Metal cation doped biochar material and application thereof in low-temperature SCR (Selective Catalytic Reduction) denitration

Abstract

The invention relates to a metal cation doped biochar material and application thereof in low-temperature SCR denitration, natural biomass is used as a raw material, biochar is prepared, oxidation treatment is performed, metal cation active components are doped, granulation and activation are performed to prepare the metal cation doped biochar material, and the metal cation doped biochar material is used for low-temperature SCR denitration and has high SCR denitration activity and catalytic stability.

Description

Technical Field:

[0001] The present invention belongs to the technical field of low-temperature SCR (Selective Catalytic Reduction) denitration, and specifically relates to a metal cation-doped biochar material and its application in low-temperature SCR denitration. Background Art:

[0002] In May 2019, five ministries and commissions including the Ministry of Ecology and Environment jointly issued the Opinions on Promoting the Implementation of Ultra-low Emissions in the Iron and Steel Industry, giving the NO x , x emission permit concentration for sintering flue gas in the iron and steel industry, and clearly stating that activated carbon (coke) and SCR denitration technology can be used for sintering flue gas denitration. At present, for low-temperature (usually 50-200°C) SCR denitration of iron and steel sintering flue gas, coal-based activated carbon is used. Under the "dual carbon" goal, activated carbon has the problem of reducing pollution but not reducing carbon emissions. Agricultural biomass such as straw can consume CO2 in the atmosphere through photosynthesis during the growth stage and is considered a carbon-neutral material. If biochar materials are prepared from agricultural biomass to replace coal-based activated carbon for low-temperature denitration of flue gas, it is expected to purify NO x while reducing CO2 emissions. Compared with single biochar denitration materials, metal cation-doped biochar is expected to achieve higher SCR denitration activity. However, so far, there are few reports on the application of metal cation-doped biochar materials in low-temperature SCR denitration. Summary of the Invention:

[0003] The present invention aims to provide a metal cation-doped biochar material and its application in low-temperature SCR denitration for low-temperature SCR denitration of NO in iron and steel sintering flue gas. The biochar material uses natural biomass as the main raw material, and through processes such as carbonization-oxidation-impregnation-granulation-drying-activation, certain mass ratios of manganese, samarium, and cerium elements are doped as active components to prepare a cation-doped biochar material with high mechanical strength, high activity, high stability, and low carbon emissions, which can achieve efficient SCR denitration under low-temperature (50-200°C) conditions.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A metal cation-doped biochar material is prepared by carbonizing-oxidizing-impregnating-granulating-drying-activating natural biomass; the mass ratio of raw materials is: biochar 50-90%, binder (coal tar) 10-40%, and the total mass percentage of manganese, samarium and cerium elements in the total mass of the catalyst is 5%-20%; the natural biomass includes agricultural biomass and forestry biomass, the agricultural biomass includes at least one of corn straw, tobacco straw, bagasse, etc., and the forestry biomass includes at least one of poplar branches, wood chips, etc.; the manganese salt includes at least one of manganese chloride, manganese nitrate, manganese sulfate, etc.; the cerium salt includes at least one of cerium chloride, cerium nitrate, cerium sulfate, etc.; the samarium salt includes at least one of samarium chloride, samarium nitrate, samarium acetate, etc.

[0006] The specific process of the preparation method of the metal cation-doped biochar material is as follows:

[0007] 1) Carbonization: Biomass powder passing through a 40-80 mesh sieve is heated to 500-800 °C at a rate of 5-15 °C / min in an anoxic atmosphere; the anoxic atmosphere is an O2 volume content of 2%-10%.

[0008] 2) Oxidation: The carbonized biochar material is crushed and passed through a 60-100 mesh sieve, and is treated in a water bath at 75-82 °C with 40-68 wt% nitric acid for 4-12 h, washed repeatedly with deionized water until neutral, and dried at 90-120 °C for 6-10 h to obtain an oxidized biochar material, which is used as a carrier.

[0009] 3) Washing: The carrier obtained in step 2) is washed with deionized water until neutral.

[0010] 4) Impregnation:

[0011] A certain proportion of manganese Salts, samarium salts and cerium salts is added to deionized water to form an aqueous solution. After stirring evenly, the material washed in step 3) is added, and impregnated under magnetic stirring for 3-4.5 h, where the total mass percentage of manganese, samarium and cerium in the total mass of the catalyst is 5%-20%, the mass of biochar + binder + doped metal elements = the total mass of the catalyst, and the molar ratios are Mn / (Mn+Sm+Ce) of 60%-90%, Sm / (Mn+Sm+Ce) of 5-20%, and Ce / (Mn+Sm+Ce) of 5-20%.

[0012] 5) Granulation: The material obtained after impregnation in step 4) is mixed evenly with the binder, and granulated under a pressure condition of 0.5-5 MPa to obtain a cylindrical sample with a diameter of 6-10 mm and a length of 5-12 mm.

[0013] 6) Drying: The sample obtained in step 5) is dried at 60-120 °C for 6-12 h.

[0014] 7) Activation: First, heat the sample obtained in step 6) from room temperature to 500 - 650 °C at a rate of 5 - 15 °C / min under a N2 atmosphere, then introduce H2O vapor with a moisture content of < 50% using N2 as the carrier gas, and activate for 30 - 90 min in this atmosphere. After activation, cool for 6 - 12 h and sieve through a 40 - 60 mesh sieve to obtain the metal cation-doped biochar material.

[0015] Application of the above metal cation-doped biochar material: Use the above metal cation-doped biochar material for SCR denitration, with the NH3 content being 100 - 700 ppm, the NO content being 100 - 700 ppm, the O2 content being 5 - 15%, and the volumetric space velocity being 400 - 30000 h -1 . It is used for SCR denitration of NO at 100 - 200 °C.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The metal cation-doped biochar material prepared by the present invention has the characteristics of high mechanical strength, low carbon emission, and high denitration efficiency at low temperature compared with commercial coal-based activated carbon catalysts (as shown in Table 1), meets the application requirements for the strength of carbon-based materials (≥420 N), and solves the problems of high CO2 emissions of current coal-based activated carbon and low denitration efficiency of single biochar-based materials.

[0018] Table 1 Comparison results of denitration performance and mechanical strength of carbon materials

[0019]

[0020] Denitration experiment conditions: Reaction temperature 100 °C, NO and NH3 concentrations 200 ppm, O2 content 5%, volumetric space velocity 2000 h -1 . Description of the drawings:

[0021] Figure 1 It is a comparison chart for the stability of SCR denitration.

[0022] Figure 2 It is a process flow chart for the preparation of the metal cation-doped biochar material of the present invention. Detailed implementation manners:

[0023] To better understand the content of the present invention, the following further illustrates the present invention in combination with the implementation manners. However, the examples given do not limit the protection scope of the present invention.

[0024] Example 1

[0025] (1) A metal cation-doped biochar material, with the raw material mass ratio as follows: 70% biochar and 30% coal tar. The preparation steps of the cation-doped biochar material are as follows:

[0026] 1) Carbonization: The corn straw biomass powder passed through a 80-mesh sieve is heated to 800 °C at a rate of 10 °C / min in an oxygen-deficient atmosphere to obtain the biochar raw material;

[0027] 2) Oxidation: The biomass char raw material is crushed and passed through a 60-mesh sieve, treated in a water bath at 80 °C with 68 wt% nitric acid for 4 h, repeatedly washed with deionized water until neutral, and dried at 90 °C for 10 h to obtain the oxygen-treated biochar material as the carrier;

[0028] 3) Washing: The carrier obtained in step 2) is washed with deionized water until neutral;

[0029] 4) Impregnation:

[0030] A certain proportion of manganese nitrate, samarium nitrate, and cerium nitrate are added to deionized water to form an aqueous solution. After stirring evenly, the material washed to neutral in step 3) is added, and impregnated for 4 h under magnetic stirring. The total mass percentage of manganese, samarium, and cerium in the total mass of the catalyst is 15%. The mass of biochar + binder + doped metal elements = the total mass of the catalyst, and the molar ratios are 70% for Mn / (Mn + Sm + Ce), 15% for Sm / (Mn + Sm + Ce), and 15% for Ce / (Mn + Sm + Ce);

[0031] 5) Granulation: The material obtained by impregnation in step 4) is mixed evenly with coal tar and granulated under a pressure condition of 2 MPa to obtain a cylindrical sample with a diameter of 8 mm and a length of 10 mm;

[0032] 6) Drying: The sample obtained in step 5) is dried at 60 °C for 6 h;

[0033] 7) Activation: Under a N2 atmosphere, the temperature is programmed to rise to 500 °C at a rate of 10 °C / min. The sample obtained in step 6) is carried into 20% H2O with N2 as the carrier gas, and activated in this atmosphere for 45 min. The activated material is cooled for 6 h to obtain the cation-doped biochar material. The compressive strength and abrasion resistance are detected.

[0034] (2) SCR denitration performance evaluation

[0035] The evaluation experimental conditions are as follows: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volumetric space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, the residual NO concentration in the flue gas after SCR denitration is detected, and the denitration efficiency is calculated. The results are shown in Table 2.

[0036] Table 2 Denitrification efficiency, pressure resistance, and wear resistance strength values of materials

[0037]

[0038] Example 2

[0039] (1) This example is a metal cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, 40wt% nitric acid is used in the oxidation process, and the granulation conditions are: molding under a pressure of 1 MPa;

[0040] (2) SCR denitrification performance evaluation

[0041] The experimental conditions are set as: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volumetric space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, the residual NO concentration in the flue gas after SCR denitrification is measured, and the denitrification efficiency is calculated. The results are shown in Table 3.

[0042] Table 3 Denitrification efficiency, pressure resistance, and wear resistance strength values of carbon materials

[0043]

[0044] Example 3

[0045] (1) This example is a metal cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the temperature is programmed to rise to 600 °C during the activation process, and the granulation conditions are: molding under a pressure of 3 MPa;

[0046] (2) SCR denitrification performance evaluation

[0047] The evaluation experimental conditions are: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volumetric space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, the residual NO concentration in the flue gas after SCR denitrification is measured, and the denitrification efficiency is calculated. The results are shown in Table 4.

[0048] Table 4 Denitrification efficiency, pressure resistance, and wear resistance strength values of materials

[0049]

[0050] Example 4

[0051] (1) This example is a cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the carbonization process is heated to 800 °C in an anoxic (O2 content 10%) atmosphere, and 20 wt% binder (coal tar) is used in the granulation process;

[0052] (2) SCR denitrification performance evaluation

[0053] The evaluation experimental conditions are as follows: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volume space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, the residual NO concentration in the flue gas after SCR denitrification is measured, and the denitrification efficiency is calculated. The results are shown in Table 5.

[0054] Table 5 Denitrification efficiency and pressure resistance and wear resistance strength values of the materials

[0055]

[0056] Example 5

[0057] (1) This example is a cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the percentage of the total mass of manganese, samarium, and cerium elements doped in the impregnation step accounts for 20% of the total mass of the catalyst, and 20 wt% binder (coal tar) is used in the granulation step and formed under a pressure condition of 5 MPa;

[0058] (2) SCR denitrification performance evaluation

[0059] The evaluation experimental conditions are as follows: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volume space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, the residual NO concentration in the flue gas after SCR denitrification is measured, and the denitrification efficiency is calculated. The results are shown in Table 6.

[0060] Table 6 Denitrification efficiency and pressure resistance and wear resistance strength values of the materials

[0061]

[0062] Example 6

[0063] (1) This example is a cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the activation step is to first increase the temperature to 500 °C at a rate of 10 °C / min under a N2 atmosphere, and then activate for 45 min under an H2O atmosphere with a water content of 40%;

[0064] (2) SCR denitrification performance evaluation

[0065] The evaluation experimental conditions are as follows: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volumetric space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, measure the NO concentration remaining in the flue gas after SCR denitrification, and calculate the denitrification efficiency. The results are shown in Table 7.

[0066] Table 7 Denitrification efficiency and pressure resistance and wear resistance strength values of the materials

[0067]

[0068] Example 7

[0069] (1) This example is a metal cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the activation step is to first increase the temperature to 500 °C at a rate of 10 °C / min under a N2 atmosphere, and then activate for 45 min under an H2O atmosphere with a water content of 50%;

[0070] (2) SCR denitrification performance evaluation

[0071] The evaluation experimental conditions are as follows: NO concentration 200 ppm, NH3 concentration 200 ppm, O2 content 5%, total gas flow rate 100 mL / min, and volumetric space velocity 2000 h -1 . In the temperature range of 50 - 200 °C, measure the NO concentration remaining in the flue gas after SCR denitrification, and calculate the denitrification efficiency. The results are shown in Table 8.

[0072] Table 8 Denitrification efficiency and pressure resistance and wear resistance strength values of the materials

[0073]

[0074] Example 8

[0075] (1) This example is a cation-doped biochar material for low-temperature NH3-SCR denitrification. The raw materials and preparation process are the same as those in Example 1, except that in this example, the doping metal element ratio is Mn / (Mn + Sm + Ce) = 60%, Sm / (Mn + Sm + Ce) = 20%, and Ce / (Mn + Sm + Ce) = 20%.

[0076] (2) SCR denitrification performance evaluation

[0077] The evaluation experimental conditions are as follows: NO concentration is 200 ppm, NH3 concentration is 200 ppm, O2 content is 5%, the total gas flow rate is 100 mL / min, and the volume space velocity is 2000 h -1 . In the temperature range of 50 - 200 °C, measure the NO concentration remaining in the flue gas after SCR denitrification, and calculate the denitrification efficiency. The results are shown in Table 9.

[0078] Table 9 Denitrification efficiency, pressure resistance, and wear resistance strength values of the materials

[0079]

[0080] Comparative Example 1

[0081] Only add the biomass described in this application, without adding a binder and metal salts, and process according to the carbonization - oxidation - granulation - drying - activation process of Example 1.

[0082] Comparative Example 2

[0083] Only add the biomass, manganese salt, cerium salt, and samarium salt described in this application, add a binder (wood tar), and do not perform oxidation. Process according to the carbonization - impregnation - granulation - drying - activation process of Example 1.

[0084] Comparative Example 3

[0085] Only add the biomass and manganese salt described in this application, add a binder (lignosulfonate), and process according to the carbonization - oxidation - impregnation - granulation - drying - activation process of Example 1.

[0086] Comparative Example 4

[0087] Only add the biomass, manganese salt, samarium salt, and binder described in this application, where the molar ratio of manganese to samarium is 7:3, without adding cerium, and process according to the carbonization - oxidation - impregnation - granulation - drying - activation process of Example 1.

[0088] Comparative Example 5

[0089] Add the biomass, manganese salt, cerium salt, samarium salt and binder described in this application, and process them according to the carbonization-oxidation-impregnation-granulation-drying process of Example 1. During carbonization, the temperature is programmed to rise to 700 °C at a rate of 10 °C / min in an N2 atmosphere and activated for 45 min.

[0090] Comparative Example 6

[0091] Add the biomass, manganese salt, cerium salt, samarium salt and binder described in this application, and process them according to the carbonization-oxidation-impregnation-granulation-drying process of Example 1. The doping metal element ratio in the impregnation step is Mn / (Mn+Sm+Ce) = 40%, Sm / (Mn+Sm+Ce) = 30%, and Ce / (Mn+Sm+Ce) = 30%.

[0092] Comparative Example 7

[0093] Add the biomass, manganese salt, cerium salt, samarium salt and binder described in this application, and process them according to the oxidation-impregnation-granulation-carbonization-activation process. Granulation is carried out first and then carbonization activation. Compared with Example 1, the mechanical strength is reduced, indicating that the adjustment of the process sequence has a poor effect on the strength.

[0094] Comparative Example 8

[0095] Only use one commercial coal-based activated carbon.

[0096] Comparative Example 9

[0097] Only use one commercial coconut shell-based activated carbon.

[0098] Perform experiments on the above-obtained carbon-based materials under the SCR denitration experimental conditions of Example 1. The denitration efficiency results are shown in Table 13, and the comparison chart of the denitration activity stability is as Figure 1 shown, and the strength numerical results are shown in Table 14.

[0099] Table 12 Comparison table of denitration efficiency between comparative examples and Example 1

[0100]

[0101] As Figure 1 shown, Example 1 shows higher activity and stability than commercial coal-based activated carbon. The comparison between Comparative Example 2 and Example 1 shows that the lack of nitric acid oxidation leads to poor denitration stability.

[0102] Table 13 Comparison table of strength numerical values between comparative examples and Example 1

[0103]

[0104] The above table result comparison shows that, compared with Example 1, in Comparative Examples 2 and 3, when other types of binders are selected, their compressive strength cannot meet the standard requirements under the same conditions. The selection of using coal tar as the binder in this application can improve the wear resistance and compressive strength of the material. Compared with Example 1, in Comparative Example 4, when cerium salt is not added and only manganese and samarium are present, the denitrification efficiency is significantly reduced. In Comparative Example 6, when the proportion of manganese is small and the proportions of samarium and cerium increase, the denitrification efficiency is lower than the optimal doping ratio of Example 1, indicating that good activity can be achieved when only manganese is the main agent and samarium and cerium are the additives for co-doping. In Comparative Example 5, when the activation temperature is too high, the denitrification efficiency is significantly reduced.

[0105] The metal cation-doped biochar material prepared by the present invention can perform SCR denitrification on NO in flue gas at a relatively low temperature (50 - 200 °C), and has high mechanical strength.

[0106] Matters not described in the present invention are applicable to the prior art.

Claims

1. A metal cation-doped biochar material applied to low-temperature SCR denitrification, characterized in that, In the metal cation-doped biochar material, the mass ratio of raw materials is as follows: biochar 40-85%, binder 10-40%, and the total mass percentage of doped manganese, samarium, and cerium elements in the total mass of the catalyst is 5%-20%; the metal cation-doped biochar material is prepared by steps of carbonization-oxidation-impregnation-granulation-drying-activation of natural biomass; The biochar is prepared by carbonizing one or more of agricultural solid wastes and forestry solid wastes; the binder is coal tar; The manganese salt includes at least one of manganese chloride, manganese nitrate, and manganese sulfate; The samarium salt includes at least one of samarium chloride, samarium nitrate, and samarium acetate; The cerium salt includes at least one of cerium chloride, cerium nitrate, and cerium sulfate.

2. The metal cation-doped biochar material according to claim 1, characterized in that, The agricultural solid wastes include at least one of corn straw, tobacco straw, and sugarcane bagasse; the forestry solid wastes are at least one of poplar branches and wood chips.

3. The metal cation-doped biochar material according to claim 1, wherein The carbonization is carried out in an anoxic atmosphere with an O2 volume content of 2%-10%, and the carbonization temperature is 500-800°C; the specific process of the activation is: first, heat up to 500-650°C in an N2 atmosphere, then introduce H2O steam with N2 as the carrier gas, the moisture content <50%, and activate for 30-90 min in this atmosphere.

4. The metal cation-doped biochar material according to claim 1, wherein The specific preparation steps of the metal cation-doped biochar material are as follows: 1) Carbonization: The biomass powder passing through a 40-80 mesh sieve is heated to 500-800°C at a rate of 5-15°C / min in an anoxic atmosphere; the anoxic atmosphere is an O2 volume content of 2%-10%; 2) Oxidation: The carbonized biochar material is crushed and passed through a 60-100 mesh sieve, treated in a water bath at 75-82°C with 40-68 wt% nitric acid for 4-12 h, repeatedly washed with deionized water until neutral, and dried at 90-120°C for 6-10 h to obtain the oxidized biochar material, which is used as a carrier; 3) Washing: The carrier obtained in step 2) is washed with deionized water until neutral; 4) Impregnation: Add a certain proportion of manganese Salt, samarium salt, and cerium salt to deionized water to form an aqueous solution. After stirring evenly, add the material washed in step 3) and impregnate it under magnetic stirring for 3 - 4.5 h. The percentage of the total mass of manganese, samarium and cerium in the total mass of the catalyst is 5% - 20%. The mass of biochar + binder + doped metal elements = the total mass of the catalyst. The molar ratios are Mn / (Mn + Sm + Ce) is 60% - 90%, Sm / (Mn + Sm + Ce) is 5 - 20%, and Ce / (Mn + Sm + Ce) is 5 - 20%. 5) Granulation: The material obtained after impregnation in step 4) is mixed evenly with the binder, and granulated under a pressure condition of 0.5-5 MPa to obtain a cylindrical sample with a diameter of 6-10 mm and a length of 5-12 mm; 6) Drying: The sample obtained in step 5) is dried at 60-120°C for 6-12 h; 7) Activation: The sample obtained in step 6) is first heated up to 500-650°C at a rate of 5-15°C / min in an N2 atmosphere, then H2O steam is introduced with N2 as the carrier gas, the moisture content <50%, and activated for 30-90 min in this atmosphere. After activation, it is cooled for 6-12 h and passed through a 40-60 mesh sieve to obtain the metal cation-doped biochar material.

5. Use of the metal cation-doped biochar material according to claim 1 in low-temperature SCR denitration, characterized in that, The SCR denitration performance evaluation is carried out using the metal cation-doped biochar material, with the reaction temperature being 50 - 200 °C, the NO content being 100 - 700 ppm, the NH3 content being 100 - 700 ppm, the O2 content being 5 - 15%, and the volumetric space velocity being 400 - 30000 h -1 .

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