JP2022034959A - Production method of acetic acid - Google Patents

Abstract

To provide a production method of acetic acid in which acetaldehyde and methyl iodide can be separated efficiently, and loss of methyl iodide is reduced.SOLUTION: A production method of acetic acid includes a membrane separation process for acquiring separately a flow rich in acetaldehyde and a flow rich in methyl iodide by using a zeolite film, from a process flow containing acetaldehyde and methyl iodide, in a production process of acetic acid. The zeolite film is preferably a BEA-type zeolite film. Preferably, the acetaldehyde concentration in the process flow is 1-99.9 mass%, and the methyl iodide concentration is 0.01-99 mass%.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for producing acetic acid.

The methanol method carbonylation process is known as an industrial method for producing acetic acid. In this process, for example, in a reaction vessel, methanol and carbon monoxide are reacted in the presence of a catalyst to produce acetic acid, and the resulting reaction mixture is combined with a steam phase containing acetic acid and a low boiling component in an evaporation vessel. It is separated into a residual liquid phase containing acetic acid and a catalyst, and the steam phase is distilled in a distillation column (de-low boiling column) to separate it into an overhead flow containing a low boiling component and an acetic acid flow, and the acetic acid flow is further purified. By doing so, the product acetic acid is obtained. In this process, acetaldehyde is by-produced during the reaction, which causes the quality of the product acetic acid to deteriorate.

Therefore, the overhead flow condensate of the delow boiling tower is separated into an aqueous phase and an organic phase with a decanter, and the aqueous phase or the organic phase is distilled in the deacetaldehyde column, and the overhead flow condensate (with acetaldehyde) is distilled. (Containing methyl iodide) is extracted with water, and the aqueous phase obtained by the extraction is distilled to separate and remove acetaldehyde.

Further, methyl iodide is a useful component that acts as an auxiliary catalyst for a metal catalyst such as a rhodium catalyst in the carbonylation process of the methanol method, and is also expensive. Therefore, the methyl iodide separated from acetaldehyde is recycled into a reactor and reused in the reaction process. However, since acetaldehyde and methyl iodide have similar boiling points, it was difficult to completely separate acetaldehyde and methyl iodide. Therefore, the methyl iodide that could not be separated was discarded together with acetaldehyde. Then, in order to compensate for the loss of methyl iodide, it is necessary to produce methyl iodide as needed and add new methyl iodide to the reactor, which causes problems such as high work load and high cost. there were.

As a method for efficiently separating acetaldehyde and methyl iodide, for example, the methods disclosed in Patent Documents 1 to 4 are known.

International Publication No. 2017-057142 Japanese Unexamined Patent Publication No. 2006-94764 Japanese Unexamined Patent Publication No. 9-40590 Japanese Unexamined Patent Publication No. 9-77697

However, even with the methods disclosed in Patent Documents 1 to 4, acetaldehyde and methyl iodide cannot be completely separated, and a method capable of more efficiently separating acetaldehyde has been desired.

Therefore, an object of the present disclosure is to provide a method for producing acetic acid, which can efficiently separate acetaldehyde and methyl iodide and reduce the loss of methyl iodide.

As a result of diligent studies to achieve the above object, the inventors of the present disclosure efficiently separate acetaldehyde and methyl iodide by separating a mixture of acetaldehyde and methyl iodide using a specific separation membrane. I found that I could do it. This disclosure relates to what has been completed with further studies based on these findings.

That is, the present disclosure comprises a membrane separation step of separating and acquiring an acetaldehyde-rich flow and a methyl iodide-rich flow from a process flow containing acetaldehyde and methyl iodide in the acetic acid production process using a zeolite membrane. A method for producing acetic acid is provided.

The zeolite membrane is preferably a BEA type zeolite membrane.

The acetaldehyde concentration in the process flow is preferably 0.1 to 99.9% by mass, and the methyl iodide concentration is preferably 0.01 to 99% by mass.

The total concentration of acetaldehyde and methyl iodide in the process flow is preferably 1% by mass or more.

The method for producing acetic acid includes a catalytic system containing a metal catalyst and methyl iodide, a carbonylation reaction step of reacting methanol with carbon monoxide in the presence of acetic acid, methyl acetate, and water to produce acetic acid.
The reaction mixture obtained in the carbonylation reaction step is subjected to one or more evaporation treatments and / or distillation treatments, and is subjected to at least a flow containing a metal catalyst, an acetic acid-rich flow, and a lower acetic acid flow. A separation process that separates into a stream rich in boiling components,
It is equipped with an acetaldehyde separation / removal system that separates acetaldehyde from at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component by one or more distillation treatments.
It is preferable that the acetaldehyde-rich flow separated in the acetaldehyde separation / removal system is subjected to the membrane separation step as the process flow.

A part of the methyl iodide-rich stream separated and obtained by the membrane separation step may be recycled to the process in the acetaldehyde separation and removal system.

The process flow preferably includes an overhead flow of a distillation column that performs the distillation treatment in the acetaldehyde separation and removal system.

A part of the flow rich in methyl iodide separated and obtained by the membrane separation step may be recycled to the distillation column.

The acetaldehyde separation / removal step is
A distillation step (A1) in which at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation to separate and obtain the first overhead flow rich in acetaldehyde and the residual liquid flow.
An extraction step (B1) in which at least a part of the condensed liquid obtained by condensing the first overhead flow is subjected to extraction and separated into an acetaldehyde-rich aqueous phase and a methyl iodide-rich organic phase.
The acetaldehyde-rich aqueous phase is subjected to distillation, and the distillation step (C1) for separating and acquiring the acetaldehyde-rich second overhead flow and the water-rich residual liquid flow is provided.
The condensed liquid obtained by condensing the second overhead flow and / or the second overhead flow may be subjected to the membrane separation step as the process flow.

The process flow preferably includes the second overhead flow.

The methyl iodide-rich flow obtained by separation in the membrane separation step may be recycled in the distillation step (A1) and / or the extraction step (B1).

The acetaldehyde separation / removal step is
At least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation, and the liquid falling from the concentrated region where methyl iodide and acetaldehyde are concentrated in the distillation column is extracted as a side flow. Distillation step (A2) and
The liquid separation step (B2) for separating the side flow into the aqueous phase and the organic phase,
The aqueous phase is subjected to distillation, and a distillation step (C2) for separating and acquiring a third overhead flow rich in acetaldehyde and a canned out liquid rich in water is provided.
Further, it may be provided with an extraction distillation step (D2) in which the acetaldehyde-rich third overhead flow is subjected to extraction distillation, and the acetaldehyde-rich fourth overhead flow and the water-rich canned liquid are separated and obtained.
One or more selected from the group consisting of the third overhead flow, the condensed liquid obtained by condensing the third overhead flow, the fourth overhead flow, and the condensed liquid obtained by condensing the fourth overhead flow. The flow may be subjected to the film separation step as the process flow.

The process flow preferably includes the fourth overhead flow.

The process flow is preferably a gas.

It is preferable to perform the membrane separation step while blowing a sweep gas to the permeation side.

The recovery rate of methyl iodide in the membrane separation step is preferably 1% by mass or more.

The methyl iodide concentration in the flow rich in methyl iodide separated and obtained by the membrane separation step is preferably higher than the methyl iodide concentration in the process flow and is preferably 1% by mass or more.

The acetaldehyde concentration in the acetaldehyde-rich stream separated and obtained by the membrane separation step is preferably higher than the acetaldehyde concentration in the process stream and is preferably 0.1% by mass or more.

The zeolite membrane is preferably provided on at least one surface of the porous substrate.

Further, the present disclosure describes the acetaldehyde-rich flow and the methyl iodide-rich flow, which separately obtain the acetaldehyde-rich flow and the methyl iodide-rich flow from the mixture containing acetaldehyde and methyl iodide using a zeolite membrane. Provide a method of manufacturing.

According to the above method for producing acetic acid, acetaldehyde and methyl iodide can be efficiently separated, so that the loss of methyl iodide can be reduced. Therefore, the work load of newly adding methyl iodide to the reaction step is also reduced.

It is a schematic flow chart which shows an example of a membrane separation process. It is a schematic flow chart which shows the other example of the membrane separation process. It is a manufacturing flow diagram which shows one Embodiment of the acetic acid manufacturing system. It is a schematic flow chart which shows an example of the acetaldehyde separation removal system. It is a schematic flow chart which shows the other example of the acetaldehyde separation removal system. It is a schematic flow diagram which shows still another example of an acetaldehyde separation removal system. It is a schematic flow diagram which shows still another example of an acetaldehyde separation removal system. It is a schematic diagram which shows the apparatus used for the separation test of Example 1. FIG.

The method for producing acetic acid according to an embodiment of the present disclosure separates an acetaldehyde-rich flow and a methyl iodide-rich flow from a process flow containing acetaldehyde and methyl iodide using a zeolite membrane in the acetic acid production process. The membrane separation step to be acquired is provided.

The zeolite membrane is a membrane formed from zeolite. The zeolite membrane mainly permeates acetaldehyde and concentrates without permeating methyl iodide. That is, the permeation flow separated and acquired in the membrane separation step is richer in acetaldehyde than the process flow (charged flow), and the concentrated flow separated and acquired is more methyl iodide than the process flow (charged flow). It is a rich flow. This is basically because the zeolite membrane allows acetaldehyde to permeate by the molecular sieving function. On the other hand, although a large amount of methyl iodide should be allowed to permeate only by the molecular sieving function, it is presumed that the adsorption characteristics of zeolite are used to make it difficult for methyl iodide to permeate. Due to the performance of such a zeolite membrane, acetaldehyde and methyl iodide can be efficiently separated.

Examples of the zeolite include A type, ferrierite, MCM-22, ZSM-5, ZSM-11, SAPO-11, mordenite, BEA type, X type, Y type, L type, FAU type, MFI type, and chabazite. , Synthetic zeolite having a skeletal structure such as offletite, and the like. Of these, BEA type zeolite, ZSM-5 type zeolite, FAU type zeolite, and MFI type zeolite are preferable, and BEA type zeolite is particularly preferable, from the viewpoint of being able to separate acetaldehyde and methyl iodide more efficiently. Since the surface of BEA type zeolite is hydrophilic, it is presumed that it is more difficult for methyl iodide to permeate. As the above-mentioned zeolite, only one kind may be used, or two or more kinds may be used.

The zeolite is not particularly limited, but may contain cations in the skeletal structure. The cation is not particularly limited, and is, for example, hydrogen ion; ammonium ion; lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion and other alkali metal ions; magnesium ion, calcium ion, barium ion and other alkalis. Earth metal ions; transition metal ions such as zinc ion, tin ion, iron ion, platinum ion, palladium ion, titanium ion, silver ion, copper ion, manganese ion and the like can be mentioned. Among them, the cation preferably contains an alkali metal ion, and more preferably potassium ion. The zeolite may contain only one kind of the cation, or may contain two or more kinds of the cation.

The zeolite membrane is preferably provided on at least one surface of the porous substrate. The porous substrate acts as a substrate for supporting the zeolite membrane. The porous substrate has pores through which acetaldehyde can permeate.

As the porous base material, known or commonly used ones can be used. Examples of the material constituting the porous substrate include inorganic substances such as silica, alumina, mullite, zirconia, cordierite, titania, silicon nitride, silicon carbide, stainless steel, copper, aluminum, titanium, and ceramics. ..

The process flow attached to the membrane separation step may be a mixture containing at least acetaldehyde and methyl iodide, and is one or more process flows selected from the process flows in all the equipment and piping in the acetic acid production process. Further, the process flow may be a liquid or a gas.

The acetaldehyde concentration in the process flow is, for example, 0.1% by mass or more, 1% by mass or more, 2% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass. % Or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 75% by mass or more, and 80% by mass or more. The acetaldehyde concentration in the process flow is, for example, 99.9% by mass or less, 99% by mass or less, 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, 70% by mass or less. It may be 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, and 5% by mass or less.

The methyl iodide concentration in the process flow is, for example, 0.01% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, and 5 It may be mass% or more, 6 mass% or more, 7 mass% or more, 10 mass% or more, 12 mass% or more, 15 mass% or more, 20 mass% or more, and 30 mass% or more. The methyl iodide concentration in the process flow is, for example, 99% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 50% by mass or less, 20% by mass or less. It may be 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, and 0.1% by mass or less.

The total concentration of acetaldehyde and methyl iodide in the process flow is not particularly limited, but is preferably 1% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, and 50% by mass. As mentioned above, it may be 60% by mass or more, 70% by mass or more, 80% by mass or more, and 85% by mass or more. The total concentration is, for example, 99% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass. Hereinafter, it may be 20% by mass or less and 10% by mass or less.

The process flow may contain other components other than acetaldehyde and methyl iodide. Examples of the other components include components that may occur in the acetic acid production process, such as carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, and methanol. , Formic acid, propionic acid, crotonaldehyde, 2-ethylcrotonaldehyde, alkanes, and alkyl iodide such as hexyl iodide and decyl iodide.

The water concentration in the process flow is, for example, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more. It may be 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more. The water concentration in the process flow is, for example, 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 50% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass. % Or less, 5% by mass or less, and 1% by mass or less.

The methyl iodide concentration in the flow rich in methyl iodide obtained by the membrane separation step is higher than the methyl iodide concentration in the process flow, for example, 1% by mass or more, 5% by mass or more, and 10% by mass or more. , 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 40% by mass or more, and 50% by mass or more. Further, the methyl iodide concentration in the flow rich in methyl iodide is, for example, 100% by mass or less, 90% by mass or less, 70% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20. It may be mass% or less, 10 mass% or less, and 5 mass% or less.

The recovery rate of methyl iodide in the film separation step ([Methyl iodide flow rate in concentrated flow / Methyl iodide flow rate in charging flow] × 100) is, for example, 1% by mass or more, 5% by mass or more, and 10% by mass. % Or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass. It may be% or more. The recovery rate of methyl iodide is, for example, 100% by mass or less, 99.5% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less. It may be 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, and 10% by mass or less.

The acetaldehyde concentration in the acetaldehyde-rich flow obtained by the membrane separation step is higher than the acetaldehyde concentration in the process flow, for example, 0.1% by mass or more, 1% by mass or more, 5% by mass or more, and 10% by mass. As mentioned above, it may be 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more. Further, the acetaldehyde concentration in the flow rich in acetaldehyde is, for example, 100% by mass or less, 99.5% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass. Hereinafter, it may be 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, and 10% by mass or less.

The recovery rate of acetaldehyde in the membrane separation step ([flow rate of acetaldehyde in permeated flow / flow rate of acetaldehyde in charged flow] × 100) is 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more. It may be 20% by mass or more, 30% by mass or more, 50% by mass or more, 60% by mass or more, 80% by mass or more, and 90% by mass or more. The recovery rate of the acetaldehyde is, for example, 100% by mass or less, 99.5% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass. % Or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, and 10% by mass or less.

Hereinafter, one embodiment of the membrane separation step will be described. FIG. 1 is a schematic flow chart showing an embodiment of the membrane separation step in the present disclosure when the process flow attached to the membrane separation step is a gas (process gas). According to this flow, for example, when the process gas is applied to the membrane separation step, the process gas is supplied to the membrane module 58 through the line 60.

The membrane separation step is performed in the membrane module 58. An inert gas such as nitrogen or helium may be blown into the permeation side of the membrane module 58 provided with the zeolite membrane as the sweep gas 70. Further, the permeation side may be depressurized by a vacuum pump, an ejector or the like. This makes it possible to increase the partial pressure difference between acetaldehyde and methyl iodide and improve the recovery rate of methyl iodide. In addition, it is possible to prevent the permeation flow that permeates the zeolite membrane from staying. The temperature and pressure of the process gas charged in the membrane separation step are not particularly limited as long as the process flow can maintain the gas state.

The membrane separation step is preferably performed in a state where the temperature of the process gas is 50 to 130 ° C. (for example, 60 to 120 ° C., preferably 70 to 110 ° C., more preferably 80 to 100 ° C.). Further, the membrane separation step is preferably performed under pressure in order to increase the partial pressure difference between acetaldehyde and methyl iodide and improve the recovery rate of methyl iodide, and the pressure is preferably absolute pressure. It is 140 to 300 kPa, more preferably 200 to 290 kPa, and even more preferably 260 to 280 kPa. By performing the membrane separation step under the above temperature range and pressure, the partial pressure difference of acetaldehyde between the concentrated flow and the permeated flow can be increased to increase the permeability of acetaldehyde, and acetaldehyde easily permeates the zeolite membrane. Acetaldehyde and methyl zeolite can be separated more efficiently.

The methyl iodide-rich flow (line 61) obtained by concentrating without permeating the zeolite membrane in the membrane separation step is cooled and condensed by the condenser 61a and supplied to the receiver 59 as a condensate. When the liquid level controller 59b detects that the liquid level in the receiver 59 has exceeded a predetermined liquid level, the valve 65b is opened, and the flow rich in methyl iodide through the lines 63, 64, 65 by the pump 63a ( Line 66) is obtained. Reference numeral 59a is a temperature controller for the capacitor 61a. Reference numeral 65a is a flow meter for the liquid passing through the line 65.

The flow rich in methyl iodide, which does not permeate the zeolite membrane and is concentrated, is directly or indirectly recycled in the reaction step and can be reused as a co-catalyst in the reaction step. The methyl iodide-rich flow (line 66) is preferably recycled into the process in the acetaldehyde separation and removal system described below, and the charging flow of the distillation column 91 (line 117) and the charging flow of the extraction column 92 (line) described later. It is more preferable to recycle to 118) or the charging flow (line 228) of the distillation column 94.

Further, the methyl iodide-rich flow (line 63) from the receiver 59 may be recovered through the line 67 by opening the valve 67b. The recovered methyl iodide-rich stream (line 67) can be recycled into a unit (for example, a distillation column such as a distillation column 93 or a distillation column 98 described later) that discharges the process gas sent through the line 60. good. Reference numeral 67a is a flow meter for the liquid passing through the line 67.

Further, the gas generated in the receiver 59 is merged with the line 71 through the line 68. The valve 69a is opened according to the value of the pressure gauge 60a, and is discharged from the line 69 through the lines 68 and 71. In the membrane module 58, the gas that has not penetrated the zeolite membrane may be discharged directly from the line 69 through the line 71. Since the gas discharged from the line 69 contains a large amount of methyl iodide, it is directly or indirectly recycled or reused in a reaction step or an appropriate part of the process. For example, it can be recycled to the exhaust gas lines 32, 37, 45 of the distillation columns 3, 5, 6 described later.

On the other hand, the acetaldehyde-rich flow that has permeated the zeolite membrane in the membrane separation step is incinerated through the line 62. 62a is a flow meter.

As described above, the process gas (line 60) is separated into an acetaldehyde-rich stream (line 62) and a methyl iodide-rich stream (lines 66, 67, 69) by the membrane separation step.

Other embodiments of the above membrane separation step will be described. FIG. 2 is a schematic flow chart showing an embodiment of the membrane separation step in the present disclosure when the process flow attached to the membrane separation step is a liquid (process liquid). According to this flow, for example, when the process liquid is applied to the membrane separation step, the process liquid is supplied to the receiver 72 through the line 60. When the liquid level controller 72a detects that the liquid level in the receiver 72 exceeds a predetermined liquid level, the valve 74b is opened, and the process liquid is described from the can-out of the receiver 72 by the pump 74a through the lines 74 and 75. Is supplied to the receiver 73. The gas content generated in the receiver 72 is connected to the line 116 or the line 227 described later through the line 76 and is disposed of.

The process liquid in the receiver 73 is supplied from the can-out of the receiver 73 to the membrane module 58 through the lines 77 and 78 by the pump 77a. At that time, the process liquid is heated by the heater 77b whose vapor amount is adjusted by the temperature controller 78a. At this time, in order to maintain the pressure at which the circulating fluid supplied through the line 81 in the receiver 73 does not vaporize, the valve 79a is opened by the pressure controller 73a, and nitrogen is supplied from the line 79 to the receiver 73. When the pressure rises more than necessary due to the operation modulation, the gas content in the receiver 73 is connected to the line 116 or the line 227 described later through the line 85 by opening the valve 85a and disposed of.

The membrane separation step is performed in the membrane module 58. An inert gas such as nitrogen or helium may be blown into the permeation side of the membrane module 58 provided with the zeolite membrane as the sweep gas 70. Further, the permeation side may be depressurized by a vacuum pump, an ejector or the like. This makes it possible to increase the partial pressure difference between acetaldehyde and methyl iodide and improve the recovery rate of methyl iodide. In addition, it is possible to prevent the permeation flow that permeates the zeolite membrane from staying. The temperature and pressure of the process gas charged in the membrane separation step are not particularly limited as long as the process flow can maintain the liquid state.

The membrane separation step is carried out in a state where the temperature of the process liquid is 10 to 180 ° C. (for example, 20 to 150 ° C., preferably 30 to 130 ° C., more preferably 50 to 110 ° C., still more preferably 70 to 90 ° C.). It is preferable to be Further, the membrane separation step is preferably performed under pressure in order to increase the partial pressure difference between acetaldehyde and methyl iodide and improve the recovery rate of methyl iodide, and the pressure is preferably absolute pressure. It is 110 to 2000 kPa, more preferably 200 to 1800 kPa, still more preferably 300 to 1500 kPa, still more preferably 400 to 1200 kPa, and particularly preferably 600 to 1000 kPa. By performing the membrane separation step under the above temperature range and pressurization, the temperature of the concentrated flow is raised and the difference in the partial pressure of acetaldehyde between the concentrated flow and the permeated flow is increased to increase the permeability and the amount of acetaldehyde. It can be increased, acetaldehyde easily permeates the zeolite membrane, and acetaldehyde and methyl iodide can be separated more efficiently.

The liquid level controller 73b detected that the liquid level in the receiver 73 exceeded a predetermined liquid level in a part of the flow (line 80) rich in methyl iodide obtained by concentrating without penetrating the zeolite membrane. At this time, while adjusting the flow rate with the flow rate controller 82a, the valve 82c is opened and the flow rich in methyl iodide is collected through the lines 82 and 83. As it passes through lines 82,83, the methyl iodide-rich stream is cooled by the capacitor 82b. In order to increase the amount of flow to the membrane module 58 and increase the efficiency (permeability) of membrane separation, the flow of the line 80 is returned to the receiver 73 through the line 81. 82d is a thermometer of the liquid passing through the line 82.

The flow rich in methyl iodide, which does not permeate the zeolite membrane and is concentrated, is directly or indirectly recycled in the reaction step and can be reused as a co-catalyst in the reaction step. The methyl iodide-rich flow (line 83) is preferably recycled into the process in the acetaldehyde separation and removal system described below, and the charge flow of the distillation column 91 described below (line 117) and the charge flow of the extraction tower 92 (line). It is more preferable to recycle to 118) or the charging flow (line 228) of the distillation column 94.

On the other hand, the acetaldehyde-rich flow separated through the zeolite membrane is directly incinerated through the line 84.

As described above, the membrane separation step separates the process liquid (line 60) into an acetaldehyde-rich stream (line 84) and a methyl iodide-rich stream (line 83).

The membrane separation step has been described as one step in the acetic acid production process, but is not limited to such an embodiment, and a flow rich in acetaldehyde from a mixture containing acetaldehyde and methyl iodide using a zeolite membrane. It can be carried out as a method for separating acetaldehyde and methyl iodide, which separates and obtains a flow rich in methyl iodide, or a method for producing a flow rich in acetaldehyde and a flow rich in methyl iodide. Preferred embodiments in the present separation method and the production method are the same as those described in the above membrane separation step.

Further, in each embodiment, by passing a solvent such as methanol, methyl acetate, acetic acid, or water through the membrane module 58 or immersing the membrane module 58 in those solvents, the membrane performance can be improved even when the membrane performance deteriorates. It can be recovered. The solvent passing solution to the membrane module 58 may be external circulation using a pump or the like, or may be flush cleaning. The membrane module 58 may be immersed in the solvent by impregnating the membrane module with the solvent and allowing it to stand. In addition, the clogging can be removed more efficiently by heating the solvent.

In the method for producing acetic acid, the acetic acid production process comprises one or more of a carbonylation reaction step of reacting methanol with carbon monoxide to produce acetic acid and a reaction mixture obtained in the carbonylation reaction step. The evaporation treatment and / or the distillation treatment has at least a separation step of separating a flow containing a metal catalyst, an acetic acid flow rich in acetic acid, and a flow rich in a lower boiling component than the acetic acid flow. May be. The carbonylation reaction step is carried out, for example, in the presence of a metal catalyst and a catalyst system containing methyl iodide. The carbonylation reaction step may be further carried out in the presence of acetic acid, methyl acetate, and water. The separation step is, for example, an evaporation step of separating the reaction mixture obtained in the carbonylation reaction step into at least a steam flow and a residual liquid flow by evaporation, and subjecting the steam flow to distillation to at least low boiling. It is preferable to have a de-low boiling step for separating and acquiring an overhead flow rich in components and a first acetic acid flow rich in acetic acid. The first acetic acid stream may be a side cut stream, a column bottom stream, or both. In the de-low boiling step, it is preferable that the steam flow is subjected to distillation to separate it into an overhead flow rich in low boiling components, a first acetic acid flow (side cut flow) rich in acetic acid, and a column bottom flow. Further, the separation step is a dehydration step in which the first acetic acid stream is subjected to distillation to separate and acquire at least a water-rich overhead flow and a second acetic acid stream richer in acetic acid than the first acetic acid stream. May have.

In the separation step, instead of the evaporation step and the delow boiling step, the reaction mixture obtained in the carbonylation reaction step is mixed with a flow containing the catalyst, an overhead flow rich in the low boiling component, and acetic acid. It may be provided with a step (evaporation de-low boiling step) of separating into a rich first acetic acid stream. Further, in the separation step, instead of the delow boiling step and the dehydration step, a delow boiling step (so-called delow boiling dehydration step) having the function of the dehydration step, that is, the steam flow is subjected to distillation. Therefore, it may be provided with a step of separating the overhead flow rich in low boiling components and the acetic acid flow dehydrated to the same water concentration as the second acetic acid flow. Therefore, the evaporation de-low boiling step may be a step having the function of the dehydration step (evaporation de-low boiling dehydration step). The acetic acid-rich acetic acid stream obtained from the delow boiling dehydration step and the evaporation delow boiling dehydration step corresponds to the second acetic acid stream.

Further, the method for producing acetic acid may further include at least one of the following steps (a) to (c).
(A) An acetic acid-rich acetic acid stream obtained in the separation step (for example, a can outflow rich in high boiling components by distilling the first or second acetic acid stream and an acetic acid stream before subject to distillation). Dehyperboiling step to separate acetic acid into a enriched third acetic acid stream (b) Acetic acid-rich acetic acid stream (eg, first or second acetic acid stream) or third acetic acid stream obtained in the separation step. (C) Acetic acid-rich acetic acid stream (for example, the first or second acetic acid stream) or the third or fourth acetic acid stream obtained in the separation step. A product process in which an acetic acid stream is distilled to obtain a fifth acetic acid stream enriched with acetic acid compared to the acetic acid stream before subject to distillation.

Further, even if the method for producing acetic acid has an acetaldehyde separation / removal system that separates acetaldehyde from at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component by one or more distillation treatments. good. Further, the acetaldehyde separation / removal system may include an extraction step of separating an aqueous phase containing acetaldehyde by one or more extraction treatments from at least a part of the acetaldehyde separated by the above one or more distillation treatments.

In the method for producing acetic acid, the acetaldehyde-rich stream separated in the distillation treatment in the acetaldehyde separation / removal system and / or the acetaldehyde-rich stream separated in the extraction process is subjected to the process flow. It is preferable to apply it to the above-mentioned film separation step. In particular, the process flow is preferably an overhead flow of a distillation column that performs the distillation treatment. Then, at least a part of the methyl iodide-rich flow separated and obtained by the membrane separation step is preferably recycled to the process in the acetaldehyde separation and removal system, and the distillation column (that is, the process flow) is discharged. It is particularly preferable to recycle it into a distillation column).

Hereinafter, an embodiment of a method for producing acetic acid including the membrane separation step will be described. FIG. 3 is an example of a production flow diagram (methanol method carbonylation process) showing an embodiment of an acetic acid production system. The acetic acid production apparatus related to this acetic acid production flow includes a reaction tank 1, an evaporation tank 2, a distillation column 3, a decanter 4, a distillation column 5, a distillation column 6, an ion exchange resin column 7, and a scrubber system 8. The acetaldehyde separation and removal system 9, the capacitors 1a, 2a, 3a, 5a, 6a, the heat exchanger 2b, the reboilers 3b, 5b, 6b, the lines 11 to 56, and the pump 57 are provided, and acetic acid is continuously applied. It is configured to be manufacturable.

In the method for producing acetic acid of the present embodiment, in the reaction tank 1, the evaporation tank 2, the distillation column 3, the distillation column 5, the distillation column 6, and the ion exchange resin column 7, the reaction step, the evaporation step (flash step), respectively, A first distillation step, a second distillation step, a third distillation step, and an adsorption removal step are performed. The first distillation step is also referred to as a de-low boiling step, the second distillation step is also referred to as a dehydration step, and the third distillation step is also referred to as a de-high boiling step. In the present embodiment, the process is not limited to the above, and in particular, the equipment of the distillation column 5, the distillation column (de-high boiling column) 6, the ion exchange resin column 7, and the acetaldehyde separation / removal system 9 (de-acetaldehyde column, etc.) is provided. It may not be incidental. Further, as will be described later, a product tower may be provided downstream of the ion exchange resin tower 7.

The reaction tank 1 is a unit for performing a reaction step. This reaction step is a step for continuously producing acetic acid by the reaction represented by the following chemical formula (1) (carbonylation reaction of methanol). In the steady operation state of the acetic acid production apparatus, there is a reaction mixture that is agitated by, for example, a stirrer in the reaction tank 1. The reaction mixture contains methanol and carbon monoxide as raw materials, a metal catalyst, a co-catalyst, water, acetic acid for production purposes, and various by-products, and the liquid phase and the gas phase are in an equilibrium state. It is in.
CH ₃ OH + CO → CH ₃ COOH (1)

The raw materials in the reaction mixture are liquid methanol and gaseous carbon monoxide. Methanol is continuously supplied to the reaction vessel 1 from the methanol reservoir (not shown) through the line 11. Carbon monoxide is continuously supplied to the reaction vessel 1 from the carbon monoxide reservoir (not shown) through the line 12. Carbon monoxide does not necessarily have to be pure carbon monoxide, and contains a small amount (for example, 5% by mass or less, preferably 1% by mass or less) of other gases such as nitrogen, hydrogen, carbon dioxide, and oxygen. May be good.

The metal catalyst in the reaction mixture is for accelerating the carbonylation reaction of methanol, and for example, a rhodium catalyst or an iridium catalyst can be used. As the rhodium catalyst, for example, a rhodium complex represented by the chemical formula ^[ Rh (CO) ₂ I ₂ ]-can be used. As the iridium catalyst, for example, an iridium complex represented by the chemical formula ^[ Ir (CO) ₂ I ₂ ]-can be used. As the metal catalyst, a metal complex catalyst is preferable. The concentration of the catalyst in the reaction mixture (in terms of metal) is, for example, 200 to 10000 mass ppm, preferably 300 to 5000 mass ppm, and more preferably 400 to 400 mass ppm with respect to the entire liquid phase (reaction mixture) of the reaction mixture. It is 2500 mass ppm.

The co-catalyst is an iodide for assisting the action of the above-mentioned catalyst, and for example, methyl iodide or ionic iodide is used. Methyl iodide may exhibit an action that promotes the catalytic action of the catalyst described above. The concentration of methyl iodide is, for example, 1 to 20% by mass, preferably 5 to 15% by mass, based on the entire liquid phase of the reaction mixture. The ionic iodide is an iodide that produces iodide ions in the reaction solution (particularly, an ionic metal iodide), and can exhibit the above-mentioned action of stabilizing the catalyst and the action of suppressing side reactions. Examples of the ionic iodide include alkali metal iodides such as lithium iodide, sodium iodide, and potassium iodide. The concentration of the ionic iodide in the reaction mixture is, for example, 1 to 25% by mass, preferably 5 to 20% by mass, based on the entire liquid phase of the reaction mixture. Further, for example, when an iridium catalyst or the like is used, a ruthenium compound or an osmium compound can also be used as the co-catalyst. The total amount of these compounds used is, for example, 0.1 to 30 mol (metal equivalent), preferably 0.5 to 15 mol (metal equivalent) with respect to 1 mol (metal equivalent) of iridium.

Water in the reaction mixture is a component necessary for producing acetic acid due to the reaction mechanism of the carbonylation reaction of methanol, and is also a component necessary for solubilizing the water-soluble component of the reaction system. The concentration of water in the reaction mixture is, for example, 0.1 to 15% by mass, preferably 0.5 to 10% by mass, more preferably 1 to 6% by mass, and further, with respect to the entire liquid phase of the reaction mixture. It is preferably 1.5 to 4% by mass. The water concentration is preferably 15% by mass or less from the viewpoint of suppressing the energy required for removing water in the acetic acid purification process and promoting the efficiency of acetic acid production. Water may be continuously supplied to the reaction tank 1 in order to control the water concentration.

The acetic acid in the reaction mixture contains acetic acid previously charged in the reaction vessel 1 before the operation of the acetic acid production apparatus, and acetic acid produced as the main product of the carbonylation reaction of methanol. Such acetic acid can function as a solvent in the reaction system. The concentration of acetic acid in the reaction mixture is, for example, 50 to 90% by mass, preferably 60 to 80% by mass, based on the entire liquid phase of the reaction mixture.

The main by-products contained in the reaction mixture include, for example, methyl acetate. This methyl acetate can be produced by the reaction of acetic acid with methanol. The concentration of methyl acetate in the reaction mixture is, for example, 0.1 to 30% by mass, preferably 1 to 10% by mass, based on the entire liquid phase of the reaction mixture.

Hydrogen iodide is also mentioned as a by-product contained in the reaction mixture. This hydrogen iodide is inevitably generated due to the reaction mechanism of the carbonylation reaction of methanol when the above-mentioned catalyst or co-catalyst is used. The concentration of hydrogen iodide in the reaction mixture is, for example, 0.01 to 2% by mass with respect to the entire liquid phase of the reaction mixture.

Examples of by-products include hydrogen, methane, carbon dioxide, acetaldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, dimethyl ether, alkanes, formic acid, and propionic acid, and hexyl iodide and decyl iodide. Examples include alkyl iodide. In addition, the reaction mixture includes metals such as iron, nickel, chromium, manganese, and molybdenum (hereinafter, may be referred to as "corrosive metals") generated by corrosion of the equipment, and other metals such as cobalt, zinc, and copper. Can be included. The above corrosive metal and other metals may be collectively referred to as "corrosive metal or the like".

In the reaction vessel 1 in which the reaction mixture as described above exists, the reaction temperature is set to, for example, 150 to 250 ° C., and the reaction pressure as the total pressure is set to, for example, 1.5 to 3.5 MPa (absolute pressure). The partial pressure of carbon monoxide is set to, for example, 0.4 to 1.8 MPa (absolute pressure), preferably 0.6 to 1.6 MPa (absolute pressure), and more preferably 0.9 to 1.4 MPa (absolute pressure). Will be done.

The vapor in the gas phase in the reaction vessel 1 during operation of the apparatus includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, and dimethyl ether. , Methanol, acetic acid, formic acid, and propionic acid. This steam can be withdrawn from the reaction vessel 1 through the line 13. By adjusting the amount of steam drawn out, it is possible to control the pressure in the reaction vessel 1, for example, the pressure in the reaction vessel 1 is maintained constant. The steam extracted from the reaction vessel 1 is introduced into the capacitor 1a.

The capacitor 1a separates the vapor from the reaction vessel 1 into a condensed component and a gas component by cooling and partially condensing the steam. The condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, propionic acid and the like, and is introduced from the condenser 1a into the reaction vessel 1 through the line 14. Will be recycled. The gas content includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid, and the condenser 1a. Is supplied to the scrubber system 8 through the line 15.

In FIG. 3, the gas content from the condenser 2a (line 20), the gas content from the condenser 3a (line 32), the gas content from the condenser 5a (line 37), and the gas content from the condenser 6a (line 45). Are all merged into the line 15 and supplied to the scrubber system 8, but only the gas from the condenser 1a may be supplied to the scrubber system 8 through the line 15 and the gas from the capacitors 3a, 5a, 6a. (Lines 32, 37, 45) may all join the line 20 and be supplied to the scrubber system 8.

As described above, acetic acid is continuously produced in the reaction vessel 1 when the apparatus is in operation. The reaction mixture containing such acetic acid is continuously withdrawn from the reaction vessel 1 and introduced into the next evaporation vessel 2 through the line 16.

The evaporation tank 2 is a unit for performing an evaporation step (flash step). In this evaporation step, the vapor flow (volatile phase) and the residual liquid flow (low volatile phase) are partially vaporized by partially evaporating the reaction mixture continuously introduced into the evaporation tank 2 through the line 16 (reaction mixture supply line). It is a process for dividing into.

Evaporation may occur by reducing the pressure without heating the reaction mixture, or by reducing the pressure while heating the reaction mixture. In the evaporation step, the temperature of the steam flow is, for example, 100 to 260 ° C, preferably 120 to 200 ° C, the temperature of the residual liquid flow is, for example, 80 to 200 ° C, preferably 100 to 180 ° C, and the pressure in the tank is, for example. It is 50 to 1000 kPa (absolute pressure).

The ratio of the vapor flow and the residual liquid flow separated in the evaporation step is, for example, 10/90 to 50/50 (vapor flow / residual liquid flow) in terms of mass ratio. The vapors produced in this step include, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, and propionic acid, as well as ethyl iodide, propyl iodide, butyl iodide, and the like. It contains hexyl iodide, alkyl iodide such as decyl iodide, and is continuously drawn from the evaporation tank 2 into the line 17 (steam flow discharge line).

A part of the steam flow extracted from the evaporation tank 2 is continuously introduced into the capacitor 2a, and the other part of the steam flow is continuously introduced into the next distillation column 3 through the line 21. The acetic acid concentration of the steam stream is, for example, 40 to 85% by mass (preferably 50 to 85% by mass), more preferably 50 to 75% by mass (for example, 55 to 75% by mass), and the methyl iodide concentration is, for example. 2 to 50% by mass (preferably 5 to 30% by mass), water concentration is, for example, 0.2 to 20% by mass (preferably 1 to 15% by mass), and methyl acetate concentration is, for example, 0.2 to 50% by mass. (Preferably 2 to 30% by mass). The hexyl iodide concentration in the steam stream is, for example, 0.1 to 10000 mass ppb, usually 0.5 to 1000 mass ppb, and often 1 to 100 mass ppb (for example, 2 to 50 mass ppb). ..

The residual liquid flow generated in this step includes the catalyst and co-catalyst (methyl iodide, lithium iodide, etc.) contained in the reaction mixture, water, methyl acetate, acetic acid, formic acid, etc. that remain without volatilization in this step. And propionic acid and the like are continuously introduced from the evaporation tank 2 to the heat exchanger 2b through the line 18 by using the pump 57. The heat exchanger 2b cools the residual liquid flow from the evaporation tank 2. The lowered residual liquid flow is continuously introduced from the heat exchanger 2b into the reaction tank 1 through the line 19 and recycled. The line 18 and the line 19 are collectively referred to as a residual liquid flow recycling line. The acetic acid concentration in the residual liquid flow is, for example, 55 to 90% by mass, preferably 60 to 85% by mass.

The condenser 2a separates the vapor flow from the evaporation tank 2 into a condensed component and a gas component by cooling and partially condensing the steam flow. The condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid, propionic acid and the like, and is introduced from the condenser 2a into the reaction vessel 1 through lines 22 and 23. And recycled. The gas content includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like, and the condenser 2a. Is supplied to the scrubber system 8 through lines 20 and 15. Where the acetic acid production reaction in the above reaction step is an exothermic reaction, part of the heat accumulated in the reaction mixture is transferred to the vapor generated from the reaction mixture in the evaporation step (flash step). The condensed matter generated by cooling the steam in the capacitor 2a is recycled to the reaction tank 1. That is, in this acetic acid production apparatus, the heat generated by the carbonylation reaction of methanol is efficiently removed by the capacitor 2a.

The distillation column 3 is a unit for performing the first distillation step, and is positioned as a so-called de-lowering boiling column in the present embodiment. The first distillation step is a step of distilling a steam stream continuously introduced into the distillation column 3 to separate and remove low boiling components. More specifically, in the first distillation step, the steam stream is distilled to separate it into an overhead stream rich in at least one low boiling component selected from methyl iodide and acetaldehyde and an acetic acid stream rich in acetic acid. ..

The distillation column 3 is composed of, for example, a rectification column such as a shelf column and a packed column. When a shelf column is adopted as the distillation column 3, the theoretical plate is, for example, 5 to 50 stages, and the reflux ratio is, for example, 0.5 to 3000 depending on the number of theoretical plates. Inside the distillation column 3, the column top pressure is set to, for example, 80 to 160 kPaG, and the column bottom pressure is set to be higher than the column top pressure, for example, 85 to 180 kPaG. Inside the distillation column 3, the column top temperature is set to, for example, 90 to 130 ° C., which is lower than the boiling point of acetic acid at the set column top pressure, and the column bottom temperature is, for example, at the set column bottom pressure. The temperature is set to 120 to 165 ° C. (preferably 125 to 160 ° C.) above the boiling point of acetic acid.

For the distillation column 3, the steam flow from the evaporation tank 2 is continuously introduced through the line 21, and the steam as an overhead flow is continuously extracted from the top of the distillation column 3 to the line 24. From the bottom of the distillation column 3, canned liquid is continuously drawn into the line 25. 3b is a reboiler. From the height position between the top and bottom of the distillation column 3, an acetic acid stream (first acetic acid stream; liquid) as a side flow is continuously withdrawn from the line 27.

The steam extracted from the top of the distillation column 3 contains a larger amount of a component having a boiling point lower than that of acetic acid (a low boiling point component) as compared with the above-mentioned canned liquid and sidestream from the distillation column 3, for example, methyl iodide. Includes hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, acetaldehyde, formic acid and the like. This vapor also contains acetic acid. Such steam is continuously introduced into the capacitor 3a through the line 24.

The condenser 3a separates the steam from the distillation column 3 into a condensed component and a gas component by cooling and partially condensing the steam. The condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like, and is continuously introduced from the condenser 3a into the decanter 4 through the line 28. The condensed component introduced into the decanter 4 is separated into an aqueous phase (upper phase) and an organic phase (methyl iodide phase; lower phase).

The aqueous phase includes water and, for example, methyl iodide, hydrogen iodide, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like. Organic phases include, for example, methyl iodide and, for example, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like.

In the present embodiment, a part of the aqueous phase is returned to the distillation column 3 through the line 29, and the other part of the aqueous phase is introduced into the reaction vessel 1 through the lines 29, 30 and 23 and recycled. A part of the organic phase is introduced into the reaction vessel 1 through the lines 31 and 23 and recycled. The other part of the organic phase and / or the other part of the aqueous phase is introduced into the acetaldehyde separation and removal system 9 through lines 31, 50 and / or lines 30, 51.

In the acetaldehyde separation / removal step using the acetaldehyde separation / removal system 9, acetaldehyde contained in at least a part (for example, an organic phase and / or an aqueous phase) of the condensate obtained by condensing the overhead flow rich in the low boiling component is used. Separation and removal is performed by a known method, for example, distillation, extraction, or a combination thereof. The separated acetaldehyde is discharged out of the device through line 53. Further, useful components (for example, methyl iodide) contained in the organic phase and / or the aqueous phase are recycled to the reaction vessel 1 through the lines 52 and 23 and reused.

FIG. 4 is a schematic flow chart showing an example of an acetaldehyde separation / removal system. According to this flow, for example, when the organic phase is treated in the acetaldehyde separation / removal step, the organic phase (charged flow) is supplied to the distillation column (first deacetaldehyde column) 91 through the line 101 for distillation, and acetaldehyde is used. The first overhead flow (line 102) rich in water and the residual liquid flow (line 103) rich in methyl iodide are separated and acquired (distillation step (A1)). The first overhead flow is condensed by the condenser 91a, a part of the condensate is refluxed to the top of the distillation column 91 (line 104), and the other part of the condensate is supplied to the extraction column 92 (line 105). .. A flow rich in methyl iodide separated and obtained by the membrane separation step may be merged with the charging flow (line 101) through line 117. Thereby, the above-mentioned flow rich in methyl iodide can be recycled in the distillation step (A1).

The condensed liquid (preparation flow) supplied to the extraction tower 92 is extracted by the water introduced from the line 109 (extraction step (B1)). By the extraction treatment, the aqueous phase rich in acetaldehyde (line 107) and the organic phase rich in methyl iodide (line 108) are separated. The acetaldehyde-rich aqueous phase (extract) obtained by the extraction treatment is supplied to the distillation column (second deacetaldehyde column) 93 through the line 107 for distillation, and is added to the acetaldehyde-rich second overhead flow (line 112) and water. The rich residual liquid flow (line 113) is separated and acquired (distillation step (C1)). Then, the second overhead flow rich in acetaldehyde is condensed by the condenser 93a, a part of the condensed liquid is refluxed to the top of the distillation column 93 (line 114), and the other part of the condensed liquid is discharged to the outside of the system (line 114). Line 115). The flow charged into the extraction tower 92 (line 105) may be joined with a flow rich in methyl iodide separated and obtained by the membrane separation step through line 118. Thereby, the above-mentioned flow rich in methyl iodide can be recycled in the extraction step (B1). Further, the above-mentioned flow rich in methyl iodide may be recycled in the distillation step (C1).

Further, the residual liquid flow rich in methyl iodide, which is the canned liquid of the first deacetaldehyde tower 91, the methyl iodide-rich raffinate (line 108) obtained in the extraction tower 92, and the can of the second deacetaldehyde tower 93. The water-rich residual liquid flow, which is the effluent, is recycled to the reaction vessel 1 through the lines 103, 111, and 113, respectively, or is recycled to an appropriate place in the process and reused. For example, the methyl iodide-rich raffinate obtained in the extraction column 92 can be recycled to the distillation column 91 through the line 110. The liquid of 113 is usually discharged to the outside as drainage. The gas (lines 106, 116) that has not been condensed in the capacitors 91a and 93a is absorbed by the scrubber system 8 or disposed of.

When the aqueous phase is treated in the acetaldehyde separation / removal step according to the flow of FIG. 4, for example, the aqueous phase (preparation flow) is supplied to the distillation column (first deacetaldehyde column) 91 through the line 101 for distillation. , The first overhead flow (line 102) rich in acetaldehyde and the residual liquid flow (line 103) rich in water are separated and acquired (distillation step (A1)). The first overhead flow is condensed by the condenser 91a, a part of the condensate is refluxed to the top of the distillation column 91 (line 104), and the other part of the condensate is supplied to the extraction column 92 (line 105). .. A flow rich in methyl iodide separated and obtained by the membrane separation step may be merged with the charging flow (line 101) through line 117. Thereby, the above-mentioned flow rich in methyl iodide can be recycled in the distillation step (A1).

The condensed liquid (preparation flow) supplied to the extraction tower 92 is extracted by the water introduced from the line 109 (extraction step (B1)). By the extraction treatment, the aqueous phase rich in acetaldehyde (line 107) and the organic phase rich in methyl iodide (line 108) are separated. The acetaldehyde-rich aqueous phase (extract) obtained by the extraction treatment is supplied to the distillation column (second deacetaldehyde column) 93 through line 107 for distillation, and is added to the acetaldehyde-rich second overhead stream (line 112) and water. Separated and acquired from the abundant residual liquid flow (line 113). Then, the second overhead flow rich in acetaldehyde is condensed by the condenser 93a, a part of the condensed liquid is refluxed to the top of the distillation column 93 (line 114), and the other part of the condensed liquid is discharged to the outside of the system (line 114). Line 115). The flow charged into the extraction tower 92 (line 105) may be joined with a flow rich in methyl iodide separated and obtained by the membrane separation step through line 118. Thereby, the above-mentioned flow rich in methyl iodide can be recycled in the extraction step (B1).

Further, the water-rich residual liquid flow which is the canned liquid of the first deacetaldehyde tower 91, the methyl iodide-rich raffinate (line 108) obtained in the extraction tower 92, and the canned liquid of the second deacetaldehyde tower 93. The water-rich residual liquid flow is recycled to the reaction vessel 1 through the lines 103, 111, 113, respectively, or is recycled to an appropriate place in the process and reused. For example, the methyl iodide-rich raffinate obtained in the extraction column 92 can be recycled to the distillation column 91 through the line 110. The liquid of 113 is usually discharged to the outside as drainage. The gas (lines 106, 116) that has not been condensed in the capacitors 91a and 93a is absorbed by the scrubber system 8 or disposed of.

A first overhead flow rich in acetaldehyde (line 102), a condensed liquid obtained by condensing the first overhead flow (lines 104, 105), an extract (107), a second overhead flow rich in acetaldehyde (line 112), And one or more of the condensed liquids (lines 114, 115) obtained by condensing the second overhead flow is a flow rich in acetaldehyde, and may be subjected to the membrane separation step as the process flow. Above all, since it is after the methyl iodide is sufficiently separated and recovered and it is difficult to separate and obtain the methyl iodide by the conventional purification of the distillation column, the process flow attached to the membrane separation step is the second overhead flow. And / or a condensed solution obtained by condensing the second overhead flow is preferable, and from the viewpoint that the zeolite membrane is superior in the recovery rate of methyl iodide and the number of facilities can be relatively reduced, the gas is used. A second overhead flow (particularly line 112) is preferred. The line 112 is an overhead flow of the distillation step (C1). Further, the process flow may be a condensed liquid (particularly, line 115) obtained by condensing a second overhead flow which is a liquid from the viewpoint of increasing the partial pressure difference between acetaldehyde and methyl iodide.

In addition to the above method, acetaldehyde contained in at least a part (for example, an organic phase and / or an aqueous phase) of the condensate obtained by condensing the overhead flow rich in the low boiling component is subjected to distillation in the distillation column. It can also be separated and removed by a distillation step (distillation step (A2)) using extraction distillation, co-boiling distillation, etc., in which the liquid falling from the concentrated region where methyl iodide and acetaldehyde are concentrated is extracted as a side flow. In the case of extraction distillation, specifically, for example, the organic phase and / or the aqueous phase (charged liquid) obtained by separating the condensed liquid of steam extracted from the top of the distillation tower 3 is distilled (extraction distillation). In the distillation column, an extraction solvent (usually water) is introduced into the concentrated area where methyl iodide and acetaldehyde are concentrated (for example, the space from the top of the column to the charging liquid supply position), and the solution is lowered from the concentrated area. The liquid (extract) to be distilled is extracted as a side flow (side cut flow). Next, this side stream is separated into an aqueous phase and an organic phase (liquid separation step (B2)), and the aqueous phase is subjected to distillation to form a third overhead flow rich in acetaldehyde and a canned liquid rich in water. (Distillation step (C2)), and acetaldehyde can be discharged to the outside of the system. Further, the acetaldehyde-rich third overhead flow is subjected to extraction distillation, the acetaldehyde-rich fourth overhead flow and the water-rich canned liquid are separated and obtained (extraction distillation step (D2)), and acetaldehyde is further concentrated. It can also be discharged to the outside of the system.

When a relatively large amount of water is present in the distillation column, the liquid falling from the concentrated region may be extracted as a side flow without introducing the extraction solvent into the distillation column. For example, a unit (such as a chimney tray) capable of receiving the liquid falling from the concentration region can be arranged in this distillation column, and the liquid received by this unit can be extracted as a side flow.

The introduction position of the extraction solvent is preferably above the supply position of the charging liquid, and more preferably near the top of the column. The extraction position of the side flow is preferably lower than the introduction position of the extraction solvent in the height direction of the column and higher than the supply position of the charging liquid. According to this method, acetaldehyde can be extracted at a high concentration from the concentrate of methyl iodide and acetaldehyde by an extraction solvent (usually water), and the area between the introduction site and the side cut site of the extraction solvent is used as an extraction region. Therefore, acetaldehyde can be efficiently extracted with a small amount of extraction solvent. Therefore, for example, the number of stages of the distillation column can be significantly reduced and the steam load can be reduced as compared with the method of extracting the extract by extraction distillation from the bottom of the distillation column (extraction distillation column). Further, since the ratio of methyl iodide (MeI / AD ratio) to acetaldehyde in the water extract can be made smaller than the method of combining the dealdehyde distillation and water extraction shown in FIG. 4 using a small amount of extraction solvent. Acetaldehyde can be removed under conditions that can suppress the loss of methyl iodide to the outside of the system.

The acetaldehyde concentration in the sidestream is much higher than the acetaldehyde concentration in the preparation liquid and the canned liquid (tower bottom liquid). Further, the ratio of acetaldehyde to methyl iodide in the sidestream is larger than the ratio of acetaldehyde to methyl iodide in the charging liquid and the canned liquid.

The organic phase (methyl iodide phase) obtained by separating the side stream may be recycled into this distillation column. In this case, the recycling position of the organic phase obtained by separating the side flow is preferably lower than the side flow extraction position in the height direction of the column, and preferably higher than the supply position of the charging liquid.

Further, a miscible solvent for the components (for example, methyl acetate) constituting the organic phase obtained by separating the condensed liquid of the vapor extracted from the top of the distillation column 3 may be introduced into the distillation column. .. Examples of the miscible solvent include acetic acid and ethyl acetate. The introduction position of the miscible solvent is preferably lower than the side flow sampling position and preferably higher than the supply position of the charging liquid in the height direction of the column. Further, the introduction position of the miscible solvent is preferably lower than the recycling position when the organic phase obtained by separating the side stream is recycled into the distillation column.

By recycling the organic phase obtained by separating the side stream into the distillation column or introducing the miscible solvent into the distillation column, the concentration of methyl acetate in the solution extracted as the side stream can be reduced. It is possible to reduce the concentration of methyl acetate in the aqueous phase obtained by separating the above solution, and thereby suppress the mixing of methyl iodide into the aqueous phase.

The theoretical stage of the distillation column is, for example, 1 to 100 stages, preferably 2 to 50 stages, more preferably 3 to 30 stages, still more preferably 5 to 20 stages, and the distillation column or extraction distillation used for conventional deacetaldehyde. Acetaldehyde can be efficiently separated and removed with a smaller number of stages as compared with the 80 to 100 stages of the column.

The mass ratio (former / latter) of the flow rate of the extraction solvent and the flow rate of the charging liquid (organic phase and / or aqueous phase obtained by separating the process flow) is in the range of 0.0001 / 100 to 100/100. It may be selected from 0.0001 / 100 to 20/100, preferably 0.001 / 100 to 10/100, more preferably 0.01 / 100 to 8/100, and even more preferably 0. It is 1/100 to 5/100.

The top temperature of the distillation column is, for example, 15 to 120 ° C., preferably 20 to 90 ° C., more preferably 20 to 80 ° C., and even more preferably 25 to 70 ° C. The column top pressure is an absolute pressure, for example, about 0.1 to 0.5 MPa. The other conditions of the above distillation column may be the same as those of the distillation column and the extraction distillation column used for the conventional deacetaldehyde.

FIG. 5 is a schematic flow chart showing an example of the acetaldehyde separation / removal system using the above-mentioned extraction distillation. In this example, the organic phase and / or the aqueous phase (preparation flow) obtained by separating the condensed liquid of steam extracted from the top of the distillation tower 3 is passed through the supply line 201 to the middle stage (with the top of the distillation tower 94) of the distillation tower 94. It is supplied to the position between the bottom of the column), and if necessary, water is introduced from the vicinity of the top of the column through the line 202 and distilled in the distillation column 94 (distillation step (A2)). A flow rich in methyl iodide separated and obtained by the membrane separation step may be merged with the charging flow (line 201) through line 228. Thereby, the above-mentioned flow rich in methyl iodide can be recycled in the distillation step (A2).

Above the supply position of the charging flow of the distillation column 94, a chimney tray 200 for receiving the liquid (extract) falling from the concentrated region where methyl iodide and acetaldehyde are concentrated in the column is arranged. .. In this extraction distillation, preferably the entire amount of the liquid on the chimney tray 200 is withdrawn and introduced into the decanter 95 through the line 208 to separate the liquids.

The aqueous phase (including acetaldehyde) in the decanter 95 is introduced into the cooling cooler 95a through the line 212 and cooled, and the methyl iodide dissolved in the aqueous phase is separated into two phases and separated by the decanter 96. Both the liquid separation in the decanter 95 and the liquid separation in the decanter 96 correspond to the liquid separation step (B2). In the liquid separation step (B2) and / or the distillation step (C2), a flow rich in methyl iodide separated and obtained by the above membrane separation step may be merged.

The aqueous phase in the decanter 96 is supplied to the distillation column 97 (de-acetaldehyde column) through line 216 for distillation, and separated into an acetaldehyde-rich third overhead stream (line 217) and a water-rich can outflow (line 218). (Distillation step (C2)). The third overhead flow is guided to the condenser 97a through the line 217 to be condensed, and a part of the condensed liquid (mainly acetaldehyde and methyl iodide) is refluxed to the top of the distillation column 97 (line 219), and the rest is discarded. Alternatively, it is supplied to the distillation column 98 (extraction distillation column) through the line 220.

Water is introduced from the vicinity of the top of the distillation column 98 through line 222, subjected to extraction distillation, and separated into an acetaldehyde-rich fourth overhead stream (line 223) and a water-rich can outflow (line 224) (line 224). Extraction distillation step (D2)). The fourth overhead flow is guided to the capacitor 98a through the line 223 to be condensed, and a part of the condensate (mainly methyl iodide) is returned to the top of the column (line 225), and the rest is recycled to the reaction system through the line 226. However, it may be removed from the system. The organic phase (methyl iodide phase) in the decanter 95 is preferably recycled in its entirety below the position of the chimney tray 200 in the distillation column 94 through lines 209 and 210. A part of the aqueous phase of the decanter 95 and the organic phase of the decanter 96 are recycled to the distillation column 94 through the lines 213, 210 and 214, 210, respectively, but may not be recycled. A part of the aqueous phase of the decanter 95 may be used as an extraction solvent (water) in the distillation column 94. A portion of the aqueous phase of the decanter 96 may be recycled to the distillation column 94 through line 210. Further, the above-mentioned flow rich in methyl iodide may be recycled in the extraction distillation step (D2).

In some cases (for example, when methyl acetate is contained in the above-mentioned charging flow), the components constituting the organic phase obtained by separating the condensed liquid of steam extracted from the top of the distillation column 3 (for example,). , Methyl acetate, etc.) and a miscible solvent (acetic acid, ethyl acetate, etc.) can be charged into the distillation column 94 through the line 215 to improve the distillation efficiency. The position of supplying the miscible solvent to the distillation column 94 is above the charging flow supply section (connecting section of the line 201) and below the connecting section of the recycling line 210. The canned liquid from the distillation column 94 is recycled into the reaction system.

The steam at the top of the distillation column 94 is guided to the condenser 94a through the line 203 to be condensed, the condensed liquid is separated by the decanter 99, the organic phase is returned to the top of the distillation column 94 through the line 206, and the aqueous phase is the line. Lead to Decanter 95 through 207.

The canned out liquid of the distillation column 97 (mainly water) and the canned out liquid of the distillation column 98 (extraction distillation column) (water containing a small amount of acetaldehyde) can be removed from the system through lines 218 and 224, respectively, or the reaction system. To recycle. The gas (lines 211,221,227) that has not been condensed by the capacitors 94a, 97a, 98a is absorbed or disposed of by the scrubber system 8.

FIG. 6 is a schematic flow chart showing another example of the acetaldehyde separation / removal system using the above-mentioned extraction distillation. In this example, the condensed liquid of steam at the top of the distillation column 94 is guided to the hold tank 100, and the entire amount thereof is returned to the top of the distillation column 94 through the line 206. Other than this, it is the same as the example of FIG.

FIG. 7 is a schematic flow chart showing still another example of the acetaldehyde separation / removal system using the above-mentioned extraction distillation. In this example, the entire amount of the liquid on the chimney tray 200 is withdrawn, introduced directly into the cooling cooler 95a through the line 208 without passing through the decanter 95, cooled, and supplied to the decanter 96. Other than this, it is the same as the example of FIG.

Sidestream containing methyl iodide and acetaldehyde (line 208), aqueous phase containing acetaldehyde (line 212), aqueous phase (line 216), steam at the top of the distillation tower 97 (line 217), and its condensate (line 219, line 219, 220), the fourth overhead flow (line 223), and one or more of the condensed liquids (lines 225 and 226) obtained by condensing the fourth overhead flow are flows rich in acetaldehyde, and the above-mentioned process flow is described above. It may be subjected to a membrane separation step. Above all, since it is after the methyl iodide is sufficiently separated and recovered and it is difficult to separate the methyl iodide by the conventional purification of the distillation column, the process flow attached to the membrane separation step is the third overhead flow. , One or more flows selected from the group consisting of a condensate obtained by condensing a third overhead flow, a fourth overhead flow, and a condensate obtained by condensing a fourth overhead flow, preferably zeolite. The fourth overhead flow (particularly, line 223), which is a gas, is preferable from the viewpoint that the membrane is superior in the recovery rate of methyl iodide and the number of facilities can be relatively small. Further, from the viewpoint that the partial pressure difference between acetaldehyde and methyl iodide can be increased and the sweep gas is not required, the condensed liquid (particularly, line 220) and / or the fourth obtained by condensing the third overhead flow which is a liquid. A condensate obtained by condensing an overhead stream (particularly line 226) is preferred. Line 217 is the overhead flow of the distillation step (C2), and line 223 is the overhead flow of the extraction distillation step (D2). Line 220 is a flow distilling from the distillation step (C2), and line 226 is a flow distilling from the extraction distillation step (D2).

In FIG. 3, the gas content generated in the condenser 3a is, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde. , And formic acid, etc., are supplied from the condenser 3a to the scrubber system 8 through the lines 32 and 15. Methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like in the gas component that has reached the scrubber system 8 are absorbed by the absorption liquid in the scrubber system 8.

The canned out liquid extracted from the bottom of the distillation column 3 contains a large amount of a component having a boiling point higher than that of acetic acid (high boiling point component) as compared with the overhead flow and the side flow from the distillation column 3, for example, propionic acid and. Includes the above-mentioned catalysts and co-catalysts accompanied by droplets. The canned liquid also contains acetic acid, methyl iodide, methyl acetate, water and the like. In the present embodiment, a part of such canned liquid is continuously introduced into the evaporation tank 2 through lines 25 and 26 and recycled, and the other part of the canned liquid is continuously introduced through lines 25 and 23 and recycled. It is continuously introduced into the reaction vessel 1 and recycled.

The first acetic acid stream continuously extracted from the distillation column 3 as a side stream is richer in acetic acid than the steam stream continuously introduced into the distillation column 3. That is, the acetic acid concentration of the first acetic acid stream is higher than the acetic acid concentration of the steam stream. The acetic acid concentration of the first acetic acid stream is, for example, 90 to 99.9% by mass, preferably 93 to 99% by mass. In addition to acetic acid, the first acetic acid stream includes, for example, methyl iodide, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, acetaldehyde, formic acid, and propionic acid, and ethyl iodide, propyl iodide, and the like. Includes butyl iodide, hexyl iodide, alkyl iodide such as decyl iodide and the like.

The connection position of the line 27 with respect to the distillation column 3 may be above the connection position of the line 21 with respect to the distillation column 3 in the height direction of the distillation column 3, as shown in the drawing. It may be lower than the connection position of the line 21 with respect to the distillation column 3 or may be the same as the connection position of the line 21 with respect to the distillation column 3. The first acetic acid stream from the distillation column 3 is continuously introduced into the next distillation column 5 through the line 27. The first acetic acid flow extracted as a side flow of the distillation column 3 and the bottom liquid of the distillation column 3 or the condensed liquid of the steam at the bottom of the distillation column 3 remain as they are without going through the distillation column 5 (dehydration step). It can also be continuously introduced into the distillation column 6 described later.

Potassium hydroxide can be supplied or added to the first acetic acid stream flowing through the line 27 through the line 55 (potassium hydroxide introduction line). Potassium hydroxide can be supplied or added as a solution such as an aqueous solution. Hydrogen iodide in the first acetic acid stream can be reduced by supplying or adding potassium hydroxide to the first acetic acid stream. Specifically, hydrogen iodide reacts with potassium hydroxide to produce potassium iodide and water. As a result, corrosion of equipment such as a distillation column due to hydrogen iodide can be reduced. Potassium hydroxide can be supplied or added to an appropriate place where hydrogen iodide is present in this process. Potassium hydroxide added during the process also reacts with acetic acid to produce potassium acetate.

The distillation column 5 is a unit for performing the second distillation step, and is positioned as a so-called dehydration column in the present embodiment. The second distillation step is a step for further purifying acetic acid by distilling the first acetic acid stream continuously introduced into the distillation column 5.

The distillation column 5 is composed of, for example, a rectification column such as a shelf column and a packed column. When a shelf column is adopted as the distillation column 5, the theoretical plate is, for example, 5 to 50 stages, and the reflux ratio is, for example, 0.2 to 3000 depending on the number of theoretical plates. Inside the distillation column 5 in the second distillation step, the column top pressure is set to, for example, 150 to 250 kPaG, and the column bottom pressure is set to be higher than the column top pressure, for example, 160 to 290 kPaG. Inside the distillation column 5 in the second distillation step, the column top temperature is set to, for example, 130 to 160 ° C., which is higher than the boiling point of water at the set top pressure and lower than the boiling point of acetic acid, and the column is set to 130 to 160 ° C. The bottom temperature is set to, for example, 150 to 175 ° C., which is a temperature equal to or higher than the boiling point of acetic acid at the set bottom pressure.

From the top of the distillation column 5, steam as an overhead flow is continuously drawn to the line 33. From the bottom of the distillation column 5, canned liquid is continuously drawn into the line 34. 5b is a reboiler. Side currents (liquid or gas) may be continuously drawn into the line 34 from a height position between the top and bottom of the distillation column 5.

The steam extracted from the top of the distillation column 5 contains a larger amount of a component having a boiling point lower than that of acetic acid (a low boiling point component) as compared with the above-mentioned canned liquid from the distillation column 5, for example, methyl iodide and iodide. Includes hydrogen, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, formic acid and the like. Such steam is continuously introduced into the capacitor 5a through the line 33.

The condenser 5a separates the steam from the distillation column 5 into a condensed component and a gas component by cooling and partially condensing the steam. Condensations include, for example, water and acetic acid. A part of the condensed portion is continuously refluxed from the capacitor 5a to the distillation column 5 through the line 35. The other part of the condensate is continuously introduced from the capacitor 5a into the reaction vessel 1 through the lines 35, 36, 23 and recycled. The gas content generated in the condenser 5a includes, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid. Is supplied from the condenser 5a to the scrubber system 8 through the lines 37 and 15. As described above, the gas component from the condenser 5a may be supplied to the scrubber system 8 without merging with the line 15. The hydrogen iodide in the gas that has reached the scrubber system 8 is absorbed by the absorption liquid in the scrubber system 8, and the reaction between the hydrogen iodide in the absorption liquid and methanol or methyl acetate produces methyl iodide, and then The liquid containing useful components such as methyl iodide is recycled from the scrubber system 8 to the reaction tank 1 through the recycling lines 48 and 23 and reused.

The canned out liquid (or sideflow) extracted from the bottom of the distillation column 5 contains more components (high boiling point components) having a higher boiling point than acetic acid in addition to acetic acid as compared with the above overhead flow from the distillation column 5. Including, for example, acetic acid anhydride, propionic acid, acetate, and iodide salts such as metal iodide salts derived from potassium iodide, corrosive metals and the like, and the above-mentioned catalysts and co-catalysts accompanied by droplets. Examples of the acetic acid salt include metal acetate salts such as potassium acetate formed when an alkali such as potassium hydroxide is supplied to the line 27 or the like. Further, a metal acetate salt formed by acetic acid and a corrosive metal such as a metal generated and liberated on the inner wall of the constituent member of the acetic acid producing apparatus can also be mentioned. Examples of the iodide salt include potassium iodide formed when an alkali such as potassium hydroxide is supplied to the line 27 or the like. Acetic acid may also be contained in this canned liquid. Such canned out liquid is continuously introduced into the next distillation column 6 through the line 34 in a second acetic acid stream. The canned out liquid (or sidestream) extracted from the bottom of the distillation column 5 also contains the corrosive metal and the like, and a compound (iodide salt) of iodine derived from the corrosive iodine and the corrosive metal and the like.

The second acetic acid stream is richer in acetic acid than the first acetic acid stream continuously introduced into the distillation column 5. That is, the acetic acid concentration of the second acetic acid stream is higher than the acetic acid concentration of the first acetic acid stream. The acetic acid concentration of the second acetic acid stream is, for example, 99.1 to 99.99% by mass as long as it is higher than the acetic acid concentration of the first acetic acid stream. Further, as described above, the second acetic acid stream may contain, for example, propionic acid, hydrogen iodide, etc. in addition to acetic acid. In the present embodiment, when the side flow is extracted, the position where the side flow is extracted from the distillation column 5 is lower than the position where the first acetic acid flow is introduced into the distillation column 5 in the height direction of the distillation column 5.

Potassium hydroxide can be supplied or added to the second acetic acid stream flowing through the line 34 through the line 56 (potassium hydroxide introduction line). Potassium hydroxide can be supplied or added as a solution such as an aqueous solution. Hydrogen iodide in the secondary acetic acid stream can be reduced by supplying or adding potassium hydroxide to the secondary acetic acid stream. Specifically, hydrogen iodide reacts with potassium hydroxide to produce potassium iodide and water. As a result, corrosion of equipment such as a distillation column due to hydrogen iodide can be reduced.

The distillation column 6 is a unit for performing the third distillation step, and is positioned as a so-called de-high boiling column in the present embodiment. The third distillation step is a step for purifying the second acetic acid stream continuously introduced into the distillation column 6 to further purify acetic acid.

The distillation column 6 is composed of, for example, a rectification column such as a shelf column and a packed column. When a shelf column is adopted as the distillation column 6, the theoretical plate is, for example, 5 to 50 stages, and the reflux ratio is, for example, 0.2 to 3000 depending on the number of theoretical plates. Inside the distillation column 6 in the third distillation step, the column top pressure is set to, for example, −100 to 150 kPaG, and the column bottom pressure is set to be higher than the column top pressure, for example, −90 to 180 kPaG. Inside the distillation column 6 in the third distillation step, the column top temperature is set to, for example, 50 to 150 ° C., which is higher than the boiling point of water at the set top pressure and lower than the boiling point of acetic acid, and the column is set to 50 to 150 ° C. The bottom temperature is set to, for example, 70 to 160 ° C., which is higher than the boiling point of acetic acid at the set bottom pressure.

From the top of the distillation column 6, steam as an overhead flow is continuously drawn into the line 38. From the bottom of the distillation column 6, canned liquid is continuously drawn into the line 39. 6b is a reboiler. A side stream (liquid or gas) is continuously drawn into the line 46 from the height position between the top and bottom of the distillation column 6. In the height direction of the distillation column 6, the connection position of the line 46 with respect to the distillation column 6 may be higher than the connection position of the line 34 with respect to the distillation column 6, but the line with respect to the distillation column 6 may be above the connection position. It may be below the connection position of 34, or may be the same as the connection position of line 34 with respect to the distillation column 6.

The steam extracted from the top of the distillation column 6 contains a component having a boiling point lower than that of acetic acid (low boiling point component) as compared with the above-mentioned canned liquid from the distillation column 6, and in addition to acetic acid, for example, iodide. Includes methyl, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, formic acid and the like. Such steam is continuously introduced into the capacitor 6a through the line 38.

The condenser 6a separates the steam from the distillation column 6 into a condensed component and a gas component by cooling and partially condensing the steam. In addition to acetic acid, the condensate contains, for example, methyl iodide, hydrogen iodide, water, methyl acetate, dimethyl ether, methanol, formic acid and the like. At least a portion of the condensed material is continuously refluxed from the capacitor 6a to the distillation column 6 through the line 40. A part of the condensed portion (distillate portion) can be recycled from the condenser 6a through the lines 40, 41 and 42 to the first acetic acid stream in the line 27 before being introduced into the distillation column 5. be. At the same time or instead, a part of the condensed portion (distillate portion) is transferred from the condenser 6a to the steam flow in the line 21 before being introduced into the distillation column 3 through the lines 40, 41, 43. It is possible to recycle.

Further, a part of the condensed portion (distilled portion) may be recycled from the capacitor 6a to the reaction tank 1 through the lines 40, 44, 23. Further, a part of the distillate from the capacitor 6a can be supplied to the scrubber system 8 and used as an absorbing liquid in the system. In the scrubber system 8, the gas after absorbing the useful component is discharged to the outside of the apparatus, and the liquid component containing the useful component is introduced or recycled from the scrubber system 8 into the reaction tank 1 through the recycling lines 48 and 23. Will be reused. In addition, a part of the distillate from the condenser 6a may be guided to various pumps (not shown) operating in the apparatus through a line (not shown) and used as a sealing liquid for the pump. Furthermore, a part of the distillate from the capacitor 6a may be constantly extracted to the outside of the device through a sampling line attached to the line 40, or may be unsteadily removed to the outside of the device when necessary. You may.

When a part of the condensed portion (distillate portion) is removed from the distillation treatment system in the distillation column 6, the amount of the distilled portion (distillate amount) is, for example, 0.01 to 30 of the condensed liquid generated in the condenser 6a. It is by mass, preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and more preferably 0.5 to 3% by mass. On the other hand, the gas content generated in the condenser 6a is, for example, carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen, oxygen, methyl iodide, hydrogen iodide, water, methyl acetate, acetic acid, dimethyl ether, methanol, acetaldehyde, and formic acid. And so on, it is supplied from the condenser 6a to the scrubber system 8 through the lines 45 and 15. As described above, the gas component from the condenser 6a may be supplied to the scrubber system 8 without merging with the line 15.

The canned out liquid extracted from the bottom of the distillation column 6 through the line 39 contains a large amount of a component having a boiling point higher than that of acetic acid (high boiling point component) as compared with the overhead flow from the distillation column 6, for example, acetic acid salt or anhydrous acetic acid. , Includes propionic acid, etc. Examples of the acetate include potassium acetate formed when an alkali such as potassium hydroxide is supplied to the line 34 or the like. Further, a metal acetate salt formed by acetic acid and a corrosive metal such as a metal generated and liberated on the inner wall of the constituent member of the acetic acid producing apparatus can also be mentioned. The canned out liquid extracted from the bottom of the distillation column 6 through the line 39 further contains the corrosive metal and the like, and a compound of iodine derived from the corrosive iodine and the corrosive metal and the like. In this embodiment, such canned liquid is discharged to the outside of the acetic acid production apparatus.

The side stream continuously drawn from the distillation column 6 to the line 46 is continuously introduced into the next ion exchange resin column 7 as a third acetic acid stream. This third acetic acid stream is richer in acetic acid than the second acetic acid stream continuously introduced into the distillation column 6. That is, the acetic acid concentration of the third acetic acid stream is higher than the acetic acid concentration of the second acetic acid stream. The acetic acid concentration of the third acetic acid stream is, for example, 99.8 to 99.99% by mass as long as it is higher than the acetic acid concentration of the second acetic acid stream. In the present embodiment, the position of extracting the side flow from the distillation column 6 is higher in the height direction of the distillation column 6 than the position of introducing the second acetic acid flow into the distillation column 6. In another embodiment, the position of extracting the side flow from the distillation column 6 is the same as or lower than the position of introducing the second acetic acid flow into the distillation column 6 in the height direction of the distillation column 6. The distillation column 6 can be replaced with a simple distillation column (evaporator), and the distillation column 6 can be omitted if impurities are sufficiently removed by the distillation column 5.

The ion exchange resin tower 7 is a purification unit for performing an adsorption removal step. In this adsorption removal step, mainly alkyl iodide (for example, ethyl iodide, propyl iodide, butyl iodide, hexyl iodide, etc.) contained in a trace amount in the tertiary acetic acid stream continuously introduced into the ion exchange resin column 7. This is a step for further purifying acetic acid by adsorbing and removing (decyl iodide, etc.).

In the ion exchange resin column 7, an ion exchange resin having an adsorptive ability to alkyl iodide is filled in the column to form an ion exchange resin bed. As such an ion exchange resin, for example, a cation exchange resin in which a part of the desorbing protons in the sulfonic acid group, the carboxyl group, the phosphonic acid group, etc., which are the exchange groups, is replaced with a metal such as silver or copper. Can be mentioned. In the adsorption removal step, for example, a third acetic acid stream (liquid) flows through the inside of the ion exchange resin tower 7 filled with such an ion exchange resin, and in the flow process, the alkyl iodide in the tertiary acetic acid stream flows. Etc. are adsorbed on the ion exchange resin and removed from the tertiary acetic acid stream. In the ion exchange resin tower 7 in the adsorption removal step, the internal temperature is, for example, 18 to 100 ° C., and the acetic acid flow rate [acetic acid treatment amount per 1 m ³ of resin volume (m ³ / h)] is, for example, 3. ~ 15 m ³ / h · m ³ (resin volume).

A fourth acetic acid stream is continuously derived from the lower end of the ion exchange resin tower 7 to the line 47. The acetic acid concentration of the fourth acetic acid stream is higher than the acetic acid concentration of the third acetic acid stream. That is, the fourth acetic acid stream is richer in acetic acid than the third acetic acid stream continuously introduced into the ion exchange resin column 7. The acetic acid concentration of the fourth acetic acid stream is, for example, 99.9 to 99.99% by mass or more as long as it is higher than the acetic acid concentration of the third acetic acid stream. In this production method, this tetracetic acid stream can be stored in a product tank (not shown).

In this acetic acid production apparatus, a so-called product column or finishing column, which is a distillation column, may be provided as a purification unit for further purifying the above-mentioned fourth acetic acid stream from the ion exchange resin column 7. When such a product tower is provided, the product tower comprises, for example, a rectification tower such as a shelf column and a packed tower. When a shelf tower is adopted as a product tower, the theoretical plate is, for example, 5 to 50 stages, and the reflux ratio is, for example, 0.5 to 3000 depending on the number of theoretical plates. Inside the product column in the refining process, the column top pressure is set to, for example, -195 to 150 kPaG, and the column bottom pressure is set to be higher than the column top pressure, for example, -190 to 180 kPaG. Inside the product column, the column top temperature is set to, for example, 50-150 ° C, which is higher than the boiling point of water at the set column top pressure and lower than the boiling point of acetic acid, and the column bottom temperature is set, for example. The temperature is set to 70 to 160 ° C., which is higher than the boiling point of acetic acid at the bottom pressure. The product tower or finishing tower can be replaced with a simple distiller (evaporator).

When the product tower is provided, all or part of the fourth acetic acid stream (liquid) from the ion exchange resin tower 7 is continuously introduced into the product tower. From the top of such a product tower, steam as an overhead stream containing trace amounts of low boiling point components (eg, methyl iodide, water, methyl acetate, dimethyl ether, crotonaldehyde, acetaldehyde, and formic acid) is continuous. It is extracted. This steam is divided into a condensed component and a gas component by a capacitor.

A portion of the condensate may be continuously refluxed to the product column and the other portion of the condensate may be recycled to the reaction vessel 1, discarded outside the system, or both. , The gas component is supplied to the scrubber system 8. Can effluent containing a trace amount of high boiling point components is continuously withdrawn from the bottom of the product column, and this can effluent is, for example, sent to a second acetic acid stream in line 34 before being introduced into the distillation column 6. And recycled. A side stream (liquid) is continuously extracted as a fifth acetic acid stream from the height position between the column top and the column bottom in the product column. The position for extracting the side flow from the product tower is lower than, for example, the position for introducing the fourth acetic acid flow into the product tower in the height direction of the product tower.

The fifth acetic acid stream is richer in acetic acid than the fourth acetic acid stream that is continuously introduced into the product column. That is, the acetic acid concentration of the fifth acetic acid stream is higher than the acetic acid concentration of the fourth acetic acid stream. The acetic acid concentration of the fifth acetic acid stream is, for example, 99.9 to 99.99% by mass or more as long as it is higher than the acetic acid concentration of the fourth acetic acid stream. This fifth acetic acid stream is stored in, for example, a product tank (not shown). The ion exchange resin tower 7 may be installed downstream of the product tower (or in addition to it) instead of being installed downstream of the distillation column 6 to treat the acetic acid flow from the product tower.

Each aspect disclosed herein can be combined with any other feature disclosed herein. Each configuration and a combination thereof in each embodiment are examples, and the configurations can be added, omitted, replaced, and other changes as appropriate without departing from the spirit of the present disclosure. Further, each invention according to the present disclosure is not limited to the embodiments or the following examples, but is limited only to the scope of claims.

Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

Example 1
A separation test was performed using the apparatus shown in FIG. As the separation membrane, a cylindrical ceramic porous substrate surface coated with the zeolite membrane shown in Table 1 was used. In the above separation test, 100 mL of the sample solution was injected into the tube with a syringe 301 so as to have a flow rate of 0.3 mL / min. The composition of the sample liquid is a mixed liquid as shown in Table 1. The injected sample liquid was heated by the ribbon heater 302, vaporized in its entirety, and supplied as gas into the membrane housing 303. Sweep gas (helium gas) 305 was blown into the separation membrane 304 installed in the membrane housing 303 at a flow rate of 10 to 100 mL / min. Then, of the gas injected into the membrane housing 303, a part of the gas that has passed through the separation membrane 304 is collected by a syringe at the sampling port 306 to collect the GC injection amount shown in Table 1, and gas chromatography analysis is performed. rice field. The remaining gas 307 that had passed through the separation membrane 304 was condensed and recovered by a liquid nitrogen trap. On the other hand, the gas 308 that did not permeate the separation membrane 304 in the membrane housing 303 was discarded. Then, the permeability [mol / m ² · s · Pa] and the permeability ratio of various components were calculated by gas chromatography analysis. The permeability ratio was determined as [acetaldehyde permeability / permeability of methyl iodide]. The results are shown in Table 1. In addition, "AD" shown in Tables 1 to 3 shows acetaldehyde, and "MeI" shows methyl iodide, respectively. Further, Na-ZSM-5 type zeolite and Silicate-1 type zeolite are a kind of MFI type zeolite.

As can be seen from Table 1, when various zeolite membranes were used as separation membranes, the permeability of methyl iodide was extremely small, the recovery rate of methyl iodide was high, and the permeability ratio was high. From this, it is shown that the zeolite membrane can efficiently separate acetaldehyde and methyl iodide.

Comparative Example 1
Experiments were performed using the acetaldehyde separation and removal system shown in FIG. A mixed solution containing acetaldehyde, methyl iodide, and water was supplied to the distillation column 91 (shelf column, actual number of columns: 80 stages, column top pressure: 0.18 MPaG, column top temperature: 52 ° C.) through line 101. Distillation was performed. The overhead flow (line 102) separated by distillation in the distillation column 91 is condensed by the condenser 91a, a part of the condensed solution is refluxed to the top of the distillation column 91 (line 104), and the rest of the condensed solution is extracted. It was supplied to the column 92 (filling column, column top pressure: 0.25 MPaG, column top temperature: 40 ° C.) (line 105). The condensed liquid supplied to the extraction tower 92 was subjected to an extraction treatment while introducing water as an extraction solvent from the line 109, and the extract separated by the extraction treatment was extracted from the line 107 and the lower phase was extracted from the line 108. The lower phase was not recycled through line 110. The above extract is supplied to a distillation column 93 (filling column, column top pressure: 0.17 MPaG, column top temperature: 85 ° C.) through a line 107 for distillation, and an overhead flow (line 112) and a can-out liquid (line 113) are distilled. ) And separated. The overhead flow of the line 112 was condensed by the condenser 93a, a part of the condensed liquid was returned to the top of the distillation column 93 (line 114), and the rest of the condensed liquid was distilled off from the line 115. The reflux ratio of the distillation column 91 was 182.2, and the reflux ratio of the distillation column 93 was 5.0. Table 2 shows the flow rates and concentrations of various components at various locations in the steady state during the experiment of Comparative Example 1.

Example 2
An experiment was conducted using the membrane separation step shown in FIG. 1 using the overhead flow (line 112) obtained in the same manner as in Comparative Example 1 as a process gas. The above process gas was supplied to the membrane module 58 through the line 60, and membrane separation was performed in an environment of a temperature of 90 ° C. and a sweep gas flow rate of 3 m ³ / h. As a separation membrane, No. 1 in Table 1 was placed on a ceramic porous substrate. The one provided with 12 BEA type zeolite membranes was used. By membrane separation, the permeated gas (line 62) and the concentrated gas (line 61) were separated. The concentrated gas was condensed by the condenser 61a and supplied to the receiver 59. A portion of the condensate in the receiver 59 was recycled to the distillation column 93 through lines 63 and 67. The recycling position to the distillation column 93 is below the top of the distillation column 93 in the height direction and above the charging position to the distillation column 93. Then, the rest of the condensed liquid in the receiver 59 was collected from the line 66. The recycling ratio [flow rate of line 67 / flow rate of line 66] was set to 5.0. The gas generated in the receiver 59 was merged with the line 61 through the lines 68 and 71, and when the pressure gauge 60a exceeded 0.17 MPa, the gas was discharged through the line 69. Table 3 shows the flow rates and concentrations of various components in various places in the steady state during the experiment of Example 2.

According to Table 2, in Comparative Example 1 which does not have the membrane separation step, it can be recognized that methyl iodide is discharged at a flow rate of 2.1 kg / h by distillation from the line 115. On the other hand, according to Table 3, in Example 2 having the above membrane separation step, it is possible to recover a flow rate of 2.0 kg / h from the line 66 out of 2.1 kg / h of methyl iodide originally discharged. I can recognize that I can do it. The recovery rate is 95.2%, and the concentration of methyl iodide in the permeated gas (line 62) to be discarded is reduced to 0.2% by mass. Therefore, according to the method for producing acetic acid of the present disclosure, the loss of methyl iodide is significantly reduced. In addition, the need for newly producing and adding methyl iodide is reduced, and the work load and cost are also reduced.

In Tables 2 and 3, the concentration of each component is shown so that the total of acetaldehyde, methyl iodide, and water is 100.0% by mass. However, in the actual acetic acid production process, each process liquid in the acetaldehyde separation / removal system may only contain acetaldehyde, methyl iodide, and water as the main components, and in addition, methanol, dimethyl ether, alkane, and crotonaldehyde. It may contain trace components such as organic iodine compounds and substances that worsen the potassium permanganate test value (permanganate thyme).

Hereinafter, variations of the invention according to the present disclosure will be described.
[Appendix 1] In the acetic acid production process, acetic acid having a membrane separation step of separating and acquiring an acetaldehyde-rich flow and a methyl iodide-rich flow from a process flow containing acetaldehyde and methyl iodide using a zeolite membrane. Production method.
[Appendix 2] The method for producing acetic acid according to Appendix 1, wherein the zeolite membrane is a BEA type zeolite membrane.
[Appendix 3] The acetaldehyde concentration in the process flow is 0.1% by mass or more (1% by mass or more, 2% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40. The method for producing acetic acid according to Appendix 1 or 2 (% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more).
[Appendix 4] The acetaldehyde concentration in the process flow is 99.9% by mass or less (99% by mass or less, 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, 70% by mass or less, 60. The acetic acid according to any one of Supplementary note 1 to 3 (% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less). Manufacturing method.
[Appendix 5] The methyl iodide concentration in the process flow is 0.01% by mass or more (0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 6% by mass or more, 7% by mass or more, 10% by mass or more, 12% by mass or more, 15% by mass or more, 20% by mass or more, or 30% by mass or more) The method for producing acetic acid according to one.
[Appendix 6] The methyl iodide concentration in the process flow is 99% by mass or less (95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 50% by mass or less, 20% by mass or less, 10). The method for producing acetic acid according to any one of Supplementary note 1 to 5 (1% by mass or less), which is 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.1% by mass or less).
[Appendix 7] The acetic acid according to any one of Supplementary note 1 to 6, wherein the acetaldehyde concentration in the process flow is 0.1 to 99.9% by mass and the methyl iodide concentration is 0.01 to 99% by mass. Manufacturing method.
[Appendix 8] The total concentration of acetaldehyde and methyl iodide in the process flow is 1% by mass or more (10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass). % Or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more).
[Appendix 9] The total concentration of acetaldehyde and methyl iodide in the process flow is 99% by mass or less (95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass). % Or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less).
[Appendix 10] The water concentration in the process flow is 0.1% by mass or more (0.5% by mass or more, 1% by mass or more, 2% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more. , 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more). The method for producing acetic acid according to any one of them.
[Appendix 11] The water concentration in the process flow is 95% by mass or less (90% by mass or less, 80% by mass or less, 70% by mass or less, 50% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass). Hereinafter, the method for producing acetic acid according to any one of Supplementary note 1 to 10, which is 5% by mass or less, or 1% by mass or less).

[Appendix 12] The membrane separation step is performed under the condition that the temperature of the process liquid is 10 to 180 ° C. (for example, 20 to 150 ° C., preferably 30 to 130 ° C., more preferably 50 to 110 ° C., still more preferably 70 to 90 ° C.). The method for producing acetic acid according to any one of Supplementary note 1 to 11, which is carried out below.
[Appendix 13] The membrane separation step is carried out under pressure (for example, 110 to 2000 kPa in absolute pressure, preferably 200 to 1800 kPa, more preferably 300 to 1500 kPa, still more preferably 400 to 1200 kPa, particularly preferably 600 to 1000 kPa). The method for producing acetic acid according to any one of Supplementary Provisions 1 to 12, which is carried out under conditions.
[Appendix 14] Methanol and carbon monoxide are reacted in the presence of a metal catalyst and a catalyst system containing methyl iodide (preferably a metal catalyst and a catalyst system containing methyl iodide, and acetic acid, methyl acetate, and water). The carbonylation reaction step to generate acetic acid and
The reaction mixture obtained in the carbonylation reaction step is subjected to one or more evaporation treatments and / or distillation treatments, and is subjected to at least a flow containing a metal catalyst, an acetic acid-rich flow, and a lower acetic acid flow. A separation process that separates into a stream rich in boiling components,
It is provided with an acetaldehyde separation / removal system that separates acetaldehyde from at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component by one or more distillation treatments.
The method for producing acetic acid according to any one of Supplementary note 1 to 13, wherein the acetaldehyde-rich flow separated in the acetaldehyde separation / removal system is subjected to the membrane separation step as the process flow.
[Appendix 15] The method for producing acetic acid according to Appendix 14, wherein the separation step comprises an evaporation step of separating the reaction mixture obtained in the carbonylation reaction step into at least a vapor stream and a residual liquid stream by evaporation.
[Appendix 16] In the separation step, (i) the separation step and the steam flow are subjected to distillation to separate and obtain at least an overhead flow rich in low boiling components and a first acetic acid flow rich in acetic acid. It has a delow boiling step, or (ii) instead of the evaporation step and the delow boiling step, the reaction mixture obtained in the carbonylation reaction step is at least with a flow containing a metal catalyst and low. The method for producing acetic acid according to Appendix 15, which comprises an evaporation-delow boiling step of separating an overhead flow rich in boiling components and an acetic acid flow rich in acetic acid.
[Appendix 17] In the de-low boiling step, the steam flow is subjected to distillation to separate it into an overhead flow rich in low boiling components, a side-cut flow, and a tower bottom flow, and the side-cut flow and / or the above. The method for producing acetic acid according to Appendix 16, wherein the column bottom flow is the first acetic acid flow.
[Appendix 18] In the separation step, (iii) the de-low boiling step and the first acetic acid stream are subjected to distillation, and at least the overhead stream rich in water and the acetic acid are enriched more than the first acetic acid stream. It has a dehydration step of separating and acquiring the second acetic acid stream, or (iv) is rich in acetic acid in the delow boiling step having the function of the dehydration step instead of the delow boiling step and the dehydration step. It has a delow boiling dehydration step of separating and acquiring an acetic acid stream, or (v) is rich in acetic acid in the evaporation delow boiling step having the function of the dehydration step instead of the evaporation delow boiling step and the dehydration step. The method for producing acetic acid according to Supplementary note 16 or 17, further comprising an evaporation-de-low boiling dehydration step of separating and acquiring an acetic acid flow.
[Supplementary Note 19] The method for producing acetic acid according to any one of Supplementary note 14 to 18, further comprising at least one step of the following (a) to (c).
(A) The acetic acid-rich acetic acid stream (for example, the first or second acetic acid stream) obtained in the separation step is distilled, and the can-out stream rich in high boiling components and the acetic acid stream before distilling are used. (B) Acetic acid-rich acetic acid stream (for example, the first or second acetic acid stream) or tertiary acetic acid obtained in the separation step. Adsorption-removal step of treating the stream with an ion exchange resin to obtain a fourth acetic acid stream (c) An acetic acid-rich acetic acid stream (eg, the first or second acetic acid stream) or a third or third acetic acid stream obtained in the separation step. 4 Product process of distilling an acetic acid stream to obtain a fifth acetic acid stream enriched with acetic acid compared to the acetic acid stream before subject to distillation.

[Appendix 20] The acetaldehyde separation / removal system comprises an extraction step of separating an aqueous phase containing acetaldehyde by one or more extraction treatments from at least a part of the acetaldehyde separated by the one or more distillation treatments. 19. The method for producing acetic acid according to any one of 19.
[Appendix 21] The acetaldehyde-rich flow separated in the distillation treatment in the acetaldehyde separation / removal system and / or the acetaldehyde-rich aqueous layer separated in the extraction treatment is used as the process flow for film separation. The method for producing acetic acid according to any one of Supplementary note 14 to 20, which is attached to the step.
[Appendix 22] A part of the methyl iodide-rich stream separated and obtained by the membrane separation step is recycled to a process in the acetaldehyde separation / removal system (particularly, a distillation column for discharging the process stream), Appendix 14 to 21. The method for producing acetic acid according to any one of 21.
[Supplementary Note 23] The method for producing acetic acid according to any one of Supplementary note 14 to 22, wherein the process flow includes an overhead flow of a distillation column for performing a distillation treatment in the acetaldehyde separation / removal system.
[Appendix 24] The method for producing acetic acid according to Appendix 23, wherein a part of the flow rich in methyl iodide separated and obtained by the membrane separation step is refluxed to the distillation column performing the distillation treatment.
[Appendix 25] The acetaldehyde separation / removal step is carried out.
A distillation step (A1) in which at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation to separate and obtain the first overhead flow rich in acetaldehyde and the residual liquid flow.
An extraction step (B1) in which at least a part of the condensed liquid obtained by condensing the first overhead flow is subjected to extraction and separated into an acetaldehyde-rich aqueous phase and a methyl iodide-rich organic phase.
The acetaldehyde-rich aqueous phase is subjected to distillation, and the distillation step (C1) for separating and acquiring the acetaldehyde-rich second overhead flow and the water-rich residual liquid flow is provided.
Of the first overhead flow, the condensed liquid obtained by condensing the first overhead flow, the acetaldehyde-rich aqueous phase, the second overhead flow, and the condensed liquid obtained by condensing the second overhead flow. One or more (preferably, the condensed liquid obtained by condensing the second overhead flow and / or the second overhead flow) is applied to the film separation step as the process flow, according to any one of Supplementary note 14 to 24. The method for producing acetic acid according to the above.
[Supplementary Note 26] The method for producing acetic acid according to Supplementary note 25, wherein the process flow includes the second overhead flow.
[Appendix 27] The methyl iodide-rich flow obtained by separation in the film separation step is one or more of the distillation step (A1), the extraction step (B1), and the distillation step (C1). 25 or 26, wherein the method for producing acetic acid according to Supplementary note 25 or 26, which is recycled in the step (preferably the distillation step (A1) and / or the extraction step (B1)).
[Appendix 28] The acetaldehyde separation / removal step is carried out.
At least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation, and the liquid falling from the concentrated region where methyl iodide and acetaldehyde are concentrated in the distillation column is extracted as a side flow. Distillation step (A2) and
A liquid separation step (B2) for separating the side flow into an aqueous phase and an organic phase,
It is provided with a distillation step (C2) in which the aqueous phase is subjected to distillation to separate and obtain a third overhead flow rich in acetaldehyde and a canned out liquid rich in water.
Further, it may be provided with an extraction distillation step (D2) in which the acetaldehyde-rich third overhead flow is subjected to extraction distillation, and the acetaldehyde-rich fourth overhead flow and the water-rich canned liquid are separated and obtained.
One or more selected from the group consisting of the third overhead flow, the condensed liquid obtained by condensing the third overhead flow, the fourth overhead flow, and the condensed liquid obtained by condensing the fourth overhead flow. The method for producing acetic acid according to any one of Supplementary note 14 to 24, wherein the flow is applied to the film separation step as the process flow.
[Appendix 29] The method for producing acetic acid according to Appendix 28, wherein in the distillation step (A2), the extraction solvent is supplied from above the position where the condensed liquid is supplied (preferably near the top of the column).
[Appendix 30] In the distillation step (A2), the extraction position of the side flow is lower than the introduction position of the extraction solvent in the height direction of the distillation column when the extraction solvent is introduced, and the condensation The method for producing acetic acid according to Appendix 28 or 29, which is above the liquid supply position.
[Supplementary Note 31] The method for producing acetic acid according to any one of Supplementary note 28 to 30, wherein the process flow includes the fourth overhead flow.
[Appendix 32] The methyl iodide-rich flow obtained by separation in the film separation step is subjected to the distillation step (A2), the liquid separation step (B2), the distillation step (C2), and the extraction distillation. The method for producing acetic acid according to any one of Supplementary note 28 to 31, which is recycled in one or more of the steps (D2) (preferably, the distillation step (A2)).

[Supplementary Note 33] The method for producing acetic acid according to any one of Supplementary note 1 to 32, wherein the process flow is a gas.
[Appendix 34] The method for producing acetic acid according to Appendix 33, wherein the membrane separation step is performed while blowing a sweep gas to the charging side.
[Appendix 35] The methyl iodide recovery rate by the membrane separation step is 1% by mass or more (5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more). ..
[Appendix 36] The methyl iodide recovery rate by the membrane separation step is 100% by mass or less (99.5% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass). Hereinafter, the acetic acid according to any one of Supplementary note 1 to 35, which is 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less). Production method.
[Appendix 37] The recovery rate of acetaldehyde in the membrane separation step is 1% by mass or more (5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 30% by mass or more, 50% by mass or more, 60). The method for producing acetic acid according to any one of Supplementary note 1 to 36, which is (% by mass or more, 80% by mass or more, or 90% by mass or more).
[Appendix 38] The recovery rate of acetaldehyde in the film separation step is 100% by mass or less (99.5% by mass or less, 95% by mass or less, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less. , 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less). Method.
[Appendix 39] The concentration of methyl iodide in the flow rich in methyl iodide separated and obtained by the membrane separation step is higher than the concentration of methyl iodide in the process flow, and is 1% by mass or more (5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more). Method for producing acetic acid.
[Appendix 40] The concentration of methyl iodide in the flow rich in methyl iodide separated and obtained by the membrane separation step is higher than the concentration of methyl iodide in the process flow and is 100% by mass or less (90% by mass or less, 70% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less). Method for producing acetic acid.
[Appendix 41] The acetaldehyde concentration in the acetaldehyde-rich stream separated and obtained by the membrane separation step is higher than the acetaldehyde concentration in the process stream, and is 0.1% by mass or more (1% by mass or more, 5% by mass). (1), 10% by mass or more, 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more) The method for producing acetic acid according to the above.
[Appendix 42] The acetaldehyde concentration in the acetaldehyde-rich stream separated and obtained by the membrane separation step is higher than the acetaldehyde concentration in the process stream and is 100% by mass or less (99.5% by mass or less, 95% by mass). Below, 93% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass. % Or less). The method for producing acetic acid according to any one of Supplementary note 1 to 41.

[Appendix 43] The method for producing acetic acid according to any one of Supplementary note 1 to 42, wherein the zeolite membrane is provided on at least one surface of a porous substrate.
[Appendix 44] The method for producing acetic acid according to Appendix 43, wherein the porous substrate is an alumina substrate.
[Appendix 45] From a mixture containing acetaldehyde and methyl iodide, a flow rich in acetaldehyde and a flow rich in methyl iodide are produced by separating and acquiring a flow rich in acetaldehyde and a flow rich in methyl iodide using a zeolite membrane. Method.

According to the method for producing acetic acid of the present disclosure, acetic acid can be industrially produced by a methanol method carbonylation process (methanol method acetic acid process).

1 Reaction tank 2 Evaporation tank 3, 5, 6 Distillation column 4 Decanter 7 Ion exchange resin tower 8 Scrubber system 9 Acetaldehyde separation and removal system 16 Reaction mixture supply line 17 Steam flow discharge line 18, 19 Residual liquid flow recycling line 54 Carbon monoxide Containing gas introduction line 55,56 Potassium hydroxide introduction line 57 Catalytic circulation pump 58 Membrane module 59,72,73 Receiver 91 Distillation column (1st deacetoaldehyde column)
92 Extraction column 93 Distillation column (second deacetaldehyde column)
94 Distillation column (extraction distillation column)
95 Decanter 96 Decanter 97 Distillation column (de-acetaldehyde column)
98 Distillation column (extraction distillation column)
99 Decanter 200 Chimney Tray

Claims (20)

A method for producing acetic acid, which comprises a membrane separation step of separating and acquiring an acetaldehyde-rich flow and a methyl iodide-rich flow from a process flow containing acetaldehyde and methyl iodide using a zeolite membrane in the acetic acid production process. The method for producing acetic acid according to claim 1, wherein the zeolite membrane is a BEA type zeolite membrane. The method for producing acetic acid according to claim 1 or 2, wherein the acetaldehyde concentration in the process flow is 0.1 to 99.9% by mass, and the methyl iodide concentration is 0.01 to 99% by mass. The method for producing acetic acid according to any one of claims 1 to 3, wherein the total concentration of acetaldehyde and methyl iodide in the process flow is 1% by mass or more. A catalytic system containing a metal catalyst and methyl iodide, and a carbonylation reaction step of reacting methanol with carbon monoxide in the presence of acetic acid, methyl acetate, and water to produce acetic acid.
The reaction mixture obtained in the carbonylation reaction step is subjected to one or more evaporation treatments and / or distillation treatments, and is subjected to at least a flow containing a metal catalyst, an acetic acid-rich flow, and a lower acetic acid flow. A separation process that separates into a stream rich in boiling components,
It is provided with an acetaldehyde separation / removal system that separates acetaldehyde from at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component by one or more distillation treatments.
The method for producing acetic acid according to any one of claims 1 to 4, wherein the acetaldehyde-rich flow separated in the acetaldehyde separation / removal system is subjected to the membrane separation step as the process flow. The method for producing acetic acid according to claim 5, wherein a part of the flow rich in methyl iodide separated and obtained by the membrane separation step is recycled into a process in the acetaldehyde separation and removal system. The method for producing acetic acid according to claim 5 or 6, wherein the process flow comprises an overhead flow of a distillation column performing a distillation treatment in the acetaldehyde separation and removal system. The method for producing acetic acid according to claim 7, wherein a part of the flow rich in methyl iodide separated and obtained by the membrane separation step is refluxed to the distillation column. The acetaldehyde separation / removal step is
A distillation step (A1) in which at least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation to separate and obtain the first overhead flow rich in acetaldehyde and the residual liquid flow.
An extraction step (B1) in which at least a part of the condensed liquid obtained by condensing the first overhead flow is subjected to extraction and separated into an acetaldehyde-rich aqueous phase and a methyl iodide-rich organic phase.
The acetaldehyde-rich aqueous phase is subjected to distillation, and the distillation step (C1) for separating and acquiring the acetaldehyde-rich second overhead flow and the water-rich residual liquid flow is provided.
The method for producing acetic acid according to claim 5, wherein the second overhead flow and / or the condensed liquid obtained by condensing the second overhead flow is subjected to the membrane separation step as the process flow. The method for producing acetic acid according to claim 9, wherein the process flow includes the second overhead flow. The production of acetic acid according to claim 9 or 10, wherein the methyl iodide-rich flow obtained by separation in the membrane separation step is recycled to the distillation step (A1) and / or the extraction step (B1). Method. The acetaldehyde separation / removal step is
At least a part of the condensed liquid obtained by condensing the flow rich in the low boiling component is subjected to distillation, and the liquid falling from the concentrated region where methyl iodide and acetaldehyde are concentrated in the distillation column is extracted as a side flow. Distillation step (A2) and
A liquid separation step (B2) for separating the side flow into an aqueous phase and an organic phase,
It is provided with a distillation step (C2) in which the aqueous phase is subjected to distillation to separate and obtain a third overhead flow rich in acetaldehyde and a canned out liquid rich in water.
Further, it may be provided with an extraction distillation step (D2) in which the acetaldehyde-rich third overhead flow is subjected to extraction distillation, and the acetaldehyde-rich fourth overhead flow and the water-rich canned liquid are separated and obtained.
One or more selected from the group consisting of the third overhead flow, the condensed liquid obtained by condensing the third overhead flow, the fourth overhead flow, and the condensed liquid obtained by condensing the fourth overhead flow. The method for producing acetic acid according to claim 5, wherein the flow is applied to the film separation step as the process flow. The method for producing acetic acid according to claim 12, wherein the process flow includes the fourth overhead flow. The method for producing acetic acid according to any one of claims 1 to 13, wherein the process flow is a gas. The method for producing acetic acid according to claim 14, wherein the membrane separation step is performed while blowing a sweep gas to the permeation side. The method for producing acetic acid according to any one of claims 1 to 15, wherein the recovery rate of methyl iodide by the membrane separation step is 1% by mass or more. Any of claims 1 to 16, wherein the methyl iodide concentration in the flow rich in methyl iodide separated and obtained by the membrane separation step is higher than the methyl iodide concentration in the process flow and is 1% by mass or more. The method for producing acetic acid according to item 1. According to any one of claims 1 to 17, the acetaldehyde concentration in the acetaldehyde-rich stream separated and obtained by the membrane separation step is higher than the acetaldehyde concentration in the process stream and is 0.1% by mass or more. The method for producing acetic acid according to the above. The method for producing acetic acid according to any one of claims 1 to 18, wherein the zeolite membrane is provided on at least one surface of a porous substrate. A method for producing an acetaldehyde-rich stream and a methyl iodide-rich stream from a mixture containing acetaldehyde and methyl iodide, which separates and obtains an acetaldehyde-rich stream and a methyl iodide-rich stream using a zeolite membrane.

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