystal layer thus grown to a desired thickness from the raw phosphoric acid aqueous solution.

[3]
The method for producing high-purity phosphoric acid according to [1] or [2], wherein phosphoric acid crystals are previously stored as seed crystals in the bottom of the container.

[4]
The method for producing high-purity phosphoric acid according to any one of [1] to [3], wherein crystallization proceeds while stirring the raw phosphoric acid aqueous solution.

[5]
The method for producing high-purity phosphoric acid according to any one of [1] to [4], wherein the crystallized phosphoric acid crystal is a semi-aqueous crystal (H ₃ PO _4. (1/2) H ₂ O).

[6]
The method for producing high-purity phosphoric acid according to any one of [1] to [5], wherein the raw phosphoric acid is purified phosphoric acid derived from wet phosphoric acid.

[7]
The method for producing high-purity phosphoric acid according to any one of [1] to [6], wherein the obtained high-purity phosphoric acid can be used for an electronic material.

[8]
The crystal apparatus is such that a container containing a raw phosphoric acid aqueous solution is stored in a cooling apparatus equipped with a cooling temperature gradient forming means, and thus after crystallizing phosphoric acid crystals in the container, The high-purity phosphoric acid according to any one of [1] to [7], wherein the residual phosphoric acid aqueous solution is discharged from a discharge port installed in the container to separate the crystallized phosphoric acid crystal layer from the phosphoric acid aqueous solution Manufacturing method.

  According to the present invention, as shown in Examples below, the amount of impurities such as Fe, Mg, and Al contained in the raw material phosphoric acid can be recrystallized and sweated only by a simple crystallization operation. Without performing the operation, it is possible to obtain high purity purified phosphoric acid reduced to about 1/10.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
(Crystallizer)
In the present invention, (a) a cylindrical, tubular or columnar container containing the raw phosphoric acid aqueous solution, and (b) a cooling temperature gradient along an axis from the bottom surface of the container toward the surface of the phosphoric acid aqueous solution A crystallizer equipped with a cooling temperature gradient forming means capable of forming a phosphoric acid crystal layer is formed by containing and cooling the raw phosphoric acid aqueous solution.

FIG. 1 is a schematic view of a crystallizer CR suitable for carrying out the present invention.
That is, the crystallizer CR basically includes a container 10 that contains a raw phosphoric acid aqueous solution, and a cooling temperature gradient forming means 20 that forms a cooling temperature gradient in the container 10.
Although the shape of the container 10 is not necessarily limited, the container 10 has, for example, a cylindrical shape, a tubular shape, a columnar shape, and the raw phosphoric acid aqueous solution 30 is accommodated therein.

  Here, if the direction from the bottom surface 12 of the container 10 toward the surface 31 of the phosphoric acid aqueous solution is expressed as “long axis (dl)”, phosphoric acid crystals are grown along this axis. (A direction perpendicular to the long axis may be indicated as “short axis (dr)”.) For example, in a container having a cylindrical shape or a tubular shape, the long axis dl is the longitudinal direction of the container. , The short axis dr coincides with the radial direction

(Cooling temperature gradient forming means)
The cooling temperature gradient forming means 20 is composed of, for example, a cooling jacket that circulates a cooling medium. The cooling temperature gradient forming means 20 cools the phosphoric acid aqueous solution 30 along the long axis dl from the bottom surface of the container toward the surface of the phosphoric acid aqueous solution. Thus, a cooling temperature gradient is formed, and the phosphoric acid crystal layer 40 is formed.

That is, in the figure, the phosphoric acid crystal that has started to crystallize from the container bottom surface 12 shows a state where it gradually grows as the phosphoric acid crystal layer 40 while maintaining the layer shape. Assuming that the bulk temperature is To and the temperature in the vicinity of the interface 40 ′ of the crystal layer is Tc, To is the temperature at which crystallization of phosphoric acid crystal does not occur ((“unsaturated temperature”)), that is, the temperature To The phosphoric acid concentration in the phosphoric acid aqueous solution is below the saturation solubility curve, and Tc is a temperature at which the phosphoric acid crystal is crystallized (referred to as “supersaturation temperature”). The concentration of phosphoric acid in the aqueous solution is equal to or higher than the saturation solubility curve.) Note that the vicinity of the interface 40 ′ of the crystal layer is mainly a mass transfer by diffusion, particularly when stirring is performed in the aqueous solution body. By conduction It is a region where heat transfer is performed, which corresponds to a boundary layer or a boundary film, where a cooling temperature gradient is considered to be formed.
In the case of phosphoric acid, naturally, To> Tc from the temperature-solubility curve. Thus, in the phosphoric acid aqueous solution contained in the container, the cooling temperature gradient (hereinafter referred to as “To → Tc”) is displayed from the bulk temperature To toward the temperature Tc in the vicinity of the interface 40 ′ of the phosphoric acid crystal layer. May be formed).

(Movement of crystal layer interface)
In the present invention, the interface 40 ′ of the formed phosphoric acid crystal layer gradually moves in the raw phosphoric acid aqueous solution 30 along the axial direction (dl) from the bottom surface 12 toward the surface 31 of the phosphoric acid aqueous solution. A cooling temperature gradient is formed in the aqueous solution to advance.

  That is, the cooling temperature gradient forming means 20 can form such a cooling temperature gradient (To → Tc) along the axis (dl) from the bottom surface of the container toward the surface of the phosphoric acid aqueous solution. And, as long as the formed cooling temperature gradient (To → Tc) can be moved so as to gradually move the phosphate crystal interface along the axis (dl), as a specific means, Without limiting, various means can be adopted.

  For example, a jacket 20 ′ as shown in FIG. 1 is used as the cooling temperature forming means 20, and the refrigerant 24 held at Tc by the jacket is circulated (or supplied). By gradually increasing the distance (depth) h of the circulating temperature Tc to the liquid level of the refrigerant, the crystal layer interface 40 'also rises. The jacket is composed of a large number of small pipe groups in the axial (dl) direction, and a refrigerant at a temperature Tc is circulated through the small pipe group corresponding to the liquid level h (hereinafter) to obtain the interface temperature h. It is also possible to circulate a medium having a temperature To in a portion exceeding.

  As schematically shown in FIG. 2, another means is to use a constant temperature cooling bath 20 ″ as the cooling temperature forming means 20. That is, the constant temperature cooling bath 20 ″ has an upper temperature To. A gas phase medium (for example, air) 22 is accommodated, and a cooling liquid phase medium 24 (with a liquid depth H) having a temperature Tc in the lower part is accommodated. In the constant temperature portion 22 of the constant temperature cooling bath 20 ″, the container 10 containing the phosphoric acid aqueous solution 30 that is first sufficiently held and the liquid temperature is To is gradually lowered toward the liquid level 25 of the cooling medium 24. First, the container bottom surface 12 is immersed in the cooling medium, and this is gradually lowered into the liquid, and the figure shows a state where the cooling medium is immersed to a depth h.

  Of course, the gas phase medium 22 and the cooling liquid phase medium 24 may be circulated as in the case of the jacket. In addition, as the said constant temperature cooling tank, another container can be installed in the said tank, and the cooling liquid phase medium 22 can also be accommodated in the said container.

  As a variation of the constant temperature cooling tank of FIG. 2, first, the inside of the tank contains only the vapor phase medium 22 having a temperature To, and the container 10 containing the phosphoric acid aqueous solution 30 is charged therein, and then the equilibrium (temperature To) and then supplying the cooling medium 24 in small amounts into the tank first, the container bottom surface 12 is first immersed in the cooling medium, and further gradually immersed in the supply cooling medium. It will be obvious that the state as shown in the figure may be obtained (however, in this case, the bottom surface of the container 10 is always in contact with the bottom surface of the constant temperature cooling tank, so that Will be a little different, just in case.) Also in this case, as the constant temperature cooling tank, another container may be further installed in the tank, and the cooling liquid phase medium 22 may be stored in the container.

  It is also preferable that a seed crystal (seed crystal) 40 ″ is accommodated or arranged in advance at the bottom of the container 10. In particular, in the first stage of crystallization, the crystallization starts smoothly due to the presence of the seed crystal. The seed crystal may be a normal phosphate crystal, but it is more preferable to use a sufficiently purified purified phosphate crystal.The purified phosphate crystal obtained by the operation of the present invention is suitable for this purpose. The amount of seed crystals is preferably thinly spread on the bottom of the container, but in some cases, the seed crystals may be placed separately at the bottom, or even more Even if it is arranged in the section, a considerable effect can be achieved.

  Further, when the crystallization operation proceeds, the liquid phase (bulk phase) internal temperature (To) should be kept uniform by gently stirring the phosphoric acid aqueous solution (mother liquor) by means such as inserting a stirrer. It is also preferable to make it.

  The material of the crystallizer is preferably a phosphoric acid resistant material, and is preferably formed of hard glass, glass lining, fluororesin, fluororesin lining metal or the like. In addition, in the container 10, since it is preferable that there is not much temperature distribution in the dr direction, it is preferable that the diameter of the container is not excessive. That is, it is also a desirable aspect that a large number of thin tubes having a small tube diameter are arranged in a bundle and used as a multi-tubular shape.

(Separation of purified phosphate crystals)
In the present invention, as described above, the deposited phosphoric acid crystal layer grown to a desired thickness is separated from the raw phosphoric acid aqueous solution.

  The phosphoric acid crystal layer thus crystallized is a purified phosphoric acid crystal from which impurities have been greatly removed, but the separation of this purified phosphoric acid crystal and the remaining liquid phase (raw phosphoric acid aqueous solution) The separation is performed by any means such as filtration, centrifugation, and centrifugal filtration.

  The container 10 is formed with one or two or more discharge ports at appropriate positions on the bottom and / or the side wall surface of the container in advance, and the remaining phosphoric acid aqueous solution is discharged from the discharge port. It is also possible to separate the crystallized phosphoric acid crystal layer from the phosphoric acid aqueous solution. In this case, mechanical solid-liquid separation means such as filtration can be omitted.

(Raw material phosphoric acid)
As the raw material phosphoric acid in the present invention, purified phosphoric acid derived from wet phosphoric acid (hereinafter sometimes referred to as “crude purified phosphoric acid”) is particularly preferable. Crude purified phosphoric acid is obtained by removing wet organic acid from activated carbon and / or oxidizing treatment to remove contained organic impurities. Further, this is treated with alcohol having about 3 to 12 carbon atoms such as isopropyl alcohol and butyl alcohol, phosphate ester, etc. In this extraction medium, the amount of metal impurities such as Fe, Mg, Al and the like is considerably reduced by solvent extraction.

  In the present invention, such roughly purified phosphoric acid is used as the raw material phosphoric acid, and is used as an aqueous solution of 70 to 90% by mass, preferably 80 to 90% by mass.

The purification operation in this case is specifically performed as follows, for example.
(1) Prepare 70-90 mass% aqueous solution 30 of the raw material phosphoric acid which consists of rough refined phosphoric acid as mentioned above,

(2) Preferably, a phosphoric acid seed crystal 40 ″ is arranged in advance on the bottom 12 of the container 10 containing the raw phosphoric acid aqueous solution 30, and the bottom is used for a jacket, a constant temperature cooling tank, or the like as described above. The cooling temperature gradient forming means is cooled by bringing it into contact with a refrigerant maintained at 2 to 8 ° C., preferably 3 to 7 ° C., more preferably 4 to 6 ° C., and crystallizes phosphoric acid crystals in a thin layer on the bottom. (In this case, the phosphoric acid crystal to be crystallized is preferably a semi-aqueous crystal (H ₃ PO _4. (1/2) H ₂ O)).

(3) The amount of refrigerant supplied to the jacket, constant temperature cooling tank, etc. little by little so that the interface 40 ′ of the phosphoric acid crystal layer thus formed gradually advances in the raw phosphoric acid aqueous solution 30 in the dl direction. Increase the cooling near the crystal interface,

(4) A high-purity phosphoric acid is produced by separating the precipitated phosphoric acid crystal layer thus grown to a desired thickness by a suitable solid-liquid separation means such as a raw phosphoric acid aqueous solution and filtration. is there.

Although the mechanism by which purified phosphoric acid of extremely high purity is produced by one-stage crystallization by the purification method of the present invention is not completely clear, the interface of the phosphoric acid crystal layer formed in the container is a raw material. Since the crystallization operation is performed so that the phosphoric acid aqueous solution gradually moves forward, the impurities in the raw phosphoric acid aqueous solution are not substantially taken into the phosphoric acid crystal layer, unlike the normal crystallization, It is presumed that this is because it always remains in the mother liquor.
According to the present invention, purified phosphoric acid with sufficiently high purity can be obtained by one-stage crystallization operation, but the operation of the present invention may be further repeated as desired.

Hereinafter, the present invention will be specifically described with reference to examples, but the technical scope of the present invention is not limited thereto.
[Example 1]
(1) An 85% by mass purified phosphoric acid aqueous solution (hereinafter also referred to as “phosphoric acid mother liquor”) having the composition shown in Table 1 was prepared as a raw material phosphoric acid.
300 g of this purified phosphoric acid aqueous solution and a needle-like crystal of purified phosphoric acid having a diameter of about 0.5 mm and a length of about 2 mm are housed in a 200 ml tall beaker which is a cylindrical container and kept at 5 ° C. It was set at the bottom of the (constant temperature cooling tank). However, at this stage, the 200 ml tall beaker is not immersed in water at 5 ° C. as a cooling medium.

(2) Water at 5 ° C. was used as a cooling medium, and this was supplied into the constant temperature water tank by a tube pump. The water as the cooling medium first comes into contact with the bottom of the tall beaker, and locally cools the portion of the phosphoric acid aqueous solution that is in contact with the cooling water through the glass wall surface of the tall beaker (mainly the bottom of the beaker). The acid crystals were deposited in layers on the bottom, which is the cooling surface.
The cooling water supply speed of the tube pump was adjusted so that the water surface rising speed of the cooling water inside the constant temperature water tank (that is, the soaking speed of the tall beaker) was extremely slow and 5 mm / hr.
That is, the vicinity of the crystal interface was cooled so that the interface of the formed phosphate crystal layer gradually advanced (in this case, increased) in the raw material phosphoric acid mother liquor.

(3) When the surface of the crystal layer reached the position of 10 mm from the phosphoric acid aqueous solution surface in the tall beaker, the cooling water supply was stopped and the phosphoric acid crystallization experiment was completed.
The crystallized phosphate crystals were centrifugally filtered, redissolved and analyzed. The analysis results are shown in Table 1. It can be seen that the purity (H ₃ PO ₄ ) of phosphoric acid is greatly improved and that Fe, Mg and Al impurities are also removed very well. Phosphoric acid was analyzed by the ammonium vanatomolybdate method, and Fe, Mg, and Al were analyzed by the atomic absorption method (the same applies hereinafter).

[Comparative Example 1]
(1) An 85% by mass purified phosphoric acid aqueous solution (also referred to as phosphoric acid mother liquor) having the same composition as in Example 1 was prepared as a raw material phosphoric acid.

(2) 300 g of this purified phosphoric acid aqueous solution was accommodated in a 200 ml tall beaker, which was accommodated in a thermostatic bath maintained at 5 ° C., and crystal phosphoric acid was gradually crystallized over 24 hours.
The precipitated phosphoric acid crystals were subjected to centrifugal filtration, redissolved and analyzed. The analysis results are shown in Table 1. The purity (H ₃ PO ₄ ) of phosphoric acid was lower than that in Example 1, and the removal rates of impurities such as Fe, Mg, and Al were particularly lower than those in Example 1.

  As shown in Table 1 above, according to the present invention, high-purity purified phosphoric acid in which the amount of impurities such as Fe, Mg, Al, etc. at the raw material phosphoric acid concentration is reduced to about 1/10 is obtained. It is possible. On the other hand, in the comparative example, a considerable amount of these impurities still remains, and it is understood that recrystallization and sweating are necessary.

  According to the present invention, the amount of impurities such as Fe, Mg, Al, etc. in the concentration of raw phosphoric acid derived from wet phosphoric acid is about 1/10 by simple operation and without further recrystallization or sweating operation. It is possible to obtain high-purity purified phosphoric acid that has been reduced to a low level, and these purified phosphoric acids can be used as they are for surface treatment applications such as electronic materials and semiconductor devices. The above availability is enormous.

It is a schematic diagram explaining the crystallizer which implements this invention. It is a schematic diagram explaining the other aspect of the crystallizer which implements this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Container which accommodates raw material phosphoric acid aqueous solution 12 Container bottom part 20 Cooling temperature gradient formation means 20 'Jacket 20 "Constant temperature cooling tank
22 Gas phase medium, etc. 24 Cooling liquid phase medium 25 Cooling liquid phase medium surface 30 Raw material phosphoric acid aqueous solution 31 Phosphoric acid aqueous solution surface 40 Phosphoric acid crystal layer 40 'Interface of phosphoric acid crystal layer 40 "Seed crystal CR crystallizer To phosphoric acid Bulk temperature of aqueous solution Tc Temperature near crystal layer h Cooling medium depth, etc. H Cooling medium depth

Claims (8)

(1) (a) A cylindrical, tubular, or columnar container that contains the raw phosphoric acid aqueous solution; and (b) a cooling temperature gradient is formed along the axis from the bottom surface of the container toward the surface of the phosphoric acid aqueous solution. In a crystallization apparatus equipped with a cooling temperature gradient forming means capable of containing and cooling the raw phosphoric acid aqueous solution, a phosphoric acid crystal layer is formed,
(2) forming a cooling temperature gradient in the aqueous solution so that the interface of the formed phosphoric acid crystal layer gradually advances in the raw phosphoric acid aqueous solution in the axial direction;
(3) A method for producing high-purity purified phosphoric acid, comprising separating the precipitated phosphoric acid crystal layer thus grown to a desired thickness from the raw phosphoric acid aqueous solution. A method for purifying phosphoric acid to obtain high purity purified phosphoric acid,
(1) Prepare an aqueous solution of 70-90% by mass of raw material phosphoric acid,
(2) Cooling the bottom of the vessel containing the raw phosphoric acid aqueous solution to crystallize phosphoric acid crystals into a thin layer on the bottom,
(3) The vicinity of the crystal interface is cooled so that the interface of the formed phosphoric acid crystal layer gradually advances in the raw phosphoric acid aqueous solution,
(4) The method for producing high purity purified phosphoric acid according to claim 1, wherein the precipitated phosphoric acid crystal layer thus grown to a desired thickness is separated from the raw phosphoric acid aqueous solution.   The method for producing high-purity phosphoric acid according to claim 1 or 2, wherein phosphoric acid crystals are previously stored as seed crystals in the bottom of the container.   The method for producing high-purity phosphoric acid according to any one of claims 1 to 3, wherein crystallization proceeds while stirring the raw phosphoric acid aqueous solution. The method for producing high-purity phosphoric acid according to any one of claims 1 to 4, wherein the crystallized phosphoric acid crystal is a semi-aqueous crystal (H ₃ PO ₄ · (1/2) H ₂ O).   The method for producing high-purity phosphoric acid according to any one of claims 1 to 5, wherein the raw phosphoric acid is purified phosphoric acid derived from wet phosphoric acid.   The method for producing high-purity phosphoric acid according to any one of claims 1 to 6, wherein the obtained high-purity phosphoric acid can be used for an electronic material. The crystal analysis apparatus vessel containing raw phosphoric acid aqueous solution is such that is accommodated in the cooling device with a cooling temperature gradient forming means, thus after the phosphate crystals was crystallized in the vessel The high-purity phosphoric acid according to any one of claims 1 to 7, wherein the crystallization phosphoric acid crystal layer and the phosphoric acid aqueous solution are separated by discharging the residual phosphoric acid aqueous solution from a discharge port installed in the container. Production method.

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