A method for reaming and deashing of waste tire pyrolysis carbon black and surface grafting modification

Abstract

The present application belongs to the technical field of solid waste resource utilization and nanomaterial modification, and particularly relates to a method for pyrolysis carbon black hole expansion and surface grafting modification of waste tires. The method provided by the present application takes the optimized pyrolysis carbon black as a precursor, and successively performs gas flow stripping pretreatment to expose the ash interface, performs chelating acid immersion (hydrochloric acid-citric acid-EDTA) to selectively remove zinc and expand pores at normal pressure and medium temperature, and then covalently grafts silane coupling agent on the surface of the carbon black through ultraviolet initiation of mercapto-alkene click reaction. The method is a full-chain modification method considering the precursor quality, pore expansion and surface chemical activation, has low energy consumption, strong general applicability of raw materials, and is suitable for high-value industrial application of the pyrolysis carbon black of waste tires.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and nanomaterial modification technology, and specifically relates to a method for pore expansion, deashing, and surface grafting modification of waste tire pyrolysis carbon black. Background Technology

[0002] The pyrolysis carbon black (rCB) produced from waste tire pyrolysis has high ash content and numerous structural defects. Its surface is covered by inorganic ash such as ZnO and SiO2, as well as residual organic tar, leading to pore blockage and deactivation of surface active sites. To achieve high-value applications of rCB in rubber, deep deashing modification and surface activation are necessary.

[0003] In existing technologies, patent CN110760204A uses a high-temperature vacuum distillation method (900-1100℃) to reduce ZnO to zinc vapor for recovery via a carbothermic reduction reaction. This method requires extremely sophisticated equipment, consumes a huge amount of energy, and the high temperature easily leads to graphitization of carbon black. Although it removes ZnO, it is ineffective against inert SiO2 ash. Patent CN112194171A uses a physical flotation process, separating ZnS by adding reagents such as zinc sulfate and butyl xanthate. This method has a long process flow, consumes a large amount of flotation reagents, and generates a large amount of wastewater. It mainly targets ZnS and has no effect on "unblocking" the micropores on the carbon black surface. Patent CN115232486A focuses on ultrafine grinding and resin granulation coating. This method does not essentially remove ash but rather masks the negative effects of ash through physical coating. It is a superficial "masking" strategy, and once the resin layer wears down, the exposed ash will still lead to performance degradation. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for pore expansion, deashing, and surface grafting modification of waste tire pyrolysis carbon black. This method is a full-chain modification approach that considers precursor quality, pore expansion, and surface chemical activation. Based on response surface methodology, this invention precisely controls the initial pore structure of rCB, utilizes atmospheric pressure chemical acid washing for pore expansion and deashing, and then introduces active functional groups through chemical grafting to achieve deep quality improvement of the pyrolysis carbon black.

[0005] The method provided by this invention specifically includes the following steps: S1. Preparation of pyrolysis carbon black precursor based on response surface methodology (RSM): Using pyrolysis temperature (A), isothermal time (B), and filling degree (C) as independent variables, and solid yield, specific surface area, and ash content as response values, a regression model is constructed to determine the process parameters; waste tires are heat-treated according to the determined process parameters to prepare the pyrolysis carbon black precursor. S2. Airflow stripping pretreatment: The pyrolysis carbon black precursor is stripped using airflow pulverization and stripping technology to obtain depolymerized carbon black powder with a median particle size D50 of 8-15 μm. S3, Chelating Acid Impregnation for Pore Enlargement: The depolymerized carbon black powder obtained in step S2 is placed in a composite acid solution containing a chelation accelerator and stirred for 1 to 2 hours under normal pressure and 50 to 70°C. After the reaction is completed, it is washed until neutral and dried to obtain pore-enlarged carbon black. S4. Click chemical grafting: The expanded pore carbon black obtained in step S3 is dispersed in an alcohol-water mixed solvent, and a coupling agent containing mercaptosilane and a photoinitiator are added. Under an inert atmosphere, the mixture is subjected to UV irradiation at room temperature and thermal reaction at 60-80°C in sequence. The coupling agent is covalently grafted onto the carbon black surface through a mercapto-alkene click chemical reaction. After drying, modified pyrolysis carbon black is obtained. The total time for the UV irradiation and thermal reaction is 2-4 hours.

[0006] In step S1, the pyrolysis behavior of waste tires directly affects the initial specific surface area and pore development of the pyrolysis carbon black precursor (rCB).

[0007] Preferably, in step S2, the airflow pulverization and stripping technology is supersonic airflow pulverization and stripping technology; further, the supersonic airflow pulverization and stripping technology adopts a fluidized bed collision airflow mill, the pulverization pressure is 0.6~0.8MPa, and the pulverization time is 10~15min. This invention uses airflow stripping treatment to replace high temperature inert atmosphere treatment. In the fluidized bed collision airflow mill, the pyrolysis carbon black precursor is carried by a high-speed collision under the pressure of 0.6~0.8MPa airflow. The residual tar layer and amorphous carbon shell layer adhering to the surface are selectively stripped by the interparticle shear force and shock wave effect. This physical stripping process has three advantages: (1) significantly reduced energy consumption - room temperature operation throughout, no heating required; (2) avoidance of surface inertization - avoidance of carbon black surface graphitization and loss of active sites caused by high temperature; (3) exposure of ash interface - the ZnO, SiO2 and other ash interfaces that were originally wrapped in the carbon black aggregates are directly exposed to the surface, opening a "fast channel" for subsequent acid penetration and reaction. After this treatment, the median particle size D50 of carbon black was sharply reduced from over 20 μm to 8–15 μm. The ash exposure rate was increased by more than 50%.

[0008] In step S3, the components of the composite acid solution include hydrochloric acid and citric acid; the chelation promoter is disodium ethylenediaminetetraacetate. The molar ratio of hydrochloric acid to citric acid is (3-5):1, and the total acid concentration of the composite acid solution is 2-4 mol / L; The amount of the chelation accelerator added is 1-3% of the mass of the pyrolysis carbon black powder; The solid-liquid ratio of pyrolysis carbon black powder to composite acid solution is 1:(6~13)g / mL.

[0009] The dissolution rate of ZnO by existing pickling processes (such as single hydrochloric acid pickling) is limited by solid-liquid interface mass transfer and dissolution equilibrium, and the efficiency of ash removal is limited for ash encapsulated by a dense carbon layer. This invention constructs a "hydrochloric acid-citric acid" composite acid system and introduces disodium ethylenediaminetetraacetate (EDTA-2Na) as a chelation promoter. Its synergistic mechanism is as follows: (1) Citric acid, as a weak organic acid, preferentially reacts with the basic oxides on the surface of depolymerized carbon black, loosening the carbon layer structure; (2) Hydrochloric acid provides a high concentration of H+. + (3) EDTA-2Na reacts with the dissolved ZnO to rapidly dissolve ZnO; 2+ A stable chelate [Zn(EDTA)] is formed. 2- This disrupts the dissolution equilibrium and drives the reaction ZnO + 2H₂O. + Zn 2+ +H2O continues to move to the right. This "dissolution-chelation" synergistic effect allows the zinc removal rate to reach over 88% under mild conditions of normal pressure and 65℃. More importantly, as the ZnO clogging the pore throats is precisely removed, the 2-50nm mesopores and micropores originally occupied by carbon black are reopened, achieving pore volume expansion—the BET specific surface area increases from less than 65m² before treatment. 2 / g restored to 71m 2 / g or more.

[0010] In step S4, the mercaptosilane coupling agent is γ-mercaptopropyltriethoxysilane or γ-mercaptopropyltrimethoxysilane; the photoinitiator is benzoin dimethyl ether or 2-hydroxy-2-methyl-1-phenylpropanone. The amount of photoinitiator added is 0.5-2% of the mass of the mercaptosilane coupling agent; The amount of the mercaptosilane coupling agent added is 2-3% of the mass of the expanded carbon black.

[0011] The expanded carbon black prepared by the waste tire pyrolysis carbon black pore-expanding deashing and surface grafting modification method has an ash content of ≤7.5% and a BET specific surface area recovery rate of ≥85%.

[0012] In step S4, the alcohol in the alcohol-water mixed solvent is one of methanol, ethanol, and isopropanol; Preferably, the volume ratio of the alcohol to water is (4~9):1.

[0013] Preferably, in step S4, the inert atmosphere is nitrogen or argon; the ultraviolet irradiation time is 30-60 min; more preferably, the ultraviolet irradiation wavelength is 365 nm.

[0014] Compared to the complex polyether-chain silane polymers used in existing technologies (which require pre-synthesis and have poor structural controllability), this invention employs commercially available mercapto-containing silane coupling agents and combines them with photoinitiation conditions to achieve functional modification of the carbon black surface. In an alcohol-water system, the mercapto-containing silane coupling agent first undergoes hydrolysis to generate silanol groups, which then condense with oxygen-containing functional groups on the carbon black surface, thereby fixing the coupling agent to the carbon black surface. Under the action of a photoinitiator and ultraviolet irradiation, the surface mercapto groups are further activated, enhancing their interfacial coupling with the unsaturated double bonds in the natural rubber molecular chain. Under photoinitiation conditions, the surface mercapto groups further participate in the radical mercapto-alkene reaction, thereby improving the interfacial bonding strength between the filler and the rubber matrix. Based on the above synergistic effects, this invention retains the technical characteristics of "click chemistry" interface regulation and helps to construct a more stable organic interfacial layer on the carbon black surface. Compared with physical adsorption or conventional silanization treatment, this modification method is beneficial to reducing the tendency of interfacial slippage and improving the reinforcing effect of pyrolysis carbon black on natural rubber.

[0015] Beneficial effects 1. This invention is the first to construct a "hydrochloric acid-citric acid" composite acid system and introduce a chelation promoter. The "dissolution-chelation" synergistic effect enables the zinc removal rate to reach more than 88% under normal pressure and mild conditions of 65℃, and achieves a significant increase in the pore volume of expanded carbon black. 2. The present invention uses physical exfoliation to obtain pyrolysis carbon black powder, which not only has low energy consumption and avoids high-temperature graphitization and loss of active sites, but also increases the ash exposure rate by more than 50%. Attached Figure Description

[0016] Figure 1 The response surface plot shows the interaction between pyrolysis temperature and isothermal time on solid-phase yield. Figure 2 This is a response surface plot showing the interaction between pyrolysis temperature and filling degree on solid-phase yield; Figure 3 This is a response surface plot showing the interaction between isothermal time and filling degree on solid yield. Detailed Implementation

[0017] In the following examples and comparative examples, the waste tire rubber powder was obtained by crushing waste tires to 40 mesh after removing steel wires and fibers; the carbon black N330 was purchased from Jiangxi Black Cat Carbon Black Co., Ltd.; and the natural rubber (NR) was purchased from Changzhou Juyuan Polymer Technology Co., Ltd., model NO.1 RSS.

[0018] Example 1 S1. Precursor Preparation: 40-mesh waste tire rubber powder was pyrolyzed in a rotary kiln. Based on RSM optimization parameters, the following settings were adopted: pyrolysis temperature 510℃, isothermal time 58min, filling degree 14%, and N2 atmosphere, to obtain pyrolyzed carbon black precursor rCB (ash content 15.8%, BET specific surface area 63.15m²). 2 / g).

[0019] S2. Airflow stripping pretreatment: Take 200g of the above-mentioned pyrolysis carbon black precursor and place it in an LHL-3 type fluidized bed airflow mill. The pulverizing pressure is 0.7MPa, the grading frequency is 35Hz, and the treatment is carried out for 15min. The median particle size D50 of the resulting depolymerized carbon black powder (Air-CB) is 9.8μm.

[0020] S3. Chelating Acid Impregnation for Pore Enlargement: Depolymerized carbon black powder was added to 2.5 L of a composite acid solution (hydrochloric acid concentration 2.8 mol / L, citric acid concentration 0.7 mol / L, containing 3.5 g EDTA-2Na), and mechanically stirred in a water bath at 65 °C for 1.5 h. The reaction solution was filtered through a 0.22 μm filter membrane, washed with deionized water until the conductivity of the filtrate was <20 μS / cm, and vacuum dried at 110 °C for 4 h to obtain expanded pore carbon black (Acid-CB). ICP analysis showed that the ash content decreased to 7.2%, the zinc removal rate was 89.1%, and the BET specific surface area increased to 71.4 m². 2 / g (recovery rate 113%).

[0021] S4. Click chemical grafting: Take 50g of the expanded pore carbon black obtained in step S3, ultrasonically disperse it in 450mL of ethanol-water mixture (volume ratio 8:2), add 1.2g of γ-mercaptopropyltriethoxysilane (KH-590) and 0.015g of dimethyl benzoate (DMPA). After purging with N2 for 30min to remove oxygen, seal the reaction bottle and place it in a UV curing oven (wavelength 365nm, light intensity 50mW / cm²). 2 The product was irradiated at room temperature for 1 hour, followed by heat treatment in a water bath at 70°C for 1 hour. The product was washed with ethanol and dried under vacuum to obtain the sample, which is the modified pyrolysis carbon black (Grafted-CB).

[0022] In step S1, a Box-Behnken design was adopted, selecting pyrolysis temperature (A), isothermal time (B), and degree of filling (C) as independent variables, and solid yield, specific surface area, and ash content as response values. As shown in Table 1, a regression model was constructed through experiments. Analysis of variance (Table 2) showed that the model was highly significant (P<0.0001). Through multi-objective joint optimization, the theoretically optimal process was determined to be a pyrolysis temperature of 513.2℃, an isothermal time of 57.6 min, and a degree of filling of 13.93%. Considering actual operation, the optimal process was modified to a pyrolysis temperature of 510℃, an isothermal time of 58 min, and a degree of filling of 14%. The precursor rCB prepared under these conditions had a high specific surface area of ​​63.15 m² / g, and the moderate ash content provided an ideal basic framework for subsequent acid washing and pore expansion.

[0023] Table 1 Response Surface Design Scheme

[0024] Table 2. Analysis of variance of the solid-phase yield response surface model

[0025] Example 2 This embodiment is the same as Embodiment 1, except that in step S2, the airflow pulverization pressure is adjusted to 0.8 MPa, the processing time is 10 min, and the median particle size D50 of the obtained Air-CB is 8.2 μm; in step S4, the silane coupling agent is replaced with γ-mercaptopropyltrimethoxysilane (KH-580).

[0026] Example 3 This embodiment is the same as Embodiment 1, except that in step S3, the concentration of hydrochloric acid in the composite acid solution is adjusted to 3.5 mol / L, the concentration of citric acid is 0.5 mol / L, and the amount of EDTA-2Na added is 2% (i.e., 4 g) of the mass of the depolymerized carbon black powder; in step S4, the photoinitiator is replaced with 2-hydroxy-2-methyl-1-phenylpropanone (HMPP).

[0027] Comparative Example 1 This comparative example is the same as Example 1, except that RSM optimization is not used, and conventional pyrolytic carbon black is used directly (the resulting pyrolytic carbon black precursor has an ash content of 18.5% and a specific surface area of ​​42 m²). 2 / g) Perform steps S2-S4.

[0028] The conventional pyrolytic carbon black refers to a pyrolysis temperature of 500℃, a constant temperature time of 60min, and a filling degree of 10%.

[0029] Due to severe initial pore collapse, the acid pickling and pore-expanding effect was limited, and the final ash content was reduced to only 11.2%.

[0030] Comparative Example 2 This comparative example is the same as Example 1, except that only steps S1-S3 of Example 1 are performed, and step (4) chemical grafting is not performed. The resulting sample is expanded pore carbon black (Acid-CB).

[0031] Comparative Example 3 Referring to the method in patent CN115232486A, the Air-CB from Example 1 was directly subjected to resin granulation. Specifically, 40 kg of process water was added to the modifier mixing tank, stirring was started at 50 rpm, and heating was then applied, maintaining the temperature at 80°C. Then, 1.5 kg of aqueous phenolic resin, 1.0 kg of triethylenetetramine, and 0.5 kg of γ-mercaptopropyltriethoxysilane were added sequentially, and the mixture was stirred for 10 minutes. The drum granulator was then started, with the speed set to 300 rpm and the temperature maintained at 80°C. Simultaneously, the feed valves for the depolymerized carbon black powder and the modifier solution were opened. The feed rate of the depolymerized carbon black powder was 10 kg / min, and the feed rate of the modifier solution was 4 kg / min. At this time, the inlet water pressure was 1.2 MPa, and the spray nozzle size was 6 mm. After granulation, the inlet air temperature of the drum dryer is adjusted to 200℃, the negative pressure inside the chamber is -0.02MPa, and the outlet air temperature is maintained at 105℃ to obtain the sample.

[0032] Comparative Example 4 Referring to the process of Example 5 of Patent CN117165103A: 40-mesh waste tire rubber powder (same as in Example 1) was heat-treated at 500°C for 30 minutes under N2 atmosphere (filling degree 14%), and then acid-washed with 5mol / L hydrochloric acid at 65°C for 1 hour (without chelation accelerator) to obtain expanded pore carbon black. Finally, the silane polymer 1 described in Patent CN117165103A was mixed at a mass ratio of 10:1 and heat-treated at 150°C for 5 minutes to obtain the sample.

[0033] Comparative Example 5 (Control without chelation promoter) The difference from Example 1 is that EDTA-2Na is not added to the composite acid solution in step S3, but the rest are the same.

[0034] Comparative Example 6 (Control without click-based chemical grafting) The difference from Example 1 is that no photoinitiator is added and no ultraviolet irradiation is performed in step S4; only conventional thermal condensation grafting is performed. The rest is the same.

[0035] Application performance testing The samples obtained in Examples 1-3, Comparative Examples 1-6, commercial N330, and unmodified rCB control group (rCB, the pyrolysis carbon black precursor prepared in Example 1) were filled into natural rubber (NR) at a ratio of 50 phr, and vulcanized at 145℃ for t. 90 (where t) 90(Time required to achieve 90% vulcanization). The mechanical property test results are shown in Table 3.

[0036] Table 3. Performance comparison of carbon black-filled NR obtained from different processing processes

[0037] Note that, except for Comparative Example 3 which is the gray content of the sample, the gray content of the others in Table 3 refers to the gray content of expanded pore carbon black.

[0038] As shown in Table 3, compared with Comparative Example 4, Example 1 exhibits an increase in 300% tensile stress from 14.2 MPa to 16.8 MPa, representing an increase of 18.3%; tensile strength from 22.5 MPa to 24.1 MPa; and tear strength from 48.3 kN·m. - ¹Increased to 54.7 kN·m - ¹. The simultaneous improvement of the above three core mechanical indicators fully demonstrates that the "airflow stripping-chelation acid impregnation-click grafting" full-chain modification method constructed in this invention significantly enhances the reinforcing effect of modified pyrolysis carbon black on rubber.

[0039] The 300% elongation stress of Example 1 is close to the level of commercial N330 carbon black (17.7 MPa). This index directly reflects the stress transfer efficiency of the filler-rubber interface under tensile deformation, indicating that the present invention constructs a stable covalent interface layer on the carbon black surface through a synergistic process, effectively inhibiting the destruction and recombination of the filler network. The 300% elongation stress of Comparative Example 5 (without chelating accelerator) is 17.9% lower than that of Example 1, and the ash content increases to 8.9%, further proving that the introduction of EDTA-2Na, through the "dissolution-chelation" synergistic effect, is a key step in achieving deep dezincification, unblocking blocked pores, and exposing active sites. The 300% elongation stress of Comparative Example 6 (without click grafting) is only 12.5 MPa, a decrease of 25.6% compared to Example 1, indicating that the interfacial bonding density formed by conventional thermal condensation grafting is insufficient, while the mercapto-olefin click chemical reaction used in the present invention can efficiently and quantitatively covalently anchor the coupling agent to the carbon black surface, achieving improved interfacial strengthening and reinforcing performance.

[0040] It is worth noting that the ash content of Example 1 (7.2%) is slightly higher than that of Comparative Example 4 (6.5%), but its comprehensive mechanical properties are significantly better than those of Comparative Example 4, indicating that simply pursuing extreme deashing is not the only way to optimize reinforcing performance. Although the high-temperature pretreatment (500℃) and high-concentration strong acid (5mol / L) used in Comparative Example 4 can further reduce the ash content, it easily causes the loss of active sites on the carbon black surface and etching of the microcrystalline structure. In contrast, the chelating acid leaching system established in this invention accurately removes ZnO blocking the pores (zinc removal rate 89.1%) under mild conditions of normal pressure and 65℃, while completely preserving the inherent skeleton structure of carbon black, achieving a process balance of "moderate deashing - structure preservation - interface strengthening".

[0041] In summary, this invention, through original innovation in the process route, avoids the limitations of high-temperature inert atmosphere pretreatment and specific synthetic coupling agents in the prior art, and achieves a breakthrough improvement in the reinforcing performance of pyrolysis carbon black with lower energy consumption and more universal raw materials.

Claims

1. A method for pore enlargement, deashing, and surface grafting modification of pyrolyzed carbon black from waste tires, characterized in that, Includes the following steps: S1. Preparation of pyrolysis carbon black precursor based on response surface methodology: Using pyrolysis temperature, isothermal time, and filling degree as independent variables, and solid yield, specific surface area, and ash content as response values, a regression model is constructed to determine the process parameters; waste tires are heat-treated according to the determined process parameters to prepare the pyrolysis carbon black precursor. S2. Airflow stripping pretreatment: The pyrolysis carbon black precursor is stripped using airflow pulverization and stripping technology to obtain depolymerized carbon black powder with a median particle size D50 of 8-15 μm. S3, Chelating Acid Impregnation for Pore Enlargement: The depolymerized carbon black powder obtained in step S2 is placed in a composite acid solution containing a chelation accelerator and stirred for 1 to 2 hours under normal pressure and 50 to 70°C. After the reaction is completed, it is washed until neutral and dried to obtain pore-enlarged carbon black. S4. Click chemical grafting: The expanded pore carbon black obtained in step S3 is dispersed in an alcohol-water mixed solvent, and a coupling agent containing mercaptosilane and a photoinitiator are added. Under an inert atmosphere, the mixture is subjected to UV irradiation at room temperature and thermal reaction at 60-80°C in sequence. The coupling agent is covalently grafted onto the carbon black surface through a mercapto-alkene click chemical reaction. After drying, modified pyrolysis carbon black is obtained. The total time for the UV irradiation and thermal reaction is 2-4 hours. In step S3, the components of the composite acid solution include hydrochloric acid and citric acid; the chelation promoter is disodium ethylenediaminetetraacetate. The amount of the chelation accelerator added is 1-3% of the mass of the pyrolysis carbon black powder; The solid-liquid ratio of pyrolysis carbon black powder to composite acid solution is 1:(6~13)g / mL.

2. The method according to claim 1, characterized in that, In step S3, the molar ratio of hydrochloric acid to citric acid is (3-5):1, and the total acid concentration of the composite acid solution is 2-4 mol / L.

3. The method according to claim 1, characterized in that, In step S2, the airflow pulverization and stripping technology is supersonic airflow pulverization and stripping technology.

4. The method according to claim 3, characterized in that, The supersonic airflow pulverization and stripping technology employs a fluidized bed impact airflow mill with a pulverization pressure of 0.6~0.8MPa and a pulverization time of 10~15min.

5. The method according to claim 1, characterized in that, In step S4, the mercaptosilane coupling agent is γ-mercaptopropyltriethoxysilane or γ-mercaptopropyltrimethoxysilane; the photoinitiator is benzoin dimethyl ether or 2-hydroxy-2-methyl-1-phenylpropanone.

6. The method according to claim 5, characterized in that, The amount of photoinitiator added is 0.5-2% of the mass of the mercaptosilane coupling agent; The amount of the mercaptosilane coupling agent added is 2-3% of the mass of the expanded carbon black.

7. The method according to claim 1, characterized in that, In step S4, the alcohol in the alcohol-water mixed solvent is one of methanol, ethanol, and isopropanol; The volume ratio of the alcohol to water is (4~9):

1.

8. The method according to claim 1, characterized in that, In step S4, the inert atmosphere is nitrogen or argon; the ultraviolet irradiation time is 30–60 min.

9. The method according to any one of claims 1-8, characterized in that, The expanded carbon black prepared by the waste tire pyrolysis carbon black pore-expanding deashing and surface grafting modification method has an ash content of ≤7.5% and a BET specific surface area recovery rate of ≥85%.

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