CN116064066A - A method and system for visbreaking and dechlorinating liquefaction of chlorine-containing waste plastics - Google Patents

Abstract

The present disclosure relates to a method and a system for liquefying, viscosity-reducing and dechlorinating chlorine-containing waste plastics, which comprises the following steps: enabling chlorine-containing waste plastic particles to enter a first screw pump for dehydration, degasification and volume reduction treatment to obtain a pretreatment material of the chlorine-containing waste plastic; enabling the pretreated material and high-temperature solvent oil to enter a second screw pump, and performing hot melting dechlorination treatment on the pretreated material to obtain a hydrogen chloride-containing gas-phase material and dechlorinated waste plastic oil; and introducing stripping gas into the second screw pump so that the gas-phase material containing hydrogen chloride is discharged from the second screw pump under the action of the stripping gas. The method can realize the dechlorination treatment of PVC-containing waste plastics while liquefying and viscosity-reducing, and the dechlorinated waste plastic liquefied oil which is convenient to convey, uniform in heat conduction and low in melt viscosity is obtained.

Description

A method and system for liquefying, viscosity-reducing and dechlorinating chlorine-containing waste plastics

Technical Field

The present disclosure relates to the technical field of waste plastic resource utilization and green environmental protection, and in particular to a method and system for liquefying, viscosity reducing and dechlorinating chlorine-containing waste plastic.

Background Art

Plastics are widely used in homes and industries and are considered an indispensable part of our modern lives. Due to the high consumption of plastics, a large amount of plastic waste is generated every year, causing serious environmental pollution. However, traditional plastic waste treatment methods, such as combustion, mechanical recycling, and waste-derived fuels, are often limited or insufficient from the perspective of energy efficiency and resource utilization. Thermochemical conversion has become a realistic alternative to traditional plastic waste treatment, among which pyrolysis recycling of waste plastics is becoming a viable route for a circular plastic economy, where pyrolysis oil can be cracked and further refined for new plastic production. When looking for solutions, controlling the pollutants generated during the conversion of plastic waste into energy or chemicals is a key factor. HCl and chlorinated compounds are very serious pollutants generated by the pyrolysis of plastic waste. They are produced during the pyrolysis process of PVC, which can cause corrosion of pipelines and cause environmental problems when discharged into the air. At the same time, the petrochemical industry usually requires a low chlorine content (<10ppm) in the pyrolysis oil for a successful refining process, so it is crucial to remove chlorine from PVC-containing waste plastics.

There are many dechlorination technologies in the existing waste plastic resource utilization technology, including thermal dechlorination technology, hydrothermal dechlorination technology, mechanochemical dechlorination and microwave radiation dechlorination technology. Among them, thermal dechlorination is the main one, that is, by controlling the heating temperature of PVC plastics to make the chlorine element in them escape in the form of hydrogen chloride to achieve the purpose of dechlorination. Alkaline dechlorination agents such as calcium oxide can also be added during the reaction process to carry out dechlorination treatment during the reaction process. However, so far, the description of thermal dechlorination has only stayed in the process flow and equipment, and no detailed description and research on the specific thermal dechlorination process parameters and dechlorination effect have been carried out.

In the process of transportation, dechlorination and pyrolysis, the plastic needs to be melted first. Due to the low thermal conductivity of plastic, when heated to the melting point of 100℃~250℃, the center temperature is still very low. If the heating continues, the external temperature can reach above 500℃ and carbonization occurs, while the internal temperature reaches the melting point, and the thermal efficiency is very low. Since the external carbonization hinders the internal decomposition, and the plastic melt has high viscosity, it is easy to stick to the wall and cause carbon deposition and coking. Therefore, in order to solve the problems of uneven heat conduction, high melt viscosity, and carbonization and coking caused by local overheating that are common in the process of waste plastic treatment, it is necessary to liquefy and reduce the viscosity of the waste plastic to form a fluid that is easy to transport, has uniform heat conduction, and has low melt viscosity.

There is no literature report on detailed research on liquefaction and viscosity reduction of waste plastics, especially on dechlorination of PVC-containing waste plastics during liquefaction and viscosity reduction.

Summary of the invention

The purpose of the present invention is to provide a method and system for liquefying and deviscosity-reducing and dechlorinating chlorine-containing waste plastics, which can achieve dechlorination of PVC-containing waste plastics while liquefying and deviscosity-reducing, and obtain dechlorinated waste plastic liquefied oil that is easy to transport, has uniform heat conduction, and has low melt viscosity.

In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a method for liquefying, viscosity reducing and dechlorinating chlorinated waste plastics, comprising the following steps: S1, allowing chlorine-containing waste plastic particles to enter a first screw pump for dehydration, degassing and volume reduction treatment to obtain a pretreated material of chlorine-containing waste plastics; S2, allowing the pretreated material and high-temperature solvent oil to enter a second screw pump, performing hot melt dechlorination treatment on the pretreated material to obtain a hydrogen chloride-containing gas phase material and dechlorinated waste plastic oil; and introducing a stripping gas into the second screw pump so that the hydrogen chloride-containing gas phase material is discharged from the second screw pump under the action of the stripping gas.

Optionally, the method further comprises: allowing the hydrogen chloride-containing gaseous material discharged from the second screw pump to enter a condensation separation device for condensation separation to obtain a condensed liquid material and a residual gaseous material after condensation; allowing the residual gaseous material after condensation to enter a primary absorber to contact with a first hydrogen chloride absorbent for a first absorption treatment of hydrogen chloride to obtain a first chlorine-containing waste liquid and a first residual gaseous material; allowing the first residual gaseous material from the primary absorber to enter a secondary absorber to contact with a second hydrogen chloride absorbent for a second absorption treatment of hydrogen chloride, a second chlorine-containing waste liquid and a second residual gaseous material, wherein the second residual gaseous material comprises dry gas and liquefied gas.

Optionally, the method further includes: allowing the hydrogen chloride absorbent to enter the secondary absorber as a second hydrogen chloride absorbent, and then allowing a portion of the hydrogen chloride absorbent in the secondary absorber to enter the primary absorber as the first hydrogen chloride absorbent; Optionally, the method further includes: allowing the second chlorine-containing waste liquid to enter the primary absorber from the secondary absorber, and be discharged together with the first chlorine-containing waste liquid in the primary absorber; Optionally, the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7, and the alkaline solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water.

Optionally, step S1 includes: allowing the chlorine-containing waste plastic to enter from the input end of the first screw pump, heating it in the first screw pump, and moving it from the input end to the output end of the first screw pump under the screw transmission and shearing action of the first screw pump, and performing the dehydration, degassing and volume reduction treatment on the chlorine-containing waste plastic during the movement.

Optionally, step S2 includes: allowing the pretreated material and the high-temperature solvent oil to enter from the input end of the second screw pump, allowing the pretreated material and the high-temperature solvent oil to be mixed and heated in the second screw pump and moved from the input end to the output end of the second screw pump under the transmission and shearing action of the screw of the second screw pump; performing the melt liquefaction, cracking and viscosity reduction and dechlorination treatment on the pretreated material during the movement process; and allowing the stripping gas to be introduced from the stripping gas inlet of the second screw pump, along the material movement direction in the second screw pump, the stripping gas inlet is close to the input end of the second screw pump and is arranged downstream of the input end of the second screw pump; allowing the hydrogen chloride-containing gas phase material in the second screw pump to be introduced from the gas phase material outlet, along the material movement direction in the second screw pump, the gas phase material outlet is arranged upstream of the output end of the second screw pump and close to the output end of the second screw pump; and allowing the dechlorinated waste plastic oil obtained by the second screw pump to be drawn out through the output end of the second screw pump.

Optionally, the chlorine-containing waste plastics include PVC and other waste plastics, and the other waste plastics are selected from one or more of LDPE, HDPE, PP and PS; the high-temperature solvent oil is selected from vacuum residue oil or distillate oil with an initial distillation point of more than 350°C, preferably selected from one or more of acid-containing crude oil, heavy crude oil, atmospheric residue oil, coker wax oil, vacuum wax oil, hydrocracking tail oil, deasphalted oil, coal tar, tank bottom oil, shale oil, coal liquefaction residue oil, waste plastic cracking wax oil and other secondary processed distillate oils.

Optionally, in step S1, the outlet temperature of the first screw pump is 100-200°C, preferably 120-160°C, and the residence time is 5-20 minutes, preferably 7-15 minutes.

Optionally, in step S2, the mass ratio of the high-temperature solvent oil to the chlorine-containing waste plastic is 0.5-10:1, preferably 1-6:1; the outlet temperature of the second screw pump is 200-450°C, preferably 275-420°C, and the residence time is 5-60 minutes, preferably 20-45 minutes; the stripping gas is nitrogen or high-temperature steam; relative to 1kg of pretreated material, the stripping gas volume of the stripping gas is 5-25L/h, preferably 10-20L/h, where material represents the pretreated material introduced into the second screw pump; the temperature of the high-temperature solvent oil is 300-450°C.

Optionally, the dechlorinated waste plastic oil has a viscosity of 50 to 10,000 mPa·s at 200° C. and a chlorine content of 100 to 800 μg/g.

The second aspect of the present disclosure provides a system for liquefying, viscosity reducing and dechlorinating chlorine-containing waste plastics, comprising a chlorine-containing waste plastics silo, a first screw pump, a second screw pump and a hydrogen chloride treatment unit; the first screw pump comprises a first input end and a first output end; the first input end is provided with a chlorine-containing waste plastics raw material inlet, and the first output end is provided with a pre-treated material outlet; the chlorine-containing waste plastics raw material inlet is connected with the outlet of the chlorine-containing waste plastics silo; the second screw pump comprises a second input end and a second output end; the second input end is provided with a pre-treated material inlet, a high-temperature solvent oil outlet and a stripping gas inlet, and along the direction of material movement in the second screw pump, the stripping gas inlet is arranged downstream of the pre-treated material inlet and the high-temperature solvent oil outlet; the pre-treated material inlet is connected with the pre-treated material outlet of the first screw pump; the second output end is provided with a hydrogen chloride-containing gas phase material outlet and a dechlorinated waste plastic oil outlet, and the hydrogen chloride-containing gas phase material outlet is connected with the inlet of the gas phase material to be treated of the hydrogen chloride absorption unit.

Optionally, the hydrogen chloride processing unit includes a condensation separation device, a primary absorber and a secondary absorber; the condensation separation device is provided with a chlorine-containing gas phase material inlet and a condensed gas phase material outlet; the chlorine-containing gas phase material inlet is formed as an inlet of the gas phase material to be treated of the hydrogen chloride absorption unit; the primary absorber is provided with a first hydrogen chloride absorbent inlet, a first hydrogen chloride mixed gas phase inlet, a first hydrogen chloride mixed gas phase outlet and a first hydrogen chloride waste liquid outlet, and the first hydrogen chloride absorbent is included in the primary absorber; the first hydrogen chloride mixed gas phase inlet is connected to the condensed gas phase material of the condensation separation device; The secondary absorber is provided with a hydrogen chloride absorbent inlet, a second hydrogen chloride mixed gas phase inlet, a hydrogen chloride absorbed gas phase outlet and a second hydrogen chloride waste liquid outlet, and the secondary absorber includes a second hydrogen chloride absorbent; the second hydrogen chloride mixed gas phase inlet is communicated with the first hydrogen chloride mixed gas phase outlet of the primary absorber, the hydrogen chloride absorbent inlet is used to introduce hydrogen chloride absorbent into the hydrogen chloride absorption unit, and the second hydrogen chloride waste liquid outlet is communicated with the first hydrogen chloride absorbent inlet of the primary absorber so that the liquid phase materials in the primary absorber and the secondary absorber are connected.

Through the above technical scheme, the present disclosure provides a method and system for liquefying, reducing viscosity and dechlorinating chlorine-containing waste plastics. The present disclosure uses solvent oil with good heat and mass transfer flow properties to disperse waste plastics, so that the heat and mass transfer flow properties of waste plastics are greatly improved, and the problems of uneven heating, slow heat transfer and severe coking of waste plastics during screw pump transportation and subsequent pyrolysis are solved. The present disclosure can melt and liquefy waste plastics and perform preliminary cracking and viscosity reduction treatment, while removing chlorine from PVC, and liquefaction, viscosity reduction and dechlorination are carried out simultaneously. Dechlorinated waste plastic liquefied oil with convenient transportation, uniform heat conduction and low melt viscosity is obtained. The present disclosure has a simple process flow, low equipment investment and good liquefaction, viscosity reduction and dechlorination effect, has significant social and economic benefits and good industrial application prospects, and can be combined with delayed coking, visbreaking, fluid catalytic cracking, catalytic hydrogenation and waste plastic pyrolysis processes.

Other features and advantages of the present disclosure will be described in detail in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

FIG1 is a process flow chart of the method for liquefying, viscosity reducing and dechlorinating chlorine-containing waste plastics provided in the present disclosure.

Description of Reference Numerals

1- chlorine-containing waste plastic silo, 2- first screw pump, 3- second screw pump, 4- condensation separation device, 5- primary absorber, 6- secondary absorber, 7- high temperature solvent oil, 8- stripping gas, 9- dechlorinated waste plastic oil, 10- dry gas, liquefied gas, 11- hydrogen chloride absorbent, 12- pipeline

DETAILED DESCRIPTION

The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

In the present disclosure, unless otherwise stated, the words "first", "second", "third", etc. are used only to distinguish different components and do not have actual meanings such as the order of connection. In the present disclosure, the directional words used, such as "upper, lower, top, bottom", generally refer to the upper and lower, top and bottom of the device in normal use. "Inside and outside" refer to the outline of the device.

The first aspect of the present disclosure provides a method for liquefying, viscosity-reducing and dechlorinating chlorine-containing waste plastics, as shown in FIG1 , comprising the following steps:

S1, allowing the chlorine-containing waste plastic particles to enter the first screw pump 2 for dehydration, degassing and volume reduction treatment to obtain pre-treated materials of the chlorine-containing waste plastic;

S2, allowing the pretreated material and high-temperature solvent oil to enter the second screw pump 3, performing hot melt dechlorination treatment on the pretreated material to obtain a hydrogen chloride-containing gas phase material and dechlorinated waste plastic oil;

Stripping gas is introduced into the second screw pump 3 so that the gaseous material containing hydrogen chloride is discharged from the second screw pump 3 under the action of the stripping gas.

The present invention uses solvent oil with good heat and mass transfer flow properties to disperse waste plastics, so that the heat and mass transfer flow properties of waste plastics are greatly improved, and the problems of uneven heating, slow heat transfer, and severe coking of waste plastics during screw pump transportation and subsequent pyrolysis are solved. The present invention can melt and liquefy waste plastics and perform preliminary cracking and viscosity reduction treatment, and remove chlorine in PVC at the same time, and liquefaction, viscosity reduction and dechlorination are carried out simultaneously. Dechlorinated waste plastic liquefied oil with convenient transportation, uniform heat conduction and low melt viscosity is obtained. The present invention has a simple process flow, low equipment investment and good liquefaction, viscosity reduction and dechlorination effect, has significant social and economic benefits and good industrial application prospects, and can be combined with delayed coking, visbreaking, fluid catalytic cracking, catalytic hydrogenation and waste plastic pyrolysis processes.

In a specific embodiment, the chlorine-containing waste plastics include PVC and other waste plastics, and the other waste plastics are selected from one or more of LDPE, HDPE, PP and PS. The present disclosure can achieve good treatment effects on chlorine-containing waste plastics with a relatively wide range of PVC content. For example, the PVC content can be more than 10% by weight. Specifically, the chlorine-containing waste plastics in the present disclosure can be PVC-containing waste plastics that have been crushed and impurity-removed.

In a specific embodiment, the high-temperature solvent oil is selected from vacuum residue oil or distillate oil with an initial distillation point of more than 350°C, preferably selected from one or more of acid-containing crude oil, heavy crude oil, atmospheric residue oil, coker wax oil, vacuum wax oil, hydrocracking tail oil, deasphalted oil, coal tar, tank bottom oil, shale oil, coal liquefaction residual oil, waste plastic cracking wax oil and other secondary processed distillate oils.

In one embodiment, as shown in FIG. 1 , the method further comprises: allowing the hydrogen chloride-containing gas phase material discharged from the second screw pump 3 to enter a condensation separation device 4 for condensation separation to obtain a condensed liquid phase material and a condensed residual gas phase material;

The remaining gas phase material after condensation enters the primary absorber 5 and contacts with the first hydrogen chloride absorbent to perform the first hydrogen chloride absorption treatment, thereby obtaining the first chlorine-containing waste liquid and the first remaining gas phase material;

The first residual gas phase material from the primary absorber 5 enters the secondary absorber 6 and contacts with the second hydrogen chloride absorbent for a second hydrogen chloride absorption treatment, the second chlorine-containing waste liquid and the second residual gas phase material, wherein the second residual gas phase material includes dry gas and liquefied gas.

The present invention condenses and separates the gaseous material containing hydrogen chloride, so that the liquid product carried in the gaseous material can be condensed and separated, thereby improving the subsequent treatment effect; and the use of a two-stage absorber further improves the absorption of hydrogen chloride, thereby preventing chlorine-containing gas from entering the air; and a small amount of gas phase produced by the initial cracking of waste plastics is finally separated through the two-stage absorption, which is convenient for subsequent treatment.

In one embodiment, as shown in FIG1 , the method further comprises: allowing the hydrogen chloride absorbent to enter the secondary absorber 6 as a second hydrogen chloride absorbent, and then allowing a portion of the hydrogen chloride absorbent in the secondary absorber 6 to enter the primary absorber 5 as the first hydrogen chloride absorbent;

Optionally, the method further comprises:

The second chlorine-containing waste liquid is allowed to enter the primary absorber 5 from the secondary absorber 6 and be discharged together with the first chlorine-containing waste liquid in the primary absorber 5 .

In a specific embodiment, the hydrogen chloride absorbent is water or an alkali solution with a pH greater than 7, and the alkali solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water.

In a preferred embodiment, as shown in Figure 1, step S1 includes: allowing the chlorine-containing waste plastic to enter from the input end of the first screw pump 2, heating it in the first screw pump 2, and moving it from the input end to the output end of the first screw pump 2 under the screw transmission and shearing action of the first screw pump 2, and performing the dehydration, degassing and volume reduction treatment on the chlorine-containing waste plastic during the movement.

In a preferred embodiment, as shown in FIG1 , step S2 comprises: allowing the pretreated material and the high-temperature solvent oil to enter from the input end of the second screw pump 3, allowing the pretreated material and the high-temperature solvent oil to be mixed and heated in the second screw pump 3 and to move from the input end to the output end of the second screw pump 3 under the transmission and shearing action of the screw of the second screw pump 3; performing the melt liquefaction, cracking and viscosity reduction and dechlorination treatment on the pretreated material during the movement; and

The stripping gas is introduced from the stripping gas inlet of the second screw pump 3, and along the material moving direction in the second screw pump 3, the stripping gas inlet is close to the input end of the second screw pump 3 and is arranged downstream of the input end of the second screw pump 3;

The gaseous material containing hydrogen chloride in the second screw pump 3 is introduced from the gaseous material outlet, and along the moving direction of the material in the second screw pump 3, the gaseous material outlet is arranged upstream of the output end of the second screw pump 3 and close to the output end of the second screw pump 3; and

The dechlorinated waste plastic oil obtained by the second screw pump 3 is led out through the output end of the second screw pump 3 .

In a specific implementation manner, in step S1, the outlet temperature of the first screw pump 2 is 100-200°C, preferably 120-160°C, and the residence time is 5-20 minutes, preferably 7-15 minutes.

In a specific embodiment, in step S2, the mass ratio of the high-temperature solvent oil to the chlorine-containing waste plastic is 10-0.5, preferably 6-1; the outlet temperature of the second screw pump (3) is 200-450°C, preferably 275-420°C, and the residence time is 5-60 minutes, preferably 20-45 minutes; the stripping gas is nitrogen or high-temperature steam; relative to 1kg of pretreated material, the stripping gas volume of the stripping gas is 5-25L/h, preferably 10-20L/h, wherein the material refers to the pretreated material introduced into the second screw pump 3; the temperature of the high-temperature solvent oil is 300-450°C.

In one embodiment, the dechlorinated waste plastic oil has a viscosity of 50 to 10,000 mPa·s at 200° C. and a chlorine content of 100 to 800 μg/g.

The second aspect of the present disclosure provides a system for liquefying, viscosity-reducing and dechlorinating chlorine-containing waste plastics, as shown in FIG1 , comprising a chlorine-containing waste plastics silo 1, a first screw pump 2, a second screw pump 3 and a hydrogen chloride treatment unit;

The first screw pump 2 includes a first input end and a first output end; the first input end is provided with an inlet for chlorine-containing waste plastic raw materials, and the first output end is provided with an outlet for pre-treated materials; the inlet for chlorine-containing waste plastic raw materials is connected to the outlet of the chlorine-containing waste plastic silo 1;

The second screw pump 3 includes a second input end and a second output end; the second input end is provided with a pre-treated material inlet, a high-temperature solvent oil outlet and a stripping gas inlet, and along the direction of material movement in the second screw pump 3, the stripping gas inlet is arranged downstream of the pre-treated material inlet and the high-temperature solvent oil outlet;

The pretreatment material inlet is connected to the pretreatment material outlet of the first screw pump 2; the second output end is provided with a hydrogen chloride-containing gas phase material outlet and a dechlorinated waste plastic oil outlet, and the hydrogen chloride-containing gas phase material outlet is connected to the inlet of the gas phase material to be treated of the hydrogen chloride absorption unit.

In one embodiment, as shown in FIG1 , the hydrogen chloride treatment unit includes a condensation separation device 4 , a primary absorber 5 and a secondary absorber 6 ;

The condensation separation device 4 is provided with an inlet for chlorine-containing gas phase material and an outlet for condensed gas phase material; the inlet for chlorine-containing gas phase material forms an inlet for gas phase material to be treated of the hydrogen chloride absorption unit;

The primary absorber 5 is provided with a first hydrogen chloride absorbent inlet, a first hydrogen chloride mixed gas phase inlet, a first hydrogen chloride mixed gas phase outlet and a first hydrogen chloride waste liquid outlet, and the primary absorber 5 includes a first hydrogen chloride absorbent; the first hydrogen chloride mixed gas phase inlet is connected to the condensed gas phase material outlet of the condensation separation device 4;

The secondary absorber 6 is provided with a hydrogen chloride absorbent inlet, a second hydrogen chloride mixed gas phase inlet, a hydrogen chloride absorbed gas phase outlet and a second hydrogen chloride waste liquid outlet. The secondary absorber 6 includes a second hydrogen chloride absorbent; the second hydrogen chloride mixed gas phase inlet is communicated with the first hydrogen chloride mixed gas phase outlet of the primary absorber 5, the hydrogen chloride absorbent inlet is used to introduce the hydrogen chloride absorbent into the hydrogen chloride absorption unit, and the second hydrogen chloride waste liquid outlet is communicated with the first hydrogen chloride absorbent inlet of the primary absorber 5 to enable the liquid phase materials in the primary absorber 5 and the secondary absorber 6 to communicate.

The devices used in the present disclosure are all conventionally selected devices in the art.

The specific process of liquefying, viscous and dechlorinating PVC waste plastics using the system shown in FIG1 includes:

After being crushed and impurity-removed, the PVC-containing waste plastic (chlorine-containing waste plastic particles) enters the first screw pump 2 from the chlorine-containing waste plastic silo 1 for dehydration, degassing and volume reduction treatment. The waste plastic (pre-treated material of chlorine-containing waste plastic) from the first screw pump 2 and the high-temperature solvent oil 7 enter the second screw pump 3 at the same time. The waste plastic is melted and liquefied and initially cracked and reduced in viscosity in the second screw pump 3, and the chlorine in the PVC is removed at the same time. Nitrogen or high-temperature steam (stripping gas) 8 is fed from the input end of the second screw pump 3 to bring out the HCl released by the PVC in the waste plastic at high temperature and a small amount of gas and liquid products (gas-phase materials containing hydrogen chloride) produced by the initial cracking of the waste plastic, and are drawn out through the output end of the second screw pump 3, and the liquid products are separated by the condensation separation device 4.

The hydrogen chloride absorption liquid 11 enters the primary absorber 5 and the secondary absorber 6, and the gaseous material from the condensation separation device 4 enters the primary absorber 5 and the secondary absorber 6 in sequence and contacts with the hydrogen chloride absorbent therein to absorb hydrogen chloride, and finally obtains dry gas and liquefied gas (second residual gaseous material) 10 without hydrogen chloride in the secondary absorber 6. The second screw pump 3 liquefies the dechlorinated waste plastic oil 9 after viscosity reduction and dechlorination, and the dry gas and liquefied gas 10 are discharged from the secondary absorber 6 through the output end of the second twin-screw pump, so that the second chlorine-containing waste liquid obtained by the secondary absorber enters the primary absorber 5 and is discharged through the pipeline 12 with the first chlorine-containing waste liquid.

The present invention is described in detail below with reference to examples, but the examples are not intended to limit the scope of application of the present invention.

The test method for the residual chlorine content in the dechlorinated waste plastic oil in the following examples and comparative examples is the coulometric method.

The test method for the viscosity of dechlorinated waste plastic oil at 200°C is the rotational viscosity test method.

The properties of the solvent oil used in the following examples are shown in Table 1

Example 1

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump to obtain a pretreated material, wherein the outlet temperature of the first screw pump is 120° C., and the residence time of the material from the inlet to the outlet in the first screw pump is 7 minutes;

Then, the pretreated material is mixed with coker wax oil (as a high-temperature solvent oil, the temperature is 350°C) at the input end of the second screw pump, the weight ratio of chlorine-containing waste plastic particles: coker wax oil is 1:3, the outlet temperature of the second screw pump is 350°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, a stripping gas (stripping gas is nitrogen) is introduced through the input end of the second screw pump, and the stripping amount is 10L/kg (chlorine-containing waste plastic particles)/h. Hot melt dechlorination treatment is carried out in the second screw pump to obtain hydrogen chloride gas phase material (including hydrogen chloride, a small amount of gas phase produced by the initial cracking of waste plastics and the carried liquid phase product) and dechlorinated waste plastic oil. The prepared dechlorinated waste plastic oil is recorded as DCI-1. The properties of the obtained dechlorinated waste plastic oil DCI-1 are shown in Table 2.

The stripping gas leads the gaseous phase material containing hydrogen chloride in the second screw pump out of the output end of the second screw pump and then is introduced into the hydrogen chloride absorption unit for absorption. The hydrogen chloride absorbent in the primary absorber and the secondary absorber is sodium hydroxide solution.

Example 2

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 120° C. and the residence time is 10 minutes;

Then, the pretreated material is mixed with coker wax oil (high temperature solvent oil, temperature is 350°C) at the input end of the second screw pump, the weight ratio of chlorine-containing waste plastic particles: coker wax oil is 1:1, the outlet temperature of the second screw pump is 350°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, a stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 10L/kg (chlorine-containing waste plastic particles)/h, and the prepared dechlorinated waste plastic oil is recorded as DCI-2. The properties of the obtained dechlorinated waste plastic oil DCI-2 are shown in Table 2. The rest of the process is the same as Example 1.

Example 3

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 140° C. and the residence time is 10 minutes;

Then, the pretreated material is mixed with coker wax oil (high temperature solvent oil, temperature is 300°C) at the input end of the second screw pump, and the weight ratio of the mixed chlorine-containing waste plastic particles: coker wax oil is 1:3, the outlet temperature of the second screw pump is 275°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, the stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 10L/kg (chlorine-containing waste plastic particles)/h. The prepared dechlorinated waste plastic oil is recorded as DCI-3. The properties of the obtained dechlorinated waste plastic oil DCI-3 are shown in Table 2. The rest of the process is the same as Example 1.

Example 4

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5% respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 150° C. and the residence time is 10 minutes;

Then the pretreated material is mixed with coker wax oil (high temperature solvent oil, temperature is 350°C) at the input end of the second screw pump, the weight ratio of mixed waste plastic: coker wax oil is 1:3, the outlet temperature of the second screw pump is 350°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment of the second screw pump, the stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 20L/kg (chlorine-containing waste plastic particles)/h. The prepared dechlorinated waste plastic oil is recorded as DCI-4. The properties of the obtained dechlorinated waste plastic oil DCI-4 are shown in Table 2. The rest of the process is the same as Example 1.

Example 5

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 17.9%, 17.9%, 35.8%, 13.4% and 15%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 150° C. and the residence time is 15 minutes;

Then, the pretreated material is mixed with coker wax oil (high temperature solvent oil, temperature is 350°C) at the input end of the second screw pump, the weight ratio of chlorine-containing waste plastic particles: coker wax oil is 1:3, the outlet temperature is 350°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, a stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 10L/kg (chlorine-containing waste plastic particles)/h, and the prepared dechlorinated waste plastic oil is recorded as DCI-5. The properties of the obtained dechlorinated waste plastic oil DCI-5 are shown in Table 2. The rest of the process is the same as Example 1.

Example 6

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 150° C. and the residence time is 7 minutes;

Then, the pretreated material is mixed with vacuum residue oil (high temperature solvent oil, temperature is 400°C) at the input end of the second screw pump, and the weight ratio of chlorinated waste plastic particles: coker wax oil is 1:3, the outlet temperature is 350°C, and the residence time is 15 minutes; during the hot melt dechlorination treatment process of the second screw pump, the stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 20L/kg (material)/h, and the prepared dechlorinated waste plastic oil is recorded as DCI-6. The properties of the obtained dechlorinated waste plastic oil DCI-6 are shown in Table 2. The rest of the process is the same as Example 1.

Example 7

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 160° C. and the residence time is 10 minutes;

Then, the pretreated material is mixed with vacuum residue oil (high temperature solvent oil, temperature is 400°C) at the input end of the second screw pump, the weight ratio of chlorinated waste plastic particles: coking wax oil is 1:3, the outlet temperature is 350°C, and the residence time is 45 minutes; during the hot melt dechlorination treatment process of the second screw pump, a stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 20L/kg (chlorinated waste plastic particles)/h, and the prepared dechlorinated waste plastic oil is recorded as DCI-7. The properties of the obtained dechlorinated waste plastic oil DCI-7 are shown in Table 2. The rest of the process is the same as Example 1.

Example 8

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5%, respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 160° C. and the residence time is 10 minutes;

Then, the pretreated material is mixed with vacuum residue oil (high temperature solvent oil, temperature is 400°C) at the input end of the second screw pump, the weight ratio of chlorinated waste plastic particles: coking wax oil is 1:3, the outlet temperature is 400°C, and the residence time is 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, a stripping gas is introduced through the input end of the second screw pump, and the stripping amount is 20L/kg (chlorinated waste plastic particles)/h, and the prepared dechlorinated waste plastic oil is recorded as DCI-8. The properties of the obtained dechlorinated waste plastic oil DCI-8 are shown in Table 2. The rest of the process is the same as Example 1.

Example 9

The method in Example 8 was used, except that the weight ratio of chlorine-containing waste plastic particles to coking wax oil was 1:9, and the rest of the process was the same as that in Example 8. The properties of the obtained dechlorinated waste plastic oil DCI-9 are shown in Table 2.

Comparative Example 1

According to the process flow shown in FIG1 , a mixed plastic containing LDPE, HDPE, PP, PS and PVC (with mass fractions of 20%, 20%, 40%, 15% and 5% respectively) is crushed and impurized to obtain chlorine-containing waste plastic particles, which are then dehydrated, degassed and reduced in volume by a first screw pump, wherein the outlet temperature of the first screw pump is 150° C. and the residence time is 10 minutes;

No solvent oil was added when passing through the second screw pump, the outlet temperature was 350°C, and the residence time was 30 minutes; during the hot melt dechlorination treatment process of the second screw pump, stripping gas was introduced through the input end of the second screw pump, and the stripping amount was 20L/kg (chlorinated waste plastic particles)/h, and the prepared liquefied waste plastic oil was recorded as DCI-0. The properties of the obtained dechlorinated waste plastic oil DCI-0 are shown in Table 2. The rest of the process is the same as Example 1.

Table 1 Properties of coker gas oil and vacuum residue

Table 2 Properties of waste plastic oil after liquefaction, viscosity reduction and dechlorination

*Note: — indicates that the viscosity exceeds the upper limit of the instrument's measurement.

According to the data in Table 2, it can be seen from the comparison between the embodiment of the present disclosure and the comparative example 1 that the process method for liquefying and reducing viscosity and dechlorinating waste plastics containing PVC provided by the present disclosure is feasible and effective, and the waste plastics can be melted and liquefied and subjected to preliminary cracking and reducing viscosity treatment, and the chlorine in the PVC can be removed at the same time, and the liquefaction and reducing viscosity and dechlorination are carried out simultaneously, and the obtained waste plastic liquefied oil has a low viscosity, a viscosity of 50 to 10000 mPa·s at 200°C, a chlorine content of 100 to 800 μg/g, and a high dechlorination rate of 90 to 98.5%. The obtained dechlorinated waste plastic liquefied oil is easy to transport, has uniform heat conduction, and has a low viscosity of the melt, which can be used as a raw material for delayed coking, visbreaking, fluidized catalytic cracking, catalytic hydrogenation, and pyrolysis of waste plastics.

According to Table 2, in the process of waste plastic treatment, increasing the outlet temperature within an appropriate range, increasing the residence time, increasing the stripping amount, and adding an appropriate amount of solvent oil are beneficial to the removal of chlorine in PVC and the reduction of the viscosity of the plastic liquefied oil. For example, comparing Examples 8 and 9, the mass ratio of high-temperature solvent oil to chlorine-containing waste plastics in Example 8 is 1 to 6:1, and the residual chlorine content of the waste plastics after dechlorination in Example 8 is lower and the dechlorination rate is higher. Comparing Examples 1 to 4 and Example 7 with Example 6, it can be seen that in Examples 1 to 4 and Example 7, the outlet temperature of the second screw pump 3 meets 275 to 420°C and the residence time meets 20 to 45 minutes, and the dechlorination rate of Examples 1 to 4 and Example 7 is higher.

The process method provided by the present disclosure has a high tolerance for the PVC content in mixed waste plastics. For example, in Example 5, a good dechlorination effect can be obtained even at a higher PVC content.

The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims (11)

1. The method for liquefying, viscosity-reducing and dechlorinating the chlorine-containing waste plastics is characterized by comprising the following steps of:

s1, enabling chlorine-containing waste plastic particles to enter a first screw pump (2) for dehydration, degasification and volume reduction treatment to obtain a pretreatment material of the chlorine-containing waste plastic;

s2, enabling the pretreated material and high-temperature solvent oil to enter a second screw pump (3), and performing hot melting dechlorination treatment on the pretreated material to obtain a hydrogen chloride-containing gas-phase material and dechlorinated waste plastic oil;

and introducing stripping gas into the second screw pump (3) so that the gas-phase material containing hydrogen chloride is discharged from the second screw pump (3) under the action of the stripping gas.

2. The method according to claim 1, characterized in that the method further comprises:

enabling the gas-phase material containing hydrogen chloride discharged from the second screw pump (3) to enter a condensation separation device (4) for condensation separation to obtain a condensed liquid-phase material and a residual gas-phase material after condensation;

enabling the condensed residual gas-phase material to enter a first-stage absorber (5) to be in contact with a first hydrogen chloride absorbent for first absorption treatment of hydrogen chloride, so as to obtain first chlorine-containing waste liquid and first residual gas-phase material;

the first residual gas-phase material from the primary absorber (5) enters the secondary absorber (6) to be contacted with a second hydrogen chloride absorbent for second absorption treatment of hydrogen chloride, and the second chlorine-containing waste liquid and the second residual gas-phase material comprise dry gas and liquefied gas.

3. The method according to claim 2, characterized in that the method further comprises:

passing the hydrogen chloride absorbent into a secondary absorber (6) as a second hydrogen chloride absorbent, and then passing a portion of the hydrogen chloride absorbent in the secondary absorber (6) into the primary absorber (5) as the first hydrogen chloride absorbent;

optionally, the method further comprises:

allowing the second chlorine-containing waste liquid to enter the primary absorber (5) from the secondary absorber (6) and be discharged together with the first chlorine-containing waste liquid in the primary absorber (5);

optionally, the hydrogen chloride absorbent is water or alkali liquor with pH greater than 7, and the alkali liquor is one or more selected from sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water.

4. The method according to claim 1, wherein step S1 comprises:

the chlorine-containing waste plastics enter from the input end of the first screw pump (2), are heated in the first screw pump (2), and move to the output end of the first screw pump (2) from the input end under the screw transmission and shearing actions of the first screw pump (2), and the dehydration, the degasification and the volume reduction treatment are carried out on the chlorine-containing waste plastics in the moving process.

5. The method according to claim 1, wherein step S2 comprises:

enabling the pretreated material and the high-temperature solvent oil to enter from the input end of the second screw pump (3), enabling the pretreated material and the high-temperature solvent oil to be mixed and heated in the second screw pump (3) and to move from the input end to the output end of the second screw pump (3) under the transmission and shearing actions of the screw of the second screw pump (3); carrying out the melting liquefaction, cracking viscosity reduction and dechlorination treatment on the pretreated material in the moving process; and

leading the stripping gas to be introduced from a stripping gas inlet of the second screw pump (3), wherein the stripping gas inlet is close to the input end of the second screw pump (3) and is arranged at the downstream of the input end of the second screw pump (3) along the moving direction of materials in the second screw pump (3);

leading the gas-phase material containing hydrogen chloride in the second screw pump (3) to be introduced from a gas-phase material outlet, wherein the gas-phase material outlet is arranged at the upstream of the output end of the second screw pump (3) and is close to the output end of the second screw pump (3) along the material moving direction in the second screw pump (3); and

and leading the dechlorinated waste plastic oil obtained by the second screw pump (3) out through the output end of the second screw pump (3).

6. The method of claim 1, wherein the chlorine-containing waste plastics comprise PVC and other waste plastics selected from one or more of LDPE, HDPE, PP and PS;

the high-temperature solvent oil is selected from vacuum residuum or distillate oil with the initial boiling point of more than 350 ℃, and is preferably one or more selected from acid-containing crude oil, heavy crude oil, atmospheric residuum, coker gas oil, vacuum wax oil, hydrocracking tail oil, deasphalted oil, coal tar, tank bottom oil, shale oil, coal liquefied residue oil, waste plastic cracking wax oil and other secondary processing distillate oil.

7. A method according to claim 1, characterized in that in step S1 the outlet temperature of the first screw pump (2) is 100-200 ℃, preferably 120-160 ℃, and the residence time is 5-20 minutes, preferably 7-15 minutes.

8. The method according to claim 1, wherein in the step S2, the mass ratio of the high-temperature solvent oil to the chlorine-containing waste plastics is 0.5-10: 1, preferably 1 to 6:1, a step of; the outlet temperature of the second screw pump (3) is 200-450 ℃, preferably 275-420 ℃, and the residence time is 5-60 minutes, preferably 20-45 minutes; the stripping gas is nitrogen or high-temperature steam; the stripping gas has a stripping gas quantity of 5 to 25L/h, preferably 10 to 20L/h, relative to 1kg of pretreatment material, wherein the material represents the pretreatment material introduced into the second screw pump (3);

the temperature of the high-temperature solvent oil is 300-450 ℃.

9. The method according to claim 1, wherein the dechlorinated waste plastic oil has a viscosity of 50-10000 mPa-s at 200 ℃ and a chlorine content of 100-800 μg/g.

10. The system for liquefying, viscosity-reducing and dechlorinating chlorine-containing waste plastics is characterized by comprising a chlorine-containing waste plastics bin (1), a first screw pump (2), a second screw pump (3) and a hydrogen chloride treatment unit;

the first screw pump (2) comprises a first input end and a first output end; the first input end is provided with a chlorine-containing waste plastic raw material inlet, and the first output end is provided with a pretreatment material outlet; the chlorine-containing waste plastic raw material inlet is communicated with the outlet of the chlorine-containing waste plastic storage bin (1);

the second screw pump (3) comprises a second input end and a second output end; the second input end is provided with a pretreatment material inlet, a high-temperature solvent oil outlet and a stripping gas inlet, and the stripping gas inlet is arranged at the downstream of the pretreatment material inlet and the high-temperature solvent oil outlet along the direction of the material movement in the second screw pump (3);

the pretreated material inlet is communicated with a pretreated material outlet of the first screw pump (2); the second output end is provided with a hydrogen chloride-containing gas-phase material outlet and a dechlorination waste plastic oil outlet, and the hydrogen chloride-containing gas-phase material outlet is communicated with an inlet of the gas-phase material to be treated of the hydrogen chloride absorption unit.

11. The system according to claim 10, wherein the hydrogen chloride treatment unit comprises a condensation separation apparatus (4), a primary absorber (5) and a secondary absorber (6);

the condensation separation device (4) is provided with a chlorine-containing gas-phase material inlet and a condensed gas-phase material outlet; the chlorine-containing gas-phase material inlet is formed as an inlet of gas-phase material to be treated of the hydrogen chloride absorption unit;

the primary absorber (5) is provided with a first hydrogen chloride absorbent inlet, a first hydrogen chloride mixed gas phase outlet and a first hydrogen chloride waste liquid outlet, and the primary absorber (5) comprises a first hydrogen chloride absorbent; the first inlet of the hydrogen chloride mixed gas phase is communicated with the condensed gas phase material outlet of the condensation separation device (4);

the secondary absorber (6) is provided with a hydrogen chloride absorbent inlet, a hydrogen chloride mixed gas phase second inlet, a gas phase outlet after hydrogen chloride absorption and a second hydrogen chloride waste liquid outlet, and the secondary absorber (6) comprises a second hydrogen chloride absorbent; the second inlet of the hydrogen chloride mixed gas phase is communicated with the first outlet of the hydrogen chloride mixed gas phase of the primary absorber (5), the hydrogen chloride absorbent inlet is used for introducing a hydrogen chloride absorbent into the hydrogen chloride absorption unit, and the second hydrogen chloride waste liquid outlet is communicated with the first hydrogen chloride absorbent inlet of the primary absorber (5) so as to enable liquid phase materials in the primary absorber (5) and the secondary absorber (6) to be communicated.

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