CN114507539B

CN114507539B - Method and system for preparing low-carbon olefin from waste plastics

Info

Publication number: CN114507539B
Application number: CN202011169445.4A
Authority: CN
Inventors: 邹亮; 徐润; 吴治国; 魏晓丽; 夏国富; 李红伟; 王志强; 王树青; 侯吉礼; 王鹏飞; 吴玉
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2020-10-28
Filing date: 2020-10-28
Publication date: 2023-05-05
Anticipated expiration: 2040-10-28
Also published as: CN114507539A

Abstract

The invention relates to a method and a system for preparing low-carbon olefin from waste plastics, wherein the waste plastics sequentially pass through a waste plastics dissolving and dechlorinating unit, and a waste plastics thermal dissolving and impurity removing unit is used for processing to obtain impurity removing and plastic containing solution; the obtained impurity-removed plastic-containing solution enters a catalytic cracking unit, and is contacted with a catalytic cracking catalyst together with optional catalytic cracking raw materials to react, and the reaction effluent is separated to obtain a catalytic cracking product comprising low-carbon olefin. The invention prepares the waste plastics into olefin monomers, so that the waste plastics are subjected to closed circulation, and the recycling of plastics is truly realized. The invention is not only helpful for solving the problem of white pollution, but also has small pollution discharge, good environmental protection and reduced carbon emission in the production process, and has good environmental benefit, social benefit and economic benefit.

Description

Method and system for preparing low-carbon olefin from waste plastics

Technical Field

The invention relates to the technical field of solid waste plastic treatment, in particular to a method and a system for preparing low-carbon olefin from waste plastic.

Background

The statistics show that the total amount of the existing waste plastics in China is about 10 hundred million tons and gradually increases at the speed of 4000 ten thousand tons per year. By 2035, about 80 million tons of waste plastics are expected to be produced worldwide. This not only causes serious environmental pollution, but even affects ecological balance in natural environment; and is also a serious waste of petrochemical resources. The existing waste plastic treatment technology mainly comprises several modes of landfill, incineration, physical recovery, chemical recovery and the like, wherein the landfill cannot essentially solve the problems due to low decomposition speed and low bulk density of waste plastic, and the underground water resource is easy to pollute; while incineration is easy to cause serious atmospheric pollution; the existing waste plastic recycling process has high cost and low economic value, and the waste plastic physical recycling development is slower due to insufficient enterprise profit.

The chemical conversion of waste plastics is an effective means for realizing the rapid recovery and conversion of waste plastics, particularly, the thermoplastic waste plastics can obtain oil products and gases through a pyrolysis process, so the pyrolysis process is one of the main process paths of the chemical conversion of the waste plastics at present.

CN106635115B discloses a method for efficiently cleaning and preparing oil by using mixed waste plastic garbage and a hydrothermal reaction system, wherein the method comprises the steps of carrying out thermal hydrolysis treatment on the mixed waste plastic garbage by using an alkaline aqueous solution under the conditions of 160-300 ℃ and 20-220 bar of pressure; the mixed waste plastic garbage contains one or more of PE, PP and PS and PET, and optionally the mixed waste plastic garbage can also comprise PVC; separating the water phase from the solid phase in the material after the hydrothermal treatment, and preparing oil from the separated solid phase. The invention not only avoids the adverse effect of PET and PVC in the mixed waste plastics on the quality of oil, but also can clean and prepare the oil with high efficiency, and can produce products with high added value, such as TA powder or particles and PS reclaimed plastics.

CN102786980B discloses a method for producing waste plastics by oil refining and a production line thereof, the method comprises the following steps: 1) Waste plastic pretreatment; 2) Cracking reaction; 3) Catalytic reaction; 4) Condensing; 5) The waste plastics are subjected to oiling treatment by the method, so that the oil yield is high, and the slag rate is low; the production line comprises a feeding device, a high-frequency electric heating reaction kettle, a catalytic tower, a cooling filtering tank, a cooling liquefying tower and an oil storage tank, wherein the feeding device is connected with the high-frequency electric heating reaction kettle, the high-frequency electric heating reaction kettle is connected with the catalytic tower through a pipeline, the catalytic tower is connected with the cooling filtering tank through a pipeline, the cooling filtering tank is connected with the cooling liquefying tower through a pipeline, and the cooling liquefying tower is connected with the oil storage tank through a pipeline.

CN107746722a discloses a method and apparatus for preparing gasoline and diesel oil by cracking waste plastics, in particular to a method and apparatus for preparing gasoline and diesel oil by cracking and upgrading oil gas by melting, dewatering, dechlorinating, cracking and upgrading by precisely controlling temperature by dissolving crushed and impurity-removed waste plastics in liquid pyrolysis oil by slurry bed, and obtaining main products of gasoline and diesel oil by cooling and fractionating, and by-products of which are small amounts of dry gas, liquefied gas and heavy oil. And part of heavy oil is directly returned to the cracking kettle for further cracking reaction, and part of heavy oil is returned as pyrolysis oil to the inlet as pyrolysis oil.

The pyrolysis process in the prior art mainly has the problem that the quality of pyrolysis oil does not reach the standard, and particularly the content of Cl and Si impurities is high. The Cl in the pyrolysis oil mainly comes from PVC decomposition in waste plastics, most of the Cl is micromolecular organic chlorine, and HCl is easily decomposed and formed in the oil quality improvement process to cause serious corrosion. In the prior art, the pyrolysis oil is mainly subjected to neutralization by adopting alkaline substances, but a large amount of solid waste is generated on the one hand, and PVC is finally converted into inorganic salt on the other hand, so that the value of the PVC is essentially reduced. Si in pyrolysis oil is mainly from decomposition of high molecular additives such as silicone oil, silicone resin, silicone rubber powder and the like and SiO ₂ The inorganic additives, which are mainly in the form of alkyl epoxy silane, are poisons for catalysts in subsequent upgrading processes, and can lead to permanent deactivation of the catalyst.

Disclosure of Invention

The invention aims to solve the problems that the pipelines and equipment in the follow-up process are easy to corrode and the catalyst is easy to deactivate due to high content of harmful elements Cl and Si in pyrolysis oil of waste plastics in the prior art.

In order to achieve the above object, the present invention provides a method for preparing low-carbon olefins from waste plastics, comprising the steps of:

(1) The waste plastics enter a waste plastics dissolving and dechlorinating unit and are fully dissolved in an organic solvent, and the dissolved materials are separated into chlorine-containing solution and dechlorinated waste plastics by a solid-liquid separation device I, wherein the organic solvent is one or more of tetrahydrofuran, ketone solvents and chlorinated aliphatic hydrocarbons; the chlorine content in the dechlorinated waste plastic is less than 20 mug/g;

(2) The dechlorinated waste plastics obtained in the step (1) enter a waste plastics thermal dissolving and impurity removing unit, are mixed with an adsorbent and solvent oil, and then undergo thermal dissolving and impurity removing at the temperature of 280-410 ℃, and the materials after thermal dissolving are separated into insoluble matters and impurity removing and plastic-containing solution through a solid-liquid separation device II; the silicon content in the impurity-removed plastic-containing solution is less than 3 mug/g;

(3) The impurity-removed plastic-containing solution obtained in the step (2) enters a catalytic cracking unit to be contacted with a catalytic cracking catalyst for reaction, and at least a low-carbon olefin product is obtained after the reaction effluent is separated, wherein the catalytic cracking catalyst is one or more of a metal oxide type catalytic cracking catalyst and a zeolite type catalytic cracking catalyst.

In the invention, the waste plastic is one or more of waste plastic in fresh household garbage, waste plastic in industrial and agricultural production and waste plastic in aged garbage, and can be one or more of waste plastic rods, waste plastic particles, waste plastic sheets and the like formed by preliminary processing of the waste plastic, preferably poor-quality waste plastic which cannot be physically recycled, and the type of the waste plastic is one or more of PE, PP, PS, PVC.

In one embodiment of the invention, the waste plastics are washed, dried and crushed before entering the waste plastics dissolution dechlorination unit, and the particle size of the crushed waste plastics is 1-200 mm, preferably 1-50 mm.

In a preferred case, the organic solvent in the step (1) is a mixed solvent composed of tetrahydrofuran and ketone solvents in any weight proportion, wherein the ketone solvents are selected from one or more of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone;

the weight ratio of the organic solvent to the waste plastic is 1:10-10:1.

In one embodiment of the present invention, the ketone solvent is selected from one or more of methyl ethyl ketone and cyclohexanone; methyl ethyl ketone is preferred;

in one embodiment of the present invention, the organic solvent is a mixed solvent of tetrahydrofuran and ketone solvent in a weight ratio of 1:3 to 3:1, and more preferably, the organic solvent is a mixed solvent of tetrahydrofuran and ketone solvent in a weight ratio of 1:2 to 2:1.

In one embodiment of the invention, the organic solvent is preheated at a temperature of 40-60 ℃, and the preheated organic solvent enters a waste plastic dissolution and dechlorination unit.

In one embodiment of the present invention, the waste plastics are sufficiently dissolved in the organic solvent at a temperature of 50-100 ℃ in the waste plastics dissolution dechlorination unit, and the residence time of the waste plastics is 30-60 min. Carrying out solid-liquid separation on the dissolved material by a solid-liquid separation device I, wherein the operation temperature of the solid-liquid separation device I is 50-100 ℃; the chlorine content in the obtained dechlorinated waste plastics is less than 20 mug/g.

In one embodiment of the invention, a solvent recovery device is arranged in the waste plastic dissolution dechlorination unit, the chlorine-containing solution obtained by the solid-liquid separation device I enters the solvent recovery device, and PVC and/or PS particles and the recovered organic solvent are obtained after precipitation treatment and separation.

In one embodiment of the present invention, in the solvent recovery device, the precipitation treatment is one or more selected from the group consisting of back extraction, simple distillation, flash evaporation and rectification.

In a preferred embodiment of the present invention, in the solvent recovery device, the precipitation treatment adopts a stripping coupling distillation mode, the stripping agent is water, the stripping temperature is 70-100 ℃, and the distillation temperature is 80-100 ℃. After the chlorine-containing solution enters a solvent recovery device and contacts with stripping agent water, dissolved PVC and/or PS are separated out in the form of solid particles, and the liquid part is an aqueous organic solvent. The water-containing organic solvent is distilled to obtain water and recovered organic solvent, and the recovered organic solvent can be reused.

In one embodiment of the invention, the stripped material is separated by filtration to obtain PVC and/or PS particles and wastewater containing organic solvent. The filtering device is one or more of a one-stage or multistage series or parallel filter press, a plate frame, a centrifugal machine and spiral extrusion desolventizing equipment.

In one embodiment of the present invention, in the step (2), the operation conditions of the waste plastic thermal dissolving and impurity removing unit are as follows: the reaction temperature is 280-410 ℃, preferably 320-390 ℃, the pressure is 0.1-5 MPa, and the residence time of the dechlorinated waste plastics is 10-60 min.

In one embodiment of the invention, the distillation range of the solvent oil is 80-550 ℃, the total aromatic hydrocarbon content in the solvent oil is higher than 50 mass percent, and the monocyclic aromatic hydrocarbon content is higher than 20 mass percent; further preferably, the content of monocyclic aromatic hydrocarbon in the solvent oil is higher than 40 mass%;

in one embodiment of the invention, the weight ratio of solvent naphtha to dechlorinated waste plastics is 1:10 to 10:1, preferably 3:1 to 7:1.

In one embodiment of the invention, the adsorbent is one or more of humus soil, red mud, dead catalyst of oil refining device, kaolin, semicoke, active carbon and gasified ash; the grain diameter is 75-150 mu m.

The humus soil is a mixture formed by rotting plant substances and various organic wastes entrained by waste plastics excavated in a landfill.

The semicoke is a solid product generated by pyrolysis of carbon-containing substances such as coal, biomass, waste plastics and the like at the temperature of 350-600 ℃.

The gasified ash is a solid product which is remained after carbonaceous substances such as coal, semicoke, coke, biomass, petroleum coke, waste plastics and the like react with gasifying agents under the conditions of normal pressure or pressurization at the temperature higher than 600 ℃.

The preferential adsorbent is one or more of waste catalytic cracking catalyst, waste catalytic cracking catalyst of catalytic cracking unit, humus soil and semicoke; further preferred are spent catalytic cracking catalysts of the catalytic cracking unit of step (3) of the present invention.

In one embodiment of the invention, the weight fraction of the adsorbent is 1-10% based on the total weight of the mixed materials in the waste plastic thermal dissolving and impurity removing unit.

In the waste plastic thermal dissolution impurity removal unit, silicon impurities in the waste plastic are removed, and the silicon impurities are removed in the original form of organic silicon polymers added in the plastic processing process, so that the influence of the silicon impurities on catalysts of subsequent processing units is effectively avoided. And the chlorine content in the waste plastics is further reduced, and the influence of chlorine impurities on a subsequent processing device is effectively avoided.

In the step (2) of the invention, the material after the thermal dissolution is separated into insoluble matters and impurity-removed plastic-containing solution by a solid-liquid separation device II, preferably the total metal content in the obtained impurity-removed plastic-containing solution is less than 5 mug/g, the silicon content is less than 2 mug/g, and the chlorine content is less than 10 mug/g.

In one embodiment of the present invention, the solid-liquid separation device II is operated at a temperature of 280 to 410 ℃.

In the step (3), the impurity-removed plastic-containing solution obtained by the solid-liquid separation device II enters a catalytic cracking unit to be contacted with a catalytic cracking catalyst for reaction, and the reaction effluent is separated to obtain low-carbon olefin, catalytic cracking naphtha, catalytic cracking gasoline, catalytic cracking diesel oil and catalytic cracking slurry oil. The low-carbon olefin comprises propylene, ethylene and butylene, which are all basic raw materials in the chemical industry and have wide application.

In one embodiment of the invention, the feed to the catalytic cracking unit comprises an optional catalytic cracking feedstock that is a petroleum hydrocarbon oil selected from at least one of vacuum wax oil, coker wax oil, deasphalted oil, residuum, gasoline, and diesel oil, and/or a mineral oil selected from at least one of coal liquefaction oil, oil sand, and shale oil.

In the present invention, "optional" means that the feed to the catalytic cracking unit includes an optional catalytic cracking feedstock, meaning that the catalytic cracking unit feed may include other catalytic cracking feedstock in addition to the de-mixed plastic-containing solution.

In the invention, the catalytic cracking unit is one or more selected from DCC, CPP, HCC, catalytic-steam cracking, THR and rapid cracking processes; the reactor is selected from one or more of fixed bed, moving bed, fluidized bed, riser and descending conveying bed.

In one embodiment of the invention, the reaction temperature of the catalytic cracking unit is 500-850 ℃, and the weight ratio of the catalyst to the oil is (1-50): 1, the mass ratio of water to oil is (0.01-1): 1, and the reaction pressure is 0.1-2 MPa. The catalytic cracking catalyst is one or more of metal oxide type catalytic cracking catalyst and zeolite type catalytic cracking catalyst.

In one embodiment of the invention, the zeolite-type catalytic cracking catalyst comprises the following components: the zeolite-type catalytic cracking catalyst comprises 1 to 50 wt% zeolite, 5 to 99 wt% inorganic oxide, and 0 to 70 wt% clay, based on the dry weight of the zeolite-type catalytic cracking catalyst.

In a preferred case, the zeolite comprises 50 to 100 wt% of a large pore zeolite comprising at least one selected from REY, REHY, USY and high silicon Y and 0 to 50 wt% of a medium pore zeolite comprising ZSM-series zeolite and/or ZRP zeolite based on the dry weight of the zeolite; the inorganic oxide comprises silicon oxide and/or aluminum oxide; the clay comprises kaolin and/or halloysite.

In one embodiment of the present invention, the metal oxide type catalytic cracking catalyst contains alumina and/or aluminosilicate, and one or more metal oxides selected from alkali metal oxides, alkaline earth metal oxides, and group VIII metal oxides.

In a preferred case, the aluminosilicate is selected from the group consisting of silica-alumina, amorphous aluminum silicate, molecular sieves.

Preferably, the metal oxide is selected from one or more of K, na, ca, fe, co, ni, mo oxides.

In another aspect, the present invention also provides a system for preparing light olefins from waste plastics in any of the above methods, comprising: the device comprises a waste plastic dissolving and dechlorinating unit, a waste plastic thermal dissolving and impurity removing unit and a catalytic cracking unit;

the waste plastic dissolving and dechlorinating unit is provided with a waste plastic inlet, an organic solvent inlet and a solid-liquid mixture outlet, the solid-liquid mixture outlet is communicated with an inlet of a solid-liquid separation device I, and the solid-liquid separation device I is provided with a chlorine-containing solution outlet and a dechlorinated waste plastic outlet;

the waste plastic thermal dissolution and impurity removal unit is provided with a dechlorination waste plastic inlet, a solvent oil inlet, an adsorbent inlet and a solid-liquid mixture outlet, the dechlorination waste plastic outlet of the solid-liquid separation device I is communicated with the dechlorination waste plastic inlet of the waste plastic thermal dissolution and impurity removal unit, the solid-liquid mixture outlet of the waste plastic thermal dissolution and impurity removal unit is communicated with the inlet of the solid-liquid separation device II, and the solid-liquid separation device II is provided with an insoluble matter outlet and an impurity removal plastic-containing solution outlet;

the catalytic cracking unit is provided with a impurity-removing plastic-containing solution inlet, an optional catalytic cracking raw material inlet and at least one low-carbon olefin outlet, and the impurity-removing plastic-containing solution outlet of the solid-liquid separation device II is communicated with the impurity-removing plastic-containing solution inlet of the catalytic cracking unit.

In one embodiment of the invention, the waste plastic dissolution dechlorination unit further comprises a solvent recovery unit, wherein the solvent recovery unit is provided with a chlorine-containing solution inlet, a PVC and/or PS particle outlet and a recovered organic solvent outlet; the chlorine-containing solution outlet of the solid-liquid separation device I is communicated with the chlorine-containing solution inlet of the solvent recovery device.

In one embodiment of the invention, the waste plastic thermal dissolving and impurity removing device is provided with an adsorbent inlet and a solvent oil inlet respectively or provided with a mixture inlet of adsorbent and solvent oil.

In one embodiment of the invention, the pore diameter of the filter screen used by the solid-liquid separation device I is 0.1-10 mm; the aperture of the filter screen used in the solid-liquid separation device II is 0.001-1 mm.

In one embodiment of the invention, the solid-liquid separation device I and the solid-liquid separation device II are one or more of various continuous automatic solid-liquid separation equipment and drying equipment with heat preservation function, oil resistance and organic solvent resistance, which are connected in series in one or more stages, or one or more of various types of filters with automatically changeable filter screens, filter presses with scrapers, cross-flow filters, horizontal screw centrifuges and screw extrusion desolventizing equipment, wherein the solid-liquid separation device I is preferably a screw extrusion desolventizing equipment connected in series with a hot air dryer, and the solid-liquid separation device II is preferably a high Wen Cuoliu filtering equipment.

The invention is characterized in that:

according to the invention, in the waste plastic dissolution and dechlorination unit, the chlorine-containing waste plastic in the waste plastic is dissolved by adopting the preferable organic solvent, and the chlorine-containing waste plastic is physically recovered while the solvent is recovered, so that the dechlorination effect is high, the solvent recovery utilization rate is high, and a large amount of solid waste is avoided while dechlorination is carried out.

The invention removes silicon impurities in the dechlorinated waste plastics in the waste plastics thermal dissolution impurity removal unit, and further reduces the chlorine content. The removed silicon impurities are removed in the original form of the organic silicon polymer added in the plastic processing process, so that the problem of deactivation of the catalyst of a subsequent processing unit is effectively avoided. The impurity-removed plastic-containing solution obtained by the waste plastic heat-dissolving impurity-removing unit reacts in the catalytic cracking unit to obtain the low-carbon olefin containing ethylene, propylene and butylene. The invention prepares the waste plastics into olefin monomers, so that the waste plastics are subjected to closed circulation, and the recycling of plastics is truly realized.

The invention is not only helpful for solving the problem of white pollution, but also has small pollution discharge, good environmental protection and reduced carbon emission in the production process, and has good environmental benefit, social benefit and economic benefit.

Drawings

FIG. 1 is a schematic diagram of the method for preparing light olefins from waste plastics.

In the figure: 1. a drying unit; 2. a crushing unit; 3. a waste plastic dissolving and dechlorinating unit; 4. a solid-liquid separation device I; 5. a waste plastic thermal dissolving and impurity removing unit; 6. a solid-liquid separation device II; 7. a fluid delivery unit; 8. a catalytic cracking unit; 9. and a solvent recovery unit.

Detailed Description

The invention will be further described with reference to the accompanying drawings, without thereby limiting the invention.

FIG. 1 is a schematic diagram of the method for preparing light olefins from waste plastics. As shown in fig. 1, the washed waste plastics are dried in a drying unit 1 and then enter a crushing unit 2 to be crushed into waste plastics particles of 1 to 200mm. The obtained waste plastic particles enter a waste plastic dissolving and dechlorinating unit 3, are fully dissolved in an organic solvent, and the dissolved materials are separated into chlorine-containing solution and dechlorinated waste plastic through a solid-liquid separation device I4. The chlorine-containing solution is sent to a solvent recovery unit 9, and the chlorine-containing plastic and the recovered organic solvent are obtained after precipitation treatment and separation. The obtained dechlorinated waste plastics enter a waste plastics thermal dissolving and impurity removing unit 5, are mixed with an adsorbent and solvent oil, and then undergo thermal dissolving and impurity removing, and the materials after thermal dissolving are separated into insoluble matters and impurity removing plastic-containing solution through a solid-liquid separation device II 6. The obtained impurity-removed plastic-containing solution enters a catalytic cracking unit 8 through a fluid conveying unit 7, and is contacted with a catalytic cracking catalyst together with optional catalytic cracking raw materials to react, and the reaction effluent is separated to obtain a catalytic cracking product comprising low-carbon olefin.

The invention is further illustrated by the following examples, which are not intended to limit the invention in any way.

In the examples, the chlorine content in the solid mixture was measured by coulometry, specifically by the method of "measuring the total chlorine content in crude oil by coulometry" (RIPP 64-90) in "petrochemical analysis method" (RIPP test method). The instrument used was a microcoulomb analyzer. The sample is a frozen crushed waste plastic powder sample.

In the examples, the chlorine content of the liquid mixture was likewise determined by means of the "coulometric determination of the total chlorine content in crude oil" (RIPP 64-90). Except that the sample was a liquid mixture.

In the examples, the silicon content of the liquid mixture was determined by the method of "additive elements in used lubricating oils, wearing metals and contaminants and determination of certain elements in base oils (inductively coupled plasma emission spectrometry) (GB 17476-1998).

Examples 1 to 5

Waste plastic A is waste plastic which is obtained by excavating aged garbage in a Guangdong landfill, crushing the waste plastic A to be less than 50mm after cleaning and drying, wherein ash content in the crushed waste plastic A is 9.5%, water content is 0, crushed particles of the waste plastic A are preheated to 60 ℃ and enter a waste plastic dissolution and dechlorination unit, the waste plastic dissolution and dechlorination unit adopts an external heating type dissolution kettle, the operating pressure is normal pressure at 60 ℃, the rotating speed of a stirring paddle is 60r/min, the waste plastic A is dissolved in an organic solvent, the residence time of the waste plastic A in the external heating type dissolution kettle is 30min, and the dissolved materials are separated into chlorine-containing solution and dechlorinated waste plastic at 60 ℃ through a spiral extrusion desolventizing device.

The organic solvent used in the example 1 is tetrahydrofuran, and the weight ratio of the organic solvent to the waste plastic A is 10:1; the chlorine content in the obtained dechlorinated waste plastics is 23 mug/g.

The organic solvent used in example 2 is methyl ethyl ketone, and the weight ratio of the organic solvent to waste plastic A is 10:1; the chlorine content in the obtained dechlorinated waste plastics is 20 mug/g.

The organic solvent used in the example 3 is cyclohexanone, and the weight ratio of the organic solvent to the waste plastic A is 10:1; the chlorine content in the obtained dechlorinated waste plastics is 25 mug/g.

The organic solvent used in example 4 was a mixture of tetrahydrofuran and methyl ethyl ketone in a weight ratio of 1:1, and the weight ratio of the organic solvent to waste plastic A was 10:1; the chlorine content in the obtained dechlorinated waste plastics is 17 mug/g.

The organic solvent used in example 5 was a mixture of tetrahydrofuran and methyl ethyl ketone in a weight ratio of 1:2, and the weight ratio of the organic solvent to waste plastic A was 10:1; the chlorine content in the obtained dechlorinated waste plastics is 19 mug/g.

Example 6

The dechlorinated waste plastics obtained in the example 4 are sent to a waste plastics thermal dissolution and impurity removal unit through a screw feeder, the waste plastics thermal dissolution and impurity removal unit adopts an external heating type dissolution kettle, and after being mixed with adsorbent and solvent oil, thermal dissolution and impurity removal are carried out at 320 ℃ and 1MPa, the residence time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and impurity removal plastic-containing solution through a screw extrusion solvent removal device (a solid-liquid separation device II). The obtained impurity-removed plastic-containing solution has a silicon content of 2.8 mug/g and a chlorine content of 1.8 mug/g.

The solvent oil is the catalytic pyrolysis diesel fraction obtained by the catalytic pyrolysis unit, the distillation range is 205-360 ℃, the total aromatic hydrocarbon content is 78.2 mass percent, and the monocyclic aromatic hydrocarbon content is 53.1 mass percent; the weight ratio of the solvent oil to the dechlorinated waste plastic is 5:1.

The adopted adsorbent is the waste catalyst of the catalytic cracking unit, and the particle size is 75-150 mu m. The weight fraction of the adsorbent is 1% based on the total weight of the mixture materials in the waste plastic thermal dissolving and impurity removing unit.

Example 7

The dechlorinated waste plastics obtained in the example 4 are sent to a waste plastics thermal dissolution and impurity removal unit through a screw feeder, the waste plastics thermal dissolution and impurity removal unit adopts an external heating type dissolution kettle, and after being mixed with adsorbent and solvent oil, the dechlorinated waste plastics are subjected to thermal dissolution and impurity removal at 300 ℃ and 2MPa, the residence time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and impurity removal plastic-containing solution through a screw extrusion solvent removal device. The obtained impurity-removed plastic-containing solution had a silicon content of 2.8. Mu.g/g and a chlorine content of 3.0. Mu.g/g.

The solvent oil is VGO of a refinery, the distillation range of the solvent oil is 275-581 ℃, the total aromatic hydrocarbon content is 45.1 mass percent, and the monocyclic aromatic hydrocarbon content is 21 mass percent; the weight ratio of the solvent oil to the dechlorinated waste plastic is 5:1.

The adsorbent is activated carbon with the particle size of 75-150 μm. The weight fraction of the adsorbent is 2% based on the total weight of the mixture materials in the waste plastic thermal dissolving and impurity removing unit.

Example 8

The dechlorinated waste plastics obtained in the example 4 are sent to a waste plastics thermal dissolution and impurity removal unit through a screw feeder, mixed with adsorbent and solvent oil, thermally dissolved and impurity removed at 300 ℃ and 2MPa, the stay time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and impurity removed plastic-containing solution through a screw extrusion solvent removal device. The obtained impurity-removed plastic-containing solution has a silicon content of 1.6 mug/g and a chlorine content of 2.9 mug/g.

The solvent oil is light catalytic cracking light cycle oil, the distillation range is 156-338 ℃, the total aromatic hydrocarbon content is 76.8 mass percent, and the monocyclic aromatic hydrocarbon content is 63.8 mass percent; the weight ratio of the solvent oil to the dechlorinated waste plastic is 5:1.

Example 9

The dechlorinated waste plastics obtained in the example 5 are sent to a waste plastics thermal dissolution and impurity removal device through a screw feeder, mixed with adsorbent and solvent oil, thermally dissolved and impurity removed at 350 ℃ and 1.5MPa, the stay time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and impurity removed plastic-containing solution through a screw extrusion and solvent removal device. The total metal content in the obtained impurity-removed plastic-containing solution is 3.6 mug/g, the silicon content is 1.6 mug/g, and the chlorine content is 1.8 mug/g.

The adsorbent is humus soil with the grain diameter of 75-150 μm. The weight fraction of the adsorbent is 1.5% based on the total weight of the mixture materials in the waste plastic thermal dissolving and impurity removing unit.

Example 10

The dechlorinated waste plastics obtained in the example 5 are sent to a waste plastics thermal dissolution and impurity removal device through a screw feeder, mixed with adsorbent and solvent oil, thermally dissolved and impurity removed at 330 ℃ and 2MPa, the stay time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and impurity removed plastic-containing solution through a screw extrusion and solvent removal device. The obtained impurity-removed plastic-containing solution has a silicon content of 2.2 mug/g and a chlorine content of 2.3 mug/g.

The solvent oil is the mixed fraction of catalytic pyrolysis diesel oil and straight-run diesel oil, the distillation range is 162-360 ℃, the total aromatic hydrocarbon content is 51 mass percent, the monocyclic aromatic hydrocarbon content is 32 mass percent, and the weight ratio of the solvent oil to dechlorinated waste plastics is 6:1.

The adsorbent is a mixture of semicoke and waste catalyst of a catalytic cracking unit in a weight ratio of 1:1, and the particle size is 75-150 mu m. The weight fraction of the adsorbent is 1.8% based on the total weight of the mixture materials in the waste plastic thermal dissolving and impurity removing unit.

Comparative example 1

The comparative example was identical to the dechlorinated waste plastics, solvent oil, and hot-dissolving impurity-removing reaction conditions employed in example 10, except that no adsorbent was employed in the comparative example.

The dechlorinated waste plastics obtained in the example 5 are sent to a waste plastics thermal dissolution and impurity removal device through a screw feeder, mixed with solvent oil, thermally dissolved at 330 ℃ and 2MPa, the residence time of the dechlorinated waste plastics is 30min, and the materials after thermal dissolution are separated into insoluble matters and plastic-containing solution through the screw extrusion and solvent removal device. The total metal content in the resulting plastic-containing solution was 13. Mu.g/g, the silicon content was 245. Mu.g/g, and the chlorine content was 3.6. Mu.g/g.

Therefore, the impurity contained in the waste plastic can be effectively removed by adopting the method for removing impurities through pyrolysis, which is beneficial to subsequent processing and utilization.

Example 11

The impurity-removed plastic-containing solution obtained in the example 9 and Daqing atmospheric residuum are sent to a catalytic cracking unit together, and the weight ratio of the impurity-removed plastic-containing solution to the Daqing atmospheric residuum is 1:2, carrying out a reaction in contact with a catalytic cracking catalyst, and separating a reaction effluent to obtain a catalytic cracking product comprising low-carbon olefin. The catalytic cracking unit adopts CPP technology of China petrochemical engineering institute of science.

The catalytic cracking catalyst is named CEP and is produced by China petrochemical catalyst division.

The catalytic cracking reaction temperature is 610 ℃, the reaction pressure is 0.08MPa,the catalyst-oil ratio is 17, the water-oil ratio is 0.4, and the airspeed is 4.0h ^-1 The catalyst regeneration temperature was 720 ℃.

The yields of the obtained products are shown in Table 1. Since the organosilicon decomposition products are mainly octamethyl cyclotetrasiloxane (D4) and decamethyl cyclopentasiloxane (D5), which are mainly concentrated in the gasoline fraction, the impurity content in the gasoline fraction is emphasized.

Example 12

The impurity-removed plastic-containing solution obtained in the example 10 is sent to a catalytic cracking unit, is contacted with a catalytic cracking catalyst to carry out catalytic cracking reaction, and is separated to obtain a catalytic cracking product comprising ethylene, propylene and butylene.

The catalytic cracking unit adopts DCC technology of China petrochemical engineering institute of science.

The catalytic cracking catalyst is CRP and is produced by China petrochemical catalyst division.

The catalytic cracking reaction temperature is 560 ℃, the reaction pressure is 0.11MPa, the catalyst-oil ratio is 12, the water-oil ratio is 0.2, and the airspeed is 4.0h ^-1 The catalyst regeneration temperature was 720 ℃.

The yields of the obtained products are shown in Table 1.

TABLE 1

Example 13

The waste plastics B are waste plastics separated from aged garbage dug out from a landfill site in Guangdong province, the separated waste plastics basically have no moisture, and the ash content is about 9.9 weight percent. Delivering the waste plastics recovered by sorting into an intermittent heat exchange dryer through a conveyor belt, wherein the temperature of the dryer is 105 ℃, and the residence time of the waste plastics in the dryer is 30min; conveying the dried waste plastics to a shearing crusher through a conveying belt, and crushing the waste plastics into fragments smaller than 10mm; the crushed waste plastics are sent to a dissolution kettle I of a dissolution dechlorination unit through a screw feeder, mixed solvent of methyl ethyl ketone and tetrahydrofuran=2:1 is sent to the dissolution kettle I together according to the proportion of plastic dissolution weight ratio of 1:5, the dissolution temperature of the dissolution kettle I is 65 ℃, the operation pressure is normal pressure, the rotation speed of a stirring paddle is 60r/min, and the waste plastics B are dissolved in the dissolution kettle I for 30min. The dissolution kettle I adopts a mode of connecting two kettles in parallel; the mixture after dissolution is sent to a high temperature filter through a discharge opening at the bottom of the dissolution kettle I, and the mixture is separated into dechlorinated waste plastics and chlorine-containing solution at 65 ℃. The chlorine-containing solution is flashed to recover the organic solvent and chlorine-containing waste plastics. The chlorine content in the obtained dechlorinated waste plastics was 8.3. Mu.g/g.

The obtained dechlorinated waste plastics are dried at 80 ℃ and are further recycled into a dissolution kettle II of a waste plastics pyrolysis impurity removal unit through a screw feeder, solvent oil is conveyed to the dissolution kettle II through a metering pump according to the proportion of plastic-to-solvent weight ratio of 1:10, a catalytic cracking balancing agent of a catalytic cracking unit is conveyed to the dissolution kettle II through the metering pump according to the proportion of the catalyst-to-plastic weight ratio of 1:10, the impurity removal reaction temperature is 350 ℃, the operating pressure is 0.5MPa, the rotating speed of a stirring paddle is 60r/min, the residence time of the dechlorinated waste plastics in the dissolution kettle is 30min, and the dissolution kettle II adopts a mode of connecting two kettles in parallel. After dissolving for a certain time, the mixture is sent to a high-temperature filter through a discharge opening at the bottom of a dissolving kettle II, and the materials after reaction are filtered at 350 ℃ to remove insoluble impurities to obtain the impurity-removing plastic-containing solution. The obtained impurity-removed plastic-containing solution has a silicon content of 1.6 mug/g and a chlorine content of 3.0 mug/g.

The impurity-removed plastic-containing solution is sent to a catalytic cracking unit. And the catalyst is contacted with a catalytic cracking catalyst to react, and the reaction product is separated to obtain a catalytic cracking product comprising low-carbon olefin, wherein the yield and part of impurity content of the obtained product are shown in table 2.

The solvent oil is distillate oil of a catalytic cracking unit, the distillation range of the solvent oil is 150-350 ℃, the total aromatic hydrocarbon content is 73 mass percent, and the monocyclic aromatic hydrocarbon content is 61 mass percent.

The catalytic cracking reaction temperature is 545 ℃, the reaction pressure is 0.11MPa, the catalyst-oil ratio is 8.9, the water-oil ratio is 0.2, and the airspeed is 4h ^-1 The catalyst regeneration temperature was 711 ℃.

Example 14

Raw material of waste plastics B, organic solvent and reaction conditions of a waste plastics dissolving and dechlorination unit, solvent oil, adsorbent and reaction conditions of a waste plastics thermal dissolving and dechlorination unit, and catalyst and reaction conditions of a catalytic cracking unit are the same as those of example 13. The difference is that the weight ratio of the impurity removing plastic-containing solution to the catalytic cracking raw material Daqing VGO is 1: 1.

The catalyst is deactivated by depositing impurities in the raw materials and carbon deposition in the reaction process on the catalyst, and in order to improve the service life of the catalyst, the catalytic cracking unit devices used in example 13 and example 14 are circulating fluidized bed devices, i.e. the deactivated catalyst is regenerated in another device, but the permanent deactivation caused by metal impurities cannot be regenerated, so that in order to maintain the stable operation of the catalytic cracking device, part of the catalyst needs to be replaced, so that the activity of the catalyst is in a relatively balanced and stable state. The catalyst replacement amount required for treating 1t of the raw oil while maintaining the original apparatus in stable operation is generally used as an index, and the catalytic cracking catalyst replacement amount in this example is 1.2kg/t.

The yields and partial impurity contents of the obtained products are shown in Table 2.

Comparative example 1

The reaction was carried out in a catalytic cracking unit using Daqing VGO, and the catalyst and reaction conditions of the catalytic cracking unit were the same as those of example 13. The yields and partial impurity contents of the obtained products are shown in Table 2.

Comparative example 2

The raw material of waste plastic B used in this comparative example, the organic solvent and reaction conditions of the waste plastic dissolution dechlorination unit, the solvent oil and reaction conditions of the waste plastic thermal dissolution dechlorination unit, and the feeding, catalyst and reaction conditions of the catalytic pyrolysis unit are the same as those of example 14. Except that the waste plastic thermal dissolving and impurity removing unit has no adsorbent.

The amount of catalyst replacement in the present comparative example was 1.25kg/t.

TABLE 2

As can be seen from comparison of the results of the comparative examples and the examples, the examples of the present invention can greatly reduce the relative content of harmful elements in oil products and obtain more light olefins.

The above description is only of any embodiment of the present invention and is not intended to limit the present invention, and various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing low-carbon olefin from waste plastics comprises the following steps:

(1) The waste plastics enter a waste plastics dissolving and dechlorinating unit and are fully dissolved in an organic solvent, and the dissolved materials are separated into chlorine-containing solution and dechlorinated waste plastics by a solid-liquid separation device I, wherein the organic solvent is one or more of tetrahydrofuran, ketone solvents and chlorinated aliphatic hydrocarbons; the chlorine content in the dechlorinated waste plastic is less than 20 mug/g; the waste plastics are one or more of PE, PP, PS, PVC;

(2) The dechlorinated waste plastics obtained in the step (1) enter a waste plastics thermal dissolving and impurity removing unit, are mixed with an adsorbent and solvent oil, and then undergo thermal dissolving and impurity removing at the temperature of 280-410 ℃, and the materials after thermal dissolving are separated into insoluble matters and impurity removing and plastic-containing solution through a solid-liquid separation device II; the silicon content in the impurity-removed plastic-containing solution is less than 3 mug/g; the distillation range of the solvent oil is 80-550 ℃, the total aromatic hydrocarbon content in the solvent oil is higher than 50 mass percent, and the monocyclic aromatic hydrocarbon content is higher than 20 mass percent; the adsorbent is one or more of humus soil, red mud, dead catalyst of oil refining device, kaolin, semicoke, activated carbon and gasified ash;

2. The method according to claim 1, wherein the waste plastics are one or more of fresh household garbage, industrial and agricultural production and aged garbage.

3. The method according to claim 1, wherein the waste plastics are washed, dried and crushed before entering the waste plastics dissolution dechlorination unit, and the crushed waste plastics have a particle size of 1-200 mm.

4. A method according to claim 3, wherein the size of the crushed waste plastics is 1-50 mm.

5. The method according to claim 1, wherein the organic solvent is a mixed solvent of tetrahydrofuran and a ketone solvent in any weight ratio, and the ketone solvent is one or more selected from methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone;

the weight ratio of the organic solvent to the waste plastic is 1:10-10:1.

6. The method according to claim 1 or 5, wherein the ketone solvent is one or more selected from methyl ethyl ketone and cyclohexanone;

the organic solvent is a mixed solvent of tetrahydrofuran and ketone solvents in a weight ratio of 1:3-3:1.

7. The process according to claim 6, wherein the ketone solvent is methyl ethyl ketone;

the organic solvent is a mixed solvent of tetrahydrofuran and ketone solvents in a weight ratio of 1:2-2:1.

8. The method according to claim 1, wherein the waste plastics are sufficiently dissolved in the organic solvent at a temperature of 50-100 ℃ in the waste plastics dissolution dechlorination unit, and the residence time of the waste plastics is 30-60 min.

9. The method according to claim 1, wherein a solvent recovery device is provided in the waste plastic dissolution dechlorination unit, the chlorine-containing solution obtained in the step (1) enters the solvent recovery device, and PVC and/or PS particles and the recovered organic solvent are obtained after precipitation treatment and separation.

10. The method according to claim 9, wherein the precipitation treatment is selected from one or more of back extraction, simple distillation and rectification in the solvent recovery device.

11. The method according to claim 9, wherein the precipitation treatment is performed by flash evaporation in the solvent recovery device.

12. The method according to claim 9, wherein in the solvent recovery device, the precipitation treatment adopts a stripping coupling distillation mode, the stripping agent is water, the stripping temperature is 70-100 ℃, and the distillation temperature is 80-100 ℃.

13. The method according to claim 1, wherein the reaction conditions of the waste plastic thermal dissolution and impurity removal unit are: the reaction temperature is 320-390 ℃, the pressure is 0.1-5 MPa, and the stay time of dechlorinated waste plastics is 10-60 min;

the content of monocyclic aromatic hydrocarbon in the solvent oil is higher than 40 mass percent;

the weight ratio of the solvent oil to the dechlorinated waste plastic is 1:10-10:1.

14. The method according to claim 13, wherein the content of monocyclic aromatic hydrocarbon in the solvent oil is higher than 40 mass%;

the weight ratio of the solvent oil to the dechlorinated waste plastic is 3:1-7:1.

15. The method of claim 1, wherein the adsorbent has a particle size in the range of 75 to 150 μm;

the weight fraction of the adsorbent is 1-10% based on the total weight of the mixture materials in the waste plastic thermal dissolving and impurity removing unit.

16. The method of claim 1, wherein the adsorbent is one or more of spent catalytic cracking catalyst, catalytic cracking unit spent catalytic cracking catalyst, humus soil, activated carbon.

17. The method according to claim 1, wherein the operating temperature of the solid-liquid separation device II is 280-410 ℃; the metal content in the obtained impurity-removed plastic-containing solution is less than 5 mug/g, the chlorine content is less than 10 mug/g, and the silicon content is less than 2 mug/g.

18. The method according to claim 1, wherein the reaction temperature of the catalytic cracking unit is 500-850 ℃, and the catalyst-to-oil weight ratio is (1-50): 1, the mass ratio of water to oil is (0.01-1): 1, and the reaction pressure is 0.1-2 MPa.

19. The method according to claim 1, wherein the feed to the catalytic cracking unit comprises an optional catalytic cracking feedstock, the catalytic cracking feedstock being a petroleum hydrocarbon oil selected from at least one of vacuum wax oil, coker wax oil, deasphalted oil, residuum, gasoline and diesel oil and/or a mineral oil selected from at least one of coal liquefaction oil, oil sand and shale oil.

20. The method according to claim 1, wherein the zeolite-type catalytic cracking catalyst has the composition: the zeolite-type catalytic cracking catalyst comprises 1 to 50 wt% zeolite, 5 to 99 wt% inorganic oxide, and 0 to 70 wt% clay, based on the dry weight of the zeolite-type catalytic cracking catalyst.

21. The method of claim 20, wherein the zeolite comprises 50-100 wt% large pore zeolite comprising at least one selected from REY, REHY, USY and high silicon Y and 0-50 wt% medium pore zeolite comprising ZSM-series zeolite and/or ZRP zeolite based on the dry weight of the zeolite;

the inorganic oxide comprises silicon oxide and/or aluminum oxide;

the clay comprises kaolin and/or halloysite.

22. The method according to claim 1, wherein the metal oxide type catalytic cracking catalyst contains alumina and/or aluminosilicate, and one or more metal oxides selected from alkali metal oxides, alkaline earth metal oxides, and group VIII metal oxides.