A composite ferrous sulfide passivating agent and preparation method thereof

Abstract

The invention relates to the technical field of passivation deodorants, and discloses a composite ferrous sulfide passivator and a preparation method thereof. The composite ferrous sulfide passivator comprises the following raw materials in percentage by mass: 4-6% sodium persulfate, 2-4% sodium percarbonate, 0.5-1% sodium nitrite, 1-2% triethanolamine, 0.5-1% quaternary ammonium surfactant, 0.3-0.7% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.2-0.4% thioacetamide, 0.2-0.4% isomeric sodium dodecylbenzene sulfonate, 0.4-0.6% sodium cocoate sarcosine, 0.5-0.8% N,N-dihydroxyethyl oleamide, and a water balance. The composite ferrous sulfide passivator provided by the invention reduces the generation of ferrous sulfide through oxidation and passivation reactions, and finally reduces the accumulation of ferrous sulfide in equipment, thereby reducing the generation of malodor; the cleaning ability and passivation efficiency are high, the equipment can be protected from corrosion, the service life of the equipment is extended, and the residual pollutants can be reduced.

Description

Technical Field

[0001] The invention relates to the field of passivation deodorants, and more specifically, to a composite ferrous sulfide passivator and a preparation method thereof. Background Art

[0002] In the crude oil processing process, the sulfur-making unit is a terminal unit of the oil refining, and its raw materials contain a large amount of hydrogen sulfide and ammonia nitrogen. These substances, especially hydrogen sulfide, produce a large amount of ferrous sulfide when in contact with the equipment, which is enriched on the tower packing, tower tray or at the bottom of some containers and pipelines, and is wrapped by the sticky impurities in the sewage and is not easily carried away by the fluid.

[0003] As the properties of crude oil become increasingly deteriorating and the number of crude oil deep processing units increases, the sulfide and ammonia nitrogen content in the sulfur-containing wastewater generated during the refining process gradually increases. The odorous environmental pollution caused by hydrogen sulfide and ammonia nitrogen during the shutdown of the unit is becoming more and more widespread and the degree of pollution is becoming more and more serious. The traditional shutdown process of the unit uses steam purging, which is directly discharged into the atmosphere. The hydrogen sulfide and ammonia nitrogen carried by the steam will cause serious pollution to the atmospheric environment and cause personal injury to the maintenance personnel. Therefore, it is very necessary to clean and deodorize the equipment and pipelines before the unit maintenance.

[0004] The existing ferrous sulfide passivation deodorant has unstable oxidation ability and is easy to decompose, which affects the sustainability of the passivation effect. The deodorant lacks ingredients that inhibit the volatilization of hydrogen sulfide and ammonia, and a certain degree of stench may still be caused during the deodorization process. The passivation of ferrous sulfide by deodorants mainly relies on chemical oxidation, and the surface of ferrous sulfide is often coated with impurities such as oil sludge, which affects the passivation effect. The deodorant lacks long-term corrosion inhibition components and may not be able to completely prevent corrosion problems during the passivation process. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a composite ferrous sulfide passivator and a preparation method thereof.

[0006] A composite ferrous sulfide passivating agent comprises the following raw materials in percentage by mass:

[0007] Sodium persulfate 4-6%, sodium percarbonate 2-4%, sodium nitrite 0.5-1%, triethanolamine 1-2%, quaternary ammonium surfactant 0.5-1%, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan 0.3-0.7%, thioacetamide 0.2-0.4%, isomeric sodium dodecylbenzene sulfonate 0.2-0.4%, sodium cocoyl sarcosine 0.4-0.6%, N,N-dihydroxyethyl oleamide 0.5-0.8%, balance water.

[0008] Preferably, the quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide.

[0009] A composite ferrous sulfide passivating agent comprises the following preferred raw materials in percentage by mass: 4% sodium persulfate, 2% sodium percarbonate, 0.5% sodium nitrite, 1% triethanolamine, 0.5% quaternary ammonium surfactant, 0.3% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.2% thioacetamide, 0.2% sodium isomeric dodecylbenzene sulfonate, 0.4% sodium cocoyl sarcosine, 0.5% N,N-dihydroxyethyl oleamide, and the balance water.

[0010] A composite ferrous sulfide passivating agent comprises the following preferred raw materials in percentage by mass: 6% sodium persulfate, 4% sodium percarbonate, 1% sodium nitrite, 2% triethanolamine, 1% quaternary ammonium surfactant, 0.7% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.4% thioacetamide, 0.4% isomeric sodium dodecylbenzene sulfonate, 0.6% sodium cocoyl sarcosine, 0.8% N,N-dihydroxyethyl oleamide, and the balance water.

[0011] A method for preparing a composite ferrous sulfide passivator comprises the following steps:

[0012] S1: In a clean container, add an appropriate amount of water, and then add triethanolamine, hexadecyltrimethylammonium bromide, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, and thioacetamide in order according to the percentage of the formula;

[0013] Stir well to ensure all solid ingredients are fully dissolved. This step is necessary to ensure all liquid ingredients are mixed evenly.

[0014] S2: Add sodium isomeric dodecylbenzene sulfonate, sodium cocoyl sarcosinate, and N,N-dihydroxyethyl oleamide to the solution of step S1 in sequence, and stir well to ensure that these surfactants are evenly dispersed in the solution.

[0015] S3: Add sodium persulfate and sodium percarbonate according to the percentage of the formula. Note that you should be particularly careful when adding sodium percarbonate to prevent it from reacting too quickly with water to produce a large number of bubbles. At the same time, ensure that all the mixtures are fully stirred.

[0016] S4: The composite ferrous sulfide passivator of the required concentration can be prepared by adding water to dilute the solution until the required concentration is reached.

[0017] Preferably, in step S1, the stirring time is 30-60 min, and the stirring temperature is 25-40°C.

[0018] Preferably, in step S2, the stirring time is 30-50 min, and the stirring temperature is 25-35°C.

[0019] Preferably, in step S3, the stirring time is 30-60 min, and the stirring temperature is 20-30°C.

[0020] The beneficial effects of the present invention are as follows: the composite ferrous sulfide passivator proposed in the present invention reduces the generation of ferrous sulfide through oxidation and passivation reactions, and ultimately reduces the accumulation of ferrous sulfide in the equipment, thereby reducing the generation of odor; it has high cleaning ability and passivation efficiency, can protect the equipment from corrosion, extend the service life of the equipment, and can reduce the residual pollutants. DETAILED DESCRIPTION

[0021] The subject matter described herein will now be discussed with reference to example embodiments. It should be understood that the discussion of these embodiments is only to enable those skilled in the art to better understand and implement the subject matter described herein, and the functions and arrangements of the elements discussed may be changed without departing from the scope of protection of the contents of this specification. Each example may omit, replace or add various processes or components as needed. In addition, the features described relative to some examples may also be combined in other examples. Example 1

[0022] In this embodiment, a composite ferrous sulfide passivator is proposed, which includes the following raw materials in mass percentage: 4% sodium persulfate, 2% sodium percarbonate, 0.5% sodium nitrite, 1% triethanolamine, 0.5% quaternary ammonium surfactant, 0.3% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.2% thioacetamide, 0.2% sodium isomeric dodecylbenzene sulfonate, 0.4% sodium cocoyl sarcosine, 0.5% N,N-dihydroxyethyl oleamide, and the balance water.

[0023] The quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide. Example 2

[0024] In this embodiment, a composite ferrous sulfide passivator is proposed, comprising the following raw materials in mass percentage: comprising the following preferred raw materials in mass percentage: sodium persulfate 6%, sodium percarbonate 4%, sodium nitrite 1%, triethanolamine 2%, quaternary ammonium surfactant 1%, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan 0.7%, thioacetamide 0.4%, isomeric sodium dodecylbenzene sulfonate 0.4%, sodium cocoyl sarcosine 0.6%, N,N-dihydroxyethyl oleamide 0.8%, and water as the balance.

[0025] The quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide.

[0026] In the above embodiment:

[0027] The sodium percarbonate (Na2CO4) and sodium persulfate (Na2S2O8) used are both highly oxidizing in chemical reactions. They can effectively oxidize ferrous sulfide (FeS) to form stable ferrous sulfate (FeSO4), thereby achieving a passivation effect. At the same time, sodium percarbonate will generate carbon dioxide (CO2) when it decomposes. This generation process has a synergistic effect with reducing the volatilization of harmful gases such as hydrogen sulfide (H2S).

[0028] Here’s how it works:

[0029] Oxidation and passivation process:

[0030] Sodium persulfate (Na2S2O8): Sodium persulfate reacts with water to form sulfuric acid and sodium peroxysulfate (Na2SO5), which then further react to form sodium sulfate (Na2SO4) and oxygen. Sodium persulfate has a very strong oxidizing property and can oxidize ferrous sulfide (FeS) into ferrous sulfate (FeSO4):

[0031] FeS+Na2S2O8→Fe(SO4)2+S+Na2O

[0032] Sodium percarbonate (Na2CO4): Sodium percarbonate generates sodium carbonate (Na2CO3) and carbon dioxide (CO2) during the hydrolysis process, while releasing oxygen. Sodium carbonate is also oxidizing and can also participate in the oxidation reaction of ferrous sulfide:

[0033] FeS+Na2CO4→FeCO3+Na2S

[0034] In fact, the hydrolysis process of sodium percarbonate is relatively complicated, and the reaction path of the generated CO2 and H2S may involve a series of intermediate reactions and chemical equilibrium.

[0035] Absorption of harmful gases such as hydrogen sulfide by carbon dioxide:

[0036] When sodium percarbonate decomposes to produce carbon dioxide, the carbon dioxide molecules react with harmful gas molecules such as hydrogen sulfide (H2S) in the environment. This is mainly based on the solubility of gases in water. Carbon dioxide dissolves in water to form carbonic acid (H2CO3), which then decomposes into bicarbonate ions (HCO3 - ) and hydrogen ions (H + Since hydrogen sulfide can dissociate into hydrogen ions and sulfur ions (H + and S2 - ), the reaction of carbon dioxide and hydrogen sulfide is more based on the interaction and chemical equilibrium of these two substances in water. In theory, this reaction may be as follows:

[0037] CO2(g)+H2S(g)⇌HCO3 - +HS -

[0038] This is a dynamic equilibrium reaction, and the generated sulfur bicarbonate (HCO3 - and HS - ) Ionic compounds may further affect the solubility and concentration of the gas, thereby reducing the escape and odor of hydrogen sulfide to a certain extent.

[0039] Through this process, sodium percarbonate and sodium persulfate, while passivating ferrous sulfide, indirectly assist in absorbing and reducing the volatilization of harmful gases such as hydrogen sulfide through the generation of carbon dioxide, which helps to reduce odor and improve environmental quality. This process actually involves complex chemical reactions and balances, and the specific effect may be affected by many factors, including reaction conditions, gas concentration, the amount of water in the solution, etc.

[0040] In the above embodiment:

[0041] The mechanism of action of sodium nitrite:

[0042] Hydrogen sulfide (H2S) is reducing and can be oxidized by strong oxidants such as sodium nitrite. The oxidation reaction is as follows:

[0043] H2S+4NaNO2→S+4NaNO3+2H2O

[0044] This reaction oxidizes hydrogen sulfide into sulfur (S), while also producing harmless sodium nitrate (NaNO3) and water (H2O). Sulfur is a solid that is more stable in the environment and does not emit the same foul odor as hydrogen sulfide.

[0045] Inhibit the formation of ferrous sulfide:

[0046] During the passivation process, sodium nitrite reduces the concentration of hydrogen sulfide by reacting with it. The reduction of hydrogen sulfide helps inhibit the formation of ferrous sulfide (FeS). This is because the formation of ferrous sulfide requires the presence of hydrogen sulfide. By reducing hydrogen sulfide, sodium nitrite indirectly reduces the precursors for the formation of ferrous sulfide, helping to prevent the accumulation of ferrous sulfide.

[0047] Synergistic effect with sodium persulfate and sodium percarbonate:

[0048] Oxidation passivation:

[0049] Sodium persulfate and sodium percarbonate both have strong oxidizing properties. They react with ferrous sulfide and oxidize it into stable ferrous sulfate. The addition of sodium nitrite can not only oxidize hydrogen sulfide, but also participate in the oxidation process of ferrous sulfide, further promoting the passivation effect.

[0050] Reduce bad odor:

[0051] By oxidizing hydrogen sulfide to sulfur, sodium nitrite reduces the volatilization of hydrogen sulfide and alleviates the odor. At the same time, sodium persulfate, sodium percarbonate and sodium nitrite work together to form an effective system, which reduces the generation of ferrous sulfide through oxidation and passivation reactions, and ultimately reduces the accumulation of ferrous sulfide in the equipment, thereby reducing the generation of odor.

[0052] In summary, sodium nitrite not only reduces odor by oxidizing hydrogen sulfide to sulfur and inhibiting the formation of ferrous sulfide, but also works synergistically with sodium persulfate and sodium percarbonate to form a complete passivation and deodorization system, thereby improving the overall treatment efficiency and effectiveness.

[0053] In the above embodiment:

[0054] The working principle of cetyltrimethylammonium bromide (CTAB):

[0055] Emulsification and dispersion: As a cationic surfactant, CTAB has good lipophilicity. In the water phase, the non-polar hydrophobic end of the CTAB molecule can interact with the oily components (such as oil, wax, etc.) in the sludge to form a stable emulsion. This helps to disperse the sludge into tiny particles, thereby improving its stability in water and facilitating subsequent cleaning and removal.

[0056] Adsorption capacity: The cationic part of CTAB can form hydrogen bonds with anions or surfactant molecules in the water phase, enhancing its adsorption capacity at the solution interface. This allows CTAB to be more effectively adsorbed on the surface of sludge, further enhancing the dispersing effect on sludge.

[0057] The working principle of polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan (G-PDDMAC):

[0058] Dual functions of emulsification, dispersion and adsorption: G-PDDMAC not only has the basic functions of cationic surfactants (such as emulsification, dispersion and adsorption), but also has the natural hydrophilicity, polymerization and biodegradability of chitosan. The introduction of chitosan provides additional hydrophilic groups (amino groups), which can enhance the affinity to the water phase and further improve the emulsification and dispersion effect.

[0059] Grafting effect: After the epichlorohydrin part in G-PDDMAC is grafted onto the chitosan molecule, it can introduce more hydrophobic groups (such as CH2CH2O-) to increase the hydrophobicity of the molecule. This enables G-PDDMAC to effectively disperse the sludge and interact with the sludge surface through the cationic part in its grafted structure, thereby improving the adsorption capacity of the sludge.

[0060] The synergistic effect of CTAB and G-PDDMAC as surfactants is mainly manifested in the following aspects:

[0061] Enhanced emulsification and dispersion effect: The hydrophobic end of CTAB works together with the hydrophilic and hydrophobic parts of G-PDDMAC to form a more stable emulsion and improve the dispersion and stability of the sludge.

[0062] Improve adsorption capacity: The two are adsorbed on the surface of the sludge together, CTAB provides cationic adsorption, and G-PDDMAC increases the hydrophilicity of the surface, synergistically enhancing the adsorption effect.

[0063] Stability: The chitosan-based portion of G-PDDMAC provides natural biodegradability and stability, allowing the composite surfactant to remain active during the passivation process and effectively remove sludge and impurities.

[0064] Through this synergistic effect, hexadecyltrimethylammonium bromide and polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan jointly improve the cleaning ability and passivation efficiency of the composite ferrous sulfide passivator, thereby more effectively removing sludge and impurities inside the equipment and improving the passivation effect.

[0065] In the above embodiment:

[0066] Thioacetamide (usually expressed as CH3NH2SH) mainly prevents further oxidation and corrosion of ferrous sulfide by forming a stable coordination compound, thereby forming a stable passivation system. The principle is as follows:

[0067] Reaction with ferrous sulfide:

[0068] When ferrous sulfide (FeS) is exposed to air, it is easily oxidized to ferrous sulfate (FeSO4), a process that may be accompanied by further oxidation and corrosion of ferrous sulfide. Thioacetamide can react with ferrous sulfide to form a more stable compound through the following reaction:

[0069] FeS+CH3NH2SH→FeS2(CH3NH2)2

[0070] Among them, FeS reacts with thioacetamide to form a coordination compound of thioacetamide and ferrous disulfide. This compound is relatively stable and not easily further oxidized or corroded in the air, thereby preventing the oxidation process of ferrous sulfide.

[0071] Synergy:

[0072] Synergistic effect with sodium persulfate (Na2S2O8):

[0073] Sodium persulfate has strong oxidizing properties. It can oxidize ferrous sulfide to form ferrous sulfate during the passivation process. At the same time, thioacetamide prevents the continued oxidation of ferrous sulfide through coordination, forming a more stable passivation system.

[0074] Synergistic effect with sodium percarbonate (Na2CO4):

[0075] Sodium percarbonate generates carbon dioxide when decomposing, which further absorbs harmful gases such as hydrogen sulfide in the environment. Thioacetamide reduces the generation and oxidation process of ferrous sulfide through coordination, reduces the production of hydrogen sulfide, and reduces odor.

[0076] Synergistic effect with triethanolamine (TEA):

[0077] As a weak alkaline substance, triethanolamine can neutralize acidic substances and reduce corrosiveness. It works synergistically with thioacetamide to further stabilize the passivation system and reduce further reaction and corrosion of ferrous sulfide.

[0078] Thioacetamide forms a stable coordination compound and synergizes with sodium persulfate, sodium percarbonate, triethanolamine and other components to prevent further oxidation and corrosion of ferrous sulfide and reduce the generation of harmful gases such as hydrogen sulfide, thus forming an effective composite ferrous sulfide passivation system. This system not only improves the passivation efficiency and reduces the emission of harmful substances, but also protects the equipment from corrosion and extends the service life of the equipment.

[0079] In the above embodiment:

[0080] As an emulsifier and dispersant, the unique action principle of isomeric sodium dodecylbenzene sulfonate (LAS) and its synergistic effect with other components are mainly reflected in the following aspects:

[0081] Emulsification: In the molecular structure of LAS, one end is a hydrophilic long carbon chain (hydrophobic group), and the other end is a lipophilic sulfonic acid group (hydrophilic group). At the oil-water interface, the hydrophobic group of the LAS molecule can attract the oil molecules, while the hydrophilic group attracts the water molecules. Through this intermolecular interaction, LAS can disperse the oil molecules from the water phase to form a stable emulsion. This allows the sludge and oil stains to be dispersed in the water and easy to clean.

[0082] Dispersing ability: Dispersing effect is an extension of emulsifying effect. When sludge or oil stains are dispersed in water, the dispersing effect of LAS can prevent the dispersed oil droplets from re-aggregating, maintain the stability of the oil droplets, and make the cleaning process more thorough.

[0083] Synergistic effect with polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan (G-PDDMAC): G-PDDMAC has surface activity and adsorption properties. Its grafted chitosan part can be adsorbed on the surface of sludge, while the epichlorohydrin grafted part may enhance its emulsification and dispersion effect. In synergy with LAS, G-PDDMAC can improve the dispersion efficiency of LAS, especially when dealing with sludge and oil stains. Their combined effect can more effectively remove impurities inside the equipment and improve the degreasing effect. At the same time, the biodegradability of chitosan also makes this synergistic effect have advantages in environmental protection.

[0084] In summary, as an emulsifier and dispersant, isomeric sodium dodecylbenzene sulfonate can more effectively remove sludge and oil stains inside the equipment due to its unique emulsifying and dispersing ability. The synergistic effect with polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan further improves the cleaning effect and reduces the residual pollutants.

[0085] In the above embodiment:

[0086] The mechanism of action of sodium cocoyl sarcosinate:

[0087] Wetting performance: Sodium cocoyl sarcosinate has good wettability and can form a stable water film with the surfaces of grease, dirt, etc. inside the equipment, enhancing the contact ability of water with these surfaces, thereby improving the cleaning effect.

[0088] Penetration: This surfactant has a certain degree of penetration and can penetrate into the micropores or fine lines of the equipment, interact with sludge or impurities, and promote their dissolution or peeling from the surface.

[0089] The mechanism of action of N,N-dihydroxyethyl oleamide:

[0090] Wetting and solubilizing properties: N,N-dihydroxyethyl oleic acid amide also has good wetting properties, which can help improve the affinity of cleaning agents to equipment surfaces. In addition, it also has strong solubilizing properties, which can increase the solubility of oil substances in aqueous solutions, thereby removing oil stains more effectively.

[0091] Emulsification and dispersing action: This surfactant can form a stable emulsion, dispersing oil into fine droplets, making them easier to rinse off with water, and also helping to peel oil from the surface of equipment.

[0092] Enhanced wetting and penetration ability: The synergistic effect of sodium cocoyl sarcosinate and N,N-dihydroxyethyl oleamide further enhances the wetting and penetration ability of the cleaning agent on impurities inside the equipment through complementary surface activity and wetting properties, allowing it to penetrate more effectively into the tiny pores of the equipment and improve the overall cleaning effect.

[0093] Synergistic emulsification and dispersion: The combined effect of these two surfactants can form a more stable emulsion system. Through emulsification and dispersion, the oil stains are broken down into smaller particles, which are easy to remove from the surface of the equipment.

[0094] Improve the overall cleaning effect: Through the complementary effect of the above properties, these two surfactants work together with other components in the composite ferrous sulfide passivator (such as emulsifiers, dispersants, etc.) to improve the cleaning ability of the composite passivator, especially for difficult-to-remove sludge and impurities, and can achieve better cleaning effects.

[0095] As surfactants, sodium cocoyl sarcosinate and N,N-dihydroxyethyl oleamide effectively improve the cleaning performance of the composite ferrous sulfide passivator through their unique wetting, penetration, emulsification and dispersion properties, as well as synergistic effects with other components in the composite passivator, which helps to clean and passivate the equipment more efficiently and thoroughly. Example 3

[0096] In this embodiment, a method for preparing a composite ferrous sulfide passivator is proposed, comprising the following steps:

[0097] S1: In a clean container, add an appropriate amount of water, and then add triethanolamine, hexadecyltrimethylammonium bromide, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, and thioacetamide in order according to the percentage of the formula;

[0098] Stir well to ensure all solid ingredients are fully dissolved. This step is necessary to ensure all liquid ingredients are mixed evenly.

[0099] The stirring time is 30-60 minutes, and the stirring temperature is 25-40°C.

[0100] S2: Add sodium isomeric dodecylbenzene sulfonate, sodium cocoyl sarcosinate, and N,N-dihydroxyethyl oleamide to the solution of step S1 in sequence, and stir well to ensure that these surfactants are evenly dispersed in the solution.

[0101] S3: Add sodium persulfate and sodium percarbonate according to the percentage of the formula. Note that you should be particularly careful when adding sodium percarbonate to prevent it from reacting too quickly with water to produce a large number of bubbles. At the same time, ensure that all the mixtures are fully stirred.

[0102] The stirring time is 30-50 minutes, and the stirring temperature is 25-35°C.

[0103] S4: The composite ferrous sulfide passivator of the required concentration can be prepared by adding water to dilute the solution until the required concentration is reached.

[0104] The stirring time is 30-60 minutes, and the stirring temperature is 20-30°C.

[0105] The above describes an embodiment of the present embodiment, but the present embodiment is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present embodiment, ordinary technicians in this field can also make many forms, all of which are within the protection of the present embodiment.

Claims

1. A composite ferrous sulfide passivator, characterized in that: The raw materials include the following mass percentages: Sodium persulfate 4-6%, sodium percarbonate 2-4%, sodium nitrite 0.5-1%, triethanolamine 1-2%, quaternary ammonium surfactant 0.5-1%, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan 0.3-0.7%, thioacetamide 0.2-0.4%, isomeric sodium dodecylbenzene sulfonate 0.2-0.4%, sodium cocoyl sarcosine 0.4-0.6%, N,N-dihydroxyethyl oleamide 0.5-0.8%, balance water.

2. A composite ferrous sulfide passivator according to claim 1, characterized in that: The quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide.

3. A composite ferrous sulfide passivator according to claim 1, characterized in that: The invention comprises the following raw materials in percentage by mass: 4% sodium persulfate, 2% sodium percarbonate, 0.5% sodium nitrite, 1% triethanolamine, 0.5% quaternary ammonium surfactant, 0.3% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.2% thioacetamide, 0.2% sodium isododecylbenzene sulfonate, 0.4% sodium cocoyl sarcosine, 0.5% N,N-dihydroxyethyl oleamide, and the balance water.

4. A composite ferrous sulfide passivator according to claim 1, characterized in that: The invention comprises the following raw materials in percentage by mass: 6% sodium persulfate, 4% sodium percarbonate, 1% sodium nitrite, 2% triethanolamine, 1% quaternary ammonium surfactant, 0.7% polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, 0.4% thioacetamide, 0.4% sodium isododecylbenzene sulfonate, 0.6% sodium cocoyl sarcosine, 0.8% N,N-dihydroxyethyl oleamide, and the balance water.

5. A method for preparing the composite ferrous sulfide passivator according to any one of claims 1 to 4, characterized in that: The steps include: S1: In a clean container, add an appropriate amount of water, then add triethanolamine, hexadecyltrimethylammonium bromide, polydiallyldimethylammonium chloride-epichlorohydrin grafted chitosan, and thioacetamide in order according to the percentage of the formula, and stir thoroughly; S2: adding sodium isomeric dodecylbenzene sulfonate, sodium cocoyl sarcosinate, and N,N-dihydroxyethyl oleamide to the solution of step S1 in sequence, and stirring thoroughly; S3: Add sodium persulfate and sodium percarbonate according to the percentage of the formula and stir thoroughly; S4: The composite ferrous sulfide passivator of the required concentration can be prepared by adding water to dilute the solution until the required concentration is reached.

6. The method for preparing a composite ferrous sulfide passivator according to claim 5, characterized in that: In step S1: the stirring time is 30-60 min, and the stirring temperature is 25-40°C.

7. The method for preparing a composite ferrous sulfide passivator according to claim 5, characterized in that: In step S2: the stirring time is 30-50 min, and the stirring temperature is 25-35°C.

8. The method for preparing a composite ferrous sulfide passivator according to claim 5, characterized in that: In step S3: the stirring time is 30-60 min, and the stirring temperature is 20-30°C.