CONVEYING A FLUID CONTAINING A (METH)ACRYLIC MONOMER BY MEANS OF A PUMP

Abstract

The present invention relates to a method for transporting a liquid F by means of a pump P, wherein the liquid F comprises at least 10% by weight of a (meth)acrylic monomer, the pump P has a pump space (3), the pump space (3) comprises at least one transport element (4) for transporting the liquid F, the transport element (4) is connected to a drive shaft (6) in such a way that the drive shaft (6) can transmit a torque to the transport element (4), the mounting of the drive shaft is effected by means of at least two sliding bearings (5) in the pump space (3) and the sliding bearings (5) are composed of tungsten carbide.

Claims

1.-15. (canceled)

16. A method for transporting a liquid F by means of a pump P, where the liquid F comprises at least 10% by weight of a (meth)acrylic monomer, the pump P has a pump space, the pump space comprises at least one transport element for transporting the liquid F, the liquid F is fed into the pump space with an entry energy, the liquid F leaves the pump space with an exit energy which is greater than the entry energy, the transport element is connected to a drive shaft in such a way that the drive shaft can transmit a torque to the transport element, and the mounting of the drive shaft is effected by means of at least two sliding bearings in the pump space, wherein the sliding bearings are composed of tungsten carbide.

17. The method according to claim 16, wherein the liquid F comprises at least 60% by weight of a (meth)acrylic monomer.

18. The method according to claim 16, wherein the liquid F comprises at least 90% by weight of a (meth)acrylic monomer.

19. The method according to claim 16, wherein the (meth)acrylic monomer is acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 4-hydroxybutyl acrylate or cyclohexyl acrylate.

20. The method according to claim 16, wherein a temperature of the liquid F is from 10 to 120° C.

21. The method according to claim 16, wherein a temperature of the liquid F is from 50 to 90° C.

22. The method according to claim 16, wherein the liquid F comprises a polymerization inhibitor.

23. The method according to claim 22, wherein the polymerization inhibitor is hydroquinone monomethyl ether, phenothiazine, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, hydroquinone or N,N′-di-sec-butyl-p-phenylenediamine.

24. The method according to claim 16, wherein the liquid F comprises from 0.001 to 1% by weight of a polymerization inhibitor.

25. The method according to claim 16, wherein the liquid F comprises from 0.01 to 0.1% by weight of a polymerization inhibitor.

26. The method according to claim 16, wherein force transmission to the drive shaft is effected by means of a magnetic coupling or a canned motor.

27. A pump P with liquid F, wherein the liquid F comprises at least 10% by weight of a (meth)acrylic monomer, the pump P has a pump space, the pump space comprises at least one transport element for transporting the liquid F, the liquid F is fed into the pump space with an entry energy, the liquid F leaves the pump space with an exit energy which is greater than the entry energy, the transport element is connected to a drive shaft so that the drive shaft can transmit a torque to the transport element, mounting of the drive shaft is effected by means of at least two sliding bearings in the pump space and the sliding bearings are composed of tungsten carbide.

28. The pump P according to claim 27, wherein the transmission of force to the drive shaft is effected by means of a magnetic coupling or a canned motor.

29. The use of a pump P for transporting a liquid F, wherein the liquid F comprises at least 10% by weight of a (meth)acrylic monomer, the pump P has a pump space, the pump space comprises at least one transport element for transporting the liquid F, the liquid F is fed into the pump space with an entry energy, the liquid F leaves the pump space with an exit energy which is greater than the entry energy, the transport element is connected to a drive shaft so that the drive shaft can transmit a torque to the transport element, mounting of the drive shaft is effected by means of at least two sliding bearings in the pump space and the sliding bearings are composed of tungsten carbide.

30. The use according to claim 29, wherein the transmission of force to the drive shaft is effected by means of a magnetic coupling or a canned motor.

Description

EXAMPLES

Example 1 (not According to the Invention)

[0043] A gaseous product gas mixture having the following composition was produced by two-stage catalytic gas-phase oxidation of propylene by molecular oxygen: [0044] 9.84% by weight of acrylic acid, [0045] 0.4% by weight of acetic acid, [0046] 4.4% by weight of water, [0047] 0.11% by weight of acrolein, [0048] 0.21% by weight of formaldehyde, [0049] 0.07% by weight of maleic anhydride together with, as
balance to 100% by weight, propionic acid, furfural, propane, propene, nitrogen, oxygen and carbon oxides.

[0050] This gaseous product gas mixture was cooled in a spray cooler (direct cooler, quench) by spraying in crude acrylic acid (4000 l/h) (the temperature of the crude acrylic acid was 95° C.; the crude acrylic acid used for direct cooling comprised, as initial concentrations, 1.1% by weight of water and 0.1% by weight of phenothiazine as polymerization inhibitor). The crude acrylic acid used for quenching was circulated via a heat exchanger by means of a circulation pump and every now and again brought back to 95° C.

[0051] A centrifugal pump model MKP 32-160 (CP-Pumpen AG, Zofingen, Switzerland) was used as circulation pump for the quench. Pump space and drive space are separated by a metal wall. The drive in the pump space was effected via a magnetic coupling. The drive shaft was mounted horizontally in the pump space using a sliding bearing composed of silicon carbide.

[0052] The cooled gas mixture, which comprised the acrylic acid to be separated off, leaving the spray cooler was fed underneath the lowermost tray into a rectification column which was equipped with 27 bubble cap trays and with a spray condenser at the top of the column. The temperature at the top of the column was 20° C. and the temperature at the bottom of the rectification column was 90° C.

[0053] The condensate obtained in the spray condenser, which consisted mainly of water, was discharged and, after addition of 0.03% by weight of hydroquinone and cooling in a heat exchanger, returned as spray liquid having a temperature of 17° C. via the spray condenser to the uppermost column tray as runback. The reflux ratio was 4.

[0054] The crude acrylic acid obtained at the bottom of the rectification column was partly discharged (430 g/h), partly (250 g/h) recirculated, after addition of 0.1% by weight of phenothiazine for the purpose of polymerization inhibition, to the rectification column on the 13th tray of the column (counted from the bottom) and partly (about 15 l/h) firstly conveyed through a heat exchanger and then recirculated at a temperature of 100° C. to the zth tray of the column (counted from the bottom) to set the column temperature.

[0055] A further part of the crude acrylic acid obtained at the bottom of the column was fed under level regulation at a temperature of 102° C. to the quench via a heat exchanger preceding the quench for the purpose of liquid equalization in the quench.

[0056] The discharged crude acrylic acid comprised 97.2% by weight of acrylic acid, 1.6% by weight of acetic acid, 0.024% by weight of propionic acid, 0.4% by weight of maleic acid, 0.005% by weight of acrolein, 0.02% by weight of furfural and 1.2% by weight of water and also 0.05% by weight of phenothiazine and 0.03% by weight of hydroquinone.

[0057] The centrifugal pump had been blocked by polymer formation within an operating time of less than 10 hours.

Example 2 (According to the Invention)

[0058] The procedure of Example 1 is repeated. The sliding bearings composed of silicon carbide are replaced by sliding bearings composed of tungsten carbide. The process can be operated without interruption.

Example 3

[0059] 1% by weight of silicon carbide (SiC) or 1% by weight of tungsten carbide (WC) was suspended in commercial acrylic acid, stabilized with 200 ppm of hydroquinone monomethyl ether (MEHQ) and in each case stored for four hours at 80° C. The concentration of hydroquinone monomethyl ether (MEHQ) was determined before and afterwards.

TABLE-US-00001 TABLE 1 MEHQ contents before and after storage at 80° C. MEHQ content MEHQ content MEHQ content Beginning End Difference Acrylic acid 193 ppm 183 ppm  −5% Acrylic acid + WC 193 ppm 168 ppm −13% Acrylic acid + SiC 193 ppm  52 ppm −72%

[0060] In the presence of silicon carbide, the polymerization inhibitor was consumed very quickly.

Example 4

[0061] 1% by weight of silicon carbide (SiC) or 1% by weight of tungsten carbide (WC) was suspended in commercial acrylic acid stabilized with 200 ppm of hydroquinone monomethyl ether (MEHQ). 0.5 ml of the respective mixture was placed in a 1.8 ml ampoule and stored at 120° C. in a convection drying oven.

[0062] In each test series, three ampoules were filled and tested for each mixture, with the average time to complete polymerization being assessed visually.

TABLE-US-00002 TABLE 2 Polymerization at 120° C. Polymerization time in the Polymerization time in the case of SiC case of WC 0.0% by weight 131 minutes  131 minutes  0.2% by weight 48 minutes 79 minutes 0.4% by weight 38 minutes 65 minutes 0.6% by weight 35 minutes 66 minutes 0.8% by weight 29 minutes 55 minutes 1.0% by weight 27 minutes 57 minutes

[0063] Silicon carbide destabilizes significantly more strongly than tungsten carbide.