CN107207392B

CN107207392B - Process for producing acetic acid

Info

Publication number: CN107207392B
Application number: CN201580074800.0A
Authority: CN
Inventors: S·L·阿夫雷戈; Y-H·刘; M·O·斯盖茨; R·D·沙弗
Original assignee: International Rayon Co
Current assignee: International Rayon Co
Priority date: 2015-01-30
Filing date: 2015-10-02
Publication date: 2021-06-08
Anticipated expiration: 2035-10-02
Also published as: SA517381989B1; KR102493740B1; MY181742A; KR20170110656A; EP3250542A1; WO2016122728A1; CN107207392A; MX2017009867A; SG11201706008YA

Abstract

The present invention relates to a carbonylation process for producing acetic acid comprising separating a vapor product stream from a carbonylation reactor to produce a crude acid product comprising acetic acid containing lithium cations and contacting the crude acetic acid product with a cation exchanger in acid form in a first treatment unit to produce an intermediate acid product; and contacting the intermediate acetic acid product with a metal-exchanged ion exchange resin having acid cation exchange sites in a second treatment device to produce purified acetic acid. Embodiments are also disclosed that relate to the operation of a processing device that includes a plurality of sampling ports.

Description

Process for producing acetic acid

RELATED APPLICATIONS

This application claims priority to U.S. provisional application serial No.62/109765 filed on 30/1/2015, and to U.S. application serial No.14/694913 filed on 23/4/2015, which claims priority to U.S. provisional application serial No.62/141490 filed on 1/4/2015, the disclosures of each of which are incorporated herein by reference in their entireties.

Background

The production of acetic acid by carbonylation comprises continuously reacting methanol and carbon monoxide in a reactor in the presence of a catalyst. The reaction mixture present in the reactor contains a transition metal, which may be a group 9 metal, which may be iridium and/or rhodium, and may further include one or more solvents, water, various stabilizers, co-catalysts, promoters, and the like. Reaction mixtures known in the art may contain acetic acid, methyl acetate, methyl iodide, hydrogen iodide promoters, and the like.

There is a complex network of interdependent equilibria in the reactor involving liquid acetic acid reaction components, including those involved in the formation of acetic acid, as well as those involved in the formation of various impurities that are also produced in the reactor. Impurities that may be present in acetic acid include Permanganate Reducing Compounds (PRCs) such as acetaldehyde. Thus, the acetic acid processes disclosed in the art may further include various purification methods and control schemes in which impurity formation is minimized and/or produced impurities are removed from the process or converted to product acetic acid.

The various impurities present in the production of acetic acid are difficult to remove. There is a need to control and monitor the purification system in various aspects of the acetic acid production process.

Summary of The Invention

In embodiments, a process comprises carbonylating at least one selected from the group consisting of methanol, dimethyl ether, and methyl acetate in a reactor in the presence of 0.1 to less than 14 weight percent of water, a rhodium catalyst, methyl iodide, and lithium iodide to form a reaction medium comprising acetic acid; separating the reaction medium into a liquid recycle stream and a vapor product stream; separating the vapor phase product stream in a primary purification line (primary purification train) in up to 2 distillation columns to produce a crude acid product comprising acetic acid containing lithium cations; contacting the crude acetic acid product with a first purification resin comprising a cation exchanger in acid form in a first treatment unit to produce an intermediate acid product; and contacting the intermediate acetic acid product in a second treatment unit with a second purification resin comprising a metal-exchanged ion exchange resin having acid cation exchange sites to produce a purified acetic acid stream, the first treatment unit, the second treatment unit, or both each comprising at least one sampling port disposed through a side of the treatment unit; obtaining a sample of the first purified resin, the second purified resin, a liquid sample of the acetic acid stream present in the processing apparatus, or a combination thereof through the respective sampling ports; and determining the concentration of the impurity in the at least one sample.

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

Drawings

FIG. 1 is a schematic diagram of a process for producing acetic acid according to one embodiment;

FIG. 2 is a schematic diagram of a series of processing devices according to one embodiment;

FIG. 3 is a cross-sectional view of a treatment device according to one embodiment; and

FIG. 4 is a cross-sectional view of a sampling device according to one embodiment; and

FIG. 5 is a block diagram illustrating the steps of loading a column of a processing plant with resin according to an embodiment.

Detailed Description

First, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, it will be apparent to those having minimal skill in the art that the methods disclosed herein may also comprise components other than those cited or specifically mentioned.

In the summary of the invention and this detailed description, each numerical value should be read on the one hand as modified by the term "about" (unless such a modification has been expressly made), and on the other hand as not having such a modification, unless the context dictates otherwise. Also, in this summary and this detailed description, it should be understood that concentration ranges recited or described as useful, suitable, etc., mean that any and every concentration (including endpoints) within the range is considered to have been described. For example, a range of "1-10" is to be read as indicating each and every possible number in succession between about 1 and about 10. Thus, even if specific numerical points within the stated ranges are explicitly identified or even if no numerical points within the stated ranges are explicitly identified, or if they refer to only a few specific numerical points, it is to be understood that the inventors intend and understand that any and all numerical points within the stated ranges are to be considered to have been mentioned, and that the inventors have knowledge of the entire ranges and all points within the stated ranges.

Throughout the specification, including the claims, the following terms have the indicated meanings, unless otherwise indicated.

As used in the specification and claims, "in the vicinity" includes "in (the position)". The term "and/or" refers to both the case of "and the case of only" or "and is used herein for simplicity only. For example, a mixture comprising acetic acid and/or methyl acetate may comprise acetic acid alone, methyl acetate alone, or both acetic acid and methyl acetate.

As used herein, the symbols representing the elements of the periodic Table and the new numbering scheme are used in accordance with those disclosed in Chemical and Engineering News, 63(5), 27 (1985). All molecular weights are weight average molecular weights unless otherwise specified.

All percentages are expressed in weight percent (wt%), based on the total weight of the particular stream present, unless otherwise specified. The room temperature was 25 ℃ and the atmospheric pressure was 101.325kPa unless otherwise specified.

For purposes herein, the percentage of exchange active sites of the resin is based on total exchange capacity in milliequivalents per gram (meq/g). For example, a cation exchange resin having a cation exchange capacity of 2meq/g (substitution of 2meq/g with silver ion) means that 100% of the active sites are substituted with silver, and 1meq/g substitution means that 50% of the active sites are substituted.

For purposes herein:

acetic acid may be abbreviated "AcOH";

methyl acetate may be abbreviated "MeAc";

methyl iodide may be abbreviated "MeI"; and

carbon monoxide may be abbreviated as "CO".

Permanganate Reducing Compounds (PRCs) refer to oxidizable compounds that cause a failure marker For Permanganate tests, as is readily understood by those skilled in the art (see "A New System For Automatic Measurement of permanate Time," Laboratory Automation and Information Management, 34, 1999, 57-67). Examples of Permanganate Reducing Compounds (PRC) include acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethyl butyraldehyde and the like, and the aldol condensation products thereof.

For purposes herein, the "overhead" of a distillation column refers to the lowest boiling condensable fraction that exits at or near the top of the distillation column. Likewise, the residue of a distillation column refers to the highest boiling fraction, which exits at or near the bottom of the distillation column. It should be understood that the resid can be taken from just above the bottom-most outlet of the distillation column, e.g., a tar, solid waste product, or trace stream where the bottom-most of the column is unusable, as would be readily understood by one skilled in the art. Likewise, the overhead stream can be taken just below the topmost outlet of the distillation column, for example where the lowest boiling fraction is a non-condensable stream or a trace stream, as will be readily understood by those skilled in the art.

As used herein, the average residence time of a column feed stream within a column refers to the total flow provided to the column divided by the total unoccupied volume present in the column, unless otherwise specified.

For purposes herein, a process vessel (which may be referred to as a column) has an inlet and an outlet. The interior of the column, also referred to herein as the internal cavity, is suitably packed with purified resin. The terms treating unit and tower are used interchangeably herein unless otherwise indicated. For purposes herein, the treating apparatus and the column other than the distillation column are used interchangeably.

As used herein, mass flow refers to kg/h unless otherwise specified, and can be measured directly or calculated from volumetric measurements. When the total mass flow rate or concentration of a component is indicated as being present "if at all," it is understood that the component may or may not be present in the stream above the measurement limit of the appropriate analytical method, as will be readily understood by those skilled in the art.

As used herein, when the mass flow rate of a fluid is "controlled" at a particular flow rate or at a flow rate proportional to the mass flow rate of another fluid, it is understood that such control includes directly altering a particular process stream, or controlling the mass flow rate of a particular fluid by altering the fluid (which directly affects the mass flow rate of the target fluid), as will be readily understood by those skilled in the art. All such ratios are expressed as mass to mass weight percent unless otherwise specified.

As used herein, a carbonylatable reactant is any material that reacts with carbon monoxide under reaction conditions to produce acetic acid or a desired product. Carbonylatable reactants include methanol, methyl acetate, dimethyl ether, methyl formate and the like.

As used herein, a low water carbonylation process is defined as a finite concentration of water in the carbonylation reactor less than or equal to about 14 weight percent.

As used herein, when at least a portion of a stream is recycled or directed back into another portion of the process, it is understood that "a portion" refers to a portion of the total mass flow of the stream. The stream may be combined with other streams (i.e., indirectly recycled), while all components initially present in the stream are present after combination.

In contrast, a stream "derived" from another stream may comprise the entire stream or may comprise less than all of the individual components originally present in the stream. A fluid "derived from" a particular stream may thus include a stream that has undergone another processing or purification prior to disposal. For example, the stream distilled prior to recycle is derived from the initial stream.

As used herein, unless otherwise specified, a limit based on a comparison between an observed effect in the presence of a certain component relative to an observed effect in the absence of the same component refers to a comparison made under substantially the same conditions, except for the presence or absence of the component (e.g., substantially the same composition, substantially the same temperature, time, and other conditions).

Impurities present in acetic acid include various iodine-containing species. Examples include alkyl iodides having 1 to about 20 carbon atoms. Alkyl iodides having higher molecular weights greater than about 6 carbons may be present in the final product at parts per billion levels. These impurities are problematic for different end uses of acetic acid and need to be removed according to different purity standards. Other impurities include different aldehydes and corrosive metals. These contaminants can be removed by contacting acetic acid with a suitable purification resin at a temperature greater than about 50 ℃ (see US 6657078). However, the use of such purified resins requires monitoring both the final product and the resin itself to prevent impurities from "penetrating" into the bed of purified resin during the production process.

While samples of the final product are readily available, samples of the purification resin used in such purification processes are hardly available, although the purification system is in operation. Furthermore, the downtime of such purification systems for obtaining resin samples is uneconomical and often questionable. However, a sampling device according to one or more embodiments of the present disclosure allows both liquid and solid purified resin samples to be obtained and analyzed at different points of the resin bed. The ability to obtain these samples allows for improved monitoring and control of the process. These sampling ports further allow prediction of when the resin will be depleted before excess impurities are present in the final product.

In particular embodiments, a method comprises providing a column comprising a lumen comprising an active purification resin located between a column inlet and a column outlet, the column further comprising one or more sample ports disposed between the column inlet and the column outlet, at least one sample port comprising a liquid sample port, a solid sample port, or both; and flowing the acetic acid stream having the first concentration of the impurity through the column at a temperature and flow rate sufficient to produce a purified acetic acid stream having a second concentration of the impurity, if any, at the column outlet that is less than the first concentration. Thus, acetic acid contacts the purification resin in a column to remove impurities and purify the acetic acid. In particular embodiments, the method further comprises opening at least one sample port prior to or while flowing the acetic acid stream through the column. In particular embodiments, the impurities comprise iodine, chromium, nickel, iron, or combinations thereof. In particular embodiments, the iodide may be an alkyl iodide. In particular embodiments, the purification resin comprises a macroporous network of a strong acid ion exchange resin having at least about 1% of its active sites in the silver or mercury form and/or a temperature of at least about 50 ℃.

In particular embodiments, opening the at least one sample port may comprise obtaining a purified resin sample through the at least one solid sample port, obtaining a liquid sample of the acetic acid stream present in the column through the at least one liquid sample port, or a combination thereof, and the method further comprises determining the concentration of the impurity in the at least one sample.

In particular embodiments, the concentration of one or more impurities is determined using gas chromatography, high pressure liquid chromatography, atomic absorption, inductively coupled plasma spectroscopy, mass spectrometry, x-ray fluorescence spectroscopy, or a combination thereof.

In a specific embodiment, the impurity concentration of one or more samples is compared to a previously determined impurity concentration value, and it is determined whether the impurity concentration indicates that the purified resin has been depleted at a point in the column corresponding to the location of the sample port from which the sample was obtained. In particular embodiments, the process may further comprise stopping the flow of acetic acid through the column. In particular embodiments, the acetic acid flow is stopped before substantially all of the active purification resin present in the column is exhausted, such that the concentration of impurities in the product acetic acid does not render the acetic acid unsuitable for a particular end use.

In particular embodiments, a second column similar to the first column may be provided, and acetic acid flows through the second column when the flow through the first column has been stopped and is thus purified in the second column.

In particular embodiments, while the flow over the column is stopped, at least a portion of the depleted resin is regenerated before resuming the flow of acetic acid through the column to produce the purified acetic acid stream. In particular embodiments, regeneration of the spent resin comprises removing at least a portion of the spent resin from the column and filling at least a portion of the column with active purification resin. In particular embodiments, the active resin used to refill at least a portion of the column comprises a previously spent resin that has been regenerated into an active purified resin. In particular embodiments, at least a portion of the spent resin is regenerated into an active purification resin within the column.

In a specific embodiment, a method comprises the steps of: (a) providing a column comprising an interior cavity defined by a plurality of sides arranged radially about a central axis and having an inlet end in fluid communication with an outlet end through the interior cavity and spaced longitudinally; (b) introducing an amount of purified resin into the lumen sufficient to fill a portion of the lumen; (c) flowing an aqueous cleaning fluid through the lumen from the outlet end to the inlet end at a flow rate and for a time sufficient to clean and/or remove fines from the purified resin; and (d) flowing the acetic acid stream having the first concentration of the impurity through the column at a temperature and flow rate sufficient to produce a purified acetic acid stream at the column outlet having a second concentration of the impurity, if any, that is less than the first concentration.

In particular embodiments, the column comprises one or more sample ports arranged between the column inlet and the column outlet, at least one sample port comprises a liquid sample port, a solid sample port, or both, and the method further comprises opening at least one sample port. In particular embodiments, the aqueous cleaning fluid is flowed for at least 60 minutes.

In particular embodiments, after step (c) of flowing the aqueous purge fluid through the column, an amount of inert gas is introduced into the column inlet to remove a portion of the purge fluid. In particular embodiments, a back-flush of acetic acid (from outlet to inlet) may then flow through the column at a flow rate and for a period of time sufficient to remove substantially all of the vapor from the internal cavity. In particular embodiments, the removal of the vapor may include opening one or more sample ports. In particular embodiments, the flow rate of the backwash stream of acetic acid is less than or equal to about 0.05 bed volumes per minute and the time period is less than or equal to about 30 minutes.

In a specific embodiment, the purified resin is pneumatically introduced into the internal cavity of the column as follows: providing fluid communication between an internal cavity and a bottom outlet of a vessel containing a slurry comprising a purified resin, and subsequently applying pressure to a headspace of the vessel in an amount sufficient to pneumatically transfer at least a portion of the slurry from the vessel to the internal cavity.

In particular embodiments, prior to loading the purified resin into the column, the interior cavity of the column and/or the headspace of the vessel is flushed with an inert gas, such as nitrogen, to remove oxygen from the space (i.e., such that the space contains less than 1 wt% oxygen).

In a specific embodiment, a method comprises: carbonylating in a reactor at least one selected from the group consisting of methanol, dimethyl ether and methyl acetate in the presence of 0.1 to less than 14 wt% of water, a rhodium catalyst, methyl iodide and lithium iodide to form a reaction medium comprising acetic acid; separating the reaction medium into a liquid recycle stream and a vapor product stream; separating the vapor product stream in a primary purification line (primary purification train) in up to 2 distillation columns to produce a crude acid product comprising acetic acid containing lithium cations; contacting the crude acetic acid product with a first purification resin comprising a cation exchanger in acid form in a first treatment unit to produce an intermediate acid product; and contacting the intermediate acetic acid product with a second purification resin comprising a metal-exchanged ion exchange resin having acid cation exchange sites in a second treatment device to produce a purified acetic acid stream, the first treatment device, the second treatment device, or both each comprising at least one sampling port disposed through a side of the treatment device; obtaining a sample of the first purified resin, the second purified resin, a liquid sample of the acetic acid stream present in the processing device, or a combination thereof through the respective sample ports; and determining the concentration of the impurity in the at least one sample.

In particular embodiments, the method further comprises comparing the impurity concentration of at least one sample to a previously determined impurity concentration value, and determining whether the impurity concentration of the sample indicates that the purified resin has been depleted at a point in the processing device corresponding to the location of the sample port from which the sample was obtained. In particular embodiments, the method further comprises stopping the flow of acetic acid through the treatment device, regenerating at least a portion of the depleted resin, and resuming the flow of acetic acid stream through the treatment device to produce a purified acetic acid stream prior to the depletion of substantially all of the active purification resin present in the treatment device.

In a specific embodiment, the metal-exchanged ion exchange resin comprises at least 1% silver occupied strong acid exchange sites. In particular embodiments, the crude acid product comprises up to 10ppm lithium.

In particular embodiments, separating the vapor product stream comprises: distilling the vapor product stream in a first distillation column and obtaining a distilled acetic acid product using side draw; and distilling the distilled acetic acid product in a second distillation column to produce a crude acid product comprising acetic acid and lithium cations. In embodiments, the method further comprises the step of: adding a potassium salt selected from the group consisting of potassium acetate, potassium carbonate, and potassium hydroxide to the distilled acetic acid product prior to distilling the distilled acetic acid product in a second distillation column; wherein at least a part of the potassium is removed by means of a cation exchanger in acid form.

In a specific embodiment, the crude acetic acid product is contacted with a cation exchanger at a temperature of from 50 ℃ to 120 ℃. In embodiments, the intermediate acetic acid product is contacted with the metal-exchanged ion exchange resin at a temperature of from 50 ℃ to 85 ℃; or a combination thereof. In embodiments, the lithium ion concentration of the intermediate acetic acid product is less than 50 ppb.

In particular embodiments, the acid form of the cation exchanger comprises a resin of an acid form strong acid cation exchange macroporous network, macroporous, or mesoporous resin. In embodiments, the process further comprises treating the purified acetic acid product with a cation exchange resin to recover any silver, mercury, palladium, or rhodium. In embodiments, the water concentration in the reaction medium is controlled to be in the range of from 0.1 to 5 weight percent, based on the total amount of reaction medium present.

In particular embodiments, the process further comprises introducing a lithium compound selected from the group consisting of lithium acetate, lithium carboxylate, lithium carbonate, lithium hydroxide, and mixtures thereof into the reactor to maintain the concentration of lithium acetate in the reaction medium at 0.3 to 0.7 wt%. In embodiments, the process further comprises maintaining the hydrogen iodide concentration in the reaction medium at from 0.1 to 1.3 wt%; the rhodium catalyst concentration in the reaction medium was maintained at 300-3000 wppm; maintaining the water concentration in the reaction medium at 0.1-4.1 wt%; maintaining the methyl acetate concentration in the reaction medium at 0.6 to 4.1 wt%; or a combination thereof.

In particular embodiments, the process further comprises controlling the butyl acetate concentration in the acetic acid product at 10wppm or less without directly removing butyl acetate from the acetic acid product. In embodiments, the butyl acetate concentration is controlled as follows: maintaining the acetaldehyde concentration in the reaction medium at 1500ppm or less; controlling the temperature in the reactor at 150-250 ℃; controlling the hydrogen partial pressure in the reactor to be 0.3-2 atm; controlling the rhodium catalyst concentration in the reaction medium at 100-3000 wppm; or a combination thereof.

In a specific embodiment, the process further comprises controlling the ethyl iodide concentration in the reaction medium at less than or equal to 750 wppm. In embodiments, the propionic acid concentration in the product acetic acid is less than 250wppm without directly removing propionic acid from the product acetic acid, wherein the ethyl iodide in the reaction medium and the propionic acid in the acetic acid product are in a weight ratio of 3: 1-1: 2 is present; wherein acetaldehyde and iodoethane are present in the reaction medium in a weight ratio of 2: 1-20: 1 is present; wherein the ethanol concentration in the methanol feed to the reactor is less than 150 wppm; or a combination thereof. In embodiments, the concentration of ethyl iodide in the reaction medium is controlled by adjusting at least one of: the hydrogen partial pressure in the carbonylation reactor, the methyl acetate concentration in the reaction medium and the methyl iodide concentration in the reaction medium.

Acetic acid production system

Processes for producing acetic acid via methanol carbonylation can be conveniently divided into three main areas: reaction systems and processes, light ends recovery/acetic acid product separation systems and processes, and product acetic acid purification systems and processes.

The acetic acid process suitable for the purposes of the present invention to produce vapor from the carbonylation reactor which is subsequently distilled in the light products column to yield acetic acid product as a side draw may vary in the system and process, including the purification streams, the recycle streams, the type and number of distillation columns used, the different purification processes used, etc. Examples of suitable methods include those described in US 3769329; US 3772156; US 4039395; US 4255591; US 4615806; US 5001259; US 5026908; US 5144068; US 5237097; US 5334755; US 5653853; US 5683492; US5831120, US 5227520; US5416237, US 5731252; US 5916422; US 6143930; US6225498, US 6255527; US 6339171; US 6657078; US 7208624; US 7223883; US 7223886; US 7271293; US 7476761; US 783871; US 7855306; US 8076507; US 20060247466; US 20090259072; US 20110288333; US 20120090981; US 20120078012; US 2012081418; US 2013261334; US 2013281735; EP 0161874; w09822420; WO 0216297; those of WO2013137236 and the like, the entire contents and disclosure of which are incorporated herein by reference. A process for producing acetic acid in accordance with embodiments disclosed herein is generally represented as process 100, which is illustrated in fig. 1.

A low water and low energy process for the production of acetic acid by the carbonylation of methanol has been developed which includes a rhodium catalyzed system operating at less than 14 wt% water and using up to 2 distillation columns in the main purification line. The purpose of this primary purification line is to remove bulk components such as water, methyl acetate, methyl iodide and hydrogen iodide from the vapor product stream of the reactor/flasher to obtain acetic acid. This main purification line receives most of the vapor stream from the reactor and obtains acetic acid as a final product. For example, the columns of the main purification line include a light product column and a drying column. This main purification line may not include a column whose main role is to remove minor components such as acetaldehyde, alkanes, and propionic acid.

The process for producing acetic acid can produce a cation that is collected in the crude acid product. These residual cations can be difficult to remove and can undesirably replace iodide in the final metal exchange guard bed. Thus, the final product may have unacceptable levels of iodide despite the use of a metal exchange guard bed. The present invention provides a method for removing cations.

The cation source may be derived from a variety of promoters, co-catalysts, additives, in situ reactions, and the like. Such as low water and low energy processes which include the use of promoters such as lithium iodide which may be formed in situ after addition of lithium acetate or other compatible lithium salt to the reaction mixture. Therefore, the process stream may contain a certain amount of lithium ions. In addition, because the process employs up to 2 distillation columns in the main purification line and preferably columns that do not include heavy product (heavies ends) material removal for the main purification, the crude acid product may contain larger alkyl iodide compounds, such as C, in addition to cations such as lithium₁₀-C₁₄Alkyl iodides. In some cases more than 10% or even more than 50% of the iodides present have a chain length of more than 10 carbon atoms. Thus, C may be present in an amount of greater than 10ppb, e.g., greater than 20ppb, greater than 50ppb, greater than 100ppb, or greater than 1ppm₁₀-C₁₄Alkyl iodides. In addition to these higher alkyl iodides, there may be typical short chain length iodide impurities found in the crude acid product of iodide-promoted carbonylation processes, including methyl iodide, HI, and iodohexane. The common iodide impurities are typically removed from the crude acid product using a metal-exchanged strong acid ion exchange resin, where the metal is, for example, silver or mercury. However, it has been found that silver or mercury in the metal-exchanged strong acid ion exchange resin can be replaced by residual lithium, resulting in lower resin capacity and efficiency and potential contamination of the product with silver or mercury.

The cations in the crude acid product may be formed by the use of organic alkali metal salt ligands, for example organic lithium salt ligands, such as those described in CN101053841 and CN1349855, the entire contents and disclosure of which are incorporated herein by reference. CN101053841 describes ligands comprising lithium acetate or lithium oxalate. CN1349855 describes a bimetallic catalyst with a metallic lithium organic ligand coordinated to a cis-dicarbonylrhodium structure. The lithium metal organic ligand may be a pyridine derivative such as lithium pyridine-2-carboxylate, lithium pyridine-3-carboxylate, lithium pyridine-4-carboxylate, lithium pyridine-3-acetate, lithium pyridine-4-acetate or lithium pyridine-3-propionate. In fact, the lithium salt component of all of these ligands is believed to produce lithium iodide in situ in the reaction medium after exposure to methyl iodide at the reaction temperature and pressure in the carbonylation reactor. At least some small portion of the lithium component will be carried into the purification system. Thus, the purification system according to the present invention can also remove lithium formed in situ from these types of organic ligands.

As a result of the use of non-lithium salts, cations may also be present, for example by using bimetallic Rh chelating catalysts having amine functionality, such as those described in CN1640543, the entire content and disclosure of which is incorporated herein by reference. According to CN16040543 the cationic species comprises N and O donor atoms and is formed from aminobenzoic acid. The amine may be quaternized with methyl iodide in situ in the reaction medium at reaction temperature and pressure to form a quaternary nitrogen cation. The quaternary nitrogen cations, like lithium cations, can be carried by the crude acid product and can be removed using the present invention prior to the metal exchange guard bed.

Particular embodiments include low water and low energy processes for producing acetic acid by carbonylating methanol, dimethyl ether, and/or methyl acetate in the presence of 0.1 to less than 14 weight percent water, a metal catalyst, methyl iodide, and lithium iodide. In a specific embodiment, a low energy process using up to 2 distillation columns (e.g., a light product column and a water removal or dehydration column, without the use of a third "heavy product column) in a main purification line and purifying the resulting acidic acid product with a cation exchanger in acid form to remove residual lithium ions, followed by treatment with a metal-exchanged ion exchange resin having acid cation exchange sites, the ion exchange resin comprising at least one metal selected from the group consisting of silver, mercury, palladium, and rhodium. The metal-exchanged ion exchange resin may have at least 1% of the strong acid exchange sites occupied by silver, mercury, palladium, and/or rhodium, for example at least 1% silver, mercury, palladium, and/or rhodium, at least 5% silver, mercury, palladium, and/or rhodium, at least 10% silver, mercury, palladium, and/or rhodium, or at least 20% silver, mercury, palladium, and/or rhodium. By using a cation exchanger to remove lithium prior to using a resin having metal-exchanged strong acid cation sites, silver, mercury, palladium, and/or rhodium from the metal-exchanged sites is reduced or eliminated from being substituted by lithium for processes using up to 2 distillation columns in the main purification line. In particular embodiments, in addition to the main purification line, other purification systems may use a distillation column to remove impurities in the reactor components, such as an aldehyde removal system in which acetaldehyde and other PRCs are removed from the methyl iodide phase prior to returning the methyl iodide to the reaction medium.

Particularly preferred methods are those that use cation exchangers to remove lithium and then iodide through a silver-exchanged cationic substrate. The crude acid product in many cases includes C which needs to be removed₁₀Or organic iodides of greater aliphatic chain length. In some cases more than 10%, for example more than 30% or even more than 50% of the iodides present have an organic chain length of more than 10 carbon atoms.

Iododecane and iodododecane are particularly popular in the absence of heavy products and other finishing equipment and are difficult to remove from the product. The silver-exchanged cationic substrates of the present invention typically remove greater than 90% of such iodides; often the crude acid product has 10-1000ppb total iodide prior to processing, which would render the product unusable for iodide sensitive applications.

Prior to the iodide removal treatment, the iodide level in the crude acid product is typically 20ppb to 1.5 ppm; while the iodide removal treatment is preferably run to remove at least about 95% of the total iodide present. In a typical embodiment, the lithium/iodide removal treatment comprises contacting the crude acid product with a cation exchanger to remove 95% or more of the lithium ions, followed by contacting the crude acid product with a silver exchanged sulfonic acid functionalized macroporous network ion exchange resin, wherein the product has an organic iodide content of greater than 100ppb prior to treatment and an organic iodide content of less than 10ppb after contact with the resin.

It has also been found that in the absence of heavy products and other finishing equipment, lithium is carried in the crude acid product. Even very small amounts of 10ppb of lithium in the crude acid product can cause problems with iodide removal. Up to 10ppm lithium, for example up to 5ppm, up to 1ppm, up to 500ppb, up to 300ppb or up to 100ppb, by weight of the crude acid product, may be present in the acid-containing crude acid product exiting the drying column of the acetic acid process (e.g., the last column of the main purification line). In terms of ranges, from 0.01ppm to 10ppm lithium may be present in the crude acid product, for example from 0.05ppm to 5ppm or from 0.05ppm to 1 ppm. Substantial amounts of lithium can be removed by using a cation exchanger in the acid form prior to introducing the crude acid product into the metal-exchanged resin. For example, greater than 90 wt% of the lithium in the stream will be removed by the cation exchanger, e.g., 95 wt% or 99 wt%. The stream leaving the acid form cation exchanger may therefore contain less than 50ppb of lithium, for example less than 10ppb or less than 5 ppb. Such removal of lithium can significantly extend the life of the metal-exchanged resin.

Reaction system and method

As shown in fig. 1, a process 100 for producing acetic acid includes a reaction system including a carbonylation reactor 104 from which a portion of the reaction medium is continuously removed via line 113 and subjected to flash evaporation or low pressure distillation in a separation system, such as flasher 112, for separating acetic acid and other volatile components from the reaction medium and recycling non-volatile components back to the reaction medium via stream 110. The volatile components of the reaction medium are then overhead via line 122 to a light product recovery/acetic acid product separation system and process which begins with a light product column 124.

As shown in fig. 1, a methanol-containing feed stream 101 and a carbon monoxide-containing feed stream 102 are introduced into a liquid phase reaction medium of a carbonylation reactor 104 in which carbonylation reactions occur in a reaction medium containing catalyst, water, methyl iodide, methyl acetate, acetic acid, iodide salts, HI and other reaction medium components.

In particular embodiments, the carbonylation reactor 104 may be a stirred vessel, a bubble column type vessel or a combination thereof, wherein the reaction liquid or slurry contents are maintained at a level consistent with normal operation. In particular embodiments, the carbon monoxide may be introduced continuously into the reaction medium of the carbonylation reactor, including below the agitator used to agitate the contents. The gaseous feed is preferably thoroughly dispersed in the reaction liquid by such stirring means. In particular embodiments, the reactor system may further comprise a number of recycle lines, wherein different components from other parts of the process and different vapor purge lines that may undergo additional processing, etc., are recycled back to the reaction medium. It is to be understood that all vents and other vapor purge lines are connected to the one or more scrubber systems 139 and that all condensable components are ultimately recycled back to the carbonylation reactor before the vapor stream is released to the atmosphere, as will be readily understood by those skilled in the art.

In particular embodiments, a gaseous purge stream 106 may be vented from the reactor 104 to a scrubber system 139 to prevent build up of gaseous byproducts and to control the carbon monoxide partial pressure and/or the total reactor pressure. The reactor system may further include a pump around loop 103 to control the reactor temperature.

In particular embodiments, the reaction medium comprises a metal catalyst, or a group 9 metal catalyst, or a catalyst comprising rhodium and/or iridium. In a particular embodiment, the reaction medium comprises a rhodium catalyst.

In particular embodiments, the rhodium component of the catalyst system is believed to be present in the form of a coordination compound of rhodium with the halogen component, which provides a ligand for at least one such coordination compound. In addition to the coordination of rhodium and halogen, it is believed that carbon monoxide will coordinate to rhodium. In particular embodiments, the rhodium component of the catalyst system may be provided by: rhodium metal, rhodium salts such as oxides, acetates, iodides, carbonates, hydroxides, chlorides, and the like, or other compounds, which result in the formation of coordination compounds of rhodium in the reaction environment, are introduced into the reaction zone. In an alternative embodiment, the carbonylation catalyst comprises rhodium dispersed in a liquid reaction medium or supported on an inert solid. Rhodium may be introduced into the reaction system in any of a number of forms, and the precise nature of the rhodium moiety in the active catalyst complex may be uncertain.

In particular embodiments, the catalyst concentration in the reactor is maintained in an amount of about 200 to about 5000 parts per million (ppm) by weight based on the total weight of the reaction medium.

In particular embodiments, the reaction medium may further comprise a halogen-containing catalyst promoter. Suitable examples include organic halides, alkyl, aryl and substituted alkyl or aryl halides. In a particular embodiment, the halogen-containing catalyst promoter is present in the form of an alkyl halide, wherein the alkyl group corresponds to the alkyl group of the feed alcohol to be carbonylated. Thus, in the carbonylation of methanol to acetic acid, the halide promoter will comprise a methyl halide, or methyl iodide (MeI). In a specific embodiment, the reaction medium comprises greater than or equal to about 5 wt% MeI based on the total weight of the reaction medium. In particular embodiments, the reaction medium comprises greater than or equal to about 5 wt% and less than or equal to about 50 wt% MeI. In particular embodiments, the reaction medium comprises greater than or equal to about 7 wt.% or 10 wt.% MeI, and less than or equal to about 30 wt.% or 20 wt.% MeI, based on the total weight of the reaction medium.

In particular embodiments, the liquid reaction medium used may comprise any solvent compatible with the catalyst system, and may comprise pure alcohol, or a mixture of alcohol feedstock and/or product carboxylic acid and/or ester of the two compounds. In a particular embodiment, the solvent used in the liquid reaction medium comprises acetic acid (AcOH). In a specific embodiment, the reaction medium comprises greater than or equal to about 50 wt.% AcOH. In particular embodiments, the reaction medium comprises greater than or equal to about 50 wt% and less than or equal to about 90 wt% AcOH. In particular embodiments, the reaction medium comprises greater than or equal to about 50 wt%, or 60 wt% AcOH, and less than or equal to about 80 wt%, or 70 wt% AcOH, based on the total weight of the reaction medium.

In a particular embodiment, the reaction medium comprises at least a finite concentration of water. In a particular embodiment, the reaction medium comprises a measurable amount of water. In a specific embodiment, the reaction medium comprises greater than or equal to about 0.001 wt% water. In particular embodiments, the reaction medium comprises greater than or equal to about 0.001 wt% and less than or equal to about 14 wt% water. In particular embodiments, the reaction medium comprises greater than or equal to about 0.05 wt%, or 0.1 wt%, or 0.5 wt%, or 1 wt%, or 2 wt%, or 3 wt%, or 4 wt% water, and less than or equal to about 10 wt% or 5 wt% water, based on the total weight of the reaction medium.

In particular embodiments, the reaction medium further comprises the carboxylic acid product and an ester of the alcohol used in the carbonylation. In a particular embodiment, the reaction medium comprises methyl acetate. In particular embodiments, the reaction medium comprises greater than or equal to about 0.5 wt.% methyl acetate (MeAc). In particular embodiments, the reaction medium comprises greater than or equal to about 1 wt% and less than or equal to about 50 wt% MeAc. In particular embodiments, the reaction medium comprises greater than or equal to about 1.5 wt%, or 2 wt%, or 3 wt% of MeAc, and less than or equal to about 20 wt%, or 10 wt% of MeAc, based on the total weight of the reaction medium.

In particular embodiments, the reaction medium further comprises additional iodide ions that are above and above the iodide ions present as hydrogen iodide. In particular embodiments, the iodide ion concentration is provided by an iodide salt, or lithium iodide (LiI). In a particular embodiment, the reaction medium is maintained at a low water concentration, wherein methyl acetate and lithium iodide are present at a concentration sufficient to act as rate promoters (see US 5001259).

In particular embodiments, at least a portion of the iodide ion concentration in the reaction medium is derived from a metal iodide salt, or an iodide salt of an organic cation, or a cation based on a quaternary amine, phosphine, or the like. In particular embodiments, the iodide is a metal salt, a group 1 or group 2 iodide salt. In particular embodiments, the reaction medium comprises an alkali metal iodide, or lithium iodide. In particular embodiments, the iodide concentration exceeds and is higher than the iodide ion present as hydrogen iodide. In particular embodiments, the reaction medium comprises an iodide salt, or lithium iodide, in an amount sufficient to produce a total iodide ion concentration of greater than about 2 wt.%. In particular embodiments, the reaction medium comprises an iodide salt, or lithium iodide, in an amount sufficient to produce a total iodide ion concentration of greater than or equal to about 2 wt.% and less than or equal to about 40 wt.%, based on the total weight of the reaction medium. In particular embodiments, the reaction medium comprises greater than or equal to about 5 wt.%, or 10 wt.%, or 15 wt.% iodide ions, and less than or equal to about 30 wt.% or 20 wt.% iodide ions, based on the total weight of the reaction medium.

In particular embodiments, the reaction medium may further comprise hydrogen, as determined by the partial pressure of hydrogen present in the reactor. In particular embodiments, the partial pressure of hydrogen in the reactor is greater than or equal to about 0.7kPa (0.1psia), or 3.5kPa (0.5psia), or 6.9kPa (1psia), and less than or equal to about 1.03MPa (150psia), or 689kPa (100psia), or 345kPa (50psia), or 138kPa (20 psia).

In particular embodiments, the reactor temperature, i.e., the temperature of the reaction medium, is greater than or equal to about 150 ℃. In particular embodiments, the reactor temperature is greater than or equal to about 150 ℃ and less than or equal to about 250 ℃. In particular embodiments, the reactor temperature is greater than or equal to about 180 ℃ and less than or equal to about 220 ℃.

In particular embodiments, the carbon monoxide partial pressure in the reactor is greater than or equal to about 200 kPa. In particular embodiments, the CO partial pressure is greater than or equal to about 200kPa and less than or equal to about 3 MPa. In particular embodiments, the CO partial pressure in the reactor is greater than or equal to about 300kPa, or 400kPa, or 500kPa and less than or equal to about 2MPa or 1 MPa. The total reactor pressure represents the combined partial pressure of all reactants, products and by-products present therein. In particular embodiments, the total reactor pressure is greater than or equal to about 1MPa and less than or equal to about 4 MPa.

In particular embodiments, liquid reaction medium is withdrawn from the carbonylation reactor 104 and introduced into the flasher 112 (which is at a pressure lower than the pressure present in the reactor) at a rate sufficient to maintain a constant level therein, and introduced into the flasher 112 at an intermediate point between its top and bottom. In the flasher, the less volatile components (i.e., catalyst solution) are withdrawn as bottoms stream 110 (primarily acetic acid, containing rhodium and iodide salts and lesser amounts of methyl acetate, methyl iodide, acetic acid and water) and recycled back to the reaction medium. The overhead of flasher 122 comprises most of the product acetic acid as well as methyl iodide, methyl acetate, water and PRC. A portion of the carbon monoxide, as well as gaseous byproducts such as methane, hydrogen, carbon dioxide, etc., may also exit at the top of the flash vessel.

Light product recovery/acetic acid product separation systems and methods

In a particular embodiment, the overhead stream from flasher 112 is directed as stream 122 to a light products column 124 (also referred to in the art as a stripping column) where distillation produces a low boiling overhead vapor stream 126 (also referred to herein as a first overhead stream 126) and a purified acetic acid product stream 128, which in embodiments is removed as a side stream. The light products column 124 further produces a high boiling residue oil stream 116, which may undergo additional purification and/or may be recycled back to the reaction medium.

In particular embodiments, first overhead 126 is condensed and then directed to overhead phase separation unit 134 (also referred to herein as an overhead decanter). In particular embodiments, the first overhead 126 comprises methyl iodide, methyl acetate, acetic acid, water, and at least one PRC. In particular embodiments, the condensed first overhead stream 126 separates into a light aqueous phase 135 (which comprises water, acetic acid, methyl iodide, methyl acetate, and at least one Permanganate Reducing Compound (PRC) such as acetaldehyde); and a heavy phase 137 (which comprises methyl iodide, methyl acetate, which may also comprise at least one PRC).

In particular embodiments, at least a portion of the heavy phase 137, at least a portion of the light phase 135, or a combination thereof is returned to the reaction medium via

lines

118 and 114, respectively. In particular embodiments, a portion of light phase stream 135 can be recycled to the reaction medium in stream 114, providing the reaction medium with water as needed. In particular embodiments, heavy phase 137 is recycled back to the reactor via 118.

In particular embodiments, the light phase 135, heavy phase 137, or a combination thereof is directed to one or more purification processes 108, such as an aldehyde removal system, via stream 142. The purified stream is then returned to the process via one or more streams, collectively 155.

Although the specific composition of the light liquid phase 135 can vary widely, some exemplary compositions are provided in table 1 below.

In one embodiment, the overhead decanter 134 is arranged and configured to maintain a low interface level to prevent excessive retention of methyl iodide. Although the specific composition of the heavy liquid phase 137 may vary widely, some exemplary compositions are provided in table 2 below.

Although not shown, a portion of the light liquid phase 135 and/or heavy liquid phase 137 may be separated and directed to an acetaldehyde or PRC removal system to recover methyl iodide and methyl acetate while removing acetaldehyde. As shown in tables 1 and 2, the light liquid phase 135 and/or heavy liquid phase 137 each comprise PRCs, and the process may include removal of carbonyl impurities, such as acetaldehyde, which may degrade the quality of the acetic acid product and may be removed in suitable impurity removal columns and absorbers, such as U.S. patent nos. 6143930; 6339171, respectively; 7223883, respectively; 7223886, respectively; 7855306, respectively; 7884237, respectively; 8889904, respectively; and U.S. publication No.2006/0011462, which are incorporated herein by reference in their entirety. Carbonyl impurities such as acetaldehyde may react with iodide catalyst promoters to form alkyl iodides such as ethyl iodide, propyl iodide, butyl iodide, pentane iodide, hexane iodide, and the like. Also, because many of the impurities originate from acetaldehyde, it is desirable to remove carbonyl impurities from the liquid light phase.

The fraction of the light liquid phase 135 and/or heavy liquid phase 137 fed to the acetaldehyde or PRC removal system may vary from 1% to 99%, such as 1-50%, 2-45%, 5-40%, 5-30%, or 5-20% of the mass flow rate of either the light liquid phase 133 and/or heavy liquid phase 134. Also in some embodiments, a portion of both the light liquid phase 135 and the heavy liquid phase 137 may be fed to an acetaldehyde or PRC removal system. The portion of the light liquid phase 135 not fed to the acetaldehyde or PRC removal system may be refluxed to the first column or recycled to the reactor as described herein. The portion of the heavy liquid phase 137 that is not fed to the acetaldehyde or PRC removal system may be recycled to the reactor. While a portion of the heavy liquid phase 137 may be refluxed to the first column, it is more desirable to return the heavy liquid phase 137 rich in methyl iodide to the reactor.

In one embodiment, a portion of the light liquid phase 135 and/or the heavy liquid phase 137 is fed to a distillation column, which is enriched in its overhead to have acetaldehyde and methyl iodide. Depending on the configuration, there may be two separate distillation columns, and the overhead of the second column may be enriched in acetaldehyde and methyl iodide. Dimethyl ether (which may be formed in situ) may also be present in the overhead. The overhead may be subjected to one or more extraction stages to remove raffinate rich in methyl iodide and extractant. A portion of the raffinate can be returned to the distillation column, the first column, the overhead decanter, and/or the reactor. For example, when the heavy liquid phase 137 is processed in a PRC removal system, it may be desirable to return a portion of the raffinate to the distillation column or reactor. Also, for example, when the light liquid phase 135 is processed in a PRC removal system, it may be desirable to return a portion of the raffinate to the first column, the overhead decanter or the reactor. In some embodiments, the extractant may be further distilled to remove water and it is returned to one or more extraction stages, containing more methyl acetate and methyl iodide than the light liquid phase 135, which may also be recycled to the reactor 104 and/or refluxed to the first column 124.

Suitable purification methods include those disclosed in US6143930, US6339171, US7223883, US7223886, US8076507, US20130303800, US20130310603, US20090036710, US20090062525, US 20120120132515, US20130026458, US201300116470, US20130204014, US20130261334, US20130264186 or US201330281735, all of which are incorporated herein by reference.

Product purification system and method

In particular embodiments, the acetic acid stream 128 may undergo further purification, for example in a drying column 130, where the acetic acid is collected as a bottoms and an aqueous overhead is collected in an overhead decanter 148, a portion of which may be refluxed back to the drying column 130 before being returned to the reactor 104. Other embodiments include directing acetic acid to a heavies column (see WO0216297), and/or contacting the product purification section of the process with one or more absorbents, adsorbents, or ion exchange resins in a resin bed or guard 200 to remove various impurities (see US6657078), and the like, as described more fully herein. As shown, the drying column 130 separates the acetic acid sidedraw 128 into a predominately aqueous overhead stream and a predominately acetic acid bottoms stream. The overhead stream is cooled and condensed in a phase separation unit, such as decanter 148, to form a light phase and a heavy phase. As shown, a portion of the light phase is refluxed and the remainder of the light phase is returned to the reactor. The heavy phase, which is typically an emulsion comprising water and methyl iodide, is preferably returned to the reactor in its entirety. Table 3 below provides an exemplary composition of the light phase of the top of the drying column.

In particular embodiments, a small amount of a basic component, such as KOH, may be added to the sidedraw 128 prior to entering the drying column 130. In other embodiments, the alkaline component may also be added to the drying column 130 at the same elevation as the stream 128 entering the drying column 130 or at an elevation above the elevation level of the stream 128 entering the drying column 130. Such addition may neutralize the HI in the column.

In particular embodiments, the drying column bottoms stream may comprise or consist essentially of acetic acid. In particular embodiments, the drying column bottoms stream comprises acetic acid in an amount greater than 90 wt%, such as greater than 95 wt% or greater than 98 wt%. In particular embodiments, such a stream will also be substantially anhydrous, e.g., containing less than 0.15 wt% water, e.g., less than 0.12 wt% water or less than 0.1 wt% water. However, as discussed, the stream may contain different levels of impurities.

In fig. 1, the crude acid product is withdrawn as a residue in the drying column bottoms stream 146. In particular embodiments, the crude acid product from the drying column 130 can be taken from the side stream at a point slightly above the bottom of the column 130. Such side streams may be withdrawn in the liquid or gas phase. When withdrawn in the gas phase, further condensation and cooling may be required before removing basic contaminants such as lithium contaminants. For example, the crude acid product may be taken as a side stream from the lower portion of the column, while the residue stream from the bottom of the drying column 130 is withdrawn and removed or recycled. This side stream contains the crude acetic acid product, which is sent to a cation exchange resin to remove lithium. This may allow the separation of the high boiling fraction from the crude acid product in the residual stream. In particular embodiments, the residue stream from process 100 is discarded or washed.

In particular embodiments, the crude acid product produced by drying column 130 is further processed by subjecting it to a series of metal-functionalized iodide removing ion exchange resins prior to storage or shipment for commercial use. In particular embodiments, the process for producing acetic acid further comprises introducing a lithium compound into the reactor to maintain the lithium acetate concentration in the reaction medium in an amount of from 0.3 to 0.7 wt.%. In a specific embodiment, an amount of lithium compound is introduced into the reactor to maintain the hydrogen iodide concentration in the reaction medium in an amount of from 0.1 to 1.3 wt.%. In a specific embodiment, the concentration of rhodium catalyst in the reaction medium is maintained at 300-3000wppm, the concentration of water in the reaction medium is maintained at an amount of from 0.1 to 4.1 wt.%, and the concentration of methyl acetate in the reaction medium is maintained at from 0.6 to 4.1 wt.%, based on the total weight of the reaction medium present in the carbonylation reactor.

In particular embodiments, the lithium compound introduced into the reactor is selected from the group consisting of lithium acetate, lithium carboxylate, lithium carbonate, lithium hydroxide, other organic lithium salts, and mixtures thereof. In particular embodiments, the lithium compound is soluble in the reaction medium. In one embodiment, lithium acetate dihydrate may be used as the source of the lithium compound.

Lithium acetate reacts with hydrogen iodide according to the following equilibrium reaction (I) to form lithium iodide and acetic acid:

lithium acetate is believed to provide improved control over the concentration of hydrogen iodide present in the reaction medium relative to other acetates, such as methyl acetate. Without being bound by theory, lithium acetate is the conjugate base of acetic acid and is therefore reactive to hydrogen iodide (via an acid-base reaction). This property is believed to result in an equilibrium in reaction (I) that favors the reaction product over and above that produced by the corresponding equilibrium of methyl acetate and hydrogen iodide. This improved equilibrium is promoted by a water concentration in the reaction medium of less than 4.1% by weight. In addition, the relatively low volatility of lithium acetate compared to methyl acetate allows the lithium acetate to remain in the reaction medium, except for volatility losses and small amounts of entrainment into the vapor crude product. In contrast, the relatively high volatility of methyl acetate allows the material to be distilled into a purification line, which makes methyl acetate more difficult to control. At low concentrations consistent with hydrogen iodide, lithium acetate is significantly easier to maintain and control in the process. Thus, a relatively smaller amount of lithium acetate may be used relative to the amount of methyl acetate required to control the concentration of hydrogen iodide in the reaction medium. It has further been found that lithium acetate is at least three times more effective than methyl acetate in promoting the oxidative addition of methyl iodide to the rhodium [ I ] complex.

In particular embodiments, the lithium acetate concentration in the reaction medium is maintained at greater than or equal to 0.3 wt%, or greater than or equal to 0.35 wt%, or greater than or equal to 0.4 wt%, or greater than or equal to 0.45 wt%, or greater than or equal to 0.5 wt%, and/or in particular embodiments, the lithium acetate concentration in the reaction medium is maintained at less than or equal to 0.7 wt%, or less than or equal to 0.65 wt%, or less than or equal to 0.6 wt%, or less than or equal to 0.55 wt%, as determined by titration to the potential endpoint according to perchloric acid.

It has been found that an excess of lithium acetate in the reaction medium can adversely affect other compounds in the reaction medium, which leads to a reduction in yield. In contrast, it has been found that a lithium acetate concentration in the reaction medium of less than about 0.3 wt.% results in a lack of control over the concentration of hydrogen iodide in the reaction medium.

In particular embodiments, the lithium compound may be introduced into the reaction medium continuously or intermittently. In particular embodiments, the lithium compound is introduced during reactor start-up. In particular embodiments, the lithium compound is introduced intermittently to replace entrainment losses.

A series of experiments were carried out to confirm the promotion of lithium acetate in the carbonylation reactor and to determine the oxidative addition of lithium acetate to the rhodium complex Li [ RhI ] for methyl iodide₂(CO)₂]The above effects confirm that lithium acetate is responsible for the reaction rateThe promotion of (1). A linear increase in the reaction rate was observed to correlate with an increase in lithium acetate concentration. This relationship is iodomethane and Li [ RhI ]₂(CO)₂]An indication of the first order promotion effect of the reaction between. These experiments further show a non-zero intercept confirming that lithium acetate is not required for the MeI-rh (i) reaction to take place, but that lithium acetate does produce a considerable promoting effect even at low concentrations.

In particular embodiments, the process may further comprise maintaining a butyl acetate concentration in the acetic acid product of 10wppm or less without directly removing butyl acetate from the product acetic acid. In particular embodiments, the butyl acetate concentration in the final acetic acid product may be maintained below 10ppm by removing acetaldehyde from the reaction medium, for example from a stream derived from the reaction medium, and/or by controlling the reaction temperature, and/or the hydrogen partial pressure, and/or the metal catalyst concentration in the reaction medium. In particular embodiments, the butyl acetate concentration in the final acetic acid product is maintained by controlling one or more of the following: the carbonylation reaction temperature is from 150 ℃ to 250 ℃, the hydrogen partial pressure of the carbonylation reactor is from 0.3atm to 2atm, the rhodium metal catalyst concentration in the reaction medium is from 100-3000wppm based on the total weight of the reaction medium, and/or the acetaldehyde concentration in the reaction medium is 1500ppm or less.

In particular embodiments, the butyl acetate concentration of the acetic acid product formed according to particular embodiments of the processes disclosed herein is less than or equal to 10wppm, or less than or equal to 9wppm, or less than or equal to 8wppm, or less than or equal to 6wppm, or less than or equal to 2wppm, based on the total weight of the acetic acid product. In particular embodiments, the acetic acid product is substantially free of butyl acetate, i.e., the butyl acetate concentration is less than 0.05wppm or undetectable by measurement means known in the art. In particular embodiments, the propionic acid concentration of the acetic acid product may also be less than 250wppm, alternatively less than 225ppm, alternatively less than 200 wppm.

In particular embodiments, the butyl acetate concentration in the acetic acid product may be controlled by controlling the acetaldehyde concentration in the reaction medium. Without wishing to be bound by theory, butyl acetate is believed to be a by-product of the aldol condensation of acetaldehyde. Applicants have found that by maintaining the acetaldehyde concentration in the reaction medium at less than 1500wppm, the butyl acetate concentration in the final acetic acid product can be controlled to less than 10 wppm. In particular embodiments, the acetaldehyde concentration in the reaction medium is maintained at less than or equal to 1500wppm, or less than or equal to 900wppm, or less than or equal to 500wppm, or less than or equal to 400wppm, based on the total weight of the reaction medium.

In particular embodiments, the butyl acetate concentration in the acetic acid product may be controlled as follows: controlling the reaction temperature of the carbonylation reactor at a temperature greater than or equal to 150 ℃, or 180 ℃, and less than or equal to 250 ℃, or 225 ℃; and/or the hydrogen partial pressure in the carbonylation reactor may be controlled to be greater than or equal to 0.3atm, or 0.35atm, or 0.4atm, or 0.5atm, and less than or equal to 2atm, or 1.5atm, or 1 atm.

While relatively high hydrogen partial pressures result in improved reaction rates, selectivities, improved catalyst activities, and reduced temperatures, applicants have found that as hydrogen partial pressures increase, the production of impurities, including butyl acetate, also increases.

In particular embodiments, the hydrogen partial pressure may be controlled as follows: the amount of hydrogen present in the carbon monoxide source is varied and/or the vent flow to the reactor is increased or decreased to achieve the desired hydrogen partial pressure within the carbonylation reactor.

A series of experiments were conducted to demonstrate the effect of hydrogen partial pressure and acetaldehyde concentration in the reaction medium on the concentration of butyl acetate in the final acetic acid product. These experiments demonstrate the correlation between the reduced butyl acetate concentration in the final acetic acid product and the relatively low acetaldehyde concentration in the reaction medium and/or the relatively low hydrogen partial pressure in the carbonylation reactor. Experiments in which the acetaldehyde concentration in the reactor was maintained below 1500ppm and the reactor hydrogen partial pressure was maintained below 0.6atm resulted in butyl acetate levels in the final acetic acid product of less than 10 wppm. Other experiments have shown that acetaldehyde concentrations in the reactor below 1500wppm and reactor hydrogen partial pressure 0.46atm result in butyl acetate concentrations in the final acetic acid product of less than 8 wppm. Similar conditions, where the hydrogen partial pressure is 0.30atm, result in butyl acetate levels below 6wppm, and 0.60atm hydrogen partial pressure results in butyl acetate concentrations below 0.2wppm in the final acetic acid product. However, comparative experiments (where the hydrogen partial pressures were 0.4 and 0.3, respectively, but no aldehyde removal system was present such that the acetaldehyde concentration in the reactor exceeded 1500wppm) resulted in butyl acetate levels of the final acetic acid product of 13wppm and 16wppm, respectively.

Applicants have further discovered that the propionic acid concentration in the final acetic acid product can be affected by the butyl acetate concentration in the acetic acid product. Thus, by controlling the butyl acetate concentration in the final acetic acid product to 10wppm or less, the propionic acid concentration in the final acetic acid product can be controlled to less than 250wppm, alternatively less than 225ppm, alternatively less than 200 wppm. Likewise, by controlling the ethanol content in the reactor feed (which may be present as an impurity in the methanol source), the propionic acid and butyl acetate concentrations in the final acetic acid product may also be controlled. In particular embodiments, the ethanol concentration in the methanol feed to the carbonylation reactor is controlled to be less than or equal to 150 wppm. In particular embodiments, the ethanol concentration in the methanol feed to the reactor, if present, is less than or equal to 100wppm, alternatively 50wppm, alternatively 25 wppm.

Applicants have further found that the formation of ethyl iodide can be affected by a number of variables, including the concentration of acetaldehyde, ethyl acetate, methyl acetate, and methyl iodide in the reaction medium. In addition, it has been found that the ethanol content in the methanol source, the hydrogen partial pressure and the hydrogen content in the carbon monoxide source affect the ethyl iodide concentration in the reaction medium, and thus the propionic acid concentration in the final acetic acid product.

In particular embodiments, the concentration of ethyl iodide in the reaction medium is maintained/controlled to less than or equal to 750wppm, or less than or equal to 650wppm, or less than or equal to 550wppm, or less than or equal to 450wppm, or less than or equal to 350 wppm. In alternative embodiments, the concentration of ethyl iodide in the reaction medium is maintained/controlled at greater than or equal to 1wppm, or 5wppm, or 10wppm, or 20wppm, or 25wppm, and less than or equal to 650wppm, or 550wppm, or 450wppm, or 350 wppm.

In particular embodiments, the propionic acid concentration in the acetic acid product can be further maintained at less than 250wppm by maintaining the ethyl iodide concentration in the reaction medium at less than or equal to 750wppm without removing propionic acid from the acetic acid product.

In particular embodiments, the concentration of ethyl iodide in the reaction medium and the propionic acid in the acetic acid product may be present in a weight ratio of 3: 1 to 1: 2, or 5: 2 to 1: 2, or 2: 1 to 1: 2 is present. In a particular embodiment, the acetaldehyde: the concentration of the iodoethane is kept at a weight ratio of 2: 1 to 20: 1, or 15: 1 to 2: 1, or 9: 1 to 2: 1.

in particular embodiments, the concentration of ethyl iodide in the reaction medium may be maintained by controlling at least one of: hydrogen partial pressure, methyl acetate concentration, methyl iodide concentration, and/or acetaldehyde concentration in the reaction medium.

A series of experiments were conducted to determine the effect of acetaldehyde and other reaction conditions on ethyl formation, which showed a relationship between acetaldehyde concentration and iodoethane concentration in the reaction medium, and a relationship between reactor concentration of iodoethane and propionic acid concentration in the final acetic acid product. Typically, an ethyl iodide concentration of less than 750wppm and an acetaldehyde concentration of less than 1500wppm in the reaction medium results in a propionic acid concentration of less than 250wppm in the acetic acid product.

Iodide removal bed/use of ion exchange resin

In particular embodiments, the product acetic acid stream may be contaminated with halides (e.g., iodides), and the lithium may be contacted with an acid form cation exchange resin under a range of operating conditions, followed by contact with a metal exchanged ion exchange resin having acid cation exchange sites comprising at least one metal selected from the group consisting of silver, mercury, palladium, and rhodium. In a specific embodiment, the ion exchange resin composition is provided in a fixed bed. The use of fixed iodide removal beds for purification of contaminated carboxylic acid streams is well documented in the art (see, e.g., U.S. Pat. Nos. 4615806; 5653853; 5731252; and 6225498, which are incorporated herein by reference in their entirety). Typically, the contaminated liquid carboxylic acid stream is contacted with the aforementioned ion exchange resin composition by flowing through a series of static fixed beds. Lithium contaminants are removed by the cation exchanger in acid form. Halide contaminants, such as iodide contaminants, are subsequently removed by reaction with the metal of the metal-exchanged ion exchange resin to form metal iodides. In some embodiments, a hydrocarbon moiety such as a methyl group (which may be bound to iodide) may esterify the carboxylic acid. For example, in the case of acetic acid contaminated with methyl iodide, methyl acetate may be produced as a byproduct of iodide removal. The formation of such esterification products typically does not adversely affect the treated carboxylic acid stream.

Similar iodide contamination problems can be present in acetic anhydride produced via rhodium iodide catalyst systems. Thus, the process of the present invention may alternatively be used to purify a crude acetic anhydride product stream.

Suitable acid form cation exchangers for use in the present invention for removing metal ion contaminants can comprise strong acid cation exchange resins, such as strong acid macroporous network resins or macroporous resins, such as

15 resin (DOW), Purolite C145, or Purolite CT 145. The resin may also be an acid form strong acid cation exchange mesoporous resin. Chelating resins and zeolites may also be used.

Suitable stable ion exchange resins utilized in connection with the present invention to prepare silver or mercury exchanged resins to remove iodide are typically of the "RSO 3H" type, which are classified as "strong acids", i.e., sulfonic acids, macroporous (macroporous) type cation exchange resins. Particularly suitable ion exchange substrates include

15，

35 and

36 resin (DOW), which is suitable for use at elevated temperatures. Other stable ion exchange substrates such as zeolites may be used as long as the material is stable in the organic medium under the conditions of interest, i.e., does not chemically decompose or release silver or mercury into the organic medium in unacceptable amounts. Zeolite cation exchange substrates are disclosed, for example, in U.S. Pat. No.5962735, the disclosure of which is incorporated herein by reference.

At temperatures greater than about 50 ℃, silver or mercury exchanged cationic substrates may tend to release small amounts of silver or mercury on the order of 500ppb or less, and thus the silver or mercury exchanged substrates are chemically stable under the conditions of interest. More preferably, the amount of silver lost is less than 100ppb into the organic medium and still more preferably less than 20ppb into the organic medium. The amount of silver lost may be somewhat higher at start-up. In any event, if desired, a bed of acid form cationic material can be placed downstream of the silver or mercury exchange material to capture any silver or mercury released, in addition to a bed of acid form cationic material upstream of the silver or mercury exchange material.

The pressure during the step of contacting with the exchange resin is limited only by the physical strength of the resin. In a particular embodiment, the contacting is carried out at a pressure of from 0.1MPa to 1MPa, such as from 0.1MPa to 0.8MPa or from 0.1MPa to 0.5 MPa. However, for convenience, it is preferred that both pressure and temperature be established so that the contaminated carboxylic acid stream is processed as a liquid. Thus, for example, when operating at atmospheric pressure, which is generally preferred on economic grounds, the temperature may vary from 17 ℃ (the freezing point of acetic acid) to 118 ℃ (the boiling point of acetic acid). It is within the ability of those skilled in the art to determine similar ranges for product streams containing other carboxylic acid compounds. The temperature of the contacting step is preferably kept low enough to minimize resin degradation. In a particular embodiment, the contacting is carried out at a temperature of from 25 ℃ to 120 ℃, such as from 25 ℃ to 100 ℃ or from 50 ℃ to 100 ℃. Some cationic macroporous network resins typically begin significant degradation (via an acid-catalyzed aromatic desulfonation mechanism) at a temperature of 150 ℃. Carboxylic acids having up to 5 carbon atoms, for example up to 3 carbon atoms, remain liquid at these temperatures. Therefore, the temperature during the contacting should be kept below the degradation temperature of the resin used. In some specific embodiments, the operating temperature is maintained below the temperature limit of the resin, consistent with liquid phase operation and the desired kinetics of lithium and/or halide removal.

The configuration of the resin bed in the acetic acid purification line may vary, but the cation exchanger should be upstream of the metal exchanged resin. In a preferred embodiment, the resin bed is disposed after the final drying tower. Preferably the resin bed is disposed at a location where the temperature of the crude acid product is low, for example below 120 ℃ or below 100 ℃. The stream contacting the acid form of the cation exchange resin and the stream contacting the metal exchange resin may be adjusted to the same or different temperatures. For example, the stream contacting the cation exchange resin in acid form can be adjusted to a temperature of 25 ℃ to 120 ℃, e.g., 25 ℃ to 85 ℃, 40 ℃ to 70 ℃, e.g., 40 ℃ to 60 ℃, while the fluid contacting the metal exchange resin can be adjusted to a temperature of 50 ℃ to 100 ℃, e.g., 50 ℃ to 85 ℃, 55 ℃ to 75 ℃, or 60 ℃ to 70 ℃. In addition to the advantages described above, lower temperature operation provides less corrosion than higher temperature operation. Lower temperature operation provides less formation of corrosion metal contaminants that, as discussed above, can reduce overall resin life. Also, because lower operating temperatures produce less corrosion, the vessel advantageously need not be made of expensive corrosion resistant metals, and lower metals such as standard stainless steel may be used.

Returning to fig. 1, the drying column bottoms stream is first passed through a cation exchange resin bed 200 to remove lithium ions. Although one cation exchange resin bed 200 is shown, it is understood that multiple cation exchange resin beds may be used in series or in parallel. The cation exchange bed may also remove other cations such as potassium present in the stream if added to the drying column 130 as potassium salts selected from potassium acetate, potassium carbonate and potassium hydroxide and corrosion metals. The resulting exchanged stream, e.g., the intermediate acid product, can then be passed through a bed of metal-exchanged ion exchange resin having acid cation exchange sites comprising at least one metal selected from the group consisting of silver, mercury, palladium, and rhodium to remove iodides from the stream to produce a purified product 146. Although the purification resin is shown via block 200, it should be understood that multiple metal-exchanged ion exchange resin beds may be used in series or in parallel. In addition to the resin beds, a heat exchanger (not shown) may be located before either resin bed to adjust the temperature of streams 146 and 182 to the appropriate temperature prior to contacting the resin beds. Similarly, the crude acetic acid product may be fed to the cation exchange resin bed from a side stream of the drying column. A heat exchanger or condenser may be located before either resin bed to adjust the fluid temperature to the appropriate temperature before contacting the resin bed.

In a specific embodiment, the flow rate through the resin bed is from 0.1 bed volume per hour ("BV/h") to 50BV/h, for example from 1BV/h to 20BV/h or from 6BV/h to 10 BV/h. The bed volume of organic medium is the volume of medium equal to the volume occupied by the resin bed. A flow rate of 1BV/h indicates that a quantity of organic liquid equal to the volume occupied by the resin bed passes through the resin bed in a period of 1 hour.

The purified acetic acid composition is obtained as a result of the resin bed treatment. The purified acetic acid composition in one embodiment comprises less than 100wppb iodides, e.g., less than 90wppb, less than 50wppb, or less than 25 wppb. In a specific embodiment, the purified acetic acid composition comprises less than 100wppb lithium, such as less than 50wppb, less than 20wppb, or less than 10 wppb. In a range aspect, the purified acetic acid composition may comprise from 0 to 100wppb of iodides, for example from 0 to 50 wppb; and/or from 0 to 100wppb of lithium, e.g., from 1 to 50 wppb. In other embodiments, the resin bed removes at least 25 wt% of the iodides from the crude acetic acid product, such as at least 50 wt% or at least 75 wt%. In one embodiment, the resin bed removes at least 25 wt% of the lithium in the crude acetic acid product, for example at least 50 wt% or at least 75 wt%.

Thus, in particular embodiments, the product acetic acid or one or more intermediate recycle streams of the process may be contacted with one or more absorbents, adsorbents, or ion exchange resins (collectively referred to herein as purification resins). Acetic acid is contacted in a resin bed or guard column 200 to remove various impurities to produce the final acetic acid product.

The impurities removed by the purification resin may include alkyl iodides. Specifically, the alkyl iodides contain from 1 to about 20 carbon atoms. Other impurities include various corrosion metals such as chromium, nickel, iron, and the like.

Purification resins suitable for the purposes of this application include macroreticular, strong acid cation exchange resins, at least 1% of their active sites being converted to the silver or mercury form. The amount of silver or mercury associated with the resin may be from 1 to 100% of the active sites of the resin, alternatively from about 25% to about 75%, alternatively at least about 50% of the active sites may be converted to the silver or mercury form (see US4615806, the contents of which are fully incorporated herein by reference). Other suitable examples include US5139981, which relates to the removal of iodide from liquid carboxylic acid contaminated with halide impurities by contacting the liquid halide contaminant acid with a silver (I) -exchanged macroporous reticular resin. Suitable examples of purification resins include amberlyst (R)15 resin (Rohm and Haas), zeolite cation ion exchange substrates (see US596273), and the like. Other suitable purification resins and methods include those disclosed in US5227524, US5801279, US5220058, EP0685445 and US6657078, the contents of which are fully incorporated herein by reference.

In particular embodiments, the acetic acid is contacted with the purification resin at a temperature of at least about 50 ℃, or from about 60 ℃ to about 100 ℃, or at a temperature of greater than or equal to about 150 ℃, depending on the type of purification resin used.

In particular embodiments, the flow rate of acetic acid through the column may be from about 0.5 to about 20 bed volumes per hour (BV/h), where a bed volume is defined as the volume occupied by the resin in the bed. In particular embodiments, the flow rate may be from about 6 to about 10BV/h, or from about 7 to 8 BV/h.

In particular embodiments, the column may contain an anion guard bed comprising pyridine or pyrrolidone resin. The terms "pyridine resin", "polymer containing a pyridine ring", "pyridine polymer", and the like are used herein to denote a polymer containing a substituted or unsubstituted pyridine ring or a substituted or unsubstituted pyridine-containing condensed ring such as a quinoline ring. In particular embodiments, the resin may comprise a high degree of crosslinking, i.e., greater than 10 wt%. Substituents include those inert to methanol carbonylation process conditions, such as alkyl and alkoxy groups. Suitable examples of insoluble pyridine ring-containing polymers include those obtained by reacting vinylpyridine with a divinyl monomer or by reacting vinylpyridine with a divinyl monomer-containing vinyl monomer, such as copolymers of 4-vinylpyridine and divinylbenzene, copolymers of 2-vinylpyridine and divinylbenzene, copolymers of styrene, vinylbenzene and divinylbenzene, copolymers of vinylpicoline and divinylbenzene, and copolymers of vinylpyridine, methyl acrylate and ethyl diacrylate (see US5334755, the disclosure of which is incorporated herein by reference).

Suitable "pyrrolidone resins", "pyrrolidone ring containing polymers", pyrrolidone polymers and the like include polymers containing substituted or unsubstituted pyrrolidone rings. Substituents may include those inert to the methanol carbonylation medium such as alkyl or alkoxy groups. Examples of the insoluble pyrrolidone ring-containing polymer include those obtained by reacting vinylpyrrolidone with a vinyl monomer containing a divinyl monomer, such as a copolymer of vinylpyrrolidone and divinylbenzene. Suitable examples of pyrrolidone polymers include those disclosed in US5466874, US5286826, US4786699, US4139688, the disclosures of which are incorporated herein by reference, and those commercially available under the trade name reillex (r) from Reilley Tar and Chemical Corporation of indianapolis, usa.

In particular embodiments, the nitrogen heterocycle-containing polymer may be crosslinked by at least 10% or at least 15% or 20%, and less than 50% or 60% or 75% to provide mechanical strength, where "degree of crosslinking" refers to the content of divinyl monomer or other crosslinking moiety in weight%.

In particular embodiments, suitable pyridine or pyrrolidone insoluble polymers include the free base form, and/or the N oxide form, and/or the quaternized form. In particular embodiments, the insoluble pyridine or pyrrolidone ring containing polymer may be in bead or granular form, or spherical form, and have a particle diameter of from 0.01 to 2mm, alternatively from 0.1 to 1mm, alternatively from 0.25 to 0.7 mm. Commercially available pyridine-containing polymers include Reillex-425(Reilly Tar and Chemical Corporation), KEX-316, KeX-501, and KEX-212(Koei Chemical Co., Ltd., product), among others.

In particular embodiments, product acetic acid is withdrawn from drying column 130 via stream 146 at or near the bottom of the column and is contacted with one or more resins in the column comprising the purified resin. As used herein, a column containing purified resin may be referred to as a purification column, a guard bed assembly or column, or simply a column. These terms are used interchangeably herein. A purification or guard bed assembly is generally indicated at 200 in fig. 1.

In a particular embodiment, as shown in fig. 2, guard bed assembly 200 can comprise one or more treatment devices, such as column 202 and column 204, each comprising inlet ends 206 and 210, respectively, and outlet ends 208 and 212, respectively. The inlet is separated from the outlet by lumens 214 and 216. A quantity of purified

resin

218 and 220 is located in the internal cavity.

Acetic acid 146 (having a first concentration of impurities) from the process is directed through lumens 214 and 216 to contact

purification resins

218 and 220 at a temperature and flow rate sufficient to produce a purified acetic acid stream 222 (where impurities at a second concentration, if any, are present, that is less than the first impurity concentration). Thus, the second concentration of the impurity may be 0 or undetectable.

In particular embodiments, the guard bed assembly may further comprise

heat exchangers

224 and 226 that control the contact temperature of the acetic acid with the purified resin. In a particular embodiment,

columns

202 and 204 are plug flow columns that flow downward from top to bottom under gravity. However, devices that flow against gravity from a bottom inlet end to a top outlet end are also contemplated.

In particular embodiments, the first column 202 can include an outlet end 208 in direct fluid communication with an inlet end 210 of the second column 204. In particular embodiments, the piping between the different units may be arranged such that any one of the multiple columns may be the first treatment unit, and any one of the remaining columns may then be arranged in series. In particular embodiments, multiple columns may be arranged in a parallel configuration.

In particular embodiments, the purified resin 218 of first column 202 may be different from the purified resin 220 of second column 204, and/or the temperature of first column 202 may be different from the temperature of second column 204, and/or the volume of lumen 214 of first column 202 may be different from the volume of lumen 216 of second column 204.

As shown in FIG. 3, in a particular embodiment, the column 400 comprises an inner cavity 402 defined by a plurality of sides 404 radially arranged about a central axis 406. In a particular embodiment, the column 400 comprises an infinite number of sides, i.e., having a circular cross-section. The column 400 further includes an inlet end 408 in fluid communication with and longitudinally spaced from an outlet end 410 through the internal cavity 402. In a particular embodiment, the column 400 further comprises a plurality of sampling ports 412 disposed through at least one side 404. The sampling port may be a solid sampling port, a liquid sampling port, or a combination thereof.

As shown in fig. 4, in a particular embodiment, each sampling port 412 comprises a first open flow path 414 between a sample inlet 416 located in the lumen 402 and a first flow control member 418 operable between an open position (as shown in flow control member 420, such as a ball of a ball valve) and a closed position (as shown in flow control member 418) located outside the lumen 402 in an external environment 422. The term "open flow path" refers to a flow path that is sized and arranged so that both liquid and solid matter pass therethrough. Thus, the relative size of the open flow path must be determined relative to the average particle size of the solid or semi-solid material to be passed therethrough.

When the flow control member is in the open position, there is fluid communication between the internal cavity 402 and the external environment 422. In particular embodiments, when the respective

flow control elements

418 and 420 are in the open position, the first flow path 414 and the second flow path 424 are both in fluid communication with the external environment 422. When the flow control member is in the closed position, fluid communication between the inner lumen 402 and the external environment 422 is prevented.

In particular embodiments, the sample port further comprises a second flow path 424 comprising a porous member 426 positioned between the sample inlet 416 and the second flow control member 420, the control member being positioned outside the lumen 402 and operable between an open position and a closed position.

In particular embodiments, the second flow path 424 comprises a portion of the first flow path 414 between the sample inlet 416 and the first flow control element 418. Thus, in particular embodiments, the second flow path may be in a "T-plane" or "Y-plane" direction away from the first flow path such that the sample exiting through the first control element 418 is drawn from the lumen 402 at the same location as the sample exiting through the second flow control element 420.

In particular embodiments, as shown in fig. 3, first flow path 414, second flow path 424, or both further comprise a heat exchanger 428 positioned between sample inlet 416 and external environment 422. In particular embodiments, the heat exchanger 428 may be removably connected to the flow path through a portion of the flow control element, as shown. Thus, heat exchanger 428, also referred to as a "sample cooler," a piece of cooling tubing in a bucket of chilled water, may be used to obtain a sample of lumen 402 when the lumen is at an elevated temperature.

In a particular embodiment, the first flow path 414 is located within a first conduit 430 having a first outlet end 432 equipped with a first valve 434 containing the first flow control member 418. In particular embodiments, the valve may be a ball valve, gate valve, and/or the like. In a specific embodiment, the first valve is a harsh environment ball valve equipped with a seat flush system 436 to prevent particulate matter, such as ion exchange resin located in the internal chamber 402, from obstructing the closing of the valve after a sample is obtained.

In a particular embodiment, the second flow path 424 is at least partially located in a second conduit 438 that is connected to the first conduit 430 at a connection point 440 and has a second outlet end 442 equipped with a second valve 444 that contains a second flow control element 420. In particular embodiments, porous element 426 is located at or proximate to connection point 440, at or proximate to second outlet end 442, or a combination thereof. In particular embodiments, the porous element comprises a screen, porous frit, filter element, or a combination thereof, generally designated 446. In particular embodiments, when a plurality of porous elements are used, the exclusion size of the elements may vary. For example, in particular embodiments, the screen or filter element 446 of the porous element 426 may be a 100 mesh screen at a first position and a 200 mesh screen at a second, downstream position, depending on the relative size of the particulate matter (e.g., purified resin) contained within the internal cavity 402.

In particular embodiments, the first open flow path 414 is sized and arranged such that both the liquid 450 and the solid 448 from the lumen 402 flow from the sample inlet 416 through the first flow control member 418 in an open position and into the external environment 422; and sizing and arranging the second flow path 424 such that the liquid 450 present in the lumen 402 flows from the sample inlet 416, through the porous member 426, through the second flow control member 420 in the open position, and into the external environment 422, while preventing at least a portion of the solid or semi-solid material 448 present in the lumen 402 from flowing through the second flow control member 420.

In a particular embodiment, at least a portion 456 of the first flow path 414 is located in a first conduit 430 that extends into the lumen 402 away from an inner surface 458 of the side 404 through which the sampling port 412 is disposed such that the sample inlet 416 is located in the lumen 402 spaced apart from the side 404.

As shown in fig. 3, in a particular embodiment, the sample inlet 416 is located at the side 404 through which the sampling port 412 is disposed.

In a particular embodiment, the inner lumen 402 has an average inner diameter 452 measured perpendicular to the central axis 406 between the opposing sides 404 that is less than 50% of an average length 454 of the inner lumen 402 measured parallel to the central axis 406 between the inlet end 408 and the outlet end 406. In particular embodiments, first conduit 430 comprises a plurality of sample inlets 416. In a particular embodiment, the plurality of sample inlets of the single first conduit 430 are all coplanar with a plane 460 perpendicular to the central axis 406.

In particular embodiments, sampling ports 412 are longitudinally (along at least a portion of one or more sides parallel to a central axis from inlet end 408 to outlet end 410) arranged at substantially equal intervals 462 along at least a portion of side 404.

In a particular embodiment, the method includes providing a column 400 according to any one or combination of embodiments disclosed herein that includes at least one, and preferably a plurality of sampling ports 412 according to any one or combination of embodiments disclosed herein, wherein the lumen 402 includes an amount of purified resin 448 at least partially filling the lumen 402. A fluid to be purified 464, such as an acetic acid stream and/or an intermediate production stream (having one or more impurities at a first concentration) is then directed through the column and contacts the purification resin 448 from the inlet end 408 through the lumen 402 at a temperature and flow rate sufficient to produce a purified liquid stream 466, such as a purified acetic acid stream and/or an intermediate production stream (having impurities at a second concentration less than the first concentration), and then through the outlet end 410.

In particular embodiments, purification resin 448 comprises a strong acid ion exchange resin in the form of a macroporous network, wherein at least about 1% of the active sites of the resin have been converted to the silver or mercury form; wherein the temperature is at least about 50 ℃, and wherein the silver or mercury exchanged ion exchange resin is effective to remove at least about 90 wt% of the C in the acetic acid stream₁-C₂₀An organic iodide.

In a particular embodiment, the purified resin 448 is present in the interior cavity 402 in a plurality of

bands

468 and 470, a first band 468 is positioned between the inlet end 408 and the second band 470, and a second band 470 is positioned between the first band 468 and the outlet end 410. In a particular embodiment, the purified resin in the first belt 468 is the same as the purified resin in the second belt 470. In an alternative embodiment, the purified resin in the first belt 468 is different from the purified resin in the second belt 470. In a particular embodiment, the purification resin in the first zone 468 is a non-functionalized macroporous network strong acid ion exchange resin, and the purification resin in the second zone 470 comprises a macroporous network strong acid ion exchange resin in which at least about 1% of the active sites of the resin have been converted to the silver or mercury form.

In particular embodiments, methods according to one or more of the particular embodiments disclosed herein further include running the first flow control member 418 from the closed position to the open position for a period of time sufficient to obtain a sample comprising the liquid 450 and the purified resin 448 from the first sampling port and then returning the first flow control member 418 to the closed position, and/or running the second flow control member 420 from the closed position to the open position for a period of time sufficient to obtain a sample comprising the liquid 450 from the first sampling port and then returning the second flow control member 420 to the closed position.

In particular embodiments, the method may further comprise analyzing the one or more samples to determine one or more concentrations of the one or more impurities at the respective sampling ports. In particular embodiments, prior to operating the valve, the method may further comprise connecting a heat exchanger to the outlet of the sampling port to obtain a sample having a reduced temperature relative to the temperature of the lumen. In particular embodiments, the process may further comprise providing a plurality of columns, wherein the outlet end of the first column is in direct fluid communication with the inlet end of the second column.

Operation and monitoring of purification columns

In particular embodiments, the sample obtained from the sample port may comprise a sample of the purified resin present in the column, a liquid sample of the acetic acid stream present in the column, or both. The arrangement of the sampling ports allows samples to be obtained at discrete points across the resin bed.

The sampling port may also be in close proximity to the final purified acetic acid stream produced by the column.

Depending on the type of sample to be analyzed, determination of the level of impurities present in the sample will be necessary. Liquid samples may be analyzed according to Gas Chromatography (GC) analysis, High Pressure Liquid Chromatography (HPLC) analysis, which is understood to include standard phase, reverse phase, ion exclusion, ion pair, size exclusion, ion exchange, and ion chromatography techniques, as will be readily understood by those skilled in the art. Any form of suitable detector may be used. Likewise, the resin sample may be extracted and/or absorbed for use in any of various chromatographic techniques, and/or may be analyzed via wet chemical techniques, atomic absorption analysis, which may include Inductively Coupled Plasma (ICP) analysis, mass spectrometry, ICP-MS, and/or the like. In one embodiment, the resin sample may be analyzed using X-ray fluorescence techniques, as will be readily understood by those skilled in the art.

In particular embodiments, the sample may be analyzed for halogens, or iodides (I) and/or different transition metals of groups 3-12, or typical acetic acid production corrosion metals such as Fe, Cr, and/or Ni, and may also be analyzed for the presence of metals or radicals (which may include silver and/or mercury) that convert the active sites of the resin.

In particular embodiments, the use of a combination of sampling ports and analysis may be used to control column operation, which may include monitoring the ability of the column to remove impurities and the diverted flow around the column before the impurity rejection or removal characteristics of the column are exhausted.

In particular embodiments, the impurity concentration of the sample can be compared to a previously determined impurity concentration value, which indicates whether the purified resin is functioning or exhausted. This information can be combined with the location of the sample port such that the impurity concentration of the sample indicates depletion of the purified resin at the point in the column corresponding to the location of the sample port from which the sample was obtained.

In particular embodiments, the resin is exhausted when acetic acid can only be purified to acceptable levels for a long period of time. In particular embodiments, a purified resin is considered to be "exhausted" when acetic acid that has been contacted with such a resin has an iodide concentration greater than 100ppb by weight, an Fe, Cr, and/or Ni concentration greater than 500ppb by weight, or a combination thereof.

Additionally, in particular embodiments, resin samples containing greater than or equal to about 10 wt% impurities are also considered depleted for purposes herein. However, it is to be understood that these levels merely reflect the current demand for product acetic acid, and that any such levels may be used. Furthermore, the levels used and the impurities analyzed (for determination) may be different from iodide and corrosion metals, depending on the fluid in which the column is placed.

In particular embodiments, an indication of a depleted column, as determined by a final purified acetic acid sample having an impurity profile above an acceptable level, may result in stopping flow through a particular column and/or diverting flow through an appropriate column.

In particular embodiments, the progression of impurities throughout the column may be used to determine the rate at which the column becomes depleted, and thus may be used to predict an estimated lifetime or to control the use of the column in the process. In one embodiment, the determination of the depleted resin proximate the end of the column, but not yet in the final purified acetic acid, can be used to terminate or divert flow around the column for resin replacement and/or resin regeneration.

In particular embodiments, the resin may be regenerated once the flow of acetic acid through the column is stopped. In particular embodiments, regeneration of the spent resin comprises removing at least a portion of the spent resin from the column and refilling at least a portion of the column with active purification resin. In particular embodiments, the reactive resin used to refill at least a portion of the column comprises a previously spent resin that has been regenerated into a reactive purified resin. In particular embodiments, at least a portion of the spent resin is regenerated to an active purified resin in the column, also referred to as in situ regeneration. Regeneration of the resin depends on the type of resin and the impurities to be removed. Regeneration methods may include contacting the resin with a suitable solvent, reagent, and/or the like.

Loading the column with resin

As shown in fig. 5, in a particular embodiment, a method 500 includes providing a column according to any one or combination of embodiments disclosed herein, comprising an internal cavity 502. The method can further include a column comprising one or more sample ports arranged between a column inlet and a column outlet, at least one sample port comprising a liquid sample port, a solid sample port, or both, and opening at least one sample port 505.

The method next includes introducing an amount of purified resin into the lumen sufficient to fill a portion of the lumen 504. In particular embodiments, filling the column comprises opening at least one sample port. In particular embodiments, the sample port may be used to purge the resin, remove vapors from the resin, flush the lumen with an inert gas during loading of the resin, and/or the like.

In particular embodiments, the resin may be placed in the column in either dry or wet form by manually transferring the resin to the top of the column or pumping the slurry into the column. In particular embodiments, the resin may be supplied as a slurry in a container such as a liquid tank, tanker truck or tanker rail car, and pneumatically transferred into the tower. Thus in a particular embodiment, the bottom outlet of the vessel containing the slurry comprising the purified resin is in fluid communication with the internal cavity. Pressure is then applied to the head space of the vessel in an amount sufficient to pneumatically transfer at least a portion of the slurry from the vessel into the internal cavity 506.

In particular embodiments, after the resin is pneumatically transferred to the column by pumping or by compressing the vessel, additional water or other solvent may be added to the vessel and the transfer process repeated to ensure that substantially all of the resin has been transferred. Prior to and/or during resin transfer, in particular embodiments, the column and/or vessel is flushed with nitrogen or another inert gas to remove oxygen 508.

In particular embodiments, the resin may then be back-washed 510 with a cleaning fluid (typically water or another solvent) to remove fines, foreign materials, and produced carryover. The cleaning may last 518 for at least 60 minutes. This backwash can be sent to waste or recycled as appropriate. The purge time may be 1 hour or more, at relatively high flow rates to ensure uniform dispersion of the resin within the column and to prevent pockets (pockets) in the resin. The cleaning fluid may then be removed from the resin as follows: pressure is applied to the top of column 512 using nitrogen or the like and maintained until the gas is blown through the column outlet, indicating that substantially all of the purge fluid has been removed.

The resin can then be back-washed once more with acetic acid 514. In particular embodiments, the acid backwash is performed at a relatively slow rate and the flow rate of acid into the bottom of the column is less than 0.05 or less than 0.04 bed volume/min 516. This backwash may be carried out until all of the vapour present in the column has been replaced by liquid. In particular embodiments, at least some of the vapor is removed through one or more open sample ports. In particular embodiments, only a portion of the lumen is initially filled with resin to allow the resin to swell, which in particular embodiments may be as high as 40% or more when the resin exchanges from water to acetic acid.

Once the resin has been backwashed, the column can be put into use as follows: an acetic acid stream having a first impurity concentration is introduced from the inlet end to the outlet end at a purification temperature and flow rate sufficient to produce a purified acetic acid stream having a second impurity concentration at the outlet end that is less than the first impurity concentration 520.

As will be apparent from the drawings and the text presented above, various embodiments can be conceived:

E1. a method, comprising:

a) providing a processing unit column comprising an internal cavity comprising an active purification resin between a column inlet and a column outlet, the column further comprising one or more sample ports disposed between the column inlet and the column outlet, at least one of the sample ports comprising a liquid sample port, a solid sample port, or both; and

b) an acetic acid stream having a first concentration of impurities is flowed through the column at a temperature and flow rate sufficient to produce a purified acetic acid stream having a second concentration of impurities, if any, at a column outlet that is less than the first concentration.

E2. The method according to embodiment E1, further comprising opening at least one sample port.

E3. The method according to embodiment E1 or E2, wherein the impurities comprise iodine, chromium, nickel, iron, or a combination thereof.

E4. The method according to any of embodiments E1-E3, wherein the purification resin comprises a macroporous network of a strong acid ion exchange resin having at least about 1% active sites in the form of silver or mercury.

E5. The method according to any one of embodiments E1-E4, wherein the temperature is at least about 50 ℃.

E6. The method according to any one of embodiments E1-E5, further comprising obtaining a sample of the purified resin through at least one solid sample port, obtaining a liquid sample of the acetic acid stream present in the column through at least one liquid sample port, or a combination thereof, and determining the concentration of the impurity in at least one sample.

E7. The method according to embodiment E6, wherein the impurity concentration is determined using gas chromatography, high pressure liquid chromatography, atomic absorption, inductively coupled plasma spectroscopy, mass spectrometry, x-ray fluorescence spectroscopy, or a combination thereof.

E8. The method of embodiment E6 or E7, further comprising comparing the impurity concentration of at least one sample to a previously determined impurity concentration value, and determining whether the impurity concentration of the sample is indicative of depletion of the purified resin at a point in the column corresponding to the location of the sample port from which the sample was obtained.

E9. The process according to any one of embodiments E1-E8, further comprising terminating the flow of acetic acid through the column.

E10. The process according to any of embodiments E1-E9, wherein the flow of acetic acid is terminated before substantially all of the active purification resin present in the column is exhausted.

E11. The method according to any of embodiments E1-E10, further comprising providing a second column comprising an internal cavity comprising an active purification resin located between a second column inlet and a second column outlet, and flowing an acetic acid stream having a first concentration of an impurity through the second column at a temperature and flow rate sufficient to produce a purified acetic acid stream having a second concentration of the impurity (if any) at the second column outlet that is less than the first concentration.

E12. The process according to any of embodiments E1-E11, further comprising regenerating at least a portion of the depleted resin and resuming flowing the acetic acid stream through the column to produce a purified acetic acid stream.

E13. The method according to embodiment E12, wherein the regeneration of the depleted resin comprises removing at least a portion of the depleted resin from the column and refilling at least a portion of the column with active purification resin.

E14. The process according to embodiment E12 or E13, wherein the reactive resin used to refill at least a portion of the column comprises a previously spent resin that has been regenerated into a reactive purified resin.

E15. The process according to any of embodiments E12-E14, wherein at least a portion of the depleted resin is regenerated to an active purified resin in a column.

E16. A method, comprising:

a. providing a treatment device tower comprising an inner cavity defined by a plurality of sides arranged radially about a central axis and having an inlet end in fluid communication with an outlet end through the inner cavity and spaced longitudinally;

b. introducing an amount of purified resin into a portion of the lumen sufficient to fill the lumen;

c. flowing an aqueous cleaning fluid through the lumen from the outlet end to the inlet end at a flow rate and for a time period sufficient to clean and/or remove fines from the purified resin; and

d. an acetic acid stream having a first concentration of impurities is flowed through the column at a temperature and flow rate sufficient to produce a purified acetic acid stream having a second concentration of impurities, if any, at less than the first concentration at the column outlet.

E17. The method according to embodiment E16, wherein the column comprises one or more sample ports arranged between the column inlet and the column outlet, the at least one sample port comprises a liquid sample port, a solid sample port, or both, and the method further comprises opening the at least one sample port.

E18. The method according to embodiment E16 or E17, wherein the aqueous cleaning fluid is flowed for at least 60 minutes.

E19. The method according to any of embodiments E16-E18, further comprising introducing an amount and pressure of inert gas into the column inlet sufficient to obtain an inert gas flow through the outlet end after step (c).

E20. The method according to any of embodiments E16-E19, further comprising directing a backwash stream of acetic acid into the outlet end at a flow rate and for a period of time sufficient to remove substantially all of the vapor from the lumen.

E21. The process according to embodiment E20, wherein the flow rate of the acetic acid reflux stream is less than or equal to about 0.05 bed volumes per minute and the time period is less than or equal to about 30 minutes.

E22. The method according to any one of embodiments E16-E21, wherein said introducing the purified resin into the internal cavity comprises providing fluid communication between the internal cavity and a bottom outlet of the vessel comprising a slurry comprising the purified resin; and pressurizing the headspace of the vessel in an amount sufficient to pneumatically transfer at least a portion of the slurry from the vessel into the internal cavity.

E23. The method according to any of embodiments E16-E22, further comprising flushing the lumen, the vessel headspace, or both with an amount of inert gas such that the lumen and/or headspace contains less than 1 wt% oxygen prior to introducing the purified resin into the lumen.

E24. A method according to any of embodiments E16-E23, wherein the impurities comprise iodine, chromium, nickel, iron, or a combination thereof;

wherein the purification resin comprises a strong acid ion exchange resin in the form of a macroporous network having at least about 1% of its active sites in the silver or mercury form;

wherein the temperature is at least about 50 ℃, or a combination thereof.

E25. A method according to any of embodiments E16-E23, wherein the impurities comprise iodine, chromium, nickel, iron, or a combination thereof;

wherein the purification resin comprises a strong acid ion exchange resin in the form of a macroporous network having at least about 1% of its active sites in the silver or mercury form; wherein the temperature is at least about 50 ℃, or a combination thereof.

E26. The process according to any of embodiments E1-E15, wherein there is provided according to any of embodiments E16-E25 a column comprising an internal cavity comprising an active purification resin located between the column inlet and the column outlet.

E27. A process comprising carbonylating at least one selected from the group consisting of methanol, dimethyl ether, and methyl acetate in a reactor in the presence of 0.1 to less than 14 weight percent of water, a rhodium catalyst, methyl iodide, and lithium iodide to form a reaction medium comprising acetic acid;

separating the reaction medium into a liquid recycle stream and a vapor product stream;

separating the vapor product stream in a main purification line in up to 2 distillation columns to produce a crude acid product comprising acetic acid containing lithium cations;

contacting the crude acetic acid product with a cation exchanger in acid form in a first treatment unit to produce an intermediate acid product; and

contacting the intermediate acetic acid product with a metal-exchanged ion exchange resin having acid cation exchange positions in a second treatment unit to produce purified acetic acid, wherein the contacting in the first treatment unit, the second treatment unit, or both is according to any one of embodiments E1-E15.

E28. A process comprising carbonylating at least one selected from the group consisting of methanol, dimethyl ether, and methyl acetate in a reactor in the presence of 0.1 to less than 14 wt% water, a rhodium catalyst, methyl iodide, and lithium iodide to form a reaction medium comprising acetic acid;

contacting the crude acetic acid product with a first purification resin comprising a cation exchanger in acid form in a first treatment unit to produce an intermediate acid product; and

contacting the intermediate acetic acid product in a second treatment unit with a second purification resin comprising a metal-exchanged ion exchange resin having acid cation exchange sites to produce a purified acetic acid stream,

the first processing device, the second processing device, or both each include at least one sampling port disposed through a side of the processing device;

obtaining a sample of the first purified resin, the second purified resin, a liquid sample of the acetic acid stream present in the processing device, or a combination thereof through the respective sample ports; and

the concentration of impurities in at least one sample is determined.

E29. The method of embodiment E27 or E28, further comprising comparing the impurity concentration of at least one sample to a previously determined impurity concentration value and determining whether the impurity concentration of the sample indicates that the purified resin has been depleted at a point in the processing device corresponding to the location of the sample port from which the sample was obtained.

E30. The process according to any of embodiments E27-E29, further comprising terminating the flow of acetic acid through the treatment plant prior to depleting substantially all of the active purification resin present in the treatment plant, regenerating a portion of the depleted resin according to any of embodiments E16-E26, and resuming the flow of the acetic acid stream through the treatment plant to produce a purified acetic acid stream.

E31. The method according to any of embodiments E27-E30, wherein the metal-exchanged ion exchange resin comprises at least 1% silver-occupied strong acid exchange sites.

E32. The process according to any one of embodiments E27-E31, wherein the crude acid product comprises up to 10ppm lithium.

E33. The method according to any one of embodiments E27-E32, wherein separating the vapor product stream comprises:

distilling the vapor product stream in a first distillation column and taking a side draw to yield a distilled acetic acid product; and

distilling the distilled acetic acid product in a second distillation column to produce a crude acid product comprising acetic acid and lithium cations.

E34. The method according to any one of embodiments E27-E33, further comprising the step of: adding a potassium salt selected from the group consisting of potassium acetate, potassium carbonate, and potassium hydroxide to the distilled acetic acid product prior to distilling the distilled acetic acid product in a second distillation column; wherein at least a portion of the potassium is removed by the cation exchanger in acid form.

E35. The process according to any one of embodiments E27-E34, wherein the crude acetic acid product is contacted with a cation exchanger at a temperature of 50 ℃ to 120 ℃.

E36. The process according to any one of embodiments E27-E35, wherein the intermediate acetic acid product is contacted with the metal-exchanged ion exchange resin at a temperature of 50 ℃ to 85 ℃; or a combination thereof.

E37. The method according to any one of embodiments E27-E36, wherein the lithium ion concentration of the intermediate acetic acid product is less than 50 ppb.

E38. The method according to any of embodiments E27-E37, wherein the cation exchanger in acid form comprises a resin of macroporous network, macroporous or mesoporous resin cation exchanged with a strong acid in acid form.

E39. The process according to any one of embodiments E27-E38, further comprising treating the purified acetic acid product with a cation exchange resin to recover any silver, mercury, palladium, or rhodium.

E40. The process according to any one of embodiments E27 to E39, wherein the water concentration in the reaction medium is controlled to be in the range of from 0.1 to 5 wt.%, based on the total amount of reaction medium present.

E41. The process according to any one of embodiments E27 to E40, further comprising introducing a lithium compound selected from the group consisting of lithium acetate, lithium carboxylate, lithium carbonate, lithium hydroxide, and mixtures thereof into the reactor to maintain the concentration of lithium acetate in the reaction medium from 0.3 to 0.7 wt%.

E42. The method according to embodiment E41, further comprising:

maintaining the concentration of hydrogen iodide in the reaction medium at 0.1 to 1.3 wt%;

the rhodium catalyst concentration in the reaction medium was maintained at 300-3000 wppm;

maintaining the water concentration in the reaction medium at 0.1-4.1 wt%;

maintaining the methyl acetate concentration in the reaction medium at 0.6 to 4.1 wt%; or a combination thereof.

E43. The process according to any one of embodiments E27-E42, further comprising controlling the concentration of butyl acetate in the acetic acid product at 10wppm or less without directly removing the butyl acetate in the acetic acid product.

E44. The process according to embodiment E43, wherein the butyl acetate concentration is controlled by maintaining the acetaldehyde concentration in the reaction medium at 1500ppm or less.

E45. The process according to embodiment E43 or E44, wherein the butyl acetate concentration is controlled by controlling the reactor temperature at 150 ℃ and 250 ℃.

E46. The process according to any of embodiments E43 to E45, wherein the butyl acetate concentration is controlled by controlling the hydrogen partial pressure in the reactor between 0.3 and 2 atm.

E47. The process according to any one of embodiments E43-E45, wherein the butyl acetate concentration is controlled by controlling the rhodium catalyst concentration in the reaction medium at 100-3000 wppm.

E48. The process according to any one of embodiments E27-E47, further comprising controlling the concentration of ethyl iodide in the reaction medium at less than or equal to 750 wppm.

E49. The process according to embodiment E48, wherein the propionic acid concentration in the product acetic acid is less than 250wppm without directly removing propionic acid from the product acetic acid.

E50. The process according to embodiment E48 or E49, wherein the ethyl iodide in the reaction medium and the propionic acid in the acetic acid product are in a weight ratio of 3: 1-1: 2 is present;

E51. the process according to any one of embodiments E48-E50, wherein acetaldehyde and iodoethane are present in the reaction medium in a weight ratio of 2: 1-20: 1 is present;

E52. the process according to any one of embodiments E48-E51, wherein the ethanol concentration in the methanol feed to the reactor is less than 150 wppm; or a combination thereof.

E53. The process according to any one of embodiments E48-E52, wherein the concentration of ethyl iodide in the reaction medium is controlled by adjusting at least one of: the hydrogen partial pressure in the carbonylation reactor, the methyl acetate concentration in the reaction medium and the methyl iodide concentration in the reaction medium.

While the embodiments have been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain specific embodiments have been shown and described and that all changes and modifications that come within the spirit of the specific embodiments are desired to be protected. It should be understood that while words such as ideal, perfect, preferred, preferential, preferred, more preferred or exemplary are used in the foregoing description to indicate that the feature may be more desirable or characteristic, it may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims, when words such as "a," "an," "at least one," or "at least a portion" are used, it is not intended that the claims be limited to only one item unless specifically stated to the contrary in the claims. When the language "at least a portion" and/or "a portion" is used, the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

1. A process for producing acetic acid comprising:

carbonylating at least one selected from the group consisting of methanol, dimethyl ether, and methyl acetate in a reactor in the presence of 0.1 to less than 14 wt% water, a rhodium catalyst, methyl iodide, and lithium iodide to form a reaction medium comprising acetic acid;

separating the vapor product stream in a main purification line in up to 2 distillation columns to produce a crude acetic acid product comprising lithium cation-containing acetic acid, wherein the crude acetic acid product comprises up to 10ppm lithium cations;

contacting the crude acetic acid product with a first purification resin comprising a cation exchanger in acid form in a first treatment device to produce an intermediate acetic acid product, wherein the intermediate acetic acid product has a lithium ion concentration of less than 50 ppb; and

contacting the intermediate acetic acid product in a second treatment unit with a second purification resin comprising a metal-exchanged ion exchange resin having acid cation exchange sites to produce a purified acetic acid stream; wherein the first processing device, the second processing device, or both each comprise at least one sampling port disposed through a side of the processing device;

obtaining a sample of the first purified resin, the second purified resin, or both, and a liquid sample of the acetic acid stream present in the processing apparatus through respective sampling ports; and

determining the concentration of impurities in at least one sample,

wherein each sampling port comprises a first open flow path between a sample inlet located in the lumen and a first flow control member located outside the lumen, the first flow control member being operable between an open position and a closed position to obtain a resin sample and optionally a liquid present within the lumen proximate the sample inlet; and a second flow path comprising a porous element located between the sample inlet and a second flow control element located outside the lumen and operable between an open position and a closed position to obtain a sample of only liquid present within the lumen immediately adjacent the sample inlet.

2. The method of claim 1, further comprising comparing the impurity concentration of at least one sample to a previously determined impurity concentration value and determining whether the impurity concentration of the sample indicates that the purified resin has been depleted at a point in the processing device corresponding to the location of the sampling port from which the sample was obtained.

3. The process according to claim 1, further comprising terminating the flow of acetic acid through the treatment device, regenerating at least a portion of the depleted resin, and resuming the flow of acetic acid stream through the treatment device to produce a purified acetic acid stream prior to the depletion of substantially all of the active purification resin present in the treatment device.

4. The process according to claim 1, wherein the metal-exchanged ion exchange resin comprises at least 1% silver occupied strong acid exchange sites.

5. The method of claim 1, wherein separating the vapor product stream comprises:

distilling the distilled acetic acid product in a second distillation column to produce a crude acetic acid product comprising acetic acid and lithium cations.

6. The method according to claim 5, further comprising the step of: adding a potassium salt selected from potassium acetate and potassium carbonate and/or potassium hydroxide to the distilled acetic acid product prior to distilling the distilled acetic acid product in a second distillation column; wherein at least a portion of the potassium is removed by the cation exchanger in acid form.

7. The process according to claim 1, wherein the crude acetic acid product is contacted with the cation exchanger at a temperature of from 50 ℃ to 120 ℃.

8. The process according to claim 1, wherein the intermediate acetic acid product is contacted with the metal-exchanged ion exchange resin at a temperature of from 50 ℃ to 85 ℃.

9. The process according to claim 1, wherein the cation exchanger in acid form comprises a resin of macroporous network, macroporous or mesoporous resin cation exchanged with a strong acid in acid form.

10. The process according to claim 1, further comprising treating the purified acetic acid product with a cation exchange resin to recover any silver, mercury, palladium, or rhodium.

11. The process according to claim 1, wherein the water concentration in the reaction medium is controlled to be from 0.1 to 5% by weight, based on the total amount of reaction medium present.

12. The process according to claim 1, further comprising introducing a lithium compound selected from the group consisting of lithium acetate, lithium carboxylate, lithium carbonate, lithium hydroxide, and mixtures thereof into the reactor to maintain the concentration of lithium acetate in the reaction medium at 0.3 to 0.7 wt%.

13. The process according to claim 1, further comprising introducing lithium acetate into the reactor to maintain the concentration of lithium acetate in the reaction medium at 0.3 to 0.7 wt%.

14. The process of claim 1 further comprising introducing lithium hydroxide into the reactor to maintain the concentration of lithium acetate in the reaction medium at 0.3 to 0.7 weight percent.

15. The process of claim 1 further comprising maintaining the hydrogen iodide concentration in the reaction medium at 0.1 to 1.3 wt.%.

16. The process as set forth in claim 1 further comprising maintaining the rhodium catalyst concentration in the reaction medium at about 300-3000 wppm.

17. The process of claim 1 further comprising maintaining the water concentration in the reaction medium at 0.1 to 4.1 weight percent.

18. The process according to claim 1, further comprising maintaining the methyl acetate concentration in the reaction medium at 0.6 to 4.1 wt.%.

19. The process according to claim 1, further comprising controlling the butyl acetate concentration in the acetic acid product at 10wppm or less without directly removing the butyl acetate from the acetic acid product.

20. The process according to claim 19, wherein the butyl acetate concentration is controlled by maintaining the acetaldehyde concentration in the reaction medium at 1500ppm or less.

21. The process as set forth in claim 19 wherein the butyl acetate concentration is controlled by controlling the reactor temperature at 150 ℃ and 250 ℃.

22. The process according to claim 19, wherein the butyl acetate concentration is controlled by controlling the hydrogen partial pressure in the reactor to 0.3 to 2 atm.

23. The process as set forth in claim 19 wherein the butyl acetate concentration is controlled by controlling the rhodium catalyst concentration in the reaction medium at 100-3000 wppm.

24. The process of claim 1, further comprising controlling the concentration of ethyl iodide in the reaction medium at less than or equal to 750 wppm.

25. The process according to claim 24, wherein the propionic acid concentration in the product acetic acid is less than 250wppm without directly removing propionic acid from the product acetic acid.

26. The process of claim 24 wherein the ethyl iodide and propionic acid in the acetic acid product in the reaction medium are present in a weight ratio of 3: 1-1: 2 is present.

27. The process according to claim 24, wherein acetaldehyde and iodoethane are present in the reaction medium in a weight ratio of 2: 1-20: 1 is present.

28. The process of claim 1, wherein the ethanol concentration in the methanol feed to the reactor is less than 150 wppm.

29. A process according to claim 24 wherein the concentration of ethyl iodide in the reaction medium is controlled by adjusting the partial pressure of hydrogen in the carbonylation reactor.

30. The process of claim 24 wherein the concentration of ethyl iodide in the reaction medium is controlled by adjusting the concentration of methyl acetate in the reaction medium.

31. The process of claim 24 wherein the concentration of ethyl iodide in the reaction medium is controlled by adjusting the concentration of methyl iodide in the reaction medium.