A method, device and application for continuously degrading plastic based on a raman spectrometer

Abstract

The application provides a method, device and application for continuously degrading plastics based on a Raman spectrometer. The application utilizes the Raman spectrometer to feed back the content ratio of alkanes and aromatic hydrocarbons in degradation products in real time, and regulates the feed, so that degradation products with relatively stable chemical components are obtained. The method for degrading plastics provided by the application solves the problems of waste plastic resource waste and environmental pollution, and on this basis, a method for preparing low-carbon olefins from plastics is provided, realizing the recycling of waste plastics, reducing pollution and reducing carbon emissions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plastic degradation, and particularly relates to a method and device for continuously degrading plastics based on a Raman spectrometer and application thereof. BACKGROUND

[0002] Plastics are high molecular materials formed by the addition or condensation polymerization of monomers. Due to the characteristics of easy processing and low cost, plastics are widely used in daily life, greatly facilitating people's life. However, due to the characteristics of not easy to degrade, the "white pollution" caused by waste plastics has become a big problem faced by human beings.

[0003] Waste plastics are resources in the wrong place. Turning waste into resources and turning "burden" into economic benefits is the only way for comprehensive utilization of waste plastics. Chemical recycling of waste plastics using supercritical fluid can degrade plastics into low-carbon olefins, and then polymerize low-carbon olefins as monomers to produce high molecular materials such as plastics and rubbers, realizing the recycling of resources. Not only can pollution be avoided, but also production costs can be reduced and enterprise competitiveness can be improved.

[0004] Plastic recycling can be divided into physical recycling and chemical recycling. Physical recycling refers to a processing method of regranulating and forming waste plastics without destroying the high molecular structure of plastics. The physical recycling process and steps are simple, and it is feasible in business. Therefore, the current mainstream plastic recycling method is physical recycling. However, physical recycling also has corresponding limitations. Physical recycling is suitable for clean and single variety materials, and waste plastics with complex components need to be sorted. In addition, the molecular chain of the plastic after physical recycling may change, so the recycled material can only be used in a degraded way.

[0005] Chemical recycling is a process of destroying the high molecular chain of waste plastics and converting it into small molecules to produce fuel or chemical products. Chemical recycling is not only suitable for complex component waste plastics, but also can "turn waste into treasure" to convert plastic garbage into chemicals, reducing the dependence on fossil energy. In solving the plastic crisis, it also reduces carbon emissions. However, until 2020, the proportion of chemical recycling in waste plastic recycling was still less than 1%. Benefiting from environmental protection policies and oil prices, the proportion of chemical recycling in waste plastic recycling methods is expected to rise to 17% by 2030, becoming the most notable method of waste plastic recycling.

[0006] Thermal degradation method is a chemical recycling method that treats waste plastics as "crude oil" for refining, and uses the thermal instability of plastics to decompose plastics into chemicals in a degradation reactor. This method can directly separate high-value olefins and aromatic hydrocarbons from the degradation products. In addition, the degradation oil can be added to the cracking reactor as a cracking raw material to prepare low-carbon olefins. SUMMARY

[0007] The waste plastic degradation process is faced with the problems of complex raw materials and uneven molecular composition, and therefore the product changes dramatically under specific degradation conditions. Therefore, it is necessary to adjust the reaction conditions in real time according to the degradation products.

[0008] To solve the above technical problems, the application provides a method and device for continuously degrading plastics based on a Raman spectrometer.

[0009] One of the purposes of the application is to provide a method for continuously degrading plastics based on a Raman spectrometer, which comprises the step of adjusting the feed flow rate by monitoring the content ratio of alkanes and aromatic hydrocarbons in the plastic degradation products online using a Raman spectrometer.

[0010] According to the application, the method for continuously degrading plastics based on a Raman spectrometer comprises the following steps:

[0011] Step (1) continuously feeding plastics and water into a degradation reactor for degradation reaction to obtain degradation products;

[0012] Step (2) detecting the content ratio of alkanes and aromatic hydrocarbons in the degradation products in real time using a Raman spectrometer, and adjusting the feed flow rate of plastics and water according to the detected content ratio of alkanes and aromatic hydrocarbons;

[0013] Step (3) gas-liquid separation after cooling the degradation products;

[0014] Optionally, the step (3) is followed by step (4) of feeding the liquid phase components obtained after gas-liquid separation into a cracking reactor, adding sulfur compounds for thermal cracking reaction to obtain low-carbon olefin products.

[0015] According to the application, the water is preferably supercritical water. Supercritical water has good solubility for nonpolar hydrocarbons, can form a "water cage" to "wrap" polyolefin molecules therein, reduce the concentration of reaction intermediates, inhibit the formation of coking and reduce the yield of aromatic hydrocarbons. After mixing with hydrocarbons, the critical temperature and pressure of supercritical water change, and in the near critical region, supercritical water can already cause plastic to be degraded and oiled.

[0016] According to the application, in the method for continuously degrading plastics based on a Raman spectrometer:

[0017] The plastics include polyolefins, preferably at least one of polyethylene, polypropylene, and polybutene, but are not limited thereto;

[0018] The low-carbon olefins include at least one of ethylene, propylene, and butene, but are not limited thereto;

[0019] The sulfur-containing compound is at least one selected from inorganic sulfide, mercaptan, sulfur-containing aliphatic hydrocarbon, and sulfur-containing heterocyclic compound, preferably at least one selected from sodium sulfide, carbon disulfide, dimethyl disulfide, and thiophene.

[0020] According to the application, in the step (1) of the method for continuously degrading plastic,

[0021] The ratio of the feed rates of the plastic and water is 1:(2-5), preferably 1:(2.5-4);

[0022] The degradation reaction is carried out under the conditions of a pressure not lower than 20 MPa, a temperature not lower than 370 DEG C, and a reaction residence time of 0.5-5 h; preferably, the degradation reaction is carried out under the conditions of a pressure of 22-40 MPa, a temperature of 380-480 DEG C, and a reaction residence time of 1-2 h;

[0023] The temperature of the material at the inlet of the degradation reactor is not lower than 140 DEG C, preferably 150-250 DEG C.

[0024] According to the application, in the step (2) of the method for continuously degrading plastic, the content ratio of alkane and aromatic hydrocarbon in the degradation product is controlled to be (2.5-5):1, preferably (3.5-5):1, by adjusting the feed flow rates of the plastic and water. When the content ratio of alkane and aromatic hydrocarbon does not satisfy the above ratio range, the water inlet valve and the feed valve are adjusted until the above ratio is satisfied. If the content ratio of alkane and aromatic hydrocarbon is lower than the above ratio, the water inlet amount is increased and / or the feed amount is decreased; if the content ratio of alkane and aromatic hydrocarbon is higher than the above ratio, the feed amount is increased and / or the water inlet amount is decreased.

[0025] The degradation product obtained in the step (1) is analyzed in real time by using a Raman spectrometer, and the specific analysis method comprises the following steps: under the excitation light of 532 nm wavelength and 40 mW laser power, the Raman signal of the sample is collected by using a CCD, and the Raman signal of the sample is collected in the range of 1400-1510 cm -1 which is the characteristic peak of alkane, and 1550-1630 cm -1 which is the characteristic peak of aromatic hydrocarbon; the contents of alkane and aromatic hydrocarbon are calculated according to the characteristic peak signals. The alkane includes but is not limited to butane, pentane, and hexane; the aromatic hydrocarbon includes but is not limited to benzene, toluene, and xylene.

[0026] According to the application, in the step (3) of the method for continuously degrading plastic based on the Raman spectrometer, the cooling operation comprises the following steps: first, cooling to 360-370 DEG C to separate part of liquid water, and then cooling to below 350 DEG C to separate liquid-phase components and gaseous components containing at least one of hydrogen, methane, carbon monoxide, carbon dioxide, ethane, and propane.

[0027] According to the application, in the step (4) of the method for continuously degrading plastic based on the Raman spectrometer,

[0028] The conditions of the thermal cracking reaction are: pressure not higher than 0.5 MPa, temperature not lower than 700 DEG C, and reaction residence time of 0.1-0.5 s; preferably, the conditions of the thermal cracking reaction are: pressure of 0.01-0.4 MPa, temperature of 750-870 DEG C, and reaction residence time of 0.18-0.25 s.

[0029] The sulfur-containing compound is used in an amount of 0.001-0.02% of the total feed into the thermal cracking reaction.

[0030] The second object of the present application is to provide a plastic degradation device which uses the above-mentioned method for continuously degrading plastic based on a Raman spectrometer.

[0031] According to the present application, the plastic degradation device comprises a degradation reactor, a Raman spectrometer and a program control system connected in sequence, and optionally a cracking reactor connected to the degradation reactor.

[0032] The degradation reactor is one of a tubular reactor and a kettle reactor; the degradation reactor can be used by selecting a part of the convection section of an industrial cracking furnace as the degradation reactor according to actual needs;

[0033] The degradation reactor is connected to an extruder through a raw material conveying pipeline 1, and a valve 1 is arranged on the raw material conveying pipeline 1, and the valve 1 is connected to the program control system through a line; according to the present application, the plastic to be degraded is extruded after being heated to a molten state by the extruder, and is conveyed to the degradation reactor by the raw material conveying pipeline 1, and the program control system adjusts the feed flow of the plastic by controlling the valve 1 according to the alkane / aromatic hydrocarbon ratio obtained by the Raman spectrometer;

[0034] The degradation reactor is connected to a water pump through a raw material conveying pipeline 2, and a valve 2 is arranged on the raw material conveying pipeline 2, and the valve 2 is connected to the program control system through a line; according to the present application, water is conveyed to the degradation reactor by the water pump through the raw material conveying pipeline 2, and the program control system adjusts the feed flow of the water by controlling the valve 2 according to the alkane / aromatic hydrocarbon ratio obtained by the Raman spectrometer;

[0035] An optional high-temperature and high-pressure visual unit is arranged at the tail of the degradation reactor for observing the degradation reaction;

[0036] The Raman spectrometer is connected to the degradation product output pipeline of the degradation reactor through a line for testing the alkane and aromatic hydrocarbon in the degradation product; the program control system adjusts the feed flow of the plastic and / or water by controlling the valve 1 and the valve 2 according to the alkane / aromatic hydrocarbon ratio measured by the Raman spectrometer;

[0037] The cracking reactor is a tubular reactor, and in addition, the cracking reactor can be used according to actual needs, and a radiation section furnace tube in an industrial cracking furnace is selected as the cracking reactor.

[0038] The cracking reactor comprises a material inlet and a cracking product discharge pipeline, and the material inlet of the cracking reactor is connected with the degradation product outlet of the degradation reactor by a pipeline.

[0039] The third object of the present application is to provide the above-mentioned plastic degradation method based on the Raman spectrometer online monitoring or the above-mentioned plastic degradation device, which is applied in plastic degradation, and is especially suitable for the degradation of waste plastics to obtain a low-carbon olefin product rich in low-carbon olefins.

[0040] In the present application, the thermal degradation of plastics is preferably carried out in supercritical water, which has good mass transfer and heat transfer performance, and can protect the plastic macromolecules by relying on the "cage effect" of water molecules while reducing the hydrocarbon partial pressure, preventing the molecular chain from breaking too fast to form too much aromatic hydrocarbon or aggravate coking. This method can greatly reduce pollution, reduce carbon emissions, reduce production costs of enterprises and improve efficiency.

[0041] The Raman spectrometer is a method for studying molecular structure by using Raman scattering. Raman spectrum is very sensitive to molecular bonds, and each molecule has a corresponding Raman spectrum. Using the Raman spectrometer, the Raman spectrum can be quickly generated, and the chemical composition of the sample can be determined in real time.

[0042] Compared with the prior art, the process method for feedback control of waste plastic degradation product content provided by the present application has the following beneficial effects:

[0043] 1) The present application uses a Raman spectrometer to adjust the reaction conditions in real time according to the degradation products, which is suitable for degrading waste plastics with complex components, and can obtain degradation products with relatively stable components and contents, avoiding too large differences in degradation products caused by changes in raw materials;

[0044] 2) In the degradation method provided by the present application, the aromatic hydrocarbon content of the degradation product is low, which can be used as a raw material to produce low-carbon olefins by cracking, increasing the source of cracking raw materials and reducing the dependence on crude oil;

[0045] 3) The method for degrading plastics provided by the present application solves the problems of waste plastic resource waste and environmental pollution, and on this basis, provides a method for preparing low-carbon olefins from plastics, realizes the recycling of waste plastics, reduces pollution, and reduces carbon emissions. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The plastic degradation device used in the present application is shown in the schematic diagram of the present application;

[0047] Figure 2The plastic degradation device used in embodiment 3 of the present application is shown in the schematic diagram. DETAILED DESCRIPTION

[0048] It is necessary to point out that the following examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application, and some non-essential improvements and adjustments to the present application made by those skilled in the art according to the content of the present application still fall within the protection scope of the present application.

[0049] In addition, it should be noted that each specific technical feature described in the following detailed description can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present application will not describe various possible combinations again.

[0050] The calculation method of the content ratio of alkanes and aromatic hydrocarbons in the degradation product of the present application is as follows:

[0051] The Raman spectrometer (Bridgetek i-Raman laser spectrometer) test conditions: using CCD to collect the Raman signal of the sample under 532 nm wavelength excitation light and 40 mW laser power, and the Raman signal intensity of the sample is collected in the range of 1400-1510 cm -1 as the alkanes characteristic peak, and 1550-1630 cm -1 as the aromatic hydrocarbons characteristic peak. The content of alkanes and aromatic hydrocarbons is calculated according to the characteristic peak signal. According to the signal intensity of alkanes and aromatic hydrocarbons obtained by the Raman spectrometer, the commonly used calculation method or program software can be used for calculation, or the following method can be used for calculation.

[0052] Standard solution preparation and testing: taking pentane and toluene as examples, standard solutions with an alkanes to aromatic hydrocarbons ratio of 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 and 5:1 are prepared respectively. After scanning by the Raman spectrometer, the Raman spectrum curves of the standard solutions with different ratios are obtained. The Raman spectrum curves of the standard solutions are smoothed by using the Smooth function of the origin software, and the baseline is flattened by using the peak analysis function. The processed Raman spectrum presents the alkanes characteristic peak in the range of 1400-1510 cm -1 , and the Raman signal intensity is I A1 , I A2 , I A3 , I A4 , I A5 , I A6 , I A7 , I A8 , and the aromatic hydrocarbons characteristic peak in the range of 1550-1630 cm -1 , and the Raman signal intensity is I B1 , I B2, I B3 , I B4 , I B5 , I B6 , I B7 , I B8 . Wherein I A1 / I B1 ~I A8 / I B8 corresponding to the standard solution of the ratio of alkane to aromatic hydrocarbon is 1.5:1~5:1, that is, the ratio of the Raman signal intensity corresponding to the standard solution is obtained. In the above standard solution, the alkane is not limited to pentane, and one or a combination of butane, pentane, hexane can be used; the aromatic hydrocarbon is not limited to toluene, and one or a combination of benzene, toluene, xylene can be used, and the Raman signal intensity of the alkane to aromatic hydrocarbon ratio at different proportions obtained can be used to calculate the alkane to aromatic hydrocarbon ratio in the degradation product in the present application.

[0053] Test and calculation of the ratio of alkane to aromatic hydrocarbon in the example: the real-time analysis of the degradation product is carried out by using the Raman spectrometer, the Raman spectrum curve of the degradation product is obtained and smoothed, then the ratio of the alkane characteristic peak intensity to the aromatic hydrocarbon characteristic peak intensity of the processed Raman spectrum signal is calculated, and I A / I B is obtained, and the ratio of the alkane to aromatic hydrocarbon concentration is calculated by using the mathematical interpolation method. For example: I A4 / I B4 is 2.9, I A5 / I B5 is 3.3, and the test result I A / I B is 3.2, then the ratio of the alkane to aromatic hydrocarbon (X) is: (3.3-3.2) / (3-X)=(3.2-2.9) / (X-2.5), and the calculation can obtain X as 2.875.

[0054] The calculation method of the liquid yield in the degradation product of the present application:

[0055] The liquid components in the degradation product include but are not limited to C5~C32 alkane and C6~C22 aromatic hydrocarbon and the like, and the calculation method of the liquid yield is as follows:

[0056] Degradation product liquid yield (%) = Degradation reactor outlet liquid weight / Plastic feed weight x 100%

[0057] Test and calculation of the triene yield in the cracking product of the present application

[0058] “Alkene” includes ethylene, propylene, butadiene, the pyrolysis reaction products are analyzed by gas chromatograph (Agilent G2070AA chemical workstation A.10.01), and the gas yield, ethylene yield, propylene yield and butadiene yield in the pyrolysis products are calculated. The specific calculation method is as follows:

[0059] Gas yield test and calculation method: the product is cooled to below 5℃, the product gas volume is measured by a flow meter, the product gas composition is analyzed by gas chromatography to obtain the gas density, and the gas yield = gas volume x gas density / plastic feed weight;

[0060] Ethylene yield test and calculation method: the ethylene content in the product gas is analyzed by gas chromatography, and the ethylene yield = gas yield x ethylene content;

[0061] Propylene yield test and calculation method: the propylene content in the product gas is analyzed by gas chromatography, and the propylene yield = gas yield x propylene content;

[0062] Butadiene yield test and calculation method: the butadiene content in the product gas is analyzed by gas chromatography, and the butadiene yield = gas yield x butadiene content.

[0063] The plastics used in the following examples and comparative examples are polyethylene PE and polypropylene PP powders, and the GPC test results are shown in Table 1:

[0064] Table 1 GPC test results of PE and PP powders

[0065] Mn Mw Mz Mw / Mn PE powder 28474 151504 660649 5.32 PP powder 49947 397084 1328004 7.95

[0066] Example 1

[0067] The following will be described Figure 1 The plastic degradation device and the method for continuously degrading plastics used in Example 1 are described.

[0068] As Figure 1 shown, the plastic degradation device used includes a degradation reactor, a Raman spectrometer, a program control system, and a pyrolysis reactor. The Raman spectrometer is connected to the program control system and connected to the degradation product outlet of the degradation reactor through a line, and the degradation product outlet of the degradation reactor is connected to the pyrolysis reactor through a pipeline. The degradation reactor is a tubular reactor, and the degradation reactor is connected to a plastic extruder through a plastic conveying pipeline, and a valve 1 is arranged on the plastic conveying pipeline, and the valve 1 is connected to the program control system through a line; the degradation reactor is connected to a water pump through a water conveying pipeline, and a valve 2 is arranged on the water conveying pipeline, and the valve 2 is connected to the program control system through a line, and the valves 1 and 2 connected to the program control system are arranged on the pipeline to regulate the input amount of plastics and water in the continuous degradation reaction process according to the ratio of alkanes and arenes in the degradation reaction process.

[0069] The method for continuous degradation of PE plastic using the above-mentioned plastic degradation device includes:

[0070] (1) A screw extruder is used to heat the plastic PE to a molten state and send it into the degradation reactor. A water pump is used to send water into the degradation reactor. The plastic undergoes a degradation reaction under high temperature and high pressure conditions in the degradation reactor to obtain degradation products.

[0071] (2) The content ratio of alkane and aromatic hydrocarbons in the degradation products was detected in real time using a Raman spectrometer, and the flow rate of plastic and water was adjusted according to the detected content ratio of alkane and aromatic hydrocarbons.

[0072] (3) After cooling the degradation products, gas-liquid separation is performed. First, the temperature is lowered to below 370℃ to separate some liquid water. Then, the temperature is lowered to below 350℃ to separate liquid phase components and gaseous components rich in hydrogen, methane, carbon monoxide, carbon dioxide, ethane and propane.

[0073] (4) The liquid phase component obtained after gas-liquid separation is sent to the pyrolysis reactor, and sulfur-containing compounds are added to carry out thermal pyrolysis reaction to obtain a product rich in low-carbon olefins.

[0074] The operating conditions and analytical results of the pyrolysis products in steps (1) to (4) above are shown in Table 2.

[0075] Example 2

[0076] The degradation apparatus and method for degrading plastics described in Example 1 were used, with the difference that after continuous degradation of PE plastic, the plastic to be degraded was changed to a mixture of PE and PP (PE to PP mass ratio of 1:1). Under the operating conditions of Example 1, the ratio of alkane to aromatic hydrocarbon content in the degradation reaction products decreased to 1.77, indicating a high aromatic hydrocarbon content, which was unsuitable as a pyrolysis feedstock for the preparation of low-carbon olefins. The water inlet flow was adjusted by a programmable control system based on feedback from a Raman spectrometer. Specific operating conditions are shown in Table 2 (Example 2), increasing the alkane to aromatic hydrocarbon ratio to 3.67, thus reducing the aromatic hydrocarbon content and allowing continued use as a pyrolysis feedstock for the preparation of low-carbon olefins. The analysis results of the pyrolysis products after pyrolysis are shown in Table 2.

[0077] Example 3

[0078] The following is combined Figure 2 This describes the plastic degradation device and the method for continuous plastic degradation used in Example 3.

[0079] like Figure 2As shown, the plastic degradation device used includes a degradation reactor, a Raman spectrometer, and a program control system. The Raman spectrometer is connected to the program control system and connected to the degradation product outlet of the degradation reactor through a line. The degradation reactor is a tubular reactor, and the degradation reactor is connected to a plastic extruder through a plastic conveying pipeline. A valve 1 is arranged on the plastic conveying pipeline, and the valve 1 is connected to the program control system through a line. The degradation reactor is connected to a water pump through a water conveying pipeline. A valve 2 is arranged on the water conveying pipeline, and the valve 2 is connected to the program control system through a line. Valves 1 and 2 connected to the program control system are arranged on the pipeline to regulate the input amount of plastic and water in the continuous degradation reaction process according to the ratio of alkanes and aromatic hydrocarbons in the degradation reaction process.

[0080] The method for continuously degrading plastic PE is specifically described by using the above plastic degradation device, which comprises the following steps:

[0081] (1) The plastic PE is heated to a molten state by using a screw extruder and is fed into a degradation reactor. Water is fed into the degradation reactor by a water pump. The plastic in the degradation reactor undergoes a degradation reaction under high temperature and high pressure conditions to obtain a degradation product;

[0082] (2) The content ratio of alkanes and aromatic hydrocarbons in the degradation product is detected in real time by using a Raman spectrometer. The flow rates of plastic and water are adjusted according to the detected content ratio of alkanes and aromatic hydrocarbons;

[0083] (3) The degradation product is cooled and gas-liquid separated. After being cooled to below 370°C, part of the liquid water is separated. Then, after being cooled to below 350°C, a liquid phase component and a gas component rich in hydrogen, methane, carbon monoxide, carbon dioxide, ethane, and propane are separated.

[0084] The operation conditions in the above steps (1) to (3) and the analysis results of the degradation product are shown in Table 2.

[0085] Comparative Example 1

[0086] According to the degradation device and the method for degrading plastic in the comparative example 2, except that the content ratio of alkanes and aromatic hydrocarbons in the degradation product is not detected by using a Raman spectrometer in the degradation reaction process, the original feed rates of plastic and water are maintained.

[0087] Comparative Example 2

[0088] According to the degradation device and the method for degrading plastic in the comparative example 3, except that the content ratio of alkanes and aromatic hydrocarbons in the degradation product is not detected by using a Raman spectrometer in the degradation reaction process, the original feed rates of plastic and water are maintained.

[0089] The operation conditions in the comparative example 2 and the analysis results of the degradation product are shown in Table 2. It can be seen that the oil yield in the degradation product is low.

[0090] Table 2 Change of content of degradation products when raw material and reaction condition change

[0091]

[0092] Note: " / " in Table 2 means that the test is not carried out

[0093] From the test results in Table 2, it can be seen that in Examples 1-3, by regulating the feeding rate of plastics and water within a certain content ratio range of alkanes and aromatic hydrocarbons, the yield of liquid components in the degradation products and the yield of low-carbon olefins after cracking can be improved, especially in Examples 1-2, the degradation reactor is connected in series with the cracking reactor, low-carbon olefins can be prepared from the degradation products, and when feedback adjustment is made by using a Raman spectrometer, the influence of changes in the feeding composition can be minimized, the relative stability of the cracking raw material is ensured, and the coking of the cracking furnace is inhibited. In Comparative Examples 1 and 2, the feeding rate is not adjusted according to the content ratio of alkanes and aromatic hydrocarbons, and the yield of oil in the degradation products and the yield of low-carbon olefins after cracking are both low, which is not suitable for preparing low-carbon olefins from cracking raw materials.

[0094] It can be seen that by using a Raman spectrometer to regulate the reaction conditions in real time according to the components of the degradation products, relatively stable degradation products in terms of components and content can be obtained, the degradation product difference caused by changes in the raw material is avoided, and the problems of waste and old plastic resource waste and environmental pollution can be effectively solved.

Claims

1. A method for continuous degradation of plastics based on Raman spectroscopy, comprising the step of using a Raman spectrometer to monitor the content ratio of alkane to aromatic hydrocarbons in the plastic degradation products online to regulate the feed flow rate; by adjusting the feed flow rate of plastic and water, the content ratio of alkane to aromatic hydrocarbons in the degradation products is controlled at (2.5~5):1; if the content ratio of alkane to aromatic hydrocarbons is lower than the above ratio, the water feed rate is increased and / or the plastic feed rate is decreased; if the content ratio of alkane to aromatic hydrocarbons is higher than the above ratio, the plastic feed rate is increased and / or the water feed rate is decreased.

2. The method according to claim 1, characterized in that, The method includes the following steps: Step (1) Plastic and water are continuously fed into the degradation reactor to carry out the degradation reaction and obtain degradation products; Step (2) Use a Raman spectrometer to detect the ratio of alkane to aromatic hydrocarbon content in the degradation products in real time, and adjust the feed flow rate of plastic and water according to the detected ratio of alkane to aromatic hydrocarbon content. Step (3) involves cooling the degradation products and then separating them into gas and liquid phases; Optionally, step (3) is followed by step (4): the liquid phase component obtained after gas-liquid separation is fed into a pyrolysis reactor, sulfur-containing compounds are added to carry out a thermal pyrolysis reaction, and a product rich in low-carbon olefins is obtained.

3. The method according to claim 2, characterized in that, The plastic includes polyolefins; and / or, The low-carbon olefins include at least one of ethylene, propylene, and butene; and / or, The sulfur-containing compound is selected from at least one of inorganic sulfides, thiols, sulfur-containing aliphatic hydrocarbons, and sulfur-containing heterocyclic compounds.

4. The method according to claim 3, characterized in that, The plastic includes at least one of polyethylene, polypropylene, and polybutene; and / or, The sulfur-containing compound is selected from at least one of sodium sulfide, carbon disulfide, dimethyl disulfide, and thiophene.

5. The method according to claim 2, characterized in that, In step (1): The ratio of the feed rates of the plastic to the water is 1:(2~5); and / or, The degradation reaction conditions are: pressure not lower than 20 MPa, temperature not lower than 370℃, and reaction residence time of 0.5~5 h; and / or, The temperature of the material entering the degradation reactor should not be lower than 140℃.

6. The method according to claim 5, characterized in that, In step (1): The feed rate ratio of the plastic to the water is 1:(2.5~4); and / or, The degradation reaction conditions are: pressure 22~40MPa, temperature 380~480℃, and reaction residence time 1~2h; and / or, The temperature of the material at the inlet of the degradation reactor is 150~250℃.

7. The method according to claim 2, characterized in that, In step (2), the ratio of alkane to aromatic hydrocarbon content in the degradation products is controlled at (3.5~5):1 by adjusting the feed flow rate of plastic and water.

8. The method according to claim 2, characterized in that, The cooling operation in step (3) includes: first cooling to 360~370℃ to separate a portion of liquid water, and then cooling to below 350℃ to separate liquid phase components and gaseous components containing at least one of hydrogen, methane, carbon monoxide, carbon dioxide, ethane, and propane.

9. The method according to claim 2, characterized in that, In step (4): The conditions for the thermal decomposition reaction are: pressure not exceeding 0.5 MPa, temperature not lower than 700℃, and reaction residence time of 0.1~0.5 s; and / or, The amount of the sulfur-containing compound used, by mass percentage, is 0.001 to 0.02% of the total feed into the thermal decomposition reaction.

10. The method according to claim 9, characterized in that, In step (4): The conditions for the thermal decomposition reaction are: pressure of 0.01~0.4MPa, temperature of 750~870℃, and reaction residence time of 0.18~0.25s.

11. The method according to any one of claims 1 to 10, characterized in that, The plastic degradation apparatus for continuous degradation of plastics using the method described herein includes a degradation reactor, a Raman spectrometer and a programmable control system connected in sequence, and optionally a pyrolysis reactor connected to the degradation reactor.

12. The method according to claim 11, characterized in that, The degradation reactor is one of a tubular reactor or a batch reactor; and / or, The degradation reactor is connected to the extruder via a raw material conveying pipeline 1. A valve is installed on the raw material conveying pipeline 1, and the valve is connected to a programmable control system via a wiring connection; and / or, The degradation reactor is connected to a water pump via a raw material delivery pipeline 2. A valve is installed on the raw material delivery pipeline 2, and the valve is connected to a programmable control system via a wiring connection; and / or, The Raman spectrometer is connected via wiring to the degradation product output pipeline of the degradation reactor for testing alkanes and aromatics in the degradation products; and / or, The pyrolysis reactor is a tubular reactor; and / or, The pyrolysis reactor includes a material inlet and a pyrolysis product discharge pipeline. The material inlet of the pyrolysis reactor is connected to the degradation product outlet of the degradation reactor by the pipeline.

13. The application of the plastic degradation method based on online monitoring by Raman spectroscopy as described in any one of claims 1 to 12 in plastic degradation.

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