METHOD FOR DRYING WET POLYMER COMPOSITION

Abstract

The invention relates to a method for drying a wet polymer composition obtained from a polymerization process, comprising: a) introducing the wet polymer composition and a drying gas into a fluidized bed dryer to form a fluidized bed of the wet polymer composition and b) heating the fluidized bed to obtain a dry polymer composition, wherein the fluidized bed further comprises an anti-fouling agent comprising inert nanoparticles.

Claims

1. A method for drying a wet polymer composition obtained from a polymerization process, comprising: a) introducing the wet polymer composition and a drying gas into a fluidized bed dryer to form a fluidized bed of the wet polymer composition and b) heating the fluidized bed to obtain a dry polymer composition, wherein the fluidized bed further comprises an anti-fouling agent comprising inert nanoparticles.

2. The method according to claim 1, wherein the fluidized bed dryer contains internal heating elements.

3. A method according to claim 1, wherein the wet polymer composition comprises powders of a polymer and residual volatile hydrocarbons used during the polymerization of the polymer, wherein the amount of the residual volatile hydrocarbons in the wet polymer composition is 5 to 50 wt %.

4. A method according to claim 1, where the wet polymer composition comprises powders of one or more polymers selected from the group consisting of polyolefins.

5. The method according to claim 1, wherein the drying gas is selected from the group consisting of nitrogen, air and carbon dioxide.

6. The method according to claim 1, wherein the amount of the anti-fouling agent is 0.1 to 5 wt % of the dry polymer composition.

7. The method according to claim 1, wherein the inert nanoparticles are selected from the group consisting of fumed silica, carbon black and organoclay.

8. The method according to claim 1, wherein the anti-fouling agent consists of the inert nanoparticles or the anti-fouling agent comprises a hydrophobic coating provided on the inert nanoparticles.

9. The method according to claim 1, wherein the method is a continuous process in which a flow of the wet polymer composition is continuously supplied to the fluidized bed dryer and a flow the dry polymer composition is continuously collected from the fluidized bed dryer.

10. The method according to claim 9, wherein the anti-fouling agent is introduced into the fluidized bed dryer together with the wet polymer composition.

11. The method according to claim 9, wherein the anti-fouling agent is introduced into the fluidized bed dryer together with the drying gas.

12. The method according to claim 1, wherein the method is a batch-process in which the wet polymer composition is supplied to the fluidized bed dryer and dried and subsequently the dry polymer composition is collected from the fluidized bed dryer.

13. The method according to claim 12, wherein the anti-fouling agent is introduced into the fluidized bed dryer together with the wet polymer composition.

14. The method according to claim 1, further comprising the polymerization process to obtain the wet polymer composition.

15. The method according to claim 1, wherein the anti-fouling agent is introduced into the fluidized bed dryer before step a) and the anti-fouling agent is not introduced into the fluidized bed dryer during or after steps a) and b).

16. The method according to claim 2, wherein the internal heating elements have a surface temperature during step b) of from 70° C. to below the melting point of polymer in the wet polymer composition.

17. The method according to claim 4, where the wet polymer composition comprises powders of one or more polymers selected from the group consisting of ethylene homopolymer, propylene homopolymer, and copolymers of ethylene or propylene with linear alpha olefins or dienes.

18. The method according to claim 6, wherein the amount of the anti-fouling agent is 0.3 to 1.5 wt %, of the dry polymer composition.

Description

EXAMPLES

Comparative Example 1

HDPE Powder with No Antifouling Additives

[0059] A crust of polymeric material was deposited on the cartridge heater after 1-hour of exposure at 110° C. The polymeric material was brushed off and collected for further analysis. The mass of polymeric material was 6 grams.

Example 2

HDPE Powder with 0.5 Weight Percent of Hydrophobic Fumed Silica

[0060] HDPE powder was mixed with fumed silica and the resulting powder mixture was fluidized and put in contact with a hot heating element under the same conditions used for Example 1. A thin layer of polymer powder was deposited on the heating element.

[0061] The polymeric material was brushed off and collected for further analysis. The mass of polymeric material was 1.4 grams.

Example 3

HDPE Powder with 1 Weight Percent of Hydrophobic Fumed Silica

[0062] HDPE powder was mixed with fumed silica and the resulting powder mixture was fluidized and put in contact with a hot heating element under the same conditions used for Example 1. A thin layer of polymer powder was deposited on the heating element. The polymeric material was brushed off and collected for further analysis. The mass of polymeric material was 0.5 grams.

[0063] Scanning electron microscopy (SEM) of the powders used in Examples 1, 2, and 3 revealed that, when present, fumed silica partially coats the surface of the polymer particles. The partial coating reduces the adhesion of the polymer particles, and their deposition onto hot surfaces. Compositional analysis of the material deposited on the heater surface indicated a relatively high concentration of fumed silica in the fouling material. In addition to partially coating the polymer particles, fumed silica also partially coats the surface of the heating elements, further reducing the deposition of polymer particles onto the heater.

[0064] The results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Amount of Amount of fouling anti-fouling material Decrease in Anti-fouling agent agent (g) fouling CE1 none 0 6.00 E2 hydrophobic fumed 0.5 wt %   1.41 77% silica E3 hydrophobic fumed 1 wt % 0.54 91% silica

[0065] Based on the mass of polymeric material deposited on the heater, 0.5% of fumed silica reduced fouling by 77%, 1% of fumed silica reduced fouling by 91%.

Example 4

Introduction of Hydrophobic Fumed Silica Only in the Beginning

[0066] A heating element coated with fumed silica and polymer powder was obtained by repeating the conditions of Example 2 (loading polymer with 0.5 wt % silica), but without brushing off any deposited material from the surface of the heater at the end of the heating cycle.

[0067] After this initial step, the coated heating element was removed from the equipment; the equipment was fully opened and cleaned to remove any traces of fumed silica and polymer powder. The coated heating element was reintroduced into the equipment along with a new load of fresh polymer powder containing no fumed silica. The silica-free polymer powder was fluidized and heated for 1 hour, and the degree of fouling was determined by measuring the amount of material deposited on the heater.

[0068] The mass of polymeric material deposited on the heater after two heating cycles was 3.0 grams. This surprising result indicates that the amount of fouling per heating cycle is comparable (1.4 grams for the first cycle, 1.6 grams for the second one), even though no silica was added with the polymer on the second cycle. Therefore, fouling can be reduced by passivating the heater elements with an initial load of fumed silica, without necessarily adding extra silica to dry more powder in subsequent drying cycles.