A production process of acetic acid according to the present invention inhibits concentration of hydrogen iodide and improves a liquid-liquid separation of an overhead from a distillation column. acetic acid is produced by distilling a mixture containing hydrogen iodide, water, acetic acid and methyl acetate in a first distillation column (3) to form an overhead and a side cut stream or bottom stream containing acetic acid, cooling and condensing the overhead in a condenser (C3) to form separated upper and lower phases in a decanter (4). According to this process, a zone having a high water concentration is formed in the distillation column above the feed position of the mixture by feeding a mixture having a water concentration of not less than an effective amount to not more than 5% by weight (e.g., 0.5 to 4.5% by weight) and a methyl acetate concentration of 0.5 to 9% by weight (e.g., 0.5 to 8% by weight) as the mixture to the distillation column and distilling the mixture. In the zone having a high water concentration, hydrogen iodide is allowed to react with methyl acetate to produce methyl iodide and acetic acid.
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0. 16. A process for producing acetic acid and for improving a liquid-liquid separation of a condensate while reducing a concentration of hydrogen iodide in an overhead and a side cut stream, comprising:
flash evaporation or flash distillation of a reaction mixture in a flasher, wherein the reaction mixture is separated in the flasher into a volatile phase component and a low-volatile phase component;
distilling a mixture containing hydrogen iodide, water, methyl iodide, acetic acid, and methyl acetate in a first distillation column to form the overhead containing a lower boiling point component, the mixture that is distilled in the first distillation column comprises said volatile phase component;
condensing the overhead from the first distillation column to form the condensate containing separated liquid phases of an aqueous phase and an organic phase;
recycling at least one selected from the aqueous phase and the organic phase to the first distillation column for reflux; and
distilling the side cut stream in a second distillation column;
wherein the mixture comprising the volatile phase component contains an effective amount of water in a concentration of not more than 5% by weight and methyl acetate in a concentration of 0.5 to 9% by weight, and is separated, in the distillation step in the first distillation column, into the overhead containing methyl iodide, the side cut stream, and a bottom stream containing acetic acid;
wherein the overhead is withdrawn from a top of the first distillation column, the bottom stream is withdrawn from a bottom of the first distillation column, and the side cut stream is withdrawn from a side of the first distillation column and is fed to the second distillation column;
wherein the overhead from the first distillation column has a concentration of hydrogen iodide of 7 ppm to 240 ppm;
wherein the side cut stream has a concentration of hydrogen iodide of 1-350 ppm, water of 0.3 to 5% by weight, and methyl acetate of 0.1 to 3% by weight;
wherein the aqueous phase of said condensate comprises: a concentration of water of 50-85% by weight; a concentration of acetic acid of 10-40% by weight; and a concentration of hydrogen iodide of 10-1000 ppm; and
wherein the organic phase of said condensate comprises: a concentration of methyl iodide of 75-98% by weight; a concentration of acetic acid of 1-10% by weight; a concentration of water of not more than 1% by weight; and a concentration of hydrogen iodide of not more than 70 ppm.
0. 1. A process for producing acetic acid, comprising:
distilling a mixture containing hydrogen iodide, water, methyl iodide, acetic acid, and methyl acetate to form an overhead containing a lower boiling point component, and
condensing the overhead to form separated liquid phases,
wherein the mixture contains an effective amount of water in a concentration of not more than 5% by weight and methyl acetate in a concentration of 0.5 to 9% by weight, and is separated, in the distillation step, into the overhead containing methyl iodide and a side cut stream or bottom stream containing acetic acid.
0. 2. The process according to
0. 3. The process according to
0. 4. The process according to
0. 5. The process according to
0. 6. The process according to
in the zone having the high water concentration, hydrogen iodide is allowed to react with methyl acetate for producing methyl iodide and acetic acid, and
the distillation provides the overhead containing the resulting methyl iodide.
0. 7. The process for producing acetic acid according to
methanol is allowed to continuously react with carbon monoxide by using a catalyst containing a group 8 metal of the Periodic Table, an ionic iodide, and methyl iodide in the presence of water,
the reaction product is separated into a low-volatile phase component and a volatile phase component by a flash distillation,
the volatile phase component as the mixture is distilled to form the overhead containing methyl iodide and the side cut stream or bottom stream containing acetic acid, and
the overhead is condensed to form an aqueous phase and an organic phase,
and wherein the volatile phase component is distilled while being adjusted to a water concentration of an effective amount and not more than 5% by weight and a methyl acetate concentration of 0.5 to 9% by weight in a distillation atmosphere of the volatile phase component in terms of a condensate or liquid form.
0. 8. The process according to
0. 9. The process according to
0. 10. The process according to
0. 11. The process according to
0. 12. The process according to
0. 13. A method for improving a liquid-liquid separation of a condensate while reducing a concentration of hydrogen iodide in an overhead and a side cut stream, comprising:
distilling a mixture containing hydrogen iodide, water, methyl iodide, acetic acid, and methyl acetate to form an overhead containing a lower boiling point component, and
condensing the overhead to give a condensate containing separated liquid phases,
wherein the mixture contains an effective amount of water in a concentration of not more than 5% by weight and methyl acetate in a concentration of 0.5 to 9% by weight.
0. 14. The method according to
0. 15. The method according to
0. 17. The process according to claim 16, wherein the mixture has a methyl acetate concentration of 0.07 to 1.2 mol/L and a water concentration of 0.28 to 2.8 mol/L, and is distilled continuously.
0. 18. The process according to claim 16, wherein the mixture contains 0.5 to 4.5% by weight of water and 0.5 to 8% by weight of methyl acetate, and is subjected to the distillation step.
0. 19. The process according to claim 16, wherein the mixture further contains dimethyl ether.
0. 20. The process according to claim 16, wherein the mixture is fed to a distillation column from an intermediate or lower position of the distillation column in height.
0. 21. The process according to claim 16, wherein a zone having a high water concentration is formed inside the first distillation column at a position upper than a position at which the mixture containing the volatile phase component is fed to the first distillation column, wherein
in the zone having the high water concentration, hydrogen iodide is allowed to react with methyl acetate for producing methyl iodide and acetic acid,
the distillation provides the overhead containing the resulting methyl iodide, and
the material of the first distillation column comprises a nickel-based alloy.
0. 22. The process for producing acetic acid according to claim 16, wherein
methanol is allowed to continuously react with carbon monoxide by using a catalyst containing a group 8 metal of the Periodic Table, an ionic iodide, and methyl iodide in the presence of water,
the reaction product is separated into a low-volatile phase component and a volatile phase component by a flash distillation,
the volatile phase component as the mixture is distilled to form the overhead containing methyl iodide and the side cut stream or bottom stream containing acetic acid, and
the overhead is condensed to form an aqueous phase and an organic phase,
and wherein the volatile phase component is distilled while being adjusted to a water concentration of an effective amount and not more than 5% by weight and a methyl acetate concentration of 0.5 to 9% by weight in a distillation atmosphere of the volatile phase component in terms of a condensate or liquid form.
0. 23. The process according to claim 16, wherein at least one member selected from the group consisting of methyl acetate, methanol and dimethyl ether, and if necessary water, is added to the volatile phase component as the mixture or a distillation atmosphere thereof as the mixture to adjust the concentrations of water and methyl acetate, and the resulting volatile phase component is distilled.
0. 24. The process according to claim 16, wherein a distillation atmosphere of a volatile phase component is formed in the distillation column at a height equal to or upper than a feed site of the volatile phase component.
0. 25. The process according to claim 16, wherein the mixture contains 1 to 4.3% by weight of water and 0.8 to 7.5% by weight of methyl acetate, and is subjected to the distillation step.
0. 26. The process according to claim 16, wherein the mixture has a hydrogen iodide concentration of 100 to 10000 ppm, and is subjected to a distillation to form the side cut stream having a hydrogen iodide concentration of 1 to 350 ppm.
0. 27. The process according to claim 16, wherein the organic phase has a methyl acetate concentration of 1 to 15% by weight, and the aqueous phase has a methyl acetate concentration of 0.4 to 8% by weight.
0. 28. The process according to claim 16, wherein the side cut stream is withdrawn from a site above the position of the feed line connected to the first distillation column.
0. 29. The process according to claim 16, wherein at least one portion of the aqueous phase and/or the organic phase is fed to the impurity-removing system to remove the impurity.
0. 30. The process according to claim 16, wherein the reflux site of the condensate in the first distillation column is located or positioned above a zone having a high hydrogen iodide concentration.
0. 31. The process according to claim 16, wherein a noncondensed component obtained when the overhead from the first distillation column is condensed is fed to a scrubber system to collect a useful component.
0. 32. The process according to claim 16, wherein the mixture comprising the volatile phase component contains an effective amount of water in a concentration of not more than 5% by weight, methyl acetate in a concentration of 0.5 to 9% by weight and acetic acid in a concentration of 35 to 75% by weight.
0. 33. The process according to claim 16, wherein the aqueous phase of the condensate comprises a concentration of hydrogen iodide of 20 to 710 ppm, and wherein the organic phase of the condensate comprises a concentration of hydrogen iodide of not more than 50 ppm.
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CH3COOCH3+H2O↔CH3OH+CH3COOH (2)
CH3OH+HI↔CH3I+H2O (3)
Further, usually, since a reflux site of the condensate (liquid reflux mixture) in the first distillation column 3 is located in an upper part (or site) of the first distillation column 3 and a distribution of the water concentration (distribution of the water concentration containing a water concentration of about 5%) is formed inside the first distillation column 3, the feed site of the condensate (liquid reflux mixture) fed from the decanter 4 to the first distillation column 3 through a reflux line 42 is located or positioned above a zone having a high water concentration and a high hydrogen iodide concentration. Specifically, the zone having high water and hydrogen iodide concentrations is formed between the feed site of the volatile component and the feed site of the liquid reflux mixture. Moreover, when the water concentration is less than 5% by weight in the head of the distillation column 3, a zone having a high hydrogen iodide concentration is not formed in the column 3. Thus, water or methyl iodide in the condensate (liquid reflux mixture) can effectively disturb the production of hydrogen iodide as a by-product in the zone having high water and hydrogen iodide concentrations.
Furthermore, even if the low-boiling stream (overhead) from the distillation column 3 is contaminated with unreacted hydrogen iodide, having a low boiling point, the unreacted hydrogen iodide can be condensed in an aqueous phase in the decanter 4 by condensing the low-boiling stream (overhead) in the condenser C3, so that the crude acetic acid stream as a side cut stream can be prevented from contamination with hydrogen iodide.
The feed amounts (supplies) of water and/or methyl acetate through the water supply line 34a and the methyl acetate supply line 35a can be calculated based on an analysis of the condensate condensed in the condenser C2 or the volatile phase component (or volatile phase) in the line 22 or 23, in particular, the water and methyl acetate concentration, and a flow rate of the volatile phase component (or volatile phase). The calculated feed amount (flow rate) of water and that of methyl acetate are fed to the line 34a and the line 35a, respectively, and thus the water and methyl acetate concentrations in the column can be adjusted to predetermined concentrations.
A portion of the condensate condensed in the condenser C3 is recycled to the reactor 1 through a recycle line 41, and another portion of the condensate is recycled to the first distillation column 3 through a reflux line 42 for reflux. More specifically, in the decanter 4, the condensate of the first overhead cooled and condensed in the condenser C3 is separated into an aqueous phase (upper phase or light phase) and an organic phase (lower phase or heavy phase); wherein the aqueous phase contains water, acetic acid, methyl acetate, hydrogen iodide, acetaldehyde, and others, and the organic phase contains methyl iodide, methyl acetate, and others. The aqueous phase (upper phase) is fed to the first distillation column 3 through the reflux line 42 for reflux. The organic phase (lower phase) is recycled to the reactor 1 through the recycle line 41.
The methyl acetate concentration is greatly involved in or engaged with the liquid-liquid separation of the condensate. In other words, since methyl acetate is miscible with both aqueous phase and organic phase, a high concentration of methyl acetate sometimes produces the uniform (or homogenous) condensate without liquid-liquid separation. The formation of the uniform or homogenous condensate fails to reuse useful methyl iodide as a catalyst system, and requires a further purification means in order to separate and collect acetic acid. In contrast, according to the present invention, as described above, since the volatile phase component (distillation system) containing a predetermined concentration of water and that of methyl acetate is distilled in the first distillation column 3 and the overhead is condensed, the aqueous phase and the organic phase can be separated clearly. Thus the present invention advantageously allows collection or reuse of a useful component and separation and removal of an impurity component.
The side cut stream (crude acetic acid stream) from the first distillation column 3 is fed to the second distillation column (dehydration column or purification column) 5 through the feed line 36 and distilled for separating into or providing a second overhead (a second lower boiling point component containing a low-boiling component such as water) withdrawn from the column top through a line 52, a bottom stream [a high-boiling component (a high-boiling impurity) containing water, a carboxylic acid having a high boiling point (such as propionic acid), a C6-12alkyl iodide (such as hexyl iodide), an aldehyde condensation product, and others] withdrawn from the column bottom through a line 51, and a side cut stream [a second liquid stream containing acetic acid (purified acetic acid stream with a high purity)] withdrawn from the side (between the column bottom and the feed site of the feed line 36) through a line 55.
The second overhead (lower boiling point fraction) is sent to the condenser C4 through a discharge line 52 and cooled and condensed. A portion of the condensate (the condensate mainly containing water) is fed to the second distillation column 5 through a reflux line 53 for reflux, and another portion thereof is recycled to the reactor 1 through a recycle line 54. The uncondensed gaseous component (gas) is discharged as an offgas.
Further, in the process shown in
Further, the condensate in the condenser C5 is fed to an extractor 7 through a line 64. In the extractor, a water-soluble component (e.g., acetaldehyde) is extracted with water fed through a water feed line 82, and thus the condensate is separated into a water-extracted phase (an aqueous phase or upper phase mainly containing acetaldehyde) and an organic phase (a lower phase or raffinate mainly containing methyl iodide). The extracted phase (aqueous phase) is fed to a fourth distillation column 8 through a line 74 and separated into a low-boiling stream (a fraction mainly containing acetaldehyde and others) from the column top and a bottom stream (a fraction mainly containing water) from the column bottom. Moreover, a portion of the organic phase (raffinate) in the extractor 7 is fed to the third distillation column 6 through lines 71, 72, and another portion thereof is recycled to the reactor 1 through recycle lines 73, 90. The bottom stream from the fourth distillation column 8 is joined to (or combined to) water of the water feed line 82 through a line 81, and used for water extraction in the extractor 7. The low-boiling stream (a fraction mainly containing acetaldehyde) from the column top of the fourth distillation column 8 is discharged as an offgas.
According to the process (or production apparatus), the water concentration and the methyl acetate concentration in the distillation system of the first distillation column 3 are adjusted to not more than 5% by weight (for example, 1 to 3% by weight) and 0.5 to 9% by weight (for example, 3 to 5% by weight), respectively, by feeding water and/or methyl acetate through the water feed line 34a and the methyl acetate feed line 35a. Thus, the zone having a high hydrogen iodide concentration can be formed in a predetermined zone in the first distillation column 3; and hydrogen iodide is allowed to contact with an ascending stream of methyl acetate (and methanol) having a low boiling point in the volatile phase component, so that the reaction can convert hydrogen iodide into methyl iodide to produce acetic acid and water as by-products. Further, in the decanter 4, since the methyl acetate content can be reduced, the aqueous phase (mainly containing acetic acid, methyl acetate and hydrogen iodide) and an organic phase (mainly containing methyl iodide and methyl acetate) can be separated with a high liquid-liquid, separation efficiency. Thus, the side cut stream (crude acetic acid stream) from the first distillation column 3 can be prevented from contamination with hydrogen iodide, a load on the second distillation column 5 can be decreased and the corrosion of the first and second distillation columns 3, 5 can be inhibited.
In this embodiment, acetic acid is produced by basically the same process as that shown in
More specifically, a vapor phase is withdrawn from a reactor 1 through a discharge line 12 and cooled in a condenser C1; the resulting condensed liquid component is returned to the reactor 1 through a reflux line 13 for reflux, and the resulting noncondensed component (gaseous component) is sent to a scrubber system 92 through a discharge line 14. Moreover, a reaction mixture in the reactor 1 is fed to a flash evaporator 2 through a feed line 11 and subjected to a flash distillation; a portion of the resulting volatile phase component is fed to a first distillation column 3 through a feed line 22, and another portion of the volatile phase component passes through a feed line 23 and cooled and condensed in a condenser C2 to produce a condensate and a noncondensed component. The condensate is recycled to the reactor 1 through a recycle line 25, and the noncondensed component (gaseous component) is fed to the scrubber system 92 through a discharge line 27. In this embodiment, the position (feed port) of a feed line 22 connected to the first distillation column 3 is located between the bottom and the intermediate of the first distillation column 3.
Moreover, in the first distillation column 3, the volatile phase component from the flash evaporator 2 is distilled to give a first overhead withdrawn from the column top, a bottom stream withdrawn from the column bottom, and a side cut stream (crude acetic acid stream) from the side. The side cut stream is withdrawn from a site above the position (feed port) of the feed line 22 connected to the first distillation column 3. The first overhead is introduced into a condenser C3 through an introduction line 32 and is cooled and condensed to give a condensed component and a noncondensed component; the condensed component (a condensate containing methyl, iodide, methyl acetate, acetic acid, acetaldehyde, and others) is fed to a decanter 4 through an introduction line 33, and the noncondensed component (a gas component mainly containing carbon monoxide, hydrogen, and others) is fed to the scrubber system 92 through a discharge line 38. A portion of the bottom stream is returned to a flash evaporator 2 through a line 37, and another portion of the bottom stream is recycled to the reactor 1 through a recycle line 31. All of the bottom stream may be returned to the flash evaporator 2 through the line 37. A condensate in the decanter 4 (in this embodiment, an aqueous phase) is returned to the first distillation column 3 through a reflux line 42 for reflux. A condensate in the decanter 4 (in this embodiment, an organic phase) is recycled to the reactor 1 through a recycle line 41.
Further, the side cut stream from the first distillation column 3 is fed to a second distillation column (dehydration column or purification column) 5 through a feed line 36 and is separated, by distillation in the second distillation column 5, into a second overhead withdrawn from the column top through a line 52, a bottom stream withdrawn from the column bottom through a line 51, and a side cut stream (high purity acetic acid stream) withdrawn from the side through a line 55. The second overhead (lower boiling point fraction) passes through a discharge line 52 and is cooled and condensed in a condenser C4 to give a condensate and a noncondensed component. A portion of the condensate (a condensate mainly containing water) is returned to the second distillation column 5 through a reflux line 53 for reflux, and another portion of the condensate is recycled to the reactor 1 through a recycle line 91. Moreover, the noncondensed component (gaseous component) is fed to the scrubber system 92 through a discharge line 56.
In the scrubber system 92, a useful component (e.g., methyl iodide, acetic acid) is collected and recycled to the reactor 1, and carbon monoxide is purified by PSA (pressure swing adsorption) or other methods and recycled to the reactor 1.
To the feed line 22 for feeding the volatile phase component to the first distillation column 3, a supply line 34b for feeding water and/or methyl acetate is connected. A high water concentration zone is formed by supplying water and/or methyl acetate through the supply line 34b and by maintaining the water concentration and methyl acetate concentration of a feeding liquid to be fed into the first distillation column 3 to predetermined ranges (for example, 1 to 3% by weight of water and 3 to 5% by weight of methyl acetate). In the zone, hydrogen iodide is concentrated and allowed to react with methyl acetate to convert into methyl iodide. Thus the first distillation column 3 can be prevented from corrosion. Since hydrogen iodide is concentrated around a water concentration of 5% by weight, hydrogen iodide cannot be concentrated if a zone having such a water concentration is not formed in the distillation column (for example, in the case where the water concentration at the top of the distillation column is less than 5% by weight due to insufficient supply of water). However, hydrogen iodide still existing in the distillation column depending on the equilibrium reaction can be converted into methyl iodide by methyl acetate. Thus, even if a zone having a water concentration of about 5% by weight is not formed, the corrosion can be inhibited. Moreover, the reaction of hydrogen iodide with methyl acetate produces methyl iodide, acetic acid and water to improve the liquid-liquid separation into an aqueous phase (light phase) and an organic phase (heavy phase) in the decanter 4.
As shown in
Further, an addition line 57a and/or 57b for adding an alkali component is connected to a feed line 36, connected to the second distillation column 5, and/or the second distillation column 5. The addition of the alkali component (an aqueous solution of an alkali such as sodium hydroxide, potassium hydroxide, or lithium hydroxide) through the addition line(s) converts hydrogen iodide into an alkali iodide, resulting in removal of hydrogen iodide.
According to such a process (or production apparatus), since not only hydrogen iodide can be converted into methyl iodide and removed in the first distillation column 3 but also hydrogen iodide can also be removed by the alkali component in the second distillation column 5, acetic acid with a high purity can be produced.
Hereinafter, steps and apparatus for producing acetic acid by carbonylation of methanol will be explained in detail.
[Carbonylation Reaction of Methanol]
In the reaction step (carbonylation reaction step), methanol is allowed to continuously react with carbon monoxide using a catalyst system (a catalyst containing a group 8 metal of the Periodic Table, a co-catalyst, and an accelerator) in the presence of water, thereby being carbonylated continuously.
The catalyst containing a group 8 metal of the Periodic Table may include, for example, a rhodium catalyst and an iridium catalyst (in particular, a rhodium catalyst). The catalyst may be used in the form of a halide (e.g., an iodide), a carboxylate (e.g., an acetate), a salt of an inorganic acid, or a complex (in particular, a form soluble in a liquid reaction medium, e.g., a complex). As the rhodium catalyst, there may be mentioned a rhodium iodide complex (for example, RhI3, [RhI2(CO)4], and [Rh(CO)2I2]), a rhodium carbonyl complex; and others. These metal catalysts may be used singly or in combination. The concentration of the metal catalyst is, for example, about 10 to 5000 ppm (on the basis of weight, the same applies hereinafter) and particularly about 200 to 3000 ppm (e.g., about 500 to 1500 ppm) in the whole liquid phase in the reactor.
As the co-catalyst or the accelerator, an ionic iodide or a metal iodide is employed which is useful for stabilization of the rhodium catalyst and inhibition of side reactions in a low water content. It is sufficient that the ionic iodide (or metal iodide) can produce an iodide ion in the liquid reaction medium. The ionic iodide (or metal iodide) may include, for example, an alkali metal iodide (e.g., lithium iodide, sodium iodide, and potassium iodide). The alkali metal iodide (e.g., lithium iodide) also functions as a stabilizer for the carbonylation catalyst (e.g., a rhodium catalyst). These co-catalysts may be used alone or in combination. Among these co-catalysts, lithium iodide is preferred. In the liquid phase system (liquid reaction medium) in the reactor, the concentration of the co-catalyst (e.g., a metal iodide) is, for example, about 1 to 25% by weight, preferably about 2 to 22% by weight, and more preferably about 3 to 20% by weight in the whole liquid phase.
As the accelerator, methyl iodide is utilized. In the liquid phase system (liquid reaction medium) in the reactor, the concentration of methyl iodide is, for example, about 1 to 20% by weight, preferably about 5 to 20% by weight, and more preferably about 6 to 16% by weight (e.g., about 8 to 14% by weight) in the whole liquid phase.
The reaction mixture usually contains methyl acetate, which is produced by a reaction of acetic acid with methanol. The proportion of methyl acetate may be about 0.1 to 30% by weight, preferably about 0.3 to 20% by weight, and more preferably about 0.5 to 10% by weight (e.g., about 0.5 to 6% by weight) in whole reaction mixture.
The reaction may be carried out, in the absence of a solvent or may usually be carried out in the presence of a solvent. As the reaction solvent, acetic acid, which is a product, is usually employed.
The water content of the reaction system may be a low concentration. The water content of the reaction system may for example be not more than 15% by weight (e.g., about 0.1 to 12% by weight), preferably not more than 10% by weight (e.g., about 0.1 to 8% by weight), more preferably about 0.1 to 5% by weight (e.g., about 0.5 to 3% by weight), and usually about 1 to 15% by weight (e.g., about 2 to 10% by weight) in the whole liquid phase in the reaction system.
The carbon monoxide partial pressure in the reactor may for example be about 2 to 30 atmospheres and preferably about 4 to 15 atmospheres. In the carbonylation reaction, hydrogen is formed (or generated) by a shift reaction between carbon monoxide and water. In order to increase the catalyst activity, hydrogen may be fed to the reactor 1, if necessary. The hydrogen partial pressure in the reaction system may for example be about 0.5 to 250 kPa, preferably about 1 to 200 kPa, and more preferably about 5 to 150 kPa (e.g., about 10 to 100 kPa) in terms of absolute pressure.
The reaction temperature may be, for example, about 150 to 250° C., preferably about 160 to 230° C., and more preferably about 180 to 220° C. Moreover, the reaction pressure (total reactor pressure) may be, for example, about 15 to 40 atmospheres.
The space time yield of acetic acid in the reaction system may be, for example, about 5 mol/Lh to 50 mol/Lh, preferably about 8 mol/Lh to 40 mol/Lh, and more preferably about 10 mol/Lh to 30 mol/Lh.
The catalyst mixture (liquid catalyst mixture) containing the catalyst system and water may be continuously fed to the reactor 1. Moreover, in order to adjust the pressure of the reactor, a vapor component (vent gas) may be withdrawn from the reactor. As described above, the vent gas may be fed to the scrubber system, if necessary, and then a useful component (e.g., methyl iodide, acetic acid) may be collected and separated by adsorption treatment and recycled to the reactor 1, and/or a useful gas component (e.g., carbon monoxide) may be separated and recycled to the reactor 1. Moreover, in order to remove part of the reaction heat, the vapor component (vent gas) from the reactor may be condensation-treated by cooling with a condenser, a heat exchanger or other means. The vapor component may be separated into a condensed component (a condensate containing acetic acid, methyl acetate, methyl iodide, acetaldehyde, water, and others) and a noncondensed component (a gaseous component containing carbon monoxide, hydrogen, and others), and the condensed component may be recycled to the reactor to control the reaction temperature of the reaction system, which is an exothermic reaction system. Moreover, the reactor 1 may be equipped with a heat-removable (or heat-removing) unit or a cooling unit (e.g., a jacket) for controlling the temperature of the reaction. The reactor is not necessarily equipped with a heat-removable or cooling apparatus. The noncondensed component may be recycled to the reactor 1, if necessary.
[Flash Evaporation]
In the flash evaporation step (flasher), the reaction mixture continuously fed from the reactor to the flasher (evaporator or flash distillation column) is separated into a volatile phase component (lower boiling point component, vapor component) and a low-volatile phase component (higher boiling point component, liquid component); wherein the volatile phase component contains acetic acid and methyl iodide, and the low-volatile phase component contains a higher boiling point catalyst component (a metal catalyst component, e.g., a metal catalyst and a metal iodide). The volatile phase component (lower boiling point component, vapor component) corresponds to the above-mentioned mixture.
The flash distillation may usually be carried out with the use of a flash distillation column. The flash evaporation step may be composed of a single step or may be composed of a plurality steps in combination. In the flash evaporation step, the reaction mixture may be separated into a vapor component and a liquid component with heating (thermostatic flash) or without heating (adiabatic flash), or the reaction mixture may be separated by combination of these flash conditions. The flash distillation may be carried out, for example, at a temperature of the reaction mixture of about 80 to 200° C. under a pressure (absolute pressure) of about 50 to 1,000 kPa (e.g., about 100 to 1,000 kPa), preferably about 100 to 500 kPa, and more preferably about 100 to 300 kPa. The formation of by-product(s) or the decrease in the catalyst activity may further be inhibited by lowering the internal temperature and/or pressure of the flash evaporator compared with those of the reactor 1.
Moreover, a portion of the volatile phase component may be recycled to the reactor (for example, as described above, a portion of the volatile phase component is heat-removed and condensed in a condenser or a heat exchanger and then recycled to the reactor).
The volatile phase component contains product acetic acid, in addition, hydrogen iodide, a co-catalyst (such as methyl iodide), methyl acetate, water, by-product(s) (e.g., an aldehyde compound such as acetaldehyde or an aldehyde condensation product, a C3-12alkanecarboxylic acid such as propionic acid, and a C6-12alkyl iodide such as hexyl iodide), and is fed to a distillation column (splitter column) for collecting acetic acid. The separated higher boiling point catalyst component (low-volatile phase component or metal catalyst component) is usually recycled to the reaction system.
[First Distillation]
The following embodiment explains distillation of the mixture and removal of hydrogen iodide in the first distillation column (distillation in the first distillation column). As far as the distillation is carried out by adjusting the water concentration and methyl acetate concentration in the mixture to predetermined concentrations, this embodiment is also applicable to other distillations (the succeeding distillation in second or third distillation column).
The volatile phase component (mixture) contains hydrogen iodide, water, methyl iodide, acetic acid, and methyl acetate. The water content of the mixture may be not less than an effective amount for forming a high water concentration zone in the distillation column and not more than 5% by weight. When the water content exceeds 5% by weight, a condensed zone of hydrogen iodide is shifted downwardly to a position for feeding the mixture (volatile phase component) to the distillation column, and thus hydrogen iodide cannot be removed effectively. The zone having a high water concentration in the distillation column is shifted upwardly to the column top direction, and hydrogen iodide cannot be removed effectively. According to the present invention, the condensed zone of hydrogen iodide can be formed above the feed position by adjusting the water concentration in the fed mixture to not more than 5% by weight, and hydrogen iodide can be effectively removed due to methyl acetate (which is concentrated above the feed position) in the mixture, so that the corrosion can be inhibited. Moreover, even if the condensed zone of hydrogen iodide is not formed in the distillation column, hydrogen iodide existing in the distillation column according to the equilibrium reaction is converted by methyl acetate, so that the corrosion can be inhibited.
The water content of the mixture may usually be about 0.5 to 4.5% by weight (e.g., about 1 to 4.3% by weight) and preferably about 1.2 to 4% by weight (e.g., about 1.5 to 3.5% by weight). According to the present invention, a high water concentration zone inside the distillation column can be formed above a position for feeding the mixture (volatile phase component) to the distillation column. Thus, hydrogen iodide is allowed to react with methyl acetate (and also methanol in the mixture and by-product methanol) at the high water concentration zone to produce methyl iodide and acetic acid.
The methyl acetate concentration in the mixture can be selected within the range from not less than an effective amount for converting hydrogen iodide into methyl iodide in the distillation column to not more than 9% by weight (0.5 to 9% by weight). When the methyl acetate concentration exceeds 9% by weight, the condensate of the overhead shows a low liquid-liquid separation. The methyl acetate concentration in the mixture may usually be about 0.5 to 8% by weight (e.g., about 0.5 to 7.5% by weight), preferably about 0.7 to 6.5% by weight (e.g., about 1 to 5.5% by weight), and more preferably 1.5 to 5% by weight (e.g., about 2 to 4.5% by weight), or may be about 0.5 to 7.2% by weight. The mixture representatively contains about 1 to 4.3% by weight (e.g., about 1.3 to 3.7% by weight) of water; and about 0.5 to 7.5% by weight (e.g., about 0.8 to 7.5% by weight), preferably about 1.2 to 5% by weight (e.g., about 1.7 to 4.5% by weight) of methyl acetate.
The methyl iodide content of the mixture may for example be about 25 to 50% by weight (e.g., about 27 to 48% by weight), preferably about 30 to 45% by weight (e.g., about 32 to 43% by weight), and more preferably about 35 to 40% by weight (e.g., about 36 to 39% by weight).
When the distillation is carried out continuously, the methyl acetate concentration in the mixture may usually be about 0.07 to 1.2 mol/L (about 0.5 to 9% by weight), preferably about 0.1 to 1.0 mol/L, and more preferably about 0.3 to 0.8 mol/L. Moreover, the water concentration in the mixture may be about 0.28 to 2.8 mol/L (about 0.5 to 5% by weight), preferably about 0.56 to 2.5 mol/L (about 1 to 4.5% by weight), and more preferably about 0.83 to 2.2 mol/L (about 1.5 to 4% by weight).
According to the present invention, since hydrogen iodide can be removed efficiently, the hydrogen iodide content of the mixture is not particularly limited to a specific one. For example, the hydrogen iodide content may be about 10 to 30000 ppm. The hydrogen iodide content of the mixture (volatile phase component) produced by the methanol carbonylation reaction may be about 100 to 10000 ppm, preferably about 200 to 7500 ppm, and more preferably about 300 to 6000 ppm (e.g., about 500 to 5000 ppm) on the basis of weight. Moreover, the acetic acid content of the mixture is not particularly limited to a specific one, and may for example be about 30 to 70% by weight (e.g., about 35 to 75% by weight), preferably about 40 to 65% by weight (e.g., about 45 to 62% by weight), and more preferably about 50 to 60% by weight (e.g., about 54 to 58% by weight).
The mixture (volatile phase component) may further contain dimethyl ether. The concentration of dimethyl ether can for example be selected from the range of 0.15 to 3% by weight, and may usually be about 0.15 to 2.5% by weight (e.g., about 0.17 to 2.3% by weight), preferably about 0.2 to 2% by weight (e.g., about 0.3 to 1.7% by weight), and more preferably about 0.5 to 1.5% by weight. Most of the remainder (residual component) of the mixture is often methanol. As described above, the mixture (volatile phase component) produced by the methanol carbonylation reaction practically contains a trace of an impurity (e.g., acetaldehyde, an aldehyde condensation product, a higher boiling point carboxylic acid such as propionic acid, and a C6-12alkyl iodide).
The total amount of each component in the mixture (volatile phase component) is 100% by weight. Moreover, although the mixture (volatile phase component) may form a vapor phase (or distillation atmosphere), the amount and concentration of the above-mentioned each component indicate those of the mixture (volatile phase component) in the form of a liquid, for example, a condensate (for example, a liquefied condensate formed by cooling at 20 to 25° C.) obtained by cooling and condensing a vapor phase mixture (a volatile phase component forming a vapor phase).
The water concentration and the methyl acetate concentration in the mixture may be adjusted by feeding (or supplying) water and/or methyl acetate. The mixture containing a predetermined concentration of water and that of methyl acetate may be directly distilled without adjusting the water concentration and the methyl acetate concentration. Moreover, water and/or methyl acetate may be fed (or supplied or added) to the mixture (volatile phase component) or in the distillation atmosphere (the distillation atmosphere in the distillation column) of the volatile phase component (mixture) to adjust a water concentration to not more than 5% by weight and a methyl acetate concentration to 0.5 to 9% by weight for distilling the volatile phase component. The water and/or methyl acetate can be fed (or supplied) to the feed line 22 or the first distillation column by using various lines connected to the first distillation column or a new line.
The adjustment (or control) of the water concentration and the methyl acetate concentration can be conducted by analyzing or detecting water and methyl acetate concentrations in the mixture (volatile phase component) introduced into the distillation column, and based on the results, and adjusting the ratio of the components of the mixture in the distillation column, or a unit or line (which is for supplying a fluid to the distillation column) by using a controller (control unit); or can also be conducted by supplying or adding water and/or methyl acetate. The unit for supplying the fluid to the distillation column may include the reactor or flasher which is located upstream of the distillation column, a decanter for feeding a condensate to the distillation column, and others.
The distillation atmosphere (the distillation atmosphere in the distillation column) of the mixture (volatile phase component) can be formed in an appropriate place inside the distillation column. In order to convert hydrogen iodide effectively, it is preferred to form the distillation atmosphere at the same height as or above the feed site of the volatile phase component.
Further, to the volatile phase component as the mixture, or to the distillation atmosphere of the volatile phase component as the mixture, at least one member selected from the group consisting of methyl acetate, methanol and dimethyl ether (a methanol source) and if necessary water may be added to form a volatile phase component (mixture) having adjusted water and methyl acetate concentrations for distilling the volatile phase component (mixture). The amounts of methyl acetate and water to be added are as described above. Moreover, the amount of methanol to be added may for example be about 0.01 to 3.8 parts by weight (e.g., about 0.1 to 3 parts by weight), preferably about 0.1 to 2.5 parts by weight (e.g., about 0.2 to 2 parts by weight), and more preferably about 0.2 to 1.5 parts by Weight (e.g., about 0.5 to 1.5 parts by weight) relative to 100 parts by weight of the mixture (volatile phase component). The amount of dimethyl ether to be added is an amount to form the dimethyl ether concentration in the mixture as described above. The amount of dimethyl ether to be added may for example be about 0.01 to 2.7 parts by weight (e.g., about 0.03 to 2 parts by weight), preferably about 0.05 to 1.5 parts by weight (e.g., about 0.07 to 1.3 parts by weight), and more preferably, about 0.1 to 1 parts by weight (e.g., about 0.2 to 0.8 parts by weight) relative to 100 parts by weight of the mixture (volatile phase component).
In the splitter column (first distillation column), the mixture (volatile phase component) is distilled (in particular, continuously distilled) and separated into an overhead containing a lower boiling point component such as methyl iodide (including methyl iodide produced by a reaction of methyl acetate with methanol), and a side cut stream or bottom stream containing acetic acid, and acetic acid is collected. In the distillation column, usually, a volatile phase component is separated as a vapor overhead (usually containing methyl iodide, methyl acetate, acetaldehyde, water, and others); a side cut stream (side stream) containing acetic acid is separated as a liquid form by side-cut; and a bottom stream (bottom liquid stream or higher boiling point component, containing acetic acid, water, propionic acid, entrained metal catalyst component, a metal halide, and others) is separated as a liquid form.
This distillation can significantly reduce the concentration of hydrogen iodide in the second overhead and the side cut stream. In particular, the side cut stream (crude acetic acid stream) having a significantly decreased concentration of hydrogen iodide can be obtained. The hydrogen iodide con centration in the side cut stream may for example be about 1 to 350 ppm, preferably about 2 to 300 ppm, and more preferably about 3 to 250 ppm.
The position of the feed line 22 connected (or joined) to the first distillation column 3 (the feed site of the volatile phase component) is not particularly limited to a specific one. For example, the position of the feed line may be in an upper part, a middle part, or a lower part of the distillation column. The mixture is practically fed to the distillation column from an intermediate or lower position of the distillation column in height. Specifically, the connecting (or joining) position of the feed line 22 (the feed site of the volatile phase component) is practically located at an intermediate or lower position of the first distillation column 3. Since feeding of the mixture in such a manner can form a high water concentration zone between at or above an intermediate position of the distillation column and below thew reflux line 42, thus the efficient contact of hydrogen iodide with methyl acetate (and methanol) can be increased, which can improve the hydrogen iodide removal efficiency. Moreover, the side cut stream (crude acetic acid stream) from the first distillation column 3 may be withdrawn from any of an upper part, a middle part, and a lower part of the distillation column, for example, the side cut stream may be withdrawn from the same height as the position (feed site) of the feed line 22 joined to the first distillation column 3 or from above or below the position (feed site) thereof. The side cut stream is usually withdrawn from a middle part or a lower part (lower part to middle part) of the distillation column, for example, a site below the connecting position of the feed line 22 (the feed site of the volatile phase component) (e.g., a site between above the column bottom and below the connecting position (feed site) of the feed line 22).
Moreover, as shown in
The bottom stream may be removed (discharged) from the bottom or lower part of the distillation column. Since the bottom stream contains a useful component such as a metal catalyst component or acetic acid, the bottom stream may be recycled to the reactor (or reaction step) or the flash evaporation step, as described above. Moreover, the bottom stream may be recycled to the reaction system or others through a storage vessel having a buffering function. The bottom stream may be fed to the second distillation column 5 for removing a high boiling point impurity such as propionic acid.
As the splitter column (distillation column), there may be used a conventional distillation column, for example, a plate column, a packed column, and a flash distillation column. A distillation column such as a plate column or a packed column may be usually employed. The material of (or for forming) the distillation column is not limited to a specific one, and a glass, a metal, a ceramic, or others can be used. In usual, a distillation column made of a metal is used practically.
For the plate column, the theoretical number of plates is not particularly limited to a specific one, and, depending on the species of the component to be separated, is about 5 to 50, preferably about 7 to 35, and more preferably about 8 to 30. Further, in order to separate acetaldehyde in the distillation column, the theoretical number of plates may be about 10 to 80, preferably about 20 to 60, and more preferably about 25 to 50. Further, in the distillation column, the reflux ratio may be selected from, for example, about 0.5 to 3,000, and preferably about 0.8 to 2,000 depending on the above-mentioned theoretical number of plates, or may be reduced by increasing the theoretical number of plates.
The distillation temperature and pressure in the splitter column (distillation column) may suitably be selected. For example, in the distillation column, the inner temperature of the column (usually, the temperature of the column top) may be adjusted by adjusting the inner pressure of the column, and may be, for example, about 20 to 180° C., preferably about 50 to 150° C., and more preferably about 100 to 140° C. The temperature of the column top can be set to a temperature lower than the boiling point of acetic acid depending on the inner pressure of the column (for example, lower than 118° C., preferably not higher than 117° C.). The temperature of the column bottom can be set to a temperature higher than the boiling point of acetic acid depending on the inner pressure of the column (for example, not lower than 130° C., preferably not lower than 135° C.).
The overhead from the first distillation column contains methyl iodide, acetaldehyde, and in addition, methyl acetate, water, methanol, acetic acid, an aldehyde or a carbonyl impurity (such as crotonaldehyde or butyraldehyde), a C2-12alkyl iodide, a C3-12alkanecarboxylic acid, and others.
[Condensation and Liquid-Liquid Separation]
The overhead from the first distillation column is cooled and condensed in a cooling unit (condenser), and the resulting condensate of the overhead can clearly be separated into an aqueous phase (light phase, upper phase) and an organic phase (heavy phase, lower phase) in a liquid-separating unit (decanter). In this manner, the separability of the overhead into the aqueous phase (light phase) and the organic phase (heavy phase) can be improved.
As described above, methyl acetate has a miscibility with both aqueous phase (light phase) and organic phase (heavy phase). The liquid-liquid separation decreases at a higher concentration of methyl acetate. Thus, the concentration of methyl acetate in the separated organic phase (heavy phase, lower phase) may be about 0.5 to 15% by weight (e.g., about 1 to 15% by weight), preferably about 1.5 to 14% by weight (e.g., about 2 to 10% by weight), and more preferably about 2 to 8% by weight (e.g., about 2.5 to 7% by weight); and the concentration of methyl acetate in the aqueous phase (light phase, upper phase) may be about 0.2 to 8.5% by weight (about 0.4 to 8% by weight), preferably about 0.5 to 7.5% by weight (e.g., about 0.6 to 6% by weight), and more preferably about 0.7 to 5% by weight (e.g., about 0.8 to 4.5% by weight) or may be about 0.4 to 8% by weight (e.g., about 1 to 5% by weight).
Moreover, the liquid-liquid separation into the aqueous phase and the organic phase is sometimes influenced by other components. In the separated organic phase (heavy phase), the concentration of methyl iodide may for example be about 75 to 98% by weight (e.g., about 76 to 98% by weight) and preferably about 78 to 97% by weight (e.g., about 80 to 96% by weight), and the concentration of acetic acid may be about 1 to 10% by weight (e.g., about 2 to 8% by weight) and preferably about 2.5 to 7.5% by weight (e.g., about 3 to 7.5% by weight). The concentration of water in the organic phase (heavy phase) is usually not more than 1% by weight. Moreover, in the aqueous phase (light phase), the concentration of water may be about 50 to 90% by weight (e.g., about 55 to 90% by weight) and preferably about 60 to 85% by weight (e.g., about 65 to 80% by weight), and the concentration of acetic acid may be about 10 to 40% by weight (e.g., 12 to 35% by weight) and preferably about 13 to 30% by weight. The sum of the percentage of all components in the organic phase (heavy phase) is 100% by weight, and that in the aqueous phase (light phase) is 100% by weight.
The concentration of hydrogen iodide in the aqueous phase (light phase) is higher than that in the organic phase (heavy phase). For example, the concentration of hydrogen iodide in the organic phase (heavy phase) is about not more than 70 ppm (for example, trace to 60 ppm), while the concentration of hydrogen iodide in the aqueous phase (light phase) is about 10 to 1000 ppm (e.g., about 50 to 800 ppm). For that reason, feeding of the aqueous phase (light phase) to the third distillation column can improve the hydrogen iodide removal efficiency. Moreover, feeding of both of the aqueous phase (light phase) and the organic phase (heavy phase) to the third distillation column can further improve the hydrogen iodide removal efficiency.
In an example shown in the figure, the organic phase (heavy phase) is recycled to the reactor 1, and the aqueous phase (light phase) is recycled to the first distillation column 3 for reflux. The organic phase (heavy phase) and/or the aqueous phase (light phase) may be recycled to the reactor 1 or may be recycled to the first distillation column 3.
[Second Distillation]
The first side cut stream (liquid crude acetic acid) usually contains acetic acid, and other components (e.g., methyl iodide, methyl acetate, water, and hydrogen iodide) which remain without separation in the first distillation column. The side cut stream (liquid crude acetic acid) from the first distillation column is usually further distilled (or dehydrated) in the second distillation column, and separated into an overhead (low-boiling content) from the column top, a bottom stream (high-boiling component such as a C3-12alkanecarboxylic acid including propionic acid) from the column bottom, and a side cut stream (purified acetic acid) from the side, and product acetic acid may be obtained as the side cut stream.
In the second distillation column, removal of hydrogen iodide by an alkali component is not necessarily needed. As described above, water and hydrogen iodide usually remain in the first side cut stream (liquid crude acetic acid). The distillation of the first side cut stream (liquid crude acetic acid) condenses hydrogen iodide in the second distillation column. Moreover, hydrogen iodide is also produced by a reaction of methyl iodide with water as shown in the above-mentioned equation (3). Thus, not only hydrogen iodide together with water is concentrated in the upper part of the second distillation column, but also hydrogen iodide is liable to be produced by a reaction of methyl iodide with water in the upper part of the second distillation column. Accordingly, it is preferable to add an alkali component for removing hydrogen iodide and for obtaining acetic acid with a further high purity. Specifically, in the second distillation column, the first side cut stream may be distilled in the presence of an alkali component (for example, an alkali metal hydroxide such as potassium hydroxide), or a mixture containing the first side cut stream and the alkali component may be distilled.
The alkali component (alkaline aqueous solution) can be added to the side cut stream or the distillation column by using various routes connected to the distillation column or a new route. In the example shown in the figure, the alkali component may be added through at least one line of addition lines 57a and 57b. Moreover, the position of the feed line 36 (or addition part) and that of an addition line 57b to the second distillation column 5 are not particularly limited. Each position may be located at the middle part of the second distillation column 5 or below or above the middle part thereof. In usual, the position of addition by the feed line 36 is practically located at or below the middle part of the second distillation column 5; the position of addition by the addition line 57b is practically located at or above the middle part of the second distillation column 5. The addition of the alkali component according to such an embodiment allows hydrogen iodide to be efficiently neutralized prior to movement or migration of hydrogen iodide to the column top of the second distillation column, even if the alkali component (non-volatile alkali component) is easily moved to the lower part of the distillation column. Thus, the concentration of hydrogen iodide at all over the distillation column including not only the lower part of the distillation column but also the upper part of the distillation column can be efficiently inhibited.
In the second distillation column, the first side cut stream may be distilled in the presence of a reactive component having a boiling point lower than that of acetic acid and converting hydrogen iodide into methyl iodide (at least one methanol or a derivative thereof, selected from the group consisting of methanol, dimethyl ether and methyl acetate, particularly, methyl acetate) in addition to the alkali component. The methanol or the derivative thereof (particularly, methyl acetate) may be contained in the first side cut stream, and is preferably added via (through) the addition lines 57a, 57b, and other routes. As described above, the reaction of methyl iodide with water easily occurs in the upper part of the distillation column, while the alkali component is easily moved to the lower part of the distillation column. Thus, the amount of the alkali component existing in the upper part of the distillation column sometimes decreases. The addition of the methanol or the derivative thereof which has a low boiling point, in combination of the alkali component can inhibit concentration of hydrogen iodide in the upper part of the distillation column with more certainty, and can remove hydrogen iodide by converting hydrogen iodide into a metal iodide or methyl iodide.
The water content of the first side cut stream (liquid crude acetic acid) is usually about 0.3 to 5% by weight (e.g., about 0.5 to 4% by weight, preferably about 0.7 to 3.5% by weight, and more preferably about 1 to 3% by weight), and the methyl acetate content thereof is about 0.1 to 3% by weight (e.g., about 0.2 to 2.5% by weight, preferably about 0.5 to 2% by weight, and more preferably about 0.7 to 1.5% by weight). The water concentration and methyl acetate concentration of the first side cut stream (liquid crude acetic acid) can also be used for removing hydrogen iodide. Specifically, water and/or acetic acid may be supplied to the side cut stream or the second distillation column, together with the addition of the alkali component or instead of the addition of the alkali component, to adjust the water concentration and the methyl acetate concentration, for converting hydrogen iodide into methyl iodide and for removing hydrogen iodide in the same manner as the first distillation. In this case, in order to increase the dehydration efficiency, supply of methyl acetate without addition of water is advantageous.
The overhead from the column top or upper part of the second distillation column 5 is usually condensed in condenser C4, and the resulting condensate may be returned to the reactor 1 and/or the second distillation column 5. When the condensate has a predetermined amount of water and can form separated liquid phases, the condensate may be separated into an aqueous phase and an organic phase in the same manner as described above and recycled to the reactor 1, the first distillation column 3 and/or the second distillation column 5. The water may be separated as a low-boiling component in the second distillation column 5, and the separated water may be fed to the reactor 1 or a water extractor 7. The higher boiling point fraction (second higher boiling point component) such as a high-boiling component (e.g., propionic acid) may be withdrawn from the column bottom or the lower part of the column, and if necessary may be returned to the reactor 1 or discharged out of the system. Moreover, if necessary, the second side cut stream (purified acetic acid stream) may further be subjected to a purification step such as distillation.
[Separation and Removal of Impurity]
The embodiment of
[Vent Gas]
The noncondensed component (vent gas component) from the condenser may be released out of the system. If necessary, the noncondensed component may be recycled to the reactor 1 directly, or may be fed to the scrubber system to separate and collect a useful component (such as methyl iodide or acetic acid) from the noncondensed component, and the useful component may optionally be recycled to the reactor 1. For the scrubber system, various separation and purification processes, such as PSA (pressure swing adsorption, pressure swing adsorption) method, may be used.
The following examples are intended to describe this invention in further detail and should by no means be interpreted as defining the scope of the invention.
In a continuous production process for acetic acid shown in
To the first distillation column (number of plates: 20, charging plate: 2nd plate from bottom), 100 parts by weight of the volatile phase component was fed, distilled at a gauge pressure of 150 KPA, a column bottom temperature of 140° C., a column top temperature of 115° C. and a reflux ratio of a light phase of 3, and liquid-liquid separated by cooling and decantation to form an aqueous phase and an organic phase. The aqueous phase (light phase, 5 parts by weight) and the organic phase (heavy phase, 38 parts by weight) were recycled to the reactor. The composition (formulation) of the column top of the first distillation column (the composition of the overhead) was as follows: 63.8% by weight of methyl iodide (MeI), 0.6% by weight of methyl acetate (MA), 23.3% by weight of water (H2O), 440 ppm of hydrogen iodide (HI), and 12.3% by weight of acetic acid. The composition of the aqueous phase (light phase) was as follows: 2.6% by weight of methyl iodide (MeI), 0.3% by weight of methyl acetate (MA), 67.0% by weight of water (H2O), 900 ppm of hydrogen iodide (HI), and 30.0% by weight of acetic acid. The composition of the organic phase (heavy phase) was as follows: 96% by weight of methyl iodide (MeI), 0.7% by weight of methyl acetate (MA), 0.3% by weight of water (H2O), 200 ppm of hydrogen iodide (HI), and 3.0% by weight of acetic acid.
From the side-cut of first distillation column (side-cut plate: 4th from bottom) and the column bottom, a side cut stream containing acetic acid and a bottom stream containing an entrained catalyst were withdrawn in a proportion of 54 parts by weight and a proportion of 3 parts by weight, respectively. The bottom stream was recycled to the reaction system. The side cut stream was fed to a second distillation column for dehydration and purification. The composition of the side cut stream was as follows: 2.9% by weight of MeI, 0.03% by weight of MA, 5.3% by weight of H2O, 970 ppm of HI, and 90.8% by weight of acetic acid.
The term “parts by weight” of a fluid (e.g., a volatile phase component, an aqueous phase (light phase) and an organic phase (heavy phase), a side cut stream and a bottom stream) indicates a flow rate per hour (the same applies hereinafter).
In the continuous reaction process, the following test pieces were placed on 3nd plate from bottom (which was the first plate above the charging plate of the first distillation column) undermost plate of the column (which was the first plate below the charging plate), and 19th plate from bottom (which was the column top). After leaving for 100 hours, each test piece was examined for a corrosion test. The weight of each test piece before and after the corrosion test was measured to determine a corrosion amount. Based on the measured corrosion amount (decrease in weight) and the area of the test piece, the corrosion rate (decrease in thickness) of the test piece per year was converted into a thickness (mm) and shown in the unit “mm/Y”.
[Test Piece]
HB2: manufactured by Oda Kaki Co., Ltd, HASTELLOY B2 (nickel-based alloy)
HC: manufactured by Oda Koki Co., Ltd, HASTELLOY C (nickel-based alloy)
SUS316L: manufactured by Umetoku Inc., SUS 316 Low Carbon (stainless steel)
The corrosion test was carried out in the same manner as in Comparative Example 1 except that the charging mixture (volatile phase component) was adjusted to a water concentration of 4% by weight and then fed to the first distillation column and that the reflux ratio in the first distillation column and the amounts of the light phase and the heavy phase recycled to the reaction system were changed depending on the water concentration.
The composition of the volatile phase component was as follows: 38.5% by weight of MeI, 0.3% by weight of MA. 4.0% by weight of H2O, 5000 ppm of HI, and 56.7% by weight of acetic acid. Moreover, the distillation was carried out at a light phase reflux ratio of 5, and the light phase (3.3 parts by weight) and the heavy phase (38.5 parts by weight) were recycled to the reaction system. The composition of the column top of the first distillation column (the composition of the overhead) was as follows: 64.3% by weight of MeI, 0.6% by weight of MA, 23.3% by weight of H2O, 470 ppm of HI, and 11.8% by weight of acetic acid. The composition of the aqueous phase (light phase) was as follows: 2.6% by weight of MeI, 0.3% by weight of MA, 68.0% by weight of H2O, 1200 ppm of HI, and 29.0% by weight of acetic acid. The composition of the organic phase (heavy phase) was as follows: 96% by weight of MeI, 0.7% by weight of MA, 0.3% by weight of H2O, 90 ppm of HI, and 3.0% by weight of acetic acid. From the first distillation column, a side cut stream containing acetic acid and a bottom stream were withdrawn in a proportion of 55.2 parts by weight and a proportion of 3 parts by weight, respectively. The composition of the side cut stream was as follows: 2.6% by weight of MeI, 0.04% by weight of MA, 2.8% by weight of H2O, 820 ppm of HI, and 93.6% by weight of acetic acid. The composition of the bottom stream was as follows: 0% by weight of MeI, 0.03% by weight of MA, 2.6% by weight of H2O, 800 ppm of HI, and 97.1% by weight of acetic acid. The column top temperature of the first distillation column was 115° C., and the column bottom temperature thereof was the same as that in Comparative Example 1.
The corrosion test was carried out in the same manner as in Comparative Example 2 except that the charging mixture (volatile phase component) was adjusted to a methyl acetate concentration of 10% by weight and then fed to the first distillation column and that the reflux ratio in the first distillation column and the amounts of the light phase and the heavy phase recycled to the reaction system were changed depending on the methyl acetate concentration. However, the charging mixture (volatile phase component) had a poor liquid-liquid separation into the light phase and the heavy phase. These phases formed a mixed phase or one phase, and the results made the operation unstable after several hours. Thus it was impossible to operate the process operation for a long period of time.
The corrosion test was carried out in the same manner as in Comparative Example 1 except that the charging mixture (volatile phase component) having appropriate methyl acetate and water concentrations in each Example is fed to the first distillation column and that the reflux ratio in the first distillation column and the amounts of the light phase and the heavy phase recycled to the reaction system were changed depending on the methyl acetate and water concentrations.
Operation conditions in each of Examples and Comparative Examples are shown in Table 1. The results of the corrosion test are shown in Table 2. The unit of numerical values in Table 2 is the corrosion rate “mm/Y”.
TABLE 1
Parts by
weight
Comparative Examples
Examples
(ppm for HI)
1
2
3
1
2
3
4
Feed
Flow rate
100
100
100
100
100
100
100
MeI
38.2
38.5
38
38
38.5
37
36
MA
0.3
0.3
10
0.5
1
4.2
7.2
Water
6.5
4
4
4
4
1.2
2
HI
5000
5000
200
4000
2000
600
300
AC
54.5
56.7
47.6
57.1
56.3
57.4
54.7
Side-
Flow rate
54
55.2
43.5
55.2
55.2
54.2
51.6
cut
MeI
2.9
2.6
2.3
1.7
4.0
3.1
2.3
MA
0.03
0.04
2.6
0.06
0.21
1.26
1.6
Water
5.3
2.8
2.8
2.8
2.7
0.7
1.2
HI
970
820
trace
290
90
20
5
AC
90.8
93.6
91.5
94.7
92.7
94.5
94.8
Column
Flow rate
58
58.3
68.5
58.3
58.3
49.2
62.2
top
MeI
63.8
64.3
54.9
64.3
63.3
72.2
57.4
MA
0.56
0.56
14.79
0.93
1.76
7.63
12.36
Water
23.3
23.3
22.6
23.3
23.4
11.9
20.9
HI
440
470
trace
240
70
70
7
AC
12.3
11.8
7.8
11.5
11.5
8.2
9.4
Column
Flow rate
3
3
3
3
3
3
3
bottom
MeI
0.0
0.0
0.0
0.0
0.2
0.1
0.0
MA
0.03
0.03
0.17
0.17
0.17
1.20
1.18
Water
5.3
2.6
2.6
2.6
2.6
0.6
1.14
HI
440
470
300
290
90
20
5
AC
94.6
97.3
96.3
97.2
97.0
98.1
97.7
Reflux
Flow rate
15
16.5
15
16.5
16.5
6.4
16.8
MeI
2.6
2.6
4
2.6
3.5
3.5
5.1
MA
0.3
0.3
8.3
0.5
0.9
4.3
7.9
Water
67
68
85
68
68.2
79
69.1
HI
900
1200
trace
710
250
70
20
AC
30.01
28.98
2.7
28.83
27.4
13.18
17.9
Upper
Flow rate
5
3.3
3.0
3.3
3.3
0.80
1.40
phase
MeI
2.6
2.6
4
2.6
3.5
3.5
5.1
(light
MA
0.3
0.3
8.3
0.5
0.9
4.3
7.9
phase)
Water
67
68
85
68
68.2
79
69.1
HI
900
1200
trace
710
250
70
20
AC
30.0
29.0
2.7
28.8
27.4
13.2
17.9
Lower
Flow rate
38
38.5
50.5
38.5
38.5
42
44
phase
MeI
96
96
73
96
94
84
79
(heavy
MA
0.7
0.7
17.1
1.15
2.2
8.2
14.2
phase)
Water
0.3
0.3
0.3
0.3
0.4
0.4
0.9
HI
110
90
trace
50
40
trace
trace
AC
3.0
3.0
9.6
2.5
3.4
7.4
5.9
TABLE 2
Position
Comparative
of test
Test
Examples
Examples
piece
piece
1
2
3
1
2
3
4
Column top
Zr
0.00
0.00
—
0.00
0.00
0.00
0.00
(19th
HB2
0.1
0.09
—
0.06
0.05
0.02
0.01
plate)
HC
0.22
0.18
—
0.12
0.09
0.05
0.02
SUS
0.54
0.3
—
0.23
0.18
0.06
0.03
316L
Charging
Zr
0.00
0.00
—
0.00
0.00
0.00
0.00
plate + 1
HB2
0.23
0.18
—
0.07
0.05
0.01
0.01
HC
0.51
0.42
—
0.18
0.09
0.04
0.02
SUS
Not
Not
—
0.51
0.22
0.06
0.04
316L
test
test
Bottom
Zr
0.00
0.00
—
0.00
0.00
0.00
0.00
(Charging
HB2
0.27
0.09
—
0.06
0.06
0.04
0.02
plate − 1)
HC
0.6
0.21
—
0.11
0.1
0.05
0.03
SUS
Not
0.6
—
0.4
0.24
0.08
0.05
316L
test
Comparative Example 3 failed to operate the apparatus stably, and the corrosion could not be evaluated.
As apparent from Table 1 and Table 2, in Comparative Example 1, corrosion developed in the whole distillation column. In Comparative Example 2, since a concentrated zone of hydrogen iodide was transferred above the charging plate due to a lower concentration of water in the charging mixture (volatile phase component), the corrosiveness of the bottom was decreased; while due to a low concentration of methyl acetate in the charging mixture (volatile phase component), corrosion developed above the charging plate. In Comparative Example 3, although the corrosiveness of the whole column was improved, the condensate (withdrawn liquid) of the overhead from the column top had a markedly low liquid-liquid separation, so that the distillation column could not be operated stably over a long period of time. In Example 1, due to a high concentration of methyl acetate in the charging mixture (volatile phase component), methyl acetate allowed to effectively react with hydrogen iodide. In particular, the test piece “HB2” showed a relatively excellent corrosion resistance in the whole column. In Example 2, due to a higher concentration of methyl acetate in the charging mixture (volatile phase component), the test piece “HB2” showed a substantially complete corrosion-resisting level (corrosion rate: not more than 0.05 mm/Y). In Examples 3 and 4, due to a further higher concentration of methyl acetate in the charging mixture (volatile phase component), each of the test pieces “HB2”, “HC” and “SUS316L” showed a complete corrosion resistance independent of the change of the water concentration.
According to the present invention, since the water concentration and the methyl acetate concentration in the distillation column are adjusted or controlled, the overhead from the distillation column can be condensed to form an aqueous phase and an organic phase while preventing corrosion of the distillation column due to hydrogen iodide. Thus, the present invention advantageously allows industrial continuous production of acetic acid.
1 . . . Reactor
2 . . . Flash evaporator
3 . . . First distillation column (splitter column)
4 . . . Decanter
5 . . . Second distillation column
34a, 34b, 35a, 35b . . . Supply line
Ueno, Takashi, Shimizu, Masahiko, Miura, Hiroyuki, Nakajima, Hidehiko
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