Fire spraying treatment method for thermal oxidation degradation of farmland polyethylene residual film and treatment device of fire spraying treatment method

Abstract

The invention discloses a flaming treatment method and device for thermal oxidation degradation of farmland polyethylene residual films, belongs to the technical field of farmland residual film degradation, and aims to solve the problem that residual film fragments which are small in size and time-consuming and labor-consuming to pick up manually are difficult to recover and degrade. The method comprises the steps of plowing, film screening and flaming treatment, and the previous two steps are repeated until the residual film turned out of the soil is less than 0.001% of the land area, so that the flaming treatment is completed. The device comprises a flame gun and a fuel supply system which are connected with each other, the flame gun is connected with the fuel supply system through an anti-explosion hose, and a fuel valve and a flame adjusting knob are sequentially arranged on the anti-explosion hose. According to the invention, the residual films with different sizes are classified and subjected to fire spraying treatment, so that the PE residual films can be quickly degraded, the release amount of volatile gas-phase products can be minimized, and the problem of new atmospheric pollutants caused by treatment of the soil residual films is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of farmland residual film degradation, and particularly relates to a flame spraying treatment method and a treatment device for thermal oxygen degradation of farmland polyethylene residual film. Background Art

[0002] Since the successful trial production of agricultural plastic mulch in my country in 1979, it has become the fourth largest agricultural production material after fertilizers, seeds and pesticides in the modern intensive agricultural production system. It has the advantages of regulating crop growth cycle, reducing chemical input, optimizing water-saving irrigation measures, and preventing pests and diseases. Polyethylene (PE) has always been the preferred substrate for the production of agricultural plastic mulch and plays an irreplaceable role in agricultural production. However, after several growing seasons, due to its difficulty in degradation, the residual mulch in the farmland will have various effects on the soil and crops, and the environmental risks caused by this have also received increasing attention. Improving the recycling rate of used PE mulch has always been an effective strategy to prevent and control residual film pollution. At present, the recycling rate of waste mulch in China is generally stable at 80% to 85%, which greatly alleviates the environmental risks brought by residual mulch. However, after large-scale centralized recycling, a small amount of residual film fragments still exist in the farmland. Under the combined effect of environmental factors (mechanical weathering and ultraviolet radiation), they continue to break and accumulate, and even become an important source of microplastics and nanoplastics, seriously threatening the health of the soil ecosystem.

[0003] The recycling of these small pieces of residual film is extremely challenging. How to reduce these smaller pieces of residual film that are difficult to pick up manually is an important issue that deserves attention.

[0004] Studies have shown that polyolefins with aliphatic structures, including PE, are more suitable for incineration than polymers with aromatic structures. The article "Theoretical studies on bond dissociation enthalpies for model compounds of typical plastic polymers" was published in Volume 167 of Environmental Science and Engineering in 2018. PE has a high carbon content and its calorific value is more than 1 times that of aromatic polymers such as polyethylene terephthalate (PET) and polyester (PES). The decomposition of its chain structure requires less energy than the decomposition of aromatic rings. The article "Thermal degradation of polymer and polymer composites" was published in Volume 9 of Handbook of Environmental Degradation of Materials in 2018. The main chain of PE is composed of saturated carbon chain structural units -CH2-CH2-. It is not easy to form secondary free radicals with poor stability during heating. Even if oxidation reaction occurs, the generated peroxide group has high thermal stability and is not easy to derive complex evolution products. The article "Analysis of volatile organic compounds produced during incineration of non-degradable and biodegradable plastics" was published in Volume 303 of Chemosphere in 2022. The volatile organic compounds (VOC) released by PE during combustion are only about one-fiftieth of those of aromatic polymers. The article "Pollution characteristics and health risk assessment of volatile organic compounds emitted from different plastic solid waste recycling workshops" was published in Volume 77 of Environment International in 2015. The VOC release of PE waste during the melting recycling process is only one-hundredth of that of polystyrene (PS) waste. The cumulative non-carcinogenic health risk index HI of the former is less than 1, and the risk can be considered negligible.

[0005] It is well known that the incineration characteristics of polymers and the formation of volatiles during incineration depend on their chemical structure, thermal oxidation degradation mechanism and incineration reaction conditions. The incineration process of thermoplastic polymers can generally be divided into four stages: softening, melting, thermal decomposition and combustion.

[0006] In the melting stage, the polymer transforms from solid phase to liquid phase, with changes in physical properties being the main factor. At higher reaction temperatures, when the heat of reaction is higher than the energy required for chain breakage, the polymer begins to decompose and produce hydroxyl, carbonyl, peroxide or hydroperoxide, etc. These small molecular compounds further react with oxygen to finally produce CO2 and H2O. Under aerobic conditions, the melting point of PE is 115℃–124℃, and it has good thermal stability below 350℃. The intense thermal decomposition temperature range only occurs between 460℃–478℃. The main evolution products in the thermal oxidative degradation process are hydrocarbon oligomers produced by the transfer of hydrogen to different positions along the polymer chain caused by the rupture of the main chain, including double bond compounds such as ethylene and propylene, and a series of low molecular weight alkanes, which will not release toxic and harmful gases such as HCl, SO2, CO, and Cl2.

[0007] In summary, how to find a simple and effective way to promote the rapid degradation of PE residual film in farmland, that is, based on the thermal oxidative degradation characteristics of PE and taking into account the controllable level of environmental risk caused by volatile thermal oxidative degradation products, has become a technical problem that researchers urgently need to solve. Summary of the invention

[0008] The purpose of the present invention is to provide a method and device for treating farmland PE residual film by thermal oxidation, so as to solve the problem that the residual film fragments are small in size and time-consuming and laborious to pick up manually, and are difficult to recycle and degrade.

[0009] In order to solve the above problems, the technical solution of the present invention is:

[0010] A method for treating farmland polyethylene residual film by thermal oxidation degradation by flame spraying, the method is divided into the following steps:

[0011] S1, turning over the soil and screening the membrane;

[0012] In the farmland area to be treated, use any agricultural implement to turn the soil so that the residual film is out of the soil and the surface area of ​​the residual film exceeds 25cm 2 The residual film is picked up manually when turning the soil, less than or equal to 25cm 2 The definition of residual membrane fragments;

[0013] S2, flame treatment;

[0014] Use a flame treatment device with temperature control and timing to treat the residual film fragments on the soil surface with flame treatment, and make sure that the total flame radiation area covers all the residual film fragments. When the flame temperature is controlled at 238℃±5℃, the flame time is between 50s±5s or 90s±5s. When the flame temperature is controlled at 337℃±5℃, the flame time is between 50s±5s or 90s±5s.

[0015] S3, repeat S1 and S2;

[0016] After the residual film is turned out of the soil, the soil turning and film screening process of S1 is repeated to turn out the residual film fragments in the soil again, and the flame spraying process of S2 is performed;

[0017] The above process is repeated for multiple rounds until the residual film fragments in the soil are less than 0.001% of the land area, and the flame treatment is completed.

[0018] Furthermore, S1 also includes a film screening step, specifically, after the residual film is turned out of the soil, the residual film on the soil surface is roughly screened using agricultural tools, which can reduce the number of cyclic operations in S3.

[0019] The flame-spraying device for thermal oxidation degradation of farmland polyethylene residual film used in the above method comprises a flame-spraying gun and a fuel supply system connected to each other; the flame-spraying gun and the fuel supply system are connected by an explosion-proof hose, on which a fuel valve and a flame regulating knob are arranged in sequence.

[0020] Furthermore, multiple groups of the flame treatment devices are evenly mounted on a trolley, a front end of the trolley bracket is provided with walking wheels, and a rear end of the trolley is provided with a floor-mounted bracket.

[0021] The beneficial effects of the present invention are as follows:

[0022] (1) The present invention classifies the residual films with different surface areas into small fragments (<4 cm 2 ) and large fragments (4–25 cm 2 ) size categories, which account for 50% and 32.3% of the total residual film in dry farmland respectively. After the flame treatment of these two size categories, most of the residual film can be degraded, and some of the residual film larger than 25cm that remain in the farmland and have not been recycled can be degraded. 2 The residual film can be picked up manually during the process of tilling the soil. It can be basically determined that the visible residual film in the farmland treated by this method has basically all undergone thermal oxidative degradation.

[0023] (2) The present invention utilizes the characteristics of PE, which has a single molecular structure, good thermal stability, and easy main chain scission when heated; finds out the narrow temperature and time range in which PE violent thermal decomposition occurs, and verifies that the volatile thermal oxidation degradation products are relatively concentrated in this temperature range, resulting in a low level of environmental risk. After the residual film of different size categories was treated with flame blasting, the mass loss was between 9.39% and 15.35%; the results of scanning electron microscope-energy spectrum analysis showed that a large number of pits, cracks and obvious rough appearance appeared on the surface of the residue, and the oxygen-carbon atomic ratio (O / C) increased significantly; Fourier transform infrared spectroscopy analysis identified the characteristic absorption of oxygen-containing functional groups (hydroxyl, keto carbonyl) and double bonds (ethylene bonds, internal double bonds); X-ray diffraction results showed that the flame blasting did not change the crystal morphology of the polymer, but increased the crystallinity; the above results all indicate that the flame blasting promotes the depolymerization of the long-chain structure of PE molecules, accompanied by the consumption of carbon and the accumulation of oxygen, to generate low molecular weight degradation products, the weight of the PE residual film is reduced, and the microscopic morphology is significantly deteriorated. In addition, compared with the lower blasting temperature treatment, a higher oxygen bond index and a smaller molecular weight and crystallinity were observed under the higher blasting temperature treatment, indicating an increase in the degree of degradation of the PE residual film.

[0024] (3) The present invention targets the PE fragments that remain in farmland after large-scale centralized recycling and are often ignored. Appropriate flame treatment is adopted to change the microscopic morphology, surface chemical functional groups, crystallinity and molecular weight of the residual film in a short period of time, promote the thermal oxidation process of the residual film, and solve the problem of the accumulation of difficult-to-degrade residual film in farmland; the flame treatment of residual films of different sizes is classified, which not only helps the rapid degradation of PE residual film, but also minimizes the release of volatile gas products, thereby preventing the treatment of soil residual film from causing new air pollution problems; and in order to match the treatment method, a corresponding treatment device is developed. In the treatment of residual film in farmland, as long as the operator cooperates with the existing agricultural tools, the residual film treatment can be achieved and the soil state can be restored, which is highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of a flame treatment device for thermal oxygen degradation of PE residual film in farmland;

[0026] Figure 2 The microscopic morphology and EDS analysis of the PE residual film (UPF) before blasting and the solid residue (SR) after blasting;

[0027] Figure 3 Infrared spectra (a) and (b) of PE residual film (UPF) before and after exposure to flame blasting and the corresponding characteristic functional group indices (c), (d), (e) and (f);

[0028] Figure 4X-ray diffraction patterns (a) and (b) of PE residual film (UPF) before and after exposure to flame blasting, as well as the change in crystallinity (c);

[0029] Figure 5 3D FTIR spectra (a), 2D FTIR spectra (b) of volatile gas phase products when PE residual film undergoes thermal oxidation degradation in the range of (30-600)℃, TG-FTIR curve fitting (c) and corresponding volatile gas phase product release (d) at characteristic temperature;

[0030] The accompanying drawings are marked as follows: 1. trolley; 2. bracket; 3. flame adjustment knob; 4. flamethrower; 5. fuel valve; 6. explosion-proof hose. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed but is merely representative of selected embodiments of the present invention.

[0033] Example 1

[0034] A method for treating farmland polyethylene residual film by thermal oxidation degradation by flame spraying, the method is divided into the following steps:

[0035] S1, soil screen

[0036] In the farmland area to be treated, use any agricultural implement to turn the soil so that the residual film is out of the soil and the surface area of ​​the residual film exceeds 25cm 2 The residual film is picked up manually when turning the soil, less than or equal to 25cm 2 is defined as residual membrane fragments.

[0037] S2. Flame treatment

[0038] Use a flame treatment device with temperature control and timing to carry out flame treatment on the residual film fragments on the soil surface. Note that the total flame radiation area covers all residual film fragment areas; when the flame temperature is controlled at 238℃±5℃, the flame time is between 50s±5s or 90s±5s; when the flame temperature is controlled at 337℃±5℃, the flame time is between 50s±5s or 90s±5s.

[0039] S3, repeat S1 and S2

[0040] After the residual film in the soil is processed, the soil turning and film screening step S1 is repeated to turn the residual film in the soil again, and then the flame spraying treatment S2 is performed;

[0041] The above process is repeated for multiple rounds until the residual film on the soil is less than 0.001% of the land area, and the flame treatment is completed.

[0042] like Figure 1 As shown, the above-mentioned flame-spraying treatment device for thermal oxidation degradation of PE residual film in farmland includes a flame-spraying gun 4 and a fuel supply system connected to each other, and the fuel supply system is generally a liquefied gas tank; the flame-spraying gun 4 and the fuel supply system are connected through an explosion-proof hose 6, and the explosion-proof hose 6 is provided with a fuel valve 5 and a flame adjustment knob 3 in sequence.

[0043] When in use, multiple groups of the flame treatment device are evenly set up on a trolley 1, the front end of the trolley 1 bracket is provided with a walking wheel, and the rear end of the trolley 1 is provided with a floor-standing bracket 2. In practice, multiple groups of explosion-proof hoses 6 are connected to the liquefied gas tank through a four-way valve.

[0044] In order to verify the effect of the present invention, the whole process of flame spraying was simulated in a laboratory environment, and the corresponding test data were collected. The specific process of the simulation test is as follows:

[0045] The experiment was conducted in a wide and flat open space.

[0046] The PE residual film raw materials used in the experiment came from farmland. The PE waste mulch film used for potato planting in the previous year was collected, thoroughly washed with distilled water, and then naturally dried in a dark place for use.

[0047] The flame blasting device used in the test was the flame blasting device of the above structure.

[0048] Experimental design L8(2 7 ) orthogonal table, setting three factors: flame temperature, flame duration and residual film size, each factor includes two levels.

[0049] Based on the polymer characteristics of PE, the two levels of flame spraying temperature were set at 238°C and 337°C respectively. During the flame spraying, an infrared thermometer (F62MAX+, Fluke) was used to measure the flame spraying temperature in real time, and each level was represented by the average value of 30 measurements.

[0050] The two levels of flame spraying time are set to 50s and 90s respectively, ensuring that the PE residual film can be observed to undergo obvious morphological changes under the set flame spraying temperature and time, showing the characteristics of melting and transparency.

[0051] The two levels of residual film size are set to small fragments (<4cm 2) and large fragments (4–25 cm 2 ), these two sizes of residual film fragments accounted for 50% and 32.3% of the total residual film in dryland farmland respectively.

[0052] The orthogonal experimental design is shown in Table 1. 7 ) orthogonal table was used for the flame test, and the eight solid residues obtained were numbered SR1–SR8 in sequence. The residue characterization data were shown as the average value of three measurements.

[0053] Table 1 Based on L8(2 7 ) Orthogonal experimental design of flame treatment scheme

[0054]

[0055] In order to facilitate the test operation and collect the test samples after the flame spraying, all the flame spraying test processes were carried out on a clean and stable high temperature resistant medium and thick steel plate (120cm×40cm×0.4cm), and the test was carried out according to the orthogonal table design scheme. The whole test process is described as follows:

[0056] Before the flame spray test, key hazardous source locations such as the liquefied gas tank, each connection of the explosion-proof hose 6, the flame spray gun 4, the fuel valve 5 and the flame adjustment knob 3 are inspected.

[0057] During the flame test, the fuel valve 5, the four-way valve and the flame adjustment knob 3 are opened in sequence, and the long-handled electronic igniter is used to ignite. The temperature can be controlled by the flame adjustment knob 3. Then the trolley is slowly moved, and the time is measured when the flame begins to contact the PE fragments. During the 50s and 90s flame time, the temperature is measured approximately every 1.5s and 3.0s respectively; the trolley is moved at a speed of 0.2m·s -1 The flamethrower moved back and forth at a speed of 1.5° and a metronome was used to maintain this speed. During the whole process, the flamethrower head was located 10 cm from the surface of the steel plate and at 40° to the horizontal direction.

[0058] After the flame spraying test, the four-way valve is closed in sequence, and the fuel valve 5 and the flame adjustment knob 3 are closed after the gas in the explosion-proof hose 6 is burned out. The solid residue obtained after the flame spraying is collected.

[0059] Necessary safety measures are taken during the entire test process. For example, the ignition personnel should maintain a certain safe distance from the flamethrower; the liquefied gas tank should be kept away from direct sunlight and kept at a safe distance of more than 5m from the medium and thick steel plate; fire-fighting equipment (foam fire extinguisher) should be equipped; after each flamethrower, the liquefied gas tank and flamethrower should be placed in a safe place.

[0060] 1. Gel Permeation Chromatography (GPC) test of polyethylene film residue (UPF) and solid residue (SR) after fire spraying.

[0061] Different flame blasting treatments have obvious effects on the thermal oxidation degradation of PE film residues. The weight average molecular weight (M w ), number average molecular weight (M n ) and peak molecular weight (M p ) all showed different degrees of decrease, as shown in Table 2:

[0062] Table 2 Gel permeation chromatography (GPC) test results of polyethylene residual film (UPF) and solid residue (SR) after fire spraying.

[0063]

[0064] In the table, a: weight average molecular weight; b: number average molecular weight; c: peak molecular weight; d: polymer polydispersity index.

[0065] It can be seen that after the PE residual film (UPF) was treated with flame spraying for 50s and 90s at 238℃ and 337℃, the weight average molecular weight, number average molecular weight and peak molecular weight were significantly reduced. Moreover, when the flame spraying temperature was 337℃, the 8 kinds of solid residues M w The value is smaller than that at 238℃, while M n The values ​​show an opposite trend, which indicates an increase in the degree of molecular chain fragmentation at higher flame temperatures.

[0066] 2. Microscopic morphology observation and EDS analysis test of polyethylene residual film (UPF) and solid residue (SR).

[0067] The solid residues obtained from the flame test were observed to have undergone significant changes in their surface microstructures, with wrinkles, cracks, holes and small particles appearing, and the surface roughness increased significantly, such as Figure 2 As shown, where:

[0068] (a)-(h) are the morphological characteristics of eight kinds of solid residues;

[0069] (i) is the morphological characteristics of the untreated PE residual film;

[0070] (j) is EDS scan and oxygen / carbon atomic ratio;

[0071] (k) and (l) are the EDS scanning results of carbon and oxygen elements, respectively.

[0072] In addition, by Figure 2(j) It can be seen that the flame treatment did not change the types of residual film elements, but increased the oxygen-carbon atomic ratio (O / C) from 0.041±0.009 to 0.086±0.016-0.147±0.011. The introduction of oxygen elements is conducive to the formation of active oxidative groups such as carbonyl, hydroxyl and carboxyl, which is an important sign of aging of PE materials. This also confirms that the method of the present invention promotes the thermal oxidation degradation process of farmland PE residual film in a short time.

[0073] 3. FTIR analysis of polyethylene residual film (UPF) and solid residue (SR).

[0074] The PE film residue before and after the fire is 3600–400 cm -1 The changes of surface functional groups within the range are as follows Figure 3 As shown:

[0075] Figures (a) and (b) show the infrared spectra of PE residual film (UPF) before and after exposure to flame treatment.

[0076] It can be seen that in addition to the unique absorption band of PE (2918cm -1 , 2849cm -1 , 1465cm -1 and 722cm -1 ), all solid residue samples were within the range of 3550–3350 cm -1 , 1750–1600cm -1 and 950–850cm -1 New characteristic absorptions appeared in the region, which were attributed to the stretching vibrations of -OH, -C=O- and -CH=CH-, respectively, which were related to the formation of γ-lactone and carboxylic acid and the oxidative chain scission in the amorphous region of the polymer.

[0077] The thermal oxidative degradation of polyolefins is a long-chain breakage process driven by both elevated temperature and oxygen. This process further triggers crosslinking and oxidation reactions, shortening the chain segments while forming oxygen-containing groups and double bonds. Therefore, the corresponding functional group index can be used as a quantitative reference for evaluating the degree of PE degradation.

[0078] In the figure, (c), (d), (e) and (f) are hydroxyl / hydroxyperoxide (HHI), ketocarbonyl (KCI), vinyl (VBI) and internal double bond index (IDBI), respectively.

[0079] It can be seen that the ketone carbonyl index of the eight residues after the fire spraying ranged from 0.135±0.019 to 0.286±0.011, which was (6.7–14.3) times that before the fire spraying. No hydroxyl, vinyl and internal double bonds were identified in the infrared spectrum of the PE residual film before the fire spraying, indicating that even after a growing season, the PE residual film in the farmland had hardly aged, while the above-mentioned characteristic functional groups appeared in the residues after the fire spraying, and the corresponding bond index ranged from 0.209±0.019 to 0.341±0.017, 0.082±0.011 to 0.152±0.021 and 0.092±0.012 to 0.182±0.019, respectively. In addition, compared with the 238°C blasting temperature, the oxygen bond index (HHI, KCI) of the residue increased significantly at the 337°C blasting temperature. On the one hand, the high temperature generated by the blasting promoted the penetration of oxygen into the PE residual film; on the other hand, highly active free radicals were formed after the main chain of the PE molecule was broken, which increased the reaction sites of the polar group and introduced more oxygen-containing functional groups. The significant increase in the double bond index (VBI, IDBI) significantly accelerated the thermal oxidation degradation process of the surface PE residual film, triggering the cross-linking and reorganization of the PE molecular chain segments.

[0080] The above results further confirmed that different flame blasting treatments caused irreversible thermal oxidative degradation of PE residual film.

[0081] 4. X-ray diffraction analysis test of polyethylene residual film (UPF) and solid residue (SR).

[0082] X-ray diffraction analysis is a reliable method to determine the crystallization pattern of polymers and infer their main degradation mechanisms. X-ray diffraction patterns of PE residual film (UPF) before and after exposure to flame blast (a), (b) and crystallinity change (c) Figure 4 shown.

[0083] according to Figure 4 From the XRD spectra in (a) and (b), it can be determined that the two basic characteristic peaks at 2θ≈21.8° and 24.0° did not shift after the flame blasting treatment. They are the diffraction peaks of the (110) and (200) crystal planes of the PE crystals, respectively. The peak positions of the above diffraction peaks remain almost unchanged, which indicates that the flame blasting treatment has no effect on the orientation of the PE residual film matrix, so that it still maintains an orthorhombic crystal structure.

[0084] However, if Figure 4 As shown in (c), compared with the PE residual film before blasting, the crystallinity of the residue after blasting is significantly increased:

[0085] When the spray temperature is 238°C, the crystallinity changes from 51.7% to 59.2%, increasing from 17.9% to 35.0%;

[0086] When the blasting temperature is 337℃, the crystallinity is slightly reduced but still higher than the residual film crystallinity before blasting, ranging from 48.6% to 50.2%.

[0087] This shows that the flame blasting treatment caused the surface temperature of the residual film to rise sharply in a short period of time. The increase in molecular internal energy and the reduction in intermolecular forces simultaneously intensified the regional movement of short chain segments in the amorphous region, which is not only conducive to grain growth, but also these short chain segments will act as new crystallization sites to produce secondary crystallization, thereby increasing the overall crystallinity. Secondly, the crystallinity after the 238°C flame blasting treatment is significantly greater than that after the 337°C flame blasting treatment, which is related to the degradation stage of the residual film at different flame blasting temperatures.

[0088] In general, flame blasting causes the chemical bonds within and between PE molecules to break, triggering a rapid chain reaction, forming more oxygen-containing groups, double bonds, chain segments and branched chains, releasing low molecular weight degradation products, producing a microcrystalline structure, and improving the overall crystallinity.

[0089] 5. Thermogravimetric-infrared analysis test of polyethylene residual film (UPF).

[0090] The thermal weight loss behavior of PE residual film samples and the evolution of volatile gas phase products during thermal oxidative degradation are shown in Figure 2. Figure 5 As shown: (a) and (b) are the 3D FTIR spectra and 2D FTIR spectra of volatile gas phase products when the PE residual film undergoes thermal oxidation degradation in the range of (30-600) °C; (c) and (d) are the TG-FTIR curve fitting of the PE residual film at characteristic temperature and the corresponding release of volatile gas phase products;

[0091] Depend on Figure 5 (a) It can be seen that when the reaction temperature is lower than 320℃, the quality of the PE residual film sample remains almost stable without obvious degradation. Its intense thermal decomposition stage occurs between (368.2 and 444.6)℃. When the temperature continues to rise to around 520℃, the thermal decomposition process is basically completed.

[0092] Depend on Figure 5 (b) It can be seen that the main gas phase products during the thermal oxidation degradation of PE residual film include long-chain aliphatic hydrocarbons, ketones / esters / carboxylic acids and CO2, etc. At the characteristic reaction temperatures of 230.2℃ and 343.8℃, the absorption intensity of the gas phase products is significantly weaker than that at 374.9℃ and 395.1℃. This means that the increase in temperature during the flame treatment will not change the thermal oxidation degradation mode of PE residual film, but will only accelerate the occurrence of this process, and different flame temperatures have different degrees of influence on the evolution of gas phase products during the degradation process.

[0093] Figure 5 (d) is based on Figure 5(c) The overall evolution characteristics of gas phase products obtained by Gaussian fitting curve, Figure 5 (d) It can be seen that the total peak area of ​​the evolved products at 374.9°C and 395.1°C is more than 10 times that at 230.2°C and 343.8°C. This means that when the PE film residues were treated at 238°C and 337°C, the film residues were in the initial stage of thermal oxidation degradation and did not release a large amount of volatile gas phase products.

[0094] Combined with the changes in molecular weight, surface micromorphology, chemical functional groups and crystallinity before and after the above-mentioned flame blasting, it can be determined that the flame blasting treatment not only promotes the thermal oxidative degradation of the PE residual film in a short period of time, but also avoids the release of a large amount of volatile gas products.

Claims

1. A method for treating farmland polyethylene residual film with flames by thermal oxidation degradation, characterized in that: The method is divided into the following steps: S1, turning over the soil and screening the membrane; In the farmland area to be treated, use any agricultural implement to turn the soil so that the residual film is out of the soil and the surface area of ​​the residual film exceeds 25cm 2 The residual film is picked up manually when turning the soil, less than or equal to 25cm 2 The definition of residual membrane fragments; S2, flame treatment; Use a flame treatment device with temperature control and timing to treat the residual film fragments on the soil surface with flame treatment, and make sure that the total flame radiation area covers all the residual film fragments. When the flame temperature is controlled at 238℃±5℃, the flame time is between 50s±5s or 90s±5s. When the flame temperature is controlled at 337℃±5℃, the flame time is between 50s±5s or 90s±5s. S3, repeat S1 and S2; After the residual film is turned out of the soil, the soil turning and film screening process of S1 is repeated to turn out the residual film fragments in the soil again, and the flame spraying process of S2 is performed; The above process is repeated for multiple rounds until the residual film fragments in the soil are less than 0.001% of the land area, and the flame treatment is completed.

2. The method for thermal oxidation degradation of polyethylene film residues in farmland according to claim 1, characterized in that: The S1 also includes a film screening step, specifically, after the residual film is turned out of the soil, the residual film on the soil surface is roughly screened using agricultural tools, which can reduce the number of cyclic operations in S3.

3. The flame-spraying treatment device for thermal oxidation degradation of polyethylene residual film in farmland used in the method according to claim 1 or 2 comprises a flame-spraying gun (4) and a fuel supply system connected to each other; characterized in that: The flame spray gun (4) is connected to the fuel supply system via an explosion-proof hose (6), and a fuel valve (5) and a flame adjustment knob (3) are sequentially arranged on the explosion-proof hose (6).

4. The flame-spraying treatment device for thermal oxidation degradation of field polyethylene residual film according to claim 3, characterized in that: A plurality of groups of flame treatment devices are evenly mounted on a trolley (1); a front end of a support of the trolley (1) is provided with a walking wheel; a rear end of the trolley (1) is provided with a support (2) that can be placed on the ground.

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