Pyrolysis reactor for the recovery of silica from polymer waste.

Abstract

A pyrolysis reactor is provided for recovering silica from silica-containing waste polymeric materials, particularly silica-containing rubber or plastic waste materials, using pyrolysis to separate the silica from at least one non-silica component of the waste polymeric materials. The waste material is fed into a pyrolysis chamber 1 where it is heated by microwave radiation to the decomposition temperature of at least one non-silica component of the waste material. The decomposition temperature is selected such that the at least one non-silica component has a higher microwave absorption rate than silica. Because silica does not absorb microwaves, heating with microwaves to remove the non-silica components, such as carbon materials, rubbers and volatile matter, leaves behind the structural and chemical integrity of the silica.

Description

[Technical field]

[0001] The present invention relates to a pyrolysis process and a pyrolysis reactor for recovering silica from silica-containing polymer waste. In particular, the present invention relates to the recovery of silica from silica-containing rubber or rubber compositions or silica-reinforced composites, especially from vehicle tires made with silica-containing rubber compounds. [Background technology]

[0002] Recycling of polymer waste, especially rubber and plastic waste, presents an environmental challenge since the volume of scrap from such materials is increasing every year. Polymer waste disposed of in landfills can remain in the environment for hundreds of years and contribute to environmental pollution. Incineration of the waste can release toxic emissions that require additional treatment. Thus, waste management of polymer waste is difficult and expensive.

[0003] For example, automobile tires are composite products of up to 14 different rubber compounds, textiles, and steel, which are made to be durable but are very difficult to recycle due to their complex structure. The most common rubbers used in tire manufacturing are natural rubber (NR), cis-polybutadiene rubber (CBR), isobutylene-isoprene copolymer rubber (i.e., butyl rubber (BR)), and styrene-butadiene copolymer rubber (SBR). These synthetic rubber compounds consist of cross-linked long-chain polymers with sulfur atoms, which chemically stabilize the elastomers, thereby limiting their degradability. In addition, the low density and elasticity of rubber makes it difficult to compress, making the material difficult to recycle and subsequently process. In addition to natural and synthetic rubber, the rubber portion of tires usually contains inorganic materials such as carbon black, plasticizers, lubricants, antioxidants, calcium carbonate, and silica, which makes sustainable waste management of used tires more complex. Furthermore, there are large differences in composition between different types of tires, for example, between passenger car tires (80% synthetic rubber, 20% natural rubber, mainly silica fillers in the tread compound) and truck tires (80% natural rubber, 20% synthetic rubber, mainly carbon black in the tread compound). Within one category of tires, further differences exist between manufacturers.

[0004] For example, the transformation of rubber waste is notoriously difficult to achieve in a way that (1) improves the efficiency and sustainability of solid waste management practices and systems, (2) recovers reusable and recyclable materials, and (3) recovers the transformation products and energy in the form of combustible biogas. When recycling waste rubber products, the valuable raw material should be maximally utilized while considering environmental sustainability. Recycling of secondary raw materials is an important resource-saving mechanism given the dwindling natural resources. In general, polymer waste forms an important source of raw materials for new production.

[0005] However, existing recycling solutions have proven to be either ineffective, energy intensive, or require significant investments in resources and infrastructure. For example, in the case of rubber, a grinding process is often used to create crumb rubber. Although seemingly simple, it is a very difficult process to determine the nature, magnitude and direction of the load, as well as to measure and quantify the consequences of the fracture. The multiple different types of elastic materials, increased temperatures, as well as the occurrence of shear resistance, can result in increased power consumption and severe wear and tear. The result is a low yield of marketable recycled material.

[0006] Cryogenic technology can reduce the energy consumption of product crushing and separation reinforcement elements for mechanical processing of rubber products and polymer waste materials in general. The main drawback of cryogenic processing methods is the high energy cost associated with the need to obtain sufficient amounts of cryogenic liquid gas and achieve and maintain low temperatures in the processing chamber. The large product size and low thermal conductivity of polymer waste materials lead to significant processing times. The cooling process as a whole and the supercooling of the outer layer of the material further significantly increase the total energy consumption while reducing the performance of the equipment. Therefore, in the overall life cycle assessment of polymer materials used in products and recycled at the end of their life, the sustainability requirements cannot be met in most cases with cryogenic recycling technology.

[0007] Another known recycling method is vulcanization, which is a chemical process for converting, for example, rubber or related polymers into a more durable material by the addition of sulfur or other equivalent curing agents or accelerators. At the same time, devulcanization is a process that reverses the polymer attributes of vulcanization. The process of regeneration is associated with significant amounts of harmful emissions. The regenerated polymer compound is composed of a gel fraction that maintains the thin network structure of the vulcanization and a sol fraction that contains relatively short segments of branched chains. Since the network structure is maintained in the regenerated vulcanization, the introduction of the regenerated polymer into the mixture to produce a new polymer material affects the strength properties of the new material. This leads to downcycling of the original material. In this respect, the regenerated material is rarely used in the same industry, which goes against the circular economy.

[0008] For example, common methods of recycling vehicle tires include crumbing the rubber, burning the tires in furnaces for tire-derived fuel (TDF), or pyrolysis to break the tires down into pyrolysis oil, carbon black, and steel used in tire manufacturing. Larger industrial tires, such as those used in earth-moving machinery, are difficult to recycle and are typically broken down into manageable sections before being recycled by any of the aforementioned processes. The equipment used to cut these tires undergoes significant wear.

[0009] Existing pyrolysis methods use maximum heat to decompose rubber at 310-540°C, which produces recovered carbon black (rCB) along with 7%-20% carbonaceous residue called char as an unwanted by-product of rubber pyrolysis. Recovered carbon black can be used, for example, as a substitute filler for virgin carbon black (vCB) in the tire manufacturing process. However, tire recycling companies struggle to produce enough recovered carbon black to reuse in tire manufacturing. Unfortunately, the presence of char reduces the performance of rCB in applications. Additionally, the volatiles produced by current pyrolysis methods are incorporated into a single condensate, which reduces the value of the feedstock.

[0010] Finally, a reverse depolymerization process is described, for example, in US9649613B2, where tires are continuously loaded into a microwave tunnel system equipped with a conveyor. The tunnel system is equipped with a number of small magnetrons, for example three magnetrons in a row of 35, each of 1.2 kW. The process is operated under a slight positive pressure to facilitate the movement of the pyrolysis gases. It is believed that the microwave energy breaks the weaker molecular bonds of the longer chain molecules, reducing them to simpler forms, which triggers the depolymerization process. Again, a holistic life cycle assessment of the recycled materials shows that in most cases such depolymerization processes are not energetically sustainable.

[0011] For example, approximately 1.5 billion metric tons of used tires are discarded worldwide each year. Global sustainability goals are driving tire manufacturers to create a circular economy. Summary of the Invention

[0012] The object of the present invention is to provide a pyrolysis method and a pyrolysis reactor for the pyrolysis of polymer waste, in particular rubber and plastic waste, which allows for sustainable polymer waste management and efficient recovery of reusable and recyclable materials, improving the environmental impact over the entire life cycle of polymer material products.

[0013] In particular, it is an object of the present invention to provide a pyrolysis method and a pyrolysis reactor for the efficient recovery of silica-containing rubber or plastic waste used in vehicle tires, which supports the circular economy model of tire manufacturing and supports the use of alternative fillers in recovered tire materials, such as recovered carbon black (rCB).

[0014] These and other objects that emerge from the following description are achieved by a pyrolysis method and a pyrolysis reactor as set forth in the attached independent claims. Preferred method details and embodiments are defined in the dependent claims.

[0015] The present invention provides a pyrolysis method and a pyrolysis reactor for recovering silica from silica-containing polymer waste, in particular from rubber or plastic waste containing silica, using pyrolysis to separate silica from at least one non-silica component of the polymer waste. The waste is fed into a pyrolysis chamber and heated by microwave radiation to the decomposition temperature of at least one non-silica component of the waste, resulting in an exothermic depolymerization reaction of the waste. The decomposition temperature is selected such that at least one non-silica component has a higher microwave absorption rate than silica at the selected temperature. Silica does not absorb microwaves, so the structural and chemical integrity of the silica remains when heated with microwaves to remove non-silica components such as carbon materials, rubber, and volatiles.

[0016] Thus, silica can be recovered from silica-containing rubber composites or silica-reinforced polymer composites by removing the carbon material, rubber, polymer and volatile matter, and the valuable volatile components can be extracted and captured.

[0017] For example, the decomposition temperature is selected from the range of 300°C to 900°C, and the carbonaceous component of the polymer waste has a high microwave absorption rate and the silica has a low microwave absorption rate. Therefore, the carbonaceous component can be recovered from the waste by decomposition, and the silica is separated from the carbonaceous component for further use.

[0018] In an advantageous variant of the pyrolysis method of the invention, an oxygenated environment and / or an inert environment and / or a negative pressure environment is applied to the pyrolysis chamber. Preferably, an inert environment and a negative pressure are applied to the pyrolysis chamber before an oxygenated environment is applied to the pyrolysis chamber.

[0019] Such an environment for recovering silica from the remaining solid residue by microwave heating and selecting the decomposition temperature as described above supports the oxidation and removal of carbonaceous materials from the waste material to obtain a silica-containing product.

[0020] The inert environment within the pyrolysis chamber does not interact with the polymer waste material during decomposition and supports the recovery of material components.

[0021] Applying negative pressure in the pyrolysis chamber allows for efficient removal or evacuation of pyrolysis gases. Evacuation of gases from the pyrolysis chamber is facilitated by pulling a partial vacuum on the off-gas line. Preferably, the negative pressure environment is less than 0.4 bar absolute, more preferably 0.1-0.3 bar. Carrying out the pyrolysis process according to the invention under negative pressure rapidly evacuates volatile components from the heated chamber or chamber zone, preventing secondary pyrolysis of volatile materials, which may cause deposition of carbonaceous residues (char) on the recovered carbon black, which was mixed into the tire during manufacture, and which helps to preserve the properties of the rCB for reuse. In addition, the negative pressure lowers the boiling point of the organic components, further preventing their secondary pyrolysis.

[0022] By applying an oxygenated environment, for example, the microwave heating process can become self-limiting, as microwave-absorbing carbon materials are oxidized. Thus, the microwave radiation for heating the waste material is selected such that the carbonaceous components of the waste material are subjected to a self-limiting process with respect to silica. This allows for the production of high-quality recovered silica that can be used as a filler in the production of tires and silica-containing rubber products, creating a circular economy in industries such as tire manufacturing.

[0023] Preferably, the microwave radiation for heating the waste material to its decomposition temperature has a power density of 30kW to 700kW per cubic meter of the pyrolysis chamber. More preferably, the microwave radiation has a power density of 100kW to 500kW per cubic meter to ensure the energy efficiency of the method and the pyrolysis of the material. In general, the microwave power selected for the pyrolysis process depends on the type of polymer waste material. For example, for tire rubber material, a power density of 50kW to 500kW per cubic meter is recommended.

[0024] In a further variant of the pyrolysis method according to the invention, the polymer waste material is subjected to successive pyrolysis by successively applying different target temperatures to the waste material, the different target temperatures corresponding to the target decomposition temperature of at least one individual non-silica component of the waste material.

[0025] This variant of the pyrolysis method focuses on the material recovery of polymer waste, in particular rubber waste, which contains several different material components, such as vehicle tyres.

[0026] The waste material is subjected to successive pyrolysis of different material components by successively applying different target temperatures corresponding to the target decomposition temperature of at least one of the plurality of individual material components. Since different material components may decompose at different temperatures, the target temperature is equal to the decomposition temperature of the particular component. Of course, two or more different components may have the same or very similar decomposition temperatures, resulting in the same target decomposition temperature for two or more different components.

[0027] Different target temperatures can be applied, for example, to successive heating steps or different heating zones of a pyrolysis reactor. In the case of successive pyrolysis, the temperature of each heating step or heating zone increases. Thus, in the course of successive pyrolysis, the target decomposition temperatures of each of the different material components of the waste material will be met. However, silica, due to its low microwave absorption, is not affected by microwave heating and remains intact.

[0028] The process according to the invention is based on the fact that during the decomposition of the different types of rubber present in the raw material, SBR decomposes mainly at high temperatures, natural rubber (NR) decomposes at low temperatures and BR can be decomposed at both high and low temperatures. Thus, during the first heating stage of the reaction at a first temperature, the main by-products formed are produced by decomposition of NR and BR, while the compounds formed during the second heating stage at a higher temperature than the first heating stage, mainly the liquid fraction, are produced by thermal decomposition of SBR and to a lesser extent BR.

[0029] During the continuous pyrolysis process, different volatile products resulting from the pyrolysis of one or more different material components at one target decomposition temperature can be extracted from the pyrolysis chamber. Thus, different volatile substances can be recovered separately from each other. In the case of successive heating steps, different volatile products can be extracted during each step. In the case of successive heating zones, different volatile products can be extracted at different locations of the pyrolysis reactor corresponding to the heating zones.

[0030] For example, according to one variation of a continuous cracking process for pyrolyzing rubber tires, primarily microwave power is used in a partial vacuum to rapidly heat the rubber to different temperatures at which depolymerization of the different rubber components (e.g., natural rubber, BR or SBR) mixed into the tire components begins. Sequential cracking of the individual rubber components at different target temperatures, along with extraction of volatile materials at different target temperatures, reduces the presence of carbonaceous residue (char) on the recovered carbon black (rCB) and allows for separation of the volatile fractions that are recovered.

[0031] The temperature of the pyrolysis reaction of the non-silica components is adjusted within a range that allows the polymer to decompose into volatile components, but is not so high that the functional properties of the silica are impaired by prolonged exposure to excessive temperatures. As previously mentioned, reaction temperatures of 300°C to 900°C are suitable for the pyrolysis process to occur. Temperatures below 650°C are suitable for the production of high quality recovered silica. The pyrolysis temperature is increased in stages and applied to the waste material, allowing the volatile components associated with each polymer in the waste material to be extracted, condensed, and separately collected. For passenger tires, preferred temperatures are, for example, first 300°C to 350°C, then 400°C to 450°C, and finally 500°C to 550°C.

[0032] Advantageously, an oxygenated environment is applied to the pyrolysis chamber at least at the highest target decomposition temperature of the continuous pyrolysis. Thus, recovering silica from the remaining solid residue comprises heating the solid residue with microwaves in an oxidizing atmosphere to oxidize and remove carbonaceous materials such as char or carbon black to obtain a silica-containing product.

[0033] Thus, preferably, the pyrolysis chamber includes subsequent heating zones, each heated to successively higher target decomposition temperatures, and an oxygenated environment is applied to the last zone of the pyrolysis chamber for complete oxidation and removal of the carbonaceous material.

[0034] Preferably, the pyrolysis process is controlled by a process control system that allows for precise differential heating of the components of the polymer waste material during successive different heating steps or during transport of the waste material through successive heating zones.

[0035] In one variation of the method for pyrolysis of polymer waste containing multiple different material components, the initial mass of silica and different non-silica components is determined before the decomposition begins. Alternatively or additionally, after pyrolysis of the different material components of the polymer waste, the ratio of products resulting from the pyrolysis of silica and different non-silica components is determined. The data of the mass of the initial components and / or the ratio of products is provided to a process control system to manage the pyrolysis process. Also, the temperature in the pyrolysis chamber can be monitored over time and / or in different zones in the chamber. For example, the power density of the microwave radiation and / or the residence time of the products resulting from the pyrolysis process are controlled according to the ratio of products resulting from the pyrolysis of the different material components and / or the temperature applied to the pyrolysis chamber.

[0036] In the pyrolysis method, the process of pyrolyzing the polymer waste material mainly uses microwave power to rapidly heat the non-silica components to a temperature at which decomposition begins. Subsequent heating to higher temperatures can be achieved by a combination of microwaves and further heating. Thus, the pyrolysis method can advantageously include a first heating step in which the waste material is heated to a first target decomposition temperature by microwave radiation as described above, and a second heating step, which is a subsequent step to heat the waste material to a second target temperature above said first decomposition temperature by microwave radiation in combination with an additional heat source. The additional heat source can be an electrically conductive heating means, an electric heating means or any other suitable heating means.

[0037] Advantageously, the last part of the volatile products obtained from the pyrolysis process is used as an additional heat source for conductively heating the waste material in the pyrolysis chamber. Thus, for example, the gases evaporated during the first heating step and the initial decomposition can be used for a second heating step.

[0038] The combination of microwaves and additional heat sources may improve the overall energy efficiency of the process. The temperatures used in the pyrolysis process vary depending on the type of polymer waste material.

[0039] For example, two subsequent heating steps serve to optimize the decomposition process of the different non-silica components of the polymer waste. In the range of low-temperature pyrolysis, gaseous organic compounds are extracted from the waste, for example by carbonization. For example, additives, oils and softeners are evaporated during the first pyrolysis. In the range of high-temperature pyrolysis, for example, natural rubber, styrene-butadiene rubber or polybutadiene rubber can be regenerated during successive decompositions.

[0040] The pyrolysis method may be carried out in a fast pyrolysis mode, where the volatile gases produced during pyrolysis are discharged from the pyrolysis reactor in less than 4 seconds, preferably less than 2 seconds. The minimum contact time of the pyrolysis gases with the high temperature environment in the reactor prevents further decomposition of the pyrolysis gases into solid compounds. This results in a large volatile yield compared to slow pyrolysis, where the carbon yield is higher. The use of the volumetric heating properties of microwave power allows the polymer waste, especially rubber, to be rapidly heated to the temperature range where the exothermic depolymerization reaction occurs. Also, in the case of silica, long exposure to high temperatures may be avoided.

[0041] In general, the functional properties of the silica recovered from silica-reinforced rubber or other polymer composites depend on the treatment temperature and duration; that is, higher treatment temperatures or longer exposure times result in reduced functional properties of the recovered silica. Thus, rapid treatment and precise control of process temperature are required, and the self-limiting nature of the microwave heating process is advantageous in achieving this.

[0042] The pyrolysis reactor of the present invention comprises a pyrolysis chamber for containing the waste material and at least one heat source for heating the waste material to the decomposition temperature of the waste material, the at least one heat source comprising a microwave radiation source. Advantageously, the pyrolysis chamber comprises an oxygen inlet and a gas outlet for applying an oxygenated environment to at least a zone of the pyrolysis chamber and extracting gas from the oxygenated environment. More advantageously, at least a zone of the pyrolysis chamber comprises an inert environment or a negative pressure environment. The zone may be a heating zone along the length of the chamber or a period within the decomposition process. When a zone is defined as a period of time, preferably, an inert environment or a negative pressure environment is applied before the oxygenated environment is applied to the pyrolysis chamber.

[0043] In one variation of the pyrolysis reactor according to the invention, the waste material is sent through the pyrolysis chamber in a continuous motion by a conveyor. Thus, the waste material can be transported along the length of the pyrolysis chamber through successive heating zones, each of which is heated to a successively higher target decomposition temperature. Furthermore, the pyrolysis gases of the waste material can be discharged from the pyrolysis chamber at intervals during the continuous motion of the waste material at different outlet ports in the pyrolysis chamber. The outlet ports can correspond to different heating zones. This allows for physical separation of different volatile non-silica products during the pyrolysis of the polymer waste material.

[0044] Furthermore, the pyrolysis reactor may provide different storage systems for the different volatile products obtained from the pyrolysis process. Each system may be connected to a different heating zone. In case of successive heating steps in the same space of the chamber, as in a batch reactor, the reactor outputs a switch between the different storage systems for each heating step.

[0045] Preferably, the pyrolysis reactor is equipped with a process control system as described above. The process control system may be connected to at least one temperature sensor in the pyrolysis chamber and / or a mass measuring device for determining the mass of different material components of the waste material. Thus, the process control system may control the continuous pyrolysis process of different material components by applying different target temperatures in succession in the pyrolysis chamber.

[0046] Furthermore, the speed of the waste material conveyor can also be controlled by the process control system. Advantageously, the conveyor is designed as a metering system with a mass measuring device for measuring the mass of the different material components of the waste material fed to the pyrolysis chamber. Data of the mass measuring device for controlling the pyrolysis process is also provided.

[0047] The reactor is sealed against the environment to prevent pyrolysis gases from escaping or oxygen from entering in an uncontrolled manner. The reactor may be purged, for example with nitrogen, prior to operation.

[0048] The pyrolysis chamber of the pyrolysis reactor may include an internal refractory lining made of a microwave transparent material. The refractory lining may contain the heat surrounding the polymer waste material being pyrolyzed. It may also distribute the microwave energy within the pyrolysis chamber to heat the product more uniformly. In an advantageous variant, the refractory lining extends only over a portion of the length of the pyrolysis chamber where the microwave radiation is introduced. The remaining portion of the pyrolysis chamber may have a double-walled construction, instead providing an additional heat source to the reactor wall.

[0049] The pyrolysis reactor may include at least one waveguide feed with a plurality of radiant outlets, which are preferably spaced apart from one another and diverged along the length of the pyrolysis chamber.

[0050] In the case of an elongated pyrolysis chamber of the pyrolysis reactor, a conveyor may be provided to feed the polymer waste material to and through the pyrolysis chamber. Thus, the polymer waste material and its compounds may be transported along the length of the pyrolysis chamber from one end to the opposite end of the chamber, respectively. Furthermore, the pyrolysis chamber may comprise several outlet ports spaced apart from one another along the length of the pyrolysis chamber to discharge the pyrolysis gases of the waste material at intervals at different outlet ports.

[0051] Alternatively, the pyrolysis reactor may comprise a pyrolysis chamber in the form of a batch reactor, where continuous pyrolysis is achieved by successive heating steps in the same chamber space. For recovering polymer waste from vehicle tires, the reactor may have a circular shape or a ring shape with a hollow center portion.

[0052] Preferred embodiments of the present invention are illustrated in the accompanying drawings, which may illustrate the principles of the present invention but do not limit the scope of the invention. [Brief description of the drawings]

[0053] [Figure 1] FIG. 1 is a schematic three-dimensional view of a first embodiment of a pyrolysis chamber and a pyrolysis reactor used in a pyrolysis method according to the present invention. [Figure 2a] FIG. 2 is a schematic diagram of a pyrolysis reactor configuration such as that described in FIG. 1. [Figure 2b] FIG. 2 is a further schematic diagram of a pyrolysis reactor configuration, such as that described in FIG. 1. [Diagram 3] Figure 3a is a schematic diagram of the pyrolysis chamber of a second embodiment of a pyrolysis reactor according to the invention, and Figure 3b is a schematic diagram of a condensation system according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Below, two embodiments of a pyrolysis reactor according to the invention are described, which are suitable for recovering silica from waste polymers containing silica, in particular waste rubber or plastics containing silica, using pyrolysis to separate the silica or silica products from at least one non-silica component of the waste polymers according to the invention.

[0055] In both embodiments, the pyrolysis reactor for the pyrolysis of polymer waste comprises a pyrolysis chamber 1 for containing the polymer waste and at least one heat source for heating the waste to a decomposition temperature of the non-silica components of the waste, the at least one heat source comprising a microwave radiation source.

[0056] The reactor embodiment shown is capable of sequential pyrolysis of polymer waste components using microwaves at partial vacuum or negative pressure, respectively. The process carried out by the reactor aims to recover non-silica components such as carbonaceous residues, polymer components and volatiles by pyrolyzing different components at different target decomposition temperatures and extracting the volatiles and other products obtained in the process at different stages of the reactor.

[0057] The described reactor embodiment may be used in particular for the pyrolysis of rubber waste, in particular used automobile tires, with the aim of complete recovery of reusable and recyclable materials. With regard to the composition of the fractions produced during the pyrolysis of vulcanized rubber, the composition of the different fractions is dominated by a mixture of aromatic, cyclic and aliphatic hydrocarbons. The main aliphatic and naphthenic compounds found in the liquid fraction of the pyrolysis of SBR are pentene, hexene, 4-ethenylcyclohexene and other C8 and C9 aliphatic compounds. In addition, 1,3-butadiene, the comonomer of SBR, is decomposed to produce reactive components such as 4-ethenylcyclohexene, which participate in secondary and tertiary reactions during pyrolysis. The amount of aliphatic compounds usually increases slowly with temperature. Thus, a similar proportion of aliphatic compounds can be obtained at different temperatures. In contrast, the amount of aromatic compounds increases significantly with increasing temperature. The main aromatic compounds in the liquid fraction are styrene, followed by ethylbenzene, benzene, toluene and xylene (BTX), and a lower proportion of methylstyrene. Benzothiazoles and thiophenes, used during rubber vulcanization, are also widely present in the liquid fraction. For the gas fraction, the main products are 1,3-butadiene, small percentages (less than 0.5%) of methane, carbon monoxide, carbon dioxide, hydrogen sulfide, methane, ethane, propene, and n-butane. The solid fraction, also called pyrolysis char, contains mainly carbon black that was mixed into the tire during manufacture, small percentages of carbonized rubber polymers, non-volatile hydrocarbons, and residual portions of rubber additives such as zinc, sulfur, clay, and silica.

[0058] Studies have shown that at low temperatures (e.g., 450°C), a large amount of carbonized rubber polymer is produced, regardless of the use of hydrogen during pyrolysis. Similarly, the solid fraction decreases with increasing temperature up to about 550°C. Further increases in temperature can increase the production of solids by about 4%. In contrast, higher temperatures have been shown to favor the production of liquid fractions. Only about 10% of the initial material yielded liquid fractions for pyrolysis carried out at an external temperature of about 450°C. On the other hand, the maximum amount of liquid fraction (about 37 wt%) was obtained at 550°C at a constant hydrogen flow rate. Pyrolysis carried out at 600°C, with or without hydrogen, resulted in a higher production of gas fractions and a decrease in the liquid fraction compared to samples obtained at 550°C. Studies using an inert atmosphere also reported an increase in the liquid fraction with temperature and a decrease or stabilization of the liquid yield at temperatures above 600°C.

[0059] The two embodiments differ mainly in the design of their pyrolysis chambers, while other features of the reactor and method steps are the same. Therefore, the description of the structural features of the reactor and the method steps suitable for both embodiments shall be considered interchangeable between the two embodiments. To enhance the clarity of the description, their repetition will be avoided.

[0060] For example, for both embodiments, it is advantageous to apply an inert or negative pressure environment to the pyrolysis chamber for recovery of non-silica components, and then apply an oxygenated environment to the pyrolysis chamber for recovery of silica. Also, in addition to the microwave radiation source, the pyrolysis reactor may include an electrically conductive heat source that serves as additional heating. Some of the volatile products generated during the pyrolysis of the polymer waste material, such as non-condensable gases, may be used to heat the walls of the pyrolysis chamber, assisting the pyrolysis process by conductive heating through the chamber walls. Alternatively, an electric heating element may also be used for this purpose. Similarly, other features and steps apply to both embodiments.

[0061] 1, 2a and 2b show an example of a pyrolysis chamber 1 of a pyrolysis reactor according to the invention. The reactor may be in the form of a continuous flow still of elongated design. For example, it may be equipped with a conveyor for feeding the polymer waste material into the pyrolysis chamber 1 and transporting the waste material and its decomposed compounds through the pyrolysis chamber 1.

[0062] For example, whole tires or tire pieces may be intermittently fed into the pyrolysis chamber 1 from a first end of the chamber. A first airlock system 9 with means for purging oxygen may be provided at the first end. Similarly, tire pieces may be fed into the still with a screw feeder.

[0063] Because the microwave energy directly heats most of the waste material, it is possible to obtain zones of product at different temperatures, each close together along the length of the reactor. This means that the reactor is effectively divided into several successive heating zones for recovering the waste material. The successive heating zones 10a-10c represent a variation of the reactor shown in Figures 2a and 2b.

[0064] This makes the system compact: the microwave power input can be instantly adjusted to adjust the temperature within a narrow temperature band, for example for optimal pyrolysis of each non-silica component in a rubber tire.

[0065] Pyrolysis gases are withdrawn at intervals along the length of the pyrolysis chamber 1 and successive gas outlet ports 2a-2c are provided at points of increasing product temperature with different gases collected corresponding to different components of the rubber. In the variant of Figures 2a and 2b, off-gases are collected from outlet ports 2a, 2b and 2c at three locations on the side of the chamber corresponding to three different product target temperatures. This allows for physical separation of the different volatility products via individual condensation systems 11a-11c associated with the outlet ports.

[0066] A multivariate process control system, such as a programmable logic controller (PLC), is used to control the pyrolysis process according to the invention. For example, the control system can measure the mass of product entering the reactor, for example through a metering system on an infeed conveyor, as well as the temperature of the pyrolysis chamber or heating zone and off-gas at various locations, and use this information to control the reactor and product temperatures and adjust microwave power to maximize production and minimize energy application.

[0067] Additionally, the mass flow rates of solid, liquid and gaseous pyrolysis products are measured using mass flow meters and load cells to determine the ratios of products obtained by the pyrolysis process. The PLC also monitors the temperature of the material, reaction vessel and volatiles exiting the reactor at the gas exit ports 2a-2c and at the various decomposition heating zones 10a-10c along the length of the reactor. Temperature sensors 19, for example in the form of thermocouples, are used. Online and offline analysis of the pyrolysis products may also be used to provide input to the control system. Based on the collected data, the process control system adjusts the application of microwave power to the reaction heating zones and the residence time of the material in the reactor. By adjusting the microwave power at the different heating zones of the reactor, the material is heated to predetermined temperatures corresponding to the target composition temperatures of the different material components, allowing these components to be decomposed in each heating zone and allowing the volatiles generated during the decomposition of that component to be collected in a dedicated condenser and storage system. In subsequent heating zones, the remaining material components are heated to successively higher target cracking temperatures, each time extracting volatile components associated with the different material components and collecting them in a separation condensation system 11. This successive cracking of the different material components allows the different hydrocarbons produced to be separated and collected, increasing the value of the produced hydrocarbon feedstock.

[0068] As shown in Figure 1, a slotted waveguide feed with multiple slots 3 extending along the length of the pyrolysis chamber 1 may be used to distribute microwave radiation along the length of the pyrolysis chamber 1. Microwave radiation may be introduced at various locations around the circumference and along the length of the chamber 1 to ensure uniform heating of the product. The slotted waveguide feed shown in Figure 1 is designed such that the slots 3 radiate a power profile where more energy is released in the zone where the initial heating stage occurs and less energy is released towards the end of the process where the material is substantially carbonized and high temperatures are maintained to ensure removal of the last traces of volatile material.

[0069] The pyrolysis chamber 1 may have an internal refractory lining 4 made from a microwave transparent material such as alumina or mullite to trap heat around the tires being pyrolyzed. It also allows the microwave energy to be distributed inside the refractory material along the periphery of the reactor for more uniform heating of the product.

[0070] The refractory lining may extend only over the portion of the length of the pyrolysis chamber where microwave power is introduced, while the remainder of the chamber may have a double-walled construction allowing for the circulation of a hot medium, such as gas or heated oil, to provide conventional heating of the reactor walls to support the process. These may be obtained, for example, by burning the non-condensable fraction of the collected volatile materials.

[0071] 2a and 2b show a variant of the pyrolysis reactor and pyrolysis method according to a first embodiment. At a first end of the pyrolysis chamber 1, silica-containing polymer waste material is introduced by a conveyor and transported along the length of the pyrolysis chamber 1.

[0072] In the course of continuous pyrolysis according to the pyrolysis method of the present invention, the pyrolysis chamber and the waste material are first heated by microwave radiation in the first heating zone 10a to a first target decomposition temperature of the first material component of the rubber, respectively, to cause an exothermic depolymerization reaction of the non-silica components of the waste material. The first target decomposition temperature may be, for example, about 350° C. The first volatile product may be discharged through the first outlet port 2a.

[0073] The residual non-silica components are then heated in a subsequent second heating zone 10b to a second target decomposition temperature higher than the first target decomposition temperature. The second target decomposition temperature may be, for example, about 450° C. The second heating zone may be heated by microwave radiation alone or by a combination of microwave radiation and an additional heat source. During the additional heating, the second volatile component may be exhausted through an outlet port 2b spaced from the outlet port 2a along the length of the chamber 1.

[0074] Thus, in a third successive heating zone 10c, a third higher target decomposition temperature may be applied and a third volatile product may be discharged through an outlet port 2c further away from the outlet port 2b along the length of the chamber. The third target decomposition temperature may be, for example, about 550°C.

[0075] Heating zones 10a-10c are separated by dashed lines for illustrative reasons, but the pyrolysis chamber 1 is designed as a continuous reactor, with subsequent heat zones merging into one another. Each heating zone has a heating port, preferably a microwave supply port 20, for heating each zone to a target decomposition temperature. Additionally, each heating zone may be equipped with a temperature sensor 19, e.g., a thermocouple, to monitor the temperature and provide temperature data to a process control system (not shown).

[0076] After passing through the outlet ports 2a-2c, each recovered volatile product enters a condensation system 11a-11c associated with the outlet port. In one embodiment, such a condensation system comprises a first condenser 13 connected to a first collection vessel 14. A vacuum pump 15 is connected to the first condenser 13 and the first collection vessel 14 and provides a negative pressure as described above. The first condenser 13 and the first collection vessel 14 thus define a low pressure side and a collection section. This section is connected to an ambient pressure section or a high pressure section comprising a second condenser 16 connected to a second collection vessel 17. Further components of the volatile products are condensed in the second condenser 16 and collected in the second collection vessel 17. A third collection vessel 18 collects non-condensable gases exiting the pyrolysis chamber 1.

[0077] Each heating zone 10a-10c connected to a condensation system 11a-11c comprises a first collection vessel 14, a second collection vessel 17 and a third collection vessel 1b, which together provide different storage systems for the different non-silica components that exit the pyrolysis chamber 1 at the outlet ports 2a-2c. The recovered components may be extracted from the vessels for further use or suitable disposal.

[0078] The pyrolysis reactors of Figures 1, 2a and 2b are designed with successive gas outlet ports 2a-2b coinciding with increasing decomposition temperatures so that different gases are collected and different volatile components can be physically separated via individual condensation systems 11a-11c. The solid products are discharged via a second airlock system 12 or a screw feeder.

[0079] Figure 2b shows a schematic diagram of a continuous flow microwave reactor for pyrolysis into tire pieces with a screw feeder. In this case, the pyrolysis gases are collected at three outlet ports 2a-2c on the side of the pyrolysis chamber 1, where the three outlet ports 2a-2c correspond to three different heating zones 10a-10c with different target decomposition temperatures. Preferentially, these temperatures are as described above.

[0080] Microwave power ensures uniform heating of the polymer waste material introduced by microwave feed ports 20 at various locations around the reactor and along the length of the reactor. A slotted waveguide feed extending along the length of the chamber can be used and designed such that the slots radiate a power profile where more energy is released during the initial heating stage and less energy is released towards the end of the process, with high temperatures maintained to ensure that the material is substantially carbonized and the last traces of volatile material are removed. The maximum product temperature is adjusted to a value that prevents thermal degradation of the silica product contained in the solid fraction in the reactor.

[0081] Instead of an internal refractory lining, the reactor may have a metal interior wall to contain the microwaves with a refractory barrier on the exterior surface to retain heat, and with an insulating and gas barrier window within the microwave feed port opening to retain heat and prevent pyrolysis gases from entering the microwave feed structure.

[0082] The application of microwave power can be adjusted instantly to adjust the target decomposition temperature within a narrow temperature band for optimal pyrolysis of each of the non-silica components in the waste material. To support the decomposition process, an inert or negative pressure environment can be applied within the three heating zones 10a-10c of the pyrolysis chamber 1.

[0083] Operating the pyrolysis process under a negative pressure environment or vacuum, respectively, rapidly evacuates the volatile components from the heated zone, prevents secondary pyrolysis of the volatile materials in the reactor, and yields high-value volatile gases that are condensed and collected as valuable hydrocarbon oils. Additionally, the negative pressure environment or vacuum lowers the boiling point of the organic components, further preventing their secondary pyrolysis. A negative pressure environment of less than 0.3 bar absolute is used, preferably 0.1-0.3 bar.

[0084] The first condenser 13 and first collection vessel 14 collect condensable hydrocarbons at reduced pressure, while the second condenser 16 and second collection vessel 17 after the vacuum pump 15 collect condensable hydrocarbons at ambient or positive pressure. The condensation system 11 can be cooled to ambient or lower temperatures using a suitable cooling medium to maximize condensation of volatile components. Non-condensable gases are collected in the third collection vessel.

[0085] At the end of the pyrolysis stage, the steel components are separated from the solid components containing carbon and silica. The silica-containing material is then exposed to microwave power in the final stage of the silica recovery process in a fourth heating zone 10d. This silica recovery heating zone 10d is provided with an oxygen inlet 21 and a gas outlet port 2d. Microwave energy is introduced through a microwave feed port 20 in the reactor wall. Preferably, insulation in the reactor wall is provided to limit heat loss. An oxidizing environment is introduced through an oxygen inlet 21 in the reactor wall to oxidize the carbonaceous material present in the oxidation stage of the pyrolysis process. The gas outlet port 2d is positioned to promote flow of the oxidizing medium through the bed of waste material. The movement of the material, combined with the flow of oxygen gas through the waste material, promotes exposure of the surface of the material for effective oxidation.

[0086] A multivariate process control system monitors the temperature of the waste material, e.g. vehicle tires, in the different cracking heating zones 10, as well as the temperature of the volatile materials leaving the chamber 1 at the gas outlet ports 2a-2c, and adjusts the application of microwave power to the cracking zones. By adjusting the microwave power in the different heating zones of the chamber, the tires are heated to a predetermined temperature, allowing the individual rubbers to be cracked in each zone and the volatile materials produced during the cracking of the rubbers to be collected in a dedicated condenser and storage system 11. In the subsequent heating zones, the residual tire material is heated to successively higher target temperatures, each time extracting the volatile components associated with the different rubbers and collecting them in a separate condensation system 11. This successive pyrolysis allows the different hydrocarbons produced to be separated and collected, increasing the value of the produced hydrocarbon feedstock. In the final oxidation stage in heating zone 10d, the microwave power is adjusted to limit the temperature of the carbonaceous material mixed with silica to the above-mentioned temperature range where the functional properties of the silica are not degraded. Finally, the solid product is discharged via a second airlock system 12 or by means of a screw feeder at the second end of the pyrolysis chamber 1.

[0087] FIG. 3 shows a schematic diagram of the pyrolysis chamber 1 of a second embodiment of a pyrolysis reactor according to the invention. The reactor has the form of a batch reactor, such as a pressure vessel that opens to accept a load of smaller tires. For example, the pyrolysis chamber 1 of the reactor may be circular and open at the top of the circular chamber. In the embodiment shown, the reactor loads a single large tire 7, such as that used by earth-moving machines. Microwave radiation is applied to the pyrolysis chamber 1 through a feed port 6 on the side of the chamber. The reactor may be provided with a pressure window 22 to allow the chamber to be operated in an inert environment, a negative pressure environment or under vacuum. An electrical element, or the combustion of some of the pyrolysis products, may provide heating of the chamber walls, assisting in the heating and preventing condensation in the vessel. The chamber may also be in the form of an annular section with a central part removed to reduce the unoccupied volume in the pyrolysis chamber 1.

[0088] In the batch reactor, for each different material component of the tire, the temperature of the waste material is raised to the target decomposition temperature in a heating step, and the volatiles collected and condensate collected in a dedicated reservoir for that component are switched into the condensate reservoir for each step of the continuous pyrolysis process. During the process, the reactor wall temperature is also raised in the heating step to prevent re-condensation of the volatiles in the reactor. A temperature sensor can be connected to the chamber 1 to record the temperature in the chamber.

[0089] At each heating step, volatile products are extracted from the pyrolysis chamber 1 through outlet ports 2a and 2b on the side, top and bottom walls of the chamber, allowing pyrolysis gases to be extracted and enter the condensation system 11 (see FIG. 3b). The condensation system 11 may, for example, condense the pyrolysis gases into pyrolysis oil. A raised metal mesh 8 may be attached to the bottom of the reactor, on which waste material is placed, allowing the pyrolysis gases to exit the chamber through the outlet port 2b in the bottom wall and at the same time preventing the waste material from clogging the gas exhaust port 2b.

[0090] The condensation system 11 may be designed in the same way as the condensation systems 11a-11c described in the first embodiment. Thus, the condensation system 11 may include a first condenser 13, a first collection vessel 14, a vacuum pump 15, a second condenser 16, a second collection vessel 17 and a third collection vessel 18. Although only one condensation system is shown in FIG. 3b, more such systems may be connected to the pyrolysis chamber 1 for different recovery products of different heating steps. As the process temperature increases to successive target temperatures at which each volatile substance is collected, the condensate may be collected in a vessel dedicated to that component, switching the condensate flow from one condensation system 11 to the next for each heating step of the successive pyrolysis processes.

[0091] A first condenser 13 and a first collection vessel 14 collect the condensable hydrocarbons under reduced pressure. A second condenser 16 and a second collection vessel 17 after a vacuum pump 15 collect the condensable hydrocarbons at ambient or positive pressure. Residual non-condensable gases are collected in a third collection vessel 18. Using a suitable cooling medium, the condensers may be cooled to ambient or low temperatures to maximize condensation of the volatile components.

[0092] The pyrolysis method and pyrolysis reactor according to the invention are based on the fact that each material component present in the polymer waste has different microwave absorption properties. The microwaves directly heat the organic compounds, sulfur and carbon black to different temperatures depending on the mix of materials present at the time. The sulfur can be heated and sublimated by the microwave energy, so that it can be evaporated from the material and removed with the pyrolysis gases at a later stage of the pyrolysis series. This results in a recycled carbon black product with a low ash content.

[0093] In contrast, the procedure for recovering silica from the remaining solid residue in a final heating step involves heating the solid residue with microwaves in an oxidizing atmosphere to oxidize and remove carbonaceous materials such as char or carbon black to obtain a silica-containing product. In the temperature range of interest, 300-900°C, the high microwave absorption of the carbonaceous components and the low microwave absorption of silica result in preferential microwave heating of the carbonaceous components relative to silica, advantageously resulting in a self-regulating process.

[0094] By carrying out the pyrolysis process in an inert environment, the vacuum formation of secondary volatile decomposition products (such as carbonaceous residues) in a negative pressure environment is limited, and high quality oil can be collected in a condenser. The temperatures selected for the successive heating steps can be, for example, about 350°C, 450°C, and 550°C for passenger car tires to recover the volatile components associated with natural rubber, butadiene rubber, and styrene butadiene rubber, respectively. To assist in the removal of pyrolysis gases, a carrier gas such as nitrogen can be introduced into the gas inlet port 21. Preferentially, the carrier gas is fed to the top of the chamber and the volatile components are extracted near the bottom of the chamber, setting up a laminar flow of gas that limits the time the volatile components are exposed to high temperatures and limits the formation of secondary pyrolysis products such as carbonaceous residues.

[0095] During the final heating step of the process, an oxidizing gas is introduced through gas inlet port 21 and the microwave power is adjusted to keep the carbon-silica mixture at the oxidation temperature until the carbonaceous solids are oxidized. Towards the end of the oxidation process, the reduction in the amount of microwave absorbing material present makes the process self-regulating.

[0096] Samples of silica recovered by the pyrolysis process according to the invention were sent to an accredited laboratory (Artis, UK) and rubber test samples prepared using the recovered silica as a reinforcing material were compared with samples reinforced with a commercial silica, Ultrasil U7000GR, commonly used to reinforce rubber in automobile tires.

[0097] The elemental analysis of the recovered silica is shown in the table below, which shows that the recovered silica has a high percentage of silica and low carbon content, proving the purity level of the recovered silica. Therefore, the higher modulus and lower energy loss could be very important to rubber compounders who use the recovered silica as a filler.

[0098] [Table 1] [Explanation of symbols]

[0099] 1 Pyrolysis chamber 2 Exit Port 3 Slots 4. Lining 5. Vibrating screen 6 Supply Port 7. Rubber Tires 8 Metal Mesh 9. First Airlock System 10 Heating Zones 11 Condensation System 12 Second Airlock System 13 First Condenser 14 First collection vessel 15 Vacuum Pump 16 Second Condenser 17 Second collection vessel 18 Third collection vessel 19 Temperature Sensor 20 Heating Port 21 Gas inlet port 22 Pressure window

Claims

1. A pyrolysis reactor for recovering silica from a waste polymer material containing silica using pyrolysis to separate silica from at least one non-silica component of the waste polymer material, the pyrolysis reactor comprising a pyrolysis chamber (1) for receiving the waste material and at least one heat source for heating the waste material to a decomposition temperature of the waste material, the at least one heat source comprising a microwave radiation source.

2. 2. The pyrolysis reactor of claim 1, wherein the pyrolysis chamber (1) comprises an oxygen inlet (21) and a gas outlet (2a) for applying an oxygenated environment to at least a zone of the pyrolysis chamber and extracting gas from the oxygenated environment.

3. 3. Pyrolysis reactor according to claim 1 or 2, wherein at least a zone of the pyrolysis chamber (1) is provided with an inert environment or a negative pressure environment.

4. 4. The pyrolysis reactor of claim 1, wherein the decomposition temperature is selected such that the at least one non-silica component has a higher microwave absorption coefficient than silica.

5. Pyrolysis reactor according to any one of claims 1 to 4, wherein an oxygenated environment and / or an inert or negative pressure environment is applied to the pyrolysis chamber (1).

6. 6. The pyrolysis reactor of claim 5, wherein an inert or negative pressure environment is applied to the pyrolysis chamber (1) before the oxygenated environment is applied to the pyrolysis chamber.

7. 7. The pyrolysis reactor according to any one of claims 1 to 6, wherein the polymer waste material is subjected to continuous pyrolysis by successively applying different target temperatures corresponding to a target decomposition temperature of at least one individual non-silica component of the waste material.

8. 8. The pyrolysis reactor of claim 7, wherein an oxygenated environment is applied within the pyrolysis chamber at a maximum target pyrolysis temperature of the continuous pyrolysis.

9. 9. The pyrolysis reactor of claim 1, wherein the target decomposition temperatures of the individual non-silica components are selected in the range of 300°C to 900°C.

10. A pyrolysis reactor according to any one of claims 1 to 9, wherein the decomposition temperature is selected such that carbonaceous non-silica components are oxidized within the pyrolysis chamber.

11. 11. The pyrolysis reactor of any one of claims 1 to 10, wherein the microwave radiation that heats the waste material to its decomposition temperature has a power density of 30kW to 700kW per cubic meter of the pyrolysis chamber.

12. 7. The pyrolysis reactor of claim 6, wherein the negative pressure environment is less than 0.4 bar.

13. 8. The pyrolysis reactor of claim 7, wherein different volatile products resulting from the pyrolysis of one or more different non-silica components of the waste material at one target decomposition temperature are extracted from the pyrolysis chamber.

14. 14. The pyrolysis reactor according to any one of claims 1 to 13, wherein the power density of the microwave radiation is controlled according to the ratio of products resulting from the pyrolysis of different material components and / or the temperature applied in the pyrolysis chamber.

15. A pyrolysis reactor according to any one of claims 1 to 14, wherein a fast pyrolysis process is used, defined as when the waste material is heated to its decomposition temperature by microwave radiation, volatile gases are produced in less than 4 seconds.

16. 16. Pyrolysis reactor according to any one of claims 1 to 15, wherein the pyrolysis chamber (1) comprises subsequent heating zones (10a, 10b, 10c), each heated to successively higher target decomposition temperatures, and an oxygenated environment is applied in the last zone of the pyrolysis chamber (1).

17. 17. The pyrolysis reactor of claim 16, wherein the waste material is conveyed through the subsequent heating zone (10a, 10b, 10c) by a conveyor.

18. Pyrolysis reactor according to any one of claims 1 to 17, wherein the waste material is transported through the pyrolysis chamber (1) in a continuous motion by a conveyor and pyrolysis gases of the waste material are discharged from the pyrolysis chamber at intervals during the continuous motion of the waste material at different outlet ports (2a, 2b, 2c) in the pyrolysis chamber (1).

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