Distillation process and apparatus with pressure-corrected temperature heat source control

Abstract

The present disclosure relates generally to methods and apparatus for separating effluent in an acetic acid production unit. Accordingly, one aspect of the present disclosure provides a method comprising introducing a feed stream comprising acetic acid and water into a distillation column through a feed inlet, separating the feed stream to form a first fraction enriched in water and a second fraction enriched in acetic acid, measuring an internal temperature and an internal pressure of the column at a location between a first outlet and a second outlet of the column, determining a corrected temperature of the column based on the measured internal pressure and internal temperature of the column, adjusting a heating rate of a heat source in thermal communication with a bottom section of the column if the corrected temperature is different from a target value, and then withdrawing at least a portion of the separated second fraction enriched in acetic acid, the fraction comprising 500-1,500 parts per million by weight (ppmw) of water.

Description

Technical Field

[0001] This disclosure generally relates to methods and apparatus for separating effluents from acetic acid production units. Background Technology

[0002] Commercially, acetic acid has been produced for many years by carbonylating methanol with carbon monoxide in the presence of a Group VIII carbonylation catalyst. Typically, carbon monoxide and methanol are contacted in a reactor in the presence of a homogeneous or heterogeneous rhodium or iridium carbonylation catalyst, methyl iodine, and water. Acetic acid product can usually be recovered by removing crude acetic acid product from the reactor and separating it from other components (such as the Group VIII metal carbonylation catalyst, methyl iodine, methyl acetate, and water) in one or more flash evaporation and / or distillation stages.

[0003] Conventionally, the effluent from the reaction zone of the acetic acid production unit is separated in a flash separation zone, such as a flash tank, to provide a feed stream containing acetic acid, “light” components such as methyl iodide and methyl acetate, and “heavy” components such as acetic anhydride and / or propionic acid. (As used herein, “light component” refers to a component with a boiling point below that of acetic acid and “heavy component” refers to a component with a boiling point above that of acetic acid). The feed stream is then transferred to a light fraction separation zone, where the light components, including water, are separated from the acetic acid product in one or more distillation columns. Finally, the heavy components are separated from the acetic acid product in one or more “heavy fraction” columns (or heavy fraction separation zones).

[0004] Because directly monitoring the composition of the product stream from a distillation column is difficult (e.g., due to cost, complexity, and measurement downtime), the composition is often inferred from the internal temperature of the column. For example, the water content of an acetic acid stream from a light fraction distillation column can be inferred from the temperature measured at a specific location within the column. The heat supplied to the distillation column is then adjusted to maintain a “target” temperature (i.e., corresponding to the desired product composition).

[0005] However, the operating pressure of such columns is generally fixed / controlled at the top of the column or even downstream of the column condenser. For example, the pressure drop within the column (i.e., relative to the fixed top pressure) can change as the overall vapor flow rate increases or decreases. Changes in plant productivity can lead to changes in vapor and liquid flow rates within the column and result in significant changes in pressure drop. When the pressure at the temperature measurement point within the column changes, the same internal column temperature will no longer indicate a fixed product stream composition. In some cases, the column pressure can even be controlled further downstream. For example, in the case of a light distillation column, the pressure can be controlled at the outlet of the light distillation washing system, and the operating pressure of the light distillation column can actually be determined by the back pressure established by intermediate equipment, which will vary according to operational adjustments. This presents further challenges when attempting to determine the appropriate temperature indicating the desired product composition.

[0006] Therefore, there is still a need to improve the separation methods for feed streams containing water and acetic acid, especially those produced by methanol carbonylation. Summary of the Invention

[0007] The scope of this disclosure is not affected in any way by the statements made in this overview.

[0008] In one aspect, this disclosure provides a method for separating a feed stream containing acetic acid and water in a distillation column, the column containing...

[0009] The bottom section that is in thermal connection with the heat source;

[0010] The feed inlet is located above the bottom section;

[0011] The first outlet is located above the feed inlet; and

[0012] The second outlet is located below the feed inlet;

[0013] Methods include

[0014] The feed stream is introduced into the tower through the feed inlet;

[0015] The feed stream is separated at a first heating rate from the heat source to form a first fraction rich in water and a second fraction rich in acetic acid.

[0016] The internal temperature of the tower was measured at a first location between the first and second outlets.

[0017] The internal pressure of the tower was measured at a second location between the first and second outlets.

[0018] The corrected temperature of the tower is determined based on the measured internal pressure and temperature; and

[0019] Determine that the correction temperature is greater than the target value, and then adjust the heat source to a second heating rate lower than the first heating rate; or

[0020] Determine that the correction temperature is below the target value, and then adjust the heat source to a second heating rate greater than the first heating rate;

[0021] At least a portion of the first fraction is extracted through the first outlet; and

[0022] At least a portion of the second fraction is taken out through the second outlet, wherein water is present in the taken-out second fraction in an amount ranging from 500 ppm to 1,500 ppm (ppmw) by weight.

[0023] In some embodiments of the method as otherwise described herein, water is present in the extracted second fraction in an amount ranging from 800 ppmw to 1,200 ppmw.

[0024] In some embodiments of the method as otherwise described herein, acetic acid is present in the extracted second fraction in an amount of at least 95 wt.% (e.g., at least 97.5 wt.% or at least 99 wt.%).

[0025] In some embodiments of the methods further described herein, the feed stream comprises 1-10 wt.% (e.g., 2-7.5 wt.% or 2-5 wt.%) of water, 90-99 wt.% (e.g., 92.5-98 wt.% or 95-98 wt.%) of acetic acid, up to 1 wt.% (e.g., up to 0.75 wt.%) of methyl iodide, and up to 5 wt.% (e.g., up to 3.5 wt.%) of methyl acetate. The feed stream may also contain heavy components, such as acetic anhydride and / or propionic acid. Acetic anhydride and / or propionic acid, such as 100-2,000 ppmw (e.g., 200-1,750 ppmw or 400-1,500 ppmw) of propionic acid, may be present.

[0026] In some embodiments of the methods further described herein, the feed stream comprises 1-10 wt.% (e.g., 2-7.5 wt.% or 2-5 wt.%) of water, 40-85 wt.% (e.g., 40-75 wt.% or 55-85 wt.%) of acetic acid, 10-25 wt.% (e.g., 15-20 wt.%) of methyl iodide, and 15-30 wt.% (e.g., 20-25 wt.%) of methyl acetate. The feed stream may also contain heavy components such as acetic anhydride and propionic acid. Acetic anhydride and / or propionic acid, such as 100-2,000 ppmw (e.g., 200-1,750 ppmw or 400-1,500 ppmw) of propionic acid, may be present.

[0027] In some embodiments of the method as otherwise described herein, the internal temperature and internal pressure of the tower are measured separately at locations between the feed inlet and the second outlet.

[0028] In some embodiments of the method as otherwise described herein, the internal temperature and internal pressure of the tower are measured individually at locations no more than 50% (e.g., no more than 45% or 40%) of the total number of theoretical stages separated from the second outlet and the first and second outlets.

[0029] In some embodiments of the method as otherwise described herein, the measured internal pressure is in the range of 0.125 MPaG to 0.5 MPaG.

[0030] In some embodiments of the method as otherwise described herein, the measured internal pressure is greater than the pressure at the top of the tower (e.g., at least 0.01 MPaG, or at least 0.02 MPaG, or at least 0.03 MPaG).

[0031] In some embodiments of the method as otherwise described herein, the measured internal temperature is in the range of 110°C to 200°C (e.g., in the range of 120°C to 190°C or 130°C to 180°C).

[0032] In some embodiments of the method as otherwise described herein, determining the correction temperature includes adding a correction factor to the measured internal tower temperature, the correction factor being based on the measured internal tower pressure.

[0033] In some embodiments of the method as otherwise described herein, the heat source comprises a reboiler.

[0034] In some embodiments of the method as otherwise described herein, adjusting the heat source includes increasing or decreasing the flow rate of steam supplied to the reboiler.

[0035] In some embodiments of the method as otherwise described herein, at least one of the following comprises zirconium: the bottom section of the column, the second outlet, the inner surface of the heat source, any connecting conduit between the second outlet and the heat source, and any internal components of the bottom section. (The term “internal components” includes any component within the column and, in this invention, includes, but is not limited to, trays and packing in the bottom section of the distillation column).

[0036] In some embodiments of the method as otherwise described herein, the bottom section of the tower and / or the second outlet contains zirconium.

[0037] In some embodiments of the method as otherwise described herein, the second outlet comprises zirconium.

[0038] In some embodiments of the method as further described herein, a second fraction is separated to produce a product stream containing acetic acid and water, and a waste stream containing heavy components such as acetic anhydride and / or propionic acid, and in particular a waste stream containing propionic acid.

[0039] In particular, the second fraction may contain acetic acid, water, and heavy components such as acetic anhydride and / or propionic acid, and the method may further include the step of passing all or part of the second fraction to a second distillation column, and particularly a "heavy fraction column," to separate the heavy components. In a preferred embodiment, the second distillation column contains...

[0040] The bottom section that is in thermal connection with the heat source;

[0041] The feed inlet located above the bottom section (“second tower feed inlet”);

[0042] The outlet located below the feed inlet (“third outlet”); and

[0043] The outlet located above the feed inlet (“Fourth Outlet”);

[0044] Methods include

[0045] All or part of the second fraction is introduced into the column through the feed inlet;

[0046] The third fraction, containing heavy components, is extracted through the outlet located below the feed inlet, and

[0047] The fourth fraction, rich in acetic acid, is extracted through the outlet located above the feed inlet.

[0048] In some embodiments, the second distillation column may include two outlets located above the feed inlet, both of which extract an acetic acid-rich fraction. One of these fractions may serve as the aforementioned fourth fraction, and preferably as the product stream, while the other, preferably a fraction with a lower flow rate, may serve as the recycle stream.

[0049] On the other hand, this disclosure provides a system for separating a feed stream containing acetic acid and water, the system comprising...

[0050] A distillation column capable of separating the feed stream to produce a first feed stream rich in water and a second feed stream rich in acetic acid, the second feed stream containing an amount of water in the range of 500 ppmw to 1,500 ppmw.

[0051] The tower contains

[0052] The bottom section that is in thermal connection with the heat source;

[0053] The feed inlet is located above the bottom section;

[0054] The first outlet is located above the feed inlet;

[0055] The second outlet is located below the feed inlet;

[0056] A temperature sensor located between the first and second outlets; and

[0057] A pressure sensor located between the first outlet and the second outlet;

[0058] The heat source includes a reboiler and a control unit, which can adjust the heating rate of the reboiler based on internal temperature measurements from a temperature sensor and internal pressure measurements from a pressure sensor.

[0059] In some embodiments of the system as otherwise described herein, the temperature sensor and the pressure sensor are each located separately between the feed inlet and the second outlet.

[0060] In some embodiments of the system as otherwise described herein, the temperature sensor and the pressure sensor are each individually isolated from the second outlet for no more than 50% (e.g., no more than 45% or 40%) of the theoretical total number of stages separating the first outlet and the second outlet.

[0061] In some embodiments, as further described herein, the system further includes a top pressure sensor capable of measuring the top pressure of the tower.

[0062] In some embodiments of the system as otherwise described herein, at least one of the bottom section of the tower, the second outlet, the inner surface of the heat source, any connecting conduit between the second outlet and the heat source, and any internal components of the bottom section comprises zirconium.

[0063] In some embodiments of the system as otherwise described herein, the bottom section of the tower and / or the second outlet contains zirconium.

[0064] In some embodiments of the system as otherwise described herein, the second outlet comprises zirconium.

[0065] Other aspects of this disclosure will be apparent to those skilled in the art from the following description. Attached Figure Description

[0066] Figure 1 This is a schematic view of a distillation system according to one embodiment of the present disclosure. Detailed Implementation

[0067] In all respects, the method disclosed herein provides improved separation of feed streams containing acetic acid and water.

[0068] Further features of the method of this disclosure will now be described with reference to the accompanying drawings.

[0069] The inventors have determined that by separating a feed stream containing acetic acid and water in a distillation column, measuring the internal pressure and internal temperature of the column, and then calculating the corrected internal temperature, a heat source in thermal communication with the bottom section of the distillation column can be adjusted to maintain the corrected internal temperature at or near a target value.

[0070] Advantageously, the target value can correspond to the water concentration of the acetic acid-rich feed stream taken from the tower, which desirablely limits the corrosivity of the system and avoids unnecessary energy consumption.

[0071] In particular, in this invention, the amount of water present in the extracted second fraction is maintained in the range of 500 ppmw to 1,500 ppmw. This range has been found to provide optimal results, minimizing or even avoiding corrosion of certain materials (e.g., zirconium) while also minimizing unnecessary energy consumption (e.g., reboiler load). As previously mentioned, water is preferably present in the extracted second fraction in an amount in the range of 800 ppmw to 1,200 ppmw.

[0072] Therefore, although distillation columns used to separate impurities from a desired component are typically operated to minimize the impurity content of the resulting desired component stream, where the desired component is acetic acid and the impurity is water, as in this invention, it is then found that a water concentration of less than 500 ppmw in the product stream can lead to increased corrosion in the system.

[0073] In particular, a mixture of acetic acid and water is known to be corrosive under the conditions of a distillation column. For this reason, at least the bottom section and second outlet of the distillation column, but generally also the auxiliary equipment at the base of the column (such as heat sources (generally including one or more reboilers), base pumps, valves, piping, etc.), can be made of or lined with corrosion-resistant materials. Zirconium is preferred. However, it has now been found that even this material can be significantly corrosive if the water concentration in the product stream (and consequently at the bottom section and second outlet of the column) is too low.

[0074] Therefore, in this invention, it is desirable not only that the water concentration is not too high to avoid or minimize the use of water for acetic acid removal in any subsequent steps to meet product specifications, but also that the concentration is not too low, as this would lead to corrosion problems. To maintain the concentration within this range, precise control of the column is required. This invention uses a defined calibration temperature not to minimize impurity levels, but to control them within the desired range.

[0075] Therefore, one aspect of this disclosure provides a method comprising introducing a feed stream containing acetic acid and water into a distillation column through a feed inlet, separating the feed stream to form a first fraction rich in water and a second fraction rich in acetic acid, measuring the internal temperature and internal pressure of the column at corresponding locations between a first outlet and a second outlet, determining a corrected temperature of the column based on the measured internal pressure and internal temperature, adjusting the heating rate of a heat source in thermal communication with the bottom section of the column if the corrected temperature differs from a target value, and removing at least a portion of the separated second fraction rich in acetic acid, said fraction containing 500-1,500 ppm (ppmw) of water by weight. As used herein, unless further defined, the water-rich fraction has a relatively greater amount of water than the corresponding acetic acid-rich fraction; and the acetic acid-rich fraction has a relatively greater amount of acetic acid than the corresponding water-rich fraction.

[0076] As described above, the feed stream contains acetic acid and water. In some embodiments further described herein, the feed stream contains a vapor fraction from the flash separation zone of the acetic acid production unit. In other embodiments further described herein, the feed stream contains a fraction from the light fractionation column in the light fractionation zone of the acetic acid production unit. The feed stream may contain any fraction from such an acetic acid-rich light fractionation column, such as the bottom fraction from the light fractionation column. As used herein, "acetic acid production unit" refers to a unit capable of producing acetic acid products. According to one embodiment of this disclosure, the acetic acid production unit includes a reaction zone, a flash separation zone, a light fractionation zone, and a heavy fractionation zone.

[0077] In some embodiments, the reaction zone of an acetic acid production unit comprises any suitable reaction unit that can be used to produce an effluent containing acetic acid. For example, in some such embodiments, the reaction zone of an acetic acid production unit includes one or more reactors in which acetic acid can be produced by carbonylating methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system. Suitable reactors for the carbonylation of methanol and / or its reactive derivatives and their configurations are generally known in the art.

[0078] For example, in some embodiments, methanol and / or its reactive derivatives are carbonylated with carbon monoxide in the presence of a Group VIII metal carbonylation catalyst and methyl iodine to produce acetic acid in the reaction zone of an acetic acid production unit. In some embodiments, the reactive derivative of methanol is, for example, methyl acetate, dimethyl ether, or methyl iodine. Methods for methanol carbonylation and Group VIII metal catalysts are generally known in the art.

[0079] In some embodiments, the carbonylation of methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system can be homogeneous or heterogeneous. For example, in some embodiments, heterogeneous carbonylation is catalyzed by a Group VIII metal carbonylation catalyst (e.g., containing rhodium and / or iridium) supported on an inert support (e.g., carbon, activated carbon). In some such embodiments, the catalyst further comprises at least one metal promoter, such as ruthenium, iron, nickel, lithium, and cobalt. In some such embodiments, the methanol reactants can be provided to the reaction zone in a liquid and / or gas phase. In some desirable embodiments, methyl iodine and optionally water are provided to the reaction zone in a gas phase.

[0080] In another example, in some embodiments, homogeneous carbonylation is catalyzed by a soluble Group VIII metal carbonylation catalyst (e.g., containing rhodium and / or iridium) in a liquid reaction composition comprising methyl iodine, methyl acetate, and water. In some such embodiments, the liquid reaction composition further comprises acetic anhydride and / or propionic acid byproducts. In this embodiment, the carbonylation catalyst may be added to the liquid reaction composition in any form that is soluble in the liquid reaction composition or convertible to a soluble form.

[0081] In some embodiments, as further described herein, the iridium-containing carbonylation catalyst is selected from IrCl3, IrI3, IrBr3, [Ir(CO)2I]2, [Ir(CO)2Cl]2, [Ir(CO)2Br]2, [Ir(CO)2I2]2. – [Ir(CO)2Br2] – [Ir(CO)2I2] – [Ir(CH3)I3(CO)2] – Ir4(CO) 12 IrCl 3.4 H2O, IrBr 3.4 H2O, Ir3(CO) 12 Iridium metal, Ir₂O₃, IrO₂, Ir(acac)(CO)₂, Ir(acac)₃, iridium acetate, [Ir₃O(OAc)₆(H₂O)₃][OAc], and hexachloroiridium acid [H₂IrCl₆]. In some desired embodiments, the catalyst comprises a chlorine-free iridium complex, such as acetate, oxalate, and acetoacetate. In some embodiments further described herein, the concentration of the iridium-containing carbonylation catalyst in the liquid reaction composition is in the range of 100 ppm to 6,000 ppm (ppmw) iridium by weight.

[0082] In certain embodiments further described herein, the rhodium-containing carbonylation catalyst is selected from [Rh(CO)₂Cl]₂, [Rh(CO)₂I]₂, [Rh(Cod)Cl]₂, rhodium(III) chloride, rhodium(III) chloride trihydrate, rhodium(III) bromide, rhodium(III) iodide, rhodium(III) acetate, rhodium dicarbonylacetylpyruvate, RhCl₃(PPh₃)₃, and RhCl(CO)(PPh₃)₂. In certain embodiments further described herein, the concentration of the rhodium-containing carbonylation catalyst in the liquid reaction composition is at least 1 ppm (i.e., at most the solubility limit of the catalyst in the liquid reaction composition or in the downstream separation zone), for example, rhodium in the range of 10 ppmw to 1,500 ppmw.

[0083] In some embodiments as further described herein, the liquid reaction composition comprises an iridium carbonylation catalyst and further comprises an auxiliary agent selected from ruthenium, osmium, and rhenium. For example, in some desirable embodiments, the liquid reaction composition comprises an iridium carbonylation catalyst and further comprises a ruthenium-containing compound soluble in the liquid reaction composition. In such embodiments, the ruthenium-containing compound may be added to the liquid reaction composition in any form soluble in the liquid reaction composition or convertible to a soluble form. In some such embodiments, the ruthenium-containing compound comprises a chlorine-free compound, such as an acetate. In some such embodiments, the ruthenium-containing compound is selected from ruthenium(III) chloride, ruthenium(III) chloride trihydrate, ruthenium(IV) chloride, ruthenium(III) bromide, ruthenium(III) iodide, ruthenium metal, ruthenium oxide, ruthenium(III) formate, [Ru(CO)3I3]-H + Ruthenium tetrachloro(II, III), ruthenium acetate(III), ruthenium propionate(III), ruthenium butyrate(III), pentacarbonylruthenium, dodecacarbonyltriruthenium, and mixed halogenated carbonylruthenium (e.g., dichlorotricarbonylruthenium(II) dimer, dibromotricarbonylruthenium(II) dimer) and other organorruthenium complexes (e.g., tetrachlorodi(4-methylisopropylphenyl)diruthenium(II), tetrachlorodi(phenyl)diruthenium(II), dichloro(cyclooctyl-1,5-diene)ruthenium(II) polymer, and tri(acetylated pyruvate)ruthenium(III)). In some desirable embodiments, the ruthenium-containing compound is free from impurities that provide or can generate in situ an ionic iodide that inhibits the reaction, such as alkali metal or alkaline earth metal salts or other metal salts.

[0084] In some embodiments, the ruthenium additive is present in the liquid reaction composition in an effective amount (e.g., at most the solubility limit of the additive in the liquid reaction composition or in the downstream separation zone).

[0085] In other embodiments, the liquid composition comprises a rhodium carbonylation catalyst and further comprises an agent selected from alkali metals and / or organic iodides (such as quaternary ammonium iodides). In some desirable embodiments, the liquid composition comprises a rhodium carbonylation catalyst and further comprises a lithium iodide agent.

[0086] In some embodiments as further described herein, the liquid reaction composition comprises a rhodium carbonylation catalyst, and methyl acetate is present in the liquid reaction composition in an amount ranging from 0.1 wt.% to 70 wt.%. In other embodiments, the liquid reaction composition comprises an iridium carbonylation catalyst, and methyl acetate is present in the liquid reaction composition in an amount ranging from 1 wt.% to 70 wt.%. In some desirable embodiments, methyl acetate is present in the liquid reaction composition in an amount ranging from 2 wt.% to 50 wt.% (e.g., 3 wt.% to 35 wt.%).

[0087] As described above, water is present in the liquid reaction composition. Those skilled in the art will recognize that water is formed in situ in the liquid reaction composition via an esterification reaction between methanol and the acetic acid product. In some embodiments, water may also be introduced into the carbonylation reaction zone (e.g., together with or separately from other components of the liquid reaction composition). In some desirable embodiments, water is present in the liquid reaction composition in an amount ranging from 0.1 wt.% to 15 wt.% (e.g., from 1 wt.% to 15 wt.% or from 1 wt.% to 8 wt.%).

[0088] As described above, heavy components such as propionic acid byproducts may also be present in the liquid reaction composition. In some embodiments, propionic acid is present in the liquid reaction composition in an amount ranging from 200 ppmw to 2,500 ppmw (e.g., from 400 ppmw to 2,000 ppmw or from 600 ppmw to 1,400 ppmw).

[0089] In some desirable embodiments, methyl iodine is present in the liquid reaction composition in an amount ranging from 1 wt.% to 20 wt.%. For example, in some such embodiments, methyl iodine is present in the liquid reaction composition in an amount ranging from 2 wt.% to 16 wt.%. In some embodiments, as further described herein, the liquid reaction composition comprises a solvent. For example, in some such embodiments, the liquid reaction composition comprises an acetic acid solvent (e.g., recycled from the separation zone of an acetic acid production unit).

[0090] As described above, acetic acid can be produced in the reaction zone by carbonylating methanol and / or its reactive derivatives with carbon monoxide. In some embodiments further described herein, the carbon monoxide supplied to the reaction zone is substantially pure. In other embodiments, the carbon monoxide supplied to the reaction zone contains one or more impurities such as carbon dioxide, methane, nitrogen, hydrogen, or an inert gas. In some embodiments further described herein, the partial pressure of carbon monoxide (e.g., in the reactor of the reaction zone) is in the range of 1 bar to 70 bar, for example, in the range of 1 bar to 35 bar.

[0091] In some embodiments further described herein, the carbonylation reaction is carried out at a total pressure in the range of 10 barg to 100 barg (e.g., in a reactor in a reaction zone). In some embodiments further described herein, the carbonylation reaction is carried out at a temperature in the range of 100°C to 300°C (e.g., in a reactor in a reaction zone). For example, in some such embodiments, the carbonylation reaction is carried out at a temperature in the range of 150°C to 210°C, or 170°C to 195°C, or 185°C to 195°C.

[0092] The carbonylation process can be carried out as a batch process or as a continuous process. In some desirable embodiments, the carbonylation process is carried out as a continuous process.

[0093] As described above, the acetic acid production unit includes a flash separation zone configured to separate crude acetic acid product from the effluent of the reaction zone. In some embodiments, as further described herein, the flash separation zone includes tanks for separating the effluent to form a liquid fraction (e.g., containing a carbonylation catalyst) and a vapor fraction containing acetic acid and water. The vapor fraction removed from the flash separation zone is transferred to a light fraction separation zone of the acetic acid production unit. In some such embodiments, the liquid removed from the tank is transferred as a recycle to the reaction zone of the acetic acid production unit.

[0094] The light fraction separation zone of the acetic acid production unit is configured to separate at least the more volatile components from the vapor fraction of acetic acid. For example, in some embodiments, acetic acid is produced in the reaction zone by carbonylating methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system, and the light fraction separation zone of the acetic acid production unit is configured to separate acetic acid and further separate methyl iodide, methyl acetate, and water, which can be recycled back to the reaction zone.

[0095] The distillation column in the method of the present invention may be located in the light fraction separation zone of an acetic acid production unit. In some embodiments, the light fraction separation zone includes a distillation column that separates a crude acetic acid product containing acetic acid and heavy components such as propionic acid from a light fraction containing methyl iodide, methyl acetate, and water. In some embodiments, the distillation column may produce a “dry” crude acetic acid stream. A “dry” or “dried” acetic acid stream, as used herein, contains up to 1,500 ppmw of water. In this embodiment, the distillation column may be the distillation column in the method of the present invention. (And in this embodiment, it may also be considered a combination of a light fraction and a drying column). In other embodiments, the light fraction separation zone includes a first distillation column and a separate drying column. For example, the light fraction separation zone may include a first distillation column that separates the crude acetic acid stream (containing acetic acid, heavy components, and residual water) from methyl acetate and methyl iodide, and a separate drying column that separates the residual water from the crude acetic acid stream to produce a “dry” crude acetic acid stream. In these embodiments, the drying column may be the distillation column in the method of the present invention. In any embodiment, the dried crude acetic acid product contains, in addition to acetic acid, a heavy component, such as propionic acid. The dried crude acetic acid stream in any embodiment can then be passed to a heavy fraction separation zone as described herein for the separation of the heavy component.

[0096] Figure 1 This is a schematic cross-sectional view of a tower according to one embodiment of this disclosure. Figure 1As shown, column 100 includes a bottom section 110 in thermal communication with a heat source 140 (i.e., providing heat to the bottom section at a heating rate) and a fractionation section 120 above the bottom section 110. Figure 1 In one embodiment, the heat source 140 includes a reboiler 142 in fluid communication with the bottom section 110 (via lines 114 and 116) and a control unit 144 capable of adjusting the heating rate of the reboiler 142. Figure 1 In one implementation, the control unit 144 is capable of regulating the amount of steam supplied from the steam source 146 to the reboiler 142.

[0097] Therefore, in some embodiments as further described herein, the heat source is a reboiler, and regulating the heat source (i.e., providing heat to the bottom section at an increased or decreased heating rate) includes regulating the amount of steam supplied to the reboiler. Of course, in other embodiments, other heat transfer media known in the art (e.g., hot oil, flue gas, process feed) may be supplied to the reboiler.

[0098] Tower 100 includes a feed inlet 122 located above a bottom section 110, a first outlet 124 located above the feed inlet 122, and a second outlet 112 located below the feed inlet 122. In some embodiments, the feed inlet is located 30-70% of the total number of theoretical levels present in the tower relative to the base of the tower. In some embodiments, the first outlet is located at least 70% (e.g., at least 80% or at least 90%) of the total number of theoretical levels present in the tower relative to the base of the tower. For example, in some such embodiments, the first outlet is located at or near the top of the tower. In some embodiments, the second outlet is located no more than 30% (e.g., no more than 20% or no more than 10%) of the total number of theoretical levels present in the tower relative to the base of the tower. For example, in some such embodiments, the second outlet is located at or near the bottom of the tower.

[0099] As described above, the column includes a fractionation section 120, which includes one or more fractionation trays (not shown). In some embodiments further described herein, the fractionation section includes at least 10 trays, such as 10-100 trays, or 10-80 trays, or 25-100 trays, or 25-80 trays, or 40-100 trays, or 40-80 trays. In some embodiments further described herein, the fractionation section includes at least 10 theoretical stages, such as 10-60 theoretical stages, or 15-60 theoretical stages, or 20-60 theoretical stages, or 10-50 theoretical stages, or 15-50 theoretical stages, or 20-50 theoretical stages, or 20-60 theoretical stages, or 20-50 theoretical stages, or 20-40 theoretical stages. In some embodiments further described herein, the fractionation section contains one or more packed beds.

[0100] Column 100 includes a temperature sensor 132 located between a first outlet 124 and a second outlet 112, and a pressure sensor 134 located between the first outlet 124 and the second outlet 112. In some embodiments as further described herein, the temperature sensor and pressure sensor are separated for no more than 10% (e.g., no more than 5% or 2.5%) of the total number of theoretical stages present in the column. In some embodiments as further described herein, both the temperature sensor and the pressure sensor are located between two adjacent trays in the fractionation section. For example, in Figure 1 In this implementation scheme, the temperature sensor and pressure sensor are located between the control tray and the adjacent tray. Figure 1 In one embodiment, temperature sensor 132 is located above pressure sensor 134. Of course, in other embodiments, the temperature and pressure sensors are located at similar distances from the base of the tower, or the pressure sensor is located above the temperature sensor. Suitable temperature and pressure sensors (i.e., capable of determining the internal temperature and internal pressure of the tower, respectively) are generally known in the art. Those skilled in the art will appreciate that the internal pressure of the tower does not necessarily need to be measured directly, but can be measured through calculations based on other suitable pressure measurements. For example, the internal pressure of the tower at a second location can be measured by combining a measurement of the pressure at the top of the tower with a measurement of the differential pressure across a suitable section of the tower to provide a measurement of the internal pressure of the tower at the second location.

[0101] exist Figure 1 In some embodiments, the temperature sensor and the pressure sensor are each located between the feed inlet 122 and the second outlet 112. In some embodiments as further described herein, the temperature sensor and the pressure sensor are each individually separated from the base of the column for no more than 50% (e.g., no more than 45% or 40%) of the total theoretical number of the separating first and second outlets.

[0102] Tower 100 may include a top pressure sensor 136. In some embodiments, the top pressure sensor is located at least 70% (e.g., at least 80% or at least 90%) of the total number of theoretical stages present in the tower, separated from the base of the tower. For example, in some such embodiments, the top pressure sensor is located at or near the top of the tower. In other embodiments, the top pressure sensor is located downstream of the first outlet of the tower. For example, in Figure 1 In one embodiment, the top pressure sensor 136 is located downstream of the first outlet 124 (i.e., configured to measure the pressure of the feed flow 126). Suitable pressure sensors and their configurations for measuring the top pressure of the tower are generally known in the art.

[0103] In some embodiments as further described herein, one or more components of the tower comprise zirconium. In some embodiments as further described herein, one or more (e.g., each) of the tower's second outlet, bottom section, reboiler, any connecting conduit between the second outlet and the heat source, and any internal components of the bottom section comprise zirconium. For example, in some embodiments, the second outlet comprises zirconium.

[0104] In operation, the feed stream is introduced into column 100 through feed inlet 122. In some embodiments further described herein, the pressure at the inlet is at least about 0.1 MPaG, for example, in the range of 0.1 MPaG-1 MPaG or 0.1 MPaG-0.5 MPaG. In some embodiments further described herein, the feed stream comprises at least a portion of the vapor fraction taken from the flash separation zone of the acetic acid production unit. In other embodiments, the feed stream comprises at least a portion of the effluent from a light fractionation column (e.g., a distillation column that separates crude acetic acid stream (containing acetic acid, heavy components, and residual water) from methyl acetate and methyl iodine).

[0105] The feed stream contains water and acetic acid. In some embodiments further described herein, the feed stream contains at least 90 wt.% acetic acid. For example, in some such embodiments, the feed stream contains 90-99 wt.%, or 92.5-98 wt.%, or 95-98 wt.% acetic acid. In some embodiments further described herein, the feed stream contains 40-85 wt.% acetic acid. For example, in some such embodiments, the feed stream contains 40-75 wt.%, or 55-85 wt.% acetic acid. In some embodiments further described herein, the feed stream contains no more than 10 wt.% water. For example, in some such embodiments, the feed stream contains 1-10 wt.%, or 2-7.5 wt.%, or 2-5 wt.% water.

[0106] In some embodiments as further described herein, the feed stream further comprises a heavy component, such as propionic acid. For example, in some such embodiments, the feed stream contains 100-2,000 ppmw (e.g., 200-1,750 ppmw or 400-1,500 ppmw) of a heavy component, such as propionic acid and / or acetic anhydride. In some such embodiments, the feed stream contains 100-2,000 ppmw (e.g., 200-1,750 ppmw or 400-1,500 ppmw) of propionic acid. In some embodiments, the feed stream further comprises one or more of methanol, methyl acetate, methyl iodine, carbon monoxide, carbon dioxide, an inert gas (e.g., nitrogen), and other reaction byproduct gases (e.g., hydrogen, methane). For example, in some such embodiments, the feed stream contains up to 1 wt.% methyl iodine (e.g., up to 0.75 wt.% or up to 0.5 wt.% methyl iodine) and up to 5 wt.% methyl acetate (e.g., up to 3.5 wt.% or up to 2 wt.% methyl acetate). In another example, in some such embodiments, the feed stream contains 10-25 wt.% methyl iodine (e.g., 15-20 wt.% methyl iodine) and 15-30 wt.% methyl acetate (e.g., 20-25 wt.% methyl acetate).

[0107] At a first heating rate in the reboiler 142 of heat source 140, the feed stream is separated to form a first fraction rich in water and a second fraction rich in acetic acid. The internal temperature of column 100 is measured by temperature sensor 132 (i.e., at a first location corresponding to the position of temperature sensor 132, as further described herein), and the internal pressure of the column is measured by pressure sensor 134 (i.e., at a second location corresponding to the position of pressure sensor 134, as further described herein). In some embodiments, the internal temperature and internal pressure of the column are each measured separately at a location between the feed inlet and the second outlet. For example, in some such embodiments, the internal temperature and internal pressure of the column are each measured separately at a location no more than 50% (e.g., no more than 45% or 40%) of the total theoretical number of stages separating the first and second outlets, separated from the second outlet.

[0108] In some embodiments further described herein, the measured internal pressure of the tower is in the range of 0.125 MPaG to 0.5 MPaG. In some embodiments, the measured internal pressure is greater than the top pressure of the tower (e.g., measured by a top pressure sensor as further described herein). For example, in some such embodiments, the measured internal pressure is at least 0.01 MPaG, or at least 0.02 MPaG, or at least 0.03 MPaG greater than the top pressure of the tower. In some embodiments further described herein, the measured internal temperature of the tower is in the range of 110°C to 200°C. For example, in some such embodiments, the measured internal temperature of the tower is in the range of 120°C to 190°C or 130°C to 180°C.

[0109] Based on the measured internal pressure and temperature of the tower, a corrected temperature for the tower is determined. In some embodiments, as further described herein, determining the corrected temperature involves adding a correction factor to the measured internal temperature of the tower.

[0110] T c =T m -F(P m )

[0111] Where T c To correct for temperature, T m For the measured internal temperature of the tower, and F(P) m The internal pressure P of the tower is based on measurements. m The correction factor. In some such implementations, the correction factor is the solution to the linear equation:

[0112] F(P m )=x*P m +y

[0113] Where x and y are real coefficients. Those skilled in the art can determine appropriate real coefficients based, for example, on product composition measured under one or more sets of distillation conditions. An example is provided in the following embodiments.

[0114] Advantageously, the inventors have determined that the correction temperature, as otherwise described herein, is strongly correlated with the water concentration present in the separated acetic acid-rich second fraction, and thus can more reliably indicate deviations from distillation conditions required to maintain the desired product composition.

[0115] Therefore, in some embodiments as further described herein, the determined correction temperature is greater than the target value, and the heat source is adjusted to a second heating rate lower than the first heating rate. In other embodiments, the determined correction temperature is less than the target value, and the heat source is adjusted to a second heating rate greater than the first heating rate. Figure 1In one implementation, the heat source 140 of the regulating tower 100 includes a control unit 144 for increasing or decreasing the amount of steam supplied from the steam source 146 to the reboiler 142.

[0116] At least a portion of the second fraction is withdrawn from column 100 as feed stream 118 through second outlet 112. As described above, the method as further described herein can be maintained to produce the withdrawn second fraction with a desired composition. The inventors have further determined that the amount of water present in the withdrawn second fraction can be maintained in the range of 500 ppmw to 1,500 ppmw, which desirously minimizes or even avoids corrosion of certain materials (e.g., zirconium) and unnecessary energy consumption (e.g., reboiler load).

[0117] Therefore, the second fraction taken out through the second outlet 112 contains water in an amount ranging from 500 ppmw to 1,500 ppmw. In some embodiments further described herein, water is present in the taken-out second fraction in an amount ranging from 800 ppmw to 1,200 ppmw. In some embodiments further described herein, acetic acid is present in the taken-out second fraction in an amount of at least 95 wt.% (e.g., at least 97.5 wt.% or at least 99 wt.%). In some embodiments further described herein, the taken-out second fraction further contains 100-2,500 ppmw (e.g., 200-2,000 ppmw or 600-1,500 ppmw) of heavy components, such as propionic acid and / or acetic anhydride, such as propionic acid containing 100-2,500 ppmw (e.g., 200-2,000 ppmw or 600-1,500 ppmw).

[0118] At least a portion of the first fraction is withdrawn from column 100 as feed stream 126 through first outlet 124. In some embodiments, the withdrawn first fraction comprises one or more of water, acetic acid, and methanol, methyl acetate, methyl iodine, carbon monoxide, carbon dioxide, inert gas (e.g., nitrogen), and other reaction byproduct gases (e.g., hydrogen, methane). In some embodiments further described herein, the first fraction comprises 5-95 wt.% (e.g., 30-50 wt.% or 70-90 wt.%) of water, 5-50 wt.% (e.g., 5-20 wt.% or 10-30 wt.%) of acetic acid, and up to 70 wt.% (e.g., up to 20 wt.% or 40-60 wt.%) of methanol, methyl acetate, methyl iodine, carbon monoxide, and carbon dioxide in a combined amount. For example, in some embodiments, the first fraction comprises 70-90 wt.% water, 10-30 wt.% acetic acid, and up to 20 wt.% methanol, methyl acetate, methyl iodine, carbon monoxide, and carbon dioxide in a combined amount. In another example, in some embodiments, the first fraction comprises 30-50 wt.% water, 5-20 wt.% acetic acid, and 40-60 wt.% methanol, methyl acetate, methyl iodine, carbon monoxide, and carbon dioxide in a combined amount.

[0119] In some embodiments as further described herein, the method further includes one or more condensers and / or coolers to condense the first fraction taken out and form a liquid fraction. Those skilled in the art will recognize that any suitable method known in the art can be used to condense the first fraction taken out into a liquid phase. For example, in some embodiments, at least one heat exchanger (e.g., supplied with water as a cooling medium) is used to condense the fraction. Components of the uncondensed overhead fraction (e.g., carbon monoxide, carbon dioxide, inert gases, reaction byproduct gases) are removed as a waste gas stream. In some embodiments, acetic acid is produced in the reaction zone by carbonylating methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system, and the waste gas stream further contains methyl iodine (e.g., present as entrained and / or evaporated methyl iodine), methyl acetate, and water.

[0120] In some embodiments, the first fraction taken out contains methyl acetate, water, and acetic acid. In some embodiments, acetic acid is produced in the reaction zone by carbonylating methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system, and the first fraction taken out further contains methyl iodine. In some embodiments, the first fraction taken out further contains entrained or dissolved gaseous components (e.g., carbon monoxide, carbon dioxide, inert gases).

[0121] In some embodiments, a portion of the first fraction is condensed and returned as a reflux stream to the distillation column, and preferably to the distillation column from which the first fraction was taken. In some embodiments, the method includes a decanter, wherein the first fraction is separated into two layers: a lower (e.g., organic) layer containing methyl acetate and methyl iodine and an upper (e.g., aqueous) layer containing water. In some embodiments, acetic acid is produced in the reaction zone by carbonylating methanol and / or its reactive derivatives with carbon monoxide in the presence of a Group VIII metal catalyst system, and the lower layer further contains methyl iodine. In some embodiments, at least a portion (e.g., all) of the upper layer from the decanter is returned to the distillation column, and preferably as a reflux stream to the distillation column from which the first fraction was taken. In some embodiments, at least a portion (e.g., all) of the upper layer from the decanter is recycled to the reaction zone. In some embodiments, exhaust gas is removed from the decanter and transferred to an exhaust gas scrubbing unit (e.g., prior to disposal).

[0122] In some embodiments, at least a portion of the extracted second fraction, comprising acetic acid and heavy components (such as propionic acid and / or acetic anhydride), is transferred to a heavy fractionation column via a feed inlet located at a midpoint in the column. In this embodiment, a waste stream containing heavy components (such as propionic acid and / or acetic anhydride) is removed from the heavy fractionation column via a heavy product outlet, and acetic acid is removed as a product stream at one or more outlets of the column (e.g., as an overhead stream from an outlet at the top of the column, or as a side-draw stream from an outlet located above the feed inlet). In some embodiments, the product stream comprises substantially acetic acid. In some embodiments, the product stream comprises substantially acetic acid and contains less than 1,500 ppmw of water. In some desirable embodiments, the product stream comprises substantially acetic acid and contains less than 1,500 ppmw of a combined total acetic anhydride, propionic acid, and water. Suitable columns that can be used as heavy fractionation columns and their configurations are generally known in the art. For example, in some embodiments, the heavy fractionation column is connected to a condenser. In another example, in some embodiments, a reboiler is connected to the base of the heavy fractionation column.

[0123] Example

[0124] The following examples illustrate specific embodiments of the present invention and its various uses. These descriptions are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0125] Example 1. Combined light fraction and drying tower

[0126] The reboiling, combined light fraction, and drying columns of the light fraction separation zone were modeled using ASPEN Plus (Aspen Technology Inc., Bedford, MA). The plate column comprises 28 theoretical stages between a first outlet at the top and a second outlet at the base. The internal pressure and temperature of the column were measured approximately six theoretical stages away from the second outlet, between two adjacent trays, and then the corrected temperature of the column was calculated using Equation I.

[0127] T c =T m -(142.35*P m -24.951)

[0128] Where T c To correct for temperature (expressed in °C), T m The measured internal temperature (in °C) and P m The measured internal temperature (in MPaG).

[0129] In baseline operation B, the pressure at the top of the column was 0.1297 MPaG, and the pressure at the base of the column was 0.1867 MPaG, providing an average pressure drop of approximately 20 mbar / theoretical level across the column. At measured internal temperatures and pressures of 146.49 °C and 0.1751 MPaG, respectively, the water concentration of the acetic acid-rich feed stream exiting the second outlet was 1,000 ppmw. Therefore, the target value corresponding to 1,000 ppmw of water is 146.5 °C.

[0130] In operation E1, the average pressure drop across the column was increased to 24 mbar / theoretical level to simulate variations in the feed flow rate into the distillation column. The top pressure of the column was maintained at 0.1297 MPaG, but the pressure at the base of the column was increased to 0.1981 MPaG. The measured internal pressure increased to 0.1848 MPaG. To maintain the corrected internal temperature at the target value of 146.5 °C, the steam supply to the column reboiler was adjusted to increase the reboiler heating rate, thereby increasing the measured internal temperature of the column to 147.85 °C, as shown in Table 1 below. By controlling the steam supply to the column reboiler to maintain the desired corrected temperature, the water concentration of the acetic acid-rich feed stream exiting the second outlet decreased only to 970 ppmw.

[0131] In comparative operation C1, the above pressure changes were simulated again, but only the steam supplied to the column reboiler was controlled to maintain the measured internal temperature at 146.49°C. As shown in Table 1 below, the resulting water concentration from the acetic acid-rich feed increased to 1,620 ppmw, significantly higher than the generally acceptable levels for commercial applications.

[0132] In operation E2, the average pressure drop across the column was reduced to 12 mbar / theoretical level to simulate variations in the feed flow rate into the distillation column. The top pressure of the column was maintained at 0.1297 MPaG, but the measured internal pressure was reduced to 0.1572 MPaG. To maintain the corrected internal temperature at the target value of 146.5 °C, the steam supply to the reboiler was adjusted to reduce the reboiler heating rate, thereby reducing the measured internal temperature of the column to 143.93 °C, as shown in Table 1 below. By controlling the steam supply to the column reboiler to maintain the desired corrected temperature, the water concentration of the acetic acid-rich feed stream exiting the second outlet increased only to 1040 ppmw.

[0133] In comparative operation C2, the above pressure changes were simulated again, but only the steam supplied to the column reboiler was controlled to maintain the measured internal temperature at 146.49°C. As shown in Table 1 below, the resulting water concentration from the acetic acid-rich feed stream decreased to 410 ppmw. At this concentration, the feed stream could corrode the distillation equipment, including the second outlet, reboiler, and bottom section. Furthermore, since water concentrations greater than 410 ppmw are acceptable for commercial applications, more energy is required to drive the distillation than necessary.

[0134] Table 1. Distillation Operation

[0135]

[0136] The entire contents of every patent and non-patent disclosure cited herein are hereby incorporated by reference, unless otherwise specified in this specification, in which case the disclosure or definition herein shall prevail.

[0137] The foregoing detailed description and accompanying drawings have been provided through explanation and illustration, and are not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

[0138] It should be understood that the elements and features listed in the appended claims can be combined in different ways to produce new claims that also fall within the scope of this disclosure. Therefore, given that the dependent claims appended below are subordinate to only a single independent or dependent claim, it should be understood, or that such dependent claims may be alternatively subordinate to any of the foregoing claims (whether independent or dependent), and such new combinations should be understood as forming part of this specification.

Claims

1. A method for separating a feed stream containing acetic acid and water in a distillation column, the column comprising: A bottom section in thermal communication with a heat source, the heat source having an inner surface; The feed inlet is located above the bottom section; The first outlet is located above the feed inlet; and The second outlet is located below the feed inlet; The method includes: The feed stream is introduced into the tower through the feed inlet; The feed stream is separated at a first heating rate from a heat source to form a first fraction rich in water and a second fraction rich in acetic acid. The internal temperature of the tower is measured at a first location between the first outlet and the second outlet. The internal pressure of the tower was measured at a second location between the first and second outlets. The corrected temperature of the tower is determined based on the measured internal pressure and internal temperature of the tower; and Determine that the corrected temperature is greater than the target value, and then adjust the heat source to a second heating rate lower than the first heating rate; or Determine that the corrected temperature is below the target value, and then adjust the heat source to a second heating rate greater than the first heating rate; At least a portion of the first fraction is extracted through the first outlet; and At least a portion of the second fraction is extracted through the second outlet. Water is present in the extracted second fraction in an amount ranging from 500 ppm to 1500 ppm (ppmw) by weight, and at least one of the bottom section of the column, the second outlet, the inner surface of the heat source, any connecting pipe between the second outlet and the heat source, and any internal components of the bottom section contains zirconium.

2. The method of claim 1, wherein water is present in the extracted second fraction in an amount ranging from 800 ppmw to 1,200 ppmw.

3. The method of claim 1, wherein acetic acid is present in the extracted second fraction in an amount of at least 95 wt.%.

4. The method of claim 1, wherein acetic acid is present in the extracted second fraction in an amount of at least 97.5 wt.%.

5. The method of claim 1, wherein acetic acid is present in the extracted second fraction in an amount of at least 99 wt.%.

6. The method of claim 1, wherein the feed stream comprises 1-10 wt.% water, 90-99 wt.% acetic acid, up to 1 wt.% methyl iodine, and up to 5 wt.% methyl acetate.

7. The method of claim 1, wherein the feed stream comprises 2-7.5 wt.% water, 92.5-98 wt.% acetic acid, up to 0.75 wt.% methyl iodine, and up to 3.5 wt.% methyl acetate.

8. The method of claim 1, wherein the feed stream comprises 1-10 wt.% water, 40-85 wt.% acetic acid, 10-25 wt.% methyl iodine, and 15-30 wt.% methyl acetate.

9. The method according to claim 1, wherein the feed stream comprises 2-7.5 wt.% water, 40-75 wt.% acetic acid, 15-20 wt.% methyl iodine and 20-25 wt.% methyl acetate.

10. The method of claim 1, wherein the internal temperature and internal pressure of the tower are each measured separately at a location between the feed inlet and the second outlet.

11. The method of claim 1, wherein the internal temperature and internal pressure of the tower are each measured individually at locations separated from the second outlet by no more than 50% of the total number of theoretical stages separating the first and second outlets.

12. The method of claim 1, wherein the measured internal pressure is in the range of 0.125 MPaG to 0.5 MPaG.

13. The method according to claim 1, wherein the measured internal temperature is in the range of 110°C to 200°C.

14. The method according to claim 1, wherein the measured internal temperature is in the range of 120°C to 190°C.

15. The method according to claim 1, wherein the measured internal temperature is in the range of 130°C to 180°C.

16. The method of claim 1, wherein determining the correction temperature comprises adding a correction factor to the measured tower internal temperature, the correction factor being based on the measured tower internal pressure.

17. The method of claim 1, wherein the heat source comprises a reboiler.

18. The method according to any one of claims 1-17, wherein at least the bottom section and the second outlet comprise zirconium.

19. The method according to any one of claims 1-17, wherein the second outlet comprises zirconium.

20. The method according to any one of claims 1-17, further comprising separating the extracted second fraction to produce a product stream comprising acetic acid and water, and a waste stream comprising heavy components.

21. A system for separating a feed stream containing acetic acid and water, the system comprising... A distillation column capable of separating the feed stream to produce a first feed stream rich in water and a second feed stream rich in acetic acid, the second feed stream containing an amount of water in the range of 500 ppmw to 1,500 ppmw. The tower comprises: The bottom section that is in thermal connection with the heat source; The feed inlet is located above the bottom section; The first outlet is located above the feed inlet; The second outlet is located below the feed inlet; A temperature sensor located between the first and second outlets; and A pressure sensor located between the first outlet and the second outlet; The heat source includes a reboiler and a control unit. The control unit is capable of adjusting the heating rate of the reboiler based on internal temperature measurements from a temperature sensor and internal pressure measurements from a pressure sensor. The heat source also has an inner surface. At least one of the following components is contained in the bottom section of the tower, the second outlet, the inner surface of the heat source, any connecting pipe between the second outlet and the heat source, and any internal component in the bottom section: zirconium.

22. The system of claim 21, wherein the temperature sensor and the pressure sensor are each located separately between the feed inlet and the second outlet.

23. The system of claim 21, wherein the temperature sensor and the pressure sensor are each individually separated from the second outlet by no more than 50% of the total number of theoretical stages separating the first outlet and the second outlet.

24. The system according to any one of claims 21-23, further comprising a top pressure sensor capable of measuring the top pressure of the tower.

25. The system according to any one of claims 21-23, wherein at least the bottom section and the second outlet comprise zirconium.

26. The system according to any one of claims 21-23, wherein the second outlet comprises zirconium.

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