Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J38/00—Regeneration or reactivation of catalysts, in general
  • B01J38/48—Liquid treating or treating in liquid phase, e.g. dissolved or suspended
  • B01J38/68—Liquid treating or treating in liquid phase, e.g. dissolved or suspended including substantial dissolution or chemical precipitation of a catalyst component in the ultimate reconstitution of the catalyst
• • 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
• • 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
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/584—Recycling of catalysts

Definitions

• This invention relates to the treatment of a catalyst-containing stream derived f rom the liquid phase oxidation of aromatic polycarboxylic acid precu rsors to produce the polycarboxylic acid Cobalt or manganese or a combination of cobalt and manganese, e g in the form of their acetates , together with a source of bromide ion provide catalysis for the catalytic liquid phase oxidation of polycarboxylic acid precursors such as paraxylene to produce the polycarboxylic acid, e g terephthalic acid
• the liqu id phase oxidation is carried out using a lower monocarboxylic aliphatic acid such as acetic acid as a solvent in which the catalyst system is dissolved
• the polycarboxylic acid produced by the oxidation process is withdrawn from the reactor as a slurry of crystals i n mother liquor comprising mainly the al iphatic carboxy c acid together with water and dissolved catalyst components and organics (including the polycarboxylic acid, precursors thereof) Further precipitation of the polycarboxylic acid is usually obtained by means of a crystall isation process before separati ng the crystals from the mother liquor
• the solids-liquid separation may be carried out by means of an integrated filtration and washing system as disclosed in EP-A-502628 and WO-A-93/24440, the entire disclosures of which are incorporated herein by this reference
• conventional practice is to recycle a major part of the mother liquor and its catalyst metal content to the oxidation reactor and to purge a minor part to avoid undue build-up of primarily organic contaminants with in the reaction system
• the mother liquor purge is treated to recover said aliphatic carboxyhc acid for recycle to the
• a process for the treatment of heavy metal catalyst-containing residue from the production of an aromatic polycarboxylic acid having a solubility in water of less than 1 % by weight at 25 D C comprising dissolving substantially all of the residue in an aqueous medium, precipitating the metal catalyst components by inclusion in the aqueous medium of metal salt-forming anions and separating the precipitate from the aqueous medium
• the metal salt-forming anions comprise carbonate and/or bicarbonate ions.
• the catalyst metal yield can be increased since catalyst metals occluded, chemically or otherwise, with the organics are taken into solution and can then be precipitated as salts, e g. carbonates and/or bicarbonates
• a process for the treatment of heavy metal catalyst-containing residue from the production of an aromatic polycarboxylic acid comprising dissolving substantially all of the residue in an aqueous medium, precipitating the metal catalyst components by inclusion in the aqueous medium of a carbonate and/or bicarbonate-containing liquor obtained following contacting a metal or ammonium hydroxide with a carbon dioxide-containing offgas derived from the oxidation reaction in which said polycarboxylic acid is produced
• aromatic polycarboxylic acid is one which has very low solubility in water, viz. less than 1% by weight at 25°C
• the aqueous medium comprises at least in part, for instance at least 10% by weight (e.g. at least 20%), an organic material-containing mother liquor derived from the hydrogenation of an aqueous solution of the polycarboxylic acid.
• an organic material-containing mother liquor derived from the hydrogenation of an aqueous solution of the polycarboxylic acid.
• the process of the present invention involves the solubilisation of substantially the whole of the residue before precipitating the catalyst metals, thus making it feasible to use an organics containing aqueous medium for dissolution of the metals and organic content of the residue
• Solubilisation of substantially all of the residue in the aqueous medium may be effected by inclusion of an alkaline agent added to the aqueous medium, for instance prior to and/or in the course of combining the residue with the aqueous medium
• the agent may comprise ammonium hydroxide or a metal hydroxide, such as sodium hydroxide.
• pH may be increased initially by the inclusion of said carbonate and/or bicarbonate reaction product in the aqueous medium either as the sole alkaline agent or in combination with another alkaline agent or agents such as ammonium hydroxide or a metal hydroxide
• the inclusion of said carbonate and/or bicarbonate reaction product in the aqueous medium is considered advantageous since the metal recovered in the form of carbonates and/or bicarbonates is of a higher quality, apparently because less oxide contamination occurs compared with use of hydroxide only in the initial solubilisation of the residue For this reason, the process of the invention may be carried out using said carbonate and/or bicarbonate reaction product as the major or sole alkaline agent in effecting initial solubilisation of the residue.
• the alkaline agent is introduced to raise the pH sufficiently, preferably to between 4 5 and 5.5 (more preferably 4 7 to 5.3), to dissolve the residue and partially neutralise the acidic content of the residue (and, where applicable, that of the aqueous medium where the latter contains acidic components as in the case where it is constituted by the mother liquor derived from said hydrogenation reaction).
• the carbonate and/or bicarbonate reaction product is added to raise the pH further to precipitate the catalyst metals and secure a pH compatible with downstream processing of the liquor remaining following separation of the solids.
• the pH is conveniently increased to about 6.5 to about 9, preferably about 7 to 8, by addition of said carbonate and/or bicarbonate reaction product.
• the downstream processing includes biological treatment, e.g.
• the pH of the liquor obtained following precipitation of the metals may be adjusted to 6.5 to 8, preferably about 7, for compatability with the biological treatment process.
• Such adjustment may involve the addition of further mother liquor derived from the hydrogenation reaction and/or other acidic component such as a mineral acid (e.g. HCI) and/or alkaline component such as caustic soda, in order to secure a suitable pH for biological treatment.
• a mineral acid e.g. HCI
• alkaline component such as caustic soda
• a process for the treatment of heavy metal catalyst-containing residue from the production of an aromatic polycarboxylic acid comprising the steps of dissolving substantially all of the residue in an aqueous medium, and precipitating the metal catalyst components by inclusion in the aqueous medium of carbonate and/or bicarbonate ions in such a way that evolution of C0 2 is substantially suppressed when the carbonate and/or bicarbonate ions are added
• the addition of the carbonate and/or bicarbonate ions is deferred until the pH of the aqueous medium has been increased by addition of an alkaline agent other than a carbonate or bicarbonate to a level such that evolution of C0 2 is substantially suppressed when the carbonate and/or bicarbonate ions are added
• the extent of dilution of the residue may be controlled such that C0 2 is suppressed upon addition of the carbonate and/or bicarbonate ions
• C0 2 suppression may also be effected by the application of overpressure during the process
• a process for the disposal of the organics content of a heavy metal catalyst-containing residue from the production of an aromatic polycarboxylic acid comprising biologically digesting the organics after neutralising the acidity of said residue for compatability with the biological treatment, the neutralisation step including dissolving said residue in aqueous medium with the aid of an alkaline agent in such a way as to precipitate the heavy metals as salts thereof, preferably as carbonate and/or bicarbonate salts
• the heavy metals may in this way be separated from the liquor (e g. for recycle to the oxidation reactor) before the liquor is further processed by biological digestion of its organic content thereby substantially eliminating the heavy metals from the sludge produced by the biological digestion process
• the metals precipitation step serves both to recover catalyst values from the residue while at the same time serving as pre-treatment neutralisation of the residue feed to the biological digestion system
• the process of the present i nvention involves producing the polycarboxylic acid by the oxidation of a precursor thereof (such as p-xylene in the case of terephthalic acid) in a solvent comprising a lower (C2-C6) aliphatic monocarboxylic acid using an oxidising agent, usually air, oxygen enriched gas or substantially pure oxygen, in the presence of a dissolved catalyst system comprising heavy metals such as cobalt and manganese and bromine ions
• the polycarboxylic acid produced is extracted from the oxidation reactor in the form of a slurry of crystals in mother liquor mainly comprising the aliphatic carboxyhc acid and, following separation of the crystals from the mother liquor (e.g using one or more integrated solids-liquid separating and water washing units such as are described in EP-A-502628 and WO-A-93/24440), the mother liquor is divided into two fractions for recycle to the oxidation reactor and for purge respectively The mother liquor purge is concentrated by removal of the
• Figure 1 is a flow sheet illustrating a process for the production of terephthalic acid
• Figure 2 is a flow sheet illustrating a catalyst recovery system in accordance with the process of the present invention
• Figure 3 is a schematic view of a scrubber unit for effecting scrubbing of off-gas from a reactor used in the production of terephthalic acid
• terephthalic acid is produced in a reactor 1 0 by reacting p-xylene (pX) with air (02) in acetic acid solvent containing some water and a dissolved catalyst system comprising heavy metals, usually cobalt and manganese, and bromine as a promoter
• pX p-xylene
• air 02
• acetic acid solvent containing some water and a dissolved catalyst system comprising heavy metals, usually cobalt and manganese, and bromine as a promoter
• the p-xylene, acetic acid and catalyst may be supplied to the reactor via a feed mix drum 12 in which these components are mixed with recycled mother liquor (M/L) from mother liquor drum 14.
• M/L mother liquor
• the oxygen/air is introduced separately into the reactor 10 via a feed line or lines (not shown). Further details of the reaction are given in our prior European Patent Applications Nos.
• the reaction is carried out at a temperature of 170-230°C and a pressure of several kg/cm 2 to 100 kg/cm 2 , eg 8-30 kg/cm 2
• the terephthalic acid is withdrawn f rom the reactor 10 in the form of a slurry of terephthalic acid crystals in mother liquor comprising acetic acid and some water
• the slurry is then subjected to crystallisation in one or more crystallisation vessels (not shown) by reducing pressure and temperature so as to precipitate further terephthalic acid
• the slurry is typically at a temperature of the order of 70 to 200°C
• the slurry next undergoes an integrated solids-liquid separation process in which the crystals are separated from the mother liquor by filtration and are washed using water or acetic acid as the wash medium
• the solids-liquid separation process is carried out in unit 18 under pressure using a filter medium across which a
• the mother liquor filtrate derived from the solids-liquid separation unit 18 via line 22 largely consists of acetic acid (typically 85 - 95% by weight) and water (typically 5 - 15% by weight)
• the mother liquor also contains soluble organic by-products and intermediates produced in the reaction, reaction catalyst and residual terephthalic acid Also with this type of filter, the wash liquor often mixes with the mother liquor stream
• the recovered mother liquor is fed to a separator 24 in which the liquor is separated from the gas used to provide the pressure difference for the filtration and washing unit 18 (e.g nitrogen)
• the gas is recovered via line 26 and the mother liquor via line 28
• the mother liquor is split into two fractions, one of which is recycled via line 30 and mother liquor drum 14 back to the reactor and the second of which is purged from the process via line 32 in order to maintain the level of impurities in the system within acceptable limits
• the mother liquor recycle fraction is typically in the range 0 7 to 0 99 (e g 0 7 to 0.95) and the purge fraction
• the mother liquor purge is fed via line 32 to a stripper stillpot 38 in which a substantial part of the solvent (acetic acid) is boiled off and fed to an acetic acid recovery process (distillation column) via line 40
• the residual liquor is fed to evaporator 42 for concentration In evaporator 42, further acetic acid is driven off via line 44 for feed to acetic acid recovery in such a way as to leave the evaporator bottoms in a fluid state for supply of the resulting residue to a catalyst recovery waste treatment system (see Figure 2) via line 46
• the residue contains, inter alia, cobalt, manganese and bromine catalyst components together with acidic organic materials
• the residue obtained from the evaporator 42 is fed via line 46 to a stirred tank 50 together with a 5% w/w caustic soda solution supplied via line 52 and an aqueous medium supplied via lines 54, 56
• the various components are shown as being fed separately to the tank 50, the residue may be slur ⁇ ed up in a portion of the aqueous medium in a slurry receiver upstream of the tank 50
• At least part, e g at least 10% by weight, of the aqueous medium is advantageously constituted by mother liquor derived from plant for purifying crude terephthalic acid by hydrogenation of an aqueous solution of the crude acid in the presence of a noble metal catalyst such as platinum and/or palladium on an inert, e.g.
• the primary mother liquor may be subjected to cooling or evaporation to precipitate further, but less pure, terephthalic acid crystals which , following separation from the secondary mother liquor, may be slur ⁇ ed in acetic acid for recycle to the oxidation reactor
• the secondary mother liquor so obtained may then be used as the aqueous medium in the catalyst recovery system
• the aqueous medium may comprise both primary and secondary mother liquor
• the mother liquor supplied to the tank will comprise primarily water but will also contain small amounts of acetic acid, benzoic acid, paratoluic acid, terephthalic acid and manganese and cobalt acetates
• the tank 50 at a temperature of about 60°C to about 80°C, 5% w/w caustic soda is added to raises the pH to for example about 5 and the metals and organics are dissolved
• the liquor obtained overflows into a precipitation tank 58 via a ba
• some precipitation of the metals as oxides may also occur especially if caustic soda is used in tank 50
• the oxides are considered to be contaminants and consequently it may be preferred to substitute at least part of the caustic soda in tank 50 with sodium carbonate and/or bicarbonate derived from the same source as that supplied via line 104
• sodium carbonate and/or bicarbonate is then used to take the pH up to 6 and beyond
• pH increase is managed in this way, we find that the catalyst metal product recovered is in the form of freely flowing purple powder
• caustic soda is used to increase pH up to neutral pH, a material is obtained which is very different in appearance, both as a suspension and as a filtered solid, to the carbonate material In this case, a fine black suspension is obtained which is difficult to filter and
• the contents of the precipitation tank 58 are passed to solids-liquid separator unit 62 which may, for instance, comprise a cla ⁇ fier producing a solids-containing underflow and a liquor overflow
• the underflow is pumped to a sludge buffer tank (not shown) and subsequently passed to a filter press to produce a relatively dry cake containing the catalyst metal carbonates and/or bicarbonates
• the catalyst metals recovered in this way may be recycled via line 64 to the oxidation reactor 10 as their carbonates and/or bicarbonates or, alternatively, before recycle they may be converted to for example acetates by reaction with acetic acid
• the unit 62 may alternatively comprise for example a centrifuge or a candle filter unit in which case the filter press may be dispensed with
• the overflow 66 from the cla ⁇ fier is mixed with additional mother liquor supplied via lines 54, 68 and passes to a final neutralisation tank 70 where, if necessary, acid (e g a mineral acid such as HCI) or alkal
• the neutralisation carried out in tank 70 will usually involve adjustment of pH within the range 6 5 to 8, preferably 7, for compatability with the downstream processing of the liquor.
• downstream processing may take various forms such as anaerobic treatment (e.g. using the UASB process - upflow anaerobic sludge blanket) followed by aerobic treatment (e.g activated sludge treatment), or wet oxidation using for example the known ZIMPRO or LOPROX processes
• the carbonate used in the treatment of the residue may be derived from a scrubber
• Figure 3 illustrates one form of scrubbing unit for use in scrubbing effluent gas from plant for the production of terephthalic acid after treatment of the effluent gas by catalytic oxidation under elevated pressure to convert methyl bromide in the effluent to bromine and/or hydrogen bromide
• the effluent gas stream is derived from the overheads condensing system associated with a reactor for the production of terephthalic acid by liquid phase oxidation of p-xylene, for example by means of the process disclosed in our prior EP-A-498591 and/or EP-A-502628 the disclosures of which are incorporated herein by this reference
• the effluent gas stream is typically at a pressure of the order of 10 to 16 bara and a temperature of the order of 40°C and typically contains, inter alia volatile organics such as methyl bromide, acetic acid and benzene, together with
• the gas stream is preheated to a temperature of the order of 250 to 300°C, mixed with a combustion assistant and fed to a catalytic combustion unit
• a convenient combustion assistant is methyl acetate which is produced as a by-product in the terephthalic acid production process
• Various other combustion assistants may be used instead or in addition, especially those which contain oxygen
• the amount of combustion assistant introduced is such that the temperature of the combusted gas stream exiting the catalytic combustion unit is of the order of 400°C or greater
• the catalyst employed in the catalytic combustion unit may comprise any suitable oxidation catalyst to secure substantially total conversion of methyl bromide to bromine and HBr while also securing, in combination with the combustion assistant (where needed), substantially total oxidation of other organics such as acetic acid and production of heat to produce the desired exit temperature
• the catalyst employed comprises a noble metal catalyst such as platinum and/or palladium supported on an inert support
• the support may be ceramic or metallic in the form of a monolith or pellets
• the bromine containing gas is subjected to a two stage scrubbing treatment allowing the bromine to be substantially completely removed before the gas is discharged from the vessel
• the scrubbing liquid is preferably caustic soda, which is converted to sodium carbonate and bicarbonate in the scrubbing vessel as a result of absorption into the hydroxide of carbon dioxide contained in the effluent gas
• the sodium (b ⁇ )carbonate resulting from the scrubbing process is then used in the recovery of catalyst metals as described above thereby making efficient use of the scrubbing liquor
• 4-CBAIc is 4-carboxybenzyl alcohol
• TA is terephthalic acid
• 4CBA is 4-carboxybenzaldehyde
• IPA is isophthalic acid
• OPA is orthophthalic acid
• BA is benzoic acid
• TMA is tnmellitic acid
• BPTC biphenylt ⁇ carboxylic acid
• p-TOL is paratoluic acid
• the resulting solution was transferred to the precipitator vessel where it was combined with a feed having a composition corresponding to the caustic scrubber liquor recovered (line 104) from the offgas scrubber system described with reference to Figure 3, namely 3 2% w/w Na 2 C0 3 /4 8% w/w NaHC0 3
• the resulting precipitate was then recovered by filtration
• the laboratory unit was operated under different temperature, pH and residence time conditions as set out below in Table 2
• the filter cake recovered from filtration was dried in air at room temperature and then analysed to determine the amounts of metals and organics present and particle size measurements were also made using a Coulter LS 130 Laser diffraction and PIDS Particle Size Analyser fitted with the Fluid Module, as supplied by Coulter Electronics Limited of Northwell Drive, Luton, Bedfordshire, England, using slurry samples of the recovered catalyst in the process filtrate as the matrix Metals contents were determined using atomic absorption and organics were quantified using high pressure liquid chromatography
• the volume mean particle size is the mean size of the particles in the sample examined on the basis of the volume of material accounted for rather than the number of particles
• the 5% quantile mentioned is a measure of the fines content of the sample It is that particle size (in microns) below which 5% of the total sample lay in the particle size distribution measured, again on a volume rather than number basis Thus a low 5% quantile figure indicates a higher fines content It is a more sensitive measure of the small particles in a sample than mean
• Table 3 reveals that use of caustic soda to adjust the dissolver pH to 6 before the addition of carbonate/bicarbonate produces a material containing significantly higher levels of organic impurities, considerably lower particle size with a higher proportion of fines, and containing more iron.
• Comparison of Examples 1 and 2 with Examples 5 and 6 reveals that use of less caustic soda to raise the dissolver pH to 4.5 produces a material of equivalent particle size and organics content but the iron content is still higher.
• Example A The procedure described in Example A above was carried using the same residue composition using, in Run 1 , 5% w/w NaOH in the dissolver vessel and 3.2% w/w Na 2 C0 3 /4.8% w/w NaHC0 3 (representative of the recovered scrubber liquor composition) in the precipitator vessel as in Example A and, in Run 2, using the 3.2% w/w Na 2 C0 3 /4.8% w/w NaHC0 3 composition in both vessels.
• Table 4 Tables 5 and 6 respectively give the analytical results obtained from Runs 1 and 2 and the metals mass balance. Table 4
• Example A the residue sample was dissolved up using demineralised water in the dissolver vessel.
• Experimental runs using the same batch of residue sample, were carried out using: Run 1 - demineralised water, and Run 2 - a sample of an aqueous mother liquor (PPML) typically derived as a purge from the hydrogenation stage of a commercially operating terephthalic acid production plant In both runs, the amount of water added (either as demineralised water or in the form of aqueous mother liquor) were substantially the same
• Example A The procedure of Example A was carried out, using the same residue and with water as the diluent, in order to illustrate the effect of temperature on the precipitation stage, particularly in terms of the amount of iron contaminant present in the Co/Mn product recovered.
• the results obtained are given in Table 9 below Table 9
• the temperature at which precipitation is carried out has a marked affect on the amount of iron contaminating the recovered catalyst product For this reason, it is preferred to operate the precipitation stage at a temperature of no greater than 70°C, more preferably no greater than 65°C and typically in the range of 20 to 60°C
• the temperature of the precipitation stage may be controlled by the temperature of the alkaline agent (e g scrubber liquor) introduced into the precipitation stage
• the precipitation vessel may be cooled during the precipitation process to maintain a temperature consistent with reduced iron recovery in the recovered catalyst product

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• 1997
  • 1997-08-08 WO PCT/GB1997/002158 patent/WO1998008605A1/en active IP Right Grant
  • 1997-08-08 BR BR9711388-3A patent/BR9711388A/pt not_active Application Discontinuation
  • 1997-08-08 KR KR10-1999-7001684A patent/KR100487035B1/ko not_active IP Right Cessation
  • 1997-08-08 EP EP97935690A patent/EP0921856A1/de not_active Withdrawn
  • 1997-08-08 DE DE69739649T patent/DE69739649D1/de not_active Expired - Lifetime
  • 1997-08-08 AU AU38584/97A patent/AU3858497A/en not_active Abandoned
  • 1997-08-08 TR TR1999/00421T patent/TR199900421T2/xx unknown
  • 1997-08-08 JP JP51106398A patent/JP3421057B2/ja not_active Expired - Fee Related
  • 1997-08-08 CN CNB971990816A patent/CN1292833C/zh not_active Expired - Fee Related
  • 1997-08-08 CA CA002264611A patent/CA2264611C/en not_active Expired - Fee Related

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