WO2015157082A1 - Minimisation du recyclage d'acide p-toluique dans une installation de purification de pta - Google Patents

Minimisation du recyclage d'acide p-toluique dans une installation de purification de pta Download PDF

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WO2015157082A1
WO2015157082A1 PCT/US2015/024093 US2015024093W WO2015157082A1 WO 2015157082 A1 WO2015157082 A1 WO 2015157082A1 US 2015024093 W US2015024093 W US 2015024093W WO 2015157082 A1 WO2015157082 A1 WO 2015157082A1
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stream
terephthalic acid
ppm
contacting
concentration
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PCT/US2015/024093
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English (en)
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Finbar Mcdonnell
Ronojoy GOHO
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Invista North America S.A.R.L.
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Publication of WO2015157082A1 publication Critical patent/WO2015157082A1/fr

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    • 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
    • C07C51/47—Separation; Purification; Stabilisation; Use of additives by solid-liquid treatment; by chemisorption

Definitions

  • the invention relates to methods for minimizing the recycle of para-toluic acid within a terephthalic acid purification plant.
  • PET Poly(ethylene terephthalate) (PET) resins are widely produced and used, for example, in beverage and food containers, themiofomiing applications, textiles, and as engineering resins.
  • PET is a polymer formed from ethylene glycol and terephthalic acid (or dimethyl terephthalate).
  • Terephthalic acid (1,4-benzenedicarboxylic acid) generally must be synthesized for use as a reactant.
  • the terephthalic acid required as a reactant for PET production is a form of
  • terephthalic acid known as "purified terephthalic acid” (PTA), which generally contains over 99.97 weight percent of terephthalic acid, and less than 25 ppm 4-carboxybenzaldehyde (4- CBA).
  • PTA purified terephthalic acid
  • purified terephthalic acid (PTA) suitable for use in PET production is generally prepared in a two-stage process comprising paraxylene oxidation followed by purification of the crude oxidation product.
  • paraxylene is oxidized (e.g., with air) to provide crude terephthalic acid (CTA), such as described, for example, in U.S. Patent No. 2,833,816 to Saffer et al. , which is incorporated herein by reference.
  • the oxidation reaction is generally conducted in a solvent comprising an aliphatic carboxylic acid ⁇ e.g., acetic acid) and in the presence of a metal catalyst ⁇ e.g., a cobalt or manganese salt or compound).
  • a solvent comprising an aliphatic carboxylic acid ⁇ e.g., acetic acid
  • a metal catalyst e.g., a cobalt or manganese salt or compound
  • the crude terephthalic acid produced by this oxidation reaction is then purified, as it is typically contaminated by such impurities as 4-carboxyberrzaldehyde, p-toluic acid, and various colored impurities that impart a yellowish color to the terephthalic acid.
  • Purification of the CTA typically requires at least one chemical transformation in addition to at least one physical procedure (e.g., crystallization, washing, etc.).
  • One common chemical transformation is hydro genation of the CTA, which can transform one of the main impurities in the CTA, 4- carboxybenzaldehyde, to p-toluic acid, which is easier to remove.
  • CTA is generally dissolved in water and subjected to hydro genation in the presence of a Group VIII noble metal hydro genation catalyst (e.g., a supported platinum or palladium catalyst) as a first step of purification.
  • a Group VIII noble metal hydro genation catalyst e.g., a supported platinum or palladium catalyst
  • the purified terephthalic acid is recovered by one or more physical procedures.
  • PTA is generally obtained via crystallization of the product from water, as a majority of the impurities, including p-toluic acid, acetic acid, and small amounts of terephthalic acid remain in the solution.
  • the PTA can be recovered by such means as filtration or centrifugation and washed to provide the pure desired material.
  • the remaining solution is referred to as "pure plant mother liquor" (PPML).
  • the 4-CBA concentration in crude terephthalic acid has to be controlled in order to allow the production of final product meeting a specification on p-toluic acid.
  • the total concentration of 4-CBA and p-toluic acid arising from the crude TA, along with the p-toluic acid recycled within the purification plant must be controlled. If the p-toluic acid contribution is reduced the 4-CBA element may be increased.
  • Increasing the 4-CBA permitted in crude TA allows economic benefits to be realized in the operation of the oxidation plant. In particular, if the severity of conditions in the oxidation reactor can be reduced, the wasteful burn of acetic acid, paraxylene and aromatic intermediates can be reduced.
  • Disclosed herein is a process that removes a portion of the p-toluic acid from the pure plant flash condensate and recycles a portion of this cleaned stream back to the crude TA feed stream before the pure plant process.
  • This process allows the 4-CBA in the crude TA to be increased from below 3000 ppm to between about 2500 ppm and 4500 ppm or about 3000 ppm to 4000 ppm without increasing p-toluic acid in the PTA, resulting in an about 7% increase in the pure plant mother liquor flows.
  • the increase in 4-CBA content in the crude TA allows for more benign oxidation conditions with a lower bum of solvent (e.g. acetic acid) and paraxylene derivatives, thus saving on raw material costs and CO/C0 2 emissions.
  • a process for increasing the concentration of 4-carboxybenzaldehyde (4-CBA) in a crude terephthalic acid stream comprising generating a flash condensate stream from a pure plant terephthalic acid system, contacting at least a portion of the flash condensate stream with an aqueous mother liquor stream from the pure plant terephthalic acid system to form a combined stream, providing the combined stream to a pure plant mother liquor solvent extraction process to separate the combined stream into an aqueous stream and organic stream, contacting the aqueous stream with an alkali to form a pH adjusted stream, contacting the pH adjusted stream with a filter to form a treated stream, contacting the treated stream with a reverse osmosis unit to form an RO permeate stream, and contacting the RO permeate stream with the crude terephthalic acid stream, wherein the concentration of 4-CBA in the crude terephthalic acid stream is between about2500 ppm and
  • the flash condensate stream can pass through a heat exchanger prior to contacting the aqueous mother liquor stream.
  • the above process results in a p-toluic acid concentration in the pure terephthalic acid between 100 ppm and 200 ppm, including 140 ppm. Further, the above process decreases acetic acid usage to between 25 and 40 kg/tonne, including 33 kg/tonne. Paraxylene usage is decreased to between 10 and 20 kg/tonne, including 13 kg/tonne, above the stoichiometric requirement of about 639 kg pX / tonne PTA, which results in a total paraxylene usage of between 649 and 659 kg pX / tonne PTA, including 652 kg Px / tonne PTA. This results in a savings of about $0.41 / tonne of PTA produced compared to known processes.
  • concentration of 4-CBA in a crude terephthalic acid stream comprising generating a flash condensate stream from a pure plant terephthalic acid system, providing at least a portion of the flash condensate stream to a pure plant mother liquor solvent extraction process to generate an aqueous stream and organic stream, contacting the aqueous stream with an alkali to form a pH adjusted stream, contacting the pH adjusted stream with a filter to form a treated stream, contacting the treated stream with a reverse osmosis unit to form an RO permeate stream, and contacting the RO permeate stream with the crude terephthalic acid stream, wherein the concentration of 4-CBA in the crude terephthalic acid stream is between 3000 ppm and 4000 ppm, including 3200 and 3500 ppm.
  • the flash condensate stream can pass through a heat exchanger prior to contacting the aqueous mother liquor stream. Further, an aqueous mother liquor stream from a pure plant system can be added to the pure plant mother liquor solvent extraction process.
  • the above process results in a p-toluic acid concentration in the pure terephthalic acid between 100 ppm and 200 ppm, including 140 ppm. Further, the above process decreases acetic acid usage to between 25 and 40 kg/tonne, including 33 kg/tonne. Paraxylene usage is decreased to between 10 and 20 kg/tonne, including 13 kg/tonne, above the
  • a process for increasing the concentration of 4-CBA in a crude terephthalic acid stream comprising generating a flash condensate stream from a pure plant terephthalic acid system, contacting at least a portion of the flash condensate stream with an azeotropic distillation stream from an azeotropic distillation process to form a combined stream, providing the combined stream to a pure plant mother liquor solvent extraction process to generate an aqueous stream and organic stream, contacting the aqueous stream with an alkali to form a pH adjusted stream, contacting the pH adjusted stream with a filter to form a treated stream, contacting the treated stream with a reverse osmosis unit to form an RO permeate stream, and contacting the RO permeate stream with the crade terephthalic acid stream, wherein the concentration of 4-CBA in the crade terephthalic acid stream is between 3000 ppm and 4000 ppm, including 3200 and 3
  • the flash condensate stream can pass through a heat exchanger prior to contacting the aqueous mother liquor stream.
  • the azeotropic distillation stream is the overheads from treating the vapor phase of an oxidation reaction system.
  • an aqueous mother liquor stream from a pure plant system can be added to the pure plant mother liquor solvent extraction process.
  • the above process results in a p-toluic acid concentration in the pure terephthalic acid between 100 ppm and 200 ppm, including 140 ppm. Further, the above process decreases acetic acid usage to between 25 and 40 kg/tonne, including 33 kg/tonne.
  • Paraxylene usage is decreased to between 10 and 20 kg/tonne, including 13 kg/tonne, above the stoichiometric requirement of about 639 kg pX / tonne PTA, which results in a total paraxylene usage of between 649 and 659 kg pX / tonne PTA, including 652 kg Px / tonne PTA. This results in a savings of about $0.41 / tonne of PTA produced compared to known processes.
  • a process for manufacturing pure terephthalic acid by air oxidation of paraxylene in an acetic acid solvent comprising contacting the paraxylene with air in an oxidation reactor containing acetic acid solvent to form a crude terephthalic acid stream, separating the crude terephthalic acid stream into a solid phase stream containing crude terephthalic acid crystals and a liquid phase stream containing acetic acid.
  • the average stoichiometric requirement for paraxylene is about 639 kg pX / tonne PTA.
  • the above process results in a p-toluic acid concentration in the pure terephthalic acid between 100 ppm and 200 ppm, including 140 ppm and a savings of about $0.41 / tonne of PTA produced compared to known processes.
  • FIGURE 1 discloses a prior art system, whereby the flash condensate from the pure plant is not treated prior to injection back into the crude terephthalic acid stream.
  • FIGURE 2 discloses one aspect of the process wherein a portion of the flash condensate from the pure plant is treated along with the aqueous mother liquor from the pure plant prior to injection into the crude terephthalic acid stream.
  • FIGURE 3 discloses another aspect of the process wherein a portion of the flash condensate from the pure plant is treated directly in the pure plant mother liquor solvent extraction process prior to injection into the crude terephthalic acid stream.
  • FIGURE 4 discloses a further aspect of the process wherein a portion of the flash condensate from the pure plant is mixed with the overheads from an azeotropic distillation system prior to injection into the crude terephthalic acid stream.
  • FIGURE 5 discloses a pure plant mother liquor solvent extraction process.
  • FIGURE 6 discloses a contamination removal process on a pure plant mother liquor aqueous stream.
  • the present invention provides systems and methods for the production of purified terephthalic acid (PTA). More specifically, the invention provides systems and methods to increase the concentration of 4-CBA in the crude terephthalic acid stream by pre-treating the flash condensate from the PTA purification process.
  • the pre-treatment is a combination of pure plant mother liquor solvent extraction (PPMLSX) on the aqueous eluent stream generated during the purification of pure plant mother liquor (PPML) that is generated during the production of PTA and contaminate removal of the PPMLSX aqueous stream.
  • PPMLSX pure plant mother liquor solvent extraction
  • PCT/US13/67304 provides an exemplary description of the PPMLSX process, which is herein incorporated by reference in its entirety.
  • U.S. Provisional Application No. 61/720,675 provides an exemplary description of the contaminate removal process, which is herein incorporated by reference in its entirety.
  • the commercial production of PTA typically begins with the liquid-phase oxidation of a p-phenylene compound to give crude ( . e. , impure) terephthalic acid.
  • the p-phenylene compound most commonly used is paraxylene (p-xylene); however, any phenylene having substituent groups subject to oxidation to form carboxyl groups at the para positions of the phenylene can be used.
  • exemplary substituent groups on the phenylene can include, but are not limited to, methyl, ethyl, propyl, isopropyl, formyl, acetyl, and combinations thereof.
  • the substituents can be the same or different.
  • the solvent used in the oxidation reaction can vary, but generally comprises acetic acid, which may optionally contain water.
  • the oxidation reaction can be conducted under any conditions wherein oxygen is available.
  • the reaction can be conducted in air, wherein the oxygen in air can serve as the oxidant, and/or in an environment enriched with pure oxygen (e.g., an all-oxygen atmosphere or an inert gas atmosphere to which some concentration of oxygen is added).
  • a transition metal catalyst and, optionally, a co-catalyst are commonly used.
  • the oxidation catalyst can vary and can, in some embodiments, comprise a heavy metal salt or compound (e.g., a cobalt, manganese, iron, chromium, and/or nickel-containing compound or salt, or a combination thereof) as described, for example, in U.S. Patent No.
  • a heavy metal salt or compound e.g., a cobalt, manganese, iron, chromium, and/or nickel-containing compound or salt, or a combination thereof
  • co-catalysts and/or promoters can also be added, including, but not limited to, a bromine-containing compound, a bromide salt, a ketone (e.g., butanone, triacetylmethane, 2,3-pentanedione, methylethylketone, acetylacetone, or a combination thereof), a metalloporphyrin, a zirconium salt, or a combination thereof.
  • a bromine-containing compound e.g., a bromide salt
  • a ketone e.g., butanone, triacetylmethane, 2,3-pentanedione, methylethylketone, acetylacetone, or a combination thereof
  • metalloporphyrin e.g., a zirconium salt, or a combination thereof.
  • Oxidation is typically conducted at elevated temperature and/or elevated pressure. Generally, the temperature and pressure must be sufficient to ensure that the oxidation reaction proceeds, but also to ensure that at least a portion of the solvent is maintained in liquid phase. Therefore, it is generally necessary to conduct the oxidation reaction under both elevated temperature and elevated pressure conditions.
  • the temperature required for the oxidation reaction may vary with the selection of the catalyst and optional co-catalyst and/or promoter. In certain embodiments, the reaction temperature is in the range of about 160 °C to about 220 °C; however, in some embodiments, the temperature can be maintained below 160 °C while still obtaining the oxidized product.
  • the reaction mixture is typically cooled (e.g. , by transferring the mixture to one or more crystallizer units, with decreased pressure).
  • the resulting mixture generally comprises a slurry from which the crude terephthalic acid can be isolated.
  • the means for isolating the crude terephthalic acid can vary and may comprise filtration,
  • the solid phase is typically washed with fresh water and/or acetic acid to give isolated crystals of crude terephthalic acid.
  • the liquid phase (typically comprising water, acetic acid, methyl acetate, and various other components) can, in some embodiments, be treated such that the acetic acid is separated from water and other low-boiling components.
  • a portion of the liquid phase is vaporized and the vapor is sent to a distillation apparatus (e.g., wherein it can undergo azeotropic distillation).
  • azeotropic distillation can be an effective method for separating acetic acid from water and is done in the presence of an organic entrainer.
  • a bottoms product will form, comprising primarily acetic acid (which can, in some embodiments, be recycled into the oxidation reaction).
  • the tops product may comprise organic entrainer, water, and methyl acetate and can subsequently be cooled to form a condensate.
  • the crude terephthalic acid is then purified to provide PTA suitable for use in the production of poly(ethylene terephthalate).
  • Various impurities are generally present in the crude terephthalic acid at this stage.
  • 4-carboxybenzaldehyde is one of the most common contaminants, as well as compounds that impart some degree of color to the crude terephthalic acid.
  • Purification of the CTA typically requires at least one chemical transformation in addition to at least one physical procedure (e.g., crystallization, washing, etc.). The chemical
  • transformation can include various processes, including but not limited to catalytic
  • hydrotreatment catalytic treatment, oxidation treatment, and/or recrystallization.
  • the most commonly used chemical transformation is hydro genation, which can transform one of the main impurities in the CTA, 4-carboxybenzaldehyde, to p-toluic acid, which is easier to remove.
  • a solvent e.g. , water
  • heat and/or pressure are required to dissolve the CTA in water.
  • a Group VIII noble metal hydrogenation catalyst e.g., a platinum, palladium, mthenium, or rhodium catalyst
  • an alternative type of catalyst e.g., a nickel catalyst
  • the catalyst can be a homogeneous or heterogeneous catalyst and can be provided in an unsupported form or can be supported on any type of material suitable for this purpose.
  • the heterogeneous catalyst employed in the purification of the crude terephthalic acid product may be a supported nobel metal catalyst, including platinum and/or palladium on an inert carbon support.
  • Support materials are generally porous materials including, but not limited to, activated carbon/charcoal, quartz powder, or a combination thereof.
  • the hydrogen source is typically hydrogen gas, although this can vary as well.
  • hydrogenation processes can, in certain cases, occur at atmospheric pressure and ambient temperature, on the commercial scale, heat and/or pressure are often applied.
  • the temperature is from about 200 °C to about 374 °C, e.g. , about 250 °C or greater.
  • the pressure is typically sufficient to maintain the CTA solution in liquid form (e.g., about 50 to about 100 atm).
  • the amount of hydrogen required to effect hydrogenation of the CTA is typically an excess of that amount required for reduction of dissolved impurities.
  • the hydrogenation can occur, for example, within a pressure vessel, hydrogenator, or plug-flow reactor or can be accomplished by flow hydrogenation, wherein the dissolved CTA is passed over a fixed bed catalyst in the presence of hydrogen.
  • the purified terephthalic acid is recovered by one or more physical procedures.
  • PTA is generally obtained via crystallization of the product from solution (e.g., water), as a majority of the impurities, including p-toluic acid, acetic acid, and small amounts of terephthalic acid remain in the solution.
  • the mixture in some embodiments is passed through one or more crystallizers and depressurized (which generally cools the mixture and evaporates some water, giving a slurry of PTA crystals).
  • the PTA can be recovered by such means as filtration and/or centrifugation, washed, and dried to provide the pure desired material.
  • the remaining solution is known as pure plant mother liquor (PPML).
  • the temperature at which this separation of PTA and PPML is conducted can vary; however, it is typically in the range of from about 70 °C to about 160 °C (e.g., about 100 °C or greater).
  • the 4-CBA concentration in crude terephthalic acid has to be controlled in order to allow the production of final product meeting a specification on p-toluic acid.
  • the total concentration of 4-CBA and p-toluic acid arising from the crude TA, along with the p-toluic acid recycled within the purification plant must be controlled. If the p-toluic acid contribution is reduced the 4-CBA element may be increased.
  • Increasing the 4-CBA permitted in crude TA allows economic benefits to be realized in the operation of the oxidation plant. In particular, if the severity of conditions in the oxidation reactor can be reduced, the wasteful burn of acetic acid, paraxylene and aromatic intermediates can be reduced.
  • Figure 1 discloses a prior art process that controls 4-CBA content via pure plant flash condensate injection into the crude terephthalic acid stream.
  • the liquor stream A from the pure plant crystallize!- 10 is passed through a heat exchanger 20 before being flashed into vapor in flasher 30.
  • the flash condensate is then injected into the crude terephthalic acid re-slurry stream 5 at points B and C, prior to the crude terephthalic acid stream being introduced into the PTA purification plant 100.
  • the 4-CBA content of the crude TA is 3000 ppm with a p-toluic acid content of 137 ppm.
  • Figure 2 discloses one aspect of the present process that controls 4-CBA content via partial treatment of the pure plant crystallizer flash condensate in a PPMLSX and contamination removal system.
  • the liquor stream A from the pure plant crystallizer 10 is passed through a heat exchanger 20 before being flashed into vapor in flasher 30.
  • the flash condensate is split into two streams Z and U, whereby stream Z is combined with the aqueous mother liquor from the pure plant Y and the combined stream X sent to a PPMLSX process 40 and contamination removal process 50, and stream U is injected into the crude terephthalic acid after the slurry step.
  • the reverse osmosis permeate stream which is the resulting treated stream Q, is sent to the crude terephthalic acid stream 5 prior to the slurry step.
  • Stream Z can be sent directly to the PPMLSX process.
  • Figure 4 discloses another aspect of the present process that controls 4-CBA content via partial treatment of the pure plant crystallizer flash condensate in a PPMLSX and contamination removal system.
  • the liquor stream A from the pure plant crystallizer 10 is passed through a heat exchanger 20 before being flashed into vapor in flasher 30.
  • the flash condensate is split into two streams Z and U, whereby stream Z is combined with the overheads G from an azeotropic distillation system 60 and the combined stream V sent to a PPMLSX process 40 and contamination removal process 50, and stream U is injected into the crude terephthalic acid after the slurry step.
  • the reverse osmosis permeate stream which is the resulting treated stream Q, is sent to the crude terephthalic acid stream 5 prior to the slurry step.
  • the aqueous mother liquor from the pure plant Y can also be sent to the PPMLSX process.
  • the azeotropic distillation overheads G are produced from the oxidation reactor 70 vapor stream I. Vapor stream I enters the azeotropic distillation system 60 at the bottom while organics from the PPMLSX process S enter the top of the azeotropic distillation system. The bottoms from the azeotropic distillation system are recycled back to the oxidation reactor 70.
  • Table 1 [00033] As shown in Table 1, the inventive process results in a total approximate raw material savings of $0.41 / tonne through increasing the 4CBA content in the crude terephthalic acid. This increase results in a decrease in paraxylene and acetic acid usage. Since current PTA plants operate at 2MM tonnes / year, the total yearly savings in these raw materials is -$800,000.
  • Figure 5 discloses the details of the PPMLSX process 40.
  • OR represents an oxidation reaction of paraxylene, such as generally described above. Other discussion of such reactions is provided, for example, in U.S. Patent Nos. 5,705,682 to Ohkashi et al ; and
  • stream B represents the overhead condensates formed during the oxidation reaction as well as the liquid and vapor phases obtained following the oxidation reaction and removal of the solid crude terephthalic acid.
  • stream B primarily comprises water and acetic acid (in liquid and/or vapor form).
  • the primary component is generally acetic acid (e.g., at least about 50% by volume) and the remainder of the stream is generally water, although small amounts (e.g., less than about 5%, less than about 2%) of organic components (e.g. , methyl acetate) can also be present in stream B.
  • the liquid and/or vapor-containing stream B is brought into contact with an organic entrainer in distillation column 30.
  • the entrainer can vary, but is advantageously a substance suitable for azeotropic distillation of a mixed solution of acetic acid and water.
  • the entrainer comprises toluene, xylene, ethylbenzene, methyl butyl ketone, chlorobenzene, ethyl amyl ether, butyl formate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, methyl acetate, n-butyl propionate, diisobutyl propionate, propanol, water, or a combination of any two or more of these or other entrainers.
  • Column 30 can be, for example, a trayed or packed column.
  • a general discussion of azeotropic distillation processes to separate water from acetic acid is provided, for example, in U.S. Patent No. 5,980,696 to Parten et al, which is incorporated herein by reference.
  • organic entrainer is used to separate acetic acid and water.
  • the acetic acid-containing phase can be removed from the bottom of the column as streams G and Jl.
  • stream G comprises about 95% acetic acid and about 5% water and does not contain a significant amount of entrainer.
  • Stream G is recycled to the column 30 through reboiler 60.
  • the hot acetic acid stream Jl leaving column 30 is passed through heat exchanger 25 prior to passage back into the oxidation reaction.
  • the organic stream Fl exiting the decanter 20 is also passed through heat exchanger 25 such that heat from acetic acid stream Jl is transferred to the organic stream Fl prior to its entry to the column 30 as stream F2.
  • organic stream F2 enters the column 30 at an increased temperature relative to the temperature upon exiting the decanter 20.
  • the vapor phase produced within column 30 generally comprises organic entrainer, as well as water and methyl acetate. Methyl acetate is advantageously removed from column 30 as it can, in some embodiments, interfere with the azeotropic separation within column 30.
  • the vapor phase can be removed from the distillation column as stream C. This stream may be condensed within condenser 40 to provide condensate stream D.
  • Condensate stream D generally comprises organic entrainer and may further comprise water, which can be removed from the mixture or maintained as a component of condensate stream D.
  • the temperature of condensate stream D can vary; however, in exemplary embodiments, stream D is between about 60 °C and about 100 °C, such as between about 70 °C and about 90 °C, between about 75 °C and about 82 °C (e.g., about 78 °C or about 80 °C in certain embodiments). It is noted that the temperature of the condensate will vary somewhat depending upon the makeup of the condensate stream D (e.g., the specific entrainer used).
  • stream Z, Y, X, and V from Figures 2-4 or a combination (herein after referred to as stream "A" for simplicity) is brought into contact with stream D in a mixer 10.
  • the weight ratio of stream A to stream D can vary and other components can be added to the mixer if desired (e.g., additional entrainer or water).
  • the ratio of stream D to stream A is about 1 : 1 to about 5: 1 (e.g., about 1.7: 1 to about 2.1 : 1).
  • the nature of the mixer 10 can vary; it can comprise an extraction column, static mixer, dynamic mixer (e.g., an agitating mixer), pump, or shaker.
  • the resulting mixture of stream A and stream D exits the mixer 10 as mixed stream E and is passed into a decanter 20.
  • the decanter can be any component which can provide for separation of an organic (e.g., entrainer-rich) stream Fl from an aqueous stream K. Sometimes, a single decanter can be used, which can reduce the capital cost of the system and reduce the degree of hydrolysis of the entrainer. Also, certain organic impurities originally present in the PPML stream A (e.g., p-toluic acid, benzoic acid, etc.) are extracted into the organic phase and thus removed via organic stream Fl. Methyl acetate (originally present in stream C from distillation column 30) is partitioned into aqueous stream Kl.
  • organic impurities originally present in the PPML stream A e.g., p-toluic acid, benzoic acid, etc.
  • Methyl acetate originally present in stream C from distillation column 30
  • the organic stream F2 is routed to the distillation column 30. Although the figures show entry of stream F2 at the middle of the distillation column, this is not intended to be limiting; stream F2 may enter the column at the top, middle, or bottom of the distillation column or at any stage in between. With the entry of certain organic components via stream F2, it is noted that the makeup of streams C and Jl leaving the distillation column 30 can be affected. Generally, the majority of the organic components that enter the distillation column via stream F2 are retained in the acetic acid phase and are removed from column 30 via stream Jl.
  • Aqueous stream Kl can be treated to allow water to be reused within the process ⁇ e.g., in the purification of CTA), recycled for other purposes, or disposed of as waste water.
  • the heated effluent water LI exiting the recovery column 70 can be passed through the heat exchanger 65 in a heat exchange relationship with the aqueous stream Kl exiting the decanter 20.
  • the aqueous stream K2 exiting the heat exchanger 65 can be delivered to the column 70 at a significantly increased temperature.
  • the temperature of stream K2 can vary such that stream K2 can comprise an aqueous liquid and/or vapor phase.
  • Provision of stream K2 at the increased temperature is beneficial in that the quantity of steam (via stream M) that must be introduced into column 70 to effectively strip the organic components can be significantly reduced.
  • Undesirable methyl acetate, which can be present in aqueous stream K2 can be stripped from the aqueous phase of the PPML extraction in certain embodiments by passing the aqueous phase K2 through recovery column 70, which is designed to strip out any residual organic material. It is noted that a small amount of the organic phase ⁇ e.g., comprising the organic entrainer) can also be present in stream K2 and in some embodiments, such residual organic material can also be removed via recovery column 70.
  • the stripping of organic material from the aqueous phase is accomplished via contacting the aqueous phase stream K2 with steam, shown as stream M entering the column 70.
  • a reboiler on column 70 can be used in place of stream M.
  • the stream to be treated generally should be heated to about 40 °C to about 140 °C, including 60 °C to 100 °C, e.g., about 95 °C.
  • Cleaned water can exit the column, e.g., at the bottom thereof, via stream L2.
  • Recovery column 70 can be further equipped with a condenser 50, which returns a reflux to the top of the column with a vapor purge and a liquid product.
  • FIG. 6 discloses the contamination removal process 50.
  • stream L2 contains impurities (e.g. carboxylic acids, metals) that make it unsuitable for use in other parts of the PTA plant.
  • impurities e.g. carboxylic acids, metals
  • fouling and scaling of reverse osmosis membranes may occur.
  • pre-treatment of stream L2 followed by reverse osmosis results in a demineralized water stream that is suitable for use in other parts of the PTA plant.
  • pre-treating L2 with an alkali solutions and micro or ultra-filtration makes reverse osmosis an economical and efficient method of obtaining demineralized water.
  • aqueous eluent stream L2 at a pH of less than or equal to 7, including 2-7, 4, 5, 6 and 7, has the following composition in Table 2:
  • Acid and salts of acid expressed as w/w concentration of the acid.
  • L2 Prior to using L2 in a reverse osmosis process, L2 is treated to remove carboxylic acids and dissolved metals, and the pH is adjusted.
  • L2 enters neutralizer 100, wherein the aqueous stream is contacted with an alkali (e.g. sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, and mixtures thereof) to raise the pH to between 8-11, including 9 and 10.
  • an alkali e.g. sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, and mixtures thereof
  • the concentration of the alkali in the aqueous stream can range from 5 wt.% to 90 wt.%, including 5 wt.% to 80 wt.%, 10 wt.% to 80 wt.%, 10 wt.% to 90 wt.%, 20 wt.% to 90 wt.%, 20 wt.% to 80 wt.%, 20 wt.% to 70 wt.%, 30 wt.% to 90 wt.%, 30 wt.% to 80 wt.%, 30 wt.% to 70 wt.%, and 30 wt.% to 60 wt.%.
  • the concentration needs to be sufficient enough to reach an alkali concentration of 500 to 2000 ppm.
  • carboxylic acids e.g acetic acid, terephthalic acid, CBA, p-toulic acid, benzoic acid
  • the dissolved and suspended carboxylic acids are converted to their respective soluble salts.
  • acetic acid is coverted to sodium acetate.
  • the dissolved metals e.g. cobalt, manganese
  • Neutralizer 100 can be any device that results in sufficient contact between stream L2 and the alkali.
  • counter-current washer, gravity feed decanter e.g. where L2 passes vertically through the alkali solution
  • static mixer sparger
  • Acid and salts of acid expressed as w/w concentration of the acid
  • the pH adjusted stream N is sent to a pre-filtration unit 120, or optionally a holding tank 110 prior to unit 120, for removal of suspended solids.
  • pH adjusted stream N is contacted with at least one pre-filtration membrane to remove the metal hydroxides to form treated stream P.
  • the pre-filtration membrane can be an ultrafiltration membrane KMS HFMTM-180 with a pore size of around 0.1 micron has a rejection performance of >99.5% for cobalt and manganese hydroxides leaving a residual ⁇ 0.05 ppm cobalt and manganese in the treated stream.
  • Typical pre-filtration units include ultra-filtration, micro-filtration, and other media filtration that removes metal hydroxides and other potentially fouling solids prior to the RO step.
  • Ultra-filtration or micro-filtration with a separation range of less than or equal to 0.1 micron including Ultra-filtration Elements such as KMS HFM 180 can provide suitable protection of the reverse osmosis membrane.
  • KMS HFM 180 can provide suitable protection of the reverse osmosis membrane.
  • Acid and salts of acid expressed as w/w concentration of the acid
  • Treated stream P next passes into reverses osmosis unit 130, where sodium, acetate, and other ionic species are removed, along with a pH reduction to between about 7-10, thereby creating a demineralized water stream Ql and Q.
  • a second reverse osmosis unit 140 can be employed with unit 130 to further reduce the concentration of sodium, acetate, and other ionic species.
  • the first pass permeate Rl is fed into unit 140, and a demineralized stream Q2 is drawn off.
  • units 130 and 140 can be used in a loop type configuration, with a portion of the unit 140 permeate R2 being recycled back to unit 130.
  • treated stream P can pass through two reverse osmosis KMS Fluid Systems TFC-SW membranes can be arranged in series, resulting in a demineralized water stream Q with 0.97 ppm of sodium and 2.49 ppm of acetate, and pH of 6.
  • the present disclosure is not limited to one or two reverse osmosis units. Additional units can be employed in series or in loop type configurations with units 130 and 140 depending on application, size of plant, and location.
  • Typical reverse osmosis units can include High Rejection Reverse Osmosis membranes, such as those used for sea water, brackish water, or waste water reclamation, including Fluid Systems® TFC®-SW, DOWTMFILMTECTMSW30HRLE-400, FLUID SYSTEMS®TFC-FR, DO WTMFILMTECTMBW30-400, Fluid Systems®TFC®-HR.
  • Fluid Systems® TFC®-SW DOWTMFILMTECTMSW30HRLE-400
  • FLUID SYSTEMS®TFC-FR DO WTMFILMTECTMBW30-400
  • Fluid Systems®TFC®-HR Fluid Systems®TFC®-HR
  • the demineralized water stream Q is substantially free of metal compounds, Mn, K, Ca, Mg, Fe, and Co (i.e. a total metal concentration, excluding the alkali sodium, between 0.01 and 1 ppm, including between 0.01 ppm and 0.1 ppm, and between 0.01 ppm and 0.05 ppm), while also having low sodium and acetate concentrations.
  • metal compounds Mn, K, Ca, Mg, Fe, and Co
  • Case B is represented by Figure 2.
  • Case C and D are represented by a drawing similar to Figure 2 however, stream B remains, having a smaller flow.
  • the difference between cases C, D and B is the magnitude of streams Z and B.
  • stream B collected pure plant flash condensate
  • stream B would be expected to be of the order of 68t/h.
  • this rate could vary depending on the specific PTA plant technology utilized.
  • 100% of this flow would be re-directed to the PPMLSX process.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

La présente invention concerne des procédés pour réduire au minimum le recyclage d'acide para-toluique (PTA) dans une installation de purification d'acide téréphtalique. Spécifiquement, les procédés décrits éliminent une partie de l'acide p-toluique du condensat de vaporisation flash d'installation pure et recycle une partie de ce flux nettoyé de retour vers le flux d'alimentation de TA brut avant le processus d'installation pure. Ce processus permet que le 4-CBA dans le TA brut soit augmenté de moins de 3000 ppm à une valeur comprise entre 3000 ppm et 4000 ppm sans augmenter l'acide p-toluique dans le PTA, ce qui conduit à une augmentation d'environ 7 % dans les flux de liqueur mère d'installation pure.
PCT/US2015/024093 2014-04-08 2015-04-02 Minimisation du recyclage d'acide p-toluique dans une installation de purification de pta WO2015157082A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6143926A (en) * 1999-09-21 2000-11-07 E. I. Du Pont De Nemours And Company Process for producing pure terephthalic acid with improved recovery of precursors, solvent and methyl acetate
US6150553A (en) * 1998-08-11 2000-11-21 E. I. Du Pont De Nemours And Company Method for recovering methyl acetate and residual acetic acid in the production acid of pure terephthalic acid
US6254779B1 (en) * 1997-03-14 2001-07-03 E. I. Du Pont De Nemours And Company Treatment of effluent streams containing organic acids

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6254779B1 (en) * 1997-03-14 2001-07-03 E. I. Du Pont De Nemours And Company Treatment of effluent streams containing organic acids
US6150553A (en) * 1998-08-11 2000-11-21 E. I. Du Pont De Nemours And Company Method for recovering methyl acetate and residual acetic acid in the production acid of pure terephthalic acid
US6143926A (en) * 1999-09-21 2000-11-07 E. I. Du Pont De Nemours And Company Process for producing pure terephthalic acid with improved recovery of precursors, solvent and methyl acetate

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