CN115244120A

CN115244120A - Method and system for depolymerizing waste plastics

Info

Publication number: CN115244120A
Application number: CN202180010602.3A
Authority: CN
Inventors: M·C·帕罗特; J·C·勒夫特; D·B·舒平; M·D·马蒂亚斯
Original assignee: Premir Plastics
Current assignee: Premir Plastics
Priority date: 2020-01-23
Filing date: 2021-01-25
Publication date: 2022-10-25
Also published as: MX2022008680A; BR112022014572A2; JP2023511372A; CA3168641A1; WO2021151071A1; EP4093814A1; JP2024028617A

Abstract

A continuous flow process and system for depolymerizing plastic. The heterogeneous mixture of plastic particles, solvent and catalyst is continuously pumped through the heating zone at a flow rate just high enough to maintain a particle velocity large enough to keep the plastic particles suspended. The temperature of the heterogeneous mixture is raised in the heating zone and maintained in a holding zone to complete depolymerization of the mixture into a homogeneous solution containing liquefied reaction products. The homogeneous solution was cooled to solidify and precipitate a solid reaction product. Separating the solid reaction product from the solvent to be recycled. Recycling the solvent for reuse as a component of the heterogeneous mixture.

Description

Method and system for depolymerizing waste plastics

Technical Field

This application claims priority to U.S. provisional application No. 62/964,948, filed on 23/1/2020, which is hereby incorporated by reference.

Background

The present invention generally relates to the depolymerization of resins, plastics or polymers. More particularly, it relates to the depolymerization of waste plastics in a continuous process.

Plastics are conventionally depolymerized in large reaction vessels, usually equipped with a heating jacket and an agitator. The depolymerization reaction is isolated in a vessel until depolymerization is complete. After depolymerization, the container is emptied and then refilled. Each batch was heated to accelerate depolymerization and then cooled to produce a viable feedstock for new polymer. Batch processes typically take from 20 minutes to 800 minutes. Continuous operation was simulated by sequentially emptying and refilling a set of reaction vessels in a cyclic manner. The constant need to fill, heat, cool, empty and repeat wastes energy and requires additional equipment to maintain the illusion of a truly continuous flow in a parallel batch process.

Disclosure of Invention

A method for depolymerizing plastic materials embodying features of the invention comprises: (a) Continuously flowing a mixture containing solid plastic particles in a solvent through a line in a heating chamber at a particle velocity sufficient to maintain the plastic particles suspended in the solvent and prevent the plastic particles from agglomerating and plugging the line; and (b) transferring heat through the line in the heating chamber to heat the mixture to a reaction temperature to begin depolymerizing the plastic particles in the solvent into a homogeneous solution comprising a liquefied reaction product.

A system for continuous depolymerization of plastic embodying features of the present invention includes a pump operating at a pump flow rate and a line through which the pump continuously feeds a heterogeneous mixture including plastic particles in a solvent at a particle velocity. The heating zone increases the temperature of the heterogeneous mixture flowing through the line to a reaction temperature of at least 150 ℃. The heterogeneous mixture containing plastic particles begins to be converted into a homogeneous solution containing liquefied reaction products (including monomers, dimers, oligomers, and/or reaction byproducts) in the heating zone.

Drawings

FIG. 1 is a block diagram of a system for depolymerizing plastic incorporating features of the present invention.

Fig. 2 is a flow chart showing the progression of a volume of plastic through a depolymerization process in the system of fig. 1.

Detailed Description

A system and method for depolymerizing plastic is shown in fig. 1 and 2. The systems and methods can be used with various plastics such as, but not limited to, PET, modified PET, PET blends, PEN, PBT, PET-G, PLA, PGA, PLGA, PEF, copolyesters, polycarbonates, polyamides (nylons), polyurethanes, and combinations and blends. Depolymerizing the plastic to the following, but not limited to: in addition, chemically useful compounds such as dioctyl terephthalate (DOTP), diisobutyl terephthalate (DITP), dibutyl terephthalate (DBTP), bisphenol A (BPA), lactate, bis (2-hydroxyethyl) terephthalamide (BHETA), and other terephthalamides.

Solid plastic particles of waste polyester material in the form of flakes, fines, granules, particles, flakes, chunks, and/or powder are mixed with a solvent and a catalyst in a mixer 10 to produce a heterogeneous mixture 12. The mixer 10 may use a stirrer (such as a propeller 13, stir bar, or other stirrer) or a recirculating solvent to mix. Or the mixture may be pre-mixed. Examples of solvents are, but are not limited to, ethylene Glycol (EG), diethylene glycol (DEG), glycol ethers, methanol, ethanol, propanol, butanol, 2-ethylhexanol, tetramethylcyclobutanediol (CBDM), cyclohexanedimethanol (CHDM), alcohols, ethanolamines, ionic liquids, polar protic solvents, polar aprotic solvents, and water. Examples of suitable catalysts include, but are not limited to: zinc salt, zinc acetate; zinc chloride; a titanium salt; a manganese salt; a magnesium salt; sodium hydroxide; potassium hydroxide; 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD); 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU); magnesium acetate; 4-Dimethylaminopyridine (DMAP); an amine; a trialkylamine; and combinations of these catalysts. The heterogeneous mixture 12 is pumped through a series of connected lines, such as pipes or tubes, by a pump 14. No agitator, auger or extruder is required to propel the mixture through the system. The pump 14 is operated at a flow rate large enough to move the mixture 12 through the system at a particle velocity large enough to maintain the particles suspended in the solvent and prevent the particles from agglomerating and plugging the lines. By operating continuously, the pump 14 causes the heterogeneous mixture to flow through the system at a steady rate, which allows the conversion of plastic to liquefied product to vary with location within the system rather than time (as in a batch system).

An optional preheat heat exchanger (preheater) 16 is used to preheat the heterogeneous mixture 12. The preheater 16 may heat the heterogeneous mixture 12 via a heat source such as a flame, steam, hot oil, or a circulating heat transfer fluid. Alternatively, a hot homogeneous solution containing liquefied product after the depolymerization reaction can be used in the preheater 16 to transfer heat to the heterogeneous mixture and cool itself down in the process.

The preheated heterogeneous mixture 12' continuously flows into and through the downstream heating chamber 18 where depolymerization begins. The heating chamber 18 may be implemented as a reactor heat exchanger that raises the temperature of the heterogeneous mixture to a reaction temperature of at least 150 ℃. The heterogeneous mixture is heated in reaction heat exchanger 18 by heat source 20. The heat source 20 may utilize microwave radiation, direct flame, electrically heated tubing, inductively heated tubing, geothermal, magnetostrictive thermoelectric, or direct heating of the heterogeneous mixture in an ohmic manner, as some examples. Or the heat source 20 may indirectly heat the heterogeneous mixture by directly heating the heat transfer fluid outside of the heating chamber 18. Examples of suitable transfer fluids are hot oils, hot fluids, molten salts and steam. The heated heat transfer fluid is then pumped through a line containing the heterogeneous mixture in the heating chamber 18. Heat is transferred from the heat transfer fluid to the heterogeneous mixture to initiate depolymerization. The heterogeneous mixture flowing through the heating chamber 18 is not in direct contact with the heat transfer fluid.

The holding tube 22 after the heating chamber 18 maintains the reaction temperature for at least one minute to complete the conversion of the heterogeneous mixture containing plastic into a homogeneous solution 24 containing liquefied product. The holding tube 22 may be implemented as an insulated spool or coil of pipe or tubing or as a jacketed pipe or vessel. Alternatively, the holding tube may be part of the heating chamber rather than a separate component. The reaction was completed in a holding tube. The exiting homogeneous solution contains solvent, spent catalyst, and depolymerized plastic in the form of liquefied reaction products, which typically include monomers, oligomers, and/or small amounts of by-products from the reaction (e.g., half-esters, half-amides, mixed esters, mixed amides).

The homogeneous solution 24 is continuously pumped through an optional preheat heat exchanger 16 to cool itself and preheat the incoming heterogeneous mixture 12. The back pressure regulator 26 maintains the system pressure (e.g., 100psi to 400 psi) above the vapor pressure of the solvent at the reaction temperature.

After flowing through the back pressure regulator 26, the homogeneous solution 24 flows through an optional cooling heat exchanger (chiller) 28 that uses cold water or other cooling heat transfer fluid from a cooling reservoir 30 to remove any excess heat that is not recycled by the preheater 16.

After the solution is cooled, it is poured into a precipitation or crystallization tank and cooled until the liquefied product precipitates as a solid reaction product 34. The solvent is then decanted, filtered, centrifuged or distilled off from the solid reaction product. The solid reaction product may then be pressure filtered to further separate it from any remaining solvent. Decantation, filtration, centrifugation or distillation of the solvent followed by pressurization for separating the solid reaction product 34 from the solvent 36 in the solution 24 is represented in fig. 1 by separator 32.

The separated solvent 36 is recycled back to the mixer 10 for reuse. An optional solvent wash, purification, or regeneration step may be required to remove reaction contaminants from the solvent supplied to the subsequent heterogeneous mixture 12. The reaction contaminants may include particles, ionic salts, anions, cations, spent catalysts, dyes, binders, components from the blend, fillers, and/or decomposed solvents. Contaminant removal 42 may occur by passing the separated solvent 36 through a filter and/or an adsorbent, such as activated carbon, ion exchange resin, diatomaceous earth, sand, zeolite, clay, silica, alumina, oxide, size exclusion, and/or tangential flow filtration. Contaminant removal 42 of solvent 36 may be an on-line or off-line process. Contaminant removal 42 may occur in the separate solvent step 36 or the homogeneous solution step 24.

Thus, the system moves the heterogeneous mixture 12 through four zones: z1-cold entry zone, where the mixture is fed into the system by pump 14; z2-a preheating zone in which the mixture is heated in a preheater 16; a Z3-heating zone in which the mixture is heated to raise its temperature to the reaction temperature; and a Z4-holding zone in which the mixture is held at the reaction temperature to complete the conversion of the heterogeneous mixture to the homogeneous solution 24. The homogeneous solution 24 is moved through a cooling zone Z5 in which the homogeneous solution is cooled in a cooler 28 or by transferring heat to the incoming heterogeneous mixture 12 in the preheater 16. The pump 14 maintains a continuous flow through the system that ensures that the particle velocity of the heterogeneous mixture is large enough to keep the particles in suspension. In this way, plastic particles do not settle in the pipeline and clog the system.

The size of the plastic particles pumped through the system can vary, but they are typically between 0.1 μm and 20,000 μm in at least one dimension. To maintain the particles in suspension, the flow rate of the pump 14 is set to ensure that the particle velocity through the system is at least 20cm/s. Particle velocities in excess of 20cm/s or 30cm/s provide a safety margin. The pump flow rate is set equal to the product of the desired particle velocity and the cross-sectional area of the pipeline (pipe or tube) through which the mixture is pumped. Lower particle velocities are possible if a mixer is installed in the line between the pump 14 and the regulator 26.

In the heating zone Z3, the heating chamber 18 raises the temperature to the reaction temperature or higher to start the depolymerization reaction, which is completed in the holding zone Z4. The length L of the holding tube 22 in the holding zone Z4 depends on its cross-sectional area a, the flow rate Q of the pump and the holding time T required for the reaction to complete at the reaction temperature: l = QT/A. The holding time may be in the range of 5 minutes to 10 minutes or even 1 minute to 60 minutes. The diameter of the line passing through the zone is from 1cm to 10cm, but may be as large as 100cm. If jacketed pipes are used, the diameter of the jacket may range from 1.1 to 5.0 times the diameter of the inner pipe through which the mixture is pumped.

Claims

1. A continuous flow process for depolymerizing plastic comprising:

(a) Continuously flowing a mixture containing solid plastic particles in a solvent through a line in a heating chamber at a particle velocity sufficient to keep the plastic particles suspended in the solvent and prevent the plastic particles from aggregating and clogging the line, wherein the solid plastic particles consist of: modified PET, PET blend, PEN, PBT, PET-G, PLA, PGA, PLGA, PEF, copolyester, polycarbonate, polyamide, polyurethane, or any combination thereof;

(b) Transferring heat through the lines in the heating chamber to heat the mixture to a reaction temperature to begin depolymerizing the plastic particles in the solvent into a homogeneous solution comprising a liquefied reaction product.

2. The continuous flow process of claim 1, wherein the solvent consists of: ethylene glycol, diethylene glycol, glycol ethers, methanol, ethanol, propanol, butanol, 2-ethylhexanol, tetramethylcyclobutanediol, cyclohexanedimethanol, an alcohol, an ethanolamine, an ionic liquid, a polar protic solvent, a polar aprotic solvent, water, or any combination thereof.

3. The continuous flow process of claim 1, wherein the liquefied reaction product comprises a monomer, dimer, or oligomer.

4. The continuous flow process of claim 1, wherein the liquefied reaction products comprise (bis (2-hydroxyethyl) terephthalate, dimethyl terephthalate, terephthalic acid, (bis (2-hydroxyethyl) naphthalate, (bis (2-hydroxyethyl) furoate), their respective oligomers, acids, half esters, mixed esters, dioctyl terephthalate, diisobutyl terephthalate, dibutyl terephthalate, bisphenol A, lactate, bis (2-hydroxyethyl) terephthalamide, other terephthalamide, or any combination thereof.

5. The continuous flow process of claim 1, wherein the reaction temperature is at least 150 ℃.

6. The continuous flow process of claim 1, wherein step (b) further comprises maintaining the mixture at the reaction temperature for at least one minute.

7. The continuous flow process of claim 1, wherein step (a) further comprises preheating the mixture in a preheating heat exchanger prior to flowing it into the heating chamber.

8. The continuous flow process of claim 7, further comprising:

(c) Flowing the homogeneous solution through a channel in the preheat heat exchanger after the homogeneous solution exits the heating chamber, wherein the homogeneous solution transfers heat to the mixture in the preheat heat exchanger.

9. The continuous flow process of claim 1, further comprising maintaining a system pressure above a vapor pressure of the solvent at the reaction temperature to prevent evaporation of the solvent.

10. The continuous flow process of claim 1, wherein step (a) further comprises mixing the solid plastic particles and the solvent with a catalyst to form the mixture.

11. The continuous flow process of claim 10, wherein the catalyst consists of: zinc salt, zinc acetate, zinc chloride, titanium salt, titanium (IV) isopropoxide, titanium (IV) n-butoxide, manganese salt, magnesium salt, sodium hydroxide, potassium hydroxide, 1,5,7-triazabicyclo [4.4.0] dec-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene, magnesium acetate, 4-dimethylaminopyridine, amine, trialkylamine, or any combination thereof.

12. The continuous flow process of claim 1, further comprising:

(c) Cooling the homogeneous solution in a cooling heat exchanger to a temperature below 50 ℃.

13. The continuous flow process of claim 12, further comprising:

(d) The cooled homogeneous solution is allowed to stand at room temperature for about 0.5 hours to 100 hours to solidify the liquefied reaction product into a solid reaction product.

14. The continuous flow process of claim 13, further comprising:

(e) Separating the solid reaction product from the solvent by one or more of decantation, filtration, centrifugation, pressurization, and distillation.

15. The continuous flow process of claim 14, further comprising:

(f) Reusing the solvent separated from the solid reaction product in the process.

16. The continuous flow process of claim 1, further comprising:

(c) Separating the solvent from the reaction product;

(d) Removing contaminants from the solvent by filtration, an adsorbent, or a combination thereof; and

(e) The solvent is reused in the process by mixing solid plastic particles in a reused solvent to form the mixture.

17. The continuous flow process of claim 16, wherein the adsorbent consists of: activated carbon, ion exchange resin, diatomaceous earth, sand, zeolite, clay, silica, alumina, oxide, or any combination thereof.

18. The continuous flow process of claim 1, wherein the plastic particles have a size of 0.1 μ ι η to 20,000 μ ι η in at least one dimension.

19. The continuous flow process of claim 1, wherein the solid plastic particles are in the form of flakes, fines, granules, particles, flakes, chunks, powder, or any combination thereof.

20. The continuous flow process of claim 1, wherein the particle velocity through the pipeline is at least 30cm/s.

21. The continuous flow process of claim 1, wherein in step (b) the mixture is indirectly heated in the conduit of the heating chamber by pumping a hot heat transfer fluid through the conduit.

22. A system for continuously depolymerizing plastic comprising:

a pump operating at a flow rate;

a line through which the pump continuously feeds a heterogeneous mixture comprising solid plastic particles in a solvent at a particle speed, wherein the solid plastic particles consist of: modified PET, PET blend, PEN, PBT, PET-G, PLA, PGA, PLGA, PEF, copolyester, polycarbonate, polyamide, polyurethane, or any combination thereof;

a heating zone that increases the temperature of the heterogeneous mixture flowing through the line to a reaction temperature of at least 150 ℃;

wherein the conversion of the heterogeneous mixture containing the solid plastic particles into a homogeneous solution containing liquefied reaction products is started in the heating zone.

23. The system of claim 22, a holding tube receiving the heated heterogeneous mixture from the heating zone, holding the reaction temperature for a holding time of at least one minute at a flow rate that completely converts the heterogeneous mixture containing the solid plastic particles into the homogeneous solution containing the liquefied reaction product.

24. The system of claim 23, wherein the holding tube is an insulated tube or a conduit.

25. The system of claim 24, wherein the holding tube is of sufficient length to ensure complete conversion of the heterogeneous mixture to the homogeneous solution containing liquefied reaction products.

26. The system of claim 25, wherein the hold time in the holding tube is between 1 minute and 60 minutes.

27. The system of claim 25, wherein the hold time in the holding tube is between 5 minutes and 10 minutes.

28. The system of claim 22, further comprising a mixer upstream of the heating zone that uses an agitator or recycled solvent to agitate the heterogeneous mixture.

29. The system of claim 22, wherein the heterogeneous mixture comprises the solid plastic particles, the solvent, and a catalyst.

30. The system of claim 22, wherein the solid plastic particles have a size of 0.1 μ ι η to 20,000 μ ι η in at least one dimension.

31. The system of claim 22, wherein the pump maintains the flow rate such that the particle velocity of the solid plastic particles exceeds 30cm/s.

32. The system of claim 31, wherein the flow rate is set equal to the product of the desired particle velocity and the cross-sectional area of the pipeline.

33. The system of claim 22, further comprising a preheat heat exchanger that indirectly preheats the heterogeneous mixture with the homogeneous solution containing the liquefied reaction product to reduce a holding time of the heterogeneous mixture in the heating zone and cool the homogeneous solution.

34. The system of claim 22, further comprising a reactor heat exchanger in the heating zone that raises the temperature of the heterogeneous mixture to the reaction temperature.

35. The system of claim 34, wherein a heat source is configured to heat a heat transfer fluid flowing through the heterogeneous mixture in the reactor heat exchanger to transfer heat to the heterogeneous mixture.

36. The system of claim 22, further comprising a back pressure regulator downstream of the heating zone that maintains a system pressure above a vapor pressure of the solvent at the reaction temperature.

37. The system of claim 22, further comprising a cooler located downstream of the heating zone and comprising a cooling heat exchanger, the homogeneous solution on one side of the heat exchanger being indirectly cooled by a cold liquid on the other side of the heat exchanger, wherein the cooler reduces the temperature of the homogeneous solution to less than 50 ℃.

38. The system of claim 22, further comprising a separator comprising a precipitation or crystallization tank, wherein the liquefied reaction product in the homogeneous solution solidifies into a solid reaction product and precipitates.

39. The system of claim 38, wherein the separator separates the solvent from the solid reaction product by one or more of decantation, filtration, centrifugation, pressurization, and distillation.

40. The system of claim 38, further comprising a contaminant removal portion located downstream of the separator, wherein the contaminant removal portion removes reaction contaminants from the solvent, and wherein the contaminant removal portion comprises a filter or an adsorbent.

41. The system of claim 40, wherein the filter comprises a size exclusion filter or a tangential flow filter.

42. The system of claim 40, wherein the adsorbent consists of: activated carbon, ion exchange resin, diatomaceous earth, sand, zeolite, clay, silica, alumina, oxide, or any combination thereof.

43. The system of claim 22, further comprising a preheater located upstream of the heating zone and a holding tube after the heating zone; wherein the preheater, the heating zone, and the holding tube each comprise a heat exchanger.

44. The system of claim 43, wherein each heat exchanger is a single shell, multiple shell, coil shell, tube-in-tube, jacketed tube, plate shell, or plate and frame heat exchanger.

45. The system of claim 22, further comprising a preheater located upstream of the heating zone and a holding tube after the heating zone; wherein the preheater, the heating zone, and the holding tube comprise segments of jacketed piping having a jacket surrounding an inner tube, wherein the jacketed piping is connected.

46. The system of claim 45, wherein the inner tube in the jacketed pipe has an inner diameter of 1cm to 100cm and the jacket has a diameter of 1.1 to 5.0 times the diameter of the inner tube.