Classifications

• • 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
• • 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
• • 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
  • C07C51/487—Separation; Purification; Stabilisation; Use of additives by treatment giving rise to chemical modification

Definitions

• the present invention relates to a process for the purification of a crude carboxylic acid slurry. More specifically, the present invention relates to a process comprising the steps of displacing at elevated temperatures, mother liquor from a crystallized product and reslurrying the crystallized product to be separated in a solid liquid displacement zone to form a purified carboxylic acid slurry; wherein the purified carboxylic acid slurry is further cooled in a cooling zone and subsequently filtered and dried in a filtration and drying zone.
• Terephthalic acid is commercially produce by oxidation, of paraxylene in the presence of a catalyst, such as, for example, Co, Mn, Br and a solvent.
• a catalyst such as, for example, Co, Mn, Br and a solvent.
• Terephthalic acid used in the production of polyester fibers, films, and resins must be further treated to remove impurities present due to the oxidation of para-xylene.
• Typical commercial process produce a crude terephthalic acid then dissolve the solid crude terephthalic acid in water at high temperatures and pressures, hydrogenating the resultant solution, cooling and crystallizing the terephthalic acid product out of solution, and separating the solid terephthalic product from the liquid as discussed in U. S. Patent No. 3,584,039 herein incorporated by reference.
• this invention provides an attractive process to produce a purified carboxylic acid slurry by utilizing a solid liquid displacement zone comprising a solid liquid separator at elevated temperatures after oxidation of a crude carboxylic acid slurry product and prior to final filtration and drying.
• a process to produce the purified carboxylic acid product is provided without the use of hydrogenation of the terephthalic acid or a process separating impurities from oxidation solvent as disclosed in US 3,584,039.
• Another example of a process for separating impurities from oxidation solvent is US 4,356,319.
• a process to produce a purified carboxylic acid slurry comprising: (a) removing impurities from a crystallized product in a solid liquid displacement zone to form a purified carboxylic acid slurry; wherein the purified carboxylic acid slurry has. a b* of less than 3.5; wherein the purified carboxylic acid slurry is formed without a hydrogenation step; (b) cooling the purified carboxylic acid slurry in a cooling zone to form a cooled purified carboxylic acid slurry; and
• a process to produce a purified carboxylic acid slurry comprises:
• the solid liquid separator is operated in a continuous mode; and wherein the solid liquid separator is operated at a pressure of less than about 70 psia;
• a process to produce a purified carboxylic acid slurry comprises: (a) optionally, removing impurities from a crude carboxylic acid slurry in an optional solid liquid displacement zone to form a slurry product;
• Figure 1 is a schematic of the inventive process for the oxidative purification of carboxylic acid wherein a liquid displacement zone is utilized after the crystallization zone.
• Figure 2 is a schematic of the inventive process for the oxidative purification of carboxylic acid wherein a liquid displacement zone is utilized after the staged oxidation zone.
• the present invention provides a process for the purification of a crude carboxylic acid slurry.
• the process comprises the steps of displacing at elevated temperatures mother liquor from a crystallized product and reslurrying the crystallized product in a solid liquid displacement zone to form a purified carboxylic acid slurry.
• Crude terephthalic acid is conventionally made via the liquid phase air oxidation of paraxylene in the presence of a suitable oxidation catalyst.
• Suitable catalysts comprises at least one selected from, but are not limited to, cobalt, bromine and manganese compounds, which are soluble in the selected solvent.
• Suitable solvents include, but are not limited to, aliphatic mono-carboxylic acids, preferably containing 2 to 6 carbon atoms, or benzoic acid and mixtures thereof and mixtures of these compounds with water.
• the solvent is acetic acid mixed with water, in a ratio of about 5:1 to about 25:1 , preferably between about 8:1 and about 20:1.
• acetic acid will be referred to as the solvent.
• a process to produce purified carboxylic acid product 230 is provided in Figure 1.
• the process comprises the following steps: (a) removing impurities from a crystallized product 160 in a solid liquid displacement zone 180 to form a purified carboxylic acid slurry 190; wherein the purified carboxylic acid slurry 190 has a b* of less than 3.5; wherein the purified carboxylic acid slurry 190 is formed without a hydrogenation step;
• the solid liquid separation zone 180, impurities, crystallized product 160, and purified carboxylic acid slurry 190 are all described subsequently in this disclosure.
• Step (a) comprises optionally removing impurities from a crude carboxylic acid slurry 30 in an optional solid liquid displacement zone 40 to form a slurry product 70;
• a crude carboxylic acid slurry 30 comprises at least one carboxylic acid, catalyst, at least one solvent, and impurities is withdrawn via line 30
• an aromatic feedstock 10 typically paraxylene is oxidized.
• the impurities typically comprise one or more of the following compounds: 4- carboxybenzaldehyde, trimellitic acid, and 2,6-dicarboxyfluorenone.
• the solvent typically comprises acetic acid, but can be any solvent that has been previously mentioned.
• the crude carboxylic acid slurry 30 is produced by oxidizing in a primary oxidation zone 20 an aromatic feed stock 10.
• the aromatic feedstock comprises paraxylene.
• the primary oxidation zone 20 comprises at least one oxidation reactor, and the crude carboxylic acid slurry 30 comprises at least one carboxylic acid.
• the carboxylic acid is terephthalic acid. Therefore, when terephthalic acid is utilized, the crude carboxylic acid slurry 30 would be referred to as crude terephthalic acid slurry.
• suitable carboxylic acids include, but are not limited to, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.
• Crude terephthalic acid slurry is conventionally synthesized via the liquid phase oxidation of paraxylene in the presence of suitable oxidation catalyst.
• suitable catalysts include, but are not limited to, cobalt, manganese and bromine compounds, which are soluble in the selected solvent.
• the crude carboxylic acid slurry in conduit 30 is fed to an optional solid liquid displacement zone 40 capable of removing a portion of the liquid contained in the crude carboxylic acid slurry 30 to produce the slurry product in conduit 70.
• the removal of a portion of the liquid to produce a slurry product in conduit 70 can be accomplished by any means known in the art.
• the solid liquid displacement zone 40 comprises a solid liquid separator that is selected from the group consisting of a decanter centrifuge, rotary disk centrifuge, belt filter, rotary vacuum filter, and the like.
• the crude carboxylic acid slurry in conduit 30 is fed to the optional solid liquid displacement zone 40 comprising a solid liquid separator.
• the solid liquid displacement zone 40 comprising a solid liquid separator.
• liquid separator is operated at temperatures between about 50°C to about
• the residence time can be any residence time suitable to remove a portion of the solvent and produce a slurry product in conduit 70.
• the optional solid liquid separator in the optional solid liquid displacement zone 40 may be operated in continuous or batch mode, although it will be appreciated that for commercial processes, the continuous mode is preferred.
• the impurities are displaced from the optional solid liquid displacement zone 40 in a mother liquor and withdrawn via line 60.
• Additional solvent is fed to the optional solid liquid displacement zone 40 via line 50 to reslurry the crude carboxylic acid slurry 30 and form a slurry product 70.
• the mother liquor is withdrawn from solid liquid displacement zone 40 via line 60 and comprises a solvent, typically acetic acid, catalyst, and bromine compounds.
• the mother liquor in line 60 may either be sent to a process for separating impurities from oxidation solvent from via lines not shown or recycled to the catalyst system via lines not shown.
• One technique for impurity removal from the mother liquor commonly used in the chemical processing industry is to draw out or "purge" some portion of the recycle stream. Typically, the purge stream is simply disposed of or, if economically justified, subjected to various treatments to remove undesired impurities while recovering valuable components. Examples of impurity removal processes include U.S. Patent # 4,939,297 and U.S. Patent 4,356,319, herein incorporated by reference.
• Step (b) comprises oxidizing the slurry product 70 or crude carboxylic acid slurry 30 in a staged oxidation zone 80 to form a staged oxidation product 110.
• the slurry product 70 or crude carboxylic acid slurry 30 is withdrawn via line 70 to a staged oxidation zone
• staged oxidation zone 80 comprises at least one staged oxidation reactor vessel.
• the crude carboxylic acid slurry 30 or slurry product 70 is fed to the staged oxidation zone 80.
• staged means that the oxidation occurs in both the primary oxidation zone 20 discussed previously as well as in the staged oxidation zone 80.
• the staged oxidation zone 80 can comprise staged oxidation reactor vessels in series.
• the crude carboxylic acid slurry 30 or slurry product 70 in the staged oxidation zone 80 comprises an oxidation reactor that is heated to between about 190°C to
• staged oxidation zone 80 preferably between 205 °C to 225°C and further oxidized with air or a source of molecular oxygen fed by line 100 to produce a staged oxidation product 110.
• oxidation in the staged oxidation zone 80 is at a higher temperature than the oxidation in the primary oxidation zone 20 to enhance the impurity removal.
• the staged oxidation zone 80 can be heated directly with solvent vapor, or steam via conduit 90 or indirectly by any means known in the art.
• the staged oxidation zone 80 is operated at a temperature and pressure sufficient that the b* color of the staged oxidation product 110 is less than about 4.
• the b* color of the staged oxidation product in conduit 110 is less than about 3.5.
• the b* color in the staged oxidation product in conduit 110 is less than about 3.
• the b* color is one of the three-color attributes measured on a spectroscopic reflectance-based instrument.
• the color can be measured by any device known in the art.
• a Hunter Ultrascan XE instrument is typically the measuring device. Positive readings signify the degree of yellow (or absorbance of blue), while negative readings signify the degree of blue (or absorbance of yellow).
• Additional air or molecular oxygen may be fed via conduit 100 to the staged oxidation zone 80 in an amount necessary to oxidize a substantial portion of the partially oxidized products such as 4-carboxybenzaldehyde (4-CBA) in the crude carboxylic acid slurry 30 or slurry product 70 to the corresponding carboxylic acid.
• 4-carboxybenzaldehyde (4-CBA) in the crude carboxylic acid slurry 30 or slurry product 70 to the corresponding carboxylic acid.
• 4-CBA 4-carboxybenzaldehyde
• at least 70% by weight of the 4- CBA is converted to terephthalic acid in the staged oxidation zone 80.
• at least 80% by weight of the 4-CBA is converted to terephthalic acid in the staged oxidation zone 80.
• Typical terephthalic acid product contains on a weight basis less than about 250 parts per million (ppm) 4-carboxybenzaldehyde and less than about 150 ppm p-toluic acid
• Impurities in the crude carboxylic acid slurry 30 or slurry product 70 go into solution as terephthalic acid particles are dissolved and re- crystallized in staged oxidation zone, 80.
• Offgas from the staged oxidation zone 80 is withdrawn via line 105 and fed to a recovery system where the solvent is removed from the offgas comprising volatile organic compounds (VOCs).
• VOCs and methyl bromide may be treated, for example by incineration in a catalytic oxidation unit.
• the staged oxidation product 110 from the staged oxidation zone 80 is withdrawn via line 110.
• Step (c) comprises crystallizing the staged oxidation product 110 in a crystallization zone 120 to form a crystallized product 160.
• the crystallization zone 120 comprises at least one crystallizer. Vapor product from the crystallization zone 120 is withdrawn via line 130, condensed in a condenser zone 150, which comprises at least one condenser and returned to the crystallization zone 120 via conduit 140. Optionally, the liquid in conduit 140 or vapor 130 in the condenser zone 150 can be recycled, or it can be withdrawn or sent to an energy recovery device. In addition, the crystallization offgas 170 from the condenser zone 150 is removed via line 170 and can be routed to a recovery system where the solvent is removed and crystallization offgas comprising VOCs and pollutants may be treated, for example by incineration in a catalytic oxidation unit.
• the staged oxidation product 110 from the staged oxidation zone 80 is withdrawn via line 110 and fed to a crystallization zone 120 comprising at least one crystallizer
• crystallized product in conduit 160 is less than 4.
• the b* color of the crystallized product in conduit 160 is less than 3.5.
• the b* color in the crystallized product in conduit 160 is less than 3.
• the crystallized product 160 from the crystallization zone 120 is withdrawn via line 160.
• the crystallized product 160 is then fed directly to a vessel and cooled to form a cooled crystallized product.
• the carboxylic acid is terephthalic acid
• the cooled crystallized product is
• terephthalic acid as a dry powder or wet cake.
• the crystallized product 160 was fed directly to a flash tank.
• the crystallized product 160 was fed directly to a flash tank.
• this invention provides an attractive process to produce a purified carboxylic acid slurry by utilizing a solid liquid displacement zone comprising a solid liquid separator at elevated temperatures after oxidation of a crude carboxylic acid slurry product and prior to final filtration and drying.
• a solid liquid displacement zone comprising a solid liquid separator at elevated temperatures after oxidation of a crude carboxylic acid slurry product and prior to final filtration and drying.
• Step (d) comprises removing in a solid liquid displacement zone 180 impurities from the crystallized product to form the purified terephthalic acid slurry.
• the solid liquid displacement zone 180 comprises a solid liquid separator which includes, but is not limited to a decanter centrifuge, rotary disk pack centrifuge and other suitable solid liquid separation devices.
• the level of impurities in the purified carboxylic acid slurry is decreased by up to 60%. It was completely unexpected that terephthalic acid of this purity could be produced utilizing the second solid liquid displacement zone 180 of the present invention without the use of a process for separating impurities from oxidation solvent as disclosed in U.S. Patent #4,939,297 or hydrogenation as disclosed in U.S. Patent #3,584,039; both of which are herein incorporated by reference.
• the crystallized product 160 is withdrawn from crystallizer zone 120 via line 160 and is fed to a solid liquid displacement zone 180 comprising a solid liquid separator to produce a purified carboxylic acid slurry in conduit 190.
• the solid liquid displacement zone 180 comprises a solid liquid separator.
• the solid liquid separator can be operated at
• solid liquid separator can be operated at 110 °C to 200 °C, preferably
• the solid liquid separator in the second solid liquid displacement zone 180 may be operated in continuous or batch mode, although it will be appreciated that for commercial processes the continuous mode is preferred.
• the impurities are displaced from the solid liquid displacement zone 180 in a mother liquor stream and withdrawn via line 185. Additional solvent is fed to the solid liquid displacement zone 180 via line 183 to reslurry the crystallized product and form the purified terephthalic acid slurry.
• the purified carboxylic acid slurry is withdrawn from displacement zone 180, via line 190.
• the purified carboxylic acid slurry in conduit 190 can then be fed to a flash tank and flash cooled to less than about 90 °C.
• Step (e) comprises cooling the purified carboxylic acid slurry in a cooling zone 200 to form a cooled purified carboxylic acid slurry 210.
• the purified carboxylic acid slurry 190 is withdrawn from solid liquid displacement zone 180 via line 190.
• the purified carboxylic acid slurry 190 is withdrawn from solid liquid displacement zone 180 via line 190.
• cooling of the purified carboxylic acid slurry can be accomplished by any means known in the art, typically the cooling zone 200 comprises a flash tank.
• Step (f) comprises filtering and drying the cooled purified carboxylic slurry 210 in a filtration and drying zone 220 to remove a portion of the solvent from the cooled carboxylic acid slurry 210 to produce the purified carboxylic acid product 230.
• the cooled, purified carboxylic acid slurry 190 is withdrawn from cooling zone 200 and fed to a filtration and drying zone 220.
• the filtration and drying zone 220 comprises a filter suitable for recovering the solid carboxylic acid and a dryer.
• the filtration can be accomplished by any means known in the art.
• a rotary vacuum filter can be used for the filtration to produce a filtration cake.
• the filtration cake goes through an initial dewatering step, is then rinsed with acid wash to remove residual catalyst, and can be dewatered again before sent to the dryers.
• the drying of the filter cake can be accomplished by any means known in the art that's capable of evaporating at least 10% of the volatiles remaining in the filter cake to produce the carboxylic acid product.
• a Single Shaft Porcupine® Processor dryer can be used.
• the solid liquid displacement zone 180 can be located after the staged oxidation zone 80 as shown in Figure 2. Even though the process zones are located in a different order, the function of the zones are the same as previously described. Impurities are displaced from the feed stream from the solid liquid displacement zone 180 via line 185.
• the feed stream to the solid displacement zone 180 is the staged oxidation product 110.
• a purified staged oxidation product 165 is produced.
• the impurities are displaced from the solid liquid displacement zone 180 in a mother liquor stream and withdrawn via line 185.
• Th e mother liquor stream 185 comprises carboxylic acid, water, a solvent, suitable oxidation catalyst(s) and bromine compounds and corrosion metals.
• the bromine compounds are used as promoters in the oxidation reaction.
• corrosion metals are iron and chromium compounds, which inhibit, reduce or entirely destroy the activity of the suitable oxidation catalyst.
• Suitable carboxylic acids are selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.
• Additional solvent is fed to the solid liquid displacement zone 180 via line 183 to reslurry the crystallized product and form the purified terephthalic acid slurry.
• the purified carboxylic acid slurry is withdrawn from the solid liquid displacement zone 180, via line 190.
• the purified carboxylic acid slurry in conduit 190 can then be fed
• process zones previously described can be utilized in any other logical order. It should also be appreciated that when the process zones are reordered that the process conditions may change.
• each embodiment can optionally include an additional step comprising decolorizing the carboxylic acid or an esterified carboxylic acid via hydrotreatment.
• the decolorizing of the purified carboxylic acid slurry or an esterified carboxylic acid can be accomplished by any means known in the art and is not limited to hydrogenation.
• the decolorizing can be accomplished by reacting a carboxylic acid that has undergone esterification treatment , for example with ethylene glycol, with molecular hydrogen in the presence of a catalyst in a reactor zone to produce a decolorized carboxylic acid solution or a decolorized ester product.
• a carboxylic acid that has undergone esterification treatment for example with ethylene glycol
• molecular hydrogen in the presence of a catalyst in a reactor zone
• the reactor zone there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen to effect intimate contact of the carboxylic acid or ester product with the catalyst in the reactor zone.
• the catalyst is usually a single Group VIII metal or combination of Group VIII metals.
• the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof.
• the reactor zone comprises a hydrogenation reactor that operates at a temperature and pressure sufficient to hydrogenate a portion of the characteristically yellow compounds to colorless derivatives
• Paraxylene was oxidized at 160°C utilizing a Co, Mn, Br catalyst
• the crude terephthalic acid slurry was crystallized and purified using the process shown in Figure 1 with the omission of Zone 180 and the crystallized product from the crystallization zone 120 was transferred directly to flash tank.
• the product was removed after filtration and drying and analyzed for 4-CBA, TMA, 2,6-DCF, percent transmittance and b*.
• the b* is one of the three-color attributes measured on a spectroscopic reflectance-based instrument.
• a Hunter Ultrascan XE instrument is typically the measuring device. Positive readings signify the degree of yellow (or absorbance of blue), while negative readings signify the degree of blue (or absorbance of yellow).
• the concentration of 4-CBA, TMA, 2,6-DCF in the terephthalic acid were analyzed via liquid chromatography. To determine the percent transmittance, a 10% solution of terephthalic acid product in 2M KOH was 52822
• Example 1 was repeated except that the crystallized product from the crystallization zone 120 was fed to a solid liquid separation zone 180 comprising a rotary disk centrifuge at a temperature of 155°C and the solvent wash was fed to the rotary disk centrifuge at a temperature of 145°C.
• the purified terephthalic acid product was collected and analyzed as in Example 1. The results are shown in Table 1.
• Desirable PTA (purified terephthalic acid) is white (which is referred to as having low color). Higher % transmittance indicates less color in the PTA.
• the human eye can detect 0.5 differences in b*.
• the 1.2 difference between the non-hydrogenation process (Example 1 ) which displays a b* of greater than about 4, and the process of the present invention (Example 2) which shows a b* less than about 3 represents a very noticeable decrease in the yellowness of the terephthalic acid slurry.
• the degree of improvement in all the measured categories is particularly surprising given the simplicity of the centrifugation in the solid liquid separation zone 180. In the past, comparable purity levels have been achieved only by utilization of a hydrogenation plant which includes numerous steps and pieces of equipment, and significant capital investment.

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• 2003
  • 2003-12-03 AU AU2003293252A patent/AU2003293252A1/en not_active Abandoned
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