Method for preparing short-chain diacid by catalytic oxidation of polyethylene with ionic liquid

Abstract

The present invention relates to the technical field of chemical synthesis, and discloses a method for preparing short-chain diacids by catalytic oxidation of polyethylene with ionic liquids, which includes the steps of: mixing an ionic liquid and polyethylene, and carrying out an oxidation reaction in an environment where nitric oxide and oxygen are present to obtain short-chain diacids. The present invention for the first time uses polyethylene as a raw material, and uses an ionic liquid as a reaction catalyst and a reaction medium to catalyze the generation of nitrogen dioxide from nitric oxide to achieve the efficient catalytic oxidation of polyethylene, obtaining short-chain diacid products with 4-12 carbon atoms, with a highest yield of over 90%, and the recycled polyethylene has little influence on the yield. This method not only solves the problem of polyethylene waste recycling, but also solves the problem of high preparation cost of short-chain diacids, greatly reducing their preparation cost.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and particularly relates to a method for preparing short-chain diacids by catalytic oxidation of polyethylene with ionic liquids. Background Art

[0002] Due to characteristics such as low cost, excellent performance, and easy processing and molding, plastics have become an indispensable part of modern life. According to statistics, nearly 80% of the plastic waste generated by humans is buried in landfills or ultimately enters nature. The natural degradation process may last for hundreds of years, which will cause great harm to human health and the ecological environment. Polyethylene (PE) is one of the most widely used plastics, and its annual output accounts for more than one-fourth of all plastic products. Due to the inert C-H bonds and C-C bonds of polyolefins, complex aggregation states, and poor solubility, its upgrading and recycling are full of challenges. Developing practical and efficient chemical methods to use these widely used polyolefin plastics as potential carbon resources and convert them into high-value-added chemicals can not only reduce the environmental and ecological burden but also contribute to the recycling of resources, which is of great significance for the sustainable development of human society.

[0003] Short-chain diacids are important chemicals, commonly used in the synthesis of high-molecular compounds and the preparation of biomedicines. For example, pimelic acid is not only used in the preparation of polymers and plasticizers but also commonly used in biochemical research, the preparation of biomedicines, and ligand synthesis. For example, it is used as biological reagents for amino acids, proteins, and culture media, nucleic acid and its derivative stains, antibiotics and vitamins, endonucleases and modifying enzymes, separation reagents for enzymes and coenzymes, and biological buffers, etc., and has wide applications and important values.

[0004] The structural formula of short-chain diacids is shown as follows:

[0005]

[0006] Traditional preparation methods usually adopt the oxidation method of cycloalkanones or cycloalkanols, using oxidants such as nitric acid to oxidize cycloalkanones or cycloalkanols to prepare the corresponding diacids, usually with higher costs, and accompanied by high energy consumption and a large amount of greenhouse gas emissions:

[0007] a. Chinese Patent CN 1938254 A discloses a method for preparing a dicarboxylic acid compound. In the presence of trifluoroacetic acid, aliphatic cyclic secondary alcohol compounds or aliphatic cyclic ketone compounds are oxidized using nitrites or nitrates to prepare aliphatic dicarboxylic acids with a yield of 100%. There are problems of high costs of cyclic ketones or alcohols and intense exothermic reactions.

[0008] b. The international patent WO 01 / 87815 A2 discloses a method for preparing aliphatic carboxylic acid compounds by oxidizing aliphatic or alicyclic ketones with molecular oxygen in the presence of a soluble manganese (II) compound, with a yield of 91.8%. However, it also has the drawback of high cost of aliphatic or alicyclic ketones.

[0009] Currently, the main domestic enterprises producing short-chain diacids (C4-C 12 ) include Nanjing Xinhua Yuan Chemical, Shandong Daoqin Chemical, Wuhan Hengjiu Chemical, etc. They mainly use the oxidation method of cyclic ketones or alcohols, and the main problems are relatively high raw material costs, violent reactions, and lack of greenness.

[0010] In recent years, with the rise of green chemistry, the demand for using environmentally friendly catalysts and solvents has been increasing continuously. Therefore, the research on new methods for synthesizing short-chain diacids (C4-C 12 ) has been gradually developing. For example, using ionic liquids as reaction systems to convert waste polymers into high-value products is a current research hotspot. These new research results are expected to play a more important role in future applications. According to the requirements of current green chemistry, we have combined the degradation of waste polyethylene with the production of high-value diacids to create a new method for preparing short-chain diacids (C4-C 12 ). Summary of the Invention

[0011] In view of the urgent need to process polyethylene and the problems of high value and high preparation cost of short-chain diacids (C4-C12), the present invention provides a method for preparing short-chain diacids by catalytic oxidation of polyethylene with ionic liquids. The method has high reaction efficiency, simple operation, and the catalyst can be reused, realizing the efficient degradation of polyethylene and the low-cost synthesis of short-chain diacids (C4-C12).

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A method for catalytic oxidation of polyethylene with ionic liquids to prepare short-chain diacids, comprising the steps of: mixing an ionic liquid and polyethylene, and carrying out an oxidation reaction in an environment where nitric oxide and oxygen are present to obtain short-chain diacids.

[0014] The present invention for the first time uses polyethylene as a raw material, and uses an ionic liquid as a reaction catalyst and a reaction medium, which has good absorption performance for nitric oxide, has good contact with polyethylene, is more likely to achieve efficient catalytic oxidation of polyethylene, and controls the carbon number of the diacid product within a certain range. Finally, the yield of short-chain diacid can reach more than 90% at most, and the carbon number of the product is controlled within the range of 4-12; among them, the ionic liquid can be recycled and reused. This method not only solves the problem of polyethylene waste recycling, but also solves the problem of high preparation cost of short-chain diacid, and greatly reduces its preparation cost.

[0015] The ionic liquid includes any one or more of [trihexyltetradecylphosphonium][benzenesulfonate], [trihexyltetradecylphosphonium][trifluoroacetate], [trihexyltetradecylphosphonium][acetate], [trihexyltetradecylphosphonium][trichloroacetate], [trihexyloctylphosphonium][benzenesulfonate], [trihexyloctylphosphonium][acetate], [trihexyloctylphosphonium][trifluoroacetate], [trihexyloctylphosphonium][trichloroacetate], [tributyloctylphosphonium][benzenesulfonate], [tributyloctylphosphonium][acetate], [tributylethylphosphonium][acetate], [tributylethylphosphonium][benzenesulfonate], [triethylbutylammonium][acetate], [triethylbutylammonium][benzenesulfonate], [tetraethylammonium][acetate], [tetraethylammonium][benzenesulfonate], [tributylethylphosphonium][trifluoroacetate], [tributylethylphosphonium][acetate].

[0016] Preferably, an ionic liquid with good absorption performance for nitric oxide and small contact tension with polyethylene is selected, including any one or more of [trihexyltetradecylphosphonium][benzenesulfonate], [trihexyltetradecylphosphonium][trifluoroacetate], [trihexyltetradecylphosphonium][acetate], [tributyloctylphosphonium][acetate], [tributylethylphosphonium][trichloroacetate], [triethylbutylammonium][acetate].

[0017] The mass ratio of the ionic liquid to polyethylene is 0.5 or more. Preferably, the mass ratio of the ionic liquid to polyethylene is 1 or more, more preferably 2 or more, and further preferably 2-6. Increasing the amount of the ionic liquid is beneficial to improving the yield, but too much has little effect on the yield but increases the cost.

[0018] The pressure of the nitric oxide is 0.1-1 MPa. Preferably, the pressure of the nitric oxide is 0.2-1 MPa, and more preferably the pressure of the nitric oxide is 0.4-0.8 MPa. The more the NO content, the more beneficial it is to the progress of the reaction and the higher the yield.

[0019] The pressure of the oxygen is 0.5-10 MPa. Preferably, the pressure of the oxygen is 1.0-5.0 MPa.

[0020] The temperature of the oxidation reaction is 80 - 160 °C, and the reaction time is 10 - 36 h. Preferably, the reaction temperature is 100 - 160 °C, and the reaction time is 12 - 30 h.

[0021] After the reaction, the ionic liquid can be recycled. The recycling of the ionic liquid includes: adding water to the reaction system to dissolve the product, and extracting the aqueous phase with dichloromethane to separate and recycle the ionic liquid and the diacid product.

[0022] The separation and purification process of the product short-chain diacid includes: adding sulfuric acid methanol solution to the diacid product separated from the ionic liquid, refluxing the reaction to methylate the product short-chain diacid, separating the dimethyl esters of each component by vacuum distillation, and then hydrolyzing to obtain the short-chain diacids of each component.

[0023] The short-chain diacids include one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, etc.

[0024] The yield of the short-chain diacid is above 30%. Preferably, the yield can be above 40%, above 50%, above 60%, above 70%, above 80%, above 90%, and the highest can reach 92%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In the present invention, the method of catalytic oxidation with ionic liquid realizes the efficient degradation of waste polyethylene under mild conditions, avoiding the use of metal catalysts. The waste polyethylene is controllably converted into high-value short-chain diacids, and the low-cost synthesis of short-chain diacids (C4 - C 12 ) is achieved through a new route. Description of the Drawings

[0027] Figure 1 It is the distribution and yield of the short-chain diacid product in Example 1.

[0028] Figure 2 It is the gas chromatogram of the short-chain diacid product in Example 1. Detailed Embodiments

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Those skilled in the art make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention, and without departing from the spirit and scope of the technical solutions of the present invention, they should all be covered within the protection scope of the present invention.

[0030] The raw materials used in the following specific embodiments are all purchased from the market. The raw materials such as ionic liquid, polyethylene, nitric oxide, etc. are purchased from companies such as Anhui Zesheng Technology Co., Ltd. and Jingong Specialties Co., Ltd., and the drug purity is chemically pure. The new polyethylene is purchased from Macklin Reagent Manufacturer, with the product number H790495, and the melting index is 12 g / 10 min (190 °C / 2.16 kg). The polyethylene waste comes from common plastic bags.

[0031] Example 1

[0032] In a 100 ml autoclave with mechanical stirring conditions, add [trihexyltetradecylphosphonium][benzenesulfonate] (20 g) and polyethylene (5 g), stir and mix, and charge 0.5 MPa of NO and 3 MPa of O2 at room temperature. Control the reaction temperature at 140 °C, the stirring rate at 200 r / min, and react for 24 h. After the reaction, add sulfuric acid methanol solution to the system, reflux for 1 h to achieve the methylation of the product diacid, separate the dimethyl esters of each component of the binary acid by vacuum distillation, and finally obtain short-chain diacids with carbon numbers from 4 to 12 through hydrolysis, with a conversion rate ≥ 99% and a yield of 91%.

[0033] The yield and product distribution are as Figure 1 shown, and the component characterization of the product is as Figure 2 shown. It can be seen that the products are all C4-12 diacids, and the yield of short-chain products is higher.

[0034] Examples 2 - 5

[0035] According to the process conditions of Example 1, control the mechanical stirring speed at 200 r / min, keep the ionic liquid, NO and O2 pressures, and reaction time the same as above, change the reaction temperature, and the product distribution and yield are shown in Table 1. It can be seen that the decrease in reaction temperature will lead to the decrease in conversion rate and yield. Too high reaction temperature will lead to the decrease in yield.

[0036] Table 1 Effects of different reaction temperatures on the oxidation reaction of polyethylene

[0037] Serial number Reaction temperature (°C) Conversion rate (%) Diacid yield (%) Example 2 80 50 38 Example 3 100 90 72 Example 4 120 ≥99 80 Example 1 140 ≥99 91 Example 5 160 ≥99 62

[0038] Examples 6 - 10

[0039] According to the process conditions of Example 1, control the mechanical stirring speed at 200 r / min, keep the ionic liquid, NO and O2 pressures, and reaction temperature the same as above, change the reaction time, and the product distribution and yield are shown in Table 2. It can be seen that the decrease in reaction time will lead to the decrease in conversion rate and yield. Too long reaction time will lead to the decrease in yield.

[0040] Table 2 Effects of different reaction times on the oxidation reaction of polyethylene

[0041] Serial number Reaction time (t) Conversion rate (%) Diacid yield (%) Example 6 6 15 7 Example 7 12 63 53 Example 8 18 82 72 Example 1 24 ≥99 91 Example 9 30 ≥99 81 Example 10 36 ≥99 69

[0042] Examples 11 - 16

[0043] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The ionic liquid, O2 pressure, reaction temperature and time are the same as above. Change the pressure of NO charged. The product distribution and yield are shown in Table 3. It can be seen that the decrease in the pressure of NO charged will lead to the decrease in conversion rate and yield. The excessive pressure of NO charged will lead to the decrease in yield.

[0044] Table 3 Influence of Different NO Charging Pressures on the Oxidation Reaction of Polyethylene

[0045] Serial number NO pressure (MPa) Conversion rate (%) Diacid yield (%) Example 11 0.1 47 42 Example 12 0.2 60 52 Example 13 0.4 85 74 Example 1 0.5 ≥99 91 Example 14 0.6 92 82 Example 15 0.8 ≥99 75 Example 16 1 ≥99 61

[0046] Examples 17 - 21

[0047] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The ionic liquid, NO pressure, reaction temperature and time are the same as above. Change the pressure of O2 charged. The product distribution and yield are shown in Table 4. It can be seen that the decrease in the pressure of O2 charged will lead to the decrease in conversion rate and yield. The increase in the pressure of O2 charged has no obvious change in yield.

[0048] Table 4 Influence of Different O2 Charging Pressures on the Oxidation Reaction of Polyethylene

[0049] Serial number <![CDATA[O2 pressure (MPa)]]> Conversion rate (%) Diacid yield (%) Example 17 1.0 67 63 Example 18 2.0 95 85 Example 19 2.5 ≥99 91 Example 1 3 ≥99 91 Example 20 4.0 ≥99 90 Example 21 5.0 ≥99 89

[0050] Examples 22 - 28

[0051] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The dosage of ionic liquid, NO and O2 pressures, reaction temperature and time are the same as above. Change the type of ionic liquid. The product distribution and yield are shown in Table 5. It can be seen that with the shortening of the cationic chain length and the increase in the polarity of the ionic liquid, the yield will decrease. Different anions also have a certain influence on the yield.

[0052] Table 5 Influence of Different Types of Ionic Liquids on the Oxidation Reaction of Polyethylene

[0053] Serial number Types of ILs Conversion rate (%) Diacid yield (%) Example 1 [Trihexyltetradecylphosphonium][benzenesulfonate] ≥99 91 Example 22 [Trihexyltetradecylphosphonium][trifluoroacetate] 92 86 Example 23 [Trihexyltetradecylphosphonium][acetate] 87 80 Example 24 [Trihexyloctylphosphonium][benzenesulfonate] ≥99 88 Example 25 [Tributyloctylphosphonium][acetate] ≥99 80 Example 26 [Tributylethylammonium][trichloroacetate] ≥99 75 Example 27 [Triethylbutylammonium][acetate] ≥99 70 Example 28 [Tetraethylammonium][benzenesulfonate] ≥99 64

[0054] Examples 29 - 34

[0055] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The types of ionic liquids, the pressures of NO and O2, the reaction temperature and time are the same as above. Change the dosage of the ionic liquid. The product distribution and yield are shown in Table 6. It can be seen that the reduction of the ionic liquid dosage will lead to the decrease of the conversion rate and the yield. The increase of the ionic liquid dosage has no obvious effect on the yield.

[0056] Table 6 Effects of Dosages of Different Ionic Liquids on the Oxidation Reaction of Polyethylene

[0057] Serial number Dosage of ILs (g) Conversion rate (%) Diacid yield (%) Example 29 0 4 1 Example 30 5 90 60 Example 31 10 ≥99 80 Example 32 15 ≥99 86 Example 1 20 ≥99 91 Example 33 25 ≥99 91 Example 34 30 ≥99 92

[0058] Example 35

[0059] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The types of ionic liquids, the dosage, the pressures of NO and O2, the reaction temperature and time are the same as above. Use the recycled ionic liquid. The product distribution and yield are shown in Table 7.

[0060] The recycled ionic liquid is obtained after the reaction in Example 1. Add water to dissolve the product, and extract the aqueous phase with dichloromethane to separate and recycle the ionic liquid and the diacid product. The recycled ionic liquid is obtained after removing dichloromethane.

[0061] It can be seen that the recycled ionic liquid still maintains high reaction activity and has no obvious effect on the reaction yield.

[0062] Table 7 Effects of the Recycled Ionic Liquid on the Oxidation of Polyethylene in the Repeated Reaction

[0063] Serial number Dosage of recycled ILs (g) Conversion rate (%) Diacid yield (%) Example 35 20 ≥99 89

[0064] Example 36

[0065] Under the process conditions of Example 1, control the mechanical stirring speed at 200 r / min. The types of ionic liquids, the dosage, the pressures of NO and O2, the reaction temperature and time are the same as above. Use the recycled polyethylene as the reactant. The product distribution and yield are shown in Table 8.

[0066] Table 8 Effects of Recycled Polyethylene as the Reactant on the Oxidation Reaction

[0067] Serial number Dosage of PE in recycled material (g) Conversion rate (%) Diacid yield (%) Example 36 5 ≥99 88

[0068] It can be seen that using the recycled polyethylene can still achieve good results and has almost no obvious effect on the reaction yield.

Claims

1. A method for preparing short-chain diacids by catalytic oxidation of polyethylene with ionic liquids, characterized in that, It includes the steps of: mixing an ionic liquid and polyethylene, and carrying out an oxidation reaction in an environment where nitric oxide and oxygen are present to obtain short-chain diacids; The ionic liquid includes any one or more of [trihexyltetradecylphosphonium][benzenesulfonate], [trihexyltetradecylphosphonium][trifluoroacetate], [trihexyltetradecylphosphonium][acetate], [trihexyltetradecylphosphonium][trichloroacetate], [trihexyloctylphosphonium][benzenesulfonate], [trihexyloctylphosphonium][acetate], [trihexyloctylphosphonium][trifluoroacetate], [trihexyloctylphosphonium][trichloroacetate], [tributyloctylphosphonium][benzenesulfonate], [tributyloctylphosphonium][acetate], [tributylethylphosphonium][acetate], [tributylethylphosphonium][benzenesulfonate], [triethylbutylammonium][acetate], [triethylbutylammonium][benzenesulfonate], [tetraethylammonium][acetate], [tetraethylammonium][benzenesulfonate], [tributylethylphosphonium][trifluoroacetate], [tributylethylphosphonium][acetate]; The temperature of the oxidation reaction is 80 to 160 °C, and the reaction time is 10 to 36 h.

2. The method for preparing short-chain diacids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, The mass ratio of the ionic liquid to polyethylene is 0.5 or more.

3. The method for preparing short-chain dibasic acids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, The pressure of the nitric oxide is 0.1 to 1 MPa.

4. The method for preparing short-chain dibasic acids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, The pressure of the oxygen is 0.5 to 10 MPa.

5. The method for preparing short-chain diacids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, After the reaction is completed, the ionic liquid can be recycled. The recycling of the ionic liquid includes: adding water to the reaction system to dissolve the product, and extracting the aqueous phase with dichloromethane to separate and recycle the ionic liquid and the diacid product.

6. The method for preparing short-chain dibasic acids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, The separation and purification process of the product short-chain diacids includes: adding a sulfuric acid methanol solution to the diacid product separated from the ionic liquid, refluxing the reaction to methylate the product short-chain diacids, separating the dimethyl esters of each component of the binary acid by vacuum distillation, and then hydrolyzing to obtain the short-chain diacids of each component.

7. The method for preparing short-chain diacids by catalytic oxidation of polyethylene with an ionic liquid according to claim 1, characterized in that, The short-chain diacids include one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid.

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