Method for the pneumatic delivery of superabsorbent particles

Abstract

A method of pneumatically conveying superabsorbent particles, wherein the superabsorbent particles have been admixed with an aqueous wax dispersion prior to the pneumatic conveying, the wax has a glass transition temperature of at least 65 C. and, based on the untreated superabsorbent particles, from 0.020% to 0.20% by weight of wax has been used.

Claims

1. A method of pneumatically conveying superabsorbent particles comprising admixing the superabsorbent particles with an aqueous wax dispersion prior to pneumatic conveying, wherein the wax has a glass transition temperature of at least 65 C. and, based on the untreated superabsorbent particles, from 0.020% to 0.20% by weight of wax is admixed.

2. The method according to claim 1, wherein the wax has a glass transition temperature of at least 80 C.

3. The method according to claim 1, wherein, based on the superabsorbent particles, from 0.035% to 0.08% by weight of wax is admixed.

4. The method according to claim 1, wherein the wax is a copolymer of 70 to 95 mol % of at least one ethylenically unsaturated hydrocarbon and 5 to 30 mol % of at least one ethylenically unsaturated carboxylic acid.

5. The method according to claim 1, wherein the superabsorbent particles have an average particle size of 250 to 500 m.

6. The method according to claim 1, wherein the superabsorbent particles have an average sphericity (ASPHT) of greater than 0.72.

7. The method according to claim 1, wherein a temperature of the superabsorbent particles during the pneumatic conveying is at least 40 C., and at least 20 C. less than the glass transition temperature of the wax.

8. The method according to claim 1, wherein an initial gas velocity in the pneumatic conveying corresponds to a Froude number of 2 to 40.

9. The method according to claim 1, wherein a conveying material load in the pneumatic conveying is from 1 to 30 kg/kg and the conveying material load is the quotient of conveying material mass flow rate and gas mass flow rate.

10. A composition comprising superabsorbent particles and wax particles, wherein the wax particles are on the surface of the superabsorbent particles, the wax particles are dispersible in water and have a glass transition temperature of at least 65 C., a proportion of the wax particles based on the superabsorbent particles is from 0.02% to 0.2% by weight, and the composition has an absorption under a pressure of 4.83 kPa (AUL0.7 psi) of at least 10 g/g.

11. The composition according to claim 10, wherein the wax has a glass transition temperature of at least 80 C.

12. The composition according to claim 10, wherein, based on the superabsorbent particles, the proportion of wax particles is from 0.035% to 0.08% by weight of wax.

13. The composition according to claim 10, wherein the wax is a copolymer of 5 to 30 mol % of at least one ethylenically unsaturated carboxylic acid and 70 to 95 mol % of at least one ethylenically unsaturated hydrocarbon.

14. The composition according to claim 10, wherein the superabsorbent particles have an average particle size of 250 to 500 m.

15. The composition according to claim 10, wherein the superabsorbent particles have an average sphericity (ASPHT) of greater than 0.72.

Description

EXAMPLES

Example 1

(1) A superabsorbent was produced analogously to example 1 of WO 2016/134905 A1. The monomer solution used additionally comprised 1.07% by weight of the disodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid.

(2) The gas inlet temperature of reaction zone (5) was 167 C., the gas outlet temperature of reaction zone (5) was 107 C., the gas inlet temperature of the internal fluidized bed (27) was 100 C., the product temperature in the internal fluidized bed (27) was 78 C., the gas outlet temperature of the condensation column (12) was 57 C., and the gas outlet temperature of the gas drying unit (37) was 47 C.

(3) The superabsorbent produced (base polymer) had a bulk density (ASG) of 0.73 g/ml, a centrifuge retention capacity (CRC) of 49.4 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 10.5 g/g, a residual monomer content of 5200 ppm, an extractables content of 4.5% by weight and a moisture content of 8.0% by weight.

(4) The superabsorbent had the following particle size distribution:

(5) TABLE-US-00001 >1000 m 0.3% by weight 850-1000 m 1.1% by weight 600-850 m 3.7% by weight 500-600 m 9.9% by weight 400-500 m 32.8% by weight 300-400 m 40.4% by weight 250-300 m 6.4% by weight 200-250 m 4.1% by weight 106-200 m 1.2% by weight <106 m 0.1% by weight

(6) The superabsorbent had a median particle size (d50) of 377 m and an average sphericity (ASPHT) of 0.81.

(7) The base polymer was subsequently surface postcrosslinked analogously to examples 11 to 15 of WO 2015/110321 A1. 2.0% by weight of ethylene carbonate, 5.0% by weight of water and 0.3% by weight of aluminum sulfate were used, based in each case on the base polymer. The product temperature was 160 C. and the height of the weir was 75%.

(8) In the cooler, after the surface postcrosslinking, first 2.35% by weight of a 0.2% by weight aqueous solution of sorbitan monolaurate and then 2.35% by weight of a dilute aqueous polymer dispersion of Poligen CE 18 (BASF SE; Ludwigshafen; Germany) were added. Poligen CE 18 is a 21% by weight aqueous wax dispersion of an ethylene-acrylic acid copolymer composed of 20% by weight of acrylic acid and 80% by weight of ethylene, stabilized with potassium hydroxide. The wax has a glass transition temperature of 80 C. The dilute aqueous polymer dispersion was calculated such that 500 ppm of wax was added in solid form, based on the superabsorbent particle on the polymer.

(9) The temperature of the superabsorbent particles at the time of addition was 75 C.

(10) The surface postcrosslinked superabsorbent produced had a bulk density (ASG) of 0.794 g/ml, a centrifuge retention capacity (CRC) of 40.1 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 32.9 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 23.3 g/g, a saline flow conductivity (SFC) of 510.sup.7 cm.sup.3s/g, a vortex of 68 s, a moisture content of 3.2% by weight, a residual monomer content of 399 ppm and an extractables content of 3.2% by weight.

(11) The surface postcrosslinked superabsorbent had the following particle size distribution:

(12) TABLE-US-00002 >850 m 0.0% by weight 710-850 m 0.4% by weight 600-710 m 2.2% by weight 500-600 m 9.0% by weight 400-500 m 36.4% by weight 300-400 m 39.2% by weight 250-300 m 7.0% by weight 200-250 m 4.0% by weight 150-200 m 1.5% by weight <150 m 0.2% by weight

(13) The superabsorbent had a median particle size (d50) of 379 m and an average sphericity (ASPHT) of 0.80.

(14) Subsequently, the superabsorbent particles were pneumatically conveyed.

(15) The conveying conduit used was a smooth pipeline of aluminum having a length of 164 m and an internal diameter of 100 mm. The conveying conduit consisted of two horizontal and two vertical sections, with the sections connected by bends. The total vertical height gain was 13 m. The conveying conduit had an internal bypass of the Intraflow type (Zeppelin Systems GmbH; Friedrichshafen; Germany). The product was conveyed into the conveying conduit by means of a CFH250 star feeder (Zeppelin Systems GmbH; Friedrichshafen; Germany).

(16) The conveying output was 7.5 t/h of superabsorbent particles, the speed of the star feeder was 13.5 rpm, the conveying air rate was 560 m.sup.3 (STP)/h, and the gas velocity was 11 m/s at the start of the conveying conduit and 11.1 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from +660 to 0 mbar, based on the ambient pressure. During the stable conveying, the pressure fluctuations were 50 mbar and the average pressure in the conveying was 560 mbar. The conveying material load was 11 kg/kg, and the Froude number at the start of the conveying was 11.

(17) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 39.5 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 31.1 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 23.1 g/g, a saline flow conductivity (SFC) of 410.sup.7 cm.sup.3s/g.

(18) The starting pressure in the conveying conduit as a function of time is shown in FIG. 2.

(19) The number of dust particles of example 1 before and after the pneumatic conveying is collated in table 1.

Example 2 (Comparative Example)

(20) The procedure was as in example 1. The amount of Poligen CE 18 added was lowered to 125 ppm, based on the superabsorbent particles.

(21) The surface postcrosslinked superabsorbent produced had a bulk density (ASG) of 0.761 g/ml, a centrifuge retention capacity (CRC) of 39.3 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 32.7 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 23.1 g/g, a saline flow conductivity (SFC) of 510.sup.7 cm.sup.3s/g, a vortex of 65 s, a moisture content of 3.1% by weight, a residual monomer content of 428 ppm and an extractables content of 3.0% by weight.

(22) The surface postcrosslinked superabsorbent had the following particle size distribution:

(23) TABLE-US-00003 >850 m 0.0% by weight 710-850 m 0.4% by weight 600-710 m 2.9% by weight 500-600 m 8.6% by weight 400-500 m 36.4% by weight 300-400 m 39.5% by weight 250-300 m 6.8% by weight 200-250 m 3.8% by weight 150-200 m 1.1% by weight <150 m 0.3% by weight

(24) The superabsorbent had a median particle size (d50) of 380 m and an average sphericity (ASPHT) of 0.80.

(25) The conveying output was 7.6 t/h of superabsorbent particles, the speed of the star feeder was 13.5 rpm, the conveying air rate was 560 m.sup.3 (STP)/h, and the gas velocity was now 7.7 m/s at the start of the conveying conduit and 16.4 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from +1600 to 0 mbar, based on the ambient pressure. The conveying material load was 12 kg/kg, and the Froude number at the start of the conveying was 7.7.

(26) Uniform operation of the pneumatic conveying with a conveying air rate of 560 m.sup.3 (STP)/h was not possible. During the unstable conveying, the pressure fluctuations were 450 mbar and the average pressure in the conveying was 1120 mbar.

(27) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 39.3 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 30.7 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 21.6 g/g, a saline flow conductivity (SFC) of 310.sup.7 cm.sup.3s/g.

(28) The starting pressure in the conveying conduit as a function of time is shown in FIG. 3.

(29) The number of dust particles of example 2 before and after the pneumatic conveying is collated in table 1.

Example 3 (Comparative Example)

(30) The procedure was as in example 1. No Poligen CE 18 was added.

(31) The surface postcrosslinked superabsorbent produced had a bulk density (ASG) of 0.78 g/ml, a centrifuge retention capacity (CRC) of 39.6 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 33.2 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 24.8 g/g, a saline flow conductivity (SFC) of 510.sup.7 cm.sup.3s/g, a vortex of 66 s, a moisture content of 3.5% by weight, a residual monomer content of 386 ppm and an extractables content of 3.0% by weight.

(32) The surface postcrosslinked superabsorbent had the following particle size distribution:

(33) TABLE-US-00004 >850 m 0.0% by weight 710-850 m 0.4% by weight 600-710 m 2.3% by weight 500-600 m 10.0% by weight 400-500 m 36.3% by weight 300-400 m 39.4% by weight 250-300 m 6.0% by weight 200-250 m 4.1% by weight 150-200 m 1.3% by weight <150 m 0.2% by weight

(34) The superabsorbent had a median particle size (d50) of 383 m and an average sphericity (ASPHT) of 0.79.

(35) The conveying output was 7.2 t/h of superabsorbent particles, the speed of the star feeder was 13.5 rpm, the conveying air rate was 560 m.sup.3 (STP)/h, and the gas velocity was now 7.5 m/s at the start of the conveying conduit and 16.4 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from 2400 to 0 mbar, based on the ambient pressure. During the conveying, the pressure fluctuations were 1000 mbar. The conveying material load was 11.3 kg/kg, and the Froude number at the start of the conveying was 7.5. The pressure peaks during the conveying were clearly audible in the form of loud banging in the conduit.

(36) Uniform operation of the pneumatic conveying with a conveying air rate of 560 m.sup.3 (STP)/h was not possible. During the very unstable conveying, the pressure fluctuations were 900 mbar and the average pressure in the conveying was 1160 mbar.

(37) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 38.6 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 32.0 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 20.6 g/g, a saline flow conductivity (SFC) of 210.sup.7 cm.sup.3s/g.

(38) The starting pressure in the conveying conduit as a function of time is shown in FIG. 4.

(39) The number of dust particles of example 3 before and after the pneumatic conveying is collated in table 1.

Example 4

(40) The base polymer from example 1 was subsequently surface postcrosslinked analogously to examples 11 to 15 of WO 2015/110321 A1. 2.0% by weight of ethylene carbonate, 5.0% by weight of water and 0.05% by weight of aluminum sulfate were used, based in each case on the base polymer. The product temperature was 159 C. and the height of the weir was 75%.

(41) In the cooler, after the surface postcrosslinking, first 4.35% by weight of a 0.23% by weight aqueous solution of aluminum lactate and then 1.66% by weight of a dilute aqueous polymer dispersion of Poligen CE 18 (BASF SE; Ludwigshafen; Germany) and sorbitan monolaurate were added. The dilute aqueous polymer dispersion was calculated such that 500 ppm of wax in solid form and 25 ppm of sorbitan monolaurate were added, based on the superabsorbent particles.

(42) The surface postcrosslinked superabsorbent produced had a bulk density (ASG) of 0.75 g/ml, a centrifuge retention capacity (CRC) of 38.1 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 34.4 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 25.9 g/g, a saline flow conductivity (SFC) of 510.sup.7 cm.sup.3s/g, a vortex of 69 s, a moisture content of 4.5% by weight, a residual monomer content of 263 ppm and an extractables content of 2.6% by weight.

(43) The surface postcrosslinked superabsorbent had the following particle size distribution:

(44) TABLE-US-00005 >850 m 0.0% by weight 710-850 m 0.1% by weight 600-710 m 2.5% by weight 500-600 m 12.5% by weight 400-500 m 38.2% by weight 300-400 m 37.4% by weight 250-300 m 5.0% by weight 200-250 m 3.0% by weight 150-200 m 0.6% by weight <150 m 0.2% by weight

(45) The superabsorbent had a median particle size (d50) of 396 m and an average sphericity (ASPHT) of 0.80.

(46) The superabsorbent particles thus obtained were pneumatically conveyed under different conditions (examples 4a to 4d).

Example 4 a

(47) The conveying output in the first conveying operation was 7.2 t/h of superabsorbent particles, the speed of the star feeder was 13.5 rpm, the conveying air rate was 550 m.sup.3 (STP)/h, and the gas velocity was now 10.7 m/s at the start of the conveying conduit and 17.3 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from 740 to 0 mbar, based on the ambient pressure. The conveying material load was 10.9 kg/kg, and the Froude number at the start of the conveying was 11. During the stable conveying, the pressure fluctuations were 50 mbar and the average pressure in the conveying was 580 mbar.

(48) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 38.7 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 34.2 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 26.2 g/g, a saline flow conductivity (SFC) of 510.sup.7 cm.sup.3s/g.

(49) The number of dust particles of example 4a before and after the pneumatic conveying is collated in table 1.

Example 4 b

(50) The conveying output in the subsequent second conveying operation was 11.2 t/h of superabsorbent particles, the speed of the star feeder was 20 rpm, the conveying air rate was 660 m.sup.3 (STP)/h, and the gas velocity was now 11.0 m/s at the start of the conveying conduit and 20.4 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from 910 to 0 mbar, based on the ambient pressure. During the conveying, the pressure fluctuations were 50 mbar. The conveying material load was 14.2 kg/kg, and the Froude number at the start of the conveying was 11. During the stable conveying, the pressure fluctuations were 50 mbar and the average pressure in the conveying was 825 mbar.

(51) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 38.6 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 33.6 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 25.3 g/g, a saline flow conductivity (SFC) of 410.sup.7 cm.sup.3s/g.

Example 4 c

(52) The conveying output in the subsequent third conveying operation was 16.4 t/h of superabsorbent particles, the speed of the star feeder was 30 rpm, the conveying air rate was 560 m.sup.3 (STP)/h, and the gas velocity was now 10.6 m/s at the start of the conveying conduit and 23.1 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from 1230 to 0 mbar, based on the ambient pressure. During the conveying, the pressure fluctuations were 50 mbar. The conveying material load was 18.3 kg/kg, and the Froude number at the start of the conveying was 10. During the stable conveying, the pressure fluctuations were 50 mbar and the average pressure in the conveying was 1160 mbar.

(53) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 38.6 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 33.0 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 24.2 g/g, a saline flow conductivity (SFC) of 410.sup.7 cm.sup.3s/g.

Example 4 d

(54) The conveying output in the subsequent fourth conveying operation was 20.8 t/h of superabsorbent particles, the speed of the star feeder was 40 rpm, the conveying air rate was 770 m.sup.3 (STP)/h, and the gas velocity was now 9.1 m/s at the start of the conveying conduit and 23.2 m/s at the end of the conveying conduit. The pressure in the conveying conduit was from 1800 to 0 mbar, based on the ambient pressure. During the conveying, the pressure fluctuations were 50 mbar. The conveying material load was 23.1 kg/kg, and the Froude number at the start of the conveying was 9. During the stable conveying, the pressure fluctuations were 200 mbar and the average pressure in the conveying was 1500 mbar.

(55) After the conveying, the superabsorbent had a centrifuge retention capacity (CRC) of 38.6 g/g, an absorption under a pressure of 21.0 g/cm.sup.2 (AUL) of 32.8 g/g, an absorption under a pressure of 49.2 g/cm.sup.2 (AUHL) of 23.9 g/g, a saline flow conductivity (SFC) of 310.sup.7 cm.sup.3s/g.

(56) The starting pressure in the conveying conduit as a function of time in examples 4a to 4d is shown in FIG. 5.

(57) TABLE-US-00006 TABLE 1 Normalized number of particles P discharged from the Heubach dustmeter in 5 l/min of dry air, normalized per min and per g of superabsorbent, classified and as sum total Normalized particle Exam- number [P/min/g] ple Sample <1 m 1 m-10 m >10 m Sum total 1 before conveying 60154 118915 3189 182258 after conveying 81525 151647 4232 237404 2*) before conveying 126543 197421 3068 327032 after conveying 266433 353877 6027 626337 3*) before conveying 419557 442039 3511 865107 after conveying 682969 602259 4377 1289605 4a before conveying 27042 71293 2231 100566 after conveying 52688 114416 5455 172559 *)comparative example