Process for the preparation of polyolefin particles

Abstract

A process for producing polyolefin particles from a polyolefin composition, comprising the steps of: a) providing a melted composition of a polyolefin and b) providing particles from the melted composition by: b1) mixing a first flow of a supercritical fluid in the melted composition in a pressure vessel to obtain a solution saturated with the supercritical fluid and b2) passing the solution from the pressure vessel through a throttling device to a spraying tower to expand the solution to obtain the polyolefin particles in the spraying tower, wherein a second flow of a supercritical fluid is injected in the throttling device, wherein the supercritical fluid is a supercritical fluid of a substance selected from the group consisting of CO.sub.2, NH.sub.3, H.sub.2O, N.sub.2O, CH.sub.4, ethane, propane, propylene, n-butane, i-butane, n-pentane, benzene, methanol, ethanol, isopropanol, isobutanol, chlorotrifluoromethane, monofluoromethane, 1,1,1,2-Tetrafluoroethane, toluene, pyridine, cyclohexane, cyclohexanol, o-xylene, dimethyl ether and SF.sub.6 and combinations thereof.

Claims

1. A process for producing polyolefin particles from a polyolefin composition, comprising the steps of: a) providing a melted composition of a polyolefin and b) providing particles from the melted composition by: b1) mixing a first flow of a supercritical fluid in the melted composition in a pressure vessel to obtain a solution saturated with the supercritical fluid and b2) passing the solution from the pressure vessel through a throttling device to a spraying tower to expand the solution to obtain the polyolefin particles in the spraying tower, wherein a second flow of a supercritical fluid is injected in the throttling device, wherein the supercritical fluid is a supercritical fluid of a substance selected from the group consisting of CO.sub.2, NH.sub.3, H.sub.2O, N.sub.2O, CH.sub.4, ethane, propane, propylene, n-butane, i-butane, n-pentane, benzene, methanol, ethanol, isopropanol, isobutanol, chlorotrifluoromethane, monofluoromethane, 1,1,1,2-Tetrafluoroethane, toluene, pyridine, cyclohexane, cyclohexanol, o-xylene, dimethyl ether, SF.sub.6, and combinations thereof, wherein the melted composition is subjected to step b) without solidification before step b), and wherein the polyolefin has Mn of 5-10 kg/mol according to size exclusion chromatography, Mw of 50-150 kg/mol according to size exclusion chromatography, a density of 915 to 935 kg/n according to ISO1183, and a melt flow rate of 0.10 g/10 min to 80 g/10 min according to ISO1133:2011 measured at 190° C. and 2.16 kg.

2. The process according to claim 1, wherein the polyolefin particles have a median particle size of 200-1000 μm, wherein the weight ratio of the supercritical carbon dioxide or SF.sub.6 to the polyolefin is 1:1 to 50:1, and wherein the polyolefin is low density polyethylene.

3. The process according to claim 1, wherein the weight ratio of the supercritical fluid to the polyolefin is 1:1 to 50:1.

4. The process according to claim 1, wherein the pressure vessel has a pressure of 100 to 1000 bar.

5. The process according to claim 1, wherein the pressure vessel has a temperature of 100 to 400° C.

6. The process according to claim 1, wherein the polyolefin is low density polyethylene.

7. The process according to claim 1, wherein the polyolefin has a MFR of 0.10 to 50 g/10 min, as determined using ISO1133:2011 (190° C./2.16 kg).

8. The process according to claim 1, wherein step a) involves polymerization of olefin monomers to obtain the melted composition of the polyolefin.

9. The process according to claim 1, wherein step a) involves the steps of providing a solid composition comprising the polyolefin and melting the solid composition.

10. The process according to claim 1, wherein the pressure vessel has a pressure of 200 to 600 bar.

11. The process according to claim 1, wherein the pressure vessel has a temperature of 150 to 350° C.

12. A method for making a masterbatch comprising using the particles obtained in claim 1, and without grinding the particles, forming a masterbatch.

13. A method for making a carpet backing comprising using the particles obtained in claim 1, and without grinding the particles, forming a carpet backing.

14. The process according to claim 1, wherein the polyolefin particles have a median particle size of 200-1000 μm; wherein the weight ratio of the supercritical fluid to the polyolefin is 1:1 to 50:1; wherein the pressure vessel has a pressure of 200 to 600 bar; wherein the pressure vessel has a temperature of 150 to 350° C.; and wherein the polyolefin has a MFR of 0.10 to 30 g/10 min as determined using ISO1133:2011 (190° C./2.16 kg).

15. The process according to claim 14, wherein step a) involves polymerization of olefin monomers to obtain the melted composition of the polyolefin.

16. The process according to claim 14, wherein the polyolefin has a MFR of 0.10 to 15 g/10 min as determined using ISO1133:2011 (190° C./2.16 kg).

17. A process for producing polyethylene particles from a polyethylene composition, comprising the steps of: a) providing a melted composition of a polyethylene and b) providing particles from the melted composition by: b1) mixing a first flow of a supercritical fluid in the melted composition in a pressure vessel to obtain a solution saturated with the supercritical fluid and b2) passing the solution from the pressure vessel through a throttling device to a spraying tower to expand the solution to obtain the polyethylene particles in the spraying tower, wherein a second flow of a supercritical fluid is injected in the throttling device, wherein the supercritical fluid is a supercritical fluid of a substance selected from the group consisting of CO.sub.2, NH.sub.3, H.sub.2O, N.sub.2O, CH.sub.4, ethane, propane, propylene, n-butane, i-butane, n-pentane, benzene, methanol, ethanol, isopropanol, isobutanol, chlorotrifluoromethane, monofluoromethane, 1,1,1,2-Tetrafluoroethane, toluene, pyridine, cyclohexane, cyclohexanol, o-xylene, dimethyl ether, SF.sub.6, and combinations thereof, wherein the polyethlene particles have a median particle size of 400-600 μm, wherein the melted composition is subjected to step b) without solidification before step b), and wherein the polyethylene Mn of 5-10 kg/mol according to size exclusion chromatography, Mw of 50-150 kg/mol according to size exclusion chromatography, a density of 915 to 935 kg/m.sup.3 according to ISO1183, and a melt flow rate of 0.10 g/10 min to 80 g/10 min according to ISO1133:2011 measured at 190° C. and 2.16 kg.

18. A process for producing polyethylene particles from a polyethylene composition, comprising the steps of: a) providing a melted composition of a polyethylene and b) providing particles from the melted composition by: b1) mixing a first flow of a supercritical fluid in the melted composition in a pressure vessel to obtain a solution saturated with the supercritical fluid and b2) passing the solution from the pressure vessel through a throttling device to a spraying tower to expand the solution to obtain the polyolefin particles in the spraying tower, wherein a second flow of a supercritical fluid is injected in the throttling device, wherein the supercritical fluid is a supercritical fluid of a substance selected from the group consisting of CO.sub.2, NH.sub.3, H.sub.2O, N.sub.2O, CH.sub.4, ethane, propane, propylene, n-butane, i-butane, n-pentane, benzene, methanol, ethanol, isopropanol, isobutanol, chlorotrifluoromethane, monofluoromethane, 1,1,1,2-Tetrafluoroethane, toluene, pyridine, cyclohexane, cyclohexanol, o-xylene, dimethyl ether, SF.sub.6, and combinations thereof, wherein the polyethylene has an Mn of 5-10 kg/mol and an Mw of 50-200 kg/mol according to size exclusion chromatography, and wherein the melted composition is subjected to step b) without solidification before step b).

Description

(1) FIG. 1 is a schematic illustration of the apparatus used for the process according to the invention.

(2) The apparatus comprises a pressure vessel 1 which can be supplied with a melted composition of polyolefin and a first flow of a supercritical fluid. In the pressure vessel 1, the melted composition and the first flow are mixed to obtain a solution saturated with the supercritical fluid.

(3) The pressure vessel 1 is connected to a throttling device (nozzle) 2 via a valve 3. The valve 3 can be opened and closed to control the transfer of the solution from the pressure vessel 1 to the throttling device 2. The throttling device 2 can be supplied with a second flow of a supercritical fluid. The solution is transferred from the throttling device through its opening with a reduced diameter to the spraying tower 4. Particles are formed in the spraying tower. The particles are collected from the bottom of the spraying tower and from a cyclone. The cyclone receives gas containing fine particles from the spraying tower and recovers the fine particles from the gas.

(4) The invention is now elucidated by way of the following examples, without however being limited thereto.

EXAMPLES

(5) The following materials were used:

(6) TABLE-US-00001 TABLE 1 Density Mw Mn MFR (kg/m.sup.3) (kg/mol) (kg/mol) (g/10 min) LDPE 1 1922T from Sabic 919 110 6.9 22 LDPE 2 2501TN00 from 925 280 20 0.75 Sabic Density is measured according to ISO1183. Mw and Mn are determined according to size exclusion chromatography.

(7) The size exclusion chromatography was performed according to ledema et. al., Polymer 54 (2013) pp. 4093-4104, section 2.2 SEC-MALS on p. 4095:

(8) The polymer samples were dissolved (0.9 mg/ml) in 1,2,4-trichlorobenzene (TCB), which was distilled prior to use, over a period of 4 h at 150° C. and stabilized with butylated hydroxytoluene (BHT) at a concentration of 1 mg/ml. The solutions were filtered at high temperature (150° C.) using a millipore filtration setup (1.2 mm) positioned in a Hereous LUT oven operating at 150° C. The separation of the polymer according to molar mass is performed with a Polymer Laboratories PL GPC210. This SEC system is operated at high temperature (column compartment at 160° C., injector compartment at 160° C., and solvent reservoir at 35° C.), and a flow of 0.5 ml/min. Eluent is 1,2,4-trichlorobenzene. Two Polymer Laboratories SEC columns with large particle size (PLGel mixed A-LS 20 mm columns) in series are used to minimize shear degradation of high molar mass polymer chains. The light scattering detector (a WYATT DAWN EOS multi-angle laser light scattering detector) is placed in line between the SEC and the refractive index detector. The used dn/dc=0.097 ml/g.

(9) MFR is measured at 190° C. and 2.16 kg according to ISO 1133:2011.

(10) A high pressure/high temperature apparatus for batch micronisation as illustrated in FIG. 1 was filled with a predetermined amount of LDPE, assembled, purged and pre-pressurized with CO2 until a pressure of approximately 5 bar was reached.

(11) The apparatus was electrically heated and the temperature was controlled to ±1° C. up to a higher temperature; subsequently CO2 was added to obtain a higher pressure. Subsequently the temperature and the pressure were adjusted up to pre-expansion conditions as summarized in Table 1 by adding CO2 until the system reached equilibrium. The apparatus was equilibrated for certain time period.

(12) In comparative experiments A-D, no additional flow of CO2 was provided to the throttling device. The valve between the pressure vessel and the throttling device was opened to pass the solution from the pressure vessel to the throttling device and then to the spraying tower which has atmospheric pressure. Particles were not obtained in the spraying tower either because the throttling device was blocked or fiber (>1 cm) was obtained, as indicated in Tables 2-1 and 2-2.

(13) In examples 1-4 according to the invention, before the valve between the pressure vessel and the throttling device was opened, supplying of a second flow of CO2 to the throttling device was started. The valve between the pressure vessel and the throttling device was opened to pass the solution from the pressure vessel to the throttling device and then to the spraying tower which has atmospheric pressure. Particles were obtained in the spraying tower, which were collected in a collecting vessel below the spraying tower. The median particle size was determined by electronic microscopy.

(14) TABLE-US-00002 TABLE 2-1 (LDPE1) CO.sub.2/ flow flow LDPE Pressure Temp LDPE CO.sub.2 (gCO.sub.2/ Particle recovery Ex (bar) (° C.) (g/s) (g/s) gLDPE) shape (%) 1 218 189 0.23 6.667 29 Powder 95.1 2 305 255 0.629 16.667 26.5 Powder 97.2 A 218 189 — — — Nozzle 0 blocked B 305 255 — — — Fiber 0 (not recovered)

(15) TABLE-US-00003 TABLE 2-2 (LDPE2) ratio CO.sub.2/ flow flow LDPE Pressure Temp LDPE CO.sub.2 (gCO.sub.2/ Particle recovery Ex (bar) (° C.) (g/s) (g/s) gLDPE) shape (%) 3 125 250 0.445 16.667 37.5 Powder 95.1 4 358 249 0.28 0.307 1.1 Powder 85.96 C 125 250 — — — Nozzle 0 blocked D 358 249 — — — Nozzle 0 blocked

(16) In Table 2-1 and 2-2, pressure and temperature are the pressure and the temperature in the pressure vessel, respectively. “flow LDPE” indicates the flow rate of LDPE to the pressure vessel. “flow CO2” indicates the total flow rate of the flow rate to the pressure vessel and the flow rate to the nozzle.

(17) In comparative experiments A-D where no side injection was used, either the nozzle was blocked or fibers were formed and particles could not be obtained. In examples 1-4 wherein the conditions were the same as A-D, respectively, except that the side injection was used, particles were successfully formed. The recovery rate indicates the amount of LDPE particles recovered in the collecting vessel, excluding the amount of LDPE particles collected by cyclone. The median particle size determined by electronic microscopy from 77 particles was 453.28 μm.

(18) The ratio CO.sub.2/LDPE indicates the amount of CO2 required for the saturation of CO2 in the melted composition and for preparing the particles. A lower CO.sub.2/LDPE ratio indicates a more economical process.

(19) Comparison of Ex 3 and 4 shows that a higher pressure leads to a lower CO.sub.2/LDPE ratio.

(20) Purity of the LDPE particles obtained by Ex 4 was measured by Headspace-Gas Chromatography/Mass Spectrometry (Headspace-GC/MS) Screening, along with LDPE2 which has not been subjected to the PGSS process according to the invention. The amounts of low molecular polyolefin (such as C10-C32 hydrocarbons) were substantially lower for the LDPE particles obtained by Ex 4 than LDPE2 which has not been subjected to the PGSS process according to the invention.