Removal of Acetal from Process Streams

Abstract

A process for producing acetic acid is provided, which can reduce the mass composition of acetaldehyde in acetic acid. The process for producing acetic acid in the present invention includes at least one distillation step that satisfies the following operating conditions: (i) the temperature in the lower part of the distillation column is 40°C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture, on a weight percent basis, wherein the mass composition of methanol in the first mixture is 2 wt% or less.

Description

Technical Field

[0001] Priority Claim This application claims priority based on U.S. Provisional Patent Application No. 63 / 034,086, filed on June 3, 2020, which is hereby incorporated by reference in its entirety for all purposes.

[0002] The present disclosure generally relates to an improved process for producing high-quality acetic acid. Specifically, the process involves, at least, distilling a first mixture comprising methanol, water, C 1 ~C 12 alkyl, and at least one permanganate reducing compound (e.g., acetaldehyde) in a distillation column under specific operating conditions for controlling the formation of acetal to reduce acetaldehyde on a mass basis. The operating conditions within the distillation column suppress or reduce acetal in the distillation column for efficiently separating acetaldehyde from the first mixture.

Background Art

[0003] The carbonylation process of methanol is a suitable industrial synthesis process for producing acetic acid. Despite the high yield of acetic acid, the process is known to generate impurities, resulting in acetic acid of low purity. One such impurity that has received significant attention is acetaldehyde, because it is quite difficult to remove, it is a precursor of several other impurities, and it has a strong influence on the purity of acetic acid. For example, acetaldehyde has a boiling point close to that of an effective cocatalyst, so simple distillation is insufficient. For the purpose of overcoming these deficiencies, several proposals have been made to remove acetaldehyde by means of an alkane or water extraction method, or by reaction with an amino compound, an oxygen-containing gas, and a hydroxyl compound. Unfortunately, despite the use of these treatments, acetaldehyde continues to be a challenging issue for obtaining high-purity acetic acid. Furthermore, the generation of impurities derived from acetaldehyde reduces the efficiency of removing acetaldehyde.

[0004] In the acetic acid production process, by-products of acetaldehyde are generated during the acetic acid production process. For example, the reaction mixture contains small amounts of by-products (impurities) such as the following: by-products of acetaldehyde (for example, butyraldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, and their aldol condensation reaction products), organic iodides (for example, C 2~12 alkyl iodides such as ethyl iodide, butyl iodide, or hexyl iodide), and others. These impurities result in low-quality acetic acid. In conventional processes, distillation columns and treatment units are used to further improve the production of high-quality acetic acid. Such treatments are beneficial for removing certain types of impurities, but there are limits with respect to some impurities in these columns and units.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, in the conventional process, the efficiency of acetaldehyde removal in the distillation column cannot be increased because acetaldehyde is not efficiently separated into the overhead distillate. Although the existing carbonylation process has a high yield, an improvement for recovering high-purity acetic acid in a safe and efficient manner is still desired.

Means for Solving the Problems

[0006] In some embodiments, the present invention provides a process for producing acetic acid by reducing impurities (including 1,1-dimethoxyethane) derived from acetaldehyde.

[0007] In some embodiments, the present invention provides a process for purifying acetic acid by using overhead extraction of a permanganate reducing compound (PRC), such as acetaldehyde (but not limited thereto), from a stream containing methanol, acetaldehyde, water, and one or more C 1 ~C 12 alkyl iodides.

[0008] In some embodiments, the present invention provides a process for producing acetic acid by efficiently separating acetaldehyde while controlling and / or adjusting the mass composition of methanol in a distillation column.

[0009] As used herein, the terms "mass composition" or "concentration" refer to the mass fraction of the substance relative to the total mass, unless otherwise specified, and are generally expressed in weight% ("wt%", or "% by weight").

[0010] In some embodiments, the present invention provides a process for purifying acetic acid by using overhead extraction of a permanganate reducing compound (PRC), such as acetaldehyde (but not limited thereto), from a stream containing methanol, acetaldehyde, water, and one or more C 1 ~C 12A process for efficiently separating PRC and methyl iodide from each other by extractive distillation of PRC in the presence of an alkyl, and a process for producing acetic acid are provided.

[0011] In some embodiments, the present invention relates to methanol, acetaldehyde, water, and one or more C-iodides 1 ~C 12 A process for efficiently separating PRC and methyl iodide from each other by distilling PRC in the presence of an alkyl without supplying additional water to the distillation column, and a process for producing acetic acid are provided.

[0012] In some embodiments, the present invention provides a process for efficiently separating PRC and methyl iodide from each other by extractive distillation of PRC, where the distillation column is operated under conditions to prevent the formation of 1,1-dimethoxyethane.

[0013] In one embodiment, acetaldehyde, one or more C-iodides 1 ~C 12A process for separating acetaldehyde from a first mixture comprising alkyl (methyl iodide), water, and methanol is disclosed, and the process includes the following steps: In a distillation column, distilling the first mixture to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottoms stream, wherein either the overhead stream or the side cut stream is withdrawn as a second mixture; separating acetaldehyde from the second mixture; and controlling the mass composition of 1,1-dimethoxyethane in the bottoms stream to 0.03 wt% or less by operating the distillation column under at least one of the following conditions (i)-(iii): (i) the temperature in the lower portion of the distillation column is 40 °C or higher; (ii) the mass composition of water in the bottoms stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the bottoms stream is greater on a weight percent basis than the mass composition of acetic acid in the first mixture; and the mass composition of methanol in the first mixture is 2 wt% or less.

[0014] In one embodiment, acetaldehyde, one or more C-iodides 1 ~C 12 A process for separating acetaldehyde from a first mixture comprising acetaldehyde, one or more C-iodides 1 ~C 12In an organic stream containing alkyl, a step of separation, and operating the distillation column under at least one of the following conditions (i) to (iii) to control the mass composition of 1,1 - dimethoxyethane in the bottom stream to 0.03 wt% or less: (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the bottom stream is 0.3 wt% or more; or (iii) the mass composition of acetic acid in the bottom stream is greater on a weight percent basis than the mass composition of acetic acid in the first mixture; and the mass composition of methanol in the first mixture is 2 wt% or less.

[0015] The present invention will be better understood with reference to the accompanying non - limiting drawings.

Brief Description of the Drawings

[0016]

Figure 1

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Modes for Carrying Out the Invention

[0017] First, in the development of such various practical embodiments, it should be noted that in order to achieve the specific purposes of the developers, numerous embodiment-specific decisions have to be made, such as achieving compliance with system-related and business-related constraints (which will vary from embodiment to embodiment). In addition, although it will be apparent to an average or reasonable person skilled in the art, the processes disclosed herein may include elements different from those cited or specifically referenced.

[0018] As is apparent from the drawings and text presented herein, various embodiments are contemplated.

[0019] The process for producing acetic acid in the present invention includes at least one distillation step that satisfies at least one of the following operating conditions: (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; and / or (iii) the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture based on the total weight. In the distillation step that satisfies such operating conditions, the formation of acetal and / or hemiacetal in the lower part of the distillation column is efficiently suppressed and / or reduced. Without being bound by theory, it is considered that under the above operating conditions, the equilibrium (reversible) reaction shifts in the direction of reducing the acetalization of acetaldehyde to acetal and / or hemiacetal. The distillation step that satisfies the above operating conditions can suppress or reduce the formation of acetal and / or hemiacetal, efficiently separate acetaldehyde, and prevent the formation of methanol, so that the mass composition of methanol in the lower part of the distillation column is 2 wt% or less.

[0020] In the present invention, a process for producing acetic acid including a distillation step that satisfies specific operating conditions can suppress or reduce the formation of acetals and / or hemiacetals in the lower portion of the distillation column. Therefore, it is possible to efficiently separate acetaldehyde distributed with acetals in the lower portion of the distillation column in the distillation step to reduce the mass composition of acetals in the product acetic acid (and thus reduce the mass composition of acetaldehyde), or a bottoms fraction having a lower mass composition of acetaldehyde can be recycled to the reactor.

[0021] Surprisingly, it has been found that under specific operating conditions in the distillation column, the formation of 1,1-dimethoxyethane in the lower stream of the distillation column can be suppressed or reduced. As found by the inventors of the present application, by operating a distillation column that satisfies at least one of the following conditions, the formation of acetals in the lower portion of the distillation column can be suppressed: (i) the temperature in the lower portion of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis. Under these operating conditions, the mass composition of methanol in the lower portion of the distillation column is suppressed to 2 wt% or less.

[0022] By conducting intensive studies, the inventors of the present invention have achieved the above-described improved process for producing high-purity acetic acid and have discovered that, in the distillation step, under specific operating conditions and when a large amount of methanol coexists with acetaldehyde, acetal is formed. It has been found that in the lower part of the distillation column, the greater the amount of methanol, the more acetal is formed. As a result, due to the reversible reaction, acetaldehyde is transferred or converted into acetal and escapes into the liquid stream at the bottom of the column. Due to its reversible nature, acetal can be reconverted into acetaldehyde by recycling. This limits the performance of removing acetaldehyde in the presence of methanol because of the trapping in the form of acetal. As a result, acetaldehyde in the mixture fed to the distillation column is distributed in the lower part of the distillation column in the form of acetal to form a second mixture, which easily undergoes back-conversion by the reversible reaction, thereby preventing the efficient separation of acetaldehyde in the distillation column.

[0023] Specifically, as found by the inventors of the present application, under certain operating conditions in the distillation column, 1,1-dimethoxyethane, which is a higher-boiling component (e.g., 64°C), is formed in the lower part of the distillation column, and as the mass composition of 1,1-dimethoxyethane increases, the removal of acetaldehyde is limited, resulting in a low-quality acetic acid product.

[0024] Therefore, the inventors of the present application conducted further studies and found the following: By maintaining high temperature, minimum water content and / or high acetic acid amount in the lower part of the distillation column, the distillation column can be operated so as to suppress or reduce the formation of acetal. Among the distillation columns satisfying these conditions, only a small amount of 1,1-dimethoxyethane is formed in the lower part of the distillation column. The small amount of 1,1-dimethoxyethane improves the removal of acetaldehyde. By reducing the amount of 1,1-dimethoxyethane in the lower stream, the abundance of acetaldehyde that can migrate through the reversible reaction decreases. Therefore, acetaldehyde can be efficiently separated, for example, by aqueous extractive distillation.

[0025] During the carbonylation of methanol, acetaldehyde or by-products of acetaldehyde present in the mixture fed to the distillation column may undergo acetalization to form acetal and / or hemiacetal. The acetalization of acetaldehyde (AcH) to an acetal (for example, 1,1-dimethoxyethane) is a two-step acid-catalyzed reaction in the methanol carbonylation system. In the first step, acetaldehyde reacts with methanol to form hemiacetal. In the second step, the hemiacetal reacts with methanol to form acetal, 1,1-dimethoxyethane, and water. The overall reaction is shown in Formula I: CH 3 CHO + 2CH 3 OH ⇔ (CH 3 O) 2 CHCH 3 + H 2 O Formula 1 The acetalization of acetaldehyde (AcH) to an acetal (for example, 1,1-dimethoxyethane) is an equilibrium (reversible) reaction as seen in the following formula:

Number

[0026] Under certain operating conditions in the distillation column (e.g., low temperature, low water conditions in the lower part of the distillation column, and / or low acetic acid mass composition), the equilibrium reaction is favorable for the acetalization of acetaldehyde. Further, the acetalization reaction may be further catalyzed in the presence of a mineral acid or a carboxylic acid, such as acetic acid. Thus, the mass composition of the acetal increases in the distillation column while recovering acetic acid from the mixture, which can cause more acetaldehyde to be distributed in the lower part of the distillation column in the form of 1,1-dimethoxyethane. To produce higher purity acetic acid, the distillation process is required to have a reduced mass composition of acetal, such as acetal (1,1-dimethoxyethane) of 0.03 wt% or less, acetal of 0.025 wt% or less, acetal of 0.02 wt% or less, or acetal of 0.01 wt% or less, in the lower stream withdrawn from the distillation column. In a range, the mass composition of acetal (1,1-dimethoxyethane) in the lower stream is preferably 0.0001 - 0.03 wt%, such as 0.0001 - 0.025 wt%, or 0.0001 - 0.02 wt%.

[0027] The present invention provides a process for reducing the mass composition of acetal (1,1-dimethoxyethane) during acetic acid purification. Without being bound by theory, the present invention can direct an equilibrium reaction in a direction that reduces the acetalization reaction towards the formation of acetal, and can reduce the amount of acetaldehyde concentrated in the lower part of the distillation column. In one embodiment, the process described herein can suppress or reduce the mass composition of acetal in a distillation step that satisfies at least one of the following operating conditions: (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the lower stream is greater, on a weight percent basis, than the mass composition of acetic acid in the first mixture. In some embodiments, a distillation step that satisfies at least one of the above operating conditions reduces the mass composition of acetal by at least 10%, for example, at least 15%, at least 20%, at least 25%, at least 30%, or at least 35%, compared to a distillation step operated without the above conditions.

[0028] By operating a distillation column that satisfies at least one of the operating conditions (i) to (iii), acetaldehyde can be efficiently separated into the overhead fraction of the distillation column, and the amount of 1,1-dimethoxyethane concentrated in the bottom stream of the distillation column is reduced. Based on these findings, the inventors of the present application have found that by controlling the operating conditions in the distillation column, it is possible to reduce or suppress the production of 1,1-dimethoxyethane, thereby enabling more acetaldehyde to be distributed to the overhead fraction of the distillation column. In addition, the operating conditions in the distillation column suppress or reduce the production of 1,1-dimethoxyethane in the bottom stream of the distillation column, and the amount of acetaldehyde recycled to the carbonylation reactor is reduced. As a result, the impurities in the product stream are reduced, and a high-quality acetic acid product can be obtained. Since the amount of 1,1-dimethoxyethane is small, acetaldehyde can be efficiently separated in the overhead fraction of the distillation column.

[0029] In addition, it has also been found that the pressure in the distillation column can affect the distillation of acetaldehyde in the mixture into the column. Using a single high-pressure distillation column operated at a distillation temperature higher than that of an atmospheric distillation column enables efficient separation of acetaldehyde in combination with the above-described operating conditions.

[0030] For operating condition (i), the temperature in the lower part of the distillation column is 40°C or higher, for example, 42°C or higher, 44°C or higher, 46°C or higher, 48°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, 100°C or higher, 110°C, or 115°C or higher. In terms of a range, the temperature in the lower part of the distillation column is in the range of 40°C to 165°C, for example, 50°C to 160°C, 60°C to 155°C, 70°C to 150°C, 80°C to 140°C, 90°C to 135°C, 100°C to 140°C, 110°C to 135°C, or 115°C to 130°C. In terms of the upper limit, the temperature in the lower part of the distillation column is less than 165°C, for example, less than 160°C, less than 155°C, less than 150°C, less than 145°C, less than 140°C, 130°C, less than 125°C, or less than 120°C. The ranges disclosed in this specification include both ends, sub-ranges, and individual numerical values.

[0031] For operating condition (ii), the mass composition of water in the lower part of the distillation column is 0.3 wt% or higher, for example, 0.4 wt% or higher, 0.5 wt% or higher, 0.6 wt% or higher, 0.8 wt% or higher, 1 wt% or higher, 1.5 wt% or higher, or 2 wt% or higher. In terms of a range, the mass composition of water in the lower part of the distillation column is in the range of 0.3 wt% to 20 wt%, for example, 0.5 wt% to 18 wt%, 0.8 wt% to 16 wt%, 1 wt% to 15 wt%, 1.5 wt% to 14 wt%, 2 wt% to 12 wt%, 3 wt% to 10 wt%, 4 wt% to 9 wt%, or 5 wt% to 9 wt%. The mass composition of water in the lower part of the distillation column is less than 20 wt%, for example, less than 18 wt%, less than 15 wt%, less than 10 wt%, or less than 5 wt%.

[0032] For operating condition (iii), the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis. The acetic acid in the first mixture mainly migrates from the upper stream to the lower stream. In some embodiments, the acetic acid in the lower stream is 3 wt% or less, for example, 2.8 wt% or less, 2.5 wt% or less, 2.2 wt% or less, 2 wt%, or 1.8 wt% or less. To achieve these mass compositions of acetic acid, more than 50%, for example, more than 60%, more than 70%, more than 80%, or more than 90% of the acetic acid in the first mixture migrates to the lower stream. The lower stream preferably has a lower water-to-acetic acid ratio (H 2 O / HOAc) than the first mixture. In one embodiment, the ratio of H 2 O / HOAc in the lower stream is from 1:10 to 1:100, for example, from 1:15 to 1:90, or from 1:20 to 1:75. The upper stream preferably has a higher water-to-acetic acid ratio (H 2 O / HOAc) than the first mixture.

[0033] Examples of distillation processes that satisfy operating conditions (i) to (iii) include various distillation columns (for example, an acetaldehyde removal column) in an acetaldehyde separation and removal system. The present invention is not limited to the above, and also includes, for example, a low-boiling component removal column, a dehydration column, or a high-boiling component removal column. In this case, the first mixture (for example, a homogeneous liquid, an aqueous phase, an organic phase, etc.) fed to the distillation column contains at least methanol, water, C 1 -C 12It contains alkyl and PRC (for example, acetaldehyde). In some embodiments, the first mixture contains about 0.001 wt% to 10 wt% of PRC (for example, acetaldehyde), 10 wt% to 85 wt% of methyl iodide in terms of mass composition, 0 wt% to 30 wt% of methyl acetate in terms of mass composition, 0 wt% to 12 wt% of acetic acid in terms of mass composition, 1 wt% to 95 wt% of water in terms of mass composition, 0 wt% to 1 wt% of dimethyl ether in terms of mass composition, and 0.0001 wt% to 2 wt% of methanol in terms of mass composition. In some embodiments, the first mixture (for example, the feed) to the distillation column has a higher mass composition of methanol than that of dimethyl ether.

[0034] In some embodiments, the pressure in the distillation column may affect the equilibrium reaction of acetal. For example, for the purpose of controlling the partial pressure of a specific component in the distillation column, purging a gas such as carbon dioxide to perform pressure control on the distillation column may affect the formation of acetal. In some embodiments, in the distillation column, the top pressure is set to, for example, 80 to 160 kPa (gauge pressure), and the bottom pressure is higher than the top pressure, so it is set to, for example, 85 to 180 kPa (gauge pressure). In some embodiments, the top temperature is set to a temperature lower than the boiling point of acetic acid at the set top pressure, for example, 90 to 130 °C, and the bottom temperature is set to a temperature higher than the boiling point of acetic acid at the set bottom pressure, for example, 120 to 165 °C (for example, 125 to 160 °C).

[0035] In one embodiment, the acetal formed in the carbonylation process can be reduced by separating the first mixture, or its derivative stream, in a distillation column operating at high pressure. In the separation of acetic acid from the crude mixture, several distillation columns are required, and by operating at least one of the several distillation columns at high pressure, the mass composition of the acetal can be reduced. In some embodiments, one of the several columns in the separation can be operated at a higher pressure than the other columns to further enhance the hydrolysis of the acetal inside that column. Embodiment

[0036] In some embodiments, the present invention provides a process for separating or removing a permanganate reducing compound (e.g., acetaldehyde) from a first mixture comprising at least methanol, water, C 1 ~C 12 alkyl (methyl iodide, and further other alkyl iodides), and a permanganate reducing compound (PRC, or PRC including acetaldehyde). The process for producing acetic acid can reduce the amount of acetaldehyde in the process stream. The process for producing acetic acid in the present invention includes at least one distillation step that satisfies at least one of the following operating conditions: (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the lower stream is greater, on a weight percent basis, than the mass composition of acetic acid in the first mixture. Here, the mass composition of methanol in the first mixture is 2 wt% or less.

[0037] In some embodiments, the process includes distilling a first mixture in a distillation step to form at least two streams selected from a top stream, a side cut stream, and a bottom stream. A distillation column that satisfies at least one of operating conditions (i) to (iii) forms a mass composition zone of PRC and at least methyl iodide and water in the top portion of the distillation column (e.g., between the top stream and the feed stream) to efficiently separate the PRC. Under the above-described operating conditions, there is little acetaldehyde distributed in the lower portion of the distillation column because the amount of acetal is small, whereby a concentration zone of PRC is formed above the lower portion of the distillation column. In the distillation column, an extractant (i.e., extraction solvent) capable of extracting PRC preferentially over methyl iodide is added to the concentration zone of PRC (e.g., high concentration zone). In some embodiments, an extraction mixture (e.g., liquefied fraction) descending from the concentration zone is withdrawn as a side cut stream.

[0038] In some embodiments, no extractant is added to the distillation column. For example, no additional water is fed to the distillation column (if reflux is used, the reflux to the distillation column is other than water). By distilling the first mixture under at least one of operating conditions (i)-(iii), at least a portion of the water in the first mixture can rise to a position above the feed port to form a second mixture containing a portion of the water, and the second mixture can be withdrawn as an upper stream. The lower stream can have a lower water content than the first mixture and can be withdrawn from a position below the feed port. The lower stream can have an acetal-to-PRC ratio lower than that of the second mixture. In this way, by distilling the first mixture, a PRC enrichment zone can be formed at a position above the feed port of the distillation column, and at least a portion of the water in the first mixture can be caused to rise (i.e., move upward) to the enrichment zone; and the stream or fluid in the enrichment zone can be withdrawn as an upper stream. In this process, the mixture descending from the enrichment zone can be withdrawn as a side cut stream.

[0039] FIG. 1 shows a continuous process 10 for producing acetic acid according to some embodiments of the present invention. In this process 10, acetic acid is produced from a reaction mixture produced by a carbonylation reaction of methanol with carbon monoxide in the presence of a catalyst system comprising a rhodium catalyst as a metal catalyst and a promoter, and further in the presence of acetic acid, methyl acetate, and a limited (i.e., restricted) amount of water. Process 10 may include at least a reactor 100, a flash vessel 200, a first distillation column 300, a first liquid-liquid separation unit 400, and a second distillation column 500. Among these steps, the present invention includes at least a reactor 100, a flash vessel 200, a first distillation column 300, and a second distillation column 500.

[0040] Those skilled in the art should understand that various process equipment, such as heat exchangers, receivers, pumps, control devices, valves, etc., are not shown in detail in FIG. 1. Unless otherwise specified, the fact that such process equipment is not shown should be understood by those skilled in the art as meaning that such process equipment would be used as optional elements.

[0041] In a reactor 100 (for example, a reaction system or reactor), a carbonylation reaction of methanol can be carried out. A flasher 200 can separate a reaction mixture containing acetic acid into a vapor phase 202 (for example, a low-boiling fraction) and a low-vapor phase 204 (for example, a high-boiling fraction). A first distillation column 300 (for example, a splitter column) can separate the vapor phase 202 into a first overhead stream 302, an acetic acid stream 304 as a side cut stream, and a bottom stream 306 (for example, a high-boiling fraction). A first liquid-liquid separation unit 400 can condense the first overhead stream 302 to form two phases. A second distillation column 500 (for example, a second distillation column) can separate a first (feed) mixture containing any one of the first overhead stream 302 (directly from the first distillation column), the aqueous phase 402 or the organic phase 404 formed in the first liquid-liquid separation unit 400 (for example, a decanter), or a combination thereof, into a second overhead stream 502, a side cut stream 504, and a bottom stream 506.

[0042] Reaction step (reactor) FIG. 1 shows a continuous process 10 for producing acetic acid. As shown, a methanol-containing feed stream 102 and a carbon monoxide-containing feed stream 104 are directed to a carbonylation reactor 100, in which a carbonylation reaction for producing acetic acid takes place. In that carbonylation reaction, a homogeneous catalyst is preferably used and it is operated on a continuous basis (for example, a continuous process).

[0043] The methanol-containing feed stream 102 may contain at least one member selected from the group consisting of methanol, dimethyl ether, and methyl acetate. The methanol-containing feed stream 102 may be partly provided from a fresh feed or may be recycled from the process 10. At least some of the methanol and / or its reactive derivatives will be converted to methyl acetate by esterification with acetic acid in a liquid medium. The amount of unreacted methanol in the reactor 100 can be low, for example, 1 wt% or less, such as 0.8 wt% or less, less than 0.5 wt%, or less than 0.3 wt%, based on the total liquid phase in the reactor 100, in order to achieve a high conversion rate.

[0044] The carbon monoxide-containing feed stream 104 may mainly contain 95 wt% or more, for example, 97 wt% or more, or 99 vol% or more of carbon monoxide. In some embodiments, trace impurities such as hydrogen, carbon dioxide, oxygen, and / or nitrogen may be present in an amount of less than 5 wt%, for example, less than 3 wt%, or less than 1 wt%. These trace impurities may also be generated by various side reactions under the operating conditions.

[0045] In some embodiments, the methanol-containing feed stream 102 and / or the carbon monoxide-containing stream 104 may contain impurities. For example, the methanol-containing feed stream 102 may contain metal ions, which can affect the purity of the methanol-containing feed stream 102. In certain embodiments, the methanol-containing feed stream 102 may have a very low metal ion content, specifically, the methanol-containing feed stream 102 may have a very low zinc ion content. The amount of metal ions in the methanol-containing feed stream 102 or the carbon monoxide-containing feed stream 104 may be less than 10 weight ppm. For example, the mass composition of the metal ions may be less than 1 ppm, less than 0.5 ppm, or less than 0.1 ppm by weight. To reduce impurities, a pretreatment step using a cation exchange resin column may be present prior to introduction into the reactor 100.

[0046] In some embodiments, a feed stream or process stream heading to the reactor 100 may be subjected to pretreatment prior to introduction into the reactor. For example, in the pretreatment step, impurities (e.g., amine-based and / or metal-based) can be removed from the feed stream or process stream heading to the reaction step. For the purposes of the processes described herein, commercially available methanol can be used. The methanol-containing feed stream can be introduced, in part, from a fresh feed from a reservoir tank (not shown), a recycled feed from the system, or a combination of the fresh feed and the recycled feed. At least some of the methanol and / or its reactive derivatives will be converted to methyl acetate by an esterification reaction with acetic acid in a liquid medium and thus will be present as methyl acetate.

[0047] The carbonylation catalyst system usually includes a metal catalyst (e.g., a cobalt catalyst, a rhodium catalyst, or an iridium catalyst), a catalyst stabilizer or reaction promoter, and a cocatalyst. These metal catalysts may be used alone or in combination. It is preferred that the metal catalyst includes a rhodium catalyst and an iridium catalyst (especially a rhodium catalyst).

[0048] The metal catalyst can be used in the form of a single metal, a metal oxide (including the metal oxide of the complex), a metal hydroxide, a metal iodide, a metal carboxylate (e.g., acetate), a metal salt of an inorganic acid (e.g., sulfate, nitrate, and phosphate), or a metal complex. In some embodiments, the metal catalyst is in a form dissolved in the liquid phase (e.g., in the form of a complex). Examples of rhodium catalysts include, for example, rhodium iodide complexes, such as {RhI 3 、[RhI 2 (CO) 4 - 、and [Rh(CO) 2 I 2 -}, and rhodium carbonyl complexes.

[0049] In some embodiments, the reaction mixture may include a catalyst stabilizer or reaction promoter. Examples of catalyst stabilizers or reaction promoters include metal iodides capable of generating iodide ions in the reaction mixture, such as alkali metal iodides (e.g., lithium iodide, sodium iodide, and potassium iodide). In some embodiments, the stabilizer may include lithium iodide. These cocatalysts or promoters may be used alone or in combination. In some embodiments, the catalyst stabilizer or reaction promoter has a mass composition of about 1 to 25 wt%, such as about 2 to 22 wt%, about 3 to 20 wt%, about 4 to 18 wt%, about 5 to 16 wt%, or about 8 to 15 wt% throughout the liquid phase in the reactor.

[0050] ​The reaction mixture contains acetic acid, methyl acetate produced by the reaction of acetic acid with the raw material methanol, and water. In addition, the reaction mixture usually contains unreacted raw material methanol. In some embodiments, the mass composition of methyl acetate in the reaction mixture is maintained at 0.5 to 30 wt%, for example, 0.3 to 20 wt%, 0.6 to 9 wt%, or 0.6 to 4.1 wt%. The mass composition of methyl acetate in the reaction mixture may be about 0.1 to 30 wt%, for example, about 0.3 to 20 wt%, about 0.5 to 10 wt%, or about 0.5 to 6 wt%.

[0051] In some embodiments, the reaction mixture contains a metal catalyst, such as cobalt, rhodium, iridium, or a combination thereof, in an amount of 200 to 3000 ppm (weight ppm), for example, 800 to 3000 wppm, 850 to 200 wppm, or 900 to 1500 wppm. In some embodiments, the mass composition of methyl iodide in the reaction mixture is maintained at 1 to 25 wt%, for example, 2 to 22 wt%, 4 to 20 wt%, 5 to 15 wt%, or 4 to 13.9 wt%. In some embodiments, the mass composition of an iodide salt, such as lithium iodide, in the reaction mixture is maintained at 1 to 25 wt%, for example, 2 to 20 wt%, 3 to 18 wt%, 4 to 15 wt%, 5 to 14 wt%. The iodide salt can be formed in situ by adding, for example, lithium acetate, lithium carbonate, lithium hydroxide, or other lithium salts of anions compatible with the reaction mixture. In some embodiments, in the process, the mass composition of lithium acetate in the reaction mixture is preferably maintained at 0.3 to 0.7 wt%, for example, 0.3 to 0.6 wt%.

[0052] There is a low amount of water in the reaction mixture. In some embodiments, the mass composition of water in the reaction mixture may be about 0.1 to 15 wt%, for example, about 0.5 to 10 wt%, about 0.8 to 5 wt%, about 1 to 3 wt%, about 1 to 10 wt%, or about 2 to 5 wt%. In some embodiments, the reaction is carried out under water-deficient conditions, and the reaction mixture contains water in an amount of 0.1 to 4.1 wt%, for example, 0.1 to 3.1 wt%, or 0.5 to 2.8 wt%. In some embodiments, the mass composition of acetic acid in the reaction mixture is generally greater than 30 wt%, for example, greater than 40 wt%, or greater than 50 wt%. The acetic acid in the reaction mixture functions as a solvent and the reactor is pre-charged with acetic acid at startup.

[0053] In the acetic acid production process, formic acid is an undesirable impurity that is produced as a by-product in the carbonylation reactor and degrades the quality of the acetic acid product. To reduce or limit the formation of formic acid, it is advisable to control the mass composition of water and further the temperature of the reactor. All of the formic acid produced by the reactor is preferably decomposed throughout the process rather than separated by distillation. In one embodiment, the formic acid can be controlled by the moisture in the reactor and / or the temperature of the reactor, such that the formic acid content in the acetic acid product is less than 200 wppm, for example, less than 180 wppm, less than 160 wppm, less than 140 wppm, less than 120 wppm, or less than 100 wppm.

[0054] The plurality of components of the reaction mixture are maintained within a predetermined limit that can sufficiently ensure the production of acetic acid and the utilization of reactants while suppressing the formation of by-products. In a continuous process, the amounts of the components are maintained within a predetermined range, and fluctuations within those ranges are expected. A person of ordinary skill in the art would readily understand the process control methods for maintaining the amounts of the components in the reaction mixture.

[0055] In some embodiments, the temperature of the carbonylation reaction may be, for example, 150°C to 250°C, for example, 175°C to 230°C, or 185°C to 205°C.

[0056] The reaction pressure (total pressure of the reactor), including the partial pressure of by-products, may be, for example, about 1.5 to 4 MPa (absolute pressure) or about 2 to 3.5 MPa (absolute pressure). In some embodiments, the partial pressure (absolute pressure) of carbon monoxide in the reactor may be 0.2 MPa to 3 MPa, for example, 0.3 MPa to 1.8 MPa, 0.4 MPa to 1.5 MPa, or 0.6 MPa to 1.2 MPa. The lower limit of the partial pressure (absolute pressure) of carbon monoxide is 0.2 MPa or more, for example, 0.3 MPa or more, 0.4 MPa or more, or 0.6 MPa or more.

[0057] In some embodiments, the partial pressure (absolute pressure) of carbon dioxide in the reactor may be 110 kPa or less, for example, 105 kPa or less, or 70 kPa or less. In some embodiments, the partial pressure (absolute pressure) of carbon dioxide in the reactor may range from 0 kPa to 110 kPa, for example, 0 kPa to 105 kPa, 0 kPa to 100 kPa, 0 kPa to 90 kPa, 0 kPa to 80 kPa, or 0 kPa to 70 kPa. The lower limit of the partial pressure (absolute pressure) of carbon dioxide can be 0 kPa, but the partial pressure (absolute pressure) of carbon dioxide may be greater than 0.1 kPa, for example, greater than 0.5 kPa, greater than 1 kPa, greater than 2 kPa, greater than 4 kPa, or greater than 5 kPa.

[0058] Carbon dioxide does not participate in the carbonylation reaction, but may be present in small amounts in the carbon monoxide-containing feed stream 104, or may be generated by the gas shift reaction. Similar to other gases, carbon dioxide can be removed by passing it through the vent stream, but as a result, there will also be a corresponding loss of useful carbon monoxide. In the implementation of acetic acid production, the mass composition of carbon monoxide in the reaction mixture in the vent stream may be at a level of 5 kmol / hr or less, for example, 4.5 kmol / hr or less or 4.1 kmol / hr or less.

[0059] Although hydrogen can increase catalytic activity, the presence of hydrogen may also generate by-products. To carry out the production of acetic acid, hydrogen may be fed into the reactor. Hydrogen may recycle the gaseous components (including hydrogen, carbon monoxide, or other gases) discharged in the process to the reactor after purifying and / or separating the gaseous components in subsequent steps if necessary. In some embodiments, the partial pressure (absolute pressure) of hydrogen in the reactor can be less than 500 kPa, for example, less than 180 kPa, less than 150 kPa, less than 135 kPa, less than 125 kPa, less than 120 kPa, or less than 105 kPa. In some embodiments, the partial pressure (absolute pressure) of hydrogen in the reactor can be in the range of 0 kPa to 500 kPa, for example, 5 kPa to 180 kPa, 5 kPa to 150 kPa, 5 kPa to 135 kPa, 5 kPa to 120 kPa, or 5 kPa to 105 kPa. Although the lower limit of the partial pressure (absolute pressure) of hydrogen can be 0 kPa, the partial pressure (absolute pressure) of hydrogen can be greater than 1 kPa, for example, greater than 2 kPa, greater than 4 kPa, or greater than 5 kPa.

[0060] In the reactor, the carbonylation reaction of methanol proceeds while maintaining the equilibrium between the liquid reaction system and the gas phase system. The liquid reaction system contains reactants and metal catalyst components, and the gas phase contains carbon monoxide, reaction products (hydrogen, methane, and carbon dioxide), and evaporated low-boiling components (for example, methyl iodide, acetic acid, and methyl acetate). The vapor component (vent gas) can be withdrawn from the top (i.e., the head) of the reactor or subjected to absorption treatment to recover condensable liquid, carbon monoxide, and / or hydrogen, which may then be recycled to the reactor.

[0061] In some embodiments, the internal pressure of the reactor 100 may be controlled by withdrawing or venting the gaseous stream 112. The gaseous stream 112 may further be processed in an absorption system 110, such as a scrubber system or a pressure swing absorption column. In some embodiments, the gaseous stream 12 may be condensed and the gaseous portion (non-condensable fraction) thereof may be fed to the absorption system 110. In some embodiments, the gaseous portion is useful for stabilizing the catalyst against settling due to its relatively high carbon monoxide content. The absorption system 110 can collect and / or recover useful components, particularly organic components, and further methyl iodide. A cooled solvent may be fed via line 116 to the top of the absorption unit 100 to recover such components in the residue 118 and return it to the reactor 100. The cooled solvent may contain acetic acid, methanol, methyl acetate, water, or a mixture thereof, and is cooled to a temperature of 20 °C or less, for example, 18 °C or less, or 10 °C or less. Any gaseous substances remaining uncollected in the residue 118 are discharged from the absorption system 110 near the top via line 114. Although only one absorber is shown for the absorption system 110, the absorption system may include multiple absorption columns and further a solvent stripping column. Furthermore, other vent streams obtained throughout the process may be collected and flowed through the absorption system 110.

[0062] One absorption system includes multiple absorption steps using, for example, different absorption solvents and / or different pressures. Such a system is described in U.S. Patent No. 8,318,977 (the entire content of which is incorporated herein by reference).

[0063] The reaction mixture (reaction liquid) may contain acetic acid, methyl iodide as a cocatalyst, methyl acetate as a reaction product of acetic acid and methanol, water, and acetaldehyde as a by-product. The reaction mixture may contain, for example, a metal catalyst component (for example, a rhodium catalyst), lithium iodide as a catalyst stabilizer, and / or methyl iodide.

[0064] In addition to the acetic acid reaction product, various by-products and / or impurities may also be formed in the reaction mixture. Furthermore, by-products derived from acetaldehyde (acetaldehyde derivatives) are also formed. Examples of acetaldehyde derivatives include, for example, the following: other aldehydes, such as butyraldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, and 2-ethylbutyraldehyde; ketones, such as acetone or methyl ethyl ketone; their aldol condensation reaction products; and C 2~12 alkyl iodides, such as ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, or hexyl iodide. Examples of by-products include the following: 3-hydroxyalkanals (for example, 3-hydroxybutanal); formic acid or C 3~12 alkanecarboxylic acids (for example, propionic acid, butanoic acid, hexanoic acid, heptanoic acid, or octanoic acid); C 3~12 alkyl alcohols, such as butyl alcohol or 2-ethylbutyl alcohol; methanol or esters of the above alkyl alcohols with acetic acid or the above carboxylic acids; ethers of methanol and / or the above alkyl alcohols (dialkyl ethers, such as dimethyl ether); and methane, and hydrocarbons having two or more carbon atoms (for example, C 2~12 alkanes). Acetaldehyde and by-products derived from acetaldehyde (for example, other aldehydes, ketones, and aldol condensation reaction products) belong to permanganate reducing compounds (PRCs). Therefore, it is preferable to separate and remove acetaldehyde, which is the main by-product from the reaction mixture, and to recover useful components (for example, methyl iodide) from the process stream.

[0065] In the present disclosure, even in a continuous reaction, acetaldehyde can be efficiently separated and removed to reduce the amount of acetaldehyde in the reactor. By reducing the amount of acetaldehyde or eliminating acetaldehyde, the generation of by-products derived from acetaldehyde is significantly prevented. Specifically, since the content of acetaldehyde separated in the overhead fraction is higher (because the amount trapped in the acetal is small), the amount of acetaldehyde in the lower stream recycled to the reactor is less. For example, the reactor may have a mass composition of PRC (typically acetaldehyde) of less than, for example, 1800 wppm, less than, for example, 1600 wppm, less than 1000 wppm, or less than 800 ppm. In some embodiments, the reactor may have a mass composition of PRC (typically acetaldehyde) of 0 to 1800 wppm, for example, 100 to 1600 wppm, 150 to 1000 wppm, or 200 to 800 wppm.

[0066] The space-time yield of acetic acid in this reaction system can be, for example, about 5 mol / L·h to 50 mol / L·h, preferably about 8 mol / L·h to 40 mol / L·h, more preferably about 10 mol / L·h to 30 mol / L·h.

[0067] This reaction system is an exothermic reaction system accompanied by heat generation, and its reaction temperature can be controlled (i.e., regulated) by installing a heat removal-capable (i.e., heat-removable) unit or a cooling unit (such as a jacket) to cool or recycle the condensate from which heat has been removed. For the purpose of removing a part of the reaction heat, it is advisable to cool the vapor (vent gas) from the reactor in a condenser, a heat exchanger, or other means for separating the vapor into a liquid component and a gaseous component, and the liquid component and / or the gaseous component can be recycled to the reactor.

[0068] In some embodiments, in the carbonylation reaction step, a pump-around reactor or an extended reactor can be used for the purpose of recovering the reaction heat. For example, a pump around reactor around the reactor can be installed at the position of the side stream from the carbonylation reactor, and a part of the reaction solution from the carbonylation reactor is fed to the pump around the reactor. Reactants selected from the group consisting of carbon monoxide and methanol, methyl acetate, methyl formate, dimethyl ether and / or mixtures can be fed to the pump around the reactor. In one embodiment, the pump around the reactor contains only the catalyst in the reaction solution, that is, no additional catalyst is introduced into the pump around the reactor. The pump around the reactor extends the carbonylation reaction to generate additional reaction heat, which can be recovered.

[0069] The carbonylation reaction is exothermic, and the temperature of the reactor should be controlled in various ways. For the purposes of the present disclosure, various suitable cooling can be used to control the temperature of the reactor. U.S. Patent No. 5,374,774 describes a cooling unit in the recycle line for the reactor. While controlling the temperature of the carbonylation reactor, an additional heat for steam generation may be generated using a pump around loop, which is also described in U.S. Patent No. 8,530,696. In some embodiments, the temperature of the reactor is controlled by condensing a part of the flash column overhead distillate returned to the reactor, which is also described in U.S. Patent No. 8,957,248.

[0070] There are no special restrictions on the materials of the carbonylation reactor 100 and its internal components, which may be metal, ceramic, glass, or a combination thereof. For example, the materials include zirconium-based materials and alloys having high corrosion resistance, and further include iron-based alloys (stainless steel), nickel-based alloys (HASTELLOY (trademark) or INCONEL (trademark)), titanium-based materials and alloys, or aluminum-based materials or alloys.

[0071] In some embodiments, the reactor 100 is self-agitating (agitable), for example, a mechanical stirring tank, a tank having ejector or pump circulation mixing, or a bubble-column type tank (in the presence or absence of a stirrer), in which a reactive liquid or slurry content is preferably automatically maintained at a predetermined level, and that level is kept substantially constant during steady operation.

[0072] Flash evaporation process In steady-state operation, the reaction mixture is continuously withdrawn from the carbonylation reactor 100 via line 120 at a rate sufficient to maintain a constant level therein and sent to the flash vessel 200. To obtain the acetic acid product, the reaction mixture withdrawn via line 120 is fed to a subsequent downstream stream flash vessel 200 (e.g., a flash evaporator, a flash tank, or a flash distillation). In some embodiments, it is also possible to employ a conversion reactor (not shown) or a pipe reactor (not shown) in the flow path between the reactor and the evaporator. The pipe reactor is described in U.S. Patent No. 5,672,744 and is used to react carbon monoxide dissolved in the reaction mixture. Chinese Patent No. 1043525C describes a conversion reactor that enables the reaction to proceed significantly further prior to subsequent flashing. From that conversion reactor, a vent stream containing gaseous components is generated, and they are typically scrubbed using a compatible solvent to recover components such as methyl iodide and methyl acetate. As described herein, the gaseous streams from the reactor 10 and the converter can be scrubbed either in combination or separately, typically using either acetic acid, methanol, or a mixture of acetic acid and methanol to prevent the loss of low-boiling components such as methyl iodide from the process.

[0073] The flasher 200 separates the reaction mixture (referred to herein as flashing or evaporation) into a vapor phase (vaporous acetic acid reaction product) 202 and a low volatility phase (residual liquid catalyst stream) 204. The vapor phase 202 contains acetic acid, methyl iodide, acetaldehyde, methyl acetate, water, or other compounds, and the low volatility phase 204 contains acetic acid, a metal (cobalt, rhodium, and / or iridium) catalyst, and a promoter compound (including lithium iodide). At least a first portion of the vapor phase is fed to a first distillation column 300, and the low volatility phase 204 is recycled to the reactor 100 of the reaction step via a recycle line. Although not shown in FIG. 1, a portion of the low volatility phase 204 may be condensed and the condensate recycled to the reactor 100.

[0074] The flow rates of both the vapor phase 202 and the low volatility phase 204 can be changed. In some embodiments, 15% to 55% of the flow into the flasher 200 (e.g., the flow of the reaction mixture via line 120) is removed as the vapor phase 202, and 45% to 85% of that flow is removed as the low volatility phase 204. The ratio between the vapor phase 202 and the low volatility phase 204 separated in the flasher 200, in terms of mass ratio, may be from 10:90 to 60:40, such as from 25:75 to 45:55, or from 30:70 to 40:60. In some embodiments, the evaporation ratio of the reaction mixture in the flasher 200 is from 10 to 60 mass%, such as from 26 to 45 mass%, from 27 to 42 mass%, or from 30 to 40 mass%.

[0075] In some embodiments, the low-volatility phase 204 contains acetic acid, a metal catalyst, a corroded metal, and various other compounds. In one embodiment, the low-volatility phase 204 contains acetic acid in an amount of 60 to 90 wt%, a metal catalyst in an amount of 0.01 to 0.5 wt%, a corroded metal (e.g., nickel, iron, and chromium) in a total amount of 10 to 2500 wppm, lithium iodide in an amount of 5 to 20 wt%, methyl iodide in an amount of 0.5 to 5 wt%, methyl acetate in an amount of 0.1 to 5 wt%, water in an amount of 0.1 to 8 wt%, acetaldehyde in an amount of 1 wt% or less (e.g., 0.0001 to 1 wt% acetaldehyde), and hydrogen iodide in an amount of 0.5 wt% or less (e.g., 0.0001 to 0.5 wt% hydrogen iodide).

[0076] In one embodiment, the vapor phase 202 contains acetic acid, methyl iodide, methyl acetate, water, acetaldehyde, and hydrogen iodide. In one embodiment, the vapor phase 202 contains acetic acid in an amount of 45 to 75 wt%, methyl iodide in an amount of 20 to 50 wt%, methyl acetate in an amount of 9 wt% or less, water in an amount of 15 wt% or less, and PRC in an amount of 5 wt% or less, based on the total weight of the vapor phase. In another embodiment, the vapor phase 202 contains acetic acid in an amount of 45 to 75 wt%, methyl iodide in an amount of 24 to 36 wt% or less, methyl acetate in an amount of 9 wt% or less, water in an amount of 15 wt% or less, and PRC in an amount of 2 wt% or less, based on the total weight of the vapor phase. In some embodiments, the vapor phase 202 contains acetic acid in an amount of 55 to 75 wt%, methyl iodide in an amount of 24 to 35 wt%, methyl acetate in an amount of 0.5 to 8 wt%, water in an amount of 0.5 to 14 wt%, and PRC in an amount of 1 wt% or less. In some embodiments, the vapor phase 202 contains acetic acid in an amount of 60 to 70 wt%, methyl iodide in an amount of 25 to 35 wt%, methyl acetate in an amount of 0.5 to 6.5 wt%, water in an amount of 1 to 8 wt%, and PRC in an amount of 0.5 wt% or less.

[0077] The mass composition of acetaldehyde in the vapor phase 202 may be in an amount of 0.005 to 1% by weight, for example, 0.01 to 0.8% by weight, or 0.01 to 0.7% by weight, based on the total weight of the vapor phase 202. In some embodiments, acetaldehyde may be present in an amount of 0.01% by weight or less. The vapor phase 202 may contain hydrogen iodide in an amount of 1% by weight or less, for example, 0.5% by weight or less, or 0.1% by weight or less, based on the total weight of the vapor phase 202. The vapor phase 202 preferably contains substantially propionic acid-free, that is, contains only 0.0001% by weight or less of propionic acid, based on the total weight of the vapor phase.

[0078] In addition to acetic acid, the vapor phase 202 also contains methyl iodide, methyl acetate, water, and PRC, for example, acetaldehyde and crotonaldehyde. The dissolved gas exiting the reactor 100 and entering the flash vessel 200 contains a portion of carbon monoxide and may further contain gaseous by-products, for example, methane, hydrogen, and carbon dioxide. Such dissolved gas is discharged from the flash vessel 200 as a part of the vapor phase 202. In one embodiment, carbon monoxide in the gaseous purge stream may be fed to the base of the flash vessel 200 to enhance the stability of rhodium.

[0079] Although not shown in FIG. 1, a part of the vapor phase 202 may be cooled and condensed in a condenser. The condensate thus obtained may be stored in a hold tank for recycling the condensate to the reactor 100. The reaction product (condensate and / or non-condensable components) cooled in the condenser is preferably fed to a liquid-liquid separation step and stored in a decanter together with the overhead distillate from the first distillation step (splitter column), and the mixture of the cooled reaction product and the overhead distillate is separated into two phases in a liquid-liquid separation unit (for example, a decanter).

[0080] In some embodiments, a part of the volatile phase 202 may be fed directly or indirectly to the distillation process without being condensed, or may be cooled and condensed in one or more condensers to form two phases (aqueous phase or organic phase) via a liquid-liquid separation process, and the aqueous phase or organic phase (at least the aqueous phase) may be directly or indirectly subjected to the distillation process. For example, a part of the volatile phase 202 may optionally be condensed as described above (and optionally subjected to liquid-liquid separation), and mixed with the condensate obtained in the liquid-liquid separation process, and the mixture may be subjected to the distillation process. If necessary, the catalyst component (metal catalyst component) and the catalyst stabilizer or reaction promoter may be separated from the low-volatile phase 204 in one or more steps and recycled to the reactor 100.

[0081] Examples of flash evaporation include isothermal flash methods (in this case, heating the reaction mixture and depressurizing), adiabatic flash methods (in this case, depressurizing the reaction mixture without heating), or combinations of their flash conditions. By such flash evaporation, the reaction mixture can be separated into a gas phase and a liquid phase. For example, flash distillation is preferably carried out at a temperature of the reaction mixture of 80 to 250°C, a pressure (absolute pressure) of the reaction mixture of 10 to 1000 kPa (for example, 100 to 1000 kPa), preferably 100 to 500 kPa, more preferably 100 to 300 kPa. Flash evaporation is preferably carried out at a temperature of, for example, 80 to 250°C, for example, 90 to 200°C, 100 to 180°C, 110 to 170°C, and 120 to 160°C. The pressure (gauge pressure) may be 0.01 to 1 MPa, for example, 0.03 to 1 MPa, 0.05 to 0.5 MPa, 0.08 to 0.3 MPa, or 0.1 to 0.2 MPa. The low-volatile phase, i.e., the catalyst liquid mixture, preferably has a temperature of, for example, 80 to 200°C, for example, 90 to 180°C, 100 to 170°C, or more preferably 130 to 160°C.

[0082] The flasher 200 may be a vertical evaporator having a torispherical, elliptical, or hemispherical head. For maintenance and access, the flasher 200 may have one or more manholes. The reaction mixture 120 may be fed tangentially to the upper portion of the flash tank 200 through one or more feed ports, as shown in U.S. Patent No. 6,599,348. Splash plates may be used at each feed port to direct the liquid portion downward. Nozzles for the reaction mixture 120 may be in the upper portion of the flasher 200, for example, above the liquid level inside the flasher 200. One or more nozzles (not shown) may be present to introduce the reaction mixture tangentially and further separate the vapor portion. In some embodiments, the flasher 200 may have a cylinder diameter where the upper portion is larger than its lower portion. The flasher 200 should have a large volume such that the reaction mixture 120 fed thereto is retained in the flasher 200 and is able to evaporate the desired carbonylation reaction product into the vapor phase 202, and then recycle the low volatility phase 204. In one embodiment, the residence time in the flasher 200 is desirably about 1 minute or more, and in some embodiments, a residence time of at least 2 minutes or more can be used.

[0083] To maintain or improve the stability of the catalyst and reduce or prevent the sedimentation of the catalyst within the flasher 200, the carbon monoxide-containing purge may be introduced into the lower section of the flasher 200, for example, below the feed nozzles or into the low volatility phase 204. The carbon monoxide-containing purge may contain greater than 60 wt%, for example, greater than 80 wt%, or greater than 90 wt% carbon monoxide. The amount of the carbon monoxide-containing purge may be an amount sufficient to dissolve carbon monoxide into the liquid retained in the lower portion of the flasher 200. In one embodiment, the carbon monoxide-containing purge is at 5 Nm 3Greater than / hr, for example, 50 Nm 3 Greater than / hr, or 100 Nm 3 It is preferably fed in an amount greater than / hr. The upper limit is 1000 Nm 3 / hr.

[0084] Even when a CO-containing purge is used to stabilize the catalyst, there may be some insoluble deposits on its internal surface. Since it is relatively expensive, the insoluble deposits of rhodium that have accumulated on the internal surface should be recovered and reused.

[0085] When the process is operating continuously, some catalyst loss can occur, so a make-up catalyst is required. The make-up catalyst may be added directly to the reactor 100, but in one embodiment, the make-up catalyst may be added to the flasher 200 or the line for the low-volatility phase 204. The make-up catalyst should be metered in at a rate sufficient to maintain a continuous reaction.

[0086] In some embodiments, a mist eliminator for optional elements may be employed near the vapor outlet to agglomerate droplets. A scrubbing section (not shown) for optional elements may be further employed at the vapor outlet of the flasher to prevent and / or reduce the entrainment of the metal catalyst or other metal components into the vapor phase 202. A washing liquid may be introduced into the scrubbing section for optional elements. In another embodiment, an in-line separator may be used in the line for the vapor phase 202 to impart a swirling motion and agglomerate the entrained liquid. The liquid may be drained back to the flasher 20 to reduce entrainment in the vapor phase 202.

[0087] In some embodiments, the low volatility phase 204 may be processed to remove corrosive metals (e.g., nickel, iron, and chromium). For example, before recycling the low volatility phase 204 back to the reactor 100, a slip stream may be passed through a bed for removing corroded metals, such as an ion exchange bed, to remove various entrained corroded metals, such as nickel, iron, chromium, and molybdenum, as described in U.S. Patent No. 5,731,252, which is hereby incorporated by reference in its entirety. Further, a bed for removing corroded metals may be used to remove nitrogen compounds, such as amines, as described in U.S. Patent No. 8,697,908, which is hereby incorporated by reference in its entirety.

[0088] The first distillation step (the first column, i.e., the splitter column) As shown in FIG. 1, the vapor phase 202 is directed to a first distillation column 300 in the first distillation step (which is also referred to as a splitter column or a light end column). To enable separation, the first distillation column 300 includes a tray column, a packed column, or a combination thereof. In embodiments using a tray column, the number of theoretical trays may range from 5 to 80 trays, for example, from 10 to 60 trays or from 15 to 50 trays. In the first distillation column 300, the vapor phase 202 (or a portion thereof) is separated into a first overhead stream 302, an acetic acid stream 304, and a bottoms stream 306. The first overhead stream 302 (overhead gas, low-boiling stream, or low-boiling fraction) is withdrawn from the top of the column or a position above the middle of the column (i.e., the upper portion), the acetic acid stream 304 is withdrawn as a side cut from a position between the upper and lower positions and mainly contains acetic acid, and the bottoms stream 306 (high-boiling stream or high-boiling fraction) is withdrawn from the bottom of the first distillation column 300 or a position below the middle of the column (i.e., the lower portion). Most of the acetic acid is removed in the acetic acid stream 304, and preferably, little or no acetic acid is recovered from the bottoms stream 306. The proportion of the first overhead stream 302 may be about 20% to 60% of the total vapor phase 202, for example, about 35% to 50%. The proportion of the acetic acid stream 304 may be about 30% to 80% of the total vapor phase 202, for example, about 40% to 70%. The proportion of the bottoms stream 306 may be about 0% to 10% of the total vapor phase 202, for example, about 0% to 3%.

[0089] The first overhead stream 302 contains at least both a permanganate reducing compound (PRC) and methyl iodide. The PRC contains at least the by-product acetaldehyde. The first overhead stream 302 usually contains methyl acetate and actually contains the following: acetic acid, methanol, water, dimethyl ether, and / or by-products derived from acetaldehyde (e.g., aldehydes, e.g., crotonaldehyde or butyraldehyde; acetaldehyde derivatives, e.g., C 2~12 alkyl iodide or C3~12 Alkanecarboxylic acids; and C 2~12 Alkanes).

[0090] In one embodiment, the first overhead stream 302 contains water in an amount of 5 wt% or more, such as 10 wt% or more, or 25 wt% or more, based on the total weight of the first overhead stream 302. In some embodiments, the water content may be up to 80 wt%. In terms of a range, the mass composition of water in the overhead distillate may be 5 wt% to 80 wt%, such as 10 wt% to 70 wt%, or 25 wt% to 60 wt%. Reducing the mass composition of water to less than 5 wt% is not advantageous because it results in a large recycle of acetic acid back to the reaction system, which in turn leads to a large recycle throughout the purification system. In addition to water, the first overhead stream 302 may further contain methyl acetate, methyl iodide, and carbonyl impurities, which are preferably concentrated in the overhead distillate removed from the acetic acid in the acetic acid stream 304. These carbonyl impurities may also be referred to herein as PRC for short.

[0091] The first overhead stream 302 from the first distillation column 300 is cooled and condensed in one or more condensers 350. The condensate 352 can be separated into two phases, an aqueous phase rich in water and an organic phase rich in methyl iodide, in a first liquid-liquid separation unit (e.g., a decanter) 400. In some embodiments, the first overhead stream 302 is cooled in a plurality of condensers arranged in series (e.g., a plurality of condensers that continuously lower the cooling temperature) to form a plurality of condensates with continuously decreasing temperatures. For example, the condensate formed in the first condenser among the plurality of condensers may have a temperature of 10°C to 120°C, such as 20°C to 110°C, 30°C to 100°C, 40°C to 90°C, 50°C to 80°C, or 60°C to 70°C. In some embodiments, the condensate formed in the second condenser among the plurality of condensers may have a temperature of -30°C to 60°C, such as -20°C to 50°C, -15°C to 45°C, -5°C to 40°C, 0°C to 30°C, or 5°C to 20°C.

[0092] In some embodiments, at least a portion of the condensate 352 is directly refluxed to the first distillation column 300. In some embodiments, at least a portion of the condensate 352 travels towards the first liquid-liquid separation unit 400 to form an aqueous phase 402 and an organic phase 404. In the first liquid-liquid separation unit 400, it is desirable to maintain conditions such that the condensate 352 separates to form the aqueous phase 402 and the organic phase 404. The phase separation should not result in the formation of a third phase where two separate phases are retained, or an emulsion between those phases.

[0093] In some embodiments, the aqueous phase 402 and / or the organic phase 404, which are part of the condensate 352, can be returned to the first distillation column 300 via the reflux line 406 or 408, respectively. Depending on the need to remove PRC (including acetaldehyde), at least a portion of the aqueous phase 402 can be fed to a second distillation column 500, and at least a portion of the organic phase 404 can be recycled to the reactor 100 via the return line 416. In some embodiments, the aqueous phase 402 and / or the organic phase 404, which are part of the condensate 352, can be returned to the reactor 100 via the return lines 414 or 416, respectively. Thus, in one embodiment, a portion of the aqueous phase 402 is returned to the first distillation column 300 for reflux via line 406, the remaining portion of the aqueous phase 402 is fed to the second distillation column 500 via line 410, and the entire portion of the organic phase 404 is returned to the reactor 100 via line 416. In another embodiment, a portion of the aqueous phase 402 is returned to the first distillation column 300 for reflux via line 406, a portion of the organic phase 404 is directed to the second distillation column 500 via line 412, and another portion of the organic phase 404 is returned to the reactor via line 416. In yet another embodiment, a portion of the aqueous phase 402 is returned to the first distillation column 300 for reflux via line 406, a portion of the aqueous phase 402 and the organic phase 404 are directed to the second distillation column 500 via lines 410 and 412, and another portion of the organic phase 404 is returned to the reactor via line 416. All of the aqueous phase 402 that is not refluxed or that remains without being fed to the second distillation column 500 is returned to the reactor 100 via line 414.

[0094] In some embodiments, some or all of the aqueous phase 402 (or a process stream derived from the aqueous phase) can be fed to the second distillation column 500, or at least a portion (or the entire organic phase) of the organic phase 404 can be fed to the second distillation column 500. In some embodiments, at least a portion of the organic phase 404 (the methyl iodide-rich organic phase) can be refluxed to the first distillation column 300 via line 406, and at least a portion of the aqueous phase 402 can be fed to the second distillation column 500 via line 410.

[0095] The reflux ratio (reflux rate / distillate rate) of the condensate 352, and the aqueous phase 402 and / or the organic phase 404 to the first distillation column 300 can be controlled to further separate or remove impurities. Due to its high water content, the aqueous phase 402 is more suitable for refluxing. When only the aqueous phase 402 and no other phase is refluxed to the first distillation column 300, the reflux ratio of the aqueous phase can be from 0.2 to 15, for example, from 1.5 to 15, from 1.8 to 10, or from 1.8 to 5. A portion of the organic phase 404 can be refluxed to the first distillation column 300 via line 408 alone or in combination with the aqueous phase 402, but it is more desirable to return the methyl iodide-rich organic phase to the reactor 100 via line 416. Thus, a portion of the organic phase 404 can be refluxed via line 408 together with the aqueous phase 402, and the total reflux can be from 0.2 to 15.

[0096] In this way, crotonaldehyde at the top of the first distillation column 300 can be controlled to less than 5.0 mass ppm, for example, less than 4.5 mass ppm, less than 4.0 mass ppm, less than 3.5 mass ppm, less than 3.0 mass ppm, less than 2.5 mass ppm, less than 2.0 mass ppm, less than 1.8 mass ppm, less than 1.5 mass ppm, less than 1.2 mass ppm, 1.0 mass ppm, or less than 0.8 mass ppm, or less than 0.5 mass ppm. In some embodiments, the first distillation column 300 is operated to have a minimum mass composition of crotonaldehyde for a higher purity acetic acid product. Crotonaldehyde causes deterioration in the test value (permanganate time) of potassium permanganate for acetic acid. Furthermore, crotonaldehyde reacts with acetaldehyde to produce 2-ethylcrotonaldehyde. Although 2-ethylcrotonaldehyde also causes deterioration in the test value of potassium permanganate for acetic acid, the degree of deterioration in the potassium permanganate test per mass unit of 2-ethylcrotonaldehyde is much smaller than that of crotonaldehyde.

[0097] In addition to the first liquid-liquid separation unit 400 (e.g., a decanter) for temporarily storing or holding the condensate and separating the condensate into two phases, a buffer tank for temporarily storing (or holding) the condensate may be used in some cases.

[0098] In some embodiments, off-gas may be vented from the liquid-liquid separation unit 400. In some embodiments, the average residence time of the condensed first overhead stream 302 in the first liquid-liquid separation unit 400 is 1 minute or more, for example, 3 minutes or more, 5 minutes or more, 10 minutes or more, and / or the average residence time is 60 minutes or less, for example, 45 minutes or less, or 30 minutes or less, or 25 minutes or less.

[0099] For example, the aqueous phase, which is mainly water, may have the following composition shown in Table 1.

[0100]

Table 1

[0101] For example, the organic phase, which is mainly methyl iodide, may have the following composition shown in Table 2.

[0102]

Table 2

[0103] A part of the organic phase 404, which is mainly methyl iodide, is returned (recycled) to the reactor 100. In some embodiments, a part of the organic phase 404 may be refluxed to the first distillation column 300 alone or together with the aqueous phase 402. The specific gravity of the organic phase 404 may be 1.3 to 2, for example, 1.5 to 1.8, 1.5 to 1.75, or 1.55 to 1.7. As described in U.S. Patent No. 6,677,480, the specific gravity measured with the organic phase 404 can be associated with the mass composition of methyl acetate in the reaction mixture. As the specific gravity decreases, the mass composition of methyl acetate in the reaction mixture increases. In some embodiments, the receiver is arranged and configured to maintain a low interface level to prevent an excessive hold-up of methyl iodide. The ratio (by weight) of the flow rate of the aqueous phase withdrawn from the receiver to that of the organic phase withdrawn from the receiver may be, for example, about 0.1 / 1 to 10 / 1, for example, about 0.3 / 1 to 3 / 1, or about 0.5 / 1 to 2 / 1, for example, about 0.7 / 1 to 1.5 / 1.

[0104] The off-gas may be vented from the first distillation column 300 and / or the liquid-liquid separation unit 400 to the absorption unit as necessary.

[0105] In a continuous process, there can be fluctuations in the flow rate, and if left unaddressed, it may cause disruptions in the process or make operation difficult. To cope with these fluctuations, it is advisable to deploy a hold tank for buffering the stream between the first distillation column 300 and the liquid-liquid separation unit 400 in the process, or a receiver for either the aqueous phase or the organic phase. When in use, the hold tank should be sized to handle fluctuations up to 20% of the flow in and out of the receiver.

[0106] Second distillation step As shown in Figure 2, direct the first mixture towards the second distillation column 400 in the second distillation step. In Figure 2, the first mixture is shown as the first overhead stream 302 from the first distillation column 300 heading towards the second distillation column, but the first mixture can be various combinations of multiple process streams. For example, the process stream introduced into the second distillation column 400 may include the first overhead stream 302 and the phases separated from it (aqueous phase 402 and / or organic phase 404), the acetic acid stream 304 and the phases separated from it, or the condensates of various streams. The first mixture is represented as the first overhead distillate 302, but it should be understood that the first mixture may include a portion of the first overhead distillate 302, including the above-mentioned liquid-liquid separated aqueous and organic phases.

[0107] In one embodiment, a portion of the first overhead distillate 302 (either the aqueous phase or the organic phase, or a combination thereof) may be introduced into the second distillation column 500, where in the second overhead distillate 502, acetaldehyde is removed, and 1,1-dimethoxyethane (including the 1,1-dimethoxyethane generated in the column) descends through column 500 and enters the bottom stream 506. The distillation can be carried out either as batch distillation or continuous distillation. To enable separation, the second distillation column 500 includes a tray column, a packed column, or a combination thereof. In a plurality of embodiments using a tray column, the number of theoretical trays may range from 1 to 100 trays, for example, from 2 to 80 trays, or from 5 to 75 trays.

[0108] In the present invention, the second distillation column 500 should satisfy at least one of the following operating conditions: (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or more; and / or (iii) the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture based on the total weight of the lower stream. By operating the second distillation column 500 under any one of the operating conditions (i) to (iii), it is possible to separate acetaldehyde into the upper stream (the second overhead stream 502 or the side cut stream 504) of the distillation column, and there is less 1,1-dimethoxyethane produced and concentrated in the lower stream of the second distillation column 500. The above-described operating conditions in the distillation column can reduce or suppress the production of 1,1-dimethoxyethane, thereby allowing more acetaldehyde to be distributed to the upper stream of the second distillation column 500. The lower stream 506 withdrawn from the second distillation column 500 can be recycled (for example, directly) to the carbonylation reactor 100, with fewer impurities (for example, acetaldehyde and / or 1,1-dimethoxyethane) for a higher purity acetic acid product. The distillation process satisfying the above conditions has a methanol mass composition in the first mixture (the aqueous part in line 410 or the organic part in line 412) to the distillation column of 2 wt% or less, for example, 1 wt% or less, or 0.5 wt% or less. In some embodiments, the first mixture (sometimes referred to as the feed mixture) to the second distillation column 500 has a methanol mass composition higher than the mass composition of dimethyl ether.

[0109] As found by the inventors of the present application, by controlling the amount of 1,1-dimethoxyethane in the lower stream of the distillation, acetaldehyde can be efficiently separated in the second distillation column 500. Since the amount of 1,1-dimethoxyethane in the lower part of the second distillation column 500 is small, it is concentrated in the lower stream withdrawn from the distillation column and contains little acetaldehyde. As a result, acetaldehyde in the first mixture or the first overhead distillate 302 (for example, the feed mixture to the second distillation column 500, which may be an aqueous phase or an organic phase) can be efficiently separated and distributed to the upper part of the distillation column to form a concentration zone of the PRC (for example, containing at least acetaldehyde). Acetaldehyde in its mass composition can be preferentially separated from the concentration zone by adding an extractant (for example, water) to the second distillation column 500. Specifically, an extractant is added to the concentration zone of the PRC to preferentially extract acetaldehyde over other components, thereby achieving efficient separation of acetaldehyde in the second distillation column 500.

[0110] For operating condition (i), the temperature in the lower part of the second distillation column 500 is 40 °C or higher, for example, 42 °C or higher, 44 °C or higher, 46 °C or higher, 48 °C or higher, 50 °C or higher, 60 °C or higher, 70 °C or higher, 80 °C or higher, 90 °C or higher, 100 °C or higher, 110 °C or higher, or 115 °C or higher. In terms of range, the temperature in the lower part of the second distillation column 500 is in the range of 40 °C to 165 °C, for example, 50 °C to 160 °C, 60 °C to 155 °C, 70 °C to 150 °C, 80 °C to 140 °C, 90 °C to 135 °C, 100 °C to 140 °C, 110 °C to 135 °C, or 115 °C to 130 °C. In terms of the upper limit, the temperature in the lower part of this distillation column is less than 165 °C, for example, less than 160 °C, less than 155 °C, less than 150 °C, less than 145 °C, less than 140 °C, 130 °C, less than 125 °C, or less than 120 °C.

[0111] For operating condition (ii), the water content in the lower part of the second distillation column 500 is 0.3 wt% or more, for example, 0.4 wt% or more, 0.5 wt% or more, 0.6 wt% or more, 0.8 wt% or more, 1 wt% or more, 1.5 wt% or more, or 2 wt% or more. In terms of range, the water content in the lower part of this distillation column is in the range of 0.3 wt% to 20 wt%, for example, 0.5 wt% to 18 wt%, 0.8 wt% to 16 wt%, 1 wt% to 15 wt%, 1.5 wt% to 14 wt%, 2 wt% to 12 wt%, 3 wt% to 10 wt%, 4 wt% to 9 wt%, or 5 wt% to 9 wt%. The water content in the lower part of the second distillation column 500 is less than 20 wt%, for example, less than 18 wt%, less than 15 wt%, less than 10 wt%, or less than 5 wt%.

[0112] For operating condition (iii), the amount of acetic acid in the lower stream is greater than the amount of acetic acid in the first mixture on a weight percent basis. The acetic acid in the first mixture mainly migrates from the upper stream to the lower stream. In some embodiments, the acetic acid in the lower stream is 3 wt% or less, for example, 2.8 wt% or less, 2.5 wt% or less, 2.2 wt% or less, 2 wt%, or 1.8 wt% or less. To achieve these amounts of acetic acid, more than 50%, for example, more than 60%, more than 70%, more than 80%, or more than 90% of the acetic acid in the first mixture migrates to the lower stream.

[0113] The distillation process that satisfies any one of operating conditions (i) to (iii) can control the amount of 1,1-dimethoxyethane in the lower stream to be 0.03 wt% or less, for example, 0.025 wt% or less, 0.02 wt% or less, 0.01 wt% or less, or 0.005 wt% or less based on the total weight of the lower stream. In some embodiments, the amount of 1,1-dimethoxyethane in the lower stream is in the range of 0.001 wt% to 0.03 wt%, for example, 0.001 wt% to 0.025 wt%, 0.004 wt% to 0.02 wt%, or 0.008 wt% to 0.015 wt% based on the total weight of the lower stream.

[0114] In some embodiments, the first mixture (e.g., the first overhead stream 302 from the first distillation column 300, or a derivative stream therefrom) to the second distillation column 500 contains a methanol amount of 2 wt% or less, such as 1.5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, 0.05 wt% or less, 0.01 wt% or less, 0.0005 wt% or less, based on the total weight of the feed mixture. In terms of range, the feed mixture to the second distillation column 500 contains a methanol amount of 0.0001 - 2 wt%, such as 0.0005 - 1.5 wt%, 0.01 - 1 wt%, 0.05 - 0.5 wt%, or 0.1 - 0.3 wt%.

[0115] As described above, under the operating conditions described in this specification, since the amount of 1,1-dimethoxyethane in the lower portion of the second distillation column 500 is small, more acetaldehyde is distributed to the upper portion of the column to form a concentration zone of PRC. In some embodiments, the first overhead stream 302 (e.g., condensate, aqueous phase, organic phase, or a combination thereof) is fed to the second distillation column 500, and by adding an extractant (e.g., water) to the concentration zone in the second distillation column 500, PRC is efficiently extracted. The extractant preferably has a composition suitable for extracting acetaldehyde from the first mixture. To facilitate the treatment, the extractant may be separable from methyl iodide using low-energy techniques including liquid-liquid separation and / or membrane separation methods. The extractant may include extracted water, a mixed solvent, or a water-soluble organic solvent (glycol, glycerin, acetone, ether, and / or ester). To keep the extraction mixture in a liquid-liquid separation state, the introduction of water is advantageous, and thus the extractant should contain 80 wt% or more of water, for example, 90 wt% or more of water, or 95 wt% or more of water. In one embodiment, the extractant is substantially free of methanol or other monoalcohols so as not to be excessive. The first (feed) mixture is efficiently distilled into the upper stream (the second overhead stream 502 or the side cut stream 504), which contains a large amount of at least methyl iodide (especially a large amount of at least methyl iodide and PRC).

[0116] The first overhead stream 302 (or its derivative stream) is distilled in a second distillation column 500 to form an upper stream and a lower stream. The upper stream may include at least one of a second overhead stream 502 and a side cut stream 504. In the second distillation column 500, an extractant (e.g., water) can be added to the second distillation column 500 via line 524 to extract PRC from the mass composition zone of PRC. The extractant preferentially extracts PRC from the mass composition zone over methyl iodide to form an extraction mixture. The extraction mixture (including PRC extracted from the mass composition zone) descending from the enrichment zone can be withdrawn as the side cut stream 504. In some embodiments, the ratio of acetaldehyde to methyl iodide in the side cut stream 504 is higher than that in the first overhead stream 302 and higher than that in the lower stream 506. The process efficiently separates PRC and methyl iodide from each other by extractive distillation of PRC in the co - presence of methyl acetate and / or acetic acid.

[0117] Under the operating conditions described herein for the second distillation column 500, little 1,1 - dimethoxyethane is produced in the lower part of the column. In some embodiments, the weight ratio of the mass composition of 1,1 - dimethoxyethane in the lower stream to the overhead stream is from 100:1 to 10:1, such as 95:1 to 15:1, 90:1 to 20:1, 80:1 to 25:1, 75:1 to 30:1, 70:1 to 40:1, or 60:1 to 50:1. In some embodiments, the weight ratio of the mass composition of 1,1 - dimethoxyethane in the lower stream to the side cut is from 100:1 to 10:1, such as 95:1 to 15:1, 90:1 to 20:1, 80:1 to 25:1, 75:1 to 30:1, 70:1 to 40:1, or 60:1 to 50:1.

[0118] In some embodiments, the first mixture fed to the second distillation column 500 may contain a total mass composition of 0.05 to 50 wt%, 0.05 to 10 wt%, 0.1 to 5 wt%, or 0.1 to 1 wt% of PRC (e.g., acetaldehyde). Thus, the target amount of PRC can be separated from the first mixture. The first mixture can be derived from the first overhead stream 302, or a portion thereof, and may further contain other components, including, but not limited to, for example, C 1 ~C 12 alkyl, acetic acid, methyl acetate, water, and / or methanol, among others. When the mixed composition is derived from portions of the aqueous and organic phases, the first mixture may have, in addition to PRC, a mass composition of 2.5 wt% to 90 wt%, for example, 10 wt% to 85 wt%, or 20 to 70 wt% of C 1 ~C 12 alkyl iodide (methyl iodide), and a mass composition of 0.5 wt% to 90 wt%, for example, 1 wt% to 90 wt%, or 1.5 wt% to 85 wt% of water. A representative C 1 ~C 12 alkyl is methyl iodide. In one embodiment, the amount of C 1 ~C 12 alkyl is greater than the mass composition of water. Importantly, within the first mixture, there exists a range where the mass compositions of PRC, C 1 ~C 12 alkyl, and water can be selected from the broad ranges disclosed herein. The composition within the first mixture may be a homogeneous liquid or a mixture of an aqueous phase and an organic phase. The composition of the first mixture may further contain up to 30 wt% of methyl acetate, for example, in an amount of 0.1 to 28 wt% or 1 to 20 wt%, up to 25 wt% of acetic acid, for example, in an amount of 0.01 to 12 wt% or 0.5 to 7.5 wt%, and up to 1 wt% of dimethyl ether, for example, in an amount of 0.001 to 1 wt% or 0.004 to 0.8 wt%.

[0119] In addition to these components, the first mixture may further contain methanol. The methanol may be unreacted methanol or may be methanol produced by a secondary reaction during the separation and / or distillation process. In one embodiment, the mass composition of methanol in the first mixture may be 2 wt% or less, for example, 1.8 wt% or less, 1.5 wt% or less, 1.1 wt% or less, 1.0 wt% or less, or 0.5 wt% or less.

[0120] As described above, in the second distillation column 500, the first overhead stream 302 (the first mixture) is distilled to form a mass composition zone (a zone having a high mass composition of PRC (particularly, acetaldehyde and methyl iodide)) at an upper position of the second distillation column 500. For example, the mass composition zone of PRC is formed above the feed line of the first mixture, which is part of the second distillation column 500. An extractant is added to the mass composition zone via line 524 to extract PRC (particularly, acetaldehyde) preferentially over other components (such as methyl iodide) in the mass composition zone, and the extraction mixture descending from the mass composition zone is withdrawn from the second distillation column 500 as a side cut stream 504. The extraction mixture has a significantly higher mass composition of PRC (particularly, acetaldehyde) than the first overhead stream 302 fed to the second distillation column 500. By withdrawing the extraction mixture as the side cut stream 504, it becomes possible to efficiently separate or remove PRC.

[0121] In some embodiments, the second distillation column 500 has actual trays greater than 10 trays, for example, greater than 15 trays, greater than 20 trays, greater than 25 trays, or greater than 30 trays. For example, in a plate distillation column having a total of 43 trays (i.e., plates), the feed plate to which the first overhead stream 302 is fed may be approximately the 1st to 20th trays, for example, approximately the 2nd to 15th trays, or approximately the 4th to 10th trays from the bottom of the distillation column. For example, in a plate distillation column having a total of 10 trays (i.e., plates), the feed plate to which the first mixture is fed may be approximately the 1st to 7th trays, for example, approximately the 1st to 5th trays, or approximately the 1st to 3rd trays from the bottom of the distillation column.

[0122] In some embodiments, the location (feed port, or feed plate or tray) at which the first mixture (e.g., the first overhead stream 302, or the aqueous / organic phase) is fed to the second distillation column 500 is changeable. In some embodiments, assuming the height level of the distillation column is "1", the first overhead stream 302 may be fed, for example, at a height level of about 0.01 / 1 to 0.7 / 1, for example, about 0.01 / 1 to 0.5 / 1, about 0.03 / 1 to 0.45 / 1, about 0.04 / 1 to 0.4 / 1, or about 0.05 / 1 to 0.35 / 1 from the bottom.

[0123] In some embodiments, the extractant can typically be added to the upper portion of the second distillation column 500. In some embodiments, the extractant can be added between the top plate of the column, or a plate located at least one plate above the top of the column or the feed tray and the feed portion of the first mixture. Assuming that the second distillation column 500 has a total of 100 plates, the feed plate of the extractant can be the top plate of the second distillation column 50 or a plate in the vicinity, for example, plates from approximately stage 0 to stage 50 from the top of the distillation column, for example, approximately stage 1 to stage 25, approximately stage 1 to stage 20, approximately stage 1 to stage 15, or approximately stage 1 to stage 10. In other words, assuming the height level of the distillation portion of the distillation column is "1", the extractant can be fed, for example, at a height level from approximately 0 / 1 (= the top of the column) to 0.5 / 1, for example, approximately 0.01 / 1 to 0.25 / 1, approximately 0.01 / 1 to 0.2 / 1, approximately 0.01 / 1 to 0.15 / 1, or approximately 0.01 / 1 to 0.1 / 1 from the top of the column.

[0124] To improve the extraction efficiency by adding the extractant countercurrently to the ascending vapor or distillate, the extractant is typically preferably added to the topmost plate of the second distillation column 500. To improve the extraction efficiency, the extractant is preferably added in the form of droplets, specifically, it is preferably added by a spray method or a sprinkler method. The extractant preferably has a temperature of, for example, about 0 to 60 °C, for example, about 10 to 50 °C, about 20 to 40 °C, or about 15 to 25 °C. The extractant can be heated or warmed, for example, heated to about 30 to 150 °C, about 50 to 110 °C, or added in the form of steam (including superheated steam).

[0125] The extractant can preferentially extract PRC (especially acetaldehyde) over other components (such as methyl iodide) in the mass composition zone. The extractant is preferably separable from the methyl iodide phase by liquid-liquid separation. In particular, the extractant can separate the extraction mixture into an upper phase and a lower phase. Specifically, examples of the extractant include aqueous extractants containing at least water, such as: water, mixed solvents containing water, and water-soluble organic solvents, such as alcohols like methanol, glycols like ethylene glycol, polyhydric alcohols like glycerin, acetone, esters, and ethers.

[0126] The extractant may contain water and at least one component selected from the group consisting of: PRC, methyl iodide, acetic acid, methyl acetate, dimethyl ether, and components present in the process (including all components, including the above-mentioned impurities). Such an extractant may be, for example, an aqueous solvent generated in the process, such as: the aqueous phase generated in the liquid-liquid separation step of the first overhead stream, an aqueous process stream, for example, the extract generated in the second liquid-liquid separation step (such as an aqueous process stream containing acetaldehyde), and other aqueous process streams containing acetaldehyde, for example, the aqueous phase generated by extracting PRC with water. The extractant may further include an aqueous solution (for example, an aqueous solution containing acetaldehyde and methyl iodide) that can be obtained by absorbing off-gas (the off-gas is generated in the process) with water.

[0127] In some embodiments, the first overhead stream 302 (or condensate, aqueous phase, organic phase, or combinations thereof) is fed to a second distillation column 500 and distilled without supplying water (excluding water in the reflux to the column) to the second distillation column 500. When distilling the first overhead stream 302, a portion of the water in the first overhead stream 302 is distributed to a location above the feed port of the second distillation column 500 to form a second mixture having an increased water content (e.g., a second mixture that can be separated into two phases by condensation) by the transfer or distribution of water.

[0128] In some embodiments, the second mixture can be withdrawn as a second overhead stream 502. Its bottom stream 506 has a lower water content than the second overhead stream 502 and is withdrawn from a location below the feed port. Specifically, the water in the first overhead stream 302 preferentially transfers to the second overhead stream 502 as the upper stream rather than the bottom stream 506. In this way, the second overhead stream 502 has a significantly higher amount of PRC (e.g., acetaldehyde) than the first overhead stream 302, i.e., the first mixture fed to the second distillation column 500. The second overhead stream 502 can be condensed and phase-separated to form an aqueous phase containing a more efficiently concentrated PRC.

[0129] The second distillation column 500 may be operated under certain conditions such that water in the first overhead stream 302 preferentially transfers to the second overhead stream 502 rather than the bottom stream 506. For example, when the second distillation column 500 is operated under the specific operating conditions described herein, a zone with a high water content is formed within the distillation column. In some embodiments, a zone containing a high concentration of PRC and methyl iodide is formed at a position above the feed port of the second distillation column 500, enabling at least a portion of the water in the first mixture to be distributed to the concentration zone. In this process, the mixture descending from the concentration zone can be withdrawn as a side cut stream 504. When PRC (including acetaldehyde) is extracted into the upper stream (the second overhead stream 502 or the side cut stream 504) on the side opposite to the bottom stream 506, a relatively small amount of the extractant can be used. For example, the flow rate ratio (by weight) of the extractant in line 524 to the first mixture (e.g., lines 410 and / or 412) can be in the following ranges: (0.0001 / 100) to (100 / 100), for example, 0.001 / 100 to 50 / 100, 0.0001 / 100 to 20 / 100, 0.001 / 100 to 10 / 100, 0.01 / 100 to 8 / 100, or 0.1 / 100 to 5 / 100. In the use of the extractive distillation process in the second distillation, PRC and iodinated C 1 ~C 12 The alkyl may be treated in an efficient way to reduce the required amount of energy.

[0130] The internal temperature of the second distillation column 500 in the second distillation step depends on its internal pressure. When the internal pressure is atmospheric pressure, the second distillation column 500 can have, for example, the following overhead temperatures: about 15 - 120 °C, for example, about 18 - 100 °C, about 20 - 90 °C, for example, about 20 - 80 °C, about 20 - 70 °C, or about 25 - 70 °C. In the second distillation step, other distillation conditions (e.g., the number of theoretical plates and reflux ratio of the distillation column) may be the same as in the distillation step. The reflux ratio (reflux: distillate) of the second distillation column 400 is 1:20 - 20:1, for example, 1:15 - 15:1, or 5:1 - 10:1.

[0131] The internal pressure of the second distillation column 500 may affect the formation of acetal in the distillation column. For example, by controlling the fluctuation of the internal pressure of the second distillation column 500, the formation of acetal can be suppressed. In some embodiments, the second distillation column 500 may be equipped with a pressure control device for controlling the pressure of the distillation column. The pressure in the distillation column (e.g., the top or bottom part of the column) can be controlled by introducing an inert gas or off - gas into the column and / or discharging non - condensable gas from the distillation column. In some embodiments, the internal pressure of the distillation column in the second distillation step (e.g., the top or bottom part of the column) is preferably as follows: for example, in absolute pressure, about 0.1 - 0.7 MPa, for example, about 0.01 - 0.6 MPa, preferably about 0.13 - 0.4 MPa, more preferably 0.15 - 0.35 MPa. In some embodiments, the internal pressure of the distillation column is 0.7 MPa or less, for example, less than 0.6 MPa, less than 0.5 MPa, less than 0.4 MPa, less than 0.3 MPa, or less than 0.2 MPa. The second distillation step can control the internal pressure of the distillation column to form a second overhead distillate rich in acetaldehyde and methyl iodide. The second overhead stream 502 may have a temperature of 15 - 110 °C, for example, 18 - 90 °C, 20 - 80 °C, or 20 - 70 °C at atmospheric pressure.

[0132] In some embodiments, the second distillation column 500 is provided with a collector tray (plate) 501, also referred to as a hat tray or chimney tray, which enables good distribution of the vapor from the first mixture to the upper zone and retention of the entire amount of the extractive mixture to be withdrawn as the side cut stream 504. In the embodiments described herein, collector trays 501 of various suitable designs can be used. The collector tray 501 is actually located where the side cut stream 504 is withdrawn, and thus, the extractant 524 is added above the collector tray 501. This makes it possible to receive the liquid descending from the upper portion of the second distillation column 500 onto the collector tray 501.

[0133] As shown in FIG. 2, the second distillation column 500 separates the components of the first mixture (from the first overhead stream) 302 by extractive distillation at a first location in the second distillation column 500. For the purposes of the disclosure contained herein, it should be understood that “from 302 of FIG. 1” in FIGS. 2-4 may include the first overhead stream 302 or a portion thereof (aqueous or organic phase) as the first mixture. In one embodiment, the feed line can be extracted using an extractant 524 introduced into an upper zone above the first location of the second distillation column 500. In some embodiments, the second overhead distillate 502 is condensed and a portion of the distillate is used as a second mixture to remove PRC. In the embodiment shown in FIG. 2, the composition of the second overhead distillate 502 may be a phase separable into an aqueous phase 523 and an organic phase 522 in an overhead receiver 520 (e.g., a decanter). In the organic phase 522, it is rich in methyl iodide and poor in water, whereas the aqueous phase 523 may contain a useful amount of PRC and water. In some embodiments, the aqueous phase 523 may be fed to the tank 600 in combination with the side cut stream 504 to remove acetaldehyde, or the aqueous phase 523 may be fed to the tank 600 separately. In yet another embodiment, a portion of the aqueous phase 523 may be used as reflux to the second distillation column 500, while the organic phase 522 containing some acetaldehyde is fed to the tank 600.

[0134] Depending on the mixing composition in the first mixture, although methyl acetate and / or acetic acid having a tendency for affinity for both PRC (including acetaldehyde) and C 1 ~C 12 alkyl (including methyl iodide) are present, acetaldehyde can be efficiently extracted into the second overhead distillate 502. In one embodiment, the amount of acetaldehyde in the upper portion of the column (including the second overhead distillate 502 and / or the side cut 504) is 5 to 1000 times, for example, 10 to 500 times or 20 to 300 times the amount in the first mixture on a weight basis.

[0135] In some embodiments, the second overhead stream 502 and / or the side cut stream 504 are condensed. The condensate can be refluxed to the overhead portion of the second distillation column 500. In some embodiments, there is also a distillate withdrawn from the overhead of the second distillation column 500, but generally, the condensed portion of the second overhead stream 502 is refluxed. The second overhead stream 502 exits the second distillation column 500 in a temperature range of 15°C to 120°C, and a condenser (or multiple condensers if necessary) lowers the second overhead stream 502 to a temperature below the boiling point of methyl iodide and condenses it. The condensed liquid 510 is accumulated in the overhead receiver 520 and refluxed via line 522. To maintain the extraction conditions, line 522 is preferably introduced into the second distillation column 500 between the location of the extractant 524 and the withdrawal location of the side draw 504 (e.g., above the collector tray 501). This reflux can be used to prevent an excess of the extractant, i.e., water, from being present in the overhead distillate 502.

[0136] A miscible solvent may be fed directly or indirectly to the column to the lower portion of the second distillation column 500. This solvent is miscible with the process stream containing methyl iodide. The miscible solvent may be at least one component selected from the group consisting of water, acetic acid, methyl iodide, and methanol. When added, the miscible solvent may be 30% or less, for example, 15% or less, or 10% or less, relative to the amount of the side cut stream 504 withdrawn from the collector tray 501.

[0137] As shown in FIG. 2, the side cut stream 504 can be collected into the tank 600. The tank 600 may be a buffer tank or, alternatively, a liquid-liquid separation tank that can receive the side cut stream 504 and separate the side cut stream 504 into multiple phases. In some embodiments, the tank 600 separates the liquid-liquid separable side cut stream 504 into an aqueous phase 602 and an organic phase 604. PRC (including acetaldehyde) is more preferably distributed into the aqueous phase 602 than into the organic phase 604. In addition, the extractant is more preferably distributed into the aqueous phase 602, and although the extractant can be recovered by subsequently treating the aqueous phase, it is not essential to recover the extractant. The organic phase may be returned to the second distillation column 500 operating under at least one of conditions (i)-(iii) or, alternatively, combined with the bottom stream 506 and returned to the reactor 100. In addition, it is desirable to reduce the methyl iodide in the aqueous phase 602 so that acetaldehyde can be discharged without further treatment.

[0138] In one embodiment, in the tank 600, the side cut 504 is separated into an aqueous phase 602 and an organic phase 604. The mass flow ratio of the aqueous phase 602 to the organic phase 604 (aqueous phase to organic phase) may be from 1:1000 to 1:1, such as from 1:900 to 1:10, or from 1:650 to 1:100. For balance, based on the mass flow, the aqueous phase 602 is preferably a stream that is less than the organic phase 604. The organic phase 604 does not contain the extractant and can be returned to the second distillation column 500.

[0139] The aqueous phase 602 has a greater amount of PRC (acetaldehyde) than the organic phase 604, and the aqueous phase 602 contains iodinated C 1 ~C 12It may contain more PRC than alkyl (methyl iodide). Taking acetaldehyde and methyl iodide as representatives, the aqueous phase 602 can have a former-to-latter ratio by weight of 2:1 to 60:1, for example, 3:1 to 45:1, 3:1 to 30:1, or 4:1 to 20:1. The composition of the aqueous phase 602 includes the following: the mass composition of PRC (acetaldehyde) is 1 to 50 wt%, for example, 5 to 45 wt%, or 10 to 35 wt%; the mass composition of water is 40 to 95 wt%, for example, 50 to 90 wt%, or 60 to 75 wt%; and C 1 ~C 12 The mass composition of alkyl (methyl iodide) is 0.01 to 15 wt%, for example, 0.1 to 10 wt%, or 0.5 to 6 wt%; the mass composition of methyl acetate is 0.1 to 25 wt%, for example, 0.5 to 20 wt%, or 0.5 to 10 wt%; the mass composition of acetic acid is 0 to 5 wt%, for example, 0.01 to 2.5 wt%, or 0.05 to 1 wt%; the mass composition of methanol is 0 to 2.5 wt%, for example, 0.01 to 2.1 wt%, or 0.05 to 2 wt%; the mass composition of acetal is 0 to 2.5 wt%, for example, 0.01 to 1.7 wt%, or 0.05 to 1.5 wt%; and the mass composition of dimethyl ether is 0 to 1.2 wt%, for example, 0.01 to 0.8 wt%, or 0.05 to 0.5 wt%.

[0140] The organic phase 604 is preferably returned to the collector tray 501 below the second distillation column 500. In one embodiment, the composition of the organic phase 604 includes the following: C 1 ~C 12The mass composition of alkyl (methyl iodide) is 0.1 to 90 wt%, for example, 5 to 85 wt%, or 10 to 80 wt%; the mass composition of methyl acetate is 0.1 to 30 wt%, for example, 0.5 to 20 wt%, or 0.5 to 10 wt%; the mass composition of PRC (acetaldehyde) is 0.01 to 15 wt%, for example, 0.5 to 10 wt%, or 0.5 to 5 wt%; the mass composition of acetic acid is 0 to 5 wt%, for example, 0.01 to 2.5 wt%, or 0.05 to 1 wt%; the mass composition of water is 0.01 to 5 wt%, for example, 0.05 to 4 wt%, or 0.5 to 3.5 wt%; the mass composition of methanol is 0 to 2.5 wt%, for example, 0.01 to 2.1 wt%, or 0.05 to 2 wt%; the mass composition of acetal is 0 to 2.5 wt%, for example, 0.01 to 1.7 wt%, or 0.05 to 1.5 wt%; and the mass composition of dimethyl ether is 0 to 1.2 wt%, for example, 0.01 to 0.8 wt%, or 0.05 to 0.5 wt%. The organic phase 604 may further contain methanol, and the additional methanol in the organic phase 604 returning to the second distillation column 500 may increase the production rate of acetal (1,1-dimethoxyethane). To control the production of acetal, the organic phase 604 is returned to the second distillation column 500, and when it contains methanol, the total mass composition of methanol in the first mixture and the organic phase is 2 wt% or less, for example, 1.5 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0.25 wt% or less. When the organic phase 604 contains more than 2 wt% of methanol, the organic phase 604 may be combined with the lower stream 506 without feeding the organic phase 604 to the second distillation column 500. For efficient operation, in one embodiment, the lower stream 506 contains a significant proportion of methyl iodide from the feed stream 302, especially when the feed stream 302 contains a portion of the organic phase 404. The lower stream 506 of the distillation column 500 contains useful methyl iodide, which is returned to the reactor 100. To achieve sufficient production, the distillation column removes 60 to 99.9%, for example, 75 to 99.5%, or 80 to 99.1% of the methyl iodide in the feed stream 302 into the lower stream 506.Upon successful removal of methyl iodide, 10 to 90% by weight, for example, 15 to 85% by weight, or 20 to 80% by weight of C iodine. 1 ~C 12 A lower stream 506 having a mass composition of alkyl (methyl iodide) is obtained. However, by doing so, the return of 1,1-dimethoxyethane to the reactor increases. To overcome these defects and use the lower stream 506 efficiently, the mass composition of water is maintained at a level sufficient to transfer or convert it to 1,1-dimethoxyethane.

[0141] The lower stream 506 is preferably withdrawn at a temperature of 30°C to 160°C, for example, 35°C to 120°C, or 40°C to 100°C.

[0142] Auxiliary removal of acetaldehyde Although acetaldehyde (including other PRCs) is removed from the feed stream 302 to the second distillation column 500, it is desirable to remove or reduce acetaldehyde using auxiliary treatment to recover either useful organic components and / or extractants. There are several available methods for achieving such auxiliary removal of acetaldehyde. For the purposes of the present invention, those auxiliary removal processes can be modified, if used, according to the requirements of the processing equipment. One aspect of the auxiliary removal of acetaldehyde is that in the process, the mass composition of 1,1-dimethoxyethane in the lower stream 506 must not be increased.

[0143] In one embodiment, acetaldehyde can be removed or reduced by purging the upper stream from the second distillation column 500 (e.g., the second overhead distillate 502 or the side cut stream 504) from the process. This can be carried out using an upper stream containing a very low amount, specifically less than 1 wt%, for example less than 0.5 wt% of methyl iodide. If the upper stream contains a high amount of methyl iodide, it is desirable to avoid purging the second mixture by employing an auxiliary acetaldehyde removal process.

[0144] In yet another embodiment, a second extraction step of the upper stream may be performed in an extractor without stages or a distillation column with stages. In this auxiliary acetaldehyde removal process, the second extraction may use a secondary extractant (additional water) to produce an extractant containing acetaldehyde and a raffinate containing methyl iodide. This allows the raffinate to be recovered and the extractant to be further discarded or purged. Under this procedure, the second extraction can be positioned as a continuous stage with the second distillation column 500. A condenser / chiller may be present between the extraction stage, i.e., between the second distillation column 500 and the extractor. The temperature of the upper stream when using a condenser / chiller may be from 10 °C to 80 °C, for example from 12 °C to 65 °C, or from 13 °C to 45 °C.

[0145] Figure 3 shows one embodiment of an auxiliary acetaldehyde removal process. As described above, the first mixture to the second distillation column 500 is represented as the first overhead distillate 302, but it should be understood that the first mixture may include a portion of the first overhead distillate 302 (including the above-described liquid-liquid separated upper and lower streams). After the first mixture is distilled and / or extracted in the second distillation column 500, a second mixture is withdrawn from the second distillation column 500 as a side cut stream 54 and introduced into a tank 600. The second overhead distillate 502 is condensed, and a portion 510 of the condensed distillate is refluxed via line 522. Water is used as an extractant 524 and introduced at the top of the second distillation column 500. The bottom stream 506 is withdrawn from the bottom of the second distillation column 500 and recycled to a tank containing at least 1.5 wt% or more water to transfer the 1,1-dimethoxyethane contained therein. The organic phase 604 from the tank 600 is recycled to the lower portion of the second distillation column 500. The organic phase 602 is richer in methyl iodide compared to the second mixture and is preferably recycled to a position below the position of the side cut stream 504 for withdrawal, for example, below the collector tray 501.

[0146] In the phase-separated side cut stream 504, a relatively large amount of acetaldehyde is contained in the aqueous phase 602 rather than in the organic phase 604. The aqueous phase 602 is a suitable extraction mixture for the second distillation column 500 due to its water content, and a portion of it can be recycled as the extractant 524. This recycled portion may constitute the entire extractant or, in combination with an additional water source, may constitute a part of the extractant. In one embodiment, the aqueous phase 602 is not used as the extractant and may be provided with a closable valve or may be removed by the process.

[0147] Since it is at a relatively high temperature similar to the side stream 504 (second mixture), the aqueous phase 602 from the tank 600 should be cooled through a condenser (cooler) and then collected in the decanter 606. As the coolant, cooling water or process water can be used. The temperature of the aqueous phase 602 is preferably -5°C to 60°C, for example, 0°C to 30°C, or 3°C to 20°C.

[0148] There may be a residual amount of methyl iodide in the decanter 606, which can be separated by liquid-liquid separation and sent to the residual stream 610. The residual stream 610 contains more methyl iodide than in the aqueous phase 608. The residual stream 610 (methyl iodide-rich heavy phase, i.e., the lower phase) formed in the decanter 606 is recycled to the second distillation column 500 either by being combined with the organic phase 604 of the tank 600 or by being independently added under the collector plate 501 of the second distillation column 500. The residual stream 610 may bypass the second distillation column 500 and return to the reactor 100 together with the lower stream 506, but it is preferable to first reduce the impurities in the residual stream 610 before returning it to the reactor 100. To avoid phase problems, it is not recommended to return the residual stream 610 to the tank 600.

[0149] In the decanter 606, a liquid stream 608 is also formed. The liquid stream 608 contains the target acetaldehyde to be removed. The mass flow ratio of the liquid stream 608 to the residual stream 610 (liquid to residual) may be 1:500 to 1:0.5, for example, 1:400 to 1:1, or 1:375 to 1:10. Although it is a relatively small stream, the liquid stream 608 contains a useful amount of acetaldehyde. The mass composition of acetaldehyde in the liquid stream 608 may be greater than 2× (twice), for example, greater than 3×, or greater than 4×, based on the amount in the residual stream 610.

[0150] The liquid stream 608 is installed to reduce the amount of acetaldehyde (e.g., purged from the process), but there may also be processes that attempt to further retain methyl iodide and / or the extractant (water) used for the extraction mixture. Accordingly, the liquid stream 608 or a portion thereof may be further subjected to separation using a third distillation column 700. In such distillation, in the third distillation column 700, a third overhead stream 702 containing acetaldehyde in an amount of 1 to 99% by weight and methyl iodide in an amount of 0.1 to 30% by weight, and a bottom stream 704 containing the extractant as the main component in an amount of 10% by weight or more and methyl iodide in an amount of 1% by weight or less are produced (assuming that each stream has a total amount of 100% by weight including impurities). A portion of the bottom stream 704 can also be returned to the second distillation column 500 via line 524 and used as an extractant. In other embodiments, the bottom stream 704 may be removed or excluded from this process.

[0151] The third distillation column 700 may have an overhead pressure (absolute) of 100 to 500 kPa, for example, 115 to 375 kPa, and 125 to 250 kPa. To efficiently separate the overhead distillate, in the third distillation column 700 at atmospheric pressure, it has an overhead temperature of 10 to 90°C, for example, 15 to 80°C, or 20 to 60°C, and / or a bottom temperature of 70 to 170°C, for example, 80 to 160°C, or 90 to 150°C. The number of stages (plate number) in the third distillation column 700, for example, 1 to 50 stages, for example, 2 to 45 stages, or 3 to 30 stages, is a sufficient number for separation. The reflux ratio (reflux:distillate) of the third distillation column 700 is 1:20 to 20:1, for example, 1:15 to 15:1, or 5:1 to 10:1.

[0152] The third overhead stream 702, i.e., its distillate, contains more acetaldehyde than the second mixture and has a lower amount of methyl iodide than the second mixture. In one embodiment, the composition of the third overhead stream 702 includes the following: the mass composition of PRC (acetaldehyde) is 45 to 99 wt%, for example, 50 to 99 wt%, or 60 to 98 wt%, iodine 1 ~C 12 The mass composition of alkyl (methyl iodide) is 0.1 to 30 wt%, for example, 0.5 to 25 wt%, or 1 to 20 wt%, the mass composition of methyl acetate is 0.1 to 25 wt%, for example, 0.5 to 20 wt%, or 0.5 to 12 wt%, the mass composition of acetic acid is 0 to 5 wt%, for example, 0 to 1.5 wt%, or 0 to 1 wt%, the mass composition of water is 0 to 5 wt%, for example, 0 to 2.5 wt%, or 0.01 to 2 wt%, the mass composition of methanol is 0 to 2.5 wt%, for example, 0.01 to 2.1 wt%, or 0.05 to 2 wt%, the mass composition of acetal is 0 to 2.5 wt%, for example, 0.01 to 1.7 wt%, or 0.05 to 1.5 wt%, and the mass composition of dimethyl ether is 0 to 1.2 wt%, for example, 0.01 to 0.8 wt%, or 0.05 to 0.5 wt%. In one embodiment, the third overhead stream 702 has this ratio which is higher than the ratio (by weight) of methyl iodide to acetic acid in the feed to the third distillation column 700. In addition to or independently of this, the third overhead stream 702 may have this ratio which is higher than the ratio (by weight) of methyl iodide to methyl acetate in the feed to the third distillation column 700.

[0153] The third overhead stream 702 has a temperature of 15 to 100 °C, 20 to 90 °C, or 35 to 75 °C at atmospheric pressure. Using a conventional condenser / cooler 710, it is advisable to condense the third overhead stream 702 and cool it to a temperature of 60 °C or lower, for example, 45 °C or lower, or 30 °C or lower. A part of the condensate can be refluxed to the third distillation column via line 706.

[0154] In one embodiment, when the extractant 524 added to the second distillation column 500 is water, its bottom stream 704 can function as an extractant because it mainly contains water. In addition to its main component, the bottom stream 704 may contain methyl acetate, as well as small amounts of acetic acid, methanol, dimethyl ether, methyl iodide, and / or acetaldehyde. This makes it possible to use part or all of the bottom stream 704 as the extractant 524 to the second distillation column 500. The bottom stream 704 may have a mass composition of water of 85 to 99.99 wt%, for example, 90 to 99.98 wt%, or 92 to 99 wt%. Methyl acetate is retained in the lower part of the third distillation column 700 and withdrawn into the bottom stream 704. The mass composition of methyl acetate in the bottom stream 704 may be 0.1 to 15 wt%, for example, 0.5 to 10 wt%, or 0.7 to 7 wt%. When other components are present, they are generally in small amounts of 5 wt% or less each. In one embodiment, the bottom stream 704 may have the following composition: the mass composition of acetaldehyde is 1 wt% or less, for example, 0.5 wt% or less, or 0.3 wt% or less; the mass composition of methyl iodide is 1.5 wt% or less, for example, 1 wt% or less, or 0.5 wt% or less; the mass composition of acetic acid is 5 wt% or less, for example, 1 wt% or less, or 0.5 wt% or less; the mass composition of methanol is 1 wt% or less, for example, 0.5 wt% or less, or 0.1 wt% or less; and / or the mass composition of dimethyl ether is 0.1 wt% or less, for example, 0.01 wt% or less, or 0.001 wt% or less. The bottom stream 704 has a temperature of 65 to 165°C, for example, 70 to 120°C, or 85 to 105°C, at atmospheric pressure.

[0155] In FIG. 3, the liquid stream 608 is depicted as being distilled, but in other implementations, the second mixture and / or the aqueous stream 602 may be distilled in the third distillation column 700 without passing through either the tank 600 or the decanter 606.

[0156] The amount of methyl iodide in the third overhead stream 702 is small, but even if methyl iodide is separated from acetaldehyde by distillation alone, methyl iodide cannot be completely recovered. Furthermore, single distillation may result in a near-limit or incremental improvement in the recovery of methyl iodide, and thus a more effective treatment offers attractive benefits for auxiliary treatment. Extraction in the presence or absence of distillation can be used as an effective process for enhancing the recovery of methyl iodide. In one embodiment, a second extractive distillation column can be used to enhance the recovery of methyl iodide. As shown in FIG. 3, the third overhead stream 702, i.e., its distillate portion, is introduced via line 712 into a fourth distillation column 800 operated as extractive distillation using a water-containing extractive mixture. The fourth distillation column 800 is operated in such a way as to obtain a methyl iodide-rich overhead stream 802 and an acetaldehyde-rich stream 804, and furthermore its extractant is water. At least a part (including all) of the bottoms stream 804 is preferably recycled, i.e., returned, as an extractive mixture to the second distillation column 500.

[0157] In one embodiment, the fourth distillation column 800 separates an overhead stream 802 having a higher ratio of methyl iodide to acetaldehyde (by weight) than the ratio in the overhead (distillate) stream 702 of the feed. The overhead stream 802 can be taken out as the overhead distillate or a stream near the overhead of the fourth distillation column 80. To maintain recovery, it may be useful to direct the overhead stream 802, either directly or indirectly, towards the reactor 100. In some embodiments, a part of the overhead stream 802 is preferably introduced into the second distillation column 500, preferably its lower portion.

[0158] For extraction, it is sufficient to add the water - extraction mixture in a counter - current direction to the top of the fourth distillation column 800 via line 810. As described in U.S. Patent No. 8,859,810 (the entire content and disclosure of which are incorporated by reference), the water - extraction mixture may contain water, glycol, glycerol, high - boiling alcohols (including mixtures thereof). In the case of water extraction distillation, the water should preferably be at the same temperature as the extraction agent. The water is preferably added as heated or warmed water having the same temperature as the extraction agent, i.e., the water to be evaporated (i.e., steam). In one embodiment, the water - extraction mixture 810 has a temperature controlled or maintained within the range of 0 to 60 °C, for example, 10 to 50 °C, or 20 to 40 °C. The weight ratio of the flow rate of the water - extraction mixture 810 to the flow rate of the top stream 802, i.e., the distillate portion thereof [the former / the latter], may be in the range of 1:1000 to 10:1, for example, 1:500 to 5:1, 1:100 to 5:1, or 1:4 to 4:1.

[0159] In the fourth distillation column 800, the top stream 802 is cooled and / or condensed, for example, by passing through a condenser 812 (indirect condenser), and the first part of the condensate 806 is returned or refluxed to the distillation column 800, while the second part of the condensate (not shown) is recycled to the reactor 100 in FIG. 1. The bottom stream 804 is a liquid stream that can be withdrawn from the lower part of the distillation column 800 (including the bottom or near the bottom), and contains acetaldehyde and the extraction agent. Since it is acetaldehyde - rich, the bottom stream 804 is purged or discharged out of the system. A part of the bottom stream 804 may be used as an extraction agent in either the second distillation column 500 and / or the fourth distillation column 800. The top stream 802 has a weight ratio of methyl iodide to acetaldehyde that is greater than that of methyl iodide to acetaldehyde in the liquid stream 804.

[0160] The fourth distillation column 800 may have a top pressure (absolute) of 100 to 500 kPa, for example, 100 to 400 kPa, and 105 to 350 kPa. In order to efficiently separate the top distillate, in the fourth distillation column 800 at atmospheric pressure, it has a top temperature of 10 to 90 °C, for example, 15 to 80 °C, or 20 to 60 °C, and / or a bottom temperature of 70 to 170 °C, for example, 80 to 160 °C, or 90 to 150 °C. The number of stages (plate number) in the fourth distillation column 800 is, for example, 1 to 50 stages, for example, 2 to 45 stages, or 3 to 30 stages, which is a sufficient number for separation. The reflux ratio (reflux: distillate) of the fourth distillation column 800 is 1:20 to 20:1, for example, 1:15 to 15:1, or 5:1 to 10:1.

[0161] In one embodiment, the fourth distillation column 800 may have, for example, less than 50 theoretical plates (or trays), and the overhead stream 802 or its condensed portion may have the following composition: the mass composition of methyl iodide is 20 to 80 wt%, for example, 30 to 75 wt%, or 40 to 65 wt%; the mass composition of PRC is 0.1 to 70 wt%, for example, 0.5 to 65 wt%, or 1 to 20 wt%; the mass composition of methyl acetate is 0.01 to 15 wt%, for example, 0.05 to 10 wt%, or 0.1 to 10 wt%; the mass composition of acetic acid is 0 to 5 wt%, for example, 0 to 3 wt%, or 0 to 1 wt%; and the mass composition of water is 0 to 10 wt%, 0 to 8 wt%, or 0.01 to 5 wt%. The mass composition of other organic substances, such as dimethyl ether and / or methanol, in the overhead stream 802 is small, for example, 1 wt% or less or 0.5 wt% or less. Further, when the fourth distillation column 800 includes less than 50 plates, the bottom stream 804 may have the following composition: the mass composition of PRC is 1 to 90 wt%, for example, 5 to 80 wt%, or 10 to 50 wt%; the mass composition of water is 10 to 95 wt%, 15 to 90 wt%, or 20 to 85 wt%; the mass composition of methyl iodide is 0 to 2 wt%, for example, 0.01 to 1.5 wt%, or 0.05 to 1 wt%; the mass composition of methyl acetate is 0.01 to 15 wt%, for example, 0.05 to 10 wt%, or 0.1 to 10 wt%; the mass composition of acetic acid is 0 to 5 wt%, for example, 0 to 3 wt%, or 0 to 1 wt%; and the mass composition of organic substances (dimethyl ether and / or methanol) is 3 wt% or less, for example, 1 wt% or less, or 0.5 wt% or less. When discharging and / or purging the bottom liquid 804 from the process, the mass ratio of acetaldehyde to methyl iodide may be 20:1 to 2000:1, for example, 35:1 to 1800:1, or 50:1 to 1000:1.

[0162] In a continuous process for manufacturing acetic acid, the process stream may contain various components that are impurities not detailed above in either the vapor stream or the liquid stream. These impurities may have been generated by side reactions in the reactor. To avoid such impurities, it is desirable to suppress the generation of impurities or purge to prevent an increase. The various process streams may contain various amounts of formic acid, higher acids, and / or hydrogen iodide.

[0163] The separation process shown in FIG. 3 may have various configurations. This includes additional units that supplement or replace the third and / or fourth distillation columns. This enables the liquid stream 608 from the decanter 606 to bypass the third distillation column 700 and be fed into the fourth distillation column 800 or fed into one or more extraction tanks. Thus, if necessary, acetaldehyde can be extracted from the liquid stream 608 using water by one or more water extraction tanks equipped with mixers and settling tanks, or by the fourth distillation column 800. In other implementations, it may not be necessary to use the third and / or fourth distillation columns to purify the liquid stream 608.

[0164] FIG. 4 shows another embodiment providing a separation process for an auxiliary acetaldehyde removal process. In one embodiment, the feed stream 302 introduced into the second distillation column 500 contains a portion of the organic phase 404 from the overhead distillate condensed in FIG. 1. Thus, the feed stream 302 contains iodinated C 1 ~C 12Alkyl (mainly represented by methyl iodide) is present in an amount of 60 to 98% by weight, for example, 60 to 95% by weight, or 75 to 93% by weight, PRC (acetaldehyde) is present in an amount up to 5% by weight, for example, up to 3% by weight, or up to 0.5% by weight, and water is present in an amount up to 3% by weight, for example, up to 1% by weight, or up to 0.8% by weight. Further, the feed stream 302 further contains a low amount of methanol, but if it is necessary to adjust the amount of methanol, a part of the aqueous phase 402 can be included in its feed line. As described above, the extractant is added via line 524 above the collector tray 501. All of the vapors at the top of the column are collected, condensed, and refluxed to the second distillation column 500.

[0165] In this embodiment, the side cut stream 504 is condensed or cooled to -5°C to 60°C and fed directly to a decanter 606 for liquid-liquid separation (thus skipping the tank 600 in FIG. 3) to obtain a residual stream 610 (containing methyl iodide) and a liquid stream 608 (containing acetaldehyde). The mass flow ratio of the liquid stream 608 to the residual stream 610 (liquid to residual) may be 1:500 to 1:0.5, for example, 1:400 to 1:1, or 1:375 to 1:10. The side cut stream 504 may have a composition suitable for phase separation. In one embodiment, the composition of the side cut stream 504 may be as follows: the mass composition of PRC is 0.1 to 90% by weight, for example, 0.2 to 65% by weight, or 0.5 to 50% by weight, iodinated C 1 ~C 12The mass composition of alkyl (methyl iodide) is 0.5 to 95% by weight, for example, 1 to 95% by weight, 5 to 90% by weight, or 10 to 60% by weight, the mass composition of methyl acetate is 0.1 to 25% by weight, for example, 0.5 to 20% by weight, or 0.5 to 10% by weight, the mass composition of acetic acid is 0 to 10% by weight, for example, 0.01 to 5% by weight, or 0.05 to 1% by weight, the mass composition of water is 0.1 to 20% by weight, for example, 0.5 to 15% by weight, or 0.5 to 8% by weight, the mass composition of methanol is 0 to 2.5% by weight, for example, 0.01 to 2.1% by weight, or 0.05 to 2% by weight, the mass composition of acetal is 0 to 2.5% by weight, for example, 0.01 to 1.7% by weight, or 0.05 to 1.5% by weight, and the mass composition of dimethyl ether is 0 to 1.2% by weight, for example, 0.01 to 0.8% by weight, or 0.05 to 0.5% by weight. The process as shown in Figure 4 further concentrates the PRC without increasing a large amount of acetal.

[0166] As shown in Figure 4, it is also possible to combine the residual stream 610 with the bottom stream 506 from the second distillation column 500. In some embodiments, the residual stream 610 may be fed to the bottom portion of the second distillation column 500. Acetic acid as a miscible solvent is fed to the bottom portion of the second distillation column 500 via the feed line 507, but in some embodiments, it may be fed below the feed position of the feed stream 302. Although not shown in Figure 4, there may be a miscible solvent fed to the second distillation column 500.

[0167] Once the liquid stream 608 is withdrawn from the decanter 606, it is fed to a third distillation column 700. Although a relatively small stream, the liquid stream 608 contains a useful amount of acetaldehyde. The mass composition of acetaldehyde in the liquid stream 608 may be greater than 2×, for example greater than 3×, or greater than 4×, based on the amount in the residual stream 610. As described above, the third distillation column 700 is operated to produce a third overhead stream 702 containing acetaldehyde in an amount of 1 to 99 wt% and methyl iodide in an amount of 0.1 to 30 wt%, and a bottom stream 704 containing an extractant as a main component in an amount of 10 wt% or more and methyl iodide in an amount of 1 wt% or less (assuming each stream totals 100 wt% including impurities). A portion of the bottom stream 704 can also be returned to the second distillation column 500 and used as an extractant. In other embodiments, the bottom stream 704 may be removed or excluded from this process.

[0168] The overhead stream 704 or its distillate contains a mass composition of acetaldehyde greater than that of the second mixture and a mass composition of methyl iodide less than that of the second mixture. In one embodiment, the composition of the third overhead stream 702 includes the following: the mass composition of PRC (acetaldehyde) is 45 to 99 wt%, for example 50 to 99 wt%, or 60 to 98 wt%, iodized C 1 ~C 12The mass composition of alkyl (methyl iodide) is 0.1 to 30% by weight, for example, 0.5 to 25% by weight, or 1 to 20% by weight; the mass composition of methyl acetate is 0.1 to 25% by weight, for example, 0.5 to 20% by weight, or 0.5 to 12% by weight; the mass composition of acetic acid is 0 to 5% by weight, for example, 0 to 1.5% by weight, or 0 to 1% by weight; the mass composition of water is 0 to 5% by weight, for example, 0 to 2.5% by weight, or 0.01 to 2% by weight; the mass composition of methanol is 0 to 2.5% by weight, for example, 0.01 to 2.1% by weight, or 0.05 to 2% by weight; the mass composition of acetal is 0 to 2.5% by weight, for example, 0.01 to 1.7% by weight, or 0.05 to 1.5% by weight; and the mass composition of dimethyl ether is 0 to 1.2% by weight, for example, 0.01 to 0.8% by weight, or 0.05 to 0.5% by weight. In one embodiment, the third overhead stream 702 has a ratio (by weight) of methyl iodide to acetic acid that is higher than the ratio in the feed to the third distillation column 700. Additionally or independently, the third overhead stream 702 may have a ratio (by weight) of methyl iodide to methyl acetate that is higher than the ratio in the feed to the third distillation column 700. Its bottom stream 704 may have a mass composition of water of 85 to 99.99% by weight, for example, 90 to 99.98% by weight, or 92 to 99% by weight. In one embodiment, the bottom stream 704 may be removed from the process or at least a portion thereof may be returned to the second distillation column 500 as an extractant.

[0169] Similar to the previous drawings, in FIG. 4, the third overhead stream 702 or its distillate portion is processed by introducing this stream into a fourth distillation column 800 operated as extractive distillation using a water-containing extractive mixture. As described above, the fourth distillation column 800 is operated in a manner using a water - extract mixture via line 812 to obtain a methyl iodide - rich fourth overhead stream 802, an acetaldehyde - rich aqueous bottom stream 804, and an extractant that is water. At least a portion (including all) of the aqueous bottom stream 804 is preferably recycled or returned to the second distillation column 500 as an extract mixture.

[0170] The materials of each member or unit associated with the distillation system (columns, valves, condensers, receivers, pumps, reboilers, and internal parts, as well as the various lines connecting this distillation system respectively) may be made of suitable substances, such as glass, metal, ceramic, or combinations thereof, and are not particularly limited to any specific one. In the present invention, the substances of the aforementioned distillation system and various lines are transition metals or transition metal-based alloys, such as iron alloys, such as stainless steel, nickel or nickel alloys, zirconium or their zirconium alloys, titanium or their titanium alloys, or aluminum alloys. Suitable iron-based alloys include those containing iron as the main component, such as stainless steel further containing chromium, nickel, molybdenum, and others. Suitable nickel-based alloys include those containing nickel as the main component and one or more of chromium, iron, cobalt, molybdenum, tungsten, manganese, and others, such as HASTELLOY (trademark) and INCONEL (trademark). Corrosion-resistant metals are particularly suitable as materials for the distillation system and various lines.

Examples

[0171] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by these examples. "MeI" represents methyl iodide, "MA" represents methyl acetate, "MeOH" represents methanol, "DME" represents dimethyl ether, "HOAc" represents acetic acid, and "AcH" represents acetaldehyde.

[0172] Example 1 The first mixture was obtained from the organic phase of the top decanter of the light end column using a semi-empirical simulator. The first mixture contained methanol (1128 ppm). Most of the first mixture was methyl iodide and methyl acetate, but the first mixture also contained acetic acid (1.83 wt%), acetaldehyde (0.186 wt%), and water (0.7 wt%). The first mixture was fed to a distillation column having 45 actual plates. The temperature at the bottom part of the distillation column was 46 °C. The column was operated at a pressure of 1 atm. The column had a collector tray for withdrawing a side cut stream. The top stream was withdrawn, condensed, and refluxed. An extraction solvent (water) was added to the upper part of the distillation. To further remove acetaldehyde, a second mixture was withdrawn from the side cut stream.

[0173] At the bottom part of the distillation column, the bottom stream was withdrawn. The distillation was continued for 100 hours and sampled periodically to examine the changes in the bottom stream. The acetal shown in Table 3 is 1,1-dimethoxyethane.

[0174]

Table 3

[0175] In Example 1, the distillation column was operated under operating condition (i) and showed high efficiency, resulting in a bottom stream containing a very low amount of 1,1-dimethoxyethane. Thus, acetaldehyde was effectively removed.

[0176] In addition to operating condition (i), since there was more acetic acid than in the first mixture, Example 1 also conformed to operating condition (iii).

[0177] Example 2 Using the same distillation column as in Example 1, a first mixture containing a very low amount of methanol (33 ppm) was used. In addition to methyl iodide and methyl acetate, the first mixture further contained acetic acid (1.83% by weight), acetaldehyde (0.196% by weight), and water (0.31% by weight).

[0178] At the lower part of the distillation column, the lower stream was withdrawn. The distillation was continued for 100 hours, and the changes in its composition are shown in Table 4. The acetal shown in Table 4 is 1,1-dimethoxyethane.

[0179]

Table 4

[0180] The distillation column in Example 2 was operated under operating condition (i), but showed high efficiency in the production of the lower stream, and 1,1-dimethoxyethane could not be detected. The lower stream was measured for 1,1-dimethoxyethane, and its detection limit was 1 ppm. Acetal was formed, but acetaldehyde was effectively removed.

[0181] Comparative Example A For the purpose of comparison with a first mixture containing a large amount of methanol, the same distillation column as in Example 1 was used. The first mixture contained methanol with a mass composition of 2.52% by weight. In addition to methyl iodide and methyl acetate, the first mixture further contained acetic acid with a mass composition of 1.83% by weight, acetaldehyde with a mass composition of 0.2% by weight, and water with a mass composition of 0.71% by weight.

[0182] Despite operating under conditions (i) and (iii), in this distillation, the mass composition of acetal in the lower stream could not be maintained below 0.03% by weight. As shown in Table 5, there was a decrease in the separation efficiency of acetaldehyde.

[0183]

Table 5

[0184] Although the present invention has been described in detail, modifications within the spirit and scope of the present invention will be readily apparent to those skilled in the art. In view of the foregoing considerations, the knowledge related to the art, and the references discussed above in connection with the "Background Art" and "Modes for Carrying Out the Invention", all of their disclosures are hereby incorporated by reference and made a part of this specification. In addition, it should be understood that the aspects of the present invention and the parts of various embodiments, as well as the various features recited in the following and / or appended claims, can be combined or interchanged either wholly or partially in any combination. In the description of the various embodiments heretofore, those embodiments related to another embodiment may be appropriately combined with other embodiments that would be evaluated by those skilled in the art. Furthermore, those skilled in the art will recognize that the foregoing description is by way of example only and is not intended to limit the present invention.

[0185] Embodiment As used hereinafter, various references to a series of embodiments should be understood as referring to those embodiments disjunctively (e.g., "Embodiments 1 to 4" should be understood as "Embodiment 1, 2, 3, or 4").

[0186] [Embodiment 1] Acetaldehyde, one or more iodinated C 1 ~C 12A method for separating acetaldehyde from a first mixture containing alkyl, water, and methanol, the method comprising distilling the first mixture in a distillation column to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottoms stream, wherein withdrawing either the overhead stream or the side cut stream as a second mixture; separating acetaldehyde from the second mixture; and operating the distillation column under at least one of the following conditions (i)-(iii): (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the bottoms stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the bottoms stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis, to control the mass composition of 1,1-dimethoxyethane in the bottoms stream to 0.03 wt% or less, the method wherein the mass composition of methanol in the first mixture is 2 wt% or less.

[0187] [Embodiment 2] The method according to Embodiment 1, wherein the mass composition of methanol in the first mixture is 1 wt% or less.

[0188] [Embodiment 3] The method according to Embodiment 1 or 2, wherein the mass composition of methanol in the first mixture is 0.5 wt% or less.

[0189] [Embodiment 4] The method according to Embodiments 1 to 3, wherein the pressure in the distillation column is 0.1 to 0.7 MPa.

[0190] [Embodiment 5] The method according to Embodiments 1 to 4, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the bottoms stream to the overhead stream is 100:1 to 10:1.

[0191] [Embodiment 6] The method according to Embodiments 1 to 5, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the lower stream to the side cut stream is from 100:1 to 10:1.

[0192] [Embodiment 7] The method according to Embodiments 1 to 6, wherein the second mixture includes a part of the overhead stream and a part of the side cut.

[0193] [Embodiment 8] The method according to Embodiments 1 to 7, wherein the step of separating acetaldehyde from the second mixture further includes feeding at least a part of the second mixture into a tank under conditions sufficient to phase-separate the second mixture into an aqueous phase and an organic phase.

[0194] [Embodiment 9] The method according to Embodiment 8, wherein the organic phase is fed to the lower part of the distillation column under at least one of conditions (i) to (iii).

[0195] [Embodiment 10] The method according to Embodiment 8 or 9, wherein the organic phase contains methanol, and the total mass composition of methanol in the organic phase and the first mixture is 2% by weight or less.

[0196] [Embodiment 11] The method according to Embodiments 1 to 10, wherein the distillation column for distilling the first mixture is an extractive distillation column, and further includes adding an extractant to the upper part of the distillation column.

[0197] [Embodiment 12] The method according to Embodiments 1 to 11, wherein under condition (ii), the mass composition of water in the lower stream is 0.6% by weight or more.

[0198] [Embodiment 13] The method according to Embodiments 1 to 12, wherein under condition (iii), the mass composition of acetic acid in the lower stream is 3% by weight or less.

[0199] [Embodiment 14] The method according to any one of Embodiments 1 to 13, wherein the distillation column has more than 10 trays.

[0200] [Embodiment 15] The method according to any one of Embodiments 1 to 14, wherein the reflux ratio of the distillation column is from 1:20 to 20:1.

[0201] [Embodiment 16] The first mixture contains acetaldehyde in a mass composition of 0.01 to 30% by weight, one or more C-iodides 1 ~C 12 alkyls in a mass composition of 0.1 to 90% by weight, water in a mass composition of 0.1 to 90% by weight, and methanol in a mass composition of 0.001 to 2% by weight, based on the total weight of the first mixture, according to the method of any one of Embodiments 1 to 15.

[0202] [Embodiment 17] The method according to any one of Embodiments 1 to 16, wherein the mass composition of methanol in the first mixture is higher than the mass composition of dimethyl ether.

[0203] [Embodiment 18] The method according to any one of Embodiments 1 to 17, wherein the distillation column is operated under conditions to prevent the formation of methanol.

[0204] [Embodiment 19] Acetaldehyde, one or more C-iodides 1 ~C 12 A method for separating acetaldehyde from a first mixture containing acetaldehyde, one or more C-iodides 1 ~C 12In an organic stream containing alkyl, a step of separation, and a distillation column are operated under at least one of the following conditions (i) to (iii): (i) the temperature in the lower part of the distillation column is 40 °C or higher; (ii) the mass composition of water in the lower stream is 0.3 wt% or higher; or (iii) the mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis, to control the mass composition of 1,1-dimethoxyethane in the lower stream to 0.03 wt% or less, and the mass composition of methanol in the first mixture is 2 wt% or less, a method.

[0205] [Embodiment 20] The method according to embodiment 19, wherein the distillation column for distilling the first mixture is an extractive distillation step, and further comprises adding an extractant to the upper part of the distillation column. The description of the claims at the time of filing is shown below. [Claim 1] Acetaldehyde, one or more iodinated C 1 ~C 12 A method for separating acetaldehyde from a first mixture containing acetaldehyde, one or more iodinated C~C alkyls, water, and methanol, the method comprising: Distilling the first mixture in a distillation column to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottom stream, wherein either the overhead stream or the side cut stream is withdrawn as a second mixture; Separating acetaldehyde from the second mixture; and Operating the distillation column under the following conditions (i) to (iii): (i) The temperature in the lower part of the distillation column is 40 °C or higher; (ii) The mass composition of water in the bottom stream is 0.3 wt% or higher; or (iii) The mass composition of acetic acid in the bottom stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis; By operating under at least one of the following conditions, controlling the mass composition of 1,1-dimethoxyethane in the lower stream to 0.03 wt% or less comprising wherein the mass composition of the methanol in the first mixture is 2 wt% or less Method. [Claim 2] The method according to claim 1, wherein the mass composition of the methanol in the first mixture is 1 wt% or less. [Claim 3] The method according to claim 1, wherein the mass composition of the methanol in the first mixture is 0.5 wt% or less. [Claim 4] The method according to claim 1, wherein the pressure in the distillation column is 0.1 to 0.7 MPa. [Claim 5] The method according to claim 1, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the lower stream to the overhead stream is 100:1 to 10:1. [Claim 6] The method according to claim 1, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the lower stream to the side cut stream is 100:1 to 10:1. [Claim 7] The method according to claim 1, wherein the second mixture comprises a part of the overhead stream and a part of the side cut. [Claim 8] The method according to claim 1, wherein the step of separating acetaldehyde from the second mixture further comprises feeding at least a part of the second mixture to a tank under conditions sufficient to phase-separate the second mixture into an aqueous phase and an organic phase. [Claim 9] The method according to claim 8, wherein the organic phase is fed to the lower part of the distillation column under at least one of conditions (i) to (iii). [Claim 10] The method according to claim 8, wherein the organic phase contains methanol, and the total mass composition of methanol in the organic phase and the first mixture is 2 wt% or less. [Claim 11] The distillation column for distilling the first mixture is an extractive distillation step, and further includes adding an extractant to an upper portion of the distillation column, the method according to claim 1. [Claim 12] The method according to claim 1, wherein, under condition (ii), a mass composition of water in the lower stream is 0.6% by weight or more. [Claim 13] The method according to claim 1, wherein, under condition (iii), a mass composition of acetic acid in the lower stream is 3% by weight or less. [Claim 14] The method according to claim 1, wherein the distillation column has more than 10 trays. [Claim 15] The method according to claim 1, wherein a reflux ratio of the distillation column is from 1:20 to 20:1. [Claim 16] The first mixture comprises, based on a total weight of the first mixture, acetaldehyde in a mass composition of 0.01 to 30% by weight, one or more C 1 ~C 12 alkyl iodides in a mass composition of 0.1 to 90% by weight, water in a mass composition of 0.1 to 90% by weight, and methanol in a mass composition of 0.001 to 2% by weight, the method according to claim 1. [Claim 17] The method according to claim 1, wherein a mass composition of the methanol in the first mixture is more than a mass composition of the dimethyl ether. [Claim 18] The method according to claim 1, wherein the distillation column is operated under conditions for preventing formation of methanol. [Claim 19] A method for separating acetaldehyde from a first mixture comprising acetaldehyde, one or more C 1 ~C 12 alkyl iodides, water, and methanol, the method comprising In a distillation column, distill the first mixture to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottoms stream, wherein the side cut stream is withdrawn as a second mixture; separating the second mixture into an aqueous stream containing acetaldehyde or an organic stream containing one or more C 1 ~C 12 alkyls, and operating the distillation column under at least one of the following conditions (i) to (iii): (i) The temperature in the lower part of the distillation column is 40 °C or higher; (ii) The mass composition of water in the bottoms stream is 0.3 wt% or more; or (iii) The mass composition of acetic acid in the bottoms stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis; controlling the mass composition of 1,1-dimethoxyethane in the bottoms stream to 0.03 wt% or less by operating under at least one of the above; including wherein the mass composition of methanol in the first mixture is 2 wt% or less, method. [Claim 20] The method according to claim 19, wherein the distillation column for distilling the first mixture is an extractive distillation column, and further includes adding an extractant to the upper part of the distillation column.

Claims

1. Acetaldehyde, one or more iodinated C １ -C １２ A method for separating acetaldehyde from a first mixture comprising acetaldehyde, one or more C1-C4 alkyl iodides, water, and methanol, the method comprising In a distillation column, distilling the first mixture to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottoms stream, wherein either the overhead stream or the side cut stream is withdrawn as a second mixture; separating acetaldehyde from the second mixture; and operating the distillation column according to the following condition (i): (i) The temperature in the lower part of the distillation column is 40 °C or higher; and optionally according to the following conditions (ii) and (iii): (ii) The mass composition of water in the bottoms stream is 0.3 wt% or more; and (iii) The mass composition of acetic acid in the bottoms stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis; by operating according to at least one of the above to control the mass composition of 1,1-dimethoxyethane in the bottoms stream to 0.03 wt% or less comprising wherein the mass composition of methanol in the first mixture is 2 wt% or less. method.

2. The method according to claim 1, wherein the mass composition of methanol in the first mixture is 1 wt% or less.

3. The method according to claim 1, wherein the mass composition of methanol in the first mixture is 0.5 wt% or less.

4. The method according to claim 1, wherein the pressure in the distillation column is 0.1 - 0.7 MPa.

5. The method according to claim 1, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the bottoms stream to the overhead stream is 100:1 to 10:

1.

6. The method according to claim 1, wherein the weight ratio of the mass composition of 1,1-dimethoxyethane in the bottoms stream to the side cut stream is 100:1 to 10:

1.

7. The method according to claim 1, wherein the second mixture comprises a portion of the overhead stream and a portion of the side cut.

8. The method according to claim 1, wherein the step of separating acetaldehyde from the second mixture further comprises feeding at least a portion of the second mixture to a tank under conditions sufficient to phase separate the second mixture into an aqueous phase and an organic phase.

9. The method according to claim 8, wherein the organic phase is fed to the lower part of the distillation column.

10. The method according to claim 8, wherein the organic phase contains methanol, and the total mass composition of methanol in the organic phase and the first mixture is 2% by weight or less.

11. The method according to claim 1, wherein the distillation column for distilling the first mixture is an extractive distillation step, and further comprises adding an extractant to an upper portion of the distillation column.

12. The method according to claim 1, wherein under condition (ii), the mass composition of water in the lower stream is 0.6% by weight or more.

13. The method according to claim 1, wherein under condition (iii), the mass composition of acetic acid in the lower stream is 3% by weight or less.

14. The method according to claim 1, wherein the distillation column has more than 10 stages.

15. The method according to claim 1, wherein the reflux ratio of the distillation column is from 1:20 to 20:

1.

16. The first mixture contains acetaldehyde in a mass composition of 0.01 to 30% by weight, one or more iodinated C １ -C １２ alkyls in a mass composition of 0.1 to 90% by weight, water in a mass composition of 0.1 to 90% by weight, and methanol in a mass composition of 0.001 to 2% by weight, according to the method of claim 1.

17. The method according to claim 1, wherein the mass composition of methanol in the first mixture is greater than the mass composition of dimethyl ether in the first mixture.

18. The method according to claim 1, wherein the distillation column is operated under conditions for preventing the production of methanol.

19. Acetaldehyde, one or more iodinated C １ -C １２ A method for separating acetaldehyde from a first mixture comprising acetaldehyde, one or more C to C alkyl iodides, water, and methanol, the method comprising Distilling the first mixture in a distillation column to form at least two streams selected from the group consisting of an overhead stream, a side cut stream, and a bottom stream, wherein withdrawing the side cut stream as a second mixture; separating the second mixture into an aqueous stream containing acetaldehyde or an organic stream containing one or more C １ -C １２ alkyls, and Operating the distillation column according to the following condition (i): (i) The temperature in the lower portion of the distillation column is 40 °C or higher; and optionally according to the following conditions (ii) and (iii): (ii) The mass composition of water in the lower stream is 0.3% by weight or more; and (iii) The mass composition of acetic acid in the lower stream is greater than the mass composition of acetic acid in the first mixture on a weight percent basis; Controlling the mass composition of 1,1 - dimethoxyethane in the lower stream to 0.03% by weight or less by operating according to at least one of the above, comprising wherein the mass composition of methanol in the first mixture is 2% by weight or less. method.

20. The method according to claim 19, wherein the distillation column for distilling the first mixture is an extractive distillation step, and further comprises adding an extractant to an upper portion of the distillation column.

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