Red mud-based catalyst for catalytic combustion of biodiesel wastewater as well as preparation method and application of red mud-based catalyst
By using Fe2O3 in red mud as active components and inert components as support, combined with binder and treatment with different calcining temperatures, an efficient red mud-based catalyst was prepared, which solved the problems of high cost and poor activity of existing catalysts and achieved efficient catalytic combustion of biodiesel wastewater.
Patent Information
- Application Number
- CN202510104411.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-23
- Publication Date
- 2025-06-03
AI Technical Summary
The existing biodiesel wastewater catalytic combustion catalysts have high costs, poor activity and unfriendly environment.
Fe2O3 in red mud is used as the catalytic active substance, inert components in red mud are used as the support, and the mechanical strength of the catalyst is increased by adding a binder, and the catalyst is finally activated by different calcining temperatures.
A red mud-based catalyst with a high specific surface area and a developed mesoporous structure has a lower reduction temperature and higher catalytic activity, which can effectively reduce the chemical oxygen demand (COD) of biodiesel wastewater, and the COD removal rate reaches 100%.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a red mud-based catalyst for catalytic combustion of biodiesel wastewater, a preparation method thereof, and an application thereof. Background Art
[0002] A large amount of biodiesel wastewater is generated during the production process of biodiesel. It is reported that approximately 0.2 - 3 L of biodiesel wastewater is produced for every liter of biodiesel produced. The global biodiesel production in 2022 was close to 52 million tons, which means that more than 10.4 million tons of biodiesel wastewater will be generated. Biodiesel wastewater is characterized by complex composition, dark color, and strong odor. A large amount of organic substances such as alcohols, organic acids, and esters contained in it result in its chemical oxygen demand (COD) reaching tens of thousands to hundreds of thousands of mg / L. Therefore, the efficient treatment of biodiesel wastewater faces great challenges.
[0003] The main organic substances in biodiesel wastewater belong to volatile organic compounds (VOCs), which turn into VOCs gas after heating and vaporization. Currently, the catalytic combustion technology is an effective method for treating high-concentration organic waste gas, with advantages such as a lower combustion temperature, high treatment efficiency, and no secondary pollution. Moreover, the heat generated by combustion can also be utilized for waste heat recovery. The design and preparation of high-performance catalysts are the key to this technology. Compared with noble metals and other non-noble metal oxides, Fe 2 O 3 is more abundant in resources, has a lower price, and is very friendly to the environment. It shows good catalytic activity and chemical stability in catalytic combustion applications. Solid waste red mud (RM) is a by-product in the aluminum industry during the production of alumina by the Bayer process, sintering process, or combined process. It contains a large amount of Fe 2 O 3 . As of 2023, the global stockpile of red mud exceeds 4 billion tons and continues to grow at an annual increment of 120 million tons. The design and development of a catalyst for catalytic combustion of biodiesel wastewater using solid waste red mud (RM) can not only realize the value addition of solid waste but also save a large amount of raw materials required for catalyst preparation, which not only protects the environment but also greatly reduces the preparation cost of the catalyst. Summary of the Invention
[0004] Regarding the catalysts for catalytic combustion of biodiesel wastewater in the prior art, there are generally problems such as high catalyst cost, poor activity, and environmental unfriendliness. The purpose of the present invention is to provide a red mud-based catalyst for catalytic combustion of biodiesel wastewater, a preparation method thereof, and an application thereof. The catalyst of the present invention mainly uses Fe 2 O 3 in red mud as the catalytically active substance, uses the inert components in red mud as the carrier, and the catalyst obtains a certain mechanical strength by adding a binder.
[0005] The technical solution adopted by the present invention is as follows:
[0006] A preparation method of a red mud-based catalyst for catalytic combustion of biodiesel wastewater, comprising the following steps:
[0007] S1: Mix the dried kaolin and the dried red mud in a mass ratio of 1-4:100 to obtain a mixed powder A.
[0008] S2: Add deionized water to the mixed powder A and stir evenly. Add the obtained mixture B into an extrusion machine to extrude into a long strip C;
[0009] S3: Dry the aged long strip C in the air, cut the dried strip into short strips, and calcine the short strips in the air to obtain a catalyst for catalytic combustion of biodiesel wastewater.
[0010] Further, in step S1, the mass ratio of the kaolin to the red mud is 2-3:1.
[0011] Further, the main components of the dried red mud include Fe 2 O 3 、Al 2 O 3 、SiO 2 、Na 2 O and TiO 2 , and by weight percentage, their proportions are 35-42%, 20-25%, 14-16%, 12-15% and 3-5% respectively, and the balance is other impurities.
[0012] Further, in step S2, the mass ratio of deionized water to the mixed powder A is 2-4:10.
[0013] Further, the diameter of the short strip in step S3 is 1-3 mm, and the length is 2-3 mm.
[0014] Further, in step S3, the calcination temperature is 300-600 °C, and the calcination time is 2-8 h.
[0015] Further, in step S3, the calcination temperature is 350 °C ± 50 °C, and the calcination time is 4-6 h.
[0016] The application of the catalyst described in the present invention in the catalytic combustion reaction of biodiesel wastewater uses a fixed-bed flow reactor for the catalytic combustion reaction. The reactor consists of two upper and lower sections. The upper section is the preheating section, and the lower section is the catalytic combustion section. Silicon carbide particles are filled in the preheating section, and the catalyst is filled in the catalytic combustion section. Air and biodiesel wastewater are first introduced into the preheating section for rapid heating to vaporize the wastewater, and the resulting raw material mixture enters the catalytic combustion section for the catalytic combustion reaction. The temperature of the catalytic combustion reaction is 300-350 °C.
[0017] Compared with the prior art, the beneficial effects achieved by the present invention are:
[0018] 1) The catalyst for catalytic combustion of biodiesel wastewater provided by the present invention is based on Fe 2 O 3 as the active component, and makes technological innovations in response to the problems of high cost, poor activity, and environmental unfriendliness of current catalytic combustion catalysts. The present invention starts from solid waste red mud (RM), through the composition and properties of red mud, and uses Fe 2 O 3 in red mud as the main active component, and uses the inert components in red mud as the carrier. Then, a binder is added to make the catalyst obtain a certain mechanical strength. Finally, the catalyst is activated by different calcination temperatures to form a red mud-based catalyst. When the calcination temperature of the catalyst does not exceed 400 °C, the red mud-based catalyst exhibits a high specific surface area of more than 60 m 2 / g and a developed mesoporous structure, which is beneficial to adsorption and diffusion. At the same time, most of the Fe 2 O 3 in the catalyst exists in an amorphous form and appears in large quantities on the catalyst surface. In addition, α-Fe 2 O 3 in the catalyst has a higher dispersion.
[0019] 2) The catalyst for catalytic combustion of biodiesel wastewater provided by the present invention has a lower reduction temperature compared with the catalyst prepared by using pure α-Fe 2 O 3 to replace red mud. The catalyst with a calcination temperature of 350 °C can well reduce the biodiesel wastewater with a chemical oxygen demand (COD) of 109159 mg / L to 0 mg / L at 320 °C, and the COD removal rate reaches 100%. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 It is the X-ray diffraction pattern of the catalysts of Examples 1-10 and Comparative Example 1 of the present invention.
[0021] Figure 2It is the X-ray photoelectron spectroscopy diagram of the catalysts of Examples 1-10, Comparative Example 1 and Comparative Example 2 of the present invention.
[0022] Figure 3 It is the H of Example 2 and Comparative Example 2 of the present invention 2 Temperature-programmed reduction diagram.
[0023] Figure 4 It is the performance diagram of the catalyst for catalytic combustion of biodiesel wastewater and the mechanical strength of the catalyst at different calcination temperatures.
[0024] Figure 5 It is the performance diagram of the catalysts of Example 2, Comparative Example 1 and Comparative Example 2 of the present invention for catalytic combustion of biodiesel wastewater and the mechanical strength of the catalyst. Detailed implementation manners
[0025] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in combination with specific examples and comparative examples.
[0026] The red mud used in the present invention comes from Xinfa Group Co., Ltd. The main components after drying include Fe 2 O 3 , Al 2 O 3 , SiO 2 , Na 2 O and TiO 2 . By weight percentage, their proportions are 39.66 wt%, 23.88 wt%, 15.73 wt%, 14.05 wt% and 4.55 wt% respectively, and the balance is other impurities.
[0027] Example 1
[0028] This example provides a method for preparing a catalyst for catalytic combustion of biodiesel wastewater. The specific preparation steps are as follows:
[0029] S1: Add 2 g of kaolin dried at 120 °C for 4 h to 100 g of red mud dried at 120 °C for 4 h and mix evenly to obtain a mixed powder A.
[0030] S2: Add 37.74 g of deionized water to the mixed powder A and stir evenly to obtain a mixture B.
[0031] S3: Add the mixture B to an extruder to extrude a long strip C with a diameter of 2 mm.
[0032] S4: Dry the aged long strip C in air at a drying temperature of 120 °C for 4 h. Cut the dried strip into short strips with a length of 2 - 3 mm. Calcinate the short strips in air at a calcination temperature of 300 °C for 6 h to finally obtain a catalyst for catalytic combustion of biodiesel wastewater, denoted as RM300. The properties of the catalyst are shown in Table 1.
[0033] The X-ray diffraction patterns of different catalysts are shown in Figure 1 , and it can be seen from the XRD results of catalyst RM1000 in Example 9 that most of the Fe 2 O 3 in catalyst RM300 exists in an amorphous form.
[0034] The X-ray photoelectron spectroscopy patterns of different catalysts are shown in Figure 2 , and it can be seen from the results of catalyst RM1000 in Example 9 that a large amount of Fe 2 O 3 appears on the surface of the catalyst, indicating that α-Fe 2 O 3 in the catalyst has a high dispersion.
[0035] Example 2
[0036] Repeat the preparation steps of the catalyst in Example 1, with the only difference being that "the calcination temperature in step S4 is replaced by 350 °C and the calcination time remains 6 h unchanged", and the other conditions remain the same. Finally, obtain a catalyst for catalytic combustion of biodiesel wastewater, denoted as RM350. The properties of the catalyst are shown in Table 1. See Figure 1 , and it can be seen from the results of catalyst RM1000 in Example 9 that most of the Fe 2 O 3 in catalyst RM350 exists in an amorphous form. See Figure 2 , and it can be seen from the results of catalyst RM1000 in Example 9 that a large amount of Fe 2 O 3 appears on the surface of the catalyst, indicating that α-Fe 2 O 3 in the catalyst has a high dispersion. See Figure 3 , and it can be seen that, compared with the catalyst Fe 2 O 3 -350 in Comparative Example 1, catalyst RM350 has a lower reduction temperature, indicating that RM350 has better catalytic reducibility.
[0037] Subject the catalyst to H 2The process of temperature-programmed reduction test is as follows: Hydrogen temperature-programmed reduction (H2-TPR) is carried out using an AutoChem II 2920 device produced by Micromeritics in the United States. Weigh about 150 mg of the catalyst sample and place it in the reaction tube. Under the condition of an Ar gas flow (30 mL / min), it is heated from room temperature to 120 °C at a heating rate of 10 °C / min for 60 min of drying pretreatment and then cooled to 50 °C. Then, 10% H 2 / 90% Ar mixed gas (50 mL / min) is introduced for 0.5 h. After the baseline is stabilized, it is heated to 800 °C at a heating rate of 10 °C / min under the atmosphere of 10% H 2 / 90% Ar (30 mL / min), and the TCD detection signal is measured.
[0038] Example 3
[0039] The preparation steps of the catalyst in Example 3 are repeated as in Example 1, with the only difference being that "the calcination temperature in step S4 is replaced by 400 °C and the calcination time remains 6 h unchanged", and the other conditions remain the same. Finally, a catalyst for catalytic combustion of biodiesel wastewater is obtained, denoted as RM400. The properties of the catalyst are shown in Table 1. See Figure 1 , compared with the results of the catalyst RM1000 in Example 9, it can be seen that most of the Fe 2 O 3 in the catalyst RM400 exists in an amorphous form. See Figure 2 , compared with the results of the catalyst RM1000 in Example 9, it can be seen that a large amount of Fe 2 O 3 appears on the surface of the catalyst, indicating that α-Fe 2 O 3 in the catalyst has a high dispersion degree.
[0040] Example 4
[0041] The preparation steps of the catalyst in Example 4 are repeated as in Example 1, with the only difference being that "the calcination temperature in step S4 is replaced by 500 °C and the calcination time remains 6 h unchanged", and the other conditions remain the same. Finally, a catalyst for catalytic combustion of biodiesel wastewater is obtained, denoted as RM500. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0042] Example 5
[0043] The preparation steps of the catalyst in Example 5 are repeated as in Example 1, with the only difference being that "the calcination temperature in step S4 is replaced by 600 °C and the calcination time remains 6 h unchanged", and the other conditions remain the same. Finally, a catalyst for catalytic combustion of biodiesel wastewater is obtained, denoted as RM600. The properties of the catalyst are shown in Table 1, Figure 1 andFigure 2 .
[0044] Example 6
[0045] The preparation steps of the catalyst in Example 6 were repeated as in Example 1, except that "the calcination temperature in step S4 was replaced with 700 °C and the calcination time remained unchanged at 6 h", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM700. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0046] Example 7
[0047] The preparation steps of the catalyst in Example 7 were repeated as in Example 1, except that "the calcination temperature in step S4 was replaced with 800 °C and the calcination time remained unchanged at 6 h", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM800. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0048] Example 8
[0049] The preparation steps of the catalyst in Example 8 were repeated as in Example 1, except that "the calcination temperature in step S4 was replaced with 350 °C and the calcination time remained unchanged at 6 h", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM900. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0050] Example 9
[0051] The preparation steps of the catalyst in Example 9 were repeated as in Example 1, except that "the calcination temperature in step S4 was replaced with 1000 °C and the calcination time remained unchanged at 6 h", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM1000. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0052] Example 10
[0053] The preparation steps of the catalyst in Example 10 were repeated as in Example 1, except that "the calcination temperature in step S4 was replaced with 1100 °C and the calcination time remained unchanged at 6 h", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM1100. The properties of the catalyst are shown in Table 1, Figure 1 and Figure 2 .
[0054] Example 11
[0055] Example 11 The preparation steps of the catalyst were repeated as in Example 1, except that "calcination was not carried out in step S4", and the other conditions remained unchanged. Finally, a catalyst for catalytic combustion of biodiesel wastewater was obtained, denoted as RM120. The properties of the catalyst are shown in Table 1. See Figure 1 , compared with the results of the catalyst RM1000 in Example 9, it can be seen that the Fe in RM120 2 O 3 mostly exists in an amorphous form. Comparing the catalysts in Examples 1-10, it can be seen that only Al(OH) exists in RM120 3 , indicating that the Al(OH) in RM120 3 will decompose after calcination. In addition, the water in the catalyst after calcination decreases, and both will lead to an increase in the specific surface area of the catalyst.
[0056] Comparative Example 1
[0057] This example provides a method for preparing a catalyst for catalytic combustion of biodiesel wastewater. The specific preparation steps are as follows:
[0058] S1: Add 2 g of kaolin dried at 120 °C for 4 h to 100 g of pure α-Fe 2 O 3 and mix evenly to obtain a mixed powder A.
[0059] S2: Add 37.74 g of deionized water to the mixed powder A and stir evenly to obtain a mixture B.
[0060] S3: Add the mixture B to an extruder to extrude a long strip C with a diameter of 2 mm.
[0061] S4: Dry the aged long strip C in air at a drying temperature of 120 °C for 4 h. Cut the dried strip into short strips with a length of 2-3 mm, and calcine the short strips in air at a calcination temperature of 350 °C for 6 h with a heating rate of 5 °C / min. Finally, a catalyst for catalytic combustion of biodiesel wastewater is obtained, denoted as Fe 2 O 3 -350. The properties of the catalyst are shown in Table 1. See Figure 2 , compared with the results of the catalyst RM1000 in Example 9, it can be seen that the Fe in Fe 2 O 3 -350 2 O 3 appears in large quantities on the surface of the catalyst, indicating that the α-Fe in the catalyst 2 O 3 has a high dispersion. See Figure 3, it can be seen that the reduction temperature of the catalyst is higher than that of RM350 in Example 2, which indicates that the catalytic reducibility of Fe 2 O 3 -350 is poor.
[0062] The test result data of the specific surface area properties of the catalysts in Examples 1-10 and Comparative Examples 1-2 of the present invention are summarized in Table 1. The X-ray diffraction patterns of the catalysts in Examples 1 to 10 and Comparative Example 1 of the present invention are as Figure 1 shown. The X-ray photoelectron spectroscopy patterns of the catalysts in Examples 1 to 10, Comparative Example 1 and Comparative Example 2 of the present invention are as Figure 2 shown.
[0063] Table 1
[0064]
[0065]
[0066] Catalytic combustion performance test:
[0067] The catalytic combustion reaction was carried out using a fixed-bed flow reactor. The reactor consists of two upper and lower sections, where the upper section is the preheating section and the lower section is the catalytic combustion section. About 70 g of silicon carbide (SiC) and 20 g of the catalyst were respectively loaded into the preheating section and the catalytic combustion section to investigate their catalytic combustion activity for biodiesel wastewater. Air and biodiesel wastewater were first introduced into the preheating section for rapid heating to vaporize the wastewater, and the obtained raw material mixture gas entered the catalytic combustion section for catalytic combustion reaction, where the air flow rate was 800 mL / min, the wastewater flow rate was 15 g / h, and the temperatures of the preheating section and the catalytic combustion section were both 320 °C.
[0068] The COD of the biodiesel wastewater was 114500 ± 7600 mg / L, and its main components were esters and alcohols. The esters mainly included methyl octanoate, methyl valerate, ethyl propylene carbonate and methyl hexanoate, and the alcohols mainly included glycerol and 3-methoxy-1,2-propanediol.
[0069] Mechanical strength test of the catalyst:
[0070] According to the Chinese standard GB / T30202.3-2013, the catalyst particles with a diameter of 2 mm and a length of 2.2 ± 0.1 mm were radially extruded to obtain the mechanical strength of the catalyst. The mechanical strength was expressed by the crushing strength (P = F / L, P (N / cm) was the radial crushing strength, F was the pressure value (N), and L was the catalyst length (cm)).
[0071] According to the above catalytic combustion performance test process, at the reaction temperature of 320 °C for the catalyst performance test, the mechanical strength of the catalysts prepared at different calcination temperatures of the present invention, i.e., the catalysts of Examples 1-10, and the performance test data of catalytic combustion of biodiesel wastewater are summarized in Figure 4 , Figure 4 . The abscissa recorded in Figure 4 is the calcination temperature during the preparation of the catalyst. The calcination temperatures of 300-1100 °C on the abscissa correspond to the catalysts of Examples 1-10 respectively. It can be seen from Figure 4 that after the biodiesel wastewater is catalytically combusted by the catalyst in Example 1, the COD is reduced to 5.52 mg / L, and the COD removal rate is 99.995%. After the biodiesel wastewater is catalytically combusted by the catalyst in Example 2, the COD is reduced to 0 mg / L, and the COD removal rate is 100%. After the biodiesel wastewater is catalytically combusted by the catalyst in Example 3, the COD is reduced to 5.02 mg / L, and the COD removal rate is 99.996%. It can be known from
[0072] that according to the above catalytic combustion performance test process and the mechanical strength test process of the catalyst, at the reaction temperature of 320 °C for the catalyst performance test, the performance of catalytic combustion of biodiesel wastewater and the results of the catalyst mechanical strength diagram of the catalysts of Example 2, Example 11 and Comparative Example 1 of the present invention are summarized in Figure 5 . Among them, after the biodiesel wastewater is catalytically combusted by the catalyst in Example 2, the COD is reduced to 0 mg / L, and the COD removal rate is 100%. After the biodiesel wastewater is catalytically combusted by the catalyst in Example 11, the COD is reduced to 10.03 mg / L, and the COD removal rate is 99.991%. After the biodiesel wastewater is catalytically combusted by the catalyst in Comparative Example 1, the COD is reduced to 10716.67 mg / L, and the COD removal rate is 90.703%. It can be known from Figure 5 that the catalyst prepared in Example 11 for catalytic combustion of biodiesel wastewater has excellent catalytic activity. Combining Figure 2 , Figure 3 and Figure 5 it can be known that compared with the catalyst in Example 2, although the surface of the catalyst prepared in Comparative Example 2 for catalytic combustion of biodiesel wastewater contains a large amount of Fe 2 O 3 , its catalytic activity is poor due to its lower specific surface area and poor catalytic reducibility.
Claims
1. A method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater, characterized in that The steps include: S1: mixing dried kaolin and dried red mud in a mass ratio of 1-4:100 to obtain mixed powder A; S2: adding deionized water to the mixed powder A and stirring evenly, adding the obtained mixture B into an extruder for extrusion to obtain a long strip C; S3: drying the aged long strip C in air, cutting the dried strip into short strips, calcining the short strips in air to obtain a catalyst for catalytic combustion of biodiesel wastewater.
2. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 1, characterized in that In step S1, the mass ratio of kaolin to red mud is 2-3:
1.
3. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 1, characterized in that The main components of the dried red mud include Fe2O3, Al2O3, SiO2, Na2O and TiO2, which account for 35-42%, 20-25%, 14-16%, 12-15% and 3-5% respectively in terms of weight percentage, and the remainder is other impurities.
4. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 1, characterized in that In step S2, the mass ratio of deionized water to mixed powder A is 2-4:
10.
5. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 1, characterized in that In step S3, the diameter of the short strip is 1-3 mm and the length is 2-3 mm.
6. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 1, characterized in that In step S3, the calcination temperature is 300-600° C., and the calcination time is 2-8 hours.
7. The method for preparing a red mud-based catalyst for catalytic combustion of biodiesel wastewater according to claim 6, characterized in that In step S3, the calcination temperature is 350°C ± 50°C, and the calcination time is 4-6h.
8. A red mud-based catalyst for catalytic combustion of biodiesel wastewater prepared by the method of any one of claims 1 to 7.
9. Use of the catalyst as claimed in claim 8 in the catalytic combustion reaction of biodiesel wastewater.
10. The use according to claim 9, characterized in that A fixed bed flow reactor is used for catalytic combustion reaction. The reactor consists of two sections, the upper section is a preheating section, and the lower section is a catalytic combustion section. The preheating section is filled with silicon carbide particles, and the catalytic combustion section is filled with the catalyst. Air and biodiesel wastewater are first introduced into the preheating section for rapid heating to vaporize the wastewater, and the resulting raw material mixed gas enters the catalytic combustion section for catalytic combustion reaction. The temperature of the catalytic combustion reaction is 300-350°C.