Method for preparing short-chain diacid by degrading polyethylene with flue gas

Abstract

The invention discloses a method for preparing short-chain diacid by degrading polyethylene with flue gas. The method comprises the following steps: mixing an ionic liquid and polyethylene, and reacting in a flue gas and air environment to obtain the short-chain diacid; the ionic liquid comprises [trihexyltetradecyl phosphorus] [benzenesulfonic acid], [trihexyltetradecyl phosphorus] [trifluoroacetic acid], [trihexyltetradecyl phosphorus] [acetic acid], [trihexyltetradecyl phosphorus] [trichloroacetic acid] and the like. The method not only can realize polyethylene degradation and flue gas denitration treatment, but also can realize efficient preparation of short-chain diacid, the concentration of NOx in the tail gas after reaction is lower than 50ppm, the process is green and pollution-free, the operation is simple, and the concept of green chemistry is practiced from multiple angles.

Description

Technical Field

[0001] This invention relates to the field of waste gas recovery technology, specifically to a method for preparing short-chain diacids by degrading polyethylene with flue gas. Background Technology

[0002] With their outstanding economic efficiency, functionality, and ease of processing, plastic products have become deeply integrated into modern life. Among various plastics, polyethylene (PE) is the most widely used, accounting for more than a quarter of the total annual production of plastics. The upgrading and recycling of this type of polyolefin material faces technological bottlenecks, mainly due to its inert carbon-hydrogen (CH) and carbon-carbon (CC) bonds in its molecular structure, its complex aggregation state, and its poor solubility. Therefore, developing efficient and practical chemical processes to treat bulk polyolefin waste as valuable carbon raw materials and transform it into high-value chemicals is not only crucial for alleviating environmental pressure and promoting resource recycling, but also for achieving sustainable development.

[0003] Short-chain diacids are an important class of chemicals with wide applications in polymer synthesis and biopharmaceutical preparation. Taking pimelic acid as an example, it is not only a raw material for the preparation of polymers and plasticizers, but also widely used in biochemical research, pharmaceutical intermediates, and ligand synthesis. Its specific uses include: as a biological reagent (such as a component of amino acids, proteins, and culture media), a nucleic acid staining agent, in the production of antibiotics and vitamins, in applications related to endonucleases / modifying enzymes, and in biological buffers required for separation reagents, enzymes, and coenzymes, demonstrating extremely high application value.

[0004] Traditional preparation methods typically employ the oxidation of cyclic ketones or alcohols, using oxidants such as nitric acid to oxidize the cyclic ketones or alcohols to prepare the corresponding diacids. This process is generally costly and involves high energy consumption and significant greenhouse gas emissions, causing substantial pollution. For example, CN1938254A describes a synthetic process for dicarboxylic acid compounds: in the presence of trifluoroacetic acid, aliphatic cyclic secondary alcohols or ketones are oxidized using nitrites or nitrates, achieving a 100% yield. However, this method faces challenges such as high cost of cyclic ketone / alcohol raw materials, intense exothermic reactions, and large NOx emissions.

[0005] International patent WO01 / 87815A2 reports another route: preparing aliphatic carboxylic acids by oxidizing aliphatic or alicyclic ketones with molecular oxygen under the catalysis of soluble manganese(II) compounds, with a yield of 91.8%. This method is also limited by the high cost of the ketone raw materials used and the problem of metal residue pollution.

[0006] In its earlier research, CN120040279A employed a method of oxidizing PE using high-purity nitric oxide and high-purity oxygen, achieving a short-chain dicarboxylic acid yield of 92%. This method suffers from problems such as vigorous reactions, high cost and hazard of high-purity nitric oxide and oxygen, and excessive concentrations of NOx and N2O pollutants in the reaction tail gas, leading to pollution emissions.

[0007] Currently, the main domestic producers of short-chain diacids (C4-C12) include Nanjing Xinhua Yuan Chemical, Shandong Daoqin Chemical, and Wuhan Hengjiu Chemical. They mainly use cyclic ketone or alcohol oxidation methods, and the main problems are high raw material costs, violent reactions, and non-green pollution in the process.

[0008] In recent years, the rise of green chemistry concepts and the deepening of synergistic treatment strategies have driven extensive exploration of green synthetic pathways for short-chain diacids (C4-C12). Among these, utilizing ionic liquid reaction systems to achieve high-value conversion of waste polymers has become a current research hotspot, and related results demonstrate significant application prospects. Summary of the Invention

[0009] This invention addresses the problems of high pollution and high cost in existing short-chain diacid preparation processes by providing a method for preparing short-chain diacids by degrading polyethylene using flue gas and air. This method not only achieves polyethylene degradation and flue gas denitrification, but also enables the efficient preparation of short-chain diacids. The NOx concentration in the tail gas after the reaction is less than 50 ppm. The process is green and pollution-free, and the operation is simple, thus practicing the concept of green chemistry from multiple perspectives.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing short-chain diacids by degrading polyethylene with flue gas includes the steps of: mixing an ionic liquid and polyethylene and reacting them in an environment of flue gas and air to obtain short-chain diacids; The ionic liquid includes any one or more of the following: [trihexyltetradecylphosphine][benzenesulfonic acid], [trihexyltetradecylphosphine][trifluoroacetic acid], [trihexyltetradecylphosphine][acetic acid], [trihexyltetradecylphosphine][trichloroacetic acid], [trihexyloctylphosphine][benzenesulfonic acid], [trihexyloctylphosphine][acetic acid], [trihexyloctylphosphine][trifluoroacetic acid], [trihexyloctylphosphine][trichloroacetic acid], [tributyloctylphosphine][benzenesulfonic acid], [tributyloctylphosphine][acetic acid], [tributylethylphosphine][acetic acid], [tributylethylphosphine][benzenesulfonic acid], [triethylbutylammonium][acetic acid], [triethylbutylammonium][benzenesulfonic acid], [tetraethylammonium][acetic acid], [tetraethylammonium][benzenesulfonic acid], [tributylethylphosphine][trifluoroacetic acid], [tributylethylphosphine][acetic acid].

[0011] Based on current requirements for green chemistry, this study explored the catalytic preparation of short-chain diacids from polyethylene in an environment of flue gas and air. A green method for preparing short-chain diacids (C4-C12) was developed, achieving highly efficient catalytic oxidation of polyethylene and controlling the carbon number of the diacid products within a specific range. The yield of short-chain diacids can reach over 80%. Simultaneously, the flue gas is treated during polyethylene degradation, resulting in NOx concentrations in the post-reaction tail gas below 50 ppm, meeting emission standards. This avoids the high costs and operational hazards associated with using pure oxygen or pure nitrogen monoxide. The preparation cost of short-chain diacids is reduced, the flue gas is treated, and the post-reaction tail gas is pollution-free, making the process green.

[0012] The preferred ionic liquids are those with good flue gas absorption performance and low contact tension with polyethylene, including one or more of the following: [trihexyltetradecylphosphine][benzenesulfonic acid], [trihexyltetradecylphosphine][trifluoroacetic acid], [trihexyltetradecylphosphine][acetic acid], [tributyloctylphosphine][acetic acid], [tributylethylphosphine][trichloroacetic acid], and [triethylbutylammonium][acetic acid].

[0013] Preferably, the pressure of the flue gas is 2-10 MPa, more preferably 5-10 MPa, and even more preferably 5-8 MPa. A higher flue gas content is beneficial for the reaction and results in a higher yield; however, due to the complex composition of the flue gas, excessive content can also lead to a decrease in yield and an increase in byproducts.

[0014] Flue gas generally refers to the mixed gas produced after fossil fuels or waste are oxidized at high temperatures in industrial combustion devices. It is a typical gas produced in industrial combustion processes that are high-temperature, oxygen-rich, and use high-sulfur fuels, such as emissions from large coal-fired boilers, refining heating furnaces, or cement rotary kilns.

[0015] The air pressure is 1-10 MPa, preferably 4-10 MPa.

[0016] The reaction temperature is 100-180℃ and the reaction time is 12-36h. Preferably, the reaction temperature is 110-170℃ and the reaction time is 18-30h.

[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 even more preferably 2 to 6. Increasing the amount of ionic liquid helps to improve the yield, but too much will not have a significant impact on the yield, but will increase the cost.

[0018] After the reaction is completed, the ionic liquid can be recycled and reused. The ionic liquid recycling includes the following steps: adding water to the reaction system to dissolve the product, extracting the aqueous phase with dichloromethane, and realizing the separation and recycling of the ionic liquid and the diacid product.

[0019] The process of separating and purifying the short-chain diacids of the product includes: adding sulfuric acid methanol solution to the reaction product, reflux reaction to methylate the short-chain diacids of the product, vacuum distillation to separate the dimethyl diacids of each component, and then hydrolysis to obtain the short-chain diacids of each component.

[0020] The short-chain diacids include one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, and dodecanoic acid.

[0021] The yield of the short-chain diacid is above 30%. Preferably, the yield can be above 40%, 50%, 60%, or 80%. In this invention, the nitrogen oxide content in the tail gas after the reaction is below 50 ppm. It can achieve denitrification of flue gas while efficiently preparing short-chain diacids, avoiding the safety issues of operation with pure oxygen and pure nitric oxide. The entire reaction process is mild, safe, green and pollution-free.

[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a flue gas degradation method, which simultaneously achieves efficient degradation of waste polyethylene under mild conditions, green and low-cost synthesis of short-chain dicarboxylic acids, and online treatment of flue gas. No pollutants are generated after the reaction, and the process is green and pollution-free. Attached Figure Description

[0023] Figure 1 The distribution and yield of the short-chain diacid products in Example 1 are shown.

[0024] Figure 2 This is a gas chromatogram of the short-chain diacid product in Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0026] All raw materials used in the following specific embodiments were purchased from the market. The ionic liquid and polyethylene were purchased from Anhui Zesheng Technology Co., Ltd., Jingong Special Products Co., Ltd., etc., and the purity of the reagents was chemically pure. The virgin polyethylene was purchased from Maclean's Reagent Manufacturer, catalog number H790495, with a melt index of 12g / 10min (190°C / 2.16kg). Virgin materials were used in Examples 1-41. The polyethylene waste used in Example 42 came from commonly used plastic bags. The flue gas originated directly from the tail gas produced by petrochemical plants, mainly containing nitrogen (70%~75%), carbon dioxide (10%~15%), water vapor (5%~10%), oxygen (3%~6%), nitrogen oxides (1000 ppm~5000 ppm), and sulfur dioxide (500 ppm~3000 ppm). The composition of tail gas from different chemical plants varies slightly, but this has no significant impact on the reaction.

[0027] Example 1 In a 100 ml autoclave equipped with mechanical stirring, 20 g of [trihexyltetradecylphosphine] and 5 g of polyethylene were added and mixed. The mixture was then purged with 5 MPa of flue gas and 5 MPa of air at room temperature. The reaction temperature was controlled at 140 °C, the stirring rate at 200 r / min, and the reaction was carried out for 24 h. After the reaction, the ionic liquid and the product diacid were separated by vacuum distillation. A sulfuric acid methanol solution was added to the system, and reflux was carried out for 1 h to achieve methyl esterification of the product diacid. Dimethyl esters of the various dicarboxylic acids were then separated by vacuum distillation. Finally, hydrolysis yielded short-chain diacids with carbon numbers from 4 to 12, with a conversion rate ≥99% and a yield of 85%.

[0028] Yield and product distribution as follows Figure 1 As shown, the compositional characterization of the product is as follows: Figure 2 As shown, the products are all C4-C. 12 The dicarboxylic acid showed a higher yield of the short-chain product. Simultaneously, the nitrogen oxides (NOx) in the tail gas after the reaction were measured. x The concentration of ions is below 50 ppm, which meets the emission standards, and the whole process is green and pollution-free.

[0029] Examples 2-7 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the ionic liquid, flue gas and air pressure, and reaction time were the same as above. The reaction temperature was varied, and the product distribution and yield are shown in Table 1. It is evident that decreasing the reaction temperature leads to a decrease in conversion rate and yield. Similarly, excessively high reaction temperatures also result in a decrease in yield.

[0030] Table 1. Effect of different reaction temperatures on the oxidation reaction of polyethylene.

[0031] Examples 8-12 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the ionic liquid, flue gas and air pressure, and reaction temperature were the same as above. The product distribution and yield were varied by changing the reaction time, as shown in Table 2. It is evident that decreasing the reaction time leads to a decrease in conversion rate and yield. Excessive reaction time results in a decrease in yield.

[0032] Table 2 Effect of different reaction times on the polyethylene oxidation reaction

[0033] Examples 13-20 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the ionic liquid, air pressure, reaction temperature, and time were the same as above. The product distribution and yield were shown in Table 3 by changing the pressure of the flue gas. It can be seen that decreasing the flue gas pressure leads to a decrease in conversion rate and yield. Excessive flue gas pressure leads to a decrease in yield.

[0034] Table 3. Effect of different flue gas injection pressures on the oxidation reaction of polyethylene.

[0035] Examples 21-27 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the ionic liquid, flue gas pressure, reaction temperature, and time were the same as above. The product distribution and yield were shown in Table 4 by changing the air pressure. It can be seen that decreasing the air pressure leads to a decrease in conversion rate and yield. Increasing the air pressure did not significantly change the yield.

[0036] Table 4. Effect of different air filling pressures on the oxidation reaction of polyethylene.

[0037] Examples 28-34 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the amount of ionic liquid, flue gas and air pressure, reaction temperature and time were the same as above. The type of ionic liquid was changed, and the product distribution and yield are shown in Table 5. It can be seen that as the cation chain length shortens and the polarity of the ionic liquid increases, the yield decreases. Different anions also have a certain impact on the yield, but the yields are all good.

[0038] Table 5. Effects of different types of ionic liquids on the oxidation reaction of polyethylene.

[0039] Examples 35-40 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the type of ionic liquid, flue gas and air pressure, reaction temperature, and time remained the same. The amount of ionic liquid was varied, and the product distribution and yield are shown in Table 6. It is evident that reducing the amount of ionic liquid leads to a decrease in conversion rate and yield. Increasing the amount of ionic liquid has no significant effect on the yield.

[0040] Table 6. Effect of different amounts of ionic liquids on the oxidation reaction of polyethylene.

[0041] Example 41 The recovered ionic liquid was obtained by adding water to dissolve the product after the reaction in Example 1, extracting the aqueous phase with dichloromethane to separate and recover the ionic liquid from the diacid product, and then removing the dichloromethane to obtain the recovered ionic liquid. Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the type and amount of ionic liquid, flue gas and air pressure, reaction temperature, and time were the same as above. Using the recovered ionic liquid, the product distribution and yield are shown in Table 7.

[0042] It is evident that the recovered ionic liquid retains high reactivity and has no significant impact on the reaction yield.

[0043] Table 7. Effect of re-reaction after ionic liquid recovery on polyethylene oxidation.

[0044] Example 42 Following the process conditions of Example 1, the mechanical stirring speed was controlled at 200 r / min, and the type and amount of ionic liquid, flue gas and air pressure, reaction temperature and time were the same as above. Recycled polyethylene was used as the reactant, and the product distribution and yield are shown in Table 8.

[0045] Table 8. Effect of recycled polyethylene as a reactant on the oxidation reaction.

[0046] It is evident that using recycled polyethylene can still achieve good results with almost no significant impact on the reaction yield.

Claims

1. A method for preparing short-chain diacids by degrading polyethylene with flue gas, characterized in that, The steps include: mixing ionic liquid and polyethylene and reacting them in an environment of flue gas and air to obtain short-chain diacids; The ionic liquid includes any one or more of the following: [trihexyltetradecylphosphine][benzenesulfonic acid], [trihexyltetradecylphosphine][trifluoroacetic acid], [trihexyltetradecylphosphine][acetic acid], [trihexyltetradecylphosphine][trichloroacetic acid], [trihexyloctylphosphine][benzenesulfonic acid], [trihexyloctylphosphine][trifluoroacetic acid], [trihexyloctylphosphine][trichloroacetic acid], [tributyloctylphosphine][benzenesulfonic acid], [tributyloctylphosphine][acetic acid], [tributylethylphosphine][acetic acid], [tributylethylphosphine][benzenesulfonic acid], [triethylbutylammonium][acetic acid], [triethylbutylammonium][benzenesulfonic acid], [tetraethylammonium][acetic acid], [tetraethylammonium][benzenesulfonic acid], [tributylethylphosphine][trifluoroacetic acid], [tributylethylphosphine][acetic acid].

2. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The pressure of the flue gas is 2-10 MPa.

3. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The air pressure is 1-10 MPa.

4. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The reaction temperature is 100-180℃, and the reaction time is 12-36h.

5. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The mass ratio of the ionic liquid to polyethylene is 0.5 or higher.

6. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, After the reaction is completed, the ionic liquid can be recycled and reused. The ionic liquid recycling includes the following steps: adding water to the reaction system to dissolve the product, extracting the aqueous phase with dichloromethane, and realizing the separation and recycling of the ionic liquid and the diacid product.

7. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, Its features are, The process of separating and purifying the short-chain diacids of the product includes: adding sulfuric acid methanol solution to the reaction product, reflux reaction to methylate the short-chain diacids of the product, vacuum distillation to separate the dimethyl diacids of each component, and then hydrolysis to obtain the short-chain diacids of each component.

8. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The short-chain diacids include one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, and dodecanoic acid.

9. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The yield of the short-chain diacid is above 30%.

10. The method for preparing short-chain diacids by degrading polyethylene with flue gas according to claim 1, characterized in that, The nitrogen oxide concentration in the exhaust gas after the reaction is below 50 ppm.

Images