A method for producing adiponitrile from waste PA-66 plastic via electrochemical hydrogen evolution coupled with electrochemical oxidation.

Abstract

A method for producing adiponitrile from waste PA-66 plastic via electrochemical hydrogen evolution coupled with electrochemical oxidation belongs to the fields of electrochemical hydrogen evolution and waste plastic recycling and upgrading. Industrial waste PA-66 plastic undergoes simple depolymerization to obtain adipic acid crystals and a hexamethylenediamine solution of acceptable purity. The hexamethylenediamine solution is directly used as the electrolyte, employing V-Ni2P catalyst, and undergoes continuous, long-term electrolysis in a constructed two-electrode electrolytic cell. Through electrolysis, hydrogen gas is obtained at the cathode, and adiponitrile is obtained at the anode, with both selectivity and yield approaching 100%. After complete reaction, the adiponitrile separates from the aqueous solution, directly yielding a high-purity adiponitrile product. This process is simple to operate, low-cost, high-return, and efficiently produces green hydrogen while upgrading waste plastics into chemicals, maximizing the utilization of renewable energy. It paves a path for the commercialization and sustainable production of high-value bulk chemicals and clean H2 fuels from PA-66 waste plastics, and has broad application prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical hydrogen evolution and waste plastic recycling and upgrading, and in particular to a method for electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to produce adiponitrile. BACKGROUND

[0002] The rapid depletion of fossil fuels and the increase in carbon emissions have become global problems faced by mankind today, and it is urgent to use alternative and sustainable energy. Hydrogen (H2) is an ideal renewable energy with high heat value and environmental protection. The production of high-purity H2 using renewable electricity through overall water splitting technology is a zero-carbon process. However, the high overpotential (1.23 V) and four-proton coupled electron transfer limit the efficiency of the oxygen evolution reaction (OER), resulting in instability of the catalyst at high energy consumption and high potential. Therefore, it has become very common to replace the OER with an oxidation reaction that is more thermodynamically favorable, which is of great significance to reduce the power consumption and improve the corresponding energy conversion efficiency, and coupling these electrosynthesis reactions with HER can simultaneously produce high-value-added products at the anode and cathode. Continuous exploration and innovation in catalyst design, reaction mechanism, and device development are expected to improve the economic feasibility and competitiveness of this hybrid water electrolysis strategy in industrial production.

[0003] Plastics have become an integral part of modern society due to their lightweight, chemical stability, and low cost. However, the continued production and use of plastics worldwide has resulted in a significant amount of unmanaged waste plastics polluting the environment at an alarming rate. Plastics are typically composed of polymers, which have high stability and resistance to degradation. The long residence time of plastic waste from production to disposal poses many serious problems and poses a significant threat to the environment, ecosystems, and human health. In the face of the urgency of plastic waste hazards, effective plastic waste disposal strategies need to be developed and proactive actions need to be taken to protect the environment and ecosystems from plastic pollution.

[0004] Polyamide-66 (PA-66), commonly known as nylon 66, is a polyamide material made from the polycondensation of hexamethylenediamine and adipic acid, one of the five engineering plastics, with a global annual demand of 1.3 million tons. Currently, PA-66 waste is mainly disposed of through landfills, but since PA-66 is not biodegradable, it accumulates in the environment, for example, 10% of the garbage in the ocean is composed of PA-66. In addition to landfilling, PA-66 can also be disposed of through incineration, but this will emit a large amount of carbon dioxide. Mechanical recycling is another option for disposing of scrap PA-66, but it is not popular due to the high cost of waste separation and cleaning. SUMMARY

[0005] In order to alleviate the plastic crisis and environmental pressure, the application discloses a method for preparing adiponitrile and green hydrogen by electrochemically oxidizing waste PA-66 plastics, which has the advantages of high utilization rate, low energy consumption, easy separation, low investment, high economic value and environmental protection, and can provide a new feasible path for alleviating the plastic crisis and industrializing the production of hydrogen by water electrolysis. The waste PA-66 is used to produce valuable AC, ADN and H2, which can open up a path for commercialization and sustainable production of high-value bulk chemicals and clean H2 fuel from PA-66 waste.

[0006] In order to achieve the above-mentioned purpose, the application provides the following technical scheme:

[0007] A method for preparing adiponitrile by electrochemically oxidizing waste PA-66 plastics coupled with hydrogen evolution, comprising the following steps:

[0008] (1) The waste PA-66 plastics are recovered, classified, pretreated, and then ground into powder in a ball mill to obtain PA-66 plastic powder;

[0009] (2) The PA-66 plastic powder is placed in a reaction device, deionized water and an acidic solution are added, and heating and stirring are carried out at a set temperature, so that the PA-66 plastic powder is depolymerized and converted into hexamethylenediamine and adipic acid;

[0010] The molar ratio of the PA-66 plastic powder to the deionized water and the acidic solution is 1: (1-5): (20-40);

[0011] The heating and stirring temperature is 100-130 DEG C, and the continuous stirring time is 2-6 h;

[0012] (3) After the reaction is completed, the temperature is cooled to room temperature, the precipitate is separated by filtration, and the filter cake is the product adipic acid; potassium hydroxide solution is added to the filtrate, and after the reaction is completed, the bottom precipitate is filtered again to obtain potassium sulfate, and the filtrate is a hexamethylenediamine solution;

[0013] (4) The depolymerized hexamethylenediamine solution is directly used as an electrolyte, a foam nickel or V-doped foam nickel catalyst is used, and electrolysis is carried out in a two-electrode electrolytic cell, so that hydrogen is obtained at the cathode and adiponitrile is obtained at the anode through electrolysis;

[0014] The electrolysis operating temperature is 20-40 DEG C, and the operating pressure is 1-3 Mpa.

[0015] Further, the waste PA-66 plastic powder has a mesh size of 16-500 mesh.

[0016] Further, the acidic solution includes hydrochloric acid solution, sulfuric acid solution and nitric acid solution.

[0017] Further, the preparation method of the V-doped foam nickel catalyst in step (4) is:

[0018] a. Ultrasonic cleaning of the foam nickel material in hydrochloric acid solution;

[0019] b. Dissolve nickel nitrate hexahydrate, ammonium fluoride, urea, and vanadium chloride in deionized water and mix well. Then immerse the treated foam nickel material in the mixed solution and transfer it to a high-pressure hydrothermal kettle for reaction. After reaction, clean and dry to obtain a precursor material;

[0020] c. Place sodium hypophosphite upstream of the tube furnace and the precursor material downstream of the tube furnace. After purging with N2, heat to 250-350°C for annealing, then naturally cool to room temperature. Clean and dry to obtain a V-doped Ni2P catalyst.

[0021] Further, the amount of nickel nitrate hexahydrate: ammonium fluoride: urea: vanadium chloride is 1.5:4:10:(0.2-0.6).

[0022] Further, the annealing time in step c is 1-3h.

[0023] A V-doped foam nickel catalyst is prepared by the above method.

[0024] Specifically, a method for electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to produce adiponitrile, comprising the following steps:

[0025] (1) The recovered waste PA-66 plastic is sorted and pretreated to remove labels, surface pigments and other impurities that may affect the purity of the subsequent product, then ground into powder in a ball mill. The fineness is determined according to the actual situation, the finer the powder, the more complete the subsequent depolymerization.

[0026] (2) A certain amount of treated PA-66 powder is placed in a reaction device, and an appropriate amount of deionized water and excess acid solution are added. Heat and stir at a set temperature for a certain time to achieve complete depolymerization of the PA-66 plastic powder and conversion to hexamethylene diamine and adipic acid;

[0027] (3) After the reaction is completed, the reaction device is placed in water to cool to room temperature, and a precipitate appears at the bottom. Filter and separate the reaction product adipic acid. Then add excess potassium hydroxide solution to the separated upper clear liquid, and after the reaction is complete, filter the precipitated potassium sulfate at the bottom again. The upper clear liquid is a hexamethylene diamine solution;

[0028] (4) The depolymerized hexamethylene diamine solution is directly used as an electrolyte, a non-noble metal bifunctional catalyst is used, and continuous long-time electrolysis is carried out in a two-electrode electrolytic cell. Through electrolysis, hydrogen with a purity of more than 99% is obtained at the cathode, and the depolymerized hexamethylene diamine can be oxidized and upgraded to adiponitrile at the anode;

[0029] (5) The electrolyte after the electrolysis reaction needs to be followed by product separation and purification. The cathode hydrogen enters a hydrogen / water separator, removes water vapor carried by the gas, and then further removes moisture through a dryer. After being adjusted to the rated pressure by a pressure stabilizing valve and an adjusting valve, the hydrogen is output and transported to the required place. The anode reaction product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the adiponitrile product and the electrolysis solution are separated, and high-purity adiponitrile product can be directly obtained.

[0030] Specifically, the PA-6 plastic powder in step (1) has a mesh size of 16-500 mesh, preferably 500 mesh.

[0031] Specifically, the acid solution in step (2) includes a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution, preferably the acid solution is a sulfuric acid solution.

[0032] Specifically, the molar mass ratio of the PA-66 powder to deionized water and the 5 mol / L sulfuric acid solution in step (2) is 1: (1-5): (20-40).

[0033] Specifically, the heating and stirring temperature range in step (2) is 80-140℃, the stirring speed is kept above 200 r / min, and the continuous stirring time is 2-6 h.

[0034] Specifically, the electrolysis operating temperature in step (4) is 20-40℃, and the operating pressure is 1-3 Mpa.

[0035] According to the above technical solution, compared with the prior art, the process provided by the present application has the following excellent effects:

[0036] 1. The depolymerized hexamethylene diamine solution is directly used as an electrolyte, a non-noble metal bifunctional catalyst V-Ni2P is used, and continuous long-time electrolysis is carried out in a two-electrode electrolytic cell. Through electrolysis, hydrogen with a purity of more than 99% is obtained at the cathode, and the depolymerized hexamethylene diamine can be oxidized and upgraded to adiponitrile, and the selectivity and yield of adiponitrile are close to 100%. After complete reaction, adiponitrile and aqueous solution are separated, and high-purity adiponitrile product can be directly obtained.

[0037] 2、Compared with the traditional landfill and incineration process, the application is more green and environmentally friendly, and will not cause additional impact on the environment; the cost of mechanical recycling and other physical recycling methods is high and the benefit is low, and the electrochemical oxidation method can convert waste plastics into valuable adipic acid and adiponitrile, while producing green hydrogen at the cathode, which has higher economic benefits.

[0038] 3、From the perspective of actual application production, the product separation after the reaction of waste plastics PA-66 is simple and low in consumption, which makes the cost of the whole recycling process lower and the benefit higher. Most importantly, the electrochemical oxidation of PA-66 can be used as an alternative to anodic oxygen evolution reaction and coupled with cathodic water electrolysis to produce hydrogen. From the perspective of energy utilization, the lower starting potential and operating potential make the energy consumption required for the same hydrogen production rate lower, and the cost of electric energy can be further reduced; in addition, compared with the low value of oxygen, it is obviously more economically valuable to convert waste plastics into high-value adiponitrile and adipic acid.

[0039] Overall, the electrochemical hydrogen evolution coupled with the electrochemical oxidation of waste PA-66 plastic to produce adiponitrile process disclosed in the application not only hopes to realize the recycling and upgrading of waste plastics, but also can cooperate with water electrolysis to produce hydrogen, which may open up a way for commercialization and sustainable production of high-value bulk chemicals and clean H2 fuel from PA-66 waste. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0041] Figure 1 is the XRD pattern of the adipic acid product prepared in Example 1.

[0042] Figure 2 is the XRD pattern of the potassium sulfate precipitate obtained in Example 1.

[0043] Figure 3 is the NMR pattern of the supernatant prepared in Example 1.

[0044] Figure 4 is the high-definition photo of the electrolyte after sufficient electrolysis in Example 1.

[0045] Figure 5 is the electrocatalytic performance comparison chart of V-Ni2P / NF, Ni2P and NiV-Pre in Example 2

[0046] Figure 6These are the LSV curves, Tafel spectra, and electrochemical impedance spectroscopy of the catalysts with different vanadium doping amounts in Example 3.

[0047] Figure 7 These are the LSV curves, Tafel spectra, and electrochemical impedance spectroscopy of the catalysts with different annealing times in Example 4.

[0048] Figure 8 This is the LSV curve of V-Ni2P as a bifunctional electrocatalyst in the dual-electrode HER||GOR and HER||OER electrolysis systems in Example 5.

[0049] Figure 9 This is a power consumption diagram for achieving different current densities in Example 5.

[0050] Figure 10 This is a graph showing the yield and conversion rate of the hydrolysis reaction under different amounts of water and H2SO4 in Example 6.

[0051] Figure 11 This is a graph showing the yield and conversion rate of the hydrolysis reaction at different reaction temperatures in Example 7.

[0052] Figure 12 This is a graph showing the hydrolysis reaction yield and conversion rate at different reaction times in Example 8.

[0053] Figure 13 This is an LSV curve at different reaction temperatures in Example 9.

[0054] Figure 14 It is a process flow diagram. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0056] This invention discloses an electrochemical oxidation process for producing adiponitrile from waste PA-66 plastic coupled with a green hydrogen production process.

[0057] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0058] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0059] Example 1

[0060] The implementation steps of the process for electrochemically oxidizing waste PA-66 plastic to adiponitrile coupled with green hydrogen production are as follows:

[0061] (1) The recovered waste PA-66 plastic is sorted and pretreated to remove labels, surface pigments, and other impurities that may affect the purity of the subsequent product. Then it is put into a ball mill for grinding and crushing into powder, obtaining PA-66 plastic powder with a mesh size of 500.

[0062] (2) 10 g of PA-66 powder is weighed into a 50 mL round-bottom flask, along with 22.7 mL of deionized water and 5.7 mL of 5 mol / L sulfuric acid solution. It is placed in an oil bath and heated to 110°C with a stirring speed of 250 r / min for 4 hours. The PA-66 plastic powder is fully depolymerized into hexanediamine and adipic acid.

[0063] (3) After the reaction is completed, the reaction device is placed in water to cool to room temperature, and a precipitate appears at the bottom. The adipic acid in the mixed solution quickly crystallizes out due to its acid insolubility. The lower precipitate is filtered, washed, and dried to obtain the product adipic acid with a purity that meets the standard. Figure 1 is the XRD pattern of the adipic acid product. Then 5 mol / L potassium hydroxide solution is added to the separated upper clear liquid until the pH is 13-14. During this period, a large amount of K2SO4 precipitates out Figure 2 is the XRD pattern of potassium sulfate precipitate, and the upper clear liquid obtained after filtering the precipitate is a hexanediamine solution Figure 3 is the NMR pattern of the supernatant;

[0064] (4) The depolymerized hexanediamine solution is directly used as an electrolyte, and a pretreated commercial nickel foam is used as a bifunctional catalyst. The pretreatment steps are as follows: The purchased commercial nickel foam with a thickness of 1 mm and 110 ppi is ultrasonically cleaned in a 2 mol / L HC1 solution for 30 minutes to remove the surface oxide layer, and then washed with ethanol and water three times to remove the oil and impurities on the surface of the NF. Continuous long-term electrolysis is carried out in a two-electrode electrolytic cell, and the electrolytic device operates at a temperature of 30°C and an operating pressure of 1 Mpa. Through electrolysis, hydrogen gas with a purity of more than 99% is obtained at the cathode, and the depolymerized hexanediamine is oxidized and upgraded to adiponitrile Figure 3 at the anode;

[0065] (5) The electrolyte after the electrolysis reaction needs to be followed by product separation and purification. The cathode hydrogen enters the hydrogen / water separator, the water vapor carried by the gas is removed, then the gas is further dehumidified by a dryer, adjusted to the rated pressure by a pressure stabilizing valve and an adjusting valve, and transported to the required place. The product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the product adiponitrile is separated from the electrolyte solution, and high-purity adiponitrile can be directly obtained. Figure 4 High-definition photo of the electrolyte after sufficient electrolysis).

[0066] Example 2

[0067] The core of the present application is to upgrade plastic monomers to chemicals at the anode, while efficiently producing green hydrogen at the cathode, maximizing the use of renewable energy. Therefore, in order to better reflect the industrialization prospect of the present application, a V-doped Ni2P catalyst with nanoflower structure composed of nanosheets with higher catalytic performance and higher stability is designed and synthesized, and the necessity of catalyst modification is explored. The specific content is as follows:

[0068] (1) Measure 10 mL of 2M hydrochloric acid solution, cut the foam nickel material with a thickness of 1mm* width of 20mm* length of 40mm in the solution and ultrasonic cleaning for 30min, to remove the surface oxide layer, then the ultrasonic foam nickel material is washed with ethanol and deionized water for three times, to remove the surface grease and impurities.

[0069] (2) Weigh 1.5mmol (436mg) of nickel nitrate hexahydrate, 4mmol (148.2mg) of ammonium fluoride, 10mmol (600.6mg) of urea, and 0.4mmol of vanadium chloride, and dissolve them in 30mL of deionized water. Stir for 30min and mix evenly. Then immerse a piece of treated foam nickel material in the mixed solution and transfer it to a 50mL high-pressure hydrothermal kettle. Hydrothermal oven to 120 ℃ for 12 h, then rinse the obtained precursor material with deionized water and ethanol several times, and then dry in an oven at 60℃ overnight to obtain the precursor material NiV-Pre;

[0070] (3) Place 0.8g of sodium hypophosphite on the upstream of the tube furnace, and place the synthesized precursor material on the downstream of the tube furnace. Purge with N2 for 20min to remove air, then heat to 300℃ at a rate of 5℃ / min under N2 atmosphere, and keep for 2h, then naturally cool to room temperature. Rinse the obtained catalyst material with deionized water and ethanol several times, then dry in an oven at 60℃ overnight to obtain the final V-doped Ni2P catalyst V-Ni2P.

[0071] Meanwhile, the undoped vanadium catalyst Ni2P was synthesized in the same way as the vanadium-doped nickel phosphide, except that vanadium chloride was not added during the synthesis. In addition, the unphosphidized catalyst NiV-Pre was synthesized.

[0072] (4) The hexamethylene diamine solution obtained in the manner provided in Example 1 was used as the electrolyte, and the three synthesized catalysts V-Ni2P, Ni2P and NiV-Pre were directly used as the anode catalyst. First, the catalysts were activated by means of CV scanning with a CHI 660E electrochemical workstation in a three-electrode system, and then a series of electrochemical tests were carried out in a three-electrode electrolytic cell. The electrolytic device was operated at a temperature of 30°C and an operating pressure of 1 Mpa. The obtained electrochemical data were analyzed to observe the changes in the activity of the modified catalysts.

[0073] (5) After the electrolytic reaction, the electrolyte needs to be subjected to subsequent product separation and purification. The cathode hydrogen enters a hydrogen / water separator, and the water vapor carried by the gas is removed. Then, after further drying by a dryer, the hydrogen is adjusted to the rated pressure by a pressure stabilizing valve and a regulating valve and is transported to the required place. The anode reaction product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the adiponitrile product and the electrolytic solution are separated, and high-purity adiponitrile product can be directly obtained.

[0074] Compared with Ni2P and NiV-Pre, the synthesized V-Ni2P / NF catalyst has better catalytic activity for anode oxidation. The potentials at 100 mA cm -2 of all samples (i.e. E100) are in the order of V-Ni2P < Ni2P < NiV-Pre, indicating that the catalytic performance decreases in turn, which shows that V doping and phosphidization are indispensable to improve the catalytic performance. Meanwhile, the lower Tafel further confirms the best AOR performance of V-Ni2P. It has the lowest Tafel slope (23.6 mV dec -1 ), which indicates that V-Ni2P is most favorable for the catalytic kinetics of AOR. At the same time, it has the lowest Rct value, which proves the descending nature of AOR kinetics, which is very consistent with the above Tafel results. In order to further study the excellent AOR activity of V-Ni2P, the double-layer capacitance value (Cdl) was calculated according to the relevant cyclic voltammetry curves (it is worth noting that the maximum Cdl value of V-Ni2P is 6.5 mF cm-2, which is 1.7 times that of Ni2P. This shows that the incorporation of V into Ni2P helps to improve the catalytic ability, as shown in the comparison of the electrocatalytic performance of V-Ni2P / NF, Ni2P and NiV-Pre. Figure 5

[0075] Example 3

[0076] ​The core of the present application is to upgrade plastic monomers to chemicals at the anode, while efficiently producing green hydrogen at the cathode, maximizing the use of renewable energy. Therefore, in order to better reflect the prospect of industrialization of the present application, a V-doped Ni2P catalyst with nanoflower structure composed of nanosheets with higher catalytic performance and higher stability is designed and synthesized, and the influence of different vanadium doping amounts on the catalyst activity is explored. The specific content is as follows:

[0077] (1) Measure 10 mL of 2M hydrochloric acid solution, cut the foam nickel material with a thickness of 1mm* width of 20mm* length of 40mm in the solution and ultrasonic cleaning for 30min, to remove the surface oxide layer, then the ultrasonic foam nickel material is washed with ethanol and deionized water for three times, to remove the surface grease and impurities.

[0078] (2) Weigh 1.5mmol (436mg) of nickel nitrate hexahydrate, 4mmol (148.2mg) of ammonium fluoride, 10mmol (600.6mg) of urea, and a certain amount of vanadium chloride dissolved in 30mL of deionized water, stir for 30min and mix evenly. Then immerse a piece of treated foam nickel material in the mixed solution, transfer it to a 50mL high-pressure hydrothermal kettle, and hydrothermal oven to 120 ℃ for 12 h, then rinse the obtained precursor material with deionized water and ethanol several times, then dry in an oven at 60℃ overnight, wherein the doping amount of vanadium chloride is 0.2mmol (31.5mg), 0.4mmol (62.9mg) and 0.6mmol (94.5mg) respectively;

[0079] (3) Place 0.8g of sodium hypophosphite on the upstream of the tube furnace, and place the synthesized precursor material on the downstream of the tube furnace, purge with N2 for 20min to remove air, then heat to 300℃ at a rate of 5℃ / min under N2 atmosphere, and keep for 2h, then naturally cool to room temperature, rinse the obtained catalyst material with deionized water and ethanol several times, then dry in an oven at 60℃ overnight, to obtain the final V-doped Ni2P catalyst, according to different vanadium doping amounts, named as 0.2-V-Ni2P, 0.4-V-Ni2P, 0.6-V-Ni2P respectively;

[0080] (4) The hexamethylene diamine solution obtained in the manner provided in Example 1 is used as the electrolyte, and the V-doped Ni2P catalyst is directly used as the anode catalyst. First, in a three-electrode system, CV scanning is performed on the catalyst with the help of a Kost CS350MA electrochemical workstation to activate the catalyst, then a series of electrochemical tests are carried out in the assembled three-electrode electrolytic cell, the electrolysis device operates at a temperature of 30℃ and an operating pressure of 1Mpa, and the obtained electrochemical data is analyzed to observe the influence of different vanadium doping amounts on the catalyst activity.

[0081] (5) The electrolyte after the electrolysis reaction needs to be followed by product separation and purification, wherein the cathode hydrogen enters the hydrogen / water separator, the water vapor carried by the gas is removed, then after further drying by the dryer, the pressure is adjusted to the rated pressure by the pressure stabilizing valve and the regulating valve, and is transported to the required place; the anode reaction product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the adiponitrile product and the electrolyte solution are separated, and the high-purity adiponitrile product can be directly obtained;

[0082] The experimental data show that the 0.4-V-Ni2P / NF catalyst shows better catalytic activity in the oxidation of hexanediamine at the anode, as shown in Figure 6 . The 0.4-V-Ni2P-2 has the best electrocatalytic performance and has the lowest initial potential. The corresponding Tafel slope shows that the 0.4-V-Ni2P-2 has the lowest Tafel slope (23.6 mV dec -1 ) compared with the 0.2-V-Ni2P-2 (43.2 mV dec -1 ) and the 0.6-V-Ni2P-2 (125.6 mV dec -1 ), indicating that it has the most favorable AOR kinetics. The electrochemical impedance spectrum (EIS) of the 0.4-V-Ni2P-2 also proves its highest catalytic capacity, with the smallest radius, which determines the smallest charge transfer resistance (Rct) on the catalyst / electrolyte interface, and the fastest charge transfer rate.

[0083] Example 4

[0084] The core of the present application is to upgrade plastic monomers to chemicals at the anode, while efficiently producing green hydrogen at the cathode, maximizing the use of renewable energy. Therefore, in order to better reflect the industrialization prospect of the present application, a V-doped Ni2P catalyst with nanoflower structure composed of nanosheets with higher catalytic performance and higher stability is designed and synthesized, and the influence of different phosphating times on the catalyst activity is explored, and the specific content is as follows:

[0085] (1) Measure 10 mL of 2M hydrochloric acid solution, cut the foam nickel material with a thickness of 1 mm* width of 20 mm* length of 40 mm in the solution and ultrasonic cleaning for 30 min, to remove the surface oxide layer, then the ultrasonic foam nickel material is cleaned with ethanol and deionized water for three times, to remove the surface grease and impurities.

[0086] (2) 1.5 mmol (436 mg) of nickel nitrate hexahydrate, 4 mmol (148.2 mg) of ammonium fluoride, 10 mmol (600.6 mg) of urea, and 0.4 mmol (62.9 mg) of vanadium chloride were weighed and dissolved in 30 mL of deionized water, and stirred for 30 min to mix uniformly. Then a piece of treated nickel foam material was immersed in the mixed solution, transferred to a 50 mL high-pressure hydrothermal kettle, and hydrothermally treated in an oven at 120 °C for 12 h. The obtained precursor material was then washed several times with deionized water and ethanol, and dried in an oven at 60 °C overnight;

[0087] (3) 0.8 g of sodium hypophosphite was placed upstream of a tube furnace, and the synthesized precursor material was placed downstream of the tube furnace. After purging with N2 for 20 min to remove air, the tube furnace was heated to 300 °C at a rate of 5 °C / min under N2 atmosphere, and kept for a certain time, and then naturally cooled to room temperature. The obtained catalyst material was washed several times with deionized water and ethanol, and dried in an oven at 60 °C overnight, to obtain the final V-doped Ni2P catalyst. The annealing time was 1 h, 2 h, and 3 h, respectively. According to the different annealing times, the catalysts were named as V-Ni2P-1, V-Ni2P-2, and V-Ni2P-3, respectively;

[0088] (4) The hexanediamine solution obtained in the manner provided in Example 1 was used as an electrolyte, and the V-doped Ni2P catalyst was directly used as an anode catalyst. First, the catalyst was activated by CV scanning in a three-electrode system with the aid of a Kost CS350MA electrochemical workstation. Then, a series of electrochemical tests were carried out in a three-electrode electrolysis cell. The electrolysis device was operated at a temperature of 30 °C and an operating pressure of 1 MPa. The obtained electrochemical data were analyzed to observe the effect of different annealing times on the activity of the catalyst.

[0089] (5) After the electrolysis reaction, the electrolyte needs to be subjected to subsequent product separation and purification. The cathode hydrogen enters a hydrogen / water separator, from which the water vapor carried by the gas is removed. After further drying by a dryer, the hydrogen is adjusted to the rated pressure by a pressure stabilizing valve and a regulating valve, and then transported to the required place. The anode reaction product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the adiponitrile product and the electrolysis solution are separated, and a high-purity adiponitrile product can be directly obtained;

[0090] The experimental data show that, compared with the samples with an annealing time of 1 h and 3 h, the sample with an annealing time of 2 h (i.e., V-Ni2P-2) shows the smallest initial potential and the lowest Tafel slope, indicating that it has the best catalytic activity, as shown in Figure 7 (LSV curve, Tafel spectrum, and electrochemical impedance spectrum of the catalysts with different annealing times).

[0091] Example 5

[0092] In order to fully illustrate the advantages of low power consumption and high energy conversion efficiency of the electrochemical hydrogen evolution coupled PA-66 waste plastic monomer oxidation process in the present application, the differences between the present electrolysis device and the water electrolysis hydrogen production device are focused on.

[0093] The hexanediamine solution obtained in the manner provided in Example 1 was used as the electrolyte, and the bifunctional catalyst V-Ni2P was directly used as the cathode and anode catalyst. First, the catalyst was activated by CV scanning with the aid of a Kost CS350MA electrochemical workstation in a three-electrode system, and then LSV scanning of the polarization curve was performed in the two-electrode electrolysis cell assembled, the operating temperature of the electrolysis device was 30°C, the operating pressure was 1 Mpa, the scanning rate was 10 mV / s, the scanning interval was 1~2.6 V, the iR compensation was set to 85%, and continuous scanning was performed multiple times until it tended to be stable.

[0094] Meanwhile, 1 mol / L potassium hydroxide was used as the electrolyte, and the same bifunctional catalyst V-Ni2P was directly used as the cathode and anode catalyst. First, the catalyst was activated by CV scanning with the aid of a Kost CS350MA electrochemical workstation in a three-electrode system, and then LSV scanning of the polarization curve was performed in the two-electrode electrolysis cell assembled, the operating temperature of the electrolysis device was 30°C, the operating pressure was 1 Mpa, the scanning rate was 10 mV / s, the scanning interval was 1~2.6 V, the iR compensation was set to 85%, and continuous scanning was performed multiple times until it tended to be stable.

[0095] Figure 8 is the LSV curve of V-Ni2P as a bifunctional electrocatalyst in a two-electrode HER||GOR and HER||OER electrolysis system. Through comparison of the two LSV curves, compared with traditional water electrolysis hydrogen production, the cathode HER coupled with the anode AOR (HER||AOR) device only needs 1.58, 1.65, 1.69 and 1.74 V to achieve current densities of 100, 200, 300 and 400 mA cm -2 , respectively, which is much smaller than the current density of traditional water splitting (HER||OER, 1.89, 1.99, 2.08 and 2.15 V). The HER||AOR system can also achieve higher industrial-grade current density (≥ 500 mA cm-2). More importantly, the V-Ni2P-based HER||AOR system needs only 1.88 V to achieve an industrial-related 800 mA cm -2 current density, which is at least 500 mV lower than water splitting. The low cell voltage of the HER||AOR system verifies the corresponding energy-saving performance and high energy conversion, which is superior to the recently reported hybrid electrolysis system. It is worth noting that, Figure 9The power consumption of the calculated HER||AOR and HER||OER systems is shown in the power consumption diagram (to reach different current densities), where the power consumption gradually increases with the increase of current density. When the current density is 400 mA cm -2 and 800 mA cm -2 , the power consumption of the HER||AOR system to produce 1 kg of H2 is 46.66 kWh and 50.55 kWh (kWh kg -1 H2), respectively, which is lower than the overall water electrolysis. This result further reveals the advantages of the hydrogen evolution reaction and the coupling process of the oxidation cycle of hexamethylene diamine in the actual electro-synthesis of high value-added chemicals.

[0096] Example 6

[0097] Exploration of PA-66 plastic hydrolysis solvent conditions in the process of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to produce adiponitrile.

[0098] (1) A certain amount of treated PA-66 powder was placed in the reaction device, and an appropriate amount of deionized water and excess acid solution was added. It was placed in an oil bath and heated to 110℃, with a rotation speed of 250 r / min, and continuously stirred for 4 hours. The PA-66 plastic powder was depolymerized into hexamethylene diamine and adipic acid. Among them, the molar mass ratio of PA-66 powder to deionized water and 5 mol / L sulfuric acid solution was 1: (1-5): (20-40), and the hydrolysis reaction yield and conversion rate under different amounts of water and H2SO4 were as shown in Figure 10 .

[0099] It was found that when the amount of sulfuric acid solution was small, the conversion rate and yield of the product were low. With the increase of the amount of sulfuric acid solution, the conversion rate and yield of the product increased significantly. The addition of sulfuric acid solution provided a good acidic environment for the depolymerization reaction of PA-66, which was beneficial to the depolymerization reaction. However, when the amount of sulfuric acid solution was too much, the conversion rate and yield of the product did not increase significantly, and it would require more potassium hydroxide solution in the subsequent process, causing waste.

[0100] At the same time, the amount of deionized water also had a significant effect on the depolymerization reaction. When the molar mass ratio of PA-66 powder to deionized water was less than 1:30, the conversion rate and yield of the product increased with the increase of the amount of deionized water. Further increasing the amount of deionized water, the conversion rate and yield of the product began to decrease. Therefore, the optimal molar mass ratio of PA-66 powder to deionized water and 5 mol / L sulfuric acid solution was 1:2.5:30, as shown in Figure 10 .

[0101] Example 7

[0102] Exploration of PA-66 plastic hydrolysis temperature conditions in the process of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to prepare adiponitrile.

[0103] (1) 10 g of PA-66 powder was weighed into a 50 mL round-bottom flask, 22.7 mL of deionized water and 5.7 mL of 5 mol / L sulfuric acid solution were added at the same time, placed in an oil bath and heated to 80℃, 90℃, 100℃, 110℃, 120℃, 130℃ and 140℃, the rotation speed was set to 250 r / min, and continuous stirring was carried out for 4 hours, and the PA-66 plastic powder was fully depolymerized into hexamethylenediamine and adipic acid.

[0104] The depolymerization temperature has a significant effect on the PA-66 depolymerization reaction. With the increase of reaction temperature, the conversion rate and yield of the product increase significantly. This is because as the temperature rises, the PA-66 powder will swell or dissolve in water, increasing the contact area with water and accelerating the depolymerization reaction rate. When the temperature rises from 80℃ to 110℃, the conversion rate and yield increase sharply, and at 110℃, the depolymerization is complete. There is no significant increase in the conversion rate and yield of the product as the temperature continues to rise. In order to maintain low energy consumption, the optimal reaction temperature is 110℃, and the hydrolysis reaction yield and conversion rate under different reaction temperatures are shown in the following figure Figure 11 .

[0105] Example 8

[0106] Exploration of PA-66 plastic hydrolysis time conditions in the process of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to prepare adiponitrile.

[0107] (1) 10 g of PA-66 powder was weighed into a 50 mL round-bottom flask, 22.7 mL of deionized water and 5.7 mL of 5 mol / L sulfuric acid solution were added at the same time, placed in an oil bath and heated to 110℃, the rotation speed was set to 250 r / min, and continuous stirring was carried out for 1, 2, 3, 4, 5, 6 hours, and the PA-66 plastic powder was fully depolymerized into hexamethylenediamine and adipic acid.

[0108] The depolymerization time also has a significant effect on the PA-66 depolymerization reaction. With the increase of reaction time, the conversion rate and yield of the product increase significantly. When the time reaches 4 hours, the conversion rate and yield of the product are the highest, and the PA-66 powder is completely depolymerized. There is no significant increase in the conversion rate and yield of the product as the time continues to extend. In order to maintain low energy consumption, the optimal reaction time is 4h, and the hydrolysis reaction yield and conversion rate under different reaction times are shown in the following figure Figure 12 .

[0109] Example 9

[0110] Exploration of PA-66 plastic electrolysis operation conditions in the process of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile.

[0111] (1) The adiponidine solution obtained in the manner provided in Example 1 was used as an electrolyte, and the bifunctional catalyst V-Ni2P was directly used as a cathode and anode catalyst. First, the catalyst was activated by CV scanning in a three-electrode system with the aid of a Kost CS350MA electrochemical workstation, and then LSV scanning of the polarization curve was performed in a two-electrode electrolysis cell assembled by the inventor, the scanning rate was 10 mV / s, the scanning interval was 1~2.6 V, the iR compensation was set to 85%, and continuous scanning was performed multiple times until it tended to be stable. The temperature of the electrolysis device was 20℃, 30℃ and 40℃.

[0112] Under different electrolysis device operation conditions, electrochemical tests were performed, and through the LSV curve test and quantitative analysis of the products, it was found that the influence of the reaction temperature on the catalytic activity and the catalytic rate was obvious. With the increase of the temperature, the transfer speed of the electrons and ions was accelerated, and the catalytic reaction rate was also obviously improved. However, high temperature also brought problems, such as faster solution evaporation rate, higher energy consumption, and greater test of the stability of the catalyst material. Considering comprehensively, the optimal temperature can be set to 30℃, and the LSV curve under different reaction temperatures is shown in Figure 13 The influence of pressure on the electrolysis reaction was not obvious, and it can be set to 1 MPa without special requirements.

[0113] Example 10

[0114] In order to fully illustrate the advantages of low cost and high return of the process of electrochemical hydrogen evolution coupled with electrochemical oxidation of PA-66 waste plastic monomer to adiponitrile in the present application, the separation cost in the present process is described.

[0115] (1) After the depolymerization reaction was completed, the reaction device was placed in water and cooled to room temperature, and a precipitate appeared at the bottom. The adipic acid in the mixed solution was quickly crystallized and precipitated due to its acid insolubility, and the lower precipitate was filtered, washed and dried to obtain the product adipic acid with a purity up to standard. Then 5 mol / L potassium hydroxide solution was added to the separated upper clear liquid until the pH was 13~14. During this period, a large amount of K2SO4 precipitated, and the upper clear liquid obtained after filtering the precipitate was adiponidine solution.

[0116] (2) The electrolyte after the electrolysis reaction needs to be followed by product separation and purification. The cathode hydrogen enters the hydrogen / water separator, and the water vapor carried by the gas is removed. Then, after further drying by a dryer, the hydrogen is adjusted to the rated pressure by a pressure stabilizing valve and an adjusting valve, and then transported to the required place. The anode reaction product adiponitrile is slightly soluble in water, so after the electrolyte is fully reacted, the adiponitrile product and the electrolysis solution are separated, and high-purity adiponitrile product can be directly obtained.

[0117] Unlike traditional commercial water electrolysis systems where power consumption is the primary cost factor, the cost of the separation system in the electrochemical hydrogen evolution coupled with the electrochemical oxidation of waste plastics is not negligible. The process design in this invention enables low-cost separation of all products. Specifically, during the depolymerization of PA-66 powder, adipic acid crystallizes out due to its acid insolubility. Simultaneously, benefiting from the excellent performance of the electrochemical catalyst V-Ni2P, at 1.40 V (vs. RHE), the selectivity and yield of adiponitrile are close to 100%, allowing all hexamethylenediamine in the solution to be converted into a separate liquid adiponitrile that separates from the aqueous solution. Figure 14 ).

[0118] In summary, the experimental results show that this electrochemical hydrogen evolution coupled with the electrochemical oxidation of waste PA-66 plastic to adiponitrile paves the way for the commercial and sustainable production of high-value bulk chemicals and clean H2 fuels from PA-66 waste, and has broad application prospects.

[0119] The above description of the disclosed embodiments enables those 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 invention is not to 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

1. A method for electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile, characterized in that, It comprises the following steps: (1) The waste PA-66 plastic is classified, pretreated, and then ground into powder in a ball mill to obtain PA-66 plastic powder; (2) The PA-66 plastic powder is placed in a reaction device, and deionized water and an acidic solution are added, and heated and stirred at a set temperature, so that the PA-66 plastic powder is depolymerized and converted into hexanediamine and adipic acid; The molar ratio of the PA-66 plastic powder to deionized water and the acidic solution is 1: (1-5): (20-40); The heating and stirring temperature is 100-130°C, and the continuous stirring time is 2-6 h; (3) After the reaction is completed, it is cooled to room temperature, and the precipitate is separated by filtration, and the filter cake is the product adipic acid; potassium hydroxide solution is added to the filtrate, and after the reaction is completed, the bottom precipitate is filtered again to obtain potassium sulfate, and the filtrate is a hexanediamine solution; (4) The depolymerized hexanediamine solution is directly used as an electrolyte, and a foam nickel or V-doped foam nickel catalyst is used in a two-electrode electrolytic cell, and through electrolysis, hydrogen is obtained at the cathode and adiponitrile is obtained at the anode; The electrolysis operating temperature is 20-40°C, and the operating pressure is 1-3 MPa.

2. The method of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile according to claim 1, characterized in that: The PA-66 plastic powder has a mesh size of 16-500 mesh.

3. The method of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile according to claim 1, characterized in that: The acidic solution comprises hydrochloric acid solution, sulfuric acid solution, and nitric acid solution.

4. The method of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile according to claim 1, characterized in that, The preparation method of the V-doped foam nickel catalyst in step (4) is as follows: a. Ultrasonic cleaning of the foam nickel material in hydrochloric acid solution; b. Dissolve nickel nitrate hexahydrate, ammonium fluoride, urea, and vanadium chloride in deionized water, and mix well; then immerse the treated foam nickel material in the mixed solution, and transfer it to a high-pressure hydrothermal kettle for reaction; after the reaction, wash and dry to obtain a precursor material; c. Place sodium hypophosphite upstream of the tube furnace, and place the precursor material downstream of the tube furnace, and then heat to 250-350°C after purging with N2, and then naturally cool to room temperature, and then wash and dry to obtain a V-doped Ni2P catalyst.

5. The method of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile according to claim 4, characterized in that, The amount of nickel nitrate hexahydrate: ammonium fluoride: urea: vanadium chloride is 1.5:4:10: (0.2-0.6).

6. The method of electrochemical hydrogen evolution coupled with electrochemical oxidation of waste PA-66 plastic to adiponitrile according to claim 4, characterized in that, The annealing time in step c is 1-3 h.

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