Method for high-selectivity preparation of synthesis gas and glyoxylic acid by photocatalysis of PET plastic

Abstract

The invention provides a method for high-selectivity preparation of synthesis gas and glyoxylic acid through photocatalysis of PET plastic. According to the method, the selectivity of a liquid product obtained by photocatalysis of the PET plastic is remarkably improved by controlling a single active oxygen species (specifically holes), and high-selectivity oxidation is realized. Furthermore, the proportion of carbon monoxide to hydrogen in the generated synthesis gas can be changed by regulating and controlling the mass ratio of cadmium sulfide to nickel aluminum hydrotalcite in the heterojunction composite material formed by compounding cadmium sulfide and nickel aluminum hydrotalcite. The method has the characteristics of low preparation cost, stable catalyst performance, simple preparation process, convenience in operation, environmental protection and the like, and has a very good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalysis of organic chemistry, and in particular to a method for preparing synthesis gas and glyoxylic acid from PET plastics with high selectivity through photocatalysis. Background Art

[0002] Plastic is a lightweight and durable material with excellent properties. As an important new material in this century, plastic is widely used in various fields and has become an indispensable part of people's daily life. The widespread use of plastics has made how to deal with waste plastics an urgent problem to be solved. In the early days, people mainly used landfill and incineration to deal with plastics, which led to the formation of a large amount of pollutants and seriously harmed the ecological environment and human health. Later, people used mechanical recycling and physical modification methods to deal with waste plastics, but this has the disadvantage of low energy efficiency. At present, relatively mature methods for processing plastics include recycling plastics through chemical upgrading and conversion methods under high temperature and high pressure, such as pyrolysis, hydrogenolysis, thermal catalysis, microwave catalysis, etc., but these methods still have problems such as high energy consumption and harsh reaction conditions.

[0003] In order to recycle waste plastics more cleanly, it is generally considered a viable option to upgrade waste plastics into high-value-added organic matter or fuels through photocatalysis, electrocatalysis, photoelectrocatalysis, etc. Studies have found that it is feasible to use sunlight to convert plastics into organic fuels, accompanied by the generation of a large amount of green hydrogen. Summary of the invention

[0004] The recycling of waste plastics disclosed in the prior art is mostly studied from the degradation efficiency of waste plastics or the rate of coupled hydrogen production, but no in-depth research is conducted on the oxidation products. How to obtain oxidation products with higher added value from the oxidation of waste plastics is very important for the recycling of waste plastics. However, it is not easy to improve the selectivity of liquid products. Various active oxygen species (such as holes, hydroxyl radicals, superoxide radicals and other oxidizing substances) easily oxidize the organic substances (such as ethylene glycol and terephthalic acid) after plastic depolymerization in different directions. Therefore, improving the selectivity of liquid products and having a higher value of synthesis gas is still a major problem in the process of photocatalytic degradation of plastics.

[0005] In order to improve the deficiencies of the prior art, the present invention provides a method for preparing synthesis gas and glyoxylic acid by photocatalytic PET plastic with high selectivity. The method significantly improves the selectivity of the liquid product obtained by photocatalytic PET plastic by controlling a single active oxygen species, thereby achieving highly selective oxidation.

[0006] In the present invention, unless otherwise defined, the term "PET" means polyethylene terephthalate.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for preparing synthesis gas and glyoxylic acid by photocatalytic PET plastic, the method comprising the following steps:

[0009] 1) subjecting PET plastic to a hydrothermal reaction to prepare a liquid product containing ethylene glycol and terephthalic acid;

[0010] 2) A heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite is used to perform a photocatalytic reaction on the liquid product of step 1) to prepare synthesis gas and glyoxylic acid.

[0011] According to an embodiment of the present invention, in step 1), the average particle size of the PET plastic is in the micron range. Exemplarily, the average particle size of the PET plastic is 50-500 microns.

[0012] According to an embodiment of the present invention, in step 1), the source of the PET plastic is not particularly limited, and can be waste PET plastic known in the art or newly prepared PET plastic. Exemplarily, the PET plastic comes from waste PET plastic bottles.

[0013] According to an embodiment of the present invention, PET plastic (such as waste PET plastic bottles) is cut and ground to obtain PET plastic powder with an average particle size of microns; illustratively, the cut PET plastic fragments are ground more finely by ball milling to obtain PET plastic powder with an average particle size of microns, which is more conducive to the hydrolysis of PET plastic into ethylene glycol and terephthalic acid during the hydrothermal reaction.

[0014] According to an embodiment of the present invention, in step 1), the temperature of the hydrothermal reaction is 180-220°C, for example, 180°C, 190°C, 200°C, 210°C or 220°C; the time of the hydrothermal reaction is not particularly defined, as long as the hydrolysis of the PET plastic can be achieved; illustratively, the time of the hydrothermal reaction is 18-36 hours, for example, 18 hours, 20 hours, 24 hours, 28 hours, 30 hours or 36 hours.

[0015] According to an embodiment of the present invention, in step 1), the hydrothermal reaction is carried out in a high-pressure reactor; illustratively, it is carried out in a high-pressure reactor with a polytetrafluoroethylene liner.

[0016] According to an embodiment of the present invention, in step 1), water is used as a solvent in the hydrothermal reaction system.

[0017] According to an embodiment of the present invention, in step 1), in the hydrothermal reaction system, the mass ratio of water to PET plastic is 60:1-20, preferably 60:1-10, for example, 60:1, 60:2, 60:3, 60:4, 60:5, 60:6, 60:7, 60:8, 60:9, 60:10, 60:12, 60:14, 60:15, 60:16, 60:18, 60:19 or 60:20.

[0018] According to an embodiment of the present invention, step 1) specifically includes the following steps:

[0019] First, add PET plastic (preferably PET plastic powder with an average particle size of micrometers) into water and stir for 30-60 minutes to obtain a suspension; then transfer the suspension to a high-pressure reactor, heat at 180-220°C for 18-36 hours, and cool to room temperature after the reaction is completed.

[0020] According to an embodiment of the present invention, the step of transferring the suspension to the autoclave is performed under an inert atmosphere. Exemplarily, the step of transferring the suspension to the autoclave is performed in a glove box filled with an inert atmosphere, so that the air in the hollow part of the liner of the autoclave can be prevented from oxidizing the hydrolysis product of the PET plastic in advance during the hydrothermal reaction.

[0021] According to an embodiment of the present invention, in step 1), after the hydrothermal reaction is completed, if there is solid waste residue at the bottom of the high-pressure reactor, a liquid product containing ethylene glycol and terephthalic acid can be collected by filtration. At this time, the solid waste residue is PET plastic that is not completely hydrolyzed. The appearance of solid waste residue can be reduced or avoided by extending the time of the hydrothermal reaction, thereby achieving complete utilization of the PET plastic.

[0022] According to an embodiment of the present invention, in step 1), the molar ratio of ethylene glycol to terephthalic acid in the liquid product containing ethylene glycol and terephthalic acid is 24:1.

[0023] According to an embodiment of the present invention, in step 1), the concentration of ethylene glycol in the liquid product containing ethylene glycol and terephthalic acid is 50-450mM, for example, 50mM, 80mM, 100mM, 130mM, 150mM, 180mM, 200mM, 230mM, 250mM, 300mM, 350mM, 400mM or 450mM.

[0024] According to an embodiment of the present invention, in step 2), the photocatalytic reaction is carried out at room temperature, that is, no additional heating treatment is required during the photocatalytic reaction.

[0025] According to an embodiment of the present invention, in step 2), the photocatalytic reaction is carried out under an inert atmosphere, that is, after the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite is mixed with the liquid product of step 1), the reaction container is sealed, and an inert gas is introduced to replace the air in the reaction container to remove the residual air in the reaction container, and then the photocatalytic reaction is carried out under the condition of the inert atmosphere.

[0026] According to an embodiment of the present invention, in step 2), during the photocatalytic reaction, the reaction container used is made of quartz, in order to prevent the reaction container from affecting the catalyst (a heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite) in absorbing ultraviolet light and visible light.

[0027] According to an embodiment of the present invention, in step 2), during the photocatalytic reaction, there is no particular definition for the selection of a light source, which may be a light source known in the art that can provide ultraviolet light and / or visible light. Exemplarily, an LED lamp is selected as a light source for the photocatalytic reaction, such as selecting at least one 50W LED lamp as a light source for the photocatalytic reaction.

[0028] According to an embodiment of the present invention, in step 2), there is no specific definition for the time of the photocatalytic reaction, as long as synthesis gas and glyoxylic acid can be produced; illustratively, the time of the photocatalytic reaction can be 12-24 hours, for example, 12 hours, 15 hours, 18 hours, 21 hours or 24 hours.

[0029] According to an embodiment of the present invention, in step 2), the mass volume ratio of the heterojunction composite material formed by the composite of cadmium sulfide and nickel aluminum hydrotalcite to the liquid product of step 1) is 2 mg: 1-20 mL, that is, 2 mg of the heterojunction composite material formed by the composite of cadmium sulfide and nickel aluminum hydrotalcite is added to 1-20 mL of the liquid product of step 1); illustratively, the mass volume ratio of the heterojunction composite material formed by the composite of cadmium sulfide and nickel aluminum hydrotalcite to the liquid product of step 1) is 2 mg: 1 mL, 2 mg: 2 mL, 2 mg: 3 mL, 2 mg: 4 mL, 2 mg: 5 mL, 2 mg: 6 mL, 2 mg: 8 mL, 2 mg: 10 mL, 2 mg: 12 mL, 2 mg: 15 mL, 2 mg: 18 mL or 2 mg: 20 mL.

[0030] According to an embodiment of the present invention, in step 2), in the heterojunction composite material formed by the cadmium sulfide and the nickel-aluminum hydrotalcite, the cadmium sulfide is loaded on the surface of the nickel-aluminum hydrotalcite.

[0031] According to an embodiment of the present invention, in step 2), in the heterojunction composite material formed by the cadmium sulfide and the nickel-aluminum hydrotalcite, the mass ratio of cadmium sulfide to nickel-aluminum hydrotalcite is 0.1-8:1, preferably 0.5-3:1, and exemplarily 0.1:1, 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1. The ratio of carbon monoxide to hydrogen in the prepared synthesis gas can be changed by regulating the mass ratio of cadmium sulfide to nickel-aluminum hydrotalcite in the heterojunction composite material formed by the cadmium sulfide and the nickel-aluminum hydrotalcite. Exemplarily, the higher the mass proportion of cadmium sulfide, the higher the molar proportion of carbon monoxide in the obtained synthesis gas; conversely, the lower the mass proportion of cadmium sulfide, the lower the molar proportion of carbon monoxide in the obtained synthesis gas.

[0032] According to an embodiment of the present invention, in step 2), the shape of the nickel aluminum hydrotalcite is not particularly defined, for example, it can be a thin sheet; the three-dimensional size of the nickel aluminum hydrotalcite is not particularly defined, illustratively, the length of the nickel aluminum hydrotalcite is 10-40nm, the width of the nickel aluminum hydrotalcite is 10-40nm, and the thickness of the nickel aluminum hydrotalcite is 2-10nm. Exemplarily, the length of the nickel aluminum hydrotalcite is 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm or 40nm; the width of the nickel aluminum hydrotalcite is 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm or 40nm; the thickness of the nickel aluminum hydrotalcite is 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm or 10nm.

[0033] According to an embodiment of the present invention, in step 2), the size of the cadmium sulfide is 2-10 nm, for example, 4-8 nm, such as 5 nm, 6 nm, 7 nm or 8 nm.

[0034] According to an embodiment of the present invention, in step 2), the morphology of the heterojunction composite material formed by the cadmium sulfide and nickel-aluminum hydrotalcite is not particularly defined, and can be, for example, a two-dimensional sheet structure.

[0035] According to an embodiment of the present invention, in step 2), the heterojunction composite material formed by the cadmium sulfide and nickel aluminum hydrotalcite has a length of 10-40 nm, a width of 10-40 nm, and a thickness of 6-18 nm.

[0036] Exemplarily, the heterojunction composite material formed by the cadmium sulfide and nickel aluminum hydrotalcite has a length of 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm or 40nm; a width of 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, 32nm, 35nm, 38nm or 40nm; and a thickness of 6nm, 8nm, 10nm, 12nm, 15nm, 16nm or 18nm.

[0037] According to an embodiment of the present invention, the synthesis gas comprises carbon monoxide and hydrogen, and the molar ratio of carbon monoxide to hydrogen is 1:2-1:5, for example, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0038] The beneficial effects of the present invention are as follows:

[0039] The present invention provides a method for preparing synthesis gas and glyoxylic acid by photocatalytic PET plastic. The method significantly improves the selectivity of liquid products obtained by photocatalytic PET plastic by controlling a single active oxygen species (specifically holes), thereby achieving highly selective oxidation. Furthermore, the ratio of carbon monoxide to hydrogen in the generated synthesis gas can be changed by regulating the mass ratio of cadmium sulfide and nickel-aluminum hydrotalcite in a heterojunction composite material formed by combining cadmium sulfide and nickel-aluminum hydrotalcite.

[0040] The method of the present invention makes plastic no longer just act as a sacrificial agent, and makes the liquid product obtained by degrading waste plastic more single and easier to separate, which can greatly reduce the difficulty of recycling and generate synthesis gas with higher value, making the degraded waste plastic have economic value.

[0041] The method of the present invention has the characteristics of low preparation cost, stable catalyst performance, simple preparation process, convenient operation, environmental protection, etc., and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The characterization results of nuclear magnetic resonance spectroscopy (hydrogen spectrum) of the liquid product obtained by catalyzing ethylene glycol and terephthalic acid with the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Example 1 are shown.

[0043] Figure 2 The selectivity of liquid products and the generation rate of gas products obtained by catalyzing ethylene glycol and terephthalic acid using the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Example 1 are shown.

[0044] Figure 3The generation rate of gas products and the proportion of carbon monoxide in the carbon-containing gas during the photocatalytic reaction of Comparative Examples 1 and 2 are shown.

[0045] Figure 4 The characterization results of nuclear magnetic resonance spectroscopy (hydrogen spectrum) of the liquid product obtained by catalyzing ethylene glycol with cadmium sulfide in Comparative Example 1 are shown.

[0046] Figure 5 The selectivity of the liquid products obtained after the photocatalytic reaction of Comparative Examples 1 and 2 is shown.

[0047] Figure 6 The graph shows the detection results of active oxygen species detected by electron paramagnetic resonance before and after illumination of the heterojunction composite material composed of cadmium sulfide of comparative example 1 and cadmium sulfide and nickel-aluminum hydrotalcite of comparative example 2.

[0048] Figure 7 This is a result graph showing the change of holes generated over time in the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite in comparative example 2 after irradiation.

[0049] Figure 8 The characterization results of nuclear magnetic resonance spectroscopy (hydrogen spectrum) of the liquid product obtained by catalyzing ethylene glycol with the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Comparative Example 2 are shown.

[0050] Fig. 9 The generation rates of carbon monoxide and hydrogen in the gas products obtained by catalyzing ethylene glycol using heterojunction composite materials composed of cadmium sulfide and nickel aluminum hydrotalcite at different mass ratios of cadmium sulfide and nickel aluminum hydrotalcite in comparative examples 2-6 and the molar ratio of carbon monoxide to hydrogen are shown.

[0051] Fig.10 The formation rate of methane in the gas product obtained by catalyzing ethylene glycol using heterojunction composite materials composed of cadmium sulfide and nickel aluminum hydrotalcite at different mass ratios of cadmium sulfide and nickel aluminum hydrotalcite in Comparative Examples 2-6 is shown. DETAILED DESCRIPTION

[0052] <Preparation method of heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite>

[0053] In step 2), the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite can be prepared by a method known in the art, that is, cadmium sulfide is in situ loaded onto the surface of nickel-aluminum hydrotalcite by a method known in the art to form a heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite.

[0054] In step 2), the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite can also be prepared by the following method:

[0055] S1) preparing nickel-aluminum hydrotalcite by coprecipitation method;

[0056] S2) In-situ growth of cadmium sulfide on the surface of the nickel-aluminum hydrotalcite obtained in step S1).

[0057] According to an embodiment of the present invention, step S1) specifically includes the following steps: dissolving a metal salt and a base in a mixed solvent of formamide and water, and performing a hydrothermal reaction to prepare the nickel-aluminum hydrotalcite.

[0058] According to an embodiment of the present invention, the metal salt is selected from nickel salts and aluminum salts; the nickel salt is selected from at least one of nickel nitrate, nickel chloride and nickel carbonate; the aluminum salt is selected from at least one of aluminum nitrate, aluminum chloride and aluminum carbonate; the molar ratio of the nickel salt to the aluminum salt is 3:1.

[0059] According to an embodiment of the present invention, the base is selected from sodium hydroxide and sodium carbonate.

[0060] According to an embodiment of the present invention, the molar ratio of the metal salt to the base is 1:1-1:5.

[0061] According to an embodiment of the present invention, the volume ratio of formamide to water is 1:30-1:15.

[0062] According to an embodiment of the present invention, the molar volume ratio of the metal salt to water is 1mmol:0.5-3mL, for example, 1mmol:0.5mL, 1mmol:1mL, 1mmol:2mL or 1mmol:2.5mL; that is, every 1mmol of metal salt is dissolved in 0.5-3mL of water.

[0063] According to an embodiment of the present invention, the temperature of the hydrothermal reaction is 80-140°C, exemplified by 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or 140°C; the time of the hydrothermal reaction is 12-36h, exemplified by 12h, 18h, 24h, 30h or 36h.

[0064] According to an embodiment of the present invention, after the hydrothermal reaction is completed, the step of washing and drying the reaction product is also included. Furthermore, the washing solvent can be deionized water and / or ethanol.

[0065] According to an embodiment of the present invention, step S1) specifically includes the following steps: dissolving nickel salt, aluminum salt, sodium carbonate and sodium hydroxide in a mixed solvent of formamide and water, and performing a hydrothermal reaction to prepare the nickel-aluminum hydrotalcite.

[0066] Exemplarily, the nickel-aluminum hydrotalcite can be prepared by the following method:

[0067] 13.1g nickel nitrate and 5.6g aluminum nitrate were dissolved in 60mL deionized water to form liquid A; 7.9g sodium carbonate and 6.0g sodium hydroxide were dissolved in 60mL deionized water to form liquid B; liquid A and liquid B were added dropwise to a mixed solvent of 32mL deionized water and 8mL formamide, the dropping speed of liquid A and liquid B was controlled to be 1-2 drops / s, and the pH of the reaction mixture was maintained between 9 and 10. After the titration was completed, the suspension in the bottle was subjected to hydrothermal reaction at 80°C for 24h; after the reaction was completed, washing and vacuum drying were performed in sequence to prepare nickel-aluminum hydrotalcite.

[0068] According to an embodiment of the present invention, step S2) specifically includes the following steps: dispersing nickel aluminum hydrotalcite in water, adding cadmium salt, mercaptopropionic acid and sulfur source to react, and preparing a heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite.

[0069] According to an embodiment of the present invention, cadmium sulfide is in-situ formed during the reaction and in-situ loaded on the surface of the nickel-aluminum hydrotalcite.

[0070] According to an embodiment of the present invention, the cadmium salt is selected from at least one of cadmium chloride, cadmium carbonate and cadmium nitrate, and is preferably cadmium chloride.

[0071] According to an embodiment of the present invention, the sulfur source is selected from sodium sulfide.

[0072] According to an embodiment of the present invention, the reaction is preferably carried out in an aqueous solvent system with a pH of 9-10.

[0073] According to an embodiment of the present invention, the reaction temperature is 100-150°C, exemplarily 100°C, 110°C or 120°C; the reaction time is 0.5-1.5h, exemplarily 0.5h, 1h or 1.5h.

[0074] According to an embodiment of the present invention, the mass ratio of the nickel aluminum hydrotalcite to the cadmium salt is 1:0.5-1:3.

[0075] According to an embodiment of the present invention, the molar ratio of the cadmium salt to the sulfur source is 1:1.

[0076] According to an embodiment of the present invention, the mass ratio of the cadmium salt to mercaptopropionic acid is 100:1.

[0077] According to an embodiment of the present invention, step S2) specifically includes the following steps:

[0078] Nickel aluminum hydrotalcite was dispersed in a three-necked flask pre-filled with 10 mL of deionized water to obtain a suspension with a concentration of 25 g / L; 456.8 mg of cadmium chloride and 340 μL of mercaptopropionic acid were added to a beaker pre-filled with 10 mL of deionized water, and 1 M sodium hydroxide solution was added dropwise to adjust the pH of the solution to between 9 and 10, the precursor solution was transferred to the three-necked flask containing nickel aluminum hydrotalcite, 480.36 mg of sodium sulfide was added, and the mixture was reacted at 100° C. for 0.5 h. After the reaction was completed, the mixture was filtered, washed, and vacuum dried in sequence to prepare a heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite.

[0079] The method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0080] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0081] Example 1

[0082] The method uses a heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite to perform a photocatalytic reaction on the hydrolyzate of PET plastic to prepare synthesis gas and glyoxylic acid, which specifically includes the following steps:

[0083] S1: waste PET plastic bottles are cut into pieces and then ball-milled to obtain 120-mesh PET plastic powder;

[0084] S2: Take 3g of the PET plastic powder obtained in step S1 and add it to 60mL of deionized water, stir for 30 minutes, transfer the suspension to a high-pressure reactor in a glove box (oxygen content <0.1%), the volume of the reactor lining is 100mL, heat at 200°C for 24h, filter the product after heating to obtain a liquid product containing terephthalic acid and ethylene glycol, wherein the molar ratio of ethylene glycol to terephthalic acid is 24:1, and the concentration of ethylene glycol in the obtained liquid product containing terephthalic acid and ethylene glycol is about 131mM, dilute with water to a concentration of ethylene glycol of 100mM, the purpose of diluting with water here is only for subsequent parallel test comparison with the comparative example, and in practical application, there is no need to dilute the liquid product, and the photocatalytic reaction can be directly carried out;

[0085] S3: Dissolve 13.1g nickel nitrate and 5.6g aluminum nitrate in 60mL deionized water to form liquid A; dissolve 7.9g sodium carbonate and 6.0g sodium hydroxide in 60mL deionized water to form liquid B; add liquid A and liquid B dropwise to a mixed solvent of 32mL deionized water and 8mL formamide, control the dropping speed of liquid A and liquid B to 1-2 drops / s, and keep the pH of the reaction mixture between 9 and 10. After the titration is completed, react the suspension in the bottle at 80°C for 24h; after the reaction is completed, wash and vacuum dry in sequence to prepare nickel-aluminum hydrotalcite;

[0086] S4: The nickel-aluminum hydrotalcite obtained in step S4 is dispersed in a three-necked flask pre-filled with 10 mL of deionized water to obtain a suspension with a concentration of 25 g / L.

[0087] S5: 456.8 mg of cadmium chloride and 340 μL of mercaptopropionic acid were added to a beaker pre-filled with 10 mL of deionized water, and 1 M sodium hydroxide solution was added dropwise to adjust the pH of the solution to between 9 and 10. The precursor solution was transferred to a three-necked flask containing nickel aluminum hydrotalcite, and 480.36 mg of sodium sulfide was added, and the mixture was reacted at 100° C. for 0.5 h. After the reaction was completed, the mixture was filtered, washed, and vacuum dried in sequence to obtain a heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite; wherein the mass ratio of cadmium sulfide to nickel aluminum hydrotalcite was 2:1;

[0088] S6: Dissolve 2 mg of the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite obtained in step S5 in 5 mL of the liquid product containing terephthalic acid and ethylene glycol obtained in step S2, put the reaction system into a quartz tube, seal it, pass argon gas to exhaust the air, turn on a 50 W LED lamp to irradiate the quartz tube, and illuminate it for 15 hours under stirring conditions.

[0089] The liquid product and gas product after the illumination are detected.

[0090] Among the gas products, CH 4 The yield reached 21.5 μmol g cat -1 h -1 , H 2 The yield reached 3038.9 μmol g cat -1 h -1 The CO yield reached 1194.7 μmol g cat -1 h -1 , CO and H 2 The molar ratio is slightly greater than 0.33, which meets the standard for forming synthesis gas.

[0091] The yield of glyoxylic acid in the liquid product reached 4.56 mmol g cat -1 h -1 , the selectivity reached 82.8%. At the same time, the concentration of the remaining ethylene glycol was also calculated to be 61.10 mM, and the conversion rate of ethylene glycol was further calculated to be 38.9%. In addition, by extending the light irradiation time, the conversion rate of ethylene glycol can be further improved.

[0092] Figure 1 The results of nuclear magnetic resonance spectroscopy (hydrogen spectrum) characterization of the liquid product obtained by catalyzing ethylene glycol and terephthalic acid with the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Example 1 are shown, based on which the types of various liquid products can be confirmed, and the yield of each product can be calculated based on the added internal standard dimethyl sulfoxide. Figure 1 It can be seen that the generated liquid products are glyoxylic acid, methanol and acetic acid. According to calculations, the PET hydrolyzate before illumination contains about 4.27mM terephthalic acid, and the liquid product after illumination still contains 4.20mM terephthalic acid. After 15 hours of illumination, the concentration of terephthalic acid has hardly changed, and it can be considered that terephthalic acid has hardly participated in the reaction.

[0093] Figure 2 The selectivity of liquid products and the generation rate of gas products obtained by catalyzing ethylene glycol and terephthalic acid using the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Example 1 are shown. Figure 2 It can be seen that among the liquid products, the selectivity of glyoxylic acid (GA) is 82.8%, the selectivity of methanol (MeOH) is 8.6%, the selectivity of acetic acid (AA) is 8.6%, and the selectivity of CH 4 The yield reached 21.5 μmol g cat -1 h -1 , CO 2 The yield reached 148.95 μmol g cat -1 h -1 , H 2 The yield reached 3038.9 μmol g cat -1 h -1 The CO yield reached 1194.7 μmol g cat -1 h -1 .

[0094] Comparative Example 1

[0095] The photocatalysis of ethylene glycol using cadmium sulfide mainly includes the following steps:

[0096] S1: 456.8 mg of cadmium chloride and 340 μL of mercaptopropionic acid were added to a beaker pre-filled with 10 mL of deionized water, and 1 M sodium hydroxide solution was added dropwise to adjust the pH of the solution to between 9 and 10, and then the solution was transferred to a three-necked flask, and 480.36 mg of sodium sulfide was added, and the mixture was reacted at 100° C. for 0.5 h. After the reaction was completed, the mixture was filtered, washed, and vacuum dried in sequence to obtain cadmium sulfide;

[0097] S2: Dissolve 2 mg of cadmium sulfide obtained in step S1 in 5 mL of 100 mM ethylene glycol aqueous solution, place the reaction system in a quartz tube, seal it, pass argon gas to exhaust all the air, turn on a 50 W LED lamp to irradiate the quartz tube, and illuminate it for 15 hours under stirring conditions.

[0098] The liquid product and gas product after the illumination are detected.

[0099] Figure 3 The generation rate of gas products and the proportion of carbon monoxide in the carbon-containing gas during the photocatalytic reaction of Comparative Example 1 are shown. Figure 3 It can be seen that in the gas product of Comparative Example 1, CH 4 The yield was 97.1 μmol g cat -1 h -1 , CO 2 The yield was 44.1 μmol g cat -1 h -1 , H 2 The yield was 674.4 μmol g cat -1 h -1 , and the CO yield was 272.6 μmol g cat -1 h -1 .

[0100] S3: Dissolve 1 mg of cadmium sulfide obtained in step S1 in 1 mL of 100 mM TEMPO (2,2,6,6-tetramethylpiperidinyl oxide) and DMPO (5,5-dimethyl-1-pyrroline-N-oxide), respectively, and use a capillary to draw the mixed solution to the standard line, purge with argon for 1 minute, and perform in-situ detection of holes and hydroxyl radicals in the reaction system before and after illumination by electron paramagnetic resonance under 50 W LED light. The detection results show that the reactive oxygen species in the reaction system include both holes and hydroxyl radicals.

[0101] Figure 4The characterization results of the nuclear magnetic resonance spectroscopy (hydrogen spectrum) of the liquid product obtained by catalyzing ethylene glycol with cadmium sulfide in Comparative Example 1 are shown, from which the types of various liquid products can be confirmed, and the yield of each product can be calculated based on the added internal standard dimethyl sulfoxide. Figure 4 It can be seen that when cadmium sulfide alone is used as a catalyst, glyoxylic acid (B), methanol (C), acetic acid (D), lactic acid (E), ethanol (F), formic acid (G) and five unknown products (*) are generated in the reaction products.

[0102] Figure 5 The selectivity of the liquid product obtained after the photocatalytic reaction of Comparative Example 1 is shown. Figure 5 It can be seen that among the liquid products of Comparative Example 1, without considering the unknown products, the selectivity of glyoxylic acid (GA) is 20.0%, the selectivity of methanol (MeOH) is 4.0%, the selectivity of acetic acid (AA) is 5.8%, the selectivity of lactic acid (LA) is 24.3%, the selectivity of ethanol (EtOH) is 21.6%, and the selectivity of formic acid (FA) is 24.3%, which indicates that none of the liquid products has high selectivity.

[0103] Figure 6 The detection result of active oxygen species detected by electron paramagnetic resonance of cadmium sulfide in comparative example 1 before and after illumination is shown. Figure 6 It can be seen that after illumination, the active oxygen species in Comparative Example 1 include both holes and hydroxyl radicals.

[0104] Comparative Example 2

[0105] S1: 2 mg of the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite obtained in step S5 of Example 1 was dissolved in 5 mL of 100 mM ethylene glycol aqueous solution, the reaction system was placed in a quartz tube, sealed, argon gas was introduced to exhaust the air, a 50 W LED lamp was turned on to irradiate the quartz tube, and the light was irradiated for 15 h under stirring conditions.

[0106] The liquid product and gas product after the illumination are detected.

[0107] Figure 3 The generation rate of gas products and the proportion of carbon monoxide in the carbon-containing gas during the photocatalytic reaction of Comparative Example 2 are shown. Figure 3 It can be seen that in the gas product of Comparative Example 2, CH 4 The yield was only 37.4 μmol g cat - 1 h -1 , CO 2 The yield was 125.0 μmol g cat -1 h -1, H 2 The yields of CO and CO reached 3081.7 μmol g cat -1 h -1 and 1152.8 μmol g cat -1 h -1 In general, the addition of nickel-aluminum hydrotalcite reduces the generation of methane, obtains synthesis gas, and obtains a glyoxylic acid solution with high selectivity.

[0108] S2: Dissolve 1 mg of the heterojunction composite material of cadmium sulfide and nickel aluminum hydrotalcite obtained in step S5 of Example 1 in 1 mL of 100 mM TEMPO (2,2,6,6-tetramethylpiperidinyl oxide) and DMPO (5,5-dimethyl-1-pyrroline-N-oxide), respectively, and inhale the above-mentioned mixed solution to the standard line with a capillary, purge with argon for 1 minute, and perform in-situ detection of holes and hydroxyl radicals in the reaction system before and after illumination by electron paramagnetic resonance under 50 W LED light. The test results show that the only active oxygen species in the reaction system are holes. It can be considered that a more single active oxygen species can significantly improve the selectivity of the product.

[0109] Figure 5 The selectivity of the liquid product obtained after the photocatalytic reaction of Comparative Example 2 is shown. Figure 5 It can be seen that in the liquid product of Comparative Example 2, the selectivity of glyoxylic acid (GA) is 87.1%, the selectivity of acetic acid (AA) is 12.4%, and the selectivity of methanol (MeOH) is 0.6% (not shown), which indicates that the obtained liquid product has a high selectivity for glyoxylic acid.

[0110] Figure 6 The graph shows the detection results of active oxygen species detected by electron paramagnetic resonance before and after illumination of the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in Comparative Example 2, from Figure 6 It can be seen that after illumination, the active oxygen species in Comparative Example 2 are only holes.

[0111] Figure 7 The result diagram of the change of the holes generated after the illumination of the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in comparative example 2 over time is shown in FIG. Figure 7 It can be seen that the peak spectrum of holes in Comparative Example 2 is significantly weakened as time goes by, which means that the concentration of holes generated gradually increases as the illumination time increases.

[0112] Figure 8The results of nuclear magnetic resonance spectroscopy (hydrogen spectrum) characterization of the liquid product obtained by catalyzing ethylene glycol with the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite in comparative example 2 are shown, based on which the types of various liquid products can be confirmed, and the yield of each product can be calculated based on the added internal standard dimethyl sulfoxide. Figure 8 It can be seen that glyoxylic acid (B), methanol (C) and acetic acid (D) are generated with selectivities of 87.1%, 0.6% and 12.4%, respectively.

[0113] Comparative Example 3

[0114] Other operations were the same as those in Comparative Example 2, except that the mass ratio of cadmium sulfide to nickel aluminum hydrotalcite was 0.5:1.

[0115] Comparative Example 4

[0116] Other operations were the same as those in Comparative Example 2, except that the mass ratio of cadmium sulfide to nickel aluminum hydrotalcite was 1:1.

[0117] Comparative Example 5

[0118] Other operations were the same as those in Comparative Example 2, except that the mass ratio of cadmium sulfide to nickel-aluminum hydrotalcite was 1.5:1.

[0119] Comparative Example 6

[0120] Other operations were the same as those in Comparative Example 2, except that the mass ratio of cadmium sulfide to nickel aluminum hydrotalcite was 3:1.

[0121] Fig. 9 The generation rates of carbon monoxide and hydrogen in the gas products obtained by catalyzing ethylene glycol using heterojunction composite materials composed of cadmium sulfide and nickel aluminum hydrotalcite at different mass ratios of cadmium sulfide and nickel aluminum hydrotalcite in comparative examples 2-6 and the molar ratio of carbon monoxide to hydrogen are shown.

[0122] Fig.10 The formation rate of methane in the gas product obtained by catalyzing ethylene glycol using heterojunction composite materials composed of cadmium sulfide and nickel aluminum hydrotalcite at different mass ratios of cadmium sulfide and nickel aluminum hydrotalcite in Comparative Examples 2-6 is shown.

[0123] from Fig. 9 and Fig.10It can be seen that with the increase of the mass ratio of cadmium sulfide and nickel-aluminum hydrotalcite, the gas product obtained by catalyzing ethylene glycol shows a phenomenon of gradually increasing molar ratio of carbon monoxide and hydrogen. This is mainly because: the higher the mass ratio of cadmium sulfide, the denser the active sites that play a reducing role, and it is easier to carry out hydrogenation reaction on the intermediate after the reaction of ethylene glycol, which leads to the generation of a higher proportion of methane gas. Methane contains more hydrogen atoms. Due to the competitiveness of the reaction, the generation ratio of hydrogen compared to carbon monoxide will show a downward trend. That is, the molar ratio of carbon monoxide to hydrogen in the generated synthesis gas can be changed by adjusting the mass ratio of cadmium sulfide and nickel-aluminum hydrotalcite in the heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite.

[0124] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing synthesis gas and glyoxylic acid by photocatalytic PET plastic, the method comprising the following steps: 1) subjecting PET plastic to a hydrothermal reaction to prepare a liquid product containing ethylene glycol and terephthalic acid; 2) A heterojunction composite material composed of cadmium sulfide and nickel-aluminum hydrotalcite is used to perform a photocatalytic reaction on the liquid product of step 1) to prepare synthesis gas and glyoxylic acid.

2. The method according to claim 1, wherein: In step 1), the average particle size of the PET plastic is in the micron range, preferably, the average particle size of the PET plastic is 50-500 microns; And / or, in step 1), the PET plastic is derived from waste PET plastic or newly prepared PET plastic.

3. The method according to claim 1 or 2, wherein: In step 1), the temperature of the hydrothermal reaction is 180-220° C.; the time of the hydrothermal reaction is 18-36 hours. And / or, in step 1), the hydrothermal reaction is carried out in a high-pressure reactor.

4. The method according to any one of claims 1 to 3, wherein: In step 1), in the hydrothermal reaction system, the mass ratio of water to PET plastic is 60:1-20; And / or, in step 1), the concentration of ethylene glycol in the liquid product containing ethylene glycol and terephthalic acid is 50-450 mM.

5. The method according to any one of claims 1 to 4, wherein: In step 2), the photocatalytic reaction is carried out under an inert atmosphere, that is, after the heterojunction composite material composed of cadmium sulfide and nickel aluminum hydrotalcite is mixed with the liquid product of step 1), the reaction container is sealed, and an inert gas is introduced to replace the air in the reaction container to remove the residual air in the reaction container, and then the photocatalytic reaction is carried out under the condition of the inert atmosphere.

6. The method according to any one of claims 1 to 5, wherein: In step 2), during the photocatalytic reaction, the light source is a light source that can provide ultraviolet light and / or visible light. And / or, in step 2), the photocatalytic reaction time is 12-24 hours.

7. The method according to any one of claims 1 to 6, wherein: In step 2), the mass volume ratio of the heterojunction composite material formed by the cadmium sulfide and nickel aluminum hydrotalcite to the liquid product of step 1) is 2 mg: 1-20 mL.

8. The method according to any one of claims 1 to 7, wherein: In step 2), in the heterojunction composite material formed by the cadmium sulfide and the nickel-aluminum hydrotalcite, the cadmium sulfide is loaded on the surface of the nickel-aluminum hydrotalcite.

9. The method according to claim 8, wherein: In step 2), in the heterojunction composite material formed by the cadmium sulfide and the nickel-aluminum hydrotalcite, the mass ratio of cadmium sulfide to nickel-aluminum hydrotalcite is 0.1-8:1; And / or, the length of the nickel aluminum hydrotalcite is 10-40 nm, the width of the nickel aluminum hydrotalcite is 10-40 nm, and the thickness of the nickel aluminum hydrotalcite is 2-10 nm; And / or, the size of the cadmium sulfide is 2-10 nm; And / or, the heterojunction composite material formed by the cadmium sulfide and nickel aluminum hydrotalcite has a length of 10-40 nm, a width of 10-40 nm, and a thickness of 6-18 nm.

10. The method according to any one of claims 1 to 9, wherein: The synthesis gas includes carbon monoxide and hydrogen, and the molar ratio of the carbon monoxide to the hydrogen is 1:2-1:5.

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