Method for preparing low-acid-value waste oil by supergravity rotating bed reinforced catalytic esterification

Abstract

The present application relates to biomass oil pretreatment, catalytic reaction engineering technology, disclose a kind of supergravity rotating bed enhanced catalytic esterification method for preparing low acid value waste oil, comprising the following steps: step 1: preparing reaction material and configuring main reaction equipment;Step 2: material premixing: the molten high acid value waste oil is added into static mixer with anhydrous methanol, and oil alcohol two-phase mixture is obtained by preliminary mixing;Step 3: oil alcohol two-phase mixture is continuously introduced into rotating packed bed reactor filled with composite solid acid catalyst in rotor packing layer;Step 4: into gas-liquid separator;Step 5: after the esterification oil of step 4 is separated methanol steam, it is sent into settling tank, and stratifies after standing.This application provides a kind of supergravity enhancement, heterogeneous catalysis, continuous, fast and efficient catalytic esterification method, realizes the rapid acid reduction of high acid value waste oil.

Description

Technical Field

[0001] This invention relates to the fields of biomass oil pretreatment and catalytic reaction engineering technology, specifically to a method for preparing low-acid-value waste oil by enhanced catalytic esterification using a high-gravity rotating bed. Background Technology

[0002] Waste oils (such as waste cooking oil and refined vegetable oil) are high-quality, inexpensive raw materials for producing renewable biomass fuels, especially sustainable aviation fuels. However, these oils undergo hydrolysis and oxidation during repeated high-temperature heating and storage, resulting in a significant increase in free fatty acid content, with acid values ​​typically reaching 50–120 mg KOH / g. Directly subjecting high-acid-value oils to subsequent catalytic conversion leads to rapid catalyst deactivation, a substantial decrease in reaction efficiency, and reduced product selectivity. Therefore, it is essential to pre-treat these oils by converting free fatty acids into fatty acid methyl esters through esterification.

[0003] Currently, traditional oil esterification processes mostly employ batch reactors and fixed-bed reactors, which have the following technical drawbacks: 1) High interphase mass transfer resistance in the reaction system, resulting in slow esterification reaction rates and reaction times lasting several hours, leading to low production efficiency; 2) Uneven mixing of catalyst and raw materials, resulting in low reaction conversion rates and difficulty in reducing the acid value to below 1 mg KOH / g; 3) Existing processes mostly use homogeneous acid catalysts such as concentrated sulfuric acid and p-toluenesulfonic acid, which lead to cumbersome subsequent separation, generate large amounts of wastewater, and corrode equipment; 4) Existing hypergravity esterification technologies are either designed for the synthesis of ordinary esters or employ homogeneous catalysts and precious metal-supported catalyst systems, which suffer from high patent barriers and high production costs. Therefore, a hypergravity process is needed for heterogeneous catalytic esterification of high-acid-value waste oils to reduce acidity and is also suitable for subsequent aviation fuel preparation. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of slow reaction rate, poor acid reduction effect, and difficulty in catalyst separation in existing waste oil esterification pretreatment processes, and to provide a supergravity-enhanced, heterogeneous catalysis, continuous, rapid and efficient catalytic esterification method to achieve rapid acid reduction of high-acid-value waste oil.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing low-acid-value waste oil by enhanced catalytic esterification using a high-gravity rotating bed, comprising the following steps: Step 1: Prepare reaction materials and configure main reaction equipment; materials include high-acid-value waste oil, anhydrous methanol as the esterification reagent, and A composite solid acid catalyst; then a static mixer, a rotating packed bed reactor, a gas-liquid separator, and a settling tank are connected in series. Step 2: Material premixing: Heat the high acid value waste oil to 50-70℃ to melt it. Add the molten high acid value waste oil and anhydrous methanol to a static mixer at a molar ratio of 4:1 to 8:1 for the free fatty acids in the high acid value waste oil. The mixture is initially mixed to obtain an oil-methanol two-phase mixture. Step 3: The oil-ethanol two-phase mixture is continuously introduced into the rotor packing layer at a liquid hourly space velocity of 0.5–2.0 h⁻¹. A rotating packed bed reactor with composite solid acid catalysts was used; then, esterification was carried out under the conditions of a hypergravity factor of 150-600, a reaction temperature of 65℃-90℃, and a reaction pressure of 0.1MPa-0.3MPa, with a single residence time of 10-30 min. Step 4: The esterified material in the rotating packed bed reactor is passed into a gas-liquid separator to separate the unreacted excess methanol vapor and obtain esterified oil. Step 5: The esterified oil after separating methanol vapor in Step 4 is sent to a settling tank, allowed to stand and separate into layers, and then the trace water generated in the reaction is removed to obtain low acid value waste oil with an acid value ≤0.5mgKOH / g.

[0006] Furthermore, in step 2, a heat transfer oil furnace or heating cylinder is used to melt the high-acid-value waste oil.

[0007] Furthermore, The preparation steps of the composite solid acid catalyst are as follows: Step S1: Dissolve tin tetrachloride and tetrabutyl titanate in anhydrous ethanol at a molar ratio of 1:1.2 to 1:2, stir to form a uniform sol, add ammonia to adjust the pH to 7 to 8, let stand for aging for 10 to 14 hours, filter and wash until no chloride ions are present, dry and calcine at 500 to 600℃ for 2 to 4 hours to obtain SnO2-TiO2 composite support; Step S2: Immerse the SnO2-TiO2 composite support in a 0.5–1.0 mol / L sulfuric acid solution for 4–6 hours, filter, dry at 100–120℃, and then calcine at 450–550℃ for 1–3 hours to obtain the desired product. Composite solid acid catalyst.

[0008] Furthermore, in step S1, tin tetrachloride and tetrabutyl titanate are dissolved in anhydrous ethanol at a molar ratio of 1:1.5.

[0009] Furthermore, the product obtained in step S2 The composite solid acid catalyst has a particle size of 2-5 mm and a specific surface area of ​​≥200 m² / g.

[0010] Furthermore, in step S2, the concentration of the sulfuric acid solution is 0.8 mol / L; the impregnation time is 5 h; and the calcination conditions are: calcination at 500℃ for 2 h.

[0011] Furthermore, the gravity factor of the rotating bed reactor is 200–400; the reaction temperature is 70–80℃; and the liquid hourly space velocity is 0.8–1.5 h⁻¹.

[0012] Furthermore, the high-acid-value waste oil is selected from at least one of waste cooking oil and refined acidified vegetable oil; the molar ratio of anhydrous methanol to free fatty acids in the high-acid-value waste oil is 5:1 to 7:1.

[0013] Furthermore, the method is used to provide low-acid-value waste oil feedstock for subsequent hydrogen-free directional conversion to produce sustainable aviation fuel.

[0014] The beneficial effects of this invention are: 1. A heterogeneous supported composite solid acid catalyst is filled in a high-gravity rotating bed. By utilizing the high-intensity shearing action of a centrifugal rotating bed, the interfacial tension between the oil and alcohol phases is broken, and the material is microfluidized. The mass transfer efficiency is increased by 10 to 15 times compared to traditional reactors, and the esterification reaction rate is significantly accelerated, with a single residence time of only 10 to 30 minutes, much faster than traditional batch processes. The high-intensity shearing and centrifugal force of hundreds of times gravity impose harsh mechanical loads on the packed catalyst particles. Conventional solid acid catalysts (such as powders and low-strength extruders) will quickly wear down and fail. This solution, through a specific SnO2 content and calcination process to form a SnO2-TiO2 composite support, possesses mechanical strength adapted to the specific stress field inside the centrifugal rotor. It truly achieves in-situ retention and long-term continuous operation of heterogeneous catalysts within the reactor, an effect that low-strength catalysts simply cannot achieve.

[0015] 2. The catalyst has high catalytic activity and strong stability. After the reaction, the catalyst is retained in the supergravity rotor, eliminating the need for subsequent separation processes, and resulting in no equipment corrosion or wastewater generation.

[0016] 3. The entire preparation process can achieve continuous operation of raw material feeding, reaction, and separation; it is simple to operate, suitable for industrial production, and the acid reduction effect is stable and controllable; the final acid value can be stably reduced to below 0.5 mg KOH / g, the reaction time is shortened by more than 80%, and it is fully compatible with the subsequent hydrogen-free directional conversion process for the preparation of sustainable aviation fuel. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific examples. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The directional terms mentioned in this invention, such as "up", "down", "front", "back", "left", "right", "inner", "outer", "side", "top" and "bottom", are only for reference to the orientation of the accompanying drawings. The directional terms used are for the purpose of explaining and understanding this invention and are not absolute limitations on the actual use.

[0020] Example 1: like Figure 1 As shown, a method for preparing low-acid-value waste oil by enhanced catalytic esterification using a high-gravity rotating bed includes the following steps: Step 1: Prepare reaction materials and configure main reaction equipment; materials include high-acid-value waste oil, anhydrous methanol as the esterification reagent, and A composite solid acid catalyst; then a static mixer, a rotating packed bed reactor, a gas-liquid separator, and a settling tank are connected in series. Step 2: Material premixing: Heat the high acid value waste oil to 50-70℃ to melt it. Add the molten high acid value waste oil and anhydrous methanol to a static mixer at a molar ratio of 4:1 to 8:1 for the free fatty acids in the high acid value waste oil. The mixture is initially mixed to obtain an oil-methanol two-phase mixture. Step 3: The oil-ethanol two-phase mixture is continuously introduced into the rotor packing layer at a liquid hourly space velocity of 0.5–2.0 h⁻¹. A rotating packed bed reactor with a composite solid acid catalyst was used. Esterification was carried out under conditions of a hypergravity factor of 150–600, a reaction temperature of 65℃–90℃, and a reaction pressure of 0.1 MPa–0.3 MPa, with a single residence time of 10–30 min. Under the influence of hypergravity, the oil and alcohol phases were sheared and broken into micron-sized droplets and liquid films by the rotor, greatly enhancing interphase mass transfer. Esterification occurred rapidly on the catalyst surface, with free fatty acids reacting with methanol to form fatty acid methyl esters, achieving rapid acid reduction. Step 4: The esterification reaction product in the rotating packed bed reactor is passed into a gas-liquid separator to separate the unreacted excess methanol vapor and obtain esterified oil; the methanol vapor is condensed and recycled. Step 5: The esterified oil after separating methanol vapor in Step 4 is sent to a settling tank, allowed to stand and separate into layers, and then the trace water generated in the reaction is removed to obtain low acid value waste oil with an acid value ≤0.5mgKOH / g.

[0021] In step 2, a heat transfer oil furnace or heating cylinder is used to melt the high-acid-value waste oil.

[0022] The preparation steps of the composite solid acid catalyst are as follows: Step S1: Dissolve tin tetrachloride and tetrabutyl titanate in anhydrous ethanol at a molar ratio of 1:1.2 to 1:2, stir to form a uniform sol, add ammonia to adjust the pH to 7 to 8, let stand for aging for 10 to 14 hours, filter and wash until no chloride ions are present, dry and calcine at 500 to 600℃ for 2 to 4 hours to obtain SnO2-TiO2 composite support; Step S2: Immerse the SnO2-TiO2 composite support in a 0.5–1.0 mol / L sulfuric acid solution for 4–6 hours, filter, dry at 100–120℃, and then calcine at 450–550℃ for 1–3 hours to obtain the desired product. Composite solid acid catalyst.

[0023] In step S1, tin tetrachloride and tetrabutyl titanate are dissolved in anhydrous ethanol at a molar ratio of 1:1.5.

[0024] The product obtained in step S2 The composite solid acid catalyst has a particle size of 2-5 mm and a specific surface area of ​​≥200 m² / g.

[0025] In step S2, the concentration of the sulfuric acid solution is 0.8 mol / L; the impregnation time is 5 h; and the calcination conditions are: calcination at 500℃ for 2 h.

[0026] The gravity factor of the rotating bed reactor is 200–400; the reaction temperature is 70–80℃; and the liquid hourly space velocity is 0.8–1.5 h⁻¹.

[0027] The high-acid-value waste oil is selected from at least one of waste cooking oil and refined acidified vegetable oil; the molar ratio of anhydrous methanol to free fatty acids in the high-acid-value waste oil is 5:1 to 7:1.

[0028] The method is used to provide low-acid-value waste oil feedstock for the subsequent hydrogen-free directional conversion to prepare sustainable aviation fuel.

[0029] This solution breaks through the mass transfer bottleneck of traditional esterification reactions, shortening the reaction time by more than 80% compared with the traditional batch reactor process, and significantly improving production efficiency. It can stably reduce the acid value of high-acid-value waste oil to below 0.5 mg KOH / g, fully meeting the raw material requirements for subsequent hydrogen-free directional conversion to prepare aviation fuel, and avoiding catalyst deactivation; The heterogeneous solid acid catalyst is used, which prevents equipment corrosion. The catalyst can be used continuously without separation and recovery. Excess methanol can be recycled and no process wastewater is generated. The entire process is continuous, the process parameters are easy to adjust, the equipment occupies a small area, and it is suitable for large-scale waste oil pretreatment.

[0030] This solution circumvents traditional homogeneous esterification process patents: it does not use homogeneous catalysts such as concentrated sulfuric acid and p-toluenesulfonic acid, but adopts heterogeneous solid acid catalysis, eliminating separation and wastewater issues; it also circumvents existing hypergravity esterification patents: it does not use patented heteropolyacid or precious metal supported catalysts, but innovates an SO4²⁻ / SnO2-TiO2 composite catalyst system, optimizing hypergravity process parameters and reactor loading methods; and it circumvents oil pretreatment patents: it is specifically designed for acid reduction of aviation fuel raw materials, achieving seamless integration between esterification pretreatment and subsequent hydrogen-free conversion processes, distinguishing it from ordinary oil esterification acid reduction processes.

[0031] The material and equipment parameters selected in this embodiment are as follows: the raw material is waste cooking oil with an acid value of 85 mgKOH / g; Material premixing: Heat the oil to 60℃ to melt, and mix the methanol and free fatty acids in a molar ratio of 6:1 statically; Reaction phase: gravity factor of 400, reaction temperature of 75℃, reaction pressure of 0.1MPa, liquid hourly space velocity of 1.0h⁻¹, residence time of 20min; Product: The acid value of the esterified oil is 0.38 mg KOH / g, the conversion rate of free fatty acids is ≥99.2%, the methanol recovery rate is 95%, and the resulting low acid value oil is directly used for subsequent hydrogen-free directional conversion to prepare SAF.

[0032] Example 2: Unlike Example 1, the material and equipment parameters selected in this example are as follows: the raw material is waste cooking oil with an acid value of 110 mg KOH / g; Material premixing: Heat the oil to 65℃ to melt, and mix the methanol and free fatty acids in a molar ratio of 7:1 statically; Reaction phase: gravity factor of 500, reaction temperature of 75℃, reaction pressure of 0.2MPa, liquid hourly space velocity of 0.8h⁻¹, residence time of 25min; Product: The esterified oil has an acid value of 0.32 mg KOH / g, a free fatty acid conversion rate of ≥99.5%, and a methanol recovery rate of 95%, making it fully compatible with the subsequent hydrogen-free SAF synthesis process.

[0033] Example 3: Unlike Example 1, the material and equipment parameters selected in this example are as follows: the raw material is waste cooking oil with an acid value of 120 mg KOH / g; Material premixing: Heat the oil to 50℃ to melt, and mix the methanol and free fatty acids in a molar ratio of 5:1 statically; Reaction phase: gravity factor of 150, reaction temperature of 65℃, reaction pressure of 0.3MPa, liquid hourly space velocity of 2.0h⁻¹, residence time of 30min; Sn:Ti = 1:1.2; Product: The acid value of the esterified oil is 0.45 mg KOH / g, the conversion rate of free fatty acids is ≥98.6%, and the methanol recovery rate is 94%.

[0034] Example 4: Unlike Example 1, the material and equipment parameters selected in this example are as follows: the raw material is waste cooking oil with an acid value of 50 mg KOH / g; Material premixing: Heat the oil to 70℃ to melt, and mix the methanol and free fatty acids in a molar ratio of 8:1 statically; Reaction phase: gravity factor of 600, reaction temperature of 90℃, reaction pressure of 0.2MPa, liquid hourly space velocity of 0.5h⁻¹, residence time of 10min; Sn:Ti = 1:2; Product: The acid value of the esterified oil is 0.29 mg KOH / g, the conversion rate of free fatty acids is ≥99.7%, and the methanol recovery rate is 96%.

[0035] Example 5: Unlike Example 1, the material and equipment parameters selected in this example are as follows: the raw material is waste cooking oil with an acid value of 70 mg KOH / g; Material premixing: Heat the oil to 60℃ to melt, and mix the methanol and free fatty acids in a molar ratio of 4:1 statically; Reaction phase: gravity factor of 300, reaction temperature of 90℃, reaction pressure of 0.2MPa, liquid hourly space velocity of 0.8h⁻¹, residence time of 20min; Sn:Ti = 1:1.5; Product: The acid value of the esterified oil is 0.41 mg KOH / g, the conversion rate of free fatty acids is ≥98.9%, and the methanol recovery rate is 95%.

[0036] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing low-acid-value waste oil by enhanced catalytic esterification using a high-gravity rotating bed, characterized in that, Includes the following steps: Step 1: Prepare reaction materials and configure main reaction equipment; materials include high-acid-value waste oil, anhydrous methanol as the esterification reagent, and A composite solid acid catalyst; then a static mixer, a rotating packed bed reactor, a gas-liquid separator, and a settling tank are connected in series. Step 2: Material premixing: Heat the high acid value waste oil to 50-70℃ to melt it. Add the molten high acid value waste oil and anhydrous methanol to a static mixer at a molar ratio of 4:1 to 8:1 for the free fatty acids in the high acid value waste oil. The mixture is initially mixed to obtain an oil-methanol two-phase mixture. Step 3: The oil-ethanol two-phase mixture is continuously introduced into the rotor packing layer at a liquid hourly space velocity of 0.5–2.0 h⁻¹. A rotating packed bed reactor with composite solid acid catalysts was used; then, esterification was carried out under the conditions of a hypergravity factor of 150-600, a reaction temperature of 65℃-90℃, and a reaction pressure of 0.1MPa-0.3MPa, with a single residence time of 10-30 min. Step 4: The esterified material in the rotating packed bed reactor is passed into a gas-liquid separator to separate the unreacted excess methanol vapor and obtain esterified oil. Step 5: The esterified oil after separating methanol vapor in Step 4 is sent to a settling tank, allowed to stand and separate into layers, and then the trace water generated in the reaction is removed to obtain low acid value waste oil with an acid value ≤0.5mgKOH / g.

2. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 1, characterized in that: In step 2, a heat transfer oil furnace or heating cylinder is used to melt the high-acid-value waste oil.

3. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 1, characterized in that: The The preparation steps of the composite solid acid catalyst are as follows: Step S1: Dissolve tin tetrachloride and tetrabutyl titanate in anhydrous ethanol at a molar ratio of 1:1.2 to 1:2, stir to form a uniform sol, add ammonia to adjust the pH to 7 to 8, let stand for aging for 10 to 14 hours, filter and wash until no chloride ions are present, dry and calcine at 500 to 600℃ for 2 to 4 hours to obtain SnO2-TiO2 composite support; Step S2: Immerse the SnO2-TiO2 composite support in a 0.5–1.0 mol / L sulfuric acid solution for 4–6 hours, filter, dry at 100–120°C, and then calcine at 450–550°C for 1–3 hours to obtain the desired product. Composite solid acid catalyst.

4. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 3, characterized in that: In step S1, tin tetrachloride and tetrabutyl titanate are dissolved in anhydrous ethanol at a molar ratio of 1:1.

5.

5. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 3, characterized in that: The product obtained in step S2 The composite solid acid catalyst has a particle size of 2-5 mm and a specific surface area of ​​≥200 m² / g.

6. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 3, characterized in that: In step S2, the concentration of the sulfuric acid solution is 0.8 mol / L; the impregnation time is 5 h; and the calcination conditions are: calcination at 500℃ for 2 h.

7. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 1, characterized in that: The gravity factor of the rotating bed reactor is 200–400; the reaction temperature is 70–80°C; and the liquid hourly space velocity is 0.8–1.5 h⁻¹.

8. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 1, characterized in that: The high-acid-value waste oil is selected from at least one of waste cooking oil and refined acidified vegetable oil; the molar ratio of anhydrous methanol to free fatty acids in the high-acid-value waste oil is 5:1 to 7:

1.

9. The method for preparing low-acid-value waste oil by enhanced catalytic esterification in a high-gravity rotating bed according to claim 1, characterized in that: The method is used to provide low-acid-value waste oil feedstock for the subsequent hydrogen-free directional conversion to prepare sustainable aviation fuel.

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