EP4642869A1

EP4642869A1 - Method for purifying pyrolysis oil, purified pyrolysis oil and use thereof

Info

Publication number: EP4642869A1
Application number: EP23837204.9A
Authority: EP
Inventors: Hang Zhou; Yuan ZOU; Sheng Jie Wang; Yi Bin XU
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2022-12-30
Filing date: 2023-12-20
Publication date: 2025-11-05
Also published as: WO2024141353A1; CN118272119A; KR20250129084A

Abstract

The present disclosure relates to a method for purifying pyrolysis oil, comprising: (i) mixing pyrolysis oil containing hydrocarbons and impurities with an extraction solution; (ii) subjecting the mixed pyrolysis oil and extraction solution to liquid-liquid separation, to obtain a hydrocarbon-containing raffinate and an impurity-containing extract liquid; (iii) mixing the raffinate with a washing solution; and (iv) subjecting the mixed raffinate and washing solution to liquid-liquid separation, to obtain a processed pyrolysis oil, wherein the extraction solution is a solution of an extracting agent in a polar solvent, the extracting agent being selected from the group of iron compounds, aluminum compounds, magnesium compounds, nickel compounds, copper compounds, zinc compounds and mixtures thereof. The present disclosure also relates to a purified pyrolysis oil and the use thereof.

Description

Method for purifying pyrolysis oil, purified pyrolysis oil and use thereof

Technical Field

The present disclosure relates to the technical field of separation, in particular to a method for separating and purifying pyrolysis oil, a purified pyrolysis oil, and the use of the purified pyrolysis oil.

Background of the Invention

Waste plastic pyrolytic conversion and utilization technology involves the conversion of waste plastics from which impurities have been removed to low-molecular-weight compounds or oligomers by pyrolysis or catalytic pyrolysis, etc. As this technology has developed, large amounts of pyrolysis oil have been produced.

Compared with naphtha, pyrolysis oil contains larger amounts of sulfur-containing compounds, chlorine-containing compounds, nitrogen-containing compounds, gums, and other solid impurities. The presence of these impurities lowers the quality of the oil product and has an impact on reprocessing of the oil product. For example, in downstream processes such as hydrocracking purification or steam cracking, the presence of chlorine-containing compounds will lead to the production of hydrogen chloride, which corrodes equipment pipelines. Sulfur-containing compounds will lead to the production of sulfur-containing harmful gases. Nitrogen-containing compounds will not only produce harmful gases such as nitrogen oxides but will also make the oil product less stable. Gums and asphaltenes will cause many problems such as scaling of equipment, reduced heat transfer efficiency and catalyst poisoning.

Known processes for removing heteroatoms from pyrolysis oil include hydrogenation removal and non-hydrogenation removal.

Non-hydrogenation methods of removing heteroatoms include nitrogen removal by acid extraction, nitrogen removal using a solvent, and nitrogen removal by adsorption, etc.

US granted patent US4960508A has disclosed a method of extracting nitrogen-containing heterocyclic compounds from petroleum. The method employs two steps, using a concentrated acid solution and a dilute acid solution separately to extract alkaline nitrogen heterocyclic compounds from petroleum.

International application publication WO2011006312A1 has disclosed an oil product purification process. In the process, a feedstock oil and a purifying agent containing water and a flocculant are added to an emulsification tank, the purifying agent and the feedstock oil being mixed and emulsified. The emulsified oil enters a separating apparatus, and a purified oil product is obtained.

US patent application publication US20210277324A1 has disclosed a method for purifying a recovered or renewable organic material containing more than 20 ppm Cl. The method comprises a step of using an aqueous solution of an alkali metal hydroxide to purify a recovered or renewable organic material, and a step of subjecting the purified recovered or renewable organic material to hydrogenation treatment.

Non-hydrogenation methods of removing heteroatoms are particularly anticipated, as they have low equipment requirements, simple processes, and low energy consumption.

Summary of the Invention

According to one aspect of the present disclosure, a method for purifying pyrolysis oil is provided, comprising:

(i) mixing pyrolysis oil containing hydrocarbons and impurities with an extraction solution;

(ii) subjecting the mixed pyrolysis oil and extraction solution to liquid-liquid separation, to obtain a hydrocarbon-containing raffinate and an impurity-containing extract liquid;

(iii) mixing the raffinate with a washing solution; and

(iv) subjecting the mixed raffinate and washing solution to liquid-liquid separation, to obtain a processed pyrolysis oil, wherein the extraction solution is a solution of an extracting agent in a polar solvent, the extracting agent being selected from the group of iron compounds, aluminum compounds, magnesium compounds, nickel compounds, copper compounds, zinc compounds and mixtures thereof.

According to another aspect of the present disclosure, a purified pyrolysis oil is provided, obtained by the following steps:

(i) mixing pyrolysis oil containing hydrocarbons and impurities with an extracting agent;

(iii) mixing the raffinate with a washing solution; and

(iv) subjecting the mixed raffinate and washing solution to liquid-liquid separation, to obtain a processed pyrolysis oil, wherein the extraction solution is a solution of an extracting agent in a polar solvent, the extracting agent being selected from the group of iron compounds, aluminum compounds, magnesium compounds, nickel compounds, copper compounds, zinc compounds and mixtures thereof. According to another aspect of the present disclosure, provided is the use of a purified pyrolysis oil as a starting material for a steam cracking process.

The method for purifying pyrolysis oil according to the present disclosure has simple steps, causes little corrosion or contamination of equipment, and has high removal rates for elements such as nitrogen and sulfur.

Brief Description of the Drawings

Fig. 1 shows a chemical circulation process according to embodiments of the present disclosure. Fig. 2 shows a method for purifying pyrolysis oil according to embodiments of the present disclosure.

Fig. 3 shows a purification system according to embodiments of the present disclosure.

Detailed description

The present disclosure is described in further detail below in conjunction with embodiments. It should be understood that the specific embodiments described here are merely used to explain the present disclosure, not to limit it.

In the description of the present disclosure, descriptions of terms such as “an embodiment”, “embodiments”, “example”, “specific example” or “examples” mean that the specific feature, structure, material or characteristic described in conjunction with the embodiment or example concerned is included in at least one embodiment or example of the present disclosure. In the present disclosure, illustrative expressions of these terms are not necessarily directed at the same embodiment or example. Furthermore, specific described features, structures, materials, or characteristics may be suitably integrated in any one or more embodiments or examples. In addition, in the absence of contradiction, those skilled in the art may integrate or combine different embodiments or examples and features of different embodiments or examples described in the present disclosure.

Definitions

The word “comprises” or “includes” used in the present disclosure is intended as an open conjunction, meaning that the named element is included, without necessarily excluding other unnamed elements. The phrase “basically consisting of...” or “essentially consisting of...” is intended to indicate the exclusion of other elements that are important to the composition in any way. The phrase “consists of...” or “consisting of...” is intended as a conjunction, meaning that all elements other than those listed are excluded, except for small amounts of impurities alone. In the present disclosure, the term “pyrolysis” means a chemical process which a polymer- containing solid mixture (such as solid waste or feedstock produced therefrom) undergoes at high temperature, in which chemical bonds are forcibly opened and smaller molecules are produced (including but not limited to hydrocarbons with 1 - 60 carbon atoms, other non-hydrocarbon organic substances, inorganic substances such as hydrogen sulfide, nitrogen oxides, sulfur oxides, etc.). For example, low density polyethylene (LDPE) can undergo pyrolysis at high temperature to produce a mixture of various hydrocarbons.

A pyrolysis product is a composition, and might be one or more of pyrolysis gas, pyrolysis oil and pyrolysis wax. The pyrolysis product might be in a gas phase, liquid phase, or solid phase at 25 °C and 1 atmosphere. A crude pyrolysis product is a product which is obtained directly from a pyrolysis process, or which has only undergone operations such as condensing, fractionation or filtration after the pyrolysis process.

Pyrolysis gas is a composition which is gaseous when measured at 25 °C and 1 atmosphere, and at least a portion thereof is obtained from pyrolysis of solid waste at a high temperature such as 300 °C - 800 °C.

Pyrolysis oil is a composition which is liquid when measured at 25 °C and 1 atmosphere, and at least a portion thereof is obtained from pyrolysis of solid waste at a high temperature such as 300 °C - 800 °C.

Pyrolysis wax is a composition which is solid when measured at 25 °C and 1 atmosphere, and at least a portion thereof is obtained from pyrolysis of solid waste at a high temperature such as 300 °C - 800 °C.

Pyrolysis gas, pyrolysis oil and/or pyrolysis wax generally contain hydrocarbons, such as saturated, unsaturated, aromatic and alicyclic hydrocarbons with different numbers of carbon atoms. Pyrolysis oil and/or pyrolysis wax might also contain other organic substances, water, gums, inorganic salts or other impurities. Pyrolysis gas generally contains one or more species such as 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-butylene, 2-butylene, 2-methyl-propylene, 1-butyne, 2-butyne and butadiene.

As used herein, the term “(meth)acrylic acid” means at least one selected from “acrylic acid” and “methacrylic acid”. “(Meth)acrylic acid ester” means at least one selected from “acrylic acid ester” and “methacrylic acid ester”. “(Meth)acrylamide” means at least one selected from “acrylamide” and “methacrylamide”. “(Meth)acrylic acid salt” means at least one selected from “acrylic acid salt’ and “methacrylic acid salt”.

In the present disclosure, extraction is a separating operation, which makes use of the fact that components of a mixture system have different solubilities in a solvent to extract a particular com- ponent/components to be separated. Extraction may be followed by a liquid-liquid separating operation.

In the present disclosure, flocculation is a separating operation, which causes suspended particles in a liquid to agglomerate and increase in size, or form flocs, in order to accelerate the clustering and sedimentation of particles and achieve the objective of separation. Flocculation may be followed by a liquid-liquid separating operation, such as sedimentation or gas flotation; or may be followed by a solid-liquid separating operation, such as filtration.

A flocculant is a chemical reagent which, when used in a mixture system, can induce flocculation in the mixture system.

Fig. 1 shows a chemical circulation process according to embodiments of the present disclosure. Waste is processed in a pretreatment unit 110 to form a feedstock suitable for a pyrolysis process. The feedstock enters a pyrolysis unit 120 and is converted by high temperature to a hydrocarbon- containing fluid and a solid residue. At least a portion of the hydrocarbon-containing fluid enters a condensing and separating unit 130 and is collected as a crude pyrolysis product. The crude pyrolysis product may comprise one or more of pyrolysis wax, pyrolysis oil and pyrolysis gas.

The abovementioned pretreatment unit 110, pyrolysis unit 120 and condensing and separating unit 130 may be integrated in a chemical circulation system 100. The chemical circulation system 100 may be configured with a heat source, a motive power apparatus and corresponding equipment such as pipelines, valves, or pumps, in order to realize operations such as heating, cooling, conveying, transfer and/or control of flow direction/flow speed.

The crude pyrolysis product may enter an after-treatment unit 140, and undergo one or more operations therein including fractionation, rectification, removal of heteroatoms, filtration, ultrafiltration, extraction, flocculation, and adsorption. After the crude pyrolysis product has been treated in the after-treatment unit 140, a refined pyrolysis product may be obtained. The refined pyrolysis product contains fewer nitrogen-containing impurities, sulfur-containing impurities, chlorine-containing im- purities, oxygen-containing impurities, ash, water, gums or asphaltenes, so is more suitable for hydrogenation treatment and subsequent steam cracking treatment.

Downstream of the after-treatment unit 140, at least a portion of the refined pyrolysis product may enter a hydrogenation treatment unit 150. The hydrogenation treatment unit 150 may operate at atmospheric pressure or high pressure and is provided with a hydrogenation catalyst. The refined pyrolysis product may be converted to a steam cracking feedstock by hydrogenation. It contains fewer olefins, alkynes, diolefins and/or aromatics, so is more suitable for directly entering a steam cracking process. In some embodiments, in addition to hydrogenating unsaturated organic substances in the refined pyrolysis product, the hydrogenation treatment unit 150 may also subject organic substances to cracking. Organic substances with larger numbers of carbon atoms (e.g., 17, 18, 19, 20 or more carbon atoms) in the refined pyrolysis product may be cracked to form organic substances with fewer carbon atoms (e.g., 10 or fewer carbon atoms). In some embodiments, the hydrogenation treatment unit 150 may also remove nitrogen-containing compounds, sulfur-containing compounds, chlorine-containing compounds, or other impurities from the refined pyrolysis product by means of a hydrogenation refining process, to increase the hydrocarbon content of the refined pyrolysis product. In other embodiments, the hydrogenation treatment unit 150 may also subject a product of hydrogenation to absorption, adsorption, or other separating operations, to remove impurities such as hydrogen sulfide, ammonia, hydrogen chloride or water.

The steam cracking feedstock enters a steam cracking unit 160, in which it undergoes a steam cracking reaction with steam at high temperature. The steam cracking reaction produces various products such as ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene or pyrolysis gasoline.

The products may be separated in a separating unit 170 into chemical industry starting materials, such as ethylene, propylene, acetylene, and butadiene. Ethylene, propylene, acetylene, and butadiene, etc. may subsequently enter an industrial process for synthesizing a polymer such as polyethylene, polypropylene, or polybutadiene, or used as a starting material to synthesize ethanol, ethylene oxide, propylene oxide, acrylonitrile, isopropanol, adipic acid, hexamethylenediamine or other chemicals.

It will be understood that in addition to the steam cracking process, at least a portion of the crude pyrolysis product may, directly or after passing through the after-treatment unit 140 and/or the hydrogenation treatment unit 150, enter another chemical industry process to produce fuel or chemical industry starting materials, such as catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refining, delayed coking, oxidative cleavage or syngas preparation. Fig. 2 is a method for purifying pyrolysis oil according to embodiments of the present disclosure. In step 210, pyrolysis oil containing hydrocarbons and impurities is mixed with an extraction solution.

The extraction solution is a solution of an extracting agent in a polar solvent. The extracting agent is selected from the group of iron compounds, aluminum compounds, magnesium compounds, nickel compounds, copper compounds, zinc compounds and mixtures thereof.

The mixing may take place in an apparatus such as a vortex mixer, an oscillating mixer, a Patterson-Kelly mixer, a DRAIS turbulent mixer, a Lbdige mixer, a screw mixer, a plate mixer, a fluidized bed mixer, a Schuggi mixer, a mixing pump, a dynamic mixer, a static mixer, a stirring kettle, or a mixer-sedimentation column. The mixing may be accompanied by stirring, gas blowing or liquid flow impingement, etc.

Step 210 may be performed once, or multiple times in succession.

A mixture can be obtained after step 210. This might exist in the form of separated layers, an emulsion, or a suspension, during mixing or after being left to stand.

Two different liquid phases, called an extract liquid and a raffinate, can be obtained via step 210. The extract liquid is a liquid phase in which impurities to be separated are dissolved. The raffinate is a hydrocarbon-containing liquid phase which remains after an extracting agent extraction operation.

According to embodiments of the present disclosure, in step 210, the pyrolysis oil containing hydrocarbons and impurities is mixed with the extraction solution at a temperature of 0 - 80 °C.

According to embodiments of the present disclosure, the extracting agent is selected from the group of iron compounds, aluminum compounds, magnesium compounds, nickel compounds, copper compounds, zinc compounds and mixtures thereof. Preferably, the extracting agent is an iron salt, an iron complex, an aluminum salt, an aluminum complex, or a mixture thereof.

The abovementioned iron salts and aluminum salts include but are not limited to iron (II), iron (III) and/or aluminum (III) chloride, bromide, iodide, perchlorate, chlorate, sulfate, hydrogen sulfate, nitrate, formate, acetate, propionate, lactate, citrate, hydrogen citrate, gluconate, benzoate, phthalate, or double salts, etc. Exemplary iron salts and aluminum salts include but are not limited to iron (II) chloride, iron (III) chloride, polyferric chloride, iron (II) sulfate, ferrous ammonium sulfate, iron (III) sulfate, ferric ammonium sulfate, polyferric sulfate, iron (II) nitrate, iron (III) nitrate, iron (II) acetate, iron (III) acetate, iron (II) lactate, iron (III) lactate, iron (III) ammonium citrate, iron (II) gluconate, aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, aluminum acetate, aluminum lactate, aluminum citrate, aluminum hydrogen citrate, polyaluminum ferric chloride, potassium aluminum sulfate, aluminum ammonium sulfate, polymeric aluminum-ferric chloride or polymeric aluminumferric sulfate.

The abovementioned iron complexes and/or aluminum complexes include but are not limited to iron acetylacetonate, iron (II) porphyrin complex, iron (III) porphyrin complex, iron (II) phthalocyanine complex, iron (III) phthalocyanine complex, iron (II) 8-hydroxyquinolate, iron (III) 8- hydroxyquinolate, potassium ferrocyanide, potassium ferricyanide, iron (III) trichloride hexaurea, iron (III) nitrate hexaurea, ferrous ethylenediamine sulfate, iron(lll) sodium ethylenediaminetetraacetate, aluminum acetylacetonate, aluminum porphyrin complex, aluminum phthalocyanine complex, tris(8-hydroxyquinoline)aluminum, or aluminum complexes based on Schiff bases.

According to embodiments of the present disclosure, the polar solvent is selected from the group of water, C1-C6 monohydric alcohols, C2-C6 dihydric alcohols, C3-C6 ketones, and mixtures thereof, and preferably selected from the group of water, methanol, ethanol, n-propanol, isopropanol, acetone and mixtures thereof.

C1-C6 monohydric alcohols are monohydric alcohols with one to six carbon atoms, including but not limited to methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tertbutanol, n-pentanol, isopentanol, neopentanol, n-hexanol, cyclopentanol, cyclohexanol or cyclopentylmethanol.

C2-C6 dihydric alcohols are dihydric alcohols with two to six carbon atoms, including but not limited to ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1 ,2-butanediol, 1 ,3-butanediol, 1,4- butanediol, 2,3-butanediol, 1 ,2-pentanediol, 1 ,5-pentanediol, 2,2-dimethyl-1 ,3-propanediol, 1 ,2- hexanediol, 1 ,6-hexanediol, 2-methyl-2,4-pentanediol, 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1 ,3-cyclohexanediol or 1 ,4-cyclohexanediol.

C3-C6 ketones are ketones with three to six carbon atoms, including but not limited to acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, 4-methyl- 2-pentanone, 2-methyl-3-pentanone, 3,3-dimethyl-2-butanone, cyclopentanone, cyclohexanone, 2- methylcyclopentanone or 3-methylcyclopentanone. According to embodiments of the present disclosure, the content of the extracting agent in the extraction solution is 0.01 - 10 wt.-%, preferably 0.1 - 8 wt.-%, and more preferably 0.15 - 5 wt.-%.

According to embodiments of the present disclosure, the weight ratio of the extraction solution to the pyrolysis oil is (0.1 - 0.5) : 1, preferably (0.15 - 0.45) : 1.

In step 230, the mixed pyrolysis oil and extraction solution are subjected to liquid-liquid separation, to obtain a hydrocarbon-containing raffinate and an impurity-containing extract liquid.

The liquid-liquid separation may employ equipment including oil-water separators, inclined-plate oil removers, inclined-pipe oil removers, coarse-graining oil removers, gas flotation oil removers, cyclones, or centrifuges. The liquid-liquid separation may be achieved by one or more of the following processes: sedimentation separation, centrifugal separation, coalescence separation, gas flotation separation and cyclonic separation.

Next, in step 250, the raffinate is mixed with a washing solution.

The introduction of the washing solution can further separate the pyrolysis oil in the raffinate from residual impurities, in particular, remove originally present impurities which steps 210 and 230 were unable to remove, as well as impurities that were newly introduced in the extraction operation, e.g., the solute and solvent in the extraction solution. The raffinate can be washed by means of the washing solution.

The mixing may take place in an apparatus such as a vortex mixer, an oscillating mixer, a Patterson-Kelly mixer, a DRAIS turbulent mixer, a Lbdige mixer, a screw mixer, a plate mixer, a fluidized bed mixer, a Schuggi mixer, a mixing pump, a dynamic mixer, a static mixer, a stirring kettle or a mixer-sedimentation column. The mixing may be accompanied by stirring, gas blowing, liquid flow impingement, etc.

Step 250 may be performed once, or multiple times in succession.

According to embodiments of the present disclosure, the raffinate is mixed with the washing solution at a temperature of 0 - 80 °C.

According to embodiments of the present disclosure, the washing solution comprises a flocculant, which comprises at least one species selected from poly(meth)acrylamide, poly(meth)acrylic acid, poly(meth)acrylic acid salt, (meth)acrylamide-(meth)acrylic acid salt copolymer, partial hydrolysate of polyacrylamide, acrylamide-(meth)acrylic acid copolymer, acrylic acid-methacrylic acid copolymer, polyethylenimine, polyethylenimine-(meth)acrylamide copolymer, polyethylenimine- (meth)acrylic acid copolymer, polyethylenimine-(meth)acrylic acid salt copolymer, sodium alginate, sodium alginate-(meth)acrylamide copolymer, sodium alginate-(meth)acrylic acid copolymer, sodium alginate-(meth)acrylic acid salt copolymer, guar gum sodium salt, guar gum sodium salt- (meth)acrylamide copolymer, guar gum sodium salt-(meth)acrylic acid copolymer, guar gum sodium salt-(meth)acrylic acid salt copolymer, chitosan, chitosan-(meth)acrylamide copolymer, chi- tosan-(meth)acrylic acid copolymer, chitosan-(meth)acrylic acid salt copolymer, polyethylene sulfonic acid (poly(vinylsulfonic acid), PVSA) salt, ethylene sulfonic acid-acrylamide copolymer, polyvinylpyrrolidone, polystyrene sulfonic acid salt, styrene sulfonic acid salt-(meth)acrylamide copolymer, lignosulfonic acid salt, lignosulfonic acid salt-(meth)acrylamide copolymer, modified cellulose, polyoxyethylene or polyoxypropylene.

In order to achieve a better flocculation rate, sedimentation rate and/or separation efficiency, according to embodiments of the present disclosure, the content of the flocculant in the washing solution is 0.001 - 0.1 wt.-%. If the flocculant content is too low, the flocculation rate and/or sedimentation rate might slow down, resulting in low separation efficiency per unit time. If the flocculant content is too high, then although the flocculation rate and/or sedimentation rate will be faster, a possible consequence is that the flocculant itself will mix into the pyrolysis oil to be purified.

According to embodiments of the present disclosure, in order to achieve a better flocculation rate, sedimentation rate and/or separation efficiency, the washing solution further comprises a pH regulator, the pH regulator being selected from alkali metal hydroxides, alkali metal carbonate salts, alkali metal bicarbonate salts, aqueous ammonia, ammonium carbonate, alkaline earth metal hydroxides, alkaline earth metal oxides and mixtures thereof.

According to embodiments of the present disclosure, the content of the pH regulator in the washing solution is 0.1 - 10 wt.-%. The pH regulator can increase the solution pH. Since a metal-based extracting agent is used, a higher pH is beneficial for hydrolysis of the extracting agent, to form a poorly soluble hydroxide precipitate. Hydrolysates can flocculate under the action of the flocculant, forming flocs with good sedimentation properties, thus increasing the separation efficiency.

According to embodiments of the present disclosure, the weight ratio of the washing solution to the raffinate is (0.1 - 0.5) : 1 , preferably (0.15 - 0.45) : 1. In step 270, the mixed raffinate and washing solution are subjected to liquid-liquid separation, to obtain a processed pyrolysis oil.

The liquid-liquid separation can split the mixed raffinate and washing solution into two phases. One phase is an organic phase containing pyrolysis oil. The other phase contains essentially no pyrolysis oil. It might contain flocculant, impurities and pH regulator (if present).

The liquid-liquid separation may employ equipment including oil-water separators, inclined-plate oil removers, inclined-pipe oil removers, coarse-graining oil removers, gas flotation oil removers, cyclones or centrifuges. The liquid-liquid separation may be achieved by one or more of the following processes: sedimentation separation, centrifugal separation, coalescence separation, gas flotation separation and cyclonic separation.

The other phase containing essentially no pyrolysis oil that results from the liquid-liquid separation may be subjected to solid-liquid separation to precipitate, sediment or process water, other solvent, residual flocculant and/or metal in this phase.

The solid-liquid separation may be performed using a known apparatus or process, e.g., a solidliquid centrifuge, a filter, a filter press, a filtration membrane, a filtration mesh, a sedimentation column, an assisted sedimentation apparatus or a separator, etc. The solid-liquid separation may be achieved by one or more of the following processes: centrifugation, gravity sedimentation, assisted sedimentation, membrane filtration, cross-flow filtration, cake filtration, through-filtration, ultrafiltration or nanofiltration.

The processed pyrolysis oil may have a low content of heteroelements such as nitrogen or sulfur. Safe, efficient, environmentally friendly and/or low-cost downstream operations are made possible by the low impurity content. Exemplary downstream operations include hydrogenation or reforming.

The abovementioned flow chart comprising steps 210, 230, 250 and 270 is merely exemplary. In addition to the abovementioned steps, some of the intermediates in the flow chart may also be processed, or new steps may be added between two adjacent steps. Alternatively, additional steps may be added before step 210 or after step 270.

For example, after step 230, the impurity-containing extract liquid may be subjected to separating operations including solvent recovery, precipitation or adsorption, etc.

Fig. 3 shows a purification system 300 according to embodiments of the present disclosure. The purification system 300 comprises an extractor 310, a first separator 320, a washer 330, a second separator 340 and a solvent recoverer 350.

The extractor 310 receives pyrolysis oil, containing hydrocarbons and impurities. The extractor 310 receives or contains an extraction solution. A mixing device is configured in the extractor 310, to mix the pyrolysis oil containing hydrocarbons and impurities with the extraction solution.

The first separator 320 is in fluid communication with the extractor 310. A valve or other component may be installed between the first separator 320 and the extractor 310, to control and/or regulate the fluid flow direction, flow speed or through-flow rate. The first separator 320 may subject the mixed pyrolysis oil and extraction solution to liquid-liquid separation, to obtain a hydrocarbon- containing raffinate and an impurity-containing extract liquid. The first separator 320 may be an apparatus including an oil-water separator, a cyclone, or a centrifuge. The first separator 320 may achieve liquid-liquid separation by one or more of the following processes: sedimentation separation, gas flotation separation and cyclonic separation.

In addition to liquid-liquid separation, the first separator 320 may also perform solid-liquid separation, in order to process insoluble substances produced during operation of the extractor 310. The first separator 320 may separate insoluble substances in the form of waste residue. The first separator 320 may comprise a solid-liquid separation apparatus, e.g., a solid-liquid centrifuge, a filter, a filter press, a filtration membrane, a filtration mesh, a sedimentation column, an assisted sedimentation apparatus or a separator, etc. The solid-liquid separation in the first separator 320 may comprise centrifugation, gravity sedimentation, assisted sedimentation, membrane filtration, cross-flow filtration, cake filtration, through-filtration, ultrafiltration or nanofiltration, etc.

The first separator 320 is in fluid communication with the washer 330. A valve or other component may be installed between the washer 330 and the first separator 320, to control and/or regulate the fluid flow direction, flow speed or through-flow rate. The washer 330 receives or contains an extraction solution. A mixing device is configured in the washer 330, to mix the raffinate from the first separator 320 with the washing solution.

The second separator 340 is in fluid communication with the washer 330. A valve or other component may be installed between the second separator 340 and the extraction washer 330, to control and/or regulate the fluid flow direction, flow speed or through-flow rate. The second separator 340 may subject the mixed raffinate and washing solution to liquid-liquid separation, to obtain purified pyrolysis oil, clear liquid, and waste residue (if present). The second separator 340 may be an ap- paratus including an oil-water separator, a cyclone, or a centrifuge. The second separator 340 may achieve liquid-liquid separation by one or more of the following processes: sedimentation separation, gas flotation separation or cyclonic separation.

In addition to liquid-liquid separation, the second separator 340 may also perform solid-liquid separation, in order to process insoluble substances produced in the washer 330. The second separator 340 may separate insoluble substances in the form of waste residue and obtain a clear liquid (containing a solvent of the washing solution and other soluble components). The second separator 340 may comprise a solid-liquid separation apparatus, e.g., a solid-liquid centrifuge, a filter, a filter press, a filtration membrane, a filtration mesh, a sedimentation column, an assisted sedimentation apparatus or a separator, etc. The solid-liquid separation in the second separator 340 may comprise centrifugation, gravity sedimentation, assisted sedimentation, membrane filtration, cross-flow filtration, cake filtration, through-filtration, ultrafiltration or nanofiltration, etc.

The solvent recoverer 350 is in fluid communication with the first separator 320, to receive the extract liquid obtained by separation therein. A valve or other component may be installed between the solvent recoverer 350 and the first separator 320, to control and/or regulate the fluid flow direction, flow speed or through-flow rate. The solvent recoverer 350 can recover one or more solvent from the extract liquid and flow it back to the extractor 310.

The depiction of the purification system 300 in Fig. 3 is merely exemplary. It will be understood that one or more of components 310 - 350 in the purification system 300 may be a single apparatus but could also be integrated apparatuses or an assembly. For example, the first separator 320 may be integrated with the extractor 310 in an assembly. As another example, the second separator 340 may be integrated with the washer 330 in an assembly.

Particular embodiments of the present disclosure are described below in conjunction with experiments.

Starting materials

Extraction solution 1 : solution of aluminum chloride in methanol, 3 g/L.

Extraction solution 2: solution of ferrous sulfate in methanol, 3 g/L.

Extraction solution 3: aqueous solution of sodium hydroxide, 10 wt.-%.

Extraction solution 4: 10 wt.-% aqueous solution of polyaluminum chloride. Extraction solution 5: made up from 1 part by volume of 10 wt.-% aqueous solution of polyaluminum chloride and 9 parts by volume of methanol.

Extraction solution 6: a solution with an aluminum chloride content of 3 g/L, made up from aluminum chloride and a water-methanol (volume ratio 1 : 4) mixture.

Washing solution 1 : 0.01 wt.-% aqueous solution of anionic polyacrylamide.

Original samples 1 and 2 of crude pyrolysis oil: pyrolysis oil obtained by pyrolysis of agricultural greenhouse film (with polyethylene as its main component) using a pyrolysis apparatus made by ourselves; the samples were pale brown or dark brown, and clear. The crude pyrolysis oils 1 and 2 were obtained from pyrolysis reactions of different batches.

Extraction: the crude pyrolysis oil and one of the extraction solutions mentioned above were mixed in a beaker in the ratio of extraction solution : crude pyrolysis oil = 0.3 : 1 (by weight), accompanied by 10 minutes of stirring. After being left to stand, the mixture split into layers, wherein a lower layer was extracting liquid, and an upper layer was raffinate. The temperature of the extraction operation was 20 °C.

Washing: the crude pyrolysis oil or the raffinate resulting from extraction was mixed with the washing solution in a beaker in the ratio of washing solution : crude pyrolysis oil/raffinate = 0.3 : 1 (by weight), accompanied by 10 minutes of stirring. The mixture was left to stand until sedimentation was essentially complete, then filtered. The temperature of the washing operation was 20 °C.

After a separating operation, a purified pyrolysis oil sample was subjected to element analysis. Nitrogen and sulfur element contents were measured in accordance with the standard oxidative combustion and chemiluminescence method of ASTM D4629-17, and the standard ultraviolet fluorescence method of ASTM D5453-19a, respectively.

The removal rate of impurity elements was calculated according to the formula below: impurity element content in purified samplex

Rem al rate = 100% x 1 towirity element cantati HI ortf inai seanrie I where the impurity element content is in units of mg/L.

The crude pyrolysis oils 1 and 2 were subjected to after-treatment operations by the abovementioned extraction solutions and washing solution. See Tables 1 - 3 for the solutions used in the specific operations, and the nitrogen and sulfur element contents of the after-treated oil samples. Table 1

Table 2

Table 3

It can be seen from the data above that the aqueous or methanol solutions of aluminum and iron salts or solutions thereof based on water-methanol mixed solvents can achieve better nitrogen removal rates for pyrolysis oil than the aqueous solution of sodium hydroxide.

It can be seen by comparing Examples 5 and 7 that based on the 70% nitrogen removal rate and 53% sulfur removal rate achieved by the extraction operation alone, the additional washing operation can reduce the residual nitrogen content to 9% of that of the original sample, and reduce the residual sulfur content to 17% of that of the original sample. Furthermore, the washing operation

Claims

following the extraction operation can remove more nitrogen element and sulfur element than the washing operation alone. It can be seen by comparing Examples 9 and 10 that the solution of the aluminum salt in the water- methanol mixed solvent can achieve better nitrogen and sulfur removal rates for pyrolysis oil than the aqueous solution of sodium hydroxide. By means of the additional washing operation, Example 11 can achieve a higher heteroatom removal rate than Example 10. Compared with an extraction operation alone or washing operation alone, the combination of the extraction operation and washing operation in the present disclosure increases the removal rates of nitrogen element and sulfur element. Claims

1. A method for purifying pyrolysis oil, comprising:

(iii) mixing the raffinate with a washing solution; and

2. The method for purifying pyrolysis oil according to claim 1, wherein the extracting agent is an iron salt, an iron complex, an aluminum salt, an aluminum complex or a mixture thereof.

3. The method for purifying pyrolysis oil according to claim 1 or 2, wherein the polar solvent is selected from water, C1-C6 monohydric alcohols, C2-C6 dihydric alcohols, C3-C6 ketones and mixtures thereof, and preferably selected from water, methanol, ethanol, n-propanol, isopropanol, acetone or mixtures thereof.

4. The method for purifying pyrolysis oil according to any one of claims 1 to 3, wherein the content of the extracting agent in the extraction solution is 0.01 - 10 wt.-%, preferably 0.1 -

8 wt.-%, and more preferably 0.15 - 5 wt.-%.

5. The method for purifying pyrolysis oil according to any one of claims 1 to 4, wherein in step (i), the weight ratio of the extraction solution to the pyrolysis oil is (0.1 - 0.5) : 1, preferably (0.15 - 0.45) : 1.

6. The method for purifying pyrolysis oil according to any one of claims 1 to 5, wherein the pyrolysis oil containing hydrocarbons and impurities is mixed with the extraction solution at a temperature of 0 - 80 °C.

7. The method for purifying pyrolysis oil according to any one of claims 1 to 6, wherein the washing solution comprises a flocculant, the flocculant comprising at least one species selected from poly(meth)acrylamide, poly(meth)acrylic acid, poly(meth)acrylic acid salt, (meth)acrylamide-(meth)acrylic acid salt copolymer, partial hydrolysate of polyacrylamide, acrylamide-(meth)acrylic acid copolymer, acrylic acid-methacrylic acid copolymer, polyethyl- enimine, polyethylenimine-(meth)acrylamide copolymer, polyethylenimine-(meth)acrylic acid copolymer, polyethylenimine-(meth)acrylic acid salt copolymer, sodium alginate, sodium al- ginate-(meth)acrylamide copolymer, sodium alginate-(meth)acrylic acid copolymer, sodium alginate-(meth)acrylic acid salt copolymer, guar gum sodium salt, guar gum sodium salt- (meth)acrylamide copolymer, guar gum sodium salt-(meth)acrylic acid copolymer, guar gum sodium salt-(meth)acrylic acid salt copolymer, chitosan, chitosan-(meth)acrylamide copolymer, chitosan-(meth)acrylic acid copolymer, chitosan-(meth)acrylic acid salt copolymer, polyethylene sulfonic acid salt, ethylene sulfonic acid-acrylamide copolymer, polyvinylpyrrolidone, polystyrene sulfonic acid salt, styrene sulfonic acid salt-(meth)acrylamide copolymer, lignosulfonic acid salt, lignosulfonic acid salt-(meth)acrylamide copolymer, modified cellulose, polyoxyethylene and polyoxypropylene.

8. The method for purifying pyrolysis oil according to claim 7, wherein the content of the flocculant in the washing solution is 0.001 - 0.1 wt.-%.

9. The method for purifying pyrolysis oil according to any one of claims 1 to 8, wherein the washing solution further comprises a pH regulator, the pH regulator being selected from alkali metal hydroxides, alkali metal carbonate salts, alkali metal bicarbonate salts, aqueous ammonia, ammonium carbonate, alkaline earth metal hydroxides, alkaline earth metal oxides and mixtures thereof.

10. The method for purifying pyrolysis oil according to claim 9, wherein the content of the pH regulator in the washing solution is 0.1 - 10 wt.-%.

11. The method for purifying pyrolysis oil according to any one of claims 1 to 10, wherein in step (iii), the weight ratio of the washing solution to the raffinate is (0.1 - 0.5) : 1 , preferably (0.15 - 0.45) : 1.

12. The method for purifying pyrolysis oil according to any one of claims 1 to 12, wherein the raffinate is mixed with the washing solution at a temperature of 0 - 80 °C.

13. The method for purifying pyrolysis oil according to any one of claims 1 to 12, wherein the pyrolysis oil containing impurities is obtained by pyrolysis of solid waste containing waste plastic.

14. A purified pyrolysis oil, obtained by the following steps:

(ii) subjecting the mixed pyrolysis oil and extraction solution to liquid-liquid separation, to obtain a hydrocarbon-containing raffinate and an impurity-containing extract liquid; (iii) mixing the raffinate with a washing solution; and

15. The use of the purified pyrolysis oil as claimed in claim 14 as a starting material for a steam cracking process.