Control of iodide in acetic acid production

Abstract

A process for the production and recovery of acetic acid in an acetic acid production system is disclosed, the process comprising contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising iodide under carbonylation conditions sufficient to form acetic acid. The liquid reaction medium comprises a carbonylation catalyst, water, and an additive comprising a bidentate phosphine dioxide, a tertiary arsine oxide, or a combination thereof. One aspect of the method includes a method for reducing water in an acetic acid production process.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is filed under the Patent Cooperation Treaty and claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 444,770, filed on February 10, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to the production of acetic acid. More specifically, the present disclosure relates to the management of hydrogen iodide (HI) levels in the production of acetic acid. Background Art

[0004] In current acetic acid production processes, the reaction mixture is removed from the reactor and separated in a flash tank into a liquid fraction and a vapor fraction comprising acetic acid produced during the carbonylation reaction. The liquid fraction can be recycled to the carbonylation reactor, and the vapor fraction can be sent to a separation unit, such as a light ends distillation column. The light ends distillation column separates the crude acetic acid product from other components. The crude acetic acid product is sent to a drying column to remove water and then further separated to recover the acetic acid.

[0005] Hydrogen iodide (HI) can be a reactive component in acetic acid production. Although process equipment typically used in acetic acid production is essentially inert to reactive components, the equipment can still be corroded or otherwise adversely affected by HI. Additionally, HI can lead to the formation of long-chain alkyl iodide impurities, such as hexyl iodide, which are difficult to remove and can complicate the recovery of acetic acid. Therefore, the presence of HI can have consequences in terms of both corrosion of process equipment and contamination of the final acetic acid product.

[0006] Methods for managing HI exist; however, there remains a need to improve upon and provide alternatives to current methods of managing HI levels. Summary of the Invention

[0007] In some embodiments, a method for producing acetic acid in an acetic acid production system comprises contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising an iodide under carbonylation conditions sufficient to form acetic acid. The liquid reaction medium comprises a carbonylation catalyst, water, and an additive. The carbonylation catalyst is selected from the group consisting of a rhodium catalyst, an iridium catalyst, and a palladium catalyst. The water is present in the liquid reaction medium at 0.1 wt % to 10 wt % based on the weight of the liquid reaction medium. The additive is present in the liquid reaction medium at a molar ratio of additive to iodide of 0.01:1 to 5.0:1, as well as an in situ generated derivative of the additive and / or a combination thereof. The additive comprises a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof. The method also includes recovering the acetic acid.

[0008] In some embodiments, a method for reducing water in an acetic acid production process comprises contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising a first amount of hydrogen iodide under carbonylation conditions sufficient to form acetic acid. The liquid reaction medium comprises a carbonylation catalyst and a first amount of water, the carbonylation catalyst being selected from the group consisting of a rhodium catalyst, an iridium catalyst, and a palladium catalyst, the first amount of water being sufficient to form an azeotropic mixture of the first amount of hydrogen iodide and the first amount of water. The method further comprises adding an additive to the liquid reaction medium at a molar ratio of additive to iodide of 0.01:1 to 5.0:1, wherein the additive forms a complex with at least a portion of the first amount of hydrogen iodide, thereby producing a second amount of hydrogen iodide. The additive comprises a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof. The method further comprises reducing the water in the liquid reaction medium to a second amount of water while maintaining an azeotropic mixture of the second amount of hydrogen iodide and the second amount of water.

[0009] The above paragraphs present a simplified overview of the presently disclosed subject matter in order to provide a basic understanding of some aspects thereof. This overview is not an exhaustive overview, nor is it intended to identify key or important elements to delineate the scope of the subject matter claimed below. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description set forth below. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

[0011] Figure 1 is a schematic diagram of an exemplary acetic acid production system according to embodiments and / or technologies disclosed herein;

[0012] Figure 2 is a schematic representation of the complexation of bis(diphenylphosphino)methane dioxide (bis-DPPMeO2) with hydrogen iodide (HI) and p-toluenesulfonic acid (PTSA) according to embodiments and / or techniques disclosed herein;

[0013] Figure 3 is a schematic representation of bis(diphenylphosphino)propane dioxide (bis-DPPPrO2) complexed with HI and PTSA according to embodiments and / or technologies disclosed herein;

[0014] Figure 4 is an overlay of FTIR spectra of decomposition of unreacted bis-DPPPrO2, HI-DPPPrO2 adduct, and HI-DPPPrO2 adduct after reaction with potassium acetate (KOAc) according to embodiments and / or technologies disclosed herein;

[0015] Figure 5 is a diagram of a vapor-liquid equilibrium (VLE) apparatus for vapor-liquid equilibrium testing according to embodiments and / or techniques disclosed herein;

[0016] Figure 6 is an overlay of UV / visible spectra of unoxidized and oxidized hydrogen iodide / acetic acid solutions according to embodiments and / or technologies disclosed herein;

[0017] Figure 7 is an overlay of comparative VLE data for TPPO and CMPO (as defined in the Examples) according to embodiments and / or technologies disclosed herein;

[0018] Figure 8 is an overlay of FTIR spectra showing the complexation of triphenylarsine oxide (Ph3AsO) with HI according to embodiments and / or technologies disclosed herein; and

[0019] Figure 9 is an overlay graph showing the decomposition of Ph3AsO-HI adduct upon addition of tetraethylammonium acetate (Et4NOAc) according to embodiments and / or technologies disclosed herein.

[0020] While the disclosed methods and systems are susceptible to various modifications and alternative forms, the drawings illustrate by way of example specific embodiments described herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the particular forms disclosed, but rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION

[0021] A detailed description of embodiments of the disclosed method follows. However, it should be understood that the described embodiments are merely examples of the method, and that the method can be implemented in various and alternative forms of the described embodiments. Therefore, the specific procedural, structural, and functional details involved in the embodiments described herein should not be construed as limiting, but merely as a basis for the claims and as a representative basis for teaching those skilled in the art to employ the disclosed method in various ways.

[0022] As used herein, the designation of the groups of the Periodic Table of the Elements is in accordance with current IUPAC conventions. The expression "HAc" is used herein as an abbreviation for acetaldehyde. The expression "MeI" is used herein as an abbreviation for methyl iodide. The expression "HI" is used herein as an abbreviation for hydrogen iodide. The expression "acac" is used herein as an abbreviation for the acetoacetate anion, i.e., H3CC(═O)CH2C(═O)O-. Unless otherwise specifically indicated, the expression "wt%" as used herein refers to the weight percentage of a particular component in the referenced composition. With respect to all ranges disclosed herein, such ranges are intended to include any combination of the upper and lower limits recited, even if a particular combination is not specifically listed.

[0023] Embodiments of the disclosed methods and systems relate to the production of acetic acid by carbonylating methanol in a carbonylation reaction. The carbonylation reaction can be represented as: CH3OH+CO→CH3COOH

[0024] Embodiments of the disclosed method include: (a) obtaining HI in an acetic acid production system; and (b) continuously introducing an additive into the system, wherein the additive interacts with the HI to form a complex. The following description sets forth the disclosed method in detail.

[0025] Embodiments of the disclosed method generally include: (a) obtaining HI in an acetic acid production system; and (b) continuously introducing an additive into the system, wherein the additive interacts with the HI to form a complex. In this context, the term "continuously" means introducing the additive frequently enough and in metered amounts to achieve a steady-state HI scavenging operation. This eliminates the wide fluctuations in scavenging efficiency that occur in conventional practice due to the occasional introduction of large amounts of additive. The following description will further elaborate on the disclosed method.

[0026] Acetic acid production

[0027] Figure 1 is a schematic diagram of an exemplary acetic acid production system 100 that performs a carbonylation reaction. In some embodiments, acetic acid system 100 may include a reaction zone 102, a light ends zone 104, a purification zone 106, and a recycle zone 108. Reaction zone 102 may include a reactor 110, a flash vessel 120, and associated equipment. Reactor 110 is a reactor or vessel in which methanol is carbonylated in the presence of a catalyst at elevated pressure and temperature to form acetic acid. Note that a "stream" discussed herein may be part of more than one functional zone.

[0028] Reaction zone 102 can include reactor 110, flash vessel 120, equipment associated with reactor 110 and flash vessel 120, and streams associated with reactor 110 and flash vessel 120. For example, reaction zone 102 can include reactor 110, flash vessel 120, and streams (or portions thereof) 111, 112, 114, 121, 126, 131, 160, 138, 139, 148. Reactor 110 is a reactor or vessel in which methanol is carbonylated in the presence of a catalyst at elevated pressure and temperature to form acetic acid. Flash vessel 120 is a tank or vessel in which the reaction mixture obtained in a reactor (e.g., reactor 110) is at least partially depressurized and / or cooled to form a vapor stream and a liquid stream. The vapor stream is a product or composition comprising a gaseous component under the conditions of the process step that formed the stream. The liquid stream can be a product or composition comprising a liquid component under the conditions of the process step that formed the stream.

[0029] Light ends section 104 can include a separation column (e.g., light ends column 130), equipment associated with light ends column 130, and streams associated with light ends column 130. For example, light ends section 104 can include light ends column 130, decanter 134, and streams 126, 131, 132, 133, 135, 136, 138, 139, 160. Light ends column 130 is a fractionation column or distillation column and includes any equipment associated with the column, including, but not limited to, heat exchangers, decanters, pumps, compressors, valves, etc.

[0030] Purification region 106 can include a drying column 140, an optional heavy ends column 150, equipment associated with drying column 140 and heavy ends column 150, and streams associated with drying column 140 and heavy ends column 150. For example, purification region 106 can include drying column 140, heavy ends column 150, and streams 136, 141, 142, 145, 148, 151, 152, 156. Heavy ends column 150 is a fractionation column or distillation column and includes any equipment associated with the column, including, but not limited to, heat exchangers, decanters, pumps, compressors, valves, etc.

[0031] Recycle zone 108 may include process streams that are recycled to reaction zone 102 and / or light ends zone 104. For example, Figure 1 , the recirculation zone 108 may include streams 121 , 138 , 139 , 148 .

[0032] In one embodiment, reactor 110 can be configured to receive a carbon monoxide feed stream 114 and a methanol feed stream 112. Feed stream 112 can include a methanol feed stream, a methyl acetate feed stream, or any mixture of the two. In the illustrated embodiment, feed stream 112 is a mixed stream. The reaction mixture in stream 111 can be removed from the reactor. Other streams can be included, such as, for example, a stream that can recycle the bottoms mixture of reactor 110 back into reactor 110, or a stream that can release gas from reactor 110. Stream 111 can include at least a portion of the reaction mixture.

[0033] In one embodiment, flash vessel 120 can be configured to receive stream 111 from reactor 110. In flash vessel 120, stream 111 can be separated into vapor stream 126 and liquid stream 121. Vapor stream 126 can be sent to light ends column 130, and liquid stream 121 can be sent to reactor 110. In one embodiment, stream 126 can have acetic acid, water, methyl iodide, methyl acetate, HI, or mixtures thereof.

[0034] In one embodiment, light ends column 130 can be a distillation column and associated equipment, such as a decanter 134, pumps, compressors, valves, and other related equipment. Light ends column 130 can be configured to receive stream 126 from flash vessel 120. In the illustrated embodiment, stream 132 is the overhead product from light ends column 130, and stream 131 is the bottom product from light ends column 130. As indicated, light ends column 130 can include a decanter 134, and stream 132 can enter decanter 134.

[0035] Stream 135 may be discharged from decanter 134 and recycled back to light ends column 130. Stream 138 may be discharged from decanter 134 and may be recycled back to reactor 110 via, for example, stream 112 or combined with any other streams fed to the reactor. Stream 139 may be recycled back to reactor 110 via, for example, stream 112. Stream 136 may be discharged from light ends column 130. Other streams may be included, such as, for example, a stream that may recycle the bottoms mixture of light ends column 130 back to light ends column 130. Streams received by or discharged from light ends column 130 may be passed through pumps, compressors, heat exchangers, and the like, as is common in the art.

[0036] In one embodiment, drying column 140 can be a vessel and associated equipment such as heat exchangers, decanters, pumps, compressors, valves, etc. Drying column 140 can be configured to receive stream 136 from light ends column 130. Drying column 140 can separate the components of stream 136 into streams 142 and 141.

[0037] Stream 142 may be discharged from drying tower 140, recycled back to the drying tower via stream 145, and / or recycled back to reactor 110 via stream 148 (e.g., via stream 112). Stream 141 may be discharged from drying tower 140 and may include dehydrated crude acetic acid product. Stream 142 may be passed through equipment, such as, for example, a heat exchanger or a separation vessel, before components of stream 142 are recycled in streams 145 or 148. Other streams may be included, such as, for example, a stream that may recycle the bottoms mixture of drying tower 140 back into drying tower 140. Streams received by or discharged from drying tower 140 may be passed through pumps, compressors, heat exchangers, separation vessels, etc., as is common in the art.

[0038] Heavy ends column 150 may be a distillation column and associated equipment, such as heat exchangers, decanters, pumps, compressors, valves, and the like. Heavy ends column 150 may be configured to receive stream 141 from drying column 140. Heavy ends column 150 may separate the components from stream 141 into streams 151, 152, and 156. Streams 151 and 152 may be sent to additional processing equipment (not shown) for further processing. Stream 152 may also be recycled, for example, to light ends column 130. Stream 156 may comprise acetic acid product.

[0039] A single column (not depicted) may be used in place of the combination of light ends distillation column 130 and drying column 140. The diameter / height ratio and number of stages of the single column may vary depending on the composition of the vapor stream from the flash separation and the desired product quality. For example, U.S. Patent No. 5,416,237, the teachings of which are incorporated herein by reference, discloses single column distillation. U.S. Patent No. 5,416,237 (the teachings of which are incorporated herein by reference) discloses single column distillation.

[0040] Alternative embodiments of acetic acid production system 100 may also be found in U.S. Patent Nos. 6,552,221, 7,524,988, and 8,076,512, the entire contents of which are incorporated herein by reference.

[0041] In one embodiment, the carbonylation reaction in reactor 110 of system 100 can be carried out in the presence of a catalyst. The catalyst can include, for example, a rhodium catalyst and an iridium catalyst.

[0042] Suitable rhodium catalysts are taught, for example, by U.S. Patent No. 5,817,869, which is incorporated herein by reference. U.S. Patent No. 5,817,869 teaches, which is incorporated herein by reference. The rhodium catalyst may include rhodium metal and a rhodium compound. In one embodiment, the rhodium compound may be selected from the group consisting of: rhodium salts, rhodium oxide, rhodium acetate, organic rhodium compounds, coordination compounds of rhodium, and the like, and mixtures thereof. In one embodiment, the rhodium compound may be selected from the group consisting of: Rh2(CO)4I2, Rh2(CO)4Br2, Rh2(CO)4Cl2, Rh(CH3CO2)2, Rh(CH3CO2)3, [H]Rh(CO)2I2, and the like, and mixtures thereof. In one embodiment, the rhodium compound may be selected from the group consisting of: [H]Rh(CO)2I2, Rh(CH3CO2)2, and the like, and mixtures thereof.

[0043] Suitable iridium catalysts are taught, for example, by U.S. Patent No. 5,932,764. Iridium catalysts may include iridium metal and iridium compounds. Examples of suitable iridium compounds include IrCl3, IrI3, IrBr3, [Ir(CO)2I]2, [Ir(CO)2Cl]2, [Ir(CO)2Br]2, [Ir(CO)4I2]-H+, [Ir(CO)2Br2]-H+, [IR(CO)2I2]-H+, [Ir(CH3)I3(CO)2]-H+, Ir4(CO)12, IrCl3.4H2O, IrBr3.4H2O, Ir3(CO)12, Ir2O3, IrO2, Ir(acac)(CO)2, Ir(acac)3, Ir(OAc)3, [Ir3O(OAc)6(H2O)3][OAc], H2[IrCl6], and the like, and mixtures thereof. In one embodiment, the iridium compound may be selected from acetates, oxalates, acetoacetates, and the like, and mixtures thereof. In one embodiment, the iridium compound may be one or more acetates.

[0044] In one embodiment, catalyst can be used together with a co-catalyst. In one embodiment, the co-catalyst can include a metal and a metal compound selected from the group comprising the following: osmium, rhenium, ruthenium, cadmium, mercury, zinc, gallium, indium and tungsten, their compound etc., and mixtures thereof. In one embodiment, the co-catalyst can be selected from ruthenium compounds and osmium compounds. In one embodiment, the co-catalyst can be one or more ruthenium compounds. In one embodiment, the co-catalyst can be one or more acetates.

[0045] The reaction rate depends on the concentration of the catalyst in the reaction mixture in reactor 110. In one embodiment, the catalyst concentration can be in the range of about 1.0 mmol to about 100 mmol catalyst per liter (mmol / l) of reaction mixture. In some embodiments, the catalyst concentration is at least 2.0 mmol / l, or at least 5.0 mmol / l, or at least 7.5 mmol / l. In some embodiments, the catalyst concentration is at most 75 mmol / l, or at most 50 mmol / l, or at most 25 mmol / l. In specific embodiments, the catalyst concentration is from about 2.0 to about 75 mmol / l, or from about 5.0 to about 50 mmol / l, or from about 7.5 to about 25 mmol / l.

[0046] In one embodiment, the carbonylation reaction in reactor 110 of system 100 can be carried out in the presence of a catalyst stabilizer. Suitable catalyst stabilizers include at least two types of catalyst stabilizers. The first type of catalyst stabilizer can be a metal iodide salt, such as lithium iodide. The second type of catalyst stabilizer can be a non-salt stabilizer. In one embodiment, the non-salt stabilizer can be a pentavalent Group 15 oxide, such as those disclosed in U.S. Patent No. 9,790,159, which is incorporated herein by reference. In one embodiment, the catalyst stabilizer can be one or more phosphine oxides. In one embodiment, the catalyst stabilizer can be CYTOP from Solvay TM 503.

[0047] The additive disclosed herein is a pentavalent Group 15 oxide. The pentavalent Group 15 oxide is soluble in acetic acid and includes bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof.

[0048] In some embodiments, the bidentate phosphine dioxide can be represented by Formula I:

[0049]

[0050] in:

[0051] P is phosphorus;

[0052] O is oxygen;

[0053] R 1 Selected from C1-C 10 alkyl;

[0054] R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Alkyl, C4-C 18 Aryl, C4-C18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other; and

[0055] Each bidentate phosphine dioxide has at least 17 carbon atoms.

[0056] In a further embodiment, R 1 is selected from C1, C3, C5, C7 and C9 alkyl groups, and R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Cyclic aromatic group.

[0057] Examples of bidentate phosphine dioxides suitable for use as pentavalent Group 15 oxides include, but are not limited to, bis(diphenylphosphino)methane dioxide (bis-DPPMeO2), bis(diphenylphosphino)propane dioxide (bis-DPPPrO2), bis(diphenylphosphino)pentane dioxide (bis-DPPPeO2), and combinations thereof.

[0058] In one or more embodiments, the bidentate phosphine dioxide exhibits a melting point, for example, greater than 100°C, or greater than 200°C, or greater than 300°C.

[0059] In one or more embodiments, the bidentate phosphine dioxide has a wavelength less than or equal to 1190 cm-1 as measured by Fourier transform infrared spectroscopy in acetonitrile at 25°C. -1 The frequency of phosphoryl groups.

[0060] In some embodiments, the tertiary arsenic oxide can be represented by Formula II:

[0061]

[0062] in:

[0063] As is arsenic;

[0064] O is oxygen; and

[0065] R 1 、R 2 , and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other.

[0066] In a further embodiment, R 1 、R2 and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Cyclic aromatic groups and combinations thereof.

[0067] Examples of phosphine oxides suitable for use as the pentavalent Group 15 oxide include, but are not limited to, triphenylarsine oxide (TPAsO), triethylarsine oxide (TEtAsO), and combinations thereof.

[0068] In one or more embodiments, the tertiary arsenic oxide exhibits a melting point greater than 100°C, or greater than 200°C, or greater than 300°C.

[0069] In some embodiments, the tertiary arsenic oxide has a pK less than or equal to 5.00. BHX , less than or equal to -20kJmol -1 ΔG° or a combination thereof, where pK BHX and ΔG° are measured in CCl4 at 25°C. pK BHX Further discussion of and ΔG° can be found in “Lewis Basicity and Affinity Scales” (C. Laurence and J. Gal, Wiley ISBN 978-0-470-74957-9, 2010), the contents of which are incorporated herein by reference.

[0070] When used, the amount of pentavalent Group 15 oxide is such that the molar ratio to the carbonylation catalyst is greater than about 0.5:1. In some embodiments, the molar ratio of pentavalent Group 15 oxide to rhodium is from about 0.5:1 to about 100:1. In some embodiments, the pentavalent Group 15 oxide may be present in the reaction mixture at about 0.005 to about 2.0 M. In some embodiments, the pentavalent Group 15 oxide may be present in the reaction mixture at about 0.01 to about 1.5 M, or 0.025 to 1.2 M.

[0071] In other embodiments, the reaction may occur in the absence of a stabilizer selected from the group consisting of metal iodide salts and non-metal stabilizers such as pentavalent Group 15 oxides. In further embodiments, the catalyst stabilizer may consist of an additive that is contacted with the reaction mixture stream 111 in the flash vessel 120.

[0072] In one embodiment, hydrogen may also be fed into reactor 110. Adding hydrogen may improve carbonylation efficiency. In one embodiment, the concentration of hydrogen in reactor 110 may be in the range of from about 0.1 mol % to about 5 mol % of carbon monoxide. In one embodiment, the concentration of hydrogen in reactor 110 may be in the range of from about 0.3 mol % to about 3 mol % of carbon monoxide.

[0073] In one embodiment, the carbonylation reaction in reactor 110 of system 100 can be carried out in the presence of water. In one embodiment, the concentration of water is from about 0.1 wt % to about 10.0 wt %, from about 0.2 wt % to about 6.0 wt %, from about 0.3 wt % to about 4.5 wt %, or from about 0.4 wt % to about 2 wt %, based on the total weight of the reaction mixture.

[0074] In one embodiment, the carbonylation reaction can be carried out in the presence of methyl acetate. Methyl acetate can be formed in situ. In an embodiment, methyl acetate can be added to the reaction mixture as a starting material. In one embodiment, the concentration of methyl acetate can be from about 2 wt % to about 20 wt % based on the total weight of the reaction mixture. In one embodiment, the concentration of methyl acetate can be from about 2 wt % to about 16 wt %. In one embodiment, the concentration of methyl acetate can be from about 2 wt % to about 8 wt %. Alternatively, methyl acetate or a mixture of methyl acetate and methanol from a byproduct stream of methanolysis of polyvinyl acetate or ethylene-vinyl acetate copolymer can be used for the carbonylation reaction.

[0075] In one embodiment, carbonylation reaction can be carried out in the presence of methyl iodide.Methyl iodide can be a catalyst promoter.In one embodiment, based on the gross weight of reaction mixture, the concentration of MeI can be about 0.6wt% to about 36wt%.In one embodiment, the concentration of MeI can be about 4wt% to about 24wt%.In one embodiment, the concentration of MeI can be about 6wt% to about 20wt%.Alternatively, MeI can be generated in reactor 110 by adding HI.

[0076] In one embodiment, methanol and carbon monoxide may be fed to reactor 110 as streams 112 and 114, respectively. The methanol feed stream to reactor 110 may come from a syngas-methanol facility or any other source. Methanol does not react directly with carbon monoxide to form acetic acid. It is converted to MeI by the HI present in reactor 110 and then reacts with carbon monoxide and water to produce acetic acid and regenerate HI.

[0077] In one embodiment, the carbonylation reaction in reactor 110 of system 100 may occur at a temperature in the range of about 120° C. to about 250° C., alternatively about 150° C. to about 250° C., alternatively about 150° C. to about 200° C. In one embodiment, the carbonylation reaction in reactor 110 of system 100 may be carried out at a pressure in the range of about 200 psia (1.38 MPa-a) to 2,000 psia (13.8 MPa-a), alternatively about 200 psia (1.38 MPa-a) to about 1,000 psia (6.9 MPa-a), alternatively about 300 psia (2.1 MPa-a) to about 500 psia (3.4 MPa-a).

[0078] In one embodiment, the reaction mixture can be removed from the reactor 110 via stream 111 and flashed in a flash vessel 120 to form a vapor stream 126 and a liquid stream 121. The reaction mixture in stream 111 can include acetic acid, methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, water, HI, heavy impurities, a catalyst, or a combination thereof. The flash vessel 120 can include any configuration for separating the vapor and liquid components via reduced pressure. For example, the flash vessel 120 can include a flash tank, a nozzle, a valve, or a combination thereof.

[0079] The flash vessel 120 may have a lower pressure than the reactor 110. In one embodiment, the flash vessel 120 may have a pressure of from about 10 psig (69 kPa-g) to 100 psig (689 kPa-g). In one embodiment, the flash vessel 120 may have a temperature of from about 100° C. to 160° C.

[0080] Vapor stream 126 can include acetic acid and other volatile components, such as methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, water, entrained HI, complexed HI and their mixtures. Liquid stream 121 can include acetic acid, methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, water, complexed HI, HI, azeotropes of HI and water and their mixtures. Specifically, this liquid stream can include catalyst, complexed HI, HI, azeotropes of HI and water and their mixtures. Liquid stream 121 can also include sufficient amounts of water and acetic acid to carry and stabilize catalyst, non-volatile catalyst stabilizer or their combination. Liquid stream 121 can be recycled to reactor 110. Vapor stream 126 can be transported to light ends column 130 for distillation.

[0081] In one embodiment, vapor stream 126 can be distilled in light ends column 130 to form overhead stream 132, crude acetic acid product stream 136, and bottoms stream 131. In one embodiment, light ends column 130 can have at least 10 theoretical stages or 16 actual stages. In an alternative embodiment, light ends column 130 can have at least 14 theoretical stages. In an alternative embodiment, light ends column 130 can have at least 18 theoretical stages. In embodiments, one actual stage can be equal to about 0.6 theoretical stages. An actual stage can be a tray or packing. The reaction mixture can be fed to light ends column 130 via stream 126 at the bottom or first stage of column 130.

[0082] Stream 132 may include acetaldehyde, water, carbon monoxide, carbon dioxide, methyl iodide, methyl acetate, methanol, and acetic acid, additives, and mixtures thereof. Stream 131 may include acetic acid, methyl iodide, methyl acetate, HI, water, and mixtures thereof. Stream 136 may include acetic acid, HI, water, heavy impurities, and mixtures thereof. Streams 132, 131, and 136, as well as other streams discussed herein, may also include additives at varying concentrations, depending on where they are added to the system.

[0083] In one embodiment, the light ends column 130 can operate at a top pressure in the range of 20 psia (138 kPa-a) to 40 psia (276 kPa-a), alternatively, the top pressure can be in the range of 30 psia (207 kPa-a) to 35 psia (241 kPa-a). In one embodiment, the top temperature can be in the range of 95° C. to 135° C., alternatively, the top temperature can be in the range of 110° C. to 135° C., alternatively, the top temperature can be in the range of 125° C. to 135° C. In one embodiment, the light ends column 130 can operate at a bottom pressure in the range of 25 psia (172 kPa-a) to 45 psia (310 kPa-a), alternatively, the bottom pressure can be in the range of 30 psia (207 kPa-a) to 40 psia (276 kPa-a).

[0084] In one embodiment, the bottom temperature of light ends column 130 can be in the range of 115° C. to 155° C., alternatively, the bottom temperature is in the range of 125° C. to 135° C. In one embodiment, crude acetic acid in stream 136 can be withdrawn from light ends column 130 as a liquid side draw. Stream 136 can be operated at a pressure in the range of 25 psia (172 kPa-a) to 45 psia (310 kPa-a), alternatively, the pressure can be in the range of 30 psia (207 kPa-a) to 40 psia (276 kPa-a). In one embodiment, the temperature of stream 136 can be in the range of 110° C. to 140° C., alternatively, the temperature can be in the range of 125° C. to 135° C. Stream 136 can be taken between the fifth and eighth actual stages of light ends column 130.

[0085] Overhead vapors in stream 132 from light ends column 130 may be condensed and separated in decanter 134 to form a light aqueous phase and a heavy organic phase. For example, the heavy organic phase may be recycled to reactor 110 in stream 138 via stream 112. Stream 138 may include acetic acid, methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, water, HI, heavy impurities, additives (optional), and combinations thereof.

[0086] For example, the light aqueous phase can be recycled to the light ends column 130 in stream 135, or can be recycled to the reactor 110 in stream 139 via stream 112. Stream 135 can include acetic acid, methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, water, HI, heavy impurities, additives (optional), and combinations thereof. The heavy organic phase in stream 138 can include methyl iodide and methyl acetate, and mixtures thereof. The light aqueous phase in streams 136 and 139 can include water (greater than 50%), acetic acid, methanol, methyl acetate, methyl iodide, carbon monoxide, carbon dioxide, heavy impurities, additives (optional), and combinations thereof. Make-up water can be introduced into the decanter 134 via stream 133. Streams 139 and 138 can be considered to be located in the light ends section 104 and the recycle section 108.

[0087] In one or more embodiments, the crude acetic acid in stream 136 can optionally undergo further purification, such as, but not limited to, drying-distillation, in drying column 140 to remove water and heavy ends distillate in stream 141. Stream 141 can be sent to heavy ends column 150, where heavy impurities such as propionic acid can be removed in stream 151, and the final acetic acid product can be recovered in stream 156.

[0088] In one embodiment, additives may be continuously introduced into the system 100 via stream 160. Figure 1126, 131, 132, 133, 135, 136, 138, 139, or a combination thereof. Thus, although Figure 1 Stream 160 is shown mixed with the vapor stream exhausted from flash vessel 120, but it is contemplated that alternative embodiments may include mixing stream 160 with any equipment or stream in reaction zone 102, light ends partition 104, recycle zone 108, or combinations thereof.

[0089] In some embodiments, the additives disclosed herein can be continuously introduced into stream 160 as a solution. In one embodiment, the additive can be continuously introduced into stream 160 as an additive solution comprising the additive and a solvent. In one embodiment, the additive solution can include an acetic acid solution. The nature of the solvent or diluent generally may not be critical, so long as the solvent or diluent does not interfere with the carbonylation reaction or the purification of acetic acid in purification zone 106.

[0090] Those skilled in the art of homogeneous processes, particularly those requiring a flash step to separate non-volatile catalysts and additives, having the benefit of this disclosure, will understand that the rate of loss of catalyst and additives associated solely with entrainment will be a function of several variables. These variables include reactor size, feed rate, flasher size, and flash rate. They will also understand that a replenishing solution of the additives disclosed herein in acetic acid ("HAc") can be concentrated to a concentration permitted by the solubility limit of the additives disclosed herein in HAc, i.e., about 50 wt%, or diluted to a few ppm.

[0091] The primary consideration is that the flow rate and concentration of the makeup stream containing the additive disclosed herein are matched so that a steady-state concentration of the additive exists in the reactor. This concentration, which typically varies by as much as 1.5 wt% from its high and low points between batch additions, is now controlled to a target range of preferably + / - 0.5 wt% and most preferably + / - 0.2 wt%. Thus, for example, in a process with a monthly loss rate of 1 wt% in the reactor, the monthly batch additions can be replaced by a continuous metered flow, corresponding to an average daily addition of approximately 0.03 wt% of the additive disclosed herein.

[0092] In one embodiment, no solvent or diluent may be used. In one embodiment, the solvent or diluent is one or more components in the liquid component of the reaction mixture in reactor 110, such as acetic acid, methanol, methyl iodide, water, or a combination thereof. In one embodiment, the solvent or diluent may be acetic acid, methanol, or both. Similarly, the amount of the solvent or diluent used in this context is not critical and can be widely adjusted according to process economics. The use of a solvent or diluent can be conducive to ensuring rapid, uniform distribution and contact of the additive with HI.

[0093] In one embodiment, it may be advantageous to use a solvent or diluent when the additive is introduced separately from the reaction mixture and any recycle stream and independently into the system 100. Such a "recycle stream" may be a product or composition recovered from a process step downstream of the flash vessel and recycled to the reactor, flash vessel, or light ends column. In an alternative embodiment, when the additive is contacted with the reaction mixture in flash vessel 120, for example by adding the additive to stream 131 prior to introducing the additive into flash vessel 120, the additive may be introduced in its original form (i.e., in undiluted form) because the liquid component of stream 131 acts as a solvent or diluent.

[0094] In one embodiment, the additive may include a catalyst stabilizer. In one embodiment, the additive may include a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof. In one embodiment, the additive may include triphenylphosphine dioxide, triphenylarsine oxide, or a combination thereof.

[0095] Without being limited by theory, it is believed that the additive (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) can interact with HI to form a complex, as discussed in the examples below. The HI complex can reduce the HI concentration in the purification zone 106 for at least the following reasons: i) the additive (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) can have a relatively high boiling point and can therefore be retained in the liquid stream 121 of the flash vessel 120, where it can inhibit or at least significantly reduce the tendency of HI to be entrained in the vapor stream 126; ii) by forming a complex with HI, the additive can act as a scavenger for HI and reduce the amount of HI that may be entrained in the vapor stream 126 and subsequently passed to the light ends section 104; and iii) even if a certain amount of HI complex is entrained in the vapor stream 126 and passed to the light ends section 104, the HI complex (which can have a relatively high boiling point) can be recovered in the bottom stream 131 of the light ends column 130. Thus, the formation of the HI complex enables system 100 to inhibit or at least reduce the transport of HI into purification zone 106 by enhancing the recovery of HI (as HI complex) in reaction zone 102 (e.g., in liquid stream 121 of flash vessel 120) and in light ends zone 104 (e.g., in bottoms stream 131 of light ends column 130).

[0096] In the case of azeotropic decomposition, the recovery of HI (as HI complexes) can also offset the effects of HI volatilization. Hydrogen iodide forms a high-boiling azeotrope in acetic acid solutions containing greater than about 5 wt% water. If the water concentration (e.g., in stream 131) is below about 5 wt%, azeotropic decomposition and HI volatilization may occur. Such volatilization may result in less HI in the bottoms stream 131 obtained in the light ends column 130 and returned to the reactor 110, which may adversely affect the reactor iodide inventory.

[0097] Additionally, in the case of azeotropic decomposition, the volatilized HI may become part of stream 136 withdrawn from light ends column 130 for purification in purification zone 106. Because the additive (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) forms a complex with HI, the continuous introduction of the additive can act as a scavenger for volatilized HI in the case of azeotropic decomposition in light ends column 130 and can inhibit or at least reduce the transfer of volatilized HI into purification zone 106. Because some additives (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) also serve as catalyst stabilizers for the carbonylation reaction in reactor 110, the reaction in reactor 110 is minimally impaired by any HI complex being recycled to reactor 110.

[0098] Without being limited by theory, it is believed that continuously introducing an additive (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) into the process at various points in the reaction zone 102 or the light ends section 104 of the system 100 reduces the likelihood of HI transfer to the purification zone 106.

[0099] In one embodiment, continuously introducing the additive (e.g., bidentate phosphine dioxide, tertiary arsenic oxide, or a combination thereof) can include continuously metering the additive in a solution (e.g., acetic acid solution) using a gas or liquid metering technique known in the art (such as a turbine flow meter, a Coriolis flow meter, an ultrasonic flow meter, a PD flow meter, or a combination thereof). Continuously metering can include uniformly injecting a known concentration of the additive in a solution (e.g., acetic acid solution).

[0100] The reaction of the additive with HI is rapid and generally quantitative at temperatures of about 10° C. In embodiments, the reaction occurs when the additive is contacted with the process stream upstream of the heavy ends distillation column.

[0101] In one embodiment, the reaction mixture in reactor 110 contains no additives other than those continuously introduced into system 100 and that have been recycled to reactor 110 .

[0102] In one embodiment, the amount of additive contacted with HI is generally not critical, as long as the additive is provided in an effective amount. An effective amount in this context refers to an amount of additive that is capable of scavenging at least a portion of the HI present at a point in the system 100. The amount of additive added is determined by the rate of depletion of the additive from the reactor, rather than by the HI concentration.

[0103] In one embodiment, the rate at which the additive is introduced into the system 100 can be adjusted based on the HI content. In some embodiments, the additive can be introduced in an amount of at least about 0.1 moles per mole of HI. In alternative embodiments, at least about 0.5 moles of additive are introduced per mole of HI, or at least about 1 mole of additive, or at least about 1.5 moles of additive are introduced per mole of HI. In alternative embodiments, the additive can be introduced in an amount of about 0.1 to about 10 moles per mole of HI. In alternative embodiments, the amount of additive is about 0.25 to about 7.5 moles, or about 0.5 to about 5 moles, or about 0.75 to about 1.5 moles per mole of HI.

[0104] In further alternative embodiments, the amount of additive is from about 1 to about 10 moles per mole of HI, or from about 1 to about 7.5 moles, or from about 1 to 5 moles. In alternative embodiments, the additive may be introduced in an amount of from about 0.1 to about 1.5 moles per mole of HI. In alternative embodiments, the amount of additive introduced may be from about 0.1 to about 1.3 moles per mole of HI, or from about 0.1 to about 1.1 moles. In further alternative embodiments, the amount of additive is from about 0.5 to about 3 moles per mole of HI, or from about 0.5 to about 2 moles, or from about 0.5 to about 1.5 moles.

[0105] Generally, if the molar amount of the additive exceeds the molar amount required to complex HI, it is not detrimental to the subsequent separation and purification of the final acetic acid product as long as the boiling point of the additive is sufficiently higher than the boiling point of vapor stream 126 discharged from flash vessel 120 and / or stream 136 discharged from light ends column 130. For example, the boiling point of the additive is sufficiently high when the boiling point of the additive is at least 15° C. higher than the boiling point of the crude acetic acid in stream 136, alternatively, at least 30° C. higher, or alternatively, at least 50° C. higher.

[0106] In certain variations of these embodiments, the additive may be introduced into flash vessel 120 in an amount of about 0.1 to about 1.5 moles per mole of HI. In alternative variations, the amount of additive is about 0.1 to about 1.3 moles per mole of HI, or about 0.1 to about 1.1 moles per mole of HI. In further alternative embodiments, the amount of additive is about 0.5 to about 3 moles per mole of HI, or about 0.5 to about 2 moles, or about 0.5 to about 1.5 moles.

[0107] In further embodiments, the additive may be introduced into the flash vessel 120 in an amount sufficient to establish an additive concentration in the liquid stream 121 of no more than 20 wt%. In alternative embodiments, the additive may be introduced to establish an additive concentration in the liquid stream 121 of no more than about 15 wt%, or no more than about 12 wt%, or no more than about 10 wt%. In other embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration in the liquid stream 121 of at least about 0.5 wt%. In alternative embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration in the liquid stream 121 of at least about 1 wt%, or at least about 2.5 wt%, or at least about 4 wt%. In particular embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration in the liquid stream 121 of from about 0.5 wt% to about 20 wt%.

[0108] In alternative embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration of from about 1 wt% to about 20 wt%, or from about 2.5 wt% to about 20 wt%, or from about 4 wt% to about 20 wt% in the liquid stream 121. In alternative embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration of from about 0.5 wt% to about 15 wt%, or from about 1 wt% to about 15 wt%, or from about 2.5 wt% to about 15 wt%, or from about 4 wt% to about 15 wt% in the liquid stream 121. In alternative embodiments, the additive may be introduced in an amount sufficient to establish an additive concentration of from about 0.5 wt% to about 12 wt%, or from about 1 wt% to about 12 wt%, or from about 2.5 wt% to about 12 wt%, or from about 4 wt% to about 12 wt% in the liquid stream 121.

[0109] The liquid stream 121 can be recycled to the reactor 110. The recycled liquid stream 121 can introduce additives into the reactor 110 and thus into the reaction mixture in the reactor 110.

[0110] In some embodiments, the amount of additive introduced into flash vessel 120 can be adjusted to establish a steady-state concentration of the additive in the reaction mixture of no more than about 20 wt%. In alternative embodiments, the additive can be introduced into flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of no more than about 17 wt%, or no more than about 15 wt%, or no more than about 12 wt%. In other embodiments, the additive can be introduced into flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of at least about 2 wt%. In alternative embodiments, the additive can be introduced into flash vessel 129 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of at least about 5 wt%, or at least about 7 wt%.

[0111] In particular embodiments, the additive may be introduced into the flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of from about 2 wt% to about 20 wt%. In alternative embodiments, the additive may be introduced into the flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of from about 5 wt% to about 20 wt%, or from about 7 wt% to about 20 wt%. In alternative embodiments, the additive may be introduced into the flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of from about 2 wt% to about 17 wt%, or from about 5 wt% to about 17 wt%, or from about 7 wt% to about 17 wt%.

[0112] In alternative embodiments, the additive may be introduced into flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of from about 2 wt% to about 15 wt%, or from about 5 wt% to about 15 wt%, or from about 7 wt% to about 15 wt%. In alternative embodiments, the additive may be introduced into flash vessel 120 in an amount sufficient to establish a steady-state concentration of the additive in the reaction mixture of from about 2 wt% to about 12 wt%, or from about 5 wt% to about 12 wt%, or from about 7 wt% to about 12 wt%.

[0113] Typically, additives may only be introduced continuously into system 100. Methods according to the present disclosure differ from the prior art in that additives may be introduced into system 100 downstream of reactor 110 and upstream of purification zone 106.

[0114] Despite the highly efficient complexation, any residual HI that might reach the light ends column 130 can be readily separated as a bottoms stream 131 from the light ends section 104. Furthermore, since HI is removed from the product stream at the earliest stages of acetic acid post-processing, side reactions caused by HI (i.e., the formation of undesirable long-chain alkyl iodide contaminants in the product stream downstream of the flash vessel) are significantly reduced. Furthermore, the reduced amount of HI in the product stream downstream of the flash vessel 120 mitigates corrosion and engineering issues. Furthermore, the additive acts as a catalyst stabilizer. Consequently, problems associated with catalyst loss due to deactivation or deposition are reduced or even avoided.

[0115] The beneficial effects of the additive on HI vaporization are not limited to the point of introduction into system 100. Rather, when the additive is circulated through system 100 by recycling liquid stream 121 from flash vessel 120 to reactor 110, its presence in the reaction mixture helps reduce the tendency of HI to vaporize in flash vessel 120, thereby helping to reduce the amount of HI that may be entrained in vapor stream 126. Thus, in cases where the process is operated continuously, the amount of additive in contact with the reaction mixture in flash vessel 120 can generally be reduced as steady-state conditions are reached. Under steady-state conditions, the amount of additive in contact with the reaction mixture in flash vessel 120 can generally be reduced to the amount necessary to maintain a desired steady-state concentration of the additive.

[0116] Certain embodiments

[0117] In some embodiments, a method for producing acetic acid in an acetic acid production system comprises contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising an iodide under carbonylation conditions sufficient to form acetic acid. The liquid reaction medium comprises a carbonylation catalyst, water, and an additive. The carbonylation catalyst is selected from the group consisting of a rhodium catalyst, an iridium catalyst, and a palladium catalyst. The water is present in the liquid reaction medium at 0.1 wt % to 10 wt % based on the weight of the liquid reaction medium. The additive is present in the liquid reaction medium at a molar ratio of additive to iodide of about 0.005 to about 2.0 M, as well as an in situ generated derivative of the additive and / or a combination thereof. The additive comprises a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof. The method also includes recovering the acetic acid.

[0118] In further embodiments of the process for producing acetic acid in an acetic acid production system, the process is further characterized by one or more of the following:

[0119] a) the additive is continuously added in the form of an acetic acid solution;

[0120] b) The bidentate phosphine dioxide can be represented by formula I:

[0121]

[0122] in:

[0123] P is phosphorus;

[0124] O is oxygen;

[0125] R 1 Selected from C1-C 10 alkyl;

[0126] R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other; and

[0127] Each bidentate phosphine dioxide has at least 17 carbon atoms; or

[0128] c) the bidentate phosphine dioxide is selected from bis(diphenylphosphino)methane dioxide (bis-DPPMeO2), bis(diphenylphosphino)propane dioxide (bis-DPPPrO2), bis(diphenylphosphino)pentane dioxide (bis-DPPPeO2) and combinations thereof.

[0129] d) the bidentate phosphine dioxide has a wavelength less than or equal to 1190 cm-1 as measured by Fourier transform infrared spectroscopy in acetonitrile at 25°C. -1 The frequency of phosphoryl groups;

[0130] e) The tertiary arsenic oxide can be represented by Formula II:

[0131]

[0132] in:

[0133] As is arsenic;

[0134] O is oxygen; and

[0135] R 1 、R 2 , and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other.

[0136] f) the tertiary arsenic oxide is selected from triphenylarsine oxide (TPAsO), triethylarsine oxide (TEtAsO), and combinations thereof;

[0137] g) the tertiary arsenic oxide has a pK less than or equal to 5.00 BHX , less than or equal to -20 kJ mol -1 ΔG° or a combination thereof, where pK BHX and ΔG° were measured in CCl4 at 25°C;

[0138] h) the additive exhibits a melting point greater than 100°C, or greater than 200°C, or greater than 300°C;

[0139] i) a molar ratio of the additive to the carbonylation catalyst greater than about 0.5:1 or within the range of 0.5:1 to 100:1;

[0140] j) the liquid reaction medium comprises water in the range of 0.1 wt% to 10 wt% based on the weight of the liquid reaction medium;

[0141] k) the liquid reaction medium comprises an additive concentration of from about 0.01 to about 1.5 M, or from 0.025 to 1.2 M;

[0142] l) the method further comprises introducing a second concentration of the one or more additives into the process downstream of the reaction zone, and in some cases, adjusting the second concentration based on downstream iodide content;

[0143] m) the second concentration comprises a molar ratio of additive to iodide of 0.05:1 to 2.0:1;

[0144] n) the acetic acid is glacial acetic acid;

[0145] o) the carbonylation conditions include a temperature in the range of 150° C. to 250° C. and a pressure in the range of 200 psig (1,380 kPag) to 2,000 psig (1,380 MPag);

[0146] p) the acetic acid production system comprises a reaction zone, a purification zone, a light ends zone, and a recycle zone, and the additive is introduced upstream of the purification zone;

[0147] q) the acetic acid production system includes a drying tower, the method further comprising continuously introducing the additive upstream of the drying tower;

[0148] r) the acetic acid production system includes a reactor, the method further comprising continuously introducing the additive into the reactor;

[0149] s) the acetic acid production system comprises a reactor and a stream in fluid communication with the reactor, the method further comprising continuously introducing the additive into the stream;

[0150] t) the acetic acid production system includes a flash vessel, the method further comprising continuously introducing the additive into the flash vessel;

[0151] u) the acetic acid production system comprises a flash vessel and a stream in fluid communication with the flash vessel, the method further comprising continuously introducing the additive into the stream;

[0152] v) the acetic acid production system includes a light ends column, the method further comprising continuously introducing the additive into the light ends column;

[0153] w) the acetic acid production system comprises a light ends column and a stream in fluid communication with the light ends column, the method further comprising continuously introducing the additive into the stream;

[0154] x) the acetic acid production system includes a drying tower, the method further comprising continuously introducing the additive into the drying tower;

[0155] y) the acetic acid production system comprises a drying tower and a stream in fluid communication with the drying tower, the method further comprising continuously introducing the additive into the stream;

[0156] z) the acetic acid production system comprises a recycle stream, the method further comprising continuously introducing the additive into the recycle stream; and

[0157] aa) The additive is introduced into the system in an amount based on the loss rate of the additive in the reactor in the system.

[0158] In some embodiments, a method for reducing water in an acetic acid production process comprises contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising a first amount of hydrogen iodide under carbonylation conditions sufficient to form acetic acid. The liquid reaction medium comprises a carbonylation catalyst and a first amount of water, the carbonylation catalyst being selected from the group consisting of a rhodium catalyst, an iridium catalyst, and a palladium catalyst, the first amount of water being sufficient to form an azeotropic mixture of the first amount of hydrogen iodide and the first amount of water. The method further comprises adding an additive to the liquid reaction medium at a molar ratio of the additive to the iodide of about 0.005 to about 2.0M, wherein the additive forms a complex with at least a portion of the first amount of hydrogen iodide, thereby producing a second amount of hydrogen iodide. The additive comprises a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof. The method further comprises reducing the water in the liquid reaction medium to a second amount of water while maintaining an azeotropic mixture of the second amount of hydrogen iodide and the second amount of water.

[0159] In further embodiments of the method for reducing water in an acetic acid production process, the method is further characterized by one or more of the following:

[0160] a) the additive is continuously added in the form of an acetic acid solution;

[0161] b) The bidentate phosphine dioxide can be represented by formula I:

[0162]

[0163] in:

[0164] P is phosphorus;

[0165] O is oxygen;

[0166] R 1 Selected from C1-C 10 alkyl;

[0167] R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other; and

[0168] Each bidentate phosphine dioxide has at least 17 carbon atoms; or

[0169] c) the bidentate phosphine dioxide is selected from bis(diphenylphosphino)methane dioxide (bis-DPPMeO2), bis(diphenylphosphino)propane dioxide (bis-DPPPrO2), bis(diphenylphosphino)pentane dioxide (bis-DPPPeO2) and combinations thereof.

[0170] d) the bidentate phosphine dioxide has a wavelength less than or equal to 1190 cm-1 as measured by Fourier transform infrared spectroscopy in acetonitrile at 25°C. -1 The frequency of phosphoryl groups;

[0171] e) The tertiary arsenic oxide can be represented by Formula II:

[0172]

[0173] in:

[0174] As is arsenic;

[0175] O is oxygen; and

[0176] R 1 、R 2 , and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other.

[0177] f) the tertiary arsenic oxide is selected from triphenylarsine oxide (TPAsO), triethylarsine oxide (TEtAsO), and combinations thereof;

[0178] g) the tertiary arsenic oxide has a pK less than or equal to 5.00 BHX , less than or equal to -20 kJ mol -1 ΔG° or a combination thereof, where pK BHX and ΔG° were measured in CCl4 at 25°C;

[0179] h) the additive exhibits a melting point greater than 100°C, or greater than 200°C, or greater than 300°C;

[0180] i) a molar ratio of the additive to the carbonylation catalyst greater than about 0.5:1 or within the range of 0.5:1 to 100:1;

[0181] j) the liquid reaction medium comprises water in the range of 0.1 wt% to 10 wt% based on the weight of the liquid reaction medium;

[0182] k) the liquid reaction medium comprises an additive concentration in the range of about 0.01 to about 1.5 M or 0.025 to 1.2 M;

[0183] l) the method further comprises introducing a second concentration of the one or more additives into the process downstream of the reaction zone, and in some cases, adjusting the second concentration based on downstream iodide content;

[0184] m) the second concentration comprises a molar ratio of additive to iodide of 0.05:1 to 2.0:1;

[0185] n) the acetic acid is glacial acetic acid;

[0186] o) the carbonylation conditions include a temperature in the range of 150° C. to 250° C. and a pressure in the range of 200 psig (1,380 kPag) to 2,000 psig (1,380 MPag);

[0187] p) the acetic acid production system comprises a reaction zone, a purification zone, a light ends zone, and a recycle zone, and the additive is introduced upstream of the purification zone;

[0188] q) the acetic acid production system includes a drying tower, the method further comprising continuously introducing the additive upstream of the drying tower;

[0189] r) the acetic acid production system includes a reactor, the method further comprising continuously introducing the additive into the reactor;

[0190] s) the acetic acid production system comprises a reactor and a stream in fluid communication with the reactor, the method further comprising continuously introducing the additive into the stream;

[0191] t) the acetic acid production system includes a flash vessel, the method further comprising continuously introducing the additive into the flash vessel;

[0192] u) the acetic acid production system comprises a flash vessel and a stream in fluid communication with the flash vessel, the method further comprising continuously introducing the additive into the stream;

[0193] v) the acetic acid production system includes a light ends column, the method further comprising continuously introducing the additive into the light ends column;

[0194] w) the acetic acid production system comprises a light ends column and a stream in fluid communication with the light ends column, the method further comprising continuously introducing the additive into the stream;

[0195] x) the acetic acid production system includes a drying tower, the method further comprising continuously introducing the additive into the drying tower;

[0196] y) the acetic acid production system comprises a drying tower and a stream in fluid communication with the drying tower, the method further comprising continuously introducing the additive into the stream;

[0197] z) the acetic acid production system comprises a recycle stream, the method further comprising continuously introducing the additive into the recycle stream; and

[0198] aa) The additive is introduced into the system in an amount based on the loss rate of the additive in the reactor in the system.

[0199] Although the disclosed methods and systems have been described in detail, it will be understood that various changes, substitutions, and modifications may be made herein without departing from the spirit and scope of the invention as defined by the appended claims. In addition, the scope of this application is not intended to be limited to the specific embodiments of the processes, machines, compositions, equipment, methods, and / or steps described in the specification. As will be readily understood by those skilled in the art from this disclosure, according to the present invention, processes, machines, compositions, equipment, methods, and / or steps that currently exist or will be developed later for performing functions substantially the same as those of the corresponding embodiments described herein or achieving substantially the same results may be utilized. Therefore, the appended claims are intended to include such processes, machines, compositions, equipment, methods, and / or steps within their scope.

[0200] Example

[0201] The following studies and examples are illustrative only and are not intended to, nor should they be construed as, limit the scope of the invention in any way.

[0202] Previously developed additives that allow for reducing the water content of the liquid reaction medium (comprising a carbonylation catalyst and hydrogen iodide) used to produce acetic acid include phosphine oxides and compound mixtures of phosphine oxides. Such phosphine oxides (e.g., triphenylphosphine oxide) are described in U.S. Patent Nos. 6,031,129 and 9,102,612, the entire teachings of which are incorporated herein by reference. Such phosphine oxides are exemplified hereinafter by triphenylphosphine oxide (TPPO). Compound mixtures of such phosphine oxides (e.g., a compound mixture of at least four phosphine oxides with a pentavalent aryl or alkyl aryl phosphine oxide comprising one or more benzoyl groups) are described in U.S. Patent Nos. 9,475,746 and 10,067,113, the entire teachings of which are incorporated herein by reference. Compound mixtures of such phosphine oxides are referred to as Cyanex TM 923, for example, formerly available from Cytec Corporation and now available from Solvay as CYTOP TM 503 is obtained and is hereinafter referred to as a compound mixture of phosphine oxides (CMPO).

[0203] bidentate phosphine dioxide

[0204] Experiments were conducted to investigate the possible chelating effects of various bidentate phosphine oxides. These studies included spectroscopic studies at room temperature and vapor-liquid equilibrium (VLE) studies, in which the extent of HI volatilization into the gas phase was determined by measuring the iodide concentration in condensed gas phase samples. Since bidentate phosphine oxides were not commercially available, they were synthesized in-house via the reaction of bis(diphenylphosphino)ethane dioxide as shown below:

[0205]

[0206] bidentate phosphine dioxide

[0207] A two-fold molar excess of 30% aqueous H2O2 was added to an appropriate mass of bidentate phosphine dissolved in acetonitrile or glacial acetic acid (GAA). Quantitative formation of dioxide was confirmed by FTIR in the acetonitrile solution, where the peak of the formed phosphoryl group (P=O) was not obscured by the solvent peak. Quantitative formation of dioxide in GAA was assumed to be similar to that in acetonitrile due to the heat released upon addition of peroxide. As shown in Table 1 below, the FTIR frequency of P=O in acetonitrile can be measured to determine basicity, as lower frequencies are associated with higher basicity. Further discussion of P-O bonds and basicity can be found in: “The Effect of Complex Formation by Phosphine Oxides on Their P-O Stretching Frequencies” (Journal of the Chemical Society, 2199-2203, 1960) and “Infrared and Raman Studies of Hydrogen Bonding in Organophosphorus Compounds-Proton Donors” (Canadian Journal of Spectroscopy, Vol. 32, No. 5, 107-114, 1987), the disclosures of which are incorporated herein by reference.

[0208] It should be noted that, somewhat surprisingly, within the bis(diphenylphosphino) series, only those with odd carbon chain lengths were soluble. Thus, bis(diphenylphosphino)ethane, bis(diphenylphosphino)butane, and bis(diphenylphosphino)hexane were all insoluble and not reported further.

[0209] Table 1

[0210] <![CDATA[R3PO]]> <![CDATA[R3PO]]> <![CDATA[P=O,cm -1 ]]> <![CDATA[Bis-DPPMeO2]]> <![CDATA[Bis-DPPMeO2]]> 1,197.7 TPPO TPPO 1,191.6 <![CDATA[Bis-DPPPrO2]]> <![CDATA[Bis-DPPPrO2]]> 1,180.8 Double-DPPPrO Double-DPPPrO 1,180.0 <![CDATA[Bis-DPPPeO2]]> <![CDATA[Bis-DPPPeO2]]> 1178.2 <![CDATA[Bis-DMePEtO2]]> <![CDATA[Bis-DMePEtO2]]> 1168.6 <![CDATA[Bis-DiCyPMeO2]]> <![CDATA[Bis-DiCyPMeO2]]> 1,160.1 <![CDATA[Double-DiCyPPRO2]]> <![CDATA[Double-DiCyPPRO2]]> 1,145.9 CMPO CMPO 1144.8 <![CDATA[Ph3AsO]]> <![CDATA[Ph3AsO]]> 885.5

[0211] These data indicate that bis(diphenylphosphino)methane dioxide (bis-DPPMeO2) has a lower basicity than the long-chain propyl and pentyl analogs (DPPPrO2 and DPPPeO2), and all three have significantly lower basicity than CMPO.

[0212] Room temperature studies in acetonitrile surprisingly revealed that p-toluenesulfonic acid (PTSA) formed 1:1 complexes with the three dioxides, where the dioxide complexed the PTSA proton in a bidentate manner, whereas HI formed a 2:1 complex where the dioxide complexed monodentately. Figure 2 For bis-DPPMeO2, and Figure 3 This phenomenon is shown diagrammatically for bis-DPPPrO2.

[0213] To ensure that the phosphoryl group was fully intact after interaction with HI and that the interaction was reversible, the HI adduct was treated with a molar equivalent of potassium acetate (KOAc). Reversibility was indicated by the reappearance of the free P=O group upon formation of potassium iodide (KI). This was observed in all cases. Figure 4 In the figure, the top spectrum is the unreacted bis-DPPPrO2, the middle spectrum is the HI-DPPPrO2 adduct, and the bottom spectrum is the spectrum of the HI-DPPPrO2 adduct after reaction with KOAc.

[0214] Vapor-Liquid Equilibrium (VLE) Studies

[0215] The VLE experiment is carried out in Figure 5 The VLE apparatus 500 is shown. The VLE apparatus 500 consists of a 50 mL single-necked flat-bottomed flask (still pot) 502, which is connected in sequence to a septum-sealed distillation head 504, an air condenser 506, a receiving tube 508, and a vent 509. The flat-bottomed flask 502 is immersed in an oil bath 512 maintained at 140°C, and the parts of the pot above the oil level, except for the distillation head 504, are wrapped with several layers of aluminum foil to ensure that condensation occurs only in the air condenser 506. All operations are carried out in air at atmospheric pressure.

[0216] The condensed vapor in the air condenser 506 was captured in a receiving tube 508 (10 mL Schlenk tube with graduations every 0.2 mL), which was cooled in an ice bath 516. Since the ice bath container consisted of a transparent beaker 518, the volume of the collected condensate 520 could be visually assessed.

[0217] In all experiments, 25 mL of a starting solution of appropriate composition was prepared in a 25 mL volumetric flask. 20 mL of this starting solution was then added to a VLE flask 502 using a 20 mL disposable syringe. This flask was connected to the rest of the apparatus via a ground glass joint and clamps, and then the VLE flask 502 was immersed in a preheated oil bath 512, with the contents stirred using a magnetic stirrer 511. The appropriate portion of the VLE apparatus 500 was quickly wrapped in aluminum foil, and then, within 5 to 10 minutes, the liquid in the flat-bottom flask 502 began to evaporate, while condensation was simultaneously performed in the air condenser 506. When 2 mL had collected in the receiving tube 508, the distillation was terminated by removing the flat-bottom flask 502 from the oil bath 512. Exactly 2 mL of condensate was collected in each experiment to ensure that variations in the condensate volume would not introduce bias into the results. The contents of the receiving tube 508 were then injected into a capped sample tube for subsequent iodide analysis.

[0218] As will be appreciated by those skilled in the art of VLE data acquisition, it is critical that the VLE apparatus 500 be operated in an adiabatic manner, wherein there is only one equilibrium stage, and wherein the vapor is not enriched in more volatile components by partial condensation. Figure 5 The suitability of the VLE apparatus 500 in the example was verified prior to use by measuring the water concentration in the vapor condensate at 5 wt% and 10 wt% water in acetic acid concentrations in the flask. After heating the sample to reflux and analyzing the condensed vapor sample, the enrichment of the more volatile water in the vapor phase matched well with previous literature values ​​shown in Table 2, where all values ​​are expressed as mole fractions.

[0219] Table 2 Validation of the VLE device by comparison with previous data

[0220] <![CDATA[Start with H2O, liquid]]> <![CDATA[H2O, vapor]]> <![CDATA[H2O 1 , steam]]> <![CDATA[H2O 2 , steam]]> 0.15 0.25 0.23 0.23 0.28 0.42 0.41 0.40

[0221] 1 Results obtained by the method disclosed in European patent application EP 0 506 240

[0222] 2 Results obtained by the method disclosed by Brown and Ah Ewald in "Liquid-Vapour Equilibria. I. The Systems Carbon Tetrachloride-cyclo-hexane and Water-Acetic Acid" (Australian Journal of Scientific Research, Vol. 3, No. 2, 306-323)

[0223] Iodide analysis

[0224] The iodide concentration in the condensed vapor sample is quantified spectrophotometrically. The iodide in the sample is oxidized to molecular iodine by the addition of hydrogen peroxide. Unlike iodide, which has no spectrophotometric characteristics in the GAA / H2O solution, molecular iodine has a strong, well-resolved absorption band centered at 475 nm, as shown in Figure 2. Figure 6 The quantitative accuracy can reach about ±20ppm.

[0225] FTIR analysis

[0226] FTIR analysis was performed on a Nicolet 6700 FTIR spectrometer equipped with a 3-reflection zinc selenide (ZnSe) attenuated total reflectance (ATR) crystal assembly. A 0.1 mL aliquot of the sample solution was removed via a microsyringe. The solution was then placed on the crystal and FTIR spectra were acquired.

[0227] Example 1 to Example 8

[0228] To simulate a low-water process, VLE experiments were conducted in the kettle at 2 wt% HO. Since HI is a 57% aqueous solution and since the in-situ generated dioxide requires aqueous HO, all VLE runs were conducted at 0.1 M HI to limit the HO in the kettle to 2 wt%. Table 3 below contains the iodide concentrations measured in the condensed vapor phase for all VLE runs, where the test conditions were 0.1 M HI, 1.3 M HO (2 wt%), and GAA, and were conducted at approximately 140°C.

[0229] Table 3

[0230]

[0231] Unlike experiments at room temperature in which HI forms a 2:1 complex in a monodentate manner, these data indicate that at 140°C, the bidentate phosphine dioxide acts in a bidentate manner in the interaction between the P═O group and HI. Examples 3 to 5 (using a 0.05 M concentration of bidentate phosphine dioxide) achieved similar inhibition of HI volatilization compared to Example 1 (using a 0.1 M concentration of CMPO). Examples 6 to 8 (using a 0.1 M concentration of bidentate phosphine dioxide) achieved similar or enhanced inhibition of HI volatilization compared to Example 2 (using a 0.2 M concentration of CMPO).

[0232] There is also strong evidence that the chelation effect increases stability. As indicated by the P=O frequencies shown in Table 1 above, the three phosphine dioxides in Examples 3 to 8 (containing two phenyl groups and one alkyl group bonded to each P atom) are electronically closer to TPPO than to CMPO.

[0233] Figure 7 The results show that at 3.3 wt% H₂O, CMPO's ability to inhibit HI volatilization increases approximately fivefold when the molar concentrations of R₃PO and HI are the same. The test conditions for these VLE experiments were 0.25 M HI, 3.3 wt% water, GAA, and varying amounts of R₃PO. Therefore, the VLE data in Table 3 above show that at the same molar concentration of P═O groups, the three bidentate phosphine dioxides match CMPO in inhibiting HI volatilization, a fact that suggests a stabilizing effect associated with chelation.

[0234] In summary, the experimental data presented above demonstrate that bidentate phosphine dioxide additives offer improvements over CMPO due to the ability to operate at half the CMPO concentration while achieving comparable suppression of HI volatility. Considering the molecular weight of these bidentate phosphine dioxides, which is approximately 420 g / mol, the mass of these bidentate phosphine dioxides required is reduced by approximately 40% compared to the CMPO molecular weight of 348 g / mol, freeing up increased reactor volume for acetic acid production. Alternatively, operating at the same molar concentration as CMPO results in only a slight reduction in available reactor volume, but with a significant reduction in volatilized HI. Both of these effects enhance the ability to operate at reactor HO concentrations as low as 2 wt%.

[0235] Tertiary arsenic oxide

[0236] Pentavalent Group 15 oxides with central atoms larger than phosphorus were analyzed based on the theory that increased polarizability and decreased electronegativity should lead to decreased double bond character, increased ionicity, and increased basicity of the M=O group.

[0237] Both triphenylarsine oxide (Ph3AsO) and triphenylantimony oxide (Ph3SbO) are commercially available. In addition, another arsenic oxide, dimethylarsinic acid shown below, is also commercially available and was analyzed to determine whether the As=O group can act as a base when part of an acidic compound.

[0238]

[0239] Another basicity manipulation method involves replacing the O atom, such as triphenylphosphine selenide (Ph3PSe), which is commercially available.

[0240] Ph3SbO and Ph3PSe were ruled out as possible additives because they are insoluble in GAA. Adding HI to a slurry of these compounds in GAA did not result in any solubility. Dimethylarsonic acid is insoluble in GAA but completely dissolved after adding HI. Ph3AsO was soluble in GAA both with and without the addition of HI.

[0241] Quantitative formation of dioxide in GAA was assumed by the heat released upon addition of peroxide being similar to that in acetonitrile. As shown in Table 4 below, the FTIR frequency of P=O in acetonitrile was determined to measure basicity, as lower frequencies are associated with higher basicity.

[0242] Table 4

[0243] <![CDATA[R3PO]]> <![CDATA[pK b ]]> <![CDATA[P=O,cm -1 ]]> TPPO 3.16 1,191.6 CMPO 3.63 1,144.8 <![CDATA[Ph3AsO]]> 4.15 885.5

[0244] The FTIR data obtained in acetonitrile solution in Table 4 above show that the P=O of Ph3AsO is greatly weakened compared to phosphine oxide, which is consistent with its expected increase in basicity. The FTIR frequency of As=O is 885 cm -1 It is almost 300 wave numbers lower than CMPO. b The results are consistent and suggest that it is at least an order of magnitude stronger base than phosphine oxide. -1 The frequency was confirmed to be the stretching vibration of As=O, because it disappeared when an aliquot of HI or PTSA was added, but reappeared when KOAc or tetraethylammonium acetate (Et4NOAc) was added to the HI or PTSA adduct. Figure 8 and Figure 9 The superimposed FTIR spectra in show some of these behaviors. Figure 8 It shows that when an equal portion of PTSA is added, the As=O frequency disappears. A 1:1 interaction is observed regardless of the H2O concentration. Figure 9 It is shown that when an aliquot of Et4NOAc is added to the adduct, the As=O frequency reappears.

[0245] Example 9 to Example 13

[0246] A series of VLE experiments were conducted under the conditions shown in Table 5 below, investigating additive-to-HI molar ratios of 1:1 and 2:1. Of particular note, at equivalent molar concentrations, PhAsO was approximately seven times more effective than CMPO in inhibiting HI volatilization. In contrast, dimethylarsonic acid exhibited poor inhibition of HI volatilization.

[0247] These data suggest that the use of PhAsO as an additive represents an improvement over CMPO, as its enhanced suppression of HI volatility would allow the reaction to be run at lower HO levels than when CMPO is used.

[0248] Table 5

[0249]

[0250] The scope of this application is not intended to be limited to the specific embodiments of the processes, devices, methods and / or steps described in the specification. The specific embodiments disclosed above are merely illustrative, as the processes and systems can be modified and practiced in different but equivalent ways, which will be apparent to those skilled in the art who benefit from the teachings herein. Although the present invention and its advantages have been described in detail, it will be understood that various changes, substitutions and modifications may be made herein without departing from the spirit and scope of the present invention as defined by the appended claims.

[0251] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to the ranges listed, any lower limit can be combined with any upper limit to list a range that is not explicitly listed, and a range from any lower limit can be combined with any other lower limit to list a range that is not explicitly listed, and similarly, a range from any upper limit can be combined with any other upper limit to list a range that is not explicitly listed. Additionally, even if not explicitly stated, a range includes each point or single value between its endpoints. Therefore, each point or single value can be combined as its own lower limit or upper limit with any other point or single value or any other lower limit or upper limit to list a range that is not explicitly listed.

[0252] All patents, test procedures, and other documents cited in this application are incorporated herein by reference in their entirety for all jurisdictions in which such incorporation is permitted. In the event of a conflict between one or more incorporated patents or publications and the present disclosure, the present specification (including definitions) will control.

Claims

1. A method for producing acetic acid in an acetic acid production system, the method comprising: a) contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising iodide under carbonylation conditions sufficient to form acetic acid, wherein the liquid reaction medium comprises: i) a carbonylation catalyst selected from the group consisting of a rhodium catalyst, an iridium catalyst and a palladium catalyst; ii) water in an amount ranging from 0.1 wt% to 10 wt% based on the weight of the liquid reaction medium; and iii) an additive having a molar ratio of additive to iodide of 0.005:1 to 2.0:1, an in situ generated derivative of said additive, or a combination thereof, wherein said additive comprises a bidentate phosphine dioxide, a tertiary arsenic oxide, or a combination thereof; and b) recovering the acetic acid.

2. The method according to claim 1, wherein the additive is added continuously in the form of an acetic acid solution.

3. The method according to claim 1, wherein the bidentate phosphine dioxide can be represented by Formula I: in: P is phosphorus; O is oxygen; R 1 Selected from C1-C 10 alkyl; R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other; and Each bidentate phosphine dioxide has at least 17 carbon atoms.

4. The method of claim 1 , wherein the bidentate phosphine dioxide is selected from the group consisting of bis(diphenylphosphino)methane dioxide (bis-DPPMeO 2 ), bis(diphenylphosphino)propane dioxide (bis-DPPPrO 2 ), bis(diphenylphosphino)pentane dioxide (bis-DPPPeO 2 ), and combinations thereof.

5. The method according to claim 1, wherein the bidentate phosphine dioxide has a wavelength less than or equal to 1190 cm-1 as measured by Fourier transform infrared spectroscopy in acetonitrile at 25°C. -1 The frequency of phosphoryl groups.

6. The method of claim 1, wherein the tertiary arsenic oxide can be represented by Formula II: in: As is arsenic; O is oxygen; and R 1 、R 2 , and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other.

7. The method of claim 1, wherein the tertiary arsenic oxide is selected from the group consisting of triphenylarsine oxide (TPAsO), triethylarsine oxide (TEtAsO), and combinations thereof.

8. The method of claim 1 , wherein the tertiary arsenic oxide has a pK less than or equal to 5.

00. BHX , less than or equal to -20 kJ mol -1 ΔG° or a combination thereof, where pK BHX and ΔG° were measured in CCl4 at 25°C.

9. The method of claim 1, wherein the additive exhibits a melting point below 100°C.

10. The process of claim 1 wherein the molar ratio of the additive to the carbonylation catalyst is greater than about 0.5:

1.

11. A method for reducing water in an acetic acid production process, the method comprising: a) contacting methanol and carbon monoxide in the presence of a liquid reaction medium comprising a first amount of hydrogen iodide under carbonylation conditions sufficient to form acetic acid, wherein the liquid reaction medium comprises: i) a carbonylation catalyst selected from the group consisting of a rhodium catalyst, an iridium catalyst and a palladium catalyst; and ii) a first amount of water, said first amount of water being sufficient to form an azeotropic mixture of said first amount of hydrogen iodide and said first amount of water; and b) adding an additive to the liquid reaction medium at a molar ratio of additive to iodide of from 0.005:1 to 2.0:1, wherein: i) the additive forms a complex with at least a portion of the first amount of hydrogen iodide, thereby producing a second amount of hydrogen iodide; and ii) the additive comprises bidentate phosphine dioxide, tertiary arsenic oxide or a combination thereof; c) reducing the water in the liquid reaction medium to a second amount of water while maintaining an azeotropic mixture of the second amount of hydrogen iodide and the second amount of water.

12. The method according to claim 11, wherein the additive is added continuously in the form of an acetic acid solution.

13. The method of claim 11, wherein the bidentate phosphine dioxide can be represented by Formula I: in: P is phosphorus; O is oxygen; R 1 Selected from C1-C 10 alkyl; R 2 、R 3 、R 4 and R 5 Each independently selected from C4-C 18 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other; and Each bidentate phosphine dioxide has at least 17 carbon atoms.

14. The method of claim 11, wherein the bidentate phosphine dioxide is selected from the group consisting of bis(diphenylphosphino)methane dioxide (bis-DPPMeO2), bis(diphenylphosphino)propane dioxide (bis-DPPPrO2), bis(diphenylphosphino)pentane dioxide (bis-DPPPeO2), and combinations thereof.

15. The method of claim 11, wherein the bidentate phosphine dioxide has a wavelength less than or equal to 1190 cm-1 as measured by Fourier transform infrared spectroscopy in acetonitrile at 25°C. -1 The frequency of phosphoryl groups.

16. The method of claim 11, wherein the tertiary arsenic oxide can be represented by Formula II: in: As is arsenic; O is oxygen; and R 1 、R 2 , and R 3 Each independently selected from C1-C 10 Alkyl, C4-C 18 Aryl, C4-C 18 Cyclic alkyl, C4-C 18 cyclic aromatic groups and combinations thereof, and can be the same as or different from each other.

17. The method of claim 11, wherein the tertiary arsenic oxide is selected from the group consisting of triphenylarsine oxide (TPAsO), triethylarsine oxide (TEtAsO), and combinations thereof.

18. The method of claim 11, wherein the tertiary arsenic oxide has a pK less than or equal to 5.

00. BHX , less than or equal to -20 kJ mol -1 ΔG° or a combination thereof, where pK BHX and ΔG° were measured in CCl4 at 25°C.

19. The method of claim 11, wherein the additive exhibits a melting point below 100°C.

20. The method of claim 11, wherein the molar ratio of the additive to the carbonylation catalyst is greater than about 0.5:1.

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