Waste plastic dechlorination method

Abstract

There is provided a process for dechlorinating waste plastic, comprising: a) adding a dechlorinating agent to waste plastic, the waste plastic comprising at least one chlorine-containing polymer; b) heating the waste plastics and a dechlorinating agent at 200-380 DEG C to obtain treated waste plastics, the dechlorinating agent being a mixture of a neutralizer and a catalyst; the neutralizer is at least one of oxides, hydroxides, carbonates, bicarbonate and basic carbonates of group 1 and group 2 metal elements, and the ratio of the total mole number of the group 1 and group 2 metal elements to the mole number of the chlorine element in the waste plastics is (0.1-0.7): 1; the catalyst is at least one metal oxide, the ratio of the total mole number of metal elements in the metal oxide to the mole number of chlorine elements in the waste plastics is (0.1-0.3): 1, and the ratio of the total mole number of the metal elements of the first group and the second group to the total mole number of the metal elements in the metal oxide is (1.0-6.0): 1.

Description

Technical Field

[0001] The present disclosure relates to a method for treating chlorine-containing waste plastics, and in particular, to a method for dechlorinating waste plastics. Background Art

[0002] Waste plastic pyrolysis conversion technology converts waste plastics into low-molecular compounds or oligomers through pyrolysis or catalytic pyrolysis. With the development of this technology, a large amount of pyrolysis oil is produced.

[0003] Waste plastic products often contain chlorine-containing plastics such as polyvinyl chloride. During the pyrolysis process, polyvinyl chloride decomposes at high temperatures and in the presence of catalysts, producing hydrogen chloride, which corrodes equipment pipes. At the same time, in the case of incomplete decomposition, chlorine elements will exist in the form of organic chlorine compounds in the final pyrolysis products, posing challenges to the subsequent purification and subsequent application of pyrolysis oil. Even for waste plastics such as polyvinyl chloride in which the proportion of chlorine-containing plastics is relatively small (for example, the polyvinyl chloride content is less than 10wt.%), the chlorine content in the pyrolysis oil can be as high as thousands or even tens of thousands of ppm.

[0004] We are particularly looking forward to a pretreatment process that can reduce the organic chlorine content of waste plastics before the pyrolysis reaction. It has low equipment requirements, a simple process, short time consumption, and low energy consumption. At the same time, this method can remove the chlorine element in the form of inorganic chlorine. Summary of the Invention

[0005] According to one aspect of the present disclosure, a method for dechlorinating waste plastics is provided, comprising:

[0006] a) adding a dechlorinating agent to waste plastics, wherein the waste plastics include at least one chlorine-containing polymer;

[0007] b) heating the waste plastic and the dechlorination agent at 200-380° C. to obtain treated waste plastic,

[0008] in,

[0009] The dechlorinating agent is a mixture of a neutralizing agent and a catalyst;

[0010] The neutralizing agent is at least one of oxides, hydroxides, carbonates, bicarbonates and basic carbonates of Group 1 and Group 2 metal elements, and the ratio of the total number of moles of the Group 1 and Group 2 metal elements to the number of moles of chlorine in the waste plastic is (0.1-0.7):1; and

[0011] The catalyst is at least one metal oxide, the ratio of the total molar number of metal elements in the metal oxide to the molar number of chlorine elements in the waste plastic is (0.1-0.3):1, and the ratio of the total molar number of the Group 1 and Group 2 metal elements to the total molar number of metal elements in the metal oxide is (1.0-6.0):1.

[0012] The method disclosed herein is particularly suitable for treating waste plastics with low chlorine content, removing chlorine as inorganic chlorine, reducing the organic chlorine content in the pyrolysis oil, and simplifying the separation of solid chlorides from the liquid pyrolysis oil. Compared to other processes, this method uses a small amount of dechlorinating agent to achieve a higher chlorine conversion rate. The treated waste plastics have a low organic chlorine content, and the generated inorganic chlorides are easy to separate. Furthermore, this method has a low dechlorination temperature and a short dechlorination time, resulting in low energy consumption. This method can be integrated into plastic pyrolysis processes and is suitable for treating mixed waste plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 shows a chemical looping process according to some embodiments of the present disclosure;

[0014] Figure 2 A method for dechlorinating waste plastics according to some embodiments of the present disclosure is shown;

[0015] Figure 3 A dechlorination system according to some embodiments of the present disclosure is shown;

[0016] Figure 4 A waste plastic processing system according to some embodiments of the present disclosure is shown. Detailed description

[0017] The present disclosure is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are not intended to limit the present disclosure.

[0018] In the description of the present disclosure, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present disclosure, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the present disclosure and the features of different embodiments or examples without contradiction.

[0019] definition

[0020] As used in this disclosure, the words "comprising" or "including" are intended as open conjunctions, meaning the inclusion of named elements but not necessarily the exclusion of other unnamed elements. The words "consisting essentially of" or "consisting essentially of" are intended to indicate the exclusion of other elements of any significance to the composition. The words "consisting of" or "consisting of" are intended as conjunctions, meaning the exclusion of all elements other than the listed elements, except for only minor impurities.

[0021] The term "waste plastic", in this disclosure includes "post-consumer plastic" and "post-industrial plastic", which are at least partially recycled.

[0022] Post-consumer plastic refers to waste plastic materials generated after plastic products have completed their intended use at least once and have been used by end consumers or manufacturers. This type of material typically comes from household, commercial, or industrial end-use products, such as beverage bottles, food packaging containers, and detergent bottles.

[0023] Post-production plastic refers to waste plastic materials generated during the manufacturing process of plastic products that are not sold to end users or used by end users, including but not limited to scraps, leftovers, waste or unused raw materials generated during processes such as injection molding, extrusion, and blow molding.

[0024] Waste plastics often appear as mixtures of two or more polymers. Waste plastics may contain at least one chlorine-containing polymer selected from the group consisting of polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, polychloroprene, poly(4-chlorostyrene), polyvinyl chloride-styrene copolymer, vinyl chloride-vinyl acetate copolymer, acrylonitrile-chlorinated polyethylene-styrene terpolymer, chlorinated polyethylene, chlorinated polypropylene, and chlorinated rubber. Waste plastics may also contain one or more of polyethylene, polypropylene, polybutene, polyisobutylene, polymethylpentene, polystyrene, polyethylene terephthalate, ethylene propylene copolymer, polyolefin elastomer, and acrylonitrile-butadiene-styrene copolymer. Waste plastics may contain organisms such as fungi, bacteria, or other microorganisms, other organic components such as oils, proteins, carbohydrates, or inorganic components such as water, dust, and inorganic salts. Waste plastics may exist in the form of fibers, granules, powder, sheets, films, foams, or other forms.

[0025] As used herein, the term "dechlorinating agent" refers to a component that reacts with chlorine-containing waste plastics under certain temperature, pressure, and / or atmospheric conditions to reduce the chlorine content in the chlorine-containing waste plastics by forming chlorides, such as hydrogen chloride, calcium chloride, ferric chloride, or aluminum chloride. The dechlorinating agent can be a single compound or a mixture of multiple compounds.

[0026] In this disclosure, the term "chlorine conversion rate" refers to the efficiency of converting chlorine into inorganic substances such as hydrogen chloride and other inorganic chlorides. The chlorine conversion rate is calculated as the ratio of the total weight of chlorine converted into inorganic substances to the total weight of chlorine in the waste plastic before treatment.

[0027] The term "oxide" in this disclosure includes both integer oxides and non-stoichiometric oxides. Non-stoichiometric oxides are for example ferrous oxide (Fe) 0.84-0.95 O.

[0028] The term "pyrolysis" as used herein refers to a chemical process in which a solid mixture containing polymers (such as solid waste or feedstock derived therefrom) is subjected to high temperatures, whereby chemical bonds are forcibly broken to produce smaller molecules (including, but not limited to, hydrocarbons of 1-60 carbon atoms, other non-hydrocarbon organic compounds, and inorganic compounds such as hydrogen sulfide, nitrogen oxides, and sulfur oxides). For example, low-density polyethylene (LDPE) can be pyrolyzed at high temperatures to produce a mixture of various hydrocarbons.

[0029] Pyrolysis products refer to a composition that may be one or more of pyrolysis gas, pyrolysis oil, and pyrolysis wax. Pyrolysis products may be in the gaseous, liquid, or solid phase at 25°C and 1 atm. Crude pyrolysis products refer to products obtained directly from the pyrolysis process or those that have undergone only condensation, fractionation, or filtration after the pyrolysis process. Pyrolysis by-products may include pyrolytic semi-coke, which is solid at 25°C and 1 atm.

[0030] Pyrolysis gas refers to a composition that is a gas when measured at 25°C and 1 atmosphere, and at least a portion of which is obtained from the pyrolysis of solid waste at high temperatures, such as 300°C to 800°C.

[0031] Pyrolysis oil refers to a composition that is liquid when measured at 25°C and 1 atmosphere, and at least a portion of which is obtained from the pyrolysis of solid waste at high temperatures, such as 300°C to 800°C.

[0032] Pyrolytic wax refers to a composition that is solid when measured at 25°C and 1 atmosphere, and at least a portion of which is obtained from the pyrolysis of solid waste at high temperatures, such as 300°C to 800°C.

[0033] Pyrolysis gas, pyrolysis oil, and / or pyrolysis wax typically contain hydrocarbons, such as saturated, unsaturated, aromatic, and aliphatic hydrocarbons with varying numbers of carbon atoms. Pyrolysis oil and / or pyrolysis wax may also contain asphaltenes, other organic matter, water, colloids, inorganic salts, or other impurities. Pyrolysis gas typically contains one or more species, including hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides, hydrogen sulfide, ammonia, hydrogen chloride, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, propane, propylene, propyne, butane, isobutane, 1-butene, 2-butene, 2-methylpropene, 1-butyne, 2-butyne, and butadiene.

[0034] Figure 1 A chemical looping process according to some embodiments of the present disclosure is shown.

[0035] The waste is processed through pretreatment unit 110 to prepare feed suitable for the pyrolysis process. Pretreatment unit 110 can perform physical and chemical operations, including screening, reshaping, cutting, washing, drying, deashing, dissolution, extraction, catalyst addition, and dechlorination. The treatment methods disclosed herein can be performed in pretreatment unit 110.

[0036] The feed enters the pyrolysis unit 120 and is converted by high temperature into a hydrocarbon-containing fluid and a solid residue. At least a portion of the hydrocarbon-containing fluid enters the condensation separation unit 130 and is collected as a crude pyrolysis product. The crude pyrolysis product may include one or more of pyrolysis wax, pyrolysis oil, and pyrolysis gas. Condensation operations that can be employed by the condensation separation unit 130 include oil spraying and partition heat exchange. The spraying oil can be derived from the pyrolysis oil produced by the pyrolysis unit 120, post-processing unit 140, or hydroprocessing unit 150.

[0037] The pretreatment unit 110, pyrolysis unit 120, and condensation separation unit 130 can be integrated into a chemical recycling system 100. The chemical recycling system 100 can be configured with a heat source, a power device, and corresponding pipes, valves, or pumps to achieve operations such as heating, cooling, transportation, transfer, and / or control of flow direction / flow rate.

[0038] The crude pyrolysis product can enter post-processing unit 140, where it undergoes one or more operations including fractionation, rectification, heteroatom removal, filtration, ultrafiltration, extraction, flocculation, and adsorption. After the crude pyrolysis product is processed in post-processing unit 140, a refined pyrolysis product can be obtained. The refined pyrolysis product contains less nitrogen-containing impurities, sulfur-containing impurities, chlorine-containing impurities, oxygen-containing impurities, ash, moisture, colloids, or asphaltenes, making it more suitable for hydroprocessing and subsequent steam cracking.

[0039] After passing through the post-processing unit 140, at least a portion of the refined pyrolysis product can enter the hydroprocessing unit 150. The hydroprocessing unit 150 can operate under normal pressure or pressure and is equipped with a hydrogenation catalyst. The refined pyrolysis product can be converted into steam cracking feed after hydrogenation. It contains fewer olefins, alkynes, diolefins and / or aromatic hydrocarbons and is more suitable for directly entering the steam cracking process. In some embodiments, in addition to hydrogenating the unsaturated organic matter in the refined pyrolysis product, the hydroprocessing unit 150 can also crack the organic matter. Organic matter with more carbon atoms (such as 17, 18, 19, 20 or more carbon atoms) in the refined pyrolysis product can be cracked into organic matter with fewer carbon atoms (such as 10 or less carbon atoms). In some embodiments, the hydroprocessing unit 150 can also remove nitrogen-containing compounds, sulfur-containing compounds, chlorine-containing compounds, oxygen-containing compounds or other impurities in the refined pyrolysis product through a hydrorefining process to increase the hydrocarbon content in the refined pyrolysis product. In some other embodiments, the hydroprocessing unit 150 may further perform absorption, adsorption or other separation operations on the hydrogenated product to remove impurities such as hydrogen sulfide, ammonia, hydrogen chloride or water.

[0040] The steam cracking feed enters the steam cracking unit 160, where it reacts with water vapor at high temperature to produce a variety of products such as ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, or pyrolysis gasoline.

[0041] The products can be separated into chemical raw materials such as ethylene, propylene, acetylene, and butadiene by separation unit 170. Ethylene, propylene, acetylene, and butadiene can subsequently be used in industrial processes to synthesize polymers such as polyethylene, polypropylene, or polybutadiene, or used as starting materials to synthesize ethanol, ethylene oxide, propylene oxide, acrylonitrile, isopropyl alcohol, adipic acid, hexamethylenediamine, or other chemicals.

[0042] It is understood that in addition to the steam cracking process, at least a portion of the crude pyrolysis product can be directly or after passing through the post-processing unit 140 and / or the hydroprocessing unit 150 to enter other chemical processes to produce fuels or chemical feedstocks, such as partial oxidation, catalytic reforming, catalytic cracking, catalytic cracking, catalytic hydrogenation, solvent refining, delayed coking, and oxidative cracking. The partial oxidation product can include synthesis gas.

[0043] Figure 2 A method 200 for dechlorinating waste plastics according to some embodiments of the present disclosure is shown, comprising step 210, step 230, and an optional step 250. In some embodiments, step 250 is not performed.

[0044] At step 210, a dechlorinating agent is added to waste plastics, the waste plastics including at least one chlorine-containing polymer.

[0045] Waste plastics may include any form of article, product, material or part thereof. A part of an article may be in the form of a sheet, extrudate, molding, film, laminate, foam, chips, flakes, granules, fibers, fabric, agglomerates, briquettes, powder, fragments, strips, or pieces of any shape, or any other form other than the original form.

[0046] The size of waste plastics can be previously reduced in a variety of ways, including shredding, shredding, rolling, grinding, pulverizing, cutting, molding, compressing, cold brittleness, or dissolving in a solvent.

[0047] In some embodiments, the dechlorinating agent is a mixture of a neutralizer and a catalyst, the neutralizer is at least one of oxides, hydroxides, carbonates, bicarbonates and basic carbonates of Group 1 and Group 2 metal elements, and the ratio of the total moles of Group 1 and Group 2 metal elements to the moles of chlorine in the waste plastic is (0.1-0.7):1; the catalyst is at least one metal oxide, the ratio of the total moles of metal elements in the metal oxide to the moles of chlorine in the waste plastic is (0.1-0.3):1, and the ratio of the total moles of Group 1 and Group 2 metal elements to the total moles of metal elements in the metal oxide is (1.0-6.0):1.

[0048] For example, when the neutralizer is composed of the aforementioned compound of a Group 1 metal element and the aforementioned compound of a Group 2 metal element, the total moles of the Group 1 and Group 2 metal elements are calculated as the sum of the moles of the Group 1 metal element and the moles of the Group 2 metal element in all the compounds. For another example, when the neutralizer is composed of the aforementioned compounds of different Group 1 metal elements, the total moles of the Group 1 and Group 2 metal elements are calculated as the sum of the moles of each Group 1 metal element in all the compounds. For another example, when the neutralizer is composed of the oxides, hydroxides, and carbonates of the same Group 2 metal element, the total moles of the Group 1 and Group 2 metal elements are calculated as the total moles of the Group 2 metal element in all the compounds.

[0049] As can be understood by technicians, neutralizing agents usually exhibit a certain alkalinity and can react with chlorine-containing plastics, intermediates produced during the decomposition of chlorine-containing plastics, or hydrogen chloride to convert elemental chlorine into solid chloride, thereby reducing or even preventing the escape of hydrogen chloride gas.

[0050] Although the term "neutralizer" is used herein to describe oxides, hydroxides, carbonates, bicarbonates, basic carbonates, or combinations thereof of Group 1 or Group 2 metal elements, this term does not exclude the catalytic effect of such substances on the decomposition of chlorine-containing plastics. Similarly, the use of the term "catalyst" does not exclude the neutralization of hydrogen chloride by the corresponding metal oxide.

[0051] Preferably, the ratio of the total molar number of Group 1 and Group 2 metal elements to the molar number of chlorine in the waste plastic is (0.4-0.6):1.

[0052] Preferably, the ratio of the total molar number of the metal elements of Group 1 and Group 2 to the total molar number of the metal elements in the metal oxide is (2.0-4.5):1.

[0053] Preferably, the neutralizing agent is lithium oxide, lithium hydroxide, lithium carbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, calcium oxide, calcium hydroxide, calcium carbonate or any mixture thereof; more preferably, the neutralizing agent is calcium oxide or calcium hydroxide.

[0054] Preferably, the catalyst is iron oxide, ferrous oxide, ferrosoferric oxide, iron oxyhydroxide, aluminum oxide, aluminum oxyhydroxide, zinc oxide, red mud or any mixture thereof; more preferably, the catalyst is α-iron oxide, γ-iron oxide, γ-aluminum oxide, δ-aluminum oxide, η-aluminum oxide and / or hexagonal zinc oxide.

[0055] There is no restriction on the form of the above-mentioned neutralizing agent and / or catalyst. Any known form neutralizing agent and / or catalyst can be used as the dechlorinating agent in the present disclosure, as long as it meets the above requirements. Nevertheless, in some embodiments, the neutralizing agent and / or catalyst used is a solid powder. As will be appreciated by those skilled in the art, the dechlorinating agent in solid powder form is easy to achieve uniform mixing with waste plastics. Meanwhile, relative to block dechlorinating agent, powder dechlorinating agent can utilize large specific surface area to achieve catalysis of waste plastics and capture of generated hydrogen chloride gas.

[0056] Without being bound by theory, the catalyst described above can promote the cleavage of carbon-chlorine bonds in chlorine-containing waste plastics under heating conditions. This cleavage of carbon-chlorine bonds may be accompanied by the production of hydrogen chloride. Therefore, the neutralizing agent used can react with hydrogen chloride to form the corresponding solid chloride, thereby converting the organic chlorine component into an easily separable inorganic chlorine component.

[0057] The dechlorinating agent is preferably in the form of solid powder so as to be fully mixed with the waste plastics.

[0058] Preferably, the chlorine-containing polymer is selected from the group consisting of polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, polychloroprene, poly(4-chlorostyrene), polyvinyl chloride-styrene copolymer, vinyl chloride-vinyl acetate copolymer, acrylonitrile-chlorinated polyethylene-styrene terpolymer, chlorinated polyethylene, chlorinated polypropylene and chlorinated rubber.

[0059] Preferably, the waste plastics also contain polyolefins, polyamides, polyesters, polyurethanes or any mixtures thereof; more preferably, the waste plastics also contain polyethylene, polypropylene, polybutene, polyisobutylene, polymethylpentene, ethylene propylene copolymer, polyolefin elastomer, polystyrene, polyamide 6, polyamide 66, polyamide 46, polyamide 6T, polyamide 11, polyamide 12, polyethylene terephthalate, polybutylene terephthalate, polyadipate / butylene terephthalate, polylactic acid, acrylonitrile-butadiene-styrene copolymer or any mixtures thereof.

[0060] Preferably, the waste plastic has a chlorine content of not more than 20 wt. %; more preferably, the waste plastic has a chlorine content of not more than 5 wt. %, based on the total weight of the waste plastic.

[0061] The chlorine content of waste plastics can be determined using a variety of analytical testing methods. For example, the oxygen bomb combustion method involves burning a sample of waste plastic in a pressurized pure oxygen atmosphere. A quantitative alkaline solution is then used to wash the solid residue and absorb the released chloride. Ion chromatography or titration is then used to determine the chloride ion concentration in the solution, ultimately providing the chlorine content of the waste plastic.

[0062] The mixing of waste plastics and dechlorinating agents can be carried out in a variety of equipment. In some embodiments, the mixing is carried out at room temperature or other temperatures not higher than the softening temperature of the waste plastics. At this point, the waste plastics are basically in solid form. The mixing of waste plastics and dechlorinating agents can be achieved by equipment such as a V-type mixer, a double-cone mixer, a horizontal ribbon mixer, a plowshare mixer, a fluidized bed mixer, a drum mixer, a vertical spiral mixer, or a shearing granulator. In other embodiments, the mixing is carried out at a temperature higher than the softening temperature of the waste plastics. At this point, the waste plastics are basically in a semi-fluid or fluid form. The mixing of waste plastics and dechlorinating agents can be achieved by equipment such as an extruder, a melt mixing kettle, a high-speed disperser, a kneader, a closed plasticator, or a planetary mixer.

[0063] In step 230, the waste plastic and the dechlorination agent are heated at 200-380°C to obtain treated waste plastic.

[0064] Without being bound by any theory, in step 230, the waste plastic and the dechlorinating agent may react at the aforementioned temperature. The carbon-chlorine bonds in the waste plastic may be broken, generating hydrogen chloride. The hydrogen chloride may further react with a neutralizing agent, such as a hydroxide, and / or a catalyst in the dechlorinating agent to generate an inorganic chloride. The specific type of inorganic chloride depends on the neutralizing agent and / or catalyst used.

[0065] Step 230 converts part of the chlorine in the waste plastic into inorganic chlorides, such as hydrogen chloride and metallic inorganic chlorides. The treated waste plastic may contain reaction products such as partially dechlorinated chlorine-containing polymers, other polymers, residual neutralizer, residual catalyst, or generated chlorides. The total chlorine in the treated waste plastic includes both inorganic chlorine in the form of inorganic chlorides and organic chlorine in the form of chlorine-containing organic compounds.

[0066] In some embodiments, the inorganic chloride is lithium chloride, sodium chloride, magnesium chloride, basic magnesium chloride, potassium chloride, calcium chloride, basic calcium chloride, ferric chloride, ferrous chloride, ferric oxychloride, aluminum chloride, zinc chloride, or any mixture thereof.

[0067] In some embodiments, step 230 also generates tail gas. The tail gas may contain hydrogen chloride. The tail gas can be absorbed using an absorption medium such as water, a salt solution, an alkaline solution, or an alkaline suspension. Examples of acceptable absorption media include aqueous potassium hydroxide solution, aqueous potassium carbonate solution, aqueous sodium hydroxide solution, aqueous sodium carbonate solution, lime milk, and organic amine solution.

[0068] In some embodiments, the tail gas contains water vapor, and the tail gas can be cooled and dehydrated by heat exchange.

[0069] The heating temperature in step 230 is important for treating chlorine-containing waste plastics. Excessively low temperatures can slow or even prevent the dechlorination process. In this case, a longer heating time is required to achieve the dechlorination effect, resulting in higher energy consumption. While excessively high temperatures can accelerate the dechlorination reaction rate of waste plastics, they may be accompanied by side reactions. For example, polyolefin components in waste plastics rapidly decompose at temperatures of 400°C or higher, causing components with lower vaporization temperatures to enter the gas phase and be lost. Furthermore, hydrogen chloride is highly corrosive to equipment at high temperatures.

[0070] Preferably, the waste plastic and the dechlorination agent are heated at 230-360°C; more preferably, the waste plastic and the dechlorination agent are heated at 250-350°C.

[0071] Preferably, step 230 lasts for 10-60 minutes, more preferably, for 15-40 minutes. The duration of step 230 does not exceed 1 hour, which is beneficial for controlling the time taken from feeding to pyrolysis of waste plastics.

[0072] In step 230, a too short treatment time causes the chlorine-containing polymer to not have enough time to absorb heat and reach the decomposition temperature, resulting in poor dechlorination effect. A longer treatment time increases energy consumption and reduces treatment efficiency.

[0073] Preferably, step 230 is performed at a pressure of 0.5-5 standard atmospheres.

[0074] Preferably, step 230 can be performed in the presence of an inert atmosphere. The inert atmosphere can contain any non-oxidizing gas, such as nitrogen, argon, and neon. The inert atmosphere does not contain oxygen or contains oxygen in an amount not exceeding 0.5% by volume. The preferred inert atmosphere is a nitrogen or argon atmosphere. Furthermore, step 230 can be performed under an inert atmosphere purge. Purge can evacuate oxygen from the system before dechlorination treatment and can also help hydrogen chloride in the system escape, reducing its corrosion to high-temperature equipment.

[0075] After step 230, the organic chlorine in the waste plastics can be converted into inorganic chlorides. The chlorine conversion rate can exceed 80%, or even 90%. Furthermore, step 230 produces less hydrogen chloride gas, which is less corrosive to equipment.

[0076] Step 210 and step 230 may be performed in the same device or in two or more devices. The devices may be a V-type mixer, a double-cone mixer, a horizontal ribbon mixer, a plowshare mixer, a fluidized bed mixer, a drum mixer, a vertical spiral mixer, a shearing granulator, an extruder, a melt mixer, a high-speed disperser, a kneader, a closed plasticator, or a planetary mixer.

[0077] Preferably, the residual amount of organochlorine in the treated waste plastic is less than 1000 ppm, even less than 500 ppm, and further less than 100 ppm.

[0078] Optionally, in step 250, the treated waste plastic is pyrolyzed at 250-600°C to obtain a crude pyrolysis product.

[0079] Step 250 can be performed in a reactor. The reactor can be a fixed bed reactor, a moving bed reactor, a bubbling bed reactor, a slurry bed reactor, a fluidized bed reactor, a trickle bed reactor, an overflow bed reactor, a rotary kiln reactor, an extruder, a falling film reactor, a wiped film reactor, or a shell and tube reactor.

[0080] Figure 3 A dechlorination system 300 is shown according to some embodiments of the present disclosure. The dechlorination system 300 may be used to implement Figure 2 The dechlorination system 300 is designed as an extruder and includes an extruder body 310, a waste plastic hopper 320, a dechlorinating agent hopper 330, an extruder vent 340, and an extruder outlet 350. The extruder body 310 mixes, heats, and propels the mixture of waste plastic and dechlorinating agent. The pressure within the extruder body 310 can be set below atmospheric pressure to facilitate the removal of volatile components.

[0081] The extruder body 310 may have one, two or more screws. The screw rotates in the extruder body 310, dividing, squeezing, stirring and shearing the heated and melted waste plastics and the dechlorinating agent to achieve sufficient mixing between the various components. The waste plastic hopper 320 is used to store waste plastics, especially waste plastics whose size has been reduced. The dechlorinating agent hopper 330 is used to store the dechlorinating agent. The waste plastic hopper 320 is close to the dechlorinating agent hopper 330 and is upstream of the material advancement direction on the extruder body 310. The extruder exhaust port 340 is arranged on the upper part of the extruder body 310, downstream of the dechlorinating agent hopper 330. The extruder exhaust port 340 is used to discharge gases or volatile components generated during the heating process, such as hydrogen chloride, water vapor, carbon dioxide, small molecular hydrocarbons or other volatile organic compounds (VOCs). The extruder exhaust port 340 can be connected to the tail gas absorption device ( Figure 3 The extruder outlet 350 is located at the end of the extruder body 310 and is used to output the processed waste plastics to the downstream.

[0082] Preferably, the extruder 310 is a twin-screw extruder, which can heat the material by means of screw heating, friction driven by screw rotation, barrel heating, and flow of heat-conducting oil in the barrel jacket.

[0083] Figure 4 The waste plastic processing system 400 according to some embodiments of the present disclosure is shown. The waste plastic processing system 400 can be used to implement Figure 2 The waste plastics processing system 400 is designed as a multi-stage series of extruders, comprising an extruder 1 body 410, a waste plastics hopper 420, a dechlorinating agent hopper 430, an extruder 1 exhaust port 440, a pipeline 450, an extruder 2 body 460, a pyrolysis catalyst hopper 470, a discharge port 480, and a gas outlet 490. Extruder 1 body 410 mixes, heats, and propels the mixture of waste plastics and dechlorinating agent. The pressure within extruder 1 body 410 can be set below atmospheric pressure to facilitate the removal of volatile components.

[0084] The extruder 1 body 410 may have one, two or more screws. The screw rotates in the extruder body 410, dividing, squeezing, stirring and shearing the heated and melted waste plastics and dechlorinating agent to achieve sufficient mixing between the various components. The waste plastic hopper 420 is used to store waste plastics, especially waste plastics whose size has been reduced. The dechlorinating agent hopper 430 is used to store the dechlorinating agent. The waste plastic hopper 420 is close to the dechlorinating agent hopper 430 and is located upstream of the material advancement direction on the extruder body 410. The exhaust port 440 of the extruder 1 is arranged on the upper part of the extruder body 410, downstream of the dechlorinating agent hopper 430. The exhaust port 440 of the extruder 1 is used to discharge gases or volatile components generated during the heating process, such as hydrogen chloride, water vapor, carbon dioxide, small molecular hydrocarbons or other volatile organic compounds (VOCs). The exhaust port 440 of the extruder 1 can be connected to the tail gas absorption device ( Figure 4 The pipe 450 is located at the end of the extruder 1 body 410 and is used to output the processed waste plastics to the extruder 2 body 460.

[0085] The extruder 2 body 460 may have one, two or more screws. The screw rotates in the extruder body 460 to divide, extrude, stir and shear the treated waste plastics and the pyrolysis catalyst to achieve sufficient mixing between the various components. In some embodiments, the extruder 2 body 460 can be heated to 250-600°C to allow the treated waste plastics to be pyrolyzed. The pyrolysis catalyst hopper 470 is used to store the pyrolysis catalyst. The pyrolysis catalyst hopper 470 is located upstream of the material advancement direction on the extruder 2 body 460. The discharge port 480 is used to output the partially pyrolyzed treated waste plastics to the downstream equipment ( Figure 4 The gas outlet 490 is used to discharge gaseous hydrocarbons and other gases generated by pyrolysis in the extruder body 460.

[0086] Preferably, the downstream equipment is configured as one or more pyrolysis units or reactors, which further pyrolyze the partially pyrolyzed treated waste plastics. Further pyrolysis can reduce the carbon-rich hydrocarbons in the solid residue, such as C18 hydrocarbons or higher hydrocarbons.

[0087] Optionally, the extruder 1 body and / or the extruder 2 body 460 is configured as a twin-screw extruder. The twin-screw extruder can heat the material by means of screw heating, screw rotation driving friction, barrel heating, and flow of heat-conducting oil in the barrel jacket.

[0088] Some specific embodiments of the present disclosure are described below with reference to experiments.

[0089] experiment

[0090] Chemical reagents:

[0091] Iron oxide, from Sinopharm Group, analytical grade.

[0092] Calcium oxide, from Sinopharm Group, analytical grade.

[0093] Calcium hydroxide, from Sinopharm Group, analytical grade.

[0094] Sodium hydroxide was from Sinopharm Group, analytical grade.

[0095] ZSM-5 molecular sieve, silicon-aluminum ratio of 40-70, from BASF, in powder form.

[0096] Polyvinyl chloride, available in solid powder form.

[0097] Low-density polyethylene, available in solid powder form.

[0098] Experimental steps:

[0099] Weigh polyvinyl chloride and low-density polyethylene and mix thoroughly to obtain a mixed plastic. Add a dechlorinating agent (if present) to the mixed plastic and mix thoroughly. Place the mixture in a reactor and introduce nitrogen protection at a flow rate of 80 mL / min. Raise the temperature at a heating rate of 10°C / min to the endpoint temperature shown in Tables 1 to 4, maintain this temperature for a period of time, and maintain the pressure in the reactor at 1.5 atmospheres during the reaction. During the reaction, the gas purged by the nitrogen flow is absorbed by a 1 mol / L NaOH solution.

[0100] After the reaction is complete, the NaOH absorption solution is weighed and analyzed for chloride ion concentration using ion chromatography. If the chloride ion concentration of the solution after absorption is greater than 5000 ppm, the solution is titrated with standard sulfuric acid solution. The amount of hydrogen chloride released is calculated based on the chloride ion concentration in the absorption solution after full absorption, and the hydrogen chloride release rate is calculated as the hydrogen chloride release divided by the weight of chlorine in the waste plastic, and is expressed as a weight percentage.

[0101] Separately, the reactor was opened and the treated waste plastic was ball-milled into a uniform powder using a SPEX 6875 liquid nitrogen cryomill. A portion of the fine powder was then dispersed by immersion in ultrapure water and shaken for 16 hours before ion chromatography analysis. The inorganic chlorine mass concentration in the treated waste plastic was determined qualitatively by retention time and quantitatively by peak area. The inorganic chlorine mass concentration was multiplied by the total weight of the treated waste plastic to obtain the inorganic chlorine weight of the treated waste plastic. Another portion of the fine powder was treated using a combustion method and the total chlorine content in the treated waste plastic was determined using a microcoulometric method (weight percentage). This total chlorine content was multiplied by the total weight of the treated waste plastic to obtain the total chlorine weight of the treated waste plastic. The residual organic chlorine weight of the treated waste plastic was calculated by subtracting the inorganic chlorine weight from the total chlorine weight of the treated waste plastic. The residual organic chlorine content was calculated by dividing the residual organic chlorine weight of the treated waste plastic by the weight of the treated waste plastic (ppm).

[0102] The weight of chlorine converted to inorganic substances (including hydrogen chloride and metal chlorides) is calculated by subtracting the weight of residual organic chlorine from the total weight of chlorine in the waste plastic before treatment. The chlorine conversion rate, expressed as a percentage, is calculated by dividing the weight of chlorine converted to inorganic substances by the total weight of chlorine in the waste plastic before treatment. Example 22 used ZSM-5 molecular sieve.

[0103] The dechlorinating agent content is calculated based on the weight of the dechlorinating agent divided by the total weight of the chlorine-containing waste plastics and the dechlorinating agent, and is expressed in weight percentage.

[0104] The material information, endpoint temperature, heating time, hydrogen chloride release rate, residual organic chlorine content and chlorine conversion rate of Examples 1 to 24 are listed in Tables 1 to 4, respectively.

[0105] Table 1

[0106]

[0107] Table 2

[0108]

[0109] Table 3

[0110]

[0111] Table 4

[0112]

[0113] For mixed waste plastics with high chlorine content (such as 3.86wt.%, 11.4wt.% or 12.3wt.% chlorine content), in the absence of a neutralizing agent and a catalyst, although long-term heating can achieve a very high chlorine conversion rate (such as 97.3% in Example 20), it takes a long time, and the chlorine element is almost entirely converted into hydrogen chloride. If a strongly alkaline neutralizing agent such as calcium oxide or calcium hydroxide is added to the system, although the amount of hydrogen chloride gas released during the treatment process of the mixed waste plastics can be reduced, the process is still time-consuming. Simultaneously, due to the high chlorine content of the waste plastics, it is necessary to add a lot of neutralizing agents, which not only produces alkali corrosion, but also has a greater impact on subsequent processes, such as producing more solid slag. Since the ZSM-5 molecular sieve does not have a neutralizing effect on hydrogen chloride, it has no significant effect on reducing the hydrogen chloride release rate.

[0114] For mixed waste plastics with low chlorine content: When using iron oxide alone as a dechlorinating agent to treat low-chlorine waste plastics, high iron oxide addition levels keep the hydrogen chloride release rate below 10%. However, the chlorine conversion rate remains around 80%. A significant amount of chlorine still exists in the form of organic chlorine.

[0115] When calcium oxide or calcium hydroxide is used alone for dechlorination, for example, when the calcium-chlorine ratio is equal to or greater than the stoichiometric ratio of 0.5, the hydrogen chloride release rate decreases as the calcium-chlorine molar ratio increases, but the chlorine conversion rate does not continue to improve. Furthermore, compared to Example 10 using calcium oxide, Example 11, which uses calcium hydroxide to dechlorinate waste plastics, achieves a lower hydrogen chloride release rate and a higher chlorine conversion rate.

[0116] As calcium hydroxide and ferric oxide are used to process mixed waste plastics simultaneously, unexpectedly, chlorine conversion does not improve along with the increase of ferric oxide addition (comparative example 1 and example 5).Similarly, comparative examples 5 and 8, when iron-chlorine ratio is 0.49, chlorine conversion does not obviously increase or decrease along with the change of calcium hydroxide addition.Example 9 also illustrates that iron-chlorine ratio is further increased to 0.57 and is also not enough to improve chlorine conversion.In other words, as needing to obtain high chlorine conversion, iron-chlorine ratio should select the numerical value lower than 0.49.Considering that ferric oxide can react with hydrogen chloride and the overall addition of dechlorinating agent should not be too high, it is suitable to select the calcium hydroxide addition with the lower calcium-chlorine ratio.

Claims

1. A method for dechlorinating waste plastics, comprising: a) adding a dechlorinating agent to waste plastics, wherein the waste plastics include at least one chlorine-containing polymer; b) heating the waste plastic and the dechlorination agent at 200-380° C. to obtain treated waste plastic, in, The dechlorinating agent is a mixture of a neutralizing agent and a catalyst; The neutralizing agent is at least one of oxides, hydroxides, carbonates, bicarbonates and basic carbonates of Group 1 and Group 2 metal elements, and the ratio of the total number of moles of the Group 1 and Group 2 metal elements to the number of moles of chlorine in the waste plastic is (0.1-0.7):1; and The catalyst is at least one metal oxide, the ratio of the total molar number of metal elements in the metal oxide to the molar number of chlorine elements in the waste plastic is (0.1-0.3):1, and the ratio of the total molar number of the Group 1 and Group 2 metal elements to the total molar number of metal elements in the metal oxide is (1.0-6.0):

1.

2. The method for dechlorinating waste plastics according to claim 1, wherein: The ratio of the total molar number of the Group 1 and Group 2 metal elements to the molar number of the chlorine element in the waste plastic is (0.4-0.6):

1.

3. The method for dechlorinating waste plastics according to claim 1, wherein: The ratio of the total molar number of the Group 1 and Group 2 metal elements to the total molar number of the metal elements in the metal oxide is (2.0-4.5):

1.

4. The method for dechlorinating waste plastics according to claim 1, wherein: The neutralizing agent is lithium oxide, lithium hydroxide, lithium carbonate, sodium hydroxide, sodium carbonate, sodium bicarbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, calcium oxide, calcium hydroxide, calcium carbonate or any mixture thereof; preferably, the neutralizing agent is calcium oxide or calcium hydroxide.

5. The method for dechlorinating waste plastics according to claim 1, wherein: The catalyst is ferric oxide, ferrous oxide, ferrosoferric oxide, ferric oxyhydroxide, aluminum oxide, aluminum oxyhydroxide, zinc oxide, red mud or any mixture thereof.

6. The method for dechlorinating waste plastics according to claim 1, wherein: The chlorine-containing polymer is selected from the group consisting of polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, polychloroprene, poly(4-chlorostyrene), polyvinyl chloride-styrene copolymer, vinyl chloride-vinyl acetate copolymer, acrylonitrile-chlorinated polyethylene-styrene terpolymer, chlorinated polyethylene, chlorinated polypropylene and chlorinated rubber.

7. The method for dechlorinating waste plastics according to claim 1, wherein: The waste plastics also contain polyolefins, polyamides, polyesters, polyurethanes or any mixtures thereof; preferably, the waste plastics contain polyethylene, polypropylene, polybutene, polyisobutylene, polymethylpentene, ethylene propylene copolymer, polyolefin elastomer, polystyrene, polyamide 6, polyamide 66, polyamide 46, polyamide 6T, polyamide 11, polyamide 12, polyethylene terephthalate, polybutylene terephthalate, polyadipate / butylene terephthalate, polylactic acid, acrylonitrile-butadiene-styrene copolymer or any mixtures thereof.

8. The method for dechlorinating waste plastics according to claim 1, wherein: The waste plastics have a chlorine content of not higher than 20 wt. %, based on the total weight of the waste plastics.

9. The method for dechlorinating waste plastics according to claim 1, wherein: In step b), the waste plastic and the dechlorination agent are heated at 230-360°C; preferably, the waste plastic and the dechlorination agent are heated at 250-350°C.

10. The method for dechlorinating waste plastics according to claim 1, wherein: Step b) lasts for 10-60 minutes; preferably, step b) lasts for 15-40 minutes.

11. The method for dechlorinating waste plastics according to claim 1, wherein: Step b) is carried out at a pressure of 0.5-5 standard atmospheres.

12. The method for dechlorinating waste plastics according to claim 1, wherein: Step b) is carried out under an inert atmosphere.

13. The method for dechlorinating waste plastics according to claim 1, wherein: The residual amount of organochlorine in the treated waste plastic is less than 1000 ppm, preferably less than 500 ppm, and more preferably less than 100 ppm.

14. The method for dechlorinating waste plastics according to claim 1, further comprising: The treated waste plastic is pyrolyzed at 250-600° C. to obtain a crude pyrolysis product.

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