A supercritical carbon dioxide corrosion inhibitor and a method of manufacturing the same

Abstract

The application provides a supercritical carbon dioxide corrosion inhibitor and a manufacturing method thereof, comprising the following general molecular structure: [three imidazoline skeleton]-[–N + R3] n –[–P(O)(OR’)2] n wherein: the three imidazoline skeleton comprises at least three independent imidazoline rings, and at least one amine group is reserved on each ring as a functionalization site; the –N + R3 group is connected to the amine group functionalization site on the three imidazoline skeleton, wherein R is independently selected from C1-C6 alkyl, aryl or a combination thereof; the –P(O)(OR')2 group is connected to the remaining amine group functionalization site on the three imidazoline skeleton, wherein R' is independently selected from C1-C6 alkyl, aryl or a combination thereof; n in the molecule is greater than or equal to 3, and all are directly anchored on the same three imidazoline skeleton through a covalent bond; so that the corrosion inhibitor of the application has greatly improved corrosion inhibition rate compared with traditional corrosion inhibitors in the extreme corrosion environment of high temperature, high salinity and supercritical CO2.

Description

Technical Field

[0001] This invention relates to the field of corrosion inhibitor technology, and in particular to a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. Background Technology

[0002] Supercritical carbon dioxide (scCO2) environments are widely used in industrial applications such as oil and gas field development, CO2-EOR (carbon dioxide enhanced oil recovery) and geological sequestration (CCS). Their high temperature (≥120℃), high pressure (>7.38MPa), high mineralization, and strong solubility significantly exacerbate the electrochemical corrosion of metallic materials such as carbon steel and alloy steel. To inhibit this type of corrosion, the industry has long relied on organic corrosion inhibitors to form adsorption films to block corrosive media. Among these, imidazoline, quaternary ammonium salts, and their compound systems are currently the mainstream technical solutions.

[0003] Existing corrosion inhibitors mostly employ monofunctional or bifunctional molecular designs. A typical example is the synergistic system of hydrocarbon-substituted imidazoline quaternary ammonium salts and polyquinoline, which can achieve a corrosion inhibition rate of around 80% under conditions of 60–120℃ and CO2 partial pressure of 1–5 MPa. However, when the ambient temperature is high, the mineralization increases, or the CO2 phase is supercritical, these molecules are prone to pyrolysis and conformational relaxation due to the flexible alkyl chains, leading to a sharp drop in the stability of the adsorption film. The corrosion inhibition rate is generally below 80%, and the thermal stability is poor. Simultaneously, their surface adsorption density is generally below 1.1 × 10⁻⁶. -6 With a concentration of mol / cm², it is difficult to form a dense and durable protective layer under extreme conditions.

[0004] In terms of the synergistic mechanism of functional groups, existing technologies mostly focus on simple combinations of single functional groups (such as nitrogen adsorption of imidazoline and electrostatic adsorption of quaternary ammonium salts) or dual groups (such as imidazoline-quaternary ammonium salts). Phosphonates are also mostly used as independent scale inhibitors. Therefore, there is a lack of systematic molecular design for the three-in-one synergistic effect of "adsorption-film formation-stabilization".

[0005] Furthermore, existing corrosion inhibitors in supercritical CO2-water coexistence systems have limitations due to the low pH (3–4) of the aqueous phase and the presence of HCO3. - High concentrations can easily trigger localized acid and pitting corrosion. Traditional molecules, lacking strong coordinating phosphonate groups, cannot effectively chelate metal ions or stabilize corrosion product films, leading to further deterioration in corrosion inhibition performance. Experimental data shows that current industrial-grade corrosion inhibitors, at a dosage of 1000 ppm, generally exhibit corrosion inhibition rates ≤80%, thermal stability ≤200℃, and surface adsorption density ≤1.2 × 10⁻⁶. -6 The concentration of mol / cm² is insufficient to meet the long-term protection requirements of deep oil and gas fields, geothermal wells, and other extreme working conditions.

[0006] In summary, existing technologies have three major flaws: Insufficient thermal stability: The flexible chain structure is prone to degradation at temperatures above 200°C, limiting its application. Low adsorption density: mono / bifunctional groups are unable to achieve high-density surface coverage; Lack of synergistic mechanism: The lack of a three-in-one molecular-level synergistic design of "adsorption-film formation-stabilization" makes it impossible to maintain film integrity under high temperature and high mineralization, resulting in a low corrosion inhibition rate (≤80%).

[0007] The above background information is disclosed only to assist in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application, nor does it necessarily provide technical teachings. In the absence of clear evidence, the novelty and inventiveness of the above application shall be deemed to be incomplete. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. This method utilizes a rigid polycyclic framework to achieve covalent anchoring of multiple functional groups, forming a synergistic system integrating adsorption, film formation, and stabilization. Consequently, the corrosion inhibitor of this application exhibits excellent high-temperature thermal stability and high surface adsorption density under extreme corrosion environments of high temperature, high mineralization, and supercritical CO2, and its corrosion inhibition rate is significantly improved compared to traditional corrosion inhibitors.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a supercritical carbon dioxide corrosion inhibitor, comprising the following general formula molecular structure: [Tripartite imidazoline skeleton]–[–N + R3] n –[–P(O)(OR')2] n in: The ternary imidazoline skeleton comprises at least three independent imidazoline rings, each ring retaining at least one amino group as a functionalization site; The –N + The R3 group is attached to the amino functionalization site on the ternary imidazoline skeleton, wherein R includes any one or more of C1–C6 alkyl and aryl groups; The –P(O)(OR')2 group is attached to the remaining amino functionalization site on the ternary imidazoline skeleton, wherein R' includes any one or more of C1–C6 alkyl and aryl groups; In the molecular structure, n≥3, and all molecules are directly anchored to the same ternary imidazoline backbone through covalent bonds, forming a ternary imidazoline-triquaternary ammonium salt-triphosphonate composite structure.

[0010] The purpose of this invention is to provide a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. By using a rigid polycyclic framework to achieve covalent anchoring of multiple functional groups, a synergistic system of "adsorption-film formation-stabilization" is formed. As a result, the corrosion inhibitor of this application not only has excellent high-temperature thermal stability and high surface adsorption density under the extreme corrosion environment of high temperature, high mineralization and supercritical CO2, but also significantly improves the corrosion inhibition rate compared with traditional corrosion inhibitors.

[0011] In some embodiments, the tri-imidazoline skeleton is formed by a ring-closing condensation reaction of at least one tricarboxylic acid and at least one triamine, wherein the molar ratio of the tricarboxylic acid to the triamine is 1:(1.1–1.5).

[0012] In some embodiments, the tricarboxylic acid includes one or more of trimellitic acid, pyromellitic acid, 1,2,4-cyclohexanetricarboxylic acid, or derivatives thereof.

[0013] In some embodiments, the ternary amine includes one or more of triethylenetetramine, tetraethylenepentamine, 1,3,5-tris(2-aminoethyl)cyclohexane or derivatives thereof.

[0014] In some implementations, the –N + At least three R3 groups are provided, the three –N groups + The R3 group is covalently attached to the amino group site on the ternary imidazoline skeleton via an alkylation reaction.

[0015] In some embodiments, at least three –P(O)(OR')2 groups are provided, and the three –P(O)(OR')2 groups are covalently linked to the remaining amino sites on the ternary imidazoline skeleton via nucleophilic substitution reaction.

[0016] On the other hand, the present invention provides a method for manufacturing a supercritical carbon dioxide corrosion inhibitor, which, in order to obtain the supercritical carbon dioxide corrosion inhibitor as described in any of the preceding claims, includes the following steps: Synthesis of S1 tri-imidazoline skeleton: Tricarboxylic acid and triamine were added to a reaction vessel at a molar ratio of 1:(1.1–1.5) and condensed at 170–200℃ under an inert atmosphere for 6–12 hours. The reaction endpoint was when the acid value was ≤3.0 mgKOH / g. The mixture was then cooled to below 80℃ to obtain the tri-imidazoline intermediate. S2 Quaternization reaction: An alkylating agent is added dropwise to the ternary imidazoline intermediate obtained in step S1, wherein the molar ratio of the alkylating agent to the ternary imidazoline intermediate is (3.0–3.5):1, and the reaction is carried out at 70–90℃ for 1–3 hours to obtain the ternary quaternary ammonium salt intermediate; S3 Phosphonate reaction: A phosphonate precursor is added to the ternary quaternary ammonium salt intermediate obtained in step S2, wherein the molar ratio of the phosphonate precursor to the quaternary ammonium salt intermediate is (3.0–3.5):1. The reaction is carried out at 100–120°C under vacuum dehydration conditions for 2–5 hours to obtain a ternary imidazoline–triquaternary ammonium salt–triphosphonate composite structure.

[0017] In some embodiments, the reaction system in step S1 is a solvent-free system, or a high-boiling-point inert solvent system is used, wherein the high-boiling-point inert solvent system includes any one or more of N-methylpyrrolidone, dimethyl sulfoxide, and ethylene glycol monobutyl ether.

[0018] In some embodiments, the alkylating agent in step S2 includes one or more of dimethyl sulfate, iodomethane, methyl chloroacetate, or tert-butane bromide.

[0019] In some embodiments, the phosphonate precursor in step S3 includes one or more of dimethyl phosphate, diethyl phosphate, diethyl phosphite, or diphenyl phosphate.

[0020] This invention provides a supercritical carbon dioxide corrosion inhibitor and its manufacturing method, which has the following beneficial effects: 1) This invention provides a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. Through a rigid polycyclic framework, multiple functional groups are covalently anchored to form a three-in-one synergistic system of "adsorption-film formation-stabilization". As a result, the corrosion inhibitor of this application not only has excellent high-temperature thermal stability and high surface adsorption density under the extreme corrosion environment of high temperature, high mineralization and supercritical CO2, but also significantly improves the corrosion inhibition rate compared with traditional corrosion inhibitors.

[0021] 2) This invention provides a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. This application achieves quaternary ammonium salt (–N) through a rigid ternary imidazoline skeleton. + Precise covalent anchoring of two functional groups, R3 and phosphonate esters (–P(O)(OR')2), constructs a three-in-one synergistic system of "adsorption-film formation-interference resistance". This system can simultaneously adapt to extreme corrosive environments of supercritical CO2, high temperature, and high mineralization. Its core mechanism of action is as follows: The ternary imidazoline skeleton is formed by three imidazoline rings covalently linked by methylene / imine groups, constructing a highly rigid three-dimensional spatial structure. On the one hand, this rigid structure can significantly restrict the free rotation and conformational relaxation of quaternary ammonium salt and phosphonate groups, suppressing the thermal motion and dissociation of molecular chain segments at high temperatures. This allows the molecule to maintain its structural integrity in a supercritical CO2 environment at high temperatures (≥120℃), providing a structural basis for the long-term stable existence of the corrosion inhibitor. On the other hand, each imidazoline ring precisely retains at least one amino functionalization site, for a total of six amino functionalization sites. Three sites are connected to quaternary ammonium salt groups, and three sites are connected to phosphonate groups, achieving a precise 1:1 equimolar anchoring ratio. This 3:3 covalent anchoring ratio avoids the waste of functional groups, and through steric hindrance optimization design, it ensures that the two types of groups do not interfere with each other, and both can efficiently contact the metal surface and the corrosive medium.

[0022] Quaternary ammonium salt group (–N) + R3 carries a strong positive charge and can be quickly adsorbed onto negatively charged metal surfaces through electrostatic attraction (Fe²⁺ is easily formed on the surface during the early stages of metal corrosion). + / Fe³ + Vacancies (exhibiting negative charge) instantly form an initial charge barrier. This barrier can effectively resist highly mineralized environments (containing Ca²⁺). + Mg² + Cl - The ion-shielding effect in (etc.) – even in high-salt media such as 5% NaCl, the strong electrostatic interaction of quaternary ammonium salts ensures rapid and robust molecular adsorption, avoiding adsorption failure due to ion competition, thus laying the foundation for subsequent film formation. Experimental data show that the surface adsorption capacity of the corrosion inhibitor in Example 1 reaches 1.8 × 10⁻⁶. -6 mol / cm², which is the traditional binary imidazoline corrosion inhibitor (8.7×10⁻⁶ mol / cm²). -7 This is 2.07 times that of (mol / cm²), confirming the high efficiency of this adsorption mechanism; The P=O bond in the phosphonate group (-P(O)(OR')2) has strong coordination ability and can react with Fe²⁺ dissolved on the metal surface. + Fe³ + and Ca² in the medium + When metal ions form stable five- or six-membered chelate rings, a dense, insoluble metal phosphonate protective film is generated. This film has extremely low permeability and can effectively block H+. + HCO3 - Cl - This chelate film allows corrosive media to penetrate the metal substrate, inhibiting pitting corrosion, crevice corrosion, and under-deposit corrosion at the source. Compared to the physical adsorption film of traditional corrosion inhibitors, this chelate film has a higher binding energy to the metal surface and a significantly improved film density, providing core protection for high corrosion inhibition rates. The π-electron system of the ternary imidazoline ring can form π–d coordination with the d orbitals of Fe atoms on the metal surface. Simultaneously, the π–π stacking of the imidazoline rings enhances the cohesion of the film layer. This dual effect significantly improves the protective film's resistance to fluid shear, effectively preventing the film from detaching under the scouring of high-speed supercritical CO2 fluid. Furthermore, the heterocyclic structure of the imidazoline ring exhibits excellent thermal stability, further enhancing the overall molecular resistance to high-temperature decomposition—Example 1 maintained a high corrosion inhibition rate of 92.3% in a supercritical CO2 environment at 120℃, while the traditional binary imidazoline corrosion inhibitor (Comparative Example 2) only achieved a corrosion inhibition rate of 68.2%, confirming the role of the framework in improving thermal stability.

[0023] In summary, the quaternary ammonium salt and phosphonate ester functional groups are covalently fixed to the same rigid imidazoline skeleton, achieving a synchronous response and synergistic effect of "adsorption-film formation-stabilization" on a single molecular structure: the rapid adsorption of the quaternary ammonium salt provides a "positioning basis" for film formation, the chelation of the phosphonate ester provides a "core barrier" for protection, and the rigid structure of the imidazoline skeleton provides a "stability guarantee" for the system. This synergistic mechanism enables the corrosion inhibitor of this application to break through the performance bottleneck of traditional corrosion inhibitors, increasing the surface adsorption density to more than 1.6 times that of traditional binary imidazoline corrosion inhibitors, while also exceeding the 80% corrosion inhibition rate threshold of traditional corrosion inhibitors, improving it by more than 12 percentage points. This not only gives the corrosion inhibitor of this application excellent high-temperature thermal stability and high surface adsorption density, but also significantly improves the corrosion inhibition rate compared to traditional corrosion inhibitors. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0025] On one hand, the present invention provides a supercritical carbon dioxide corrosion inhibitor, comprising the following general formula molecular structure: [Tripartite imidazoline skeleton]–[–N + R3] n –[–P(O)(OR')2] n in: The ternary imidazoline skeleton contains at least three independent imidazoline rings, each ring retaining at least one amino group as a functionalization site, with a total number of functionalized amino groups ≥ 6; The –N + The R3 group is attached to the amino functionalization site on the ternary imidazoline skeleton, wherein R includes any one or more of C1–C6 alkyl and aryl groups, preferably C1–C4 alkyl. The –P(O)(OR')2 group is attached to the remaining amino functionalization site on the ternary imidazoline skeleton, wherein R' includes any one or more of C1–C6 alkyl and aryl groups, preferably C2–C4 alkyl. In the molecular structure, n≥3, and all molecules are directly anchored to the same ternary imidazoline backbone through covalent bonds, forming a ternary imidazoline-triquaternary ammonium salt-triphosphonate composite structure.

[0026] The purpose of this invention is to provide a supercritical carbon dioxide corrosion inhibitor and its manufacturing method. By using a rigid polycyclic framework to achieve covalent anchoring of multiple functional groups, a synergistic system of "adsorption-film formation-stabilization" is formed. As a result, the corrosion inhibitor of this application not only has excellent high-temperature thermal stability and high surface adsorption density under the extreme corrosion environment of high temperature, high mineralization and supercritical CO2, but also significantly improves the corrosion inhibition rate compared with traditional corrosion inhibitors.

[0027] Preferably, the amino functionalization site includes either a primary amine functionalization site or a secondary amine functionalization site, with a secondary amine site being preferred.

[0028] Preferably, the ternary imidazoline skeleton is formed by a ring-closing condensation reaction of at least one tricarboxylic acid and at least one triamine, wherein the molar ratio of the tricarboxylic acid to the triamine is 1:(1.1–1.5).

[0029] Preferably, the tricarboxylic acid includes one or more of trimellitic acid, pyromellitic acid, 1,2,4-cyclohexanetricarboxylic acid, or their derivatives.

[0030] Preferably, the ternary amine comprises any one or more of triethylenetetramine, tetraethylenepentamine, 1,3,5-tris(2-aminoethyl)cyclohexane or its derivatives.

[0031] Preferably, the –N + At least three R3 groups are provided, the three –N groups + The R3 group is covalently attached to the amino group site on the ternary imidazoline skeleton via an alkylation reaction.

[0032] Preferably, at least three –P(O)(OR')2 groups are provided, and the three –P(O)(OR')2 groups are covalently linked to the remaining amino sites on the ternary imidazoline skeleton through a nucleophilic substitution reaction.

[0033] On the other hand, the present invention provides a method for manufacturing a supercritical carbon dioxide corrosion inhibitor, which, in order to obtain the supercritical carbon dioxide corrosion inhibitor as described in any of the preceding claims, includes the following steps: Synthesis of S1 tri-imidazoline skeleton: Tricarboxylic acid and triamine were added to a reaction vessel at a molar ratio of 1:(1.1–1.5) and condensed at 170–200℃ under an inert atmosphere for 6–12 hours. The reaction endpoint was when the acid value was ≤3.0 mgKOH / g. The mixture was then cooled to below 80℃ to obtain the tri-imidazoline intermediate. S2 Quaternization reaction: An alkylating agent is added dropwise to the ternary imidazoline intermediate obtained in step S1, wherein the molar ratio of the alkylating agent to the ternary imidazoline intermediate is (3.0–3.5):1, and the reaction is carried out at 70–90℃ for 1–3 hours to obtain the ternary quaternary ammonium salt intermediate; S3 Phosphonate reaction: A phosphonate precursor is added to the ternary quaternary ammonium salt intermediate obtained in step S2, wherein the molar ratio of the phosphonate precursor to the quaternary ammonium salt intermediate is (3.0–3.5):1. The reaction is carried out at 100–120°C under vacuum dehydration conditions for 2–5 hours to obtain a ternary imidazoline–triquaternary ammonium salt–triphosphonate composite structure.

[0034] Preferably, the dropping rate of the alkylating agent in step S2 is 0.5–1.0 mol / h.

[0035] Preferably, the reaction system in step S1 is a solvent-free system, or a high-boiling-point inert solvent system is used, wherein the high-boiling-point inert solvent system includes any one or more of N-methylpyrrolidone, dimethyl sulfoxide, and ethylene glycol monobutyl ether.

[0036] Preferably, the alkylating agent in step S2 includes one or more of dimethyl sulfate, iodomethane, methyl chloroacetate, or tert-butane bromide.

[0037] Preferably, the phosphonate precursor in step S3 includes one or more of dimethyl phosphate, diethyl phosphate, diethyl phosphite, or diphenyl phosphate.

[0038] Example 1 The method for manufacturing the supercritical carbon dioxide corrosion inhibitor provided in Example 1 includes the following manufacturing steps: Synthesis of the S1 tri-imidazoline skeleton: 1.0 mol trimellitic acid and 1.2 mol triethylenetetramine were added to a reaction vessel. A solvent-free system was used, and the condensation reaction was carried out at 190℃ under nitrogen protection (purity ≥99.99%) by vacuum dehydration (vacuum degree ≤-0.08MPa) for 10 hours. Samples were taken every 2 hours to determine the acid value by potentiometric titration according to GB / T 1668-2008. The reaction endpoint was determined when the acid value was ≤2.0 mgKOH / g. The mixture was cooled to below 80℃ to obtain the tri-imidazoline intermediate. The chemical reaction formula for step S1 (closed-ring condensation reaction): C9H6O6 (triphenyl benzoic acid) + 3C6H 18 N4 (triethylenetetramine) → C9H3[C(O)-N(CH2CH2NHCH2CH2NH)-C2H2N]3 (ternary imidazoline intermediate) + 3H2O↑; S2 Quaternization reaction: 3.2 mol of dimethyl sulfate was added dropwise to the ternary imidazoline intermediate obtained in step S1 at a rate of 0.8 mol / h, and the reaction was stirred at 85℃ for 1.5 hours to obtain the ternary quaternary ammonium salt intermediate; The chemical reaction formula for step S2 (quaternization reaction): C9H3[C(O)-N(CH2CH2NHCH2CH2NH)-C2H2N]3 (ternary imidazoline intermediate) + 3(CH3)2SO4 (dimethyl sulfate) → C9H3[C(O)-N(CH2CH2NHCH2CH2N] + (CH3)3)-C2H2N]3·3CH3SO4 - (Ternary quaternary ammonium salt intermediate); S3 Phosphate Esterification Reaction: 3.3 mol of diethyl phosphate was added to the ternary quaternary ammonium salt intermediate obtained in step S2, and the reaction was carried out at 115℃ under vacuum dehydration conditions (vacuum degree ≤ -0.09MPa) for 4 hours. After the reaction was completed, the unreacted raw materials were removed by vacuum distillation at 140℃ under vacuum degree ≤ -0.095MPa to obtain a ternary imidazoline-triquaternary ammonium salt-triphosphate ester composite corrosion inhibitor.

[0039] The chemical reaction formula for step S3 (phosphonate esterification reaction): C9H3[C(O)-N(CH2CH2NHCH2CH2N + (CH3)3)-C2H2N]3·3CH3SO4 - (Ternary quaternary ammonium salt intermediate) + 3(C2H5O)2P(O)OH (diethyl phosphate) → C9H3[C(O)-N(CH2CH2NHCH2CH2N] +(CH3)3)-C2H2N]3[C(O)-N(CH2CH2NHCH2CH2P(O)(OC2H5)2)-C2H2N]3·3CH3SO4 - (Finished product) + 3H2O↑.

[0040] The supercritical carbon dioxide corrosion inhibitor provided in Example 1 was manufactured according to the above-described method for manufacturing supercritical carbon dioxide corrosion inhibitors. The chemical structural formula of the supercritical carbon dioxide corrosion inhibitor is: C9H3[C(O)-N(CH2CH2NHCH2CH2N] + (CH3)3)-C2H2N]3–[N(CH2CH2NHCH2CH2P(O)(OC2H5)2)-C2H2N]3·3CH3SO4 - The chemical structure uses the benzene ring of trimellitic acid as the core bridging skeleton, which is connected to the imidazoline ring derived from triethylenetetramine via imide bonds to form a ternary imidazoline skeleton; the secondary amine sites of the three imidazoline ring side chains combine with the -CH3 provided by dimethyl sulfate to form -N + The (CH3)3 quaternary ammonium group, with the remaining three secondary amine sites forming NP covalent bonds with the -P(O)(OC2H5)2 group of diethyl phosphate, and the sulfate ion (CH3SO4) - To balance the anions, all functional groups are uniformly anchored on the ternary imidazoline skeleton, ensuring the synergistic effect of "adsorption-film formation-stability".

[0041] Comparative Example 1 The binary imidazoline quaternary ammonium salt-phosphonate corrosion inhibitor provided in Comparative Example 1 includes the following manufacturing steps: Synthesis of S1 diimidazoline skeleton: 1.0 mol sebacic acid and 1.1 mol diethylenetriamine were added to a reaction vessel. In a solvent-free system, the reaction was carried out at 185 °C under nitrogen protection (purity ≥99.99%) for 8 hours in an azeotropic dehydration reaction. The reaction endpoint was determined by an acid value ≤5.0 mgKOH / g. The acid value was determined by potentiometric titration according to GB / T 1668-2008. The mixture was cooled to below 80 °C to obtain the diimidazoline intermediate. S2 Quaternization reaction: 2.2 mol of dimethyl sulfate was slowly added dropwise to the di-imidazoline intermediate obtained in step S1 at a rate of 0.6 mol / h, and the reaction was stirred at 80 °C for 2 hours to obtain the di-quaternary ammonium salt intermediate; S3 Phosphonate esterification reaction: 2.2 mol of diethyl phosphate was added to the binary quaternary ammonium salt intermediate obtained in step S2, and the reaction was carried out at 110℃ under vacuum dehydration (vacuum degree ≤ -0.09MPa) for 3 hours. After removing impurities by vacuum distillation, the binary imidazoline quaternary ammonium salt-phosphonate corrosion inhibitor was obtained.

[0042] Comparative Example 2 The conventional binary imidazoline corrosion inhibitor provided in Comparative Example 2 includes the following manufacturing steps: Synthesis of the binary imidazoline skeleton: 1.0 mol sebacic acid and 1.1 mol diethylenetriamine were added to a reaction vessel and subjected to azeotropic dehydration and ring-closure reaction at 185 °C under nitrogen protection (purity ≥99.99%) for 8 hours in a solvent-free system. The reaction endpoint was an acid value ≤5.0 mgKOH / g. The acid value was determined by potentiometric titration according to GB / T 1668-2008. After cooling, a conventional binary imidazoline corrosion inhibitor was obtained directly.

[0043] Experimental methods 1. Determination of corrosion inhibition rate (%) (weight loss method), including the following steps: (1) Pretreatment of test pieces: Q235 carbon steel test pieces (50mm×25mm×2mm) were polished with 400#, 800# and 1200# sandpaper until the surface was bright. They were then ultrasonically degreased with acetone for 15 minutes, dehydrated with anhydrous ethanol, dried in an oven at 105℃ for 2 hours, cooled to room temperature in a desiccator, and accurately weighed with an electronic balance with an accuracy of 0.0001g (recorded as the initial mass m1). (2) Corrosion test: The test piece was placed in a 5% NaCl corrosive medium containing 1000ppm corrosion inhibitor and placed in a high-temperature and high-pressure reactor. Nitrogen gas (purity ≥99.99%) was first introduced to replace the air in the reactor 3 times (each replacement pressure 0.5MPa, pressure held for 5min and then vented). Then CO2 gas was introduced and the temperature and pressure were increased to the supercritical state (temperature 120℃, pressure 8.0MPa, satisfying the supercritical conditions of CO2: T≥31.1℃, P≥7.38MPa). The stirring rate was controlled at 150r / min and constant temperature and pressure were maintained for 72h. (3) Post-treatment and weighing: After the experiment, the sample was allowed to cool naturally to room temperature, and CO2 was slowly released. The sample was then removed. According to GB / T16545-2015 standard, 5% hydrochloric acid-0.5% hexamethylenetetramine solution (with a clear rust remover formula) was used to remove the surface corrosion products. The sample was washed three times with deionized water, dehydrated with anhydrous ethanol, dried in an oven at 105℃ for 2 hours, and then accurately weighed again after the desiccator cooled to room temperature (recorded as the final mass m2). (4) Calculation method: Corrosion rate ν = (m1 - m2) / (S × t) (where: ν is the corrosion rate, in g / (m²·h); S is the total surface area of ​​the specimen, in m²; t is the experimental time, in h). Corrosion inhibition rate η (%) = [(ν0-ν1) / ν0] × 100% (where: ν0 is the corrosion rate of the blank sample, and ν1 is the corrosion rate of the sample with added chemicals). The blank sample was tested under the same conditions as the chemically treated sample, except that the corrosive medium did not contain any corrosion inhibitor, and its corrosion inhibition rate was 0, which was used as the calculation benchmark.

[0044] 2. Surface adsorption capacity (mol / cm²) determination The adsorption behavior of corrosion inhibitor molecules on the carbon steel modified electrode surface was monitored in real time using a quartz crystal microbalance (QCM-D, model Q-SenseE4). The experiment was conducted in situ in the aforementioned supercritical CO2 simulated corrosion environment. Specific steps are as follows: (1) Electrode pretreatment: The surface of the gold-plated quartz crystal sensor was deposited with Q235 carbon steel film (simulating carbon steel substrate) by magnetron sputtering, and then ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min in sequence. After being dried with nitrogen, it was ready for use. (2) Baseline correction: The pretreated sensor was installed in the QCM-D test chamber and a 5% NaCl corrosion medium without corrosion inhibitor was introduced. The temperature and pressure were increased to 120℃ and 8.0MPa supercritical CO2 conditions. The monitoring was stable for 30 minutes, and the frequency shift value (Δf0) of the quartz crystal was recorded as the baseline correction data to eliminate the interference of the medium itself, spontaneous adsorption of the electrode substrate and temperature and pressure changes. (3) Adsorption test: Inject 5% NaCl corrosion medium containing 1000ppm target corrosion inhibitor into the test chamber, keep the supercritical CO2 conditions unchanged, continuously monitor the oscillation frequency shift (Δf) of the quartz crystal until the frequency stabilizes (frequency change ≤0.5Hz within 30min), and stop the test; (4) Calculation method: Effective frequency offset Δf ( efficient ) =Δf-Δf0 (subtract baseline interference); The adsorption mass change is calculated based on the Sauerbrey equation: Δm = -C6 × Δf ( efficient ) / n (where: Δm is the adsorption mass change, in ng / cm²; C6 is the quartz crystal sensitivity constant, taken as 17.7 ng·cm²) - ²·Hz - ¹; n is the harmonic order, taken as the 3rd harmonic to ensure that the adsorption layer meets the applicable premise of the Sauerbrey equation of "uniform and dense, with a thickness much smaller than the crystal thickness"). Surface adsorption capacity per unit area Γ (mol / cm²) = (Δm × 10⁻⁶) -9 g / ng) / (M×10 4 (cm² / m²) ÷ M1 (where: Δm is in ng / cm², multiply by 10 to convert to g / cm²) -9 M represents the effective area of ​​the sensor, in cm²; M1 represents the molecular weight of the corrosion inhibitor, in g / mol. After calibration, the surface adsorption amount Γ≈0 of the blank sample (without corrosion inhibitor) is consistent with the theoretical expectation.

[0045] The experimental data obtained from the above experimental methods used in Example 1 and Comparative Examples 1-2 are shown in Table 1 below: Table 1. Experimental data for Example 1 and Comparative Examples 1-2 This application employs a weight loss method under 120℃, 0.8MPa high pressure, and 5% NaCl high-salt corrosive medium conditions. These experimental conditions simulate harsh actual corrosion scenarios such as deep oil wells, supercritical CO2 flooding wells, and high-temperature chemical CO2 treatment equipment (combining the triple harsh characteristics of supercritical fluid erosion, high chloride ion concentration, and high temperature, making the corrosiveness far stronger than conventional ambient temperature and pressure environments). Table 1 shows that the corrosion inhibitor in Example 1, at a dosage of 1000ppm, achieved a corrosion inhibition rate as high as 92.3%, an increase of 12.8 percentage points compared to Comparative Example 1 (79.5%), representing a relative improvement of 16.1%; and an increase of 24.1 percentage points compared to Comparative Example 2 (68.2%), representing a relative improvement of 35.3%. This demonstrates that the corrosion inhibitor in this application exhibits significantly better corrosion inhibition performance than the inhibitors in Comparative Examples 1-2, effectively resisting corrosion in supercritical CO2 high-temperature and high-salt environments, and better meeting the anti-corrosion requirements of actual harsh working conditions. The surface adsorption capacity per unit area of ​​the corrosion inhibitor in Example 1, as shown in Table 1, reaches 1.8 × 10⁻⁶. -6 mol / cm², compared to Comparative Example 1 (1.1 × 10⁻⁶ mol / cm²), -6 The efficiency (mol / cm²) increased by 63.6%, compared to Comparative Example 2 (8.7 × 10⁻⁶ mol / cm²). -7 The corrosion inhibitor concentration (mol / cm²) increased by 106.9%. This data directly corroborates the effectiveness of the core design of this application: the ternary imidazoline rigid framework successfully anchors multiple quaternary ammonium groups and phosphonate groups, forming a "adsorption-film formation-stabilization" synergistic system, which enables the corrosion inhibitor molecules to be more tightly and fully adsorbed on the carbon steel surface. The quaternary ammonium groups are rapidly anchored through electrostatic interaction, and the phosphonate groups are strengthened through coordination interaction, ultimately forming a dense adsorption protective film that effectively blocks chloride ion penetration and supercritical CO2 corrosion, providing a solid mechanistic support for the high corrosion inhibition rate. Crucially, the corrosion inhibition rate and surface adsorption capacity tests in Table 1 were conducted in situ in a supercritical CO2 and 5% NaCl corrosive medium at 120℃, 8.0MPa, precisely matching the actual high-temperature, high-salt supercritical operating conditions. Example 1 maintained a high corrosion inhibition rate of 92.3% under these extreme conditions, indicating that the rigid ternary imidazoline framework in its molecular structure effectively inhibits molecular decomposition or configurational collapse at high temperatures, demonstrating excellent high-temperature stability. In contrast, Comparative Examples 1-2, under the same operating conditions, not only showed significantly lower corrosion inhibition rates but also significantly lower surface adsorption capacity than Example 1. This indicates that traditional corrosion inhibitors, due to their simple framework structure and limited number of functional groups, are prone to adsorption-desorption and molecular degradation in high-temperature supercritical environments, leading to decreased adsorption capacity and reduced corrosion inhibition performance.

[0046] In summary, the corrosion inhibitor of this application, through the innovative design of a ternary composite structure, simultaneously solves the three core pain points of traditional corrosion inhibitors in supercritical CO2 high-temperature and high-salt environments: "low corrosion inhibition rate", "poor high-temperature stability" and "weak adsorption capacity". This significantly broadens the application scenarios of corrosion inhibitors, making them particularly suitable for harsh corrosive environments such as supercritical CO2 oil recovery in oil fields and high-temperature chemical CO2 treatment, and has important industrial application value.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A supercritical carbon dioxide corrosion inhibitor, characterized in that, Including the following general formula molecular structures: [Tripartite imidazoline skeleton]–[–N + R3] n –[–P(O)(OR')2] n in: The ternary imidazoline skeleton comprises at least three independent imidazoline rings, each ring retaining at least one amino group as a functionalization site; The –N + The R3 group is attached to the amino functionalization site on the ternary imidazoline skeleton, wherein R includes any one or more of C1–C6 alkyl and aryl groups; The –P(O)(OR')2 group is attached to the remaining amino functionalization site on the ternary imidazoline skeleton, wherein R' includes any one or more of C1–C6 alkyl and aryl groups; In the molecular structure, n≥3, and all molecules are directly anchored to the same ternary imidazoline backbone through covalent bonds, forming a ternary imidazoline-triquaternary ammonium salt-triphosphonate composite structure.

2. The supercritical carbon dioxide corrosion inhibitor according to claim 1, characterized in that, The ternary imidazoline skeleton is formed by a ring-closing condensation reaction of at least one ternary carboxylic acid and at least one ternary amine, wherein the molar ratio of the ternary carboxylic acid to the ternary amine is 1:(1.1–1.5).

3. The supercritical carbon dioxide corrosion inhibitor according to claim 2, characterized in that, The tricarboxylic acid includes any one or more of trimellitic acid, pyromellitic acid, 1,2,4-cyclohexanetricarboxylic acid, or their derivatives.

4. The supercritical carbon dioxide corrosion inhibitor according to claim 2, characterized in that, The ternary amine includes any one or more of the following: triethylenetetramine, tetraethylenepentamine, 1,3,5-tris(2-aminoethyl)cyclohexane or its derivatives.

5. The supercritical carbon dioxide corrosion inhibitor according to claim 1, characterized in that, The –N + At least three R3 groups are provided, the three –N groups + The R3 group is covalently attached to the amino group site on the ternary imidazoline skeleton via an alkylation reaction.

6. The supercritical carbon dioxide corrosion inhibitor according to claim 5, characterized in that, The –P(O)(OR')2 group is provided in at least three forms, and the three –P(O)(OR')2 groups are covalently linked to the remaining amino sites on the ternary imidazoline skeleton through a nucleophilic substitution reaction.

7. A method for manufacturing a supercritical carbon dioxide corrosion inhibitor, characterized in that, The method for manufacturing a supercritical carbon dioxide corrosion inhibitor as described in any one of claims 1-6 comprises the following steps: Synthesis of S1 tri-imidazoline skeleton: Tricarboxylic acid and triamine were added to a reaction vessel at a molar ratio of 1:(1.1–1.5) and condensed at 170–200℃ under an inert atmosphere for 6–12 hours. The reaction endpoint was when the acid value was ≤3.0 mgKOH / g. The mixture was then cooled to below 80℃ to obtain the tri-imidazoline intermediate. S2 Quaternization reaction: An alkylating agent is added dropwise to the ternary imidazoline intermediate obtained in step S1, wherein the molar ratio of the alkylating agent to the ternary imidazoline intermediate is (3.0–3.5):1, and the reaction is carried out at 70–90℃ for 1–3 hours to obtain the ternary quaternary ammonium salt intermediate; S3 Phosphonate reaction: A phosphonate precursor is added to the ternary quaternary ammonium salt intermediate obtained in step S2, wherein the molar ratio of the phosphonate precursor to the quaternary ammonium salt intermediate is (3.0–3.5):

1. The reaction is carried out at 100–120°C under vacuum dehydration conditions for 2–5 hours to obtain a ternary imidazoline–triquaternary ammonium salt–triphosphonate composite structure.

8. The method for manufacturing the supercritical carbon dioxide corrosion inhibitor according to claim 7, characterized in that, The reaction system described in step S1 is a solvent-free system or a high-boiling-point inert solvent system, wherein the high-boiling-point inert solvent system includes any one or more of N-methylpyrrolidone, dimethyl sulfoxide, and ethylene glycol monobutyl ether.

9. The method for manufacturing the supercritical carbon dioxide corrosion inhibitor according to claim 7, characterized in that, The alkylating agent mentioned in step S2 includes one or more of dimethyl sulfate, iodomethane, methyl chloroacetate, or tert-butane bromide.

10. The method for manufacturing the supercritical carbon dioxide corrosion inhibitor according to claim 7, characterized in that, The phosphonate precursor in step S3 includes one or more of dimethyl phosphate, diethyl phosphate, diethyl phosphite, or diphenyl phosphate.

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