A method of preventing corrosion by petroleum acids in heavy distillate oils

Abstract

The application provides a method for preventing corrosion of petroleum acid in heavy distillate oil, and relates to the technical field of petroleum refining processing. The method comprises the following steps: adding a deacidification corrosion inhibitor into the heavy distillate oil, increasing the oil temperature to 140-170 DEG C, and generating an amide compound through an amidation reaction; wherein the deacidification corrosion inhibitor is a polyethylene polyamine; further increasing the oil temperature to 200-260 DEG C, and generating an imidazoline compound through a cyclization dehydration reaction. The method realizes a consecutive reaction process of the amidation reaction and the cyclization dehydration reaction through temperature change operation, ingeniously utilizes the further reaction of the deacidification product to generate a corrosion inhibitor, and constructs a deacidification-corrosion synergistic corrosion prevention mechanism.

Description

Technical Field

[0001] This invention relates to the field of petroleum refining and processing technology, and in particular to a method for preventing petroleum acid corrosion in heavy distillate oils. Background Technology

[0002] Petroleum acids generally refer to naphthenic acids and other organic acids. The total amount of naphthenic acids in petroleum acids can account for 90% or even higher of the composition. It is generally believed that naphthenic acid corrosion usually occurs in high-flow-rate process media with an acid value greater than 0.5 mg KOH / g and a temperature between 220 and 400°C. It often occurs in parts such as trays, tower walls, furnace tubes, oil transfer lines, and high-temperature pipelines. The most severely corroded areas often occur in the casing, inlet ring, and impeller of circulating pumps or high-temperature feed pumps, easily causing circular or elliptical corrosion pits or corrosion perforations. The corrosion in local flow areas is sharp and edgy, causing equipment and pipeline damage, leading to leaks, fires, and other dangerous situations.

[0003] To prevent petroleum acid corrosion, methods such as deacidification, corrosion inhibition, and material upgrading can generally be used. Regarding deacidification technology, various techniques have been developed both domestically and internationally. One approach involves the destructive removal of carboxyl groups from petroleum acid molecules, including thermal decomposition / catalytic decomposition deacidification, organic amine / quaternary alkali solution methods, catalytic hydrogenation deacidification, and esterification. Another approach involves the overall separation and recovery of petroleum acid resources, including adsorption separation / membrane separation, alcohol-ammonia method / alkali washing method, and solvent extraction.

[0004] For corrosion inhibition technology, industrial applications typically involve applying corrosion inhibitors to areas with severe corrosion. The polar groups in the inhibitor molecules possess unshared electrons that can form coordinate bonds with empty metal orbitals, resulting in adsorption. Simultaneously, the non-polar groups in the inhibitor molecules are oriented away from the metal surface, forming a hydrophobic film that isolates the petroleum acid from the metal surface, hindering the occurrence of electrochemical corrosion reactions. For material upgrades, commonly used carbon steel in industrial equipment is typically replaced with 316L or 317L stainless steel to improve the equipment's corrosion resistance; however, this method is costly. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preventing petroleum acid corrosion in heavy distillate oils. This method requires only the addition of a deacidifying agent and utilizes a simple and feasible variable-temperature operation and reactive distillation apparatus to achieve a two-step series of reactions carried out online continuously. The first step, amidation reaction, removes naphthenic acids from the distillate oil, and the second step, cyclization dehydration reaction, forms an imidazoline-type high-temperature corrosion inhibitor to protect the metal wall, thus constructing a deacidification-corrosion inhibition synergistic anti-corrosion mechanism and achieving a dual-effect protection measure with a single agent.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] This invention provides a method for preventing petroleum acid corrosion in heavy distillate oils, comprising the following steps:

[0008] S1. Add a deacidifying preservative to heavy distillate oil, raise the oil temperature to 140-170℃, and an amidation reaction occurs to obtain amide compounds; wherein the deacidifying preservative is a polyethylene polyamine.

[0009] S2. Raise the oil temperature to 200-260℃ to further induce a cyclization and dehydration reaction, yielding imidazoline compounds.

[0010] The following is a detailed explanation:

[0011] Step S1: The first step of amidation and deacidification reaction.

[0012] Adding a deacidifying and corrosion-preventing agent based on polyethylene polyamine to heavy distillate oil and raising the oil temperature to 140-170℃, the alkaline polyethylene polyamine acts as a deacidifying agent and reacts with petroleum acid through an amidation reaction to form neutral amide compounds. The reaction equation is shown below, which reduces the acid value of the distillate oil and inhibits the corrosion rate of petroleum acid.

[0013]

[0014] Heavy distillate refers to distillate extracted from the side stream of a refinery vacuum distillation tower, including but not limited to vacuum distillate from the fourth vacuum distillation line, vacuum distillate from the third vacuum distillation line, and vacuum residue.

[0015] In some embodiments, the polyethylene polyamine is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine, more preferably diethylenetriamine.

[0016] In some embodiments, the molar ratio of the amount of the deacidifying preservative added to the distillate oil to the naphthenic acid content in the distillate oil is 1-2:1, preferably 1.05:1. During the synthesis process, appropriately increasing the amine content generally facilitates the synthesis of imidazoline, while also suppressing side reactions and improving product yield.

[0017] In some embodiments, the amidation reaction is carried out at a pressure of 0.5-2 MPa and for a time of 0.5-3 h.

[0018] Step S2: The second cyclization and dehydration reaction stage.

[0019] The distillate oil temperature is raised to 200-260℃, and then passed through a reactive distillation unit. The amide compounds obtained from the first step of the deacidification reaction become reactants in the second step, undergoing a cyclization and dehydration reaction at an even higher temperature to generate imidazoline compounds. The reaction equation is shown below. Under higher temperature conditions, the amide compounds accelerate the dehydration of cycloalkanes to form imidazoline compounds. These compounds can act as corrosion inhibitors, adhering to metal surfaces to prevent corrosion from petroleum acids.

[0020]

[0021] In some implementations, the oil temperature is raised to 200-260°C using a heat exchanger or a heating furnace.

[0022] In some embodiments, the cyclization dehydration reaction is carried out at a pressure of 0.5-2 MPa and for a time of 0.5-3 h.

[0023] In some implementations, the cyclization dehydration reaction is carried out using a reactive distillation apparatus.

[0024] Preferably, the reactive distillation apparatus is a device capable of simultaneously carrying out reaction and separation. The apparatus consists of a bottom reaction vessel and an upper distillation column. The raw material is fed from the middle of the reactive distillation apparatus, entering the reaction vessel downwards for cyclization and dehydration reaction. Water in the reaction product is in the gas phase, rising upwards through the distillation column section and exiting the apparatus at the top of the column. By disrupting the reversible reaction equilibrium, the conversion rate and reaction rate are increased.

[0025] Technical effects:

[0026] (1) This invention realizes a series of reaction processes of amidation reaction and cyclization dehydration reaction through temperature-variable operation, and cleverly utilizes the deacidification products to further react and generate corrosion inhibitors, thus constructing a deacidification-corrosion inhibition synergistic anti-corrosion mechanism, forming protective measures from two aspects: petroleum acid concentration and corrosion contact sites.

[0027] (2) The present invention only requires one additive to achieve the effect of first deacidification and then corrosion inhibition. The corrosion inhibition effect strengthens the inhibition effect on naphthenic acid corrosion, while reducing the need for deacidification effect of distillate oil, thus reducing the amount of deacidifying agent used, reducing costs and reducing the impact on nitrogen content of distillate oil.

[0028] (3) The present invention can enhance the two-stage cyclization dehydration reaction by means of reactive distillation process, promote the generation of imidazoline type corrosion inhibitors, and further improve the corrosion inhibition effect.

[0029] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0030] Figure 1 The image shows the infrared spectrum of the pre-de-oxidized extract.

[0031] Figure 2 The infrared spectrum of the extract after the first-stage desulfurization is shown.

[0032] Figure 3 The infrared spectrum of the extract after the second-stage removal of the four-stage precipitate is shown.

[0033] Figure 4 Infrared spectra of cycloalkanoic acids, amides, and imidazoline compounds as standards. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0035] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0036] The reduced-grade fourth-line distillate oil comes from the refinery of Sinopec Qilu Branch.

[0037] The cycloalkanoic acid comes from Sinopharm Chemical Reagent Co., Ltd.

[0038] Corrosion rate test method:

[0039] The corrosion rate was calculated by measuring the change in mass of the specimen before and after the test, and the corrosion rate V was calculated using the following formula. L :

[0040]

[0041] In the formula: V L G is the corrosion rate, mm / a; G0 is the mass of the specimen before corrosion, g; G is the mass of the specimen after corrosion, g; S is the surface area of ​​the specimen, cm². 2 t represents the corrosion time, in hours; d represents the density of the metal sample, expressed as 7.86 g / cm³. 3 calculate.

[0042] Example 1

[0043] Experiments were conducted in a high-pressure reactor. Diethylenetriamine was added to the reduced-tetrafluoroethylene (RTE) fraction oil at a dosage of 2000 ppm. The oil temperature was first raised to 160°C, and the system pressure was maintained at 1 MPa for 2 hours. Samples were then taken and solvent extracted to obtain the first-stage RTE-removed extract. Next, the oil temperature in the reactor was raised to 260°C and run for 30 minutes, with the pressure maintained at a slight positive / negative pressure to simulate the process conditions of a reactive distillation unit. After the reaction, samples were taken and solvent extracted to obtain the second-stage RTE-removed extract. Infrared spectroscopy analysis was performed on the RTE-removed extract before deacidification, the first-stage RTE-removed extract after deacidification, and the second-stage RTE-removed extract. Infrared spectra were obtained, as shown below. Figures 1-3 As shown.

[0044] The specific operation of the solvent extraction described above is as follows: First, heat the raw oil or de-treated oil to 80°C and start stirring. Then, gradually add 95% ethanol to the oil at a volume ratio of 1.5:1. Maintain the solution temperature at 80°C and stir for 20 minutes. Then, stop heating and stirring, allowing the ethanol and oil to separate into layers. Next, take the supernatant and heat it to evaporate the ethanol solvent, obtaining the naphthenic acid or deacidification product extract. Simultaneously, perform liquid-phase extraction again on the lower oil phase and mix the secondary extract with the primary extract to fully extract the naphthenic acid or deacidification product from the oil.

[0045] Example 2

[0046] Naphthenic acid and reduced-pressure fourth-line distillate oil were blended in a certain ratio to obtain a corrosive medium with an acid value of 7 mg KOH / g. 300g of this medium was placed in an autoclave, and diethylenetriamine was added at a molar ratio of 1:1.05 to the naphthenic acid content in the corrosive medium. A 20# carbon steel sheet was cleaned, weighed, and attached to a stirring paddle. The oil temperature was raised to 160℃ at 150 rpm, and the system pressure was maintained at 1 MPa. After 2 hours of operation, the oil temperature in the autoclave was raised to 260℃ and operated for 30 minutes, maintaining the system pressure at 1 MPa. After the reaction was complete, the 20# carbon steel sheet was removed, and the surface of the sheet was cleaned with petroleum ether and ethanol, dried, and the mass change of the sheet before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.1631 mm / a.

[0047] Example 3

[0048] A corrosive medium with an acid value of 7 mg KOH / g was prepared by blending naphthenic acid and reduced-pressure distillate oil in a certain ratio. 300g of this medium was placed in an autoclave, and diethylenetriamine with a molar ratio of 1:1.05 to the naphthenic acid content in the corrosive medium was added. A 20# carbon steel sheet was cleaned, weighed, and attached to a stirring paddle. The oil temperature was raised to 160℃ at 150 rpm, and the system pressure was maintained at 1 MPa. After 2 hours of operation, the oil temperature in the autoclave was raised to 260℃ and operated for 30 minutes, with the autoclave pressure maintained at a slightly positive pressure (to promptly remove water generated during the deacidification reaction and promote a shift in the reaction equilibrium towards the positive deacidification direction) to simulate the process conditions of a reactive distillation unit. After the reaction, the 20# carbon steel sheet was removed, and the surface of the sheet was cleaned with petroleum ether and ethanol, dried, and the mass change of the sheet before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.1272 mm / a.

[0049] Comparative Example 1

[0050] A corrosive medium with an acid value of 7 mg KOH / g was prepared by blending naphthenic acid and reduced-pressure fourth distillate oil in a certain proportion. 300g of this medium was placed in an autoclave, and diethylenetriamine with a molar ratio of 1:1.05 to the naphthenic acid content in the corrosive medium was added. A 20# carbon steel sheet was cleaned, weighed, and attached to a stirring paddle. The oil temperature was raised to 160℃ at a stirring speed of 150 rpm, and the system pressure was maintained at 1 MPa. After 2.5 hours of operation, the 20# carbon steel sheet was removed, and the surface of the sheet was cleaned with petroleum ether and ethanol, dried, and the mass change of the sheet before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.2283 mm / a.

[0051] Comparative Example 2

[0052] Naphthenic acid and reduced-pressure fourth-line distillate oil were blended in a certain proportion to obtain a corrosive medium with an acid value of 7 mg KOH / g. 300g of this medium was placed in an autoclave. A 20# carbon steel sheet was cleaned, weighed, and attached to a stirring paddle. The oil temperature was raised to 160℃ at a stirring speed of 150 rpm, while maintaining a system pressure of 1 MPa. After 2 hours of operation, the oil temperature in the autoclave was raised to 260℃ and operated for 30 minutes, while maintaining a system pressure of 1 MPa. After the reaction was completed, the 20# carbon steel sheet was removed, and the surface of the sheet was cleaned with petroleum ether and ethanol, then dried. The mass change of the sheet before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.3976 mm / a.

[0053] Infrared spectroscopy analysis was performed on standard samples of cycloalkanoic acids, amide compounds (amide compounds obtained by reacting cycloalkanoic acids with diethylenetriamine), and imidazoline compounds (obtained by further cyclization and dehydration of amide compounds) to obtain infrared spectra. For example... Figure 4 As shown, the characteristic absorption peak of the carboxyl group in cycloalkanoic acid molecules is located at 1705 cm⁻¹. -1Around 1650 cm⁻¹, the characteristic absorption peak of the amide group in amide compounds is located at 1650 cm⁻¹. -1 The characteristic absorption peak of the imidazoline ring in imidazoline compounds is located at 1605 cm⁻¹. -1 The infrared spectra of carboxylic acids, from cycloalkanoic acids to amides and then to imidazoline compounds, show a downward shift in the characteristic peaks of carboxylic acids. Therefore, this pattern can be used to assess the reaction progress and product distribution during the deacidification process of distillate oils. Thus, in Example 1, as... Figure 2 , Figure 3 As shown, the majority of the products from the first-stage deacidification process are amide compounds, with a small amount of imidazoline compounds. However, imidazoline compounds are clearly visible in the products from the second-stage deacidification process. The results indicate that the imidazoline compounds generated during the second-stage deacidification reaction can effectively protect these areas by forming corrosion inhibitors, thus enabling the deacidifying agent to possess a synergistic deacidification-corrosion inhibition mechanism.

[0054] Comparative Example 2 shows the corrosion process without the addition of a deacidifying agent; Comparative Example 1 shows the corrosion process when only the first stage of deacidification reaction is carried out; Example 2 shows the corrosion process when a two-stage reaction is carried out; and Example 3 shows the corrosion process when a two-stage reaction is carried out and the cyclization dehydration reaction is enhanced by reactive distillation.

[0055] The experimental results show that the corrosion rate of naphthenic acid in Comparative Example 2 was 0.3976 mm / a, in Comparative Example 1 it was 0.2283 mm / a, in Example 2 it was 0.1631 mm / a, and in Example 3 it was 0.1272 mm / a. It can be seen that the corrosion inhibition rate was 42.58% when only the first-stage deacidification reaction was carried out, 58.98% when the two-stage reaction was carried out, and 68.01% when the two-stage reaction was enhanced by reactive distillation. The results indicate that compared to simply carrying out the deacidification reaction, the two-stage reaction with variable temperature operation to achieve synergistic corrosion prevention through deacidification and corrosion inhibition can suppress the corrosion process to a greater extent. Simultaneously, the reactive distillation process can enhance the cyclization and dehydration reaction, promote the formation of imidazoline-type corrosion inhibitors, and further improve the corrosion inhibition effect.

[0056] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method of preventing corrosion by petroleum acids in heavy distillate oil, characterized by, Includes the following steps: S1. Add a deacidifying preservative to heavy distillate oil, raise the oil temperature to 140-170℃, and an amidation reaction occurs to obtain amide compounds; wherein the deacidifying preservative is polyethylene polyamine; the reaction pressure of the amidation reaction is 0.5-2MPa, and the reaction time is 0.5-3h. S2. Raise the oil temperature to 260℃ to further induce a cyclization and dehydration reaction, yielding imidazoline compounds; the reaction pressure for the cyclization and dehydration reaction is 0.5-2 MPa, and the reaction time is 0.5-3 h. The cyclization dehydration reaction is carried out by a reactive distillation unit, which consists of a bottom reaction vessel and a middle and upper distillation column. The raw material is fed from the middle of the reactive distillation unit and enters the reaction vessel downwards to carry out the cyclization dehydration reaction. The water in the reaction product is in the gas phase and rises through the distillation column section, leaving the unit at the top of the column.

2. The method of claim 1, wherein, Heavy distillate oils include one of the following: reduced pressure fourth-line distillate oil, reduced pressure third-line distillate oil, and vacuum residue oil.

3. The method of claim 1, wherein, The polyethylene polyamine is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine.

4. The method of claim 3, wherein, The polyethylene polyamine is diethylenetriamine.

5. The method of claim 1, wherein, The molar ratio of the amount of deacidifying preservative added to the distillate oil to the naphthenic acid content in the distillate oil is 1-2:1.

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