Separation Process of a Mixture Acetone , Dichloromethane and Trifluoroacetic Acid/Acetone Azeotrope

Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 601 458 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) intci.6: C08J 11/02, B01D 3/14, of the grant of the patent: B01D3/36, D01F 13/04 26.08.1998 Bulletin 1998/35 // C08G63/81 (21) Application number: 93119353.6

(22) Date of filing: 01.12.1993

(54) Separation process of a mixture acetone , dichloromethane and trifluoroacetic acid/acetone azeotrope Verfahren zurTrennung einer Mischung aus Aceton, Dichlormethan und dem Azeotrop Aceton/ Trifluoressigsaure Procede de separation d'un melange acetone, dichloromethane et azeotrope acetone/acide trifluoroacetique

(84) Designated Contracting States: • Maier, Thomas Robert DE FR GB IT Brecksville, Ohio 44141 (US) • Chawla, Surendra Kumar (30) Priority: 07.12.1992 US 986201 Copley, Ohio 44321 (US)

(43) Date of publication of application: (74) Representative: Leitz, Paul 15.06.1994 Bulletin 1994/24 Goodyear Technical Center-Luxembourg Patent-Department (73) Proprietor: THE GOODYEAR TIRE & RUBBER L-7750 Colmar-Berg (LU) COMPANY Akron, Ohio 44316-0001 (US) (56) References cited: EP-A- 0 359 692 (72) Inventors: • Hahn, Bruce Raymond • DATABASE WPIL, no. 88-212 207, DERWENT Hudson, Ohio 44236 (US) PUBLICATIONS LTD., London; & SU-A-1 366 173 (MOSCOW FINE CHEM. TECHN.)

DO 00

o CO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU

Printed by Jouve, 75001 PARIS (FR) 1 EP 0 601 458 B1 2

Description trope to break the water/trifluoroacetic acid azeotrope producing a mixture of trifluoroacetic acid and Background of the Invention a water/sulfuric acid complex; (6) fractionally distilling the mixture of trifluoroacetic United States Patent 5,061 ,425 discloses a process 5 acid and the water/sulfuric acid complex to separate for producing high modulus, high tenacity polyethylene the trifluoroacetic acid from the water/sulfuric acid terephthalate (PET) filament by spinning a solution of complex. PET in a mixed solvent system containing trifluoroacetic acid and dichloromethane through a die and into a co- Detailed Description of the Invention agulation medium containing acetone. This results in 10 the formation of a mixture of acetone, trifluoroacetic ac- Mixtures of acetone, dichloromethane, and trifluor- id, and dichloromethane. United States Patent oacetic acid are technically comprised of free acetone, 4,792,573, United States Patent 4,917,845, and United free dichloromethane, and a trifluoroacetic acid/acetone States Patent 4,957,945 disclose a technique for pro- azeotrope. There is no free trifluoroacetic acid in such ducing ultra-high molecular weight polyester resin. One is mixtures (all of the trifluoroacetic acid is in the trifluoro- of the techniques disclosed in these patents also results acetic acid/acetone azeotrope). In the first step of the in the formation of a mixture of acetone, trifluoroacetic process of this invention, the three component mixture acid, and dichloromethane. In commercial operations it is fractionally distilled to recover the dichloromethane. is important to be able to recycle such solvent mixtures This fractional distillation is typically conducted at a tem- to make the process commercially and environmentally 20 perature of 41 °C (the boiling point of dichloromethane). feasible. In other words, the organic solvents must be However, this temperature will vary if the fractional dis- used, collected, separated, and re-used in a closed con- tillation is not carried out under atmospheric pressure. tinuous system. For instance, the dichloromethane will boil at a lower It is unfortunately not an easy task to separate the temperature at reduced pressures and will boil at higher three organic solvents present in such mixtures. This is 25 temperatures under increased pressures. In any case, because a trifluoroacetic acid/acetone azeotrope forms the dichloromethane is boiled off and recovered in this making quantitative separation by fractional distillation fractional distillation step. Afterthe dichloromethane has impossible. been removed, the remaining components in the solvent mixture are the free acetone and the trifluoroacetic acid/ Summary of the Invention 30 acetone azeotrope. In the second step of the process, the mixture of This invention discloses a process for separating trifluoroacetic acid/acetone azeotrope and free acetone acetone, dichloromethane and trifluoroacetic acid from remaining after the first step is fractionally distilled to re- a mixture of acetone, dichloromethane, and a trifluoro- move and recover the free acetone from the mixture. acetic acid/acetone azeotrope comprising the steps of: 35 Since acetone has a boiling point of 56°C, this fractional distillation step will typically be carried out at that tem- (1) fractionally distilling the mixture of acetone, perature under atmospheric pressure. After all of the dichloromethane, and the trifluoroacetic acid/ace- free acetone has been recovered, only the trifluoroace- tone azeotrope to separate the dichloromethane tic acid/acetone azeotrope remains. from a mixture of the trifluoroacetic acid/acetone 40 At this point, at least about 1 6 parts of water is add- azeotrope and free acetone; ed to the trifluoroacetic acid/acetone azeotrope per 1 00 (2) fractionally distilling the mixture of the trifluoro- parts by volume of the trifluoroacetic acid/acetone aze- acetic acid/acetone azeotrope and free acetone to otrope. The water breaks the trifluoroacetic acid/ace- separate the free acetone from the trifluoroacetic tone azeotrope and produces a mixture of free acetone acid/acetone azeotrope; 45 and a water/trifluoroacetic acid azeotrope. This will typ- (3) adding at least 1 6 parts of water to the trifluoro- ically be accomplished by adding from 16 parts to 350 acetic acid/acetone azeotrope per 100 parts by vol- parts of water per 100 parts by volume of the trifluoro- ume of the trifluoroacetic acid/acetone azeotrope to acetic acid/acetone azeotrope. It is more typical to add break the trifluoroacetic acid/acetone azeotrope from 1 6 parts to 1 00 parts of water to the trifluoroacetic producing a mixture of free acetone and a water/ so acid/acetone azeotrope per 1 00 parts by volume of the trifluoroacetic acid azeotrope; azeotrope. It is normally preferred to add from 16 parts (4) fractionally distilling the mixture of free acetone to 30 parts of water to the trifluoroacetic acid/acetone and the water/trifluoroacetic acid azeotrope to sep- azeotrope per 100 parts by volume of the azeotrope. It arate the free acetone from the water/trifluoroacetic is beneficial to minimize the amount of water added acid azeotrope; 55 while still using an amount which ensures that the trif- (5) adding at least 10 parts of sulfuric acid to the luoroacetic acid/acetone azeotrope is completely bro- water/trifluoroacetic acid azeotrope per 100 parts ken. by volume of the water/trifluoroacetic acid azeo- The mixture of free acetone and the water/trifluoro-

2 3 EP 0 601 458 B1 4 acetic acid azeotrope can then be fractionally distilled of the mixture of acetone, dichloromethane and the tri- to recover the free acetone from the mixture. This frac- fluoroacetic acid/acetone azeotrope was then heated in tional distillation is, of course, preferably carried out un- a round bottom flask equipped with a small Vigreux col- der atmospheric pressure at a temperature of 56°C. Af- umn. The mixture was fractionally distilled and at a tem- ter the free acetone is removed and recovered, only the 5 perature of about 40°C, a dichloromethane fraction was water/trifluoroacetic acid azeotrope remains. collected. After all of the dichloromethane had been sep- The water/trifluoroacetic acid azeotrope is broken arated from the mixture, the temperature was allowed by the addition of sulfuric acid. This is carried out by add- to increase to about 56°C. At that point, an acetone frac- ing at least 10 parts by volume of sulfuric acid to the tion was collected. Titrations of the dichloromethane water/trifluoroacetic acid azeotrope per 1 00 parts by vol- 10 fraction and the acetone fraction collected with a sodium ume of the water/trifluoroacetic acid azeotrope. Typical- hydroxide (NaOH) solution showed only a trace amount ly, from 10 parts to 140 parts of sulfuric acid is added of acid. The 111 .5 ml of residue in the pot was found to per 1 00 parts by volume of the water/trifluoroacetic acid be 5.01 molar trifluoroacetic acid. This showed that the azeotrope. Preferably, from 20 parts to 70 parts of sul- residue in the pot was a 3/2 by volume trifluoroacetic furic acid will be added to the water/trifluoroacetic acid is acid/acetone azeotrope (within experimental error). azeotrope per 100 parts by volume of the azeotrope. It At this point 20 ml of water was added to the trifluor- is normally most preferred to add from 30 parts to 50 oacetic acid/acetone azeotrope in the round bottom parts of sulfuric acid to the water/trifluoroacetic acid aze- flask. The distillation was continued and additional ace- otrope per 100 parts by volume of the azeotrope. After tone was collected at a temperature of 56°C. The tem- the water/trifluoroacetic acid azeotrope is broken by the 20 perature was then increased and a small fraction was addition of sulfuric acid, a mixture of free trifluoroacetic collected at a temperature over the range of 70°C to acid and a water/sulfuric acid complex is formed. 78°C. The fraction collected at 56°C contained only a The free trifluoroacetic acid can then be removed trace amount of acid and the small fraction collected from the mixture of free trifluoroacetic acid and the wa- from 70°C to 78°C contained 2.8% trifluoroacetic acid ter/sulfuric acid complex by fractional distillation. This 25 by weight. The pot was then cooled and 40 ml of con- fractional distillation will typically be carried out under centrated sulfuric acid was subsequently added. The atmospheric pressure at a temperature of 72°C. As ex- flask was then heated to 72°C and 29 ml of a trifluoro- plained before, the temperature at which the fractional acetic acid fraction was collected. Titration showed this distillation is carried out will vary under increased or de- fraction to be virtually pure trifluoroacetic acid. creased pressures. After the trifluoroacetic acid is re- 30 This example shows that the procedure of this in- moved and recovered by fractional distillation, only the vention can be successfully used for separating ace- water/sulfuric acid complex remains. tone, dichloromethane and trifluoroacetic acid from a Water can then be removed from the water/sulfuric mixture of acetone, dichloromethane and a trifluoroace- acid complex by boiling it out or by simply allowing it to tic acid/acetone azeotrope. Very high levels of purity can evaporate. By utilizing this procedure of water removal, 35 be realized by utilizing distillation columns having a concentrated sulfuric acid can be produced. The con- large number of theoretical plates. centrated sulfuric acid produced by such a procedure While certain representative embodiments and de- can then be recycled for utilization in breaking the water/ tails have been shown for the purpose of illustrating the trifluoroacetic acid azeotrope in the fifth step of the proc- subject invention, it will be apparent to those skilled in ess of this invention. In utilizing this process, the sulfuric 40 this art that various changes and modifications can be acid, water, trifluoroacetic acid, dichloromethane, and made therein without departing from the scope of the acetone can all be reused as part of a closed, continu- subject invention. ous separation procedure. This invention is illustrated by the following example which is merely for the purpose of illustration and is not 45 Claims to be regarded as limiting the scope of the invention or the manner in which it can be practiced. This working 1 . A process for separating acetone, dichloromethane example illustrates the practicality and the operability of and trifluoroacetic acid from a mixture of acetone, the present invention. dichloromethane, and a trifluoroacetic acid/acetone 50 azeotrope which is characterized by the steps of: Example (1 ) fractionally distilling the mixture of acetone, A solution containing 50 weight percent trifluoro- dichloromethane, and the trifluoroacetic acid/ acetic acid and 50 weight percent dichloromethane was acetone azeotrope to separate the dichlo- prepared. A mixture of acetone, dichloromethane, and romethane from a mixture of the trifluoroacetic a trifluoroacetic acid/acetone azeotrope was then pre- acid/acetone azeotrope and free acetone; pared by mixing 1 00 ml of the trifluoroacetic acid/dichlo- (2) fractionally distilling the mixture of the trif- romethane solution with 500 ml of acetone. The 600 ml luoroacetic acid/acetone azeotrope and free

3 5 EP 0 601 458 B1 6

acetone to separate the free acetone from the parts by volume of the water/trifluoroacetic acid trifluoroacetic acid/acetone azeotrope; azeotrope; and in that from 16 parts to 30 parts of (3) adding at least 16 parts of water to the trif- water is added in step (3) per 100 parts by volume luoroacetic acid/acetone azeotrope per 100 of the trifluoroacetic acid/acetone azeotrope. parts by volume of the trifluoroacetic acid/ace- 5 tone azeotrope to break the trifluoroacetic acid/ 7. A process as specified in any of the preceding acetone azeotrope producing a mixture of free claims characterized in that the mixture of acetone, acetone and a water/trifluoroacetic acid azeo- dichloromethane, and the trifluoroacetic acid/ace- trope; tone azeotrope is fractionally distilled in step (1 ) un- (4) fractionally distilling the mixture of free ac- 10 der atmospheric pressure at a temperature of 41 °C. etone and the water/trifluoroacetic acid azeotrope to separate the free acetone from the wa- 8. A process as specified in any of the preceding ter/trifluoroacetic acid azeotrope; claims characterized in that the mixture of the trif- (5) adding at least 10 parts of sulfuric acid to luoroacetic acid/acetone azeotrope and free ace- the water/trifluoroacetic acid azeotrope per 1 00 15 tone is fractionally distilled in step (2) under atmos- parts by volume of the water/trifluoroacetic acid pheric pressure at a temperature of 56°C. azeotrope to break the water/trifluoroacetic acid azeotrope producing a mixture of trifluoro- 9. A process as specified in any of the preceding acetic acid and a water/sulfuric acid complex; claims characterized in that the mixture of free ac- (6) fractionally distilling the mixture of trifluoro- 20 etone and the water/trifluoroacetic acid azeotrope acetic acid and the water/sulfuric acid complex is fractionally distilled in step (4) under atmospheric to separate the trifluoroacetic acid from the wa- pressure at a temperature of 56°C. ter/sulfuric acid complex. 10. A process as specified in any of the preceding 2. A process as specified in claim 1 characterized in 25 claims characterized in that the mixture of trifluoro- that the concentration of the sulfuric acid in the wa- acetic acid and the water/sulfuric acid complex is ter/sulfuric acid complex separated from the trifluor- fractionally distilled in step (6) under atmospheric oacetic acid in step (6) is increased by removing a pressure at a temperature of 72°C. portion of the water therefrom by evaporation or boiling to produce a concentrated sulfuric acid so- 30 lution, and in that the concentrated sulfuric acid so- Patentanspriiche lution is utilized as the source of the sulfuric acid employed in step (5). 1. Verfahren zur Abtrennung von Aceton, Dichlorme- than und Trifluoressigsaure aus einer Mischung von 3. A process as specified in claim 2 characterized in 35 Aceton, Dichlormethan und einem Trifluoressigsau- that the water removed from the water/sulfuric acid re/ Aceton-Azeotrop, welches durch die folgenden complex is utilized as the source of the water em- Stufen gekennzeichnet ist: ployed in step (3). (1) fraktionierte Destination der Mischung von 4. A process as specified in any of the preceding 40 Aceton, Dichlormethan und dem Trifluoressig- claims characterized in that from 10 parts to 140 saure/Aceton-Azeotrop, urn das Dichlorme- parts of sulfuric acid is added in step (5) per 100 than von einer Mischung des Trifluoressigsau- parts by volume of the water/trifluoroacetic acid re/ Aceton-Azeotrops und von f reiem Aceton zu azeotrope; and in that from 16 parts to 350 parts of trennen; water is added in step (3) per 100 parts by volume 45 (2) fraktionierte Destination der Mischung des of the trifluoroacetic acid/acetone azeotrope. Trifluoressigsaure/Aceton-Azeotrops und des freien Acetons, urn das freie Aceton von dem 5. A process as specified in any of the preceding Trifluoressigsaure/Aceton-Azeotrop zu tren- claims characterized in that from 20 parts to 70 nen; parts of sulfuric acid is added in step (5) per 100 50so (3) Zugabe von mindestens 16 Teilen Wasser parts by volume of the water/trifluoroacetic acid pro 100 Volumenteile des Trifluoressigsaure/ azeotrope; and in that from 16 parts to 100 parts of Aceton-Azeotrops zu dem Trifluoressigsaure/ water is added in step (3) per 100 parts by volume Aceton-Azeotrop, urn das Trifluoressigsaure/ of the trifluoroacetic acid/acetone azeotrope. Aceton-Azeotrop unter Bildung einer Mischung 55 von freiem Aceton und einem Wasser/Trifluor- 6. A process as specified in any of the preceding essigsaure-Azeotrop zu brechen; claims characterized in that from 30 parts to 50 (4) fraktionierte Destination der Mischung von parts of sulfuric acid is added in step (5) per 100 freiem Aceton und dem Wasser/Trifluoressig-

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saure-Azeotrop, urn das freie Aceton von dem 7. Verfahren nach irgendeinem der vorangehenden Wasser/Trifluoressigsaure-Azeotrop zu tren- Anspruche, dadurch gekennzeichnet, da(3 die Mi- nen; schung von Aceton, Dichlormethan und dem (5) Zugabe von mindestens 10 Teilen Schwe- Trifluoressigsaure/Aceton-Azeotrop in Stufe (1) un- felsaure pro 100 Volumenteile des Wasser/ 5 ter Atmospharendruck bei einer Temperatur von Trifluoressigsaure-Azeotrops zu dem Wasser/ 41 °C fraktioniert destilliert wird. Trifluoressigsaure-Azeotrop, urn das Wasser/ Trifluoressigsaure-Azeotrop unter Bildung ei- 8. Verfahren nach irgendeinem der vorangehenden ner Mischung von Trifluoressigsaure und ei- Anspruche, dadurch gekennzeichnet, dal3 die Mi- nem Wasser/Schwefelsaure-Komplex zu bre- 10 schung des Trifluoressigsaure/Aceton-Azeotrops chen; unddesfreien Acetons in Stufe (2) unter Atmospha- (6) fraktionierte Destination der Mischung von rendruck bei einer Temperatur von 56°C fraktioniert Trifluoressigsaure und dem Wasser/Schwefel- destilliert wird. saure-Komplex, urn die Trifluoressigsaure von dem Wasser/Schwefelsaure-Komplex zu tren- is 9. Verfahren nach irgendeinem der vorangehenden nen. Anspruche, dadurch gekennzeichnet, dal3 die Mi- schung von freiem Aceton und dem Wasser/Trifluo- 2. Verfahren nach Anspruch 1 , dadurch gekennzeich- ressigsaure-Azeotrop in Stufe (4) unter Atmospha- net, dal3 die Konzentration der Schwefelsaure in rendruck bei einer Temperatur von 56°C fraktioniert dem Wasser/Schwefelsaure-Komplex, der in Stufe 20 destilliert wird. (6) von der Trifluoressigsaure getrennt wird, durch Entfernung eines Teiles des Wassers daraus durch 10. Verfahren nach irgendeinem der vorangehenden Verdampfung oder Kochen erhoht wird, urn eine Anspruche, dadurch gekennzeichnet, dal3 die Mi- konzentrierte Schwefelsaure-Losung herzustellen, schung von Trifluoressigsaure und dem Wasser/ und dal3 die konzentrierte Schwefelsaure-Losung 25 Schwefelsaure-Komplex in Stufe (6) unter Atmo- als Quelle fur die Schwefelsaure, die in Stufe (5) spharendruck bei einer Temperatur von 72°C frak- eingesetzt wird, verwendet wird. tioniert destilliert wird.

3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, dal3 das aus dem Wasser/Schwefelsaure- 30 Revendications Komplex entfernte Wasser als Quelle fur das in Stu- fe (3) verwendete Wasser eingesetzt wird. 1. Procede pour separer de I'acetone, du dichloromethane et de I'acide trifluoracetique d'un melange 4. Verfahren nach irgendeinem der vorangehenden d'acetone, de dichloromethane et d'un azeotrope Anspruche, dadurch gekennzeichnet, dal3 10 Teile 35 acide trifluoracetique/acetone, qui se caracterise bis 140 Teile Schwefelsaure pro 100 Volumenteile par les etapes consistant a: des Wasser/Trifluoressigsaure-Azeotrops in Stufe (5) zugegeben werden; und dal3 16 Teile bis 350 (1) soumettre a une distillation fractionnee le Teile Wasser pro 100 Volumenteile Trifluoressig- melange d'acetone, de dichloromethane et de saure/Aceton-Azeotrop in Stufe (3) zugegeben 40 I'azeotrope acide trifluoracetique/acetone pour werden. separer le dichloromethane d'un melange de I'azeotrope acide trifluoracetique/acetone et 5. Verfahren nach irgendeinem der vorangehenden d'acetone libre; Anspruche, dadurch gekennzeichnet, dal3 20 Teile (2) soumettre a une distillation fractionnee le bis 70 Teile Schwefelsaure pro 100 Volumenteile 45 melange de I'azeotrope acide trifluoracetique/ des Wasser/Trifluoressigsaure-Azeotrops in Stufe acetone et d'acetone libre pour separer I'ace- (5) zugegeben werden; und dal3 16 Teile bis 100 tone libre de I'azeotrope acide trifluoracetique/ Teile Wasser pro 100 Volumenteile Trifluoressig- acetone; saure/Aceton-Azeotrop in Stufe (3) zugegeben (3) ajouter au moins 16 parties d'eau a I'azeo- werden. 50 trope acide trifluoracetique/acetone par 100 parties en volume de I'azeotrope acide trifluo- 6. Verfahren nach irgendeinem der vorangehenden racetique/acetone pour rompre I'azeotrope aci- Anspruche, dadurch gekennzeichnet, dal3 30 Teile de trifluoracetique/acetone et obtenir un me- bis 50 Teile Schwefelsaure pro 100 Volumenteile lange d'acetone libre et d'un azeotrope eau/aci- Wasser/Trifluoressigsaure-Azeotrop in Stufe (5) 55 de trifluoracetique; zugegeben werden; und dal3 16 Teile bis 30 Teile (4) soumettre a une distillation fractionnee le Wasser pro 100 Volumenteile Trifluoressigsaure/ melange d'acetone libre et de I'azeotrope eau/ Aceton-Azeotrop in Stufe (3) zugegeben werden. acide trifluoracetique pour separer I'acetone li-

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bre de I'azeotrope eau/acide trifluoracetique; qu'on soumet le melange d'acetone, de dichlorome- (5) ajouter au moins 10 parties d'acide sulfuri- thane et de I'azeotrope d'acide trifluoracetique a que a I'azeotrope eau/acide trifluoracetique par une distillation fractionnee a I'etape (1) sous pres- 1 00 parties en volume de I'azeotrope eau/acide sion atmospherique, a une temperature de 41 °C. trifluoracetique pour rompre I'azeotrope eau/ 5 acide trifluoracetique et obtenir un melange 8. Procede tel que specifie dans I'une quelconque des d'acide trifluoracetique et d'un complexe eau/ revendications precedentes, caracterise en ce acide sulfurique; qu'on soumet le melange de I'azeotrope acide tri- (6) soumettre a une distillation fractionnee le fluoracetique/acetone et de I'acetone libre a une melange d'acide trifluoracetique et du comple- 10 distillation fractionnee a I'etape (2) sous pression xe eau/acide sulfurique pour separer I'acide tri- atmospherique a une temperature de 56°C. fluoracetique du complexe eau/acide sulfurique. 9. Procede tel que specifie dans I'une quelconque des revendications precedentes, caracterise en ce 2. Procede selon la revendication 1 , caracterise en ce is qu'on soumet le melange d'acetone libre et de qu'on augmente la concentration de I'acide sulfuri- I'azeotrope eau/acide trifluoracetique a une distilla- que dans le complexe eau/acide sulfurique separe tion fractionnee a I'etape (4) sous pression atmos- de I'acide trifluoracetique a I'etape (6) en en retirant pherique, a une temperature de 56°C. une partie de I'eau par evaporation ou par ebullition pour obtenir une solution concentree d'acide sulfu- 20 10. Procede tel que specifie dans I'une quelconque des rique et en ce qu'on utilise la solution concentree revendications precedentes, caracterise en ce d'acide sulfurique comme source de I'acide sulfuri- qu'on soumet le melange de I'acide trifluoracetique que utilise a I'etape (5). et du complexe eau/acide sulfurique a une distillation fractionnee a I'etape (6) sous pression atmos- 3. Procede tel que specifie a la revendication 2, carac- 25 pherique, a une temperature de 72°. terise eh ce que I'eau retiree du complexe eau/acide sulfurique est utilisee comme source de I'eau em- ployee dans I'etape (3).

4. Procede tel que specifie dans I'une quelconque des 30 revendications precedentes, caracterise en ce qu'on ajoute de 1 0 parties a 1 40 parties d'acide sulfurique a I'etape (5) par 100 parties en volume de I'azeotrope eau/acide trifluoracetique et en ce qu'on ajoute de 16 parties a 350 parties d'eau a I'etape 35 (3) par 100 parties en volume de I'azeotrope acide trifluoracetique/acetone.

5. Procede tel que specifie dans I'une quelconque des revendications precedentes, caracterise en ce 40 qu'on ajoute de 20 parties a 70 parties d'acide sulfurique a I'etape (5) par 100 parties en volume de I'azeotrope eau/acide trifluoracetique et en ce qu'on ajoute de 16 parties a 100 parties d'eau a I'etape (3) par 100 parties en volume de I'azeotrope acide 45 trifluoracetique/acetone.

6. Procede tel que specifie dans I'une quelconque des revendications precedentes, caracterise en ce qu'on ajoute de 30 parties a 50 parties d'acide sul- 50 furique a I'etape (5) par 100 parties en volume de I'azeotrope eau/acide trifluoracetique et en ce qu'on ajoute de 16 parties a 30 parties d'eau a I'etape (3) par 100 parties en volume de I'azeotrope acide trifluoracetique/acetone.

7. Procede tel que specifie dans I'une quelconque des revendications precedentes, caracterise en ce