Acetic acid production method and acetic acid production apparatus

Abstract

To provide a recovery method of ethyl iodide by-produced in a production process of acetic acid.SOLUTION: A production method of acetic acid includes a reaction step for carbonylating methanol with carbon monoxide to produce acetic acid, a flash evaporation step for separating a vapor phase fraction containing the acetic acid from a reaction product solution flowing in from the reaction step, and a light-end distillation step for producing a bottom liquid and an overhead effluent to be recycled to the reaction step from the vapor phase fraction. The production method further includes an excess water removal step for distilling a water phase discharged from the light-end distillation step to remove the excess water by-produced in the reaction step and separating at least methyl iodide, methyl acetate, and ethyl iodide to recycle to the reaction step or / and the light-end distillation step and a separation step for separating and removing water from a water phase containing at least ethyl iodide discharged from the excess water removal step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing acetic acid and an acetic acid production apparatus.

Background Art

[0002] The present invention relates to a method for recovering ethyl iodide by-produced in an acetic acid production process. The acetic acid product stream in the acetic acid production process is separated into acetic acid and impurities through a plurality of distillation columns. In the separation, reaction raw materials such as a reaction solvent and a cocatalyst are recycled from the distillation step to the reaction step or the like, but a part of the water separated in the distillation step is discarded outside the system. For example, in Patent Document 1, it is disclosed that the aqueous phase discharged from the excess water removal distillation column in the acetic acid production process is discharged outside the reaction system.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The acetic acid product stream contains various impurities generated in the reaction process, one of which is ethyl iodide. Ethyl iodide may be contained in trace amounts in the above-mentioned discarded water. Ethyl iodide forms hydrogen iodide through a catalyst, and hydrogen iodide reacts with methanol, which is a reaction raw material, to produce methyl iodide, which is a cocatalyst for the reaction. Therefore, if ethyl iodide is discharged outside the reaction system, as a result, methyl iodide decreases, leading to a loss of the cocatalyst. Furthermore, since ethyl iodide contains iodine, it is not preferable from an environmental aspect to discard it.

[0005] To avoid this, it is also conceivable to improve the distillation column (the number of theoretical plates, reflux ratio, temperature, pressure conditions, etc.) to enhance the separation efficiency of ethyl iodide. However, since ethyl iodide is a trace component, improving the distillation column may involve complications due to an increase in the number of theoretical plates and enlargement of the column, which is not practical in terms of cost-effectiveness.

[0006] Therefore, as a result of intensive studies by the present inventors, by separately providing a separation means for partially removing water from the aqueous phase containing ethyl iodide discharged from this distillation column in a conventional distillation column (Excess Water Column) for separating excess water, it has been found that the recovery efficiency of ethyl iodide can be simply improved without significantly modifying the distillation column.

[0007] That is, the present invention can significantly improve the recovery efficiency of ethyl iodide without significantly modifying the conventional distillation column.

Means for Solving the Problems

[0008] A method for producing acetic acid according to one aspect of the present invention includes a reaction step of subjecting methanol to carbonylation with carbon monoxide to produce acetic acid, a flash evaporation step of separating a vapor-phase fraction containing acetic acid from the reaction product liquid flowing in from the reaction step, and a light-end distillation step of producing a bottoms liquid and a top product liquid circulated to the reaction step from the vapor distillation. The method is a method for producing acetic acid, and includes an excess water removal step of distilling the aqueous phase discharged from the light-end distillation step to remove excess water by-produced in the reaction step and separating at least methyl iodide, methyl acetate, and ethyl iodide and recycling them to the reaction step and / or the light-end distillation step, and a separation step of separating and removing water from the aqueous phase containing at least ethyl iodide discharged from the excess water removal step, thereby removing water.

[0009] Further, an acetic acid production apparatus according to another aspect of the present invention includes a reactor that performs a carbonylation reaction to carbonylate methanol with carbon monoxide to produce acetic acid, a flash evaporation unit that separates a gas-phase fraction containing acetic acid from a reaction product liquid flowing in from the reaction step, and a light-end distillation unit that produces a bottoms liquid and a top product liquid to be circulated to the reaction step from the gas-phase distillation. The acetic acid production apparatus has an excess water removal unit that distills the aqueous phase discharged from the light-end distillation unit to remove excess water by-produced in the reactor and separates at least methyl iodide, methyl acetate, and ethyl iodide and recycles them to the reactor and / or the light-end distillation unit, and a separation unit that separates and removes water from the aqueous phase containing at least ethyl iodide discharged from the excess water removal unit.

Advantages of the Invention

[0010] According to one aspect of the present invention, there are provided a method for producing acetic acid that is environmentally friendly and can significantly improve the recovery efficiency of ethyl iodide without significantly improving a conventional distillation column, and an acetic acid production apparatus to which the production method is applied.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] According to a first aspect of the present invention, there is provided a method for producing acetic acid, comprising: a reaction step of subjecting methanol to carbonylation with carbon monoxide to produce acetic acid; a flash evaporation step of separating a gas-phase fraction containing acetic acid from a reaction product liquid flowing in from the reaction step; a light-end distillation step of producing a bottoms liquid and a top product liquid to be circulated to the reaction step from the gas-phase distillation, wherein water in the aqueous phase discharged from the light-end distillation step is distilled to remove excess water by-produced in the reaction step, and at least methyl iodide, methyl acetate, and ethyl iodide are separated and recycled to the reaction step and / or the light-end distillation step; and a separation step of separating and removing water from the aqueous phase containing at least ethyl iodide discharged from the excess water removal step.

[0013] An acetic acid production apparatus to which this production method is applied includes a reactor that performs a carbonylation reaction of carbonylating methanol with carbon monoxide to produce acetic acid, a flash evaporation unit that separates a gas-phase fraction containing acetic acid from a reaction product liquid flowing in from the reaction step, and a light-end distillation unit that produces a bottoms liquid and a top product liquid to be circulated to the reaction step from the gas-phase distillation. The apparatus further includes an excess water removal unit that distills the aqueous phase discharged from the light-end distillation unit to remove excess water by-produced in the reactor and separates and recycles at least methyl iodide, methyl acetate, and ethyl iodide to the reactor and / or the light-end distillation unit, and a separation unit that separates and removes water from the aqueous phase containing at least ethyl iodide discharged from the excess water removal unit. A specific example thereof is shown in FIG. 1. An aspect of the present invention will be described based on FIG. 1.

[0014] [First Embodiment] The acetic acid production apparatus 10 according to the first embodiment of the present invention will be described with reference to FIG. 1. In the first embodiment of the present invention, a heterogeneous system using a solid catalyst will be described as an example, but the present invention is not limited thereto, and a homogeneous system using a noble metal catalyst dissolved in a liquid phase may also be used.

[0015] As shown in Fig. 1, the acetic acid production apparatus 10 includes a reactor 1 that performs a carbonylation reaction to carbonylate methanol with carbon monoxide to produce acetic acid, a flash evaporation unit 2 such as a flash evaporator that separates a gas-phase fraction containing acetic acid from the reaction product liquid flowing in from the reactor 1, a first light-end distillation unit 3 that further removes light components from the gas-phase fraction separated by the flash evaporation unit 2 by distillation, and a second light-end distillation unit 11 that removes components other than water from the discharge stream from the first light-end distillation unit 3.

[0016] Furthermore, it has a separation unit 12 that recovers components other than water from the bottoms stream from the second light-end distillation unit 11 and discharges residual water not containing ethyl iodide, and a reflux unit 13 that returns the components containing ethyl iodide recovered by the separation unit 12 to the flash evaporation unit 2.

[0017] Methanol and carbon monoxide are introduced into the reactor 1, and acetic acid is produced by their reaction. Specifically, in the reactor 1, a solid catalyst is dispersed and present in the liquid phase. The liquid phase contains acetic acid as a solvent, methyl iodide as a reaction promoter, methanol as a reaction raw material, and various reaction by-products (methyl acetate, acetaldehyde, water, etc.). Carbon monoxide gas is blown into the above reaction liquid in which the solid catalyst is dispersed. For example, under conditions of a reaction temperature of 150 to 200 °C and a reaction pressure of about 1 to 6 MPa, methanol reacts with carbon monoxide to produce acetic acid.

[0018] The reaction product liquid of the reactor 1 is taken out through a screen or the like and introduced into the flash evaporation unit 2. Then, a part of the reaction product liquid is vaporized by flash evaporation to form a gas phase and a liquid phase. The gas phase generated by flash evaporation flows into the subsequent first light-end distillation unit 3.

[0019] The off-gas discharged from the top of the reactor 1 is introduced from the bottom into the methyl iodide absorption section 7. The off-gas introduced into the methyl iodide absorption section 7 comes into contact with the liquid methanol that has been dropped from the top of the methyl iodide absorption section 7, and the methyl iodide is absorbed into the liquid methanol. The methanol-containing liquid that has absorbed methyl iodide and the like is returned to the reactor 1. Further, the off-gas from which methyl iodide and the like have been removed, discharged from the top or the like of the methyl iodide absorption section 7, is appropriately treated in the waste treatment section 9 and then discharged out of the reaction system.

[0020] Furthermore, instead of the gas phase discharged from the first light-end distillation section 3, the gas phase discharged as a discharge stream from the second light-end distillation section 11 is led to the methyl iodide absorption section 8 and introduced from the bottom. The methanol-containing liquid that has absorbed methyl iodide and the like is returned to the reactor 1. Further, the off-gas from which methyl iodide and the like have been removed, discharged from the top or the like of the methyl iodide absorption section 8, is appropriately treated in the waste treatment section 9 and then discharged out of the reaction system.

[0021] The liquid phase generated by flash evaporation is returned to the reactor 1.

[0022] In the first light-end distillation section 3, the gas phase flowing in from the flash evaporation section 2 is separated by distillation. By ensuring that a part of acetic acid, which has the lowest volatility among the components constituting the gas phase flowing in from the flash evaporation section 2, is included in the discharge stream, all other gas phase components such as water and permanganate-reducing compounds can be included in the discharge stream. Most of the acetic acid contained in the gas phase in the flash evaporation section 2 is taken out as a bottoms liquid from below the first light-end distillation section 3 and led to a heavy fraction distillation section 5 such as a heavy fraction distillation column that performs a heavy fraction removal step.

[0023] In the heavy fraction distillation section 5, impurities such as propionic acid with a boiling point lower than that of acetic acid are removed by distillation. The acetic acid taken out as a discharge stream from the heavy fraction distillation section 5 is appropriately purified in the product acetic acid purification section 6 and then separated and recovered as a product. The impurities taken out as a bottoms liquid from the lower part of the heavy fraction distillation section 5 are appropriately treated in the waste treatment section 9 and then discarded. Note that the bottoms liquid taken out from the lower part of the heavy fraction distillation section 5 may be configured to be refluxed to the reactor 1.

[0024] In the acetic acid production apparatus of the present invention, it has a separation section 12 and a reflux section 13 that returns the component containing ethyl iodide recovered in the separation section 12 to the flash evaporation section 2, and discharges residual water outside the system. That is, components other than water are recovered in the second light end distillation section 11 and returned to the flash evaporation section 2. The separation section 12 recovers ethyl iodide from water containing a trace amount of ethyl iodide, and the water containing no ethyl iodide is discarded as wastewater. Fig. 2 shows the specific configuration of the separation section 12 used in the present invention. In this system, reflux is basically unnecessary, and the condensate condensed by the condenser is recycled to the reaction system, so a stripper column can be adopted. In addition, since the throughput of this system is small and the required column diameter can be small, the dehydration section 15, the condenser 16, and the kettle type reboiler 17 can be integrated. By adopting the integrated type with this kettle type reboiler, the pressure in the reboiler can be made lower than that of a thermosyphon type reboiler, and the boiling point rise can be suppressed. Therefore, as a result, it is easier to ensure a temperature difference, and there is an advantage that the heat transfer area can be reduced. Furthermore, since the number of installed devices is also small, there is also an effect of reducing the construction cost. Further, for the condenser 16, by integrating it with the dehydration section 15, a receiver becomes unnecessary. In the present invention, a general stripper column in which the dehydration section 15 and the condenser 16 and the kettle type reboiler 17 are separated can also be used, but by applying an integrated stripper column, the above-mentioned advantages can be obtained. By using such a recovery column 12, ethyl iodide is recovered at a recovery rate of 99.9% or more and recycled to the reaction system.

[0025] The separation unit 12, which is this separation means, is a stripper column or a vapor permeation separation membrane 18. As the stripper type column, for example, an atmospheric pressure stripper, a pressurized stripper, etc. can be used. Fig. 3 shows the configuration of the vapor permeation separation membrane 18. As described above, when the recycled water from the second light end column passes through the vapor permeation separation membrane 18 of the separation unit, ethyl iodide that does not pass through the separation membrane is recycled by returning to the reaction system, and the passed unnecessary water is discarded as waste liquid.

[0026] The type of the vapor permeation separation membrane (also called a vapor separation membrane) that constitutes the separation membrane dehydration unit may be appropriately determined according to the type of components that constitute the water-soluble organic substance and various conditions such as the temperature and pressure of the distillate vapor to be introduced. For example, in the case of an inorganic type, zeolite membranes, carbon membranes, ceramic porous membranes, etc. can be mentioned. Further, in the present invention, a vapor permeation separation membrane that selectively permeates water (water vapor) and can efficiently separate it from other components can be used. In particular, when the raw material is a two-component system of a water-soluble organic substance such as acetic acid and water, a zeolite membrane that permeates water (water vapor) and separates it from acetic acid etc. in a vapor state can be used as the vapor permeation separation membrane. As the zeolite membrane, for example, membranes using zeolites such as type A membrane, Y type, mordenite type, chabazite type, etc. can be mentioned.

[0027] The configuration (pore diameter, shape, porous / non-porous, etc.) of the vapor permeation separation membrane is not particularly limited, and like the type of the vapor permeation separation membrane described above, it may be appropriately determined according to the type of components that constitute the raw material and various conditions such as the temperature and pressure of the water-soluble organic substance to be introduced. Further, the vapor permeation separation membrane may be used in a form such as a multi-tubular so-called separation membrane module.

[0028] [Second Embodiment] The above-described aspect is an example in which a separation unit (stripper column or membrane separation) as a separation means is added to the excessive water removal unit of the conventional specifications. However, even when only one excessive water removal unit is improved without adding an independent separation unit, ethyl iodide can also be recovered.

[0029] That is, according to another embodiment of the present invention, there is provided a method for producing acetic acid, comprising: a reaction step of subjecting methanol to carbonylation with carbon monoxide to produce acetic acid; a flash evaporation step of separating a gas-phase fraction containing acetic acid from a reaction product liquid flowing in from the reaction step; and a light-end distillation step of producing a bottoms liquid and a top effluent to be circulated to the reaction step from the gas-phase distillation. In the method, an aqueous phase discharged from the light-end distillation step is distilled to remove excess water by-produced in the reaction step, and at least methyl iodide, methyl acetate, and ethyl iodide are separated and recycled to the reaction step and / or the light-end distillation step by an excess water removal step.

[0030] However, it has been found that, in order to obtain the same recovery efficiency of ethyl iodide as in the first embodiment of the present invention having a separation section, the number of theoretical plates of the distillation column in the excess water removal step increases significantly. That is, in the first embodiment, the number of theoretical plates of the distillation column and the stripper column is 20 to 60, while in the second embodiment, which is only the distillation column, the number of theoretical plates is 120 to 200.

[0031] Therefore, it can be seen that in order to effectively recover ethyl iodide, it is more preferable to add a separation section (stripper column or membrane separation) as a separation means to the excess water removal section as in the first embodiment.

Explanation of Reference Numerals

[0032] 1 Reactor 2 Flash Evaporation Section 3 First Light-End Distillation Section 5 Heavy Fraction Distillation Section 6 Product Acetic Acid Purification Section 7, 8 Methyl Iodide Absorption Section 9 Waste Treatment Section 10 Acetic Acid Production Apparatus 11 Second Light-End Distillation Section 12 Separation Section (Stripper Column) 13 Reflux Section 14 Flow path 15 Dehydration section 16 Condenser 17 Kettle type reboiler 18 Vapor permeation separation membrane

Claims

1. A reaction step of performing a carbonylation reaction for carbonylating methanol with carbon monoxide to produce acetic acid, a flash evaporation step of separating a gas-phase fraction containing acetic acid from the reaction product liquid flowing in from the reaction step, and a light-end distillation step of producing a bottoms liquid and a top discharge liquid to be circulated to the reaction step from the gas-phase fraction. A method for producing acetic acid, comprising: a step of removing excess water by-product in the reaction step by distilling the top discharge liquid discharged from the light-end distillation step, and producing a first stream containing at least methyl iodide, methyl acetate, and ethyl iodide, and a second stream containing the excess water and at least ethyl iodide, wherein the first stream is recycled to the reaction step and / or the light-end distillation step; and a separation step of separating and removing water from the second stream discharged from the excess water removal step. A method for producing acetic acid, characterized in that water is removed.

2. The method for producing acetic acid according to claim 1, wherein the separation means in the separation step is a stripper column or a steam permeation separation membrane.

3. The method for producing acetic acid according to claim 2, wherein the steam permeation separation membrane is selected from a zeolite membrane, a carbon membrane, and a ceramic porous membrane.

4. A reaction step of performing a carbonylation reaction for carbonylating methanol with carbon monoxide to produce acetic acid, a flash evaporation step of separating a gas-phase fraction containing acetic acid from the reaction product liquid flowing in from the reaction step, and a light-end distillation step of producing a bottoms liquid and a top discharge liquid to be circulated to the reaction step from the gas-phase fraction. A method for producing acetic acid, comprising: a step of removing excess water by-product in the reaction step by distilling the top discharge liquid discharged from the light-end distillation step, and producing a first stream containing at least methyl iodide, methyl acetate, and ethyl iodide, and a second stream containing the excess water and at least ethyl iodide, wherein the first stream is recycled to the reaction step and / or the light-end distillation step; and a step of removing water by the excess water removal step. Furthermore, a step of separating ethyl iodide from the second stream discharged from the excess water removal step through a separation unit having a stripper column or a steam permeation separation membrane; A method for producing acetic acid, characterized by comprising the above steps.

5. The method for producing acetic acid according to claim 4, wherein the number of theoretical plates of the distillation column in the excess water removal step is 20 to 60 plates.

6. A reactor that performs a reaction step including a carbonylation reaction in which methanol is carbonylated with carbon monoxide to produce acetic acid, a flash evaporation unit that separates a gas-phase fraction containing acetic acid from the reaction product liquid flowing in from the reaction step, and a light-end distillation unit that produces a bottoms liquid and a top discharge liquid that is circulated to the reaction step from the gas-phase fraction, and an acetic acid production apparatus having: An excess water removal unit that distills the top discharge liquid discharged from the light-end distillation unit to remove excess water by-produced in the reactor, and generates a first stream containing at least methyl iodide, methyl acetate, and ethyl iodide, and a second stream containing the excess water and at least ethyl iodide, wherein the first stream is recycled to the reactor and / or the light-end distillation unit; A separation unit configured to separate and remove water from the second stream discharged from the excess water removal unit; An acetic acid production apparatus, characterized by comprising:

7. The acetic acid production apparatus according to claim 6, wherein the separation means in the separation unit is a stripper column or a steam permeation separation membrane.

8. The acetic acid production apparatus according to claim 7, wherein the steam permeation separation membrane is selected from a zeolite membrane, a carbon membrane, and a ceramic porous membrane.

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