Preparation method of corrosion inhibitor for fractionation system

Abstract

The invention relates to the technical field of corrosion inhibitors, in particular to a preparation method of a corrosion inhibitor for a fractionation system. The preparation method of the fractionation system corrosion inhibitor comprises the following specific steps: firstly, under the protection of nitrogen, fatty acid and organic amine are subjected to an acylation dehydration reaction and a cyclization reaction to obtain an intermediate material, then the intermediate material reacts with 3, 4-dihydroxybenzaldehyde, a catechol group having a strong adsorption effect on metal is introduced into a molecular structure, and the fractionation system corrosion inhibitor is obtained. And the fractionation system corrosion inhibitor with relatively high corrosion inhibition efficiency is obtained. A catalyst is added in the reaction process of fatty acid and organic amine, the catalyst is further modified, the catalytic reaction rate is increased, the corrosion inhibition efficiency is further improved, and the corrosion inhibitor obtained through the method is applied to a fractionation system and has high corrosion inhibition efficiency under the conditions of high temperature, high acid, high salt and the like.

Description

Technical Field

[0001] The present application relates to the technical field of corrosion inhibitors, and in particular to a method for preparing a corrosion inhibitor for a fractionation system. Background Art

[0002] In recent years, with the increasing trend of heavier and inferior crude oil, the proportion of high-acid, high-sulfur and high-salt crude oil processed by refineries has become increasingly higher, causing more and more serious corrosion of equipment such as refinery distillation systems. Phenomena such as pipe wall thinning, leakage and salt deposition have occurred, seriously affecting the normal operation of distillation systems and other equipment, and posing great safety hazards to production. Therefore, the research and development of corrosion inhibitors suitable for distillation systems has very important theoretical significance and practical application value.

[0003] Commonly used corrosion inhibitors for fractionation systems include imidazoline, triazole and pyridine compounds, but triazole corrosion inhibitors have poor oil solubility and are not suitable for oil system corrosion protection. Pyridine corrosion inhibitors are highly toxic, increasing the pressure on environmental management. Imidazoline corrosion inhibitors have the advantages of good thermal stability, high corrosion inhibition efficiency and low toxicity, so they have become the most promising corrosion inhibitors at present.

[0004] Imidazoline corrosion inhibitors have excellent performance, but the process control is difficult during the synthesis process. For example, when using the solvent dehydration method, if the dehydration is not thorough, it will not only affect the ring formation of imidazoline, but also may cause the hydrolysis of the imidazoline ring, which not only increases the cost and energy consumption, but also greatly reduces the corrosion inhibition performance.

[0005] In order to improve the corrosion inhibition performance of the imidazoline corrosion inhibitor, it is necessary to promote the formation of the imidazoline ring and reduce the hydrolysis of the imidazoline ring. Therefore, it is necessary to accelerate the ring formation rate or effectively remove the water generated during the reaction. The commonly used method is to use a high-efficiency catalyst and a water separator. The application document with publication number CN117567375A discloses a tall oil amine ethyl imidazoline corrosion inhibitor and a preparation method thereof, which uses a 5A molecular sieve as a carrier and a solid acid with 3,4,5-trifluorophenylboric acid as an active component as a catalyst to accelerate the reaction rate. However, the 5A molecular sieve has a rich void structure and may absorb moisture during the reaction, which is not conducive to the removal of moisture. In addition, the 5A molecular sieve itself does not have catalytic performance, which may reduce the corrosion inhibition performance. Summary of the invention

[0006] In order to improve the corrosion inhibition performance of the corrosion inhibitor, the present application provides a method for preparing a corrosion inhibitor for a fractionation system.

[0007] A method for preparing a corrosion inhibitor for a fractionation system comprises the following steps: S1: Mix fatty acid and water separator, heat to 140-170°C under nitrogen protection, and stir continuously, add organic amine, react for 1-2h, program temperature rise to 190-220°C, install water separator, react for 3-8h, and then distill under reduced pressure to obtain intermediate material; S2: Dissolve the intermediate material in anhydrous ethanol, heat to 50-75°C, slowly add anhydrous ethanol solution containing 3,4-dihydroxybenzaldehyde, react for 4-8 hours, cool the reaction solution and filter it under reduced pressure, wash the product with n-hexane and vacuum dry it to obtain.

[0008] In the above technical scheme, fatty acids and organic amines are first acylated and dehydrated under nitrogen protection, and then programmed temperature cyclodehydration is performed, and an intermediate material is obtained by vacuum distillation. Then, the intermediate material reacts with 3,4-dihydroxybenzaldehyde to graft the catechol group onto the intermediate material molecule, and a carbon-nitrogen double bond is formed at the same time. In the above corrosion inhibitor preparation process, on the one hand, cyclodehydration forms a five-membered heterocyclic compound, which has a conjugated system that is easy to provide π electrons in its molecular structure, and the nitrogen atom in the heterocyclic ring has a high electronegativity and a large electron density, which can form a strong coordination bond with the empty orbital of the metal atom on the metal surface, thereby forming a stable adsorption film. Secondly, the hydroxyl group in the catechol group can form hydrogen bonds with the metal surface, so that the catechol group can be firmly adsorbed on the metal surface, and the large π conjugated system formed by the benzene ring and the carbon-nitrogen double bond further increases the adsorption of the corrosion inhibitor molecule on the metal surface, forming a stronger coordination bond. Therefore, the conjugated system and heteroatoms of the five-membered heterocyclic ring and the hydroxyl group and large π conjugated system of catechol can make the corrosion inhibitor molecule firmly adsorbed on the metal surface, and interact strongly with the atoms on the metal surface through hydrogen bonds and coordination bonds to form a stable protective film, change the charge distribution and interface properties of the metal surface, and stabilize the energy state of the metal surface, thereby increasing the activation energy of the corrosion reaction and inhibiting corrosion on the metal surface. Thirdly, the fatty acid has a long-chain alkyl group, which can be perpendicular to the metal surface to form a hydrophobic protective film covering the metal surface, hindering and shielding the diffusion of the corrosive medium to the metal surface, and reducing the contact between the corrosive medium and the metal surface, so it is beneficial to reduce the corrosion rate and improve the corrosion inhibition performance.

[0009] In addition, a certain amount of water will be produced during the acylation dehydration and cyclization dehydration processes. If it cannot be removed in time, the reaction rate will be reduced, and even the number of imidazoline rings will be reduced, and the interaction force with the metal surface will be weakened. Therefore, the corrosion inhibition performance will also be reduced. Therefore, a water separator is added during the acylation and cyclization processes so that the water produced during the reaction and the water separator can be evaporated in the form of an azeotrope, reducing the influence of water molecules on the product.

[0010] Preferably, the fatty acid in step S1 is one or more of dodecanoic acid, tetradecanoic acid, hexadecanoic acid and octadecanoic acid; the organic amine is one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine; and the water-separating agent is toluene or xylene.

[0011] Preferably, the molar ratio of the fatty acid to the organic amine in step S1 is 1:(1-1.4).

[0012] Preferably, in step S1, the rate of the programmed temperature increase is 2-8°C / min.

[0013] Preferably, in step S2, the mass ratio of the intermediate material to 3,4-dihydroxybenzaldehyde is 1:(0.35-0.46).

[0014] Further preferably, a catalyst is added in step S1, wherein the catalyst is boric acid, and the amount of the catalyst added is 1%-10% of the sum of the mass of the fatty acid and the organic amine.

[0015] In the above technical scheme, boric acid has the advantages of safety, environmental protection and low cost. Boric acid as a catalyst can indeed increase the reaction rate of fatty acids and organic amines. However, when fatty acids are changed to aromatic carboxylic acids and organic amines are aromatic amines, more boric acid catalysts need to be added to achieve a higher reaction rate.

[0016] Further preferably, the catalyst is modified by a method comprising the following steps: (1) Add a dispersant to an aqueous solution of aluminum nitrate, add an ammonium carbonate solution dropwise under vigorous stirring until the pH is acidic, continue stirring for 0.5-1h, age for 12-48h, filter and dry to obtain a dry gel powder, add n-butanol to the dry gel powder, reflux for 1-3h, distill and filter, and calcine at 600-1000°C for 1-3h to obtain nano alumina; (2) Dissolve boric acid in water, add nano-alumina, heat to 50-65°C, stir for 1-5 hours, rotary evaporate and dry.

[0017] By adopting the above technical scheme, firstly, the nano-alumina obtained by the sol-gel method has a larger specific surface area and a higher loading amount of boric acid, and the organic functional groups of boric acid can be "anchored" on the surface of the nano-alumina to form a catalytic center. Therefore, after loading, the catalytic ability will be enhanced, which is beneficial to the acylation and cyclization reactions, thereby helping to improve the corrosion inhibition performance; secondly, the surface of the nano-alumina contains certain acidic and alkaline sites, which itself has a certain catalytic ability and can synergize with boric acid to improve the catalytic efficiency, thereby also helping to improve the corrosion inhibition performance of the corrosion inhibitor.

[0018] Preferably, in step (2), the mass ratio of boric acid to nano-alumina is 1:(0.5-2).

[0019] Further preferably, in step (1), the nano-alumina is modified by a method comprising the following steps: Disperse nano-alumina in anhydrous ethanol to obtain a suspension, mix a silane coupling agent with water, slowly drop glacial acetic acid while stirring to make the solution acidic to obtain a silane hydrolyzate, slowly drop the silane hydrolyzate into the suspension, stir at 70-90°C until it becomes viscous, wash with anhydrous ethanol, filter, and dry.

[0020] By adopting the above technical scheme, the nano-alumina is hydrophobically modified by a silane coupling agent, which can reduce the adsorption of water molecules by the nano-alumina in the acylation dehydration and cyclization dehydration reactions, making it easier for the water molecules to evaporate, thereby making it easier to cyclize and improving its corrosion inhibition performance.

[0021] Preferably, the silane coupling agent is one or more of vinyl triethoxysilane, vinyl trimethoxysilane and γ-methacryloxypropyl trimethoxysilane; and the mass ratio of the nano-alumina to the silane coupling agent is 100:(2-6).

[0022] The above technical solution of the present application includes at least the following beneficial effects: 1. The corrosion inhibitor obtained by the preparation method of the present application has strong adsorption to the metal surface and high corrosion inhibition efficiency.

[0023] 2. In the present application, boric acid is loaded on nano-alumina as a catalyst to increase the reaction rate of fatty acids and organic amines, thereby improving the corrosion inhibition efficiency.

[0024] 3. The present application performs hydrophobic modification on nano-alumina to reduce the adsorption of water during the acylation and cyclization reactions, making it easier to remove the water produced by the reactions, thereby being more conducive to the formation of imidazoline rings and further improving its corrosion inhibition performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the corrosion inhibition efficiency of the corrosion inhibitor for the distillation system obtained by the preparation method of Examples 1-9 and Comparative Example 1. DETAILED DESCRIPTION

[0026] The present application is further described in detail below with reference to the embodiments.

[0027] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0028] Example Example 1 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment comprises the following steps: S1: Add 20 g of dodecanoic acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 140°C, and stir continuously. Add 14.4 g of diethylenetriamine, react for 2 h, and then heat to 220°C at a rate of 2°C / min. Install a water separator and react for 3 h until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 h to remove unreacted diethylenetriamine and xylene to obtain an intermediate material. S2: Weigh 10 g of the intermediate material and 100 mL of anhydrous ethanol, place them in a flask, heat to 50°C, stir to dissolve, slowly add 50 mL of anhydrous ethanol solution containing 3.5 g of 3,4-dihydroxybenzaldehyde, react for 8 hours, cool the reaction solution, filter it under reduced pressure, remove the filtrate, wash the product with n-hexane, and dry it in vacuum to obtain the product.

[0029] Example 2 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment comprises the following steps: S1: Add 22.8 g of tetradecanoic acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 170°C, and stir continuously. Add 14.6 g of triethylenetetramine, react for 1 hour, and then heat to 190°C at a rate of 8°C / min. Install a water separator and react for 8 hours until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted triethylenetetramine and xylene to obtain an intermediate material. S2: Weigh 10 g of the intermediate material and 100 mL of anhydrous ethanol, place them in a flask, heat to 75°C, stir to dissolve, slowly add 50 mL of anhydrous ethanol solution containing 4.6 g of 3,4-dihydroxybenzaldehyde, react for 4 hours, cool the reaction solution, filter it under reduced pressure, remove the filtrate, wash the product with n-hexane, and dry it in vacuum to obtain the product.

[0030] Example 3 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment comprises the following steps: S1: Add 28.5 g of octadecanoic acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 160°C, and stir continuously. Add 22.7 g of tetraethylene pentamine, react for 1 hour, and then heat to 200°C at a rate of 5°C / min. Install a water separator and react for 4 hours until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted tetraethylene pentamine and xylene to obtain an intermediate material. S2: Weigh 10 g of the intermediate material and 100 mL of anhydrous ethanol, place them in a flask, heat to 60°C, stir to dissolve, slowly add 50 mL of anhydrous ethanol solution containing 4 g of 3,4-dihydroxybenzaldehyde, react for 4 hours, cool the reaction solution, filter it under reduced pressure, remove the filtrate, wash the product with n-hexane, and dry it in vacuum to obtain the product.

[0031] Example 4 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment comprises the following steps: S1: Add 28.5 g of octadecanoic acid, 0.51 g of boric acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 160°C, and stir continuously. Add 22.7 g of tetraethylene pentamine, react for 1 hour, and then heat to 200°C at a rate of 5°C / min. Install a water separator and react for 4 hours until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted tetraethylene pentamine and xylene to obtain an intermediate material. S2: Weigh 10 g of the intermediate material and 100 mL of anhydrous ethanol, place them in a flask, heat to 60°C, stir to dissolve, slowly add 50 mL of anhydrous ethanol solution containing 4 g of 3,4-dihydroxybenzaldehyde, react for 4 hours, cool the reaction solution, filter it under reduced pressure, remove the filtrate, wash the product with n-hexane, and dry it in vacuum to obtain the product.

[0032] Example 5 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment is different from that of Embodiment 4 in that: S1: Add 28.5 g of octadecanoic acid, 5.12 g of boric acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 160°C, and stir continuously. Add 22.7 g of tetraethylene pentamine, react for 1 hour, and then heat to 200°C at a rate of 5°C / min. Install a water separator and react for 4 hours until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted tetraethylene pentamine and xylene to obtain an intermediate material. The remaining steps are the same as those in Example 4; The boric acid is modified by a method comprising the following steps: (1) Aluminum nitrate nonahydrate is dissolved in deionized water to prepare an aluminum nitrate solution with a concentration of 0.2 mol / L; ammonium carbonate is dissolved in deionized water to prepare an ammonium carbonate solution with a concentration of 2 mol / L; 100 mL of the aluminum nitrate solution is weighed, 2 mL of polyethylene glycol octylphenyl ether is added, and the ammonium carbonate solution is added dropwise to the mixed solution under vigorous stirring, and the addition is stopped when the pH value is acidic, and the stirring is continued for 0.5 h, aged for 48 h, filtered, and dried to obtain a dry gel powder, and n-butanol is added to the dry gel powder, vigorously stirred and refluxed for 1 h, the n-butanol is distilled off, filtered, and calcined at 600° C. for 3 h to obtain nano alumina; (2) Weigh 1 g of boric acid and dissolve it in 50 mL of deionized water. Add 2 g of nano-alumina while stirring. Heat to 50°C and stir for 5 h. Then use a rotary evaporator at 70°C under negative pressure to evaporate the water. Then dry the mixture.

[0033] Example 6 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment is different from that of Embodiment 4 in that: S1: Add 28.5 g of octadecanoic acid, 2.56 g of boric acid and 50 mL of xylene to a three-necked flask, introduce nitrogen, heat to 160°C, and stir continuously. Add 22.7 g of tetraethylene pentamine, react for 1 hour, and then heat to 200°C at a rate of 5°C / min. Install a water separator and react for 4 hours until no water is produced in the water separator. Then, perform vacuum distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted tetraethylene pentamine and xylene to obtain an intermediate material. The remaining steps are the same as those in Example 4; The boric acid is modified by a method comprising the following steps: (1) Aluminum nitrate nonahydrate is dissolved in deionized water to prepare an aluminum nitrate solution with a concentration of 0.2 mol / L; ammonium carbonate is dissolved in deionized water to prepare an ammonium carbonate solution with a concentration of 2 mol / L; 100 mL of the aluminum nitrate solution is weighed, 2 mL of polyethylene glycol octylphenyl ether is added, and the ammonium carbonate solution is added dropwise to the mixed solution under vigorous stirring, and the addition is stopped when the pH value is acidic, and the stirring is continued for 1 hour, and the mixture is aged for 12 hours, and then filtered and dried to obtain a dry gel powder, and n-butanol is added to the dry gel powder, and the mixture is vigorously stirred and refluxed for 3 hours, the n-butanol is distilled off, filtered, and calcined at 1000° C. for 1 hour to obtain nano-alumina; (2) Weigh 1 g of boric acid and dissolve it in 50 mL of deionized water. Add 0.5 g of nano-alumina while stirring. Heat to 65°C and stir for 1 h. Then use a rotary evaporator at 70°C to evaporate the water under negative pressure. Then dry the mixture.

[0034] Example 7 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment is the same as that of embodiment 6; The modification method of the boric acid is different from that of Example 6 in that: (2) Weigh 1g of boric acid and dissolve it in 50mL of deionized water. Add 1g of nano-alumina while stirring. Heat to 60°C and stir for 2h. Then use a rotary evaporator at 70°C to evaporate the water under negative pressure. Then dry it. The remaining steps are the same as those in Example 6.

[0035] Example 8 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment is the same as that of embodiment 7; The modification method of boric acid in this embodiment is the same as that in Example 7; The nano-alumina described in this embodiment is modified by a method comprising the following steps: Weigh 10 g of nano-alumina, add 50 mL of anhydrous ethanol, and ultrasonically disperse for 2 hours to obtain a suspension; weigh 0.2 g of vinyltriethoxysilane, add 10 mL of deionized water, slowly add glacial acetic acid while stirring to make the solution acidic to obtain a silane hydrolyzate, slowly drop the silane hydrolyzate into the suspension, stir at 70°C until it becomes viscous, wash with anhydrous ethanol, filter, and dry.

[0036] Example 9 The preparation method of the corrosion inhibitor for the fractionation system of this embodiment is the same as that of embodiment 7; The modification method of boric acid in this embodiment is the same as that in Example 7; The nano-alumina described in this embodiment is modified by a method comprising the following steps: Weigh 10 g of nano-alumina, add 50 mL of anhydrous ethanol, and ultrasonically disperse for 2 hours to obtain a suspension; weigh 0.6 g of γ-methacryloxypropyltrimethoxysilane, add 10 mL of deionized water, slowly add glacial acetic acid while stirring to make the solution acidic to obtain a silane hydrolyzate, slowly drop the silane hydrolyzate into the suspension, stir at 90°C until it becomes viscous, wash with anhydrous ethanol, filter, and dry.

[0037] Comparative Example Comparative Example 1 The preparation method of the corrosion inhibitor for the fractionation system of this comparative example comprises the following steps: Add 20 g of dodecanoic acid and 50 mL of xylene into a three-necked flask, introduce nitrogen, heat to 140°C, and stir continuously. Add 14.4 g of diethylenetriamine and react for 2 hours. Then, heat to 220°C at a rate of 2°C / min. Install a water separator and react for 3 hours until no water is produced in the water separator. Then, perform reduced pressure distillation, cool to 140°C, and keep warm for 2 hours to remove unreacted diethylenetriamine and xylene.

[0038] Performance testing Corrosion inhibition performance test method The corrosion inhibition performance of the distillation system corrosion inhibitor obtained by the preparation method of Examples 1-9 and Comparative Example 1 was determined by the static hanging plate weight loss method. The corrosion rate was calculated by measuring the change in mass of the steel sheet before and after corrosion, and then the corrosion inhibition efficiency was calculated. The higher the corrosion inhibition efficiency, the better the corrosion inhibition performance of the distillation system corrosion inhibitor.

[0039] Simulation of corrosion environment: In actual production, the corrosive media in the circulating reflux system at the top of the distillation tower are mainly chlorides, sulfides and other compounds. The oil circulating reflux at the top of the distillation tower is generally acidic and has a high temperature. This test uses 1000μg / gHCl-500μg / g(NH4)2S-white oil as the corrosive medium to simulate the corrosion environment of the circulating reflux system at the top of the distillation tower, and uses ammonia water to adjust the pH to 5.5.

[0040] Specific corrosion test steps: (1) The steel sheet was polished with sandpaper, cleaned with acetone and anhydrous ethanol, air-dried, and weighed after drying to constant weight. The steel sheet was then hung in a container containing a corrosive medium and immersed at 135°C for 12 h. (2) Take out the steel sheet, wash it with distilled water, then with acetone and anhydrous ethanol, then dry it in the air until it reaches a constant weight and weigh it; (3) Calculate the corrosion rate of the steel sheet based on the weight loss of the steel sheet, and then calculate the corrosion inhibition efficiency; Corrosion rate v=m0-m1 / st, where m0 is the mass before weight loss, g; m1 is the mass after weight loss, g; s is the surface area of ​​the steel sheet, m2; t is the corrosion time, h.

[0041] Corrosion inhibition efficiency η = v0-v1 / v0×100%, where v0 is the corrosion rate of the steel sheet in the blank test, g / (㎡•h); v1 is the corrosion rate of the steel sheet when the fractionation system corrosion inhibitor is added, g / (㎡•h). The calculation results are as follows: Figure 1 shown.

[0042] In the above corrosion test, the distillation system corrosion inhibitor prepared by Examples 1-9 and Comparative Example 1 was first dissolved in ethanol and then added to the corrosive medium. The amount of distillation system corrosion inhibitor added was 50 ppm. At the same time, a blank comparison test was performed, that is, the corrosion test was performed without adding the corrosion inhibitor.

[0043] Results Analysis from Figure 1 It can be seen from the data of Comparative Example 1 and Examples 1-3 that the introduction of catechol groups greatly improves the corrosion inhibition efficiency. The reason may be that the catechol groups make the corrosion inhibitor more adsorbable to the metal surface and more interactive with the metal atoms, so the protective film formed is more stable and the corrosion inhibition efficiency is higher; in addition, when the alkyl side chain is longer, the corrosion inhibition efficiency is higher, which may be because the alkyl side chain hinders the diffusion of the corrosive medium to the metal surface. The corrosion inhibition efficiency of the biodegradable corrosion inhibitor obtained by the preparation method of the embodiment is greater than 80%. After modification, the corrosion inhibition efficiency is improved, and the maximum can exceed 95%.

[0044] from Figure 1It can be seen from the data of Examples 3-7 that adding a catalyst during the reaction of fatty acids and organic amines is beneficial to improving the corrosion inhibition efficiency, and when boric acid is loaded on nano-alumina, the corrosion inhibition efficiency is further improved. This may be because boric acid loaded on nano-alumina can improve the catalytic performance, accelerate the reaction rate, and is more conducive to the formation of an imidazoline ring.

[0045] from Figure 1 It can be seen from the data of Examples 7-9 that the corrosion inhibition efficiency of the corrosion inhibitor can be improved within a certain range by modifying the nano-alumina.

[0046] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing a corrosion inhibitor for a fractionation system, characterized in that: The steps include: S1: Mix fatty acid and water separator, heat to 140-170°C under nitrogen protection, and stir continuously, add organic amine, react for 1-2h, program temperature rise to 190-220°C, install water separator, react for 3-8h, and then distill under reduced pressure to obtain intermediate material; S2: Dissolve the intermediate material in anhydrous ethanol, heat to 50-75°C, slowly add anhydrous ethanol solution containing 3,4-dihydroxybenzaldehyde, react for 4-8 hours, cool the reaction solution and filter it under reduced pressure, wash the product with n-hexane and vacuum dry it to obtain.

2. The method for preparing a corrosion inhibitor for a fractionation system according to claim 1, characterized in that: In step S1, the fatty acid is one or more of dodecanoic acid, tetradecanoic acid, hexadecanoic acid and octadecanoic acid; the organic amine is one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine; and the water-separating agent is toluene or xylene.

3. The method for preparing a corrosion inhibitor for a fractionation system according to claim 1, characterized in that: The molar ratio of the fatty acid to the organic amine in step S1 is 1:(1-1.4).

4. The method for preparing a corrosion inhibitor for a fractionation system according to claim 1, characterized in that: In step S1, the rate of the programmed temperature increase is 2-8°C / min.

5. The method for preparing a corrosion inhibitor for a fractionation system according to claim 1, characterized in that: In step S2, the mass ratio of the intermediate material to 3,4-dihydroxybenzaldehyde is 1:(0.35-0.46).

6. The method for preparing a corrosion inhibitor for a fractionation system according to claim 1, characterized in that: In step S1, a catalyst is also added, wherein the catalyst is boric acid, and the amount of the catalyst added is 1%-10% of the sum of the mass of the fatty acid and the organic amine.

7. The method for preparing a corrosion inhibitor for a fractionation system according to claim 6, characterized in that: The catalyst is modified by a method comprising the following steps: (1) Add a dispersant to an aqueous solution of aluminum nitrate, add an ammonium carbonate solution dropwise under vigorous stirring until the pH is acidic, continue stirring for 0.5-1h, age for 12-48h, filter and dry to obtain a dry gel powder, add n-butanol to the dry gel powder, reflux for 1-3h, distill and filter, and calcine at 600-1000°C for 1-3h to obtain nano alumina; (2) Dissolve boric acid in water, add nano-alumina, heat to 50-65°C, stir for 1-5 hours, rotary evaporate and dry.

8. The method for preparing a corrosion inhibitor for a fractionation system according to claim 7, characterized in that: In step (2), the mass ratio of boric acid to nano-alumina is 1:(0.5-2).

9. The method for preparing a corrosion inhibitor for a fractionation system according to claim 7, characterized in that: In step (1), the nano-alumina is modified by a method comprising the following steps: Disperse nano-alumina in anhydrous ethanol to obtain a suspension, mix a silane coupling agent with water, slowly drop glacial acetic acid while stirring to make the solution acidic to obtain a silane hydrolyzate, slowly drop the silane hydrolyzate into the suspension, stir at 70-90°C until it becomes viscous, wash with anhydrous ethanol, filter, and dry.

10. The method for preparing a corrosion inhibitor for a fractionation system according to claim 9, characterized in that: The silane coupling agent is one or more of vinyl triethoxysilane, vinyl trimethoxysilane and γ-methacryloxypropyl trimethoxysilane; the mass ratio of the nano-alumina to the silane coupling agent is 100:(2-6).

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