Method for preparing vinyl-terminated polymer by means of rapid laser pyrolysis of polyolefin

Abstract

The present invention belongs to the field of resource utilization of waste plastics. Specifically disclosed is a method for preparing a vinyl-terminated polymer by means of rapid laser pyrolysis of a polyolefin. The preparation method comprises the following steps: first, taking a polyolefin as a raw material, and adding a light-absorbing agent having a certain concentration thereto by means of the processes of melting and mixing; and then, under the protection of an inert gas, initiating high-temperature decomposition of the polyolefin by means of laser irradiation, and condensing and collecting a decomposition product, thereby obtaining a vinyl-terminated polymer. The polyolefin pyrolysis technique provided by the present invention realizes rapid pyrolysis of a polyolefin by means of laser heating, and is simple in terms of process, controllable and pollution-free during implementation, and high in terms of product yield. Characterized by rapidness and uniformity, laser heating has no heat transfer limitation or temperature gradient, reduced energy consumption during cracking, and improved cracking efficiency in comparison with traditional heating modes; and a high proportion of a vinyl-terminated polymer product is obtained, and separation is not required.

Description

A method for preparing vinyl-terminated polymers by laser rapid pyrolysis of polyolefins Technical Field

[0001] The invention belongs to the technical field of waste plastic recycling and resource utilization, and particularly relates to a method for preparing vinyl-terminated polymers by laser rapid pyrolysis of polyolefins. Background Art

[0002] Plastics play an indispensable role in contemporary society, but their short lifespan and growing demand for use have created a significant imbalance between production and recycling. The large-scale disposal of single-use plastics, particularly packaging materials, ground films, and plastic bags, has caused serious pollution to the natural environment and a significant consumption of non-renewable resources. The production, use, and disposal rates of polyolefins, such as polyethylene, polypropylene, and polystyrene, account for a large proportion of all plastics, and the resulting plastic waste poses a serious challenge to recycling. Currently, the main treatment methods for single-use waste plastics include landfilling, incineration, and downgrading, but these treatment methods cannot achieve efficient resource utilization and are prone to secondary pollution. Therefore, it is urgent to develop green and efficient chemical recycling technologies to alleviate the environmental and resource pressures caused by waste plastics.

[0003] Chemically inert polyolefins lack suitable solvents for chemical recovery, making efficient and selective degradation and recycling difficult. Pyrolysis is a versatile and effective method for converting waste polyolefins into high-value-added products. Traditional pyrolysis involves a thermochemical process that decomposes polyolefin polymers into a mixture of gaseous and liquid hydrocarbons and coke at high temperatures and in the absence of oxygen (typically above 500°C). However, traditional direct pyrolysis technology suffers from low efficiency, high energy consumption, and often complex product distribution due to its slow heating rate and limitations on heat and mass transfer. To improve product selectivity, a two-step pyrolysis process has been proposed. Artetxe et al. (Artetxe. M, Lopez. G, Elordi. G, Amutio. M, Bilbao. M, Olazar. M. Production of Light Olefins from Polyethylene in a Two-Step Process: Pyrolysis in a Conical Spouted Bed and Downstream High-Temperature Thermal Cracking[J]. Industrial & Engineer Chemistry Research, 2021, 51, 13915-13923) employed a two-step pyrolysis process to selectively produce light olefins from high-density polyethylene. They first fed the plastic into a conical spouted bed reactor (CSBR) at 500°C to produce a high yield of wax (93%). The wax produced in the first step was then cracked in a quartz reactor at 900°C with a short residence time (0.016–0.032 s), resulting in a yield of light olefins (C2–C4) as high as 77 wt%. However, the large energy input and relatively complex process flow have limited the expansion of this technology. Adding a catalyst to the pyrolysis process can lower the reaction temperature and improve product selectivity, but the cost and lifespan of the catalyst place higher demands on the pyrolysis reaction, and catalytic pyrolysis is difficult to process with highly polluting polyolefin waste.

[0004] There are reports on the use of new pyrolysis technologies for the pyrolysis of polyolefins, such as microwave heating, infrared heating, pulsed electric heating, etc. Jie et al. (Jie X, Li W, Slocombe D, Gao Y, Banerjee I, Gonzalez-Cortes S, Yao B, AlMergen H, Alshihri S, Dilworth J, Thomas J, Xiao T, Edwards P. Microwave-initiated catalytic deconstruction of plastic waste into hydrogen and high-value carbons [J]. Naturecatalysis, 2020 (3) (11), 902-912) used microwave-induced FeAlO X Catalytic deconstruction of waste polyolefins to generate hydrogen and high-value carbon materials. This method has a fast reaction rate and can achieve high-value conversion of waste plastics within 30-90 seconds, with hydrogen production as high as 55.6mmol / g plastic (Concentration accounts for ~90 vol%), and more than 92% of the residual carbon is composed of carbon nanotubes. Patent 202110588868.8 discloses a method for the rapid pyrolysis and catalytic pyrolysis of waste plastics using infrared heating. This method not only solves the problems of slow heating rate and uneven heating of raw materials in existing pyrolysis technologies, but also achieves flexible regulation of the pyrolysis and catalytic pyrolysis temperatures by separating the pyrolysis and catalytic reactions of the plastics, slowing the deactivation rate of catalyst carbon deposition and improving the quality of the pyrolysis products.

[0005] Controlling the process conditions during the pyrolysis process can generate different types of products. By regulating the temperature and degradation time, end-group ethylene polymers can be generated in a targeted manner. The preparation of ethylene-terminated polymers by thermal degradation can achieve the upgrading and utilization of waste polyolefins. This technology is not only simple in process but also has potential economic value and environmental benefits. Sawaguchi et al. (Sawaguchi T, Suzuki Y, Sakaki A, Saito H, Yano S, Seno M. Chemical recycling of commodity vinyl polymers: selective preparation of end-reactive oligomers by controlled thermal degradation, 2000 (49), 921-925) proposed the preparation of low molecular weight polymers with end-group vinyl double bonds by controlled thermal degradation of isotactic polypropylene (iPP). However, the pyrolysis method used was traditional external electric heating, and the products needed to be purified, which was difficult to separate.

[0006] Proposing a pyrolysis technology with high efficiency, low energy consumption, high added value, and considerable cost-effectiveness is a significant undertaking for the upcycling and recycling of plastic waste. Conventional pyrolysis technologies, due to shortcomings such as poor heat transfer efficiency, uneven temperature distribution, and long pyrolysis reaction times, struggle to effectively prevent secondary reactions between products. This results in a complex final product structure, making separation difficult and reducing the economic value of further utilization. Therefore, developing a fast pyrolysis technology that is not limited by heat transfer and has a short residence time to produce polymers rich in terminal double bonds is of great significance in this technical field.

[0007] Summary of the Invention

[0008] To address the shortcomings of existing methods, the present invention provides a method for preparing vinyl-terminated polymers by laser rapid pyrolysis of polyolefins. This method utilizes lasers to locally heat the polyolefin, resulting in rapid temperature increase and decrease, uniform and controllable temperature, high efficiency, low energy consumption, and a pure, selective, and value-added product.

[0009] To achieve this object, the present invention is achieved through the following technical solutions.

[0010] First, polyolefin plastics are insensitive to infrared light and have a low absorption rate. Directly irradiating and heating them with infrared lasers makes it difficult to rapidly decompose them. The present invention, by doping the polyolefin with a certain concentration of a light absorber, increases the polyolefin's absorption coefficient to laser energy. This allows the polyolefin material in the irradiated area to efficiently absorb the laser energy and convert it into heat, causing the polyolefin material to rapidly heat up and undergo thermal decomposition in a very short time, effectively improving energy utilization efficiency.

[0011] Secondly, the temperature of the polyolefin raw material only occurs on the material surface in the laser irradiated area, and the temperature of the non-irradiated area and the environment remains unchanged. The laser thermal cracking reaction of polyolefin only occurs in the irradiated high-temperature area, and the gradual decomposition of the polyolefin material is achieved through the rapid movement of the laser spot.

[0012] Again, the irradiated raw materials are cracked in the high-temperature area and the cracking products erupt and escape in the form of steam, leaving the laser irradiation surface and rapidly cooling away from the high-temperature area with the purge air flow. The rapid decrease in the temperature of the pyrolysis products can effectively avoid the occurrence of secondary reactions, which is conducive to retaining the terminal ethylene structure generated by the cracking reaction and effectively improving the product selectivity.

[0013] Finally, the pyrolysis products and the purge gas enter the condensation collection device, and some of the products that form solids and liquids are collected in the condensation device, while the gases that cannot be condensed enter the gas collection device.

[0014] A method for preparing a vinyl-terminated polymer by laser pyrolysis of polyolefins comprises the following steps:

[0015] (1) Using polyolefin plastics as raw materials, a certain concentration of light absorber is added during the melt mixing process;

[0016] (2) The polyolefin raw material mixed with the light absorber is prepared into a sheet of a certain thickness by hot pressing;

[0017] (3) The polyolefin is placed in a laser pyrolysis reaction device, and under the protection of inert gas, the polyolefin is rapidly pyrolyzed by laser irradiation;

[0018] (4) The decomposition products enter the condensation collection device along with the inert gas, and are condensed and collected to obtain ethylene-terminated polymers.

[0019] Preferably, in step (1), the polyolefin is high-density polyethylene, low-density polyethylene, polypropylene, polystyrene or a mixture thereof.

[0020] Preferably, in step (1), the mixing process uses an extruder or an internal mixer to uniformly mix the polyolefin and the light absorber through a melt mixing process.

[0021] Preferably, in step (1), the light absorber used is a thermally stable black inorganic material that does not decompose under laser irradiation, such as carbon black, graphite, graphene, carbon nanotubes, ferroferric oxide, copper oxide, manganese dioxide, etc., and more preferably carbon black powder.

[0022] Preferably, in step (1), the mass concentration of the light absorber used is in the range of 0.01% to 10.0%.

[0023] Preferably, in step (2), the hot pressing process is performed at a temperature in the range of 150-250° C. to form a sheet / plate with a thickness of 0.1-5.0 mm.

[0024] Preferably, in step (3), the inert gas used is one of nitrogen, argon and helium.

[0025] Preferably, in step (3), the laser used is an infrared laser, which can convert light energy into heat energy through a light-absorbing medium.

[0026] Preferably, in step (3), the laser pyrolysis reaction device used is a quartz glass cylinder having an inert gas inlet and a pyrolysis product outlet, the cylinder diameter is 30-500 mm, the front end of the quartz glass cylinder is connected to an inert gas purge device, and the rear end is connected to a condensation collection device, and the polyolefin sheet / plate mixed with the light absorber is placed inside the quartz glass cylinder.

[0027] Preferably, after placing the polyolefin sheet / plate containing the light absorber into the laser pyrolysis reactor, an inert gas is introduced into the reactor. After the air is exhausted, the laser is started and the inert gas is kept flowing. The laser is irradiated through the quartz glass onto the polyolefin sheet / plate mixed with the light absorber in the cylinder, inducing rapid pyrolysis of the polyolefin and generating pyrolysis product vapor. The product vapor enters the condensation collection device through a conduit.

[0028] Preferably, the movement of the laser spot is achieved by controlling the rotation of the galvanometer, and the scanning rate of the laser spot is not less than 3 mm / s. More preferably, the laser scanning rate is 5-15 mm / s.

[0029] Preferably, the laser power used is 10-1000W, more preferably the laser power is 100W.

[0030] Preferably, in step (4), the temperature of the condensation collection device is set between -30 and 30 °C, and the pyrolysis products enter the cooling device along with the inert gas to be cooled and collected in the cooling device.

[0031] Advantages and beneficial effects of the preparation method and the prepared product of the present invention:

[0032] 1. The present invention can achieve rapid temperature increase / decrease and continuous pyrolysis of polyolefin materials in a limited area through laser heating and movement of the light spot.

[0033] 2. The present invention improves the light absorption efficiency of polyolefin materials by adding light absorbers. Photothermal conversion occurs in the irradiated area of ​​the plastic, without heat transfer resistance and temperature gradient limitations. By controlling the concentration of the light absorber and the laser parameters, the pyrolysis temperature and time can be precisely controlled.

[0034] 3. The present invention realizes a controllable pyrolysis process of polyolefin materials through a relatively high pyrolysis temperature and an extremely short pyrolysis time. The rapid heating of the raw materials and the rapid cooling of the products greatly reduce the occurrence of secondary reactions. The pyrolysis reaction products contain a high content of terminal vinyl structures.

[0035] 4. The laser in the present invention acts directly on the raw material, and the heat converted by the laser is almost all used for cracking the plastic. There is no external heat dissipation process, which can greatly reduce the energy consumption in the pyrolysis process and has a high energy utilization rate.

[0036] 5. The present invention can process uncleaned polyolefin materials containing impurities, and there is no need to clean and classify the polyolefins in advance, which greatly reduces the pretreatment cost of waste plastics.

[0037] 6. The pyrolysis apparatus and process of the present invention are simple. The pyrolysis products escape the reaction zone as vapor, while the light absorber and impurities in the raw materials remain within the raw materials, making product separation easy. Furthermore, the quality of the inert light absorber remains unchanged and can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a diagram showing the connection of equipment for preparing vinyl terminated polymers by laser pyrolysis of polyolefins in the present invention;

[0039] FIG2 is a comparison of Fourier transform infrared spectra (FTIR) of solid products and raw materials obtained by pyrolyzing HDPE in Example 1 and Examples 4-11 of the present invention;

[0040] FIG3 is a nuclear magnetic resonance (NMR) spectrum of solid products prepared by pyrolyzing HDPE in Example 1 and Examples 4-11 of the present invention;

[0041] FIG4 is a comparison of Fourier transform infrared (FTIR) spectra of the solid product prepared by pyrolysis of LDPE / PP in Example 2-3 of the present invention and the raw material;

[0042] FIG5 is a nuclear magnetic resonance spectrum (NMR) of a solid product prepared by pyrolyzing LDPE in Example 2 of the present invention;

[0043] FIG6 is a nuclear magnetic resonance spectrum (NMR) of a solid product prepared by pyrolysis of PP in Example 3 of the present invention;

[0044] Figures 7a and 7b are scanning electron microscope images (SEM) of carbon black before and after pyrolysis reaction in Example 1 of the present invention;

[0045] FIG8 is a Raman spectrum of carbon black before and after pyrolysis reaction in Example 1 of the present invention.

[0046] Specific implementation methods

[0047] The present invention is further described in detail below with reference to the accompanying drawings and examples. However, it should be understood that these drawings and examples are intended to illustrate the present invention only and do not constitute any limitation. Unless otherwise specified, process parameters may be conventionally used. All raw materials, reagents, etc., for which the manufacturer is not indicated, are commercially available conventional products.

[0048] Figure 1 is a schematic diagram of the laser pyrolysis reaction device used in the present invention, which includes an inert gas purge device, a reaction device, a condensation collection device, and a filtration device. The components in Figure 1 are an inert gas storage tank 1, an airflow pressure gauge 2, a flow meter 3, a flange 4, a quartz glass cylinder 5, a laser 6, a condenser 7, a sample collector 8, and a filter 9. The inert gas storage tank 1 is connected to the flange 4 at the inlet of the quartz glass cylinder 5 via a pipe. The airflow pressure gauge 2 and the flow meter 3 are connected to the pipe between the inert gas storage tank 1 and the quartz glass cylinder 5. The laser 6 is installed on the outside of the quartz glass cylinder 5. The flange 4 at the outlet of the quartz glass cylinder 5 is connected to the collector 8 disposed in the condenser 7, and the collector 8 is connected to the filter 9.

[0049] The laser pyrolysis reaction devices in the following embodiments all adopt the above structure.

[0050] Example 1

[0051] 1) 47 g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5 mm thick HDPE / CB composite sheet.

[0052] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. The condensed products were collected to yield ethylene-terminated polyethylene.

[0053] Example 2

[0054] 1) 45.5 g of LDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was uniformly mixed, it was pressed at 160°C and 15 MPa to form a 0.5 mm thick LDPE / CB composite sheet.

[0055] 2) After placing the LDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 50 W, and a laser scanning rate of 5 mm / s. The laser spot was directed onto the LDPE flakes mixed with carbon black in a glass cylinder, causing the LDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then condensed and collected.

[0056] Example 3

[0057] 1) 45g of PP was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 200°C and 15 MPa to form a 0.5mm thick PP / CB composite sheet.

[0058] 2) After placing the PP / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 60 W, and a laser scanning rate of 5 mm / s. The laser spot was directed onto the PP flakes mixed with carbon black in a glass cylinder, causing the PP to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. After condensation, they were collected to yield allyl-terminated polypropylene.

[0059] Example 4

[0060] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% graphene (G) was added. After the mixture was uniformly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / G composite sheet.

[0061] 2) After placing the HDPE / G flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then collected and condensed.

[0062] Example 5

[0063] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon nanotubes (CN) were added. After the mixture was uniformly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CN composite sheet.

[0064] 2) After placing the HDPE / CN sheet in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE sheet mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then condensed and collected.

[0065] Example 6

[0066] 1) 47g of HDPE was melt-blended in an internal mixer, and 0.1% carbon black (CB) was added. After the mixture was uniformly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0067] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. The condensed products were collected to yield ethylene-terminated polyethylene.

[0068] Example 7

[0069] 1) 47g of HDPE was melt-blended in an internal mixer, and 10% carbon black (CB) was added. After the mixture was uniformly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0070] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 20 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. The condensed products were collected to yield ethylene-terminated polyethylene.

[0071] Example 8

[0072] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0073] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 1064 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. The condensed products were collected to yield ethylene-terminated polyethylene.

[0074] Example 9

[0075] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0076] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 15 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then condensed and collected.

[0077] Example 10

[0078] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0079] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 30 mm / s. The laser spot was directed onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. The condensed products were collected to yield ethylene-terminated polyethylene.

[0080] Example 11

[0081] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0082] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 60 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then collected and condensed.

[0083] Example 12

[0084] 1) 47g of HDPE was melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5mm thick HDPE / CB composite sheet.

[0085] 2) After placing the HDPE / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 10 W, and a laser scanning rate of 5 mm / s. The laser spot was directed onto the HDPE flakes mixed with carbon black in a glass cylinder, causing the HDPE to rapidly heat up and pyrolyze. The pyrolysis products vaporized under the influence of the high temperature and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then condensed and collected.

[0086] Example 13

[0087] 1) 47g HDPE milk bottle (PSW-H) was used as the raw material. 1% carbon black (CB) was added to the mixture via melt blending in an internal mixer. After the mixture was thoroughly mixed, it was pressed at 180°C and 15 MPa to form a 0.5 mm thick PSW-H / CB composite sheet.

[0088] 2) After placing the PSW-H / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following laser parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 100 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the PSW-H flakes mixed with carbon black in a glass cylinder, causing the PSW-H to rapidly heat up and pyrolyze. The pyrolysis products vaporized at high temperatures and escaped into a condenser at -20°C along with the nitrogen flow. They were then condensed and collected to yield ethylene-terminated polyethylene.

[0089] Example 14

[0090] 1) 45.5g of LDPE packaging bags (PSW-L) were melt-blended in an internal mixer, and 1% carbon black (CB) was added. After the mixture was uniformly mixed, it was pressed at 160°C and 15 MPa to form a 0.5mm thick PSW-L / CB composite sheet.

[0091] 2) After placing the PSW-L / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following parameters: a wavelength of 915 nm, a laser spot diameter of 1.5 mm, a laser power of 50 W, and a laser scanning rate of 5 mm / s. The laser spot was irradiated onto the PSW-L flakes mixed with carbon black in a glass cylinder, causing the PSW-L to rapidly heat up and pyrolyze. The pyrolysis products vaporized at high temperatures and escaped into a condenser at -20°C along with the nitrogen flow. Ethylene-terminated polyethylene was then collected and condensed.

[0092] Example 15

[0093] 1) 45g PP lunch box (PSW-P) was used as the raw material. 1% carbon black (CB) was added to the mixture via melt blending in an internal mixer. After the mixture was thoroughly mixed, it was pressed at 200°C and 15 MPa to form a 0.5 mm thick PSW-P / CB composite sheet.

[0094] 2) After placing the PSW-P / CB flakes in a laser pyrolysis reactor, nitrogen was introduced into the reactor. After the air was exhausted, the laser was activated using the following parameters: wavelength 915 nm, laser spot diameter 1.5 mm, laser power 60 W, and laser scanning rate 5 mm / s. The laser spot was irradiated onto the PSW-P flakes mixed with carbon black in a glass cylinder, causing the PSW-P to rapidly heat up and pyrolyze. The pyrolysis products vaporized and escaped under the influence of the high temperature. They were then transported along with the nitrogen flow into a condenser at -20°C, where they were condensed and collected to yield ethylene-terminated polyethylene.

[0095] Product structure characterization

[0096] Table 1 shows the laser rapid pyrolysis conditions and the test results for the cracking product yields and quality in Examples 1-15. As can be seen from Table 1, under the experimental conditions described herein, the solid product yields of laser pyrolysis polyolefins ranged from 60% to 80%, with molecular weights between 1000 and 2000, a molecular weight distribution close to 2, and a terminal double bond content close to 100%. Furthermore, the test results (Examples 12-15) indicate that the presence of impurities in the feedstock did not significantly interfere with the selectivity and quality of the products.

[0097] Figure 2 is a Fourier infrared spectrum of the solid product and raw material HDPE prepared in Example 1 and Examples 4-11. As can be seen from Figure 2, by pyrolyzing HDPE with the technology of the present invention, the 1641cm -1 The stretching vibration peak of C=C bond is 3076cm -1 The stretching vibration peak of the CH bond in -CH=CH2 is 991cm -1 and 910cm-1 The peak at -CH=CH2 is the deformation vibration peak of the CH bond, which indicates that a large number of terminal vinyl functional groups are generated in the molecular chain of the solid product prepared by the present invention.

[0098] Figure 3 shows the NMR spectra of the solid products prepared in Example 1 and Examples 4-11. The average number of terminal vinyl groups in each molecule (f) was calculated by the ratio of the integrated area I1 of vinyl hydrogen (δ = 4.90-5.02 ppm) to the integrated area I2 of methyl hydrogen (δ = 0.80-0.92 ppm). c =3I1 / 2I2), it was calculated that the content of ethylene-terminated polyethylene prepared in Example 1 and Examples 4-11 was close to 100%.

[0099] Figure 4 is a Fourier transform infrared spectrum of the solid product and the raw material LDPE / PP prepared in Example 2-3. -1 The stretching vibration peak of C=C bond is 3078cm -1 The stretching vibration peak of the CH bond in -CH=CH2 is 991cm -1 and 910cm -1 The peak at 1650cm is the deformation vibration peak of the CH bond in -CH=CH2 and the infrared spectrum of the solid product of PP pyrolysis. -1 The stretching vibration peak of C=C bond is 3074cm -1 The stretching vibration peak of the CH bond in -C=CH2 is 887cm -1 It can be seen from the deformation vibration peak of the CH bond in -C=CH2 that the vinyl-terminated polymer produced by the technology of the present invention is widely applicable to different types of polyolefin materials.

[0100] Figure 5 is the NMR spectrum of the solid product prepared in Example 2. The average number of terminal vinyl groups in each molecule (f c =3I1 / 2I2), it was calculated that the content of ethylene-terminated polyethylene prepared in Example 9 was 90.51%, which was relatively low because the presence of the side groups increased the number of methyl hydrogens.

[0101] Figure 6 is the NMR spectrum of the solid product prepared in Example 3. The average number of allyl groups per molecule (f) was calculated by the ratio of the integrated area I3 of the methyl carbon connected to the terminal double bond (δ = 22.37 ppm) to the integrated area I4 of the terminal methyl carbon (δ = 14.59 ppm). c=2I3 / (I3+I4)), it was calculated that the content of the allyl-terminated polypropylene prepared in Example 3 was 176.4%, indicating that the molecular chain of the solid product prepared by the present invention contained a large number of molecular structures with allyl groups at both ends.

[0102] Figures 7a, 7b, and 8 show scanning electron micrographs and Raman spectra of the carbon black absorber before and after laser pyrolysis in Example 1. As can be seen from the figures, the carbon black structure undergoes minimal structural changes after pyrolysis (Figure 7a before and after pyrolysis, Figure 7b), while the degree of graphitization increases slightly, with the degree of increase increasing with increasing laser power. This demonstrates that the carbon black additive can be recycled multiple times.

[0103] Table 1 and the accompanying figures demonstrate that the method of the present invention can achieve high-value recovery of waste polyolefins, addressing environmental pollution issues while also producing high-value ethylene-terminated polymers. This method significantly expands the scope of resource utilization for waste plastics.

[0104] Table 1

[0105]

[0106] The above content is only a basic description of the patent concept of the present invention, and any equivalent transformations made according to the technical solution of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins, characterized in that: The following steps are involved: (1) Using polyolefin plastics as raw materials, light absorbers are added during the melt mixing process; (2) The polyolefin raw material mixed with the light absorber is pressed into a polyolefin sheet / plate through a hot pressing process; (3) The polyolefin sheet / plate is placed in a laser pyrolysis reaction device, and under the protection of inert gas, the polyolefin is rapidly pyrolyzed by laser irradiation; (4) The decomposition products enter the condensation collection device along with the inert gas, and are condensed and collected to obtain ethylene-terminated polymers.

2. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (1), the polyolefin plastic is one or more of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS); The mixing process uses an extruder or an internal mixer to mix the polyolefin and the light absorber uniformly through a melt mixing process.

3. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (1), the light absorber used is a thermally stable black inorganic material that does not decompose under laser irradiation; the light absorber includes carbon black, graphite, graphene, carbon nanotubes, ferrosoferric oxide, copper oxide or manganese dioxide; The mass percentage concentration of the light absorber is 0.01% to 10.0%.

4. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (2), the hot pressing process is performed at a temperature in the range of 150-250° C. to form a sheet / plate with a thickness of 0.1-5.0 mm.

5. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (3), the inert gas is one of nitrogen, argon or helium; The laser used is an infrared laser.

6. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (3), the laser pyrolysis reaction device is a quartz glass cylinder having an inert gas inlet and a pyrolysis product outlet, the cylinder diameter is 30-500 mm, the front end of the quartz glass cylinder is connected to an inert gas purge device, the rear end is connected to a condensation collection device, and the polyolefin sheet / plate mixed with the light absorber is placed inside the quartz glass cylinder.

7. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1 or 6, characterized in that: After placing the polyolefin sheet / plate containing the light absorber into the laser pyrolysis reactor, an inert gas is introduced into the reactor. After the air is exhausted, the laser is started and the inert gas is kept flowing. The laser is irradiated through the quartz glass onto the polyolefin sheet / plate mixed with the light absorber in the cylinder, causing rapid pyrolysis of the polyolefin and generating pyrolysis product vapor. The product vapor enters the condensation collection device through the conduit.

8. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1 or 7, characterized in that: The movement of the laser spot is achieved by controlling the rotation of the galvanometer, and the scanning rate of the laser spot is not less than 3 mm / s.

9. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1 or 7, characterized in that: The laser power used is 10~1000W.

10. The method for preparing vinyl terminated polymers by laser rapid pyrolysis of polyolefins according to claim 1, characterized in that: In step (4), the temperature of the condensation collection device is set between -30 and 30 °C, and the pyrolysis products enter the cooling device along with the inert gas to be cooled, and are condensed into solids in the cooling device and collected.

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