Method for refining pyrolysis oil, refined pyrolysis oil and use thereof

Abstract

The present disclosure relates to a method for refining pyrolysis oil, a refined pyrolysis oil obtained by the method, and the use of the refined pyrolysis oil in steam cracking or partial oxidation. The method comprises the steps (i) subjecting crude pyrolysis oil containing hydrocarbons and impurities to a separating operation and thereby forming refined pyrolysis oil and waste liquid, and (ii) subjecting the waste liquid to advanced oxidation treatment and filtering the treated waste liquid, wherein the separating operation comprises using a washing solution to wash the crude pyrolysis oil, the washing solution being an aqueous solution of a transition metal compound or an aluminum compound.

Description

[0001] Method for refining pyrolysis oil, refined pyrolysis oil and use thereof

[0002] Technical Field

[0003] The present disclosure relates to the technical field of separation, in particular to a method for refining pyrolysis oil, a refined pyrolysis oil, and the use of the refined pyrolysis oil.

[0004] Background Art

[0005] 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.

[0006] 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 also 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.

[0007] Although purification and refining processes for pyrolysis oil reduce the impurity content of the pyrolysis oil, they also produce waste water with a high content of organic matter. A very large number of different types of organic matter, each with different properties, is contained in this waste water, and it is difficult to reduce the chemical oxygen demand (COD) by conventional treatment to suit physical, chemical or biochemical treatment processes.

[0008] A pyrolysis oil after-treatment process which is capable of removing the heteroatom content by a simple procedure, with low energy consumption and low demands on equipment, and which produces waste water that can be treated conveniently, would be especially desirable.

[0009] Summary of the Invention

[0010] According to one aspect of the present disclosure, a method for refining pyrolysis oil is provided, comprising:

[0011] (i) subjecting crude pyrolysis oil containing hydrocarbons and impurities to a separating operation and obtaining refined pyrolysis oil and waste liquid; and

[0012] (ii) subjecting the waste liquid to advanced oxidation treatment and filtering the treated waste liquid, wherein the separating operation comprises using a washing solution to wash the crude pyrolysis oil, the washing solution being an aqueous solution of a transition metal compound or an aluminum compound.

[0013] According to another aspect of the present disclosure, a refined pyrolysis oil obtained by the method for refining pyrolysis oil is provided. According to another aspect of the present disclosure, the use of the refined pyrolysis oil in steam cracking or partial oxidation is provided.

[0014] The method for refining pyrolysis oil according to the present disclosure has simple steps, causes little corrosion or contamination of apparatus, and has high removal rates for elements such as nitrogen and sulfur; furthermore, the waste liquid resulting from treatment has a low chemical oxygen demand, so is suitable for downstream treatment.

[0015] Brief Description of the Drawings

[0016] Fig. 1 shows a chemical circulation process according to embodiments of the present disclosure.

[0017] Fig. 2 shows a method for refining pyrolysis oil according to embodiments of the present disclosure; and

[0018] Fig. 3 shows a refining system according to embodiments of the present disclosure.

[0019] Detailed description

[0020] 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.

[0021] 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.

[0022] Definitions

[0023] 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.

[0024] In the present disclosure, the term "pyrolysis" refers to a chemical process which a solid mixture (e.g. solid waste or feedstock made therefrom) containing polymers undergoes at a high temperature, in which chemical bonds are forcibly opened and smaller molecules (including but not limited to hydrocarbons with 1 - 60 carbon atoms, other non-hydrocarbon organic substances, and inorganic substances such as hydrogen sulfide, nitrogen oxides and sulfur oxides, etc.) are produced. For example, low density polyethylene (LDPE) can undergo pyrolysis at a high temperature to produce a mixture of various hydrocarbons.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 of hydrogen, oxygen, nitrogen, nitrogen oxides, sulfur oxides, hydrogen sulfide, ammonia, hydrogen chloride, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, propane, propylene, propyne, butane, isobutane, 1 -butene, 2-butene, 2-methyl-propene, 1 -butyne, 2-butyne and butadiene, etc.

[0030] 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”.

[0031] 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 component / components to be separated. Extraction may be followed by a liquid-liquid separating operation.

[0032] In the present disclosure, flocculation is a separating operation, which causes suspended particles in a liquid to gather together 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.

[0033] A flocculant is a chemical reagent which, when used in a mixture system, can induce flocculation in the mixture system.

[0034] In the present disclosure, advanced oxidation is a new technique for treating highly concentrated toxic and harmful pollutants in liquid, especially in waste water; this technique causes organic substances in a system to be oxidized and thereby degraded to species that are relatively harmless to the environment, such as water, carbon dioxide, nitrogen, nitrate ions and sulfate ions. Advanced oxidation can be accompanied by a subsequent solid-liquid separating operation, such as flocculation or filtration.

[0035] Fig. 1 shows a chemical circulation process according to embodiments of the present disclosure.

[0036] 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.

[0037] The pretreatment unit 110, pyrolysis unit 120, and condensing and separating unit 130 mentioned above may be integrated in a chemical circulation system 100. The chemical circulation system 100 may be equipped 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.

[0038] 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 impurities, oxygen-containing impurities, ash, water, gums or asphaltenes, and is more suitable for hydrogenation treatment and subsequent steam cracking treatment.

[0039] 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 contains 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 aromatic hydrocarbons, so is more suitable for direct entry into 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.

[0040] 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.

[0041] 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.

[0042] 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 partial oxidation, catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refining, delayed coking or oxidative cleavage. A product of partial oxidation may comprise syngas.

[0043] Fig. 2 shows a method for refining pyrolysis oil according to embodiments of the present disclosure.

[0044] In step 210, crude pyrolysis oil containing hydrocarbons and impurities is subjected to a separating operation, and refined pyrolysis oil and waste liquid are obtained.

[0045] The impurities in the crude pyrolysis oil may comprise nitrogen-containing organic compounds, chlorine- containing organic compounds, sulfur-containing organic compounds, bromine-containing organic compounds, silica, iron oxides, alumina, hydrated alumina, salts, water, etc. As typical impurities in crude pyrolysis oil, nitrogencontaining organic compounds and chlorine-containing organic compounds may be present in the oil phase, or may be dispersed in the oil phase in the form of suspended matter or an emulsion, etc., or may be present in the form of sediment or other insoluble matter.

[0046] The refined pyrolysis oil may have a low content of heteroatoms such as nitrogen or chlorine. 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.

[0047] Preferably, the refined pyrolysis oil has a chlorine content not exceeding 30 ppm and a nitrogen content not exceeding 300 ppm.

[0048] The separating operation comprises using a washing solution to wash the crude pyrolysis oil, the washing solution being an aqueous solution of a transition metal compound or an aluminum compound.

[0049] The washing solution is preferably an aqueous solution of a ferrous salt or an aluminum salt, more preferably an aqueous solution of ferrous sulfate, an aqueous solution of aluminum sulfate, or an aqueous solution of ferrous sulfate and aluminum sulfate.

[0050] The transition metals mentioned here include but are not limited to chromium, manganese, iron, cobalt, nickel and copper.

[0051] The abovementioned transition metal compounds or aluminum compounds include but are not limited to chloride, bromide, iodide, perchlorate, chlorate, sulfate, hydrogen sulfate, nitrate, formate, acetate, propionate, lactate, citrate, hydrogen citrate, gluconate, benzoate, phthalate, double salts or complexes, etc.

[0052] Exemplary ferrous salts and aluminum salts include but are not limited to iron(ll) chloride, iron(ll) sulfate, ammonium iron(ll) sulfate, iron(ll) nitrate, iron(ll) acetate, iron(ll) lactate, iron(ll) gluconate, aluminum chloride, polyaluminum chloride, aluminum sulfate, aluminum nitrate, aluminum acetate, aluminum lactate, aluminum citrate, aluminum hydrogen citrate, potassium aluminum sulfate or aluminum ammonium sulfate.

[0053] Due to the action of the transition metal compound or aluminum compound, some of the organic matter in the crude pyrolysis oil forms complexes with the metal and therefore enters the aqueous phase. Thus, the content of impurities in the crude pyrolysis oil decreases.

[0054] According to some embodiments of the present disclosure, the content of the transition metal compound or aluminum compound in the washing solution is 0.01 - 10 wt%, preferably 0.1 - 8 wt%, more preferably 0.15 - 5 wt%.

[0055] According to some embodiments of the present disclosure, the weight ratio of the washing solution to the crude pyrolysis oil is (0.1 - 0.5) : 1, preferably (0.15 - 0.45) : 1. According to some embodiments of the present disclosure, the washing is performed at a temperature of 0 -

[0056] 80°C.

[0057] According to some embodiments of the present disclosure, the washing may include a liquid-liquid separating operation, to achieve phase separation of the refined pyrolysis oil and the waste liquid. The liquid-liquid separation may employ equipment including an oil-water separator, an inclined-plate oil remover, an inclined-tube oil remover, a coarse granulation oil remover, a gas flotation oil remover, a cyclone or a centrifuge. 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.

[0058] In addition to washing, the separating operation of step 210 may also comprise physical / chemical operations such as extraction, stripping, evaporation, sedimentation and adsorption.

[0059] Preferably, the separating operation of step 210 further comprises: using an extracting agent to subject the crude pyrolysis oil to extraction, the extracting agent being water, an aqueous solution of an acid, an aqueous solution of a base, an aqueous solution of a metal salt, or an organic extracting agent.

[0060] Acids include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid and citric acid. Bases include but are not limited to sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonia. Metal salts include chlorides, bromides, iodides, carbonates, bicarbonates, sulfates, bisulfates, nitrates, phosphates, formates, acetates, citrates, dibasic citrates and monobasic citrates of alkali metals, alkaline earth metals, aluminum, tin and transition metals.

[0061] Preferably, the organic extracting agent is an alcohol, a ketone, an amide, a nitrile, dimethyl sulfoxide, pyridine, substituted pyridine, or any mixture thereof. The organic extracting agent has high polarity, and is able to dissolve some polar organic substances, inorganic salts and / or other inorganic substances (such as water, acids, sulfides and ammonia). Alcohols include but are not limited to methanol, ethanol, n-propanol, isopropanol, n-butanol and cyclohexanol. Ketones include but are not limited to acetone, methyl ethyl ketone, cyclohexanone and benzophenone. Amides include but are not limited to N,N-dimethylformamide and N,N-dimethylacetamide. Nitriles include but are not limited to acetonitrile and propionitrile.

[0062] The abovementioned extracting agent has high polarity. When it is mixed with the crude pyrolysis oil, two different phases can be formed. Organic substances with high polarity (such as certain compounds containing nitrogen heterocycles or compounds containing sulfur) might be concentrated in the phase of the extracting agent.

[0063] 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 Lddige 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.

[0064] Step 210 may be performed once, or multiple times in succession.

[0065] Preferably, the crude pyrolysis oil is obtained by pyrolysis of solid waste containing waste plastic.

[0066] In step 230, the waste liquid subjected to advanced oxidation treatment, and the treated waste liquid is filtered.

[0067] The waste liquid resulting from treatment in step 230 may have a chemical oxygen demand lower than 5000 ppm. It can be converted to a liquid stream with a low organic matter content and low toxicity by a biochemical treatment process, a chemical treatment process or a physical treatment process. According to some embodiments of the present disclosure, step 230 specifically comprises: adding an oxidant based on active oxygen to the waste liquid; adjusting the pH of the waste liquid to 7 - 9; adding a flocculant to the waste liquid; and filtering the waste liquid to which the flocculant has been added.

[0068] The oxidant based on active oxygen can fully oxidize organic matter in the waste liquid under the abovementioned process conditions, reducing the chemical oxygen demand. Since an aqueous solution of a transition metal compound or an aluminum compound is used as the washing solution in step 210, the transition metal compound or aluminum compound can form a hydroxide with hydroxide ions after the advanced oxidation treatment; a precipitate is formed in the presence of the flocculant, and some of the organic matter is adsorbed, achieving the effect of further reducing the chemical oxygen demand.

[0069] Preferably, the oxidant based on active oxygen is ozone, an aqueous solution of hydrogen peroxide, an adduct of urea and hydrogen peroxide, calcium peroxide, magnesium peroxide, sodium percarbonate, persulfuric acid, a persulfuric acid salt, peroxyacetic acid, a peroxyacetic acid salt, or a mixture thereof. The oxidant based on active oxygen can introduce strongly oxidative species such as ozone, hydrogen peroxide and / or hydroxyl free radicals, or introduce strongly oxidative species such as ozone, hydrogen peroxide and / or hydroxyl free radicals after reacting with waste liquid components such as water, transition metal ions and / or aluminum ions.

[0070] Exemplary flocculants include 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, chitosan-(meth)acrylic acid copolymer, chitosan-(meth)acry lie acid salt copolymer, polyethylene sulfonic acid (poly (viny Isulfonic 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.

[0071] Preferably, the flocculant comprises poly(meth)acrylamide, polyethylenimine or polyethylenimine- (meth)acrylamide copolymer.

[0072] The order of the abovementioned steps may be swapped or reversed. For example, one option is to first add an oxidant based on active oxygen, then adjust the pH of the waste liquid to 7 - 9, add a flocculant, and finally perform filtration; another option is to first adjust the pH of the waste liquid to 7 - 9, then add an oxidant based on active oxygen, add a flocculant, and finally perform filtration.

[0073] Alternatively, step 230 may comprise: adding a flocculant to the waste liquid; irradiating the waste liquid with ultraviolet rays of wavelength 150 - 400 nm; and filtering the irradiated waste liquid.

[0074] The abovementioned ultraviolet oxidation process utilizes ultraviolet irradiation to produce oxidizing species in the waste liquid, thus achieving oxidation of organic matter.

[0075] Exemplary flocculants include at least one species selected from poly(meth)acrylamide, poly (meth)acrylic acid, poly (meth)acry lie 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, chitosan-(meth)acrylic acid copolymer, chitosan-(meth)acrylic acid salt copolymer, polyethylene sulfonic acid (poly (viny Isulfonic 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.

[0076] Preferably, the flocculant comprises poly(meth)acrylamide, polyethylenimine or polyethylenimine- (meth)acrylamide copolymer.

[0077] Ultraviolet irradiation can cause water in the waste liquid to undergo a photochemical reaction, generating strongly oxidative hydroxyl free radicals, which can oxidize organic matter in the waste liquid quickly and efficiently.

[0078] Preferably, during or before irradiation with ultraviolet rays of wavelength 150 - 400 nm, a photocatalyst such as titania is added to the waste liquid.

[0079] Preferably, during or before irradiation with ultraviolet rays of wavelength 150 - 400 nm, an oxidant such as ozone or hydrogen peroxide is added to the waste liquid.

[0080] Alternatively, step 230 may comprise: adding a flocculant to the waste liquid; applying ultrasonic waves of 15 kHz - 1 MHz to the waste liquid; and filtering the waste liquid to which ultrasonic waves have been applied.

[0081] The abovementioned ultrasonic oxidation process utilizes sound waves to produce a localized high- temperature, high-pressure environment in the waste liquid, generating oxidizing species and thus achieving oxidation of organic matter.

[0082] Exemplary flocculants include at least one species selected from poly(meth)acrylamide, poly (meth)acrylic acid, poly (meth)acry lie 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, chitosan-(meth)acrylic acid copolymer, chitosan-(meth)acrylic acid salt copolymer, polyethylene sulfonic acid (poly (viny Isulfonic 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.

[0083] Preferably, the flocculant comprises poly(meth)acrylamide, polyethylenimine or polyethylenimine- (meth)acrylamide copolymer.

[0084] Ultrasonic treatment can cause strongly oxidative hydroxyl free radicals to form locally in the waste liquid, and these can oxidize organic matter in the waste liquid quickly and efficiently.

[0085] The filtration in step 230 may be one or more of membrane filtration, cross-flow filtration, cake filtration, through-filtration, ultrafiltration or nanofiltration.

[0086] Before filtration, the treated waste liquid may be subjected to an operation such as settlement, assisted settlement or centrifugation.

[0087] The abovementioned flow chart comprising steps 210 - 230 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 230.

[0088] For example, after step 230, the refined pyrolysis oil may be subjected to a separating operation such as stripping, rectification, fractionation, sedimentation or adsorption.

[0089] Fig. 3 shows a pyrolysis oil refining system 300 according to embodiments of the present disclosure. The pyrolysis oil refining system 300 can serve as the after-treatment unit 140 in Fig. 1, or a component thereof.

[0090] The pyrolysis oil refining system 300 comprises a mixing and phase separation unit 310, a mixing and washing unit 320, a rectification unit 330, an advanced oxidation unit 340, a sedimentation unit 350 and a filtration unit 360.

[0091] The mixing and phase separation unit 310 receives pyrolysis oil containing hydrocarbons and impurities, and an extracting agent. Such pyrolysis oil may come from a special storage tank or be delivered via a pipeline from a pyrolysis reactor. In the latter case, the whole of or part of the pyrolysis oil refining system 300 may be integrated with a pyrolysis system.

[0092] The mixing and phase separation unit 310 performs a liquid-liquid extracting operation. After phase separation, an oil phase containing 10 - 90 wt% hydrocarbons is delivered as a raffinate to the mixing and washing unit 320, and another phase containing impurities is delivered as an extract liquid to the rectification unit 330. The extract liquid also contains the extracting agent. The mixing and phase separation unit 310 may be an apparatus including an oilwater separator, a cyclone or a centrifuge. The mixing and phase separation unit 310 may achieve liquid-liquid separation by one or more of the following processes: sedimentation separation, gas flotation separation and cyclonic separation.

[0093] In addition to the oil phase from the mixing and phase separation unit 310, the mixing and washing unit 320 also receives a washing agent. In the mixing and washing unit 320, the washing agent and the raffinate are thoroughly mixed. The mixing and washing unit may employ mechanical stirring, pipeline throttling, tube-type static mixing, jet impingement or another method to achieve thorough mixing of the two phases. The mixing and washing unit may be equipped with internal members such as a stirring paddle, a bubbler, helical fixed internal members, interleaved fixed internal members, a high-pressure pump, etc. During mixing, some of the nitrogen / sulfur / chlorine compounds present in the raffinate, and the extracting agent introduced in the abovementioned liquid-liquid extracting operation, are further removed. The mixing and washing unit 320 outputs refined pyrolysis oil and an aqueous phase. The small amount of remaining organic matter in the aqueous phase will enter downstream units for further treatment. The refined pyrolysis oil can enter a storage tank to be collected, a physical treatment unit to undergo a separating operation such as stripping, rectification, fractionation, sedimentation or adsorption, or a chemical treatment unit to undergo hydrogenation, chorine removal, nitrogen removal, sulfur removal or other chemical treatment. Alternatively, if the chemical components of the refined pyrolysis oil meet the feedstock requirements of a steam cracking or catalytic cracking process, they may directly enter a cracking reactor to undergo a corresponding operation.

[0094] The rectification unit 330 may comprise a plate column or a packed column. The rectification unit 330 subjects the extract liquid to rectification to recover the extracting agent. The recovered extracting agent can continue to serve as input to the mixing and phase separation unit 310. A small amount of waste liquid or solid waste is also obtained through treatment of the extract liquid in the rectification unit 330.

[0095] The advanced oxidation unit 340 subjects the aqueous phase to advanced oxidation treatment. The advanced oxidation treatment comprises the Fenton process, ozone oxidation, ultrasonic oxidation, ultraviolet oxidation, etc. Depending on the advanced oxidation process specifically chosen, the advanced oxidation unit 340 may be equipped with different components (such as an ultrasound generator, a low-pressure ultraviolet lamp, a medium-pressure ultraviolet lamp or an ozone generator) or receive different input materials (oxidants based on active oxygen such as an aqueous solution of hydrogen peroxide, an adduct of urea and hydrogen peroxide, calcium peroxide, peroxyacetic acid or ozone). After being treated in the advanced oxidation unit 340, the aqueous phase enters the sedimentation unit 350.

[0096] The sedimentation unit 350 can subject the aqueous phase to operations such as flocculation and settlement. The sedimentation unit 350 may take the form of a horizontal flow sedimentation tank, a vertical flow sedimentation tank, a radial flow sedimentation tank, an inclined-tube packed sedimentation tank, etc.

[0097] The filtration unit 360 filters the aqueous phase that has passed through the sedimentation unit 350, to obtain solid waste and waste liquid with a low organic matter content. The waste liquid has good direct biodegradability, so is able to meet the requirements of waste water treatment plants. The waste liquid may be further treated in a downstream apparatus or plant, such as a centralized waste water treatment plant. The solid waste comes from insoluble matter produced by operations such as flocculation and sedimentation, and may contain transition metals, sludge, microbes, water, dust, carbon particles, etc.

[0098] The depiction of the pyrolysis oil refining system 300 in Fig. 3 is merely exemplary. It will be understood that one or more of components 310 - 360 in the pyrolysis oil refining system 300 may be a single apparatus but could also be integrated apparatuses or an assembly. For example, the sedimentation unit 350 may be integrated with the filtration unit 360 in an assembly. As another example, the advanced oxidation unit 340, the sedimentation unit 350 and the filtration unit 360 may be integrated in an assembly.

[0099] The present disclosure further relates to a refined pyrolysis oil obtained by the method for refining pyrolysis oil. The present disclosure further relates to the use of the refined pyrolysis oil in steam cracking or partial oxidation. Particular embodiments of the present disclosure are described below in conjunction with experiments.

[0100] Chemical reagents

[0101] Extracting agent 1 : 10 wt% aqueous solution of sodium hydroxide.

[0102] Extracting agent 2: dimethyl sulfoxide.

[0103] Washing agent 1: deionized water.

[0104] Washing agent 2: 1 wt% aqueous solution of ferrous sulfate.

[0105] 10 wt% dilute sulfuric acid and 10 wt% aqueous solution of sodium hydroxide are both used to adjust the pH of the aqueous system.

[0106] 10 wt% aqueous solution of polyaluminum chloride.

[0107] Flocculant: 0.1 wt% aqueous solution of polyacrylamide.

[0108] Oxidant: 7.9 wt% aqueous solution of hydrogen peroxide.

[0109] 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 and clear. Original samples 1 and 2 were collected after pyrolysis of different batches. Compared with the agricultural greenhouse film used to produce original material 1, a greater amount of waste polyvinyl chloride (PVC) plastic was mixed into the agricultural greenhouse film used to produce original sample 2.

[0110] 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 extract liquid, and an upper layer was raffinate. The temperature of the extraction operation was 20°C.

[0111] 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.

[0112] After a separating operation, a purified pyrolysis oil sample was subjected to element analysis. Nitrogen and chlorine element contents were measured in accordance with the oxidative combustion and chemiluminescence method described in standard ASTM D4629-17, and the ultraviolet fluorescence method described in standard ASTM D6643-14 (2019) E1, respectively.

[0113] Crude pyrolysis oils 1 and 2 were subjected to different separating operations in Examples 1 - 8. Impurity element contents of oil samples obtained after separation, and impurity element removal rates of the corresponding separating operations, are recorded in Table 1 and Table 2.

[0114] The removal rate of impurity elements was calculated according the formula below:

[0115] / Impurity element content in refined pyrolysis oil\

[0116] Removal rate = 100% x I 1 - - - - - - - -)

[0117] \ Impurity element content in crude pyrolysis oil / where the impurity element content is in units of mg / L.

[0118] Extraction and / or washing treatment of the crude pyrolysis oil produces waste water. When an aqueous solution was used for the extracting operation, the waste water resulting from the extracting operation was merged with the waste water resulting from the washing operation. The merged waste water was subjected to subsequent treatment. When an aqueous solution was not used for the extracting operation, or no extracting operation was performed, only the waste water resulting from the washing step was subjected to subsequent treatment.

[0119] The subsequent treatment was flocculation sedimentation or advanced oxidation treatment and was aimed at reducing the chemical oxygen demand. The waste waters produced in Examples 1, 3, 5 and 7 were separately subjected to the two types of treatment mentioned above; the chemical oxygen demand values of the water samples after treatment are recorded in Table 3. In Examples 9, 12, 15 and 18, the waste water was not subjected to any treatment. In Examples 10, 13, 16 and 19, the waste water was subjected to flocculation sedimentation treatment. In Examples 14 and 20, the waste water was subjected to advanced oxidation treatment. Since sodium hydroxide solution was used in the extracting operations of Examples 1 and 5, the waste water was strongly basic and unsuitable for the Fenton process, so the waste waters obtained in Examples 1 and 5 were not subjected to advanced oxidation treatment.

[0120] Flocculation sedimentation: 10 wt% dilute sulfuric acid was added first to adjust the pH of the waste water to about 9, then an amount of 10 wt% polyaluminum chloride solution equivalent to 5% of the mass of the waste water and an amount of 0.1 wt% polyacrylamide solution equivalent to 2% of the mass of the waste water were separately added, stirring was performed slowly to form sedimentation flocs, then filtration was performed; the filtrate was the treated waste water.

[0121] Advanced oxidation: using the Fenton process, an amount of 7.9 wt% hydrogen peroxide solution equivalent to 10% of the mass of the waste water was added first; after thorough stirring, 10 wt% sodium hydroxide solution was used to adjust the pH value of the waste water to about 8, then an amount of 0.1 wt% polyacrylamide solution equivalent to 2% of the mass of the waste water was added, stirring was performed slowly to form sedimentation flocs, then filtration was performed; the filtrate was the treated waste water.

[0122] The chemical oxygen demand (COD) was determined in accordance with the dichromate method described in national environment protection standard HJ 828-2017 of the People's Republic of China.

[0123] Table 1 Table 2 Table 3

[0124] Table 4

[0125] The advanced oxidation in the experiments above includes an oxidation step and a flocculation sedimentation step. It can be seen by comparing Examples 13 and 14 or Examples 19 and 20 that the oxidation step can effectively reduce the COD value. Compared with the joint use of aqueous sodium hydroxide solution and deionized water, the use of dimethyl sulfoxide alone or the use of aqueous ferrous salt solution alone, the combination of dimethyl sulfoxide and aqueous ferrous salt solution can achieve better nitrogen and chlorine removal rates for pyrolysis oil. Furthermore, this combination avoids corrosion of equipment by sodium hydroxide solution.

[0126] Examples 4 and 8 also reduce the nitrogen element content and chlorine element content of the oil samples.

[0127] The chemical oxygen demand values indicate that waste water with a high organic matter content is produced in the extracting or washing operation. Flocculation sedimentation and advanced oxidation can both achieve a reduction in the chemical oxygen demand of the waste water. Further, it can be seen by comparing Examples 13 or 14 or Examples 19 and 20 that compared with the flocculation sedimentation method, advanced oxidation can considerably reduce the chemical oxygen demand of the waste water resulting from treatment of pyrolysis oil. The treated waste water is convenient for subsequent biochemical treatment.

Claims

Claims1. A method for refining pyrolysis oil, comprising:(I) subjecting crude pyrolysis oil containing hydrocarbons and impurities to a separating operation and thereby forming refined pyrolysis oil and waste liquid, and(ii) subjecting the waste liquid to advanced oxidation treatment and filtering the treated waste liquid, wherein the separating operation comprises using a washing solution to wash the crude pyrolysis oil, the washing solution being an aqueous solution of a transition metal compound or an aluminum compound.

2. The method for refining pyrolysis oil according to claim 1, wherein the washing solution is an aqueous solution of a ferrous salt or an aluminum salt, preferably an aqueous solution of ferrous sulfate, an aqueous solution of aluminum sulfate, or an aqueous solution of ferrous sulfate and aluminum sulfate.

3. The method for refining pyrolysis oil according to claim 1 or 2, wherein the separating operation further comprises: using an extracting agent to subject the crude pyrolysis oil to extraction, the extracting agent being water, an aqueous solution of an acid, an aqueous solution of a base, an aqueous solution of a metal salt, or an organic extracting agent.

4. The method for refining pyrolysis oil according to claim 3, wherein the organic extracting agent is an alcohol, a ketone, an amide, a nitrile, dimethyl sulfoxide, pyridine, substituted pyridine, or any mixture thereof.

5. The method for refining pyrolysis oil according to any one of claims 1 to 4, wherein the step of subjecting the waste liquid to advanced oxidation treatment comprises: a1) adding an oxidant based on active oxygen to the waste liquid, b1) adjusting the pH of the waste liquid to 7 - 9, and d) adding a flocculant to the waste liquid or a2) adding a flocculant to the waste liquid, and b2) irradiating the waste liquid with ultraviolet rays of wavelength 150 - 400 nm or a3) adding a flocculant to the waste liquid, and b3) applying ultrasonic waves of 15 kHz - 1 MHz to the waste liquid.

6. The method for refining pyrolysis oil according to claim 5, wherein the oxidant based on active oxygen is ozone, an aqueous solution of hydrogen peroxide, an adduct of urea and hydrogen peroxide, calcium peroxide, magnesium peroxide, sodium percarbonate, persulfuric acid, a persulfuric acid salt, peroxyacetic acid, a peroxyacetic acid salt, or a mixture thereof.

7. The method for refining pyrolysis oil according to claim 5 or 6, wherein the flocculant comprises poly(meth)acrylamide, polyethylenimine or polyethylenimine-(meth)acrylamide copolymer.

8. The method for refining pyrolysis oil according to anyone of claims 1 to 7, wherein the treated waste liquid has a chemical oxygen demand not exceeding 5000 ppm.

9. The method for refining pyrolysis oil according to anyone of claims 1 to 8, wherein the refined pyrolysis oil has a chlorine content not exceeding 30 ppm and a nitrogen content not exceeding 300 ppm.

10. The method for refining pyrolysis oil according to anyone of claims 1 to 9, wherein a filter press is used in step (ii) to filter the treated waste liquid.11 . The method for refining pyrolysis oil according to anyone of claims 1 to 10, wherein the weight ratio of the washing solution to the crude pyrolysis oil in step (I) is (0.1 - 0.5) : 1, preferably (0.15 - 0.45) : 1.

12. The method for refining pyrolysis oil according to anyone of claims 1 to 11, wherein the crude pyrolysis oil is manufactured by pyrolysis of waste plastic.

13. A refined pyrolysis oil manufactured by the method for refining pyrolysis oil as claimed in any one of claims 1 to 12.

14. The use of the refined pyrolysis oil according to claim 13 in steam cracking process or a partial oxidation process.

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