Decomposition of halogenated plastics by microwave irradiation

Abstract

A method for processing a feedstock, the feedstock comprising halogenated polymer particles, the halogenated polymer particles having a polymer type with a first predetermined solubility parameter. The method includes pre-treating the feedstock by adding a solvent to the feedstock, the solvent having a second predetermined solubility parameter, the second predetermined solubility parameter substantially matching the first solubility parameter. After pre-treatment, the method further comprises irradiating the feedstock with microwaves using a microwave reactor.

Description

[Technical Field]

[0001] The present invention relates to the treatment of plastics, in particular to the depolymerization of halogenated plastics. Aspects of the present invention relate to the treatment of plastic raw materials, in particular to the pretreatment of plastic raw materials prior to microwave irradiation in a pyrolysis process. [Background technology]

[0002] Polyvinyl chloride (PVC) and other halogen-containing plastics have been produced and used worldwide for at least 50 years. Once these materials reach the end of their intended useful life, they can be mechanically recycled by molding them into new shapes and structures; however, there is a finite number of times mechanical recycling can be used before more permanent recycling or disposal solutions are needed. Chemical recycling is the process of converting waste plastics into their constituent chemical components so they can be used to manufacture new plastics and other chemical products. Alternatively, plastics can be disposed of in landfills or used as a fuel source for generating electricity in waste-to-energy facilities.

[0003] Chemical recycling and power generation both pose significant challenges for PVC and other halogen-containing plastics. Both processes require breaking the chemical bonds within the plastic, resulting in depolymerization, which creates smaller molecules that can be burned or recovered as chemical products. Temperatures of 250–500°C are typically required to break the bonds and achieve depolymerization of PVC. The depolymerization product is an acid-rich liquid stream that contains most of the chlorine from the original plastic, a hydrocarbon liquid fraction, a non-condensable gas fraction, and residual solids.

[0004] Conventional processing techniques for recycling PVC involve contacting granular or powdered plastic with a hot gas medium. Larger particles cannot be handled due to their inherently low thermal conductivity, so an additional shredding or crushing step is required to reduce the size of these larger particles to less than 10 mm. The hot gas must (i) be at a temperature higher than the temperature required for depolymerization (typically 500-600°C) to ensure sufficient heat transfer, and (ii) contain oxygen below the lower flammability limit of the flammable products (typically less than 2%). Heat is transferred from the gas to the plastic, providing the energy needed to heat the plastic and break its chemical bonds. The depolymerization products are produced in the form of vapor and converted to hot inert gases in the reactor. Because the typical boiling point of the acid-rich products is around 100-120°C, they remain in vapor form in the reactor and are transported into the hot gas medium along with the remaining solids. Separation of the remaining solids is performed before cooling and condensing the product to recover the liquid component. The presence of large amounts of hot acid creates a highly corrosive environment that is very difficult to handle in a robust manner using conventional cooling and condensing equipment. Acidic products are also difficult to handle in the high temperature regions of the process during primary depolymerization.

[0005] The residual solids have a high carbon content derived from the carbon skeleton of the PVC. They have a high surface area and contain components of the polymer that have not been depolymerized, as well as residual inorganic additives from the original polymer, such as pigments. The high temperature environment in which depolymerization occurs, combined with the presence of solid residues, further decomposes the hydrocarbon products, triggering side reactions that promote the formation of chlorinated hydrocarbons, thereby reducing their inherent value.

[0006] As a result, chemical recycling of PVC using conventional heating or combustion technologies is not currently practiced. Alternative technological approaches are required that maximize the quality of the resulting hydrocarbon phase while overcoming the inherent challenges of processing an acidic product.

[0007] Microwave heating is one method that can transfer energy to PVC while maintaining a cool environment during the depolymerization process. Previous approaches have attempted to utilize this technology, but found that microwave absorption levels within PVC were relatively low. As a result, additives were required to absorb the microwaves and transfer heat to the plastic in traditional ways. US Patent No. 5,387,321 uses carbonaceous materials for this purpose. US Patent No. 2013,016,5710 describes the use of photosensitizers to heat the plastic. WO Patent No. 2007,530,888 details the use of microwave-absorbing substances incorporated into the raw material. All of these innovations, and others like them, mean that the temperature of the environment surrounding the plastic is high, thus preventing the formation of high-quality hydrocarbon products that can be achieved in a cool environment.

[0008] Alternative approaches to overcoming the poor microwave absorption include using microwaves to generate plasma, as described in US20190284476, or an electric arc, as described in CN111097350. In both cases, the energy is transferred to the plastic by the high-temperature environment of the plasma or electric arc, not directly by the microwaves themselves. These approaches do not maintain a cool environment, resulting in a lower-quality product from the depolymerization process.

[0009] Other innovations have attempted to use microwave heating more directly, without the use of microwave-absorbing additives: JPH10185140 uses a microwave-heated moving bed and adds a dispersing medium to improve the flow of plastics and decomposition products through the reactor.

[0010] JPH0971683 describes a process that utilizes a mixed waste material containing pre-existing iron- and copper-based microwave-absorbing species, dispersing PVC-containing waste material in the air during processing. This document describes the use of multiple microwave sources to uniformly heat the chlorine-containing waste material. This results in a widely dispersed electric field within the reactor, resulting in low power density. In this case, the power density is too low to induce direct thermal decomposition of PVC without the unique microwave-absorbing additives taught in this application.

[0011] Processes that rely on moving beds or dispersed solids in a gas have three major drawbacks: (1) precise control of particle size is required for the process to function effectively; (2) the residence time of the plastic in the reactor cannot be precisely controlled, resulting in different levels of energy absorption and variable product quality; and (3) residual solids can become entrained in the product vapor, requiring additional separation stages in the system.

[0012] Several innovations have attempted "wet" processes. These processes utilize chemical reactions, rather than high temperatures, to break bonds and separate chlorine. For this purpose, glycolysis or acidolysis reactions are typically used at temperatures up to 200 °C. CN102127246 reports a wet process using microwave heating to separate heteroatoms, and JP4605602 reports a glycolysis process to remove halogen atoms from plastics. In both cases, the chlorine product must be separated from the reaction medium; hydrocarbon products are not present, as in thermal depolymerization processes.

[0013] WO0228609 describes adding a liquid to loosen scrap tire fragments before shearing to separate the rubber and metal. Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention was conceived against this background. [Means for solving the problem]

[0015] In one aspect of the invention, a method is provided for processing a feedstock, the feedstock comprising halogenated polymer particles, the halogenated polymer particles having a polymer type with a first predetermined solubility parameter.

[0016] The method includes pre-treating the feedstock by adding a solvent to the feedstock, the solvent having a second predetermined solubility parameter, the second predetermined solubility parameter substantially matching the first solubility parameter, and after pre-treatment, irradiating the feedstock with microwaves using a microwave reactor.

[0017] In another aspect, there is provided a method for pre-treating a plastic raw material to improve or enhance the ability of the plastic raw material to directly absorb microwave radiation before the plastic raw material is subjected to microwave pyrolysis.

[0018] The method may include adding a solvent to the feedstock.

[0019] The solvent can be added by spraying, pouring, mixing, or other suitable means that ensures contact between the ingredients and the solvent.

[0020] The solvent has a second predetermined solubility parameter that substantially matches the solubility parameter of the plastic raw material (i.e., the first predetermined solubility parameter). Preferably, the solvent has a solubility parameter that is within + / - 1.0 MPa of the solubility parameter of the plastic raw material. 0.5 In some cases, the solvent may have a solubility parameter value within + / - 5.0 MPa of the solubility parameter of the plastic raw material. 0.5 The solubility parameter may be within the range of

[0021] The solvent may include a swelling agent. The swelling agent may be liquid. The solvent may comprise 5 mass percent of the total feedstock sent to the microwave reactor for microwave pyrolysis. Preferably, the solvent added to the feedstock is present in an amount ranging from 0.1% to 20% per unit mass of the feedstock.

[0022] The plastic feedstock may include polyvinyl chloride (PVC). The feedstock particle size may be greater than 10 mm. The feedstock particle size may be less than 20 mm. The feedstock particle size may be less than 50 mm. The feedstock may be delivered to the microwave reactor by a batch process or a continuous process. The feedstock may be delivered to the microwave reactor by a conveying system.

[0023] Also provided is a method for recycling or depolymerizing plastic materials using microwave pyrolysis, which may include pre-treating the plastic feedstock as described in any of the paragraphs above.

[0024] The method may include delivering microwave radiation to a pretreated plastic feedstock in a microwave reactor, i.e., supplying power to the microwave reactor to irradiate the feedstock with microwaves. The method may include irradiating the pretreated plastic feedstock in the microwave reactor with microwaves in the absence of a dispersing medium that absorbs and delivers the microwave radiation to the plastic feedstock. Thus, the method may include using microwave radiation to directly heat the pretreated plastic feedstock.

[0025] The method can include delivering the pre-treated plastic feedstock to a microwave reactor via a conveying system, which can consist of an auger, a fixed conveyor, or a segmented conveyor.

[0026] The feedstock may be passed through an electromagnetic filter before entering the microwave reactor and / or after exiting the microwave reactor. The electromagnetic filter(s), if multiple, each provide an attenuation of about -60 dB. The electromagnetic filter(s), if multiple, each provide an attenuation of at least -40 dB, preferably at least -60 dB.

[0027] The microwave reactor is 6 -10 8 W / m 3 , more preferably 10 7 -10 8 W / m 3 can be controlled to produce a power density of

[0028] The method may further comprise extracting the gaseous products of depolymerization of the feedstock. The gaseous and vaporous products may be extracted using a sweep gas passed through the microwave reactor. The sweep gas may be inert.

[0029] The interior of the microwave reactor is maintained below 70°C, preferably below 50°C, during the microwave pyrolysis process. The temperature of the microwave reactor is maintained by a sweep gas. Performing the depolymerization process in a low-temperature environment overcomes a number of challenges: (1) The acidic products condense directly when discharged into the cold ambient environment and can be recovered without contact with heat exchange surfaces that can corrode. (2) The hydrocarbon products condense and solidify directly when discharged into the cold ambient environment, limiting further degradation and side reactions to form chlorinated hydrocarbons.

[0030] An apparatus for carrying out a microwave pyrolysis process on a plastic feedstock is provided, the apparatus comprising a microwave reactor for heating the plastic feedstock, and a conditioning or pre-treatment section for pre-treating the plastic feedstock before it is fed to the microwave reactor.

[0031] The plastic raw material may be mixed with a solvent in the preparation section. The solvent may have a solubility parameter that substantially matches the solubility parameter of the plastic raw material. Preferably, the solvent has a solubility parameter that is within + / - 1.0 MPa of the solubility parameter of the plastic raw material. 0.5 In some cases, the solvent may have a solubility parameter value within + / - 5.0 MPa of the solubility parameter of the plastic raw material. 0.5 The solubility parameter may be within the range of

[0032] The solvent may be selected from the group consisting of acetone, toluene, tetralin, dichloromethane, and methyl ethyl ketone.

[0033] Mixing the plastic raw materials with the solvent in the conditioning section allows for effective direct heating of the plastic by the subsequent microwave field, while maintaining a cool ambient environment for the plastic raw materials. This approach directly overcomes the limitations of prior art techniques that rely on the use of microwave-absorbing additives or dispersion of raw materials within a fluidized medium, allowing the microwave field to be used to indirectly heat the raw materials.

[0034] Further provided is a method for processing a plastic feedstock, the method comprising providing a feedstock comprising halogenated polymer particles, passing the feedstock to a microwave reactor, irradiating the feedstock in the reactor with microwave energy, and maintaining a temperature within the reactor below a predetermined temperature (70°C, more preferably 50°C). The method may include initiating pyrolysis of the feedstock by irradiating the feedstock in the microwave reactor with microwave energy. The method may include maintaining a temperature within the microwave reactor below a predetermined temperature (70°C, more preferably 50°C) during pyrolysis of the feedstock.

[0035] The method may include passing a sweep gas into the microwave reactor at a temperature below the predetermined temperature to assist in maintaining the microwave reactor below the predetermined temperature.

[0036] The particle size of the raw material can be greater than 10 mm. The particle size of the raw material can be less than 20 mm. The particle size of the raw material can be less than 50 mm.

[0037] The feedstock may have a polymer type having a first predetermined solubility parameter. The method may further include pretreating the feedstock by adding a solvent to the feedstock prior to irradiating the feedstock in the microwave reactor. The solvent has a second predetermined solubility parameter, the second predetermined solubility parameter substantially matching the first solubility parameter.

[0038] The second solubility parameter is + / - 5.0 MPa 0.5 The second solubility parameter may match the first solubility parameter within + / - 1.0 MPa. 0.5 The first solubility parameter may be met within a range of 0.1 to 1.0 sq. m.

[0039] The solvent added to the feedstock may account for more than 0.1% by mass of the feedstock. The solvent added to the feedstock may account for less than 20% by mass of the feedstock.

[0040] The processing method is to process the plastic raw material by at least 10 7 W / m 3 The material can be exposed to a high-intensity electric field that maintains an average power density of 10-50 seconds. The residence time of the material within the high-intensity electric field is precisely controlled and can be adjusted from 10 to 50 seconds. The high-intensity electric field and precise residence time control minimize overheating of the PVC and promote cool ambient temperatures of 50-70°C.

[0041] The inert gas is supplied at atmospheric temperature and can be used to entrain the acidic products produced in the microwave pyrolysis process and to directly condense and entrain the organic products.

[0042] Entrained products can be removed from the microwave reactor in a direct contact separator, which uses a circulating stream of cold water or weak hydrochloric acid solution to absorb the acid components of the product vapor and directly condense the organic products. Direct contact separators can use a secondary organic liquid, such as kerosene, in addition to the aqueous humor to aid in the absorption of the organic products and to displace polymeric wax products that can contaminate internal parts in the condenser.

[0043] The product from the direct contact condenser flows by gravity to the phase separator, where the organic product is removed from the top along with the organic liquid used in the direct contact separator, and the acidic product is removed at the bottom of the phase separator by water or an acidic solution added to the direct contact separator.

[0044] In another aspect, the invention relates to a product produced by the method of any of the preceding paragraphs, particularly an organic product produced by the method of any of the preceding paragraphs. [Brief explanation of the drawings]

[0045] In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which like features are assigned like reference numerals, in which: [Figure 1] FIG. 1 is a process flow diagram illustrating an exemplary apparatus according to the present invention. [Figure 2] FIG. 2 is a process flow diagram illustrating an alternative configuration of an apparatus according to the present invention. [Figure 3] FIG. 3 is a schematic diagram showing an alternative configuration of the device according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] Examples of the present invention include a dry process for the depolymerization of PVC using microwave heating to produce an acid-rich product and a liquid hydrocarbon product.

[0047] Figures 1 and 2 are process flow diagrams each showing an embodiment of a process according to the invention, also referred to as a depolymerization process. Figure 3 also shows an embodiment of a process according to the invention, namely a setup allowing batch depolymerization of PVC with added blowing agent. This setup may be a laboratory scale setup.

[0048] First, Figure 1 shows the depolymerization process (in this example, the PVC depolymerization process).

[0049] 1, a feedstock 12 to be processed, including waste plastic such as PVC, is added to a feedstock conditioning section 10 along with an expanding agent 14. The conditioned feedstock 16 is conveyed through an electromagnetic filter 22 to a microwave reactor 20, where microwave heating of the conditioned feedstock 16 occurs. Microwave reactor 20 is powered by a microwave power supply 26.

[0050] Depolymerization of conditioned feed 16 produces hydrocarbon product 34, aqueous / acid product 32, gas phase 56, and solid residue 52. Hydrocarbon product 34, aqueous / acid product 32, and gas phase 56 pass through direct contact separator 40, where hydrocarbon product 34 and aqueous / acid product 32 are condensed and removed. Coolant in the form of aqueous fluid 52 and hydrocarbon fluid 54 is used in direct contact separator 40 to condense hydrocarbon product 34 and aqueous / acid product 32.

[0051] Residual solid feedstock 52 that is not depolymerized in microwave reactor 20 is conveyed from microwave reactor 20 through a second electromagnetic filter 24 that provides an attenuation of -60 bB. The solid residue 52 is deposited in a cooling screw 53 and cooled before exiting the PVC depolymerization process.

[0052] The gas phase 56 passes through a recirculation fan 60 before re-entering the PVC depolymerization process at either end of the microwave reactor 20 via two electromagnetic filters 22, 24 or exiting the process as exhaust gas.

[0053] FIG. 2 illustrates a PVC depolymerization process according to another embodiment of the present invention.

[0054] The process feedstock 112 is comprised of waste plastics, such as PVC. The process feedstock 112 has particle sizes ranging from 1 mm to 50 mm, but typically has an average particle size of 20 mm. To determine the particle size distribution of the waste plastic feedstock 112 being processed, a sieve analysis using a sieve array with various sieve sizes can be performed on samples from each batch of waste plastic feedstock 112. In this example, the sieve analysis is performed using standard procedures: weighing a representative sample of the mixed waste plastic feedstock 112 to determine the total mass, placing the sample on the top sieve of a sieve array with decreasing mesh size, shaking the array thoroughly, weighing the portion of the sample retained on each sieve, and dividing the mass of the sample per sieve by the total mass to calculate the percentage of sample at each sieve size.

[0055] In some embodiments, a sieving step (not shown) is performed at the beginning of the process before conditioning the waste plastic feedstock 112 to control the particle size being processed. The sieving step may include an appropriately sized aggregate screening system for sieving the waste plastic feedstock 112. Preferably, the largest mesh of the screening system has a sieve size of 50 mm (2 inches). In other embodiments, the largest mesh may be configured with a different sieve size (e.g., 20 mm). Such processes known in the art can obtain granular waste plastic feedstock 112 of a known maximum particle size. Typically, waste plastic feedstock 112 is commercially available in granular form with a defined size.

[0056] The process of the present invention has the advantage of being able to process larger particle sizes of waste plastic feedstock 112 compared to conventional thermal recycling technologies, which typically require particle sizes less than 10 mm. Small particles are necessary when conventional heat transfer is the rate-limiting step in the process, as is the case with conventional thermal processing technologies. When particles less than 100 mm are heated with microwaves, energy transfer is instantaneous and there are no thermal conductivity limitations. As a result, there is no limitation on the particle size that can be heated due to thermal conductivity limitations, and the overall process system has the advantage that a size reduction step to precondition the waste plastic feedstock 112 is not required. Larger particles also facilitate separation of solid and liquid / vapor products, providing an additional benefit to the process system that does not require an intensive solid separation stage after the heating section.

[0057] 2, the PVC depolymerization process includes a feedstock conditioning section 110 in which waste plastic feedstock 112 is contacted with a blowing agent 114. In this embodiment, the feedstock conditioning section 110 includes a feed hopper (not shown) into which the waste plastic feedstock 112 is transferred in batches before contacting with the blowing agent 114. It will be appreciated that in other embodiments, other suitable equipment may be used for contacting the waste plastic feedstock 112 with the blowing agent 114. Those skilled in the art will appreciate that other suitable equipment and methods exist for contacting a liquid and a solid.

[0058] The adjustment of waste plastic raw material 112 is carried out within the Hildebrand solubility parameter of the plastic of waste plastic raw material 112 within + / - 1.0MPa. 0.5 The optimum liquid blowing agent 114 has a Hildebrand solubility parameter value within + / - 5.0 MPa of the plastic of the waste plastic raw material 112. 0.5Using a liquid swelling agent 114 with a Hildebrand solubility parameter that falls within the range of 1 / 2 of the Hildebrand solubility parameter will work effectively because materials with similar Hildebrand solubility parameters are more likely to be miscible and cause swelling of the plastic.

[0059] The Hildebrand solubility parameter of PVC is 19.5 MPa. 0.5 The waste plastic raw material 112 in the preparation section 110 is prepared using, for example, acetone (Hildebrand solubility parameter is 19.9 MPa 0.5 ) or toluene (Hildebrand solubility parameter is 18.3 Pa 0.5 A liquid swelling agent 114 in the form of a ketone such as dichloromethane (Hildebrand solubility parameter is 20.2 MPa) can be used. 0.5 ) and methyl ethyl ketone (MEK) (Hildebrand solubility parameter is 19.3 MPa) 0.5 ) is another example of a liquid blowing agent 114 that can be used with PVC. Other suitable liquid blowing agents 114 can also be used in the conditioning section 110. For example, other aromatic hydrocarbons, tetralin, or crude hydrocarbon products produced by depolymerization processes can be used. The liquid blowing agent 114 used in the conditioning section 110 is preferably at 100% concentration, undiluted.

[0060] The liquid blowing agent 114 typically accounts for 5% by weight (dry weight) of the total waste plastic feedstock 112 added to the microwave reactor 120 (i.e., 50 g of liquid blowing agent 114 is added for every 1 kg of waste plastic feedstock 112). A dosage of liquid blowing agent 114 below 0.1% by weight typically does not result in any improvement in microwave absorption behavior, while concentrations above 20% by weight do not provide any additional benefit and require more energy for processing.

[0061] Upon contact with the waste plastic feedstock 112, the liquid swelling agent 114 diffuses into the plastic. The polymer chains of the waste plastic in the feedstock 112 are pulled apart by the liquid swelling agent 114, causing the polymer matrix to expand. Thus, the use of the liquid swelling agent 114 promotes chain mobility and enhances the effectiveness of subsequent microwave heating of the waste plastic feedstock 112.

[0062] To adequately condition the waste plastic feedstock 112, the liquid blowing agent 114 may be allowed to contact the plastic for 15 seconds to 15 minutes before proceeding to the next stage of the PVC depolymerization process. Typically, 1 to 2 minutes of contact time between the waste plastic feedstock 112 and the liquid blowing agent 114 is sufficient before proceeding. In this example, the conditioning of the waste plastic feedstock 112 is performed at room temperature, although other temperatures can be used.

[0063] While known systems use microwave susceptors to improve microwave heating behavior, the process of the present invention allows for and improves the direct interaction of microwave energy with the polymer chains that make up the waste plastic of the feedstock 112. As explained above, the use of a blowing agent to condition the feedstock overcomes the limited polymer chain mobility, allowing for effective microwave heating.

[0064] Direct microwave heating maintains a consistent temperature profile within the plastic of the feedstock 112, helping to avoid hot spots. Hot spots form when there are significant temperature gradients within the plastic, which occurs when microwave-absorbing and microwave-transparent materials are placed adjacent to one another. The addition of microwave susceptors to the plastic results in hot spots, resulting in localized high temperatures that lead to poor control of the depolymerization process and significant degradation of the primary depolymerization product. Eliminating hot spots maintains the quality of the primary depolymerization product, which is achieved by distributing microwave energy throughout the entire volume of the plastic, rather than in a limited number of microwave-absorbing zones, according to the present invention. Therefore, conditioning the plastic feedstock 112 with a leavening agent prior to microwave heating promotes microwave absorption throughout the entire volume of the plastic, eliminating hot spots.

[0065] Continuing with reference to FIG. 2, once the waste plastic feedstock is conditioned in the conditioning section 110, the conditioned waste plastic feedstock 116 (hereafter referred to as conditioned feedstock 116) is transferred via a feed hopper (not shown) to a conveying system (not shown), which transports the conditioned feedstock 116 to a microwave reactor feed system (not shown). The conveying system can take the form of an auger, a fixed conveyor, or a segmented conveyor. The conveying system can be an off-the-shelf component, and numerous options are available, as detailed in Beneroso et al., Chemical Engineering Journal 316 (207) 481-498, "Microwave Pyrolysis of Biomass for Bio-Oil Production: A Scalable Processing Concept." According to Beneroso et al., suitable conveying options for processing PVC include linear conveyors, fixed rotary conveyors, and auger-based processes. The fixed linear conveyor system detailed in WO2017178793A1 is another example of a suitable transport system, and WO2015110797A3 details an alternative configuration of a suitable auger-based transport system.

[0066] Before entering the microwave reactor 120, the conveyor and conditioned feedstock 116 pass through an electromagnetic filter 122 that provides -60 dB of microwave attenuation. The electromagnetic filter 122 is designed based on the geometry of the microwave reactor 120 and conveyor using established electromagnetic principles. A separate -60 dB electromagnetic filter 124 for the solids stream exiting the microwave reactor 120 is located on the outlet side of the microwave reactor 120. The electromagnetic filters 122, 124 function as the inlet and outlet gates for the microwave reactor 120, allowing the conditioned feedstock 116 to enter and exit while preventing microwave leakage.

[0067] The microwave reactor feed system is capable of handling particle sizes ranging from 1 mm to 50 mm. The microwave reactor feed system delivers the conditioned feedstock 116 to the reactor section of the microwave reactor 120.

[0068] Depolymerization of the conditioned feedstock 116 occurs in the reactor section of the microwave reactor 120. Microwave heating occurs directly in the presence of an inert gas below 50° C., creating a cool ambient environment.

[0069] The reactor section of the microwave reactor 120 includes a microwave power supply 126 for microwaves that support a high intensity electric field, with a power density during the heating phase typically exceeding 10 7 W / m 3 More than 10 6 -10 8 W / m 3 The electric field strength in the microwave reactor 120 is controlled to uniformly heat the plastic. The electric field strength in the microwave reactor 120 is controlled to achieve a microwave power density that favors the formation of high-value organic products and minimizes side reactions that produce chlorinated hydrocarbons. To minimize side reactions and secondary decomposition and to minimize heat loss to the reactor that would otherwise compromise the cool surrounding environment, a microwave power density of 10 7 W / m 3 A power density (power / volume) value exceeding this is required.

[0070] The microwave power supply 126 has a cooling water supply 127 in the range of 18-25°C that removes excess heat and reflected power from the transformer.

[0071] The PVC depolymerization process in microwave reactor 120 is continuous and operates at 1-10 kg / h of conditioned feed 116 when using a microwave frequency of 2450 + / - 20 MHz, and 50-2000 kg / h of conditioned feed 116 when operating at 905 + / - 20 MHz.

[0072] The operating frequency of the microwave reactor 120 is 885-925 MHz in this embodiment, but may vary in other embodiments. For example, in some embodiments, the operating frequency is 2430-2470 MHz or 420-450 MHz. The reactor of the microwave reactor 120 can be sized according to the principles detailed in Robinson et al., Chemical Engineering Research and Design, 88 (2010) 46-154, "Scale-Up and Design of a Continuous Microwave Processing System for the Treatment of Oil-Contaminated Drill Cuttings," and the power density ranges specified above. Specifically, the iterative procedure outlined on page 149 of Robinson et al. illustrates a procedure that can be followed to achieve a high, uniform power density within a nuclear reactor, and Figures 8, 9, 10, and 14 show examples of the resulting electric field and power density distributions that may be achieved.

[0073] The residence time in the microwave reactor 120 is controlled by adjusting the conveyor speed and is typically 10 to 50 seconds. The absorbed energy is adjusted by varying the depth of the conditioned feedstock 116 on the conveyor and the applied power at a given conveying speed. When the liquid blowing agent concentration is greater than 20%, an energy input of greater than 3.5 kJ / g is required. Without the use of a liquid blowing agent 114, an energy input of 2 to 3 kJ / g is required to depolymerize all halogen-containing plastics in the waste plastic feedstock 112.

[0074] The amount of energy absorbed by the conditioned feedstock 116 can be adjusted by varying any of several factors, including, but not limited to, the power input, the flow rate of the conditioned feedstock 116, the volume in which the power is absorbed, the configuration of the delivery system, and the cross-sectional shape of the microwave reactor 120.

[0075] The speed of the conveying device controls the residence time of the conditioned feedstock 116 in the microwave reactor 120. The conditioned feedstock 116 cannot remain in the reactor longer or shorter than the conveyor allows. This is in contrast to fluidized bed or stirred tank reactors, which have an inherent residence time distribution. By precisely controlling the residence time, the exact amount of energy to the conditioned feedstock 116 can be adjusted to achieve depolymerization while minimizing side reactions. The energy delivered to the plastic in the conditioned feedstock 116 is a function of the microwave power and the flow rate of the plastic in the microwave reactor 120.

[0076] An inert sweep gas 118 is supplied to the microwave reactor 120 with an injection point located at the inlet of an electromagnetic filter 122. The temperature of the gas 118 is typically below 30° C. when injected into the microwave reactor 120, thereby maintaining the temperature in the headspace of the reaction zone region of the microwave reactor 120 below 50° C., i.e., a low temperature environment. In this embodiment, nitrogen is used as the sweep gas, although in other embodiments, other inert gases such as CO or argon may be used alone or in combination.

[0077] In this embodiment, the PVC depolymerization process is carried out at atmospheric pressure, although sub-atmospheric pressures (i.e., high vacuum environments) may be acceptable in other embodiments.

[0078] The depolymerization products (in the form of acidic products 132 and hydrocarbon (organic) products 134) are condensed directly in the low temperature environment of the microwave reactor 120, entrained in the inert sweep gas 118, and removed via the extraction manifold 130. The extraction manifold 130 is designed to allow precipitation of the condensed acidic products 132 and hydrocarbon products 134, which are sent to a phase separation vessel 140 rather than being returned to the microwave reactor 120.

[0079] Downstream of the manifold 130, the acidic products 132 and hydrocarbon products 134 are further cooled and condensed in a direct contact condenser 150, where they are directed through a phase separator 140. Within the condenser 150, two contact fluids are typically used as cooling media: water or a water / acid mixture (aqueous fluid) 152 to facilitate the removal of the acidic products 132 from the PVC pyrolysis, and an organic solvent (organic fluid) 154 to facilitate the removal of the organic pyrolysis (hydrocarbon) products 134. The recovered hydrocarbon products 134 and / or acidic products 132 can be used as cooling media for the direct contact condenser 150. Freshly supplied make-up aqueous and / or organic liquids can also be used as cooling media.

[0080] The acid product is produced in the same way as in conventional thermal technology, where the acid is produced in vapor form at a temperature of approximately 500 °C. In this state, the acid is highly corrosive, and subsequent cooling and condensation is extremely difficult, requiring metal heat transfer surfaces.

[0081] In the process of the present invention, the reactor environment temperature is maintained below 50°C, for example, and the acid condenses in the sweep gas when the boiling point of the acid product exceeds 100°C. Upon condensation, the acid forms small droplets that are entrained in the sweep gas and carried out of the reactor. The low temperature of the acid-containing sweep gas allows the use of structural materials to handle products that are not possible with conventional techniques. According to the present invention, a direct-contact cooling vessel can be placed immediately downstream of the reactor. The direct-contact cooling vessel can be made from glass-reinforced plastic or other polymer-lined vessels that are resistant to the acid product. The low-temperature environment made possible by the present invention therefore allows for safe handling of the acid in a manner not possible with conventional techniques.

[0082] The organic products are formed in the same manner as conventional thermal processes. In conventional processes, the organic products are generated in vapor form at temperatures of approximately 500°C. Under these conditions, the organic products are prone to secondary and tertiary decomposition reactions, potentially forming undesirable by-products such as chlorinated hydrocarbons, benzene, and carbon-rich chars. In the present invention, the organic products are generated at the reaction temperature, condensed and solidified in a cool ambient environment, and then entrained in a sweep gas. The low temperature and rapid condensation of the organic products prevent secondary reactions and preserve the basic chemical properties of the hydrocarbon products from the thermal decomposition process. The organic products resulting from the present process are enriched in naphthalene, which, upon purification, yields a stable solid product at room temperature. Naphthalene can be functionalized in subsequent reaction steps to produce, for example, naphthalene epoxides and naphthoquinones, providing a platform for the production of dyes, pesticides, and pharmaceuticals.

[0083] The liquid product from direct contact condenser 150 flows by gravity to phase separator 140, where hydrocarbon product 134, organic fluids 154, and recovered expansion agent 114 are removed from the top of separator 140 via a weir (not shown). Aqueous / acidic product 132 and aqueous fluids 152 are removed from the bottom of separator 140 via a standpipe (not shown).

[0084] After passing through a demister (not shown), the non-condensable gas 156 enters the recirculation system on the suction side of a recirculation fan 160, which returns the gas 156 to the process section. Figure 2 shows the gas 156 being recirculated to the conveying system after the second electromagnetic filter 124. However, it should be noted that the gas 156 may be recirculated at both ends of the conveying system, i.e., before the first electromagnetic filter 122 and after the second electromagnetic filter 124. The gas 156 may only be recirculated to the conveying system before the first electromagnetic filter 122.

[0085] The gas 156 is used to maintain both an inert atmosphere and a cool environment within the microwave reactor 120, while also acting as an entrainment medium to remove condensed droplets from the microwave reactor 120. The recycle system includes bleed points that allow the gas 156 to be diverted to a scrubber 170, flared, or used as combustion fuel. Refilling of the recycle gas 156 can be accomplished using compressed nitrogen from a cylinder bank (not shown).

[0086] Residual solid feedstock 128 that is not depolymerized within microwave reactor 120 is conveyed from microwave reactor 120 through a second electromagnetic filter 124 that provides an attenuation of −60 bB. The solid residue 128 passes through a discharge buffer 180 and enters a cooling screw (not shown) where it is cooled before exiting the PVC depolymerization process.

[0087] While Figures 1 and 2 show a continuous process for the depolymerization of PVC, Figure 3 shows a batch microwave process for the depolymerization of PVC in combination with a suitable blowing agent (i.e., "expanded PVC"). Suitable blowing agents are as described above with respect to Figure 2.

[0088] The system consists of a microwave generator 210 operating at a frequency of 2.45 GHz and delivering up to 6 kW of output power. A three-stub tuner 220 is used to tune the process to maximize the forward power absorbed by the expanded PVC 280 through impedance matching. The microwaves are transmitted to a single-mode microwave cavity 240 using a waveguide 230, preferably a rectangular waveguide in the form of a WR340 or WR430 waveguide. A chamber 270, which may take the shape of a quartz reactor tube, is placed within the cavity 240 and contains the pre-expanded PVC 280. A short-circuit tuner 260 is used to position the expanded PVC 280 within the peak electric field region within the single-mode microwave cavity 240. The reactor tube 270 is housed within an electromagnetic filter / choke 250 to contain the microwave field. The system is purged with nitrogen to maintain an inert environment. The depolymerization products from chamber 270 may be condensed and recovered using known condensation devices.

[0089] Similar to the processes in Figures 1 and 2, the apparatus detailed in Figure 3 allows microwaves to be used to directly heat expanded PVC 280 without the need for commonly used microwave absorbing additives such as carbon, metal oxides or silicon carbide.

[0090] Additional advantages of the present invention are:

[0091] The ability to accommodate a wide particle size range of feedstock. The conveying system can handle any shredded material, and particle size is not critical to the process function or conveying method. The microwave depolymerization process uses an electric field to directly heat plastics at the molecular level, making it independent of thermal conductivity. Unlike conventional heating, the microwave heating process does not require a large surface area for heat transfer, eliminating the need for small particle sizes as in conventional processes. The microwave depolymerization process allows for the use of larger particle sizes, eliminating the need for size reduction of the feedstock. Using larger particle sizes makes separation of solid char from the process product less demanding because the solids are not entrained in the gas stream as in conventional thermal depolymerization processes. As a result, the microwave depolymerization process makes the separation of solid residues simpler and less demanding. This, combined with the elimination of the size reduction step, means fewer key plant items are required for the microwave depolymerization process. This reduces the process footprint and capital and operating costs.

[0092] Direct condensation is promoted within the process, and condensate is removed in the reactor outlet manifold and direct contact condenser. This prevents condensate from re-entering the reactor and eliminates the need for trace heating of the reactor and manifold walls. Trace heating does not allow for the maintenance of a cool ambient environment, and the present invention overcomes this limitation.

[0093] The process described does not require an additional dispersion medium, which allows for the use of larger sized feedstocks and also allows the surrounding environment to remain cool.

[0094] The present invention does not require contact between hot gas and solids. Conventional heating techniques based on fluidized or entrained bed systems require hot inert gas to be supplied at a rate sufficient to fluidize or agitate the plastic, making gas-solid contact a key feature of the process. The present invention does not require gas-solid contact; the role of the gas is not to interact with the plastic itself, but to condense and capture released products.

[0095] The following variations of the above process are possible: Transportation method Condensate / liquid separation system Fluids used for direct condensation Control System Electromagnetic filter characteristics ·Residue cooling technology

Claims

1. 1. A method for treating a feedstock (112), the feedstock (112) comprising halogenated polymer particles, the halogenated polymer particles having a polymer type with a first predetermined solubility parameter; pre-treating the feedstock (112) by adding a solvent (114) to the feedstock (112), the solvent (114) having a second predetermined solubility parameter, the second predetermined solubility parameter substantially matching the first solubility parameter; After pretreatment, the raw material (112) is irradiated with microwaves using a microwave reactor (120).

2. 2. The method of claim 1, wherein the second solubility parameter is within a range of + / - 5.0 MPa. ０．５ wherein the first solubility parameter is within

3. 2. The method of claim 1, wherein the second solubility parameter is within a range of + / - 1.0 MPa. ０．５ wherein the first solubility parameter is within

4. 4. The method of claim 1, wherein the solvent (114) added to the feedstock (112) comprises more than 0.1% per unit mass of the feedstock (112).

5. 5. The method of claim 1, wherein the solvent (114) added to the feedstock (112) comprises less than 20% by mass of the feedstock.

6. 6. The method of any one of claims 1 to 5, wherein the solvent (114) is selected from the group consisting of acetone, toluene, tetralin, dichloromethane, and methyl ethyl ketone.

7. 7. The method of any one of claims 1 to 6, wherein the raw material (112) comprises polyvinyl chloride.

8. 8. The method of any one of claims 1 to 7, wherein the particle size of the raw material (112) is greater than 10 mm.

9. 9. The method of claim 8, wherein the particle size of the raw material (112) is less than 20 mm.

10. 9. The method of claim 8, wherein the particle size of the raw material (112) is less than 50 mm.

11. 11. The method of any one of claims 1 to 10, wherein the feedstock (112) is fed to the microwave reactor (120) by a batch process.

12. 11. The method of any one of claims 1 to 10, wherein the feedstock (112) is fed to the microwave reactor (120) in a continuous process.

13. 13. The method according to claim 11 or 12, wherein the raw material (112) is delivered to the microwave reactor (120) by a conveying system.

14. 14. The method according to any one of claims 11 to 13, wherein the feedstock (112) is fed to the microwave reactor (120) through an electromagnetic filter device (122) and / or is conveyed out of the microwave reactor (120) through an electromagnetic filter device (124).

15. A method according to claim 14, wherein the or each electromagnetic filter device (122, 124) provides an attenuation of at least -40 dB, preferably at least -60 dB.

16. 16. The method of any one of claims 1 to 15, wherein the feedstock (112) is pretreated in the absence of a dispersing medium that absorbs microwave radiation.

17. 17. The method of claim 1, wherein the microwave reactor (120) is ６ -10 ８ W / m ３ , preferably 10 ７ -10 ８ W / m ３ The method is controlled to produce a power density of

18. 18. The method of any one of claims 1 to 17, further comprising extracting gaseous products of depolymerization of the feedstock (112).

19. 20. The method of claim 18, wherein gaseous and vaporous products are extracted using a sweep gas (118) flowed through the microwave reactor (120).

20. 20. The method of claim 19, wherein the sweep gas (118) is inert.

21. 21. The method of any one of claims 1 to 20, comprising maintaining the interior of the microwave reactor (120) at a temperature below 70°C, preferably below 50°C, while the feedstock (112) is irradiated.

22. 22. The method of claim 21 when dependent on claim 19 or claim 20 when dependent on claim 21, wherein the temperature of the microwave reactor (120) is maintained by the sweep gas (118).

23. A method for treating plastic raw materials (112), comprising the steps of: Providing a feedstock (112) comprising halogenated polymer particles; sending said feedstock (112) to a microwave reactor (120); initiating pyrolysis of the feedstock (112) by exposing the feedstock (112) to microwave energy in the microwave reactor (120); maintaining the temperature in the microwave reactor (120) below a predetermined temperature of 70°C during pyrolysis of the feedstock (112); A method comprising:

24. 24. The method of claim 23, wherein the temperature is maintained below 50°C.

25. 25. The method of claim 23 or 24, further comprising passing a sweep gas (118) into the microwave reactor (120) at a temperature below the predetermined temperature to help maintain the microwave reactor (120) below the predetermined temperature.

26. 26. The method of any one of claims 23 to 25, wherein the particle size of the raw material (112) is greater than 10 mm.

27. 27. The method of claim 26, wherein the particle size of the raw material (112) is less than 20 mm.

28. 27. The method of claim 26, wherein the particle size of the raw material (112) is less than 50 mm.

29. 29. The method of any one of claims 23 to 28, comprising: the feedstock (112) has a polymer type with a first predetermined solubility parameter; The method further comprises pre-treating the feedstock (112) by adding a solvent (114) to the feedstock (112) prior to irradiating the feedstock (112) in the microwave reactor (120), the solvent (114) having a second predetermined solubility parameter; The method, wherein the second predetermined solubility parameter substantially matches the first solubility parameter.

30. 30. The method of claim 29, wherein the second solubility parameter is + / - 5.0 MPa. ０．５ wherein the first solubility parameter is within

31. 31. The method of claim 30, wherein the second solubility parameter is within a range of + / - 1.0 MPa. ０．５ wherein the first solubility parameter is within

32. 32. The method of any one of claims 29 to 31, wherein the solvent (114) added to the feedstock (112) accounts for more than 0.1% per unit mass of the feedstock (112).

33. 33. The method of any one of claims 29 to 32, wherein the solvent (114) added to the feedstock (112) accounts for less than 20% by mass of the feedstock (112).

34. 34. An organic product (134) produced by the method of any one of claims 1 to 33.

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