A bactericidal corrosion inhibitor of polyhexamethylene biguanide inorganic salt, a preparation method and application thereof in oilfield produced water

Abstract

This invention relates to the field of oilfield water treatment technology, specifically a bactericide and corrosion inhibitor based on polyhexamethylene biguanide (PHBQ), its preparation method, and its application in oilfield produced water. The PHBQ of this invention comprises a compound system of PHBQ hydrochloride and zinc sulfate-sodium molybdate. Using PHBQ as the synthesis substrate, this bactericide and corrosion inhibitor offers advantages such as high stability, biodegradability, low cost, and environmental friendliness. The compound system of sodium molybdate and zinc sulfate not only effectively inhibits corrosion but also reduces costs. Due to its limited water solubility, this agent is a slow-release, long-acting bactericide and corrosion inhibitor that can adsorb onto the surface of metal materials, slowly releasing PHBQ to inhibit bacterial biofilm formation, effectively kill microorganisms in water, and inhibit metal corrosion.

Description

Technical Field

[0001] This invention relates to the field of oilfield water treatment technology, specifically to a polyhexamethylene biguanide inorganic salt bactericide and corrosion inhibitor for oilfield water treatment systems with high microbial content and severe corrosion, its preparation method, and its application in oilfield produced water. Background Technology

[0002] Corrosion is a material failure phenomenon widely found in marine, oilfield, and freshwater environments, posing threats to daily life and almost all industrial sectors. It is estimated that the global cost of corrosion is $2.5 trillion, and in my country, the annual economic losses due to corrosion account for approximately 5% of the GDP. Microbial corrosion accounts for about 20% of these economic losses, especially in the oilfield development sector where the diversity of microorganisms is vast. This further reduces the lifespan of metal materials and equipment, significantly increasing economic, environmental, and safety risks. Currently, it is widely believed that microbial corrosion is closely related to biofilms formed by microorganisms. Microorganisms tend to grow on material surfaces, accumulating in the form of biofilms to capture nutrients from the environment, providing conditions for their growth and metabolism. This allows microorganisms to operate independently of the external environment, with minimal external interference. Simultaneously, biofilms attached to metal surfaces can alter the physicochemical properties of the metal surface, promoting electrochemical corrosion and further reducing the service life of equipment.

[0003] Microbial corrosion in oilfields is primarily caused by bacteria, including sulfate-reducing bacteria (SRB), saprophytic bacteria (TGB), and iron bacteria (FB). SRB is an anaerobic bacterium that oxidizes carbonaceous organic compounds or hydrogen, reducing sulfates to produce H2S. It has a wide pH range of survival, between 5.5 and 9.0. Sulfate-reducing bacteria commonly found in oilfields are typically *Vibrio desulfonati*, which mainly adhere to pipe walls in groups or colonies. They have a depolarizing effect on metal surfaces, accelerating corrosion of pipelines and equipment. The corrosion product, FeS, can further clog pipelines and injection wells, posing the greatest threat to oilfield surface systems. TGB, also known as slime-forming bacteria, is an aerobic heterotrophic bacterium that secretes large amounts of slime that adheres to pipelines and equipment, causing biofouling and clogging injection wells and filters. It also creates oxygen concentration cells, leading to corrosion of equipment and pipelines, and provides a suitable environment for sulfate-reducing bacteria to survive and reproduce. FB is a type of saprophytic bacteria that is widely distributed. It mainly oxidizes ferrous iron into ferric iron and uses the energy released from the oxidation of iron to meet its survival needs. It is more harmful than ordinary saprophytic bacteria, as it accelerates the corrosion of equipment and pipelines and causes blockages in water injection wells and filters.

[0004] Numerous methods exist for protecting against microbial corrosion, with chemical methods being one of the simplest and most effective. Bactericides, also known as biocides, bactericides, algaecides, and microbial agents, are chemical preparations that effectively control or kill microorganisms in water systems. Currently, the bactericides used in oil fields are generally those used in domestic and industrial circulating water systems. Based on their bactericidal mechanism, they can be divided into oxidizing and non-oxidizing bactericides. Oxidizing bactericides include chlorine, ozone, sodium hypochlorite, and chlorine dioxide, which utilize their strong oxidizing power to destroy the cell structure of microorganisms or inhibit their metabolic processes. However, due to their lower safety and tendency to cause chemical corrosion, they are rarely used in practice. Non-oxidizing bactericides can be classified into aldehydes and ketones, quaternary ammonium salts, quaternary phosphate salts, organosulfur compounds, and compound formulations. In recent years, organic guanidine and heterocyclic bactericides have been gradually developed and have shown good bactericidal effects.

[0005] Currently, most oilfields in my country have entered the secondary oil recovery stage. With the continuous increase in produced fluid water content and water drive water consumption, microbial corrosion is becoming more prevalent. To prevent damage to equipment, tubing, and formations from injected water, the requirements for produced water reinjection are becoming more stringent, and the demand for bactericides is also constantly increasing. In Jiangsu Oilfield, the water body has a high content and variety of microorganisms. Previously, quaternary ammonium salt bactericides were mainly used, leading to increased bacterial resistance. At some water treatment stations, the number of sulfate-reducing bacteria, iron bacteria, and saprophytic bacteria has reached the order of 10 to the power of 5, which has deteriorated the water quality and caused numerous corrosion problems. Currently, the corrosion rate at some stations has exceeded 0.076 mm / a. Therefore, there is an urgent need to develop a bactericide and corrosion inhibitor that can kill microorganisms in the water and inhibit corrosion to ensure the safe operation of oilfield injection and production. Summary of the Invention

[0006] This invention addresses the increasingly severe microbial corrosion in existing oilfield water treatment systems, which necessitates higher requirements for bactericides. It provides a polyhexamethylene biguanide inorganic salt bactericide and corrosion inhibitor, its preparation method, and its application in oilfield produced water. This invention enables the slow release of polyhexamethylene biguanide in the water treatment system during oilfield water sterilization, effectively killing bacteria in the water while inhibiting the formation of bacterial biofilms, significantly alleviating equipment corrosion, and extending equipment lifespan.

[0007] The present invention first provides a bactericidal and corrosion inhibitor of polyhexamethylene biguanide inorganic salt, characterized in that it comprises a compound system of polyhexamethylene biguanide hydrochloride and zinc sulfate-sodium molybdate.

[0008] Furthermore, the mass ratio of the polyhexamethylene biguanide hydrochloride compound system with zinc sulfate and sodium molybdate is 10:2-6.

[0009] The bactericide and corrosion inhibitor of this invention uses polyhexamethylene biguanide as a synthetic substrate, possessing advantages such as high stability, biodegradability, low cost, and environmental friendliness. The compound system of sodium molybdate and zinc sulfate not only effectively inhibits corrosion but also reduces costs. Due to its limited water solubility, this agent is a slow-release, long-acting bactericide and corrosion inhibitor that can adsorb onto the surface of metal materials, slowly releasing polyhexamethylene biguanide to inhibit the formation of bacterial biofilms, effectively kill microorganisms in water, and inhibit metal corrosion.

[0010] To further achieve the objectives of this invention, the present invention also provides a method for preparing the above-mentioned polyhexamethylene biguanide inorganic salt bactericide and corrosion inhibitor, characterized in that: after mixing an aqueous solution of polyhexamethylene biguanide hydrochloride with an aqueous solution of a zinc sulfate and sodium molybdate compound system, the mixture is decanted to remove water, the precipitate is washed with deionized water and vacuum dried, and finally the dried material is ground into a fine powder to obtain polyhexamethylene biguanide inorganic salt.

[0011] Furthermore, the concentration of the polyhexamethylene biguanide hydrochloride aqueous solution is 60–100 g / L.

[0012] Furthermore, the concentration of the aqueous solution of the zinc sulfate-sodium molybdate compound system is 80-240 g / L, and the mass ratio of zinc sulfate to sodium molybdate is 1:1.5-3.

[0013] Furthermore, the vacuum drying temperature is 75–85°C, and the drying time is more than 24 hours.

[0014] Furthermore, the preparation method of the polyhexamethylene biguanide hydrochloride is as follows: guanidine hydrochloride and 1,6-hexanediamine are dissolved in deionized water and mechanically stirred and mixed. At the same time, the mixture is heated to continuously evaporate the water. The temperature is raised to 100-120 ℃ and stirred at a constant temperature for 3-4 h. Then, the temperature is raised to 160-180 ℃ and reacted for 3-6 h to obtain a solid phase. Distilled water is added to the solid phase until it is completely dissolved. Then, saturated sodium chloride aqueous solution is added to the solution and the precipitate is filtered. The supernatant is removed by centrifugation. The solid phase is vacuum dried at 75-85 ℃ for more than 24 h to obtain polyhexamethylene biguanide hydrochloride.

[0015] As a preferred embodiment of the preparation method of the above-mentioned polyhexamethylene biguanide hydrochloride, the weight ratio of guanidine hydrochloride to 1,6-hexanediamine is 1:1 to 3;

[0016] In a further preferred embodiment, the weight ratio of guanidine hydrochloride to 1,6-hexanediamine is 1:1.1 to 1.5.

[0017] This invention discloses a method for preparing a bactericidal and corrosion inhibitor of polyhexamethylene biguanide inorganic salt. The method involves reacting guanidine hydrochloride with 1,6-hexanediamine to generate polyhexamethylene biguanide hydrochloride, which is then reacted with a compound system of sodium molybdate and zinc sulfate to generate polyhexamethylene biguanide inorganic salt. Using polyhexamethylene biguanide as the synthesis substrate offers advantages such as high stability, biodegradability, low cost, and environmental friendliness. The compound system of sodium molybdate and zinc sulfate not only effectively inhibits corrosion but also reduces costs. This agent has limited water solubility and is a slow-release, long-acting bactericidal and corrosion inhibitor that can adsorb onto the surface of metal materials, slowly releasing polyhexamethylene biguanide to inhibit bacterial biofilm formation, effectively kill microorganisms in water, and inhibit metal corrosion.

[0018] The third objective of this invention is to apply the aforementioned polyhexamethylene biguanide inorganic salt bactericide and corrosion inhibitor to oilfield water treatment systems. It is primarily used in surface treatment systems for produced water, reinjection tubing, or annular water systems. Through periodic and quantitative addition during production operations, it gradually dissolves into the produced fluid, protecting downhole tubing and surface pipelines. The particle size of the agent can be adjusted based on factors such as bottomhole temperature, fluid velocity, fluid corrosivity, and required concentration to control the release rate and achieve optimal protective effect and duration. Attached Figure Description

[0019] Figure 1 The images show the FT-IR spectra of the polyhexamethylene biguanide inorganic salt and polyhexamethylene biguanide hydrochloride prepared in Example 1.

[0020] Figure 2 Figures show the corrosion phenomena of N80 pads in Comparative Example 1 and Example 1. In particular, Figure (a) shows the morphology of the pad after corrosion in Comparative Example 1, (b) shows the 3D diagram of pitting corrosion in Comparative Example 1, (c) shows the morphology of the pad after corrosion in Example 1, and (d) shows the 3D diagram of pitting corrosion in Example 1.

[0021] Figure 3 This is a test diagram of the sustained-release performance of the polyhexamethylene biguanide-inorganic salt of the present invention. Detailed Implementation

[0022] The present invention will now be described in more detail through specific embodiments; however, these embodiments are not intended to limit the scope of the invention in any way. Example 1

[0023] (1) Weigh 20.0 g of guanidine hydrochloride and 22 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water until completely dissolved. Add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0024] (2) Dissolve 3.0 g of zinc sulfate and 9.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0025] (3) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt.

[0026] like Figure 1 The image shown is the FT-IR plot of this embodiment. Figure 1 It can be seen that the polyhexamethylene biguanide hydrochloride synthesized in step (1) has a temperature range of 3000-3500 cm⁻¹. -1 A broad peak appears at 2930 and 2860 cm⁻¹, mainly due to the stretching vibrations of -NH, -CH₂, and -OH. -1 The absorption peaks at 1540-1660 cm⁻¹ are asymmetric and symmetric absorption peaks due to the -CH₂ stretching vibration. -1 The presence of a strong stretching vibration peak at C=N indicates the successful synthesis of polyhexamethylene biguanide hydrochloride. Step (2) shows a comparison of the infrared spectrum of polyhexamethylene biguanide hydrochloride synthesized in step (1) with that of the inorganic salt. The main difference lies in the fingerprint region, specifically at 1090 cm⁻¹. -1 A stretching vibration peak of the S=O bond appeared at 830 cm⁻¹. -1 MoO4 appears at [location] 2- The corresponding vibration peaks indicate that the polyhexamethylene biguanide-inorganic salt composite system was successfully prepared. Example 2

[0027] (1) Weigh 20.0 g of guanidine hydrochloride and 30 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 100 °C, maintain the temperature and stir for 4 h. Then react at 180 °C for 3 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0028] (2) Dissolve 3.0 g of zinc sulfate and 6.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0029] (3) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Example 3

[0030] (1) Weigh 20.0 g of guanidine hydrochloride and 28 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature is raised to 110 °C, maintain the temperature and stir for 4 h. Then react at 170 °C for 4 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 75 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0031] (2) Dissolve 3.0 g of zinc sulfate and 7.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0032] (3) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 85 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Example 4

[0033] (1) Weigh 20.0 g of guanidine hydrochloride and 40 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature is raised to 110 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 6 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 85 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0034] (2) Take 2.0 g of zinc sulfate and 5.0 g of sodium molybdate and dissolve them in 50 mL of deionized water. Mix them evenly while stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0035] (3) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 85 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Example 5

[0036] (1) Weigh 20.0 g of guanidine hydrochloride and 60 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter to remove the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0037] (2) Dissolve 2.0 g of zinc sulfate and 2.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0038] (3) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Example 6

[0039] (1) Weigh 20.0 g of guanidine hydrochloride and 20 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter to remove the precipitate, centrifuge to remove the supernatant, and vacuum dry at 75 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0040] (2) Dissolve 3.0 g of zinc sulfate and 9.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0041] (3) Dissolve 12 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 85℃ for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt.

[0042] Comparative Example 1

[0043] This comparative example is used to compare the bactericidal effect with that of conventional non-oxidizing bactericides.

[0044] Dissolve 1 g of dodecyl dimethyl benzyl ammonium chloride in 100 mL of deionized water to prepare a 10000 mg / L dodecyl dimethyl benzyl ammonium chloride solution. Add a certain amount of this solution to the experimental water sample to test its bactericidal performance. The experimental water sample was a fine filtration outlet water sample from a site in Jiangsu Oilfield, containing 11000 SRB / mL, 600 TGB / mL, and 600 FB / mL. Comparative Example 2

[0045] This comparative example is used to compare the corrosion inhibition effect with that of conventional inorganic corrosion inhibitors.

[0046] Dissolve 1 g of sodium molybdate in 100 mL of deionized water to prepare a 10000 mg / L sodium molybdate solution. Add a certain amount of this solution to the experimental water sample to test its corrosion inhibition performance. The experimental water sample was the outlet water sample from a three-phase separator at a site in Jiangsu Oilfield, with a total salinity of 19213 mg / L. Comparative Example 3

[0047] This comparative example is used to compare the corrosion inhibition effect with that of polyhexamethylene biguanide hydrochloride-zinc chloride.

[0048] (1) Weigh 20.0 g of guanidine hydrochloride and 24 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0049] (2) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 12 g of zinc chloride under mechanical stirring, decant the upper layer of water to remove the reaction solution, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, and grind it into fine powder using an agate mortar to obtain polyhexamethylene biguanide-zinc chloride. Comparative Example 4

[0050] This comparative example is used to compare the corrosion inhibition effect with that of polyhexamethylene biguanide hydrochloride-zinc sulfate.

[0051] (1) Weigh 20.0 g of guanidine hydrochloride and 24 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0052] (2) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 12 g of zinc sulfate under mechanical stirring, decant the upper layer of water to remove the resulting reaction solution, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, and grind it into fine powder using an agate mortar to obtain polyhexamethylene biguanide-zinc sulfate. Comparative Example 5

[0053] This comparative example is used to compare the corrosion inhibition effect with that of polyhexamethylene biguanide hydrochloride-sodium molybdate.

[0054] (1) Weigh 20.0 g of guanidine hydrochloride and 24 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0055] (2) Dissolve 20 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 12 g of sodium molybdate under mechanical stirring, decant the upper layer of water from the resulting reaction solution, wash it three times with deionized water, vacuum dry it at 80 °C for 24 h, and grind it into fine powder using an agate mortar to obtain polyhexamethylene biguanide sodium molybdate. Comparative Example 6

[0056] (1) Weigh 20.0 g of guanidine hydrochloride and 10 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0057] (2) Dissolve 1.0 g of zinc sulfate and 9.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0058] (3) Dissolve 12 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Comparative Example 7

[0059] (1) Weigh 20.0 g of guanidine hydrochloride and 24 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0060] (2) Dissolve 3.0 g of zinc sulfate and 12.0 g of sodium molybdate in 50 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0061] (3) Dissolve 12 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 100 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt. Comparative Example 8

[0062] (1) Weigh 20.0 g of guanidine hydrochloride and 75 g of 1,6-hexanediamine respectively, dissolve them in deionized water and add them to a three-necked flask equipped with a mechanical stirrer. Slowly raise the temperature to allow the water to evaporate continuously. When the temperature reaches 120 °C, maintain the temperature and stir for 4 h. Then react at 160 °C for 5 h. Add an appropriate amount of distilled water to dissolve the precipitate, add saturated sodium chloride aqueous solution, filter the precipitate, centrifuge to remove the supernatant, and vacuum dry at 80 °C for 24 h to obtain polyhexamethylene biguanide hydrochloride solid.

[0063] (2) Dissolve 0.3 g of zinc sulfate and 0.9 g of sodium molybdate in 5 mL of deionized water and mix them evenly with stirring to obtain a zinc sulfate-sodium molybdate composite system.

[0064] (3) Dissolve 12 g of polyhexamethylene biguanide hydrochloride obtained in step (1) in 200 mL of deionized water, add 10 mL of zinc sulfate-sodium molybdate composite system obtained in step (2) under mechanical stirring, decant the resulting reaction solution to remove the upper layer of water, wash it 3 times with deionized water, vacuum dry it at 80 °C for 24 h, grind it into fine powder using an agate mortar, and obtain polyhexamethylene biguanide-inorganic salt.

[0065] 1. Evaluation of bactericidal performance

[0066] Table 1 shows the bactericidal performance test results of Comparative Example 1 and Examples 1-6. The water sample used was the water sample described in Comparative Example 1, which contained 11,000 SRB / mL, 600 TGB / mL, and 600 FB / mL. The bactericidal performance of the bactericides in each comparative example and example was tested using the method specified in "Q / SHCG 132—2017 Technical Requirements for Bactericides for Oilfield Produced Water Treatment". The number of bacteria in the raw water was determined by secondary bacterial count using the dilution method, and the three-tube parallel method was used to determine whether the added bactericide could completely kill the bacteria ("+" indicates the presence of bacteria, "-" indicates the absence of bacteria). As can be seen from Table 1, at 50 ppm, polyhexamethylene biguanide-inorganic salt has a certain inhibitory effect on TGB and FB. At 80 ppm, polyhexamethylene biguanide-inorganic salt can completely kill SRB, TGB, and FB. At 50 ppm, the bactericidal effect of Examples 1-6 is significantly better than that of the comparative examples.

[0067] Table 1 Evaluation of bactericidal performance

[0068]

[0069] 2. Evaluation of corrosion inhibition performance

[0070] Table 2 shows the corrosion inhibition performance test results of Comparative Examples 2-5 and Examples 1, 3, and 4. The water sample used was the same as that described in Comparative Example 2, with a salinity of 19213 mg / L, a calcium chloride type, and containing sodium ions (5867 mg / L), calcium ions (1252 mg / L), magnesium ions (99 mg / L), barium ions (67 mg / L), chloride ions (10989 mg / L), sulfate ions (314 mg / L), and bicarbonate ions (625 mg / L). Weight loss analysis was performed on the steel sheets before and after corrosion according to the method in GB / T 35509-2017 "Application and Evaluation of Corrosion Inhibitors in Oil and Gas Fields," and the corrosion rate was calculated. The results are shown in Table 2. Table 2 shows that the polyhexamethylene biguanide-inorganic salt provided by this invention has good corrosion inhibition performance, maintaining a corrosion inhibition rate of over 80% at conventional water treatment system temperatures. Compared to Comparative Example 5, the addition of zinc sulfate, synergistically inhibiting corrosion with sodium molybdate, reduces both the corrosion rate and cost. The corrosion rate is as low as 0.011 mm / a, and the corrosion inhibition rate reaches 88.54%, which can meet the equipment corrosion protection requirements.

[0071] Table 2

[0072] serial number Temperature, °C Concentration, ppm Corrosion rate, mm / a Corrosion inhibition rate, % blank 35 0 0.096 0 Comparative Example 2 35 40 0.077 19.79 Comparative Example 3 35 40 0.032 66.67 Comparative Example 4 35 40 0.029 69.80 Comparative Example 5 35 40 0.027 71.88 Comparative Example 6 55 40 0.043 72.08 Comparative Example 7 55 40 0.039 74.68 Example 1 35 40 0.011 88.54 blank 45 0 0.121 0 Example 3 45 40 0.018 85.12 blank 55 0 0.154 0 Example 4 55 40 0.029 81.17 Example 5 55 40 0.038 75.32 Example 6 55 40 0.036 76.62

[0073] like Figure 2 The image shows the corrosion phenomenon of N80 coating plates in Comparative Example 1 and Example 1. The water sample used was the water sample described in Comparative Example 2, and the water sample temperature was 35 °C. Figure 2 It can be seen that the surface of the hanging plate in Example 1 is smoother, with almost no pitting corrosion and a maximum depth of 0.97 mm. This shows that the polyhexamethylene biguanide inorganic salt provided by the present invention has good corrosion inhibition properties and can be adsorbed on the surface of the hanging plate to effectively prevent equipment corrosion.

[0074] 10 mg of polyhexamethylene biguanide inorganic salt was placed in 50 mL of deionized water. The concentration of polyhexamethylene biguanide inorganic salt in the deionized water at different times was measured using a UV-Vis spectrophotometer at a wavelength of 230 nm. The test results are as follows. Figure 3 As shown, polyhexamethylene biguanide inorganic salts are released rapidly in the initial stage, and then slowly over time. After 48 hours, the concentration in the water reaches 84.9 mg / L, and the release rate reaches 42.7%.

Claims

1. A bactericidal and corrosion inhibitor of polyhexamethylene biguanide inorganic salt, characterized in that, The invention comprises a compound system of polyhexamethylene biguanide hydrochloride and zinc sulfate-sodium molybdate; the mass ratio of polyhexamethylene biguanide hydrochloride to the zinc sulfate and sodium molybdate compound system is 10:2-6; the preparation method of polyhexamethylene biguanide hydrochloride is as follows: guanidine hydrochloride and 1,6-hexanediamine are dissolved in deionized water and mechanically stirred and mixed, while the mixture is heated to continuously evaporate the water. The mixture is heated to 100-120℃ and stirred at a constant temperature for 3-4 h, then heated to 160-180℃ and reacted for 3-6 h to obtain a solid phase. Distilled water is added to the solid phase until it is completely dissolved. Then, saturated sodium chloride aqueous solution is added to the solution, the precipitate is filtered, the supernatant is removed by centrifugation, and the solid phase is vacuum dried at 75-85℃ for more than 24 h to obtain polyhexamethylene biguanide hydrochloride.

2. The bactericidal and corrosion-inhibiting agent of polyhexamethylene biguanide inorganic salt according to claim 1, characterized in that, The weight ratio of guanidine hydrochloride to 1,6-hexanediamine is 1:1 to 3.

3. The bactericidal and corrosion-inhibiting agent of polyhexamethylene biguanide inorganic salt according to claim 2, characterized in that, The weight ratio of guanidine hydrochloride to 1,6-hexanediamine is 1:1.1 to 1.

5.

4. A method for preparing a bactericidal and corrosion-inhibiting agent of polyhexamethylene biguanide inorganic salt as described in claim 1, 2, or 3, characterized in that, After mixing the aqueous solution of polyhexamethylene biguanide hydrochloride with the aqueous solution of zinc sulfate and sodium molybdate, the mixture was decanted to remove water, the precipitate was washed with deionized water and vacuum dried, and finally the dried material was ground into fine powder to obtain polyhexamethylene biguanide-inorganic salt.

5. The preparation method according to claim 4, characterized in that, The concentration of the polyhexamethylene biguanide hydrochloride aqueous solution is 60–100 g / L.

6. The preparation method according to claim 4, characterized in that, The concentration of the aqueous solution of the zinc sulfate-sodium molybdate compound system is 80-240 g / L, and the mass ratio of zinc sulfate to sodium molybdate is 1:1.5-3.

7. The preparation method according to claim 4, characterized in that, Vacuum drying is performed at a temperature of 75–85°C for at least 24 hours.

8. The application of the polyhexamethylene biguanide inorganic salt bactericide and corrosion inhibitor as described in claim 1, 2 or 3 in an oilfield water treatment system.

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