Process for melting plastic for subsequent feeding to a processor via a melt pump

Patent metadata

Field	Value
Publication number	US-12291676-B2
Application number	US-202017776275-A
Country	US
Kind code	B2
Filing date	Nov 2, 2020
Priority date	Nov 14, 2019
Publication date	May 6, 2025
Grant date	May 6, 2025

Abstract

Process for feeding plastic material, e.g. a plastic waste, to a processor such as a thermochemical reactor, e.g. a pyrolysis reactor. The process comprises an optional shredder or disintegrator ( 1 ), a conveying system ( 2 ), a feed hopper ( 3 ) with a lock hopper or rotary valve, a melting tank ( 6 ) with an agitator ( 5 ) followed by a melt pump ( 7 ) for the delivery of molten plastic to the processor. The advantage of the current process includes the ability to supply a consistent, metered flow to the processor, independent of the recycled plastic's melt properties, or the form or particle size and distribution of the plastic material.

First claim

What is claimed is:

1. A process comprising:
conveying a quantity of plastic material into a feed hopper via a screw conveyor or an air conveyor;
supplying a controlled amount of the plastic material directly into a melting tank from the feed hopper using a rotary valve control mechanism, wherein the rotary valve control mechanism forms a gas seal between the feed hopper and the melting tank, wherein the rotary valve provides a seal against a backflow of a gas from the melting tank, and wherein the rotary valve controls the quantity of the plastic material supplied into the melting tank;
melting the plastic material in the melting tank at a temperature from 200° C. to 300° C. while agitating the plastic material using a melting tank agitator to form a molten plastic material and a gas mixture;
supplying the gas mixture to a condenser, wherein the gas mixture is contacted by a recirculated liquid in the condenser that strips out acid gases and other water-soluble gases, and wherein other gases not stripped out are compressed and at least partially sent back to the melting tank;
withdrawing the molten plastic material using a melt pump fluidically connected to the melt tank; and
supplying the molten plastic material into a processor in a controlled metered flow using the melt pump.

2. The process of claim 1 , wherein the plastic material is in the form of chips, pellets, and/or beads.

3. The process of claim 1 , wherein the melting tank does not include an extruder.

4. The process of claim 1 , wherein the control mechanism comprises a double-flap valve and/or a lock hopper.

5. The process of claim 1 , wherein the temperature in the melting tank is from 200° C. to 250° C.

6. The process of claim 1 , wherein the pressure of the melting tank is less than 1,034 kilopascal-gauge (150 psig).

7. The process of claim 1 , wherein the gas mixture from the melting tank comprises at least one gas selected from the group consisting of nitrogen, a hydrocarbon gas, an acid gas, and combinations thereof.

8. The process of claim 7 , wherein the gas mixture comprises the acid gas and wherein recirculating liquid comprises water that at least partially removes the acid gas from the gas mixture upon contact in the condenser.

9. The process of claim 7 , wherein the gas mixture comprises the hydrocarbon gas and wherein the hydrocarbon gas is separated from the gas mixture and then at least partly recycled to the melting tank.

10. The process of claim 1 , wherein the melt pump meters the feed of the molten plastic material to the processor.

11. The process of claim 1 , wherein the melt pump maintains a liquid seal between the processor and the melting tank.

12. The process of claim 1 , wherein the melt pump comprises a screw pump or a gear positive displacement pump.

13. The process of claim 1 , wherein the plastic material does not contain a condensation polymer wherein the condensation polymer is polyethylene terephthalate, polyamide or polyurethane.

14. The process of claim 1 , wherein the plastic material does not contain a compounded waste.

15. The process of claim 1 , wherein the plastic material comprises at least one material selected from the group consisting of a polyolefin, a polyolefin blend, and combinations thereof.

16. The process of claim 1 , wherein the melting tank agitator comprises a mechanical mixer, wherein the melting tank agitator is configured to mix the molten plastic material in the melting tank.

17. The process of claim 1 , wherein heat to the melting tank is provided by heating coils within the melting tank.

18. The process of claim 1 , wherein the plastic material is introduced through a lock hopper system that purges air from the plastic material before the plastic material is introduced to the melting tank.

19. The process of claim 1 , wherein the processor is a pyrolysis reactor.

20. The process of claim 1 , wherein the plastic material does not contain more than 10 percent polyethylene terephthalate, wherein the plastic material does not contain more than 10 percent polyamide, wherein the plastic material does not contain more than 10 percent PCT, wherein the plastic material does not contain more than 10 percent PVDC, wherein the plastic material does not contain more than 10 percent polyester, and wherein the plastic material does not contain more than 10 percent polyurethane.

21. The process of claim 1 , wherein after adding a pyrolysis oil to the melting tank the molten plastic material has a viscosity of less than 20 MM centipoise.

22. The process of claim 1 , comprising adding a pyrolysis oil to the mixing tank.

23. A process comprising:
conveying a quantity of plastic material into a feed hopper via a screw conveyor or an air conveyor;
supplying in a continuous manner a controlled amount of the plastic material into a melting tank from the feed hopper using a rotary valve control mechanism, wherein the rotary valve control mechanism forms a gas seal between the feed hopper and the melting tank, wherein the rotary valve provides a seal against a backflow of a gas from the melting tank, and wherein the rotary valve controls the quantity of the plastic material supplied into the melting tank;
melting the plastic material in the melting tank at a temperature from about 200° C. to about 300° C. while agitating the plastic material using a melting tank agitator to form a molten plastic material and a gas mixture,
supplying the gas mixture to a condenser, wherein the gas mixture is contacted by a recirculated liquid in the condenser that strips out acid gases and other water-soluble gases, and wherein other gases not stripped out are compressed and at least partially sent back to the melting tank;
withdrawing the molten plastic material using a melt pump fluidically connected to the melt tank, wherein the molten plastic material has a melt viscosity in between 1000 cP and 20 MM cP; and
supplying the molten plastic material into a processor in a controlled metered flow using the melt pump.

24. The process of claim 23 , wherein the molten plastic material has a solid content of less than 30% wt/wt, wherein the solids are less than 4 cm.

Assignees

• Exxonmobil Chemical Patents Inc

Inventors

• Reimers Jay L

Classifications

• C10G2300/1003

  Waste materials · CPC title

• C10G1/10

  from rubber or rubber waste · CPC title

• C10B47/16 Primary

  with indirect heating means both inside and outside the retorts · CPC title

• B29B2017/0496

  Pyrolysing the materials · CPC title

• B29B17/04

  Disintegrating plastics, {e.g. by milling}(B29B9/02, B29B11/02, B29B13/10, {B29B17/02} take precedence) · CPC title