Method for controllably preparing high-added-value uniform long-chain polycarboxylic acid through oxidative degradation of waste polyolefin

Abstract

The invention belongs to the technical field of waste high polymer material recovery, and provides a method for controllably preparing high-added-value uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefin, which comprises the following steps: adding a waste polyolefin material into an oxidant solution, and heating in a closed reaction container for oxidative degradation reaction, the oxidative degradation reaction temperature is controlled to be not lower than 80 DEG C and not higher than the thermal decomposition temperature of polyolefin in air, and the main component of the obtained degradation product is long-chain polycarboxylic acid with the number-average molecular weight of 800 g / mol or above; the molecular weight and the molecular weight distribution index of the long-chain polycarboxylic acid can be adjusted by adjusting the size of the waste polyolefin material or / and adjusting oxidative degradation conditions; according to the method, the conversion rate for converting the waste polyolefin into the long-chain polycarboxylic acid through oxidative degradation is 90% or above. The method can effectively control the degree of the oxidative degradation reaction of the waste polyolefin and the uniformity of the reaction, improve the carbon yield and increase the uniformity of the molecular weight of the oxidative degradation product of the mixed polyolefin.

Description

Technical Field

[0001] The invention belongs to the technical field of waste polymer material recovery and relates to a method for controllably preparing high-value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefin. Background Art

[0002] Polyolefins, including the widely used polypropylene (PP), high-density polyethylene (HDPE) and low-density polyethylene (LDPE), account for 50% of the total plastics. The high upper limit temperature of polyolefin polymerization makes it difficult to depolymerize into ethylene or propylene monomers; at the same time, the polyolefin chain is composed of stable CC bonds and CH bonds, lacks weak bonds associated with heteroatoms, and therefore cannot provide sites for selective chain breaking. This greatly increases the difficulty of recycling waste polyolefins and limits their recycling and value-added into relatively high value-added products. The main chemical recovery strategy for waste polyolefins is to convert them into fuel oil, lubricating oil, etc., whose main components are hydrocarbons, by pyrolysis / catalytic cracking / hydrogenolysis. Although researchers have made some progress in efficient catalysts and tandem reactions, the value of hydrocarbons is limited.

[0003] Introducing heteroatoms such as oxygen or nitrogen into hydrocarbons can greatly increase their value. Recently, some researchers have tried to introduce heteroatoms such as oxygen or nitrogen into waste polyolefins to convert them into high value-added products. For example, Hartwig et al. used organometallic complex catalysts to embed oxygen-containing functional groups and nitrogen-containing functional groups into polyolefins without reducing the molecular weight of waste polyolefins. The resulting modified polyolefins can be directly used as adhesives or coatings, but the catalyst used in this method is expensive. In contrast, oxidative degradation is a more flexible way to introduce heteroatoms, but the selectivity of oxidative degradation of polyolefins is poor, and the oxidative degradation products are mostly short-chain mixed carboxylic acids of C1-C8, which have limited value. In addition, the oxidative degradation of polyolefins into short-chain mixed carboxylic acids requires harsh reaction conditions, such as high temperature, high pressure or long reaction time, resulting in low carbon yield of the reaction, and a large amount of greenhouse gas carbon dioxide is also produced during the reaction. For example, Jiao et al. first deeply oxidized polystyrene (PS) or PP into small molecular acids, and then reacted with ammonia to generate nitrile and amide compounds. Although this method can increase the value of the product, the entire oxidative degradation reaction still has the problem of low carbon yield due to the deep oxidative degradation of PS or PP into small molecular acids. Therefore, a challenging problem currently faced by oxidative degradation of polyolefins is how to control the degree of oxidative degradation of polyolefins and improve the carbon yield of the reaction.

[0004] In addition, plastic waste in real life is composed of a variety of polymers, such as PP, PE, polyester, polyvinyl chloride (PVC) and PS. This complex mixed plastic further increases the difficulty of recycling. The simultaneous conversion of mixed plastics is a sustainable solution that can reduce the front-end sorting operations and the back-end separation operations of degradation products, which is conducive to improving the recycling efficiency. For polyolefins, the differences in properties between different polyolefins will cause differences in their oxidative degradation conditions and degradation products, thereby increasing the complexity and separation difficulty of the products. Taking PP and PE as an example, the difference in melting points between the two makes PP require higher oxidative degradation conditions than PE. The oxidative degradation products of PE are usually mixed diacids of C4 to C10, while the oxidative degradation products of PP are acetic acid, propionic acid and acetone, etc. Therefore, the oxidative degradation of mixed polyolefins of PP and PE is more challenging than the oxidative degradation of single PP or PE, and it is difficult to achieve relatively uniform oxidative degradation of mixed polyolefins. Summary of the invention

[0005] In view of the problems faced by existing waste polyolefin oxidative degradation recovery methods, such as the difficulty in controlling the oxidative degradation degree of polyolefins, low reaction carbon yield, the products being mostly mixed short-chain carboxylic acids, the product value to be improved, great difficulty in separation and purification, and in particular the difficulty in achieving relatively uniform oxidative degradation of mixed polyolefins, the present invention provides a method for controllably preparing high-value-added uniform long-chain polycarboxylic acids through oxidative degradation of waste polyolefins, so as to convert waste polyolefins into high-value long-chain polycarboxylic acids through oxidative degradation reactions, better control the degree of oxidative degradation reactions of waste polyolefins and the uniformity of the reactions, improve the carbon yield, and effectively increase the uniformity of the molecular weight of oxidative degradation products of mixed polyolefins.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing high-value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins, the method comprising the following steps: adding waste polyolefins to an oxidant solution, heating in a closed reaction container for oxidative degradation reaction, controlling the oxidative degradation reaction temperature to be not less than 80°C and not higher than the thermal decomposition temperature of polyolefins in air, wherein the main component of the obtained degradation product is a long-chain polycarboxylic acid with a number average molecular weight of more than 800 g / mol; the molecular weight and molecular weight distribution index of the long-chain polycarboxylic acid can be adjusted by adjusting the size of the waste polyolefins and / or adjusting the oxidative degradation conditions; the method has a conversion rate of more than 90% for oxidative degradation of waste polyolefins into long-chain polycarboxylic acids;

[0008] The oxidant includes at least one of hydrogen peroxide, nitric acid, and potassium permanganate; the concentration of the oxidant in the oxidant solution is 2 wt% to 65 wt%, and preferably 10 wt% to 40 wt%; the waste polyolefin material is the original waste polyolefin material or the pretreated waste polyolefin material.

[0009] In the above technical solution, the conversion rate of oxidatively degrading waste polyolefin into long-chain polycarboxylic acid refers to the ratio of the mass of long-chain polycarboxylic acid in the oxidative degradation product to the mass of the waste polyolefin material. The concept of this conversion rate is equivalent to the concept of mass yield, that is, the mass yield of long-chain polycarboxylic acid by the above method is above 90%. Since the long-chain polycarboxylic acid obtained by the above technical solution is an oligomeric polycarboxylic acid in paste or wax form, therefore, the mass yield of the long-chain carboxylic acid refers to the mass percentage of the paste or wax degradation product in the degradation product to the waste polyolefin material.

[0010] In the above technical solution, when the waste polyolefin material is the original waste polyolefin material, in order to increase the uniformity of the oxidative degradation reaction, it is preferably that after adding the original waste polyolefin material into the oxidant solution, it is first heated in a closed reaction vessel to a state where the original waste polyolefin material is broken into powder (preferably micron-sized powder) at a temperature lower than the oxidative degradation temperature, and then the temperature is raised to the oxidative degradation temperature for oxidative degradation.

[0011] In the above technical solution, the pretreated waste polyolefin material is obtained by mechanically crushing / or solvent-crushing the original polyolefin material into a powder state. Among them, solvent-crushing the original polyolefin material into a powder state means adding the raw waste polyethylene material into the crushing solvent and heating it until the original waste polyolefin material is transformed into a powder state. The crushing solvent includes toluene, xylene, chlorobenzene, or 1,3,5-trichlorobenzene. Usually, the heating temperature during solvent-crushing can be controlled as T, (t - 20)°C ≤ T2 ≤ (t + 60)°C, where t is the melting point of the polyolefin. For example, the heating temperature during solvent-crushing can be 100 - 180°C, but the feasible heating temperature range for solvent-crushing is not limited to this range. During solvent-crushing, the amount of the crushing solvent used should at least ensure that the crushing solvent completely submerges the original waste polyolefin material. Usually, the mass ratio of the original waste polyolefin material to the volume of the solvent is 1 g:(5 - 20) mL, but the feasible mass ratio of the original waste polyolefin material to the volume of the solvent is not limited to the above range. Further, in the above technical solution, after solvent-crushing is completed, solid-liquid separation is carried out to recover the solvent-crushing solvent, and the recovered solvent-crushing solvent is recycled for the solvent-crushing of the original waste polyolefin material, thereby reducing the solvent-crushing cost of the waste polyolefin.

[0012] In the above technical solution, the size of the pretreated waste polyolefin material is preferably on the micron scale. When using mechanical crushing, it is best to screen the product after mechanical crushing of the original waste polyolefin material to increase the size uniformity of the obtained pretreated waste polyolefin material.

[0013] The molecular weight distribution range of the long-chain polycarboxylic acid prepared by the above technical solution is relatively narrow, and the molecular weight distribution index of the long-chain polycarboxylic acid is between 1.2 and 2.0. The number-average molecular weight of the long-chain polycarboxylic acid can be adjusted by controlling the size of the waste polyolefin material and the oxidative degradation conditions according to actual application requirements. Usually, the number-average molecular weight of the long-chain polycarboxylic acid is between 800 and 10,000 g / mol. For example, it can be between 800 and 2,000 g / mol, between 2,000 and 4,000 g / mol, between 4,000 and 6,000 g / mol, between 6,000 and 8,000 g / mol, between 8,000 and 10,000 g / mol, etc. No matter which molecular weight range the number-average molecular weight of the polycarboxylic acid is in, the molecular weight distribution index of the long-chain polycarboxylic acid is between 1.2 and 2.0.

[0014] The number of carboxyl groups on each molecular chain of the long-chain polycarboxylic acid prepared by the above technical solution is more than 2. The carboxyl group content of the long-chain polycarboxylic acid decreases with the increase of the number-average molecular weight of the long-chain polycarboxylic acid. Usually, the carboxyl group content of the long-chain polycarboxylic acid is above 0.1 mmol / g. When the number-average molecular weight of the long-chain polycarboxylic acid is between 800 and 2,000 g / mol, the carboxyl group content of the long-chain polycarboxylic acid is above 2.0 mmol / g.

[0015] In the above technical solution, the degree of degradation of polyolefin is related to the oxidative degradation conditions (for example, the concentration of the oxidant solution, the dosage of the oxidant solution, the type of oxidant, the temperature of the oxidative degradation reaction, the time of the oxidative degradation reaction) and the size of the waste polyolefin material (for example, the size and size distribution). Therefore, in practical applications, by controlling one or more of these two types of factors, namely the oxidative degradation conditions and the size of the waste polyolefin material, this method can adjust the degree of oxidative degradation of polyolefin, and further adjust the molecular weight and molecular weight distribution index of the long-chain polycarboxylic acid in the degradation product. Generally, when the oxidative degradation time, the type of oxidant, the concentration and dosage of the oxidant solution are certain, the higher the temperature of the oxidative degradation reaction, the lower the molecular weight of the degradation product; when the oxidative reaction temperature, the type of oxidant, the concentration and dosage of the oxidant solution are certain, as the oxidative degradation reaction time gradually increases, the molecular weight of the degradation product first decreases rapidly and then remains stable within a certain time range. Continuing to increase the oxidative degradation reaction time, the degradation product will be further deeply oxidized and degraded into small molecule products and carbon dioxide. Generally, the more uniform the size of the waste polyolefin material, the smaller the molecular weight distribution index of the long-chain polycarboxylic acid in the degradation product. For example, when the temperature of the oxidative degradation reaction is 80-180 °C, the oxidative degradation reaction time is usually 1.5-2.5 h. Of course, the oxidative degradation reaction temperature and time of the above technical solution are not limited to this range. The specific degradation reaction temperature and oxidative degradation reaction time can be comprehensively determined according to factors such as the type of polyolefin of the waste polyolefin material, the size of the waste polyolefin material, the oxidative degradation efficiency, energy consumption, the number average molecular weight of the long-chain polycarboxylic acid in the degradation product, and the mass yield of the long-chain polycarboxylic acid.

[0016] In the above technical solution, the dosage of the oxidant solution should at least ensure that the oxidant solution completely immerses the waste polyolefin material. Generally, the mass ratio of the waste polyolefin material to the volume of the oxidant solution can be controlled at 1 g:(1-20) mL. However, the feasible mass ratio of the waste polyolefin material to the volume of the oxidant solution is not limited to the above range.

[0017] In the above technical solution, the polyolefin is a single polyolefin material or a mixed polyolefin material, and the polyolefin material includes polyethylene, polypropylene or polyolefin elastomer. The polyethylene includes, but is not limited to, low-density polyethylene, high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, metallocene linear low-density polyethylene. The mixed polyolefin material refers to a mixture of different polyolefins. For example, a mixture of polyethylene and polypropylene.

[0018] In the above technical solution, when the polyolefin is a mixed polyolefin, the determination method of the solvent fragmentation temperature T is: (t1 - 20) °C ≤ T ≤ (t1 + 60) °C, where t1 is the melting point of the polyolefin with the highest melting point in the mixed polyolefin material.

[0019] The present invention has been verified through experiments that the molecular weight distribution range of the long-chain polycarboxylic acid prepared by the above technical solution is relatively narrow, and the molecular weight distribution index of the long-chain polycarboxylic acid is between 1.2 and 2.0, and phase separation does not occur in the obtained long-chain polycarboxylic acid. The above characteristics enable the long-chain polycarboxylic acid prepared by the above technical solution to be directly applied without the need for product separation and purification operations before application. For example, the obtained long-chain polycarboxylic acid can be directly applied as a high-performance or multifunctional material. For instance, when the long-chain polycarboxylic acid is waxy, it can be directly applied as a wax product. Of course, according to different application requirements, the long-chain polycarboxylic acid prepared by the above technical solution can also be used after separation and purification. The long-chain polycarboxylic acid prepared by the above technical solution can be prepared into long-chain fatty esters through esterification for application. For example, the obtained long-chain polycarboxylic acid can be directly esterified with an alcohol (such as ethanol) to prepare long-chain fatty esters, and the obtained long-chain fatty esters can be used as plasticizers. The long-chain polycarboxylic acid prepared by the above technical solution can also be prepared into long-chain polyaliphatic amines through nitro reduction for application.

[0020] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0021] 1. The present invention provides a method for controllably preparing high-value-added uniform long-chain polycarboxylic acids by oxidative degradation of waste polyolefins. In this method, waste polyolefin materials are added to an oxidant solution, and an oxidative degradation reaction is carried out by heating in a sealed reaction vessel. The temperature of the oxidative degradation reaction is controlled to be not lower than 50 °C and not higher than the thermal decomposition temperature of the polyolefin in air. The main component of the obtained degradation product is long-chain polycarboxylic acids with a number-average molecular weight of more than 800 g / mol. The molecular weight and molecular weight distribution index of the long-chain polycarboxylic acids can be adjusted by adjusting the size of the waste polyolefin materials and / or adjusting the oxidative degradation conditions. The conversion rate of converting waste polyolefins into long-chain polycarboxylic acids by oxidative degradation in this method is more than 90%. The oxidant includes at least one of hydrogen peroxide, nitric acid, and potassium permanganate. The concentration of the oxidant in the oxidant solution is preferably 10 wt% - 40 wt%. The waste polyolefin materials are raw waste polyolefin materials or pretreated waste polyolefin materials. The present invention processes the waste polyolefin materials into fine powders by means of crushing and pretreatment of the waste polyolefin materials or heating and crushing the raw polyolefin materials in the reaction vessel under conditions lower than the oxidative degradation temperature, which is beneficial to promoting mass transfer and heat transfer of the oxidative degradation reaction and improving the uniformity and efficiency of the oxidative degradation reaction. On this basis, the present invention effectively controls the degree of oxidative degradation and uniformity of waste polyolefins by screening the types and concentrations of oxidants and cooperating with appropriate temperature, pressure, time, etc. of the degradation reaction, that is, effectively regulates the molecular weight and molecular weight distribution index of the long-chain polycarboxylic acids in the degradation product. In particular, long-chain polycarboxylic acids with a number-average molecular weight between 800 and 10,000 g / mol and a relatively narrow molecular weight distribution range can be prepared. On the one hand, the added value of the long-chain polycarboxylic acids obtained by the method of the present invention is much higher than that of the fuel oil prepared by existing waste polyolefin recycling technologies such as pyrolysis, catalytic cracking, and hydrocracking. On the other hand, the method of the present invention also solves the problems existing in the recovery of waste polyolefins by oxidative degradation in the prior art, such as difficult control of the degree of oxidative degradation, mostly mixed short-chain carboxylic acids in the products, and low carbon yield. On the other hand, the method of the present invention realizes the uniform and controllable oxidative degradation of waste polyolefins by relying on an oxidant solution at a low concentration level (10 wt% - 40 wt%), and has the advantage of low catalyst cost, which can overcome the problem of high catalyst cost in the oxidative degradation or modification of waste polyolefins using high-concentration oxidants or organometallic catalysts in the prior art.

[0022] 2. The method of the present invention can achieve uniform oxidative degradation of mixed waste polyolefins to obtain polybasic long-chain carboxylic acids with a narrow molecular weight distribution range, and can solve the problems existing in the prior art that the degradation products of different types of polyolefins are different and the molecular weight distribution range of the degradation products is wide when oxidatively degrading different types of mixed waste polyolefins. This is beneficial to reducing or omitting the sorting operation before the degradation of mixed waste polyolefins and the product separation operation after the degradation, can simplify the degradation operation process of mixed waste polyolefins, improve the recycling efficiency of mixed waste polyolefins and reduce the recycling cost of mixed waste polyolefins.

[0023] 3. The present invention has confirmed through experiments that the molecular weight distribution range of the long-chain polybasic carboxylic acids obtained by oxidatively degrading waste polyolefins by the method of the present invention is narrow, the molecular weight distribution index of the long-chain polybasic carboxylic acids is between 1.2 and 2.0, and no phase separation phenomenon occurs in the obtained long-chain polybasic carboxylic acids. This enables the obtained long-chain polybasic carboxylic acids to be directly applied without the need for product separation and purification operations before application. For example, the long-chain polybasic carboxylic acids obtained by the method of the present invention can be directly esterified to prepare long-chain fatty esters for application, and the prepared long-chain fatty esters can be used as plasticizers. The long-chain polybasic carboxylic acids obtained by the method of the present invention can also be directly subjected to nitro reduction to prepare long-chain polybasic fatty amines for application, and the long-chain polybasic carboxylic acids obtained by the method of the present invention can also be directly used as applications of high-performance or multifunctional materials, such as directly used as wax products. The present invention can solve the problem that the composition of the degradation products obtained by oxidatively degrading waste polyolefins in the prior art is complex or the molecular weight distribution range is wide and special separation operations are required before application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 are the photos of the waste HDPE bottle chips after solvent fragmentation with different solvents and the photos of the degradation products in Example 1.

[0025] Figure 2 is in Example 1 Figure 2 are the photos of the waste HDPE bottle chips after solvent fragmentation and mechanical pulverization with xylene and the photos of the degradation products.

[0026] Figure 3 are the photos of the degradation products obtained by oxidatively degrading waste HDPE under different reaction conditions in Example 2.

[0027] Figure 4 are the infrared spectra of LDPE and DLDPE in Example 3.

[0028] Figure 5 Figures (a) and (b) of are the proton nuclear magnetic resonance spectrum and carbon spectrum of DLDPE in Example 3.

[0029] Figure 6It is the molecular weight and molecular weight distribution of DLDPE obtained by GPC analysis in Example 3.

[0030] Figure 7 It is the SEM image of the degradation product DPP1 / PE1 in Example 4.

[0031] Figure 8 It is the molecular weight and molecular weight distribution of the degradation product DPP1 / PE1 obtained by GPC analysis in Example 4. Detailed implementation manners

[0032] The following further illustrates the method for controllably preparing high-value-added uniform long-chain polycarboxylic acids by oxidative degradation of waste polyolefins according to the present invention through examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art still fall within the protection scope of the present invention when making some non-essential improvements and adjustments to the present invention based on the above-mentioned invention content for specific implementation.

[0033] It is worth noting that in the following examples and comparative examples:

[0034] (1) The mass yield Y of the degradation product of waste polyolefins refers to the mass yield of the solid or / and paste or / and wax-like degradation product obtained after oxidative degradation of waste polyolefins. The calculation formula for the mass yield Y of the degradation product of waste polyolefins is:

[0035]

[0036] In the above formula, W1 is the mass of the solid / and paste or / and wax-like degradation product (when the degradation product is solid, W1 is the mass of the solid degradation product; when the degradation product is paste, W1 is the mass of the paste degradation product; when the degradation product is wax-like, W1 is the mass of the wax-like degradation product; when the degradation product contains at least two of solid, paste and wax-like degradation products, W1 is the total mass of at least two of solid, paste and wax-like degradation products), and W2 is the mass of the waste polyolefins.

[0037] The concept of this mass yield is equivalent to the concept of the conversion rate of converting waste polyolefins into long-chain polycarboxylic acids by oxidative degradation described above.

[0038] (2) The carboxyl group content a of the degradation product COOH It is determined according to the method in the industry standard NB / SH / T 0809-2010.

[0039] (3) The number of carboxyl groups N on each average molecular chain of the degradation product acid The calculation formula is:

[0040] N acid= a COOH × M n

[0041] In the above formula, Mn is the number-average molecular weight of the degradation product, and Mn is obtained by measurement with gel permeation chromatography (GPC).

[0042] Example 1

[0043] In this example, the effects of different crushing methods on the crushing effect of waste polyolefins and the subsequent oxidative degradation effect were investigated.

[0044] 1. Solvent crushing method

[0045] (1) According to the ratio of adding 5 mL of solvent per 1 g of waste high-density polyethylene (HDPE) bottle chips, the waste HDPE bottle chips were respectively placed in xylene, dodecane, and γ-valerolactone of the same volume, heated at 120 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain HDPE after solvent crushing.

[0046] Photos of the waste HDPE bottle chips after solvent crushing with different solvents are as Figure 1 It can be seen that Figure 1 It can be seen that: after the waste HDPE bottle chips were treated with xylene, they changed from the original blocky shape to fine powders with relatively uniform sizes, and the powder particle size was about 200 μm, and the crushing effect was excellent; after the waste HDPE bottle chips were treated with dodecane, most of the waste HDPE bottle chips were swollen by dodecane and the volume increased, and they were not crushed into smaller sizes, and only a small part of the waste HDPE bottle chips had a certain crushing effect; after the waste HDPE bottle chips were treated with γ-valerolactone, the waste HDPE bottle chips remained in the original blocky shape and there was no crushing effect.

[0047] (2) According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of the crushed HDPE, the HDPE crushed by xylene in step (1) and the nitric acid aqueous solution with a concentration of 25 wt% were added to a hydrothermal reaction kettle, the hydrothermal reaction kettle was sealed, heated to 140 °C and maintained at this temperature for 2 h for oxidative degradation reaction. The degradation products were mainly a homogeneous and transparent yellow paste, and there were also a small amount of small molecules soluble in water. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water and dried in an oven at 80 °C.

[0048] According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of crushed HDPE, the HDPE crushed by dodecane and γ-valerolactone in step (1) was respectively added into a hydrothermal reaction kettle, and then a nitric acid aqueous solution with a concentration of 25 wt% was added. The hydrothermal reaction kettle was sealed, heated to 140 °C and maintained at this temperature for 2 h for oxidative degradation reaction. The degradation product was in a solid state. It was cooled to room temperature, filtered and the solid product was collected. The solid product was washed with water and dried in an oven at 80 °C.

[0049] The photos of the degradation products obtained after oxidative degradation of HDPE crushed by different solvents are as Figure 1 shown. It can be seen from Figure 1 that when xylene is used for crushing, the degradation product is a uniform, transparent yellow paste; when dodecane and γ-valerolactone are used for crushing, the degradation product still remains in a solid state. Since the molecular weight of the solid degradation product is higher than that of the paste degradation product, it can be seen from the properties of the degradation product that the smaller and more uniform the size of the crushed polyolefin is, the more beneficial it is to improve the subsequent oxidative degradation effect.

[0050] 2. Mechanical crushing method

[0051] The waste HDPE bottle chips were mechanically crushed by a crusher. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of crushed HDPE, the mechanically crushed waste HDPE bottle chips and a nitric acid aqueous solution with a concentration of 25 wt% were added into a hydrothermal reaction kettle. The hydrothermal reaction kettle was sealed and heated to 140 °C and maintained at this temperature for 2 h for oxidative degradation reaction. The degradation product was mainly in a solid state and there was also a small amount of semi-transparent paste. It was cooled to room temperature, filtered and the solid and paste products were collected. The collected solid and paste were washed with water and dried in an oven at 80 °C.

[0052] Figure 2 are the photos of the waste HDPE bottle chips after solvent crushing and mechanical crushing and the photos of the degradation products. It can be seen from Figure 2It can be seen that due to the good toughness of waste HDPE, the size difference after mechanical crushing is large, most of them still maintain a large size, and a small part is crushed into powder. After being crushed by xylene solvent, the waste HDPE bottle flakes are crushed into relatively uniform and small powders. The waste HDPE bottle flakes crushed by these two crushing methods were oxidatively degraded under the same reaction conditions. The results showed that after oxidative degradation, the degradation products of the waste HDPE bottle flakes after mechanical crushing were mainly white hard block substances, and there was a small amount of translucent paste, which indicated that the uniformity of the degradation products was poor, the molecular weight distribution of the degradation products was wide, and there were solid large molecular weight degradation products and paste-like degradation products with relatively lower molecular weight. The oxidative degradation products of the waste HDPE bottle flakes after being crushed by xylene solvent were uniform and transparent pastes, which indicated that the waste HDPE bottle flakes after being crushed by xylene solvent underwent a more uniform oxidative degradation reaction than mechanical crushing. It can be seen from this that the size of waste polyolefins and their uniformity will affect the uniformity of the oxidative degradation reaction. In practical applications, when mechanical crushing is adopted, the crushed waste polyolefins can be screened to increase the uniformity of the size of the crushed waste polyolefins, thereby promoting the uniformity of the oxidative degradation reaction.

[0053] Example 2

[0054] In this example, the oxidative degradation effects of waste polyolefins under different concentrations of nitric acid and different pressure conditions were investigated.

[0055] (1) Reaction under normal pressure using concentrated nitric acid: waste HDPE is placed in xylene at a ratio of 5 mL of xylene per 1 g of waste HDPE bottle flakes, heated at 120° C. for 30 min, cooled to room temperature, filtered, and dried in an oven at 80° C. to obtain HDPE powder with a particle size of about 200 μm. HDPE powder and a 68 wt% nitric acid aqueous solution are added to a round-bottom flask at a ratio of 5 mL of nitric acid aqueous solution per 1 g of HDPE powder, and the round-bottom flask is placed in an oil bath at 120° C. and heated under reflux for 12 h under magnetic stirring for oxidative degradation reaction, the degradation product is solid, cooled to room temperature, filtered and collected, washed with water, and dried in an oven at 80° C.

[0056] (2) React in a hydrothermal reactor with concentrated nitric acid: According to the ratio of adding 5 mL of xylene per 1 g of waste HDPE bottle chips, put the waste HDPE into xylene, heat at 120 °C for 30 min, cool to room temperature, filter, and dry in an oven at 80 °C to obtain HDPE powder with a particle size of about 200 μm. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of HDPE powder, add the HDPE powder and nitric acid aqueous solution with a concentration of 68 wt% into the hydrothermal reactor, seal the hydrothermal reactor, heat to 140 °C and maintain at this temperature for 2 h for oxidative degradation reaction. The degradation product is mainly a dark black paste. Cool to room temperature, pour out the liquid in the hydrothermal reactor, take out the dark black paste adhering to the hydrothermal reactor, wash it with water and dry it in an oven at 80 °C.

[0057] (3) React in a hydrothermal reactor with low-concentration nitric acid: According to the ratio of adding 5 mL of xylene per 1 g of waste HDPE bottle chips, put the waste HDPE into xylene, heat at 120 °C for 30 min, cool to room temperature, filter, and dry in an oven at 80 °C to obtain HDPE powder with a particle size of about 200 μm. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of HDPE powder, add the HDPE powder and nitric acid aqueous solution with a concentration of 18 wt% into the hydrothermal reactor, seal the hydrothermal reactor, heat to 140 °C and maintain at this temperature for 2 h for oxidative degradation reaction. The degradation product is a uniform and transparent yellow paste. Cool to room temperature, pour out the liquid in the hydrothermal reactor, take out the paste adhering to the hydrothermal reactor, wash it with water and dry it in an oven at 80 °C.

[0058] Figure 3 are the photos of the degradation products obtained by oxidatively degrading waste HDPE under different reaction conditions in this example. It can be seen from Figure 3 that when degrading waste HDPE at atmospheric pressure, even using concentrated nitric acid (nitric acid aqueous solution with a concentration of 68 wt%) as the oxidant, the oxidative degradation rate is still very slow. After reflux reaction at atmospheric pressure for 12 h, the obtained degradation product is still in powder state, indicating that the molecular weight of the degradation product is relatively large; when using concentrated nitric acid (nitric acid aqueous solution with a concentration of 68 wt%) as the oxidant to degrade waste HDPE in a sealed hydrothermal reactor, the obtained degradation product is a dark black paste, and the mass yield of the degradation product is only 65%, indicating that the reaction is too violent and there are more small-molecule water-soluble products and gaseous products; when using low-concentration nitric acid (nitric acid aqueous solution with a concentration of 18 wt%) as the oxidant to degrade waste HDPE in a sealed hydrothermal reactor, the degradation product is a uniform and transparent yellow paste, which indicates that the molecular weight of the degradation product is relatively low and the uniformity of the degradation product is good (the molecular weight distribution range is relatively narrow), and the mass yield of the degradation product is 118%.

[0059] The experimental results of this example show that when using a low-concentration nitric acid aqueous solution to oxidatively degrade waste HDPE in a closed reaction kettle, not only can the oxidative degradation efficiency be improved, but also the degree of oxidative degradation can be controlled at an appropriate level to ensure the uniformity of the degree of oxidative degradation, and the mass yield of the degradation products can be effectively increased.

[0060] Example 3

[0061] In this example, the method described in the present invention was used to oxidatively degrade waste low-density polyethylene (LDPE) and the degradation products were characterized.

[0062] According to the ratio of adding 5 mL of xylene per 1 g of the original waste LDPE, the original waste LDPE was put into xylene, heated at 120 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain LDPE powder with a particle size of about 200 μm. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of LDPE powder, the LDPE powder and a nitric acid aqueous solution with a concentration of 25 wt% were added to a hydrothermal reaction kettle, and the hydrothermal reaction kettle was sealed and heated to 140 °C and maintained at this temperature for 2 h for the oxidative degradation reaction. The degradation products were mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste-like oxidative degradation products adhering to the hydrothermal reaction kettle were taken out, washed with water and dried in an oven at 80 °C. The oxidative degradation products were denoted as DLDPE.

[0063] FT-IR tests were carried out on LDPE and DLDPE, and the results are as Figure 4 shown. It can be seen from Figure 4 that DLDPE shows a characteristic peak of the carbonyl group of the carboxyl group at 1714 cm -1 . DLDPE was further characterized by proton nuclear magnetic resonance (¹H NMR) and carbon-13 nuclear magnetic resonance (¹³C NMR). The ¹H NMR spectrum of DLDPE is as shown in Figure 5 Figure (a). In the ¹H NMR spectrum, the characteristic peak at 0 - 2 ppm is the signal of the hydrogen on the methylene group in DLDPE, indicating that DLDPE retains some methylene fragments originally in LDPE. The characteristic peak at 2.0 - 3.0 ppm is the signal of the hydrogen on the carbon connected to the carbonyl group, and the broad peak at 8.0 ppm is the signal of the active hydrogen on the carboxyl group. The ¹³C NMR spectrum of DLDPE is as shown in Figure 5 Figure (b). The characteristic peak at 0 - 20 ppm is the peak of aliphatic carbon, and the characteristic peak at 179.9 ppm is the peak of carboxyl carbon, indicating that DLDPE contains a large amount of carboxyl groups.

[0064] GPC was used to analyze the molecular weight and molecular weight distribution of DLDPE, and the results are as Figure 6As shown, the number-average molecular weight Mn of DLDPE is 1013 g / mol, and the molecular weight distribution index is 1.77, indicating that DLDPE is an oligomer containing carboxyl groups. The carboxyl group content in DLDPE was determined to be 4.2 mmol / g by acid-base titration, and further the number N of carboxyl groups on each molecular chain of DLDPE was calculated. acid The value of N is 4.2, indicating that DLDPE is mainly a long-chain polycarboxylic acid with more than 2 carboxyl groups. Long-chain polycarboxylic acid is a high-value fine chemical, and its chemical synthesis is relatively difficult. In this invention, high-value long-chain polycarboxylic acid is obtained by oxidative degradation of waste polyolefins. Compared with the prior art, this invention can improve the value of the degradation products of waste polyolefins.

[0065] Example 4

[0066] In this example, the oxidative degradation effect of the method described in this invention on the mixed waste polyolefins of waste LDPE and waste PP was investigated.

[0067] The molecular chain of PP contains methyl side groups, which makes it have higher rigidity and crystallinity. The intermolecular force between the molecular chains of PP is relatively strong, and the melting point of PP is 160 °C. The molecular chain of PE is composed of a large number of methylene groups, with good flexibility of the molecular chain, and the melting point is 120 °C. At the same time, PP contains a large number of tertiary carbons, which are more likely to undergo free radical reactions than the large number of secondary carbons in PE. The differences in physical and chemical properties between PP and PE make the mixed degradation of the two more difficult. The mixture of PP and PE is the most difficult-to-degrade mixed polyolefin recognized in the art. In this example, the mixed waste polyolefins of waste LDPE and waste PP were oxidatively degraded to investigate the oxidative degradation effect of the method described in this invention on the mixed polyolefins.

[0068] 1. Experimental group: According to the ratio of adding 5 mL of xylene per 1 g of waste mixed polyolefins (the waste mixed polyolefins are composed of original waste PP and original waste LDPE in a mass ratio of 1:1, abbreviated as LDPE / PP), add LDPE / PP to xylene, heat at 120 °C for 30 min, cool to room temperature, filter, and dry in an oven at 80 °C to obtain LDPE / PP mixed powder with a particle size of about 200 μm. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of PP / LDPE mixed powder, add the PP / LDPE mixed powder and 25 wt% nitric acid aqueous solution to a hydrothermal reaction kettle, close the hydrothermal reaction kettle, heat to 140 °C and maintain at this temperature for 2 h for oxidative degradation reaction. The degradation products are mainly a homogeneous transparent yellow paste. Cool to room temperature, pour out the liquid in the hydrothermal reaction kettle, take out the paste-like oxidative degradation products adhering to the hydrothermal reaction kettle, wash with water and dry in an oven at 80 °C, and record the degradation products as DPP1 / PE1.

[0069] From the optical picture of the degradation product DPP1 / PE1, DPP1 / PE1 is a uniform yellow transparent paste, as shown in the small picture at the lower left corner of Figure 7 , indicating that the degradation degree of the two is relatively uniform. Further, a scanning electron microscope (SEM) test was carried out on DPP1 / PE1, and the results are as shown in Figure 7 . The SEM picture shows that DPP1 / PE1 is very uniform without obvious phase separation, indicating that DPP1 / PE1 has good compatibility and can be directly used in the back end without further separation and purification, without additional separation and purification steps. The molecular weight and molecular weight distribution of DPP1 / PE1 were analyzed by GPC, and the results are as shown in Figure 8 . As can be seen from Figure 8 , there is only one peak on the GPC curve of DPP1 / PE1, indicating that in this example, the waste PP / waste LDPE mixed polyolefin is oxidatively degraded, and the molecular weights of the obtained degradation products are close, and the molecular weight distribution range is narrow.

[0070] 2. Control group: According to the ratio of adding 5 mL of xylene per 1 g of waste mixed polyolefin (the waste mixed polyolefin is composed of original waste PP and original waste LDPE in a mass ratio of 1:1, abbreviated as LDPE / PP), add LDPE / PP to xylene, heat at 120 °C for 30 min, cool to room temperature, filter, and dry in an oven at 80 °C to obtain LDPE / PP mixed powder with a particle size of about 200 μm. According to the ratio of adding 5 mL of nitric acid aqueous solution per 1 g of PP / LDPE mixed powder, add the PP / LDPE mixed powder and 68 wt% nitric acid aqueous solution to a round-bottom flask, place the round-bottom flask in an oil bath at 120 °C, and heat under magnetic stirring and reflux for 12 h for oxidative degradation reaction. The degradation product contains both solid products and paste-like substances. Cool to room temperature, filter and collect the solid and paste-like products, wash the solid and paste-like products with water, and dry in an oven at 80 °C.

[0071] Judging from the properties of the degradation products, when the waste PP / waste LDPE mixed polyolefin is degraded with concentrated nitric acid under normal pressure, the molecular weights of the degradation products vary greatly, and the compatibility of the degradation products is poor, and the products are inhomogeneous. From the comparison between the above experimental group and the control group, it can be seen that the method of the present invention can well oxidatively degrade the mixed waste polyolefin into degradation products with close molecular weights, and can solve the problem that it is difficult or even impossible to achieve relatively uniform oxidative degradation of the mixed polyolefin in the prior art, and it is impossible to obtain degradation products with a narrow molecular weight distribution range.

[0072] Example 5

[0073] The original waste LDPE was added to xylene at a ratio of 5 mL of xylene per 1 g of the original waste LDPE, heated at 120 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized LDPE powder. The LDPE powder and a nitric acid aqueous solution with a concentration of 10 wt% were added to a hydrothermal reaction kettle at a ratio of 5 mL of the nitric acid aqueous solution per 1 g of the LDPE powder. The hydrothermal reaction kettle was sealed and heated to 120 °C and maintained at this temperature for 2 h for the oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0074] In this example, the mass yield of the long-chain polycarboxylic acid was 120%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1145 g / mol, the molecular weight distribution index was 1.94, the carboxyl group content of the long-chain polycarboxylic acid was 3.7 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 4.2.

[0075] Example 6

[0076] The original waste HDPE was added to chlorobenzene at a ratio of 5 mL of chlorobenzene per 1 g of the original waste HDPE, heated at 100 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized HDPE powder. The HDPE powder and a nitric acid aqueous solution with a concentration of 35 wt% were added to a hydrothermal reaction kettle at a ratio of 2 mL of the nitric acid aqueous solution per 1 g of the HDPE powder. The hydrothermal reaction kettle was sealed and heated to 160 °C and maintained at this temperature for 1.5 h for the oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0077] In this example, the mass yield of the long-chain polycarboxylic acid was 114%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1234 g / mol, the molecular weight distribution index was 1.83, the carboxyl group content of the long-chain polycarboxylic acid was 3.5 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 4.3.

[0078] Example 7

[0079] The raw waste LDPE was added to 1,3,5-trichlorobenzene at a ratio of 5 mL of 1,3,5-trichlorobenzene per 1 g of raw waste LDPE, heated at 180 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized LDPE powder. The LDPE powder and 40 wt% hydrogen peroxide aqueous solution were added to a hydrothermal reaction kettle at a ratio of 10 mL of hydrogen peroxide aqueous solution per 1 g of LDPE powder. The hydrothermal reaction kettle was sealed and heated to 150 °C and maintained at this temperature for 2.5 h for oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0080] In this example, the mass yield of the long-chain polycarboxylic acid was 106%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1154 g / mol, the molecular weight distribution index was 1.74, the carboxyl content of the long-chain polycarboxylic acid was 3.7 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 4.3.

[0081] Example 8

[0082] The raw waste PP was added to xylene at a ratio of 5 mL of xylene per 1 g of raw waste PP, heated at 80 °C for 120 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized PP powder. The PP powder and 30 wt% potassium permanganate aqueous solution were added to a hydrothermal reaction kettle at a ratio of 5 mL of potassium permanganate aqueous solution per 1 g of PP powder. The hydrothermal reaction kettle was sealed and heated to 130 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0083] In this example, the mass yield of the long-chain polycarboxylic acid was 105%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1056 g / mol, the molecular weight distribution index was 1.97, the carboxyl content of the long-chain polycarboxylic acid was 3.4 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 3.6.

[0084] Example 9

[0085] According to the ratio of adding 5 mL of 1,3,5-trichlorobenzene per 1 g of the original waste POE, the original waste POE was added to xylene, heated at 110 °C for 60 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized POE powder. According to the ratio of adding 20 mL of nitric acid aqueous solution per 1 g of POE powder, the LDPE powder and the nitric acid aqueous solution with a concentration of 40 wt% were added to a hydrothermal reaction kettle, and the hydrothermal reaction kettle was sealed and heated to 100 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0086] In this example, the mass yield of the long-chain polycarboxylic acid was 107%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1024 g / mol, the molecular weight distribution index was 1.84, the carboxyl group content of the long-chain polycarboxylic acid was 3.4 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 3.5.

[0087] Example 10

[0088] According to the ratio of adding 5 mL of xylene per 1 g of the original waste LDPE, the original waste LDPE was added to xylene, heated at 130 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized LDPE powder. According to the ratio of adding 15 mL of nitric acid aqueous solution per 1 g of LDPE powder, the LDPE powder and the nitric acid aqueous solution with a concentration of 10 wt% were added to a hydrothermal reaction kettle, and the hydrothermal reaction kettle was sealed and heated to 140 °C and maintained at this temperature for 2.5 h for oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0089] In this example, the mass yield of the long-chain polycarboxylic acid was 105%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1056 g / mol, the molecular weight distribution index was 1.88, the carboxyl group content of the long-chain polycarboxylic acid was 3.4 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 3.6.

[0090] Example 11

[0091] According to the proportion of adding 5 mL of xylene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of original waste LDPE and original waste PP in a mass ratio of 1:1), the mixed waste polyolefins are added to xylene, heated at 140 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the proportion of adding 15 mL of nitric acid aqueous solution per 1 g of mixed waste polyolefin powder, the mixed waste polyolefin powder and nitric acid aqueous solution with a concentration of 35 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 150 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0092] In this example, the mass yield of the long-chain polycarboxylic acid is 117%, the number-average molecular weight Mn of the long-chain polycarboxylic acid is 1145 g / mol, the molecular weight distribution index is 1.74, the carboxyl group content of the long-chain polycarboxylic acid is 3.0 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid is 3.4.

[0093] Example 12

[0094] According to the proportion of adding 10 mL of 1,3,5-trichlorobenzene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of original waste LDPE and original waste PP in a mass ratio of 2:1), the mixed waste polyolefins are added to 1,3,5-trichlorobenzene, heated at 180 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the proportion of adding 2 mL of nitric acid aqueous solution per 1 g of mixed waste polyolefin powder, the mixed waste polyolefin powder and nitric acid aqueous solution with a concentration of 40 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 160 °C and maintained at this temperature for 2.5 h for oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0095] In this example, the mass yield of the long-chain polycarboxylic acid is 104%, the number-average molecular weight Mn of the long-chain polycarboxylic acid is 1257 g / mol, the molecular weight distribution index is 1.41, the carboxyl group content of the long-chain polycarboxylic acid is 2.8 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid is 3.5.

[0096] Example 13

[0097] According to the ratio of adding 5 mL of xylene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of original waste LDPE and original waste PP in a mass ratio of 1:5), the mixed waste polyolefins are added to xylene, heated at 140 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the ratio of adding 15 mL of nitric acid aqueous solution per 1 g of mixed waste polyolefin powder, the mixed waste polyolefin powder and a nitric acid aqueous solution with a concentration of 20 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 140 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0098] In this example, the mass yield of the long-chain polycarboxylic acid is 113%, the number-average molecular weight Mn of the long-chain polycarboxylic acid is 1042 g / mol, the molecular weight distribution index is 1.97, the carboxyl group content of the long-chain polycarboxylic acid is 3.0 mmol / g, and the number of carboxyl groups N acid on each molecular chain is 3.1.

[0099] Example 14

[0100] According to the ratio of adding 20 mL of xylene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of original waste LDPE, original waste PP, and original waste HDPE in a mass ratio of 1:1:1), the mixed waste polyolefins are added to xylene, heated at 140 °C for 60 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the ratio of adding 15 mL of potassium permanganate aqueous solution per 1 g of mixed waste polyolefin powder, the mixed waste polyolefin powder and a potassium permanganate aqueous solution with a concentration of 30 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 160 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0101] In this example, the mass yield of the long-chain polycarboxylic acid is 118%, the number-average molecular weight Mn of the long-chain polycarboxylic acid is 1011 g / mol, the molecular weight distribution index is 1.67, the carboxyl group content of the long-chain polycarboxylic acid is 3.2 mmol / g, and the number of carboxyl groups N acid on each molecular chain is 3.2.

[0102] Example 15

[0103] According to the proportion of adding 30 mL of chlorobenzene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of raw waste LDPE, raw waste POE, and raw waste HDPE in a mass ratio of 1:2:1), the mixed waste polyolefins are added to xylene, heated at 180 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the proportion of adding 2 mL of nitric acid aqueous solution per 1 g of the mixed waste polyolefin powder, the mixed waste polyolefin powder and an aqueous potassium permanganate solution with a concentration of 40 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 130 °C and maintained at this temperature for 2.5 h for the oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acids.

[0104] In this example, the mass yield of the long-chain polycarboxylic acids is 106%, the number-average molecular weight Mn of the long-chain polycarboxylic acids is 1149 g / mol, the molecular weight distribution index is 1.88, the carboxyl group content of the long-chain polycarboxylic acids is 3.3 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid is 3.8.

[0105] Example 16

[0106] According to the proportion of adding 30 mL of xylene per 1 g of mixed waste polyolefins (the mixed waste polyolefins are composed of raw waste LDPE, raw waste HDPE, raw waste LLDPE, and waste PP in a mass ratio of 1:1:3:2), the mixed waste polyolefins are added to xylene, heated at 160 °C for 30 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized mixed waste polyolefin powder. According to the proportion of adding 5 mL of nitric acid aqueous solution per 1 g of the mixed waste polyolefin powder, the mixed waste polyolefin powder and an aqueous nitric acid solution with a concentration of 35 wt% are added to a hydrothermal reaction kettle. The hydrothermal reaction kettle is sealed and heated to 150 °C and maintained at this temperature for 2.5 h for the oxidative degradation reaction. The degradation products are mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle is poured out, and the paste adhering to the hydrothermal reaction kettle is taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acids.

[0107] In this example, the mass yield of the long-chain polycarboxylic acids is 122%, the number-average molecular weight Mn of the long-chain polycarboxylic acids is 966 g / mol, the molecular weight distribution index is 1.51, the carboxyl group content of the long-chain polycarboxylic acids is 3.5 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid is 3.4.

[0108] Example 17

[0109] The raw waste LDPE was added to xylene at a ratio of 5 mL of xylene per 1 g of raw waste LDPE, heated at 110 °C for 60 min, cooled to room temperature, filtered, and dried in an oven at 80 °C to obtain micron-sized LDPE powder. The LDPE powder and a nitric acid aqueous solution with a concentration of 10 wt% were added to a hydrothermal reaction kettle at a ratio of 20 mL of nitric acid aqueous solution per 1 g of LDPE powder. The hydrothermal reaction kettle was sealed and heated to 80 °C and maintained at this temperature for 2 h for oxidative degradation reaction. The degradation product was mainly a uniform wax-like substance. It was cooled to room temperature, filtered to collect the wax-like substance, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid. This wax-like long-chain polycarboxylic acid can be directly used in oxidized wax products.

[0110] In this example, the mass yield of the long-chain polycarboxylic acid was 124%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 9845 g / mol, the molecular weight distribution index was 1.97, the carboxyl group content of the long-chain polycarboxylic acid was 0.4 mmol / g, and the number of carboxyl groups N on each average molecular chain acid was 3.9.

[0111] Example 18

[0112] The raw waste LDPE was added to a 25 wt% nitric acid solution at a ratio of 20 mL of nitric acid aqueous solution per 1 g of raw waste LDPE. It was heated in a sealed reaction vessel at 50 °C until the raw waste LDPE was broken into a powder state, and then the sealed reaction vessel was heated to 150 °C and maintained at this temperature for 2 h for oxidative degradation reaction. The degradation product was mainly a uniform transparent yellow paste. It was cooled to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water, and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0113] In this example, the mass yield of the long-chain polycarboxylic acid was 104%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1041 g / mol, the molecular weight distribution index was 1.78, the carboxyl group content of the long-chain polycarboxylic acid was 3.4 mmol / g, and the number of carboxyl groups N on each average molecular chain acid was 3.5.

[0114] Example 19

[0115] The original waste PP was added to a 35 wt% nitric acid solution at a ratio of 15 mL of nitric acid aqueous solution per 1 g of the original waste PP. The mixture was heated in a sealed reaction vessel at 50 °C until the original waste PP was broken into a powder state. Subsequently, the sealed reaction vessel was heated to 130 °C and maintained at this temperature for 1.5 h for oxidative degradation reaction. The degradation product was mainly a homogeneous and transparent yellow paste. After cooling to room temperature, the liquid in the hydrothermal reaction kettle was poured out, and the paste adhering to the hydrothermal reaction kettle was taken out, washed with water and dried in an oven at 80 °C to obtain long-chain polycarboxylic acid.

[0116] In this example, the mass yield of the long-chain polycarboxylic acid was 114%, the number-average molecular weight Mn of the long-chain polycarboxylic acid was 1174 g / mol, the molecular weight distribution index was 1.97, the carboxyl group content of the long-chain polycarboxylic acid was 2.9 mmol / g, and the number of carboxyl groups N on each molecular chain on average acid was 3.4.

Claims

1. A method for preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins, characterized in that: The following steps are involved: Adding waste polyolefin material to an oxidant solution, heating in a closed reaction container for oxidative degradation reaction, controlling the oxidative degradation reaction temperature to be not less than 80° C. and not higher than the thermal decomposition temperature of polyolefin in air, wherein the main component of the obtained degradation product is a long-chain polycarboxylic acid with a number average molecular weight of more than 800 g / mol; the molecular weight and molecular weight distribution index of the long-chain polycarboxylic acid can be adjusted by adjusting the size of the waste polyolefin material and / or adjusting the oxidative degradation conditions; the method has a conversion rate of more than 90% for oxidative degradation of waste polyolefin into long-chain polycarboxylic acid; The oxidant comprises at least one of hydrogen peroxide, nitric acid and potassium permanganate; the concentration of the oxidant in the oxidant solution is 2wt% to 65wt%, and the concentration of the oxidant is preferably 10wt% to 40wt%; the waste polyolefin material is original waste polyolefin material or pretreated waste polyolefin material.

2. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to claim 1, characterized in that: When the waste polyolefin material is original waste polyolefin material, after the original waste polyolefin material is added to the oxidant solution, it is first heated in a closed reaction container under conditions below the oxidative degradation temperature until the original waste polyolefin material is broken into a powder state, and then the temperature is raised to the oxidative degradation temperature for oxidative degradation.

3. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to claim 1, characterized in that: The pretreated waste polyolefin material is obtained by mechanically crushing or / and solvent crushing the original polyolefin material into a powder state.

4. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to claim 3, characterized in that: Crushing the original polyolefin material solvent into powder state means that the raw waste polyethylene material is added into the crushing solvent and heated until the original waste polyolefin material is converted into powder state, and the crushing solvent includes toluene, xylene, chlorobenzene or 1,3,5-trichlorobenzene.

5. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to claim 4, characterized in that: After the solvent crushing is completed, the solid and liquid are separated, the solvent crushing solvent is recovered, and the recovered solvent crushing solvent is recycled for the solvent crushing of the original waste polyolefin material.

6. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to any one of claims 1 to 5, characterized in that: The time of the oxidative degradation reaction is controlled to be 1.5 to 2.5 hours.

7. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to any one of claims 1 to 5, characterized in that: The ratio of the mass of the waste polyolefin material to the volume of the oxidant solution is controlled to be 1 g: (1-20) mL.

8. The method for controllably preparing high value-added uniform long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to any one of claims 1 to 5, characterized in that: The polyolefin material is a single polyolefin material or a mixed polyolefin material, and the polyolefin material includes polyethylene, polypropylene or polyolefin elastomer.

9. The method for preparing high value-added long-chain polycarboxylic acid by oxidative degradation of waste polyolefins according to any one of claims 1 to 5, characterized in that: The long-chain polycarboxylic acid obtained by oxidative degradation of waste polyolefins can be directly mixed and applied or applied after separation. The long-chain polycarboxylic acid obtained by oxidative degradation of waste polyolefins can be prepared into long-chain fatty esters through esterification or long-chain polycarboxylic acid can be prepared into long-chain fatty amines through nitro reduction.

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