Method and device for preparing urea through photocatalysis and piezoelectric catalysis of CO2

Abstract

The invention relates to a method and device for preparing urea through photocatalysis and piezoelectric catalysis of CO2, and the method comprises the following steps: adding a catalyst into water, introducing CO2 and N2 into the water, and reacting under the action of illumination and ultrasonic waves to obtain a urea solution; the light intensity of illumination ranges from 200 mW / cm < 2 > to 300 mW / cm < 2 >; the catalyst is selected from one or more of CdS (cadmium sulfide), ZnO (zinc oxide), WO3 (tungsten trioxide), BiOCl (bismuth oxychloride) and Bi4NbO8Cl (bismuth oxychloride). The technical problem to be solved is to provide a method for preparing urea by photocatalysis and piezoelectric catalysis of CO2, according to the method, under the action of illumination, ultrasonic waves and a catalyst, photocatalysis and piezoelectric catalysis of CO2 are combined, urea synthesis can be carried out at normal temperature and normal pressure, the yield of urea can be improved, and a new direction is developed for green and efficient synthesis of urea. Furthermore, the device can integrate air carbon capture coupling photocatalysis and piezoelectric catalysis CO2 preparation of urea into a set of continuous device, a large amount of energy input is not needed, multi-step separation can be avoided, the device is simple, and the cost can be greatly reduced.

Description

Technical Field

[0001] The present invention relates to the field of urea synthesis, and in particular to photocatalytic and piezoelectric catalytic CO 2 Method and apparatus for preparing urea. Background Art

[0002] Urea (NH 2 ) 2 CO) is an important chemical product, widely used in agricultural fertilizers, chemical raw materials and pharmaceutical fields. However, the traditional industrial urea synthesis method is to synthesize ammonia from nitrogen and hydrogen through the Haber-Bosch process, and then react ammonia with carbon dioxide to produce urea. This method requires high temperature and high pressure conditions, high energy consumption and large carbon emissions.

[0003] In recent years, efforts have been made to explore green chemistry to achieve sustainable development, and the use of mild technical means to synthesize urea has become an emerging research direction, such as photocatalysis and electrocatalysis. Photocatalysis can directly use nitrogen as a nitrogen source to catalyze the reaction with carbon dioxide and water under mild light to obtain urea, which can fundamentally avoid dependence on and consumption of ammonia, and can further avoid the demand for hydrogen in the process of synthesizing ammonia, as well as high emissions and high energy consumption. However, there are problems such as low light utilization.

[0004] Electrocatalysis uses an electrolytic cell to electrolyze nitrogen-containing solutions and carbon-containing solutions to obtain urea. It can utilize an electrochemical reaction to produce urea in a one-step CN coupling reaction, but there are problems such as complex reaction conditions, strong competitiveness of side reactions, and low urea yield.

[0005] Although photocatalytic, electrocatalytic, and even photoelectrocatalytic synthesis of urea avoids the traditional problems of high temperature, high pressure, high energy consumption, and high emissions, there are still problems such as low urea yield, low synthesis efficiency, poor catalyst selectivity, and difficulty in achieving large-scale industrial synthesis.

[0006] Therefore, it is of great significance to develop a high-yield, efficient and environmentally friendly urea synthesis method to achieve green and sustainable synthesis of urea. Summary of the invention

[0007] The main purpose of the present invention is to provide a photocatalytic and piezoelectric catalytic CO 2 Method and device for preparing urea. The technical problem to be solved is how to provide a photocatalytic and piezoelectric catalytic CO 2 A method for preparing urea, wherein the method combines photocatalysis and piezoelectric catalysis with mechanical stress provided by light and ultrasound and the action of a catalyst to produce urea. 2 The combination of these two technologies can not only synthesize urea at room temperature and pressure, but also improve the CO 2 and N 2The yield of synthetic urea has been improved, which has opened up a new direction for the sustainable development of green and efficient synthetic urea. 2 Urea production device, captures CO from air 2 and CO 2 The two independent process steps of catalytic conversion to synthesize urea are integrated into a continuous device, which does not require a large amount of energy input, high temperature and high pressure, can avoid multi-step separation, and can simplify the urea synthesis process and improve applicability.

[0008] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions. 2 A method for preparing urea, comprising the following steps:

[0009] The catalyst is added to water to convert CO 2 and N 2 Pass it into water, and under the action of light and ultrasound, it reacts to obtain urea solution;

[0010] The light intensity of the illumination is 200-300 mW / cm 2 ;

[0011] The catalyst is selected from CdS, ZnO, WO 3 , BiOCl and Bi 4 NbO 8 One or more of Cl.

[0012] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0013] Preferably, in the aforementioned method, the CO 2 and N 2 The molar ratio is 0.8 to 1:1.

[0014] Preferably, in the aforementioned method, the light source of the illumination is selected from a xenon lamp, sunlight or an incandescent lamp.

[0015] Preferably, in the aforementioned method, the reaction time is 4 to 8 hours.

[0016] Preferably, in the aforementioned method, the frequency of the ultrasonic wave is 80-100 kHz.

[0017] Preferably, in the aforementioned method, the mass ratio of the catalyst to the water is 0.01:1-10.

[0018] The purpose of the present invention and the technical problem solved are achieved by adopting the following technical solutions. 2A device for preparing urea, comprising CO 2 Catalytic conversion unit, the CO 2 The catalytic converter unit includes:

[0019] The reactor is provided with a CO 2 Inlet and N 2 Air inlet; the reactor is made of quartz or glass;

[0020] A light source system is arranged on the top or above the reactor; the light source system comprises a light emitting element and a current control element, the current control element is connected to the light emitting element to control the light intensity of the light emitting element;

[0021] An ultrasonic system is used to provide ultrasonic waves to the reactor.

[0022] Preferably, the aforementioned device further comprises:

[0023] An air carbon capture unit, the air carbon capture unit comprising:

[0024] Air compressor;

[0025] An adsorption system is disposed downstream of the air compressor, wherein the adsorption system is provided with an adsorbent; the adsorbent comprises a carbon material supported by tetraethylenepentamine and a layered double hydroxide;

[0026] a heating element, wherein the heating element heats the adsorption system;

[0027] CO 2 Export, the CO 2 Export and the CO 2 Air inlet connection.

[0028] Preferably, in the aforementioned device, the ultrasonic system comprises a plurality of ultrasonic transducers connected in series; the ultrasonic system further comprises a circuit control element; the circuit control element is connected to each of the ultrasonic transducers to control the frequency of the ultrasonic transducers;

[0029] The device also includes a catalyst mesh layer; the catalyst mesh layer is placed inside the reactor and is used to load the catalyst;

[0030] The ultrasonic system is placed below the catalyst mesh layer.

[0031] Preferably, in the aforementioned device, the ultrasonic system is an ultrasonic cleaner; and the reactor is placed in the ultrasonic cleaner.

[0032] By means of the above technical solution, the present invention proposes a photocatalytic and piezoelectric catalytic CO 2The method and device for preparing urea have at least the following advantages:

[0033] The present invention proposes a photocatalytic and piezoelectric catalytic CO 2 A method for preparing urea, wherein the method combines photocatalysis and piezoelectric catalysis with mechanical stress provided by light and ultrasound and the action of a catalyst to produce urea. 2 The combination of these two technologies can not only synthesize urea at room temperature and pressure, but also improve the CO 2 and N 2 The yield of synthetic urea has opened up a new direction for the sustainable development of green and efficient synthetic urea.

[0034] The present invention proposes a photocatalytic and piezoelectric catalytic CO 2 A device for preparing urea comprises a light source system and an ultrasonic system. The light source system comprises a light emitting element and a current control element. The current control element is connected to the light emitting element to control the light intensity of the light emitting element. The ultrasonic system is used to provide ultrasonic waves to the reactor. The device is simple and has the advantages of efficient synergistic catalysis, multi-energy utilization of light energy and mechanical energy, etc., and can greatly reduce costs.

[0035] The air carbon capture coupling photocatalysis and piezoelectric catalysis CO 2 Urea production device, captures CO from air 2 and CO 2 The two independent process steps of catalytic conversion and urea synthesis are integrated into a continuous device, which does not require a large amount of energy input and does not require high temperature and high pressure. It can avoid multi-step separation, improve urea selectivity and yield, and has a simple device that can greatly reduce costs.

[0036] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The photocatalytic and piezoelectric catalytic CO 2 Schematic diagram of a device for preparing urea;

[0038] Figure 2 The present invention provides a set of air carbon capture coupling photocatalysis and piezoelectric catalysis CO 2 Schematic diagram of a device for preparing urea;

[0039] Figure 3 It is a standard curve diagram of urea concentration and absorbance of Example 1 of the present invention. DETAILED DESCRIPTION

[0040] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a photocatalytic and piezoelectric catalytic CO 2 The specific implementation, structure, characteristics and efficacy of the method and device for preparing urea are described in detail below.

[0041] The first aspect of the present invention provides a photocatalytic and piezoelectric catalytic CO 2 A method for preparing urea, comprising the following steps:

[0042] The catalyst is added to water to convert CO 2 and N 2 Pass it into water and react to obtain urea solution under the action of light and ultrasound. The light intensity is 200-300mW / cm 2 ; The catalyst is selected from CdS, ZnO, WO 3 , BiOCl and Bi 4 NbO 8 One or more of Cl.

[0043] The inventors found that photocatalysis can absorb light energy to generate electron-hole pairs, and the photogenerated electrons drive CO 2 and N 2 The intermediate product is co-reduced and further reacts to form urea, and the holes participate in the water oxidation part. However, the efficiency of photocatalysis is low and the catalyst is easily deactivated. Piezoelectric catalysis can use the catalyst (piezoelectric material) to generate an electric field under the mechanical stress provided by ultrasound to drive CO 2 and N 2 The inventors further discovered that the combination of photocatalysis and piezoelectric catalysis can generate urea. 2 The piezoelectric field is generated under the mechanical stress provided by ultrasound. The piezoelectric catalysis can more efficiently promote the separation of photogenerated electron-hole pairs generated by photocatalysis, reduce recombination, enhance catalytic activity, and form a two-way promotion effect. In particular, when the light intensity is 200-300mW / cm 2 Ultrasonic waves provide mechanical stress, and the catalyst is selected from CdS, ZnO, WO 3 , BiOCl and Bi 4 NbO 8 Under the action of one or more of Cl, the synergistic effect of photocatalysis and piezoelectric catalysis can promote the conversion of water, CO 2 and N 2 Directed conversion into urea can not only reduce by-products and improve catalytic efficiency, but also utilize renewable energy (light and mechanical energy) to reduce carbon emissions. The simultaneous use of light energy and mechanical energy can further broaden the scope of energy utilization.

[0044] In the present invention, the CO2 and N 2 The molar ratio of CO is 0.8 to 1:1, which can maintain the balance of reactants, inhibit side reactions, and optimize reaction kinetics. 2 and N 2 They are the two main raw materials for urea synthesis, and their molar ratio directly affects the formation of intermediates and the reaction path. 2 This may lead to an increase in by-products (such as CO and HCOOH), while excess N 2 May reduce CO 2 The conversion efficiency of CO 2 and N 2 The molar ratio of 0.8 to 1:1 not only helps to balance CO 2 Reduction and N 2 The activation rate is increased, side reactions are reduced, and the synergistic effect of photocatalysis and piezocatalysis is promoted to 2 and N 2 At the same time, it is activated into reactive intermediates (such as CO, NH 3 or NH 2 ).

[0045] In the present invention, the light source of the illumination is selected from xenon lamp, sunlight or incandescent lamp. The xenon lamp, sunlight or incandescent lamp with a wide spectrum light source is better suitable for the catalyst with a wide spectrum response of the present invention.

[0046] In the present invention, the reaction time is 4 to 8 hours, which can ensure sufficient conversion of the reactants while avoiding excessive reaction leading to an increase in by-products. The activity of photocatalysis and piezoelectric catalysts is higher in the initial stage of the reaction, but may decrease over time due to catalyst deactivation or surface passivation. A reaction time of 4 to 8 hours is conducive to completing the main reaction when the catalyst activity is higher. A reaction time that is too short may lead to low energy utilization, while a reaction time that is too long will increase energy consumption. A reaction time of 4 to 8 hours is conducive to achieving a balance between energy efficiency and reaction completion.

[0047] In the present invention, the frequency of the ultrasonic wave is 80-100kHz, which can effectively generate a piezoelectric field, promote charge separation, and is suitable for the resonant frequency of the catalyst of the present invention, which can maximize the conversion efficiency of mechanical energy to electrical energy. When the ultrasonic wave propagates in the liquid, it will produce a cavitation effect (the formation and rupture of bubbles), which promotes the mixing and mass transfer of reactants. The frequency of 80-100kHz can produce a moderate cavitation effect in the liquid, avoiding energy dissipation caused by too high frequency or insufficient cavitation effect caused by too low frequency, and is less destructive to the reaction system, suitable for long-term reaction (such as 4-8h), and can also effectively disperse the catalyst to prevent its agglomeration, while promoting the adsorption and activation of reactants on the catalyst surface.

[0048] In the present invention, the mass ratio of the catalyst to the water is 0.01:1-10, the catalyst has good dispersibility, a large contact area with the reactants, can balance the catalyst dosage and the reactant concentration, can effectively utilize the catalyst active sites, and avoid catalyst agglomeration.

[0049] According to the present invention, in order to further recycle the catalyst, the catalyst is loaded on a catalyst mesh layer and then dispersed in an aqueous solution.

[0050] According to the present invention, in order to ensure the accuracy of the urea yield prepared, the CO 2 and N 2 Before the reaction, the reactor was evacuated to remove the air inside the reactor.

[0051] The second aspect of the present invention provides a photocatalytic and piezoelectric catalytic CO 2 A device for preparing urea, comprising: Figure 1 Parts shown:

[0052] CO 2 A catalytic conversion unit comprising:

[0053] Reactor 9, the top of which is provided with a CO 2 Inlet holes 91 and N 2 The gas inlet 92, the reactor 9 is made of quartz or glass;

[0054] A light source system 95 is disposed on or above the reactor 9; the light source system 95 comprises a light emitting element and a current control element, wherein the current control element is connected to the light emitting element to control the light intensity of the light emitting element;

[0055] An ultrasonic system 96, the ultrasonic system 96 is used to provide ultrasonic waves to the reactor 9;

[0056] The air carbon capture unit 7 comprises:

[0057] Air compressor 5;

[0058] An adsorption system 7 is disposed downstream of the air compressor 5, and the adsorption system 7 is provided with an adsorbent; the adsorbent includes a carbon material supported by tetraethylenepentamine and a layered double hydroxide;

[0059] A heating element 73, wherein the heating element 73 heats the adsorption system 7;

[0060] CO 2 Outlet 72, the CO 2 The outlet 72 is connected to the CO 2 The air inlet 91 is connected.

[0061] According to a preferred embodiment of the present invention, the ultrasonic system 96 includes a plurality of ultrasonic transducers connected in series; the ultrasonic system also includes a circuit control element; the circuit control element is connected to each of the ultrasonic transducers to control the frequency of the ultrasonic transducers;

[0062] The device further comprises a catalyst mesh layer 93; the catalyst mesh layer 93 is placed inside the reactor 9 and is used to load the catalyst;

[0063] The ultrasonic system is placed below the catalyst mesh layer 93 .

[0064] According to a preferred embodiment of the present invention, the ultrasonic system is an ultrasonic cleaner; the reactor is placed in the ultrasonic cleaner.

[0065] According to a particularly preferred embodiment of the present invention, the photocatalytic and piezoelectric catalytic CO 2 The device for preparing urea is air carbon capture coupled with photocatalysis and piezoelectric catalysis CO 2 A device for preparing urea, comprising: Figure 2 The components connected in sequence are as shown: the solar panel 1 is connected to the wind turbine 2 to charge the battery 3 together, and to supply power to the downstream air compressor 5 and the heater 73; the downstream of the battery 3 is connected to the inverter 4 to convert the current into stable alternating current; the downstream of the inverter 4 is connected to the air compressor 5, and the air compressor 5 compresses the air into high-pressure gas; the air compressor 5 controls the gas to pass into the adsorption bed 7 through the electric control valve 6, and the adsorbent on the adsorption bed 7 reacts with CO 2 The heater 73 is placed under the adsorption bed to heat the adsorption bed 7 and release CO 2 The adsorption bed 7 is connected to a gas pipeline through a control valve 71 to control the excess gas after adsorption to be discharged into the air. The adsorption bed 7 is connected to a gas pipeline through a control valve 72 to control the desorbed CO 2 into the reactor 9, the top of which is provided with a CO 2 Inlet holes 91 and N 2 Inlet 92, CO 2 Air inlet 91 and CO 2The outlet 72 is connected, and the side wall of the reactor 9 allows water to enter the reactor 9 through the control valve 8. The material of the reactor 9 is quartz or glass. The catalyst mesh layer 93 is placed inside the reactor 9. The catalyst mesh layer 93 is provided with a catalyst. The light source system 95 is arranged on the top of the reactor 9. The light source system 95 includes a light-emitting element and a current control element. The ultrasonic system 96 is used to provide ultrasonic waves to the reactor 9. The ultrasonic system 96 includes a plurality of ultrasonic transducers connected in series. The ultrasonic system also includes a circuit control element. The circuit control element is connected to each of the ultrasonic transducers to control the frequency of the ultrasonic transducer. The ultrasonic system is placed below the catalyst mesh layer 93. The bottom of the reactor 9 is connected to the PVC pipe through a control valve 94 to control the collection of the urea solution.

[0066] The present invention will be further described below in conjunction with specific embodiments, but this should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by technicians in this field based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0067] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well known to those skilled in the art; unless otherwise specified, the methods described are all methods well known in the art. Unless otherwise defined, the technical terms or scientific terms used should have the common meanings understood by ordinary technicians in the field to which the present invention belongs.

[0068] Preparation Example 1

[0069] Used to illustrate the preparation of catalyst CdS

[0070] Add 1 mmol of CdCl in 50 mL of deionized water 2 2.5H 2 O and 2mmol of thiourea, stirred for 30 minutes, 1mol / L NaOH was used to adjust the pH value of the solution to 11, and the resulting solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, reacted at 180°C for 12 hours, and cooled to room temperature after the reaction. The product after the reaction was washed with deionized water and ethanol, and then vacuum dried at 60°C to obtain rod-shaped CdS nanomaterials.

[0071] Preparation Example 2

[0072] Used to illustrate the preparation of ZnO catalyst

[0073] 1 mmol of Zn(NO 3 ) 2 6H 2O was dissolved in 30 mL of deionized water and stirred evenly. 2 mol / L of NaOH was added to adjust the pH of the solution to 11. The resulting solution was transferred to a polytetrafluoroethylene-lined autoclave. The reaction was carried out at 180 °C for 12 hours, cooled to room temperature, centrifuged and the precipitate was washed, and dried at 60 °C to obtain ZnO nanomaterials.

[0074] Preparation Example 3

[0075] For the description of catalyst WO 3 Preparation

[0076] 2mmol Na 2 WO 4 ·2H 2 O was dissolved in 20 mL of deionized water. The pH value was adjusted to 10 with 2 mol / L NaOH solution and stirred for 30 minutes. The solution was transferred to a polytetrafluoroethylene autoclave and reacted at 200 °C for 12 hours. After the reaction, it was cooled to room temperature, centrifuged and washed, and dried at 60 °C to obtain WO 3 Nanoparticles.

[0077] Example 1

[0078] 50 mg of the catalyst CdS supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. CO at a molar ratio of 1:1 was introduced. 2 and N 2 The mixed gas was tested for the pressure in the reactor. When positive pressure appeared, ventilation was stopped immediately. At this time, the mixed gas filled the reactor. The reactor was placed in an ultrasonic cleaner with a frequency of 80 kHz. A 300 mW xenon lamp was turned on at the same time to illuminate the reactor from the top. The reaction was continued for 8 h. After that, 1 mL of the solution in the reactor was taken out for urea determination. The results are shown in Table 1.

[0079] Example 2

[0080] 50 mg of ZnO catalyst supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. The reactor was evacuated and then CO at a molar ratio of 0.8:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears. At this time, the mixed gas fills the reactor. Place the reactor in an ultrasonic cleaner, set the frequency of the ultrasonic cleaner to 100kHz, and turn on a 240mW xenon lamp at the same time. Illuminate from the top of the reactor and react for 6h. Then take out 1mL of the solution in the reactor for urea determination. The results are shown in Table 1.

[0081] Example 3

[0082] 50 mg of catalyst WO loaded on the catalyst mesh layer 3 Dispersed in 50 mL of aqueous solution, added to a 50 mL quartz reactor, the reactor was evacuated, and then CO at a molar ratio of 0.9:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears, at this time the mixed gas fills the reactor, place the reactor in an ultrasonic cleaner, set the frequency of the ultrasonic cleaner to 100kHz, and turn on a 200mW xenon lamp at the same time, shining it from the top of the reactor, react for 4h, then take out 1mL of the solution in the reactor for urea determination. The results are shown in Table 1.

[0083] Comparative Example 1

[0084] 50 mg of the catalyst CdS supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. The reactor was evacuated and then CO at a molar ratio of 1:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears. At this time, the mixed gas fills the reactor. Turn on the 300mW xenon lamp and illuminate the reaction from the top of the reactor for 8h. Then take out 1mL of solution in the reactor for urea determination. The results are shown in Table 1.

[0085] Comparative Example 2

[0086] 50 mg of the catalyst CdS supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. The reactor was evacuated and then CO at a molar ratio of 1:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears, at this time the mixed gas fills the reactor, place the reactor in an ultrasonic cleaner, set the frequency of the ultrasonic cleaner to 80kHz, and cover the reactor with a black plastic bag, let the reactor react in a dark environment for 8h, then take out 1mL of solution in the reactor for urea determination, the results are shown in Table 1.

[0087] Comparative Example 3

[0088] 50 mg of ZnO catalyst supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. The reactor was evacuated and then CO at a molar ratio of 0.8:1 was introduced. 2 and N 2Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears. At this time, the mixed gas fills the reactor. Turn on the 240mW xenon lamp and shine it from the top of the reactor. React for 6h, then take out 1mL of solution in the reactor for urea determination. The results are shown in Table 1.

[0089] Comparative Example 4

[0090] 50 mg of ZnO catalyst supported on the catalyst mesh layer was dispersed in 50 mL of aqueous solution and added into a 50 mL quartz reactor. The reactor was evacuated and then CO at a molar ratio of 0.8:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears, at this time the mixed gas fills the reactor, place the reactor in an ultrasonic cleaner, set the frequency of the ultrasonic cleaner to 100kHz, react for 6h, then take out 1mL of the solution in the reactor for urea determination, the results are shown in Table 1.

[0091] Comparative Example 5

[0092] 50 mg of catalyst WO loaded on the catalyst mesh layer 3 Dispersed in 50 mL of aqueous solution, added to a 50 mL quartz reactor, the reactor was evacuated, and then CO at a molar ratio of 0.9:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears. At this time, the mixed gas fills the reactor. Turn on the 200mW xenon lamp and shine it from the top of the reactor. React for 4h, then take out 1mL of solution in the reactor for urea determination. The results are shown in Table 1.

[0093] Comparative Example 6

[0094] 50 mg of catalyst WO loaded on the catalyst mesh layer 3 Dispersed in 50 mL of aqueous solution, added to a 50 mL quartz reactor, the reactor was evacuated, and then CO at a molar ratio of 0.9:1 was introduced. 2 and N 2 Mixed gas, detect the pressure of the reactor, stop ventilation immediately when positive pressure appears, at this time the mixed gas fills the reactor, place the reactor in an ultrasonic cleaner, set the frequency of the ultrasonic cleaner to 100kHz, react for 4h, then take out 1mL of the solution in the reactor for urea determination, the results are shown in Table 1.

[0095] Test Case

[0096] Urea determination method: Take 1 mL of the solution after the reaction, add 1 mL of color reaction solution A (1.25 g of diacetyl oxime and 25 mg of thiosemicarbazide in 250 mL of deionized water) and 2 mL of color reaction solution B (50 mL of phosphoric acid, 125 mL of concentrated sulfuric acid and 50 mg of FeCl in 500 mL of deionized water). 3 ), color development at 100°C for 15 minutes and then stand for 5 minutes. Subsequently, a glass cuvette was used to perform a spectrum scan in the range of 400-800 nm using an ultraviolet spectrometer, and the absorbance value at 525 nm was recorded and compared with the standard curve to finally obtain the concentration of urea.

[0097] The standard curve of urea was obtained by the following method:

[0098] Prepare standard solutions with urea concentrations of 0.1 μg / mL, 0.5 μg / mL, 1.0 μg / mL, 2.0 μg / mL, 10.0 μg / mL, and 20.0 μg / mL, respectively, perform colorimetric determination using the above determination method, record the absorbance values ​​at the corresponding wavelengths, and draw a standard curve of the target product urea. The equation of the fitted standard curve is: y=0.05182x+0.04356, R 2 =0.9911, as shown in the attached Figure 3 shown.

[0099] The urea yield was calculated using the following formula:

[0100] R urea =(C urea ×V) / (t×m)

[0101] Where: C urea — represents the concentration of urea in the solution after the reaction is completed, in μg / mL;

[0102] V—indicates the volume of the solution after the reaction is completed, in mL;

[0103] m—represents the mass of the catalyst, in g;

[0104] t—represents reaction time, in h.

[0105] Table 1 Urea productivity of Examples and Comparative Examples

[0106] serial number catalyst <![CDATA[CO 2 Conversion method]]> Urea yield (μg / g / h) Example 1 CdS Photo-piezocatalysis 198 Comparative Example 1 CdS Photocatalysis 34 Comparative Example 2 CdS Piezoelectric Catalysis 58 Example 2 ZnO Photo-piezocatalysis 102 Comparative Example 3 ZnO Photocatalysis 45 Comparative Example 4 ZnO Piezoelectric Catalysis 41 Example 3 <![CDATA[WO 3 ]]> Photo-piezocatalysis 88 Comparative Example 5 <![CDATA[WO 3 ]]> Photocatalysis 26 Comparative Example 6 <![CDATA[WO 3 ]]> Piezoelectric Catalysis 32

[0107] The test data of the embodiments and comparative examples of the present invention show that the present invention uses photocatalysis and piezoelectric catalysis to produce CO 2 The method for preparing urea not only combines photocatalysis with piezoelectric catalysis to produce CO 2 The combination enables urea synthesis to be carried out at room temperature and pressure, and can increase CO 2 and N2 The yield of synthetic urea. Especially when the catalyst is CdS, the urea yield obtained by photo-piezoelectric catalysis is 198μg / g / h, which is a significant improvement, opening up a new direction for green and efficient synthetic urea to achieve sustainable development and has great potential.

[0108] The technical features in the claims and / or the specification of the present invention can be combined, and the combination is not limited to the combination obtained by reference in the claims. The technical solution obtained by combining the claims and / or technical features is also within the protection scope of the present invention.

[0109] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing urea from CO2 by photocatalysis and piezoelectric catalysis, characterized in that: It includes the following steps: The catalyst is added into water, CO2 and N2 are introduced into the water, and under the action of light and ultrasound, a urea solution is obtained by reaction; The light intensity of the illumination is 200-300 mW / cm 2 ; The catalyst is selected from one or more of CdS, ZnO, WO3, BiOCl and Bi4NbO8Cl.

2. The method according to claim 1, characterized in that: The molar ratio of CO2 to N2 is 0.8 to 1:

1.

3. The method according to claim 1, characterized in that The light source of the illumination is selected from a xenon lamp, sunlight or an incandescent lamp.

4. The method according to claim 1, characterized in that: The reaction time is 4 to 8 hours.

5. The method according to claim 1, characterized in that The frequency of the ultrasonic wave is 80-100 kHz.

6. The method according to claim 1, characterized in that The mass ratio of the catalyst to the water is 0.01:1-10.

7. A device for preparing urea from CO2 by photocatalysis and piezoelectric catalysis, characterized in that: It includes a CO2 catalytic conversion unit, and the CO2 catalytic conversion unit includes: A reactor, wherein a CO2 inlet and a N2 inlet are arranged on the top of the reactor; the reactor is made of quartz or glass; A light source system is arranged on the top or above the reactor; the light source system comprises a light emitting element and a current control element, the current control element is connected to the light emitting element to control the light intensity of the light emitting element; An ultrasonic system is used to provide ultrasonic waves to the reactor.

8. The device according to claim 7, characterized in that It also includes An air carbon capture unit, the air carbon capture unit comprising: Air compressor; An adsorption system is disposed downstream of the air compressor, wherein the adsorption system is provided with an adsorbent; the adsorbent comprises a carbon material supported by tetraethylenepentamine and a layered double hydroxide; a heating element, wherein the heating element heats the adsorption system; A CO2 outlet is connected to the CO2 inlet.

9. The device according to claim 7, characterized in that The ultrasonic system comprises a plurality of ultrasonic transducers connected in series; the ultrasonic system further comprises a circuit control element; the circuit control element is connected to each of the ultrasonic transducers to control the frequency of the ultrasonic transducers; The device also includes a catalyst mesh layer; the catalyst mesh layer is placed inside the reactor and is used to load the catalyst; The ultrasonic system is placed below the catalyst mesh layer.

10. The device according to claim 7, characterized in that The ultrasonic system is an ultrasonic cleaner; the reactor is placed in the ultrasonic cleaner.

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