A method for electrocatalytic hydrogen production coupled with waste plastic to form potassium formate and potassium terephthalate

Abstract

The application discloses a method for producing hydrogen by coupling formic acid potassium and terephthalic acid potassium from electrocatalytic waste plastics. The method comprises the following steps: dissolving the waste plastics into an alkaline solution by a certain treatment method; adopting a three-electrode system; taking the alkaline solution containing the waste plastics as an electrolyte; and performing electrocatalytic oxidation in an H-shaped electrolytic tank. The three-electrode system comprises a working electrode, a counter electrode and a reference electrode, and the electrolyte jointly constitutes an electrocatalytic reaction device. During the reaction process under a constant voltage, hydrogen can be collected at a cathode, and formic acid potassium and terephthalic acid potassium can be obtained at an anode. The production process is clean and pollution-free. Meanwhile, the high-value-added chemicals, formic acid potassium and terephthalic acid potassium, converted from the waste plastics can be further used as industrial raw materials. The clean gas, hydrogen, produced can be used as energy, and the method has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrochemical catalytic oxidation and hydrogen production by electrolysis of water, and particularly relates to a method for producing hydrogen by coupling electrocatalysis of waste plastic into potassium formate and potassium terephthalate. BACKGROUND

[0002] Plastics are widely used in various aspects of national economy and daily life due to their good use performance, easy molding and processing, and low cost, and are important and indispensable basic materials. Large-scale production and use of plastics have facilitated people's daily life, but have also caused a large amount of plastic waste, which not only causes white pollution but also causes ecological environmental risk to accumulate year by year, seriously threatening water and soil safety and human health. At the same time, if petroleum-based synthetic plastic products cannot be effectively recycled and recycled, it is also a great waste of petroleum resources.

[0003] Polyester is the second largest (China is the largest) thermoplastic polymer material in the world, and especially polyethylene terephthalate (PET) has outstanding advantages such as excellent physical and mechanical properties, electrical insulation, fatigue resistance, friction resistance and dimensional stability, and is the main raw material for synthetic polyester, accounting for more than 80% of the total synthetic fiber; at the same time, PET has the characteristics of no odor, no smell, no toxicity, and can directly contact food-grade products, and is widely used in food, catering and various packaging products. At present, most of the PET plastic products are disposable consumer goods, which are difficult to degrade under natural conditions after being discarded, and their recycling is mainly realized through physical regeneration and chemical recycling. Among them: physical regeneration reduces the molecular weight of the regenerated product due to the double action of heat and mechanical processing, and is difficult to be recycled for multiple times, and is also not suitable for the treatment of waste fibers with complex composition. Chemical recycling refers to the depolymerization of waste PET plastic long molecular chains into monomers or the cracking of small molecular organic matter under specific chemical or biochemical conditions, and then the raw materials are refined to obtain upgraded products. Chemical recycling is expected to realize the "closed" recycling of waste plastics in theory, and has received widespread attention from the scientific and industrial communities in recent years

[0004] The chemical formula of PET is (C 10 H8O4) nPET plastics can be chemically hydrolyzed to produce terephthalic acid (PTA) and ethylene glycol (EG) under alkaline conditions, but there are problems such as difficult separation of generated products. In recent years, under the action of catalysts, EG is catalytically upgraded to formic acid and other high-value, easily separated chemicals under specific chemical conditions such as light and electricity, becoming a very promising PET high-value recycling approach. For example, the literature (Photoreforming of Nonrecyclable Plastic Waste over a Carbon Nitride / Nickel Phosphide Catalyst) reports that PET plastics are converted into valuable formate and acetate through photocatalytic conversion. Although the method is perfect, the process still has problems of low space production rate and poor selectivity for single high-value oxidation products.

[0005] Electrocatalysis can be driven by renewable energy (solar, wind and water power), and under mild conditions, clean hydrogen is produced at the cathode, and organic compounds at the anode are efficiently and selectively oxidized and upgraded to high-value oxygen-containing chemicals such as potassium formate, acetic acid, 2,5-furan carboxylic acid and other carbonyl compounds. However, there are few reports on the use of electrocatalysis to upgrade and convert waste PET into high-value chemicals. SUMMARY

[0006] In view of the shortcomings and deficiencies of the prior art, the purpose of the present application is to overcome the problems of low recycling efficiency, poor selectivity, high cost and downgrading of waste plastics. After hydrolysis of waste plastics in an alkaline solution, terephthalate and ethylene glycol are generated, and the ethylene glycol is further catalytically oxidized to formate in the electrolysis process. The present application provides a method for electrocatalytic oxidation of waste plastics to potassium formate and potassium terephthalate, which has the advantages of green environmental protection, simple production process, low catalyst cost, high reaction efficiency, high product purity and easy separation.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] 1. The present application provides a method for electrocatalytic oxidation of waste plastics to potassium formate and potassium terephthalate, which has the advantages of green environmental protection, simple production process, low catalyst cost, high reaction efficiency, high product purity and easy separation.

[0009] 2.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the waste plastics are one or more of waste PET plastic bottles, waste PET packaging materials, PET / PE mixed films, and fiber grade waste PET (polyester microfibers).

[0010] 3.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the waste plastics are treated by dissolving in an alkaline solution by one or more of heating, ultrasonic, stirring, microwave, and mechanical ball milling. Preferably, the heating temperature is 80-180℃, and the time is 2-24h. The alkaline solution is a 2-10M KOH or NaOH solution with a volume of 50-100mL.

[0011] 4.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the working electrode is a porous foam metal loaded metal oxide / hydroxide, the reference electrode is Hg / HgO, and the counter electrode is a platinum wire; wherein the metal comprises one or more of cobalt, nickel, manganese, iron, copper, and aluminum.

[0012] 5.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the porous foam metal comprises one of foam nickel, foam iron, foam copper, foam nickel-iron (7:3), foam nickel-copper (8:2), and foam cobalt-nickel (3:7). Preferably, the thickness of the foam metal is 3-5mm, and the size is (1-3)×(1-3)cm.

[0013] 6.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the mass of the waste plastics is 0.002-2kg, and the molar concentration of the hydrolysis product ethylene glycol is 10-1000mM. Preferably, the molar concentration of the ethylene glycol is 50-500mM.

[0014] 7.The method of electrocatalytic waste plastics for hydrogen production by coupling of potassium formate and potassium terephthalate, wherein the electrolysis is constant voltage electrolysis. Preferably, the working voltage is 1.1-1.5V, and the reaction time is 1-20h.

[0015] Compared with the prior art, the advantages of the present application include:

[0016] (1) The present application catalytically oxidizes waste plastics into potassium formate and potassium terephthalate by an electrocatalytic method, and couples hydrogen production, thereby producing high-value chemical products while reducing the voltage of water splitting for hydrogen production. Compared with other methods, the present application has greater economic benefits and is more suitable for industrialization and large-scale promotion.

[0017] (2)The application can be carried out at normal temperature and pressure, the selectivity and conversion rate of the product are high, the product does not need a complicated separation and purification process, and a large amount of potassium formate and potassium terephthalate can be obtained by a simple method, which is suitable for industrial implementation and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a scanning electron microscope image of the electrocatalyst in Example 1 of the application.

[0019] Figure 2 is a linear sweep voltammetry curve of the electrocatalytic process of the hydrolysis solution of the waste PET packaging material in Example 2 of the application.

[0020] Figure 3 is a current density, charge and time curve in Example 4 of the application.

[0021] Figure 4 is a high performance liquid chromatogram in Example 4 of the application. DETAILED DESCRIPTION

[0022] The application will be further described in detail below in combination with examples and drawings, but the embodiments of the application are not limited thereto.

[0023] Example 1

[0024] Preparation of nickel hydroxide / copper hydroxide / copper oxide electrode material loaded on foamed nickel-copper (8:2)

[0025] 1. Foamed nickel-copper (8:2) with a thickness of 2 mm and a size of 2 cm x 2 cm is ultrasonically washed with anhydrous ethanol, analytical pure acetone and deionized water for 15 min each;

[0026] 2. 50 mL of a reaction solution containing 3 mM copper chloride and 5% mass fraction of hydrogen peroxide is prepared, then the cleaned foamed nickel-copper is soaked in the solution for 10 min, after the reaction is completed, the surface is washed with deionized water and dried at 80℃ to obtain the working electrode foamed nickel-copper loaded nickel hydroxide / copper hydroxide / copper oxide.

[0027] Example 2

[0028] Electrochemical activity test of foamed nickel-copper (8:2) loaded nickel hydroxide / copper hydroxide / copper oxide as working electrode

[0029] (1) 0.2 kg of waste PET packaging material is crushed and dissolved in 50 mL of 2M KOH solution, and heated in a 90℃ oil bath for 20 h to obtain a mixed solution of potassium terephthalate and ethylene glycol, and the molar concentration of ethylene glycol is 100 mM.

[0030] (2) Using a three-electrode system, catalytic oxidation was carried out in an H-type electrolytic cell; nickel hydroxide / copper hydroxide / copper oxide was used as the working electrode, Hg / HgO was used as the reference electrode, and platinum wire was used as the counter electrode; the alkaline solution containing terephthalic acid potassium and ethylene glycol dissolved in step 1 was used as the anode electrolyte, and 2M KOH solution was used as the cathode electrolyte, which together constituted the electrocatalytic reactor.

[0031] (3) At room temperature and atmospheric pressure, the reaction was continuously stirred for 2h at a constant voltage of 1.47V vs. RHE. Hydrogen was collected at the cathode during the reaction, and the reaction product was detected at the anode by high performance liquid chromatography after the reaction was completed, and the yield of potassium formate was 96%.

[0032] Example 3

[0033] Preparation of foam cobalt-nickel (3:7) loaded nickel hydroxide / cobalt hydroxide / iron oxide electrode material

[0034] 1. Foam cobalt-nickel (3:7) with a thickness of 3mm and a size of 2.5cm x 2cm was ultrasonically washed with anhydrous ethanol, analytical pure acetone and deionized water for 15min;

[0035] 2. A reaction solution containing 3mM ferric chloride and 5% mass fraction of hydrogen peroxide was prepared in 50mL, and then the cleaned foam cobalt-nickel was immersed in the solution and reacted for 10min; after the reaction was completed, it was taken out, the surface was washed with deionized water, and was dried at 80℃ to obtain the working electrode foam cobalt-nickel loaded nickel hydroxide / cobalt hydroxide / iron oxide.

[0036] Example 4

[0037] Electrochemical activity test of foam cobalt-nickel (3:7) loaded nickel hydroxide / cobalt hydroxide / iron oxide as working electrode

[0038] (1) 0.1kg of fiber grade waste PET (polyester microfiber) was crushed and dissolved in 50mL, 5MKOH solution, and heated and stirred in a 100℃ oil bath for 16h to obtain a mixed solution of terephthalic acid potassium and ethylene glycol, and the molar concentration of ethylene glycol was 50mM.

[0039] (2) Using a three-electrode system, catalytic oxidation was carried out in an H-type electrolytic cell; nickel hydroxide / cobalt hydroxide / iron oxide was used as the working electrode, Hg / HgO was used as the reference electrode, and platinum wire was used as the counter electrode; the alkaline solution containing terephthalic acid potassium and ethylene glycol dissolved in step 1 was used as the anode electrolyte, and 5M KOH solution was used as the cathode electrolyte, which together constituted the electrocatalytic reactor.

[0040] (3) At room temperature and normal pressure, continuously stirring the reaction for 5h at a constant voltage of 1.47V vs. RHE, collecting hydrogen gas at the cathode during the reaction. After the reaction, detecting the anode reaction product by high performance liquid chromatography, the yield of potassium formate is 97%.

[0041] Example 5

[0042] Preparation of nickel hydroxide / aluminum hydroxide / iron hydroxide / iron oxide electrode material supported by nickel-iron foam (7:3)

[0043] 1. Ultrasonic washing the nickel-iron foam (7:3) with a thickness of 3mm and a size of 3cm x 3cm with anhydrous ethanol, analytical pure acetone and deionized water for 15min each;

[0044] 2. Preparing 50mL of a reaction solution containing 3mM aluminum chloride and 5% mass fraction of hydrogen peroxide, then immersing the cleaned nickel-iron foam into the solution for reaction for 10min; after the reaction, taking it out, rinsing the surface with deionized water and drying at 80℃ to obtain the working electrode nickel hydroxide / aluminum hydroxide / iron hydroxide / iron oxide.

[0045] Example 6

[0046] Electrochemical activity test of nickel hydroxide / aluminum hydroxide / iron hydroxide / iron oxide supported by nickel-iron foam (7:3) as working electrode

[0047] (1) Dissolving 0.4kg of crushed waste PET plastic bottles into 50mL of 8M KOH solution, heating and stirring in a 120℃ oil bath for 12h to obtain a mixed solution of potassium terephthalate and ethylene glycol, and the molar concentration of ethylene glycol is 200mM.

[0048] (2) Using a three-electrode system to perform catalytic oxidation in an H-type electrolytic cell; the nickel hydroxide / aluminum hydroxide / iron hydroxide / iron oxide is the working electrode, Hg / HgO is the reference electrode, platinum wire is the counter electrode, the alkaline solution containing potassium terephthalate and ethylene glycol dissolved in step 1 is the anode electrolyte, and 8M KOH solution is the cathode electrolyte, which together constitute an electrocatalytic reactor.

[0049] (3) At room temperature and normal pressure, continuously stirring the reaction for 10h at a constant voltage of 1.47V vs. RHE, collecting hydrogen gas at the cathode during the reaction. After the reaction, detecting the anode reaction product by high performance liquid chromatography, the yield of potassium formate is 95%.

[0050] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be included in the protection scope of the present application.

Claims

1. A method for electrocatalytic conversion of waste plastics into hydrogen coupled with production of potassium formate and potassium terephthalate, characterized by: The waste plastic is dissolved into an alkaline solution by treatment, and an H-shaped electrolytic tank is used for electrocatalytic oxidation by taking the alkaline solution containing the waste plastic as an electrolyte by using a three-electrode system; the three-electrode system is composed of a working electrode, a counter electrode, a reference electrode and an electrolyte, and collectively forms an electrocatalytic reaction device; hydrogen can be collected at the cathode during the reaction under a constant voltage, and potassium formate and potassium terephthalate are obtained at the anode after the reaction; the working voltage is 1.47 V, and the reaction time is 2-5 h; the working electrode is a nickel / copper hydroxide / copper oxide foam supported on nickel / copper.

2. A method of electrocatalytic hydrogen production from waste plastic coupled with potassium formate and potassium terephthalate according to claim 1, characterized in that, The waste plastic is one or more of waste PET plastic bottles, waste PET packaging materials, PET / PE mixed films and fiber-grade waste PET polyester microfibers.

3. A method of electrocatalytic hydrogen production from waste plastic coupled with potassium formate and potassium terephthalate according to claim 1, characterized in that, The waste plastic is dissolved into an alkaline solution by treatment, and an H-shaped electrolytic tank is used for electrocatalytic oxidation by taking the alkaline solution containing the waste plastic as an electrolyte by using a three-electrode system; the three-electrode system is composed of a working electrode, a counter electrode, a reference electrode and an electrolyte, and collectively forms an electrocatalytic reaction device; hydrogen can be collected at the cathode during the reaction under a constant voltage, and potassium formate and potassium terephthalate are obtained at the anode after the reaction; the working voltage is 1.47 V, and the reaction time is 2-5 h; the working electrode is a nickel / copper hydroxide / copper oxide foam supported on nickel / copper.

4. The method of claim 1, wherein the method of electrocatalytic hydrogen production from formic acid and terephthalic acid is characterized by, The heating temperature is 60-200 DEG C, and the time is 0.5-24 h.

5. The method of claim 1, wherein the method of electrocatalytic hydrogen production from formic acid and terephthalic acid is characterized by, The reference electrode is Hg / HgO, and the counter electrode is a platinum wire.

6. A method of electrocatalytic waste plastic to potassium formate and potassium terephthalate coupling for hydrogen production according to claim 1, characterized in that, The thickness of the foam metal is 1-5 mm, and the size is (1-5) × (1-5) cm.

7. The method for producing hydrogen from electrocatalytic waste plastics by coupling potassium formate and potassium terephthalate according to claim 1, characterized in that, The molar concentration of the hydrolysis product ethylene glycol is 10-1000 mM.

8. The method of claim 1, wherein the electrocatalytic waste plastic is potassium formate and potassium terephthalate coupled to produce hydrogen, and wherein the method further comprises: The alkaline solution is a 1-10 M KOH or NaOH solution with a volume of 50-200 mL; and the mass of the waste plastic is 0.002-2 kg. ​

Images