EP0879221A1 - Production d'acides carboxyliques aromatiques - Google Patents

Production d'acides carboxyliques aromatiques

Info

Publication number
EP0879221A1
EP0879221A1 EP97900351A EP97900351A EP0879221A1 EP 0879221 A1 EP0879221 A1 EP 0879221A1 EP 97900351 A EP97900351 A EP 97900351A EP 97900351 A EP97900351 A EP 97900351A EP 0879221 A1 EP0879221 A1 EP 0879221A1
Authority
EP
European Patent Office
Prior art keywords
water
acid
monocarboxylic acid
stream
bromine
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97900351A
Other languages
German (de)
English (en)
Inventor
Ian Charles Jeffery
John Arthur Turner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
EIDP Inc
Original Assignee
EI Du Pont de Nemours and Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9601493.1A external-priority patent/GB9601493D0/en
Priority claimed from GBGB9602050.8A external-priority patent/GB9602050D0/en
Priority claimed from GBGB9602458.3A external-priority patent/GB9602458D0/en
Priority claimed from PCT/GB1996/001261 external-priority patent/WO1996039595A1/fr
Priority claimed from GBGB9620494.6A external-priority patent/GB9620494D0/en
Application filed by EI Du Pont de Nemours and Co filed Critical EI Du Pont de Nemours and Co
Publication of EP0879221A1 publication Critical patent/EP0879221A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
    • F23G7/06—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of waste gases or noxious gases, e.g. exhaust gases
    • F23G7/07—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of waste gases or noxious gases, e.g. exhaust gases in which combustion takes place in the presence of catalytic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8659—Removing halogens or halogen compounds
    • B01D53/8662—Organic halogen compounds
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
    • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
    • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
    • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2209/00—Specific waste
    • F23G2209/14—Gaseous waste or fumes
    • F23G2209/142—Halogen gases, e.g. silane
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J2215/00—Preventing emissions
    • F23J2215/30—Halogen; Compounds thereof
    • 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

Definitions

  • This invention relates to a process for the production of an aromatic carboxylic acid , especially dicarboxylic acids such as terephthalic acid and isophthahc acid, by the liquid-phase oxidation of a precursor (e g p-xylene) of said carboxylic acid I n a widely practised method of producing terephthalic acid , p-xylene is oxidised under elevated temperature and pressure conditions in a liquid phase reaction using air or other source of oxygen , the oxidation being carried out in a reaction solvent comp ⁇ sing a C2 - C6 monocarboxylic acid, such as acetic acid , in the presence of a catalyst system comprising one or more heavy metal compounds and one or more promoter compounds including bromine Water is present in the reaction solvent and is formed as a result of the oxidation reaction The oxidation reaction is accompanied by evolution of a reaction offgas which generally comprises inter alia nitrogen unreacted oxygen , carbon dioxide , carbon monoxide and methyl bromide Because the reaction
  • the present invention is concerned with the treatment of the offgas derived from the oxidation reactor
  • a process for the production of an aromatic carboxylic acid comprising oxidising a precursor of the aromatic carboxylic acid in a liquid-phase C2 - C6 monocarboxylic acid solvent containing water and in the presence of a catalyst system containing one or more heavy metals and bromine, withdrawing from the reaction an overheads gaseous stream at elevated pressure containing inter alia water, monocarboxylic acid and gaseous by-products including methyl bromide and feeding the high pressure gaseous stream to means for removing said monocarboxylic acid from the overheads stream to produce a high pressure monocarboxylic acid-depleted gaseous stream containing inter alia water and methyl bromide; effecting high temperature combustion of the high pressure monocarboxylic acid-depleted gaseous stream so as to convert the methyl bromide to bromine and/or hydrogen bromide; and passing the treated gas containing bromine and/or hydrogen bromide to an energy recovery system
  • the pressure and temperature conditions are controlled so as to prevent condensation of bromine and/or hydrogen bromide on passage through the energy recovery system
  • the gas stream is passed to the energy recovery system without scrubbing the gas stream
  • the temperature of the treated gas stream is maintained and corrosion is suppressed by control of the temperature and pressure conditions to ensure the potentially corrosive bromine compound(s) remain in the gaseous phase during passage through the energy recovery system.
  • the energy recovery system eg a gas turbine
  • the energy recovery system may be fabricated using more conventional materials such as high chrome or austenitic stainless steels.
  • At least part of the gas stream Prior to introduction into the energy recovery system, at least part of the gas stream may be used to preheat the gas stream upstream of the combustion step.
  • the treated gas is treated to remove substantially all of the bromine species and/or hydrogen bromide.
  • the monocarboxylic acid is removed from the overheads gas stream to such an extent that the water content of the resulting gas stream exceeds its monocarboxylic acid content.
  • the means for removing monocarboxylic acid from the overheads stream conveniently includes a separation column in which water/monocarboxylic acid distillation is effected e g a packed or trayed distillation or rectification column capable of effecting a separation whereby at least 95% , more preferably about 98% and most prefera bly at least about 99%, by weight of the monocarboxylic acid solvent is removed from the gaseous overheads stream from the oxidation reaction
  • the separation column is preferably operated at the same, or close to the, pressure at which the oxidation reaction is conducted
  • the separation column may be mounted separately from the oxidation reactor with suitable pipework connecting the reactor to the column for the supply of the overheads stream to the latter
  • the separation column may be mounted directly above and integrated with the oxidation reactor
  • the high pressure gaseous overheads stream derived from the oxidation reactor vapor (which typically contains, in addition to water and monocarboxylic acid , residual oxgyen by-product gases such as methyl bromide and methyl acetate formed as a result of the oxidation , carbon dioxide, carbon monoxide and nitrogen) is passed to the separation column to remove most of the monocarboxylic acid solvent Consequently, the offgas stream discharged from the separation column will be at high pressure and will contain, in addition to a significant amount of water in the form of steam, residual oxgyen , by-product gases such as such as methyl bromide (typically present in an amount in the range of 25 to 125 ppm) and methyl acetate formed as a result of the oxidation, carbon dioxide , carbon monoxide and nitrogen As such therefore , the high pressure offgas stream discharged from the separation column constitutes a significant source of energy which can be extracted by suitable means such as an expander
  • the residual oxygen content of gaseous overheads stream withdrawn from the oxidation reactor constitutes about 3 to 8% by volume of the non-condensibles present in the overheads stream
  • the liquid phase oxidation process is carried out in such a way that the amount of residual oxygen in the offgas is sufficient under normal operating conditions to avoid the need to supply further oxygen under pressure to the offgas treatment process while ensuring that there is substantially no risk of oxygen starvation in the offgas treatment without giving rise to potentially hazardous conditions that can obtain if the gaseous overheads stream contains excessive oxygen
  • scrubbing of the high pressure monocarboxylic acid-depleted gaseous stream with liquor may be effected upstream of the combustion zone in order to recover at least in part any volatile precursor or precursors of said aromatic carboxylic acid which would otherwise be entrained in the gaseous stream passing to the combustion step
  • the means for removing said monocarboxylic acid from the overheads stream comprises a separation column
  • such scrubbing may be effected within the separation column , conveniently using water which has been recovered from the treated gas after passage through the energy recovery system and may optionally be preheated upstream of said scrubbing
  • the combustion step (preferably catalytic combustion) of the present invention serves to eliminate combustible components and carbon monoxide present in the high pressure offgas stream before it is directed to the energy recovery means and contributes to elevation of the offgas temperature prior to the energy recovery system thereby increasing power recovery and avoiding dewing of corrosive bromine species e g HBr in the system Additional temperature elevation may be provided by indirect heating via steam or a fired heater, direct firing of fuel and/or injection of a support fuel such as methyl acetate methanol methane , propane butane, etc
  • the offgas stream is preferably contacted with a suitable catalyst so that at least a substantial proportion of the combustible components and carbon monoxide is converted to environmentally acceptable forms
  • the combustion step also results in conversion of methyl bromide to bromine and/or hydrogen bromide which can be highly corrosive but, in accordance with the invention are passed through the energy recovery system under controlled conditions instead of being scrubbed from the offgas thus avoiding the inevitable substantial reduction m the temperature which would be necessary if scrubbing of the offgas is to be undertaken before passage through the energy recovery means coupled with the necessary reheating prior to passing the scrubbed offgas stream to the energy recovery system
  • the offgas stream may be condensed to recover water for recycle within the overall process for the production of the aromatic carboxylic acid
  • the recovered water may for instance be used as a reflux in the separation column for separating the monocarboxylic acid from the high pressure gaseous overheads stream, and/or solvent for dissolution of crude carboxylic acid in preparation for purification of the aromatic carboxylic acid by hydrogenation , for example in the manner disclosed in our prior EP-A-498591 and/or EP-A-502628
  • the offgas stream may be desuper eated to a temperature corresponding to or close to the dewpoint of the stream and scrubbed to remove the bromine and HBr components (e.g . using an aqueus caustic soda) while retaining the water content within the offgas stream
  • the scrubbed offgas stream at the dewpoint temperature may then be condensed to remove its water content.
  • the offgas stream obtained following separation of the monocarboxylic acid in said separation column is at a pressure in the range of 5 to 25 bara (for instance between 10 and 16 bara) and a temperature of the order of 160 to 200°C (e.g . about 177°C and 14 bara) .
  • the offgas stream from the separation column Prior to combustion thereof, the offgas stream from the separation column is conveniently heated directly or indirectly (eg by means of high pressure steam , heating oil , heat exchange between the offgas stream upstream and downstream of the combustion step, passage through a fuel-fired heater or by direct firing of fuel into the gas stream) to an elevated temperature, usually in the range of 250 to 450°C (typically about 300°C)
  • combustion assistant is preferably pre-mixed with the gas stream prior to entry into the combustion zone.
  • the combustion assistant is preferably, but need not necessarily be, one including one or more oxygen atoms per molecule.
  • Various assistants may be used, eg methanol , methyl acetate, hydrogen, natural gas, methane , propane, butane or mixtures thereof
  • methyl acetate it is conveniently derived from the terephthalic acid production process as it is generated as a by-product of the liquid phase oxidation of p-xylene in acetic acid solvent.
  • methane it may be derived from an anaerobic process for the treatment of effluent produced in the manufacture of the aromatic carboxylic acid, e.g . terephthalic acid. If desired, additional air may be introduced into the combustion zone to promote oxidation.
  • the combustion step is carried out with regard to ensuring that, during the subsequent expansion on passage through the energy recovery system bromine and HBr derived from the methyl bromide constituent of the effluent gas stream remain in the gas phase thereby avoiding dew point corrosion conditions in the energy 5 recovery system
  • the combustion step is carried out in the presence of a catalyst and the temperature of the treated offgas stream exiting the oxidation zone will be in the range from about 250 to about 700°C , e g 350 to 700°C , and will depend on whether or not the gas stream is preheated before introduction into the catalytic oxidation zone and whether or not a combustion assistant is employed
  • a combustion assistant is employed for
  • the catalytic oxidation may be conducted in such a way that the temperature of the treated gas exiting the catalytic oxidation zone is of the order of 400°C or greater Where no combustion assistant is used , or where the combustion assistant is one which is easily or relatively easily oxidised (e g methanol , methyl acetate or hydrogen) the exit temperature may be in the range of about 250 to about
  • the temperature of the gas stream following combustion will typically be in excess of 700 ⁇ > C usually in excess of 800°C and conveniently the liquid phase oxidation process is operated so that the oxygen content of the gaseous overheads stream withdrawn from the oxidation reactor is increased eg in excess of 5 5% by volume relative to the non-condensible components in the overheads stream thereby avoiding the need for separate supply of pressurised oxygen to the combustion step under normal operating conditions of the liquid phase oxidation process
  • the combustion process will be carried out using operating 0 conditions (eg temperature, space velocity, catalyst composition) selected to ensure that methyl bromide is substantially completely converted to HBr and Br 2 , the aim being to minimise or avoid the production of underconversion brominated aromatic compounds which have high dew points
  • operating 0 conditions eg temperature, space velocity, catalyst composition
  • pressure and temperature conditions are controlled so as to prevent condensation of the HBr and/or Br 2 5 compound(s) on passage through the energy recovery system
  • the energy recovery system may produce an output in mechanical or electrical form and may for instance be used to power other equipment in the production plant such as a compressor forming part of the system for feeding air oxygen-enriched air oxygen-containing gas or oxygen to the reactor in which the liquid phase oxidation is carried out
  • an aromatic carboxylic acid such as terephthalic acid
  • a process for the production of an aromatic carboxylic acid comprises oxidising a precursor of said aromatic carboxylic acid (e g paraxylene) in a reaction medium comprising a monocarboxylic acid (e g acetic acid) to produce a slurry of crude aromatic carboxylic acid in said aliphatic acid, recovering the crude acid from said slurry, dissolving the recovered crude acid in water, purifying the crude acid by a reaction comprising contacting the solution with hydrogen , and separating the purified acid from the mother liquor component of said solution , the steps of withdrawing from the reaction zone a high pressure gaseous overheads stream containing inter alia monocarboxylic acid water and methyl bromide, separating substantially all of the monocarboxylic acid from said overheads stream in a separation column to which aqueous mother liquor obtained from said purification reaction is also supplied whereby a high pressure offgas stream is obtained which contains inter
  • the treated gas has a bromine content of less than 4 ppm vol/vol
  • the aqueous mother liquor separated from the purified aromatic acid e g by means of filtration equipment such as that disclosed in our prior International Patent Application No WO 93/24440, contains various impurities, reaction intermediates and also said aromatic carboxylic acid in suspended and dissolved forms
  • impurities, reaction intermediates and dissolved aromatic carboxylic acid content can be separated from the water content of the aqueous mother liquor and returned to the oxidation reactor as bottoms product from the column along with the monocarboxylic acid recovered by means of the column
  • the mother liquor recovered from the purification reaction may be treated, e g by cooling or evaporation , to recover therefrom crystals of less pure aromatic carboxylic acid , and at least part of the mother liquor supplied to the separation column may comprise the secondary mother liquor obtained following such treatment
  • primary mother liquor recovered from the purification reaction may be recycled to the separation column without cooling the same to any signficant extent although it may be filtered before introduction into the separation column in order to remove any suspended fines
  • the crude acid is separated from said monocarboxylic acid by replacing the monocarboxylic acid in said slurry with water to produce a wet deposit of crude acid containing water for use in the subsequent purification of the crude acid (i e by hydrogenation of an aqueous solution formed from said wet deposit) , replacement of the monocarboxylic acid with water being effected by means of
  • the integrated separation and water washing filter may comprise a gas pressurised belt filter, a gas pressurised rotary cylindrical filter, a hydraulically pressurised multi-celled pressure drum filter or a centrifuge provided with washing facilities I n each instance, the washing operation may be carried out in stages, preferably in countercurrent fashion so that the filter cake is washed with water of increasing purity as it advances downstream from the location at which separation of the crystals from the mother liquor takes place
  • the filter operates with a pressure differential in the range of 0 1 to 1 5 bara (preferably between 0 3 and 7 bara), preferably such that the pressure on the lower pressure side thereof is no less than one bara although we do not exclude the possibility of the lower pressure side being at sub-atmospheric pressure.
  • Another aspect of the invention is concerned with the removal from the gas stream of bromine and/or hydrogen bromide following high temperature particularly with the aim of processing the gas stream to remove the bromine components so that any discharge to atmosphere is substantially free of such components
  • processing may for instance be effected by desuperheating the gas stream using water and contacting the gas stream with a suitable aqueous scrubbing media in a scrubbing section to remove the Br ; and HBr HBr for instance may be removed by countercurrent contact with HBr solution or it may be removed simply by contact with water, e g a water spray, while at the same time desuperheating the treated gas
  • Contacting the treated gas with HBr solution is for instance appropriate where the aim is to recover HBr for reuse as part of the catalyst system employed in the oxidation reactor.
  • water may be used. If used , it is preferred that sufficient water is employed to irrigate the pipeline transporting the water treated gas downstream and thereby prevent corrosion problems.
  • Br 2 may be removed by countercurrent contact with an aqueous solution of components such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium bromide , sodium formate, sodium sulphite , urea or mixtures containing any combination of two or more of these compounds (e.g sodium hydroxide and sodium sulphite).
  • the aromatic carboxylic acid may be terephthalic acid, in which the case the precursor thereof which is oxidised to produce terephthalic acid will be p-xylene
  • the aromatic carboxylic acid may be isophthalic acid (precursor m-xylene) or 2,6-naphthalene-dicarboxylic acid (precursor 2,6-dimethylnaphthalene).
  • the oxidation reaction is typically carried out at a temperature in the range of about 120°C to about 240°C and a pressure which is at least sufficient to maintain the reaction mixture under liquid phase conditions, typically 5 bara to 30 bara
  • the promoter component of the catalyst system contains bromine and is typically in the form of hydrogen bromide, molecular bromine, sodium bromide and/or suitable organic bromide compounds well known to those in the art.
  • the heavy metal components of the catalyst system usually in the form of cobalt and/or manganese compounds, for example cobalt and/or manganese carbonate.
  • an aromatic carboxylic acid such as terephthalic acid
  • a process for the production of an aromatic carboxylic acid comprises oxidising a precursor of said aromatic carboxylic acid (e.g. paraxylene) in a reaction medium comprising an aliphatic monocarboxylic acid (e.g acetic acid) to produce a slurry of crude aromatic carboxylic acid in said aliphatic acid, and replacing the aliphatic monocarboxylic acid in said slurry with water to produce a wet deposit of crude aromatic carboxylic acid containing water for use in the subsequent purification of the crude carboxylic acid (e .g.
  • processing of the overheads stream conveniently includes the step of separating water and aliphatic monocarboxylic acid in a separation column to allow recovered aliphatic acid to be recycled to the reactor
  • aqueous mother liquor derived from purification of the crude aromatic carboxylic acid is also supplied to the distillation column , preferably as reflux, whereby impurities, reaction intermediates and aromatic carboxylic acid present in the aqueous mother liquor are passed to the oxidation reaction together with aliphatic monocarboxylic acid and the water content of the gaseous effluent stream includes water derived from said aqueous mother liquor
  • FIG. 1 is a schematic flow diagram illustrating one embodiment of the invention as applied to the treatment of an effluent gas stream derived from plant for the production of terephthalic acid
  • Figure 2 illustrates a scrubbing unit for reducing the bromine/hydrogen bromide content of the effluent gas
  • the effluent gas stream entering the treatment plant via line 10 is derived from a distillation column or rectifier D associated with a reactor R for the production of terephthalic acid by liquid phase oxidation of p-xylene , for example by means of the process disclosed in our p ⁇ or EP-A-498591 and/or EP-A-502628
  • catalysed liquid phase oxidation of paraxylene is carried out in a solvent comprising acetic acid to produce terephthalic acid, the catalyst system comprising heavy metals such as cobalt and manganese and bromine promoter
  • the temperature of the liquid phase reaction is controlled by withdrawing a vapour phase overheads stream from the reactor comprising the acetic acid , water, gaseous by-products including methyl bromide and methyl acetate, and gases such as nitrogen, carbon monoxide carbon dioxide and unreacted oxygen Following processing involving removal of a large proportion of the acetic acid, an offgas or gas
  • Processing of the overheads stream in the illustrated embodiment comprises passing the gaseous stream to the column D which serves to effect the separation of acetic acid from water
  • Column D is operated so that the heavy components such as acetic acid are recovered as a liquid phase bottoms product while the light components such as water, gaseous by-products such as methyl bromide and methyl acetate and gases such as nitrogen , carbon monoxide, carbon dioxide and oxygen are recovered as a gaseous phase tops product constituting the high pressure gaseous offgas stream which is to be treated
  • Water in the resulting offgas stream is in the form of steam
  • the overheads stream withdrawn from the oxidation reactor may contain acetic acid and water in the proportion of 70 to 95% acetic acid to 30 to 5% water (on a weight to weight basis)
  • the high pressure offgas stream recovered from the column D will typically contain acetic acid and water in the proportion of 0 5 to 1 0 wt% acetic to 99 5 to 99 0 wt% water as steam
  • the acetic acid-rich bottoms product from the column D is returned to the oxidation reactor R via line 1 1
  • This bottoms product will comprise acetic acid and some water and may also contain other organics such as precursors, e g paratoluic acid , of terephthalic acid routed to the column D in the manner described below
  • the tops product namely the high pressure offgas comprising steam as a primary component, is removed via line 1 0
  • a feature of the process disclosed in EP-A-498591 and EP-A-502628 is the handling of the aqueous mother liquor produced in the purification process
  • the purification process involves the hydrogenation of an aqueous solution of crude terephthalic acid obtained from the oxidation of paraxylene, crystallisation of purified terephthalic acid and separation of the purified crystals from the aqueous mother liquor
  • the resulting aqueous mother liquor contains impurities and intermediates such as paratoluic acid and in prior processes was treated as a waste
  • EP-A-498591 and EP-A-502628 teach recycle of at least part of this primary mother liquor to the distillation column associated with the oxidation reactor conveniently as reflux in such a way that high boiling point impurities such as paratoluic acid are recovered in the acetic acid-rich bottom product withdrawn from the column for recycle to the oxidation reactor
  • the mother liquor recovered from the purification process may be recycled to the distillation column with or without treatment
  • Such treatment where employed,
  • the integrated solids separation and water washing apparatus may comprise a belt filter unit operated with the slurry side under superatmospheric conditions, or a pressurised rotary cylindrical filter unit operated with the slurry side under superatmospheric conditions, or a pressure drum filter unit (e g a BHS-Fest pressure filter drum formed with a plurality of slurry receiving cells in which the mother liquor is displaced from filter cake by water under hydraulic pressure supplied to the cells)
  • a pressure drum filter unit e g a BHS-Fest pressure filter drum formed with a plurality of slurry receiving cells in which the mother liquor is displaced from filter cake by water under hydraulic pressure supplied to the cells
  • the effluent gas stream is typically at a pressure of the order of 10 to 16 bara and a temperature of the order of 170 to 190°C
  • the gas stream is preheated in heat exchanger 12 using for example high pressure steam as the heat source Typically the temperature of the gas stream following such heat exchange is of the order of 250 to 450°C , preferably 300 to 400°C
  • the gas stream then enters a mixer 14 into which a combustion assistant is also introduced via line 16 , the combined gas stream and combustion assistant then being fed to a catalytic combustion unit 1 8 with a space velocity of the order of 1 0 3 to 5 x 1 0 4 h ' preferably 5 x 1 0 3 to 2 x 10* h '
  • 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 - eg methanol
  • the amount of combustion assistant introduced is such that the temperature of the combusted gas stream exiting the catalytic combustion unit 18 ts of the order of 400°C or greater, typically of the order of 480°C
  • a feedback arrangement comprising valve 20 in line 16, temperature sensor 22 and appropriate control equipment is used to regulate the supply of combustion assistant to the mixer 14 so that the desired temperature is maintained at the exit of the unit 18
  • the catalyst employed in the catalytic combustion unit 1 8 may comprise any suitable oxidation catalyst, usually in solid form , 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, elimination of carbon monoxide 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 a suitable support which may be inert
  • the support may be ceramic or metallic in the form of a monolith or pellets
  • Suitable commercial catalysts are available from catalyst manufacturers such as Johnson Matthey (e g Halocat AH/HTB-1 0 or LHC catalyst) , Allied Signal/Degussa (e g HDC-2 or T2-HDC catalyst) and Engelhard (e g VOCAT 300H or VOCAT 450H catalyst)
  • the treated gas stream typically has a temperature of the order of 400 to 700°C and a pressure only marginally lower than the untreated gas stream , ie about 9 5 to 15 5 bara in the case where the untreated gas stream has a pressure of the order of 1 0 to 16 bara
  • the treated gas is then passed through expander 24 in which the energy content of the gas stream is converted into mechanical power which, via shaft 26 , can be employed appropriately within the terephthalic acid production process, for instance as power input for an air compressor for feeding air under pressure to the oxidation reactor of the production process or for generation of electric power for distribution either within the plant or to other users
  • the gas stream temperature is typically of the order of 140 to 220°C (eg about 170 to 200°C) and its pressure is near atmospheric, eg about 1 2 bara
  • the temperature and pressure conditions employed are such that the bromine and HBr derived from methyl bromide in the course of the catalytic combustion remain in the gas phase thereby avoiding
  • the gas stream is processed to remove the bromine components so that any discharge to atmosphere is substantially free of such components
  • processing may for instance be effected by desuperheating the gas stream in unit 28 using water and contacting the gas stream with a suitable aqueous scrubbing media in a scrubbing section 30 to remove the Br 2 and HBr HBr for instance may be removed by countercurrent contact with HBr solution and Br 2 may be removed by countercurrent contact with an aqueous solution of components such as sodium hydroxide , sodium carbonate, sodium bicarbonate , sodium bromide, sodium formate , sodium sulphite or mixtures containing any combination of two or more of these compounds (e g sodium hydroxide and sodium sulphite)
  • the water used for desuperheating may also be employed in the scrubbing section
  • the cleaned offgas typically containing 40 to 70% by weight water vapour
  • a cooling water exchanger 32 for example, to recover a major proportion and preferably substantially all of the water there
  • the scrubbing liquid employed may be any suitable liquid capable of removing bromine from the effluent gas, including the chemicals specified above
  • the scrubbing liquid is circulated around a loop including the upper section 52, exit line 62, pump 64 and inlet line 66 so that the liquid flows countercurrent to the direction of gas flow passing up through the vessel 50
  • a second recirculatory flow of scrubbing liquid is established in the lower part of the vessel 50 again in countercurrent relation to the gas flow, by means of outlet line 68, pump 70 and return line 72
  • Spent scrubbing liquid is purged from the system via line 74 and make-up liquid is supplied via line 76
  • the amount of scrubbing liquid pumped through the vessel per unit time will generally be far in excess of that being purged, e g a ratio of at least 20 1 e g at least 30 1 (typically of the order of 40 1 )
  • a purge line 78 interconnects the outlet of pump 64 and line 72 so that scrubbing liquid collecting
  • the HBr scrubbing process may be integrated with the Br 2 process by incorporating a further packing section into the scrubbing tower beneath the sections 52 and 54 so that the gas stream initially passes through the HBr scrubbing section
  • the scrubbing liquor may be an aqueous solution of HBr flowing in a recirculatory loop as described above in relation to sections 52 and 54 with suitable purging and make-up of the loop
  • the HBr purge may for instance be supplied to catalyst make up From the foregoing , it will be seen that 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 may be any suitable liquid for effecting bromine removal , with alkali metal compounds being preferred Where for example the liquid is caustic soda , this is converted to sodium carbonate and bicarbonate in the scrubbing vessel as a

Abstract

On traite un effluent gazeux contenant des constituants organiques dont un acide carboxylique aliphatique et du bromure de méthyle, des gaz dont l'azote, l'oxygène, le monoxyde et le dioxyde de carbone et de l'eau, en particulier quand ce gaz provient de la production d'un acide carboxylique aromatique tel que l'acide téréphtalique, dans le but d'éliminer sensiblement tout l'acide carboxylique aliphatique qu'il contient, et on lui fait subir ensuite une combustion à haute température, éventuellement en présence d'un catalyseur d'oxydation ou d'un auxiliaire de combustion, ou des deux, pour effectuer la conversion complète du bromure de méthyle qu'il contient en HBr ou Br2, ou les deux. Le courant de gaz ainsi obtenu est transmis à un appareil de conversion d'énergie tel qu'une turbine à gaz, après quoi il est épuré pour éliminer le HBr ou le Br2, ou les deux.
EP97900351A 1996-01-25 1997-01-15 Production d'acides carboxyliques aromatiques Withdrawn EP0879221A1 (fr)

Applications Claiming Priority (13)

Application Number Priority Date Filing Date Title
GBGB9601493.1A GB9601493D0 (en) 1996-01-25 1996-01-25 Effluent gas treatment
GB9601493 1996-01-25
GBGB9602050.8A GB9602050D0 (en) 1996-02-01 1996-02-01 Effluent gas treatment
GB9602050 1996-02-01
GB9602458 1996-02-07
GBGB9602458.3A GB9602458D0 (en) 1996-02-07 1996-02-07 Effluent gas treatment
PCT/GB1996/001261 WO1996039595A1 (fr) 1995-06-05 1996-05-28 Traitement de gaz d'effluent
WOPCT/GB96/01261 1996-05-28
GBGB9620494.6A GB9620494D0 (en) 1996-10-02 1996-10-02 Production of aromatic carboxylic acids
GB9620494 1996-10-02
US2778496P 1996-10-04 1996-10-04
US27784P 1996-10-04
PCT/GB1997/000104 WO1997027168A1 (fr) 1996-01-25 1997-01-15 Production d'acides carboxyliques aromatiques

Publications (1)

Publication Number Publication Date
EP0879221A1 true EP0879221A1 (fr) 1998-11-25

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP97900351A Withdrawn EP0879221A1 (fr) 1996-01-25 1997-01-15 Production d'acides carboxyliques aromatiques

Country Status (3)

Country Link
EP (1) EP0879221A1 (fr)
CA (1) CA2273958A1 (fr)
WO (1) WO1997027168A1 (fr)

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