JP2009114064A - High purity phosphoric acid and method for producing the same - Google Patents

Abstract

The present invention provides a high-purity phosphoric acid having a very low content of antimony and sulfide ions, which are impurity metals that have been conventionally difficult to remove, and a method for producing the same.
The high-purity phosphoric acid of the present invention is characterized in that Sb is 200 ppb or less and sulfide ions are 200 ppb or less as impurity contents when the concentration of H ₃ PO ₄ is converted to 85% by weight. And The high purity phosphoric acid of the present invention is an etching solution for a semiconductor element having a silicon nitride film, an etching solution for a liquid crystal display panel having an alumina film, a metal aluminum etching solution, an alumina etching solution for ceramics, a phosphate glass raw material for optical fiber glass, It is useful as a food additive.
[Selection figure] None

Description

  The present invention relates to high-purity phosphoric acid and a method for producing the same. Furthermore, high-purity phosphoric acid that is substantially free of impurities that degrade the electrical characteristics of the microelements and that is suitably used for removing the silicon nitride film or the like by etching in the electronics industry, for example, in the semiconductor manufacturing process, and It relates to the manufacturing method. The high-purity phosphoric acid of the present invention has a low impurity content, so that it can be used as a metal aluminum etching solution, an etching solution for liquid crystal, an alumina etching solution for ceramics, and a phosphate glass raw material for optical fiber glass in addition to semiconductor etching. Is also a suitable material.

  It is known that phosphoric acid production methods include a dry method and a wet method. The method for producing dry phosphoric acid can be obtained by using phosphorus ore as a raw material, reducing it in an electric furnace, burning the obtained yellow phosphorus to diphosphorus pentoxide, and hydrating it. On the other hand, the wet phosphoric acid production method is a method in which phosphorous ore is decomposed with sulfuric acid, calcium sulfate produced is separated to produce dilute phosphoric acid, and then concentrated to a high concentration. Any phosphoric acid obtained by any method requires a high-purity product when used as an electronic material.

  Since dry phosphoric acid is produced via yellow phosphorus, it is said that the phosphorous ore-derived impurities are less mixed and the quality is better than that obtained by the wet method. High purity phosphoric acid having a purity of 75 to 85% by weight obtained by such a dry method is used for etching semiconductors. In this case, if phosphoric acid contains a large amount of impurity metals such as antimony and arsenic, depending on the semiconductor manufacturing apparatus, these impurity metal fine particles may remain on the silicon wafer, causing problems in subsequent processes, There may be a problem that a process for cleaning the fine particles on the wafer becomes necessary. Therefore, higher purity phosphoric acid is required.

As a method for purifying dry phosphoric acid, hydrogen sulfide is added to 75 to 85% by weight of phosphoric acid containing antimony and arsenic as impurity metals and H ₃ PO ₄ to produce precipitates of impurity metals, which are separated. After that, a method for purifying phosphoric acid for electric semiconductors in which such a separation operation is performed at least at 60 ° C. is known (see Patent Document 1). According to such a purification method, the purified phosphoric acid contains 13 to 20 ppm of antimony and 0.1 to 0.02 ppm of arsenic when the concentration of phosphoric acid is converted to 85% by weight.

Also known is a method of removing arsenic by bringing phosphoric acid and hydrogen halide into contact with each other (see Patent Document 2). According to this method, arsenic in phosphoric acid can be removed to 1 ppm or less. Further, when phosphoric acid and hydrogen halide are brought into contact with each other in the presence of a compound capable of generating hydrogen halide under acidic conditions, the arsenic removal effect is further enhanced, and arsenic in phosphoric acid can be reduced to 0.1 ppm or less. ing. However, according to the examples of this patent document, arsenic in phosphoric acid has been removed only to about 0.07 to 0.8 ppm at a P ₂ O ₅ concentration (65%). It is not something that can be answered enough. In addition, this method requires hydrogen peroxide, and there is a disadvantage that arsenic cannot be removed sufficiently unless iron chloride or tin chloride is used before blowing hydrogen chloride.

  Apart from the above method, a technique for purifying phosphoric acid by a crystallization method is widely known (for example, see Patent Document 3). This patent document discloses a method of repeating a series of crystallization purification operations consisting of a crystallization operation, a separation operation from a mother liquor, and a melting operation three times in order to purify phosphoric acid to a desired purity. In addition, knowledge on basic physical properties data for purifying phosphoric acid by crystallization operations, such as saturation solubility, correlation between supersaturation and growth rate, hygroscopicity of phosphoric acid hemihydrate crystals, and precipitation rate of crystals in phosphoric acid (non-patent literature) 1) and knowledge about application examples in a fluidized bed crystallizer (see Non-Patent Document 2) are also known. However, the purity of phosphoric acid obtained by the crystallization operation is not clearly described. In addition, the crystallization operation has problems such as high cost.

Japanese Unexamined Patent Publication No. 1-113109 International Publication No. 00/40507 Pamphlet Japanese Patent Publication No. 44-14692

Oimura et al., "Toyo Soda Report", 10, 2, 21 (1966) Aoyama et al., Proceedings of a Conference of Industrial Crystallization, pp. 413-420 (1976)

  Accordingly, an object of the present invention is to provide high-purity phosphoric acid having a very low content of antimony and sulfide ions, which are impurity metals that have been difficult to remove, and a method for producing the same.

The present invention provides high-purity phosphoric acid characterized in that Sb is 200 ppb or less and sulfide ions are 200 ppb or less as impurity content when the concentration of H ₃ PO ₄ is converted to 85% by weight. Thus, the object is achieved.

  In addition, the present invention is obtained in the first step and the first step in which hydrogen sulfide gas is excessively blown into the crude phosphoric acid containing the impurity metal and the impurity metal contained in the crude phosphoric acid is precipitated as a sulfide. A second step of filtering phosphoric acid; and a third step of removing phosphorous acid contained in phosphoric acid by bringing phosphoric acid and air into contact with each other in the removal tower after completion of the second step. And the said objective is achieved by providing the manufacturing method of high purity phosphoric acid characterized by performing a 2nd process at 59 degrees C or less.

  As described above in detail, the high-purity phosphoric acid of the present invention has extremely low contents of antimony and sulfide ions, which are impurity metals that have been conventionally difficult to remove. The high purity phosphoric acid of the present invention is an etching solution for a semiconductor element having a silicon nitride film, an etching solution for a liquid crystal display panel having an alumina film, a metal aluminum etching solution, an alumina etching solution for ceramics, a phosphate glass raw material for optical fiber glass, It is useful as a food additive. Further, according to the production method of the present invention, such high-purity phosphoric acid can be produced easily and economically.

It is explanatory drawing which shows the analysis method of sulfide ion.

Hereinafter, the present invention will be described in detail. Unless otherwise specified, “%”, “ppb”, and “ppm” are based on weight in the following description. The phosphoric acid in the present invention, the component represented by the general formula H ₃ PO _4, is a mixed liquid of any ratio of H ₂ O. The high-purity phosphoric acid of the present invention is obtained by a dry method or a wet method, and refers to that having a H ₃ PO ₄ concentration of 75 to 89%. In the dry method, the crude phosphoric acid obtained by burning yellow phosphorus and further hydrating it is purified to obtain high-purity phosphoric acid. In the wet method, the phosphorus ore is decomposed with a strong inorganic acid and then concentrated. The crude phosphoric acid obtained is purified to give high purity phosphoric acid. The concentration of high-purity phosphoric acid is measured by a titration method with sodium hydroxide specified in JIS K-1449. The concentration of phosphoric acid is expressed as a mass ratio of elements per unit phosphoric acid mass.

  The high-purity phosphoric acid of the present invention is a material suitable as an etching solution for the surface of metals and the like because of its strong corrosiveness to various metals. Since phosphoric acid has a lower vapor partial pressure than other mineral acids, it is not easy to purify by applying a distillation method. Moreover, it is practically very difficult to purify industrially. In spite of such difficulty in purification, the high purity phosphoric acid according to the present invention has a low content of Sb, which is an impurity metal.

Specifically, the high-purity phosphoric acid of the present invention has an Sb content of 200 ppb or less, preferably 100 ppb or less, more preferably 50 ppb or less, as the impurity content when the concentration of H ₃ PO ₄ is converted to 85%. is there. When Sb exceeds 200 ppb, for example, when the high-purity phosphoric acid of the present invention is used as an etching solution for an electronic device such as a semiconductor element or a liquid crystal display panel, Sb particles adhere to the surface of a silicon wafer or the like. The disadvantages may occur.

In addition to the Sb content being not more than the aforementioned value, the high purity phosphoric acid of the present invention has a sulfide ion of 200 ppb or less as an impurity content when the concentration of H ₃ PO ₄ is converted to 85%. As is apparent from the method for producing high-purity phosphoric acid described later, in a preferred embodiment of the present invention, hydrogen sulfide is used as a means for removing impurity metals in phosphoric acid. As a result, sulfide ions may inevitably remain in the phosphoric acid after the impurity metal is removed. There are also sulfides such as arsenic sulfide and antimony sulfide that cannot be removed in the filtration step. When high purity phosphoric acid in such a state is used for etching an Ag-based thin film or an Ag-based electrode provided on a reflective film of a reflective liquid crystal display panel, for example, if the content of sulfide ions exceeds 200 ppb, Product ions may react with silver to produce silver sulfide, which may cause problems in product quality and the like. On the other hand, in the high purity phosphoric acid of the present invention, the content of the impurity metal is extremely small, and furthermore, the content of the sulfide ion used for removing the impurity metal is also very small. Does not occur. That is, the high-purity phosphoric acid of the present invention satisfies both the contradictory requirements of reducing impurity metals and reducing sulfide ions. The sulfide ion referred to here is the total sulfide contained in phosphoric acid, specifically, sulfides such as antimony sulfide and arsenic sulfide generated when hydrogen sulfide is blown into phosphoric acid, and remain. It contains hydrogen sulfide.

The high-purity phosphoric acid of the present invention preferably has an As content of 10 ppb or less, particularly 2 ppb or less, as the impurity content when the concentration of H ₃ PO ₄ is converted to 85%, for the same reason as in the case of Sb. . The content of As or Sb in phosphoric acid is measured with an instrument (ICP-HYD) in which a hydride generator (HYD) is connected to an ICP emission spectroscopic analyzer. Details of the measurement method will be described in detail in Examples described later. A method for quantifying sulfide ions will also be described in detail in the examples described later.

  Metal ions such as Sb and As are originally contained in yellow phosphorus, and they continue to be contained in crude phosphoric acid. Therefore, from the viewpoint of obtaining high-purity phosphoric acid, it is preferable to originally use high-purity yellow phosphorus as a raw material. However, it is very difficult to obtain purified yellow phosphorus until Sb and As are in the order of ppb.

  The use of the high purity phosphoric acid of the present invention is not particularly limited. For example, an etching solution used to remove a silicon nitride film in a manufacturing process of a semiconductor element, an etching solution used to remove an alumina film in a manufacturing process of a liquid crystal display panel, a metal aluminum etching solution, an alumina etching solution for ceramics, It is suitably used as a phosphate glass raw material for optical fibers.

  In particular, when a high purity phosphoric acid of the present invention is used to remove a silicon nitride film by etching in a semiconductor manufacturing process that requires microfabrication, impurities derived from Sb remain on the etched silicon wafer. Absent. In addition to Sb, As, Fe, Mn, Na and the like are also known as impurities contained in phosphoric acid. However, in the field of semiconductor microfabrication, particularly microfabrication with a line width of 0.5 μm or less, Sb It has been found by the present inventors that impurities derived from impurities, in particular impurities derived from Sb, have the most adverse effects. Therefore, the high-purity phosphoric acid of the present invention having a small Sb content is extremely useful as an etching solution used for semiconductor microfabrication. For the same reason, the high-purity phosphoric acid of the present invention is extremely useful as an etching solution used for fine processing of electronic circuits of liquid crystal display panels.

  Next, the manufacturing method of the high purity phosphoric acid of this invention is demonstrated. The manufacturing method of the present invention roughly includes first, second and third steps. In the first step, hydrogen sulfide gas is blown into a crude phosphoric acid containing an impurity metal such as Sb or As in a large excess, and then the impurity metal contained in the crude phosphoric acid is precipitated as a sulfide (absorption). Process). The second step is a step (filtering step) of filtering the crude phosphoric acid obtained in the first step. It is important that all these steps be performed at 59 ° C. or lower. Furthermore, after the 2nd process completion | finish, it consists of the 3rd process (deaeration process) which makes phosphoric acid and air contact in a removal tower, and removes the hydrogen sulfide gas contained in phosphoric acid. The production method of the present invention can naturally produce high-purity phosphoric acid continuously and efficiently. Hereinafter, each process is explained in full detail.

First, the first step will be described. The crude phosphoric acid used in the first step may be obtained by a dry method or may be obtained by a wet method, but a crude phosphoric acid obtained by a dry method is preferred. Even crude phosphoric acid obtained by any method, Sb content when converted to the concentration of H ₃ PO ₄ to 85% by weight is about 1-10 ppm, also As content is about 10~100ppm . When manufacturing crude phosphoric acid by a dry method, it is as follows, for example. The raw material yellow phosphorus (P ₄ ) is not particularly limited as long as it is industrially available. The yellow phosphorus usually contains about 4 to 40 ppm of Sb. Of course, yellow phosphorus containing more Sb than this may be used as a raw material.

In a combustion furnace, liquid yellow phosphorus is combusted by air to generate diphosphorus pentoxide gas. Subsequently, the produced phosphorous pentoxide gas is hydrated to produce crude phosphoric acid. The reaction formula is as follows.
P ₄ + 5O ₂ → P ₄ P ₁₀ (1)
P ₄ O ₁₀ + 6H ₂ O → 4H ₃ PO ₄ (2)

  When producing crude phosphoric acid by a wet method, for example, the following operation is performed. In general, the process for producing wet phosphoric acid involves decomposing phosphate ore with sulfuric acid, separating the produced calcium sulfate and first producing diluted phosphoric acid to a concentration of about 40%, and arsenic and solids in phosphoric acid. The arsenic process that separates and removes the components, then the oxidation process that oxidatively decomposes organic substances dissolved in phosphoric acid, the extraction washing process that mixes phosphoric acid and isopropyl alcohol and separates them into the extract and the extraction residue, A Na removal step in which Na content is adsorbed and removed by an ion exchange resin, a Deisopropyl alcohol step in which Na from the extract from which the phosphoric acid and isopropyl alcohol have been separated is separated, and a small amount of isopropyl alcohol and fluorine remaining in the phosphoric acid. Defluorination / isopropyl alcohol process to separate the organic matter, organic matter that was not removed in the oxidation-reduction process is removed with activated carbon, phosphoric acid 5%, a concentration step of concentrating the 85%. Various processes for producing wet phosphoric acid have been proposed. In the present invention, phosphoric acid before the dearsenic process is used as crude phosphoric acid.

Next, hydrogen sulfide gas is blown into the crude phosphoric acid. As a result of the examination by the present inventors, the temperature of the crude phosphoric acid when the hydrogen sulfide gas is blown is extremely important in the present invention. Specifically, the temperature of the crude phosphoric acid when the hydrogen sulfide gas is blown is set to 59 ° C. or less. This temperature is preferably as low as possible and is determined in consideration of the freezing point of phosphoric acid. For example, when the concentration of H ₃ PO ₄ is 85 wt% phosphoric acid, it is usually preferably 20 to 59 ° C., particularly preferably 20 to 40 ° C. As a result of the study by the present inventors, a large amount of antimony sulfide produced by the reaction between the hydrogen sulfide gas and Sb can be obtained by setting the temperature of the crude phosphoric acid to be equal to or lower than the above temperature when or after the hydrogen sulfide gas is blown. It has been found that it can be precipitated and the content of Sb present in phosphoric acid can be very low.

  In blowing hydrogen sulfide gas, it has been found that it is also important to supply these in excess. There is no particular upper limit to these supply amounts, and the greater the excess, the more the production of sulfides of Sb and As is promoted. However, even if the supply is too large, the formation of sulfide is saturated. In consideration of production costs, it is best to keep the upper limit of the supply amount within the solubility in phosphoric acid when hydrogen sulfide gas is used.

As a method of blowing hydrogen sulfide gas into the phosphoric acid, a method is performed in which crude phosphoric acid is caused to flow down from the upper part of the absorption tower and hydrogen sulfide gas is raised from the lower part of the absorption tower so that both are brought into countercurrent contact with each other. However, phosphoric acid and hydrogen sulfide gas may be contacted in a cocurrent manner. According to such a method, hydrogen sulfide gas can be efficiently reacted with impurities in phosphoric acid. In this case, it is preferable to fill the inside of the absorption tower with various packing materials such as terrarette and saddle to ensure sufficient contact between phosphoric acid and hydrogen sulfide gas. By blowing hydrogen sulfide gas, Sb and As and other impurity metals are produced as water-insoluble sulfides and are precipitated in the crude phosphoric acid. The reaction formula of hydrogen sulfide gas with Sb and As is as follows.
Sb ₂ O ₃ + 3H ₂ S → Sb ₂ S ₃ + 3H ₂ O (3)
Sb ₂ O ₅ + 5H ₂ S → Sb ₂ S ₅ + 5H ₂ O (4)
_{As 2 O 3 + 3H 2 S} → As 2 S 3 + 3H 2 O (5)
As ₂ O ₅ + 5H ₂ S → As ₂ S ₅ + 5H ₂ O (6)

The crude phosphoric acid after blowing hydrogen sulfide gas is subjected to the second step. Prior to that, it is preferable to age the crude phosphoric acid obtained in the first step. By this aging, sulfides of Sb and As can be sufficiently precipitated. The aging time is 1 to 10 hours, but the sulfide can be sufficiently precipitated by operating in the process usually in 2 to 4 hours. No special operation is required for aging, and the crude phosphoric acid in the tank is heated to the temperature in the hydrogen sulfide blowing operation. For example, when the concentration of H ₃ PO ₄ is 85 wt% phosphoric acid, it is 59 ° C. or less, preferably What is necessary is just to hold | maintain for a predetermined time at about 20-40 degreeC.

The sulfide filtration step, which is the second step, is also performed at 59 ° C. or lower, as in the first step. The filtration temperature is determined in consideration of the freezing point of phosphoric acid, the viscosity, and the capacity of the filter (filtration area). For example, when the concentration of H ₃ PO ₄ is 85 wt% phosphoric acid, it is usually preferably 20 to 59 ° C., particularly preferably 20 to 40 ° C. Since high-purity phosphoric acid is a viscous liquid at room temperature at a high concentration, it is advantageous to increase the temperature and lower the viscosity for filtration. However, if the temperature of phosphoric acid is raised too much, the solubility of sulfides precipitated in phosphoric acid increases, and the precipitated sulfides are dissolved in phosphoric acid.

  The filtration method is not particularly limited. Since the filtration temperature is relatively low, that is, the viscosity of phosphoric acid is high, it is advantageous that the filtration device used has a large filtration area. Examples of the filtration method include pressure filtration and vacuum filtration. In particular, leaf-shaped pressure filtration such as an ultra filter press is preferred. This ultra filter press can remove sulfides of Sb and As.

The phosphoric acid obtained by filtration is transparent, and the Sb is 200 ppb or less as the impurity content when the concentration of H ₃ PO ₄ is converted to 85%. The As content is 10 ppb or less.

  When hydrogen sulfide gas is used to remove the impurity metal, the resulting phosphoric acid contains excess hydrogen sulfide. Therefore, in order to remove this, air is ventilated in phosphoric acid as a third step. Thereby, the concentration of sulfide ions is lowered to 200 ppb or less, and the phosphoric acid of the present invention purified to a high purity is obtained.

  As a method of removing excess hydrogen sulfide in phosphoric acid, for example, phosphoric acid is allowed to flow down from the upper part of the removing tower and air is raised from the lower part of the removing tower to bring them into countercurrent contact with each other. It is preferable to use a method for removing the contained hydrogen sulfide gas. Moreover, you may make phosphoric acid and air contact in parallel flow. In this case, it is preferable to fill the inside of the removal tower with various packing materials such as terrarette and saddle to ensure sufficient contact between phosphoric acid and air. Since high-purity phosphoric acid has a high viscosity as described above, a heat removal method in which air is blown into a heating kettle is usually performed to remove the impurity gas dissolved in the phosphoric acid. On the other hand, the present inventors can surprisingly easily remove hydrogen sulfide gas dissolved in phosphoric acid having high viscosity by using a removal tower packed with packing. I found out. Moreover, according to this method, hydrogen sulfide gas can be removed economically.

  In the third step (deaeration step), the temperature of phosphoric acid may be set to a temperature equal to or higher than the freezing point, but is usually 25 ° C. or higher, and preferably 50 to 65 ° C. Thereby, the dissolved hydrogen sulfide gas in phosphoric acid can be almost completely released. Further, depending on the concentration of dissolved hydrogen sulfide gas in phosphoric acid and the amount of phosphoric acid treated, a plurality of removal towers may be juxtaposed and connected in series. In this case, phosphoric acid and air are contacted countercurrently or in a cocurrent manner in each removal tower.

  The present invention is not limited to the embodiment. For example, the method for obtaining the high purity phosphoric acid of the present invention is not limited to the method described above, and any method may be used as long as the content of Sb and sulfide ions can be set to the values described above.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
(1) First Step Liquid yellow phosphorus was burned with air in a combustion tower, and the produced phosphorous pentoxide gas was hydrated to produce crude phosphoric acid. Yellow phosphorus was supplied to the combustion tower with a burner, and air was blown in excessively to complete combustion. The combustion gas was cooled and hydrated as it passed through the cooling tower. As a result, crude phosphoric acid having a concentration of 86% by weight of H ₃ PO ₄ was obtained. The crude phosphoric acid contained 4 ppm Sb and 40 ppm As.

The produced crude phosphoric acid (86%) is adjusted to 35 ° C., and the crude phosphoric acid is supplied from the upper part of the absorption tower packed with a packing (terrarette), and excess hydrogen sulfide gas is blown from the lower part to The acid and hydrogen sulfide gas were in full contact in countercurrent. As a result, water-insoluble sulfides of Sb and As were formed as precipitates. The amount of hydrogen sulfide gas blown was 10 times equivalent to the total equivalent of Sb and As when the concentration of crude phosphoric acid (H ₃ PO ₄ ) was converted to 85%.

  Crude phosphoric acid containing water-insoluble sulfide was aged at about 35 ° C. for 2 hours.

(2) Second Step Crude phosphoric acid after completion of aging was subjected to pressure filtration with a leaf filter (ultra filter press) to remove insoluble sulfides to obtain clear phosphoric acid. The temperature of phosphoric acid during filtration was 30 ° C.

(3) Third step The obtained clear phosphoric acid is heated to 60 ° C., supplied from the upper part of the removal tower packed with packing (terrarette), and air is blown in from the lower part. And were in sufficient countercurrent contact. Thus, after removing excess hydrogen sulfide dissolved in phosphoric acid, pure water was added to obtain high-purity phosphoric acid having a H ₃ PO ₄ concentration of 85% by weight.

[Example 2]
(1) First Step Crude phosphoric acid was obtained in the same manner as in Example 1. The crude phosphoric acid contained 4 ppm Sb and 40 ppm As. The generated crude phosphoric acid (86%) is adjusted to 58 ° C., and the crude phosphoric acid is supplied from the upper part of the absorption tower packed with the packing (terrarette), and excess hydrogen sulfide gas is blown from the lower part to The acid and hydrogen sulfide gas were in full contact in countercurrent. As a result, water-insoluble sulfides of Sb and As were formed as precipitates. The amount of hydrogen sulfide gas blown was 10 times equivalent to the total equivalent of Sb and As when the concentration of crude phosphoric acid (H ₃ PO ₄ ) was converted to 85%.

  Crude phosphoric acid containing water-insoluble sulfide was aged at about 55 ° C. for 2 hours.

(2) Second Step Crude phosphoric acid after completion of aging was subjected to pressure filtration with a leaf filter (ultra filter press) to remove insoluble sulfides to obtain clear phosphoric acid. The temperature of phosphoric acid during filtration was 52 ° C.

(3) Third step The obtained clear phosphoric acid is heated to 60 ° C., supplied from the upper part of the removal tower packed with packing (terrarette), and air is blown in from the lower part. And were in sufficient countercurrent contact. Thus, excess hydrogen sulfide dissolved in phosphoric acid was removed, and then pure water was added to obtain high purity phosphoric acid having a H ₃ PO ₄ concentration of 85% by weight.

Example 3
(1) First Step Crude phosphoric acid was obtained in the same manner as in Example 1. The crude phosphoric acid contained 4 ppm Sb and 40 ppm As. The produced crude phosphoric acid (86%) is adjusted to 40 ° C., and the crude phosphoric acid is supplied from the upper part of the absorption tower packed with the packing (terrarette), and excess hydrogen sulfide gas is blown from the lower part to The acid and hydrogen sulfide gas were in full contact in countercurrent. As a result, water-insoluble sulfides of Sb and As were formed as precipitates. The amount of hydrogen sulfide gas blown was 10 times equivalent to the total equivalent of Sb and As when the concentration of crude phosphoric acid (H ₃ PO ₄ ) was converted to 85%.

  Crude phosphoric acid containing water-insoluble sulfide was aged at about 38 ° C. for 2 hours.

(2) Second Step Crude phosphoric acid after completion of aging was subjected to pressure filtration with a leaf filter (ultra filter press) to remove insoluble sulfides to obtain clear phosphoric acid. The temperature of phosphoric acid during filtration was 36 ° C.

(3) Third step The obtained clear phosphoric acid is heated to 60 ° C., supplied from the upper part of the removal tower packed with packing (terrarette), and air is blown in from the lower part. And were in sufficient countercurrent contact. Thus, excess hydrogen sulfide dissolved in phosphoric acid was removed, and then pure water was added to obtain high-purity phosphoric acid having a concentration of 85 wt% of H ₃ PO ₄ .

Example 4
(1) First Step Crude phosphoric acid was obtained in the same manner as in Example 1. The crude phosphoric acid contained 4 ppm Sb and 40 ppm As. The produced crude phosphoric acid (86%) is adjusted to 35 ° C., and the crude phosphoric acid is supplied from the upper part of the absorption tower packed with a packing (terrarette), and excess hydrogen sulfide gas is blown from the lower part to The acid and hydrogen sulfide gas were in full contact in countercurrent. As a result, water-insoluble sulfides of Sb and As were formed as precipitates. The amount of hydrogen sulfide gas blown was 10 times equivalent to the total equivalent of Sb and As when the concentration of crude phosphoric acid (H ₃ PO ₄ ) was converted to 85%.

  Crude phosphoric acid containing water-insoluble sulfide was aged at about 35 ° C. for 2 hours.

(2) Second Step Crude phosphoric acid after completion of aging was subjected to pressure filtration with a leaf filter (ultra filter press) to remove insoluble sulfides to obtain clear phosphoric acid. The temperature of phosphoric acid during filtration was 30 ° C.

(3) Third step The obtained clear phosphoric acid is heated to 40 ° C., supplied from the upper part of the removal tower packed with packing (terrarette), and air is blown in from the lower part. And were in sufficient countercurrent contact. Thus, excess hydrogen sulfide dissolved in phosphoric acid was removed, and then pure water was added to obtain high-purity phosphoric acid having a concentration of 85 wt% of H ₃ PO ₄ .

[Comparative Example 1]
(1) First Step Crude phosphoric acid was obtained in the same manner as in Example 1. The crude phosphoric acid contained 4 ppm Sb and 40 ppm As. The produced crude phosphoric acid (86%) was adjusted to 65 ° C., and excess hydrogen sulfide was blown into it. As a result, water-insoluble sulfides of Sb and As were formed as precipitates. Blowing amount of hydrogen sulfide was 10 equivalents with respect to the total equivalents of Sb and As when the concentration of the crude phosphoric acid (H ₃ PO ₄₎ was converted to 85%.

  Crude phosphoric acid containing water-insoluble sulfide was aged at about 64 ° C. for 2 hours.

(2) Second Step Crude phosphoric acid after completion of aging was subjected to pressure filtration with a leaf filter (ultra filter press) to remove insoluble sulfides to obtain clear phosphoric acid. The temperature of phosphoric acid during filtration was 63 ° C.

(3) Third step The obtained clear phosphoric acid is heated to 60 ° C., supplied from the upper part of the removal tower packed with packing (terrarette), and air is blown in from the lower part. And were in sufficient countercurrent contact. As a result, excess hydrogen sulfide dissolved in phosphoric acid was removed, and then pure water was added to obtain 85% high-purity phosphoric acid.

[Performance evaluation]
About the phosphoric acid obtained by the Example and the comparative example, content of Sb and As was analyzed with the following method. The content of sulfide ions was also analyzed. These results are shown in Table 1 below.

[Sb analysis method]
(1) Weigh 50.0 g of sample into a 200 ml beaker and add water to make about 100 ml. In order to prevent bumping, put a few stones, cover with a watch glass, and boil on an electric heater to reduce the liquid volume to about 50 ml or less.
(2) {Sample preparation method when using ICP (JY238)}
After cooling, transfer to a 100 ml volumetric flask, add 10 ml of hydrochloric acid (arsenic-free 35-37%), add water and adjust the liquid level to the marked line, then shake the volumetric flask. Separately, a blank solution and a standard solution (Sb 0.2 ppm) prepared by adding 10 ml of hydrochloric acid (arsenic-free 35 to 37%) to a 100 ml volumetric flask are also prepared.
(3) Using a standard solution (Sb 0.2 ppm), the Sb content is measured by an ICP analyzer (reduction vaporization method) (wavelength: 231.147 nm).
(4) The measured value of Sb is calculated from the following equation.
Sb measurement value (ppb) = reading value (ppb) × 100 / sample (g)

The operation procedure of the ICP-HYD method is as follows.
Turn on the power of the ICP body and keep it stable for at least 1 hour before use.
1) Preparation of solution [1] HCl (arsenic-free 35 to 37%) is added to the blank solution, the standard solution, and the sample solution so as to be 1 mol (added at a rate of 10 ml of HCl in 100 ml).
[2] 1% NaBH ₄ : 10 g of NaBH ₄ is precisely weighed, placed in a 1000 ml beaker together with 20 g of NaOH, dissolved by adding about 500 ml of water, and diluted to 1000 ml with water.
[3] Cleaning solution: HCl 2 mol
2) Conditions of ICP-HYD Power: 1.0 kW or 1.2 kW
Plasma gas: 12-14 l / min
Nebulizer gas: 0.6 l / min The pressure is close to zero.
Sheath gas: 0.4 l / min
When the plasma is stable, place the tube in the cleaning solution and NaBH ₄ solution.
3) Measurement [1] Set the HYD method file for Sb measurement.
[2] A calibration curve is prepared by measuring the blank solution and the standard solution in this order, and then the sample solution is measured.

[As analysis method]
A 0.1 ppm solution of As is prepared as a standard solution. Further, 193.696 nm is used as the measurement wavelength of the ICP analyzer. The rest is the same as the Sb analysis method described above.

[Method of analyzing sulfide ions]
(1) The apparatus shown in FIG. 1 was used. The apparatus includes a hydrogen sulfide gas generation bottle 1 and a detector tube 2. The detection tube 2 includes a small diameter portion and a large diameter portion connected to the lower end of the small diameter portion. The upper and lower ends of the detection tube 2 are open. The detector tube 2 has a volume scale of 0 to 1.5 ml, and one scale is 0.01 ml. 100 g of a sample is weighed in the generation bottle 1 and 40 ml of stannous chloride solution (8 g of stannous chloride dissolved in 500 g of 36% hydrochloric acid and made up to 1 liter with water) and 4 g of sandy zinc are added. As a result, hydrogen sulfide gas is generated in the generation bottle 1. A detection tube 2 filled with lead acetate silica gel is immediately connected to the bottle 1. A rubber plug 3 is used for connection. For lead acetate silica gel, dissolve 5 g of lead acetate in 500 ml of methyl alcohol, add 500 g of white silica gel (500-297 microns) to this, mix well, leave it for about 10 minutes, and spread it on a stainless steel vat to form a thin layer. It was obtained by natural drying. Absorbent cotton 4 is packed in the upper and lower ends of the small-diameter portion of the detection tube 2, and lead acetate silica gel is filled in the meantime. Absorbent cotton 4 is also packed in the lower end opening of the large diameter portion of the detection tube 2. This absorbent cotton 4 is used to prevent the mist of the sample contained in the generating bottle 1 from rising in the detection tube 2.
(2) The hydrogen sulfide gas rises in the detection tube 2 and changes the white lead acetate filled in the detection tube 2 to brown lead sulfide. As a result, the inside of the detection tube 2 gradually changes from white to brown upward. After leaving the generating bottle 1 in a 35-40 ° C. water bath for about 1 hour, the detection tube 2 is removed. Tap the lower end of the removed detection tube 2 on the desk several times and read the volume changed to brown to 0.01 ml.
(3) Separately from the operations of (1) and (2), a calibration curve is created between the volume changed to brown and the amount (mg) of hydrogen sulfide. To prepare a calibration curve, first prepare a hydrogen sulfide standard comparative solution. The preparation method is as follows. First, 7 g of sodium sulfide is dissolved in a sodium hydroxide solution (6 w / v%) to prepare a stock solution made 1 liter with water. Determine the titer by iodometric titration of the stock solution. Based on the determined titer, accurately extract 10 mg of hydrogen sulfide from the stock solution. Water is added to the collected stock solution to make 1 liter, and this is used as a standard comparison solution. One milliliter of the standard comparison solution contains 0.01 mg of H ₂ S.
(4) Take 0 ml (hydrogen sulphide 0 mg), 1.0 ml (hydrogen sulphide 0.01 mg), 5.0 ml (hydrogen sulphide 0.05 mg) of the prepared standard comparative solution, put it in a generation bottle, add water to it. About 50 ml. Further, 50 ml of stannous chloride solution and 4 g of sandy zinc are added to generate hydrogen sulfide gas. Next, the operations of (1) and (2) are performed, and the volume of the detection tube 2 turned brown is obtained when the standard comparison solutions are 0 ml, 1.0 ml, and 5.0 ml, respectively. From these results, a calibration curve is created between the volume of the detection tube 2 turned brown and the amount (mg) of hydrogen sulfide.
(5) Calculation of measurement value The amount (mg) of hydrogen sulfide is obtained from the volume of the detection tube 2 that has turned brown and the calibration curve read in (2). Then, the amount of sulfide ions (ppb) is obtained with two significant digits from the following equation.

  As is apparent from the results shown in Table 1, it can be seen that the high-purity phosphoric acid (product of the present invention) of each Example has a very low content of Sb and As and sulfide ions. On the other hand, it can be seen that the phosphoric acid of the comparative example contains a large amount of Sb and As and the content of sulfide ions is also high.

Claims (9)

A high-purity phosphoric acid characterized in that Sb is 200 ppb or less and sulfide ions are 200 ppb or less as an impurity content when the concentration of H ₃ PO ₄ is converted to 85% by weight.   A first step of excessively blowing hydrogen sulfide gas into the crude phosphoric acid and precipitating the impurity metal contained in the crude phosphoric acid as a sulfide, and a second step of filtering the phosphoric acid obtained in the first step And a third step of removing the hydrogen sulfide gas contained in the phosphoric acid by bringing phosphoric acid and air into contact with each other in the removal tower after completion of the second step, and the first and second steps. The high-purity phosphoric acid according to claim 1, which is obtained by performing at 59 ° C. or lower.   The high-purity phosphoric acid according to claim 1 or 2, wherein the crude phosphoric acid is dry phosphoric acid obtained by burning yellow phosphorus to generate gas of diphosphorus pentoxide and then hydrating the gas.   The high purity phosphoric acid according to any one of claims 1 to 3, which is used for etching an electronic device.   A hydrogen sulfide gas is excessively blown into the crude phosphoric acid containing the impurity metal, the first step of precipitating the impurity metal contained in the crude phosphoric acid as a sulfide, and the phosphoric acid obtained in the first step is filtered. Including a second step and a third step of bringing phosphoric acid and air into contact with each other in the removal tower after the second step to remove hydrogen sulfide gas contained in the phosphoric acid, and the first and second steps. Is carried out at a temperature of 59 ° C. or less.   The method for producing high-purity phosphoric acid according to claim 4, wherein an aging step is performed between the first step and the second step.   The method for producing high-purity phosphoric acid according to claim 5 or 6, wherein the first step is performed by bringing crude phosphoric acid and hydrogen sulfide gas into contact with each other in an absorption tower packed with a packing material.   The method for producing high-purity phosphoric acid according to any one of claims 5 to 7, wherein the third step is performed by bringing phosphoric acid and air into contact with each other in a removal tower packed with a packing.   The crude phosphoric acid containing the impurity metal is dry phosphoric acid obtained by burning yellow phosphorus to generate gas of diphosphorus pentoxide and then hydrating the gas. The manufacturing method of high purity phosphoric acid of description.

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