Method for purifying unsaturated carboxylic acid anhydride by distillation

Abstract

The present invention relates to a process for the distillative removal of unsaturated carboxylic acid anhydrides of general formula (I) RC(O)-OC-(O)-R, wherein R is an unsaturated organic group having 2 to 12 carbon atoms, which unsaturated carboxylic acid anhydrides are discharged in gaseous form from a side draw and condensed in a liquid circulating stream atomized with the unsaturated carboxylic acid anhydrides.

Description

[Technical field]

[0001] The present invention relates to a process for removing unsaturated carboxylic acid anhydrides by distillation.

[0002] Prior Art EP-2032518 B1 describes a process for the continuous preparation of carboxylic acid anhydrides, which are obtained in a side stream, preferably between the middle and lower regions of a rectification column.

[0003] CN-107963966 A describes an apparatus for producing methacrylic anhydride, in which the methacrylic anhydride is obtained at the bottom outlet of a rectification column.

[0004] The disadvantage of the mentioned process is that in order to obtain pure methacrylic anhydride, the target product must subsequently undergo further purification and distillation steps to separate it from high-boiling secondary components, including process stabilizers.

[0005] The object of the present invention is therefore to provide a simplified method for removing unsaturated carboxylic acid anhydrides, which makes it possible to dispense with further purification steps and which gives the target product (i.e. the unsaturated carboxylic acid anhydride) in a highly pure form. Moreover, the method should ensure that polymerization of the target product is avoided.

[0006] Summary of the Invention This object is achieved in that, during purification by distillation, the unsaturated carboxylic acid anhydride is discharged in gaseous form by side withdrawal and condensed ("quenched") in a cooled liquid stream, which is a liquid circulation stream of the unsaturated carboxylic acid anhydride.

[0007] As a result, impurities are eliminated, since the gaseous stream from the distillative purification unit is substantially purer than the liquid stream, and no further auxiliaries are used that could reduce the purity of the gaseous target product (the unsaturated carboxylic acid anhydride).

[0008] Thus, the present invention provides General formula (I) RC(O)-OC-(O)-R (I) The present invention relates to a process for removing an unsaturated carboxylic anhydride of the formula (I) by distillation, wherein R is an unsaturated organic group having 2 to 12 carbon atoms, characterized in that the unsaturated carboxylic anhydride of the formula (I) is discharged in gaseous form from a side stream withdrawal and condensed in a liquid circulation stream sprayed with the unsaturated carboxylic anhydride of the formula (I).

[0009] Detailed Description of the Invention The unsaturated carboxylic acid anhydride of general formula (I) as defined above is preferably (meth)acrylic anhydride. The term (meth)acrylic anhydride includes the compounds methacrylic anhydride and acrylic anhydride.

[0010] In the context of the present invention, the term "circulation stream" is understood to mean any circulation of said unsaturated carboxylic acid anhydride of general formula (I) in a unit operating for the removal of said unsaturated carboxylic acid anhydride of general formula (I) or in a unit associated therewith.

[0011] Any distillative purification apparatus can be used in the process according to the invention, for example a rectification column having an upper section, a middle section and a lower section.

[0012] Preferably, the rectification column has 5 to 50 separation stages. In the present invention, the number of separation stages should be understood to mean the number of trays multiplied by its plate efficiency in a plate column or the number of theoretical separation stages in the case of a structured packed column or a column containing random packing.

[0013] Examples of trays in rectification columns containing trays include bubble cap trays, sieve trays, tunnel trays, valve trays, slit trays, sieve slit trays, sieve bubble cap trays, nozzle trays, centrifugal trays, examples of random packing in rectification columns containing random packing include Raschig rings, Lessing rings, Pall rings, Berl saddles, Intalox saddles, and examples of structured packing in rectification columns containing structured packing include structured packing including Mellapak (Sulzer), Rombopak (Kuehni) and Montz-Pak (Montz) types and catalyst bags, e.g. Katapak (Sulzer).

[0014] Rectification columns containing combinations of sections of trays, sections of random packing and / or sections of structured packing may be used as well.

[0015] It is preferred to use a rectification column containing random and / or structured packing, which may be manufactured from any material suitable for this purpose, including, inter alia, stainless steel and inert materials.

[0016] Preferably, the rectification column is operated under vacuum at a pressure between 1 and 500 mbar absolute, preferably at a pressure between 1 and 100 mbar absolute. The temperature at the bottom of the rectification column is a result of the prevailing system pressure.

[0017] The low boiling impurities are taken off from the top of the rectification column, while the high boiling impurities are discharged from the bottom of the rectification column. The target product (i.e., the unsaturated carboxylic acid anhydride of the general formula (I)) is preferably discharged in a side draw below the central region of the rectification column.

[0018] The rectification column may be interconnected with other devices, for example further devices for substance separation and / or reactors. A reaction zone may be located within the rectification column. The rectification column may be subdivided into two or more separation segments that perform different tasks.

[0019] The process according to the invention preferably uses an apparatus having a container connected to the purification apparatus by distillation via an attachment and sealed against the atmosphere. This container can be configured without a cooling element, preferably with a cooling element (as a heat exchanger). The apparatus also has an outlet line through which the liquid target product (the unsaturated carboxylic anhydride of general formula (I)) is taken off, which is preferably further cooled via a heat exchanger and partially returned to the apparatus via the inlet line (recycle stream).

[0020] Preferably, a nozzle is located at the end of the inlet line, and the liquid target product is sprayed into the vessel, thus generating a negative pressure so that the gaseous target product (the unsaturated carboxylic anhydride of general formula (I)) can be better condensed from the distillation purification device. The filling level of the circulating liquid target product in the vessel is constantly maintained, which is preferably achieved by means of an automatically adjusted filling level measurement. Excess liquid target product is removed via a pipeline and collected in a target product vessel.

[0021] The fittings used, which connect the vessel with the purification apparatus by distillation, can be valves, ball valves or flaps, which can be adjusted manually or preferably automatically. As regulating variables in this case, measuring and regulating points, preferably temperature measuring points, located in the purification apparatus by distillation are used. The measuring points can be located above, at the same level or below, preferably above, the fittings connecting the vessel with the purification apparatus by distillation or the side draw. Preferably, the side draw is regulated by a temperature regulating valve.

[0022] The device may have further connections that can be used for measuring instruments (e.g. pressure and temperature sensors) or sight glasses. The device may be manufactured from any material suitable for this purpose. These include, inter alia, stainless steel and inert materials.

[0023] In order to avoid undesired polymerization of the unsaturated carboxylic anhydride of the above general formula (I), a polymerization inhibitor is optionally added.Preferred polymerization inhibitors that can be used include, inter alia, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, phenothiazine, hydroquinone, hydroquinone monomethyl ether, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl (TEMPOL), 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, para-substituted phenylenediamines such as N,N'-diphenyl-p-phenylenediamine, 1,4-benzoquinone, 2,6-di-tert-butyl-α-(dimethylamino)-p-cresol, 2,5-di-tert-butylhydroquinone, or a mixture of two or more of these polymerization inhibitors.

[0024] The inhibitor is preferably metered at the top of the column.

[0025] The high boilers, e.g. the inhibitors added, can be discharged from the bottom of the column in a conventional manner, for example by means of a thin-film evaporator or a similar device for carrying out the task of recycling the evaporated substances to the rectification column and discharging the non-evaporated high boilers.

[0026] The process according to the invention allows said unsaturated carboxylic anhydrides of general formula (I) to be obtained by simple separation in high purity and without losses due to undesired polymerization, the polymerization of which can, if desired, be subsequently stabilized by means of a polymerization inhibitor for storage. [Brief description of the drawings]

[0027] [Figure 1] Schematic diagram of the method according to the present invention. [Diagram 2] FIG.

[0028] An embodiment of the method according to the invention is shown diagrammatically in FIG.

[0029] The unsaturated carboxylic anhydride (1) of general formula (I) to be purified reaches the lower part of the rectification column (2), where in the separation zone (2a) components (3) with a lower boiling point than the unsaturated carboxylic anhydride of general formula (I) are removed. In the separation zone (2b) of the rectification column, the unsaturated carboxylic anhydride of general formula (I) is separated from the components (4) with a higher boiling point than the unsaturated carboxylic anhydride of general formula (I). The unsaturated carboxylic anhydride of general formula (I) is taken off in gaseous form from the side draw between the separation zones (2a) and (2b) via the temperature control valve (5) and is then condensed directly in a container for the atomized liquid target product (i.e. the unsaturated carboxylic anhydride of general formula (I) coming from the circulation stream). The liquid target product is recycled to the container (6) by means of the pump (7). A heat exchanger (8) cools the liquid target product. The target product is removed from the circulation (9) as controlled by the filling level and fed to a target product vessel.

[0030] The following examples illustrate the methods according to the invention without, however, limiting them. EXAMPLES

[0031] Example 1: Purification of methacrylic anhydride The purification of methacrylic anhydride as the unsaturated carboxylic acid anhydride of the general formula (I) was carried out in the lower part of a rectification column according to FIG.

[0032] The rectification column had 12 separation stages in the separation zone (2a) and 8 in the separation zone (2b). The column had an internal diameter of 100 mm and was equipped with structured packing from Sulzer, type CY (separation zone 2a) and structured packing from Montz, type BSH 400 (separation zone 2b). The pressure at the bottom of the column was 35 mbar. At stationary conditions, a temperature profile was set from 164° C. (bottom) to 66° C. (top of separation zone 2a). The outflow of methacrylic anhydride at the side draw (between separation zones 2a and 2b) and the heating steam capacity of the bottom evaporator were thermoregulated in the respective zones.

[0033] Phenothiazine was used as a process stabilizer and was dissolved in acetic acid and added to the return flow to the fractionator via its top. A falling film evaporator served as the evaporator.

[0034] In the side draw, gaseous methacrylic anhydride was condensed into the already present atomized liquid methacrylic anhydride. The pressure in the vessel was 25 mbar (absolute); the pressure in the rectification column at the point of the draw before the valve (5) was 30 mbar (absolute). The liquid methacrylic anhydride was cooled to a temperature of 10° C. in a tube-coil heat exchanger (8) operated with cold brine. Clear, colorless (platinum-cobalt color number 5) methacrylic anhydride with a purity of 99.7% (GC analysis) was withdrawn via the outlet line.

[0035] Example 2: Purification of acrylic anhydride The purification of acrylic anhydride as the unsaturated carboxylic anhydride of general formula (I) was carried out in the same lower part of the rectification column according to FIG. 1 as described in Example 1. The pressure at the bottom of the column was 35 mbar. At stationary conditions, a temperature profile was set from 164° C. (bottom) to 54° C. (top of separation zone 2a). The outflow of acrylic anhydride at the side draw (between separation zones 2a and 2b) and the heating steam capacity of the bottom evaporator were temperature-regulated in the respective zones. Phenothiazine was used as a process stabilizer, which was dissolved in acetic acid and added to the return flow to the rectification column via its top. A falling-film evaporator served as the evaporator.

[0036] In the sidestream withdrawal, gaseous acrylic anhydride was condensed into the already present atomized liquid acrylic anhydride. The pressure in the vessel was 25 mbar (absolute); the pressure in the rectification column at the point of withdrawal before the valve (5) was 30 mbar (absolute). The liquid acrylic anhydride was cooled to a temperature of 10° C. in a tube coil heat exchanger (8) operated with cold brine. Clear, colorless (platinum-cobalt color number 6) acrylic anhydride with a purity of 99.7% (GC analysis) was withdrawn via the outlet line.

[0037] Comparative Example 1: Purification of methacrylic anhydride The purification of methacrylic anhydride as the unsaturated carboxylic acid anhydride of the general formula (I) was carried out in the lower part of a rectification column according to FIG.

[0038] The rectification column had 12 separation stages in the separation zone (2a) and 8 in the separation zone (2b). The column had an internal diameter of 100 mm and was equipped with structured packing from Sulzer, type CY (separation zone 2a) and structured packing from Montz, type BSH 400 (separation zone 2b). The pressure at the bottom of the column was 35 mbar. At stationary conditions, a temperature profile was set from 164° C. (bottom) to 66° C. (top of separation zone 2a). The outflow of methacrylic anhydride at the side draw (between separation zones 2a and 2b) and the heating steam capacity of the bottom evaporator were thermoregulated in the respective zones.

[0039] Phenothiazine was used as a process stabilizer and was dissolved in acetic acid and added to the return flow to the fractionator via its top. A falling film evaporator served as the evaporator.

[0040] Liquid methacrylic anhydride was withdrawn via the side draw. The liquid methacrylic anhydride was cooled to a temperature of 10° C. in a tube coil heat exchanger (8) operated with cold brine. Methacrylic anhydride was withdrawn via the outlet line as a clear, pale yellow liquid (platinum-cobalt color number 35) having a purity of 99.2% (GC analysis).

[0041] Comparative Example 2: Purification of acrylic anhydride The purification of acrylic anhydride as the unsaturated carboxylic acid anhydride of general formula (I) was carried out in the same lower part of the rectification column according to FIG.

[0042] The pressure at the bottom of the column was 35 mbar. At stationary conditions, a temperature profile was set from 164° C. (bottom) to 54° C. (top of separation zone 2a). The outflow of acrylic anhydride at the side draw (between separation zones 2a and 2b) and the heating steam capacity of the bottom evaporator were thermoregulated in the respective zones. Phenothiazine was used as a process stabilizer, dissolved in acetic acid and added via the top to the return flow to the rectification column. A falling film evaporator served as the evaporator.

[0043] Liquid acrylic anhydride was withdrawn via the side draw. The liquid acrylic anhydride was cooled to a temperature of 10° C. in a tube coil heat exchanger (11) operated with cold brine. Acrylic anhydride was withdrawn via the outlet line as a clear, pale yellow liquid (platinum-cobalt color number 38) having a purity of 99.1% (GC analysis). [Explanation of symbols]

[0044] 1 Unsaturated carboxylic anhydride of general formula (I) to be purified, 2 Rectification column, 2a, 2b Separation zones, 3 Components having a lower boiling point than the unsaturated carboxylic anhydride of general formula (I), 4 Components having a higher boiling point than the unsaturated carboxylic anhydride of general formula (I), 5 Temperature control valve, 6 Vessel, 7 Pump, 8 Heat exchanger, 9 Removal of the target product

Claims

1. General formula (I) RC(O)-OC(O)-R (I) 1. A process for removing by distillation an unsaturated carboxylic anhydride of formula (I) wherein R is an unsaturated organic radical having 2 to 12 carbon atoms, characterized in that the unsaturated carboxylic anhydride of formula (I) is discharged in gaseous form from a side draw and condensed in a sprayed liquid circulation stream of the unsaturated carboxylic anhydride of formula (I).

2. 2. The process according to claim 1, characterized in that the unsaturated carboxylic acid anhydride of general formula (I) is (meth)acrylic anhydride.

3. 3. The process according to claim 1 or 2, characterized in that the temperature of the liquid circulation stream of the unsaturated carboxylic acid anhydride of general formula (I) is lower than the condensation temperature of the unsaturated carboxylic acid anhydride of general formula (I).

4. 4. The process according to claim 1, wherein the temperature of the liquid circulating stream of unsaturated carboxylic acid anhydride of general formula (I) is between minus 50° C. (−50° C.) and 200° C.

5. 5. The process according to claim 1, wherein the temperature of the liquid circulating stream of unsaturated carboxylic acid anhydride of general formula (I) is between minus 10° C. (−10° C.) and 50° C.

6. 6. The process according to claim 1, characterized in that the pressure during the removal of the unsaturated carboxylic anhydride of general formula (I) is between 1 mbar and 500 mbar (absolute).

7. 7. The process according to claim 1, characterized in that the pressure during the removal of the unsaturated carboxylic anhydride of general formula (I) is between 1 mbar and 100 mbar (absolute).

8. 8. The process according to claim 1, characterized in that the distillative removal of the unsaturated carboxylic anhydride of general formula (I) is carried out in a rectification column having an upper section, a middle section and a lower section, and the side draw is located in the middle section or below the middle section.

9. 9. The method of claim 8, wherein the rectification column has measuring and adjusting points for adjusting the sidestream withdrawal.

10. 10. The method of claim 9, wherein the sidestream withdrawal is regulated via a thermostatic valve.

11. 11. The process according to claim 1, wherein the distillative removal of the unsaturated carboxylic anhydride of formula (I) is carried out in the presence of a polymerization inhibitor.

12. 12. The method of claim 11, wherein the polymerization inhibitor is selected from the group consisting of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, phenothiazine, hydroquinone, hydroquinone monomethyl ether, 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl (TEMPOL), 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, para-substituted phenylenediamines, 1,4-benzoquinone, 2,6-di-tert-butyl-α-(dimethylamino)-p-cresol, 2,5-di-tert-butylhydroquinone, or a mixture of two or more of these polymerization inhibitors.

13. The removal by distillation of the unsaturated carboxylic anhydride of general formula (I) is carried out in a rectification column having an upper section, a middle section and a lower section, 13. The process according to claim 11 or 12, characterized in that the polymerization inhibitor is added at the top of the column.

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