Waste plastic continuous depolymerization device and waste plastic recovery method

Abstract

The invention discloses a waste plastic continuous depolymerization device and a waste plastic recycling method, and belongs to the technical field of waste plastic recycling, the waste plastic continuous depolymerization device comprises a raw material treatment device, a primary depolymerization reactor, a secondary depolymerization reactor and a separation device, the raw material treatment device is used for converting waste plastic into melt; the first-stage depolymerization reactor is used for converting the melt into a first-stage gas phase product and a first-stage liquid phase product; the second-stage depolymerization reactor is used for converting the first-stage liquid-phase product into a second-stage gas-phase product and a second-stage liquid-phase product, the first-stage gas-phase product and the second-stage gas-phase product are used as gas-phase products, and the second-stage liquid-phase product is used as a liquid-phase product; and the separation device is used for separating and recovering the gas-phase product and the liquid-phase product. By means of the first-stage depolymerization reactor and the second-stage depolymerization reactor which are continuously arranged, continuous depolymerization recovery of waste plastics is achieved, the conversion rate of gas-phase products is increased, and the device has the advantages of being high in efficiency, low in cost, high in additional value and the like.

Description

Technical Field

[0001] The invention relates to the technical field of waste plastic recycling, in particular to a waste plastic continuous depolymerization device and a waste plastic recycling method. Background Art

[0002] With the rapid development of the plastics industry, plastic products have been widely used in people's daily lives, greatly promoting social progress and economic development. However, behind this prosperity lies a serious environmental problem - the amount of waste plastics is increasing at an unprecedented rate. If these waste plastics are not handled in a timely and effective manner, they will not only cause long-term pollution to the natural environment and destroy the ecological balance, but also waste a lot of precious resources, which runs counter to the current concept of circular economy.

[0003] At present, the treatment methods of waste plastics mainly include traditional means such as landfill and incineration. Although these methods have alleviated the accumulation problem of waste plastics to a certain extent, their treatment efficiency is low and they are often accompanied by serious secondary pollution risks, such as soil pollution, air pollution and water pollution, which further aggravates the environmental burden. Therefore, it is particularly urgent to explore a more efficient and environmentally friendly waste plastic treatment technology.

[0004] In the field of waste plastic recycling, depolymerization technology is seen as a potential solution. Through depolymerization, the molecular chains of waste plastics can be broken and converted into small molecular compounds, thereby achieving resource reuse. However, the existing waste plastic depolymerization technology still faces many challenges. On the one hand, the depolymerization efficiency is low and the product quality is uneven, which makes it difficult to meet the needs of industrial production; on the other hand, the high cost limits the widespread application of these technologies. In addition, the continuous depolymerization process of waste plastics involves complex process links, such as feed control, reaction condition optimization, product separation and purification, etc., which puts extremely high demands on the design and operation of the equipment, and continuous production is difficult.

[0005] In view of this, developing an efficient, continuous and environmentally friendly waste plastic depolymerization device has become the key to solving the current problem of waste plastic treatment. Summary of the invention

[0006] The purpose of the present invention is to provide a waste plastic continuous depolymerization device and a waste plastic recycling method to solve the problems existing in the above-mentioned prior art. By continuously arranging a primary depolymerization reactor and a secondary depolymerization reactor, continuous depolymerization and recycling of waste plastics can be achieved, and the conversion rate of gas phase products can be improved. The device has the characteristics of high efficiency, low cost and high added value.

[0007] To achieve the above object, the present invention provides the following solutions: The present invention provides a waste plastic continuous depolymerization device, comprising a raw material processing device, a primary depolymerization reactor, a secondary depolymerization reactor and a separation device, wherein the raw material processing device is used to convert the waste plastic into a melt; the primary depolymerization reactor is used to convert the melt into a primary gas phase product and a primary liquid phase product; the secondary depolymerization reactor is used to convert the primary liquid phase product into a secondary gas phase product and a secondary liquid phase product, the primary gas phase product and the secondary gas phase product are used as gas phase products, and the secondary liquid phase product is used as a liquid phase product; and the separation device is used to separate and recover the gas phase product and the liquid phase product.

[0008] In one embodiment, the raw material processing device includes a pretreatment silo and an extruder, wherein the pretreatment silo is used to hold waste plastics that have been screened and crushed into granules, sheets or strips, and the extruder is used to melt and extrude the waste plastics in the pretreatment silo and feed them into the primary depolymerization reactor.

[0009] In one embodiment, the raw material processing device further comprises a feeder, wherein an inlet of the feeder is connected to the pretreatment silo, and an outlet of the feeder is connected to the extruder.

[0010] In one embodiment, the extruder is a twin-screw extruder with a nitrogen protection device.

[0011] In one embodiment, a filter is further included, wherein the filter is disposed between the primary depolymerization reactor and the secondary depolymerization reactor, and the filter is used to filter the waste catalyst and other impurities.

[0012] In one embodiment, the separation device comprises a gas-liquid separator, and the gas-liquid separator is used to separate the gas phase product from the liquid phase product.

[0013] In one embodiment, the separation device further comprises a distillation tower and an online chromatograph, wherein the online chromatograph is used to analyze the components of the liquid product separated by the gas-liquid separator, and the distillation tower is used to separate and recover the liquid product according to the analysis result of the online chromatograph.

[0014] The present invention provides a method for recycling waste plastics, comprising the following steps: S1, converting waste plastic into melt; S2, converting the melt into a primary gas phase product and a primary liquid phase product through a depolymerization reaction; S3, converting the primary liquid phase product into a secondary gas phase product and a secondary liquid phase product through a depolymerization reaction, wherein the primary gas phase product and the secondary gas phase product are used as gas phase products, and the secondary liquid phase product is used as a liquid phase product; S4. Separate and recover the gas phase product and the liquid phase product.

[0015] In one embodiment, in step S1, waste plastics are screened and crushed into granular, flaky or strip raw materials with a mesh size of not less than 5, and a catalyst is added to the pretreated raw materials at a weight ratio of 1% to 5%. The waste plastics are converted into a melt by melt extrusion at 180° C. to 250° C. under nitrogen protection.

[0016] In one embodiment, in step S3, a highly selective catalyst is used, the operating temperature is 150° C. to 300° C., and the residence time is not less than 15 min to 20 min.

[0017] Compared with the prior art, the present invention has achieved the following technical effects: The present invention converts the raw materials of waste plastics into melts after processing, and then realizes continuous depolymerization and recovery of the waste plastics through a continuously arranged primary depolymerization reactor and a secondary depolymerization reactor. During depolymerization, the secondary depolymerization reactor is used to continue to depolymerize the primary liquid phase product produced by the primary depolymerization reactor, and the gas phase product finally obtained includes the primary gas phase product and the secondary gas phase product, thereby improving the conversion rate of the gas phase product, and has the characteristics of high efficiency, low cost and high added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 Schematic diagram of a continuous depolymerization device for waste plastics in an embodiment of the present invention; Among them, 1. pretreatment silo; 2. feeder; 3. extruder; 4. primary depolymerization reactor; 5. secondary depolymerization reactor; 6. gas-liquid separator; 7. online chromatograph; 8. distillation tower; 9. filter. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The purpose of the present invention is to provide a waste plastic continuous depolymerization device and a waste plastic recycling method to solve the problems existing in the prior art. By continuously arranging a primary depolymerization reactor and a secondary depolymerization reactor, continuous depolymerization and recycling of waste plastics can be achieved, and the conversion rate of gas phase products can be improved. The device has the characteristics of high efficiency, low cost and high added value.

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The primary depolymerization reactor and the secondary depolymerization reactor mentioned in the present invention refer to equipment used to degrade polymers into smaller molecules. The working principle is to provide appropriate chemical and physical conditions to break the polymer chain and generate smaller molecules. These smaller molecules are usually called oligomers, which have a low molecular weight and can be used for further processing or recycling. In the plastic recycling process, the depolymerization reactor can degrade the discarded plastic into small molecules, which are convenient for further processing and reuse.

[0024] The waste plastics mentioned in the present invention mainly refer to waste plastics such as high-density polyethylene (HDPE), high-pressure low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and polystyrene (PS). The above waste plastics are depolymerized. Such waste plastics account for the largest proportion of discarded plastics. The present invention can achieve high added value recycling of such plastics, which is of great significance for solving the current white pollution problem.

[0025] like Figure 1As shown, the present invention provides a waste plastic continuous depolymerization device, including a raw material processing device, a primary depolymerization reactor 4, a secondary depolymerization reactor 5 and a separation device. The raw material processing device may include multiple groups of equipment, and the waste plastic is pre-treated to be broken into a certain size so as to facilitate heating and melting, thereby converting the waste plastic into a melt. The primary depolymerization reactor 4 is used to convert the melt into a primary gas phase product and a primary liquid phase product. During the depolymerization reaction, a catalyst may be added and an appropriate reaction temperature may be reached. Specifically, the depolymerization reaction parameters known in the art may be used. The product of the primary depolymerization reactor 4 enters the secondary depolymerization reactor 5. The secondary depolymerization reactor 5 is used to continue the depolymerization reaction of the primary liquid phase product to convert it into a secondary gas phase product and a secondary liquid phase product. During the depolymerization reaction, a catalyst may be added and an appropriate reaction temperature may be reached. Specifically, the depolymerization reaction parameters known in the art may be used. The primary gas phase product basically no longer reacts in the secondary depolymerization reactor 5. At this time, most of the products are gas phase products composed of the primary gas phase product and the secondary gas phase product, and only a small amount of the secondary liquid phase product is used as a liquid phase product. The separation device is used to separate and recover gas phase products and liquid phase products, and the recovered products are then subjected to subsequent treatment.

[0026] The present invention converts the raw materials of waste plastics into melts after processing, and then realizes continuous depolymerization and recovery of waste plastics through a continuously arranged primary depolymerization reactor 4 and a secondary depolymerization reactor 5. During depolymerization, the secondary depolymerization reactor 5 is used to continue to depolymerize the primary liquid phase product produced by the primary depolymerization reactor 4, and the gas phase product finally obtained includes the primary gas phase product and the secondary gas phase product, thereby improving the conversion rate of the gas phase product, and has the characteristics of high efficiency, low cost and high added value.

[0027] The present invention is suitable for high-value-added recycling of waste plastics, and has a good promoting effect on reducing white pollution, practicing the concept of circular economy, and achieving the "dual carbon" goal.

[0028] In one embodiment, the raw material processing device includes a pretreatment silo 1 and an extruder 3. The pretreatment silo 1 is used to contain waste plastics that have been screened and crushed into granules, sheets or strips. After entering the extruder 3, the waste plastics are heated and melted by the extruder 3 and then extruded, and then fed to the primary depolymerization reactor 4. During the extrusion process, on the one hand, continuous extrusion can be achieved, which is convenient for continuous and stable feeding to the subsequent primary depolymerization reactor 4; on the other hand, the waste plastics are heated to a molten state, which preheats the subsequent primary depolymerization reactor 4 and improves the efficiency of the depolymerization reaction.

[0029] In one embodiment, the raw material processing device further comprises a feeder 2, the inlet of the feeder 2 is connected to the pretreatment silo 1, and the outlet of the feeder 2 is connected to the extruder 3. The function of the feeder 2 is to transfer the waste plastics in the pretreatment silo 1 to the extruder 3 according to the feeding speed requirement. The feeder 2 can be a feeder 2 with a screw conveying structure, which can continuously supply the waste plastics to the extruder 3, and adjust the feeding speed and feeding amount by adjusting the rotation speed of the screw conveying structure according to the demand.

[0030] In one embodiment, the extruder 3 uses a twin-screw extruder with a nitrogen protection device. The nitrogen protection device can provide a nitrogen atmosphere to prevent air oxidation from affecting the composition of the plastic. The twin-screw extruder has good feeding performance, mixing and plasticizing performance, exhaust performance, extrusion stability and other characteristics, and can stably and continuously provide the melt of waste plastics to the primary depolymerization reactor 4.

[0031] In one embodiment, a filter 9 is further included. The filter 9 is arranged between the primary depolymerization reactor 4 and the secondary depolymerization reactor 5. The material discharged from the primary depolymerization reactor 4 is filtered by the filter 9 before entering the secondary depolymerization reactor 5. The filter 9 is used to filter the waste catalyst and other impurities used in the primary depolymerization reaction process and the secondary depolymerization reaction process to improve the purity of the product obtained by subsequent separation.

[0032] In one embodiment, the separation device includes a gas-liquid separator 6, which is used to separate gas phase products from liquid phase products. The separated gas phase products can be directly recovered, and the separated liquid phase products can be subsequently separated. The gas-liquid separator 6 can be a centrifugal gas-liquid separator or a pipeline gas-liquid separator, etc. The working principle of the former is based on centrifugal force. When the gas-liquid mixture enters the separator, the mixture is subjected to the centrifugal force in the rotating chamber, and the liquid particles are thrown to the outer wall, while the gas is lighter and remains in the central area. By adjusting the rotation speed and the chamber design, liquid and solid particles can be effectively separated, thereby achieving the purpose of purifying the gas. The working principles of the latter mainly include the following two types: Gravity separation: The gas-liquid mixture enters the separator through a reasonably designed structure. According to the density difference between the two phases, the lighter gas usually rises to the top, while the heavier liquid sinks to the bottom. Using the effect of gravity, the gas naturally separates from the liquid at the top, thereby achieving effective separation of gas and liquid; Inertial separation: When the gas-liquid mixture passes through the gas-liquid separator 6, due to the different inertia of the gas and liquid, the two will produce different flow patterns in the equipment, achieving inertial separation. Inertial separation can make the gas and liquid move along different paths in the equipment and finally separate.

[0033] In one embodiment, the separation device further includes a fractionation tower 8 and an online chromatograph 7. The online chromatograph 7 is used to analyze the components of the liquid phase product separated by the gas-liquid separator 6, and the fractionation tower 8 is used to separate and recover the liquid phase product according to the analysis results of the online chromatograph 7. The fractionation tower 8 effectively separates the light components and the heavy components therein by heating and cooling based on the boiling point differences of various components in the liquid phase product. The main controlled parameters of the fractionation tower 8 include pressure and temperature. The pressure affects the boiling point of the components, thereby affecting their evaporation rate. Generally, the lower the pressure in the fractionation tower 8, the faster the component evaporation rate and the better the separation effect. The temperature needs to be gradually increased during the fractionation process so that different components evaporate in different temperature gradients. Too high a temperature will cause some components to evaporate in a lower temperature gradient, affecting the separation effect.

[0034] like Figure 1 As shown, the present invention provides a waste plastic recycling method, which can use the waste plastic continuous depolymerization device as described above, or other equipment, including the following steps: S1, converting waste plastics into melt, which can be crushed before being converted into melt to improve melting efficiency, and an extruder 3 can be used to ensure continuous and stable feeding; S2, converting the melt into a primary gas phase product and a primary liquid phase product through a depolymerization reaction; S3, converting the primary liquid phase product into a secondary gas phase product and a secondary liquid phase product through a depolymerization reaction, wherein the primary gas phase product and the secondary gas phase product are used as gas phase products, and the secondary liquid phase product is used as a liquid phase product; S4, separating and recovering the gas phase product and the liquid phase product. During separation, the gas phase product and the liquid phase product can be separated by a gas-liquid separator 6 first, and then the different components of the liquid phase product can be separated as needed.

[0035] In one embodiment, in step S1, waste plastics are screened and crushed into granular, flaky or strip raw materials with a mesh size of not less than 5, and a catalyst is added to the pretreated raw materials at a weight ratio of 1% to 5%. The waste plastics are converted into a melt by melt extrusion at 180° C. to 250° C. under nitrogen protection.

[0036] In one embodiment, in step S3, a highly selective catalyst is used, the operating temperature is 150° C. to 300° C., and the residence time is not less than 15 min to 20 min.

[0037] In one embodiment, the present invention provides the following steps: S11, screening and crushing the waste plastics into granular, flake or strip raw materials with a mesh size of not less than 5, and entering the pretreatment silo 1. This step is mainly to convert the recycled waste plastics into raw materials that can be smoothly fed; S12, the pretreated raw material is added with a catalyst at a ratio of 1% to 5% (mass ratio of the raw material) through a feeder 2, the catalyst adopts a catalytic cracking balance agent (FCC unit waste catalyst, i.e., fluidized cracking unit waste catalyst, which has a lower cost), and then enters an extruder 3 with a nitrogen protection device, is melt-extruded at 180° C. to 250° C., and is fed to a primary depolymerization reactor 4. This process requires sealing and nitrogen protection; S13, the primary depolymerization reactor 4 is heated by electromagnetic induction, which can achieve rapid heating, and the operating temperature is 300°C~450°C. The melt is extruded, sealed and continuously transported by the extruder 3 in step S12, and the residence time in the primary depolymerization reactor 4 is ensured to be not less than 10min~15min. The main function of this step is to convert the raw material melt into a primary gas phase product and a primary liquid phase product, and the conversion rate is greater than 96%. The depolymerization product is flammable. In order to ensure operational safety and prevent carbon deposition, the melt needs to be vacuumed before entering the previous stage depolymerization reactor 4; S14, the primary gas phase product and the primary liquid phase product in step S13 are filtered out by filter 9 to remove waste catalyst and other impurities in the raw materials and then enter the secondary depolymerization reactor 5, the secondary depolymerization reactor 5 is a fixed bed reactor, and uses a high-selectivity catalyst (specifically a loaded nickel-type molecular sieve catalyst, the main function of which is to greatly increase the proportion of gas phase products during the depolymerization catalytic process), the operating temperature is 150°C to 300°C, the residence time is not less than 15min to 20min, the main function of this step is to further convert the primary liquid phase product in step S13 into secondary gas phase products and secondary liquid phase products, and the gasification rate exceeds 90%. In order to ensure operational safety and prevent carbon deposition, the reactor needs to be vacuumed before the operation; S15. The final product in step S14 is separated into gas phase product and liquid phase product by gas-liquid separator 6. The gas phase product is directly recovered, and the liquid phase product first enters online chromatograph 7 to analyze the component ratio, and then enters distillation tower 8 for separation and recovery. The operating parameters of distillation tower 8 are set according to the analysis results.

[0038] The whole process of the invention is carried out under closed and oxygen-free conditions. A low-cost FCC balance agent is used as a catalyst in the primary depolymerization process, and a high-activity and high-selectivity catalyst is used in the secondary depolymerization process. The whole depolymerization process has a high conversion rate and very little carbon deposition, and continuous depolymerization and recovery of waste plastics is achieved. The yield of gas phase products exceeds 90%, and the invention has the characteristics of high efficiency, low cost, high added value, etc.

[0039] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A waste plastic continuous depolymerization device, characterized in that: include: A raw material processing device, the raw material processing device is used to convert waste plastics into a melt; A primary depolymerization reactor, the primary depolymerization reactor is used to convert the melt into a primary gas phase product and a primary liquid phase product; A secondary depolymerization reactor, wherein the secondary depolymerization reactor is used to convert the primary liquid phase product into a secondary gas phase product and a secondary liquid phase product, wherein the primary gas phase product and the secondary gas phase product serve as gas phase products, and the secondary liquid phase product serves as a liquid phase product; and a separation device, wherein the separation device is used to separate and recover the gas phase product and the liquid phase product.

2. The waste plastic continuous depolymerization device according to claim 1, characterized in that: The raw material processing device includes a pretreatment silo and an extruder. The pretreatment silo is used to contain waste plastics that have been screened and crushed into granules, sheets or strips. The extruder is used to melt and extrude the waste plastics in the pretreatment silo and feed them into the primary depolymerization reactor.

3. The waste plastic continuous depolymerization device according to claim 2 is characterized in that: The raw material processing device further comprises a feeder, wherein the inlet of the feeder is connected to the pretreatment silo, and the outlet of the feeder is connected to the extruder.

4. The waste plastic continuous depolymerization device according to claim 2, characterized in that: The extruder is a twin-screw extruder with a nitrogen protection device.

5. The waste plastic continuous depolymerization device according to claim 1, characterized in that: The invention also comprises a filter, which is arranged between the primary depolymerization reactor and the secondary depolymerization reactor, and is used for filtering the waste catalyst and other impurities.

6. The waste plastic continuous depolymerization device according to claim 1, characterized in that: The separation device comprises a gas-liquid separator, and the gas-liquid separator is used to separate the gas phase product from the liquid phase product.

7. The waste plastic continuous depolymerization device according to claim 6, characterized in that: The separation device also includes a fractionation tower and an online chromatograph. The online chromatograph is used to analyze the components of the liquid phase product separated by the gas-liquid separator, and the fractionation tower is used to separate and recover the liquid phase product according to the analysis result of the online chromatograph.

8. A method for recycling waste plastics, characterized in that: The following steps are involved: S1, converting waste plastic into melt; S2, converting the melt into a primary gas phase product and a primary liquid phase product through a depolymerization reaction; S3, converting the primary liquid phase product into a secondary gas phase product and a secondary liquid phase product through a depolymerization reaction, wherein the primary gas phase product and the secondary gas phase product are used as gas phase products, and the secondary liquid phase product is used as a liquid phase product; S4. Separate and recover the gas phase product and the liquid phase product.

9. The method for recycling waste plastics according to claim 8, characterized in that: In step S1, waste plastics are screened and crushed into granular, flaky or strip raw materials with a mesh size of not less than 5, and a catalyst is added to the pretreated raw materials at a weight ratio of 1% to 5%. The waste plastics are converted into a melt by melt extrusion at 180° C. to 250° C. under nitrogen protection.

10. The method for recycling waste plastics according to claim 8, characterized in that: In step S3, a highly selective catalyst is used, the operating temperature is 150°C to 300°C, and the residence time is not less than 15min to 20min.

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