A method for preparing a wear-resistant and high-strength catalyst

Abstract

This invention discloses a method for preparing a wear-resistant and high-strength catalyst. During the preparation of titanium dioxide, the addition of activated carbon increases the specific surface area of ​​the titanium dioxide support, adjusts the mesoporous structure and pore size distribution, and improves the bonding ability between the titanium dioxide support and the active metal. Modification of titanium dioxide enhances its toughness and reduces its coefficient of thermal expansion, resulting in a catalyst with excellent wear resistance. The addition of silicon powder during the preparation process effectively increases the catalyst's compressive strength and wear resistance. Experiments show that adding a small amount of silicon carbide further improves the catalyst's mechanical strength and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of SCR denitrification catalyst technology, specifically to a method for preparing a wear-resistant and high-strength catalyst. Background Technology

[0002] Flue gas denitrification is divided into selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). SCR denitrification technology has the advantages of high denitrification rate, good selectivity, maturity and reliability, and is the mainstream denitrification technology for coal-fired units.

[0003] The most critical component in an SCR denitrification system is the catalyst. Currently, high-temperature catalysts are commonly used, with TiO2 as the carrier and V2O5 to WO3 (MoO3) as the main components. SCR denitrification catalysts are primarily used for the removal of nitrogen oxides from flue gas in coal-fired boilers. Nitrogen oxides react with ammonia in the catalyst under certain temperature conditions to produce nitrogen and water. The flue gas contains a large amount of dust and particulate matter. During the denitrification process, the catalyst is subjected to prolonged erosion by the flue gas, causing its physical structure to break down and failing to meet denitrification requirements. This leads to a decrease in overall denitrification efficiency, necessitating catalyst replacement. According to relevant statistics, the catalyst replacement cycle is three years. Therefore, improving the catalyst's wear resistance is crucial to extending its service life. Summary of the Invention

[0004] In view of the problems existing in the background technology, the present invention provides a method for preparing a wear-resistant and high-strength catalyst. The catalyst prepared has high denitrification efficiency and excellent wear resistance.

[0005] This invention is implemented through the following technical solutions:

[0006] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0007] S1. Preparation of modified titanium dioxide;

[0008] S2. Material Preparation: The main components are prepared according to the following weight proportions:

[0009] Modified titanium dioxide 82-92 parts, ammonium metavanadate 0.5-1 parts, ammonium metatungstate 3-5 parts, silicon powder 3-6 parts, and auxiliary materials 5-8 parts;

[0010] S3. Dissolve ammonium metavanadate and ammonium metatungstate in water to prepare an active component solution;

[0011] S4. Mix the modified titanium dioxide, silicon powder and auxiliary materials to obtain a mixture. Add the active component solution to the mixture and knead to obtain mud. Continue to dehumidify and unload the material into a storage box for aging for 24 hours after the temperature drops below 35℃.

[0012] S5. After aging, the clay is extruded into shape according to the required number of holes and length. The extruded unit strips are placed in the drying cart with cardboard spacers. After the drying cart is full of unit strips, they are put into the drying room for drying. After drying, the moisture content is tested.

[0013] S6. Place the qualified unit strips into a mesh belt kiln for calcination. After calcination, a wear-resistant and high-strength catalyst is obtained.

[0014] Furthermore, the preparation of modified titanium dioxide in S1 includes the following steps:

[0015] S101. Dissolve titanium oxysulfate in deionized water, add urea and activated carbon, react at 85°C for 10 hours to obtain a precipitate, filter, wash with deionized water until pH value is 7, dry at 110°C for 6 hours, and calcine at 500°C for 5 hours to obtain titanium dioxide.

[0016] S102. Add titanium dioxide and organosilicon coupling agent to ethanol, mix at high speed for 30 min, add stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate ethanol by rotary evaporation to obtain modified titanium dioxide.

[0017] Furthermore, in S101, the molar ratio of titanium oxysulfate to urea is 1:2, and the amount of activated carbon used is 5-15% of the weight of titanium oxysulfate.

[0018] Furthermore, in S102, the mass ratio of titanium dioxide, organosilicon coupling agent, and stearic acid is 10:(0.05-0.15):(0.8-1.2), and the amount of ethanol used is 1.5-2.5 times the weight of titanium dioxide.

[0019] Furthermore, the excipients in S2 also include silicon carbide, hydrated alumina, and carboxymethyl cellulose.

[0020] Furthermore, the mass ratio of silicon carbide, hydrated alumina and carboxymethyl cellulose is 1:(2-4):(2-4).

[0021] Furthermore, in step S4, the mixing temperature is increased to 95℃ at a rate of 15℃ / h and maintained for 1-2 hours, and the mixing mill speed is 1500-2000 rpm; during dehumidification, the mixing mill speed is reduced to 500-550 rpm.

[0022] Furthermore, in step S5, the extrusion pressure is 1.5-2.0 MPa, the extrusion speed is 0.8-1.2 m / min, the temperature in the drying room is 45-55℃, the ambient humidity is >95%, and the drying time is 10-15 days.

[0023] Furthermore, in step S5, after drying, the moisture content is tested by using a gravimetric method to test the moisture content of the dried unit strip. A moisture content of less than 6% is considered acceptable.

[0024] Furthermore, in step S6, the mesh belt kiln is heated from room temperature to 500-550℃ and maintained for 8-12 hours, with the overall calcination time being 36-48 hours.

[0025] The beneficial effects of this invention are:

[0026] 1. In the preparation method of the present invention, the addition of activated carbon during the preparation of titanium dioxide increases the specific surface area of ​​the titanium dioxide support, adjusts the mesoporous structure and pore size distribution, and improves the bonding ability between the titanium dioxide support and the active metal; by modifying titanium dioxide, its toughness is enhanced and the coefficient of thermal expansion is reduced, so that the catalyst has excellent wear resistance.

[0027] 2. In the preparation method of the present invention, the addition of silicon powder effectively increases the catalyst's compressive strength and wear resistance. Through experiments, the present invention has found that adding a small amount of silicon carbide during the preparation process is beneficial to further improve the catalyst's mechanical strength and wear resistance. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0031] S1. Preparation of modified titanium dioxide;

[0032] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and 50g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0033] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0034] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0035] 85 parts modified titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 6 parts silicon powder, 1 part silicon carbide, 3 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0036] S3. Dissolve ammonium metavanadate and ammonium metatungstate in 20 parts of deionized water to prepare an active component solution;

[0037] S4. Mix the modified titanium dioxide, silicon powder and auxiliary materials to obtain a mixture. Add the active component solution to the mixture and knead it. The kneading temperature is increased to 95℃ at 15℃ / h and maintained for 2h. The kneading machine speed is 1800 rpm to obtain mud. Continue to dehumidify. When dehumidifying, reduce the kneading machine speed to 550 rpm. When the temperature drops below 35℃, unload the material and put it into a storage box for aging for 24h.

[0038] S5. After aging, the clay material is extruded into strips with a cross-section of 150*150mm, 13 holes*13 holes, and a length of 500mm. The extrusion pressure is 1.8MPa and the extrusion speed is 1.0m / min. The extruded unit strips are placed in a drying trolley with cardboard spacers. After the drying trolley is full of unit strips, they are placed in a drying room for drying. The temperature in the drying room is 50℃, the ambient humidity is >95%, and the drying time is 15 days. After drying, the moisture content of the dried unit strips is tested by gravimetric method. A moisture content of <6% is considered qualified.

[0039] S6. Place the qualified unit strips into a mesh belt kiln for calcination. The mesh belt kiln is heated from room temperature to 550℃ and maintained for 12 hours. After calcination, the wear-resistant and high-strength catalyst is obtained.

[0040] Example 2

[0041] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0042] S1. Preparation of modified titanium dioxide;

[0043] S101. Dissolve 300g of titanium oxysulfate in 1500ml of deionized water, add 225g of urea and 24g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0044] S102. Add 100 parts of titanium dioxide and 0.15 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 12 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0045] The remaining steps are the same as in Example 1.

[0046] Example 3

[0047] S1. Preparation of modified titanium dioxide;

[0048] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and 50g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0049] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0050] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0051] 88 parts modified titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 5 parts silicon powder, 1 part silicon carbide, 4 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0052] The remaining steps are the same as in Example 1.

[0053] Comparative Example 1

[0054] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0055] S1. Preparation of modified titanium dioxide;

[0056] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and react at 85℃ for 10 hours to obtain a precipitate. After filtration, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0057] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0058] The remaining steps are the same as in Example 1.

[0059] Comparative Example 2

[0060] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0061] S1. Preparation of titanium dioxide: 500g of titanium oxysulfate was dissolved in 1500ml of deionized water, 375g of urea and 50g of activated carbon were added, and the mixture was reacted at 85℃ for 10 hours to obtain a precipitate. After filtration, the precipitate was washed with deionized water until the pH value was 7, dried at 110℃ for 6 hours, and calcined at 500℃ for 5 hours to obtain titanium dioxide.

[0062] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0063] 85 parts titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 6 parts silicon powder, 1 part silicon carbide, 3 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0064] S3. Dissolve ammonium metavanadate and ammonium metatungstate in 20 parts of deionized water to prepare an active component solution;

[0065] S4. Mix titanium dioxide, silicon powder and auxiliary materials to obtain a mixture. Add the active component solution to the mixture and knead it. The kneading temperature is increased to 95℃ at 15℃ / h and maintained for 2h. The kneading machine speed is 1800 rpm to obtain mud. Continue to dehumidify. When dehumidifying, reduce the kneading machine speed to 550 rpm. When the temperature drops below 35℃, unload the material and put it into a storage box for aging for 24h.

[0066] The remaining steps are the same as in Example 1.

[0067] Comparative Example 3

[0068] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0069] S1. Preparation of modified titanium dioxide;

[0070] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and 50g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0071] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0072] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0073] 85 parts modified titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 1 part silicon carbide, 3 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0074] The remaining steps are the same as in Example 1.

[0075] Comparative Example 4

[0076] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0077] S1. Preparation of modified titanium dioxide;

[0078] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and 50g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0079] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0080] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0081] 85 parts modified titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 6 parts silica powder, 3 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0082] The remaining steps are the same as in Example 1.

[0083] Comparative Example 5

[0084] A method for preparing a wear-resistant and high-strength catalyst includes the following steps:

[0085] S1. Preparation of modified titanium dioxide;

[0086] S101. Dissolve 500g of titanium oxysulfate in 1500ml of deionized water, add 375g of urea and 50g of activated carbon, react at 85℃ for 10 hours to obtain a precipitate, filter, wash with deionized water until the pH value is 7, dry at 110℃ for 6 hours, and calcine at 500℃ for 5 hours to obtain titanium dioxide.

[0087] S102. Add 100 parts of titanium dioxide and 0.1 parts of organosilicon coupling agent KH550 to 200 parts of ethanol, mix at high speed for 30 min, add 10 parts of stearic acid, continue mixing for 30 min, grind for 2 h, and evaporate the ethanol by rotary evaporation to obtain modified titanium dioxide.

[0088] S2. Material Preparation: The main components are prepared according to the following weight fractions:

[0089] 85 parts modified titanium dioxide, 1.0 part ammonium metavanadate, 4 parts ammonium metatungstate, 6 parts silicon powder, 5 parts silicon carbide, 3 parts hydrated alumina and 3 parts carboxymethyl cellulose;

[0090] The remaining steps are the same as in Example 1.

[0091] Experimental Example 1

[0092] Wear rate test

[0093] The catalysts prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to wear rate tests. Referring to the determination of wear rate in GB / T315877-2015, the specific procedures were as follows: Two samples with a height of 100 mm were cut, serving as the test sample and the control sample. The samples were dried in a constant temperature oven at 105±2℃ for 2 hours, removed, and allowed to cool naturally to room temperature before weighing. The samples were then wrapped in kaolin cotton and placed in the sample chamber. The air velocity in the catalyst channel was 14.5±0.5 m / s, and the abrasive concentration was 50±5 g / m³. 3 Stop after 2 hours. Remove the sample and place it in an oven at 105±2℃ for 2 hours. After removing it and allowing it to cool naturally to room temperature, weigh it to an accuracy of 0.01g.

[0094] The formula for calculating the wear rate is as follows:

[0095]

[0096] In the formula:

[0097] ξ represents the wear rate of the sample, % / kg;

[0098] m1 is the weight of the sample before testing, in grams;

[0099] m2 is the weight of the sample after the test, in grams;

[0100] m3 is the weight of the control sample before the test, in grams;

[0101] m4 is the weight of the control sample after the test, in grams;

[0102] m is the weight of the abrasive, in kg.

[0103] The test results are shown in Table 1.

[0104] Table 1. Results of catalyst attrition rate tests for Examples 1-3 and Comparative Examples 1-5.

[0105] Group Abrasion resistance (%) / kg Example 1 0.05 Example 2 0.06 Example 3 0.06 Comparative Example 1 0.05 Comparative Example 2 0.09 Comparative Example 3 0.16 Comparative Example 4 0.10 Comparative Example 5 0.06

[0106] As shown in Table 1, the catalysts prepared in Examples 1-3 of this invention exhibit significantly better wear resistance than those in Comparative Examples 2-4. In Comparative Example 1, no activated carbon was added during the titanium dioxide preparation process, so its impact on the catalyst's wear resistance was minimal. In Comparative Example 2, the prepared titanium dioxide was directly used in catalyst preparation without modification, resulting in increased wear resistance but decreased wear resistance. In this invention, titanium dioxide is modified, and when mixed with other components, the connectivity between components is increased, improving the catalyst's density. Calcination enhances the catalyst's toughness, reduces its thermal expansion coefficient, and improves its wear resistance. In Comparative Example 3, no silicon powder was added during preparation, resulting in a significant increase in wear resistance but a significant decrease in wear resistance. This indicates that the addition of silicon powder greatly improves the catalyst's wear resistance. In Comparative Example 4, no silicon carbide was added, resulting in an increase in catalyst wear resistance compared to Example 1, but a certain decrease in wear resistance. This shows that the addition of silicon carbide can improve the catalyst's compressive strength, which is beneficial for improving wear resistance. In Comparative Example 5, the amount of silicon carbide was increased, but its wear resistance was not much different from that in Example 1. It can be seen that increasing the amount of silicon carbide did not bring about the unexpected technical effect.

[0107] Experimental Example 2

[0108] Denitrification catalytic activity test

[0109] Test subjects: catalysts prepared in Example 1 and Comparative Examples 1-2.

[0110] Test conditions: Flue gas composition was NO (400 mg / Nm³). 3 ), NH3 (400mg / Nm 3 ), O2 (5%), SO2 (100mg / Nm 3 N2 is the balance gas, and the space velocity is 3000 h⁻¹. -1 The catalyst has 5*5 pores and a length of 500mm.

[0111] NO was detected at inlet and outlet temperatures of 140℃, 160℃, 180℃, and 200℃ respectively. X The concentration of the flue gas was detected using a Testo portable flue gas analyzer, and the results are shown in Table 2.

[0112] Table 2. Activity test results of the catalysts prepared in Example 1 and Comparative Examples 1-2

[0113]

[0114] As shown in Table 2, the catalyst prepared in this invention exhibits higher denitrification efficiency compared to Comparative Examples 1 and 2. Comparative Example 1, which prepared titanium dioxide without activated carbon, had the lowest denitrification efficiency. In this invention, activated carbon was added as a template agent during titanium dioxide preparation, participating in the entire reaction process. It was then burned off during calcination, thus acting as a pore-forming agent, increasing the specific surface area of ​​the titanium dioxide support, adjusting the mesoporous structure and pore size distribution, and improving the bonding ability between the titanium dioxide support and the active metal. Therefore, the denitrification efficiency of the catalyst in Example 1 of this invention is significantly higher than that in Comparative Example 1. The catalyst in Comparative Example 2, prepared without modification of titanium dioxide, also had a lower denitrification efficiency than that in Example 1. This demonstrates that the modification of titanium dioxide in this invention helps improve the catalyst's bonding ability with the active metal.

[0115] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a wear-resistant, high-strength catalyst, characterized in that, Includes the following steps: S1. Preparation of modified titanium dioxide: Titanium sulfate oxysulfate was dissolved in deionized water, urea and activated carbon were added, and the mixture was reacted at 85℃ for 10 hours to obtain a precipitate. After filtration, the precipitate was washed with deionized water until the pH value was 7, dried at 110℃ for 6 hours, and calcined at 500℃ for 5 hours to obtain titanium dioxide. Titanium dioxide and organosilicon coupling agent were added to ethanol, and the mixture was mixed at high speed for 30 minutes. Stearic acid was added, and the mixture was mixed for another 30 minutes. The mixture was then ground for 2 hours. The ethanol was then evaporated by rotary evaporation to obtain modified titanium dioxide. S2. Material Preparation: The main components are prepared according to the following weight proportions: Modified titanium dioxide 82-92 parts, ammonium metavanadate 0.5-1 parts, ammonium metatungstate 3-5 parts, silicon powder 3-6 parts, and auxiliary materials 5-8 parts; S3. Dissolve ammonium metavanadate and ammonium metatungstate in water to prepare an active component solution; S4. Mix the modified titanium dioxide, silicon powder and auxiliary materials to obtain a mixture. Add the active component solution to the mixture and knead to obtain mud. Continue to dehumidify and unload the material into a storage box for aging for 24 hours after the temperature drops below 35℃. S5. After aging, the clay is extruded into shape according to the required number of holes and length. The extruded unit strips are placed in the drying cart with cardboard spacers. After the drying cart is full of unit strips, they are put into the drying room for drying. After drying, the moisture content is tested. S6. Place the qualified unit strips into a mesh belt kiln for calcination. After calcination, a wear-resistant and high-strength catalyst is obtained.

2. The method according to claim 1, characterized in that, In S1, the molar ratio of titanium oxysulfate to urea is 1:2, and the amount of activated carbon used is 5-15% of the weight of titanium oxysulfate.

3. The method according to claim 1, characterized in that, In S1, the mass ratio of titanium dioxide, organosilicon coupling agent, and stearic acid is 10:(0.05-0.15):(0.8-1.2), and the amount of ethanol used is 1.5-2.5 times the weight of titanium dioxide.

4. The method according to claim 1, characterized in that, The excipients in S2 include silicon carbide, hydrated alumina, and carboxymethyl cellulose.

5. The method according to claim 4, characterized in that, The mass ratio of silicon carbide, hydrated alumina and carboxymethyl cellulose is 1:(2-4):(2-4).

6. The method according to claim 1, characterized in that, In step S4, during mixing, the temperature is increased to 95℃ at a rate of 15℃ / h and maintained for 1-2 hours, with the mixer speed at 1500-2000 rpm; during dehumidification, the mixer speed is reduced to 500-550 rpm.

7. The method according to claim 1, characterized in that, In step S5, the extrusion pressure is 1.5-2.0 MPa, the extrusion speed is 0.8-1.2 m / min, the temperature in the drying room is 45-55℃, the ambient humidity is >95%, and the drying time is 10-15 days.

8. The method according to claim 1, characterized in that, In step S5, after drying, the moisture content is tested by weight method. The moisture content of the dried unit strip is less than 6%, which is considered qualified.

Images