MXPA99007946A - Method for extracting (meth)acrylic acid - Google Patents

Abstract

The invention relates to a method for extracting an aqueous solution containing (meth)acrylic acid. Said solution is brought into contact with a solution containing at least one extracting agent which can be converted into (meth)acrylic acid and forms a miscibility gap with the aqueous solution to produce an organic phase containing (meth)acrylic acid and extraction agent and an aqueous phase.

Description

ACRYLIC ACID (MET) EXTRACTION The present invention relates to a process for extracting an aqueous solution containing (meth) acrylic acid by contacting it with a solution containing at least one extractant that can be converted to (meth) acrylic acid in one or more steps and an interval or lack of miscibility with the aqueous solution. The term "(meth) acrylic acid" used in this application refers to acrylic acid and methacrylic acid. Due to its unsaturated monoethylenic bond, - very reactive and acid function, methacrylic acid is a monomer useful for the preparation of polymers, for example for aqueous dispersions of polymers suitable for adhesives. This also applies to acrylic acid. Methacrylic acid is obtained by, inter alia, gaseous phase oxidation of 1-butene, isobutene, isobutyraldehyde, isobutyric acid, isobutene, MTBE and / or methacrolein with oxygen or oxygen-containing gases in the presence of catalysts, eg multiple oxides. metals containing the elements molybdenum and vanadium in the form of oxide. The oxidation is carried out at elevated temperatures and, owing to the considerable reaction heat, preferably with dilution of the reactants with inert gases such as N2, C02 and / or hydrocarbons and / or steam. However, these processes do not provide the pure methacrylic acid but a mixture of reaction gases which, in addition to the methacrylic acid, contains the starting materials, for example non-converted methacrolein, steam, inert diluent gases (for example nitrogen) and by-products (by examples are carbon oxides), lower aldehydes, for example formaldehyde, high-boiling substances, for example citraconic acid and, in particular acetic acid, from which methacrylic acid can subsequently be isolated (see, for example EP-A 253 409 and DE-A 19 62 431). However, other possible starting compounds are those of which the initial real C4 compound, eg, methacrolein, is initially formed as an intermediate during gas phase oxidation. An example is tert-butanol methyl ether (MTBE). For the preparation of methacrolein it is also possible to subject formaldehyde and propionaldehyde to a condensation reaction and obtain methacrolein by subsequent distillation. This process is described in EP-B 58 927. The methacrolein thus obtained can be converted into methacrylic acid in a conventional manner by catalytic oxidation in the gas phase. A reaction of this type is described, inter alia, in EP-B 297 445. Acrylic acid can be obtained in a similar manner starting from the corresponding C3 compounds, in particular propene or acrolein, or both. If it is intended to isolate the (meth) acrylic acid from the resulting reaction gas mixture by extraction, the gaseous mixture of the reaction is first subjected to a condensation step and then extracted. In this way, EP-B 345 083 describes this process which consists of an extraction step of methacrylic acid in which methacrylic acid is extracted with a saturated hydrocarbon of 6 to 9 carbon atoms. According to EP-A 710 643, in a process for the purification of methacrylic acid, an aqueous solution of methacrylic acid obtained by cooling and condensation of the reaction gas is extracted from the aqueous solution by adding an organic solvent, preferably an aliphatic hydrocarbon from 5 to 9 carbon atoms, an aromatic hydrocarbon and an ester or a mixture thereof. Japanese Patent JP 57 095 938 discloses the extraction of acrylic acid from an aqueous solution diluted by extraction by means of an oxygen-containing solvent and a tertiary amine. Examples are trioctylamine and 2,6-dimethyl-4-heptanol. However, all these processes are disadvantageous in that the extraction of (meth) acrylic acid is carried out in each case using an auxiliary that, on the one hand, it can not be obtained without additional costs and, in addition, in this process additional steps are required to separate this auxiliary again, giving rise to additional costs and additional energy consumption. None of the processes of the prior art write the possibility of extracting (meth) acrylic acid by means of a solution without auxiliary. The extractants used to date are simply auxiliaries that can not be converted to (meth) acrylic acid. Thus, an object of the present invention is to provide a process for extracting an aqueous solution containing (meth) acrylic acid, which process can be carried out without auxiliaries and, in addition, can be carried out using conventional apparatuses and with comparatively low energy consumption. We have found that this objective is achieved by the process according to the invention. The present invention, therefore, relates to a process for extracting an aqueous solution containing acid (met) acrylic by contacting it with a solution containing at least one extractant that can be converted to (meth) acrylic acid and forms a miscibility range with the aqueous solution, where an organic phase containing the acid is obtained ( met) acrylic and extractant, and an aqueous phase. As defined in, inter alia, the claims, the term extractant includes all substances that can be converted to (meth) acrylic acid in one or more steps and at the same time forms a miscibility range with the aqueous solution containing the (meth) acrylic acid. Specific examples are alkanes, alkanols, alkenes or alkenes of 3 or 4 carbon atoms or mixtures of two or more thereof which can be converted to (meth) acrylic acid and forms a miscibility range with the aqueous solution defined above. The substances suitable for this purpose are preferably (meth) acrolein, isobutene, propene, propane, butane, isobutyraldehyde, methyl ether of tert-butanol (MTBE) or a mixture of two or more thereof. The use of (meth) acrolein is particularly preferred. The solution containing at least one extractant that can be converted to (meth) acrylic acid consists entirely of this extractant or contains it as a mixture with other substances, for example water or acetic acid, or both. The solution may also contain impurities that arise from the process of preparation of the components and, therefore, do not need to be purified before extraction.

Additives that improve the extraction effect can also be added to this solution. Examples are defoamers, for example tallow fatty alcohol and other polyalcohols, emulsifiers such as alkali metal chlorides and surfactants and substances extending the range of miscibility, for example higher alkanes, in particular those having from 4 to 14 carbon atoms. . In principle, there are no restrictions with respect to the concentration of extractant that is contained in this solution and can be converted to (meth) acrylic acid, but the concentration of this extractant in the solution is preferably from about 50 to 100, particularly preferably from 70 to about 99.9, in particular from about 90 to about 97% by weight. In any case, the solution defined above must have a miscibility interval with the aqueous solution containing the (meth) acrylic acid. Particularly if the novel process is integrated into a process for the preparation of (meth) acrylic acid or is operated in combination with such a process, this is preferable, if the solution used to extract acid (met) acrylic and contains at least one extractant that can be converted to (meth) acrylic acid is a solution that can be used as an initial material for the synthesis of (meth) acrylic acid and preferably has a concentration from 50 to 100% by weight of the extractant. This is particularly preferably a solution containing (meth) acrolein. The mixture of the reaction gas which is obtained by oxidation of the C3 / C4 compounds in the first stage and still contains the initial material can, after the condensation of the mixture, also be used as the solution containing at least one agent Extractant that can be converted into (meth) acrylic acid to extract the (meth) acrylic acid. The extractant contained in the solution and which is present in a certain amount in the aqueous phase after the extraction is preferably recovered by a thermal separation method, for example by steam stripping or an inert gas, for example nitrogen, air , carbon dioxide, gas outlet - acid preparation (meth) acrylic or a mixture of two or more thereof, or by recovery by distillation. The extractant is transferred almost completely to the gas phase and can then be used for the preparation of (meth) acrylic acid, if necessary after passing through other stages (of treatment) In the same way, there are no restrictions with respect to the concentration of (meth) acrylic acid in the aqueous solution The content of (meth) acrylic acid in this solution preferably it is from about 0.01 to about 80, particularly preferably from about 1 to about 40, in particular from about 5 to about 20% by weight In addition to the (meth) acrylic acid and water, this solution, particularly if obtained in industrial form of the preparation of (meth) acrylic acid, may contain a small amount, as a rule less than about 3% by weight, of the initial material used for the preparation of (meth) acrylic acid and a small amount, as a general rule less than 10% by weight of acetic acid.As already mentioned, an organic phase containing (meth) acrylic acid and the extractant is obtained in The extraction is preferably carried out in such a way that the total or almost total amount of the (meth) acrylic acid used is present in this phase. In addition to (meth) acrylic acid, the organic phase contains the extractant and also small amounts of water, acetic acid and high-boiling substances. The resulting aqueous phase may also contain small amounts of (meth) acrylic acid, extractant and acetic acid, which however can be separated from the predominant part by thermal separation methods. According to a preferred embodiment of the novel process, the organic phase containing (meth) acrylic acid and extractant is subjected to a method of thermal separation, for example by steam stripping or with an inert gas, for example nitrogen, air, carbon dioxide, an exit gas formed in the oxidation of the starting materials for the preparation of (meth) acrylic acid or a mixture of these inert gases, or by distillation of the extractant and water mixture. In this process, on the one hand the (meth) acrylic acid together with the high-boiling substances and the acetic acid, are separated from the predominant part of the extractant and water. There are no specific limitations regarding the temperature at which the novel process can be performed. The only precondition is that, at the chosen temperature and pressure, it is possible for two phases, an organic phase and an aqueous phase to form. In general, the novel process is performed from about 0 to about 150 ° C, preferably from about 30 to about 80 ° C, in particular from about 50 to about 70 ° C, using temperatures above about 68 ° C at a pressure superatmosferica when (met) acroleina is used as extractant agent. If other extractant agents are used, the temperature and / or pressure should be modified depending on the extractant agent.

In general, all devices used for extraction, as described for example in Ullmanns Encyklopadie der Technischen Chemie, 4th edition, vol. 2, page 546 et seq., In particular page 560 et seq. (1972), can be used to perform the novel process. Specific examples are mixer-settler apparatus, extraction columns, extraction columns by spray towers, columns of pulsed and unpulsed trays and packed columns and extraction columns with agitation or extraction devices using centrifugal forces. The aqueous solution containing (meth) acrylic acid and the solution containing at least one extractant that can be converted to (meth) acrylic acid can be contacted with each other at co-current, cross current or countercurrent, with the preferred contact by the countercurrent method. The extraction can be carried out in one or more stages, and it is also possible to use combinations of the extraction apparatuses. The process according to the invention can be carried out continuously or in batches, with the continuous process being preferred. It is also possible to perform the novel extraction process as part of a process for the preparation of (meth) acrylic acid. The amount of (meth) acrylic acid to be extracted corresponds, as a rule, to the amount of (meth) acrylic acid that was not condensed in the condensation of the reaction mixture obtained directly in the preparation of (meth) acrylic acid by oxidation in gas phase. As already mentioned, the extractant agent that is used for the extraction of preference is recovered after passing through the extraction. Particularly suitable methods for recovering this part of the extractant which is dissolved in the aqueous phase are the thermal separation methods, for example by steam stripping or with an inert gas, for example nitrogen, air, carbon dioxide, a gas of output formed in the oxidation of the starting materials for the preparation of (meth) acrylic acid or a mixture of these inert gases, or the distillation of the extractant and water mixture. The stripping process is generally carried out at temperatures from about 30 to about 100 ° C, preferably from about 50 to about 80 ° C, and at a pressure from about 1 to about 1.5 x 105 Pa. For other purposes the temperatures must be modified in frequency The type of trawl used is not subject to a specific restriction, and it is possible to use any conventional trawl device that allows gas-liquid contact, for example packed towers, sieve tray towers, bubble tower towers or towers of aspersion. Other readily usable spraying apparatuses are described under the keyword absorption column in EP-A 706 986, in column 3, lines 11 to 38, and in the prior art mentioned herein, which are hereby incorporated in their entirety. as reference. As already mentioned, the (meth) acrylic acid contained in the organic phase is recovered in the same way by a thermal separation method, preferably by subjecting the organic phase to a stage for the condensation of acid (met) acrylic. This stage provides the condemned containing the highest amount of (meth) acrylic acid present in the organic phase and the greatest amount of acetic acid, while the extractant generally contained in the organic phase is converted to the gaseous state. For this purpose, the organic phase is fed to a thermal separation method which is operated at a temperature at which the above objective is achieved, namely, the separation of the largest amount of (meth) acrylic acid from the main amount of the extractant agent. These separation methods are known from the prior art and are described, for example, inter alia in the German applications open to the public DOS 4 235 321 and DOS 3 721 865 for the condensation of the gaseous reaction mixture obtained in the preparation of (meth) acrylic acid. To prevent or reduce the tendency of the (meth) acrylic acid or the extractant, or both, to polymerize, it is also possible to add to the solutions used in the present process, for example, phenothiazine, hydroquinone or a derivative thereof. As is evident from the foregoing, the problem of the azeotropic acid (meth) acrylic and water mixture can be overcome in a simple manner by means of the novel process by adding extractants which can be converted to (meth) acrylic acid. With this process, expensive and energy-consuming separation steps included in the distillation are omitted. In addition pollution problems due to the treatment of the auxiliary are avoided. The following examples illustrate the present invention.

EXAMPLES Example 1 An aqueous solution containing 10.3% by weight of methacrylic acid and 2.2% by weight of acetic acid was extracted with an aqueous solution containing methacrolein with a methacrolein content of 92% by weight by the countercurrent method in a cascade Three stage mixer-settler that was operated at 50 ° C. A stay time of 30 minutes was sufficient for the separation of the phases. The organic phase obtained contained a total amount of methacrylic acid introduced, the concentration thereof in the phase was 17.6% by weight, 361 g of (meth) acrylic acid were extracted.

Example 2 63.0 g of the aqueous solution containing 10.3% by weight of methacrylic acid and 2.2% by weight of acetic acid were extracted in one step with 300 g of an organic methacrolein solution. The methacrolein solution contained 7% by weight of water. 580 g of aqueous phase were obtained containing 1.7% by weight of methacrylic acid and 1.2% by weight of acetic acid. In the extraction step, the methacrolein solution was charged with 14.4% by weight of methacrylic acid and 1.1% by weight of acetic acid.

Example 3 449 g of the aqueous solution containing 1.7% by weight of methacrylic acid and 1.2% by weight of acetic acid were extracted in one step with 212 g of an organic methacrolein solution. The methacrolein solution contained 7% by weight of water. 434 g of aqueous phase were obtained containing 0.37% by weight of methacrylic acid and 1.2% by weight of acetic acid. In the extraction step the methacrolein solution was loaded with 2.9% by weight of methacrylic acid and 0.73% by weight of acetic acid.

Example 4 328 g of an aqueous solution containing 0.37% by weight of methacrylic acid and 1.2% by weight of acetic acid were extracted in one step with 156 g of an organic methacrolein solution. The i-etacrolein solution contained 7% by weight of water. 325 g of aqueous phase were obtained containing 0.06% by weight of methacrylic acid and 0.68% by weight of acetic acid. In the extraction step the methacrolein solution was loaded with 0.65% by weight of methacrylic acid and 0.56% by weight of acetic acid.

Example 5 3.49 kg / h of a first aqueous solution containing 10.3% by weight of methacrylic acid and 2.2% by weight of acetic acid were extracted by the countercurrent method in a 3-stage mixer-settler system with 1.63 kg / hr. a first solution of methacrolein that was introduced in the third settler. The first methacrolein solution contained 7% by weight of water. The first aqueous solution was contacted in the first extraction stage (first settler) with a third methacrolein solution after a second settler. The second aqueous solution discharged from the first settler was contacted with a second methacrolein solution leaving a third settler. The third aqueous solution leaving the second settler was contacted in the third stage with the first methacrolein solution. From the third settler 3 kg / h of a fourth aqueous phase were obtained. This fourth aqueous solution contained 0.8% by weight of (meth) acrylic acid and 1.5% by weight of acetic acid. From the first settler, 2 kg / h of the fourth methacrolein solution were obtained. This fourth methacrolein solution contained 17.6% by weight of methacrolein and 1.6% by weight of acetic acid. The phase separation between the aqueous solutions and the methacrolein solutions was complete after less than 3 minutes in all the examples. All exemplary experiments were carried out at a temperature of 50 ° C and atmospheric pressure.

Claims (1)

1. CLAIMS A process for extracting an aqueous solution containing (meth) acrylic acid by contacting it with a solution containing at least one extractant that can be converted to (meth) acrylic acid and forms a miscibility range with the aqueous solution, wherein an organic phase is obtained which contains the (meth) acrylic acid and the extractant and an aqueous phase. The process as recited in claim 1, wherein the solution contains the one or more extractant, which can be converted to (meth) acrylic acid in a concentration of 50 to 100% by weight. The process as recited in claim 1 or 2, wherein the one or more extractants that can be converted to (meth) acrylic acid are (meth) acrolein, isobutene, propene, propane, butane, isobutyraldehyde, methyl ether ter-butanol (MTBE) or a mixture of two or more thereof. The process as mentioned in any of the preceding claims, wherein the aqueous solution containing (meth) acrylic acid contains the latter in a concentration from 0.01 to 80% by weight. The process as mentioned in any of the preceding claims, wherein the solution containing at least one extractant agent, which can be converted to (meth) acrylic acid and forms a miscibility range with the aqueous solution, is a solution that can be used as initial material for the preparation of (meth) acrylic acid. The process as mentioned in any of the preceding claims, wherein the extraction is performed in a mixer-settler apparatus, a packed extraction column, an extraction column with spray towers, a column of pulsed or non-pulsed plates or column packed, an extraction column with agitation or an extraction apparatus that uses centrifugal forces. The process as mentioned in any of the preceding claims, wherein the extraction is carried out continuously. The process as mentioned in any of the preceding claims, wherein the extraction is carried out countercurrently. The process as mentioned in any of the preceding claims, wherein the aqueous phase is subjected to a thermal separation method, obtaining a gas containing the extractant and residual water. The process as mentioned in any of the preceding claims, wherein the organic phase containing (meth) acrylic acid and the extractant is subjected to a thermal separation method, a liquid phase containing (meth) acrylic acid being obtained and a gaseous phase containing the extractant agent.