Steam cracking device for converting plastic waste into olefin

Abstract

Disclosed is an integrated cracking unit for producing C2-C4 olefins based on the integrated use of renewable feedstock and at least plastic waste feedstock which is converted to crude gas at high efficiency.

Description

Technical Field

[0001] This disclosure relates to an integrated pyrolysis unit for producing C2-C4 olefins. More specifically, this disclosure relates to an integrated pyrolysis unit based on renewable feedstocks and plastic waste feedstocks. Background Technology

[0002] Cracking units are a key aspect of the petrochemical industry. They are the first step in producing downstream products such as resins and plastics by traditionally “cracking” fossil fuel-based materials.

[0003] However, fossil fuel-based feedstocks have raised growing concerns about sustainability.

[0004] Therefore, attempts to use non-fossil pyrolysis feedstocks were evaluated in order to improve circularity and sustainability.

[0005] Chemical recycling, such as chemical recycling in the form of plastic raw materials, includes the following steps: collecting plastic waste, then heating the plastic waste to break down the polymer to obtain smaller organic molecules, which are then recycled in the petrochemical industry.

[0006] Typically, the main effluent from the pyrolysis step is a liquid stream, also known as pyrolysis oil, which can undergo a steam cracking step to produce a gaseous fraction consisting of C2-C4 olefins. However, in terms of plastic waste feedstock, the overall yield of olefins, particularly ethylene and propylene, remains at around 35%, which is not entirely satisfactory.

[0007] Furthermore, since a large amount of plastic waste is degraded into pyrolysis oil, the steam cracking step will require a correspondingly large amount of specific energy to produce the desired olefins.

[0008] In view of the above, it would be important to develop a cracking unit capable of producing C2-C4 olefins from non-fossil feedstocks in high yield. Summary of the Invention

[0009] In one aspect, this disclosure provides a steam cracking apparatus comprising:

[0010] - At least one electric furnace for depolymerizing polyolefin-based plastic waste, said furnace operating with a crude gas efficiency of at least 70% based on the polyolefin content in the plastic waste, and

[0011] - At least one furnace for renewable feedstock having a final boiling point (FBP) of less than 550°C, and optionally,

[0012] - Hydrogenation unit.

[0013] More specifically, the pyrolysis apparatus may include:

[0014] - At least one electric furnace for depolymerizing polyolefin-based plastic waste, said furnace operating with a crude gas efficiency of at least 70% based on the polyolefin content in the plastic waste;

[0015] - At least one furnace for a renewable feedstock having a final boiling point (FBP) of <550°C; and

[0016] - At least one electric furnace for steam cracking of materials other than plastic waste and renewable raw materials;

[0017] - A quench / fractionation unit that receives the output of the furnace and produces a light hydrocarbon stream and a heavy liquid stream;

[0018] - The pyrolysis back-end separation unit receives light hydrocarbon streams from the quench / fractionation unit;

[0019] - Optionally, a hydrogenation unit is fed with a heavy liquid stream from a quench / fractionation unit and its output is connected to an electric furnace for steam cracking of feedstocks other than plastic waste and renewable materials; the apparatus is characterized in that the crude gas from the plastic waste furnace bypasses the quench / fractionation unit and is sent to a separation unit at the rear end of the pyrolyzer.

[0020] According to one specific implementation, the cracking unit also includes a hydrotreating / hydrocracking unit to upgrade heavy cracking residues and pyrolysis oil feed (Pyroil, PFO, HVGO, etc.).

[0021] As described above, in one specific embodiment, the pyrolysis unit also includes at least one other electric furnace for feedstocks other than plastic waste or renewable feedstocks (e.g., fossil-based feedstocks such as naphtha or natural gas). Attached Figure Description

[0022] Figure 1 This is a flow chart showing the integrated steam cracking unit according to the present disclosure. Detailed Implementation

[0023] In one particular embodiment, the electric furnace for depolymerizing polyolefin-based plastic waste is operated at a temperature of 400 to 750°C with plastic waste raw material comprising polyolefin with a polymer content greater than 80 wt% based on the plastic waste raw material.

[0024] Preferably, the plastic waste raw material is characterized in that: (a) based on the total weight of the polymer waste raw material, the total content of polyolefins, especially polypropylene (PP) and polyethylene (PE), is greater than 85 wt%, more preferably greater than 90 wt%, and especially greater than 95 wt%.

[0025] Preferably, based on the total amount of plastic waste raw materials, the upper limit of polyolefin content is 99 wt%, more preferably 98 wt%, and especially 97 wt%.

[0026] Furthermore, the total ash content of the plastic waste raw material is preferably less than 10 wt%, more preferably less than 5 wt%, and most preferably less than 3 wt%, defined as the residue after heating the polymer waste raw material in air at 800°C for 120 hours. Preferably, the plastic waste raw material is further characterized in that (i) for the case where the polymer waste raw material is in shredded form, the bulk density is 70 to 500 g / l, preferably 100 to 450 g / l, or for the case where the polymer waste raw material is in granular form, the bulk density is 300 to 700 g / l, the bulk density being determined according to DIN 53466. It has been found that the above-mentioned bulk density values ​​greatly contribute to achieving a continuous, defect-free depolymerization method and preventing feed line blockage and reactor fouling. In addition, it also helps to obtain low amounts of residue and enhanced depolymerization reaction, thereby increasing the yield of the desired product.

[0027] In a preferred embodiment, the plastic waste raw material is further characterized by: (i) a total volatile matter (TV) content of less than 4%, preferably less than 3%, measured as the weight loss of a 10 g sample after 2 hours at 200 mbar and 100°C.

[0028] In addition to the polyolefin components described above, the polymer waste raw materials used in the methods of this disclosure may include substantially all polymer materials, particularly those formed from synthetic polymers. Non-limiting examples include polyolefins other than PE and PP, such as polybutene-1 and ethylene-propylene elastomers, polystyrene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamide, polycarbonate, polyurethane, polyester, natural and synthetic rubber, tires, filled polymers, composite materials and plastic alloys, and plastics dissolved in solvents.

[0029] However, according to this disclosure which aims to maximize the production of light gaseous olefins, the plastic raw material is preferably composed mainly of polyolefins, and non-polyolefin polymer materials may be present only in an amount of less than 10%, preferably less than 5%, of the total amount of plastic waste raw material.

[0030] As described above, the polymer waste raw material can consist of one type of polyolefin waste, or it can be a mixture of two or more different polymer wastes. An embodiment in which the polyolefin waste is entirely composed of polyethylene (PE) is particularly preferred.

[0031] Polymer waste feedstock can be provided in a variety of different forms. In smaller-scale operations, polymer waste feedstock can be in powder form. In larger-scale operations, polymer waste feedstock can be in granular, flake, and powder form, for example, those with a particle size of 1 to 30 mm comprising at least 80 wt% (preferably 85%, 90%) of the feedstock, preferably 2 to 20 mm, more preferably 2 to 8 mm, or, when in the form of shredded flakes and / or film fragments, preferably with a particle size of 1 to 20 mm. In the context of this disclosure, having a particle size within a defined range means that 90 wt% of the particles have a particle size within the defined range. Particle size can be determined by sieving or by using a Beckman Coulters LS13320 laser diffraction particle size analyzer.

[0032] The plastic waste disclosed above is primarily composed of plastic materials and is typically named after the type of polymer that forms the main component of the polymer waste. Preferably, the plastic waste used as a raw material in the methods of this disclosure comprises more than 50 wt%, preferably more than 6 wt%, and more preferably more than 70 wt% of polymer materials by weight. Other components in the polymer waste raw material may be, for example, additives such as fillers, reinforcing materials, processing aids, plasticizers, pigments, light stabilizers, lubricants, impact modifiers, antistatic agents, inks, antioxidants, pigments, etc.

[0033] In one specific embodiment, the polymer waste used in the method of this disclosure preferably comprises polyolefins and polystyrene, such as high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), ethylene-propylene-diene monomer (EPDM), polypropylene (PP), and polystyrene (PS). Particularly preferred are polymer wastes comprising mixtures of polyolefins and polystyrene.

[0034] Other non-polyolefin polymer wastes, such as polyamides, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), nylon, and fluorinated polymers, can also be used in the methods of this disclosure. If present in the polymer waste, these polymers are preferably present in an amount of less than 10%, and especially less than 5%, of the total dry weight of the polymer waste raw material.

[0035] Preferably, the polymer waste is substantially free of thermosetting polymers. In this respect, "substantially free" means that the content of thermosetting polymers is less than 10 wt% of the polymer waste raw material, and even more preferably less than 5 wt%.

[0036] The polymer waste used in the methods of this disclosure is preferably selected from single plastic waste, mixed plastic waste, and rubber waste. Single plastic waste, substandard single virgin plastic, mixed plastic waste, rubber waste, or mixtures thereof are preferred. Substandard single virgin plastic, mixed plastic waste, or mixtures thereof are particularly preferred.

[0037] Polymer waste may also contain limited amounts of non-pyrolytic components, such as water, glass, stone, and metal, as contaminants. "Limited amount" preferably means less than 15 wt% of the total weight of the dry polymer waste raw material, more preferably less than 10 wt%.

[0038] The polymer waste may optionally be extruded before being used as a raw material in the methods of this disclosure. In some preferred embodiments, the polymer waste is granulated, and the granules are used as a raw material in the methods of this disclosure. In other preferred embodiments, the polymer waste is used in a molten state, for example at a temperature of 200°C to 300°C.

[0039] The polymer waste used as a particularly preferred type of raw material in the method of this disclosure is characterized by the following features:

[0040] i) Based on the total weight of the polymer waste raw materials, the content of polyolefins, especially polypropylene (PP) and / or polyethylene (PE) in the polymer waste is greater than 80 wt%, preferably greater than 85 wt%, more preferably greater than 90 wt%, and especially greater than 95 wt%.

[0041] ii) The polymer waste is shredded and optionally compacted polymer waste in the form of powder, flakes or agglomerates with a bulk density of 70 to 500 g / l, preferably 100 to 450 g / l, more preferably 200 to 440 g / l, especially 250 to 400 g / l, or the polymer waste is in the form of granules and has a bulk density of 250 to 700 g / l, the bulk density being determined according to DIN 53466;

[0042] iii) Total volatile matter (TV) content, measured as the weight loss of 10 g sample after 2 hours at 100°C and 200 mbar, is less than 5%, preferably less than 3%, more preferably less than 2%, and especially less than 1%.

[0043] iv) Based on the total weight of the polymer waste, the amount of polar polymer contaminants in the polymer waste is less than 5 wt%, more preferably less than 3 wt%;

[0044] v) Based on the total weight of the polymer waste, the amount of cellulose, wood and / or paper in the polymer waste is less than 5 wt%, more preferably less than 3%;

[0045] vi) Based on the total weight of the polymer waste, the total chlorine content is less than 1.0 wt%, preferably less than 0.5 wt%, and more preferably less than 0.1 wt%.

[0046] vii) The total ash content of the polymer waste raw material is less than 10 wt%, more preferably less than 5 wt%, and most preferably less than 3 wt%, defined as the residue after heating the polymer waste in air at 800°C for 120 hours. In other preferred embodiments, the ash content is 0.01 to 2 wt%, preferably 0.02 to 1.5 wt%, and more preferably 0.05 to 1.0 wt%.

[0047] In a preferred embodiment of this disclosure, the polymer waste used as a raw material in the method of this disclosure is limited by an upper limit on the amount of minor components, ingredients, or impurities expressed as a weight percentage. Preferably, the lower limit of the amount of these components, ingredients, or impurities in the preferred polymer waste is below the detection limit, or the lower limit is 0.001 wt%, 0.01 wt%, or 0.1 wt%.

[0048] Various technologies are known for separating materials from polymer waste streams. Moving beds, rotary drums, screens, and air separators are used to differentiate materials by size, weight, and density. Advanced classification of plastic waste using spectroscopic techniques (MIR, NIR [near-infrared]), X-ray, or fluorescence spectroscopy provides high-quality plastic waste streams with high polyolefin content.

[0049] Automatic separation technologies for waste plastics include dry sorting, electrostatic sorting, mechanical sorting methods (involving centrifugal force, specific gravity, elasticity, particle shape, selective crushing and mechanical properties), wet sorting (such as flotation sorting) and chemical sorting methods.

[0050] Suitable raw materials used in the methods of this disclosure can be obtained by applying any known sorting technique, such as those summarized in B. Ruj et al.: Sorting of plastic waste for effective recycling, Int. J. Appl. Sci. Eng. Res 4, 2015, 564-571.

[0051] Depolymerization

[0052] According to this disclosure, a method for depolymerizing plastic waste includes pyrolyzing the plastic waste at a temperature preferably 350 to 750°C, more preferably 420 to 700°C, more preferably 460 to 680°C, and especially 500 to 680°C. In particular, when depolymerization is solely pyrolysis, the temperature is preferably maintained in the range of 500°C to 700°C, more preferably in the range of 500 to 600°C.

[0053] The depolymerization method can be either thermal depolymerization or thermal catalytic depolymerization.

[0054] If a catalyst is present, it is selected from those containing an acidic compound as the active component, preferably selected from metal oxides, heteropolyacids, mesoporous silica, aluminosilicate catalysts, such as halloysite and kaolinite, and preferably selected from optionally modified zeolites. Among these, synthetic Y-type zeolites and ZSM-5 are particularly preferred.

[0055] A preferred type of catalyst comprises an acidic compound as the active component, which is deposited on a particulate, nonporous support by means of a coating agent.

[0056] Preferably, the catalyst of this disclosure is in particulate form. A particulate, non-porous support selected from sand, glass beads, and metal particles is preferred. The particulate, non-porous support can have any shape, such as spherical, cylindrical, or any non-uniform shape. In addition to being particulate, the support used in the catalyst of this invention is also non-porous. Within the meaning of this disclosure, non-porous should be understood as impermeable to gases (e.g., air) or liquids (e.g., water). To specifically design the catalyst of this disclosure for mixing with polymer waste undergoing depolymerization, the support preferably has an average particle size D50 of 0.2 to 20 mm, preferably 0.5 to 10 mm, more preferably 1 to 8 mm, and most preferably 1 to 6 mm, as determined by sieve analysis according to ISO 3310-1 / ASTM E11. Retsch's test sieve equipment with a braided wire mesh sieve (Ø 125 mm - 20 μm) is an example of a usable sieving device.

[0057] The sand is a preferred type of non-porous granular carrier, and preferably has the following particle size distribution:

[0058] Minimum maximum <3000µm 70% 90% >1400µm 40% 80% >1000µm 50% 80% <1000µm 0% 20%

[0059] The acidic compound of the catalyst disclosed herein is preferably selected from Al / Si mixed oxides, Al2O3, aluminosilicates, silica, and zeolites. Particularly preferred Al / Si mixed oxides in this disclosure refer to materials containing a mixture of Al2O3 and SiO2 having a neutral structure.

[0060] The particularly preferred zeolites mentioned in this disclosure are understood to be crystalline microporous aluminosilicates, which are composed of a general formula M n +x / n [AlO2]-x(SiO2) y The H₂O is composed of coplanar SiO₄⁻ and AlO₄⁻ tetrahedra, where n is the charge of the cation M, which is usually an alkali metal, alkaline earth metal, or hydrogen ion, preferably selected from H₂O. + Na + Ca2 + K+ and Mg2 + The ion is defined by z, and z defines the number of water molecules bound into the crystal structure. Zeolites differ from mixed Al / Si oxides in the pore structure and ionic properties they define. In a particularly preferred embodiment, the zeolite used as the acid compound is selected from zeolite Y, zeolite β, zeolite A, zeolite X, zeolite L, and mixtures thereof, especially zeolite Y and zeolite β. The listed zeolites are known and commercially available. Zeolites in which the metal ion M is replaced by hydrogen are particularly preferred. Other specific examples of suitable zeolite-type components used in this disclosure include, but are not limited to, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, TS-1, TS-2, SSZ-46, MCM-22, MCM-49, FU-9, PSH-3, ITQ-1, EU-1, NU-10, silica zeolite-1, silica zeolite-2, boron zeolite-C, boron zeolite-D, BCA, and mixtures thereof.

[0061] In a particularly preferred embodiment, the acidic compound is an Al / Si mixed oxide. The composition of the Al / Si mixed oxide used as a support can be adjusted as needed. However, depolymerization is particularly effective when the acidic compound contains specific amounts of Al₂O₃ and SiO₂. Therefore, in a preferred embodiment, the amount of Al₂O₃ contained in the acidic compound is 20 to 99 wt%, preferably 30 to 80 wt%, and especially 40 to 70 wt%, based on the total weight of the acidic compound. Furthermore, based on the total weight of the acidic compound, the acidic compound preferably contains 1 to 80 wt%, preferably 20 to 70 wt%, and especially 30 to 60 wt% of SiO₂.

[0062] Preferably, the acidic compound comprises an excess of Al2O3 relative to SiO2. More preferably, embodiments in which the weight ratio of Al2O3 to SiO2 in the acidic compound is 99:1 to 30:70, preferably 9:1 to 3:2, and particularly 4:1 to 3:2.

[0063] The SiO2 and Al2O3 contents of acidic compounds can be determined by using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0064] The coating agent used in the catalyst of this disclosure is preferably selected from oil, inorganic hydrogel, or a combination thereof. As an inorganic hydrogel, silica hydrogel is preferred. Regarding the oil used as the coating agent, a non-aromatic white mineral oil is preferred, and preferably based on isoparaffins. In a preferred embodiment, the oil used has a kinematic viscosity of 140 to 180 mm² / s, preferably 150 to 170 mm² / s, at 20°C, and / or a kinematic viscosity of 40 to 80 mm² / s, preferably 50 to 70 mm² / s, at 40°C, and / or a kinematic viscosity of 5 to 15 mm² / s, preferably 7 to 10 mm² / s, at 100°C. The kinematic viscosity can be determined according to ISO 3104.

[0065] Based on the amount of acidic compound, the preferred amount of coating agent is 1 to 300%, more preferably 2 to 150 wt%, more preferably 5 to 100 wt%, and most preferably 10 to 80 wt%. For hydrogels, the amount to be used refers to the dry weight.

[0066] In another preferred embodiment, the active compound is included in the catalyst of this disclosure in an amount of 0.5 to 6 wt%, preferably 2 to 4 wt%, based on the total weight of the catalyst.

[0067] The catalyst disclosed herein is preferably obtained by mixing a particulate nonporous support and a coating agent, and then adding an acidic compound in powder form to the resulting mixture. Optionally, the mixture may be heat-treated to obtain the catalyst. The heat treatment may be carried out, for example, at a temperature of 100 to 800°C, preferably 150 to 600°C. In a preferred embodiment, the particulate nonporous support undergoes a drying step before being mixed with the coating agent.

[0068] In a preferred embodiment, the catalyst is obtained by a method comprising the steps of: (a) mixing a particulate nonporous support and a coating agent; and (b) adding an acidic compound in powder form to the mixture of step (a).

[0069] In a particularly preferred embodiment, the catalyst is characterized as follows: (a) sand as a particulate, nonporous support; (b) an Al / Si mixed oxide or zeolite as an acidic compound; and (c) a mineral oil or silica hydrogel as a coating agent.

[0070] In addition to the catalyst components mentioned above, the catalyst package may also include a co-catalyst (e.g., clay) component and / or a solid base component, such as a metal hydroxide.

[0071] The gaseous effluent from the pyrolysis reactor is then collected and separated into gaseous and liquid depolymerization products.

[0072] The collected gaseous fraction can be separated into liquid and gaseous depolymerization products by condensation. Therefore, the liquid and gaseous depolymerization products can be further processed.

[0073] The method of this disclosure can produce little to no carbon. Therefore, in a preferred embodiment, the residue of the depolymerization method of this disclosure has a carbon content of less than 5 wt%, preferably less than 2 wt%, based on the total weight of the product.

[0074] The obtained liquid depolymerization products can be further separated. Therefore, the pyrolysis apparatus preferably also includes a step of distilling the liquid depolymerization products.

[0075] The method disclosed herein produces depolymerization products with high gas content.

[0076] Specifically, the amount of gaseous depolymerization products is at least 70 wt% of the total polyolefin content in the plastic waste, preferably greater than 75 wt%, more preferably greater than 80 wt%, and especially greater than 85 wt%.

[0077] In one particular embodiment, the amount of C2-C4 olefins in the gaseous depolymerization products is equal to or greater than 50 wt%, based on the total amount of hydrocarbons. Preferably, the amount of olefinic C2-C4 compounds is equal to or greater than 55%, more preferably greater than 60%, and especially greater than 65%, based on the total amount of hydrocarbons in the gaseous depolymerization products.

[0078] In one specific embodiment, the percentage of ethylene relative to the total amount of olefinic C2-C4 compounds is greater than 28 wt%, preferably greater than 30 wt%.

[0079] Furthermore, based on the total amount of hydrocarbons, the amount of C2-C4 hydrocarbons in the gaseous fraction of the depolymerization product is preferably higher than 80%, more preferably higher than 85%, and especially higher than 90%.

[0080] Gaseous products containing light olefins and light alkanes can be directly transferred to a separation unit at the back end of the pyrolyte, where the olefins are separated from other hydrocarbon components.

[0081] In a preferred embodiment, the gaseous product is sent to a cleaning / purification unit to remove contaminants before being fed to the separation unit. Such a unit may consist of several sections for removing contaminants such as HCl, HCN, H2S, H2O, NH3, COS, MeCl, MeSH, NOx, etc. An alkaline scrubber section is an example of a conventional unit suitable for this purpose.

[0082] exist Figure 1 In an alternative embodiment not shown, the gaseous stream from the cleaning / purification section may be fed to the quenching section of the steam pyrolyzer.

[0083] Once separated, the olefins and other hydrocarbon components can undergo various uses. Olefins, such as ethylene and propylene, can be used in polymerization processes and thus reintroduced into the plastics cycle. Unsaturated C4 hydrocarbons can be used in polymerization or undergo steam cracking steps, preferably after a hydrogenation step in a hydrogenation unit.

[0084] Saturated hydrocarbons, such as ethane, propane, and butane, can be fed directly to another steam cracking furnace in a conventional manner.

[0085] The liquid depolymerization products obtained from the distillation unit can also be sent to another steam cracking furnace. However, it is particularly preferred to perform a hydrotreating / hydrocracking step on the liquid products to upgrade the pyrolysis oil.

[0086] Plastic waste depolymerization furnace

[0087] The depolymerization method according to this disclosure can be carried out in a reactor comprising: (a) a feeding device for introducing polymer waste and catalyst into the reactor; (b) a pyrolysis device equipped with a heating unit, a gas discharge unit and a solid discharge unit; and (c) a condensation unit.

[0088] In a preferred embodiment, the reactor may include more than one pyrolysis unit.

[0089] In principle, any type of reactor used for pyrolysis can be used, provided that heating is generated by electricity. Examples include screw reactors, fluidized bed reactors, circulating gas-phase reactors with and without catalysts, slurry loop reactors or stirred tank reactors, fixed bed reactors, and fluidized bed reactors.

[0090] It can be, for example, a stirred vessel with rotating blades, or preferably, a horizontal screw reactor equipped with a screw for uniformly mixing the polymer waste in the pyrolysis unit throughout the depolymerization process. In the latter case, the residence time of the solids in the pyrolysis unit can be precisely defined by adjusting the rotational speed of the screw. Examples of screw reactors suitable for this disclosure are described in WO2017 / 173473, which is incorporated herein by reference, showing a particular type of screw in which a heating fluid flows.

[0091] In such a reactor, gas discharge units are distributed throughout the pyrolysis unit, and are provided with outlets for discharging depolymerized gaseous fractions and inlets for introducing clean gas into the pyrolysis unit.

[0092] Preferably, the gas exhaust unit is equipped with a filter membrane to prevent solids from remaining in the gaseous portion after being discharged from the pyrolysis unit. The gas exhaust unit is preferably made of metal or ceramic particles or fibrous materials.

[0093] In another embodiment, the electric furnace operating as a depolymerization reactor is of the type described in WO2022 / 136333, the relevant portions of which are incorporated herein by reference. Specifically, heat is supplied to the reactor via a circulating molten salt, the melting of which is achieved through electric heating.

[0094] In a preferred embodiment, the condensation unit includes several condensers, preferably operating at different temperatures. The temperature of the condensers can be set according to the boiling point of the condensate.

[0095] Polymer waste feedstock and catalyst (if used) are introduced into the pyrolysis unit via at least one feed device, and then heated to achieve depolymerization. Gaseous fractions generated during depolymerization are discharged through the outlet of the gas discharge unit and conveyed to the condensation unit for further processing. Any solid residues from depolymerization are discharged through the solids discharge unit. Clean gas for cleaning the gas discharge unit and the pyrolysis unit can be introduced through the inlet of the gas discharge unit.

[0096] Depolymerization products

[0097] The gaseous fractions produced during pyrolysis are separated into liquid and gaseous depolymerization products by condensation, for example.

[0098] The method disclosed herein produces depolymerization products with surprisingly high selectivity for gaseous fractions.

[0099] Liquid depolymerization products

[0100] The obtained liquid depolymerization products, especially when operated in the presence of a catalyst, exhibit surprisingly low contents of aromatic compounds, particularly surprisingly low contents of polycyclic aromatic compounds and asphaltenes. Therefore, the liquid depolymerization products obtained by the method of this disclosure are characterized by low contents of aromatic and olefinic components and high purity.

[0101] Preferably, the content of aromatic compounds in the obtained liquid depolymerization product is less than 10 mol%, more preferably less than 5 mol%, and particularly not more than 3 mol%. The content of aromatic components is measured as the content of aromatic protons in mol% by 1H-NMR spectroscopy.

[0102] Furthermore, the liquid depolymerization product obtained by the depolymerization method of this disclosure is characterized by a low content of olefins. Based on the total number of hydrocarbon protons, the content of olefins in the liquid depolymerization product is preferably less than 7 mol%, more preferably less than 5 mol%, and even more preferably less than 3 mol%; the content of olefins is determined based on the content of olefin protons as determined by 1H-NMR spectroscopy.

[0103] The liquid depolymerization product obtained by the method of this disclosure preferably has a boiling point range of 30 to 550°C, more preferably 50 to 250°C. By separation techniques, such as distillation, the depolymerization product can be separated into hydrocarbon fractions with different boiling point ranges, such as light naphtha fractions mainly containing C5 and C6 hydrocarbons with a boiling point range of 30°C to 130°C, and fractions mainly containing C6 to C6 hydrocarbons with a boiling point range of 130°C to 220°C. 12 Heavy naphtha fractions of hydrocarbons, mainly containing C9 to C6 hydrocarbons with boiling points ranging from 220°C to 270°C. 17 The kerosene fraction of hydrocarbons, or separated into other high-boiling fractions, such as diesel fuel, fuel oil or wax oil.

[0104] Preferably, the liquid depolymerization product contains little to no solid residue. In a preferred embodiment, the residue content of the liquid depolymerization product upon evaporation, as determined according to ASTM D381, does not exceed 5 ppm (w).

[0105] gaseous depolymerization products

[0106] The obtained gaseous depolymerization products showed surprisingly low contents of low-molecular-weight hydrocarbons, such as methane or ethane. Conversely, surprisingly, the gaseous depolymerization products contained unusually high contents of higher olefins, such as ethylene, propylene, and butene, which are typically required for polyolefin production.

[0107] As described above, based on the total amount of hydrocarbons in the gaseous depolymerization products, the amount of olefinic C2-C4 compounds is preferably equal to or greater than 55%, preferably greater than 60%, and especially greater than 65%. Therefore, the gaseous depolymerization products obtained by the method of this disclosure are characterized by high contents of any one of ethylene, propylene, and butene, and also by low contents of saturated low-molecular-weight hydrocarbons, particularly those of the general formula C... n H 2n+2 Hydrocarbons, where n is a real number from 1 to 4.

[0108] In a preferred embodiment, the gaseous depolymerization product of the method of this disclosure is characterized in that, based on the total weight of the gaseous depolymerization product after step (e) of the method of this disclosure, the CO content is at most 2 wt%, preferably at most 1 wt%, more preferably at most 3 wt%, most preferably at most 2 wt%, and especially at most 0.1-0.5 wt%.

[0109] In a preferred embodiment, the gaseous depolymerization product of the method of this disclosure is characterized in that, based on the total weight of the gaseous depolymerization product after step (e) of the method of this disclosure, the CO2 content is at most 5 wt%, preferably at most 3 wt%, and more preferably at most 2 wt%.

[0110] As already explained, the gaseous fraction can therefore be used directly as a feedstock for further processing downstream of the pyrolysis unit (e.g., in a crude gas compressor) to obtain a purified monomer stream, which can then be used for subsequent polymer production, thus allowing bypassing the typically required high-energy-consuming stream pyrolysis furnace while reducing CO2 output. In particular, using the method of this disclosure, the total yield of C2 / C3 olefins can be in the range of 60 to 70 wt%, depending on the amount of plastic waste feedstock.

[0111] Renewable feedstock furnace

[0112] The furnace operating with renewable raw materials can be one of those furnaces commonly used in the art. The reactor can be the same as that used for waste plastic furnaces, so, for example, in this case, a reactor disclosed in WO2017 / 173473 can also be used.

[0113] In terms of operation, it can be operated with bio-naphtha and / or biodiesel as the target products. For example... Figure 1 As shown, the liquid output products of this furnace can be combined with the liquid outputs of other furnaces and sent to the fractionation stage. Subsequently, the pyrolysis fuel oil fraction (PFO) can undergo a hydrotreating / hydrocracking stage and then be reintroduced into a conventional naphtha furnace, where it can be converted into light products including olefins.

[0114] The renewable feedstock used in the renewable feedstock furnace is preferably derived from biomass and may preferably include oils and fats from one or both animal and plant sources. Oils and fats may include rapeseed oil, palm oil, palm kernel oil, olive oil, soybean oil, sesame oil, castor oil, jatropha oil, corn oil, and other vegetable oils, terpenes, fish oil, lard, and beef tallow. Oils and fats collected from certain types of algae, such as animal fats, and mixtures thereof may be used. Additionally, waste cooking oils, such as tempura oil, may also be used. Oils and fats that solidify at room temperature (e.g., lard and beef tallow) can be melted and liquefied by preheating, so that the oils and fats may be liquid or solid.

[0115] Although various methods for producing biofuels (including transesterification) are available, the furnace will preferably be operated according to hydrotreating or catalyst-assisted pyrolysis methods.

[0116] Hydrotreating is a process performed under high pressure, such as 10 MPa. Oxygen in the feedstock fat is primarily removed as water, and the unsaturated bonds derived from the unsaturated oil are saturated to obtain a hydrocarbon oil with a boiling point range similar to that of light oils.

[0117] In catalyst-assisted cracking, various options are possible. For example, a fluidized bed catalytic cracking unit with a reaction zone, separation zone, stripping zone, and regeneration zone can be used, and a feedstock containing biomass can be added to the reaction zone at an outlet temperature of 480 to 540°C. In this method, a solid acid catalyst, such as ultrastable Y-type zeolite or silica-alumina oxide, can be used. Alternatively, when using a solid acid catalyst heated to a temperature range of 350 to 450°C, liquid oil can be used in the reaction vessel. Upon contact with the solid acid catalyst, oxygen-containing components are removed from the oil and catalytically cracked to produce a hydrocarbon mixture mainly composed of olefins and alkanes with 9 to 24 carbon atoms, having a final boiling point (FBP) of less than 550°C, preferably less than 450°C, more preferably less than 350°C, even more preferably less than 300°C, and especially less than 250°C.

[0118] In a preferred aspect, a decarboxylation / decomposition catalyst as described in WO2010050186A1 is used, the relevant portion of which is incorporated herein by reference. The catalysts disclosed and used therein are capable of cracking and decomposing fats and oils to primarily produce C8-C24 hydrocarbons.

[0119] It will be apparent to those skilled in the art that the pyrolysis unit of this disclosure is capable of producing olefins, particularly ethylene and propylene, in very high yields using non-fossil feedstocks, which increases the sustainability of the method.

[0120] As mentioned above, the integrated pyrolysis unit also includes at least one other electric furnace for feedstocks other than plastic waste (e.g., fossil-based feedstocks such as naphtha or natural gas). With the presence of this additional furnace operating in a conventional manner, the integrated pyrolysis unit is well-equipped to process any type of feedstock, thus increasing versatility while also ensuring greater sustainability and circularity.

[0121] Reference Figure 1 As can be seen, the plastic waste fed into the furnace originates from the initial stages of sorting, washing, and pretreatment (e.g., grinding). These operations can be carried out in the same unit, which can be located in the same steam pyrolysis unit site or elsewhere.

[0122] Steam pyrolyzers can be equipped with several furnaces with dedicated feedstocks. In addition to furnaces for plastic waste and renewable feedstocks, there are more conventional furnaces for fossil-based feedstocks such as naphtha and LNG / butane / propane. Furthermore, there are recirculated gas furnaces that receive the heavy portion of the pyrolyzer's downstream separation unit.

[0123] All liquid output from the furnace is directed to a quench / fractionation unit, which generates two streams: a light hydrocarbon stream that is fed to a downstream separation unit, and a heavy liquid stream (PFO) that is reintroduced into the naphtha furnace after undergoing hydrotreating / cracking purification steps.

[0124] In addition to the liquid output, the plastic waste furnace also produces a gaseous stream (crude gas), which passes through adsorption columns, such as Selexsorb for removing heteroatom impurities, Cl-guard for removing halogens, and Si-guard for removing silicon compounds. Optionally, the crude gas is also directed to an alkaline scrubber for removing acidic components, thus becoming a clean gas stream entering the downstream separation unit of the pyrolysis unit. As described, the latter unit produces olefins and other products that can be readily used for specific purposes such as olefin polymerization. Optionally, after the hydrogenation step, a portion of the separated products is alternatively reintroduced into the recycle gas furnace.

[0125] Finally, the pyrolysis unit is also equipped with a system for removing, processing, and disposing of solid carbonaceous products (Char) generated in the plastic waste furnace.

[0126] This disclosure will be explained in more detail with reference to the embodiments provided below.

[0127] Example

[0128] The following analytical methods were used:

[0129] 1) GC MS is used for liquid and gas analysis.

[0130] 2) After decoking the reactor residue at 800℃, the carbon residue is determined based on mass balance.

[0131] 3) Simulated distillation (SimDist) analysis was used to characterize the liquid content according to ASTM D 7213:2012. Final boiling point (FBP), boiling temperature at 50%, and initial boiling point (IBP) were obtained from SimDist.

[0132] 4) The total content of unsaturated components in liquid condensates is characterized by bromine value determination using an 848 Titrino Plus (Metrohm AG, Herisau, Switzerland) equipped with a dual PT wire electrode with an integrated PT1000 temperature sensor and a 10 ml burette, according to ASTM D1159-01 (as described in Metrohm Application Bulletin 177 / 5e, December 2018). Bromine value (BrNo.) indicates the amount of bromine absorbed (in grams) from 100 grams of sample.

[0133] 5) 1H-NMR analysis was performed by dissolving the liquid condensate sample in CDCl3 and characterizing the sample using proton NMR spectroscopy. Aromatic, alkene, and aliphatic protons were designated according to the chemical shifts summarized in Table 1:

[0134] Table 1 – Integration region in 1H-NMR spectra

[0135] Peak attribution 1H chemical shift (ppm) <![CDATA[I1 (Aromatic protons)]]> 8.25–7.27 <![CDATA[CDCl3 - Solvent]]> 7.26 <![CDATA[I2 (Aromatic protons)]]> 7.25–6.60 <![CDATA[I3 (olefinic proton – type 2)]]> 6.60–5.95 <![CDATA[I4 (olefinic proton – type 1)]]> 5.95–5.67 <![CDATA[I5 (olefinic proton – type 2)]]> 5.67–5.35 <![CDATA[I6 (olefinic proton – type 3)]]> 5.35–5.15 <![CDATA[I7 (olefinic proton – type 1)]]> 5.15–4.85 <![CDATA[I8 (olefinic proton – type 4)]]> 4.85–4.40 <![CDATA[I9… (alkane protons)]]> 4.40–0.25

[0136] Assume that the listed types of olefinic protons correspond to the following structures:

[0137]

[0138] The amounts of aromatic, alkene, and aliphatic protons can be determined based on the integral of a specified peak using the following equation:

[0139] Aromatic protons mol% = [(I1+I2) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)] %

[0140] The proton type of alkenes is calculated as follows: 1 mol% = [(I₄+I₇) / (I₁+I₂+I₃+I₄+I₅+I₆+I₇+I₈+I₁)] %

[0141] The proton type of alkenes is 2 mol% = [(I3+I5) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)] %

[0142] The proton type of alkenes is 3 mol% = [(I6) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)] %

[0143] The proton type of alkenes is 4 mol% = [(I8) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)] %

[0144] The percentage of protons in alkanes (mol%) is calculated as follows: [(I9) / (I1+I2+I3+I4+I5+I6+I7+I8+I9)] %

[0145] 6) The water content of the catalyst was determined on 0.5 to 1 g samples at 180 °C using Sartorius MA45 (Sartorius AG, Göttingen, Germany).

[0146] 7) To determine the pH of the hydrodepolymerization product, a liquid sample of the hydrodepolymerization product was extracted with water at a water:sample volume ratio of 1:5 and the pH of the aqueous solution was measured.

[0147] 8) The characteristics of the organic waste raw materials used were determined as follows:

[0148] Because the composition of organic waste can vary, samples of 20 to 100 g of polymer waste were ground and analyzed. Alternatively, granular samples of polymer waste were analyzed using the following methods:

[0149] i) Total volatile matter (TV) is measured as the weight loss of a 10 g sample after 2 hours at 100 °C and 200 mbar.

[0150] ii) Determine the water content by Karl Fischer titration using a device from Metrohm 915 KFTi-Touch equipped with a PT100 indicator electrode for volumetric KF titration, in accordance with Metrohm Application Bulletin 77 / 3e conforming to ASTM E203.

[0151] iii) IR spectroscopy is used for qualitative identification of various polymers (PP, PE, PS, PA, PET, PU, ​​polyester) and additives, such as CaCO3.

[0152] iv) Standard elemental analysis was used to determine the wt% of H, C, N (DIN 51732: 2014-07) and S (tube furnace, ELTRA GmbH, Haan, Germany, DIN 51724-3: 2012-07).

[0153] v) 1H-NMR is used to determine the composition of polymers soluble in solvents sufficient to record 1H-NMR spectra: PE / PP equilibrium (including copolymers), PET, PS.

[0154] vi) Determine the ash content of plastics at 800°C according to DIN EN ISO 3451-1 (2019-05).

[0155] vii) Determine the bulk density of polymer waste according to DIN 53466.

[0156] viii) Corrosivity was determined by the pH value of the aqueous solution (5 g sample in 50 ml distilled water) after 3 h of contact.

[0157] ix) Inductively coupled plasma atomic emission spectrometry (ICP-AES) is used for quantitative elemental determination (total chlorine content, Si or metal content).

[0158] x) The ash content of liquid feedstocks (e.g., pyrolysis oil) is measured according to ASTM D482-19.

[0159] raw material:

[0160] Some of the following organic wastes are used as raw materials:

[0161] A: Granular agricultural and industrial packaging films.

[0162] The average raw material characteristics of the three samples are summarized in Table 2.

[0163] Table 2:

[0164]

[0165] *) Other contents include inorganic, polymeric or organic pollutants and volatile components.

[0166] Ash content: Ash content

[0167] TV: Total Volatile Matter

[0168] BD: Bulk Density

[0169] CL: Total chlorine content

[0170] PE: Polyethylene content

[0171] PP: Polypropylene content

[0172] PET: Polyethylene terephthalate content

[0173] PS: Polystyrene content

[0174] PA: Polyamide content

[0175] Other content: content of other pollutants

[0176] The following examples illustrate the thermal depolymerization of plastic waste in an electric furnace. It is evident that the large amount of gaseous products allows for efficient separation into individual components at the downstream end of the pyrolysis unit.

[0177] Depolymerization

[0178] The raw materials are introduced into a reactor equipped with an electric heating unit, a gas discharge unit, and a solid discharge unit; a condenser and a screw are used to uniformly mix the reactor contents during depolymerization. The depolymerization conditions are summarized in Table 3. The obtained gaseous fraction is further separated into liquid and gaseous depolymerization products by condensation. The amounts of the obtained fractions are also given in Table 3.

[0179] Table 3: Process Parameters and Quality Balance (a)

[0180]

[0181] (a)(a) The amount not accounted for to 100% was due to loss; (b) A large amount of wax floated in the heterogeneous liquid; +) The liquid is a combination of all fractions and may contain some waxy solid particles and agglomerates, which will disappear when heated to >50°C.

[0182] The above data show that the catalyst of this disclosure produces a large amount of gaseous depolymerization products and maintains good performance even when heterogeneous materials are added to the feedstock. The analytical results of the gaseous depolymerization products are summarized in Table 4.

[0183] Table 4: Mass balance of gaseous depolymerization products

[0184]

[0185] HC: Hydrocarbon

[0186] Olefins: the sum of ethylene, propylene, and butene

[0187] Olefins / HC: Percentage of all olefins relative to total hydrocarbons

[0188] As shown in Table 4, the method of this disclosure produces gaseous depolymerization products containing a large amount of monomers, which can be used as polymerization feedstock after purification. Any saturated gaseous hydrocarbons can be processed back into the steam cracking furnace in the usual manner.

[0189] The following examples illustrate the thermocatalytic depolymerization of plastic waste in an electric furnace. It is evident that the large amount of gaseous products allows for efficient separation into individual components at the downstream end of the pyrolysis unit.

[0190] raw material :

[0191] Some of the following organic wastes are used as raw materials:

[0192] A1: Granular agricultural and industrial packaging film.

[0193] A2) Shredded multilayer PEX pipe waste with aluminum layer (particle size <20 mm)

[0194] B) Shredded PEX pipe waste with EVOH (particle size <20 mm)

[0195] C) Shredded PEX pipe waste with an aluminum layer (particle size <20 mm)

[0196] D) Shredded single-layer PEX pipe waste (particle size <20 mm)

[0197] E) Shredded cross-linked waste from high-voltage cables (particle size <20 mm)

[0198] F) Mixed plastic waste from household packaging, consisting of shredded and granular materials (comparison)

[0199] The characteristics of the raw materials are summarized in Table 5.

[0200] Table 5:

[0201]

[0202] *) Other contents include inorganic, polymeric or organic pollutants and volatile components.

[0203] The catalyst used in the examples of using silica hydrogel coating agents was prepared as follows:

[0204] 25.0 kg of sand was placed in a 60 L steel drum fitted with a nut and equipped with a Teflon insert. 500 ml of water (corresponding to 2.0 wt% relative to the sand) was added, and the drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). 24.5 kg of the resulting mixture was placed in another drum, and 1000 g of a 1:1 ground mixture of free-flowing silica hydrogel and acidic compound (corresponding to a 2 wt% loading) was added. The drum was placed on a rotary ring mixer and rotated for 1 hour (approximately 100 rpm). At the end of the mixing process, a free-flowing catalyst was obtained, in which the acidic compound particles were uniformly distributed on the surface of the sand particles. The resulting mixture was vacuum dried at 120 °C for 6 h.

[0205] Silica hydrogels were prepared according to the procedure described in Example 1 of EP1290042. The solids content of the hydrogel sample was 20 wt%. The D50 of the milled mixture of silica hydrogel and acidic component was 80-100 μm according to ASTM D4438.

[0206] Table 6 summarizes the catalysts used, with the amount of acidic compounds given as wt% relative to sand.

[0207] Table 6

[0208]

[0209] Acidic compounds:

[0210] Zeolystβ (CP811E-75) is commercially available from PQ Corporation, Malvern, PA, USA.

[0211] Depolymerization

[0212] The same equipment as described in the preceding examples was used. The depolymerization conditions are summarized in Table 7. The obtained gaseous fraction was further separated into liquid and gaseous depolymerization products by condensation. The amounts of the obtained fractions are also given in Table 7.

[0213] Table 7: Process Parameters and Quality Balance (a)

[0214]

[0215] (a) (a) The amount not accounted for to 100% was due to loss; (b) A large amount of wax floated in the heterogeneous liquid; +) The liquid is a combination of all fractions and may contain some waxy solid particles and agglomerates, which will disappear when heated to >50°C*.

[0216] The above data show that the method of this disclosure produces a large amount of gaseous depolymerization products, and maintains good performance even when heterogeneous materials are added to the feedstock. The analytical results of the gaseous depolymerization products are summarized in Table 8.

[0217] Table 8: Mass Balance of Gaseous Depolymerization Products

[0218]

[0219] *） The catalyst used in three consecutive operations maintained good selectivity and was then regenerated by heating it in air to 800°C and sieving out smaller particles (ash) of <500 μm.

[0220] HC: Hydrocarbon

[0221] Olefins: the sum of ethylene, propylene, and butene

[0222] Olefins / HC: Percentage of all olefins relative to total hydrocarbons

[0223] As can be seen from Table 8, the method of this disclosure produces gaseous depolymerization products, which contain a large number of monomers and can be used as polymerization raw materials after purification.

Claims

1. A steam pyrolysis apparatus, comprising: - At least one electric furnace for depolymerizing polyolefin-based plastic waste, said furnace operating with a crude gas efficiency of at least 70% based on the polyolefin content in the plastic waste; - At least one furnace for renewable feedstock having a final boiling point (FBP) of <550°C; and - At least one electric furnace for steam cracking of materials other than plastic waste and renewable raw materials; - A quench / fractionation unit that receives the output of the furnace and produces a light hydrocarbon stream and a heavy liquid stream; - A pyrolysis back-end separation unit that receives the light hydrocarbon stream from the quench / fractionation unit; - Optionally, a hydrogenation unit is fed with the heavy liquid stream from the quench / fractionation unit and its output is connected to the electric furnace for steam cracking of materials other than plastic waste and renewable feedstocks; the apparatus is characterized in that the crude gas from the plastic waste furnace bypasses the quench / fractionation unit and is sent to the separation unit at the rear end of the cracker.

2. The steam cracking apparatus according to claim 1, further comprising a hydrogenation unit for performing hydrogenation / hydrocracking to upgrade the liquid depolymerization product (pyrolysis oil) from one or both of the plastic waste furnace and the renewable feed furnace.

3. The steam pyrolysis apparatus according to any one of the preceding claims, wherein the plastic waste feedstock is characterized in that: (a) the total content of polyolefins, particularly polypropylene (PP) and polyethylene (PE), based on the polymer content of the plastic waste feedstock is greater than 85 wt%.

4. The steam pyrolysis apparatus according to any one of the preceding claims, wherein the polyolefin content is at an upper limit of 99 wt%, more preferably 98 wt%, and especially 97 wt%, based on the total amount of plastic waste raw material.

5. The steam pyrolysis apparatus according to any one of the preceding claims, wherein the polymer content of the plastic waste raw material is entirely composed of polyethylene (PE).

6. The steam cracking apparatus according to any one of the preceding claims, wherein the depolymerization reaction is carried out in the plastic waste furnace at a temperature of 350 to 750°C, preferably 420 to 700°C.

7. The steam cracking apparatus according to any one of the preceding claims, wherein the depolymerization reaction in the plastic waste furnace is thermocatalyzed.

8. The steam cracking apparatus according to claim 7, wherein the catalyst is selected from those containing an acidic compound as an active component, and the acidic compound is preferably selected from metal oxides, heteropoly acids, mesoporous silica, aluminosilicate catalysts and zeolites.

9. The steam cracking apparatus according to claim 8, wherein the catalyst comprises an acidic compound as an active component, which is deposited on a particulate nonporous support by means of a coating agent.

10. The steam cracking apparatus according to any one of the preceding claims, wherein the plastic waste furnace operates at an efficiency of greater than 75 wt%, more preferably greater than 80 wt%, in crude gas production based on the polyolefin content in the plastic waste.

11. The steam cracking apparatus according to claim 10, wherein, based on the total amount of hydrocarbons, the amount of C2-C4 olefins in the crude gas depolymerization products is equal to or greater than 50 wt%.

12. The steam cracking apparatus according to claim 11, wherein the CO2 content is at most 5 wt%, preferably at most 3 wt%, and more preferably at most 2 wt%, based on the total weight of the crude gaseous depolymerization products.

13. The steam pyrolysis apparatus of claim 1, wherein the crude gas is sent to a cleaning / purification unit to remove contaminants before being sent to the downstream separation unit of the pyrolysis unit.

14. The steam cracking apparatus of claim 13, wherein the crude gas is directed to an adsorption column, such as Selexsorb for removing heteroatom impurities, Cl-guard for removing halogens, and Si-guard for removing silicon compounds.

15. The steam cracking apparatus according to one or more of claims 13 and 14, wherein the crude gas is directed to an alkaline scrubber for removing acidic components.

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