HK1184778A - Process and system for supplying vapor from drying column to light ends column - Google Patents

Description

Method and system for feeding vapor from a drying column to a light ends column

Priority requirement

The present invention claims priority from U.S. application No. 12/857,323 filed on 8/16/2010, the entire contents and disclosure of which are incorporated herein by reference.

Technical Field

The present invention relates to a method of heating a light ends column by directing one or more vapor side streams from a drying column to the light ends column. The invention also relates to carbonylation processes for producing acetic acid in which one or more vapor side streams from a drying column provide the energy required to drive separation in a light ends column.

Background

A widely used and successful commercial process for the synthesis of acetic acid involves the catalytic carbonylation of methanol with carbon monoxide. The catalyst comprises rhodium and/or iridium and a halogen promoter, typically methyl iodide. The reaction is carried out by continuously bubbling carbon monoxide through a liquid reaction medium in which the catalyst is dissolved. The reaction medium comprises acetic acid, methyl acetate, water, methyl iodide and a catalyst. Conventional commercial processes for the carbonylation of methanol include those described in U.S. Pat. nos. 3,769,329, 5,001,259, 5,026,908, and 5,144,068, the entire contents and disclosures of which are incorporated herein by reference. Another conventional methanol carbonylation process includes that described in Jones, J.H. (2002), "The Cativa^TMProcess for the manufacturing of Acetic Acid, "Platinum Metals Review, 44(3):94-105 described Cativa^TMMethods, the entire contents and disclosure of which are incorporated herein by reference.

The crude acetic acid product from the reactor is treated in a purification section to remove impurities and recover acetic acid. These impurities, which may be present in trace amounts, affect the quality of the acetic acid, particularly as the impurities are recycled through the reaction process, which can lead to, among other things, the accumulation of these impurities over time. Conventional purification techniques for removing these impurities include treating the acetic acid product stream with oxidants, ozone, water, methanol, activated-carbon, amines, and the like. This treatment may also be combined with distillation of the crude acetic acid product. Generally, in many chemical processes, such as acetic acid production, distillation columns consume large amounts of energy. The distillation columns may each independently receive the energy required to drive the separation within the column. The present invention provides a new and improved process to advantageously increase the overall efficiency of an acetic acid production process by providing the energy required to drive the separation in a separation system, preferably a light ends column, from another location within the system.

Disclosure of Invention

The present invention relates to advantageously increasing the overall efficiency of an acetic acid production process by providing the energy required to drive the separation in a separation system, preferably a light ends column, from another location within the system. It has now been found that the energy in the drying column can be advantageously controlled and transferred to other parts of the separation system, in particular the light ends column. For example, in a first embodiment, the present invention relates to a carbonylation process for producing acetic acid comprising the steps of: the crude product stream is purified in a light ends column to produce a product stream, which is directed to a drying column to produce a dried product stream and one or more vapor side streams, wherein the one or more vapor side streams provide energy to one or more separation systems.

In a second embodiment, the present invention is directed to a process for heating a light ends column comprising the steps of: reacting carbon monoxide with at least one reactant in a first reactor comprising a reaction medium to produce a crude product stream comprising acetic acid, wherein the at least one reactant is selected from the group consisting of methanol, methyl acetate, methyl formate, dimethyl ether, and mixtures thereof, and wherein the reaction medium comprises water, acetic acid, methyl iodide, methyl acetate, and a catalyst, purifying the crude product stream in a light ends column to produce a product stream, directing the product stream to a drying column to produce a dried product stream and one or more vapor side streams, and directing the one or more vapor side streams to the light ends column, wherein the one or more vapor side streams heat the crude product stream in the light ends column. In some embodiments, the reboiler is not connected to a bottom portion of the light ends column. In some embodiments, the drying column is connected to a reboiler.

In a third embodiment, the present invention relates to a carbonylation process for producing acetic acid comprising the steps of: purifying the crude product stream in a light ends column to remove methyl iodide and methyl acetate and produce a product stream having a lower concentration of methyl iodide and methyl acetate than the crude product stream, and withdrawing the product stream from a side draw of the light ends column, directing the product stream to a drying column to produce a dried product stream and one or more vapor side streams, wherein the one or more vapor side streams from the drying column heat the crude product stream in the light ends column.

In a fourth embodiment, the present invention is directed to a process for heating a light ends column comprising the steps of: the method includes purifying a crude product stream in a light ends column to produce a product stream, directing the purified product stream to a drying column to produce a dried product stream, and transferring heat from the drying column to the light ends column. In some embodiments, the step of transferring heat further comprises withdrawing one or more vapor side streams from the drying column and directing the one or more vapor side streams to the light ends column.

Drawings

The invention will be better understood with reference to the non-limiting drawings, in which

Fig. 1 illustrates an exemplary scheme according to one embodiment of the present invention.

Detailed Description

The present invention generally relates to at least some of the energy requirements for feeding a portion of the separation system in an acetic acid production process from one or more vapor side streams of a drying column. In a preferred embodiment, one or more vapor side streams are directed to the light ends column and the energy required to drive the separation therein is provided. In other words, some embodiments of the invention involve transferring heat, preferably excess heat, from the drying column to drive the separation in the light ends column. In conventional systems, a portion of the energy required to drive the separation in the light ends column is provided by the crude acetic acid product fed to the column. The crude acetic acid product is typically in the vapor phase. For conventional systems, the light ends column may also receive energy from a separate reboiler at the base of the light ends column, in addition to the energy provided from the crude acetic acid product.

The present invention advantageously improves the efficiency of acetic acid production by eliminating the need for a reboiler and using energy in one or more vapor streams from the drying column to drive the separation of the light ends column. In a preferred embodiment, the one or more vapor side streams are obtained from the drying column and more preferably from the base of the drying column. The one or more vapor side streams each can comprise acetic acid and water. Similar to the crude acetic acid product fed to the light ends column, one or more vapor side streams are fed directly to the light ends column.

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated 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 and will be routine to those skilled in the art having the benefit of this disclosure.

The present invention may be appreciated in connection with, for example, the carbonylation of methanol with carbon monoxide in a homogeneous catalytic reaction system comprising a reaction solvent, methanol and/or reactive derivatives thereof, a group VIII catalyst, at least a finite concentration of water, and optionally an iodide salt.

Suitable group VIII catalysts include rhodium and/or iridium catalysts. As is well known in the art, when a rhodium catalyst is used, the rhodium catalyst may be added in any suitable form such that the rhodium is present in the catalyst solution as comprising [ Rh (CO ]₂I₂]-equilibrium mixtures of anions. Optionally, the catalyst may be a rhodium dicarbonyl diiodo anion ionically bound to a suitable resin, for example, polyvinylpyridine. The iodide salt optionally maintained in the reaction mixture of the processes described herein may be in the form of a soluble salt or a phosphonium salt of an alkali or alkaline earth metal or quaternary ammonium. In certain embodiments, the catalyst co-promoter is lithium iodide, lithium acetate, or mixtures thereof. The salt co-promoter may be added as a non-iodide salt that will produce an iodide salt. The iodide catalyst stabilizer may be introduced directly into the reaction system. Alternatively, the iodide salt may be generated in situ because under the operating conditions of the reaction system, a wide range of non-iodide salt precursors will react with methyl iodide to produce the corresponding co-promoter iodide salt stabilizer. For additional details regarding rhodium catalysis and iodide salt generation, see U.S. Pat. nos. 5,001,259; 5,026,908; and 5,144,068, the entire contents of which are incorporated herein by reference.

When an iridium catalyst is used, the iridium catalyst may include any iridium-containing compound that is soluble in the liquid reaction composition. The iridium catalyst may be added to the liquid reaction composition for the carbonylation reaction in any suitable form which is soluble in the liquid reaction composition or convertible to a soluble form. Examples of suitable iridium-containing compounds that may be added to the liquid reaction composition include: IrCl₃，IrI₃，IrBr₃，[Ir(CO)₂I]₂，[Ir(CO)₂Cl]₂，[Ir(CO)₂Br]₂，[Ir(CO)₂I₂]^-H⁺，[Ir(CO)^- ₂Br₂]^-H⁺，[Ir(CO)₂I₄]^-H⁺，[Ir(CH₃)I₃(CO)₂]^-H⁺，Ir₄(CO)₁₂，IrCl₃·3H₂O，IrBr₃·3H₂O, iridium metal, Ir₂O₃Ir (acetylacetonate) (CO)₂Ir (acetylacetonate)₃Iridium acetate, [ Ir ]₃O(OAc)₆(H₂O)₃][OAc]And hexachloroiridic acid [ H ]₂IrCl₆]. Chloride-free iridium complexes such as acetates, oxalates and acetoacetates are generally used as starting materials. The iridium catalyst concentration in the liquid reaction composition may be 100-6000 wppm. The carbonylation of methanol using iridium catalysts is well known and is described in its entirety in U.S. patent nos. 5,942,460; 5,932,764; 5,883,295; 5,877,348, respectively; 5,877,347 and 5,696,284, which are incorporated herein by reference in their entirety.

The halogen co-catalyst/promoter is typically used in combination with the group VIII metal catalyst component. Methyl iodide is preferred as the halogen promoter. Preferably, the concentration of halogen promoter in the liquid reaction composition is from 1 to 50% by weight, preferably from 2 to 30% by weight.

The alkyl halide promoter may be combined with a salt stabilizer/co-promoter compound which may include a salt of a group IA or group IIA metal, or a quaternary ammonium or phosphonium salt. Particularly preferred are iodide salts or acetate salts, for example, lithium iodide or lithium acetate.

Other promoters and co-promoters may be used as part of the catalytic system of the present invention, as described in european patent publication EP0849248, the entire contents of which are incorporated herein by reference. Suitable promoters are selected from ruthenium, osmium, tungsten, rhenium, zinc, cadmium, indium, gallium, mercury, nickel, platinum, vanadium, titanium, copper, aluminum, tin, antimony, and more preferably from ruthenium and osmium. Specific co-promoters are described in U.S. Pat. No. 6,627,770, the entire contents of which are incorporated herein by reference.

The promoter may be present in an effective amount up to the limit of its solubility in the liquid reaction composition and/or any liquid process streams recycled to the carbonylation reactor from the acetic acid recovery stage. When used, the promoter is suitably present in the liquid reaction composition in a molar ratio of promoter to metal catalyst of from 0.5:1 to 15:1, preferably from 2:1 to 10:1, more preferably from 2:1 to 7.5: 1. A suitable promoter concentration is 400-5000 wppm.

In one embodiment, the temperature of the carbonylation reaction in the first reactor 105 is preferably from 150 ℃ to 250 ℃, for example, from 155 ℃ to 235 ℃, or from 160 ℃ to 220 ℃. The pressure of the carbonylation reaction is preferably in the range of from 10 to 200bar, preferably from 10 to 100bar, most preferably from 15 to 50 bar. Acetic acid is typically produced in a liquid phase reaction at a temperature of about 160 ℃ and 220 ℃ and a total pressure of about 20 to about 50 bar.

Fig. 1 shows an exemplary carbonylation system 100 for producing acetic acid according to an embodiment of the present invention. Other carbonylation systems that may be used in embodiments of the present invention include those described in U.S. Pat. nos. 7,223,886, 7,005,541, 6,6657,078, 6,339,171, 5,731,252, 5,144,068, 5,026,908, 5,001,259, 4,994,608, and U.S. publication nos. 2008/0287706, 2008/0293966, 2009/0107833, 2009/0270651, the entire contents and disclosures of which are incorporated herein by reference. The system 100 includes a carbonylation section 101 and a purification section 102. It is to be understood that the carbonylation section 101 shown in figure 1 is exemplary and that other moieties may be used within the scope of the present invention.

Carbonylation section 101 includes carbon monoxide feed stream 103, reactant feed stream 104, reactor 105, flasher 106 and recovery unit 107. Carbon monoxide and at least one reactant are preferably continuously fed to reactor 105 via feed streams 103 and 104, respectively. Reactant feed stream 104 can supply at least one reactant selected from methanol, methyl acetate, methyl formate, dimethyl ether, and/or mixtures thereof to reactor 105. In a preferred embodiment, reactant feed stream 104 may supply methanol and/or methyl acetate. Optionally, reactant feed stream 104 can be connected to one or more vessels (not shown) that store fresh reactants for the carbonylation process. Further, although not shown, there may be a methyl iodide storage vessel and/or a catalyst vessel connected to reactor 105 to supply fresh methyl iodide and catalyst as needed to maintain reaction conditions.

One or more recycle feed streams 108, 108', preferably from the purification section, may be fed to reactor 105. Although two recycle feed streams 108, 108' are shown in fig. 1, there may be multiple streams that are separately fed to reactor 105. As discussed below, the recycle feed stream 108 may comprise components of the reaction medium, as well as residual and/or entrained catalyst and acetic acid.

Optionally, there may be at least one fresh water stream (not shown) that may be fed to reactor 105.

In a preferred embodiment, reactor 105 is a liquid phase carbonylation reactor. Reactor 105 is preferably a stirred vessel or bubble-column type vessel with or without an agitator, wherein the liquid content of the reaction is preferably automatically maintained at a predetermined level, which preferably remains substantially constant during normal operation. Fresh methanol from feed stream 104, carbon monoxide from feed stream 103, and recycle stream 108, along with optional methyl iodide stream, catalyst stream, and/or water stream, are continuously introduced into reactor 105, as needed to maintain a water concentration in the reaction medium of at least 0.1wt.% to 14 wt.%.

In a typical carbonylation process, carbon monoxide is preferably introduced continuously into the carbonylation reactor through a sparger, and desirably below an agitator which may be used to agitate the contents. The gaseous feed is preferably well dispersed throughout the reaction liquid by means of stirring. A gaseous/vapor purge stream 109 is desirably vented from reactor 105 to avoid the build up of gaseous side-products, inerts, and to maintain a set partial pressure of carbon monoxide at a given total reactor pressure. The temperature of the reactor can be controlled and the carbon monoxide feed introduced at a rate sufficient to maintain the total reactor pressure. Gaseous purge stream 109 can be scrubbed with acetic acid and/or methanol in recovery unit 107 to recover low boiling components, such as methyl iodide. The gaseous purge stream 109 may be condensed and fed to a recovery unit 107 which may return low boiling components 110 to the top of the reactor 105. The low boiling components 110 may comprise methyl acetate and/or methyl iodide. The carbon monoxide in the gaseous purge stream 109 can be purged in line 111 or fed to the base of the flasher 106 via line 111' to improve rhodium stability.

Carbonylation product is withdrawn from carbonylation reactor 105 at a rate sufficient to maintain a constant level therein and provided to flasher 106 via stream 112. In flasher 106, the carbonylation product is separated in a flash separation step with or without added heat to obtain a crude product stream 113 comprising acetic acid, and a catalyst recycle stream 114 comprising the catalyst containing solution preferably recycled to the reactor via stream 108. As noted above, the catalyst-containing solution comprises primarily acetic acid, rhodium catalyst, and iodide salt, along with small amounts of methyl acetate, methyl iodide, and water. The crude product stream 113 comprises acetic acid, methyl acetate, methyl iodide, water, alkanes, and permanganate reducing compounds (PRC's). PRC's may include, for example, compounds such as acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethyl butyraldehyde and the like, and the aldol condensation products thereof. The dissolved gases leaving reactor 105 and entering flasher 106 comprise a portion of the carbon monoxide and may also comprise gaseous side-products such as methane, hydrogen, and carbon dioxide, and inerts such as nitrogen and argon, and oxygen. Such dissolved gases exit flash vessel 106 as part of crude product stream 113. Crude product stream 113 from flasher 106 is directed to purification section 102.

In one embodiment, purification section 102 comprises light ends column 120 and drying column 130. In other embodiments, purification section 102 may comprise one or more columns for removal of PRC's, guard beds, blowdown scrubber, and/or heavy ends column. PRC removal columns are described in U.S. patent nos. 6,143,930, 6,339,171, and 7,223,886, and U.S. publication nos. 2005/0197513, 2006/0247466, and 2006/0293537, the entire contents and disclosures of which are incorporated herein by reference. Guard beds are described in U.S. patent nos. 4,615,806, 4,894,477, and 6,225,498, the entire contents and disclosures of which are incorporated herein by reference.

The crude product stream 113 from the carbonylation section 101 is fed to a light ends column 120 to obtain a low boiling overhead vapor stream 121, a product side stream 122, and an optional bottoms stream 123. The temperature at the base of light ends column 120, i.e., the temperature of optional exiting bottoms stream 123, is preferably in the range of 120 ℃ to 170 ℃. In addition, the temperature at the top of the light ends column, i.e., the temperature of the low boiling overhead vapor stream 121, is preferably in the range of 100 ℃ to 145 ℃.

The low boiling overhead vapor stream 121 may comprise methyl iodide, methyl acetate, water, PRC's, acetic acid, alkanes, and dissolved gases. As shown, the low boiling overhead vapor stream 121 is preferably condensed and directed to an overhead phase separation unit, as shown by overhead receiver or decanter 124. It is desirable to maintain such conditions that the low boiling overhead vapor stream 121, once in decanter 124, will separate into a light phase 125 and a heavy phase 126. Non-condensable gases may be removed via vent stream 127 and optionally fed to one or more scrubbers (not shown) to recover any low boiling components.

Light phase 125 preferably comprises water, acetic acid, and PRC's, as well as methyl iodide and methyl acetate. As shown in fig. 1, light phase 125 may be refluxed to light ends column 120. A portion of the light phase 125 can also be separated and treated in one or more columns (not shown) to remove PRC's via line 128. Optionally, a portion of light phase 125 may also be returned to carbonylation section 101 and co-fed with recycle stream 108' to reactor 105. The heavy phase 126 from decanter 124 may be conveniently recycled, either directly or indirectly via recycle stream 108' to reactor 105. For example, a portion of heavy phase 126 and a slip stream (not shown) may be recycled to reactor 105, typically a small amount, e.g., 5-40vol.%, or 5-20vol.% of heavy phase 126 is directed to one or more columns to remove PRC's.

The product side stream 122 from the light ends column may comprise acetic acid and water. In one embodiment, the product side stream 122 can comprise at least 70wt.%, e.g., at least 80wt.% or at least 85wt.% acetic acid, and can comprise less than 15wt.%, e.g., less than 10wt.% or less than 5wt.% water. In terms of ranges, product stream 122 comprises from 0.01wt.% to 20wt.%, from 0.1wt.% to 10wt.%, or from 1wt.% to 5wt.% water. Product side stream 122 is preferably withdrawn from light ends column 120 in the liquid phase and at a temperature of 115 ℃ to 160 ℃, e.g., 125 ℃ to 155 ℃. The product side stream 122 can be fed to a drying column 130 to obtain a dried product stream 131 and an overhead stream 132 comprising primarily separated water. The dried purified product stream 131 preferably comprises acetic acid in an amount greater than 90wt.%, e.g., greater than 95wt.% or greater than 98 wt.%. Optionally, the dried purified product stream 131 can be further processed in one or more guard beds (not shown) and/or a heavy ends column (not shown) to further remove impurities. The overhead stream 132 of the drying column may be condensed and separated in a receiver 133. A portion of the liquid from receiver 133 can be refluxed to drying column 130 via line 134 and another portion can be returned to carbonylation section 101 via line 135. The temperature at the base of the drying column 130, i.e. the temperature of the exiting dried purified product stream 131, is preferably in the range of 130 ℃ to 185 ℃. Further, the temperature at the top of the drying column 130, i.e., the temperature of the overhead stream 132, is preferably in the range of 110 ℃ to 150 ℃.

The external energy introduced to separate the components of the product side stream 122 in the drying column 130 (e.g., heat exchange from a reboiler or direct injection energy) is typically more than that required for the light ends column 120. In one embodiment, the reboiler 136 of the drying column 130 provides substantially the same amount of energy under normal or partial conditions, and thus may result in excess potential energy that can be used as an external source of energy to drive the separation in the light ends column 120. As shown in fig. 1, reboiler 136 may be used to supply the energy requirements of drying column 130. The partially dried purified product stream 131 can be recycled to the drying column 130 through reboiler 136.

Returning to the light ends column 120, because the optional light ends column bottoms stream 123 will typically contain heavies, acetic acid, water, and entrained catalyst, it may be advantageous to recycle all or a portion of the light ends column bottoms stream 123 to the reactor 105 via one or more recycle streams 108. Light ends bottoms stream 123 can be combined with catalyst recycle stream 114 from flasher 106 and returned to reactor 105 together as shown in fig. 1. Optionally, light ends bottoms stream 123 can be fed to the base of flasher 106.

In conventional systems, the energy to drive the separation in the light ends column may be supplied by the heat of the crude product stream and/or the reboiler. Crude product stream 113 exits flasher 106 at a temperature from 115 ℃ to 170 ℃, e.g., from 125 ℃ to 165 ℃ or from 130 ℃ to 160 ℃. In an exemplary embodiment, the energy required to drive the separation in the light ends column is at least 6,000,000BTU/hr, for example, at least 10,000,000BTU/hr, or at least 15,000,000 BTU/hr.

When operating at steady state conditions or in normal operation, the crude product stream 113 typically provides sufficient energy to drive the separation in the light ends column 120. However, outside of normal operating or partial operating conditions, such as in a start-up or reactor shutdown mode, the crude product stream 113 alone may not provide sufficient energy to drive the separation in the light ends column. Under these conditions, a separate reboiler is typically required to supply energy to the light ends column base to drive the separation. Even under normal conditions, additional energy may need to be supplied to the light ends column beyond the capacity of the crude product stream.

During the production of acetic acid, the process is preferably operated continuously under normal steady state conditions. However, the process may be operated under partial conditions (partial conditions) due to start-up, reactor shut-down, reduced reactor rate, trip (trip), or improper distillation train (upset). When operating under these partial conditions and outside of on-stream operation, the energy required to drive the separation in the light ends column requires a source other than the crude product stream 113. Embodiments of the present invention use one or more vapor streams 140 from drying column 130 to advantageously provide the energy to drive the separation in light ends column 120. Preferably, the one or more vapor streams 140 allow the light ends column to operate at normal and partial conditions. More preferably, the one or more vapor streams 140 allow the light ends column to be operated without the need for a special reboiler.

During normal operation, the one or more vapor side streams 140 can provide a small portion of the energy required to drive the separation in the light ends column, i.e., less than 50% of the total required energy. In terms of ranges, the one or more vapor side streams 140 can provide from 1% to 50%, e.g., from 1% to 25%, of the total required energy. The light ends column may use energy from both the crude product stream 113 and the one or more vapor side streams 140. In one embodiment, the one or more vapor side streams 140 may provide energy from the excess potential of the drying column 130 when the energy from the flasher 106 is insufficient to drive the separation in the light ends column 120.

During part of the operation, the one or more vapor side streams 140 can provide a majority of the energy required to drive the separation in the light ends column. Under certain conditions providing little to no crude product stream 113 to the light ends column, the one or more vapor side streams 140 can provide all of the energy required to drive the separation in the light ends column. In a preferred embodiment, under partial conditions, the one or more vapor side streams 140 can provide from 1% to 100%, e.g., from 10% to 85%, of the total energy required to drive the separation in the light ends column. The one or more vapor side streams 140 preferably provide at least 20%, e.g., at least 50% or at least 70% of the total energy required for the light ends column. In some embodiments, for example during reactor shutdown operations, the one or more vapor side streams 140 can provide from 90% to 100% of the total energy required to drive the separation in the light ends column. Further, during a distillation system start-up, the one or more vapor side streams 140 can provide from 1% to 100% of the total energy required to drive the separation in the light ends column. In some embodiments, for example, during initial reactor start-up operations, the one or more vapor side streams 140 can provide 50% to 100% of the energy required to drive the separation in the light ends column. In some embodiments, the one or more vapor side streams 140 can provide from 1% to 50% of the energy required to drive the separation in the light ends column during reactor start-up operations. In other embodiments, the drying column 130 can supply 1-60% of the energy to the light ends column 120 when the reactor feed rate is reduced by 50% or less from normal operating conditions. Providing external energy from drying column 130 during a reactor trip allows the distillation system to be maintained in a stable, robust condition so that the reactor can be restarted and restarted to produce acetic acid product at normal operating rates more quickly.

In one embodiment, the drying column may have excess potential and the one or more vapor side streams 140 may transfer the excess energy and/or potential. Excess energy or potential refers to the energy provided to the drying column from the reboiler that is not used to drive the separation in the drying column and may vary depending on the conditions of the process. In one embodiment, at least 3%, for example, at least 20% or at least 45% of the latent energy from the drying column may be transferred. In a preferred embodiment, one or more vapor streams 140 can transfer the full excess potential from the drying column.

One or more vapor side streams 140 are withdrawn from the lower portion 137 of the drying column 130 and directed to the lower portion 129 of the light ends column 120. Preferably, lower section 137 of the drying column is taken at a location below where purified product stream 122 is fed to drying column 130. In one embodiment, one or more vapor streams are withdrawn from the base portion of the drying column in close proximity to the vapor in which the return feed from reboiler 136 is fed to the drying column. When the one or more vapor side streams 140 are directed to the lower portion 129 of the light ends column 120, the one or more vapor side streams are fed into the light ends column 120 at a location below where the product side stream 122 is withdrawn. In some embodiments, light ends column 120 contains a number of trays (not shown) layered throughout the length of the column. In some embodiments, one or more vapor side streams are fed into the light ends column 120 at a location below the first tray (or first packing portion) of the base. In some embodiments, one or more vapor side streams are fed into the light ends column 120 at a location below the tenth tray from the base. In some embodiments, one or more vapor side streams are fed to the light ends column 120 at a location where stream 122 exits below the light ends column.

The one or more vapor side streams 140 comprise acetic acid and water. In some embodiments, the one or more vapor side streams 140 comprise a major portion of acetic acid and a minor portion of water. In terms of ranges, the one or more vapor side streams 140 comprise 90wt.% to 99.9wt.%, e.g., 95wt.% to 99.95wt.% acetic acid, and 0.01wt.% to 10wt.%, e.g., 0.05wt.% to 1wt.% water. Preferably, the composition of the one or more vapor side streams 140 has a lower water content than the product side stream 122 fed from the light ends column 120 to the drying column 130. The one or more vapor side streams preferably have a temperature of from 130 ℃ to 185 ℃, e.g., from 130 ℃ to 180 ℃, from 150 ℃ to 180 ℃, from 155 ℃ to 180 ℃, or from 160 ℃ to 175 ℃, and can have a pressure of from 2.5atm to 5atm, e.g., from 3atm to 4.5 atm. In one embodiment, it is preferred that the one or more vapor side streams 140 have a temperature that is higher than the crude acetic acid product 113, e.g., at least 5 ℃, 10 ℃, 20 ℃, or 30 ℃ higher. In another embodiment, it is preferred that the one or more vapor side streams 140 have a higher temperature than the product side stream 122.

The acetic acid fed in the one or more vapor streams 140 is preferably separated in the light ends column 120 and returned to the drying column 130 and ultimately withdrawn as a dried purified product stream 131. In a preferred embodiment, when column 130 is not in internal reflux mode, without dried purified product stream 131, the acetic acid directed to the one or more vapor streams is in a lesser amount than the acetic acid vaporized in base region 137 of drying column 130.

In some embodiments, a portion of the light ends bottoms stream 123 can be directed to other portions of the system, depending on the operating conditions of the system. For example, during reactor shutdown operations, a portion of the light ends column bottoms stream 123 can be introduced to the light ends column 120 via return line 141. The return line 141 preferably enters the light ends column 120 at or below the location where the product side stream 122 is withdrawn. In some embodiments, a portion of the side stream 122 can be returned to the light ends column 120. As noted above, the one or more vapor streams 140 have a majority of the acetic acid. Thus, the concentration of acetic acid in the bottoms stream 123 may be expected to increase the amount of acetic acid returned to the reactor 105. Return 141 further introduces a portion of acetic acid rich bottoms stream 123 to light ends column 120 in order to facilitate return of acetic acid to drying column 130.

In conventional processes, a portion of product stream 122 may be distributed and returned to light ends column 120 at a lower tray. This is referred to as the reflux stream to the lower portion of the light ends column 120 and provides scrubbing to the lower portion for removal of entrained catalyst (typically at wppm levels). In addition, the reflux stream provides a working base inventory (working base inventory) in the lower portion 129 of the light ends column 120. In embodiments of the present invention, the use of a portion of stream 123 for this purpose via line 141 can reduce and/or eliminate the need for a reflux stream from product stream 122. Advantageously, embodiments of the present invention may allow a higher net percentage of stream 122 to be sent to drying column 130. Stream 141 can reduce the rectification duty for light ends column 120 by a marginal amount (a marginalamount).

In other embodiments, a portion of the light ends bottoms stream 123 can be directed to the drying column 130 via line 142. Line 142 can be co-fed with side stream 122 or optionally fed separately to drying column 130. For example, during the overall cycle operation of the drying column, the portion of the light ends bottoms stream 123 in line 142 can provide direct recycle to maintain the liquid inventory at the base of the drying column 130.

In some embodiments, the present process further comprises adjusting one or more vapor side streams 140. Modulation of the one or more vapor side streams 140 can be achieved through one or more valves 143. In some embodiments, the one or more valves include a manual check type valve, a flow control type valve, a positive isolation type valve, and combinations thereof. While not being limited by a particular theory, the presence of one or more valves provides the ability to control the light ends column base temperature and/or inhibit cross-contamination/reflux into the drying column. In some embodiments, one or more valves 143 provide the ability to regulate the unidirectional flow of one or more vapor side streams 140 to the lower vapor portion 129 of the light ends column 120. Advantageously, the one or more valves 143 inhibit the reverse flow of any material at the base of the light ends column 120 from entering the drying column 130.

In order that the invention disclosed herein may be more effectively understood, the following non-limiting examples are provided. The following examples describe various embodiments of the process of the present invention.

Examples

Using ASPEN Radfrac^TMA computer model simulating the method illustrated in part 102 of fig. 1 under normal operating conditions. For normal operating conditions, the light ends column receives heat from one or more vapor streams from the drying column without receiving any heat from a specialized reboiler (within Radfrac modeling capability) attached to the base of the light ends column.

Example 1

At the designed production rate for acetic acid production, the reboiler of the drying column provides sufficient energy to the drying column to drive the separation without excessive energy. The energy required to drive the separation in the light ends column is provided by energy from the flasher.

Example 2

When the production rate of example 1 was reduced by half, the energy from the flash vessel provided about 90% of the total energy required to drive the separation in the light ends column. The light ends column requires about an additional 10% of the energy. The drying tower has a relatively excess energy of about 38% available. The one or more vapor side streams transfer a portion of the excess energy from the drying column to the light ends column and provide about 10% of the additional energy needed to drive the separation in the light ends column.

Example 3

When the production rate of example 1 is one-quarter, the energy from the flash provides about 25% of the total energy required to drive the separation in the light ends column. The light ends column requires about an additional 75% of the energy. The drying column has a relative excess of energy available of about 49%, and one or more vapor side streams transfer a portion of the excess energy from the drying column to the light ends column and provide about 75% of the additional energy needed to drive the separation in the light ends column.

Example 4

No energy is provided from the flasher to the light ends column during some conditions when the reactor is tripped and the purification section remains operational. The drying column has a relatively excess energy of about 49% available, and one or more vapor side streams divert a portion of the excess energy from the drying column and provide the energy needed to drive the separation in the light ends column.

Example 5

No energy is provided from the flasher to the light ends column during part of the conditions when the purification section is on-stream prior to reactor on-stream. The drying column has a relatively excess energy of about 49% available, and one or more vapor side streams divert a portion of the excess energy from the drying column to provide the energy needed to drive the separation in the light ends column. The total energy required under these conditions may be less than the energy required under some of the conditions described in example 4. It is expected that changing the reactor operating rate in example 4 will also change the total energy required for the light ends column.

Example 6

During the portion of the conditions when the reactor and purification sections are being driven in, the energy from the flasher provides about 25% of the total energy required to drive the separation in the light ends column. Similar to example 3, the light ends column requires about an additional 75% of the total energy. The drying column has a relatively excess of energy of about 49% available, and one or more vapor side streams divert a portion of the excess energy to provide the energy needed to drive the separation in the light ends column.

Example 7

During the portion of the conditions when the reactor and purification sections continued to transition to the operating rate of example 1, the energy from the flasher provided about 85% of the total energy required to drive the separation in the light ends column. The light ends column requires about an additional 15% of the energy. The drying column has a relatively excess energy of about 49% available, and one or more vapor side streams divert a portion of the excess energy from the drying column to provide the energy needed to drive the separation in the light ends column.

Although the present invention has been described in detail, various modifications within the spirit and scope of the invention will be apparent to those skilled in the art. The disclosures of which are incorporated herein by reference, in light of the foregoing discussion, the knowledge in the art, and the references discussed above in connection with the background and the detailed description of the invention. Furthermore, it is to be understood that various aspects of the invention as well as various portions of the various embodiments and features recited herein and/or in the appended claims may be combined or interchanged either in part or in whole. In the foregoing description of the various embodiments, those embodiments which refer to another embodiment may be combined with other embodiments as appropriate, as will be recognized by those skilled in the art. Furthermore, those skilled in the art will recognize that the foregoing description is by way of example only, and is not intended to limit the present invention.

Claims (23)

1. A carbonylation process for producing acetic acid, said process comprising the steps of:

purifying the crude product stream in a light ends column to produce a product stream; and

directing the product stream to a drying column to produce a dried product stream and one or more vapor side streams;

wherein the one or more vapor side streams provide energy to the one or more separation systems.

2. The method according to claim 1, further comprising directing one or more vapor side streams to the light ends column.

3. The process according to claim 2, wherein the one or more vapor side streams are withdrawn from a lower portion of the drying column.

4. The process according to claim 2, wherein the one or more vapor side streams are fed to a base of the light ends column.

5. The process according to claim 2, wherein the reboiler is not connected to the bottom portion of the light ends column.

6. The process according to claim 1, wherein the one or more vapor side streams heat a crude product stream in the light ends column.

7. The process according to claim 1, wherein the drying column is connected to a reboiler.

8. The process according to claim 1, wherein the one or more vapor side streams comprise acetic acid and water.

9. The process according to claim 8, wherein the one or more vapor side streams comprise acetic acid in an amount from 90wt.% to 99.9 wt.%.

10. The process according to claim 8, wherein the one or more vapor side streams comprise water in an amount from 0.01wt.% to 10 wt.%.

11. The method according to claim 1, wherein the one or more vapor side streams have a temperature from 130 ℃ to 185 ℃.

12. The process according to claim 1, wherein the one or more vapor side streams are fed to a base of the light ends column.

13. The process according to claim 1, wherein the light ends column is operated at a base temperature in the range of from 120 ℃ to 170 ℃.

14. The process according to claim 1, wherein from 1% to 50% of the total amount of energy required to drive the separation in the light ends column is provided by the one or more vapor side streams.

15. The process according to claim 1, wherein 50% to 100% of the total amount of energy required to drive the separation in the light ends column is provided by the one or more vapor side streams.

16. The method of claim 1, further comprising the steps of:

reacting carbon monoxide with at least one reactant in a first reactor comprising a reaction medium to produce a crude product stream comprising acetic acid,

wherein the at least one reactant is selected from the group consisting of methanol, methyl acetate, methyl formate, dimethyl ether and mixtures thereof, and

wherein the reaction medium comprises water, acetic acid, methyl iodide, methyl acetate and a catalyst.

17. A carbonylation process for producing acetic acid, said process comprising the steps of:

purifying the crude product stream in a light ends column to remove methyl iodide and methyl acetate and produce a product stream having a lower concentration of methyl iodide and methyl acetate than the crude product stream;

withdrawing a product stream from a side draw of the light ends column; and

directing the product stream to a drying column to produce a dried product stream and one or more vapor side streams;

wherein one or more vapor side streams from the drying column heat the product stream in the light ends column.

18. The process according to claim 17, wherein the one or more vapor side streams comprise acetic acid and water.

19. The method according to claim 17, wherein the one or more vapor side streams have a temperature from 130 ℃ to 185 ℃.

20. A method of heating a light ends column, the method comprising the steps of:

purifying the crude product stream in a light ends column to produce a product stream;

directing the purified product stream to a drying column to produce a dried product stream; and

transferring heat from the drying column to the light ends column.

21. The method of claim 20, wherein the step of transferring heat further comprises:

withdrawing one or more vapor side streams from the drying column; and

one or more vapor side streams are directed to the light ends column.

22. The process according to claim 20, wherein the one or more vapor side streams comprise acetic acid and water.

23. The method according to claim 20, wherein the one or more vapor side streams have a temperature from 130 ℃ to 185 ℃.