TWI865666B - Method for producing purified hydrogen cyanide - Google Patents

Abstract

The present invention provides a method for producing purified hydrogen cyanide, which is capable of safely and stably purifying hydrogen cyanide while reducing the use of materials with high corrosion resistance in hydrogen cyanide purification equipment or components. The method for producing purified hydrogen cyanide of the present invention comprises: a step (A) of mixing crude hydrogen cyanide gas (1) with crude acrylonitrile gas (2) obtained by ammonia oxidation to form a crude mixed gas (3); and a step (B) of mixing the crude mixed gas (3) with an aqueous sulfuric acid solution (4) to neutralize and remove unreacted ammonia contained in the crude mixed gas (3) to obtain a deamination step. The present invention further comprises a step (B) of treating the gas (5), a step (C) of allowing the deaminated gas (5) to be absorbed by water (6) to obtain a crude mixed solution (7), a step (D) of separating the aqueous layer (8) from the crude mixed solution (7) to obtain an organic layer (9) containing hydrogen cyanide and acrylonitrile, and a step (E) of distilling the organic layer (9) to obtain purified hydrogen cyanide (11).

Description

Method for producing purified hydrogen cyanide

The present invention relates to a method for producing purified hydrogen cyanide by purifying crude hydrogen cyanide containing impurities such as unreacted residual components of synthetic raw materials to obtain purified hydrogen cyanide.

Hydrogen cyanide is widely used as a raw material for various compounds or pesticides. As an industrial method for producing hydrogen cyanide, for example, the Andrussow process is known, which is ammonia oxidation by reacting a mixture of methane, ammonia and air. In addition, there is also a method of obtaining hydrogen cyanide produced as a by-product when manufacturing acrylonitrile by ammonia oxidation using propyl ether or propane as a raw material, which is called the Sohio process.

Hydrogen cyanide synthesized by the ammoxidation of methane as described above may be crude hydrogen cyanide containing impurities such as unreacted residual components such as methane or ammonia, oxygen, etc., which are the synthesis raw materials. In order to obtain high-purity hydrogen cyanide, the crude hydrogen cyanide is purified.

Hydrogen cyanide is easy to polymerize in the presence of alkali, and the polymerization is further accelerated by heat. Due to the runaway reaction, there is a risk of blocking the line in the purification process, and further causing a fire or explosion. Therefore, crude hydrogen cyanide is purified by pH adjustment, etc. to reduce the risk of polymerization.

For example, Patent Document 1 describes a method for simultaneously producing acrylonitrile and hydrogen cyanide, wherein an acrylonitrile production process and a hydrogen cyanide production process are operated simultaneously, and by combining the product flows from the two processes, recovering and purifying them, the polymerization of relatively high concentration hydrogen cyanide can be substantially prevented.

The schematic flow of the method described in the above-mentioned patent document 1 is shown in FIG2. As shown in FIG2, in the method described in the above-mentioned patent document 1, the acrylonitrile product 22 from the acrylonitrile synthesis reactor is neutralized by spraying a sulfuric acid aqueous solution 23 in a quench column 100, and then mixed with the hydrogen cyanide product 21 from the hydrogen cyanide synthesis reactor and water 25 in an absorption column 200, and the pH is adjusted by adding an acid 26 to obtain a mixed product. After the non-absorbed compounds of the mixed product are separated and removed as exhaust gas 24 in the absorption column 200, the acid 26 is added to adjust the pH even in the recovery column 300 to be transferred. Moreover, before the mixed product is transferred to the decanter 400, the pH is adjusted by the acid 26, and the water layer is separated and refluxed to the recovery column 300. The organic layer is supplied to the head column 500, and after adjusting the pH with the acid 26, separation is performed to obtain separated crude hydrogen cyanide 31 and separated crude acrylonitrile 32. The separated crude hydrogen cyanide 31 is further distilled to obtain purified hydrogen cyanide. Prior art literature Patent literature

Patent document 1: Japanese Patent Publication No. 2011-513425

Invention Problems to be Solved

However, the mixture prepared by adjusting the pH of hydrogen cyanide and sulfuric acid is prone to corroding carbon steel, a material commonly used in factory piping or containers. Therefore, from the perspective of safe operation of the purification process, it is necessary to frequently replace equipment or components in the steps that come into contact with the mixture, or to use highly corrosion-resistant materials such as stainless steel. Even in the above-mentioned patent document 1, it is recorded that when hydrogen cyanide is recovered and purified by the method described in the document, in order to protect the equipment that comes into contact with hydrogen cyanide of a higher concentration than in the conventional Soheiau process for the production of acrylonitrile, the recovery and purification equipment should be made of a material having higher corrosion resistance than the carbon steel generally used for factory piping or containers, such as stainless steel.

However, frequent replacement of plant equipment or components is not good because it increases the equipment cost and the burden of replacement work, which in turn leads to a decrease in the production efficiency of purified hydrogen cyanide. On the other hand, since stainless steel and other materials with high corrosion resistance are expensive, when used as a component material of the above-mentioned recovery and purification equipment, or in a separate purification equipment for hydrogen cyanide, the equipment cost for obtaining purified hydrogen cyanide increases. Accordingly, a method for obtaining purified hydrogen cyanide at low cost, safely, and stably with high quality is being sought.

The present invention is completed to solve the above-mentioned problems, and aims to provide a method for producing purified hydrogen cyanide that can reduce the use of highly corrosion-resistant materials in hydrogen cyanide purification equipment or components, and can safely and stably purify hydrogen cyanide. Means for solving the problem

The present invention is based on the discovery that in the production of purified hydrogen cyanide, by incorporating a specified step in the purification process of acrylonitrile into the purification process of crude hydrogen cyanide, the material used for the purification equipment or its components can be reduced to a point where it is necessary to use a material with high corrosion resistance instead of the usual carbon steel.

That is, the present invention provides the following [1] to [8]. [1] A method for producing purified hydrogen cyanide, comprising: a step (A) of mixing crude hydrogen cyanide gas with crude acrylonitrile gas obtained by ammoxidation to obtain a crude mixed gas, a step (B) of mixing the crude mixed gas with an aqueous sulfuric acid solution to neutralize and remove unreacted ammonia contained in the crude mixed gas to obtain a deaminated gas, a step (C) of allowing the deaminated gas to be absorbed by water to obtain a crude mixed liquid, a step (D) of separating the aqueous layer from the crude mixed liquid to obtain an organic layer containing hydrogen cyanide and acrylonitrile, and a step (E) of distilling the organic layer to obtain purified hydrogen cyanide. [2] The method for producing purified hydrogen cyanide as described in [1] above, wherein the crude mixed gas contains 2.5 to 9.0 mol of acrylonitrile per 1 mol of hydrogen cyanide. [3] The method for producing purified hydrogen cyanide as described in [1] or [2] above, wherein the concentration of hydrogen cyanide in the crude mixed liquid is 0.1 to 20.0 mass %. [4] The method for producing purified hydrogen cyanide as described in any one of [1] to [3] above, wherein in the step (B), the crude mixed gas and the aqueous sulfuric acid solution are mixed by flowing the crude mixed gas into the aqueous sulfuric acid solution. [5] A method for producing purified hydrogen cyanide as described in any one of [1] to [4] above, wherein the step (C) is carried out in a carbon steel manufacturing facility. [6] A method for producing purified hydrogen cyanide as described in any one of [1] to [5] above, wherein the step (D) is carried out in a carbon steel manufacturing facility. [7] A method for producing purified hydrogen cyanide as described in any one of [1] to [6] above, wherein the crude hydrogen cyanide gas is obtained by ammoxidation of a synthetic raw material containing methanol. [8] A method for producing purified hydrogen cyanide as described in any one of [1] to [7] above, wherein the crude acrylonitrile gas is obtained by ammoxidation of a synthetic raw material containing propylene. Effect of the Invention

According to the method for producing purified hydrogen cyanide of the present invention, by reducing the need to use highly corrosion-resistant materials in hydrogen cyanide purification equipment or components, equipment costs can be suppressed, and hydrogen cyanide can be purified safely and stably, resulting in an increase in the production efficiency of purified hydrogen cyanide.

The following is a description of the method for producing purified hydrogen cyanide of the present invention with reference to the drawings. FIG1 shows a schematic flow chart of the method for producing purified hydrogen cyanide of the present invention. The method for producing purified hydrogen cyanide of the present invention is characterized by comprising: a step (A) of mixing crude hydrogen cyanide gas 1 with crude acrylonitrile gas 2 obtained by ammoxidation to obtain a crude mixed gas 3, a step (B) of mixing the crude mixed gas 3 with an aqueous sulfuric acid solution 4 to neutralize and remove unreacted ammonia contained in the crude mixed gas 3 to obtain a deaminated gas 5, a step (C) of allowing the deaminated gas 5 to be absorbed by water 6 to obtain a crude mixed solution 7, a step (D) of separating a water layer 8 from the crude mixed solution 7 to obtain an organic layer 9 containing hydrogen cyanide and acrylonitrile, and a step (E) of distilling the organic layer 9 to obtain purified hydrogen cyanide 11. That is, the method for producing purified hydrogen cyanide of the present invention includes steps (A) to (E) in order as shown in FIG1 . By purifying crude hydrogen cyanide through such steps, the use of materials with high corrosion resistance in hydrogen cyanide purification equipment or components can be reduced, thereby suppressing equipment costs. In addition, hydrogen cyanide can be purified safely and stably. The following is an explanation of steps (A) to (E) in order.

[Step (A)] Step (A) is a mixing step of mixing crude hydrogen cyanide gas 1 with crude acrylonitrile gas 2 obtained by ammoxidation to form a crude mixed gas 3. As described above, since hydrogen cyanide is dangerous to polymerize in the presence of alkali, it is necessary to keep it in a neutral to acidic state in an acid such as sulfuric acid, but a high concentration of hydrogen cyanide and an acid such as sulfuric acid in a mixed state easily corrodes carbon steel. From this point of view, in the present invention, the crude hydrogen cyanide gas 1 and the crude acrylonitrile gas 2 are mixed to form a crude mixed gas 3 before mixing with an aqueous sulfuric acid solution for inhibiting the polymerization of hydrogen cyanide.

<Crude hydrogen cyanide gas> The supply source of the crude hydrogen cyanide gas 1 is not particularly limited, and may be a gas containing hydrogen cyanide produced by a known hydrogen cyanide synthesis method. As industrial production methods for hydrogen cyanide, in addition to the Andrussow method mentioned above, there are also known methods using methane as a raw material, namely the so-called BMA method (also known as the Degussa method), or ammoxidation of methanol, etc.

The Andrussow process is a process in which a mixture of methane, ammonia and air (oxygen) is reacted at a high temperature of about 800-1000°C in the presence of a catalyst such as a rhodium-platinum catalyst. This reaction is the ammoxidation of methane and proceeds as shown in the following reaction formula (1).

The BMA method is a method in which a reaction is carried out in a bundle of alumina tubes coated with a platinum catalyst at a high temperature of about 1300°C in the absence of air (oxygen). This reaction is carried out as shown in the following reaction formula (2).

In the method of ammoxidation of methanol, the reaction is carried out as shown in the following reaction formula (3). In this method, a mixture of methanol, ammonia and air (oxygen) can be reacted in the presence of a catalyst such as molybdenum or bismuth, or a composite oxide catalyst of other metals at a lower temperature of about 300 to 600°C than the above reaction formulas (1) and (2).

Among these methods for producing hydrogen cyanide, from the viewpoint of energy efficiency, etc., a method for producing hydrogen cyanide by ammoxidation of methanol at a relatively low reaction temperature is preferred. Accordingly, the crude hydrogen cyanide gas 1 is preferably obtained by ammoxidation of a synthetic raw material containing methanol. In addition, the pressure during the reaction is preferably normal pressure to 1 MPaG, more preferably normal pressure to 0.5 MPaG, and even more preferably normal pressure to 0.2 MPa. In addition, the retention time of the product in the synthesis reactor is preferably 0.1 to 60 seconds, more preferably 0.1 to 50 seconds, and even more preferably 0.1 to 30 seconds.

Crude hydrogen cyanide gas 1 is a gas containing impurities such as unreacted residual components of synthetic raw materials, mixed components during production, and by-products in addition to hydrogen cyanide. Crude hydrogen cyanide gas 1 can be directly supplied to the generated gas discharged from the synthesis reactor of hydrogen cyanide. When the temperature of the generated gas is high, it is preferably cooled to a temperature at which it can be safely mixed with crude acrylonitrile gas 2 before being supplied to the mixing step. The aforementioned temperature is preferably set to below 250°C, and from the perspective of safety and energy efficiency, it is more preferably 100-230°C, and more preferably 150-200°C.

<Crude acrylonitrile gas> Crude acrylonitrile gas 2 is obtained by ammoxidation. As a method for producing acrylonitrile by ammoxidation, a known method can be applied. Among these methods, the above-mentioned Sohio method is generally used. Usually, a mixture of propylene, ammonia and air is reacted at a temperature of about 350 to 500°C in the presence of a catalyst such as molybdenum or bismuth, or a complex oxide catalyst of other metals. As a method for producing acrylonitrile, from the perspective of production efficiency, a method for producing by ammoxidation of propylene is preferred. Accordingly, crude acrylonitrile gas 2 is preferably obtained by ammoxidation of a synthetic raw material containing a propylene group.

In addition, methanol may be included in the synthetic raw material containing propylene in the production of acrylonitrile. Although the content of hydrogen cyanide in the crude acrylonitrile gas 2 can be increased by this, the ammoxidation of the synthetic raw material containing methanol together with the propylene leads to an increase in the load or energy cost of the acrylonitrile synthesis reactor, and there is also a case where the catalyst is easily deactivated. Accordingly, when the amount of hydrogen cyanide in the crude mixed gas 3 is increased, the amount of methanol supplied together with the propylene as a synthetic raw material in the acrylonitrile synthesis reactor is relatively increased, as described above, it is preferably increased by adjusting the supply amount of the generated gas discharged from the hydrogen cyanide synthesis reactor in other ways.

Crude acrylonitrile gas 2 is a gas containing impurities such as unreacted residual components of synthetic raw materials or mixed components during production, other than acrylonitrile, and by-products such as acetonitrile or hydrogen cyanide. Crude acrylonitrile gas 2 can be directly supplied to the generated gas discharged from the acrylonitrile synthesis reactor. When the temperature of the generated gas is high, it is preferably cooled to a temperature at which it can be safely mixed with crude hydrogen cyanide gas 1 before being supplied to the mixing step. The temperature is preferably set to 250°C or less, and from the perspective of safety and energy efficiency, it is more preferably 100-240°C, and more preferably 150-230°C. Since the crude acrylonitrile gas 2 may contain tar or heavy distillate from modified products or polymers of acrylonitrile as impurities, it is preferably washed with water to separate and remove such tar or heavy distillate. The washing can be performed, for example, in an absorption tower into which water flows. The crude acrylonitrile gas 2 washed with water is preferably cooled to below 100°C, more preferably to below 95°C, and even more preferably to below 85°C.

As described above, the crude hydrogen cyanide gas 1 and the crude acrylonitrile gas 2 are preferably mixed after being cooled to a temperature lower than the temperature of the generated gas in the synthesis reactor from the viewpoint of the safety of the mixing operation, so as to obtain the crude mixed gas 3.

<Crude mixed gas> The crude mixed gas 3 preferably contains 2.5 to 9.0 mol of acrylonitrile relative to 1 mol of hydrogen cyanide, more preferably 2.6 to 6.0 mol, and even more preferably 2.8 to 5.0 mol. If the amount of acrylonitrile is 2.5 mol or more relative to 1 mol of hydrogen cyanide, hydrogen cyanide is sufficiently diluted with acrylonitrile, and in order to suppress the polymerization of hydrogen cyanide, it becomes easy to suppress the corrosion of carbon steel even when mixed with sulfuric acid. In addition, from the perspective of the production efficiency of purified hydrogen cyanide, the upper limit of the amount of acrylonitrile relative to 1 mol of hydrogen cyanide is preferably 9.0 mol or less.

In addition, the molar amount of acrylonitrile relative to 1 mole of hydrogen cyanide in the crude mixed gas 3 of the present invention, that is, since the molar ratio of acrylonitrile to hydrogen cyanide in the crude mixed gas 3 is difficult to determine by actual analytical measurement, it is a calculated value based on the charged amounts of acrylonitrile and hydrogen cyanide in each synthetic raw material produced and the assumed yield.

[Step (B)] Step (B) is a deamination step of mixing the crude mixed gas 3 obtained in step (A) with an aqueous sulfuric acid solution 4 to neutralize and remove the unreacted ammonia contained in the crude mixed gas 3, thereby obtaining a deamination treated gas 5. In this way, by deaminating the crude mixed gas 3 with an aqueous sulfuric acid solution 4, it is not necessary to perform a deamination treatment for removing the unreacted ammonia of the synthesis raw material of hydrogen cyanide in the subsequent steps.

The mixing of the crude mixed gas 3 and the aqueous sulfuric acid solution 4 is preferably carried out by flowing the crude mixed gas 3 into the aqueous sulfuric acid solution 4. For example, the crude mixed gas 3 can be introduced into a sulfuric acid tank filled with the aqueous sulfuric acid solution 4 and mixed with the aqueous sulfuric acid solution 4. In such a method, the unreacted ammonia of the synthetic raw material contained in the crude mixed gas 3 is neutralized with sulfuric acid by contacting the crude mixed gas 3 with a sufficient amount of the aqueous sulfuric acid solution 4, and the ammonium sulfate generated is removed as an aqueous solution. The concentration of sulfuric acid in the aqueous sulfuric acid solution 4 varies depending on the amount of unreacted ammonia contained in the crude mixed gas 3, but from the perspective of efficient removal of ammonia and safety of operation, it is preferably 0.1 to 20.0 mass%, more preferably 1.0 to 10.0 mass%, and even more preferably 2.0 to 7.0 mass%. The temperature of the sulfuric acid tank is preferably 30 to 100°C, more preferably 50 to 95°C, and even more preferably 70 to 90°C from the viewpoint of efficiently performing the deamination treatment of the crude mixed gas 3.

[Step (C)] Step (C) is an absorption step in which the deaminated gas 5 obtained in step (B) is absorbed by water 6 to obtain a crude mixed solution 7. In step (C), the deaminated gas 5 from which ammonia is fully removed is absorbed by water 6, and the gas not absorbed by water is separated and removed as waste gas.

The crude mixed solution 7 is fully free of ammonia, and the pH is below 7.00, preferably 4.00 to 6.50, and more preferably 5.00 to 6.00, and hydrogen cyanide is in a stable state of inhibiting polymerization. Therefore, in step (C), it is not necessary to add an acidic liquid such as sulfuric acid again to adjust the pH. The concentration of hydrogen cyanide in the crude mixed solution 7 is preferably 0.1 to 20.0 mass%, more preferably 0.3 to 10.0 mass%, and even more preferably 0.5 to 5.0 mass%, from the perspective of efficient production of purified hydrogen cyanide and safety of operation in which polymerization of hydrogen cyanide is fully inhibited.

Furthermore, from the viewpoint of sufficiently dissolving hydrogen cyanide in the crude mixed liquid 7 and efficiently producing purified hydrogen cyanide, the crude mixed liquid 7 is preferably cooled to 50°C or less, more preferably to 1 to 35°C, and even more preferably to 5 to 25°C.

As mentioned above, although the crude mixed solution 7 is adjusted to neutral to acidic in the sulfuric acid aqueous solution, the carbon steel is not easily corroded when the hydrogen cyanide is diluted in a state of mixing with acrylonitrile. Accordingly, in step (C), although the corrosion resistance is high, it is not necessary to use expensive materials, such as stainless steel equipment such as SUS304 or SUS316, and carbon steel equipment can be used. The method of the present invention has the advantage of suppressing equipment costs in this regard.

The crude mixed liquid 7 obtained by absorbing the deaminated gas 5 with water 6 contains, in addition to hydrogen cyanide and acrylonitrile, acetonitrile, a by-product of the production of acrylonitrile. In order to separate and remove the acetonitrile, it is also preferable to undergo a stripping treatment. The recovered liquid containing hydrogen cyanide and acrylonitrile after the separation and removal of acetonitrile is also combined as the crude mixed liquid 7 and provided to the following step (D).

[Step (D)] Step (D) is a liquid-liquid separation step of separating the aqueous layer 8 from the crude mixed solution 7 obtained in step (C) to obtain an organic layer 9 containing hydrogen cyanide and acrylonitrile. In step (D), the organic layer 9 is a state where hydrogen cyanide is diluted with acrylonitrile, and the pH is maintained below 7.00, and there is no need to add an acid or the like for inhibiting the polymerization of hydrogen cyanide. The pH of the organic layer 9 is preferably 4.00 to 6.50, and more preferably 5.00 to 6.00.

Even in step (D), similar to step (C), since hydrogen cyanide is diluted in a state of being mixed with acrylonitrile, it will not easily corrode carbon steel, so it is not necessary to use equipment made of highly corrosion-resistant materials, and carbon steel equipment can be used. The method of the present invention has the advantage of suppressing equipment costs in this regard.

A trace amount of acrylonitrile or hydrogen cyanide, acetonitrile, etc. is dissolved in the separated water layer 8. The separated water layer 8 can be recovered to improve the yield of purified hydrogen cyanide, and can also be combined with the crude mixed solution 7 for circulation.

[Step (E)] Step (E) is a distillation step for distilling the organic layer 9 obtained in step (D) to obtain purified hydrogen cyanide 11. In step (E), hydrogen cyanide and acrylonitrile contained in the organic layer 9 are separated by distilling the organic layer 9 to obtain purified hydrogen cyanide 11.

In step (E), since the distillation equipment used for purifying hydrogen cyanide is in contact with high-concentration hydrogen cyanide, in order to suppress the corrosion of the equipment and obtain highly purified hydrogen cyanide, it is preferably made of a material with high corrosion resistance such as stainless steel. In addition, in order to suppress the polymerization of hydrogen cyanide in the distillation step and stabilize it, the organic layer 9 is preferably distilled by adding an acid. Examples of additives for stabilizing hydrogen cyanide include glycolic acid, acetic acid, sulfurous acid gas, phosphoric acid, etc. When an acid is added, the pH of the organic layer 9 after the addition is preferably 3.50 to 6.00, and more preferably 4.00 to 5.50.

The distillate containing hydrogen cyanide recovered by separating and removing acrylonitrile can be further refined to produce purified hydrogen cyanide 11 with high purity. In addition, the dehydrocyanide treatment liquid 12 containing acrylonitrile can be further refined to produce purified acrylonitrile with high purity by, for example, performing liquid-liquid separation treatment again, drying the obtained organic layer, and further refining. Example

Although the following describes an embodiment of the present invention, the present invention is not limited to the embodiment. [Example 1] Purified hydrogen cyanide is produced according to the process shown in FIG1. The crude acrylonitrile gas 2 at 230°C obtained by ammoxidation of propylene is washed with water and cooled to 85°C, and then mixed with the crude hydrogen cyanide gas 1 at 200°C obtained by ammoxidation of methanol to obtain a crude mixed gas 3 (step (A)). The ratio of acrylonitrile to hydrogen cyanide contained in the crude mixed gas 3 is such that 2.83 mol of acrylonitrile is obtained per 1 mol of hydrogen cyanide. The crude mixed gas 3 is mixed with a sulfuric acid aqueous solution 4 having a sulfuric acid concentration of 5.0 mass % in a sulfuric acid tank (85°C) to obtain a deaminated gas 5 at 85°C (step (B)). Then, the deaminated gas 5 is absorbed by water to obtain a crude mixed liquid 7 at about 20°C (step (C)). The crude mixed liquid 7 is separated by stripping treatment to remove acetonitrile, and a recovered liquid containing hydrogen cyanide and acrylonitrile is returned, which is also used as a combined liquid. The pH of the crude mixed liquid 7 is 5.95. In addition, the pH is the arithmetic mean of the values measured three times on a desktop pH meter ("F-71S", Horiba, Ltd., temperature correction (20°C)) (the same applies hereinafter). Next, the crude mixed solution 7 is liquid-separated into an organic layer 9 and an aqueous layer 8 (step (D)). The aqueous layer 8 is recovered and returned and also merged with the crude mixed solution 7. The concentration of hydrogen cyanide contained in the crude mixed solution 7 is about 1.8% by mass. The pH of the organic layer 9 is 5.63. Furthermore, after adding acetic acid and sulfurous acid gas to the organic layer 9 (pH 4.32), it is distilled to obtain purified hydrogen cyanide (step (E)). Still, the concentration of hydrogen cyanide contained in the organic layer 9 is about 8.3% by mass.

Each device for performing step (C) and step (D) is made of carbon steel, and in other steps, the devices and components in contact with hydrogen cyanide are made of stainless steel (SUS304).

Even when the carbon steel absorption tower for step (C) was used for one year (maximum 10,000 tons/year of purified hydrogen cyanide production), no corrosion was observed to progress, and no clogging due to polymerization of hydrogen cyanide was observed in the absorption tower and the lines before and after it. From this, it can be seen that by mixing crude hydrogen cyanide gas and crude acrylonitrile gas and then performing deamination treatment, the use of expensive materials with high corrosion resistance in the production equipment of purified hydrogen cyanide can be reduced, and the polymerization of hydrogen cyanide can be efficiently suppressed. Therefore, according to the production method of the present invention, compared with the case of purifying crude hydrogen cyanide alone, the equipment cost can be suppressed, and purified hydrogen cyanide can be obtained safely and stably.

1: Crude hydrogen cyanide gas 2: Crude acrylonitrile gas 3: Crude mixed gas 4: Sulfuric acid aqueous solution 5: Deamination treatment gas 6: Water 7: Crude mixed solution 8: Water layer 9: Organic layer 11: Purified hydrogen cyanide 12: Dehydrocyanide treatment solution 21: Hydrogen cyanide product 22: Acrylonitrile product 23: Sulfuric acid aqueous solution 24: Waste gas 25: Water 26: Acid 31: Separation of crude hydrogen cyanide 32: Separation of crude acrylonitrile 100: quenching column 200: absorption column 300: recovery column 400: decanter 500: head column

[Figure 1] is a schematic flow chart of the method for producing purified hydrogen cyanide of the present invention. [Figure 2] is a schematic flow chart of the method for simultaneously producing acrylonitrile and hydrogen cyanide described in Patent Document 1.

1: Crude hydrogen cyanide gas

2: Crude acrylonitrile gas

3: Rough mixed gas

4: Aqueous solution of sulfuric acid

5: Deamination of gas treatment

6: Water

7: Crude mixed liquid

8: Water layer

9: Organic layer

11: Purification of hydrogen cyanide

12: Decyanation treatment liquid

Claims (5)

A method for producing purified hydrogen cyanide comprises: a step (A) of mixing crude hydrogen cyanide gas obtained by ammoxidation of methanol with crude acrylonitrile gas obtained by ammoxidation to obtain a crude mixed gas; a step (B) of mixing the crude mixed gas with an aqueous sulfuric acid solution to neutralize and remove unreacted ammonia contained in the crude mixed gas to obtain a deaminated gas; a step (B) of allowing the deaminated gas to be absorbed by water and passing through a stripping process for separating and removing acetonitrile. The invention further comprises a step (C) of obtaining a crude mixed solution containing hydrogen cyanide and acrylonitrile by treating the crude mixed solution with water to obtain an organic layer containing hydrogen cyanide and acrylonitrile; a step (D) of separating the aqueous layer from the crude mixed solution to obtain an organic layer containing hydrogen cyanide and acrylonitrile; and a step (E) of distilling the organic layer to obtain purified hydrogen cyanide; wherein the step (D) is carried out in a carbon steel device, the organic layer is a state in which hydrogen cyanide is diluted with acrylonitrile, and the concentration of hydrogen cyanide in the crude mixed solution is 0.1-20.0 mass %. The method for producing purified hydrogen cyanide as claimed in claim 1, wherein the crude mixed gas contains 2.5 to 9.0 moles of acrylonitrile relative to 1 mole of hydrogen cyanide. The method for producing purified hydrogen cyanide as claimed in claim 1, wherein in the aforementioned step (B), the aforementioned crude mixed gas is flowed into the aforementioned aqueous sulfuric acid solution to mix the aforementioned crude mixed gas with the aforementioned aqueous sulfuric acid solution. The method for producing purified hydrogen cyanide as claimed in claim 1, wherein the aforementioned step (C) is carried out in a carbon steel manufacturing facility. A method for producing purified hydrogen cyanide as claimed in claim 1 or 2, wherein the crude acrylonitrile gas is obtained by ammoxidation of a synthetic raw material containing a propylene group.

Images