JP7599499B2 - Process and system for depolymerization of waste plastics - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62/964,948, filed January 23, 2020, the contents of which are incorporated herein by reference.

FIELD OF THEINVENTION This invention relates generally to the depolymerization of resins, plastics, or polymers, and more particularly to the depolymerization of waste plastics in a continuous process.

Traditionally, depolymerization of plastics is carried out in large reaction vessels, usually equipped with a heating jacket and an agitator. The depolymerization reaction is contained in the vessel until the depolymerization is complete. After depolymerization, the vessel is emptied and refilled. Each batch is heated to accelerate the depolymerization and then cooled to produce a viable feedstock for new polymer. Batch processing typically takes anywhere from 20 minutes to 800 minutes. Continuous operation is simulated by sequentially emptying and refilling groups of reaction vessels in a round robin fashion. The continuous need to fill, heat, cool, empty and repeat wastes energy and requires additional equipment to keep the parallel batch process looking like it is actually flowing continuously.

Overview A process embodying features of the invention for depolymerizing plastics includes the steps of: (a) continuously flowing a mixture including solid plastic particles in a solvent through a line within a heated chamber at a particle velocity great enough to maintain the plastic particles suspended in the solvent and to prevent the plastic particles from agglomerating and clogging the line; and (b) transferring heat through the line within the heated chamber to heat the mixture to a reaction temperature to initiate depolymerization of the plastic particles in the solvent into a homogenous solution including a liquefied reaction product.

A system embodying features of the invention for continuous depolymerization of plastics includes a pump operating at a pumping flow rate and a line through which the pump continuously delivers a heterogeneous mixture comprising particles of plastic in a solvent at a particle rate. A heating zone raises the temperature of the heterogeneous mixture flowing through the line to a reaction temperature of at least 150° C. Conversion of the heterogeneous mixture comprising plastic particles to a homogeneous solution comprising a liquefied reaction product comprising monomers, dimers, oligomers, and/or reaction by-products is initiated in the heating zone.

FIG. 1 is a block diagram of a system embodying features of the present invention for depolymerizing plastics.

FIG. 2 is a flow chart illustrating the progression of a volume of plastic undergoing a depolymerization process in the system of FIG.

DETAILED DESCRIPTION A system and process for depolymerizing plastics is shown in Figures 1 and 2. The system and process can be used with a variety of plastics, including, 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. Depolymerize plastics to, but are not limited to, the following: bis(2-hydroxyethyl)terephthalate (BHET), dimethyl terephthalate (DMT), terephthalic acid (TA), bis(2-hydroxyethyl)naphthalate (BHEN), bis(2-hydroxyethyl)furanoate (BHEF), their respective oligomers, acids, half esters, mixed esters, etc. Additionally, 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 can be included.

Solid plastic particles of waste polyester material in the form of flakes, fines, granules, granules, lumps, chunks, and/or powder are mixed with a solvent and catalyst in a mixer 10 to produce a heterogeneous mixture 12. The mixer 10 can use an agitator such as a propeller 13, stirrer, or other agitator, or a recirculating solvent to effect the mixing. Alternatively, the mixture can be premixed. Examples of solvents include, but are not limited to, ethylene glycol (EG), diethylene glycol (DEG), glycol ethers, methanol, ethanol, propanol, butanol, 2-ethylhexanol, tetramethylcyclobutanediol (CBDM), cyclohexanedimethanol (CHDM), alcohols, ethanolamine, ionic liquids, polar protic solvents, polar aprotic solvents, and water. Examples of suitable catalysts include, but are not limited to, zinc salts, zinc acetate; zinc chloride; titanium salts; manganese salts; magnesium salts; 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); amines; trialkylamines; and combinations of these catalysts. The heterogeneous mixture 12 is pumped by pump 14 through a series of connected lines, such as tubes or pipes. No agitators, augers, or extruders are required to advance the mixture through the system. Pump 14 operates at a flow rate high enough to move mixture 12 through the system at a particle velocity high enough to keep the particles suspended in the solvent and to prevent the particles from agglomerating and clogging the lines. The pump 14 operates continuously without stopping, allowing the heterogeneous mixture to flow through the system at a steady rate, making the conversion of the plastic to a liquefied product a function of position in the system rather than a function of time as in a batch system.

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

The preheated heterogeneous mixture 12' flows continuously into the downstream heating chamber 18 through which the depolymerization is initiated. The heating chamber 18 can be realized as a reactor heat exchanger that raises the temperature of the heterogeneous mixture to a reaction temperature of at least 150°C. The heterogeneous mixture is heated in the reaction heat exchanger 18 by a heat source 20. The heat source 20 may directly heat the heterogeneous mixture with microwave radiation, direct flame, electric heating pipes, induction heating pipes, geothermal heat, magnon drag thermoelectric, or ohmic, as some examples. Alternatively, the heat source 20 may indirectly heat the heterogeneous mixture by directly heating a heat transfer fluid that is external to the heating chamber 18. Examples of suitable transfer fluids include thermal oil, thermal fluid, molten salt, and steam. The heated heat transfer fluid is then pumped through the lines containing the heterogeneous mixture in the heating chamber 18. Heat is transferred from the heat transfer fluid to the heterogeneous mixture, initiating depolymerization. The heterogeneous mixture flowing through the heating chamber 18 is not directly contacted by the heat transfer fluid.

The holding tube 22 following the heating chamber 18 maintains the reaction temperature for at least one minute to complete the conversion of the heterogeneous mixture containing the plastic to a homogeneous solution 24 containing the liquefied product. The holding tube 22 can be realized by 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 is completed within the holding tube. The emerging homogeneous solution contains the solvent, spent catalyst, and the depolymerized plastic in the form of a liquefied reaction product, typically including monomers, oligomers, and/or minor 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. A backpressure regulator 26 maintains a system pressure above the vapor pressure of the solvent at the reaction temperature, e.g., 100 psi to 400 psi.

After flowing through the backpressure regulator 26, the homogenous solution 24 flows through an optional chilling heat exchanger 28, which uses cold water or other cooling heat transfer fluid from a chilled reservoir 30 to remove any excess heat not regenerated by the preheater 16.

After the solution is cooled, it is poured into a settling or crystallizing tank and cooled until the liquefied product precipitates as a solid reaction product 34. The solvent is then decanted, filtered, centrifuged, or distilled away from the solid reaction product. The solid reaction product may then be filter pressed for further separation from the remaining solvent. The decantation, filtration, centrifugation, or distillation of the solvent, followed by pressing, to separate the solid reaction product 34 in solution 24 from the solvent 36 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 feeding the subsequent heterogeneous mixture 12. The reaction contaminants may include particulates, ionic salts, anions, cations, spent catalysts, dyes, adhesives, components from blends, fillers and/or decomposed solvent. Decontamination 42 may occur by passing the separated solvent 36 through a filter and/or over an adsorbent such as activated carbon, ion exchange resins, diatomaceous earth, sand, zeolites, clays, silica, alumina, oxides, size exclusion and/or tangential flow filtration. Decontamination 42 of the solvent 36 may be an in-line or offline process. Decontamination 42 may occur at the separated solvent step 36 or at the homogeneous solution step 24.

Thus, the system moves the heterogeneous mixture 12 through four zones: Z1 - a cold entry zone where the mixture is fed into the system by pump 14, Z2 - a preheat zone where the mixture is heated in preheater 16, Z3 - a heating zone where the mixture is heated to raise its temperature to the reaction temperature, and Z4 - a holding zone where the mixture is maintained at the reaction temperature to complete the conversion of the heterogeneous mixture to a homogeneous solution 24. The homogeneous solution 24 is moved through a cooling zone Z5 where the homogeneous solution is cooled in a chiller 28 or by the transfer of heat to the incoming heterogeneous mixture 12 in preheater 16. The pump 14 maintains a continuous flow rate through the system that ensures a particle velocity of the heterogeneous mixture that is great enough to keep the particles suspended. That way, the plastic particles do not settle in the lines and clog the system.

The size of the plastic particles pumped through the system can vary, but are typically between 0.1 μm and 20,000 μm in at least one dimension. To keep the particles suspended, the flow rate of the pump 14 is set to ensure a particle velocity of at least 20 cm/s through the system. Particle velocities above 20 cm/s or 30 cm/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 line (pipe or tubing) 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 heating zone Z3, heating chamber 18 raises the temperature to or above the reaction temperature to initiate the depolymerization reaction, which is completed in holding zone Z4. The length L of holding tube 22 in holding zone Z4 depends on its cross-sectional area A, the pump flow rate Q, and the holding time T required at the reaction temperature to complete the reaction, i.e., L=QT/A. Holding times can range from 5 minutes to 10 minutes, or alternatively from 1 minute to 60 minutes. The diameter of the lines passing through the zones is 1 cm to 10 cm, but can be as large as 100 cm. If jacketed piping is used, the diameter of the jacket can range from 1.1 to 5.0 times the diameter of the inner pipe through which the mixture is pumped.
The present invention provides, for example, the following items.
(Item 1)
1. A continuous flow process for depolymerizing plastics, the process comprising:
(a) continuously flowing a mixture comprising solid plastic particles in a solvent through a line in a heated chamber at a particle velocity sufficient to maintain suspension of the plastic particles in the solvent and to prevent the plastic particles from agglomerating and clogging the line, wherein the solid plastic particles are comprised of modified PET, PET blends, PEN, PBT, PET-G, PLA, PGA, PLGA, PEF, copolyesters, polycarbonates, polyamides, polyurethanes, or any combination thereof;
(b) transferring heat through the lines of the heating chamber to heat the mixture to a reaction temperature to initiate depolymerization of the plastic particles in the solvent into a homogenous solution containing a liquefied reaction product;
A continuous flow process comprising:
(Item 2)
2. The continuous flow process of claim 1, wherein the solvent comprises ethylene glycol, diethylene glycol, glycol ethers, methanol, ethanol, propanol, butanol, 2-ethylhexanol, tetramethylcyclobutanediol, cyclohexanedimethanol, alcohols, ethanolamine, ionic liquids, polar protic solvents, polar aprotic solvents, water, or combinations thereof.
(Item 3)
2. The continuous flow process of claim 1, wherein the liquefied reaction product comprises a monomer, a dimer, or an oligomer.
(Item 4)
2. The continuous flow process of claim 1, wherein the liquefied reaction product comprises bis(2-hydroxyethyl)terephthalate, dimethyl terephthalate, terephthalic acid, bis(2-hydroxyethyl)naphthalate, bis(2-hydroxyethyl)furanoate, their respective oligomers, acids, half esters, mixed esters, dioctyl terephthalate, diisobutyl terephthalate, dibutyl terephthalate, bisphenol A, lactate, bis(2-hydroxyethyl)terephthalamide, other terephthalamides, or any combination thereof.
(Item 5)
2. The continuous flow process of claim 1, wherein the reaction temperature is at least 150° C.
(Item 6)
2. The continuous flow process of claim 1, wherein step (b) further comprises holding the mixture at the reaction temperature for at least 1 minute.
(Item 7)
2. The continuous flow process of claim 1, wherein step (a) further comprises preheating the mixture in a preheating heat exchanger prior to flowing the mixture into the heating chamber.
(Item 8)
(c) passing the homogeneous solution through passages in the preheating heat exchanger after the homogeneous solution leaves the heating chamber, and the homogeneous solution transferring heat to the mixture in the preheating heat exchanger.
8. The continuous flow process of claim 7, further comprising:
(Item 9)
13. The continuous flow process of claim 1, further comprising maintaining a system pressure above the vapor pressure of the solvent at the reaction temperature to prevent the solvent from evaporating.
(Item 10)
2. 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.
(Item 11)
11. The continuous flow process of item 10, wherein the catalyst comprises zinc salts, zinc acetate, zinc chloride, titanium salts, titanium (IV) isopropoxide, titanium (IV) n-butoxide, manganese salts, magnesium salts, 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, amines, trialkylamines, or any combination thereof.
(Item 12)
(c) cooling the homogeneous solution to a temperature below 50° C. in a cooling heat exchanger.
2. The continuous flow process of claim 1, further comprising:
(Item 13)
(d) allowing the cooled homogenous solution to settle at room temperature for a period of between about 0.5 hours and 100 hours to solidify the liquefied reaction product into a solid reaction product.
13. The continuous flow process of claim 12, further comprising:
(Item 14)
(e) separating the solid reaction product from the solvent by one or more of decantation, filtration, centrifugation, pressing, and distillation.
14. The continuous flow process of claim 13, further comprising:
(Item 15)
(f) recycling the solvent separated from the solid reaction product within the process.
15. The continuous flow process of claim 14, further comprising:
(Item 16)
(c) separating the solvent from the reaction product;
(d) removing contaminants from the solvent by filtration, adsorption, or a combination thereof; and
(e) reusing the solvent within the process by mixing the recycled solvent with solid plastic particles to form the mixture.
2. The continuous flow process of claim 1, further comprising:
(Item 17)
17. The continuous flow process of claim 16, wherein the adsorbent comprises activated carbon, ion exchange resin, diatomaceous earth, sand, zeolite, clay, silica, alumina, oxide, or any combination thereof.
(Item 18)
2. The continuous flow process of claim 1, wherein the plastic particles have a size between 0.1 μm and 20,000 μm in at least one dimension.
(Item 19)
2. The continuous flow process of claim 1, wherein the solid plastic particles are in the form of flakes, fines, granules, granules, lumps, chunks, powder, or any combination thereof.
(Item 20)
2. The continuous flow process of claim 1, wherein the particle velocity through the line is at least 30 cm/s.
(Item 21)
2. The continuous flow process of claim 1, wherein in step (b), the mixture is indirectly heated in the lines of the heating chamber by pumping a hot heat transfer fluid through the lines.
(Item 22)
1. A system for continuous depolymerization of plastics, comprising:
A pump operating at a certain flow rate,
a line in which the pump continuously delivers a heterogeneous mixture comprising solid plastic particles in a solvent at a particle velocity, the solid plastic particles being comprised of modified PET, PET blends, PEN, PBT, PET-G, PLA, PGA, PLGA, PEF, copolyesters, polycarbonates, polyamides, polyurethanes, or any combination thereof; and
A heating zone for raising the temperature of the heterogeneous mixture flowing through the line to a reaction temperature of at least 150° C.
wherein conversion of the heterogeneous mixture comprising the solid plastic particles to a homogeneous solution comprising a liquefied reaction product is initiated in the heating zone.
(Item 23)
23. The system of claim 22, wherein a holding tube receives the heated heterogeneous mixture from the heating zone to maintain the reaction temperature at the flow rate for a holding time of at least 1 minute to completely convert the heterogeneous mixture comprising the solid plastic particles into the homogeneous solution comprising the liquefied reaction product.
(Item 24)
24. The system of claim 23, wherein the holding tube is an insulated pipe or tubing.
(Item 25)
25. The system of claim 24, wherein the length of the holding tube is long enough to ensure that the conversion of the heterogeneous mixture to the homogeneous solution containing the liquefied reaction product is complete.
(Item 26)
26. The system of claim 25, wherein the retention time in the holding tube is between 1 minute and 60 minutes.
(Item 27)
26. The system of claim 25, wherein the retention time in the holding tube is between 5 minutes and 10 minutes.
(Item 28)
23. The system of claim 22, further comprising a mixer upstream of the heating zone that uses an agitator or recirculating solvent to agitate the heterogeneous mixture.
(Item 29)
23. The system of claim 22, wherein the heterogeneous mixture comprises the solid plastic particles, the solvent, and a catalyst.
(Item 30)
23. The system of claim 22, wherein the solid plastic particles have a size between 0.1 μm and 20,000 μm in at least one dimension.
(Item 31)
23. The system of claim 22, wherein the pump maintains the flow rate such that the particle velocity of the solid plastic particles exceeds 30 cm/s.
(Item 32)
32. The system of claim 31, wherein the flow rate is set equal to the product of a desired particle velocity and a cross-sectional area of the line.
(Item 33)
23. The system of claim 22, further comprising a preheating heat exchanger that indirectly preheats the heterogeneous mixture with the homogeneous solution containing the liquefied reaction product to reduce retention time of the heterogeneous mixture in the heating zone and to cool the homogeneous solution.
(Item 34)
23. 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.
(Item 35)
35. The system of claim 34, wherein a heat source is configured to heat a heat transfer fluid flowing past the heterogeneous mixture in the reactor heat exchanger to transfer heat to the heterogeneous mixture.
(Item 36)
23. The system of claim 22, further comprising a backpressure regulator downstream of the heating zone to maintain a system pressure above the vapor pressure of the solvent at the reaction temperature.
(Item 37)
23. The system of claim 22, further comprising a cooling device downstream of the heating zone, the cooling device including a heat exchanger for cooling, the homogeneous solution on one side of the heat exchanger being indirectly cooled by a cold liquid on the other side, the cooling device reducing the temperature of the homogeneous solution to below 50°C.
(Item 38)
23. The system of claim 22, further comprising a separator comprising a precipitator or crystallizer, wherein the liquefied reaction product in the homogeneous solution solidifies and precipitates into a solid reaction product.
(Item 39)
40. The system of claim 38, wherein the separator separates the solvent from the solid reaction product by one or more of decantation, filtration, centrifugation, pressing, and distillation.
(Item 40)
40. The system of claim 38, further comprising a contaminant removal section downstream of the separator, the contaminant removal section removing reactive contaminants from the solvent, the contaminant removal section comprising a filter or an adsorbent.
(Item 41)
41. The system of claim 40, wherein the filter comprises a size exclusion filter or a tangential flow filter.
(Item 42)
41. The system of claim 40, wherein the adsorbent comprises activated carbon, ion exchange resin, diatomaceous earth, sand, zeolite, clay, silica, alumina, oxide, or any combination thereof.
(Item 43)
23. The system of claim 22, further comprising a preheater upstream of the heating zone and a holding tube following the heating zone; and wherein the preheater, the heating zone, and the holding tube each comprise a heat exchanger.
(Item 44)
44. The system of claim 43, wherein each heat exchanger is a tube-in-shell, tubes-in-shell, coil-in-shell, tube-in-tube, jacketed piping, plattura, plate-and-shell, or plate-and-frame heat exchanger.
(Item 45)
23. The system of claim 22, further comprising a preheater upstream of the heating zone and a holding tube after the heating zone; the preheater, the heating zone, and the holding tube comprising a plurality of jacketed pipes having a jacket around an inner tube, the jacketed pipes being connected.
(Item 46)
Item 46. The system of item 45, wherein the inner diameter of the inner pipe in the jacketed piping is between 1 cm and 100 cm, and the diameter of the jacket is between 1.1 times and 5.0 times the diameter of the inner pipe.

Claims (19)

1. A continuous flow process for depolymerizing plastics, the process comprising:
(a ) providing a continuous loop flow line including: (i) a cold entry zone, (ii) a preheat zone, (iii) a heating zone, (iv) a holding zone, and (v) a cooling zone;
(b) continuously flowing a heterogeneous mixture comprising solid plastic particles, a catalyst and a solvent sequentially through the cold entry zone, the preheat zone and then the heating zone of the line , the heterogeneous mixture flowing at a velocity sufficient to ensure a particle velocity of at least 30 cm/s in the cold entry, preheat and heating zones to maintain suspension of the plastic particles in the solvent and to prevent the plastic particles from agglomerating and clogging the line, the plastic particles being selected from the group consisting of polyethylene terephthalate, modified polyethylene terephthalate, polyethylene terephthalate blends, polyethylene naphthalate, polybutylene terephthalate, polyethylene terephthalate glycol, polylactic acid, polyglycolic acid, poly D,L-lactic acid-glycolic acid copolymer, polyethylene 2,5-furandicarboxylate, copolyester, polycarbonate, polyamide, or any combination thereof, and the solvent comprises ethylene glycol, diethylene glycol, glycol ether, 2-ethylhexanol, tetramethylcyclobutanediol, cyclohexanedimethanol, alcohols, ethanolamine, ionic liquids, polar protic solvents, polar aprotic solvents, or combinations thereof;
( c ) transferring heat through the lines of the heating zone to heat the heterogeneous mixture to a reaction temperature of at least 150° C. to initiate depolymerization of the plastic particles in the solvent into a homogeneous solution comprising a liquefied reaction product;
( d ) holding the mixture at the reaction temperature in the holding zone for at least 1 minute; and ( e ) flowing the homogeneous solution through the cooling zone to cool the homogeneous solution .
A continuous flow process comprising : The continuous flow process of claim 1, wherein the liquefied reaction product comprises a monomer, a dimer, or an oligomer. The continuous flow process of claim 1, wherein the liquefied reaction product comprises (bis(2-hydroxyethyl)terephthalate, dimethyl terephthalate, terephthalic acid, (bis(2-hydroxyethyl)naphthalate, (bis(2-hydroxyethyl)furanoate, their respective oligomers, acids, half esters, mixed esters, dioctyl terephthalate, diisobutyl terephthalate, dibutyl terephthalate, bisphenol A, lactate, bis(2-hydroxyethyl)terephthalamide, other terephthalamides, or any combination thereof. The continuous flow process of claim 1, further comprising maintaining a system pressure above the vapor pressure of the solvent at the reaction temperature to prevent the solvent from evaporating. The continuous flow process of claim 1, wherein the catalyst comprises zinc salts, zinc acetate, zinc chloride, titanium salts, titanium (IV) isopropoxide, titanium (IV) n-butoxide, manganese salts, magnesium salts, 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, amines, trialkylamines, or any combination thereof. (e) cooling the homogeneous solution in a cooling heat exchanger to a temperature below 50° C.;
(f) allowing the cooled homogenous solution to settle at room temperature for a period of between about 0.5 hours and 100 hours to solidify the liquefied reaction product into a solid reaction product;
10. The continuous flow process of claim 1, further comprising: (g) separating the solid reaction product from the solvent by one or more of decanting, filtration, centrifugation, pressing, and distillation; and (h) recycling the solvent separated from the solid reaction product within the process. (e) separating the solvent from the reaction product;
10. The continuous flow process of claim 1, further comprising: (f) removing contaminants from the solvent by filtration or adsorption; and (g) reusing the solvent in the process by mixing the recycled solvent with solid plastic particles to form the mixture. The continuous flow process of claim 1, wherein the plastic particles have a size between 0.1 μm and 20,000 μm in at least one dimension. 1. A system for continuous depolymerization of plastics, comprising:
A pump operating at a certain flow rate;
A line including (i) a cold entry zone, (ii) a preheating heat exchanger, (iii) a heating zone, and (iv) a holding tube, wherein the pump continuously supplies a heterogeneous mixture including solid plastic particles, a catalyst, and a solvent at the flow rate, the flow rate being sufficient to ensure a particle velocity of at least 30 cm/s in the cold entry zone, the preheating heat exchanger, and the heating zone, and the solid plastic particles are selected from the group consisting of polyethylene terephthalate, modified polyethylene terephthalate, polyethylene terephthalate blends, polyethylene naphthalate, polybutylene terephthalate, polyethylene terephthalate glycol, polylactic acid, polyglycolic acid, poly D,L-lactic acid-glycolic acid copolymer, polyethylene a line consisting of 2,5-furandicarboxylate, copolyester, polycarbonate, polyamide, or any combination thereof, and the solvent consists of ethylene glycol, diethylene glycol, glycol ether, 2-ethylhexanol, tetramethylcyclobutanediol, cyclohexanedimethanol, alcohols, ethanolamine, ionic liquids, polar protic solvents, polar aprotic solvents, or combinations thereof;
a heating zone which raises the temperature of the heterogeneous mixture flowing through the line to a reaction temperature of at least 150° C., where conversion of the heterogeneous mixture containing the solid plastic particles to a homogeneous solution containing a liquefied reaction product is initiated in the heating zone;
a holding tube receiving the heated heterogeneous mixture from the heating zone to maintain the reaction temperature within the holding tube at the flow rate for a retention time of at least one minute to complete conversion of the heterogeneous mixture comprising the solid plastic particles to the homogeneous solution comprising the liquefied reaction product; and a preheating heat exchanger for preheating the heterogeneous mixture upstream of the heating zone, the preheating heat exchanger indirectly preheating the heterogeneous mixture with the homogeneous solution comprising the liquefied reaction product to cool the homogeneous solution. The system of claim 9, further comprising a mixer upstream of the heating zone that agitates the heterogeneous mixture using an agitator or recirculating solvent. The system of claim 10, wherein the holding tube is an insulated pipe or tubing having a length sufficient to ensure that the conversion of the heterogeneous mixture to the homogeneous solution containing the liquefied reaction product is complete. The system of claim 11, wherein the retention time in the holding tube is between 1 minute and 60 minutes. The system of claim 9, further comprising a reactor heat exchanger in the heating zone that raises the temperature of the heterogeneous mixture to the reaction temperature, and a heat source configured to heat a heat transfer fluid flowing past the heterogeneous mixture in the reactor heat exchanger to transfer heat to the heterogeneous mixture. The system of claim 9 further comprises a contaminant removal section downstream of the heating zone, the contaminant removal section including a filter or adsorbent, the contaminant removal section configured to remove reaction contaminants from the solvent. The system of claim 9 further comprises a cooling device downstream of the heating zone, the cooling device including a cooling heat exchanger, the homogeneous solution on one side of the cooling heat exchanger being indirectly cooled by a cold liquid on the other side, the cooling device reducing the temperature of the homogeneous solution to less than 50°C. The system of claim 9 further comprising a separator including a settling tank or crystallizer, in which the liquefied reaction product in the homogeneous solution solidifies and precipitates into a solid reaction product. The system of claim 9, wherein the heating zone includes a heat exchanger, and the heating zone heat exchanger and the preheating heat exchanger are each a tube-in-shell, tubes-in-shell, coil-in-shell, tube-in-tube, jacketed piping, plattura, plate-and-shell, or plate-and-frame heat exchanger. The system of claim 9, wherein the heating zone and the preheating heat exchanger each include a plurality of jacketed pipes having a jacket around an inner tube, and the jacketed pipes are connected. The system of claim 18, wherein the inner diameter of the inner pipe in the jacketed piping is between 1 cm and 100 cm, and the diameter of the jacket is between 1.1 and 5.0 times the diameter of the inner pipe.

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