CN116536681A - A green hydrogen production process coupled with electrochemical oxidation of waste PBT plastics to succinic acid - Google Patents

Abstract

The invention discloses a coupling green hydrogen production process for preparing succinic acid by electrochemical oxidation of waste PBT plastic, and belongs to the fields of electrochemical synthesis and plastic recovery. Collecting, classifying, removing impurities and grinding the industrial waste PBT plastic into powder, and putting the powder into an alkaline medium for depolymerization; and (3) continuously electrolyzing the depolymerization solution serving as an electrolyte by taking a non-noble metal catalyst as an anode and taking a Pt/C catalyst as a cathode to obtain hydrogen with the purity of more than 99% at the cathode, and oxidizing and upgrading the 1, 4-butanediol into succinic acid at the anode. Adjusting the pH value of the electrolyzed solution to be acidic, and separating out terephthalic acid; and distilling or complexation extracting the residual solution to obtain the high-purity succinic acid product. Compared with the traditional electrolytic hydrogen production process, the process is simple to operate, has obvious energy-saving effect, realizes the green recovery of waste PBT and the conversion to high-added-value products, can greatly improve the market competitiveness and economic benefit of the electrolytic hydrogen production industry, and has wide application prospect.

Description

A green hydrogen production process coupled with electrochemical oxidation of waste PBT plastics to succinic acid

technical field

The invention belongs to the fields of electrochemical synthesis and plastic recycling, and in particular relates to a coupled green hydrogen production process for preparing succinic acid by electrochemical oxidation of waste PBT plastics.

Background technique

Polybutylene terephthalate (PBT) is a polyester made by polycondensation of terephthalic acid and 1,4-butanediol. It has been modified by various additives and blended with other resins to obtain good Comprehensive properties such as heat resistance, flame retardancy, electrical insulation and good processing performance, and then widely used in electrical appliances, automobiles, aircraft manufacturing, communications, home appliances, transportation and other industries, such as integrated circuit sockets, printed circuit boards, computer keyboards , electrical switches, protectors, car bumpers, carburetors, spark plugs, etc., and has gradually become one of the five major engineering plastics. With the gradual expansion of the application of PBT plastics, the pollution caused by waste plastics to the environment is also highlighted. According to statistics, since the 1950s, the world has produced more than 8 billion tons of plastics. The United Nations Environment Program (UNEP) estimates By 2050, the global production of primary plastics will reach 34 billion tons. However, so far, only 9% of the billions of tons of plastic waste generated globally have been recycled, and only 12% of the remaining plastic has been incinerated. The slow rate of degradation over the years. According to the United Nations, at least 85% of beach litter around the world is plastic waste. These waste plastics will cause irreversible damage to the soil, human body and marine ecosystem. Therefore, how to properly depolymerize the plastic crisis and realize the recycling of waste plastics is imminent.

In addition, with the emergence of fossil energy resource problems and the intensification of environmental pressure, how to find alternative new energy sources has become an inevitable way to promote global sustainable development. As a green and clean emerging energy, hydrogen energy may become an important energy source on the world energy stage in the 21st century. With the rapid development of renewable energy such as solar energy, wind energy, and nuclear energy, the cost of direct electric energy is expected to further decrease in the future, and hydrogen production from electrolyzed water is compared with coal-to-hydrogen, methane steam reforming, and industrial tail gas hydrogen production that are commonly used in industry today. And other processes are gradually showing their own advantages and market competitiveness. However, at present, the overall cost and scale of hydrogen production by electrolysis of water still have a gap with coal-to-hydrogen and other processes. How to solve the problems of expensive catalysts and high power consumption costs will also become the key to the development of hydrogen production by electrolysis of water.

In order to solve the above problems, Chinese invention patent ZL201910941831.1 discloses a PET plastic waste recycling, chopping, cooking, heating and stirring, separation, and then soaking and washing with sodium hydroxide and hydrochloric acid solution, melting and then adding modified elastic body, adding coupling agent, lubricant and antioxidant, heating and kneading to obtain a usable PET composite material. In addition, Chinese invention patent ZL202210400007.7 discloses a preparation method of an engineering enzyme complex that efficiently degrades PET plastics. MHETase in the engineering enzyme complex can degrade MHET that leads to IsPETase substrate inhibition, and hydrophobin4 pulls the compound to PET plastics Surface, thereby significantly improving the degradation environment of IsPETase, and its degradation efficiency is about 5 times higher than that of IsPETase with the highest degradation rate through directed evolution. However, the current enzyme-catalyzed plastic conversion is mainly in the laboratory stage. Compared with physical recycling and enzyme catalysis, the electrochemical recycling process seems to have more application potential and economic competitiveness, and can realize the recycling of valuable chemicals and green upgrade. Chinese invention patent ZL202010499309.5 discloses a plastic recycling method of electrochemical oxidation of PET plastics to succinic acid coupled with green hydrogen production, and has achieved good energy-saving effects and economic value. However, the recycling and upgrading of PBT plastics has not been reported yet.

Contents of the invention

In view of this, the present invention discloses a process for producing succinic acid coupled green hydrogen by electrochemical oxidation of waste PBT plastics, which is expected to be a Alleviating the plastic crisis and the industrial development of hydrogen production by electrolysis of water provide new feasible paths.

In order to achieve the above object, the present invention provides the following technical solutions:

A green hydrogen production process coupled with electrochemical oxidation of waste PBT plastics to produce succinic acid, comprising the following steps:

Step 1. Industrial waste PBT plastics are sorted and collected, pre-treated to remove labels, surface pigments and other impurities that will affect the purity of subsequent products, and then put into a ball mill for grinding and crushing into powder. The mesh number is determined according to the actual situation. finer, the more thorough the follow-up depolymerization.

Step 2, the processed powder PBT is placed in the reaction device, and an excessive amount of alkaline potassium hydroxide/sodium hydroxide aqueous solution is added at the same time. The concentration range of the solution is 0.1 mol/L~10 mol/L. Depolymerization reaction is more likely to occur, when the excess will accelerate the corrosion of the electrolytic device. Heat the device to the range of 70°C~140°C and keep stirring at a speed of more than 400 rpm for more than 2~48 hours to achieve sufficient depolymerization of PBT plastic powder and conversion into 1,4-butanediol and terephthalic acid .

Step 3, the potassium hydroxide/sodium hydroxide solution after hydrolysis is directly used as electrolyte, adopts non-precious metal anode catalyst (metal oxide, sulfide, phosphide, selenide of Ni base or Co base, also can select bimetallic Layered hydroxide, metal-organic framework and other catalysts) and Pt/C catalyst (or other non-precious metal-based catalysts) are used as cathode catalysts for continuous electrolysis in a two-electrode electrolysis cell similar to an electrolysis device. The operating temperature of the electrolysis device The temperature is 30℃~85℃, and the operating pressure is 1~3 MPa.

Step 4. Considering the instantaneous fluctuation of the concentration of the reaction substrate in the electrolyte, in order to maintain the continuous operation of the device and the stability of the electrolysis rate, a segmented electrolysis device design can be adopted, wherein the first segment contains a high concentration of 1,4-butane The electrolysis of the diol electrolyte, when the current density is affected by the concentration, is transferred to the second electrolysis device and carried out in steps, thereby ensuring the energy utilization efficiency of the electrolysis device, and at the same time achieving as much conversion of 1,4-butanediol to succinic acid Through electrolysis, hydrogen with a purity of more than 99% can be obtained at the cathode, and the depolymerized 1,4-butanediol can be oxidized and upgraded to succinic acid at the anode.

Step 5. The electrolyte from the electrolysis system needs to undergo subsequent product separation and purification, in which the cathode hydrogen enters the hydrogen/water separator to remove the water vapor carried by the gas, and then goes through the dryer for further dehumidification, and then passes through the regulator valve and regulation The valve is adjusted to the rated pressure output, and transferred to the required place; the fully reacted electrolyte is transferred to the sedimentation tank, and hydrochloric acid is added to adjust the pH to 3~4, so that terephthalic acid can be crystallized, and then filtered, washed and dried To obtain the terephthalic acid product with the purity up to the standard, the main component of the supernatant electrolyte liquid is succinic acid, and the high-purity succinic acid product required by industry can be obtained through various methods such as distillation, complex extraction, electrodialysis or membrane separation.

It can be known from the above-mentioned technical solutions that, compared with the prior art, the electrochemical oxidation of waste PBT plastics to succinic acid coupling green hydrogen production process provided by the present invention has the following excellent effects:

Compared with the traditional landfill and incineration process, the present invention is more low-carbon and environmentally friendly, and will not cause additional damage to the environment; compared with the current physical recycling method, the electrochemical oxidation method upgrades the plastic cycle to high added value High-quality succinic acid and terephthalic acid products have higher economic and environmental benefits. And from the perspective of application, the scale of the device is small, the investment is small, and the benefit is higher. The scale and processing capacity of the device can be flexibly designed according to the demand. Most importantly, the electrochemical oxidation of PBT can be used as a substitute for the anode oxygen evolution reaction and coupled with cathodic electrolysis of water to produce hydrogen. From the perspective of energy utilization, the lower initial potential and operating potential make the The required energy consumption is lower, and the cost of electric energy can be further reduced; coupled with the low value compared to oxygen, it is obviously more economical to go from waste plastics to high value-added terephthalic acid and succinic acid. In general, the electrochemical oxidation of waste PBT plastics to succinic acid coupling green hydrogen production process disclosed in the present invention is not only expected to realize the recycling and upgrading of waste plastics, but also can be combined with electrolysis of water to produce hydrogen, with lower power consumption and significant operating costs. It provides a new feasible solution for the industrialization of commercial electrolyzed water, and has broad application prospects.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is a flow chart of the coupled green hydrogen production process by electrochemical oxidation of waste PBT plastics to succinic acid in Example 1.

Fig. 2 is a comparison diagram of the polarization curves of PBT oxidation coupling green hydrogen production and integral water electrolysis in Example 3.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The embodiment of the invention discloses a green hydrogen production process coupled with electrochemical oxidation of waste PBT plastics to produce succinic acid.

For a better understanding of the present invention, the present invention will be further specifically described below through the following examples, but it should not be construed as a limitation of the present invention. For some non-essential improvements and adjustments made by those skilled in the art according to the above-mentioned content of the invention, It is also considered to fall within the protection scope of the present invention.

In the following, the technical solutions of the present invention will be further described in conjunction with specific embodiments.

Example 1

As shown in Figure 1, the implementation steps of a green hydrogen production process coupled with electrochemical oxidation of waste PBT plastics to succinic acid are as follows:

Step 1. Industrial waste PBT plastics are sorted and collected, pre-treated to remove labels, surface pigments and other impurities that will affect the purity of subsequent products, crushed by a crusher, and further put into a ball mill for grinding at high speed into powder , The mesh number of PBT powder reaches 200 mesh.

Step 2. Here, a small-scale test is carried out in the laboratory. 100 g of the processed powder PBT is placed in a round-bottomed flask, and the configured 2 mol/L potassium hydroxide aqueous solution is added at the same time, placed in an oil bath and heated. Heating to 110°C, setting the rotation speed at 600 rpm, and continuously stirring for 12 hours, the PBT plastic powder was fully depolymerized into 1,4-butanediol and terephthalic acid.

Step 3, the fully depolymerized solution is directly used as electrolyte, and the anode catalyst of the electrolysis system adopts commercial foamed nickel, and its pretreatment method is: commercially purchased foamed nickel is placed in 2 mol/L hydrochloric acid solution for 30 minutes, Then rinse with ethanol, water and dry to remove the surface oxide layer. For the cathode catalyst, a commercially purchased 20% Pt/C catalyst was used, which was immobilized on carbon fiber paper through Nifion dispersion and used as the cathode catalyst.

Step 4. Carry out continuous electrolysis in a two-electrode electrolysis cell similar to the water electrolysis device. The operating temperature of the electrolysis device is 30° C. and the operating pressure is 1 MPa. In the three-electrode system, the electrochemical workstation is used to apply voltage. First, the cathode catalyst and the anode catalyst are activated by CV scanning, and then a voltage of 1.6 V is applied to the two-electrode system. The continuous electrolysis test is carried out by the transverse potential test method. As the concentration of 1,4-butanediol in the electrolyte decreases, after 20 hours of continuous electrolysis, the 1,4-butanediol in the electrolyte is completely oxidized to succinic acid. For the sake of simplicity, the cascade design of the electrolysis device is not carried out. In the actual industry, considering the operation stability and efficiency of the device, it can be designed separately.

Step 5. Pump the electrolyte from the electrolysis system to the separation system. First, add 1mol/L hydrochloric acid into the sedimentation tank until the pH of the solution is adjusted to 3~4. The terephthalic acid in the electrolyte is insoluble due to its acid insolubility However, crystallization occurs quickly, and the lower layer of precipitate is filtered, washed and dried to obtain a pure terephthalic acid product. The main component of the upper layer of electrolyte is succinic acid. Here, a vacuum distillation device is used to obtain high-purity succinic acid products required by industry. . As for the cathode gas phase product-hydrogen, it is sent to the hydrogen/water separator to remove the water vapor carried by the gas, and then after further dehumidification by the dryer, it is adjusted to the rated pressure output through the pressure stabilizing valve and the regulating valve.

Example 2

The core of the present invention lies in the oxidation of PBT in the electrolysis system and the cathodic hydrogen evolution reaction. Therefore, in order to better reflect the significant energy-saving effect of the present invention in the actual industry, a non-noble metal with higher catalytic performance and lower cost was redesigned and synthesized. base catalyst, the specific content is as follows:

Step 1. Industrial waste PBT plastics are collected, classified, pre-treated, and ground into powder.

Step 2. Add powder PBT to the reaction device, and add excess alkaline potassium hydroxide aqueous solution at the same time, heat the device to above 110°C and keep stirring at 600 rpm for more than 12 hours to achieve sufficient depolymerization of PBT plastic powder For 1,4-butanediol and terephthalic acid.

Step 3. Design and synthesize cathode and anode catalysts. Here, non-precious metal-based NiCo-LDH/NF bifunctional catalysts are directly used as cathode and anode catalysts. The synthesis method is as follows: Commercial nickel foam (2*4 cm ^-2 ) is placed in 2 mol/L hydrochloric acid solution for 30 minutes, then washed with ethanol and water and dried to remove the surface oxide layer; weigh 0.291g Ni(NO ₃ ) ₂ ·6H ₂ O, 0.290 g Co(NO ₃ ) ₂ · 6H ₂ O and 0.3 g urea were dissolved in 30 mL of water, stirred for 30 minutes until completely dissolved, and the solution was transferred together with the treated foamed nickel into a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure hydrothermal kettle. Keep in the oven for 12 h. After cooling, washing with deionized water and ethanol in sequence, and drying overnight, the NiCo-LDH/NF catalyst was obtained, which was then directly used as an anode and cathode catalyst.

Step 4. Build a two-electrode system electrolysis device, which is similar to the water electrolysis device, except that an ion exchange membrane is not required to separate the cathode and anode. The operating temperature of the electrolysis device is 30°C and the operating pressure is 1 MPa. In the three-electrode system, the catalyst was activated by CV scanning with Chenhua 760E electrochemical workstation, and then replaced with a two-electrode system, and the continuous electrolysis test was carried out at a voltage of 1.6 V by using the transverse potential test method. The concentration of 1,4-butanediol in the electrolyte decreased and decreased, and after 15 hours of continuous electrolysis, the 1,4-butanediol in the electrolyte was completely oxidized to succinic acid.

Compared with the nickel foam and Pt/C catalyst used in Example 1, the synthesized NiCo-LDH/NF catalyst has better catalytic activity for anodic oxidation, and the cathode is also comparable to the Pt/C catalyst, but the cost is lower. Therefore, the overall results show that at a voltage of 1.6 V, the current density is higher than in Example 1, and the time for 1,4-butanediol to be completely oxidized to succinic acid is also shortened.

Step 5. The electrolyte from the electrolysis system is pumped to the separation system. First, the pH is adjusted to 3~4 in the sedimentation tank, and the terephthalic acid crystallizes out, and then filtered, washed and dried to obtain a product with a purity standard, and the upper layer is electrolyzed The liquid supernatant uses a vacuum distillation device to obtain high-purity succinic acid products required by industry. The purification of cathode hydrogen adopts the same process steps as in Example 1.

Example 3

In order to give full feedback on the energy-saving advantages of the electrochemical oxidation of waste PBT plastic coupled with the green hydrogen production process disclosed in the present invention, the difference between the polarization curve in the electrolysis device and the hydrogen production device by electrolysis of water was mainly studied.

In the manner provided in Example 1, the solution dissolved with 1,4-butanediol and terephthalic acid was obtained as the electrolyte, and the non-noble metal-based NiCo-LDH/NF bifunctional catalyst was directly used as the cathode and anode catalyst, and Chenhua The 760E electrochemical workstation performs CV scanning to pre-activate the catalyst, and then replaces it with a two-electrode system to perform LSV scanning of the polarization curve. The scanning rate is 10 mV/s, the scanning interval is 0-1.8 V, and the iR compensation is set to 85%. , continuously scan for several times until it tends to be stable.

In order to compare commercial water electrolysis, the same NiCo-LDH/NF bifunctional catalyst was directly used as the cathode and anode catalyst, the electrolyte was 2 mol/L potassium hydroxide, and the same method was first used for CV scanning activation, and then replaced with two electrodes System, conduct polarization curve LSV scanning, the scanning rate is 10 mV/s, the scanning interval is 0-2.0 V, the iR compensation is set to 85%, and the scanning is performed several times continuously.

Through the comparison of the two LSV curves (Fig. 2), it can be clearly observed that to achieve the same current density, the energy input required for the PBT plastic oxidation coupled green hydrogen production system is significantly smaller than that of the water electrolysis device, especially at 200 mA cm ^-2 And the industrial current density of 400 mAcm ^-2 , the energy consumption can save 250 mV and 300 mV respectively, which is obviously more energy-saving advantage, and surpasses most of the reported electrolytic water systems.

Example 4

In fact, unlike the traditional commercial water electrolysis system which is dominated by electricity consumption cost, the cost of the separation system of waste PBT plastic electrochemical oxidation coupled with green hydrogen production process cannot be ignored, especially the separation of liquid phase products proposed here Explore its separation process.

Adopt the step of embodiment 1 to carry out electrochemical oxidation and the hydrogen evolution reaction of negative electrode to PBT depolymerization liquid, after the completion of the reaction, the electrolytic solution is transported to the separation system, at first, hydrochloric acid solution is added in the sedimentation tank, and the pH is adjusted to 3 ~ 4, The rapid crystallization of terephthalic acid, followed by filtration, washing and drying to obtain a product with a purity up to the standard, there is not much room for optimal design, and the calcium salt method is used for the upper electrolyte liquid, that is, calcium ions are added to make it It is calcified, followed by acid hydrolysis, ion exchange purification, and crystallization.

Bipolar membrane electrodialysis, sugar extraction combined with crystallization separation and purification, complex extraction, etc. can also be used. These methods have been reported in various literatures, but different methods are used according to different product concentration requirements. Electrodialysis The method has high product purity but high cost, and complex extraction is a more commonly used method.

The final succinic acid product and terephthalic acid product were obtained in the above manner.

Example 5

Exploration of the hydrolysis conditions of PBT plastic in the coupled green hydrogen production process of electrochemical oxidation of waste PBT to succinic acid.

Step 1. Put 100 g of the processed PBT powder into a round bottom flask, and add 0.5 mol/L, 1 mol/L, 2 mol/L, 5 mol/L and 10 mol/L of hydrogen at the same time Potassium oxide aqueous solution was placed in an oil bath and heated to 110°C, the rotation speed was set at 600 rpm, and the stirring continued for 12 hours. The PBT plastic powder was fully depolymerized into 1,4-butanediol and terephthalic acid.

Studies have found that the increase of potassium hydroxide concentration can promote the depolymerization of PBT plastics, but the depolymerization of PBT plastics can also be achieved at low concentrations, but the required stirring time is longer and the monomer concentration in the solution is relatively low , according to the actual needs of the subsequent electrolysis system, the concentration of potassium hydroxide solution can be adjusted.

Example 6

Exploration of the hydrolysis temperature of PBT plastic in the coupled green hydrogen production process of electrochemical oxidation of waste PBT to succinic acid.

Step 1. Put 100 g of the processed PBT powder into a round bottom flask, add the prepared 2 mol/L potassium hydroxide aqueous solution at the same time, place it in an oil bath and heat it. Here, the oil is controlled by adjusting the variable. The bath temperature is 70°C, 90°C, 110°C, 130°C and 140°C, the rotation speed is set at 600 rpm, and the stirring is continued for 12 hours. The PBT plastic powder is also fully depolymerized into 1,4-butanediol and terephthalic acid. .

It was found that the increase of oil bath temperature promoted the depolymerization of PBT plastics. As the temperature increased, the rate of depolymerization was accelerated, and the depolymerization of PBT plastics was also more sufficient, but the temperature was too high, on the one hand, it would increase the thermal utility The other aspect will reduce the stability of the depolymerized monomer.

Example 7

Exploration on the hydrolysis speed and stirring time of PBT plastics in the green hydrogen production process coupled with electrochemical oxidation of waste PBT to succinic acid.

Step 1. Put 100 g of the processed PBT powder into a round bottom flask, add the prepared 2 mol/L potassium hydroxide aqueous solution at the same time, place it in an oil bath and heat it to 100°C. Here, adjust the variable , control the stirring speed to 400 rpm, 500 rpm, 600 rpm, 700 rpm and 800 rpm, and continuously stir for 12 hours. The PBT plastic powder is also fully depolymerized into 1,4-butanediol and terephthalic acid.

It was found that the depolymerization of PBT plastics will be promoted with the increase of the rotational speed, but too high a rotational speed will also increase the cost and affect the stability of the device, generally set at 500 and 600 rpm. In addition, the stirring time is also used as a research variable. When the stirring time is 2 h, the depolymerization of PBT has already occurred, but the concentration of the depolymerization monomer in the solution is relatively low. With the extension of the stirring time, the depolymerization The concentration of the polymer monomer increases gradually, and the higher the concentration, the longer the operation time of the subsequent electrolysis device, and the higher the current density of stable operation, so it is usually set to 12 hours.

Example 8

The types of depolymerization solutions for PBT plastics in the coupled green hydrogen production process by electrochemical oxidation of waste PBT to succinic acid were studied.

Step 1. Put 100 g of the processed PBT powder into a round-bottomed flask, and at the same time add the prepared 2mol/L potassium hydroxide and sodium hydroxide aqueous solutions, place in an oil bath and heat to 100°C. Control the stirring speed at 600 rpm and continue stirring for 12 hours, the PBT plastic powder is also fully depolymerized into 1,4-butanediol and terephthalic acid.

As a result, it was found that the impact of the two alkaline solutions on the depolymerization effect was basically the same, but in the implementation process, terephthalic acid would react with the lye to generate sodium terephthalate or potassium terephthalate, but due to the subsequent separation After the process adjusts the pH, the terephthalic acid can be directly precipitated, and the separation of the product will not be affected.

Example 9

In order to study the universal applicability of the catalyst in the electrochemical oxidation of waste PBT plastic coupled with the green hydrogen production process disclosed in the present invention, the influence of different catalysts on the overall process energy saving effect and product selectivity was mainly studied.

Obtain the solution _that is dissolved with 1,4 _- butanediol and terephthalic acid as electrolyte in the manner provided in Example 1, directly As the cathode and anode catalysts, Chenhua 760E electrochemical workstation was used for CV scanning to preactivate the catalysts, and then replaced with a two-electrode system, and the polarization curve LSV scanning was performed, the scanning rate was 10 mV/s, and the scanning interval was 0~1.8 V, iR compensation is set to 85%, and it is scanned several times until it becomes stable.

In order to compare commercial water electrolysis, the same non-precious metal-based NiS _x /NF, NiP _x /NF and NiSe/NF bifunctional catalysts were directly used as cathode and anode catalysts, and the electrolyte was 2 mol/L potassium hydroxide, in the same way Firstly, CV scan activation was performed, and then switched to a two-electrode system, and the polarization curve LSV scan was performed at a scan rate of 10 mV/s, with a scan range of 0-2.0 V, iR compensation set at 85%, and multiple consecutive scans.

The study found that the three catalysts can realize the oxidation upgrade of PBT plastic to succinic acid, and the catalytic performance is very good, especially at the industrial current density of 200 mA cm ^-2 and 400 mA cm ^-2 , the required electrode voltage is significantly less than Anodic oxygen evolution reaction for commercial water electrolysis.

Example 10

The effects of different catalysts on the energy saving effect and product selectivity of the overall process were continued to be studied.

In the manner provided in Example 1, a solution dissolved with 1,4-butanediol and terephthalic acid was obtained as an electrolyte, and a non-noble metal-based NiCo-MOF/NF catalyst and a NiCo-LDH/NF bifunctional catalyst were directly used as the cathode And the anode catalyst, its synthesis method is obtained from the literature, and the prepared catalyst is usually a nano-array structure. Chenhua 760E electrochemical workstation was used to perform CV scanning to pre-activate the catalyst, and then switch to a two-electrode system to perform LSV scanning of the polarization curve. The scanning rate was 10 mV/s, the scanning range was 0-1.8 V, and the iR compensation was set. It is 85%, and it is scanned several times continuously until it becomes stable.

Through the test of the LSV curve and the test of the product, it is found that both catalysts can realize the oxidation upgrade of PBT plastic to succinic acid, and have high Faradaic efficiency and excellent catalytic performance, especially at industrial current densities. The electrode voltage is also significantly smaller than the anodic oxygen evolution reaction of commercial electrolyzed water.

Example 11

The effect of the reaction conditions of the electrolysis system on the oxidation upgrade of PBT plastics was studied.

Obtain the solution that is dissolved with 1,4-butanediol and terephthalic acid as electrolytic solution in the manner that embodiment 1 provides, directly as cathode and anode catalyst with non-noble metal-based NiCo-LDH/NF bifunctional catalyst, its synthetic method is obtained from the literature, and the prepared catalysts are usually nano-array structures. Chenhua 760E electrochemical workstation was used to perform CV scanning to pre-activate the catalyst, and then switch to a two-electrode system to perform LSV scanning of the polarization curve. The scanning rate was 10 mV/s, the scanning range was 0-1.8 V, and the iR compensation was set. It is 85%, and it is scanned several times continuously until it becomes stable. The electrolysis device simulates a commercial water electrolysis device, and its reaction temperature control variables are 25°C, 50°C, 65°C, and 85°C. The pressure is set to 1MPa, 2MPa, 3MPa through the control variable.

Electrochemical tests were carried out under different operating conditions of the electrolysis device. Through the test of the LSV curve and the quantitative analysis of the product, it was found that the influence of the reaction temperature on the catalytic activity and the catalytic rate is obvious. As the temperature increases, electrons and ions The transfer speed is accelerated, and the catalytic reaction rate is also significantly improved, but considering the energy consumption required by high temperature and the evaporation rate of water vapor, it can usually be set to 65 °C. The influence of the pressure on the electrolysis device is not obvious, and it can be set to 1 MPa if there is no special requirement.

In addition, as an important chemical raw material, succinic acid has a wide range of applications and high value in the fields of food, chemical industry and medicine, which means that PBT plastics can be recovered by electrochemical methods while obtaining high value-added products. Fine chemicals, while reducing the cost of hydrogen production by electrolysis of water, have broad application prospects.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. The technology for preparing succinic acid by electrochemical oxidation of waste PBT plastic is characterized by comprising the following steps:

step 1), collecting, classifying, removing impurities and grinding the industrial waste PBT plastic into powder for later use;

step 2) adding excessive alkaline aqueous solution into the PBT powder treated in the step 1), heating and continuously stirring to fully depolymerize the PBT plastic powder into 1, 4-butanediol and terephthalic acid;

step 3) continuously electrolyzing the depolymerized alkaline aqueous solution serving as electrolyte by taking a non-noble metal catalyst as an anode and a Pt/C catalyst as a cathode to obtain hydrogen at the cathode, wherein the anode oxidatively upgrades the depolymerized 1, 4-butanediol into succinic acid;

and 4) regulating the pH value of the solution subjected to the electrolysis in the step 3) to be acidic so as to crystallize and separate terephthalic acid, and separating and purifying the residual electrolyte to obtain a high-purity succinic acid product.

2. The process for preparing succinic acid by electrochemical oxidation coupling green hydrogen production by using waste PBT plastic according to claim 1, wherein in the step 2), the heating temperature is 70-140 ℃, the stirring time is 2-48 h, and the stirring rotation speed is 400-800 r/min.

3. The process for preparing succinic acid coupling green hydrogen production by electrochemical oxidation of waste PBT plastic according to claim 1 or 2, wherein the alkaline aqueous solution is potassium hydroxide or sodium hydroxide, and the concentration of the alkaline aqueous solution is 0.1 mol/L-10 mol/L.

4. The process for preparing succinic acid coupling green hydrogen by electrochemical oxidation of waste PBT plastic according to claim 1, wherein the electrolysis in the step 3) adopts a sectional type electrolysis device; wherein,,

the first section is the electrolysis of the high-concentration 1, 4-butanediol-containing electrolyte, when the current density is attenuated to 80%, the electrolyte is transferred to a second electrolysis device to be carried out in a gradient manner, so that the energy utilization efficiency of the electrolysis device is ensured, and the conversion of 1, 4-butanediol into succinic acid is realized.

5. The process for preparing succinic acid coupling green hydrogen by electrochemical oxidation of waste PBT plastic according to claim 1 or 4, wherein the non-noble metal catalyst is Ni-based or Co-based metal oxide, sulfide, phosphide, selenide or bi-metal layered hydroxide, or metal organic framework.

6. The process for preparing succinic acid by electrochemical oxidation coupling green hydrogen production from waste PBT plastic according to claim 5, wherein the electrolysis operation temperature in the step 3) is 30-85 ℃ and the operation pressure is 1-3 MPa.

7. The process for preparing succinic acid by electrochemical oxidation coupling green hydrogen production by using waste PBT plastic according to claim 1, wherein hydrogen generated by a cathode in electrolysis is required to pass through a water/gas separation device and a drying device to remove water vapor carried by the gas.

8. The process for preparing succinic acid by electrochemical oxidation coupling green hydrogen production according to claim 1, wherein the separation and purification process in the step 4) comprises complex extraction, aqueous two-phase extraction, calcium salt method, direct crystallization method, ion exchange method, electrodialysis method or distillation method.