SE187964C1

SE187964C1 -

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Publication number: SE187964C1
Authority: SE
Publication date: 1963-01-01

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Uppfinnare: D E Burney, J 0 Knobloch och H P Liao Prioritet begard frdn den 19 november 1957 (USA) Foreliggande uppfinning avser ett forbattrat forfarande for separering av blandningar som innehaller bensenpolykarbonsyror, av vilka minst en men icke alla kan bilda en intramolekylar anhydrid. Inventors: D Burney, J. Knobloch and H. P Liao Priority Required as of November 19, 1957 (USA) The present invention relates to an improved process for separating mixtures containing benzene polycarboxylic acids, at least one but not all of which may form an intramolecular anhydride.

Den expanderande plastindustrien her medfort ett alltmer okande behov av olika bensenpolykarbonsyror. Speciellt o-ftalsyra, isoftalsyra, tereftalsyra och trimellitsyra anvandas med gott result:at Arid framstallning av mjukningsmedel, alkydfarger och hartser samt for framstallning av polyesterfilmer och -fibrer av hog kvalitet. Dessa produkter erfordra emellertid ofta, att bensenpolykarbonsyran (den »aromatiska syram) foreligger i ren form och aven fri Iran isomera och homologa aromatiska syror. Genom att bensenpolykarbonsyror vanligen framstallas genom en oxidationsreaktion, varvid motsvarande polyalkylsubstituerade aromatiska kolvate anvandes sasom utgangsmaterial, ha de narliggande kokpunkterna fiOr de olika polyalkylsubstituerade aromatiska foreningarna effektivt forhindrat isolering och oxidation av ett enda polyalkylsubstituerat aromatiskt kolvate sasom en vag till framstallning av en enda ren bensenpolykarbonsyra. Det är darfor ntidvandigt aft oxidera en blandning av alkylsubstituerade aromatiska kolvaten °ch att darefter separera blandningen av bensenpolykarbonsyror. Fiera separeringsforfaranden, vilka innefatta fraktionerad destillation, selektiv extraktion och selektiv reaktion med alkoholer eller kvavebaser, ha foreslagits eller anvants. Fastan vissa av dessa forfaranden go forhallandevis gott resultat, ha sadana olagenheter som korroderande syraangor eller syralOsningar och den dyrbara utrustningen och de dyrbara reaktionskomponenterna skapat ett behov av forbattrade forfaranden for separering av aromatiska syror. The expanding plastics industry here has led to an ever-increasing need for various benzene polycarboxylic acids. Especially o-phthalic acid, isophthalic acid, terephthalic acid and trimellitic acid are used with good results: at Arid production of plasticizers, alkyd paints and resins and for the production of high quality polyester films and fibers. However, these products often require that the benzene polycarboxylic acid (the "aromatic acid") be present in pure form and also free Iran isomeric and homologous aromatic acids. Because benzene polycarboxylic acids are usually produced by an oxidation reaction, using the corresponding polyalkyl-substituted aromatic hydrocarbons as starting materials, the adjacent boiling points of the various polyalkyl-substituted aromatic compounds have effectively prevented the isolation and oxidation of a single carbonyl arbyl monoalkylene aroma to a polyalkyl aroma. It is therefore necessary to oxidize a mixture of alkyl-substituted aromatic hydrocarbons and then separate the mixture of benzene polycarboxylic acids. Several separation processes, which include fractional distillation, selective extraction and selective reaction with alcohols or nitrogen bases, have been proposed or used. Although some of these processes have been relatively successful, such anomalies as corrosive acid vapors or acid solutions and the expensive equipment and components have created a need for improved processes for separating aromatic acids.

Foreliggande uppfinning avser ett forbattrat forfarande for separering av bensenpolykarbonsyror, vilket är bade smidigt och hogeffektivt och kan tillampas samtidigt med andra separeringsforfaranden. Enligt uppfinningen extraheras en bensenpolykarbonsyra, som kan bilda en intramolekylar anhydrid, ur en blandning med andra bensenpolykarbonsyror. Enligt en utforingsform av uppfinningen kunna ofullstandigt oxiderade alkylsubstituerade aromatiska foreningar atervinnas och aterfOras till wddationssteget. Uppfinningen avser sarskilt separering av ortoftalsyra fran isoftal- och tereftalsyra och aven separering av eventuellt bildad bensoesyra. Vidare omfattar uppfinningen separering och utvinning av trimellitsyra ur en blandning av bensenpolykarbonsyror. The present invention relates to an improved process for the separation of benzene polycarboxylic acids, which is both flexible and highly efficient and can be applied simultaneously with other separation processes. According to the invention, a benzene polycarboxylic acid, which can form an intramolecular anhydride, is extracted from a mixture with other benzene polycarboxylic acids. According to one embodiment of the invention, incompletely oxidized alkyl-substituted aromatic compounds can be recovered and recycled to the addition step. The invention relates in particular to the separation of orthophthalic acid from isophthalic and terephthalic acid and also to the separation of any benzoic acid formed. The invention further comprises the separation and recovery of trimellitic acid from a mixture of benzene polycarboxylic acids.

Vid utforande av foreliggande uppfinning upphettar man en blandning, som innehaller bensenpolykarbonsyror, av vilka minst en men icke alla ha formaga att bilda en intramolekylar anhydrid (dvs. uppvisar minst 2 orto-orienterade karboxylgrupper), fOr bildning ay en sadan anhydrid, varefter anhydriden extraheras med ett aromatiskt losningsmedel. Fastan bensenpolykarbonsyror, vilka uppvisa minst 2 orto-orienterade karboxylgrupper, vanligen aro fran ungefar 5 till ungefar 15 ganger sá losliga i aromatiska lOsningsmedel som deras isomerer, vilka icke uppvisa denna ken-figuration, blir orto-polykarbonsyran, om den fiirst dehydratiseras, mer an 100 ganger sã loslig som flagon av doss isomerer. Losligheten i aromatiska losningsmedel av bensen-trikarbonsyror, vilka uppvisa minst 2-orto-orienterade karboxylgrupper, okas med andra ord med en faktor fran ungefar 20 till ungeffir 80 enb art genom Overforing av syran till motsvarande anhydrid. Till fOljd liarav är det genom extraktion av anhydriden i stallet for av syran mOjligt aft anvanda endast 1/20 till 1/80 sa stor mangd losningsmedel som tidigare, varvid man pa samma gang uppnar en finare separering mellab polykarbonsyror, vilka kunna bilda anhydrider, och polykarbonsyror, vilka icke kunna Ora detta. Enligt en sarskilt lamplig utforingsform av uppfinningen bestar det aroma- 2— — tiska losningsmedlet av den blandning av aromatiska foreningar (en blandning av alkylsubstituerade aromatiska fOreningar), som oxideras till blandningen av bensenpolykarbonsyror. Enligt denna utforingsform lOsas aven partiellt oxiderade alkylsubstituerade aromatiska foreningar i det aromatiska losningsmedlet och kunna efter isoleringen av polykarbonsyraanhydriden aterforas till oxidationen, upplosta i losningsmedlet. Enligt en annan mycket la.mplig utforingsform av uppfinningen, vid vilken blandningen av bensenkarbonsyror innehaller bade bensoesyra och en polykarbonsyra, som kan bilda en intramolekylar anhydrid, extraherar man forst bensoesyran (som dr mycket lattloslig i aromatiska losningsmedel) ur blandningen med ett aromatiskt losningsmedel vid en temperatur, som Egger under anhydridbildningstemperaturen. Det fOrsta raffinatet upphettas sedan for dehydratisering av den bensenpolykarbonsyra, som kan bilda en intramolekylar anhydrid, varefter den intramolekylara anhydriden extraheras ur det forsta raffinatet med ett aromatiskt losningsmedel. In the practice of the present invention, a mixture containing benzene polycarboxylic acids is heated, at least one but not all of which are capable of forming an intramolecular anhydride (i.e., having at least 2 ortho-oriented carboxyl groups), to form such an anhydride, after which the anhydride is extracted. with an aromatic solvent. Although benzene polycarboxylic acids, which have at least 2 ortho-oriented carboxyl groups, are usually from about 5 to about 15 times as soluble in aromatic solvents as their isomers, which do not have this configuration, the ortho-polycarboxylic acid, if first dehydrated, becomes more 100 times as soluble as the flag of doss isomers. In other words, the solubility in aromatic solvents of benzene tricarboxylic acids, which have at least 2-ortho-oriented carboxyl groups, is increased by a factor of from about 20 to about 80 units by transfer of the acid to the corresponding anhydride. As a result, by extracting the anhydride instead of the acid, it is possible to use only 1/20 to 1/80 as much solvent as before, thereby achieving a finer separation between polycarboxylic acids, which can form anhydrides, and polycarboxylic acids, which can not ora this. According to a particularly suitable embodiment of the invention, the aromatic solvent consists of the mixture of aromatic compounds (a mixture of alkyl-substituted aromatic compounds) which is oxidized to the mixture of benzene polycarboxylic acids. According to this embodiment, even partially oxidized alkyl-substituted aromatic compounds are dissolved in the aromatic solvent and, after the isolation of the polycarboxylic anhydride, can be returned to the oxidation, dissolved in the solvent. According to another very suitable embodiment of the invention, in which the mixture of benzenecarboxylic acids contains both benzoic acid and a polycarboxylic acid, which can form an intramolecular anhydride, the benzoic acid (which is very readily soluble in aromatic solvents) is first extracted from the mixture with an aromatic solvent. a temperature which Egger below the anhydride formation temperature. The first raffinate is then heated to dehydrate the benzene polycarboxylic acid which may form an intramolecular anhydride, after which the intramolecular anhydride is extracted from the first raffinate with an aromatic solvent.

FOreliggande ferfarande uppvisar viktiga fordelar utover tidigare kanda forfaranden, vid vilka man fiirsokt separera blandningar av bensenkarbonsyror utan att forst omvandla orto-orienterade syror till deras intramolekylara anhydrider. Forst -och framst ar det pa grund ay den kraftigt okade losligheten hos anhydriderna mojligt att anvanda endast en ringa del av den lbsningsmedelsmangd, som tidigare varit nodvandig, med atfoljande forbattrad separering och minskade investeringskostnader fOr utrustning och minskade arbetskostnader. For det andra Or fOrfarandet mycket smidigt och kan anvandas vid separering av blandningar av bensenkarbonsyror med mycket varierande sammansattning och erhallna frail olika kallor. FOrfarandet kan vidare tillampas samtidigt med andra separeringsforfaranden, sasom vattenextraktion eller selektiv fOrestring oiler liknande, for ytterligare separering av raffinatet. For det tredje och till skillnad Iran vattenextraktion losa aromatiska foreningar joke de tungmetalloxidationskatalysatorer, vilka anvandas for oxidation av polyalkylsubstituerade aromatiska foreningar med molekylart syre, vilket ytterligare forenklar reningen av bensenpolykarbonsyrorna. Annu en fordel ar aft ofullstandigt oxiderade alkylsubstituerade aromatiska fOreningar aro mer losliga i aromatiska lbsningsmedel an de fullstandigt oxiderade polykarbonsyrorna och foljaktligen kunna upplosas tillsammans med anhydriden och efter isolering av derma kunna aterforas till oxidationssteget, om sã onsk-as. Ett exempel pa den sistnamnda fordelen är oxidation av en xylen till en ftalsyra, dar oxidationsmellanprodukten (toluensyra) är loslig i aromatiska foreningar i en mangd av ungerar 15 g/100 g vid 25° C, medan den mest lattlosliga ftalsyran har en loslighet av endast ungefax 0,1 g vid donna teinperatur. Slutligen betinga aromatiska losningsmedel lag kostnad, Oro lattillgangliga och mycket stabila. The present process has important advantages over prior art processes which attempt to separate mixtures of benzenecarboxylic acids without first converting ortho-oriented acids to their intramolecular anhydrides. First and foremost, due to the greatly increased solubility of the anhydrides, it is possible to use only a small part of the amount of solvent previously required, with consequent improved separation and reduced investment costs for equipment and reduced labor costs. Secondly, the process is very flexible and can be used in separating mixtures of benzenecarboxylic acids with very different composition and obtaining from different sources. The process can further be applied simultaneously with other separation processes, such as water extraction or selective esterification or the like, for further separation of the raffinate. Third, and unlike Iran water extraction, aromatic compounds release the heavy metal oxidation catalysts used for the oxidation of polyalkyl-substituted aromatic compounds with molecular oxygen, which further simplifies the purification of benzene polycarboxylic acids. Another advantage is that incompletely oxidized alkyl-substituted aromatic compounds are more soluble in aromatic solvents than the fully oxidized polycarboxylic acids and consequently can be dissolved together with the anhydride and after isolation thereof can be returned to the oxidation step, if desired. An example of the latter advantage is the oxidation of a xylene to a phthalic acid, where the oxidation intermediate (toluic acid) is soluble in aromatic compounds in an amount of about 15 g / 100 g at 25 ° C, while the most readily soluble phthalic acid has a solubility of only approximately 0.1 g at this temperature. Finally, aromatic solvents require law cost, Concerns readily available and very stable.

Den anmarkningsvdrda selektiviteten has aro matiska losningsmedel for bensenpolykarbonsyraanhydrider gentemot deras hydratiserade former framgar av nedanstaende tabell I. Om ortoftalsyra tages sasom ett exempel, loser sig ungefar 50 ganger sa stor mangd anhydrid som syran vid en given temperatur. Vid trimellitsyraanhydrid är losligheten ungefar 35 ganger sa stor. Andra anhydrider upptrada pa liknande salt. The remarkable selectivity of aromatic solvents for benzene polycarboxylic anhydrides over their hydrated forms is shown in Table I below. With trimellitic anhydride, the solubility is about 35 times as great. Other anhydrides appeared on similar salt.

Tabell I. Table I.

Loslighet av aromatiska syror och anhydrider i ett aromatiskt losningsmedel i g/100 g losningsmedel. Solubility of aromatic acids and anhydrides in an aromatic solvent in g / 100 g solvent.

Temp °C 0 Bensoe- syrat o-ftalsyraTrimellitsyra AnhyAnhy- Syra2Syra, drid 1,90, 10,00,083 4,3 0,01 0,36 20,0,16 20,0,62 60 39 0,23,7 1, 80 70,6 2,0 100 113,6 16,4 10,3 11,6 160 180 37 200 6 1- I bensen 2 I bensen I bensen I xylener I xylener Av nedanstaende tabell II framgar, att aromatiska kolvaten halt allmant ha en kokpunkt, som Egger mycket ndra kokpunkten for deras isomerer och homologer. Endast 8° skiljer den lagst kokande frail den meat hogkokande C-aromatiska f oreningen och alla 22 isomererna av en C-aromatisk forming koka inom ett temperaturomrade av 35° C. Harav framgar att separering av en enda aromatisk forening genom fraktionerad destillation ur en blandning Or svar att genomfora och ekonomiskt outforbar i teknisk skala. Av denim_ orsak är det nodvandigt att framstalla en fraktion, som kokar Mom jamfOrelsevis snava granser, av blandade alkylsubstituerade aromatiska kolvaten, att darefter oxidera hela fraktionen och slutligen separera den bildade blandningen av bensenkarbonsyror. Temp ° C 0 Benzoic acid o-phthalic acidTrimellitic acid AnhyAnhy- Acid2Acid, drid 1.90, 10.00.083 4.3 0.01 0.36 20.0.16 20.0.62 60 39 0.23.7 1, 80 70.6 2.0 100 113.6 16.4 10.3 11.6 160 180 37 200 6 1- I benzene 2 I benzene I benzene I xylenes I xylenes Table II below shows that aromatic hydrocarbons generally have a boiling point, as Egger greatly changes the boiling point of their isomers and homologues. At only 8 °, the lowest boiling frail separates the meat high boiling C aromatic compound and all 22 isomers of a C aromatic forming boil within a temperature range of 35 ° C. This shows that separation of a single aromatic compound by fractional distillation from a mixture Or answers to implement and financially unforeseeable on a technical scale. For denim reason, it is necessary to prepare a fraction, which boils Mom comparatively narrow borders, of mixed alkyl-substituted aromatic hydrocarbons, then to oxidize the whole fraction and finally to separate the resulting mixture of benzenecarboxylic acids.

Tabell II anger aven de syror, vilka bildats genom oxidation av ifragavarande aromatiska kolvaten, och anger, out den aromatiska syran kan bilda en intramolekylar anhydrid. Dot bOr observeras, att karbonsyraanhydriderna erhallas genom upphettningbensenkarbonsyror med minst tva karboxylgrupper, vilka sta i orto-stallning till varandra. Foljaktligen kan endast orto-ftalsyra av de tre xylenoxidationsprodukterna underkastas dehydratisering genom upphettning. Intermolekylara anhydrider, sasom bensoesyraanhydrid, existera givetvis men kunna icke framstallas genom enkel upphettning. Table II also lists the acids formed by oxidation of the aromatic hydrocarbons in question, and indicates that the aromatic acid may form an intramolecular anhydride. It should be noted that the carboxylic anhydrides are obtained by heating benzenecarboxylic acids having at least two carboxyl groups, which are in orthotics to each other. Consequently, only orthophthalic acid of the three xylene oxidation products can be subjected to dehydration by heating. Intermolecular anhydrides, such as benzoic anhydride, do exist, of course, but cannot be produced by simple heating.

Blandade alkylsubstituerade aromatiska kolvaten erhallas vanligen genom destillation av pet- - - Tabell II Aromatiska syror genom oxidation av alkylsubstituerade aromatiska kolvaten* Formel KPS** Alkylsubstituerat aromatiskt kolvate Kokpunkt °C vid at- mosfarstryck Bildad syra Bildar anbydrid Css 1 Bensen 80,103 C71-18 1 Metylbensen (toluen) 110,623 Bensoesyra C81-11.0 1 Etylbensen 136,187 Bensoesyra 2 1,4-dimetylbensen (p-xylen) 138,348 Tereftalsyra 3 1,3-dimetylbensen (m-xylen) 139,102 Isoftalsyra 4 1,2-dimetylbensen (o-xylen) 144,414 Ortoftalsyra Ja C sH12 1 Isopropylbensen (kumen) 152,393 Bensoesyra 2 n-propylbensen 159,216 Bensoesyra 3 1-mety1-3-etylbensen 161,301 Isoftalsyra 4 1-mety1-4-etylbensen 161,98Tereftalsyra 1,3,5-trimetylbensen (mesitylen) 164,711 Trimesinsyra 6 1-mety1-2-etylbensen 165,1o-ftalsyra Ja 7 1,2,4-trimetylbensen (pseudokumen) 169,347 Trimellitsyra Ja 8 1,2,3-trimetylbensen (hemimelliten) 176,080 Hemimellitsyra Ja C3.01-13.4 1 tert.-butylbensen (2-feny1-2-metylpropan) 169,113 Bensoesyra 2 Isobutylbensen (1-feny1-2-metylpropan) 172,7Bensoesyra 3 sek.-butylbensen (2-fenylbutan) 173,299 Bensoesyra 4 1-mety1-3-isopropylbensen (m-cymen) 175,200 Isoftalsyra 1-mety1-4-isopropylbensen (p-eymen) 177,100 Tereftalsyra 6 1-metyl-2-isopropylbensen (o-cymen) 178,300 o-ftalsyra Ja 7 1,3-dietylbensen 181,1isoftalsyra 8 1-mety1-3-propylbensen 182,000 isoftalsyra 9 n-butylbensen (1-fenylbutan) 183,267 Bensoesyra 1-mety1-4-propylbensen 183,4Tereftalsyra 11 1,2-dietylbensen 183,480 o-ftalsyra Ja 12 1,3-dimety1-5-etylbensen 183,7trimesinsyra 13 1,4-dietylbensen 183,780 Tereftalsyra 14 1-mety1-2-propylbensen 184,000 o-f talsyra Ja 1,4-dimety1-2-etylbensen 186,9trimellitsyra Ja 16 1,3-dimety1-4-etylbensen 188,4trimellitsyra Ja 17 1,2-dimety1-4-etylbensen 189,7trimellitsyra Ja 18 1,3-dimety1-2-etylbensen 190,0hemimellitsyra Ja 19 1,2-dimety1-3-etylbensen 193,9hemimellitsyra Ja 1,2,4,5-tetrametylbensen (duren) 196,000 pyromellitsyra Ja 21 1,2,3,5-tetrametylbensen (isoduren) 197,9prenit8yra Ja 22 1,2,3,4-tetrametylbensen (preniten) 205,04 mellofan-syra Jo Uppgiftskalla: * National Bureau of Standards Circular 461, 1947 ** Kokpunktsfoljd roleumkolvaten eller genom extraktion av dessa med ett selektivt losningsmedel. De kunna aven fraktioneras eller extraheras ur ett hydroformat, som bildats genom katalytisk reformering (aromatisering) av petroleumkolvaten med exempelvis en platina-aluminiumoxid- eller molybdenoxidaluminiumoxidkatalysator. En petroleumkolvateblandning hydroformeras lampligen katalytiskt och den aromatiska delen extraheras ur hydroformatet med ett selektivt losningsmedel, sasom dietylenglykol, fenol, svaveldiwdd eller liknande. Det aromatiska extraktet fraktioneras sedan, om sä erfordras, for aft avlagsna eventuell bensen och toluen och aterstoden onderas i sin helhet eller omdestilleras forst for beredning av en oxidationsutgangsblandning med ett Onskat snavt kok- punktsomrade. En petroleumkolvateblandning, som exempelvis kokar radian 70 och ungefar 145° C kan hydroformeras till en pa aromatiska kolvaten rik fraktion med liknande kokpunktsomra.cle, som sedan underkastas extraktion med dietylenglykol, varvid man utvinner en till mer an 99 % ren aromatisk fraktion, som bestir av bensen, toluen, etylbensen och de tre xylenerna. Fraktionerad destination av det aromatiska extraktet ger i huvudsak rena bensen- och toluenftaktioner samt en Craromatisk fraktion, som kokar mellan 136 och 145° C och liar en genomsnittltg sammansattning av ungefar 23,6 vildprocent orto-xylen, 45,4 % meta-xylen, 18,0 Vc, paraxylen och 13,0 % etylbensen med ett spar toluen. Ytterligare separering av Cs-fraktionen kan en- 4— — dast astadkommas genom dyrbar och besvarlig lagtemperaturkristallisation eller genom ultrafraktionering. Pa liknande Batt erhallas mer hogkokande aromatiska fraktioner frau mer hogkokande petroleumfraktioner eller -reformat. Sammansattningen av de mer hogkokande fraktionerna regleras pa samma Batt som vid xylenerna av den ursprungliga sammansdttningen av petroleumkolvdtehlandningen samt av jamvikten och graden av narhet till jamvikt vid hydroformeringen. Mixed alkyl-substituted aromatic hydrocarbons are usually obtained by distillation of pet- - - Table II Aromatic acids by oxidation of alkyl-substituted aromatic hydrocarbons * Formula KPS ** Alkyl-substituted aromatic hydrocarbon Boiling point ° C at atmospheric pressure Pressure Formed acid C Methylbenzene (toluene) 110,623 Benzoic acid C81-11.0 1 Ethylbenzene 136,187 Benzoic acid 2 1,4-dimethylbenzene (p-xylene) 138,348 Terephthalic acid 3 1,3-dimethylbenzene (m-xylene) 139,102 Isophthalic acid 4 1,2-dimethylbenzene) 144,414 Orthophthalic acid Yes C sH12 1 Isopropylbenzene (cumene) 152,393 Benzoic acid 2 n-propylbenzene 159,216 Benzoic acid 3 1-methyl-3-ethylbenzene 161,301 Isophthalic acid 4 1-methyl-4-ethylbenzene 161,98Terephthalic acid 1,3,511-trimethylene) Trimesic acid 6 1-methyl-2-ethylbenzene 165,1o-phthalic acid Ja 7 1,2,4-trimethylbenzene (pseudocumene) 169,347 Trimellitic acid Ja 8 1,2,3-trimethylbenzene (hemimellite) 176,080 Hemimellitic acid Ja C3.01-13.4 1 tert .-butylbenzene (2-phenyl-2-methyl 1propane) 169.113 Benzoic acid 2 Isobutylbenzene (1-phenyl-2-methylpropane) 172.7Benzoic acid 3 sec.-butylbenzene (2-phenylbutane) 173,299 Benzoic acid 4 1-methyl-3-isopropylbenzene (m-cymene) 175,200 Isophthalic acid 1-methyl- -isopropylbenzene (p-eymen) 177,100 Terephthalic acid 6 1-methyl-2-isopropylbenzene (o-cymene) 178,300 o-phthalic acid Yes 7 1,3-diethylbenzene 181.1isophthalic acid 8 1-methyl-3-propylbenzene 182,000 isophthalic acid 9 n-butylbenzene (1-phenylbutane) 183,267 Benzoic acid 1-methyl-4-propylbenzene 183,4Terephthalic acid 11 1,2-diethylbenzene 183,480o-phthalic acid Yes 12 1,3-dimethyl-5-ethylbenzene 183,7trimesic acid 13 1,4-diethylbenzene 183,780 Terephthalic acid 14 1-methyl-2-propylbenzene 184,000 or tallic acid Ja 1,4-dimethyl-2-ethylbenzene 186,9trimellitic acid Ja 16 1,3-dimethyl-4-ethylbenzene 188.4trimellitic acid Ja 17 1,2-dimethyl-4-ethylbenzene 189, 7trimellitic acid Ja 18 1,3-dimethyl-2-ethylbenzene 190,0hemimellitic acid Ja 19 1,2-dimethyl-3-ethylbenzene 193,9hemimellitic acid Ja 1,2,4,5-tetramethylbenzene (durene) 196,000 pyromellitic acid Ja 21 1,2, 3,5-tetramethylbenzene ( isoduren) 197.9prenit8yra Yes 22 1,2,3,4-tetramethylbenzene (prenitene) 205.04 mellophanic acid Jo Information source: * National Bureau of Standards Circular 461, 1947 ** Boiling point follow the roleum carbonates or by extraction of these with a selective solvent . They can also be fractionated or extracted from a hydroformate formed by catalytic reforming (aromatization) of the petroleum carbonates with, for example, a platinum-alumina or molybdenum-alumina catalyst. A petroleum hydrocarbon mixture is suitably catalytically hydroformed and the aromatic moiety is extracted from the hydroformate with a selective solvent such as diethylene glycol, phenol, sulfur dioxide or the like. The aromatic extract is then fractionated, if necessary, to remove any benzene and toluene and the residue is submerged in its entirety or first redistilled to prepare an oxidation starting mixture with a desired narrow boiling point range. A petroleum carbonate mixture boiling, for example, radian 70 and about 145 ° C can be hydroformed to a fraction rich in aromatic hydrocarbons with similar boiling point ranges, which is then subjected to extraction with diethylene glycol, yielding a more than 99% pure aromatic fraction which of benzene, toluene, ethylbenzene and the three xylenes. Fractional distillation of the aromatic extract gives essentially pure benzene and toluene actions, as well as a chromatic fraction which boils between 136 and 145 ° C and has an average composition of about 23.6% ortho-xylene, 45.4% meta-xylene, 18.0 Vc, paraxylene and 13.0% ethylbenzene with a saving of toluene. Further separation of the Cs fraction can be achieved only by expensive and costly layer temperature crystallization or by ultrafractionation. Similarly, more high-boiling aromatic fractions are obtained from more high-boiling petroleum fractions or reforms. The composition of the higher boiling fractions is regulated in the same way as in the case of the xylenes by the initial composition of the petroleum flask landings and by the equilibrium and degree of proximity to equilibrium during hydroformation.

Oxidation av blandningen av aromatiska foreningar kan utforas pa nagot i och fOr sig kant satt, t. ex. pade sktt, som beskrivas i Chemical Week, 6 april 1957, sid. 33-42. Man kan salunda exempelvis anyanda sig av salpetersyraoxidation, katalytisk luftoxidation av xylener med moleky- lärttill toluensyror med efterfoljande sal- petersyraoxidation till ftalsyror, katalytisk oxidation av xylener med molekyldrt syre till toluensyror, fi5restring av toluensyrorna och fortsatt katalytisk oxidation med molekyldrt syre till monometylftalat saint slutligen hydrolys till motsvarande syra eller ocksa direkt oxidation med molekyldrt syre till polykarbonsyran i en mattad monokarbonsyra (dvs. en paraffinkolvdtesyra eller naftensyra, innehallande 2 till ungefar 8 kolatomer i molekylen, t. ex. dttiksyra, propionsyra, kaprylsyra eller cyklobutankarbonsyra) i narvaro av en tungmetallmddationskatalysator och brom. Sistndmnda forfarande är speciellt lampligt for framstallning av bensenpolykarbonsyror, eftersom det genomfbres i ett enda steg och gor det mOjligt att anvanda luft sasom enda oxidationsmedel saint dessutom utfOres med billiga katalysatorer, sasom mangan, kobolt, jarn eller nickel, med exempelvis ammoniurnbromid. Oxidation of the mixture of aromatic compounds can be carried out in any way per se, e.g. pade sktt, described in Chemical Week, April 6, 1957, p. 33-42. These may include, for example, nitric acid oxidation, catalytic air oxidation of xylenes with molecular to toluic acids with subsequent nitric acid oxidation to phthalic acids, catalytic oxidation of xylenes with molecular oxygen to toluic acids, filtration of the toluic acids and further monolithic acid. hydrolysis to the corresponding acid or also direct oxidation with molecular oxygen to the polycarboxylic acid in a matt monocarboxylic acid (ie a paraffinic carbonic acid or naphthenic acid, containing 2 to about 8 carbon atoms in the molecule, eg acetic acid, propionic acid, caprylic acid or cyclobutanecarboxylic acid) heavy metal conversion catalyst and bromine. The latter process is particularly suitable for the production of benzene polycarboxylic acids, since it is carried out in a single step and makes it possible to use air as a single oxidizing agent and also to be carried out with inexpensive catalysts such as manganese, cobalt, iron or nickel, for example ammonium bromide.

Isoleringen av blandningen av bensenpolykarbonsyror ur en oxidationsblandning kan utf6ras pa olika satt, beroende pa -vilken aromatisk utgangsblandning, son).- oxideras, och :pa naturen av oxidationsmedlet. Salunda- kan exempelvis losningsmedel och vatten fran oxidationen helt enkelt avdestilleras eller avdunstas, varvid karbonsyrafraktionen erhalles sasom aterstod. Man kan alternativt littera en reaktionsblandning, lampligen medan den befinner sig vid en temperatur under ungefdr 100° C, for avskiljning av blandningen av aromatiska syror, eller kan filtrera den .vid en temperatur Over ungefar 100° C fOr avskiljlaing av en forsta fast fraktion, som innehaller Ditisliga aromatiska syror, sasom isoftalsyra och tereftalsyra, varefter filtratet avkyles eller destilleras for isolering av en andra blandning av .polykarbonsyror, vilken sedan behandlas enligt foreliggande uppf inning. Man kan givetvis i stallet tbr filtering anydrida ekvivalenta metoder for separering av fasta och flytande laser fran varandra, sasom centrifugering, dekantering och eyklonseparering. Den blandade bensenpolykar-bonsyrafraktionen kan vid denna tidpunkt tvattas Tiled vatten eller nagot annat losningsmedel fOr -avskiljning av vattenlosliga fOroreningar, vilka kunna vara narvarande till foljd av den utfOrda -oxidationen. The isolation of the mixture of benzene polycarboxylic acids from an oxidizing mixture can be carried out in different ways, depending on which starting aromatic mixture is oxidized, and on the nature of the oxidizing agent. Salunda, for example, solvent and water from the oxidation can simply be distilled off or evaporated, the carbonic acid fraction being obtained as remaining. Alternatively, a reaction mixture may be allowed, preferably while at a temperature below about 100 ° C, to separate the mixture of aromatic acids, or it may be filtered at a temperature above about 100 ° C to separate a first solid fraction. containing ditislic aromatic acids, such as isophthalic acid and terephthalic acid, after which the filtrate is cooled or distilled to isolate a second mixture of polycarboxylic acids, which is then treated according to the present invention. Of course, instead of filtering, one can use any equivalent methods for separating solid and liquid lasers from each other, such as centrifugation, decantation and eiclone separation. The mixed benzene polycarbonic acid fraction may at this time be washed with water or some other solvent to separate water-soluble contaminants which may be present as a result of the oxidation carried out.

Om den blandade bensenkarbonsyrafraktionen innehaller bensoesyra och/eller en alkylsubstituerad bensoesyra, som bildas genom ofullstandig oxidation, kunna dessa syror lampligen extraheras ur syrablandningen fbre dehydratiseringen genom tvdttning med en ringa mangd av ett aromatiskt lbsningsmedel vid en temperatur under anhydridbildningstemperaturen fOr varje ndrvarande ortopolykarbonsyra. Med undatag for vissa tert.-alkylsubstituerade orto-polykarbonsyror, vilka dehydratisera vid ldgre temperatur, dr en extraktionstemperatur under ungefar 165° C tillracklig for att forhindra dehydratisering av orto-polykarbonsyror. Eftersom bensoesyra Or loslig i en mangd av 12,2 g per 100 g bensen vid 25° C och alkylsubstituerade bensoesyror dro till och med mer losliga framgar det klart, aft endast en jainforelsevis ringa mangd aromatiskt lOsningsmedel be-hover anvandas och att extraktionstemperaturen till och med kan vara under ungefar 50° C, sä att man undviker upplbsning av namnvarda mangder andra karbonsyror. If the mixed benzenecarboxylic acid fraction contains benzoic acid and / or an alkyl-substituted benzoic acid, which is formed by incomplete oxidation, these acids can be conveniently extracted from the acid mixture before dehydration by washing with a small amount of an aromatic solvent at a temperature below anhydride. With the exception of certain tert-alkyl-substituted ortho-polycarboxylic acids, which dehydrate at lower temperatures, an extraction temperature below about 165 ° C is sufficient to prevent dehydration of ortho-polycarboxylic acids. Since benzoic acid is soluble in an amount of 12.2 g per 100 g of benzene at 25 ° C and alkyl-substituted benzoic acids were even more soluble, it is clear that only a relatively small amount of aromatic solvent needs to be used and that the extraction temperature to may be below about 50 ° C, so that the accumulation of significant amounts of other carbonic acids is avoided.

Upphettningen av blandningen av bensen-polykarbonsyror for dehydratisering av de syror, vilka kunna bilda intramolekyldra anhydrider, kan utforas i vakuum eller vid atmosfarstryck eller hogre tryck och underldttas, cm den utf Ores i nOrvaro av ett med vatten oblandbart losningsmedel, som kokar Over vattnets kokpunkt (100° C). Kolvdten dro lampliga for detta andamal och bade paraffinkolvaten och aromatiska kolvdten kunna anvandas for utforande av dehydratiseringen pa en ldmpligt kort tidrymd. Den anvanda vatskan Mir ldmpligen ha en kokpunkt, som icke är vasentligt lagre an. 10 eller 20° C under dehydratiseringstemperaturen for den i varje sarskilt fall ifragakommande orto-polykarbonsyran. Cymener arc sarskilt ldmpliga for dehydratisering av orto-ftalsyra till ftalsyraanhydrid, medan duren eller preniten och mer hogkokande aromatiska foreningar lampligen anyandas vid dehydratisering av trikarbonsyror, sasom trimellitsyra. Mer lagkokande aromatiska fOreningar kunna emellertid anvandas och Oven xylen dehydratiserar 90 % trimellitsyra Mom 15 minuter vid 225° C. Endast 1 eller 2 % av vatskan erfordras men stone mangd kan anvandes, om dehydratiseringen och extraktionen utfbras samtidigt. Dehydratiseringskdrlet forses med en aterflodeskylare for aterflode av endast den med vatten oblandbara fasen till kdrlet. Dehydratiseringen Or avslutad, nar ytterligare vatten icke _utvecklas. The heating of the mixture of benzene-polycarboxylic acids for dehydration of the acids which may form intramolecular anhydrides may be carried out in vacuo or at atmospheric pressure or higher pressure and subjected to the presence of a water-immiscible solvent boiling above the boiling point of water. (100 ° C). The flask was suitable for this purpose and both the paraffin flasks and aromatic flasks could be used to carry out the dehydration in a remarkably short period of time. The used liquid Mir ldmpligen have a boiling point, which is not substantially lower. 10 or 20 ° C below the dehydration temperature of the ortho-polycarboxylic acid in each particular case. Cymenes are particularly suitable for the dehydration of orthophthalic acid to phthalic anhydride, while duren or prenite and more boiling aromatic compounds are suitably different in the dehydration of tricarboxylic acids, such as trimellitic acid. However, more low boiling aromatic compounds can be used and Oven xylene dehydrates 90% trimellitic acid Mom 15 minutes at 225 ° C. Only 1 or 2% of the liquid is required but stone amount can be used, if the dehydration and extraction are performed simultaneously. The dehydration vessel is provided with a reflux condenser for refluxing only the water-immiscible phase of the vessel. Dehydration Or terminated when additional water does not develop.

Polykarbonsyrafraktionen, som innehaller den genom dehydratiseringen bildade intrarnolekyldra anhydriden, underkastas sedan extraktion med ett aromatiskt lbsningsmedel. Eftersom losligheten av bensenkarbonsyror eller bensenkarb onsyraanhydrider i arornatiska losningsmedel Or i huvudsak oberoende av naturen av det aromatiska losningsmedlet, kan varje aromatisk forening med en kokpunkt, som lampligen ligger under 200° C anvandes bade sasom losningsmedel for anhydriden, som losningsmedel for bensoesyran och fOr alkylsubstituerade bensoesyrorna samt for un- — — derlattande av dehydratiseringen. De i tabell II angivna foreningarna eller varje blandning darav kunna anvandas. Losningsmedlet kan innehalla en mindre mangd icke aromatiska kolvaten, vilka icke fOrAndra de aromatiska losningsmedlens selektivitet. The polycarboxylic acid fraction, which contains the intranolecular anhydride formed by the dehydration, is then subjected to extraction with an aromatic solvent. Since the solubility of benzenecarboxylic acids or benzenecarboxylic acid anhydrides in aromatic solvents Or is substantially independent of the nature of the aromatic solvent, any aromatic compound having a boiling point suitably below 200 ° C can be used both as anhydride solvent, as a solvent for the benzoic acid substituents and the benzoic acids and for omitting the dehydration. The compounds listed in Table II or any mixture thereof may be used. The solvent may contain a minor amount of non-aromatic hydrocarbons which do not alter the selectivity of the aromatic solvents.

Oberoende av om bensoesyra extraheras forst ur blandningen eller icke är det, sasom ovan an- givits, mycket onskvart att extrahera den intra- molekylara anhydriden ur blandningen av aromatiska syror med ett losningsmedel, vilket bestar av en del av den aromatiska utgangsblandning, som senare skall oxideras. Genom att fOrfara ph detta satt losas ofullstandigt o3dderade aromatiska fore- ningar, sasom toluensyror och metylftalsyror, i losningsmedlet och kvarstanna i detta aven efter kristalliseringen av anhydriden samt kunna caterforas tillsammans med lOsningsmedlet till oxidationssteget. Regardless of whether or not benzoic acid is extracted first from the mixture, as indicated above, it is very difficult to extract the intramolecular anhydride from the mixture of aromatic acids with a solvent, which consists of a part of the starting aromatic mixture, which will later be oxidized. By carrying out this process, incompletely undiluted aromatic compounds, such as toluic acids and methylphthalic acids, are dissolved in the solvent and remain therein even after the crystallization of the anhydride and can be caterforas together with the solvent to the oxidation step.

Mangden och temperaturen av det aromatiska losningsmedel, som anvandes for extraktionen av anhydriden, beror pa den speciella losligheten av denna anhydrid, visad i tabell I. Det har i allmanhet visat sig lampligt att anvanda en temperatur Iran ungefar 20 till ungefar 200° C och foretradesvis mellan 50 och 100° C, varigenom den erforderliga mangden losningsmedel reduceras. Om sa erfordras, anvandes tryck for att halla losningsmedlet i flytande fas. Exempelvis ftalsyraanhydrid loser sig i en mangd av 3,4 g per 100 g losningsmedel i toluen vid 25° C, i en mangd av 39 g vid 100° C och i en mangd av ungefar 1000 g vid 200° C. Dess liislighet i andra aromatiska foreningar Egger vid ungefar + 20 % av dess loslighet i toluen. Trimellitsyraanhydrid är nagot mind-re loslig an ftalsyraanhydrid. Extraktionen kan antingen utforas i dehydratiseringskarlet eller i ett sarskilt kart varvid det anvanda karlet lampligen Or forsett med omr8rarorgan for att intim kontakt skall astadkommas mellan det aromatiska losningsmedlet och polykarbonsyrablandningen. Efter extraktionen separerar man extraktet frau det olosta bensenpolykarbonsyraraffinatet genom filtrering vid en temperatur nara extraktionstemperaturen. The amount and temperature of the aromatic solvent used for the extraction of the anhydride depends on the particular solubility of this anhydride, shown in Table I. In general, it has been found suitable to use a temperature of about 20 to about 200 ° C and preferably between 50 and 100 ° C, thereby reducing the amount of solvent required. If required, pressure was applied to keep the solvent in the liquid phase. For example, phthalic anhydride dissolves in an amount of 3.4 g per 100 g of solvent in toluene at 25 ° C, in an amount of 39 g at 100 ° C and in an amount of about 1000 g at 200 ° C. aromatic compounds Egger at about + 20% of its solubility in toluene. Trimellitic anhydride is slightly less soluble than phthalic anhydride. The extraction can be carried out either in the dehydration vessel or in a special card, the vessel used being suitably provided with stirring means for establishing intimate contact between the aromatic solvent and the polycarboxylic acid mixture. After extraction, the extract is separated from the undissolved benzene polycarboxylic acid raffinate by filtration at a temperature close to the extraction temperature.

Polykarbonsyraanhydriden isoleras lampligen ur extraktet genom avkylning och kristallisering av detta med efterfoljande avfiltrering av anhydridkristallerna. Kristalliseringen kan utforas genom kylning till en temperatur av ungefar 0 till ungefar 60° C, och nar tva anhydrider aro narvarande, t. ex. ftalsyra- och trimellitsyraanhydrid, kan en partiell separering mellan dessa tva anhydrider utforas genom kylning av extraktet till lampligen migefar 30-60° C for kristallisering av en trimellitsyraanhydridrik fraktion med efterfoljande kylning till ungefar 0-30° C for isolering av en ftalsyraanhydridrik fraktion. Den kristalliserade anhydriden är fororenad med en ringa mangd losningsmedel, som kan avlagsnas genom destination eller genom torkning i luft eller i vakuum. The polycarboxylic anhydride is suitably isolated from the extract by cooling and crystallizing it with subsequent filtration of the anhydride crystals. The crystallization can be carried out by cooling to a temperature of about 0 to about 60 ° C, and when two anhydrides are present, e.g. phthalic acid and trimellitic anhydride, a partial separation between these two anhydrides can be performed by cooling the extract to approximately 30-60 ° C for crystallization of a trimellitic anhydride-rich fraction with subsequent cooling to about 0-30 ° C to isolate a phthalic anhydride-rich fraction. The crystallized anhydride is contaminated with a small amount of solvent, which can be removed by distillation or by drying in air or in vacuum.

Andra metoder for isolering av den intramolekylara anhydriden innefatta exempelvis destilla tion eller indunstning av extraktet for avskiljning av det aromatiska losningsmedlet eller indunstning av extraktet vid lagre tryck for avdrivning av hela mangden eller en del av losningsmedlet. Other methods of isolating the intramolecular anhydride include, for example, distillation or evaporation of the extract to separate the aromatic solvent or evaporation of the extract at lower pressures to evaporate all or part of the solvent.

Efter extraktion och isolering av anhydridenkan .losningsmedlet antingen aterforas till extraktions- steget, destilleras for separering av ofullstandigt oxiderade aromatiska fOreningar eller (om losningsmedlet besthr av en del av oxidationsut- gangsblandningen) foras direkt till oxidations- steget. Hela eller en del av losningsmedlet kan behandlas med aktiverat trakol for adsorption av eventuella fargade oxidationsbiprodukter, vilka kunna vara losta i losningsmedlet och vilka ham-ma den katalytiska oxidationen. Om det aroma- tiska losningsmedlet skall aterforas till extraktionen eller oxidationssteget Or det mycket lampligt att avlagsna oxidationsbiprodukter frail hela eller en del av den aterforda losningsmedelsstrbmmen. After extraction and isolation of the anhydride, the solvent can either be returned to the extraction step, distilled to separate incompletely oxidized aromatic compounds or (if the solvent consists of a part of the oxidation starting mixture) passed directly to the oxidation step. All or part of the solvent can be treated with activated trachol for adsorption of any colored oxidation by-products, which may be dissolved in the solvent and which inhibit the catalytic oxidation. If the aromatic solvent is to be returned to the extraction or oxidation step, it is very convenient to remove oxidation by-products from all or part of the recovered solvent stream.

Uppfinningen askadliggores narmare medelst foljande exempel, van i temp eraturerna angivas i Celsiusgrader. The invention is further illustrated by the following examples, the temperatures are given in degrees Celsius.

Exempel 1. Forfarandet tillampades forst pa en syntetisk blandning av bensendikarbonsyror, vii- ken i sammansattning motsvarade en blandning, som framstallts genom oxidation av en Craromatisk fraktion med kokintervallet 136-145° me- delst luft vid 200° och 28 at tryck i ett attiksyra- losningsmedel och i narvaro av en manganbromidkatalysator med efterfOljande avfiltrering av storsta delen isoftalsyra och tereftalsyra frail reak- tionsmediet vid 200° under tryck, avdunstning av attiksyran och vattnet frail filtratet vid 118° och extraktion av bensoesyran ur den isolerade bensenkarbonsyrablandningen med 1/4 viktdel toluen per del blandning vid 25°. Den syntetiska blandningen hade foljande sammansattning: Ortoftalsyra 34,00 viktdelar Isoftalsyra 2,00 Tereftalsyra 2,00 38,00 viktdelar Ovannamnda blandning overfordes till kokaren (reboiler) i en tiobottnars destillationskolonn med en toppaterflOdeskylare, som var anordnad att hterfora icke vattenhaltigt destillat till kolonnen. 2,6 delar xylen sattes till kolonnen och kokaren upphettades till 178-185°, vid vilken temperatur xylenen kokade och ortoftalsyran dehydratiserades. mom 15 minuter tillvaratogos 3,6 delar vatten i aterflodeskylaren. Den teoretiska mangd vatten, som kan avlagsnas, uppghr till 3,69 delar. Fort-salt upphettning gay icke ytterligare vattenmangd. Example 1. The process was first applied to a synthetic mixture of benzenedicarboxylic acids, which in composition corresponded to a mixture prepared by oxidation of a chromatic fraction with a boiling range of 136-145 ° with air at 200 ° and 28 ° C in an attic acid. solvent and in the presence of a manganese bromide catalyst with subsequent filtration of most of the isophthalic acid and terephthalic acid from the reaction medium at 200 ° under pressure, evaporation of the attic acid and water from the filtrate at 118 ° and extraction of the benzoic acid from the isolated mixture with benzenecarboxylic acid toluene per part mixture at 25 °. The synthetic mixture had the following composition: Orthophthalic acid 34.00 parts by weight Isophthalic acid 2.00 Terephthalic acid 2.00 38.00 parts by weight The above mixture was transferred to the boiler (reboiler) in a ten-bottom distillation column with a topater liquid cooler arranged to distill carbon to water. . 2.6 parts of xylene were added to the column and the digester was heated to 178-185 °, at which temperature the xylene boiled and the orthophthalic acid was dehydrated. 15 minutes, 3.6 parts of water were recovered in the backflow cooler. The theoretical amount of water that can be removed amounts to 3.69 parts. Fast-salt heating gay no additional amount of water.

Kokarinnehallet avkyldes till 20° och bildade en fast massa. Denna uttogs, pulveriserades och overfordes till ett slutet glasextraktionskarl. 260 viktdelar toluen tillsattes och den resulterande uppslamningen omrordes 15 minuter vid 85°. The contents of the boiler were cooled to 20 ° and formed a solid mass. This was taken out, pulverized and transferred to a closed glass extraction vessel. 260 parts by weight of toluene were added and the resulting slurry was stirred for 15 minutes at 85 °.

Uppslamningen avkyldes till 600 och filtrerades, varefter filterkakan tvattades med 17,5 delar toluen och lufttorkades. Filterkakan vagde 3,96 de- -6— — Tar, motsvarande 99,0 % av de tillforda 4,00 de-lama iso- och tereftalsyra. Produkten hade syratalet 659, vilket motsvarar det teoretiska iso- och tereftalsyratalet 675. The slurry was cooled to 600 and filtered, after which the filter cake was washed with 17.5 parts of toluene and air dried. The filter cake weighed 3.96 parts, corresponding to 99.0% of the required 4.00 parts of iso- and terephthalic acid. The product had the acid number 659, which corresponds to the theoretical iso- and terephthalic acid number 675.

Avdunstning av filtratet gay 28,60 delar ftalsyraanhydrid, vilket utgor 94,5 % av den teoretiska mangden 29,50 delar. Produkten hade syratalet 757. Eftersom det teoretiska syratalet for ftalsyraanhydrid är 759, hade den erhallna produkten hogre renhetsgrad an 97,0 % Exempel 2. En blandning av aromatiska foreningar, erhallen av ett petroleumreformat och med kokpunkten mellan ungefar 164 och 179°, innehaller C,- och C-aromatiska kolvaten och bestar huvudsakligen av pseudokumen med nagot mindre mangd mesitylen och en smarre mangd andra aromatiska kolvaten. Nar en sadan blandning mdderas, erhaller man en blandning av trimellitsyra och trimesinsyra och en ovasentlig mangd av andra aromatiska syror. Trimellitsyra men icke trimesinsyra kan bilda en intramolekylar anhydrid. Evaporation of the filtrate gay 28.60 parts of phthalic anhydride, which represents 94.5% of the theoretical amount of 29.50 parts. The product had an acid number of 757. Since the theoretical acid number for phthalic anhydride is 759, the product obtained had a higher degree of purity of 97.0% Example 2. A mixture of aromatic compounds, obtained from a petroleum reformate and having a boiling point between about 164 and 179 °, contains C , - and C-aromatic hydrocarbons and consists mainly of pseudocumens with a slightly lesser amount of mesitylene and a smarter amount of other aromatic hydrocarbons. When such a mixture is moderated, a mixture of trimellitic acid and trimesic acid and an insignificant amount of other aromatic acids are obtained. Trimellitic acid but not trimesic acid can form an intramolecular anhydride.

En syntetisk blandning, innehallande kanda mangder trimellitsyra och trirnesinsyra, framstalldes for att utgora ett duplikat till denna blandning. Den hade foljande sammansattning- Trimesinsyra (2,4 mol) 5,279 viktdelar Trimellitsyra (4,7 mol) 10,088» 15,367 viktdelar Blandningen infordes i kokaren (reboiler) i en tiobottnars destillationskolonn, anordnad for Aterflode av endast icke vattenhaltigt destillat. 10 de-Jar (9,8 mol) attiksyraanhydrid och 125 delar xylen tillsattes for att underlatta dehydratiseringen. Blandningen kokades en. timme vid atmosfarstryck. A synthetic mixture, containing known amounts of trimellitic acid and trirnesic acid, was prepared to be a duplicate of this mixture. It had the following composition: Trimesic acid (2.4 moles) 5.279 parts by weight Trimellitic acid (4.7 moles) 10.088 »15.367 parts by weight 10 de-Jar (9.8 moles) of acetic anhydride and 125 parts of xylene were added to facilitate dehydration. The mixture was boiled one. hour at atmospheric pressure.

Materialet i kokaren avdrogs och filtrerades vid kokpunkten for separering av den olosliga trimesinsyran. Etter torkning av trimesinsyran vagde den 5,237 viktdelar och hade syratalet 802 (teoretiskt 801), motsvarande en separeringsgrad Over 99 %. En infrarod analys visade icke narvaro ens av spar trimellitsyra eller trimellitsyraanhydrid. The material in the digester was removed and filtered at the boiling point to separate the insoluble trimesic acid. After drying the trimesic acid, it weighed 5,237 parts by weight and had an acid number of 802 (theoretical 801), corresponding to a degree of separation of over 99%. An infrared analysis did not even show the presence of sparse trimellitic acid or trimellitic anhydride.

Av ovanstiende beskrivning och exempel framgar det klart, att foreliggande forfarande fullstandigt uppfyller ovan angivna krav och mojliggor en i det narmaste kvantitativ separering av bensenpolykarbonsyror, vilka kunna bilda intramolekylara anhydrider, fran sadana bensenpolykarbonsyror, -vilka icke kunna bilda anhydrider av delta slag. From the above description and examples it is clear that the present process completely meets the above requirements and enables an almost quantitative separation of benzene polycarboxylic acids, which can form intramolecular anhydrides, from such benzene polycarboxylic acids, which cannot form anhydrides of delta kinds.

Claims

Patent claim Ak:

A process for separating a mixture containing benzene polycarboxylic acids, at least one but not all of which may form an intramolecular anhydride, may be characterized in that the mixture is heated to dehydrate the benzene polycarboxylic acid which may form the intramolecular anhydride. from the mixture with an aromatic solvent and isolate the extracted benzene polycarboxylic anhydride.

2. Process according to claim 1, characterized in that the aromatic solvent consists of a mixture of alkyl-substituted aromatic compounds, which can be oxidized to said mixture of benzene polycarboxylic acids.

3. A process according to claim 1, characterized in that the anhydride is extracted at elevated temperature and isolated by cooling the extract and crystallizing the benzene polycarboxylic anhydride therefrom.

4. A process according to claim 1, characterized in that the mixture consisting of benzene polycarboxylic acids constitutes at least part of the products obtained by oxidation of alkyl-substituted aromatic compounds with a boiling range of about 164 to 179 ° C, and from the isolated anhydride of trimellitic anhydride.

5. A process for separating a mixture consisting of benzoic acid and benzene polycarboxylic acids, according to claim 1, characterized in that benzoic acid is extracted from the mixture with an aromatic solvent at a temperature below the dehydration temperature, whereby a first raffinate is obtained. dehydration of the benzene polycarboxylic acid, which can form the intramolecular anhydride, extracts the anhydride from the first raffinate with an aromatic solvent and isolates the benzene polycarbonic anhydride from the extract.

6. A process according to claim 5, characterized in that the mixture consisting of benzoic acid and benzene polycarboxylic acids constitutes at least part of the products obtained by oxidation of alkyl-substituted aromatic compounds with a boiling range between about 136 and 145 ° C, and that the isolated anhydride consists of phthalic anhydride. Request publications: Patents from Germany 948 503; USA. 2 741 63 3.