Preparation method of high-concentration naphthalene sodium for plastic recovery

Abstract

The invention belongs to the field of composite material molding processes, and particularly relates to a preparation method of high-concentration naphthalene sodium for plastic recovery, which is technically characterized in that the plastic recovery comprises the following steps: crushing recovered polyester plastics into particles, cleaning and drying; under the protection of inert gas, adding the particles into a high-concentration sodium naphthalene solution; controlling the temperature of the system in the reaction kettle to be 20-40 DEG C, continuously stirring and reacting for 2-6 hours, and decomposing the polyester plastics into low-molecular-weight compounds by using the high-concentration naphthalene sodium solution; after the reaction is finished, separating a reaction product by using a filtering method, and recovering the solvent through distillation; the final product is a renewable raw material monomer; sodium naphthalene is a sodium naphthalene solution, and the concentration is greater than or equal to 2mol / L; the solvent of the sodium naphthalene solution is tetrahydrofuran or a mixture of tetrahydrofuran and methylbenzene; the solvent component is determined by particle size distribution of sodium. The prepared high-concentration sodium naphthalene solution has higher purity and more stable reaction performance, and is suitable for the field of plastic recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic recycling, and in particular relates to a method for preparing high-concentration sodium naphthalene for plastic recycling. Background Art

[0002] In the field of plastic recycling, especially for the chemical degradation of polyester (such as PET) plastics, sodium naphthalene solution has significant application potential as a strong reducing agent. The concentration of sodium naphthalene solution directly affects its reducing ability and the efficiency of decomposing plastic molecular chains. Usually in organic reactions, the concentration of sodium naphthalene solution is in the range of 0.1~2.0 mol / L. High-concentration sodium naphthalene solution has stronger reducing ability, can provide more electrons, and form a more intense reducing environment.

[0003] For the recycling and degradation of polyester plastics, high concentrations of sodium naphthalene solution can accelerate the breakage of plastic molecules, thereby improving the recycling efficiency and monomer yield. For example, studies have shown that in the reduction reaction of certain aromatic compounds, the use of 2 mol / L sodium naphthalene solution increased the reaction yield by 20% to 30% compared to 1 mol / L solution. Similarly, in the plastic recycling process, the use of 2 mol / L sodium naphthalene solution can provide more active sites, effectively accelerate the degradation reaction of the polymer chain, and improve the recovery rate and purity of the final product. This is especially important for plastic degradation reactions that require a strong reducing environment, because high concentrations of sodium naphthalene solution can not only accelerate the reaction, but also improve the selectivity of the reaction and reduce the formation of by-products.

[0004] In addition, high-concentration sodium naphthalene solution can help reduce unnecessary side reactions in complex reaction systems and improve the selectivity of target products. For example, in a specific organic synthesis reaction, a 2 mol / L sodium naphthalene solution increases the selectivity of the target product from 70% of a 1 mol / L solution to 85%. Similarly, in the process of plastic recycling and degradation, the use of a higher concentration of sodium naphthalene solution can effectively control the degradation reaction, allowing polyester plastics to be more thoroughly decomposed into low molecular weight monomers, such as ethylene glycol and terephthalic acid, thereby improving the recycling rate of resources.

[0005] Therefore, in the recycling of polyester plastics, the use of high-concentration sodium naphthalene solution can not only improve the reaction rate and product selectivity, but also enhance the efficiency of the entire degradation process, providing a technical guarantee for achieving more efficient and economical plastic recycling. However, since the preparation of sodium naphthalene is an exothermic reaction, local overheating can cause tetrahydrofuran to volatilize or decompose and oxidize, generating by-products, affecting the purity of sodium naphthalene, and it is impossible to obtain a high-concentration sodium naphthalene solution. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing high-concentration sodium naphthalene for plastic recycling, solve the problems raised by the background technology, and be able to prepare a sodium naphthalene solution with a concentration of ≥2 mol / L to meet the demand for plastic recycling at a higher concentration, greatly improve the activity of the reaction, reduce the amount of solvent used, and enhance the reducing ability of the solution, so as to be suitable for larger-scale or efficient organic synthesis reactions.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions: The present invention provides a method for preparing high-concentration sodium naphthalene for plastic recycling, wherein the sodium naphthalene is a sodium naphthalene solution with a concentration of ≥2 mol / L; The plastic recycling comprises the following steps: The recycled polyester plastics are crushed into granules, cleaned and dried; Under the protection of inert gas, the above particles are added into a high concentration sodium naphthalene solution; The system temperature is controlled at 20-40°C in the reactor, and the reaction is stirred continuously for 2-6 hours. The high concentration of sodium naphthalene solution decomposes the polyester plastic into low molecular weight compounds. After the reaction is completed, the reaction product is separated by filtration and the solvent is recovered by distillation; The final product is a renewable raw material monomer; The solvent of the sodium naphthalene solution is tetrahydrofuran or a mixture of tetrahydrofuran and toluene; The solvent composition is determined by the particle size distribution of the sodium.

[0008] Further, the renewable raw material monomers include ethylene glycol and terephthalic acid.

[0009] Further, the ratio of toluene to tetrahydrofuran is determined by the particle size distribution of sodium, including: When the particle size distribution of sodium is (D90-D10) / D50≤1 When, the solvent component contains only tetrahydrofuran; When the particle size distribution of sodium is (D90-D10) / D50>1 When the solvent component comprises tetrahydrofuran and toluene.

[0010] Furthermore, when the particle size distribution of sodium (D90-D10) / D50>1 When the toluene content in the solvent component is determined by the following formula: P=(x-1) / x ; in, P is the volume percentage of toluene in the solvent, the unit is 1; x for (D90-D10) / D50 The value of is in units of 1.

[0011] Further, a method for preparing high-concentration sodium naphthalene for plastic recycling comprises the following steps: dissolving naphthalene in a solvent to obtain naphthalene-solvent; Under nitrogen protection, sodium was dissolved in naphthalene-solvent and stirred to obtain a green solution; Control the reaction temperature at 10-15°C, continue stirring the green solution, and react for 2-4 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

[0012] Furthermore, when the solvent is a mixture of tetrahydrofuran and toluene, naphthalene is added in batches.

[0013] Further, the naphthalene is added in batches, including: the mass of naphthalene added each time is calculated by the following formula: m / M = p / (p+1) ; Wherein, m is the mass of naphthalene added each time, in g; M is the total mass of naphthalene added, in g; P is the volume percentage of toluene in the solvent, and the unit is 1.

[0014] Furthermore, the average particle size of the sodium is 1-4 mm.

[0015] Further, the green solution is continuously stirred, and the stirring rate is calculated according to the following formula: N=N 0 ·(1+x) / x ; in, N 0 is the stirring rate when dissolving naphthalene in the solvent, in rpm; N is the stirring rate of the green solution during continuous stirring, in rpm; x for (D90-D10) / D50 The value of is in units of 1.

[0016] Furthermore, in the sodium naphthalene solution, the molar ratio of naphthalene to sodium is 1:(1-1.2).

[0017] Furthermore, the nitrogen protection first uses a large flow of nitrogen to drive out the air in the system, and then reduces the nitrogen flow.

[0018] In summary, the present invention has the following beneficial effects: The invention successfully solves the problems of low concentration, difficult to control reaction rate, many impurities and poor stability in the preparation of traditional sodium naphthalene solution by dynamically adjusting solvent components, automatically adjusting stirring rate, optimizing sodium particle size distribution and enhancing nitrogen protection measures. The prepared high-concentration sodium naphthalene solution has higher purity and more stable reaction performance, and is suitable for efficient organic synthesis reaction. DETAILED DESCRIPTION

[0019] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, a preparation method of high-concentration sodium naphthalene for plastic recycling proposed by the present invention, its specific implementation method, characteristics and effects are described in detail as follows.

[0020] In the traditional preparation process of sodium naphthalene, the solution concentration is low, resulting in insufficient reaction efficiency and unable to adapt to the plastic recycling needs under high concentration conditions. When the sodium particle size distribution is uneven, the reaction rate is difficult to stably control, which can easily lead to problems of over-fast or over-slow reactions, resulting in increased side reactions or incomplete reactions. In the preparation process of sodium naphthalene, the use of a single solvent often cannot simultaneously take into account the reaction requirements of sodium with different particle sizes, thereby affecting the uniformity and efficiency of the reaction.

[0021] In the traditional preparation process, nitrogen protection is insufficient, and residual oxygen and moisture in the air may lead to sodium oxidation or the production of side reactions, affecting the purity and stability of the sodium naphthalene solution.

[0022] In order to solve the above problems, the present specific embodiment provides a method for preparing high-concentration sodium naphthalene for plastic recycling, wherein the sodium naphthalene is a sodium naphthalene solution with a concentration of ≥2 mol / L; Plastic recycling includes the following steps: The recycled polyester plastics are crushed into granules, cleaned and dried; Under the protection of inert gas, the above particles are added into a high concentration sodium naphthalene solution; The system temperature is controlled at 20-40°C in the reactor, and the reaction is stirred continuously for 2-6 hours. The high concentration of sodium naphthalene solution decomposes the polyester plastic into low molecular weight compounds. After the reaction is completed, the reaction product is separated by filtration and the solvent is recovered by distillation; The final product is a renewable raw material monomer; The solvent of the sodium naphthalene solution is tetrahydrofuran or a mixture of tetrahydrofuran and toluene; The solvent composition is determined by the particle size distribution of the sodium.

[0023] It can be understood that high concentration sodium naphthalene solution (≥2mol / L) can provide stronger reducing power for plastic recycling reaction, reduce the volume of solvent required for reaction, and thus improve the efficiency of reaction system. Higher concentration means that reaction can be carried out in a smaller volume of solvent, which helps to improve reaction speed and reaction yield.

[0024] This specific embodiment determines the solvent composition based on the particle size distribution of sodium. By adjusting the composition of the solvent according to the particle size distribution of sodium (D90, D10 and D50), the effectiveness of sodium particles of different sizes in the reaction is ensured. For example, large particles of sodium take longer to dissolve and react, while small particles of sodium react faster. By adjusting the ratio of tetrahydrofuran (THF) and toluene, different particle sizes of sodium can be adapted, thereby optimizing the reaction rate and reducing side reactions and local overheating.

[0025] Tetrahydrofuran has a low boiling point. When the reaction is locally overheated, it is easy to cause local tetrahydrofuran solvent volatilization or decomposition, oxidation, and reduce the concentration and purity of the sodium naphthalene solution. After adding toluene, the boiling point of toluene is relatively high, and it can form an azeotropic system with tetrahydrofuran, thereby increasing the overall boiling point of the solvent system and avoiding solvent volatilization and decomposition caused by local overheating.

[0026] Precisely control the composition of the solvent: Using a mixture of tetrahydrofuran and toluene, the reaction conditions of naphthalene and sodium can be optimized by adjusting the polarity of the solvent. Toluene is a non-polar solvent, and tetrahydrofuran is a weakly polar solvent. Their combination can provide a suitable dissolution and reaction environment for sodium particles of different particle sizes. This method of precisely controlling the solvent composition ensures the uniformity and stability of the reaction process and reduces fluctuations in the reaction rate.

[0027] By adjusting the ratio of tetrahydrofuran and toluene, the reaction rate of sodium can be better controlled, avoiding the problem of local high temperature or sodium surface passivation caused by too fast reaction. The stable and controllable reaction rate effectively avoids the occurrence of side reactions, thereby improving the purity of the sodium naphthalene solution.

[0028] By adjusting the ratio of toluene and tetrahydrofuran, the heat distribution generated during the reaction can be effectively controlled. Toluene has a high boiling point (110.6°C), which can reduce the risk of solvent volatilization during the reaction and maintain the stability of the reaction temperature, especially when high-temperature operation is required, to prevent reaction instability caused by solvent boiling.

[0029] Exemplarily, the ratio of toluene to tetrahydrofuran is determined by the particle size distribution of sodium, including: When the particle size distribution of sodium is (D90-D10) / D50≤1 When, the solvent component contains only tetrahydrofuran; When the particle size distribution of sodium is (D90-D10) / D50>1 When the solvent component comprises tetrahydrofuran and toluene.

[0030] It can be understood that in this embodiment, the composition of the solvent is selected according to the particle size distribution of the sodium. When the particle size of the sodium is relatively uniform, that is, (D90−D10) / D50≤1) , only tetrahydrofuran (THF) can meet the reaction requirements; when the particle size difference is large (i.e. (D90−D10) / D50>1) , adding toluene can better adapt to the dissolution and reaction requirements of larger and smaller sodium particles. This makes the solvent selection more flexible and targeted, ensuring a more efficient preparation of sodium naphthalene solution.

[0031] When the particle size distribution of sodium is wide, the reaction rates of large and small particles of sodium are significantly different, which can easily lead to uneven reaction or local overheating. By adding toluene, the dissolution and reaction rate of sodium can be better adjusted in the non-polar environment of the solvent, so that sodium particles of different particle sizes can react more evenly and avoid the problem of too fast or too slow reaction rate.

[0032] The mixed solvent of toluene and tetrahydrofuran can provide a more stable environment in the preparation of high-concentration sodium naphthalene solution. Since toluene has a high boiling point (110.6°C) and good solubility, when toluene is added, the mixed solvent can improve the stability of the solution and allow the sodium naphthalene solution to exist at a higher concentration (≥2mol / L), ensuring that the prepared high-concentration sodium naphthalene solution will not have the problem of solvent volatilization too quickly.

[0033] When the sodium particle size distribution is large, the smaller particles of sodium will react first and quickly, while the larger particles of sodium will react slowly. If only tetrahydrofuran is used, the strong polarity of the solvent may exacerbate this imbalance and cause an overly rapid reaction. By adding toluene, the reaction rate can be slowed down, providing a smoother reaction process, reducing the risk of a runaway reaction, and improving the safety of the entire reaction process.

[0034] Tetrahydrofuran is a weakly polar solvent, while toluene is a non-polar solvent. By combining the two, the polarity of the solvent can be adjusted so that it can adapt to the generation of sodium naphthalene and better match the reaction conditions of sodium particles of different sizes. This is conducive to the dissolution of naphthalene and avoids the limitations of a single solvent in the reaction of sodium particles of different particle sizes, providing a more compatible solvent system.

[0035] By adjusting the ratio of toluene to tetrahydrofuran according to the particle size distribution, the reaction rate and temperature control can be optimized, ensuring a more uniform and stable reaction process, reducing the occurrence of side reactions, and thus improving the purity and yield of sodium naphthalene. Especially in the case of a wide particle size distribution, toluene can provide a more uniform reaction environment, avoiding local overreaction or incomplete reaction of sodium.

[0036] Toluene has a high boiling point, which can remain stable in high-temperature reactions, reducing the risk of premature solvent volatilization, thereby ensuring stable control of the reaction temperature. The low boiling point of tetrahydrofuran helps to provide suitable solubility and reactivity at low temperatures, while the high boiling point of toluene ensures that the solution remains stable at high temperatures. This adjustment of the solvent ratio can better control the temperature changes in the reaction system and improve the stability of the reaction.

[0037] Exemplarily, when the particle size distribution of sodium is (D90-D10) / D50>1 When the toluene content in the solvent component is determined by the following formula: P=(x-1) / x ; in, P is the volume percentage of toluene in the solvent, the unit is 1; x for (D90-D10) / D50 The value of is in units of 1.

[0038] It can be understood that this formula automatically determines the volume percentage of toluene based on the particle size distribution of sodium. When the particle size distribution is larger, x The value increases, the proportion of toluene P=(x−1) / x This means that the toluene content in the reaction system increases dynamically according to actual needs, can adapt to different sodium particle distributions, and optimize reaction conditions. Through this formula, the proportion of toluene increases with x No matter how the particle size distribution of sodium changes, the toluene content can be reasonably adjusted to ensure the stability of the solvent system.

[0039] When the particle size distribution of sodium is wide, large particles of sodium require more toluene as a solvent, because toluene is a non-polar solvent and is suitable for dissolving large particles of sodium, allowing it to react more smoothly. x>1 When the toluene content increases, the proportion of toluene increases with the difference in particle size distribution, which can ensure that the dissolution reaction of large and small sodium particles is more uniform and avoid excessive local reaction or incomplete dissolution.

[0040] By adding toluene, the overall polarity of the solvent is weakened, which is suitable for controlling the reaction rate of sodium, especially for larger particle size sodium, which requires a slower reaction environment. The formula ensures that as the difference in particle size increases, the proportion of toluene increases, which helps to avoid side reactions or local overheating caused by too fast a reaction rate. When the sodium particles are too small or too large, if only tetrahydrofuran is used, the reaction rate may be uneven, resulting in overreaction or even passivation of the local sodium particle surface. After adding an appropriate amount of toluene, the polarity of the solution is reduced, the reaction is mild and uniform, and the occurrence of passivation and side reactions is effectively reduced, thereby improving the purity and stability of the sodium naphthalene solution.

[0041] When the particle size distribution is wide, the sodium particles in the high-concentration sodium naphthalene solution may be difficult to completely dissolve and react. By appropriately increasing the proportion of toluene, the solubility of the solution can be enhanced to ensure that the sodium naphthalene still maintains good stability and uniformity at high concentrations.

[0042] An exemplary method for preparing high-concentration sodium naphthalene for plastic recycling comprises the following steps: dissolving naphthalene in a solvent to obtain naphthalene-solvent; Under nitrogen protection, sodium was dissolved in naphthalene-solvent and stirred to obtain a green solution; Control the reaction temperature at 10-15°C, continue stirring the green solution, and react for 2-4 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

[0043] It can be understood that carrying out the reaction under nitrogen protection can effectively prevent sodium from coming into contact with oxygen and moisture in the air, thereby preventing sodium from being oxidized into sodium oxide or reacting with water to generate hydrogen, thereby ensuring that the formation reaction of sodium naphthalene proceeds smoothly; nitrogen protection can reduce the generation of impurities during the reaction, avoid the formation of a passivation layer on the surface of sodium, ensure that sodium can fully react, and improve the purity and stability of the sodium naphthalene solution.

[0044] Controlling the reaction temperature at 10-15°C can effectively reduce the reaction rate and prevent overheating or side reactions caused by too fast a reaction. Low temperature helps to avoid violent exothermic phenomena and makes the reaction more stable and controllable; under low temperature conditions, the probability of side reactions (such as side reactions between solvents and sodium or naphthalene) is lower, which further improves the quality of the sodium naphthalene solution while maintaining the stability of the solution.

[0045] Evenly mix the reactants: By continuous stirring, the sodium can be evenly distributed in the naphthalene-solvent solution, ensuring sufficient contact between the sodium and naphthalene, avoiding excessive local reaction rate or incomplete dissolution of sodium particles, ensuring the uniformity of the reaction, and helping to accelerate the dissolution and reaction of sodium, especially in a low temperature environment. Stirring maintains a stable reaction rate and prevents sodium from agglomerating or unevenly dispersing during the reaction.

[0046] Due to the optimization of reaction conditions (low temperature, nitrogen protection, stirring, etc.), this method can stably prepare high-concentration (≥2 mol / L) sodium naphthalene solution, which is suitable for subsequent organic synthesis applications and improves the practicality and economic benefits of the product.

[0047] For example, when the solvent is a mixture of tetrahydrofuran and toluene, naphthalene is added in portions.

[0048] In some preferred embodiments, naphthalene is added in batches, including: the mass of naphthalene added each time is calculated by the following formula: m / M =p / (p+1) ; Wherein, m is the mass of naphthalene added each time, in g; M is the total mass of naphthalene added, in g; P is the volume percentage of toluene in the solvent, and the unit is 1.

[0049] It is understandable that this method of adding naphthalene based on the toluene ratio can adjust the amount of naphthalene added each time according to the mixing ratio of toluene and tetrahydrofuran, so that the reaction rate and conditions match the actual situation of the solvent system, thereby improving the efficiency and stability of the reaction.

[0050] Exemplarily, the average particle size of the sodium is 1 to 4 mm.

[0051] Exemplarily, the green solution is continuously stirred, and the stirring rate is calculated according to the following formula: N=N 0 ·(1+x) / x ; in, N 0 is the stirring rate when dissolving naphthalene in the solvent, in rpm; N is the stirring rate of the green solution during continuous stirring, in rpm; x for (D90-D10) / D50 The value of is in units of 1.

[0052] It can be understood that when the particle size distribution parameter x When the size of the sodium particles is relatively uniform, the stirring rate in the formula N Close to initial stirring rate N 0, to ensure uniform mixing. x When the particle size is larger (i.e., when the particle size distribution is wider), the stirring rate will automatically increase to ensure that the large and small particles of sodium can be better evenly dispersed and reacted in the solution.

[0053] By adjusting the stirring rate through the formula, the reaction system can always maintain the best mixing state when sodium particles of different particle size distributions exist. This adaptability greatly improves the uniformity and efficiency of the reaction.

[0054] Large and small particles of sodium react at different rates in solution, with larger particles reacting slower and smaller particles reacting faster. x Increase stirring rate N The increase effectively prevents local overheating caused by the local rapid reaction of small-particle sodium and avoids side reactions or incomplete reactions caused by uneven mixing during the reaction.

[0055] A higher stirring rate helps to evenly distribute heat in various parts of the solution, reduces excessive temperatures caused by intense local reactions, and improves the stability and safety of the reaction.

[0056] This formula takes into account the particle size distribution of sodium, ensuring that the stirring rate is increased when the particle size distribution is wide. Larger particles require more mixing power to ensure that they are fully dissolved and in full contact with the solution, while smaller particles react faster. By dynamically adjusting the stirring rate, it can be ensured that sodium particles of different particle sizes can participate in the reaction under optimal conditions, improving the overall reaction efficiency.

[0057] Different particle size distributions will lead to inconsistent reaction rates of sodium particles in solution. By adjusting the stirring rate, these differences can be balanced to ensure a smooth reaction and avoid fluctuations in reaction rate caused by some sodium particles reacting too quickly or too slowly.

[0058] By adjusting the stirring rate according to the formula, it is possible to ensure that the sodium particles are evenly dispersed in the solution, avoid side reactions caused by insufficient mixing of the particles, thereby improving the purity of the sodium naphthalene solution, helping to ensure that the dissolved naphthalene and sodium in the entire reaction system are fully mixed, and the resulting sodium naphthalene solution is more uniform, which helps to ensure the quality consistency of the final product.

[0059] Since the reaction of sodium releases heat during the reaction, increasing the stirring rate can better control the reaction temperature, avoid excessive local temperature, and improve the safety of the reaction. Especially in the preparation of high-concentration sodium naphthalene solution, the adjustment of the stirring rate helps to dissipate heat, maintain temperature balance, and prevent high temperature from causing solvent volatilization or sodium naphthalene decomposition.

[0060] Continuous stirring not only promotes the mixing of materials, but also improves the uniform transfer of heat, so that the heat generated during the reaction is quickly dispersed, reducing the phenomenon of local temperature unevenness and ensuring the temperature consistency of the entire reaction system.

[0061] When the particle size distribution is uneven, small particles of sodium will react faster, which may lead to faster reaction speed and unstable reaction system. By increasing the stirring rate, this over-fast reaction can be effectively suppressed, ensuring a more controllable reaction process and reducing safety risks in operation.

[0062] This formula is based on the particle size distribution of sodium x Automatically adjust the stirring rate, reducing the necessity of manual adjustment of the stirring rate, reducing the complexity of operation, and making the reaction process more stable and predictable.

[0063] Exemplarily, in the sodium naphthalene solution, the molar ratio of naphthalene to sodium is 1:(1-1.2).

[0064] For example, in nitrogen protection, first use a large flow of nitrogen to drive out the air in the system, and then reduce the nitrogen flow.

[0065] It is understandable that before the reaction starts, the reactor is filled with air (containing oxygen and moisture), and a large flow of nitrogen can quickly drive out the oxygen and moisture in the system, forming a pure inert environment and preventing sodium from reacting with oxygen or moisture.

[0066] During the reaction, the nitrogen flow rate can be reduced to a moderate level to maintain an inert environment within the system while reducing gas consumption. Maintaining a low flow rate can effectively prevent air from re-entering the reactor.

[0067] Depending on the size of the reactor, the nitrogen flow rate can be adjusted as follows: 1~5L volume: The large flow exhaust stage uses 30~40 L / min, the exhaust time is 5~10 minutes, and the subsequent nitrogen flow rate is adjusted to 0.5~1 L / min.

[0068] 10~20L volume: The large flow exhaust stage uses 40~50L / min, the exhaust time is 10~15 minutes, and the subsequent nitrogen flow is adjusted to 2~3L / min.

[0069] 50 L or above: The large flow exhaust stage uses 50 L / min or above, the exhaust time is 15 minutes or more, and the subsequent nitrogen flow rate is adjusted to 3~5 L / min.

[0070] During low temperature reactions (e.g. 10-15°C), the nitrogen flow rate should be slightly higher (recommended to be in the range of 1-3 L / min) to ensure that an inert environment can be maintained under low temperature conditions.

[0071] Example 1 A method for preparing high-concentration sodium naphthalene for plastic recycling, wherein the sodium naphthalene solution comprises: 5.12 kg of naphthalene, 0.94 kg of sodium, and 17.8 kg of solvent; Among them, the average particle size of sodium is 2.5mm; its particle size distribution is: (D90-D10) / D50=1.2; Then, according to the formula P=(x-1) / x Calculation shows that in the solvent, tetrahydrofuran is 14.83 kg and toluene is 2.96 kg.

[0072] The preparation method provided in this embodiment comprises the following steps: S1, dissolving naphthalene in a solvent to obtain naphthalene-solvent; S2, under nitrogen protection, sodium was dissolved in naphthalene-solvent, stirred at a stirring rate of 400 rpm to obtain a green solution; S3, control the reaction temperature at 15°C, continue stirring the green solution, and react for 4 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

[0073] Wherein, naphthalene is added in batches, including: the mass of naphthalene added each time is calculated by the following formula, m / M =p / (p+1) ; Wherein, m is the mass of naphthalene added each time, in g; M is the total mass of naphthalene added, in g; P is the volume percentage of toluene in the solvent, the unit is 1; Then, the amount of naphthalene added each time is 0.74 kg.

[0074] The stirring rate in step S3 is given by the formula N=N 0 ·(1+x) / x calculate; in, N 0 is the stirring rate when dissolving naphthalene in the solvent, in rpm; N is the stirring rate of the green solution during continuous stirring, in rpm; x for (D90-D10) / D50 The value of is in units of 1.

[0075] Then the stirring rate in step S3 is 733 rpm.

[0076] Example 2 A method for preparing high-concentration sodium naphthalene for plastic recycling, wherein the sodium naphthalene solution comprises: 5.12 kg of naphthalene, 0.94 kg of sodium, and 17.8 kg of solvent; Among them, the average particle size of sodium is 2.5mm; its particle size distribution is: (D90-D10) / D50=1.2; Then, according to the formula P=(x-1) / x Calculation shows that in the solvent, tetrahydrofuran is 14.83 kg and toluene is 2.96 kg.

[0077] The preparation method provided in this embodiment comprises the following steps: S1, dissolving naphthalene in a solvent to obtain naphthalene-solvent; S2, under nitrogen protection, sodium was dissolved in naphthalene-solvent, stirred at a stirring rate of 400 rpm to obtain a green solution; S3, control the reaction temperature at 10°C, continue stirring the green solution, and react for 3 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

[0078] Wherein, naphthalene is added in batches, including: the mass of naphthalene added each time is calculated by the following formula, m / M =p / (p+1) ; Wherein, m is the mass of naphthalene added each time, in g; M is the total mass of naphthalene added, in g; P is the volume percentage of toluene in the solvent, the unit is 1; Then, the amount of naphthalene added each time is 0.74 kg.

[0079] The stirring rate in step S3 is given by the formula N=N 0 ·(1+x) / x calculate; in, N 0 is the stirring rate when dissolving naphthalene in the solvent, in rpm; N is the stirring rate of the green solution during continuous stirring, in rpm; x for (D90-D10) / D50 The value of is in units of 1.

[0080] Example 3 A method for preparing high-concentration sodium naphthalene for plastic recycling, wherein the sodium naphthalene solution comprises: 6 kg of naphthalene, 1.316 kg of sodium, and 17.8 kg of solvent; Among them, the average particle size of sodium is 2.5mm; its particle size distribution is: (D90-D10) / D50=0.9; Then, the solvent is tetrahydrofuran, which is 17.8 kg.

[0081] The preparation method provided in this embodiment comprises the following steps: S1, dissolving naphthalene in a solvent to obtain naphthalene-solvent; S2, under nitrogen protection, sodium was dissolved in naphthalene-solvent, stirred at a stirring rate of 400 rpm to obtain a green solution; S3, the reaction temperature was controlled at 15°C, the green solution was continuously stirred at a stirring rate of 400 rpm, and the reaction was continued for 4 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

[0082] Comparative Example 1 The same as Example 1, except that the solvent is 17.8 kg of tetrahydrofuran.

[0083] Comparative Example 2 The same as Example 1, except that naphthalene is added at one time.

[0084] Comparative Example 3 The same as Example 1, except that the stirring rate of step S3 is 400 rpm.

[0085] The sodium naphthalene solutions prepared in Examples 1 to 3 and Comparative Examples 1 to 3 are used for the recovery of waste plastics, specifically comprising the following steps: adding 50 g of the prepared waste PET particles into the pre-prepared 2 mol / L sodium naphthalene solution, filling the reactor with nitrogen to exclude air and protect the reaction system, controlling the reaction temperature at 30° C., setting the stirring rate to 300 rpm to ensure that the solution is in full contact with the plastic particles, and reacting for 4 hours to obtain a monomer of a renewable raw material.

[0086] Performance Testing The purity, concentration and stability of the sodium naphthalene solutions of Examples 1 to 3 and Comparative Examples 1 to 3 were tested, and the test results are shown in Table 1.

[0087] The test method is as follows: 1. Purity test of sodium naphthalene solution: High performance liquid chromatography (HPLC) was used to detect the naphthalene and impurity content in the sodium naphthalene solution. After diluting the sodium naphthalene solution to a suitable concentration, it was injected into the HPLC equipment to detect and analyze the purity of the naphthalene in the solution, record the peak area of ​​naphthalene, and calculate its relative purity.

[0088] The detection conditions included: the mobile phase was methanol / water (80:20), the column temperature was 25°C, and the detection wavelength was 254 nm.

[0089] 2. Concentration test of sodium naphthalene solution: The concentration of the sodium naphthalene solution is determined by titration. Take a certain volume of the sodium naphthalene solution, use a standard acid solution (such as 0.1 mol / L HCl) to titrate, calculate the number of moles of sodium naphthalene generated by the reaction, and determine the concentration of the solution.

[0090] The titration endpoint is determined by a pH indicator or potentiometric titration.

[0091] 3. Stability test: Each sample was stored in a sealed container at room temperature (25°C), and samples were taken regularly to test its purity and concentration, and its trend over time was observed to evaluate the long-term stability of each sample.

[0092] 4. Purity test of monomers of renewable raw materials: ethylene glycol: analyzed by gas chromatography (GC), the purity is 99.2%, and the yield is 90%; terephthalic acid: analyzed by high performance liquid chromatography (HPLC), the purity is 98.5%, and the yield is 85%.

[0093] Table 1. Purity, concentration and stability of sodium naphthalene solutions of Examples 1 to 3 and Comparative Examples 1 to 3

[0094] Results Analysis Embodiments 1, 2, and 3 all adopt the method of adding naphthalene in batches, and through the optimization of stirring speed, the purity and concentration of sodium naphthalene solution are significantly improved. Especially in embodiment 1, through the stirring speed optimized by calculation and the addition of naphthalene in batches, the purity of the final sodium naphthalene solution reaches 98.5%, and the concentration is also maintained at 2.05mol / L.

[0095] Comparative Example 1 used tetrahydrofuran as a single solvent. Although a sodium naphthalene solution was prepared, its purity (95.3%) and concentration (1.92 mol / L) were significantly lower than those of the optimized example.

[0096] Comparative Example 2: Naphthalene was added all at once, resulting in an excessively fast local reaction rate, which led to an increase in side reactions. The purity of the solution was only 90.5%, and the concentration was 1.85 mol / L, indicating the importance of adding naphthalene in batches.

[0097] Comparative Example 3 The stirring rate was not optimized. Although the concentration of the sodium naphthalene solution was close to the expected value, the purity decreased (92.1%) due to insufficient stirring and uneven reaction.

[0098] Stability test: After storage for 1 month, the concentration of the sodium naphthalene solution of Examples 1, 2, and 3 only slightly decreased, indicating that the sodium naphthalene solution has good long-term stability under the conditions of adding naphthalene in batches and reasonably controlling the stirring rate.

[0099] The concentrations of the sodium naphthalene solutions of Comparative Examples 1 to 3 decreased after storage, especially in Comparative Example 2, where the solution quality was poor and the concentration decreased more after storage (1.77 mol / L).

[0100] Example 1 and Example 2 show that the preparation method of adding naphthalene in batches and adjusting the stirring rate according to the particle size distribution can significantly improve the purity and concentration of the sodium naphthalene solution, and ensure the stability and controllability of the reaction.

[0101] Example 3 shows that a high concentration and high purity sodium naphthalene solution can be obtained by using only tetrahydrofuran without toluene, but a mixed solvent system (such as Examples 1 and 2) shows better effects in some cases.

[0102] The comparative experiment emphasized the importance of optimizing the stirring rate and adding naphthalene in batches. Without taking optimization measures, the purity and concentration of the sodium naphthalene solution decreased significantly, and the long-term storage stability was also poor.

[0103] And through the above performance test results, it can be known that the high concentration sodium naphthalene solution provided by the present invention not only improves the reaction rate when recycling plastics, but also effectively reduces the generation of by-products, showing the good application prospect of high concentration sodium naphthalene solution in the recycling of polyester plastics. This process provides an efficient and economical solution for the resource utilization of waste plastics.

[0104] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been shown as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing high-concentration sodium naphthalene for plastic recycling, characterized in that: The plastic recycling comprises the following steps: The recycled polyester plastics are crushed into granules, cleaned and dried; Under the protection of inert gas, the above particles are added into a high concentration sodium naphthalene solution; The system temperature is controlled at 20-40°C in the reactor, and the reaction is stirred continuously for 2-6 hours. The high concentration of sodium naphthalene solution decomposes the polyester plastic into low molecular weight compounds. After the reaction is completed, the reaction product is separated by filtration and the solvent is recovered by distillation; The final product is a renewable raw material monomer; Wherein, the sodium naphthalene is a sodium naphthalene solution with a concentration of ≥2 mol / L; The solvent of the sodium naphthalene solution is tetrahydrofuran or a mixture of tetrahydrofuran and toluene; The solvent composition is determined by the particle size distribution of the sodium.

2. A method for preparing high-concentration sodium naphthalene for plastic recovery according to claim 1, characterized in that: The ratio of toluene to tetrahydrofuran is determined by the particle size distribution of sodium, including: When the particle size distribution of sodium is (D90-D10) / D50≤1 When, the solvent component contains only tetrahydrofuran; When the particle size distribution of sodium is (D90-D10) / D50>1 When the solvent component comprises tetrahydrofuran and toluene.

3. A method for preparing high-concentration sodium naphthalene for plastics recovery according to claim 2, characterized in that, When the particle size distribution of sodium is (D90-D10) / D50>1 When the toluene content in the solvent component is determined by the following formula: P = (x-1) / x ； in, P is the volume percentage of toluene in the solvent, the unit is 1; x for (D90-D10) / D50 The value of is in units of 1.

4. A method for preparing high-concentration sodium naphthalene for plastic recovery according to claim 3, characterized in that: The steps include: dissolving naphthalene in a solvent to obtain naphthalene-solvent; Under nitrogen protection, sodium was dissolved in naphthalene-solvent and stirred to obtain a green solution; Control the reaction temperature at 10-15°C, continue stirring the green solution, and react for 2-4 hours; After the reaction is completed, the sodium naphthalene solution is filled and sealed with petroleum ether.

5. A method for preparing high-concentration sodium naphthalene for plastic recovery according to claim 3, characterized in that, When the solvent is a mixture of tetrahydrofuran and toluene, naphthalene is added in batches.

6. A method for preparing high-concentration sodium naphthalene for plastic recycling according to claim 5, characterized in that: The naphthalene is added in batches, including: the mass of naphthalene added each time is calculated by the following formula: m / M =p / (p+1) ; Wherein, m is the mass of naphthalene added each time, in g; M is the total mass of naphthalene added, in g; P is the volume percentage of toluene in the solvent, and the unit is 1.

7. A method for preparing high-concentration sodium naphthalene for plastic recycling according to claim 1, characterized in that: The average particle size of the sodium is 1-4 mm.

8. A method for preparing high-concentration sodium naphthalene for plastic recycling according to claim 1, characterized in that: The green solution is continuously stirred, and the stirring rate is calculated according to the following formula: N=N 0 ·(1+x) / x ； in, N 0 is the stirring rate when dissolving naphthalene in the solvent, in rpm; N is the stirring rate of the green solution during continuous stirring, in rpm; x for (D90-D10) / D50 The value of is in units of 1.

9. A method for preparing high-concentration sodium naphthalene for plastic recycling according to claim 1, characterized in that: In the sodium naphthalene solution, the molar ratio of naphthalene to sodium is 1:(1-1.2).

10. The method for preparing high-concentration sodium naphthalene for plastic recycling according to claim 4, characterized in that: The nitrogen protection is performed by first using a large flow rate of nitrogen to drive out the air in the system, and then reducing the nitrogen flow rate.

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