PROCESS FOR PRODUCING HYDROXYALKYL (METH)ACRYLATE ESTERS BY OXIDATIVE CLEAVAGE OF METHACROLEIN ACETALS

Abstract

A process can be used for producing hydroxyalkyl (meth)acrylate esters, in particular hydroxyethyl methacrylate (HEMA). The process involves a first reaction of (meth)acrolein with at least one polyhydric alcohol, in particular ethylene glycol, in the presence of a first catalyst C1, wherein a first reaction product containing a cyclic acetal is obtained. The process then involves a second reaction of the first reaction product with oxygen in the presence of a second catalyst C2, wherein a second reaction product containing at least one hydroxyalkyl (meth)acrylate ester is obtained. After the first reaction, water and optionally further components, in particular (meth)acrolein and/or the polyhydric alcohol, e.g. ethylene glycol, are at least partially removed from the first reaction product.

Claims

1: A process for producing hydroxyalkyl (meth)acrylate esters, the process comprising: a) reacting (meth)acrolein with at least one polyhydric alcohol in the presence of a first catalyst C1, wherein a first reaction product comprising at least one cyclic acetal is obtained; b) at least partially removing water from the first reaction product; and c) reacting the first reaction product with oxygen in the presence of a second catalyst C2, wherein a second reaction product comprising at least one hydroxyalkyl (meth)acrylate ester is obtained.

2: The process according to claim 1, wherein the process is a continuous process for producing hydroxyalkyl (meth)acrylate esters.

3: The process according to claim 1, wherein the reaction in a) is carried out in the presence of at least one acidic compound as the first catalyst C1, selected from the group consisting of Brønsted acids and Lewis acids, wherein the first catalyst C1 is present in heterogeneous or homogeneous form and comprises at least one acidic group that has a pKa of less than or equal to 5.

4: The process according to claim 1, wherein the at least one fir catalyst C1 is selected from the group consisting of phosphoric acid, sulfuric acid, sulfonic acid, carboxylic acid, and an ion-exchange resin containing at least one acidic group selected from the group consisting of sulfonic acids and carboxylic acids.

5: The process according to claim 1, wherein the reaction in a) is carried out with a molar ratio of (meth)acrolein to polyhydric alcohol(s) within a range from 1:50 to 50:1.

6: The process according to claim 1, wherein, in b), unreacted (meth)acrolein and/or unreacted polyhydric alcohol are removed from the first reaction product and recycled into the reaction in a).

7: The process according to claim 1, wherein, in b), in a first separation, (meth)acrolein and at least some of the water are removed from the first reaction product.

8: The process according to claim 1, wherein, in b), in at least two separations, water, unreacted (meth)acrolein and unreacted polyhydric alcohol are removed from the first reaction product comprising at least one cyclic acetal.

9: The process according to claim 1, wherein the reaction in c) is carried out in the presence of a metal-containing and/or metalloid-containing, heterogeneous catalyst system as the second catalyst C2.

10: The process according to claim 1, wherein the at least one second catalyst C2 is a heterogeneous catalyst comprising one or more support materials and one or more active components, wherein the one or more support materials are selected from the group consisting of activated charcoal, silicon dioxide, aluminium oxide, titanium dioxide, alkali metal oxide, alkaline earth metal oxide, and a mixture thereof, and wherein the one or more active component comprise at least one element selected from the group consisting of palladium, platinum, iridium, rhodium, ruthenium, gold, cobalt, nickel, zinc, copper, iron, selenium, tellurium, arsenic, antimony, bismuth, germanium, tin, and lead, wherein the at least one element is present in elemental form, as an alloy, or in the form of a compound thereof in any desired oxidation state.

11: The process according to claim 1, wherein the at least one second catalyst C2 is a heterogeneous catalyst comprising silicon dioxide and/or aluminium oxide as a support material, and comprising as an active component at least one element selected from the group consisting of palladium, bismuth, and tellurium, wherein the at least one element can be present in elemental form, as an alloy, or in the form of a compound thereof in any desired oxidation state.

12: The process according to claim 1, wherein the at least one second catalyst C2 is a heterogeneous catalyst comprising silicon dioxide and/or aluminium oxide as a support material, and an active component, wherein the active component is palladium and at least one further element selected from the group consisting of selenium, tellurium, and bismuth, wherein the at least one further element can be present in elemental form, as an alloy, or in the form of an oxide thereof in any desired oxidation state.

13: The process according to claim 1, wherein, in the reaction in c), a reaction mixture comprising the first reaction product and the second catalyst C2 is contacted with an oxygen-containing gas, wherein an oxygen-containing offgas is obtained in c), wherein the oxygen-containing offgas is cooled at least once, and wherein the oxygen-containing offgas has an oxygen content within the range from 1% to 10% by volume based on the total oxygen-containing offgas.

14: The process according to claim 1, wherein a reaction mixture comprising the first reaction product and the second catalyst C2 is used in the reaction in c), said reaction mixture having a content of polyhydric alcohol(s) of less than 10% by weight based on the reaction mixture in c).

15: The process according to claim 1, wherein the reaction in a) is carried out within a temperature range from −50° C. to 100° C. and the reaction in c) is carried out within a temperature range from 0° C. to 120° C., and wherein the reaction in a) is carried out at a temperature that is at least 15° C. lower than the temperature in the reaction in c).

16: The process according to claim 1, wherein the reaction in a) is carried out within a pressure range from 0.5 to 10 bar and the reaction in c) is carried out within a pressure range from 1 to 50 bar, and wherein the reaction in c) is carried out at a pressure that is at least 0.1 bar higher than the pressure in the reaction in a).

17: The process according to claim 5, wherein the reaction in a) is carried out with a molar ratio of (meth)acrolein to polyhydric alcohol(s) within a range from 1:3 to 3:1.

Description

DESCRIPTION OF THE FIGURES

[0096] FIG. 1 shows by way of example a possible schematic flow diagram of the process according to the invention. The designations here are defined as follows: [0097] 1 (Meth)acrolein stream from 3 or 7 [0098] 2 Dialcohol stream [0099] 3 Reactor, first step, formation of the cyclic acetal [0100] 4 Optional recycling stream ((meth)acrolein) [0101] 5 Decanter [0102] 6 Removal of water [0103] 7 Distillation column, separation of (meth)acrolein and water [0104] 8 Crude stream of first reaction product (cyclic acetal) [0105] 9 Optional recycling stream (dialcohol) [0106] 10 Distillation column, separation of acetal from dialcohol and high boilers [0107] 11 Acetal stream from second reaction step, optional addition of stabilizer and solvent to second reaction step possible here [0108] 12 Metering-in of air for oxidation of the acetal [0109] 13 Reactor, second step, formation of the hydroxyalkyl (meth)acrylate ester [0110] 14 Optional recycling stream (acetal and/or solvent) [0111] 15 Offgas line [0112] 16 Distillation column, separation of acetal and/or solvent [0113] 17 Discharge of high boilers from the first reaction step [0114] 18 Crude stream of second reaction product (hydroxyalkyl (meth)acrylate ester)

EXPERIMENTAL SECTION

Example 1a—Continuous Production of the Cyclic Acetal (2-isopropenyl-1,3-dioxolane) Based on Methacrolein and Ethylene Glycol/Methacrolein on a Distillation Column

[0115] A jacketed loop reactor containing a 5 kg quantity of active catalyst and having a total volume of 25 L was used. The catalyst (C1) used was a sulfonic acid resin from Lanxess (K2431). The reactor was controlled via the jacket (operated with Aral antifreeze coolant) such that the internal temperature was 2-3° C. The reactor was connected to a distillation column (DN 150 mm, height 6 m) packed with Sulzer DX packing (HETP 60 mm, ˜16.6 theoretical plates per metre packing height).

[0116] Ethylene glycol (EG) (15 kg/h, 242 mol/h), to which 100 ppm of TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperdine-1-oxyl) was added, was metered directly into the reactor (3), whereas the methacrolein (MAL) together with the outflow from the reactor was fed onto a distillation column (7). This resulted in both the methacrolein (MAL) and the reaction product being dewatered, which was advantageous for reaction control. The hetero-azeotrope of methacrolein and water collected at the head of the column, which on cooling separates into two phases. The methacrolein was fed via a decanter (5) back into the reactor (3). The amount of fresh methacrolein was adjusted so that the amount of methacrolein fed into the reactor was 17.25 kg (246 mol) per hour. The molar ratio of methacrolein to ethylene glycol was thus 1.02 and the LHSV (liquid hourly space velocity) was 6.4 ((kg MAL+kg EG)/(kg cat.*hr)).

[0117] The contents of the loop reactor were circulated via a pump such that the internal circulation ensured thorough mixing of the reactants; at low circulation flow rates, the formation of two phases was observed. To improve mixing, a static mixer was installed in front of the catalyst bed. The dwell time in the reactor was nearly 45 minutes and the reaction mixture in the reactor outflow had a composition of 40% by weight of methacrolein, 34% by weight of ethylene glycol, 21% by weight of acetal, 3% by weight of water and 2% by weight of secondary components. The secondary components are in particular high-boiling products of the addition of glycol or water to the acetal.

[0118] The reactor was started up over a period of 3 hours and was then operated with these parameters continuously and stably for 12 hours. Methacrolein conversion was 26% and selectivity in respect of the acetal was 92%.

Example 1b—Continuous Removal of Methacrolein and Water from the Product Mixture from Example 1a

[0119] The reaction outflow from Example 1a (32.25 kg/h) was mixed with fresh methacrolein and fed into a distillation column (7) (DN 150 mm, height 6 m) packed with Sulzer DX packing (HETP 60 mm, ˜16.6 theoretical plates per metre packing height). The column was operated at a pressure of 90 mbar, a bottoms temperature of 90° C., a distillate temperature of 5° C. and a reflux ratio of 1. Connected at the head of the column was a decanter (5), by means of which the resulting hetero-azeotrope of methacrolein and water (98.8% by weight of MAL and 1.2% by weight of water) was separated.

[0120] The aqueous phase in the decanter consisted of 93.9% by weight of water and 6.1% by weight of methacrolein. The aqueous phase was stripped from time to time, yielding a methacrolein-free aqueous bottoms. This bottoms can be treated biologically or incinerated. The organic phase of the decanter (5) was recycled into the reaction (reactor 3).

[0121] The bottoms of the distillation column (7) (18.4 kg/h) consisted of the cyclic acetal (37% by weight), ethylene glycol (60% by weight) and the high-boiling by-products mentioned under 1a (3% by weight).

[0122] The fresh methacrolein was loaded onto the distillation column (7) in a manner that ensured almost total removal of the methacrolein and water azeotrope from the bottoms of column 7. This achieved depletion of the methacrolein in the bottoms discharge (from 7) to a level of below 1000 ppm.

Example 1c—Continuous Production of the Cyclic Acetal (2-isopropenyl-1,3-dioxolane) Based on Methacrolein and Ethylene Glycol/Methacrolein in the Reactor

[0123] A jacketed loop reactor containing a 5 kg quantity of active catalyst and having a total volume of 25 L was used. The catalyst (C1) used was a sulfonic acid resin from Lanxess (K2431). The reactor was controlled via the jacket (operated with Aral antifreeze coolant) such that the internal temperature was 2-3° C.

[0124] The ethylene glycol (15 kg/h, 242 mol/h) and the methacrolein (17.25 kg/h, 246 mol/h) were metered into the reactor (3) with 100 ppm of TEMPOL. The molar ratio of methacrolein to ethylene glycol was thus 1.02 and the LHSV was 6.4 ((kg MAL+kg EG)/(kg cat.*hr)). The contents of the loop reactor were circulated via a pump such that the internal circulation ensured thorough mixing of the reactants; at low circulation flow rates, the formation of two phases was observed. To improve mixing, a static mixer was installed in front of the catalyst bed.

[0125] The dwell time in the reactor (3) was nearly 45 minutes and the reaction mixture at the outflow had a composition of 40% by weight of methacrolein, 34% by weight of ethylene glycol, 21% by weight of acetal, 3% by weight of water and 2% by weight of secondary components. The secondary components are in particular high-boiling products of the addition of glycol or water to the acetal.

[0126] The reactor was started up over a period of 3 hours and was then operated with these parameters continuously and stably for 12 hours. Methacrolein conversion was thus 26% and selectivity in respect of the acetal was 92%.

Example 1d—Continuous Removal of Methacrolein and Water from the Product Mixture from Example 1c

[0127] The reaction outflow from Example 1c (32.25 kg/h) was fed into a distillation column (7) (DN 150 mm, height 6 m) packed with Sulzer DX packing (HETP 60 mm, ˜16.6 theoretical plates per metre packing height). The column was operated at a pressure of 85 mbar, a bottoms temperature of 88° C., a distillate temperature of 5° C. and a reflux ratio of 2.5. Connected at the head of the column was a decanter (5), by means of which the resulting hetero-azeotrope of methacrolein and water (98.8% by weight of MAL and 1.2% by weight of water) was separated.

[0128] The aqueous phase in the decanter consists of 93.5% by weight of water, 6.1% by weight of methacrolein and 0.4% by weight of acetal. The aqueous phase was stripped from time to time, yielding a methacrolein-free aqueous bottoms. This bottoms can be treated biologically or incinerated. The organic phase of the decanter was recycled into the reaction (3) and contained 2.3% by weight of acetal here.

[0129] The bottoms of the distillation column (7) (18.4 kg/h) consisted of the cyclic acetal (36% by weight), ethylene glycol (61% by weight) and the high-boiling by-products mentioned under 1a (3% by weight). Although depletion of methacrolein and water in the bottoms to below 1000 ppm was achieved, there was some loss of acetal in the decanter (5).

Example 1e—Batchwise Production of the Cyclic Acetal (2-isopropenyl-1,3-dioxolane) Based on Methacrolein and Ethylene Glycol/with the Aid of an Inert Azeotropic Entrainer

[0130] A glass apparatus fitted with a Dean-Stark apparatus was charged with 315 g of methacrolein (4.5 mol), 279 g of ethylene glycol (4.5 mol), 500 g of hexane and 5.2 g of phosphoric acid (1 mol %). The reaction mixture was stabilized with 0.4 g of TEMPOL and 0.4 g of 4-methoxyphenol in each case. The mixture was heated to 80° C. for 6 hours, resulting in the removal of the water liberated in the reaction by the hexane entrainer. In the separation part of the Dean-Stark apparatus, a water-rich fraction was additionally collected, and the condensed organic fraction consisting of hexane and methacrolein was continuously recycled into the reaction part of the apparatus. After 6 hours the reaction was stopped.

[0131] Methacrolein conversion was approx. 70% and selectivity was approx. 48%. Not long after the start of the reaction, a dark-coloured turbidity developed in the reaction vessel at the phase boundary between methacrolein/hexane and ethylene glycol, which increased as the reaction progressed. The turbidity here was due in particular to high-boiling polymers formed from methacrolein and glycol and to products of the addition of glycol to the 4-position of methacrolein or the acetal thereof. Increasing the amount of catalyst or scale-up of the reaction to a larger scale accelerated the formation of these high boilers.

[0132] The acetal yields obtained with this methodology were essentially unsatisfactory, particularly with regard to space-time yield. The principle of water removal by means of an entrainer and by means of removal of a methacrolein-water azeotrope is however demonstrated.

Example 2—Synthesis of the Catalyst (C2) for the Oxidation of 2-Isopropenyl-1,3-Dioxolane to Hydroxyethyl Methacrylate (HEMA) Example 2a

[0133] 0.90 g of bismuth pentahydrate and 0.36 g of telluric acid were suspended, with stirring, in a glass apparatus. HNO.sub.3 (60%) was added dropwise until everything had dissolved and the formation of unstable suboxides was prevented. 20.0 g of palladium on alumina (5% by weight Pd) was added and the suspension heated to 60° C. On reaching this temperature, the mixture was stirred for one hour. To this was added dropwise 10.0 g of a hydrazine monohydrate solution. The suspension was heated to 90° C. and stirred for another hour. After cooling to room temperature, the black solid was filtered off and washed with four 100 mL portions of distilled water. The conductivity of the liquid from the last wash was less than 100 μS/cm, which showed that the dopants had been taken up quasi-quantitatively.

[0134] The solid was dried at 105° C. for 10 h, affording the final catalyst. The stoichiometry was Pd1.00Bi0.20Te0.17@Al2O3.

Example 2b

[0135] The synthesis was carried out in analogous manner to Example 2a, without addition of telluric acid.

Example 2c

[0136] The synthesis was carried out in analogous manner to Example 2a, without addition of bismuth nitrate pentahydrate.

Example 2d

[0137] The synthesis was carried out in analogous manner to Example 2a, with addition of twice the amount of telluric acid.

Example 2e

[0138] The synthesis was carried out in analogous manner to Example 2a, with addition of twice the amount of bismuth nitrate pentahydrate.

Example 2f

[0139] The synthesis was carried out in analogous manner to Example 2a, with addition of twice the amount of bismuth nitrate pentahydrate and telluric acid.

Example 3—Oxidation of 2-isopropenyl-1,3-dioxolane to Hydroxyethyl Methacrylate (HEMA)

Example 3a

[0140] Into a 130 mL steel autoclave with stirrer unit was weighed 400 mg of catalyst (C2) from Example 2a and a 25% by weight solution of 2-isopropenyl-1,3-dioxolane in toluene stabilized with 200 ppm of TEMPOL. The autoclave was closed, pressurized to 37 bar with 7% oxygen in nitrogen (0.6 equivalents of oxygen per equivalent of acetal) and placed in a pre-tempered oil bath at 70° C. The reaction was stirred for 4 h and then stopped by cooling with dry ice. The pressure in the autoclave was carefully released and the reaction mixture was analysed by gas chromatography (GC).

[0141] Conversion was 54% and selectivity in respect of 2-hydroxyethyl methacrylate was 84%. This corresponds to a space-time yield of 3.8 mol HEMA/kg catalyst per hour. Ethylene dimethacrylate could not be detected by gas chromatography (GC).

Example 3b

[0142] The oxidation was carried out as in Example 3a, but using ethyl acetate as solvent. After a reaction time of 2 hours, conversion was 91%, selectivity was 88% and the space-time yield was 19.6 mol HEMA/kg catalyst per hour. Ethylene dimethacrylate could not be detected by gas chromatography.

Example 3c

[0143] The oxidation was carried out as in Example 3a, but with the catalyst from Example 2b. Conversion was 12% and selectivity was 79%.

Example 3d

[0144] The oxidation was carried out as in Example 3a, but with the catalyst from Example 2c. Conversion was 73%, selectivity was 78% and the space-time yield was 7.1 mol HEMA/kg catalyst per hour.

Example 3e

[0145] The oxidation was carried out as in Example 3a, but with the catalyst from Example 2d. Conversion was 20%, selectivity was 84% and the space-time yield was 2.1 mol HEMA/kg catalyst per hour.

Example 3f

[0146] The oxidation was carried out as in Example 3a, but with the catalyst from Example 2e. Conversion was 83%, selectivity was 59% and the space-time yield was 6.1 mol HEMA/kg catalyst per hour.

Example 3g

[0147] The oxidation was carried out as in Example 3a, but with the catalyst from Example 2f. Conversion was 59%, selectivity was 71% and the space-time yield was 5.3 mol HEMA/kg catalyst per hour.

Example 3h

[0148] The oxidation was carried out as in Example 3a, but using ethylene glycol as solvent. After a reaction time of 2 hours, conversion was 99%, selectivity was 55% and the space-time yield was 7.06 mol HEMA/kg catalyst per hour.

[0149] The main side reaction observed was hydrogenation of 2-hydroxyethyl methacrylate. Selectivity in this reaction was 30%. The example demonstrates that, for reaction control and for the achievement of high selectivities and yields, it is advantageous to monitor and reduce the concentration of the alcohol (reactant in the first step), since the side reaction to the undesired, hydrogenated by-product can otherwise increase.

Example 3i

[0150] The oxidation was carried out as in Example 3a, but with the reaction carried out at atmospheric pressure and with the gas amount chosen such that there was a continued excess of oxygen. After a reaction time of 4 hours, almost no conversion was present. The reaction time was extended to 48 hours, wherein conversion of approx. 50% was observed, with selectivity of 83%.

[0151] This demonstrates that reaction at lower pressures, although possible, is economically unviable.

Example 3j

[0152] The oxidation was carried out as in Example 3a, but with the reaction carried out at 50° C. After a reaction time of 4 hours, conversion was 29% and selectivity was 83%. On lowering the temperature, an almost linear decrease in reaction rate was observed.

[0153] This demonstrates that reaction at low temperatures, although possible, is economically unviable.