Europaisches Patentamt

(19) J» European Patent Office (îj) Publication number: O 002 382 Office européen des brevets Bl

® EUROPEAN PATENT SPECIFICATION

@ Date of publication of patent spécification: 14.10.81 ® Int. CI.3: C07 C 51/46, C07C 51/48, @ Application number: 78300736.2 C 07 C 57/04, C 07 C 53/08 @ Date offiling: 05.12.78

(§) Acrylic acid recovery and purification.

(30) Priority: 05.1 2.77 US 857147 (73) Proprietor: THE STANDARD OIL COMPANY Midland Building Cleveland, Ohio 441 1 5 (US) @ Date of publication of application: 13.06.79 Bulletin 79/12 @ Inventor: Wagner, David Rudolph 3613 West 120, Street @ Publication of the grant of the European patent: Cleveland Ohio 441 1 1 Cuyahoga County (US) 14.10.81 BiMIetin 81/41

@ Représentative: Smith, Sydney et al, @ Designated Contracting States: Elkington and Fife High Holborn House 52/54 BE CH DE FR GB NL High Holborn London WC1V6SH (GB) (56) Références cited: US -A -3 433 831 US - A - 3 478 093 US - A - 3 830 707 US-A-3859175

00 co Cl o o Q Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. it shall not be deemed to have been filed until the opposition fee has been ÎJ! paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. This invention relates to the recovery and separation. It has been discovered that capital purification of acrylic acid. cost reduction and energy savings may be Acrylic acid is produced from the vapour obtained by the process according to the inven- phase oxidation of propylene or acrolein over an tion. oxidation catalyst. The gaseous reactor effluent The process according to the invention there- is then cooled and/or absorbed in water to fore comprises the steps of: obtain an aqueous solution containing from (a) contacting an aqueous solution, obtained 10-80% by weight acrylic acid, acetic acid, from the process of oxidation of propylene and various impurities. or acrolein, with a solvent which has an The separation of acrylic acid from this azeotropic boiling point with water below aqueous stream has been difficult due to the the boiling point of acrylic acid, in a first relative volatilities of acrylic acid, acetic acid column to obtain a first overhead stream of and water, which prevent simple fractional dis- solvent, acrylic acid, acetic acid and water tillation. and Several different processes have been (b) distilling said first stream in a solvent proposed to perform this separation. For recovery column having distillation trays, to example, U.S. Patent No. 3,830,707 discloses a obtain a second overhead vapour stream of process in which a specific entrainer which is solvent and water which vapour stream is isooctane or nitroethane is used to perform an condensed and a portion thereof is re- azeotropic distillation. The entrainer allows the cycled to the solvent recovery column as re- removal of acetic acid overhead, while sub- flux and the remainder returned to the first stantially purified acrylic acid is removed as a column for re-use, and a bottoms stream of bottoms product. Other entrainers that have acrylic acid; been proposed have also included benzene and characterised in that toluene. (c) a vapour stream which contains acrylic acid Another method for separation of acrylic acid and acetic acid is removed from below the has been solvent extraction. The acrylic acid, feed tray of the solvent recovery column, acetic acid and water are extracted from the and aqueous solution by countercurrent extraction. (d) the vapour stream is rectified to separate Many different types of solvents have been and remove acetic acid. proposed for this extraction, some of which may The invention will now be further described also be used as entrainers. Among typical by reference to the accompanying drawings, in extraction solvents have been phosphates; ali- which phatic or aromatic hydrocarbons; ethers such as Figure 1 shows the prior art method of diphenol ether; alcohols and esters. U.S. Patent separating acrylic acid by extraction and Figure No. 3,859,175, although directed to a dual 2 shows one embodiment of the process solvent system for entrainment, discloses as according to the present invention. prior art the extraction of acrylic acid using a Referring to Figure 1, the aqueous solution solvent mixture of methylethyl ketone and either obtained in the process for production of acrylic a xylene or ethyl benzene. Typically, such sol- acid from the oxidation of propylene or acrolein vent extraction systems can be divided into is passed through line 100 to extraction column those solvents that have a boiling point higher 102. A solvent enters the extraction column at than acrylic acid and those that boil at a the bottom through line 104 and contacts the temperature lower than the boiling point of aqueous solution countercurrently to extract the acrylic acid. acrylic acid. The extract, comprising the sol- A third method for recovery of acrylic acid vent, acrylic acid, acetic acid and water leaves has been the combination of extraction followed the extraction column through line 106 and is by entrainment such as is described in U.S. sent to a solvent recovery column 110. The Patent No. 3,433,831. residue not extracted, being various impurities An alternative process is described in U.S. dissolved solvent and water leaves the extrac- Patent No. 3,478,093, in which a vapour tion column through line 108. stream of acrylic acid and acetic acid is removed In the solvent recovery column 110 distilla- from a distillation column containing acrylic tion is carried out. The column is heated through acid, acetic acid, solvent and water. exchanger 120. A vapour stream of solvent and A major disadvantage of recovery systems water leaves the solvent recovery column in line using solvents that have a boiling point higher 112 and is passed to condenser 114. Here the than that of acrylic acid, has been the need for a solvent and water are condensed, a portion large amount of heat usage in performing the being returned to the solvent recovery column separation. The present invention provides a through line 116 as reflux. The remaining sol- method for both reducing the size of the final vent and water is returned to the extraction column needed in the separation process and column through line 104 for reuse. Acetic acid, eliminating the heat necessary for this final acrylic acid and a minor amount of solvent leaves the solvent recovery column through line The operating parameters and particular con- 118 and passes to the final separation column struction of the first column depend on whether 122. In the final separation column, another dis- the process uses extraction or entrainment, and tillation is performed, with heat being added to the specific type of solvent. Typically, this the column through exchanger 134. A vapour column is operated at atmospheric or sub- stream which contains acetic acid is removed atmospheric conditions. The various column de- overhead through line 124. This vapour stream signs based on specific solvents are known in is condensed in condenser 126 and the con- the art. densed liquid can be recycled back to the The solvent recovery column is essential to column through line 128 or a portion removed the present invention. The distillation necessary from the system through line 130. Sub- to recover and recycle solvent for further use is stantially purified acrylic acid is removed from carried out in this column. Again, the precise the final separation column through line 132. column design will depend on the type of sol- Figure 2, which is an embodiment of the vent used and the composition of the extract or present invention sl---3ws the advantages over entrained liquid from the first column. the prior art. The numbers of the various The extract is normally fed to the upper half streams and equipment which are the same as of the solvent recovery column. The distillation in Figure 1 have been retained. Referring is carried out in this column, usually at pressures specifically to the solvent recovery column 110, from 13332.2 to 53328.8 Pa (100 to 400 mm it can be seen that the solvent and water are Hg). The lower pressures allow lower temper- removed overhead through line 112 to con- atures to be used in the distillation, thus pre- denser 114 as in the previous figure. However, a venting undesirable polymerization of the acrylic vapour side-stream is removed through line 140 acid. and passed to a much smaller column 142. The overhead stream from the solvent Without the addition of heat, acetic acid passes recovery column contains solvent and water. overhead and is removed from the column This vapour stream is then condensed. A portion through line 144. This overhead stream then is is recycled to the solvent recovery column as re- sent to condenser 146 and the condensed flux, while the remainder is returned to the liquid is both used as reflux through line 148 extraction or entrainment column for solvent back to the column, and removed from the reuse. system through line 150. The bottoms stream It has been discovered that the concentra- of column 142 contains acrylic acid and acetic tion of acetic acid in the solvent recovery acid. The stream is returned to the solvent column reaches a maximum below the feed recovery column through line 152. Acrylic acid tray. Specifically, this maximum occurs between is removed from the solvent recovery column 1/4 to 1/2 of the number of trays in the column bottoms through line 1 54. A portion is sent to counting from the bottom of the column. By indirect heat exchange in exchanger 156 to pro- removing the vapours at this point in the vide the heat necessary to reboil the column. column, the acetic acid may be separated from It can thus be seen that acetic acid can be the acrylic acid without the application of addit- separated from acrylic acid in a much smaller ional heat. Further, the number of trays column recuring less energy. necessary for this separation is greatly reduced. It is pr\<::rred that the invention is used with The vapour stream is passed to a small recti- recovery systems which use a solvent for fication column, typically having three to twelve extraction of acrylic acid, acetic acid and water. trays, preferably three to ten trays. Acetic acid is The solvents used in the present invention removed as a vaporous overhead, condensed are those known in the art which can extract and removed from the system. A portion of this acrylic acid. The solvent must have an azeo- condensed liquid is returned to the column as tropic boiling point with water below the boiling reflux. The bottoms stream of this small recti- point of acrylic acid. This is required so that the fying column, being acrylic acid and acetic acid, solvent and water can be removed overhead in is returned to the solvent recovery column at a the solvent recovery column. There are point below the vapour removal. many solvents that meet this requirement, such The vapour stream may also contain some as those mentioned in the description of the solvent. This solvent, if present, will then appear prior art processes in U.S. Patent No. 3,478,093. in the vaporous overhead of the rectification These include, for example, benzene, diiso- column. If pure acetic acid is desired, this propyl ether and toluene. The solvent may also vaporous overhead should be passed to another be a combination of two or more solvents such column for solvent separation. as described in U.S. Patent No. 3,433,831. By using the process of the present inven- In a second embodiment, the present inven- tion, the size of the final column for the tion is also applicable to entrainment recovery separation of acetic acid from acrylic acid is systems in which distillation with a solvent greatly reduced. Further, the equipment rather than extraction is performed in the first necessary to reboil this column has been elimin- column. In this process, the overhead stream ated. Although somewhat more heat may be re- from the distillation column will contain sol- quired in the solvent recovery column, the total vent, acetic acid, water and some acrylic acid. amount of heat necessary to perform the com- plete operation of solvent recovery and acetic from the process of oxidation of propylene acid separation is substantially reduced. or acrolein, with a solvent which has an azeotropic boiling point with water below Example the boiling point of acrylic acid, in a first An aqueous solution obtained from the oxi- column to obtain a first overhead stream of dation reaction of propylene, comprising solvent, acrylic acid, acetic acid and water approximately 55% by weight acrylic acid, and water, acetic acid and some impurities was sent (b) distilling said first stream in a solvent to the top of a first column. In this column, the recovery column having distillation trays, to aqueous stream was contacted counter- obtain a second overhead vapour stream of currently with diisopropyl ether having a boiling solvent and water which vapour stream is point of 67.5°C. The extract was removed condensed and a portion thereof is re- overhead and had the following composition: cycled to the solvent recovery column as re- flux and the remainder returned to the first column for re-use, and a bottoms stream of acrylic acid; characterised in that (c) a vapour stream which contains acrylic acid and acetic acid is removed from below the feed tray of the solvent recovery column, and (d) the vapour stream is rectified to separate and remove acetic acid. 2. A method as claimed in claim 1 in which the solvent has a boiling point below that of acrylic acid. This stream was passed to the 15th stage of 3. A method as claimed in claim 2 in which a solvent recovery column having 19 distilla- extraction is performed in the column of step tion stages. The bottom of the column was re- (a). boiled to provide the heat necessary for distilla- 4. A method as claimed in claim 2 in which tion. An overhead stream containing all of the entrainment involving distillation with the sol- solvent, water and about 10% of the acetic acid vent is performed in the column of step (a). was removed and condensed in a condenser. A 5. A method as claimed in any of claims 1 to portion of the condensed liquid was used for re- 4 in which the vapour stream of step (c) is flux, the remainder being recycled back to the removed from the solvent recovery column at a extraction column. point between 1/4 to 1/2 of the total number of A vapour stream was removed from the 7th trays within the column, counting from the stage of the solvent recovery column. This bottom of the column. vapour stream had a composition of about 80% 6. A method as claimed in any of claims 1 to acrylic acid and about 20% acetic acid. The 5 in which rectification of the vapour stream is vapour stream was then passed to the bottom carried out in a second column to obtain a of a column having four stages. second overhead stream of acetic acid, and a Without the addition of heat, acetic acid was bottoms stream of acrylic acid and acetic acid, removed overhead as a vapour stream. This which bottoms stream is returned to the sol- stream was condensed, with a portion of the vent recovery column at a point below the condensed liquid being used as reflux and the vapour removal. remainder removed from the system. Approxi- 7. A method as claimed in claim 6 in which mately 90% of the acetic acid contained in the the second column has from three to ten trays. feed to the solvent recovery unit was removed in this manner. The bottoms of the small rectifying column, containing acetic acid and acrylic acid, was then returned to the 7th stage tray of the solvent 1. Procédé de séparation d'acide acrylique à recovery column. partir d'une solution aqueuse d'acide acrylique By removing the acetic acid in this manner, a et d'acide acétique comprenant les étapes de: bottoms stream of 99,9% acrylic acid could be (a) mise en contact d'une solution aqueuse ob- recovered from the solvent recovery column. tenue à partir du procédé d'oxydation de propylène ou d'acroléine, avec un solvant qui a un point d'ébullition azéotropique avec l'eau inférieur au point d'ébullition de l'acide acrylique dans une première colonne afin 1. A method for separating acrylic acid from d'obtenir en tête de colonne un premier an aqueous solution of acrylic acid and acetic courant de solvant, d'acide acrylique, acid comprising the steps of: d'acide acétique et d'eau et. (a) contacting an aqueous solution, obtained (b) de distillation de ce premier courant dans une colonne de récupération de solvant ersten Kolonne mit einem Lösungsmittel in ayant des plateaux de distillation pour ob- Berührung gebracht wird, das einen azeo- tenir un second courant de vapeur en tête tropen Siedepunkt mit Wasser unterhalb de colonne constitué de solvant et d'eau, ce des Siedepunkts der Acrylsäure hat, wo- courant de vapeur étant condensé et une durch ein erstes Kopfprodukt aus Lösungs- partie de celui-ci étant recyclée dans la mittel, Acrylsäure, Essigsäure und Wasser colonne de récupération de solvant sous erhalten wird, und forme de reflux et le restant étant ramené (b) dieses erste Produkt in einer Lösungs- dans la première colonne pour sa ·réutiIisa- mittelrückgewinnungskolonne mit Destilla- tion, et un courant de queues constitué tionsböden destilliert wird, wodurch ein d'acide acrylique, zweites dampfförmiges Überkopfprodukt caracterisé par le fait que aus Lösungsmittel und Wasser erhalten (c) l'on sépare un courant de vapeur qui con- wird, das kondensiert wird un teilweise tient l'acide acrylique et l'acide acétique à als Rückfluß der Lösungsmittelrückgewin- partir d'une zone située au-dessous du nungskolonne wieder zugeführt wird, plateau d'alimentation de la colonne de während die Restmenge der ersten Kolonne récupération de solvant et, zur Wiederverwendung zugeführt wird, und (d) on rectifie le courant de vapeur pour séparer zusätzlich ein Acrylsäure-Bodenprodukt et éliminer l'acide acétique. erhalten wird, 2. Procédé selon la revendication 1, carac- durch gekennzeichnet, daß térisé par le fait que le solvant a un point (c) ein Acrylsäure und Essigsäure enthaltendes d'ébullition inférieur à celui de l'acide acrylique. Dampfprodukt unterhalb des Bodens der 3. Procédé selon la revendication 2, carac- Lösungsmittelrückgewinnungskolonne ab- terisé, par le fait qu'on effectue une extraction gezogen wird, bei dem die Kolonne gespeist dans la colonne de l'étape a). wird, und 4. Procédé selon la revendication 2, carac- (d) dieses Dampfprodukt zur Abtrennung und térisé par le fait qu'on effectue un entrainement Entfernung von Essigsäure rektifiziert wird. comportant une distillation avec le solvant dans 2. Verfahren gemäß Anspruch 1, dadurch la colonne de l'étape a). gekennzeichnet, daß das Lösungsmittel einen 5. Procédé selon l'une des revendications 1 à Siedepunkt unterhalb des Siedepunkts der 4, caractérisé par le fait que le courant de Acrylsäure hat. vapeur de l'étape c) est éliminé de la colonne 3. Verfahren gemaß Anspruch 2, dadurch ge- de récupération du solvant et un point situé kennzeichnet, daß die Extraktion in der Ko- entre le 1/4 et la moitié du nombre total de lonne der Stufe (a) durchgeführt wird. plateaux dans la colonne, en comptant à partir 4. Verfahren gemäß Anspruch 2, dadurch ge- du fond de la colonne. kennzeichnet, daß die das Abziehen umfassende 6. Procédé selon l'une des revendications 1 à Destillation mit dem Lösungsmittel in der 5, caractérisé par le fait que la rectification du Kolonne der Stufe (a) durchgeführt wird. courant de vapeur est effectuée dans une 5. Verfahren gemäß irgendeinem der An- seconde colonne pour obtenir un second sprüche 1 bis 4, dadurch gekennzeichnet, daß courant d'acide acétique en tête de colonne et das dampfförmige Produkt der Stufe (c) aus des un courant de queues constitué d'acide Lösungsmittelrückgewinnungskolonne an ei- acrylique et d'acide acétique, ce courant de nem Punkt zwischen 1/4 bis 1/2 der Gesamt- queues étant renvoyé dans la colonne de zahl der Böden in der Kolonne abgezogen wird, récupération de solvant en un point situé au- gezählt vom unteren Ende der Kolonne. dessous du point d'élimination de la vapeur. 6. Verfahren gemäß irgendeinem der An- 7. Procédé selon la revendication 6, carac- sprüche 1 bis 5, dadurch gekennzeichnet, daß térisé par le fait que la seconde colonne com- die Rektifizierung des Dampfstromes in einer porte de 3 à 10 plateaux. zweiten Kolonne durchgeführt wird, um ein zweites, Essigsäure enthaltendes Kopfprodukt und ein Acrylsäure und Essigsäure enthaltendes Bodenprodukt zu erhalten, wobei das Bodenpro- dukt wieder der Lösungsmittelrückge- 1. Verfahren zur Abtrennung von Acrylsäure winnungskolonne an einem Punkt unterhalb der aus einer Acrylsäure und Essigsäure enthal- Dampfabtrennung zugeführt wird. tenden wäßrigen Lösung, wobei 7. Verfahren gemäß Anspruch 6, dadurch ge- (a) ein durch Oxydation von Propylen oder kennzeichnet, daß die zweite Kolonne drei bis Acrolein erhaltene wäßrige Lösung in einer zehn Böden aufweist.