A method for removing chlorine from a chlorine-containing plastic by plasma and recovering by-products

Abstract

The application discloses a method for removing Cl element in chloroplast and recycling byproducts. The method can realize the dechlorination pretreatment of chloroplast at room temperature, and the specific method is as follows: the chloroplast is placed in a plasma reactor, and the plasma reactor is discharged in an inert gas. The plasma active group generated by the inert gas has high energy, and can effectively destroy the chemical bond of the chloroplast. The Cl free radicals and H free radicals generated by the breaking of C-Cl bond and C-H bond combine to generate HCl gas, and the H free radicals combine to generate H2. At the same time, the unsaturation of the solid product is increased, and the polyalkene structure and the aromatic hydrocarbon structure are formed, and the removal of the Cl element in the chloroplast is completed. The method has low energy consumption and low requirement on the reaction device. The process flow is simple, the byproduct is single and has high purity, the Cl element can be efficiently removed, the HCl and H2 byproducts can be collected, waste is turned into treasure, and two goals are achieved at one time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental protection and chemical material preparation, and particularly relates to a method for removing Cl element in Cl-containing plastics by plasma and recycling by-products (HCl and H2), which can be used for pretreatment of Cl-containing plastics and preparation of HCl and H2. BACKGROUND

[0002] Plastic products are widely used in daily life and building materials, at the same time, which also makes the amount of waste plastics increase day by day. As of 2019, the annual output of plastics in the world has reached 368 million tons, of which about 79% is discarded without proper treatment. Cl-containing plastics are mainly polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). Among them, PVC plastic is the third most widely used plastic in the world, and according to statistics, the annual output of PVC plastic accounts for 9.8% of the annual output of plastics in Europe. At present, the disposal and treatment of waste plastics in China are mainly carried out by landfill method and thermal chemical disposal method (incineration power generation and pyrolysis gasification). Landfill method will cause waste of land resources, so the reduction of waste volume is crucial. For thermal chemical disposal technology, due to the relatively high content of Cl element in waste plastics, plastics are prone to generate HCl pollutants under high temperature conditions, which can corrode heat exchangers, and the emission of HCl will also cause acid rain problem, causing serious harm to the environment. At the same time, in the high-temperature oxygen environment, Cl-containing plastics provide Cl source for toxic and harmful dioxin pollutants, leading to the generation of dioxin, which causes great harm to the ecology. Therefore, it is crucial to find a pretreatment method for Cl-containing plastics to reduce the volume of plastics and remove Cl element.

[0003] Currently, the removal of Cl element in chloroplasts is mainly carried out in two ways. One is to place the chloroplasts in a high-temperature inert or vacuum environment for pyrolysis dechlorination (Jiang H., Huo R., and Zhang Z. et al., 2022. Dechlorination performance in chemical looping conversion of polyvinylchloride plastic waste using K / Na / Ca-modified iron ore oxygen carriers. Journal of Environmental Chemical Engineering, 10(2): 107314.), but this method requires a higher temperature, generally 500-900℃, and has high energy consumption. The second is to place the chloroplasts in a high-pressure environment for hydrothermal dechlorination (Yu Y., Zhu B, and Li P. et al, 2022. Hydrothermal carbonization of food waste digestates and polyvinyl chloride: focus on dechlorination performance and fuel characteristics. Biomass Conversion and Biorefinery, 1-8.), which requires a lower temperature (160-300℃) but high working pressure (0.1-19MPa), high requirements for reaction devices, and safety hazards. Therefore, it is urgent to find an efficient pretreatment method for chloroplasts that can simultaneously achieve efficient and low-energy removal of Cl element and recover by-products. SUMMARY

[0004] In order to solve the problems of atmospheric pollution and pipeline corrosion caused by the thermal chemical disposal of chloroplasts, the present application provides a method for removing Cl element in chloroplasts by plasma and recovering by-products (HCl and H2), which can better realize the resource disposal of chloroplasts.

[0005] In order to achieve the above invention purposes, the present application adopts the following technical solutions:

[0006] A method for removing Cl element in chloroplasts by plasma and recovering by-products (HCl and H2), which can realize the dechlorination pretreatment of chloroplasts at room temperature, the steps are as follows:

[0007] 1. Put the chlorine-containing plastics into a plasma reactor, discharge the plasma reactor in inert gas, the active particles of plasma act on the chlorine-containing plastics and produce HCl and H2, the produced gas is carried out of the reactor by the inert gas introduced into the reactor;

[0008] 2. The gas flowing out of the reactor passes through a gas washing device filled with deionized water and is discharged from the reaction system, HCl is collected in the form of hydrochloric acid solution; H2 and the carrier gas are collected by a gas bag, and the H2 in the mixed gas is separated and disposed by ion liquid membrane method to obtain high-purity H2;

[0009] 3. After the reaction is completed, the solid product is collected, which is the product after the Cl removal treatment of the chlorine-containing plastics.

[0010] In the above technical solution, further, in step 1, the chlorine-containing plastics can be any chlorine-containing plastics such as PVC and PVDC, or a mixture of various chlorine-containing and non-chlorine-containing plastics. The discharge time, discharge power and discharge mode (AC / pulse) of the plasma reactor can be adjusted to select the optimal treatment condition for different plastic components.

[0011] The invention principle of the present application is:

[0012] As the fourth form of matter, plasma can produce various active particles through dissociation, electron collision, excitation and ionization. The active particles can break the chemical bonds of polymers at room temperature to produce various free radicals, and the free radicals can produce high-value target products through recombination reaction. In general, the low-energy and high-activity characteristics of low-temperature plasma technology can meet the removal of Cl elements in chlorine-containing plastics and effectively make up for the shortcomings of the existing chlorine-containing plastic dechlorination pretreatment method.

[0013] The plasma active groups (nitrogen gas positive ions, nitrogen gas metastable substances and electrons, etc.) produced in the inert atmosphere (taking nitrogen as an example) have high energy, which can effectively break the chemical bonds of chlorine-containing plastics. The Cl free radicals and H free radicals produced by the breaking of C-Cl bonds and C-H bonds combine to generate HCl gas, and the H free radicals combine to generate H2, while the unsaturation of the solid product increases and forms polyalkene structure and aromatic structure, completing the removal of Cl elements in chlorine-containing plastics.

[0014] Compared with the prior art, the present application has at least the following beneficial effects:

[0015] 1. Low energy consumption and low requirement for reaction device. The present application supports the Cl element removal pretreatment of chlorine-containing plastics at room temperature, without the need for high temperature and high pressure environment, and has no special requirements for the reaction device.

[0016] 2. The process flow is simple. The present application can realize one-stage disposal of chloroplastics, without complicated steps, and is easy to operate.

[0017] 3. HCl and H2 by-products can be collected while efficiently removing Cl elements. The present application not only realizes pre-disposal of Cl elements in chloroplastics, but also realizes recovery of high-value-added HCl solution and H2, which turns waste into treasure and achieves two goals at once.

[0018] 4. The by-products are single and high in purity. The gas products under the action of the present application are only HCl and H2, and the gas collected after the HCl is absorbed by deionized water is a mixed gas of high-purity H2 and carrier gas. High-purity H2 can be obtained by ion liquid membrane method separation and disposal of H2 in the mixed gas. BRIEF DESCRIPTION OF DRAWINGS

[0019] The present application will be further described below in combination with the drawings and examples.

[0020] Figure 1 It is a flowchart of a method for removing Cl elements in chloroplastics (taking PVC as an example) by plasma and recycling HCl.

[0021] Figure 2 It is an effect diagram of removing Cl elements in chloroplastics (taking PVC as an example) by plasma under different discharge conditions and recycling HCl and H2.

[0022] Figure 3 It is an effect comparison diagram of removing Cl elements in chloroplastics (taking PVC as an example) by a thermal disposal method and recycling HCl and H2. DETAILED DESCRIPTION

[0023] The present application will be further described below in combination with the drawings and specific examples.

[0024] Example 1

[0025] 0.5g of PVC plastic was placed in the discharge area of the plasma reactor, and an inert carrier gas was introduced into the reactor at a gas velocity of 100mL / min until the reactor and the gas washing bottle containing 100mL of deionized water were filled with the inert carrier gas.

[0026] The plasma discharge power was turned on, and the PVC plastic was discharged for 20min under a discharge power of 180W. The PVC plastic underwent chain scission reaction under the action of plasma active substances to generate Cl free radicals and H free radicals, and then the free radicals recombined to generate HCl and H2 gas.

[0027] The HCl gas flowed through the gas washing device containing deionized water to be collected in the form of hydrochloric acid, and the yield was 0.53g / g pvc .

[0028] H2 and nitrogen carrier gas are collected in a gas bag. The H2 in the mixture is then separated using methods such as ion-liquid membrane separation to obtain H2 with high purity, yielding a yield of 2.32 mmol / g. pvc .

[0029] After the reaction is complete, the solid product in the reactor is collected. This solid product is the substance after HCl removal from PVC plastic. Under this condition, the HCl removal rate can reach 97.76%.

[0030] Example 2

[0031] The difference from Example 1 is that the plasma reactor is operated at a discharge power of 150W.

[0032] The yield of HCl produced by this method is 0.50 g / g. pvc The H2 yield was 2.01 mmol / g. pvc The Cl removal rate was 97.3%.

[0033] Example 3

[0034] The difference from Example 1 is that the plasma reactor operates at a discharge power of 120W.

[0035] The yield of HCl produced by this method is 0.45 g / g. pvc The H2 yield was 1.69 mmol / g. pvc The Cl removal rate was 96.76%.

[0036] Example 4

[0037] The difference from Example 1 is that the PVC was treated in the plasma reactor for 40 minutes.

[0038] The yield of HCl produced by this method is 0.56 g / g. pvc The H2 yield was 2.94 mmol / g. pvc The Cl removal rate was 97.94%.

[0039] The Cl element removal efficiency and three-phase product distribution achievable by the method of this invention are as follows: Figure 2 .

[0040] Depend on Figure 2 It can be seen that the Cl removal rate, HCl, and H2 yield all increase with increasing discharge power. Specifically, the Cl removal rate (mass of Cl removed / total mass of Cl in PVC) reaches 96.76% at a discharge power of 120W; the HCl yield is as high as 53.4wt% at 180W, meaning 534kg of HCl can be collected per ton of plastic treated; and the H2 yield is a maximum of 2.32mmol / g at 180W, meaning 51.97mg / g can be collected per ton of plastic treated.3 H2 (standard case).

[0041] By Figure 2 and Figure 3 It can be seen from the comparison that the Cl removal rate and HCl yield of the method of the present application at a discharge power of 150 W are comparable to the effect of high-temperature pyrolysis of PVC at 400 ℃, and the H2 yield of the method of the present application is significantly better than the effect of high-temperature pyrolysis of PVC at 400 ℃.

Claims

1. A method for removing chlorine from a chlorine-containing plastic by plasma and recovering by-products, characterized by, The method comprises the following steps: 1) placing the chlorine-containing plastic into a plasma reactor, discharging the plasma reactor in an inert gas, and allowing the active particles of the plasma to act on the chlorine-containing plastic and produce HCl and H2, and the produced gas is carried out of the reactor by the inert gas introduced into the reactor; 2) the gas flowing out of the reactor passes through a gas washing device containing deionized water and is discharged from the reaction system, and the HCl is collected in the form of hydrochloric acid solution; the H2 and the carrier gas are collected by a gas bag, and the H2 in the mixed gas is separated and disposed to obtain high-purity H2; 3) after the reaction is completed, the solid product is collected, and the product is the product after the chlorine-containing plastic is treated by removing Cl; The chlorine-containing plastic is PVC, PVDC or a mixture of the two.

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