Process for preparing (meth)acrylates

Abstract

Process for preparing (meth)acrylates of the formula (I)
CH.sub.2C(R.sup.1)COOR.sup.2(I)
in which R.sup.1 is hydrogen or methyl and
R.sup.2 is a saturated or unsaturated, linear or branched, aliphatic or cyclic alkyl radical having 6 to 22 carbon atoms, or a (C.sub.6-C.sub.14)-aryl-(C.sub.1-C.sub.8)-alkyl radical;
by reacting a (meth)acrylate of the formula II
CH.sub.2C(R.sup.1)COOR.sup.3(II)
with an alcohol of the formula (III)
HOR.sup.2(III)
in the presence of an amount of a suitable catalyst which catalyzes the reaction and of an amount of a phenolic polymerization inhibitor or a combination of two or more phenolic polymerization inhibitors which is sufficient to inhibit undesired polymerization;
the reaction being undertaken with input or introduction into the reaction mixture resulting from the reaction of an amount of oxygen or of an oxygenous gas mixture sufficient to inhibit undesired polymerization, and the process is characterized in that
the specific total oxygen input is less than or equal to 1.0 l/kg, measured in liters of oxygen per kilogram of (meth)acrylate of the formula (I), where the volume of oxygen introduced is calculated at a temperature of 25 C. and a pressure of 101 325 pascal. The resulting (meth)acrylates can surprisingly be processed to particularly high molecular weight emulsion polymers which are, for example, outstandingly suitable for use as flow resistance reducers in mineral oil extraction.

Claims

1. A process for preparing a (meth)acrylate of formula (I)
CH.sub.2C(R.sup.1)COOR.sup.2(I) wherein R.sup.1 is hydrogen or methyl, and R.sup.2 is a saturated or unsaturated, linear or branched, aliphatic or cyclic alkyl radical having 6 to 22 carbon atoms, or a (C.sub.6-C.sub.14)-aryl-(C.sub.1-C.sub.8)-alkyl radical, the process comprising: reacting a (meth)acrylate of formula II
CH.sub.2C(R.sup.1)COOR.sup.3(II) wherein R.sup.1 is hydrogen or methyl and R.sup.3 is methyl, with an alcohol of formula (III)
HOR.sup.2(III) wherein R.sup.2 is a saturated or unsaturated, linear, branched or cyclic alkyl radical having 6 to 22 carbon atoms, or a (C.sub.6-C.sub.14)-aryl-(C.sub.1-C.sub.8)-alkyl radical, in the presence of an amount of a suitable catalyst which catalyses the reaction and in the presence of an amount of a phenolic polymerization inhibitor or a combination of two or more phenolic polymerization inhibitors which is sufficient to inhibit undesired polymerization, to form a reaction mixture, the reaction undertaken with introduction into the reaction mixture resulting from the reacting, of an amount of oxygen or of an oxygenous gas mixture sufficient to inhibit undesired polymerization, wherein a specific total oxygen input is less than or equal to 1.0 l/kg, measured in liters of oxygen per kilogram of (meth)acrylate of formula (I), where the volume of oxygen introduced is calculated at a temperature of 25 C. and a pressure of 101,325 pascal, and wherein the reacting is performed continuously.

2. The process according to claim 1, wherein the reacting of the alcohol of formula (III) to (meth)acrylate of formula (I) is carried out in a reaction vessel having a reactor volume of greater than or equal to 0.25 m.sup.3.

3. The process according to claim 1, wherein the (meth)acrylate of formula (I), after the reacting has ended, is isolated by distillation.

4. The process according to claim 1, wherein R.sup.2 is a linear or branched alkyl radical having 8 to 12 carbon atoms or a (C.sub.6-C.sub.12)-aryl-(C.sub.1-C.sub.4)-alkyl radical.

5. The process according to claim 1, wherein R.sup.2 is a 2-ethylhexyl radical.

6. The process according to claim 1, wherein the catalyst is tetraisopropyl titanate, tetrakis(ethylhexyl) titanate, zirconium acetylacetonate, a dialkyltin compound, a lithium compound, optionally in combination with a calcium compound, or an acid.

7. The process according to claim 1, wherein the phenolic inhibitor is hydroquinone and/or hydroquinone monomethyl ether.

8. The process according to claim 1, wherein the oxygenous gas mixture introduced into the reaction mixture is oxygenous lean air having a content of less than or equal to 5% oxygen (v/v).

9. The process according to claim 1, wherein the specific total oxygen input is less than or equal to 0.5 liter of oxygen per kilogram of product of the formula (I).

10. The process according to claim 1, wherein the specific total oxygen input is less than or equal to 0.3 liter of oxygen per kilogram of product of the formula (I).

11. The process according to claim 1, wherein the specific total oxygen input is less than or equal to 0.2 liter of oxygen per kilogram of product of the formula (I).

12. The process according to claim 1, wherein the catalyst is tetraisopropyl titanate or tetrakis(ethylhexyl) titanate.

13. The process according to claim 1, wherein the catalyst is tetraisopropyl titanate.

14. The process according to claim 1, wherein the catalyst is tetrakis(ethylhexyl) titanate.

15. The process according to claim 1, wherein the catalyst is zirconium acetylacetonate.

16. The process according to claim 1, wherein the catalyst is a dialkyltin compound.

17. The process according to claim 1, wherein the process is performed without a further solvent.

18. The process according to claim 1, wherein a concentration of the phenolic polymerization inhibitor is less than 50 ppm, based on the (meth)acrylate of formula (I).

19. The process according to claim 1, wherein the alcohol of formula III and the (meth)acrylate of formula II are combined with the catalyst and polymerization inhibitor in a reaction vessel such that a weight ratio of alcohol of formula III:(meth)acrylate of formula II is in a range of from 1:1.5 to 1:10, to form the reaction mixture.

20. A process for preparing a (meth)acrylate of formula (I)
CH.sub.2C(R.sup.1)COOR.sup.2(I) wherein R.sup.1 is hydrogen or methyl, and R.sup.2 is a saturated or unsaturated, linear or branched, aliphatic or cyclic alkyl radical having 6 to 22 carbon atoms, or a (C.sub.6-C.sub.14)-aryl-(C.sub.1-C.sub.8)-alkyl radical, the process comprising: reacting a (meth)acrylate of formula II
CH.sub.2C(R.sup.1)COOR.sup.3(II) wherein R.sup.1 is hydrogen or methyl and R.sup.3 is methyl, with an alcohol of formula (III)
HOR.sup.2(III) wherein R.sup.2 is a saturated or unsaturated, linear, branched or cyclic alkyl radical having 6 to 22 carbon atoms, or a (C.sub.6-C.sub.14)-aryl-(C.sub.1-C.sub.8)-alkyl radical, in the presence of an amount of a suitable catalyst which catalyses the reaction and in the presence of an amount of a phenolic polymerization inhibitor or a combination of two or more phenolic polymerization inhibitors which is sufficient to inhibit undesired polymerization, to form a reaction mixture, the reaction undertaken with introduction into the reaction mixture resulting from the reacting, of an amount of an oxygenous gas mixture sufficient to inhibit undesired polymerization, wherein a specific total oxygen input is less than or equal to 1.01/kg, measured in liters of oxygen per kilogram of (meth)acrylate of formula (I), where the volume of oxygen introduced is calculated at a temperature of 25 C. and a pressure of 101,325 pascal, the oxygenous gas mixture introduced into the reaction mixture is oxygenous lean air having a content of less than or equal to 5% oxygen (v/v), and wherein the reacting is performed continuously.

Description

EXAMPLES

Example 1

Preparation of 2-Ethylhexyl Methacrylate by a Batch Process

(1) A 12 m.sup.3 stirred tank reactor with stirrer, steam heater, distillation column and condenser is initially charged with 4200 kg of 2-ethylhexanol, 5000 kg of methyl methacrylate (MMA), 0.840 kg of hydroquinone monomethyl ether as an inhibitor and 28 kg of tetra-isopropyl titanate as a catalyst, which are stirred while constantly introducing air (14 m.sup.3/h).

(2) To stabilize the column, over the entire reaction phase, a total of 160 kg of MMA which contains 0.2 kg of hydroquinone monomethyl ether are metered into the column reflux. The mixture is heated to boiling temperature (beginning at approx. 90 C.), in the course of which the column is initially operated with full reflux. As soon as the temperature at the top of the column falls below 70 C., the methanol-MMA mixture formed is drawn off with variable reflux ratio (2:1-10:1). After approx. 3 hours and the removal of approx. 1200 l of methanol-MMA mixture, the reaction is very substantially complete (conversion >90%). As a result of the removal of the low-boiling components, the product temperature has risen to 116 C.

(3) Up to a product temperature of 130 C., excess MMA is subsequently drawn off with a reflux ratio of 1:2 under standard pressure over a period of about 2 hours.

(4) Thereafter, the MMA which still remains is removed completely under adjusted vacuum (1000-30 mbar) at a constant bottom temperature of 120 C. and without reflux. The air introduction is reduced to 4 m.sup.3/h in the vacuum phase. When no further MMA distillate is obtained with the best vacuum over a period of 30 minutes, the vacuum is broken (duration about 2 hours).

(5) The vessel contents, consisting of the catalyst-containing 2-ethylhexyl MA, are subsequently stabilized with 2.5 kg of Irganox 1076, and 2-ethylhexyl MA is distilled off with a reflux ratio of 1:10 under the best possible vacuum (approx. 30 mbar) and an average bottom temperature of 130 C.-140 C. The air introduction of 4 m.sup.3/h is maintained; the distillation step is complete after about 2 hours.

(6) With a bottom residue of approx. 800 kg, 4900 kg of pure ester are obtained with the following composition (determined by gas chromatography):

(7) 2-ethylhexyl MA: 99.4%

(8) 2-ethylhexanol: 0.17%

(9) MMA: 0.1%

Example 2

Preparation of 2-Ethylhexyl Methacrylate by a Batch Process

(10) A 20 m.sup.3 stirred tank reactor with a stirrer, distillation column and condenser is initially charged with 8030 kg of methyl methacrylate (MMA), 7890 kg of 2-ethylhexanol, 364 g of hydroquinone monomethyl ether and 36 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl as inhibitors, and also 90 kg of 2-ethylhexyl titanate as a catalyst, and stirred with constant introduction of a gas mixture composed of 95% N.sub.2 and 5% O.sub.2 (10 m.sup.3/h).

(11) To stabilize the column, over the entire reaction phase, a total of 908 kg of MMA which contain 908 g of hydroquinone monomethyl ether and 90 g of 4-hydroxy-2,2,6,6-tetamethylpiperidine 1-oxyl are metered into the column reflux. The mixture is heated to boiling temperature (approx. 100 C.). At a constant reflux ratio of 1:1, the methanol-MMA mixture formed is drawn off. During the reaction phase, 2800 kg of MMA are metered continuously into the reactor. After approx. 3 h, the reaction is very substantially complete.

(12) Up to a product temperature of 130 C., excess MMA is subsequently drawn off at a reflux ratio of 0.2:1; the pressure is lowered continuously down to 40 mbar. The gas mixture introduction in the vacuum phase is reduced to 5 m.sup.3/h. The vacuum is broken when a pressure of 40 mbar is attained at a bottom temperature of 110 C. or higher (approx. 3 h). The tank contents are subsequently cooled to 80 C. and pumped into an intermediate tank.

(13) The crude product is pumped out of the intermediate tank into a thin-film evaporator. The pure product is removed there at a pressure of 5 mbar. The product is condensed and collected in a tank.

(14) A pure product is obtained with the following composition (determined by gas chromatography):

(15) 2-EHMA 99.1%

(16) 2-ethylhexanol 0.3%

(17) MMA 0.5%

Example 3

Preparation of 2-Ethylhexyl Methacrylate by a Continuous Process

(18) 2-Ethylhexyl methacrylate is prepared continuously in a stirred tank battery consisting of three stirred tanks connected in series, each of capacity 2.1 m.sup.3, comprising a first column unit for removing the methanol-methyl methacrylate mixture formed and a second column unit for removing low-boiling components. The stirred tank battery is supplied continuously with 700 l/h of 2-ethylhexanol, 600 l/h of methyl methacrylate (MMA) and 15 kg/h of a 50% solution of 2-ethylhexyl titanate in MMA, which has been stabilized with 525 ppm of hydroquinone monomethyl ether.

(19) Additionally metered into the system are 15 l/h of 3.5% hydroquinone monomethyl ether in MMA via reaction stage 1.

(20) The individual reaction stages are supplied with stabilization air of in each case 450 l/h of fresh air. The vapours from the stirred tank which have been freed of methanol in the first distillation column are fed to the 1st stirred tank via the column bottom.

(21) Under these reaction conditions (pressure 500 mbar), a reaction temperature of 107 C. is established in the first stirred tank. The reaction temperature is 125 C. in the 2nd stirred tank and 136 C. in the 3rd stirred tank.

(22) The methanol formed is drawn off continuously as a methanol-MMA mixture at a rate of 240 l/h via the first distillation column with a circulation evaporator. The effluent of the 1st reaction vessel is passed on into the 2nd reaction vessel, and the effluent of the 2nd reaction vessel into the 3rd reaction vessel.

(23) The effluent of the 3rd reaction vessel is fed continuously to the thin-film evaporator of the low boiler column, in which unconverted 2-ethylhexanol, MMA and methanol are drawn off as distillate (350 l/h) and fed back to the first distillation column.

(24) The bottom effluent of the low boiler column is 1000 kg/h and has a composition of 98.1% 2-ethylhexyl methacrylate, 1.0% MMA and 0.7% 2-ethylhexanol and, to a smaller degree, high boilers and reactants.

Emulsion polymerization of 2-ethylhexyl methacrylate

(25) The 2-ethylhexyl methacrylate prepared according to Examples 1 to 3 was in each case polymerized by emulsion polymerization.

(26) To this end, 400 g of the 2-ethylhexyl methacrylate prepared were processed to an emulsion by means of an Ultra-Turrax at 4000 rpm for 3 minutes with

(27) TABLE-US-00001 18 g of sodium lauryl sulphate 0.6 g of K.sub.3PO.sub.43 H.sub.2O in 50 g of dist. water 0.6 g of KH.sub.2PO.sub.4 in 50 g of dist. water 0.06 g of ammonium peroxodisulphate (APS) in 50 g of dist. water 373 g of dist. water.

(28) The emulsion was transferred to the initial charge of a polymerization vessel which was cooled to circulation temperature 5 C. Simultaneously, nitrogen was introduced into the reaction mixture which was stirred at 100 rpm. Subsequently, the metered addition of a solution of 0.072 g FeSO.sub.4.7 H.sub.2O in 100 g of dist. water over 20 hours was commenced. After the end of feeding, 24 g of Triton X 305 (70% strength) in 24 g of dist. water were added. Subsequently, the dispersion was filtered through a stainless steel screening fabric with MW 0.09 mm.

(29) The specific viscosity .sub.spec/c was determined based on DIN 51562 in THF as a solvent. The concentration was selected so as to achieve a relative viscosity in the range of 1.1-1.2. The particle radius was determined as the r.sub.N5 value with an N5 Submicron Particle Size Analyzer from Beckman Coulter according to the manufacturer's instructions.

(30) The analytical data of the monomers and of the polymer dispersions obtained from the monomers can be taken from the table which follows:

(31) TABLE-US-00002 EHMA characterization and resulting homopolymer Air/O2 Total O2 input content [%] [l/kg EHMA] Monomer on including Example preparation degassing 1 18 2.4 2 5 0.2 3 18 0.2 Stabilization of the Characterization of the Dry monomer used TempolMA* resulting polymer dispersion rN5 content Example HQME [ppm] Tempol [ppm] [PPM] .sub.spec/c in THF [ml/g] [nm] [%] pH 1 23.5 715 66 39.7 7.1 2 10 <1 4.5 1464 52 39.6 7.2 3 1 <1 <1 1369 69 39.6 7.2 *TempolMA is a conversion product inevitably formed in the transesterification by reaction of Tempol with methyl methacrylate.