Method for processing char derived from recycled plastics

Abstract

1. A process for recovering carbon contained in char (solid carbonaceous residue) obtained from the pyrolysis of mixed plastic waste or secondary raw materials that are the end product of recycling and / or processing of plastic waste, the process comprising the steps of: (A) heating the char in the presence of carbon dioxide in a gasification reactor to a predetermined temperature in the range of below 950°C and above 600°C (preferably not more than 850°C); (B) continuing heating the char in the presence of CO2 within said temperature range, preferably in the range of 750°C to 850°C, while holding it in the reactor for a predetermined residence time, to produce an outflow gas stream (effluent) comprising CO in addition to unreacted CO2 and optionally H2; and (C) sending at least a portion of the gas stream (effluent) leaving the reactor and comprising CO, unreacted CO2, and optionally H2 to at least one subsequent operational unit selected from a unit for separating CO from CO2, a unit for direct use of the outflow stream, or a storage unit.

Description

[Technical Field]

[0001] The present invention relates to a method for treating the "char" (solid carbonaceous residue) obtained by pyrolysis of mixed plastic waste (a mixture of two, three or more recycled plastics differing in chemical and / or physical and / or structural properties, such as density, branching or lack thereof, crystallinity, etc.) and maximizing material recovery from the pyrolysis process.

[0002] More particularly, the present invention relates to a method for treating char obtained from the pyrolysis and / or catalytic pyrolysis of mixed plastic waste or from the pyrolysis of mixed plastics as defined above with CO2, preferably recovered from the same pyrolysis process or from a process that produces it (other industrial / civilian cycle), in order to produce CO and, optionally, synthesis gas (a mixture mainly comprising CO, H2, CH4, with minor amounts of CO2).

[0003] More particularly, the present invention relates to a method for recovering carbon from "char" obtained from the pyrolysis of mixed plastics or mixed plastic waste as defined above, by producing CO and optionally synthesis gas, which is carried out at temperatures below 950°C and which provides high carbon recovery from the char, e.g. approaching 100% by weight, thereby improving material recovery from mixed plastic waste and / or mixed plastics as defined above. [Background technology]

[0004] As is well known, material recovery from mixed plastic waste that cannot be mechanically recycled is mainly achieved by two different chemical recycling methods, which are industrially applicable and allow the polymeric materials to be returned to their original state as monomers or precursors.

[0005] The first method involves the direct high temperature vaporization of this plastic waste using vaporizers such as water vapor (H2O), oxygen / air (O2 / air), carbon dioxide (CO2) etc. to produce synthesis gas (syngas).The second method involves the thermal decomposition and / or catalytic pyrolysis of said polymeric materials.

[0006] The choice of method for recycling plastics depends primarily on the main product to be obtained: in the case of direct gasification of plastics, the goal is to obtain synthesis gas for use in the Fischer-Tropsch reaction and other subsequent reactions, while in the case of thermal decomposition of plastics, the goal is to obtain hydrocarbon oils that can be sent to cracking processes to obtain materials that can ultimately be used to produce polymeric products.

[0007] Pyrolysis is the preferred recovery method for plastics recycling because it does not produce tar (a dark, viscous liquid) and is performed at lower temperatures (approximately 500–600 °C) than direct vaporization. Direct vaporization, on the other hand, is performed at temperatures above 600 °C and generally produces tar in the process of producing synthesis gas as the primary product. However, the pyrolysis process also produces a significant amount of marketable by-product, "char," which typically accounts for approximately 5% by weight of the hydrocarbon oil, but can reach up to 20%.

[0008] There are many factors that make this by-product difficult to control in the pyrolysis process. The physical state of char is a fine powder, which makes it difficult to handle. To facilitate handling in subsequent processes, the char powder must undergo compression and granulation processes, which are very often carried out using binders. Finely dispersed powders can also have ignitable / explosive properties under certain conditions.

[0009] Furthermore, char from mixed plastics is composed mainly of carbon and hydrogen, and of inorganic (ash) matter, the latter consisting of oxides and / or carbonates of various metals such as Ca, Na, K, Fe, Si, Al and others (e.g. titanium, zinc, chromium, manganese, copper, nickel).The composition of the carbonaceous fraction is highly unstable, due to the highly variable chemical composition of the mixed plastic waste used for pyrolysis and the fact that the pyrolysis process itself can be carried out in very different ways.

[0010] Thus, the chemical composition of the char obtained from the pyrolysis of mixed plastics is highly variable, limiting its use as a raw material. The primary applications include as an inert material in the production of activated carbon or as a catalyst support (including functionalized ones), due to the large specific surface area and pore volume, especially in the case of biochar (a by-product of the pyrolysis of biomass, e.g., lignite).

[0011] To the applicant's knowledge, the second most common recycling destination for char obtained from the pyrolysis of mixed plastics is the cement or steel industry, due both to its very diverse composition and to its high content of inorganic compounds (ash).

[0012] However, the above-mentioned uses are limited, and therefore most of the char obtained by pyrolysis of mixed plastics has very limited uses, and when the market becomes saturated and there are no takers, it will be managed as waste.

[0013] In all the above cases, the carbon content of the pyrolysis char represents a substantial loss of material in the process of recycling mixed plastic waste by pyrolysis, which results in a decrease in the final yield (i.e., the weight of hydrocarbon oils and gases produced as a percentage of the total weight of all products, including by-products such as char). This phenomenon is more pronounced the higher the carbon content in the char and the greater the amount of char produced in the pyrolysis process.

[0014] The applicant therefore aimed to find a means to overcome the above-mentioned problems, which are mainly related to the limited scope of treatment and recycling of the char obtained from the pyrolysis of mixed plastic waste, i.e. to recover the char, or a large part of it, produced by the pyrolysis of mixed plastics, while also recovering the CO2 (in whole or in part) produced in the pyrolysis process.

[0015] Applicant has now surprisingly discovered that by utilizing a reaction known as the "Boudouard Equilibrium" within a specific temperature range, it is possible to recover a significant portion of the char produced from the pyrolysis of mixed plastics or mixed plastic waste, thereby enabling the char to be used as a raw material despite variations in the composition of the mixed plastic waste and the char derived therefrom, thereby solving the aforementioned problems associated with the management and / or handling of the char.

[0016] The Boudouard equilibrium, or Boudouard reaction, is a disproportionation reaction between carbon dioxide, carbon monoxide, and carbon (e.g., graphite) that was studied by the French chemist Octave Leopold Boudouard in 1905 (2CO ←→ CO 2 + C). It is now known through literature that the Boudouard reaction can be carried out using specific chars, such as biochars, chars obtained by tire pyrolysis, or chars obtained from limited mixtures of individual plastics (maximum ternary mixtures). These do not suffer from the large compositional variations that occur with mixed plastic waste.

[0017] Below are some related prior art documents: The paper "CO2 Gasification Reactivity and Syngas Production of Greek Lignite Coal and Ex-Situ Produced Chars under Non-Isothermal and Isothermal Conditions," Energies 2022, 15, 679, presents a study on the conversion of Greek lignite coal to synthesis gas (syngas) containing CO, H2, CH4, and CO2. The pyrolysis of the lignite coal (Greek lignin) and its gasification in the presence of CO2 using biochar (biomass char) derived from the lignite coal were investigated at various temperatures. Pyrolysis was performed on the lignite coal to remove weakly bound functional groups in the lignin and obtain a solid fuel more suitable for gasification. Specifically, the paper outlines the syngas yields obtained from these pyrolysis materials (biochar) under various conditions at 300°C, 500°C, and 800°C compared to untreated lignite (unpyrolyzed). The material recovery (understood as reacted carbon) determined by thermogravimetric analysis varies between about 48% and about 84% by weight in the temperature range of 650°C to 920°C, depending on the type of biochar used. The paper does not provide or disclose any process description applicable to chars obtained from the pyrolysis of mixed plastics, since mixed plastics, due to their compositional characteristics, cannot be compared to the pyrolysis residues of lignite.

[0018] The ENEA report RSE / 2009 / 187 presents the results of thermogravimetric analyses carried out on several fossil coal samples. Their reactivity towards CO2 via the Boudouard reaction at temperatures of 900 °C, 1000 °C and 1100 °C is also evaluated. Therefore, the report does not specifically investigate the behavior of the pyrolysis residues (chars) of mixed plastic waste.

[0019] The paper "Waste-tire pyrolysis and gasification via the reverse Boudouard reaction: derivation of empirical kinetics from TGA data" - Thermochimica Acta 708 (2022) 179104, presents a kinetic study of tire pyrolysis and the resulting char gasification via the Boudouard reaction. Mass recoveries of approximately 85% were obtained above 900 °C, and approximately 70–75% at approximately 850 °C. However, when char obtained from tire pyrolysis is gasified via the Boudouard reaction, the resulting gas always contains toxic sulfur compounds due to the high sulfur content of the char, resulting in expensive subsequent gas purification operations. Therefore, industrial interest in recovering materials from char via this route is low. Even in this case, no process applicable to char obtained from the pyrolysis of mixed plastics has been described or disclosed.

[0020] The paper "CO2-assisted gasification of polyethylene terephthalate with focus on syngas evolution and solid yield" - Applied Energy 276 (2020) 115508 reports the results of a study on the direct gasification of PET using carbon dioxide, using only a single type of plastic. The article states that the absence of ash (present in mixed plastic waste char, albeit with variable composition) and high carbon content make PET-derived char a promising precursor for carbon materials. Therefore, this paper is concerned with the direct gasification of polymers, rather than the gasification of pyrolysis residues of mixed plastics, which have widely varying compositions and high ash contents.

[0021] The paper "A Critical Review of SCWG in the Context of Available Gasification Technologies for Plastic Waste" - Appl. Sci. 2020, 10, 6307 describes a process for direct vaporization of various materials using water under supercritical conditions, including plastic waste. Therefore, it does not describe CO2 vaporization of mixed plastic pyrolysis char. Furthermore, a challenge with direct vaporization of various plastic materials is the production of highly viscous tar and pitch, which contaminate the equipment and are difficult to recover.

[0022] The paper "Performance Prediction of Waste Polyethylene Gasification Using CO2 in a Bubbling Fluidized Bed: A Modeling Study" - Chem. Biochem. Eng. Q., 32 (3) 349-358 (2018) describes the results of simulating the gasification of pure polyethylene waste in a fluidized bed reactor using ASPEN PLUS software. The gasification was performed in the presence of CO2. This type of waste is completely different from the pyrolysis residue of mixed plastics, containing only polyethylene and no mixed plastics. In this direct gasification, all polyethylene is converted to syngas, and a new start is required to reach the polymer chain. Therefore, CO2 gasification of the pyrolysis char of mixed plastics is not described.

[0023] MV Gil et al., "Intrinsic char reactivity of plastic waste (PET) during CO2 gasification," Fuel Processing Technology, ELSEVIER BV, NL, vol. 91, no. 11, November 1, 2010, pp. 1776-1781, discloses the partial CO2 vaporization of inorganic-free PET pyrolysis residues at temperatures between 925°C and 1125°C. The purpose of this study was to investigate how the porosity of the sample affects the vaporization rate at that temperature; no studies have been conducted at lower temperatures on mixed plastic pyrolysis chars containing inorganic components.

[0024] WO2021 / 163110 discloses a method for the partial oxidation of plastic pyrolysis residues using an oxygen-enriched oxidizing agent, which may optionally contain CO2 as a carrier. The objective is to produce CO2 by partial oxidation using oxygen as a reactant. In partial oxidation, where CO2 is the primary product, the reaction should be carried out with an oxygen amount less than half the number of moles of carbon in the residue to maximize the conversion rate to CO2 and suppress CO2 production. When there are more than half the number of moles of oxygen in the residue, CO2 production begins and continues to increase until the number of moles of oxygen is equal to or greater than the number of moles of carbon, at which point CO2 production reaches its maximum and CO2 production is effectively zero (complete oxidation). Summary of the Invention [Problem to be solved by the invention]

[0025] The object of the present invention is to realize an industrially feasible process that allows the char obtained by pyrolysis of mixed plastic waste, which generally contains three or more types of plastics with different chemical and / or physical properties and structures (e.g., density, branching, crystallinity, etc.), to be recycled as a raw material, and / or at the same time allows the recovery of the carbonaceous material in the char, thereby enabling: - Eliminating the need for granulation and solidification of the char powder discharged from the pyrolysis plant, thereby simplifying the pyrolysis process and reducing costs; and / or - Recovering at least a significant portion of the carbon contained in the char by converting it into useful products for the production of raw materials from waste plastics again, thereby improving the overall material recovery rate of the pyrolysis process of mixed plastic waste from a circularity perspective; and / or - Further improving the overall material yield of the pyrolysis process of mixed plastic waste by using other by-products obtained in the pyrolysis process, such as potassium salts, CO2, etc., or increasing the circularity of the process by using materials obtained in other production steps (including civil uses).

[0026] Another object of the present invention is to identify and develop a process for treating char obtained from the pyrolysis of mixed plastic materials with CO2, which maximizes the conversion of carbon present in the char residue of said pyrolysis process, while allowing the recovery of the CO2 produced. This process is particularly useful when applied to mixed plastics pyrolysis plants, as it allows improving the plant's yield and reducing the amount of powder residue that has to be handled. [Means for solving the problem]

[0027] One or more of these objectives may be achieved by the suitable process described herein.

[0028] The applicant has indeed found a specific method for recycling char obtained from thermal and / or catalytic pyrolysis of mixed plastic waste, and also for recycling carbon dioxide produced by thermal and / or catalytic pyrolysis or CO2 produced by other industrial / civilian cycles, which achieves one or more of the above-mentioned objectives and makes it possible to solve the above-mentioned technical problems by reacting said char with CO2 in a specific temperature range to produce CO via the Boudouard reaction, as claimed in the present specification.

[0029] To the best of the applicant's knowledge, there is currently no known process for the pyrolysis of mixed plastic waste, in particular a mixture containing more than three types of plastics with different chemical and / or physical and structural properties (e.g. density, branching or non-branching, crystallinity, etc.), which maximizes the yield of the pyrolysis process by treating with CO2 to produce carbon monoxide (CO) in order to make the corresponding char valuable as a raw material, and avoids the loss of the raw materials contained in said char when used as a reducing agent or in industrial applications, or their disposal if they cannot be recycled.

[0030] It is therefore a first object of the present invention to provide a method for recovering the carbon contained in char (solid carbonaceous residue) from the thermal and / or catalytic pyrolysis of mixed plastic waste or secondary raw materials that are the end product of (and thus obtained from) plastic waste recycling and / or processes, or from char obtained from the pyrolysis of mixed plastics, through the production of CO and optionally synthesis gas, said method comprising the following steps: (A) heating the char in the presence of carbon dioxide in a gasification reactor to a prefixed temperature in the range of less than 950°C and greater than 600°C, preferably less than or equal to 900°C, more preferably less than or equal to 850°C; (B) continuing heating the char in the presence of CO within the temperature range, preferably between 750°C and 850°C, for a prefixed residence time of the char in the reactor to produce an outflow gas stream (effluent) comprising CO in addition to unreacted CO and optionally H; (C) sending at least a portion of the gas stream (effluent) leaving the reactor, comprising CO, unreacted CO, and optionally H, to at least one subsequent operational unit selected from a unit for separating CO from CO, a unit for direct use of the outflow stream, or a storage unit.

[0031] The mixed plastic waste from which the char used in the present invention is derived via pyrolysis comprises or consists essentially of a mixture of two, three, or even more than three recycled plastics that differ in chemical and / or physical and / or structural characteristics, such as density, presence of branching, crystallinity, etc.

[0032] Furthermore, the char derived from the pyrolysis of the above-mentioned plastic waste also generally contains inorganic materials (ash) formed by oxides and / or carbonates of various metals such as Ca, Na, K, Fe, Si, Al and others (e.g., titanium, zinc, chromium, manganese, copper, nickel).

[0033] In step (A), the predetermined temperature is generally the temperature at which CO production begins to be detected due to vaporization of char with CO2 as a vaporizing agent.

[0034] Advantageously, in step (B), the temperature is less than or equal to 850°C and greater than 600°C.

[0035] In a preferred embodiment, the char subjected to steps (A) and (B) of the method of the present invention is a char produced from a pyrolysis process of mixed plastic waste or secondary raw materials obtained from the recycling and / or processing of plastic waste.

[0036] In some embodiments, step (C) provides for sending only a portion of the effluent gas stream to at least one subsequent unit for separating CO from CO. In this case, it is further preferred that the remaining portion of the gas stream leaving the reactor is recycled within said gasification reactor, where it may be replenished with fresh make-up CO.

[0037] In step (A), CO2 in the vaporization reactor is the vaporization / vaporization agent and is the only or main reactant.

[0038] In step (A), the oxidation of the carbon contained in the char occurs with CO2 as reactant (reverse Boudouard reaction) according to the following reaction: C+CO2→2CO

[0039] The above reaction is completely different from the reaction C + 1 / 2O2 → CO (partial oxidation).

[0040] In step (A), the CO in the vaporization reactor may be a gaseous stream of pure CO, or may be a gaseous stream containing a predominant amount of CO compared to the total amount of other gases (hereinafter also referred to as carbon dioxide-based gases) that may be contained in the stream. If the gaseous stream containing a predominant amount of CO also contains gaseous oxygen, the amount of oxygen is 5% by volume or less relative to the total volume of the CO-containing gas, and is an amount such that the gaseous oxygen is considered, in any way, an impurity rather than a reactant.

[0041] In fact, oxygen is an undesirable but acceptable substance in the process of the present invention, present as an impurity like other substances, because the source of CO2 can be varied and because removing oxygen and other impurities to obtain a CO2 stream with negligible (or insignificant, e.g., less than 0.1% by volume) oxygen levels would be costly in the process.

[0042] The CO2-based gas or CO2-based gas stream is preferably gases containing mainly CO2, for example technical grade CO2, or gases containing mainly CO2 in an amount of 80-90% by volume and containing negligible or small amounts, for example less than 1% by volume, of other gases, such as O2, N2, etc., as impurities; A gas containing primarily CO2 (e.g., about 50% to 70% by volume), with the remainder being CO; Recycled CO2 and recycled gases containing CO (e.g., recycling of gases leaving the vaporization reactor); CO2 or CO2 stream obtained from a pyrolysis unit after separation of CO2 from other gases You can choose from;

[0043] In a preferred embodiment, impure CO is used in step (A), i.e., in a gas stream containing a predominance of CO relative to other gases, such as CO gas as defined above, or a gas stream containing CO as the main component, but free of N and / or O and / or other gases other than CO and CO. Optionally, the gas stream may also contain CO in a smaller amount than CO.

[0044] In step (A), the heating of the char comprises: In the reactor -Suitably preheated pure / substantially pure CO2, or -Properly preheated CO2 gas To supply externally heating the reactor; Use a combination of the above two modes (external heating of the reactor and heated gas supply), or Other methods as described below This may be accomplished by heating the reactor by

[0045] In step (B), heating may be continued by directly heating the reactor surface containing the char, by contacting the char with a hot stream of CO2-based gas and then feeding it to the reactor, by using a combination of the two, or by other methods as described below.

[0046] In step (B), the CO2 present in the reactor is Fresh CO2 flow (replenishment CO2), present in a gas stream that contains a large amount of CO2 relative to other gases (also referred to herein as a CO2-based gas stream); or The flow formed by their combination may be.

[0047] Such a CO2-based gas stream used in step (B) may be, for example, a portion of the gas stream (effluent) leaving the gasification reactor containing unreacted CO2 and CO (hereinafter also referred to as recycle stream); a CO2 stream obtained from a pyrolysis unit after fractionation of CO2 from other gases.

[0048] In a preferred embodiment, in step (B), the CO in the vaporization reactor is included in a recycle stream of a portion of the gas exiting said vaporization reactor, optionally combined with fresh make-up CO. In this case, step (C) preferably further comprises subjecting the non-recycled portion of the gas exiting the reactor to a separation step for separating CO and optionally H from a residual gas product comprising unreacted CO present in said non-recycled portion of the gas exiting the reactor.

[0049] In a preferred embodiment, the process for recovering carbon from char (solid carbonaceous residue) resulting from thermal and / or catalytic pyrolysis of mixed plastic waste or secondary raw materials obtained from recycling and / or processing of plastic waste, or char from pyrolysis of mixed plastics, through the production of CO and optionally synthesis gas, comprises the following steps: (A) heating the char in a gasification reactor and in the presence of carbon dioxide to a prefixed temperature comprised between 600°C and 850°C, wherein the temperature is the temperature at which CO production begins to be detected; (B) continuing heating the char in the presence of CO within the temperature range, preferably in the range of 750°C to 850°C, for a prefixed residence time of the char in the reactor to produce an outflow gas stream (effluent) comprising CO in addition to unreacted CO and optionally H; and (C) sending at least a portion of the gas stream (effluent) leaving the reactor, comprising CO, unreacted CO, and possibly H, to at least one subsequent operational unit for separating CO from CO, and recycling another portion of the effluent comprising CO and CO (not the recycled portion), optionally combined with fresh make-up CO, into the reactor.

[0050] The preferred embodiment described above, in which a portion of the exhaust gas from the reactor containing CO and CO2 is recycled and the non-recycled exhaust gas is sent to the separator, has the following advantages: less gas needs to be sent to the separator to separate the CO and CO2, and also savings can be made in heating, since the char is heated by the gas stream entering the reactor.

[0051] Thus, the end product of the process for treating char obtained from the pyrolysis of mixed plastic waste, after separation of CO2 from CO, is: A gas consisting mainly of carbon monoxide and optionally H2, and Inorganic compounds (hereinafter also referred to as inerts or ash) present in mixed plastic waste and / or added during the pyrolysis process. These are usually solid residues consisting of carbonates and / or metal oxides.

[0052] Metals that may be present in the solid residue (due to their initial presence in the char) include, for example, Ca, Ti, Na, K, Al, Si, and / or others such as zinc, chromium, manganese, copper, nickel, and combinations thereof.

[0053] The final gas obtained in step (C), after separation of CO from CO2, consisting mainly of CO and optionally also containing H2, can be stored for further use or sent directly to a plant or Fischer-Tropsch synthesis-based process to produce other chemicals such as methanol.

[0054] Thus, using the process subject matter of the present application, it is possible to recover a large portion of the mass of char obtained from pyrolysis, regardless of the variability in the chemical composition of the char and / or the high or low ash content in said char, indicating that ash content does not adversely affect carbon recovery.

[0055] In the process subject of the present invention, it is also possible to recycle as raw material the carbon dioxide obtained from the upstream pyrolysis process (or other process) from which the char originates, eliminating the processing operations (granulation or pelletization) of the char leaving the pyrolysis plant.

[0056] According to the present invention, the singular indefinite article "one" is intended to also include the meaning "at least one" unless otherwise specified.

[0057] In this application, percentages are to be understood as percentages by mass, unless otherwise specified.

[0058] According to the present invention, the term "char" generally refers to any solid residue resulting from the pyrolysis of mixed plastic waste or SRM "secondary raw material", not only in powder form, but also from the recycling and / or processing of plastic waste of any nature and / or composition as defined below.

[0059] As mentioned above, the char obtained from the pyrolysis of mixed plastic waste is mainly composed of a portion composed of carbon and hydrogen, a portion composed to a lesser extent of oxygen, nitrogen and traces of sulfur, and an inorganic portion composed of oxides and / or carbonates and oxides of various metals such as Ca, Na, K, Fe, Si, Al and / or other metals such as titanium, zinc, chromium, manganese, copper, nickel, etc., with a content of inorganic compounds (ash) that can reach a composition of up to 70% by weight.

[0060] The typical composition of char obtained from the pyrolysis of plastic waste may contain only about 30 wt% carbon, whereas the carbon content measured by CHNS analysis is usually between 40 and 70 wt%.

[0061] In the present invention, the term "mixed plastic waste" refers to the overall mixed plastic waste resulting from the sorting of general plastic waste, the mechanical recycling of packaging and / or plastic parts of electrical and electronic equipment, as well as plastic material from the industrial post-consumer and automotive sectors, all of which are characterized by a high degree of structural heterogeneity and a significant variation in chemical composition, both in terms of the type of polymer and the type of inorganic and organic additives (which form char ash).

[0062] According to the present invention, the term "secondary raw materials (SRM)" means materials consisting of plastic processing scrap / waste or materials originating from the recovery and recycling of plastic material waste.

[0063] Preferably, the characteristics of said secondary raw materials are those defined in Italian standard UNI 10667-18.

[0064] Generally, mixed plastics, such as those found in secondary raw materials and mixed plastic waste, may also contain non-plastic materials such as paper (cellulose), but in amounts much less than the total plastic content. The maximum cellulose (paper) content may be, for example, 12% by weight relative to the total weight of the plastic mixture.

[0065] Obviously, the above definition does not include the tire plastics used, and therefore the char obtained from pyrolysis used in the present invention is not a char obtained from tire pyrolysis, which, as mentioned above, has a high sulfur content and can lead to the formation of toxic sulfur compounds when vaporized at the temperatures envisaged in the process of the present invention.

[0066] The vaporization reactor used in the process of the present invention comprises, or preferably consists of, a horizontal cylinder, although this is not intended to be a limitation of the present invention and other reactor configurations may be provided, such as a vertically oriented fluidized bed cylinder.

[0067] The gasification reactor is then generally equipped with agitation / mixing means and / or a fluidization system, such as a fluidized bed, to facilitate contact of all solids (char) with the carbon dioxide.

[0068] In particular, the vaporization reactor can be any fluidized bed reactor.

[0069] In a preferred embodiment, the gasification reactor includes a screw therein as an agitation / mixing means, which also allows the char to advance / move along the gasification reactor during a continuous process.

[0070] The heating temperature of the char in the gasification reactor in steps (A) and / or (B) may advantageously be comprised between 700°C and 950°C, more preferably between 700-750°C and 900°C, and even more preferably between 700-750°C and 850°C.

[0071] The CO2 or CO2-based gas is preferably heated before being fed to the reactor. Upon entering the reactor, the CO2 and / or CO2-based gas may be at a temperature between 600°C and 950°C, inclusive, preferably between 700°C and 950°C, more preferably between 700-750°C and 900°C, and preferably between 700-750°C and 850°C, inclusive.

[0072] The heating to which the char is subjected in the gasification reactor in steps (A) and / or (B) can be carried out by any internal and / or external heating method (heating outside the reactor) known to those skilled in the art, and by any heating means or combination of heating means, such as irradiation by direct flame, irradiation by convection with hot gases or flue gases, heating by microwave, etc., without departing from the scope of the present invention.

[0073] In a preferred embodiment, the heating of the char from the pyrolysis of mixed plastic waste is done indirectly by a heating fluid external to the reactor, such as by feeding flue gas (hot gas) from the pyrolyzer furnace into the reactor chamber.

[0074] In another, particularly more preferred embodiment, said heating is carried out by electrically resistant means, for example arranged in the electricity of the reactor.

[0075] In another embodiment, heating of the char in the gasification reactor can be carried out by heating gases comprising or formed primarily from CO2 entering the reactor.

[0076] Heating of the pure CO or the above gas containing CO as defined above fed to the vaporization reactor can be carried out via a heating liquid in a heat exchanger or via a heating means such as, for example, a resistor.

[0077] In one embodiment, heating of the CO or CO-containing gas supplied to the vaporization reactor is carried out in an external heat exchanger, preferably a shell-and-tube heat exchanger, operating at 800°C to 1100°C, preferably 825°C to 950°C, and even more preferably 850°C.

[0078] In a preferred embodiment, the hot gas containing the CO2 or CO2 as defined above is heated outside the heat exchanger and counter-fed to the solids (char) conveyed by a cochlea (often called a screw conveyor or auger) and subjected to a mixing process in order to increase the amount of heat supplied to the pyrolysis gasifier (i.e., gasification reactor) for the gasification reaction and to promote intimate contact of all the solids (char) with the heated gas.

[0079] In the above embodiment, any fluidized bed reactor may be used for this purpose, but a screw / auger / cochlear reactor is preferred, and even more preferred is a configuration with external heating by gas in addition to cylinder heating.

[0080] In a preferred arrangement, heating may be achieved by means of electrical resistance.

[0081] The total pressure during the char gasification reaction (measured as the average of the gas stream pressure entering the reactor and the outlet pressure leaving the reactor) may comprise from 0.2 bar absolute to 1.5 bar absolute, preferably from 0.5 bar absolute to 1.2 bar absolute, and more preferably from 0.85 bar absolute to 1.05 bar absolute.

[0082] The residence time of the char in the gasification reactor can be 0.5 to 10 hours, preferably 2 to 8 hours, and more preferably 5 to 7 hours.

[0083] The residence time of the char in the reactor corresponds to the time it takes for the char to exit the reactor after it enters the reactor.

[0084] The residence time when feeding char continuously is set to achieve a specific conversion, e.g., complete, substantially complete, or partial conversion, of the carbon contained in the char, particularly the non-inert portion of the char (i.e., carbon in its non-salted form). This conversion is measured by performing CHNS analysis on both the initial char, the char entering the reactor, and the residual char leaving the reactor, and calculating the difference.

[0085] When char is fed in batch mode, the residence time refers to the time that the char remains in the reactor until a decrease in the CO concentration in the effluent is confirmed, under the condition that the total flow rate of CO2 fed to the reactor is constant.

[0086] The total amount of CO2 fed to the gasification reactor (fresh CO2 plus CO2 recycled from the process) depends on the carbon content present in the char.

[0087] As already mentioned, the carbon content is generally measured using standard analytical techniques (CHNS elemental analysis, temperatures up to 1100° C.).

[0088] It is understood that other techniques may be used to determine carbon content without departing from the scope and protection of the present invention.

[0089] The total amount of CO2 fed to the gasification reactor (including the amount of make-up CO2 and the amount resulting from any recycle) relative to the carbon in the char determined analytically (e.g., by CHNS) is expressed as a CO2 / C mass ratio, which may advantageously be 1, preferably 1-150, more preferably 10-140, and even more preferably 100-120.

[0090] As mentioned above, the gas (effluent) leaving the vaporization reactor is preferably (recycled gas stream) is partially recycled to the vaporization reactor. In this case, the recycled gas preferably passes through a heating system outside the vaporization reactor. The heating system heats the recycled gas before entering the vaporization reactor to a predetermined reaction temperature, generally between 750°C and 950°C, preferably between 800°C and 900°C, and even more preferably 850°C; and A portion (non-recycled portion) is first sent to the heat recovery unit (gas flow to the heat recovery unit), which cools the non-recycled portion, after which it is sent to a separator for a separation step. The distribution of the effluent stream described above is not accompanied by any change in composition.

[0091] This cooling in the heat recovery unit of the non-recycled portion of the gas leaving the vaporization reactor is advantageously carried out by giving up some of its warmth to heat a portion of the CO2 gas stream (make-up CO2).

[0092] The volume ratio between the recycled gas stream going to the gasification reactor and the non-recycled gas stream that is optionally sent to the heat recovery unit for cooling and then separated is 1-20, preferably 2-10, more preferably 2-8.

[0093] The cooled portion of the gas stream exiting the heat recovery unit is optionally subjected to separation, as described above, to remove CO and optionally H from other gas products, which generally include unreacted CO.

[0094] This separation can be carried out by one of the methods known in the art.

[0095] To selectively absorb the subsequently released CO2, for example, separation methods based on physical solvents, such as the Rectisol® method using methanol, can be conveniently used. Methods based on selective absorption by alkaline solvents that chemically bind to CO2 with relatively weak chemical bonds (e.g., methods using solutions of monoethanolamine (MEA) or diethanolamine (DEA) or diisopropanolamine (DIPA), methyldiethanolamine, and diglycolamine (DGA)) can also be used for this purpose. Mixtures of the above alkanolamines may also be used. The operating conditions for the separation processes are known and widely described in the literature. Furthermore, due to the high concentration (>10% by volume) of CO2 to be separated and recycled in the treated stream, physical methods based on adsorption (pressure swing adsorption) can also be conveniently used.

[0096] Subsequently, in one embodiment, the (unreacted) carbon dioxide separated as described above is first combined (mixed) with the directly recycled gas exiting the vaporization reactor, then integrated (mixed) with CO2 coming from an external source (e.g., fresh make-up CO2, CO2 obtained from a pyrolysis plant, or a combination thereof), and the total CO2 is then heated to 800°C to 1100°C, preferably 825°C to 950°C, more preferably 840°C to 870°C, and then reintroduced into the reactor.

[0097] Heating of the total CO stream can be carried out, for example, in a heat exchanger using hot gases (e.g., flue gases), or in an alternative arrangement, or by means of electrical resistance, preferably using hot gases.

[0098] It is understood that the char treatment process of the present invention can be applied to any type of char from the pyrolysis of mixed plastic waste having any composition with respect to carbon content and ash / metals content, which have unexpectedly been found to be irrelevant for all or substantially all carbon recovery purposes.

[0099] This is extremely useful in that it makes the invention widely applicable, as it allows the invention to be applied regardless of the type of char (carbonized material) produced by pyrolysis of mixed plastic waste, its composition and / or the composition of the plastic, or the type of process used to produce it.

[0100] In one embodiment, a pyrolysis process upstream of the above-mentioned char recovery process by gasification is carried out on mixed plastics containing more than 5% by weight, preferably more than 15% by weight, and more preferably 25% by weight, of PET (polyethylene terephthalate). Indeed, in the pyrolysis reactor, part of the PET is converted into CO2. This CO2 can be recovered from the gases produced by pyrolysis (by one of the methods known in the art, for example by using a membrane or an amine solution) and used in a gasification reactor (pyrolyzer) to vaporize the char from the pyrolysis reactor by using CO2 as a vaporizing agent. This allows the recovery of CO2, which would otherwise be removed as a useful substance resulting from the pyrolysis of PET, and thus also increases the overall yield of the pyrolysis process of mixed plastic waste as defined above.

[0101] According to another method, potassium, sodium and / or calcium salts (inorganic and / or organic), such as carbonates, bicarbonates, acetates, oxalates, etc., can be added to the pyrolysis process of the mixed plastic waste or SRM waste from which the char is derived that is subjected to this treatment method, with potassium carbonate and bicarbonates being preferred.

[0102] In a preferred embodiment, the char treated by the method according to the invention is the product of the pyrolysis of mixed plastic waste or the pyrolysis of mixed plastics, which is carried out by adding potassium carbonate as a pyrolytic dehalogenating agent, which is conveniently added when halogenated polymers (e.g. PVC (polyvinyl chloride)) are present in the feedstock fed to the pyrolysis.

[0103] The salt (potassium carbonate) contains 0.2 mol of cation in the final char. カチオン / kg~2mol カチオン / kg, preferably 0.4 mol カチオン / kg~1mol カチオン / kg, more preferably 0.5 mol カチオン / kg.

[0104] It should be noted that char obtained from pyrolysis of mixed plastic waste has shown high material recovery of over 90% at a temperature of 850°C by simple TGA analysis, while prior literature has revealed lower material recovery of lignite char by TGA analysis at the same temperature.

[0105] Therefore, char obtained from the pyrolysis of mixed plastic waste as defined above is particularly suitable and more favorable for gasification in the presence of CO2 than biochar from lignin.

[0106] It should also be noted that, with regard to char from fossil fuel coal, the char resulting from pyrolysis of mixed plastic waste is a different material and more suitable for gasification in the presence of CO2 than coal, due to milder operating conditions than coal.

[0107] The process of the present invention is completely different from the processes described in the literature for the direct gasification of plastics. As mentioned above, it should be noted that in the pyrolysis process, the plastic material is not converted into CO but into a hydrocarbon mixture of various compositions that can be used as a feedstock in the cracking plant, thus shortening the recycling chain compared to obtaining a synthesis gas obtained by converting all of the plastics by direct gasification of plastics.

[0108] In contrast, in the applicant's process, only a portion of the carbon contained in the char is intended to produce CO. A small portion, typically less than 10 percent, of the total carbon in the pyrolysis feedstock is found in the residue (char), while the remainder is found in hydrocarbon compounds, which are the main product of pyrolysis and are used as feedstock in the steam cracking plant. Therefore, in the present application, only the resulting char is vaporized with CO to maximize material recovery in the pyrolysis process.

[0109] As mentioned above, the process of direct gasification of plastics is conceptually different from the process of pyrolysis of mixed plastic waste combined with the process of gasification of only the produced char.

[0110] The char treatment method can therefore be integrated into processes for pyrolysis under pressure or vacuum of mixed plastics or mixed plastic waste known in the art, such as those described in e.g. ES2389799, WO2013 / 187788.

[0111] In the pyrolysis process, dehalogenation treatments known to those skilled in the art can be carried out by adding a dehalogenating agent (e.g., potassium carbonate) during the heating and temperature maintenance stages, thereby obtaining hydrocarbon residues and / or oils with reduced, optionally negligible, halogen (e.g., chlorine) content, and such treatments do not depart from the scope of the present invention.

[0112] It is therefore another object of the present invention to provide a method for the pyrolysis and / or catalytic pyrolysis of mixed plastic waste or secondary raw materials or from the pyrolysis of mixed plastics, which method comprises a subsequent step of treating the char obtained by said pyrolysis method as described so far.

[0113] In one embodiment, the mixed plastics pyrolysis process is that described in applicant's pending application WO2023126824A1, which is incorporated herein by reference in its entirety. The pyrolysis process comprises: a step of subjecting the mixed plastic waste of variable composition to a pyrolysis reactor in the substantial absence of oxygen to a temperature comprised between 330°C and 580°C and a pressure comprised between atmospheric pressure and 13 bar; maintaining the material in the pyrolysis reactor at a temperature comprised between 330°C and 580°C for a time sufficient to produce at least one effluent in the pyrolysis reactor in a gaseous state, wherein the pressure is adjustable according to the composition of the substantially plastic material and / or the product of the pyrolysis process; adjusting the pressure in the pyrolysis reactor as a function of the composition of the substantially plastic material and / or the products of the pyrolysis process, while maintaining the pressure at a value comprised between atmospheric pressure and 13 bar a; a step of partially or completely condensing the effluent in gaseous state to form at least a fluid that is in liquid state at 25°C and contains hydrocarbons that are at least 10% by weight of the weight of the material fed, wherein the pressure adjustment is preferably carried out with respect to the H / C ratio (H / C index) and / or the carbon index of the mixed plastic waste of variable composition. [Brief explanation of the drawings]

[0114] [Figure 1] FIG. 1 shows a block diagram of a process for treating char obtained from the pyrolysis of mixed plastics according to the present invention, integrated into any mixed plastics pyrolysis process. DETAILED DESCRIPTION OF THE INVENTION

[0115] Referring to FIG. 1, an embodiment of the pyrolysis process according to the present invention is illustrated, including the treatment of relative char according to the present invention.

[0116] The mixed plastic waste, which has been suitably pre-treated by screening, washing, removal of non-organic solid particles (e.g., ferrous materials and crushed stone), and optionally by crushing, is placed in a container (1-MP) and then fed as stream 1 to a pyrolysis unit (2-PY) comprising at least one pyrolysis reactor.

[0117] The pyrolysis process produces a stream of volatile compounds (Py gas) 2 and char 4 at a selected pyrolysis temperature.

[0118] The generated volatile compounds (Py-gas) stream 2 is sent to the 3-CD condenser, from where a liquid compound (liquid product) stream 3, consisting mainly of hydrocarbon oils, which is the main product of the thermal cracking and which is subsequently sent to the cracking; and A gas stream 10 (gaseous product), which contains CO2 and is therefore advantageously used in the char treatment step according to the invention. comes out.

[0119] The char produced in the pyrolysis of the mixed plastic waste is then sent as stream 4 to the above-mentioned gasifier 4-GB (gasification reactor) and heated at a given temperature, preferably below 950°C, more preferably below 850°C, in the presence of CO from stream 50 under the conditions described above, to produce a resultant gas stream 60 (effluent) comprising CO, unreacted CO and optionally H.

[0120] The CO2 stream 50 fed to the vaporization reactor 4-GB comes mainly from the gas stream 10 exiting the condenser 3-CD. Before entering the vaporization reactor 4-GB, this stream 10 is used as fuel in a heating system 5-HT external to the vaporization reactor 4-GB.

[0121] In heating system 5-HT, a stream of heating fluid 100 (designated as "heating means" in FIG. 1) is heated and sent to pyrolysis unit 2-PY, where said fluid stream provides the heat required for the pyrolysis process, from whence it returns in a continuous recycle to unit 5-HT, where it is further heated for re-passage to unit 2-PY. Additionally, in unit 5-HT, as a result of the combustion of stream 10, a stream of very hot gases 200 is produced (designated "hot gases" in FIG. 1), which is sent to unit 4-GB to provide the high temperature heat required by the pyrolysis gasification reaction of char stream 4 produced by pyrolysis.

[0122] After transferring heat to pyrolysis vaporization unit 4-GB, the hot flue gas 200 returns to unit 5-HT where it is combined with flue gas 20 that provided heat to heating fluid stream 100 used in unit 2-PY and is cooled by preheating combustion air stream 11 used to combust stream 10 in unit 5-HT before being sent to unit 7-SF for separation of CO2 from the flue gas. In unit 7-SF, flue gas stream 20 is separated into two streams: CO2-depleted hot gas stream 21 which is injected into the atmosphere, and CO2 from pyrolysis stream 30.

[0123] Stream 30 of CO2 from the pyrolysis is mixed with recycled stream 40 of CO2 and then sent to pyrolysis vaporization unit 4-GB. In unit 4-GB, which is also fed with char stream 4, total CO2 stream 50 reacts with the non-inert fraction of char stream 4 and is converted into a mixed gas stream of CO2 and CO 60. Part of this mixed gas is sent to CO separator 6-SP, and part is recycled in unit 4-GB, where it is mixed with total CO2 stream 50 and then heated by means of hot gas 200 from unit 5-HT in a heat exchanger (not shown in Figure 1 but present in unit 4-GB) before being sent again to unit 5-HT.

[0124] Some illustrative, but non-limiting, examples of the present invention are set forth below. [Example]

[0125] The gases used in the examples are as follows: CO2 Purity: 4.8 (potency > 99.9980%) O2: Less than 5 ppm N2: Less than 10 ppm CH4: Less than 5 ppm H2O: Less than 10 ppm He (gas chromatograph carrier) Purity: 5.5~99.9995% O2: approx. 0.5 ppm CO+CO2: non-existent N2: Less than 1 ppm H2: Less than 0.5 ppm Hydrocarbons: None H2O: Less than 3 ppm

[0126] Preparation 1: Chars obtained from pyrolysis of mixed plastics and associated CHNS analysis The chars used in the examples of this application were prepared as described below.

[0127] Samples of mixed plastic secondary raw materials (SRM) were ground as reported below.

[0128] As an applicable example, but not limited to, secondary raw material SRM from waste sorting of mixed plastic waste with the composition shown in Table 1 was used.

[0129] Because plastic waste compositions are inherently variable, the composition ranges and average values ​​used are shown in Table 1. The secondary material complies with UNI 10667-18, which is referenced for further analytical details. Note that for purposes of this invention, the composition of the initial plastic mixture is not critical, since mixed plastic waste does not have a constant and defined composition. Any mixed plastic waste / scrap mixture can be used without departing from the scope of this invention.

[0130] [Table 1]

[0131] The SRM was milled in a Retsch ultracentrifugal mill model ZM200 using a 2 mm port grid and the rotation speed set at 12000 rpm.

[0132] The resulting material was used as is and subjected to pyrolysis (described below) without further physical and / or chemical treatment.

[0133] 25 grams of the mixed plastics obtained above were introduced into a tubular reactor with a diameter of 19 mm and a length of 30 cm. The reactor was then inserted vertically into an electric furnace. The lower end of the reactor was connected to a flow meter through which nitrogen passed, and the upper end was connected to a pressure control valve, which in turn was connected to a collection flask equipped with a vent, which in turn was connected to a gas meter.

[0134] The reactor was subjected to a nitrogen flux of 60 cc / min and heated to 240° C. Once 240° C. was reached, the nitrogen flow was discontinued, heated to 380° C. and pressurized to 1 bar g.

[0135] Once 380°C was reached, the reactor was held under these conditions for 3 hours.

[0136] After 3 hours, the reactor was heated to 430°C and once 430°C was reached, the reactor was held at these conditions for 3 hours.

[0137] After 3 hours, the reactor was heated to 480°C and, once 480°C was reached, the reactor was maintained at these conditions until no further production of volatiles (gases) was observed, i.e., 3 hours.

[0138] After 3 hours, the reactor was gradually let down to atmospheric pressure and cooling to room temperature was commenced by flushing again with nitrogen at 60 cc / min.

[0139] Once room temperature was reached, the reactor was disconnected and opened and the collected residue was the char obtained from the pyrolysis of SRM.

[0140] The above pyrolysis procedure was repeated multiple times to obtain a sufficient amount of char (10 grams) for carrying out the experiments, and multiple char samples were obtained.

[0141] The various char samples obtained were then mixed to obtain the char samples used in the experimental part of this application, which were subjected to elemental analysis (CHNS), the results of which are summarized in Table 2.

[0142] [Table 2]

[0143] Elemental analysis (CHNS analysis) was performed using an organic elemental analyzer manufactured by Organic Elemental Analyzer instrument, "Unicube" model under the trade name Elementar. It will be appreciated that other elemental analyzers may be used without departing from the scope of the present invention. Before the analysis was carried out, the char samples were dried in an oven at a temperature of 110°C to remove traces of water therein. 2 mg ± 0.2 mg of sample and 2 mg ± 0.2 mg of WO3 (as required by the analytical technique of the instrument) are placed inside the sample holder and introduced into the combustion reactor of the instrument. Then, a procedure is started in which the instrument is heated to 1100° C. At the end of the cycle, after cooling, the instrument directly provides the % of C, H, N, S in the sample.

[0144] The ash content was measured according to the following gravimetric method. Approximately 1 g of char sample, previously dried in an oven at 110 °C and weighed accurately, was placed in a ceramic crucible. Prior to this analysis, the crucible was dried in a muffle furnace at 650 °C for 3 h, cooled, and then weighed. The crucible containing the char sample was then placed in a muffle furnace in the presence of air and heated to a temperature of 750°C, at which point the system was maintained for 3 hours. After 3 hours, the crucible was removed from the muffle furnace and placed in a desiccator until cooled to room temperature, then reweighed. The percentage of ash present in the char samples is shown in Table 2. The percentage was determined via the following relationship:

[0145] %Ash=[(AB) / C]×100 During the ceremony, A: Mass of crucible including ash (in grams) B: Mass of the crucible (in grams) C: Mass of the test sample (in grams)

[0146] The oxygen values ​​reported in Table 2 were calculated by difference according to the following relationship: %Oxygen(O)=100-(%C+%H+%N+%S+%Ash)

[0147] Metals in the char samples were determined using the following: Milestone microwave mineralizer (for metal analysis), ETHOS UP model (conditions: power 1800 W, temperature 210°C, time 35 min): The char sample was digested using a solution of aqua regia (HCl:HNO3 = 3:1), hydrogen peroxide, and hydrofluoric acid in a microwave digester, Ethos UP. Agilent Technologies MPAES Microwave Plasma Atomic Emission Spectroscopy (for metal analysis), Model 42-10 MP-AES

[0148] Metal analysis gave the following results, reported in Table 3:

[0149] [Table 3]

[0150] The pyrolysis method described above is merely one example for obtaining char and is in no way limiting of the present invention. Virtually any pyrolysis method known to those skilled in the art can be used to produce char from the pyrolysis of mixed plastics.

[0151] Examples 1-4 of char decomposition using TGA Example 1: TGA of char in the presence of carbon dioxide at 750°C Char samples obtained from the pyrolysis of the plastic described in Preparation 1 were subjected to thermogravimetric analysis TGA in the presence of carbon dioxide. The instrument used is a TA Instrument Q 500 V20. Approximately 10 mg of a precisely weighed sample was placed in the crucible of the instrument and subjected to heating according to the following method provided by the TGA analysis method. 1- Reflux gas: CO2, flow rate 60 ml / min 2- Heat to 40℃ 3- Keep at 40℃ for 5 minutes 4- Heat to 750°C at 10°C / min 5- Isothermal at 750°C for 360 minutes 6- After 360 minutes, replace the CO2 with nitrogen at the same flow rate and cool to 50°C at 50°C / min. 7- Isothermal at 50℃ for 40 minutes, analysis completed

[0152] The final residue of the sample after carbon dioxide flow analysis was 33 wt% based on the initial char sample weight.

[0153] TGA (thermogravimetric analysis) performed at 750 °C with CO2 injection showed that the residue (33%) was in perfect agreement with the ash content (32%) determined by elemental analysis and the crucible method. This indicates that the mass of the remaining char (67%) reached 100% through reaction with CO2, confirming that the carbon in the char obtained by pyrolysis of mixed plastic waste was completely vaporized.

[0154] Example 2: TGA of char in the presence of carbon dioxide at 800°C In Example 2, the same char and the same equipment as described in Example 1 were used. Approximately 10 mg of precisely weighed sample was placed in the instrument crucible and heated according to the method described above in Example 1, but at a higher T and for a shorter time as reported below. 1- Reflux gas: CO2, flow rate 60 ml / min 2- Heat to 40℃ 3- Keep at 40℃ for 5 minutes 4- Heat to 800°C at 10°C / min 5- Isothermal at 800°C for 200 minutes 6- After 200 minutes, replace the CO2 with nitrogen at the same flow rate and cool to 50°C at 50°C / min. 7- Isothermal at 50℃ for 40 minutes, analysis completed

[0155] The final residue of the sample after carbon dioxide injection and analysis was 32.1 wt% of the initial char sample weight. The residue obtained in the TGA with CO2 flushing (32.1%) is in perfect agreement with the ash content in the char (33%) obtained by elemental analysis using the crucible method and calculation of the ash percentage. This indicates that the residual mass reacted with CO2 and confirms the complete vaporization of the carbon not contained in the ash in the char obtained from the pyrolysis of mixed plastic waste.

[0156] Example 3: TGA of char in the presence of carbon dioxide at 700°C In Example 3, the same char and equipment as described in Example 1 were used. Approximately 10 mg of precisely weighed sample was placed in the instrument crucible and heated according to the method described above in Example 1, but at a lower T, as reported below. 1- Reflux gas: CO2, flow rate 60 ml / min 2- Heat to 40℃ 3- Keep at 40℃ for 5 minutes 4- Heat to 700°C at 10°C / min 5- Isothermal at 700°C for 360 minutes 6- After 360 minutes, replace the CO2 with nitrogen at the same flow rate and cool to 50°C at 50°C / min. 7- Isothermal at 50℃ for 40 minutes, analysis completed

[0157] The final residue of the sample after carbon dioxide flow analysis was 36.8 wt.% based on the initial char sample weight. This analysis shows a residue of 36.8%, which is slightly higher than the ash content in the char (33%) obtained from elemental analysis and calculation of the ash percentage by the crucible method at 750°C, but still indicates a clear reaction between the remaining char mass (63.2%) and CO2 to reach 100%.

[0158] Example 4 (Comparative): TGA of char in the presence of N2 at 920°C or in the presence of air at 850°C In Example 4, the same char and equipment were used as described in Example 1, except that in this case the analysis was carried out first in the presence of nitrogen and then in the presence of air, and the sample was heated to 920°C in the following manner. 1- Reflux gas: N2, flow rate 60 ml / min 2- Heat to 40℃ 3- Keep at 40℃ for 5 minutes 4- Heat to 920°C at 10°C / min 5- 920℃, isothermal for 10 minutes 6- Cool to 400°C at 20°C / min 7- 400℃, isothermal for 5 minutes 8- Replace N2 with air at a flow rate of 60 ml / min 9- Heat to 850°C at 20°C / min 10- 850℃, isothermal for 5 minutes 11- After 5 minutes, replace the air gas with nitrogen at the same flow rate and cool to 50°C at 50°C / min. 12- Isothermal at 50℃ for 40 minutes, analysis completed

[0159] Analysis performed in this way showed that char under inert atmosphere (flushing with N2) showed an initial mass loss of about 24% upon heating alone, which was attributed to heavy compounds that evaporated or decomposed when heated to 920°C.

[0160] Subsequent combustion of carbon occurs by replacing the nitrogen with air, resulting in a final residue of approximately 31.4% at 850 °C, which is comparable to the ash content in char (33%) obtained when calculating the ash percentage using the crucible method.

[0161] Therefore, the tests performed in Examples 1-3 highlight the reactivity of CO2 with the carbon present in the char.

[0162] Examples 5-10: Char vaporization Example 5: Gasification of char obtained from pyrolysis of SRM of mixed plastics at 750°C with CO production The char from Example 1 was subjected to reaction with CO in a tubular reactor in a small laboratory setup as described below. Reactor material: Quartz The reactor had an inner diameter of 10 mm and a length of 200 mm, and a quartz wool partition was inserted in the middle of the tube. The reactor was mounted in a cylindrical electric furnace equipped with a control thermocouple. The lower end of the reactor was connected to a Brooks Model 5850 Series flow meter and controller, which was used to supply CO2.

[0163] Instead, the reactor outlet was connected to a gas chromatograph for analysis of the effluent gases. Agilent Technologies Gas Chromatograph, Model GC1540A, equipped with a Porapak N column (2.5 m length) and molecular sieves (5 m length). Gas analysis conditions: Head flow pressure: 63 psi Temperature ramp: 35°C for 0.7 minutes, then increased to 75°C in 1 minute; Hold at 75°C for 4 minutes; cool to 50°C and then to 35°C; hold at 35°C for 2.2 minutes Carrier: Helium (He)

[0164] Approximately 100 mg of accurately weighed char from Example 1 was loaded into the reactor (on the quartz wool partition) and heated from room temperature to 700°C at a rate of 10°C / min under a CO flow of 20 Nml / min, and then continued to heat at a rate of 5°C / min up to 750°C.

[0165] The reactor was maintained at 750°C and cooled 260 minutes after the start of heating. Cooling to room temperature was achieved by replacing the CO2 flow with N2 at the same flow rate. Therefore, CO2 was supplied to the reactor for 260 minutes, with a total volume of 5.2 liters.

[0166] The gas discharged from the reactor was analyzed inline during the reaction using the aforementioned analyzer (gas chromatograph). The results showed that the maximum concentration of CO in CO2 was 20% (volume ratio), with the remainder consisting of CO2, reaching 100% by volume.

[0167] The carbon conversion to char, as determined by the following report, was 93 wt %.

[0168]

number

[0169] During the ceremony, A is the weight of the char sample loaded into the reactor; B is the final weight of the char residue left in the reactor; %Ash is the percentage of ash contained in the char sample measured as above gravimetrically at 750°C (32%) in a muffle furnace

[0170] Example 6: Gasification of char obtained from pyrolysis of SRM of mixed plastics at 750°C with CO production Example 6 was carried out under the same conditions and using the same equipment as Example 5, but with a different commercially available char derived from waste plastics. This char was called "Pyrolysis Char Neoliquid" and was supplied by Neoliquid Advanced Biofuels and Biochemicals, Guadalajara, Spain.

[0171] The char was subjected to analysis as described above (combustion in a muffle furnace at 750°C for CHSN and ash determination) with the results shown in Table 4.

[0172] [Table 4]

[0173] The gas exiting the reactor was analyzed by an in-line analyzer, and the results showed that the maximum concentration of CO in CO2 was 12% (vol / vol), with the remaining volume being composed of CO2, reaching 100% by volume. After vaporization, the carbon conversion was measured using the same method as described in Example 5 and was found to be 90%.

[0174] Example 7: Gasification of char obtained from pyrolysis of SRM of mixed plastics at 750°C with CO production Example 7 was carried out under exactly the same conditions and with the same equipment as Example 5. However, the char used was that obtained by Preparation 1 using SRM having the composition shown in Table 1, to which 20 wt % of PET (polyethylene terephthalate) was added. The resulting char was analyzed as described above (combustion in a muffle furnace at 750° C. for CHSN and ash determination) and its composition is shown in Table 5.

[0175] This composition shows that the O2 content of char from pyrolysis of PET-containing mixed feedstocks is not higher than that of other types of char used conventionally, indicating that PET is already decomposed and releases CO2 during pyrolysis.

[0176] [Table 5]

[0177] The gas exiting the reactor was analyzed by an in-line analyzer, and the maximum concentration of CO in CO2 was found to be 16% (vol / vol). After vaporization, the carbon conversion was measured using the same method as described in Example 5 and was found to be 90%.

[0178] Example 8: Gasification of char obtained from pyrolysis of SRM of mixed plastics at 750°C with CO production Example 8 was carried out under exactly the same conditions and with the same equipment as Example 5. However, the char used was the char obtained by Preparation 1 using SRM having the composition shown in Table 1, to which 7 wt % of potassium carbonate was added. The resulting char was analyzed as described above (combustion in a muffle furnace at 750°C for CHNS and ash determination), with the results shown in Table 6.

[0179] [Table 6]

[0180] The gas exiting the reactor was analyzed by an in-line analyzer, and the results showed that the maximum concentration of CO in CO2 was 22% (vol / vol), with the remainder consisting of CO2 reaching 100% by volume. After vaporization, the carbon conversion was measured using the same method as in Example 5 and was found to be 99.9%.

[0181] Example 9: Gasification of char obtained from pyrolysis of SRM of mixed plastics at 700°C with CO production Example 9 was carried out under the same conditions as Example 8, except for the reaction temperature. The reactor was heated from room temperature to 650°C at a rate of 10°C / min. After reaching 650°C, it continued to heat at a rate of 5°C / min to 700°C. The reactor was kept at 700°C and cooled 260 minutes after the start of heating. Cooling to room temperature was achieved by replacing the CO2 flow with N2 at the same flow rate. Therefore, CO2 was supplied to the reactor for 260 minutes, for a total volume of 5.2 liters.

[0182] The gas exiting the reactor was analyzed by an in-line analyzer, and the results showed that the maximum concentration of CO in CO2 was 20% (vol / vol), with the remainder consisting of CO2 reaching 100% by volume. After vaporization, the carbon conversion was measured using the same method as described in Example 5 and was found to be 93%.

[0183] Examples 5-9 show how high carbon conversions are already achieved at 750° C. and with different char types. By using potassium salt, which is usually used as a dehalogenating agent, in the thermal decomposition, it is possible to increase the conversion rate (Example 8) or reduce the vaporization temperature to 700°C (Compare Example 9 with Example 5).

[0184] Example 10: Gasification of char obtained from pyrolysis of mixed plastic SRM at 750°C To simulate the recycling process of CO-containing reaction gas, Example 10 was carried out using the same conditions, operation method, and equipment as Example 5. However, instead of CO, the char was heated while flowing a CO mixed gas containing 16.26 vol% CO supplied by SIAD at 20 Nml / min. Therefore, a total of 4.355 N liters of CO2 was fed to the reactor for 260 minutes, and a total of 0.845 N liters of CO was fed.

[0185] The gas exiting the reactor was subjected to analysis as in the previous examples. The maximum CO produced was calculated by subtracting the CO present in the feed and was 17% by volume. Under these conditions, the carbon conversion to char was 91%.

[0186] A comparison of the conversion data from Example 5 with that from Example 10 shows that the values ​​are substantially similar, indicating that operating with a mixture of CO and CO rather than CO alone does not result in a substantial reduction in the rate at which carbon in the char is converted to CO under the operating conditions of the present process. This is despite the fact that the reaction to produce CO is an equilibrium reaction. It is therefore possible to recycle the gas leaving the vaporization reactor to the reactor.

[0187] [Table 7]

Claims

1. A process for recovering carbon contained in char (solid carbonaceous residue) obtained from the pyrolysis of mixed plastic waste or from the pyrolysis of secondary raw materials that are the end products of recycling and / or processing of plastic waste, or from the pyrolysis of mixed plastics, through the production of CO and, optionally, synthesis gas, comprising: (A) heating the char in the presence of carbon dioxide in a gasification reactor to a prefixed temperature ranging from below 950°C to above 600°C; (B) adding CO 2 to the char during a predetermined residence time of the char in the reactor at a temperature within the range of 750°C to 850°C. ２ and continuing to heat the char in the presence of ２ In addition to CO, and ２ generating an outflow gas stream (effluent) which may include: (C) CO, unreacted CO ２ , and optionally H ２ and treating at least a portion of the gas stream (effluent) exiting the reactor with CO ２ to at least one subsequent operational unit selected from a unit for separating CO from the outflow stream, a unit for direct use of the outflow stream, or a storage unit. A process involving:

2. 2. The process according to claim 1, wherein the char subjected to steps (A) and (B) of the process according to the invention is a char obtained from a pyrolysis process of mixed plastic waste or a pyrolysis process of secondary raw materials obtained from the recycling and / or processing of plastic waste.

3. In the step (C), CO and unreacted CO ２ and wherein only a portion of the gas stream exiting the reactor containing CO ２ and the remaining portion of the gas stream exiting the reactor is fed to at least one subsequent unit for separating CO from the ２ 3. The process of claim 1 or claim 2, wherein the molten metal is recycled to the vaporization reactor, where the molten metal is optionally replenished.

4. The CO in the vaporization reactor in step (A) ２ However, it is not pure and has a higher CO content than other gases contained in the gas stream. ２ The method according to any one of claims 1 to 3, wherein the gas stream contains a predominant amount of

5. 5. The process according to any one of claims 1 to 4, wherein the gasification reactor comprises or consists of a horizontal cylinder for facilitating contact of all solids (char) with carbon dioxide, said horizontal cylinder preferably being equipped with stirring / mixing / moving means and / or a fluidization system, preferably a fluidized bed.

6. 6. The process of claim 5, wherein the stirring / mixing / moving means is in the form of a screw.

7. 7. The process according to any one of claims 1 to 6, wherein the temperature of heating of the char in the gasification reactor in phases (A) and / or (B) is between 700°C and 950°C, preferably between 700-750°C and 900°C, more preferably between 700-750°C and 850°C.

8. 8. The process of any one of claims 1 to 7, wherein the total pressure of the char gasification reaction is from 0.2 bar absolute to 1.5 bar absolute, preferably from 0.5 bar absolute to 1.2 bar absolute, more preferably from 0.85 bar absolute to 1.05 bar absolute.

9. 9. The process of any one of claims 1 to 8, wherein the residence time of the char in the gasification reactor is from 0.5 hours to 10 hours, preferably from 2 hours to 8 hours, more preferably from 5 hours to 7 hours.

10. CO ２ CO fed to the gasification reactor relative to the carbon in the char as determined by analysis, expressed as a CO / C weight ratio. ２ The process according to any one of claims 1 to 9, wherein the total amount of is from 1 to 150, preferably from 10 to 140, more preferably from 100 to 120.

11. 11. The process according to any one of claims 2 to 10, wherein the portion of the gas (effluent) leaving the gasification reactor to be recycled is passed through a heating system external to the gasification reactor, which heats the portion to a predetermined reaction temperature before entering the gasification reactor.

12. 12. The process of any one of claims 2 to 11, wherein the non-recycled portion of the gas (effluent) exiting the gasification reactor is sent to a heat recovery unit which cools it before subjecting it to the separation step.

13. 13. The process of any one of claims 1 to 12, wherein the volume ratio of the recycle stream of the gasification reactor to the non-recycle stream subjected to separation is from 1 to 20, preferably from 2 to 10, more preferably from 2 to 8.

14. 14. Thermal and / or catalytic pyrolysis process of mixed plastics or of secondary raw materials that are the end product of recycling and / or processing of plastic waste or from mixed plastics pyrolysis, said process further comprising treating char obtained from said pyrolysis process by means of an organic carbon recovery process as defined in any one of claims 1 to 13.

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