A method for the production of benzoic acid by the selective oxidative degradation of polystyrene

Abstract

The present invention discloses a method for selectively oxidizing and degrading polystyrene to produce benzoic acid. In the present invention, nitric acid or a nitrate solution is used as an oxidant to convert polystyrene into high-value chemical raw materials of small molecules, namely benzoic acid. Through the carbon-centered free radicals generated at the weak sites on the carbon chain of polystyrene, the introduction of oxygen-containing functional groups is caused under the oxidation of nitric acid and nitrate solutions, thereby causing the cleavage of C-C bonds and resulting in the selective oxidation and degradation of polystyrene. The reaction conditions of this process are mild, the yield and selectivity of the main product benzoic acid are relatively high, and the impact on the environment is small, providing a new method for the resource-based high-value recycling of polystyrene.

Description

Technical Field

[0001] The present invention belongs to the fields of environmental protection and comprehensive utilization of resources, and particularly relates to a method for selectively oxidizing and degrading polystyrene to produce benzoic acid. Background Art

[0002] Due to its excellent properties, polystyrene plays an important role in life and production, and is one of the most widely used types of plastics. Polystyrene products include a large number of disposable products, with a large usage and waste volume. Since polystyrene is difficult to degrade naturally, the resulting microplastic pollution and resource waste problems cannot be underestimated. At the same time, since the raw materials for producing polystyrene come from fossil energy, there is huge application potential. Compared with polyester plastics, polystyrene is connected by C-C bonds with relatively higher bond energy, making it more difficult to degrade. However, polystyrene has electron-rich conjugated aromatic ring units and activated benzylic C-H bonds for selective depolymerization and conversion, which also brings more possibilities for the resource recovery and utilization of polystyrene.

[0003] Currently, the methods applied to the recycling of polystyrene mainly include mechanical recycling and chemical cracking. Mechanical recycling produces plastic pellets from polystyrene through physical processes such as crushing, extrusion, and regranulation for continued use in the production of plastic products. However, this method has high requirements for raw materials, and the quality of the recycled plastics produced is low, with limited application fields. Chemical cracking refers to heating polystyrene to a certain temperature in an inert atmosphere to depolymerize it, thereby generating products such as fuel gas, fuel oil, or wax. However, this method has the problem of high separation and purification costs for the complex mixture of gases, liquid hydrocarbons, and coke produced.

[0004] In view of the problems existing in the above two methods, current research shows that an oxidative degradation method can be adopted. By introducing oxygen-containing functional groups, the carbon chain of polystyrene can be promoted to break, and it can be converted into small molecule chemicals that are easy to recycle, thereby realizing the high-value utilization of polystyrene resources. At the same time, the oxidative degradation method can also be applied to the treatment of microplastics in water, providing a good solution to the problem of microplastic pollution in the environment.

[0005] The reaction process of polystyrene oxidative degradation can be achieved in the gas phase or the liquid phase. It is reported that heating polystyrene in an oxidative gas atmosphere can oxidatively degrade polystyrene to produce benzoic acid at a lower temperature compared to simple thermal cracking. However, this method has the problems of high reaction pressure and low yield. There is also research on oxidatively degrading polystyrene by using oxidants such as sodium hydroxide, hydrogen peroxide, potassium permanganate, and persulfate by heating to an appropriate temperature or adding a catalyst. Compared with gas-phase reactions, the oxidation of polystyrene in liquid-phase reactions is more complete, with higher conversion rates and product yields.

[0006] Based on the dual properties of polystyrene pollution and resources, according to the treatment method of liquid-phase oxidation degradation of polystyrene, nitric acid and nitrate solutions are used as oxidants to selectively oxidize and degrade polystyrene, and efficiently convert it into high-value chemical raw material benzoic acid, thereby realizing the resource utilization, harmless treatment and high-value utilization of polystyrene. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for producing benzoic acid by selectively oxidizing and degrading polystyrene. The present invention uses nitric acid and nitrate solutions as oxidants to selectively oxidize and treat polystyrene, and degrades it to obtain small molecule chemical raw material benzoic acid.

[0008] A method for producing benzoic acid by selectively oxidizing and degrading polystyrene proposed by the present invention comprises the following specific steps:

[0009] (1) Add polystyrene into a hydrothermal reaction kettle, and at the same time add nitric acid or nitrate solution to obtain a mixture;

[0010] (2) Heat the mixture obtained in step (1) to 100°C to 300°C and continuously stir;

[0011] (3) After the temperature in step (2) reaches any temperature value in the preset range of 100°C to 300°C, maintain the reaction for 0.5 to 20 hours and continuously stir;

[0012] (4) After the reaction in step (3) ends, cool down;

[0013] (5) After cooling down to room temperature in step (4), filter and separate the obtained product to obtain a solid product;

[0014] (6) The solid product obtained in step (5) is dried to remove moisture to obtain the product benzoic acid.

[0015] In the present invention, the polystyrene described in step (1) includes but is not limited to any one of plastic products made of polystyrene such as plastic beverage cup lids, food packaging, tableware containers, foam plastic boxes, sound insulation boards, expanded polystyrene particles, electronic and electrical components, home decorations, disposable cell culture dishes, plastic toys or extruded polystyrene particles.

[0016] In the present invention, the nitrate solution described in step (1) includes but is not limited to one or several of copper nitrate solution, sodium nitrate solution, potassium nitrate solution, iron nitrate solution, cobalt nitrate solution, manganese nitrate solution or zirconium nitrate solution, etc., and the concentration is any concentration in the range of 1 mol / L to 10 mol / L (calculated as nitrate).

[0017] The beneficial effects of the present invention are as follows: The present invention uses a nitric acid and nitrate solution as an oxidant in a selective oxidation process to degrade the high molecular polymer polystyrene into small molecule high-value chemical raw material benzoic acid at a certain temperature. This process has a simple operation process, relatively mild reaction conditions, less environmental impact, and a high yield of benzoic acid, providing a new method for the resource utilization of polystyrene. The present invention discloses a method for selectively oxidizing and degrading polystyrene using a nitric acid and nitrate solution. This method has mild reaction conditions, requires a relatively low temperature, produces less environmental impact, and has a high yield, selectivity, and economic benefits of the product benzoic acid, providing a new and sustainable method for the resource recovery and utilization of polystyrene, which has a positive significance for solving the environmental pollution and energy waste problems of polystyrene. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the basic process flow chart of the process of the present invention. EMBODIMENTS

[0019] The following examples are used to further illustrate the present invention and are not intended to limit the present invention. Example 1:

[0020] (1) After crushing a disposable plastic cup lid, add it to a hydrothermal reaction kettle, and at the same time add a 3 mol / L nitric acid solution;

[0021] (2) Heat the mixture of the disposable plastic cup lid and the nitric acid solution in step (1) to 210 °C and continuously stir;

[0022] (3) After the temperature in step (2) reaches the preset value of 210 °C, maintain the reaction for 2 hours and continuously stir;

[0023] (4) After the reaction in step (3) ends, cool down;

[0024] (5) After cooling down to room temperature in step (4), filter and separate the obtained product;

[0025] (6) Dissolve the solid product obtained by filtration in step (5) in ethyl acetate and perform GC-MS and GC-FID analyses on the products and yields therein. The results show that the main product is benzoic acid, and the yield is 50.8 mol%. Example 2:

[0026] (1) Add extruded polystyrene plastic particles to a hydrothermal reaction kettle, and at the same time add a copper nitrate solution with a nitrate concentration of 6.5 mol / L;

[0027] (2) Heat the mixture of the extruded polystyrene plastic particles and the copper nitrate solution in step (1) to 180 °C and continuously stir.

[0028] (3) After the temperature in step (2) reaches the preset value of 180 °C, maintain the reaction for 6 hours and continuously stir.

[0029] (4) After the reaction in step (3) ends, cool down the temperature.

[0030] (5) After cooling down to room temperature in step (4), filter and separate the obtained product.

[0031] (6) Dissolve the solid product obtained by filtration in step (5) in ethyl acetate and perform GC-MS and GC-FID analyses on the products and yields therein. The results show that the main product is benzoic acid and the yield is 46.6 mol%. Example 3:

[0032] (1) Crush the foam plastic board and add it to the hydrothermal reaction kettle, and at the same time add a 5 mol / L nitric acid solution.

[0033] (2) Heat the mixture of the foam plastic board and the nitric acid solution in step (1) to 150 °C and continuously stir.

[0034] (3) After the temperature in step (2) reaches the preset value of 150 °C, maintain the reaction for 12 hours and continuously stir.

[0035] (4) After the reaction in step (3) ends, cool down the temperature.

[0036] (5) After cooling down to room temperature in step (4), filter and separate the obtained product.

[0037] (6) Dissolve the solid product obtained by filtration in step (5) in ethyl acetate and perform GC-MS and GC-FID analyses on the products and yields therein. The results show that the main product is benzoic acid and the yield is 64.8 mol%. Example 4:

[0038] (1) Crush the disposable plastic petri dish and add it to the hydrothermal reaction kettle, and at the same time add a 4 mol / L nitric acid solution.

[0039] (2) Heat the mixture of the disposable plastic petri dish and the nitric acid solution in step (1) to 180 °C and continuously stir.

[0040] (3) After the temperature in step (2) reaches the preset value of 180 °C, maintain the reaction for 4 hours and continuously stir.

[0041] After the reaction in step (3) ends, cool down to lower the temperature.

[0042] (5) After the cooling in step (4) reaches room temperature, filter and separate the obtained product.

[0043] (6) Dissolve the solid product obtained by filtration in step (5) in ethyl acetate and conduct GC-MS and GC-FID analyses on the products and yields therein. As a result, it is found that the main product is benzoic acid and the yield is 70.0 mol%.

Claims

1. A method for the selective oxidation degradation of polystyrene to produce benzoic acid with nitric acid and nitrate solutions, characterized in that The specific steps are as follows: (1) Add polystyrene into a hydrothermal reactor, and simultaneously add nitric acid or a nitrate solution to obtain a mixture; the nitrate solution is one or more of a copper nitrate solution, a sodium nitrate solution, a potassium nitrate solution, an iron nitrate solution, a cobalt nitrate solution, a manganese nitrate solution, or a zirconium nitrate solution, and the concentration is any concentration from 1 mol / L to 10 mol / L (calculated based on nitrate); (2) Heat the mixture obtained in step (1) to 100°C - 300°C and continuously stir; (3) After the temperature in step (2) reaches any temperature value within the preset range of 100°C - 300°C, maintain the reaction for 0.5 - 20 hours and continuously stir; (4) After the reaction in step (3) ends, cool down the temperature; (5) After cooling down to room temperature in step (4), filter and separate the obtained product to obtain a solid product; (6) The solid obtained by filtration in step (5) is dried to remove moisture to obtain the product benzoic acid.

2. The method according to claim 1, wherein: The polystyrene described in (1) includes but is not limited to any one or more of plastic beverage cup lids, food packaging, tableware containers, foam plastic boxes, sound insulation boards, expanded polystyrene particles, electronic and electrical components, home decorations, disposable cell culture dishes, plastic toys, or extruded polystyrene particles.

Images