WO2016055466A1 - Method for recovering methyl acetate - Google Patents

Method for recovering methyl acetate Download PDF

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Publication number
WO2016055466A1
WO2016055466A1 PCT/EP2015/073033 EP2015073033W WO2016055466A1 WO 2016055466 A1 WO2016055466 A1 WO 2016055466A1 EP 2015073033 W EP2015073033 W EP 2015073033W WO 2016055466 A1 WO2016055466 A1 WO 2016055466A1
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WO
WIPO (PCT)
Prior art keywords
organic solvent
stream
derivative
sump
purified
Prior art date
Application number
PCT/EP2015/073033
Other languages
French (fr)
Inventor
Christopher Howard Jackson
Antony Peter John Limbach
Anuj Gupta
Iain James Olson ROBERTS
Original Assignee
Invista Technologies S.À R.L.
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Application filed by Invista Technologies S.À R.L. filed Critical Invista Technologies S.À R.L.
Publication of WO2016055466A1 publication Critical patent/WO2016055466A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/009—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping in combination with chemical reactions
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
    • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
    • B01D3/38—Steam distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency

Definitions

  • the present invention relates to a process and apparatus for the production of an aromatic dicarboxylic acid.
  • Aromatic dicarboxylic acids are commonly manufactured by the catalytic oxidation of a hydrocarbon precursor in an organic solvent.
  • An example is terephthalic acid (TA), which is widely used in the manufacture of polyesters, such as poly(ethylene terephthalate) (PET).
  • PET poly(ethylene terephthalate)
  • the TA required as a reactant for PET production is known as "purified terephthalic acid” (PTA) and generally contains over 99.97 wt%, preferably over 99.99 wt%, of terephthalic acid, and less than 25 ppm 4- carboxybenzaldehyde (4-CBA).
  • PTA suitable for use in PET production is generally prepared in a two-stage process. First, p-xylene is oxidized (e.g.
  • CTA "crude terephthalic acid”
  • a metal catalyst e.g. a cobalt and/or manganese salt or compound
  • CTA "crude terephthalic acid”
  • the CTA produced by this oxidation reaction is then purified, as it is typically contaminated by impurities such as 4-CBA, p-toluic acid, and various coloured impurities that impart a yellowish colour to the TA.
  • Purification of the CTA typically requires at least one chemical transformation (e.g. hydrogenation) in addition to at least one physical procedure (e.g. crystallization, washing, etc.) to yield PTA.
  • PTA is generally considered to be a commodity item, with several million tonnes being produced annually, and it is therefore desirable for manufacturers to reduce their costs to maximise the economy and efficiency of PTA production. This can be achieved both by reducing capital costs (e.g. equipment costs) and variable costs (e.g. costs associated with waste disposal, use of starting materials, organic solvent, heating fuel and demineralised water).
  • capital costs e.g. equipment costs
  • variable costs e.g. costs associated with waste disposal, use of starting materials, organic solvent, heating fuel and demineralised water.
  • WO 96/06065 describes the azeotropic distillation of acetic acid from the overhead vapour stream of an oxidation reaction to produce TA.
  • An entrainer such as isobutyl acetate or n-propyl acetate, is used to facilitate the removal of water from the acetic acid.
  • the tops product from the distillation is passed to a separate condenser.
  • the resulting condensate is separated into an organic phase, which is returned to the distillation, and an aqueous phase, from which the entrainer is recovered for recycle to the distillation and methyl acetate is recovered for subsequent processing.
  • the process may be designed to recover organic solvent, use it on scrubbing duties to recover its derivatives from effluent gas streams, and subsequently recycle it to the oxidation reaction to achieve both of the above aims.
  • the present invention provides a method for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent in a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent in an oxidation reactor, comprising the steps of:
  • the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step ii) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i), and, optionally,
  • the present invention further provides an apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising:
  • a stripping device comprising:
  • a sump positioned to receive liquid from the stripping column
  • a condenser positioned to receive an overhead stream from the stripping column; and a first process stream inlet;
  • a substantially vertical internal weir separating a purified organic solvent reservoir from a contaminated organic solvent reservoir; a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir;
  • a purified organic solvent stream outlet for removing a purified organic solvent stream from the purified organic solvent reservoir.
  • the present invention further provides an apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising:
  • a stripping device configured to receive a first process stream and comprising:
  • a condenser positioned to receive an overhead stream from the stripping column, and an oxidation reactor for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent,
  • apparatus further comprises:
  • the stripping column and sump typically form an integrated unit, i.e. they are not discrete units separated by connecting pipework but instead are joined directly to one another.
  • the stripping column, sump and condenser form an integrated unit. These configurations remove the need for any pipework connecting the sump and the stripping column, and the stripping column and the condenser, and thus reduce the capital cost of the manufacturing plant.
  • the method of the invention further comprises the step of feeding a liquid stream comprising the derivative of the organic solvent from the condenser or an upper region of the stripping column to the oxidation reactor. As mentioned above, recovering the derivative of the organic solvent in this way and recycling it to the oxidation reactor contributes to minimising the consumption of organic solvent by its conversion to this derivative.
  • the invention further comprises feeding the purified organic solvent stream to a scrubbing stage to remove the derivative of the organic solvent from a gaseous stream.
  • a purified organic solvent stream (as opposed to an organic solvent stream that has not been purified) on scrubbing duties increases the recovery of the derivative of the organic solvent from the gaseous stream.
  • the purified organic solvent stream is cooled prior to feeding it to the scrubbing stage. This further increases the recovery of the derivative of the organic solvent from the gaseous stream.
  • the present invention further provides a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in an organic solvent, comprising the steps of:
  • mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step III) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II), and, optionally,
  • mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step IV) is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II).
  • Figure 1 is a schematic of a process and apparatus according to the invention.
  • terephthalic acid suitable for use in PET production i.e. purified terephthalic acid
  • a metal catalyst e.g. a cobalt and/or manganese salt or compound
  • the crude terephthalic acid produced by this oxidation reaction is then purified to remove impurities, such as 4-CBA and p-toluic acid, to yield purified terephthalic acid.
  • Purification of crude terephthalic acid typically requires at least one chemical transformation (e.g. hydrogenation) in addition to at least one physical procedure (e.g. crystallization, washing, etc.).
  • the aromatic dicarboxylic acid produced in the present invention may be selected from terephthalic acid, orthophthalic acid and isophthalic acid.
  • the aromatic dicarboxylic acid is preferably terephthalic acid.
  • the hydrocarbon precursor is a compound that may be oxidised to form the aromatic dicarboxylic acid.
  • the hydrocarbon precursor is typically benzene or naphthalene substituted with groups such as Ci-6alkyl, formyl, or acetyl in the positions of the carboxylic acid substituents in the desired end product.
  • Preferred hydrocarbon precursors are Ci-6alkyl-substituted benzene, in particular p-xylene.
  • the organic solvent is typically an aliphatic carboxylic acid, such as acetic acid, or a mixture of such aliphatic carboxylic acid(s) and water.
  • the derivative of the organic solvent is a compound that is formed from the organic solvent as a by-product of the oxidation reaction.
  • the organic solvent is acetic acid
  • the derivative of the organic solvent may be methyl acetate.
  • the oxidation reaction may be carried out under any conditions wherein oxygen is available, e.g. the reaction can be carried out in air.
  • the reaction catalyst typically comprises soluble forms of cobalt and/or manganese (e.g. their acetates), with a source of bromine, such as hydrogen bromide, used as a promoter.
  • the temperature of the oxidation reaction is typically in the range of about 100-250 °C, preferably about 150-220 °C. Any conventional pressure may be used for the reaction, suitably to maintain the reaction mixture in a liquid state.
  • An oxidation stage which typically comprises an oxidation reactor, performs the function of catalytically oxidizing the hydrocarbon precursor in the organic solvent, thus forming a product stream and a vent gas.
  • the product stream is typically transferred to a crystallisation stage, which typically comprises at least a first crystalliser and a second crystalliser, to form a first slurry of crude aromatic dicarboxylic acid crystals and an overhead vapour.
  • the first slurry of crude aromatic dicarboxylic acid crystals is typically passed to a separation stage in which a mother liquor is separated from the crude aromatic dicarboxylic acid crystals, which may then be mixed with an aqueous liquid to form a second slurry of crude aromatic dicarboxylic acid crystals.
  • This second slurry of crude aromatic dicarboxylic acid crystals is typically transferred to a purification plant, heated and subjected to hydrogenation, before being cooled to form a slurry of purified aromatic dicarboxylic acid crystals.
  • the vent gas from the oxidation stage is typically separated in a distillation stage into an organic solvent-rich liquid stream and a water-rich vapour stream.
  • the organic solvent-rich liquid stream from the distillation stage typically comprises 80-95 % w/w organic solvent and is typically returned to the oxidation stage.
  • the water-rich vapour stream from the distillation stage typically comprises 0.1-5.0 % w/w organic solvent and is typically condensed to form a condensate stream and an overhead gas in a condensing stage.
  • a portion of the condensate stream is typically used as a source of the aqueous liquid used to form the second slurry of crude aromatic dicarboxylic acid crystals mentioned above.
  • a portion of the condensate stream also typically forms a source of wash fluid for the purified aromatic dicarboxylic acid crystals from the purification plant.
  • the stripping device comprises a stripping column and sump, which is positioned to collect liquid from the bottom of the stripping column.
  • the stripping column is typically a distillation column comprising at least one theoretical separation stage, which can be provided by trays, such as sieve, valve or bubble cap trays, structured packing or other suitable structures that provide surfaces for mass transfer between gaseous and liquid phases within the column.
  • the sump may comprise a substantially vertical internal weir for separating a purified organic solvent reservoir from a contaminated organic solvent reservoir. Accordingly, when the stripping device is in use, the purified organic solvent reservoir contains purified organic solvent and the contaminated organic solvent reservoir contains contaminated organic solvent.
  • purified organic solvent refers to a body or stream of liquid comprising the organic solvent in which the mass concentration of the derivative of the organic solvent is decreased relative to the mass concentration of the derivative of the organic solvent in the first process stream.
  • at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% by mass of the purified organic solvent stream is the organic solvent and less than 5%, or less than 2%, or less than 1 %, or less than 0.5%, or less than 0.2%, or less than 0.1 % by mass of the purified organic solvent stream is the derivative of the organic solvent.
  • the balance of the purified organic solvent stream is typically water, although minor amounts (e.g. less than 1 % by mass of each) of impurities (e.g.
  • contaminated organic solvent refers to a body or stream of liquid in which the mass concentration of the derivative of the organic solvent is greater than in the purified organic solvent.
  • mass concentration refers to the mass (or mass flow rate) of a given component as a fraction of the mass (or mass flow rate) of a given body (or stream) of liquid.
  • the ratio of the mass concentration of the derivative of the organic solvent in the contaminated organic solvent to the mass concentration of the derivative of the organic solvent in the purified organic solvent may be greater than 1 :1 , or greater than or equal to 2:1 , or greater than or equal to 3:1 , or greater than or equal to 4:1 , or greater than or equal to 5:1 , or greater than or equal to 6:1 , or greater than or equal to about 7:1 , or greater than or equal to about 8:1 , or greater than or equal to about 9:1 , or greater than or equal to about 10:1 and may be less than or equal to about 50:1 , or less than or equal to about 100:1 .
  • substantially vertical means that the weir is oriented such that it is effective in separating two reservoirs of organic solvent that are disposed in the bottom of the sump; it does not require that the weir is perpendicular to the horizontal (e.g. it may be between 70° and 1 10° to the horizontal, or between 80° and 100° to the horizontal, or about 90° to the horizontal).
  • the stripping device may be operated such that purified organic solvent may flow over the weir into the contaminated organic solvent reservoir, such that the contaminated organic solvent reservoir is effectively diluted by addition of the purified organic solvent (i.e. the mass concentration of the derivative of the organic solvent in the contaminated organic solvent reservoir is reduced).
  • the purified organic solvent stream and a contaminated organic solvent stream may be removed from the sump via outlets that are in fluid communication with the purified organic solvent reservoir and the contaminated organic solvent reservoir respectively. Accordingly, the outlet for removing the purified organic solvent stream and the outlet for removing the contaminated organic solvent stream may be located in the lower sections of the purified organic solvent reservoir and the contaminated organic solvent reservoir respectively. These streams may then be used elsewhere in the process.
  • the purified organic solvent stream is typically transferred under high pressure to a scrubbing stage or to the oxidation reactor.
  • the contaminated organic solvent is typically transferred under low pressure to other duties or recycled to a higher position in the stripping device.
  • the stripping column and sump typically form an integrated unit.
  • liquid from the stripping column falls into the sump without passing through any intermediate pipework.
  • the sump may further comprise a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir.
  • the deflector baffle may be positioned above the contaminated organic solvent reservoir and angled such that liquid falling onto the deflector baffle subsequently falls into the purified organic solvent reservoir.
  • the first process stream is typically directed to the stripping column, which separates the derivative of the organic solvent from the organic solvent itself, thus providing an overhead stream in which the mass concentration of the derivative of the organic solvent is increased and a bottoms stream (the purified organic solvent stream) in which the mass concentration of the derivative of the organic solvent is decreased relative to the mass concentration of the derivative of the organic solvent in the first process stream.
  • the first process stream may be directed to the sump at a height above the level of the liquid in the sump, which typically results in partial flashing of the first process stream to generate a vapour that enters the bottom of the stripping column.
  • the stripping device may comprise one or more inlets for receiving one or more process streams.
  • a first condensate stream derived from condensation of an overhead vapour stream from a first crystalliser may be fed to a first condensate stream inlet.
  • the first condensate stream inlet may be positioned in the sump such that liquid derived from the first condensate stream enters the contaminated organic solvent reservoir.
  • a second condensate stream derived from condensation of an overhead vapour stream from a second crystalliser may be fed to a second condensate stream inlet.
  • the second condensate stream inlet may be positioned in the sump such that liquid derived from the second condensate stream enters the contaminated organic solvent reservoir.
  • One or both of the first and second condensate stream inlets may be positioned below the baffle (if present) and above the contaminated organic solvent reservoir.
  • the contaminated organic solvent reservoir may replace a solvent drum for collecting streams of contaminated organic solvent, thus further reducing the capital cost of the process.
  • a contaminated organic solvent stream may be fed from the contaminated organic solvent reservoir to a higher point in the stripping device (i.e. to an inlet in the stripping device) via an external fluid pathway (i.e. the fluid pathway is external to the stripping device).
  • the contaminated organic solvent stream may be fed from the contaminated organic solvent reservoir to the stripping column (i.e. to an inlet in the stripping column).
  • a clean organic solvent stream may be fed to the purified organic solvent reservoir (i.e. to an inlet in or above the purified organic solvent reservoir).
  • the overhead stream from the stripping column is passed to a condenser.
  • the stripping column, sump and condenser preferably form an integrated unit to avoid the need for any intermediate pipework connecting each unit together. Accordingly, vapour from the stripping column rises into the condenser without passing through any intermediate pipework.
  • the condenser may be designed such that condensate from the condenser may fall down to the stripping column.
  • the condenser is typically supplied with a cold water feed to condense at least a portion of the volatile components of the vapour, forming a liquid stream and a vapour stream, which comprise the derivative of the organic solvent that is stripped from the first process stream.
  • the liquid stream may be withdrawn from the condenser or an upper region of the stripping column (e.g. from the top tray of the stripping column) and fed to the oxidation reactor to effect recycling of the derivative of the organic solvent to the oxidation reactor.
  • the liquid stream may be combined with other streams (e.g. one or more bottoms streams from the scrubbing stage) and/or treated on its path to the oxidation reactor.
  • the liquid stream may be fed directly to the oxidation reactor, i.e. it is not subjected to any intermediate treatment to alter its composition on its path to the oxidation reactor.
  • the invention preferably does not employ an entrainer in the stripping device.
  • the invention preferably does not employ isobutyl acetate, n-propyl acetate, or an entrainer with a boiling point intermediate those of isobutyl acetate and n-propyl acetate in the stripping device.
  • the scrubbing stage may remove the derivative of the organic solvent from a gaseous stream.
  • "remove” refers to partial or complete removal of the specified component from the specified stream. Accordingly, 10%, or 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 95%, or 99% by mass of the specified component may be removed from the specified stream. Typically, this is achieved by feeding the gaseous stream to a lower region of a scrubbing device, usually below a scrubbing column within the device but above the level of any liquid in the sump of the scrubbing device, and feeding one or more liquid streams (e.g.
  • an organic solvent stream and a water stream to a higher region of the scrubbing device, usually above the scrubbing column, optionally via an irrigation system.
  • a liquid bottoms stream comprising the derivative of the organic solvent may be recovered from the scrubbing device.
  • one or more bottoms streams, which comprise the derivative of the organic solvent may be transferred from the scrubbing stage to the oxidation reactor to effect recycling of the derivative of the organic solvent to the oxidation reactor.
  • the bottoms stream(s) may be combined with other streams (e.g. the liquid stream from the condenser or an upper region of the stripping column) and/or treated on its path to the oxidation reactor.
  • the bottoms stream(s) may be transferred directly to the oxidation reactor, i.e. it is not subjected to any intermediate treatment to alter its composition on its path to the oxidation reactor.
  • the scrubbing stage may comprise at least one of a pressurised scrubberfor removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream.
  • the pressurised scrubber is typically operated at a pressure of at least 2.5 barA, or at least 5 barA, or at least 7.5 barA, or at least 10 barA, or at least 12.5 barA, typically up to a pressure of 20 barA, or 30 barA, or 40 barA, or 50 barA.
  • the atmospheric scrubber is typically operated at a pressure of about 1 barA, i.e. at about atmospheric pressure.
  • the overhead gas is typically derived from the vent gas from the oxidation stage by passing the vent gas through a distillation stage and a condensing stage to remove water and organic solvent and comprises materials such as unreacted hydrocarbon precursor (e.g. p-xylene) in addition to the derivative of the organic solvent.
  • unreacted hydrocarbon precursor e.g. p-xylene
  • the purified organic solvent stream is cooled prior to feeding it to the scrubbing stage, thus further increasing the recovery of the derivative of the organic solvent from the gaseous stream.
  • This may be achieved by transferring heat (e.g. in a heat exchanger) from the purified organic solvent stream to a bottoms stream transferred from the scrubbing stage, preferably from the pressurised scrubber. This bottoms stream may then be transferred to the oxidation reactor.
  • a control system may be included to re-route this stream back to the stripping device rather than the oxidation reactor if required.
  • the purified organic solvent stream may be further cooled using a cold water feed (e.g. in a heat exchanger) prior to feeding it to the scrubbing stage.
  • the vapour stream from which the derivative of the organic solvent is removed in the atmospheric scrubber may be transferred to the atmospheric scrubber from the condenser (i.e. it may be the vapour stream formed in the condenser).
  • a bottoms stream from the atmospheric scrubber may be transferred to the oxidation reactor.
  • the scrubbed vapour stream from the atmospheric scrubber may be subject to further treatment, for example in a further scrubbing column using water.
  • a contaminated organic solvent stream from the sump of the stripping device may be transferred to a solvent stripping device comprising a still pot and a stripping column in which a vapour stream comprising the organic solvent, water, and the derivative of the organic solvent is separated from residues (e.g. isophthalic acid, orthophthalic acid, p-toluic acid, benzoic acid, 4- carboxybenzaldehyde, bromides (e.g. hydrogen bromide), catalyst components or a mixture of two or more of these components).
  • the contaminated organic solvent stream is typically transferred to the stripping column of the solvent stripping device as a scrubbing fluid.
  • the vapour stream from the solvent stripping device may be transferred to the stripping device.
  • the first process stream may be selected from any one of the streams mentioned above that is directed to the stripping device or may be another stream comprising the organic solvent, water, and the derivative of the organic solvent.
  • the first process stream may be selected from the first condensate stream derived from condensation of an overhead vapour stream from a first crystalliser, the second condensate stream derived from condensation of an overhead vapour stream from a second crystalliser, the contaminated organic solvent stream fed from the contaminated organic solvent reservoir to a higher point in the stripping device via an external fluid pathway, and the vapour stream from the solvent stripping device.
  • FIG. 1 is a schematic of a process and apparatus according to a preferred embodiment of the present invention.
  • Stripping device 10 is made up of sump 20, stripping column 30 and condenser 40, which form an integrated unit.
  • Weir 22 divides a lower region of sump 20 into purified organic solvent reservoir 24 and contaminated organic solvent reservoir 26.
  • Deflector baffle 28 is positioned above contaminated organic solvent reservoir 26 such that liquid falling from stripping column 30 is directed into purified organic solvent reservoir 24.
  • Clean organic solvent (preferably acetic acid) stream 24b is fed via an inlet to purified organic solvent reservoir 24.
  • Purified organic solvent stream 24a is removed via an outlet from purified organic solvent reservoir 24 to high-pressure pump 50, which transfers purified organic solvent stream 50a to heat exchanger 70, in which it is cooled by pressurised scrubber bottoms stream 80a.
  • Purified organic solvent stream 70a is fed to pressurised scrubber 80 to remove the organic solvent derivative (preferably methyl acetate) from overhead gas stream 80b, which is derived from oxidation reactor vent gas stream 100a.
  • Pressurised scrubber vent gas stream 80c is removed for further treatment.
  • Pressurised scrubber bottoms stream 70c is fed to oxidation reactor 100.
  • Purified organic solvent stream 70b is fed to atmospheric scrubber 90 to remove the derivative of the organic solvent from condenser vapour stream 40b.
  • Atmospheric scrubber bottoms stream 90a is fed to oxidation reactor 100. Atmospheric scrubber vent stream 90b is removed for further treatment. Contaminated organic solvent stream 26a is removed via an outlet from contaminated organic solvent reservoir 26 to low-pressure pump 60. Contaminated organic solvent stream 60b is fed to solvent stripping device 110. Vapour stream 1 10a from solvent stripping device 110 is fed to an inlet in sump 20 above deflector baffle 28 and a residue stream (not shown) is removed from solvent stripping device 1 10. Contaminated organic solvent stream 60a is fed to an inlet in stripping column 30. Liquid stream 40a is fed from condenser 40 to oxidation reactor 100.
  • Oxidation reactor product stream 100b is fed to a first crystalliser and a second crystalliser (not shown).
  • First condensate stream 20a and second condensate stream 20b which are derived from condensation of overhead vapour streams from the first crystalliser and the second crystalliser, are fed to inlets in sump 20 positioned such that liquid derived from first condensate stream 20a and second condensate stream 20b enters contaminated organic solvent reservoir 26.

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Abstract

The present invention provides a method for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent in a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent in an oxidation reactor, comprising the steps of: i) feeding the first process stream to a stripping device comprising a stripping column and sump; ii) removing a purified organic solvent stream from the sump; and iii) transferring an overhead stream from the stripping column to a condenser, wherein the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step ii) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i), and, optionally, wherein the mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step iii)is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i). The present invention further provides apparatus for carrying out the method, and a process for the production of an aromatic dicarboxylic acid incorporating the method.

Description

METHOD FOR RECOVERING METHYL ACETATE
TECHNICAL FIELD
The present invention relates to a process and apparatus for the production of an aromatic dicarboxylic acid.
BACKGROUND ART
Aromatic dicarboxylic acids are commonly manufactured by the catalytic oxidation of a hydrocarbon precursor in an organic solvent. An example is terephthalic acid (TA), which is widely used in the manufacture of polyesters, such as poly(ethylene terephthalate) (PET). The TA required as a reactant for PET production is known as "purified terephthalic acid" (PTA) and generally contains over 99.97 wt%, preferably over 99.99 wt%, of terephthalic acid, and less than 25 ppm 4- carboxybenzaldehyde (4-CBA). On the commercial scale, PTA suitable for use in PET production is generally prepared in a two-stage process. First, p-xylene is oxidized (e.g. using air) in the presence of a metal catalyst (e.g. a cobalt and/or manganese salt or compound) to provide "crude terephthalic acid" (CTA), as described in, for example, US 2,833,816. Second, the CTA produced by this oxidation reaction is then purified, as it is typically contaminated by impurities such as 4-CBA, p-toluic acid, and various coloured impurities that impart a yellowish colour to the TA. Purification of the CTA typically requires at least one chemical transformation (e.g. hydrogenation) in addition to at least one physical procedure (e.g. crystallization, washing, etc.) to yield PTA.
PTA is generally considered to be a commodity item, with several million tonnes being produced annually, and it is therefore desirable for manufacturers to reduce their costs to maximise the economy and efficiency of PTA production. This can be achieved both by reducing capital costs (e.g. equipment costs) and variable costs (e.g. costs associated with waste disposal, use of starting materials, organic solvent, heating fuel and demineralised water).
It is therefore desirable to minimise the consumption of organic solvent (e.g. acetic acid) by designing the manufacturing process to recover and recycle the organic solvent. WO 96/06065 describes the azeotropic distillation of acetic acid from the overhead vapour stream of an oxidation reaction to produce TA. An entrainer, such as isobutyl acetate or n-propyl acetate, is used to facilitate the removal of water from the acetic acid. The tops product from the distillation is passed to a separate condenser. The resulting condensate is separated into an organic phase, which is returned to the distillation, and an aqueous phase, from which the entrainer is recovered for recycle to the distillation and methyl acetate is recovered for subsequent processing.
As derivatives of the organic solvent such as methyl acetate accumulate to a steady state level within the oxidation reaction, the consumption of organic solvent by its conversion to these derivatives can be minimised by designing the process to also recover these derivatives and recycle them to the oxidation reaction. Accordingly, the process may be designed to recover organic solvent, use it on scrubbing duties to recover its derivatives from effluent gas streams, and subsequently recycle it to the oxidation reaction to achieve both of the above aims.
It is an object of the present invention to provide a more economic and efficient process and apparatus for the manufacture of aromatic dicarboxylic acids. Further objects will be apparent from the description below. DISCLOSURE OF THE INVENTION
The present invention provides a method for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent in a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent in an oxidation reactor, comprising the steps of:
i) feeding the first process stream to a stripping device comprising a stripping column and sump;
ii) removing a purified organic solvent stream from the sump; and
iii) transferring an overhead stream from the stripping column to a condenser,
wherein the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step ii) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i), and, optionally,
wherein the mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step iii) is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i).
The present invention further provides an apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising:
a stripping device comprising:
a stripping column;
a sump positioned to receive liquid from the stripping column;
a condenser positioned to receive an overhead stream from the stripping column; and a first process stream inlet;
wherein the sump comprises
a substantially vertical internal weir separating a purified organic solvent reservoir from a contaminated organic solvent reservoir; a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir; and
a purified organic solvent stream outlet for removing a purified organic solvent stream from the purified organic solvent reservoir.
The present invention further provides an apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising:
a stripping device configured to receive a first process stream and comprising:
a stripping column;
a sump positioned to receive liquid from the stripping column; and
a condenser positioned to receive an overhead stream from the stripping column, and an oxidation reactor for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent,
wherein the apparatus further comprises:
means for transferring a stream comprising the derivative of the organic solvent from the condenser or an upper region of the stripping column to the oxidation reactor.
The stripping column and sump typically form an integrated unit, i.e. they are not discrete units separated by connecting pipework but instead are joined directly to one another. Preferably, the stripping column, sump and condenser form an integrated unit. These configurations remove the need for any pipework connecting the sump and the stripping column, and the stripping column and the condenser, and thus reduce the capital cost of the manufacturing plant. Preferably, the method of the invention further comprises the step of feeding a liquid stream comprising the derivative of the organic solvent from the condenser or an upper region of the stripping column to the oxidation reactor. As mentioned above, recovering the derivative of the organic solvent in this way and recycling it to the oxidation reactor contributes to minimising the consumption of organic solvent by its conversion to this derivative.
Preferably, the invention further comprises feeding the purified organic solvent stream to a scrubbing stage to remove the derivative of the organic solvent from a gaseous stream. The use of a purified organic solvent stream (as opposed to an organic solvent stream that has not been purified) on scrubbing duties increases the recovery of the derivative of the organic solvent from the gaseous stream. In addition, as the amount of the derivative of the organic solvent in the purified organic solvent stream is reduced, the loss of the derivative of the organic solvent by evaporation of the derivative of the organic solvent from the purified organic solvent stream is reduced. It is further preferred that the purified organic solvent stream is cooled prior to feeding it to the scrubbing stage. This further increases the recovery of the derivative of the organic solvent from the gaseous stream.
The present invention further provides a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in an organic solvent, comprising the steps of:
I) oxidising the hydrocarbon precursor in the organic solvent in the presence of a metal catalyst to provide an aromatic dicarboxylic acid;
wherein the process further comprises the steps of:
II) feeding a first process stream comprising the organic solvent, water, and a derivative of the organic solvent in the process for the production of an aromatic dicarboxylic acid to a stripping device comprising a stripping column and a sump;
III) removing a purified organic solvent stream from the sump; and
IV) transferring an overhead stream from the stripping column to a condenser,
wherein the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step III) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II), and, optionally,
wherein the mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step IV) is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II).
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic of a process and apparatus according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention are described herein. It will be recognised that features specified in each embodiment may be combined with other specified features to provide further embodiments.
It will be appreciated that the general operation of a process and apparatus for the production of an aromatic dicarboxylic acid by the catalytic oxidation of a hydrocarbon precursor in an organic solvent is well known. For example, as discussed above, terephthalic acid suitable for use in PET production (i.e. purified terephthalic acid) is generally prepared in a two-stage process. First, p-xylene is oxidized (e.g. in air) in the presence of a metal catalyst (e.g. a cobalt and/or manganese salt or compound) to provide crude terephthalic acid. Second, the crude terephthalic acid produced by this oxidation reaction is then purified to remove impurities, such as 4-CBA and p-toluic acid, to yield purified terephthalic acid. Purification of crude terephthalic acid typically requires at least one chemical transformation (e.g. hydrogenation) in addition to at least one physical procedure (e.g. crystallization, washing, etc.). Production of an aromatic dicarboxylic acid
The aromatic dicarboxylic acid produced in the present invention may be selected from terephthalic acid, orthophthalic acid and isophthalic acid. The aromatic dicarboxylic acid is preferably terephthalic acid. The hydrocarbon precursor is a compound that may be oxidised to form the aromatic dicarboxylic acid. Thus, the hydrocarbon precursor is typically benzene or naphthalene substituted with groups such as Ci-6alkyl, formyl, or acetyl in the positions of the carboxylic acid substituents in the desired end product. Preferred hydrocarbon precursors are Ci-6alkyl-substituted benzene, in particular p-xylene. The organic solvent is typically an aliphatic carboxylic acid, such as acetic acid, or a mixture of such aliphatic carboxylic acid(s) and water. The derivative of the organic solvent is a compound that is formed from the organic solvent as a by-product of the oxidation reaction. For instance, when the organic solvent is acetic acid, the derivative of the organic solvent may be methyl acetate. The oxidation reaction may be carried out under any conditions wherein oxygen is available, e.g. the reaction can be carried out in air. The reaction catalyst typically comprises soluble forms of cobalt and/or manganese (e.g. their acetates), with a source of bromine, such as hydrogen bromide, used as a promoter. The temperature of the oxidation reaction is typically in the range of about 100-250 °C, preferably about 150-220 °C. Any conventional pressure may be used for the reaction, suitably to maintain the reaction mixture in a liquid state.
An oxidation stage, which typically comprises an oxidation reactor, performs the function of catalytically oxidizing the hydrocarbon precursor in the organic solvent, thus forming a product stream and a vent gas. The product stream is typically transferred to a crystallisation stage, which typically comprises at least a first crystalliser and a second crystalliser, to form a first slurry of crude aromatic dicarboxylic acid crystals and an overhead vapour. The first slurry of crude aromatic dicarboxylic acid crystals is typically passed to a separation stage in which a mother liquor is separated from the crude aromatic dicarboxylic acid crystals, which may then be mixed with an aqueous liquid to form a second slurry of crude aromatic dicarboxylic acid crystals. This second slurry of crude aromatic dicarboxylic acid crystals is typically transferred to a purification plant, heated and subjected to hydrogenation, before being cooled to form a slurry of purified aromatic dicarboxylic acid crystals. The vent gas from the oxidation stage is typically separated in a distillation stage into an organic solvent-rich liquid stream and a water-rich vapour stream. The organic solvent-rich liquid stream from the distillation stage typically comprises 80-95 % w/w organic solvent and is typically returned to the oxidation stage. The water-rich vapour stream from the distillation stage typically comprises 0.1-5.0 % w/w organic solvent and is typically condensed to form a condensate stream and an overhead gas in a condensing stage. A portion of the condensate stream is typically used as a source of the aqueous liquid used to form the second slurry of crude aromatic dicarboxylic acid crystals mentioned above. A portion of the condensate stream also typically forms a source of wash fluid for the purified aromatic dicarboxylic acid crystals from the purification plant.
Stripping device
The stripping device comprises a stripping column and sump, which is positioned to collect liquid from the bottom of the stripping column. The stripping column is typically a distillation column comprising at least one theoretical separation stage, which can be provided by trays, such as sieve, valve or bubble cap trays, structured packing or other suitable structures that provide surfaces for mass transfer between gaseous and liquid phases within the column. The sump may comprise a substantially vertical internal weir for separating a purified organic solvent reservoir from a contaminated organic solvent reservoir. Accordingly, when the stripping device is in use, the purified organic solvent reservoir contains purified organic solvent and the contaminated organic solvent reservoir contains contaminated organic solvent. As used herein, "purified organic solvent" refers to a body or stream of liquid comprising the organic solvent in which the mass concentration of the derivative of the organic solvent is decreased relative to the mass concentration of the derivative of the organic solvent in the first process stream. Typically, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% by mass of the purified organic solvent stream is the organic solvent and less than 5%, or less than 2%, or less than 1 %, or less than 0.5%, or less than 0.2%, or less than 0.1 % by mass of the purified organic solvent stream is the derivative of the organic solvent. The balance of the purified organic solvent stream is typically water, although minor amounts (e.g. less than 1 % by mass of each) of impurities (e.g. organic impurities) may be present. As used herein, "contaminated organic solvent" refers to a body or stream of liquid in which the mass concentration of the derivative of the organic solvent is greater than in the purified organic solvent. As used herein, "mass concentration" refers to the mass (or mass flow rate) of a given component as a fraction of the mass (or mass flow rate) of a given body (or stream) of liquid. In particular, the ratio of the mass concentration of the derivative of the organic solvent in the contaminated organic solvent to the mass concentration of the derivative of the organic solvent in the purified organic solvent may be greater than 1 :1 , or greater than or equal to 2:1 , or greater than or equal to 3:1 , or greater than or equal to 4:1 , or greater than or equal to 5:1 , or greater than or equal to 6:1 , or greater than or equal to about 7:1 , or greater than or equal to about 8:1 , or greater than or equal to about 9:1 , or greater than or equal to about 10:1 and may be less than or equal to about 50:1 , or less than or equal to about 100:1 . As used here, "substantially vertical" means that the weir is oriented such that it is effective in separating two reservoirs of organic solvent that are disposed in the bottom of the sump; it does not require that the weir is perpendicular to the horizontal (e.g. it may be between 70° and 1 10° to the horizontal, or between 80° and 100° to the horizontal, or about 90° to the horizontal). The stripping device may be operated such that purified organic solvent may flow over the weir into the contaminated organic solvent reservoir, such that the contaminated organic solvent reservoir is effectively diluted by addition of the purified organic solvent (i.e. the mass concentration of the derivative of the organic solvent in the contaminated organic solvent reservoir is reduced). The purified organic solvent stream and a contaminated organic solvent stream may be removed from the sump via outlets that are in fluid communication with the purified organic solvent reservoir and the contaminated organic solvent reservoir respectively. Accordingly, the outlet for removing the purified organic solvent stream and the outlet for removing the contaminated organic solvent stream may be located in the lower sections of the purified organic solvent reservoir and the contaminated organic solvent reservoir respectively. These streams may then be used elsewhere in the process. Specifically, the purified organic solvent stream is typically transferred under high pressure to a scrubbing stage or to the oxidation reactor. The contaminated organic solvent is typically transferred under low pressure to other duties or recycled to a higher position in the stripping device.
As mentioned above, the stripping column and sump typically form an integrated unit. Thus, liquid from the stripping column falls into the sump without passing through any intermediate pipework. The sump may further comprise a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir. Thus, the deflector baffle may be positioned above the contaminated organic solvent reservoir and angled such that liquid falling onto the deflector baffle subsequently falls into the purified organic solvent reservoir.
The first process stream is typically directed to the stripping column, which separates the derivative of the organic solvent from the organic solvent itself, thus providing an overhead stream in which the mass concentration of the derivative of the organic solvent is increased and a bottoms stream (the purified organic solvent stream) in which the mass concentration of the derivative of the organic solvent is decreased relative to the mass concentration of the derivative of the organic solvent in the first process stream. However, the first process stream may be directed to the sump at a height above the level of the liquid in the sump, which typically results in partial flashing of the first process stream to generate a vapour that enters the bottom of the stripping column. The stripping device may comprise one or more inlets for receiving one or more process streams. For instance, a first condensate stream derived from condensation of an overhead vapour stream from a first crystalliser may be fed to a first condensate stream inlet. The first condensate stream inlet may be positioned in the sump such that liquid derived from the first condensate stream enters the contaminated organic solvent reservoir. In addition, a second condensate stream derived from condensation of an overhead vapour stream from a second crystalliser may be fed to a second condensate stream inlet. The second condensate stream inlet may be positioned in the sump such that liquid derived from the second condensate stream enters the contaminated organic solvent reservoir. One or both of the first and second condensate stream inlets may be positioned below the baffle (if present) and above the contaminated organic solvent reservoir. Thus, the contaminated organic solvent reservoir may replace a solvent drum for collecting streams of contaminated organic solvent, thus further reducing the capital cost of the process. A contaminated organic solvent stream may be fed from the contaminated organic solvent reservoir to a higher point in the stripping device (i.e. to an inlet in the stripping device) via an external fluid pathway (i.e. the fluid pathway is external to the stripping device). In particular, the contaminated organic solvent stream may be fed from the contaminated organic solvent reservoir to the stripping column (i.e. to an inlet in the stripping column). A clean organic solvent stream may be fed to the purified organic solvent reservoir (i.e. to an inlet in or above the purified organic solvent reservoir).
The overhead stream from the stripping column is passed to a condenser. As mentioned above, the stripping column, sump and condenser preferably form an integrated unit to avoid the need for any intermediate pipework connecting each unit together. Accordingly, vapour from the stripping column rises into the condenser without passing through any intermediate pipework. Similarly, the condenser may be designed such that condensate from the condenser may fall down to the stripping column. The condenser is typically supplied with a cold water feed to condense at least a portion of the volatile components of the vapour, forming a liquid stream and a vapour stream, which comprise the derivative of the organic solvent that is stripped from the first process stream. The liquid stream may be withdrawn from the condenser or an upper region of the stripping column (e.g. from the top tray of the stripping column) and fed to the oxidation reactor to effect recycling of the derivative of the organic solvent to the oxidation reactor. The liquid stream may be combined with other streams (e.g. one or more bottoms streams from the scrubbing stage) and/or treated on its path to the oxidation reactor. Alternatively, the liquid stream may be fed directly to the oxidation reactor, i.e. it is not subjected to any intermediate treatment to alter its composition on its path to the oxidation reactor.
As the primary aim of the invention is to recover a derivative of an organic solvent from the first process stream, rather than separate the water from the organic solvent, the invention preferably does not employ an entrainer in the stripping device. In particular, the invention preferably does not employ isobutyl acetate, n-propyl acetate, or an entrainer with a boiling point intermediate those of isobutyl acetate and n-propyl acetate in the stripping device. Scrubbing stage
The scrubbing stage may remove the derivative of the organic solvent from a gaseous stream. As used herein, "remove" refers to partial or complete removal of the specified component from the specified stream. Accordingly, 10%, or 20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 95%, or 99% by mass of the specified component may be removed from the specified stream. Typically, this is achieved by feeding the gaseous stream to a lower region of a scrubbing device, usually below a scrubbing column within the device but above the level of any liquid in the sump of the scrubbing device, and feeding one or more liquid streams (e.g. an organic solvent stream and a water stream) to a higher region of the scrubbing device, usually above the scrubbing column, optionally via an irrigation system. A liquid bottoms stream comprising the derivative of the organic solvent may be recovered from the scrubbing device. Thus, one or more bottoms streams, which comprise the derivative of the organic solvent, may be transferred from the scrubbing stage to the oxidation reactor to effect recycling of the derivative of the organic solvent to the oxidation reactor. The bottoms stream(s) may be combined with other streams (e.g. the liquid stream from the condenser or an upper region of the stripping column) and/or treated on its path to the oxidation reactor. Alternatively, the bottoms stream(s) may be transferred directly to the oxidation reactor, i.e. it is not subjected to any intermediate treatment to alter its composition on its path to the oxidation reactor.
The scrubbing stage may comprise at least one of a pressurised scrubberfor removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream. The pressurised scrubber is typically operated at a pressure of at least 2.5 barA, or at least 5 barA, or at least 7.5 barA, or at least 10 barA, or at least 12.5 barA, typically up to a pressure of 20 barA, or 30 barA, or 40 barA, or 50 barA. The atmospheric scrubber is typically operated at a pressure of about 1 barA, i.e. at about atmospheric pressure. The overhead gas is typically derived from the vent gas from the oxidation stage by passing the vent gas through a distillation stage and a condensing stage to remove water and organic solvent and comprises materials such as unreacted hydrocarbon precursor (e.g. p-xylene) in addition to the derivative of the organic solvent.
As mentioned above, it is preferred that the purified organic solvent stream is cooled prior to feeding it to the scrubbing stage, thus further increasing the recovery of the derivative of the organic solvent from the gaseous stream. This may be achieved by transferring heat (e.g. in a heat exchanger) from the purified organic solvent stream to a bottoms stream transferred from the scrubbing stage, preferably from the pressurised scrubber. This bottoms stream may then be transferred to the oxidation reactor. A control system may be included to re-route this stream back to the stripping device rather than the oxidation reactor if required. The purified organic solvent stream may be further cooled using a cold water feed (e.g. in a heat exchanger) prior to feeding it to the scrubbing stage. The vapour stream from which the derivative of the organic solvent is removed in the atmospheric scrubber may be transferred to the atmospheric scrubber from the condenser (i.e. it may be the vapour stream formed in the condenser). A bottoms stream from the atmospheric scrubber may be transferred to the oxidation reactor. The scrubbed vapour stream from the atmospheric scrubber may be subject to further treatment, for example in a further scrubbing column using water.
Solvent stripping device
A contaminated organic solvent stream from the sump of the stripping device may be transferred to a solvent stripping device comprising a still pot and a stripping column in which a vapour stream comprising the organic solvent, water, and the derivative of the organic solvent is separated from residues (e.g. isophthalic acid, orthophthalic acid, p-toluic acid, benzoic acid, 4- carboxybenzaldehyde, bromides (e.g. hydrogen bromide), catalyst components or a mixture of two or more of these components). The contaminated organic solvent stream is typically transferred to the stripping column of the solvent stripping device as a scrubbing fluid. The vapour stream from the solvent stripping device may be transferred to the stripping device.
First process stream
The first process stream may be selected from any one of the streams mentioned above that is directed to the stripping device or may be another stream comprising the organic solvent, water, and the derivative of the organic solvent. In particular, the first process stream may be selected from the first condensate stream derived from condensation of an overhead vapour stream from a first crystalliser, the second condensate stream derived from condensation of an overhead vapour stream from a second crystalliser, the contaminated organic solvent stream fed from the contaminated organic solvent reservoir to a higher point in the stripping device via an external fluid pathway, and the vapour stream from the solvent stripping device.
The invention will be further described with reference to the figures.
Figure 1 is a schematic of a process and apparatus according to a preferred embodiment of the present invention. Stripping device 10 is made up of sump 20, stripping column 30 and condenser 40, which form an integrated unit. Weir 22 divides a lower region of sump 20 into purified organic solvent reservoir 24 and contaminated organic solvent reservoir 26. Deflector baffle 28 is positioned above contaminated organic solvent reservoir 26 such that liquid falling from stripping column 30 is directed into purified organic solvent reservoir 24. Clean organic solvent (preferably acetic acid) stream 24b is fed via an inlet to purified organic solvent reservoir 24.
Purified organic solvent stream 24a is removed via an outlet from purified organic solvent reservoir 24 to high-pressure pump 50, which transfers purified organic solvent stream 50a to heat exchanger 70, in which it is cooled by pressurised scrubber bottoms stream 80a. Purified organic solvent stream 70a is fed to pressurised scrubber 80 to remove the organic solvent derivative (preferably methyl acetate) from overhead gas stream 80b, which is derived from oxidation reactor vent gas stream 100a. Pressurised scrubber vent gas stream 80c is removed for further treatment. Pressurised scrubber bottoms stream 70c is fed to oxidation reactor 100. Purified organic solvent stream 70b is fed to atmospheric scrubber 90 to remove the derivative of the organic solvent from condenser vapour stream 40b. Atmospheric scrubber bottoms stream 90a is fed to oxidation reactor 100. Atmospheric scrubber vent stream 90b is removed for further treatment. Contaminated organic solvent stream 26a is removed via an outlet from contaminated organic solvent reservoir 26 to low-pressure pump 60. Contaminated organic solvent stream 60b is fed to solvent stripping device 110. Vapour stream 1 10a from solvent stripping device 110 is fed to an inlet in sump 20 above deflector baffle 28 and a residue stream (not shown) is removed from solvent stripping device 1 10. Contaminated organic solvent stream 60a is fed to an inlet in stripping column 30. Liquid stream 40a is fed from condenser 40 to oxidation reactor 100.
Oxidation reactor product stream 100b is fed to a first crystalliser and a second crystalliser (not shown). First condensate stream 20a and second condensate stream 20b, which are derived from condensation of overhead vapour streams from the first crystalliser and the second crystalliser, are fed to inlets in sump 20 positioned such that liquid derived from first condensate stream 20a and second condensate stream 20b enters contaminated organic solvent reservoir 26.

Claims

A method for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent in a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent in an oxidation reactor, comprising the steps of:
i) feeding the first process stream to a stripping device comprising a stripping column and a sump;
ii) removing a purified organic solvent stream from the sump; and
iii) transferring an overhead stream from the stripping column to a condenser,
wherein the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step ii) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i), and, optionally,
wherein the mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step iii) is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step i).
The method of claim 1 , wherein the aromatic dicarboxylic acid is terephthalic acid.
The method of claim 2, wherein the organic solvent is acetic acid.
The method of claim 3, wherein the derivative of the organic solvent is methyl acetate.
The method of any preceding claim, wherein the stripping column, sump and condenser form an integrated unit.
The method of any preceding claim, further comprising the step of:
iv) feeding a liquid stream comprising the derivative of the organic solvent from the condenser or an upper region of the stripping column to the oxidation reactor.
7. The method of any preceding claim, further comprising the step of:
v) feeding the purified organic solvent stream to a scrubbing stage to remove the derivative of the organic solvent from a gaseous stream. 8. The method of claim 7, wherein the scrubbing stage comprises a pressurised scrubber for removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and/or an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream.
9. The method of claim 7 or claim 8, further comprising the step of:
vi) transferring one or more bottoms streams from the scrubbing stage to the oxidation reactor.
10. The method of any one of claims 7-9, further comprising the step of:
vii) cooling the purified organic solvent stream prior to feeding it to the scrubbing stage. 1 1. The method of claim 10, wherein the scrubbing stage comprises a pressurised scrubber for removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and step vii) comprises transferring heat from the purified organic solvent stream to a bottoms stream transferred from the pressurised scrubber to the oxidation reactor.
12. The method of any one of claims 7-1 1 , wherein the scrubbing stage comprises an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream transferred to the atmospheric scrubber from the condenser. 13. The method of any preceding claim, further comprising the steps of:
viii) feeding a contaminated organic solvent stream from the sump to a solvent stripping device; and
ix) transferring a vapour stream from the solvent stripping device to the stripping device. 14. The method of any preceding claim, wherein the sump comprises a substantially vertical internal weir separating a purified organic solvent reservoir from a contaminated organic solvent reservoir.
15. The method of claim 14, wherein the sump further comprises a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir.
16. The method of claim 14 or claim 15, wherein the ratio of the mass concentration of the derivative of the organic solvent in the contaminated organic solvent to the mass concentration of the derivative of the organic solvent in the purified organic solvent is greater than or equal to about 2:1 , or greater than or equal to about 5:1 , or greater than or equal to about 7:1.
17. The method of any one of claims 14-16, further comprising the step of:
x) feeding a first condensate stream derived from condensation of an overhead vapour stream from a first crystalliser to a first condensate stream inlet in the sump positioned such that liquid derived from the first condensate stream enters the contaminated organic solvent reservoir.
18. The method of claim 17, further comprising the step of:
xi) feeding a second condensate stream derived from condensation of an overhead vapour stream from a second crystalliser to a second condensate stream inlet in the sump positioned such that liquid derived from the second condensate stream enters the contaminated organic solvent reservoir.
19. The method of any one of claims 14-18, further comprising the step of:
xii) feeding a contaminated organic solvent stream from the contaminated organic solvent reservoir to the stripping column via an external fluid pathway.
20. The method of any one of claims 14-19, further comprising the step of:
xiii) feeding a clean organic solvent stream to the purified organic solvent reservoir. 21. An apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising: a stripping device comprising:
a stripping column;
a sump positioned to receive liquid from the stripping column;
a condenser positioned to receive an overhead stream from the stripping column; and a first process stream inlet;
wherein the sump comprises
a substantially vertical internal weir separating a purified organic solvent reservoir from a contaminated organic solvent reservoir;
a deflector baffle positioned such that liquid from the stripping column is directed into the purified organic solvent reservoir; and
a purified organic solvent stream outlet for removing a purified organic solvent stream from the purified organic solvent reservoir. 22. The apparatus of claim 21 , wherein the stripping column, sump and condenser form an integrated unit.
23. The apparatus of claim 21 or claim 22, wherein the sump further comprises an outlet for removing a contaminated organic solvent stream.
24. The apparatus of claim 23, wherein the stripping column further comprises an inlet for receiving a portion of the contaminated organic solvent stream.
25. The apparatus of any one of claims 21 -24, wherein the sump further comprises a first condensate stream inlet wherein, optionally, the first condensate stream inlet is positioned between the deflector baffle and the contaminated organic solvent reservoir such that liquid derived from a first condensate stream entering the first condensate stream inlet enters the contaminated organic solvent reservoir.
26. The apparatus of claim 25, wherein the sump further comprises a second condensate stream inlet wherein, optionally, the second condensate stream inlet is positioned between the deflector baffle and the contaminated organic solvent reservoir such that liquid derived from a second condensate stream entering the second condensate stream inlet enters the contaminated organic solvent reservoir.
27. The apparatus of any one of claims 21-26, wherein the sump further comprises an inlet for receiving a clean organic solvent stream, wherein, optionally, the inlet for receiving the clean organic solvent stream is positioned such that the clean organic solvent stream enters the purified organic solvent reservoir.
28. The apparatus of any one of claims 21 -27, wherein the first process stream inlet is in the stripping column or in the sump.
29. The apparatus of any one of claims 21 -28, wherein the condenser or an upper region of the stripping column comprises a liquid stream outlet for removing a liquid stream comprising the derivative of the organic solvent from the stripping device.
30. The apparatus of any one of claims 21 -29, wherein the condenser comprises a vapour stream outlet for removing a vapour stream comprising the derivative of the organic solvent from the condenser.
31. An apparatus for recovering a derivative of an organic solvent from a first process stream comprising the organic solvent, water, and the derivative of the organic solvent, comprising: a stripping device configured to receive a first process stream and comprising: a stripping column;
a sump positioned to receive liquid from the stripping column; and
a condenser positioned to receive an overhead stream from the stripping column, and an oxidation reactor for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in the organic solvent,
wherein the apparatus further comprises:
means for transferring a stream comprising the derivative of the organic solvent from the condenser to the oxidation reactor. 32. The apparatus of claim 31 , wherein the stream comprising the derivative of the organic solvent is a liquid stream.
33. The apparatus of claim 31 or claim 32, further comprising:
a scrubbing stage for removing the derivative of the organic solvent from a gaseous stream, and
means for transferring a purified organic solvent stream from the stripping device to the scrubbing stage to remove the derivative of the organic solvent from the gaseous stream.
34. The apparatus of claim 33, wherein the scrubbing stage comprises a pressurised scrubber for removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and/or an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream.
35. The apparatus of claim 33 or claim 34, further comprising:
means for transferring one or more bottoms streams from the scrubbing stage to the oxidation reactor.
36. The apparatus of any one of claims 33-35, further comprising means for cooling the purified organic solvent stream.
37. The apparatus of claim 36, wherein the scrubbing stage comprises a pressurised scrubber for removing the derivative of the organic solvent from an overhead gas derived from a vent gas from the oxidation reactor and the means for cooling the purified organic solvent stream comprises a means for transferring heat from the purified organic solvent stream to a bottoms stream transferred from the pressurised scrubber to the oxidation reactor.
38. The apparatus of any one of claims 33-37, wherein the scrubbing stage comprises an atmospheric scrubber for removing the derivative of the organic solvent from a vapour stream transferred to the atmospheric scrubber from the condenser.
39. The apparatus of claim 38, further comprising:
a solvent stripping device,
means for feeding a contaminated organic solvent stream from the sump to the solvent stripping device, and
means for transferring a vapour stream from the solvent stripping device to the stripping device.
40. The apparatus of any one of claims 31-39, further comprising a substantially vertical internal weir separating a purified organic solvent reservoir from a contaminated organic solvent reservoir.
41. The apparatus of claim 40, further comprising:
means for feeding a first condensate stream derived from condensation of a vapour stream from a first crystalliser to the sump positioned such that liquid derived from the first condensate stream enters the contaminated organic solvent reservoir.
42. The apparatus of claim 41 , further comprising:
means for feeding a second condensate stream derived from condensation of a vapour stream from a second crystalliser to the sump positioned such that liquid derived from the second condensate stream enters the contaminated organic solvent reservoir.
43. The apparatus of any one of claims 40-42 further comprising:
means for feeding a contaminated organic solvent stream from the contaminated organic solvent reservoir to the stripping column via an external fluid pathway.
44. The apparatus of any one of claims 40-43 further comprising:
means for feeding a clean organic solvent stream to the purified organic solvent reservoir.
45. A process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in an organic solvent, comprising the steps of:
I) oxidising the hydrocarbon precursor in the organic solvent in the presence of a metal catalyst to provide an aromatic dicarboxylic acid;
wherein the process further comprises the steps of: II) feeding a first process stream comprising the organic solvent, water, and a derivative of the organic solvent in the process for the production of an aromatic dicarboxylic acid to a stripping device comprising a stripping column and a sump;
III) removing a purified organic solvent stream from the sump; and
IV) transferring an overhead stream from the stripping column to a condenser,
wherein the mass concentration of the derivative of the organic solvent in the purified organic solvent stream removed from the sump in step III) is lower than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II), and, optionally,
wherein the mass concentration of the derivative of the organic solvent in the overhead stream transferred to the condenser in step IV) is greater than the mass concentration of the derivative of the organic solvent in the first process stream fed to the stripping device in step II).
PCT/EP2015/073033 2014-10-07 2015-10-06 Method for recovering methyl acetate WO2016055466A1 (en)

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