A heat preservation pyrolysis process of bamboo chips and high-density polyethylene mixed material

Abstract

The present application relates to a kind of bamboo chip and high-density polyethylene mixed material heat preservation pyrolysis process, it relates to biomass and waste plastic resource technology field.The process includes that bamboo chip is mixed with high-density polyethylene according to mass ratio 1:1, the temperature corresponding to maximum pyrolysis rate is determined as peak value heat preservation temperature by multiple heating rate thermogravimetric analysis, linear heating and peak value heat preservation two-stage pyrolysis procedure are used to carry out pyrolysis, and process rationality is verified by multidimensional dynamics and thermodynamics analysis.The present application can be carried out heat preservation treatment at the temperature corresponding to maximum pyrolysis rate, fully utilize the interaction between biomass and plastic, avoid unnecessary later high-temperature heating, to significantly improve pyrolysis oil yield and reduce whole process energy consumption.

Description

Technical Field

[0001] This invention relates to the field of biomass and waste plastic resource utilization technology, specifically to a heat-insulating pyrolysis process for a mixture of bamboo chips and high-density polyethylene. Background Technology

[0002] With increasing global emphasis on renewable resource utilization and waste resource recovery technologies, the treatment of biomass and waste plastics has become a current research hotspot. The large amount of bamboo shavings generated during bamboo processing is typically considered agricultural and forestry waste, and improper disposal can easily lead to environmental pollution and resource waste. On the other hand, high-density polyethylene (HDPE), a common general-purpose plastic, produces large-volume waste that is difficult to degrade. Traditional landfill and incineration methods not only occupy land but also release greenhouse gases and toxic substances, posing a threat to the ecological environment. Currently, thermochemical conversion technologies for biomass-plastic mixtures, especially co-pyrolysis, are considered a promising resource recovery pathway. In the field of pyrolysis processes, the "heating + holding" strategy to achieve energy saving and efficiency has been reported in relevant studies. For example, some studies have analyzed thermogravimetric experimental data at a single heating rate, constructed a pyrolysis function model using specific equations, and determined the critical temperature based on the transition point from one model to another. Holding at this temperature achieves pyrolysis. This process, applied to plastic-plastic mixtures, validated the application of the "critical temperature holding" strategy in the pyrolysis process.

[0003] However, the aforementioned processes are mainly applicable to plastic-plastic systems, and the determination of their critical temperature depends solely on the transition point of the pyrolysis function model at a single heating rate, making the verification methods relatively limited. In practical waste resource utilization scenarios, more complex biomass-plastic hybrid systems often need to be processed. Existing co-pyrolysis processes lack scientific basis for selecting the holding temperature when handling such complex systems, leading to low energy efficiency and unstable product distribution during process implementation. Therefore, for biomass-plastic composite systems like bamboo chips and high-density polyethylene, developing a pyrolysis process that fully utilizes the interaction between the two based on their co-pyrolysis behavior, and scientifically analyzing the energy-saving process using multi-dimensional analytical methods (such as multi-heating rate kinetic analysis and thermodynamic parameter verification), is of great significance for promoting the green and comprehensive utilization of biomass and waste plastics. Summary of the Invention

[0004] This invention provides a thermal insulation pyrolysis process for a mixture of bamboo chips and high-density polyethylene, which solves the technical problems of low energy utilization efficiency and unstable product distribution caused by the lack of scientific basis for selecting the thermal insulation temperature in biomass-plastic co-pyrolysis processes. To achieve the above objectives, this invention provides the following technical solution: This invention provides a heat-insulating pyrolysis process for a mixture of bamboo chips and high-density polyethylene, comprising the following steps: Step 1: Dry, grind, and sieve the bamboo shavings and high-density polyethylene separately, then weigh them precisely at a mass ratio of 1:1 and mix them physically evenly to obtain a PE / BP mixed sample; Step 2: Perform thermogravimetric analysis on the PE / BP mixed sample at multiple heating rates to obtain its thermogravimetric (TG) and differential thermogravimetric (DTG) curves under nitrogen atmosphere at heating rates of 10 K / min, 20 K / min and 30 K / min, respectively. Step 3: Based on the DTG curve, determine the temperature corresponding to the maximum pyrolysis rate at a heating rate of 10 K / min as the peak holding temperature Tm. m It is 732.25 K; Step 4: The PE / BP mixed sample is pyrolyzed in a pyrolysis reactor under an inert atmosphere according to a two-stage pyrolysis procedure of "linear heating and peak holding". First stage: Heating from room temperature to peak holding temperature Tm at a constant heating rate of 10 K / min; Second stage: Hold at the peak holding temperature Tm for 6 minutes to allow the pyrolysis reaction to proceed fully; Step 5: Based on the multi-heating rate thermogravimetric data obtained in Step 2, the apparent activation energy of the PE / BP mixture sample at different conversion rates was calculated using three model-free equal conversion methods: the Flynn-Wall-Ozawa method, the Kissinger-Akahira-Sunose method, and the Starink method. The apparent activation energy variation curves at different conversion rates were obtained, and a comparative analysis was performed to verify the energy-saving rationality of the peak insulation temperature Tm. The analysis revealed that throughout the entire conversion rate range, the activation energy of the PE / BP mixture was significantly lower than that of pure HDPE. Especially in the conversion rate range of α = 0.3–0.6, the activation energy of the mixture decreased by 15%–25% compared to pure HDPE, indicating a significant interaction between bamboo chips and HDPE. In the conversion rate range of α = 0.7–0.8 corresponding to the peak temperature Tm (732.25 K), the upward trend of the activation energy of the mixture slowed significantly, indicating that the reaction entered a steady-state stage within this temperature range, and further heating would not significantly reduce the energy barrier, thus verifying the energy-saving rationality of insulation at this peak temperature. Step 6: Based on the kinetic analysis results of Step 5, calculate the enthalpy change ΔH, Gibbs free energy change ΔG, and entropy change ΔS of the PE / BP mixed sample at different conversion rates. Verify the thermodynamic stability of the insulation at the peak insulation temperature Tm using thermodynamic parameters. The analysis shows that in the conversion rate range α=0.7~0.8 corresponding to the peak temperature, the ΔH value of the PE / BP mixture tends to be stable, the ΔG value fluctuates very little, and ΔS remains in a stable positive range. This indicates that insulation at this stage can not only meet the stable energy requirements of the system's continuous reaction, but also conforms to the thermodynamic law that the reaction proceeds in the direction of increasing disorder. From an energy perspective, the rationality of the peak insulation process is verified. Step 7: After the pyrolysis reaction is completed, collect and separate the pyrolysis oil, pyrolysis gas and solid residue.

[0005] This invention provides a thermal insulation pyrolysis process for a mixture of bamboo chips and high-density polyethylene (HDPE). This process ensures uniformity of the raw materials during pyrolysis by precisely weighing and physically mixing the bamboo chips and HDPE at a 1:1 mass ratio, thus providing a stable material basis for subsequent pyrolysis reactions. Thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG) curves at different heating rates under a nitrogen atmosphere are obtained, providing experimental evidence for determining optimal pyrolysis conditions. Based on the DTG curves, the temperature corresponding to the maximum pyrolysis rate at a heating rate of 10 K / min is determined as the peak holding temperature Tm, which is 732.25 K. This temperature reflects the most intense temperature range of the pyrolysis reaction of the mixture. A two-stage pyrolysis procedure of "linear heating + peak holding" is adopted. In the first stage, the temperature is heated from room temperature to the peak holding temperature Tm at a constant heating rate of 10 K / min. In the second stage, the temperature is held at the peak holding temperature Tm for 6 minutes, allowing the pyrolysis reaction to proceed fully and avoiding the energy waste caused by continuously heating to higher temperatures in traditional processes. Based on thermogravimetric data from multiple heating rates, three model-free equal conversion methods—Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink—were used to calculate the apparent activation energy of PE / BP mixed samples at different conversion rates, and comparative analysis was conducted to verify the energy-saving rationality of the peak holding temperature Tm. Multi-dimensional kinetic analysis improved the scientific rigor and universality of temperature selection. Based on the kinetic analysis results, the enthalpy change ΔH, Gibbs free energy change ΔG, and entropy change ΔS of the PE / BP mixed samples at different conversion rates were calculated. The thermodynamic stability of the holding temperature at the peak holding temperature Tm was verified using thermodynamic parameters, achieving a dual-dimensional demonstration of process rationality from the perspectives of energy efficiency and reaction stability. After the pyrolysis reaction, the pyrolysis oil, pyrolysis gas, and solid residue were collected and separated, completing the entire pyrolysis process. This process fully utilizes the interaction between bamboo chips and high-density polyethylene by maintaining the temperature at the maximum pyrolysis rate, avoiding the energy waste caused by continuing to raise the temperature to pursue the final small amount of conversion. This significantly improves the yield and quality of pyrolysis oil, while reducing the energy consumption of the entire process, and realizing the efficient resource utilization of bamboo chips and waste plastics. Attached Figure Description

[0006] Figure 1 Thermogravimetric curves of bamboo chips, high-density polyethylene, and mixed samples provided for embodiments of the present invention.

[0007] Figure 2 Thermogravimetric diagrams of the peak heat preservation pyrolysis process and the conventional process for mixed samples provided in the embodiments of the present invention.

[0008] Figure 3 The activation energy variation diagram of bamboo chips, high-density polyethylene, and mixed samples provided in the embodiments of the present invention.

[0009] Figure 4 The diagram shows the activation energy changes of three model-free methods for bamboo chips, high-density polyethylene, and mixed samples provided in the embodiments of the present invention.

[0010] Figure 5 The thermodynamic parameter variation diagram of bamboo chips, high-density polyethylene, and mixed samples provided in the embodiments of the present invention.

[0011] Figure 6 This is a schematic diagram of a pyrolysis reactor provided in an embodiment of the present invention.

[0012] Figure 7 Energy consumption measurement diagrams for conventional pyrolysis process and peak heat preservation pyrolysis process provided in the embodiments of the present invention.

[0013] Table 1 shows the proportions of pyrolysis oil, pyrolysis gas, and residue under conventional pyrolysis process and peak heat preservation pyrolysis process provided in the embodiments of the present invention. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] like Figure 1-7 Unless otherwise specified, all materials, reagents and instruments used in this invention are commercially available.

[0016] Bamboo shavings were obtained from bamboo processing residues, and after natural air drying, they were dried in a vacuum drying oven at 105℃ for 12 hours. High-density polyethylene was obtained from recycled plastic fragments, which were washed, air-dried, and also vacuum-dried at 105℃ for 12 hours. All raw materials were ground and passed through a 35-mesh standard sieve. Thermogravimetric analysis was performed using a thermogravimetric analyzer, with nitrogen purity ≥99.999%. The pyrolysis reaction was carried out in a tube furnace equipped with a quartz tube, quartz boat, and condensation system. The condensation system used a low-temperature circulating pump to maintain the cold trap temperature at 263.15 K.

[0017] Example 1 (corresponding to steps 1-4, 7) This embodiment provides a heat-insulating pyrolysis process for a mixture of bamboo chips and high-density polyethylene.

[0018] 20.0 g each of dried, ground, and sieved bamboo shavings and high-density polyethylene (HDPE) were mixed evenly to obtain a PE / BP mixed sample. The sample was placed in a thermogravimetric analyzer, and non-isothermal thermogravimetric experiments were conducted under a nitrogen atmosphere at heating rates of 10 K / min, 20 K / min, and 30 K / min. TG and DTG curves were recorded. Based on the DTG curve at a heating rate of 10 K / min, the peak holding temperature corresponding to the maximum pyrolysis rate was determined to be 732.25 K.

[0019] A thermogravimetric analysis was conducted to compare the conventional pyrolysis process and the peak heat preservation pyrolysis process.

[0020] Experiments were conducted in a thermogravimetric analyzer at a heating rate of 10 K / min. With the conventional process, mass loss slowed down at 793.15 K, with a residual mass of approximately 12.25%. With the peak holding process, heating to 732.25 K followed by a 6-minute hold resulted in mass loss equilibrium, and the residual mass was essentially the same as that of the conventional process at 793.15 K. Relevant thermogravimetric curves are shown below. Figure 2 As shown.

[0021] A 20.0 g PE / BP mixed sample was spread evenly in a quartz boat and placed in a tube furnace. Nitrogen gas was introduced, and the tube furnace was heated according to both conventional pyrolysis and peak holding pyrolysis processes by setting a heating program. The peak holding pyrolysis process involved heating to 732.25 K at a heating rate of 10 K / min and holding at that temperature for 6 minutes. The volatiles produced by pyrolysis were condensed and collected as pyrolysis oil through a condensation system (263.15 K). The uncondensed gas was used as pyrolysis gas, and the solid residue was weighed after cooling.

[0022] The results showed that the pyrolysis oil yield was 64.5%, the pyrolysis gas yield was 18.87%, and the solid residue yield was 16.63%. Thermogravimetric analysis (TGA) curves showed that the mass loss stabilized after 6 minutes of holding at that temperature, and the residual mass was basically consistent with that of the conventional process (heating to 793.15 K). Energy consumption monitoring showed that the total power consumption for the entire process was 134.57 Wh, a 13.1% reduction compared to the conventional process (154.86 Wh).

[0023] Table 1

[0024] Example 2 (corresponding to steps 2 and 3) This embodiment analyzes the pyrolysis characteristics of bamboo chips, high-density polyethylene and their mixtures.

[0025] At a heating rate of 10 K / min, the initial pyrolysis temperature of high-density polyethylene was 702.35 K, the peak temperature was 725.35 K, the maximum pyrolysis rate was 26.84% / min, and the termination temperature was 739.45 K. The initial pyrolysis temperature of bamboo chips was 577.35 K, the peak temperature was 628.95 K, the maximum pyrolysis rate was 9.89% / min, and the termination temperature was 648.15 K. The initial pyrolysis temperature of the mixed sample was 682.85 K, the peak temperature was 732.25 K, the maximum pyrolysis rate was 12.52% / min, and the termination temperature was 747.25 K. The relevant thermogravimetric curves are shown below. Figure 1 As shown.

[0026] Example 3 (corresponding to step 5) In this embodiment, three model-free methods, FWO, KAS, and Starink, are used to calculate the activation energy of the sample.

[0027] Thermogravimetric analysis (TGA) of bamboo chips, high-density polyethylene (HDPE), and their mixtures at heating rates of 10, 20, and 30 K / min was performed to obtain the apparent activation energy at different conversion rates. The results showed a significant consistency in the trends and magnitudes of the activation energies calculated by the three methods. Throughout the entire conversion range, the activation energy of the PE / BP mixture was lower than that of pure HDPE. In the conversion range α = 0.3–0.6, the activation energy of the mixture decreased by 15%–25% compared to pure HDPE. The interaction-induced energy reduction effect was significant, indicating that the free radical fragments generated by the pyrolysis of bamboo chips could promote the breakage of the HDPE long chains, thereby lowering the overall reaction energy barrier. In the conversion range α = 0.7–0.8 corresponding to the peak temperature of 732.25 K, the upward trend of the activation energy of the mixture slowed significantly. This phenomenon indicates that within this temperature range, the reaction enters a steady-state stage, and the conversion of the residual components no longer requires a significant increase in energy input. Therefore, holding the temperature at this point allows the reaction to proceed fully under optimal energy efficiency conditions, avoiding the energy waste caused by continuing to raise the temperature to pursue a small final conversion. The relevant activation energy change curves are as follows: Figure 3 , Figure 4 As shown.

[0028] Example 4 (corresponding to step 6) This embodiment calculates the thermodynamic parameters of the sample.

[0029] Based on the kinetic analysis results, the enthalpy change ΔH, Gibbs free energy change ΔG, and entropy change ΔS of bamboo chips, high-density polyethylene (HDPE), and their mixtures at different conversion rates were calculated. The results show that within the conversion rate range α = 0.7–0.8 corresponding to the peak temperature, the ΔH value of the PE / BP mixture tends to be stable, the ΔG value fluctuates very little, and ΔS remains within a stable positive range. The relevant thermodynamic parameter variation curves are shown below. Figure 5As shown. Specific analysis revealed: Evolution characteristics of enthalpy change (ΔH): ΔH represents the energy required for reactants to form an activated complex. The closer its value is to the activation energy, the lower the reaction barrier. Calculation results show that throughout the entire conversion range (α=0.1~0.9), the ΔH value of the PE / BP mixture is consistently lower than that of pure HDPE, and its trend is highly consistent with the activation energy. Particularly in the conversion range corresponding to the peak temperature (α=0.7~0.8), the ΔH value tends to stabilize, remaining within a narrow range of approximately 180~190 kJ / mol. This plateau phenomenon indicates that at this stage, the heat absorption requirement of the reaction system reaches a steady state; further heating will not significantly reduce the energy barrier and may even lead to energy waste.

[0030] The evolution of Gibbs free energy change (ΔG): ΔG reflects the total energy required for the formation of the activated complex in the reaction system, and its positive value indicates the ease with which the reaction proceeds. Analysis shows that the ΔG value of the PE / BP mixture is slightly higher than that of pure HDPE in the low conversion stage (α<0.5), but significantly decreases in the high conversion stage (α>0.6), and remains relatively stable throughout the entire conversion range (approximately 160~170 kJ / mol). Especially in the α=0.7~0.8 range, the ΔG value fluctuates very little, indicating that the spontaneity of the reaction tends to be uniform in this stage, and the reaction process can be maintained without additional energy input.

[0031] The evolution characteristics of entropy change (ΔS): ΔS represents the change in disorder of the reaction system from the initial state to the activated complex state. A positive ΔS value means that the activated complex has a higher degree of disorder than the initial reactants, which is conducive to the formation of volatile products. The results show that the ΔS value of the PE / BP mixture is positive and gradually increases in the low conversion stage, indicating that the molecular disorder increases in the early stage of the reaction and the release of volatiles is active; after entering the high conversion stage (α>0.6), the ΔS value is maintained in a stable positive range (about 25~35 J / (mol·K)), indicating that the evolution of disorder in the reaction system tends to be stable and the formation rate and diffusion behavior of volatile products reach a dynamic equilibrium. The stability of ΔS is particularly prominent in the range corresponding to the peak temperature (α=0.7~0.8), indicating that if the temperature is maintained at this temperature, the reaction can continue to proceed in the direction that is conducive to the release of volatiles.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat-insulating pyrolysis process for a mixture of bamboo chips and high-density polyethylene, characterized in that, Includes the following steps: Step 1: Dry, grind, and sieve the bamboo shavings and high-density polyethylene separately, then weigh them precisely at a mass ratio of 1:1 and mix them physically evenly to obtain a PE / BP mixed sample; Step 2: Perform thermogravimetric analysis on the PE / BP mixed sample at multiple heating rates to obtain its thermogravimetric (TG) and differential thermogravimetric (DTG) curves under nitrogen atmosphere at heating rates of 10 K / min, 20 K / min and 30 K / min, respectively. Step 3: Based on the DTG curve, determine the temperature corresponding to the maximum pyrolysis rate at a heating rate of 10 K / min as the peak holding temperature Tm, where Tm is 732.25 K; Step 4: The PE / BP mixed sample is pyrolyzed in a pyrolysis reactor under an inert atmosphere according to a two-stage pyrolysis procedure of "linear heating and peak holding". First stage: Heating from room temperature to the peak holding temperature Tm at a constant heating rate of 10 K / min; Second stage: Hold at the peak holding temperature Tm for 6 minutes to allow the pyrolysis reaction to proceed fully; Step 5: Based on the multi-heating rate thermogravimetric data obtained in Step 2, the apparent activation energy of the PE / BP mixed sample at different conversion rates was calculated using three model-free equal conversion methods: the Flynn-Wall-Ozawa method, the Kissinger-Akahira-Sunose method, and the Starink method. Comparative analysis was then performed to verify the energy-saving rationality of the peak insulation temperature Tm. Specifically, in the conversion rate range of α = 0.3~0.6, the activation energy of the mixture decreased by 15%~25% compared to pure high-density polyethylene; in the conversion rate range of α = 0.7~0.8, the upward trend of the activation energy of the mixture slowed down. Step 6: Based on the kinetic analysis results of Step 5, calculate the enthalpy change ΔH, Gibbs free energy change ΔG, and entropy change ΔS of the PE / BP mixed sample at different conversion rates, and verify the thermodynamic stability of the insulation at the peak insulation temperature Tm using thermodynamic parameters; wherein, in the conversion rate range of α = 0.7~0.8, the ΔH value of the PE / BP mixed sample tends to be stable, the ΔG value fluctuates very little, and the ΔS remains in a stable positive range; Step 7: After the pyrolysis reaction is completed, collect and separate the pyrolysis oil, pyrolysis gas and solid residue.

2. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene mixture according to claim 1, characterized in that, The calculation results of the Flynn-Wall-Ozawa method, Kissinger-Akahira-Sunose method, and Starink method described in step 5 are used for mutual verification.

3. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene composite material according to claim 1, characterized in that, In step 1, the drying temperature of bamboo chips and high-density polyethylene is 105°C, and the drying time is 12 hours.

4. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene composite material according to claim 1, characterized in that, In step 1, the standard sieve used for sieving is 35 mesh, and the particle size of the screened particles is less than 0.5 mm.

5. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene composite material according to claim 1, characterized in that, The inert atmosphere in step 4 is a nitrogen atmosphere, and the nitrogen flow rate is 200 mL / min.

6. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene mixture according to claim 1, characterized in that, The pyrolysis reactor in step 4 is a tubular furnace, which is equipped with a quartz tube and a quartz boat.

7. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene composite material according to claim 1, characterized in that, In step 4, the pyrolysis reactor is connected to a condensation system, the temperature of which is 263.15 K.

8. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene mixture according to claim 1, characterized in that, After the pyrolysis process in step 4 is completed, the mass loss of the PE / BP mixed sample reaches equilibrium.

9. The heat-insulating pyrolysis process for the bamboo shavings and high-density polyethylene mixture according to claim 1, characterized in that, The yield of pyrolysis oil collected in step 7 is 64.5%.

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