NITRATE REMOVAL FROM WATER BODIES USING ELECTROCATALYTIC HYDROGEN EVOLUTION AND CATALYTIC HYDROGENATION

Abstract

A denitrification system for removing nitrates in a water body by electrocatalytic hydrogen evolution and catalytic hydrogenation is disclosed. The denitrification system includes an electrolytic cell and a three-electrode system inserted into the electrolytic cell. The electrolytic cell contains electrolyte solution, and the denitrification catalyst is dispersed and suspended in the electrolyte solution. The three-electrode system includes a working electrode, a counter electrode and a reference electrode. The counter electrode adopts Pt sheet, the working electrode adopts the catalyst Ni.sub.3S.sub.2—NF, and the preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows: (i) cutting a certain size nickel mesh and cleaning it; (ii) adding the cleaned nickel mesh into thiourea solution; (iii) reacting under hydrothermal conditions, and washing and drying to obtain the catalyst Ni.sub.3S.sub.2—NF. The invention avoids the hazards of storing and transporting hydrogen storage and realizes the efficient removal of nitrate in water by electrocatalytic hydrogen evolution and catalytic hydrogenation.

Claims

1. A denitrification system for efficiently removing nitrate in a water body by electrocatalytic hydrogen evolution and catalytic hydrogenation, comprising an electrolytic cell and a three-electrode system inserted into the electrolytic cell, wherein the electrolytic cell contains an electrolyte solution, and the three-electrode system comprises a working electrode, a counter electrode and a reference electrode, and the counter electrode adopts a Pt sheet, a denitrification catalyst is dispersed and suspended in the electrolyte solution, the working electrode adopts a catalyst Ni.sub.3S.sub.2—NF, and preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows: (1) cutting and cleaning a nickel mesh to obtain a cleaned nickel mesh; (2) adding the cleaned nickel mesh in step (1) into a thiourea solution to obtain a soaked nickel mesh, and then placing the soaked nickel mesh under hydrothermal conditions; (3) washing and drying the soaked nickel mesh in step

2. The denitrification system according to claim 1, wherein the denitrification catalyst is PdCu-AC, and the PdCu-AC is an activated carbon supported with metal palladium and copper, and preparation steps of the PdCu-AC are as follows: (1) adding an activated carbon into nitric acid to obtain a first mixture, heating the first mixture in a water bath, filtering the first mixture obtain a filtered substance and drying the filtered substance to obtain a pretreated activated carbon AC; (2) adding the pretreated activated carbon AC, palladium chloride PdCl.sub.2 and copper nitrate into ethanol to obtain a second mixture and stirring the second mixture evenly; (3) stirring the second mixture obtained in step (2) at room temperature until the ethanol is evaporated to obtain a third mixture, and drying the third mixture to obtain powder; (4) calcining the powder obtained in step (3) in a tubular furnace to obtain the PdCu-AC.

3. The denitrification system according to claim 2, wherein the nitric acid in step (1) is 10%-45% dilute nitric acid, a temperature of the water bath is 60-100° C., the heating lasts for 4-6 h, the filtering is performed by a vacuum suction filtration, and the drying is performed at 100-120° C. for 2-4 h.

4. The denitrification system according to claim 2, wherein the copper nitrate in step (2) is copper nitrate trihydrate Cu(NO.sub.3).sub.2.3H.sub.2O, and a mass ratio of the AC, the PdCl.sub.2 and the Cu(NO.sub.3).sub.2.3H.sub.2O is 1: (0.0835-0.167):(0.0945-0.189).

5. The denitrification system according to claim 2, wherein the drying described in step (3) is performed in an oven at 60-100° C. for 10-12 h.

6. The denitrification system according to claim 2, wherein the calcining in step (4) is carried out in the tubular furnace under a nitrogen atmosphere, and a temperature is raised to 400° C. at a heating rate of 1° C./min for 2-4 h.

7. The denitrification system according to claim 1, wherein the cleaning of the nickel mesh in step (1) is as follows: ultrasonic cleaning the nickel mesh in 30 ml of acetone and 30 ml of hydrochloric acid for 10-15 min in turn, and then cleaning the nickel mesh three times with ethanol and water respectively.

8. The denitrification system according to claim 1, wherein a concentration of the thiourea solution in step (2) is 0.10-0.20 M, a hydrothermal temperature is 120-150° C., and a hydrothermal time is 4-6 h.

9. The denitrification system according to claim 1, wherein the washing described in step (3) is to wash the soaked nickel mesh three times with ethanol, and the drying is a vacuum drying at room temperature.

10. A method of using the denitrification system according to claim 1 in a removal of nitrate from the water body, comprising: dispersing and suspending 1 g of the denitrification catalyst in 100 ml of the electrolyte solution, and starting an electrochemical workstation electrically connected to the three-electrode system for a reaction for 5 h; wherein the electrolyte solution is a solution containing sodium nitrate and sodium sulfate, a concentration of the sodium nitrate in the electrolyte solution is 100 mg-N/L, a concentration of the sodium sulfate in the electrolyte solution is 0.1 M.

11. The method according to claim 10, wherein the denitrification catalyst is PdCu-AC, and the PdCu-AC is an activated carbon supported with metal palladium and copper, and preparation steps of the PdCu-AC are as follows: (1) adding an activated carbon into nitric acid to obtain a first mixture, heating the first mixture in a water bath, filtering the first mixture obtain a filtered substance and drying the filtered substance to obtain a pretreated activated carbon AC; (2) adding the pretreated activated carbon AC, palladium chloride PdCl.sub.2 and copper nitrate into ethanol to obtain a second mixture and stirring the second mixture evenly; (3) stirring the second mixture obtained in step (2) at room temperature until the ethanol is evaporated to obtain a third mixture, and drying the third mixture to obtain powder; (4) calcining the powder obtained in step (3) in a tubular furnace to obtain the PdCu-AC.

12. The method according to claim 11, wherein the nitric acid in step (1) is 10%-15% dilute nitric acid, a temperature of the water bath is 60-100° C., the heating lasts for 4-6 h, the filtering is performed by a vacuum suction filtration, and the drying is performed at 100-120° C. for 2-4 h.

13. The method according to claim 11, wherein the copper nitrate in step copper nitrate trihydrate Cu(NO.sub.3).sub.2.3H.sub.2O, and a mass ratio of the AC, the PdCl.sub.2 and the Cu(NO.sub.3).sub.2.3H.sub.2O is 1: (0.0835-0.167):(0.0945-0.189).

14. The method according to claim 11, wherein the drying described in step (3) is performed in an oven at 60-100° C. for 10-12 h.

15. The method according to claim 11, wherein the calcining in step (4) is carried out in the tubular furnace under a nitrogen atmosphere, and a temperature is raised to 400° C.. at a heating rate of 1° C./min for 2-4 h.

16. The method according to claim 10, wherein the cleaning of the nickel mesh in step (1) is as follows: ultrasonic cleaning the nickel mesh in 30 ml of acetone and 30 ml of hydrochloric acid for 10-15 min in turn, and then cleaning the nickel mesh three times with ethanol and water respectively.

17. The method according to claim 10, wherein a concentration of the thiourea solution in step (2) is 0.10-0.2.0 M, a hydrothermal temperature is 120-150° C., and a hydrothermal time is 4-6 h.

18. The method according to claim 10, wherein the washing described in step (3) is to wash the soaked nickel mesh three times with ethanol, and the drying is a vacuum drying at room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a structural diagram of the denitrification system of the invention;

[0027] FIG. 2 is a transmission electron microscope (TEM) image of the denitrification chemical catalyst in embodiment 1;

[0028] FIG. 3 is a TEM image of the denitrification chemical catalyst in embodiment 2;

[0029] FIG. 4 is a TEM image of the denitrification chemical catalyst in embodiment 3;

[0030] FIG. 5 is a comparison diagram of denitrification effects in embodiments 1-3 and comparative example 1;

[0031] FIG. 6 is a diagram showing leaching percentage of the denitrification catalyst supported with metal during six regeneration cycles in embodiment 1;

[0032] FIG. 7 is a denitrification effect diagram of six regeneration cycles in embodiment 1; and

[0033] FIG. 8 is a comparison diagram of denitrification effects of embodiment 1 and comparative examples 1-2.

[0034] In the drawings:

[0035] 1. electrolytic cell

[0036] 11. denitrification catalyst

[0037] 21. working electrode

[0038] 22. counter electrode

[0039] 23. reference electrode

[0040] 3. electrochemical workstation

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The features of the invention are further described through the implementation embodiments, but the claims of the invention are not limited.

Embodiment 1

[0042] A denitrification system for efficiently removing nitrate in a water body by electrocatalytic hydrogen evolution and catalytic hydrogenation is provided. As shown in FIG. 1, the system includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1.

[0043] The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution, and the denitrification catalyst 11 is an activated carbon PdCu-AC supported with metal palladium and copper, and the preparation steps of the PdCu-AC are as follows:

[0044] (1) 25 g of activated carbon powder is added to 500 ml of 10% dilute nitric acid, heated in a water bath at 80° C. for 4 h, and then filtered by vacuum suction filtration to obtain a solid, and finally the solid is put in an oven for drying at 100° C. for 4 h to obtain a pretreated AC;

[0045] (2) 0.0835 g of PdCl.sub.2, 0.0945 g of Cu(NO.sub.3).sub.2.3H.sub.2O and 1 g of the pretreated AC are added into 10 ml of ethanol and stirred evenly;

[0046] (3) the mixture obtained in step (2) is stirred at room temperature until the ethanol is evaporated, and the obtained solid is dried in the oven at 80° C. for 12 h; and

[0047] (4) the product obtained in step (3) is placed in a tubular furnace, heated to 400° C. at a heating rate of 1° C./min under a nitrogen atmosphere and calcined for 2 h to obtain an activated carbon catalyst (5% PdCu-AC) supported with palladium and copper. The TEM image of the catalyst is shown in FIG. 2.

[0048] The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23. The counter electrode adopts Pt sheet. The working electrode 21 adopts the catalyst Ni.sub.3S.sub.2—NF, and the preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows:

[0049] (1) a nickel mesh is cut to have a size of 2.5—2.5 cm, which is first ultrasonic cleaned with 30 ml of acetone for 10 min, and then cleaned using ultrasound with 30 ml of 3 M hydrochloric acid for 10 min, and finally washed with ethanol and deionized water for 3 times respectively;

[0050] (2) the cleaned nickel mesh in step (1) is added to 20 ml of 0.15M thiourea solution and transferred to a reactor, and kept airtight for 5 h at 150° C.;

[0051] (3) Ni.sub.3S.sub.2—NF is obtained by washing the material obtained in step (2) three times with ethanol and vacuum drying at room temperature.

[0052] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution. The concentration of sodium nitrate in the electrolyte solution is 100 mg-N/L, and the concentration of sodium sulfate is 0.1 M. And 1 g of denitrification catalyst, i.e., 5% PdCu-AC prepared above, is suspended in the electrolyte solution. The electrochemical workstation CH1760D 3 electrically connected to the three-electrode system is engaged to perform the denitrification reaction for 5 h. The denitrification effect is shown in FIG. 5, wherein the abscissa of FIG. 5 shows the denitrification catalyst with different metal supporting contents. The left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

[0053] The 5% PdCu-AC denitrification catalyst after the denitrification reaction is recycled for repeatedly performing the above application operations 6 times. The metal content in the reaction solution during each reaction is tested for further analyzing the structural stability of the material. The result is shown in FIG. 6, and the denitrification effect of each reaction is shown in FIG. 7. The abscissa of FIG. 6 represents the reaction times, and the ordinate represents the precipitation percentage of metal Pd and Cu in the reaction solution. The abscissa of FIG. 7 shows the recycling times of denitrification catalyst: The left ordinate is the proportion of reaction products, and the right ordinate is the removal rate of nitrate. It can be seen from FIG. 6 that the metal content in the reaction solution remains low after six times of recycling, which indicates that the structure stability of the 5% PdCu-AC denitrification catalyst is high. FIG. 7 shows that the 5% PdCu-AC denitrification catalyst still has high denitrification effect after six times of recycling, which indicates that the structure stability of PdCu-AC denitrification catalyst is consistent with the denitrification effect stability thereof.

Embodiment 2

[0054] A denitrification system for efficiently removing nitrate in a water body by electrocatalytic hydrogen evolution and catalytic hydrogenation includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1.

[0055] The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution. The denitrification catalyst 11 is an activated carbon PdCu-AC supported with metal palladium and copper, and the preparation steps of the PdCu-AC are as follows:

[0056] (1) 25 g of activated carbon powder is added to 500 ml of 10% dilute nitric acid, heated in water bath at 80° C. for 4 h, and then filtered by vacuum suction filtration to obtain a solid, and finally the solid is put in an oven for drying at 100° C. for 4 h to obtain a pretreated AC;

[0057] (2) 0.0167 g of PdCl.sub.2, 0.0189 g of Cu(NO.sub.3).sub.2.3H.sub.2O and 1 g of the pretreated AC are added into 10 ml of ethanol and stirred evenly;

[0058] (3) the mixture obtained in step (2) is stirred at room temperature until the ethanol is evaporated, and the obtained solid is dried in the oven at 80° C. for 12 h;

[0059] (4) the product obtained in step (3) is placed in a tubular furnace, heated to 400° C. at a heating rate of 1° C./min under a nitrogen atmosphere and calcined for 2 h to obtain an activated carbon catalyst (1% PdCu-AC) supported with palladium and copper. The TEM image of the catalyst is shown in FIG. 3.

[0060] The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23. The counter electrode 22 adopts Pt sheet, the working electrode 21 adopts the catalyst Ni.sub.3S.sub.2—NF, and the preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows:

[0061] (1) a nickel mesh is cut to have a size of 2.5×2.5 cm, which is first ultrasonically cleaned with 30 ml of acetone for 10 min, and then cleaned using ultrasound with 30 ml of 3 M hydrochloric acid for 10 min, and finally washed with ethanol and deionized water for 3 times;

[0062] (2) the cleaned nickel mesh in step (1) is added to 20 ml of 0.15M thiourea solution and transferred to a reactor, and kept airtight for 5 h at 150° C.;

[0063] (3) Ni.sub.3S.sub.2—NF is obtained by washing the material obtained in step three tunes with ethanol and vacuum drying at room temperature.

[0064] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution. The concentration of sodium nitrate in the electrolyte solution is 100 mg-N/L, and the concentration of sodium sulfate is 0.1 M, and 1 g of denitrification catalyst, i.e., 1% PdCu-AC prepared above, is suspended in the electrolyte solution. The electrochemical workstation CH1760D electrically connected to the three-electrode system is started to perform the denitrification reaction for 5 h. The denitrification effect is shown in FIG. 5, wherein, the abscissa of FIG. 5 shows the denitrification catalyst with different metal supporting contents. The left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

Embodiment 3

[0065] A denitrification system for efficiently removing nitrate in a water body by electrocatalytic hydrogen evolution and catalytic hydrogenation includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1.

[0066] The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution. The denitrification catalyst 11 is an activated carbon PdCu-AC supported with metal palladium and copper, and the preparation steps of the PdCu-AC are as follows:

[0067] (1) 25 g of activated carbon powder is added to 500 ml of 10% dilute nitric acid, heated in water bath at 80° C. for 4 h, and then filtered by vacuum suction filtration to obtain a solid, and finally the solid is put in an oven for drying at 100° C. for 4 h to obtain a pretreated AC;

[0068] (2) 0.167 g of PdCl.sub.2, 0.189 g of Cu(NO.sub.3).sub.2.3H.sub.2O and 1 g of the pretreated AC are added into 10 ml of ethanol and stirred evenly;

[0069] (3) the mixture obtained in step (2) is stirred at room temperature until the ethanol is evaporated, and the obtained solid is dried in the oven at 80° C. for 12 h;

[0070] (4) the product obtained in step (3) is placed in a tubular furnace, heated to 400° C. at a heating rate of 10° C./min under a nitrogen atmosphere and calcined for 2 h to obtain an activated carbon catalyst (10% PdCu-AC) supported with palladium and copper. The TEM image of the catalyst is shown in FIG. 4.

[0071] The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23, and the counter electrode 22 adopts Pt sheet, the working electrode 21 adopts the catalyst Ni.sub.3S.sub.2—NF, and the preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows:

[0072] (1) a nickel mesh is cut to have a size of 2.5×2.5 cm, which is first ultrasonic cleaned with 30 ml of acetone for 10 min, and then ultrasonic cleaned with 30 ml of 3 M hydrochloric acid for 10 min, and finally washed with ethanol and deionized water for 3 times respectively;

[0073] (2) the cleaned nickel mesh in step (1) is added to 20 ml of O.15M thiourea solution and transferred to a reactor, and kept airtight for 5 h at 150° C.;

[0074] (3) Ni.sub.3S.sub.2—NF is obtained by washing the material obtained in step (2) three times with ethanol and vacuum drying at room temperature.

[0075] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution, the concentration of sodium nitrate in the electrolyte solution is 100 mg:N/L, and the concentration of sodium sulfate is 0.1 M, and 1 g of denitrification catalyst, i.e., 10% PdCu-AC prepared above, is suspended in the electrolyte solution, and the electrochemical workstation CH 760D electrically connected to the three-electrode system is started to perform denitrification reaction for 5 h, the denitrification effect is shown in FIG. 5, wherein, the abscissa of FIG. 5 shows the denitrification catalyst with different metal supporting contents, the left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

Comparative Example 1

[0076] A denitrification system for removing nitrate in water body, includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1. The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution. The denitrification catalyst 11 is an activated carbon AC. The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23. The counter electrode 22 adopts Pt sheet, the working electrode 21 adopts the catalyst Ni.sub.3S.sub.2—NF, and the preparation steps of the catalyst Ni.sub.3S.sub.2—NF are as follows:

[0077] (1) a nickel mesh is cut to have a size of 2.5×2.5 cm, which is first ultrasonic cleaned with 30 ml of acetone for 10 min, and then ultrasonic cleaned with 30 ml of 3 M hydrochloric acid for 10 min, and finally washed with ethanol and deionized w Tater for 3 times respectively;

[0078] (2) the cleaned nickel mesh in step (1) is added to 20 ml of 0.15M thiourea solution and transferred to a reactor, and kept airtight for 5 h at 150° C.;

[0079] (3) Ni.sub.3S.sub.2—NF is obtained by washing the material obtained in step (2) three times with ethanol and vacuum drying at room temperature.

[0080] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution, the concentration of sodium nitrate in the electrolyte solution is 100 mg:N/L, and the concentration of sodium sulfate is 0.1 M, and 1 g of AC is suspended in the electrolyte solution, and the electrochemical workstation CHI760D electrically connected to the three-electrode system is started to perform denitrification reaction for 5 h, the denitrification effect is shown in FIG. 5, wherein, the abscissa of FIG. 5 shows the denitrification catalyst with different metal supporting contents, the left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

[0081] By comparing the embodiments 1-3 with the comparative example 1, it can be seen that the activated carbon PdCu-AC supported with metal palladium and copper has a better denitrification effect than the activated carbon AC when using as the denitrification catalyst. PdCu-AC can achieve the optimal denitrification effect when the metal supporting content of PdCu-AC is 5%. The optimal denitrification effect obtained under this supporting content is attributed to the highly dispersed metal active components on the support, thus having sufficient catalytic active sites.

Comparative Example 2

[0082] A denitrification system for removing nitrate in water body, includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1. The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution, and the denitrification catalyst 11 is an activated carbon PdCu-AC supported with metal palladium and copper, and the PdCu-AC is prepared by the method in embodiment 1. The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23, and the counter electrode 22 adopts Pt sheet, the working electrode 21 adopts graphite carbon.

[0083] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution, the concentration of sodium nitrate in the electrolyte solution is 100 mg-N/L, and the concentration of sodium sulfate is 0.1 M, and 1 g of denitrification catalyst, i.e., 5% PdCu-AC, is suspended in the electrolyte solution, and the electrochemical workstation CHI760D 3 electrically connected to the three-electrode system is started to perform denitrification reaction for 5 h, the denitrification effect is shown in FIG. 8, wherein, the abscissa of FIG. 8 shows different working electrodes, the left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

Comparative Example 3

[0084] A denitrification system for removing nitrate in water body, includes the electrolytic cell 1 and a three-electrode system inserted into the electrolytic cell 1. The electrolytic cell 1 contains electrolyte solution, and the denitrification catalyst 11 is dispersed and suspended in the electrolyte solution, and the denitrification catalyst 11 is an activated carbon PdCu-AC supported with metal palladium and copper, and the PdCu-AC is prepared by the method in embodiment 1. The three-electrode system includes the working electrode 21, the counter electrode 22 and the reference electrode 23, and the counter electrode 22 adopts Pt sheet, the working electrode 21 adopts nickel foam NF.

[0085] The above denitrification system is applied to the removal of nitrate in water, and the specific steps are as follows: 100 ml of solution containing sodium nitrate and sodium sulfate is used as electrolyte solution, the concentration of sodium nitrate in the electrolyte solution is 100 mg-N/L, and the concentration of sodium sulfate is 0.1 M, and 1 g of denitrification catalyst, i.e., 5% PdCu-AC, is suspended in the electrolyte solution, and the electrochemical workstation CHI760D 3 electrically connected to the three-electrode system is started to perform denitrification reaction for 5 h, the denitrification effect is shown in FIG. 8, wherein, the abscissa of FIG. 8 shows different working electrodes, the left ordinate is the proportion of reaction products, and the right ordinate is the nitrate removal rate.

[0086] By comparing the embodiment 1 with the comparative examples 1-2, the denitrification system can achieve the optimal denitrification effect when using Ni.sub.3S.sub.2—NF material instead of graphite carbon and NE as working electrode.

[0087] It can be understood that the above specific description of the invention is only used to illustrate the invention and is not limited to the technical solution described in the embodiment of the invention. Those of ordinary skill in the art should understand that the invention can still be modified or equivalently replaced in order to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the invention.