METHOD FOR INHIBITING CORROSION IN THE CRUDE OIL DISTILLATION PROCESS.

Abstract

The invention presented consists of a method of corrosion protection in crude oil refining process units contaminated with organic chlorides through the application of anti-corrosion compounds based on rare earth salts, such as neodymium and praseodymium salts, used as additives, with the distinctive element of being nitrogen-free and suitable for high-temperature service, designed to extend the useful life of the facilities and processes associated with oil refining and the petrochemical industry.

Description

The present invention belongs to the technical field of chemistry. Specifically, it relates to the technical field of means for preventing corrosion of metallic materials and scaling in general, and more particularly to a method for inhibiting corrosion in crude oil distillation processes. BACKGROUND Crude oil can become contaminated with organic chlorides due to the injection of additives at production wells. These additives persist until the crude is transported to the storage tanks of refinery crude units. Organic chlorides in crude oil cannot be removed during the desalting process, so they remain in the process until distillation, and many even reach hydrotreating. During naphtha hydrotreating, organic chlorides are transformed into hydrogen chloride (HCl), which reacts with ammonia (NH3) to form ammonium chloride salts (NH4Cl). The precipitation of NH4Cl is proportional to the organic chloride content in the feed.The temperatures reached in the reactor prevent salt precipitation within it, and these salts are transported along with the product. However, the temperature drop in subsequent sections of the process promotes salt precipitation. These sections generally correspond to the heat exchangers. Dry NH4Cl salts are not corrosive on their own, but they cause fouling and clogging in the heat exchanger tubes. One characteristic observed in the analyzed product layers is their high hygroscopic potential, typical of these salts. This condition promotes moisture attraction, giving the salts a high corrosive potential that generates corrosion processes under deposits. In the specialized literature, several methods exist for corrosion protection in crude oil refining processes. Prior art includes a large number of published patents, generally related to the use of nitrogen compounds for corrosion control. In recent years, various compounds have been developed and evaluated as corrosion inhibitors for metals exposed to corrosive media such as chloride-rich water and acidic solutions, among others. These fluids are also found in refining processes. One of the most common methods used to combat corrosion is the use of nitrogen compound inhibitors. US patent 3907578A describes corrosion-inhibiting compositions comprising a mixture of carboxylic acid salts and aliphatic amines. The composition is exemplified by a salt of a dicarboxylic acid and amylamine with a volatile cyclic amine comprising a mixture of pyridine, picoline, lutidine, aniline, quinoline, isoquinoline, toluidine, and heavy pyridine. However, these are nitrogen compounds that can contribute nitrogen to the process in addition to promoting the precipitation of ammonium salts. Another patent, US patent 4992210A, describes the use of amines added to the wash water of the desalting process to promote chloride removal from the crude oil feed before distillation. Another patent that describes a method of corrosion control in crude oil refining processes through the addition of chemicals is WO2017189801A1.The corrosion control agent comprises an amine and an alcohol. The process involves adding the amine and the alcohol to the upper system of the oil recovery unit, either separately or in combination. Another method for preventing corrosion by ammonium salts is described in US patent 4141816A, where the deposition of ammonium chloride from gas streams is prevented by maintaining the gas stream temperature above the deposition temperature for ammonium chloride at operating pressure. This method, while effective, is neither flexible nor robust, as the process cannot always be operated under the desired conditions due to variability in crude oil feeds, pressures, equipment capacities, and other factors. The invention is particularly useful in hydrocarbon hydrogen treatment processes where hydrogen recycle streams containing ammonium chloride or ammonium chloride-forming constituents must be recompressed before being recycled to the hydrogen treatment process. US Patent 4855035A describes a method for corrosion control in crude oil distillation units operated at a temperature above the nominal aqueous dew point and in contact with a crude oil feed stream containing sulfur oxides, ammonia, and a hydrochloric acid neutralizing amine, the process comprising maintaining a chloride level in said crude oil feed stream sufficient to provide a molar ratio of ammonium chloride to ammonium bisulfate greater than approximately 20 in said net column upper transfer line. US patent 20120190906A1 describes a process for the absorption of organic chlorides. According to the invention, organic chlorides are removed from hydrocarbon and / or hydrogen streams by contacting the streams with a zeolite 13X molecular sieve for a time sufficient for the chemically combined chlorine to adsorb onto the molecular sieves. Zeolite 13X molecular sieves with a Si / Al ratio of less than 1.25 have been found to have improved organic chloride adsorption compared to zeolite 13X with Si / Al ratios of 1.25 and higher. However, challenges in the development of this invention persist; specifically, a solution is needed to prevent chloride corrosion or the further deposition of ammonium salts to avoid or minimize corrosion and scaling potential, even in the presence of organic chlorides in crude oil. The use of a powerful water scrubbing system is certainly a good step in the right direction for removing as many salts as possible. Ammonium salts are generally readily soluble in water, but they often cannot be completely removed in the presence of hydrocarbons. Process units that suffer from ammonium salt scaling or corrosion include crude oil distillation units, hydrocrackers, hydrotreators, and reforming units. OBJECT OF THE INVENTION Accordingly, there is a need for a corrosion inhibitor that promotes protection against hydrochloric acid caused by the presence of organic chlorides in crude oil, not removed in the desalting process, without the disadvantage of providing nitrogen compounds that react with chlorides to cause the precipitation of ammonium salts. The present invention relates to a method of corrosion protection through the application of corrosion inhibitors in the form of rare-earth salts. These inhibitors are distinguished by being nitrogen-free, possessing adsorption properties for iron cations, and are suitable for high-temperature service. They are designed to extend the service life of facilities and processes associated with petroleum refining and the petrochemical industry. Additionally, the invention aims to improve the environmental sustainability of refining and petrochemical processes by replacing other highly toxic inhibitors such as chromates (CrO₄), mercurates, and nitrites. The objectives of the present invention referred to above, and even others not mentioned, will be evident from the description of the invention and the figures that accompany it for illustrative and non-limiting purposes, which are presented below. BRIEF DESCRIPTION OF THE FIGURES Figure 1. Schematic of the corrosion protection method in the crude oil unit. Figure 2. Graph showing the percentage of corrosion inhibition efficiency. Figures 3a-3d. Elemental EDS analysis of the different morphologies of the layer formed by rare earth salts observed on the surface of API X70 steel Figure 4. Variation of open circuit potential vs time at different neodymium concentrations DESCRIPTION OF THE INVENTION The present invention describes a method applicable to rare-earth-based anticorrosive compounds as additives for corrosion control in crude oil refining processes. Specifically, it relates to the application of neodymium and praseodymium salts after their extraction, for injection into refining processes to control corrosion caused by the presence of organic chlorides in crude oil. Since organic chlorides cannot be conventionally removed during desalting, they promote the formation of hydrochloric acid (HCl) in the upper dome of the distillation tower. As the pH decreases due to the presence of these acids, nitrogen compounds are conventionally applied to neutralize the pH and control corrosion.However, the application of nitrogen compounds leads to the precipitation of ammonium chlorides and sulfides in the preheating trains of subsequent processes, mainly in the washing lines of hydrotreating plants. These are hygroscopic salts that promote localized corrosion in the presence of moisture and free water, as well as clogging and scaling. This method has strong applicability in the crude oil refining industry due to problems of high concentrations of organic chlorides in crude oil, which cause severe problems of precipitation, fouling and corrosion due to chloride hydrolysis processes. One of the novel aspects of this invention is the method comprising the step of applying a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, more preferably the mixture comprising 20% ​​neodymium and 16% praseodymium, which are rare earth compounds that, being nitrogen-free and capable of being used at high temperatures, allow avoiding subsequent problems of excess nitrogen in fuels after reforming, since one measure to counteract corrosion in the previous processes is to use traditional corrosion inhibitor systems derived from amines; this causes an excess of nitrogen and therefore the concentration specifications of this nitrogen fall outside the established ranges, in addition to the problems of corrosion and clogging in process equipment. The anti-corrosive composition of neodymium and praseodymium salts is made from rare-earth oxides, obtained optionally, but not exclusively, from the recycling and processing of permanent magnets. The sources of these rare-earth oxides are dissolved in HCl solution and then dried at 60 °C to obtain the rare-earth salts. In a preferred aspect of the invention, the anticorrosive composition of the present invention comprises: a) a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, more preferably the mixture comprises 20% neodymium and 16% praseodymium; said salts are preferably in powder form; b) an antifoaming agent present between 1 and 3% by weight, preferably a cationic surfactant; c) a pH adjusting agent present between 1 and 3% by weight, preferably selected from hydrochloric acid. The anti-corrosive mixture may have an acidic pH of around 3, so it is necessary to adjust it to 7; d) a solvent, preferably water. The mixture of neodymium and praseodymium salts is diluted in a solvent, usually water, and injected into the top of the distillation column. To achieve corrosion protection efficiencies above 90%, it is recommended to use dosages ranging from 80 ppm to 500 ppm. This has been determined through testing, which has shown that above 500 ppm, efficiency decreases due to an excess concentration of Nd3+ cations that promotes competitive adsorption for forming the protective layer. The invention developed consists of an anti-corrosion method based on neodymium and praseodymium salts to be used as corrosion inhibitors for crude oil refining processes, mainly in primary units. The method involves extracting praseodymium and neodymium salts from rare-earth oxides, obtaining them in powder form for use as chemical additives in injection systems. The best known efficiency is achieved when the inhibitor salts are extracted from permanent magnets through a digestion, extraction, and drying process. Once the salts are in powder form, such as neodymium and praseodymium salts, they are added to a solvent, which can be water with the addition of an antifoaming agent, at a concentration of 1 to 3% by weight. The salt concentration in the fluid transported during the refining process can vary from 100 ppm to 500 ppm. It is important to note that this concentration must be calculated based on the salts themselves, not the dilution. For the application of the anti-corrosive composition, an injection medium is used with a dosing pump which injects said composition in the range of the indicated concentrations. The anti-corrosion method involves injecting an anti-corrosion composition comprising a mixture of neodymium and praseodymium salts, previously dissolved in a solvent, into the outlet line of the upper dome of the distillation column in a refinery's primary unit. In this area, due to the formation of hydrochloric acid (HCl) caused by the presence of organic chlorides, the pH can drop to as low as 3, leading to serious corrosion problems. In this case, the injection of the anti-corrosion composition neutralizes the pH of the aqueous phase. The protection provided by this anti-corrosion method focuses primarily on the action of Nd3+ cations in the process, modifying and deactivating the corrosion process. This can be attributed to the formation or deposition of a Nd oxide film on the metal surface. Generally, the precipitation of the oxide layer is due to the hydrolysis reactions of the metal cations with the OH- ions produced at the cathodic sites.The increase in pH of the cathodic sites causes the precipitation of compounds of the type Me(OH)3, which are subsequently transformed into more stable metal oxides (Me2O3). Nd3+ ions protect steel by adsorbing onto the metal surface, forming a thin layer of oxyhydroxides. However, the presence of imperfections may cause cracking and detachment of this protective layer, resulting in the observed stacked layer morphologies. In the case of small imperfections such as pores (cathode sites), Nd3* ions can precipitate and seal them, causing the formation of small crystals identified as protrusions. These protrusions may be the result of the formation of a film of Nd(OH)3 and NdzOa. The inhibition mechanism of these salts on iron alloys is due to the adsorption process that forms neodymium cations, creating a protective layer composed of Nd oxides / hydroxides 200 to 400 nm thick on metallic surfaces, and their presence is able to reduce the exchange of electrons with oxidizing species. The next injection point in the refining processes is in the hydrotreating wash water lines, where corrosion can occur due to the carryover of sulfur compounds and other corrosive agents. The method for inhibiting corrosion in crude oil distillation processes finds its advantageous element by applying the anti-corrosive composition of the invention to specific areas or points of the crude oil; in particular, the process consists of the following steps: a) Dosing to a washing line of a desalter a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, in dosage ranges from 80 ppm to 500 ppm; said desalter is in fluid communication with a mixing valve that feeds it with crude oil from a primary preheating train which in turn is fed by a crude oil storage tank of a crude oil unit; b) To dose a top-mounted accumulator unit with a composition comprising a mixture of neodymium and praseodymium salts at a preferred concentration of between 15 and 25%, and between 10 and 20%, respectively, in dosage ranges from 80 ppm to 500 ppm; said accumulator equipment is fed by the outlet of the desalted crude that passes through a pre-flash unit where it in turn distributes the crude to a preheating train of a distillation tower and passes through a furnace to enter a distillation tower, also from the same line as the pre-flash, it has an upper outlet that feeds directly to the fractionating distillation tower and the fractionated light naphtha exits through the upper dome of the distillation tower c) Dosing into the wash water of the preheating trains of the hydrotreating units of a crude unit a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively in dosage ranges from 80 ppm to 500 ppm. In an additional aspect considered in the present invention, a crude oil treatment unit is contemplated, which is detailed according to Figure 1, where the crude oil unit comprises a crude oil storage tank (1), which has an outlet to a primary preheating train (2) to distribute the fluid through a mixing valve (3) and enter a desalter (4) specially configured as a first injection point of a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively in dosage ranges from 80 ppm to 500 ppm, in the desalter wash water line.Subsequently, the desalted crude oil outlet passes through a pre-flash unit (5) where it distributes the crude oil to a preheating train of the distillation tower (6) and passes through a furnace (7) to enter a distillation-fractionation tower (8). Also from the same line as the pre-flash, it has an upper outlet that feeds directly to the distillation-fractionation tower (8), and the fractionated light naphtha exits through the upper dome (9) of the distillation tower, where it continues to an upper top accumulator unit (10), which is configured to receive a second dosage ranging from 80 ppm to 500 ppm of a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, in its wash water lines.It is in this zone where HCl can accumulate due to the entrainment and breakdown of organic chlorides in the crude oil; therefore, it is the most important area where the rare-earth-based anti-corrosion composition should be applied. Subsequently, the flow passes through a separator with a heavy naphtha outlet (11) and an upper light naphtha outlet (12). A third dosage, ranging from 80 ppm to 500 ppm, of a composition comprising a mixture of neodymium and praseodymium salts at a preferred concentration of 15–25% and 10–20%, respectively, is applied to the wash water of the hydrotreator preheating trains (13), where ammonium chlorides and ammonium sulfides typically form when nitrogen-based corrosion inhibitors are applied. The examples presented are illustrative and not limiting, since a person skilled in the art will understand that there are variations that fall within the scope of protection of the present invention. Example 1. The corrosion protection process based on the application of neodymium and praseodymium salts was evaluated through electrochemical tests under acidic conditions, corresponding to the upper dome of the distillation column (9) and the top accumulator (10). This electrochemical test consisted of an electrochemical measurement of the inhibition efficiency from 100 ppm to 1000 ppm in an acidic medium with the addition of 8% HCl and a pH of 3.5, to simulate the most aggressive conditions. The results indicated that an increase in the concentration of the corrosion inhibitor increases the protection efficiency from 100 to 250 ppm; however, at 500 ppm the efficiency decreases, due to an excess concentration of Nd3* cations that promotes adsorption competition to form the protective layer. Example 2. Figure 3 describes an analysis of the protective layer performed using X-ray scattering scanning electron microscopy. A point analysis of the main morphologies identified (Figure 3) showed that the layer adhered to the surface (point 1) had an elemental composition of Fe = 92%, Nd = 3%, and O = 5% (wt%). The crystals protruding from the surface (point 2) had an elemental composition of Fe = 7%, Nd = 60%, and O = 33%. The morphologies with the appearance of stacked layers (point 3) had an elemental composition of Fe = 54%, Nd = 7%, and O = 39%. Based on the morphology of point 3, it is possible to deduce that the layer adhered to the metal surface had a thickness between approximately 200 and 400 nm. Example 3. Figure 4 shows the open-circuit potential variations over time in an acidic HCl solution at pH 3. The shift to a more positive potential indicates metal passivation, which, in the presence of a corrosion inhibitor, occurs through the formation of a protective layer on the metal surface. It can be seen that a Nd concentration of 0.0005 M provides the most positive potential, offering the best protection. It is also observed that, regardless of the Nd3* ion concentration, the OCP values ​​remain within a 25 mV band.It has been suggested that a shift in OCP values ​​greater than ± 85 mV, with respect to the blank, is typical of anodic or cathodic inhibitors, depending on the direction of the shift; otherwise, they are mixed inhibitors. However, the results of this study show a variation in OCP values ​​less than 85 mV; this reaffirms that Nd3* ions act as a mixed inhibitor with a strong predominant cathodic effect. Although the foregoing description was made taking into account the preferred embodiments of the invention, those skilled in the art should be aware that any modification of form and detail will be considered within the spirit and scope of the present invention. The terms in which this specification has been drafted should always be taken in a broad and non-restrictive sense. The materials, form, and description of the elements may be varied provided that this does not alter the essential characteristics of the model.

Claims

1. A method for inhibiting corrosion in crude oil distillation processes, characterized in that it comprises the following steps: administering a mixture of neodymium and praseodymium salts at a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, in a wash water line of the desalter, at the outlet of the top dome of the distillation tower and the top-top accumulator, and in the wash water line of the preheating trains of the crude oil refining processes.

2. The method for inhibiting corrosion in crude oil distillation processes according to claim 1, characterized in that it is applied to dosage ranges of between 100 and 500 ppm, preferably 250 ppm at at least one of the aforementioned points.

3. A composition for inhibiting corrosion in crude oil distillation processes, characterized in that it comprises a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 to 25%, and between 10 to 20%, respectively, more preferably the mixture comprises 20% neodymium and 16% praseodymium; said salts are preferably in powder form.

4. The composition for inhibiting corrosion in crude oil distillation processes according to claim 3, characterized in that it may contain an agent for adjusting the pH.

5. The composition for inhibiting corrosion in crude oil distillation processes according to claim 3, characterized in that it may contain an antifoaming agent.

6. The composition for inhibiting corrosion in crude oil distillation processes according to claim 3, characterized in that the mixture is diluted and applied with a solvent, preferably water.

7. The composition for inhibiting corrosion in crude oil distillation processes according to claim 3, characterized in that the antifoaming agent is present between 1 and 3% by weight, preferably a cationic surfactant; and the pH adjusting agent is present between 1 and 3% by weight, preferably selected from hydrochloric acid.

8. The composition for inhibiting corrosion in crude oil distillation processes according to the preceding claim, characterized in that the neodymium and praseodymium are in powder form.

9. A crude oil treatment unit, comprising a crude oil storage tank (1), which has an outlet to a primary preheating train (2) to distribute the fluid through a mixing valve (3) and into a desalter (4), characterized in that it is specially configured to inject a composition comprising a mixture of neodymium and praseodymium salts at a preferred concentration of between 15 and 25%, and between 10 and 20%, respectively, in dosage ranges from 80 ppm to 500 ppm, into the desalter wash water line; the outlet of the desalted crude oil passes through a preflash unit (5) where it in turn distributes the crude oil to a preheating train of the distillation tower (6) and passes through a furnace (7) to enter a distillation-fractionating tower (8), also on the same line as the preflash unit,It has an upper outlet that feeds directly to the fractionating distillation tower (8), and the fractionated light naphtha exits through the top dome (9) of the distillation tower, where it continues to an upper-head accumulator unit (10). This unit is configured to receive a second dosage, ranging from 80 ppm to 500 ppm, of a composition comprising a mixture of neodymium and praseodymium salts at a preferred concentration of 15 to 25% and 10 to 20%, respectively, in its wash water lines. It is in this area that HCl can accumulate due to the entrainment and breakdown of organic chlorides in the crude oil; therefore, it is the most critical area where the rare-earth-based anti-corrosion composition should be applied. Subsequently,The flow passes through a separator having a heavy naphtha outlet (11) and an upper light naphtha outlet (12). A third dosage, ranging from 80 ppm to 500 ppm, of a composition comprising a mixture of neodymium and praseodymium salts in a preferred concentration of between 15 and 25% and between 10 and 20%, respectively, is applied to the wash water of the hydrotreator preheating trains (13), where ammonium chlorides and ammonium sulfides are generally formed when nitrogen-based corrosion inhibitors are applied.