Depolymerization utilizing a continuous back-mixed reactor

Abstract

Embodiments of the present disclosure are directed towards depolymerization and specifically depolymerization utilizing a continuous back-mixed reactor.

Description

DEPOLYMERIZATION UTILIZING A CONTINUOUS BACK-MIXED REACTOR Field of Disclosure

[0001] Embodiments of the present disclosure are directed towards depolymerization and specifically depolymerization utilizing a back-mixed reactor. Background

[0002] Waste plastics are often diverted to landfills or are incinerated, with a smaller fraction being diverted to recycling. Recycling of waste plastics can occur through a process, such as a pyrolytic process or a catalytic depolymerization process, in which the plastic is converted into solid, liquid, and / or gaseous materials. However, there is a need for improved methods and systems directed toward waste plastic processing. Summary

[0003] The present disclosure provides various embodiments, including without limitation:

[0004] A method for depolymerization utilizing a continuous back-mixed reactor, the method including: transferring polymer to a continuous back-mixed reactor; contacting the polymer with a depolymerization catalyst in the continuous back-mixed reactor; solvating contents of the continuous back-mixed reactor with depolymerized components of the polymer; and transferring contents of the continuous back-mixed reactor to a subsequent unit operation vessel. Brief Description of Drawings

[0005] Figure 1 is a schematic diagram of a depolymerization system utilizing a continuous back-mixed reactor according to an embodiment of the present disclosure.

[0006] Figure 2 is a schematic diagram of a depolymerization system utilizing a continuous back-mixed reactor according to an embodiment of the present disclosure.

[0007] Figure 3 is a schematic diagram of a depolymerization system utilizing a continuous back-mixed reactor according to an embodiment of the present disclosure.

[0008] Figure 4 is a data plot of hydrocarbon viscosity according to an embodiment of the present disclosure.

[0009] Figure 5 illustrates the C1-C4 and C5-C25 product selectivities as functions of temperature at fixed residence time for the thermal pyrolysis of polyethylene in a tubular reactor.

[0010] Figure 6 illustrates molar vapor fraction vs carbon number according to an embodiment of the present disclosure. Detailed Description

[0011] The present disclosure is directed toward methods and systems for depolymerization and specifically depolymerization utilizing continuous back-mixed reactor.

[0012] “Depolymerization”, as used herein, refers to breaking down a polymer into smaller components. Depolymerization methods can be challenging due to the high viscosities experienced during processing, e.g., pumping, mixing, contacting the polymer with a catalyst, et cetera, of the polymer. Previous depolymerization methods have achieved relatively lower viscosities by utilizing a depolymerization solvent feed. However, the fed depolymerization solvent can participate in the depolymerization chemistry, the fed depolymerization solvent can be extremely costly for the required solvent concentrations, and the fed depolymerization solvent can dilute species within a depolymerization reactor, thus providing lower depolymerization rates and / or requiring larger equipment sizes.

[0013] Advantageously, the methods and systems for depolymerization, as disclosed herein, provide relatively lower viscosities that are suitable for depolymerization processing. Additionally, the methods and systems disclosed herein, do not utilize a continuous feed depolymerization solvent.

[0014] As mentioned, the present disclosure is directed toward methods and systems for depolymerization utilizing a continuous back-mixed reactor. In other words, methods and systems for depolymerization, as disclosed herein, are continuous, as opposed to batch processes. Continuous back-mixed reactors are well known. For example, one or more embodiments provide that the continuous back-mixed reactor can be a continuous stirred-tank reactor (CSTR); one or more embodiments provide that the continuous back-mixed reactor can be a loop reactor.

[0015] The continuous back-mixed reactor can provide an exponential residence time distribution of product. At a steady state, this exponential residence time distribution, when applied for depolymerization as discussed herein, can yield a distribution of smaller components that range from relatively longer polymer chains, such as C100to C5000for example, to relatively shorter chain hydrocarbons, e.g., C1to C25. Therefore, for particular feed conditions and / or operating conditions, the continuous back-mixed reactor can advantageously utilize the feed, i.e. polymer, to solvate contents of the continuous back-mixed reactor. As such, embodiments provide that the methods and systems discussed herein do not utilize a continuous fed depolymerization solvent. In other words, depolymerization solvent is notcontinuously fed to the continuous back-mixed reactor, e.g., the continuous back- mixed reactor does not include a continuous feed of depolymerization solvent.

[0016] While the continuous back-mixed reactor does not include a continuous feed of depolymerization solvent, one or more embodiments provided that a startup solvent may be utilized. For example, a startup solvent may be added to the continuous back-mixed reactor upon initiation of the continuous depolymerization methods discussed herein. Different startup solvents may be utilized for various applications. Different amounts of the startup solvent may be utilized for various applications.

[0017] Figure 1 is a schematic diagram of a depolymerization system 100 utilizing a continuous back-mixed reactor 102 according to an embodiment of the present disclosure. The continuous back-mixed reactor 102 shown in Figure 1 is a CSTR; however, embodiments are not so limited. For example, one or more embodiments provide that the continuous back-mixed reactor 102 is a loop reactor. Loop reactors are well known back-mixed reactors. The continuous back-mixed reactor 102 can have different configurations, e.g., sizes and / or shapes, for various applications.

[0018] The continuous back-mixed reactor 102 can operate, e.g., have a steady state temperature, at a temperature from 10 °C to 450 °C. All individual values and subranges from 10 °C to 450 °C are included; for example, the continuous back-mixed reactor can operate at a temperature from a lower limit of 10, 15, or 20 °C to an upper limit of 450, 400, 350, 300, 250, 200, 150, 125, or 100 °C. One or more embodiments provide that polymer may be depolymerized in the continuous back-mixed reactor by thermal pyrolysis. One or more embodiments provide that polymer may be depolymerized in the absence of a depolymerization catalyst.

[0019] The continuous back-mixed reactor 102 can operate, e.g., have a steady state pressure, at a pressure from 1 bar to 50 barg. All individual values and subranges from 1 bar to 50 barg are included; for example, the continuous back- mixed reactor can operate at a pressure from a lower limit of 1, 1.5, or 2 barg to an upper limit of 50, 40, 30, 20, 10, 8, or 5 barg.

[0020] The continuous back-mixed reactor 102 can have different residence times for various applications. The continuous back-mixed reactor 102 can have a residence time from 0.03 hours to 72 hours. All individual values and subranges from 0.03 hours to 72 hours are included; for example, the continuous back-mixed reactor can have a residence time from a lower limit of 0.03, 0.05, 0.2, 0.5, 1, 3, or 5 hours to an upper limit of 72, 48, or 24 hours.

[0021] The continuous back-mixed reactor 102 can have different flow rates for various applications. The back-mixed reactor 102 can have a flow rate from 10 liters / minute (l / min) to 10,000 l / min. All individual values and subranges from 10 l / min to 10,000 l / min are included; for example, the continuous back-mixed reactor can have a flow rate from a lower limit of 10, 100, or 1,000 l / min to an upper limit of 10,000, 8,000, or 5,000 l / min. The flow rate can be calculated as a quotient of a volume of the continuous back-mixed reactor and a residence time of the continuous back-mixed reactor.

[0022] The depolymerization system 100 can include a polymer input 104. The polymer input 104 can be utilized to provide polymer, for depolymerization, to the continuous back-mixed reactor 102. Embodiments provide that various polymers may be utilized. The polymer can include recycled and / or reclaimed polymer. The polymer can include mixtures of polyolefins, e.g., mixtures of polyolefins that are obtained from a recycling process. The polymer can be a homopolymer, a copolymer, a terpolymer, or a combination thereof, for example. Examples of the polymer include, but are not limited to, polyolefins, such as polyethylene and polypropylene, vinyl polymers, such as poly(vinyl chloride), acrylonitrile, butadiene and styrene homopolymer and interpolymers, acrylics, such as poly(methyl methacrylate), fluorocarbon polymer, polyesters, such as poly(ethylene terephthalate) and poly(bisphenol-A carbonate), polyethers, polyamides, such as Nylon 66, polysaccharides, silicones, such as poly(dimethylsiloxane), thermoplastic elastomers, such as ethylene-propylene rubber, and terpolymers, such as ethylene / VA / CO, among other polymers. One or more embodiments provide that the polymer is a polyolefin. One or more embodiments provide that the polymer is polyethylene, polypropylene, or a combination thereof. One or more embodiments provide that the polymer is polyethylene. One or more embodiments provide that the polymer is polypropylene.

[0023] The polymer can be input to the to the continuous back-mixed reactor 102 continuously, e.g., in a steady state operation. Different amounts of polymer, e.g., different polymer flow rates, can be input (continuously) to the to the continuous back-mixed reactor 102 for various applications.

[0024] The polymer can be input to the to the continuous back-mixed reactor 102 via an extruder, a pump, and / or a conveyor, among other well-known polymer inputs. One or more embodiments provide that the polymer input 104 can have a viscosity from 1 to 10,000,000 centipoise (cP). All individual values and subranges from 1 to 10,000,000 cP are included; for example, the polymer input can have viscosity from a lower limit of 1, 100, or 1,000 cP to an upper limit of 10,000,000,5,000,000, 1,000,000, 750,000, 500,000, or 250,000 cP. Viscosity can be determined according to ASTM D5225-22.

[0025] As an example, the polymer can have an average from 200 to 150,000 carbons per polymer molecule. All individual values and subranges from 200 to 150,000 carbons per polymer molecule are included; for example, the polymer can have an average from a lower limit of 200, 500, 1,000, 2,000, 4,000, or 5,000 carbons per polymer molecule to an upper limit of 150,000, 130,000, or 100,000 carbons per polymer molecule.

[0026] The depolymerization system 100 can include a depolymerization catalyst input 106. While Figure 1 shows the depolymerization catalyst input 106 and the polymer input 104 as two distinct inputs, embodiments are not so limited. For instance, one or more embodiments provide that both the polymer and the depolymerization catalyst may be input to the continuous back-mixed reactor 102 by a single input.

[0027] Different depolymerization catalysts may be utilized for various applications. The depolymerization catalyst can comprise a zeolite. The depolymerization catalyst can comprise a metal. The metal can be a transition metal. One or more embodiments provide that the depolymerization catalyst comprises a transition metal from Groups 3-12. One or more embodiments provide that the depolymerization catalyst comprises Pt, Pd, Ni, Co, Fe, Mo, W, Ti, Cr, V, Zr, Ru, Hf, Sc, or a combination thereof. One or more embodiments provide that the depolymerization catalyst comprises Pt. The metal can be from 0.01 weight percent (wt %) to 30 wt % of the depolymerization catalyst based upon the total weight of the depolymerization catalyst.

[0028] The depolymerization catalyst can be a supported catalyst. One or more embodiments provide that the support can be a metal oxide. Examples of metal oxides include SrTiO3, TiO2, MgO, WO3, ZrO2, amorphous aluminosilicate, and modified zeolite. The depolymerization catalyst can be Pt on a metal oxide support, a Pt alloy catalyst, a NiMo catalyst, a CoMo catalyst, or a combination thereof. The support can include SiO2, Al2O3, AlPO4, ZrO2, SiO2, Al2O3, or combinations thereof. In one or more embodiments, the support may comprise microporosity (Zeotype structure). In one or more embodiments, the support maybe amorphous.

[0029] The depolymerization catalyst can include a sulfided catalyst. An example of a sulfied catalyst is sulfided NiCoMo, among others.

[0030] Different amounts of depolymerization catalyst, e.g., different catalyst flow rates, can be input (continuously) to the to the continuous back-mixed reactor 102 for various applications. A weight ratio of depolymerization catalyst tohydrocarbons in the reactor 102 can be from 0.9:1 to 1:400, 1:100,000, or 1:3,000,000.

[0031] Contacting the polymer and the depolymerization catalyst in the continuous back-mixed reactor 102 can provide that contents of the continuous back- mixed reactor are solvated with depolymerized components of the polymer. For instance, contacting the polymer and the depolymerization catalyst in the continuous back-mixed reactor 102 can provide that naphtha, e.g., C5to C12hydrocarbons, is made in the continuous back-mixed reactor 102 by depolymerization. The naphtha made in the continuous back-mixed reactor 102 can solvate contents of the back- mixed reactor. As previously mentioned, advantageously for particular feed conditions and / or operating conditions, the continuous back-mixed reactor can advantageously utilize the feed, i.e., polymer, to solvate contents of the continuous back-mixed reactor.

[0032] One or more embodiments provide that the depolymerization catalyst is not utilized in the continuous back-mixed reactor 102. For embodiments where the depolymerization catalyst is not utilized, contents of the continuous back-mixed reactor can be solvated by thermal degradation of the input polymers.

[0033] The depolymerization system 100 can include a continuous back- mixed reactor output 108. Embodiments of the present disclosure provide that the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to a subsequent unit operation vessel. Various subsequent unit operation vessels may be utilized for different applications. For example, the subsequent unit operation vessel may be a reactor, e.g., a tubular reactor, a CSTR, a fixed bed reactor, a fluidized bed reactor, or the subsequent unit operation vessel may be a separator.

[0034] As shown in Figure 1, the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to tubular reactor 110. The continuous back-mixed reactor output 108 is a liquid. The continuous back-mixed reactor output 108 can include a combination of components obtained from depolymerization of the input polymer and depolymerization catalyst suspended therein.

[0035] The continuous back-mixed reactor output 108 can have a viscosity from 1 to 50,000 cP. All individual values and subranges from 1 to 50,000 cP are included; for example, the continuous back-mixed reactor output can have viscosity from a lower limit of 1, 5, or 10 cP to an upper limit of 50,000, 25,000, 10,000, 5,000, or 1,000 cP. One or more embodiments provide that the continuous back-mixed reactor output has a viscosity from 10 to 1,000 cP. One or more embodimentsprovide that the continuous back-mixed reactor output has a viscosity from 5 to 5,000 cP.

[0036] One or more embodiments of the present disclosure provide that the continuous back-mixed reactor output 108 can contain from 1 wt% to 90 wt% of C1to C25hydrocarbons based upon a total weight of the continuous back-mixed reactor output. All individual values and subranges from 1 wt% to 90 wt% are included; for example, the continuous back-mixed reactor output can contain from a lower limit of 1, 3, or 5 wt% to an upper limit of 90, 85, or 80 wt% of C1to C25hydrocarbons based upon the total weight of the continuous back-mixed reactor output.

[0037] The continuous back-mixed reactor 102 and the tubular reactor 110 are in series reactors. The tubular reactor may be a plug flow tubular reactor (PFTR). The tubular reactor may be a laminar flow tubular reactor. Tubular reactors are well known. The tubular reactor 110 can have different configurations, e.g., sizes and / or shapes, for various applications. The tubular reactor 110 is a continuous flow vessel. While Figure 1 illustrates a single tubular reactor 110, embodiments are not so limited. For instance, one or more embodiments provide that a plurality of in series tubular reactors are utilized. One or more unit operations, e.g., a flash drum, may be located in between each of the plurality of in series tubular reactors.

[0038] The tubular reactor 110 can operate, e.g., have a steady state temperature, at a temperature from 10 °C to 420 °C. All individual values and subranges from 10 °C to 420 °C are included; for example, the tubular reactor can operate at a temperature from a lower limit of 10, 15, or 20 °C to an upper limit of 420, 375, or 325 °C.

[0039] The tubular reactor 110 can have different residence times for various applications. The continuous back-mixed reactor 102 can have a residence time from 2 minutes to 72 hours. All individual values and subranges from 2 minutes to 72 hours are included; for example, the tubular reactor can have a residence time from a lower limit of 2, 5, 10, 30, 45, or 60 minutes to an upper limit of 72, 48, 24, or 12 hours.

[0040] The tubular reactor 110 can have different flow rates for various applications. The tubular reactor 110 can have a flow rate from 10 liters / minute (l / min) to 10,000 l / min. All individual values and subranges from 10 l / min to 10,000 l / min are included; for example, the tubular reactor can have a flow rate from a lower limit of 10, 100, or 1,000 l / min to an upper limit of 10,000, 8,000, or 5,000 l / min. The flow rate can be calculated as a quotient of a volume of the tubular reactor and a residence time of the tubular reactor.

[0041] The depolymerization system 100 can include a tubular reactor output 112. Embodiments of the present disclosure provide that the tubular reactor output 112 can be utilized to transfer contents of the tubular reactor to a downstream unit operation 114.

[0042] Embodiments provide that the tubular reactor output 112 can comprise a C1to C25hydrocarbon stream. The C1to C25hydrocarbon stream can be made by depolymerization of the polymer in the continuous back-mixed reactor 102 and the tubular reactor 110. In other words, the polymer that is input via polymer input 104 is broken down into smaller components in the continuous back-mixed reactor 102 and the tubular reactor 110 to make the C1to C25hydrocarbon stream.

[0043] One or more embodiments of the present disclosure provide that the C1to C25hydrocarbon stream contains from 35 wt% to 95 wt% of C10to C25hydrocarbons based upon a total weight of the C1to C25hydrocarbon stream. All individual values and subranges from 35 wt% to 95 wt% are included; for example, the C1to C25hydrocarbon stream can contain from a lower limit of 35, 40, or 45 wt% to an upper limit of 95, 85, or 75 wt% of C10to C25hydrocarbons based upon the total weight of the C1 to C25 hydrocarbon stream.

[0044] The tubular reactor output 112 can have a viscosity from 0.01 to 50,000 cP. All individual values and subranges from 0.01 to 50,000 cP are included; for example, the tubular reactor output can have viscosity from a lower limit of 0.01, 0.1, 0.5, 1, 5, or 10 cP to an upper limit of 50,000, 25,000, 10,000, 5,000, or 1,000 cP. One or more embodiments provide that the tubular reactor output has a viscosity from 10 to 1,000 cP. One or more embodiments provide that the tubular reactor output has a viscosity from 5 to 5,000 cP.

[0045] As mentioned, the tubular reactor output 112 can be utilized to transfer contents of the tubular reactor to a downstream unit operation 114. The downstream unit operation 114 can be a cracker, e.g., a steam cracker. Steam cracking is a well know process. Steam cracking can utilize heat, sometimes supplemented by high pressure and / or catalysts, to break hydrocarbon molecules, e.g., the tubular reactor output 112, down into lighter molecules. For a number of cracking applications, it is desirable to provide hydrocarbon streams comprising C25 hydrocarbons and / or smaller hydrocarbons, as hydrocarbons larger than C25hydrocarbon may introduce undesirable processing issues.

[0046] Figure 2 is a schematic diagram of a depolymerization system 200 utilizing a continuous back-mixed reactor 102 according to an embodiment of the present disclosure. The continuous back-mixed reactor 102 can be as described for Figure 1.

[0047] As shown in Figure 2, the depolymerization system 200 can include a continuous back-mixed reactor output 108. As previously mentioned, embodiments of the present disclosure provide that the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to a subsequent unit operation vessel. Various subsequent unit operation vessels may be utilized for different applications. For example, the subsequent unit operation vessel may be a reactor, e.g., a tubular reactor, a CSTR, a fixed bed reactor, a fluidized bed reactor, or the subsequent unit operation vessel may be a separator.

[0048] As shown in Figure 2, the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to separator 216. The continuous back-mixed reactor output 108 is a liquid. The continuous back-mixed reactor output 108 can include a combination of components obtained from depolymerization of the input polymer and depolymerization catalyst suspended therein.

[0049] One or more embodiments provide that separator 216 is a flash drum. The flash drum can be operated at various temperatures and pressures for different applications. The flash drum can provide that the contents of the flash drum, i.e., contents of the continuous back-mixed reactor 102 transferred to the separator 216, include a vapor phase and a liquid phase. In general, the vapor phase can include relatively lighter hydrocarbons, e.g., C1 to C25 hydrocarbons, and the liquid phase can include relatively heavier hydrocarbons, e.g., hydrocarbons greater than C25.

[0050] One or more embodiments of the present disclosure provide that the vapor phase of hydrocarbons in the separator 216 can contain from 35 wt% to 95 wt% of C10to C25hydrocarbons based upon a total weight of the vapor phase of hydrocarbons in the separator. All individual values and subranges from 35 wt% to 95 wt% are included; for example, vapor phase of hydrocarbons in the separator can contain from a lower limit of 35, 40, or 45 wt% to an upper limit of 95, 85, or 75 wt% of C10to C25hydrocarbons based upon the total weight of the vapor phase of hydrocarbons in the separator.

[0051] The depolymerization system 200 can include a vapor phase output 218. The vapor phase output 218 can be utilized to transfer the vapor phase contents of separator 216 to a downstream unit operation 114. As previously mentioned, the downstream unit operation 114 can be a cracker, e.g., a steam cracker. Steam cracking can utilize heat, sometimes supplemented by high pressure and / or catalysts, to break hydrocarbon molecules, e.g., the vapor phase contents of separator, down into lighter molecules.

[0052] The depolymerization system 200 can include a liquid phase output 220. The liquid phase output 220 can be utilized to transfer the liquid phase contents of separator 216 back to the continuous back-mixed reactor 102. As shown in Figure 2, a pump 224 can be utilized to transfer the liquid phase contents of separator 216 back to the continuous back-mixed reactor 102. In one or more embodiments, a fraction of the liquid phase output 220 can also be utilized to transfer the liquid phase contents of separator 216 to a downstream unit operation 114. As previously mentioned, the downstream unit operation 114 can be a cracker, e.g., a steam cracker.

[0053] Returning, e.g., recycling, the liquid phase contents of separator 216 back to the continuous back-mixed reactor 102 can help provide for a greater overall relative proportion of lighter hydrocarbons, e.g., C1to C25hydrocarbons, for depolymerization of the polymer, as compared to not utilizing the return of liquid phase contents of separator 216 back to the continuous back-mixed reactor 102. Returning the liquid phase contents of separator 216 back to the continuous back- mixed reactor 102 can be accomplished without utilizing additional solvent.

[0054] Figure 3 is a schematic diagram of a depolymerization system 300 utilizing a continuous back-mixed reactor 102 according to an embodiment of the present disclosure. The continuous back-mixed reactor 102 can be as described for Figure 1.

[0055] As shown in Figure 3, the depolymerization system 300 can include a continuous back-mixed reactor output 108. As previously mentioned, embodiments of the present disclosure provide that the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to a subsequent unit operation vessel. Various subsequent unit operation vessels may be utilized for different applications. For example, the subsequent unit operation vessel may be a reactor, e.g., a tubular reactor, a CSTR, a fixed bed reactor, a fluidized bed reactor, or the subsequent unit operation vessel may be a separator.

[0056] As shown in Figure 3, the continuous back-mixed reactor output 108 can be utilized to transfer contents of the continuous back-mixed reactor 102 to reactor 326. The reactor 326 is a continuous back-mixed reactor. The continuous back-mixed reactor output 108 is a liquid. The continuous back-mixed reactor output 108 can include a components obtained from depolymerization of the input polymer. Figure 3 illustrates that two continuous back-mixed reactors may be utilized in series.

[0057] The depolymerization system 300 can include a depolymerization catalyst filter 328. Catalyst filters are well known. The depolymerization catalyst filter328 can provide that depolymerization catalyst from the continuous back-mixed reactor 102 is not transferred to the reactor 326.

[0058] The reactor 326 can be various types of reactors for different applications. For example, the reactor 326 can be a back-mixed reactor, a fixed bed reactor, or a fluidized bed reactor. One or more embodiments provide that the reactor 326 is a CSTR.

[0059] The reactor 326 can include a second catalyst input 330. Different second catalysts may be utilized for various applications. The second catalyst can be a hydrogenation catalyst and / or a depolymerization catalyst. The second catalyst can comprise a zeolite. The second catalyst can comprise a metal. The metal can be a transition metal. One or more embodiments provide that the second catalyst comprises a transition metal from Groups 3-12. One or more embodiments provide that the second catalyst comprises Pt, Pd, Ni, Co, Fe, Mo, W, Ti, Cr, V, Zr, Ru, Hf, Sc, or a combination thereof. One or more embodiments provide that the second catalyst comprises Pt. The metal can be from 0.01 weight percent (wt %) to 30 wt % of the second catalyst based upon the total weight of the second catalyst.

[0060] The second catalyst can be a supported catalyst. One or more embodiments provide that the support can be a metal oxide. Examples of metal oxides include SrTiO3, TiO2, MgO, WO3, ZrO2, amorphous aluminosilicate, and modified zeolite. The second catalyst can be Pt on a metal oxide support, a Pt alloy catalyst, a NiMo catalyst, a CoMo catalyst, or a combination thereof. The support can include SiO2, Al2O3, AlPO4, ZrO2, SiO2, Al2O3, or combinations thereof. In one or more embodiments, the support may comprise microporosity (Zeolite structure). In one or more embodiments, the support may be amorphous.

[0061] The second catalyst can include a sulfided catalyst. An example of a sulfied catalyst is sulfided NiCoMo, among others.

[0062] One or more embodiments of the present disclosure provide that the second catalyst is different than the depolymerization catalyst, e.g., as discussed with Figure 1. In other words, one or embodiments of the present disclosure provide that the depolymerization system 300 utilizes two or more distinct catalysts, where one catalyst is utilized in the continuous back-mixed reactor 102 and another catalyst is utilized in the reactor 326. However, embodiments are not so limited.

[0063] Different amounts of second catalyst, e.g., different catalyst flow rates, can be input (continuously) to the to the reactor 326 for various applications. A weight ratio of second catalyst to hydrocarbons in the reactor 326 can be from 0.9:1 to 1:400, 1:100,000, or 1:3,000,000.

[0064] Contacting the contents of reactor 326 and the second catalyst in the reactor 326 can provide that contents of the reactor 326 are further depolymerized, as compared to the contents of the continuous back-mixed reactor 102.

[0065] The reactor 326 can include a return line 332. The return line 332 can be utilized to transfer a portion of the contents of the reactor 326 to the continuous back-mixed reactor 102. Various portions of the contents of the reactor 326 can be transferred to the continuous back-mixed reactor 102 for different applications. Transferring a portion of the contents of the reactor 326 to the continuous back- mixed reactor 102 can provide that hydrocarbons are contacted with both the depolymerization catalyst and the second catalyst multiple times during the depolymerization process.

[0066] The depolymerization system 300 can include a second catalyst filter 334. The second catalyst filter 334 can provide that second catalyst from the reactor 326 is not transferred to the continuous back-mixed reactor 102.

[0067] The depolymerization system 300 can include a reactor output 336. The reactor output 336 can be utilized to transfer a portion of the contents of the reactor 326 to a downstream unit operation 114. Various portions of the contents of the reactor 326 can be transferred to the downstream unit operation 114 for different applications. As previously mentioned, the downstream unit operation 114 can be a cracker, e.g., a steam cracker. Steam cracking can utilize heat, sometimes supplemented by high pressure and / or catalysts, to break hydrocarbon molecules, e.g., the a portion of the contents of reactor 326, down into lighter molecules.

[0068] Figure 4 is a data plot of hydrocarbon viscosity according to an embodiment of the present disclosure. The data plot of hydrocarbon viscosity is shown at four different temperatures for various conversion percentages. Aspen Plus V10 (obtained from Aspen Technology) was utilized to perform computations to obtain values for the data plot of Figure 4. For the computations, a continuous back- mixed reactor was utilized; the polymer was defined to have a uniformly distributed (all polymer had the same initial length) number average molecular weight of 100 kg / mol. The computations valued all bonds as being equally likely to break and provided that only normal paraffins were formed. The conversion percentages are defined as the weight fraction of the feed polymer existing with carbon number between 1 and 25. The pressure of the continuous back-mixed reactor was 20 bar. Data plot 440 corresponds to a temperature of 100 °C, data plot 442 corresponds to a temperature of 200 °C, data plot 444 corresponds to a temperature of 300 °C, and data plot 446 corresponds to a temperature of 400 °C.

[0069] As shown in Figure 4, the data plots for depolymerizations utilizing the continuous back-mixed reactor provide advantageous lower viscosities, while not utilizing a continuous feed depolymerization solvent.

[0070] Depolymerization was modeled using python for the reactor model and Aspen Plus V10 for the vapor liquid equilibria and viscosity predictions as follows. The model included a depolymerization chemistry utilizing a monodisperse linear polymer feed where all structural changes occurred according to the following kinetic expression: ^^՜^^^^^ି^^^^ ^^^ ^ ^ 1 ^^^ ^ ^ ^ െ 1

[0071] For the kinetic expression, Pxindicates a molar concentration of species of length “x.” The rate of this reaction was assumed to be the same for all species, and the specific value used to describe the chemistry depends on catalyst choice and process temperature. Reported conversions are defined as a weight fraction of material in the C1to C25range.

[0072] Selectivity and viscosity are reported as functions of reactor design choices, temperatures, and pressures. In these cases, the feed was a monodisperse linear polyolefin feed with a number average molecular weight of 100 kg / mole. It was assumed that reaction only occurred in the liquid phase, and thus temperature and pressure affect the selectivity through changes in the vapor liquid equilibria of the reaction mixture. Vapor-liquid equilibrium and liquid phase viscosity calculations for a specific reaction mixture composition were performed using the Aspen Plus V10 (obtained from Aspen Technology) with the PC-SAFT equation of state and Aspen default pure component and binary PC-SAFT parameters. The n-paraffinic components C1to C25were taken from the APV121 Aspen PLUS databank. The paraffinic components C25+were considered as lumps with a minimum of 25 and a maximum of 100 different components per lump depending on the carbon number. These lumped components were defined as oligomeric species in Aspen PLUS based on a polyethylene repeat unit.

[0073] Figure 5 illustrates the C1-C4and C5-C25product selectivities as functions of temperature at fixed residence time for the thermal pyrolysis of polyethylene in a tubular reactor. The points correspond to experimental results at 500 °C, 600 °C, 700 °C and 800 °C. This data was used to fit an Arrhenius rate expression for the chemistry discussed above. With this rate constant, the selectivities are calculable as a function of temperature, e.g., corresponding to the lines in Figure 5. The model reproduced the observed selectivities to support the above chemistry description for describing depolymerization.

[0074] Figure 6 illustrates molar vapor fraction vs carbon number according to an embodiment of the present disclosure. The molar vapor fraction is defined as the moles of a component in the vapor phase divided by the total number of moles of the same component in both liquid and vapor phases. This ratio depends on temperature, pressure, and reactor configuration, e.g., as discussed with Figure 4. Figure 6 illustrates molar vapor fraction vs carbon number for reaction mixture compositions in the back-mixed reactor corresponding to a conversion of 20%, 40%, 60%, 80% and 100% at a temperature of 200 °C and a pressure of 20 bara.

Claims

Claims What is claimed is:

1. A method for depolymerization utilizing a continuous back-mixed reactor, the method comprising: transferring polymer to a continuous back-mixed reactor; depolymerizing the polymer in the continuous back-mixed reactor; solvating contents of the continuous back-mixed reactor with depolymerized components of the polymer; and transferring contents of the continuous back-mixed reactor to a subsequent unit operation vessel.

2. The method of claim 1, wherein depolymerizing the polymer in the continuous back-mixed reactor includes contacting the polymer with a depolymerization catalyst in the continuous back-mixed reactor.

3. The method of claim 1, wherein the subsequent unit operation vessel is a reactor.

4. The method of claim 3, wherein the reactor is a tubular reactor.

5. The method of claim 3, wherein the reactor is a second continuous back- mixed reactor.

6. The method of claim 5, wherein the second continuous back-mixed reactor contains a second catalyst.

7. The method of claim 1, wherein the subsequent unit operation vessel is a separator.

8. The method of claim 7, further comprising transferring a liquid phase from the separator to the continuous back-mixed reactor.

9. The method of claim 8, further comprising transferring a vapor phase from the separator to a steam cracker.

10. The method of claim 1, further comprising transferring a C1to C25hydrocarbon stream from the subsequent unit operation vessel to a steam cracker.

11. The method of claim 1, wherein the method does not utilize a continuous feed depolymerization solvent.

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