AES continuous synthesis process with low energy consumption and high conversion rate

Abstract

The invention discloses an AES continuous synthesis process with low energy consumption and high conversion rate. The AES continuous synthesis process comprises the following steps: step 1, raw material pretreatment; step 2, continuous etherification reaction; step 3, waste heat recovery; step 4, continuous sulfation reaction; step 5, performing vacuum degassing; step 6, neutralizing and refining; and step 7, drying and packaging. Through a continuous synthesis process, the production efficiency and the product quality of the AES are remarkably improved. Firstly, the raw material pretreatment step ensures the purity and activity of reactants, and lays a solid foundation for subsequent continuous reaction; according to the continuous etherification reaction, the efficient mass transfer characteristic of the microchannel reactor is utilized, the reaction process is accelerated, the conversion rate is increased, and meanwhile generation of by-products is reduced. The waste heat recovery step not only reduces the energy consumption, but also provides preheating for subsequent SO3 preparation, and further improves the energy utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of continuous AES synthesis technology, specifically a low-energy-consumption, high-conversion-rate continuous AES synthesis process. Background Technology

[0002] Sodium fatty alcohol polyoxyethylene ether sulfate (AES) is an important anionic surfactant widely used in detergents, cosmetics, and other fields. Traditional AES synthesis processes often employ batch reactions, resulting in high energy consumption, low conversion rates, and numerous byproducts. For example, existing patent 202211605126.2 discloses a high-impact flame-retardant AES resin and its preparation method, and existing patent 201811024807.3 discloses a method for synthesizing thickening-type low-freezing-point sodium fatty alcohol polyoxyethylene ether sulfate. Traditional sulfonation processes suffer from low SO3 utilization and ineffective heat recovery, leading to high energy consumption. Batch etherification reactions require prolonged high temperature and pressure, resulting in high ethylene oxide residue rates and impacting product quality. Furthermore, existing continuous processes suffer from insufficient precision in reaction parameter control and cumbersome separation and purification steps, further limiting production efficiency and product quality. Summary of the Invention

[0003] The purpose of this invention is to provide a low-energy-consumption, high-conversion-rate continuous synthesis process for AES to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a low-energy-consumption, high-conversion-rate continuous synthesis process for AES, comprising the following steps:

[0005] Step 1: Raw material pretreatment: The fatty alcohol and catalyst are mixed, heated, stirred evenly, and then dehydrated; at the same time, ethylene oxide (EO) is pressurized to 0.4-0.8 MPa through a nitrogen pressurization device to maintain it in a liquid state for later use; KOH catalyst promotes the etherification reaction, vacuum dehydration avoids moisture affecting the reaction activity, and pressurized EO ensures that it is accurately metered into the reactor in a liquid state;

[0006] Step 2, Continuous etherification reaction: The pretreated fatty alcohol and liquid EO are respectively delivered to the first microchannel reactor through metering pumps to carry out ring-opening addition reaction to generate fatty alcohol polyoxyethylene ether (AEO); the high mass transfer efficiency of the microchannel reactor accelerates the mixing of EO and fatty alcohol, and under high temperature and high pressure conditions, KOH catalyzes the etherification reaction of EO and fatty alcohol, improving the reaction rate and conversion rate.

[0007] Step 3, Waste Heat Recovery: The fatty alcohol polyoxyethylene ether (AEO) after the etherification reaction is passed through a heat exchanger to exchange heat with the high-temperature SO2 / air mixture generated by the sulfur combustion furnace. The recovered heat cools the fatty alcohol polyoxyethylene ether (AEO) to 40-45℃, while the SO2 / air mixture is cooled to 420-430℃ and then sent to the conversion furnace for SO3 preparation. The waste heat recovery device using superconducting heat pipes achieves cascade utilization of heat, reduces subsequent cooling energy consumption, and preheats the SO2 mixture to improve conversion efficiency.

[0008] Step 4, Continuous sulfation reaction: The cooled fatty alcohol polyoxyethylene ether (AEO) enters the second microchannel reactor and undergoes a sulfation reaction with gaseous SO3 to generate fatty alcohol polyoxyethylene ether sulfate (AESA). The homogeneous reaction environment of the microchannel reactor reduces local overheating, controls the SO3 concentration to avoid over-sulfonation, and ensures reaction selectivity and conversion rate.

[0009] Step 5, Vacuum Degassing: The sulfation product is degassed under vacuum through a falling film evaporator to remove residual SO3 and by-product dioxane; the degassed gas is mixed with dry air through a venturi tube and then incinerated in a sulfur combustion furnace; vacuum degassing effectively reduces the sulfate content in the product (≤0.3%), and the removed organic matter decomposes at high temperature in the sulfur combustion furnace, reducing environmental pollution;

[0010] Step Six: Neutralization and Purification: The degassed fatty alcohol polyoxyethylene ether sulfate (AESA) enters the neutralization reactor. A 30% NaOH aqueous solution is added to adjust the pH to 7-8, and deionized water is added to dilute the AES concentration to 70%. The neutralization product is filtered through a membrane separation system to remove unreacted impurities and catalyst residues. Precise control of the neutralization pH prevents product hydrolysis, and membrane separation technology efficiently removes microparticles, improving product purity.

[0011] Step 7, Drying and Packaging: The refined fatty alcohol polyoxyethylene ether sulfate (AES) solution is dried in a spray drying tower to obtain powdered AES product, which is then packaged and stored. Spray drying quickly removes moisture, and the high temperature further kills microorganisms, ensuring product stability.

[0012] Preferably, the fatty alcohol in step one is C14. 12 -C 14 The preferred catalyst is KOH, which is used at 0.3-0.5% of the mass of the fatty alcohol. The heating temperature is 60-80℃, and the water content is removed by a vacuum dehydration system to ≤0.1%.

[0013] Preferably, in step two, the reaction temperature of the first microchannel reactor is controlled at 175-190℃, the pressure at 1.1-1.5MPa, and the residence time at 6.5-12.5 minutes.

[0014] Preferably, the temperature of the high-temperature SO2 / air mixture in step three is 600-650℃.

[0015] Preferably, in step four, the volume concentration of gaseous SO3 is 5%, with the remainder being air, and the parameters for the sulfation reaction are: the reaction is carried out at a temperature of 40-45℃ and a pressure of 0.2MPa.

[0016] Preferably, in step five, the vacuum degassing control temperature is 50-60℃ and the vacuum degree is -40 to -80kPa.

[0017] Preferably, in step six, the pore size of the membrane separation system is 0.1-0.5 μm.

[0018] Preferably, in step seven, the drying conditions of the spray drying tower are as follows: the inlet temperature is 180-200℃ and the outlet temperature is 80-90℃.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention significantly improves the production efficiency and product quality of AES through a continuous synthesis process. First, the raw material pretreatment step ensures the purity and activity of the reactants, laying a solid foundation for subsequent continuous reactions. The continuous etherification reaction utilizes the efficient mass transfer characteristics of a microchannel reactor, accelerating the reaction process, increasing conversion rate, and reducing by-product formation. The waste heat recovery step not only reduces energy consumption but also provides preheating for subsequent SO3 preparation, further improving energy utilization efficiency. The continuous sulfation reaction is carried out in a microchannel reactor, ensuring reaction uniformity and selectivity, avoiding over-sulfonation, thereby improving product purity and conversion rate. The vacuum degassing step effectively removes residual SO3 and by-product dioxane, reducing the sulfate content in the product and minimizing environmental pollution. The neutralization and purification steps, through precise control of the neutralization pH and membrane separation technology, further improve product purity and stability. Finally, the drying and packaging steps employ spray drying technology to rapidly remove moisture, ensuring product stability and storability. Compared with existing technologies, this invention not only significantly reduces energy consumption and increases conversion rate but also reduces by-product formation, improving product quality and purity. Therefore, this invention has broad application prospects and significant economic benefits in the field of continuous AES synthesis. Attached Figure Description

[0021] Figure 1 This is a flowchart of the synthesis process of the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1 This invention provides a low-energy-consumption, high-conversion-rate continuous synthesis process for AES, comprising the following steps:

[0024] Step 1: Raw material pretreatment: The fatty alcohol and catalyst are mixed, heated, stirred evenly, and then dehydrated. Simultaneously, ethylene oxide (EO) is pressurized to 0.4-0.8 MPa using a nitrogen pressurization device to maintain it in a liquid state for later use. KOH catalyst promotes the etherification reaction, vacuum dehydration prevents moisture from affecting the reaction activity, and pressurized EO ensures accurate metering into the reactor in liquid form. The preferred fatty alcohol is C4. 12 -C 14 The preferred catalyst is KOH, which is used at 0.3-0.5% of the mass of the fatty alcohol. The heating temperature is 60-80℃, and the water content is removed by a vacuum dehydration system to ≤0.1%.

[0025] Step 2, Continuous Etherification Reaction: The pretreated fatty alcohol and liquid EO are separately pumped into the first microchannel reactor for a ring-opening addition reaction to generate fatty alcohol polyoxyethylene ether (AEO). The high mass transfer efficiency of the microchannel reactor accelerates the mixing of EO and fatty alcohol. Under high temperature and high pressure conditions, KOH catalyzes the etherification reaction of EO and fatty alcohol, improving the reaction rate and conversion rate. The reaction temperature in the first microchannel reactor is controlled at 175-190℃, the pressure at 1.1-1.5MPa, and the residence time at 6.5-12.5 minutes.

[0026] Step 3, Waste Heat Recovery: The fatty alcohol polyoxyethylene ether (AEO) after the etherification reaction is passed through a heat exchanger to exchange heat with the high-temperature SO2 / air mixture generated by the sulfur combustion furnace. The recovered heat cools the fatty alcohol polyoxyethylene ether (AEO) to 40-45℃, while the SO2 / air mixture is cooled to 420-430℃, and then sent to the conversion furnace for SO3 production. A superconducting heat pipe waste heat recovery device is used to achieve cascaded utilization of heat, reducing subsequent cooling energy consumption, and preheating the SO2 mixture to improve conversion efficiency. The temperature of the high-temperature SO2 / air mixture is 600-650℃.

[0027] Step 4, Continuous Sulfation Reaction: The cooled fatty alcohol polyoxyethylene ether (AEO) enters the second microchannel reactor and undergoes a sulfation reaction with gaseous SO3 to generate fatty alcohol polyoxyethylene ether sulfate (AESA). The homogeneous reaction environment of the microchannel reactor reduces local overheating, controls the SO3 concentration to avoid over-sulfonation, and ensures reaction selectivity and conversion rate. The volume concentration of gaseous SO3 is 5%, with the remainder being air. The sulfation reaction parameters are: reaction is carried out at a temperature of 40-45℃ and a pressure of 0.2 MPa.

[0028] Step 5, Vacuum Degassing: The sulfation product is degassed under vacuum using a falling film evaporator to remove residual SO3 and by-product dioxane; the degassed gas is mixed with dry air through a venturi tube and then incinerated in a sulfur combustion furnace; vacuum degassing effectively reduces the sulfate content in the product (≤0.3%), and the removed organic matter decomposes at high temperatures in the sulfur combustion furnace, reducing environmental pollution; the vacuum degassing temperature is controlled at 50-60℃ and the vacuum degree is -40 to -80 kPa;

[0029] Step Six: Neutralization and Purification: The degassed fatty alcohol polyoxyethylene ether sulfate (AESA) enters the neutralization reactor. A 30% NaOH aqueous solution is added to adjust the pH to 7-8, and deionized water is added to dilute the AES concentration to 70%. The neutralization product is filtered through a membrane separation system to remove unreacted impurities and catalyst residue. Precise control of the neutralization pH prevents product hydrolysis, and membrane separation technology efficiently removes microparticles, improving product purity. The pore size of the membrane separation system is 0.1-0.5 μm.

[0030] Step 7, Drying and Packaging: The refined fatty alcohol polyoxyethylene ether sulfate (AES) solution is dried in a spray drying tower to obtain powdered AES product, which is then packaged and stored. Spray drying quickly removes moisture and further kills microorganisms under high temperature conditions to ensure product stability. The drying conditions of the spray drying tower are 180-200℃ at the inlet and 80-90℃ at the outlet.

[0031] Example 1:

[0032] Ingredients: C 12 1000 kg of fatty alcohol, 3 kg of KOH, 350 kg of EO, and SO3 gas (5% volume concentration).

[0033] Includes the following steps:

[0034] Step 1: Raw material pretreatment: Mix fatty alcohol with catalyst, heat, stir evenly, and then dehydrate; at the same time, pressurize ethylene oxide (EO) to 0.4-0.8 MPa through a pressurized nitrogen device and keep it in liquid state for later use; the heating temperature is 60-80℃, and the water content is removed by a vacuum dehydration system to ≤0.1%;

[0035] Step 2, Continuous etherification reaction: The pretreated fatty alcohol and liquid EO are respectively delivered to the first microchannel reactor through metering pumps to carry out ring-opening addition reaction to generate fatty alcohol polyoxyethylene ether (AEO); the reaction temperature in the first microchannel reactor is controlled at 180℃, the pressure at 1.5MPa, and the residence time at 8 minutes.

[0036] Step 3, Waste Heat Recovery: The fatty alcohol polyoxyethylene ether (AEO) after the etherification reaction is passed through a heat exchanger to exchange heat with the high-temperature SO2 / air mixture generated by the sulfur combustion furnace. The recovered heat cools the fatty alcohol polyoxyethylene ether (AEO) to 40-45℃, while the SO2 / air mixture is cooled to 420-430℃ and then sent to the conversion furnace for SO3 preparation; the temperature of the high-temperature SO2 / air mixture is 600-650℃.

[0037] Step 4, Continuous sulfation reaction: The cooled fatty alcohol polyoxyethylene ether (AEO) enters the second microchannel reactor and undergoes a sulfation reaction with gaseous SO3 to generate fatty alcohol polyoxyethylene ether sulfate (AESA); the volume concentration of gaseous SO3 is 5%, with the remainder being air. The parameters for the sulfation reaction are: temperature 43℃, 0.2MPa, and SO3 flow rate 10.49L / min.

[0038] Step 5, Vacuum Degassing: The sulfation product is degassed under vacuum using a falling film evaporator to remove residual SO3 and by-product dioxane; the degassed gas is mixed with dry air through a venturi tube and then incinerated in a sulfur combustion furnace; the vacuum degassing temperature is controlled at 60℃ and the vacuum degree is -85kPa.

[0039] Step Six: Neutralization and Purification: The degassed fatty alcohol polyoxyethylene ether sulfate (AESA) enters the neutralization reactor. A 30% NaOH aqueous solution is added to adjust the pH to 7-8, and deionized water is added to dilute the AES concentration to 70%. The neutralization product is filtered through a membrane separation system to remove unreacted impurities and catalyst residue. Precise control of the neutralization pH prevents product hydrolysis, and membrane separation technology efficiently removes microparticles, improving product purity. The pore size of the membrane separation system is 0.1-0.5 μm.

[0040] Step 7, Drying and Packaging: The refined fatty alcohol polyoxyethylene ether sulfate (AES) solution is dried in a spray drying tower to obtain powdered AES product, which is then packaged and stored. Spray drying quickly removes moisture and further kills microorganisms under high temperature conditions to ensure product stability. The drying conditions of the spray drying tower are 180-200℃ at the inlet and 80-90℃ at the outlet.

[0041] Results: AES conversion rate was 99.2%, sulfate content was 0.28%, and energy consumption was reduced by 32% compared with traditional processes.

[0042] Example 2:

[0043] Ingredients: C 14 800 kg of fatty alcohol, 4 kg of KOH, 300 kg of EO, and SO3 gas (5% volume concentration).

[0044] Includes the following steps:

[0045] Step 1: Raw material pretreatment: Mix fatty alcohol with catalyst, heat, stir evenly, and then dehydrate; at the same time, pressurize ethylene oxide (EO) to 0.4-0.8 MPa through a pressurized nitrogen device and keep it in liquid state for later use; the heating temperature is 60-80℃, and the water content is removed by a vacuum dehydration system to ≤0.1%;

[0046] Step 2, Continuous etherification reaction: The pretreated fatty alcohol and liquid EO are respectively delivered to the first microchannel reactor through metering pumps to carry out ring-opening addition reaction to generate fatty alcohol polyoxyethylene ether (AEO); the reaction temperature in the first microchannel reactor is controlled at 190℃, the pressure at 1.1MPa, and the residence time at 6.5 minutes.

[0047] Step 3, Waste Heat Recovery: The fatty alcohol polyoxyethylene ether (AEO) after the etherification reaction is passed through a heat exchanger to exchange heat with the high-temperature SO2 / air mixture generated by the sulfur combustion furnace. The recovered heat cools the fatty alcohol polyoxyethylene ether (AEO) to 40-45℃, while the SO2 / air mixture is cooled to 420-430℃ and then sent to the conversion furnace for SO3 preparation; the temperature of the high-temperature SO2 / air mixture is 600-650℃.

[0048] Step 4, Continuous sulfation reaction: The cooled fatty alcohol polyoxyethylene ether (AEO) enters the second microchannel reactor and undergoes a sulfation reaction with gaseous SO3 to generate fatty alcohol polyoxyethylene ether sulfate (AESA); the volume concentration of gaseous SO3 is 5%, and the remainder is air. The parameters for the sulfation reaction are: temperature 40℃, 0.2MPa, and SO3 flow rate 9.8L / min.

[0049] Step 5, Vacuum Degassing: The sulfation product is degassed under vacuum using a falling film evaporator to remove residual SO3 and by-product dioxane; the degassed gas is mixed with dry air through a venturi tube and then incinerated in a sulfur combustion furnace; the vacuum degassing temperature is controlled at 55℃ and the vacuum degree is -70kPa.

[0050] Step Six: Neutralization and Purification: The degassed fatty alcohol polyoxyethylene ether sulfate (AESA) enters the neutralization reactor. A 30% NaOH aqueous solution is added to adjust the pH to 7-8, and deionized water is added to dilute the AES concentration to 70%. The neutralization product is filtered through a membrane separation system to remove unreacted impurities and catalyst residue. Precise control of the neutralization pH prevents product hydrolysis, and membrane separation technology efficiently removes microparticles, improving product purity. The pore size of the membrane separation system is 0.1-0.5 μm.

[0051] Step 7, Drying and Packaging: The refined fatty alcohol polyoxyethylene ether sulfate (AES) solution is dried in a spray drying tower to obtain powdered AES product, which is then packaged and stored. Spray drying quickly removes moisture and further kills microorganisms under high temperature conditions to ensure product stability. The drying conditions of the spray drying tower are 180-200℃ at the inlet and 80-90℃ at the outlet.

[0052] Results: AES conversion rate was 99.5%, sulfate content was 0.25%, and energy consumption was reduced by 35%.

[0053] Comparative example:

[0054] A traditional batch process was used, with the etherification reaction temperature at 160℃, pressure at 1.0MPa, and reaction time at 4 hours; the sulfation reaction employed a falling film sulfonator with an SO3 concentration of 3%. Results showed an AES conversion rate of 95.3%, a sulfate content of 0.52%, and energy consumption 40% higher than that of this invention.

[0055] In summary, this invention significantly improves the production efficiency and product quality of AES through a continuous synthesis process. First, the raw material pretreatment step ensures the purity and activity of the reactants, laying a solid foundation for subsequent continuous reactions. The continuous etherification reaction utilizes the efficient mass transfer characteristics of a microchannel reactor, accelerating the reaction process, increasing conversion rate, and reducing byproduct formation. The waste heat recovery step not only reduces energy consumption but also provides preheating for subsequent SO3 preparation, further improving energy utilization efficiency. The continuous sulfation reaction, carried out in a microchannel reactor, ensures reaction uniformity and selectivity, avoiding over-sulfonation, thereby improving product purity and conversion rate. The vacuum degassing step effectively removes residual SO3 and byproduct dioxane, reducing sulfate content in the product and minimizing environmental pollution. The neutralization and purification steps, through precise control of neutralization pH and membrane separation technology, further improve product purity and stability. Finally, the drying and packaging steps employ spray drying technology to rapidly remove moisture, ensuring product stability and shelf life. Compared with existing technologies, this invention not only significantly reduces energy consumption and improves conversion rate, but also reduces the generation of by-products and improves product quality and purity. Therefore, this invention has broad application prospects and significant economic benefits in the field of continuous AES synthesis.

[0056] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low energy, high conversion, continuous synthesis process for AES, characterized in that: The method comprises the following steps: Step one, raw material pretreatment: mix the fatty alcohol with the catalyst, heat and stir until uniform, and then dehydrate; at the same time, pressurize the liquid ethylene oxide EO to 0.4-0.8 MPa by means of pressurized nitrogen gas device and maintain the liquid state for standby; Step two, continuous etherification reaction: deliver the pretreated fatty alcohol and the liquid EO to the first microchannel reactor by means of metering pumps respectively to generate the fatty alcohol polyoxyethylene ether AEO by ring-opening addition reaction; Step three, waste heat recovery: deliver the etherification product fatty alcohol polyoxyethylene ether AEO to the heat exchanger to exchange heat with the high-temperature SO2 / air mixture gas generated by the sulfur burning furnace, recover the heat to cool the fatty alcohol polyoxyethylene ether AEO to 40-45℃, and at the same time, cool the SO2 / air mixture gas to 420-430℃ and deliver it to the conversion furnace for SO3 preparation; Step four, continuous sulfation reaction: deliver the cooled fatty alcohol polyoxyethylene ether AEO to the second microchannel reactor to perform sulfation reaction with gaseous SO3 to generate the fatty alcohol polyoxyethylene ether sulfate AESA; Step five, vacuum degassing: deliver the sulfation product to the falling-film evaporator to perform vacuum degassing to remove residual SO3 and by-product dioxane; deliver the removed gas to the Venturi tube to mix with dry air and then deliver it to the sulfur burning furnace for incineration treatment; Step six, neutralization and refining: deliver the degassed fatty alcohol polyoxyethylene ether sulfate AESA to the neutralization reactor, add 30% NaOH aqueous solution to adjust the pH to 7-8, and at the same time, add deionized water to dilute the fatty alcohol polyoxyethylene ether sulfate AES to a concentration of 70%; filter the neutralization product by means of the membrane separation system to remove unreacted impurities and catalyst residues; Step seven, drying and packaging: deliver the refined fatty alcohol polyoxyethylene ether sulfate AES solution to the spray drying tower to dry to obtain the powdery AES product, and then package it for storage.

2. The low energy high conversion AES continuous synthesis process according to claim 1, characterized in that: The fatty alcohol in step one is preferably C 12 -C 14 The fatty alcohol in step one is preferably C The catalyst is preferably KOH, and the amount used is 0.3-0.5% of the mass of the fatty alcohol; the heating temperature is 60-80°C, and the water is removed by a vacuum dehydration system until the water content is ≤0.1%.

3. The low energy intensive high conversion AES continuous synthesis process according to claim 1, wherein: In the step two, the first microchannel reactor controls the reaction temperature to be 175-190℃, the pressure to be 1.1-1.5 MPa, and the residence time to be 6.5-12.5 minutes.

4. The low energy, high conversion, continuous synthesis process of AES according to claim 1, characterized in that: In the step three, the temperature of the high-temperature SO2 / air mixture gas is 600-650℃.

5. The low energy, high conversion, continuous synthesis process of AES according to claim 1, characterized in that: In the step four, the gaseous SO3 has a volume concentration of 5% and the rest is air, and the sulfation reaction parameters are as follows: the reaction is performed at a temperature of 40-45℃ and a pressure of 0.2 MPa.

6. The low energy, high conversion, continuous synthesis process of AES according to claim 1, characterized in that: In the step five, the vacuum degassing controls the temperature to be 50-60℃ and the vacuum degree to be -40 to -80 kPa.

7. The method of claim 1, wherein the process is a continuous process for the synthesis of AES with low energy consumption and high conversion rate, characterized in that: In the step six, the membrane separation system has a pore size of 0.1-0.5 μm.

8. The method of claim 1, wherein the process is a continuous process for the synthesis of AES with low energy consumption and high conversion rate, characterized in that: In the step seven, the spray drying tower has a drying condition of drying at an inlet temperature of 180-200℃ and an outlet temperature of 80-90℃.

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