Method for degrading high concentration organic waste water by cold plasma under catalyst action

Abstract

This invention relates to the field of wastewater treatment catalyst technology, and particularly to a method for preparing and applying a CeO2-LaCoO3 / Al2O3 catalyst. The method involves mixing La(NO3)2•6H2O, Co(NO3)3•6H2O, and anhydrous citric acid, filtering the mixture, and then calcining it in air to obtain LaCoO3. LaCoO3 and Al2O3 are then mixed, water is added, the mixture is stirred and ultrasonically vibrated, filtered, and dried to obtain a mixed powder of LaCoO3 and Al2O3. CeO2 is then mixed with the mixed powder of LaCoO3 and Al2O3 and calcined to obtain the CeO2-LaCoO3 / Al2O3 catalyst. Under the catalytic action of the catalyst described in this invention, high-concentration papermaking organic wastewater is degraded with a degradation efficiency of up to 76%, which is at least 10% higher than the degradation efficiency achieved using LaCoO3 / Al2O3.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment catalyst technology, and in particular to a method for preparing a CeO2-LaCoO3 / Al2O3 catalyst and its application. Background Technology

[0002] Paper mill wastewater is a type of industrial wastewater that is difficult to treat. It contains a large amount of organic matter, and the chemical oxygen demand (COD) concentration is above 5000 mg / L. Traditional treatment methods and general oxidation methods can only reduce the COD of the effluent to a certain extent, which is not ideal. Therefore, it is necessary to explore new technologies and methods to fully degrade this type of wastewater.

[0003] Cold plasma catalytic reaction technology is a new technology that integrates physics, chemistry, biology, and environmental ecology. Under normal temperature conditions, when ionized gases have equal positive and negative charges, they are classified as cold plasma. Its composition includes ions, electrons, free radicals, etc. In particular, it produces a large number of ozone molecules when in contact with air, thus exhibiting overall electrical neutrality. However, it readily reacts with other substances, is relatively reactive, and reacts rapidly.

[0004] In the process of cold plasma treatment of wastewater, the addition of different types of catalysts can significantly affect the removal efficiency of target pollutants. Summary of the Invention

[0005] In order to improve the degradation effect of cold plasma on high-concentration papermaking wastewater, this invention provides a method for preparing CeO2-LaCoO3 / Al2O3 catalyst and its application.

[0006] This invention is achieved through the following technical solution: a method for preparing a CeO2-LaCoO3 / Al2O3 catalyst, comprising the following steps:

[0007] 1) Dissolve La(NO3)3·6H2O and Co(NO3)2·6H2O in deionized water and stir to mix; slowly add anhydrous citric acid to the mixed solution, stir to mix, and filter; then calcine in air at 600-700℃ for 2-5 hours to obtain LaCoO3, grind it into powder and set aside for use;

[0008] 2) Weigh Al2O3, calcine it at 600-700℃ for 2 hours, and then grind it into Al2O3 particles; mix LaCoO3 and Al2O3, add water, stir and sonicate, then filter and dry to obtain a mixed powder solid of LaCoO3 and Al2O3; mix CeO2 with the mixed powder solid of LaCoO3 and Al2O3, and calcine it at 600-850℃ for 2-5 hours to obtain CeO2-LaCoO3 / Al2O3 catalyst.

[0009] As a further improvement to the preparation method of the present invention, the molar ratio of La(NO3)3·6H2O and Co(NO3)2·6H2O is 1:1-2.

[0010] As a further improvement to the preparation method of the present invention, the molar ratio of the anhydrous citric acid to the total molar of La(NO3)3·6H2O and Co(NO3)2·6H2O is 1-5:1.

[0011] As a further improvement to the preparation method of the present invention, the mass ratio of LaCoO3 to Al2O3 is 1:3-4.

[0012] As a further improvement to the preparation method of the present invention, the amount of CeO2 added is 5-8 wt% of the total mass of the mixed powder of LaCoO3 and Al2O3.

[0013] The present invention further provides the application of the CeO2-LaCoO3 / Al2O3 catalyst prepared by the above-mentioned method in the catalytic oxidation and degradation of wastewater.

[0014] As a further improvement to the application technology solution of the present invention, the wastewater is papermaking wastewater.

[0015] The preparation method and application of the CeO2-LaCoO3 / Al2O3 catalyst provided by this invention have the following advantages compared with the prior art:

[0016] The physical properties of the synthesized ozone catalysts LaCoO3 / Al2O3 and CeO2-LaCoO3 / Al2O3 were compared and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray electron spectroscopy (XPS). Furthermore, the degradation of papermaking wastewater before and after treatment was characterized using three-dimensional fluorescence spectroscopy, and the COD at different reaction times was measured. These results demonstrate that cold plasma significantly enhances the degradation of high-concentration papermaking wastewater under the catalytic action of the CeO2-LaCoO3 / Al2O3 catalyst. Under the catalytic action of CeO2-LaCoO3 / Al2O3, the degradation efficiency of high-concentration papermaking organic wastewater reached 76%, which is at least 10% higher than that achieved using LaCoO3 / Al2O3. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 SEM images of the CeO2-LaCoO3 / Al2O3 catalyst prepared for this example are shown. The images clearly show small particles of rare earth oxide CeO2 distributed as dopants on the surface of LaCoO3 / Al2O3. CeO2 has a high oxygen vacancy content, enabling it to effectively adsorb ozone and decompose it at these vacancy sites to produce active substances. LaCoO3 / Al2O3 uses Al2O3 as a support to load LaCoO3, which exhibits broad-spectrum low-temperature catalytic activity, significantly improving the oxidation efficiency of ozone on organic matter. By loading a small amount of rare earth oxide CeO2 onto the surface of the composite binary catalyst LaCoO3 / Al2O3, cold plasma can not only ionize humid air to generate more ozone molecules under the excitation of CeO2, but also accelerate the dissociation of ozone molecules, thereby efficiently promoting the degradation of organic matter by the oxidation catalytic system.

[0020] Figure 2 The XRD diffraction patterns of LaCoO3 / Al2O3 prepared in Comparative Example 1 and CeO2-LaCoO3 / Al2O3 prepared in Example 1 are shown. As can be seen from the figures, the characteristic peaks of LaCoO3 appear at 23°, 33°, 40°, 47°, and 59°, corresponding to the (012), (104), (202), (024), and (018) crystal planes, which are very consistent with the standard diffraction pattern of LaCoO3 (JCPDS48-0123). Compared with LaCoO3 / Al2O3, the XRD diffraction pattern of CeO2-LaCoO3 / Al2O3 shows the addition of characteristic peaks of CeO2. The characteristic peaks of CeO2 appear at angles of 33°, 47°, 56°, 59°, 69°, and 79°, corresponding to the (111), (200), (220), (311), (222), and (331) crystal planes. This matches the standard spectrum of CeO2 (JCPDS 89-8436) very well, proving that CeO2 has been successfully loaded onto LaCoO3 / Al2O3.

[0021] Figure 3 The three-dimensional fluorescence spectra of the LaCoO3 / Al2O3 catalyst prepared in Comparative Example 1 and the CeO2-LaCoO3 / Al2O3 catalyst prepared in Example 1 before and after degradation of papermaking wastewater are shown. Figure 3 (a)- Figure 3(d) It can be seen that the fluorescence peak of the papermaking wastewater raw liquid mainly appears in the V region, which represents humic acids. This indicates that the wastewater mainly contains humic acid organic matter that is difficult to degrade. Moreover, under the action of different catalysts, the fluorescence peak in the spectrum is constantly changing, and the overall fluorescence intensity is continuously decreasing. Figure 3 (b)~ Figure 3 (e) are three-dimensional fluorescence contour plots for ozone catalysis alone, a binary catalyst with 30% LaCoO3 loading (LaCoO3 / Al2O3) at an addition of 0.5 g / L, and a ternary catalyst with 30% LaCoO3 loading and 5% CeO2 loading (CeO2-LaCoO3 / Al2O3) at additions of 0.5 g / L and 0.7 g / L, respectively, after 4 h of catalysis. Figure 3 (a) Figure 3 (b) and Figure 3 (c) The comparison shows that after catalytic treatment, the intensity of peak A of humic acid, which represents substances in the humic acid region, weakens, but peak B, which represents weak fulvic acid, also appears. Figure 3 (c) indicates that the intensity of peaks A and B decreases when the binary catalyst LaCoO3 / Al2O3 is added; Figure 3 (d) indicates that when CeO2 is added to form a ternary catalyst CeO2-LaCoO3 / Al2O3, peak A gradually disappears, indicating that the oxidation effect of CeO2 on humic acid is relatively obvious. When the amount of ternary catalyst added is 0.5 g / L, peak A basically disappears. When the amount added is increased to 0.7 g / L, peak A disappears completely. Figure 3 (e) indicates that a small amount of humic acid was converted into fulvic acid.

[0022] Figure 4 This section compares the degradation performance of different catalysts at different times. Figure 4 It can be seen that when both CeO2-LaCoO3 / Al2O3 and LaCoO3 / Al2O3 are added at a concentration of 0.5 g / L, the COD degradation rate of wastewater continuously increases over time. CeO2-LaCoO3 / Al2O3 achieves a COD degradation rate of 73.5% after 2 hours, then increases slowly, reaching a near-limit of 76% after 3 hours. LaCoO3 / Al2O3 achieves a COD degradation rate of 54.5% after 2 hours, increasing to 63.5% after 3 hours. Compared to CeO2-LaCoO3 / Al2O3 after 3 hours, LaCoO3 / Al2O3's COD degradation rate is more than 10% lower. Ozone oxidation alone achieves a COD degradation rate of 36.5% after 2 hours and 39.0% after 3 hours. Therefore, CeO2-LaCoO3 / Al2O3 exhibits a significant advantage in catalytic degradation.

[0023] Figure 5The effect of different dosages of the CeO2-LaCoO3 / Al2O3 catalyst prepared for this example on the degradation rate of papermaking wastewater after 2 hours was investigated. Figure 5 It can be seen that with the increase of the dosage, the COD degradation rate first increases sharply and then increases slowly. When the catalyst dosage increases from 0.1 g / L to 0.5 g / L, the COD degradation rate increases rapidly, reaching 73.5% at 0.5 g / L. However, with further increases in dosage, the increase in COD degradation rate becomes very slow, reaching 76.5% at 0.7 g / L. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0026] This invention provides a specific embodiment of a method for preparing a CeO2-LaCoO3 / Al2O3 catalyst, comprising the following steps:

[0027] 1) Dissolve La(NO3)3·6H2O and Co(NO3)2·6H2O in deionized water and stir to mix; slowly add anhydrous citric acid to the mixed solution, stir and react for 4 hours, filter; then calcine in air at 600-700℃ for 2-5 hours to obtain LaCoO3, grind it into powder with a particle size of 0.2-0.3 mm, and set aside for use;

[0028] 2) Weigh Al2O3 and calcine it at 600-700℃ for 2 hours, then grind it into Al2O3 particles with a particle size of 0.1-0.2 mm; mix LaCoO3 and Al2O3, add water, stir and sonicate, then filter and dry to obtain a mixed powder solid of LaCoO3 and Al2O3; mix CeO2 with the mixed powder solid of LaCoO3 and Al2O3 and calcine it at 600-850℃ for 2-5 hours to obtain CeO2-LaCoO3 / Al2O3 catalyst, and grind it into a mixed powder solid with a particle size of 0.2-0.3 mm.

[0029] Before mixing LaCoO3 and Al2O3, the present invention calcines Al2O3 to transform its loose amorphous structure into a slightly more regular crystalline structure.

[0030] In another embodiment of the present invention, the molar ratio of La(NO3)3·6H2O and Co(NO3)2·6H2O is 1:1-2.

[0031] In one embodiment of the present invention, the molar ratio of the anhydrous citric acid to the total molar of La(NO3)3·6H2O and Co(NO3)2·6H2O is 1-5:1.

[0032] In another embodiment of the present invention, the mass ratio of LaCoO3 to Al2O3 is 1:3-4.

[0033] In one embodiment of the present invention, the amount of CeO2 added is 5-8 wt% of the total mass of the mixed powder of LaCoO3 and Al2O3.

[0034] This invention also provides a method for preparing a CeO2-LaCoO3 / Al2O3 catalyst and its application in the catalytic oxidation and degradation of wastewater. Preferably, the wastewater is papermaking wastewater.

[0035] The specific embodiments of the present invention will be described in detail below.

[0036] The experimental reagents, instruments, equipment, and wastewater used in the various embodiments and comparative examples provided by this invention are as follows:

[0037] (1) Experimental reagents

[0038] γ-alumina, chemically pure, purchased from Zhongke New Materials Co., Ltd.; La(NO3)3·6H2O, chemically pure, purchased from Tianjin Guangfu Fine Chemical Research Institute; Co(NO3)2·6H2O, analytical grade, purchased from Tianjin Fuchen Chemical Reagent Factory; citric acid, analytical grade, purchased from Tianjin Kemio Chemical Reagent Co., Ltd.; cerium oxide, chemically pure, purchased from Shanghai Yaoge Alloy Materials Co., Ltd.

[0039] (2) Main instruments and equipment

[0040] Cold plasma generator, Hebei Haoyong Environmental Protection Technology Co., Ltd.; X-ray diffractometer TD-3700, Dandong Tongda Technology Co., Ltd.; Scanning electron microscope KYKY-3700, Beijing Zhongke Keyi Technology Development Co., Ltd.; FLS1000 three-dimensional fluorescence spectrometer, made in the UK; HPGS1600X tubular high-temperature furnace, Zhengzhou Kejia Electric Furnace Co., Ltd.

[0041] (3) Wastewater sources

[0042] The initial COD value of the raw wastewater from Guansen Paper Industry Co., Ltd. in Datong City, Shanxi Province, is 5500 mg / L.

[0043] Example 1

[0044] A method for preparing a CeO2-LaCoO3 / Al2O3 catalyst includes the following steps:

[0045] 1) Dissolve 3.464g of La(NO3)3·6H2O and 2.842g of Co(NO3)2·6H2O in deionized water, slowly add 9.216g of anhydrous citric acid to the mixed solution, stir and mix at 80℃ for 4h, filter; then calcine in air at 700℃ for 2h to obtain LaCoO3, and grind it into powder particles with a particle size of 0.2-0.3mm;

[0046] 2) Weigh 8.256g of γ-Al2O3, and then weigh 30% of the total mass of γ-Al2O3, LaCoO3. Calcinate at 600℃ for 2h. Mix LaCoO3 and Al2O3, add water, stir and sonicate, then filter and dry to obtain LaCoO3 / Al2O3. Remove and grind into a mixed powder solid with a particle size of 0.1-0.2mm. Weigh 5wt% of the total mass of LaCoO3 / Al2O3, mix CeO2 with LaCoO3 / Al2O3, and then calcine at 700℃ for 2h to obtain the ternary catalyst CeO2-LaCoO3 / Al2O3 supported on CeO2. Remove and grind into a mixed powder solid with a particle size of 0.2-0.3mm.

[0047] Comparative Example 1

[0048] A method for preparing a LaCoO3 / Al2O3 catalyst includes the following steps:

[0049] 1) Dissolve 3.464g of La(NO3)3·6H2O and 2.842g of Co(NO3)2·6H2O in deionized water, slowly add 9.216g of anhydrous citric acid to the mixed solution, stir and mix at 80℃ for 4h, filter; then calcine in air at 700℃ for 2h to obtain LaCoO3, and grind it into powder particles with a particle size of 0.2-0.3mm;

[0050] 2) Weigh 8.256g of γ-Al2O3, and weigh LaCoO3, which accounts for 30% of the total mass of γ-Al2O3. Place them at 600℃ for 2h, mix LaCoO3 and Al2O3, add water, stir and ultrasonically vibrate, then filter, dry, and place at 700℃ for 2h to obtain LaCoO3 / Al2O3. Take it out and grind it into a mixed powder solid with a particle size of 0.1-0.2mm.

[0051] Experimental Example 1

[0052] 0.5g of the prepared LaCoO3 / Al2O3 and 0.5g of the prepared CeO2-LaCoO3 / Al2O3 were weighed and placed in Ф50 plastic columnar tubes, respectively. Then, 1L of raw papermaking wastewater (the wastewater in all three tubes was identical) was added to each of the three tubes. The initial COD of the wastewater was as high as 5500mg / L. One tube contained no catalyst, while the other two tubes contained the corresponding catalysts, each added at a rate of 0.5g / L. A cold plasma generator was then turned on, and the plasma was introduced at a rate of 1L / s. Samples were removed every 30 minutes to measure COD and calculate the degradation rate. The reaction time was 2 hours. Specific results are shown in Table 1 below. Figure 4 As shown.

[0053] Table 1 Comparison of the effects of adding different catalysts

[0054] Catalyst types COD (mg / L) after 2 hours COD degradation rate / % <![CDATA[CeO2-LaCoO3 / Al2O3]]> 1475.5 73.5 <![CDATA[LaCoO3 / Al2O3]]> 2502.5 54.5 Catalyst-free 3492.5 36.5

[0055] As shown in Table 1, CeO2-LaCoO3 / Al2O3 prepared by the method described in this invention exhibits the highest ozone oxidation degradation effect.

[0056] Experimental Example 2

[0057] 0.7 g of the prepared LaCoO3 / Al2O3 and 0.7 g of the prepared CeO2-LaCoO3 / Al2O3 were weighed and placed in Ф50 plastic columnar tubes, respectively. Then, 1 L of raw papermaking wastewater (the wastewater in all three tubes was identical) was added to each of the three tubes. The initial COD of the wastewater was as high as 5500 mg / L. One tube contained no catalyst, while the other two tubes contained the corresponding catalysts, each at a concentration of 0.7 g / L. A cold plasma generator was then turned on, and the plasma was introduced at a rate of 1 L / s. Samples were removed every 30 minutes and characterized using three-dimensional fluorescence spectroscopy (EEM). COD was measured simultaneously, and the degradation rate was calculated. The reaction time was 2 hours. Specific results are shown in Table 2 below.

[0058] Table 2 Comparison of the effects of adding different catalysts

[0059] Catalyst types COD (mg / L) COD degradation rate / % <![CDATA[CeO2-LaCoO3 / Al2O3]]> 1457.5 76.5 <![CDATA[LaCoO3 / Al2O3]]> 2376.0 56.8 Catalyst-free 3399.0 37.7

[0060] As shown in Table 2, when the amount of CeO2-LaCoO3 / Al2O3 added is 0.7 g / L, the COD degradation rate of ozone oxidation is about 3% higher than that when the amount added is 0.5 g / L.

[0061] This invention Figure 3In the study, the fluorescent emission regions are divided into five categories: aromatic protein I region, aromatic protein II region, fulvic acid region, soluble microbial metabolite region, and humic acid region. The corresponding excitation wavelengths and emission wavelengths are shown in Table 3 below.

[0062] Table 3. Organic species represented by the five fluorescent regions

[0063]

[0064] Experimental Example 3

[0065] Weigh out 0.1g, 0.2g, 0.3g, 0.4g, 0.5g, 0.6g, and 0.7g of CeO2-LaCoO3 / Al2O3 prepared in Example 1, and place them into Ф50 plastic columnar tubes. Then, add 1L of raw papermaking wastewater (catalyst addition amounts of 0.1g / L, 0.2g / L, 0.3g / L, 0.4g / L, 0.5g / L, 0.6g / L, and 0.7g / L, respectively) to each tube. The initial COD of the wastewater was as high as 5500mg / L. A cold plasma generator was then turned on, and the plasma was introduced at a rate of 1L / s. The COD was measured, and the degradation rate was calculated. When the catalyst addition amount was 0.7g / L, the degradation rate reached approximately the limit of 76.5% after 2 hours. See the detailed results below. Figure 5 .

[0066] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. The application of a CeO2-LaCoO3 / Al2O3 catalyst in the catalytic cold plasma oxidation degradation of wastewater, characterized in that, The preparation method of the CeO2-LaCoO3 / Al2O3 catalyst includes the following steps: 1) Dissolve La(NO3)3•6H2O and Co(NO3)2•6H2O in deionized water and stir to mix; slowly add anhydrous citric acid to the mixed solution, stir to mix, and filter; then calcine in air at 600-700℃ for 2-5 hours to obtain LaCoO3, grind it into powder and set aside for use; 2) Weigh Al2O3, calcine it at 600-700℃ for 2 hours, and then grind it into Al2O3 particles; mix LaCoO3 and Al2O3, add water, stir and sonicate, then filter and dry to obtain a mixed powder solid of LaCoO3 and Al2O3; mix CeO2 with the mixed powder solid of LaCoO3 and Al2O3, and calcine it at 600-850℃ for 2-5 hours to obtain CeO2-LaCoO3 / Al2O3 catalyst.

2. The application as described in claim 1, characterized in that, The molar ratio of La(NO3)3•6H2O and Co(NO3)2•6H2O is 1:1-2.

3. In the application as described in claim 1, the molar ratio of the anhydrous citric acid to the total molar of La(NO3)3•6H2O and Co(NO3)2•6H2O is 1-5:

1.

4. In the application described in claim 1, the mass ratio of LaCoO3 to Al2O3 is 1:3-4.

5. In the application as described in claim 1, the amount of CeO2 added is 5-8 wt% of the total mass of the mixed powder of LaCoO3 and Al2O3.

6. The application as described in claim 1, characterized in that, The wastewater is papermaking wastewater.

Images