Process for preparing unsaturated symmetric carboxylic anhydrides

Abstract

The invention relates to a process for simultaneously preparing symmetric carboxylic anhydrides of the general formulae R-C(O)-O-C(O)-R (I) and R'R"HC-C(O)-O-C(O)-CHR'R" (II) by reacting an unsaturated carboxylic acid with a ketene, wherein (a) the unsaturated carboxylic acid (III) is reacted with the ketene in a first reaction region to give a crude anhydride mixture, (b) the crude anhydride mixture obtained in step (a) is converted further in a second reaction region, preferably in the presence of a catalyst, (c) the symmetric anhydrides (I) and (II) are isolated in a rectification from the mixture obtained in step (b), and (d) unconverted mixed anhydride obtained in the rectification in step (c) is returned to the first reaction region and / or to the second reaction region.

Description

[0001] Method for the production of unsaturated symmetrical carboxylic acid anhydrides

[0002] Field of invention

[0003] The invention describes a process for the simultaneous production of unsaturated symmetrical carboxylic acid anhydrides of the general formulas RC(O)-OC(O)-R (I) and R'R“HC-C(O)- OC(O)-CHR'R“ (II) by reacting an unsaturated carboxylic acid with a ketene.

[0004] State of the art

[0005] German patent DE-A-3510035 describes a process for the continuous production of unsaturated carboxylic anhydrides by an acid-catalyzed re-anhydridation reaction of acetic anhydride with an unsaturated carboxylic acid in the middle section of a distillation column. To achieve complete conversion, acetic anhydride is used in an excess of 0.1 to 0.5 moles per mole of carboxylic acid, resulting in a mixture of acetic acid and acetic anhydride at the column head, meaning that pure acetic acid is not obtained. The product formed in this way is contaminated by the catalyst, which must be removed in a subsequent process step.

[0006] US Patent 4,857,239 describes a process for the production of methacrylic anhydride, in which the molar ratio of methacrylic acid to acetic anhydride is 2.1 to 3 and a polymerization inhibitor is added to the distillation column. The process is carried out batchwise. A further disadvantage is that the excess starting material is wasted.

[0007] US Patent 2003 / 001827 describes a batch process for the production of methacrylic anhydride, wherein the initial molar ratio of methacrylic acid to acetic anhydride is preferably 9 to 11. The acetic acid produced is immediately removed, and the released reactor contents are replenished with acetic anhydride. Inhibitors are added to the reactor and the column to prevent polymerization. Numerous byproducts are formed, which cannot be completely removed.

[0008] EP 2 032 519 describes a process for the continuous production of unsaturated carboxylic anhydrides, in which complete conversion of the unsaturated carboxylic acid used is achieved and the resulting unsaturated carboxylic anhydride is obtained in high purity. Furthermore, polymerization is largely avoided in all stages, and the space-time yield of the reaction is increased compared to the processes described above.

[0009] The objective is to provide a further improved process for the continuous (or semi-continuous) production of unsaturated symmetrical carboxylic anhydrides, achieving a higher space-time yield of the anhydride compared to EP2032519. Furthermore, the formation of byproducts (especially acetic acid) should be suppressed. Summary of the invention

[0010] Surprisingly, the inventors have succeeded in developing a by-product-free process for the simultaneous production of symmetrical carboxylic acid anhydrides of the general formulas RC(O)-OC(O)-R (I) and R'R“HC-C(O)-OC(O)-CHR'R“ (II).

[0011] Specifically, the invention relates to a process for the simultaneous production of symmetrical carboxylic acid anhydrides of the general formula

[0012] RC(O)-OC(O)-R (I) and

[0013] R'R“HC-C(O)-OC(O)-CHR'R“ (II) in which R represents an unsaturated organic residue with 2 to 12 C atoms, wherein R' and R“ are the same or different and represent hydrogen or a Ci to C4 alkyl residue, and wherein R' and R“ are different from R, by reaction of an unsaturated carboxylic acid of the general formula

[0014] R-COOH (III), in which R has the meaning given above, with a ketene of the general formula

[0015] R'R“C=C=O (IV), in which R' and R“ have the meanings given above, where

[0016] (a) the unsaturated carboxylic acid (III) is reacted with the ketene (IV) in a first reaction area to form a crude anhydride mixture,

[0017] (b) the crude anhydride mixture obtained in step (a) is further reacted in a second reaction area, preferably in the presence of at least one catalyst,

[0018] (c) the symmetrical anhydrides (I) and (II) are isolated by rectification from the mixture obtained in step (b), and

[0019] (d) unreacted mixed anhydride obtained during rectification in step (c) is returned to the first reaction area and / or to the second reaction area.

[0020] By combining the aforementioned process features, complete conversion of the reactants and high purity of the products are achieved, and polymerization is largely avoided in all areas, since, among other things, long residence times of the formed unsaturated anhydride in the column sump are excluded.

[0021] Due to the complete conversion in the first reaction area, the rectification column remains almost free of free carboxylic acids.

[0022] Detailed description of the invention

[0023] Suitable unsaturated carboxylic acids for the process according to the invention have an unsaturated organic residue with 2 to 12, preferably 2 to 6, and particularly preferably 2 to 4 carbon atoms. Suitable alkenyl groups are, in particular, the vinyl, allyl, 2-methyl-2-propene, 2-butenyl, 2-pentenyl, 2-decenyl, 1-undecenyl, and 9,12-octadecadienyl groups. The vinyl and allyl groups are particularly preferred.

[0024] Particularly preferred carboxylic acids include (meth)acrylic acids. The term "(meth)acrylic acid" is well-known in the field, encompassing not only acrylic acid and methacrylic acid but also derivatives of these acids. These derivatives include, among others, β-methylacrylic acid (butenoic acid, crotonic acid), α-β-dimethylacrylic acid, β-ethylacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, 1-(trifluoromethyl)acrylic acid, and β-β-dimethylacrylic acid. Acrylic acid (propenoic acid) and methacrylic acid (2-methylpropenoic acid) are preferred.

[0025] The molar ratio of the reactants, that is, of unsaturated carboxylic acid of formula (III) to ketene of formula (IV), is usually 1 :4 to 1 :0.5, preferably 1 :1.

[0026] The unsaturated carboxylic anhydride of formula (I) is preferably (meth)acrylic anhydride, prepared by reacting a ketene of formula CH₂=C=O and (meth)acrylic acid. The carboxylic anhydride of formula (II) is preferably acetic anhydride.

[0027] In the process according to the invention, the (meth)acrylic anhydride can be withdrawn between the middle and the lower part of the rectification column and the acetic anhydride can be withdrawn at the column head.

[0028] Suitable ketenes for the process according to the invention have the general formula (IV) R'R" C=C=O, wherein R' and R" are the same or different and represent hydrogen or a Ci to C4 alkyl group. Preferably, CH2=C=O is used as the ketene.

[0029] The production of ketene is carried out according to common procedures known from general technical literature, for example from H. Held, A. Rengstl and D. Mayer, Acetic Anhydride and Mixed Fatty Acid Anhydrides in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed., Wiley VCH, Weinheim, 2003, pp. 184-185.

[0030] For example, the ketene used as a reactant is obtained by thermal cleavage of a carboxylic acid of the general formula R'R"CH-COOH (V), where R' and R" have the meanings mentioned above, in a ketene furnace in the presence of a conventional catalyst such as triethyl phosphate. The thermal cleavage is carried out under generally accepted temperature and pressure conditions.

[0031] The thermal cleavage of acetic acid is preferred, yielding CH2=C=O as the ketene.

[0032] Figure 1 shows a plant for the continuous production of unsaturated carboxylic acid anhydrides as known from the prior art, see EP 2 032 519.

[0033] Figure 2 shows an apparatus suitable for the method according to the invention.

[0034] The ketene is produced in a step preceding the process according to the invention, see reaction area (3) of Fig. 2. The obtained ketene is separated by conventional methods and reacted with an unsaturated carboxylic acid of the general formula R-COOH (III), where R has the meaning mentioned above, in a first reaction area or reactor (1) (process step (a) of the process according to the invention). This first reaction area (1) need not necessarily be connected to the other components of the apparatus, but may be.

[0035] The reaction in the first reaction area is carried out at temperatures in the range of 40 to 100 °C, particularly at 50 to 90 °C, and especially preferably at 70 to 85 °C.

[0036] The resulting crude anhydride mixture, consisting of symmetrical and mixed anhydrides, is further reacted in a second reaction area or reactor (2) (process step (b) of the process according to the invention), wherein "reacted" is understood to mean the establishment of equilibrium between all reactants. The second reaction area (2) can be located outside and / or inside the rectification column and / or be included in the first reaction area (1).

[0037] Preferably the second reaction area / reaction area (2) is located outside the rectification column.

[0038] The reaction in the second reaction zone is carried out at temperatures in the range of 30 to 120 °C, particularly at 40 to 100 °C, and especially preferably at 50 to 80 °C. The reaction temperature depends on the set system pressure. If reaction zone (2) is located inside the column, the reaction is preferably carried out at a pressure of 5 to 100 mbar (absolute), particularly at 10 to 50 mbar (absolute), and especially preferably at 20 to 40 mbar (absolute).

[0039] If reaction area (2) is located outside the column and separate from reaction area (1), different pressure and temperature conditions can be selected there. This has the advantage that the reaction parameters of reactor (2) can be set independently of the operating conditions in the column and in reaction area (1).

[0040] The reaction time depends on the reaction temperature; the residence time in the reaction area (2) for a single pass is preferably 0.5 to 15 minutes and particularly preferably 1 to 5 minutes.

[0041] The reaction mixture may include other components besides the reactants, such as solvents, catalysts and polymerization inhibitors.

[0042] Between process step (a) in a first reaction area (1) and process step (b) in a second reaction area (2), the crude anhydride mixture can be temporarily stored. During such temporary storage, the dynamic equilibrium of all reactants can be established.

[0043] Finally, the symmetrical anhydrides of general formulas (I) and (II) are isolated by rectification (see rectification column (7) in Fig. 2), see process step (c) of the process according to the invention. Mixed anhydride obtained during rectification is recycled in process step (d) to the first and / or second reaction area (see stream (11) in Fig. 2).

[0044] In the second reaction area (see reaction area (2) of Fig. 2) at least one catalyst is preferably present.

[0045] If a catalyst is used within the second reaction area (2) and this second reaction area is located within the rectification column, the catalyst can in principle be used in any area of ​​the rectification column, but preferably in the middle area.

[0046] Preferably, however, the catalyst is provided in a reaction area (2) located outside the column and arranged separately from reaction area (1). This arrangement of the catalyst area is preferred. The crude anhydride mixture is preferably continuously passed through the catalyst area. This continuously produces the unsaturated carboxylic anhydride of formula (I), for example (meth)acrylic anhydride, as well as a carboxylic anhydride of formula (II), which corresponds to the symmetrical anhydride of the carboxylic acid from formula (III), for example acetic anhydride, which can be sold as a valuable material.

[0047] Homogeneous catalysts can preferably be added to the top of the column or to the reaction zone (2). Magnesium bromide (preferably anhydrous) and triflate salts of all rare earth elements are particularly suitable as homogeneous catalysts.

[0048] Heterogeneous catalysts are particularly preferred in reaction area (2). Acidic fixed-bed catalysts, especially acidic ion exchangers (cation exchangers), are particularly suitable as heterogeneous catalysts. Particularly suitable acidic ion exchangers include cation exchange resins such as styrene-divinylbenzene polymers containing sulfonic acid groups. Suitable cation exchange resins are commercially available from Rohm & Haas under the trade name Amberlyst®, from Dow under the trade name Dowex®, and from Lanxess under the trade name Lewatit®.

[0049] The amount of catalyst in L is preferably 1 / 10 to 2 times, particularly preferably 1 / 5 to 1 / 2, the amount of unsaturated carboxylic anhydride of formula I to be produced in L / h.

[0050] Stabilizers / polymerization inhibitors can be used to stabilize reactants, intermediates and / or products.

[0051] Preferred polymerization inhibitors include, among others, 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-alpha-(dimethylamino)-p-cresol, 2,5-di-tert-butylhydroquinone, or mixtures of two or more of these stabilizers. Phenothiazine is particularly preferred.

[0052] The inhibitor can be added to the feed of the unsaturated carboxylic acid of general formula (III), before reaction section (1), before reaction section (2) and / or to the rectification column, preferably at its head.

[0053] Furthermore, in the rectification step (c), a high-boiling, inert substance with a boiling point higher than the boiling points of the components involved in the reaction can be used as a boiling oil to ensure the distillative separation of the acid anhydride formed without polymerization.

[0054] However, the boiling point of the boiling oil should not be too high in order to reduce the thermal stress on the acid anhydride formed. The boiling oil is located in the bottom of the column to avoid long residence times for the polymerization-prone target product.

[0055] Generally, the boiling point of boiling oil at normal pressure (1013 mbar) is between 200 and 400 °C, especially between 240 and 290 °C.

[0056] Suitable boiling oils include, among others, higher-chain unbranched paraffins with 12 to 20 carbon atoms, aromatic compounds such as Diphyl (eutectic mixture of 75% biphenyl oxide and 25% biphenyl), alkyl-substituted phenols or naphthalene compounds, Sulfolan (tetrahydrothiophene-1,1-dioxide) or mixtures of these.

[0057] Suitable examples are the following boiling oils: n-Paraffin C14 1-Methylnaphthalene

[0058] 75% biphenyl oxide + 25% biphenyl = diphyl

[0059] Particularly preferred are 2,6-di-tert-butyl-para-cresol, 2,6-di-tert-butyl-phenol, sulfolan, diphyl or mixtures thereof, sulfolan being especially preferred.

[0060] A rectification column is used for the purification of the crude anhydride mixture according to process step (c) of the present invention. Preferably, a rectification column is used that has 5 to 15 separation stages each in the upper, middle, and lower sections. Preferably, the number of separation stages is 10 to 15 in the upper section and 8 to 13 in the middle and lower sections.

[0061] In the present invention, the number of separation stages is defined as the number of trays in a tray column multiplied by the tray efficiency, or the number of theoretical separation stages in the case of a packed column or a column with packing materials.

[0062] Examples of rectification columns with trays include bubble-cap trays, sieve trays, tunnel trays, valve trays, slotted trays, sieve-slotted trays, sieve bubble-cap trays, nozzle trays, and centrifugal trays. Examples of packed rectification columns include Raschig rings, Lessing rings, Pall rings, Berl saddles, and Intalox saddles. Examples of packed rectification columns include Mellapak (Sulzer), Rombopak (Kühni), Montz-Pak (Montz), and packings with catalyst pockets, such as Katapak (Sulzer). A rectification column with combinations of tray sections, packed sections, and / or packed sections can also be used.

[0063] A rectification column with packings and / or packings is preferably used.

[0064] The rectification column can be made from any suitable material. This includes, among others, stainless steel and inert materials.

[0065] The return of unreacted mixed anhydride to the reaction area in step (d) is carried out, for example, by means of a pump.

[0066] High-boiling substances and added inhibitors can be removed from the column sump by conventional methods, for example by a thin-film evaporator or an apparatus designed for similar tasks, which returns evaporating substances to the rectification column and removes non-evaporating high-boiling substances or salts.

[0067] The method according to the invention can be operated continuously or semi-continuously.

[0068] A preferred embodiment of the method according to the invention is shown schematically in Fig. 2.

[0069] The production of ketene (here: CH2=C=O) takes place in reaction area (3) according to the procedures described above.

[0070] The subsequent reaction of this ketene with (meth)acrylic acid (= (M)AS) takes place in a first reaction chamber (1). For the preparation of (meth)acrylic anhydride from ketene CH2=C=O and (meth)acrylic acid, the reaction temperature in reaction chamber (1) is preferably 40 to 100 °C, particularly preferably 50 to 90 °C and most preferably 70 to 85 °C.

[0071] The crude anhydride mixture (4) obtained from process step (a) in reaction area (1) is now fed to the second reaction area (2), where the further reaction takes place according to process step 8b).

[0072] The temperature of the reactants can be adjusted via a heat exchanger (5) in the feed. The reactor (2) is preferably a flow-tube reactor containing a fixed-bed catalyst. An acidic ion exchanger is preferably used as the fixed-bed catalyst.

[0073] The reactor outflow (6) from the second reaction section (2) is fed into the rectification column (7), preferably below the reflux stream from the upper section (7a) of the column. The separation of the components takes place in the column (7).

[0074] To prevent polymerization, at least one polymerization inhibitor is preferably added both at the top of the column (7) and in the (M)AS feed. In the upper section (7a), the low-boiling acetic anhydride is separated from the middle-boiling component (mixed anhydride), drawn off at the top, and recovered as a valuable material.

[0075] In the middle section (7b) of the column, the separation of the medium-boiling components against (meth)acrylic anhydride (= (M)AAH) takes place, with (M)AAH being preferentially withdrawn in gaseous form between the middle and lower sections. In the lower section (7c) of the column, (M)AAH is separated from the boiling oil (8) in the sump. High-boiling components in the sump can be removed by conventional methods (9), for example, by a thin-film evaporator or a similar apparatus that returns evaporating substances to the rectification column and removes non-evaporating high-boiling components.

[0076] The liquid stream resulting from the upper section (7a) is completely drawn off from the column and collected separately. The mixed anhydride (4) is fed to the reactor (2) as a recirculated stream (10). Alternatively, the recirculated stream (10) can also be fed completely or partially to the reaction section (1) via line (11), provided that both reaction steps are carried out in a common system. Alternatively, the mixed anhydride (4) can be temporarily stored or transported in a tank, provided that the system components are spatially separated.

[0077] The following examples illustrate the method according to the invention without limiting it to these.

[0078] Examples

[0079] Comparison example 1:

[0080] A plant for the production of (meth)acrylic anhydride, as described in EP 2 032 519, was brought to a steady and stable state of maximum capacity utilization, and the parameters at which operation is just barely possible were recorded. The plant is shown in Fig. 1.

[0081] During steady-state operation, reactor 2 was fed with 363.2 g / h MAS and 255.2 g / h acetic anhydride. 309.7 g / h MAAH with a purity greater than 99% was withdrawn via the column draw-off. A distillate of 237.5 g / h was collected at the column head, containing 91.6% acetic acid, 6.3% acetic anhydride, and 2.1% methacrylic acid. At maximum capacity, the condenser at the column head cooled the distillate to 18°C; the loss via the exhaust gas downstream of the condenser was 32 g / h. Thermocouples located between the packing elements (7a, b, and c) recorded a continuous temperature profile of the column, including the top and bottom temperatures as well as the product discharge temperature.

[0082] Example 1:

[0083] The plant from Comparative Example 1 was modified as shown in Figure 2. Acid-free mixed anhydride (from ketene and methacrylic acid) is used as feed for the column. The feed is increased until comparable loading parameters are reached in the column as in Comparative Example 1. The column is then operated at steady state with these parameters. During steady state operation, 1000 g / h of mixed anhydride is fed into the column via line 6. From this, 598 g / h of methacrylic anhydride of identical quality to that in Comparative Example 1 can be isolated. At the top of the column, 370.6 g / h of acetic anhydride distillate with a purity of >99% is produced. At maximum capacity, the condenser at the top of the column can cool the distillate to 22°C; the loss via the exhaust gas downstream of the condenser was 29.8 g / h (the exhaust gas consists of pure acetic anhydride).As in comparative example 1, an increase in the feed rate resulted in a significant increase in flue gas losses, thus establishing a comparable operating point. The calculated column load and spray density, along with the steady-state operating parameters, can be found in Table 1 for direct comparison and demonstrate that the column operates under comparable conditions. The plant capacity was increased by a factor of 1.93 while simultaneously producing the valuable acetic anhydride.

[0084] Table 1: Comparison of the operating parameters of the comparative example and the example according to the invention.

Claims

Patent claims 1. Process for the simultaneous preparation of symmetrical carboxylic acid anhydrides of the general formulas RC(O)-OC(O)-R (I) and R'R“HC-C(O)-OC(O)-CHR'R“ (II) in which R represents an unsaturated organic residue with 2 to 12 C atoms, wherein R' and R“ are the same or different and represent hydrogen or a Ci to C4 alkyl residue, and wherein R' and R“ are different from R by reaction of an unsaturated carboxylic acid of the general formula R-COOH (III), in which R has the meaning given above, with a ketene of the general formula R'R“C=C=O (IV), in which R' and R“ have the meanings given above, characterized in that (a) the unsaturated carboxylic acid (III) is reacted with the ketene (IV) in a first reaction area to form a crude anhydride mixture, (b) the crude anhydride mixture obtained in step (a) is further reacted in a second reaction area, preferably in the presence of at least one catalyst, (c) the symmetrical anhydrides (I) and (II) are isolated by rectification from the mixture obtained in step (b), and (d) unreacted mixed anhydride obtained during rectification in step (c) is returned to the first reaction area and / or to the second reaction area.

2. Method according to claim 1, characterized in that the molar ratio of unsaturated carboxylic acid of formula (III) to ketene of formula (IV) is 1 :4 to 1 :0.5, preferably 1 :1 , amounts.

3. Method according to one of claims 1 or 2, characterized in that the unsaturated carboxylic anhydride of formula (I) is (meth)acrylic anhydride produced by reaction of a ketene of formula CH2=C=O and (meth)acrylic acid.

4. Method according to claim 3, characterized in that the carboxylic acid anhydride of formula (II) is acetic acid anhydride.

5. The process according to claim 4, characterized in that the (meth)acrylic anhydride is obtained in the rectification column used for process step (c) between the middle and the lower part of the rectification column and the acetic anhydride is withdrawn at the column head.

6. Method according to one of the preceding claims, characterized in that the second reaction area is spatially separated from the first reaction area and is arranged outside the rectification column used for process step (c).

7. Method according to one of the preceding claims, characterized in that the reaction in the second reaction area is carried out at temperatures in the range of 30 to 120 °C, in particular at 40 to 100 °C, and particularly preferably at 50 to 80 °C.

8. Method according to one of the preceding claims, characterized in that an intermediate storage of the crude anhydride mixture takes place between process step (a) and process step (b).

8. Method according to one of the preceding claims, characterized in that a heterogeneous catalyst is used in the second reaction area.

10. Method according to claim 8, characterized in that an acidic fixed-bed catalyst is used in the second reaction area.

11. Method according to one of claims 8 or 9, characterized in that a cation exchanger is used as a catalyst in the second reaction area.

12. Method according to one of the preceding claims, characterized in that in the rectification step (c) a high-boiling, inert substance with a boiling point higher than the boiling points of the components involved in the reaction is used as the boiling oil.

13. Method according to claim 12, characterized in that 2,6-di-tert-butyl paracresol, 2,6-di-tert-butylphenol, sulfolane or diphyl or mixtures thereof are used as the boiling oil.

14. Method according to one of claims 12 or 13, characterized in that the boiling oil is Sulfolan is used.

15. A process according to one of the preceding claims, characterized in that high-boiling components are removed from the column sump in the rectification column used for process step (c) and evaporating substances are returned to the column.

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