Sulfate reducing bacteria soluble extracellular polymeric substance (S-EPS) with corrosion inhibition function and extraction method thereof

Abstract

The invention provides a sulfate reducing bacteria soluble extracellular polymeric substance (S-EPS) with a corrosion inhibition function and an extraction method thereof, and belongs to the technical field of metal corrosion protection. The S-EPS is extracted from natural microorganism sulfate reducing bacteria, is separated and extracted by adopting a simple centrifugal method, and is purified by adopting a dialysis method, so that the soluble extracellular polymeric substance with a corrosion inhibition function is obtained. The extraction process is simple, no toxic chemical reagent is added, and the method is environment-friendly. The S-EPS serving as a corrosion inhibitor can have a good corrosion inhibition effect on EH40 steel in both aerobic and anaerobic environments, the corrosion inhibition rates are 88.5% and 80.9% respectively, the protection effect is stable, and the corrosion inhibition performance is excellent.

Description

Technical Field

[0001] The present invention belongs to the field of corrosion protection, and in particular relates to a sulfate-reducing bacteria soluble extracellular polymer (S-EPS) with corrosion inhibition function and an extraction method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Corrosion is a major hazard in modern industry. Corrosion inhibitors are widely used because they effectively suppress corrosion. Traditional corrosion inhibitors, such as chromates and nitrites, pose significant environmental risks, high costs, and harmful effects on the human body, making them difficult to meet the demands of green and safe development. In recent years, green corrosion inhibitors, such as natural organic matter and microbial products, have gained increasing attention. Extracellular polymeric substances (EPS) secreted by microorganisms, among others, show promising application prospects due to their renewable and eco-friendly nature.

[0004] Previous studies have shown that extracellular polymeric substances (EPS) secreted by Desulfuricans have a moderate corrosion-inhibiting effect on carbon steel, demonstrating the potential of microbial-derived natural corrosion inhibitors. However, these studies have limited exploration of culture conditions and EPS extraction methods, resulting in an incomplete understanding of the composition and mechanism of action of EPS. Consequently, the resulting EPS samples still contain corrosive components, resulting in unstable and limited corrosion inhibition performance. Therefore, further optimization of EPS extraction conditions is needed to enhance its application feasibility and slow-release performance. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a sulfate-reducing bacteria soluble extracellular polymer (S-EPS) with corrosion inhibition function and an extraction method thereof. The S-EPS provided by the present invention is a natural, green and efficient corrosion inhibitor. The extraction method is simple to operate and has excellent corrosion inhibition effect. It is extracted and separated from natural microorganisms, and its components are non-toxic, safe and environmentally friendly.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function, comprising: inoculating sulfate-reducing bacteria into a culture medium, culturing, and collecting bacterial liquid; The bacterial solution is centrifuged, the supernatant is taken, and filtered to sterilize to obtain a crude S-EPS extract; The crude S-EPS extract is dialyzed and freeze-dried to obtain the product.

[0007] The present invention has found through systematic research and experimental exploration of various corrosive microorganisms that: from typical corrosive microorganisms - sulfate-reducing bacteria Desulfovibrio ferrophilus The soluble extracellular polymers (S-EPS) extracted from IS5 have a better inhibitory effect on salt corrosion of EH40 steel under aerobic or anaerobic conditions.

[0008] The second aspect of the present invention provides the sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function extracted by the above method.

[0009] The third aspect of the present invention provides a natural green corrosion inhibitor, comprising: the above-mentioned sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function.

[0010] A fourth aspect of the present invention provides a method for using a natural green corrosion inhibitor, comprising: Under aerobic or anaerobic conditions, the steel is placed in a solution containing soluble extracellular polymers S-EPS of sulfate-reducing bacteria with corrosion inhibition function and NaCl to obtain the product; Among them, the concentration of S-EPS is 0.1-0.3 g·l -1 .

[0011] The fifth aspect of the present invention provides the use of the above-mentioned sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function or the above-mentioned natural green corrosion inhibitor in inhibiting steel corrosion in an aerobic or anaerobic environment.

[0012] Beneficial effects of the present invention (1) The present invention discovered for the first time that the soluble extracellular polymer S-EPS of sulfate-reducing bacteria has a good inhibitory effect on salt corrosion of EH40 steel under aerobic or anaerobic conditions. The corrosion inhibition film formed is dense and has excellent corrosion inhibition performance, and can be used as a natural green corrosion inhibitor.

[0013] (2) The present invention successfully extracted a natural and highly effective corrosion inhibitor from the metabolites of marine corrosive microorganisms. The extraction operation is simple and does not require any additional toxic or harmful chemical reagents, making it environmentally friendly. Under aerobic or anaerobic conditions, the product exhibits a stable corrosion inhibition effect on EH40 steel, forming a dense corrosion inhibition film with excellent corrosion inhibition performance.

[0014] (3) The extraction method of the present invention is simple, practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0016] Figure 1 Extraction of sulfate-reducing bacteria in Example 1 of the present invention D. ferrophilus Macro picture of S-EPS powder.

[0017] Figure 2 Electrochemical impedance spectroscopy (EIS) diagrams of EH40 steel immersed in 3.5% NaCl solutions containing no S-EPS and 0.1 g·l-1 S-EPS for 14 days under aerobic conditions in Example 2 of the present invention, a: Nyquist plot; b: Bode plot.

[0018] Figure 3 Electrochemical impedance spectroscopy (EIS) diagrams of EH40 steel immersed in 3.5% NaCl solutions containing no S-EPS and 0.1 g·l-1 S-EPS for 14 days under anaerobic conditions in Example 3 of the present invention, a: Nyquist plot; b: Bode plot.

[0019] Figure 4 The EH40 steel in Examples 2 and 3 of the present invention was immersed in "no S-EPS and 0.1 g·l -1 Potentiodynamic polarization curves of S-EPS in 3.5% NaCl solution for 14 days, a: Nyquist plot; b: Bode plot. DETAILED DESCRIPTION

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0021] A method for extracting sulfate-reducing bacteria soluble extracellular polymers (S-EPS) with corrosion inhibition function, comprising: inoculating sulfate-reducing bacteria into a culture medium, culturing, and collecting bacterial liquid; The bacterial solution is centrifuged, the supernatant is taken, and filtered to sterilize to obtain a crude S-EPS extract; The crude S-EPS extract is dialyzed and freeze-dried to obtain the product.

[0022] Too high or too low a strain inoculation rate will affect the fermentation effect. Therefore, the present invention is to Desulfovibrio ferrophilus The inoculation rate of IS5 was studied, and preferably, the inoculation rate was 1%-1.5% to obtain a better fermentation effect.

[0023] Different culture medium compositions can affect the morphology, growth rate, production of metabolites and other aspects of microorganisms. Therefore, the present invention studies the composition and ratio of the culture medium. Preferably, the culture medium is composed of the following raw materials: 0.5-0.8 g of dipotassium hydrogen phosphate, 1-1.2 g of ammonium chloride, 1-3 g of calcium sulfate, 2-2.4 g of magnesium sulfate, 5-8 g of sodium citrate, 4-6 ml of sodium lactate, 1-1.2 g of yeast powder, and 1000-1100 ml of water to better promote sulfate-reducing bacteria. Desulfovibrio ferrophilus IS5 growth.

[0024] The culture medium temperature not only affects the growth rate and reproduction efficiency of the strain, but also affects the metabolic activity, enzyme activity and other characteristics of the strain. Therefore, the present invention studies the culture conditions. Preferably, the culture condition is static culture in a constant temperature incubator at 37°C in the dark for 11 days.

[0025] Centrifugation is a key step in separating bacterial liquid from bacterial cells. Therefore, the present invention studies the speed and time of centrifugation. Preferably, the centrifugation condition is 5000-6000 g for 10-15 min to better separate the crude S-EPS extract.

[0026] Dialysis can effectively improve the purity of S-EPS. To this end, the present invention studies the specifications of the dialysis bag and the purification time. Preferably, the dialysis condition is to purify in a 10,000 Da dialysis bag for 72-84 h to obtain high-purity S-EPS.

[0027] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0028] In the following examples, sulfate-reducing bacteria Desulfovibrio ferrophilus IS5 (DSM 15579, purchased from DSMZ (German Collection of Microorganisms and Cell Cultures GmbH)).

[0029] Example 1 The extraction of soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function comprises the following steps: (1) Add 10 ml D. ferrophilus The bacterial solution was inoculated into 1000 ml of culture medium (containing 0.5 g K2HPO4, 1 g NH4Cl, 1 g CaSO4, 2 g MgSO4, 5 g sodium citrate, 4 ml sodium lactate and 1 g yeast powder, 1000 ml deionized water); (2) Culture in a constant temperature incubator at 37°C in the dark D. ferrophilus 11 days to the peak bacterial count; (3) Centrifuge at 5000 g for 15 min, filter the supernatant through 0.22 μm to obtain the crude S-EPS extract; (4) The crude S-EPS extract from step (3) was purified using a 10,000 Da dialysis bag for 72 h (changing water every 12 h), and then freeze-dried to obtain purified S-EPS powder.

[0030] The sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function prepared in Example 1 was used as a natural green corrosion inhibitor.

[0031] Example 2 The extraction of soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function comprises the following steps: (1) Add 12 ml D. ferrophilus The bacterial solution was inoculated into 1000 ml of culture medium (containing 0.5 g K2HPO4, 1 g NH4Cl, 1 g CaSO4, 2 g MgSO4, 5 g sodium citrate, 4 ml sodium lactate and 1 g yeast powder, 1000 ml deionized water); (2) Culture in a constant temperature incubator at 37°C in the dark D. ferrophilus 11 days to the peak bacterial count; (3) Centrifuge at 5000 g for 15 min, filter the supernatant through 0.22 μm to obtain the crude S-EPS extract; (4) The crude S-EPS extract from step (3) was purified using a 10,000 Da dialysis bag for 72 h (changing water every 12 h), and then freeze-dried to obtain purified S-EPS powder.

[0032] The sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function prepared in Example 1 was used as a natural green corrosion inhibitor.

[0033] Example 3 The extraction of soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function comprises the following steps: (1) Add 15 ml D. ferrophilus The bacterial solution was inoculated into 1000 ml of culture medium (containing 0.5 g K2HPO4, 1 g NH4Cl, 1 g CaSO4, 2 g MgSO4, 5 g sodium citrate, 4 ml sodium lactate and 1 g yeast powder, 1000 ml deionized water); (2) Culture in a constant temperature incubator at 37°C in the dark D. ferrophilus11 days to the peak bacterial count; (3) Centrifuge at 5000 g for 15 min, filter the supernatant through 0.22 μm to obtain the crude S-EPS extract; (4) The crude S-EPS extract from step (3) was purified using a 10,000 Da dialysis bag for 72 h (changing water every 12 h), and then freeze-dried to obtain purified S-EPS powder.

[0034] The sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function prepared in Example 1 was used as a natural green corrosion inhibitor.

[0035] Example 4 Study Example 1: Effect of S-EPS on the electrochemical corrosion behavior and corrosion inhibition effect of EH40 steel under aerobic conditions (14-day test): (1) Experimental setup: 300 ml wide-mouth bottle, three-electrode system (working electrode: EH40 (Φ 5 mm), working surface (0.196 cm2), auxiliary electrode: graphite electrode, φ15 mm, reference electrode: Ag / AgCl (3 M KCl). Electrode treatment: The working electrode, except the working surface, was sprayed with waterproof coating and sealed with epoxy resin.

[0036] (2) The electrolyte was a 3.5% NaCl solution containing either S-EPS or 0.1 g·l-1 S-EPS.

[0037] (3) Tested using PARSTAT P1000A electrochemical workstation: EIS: After the open circuit potential (OCP) is stabilized, the sinusoidal signal is 5-15 mV and the scanning frequency range is 10-2~105 Hz.

[0038] Potentiodynamic polarization: Scan range: -250~+250 mV vs. OCP, scan rate 0.1667 mV / s The experimental device was placed in a 30℃ constant temperature box. Figure 2 As shown in the figure, after adding S-EPS, the Nyquist arc radius increased significantly (vs blank group), indicating that S-EPS can effectively inhibit the corrosion of EH40 steel under aerobic conditions, the corrosion inhibition film has good adhesion effect, and the corrosion inhibition effect is excellent. The 14-day corrosion inhibition rate is calculated by formula (1): IE (%): IE =( R’ ct‒ R ct) / R’ ct(1) Where: R’ ct and R ct represents the charge transfer resistance with and without S-EPS, respectively.

[0039] The experimental results show that: under aerobic conditions on the 14th day, the corrosion inhibition rate of S-EPS on EH40 steel reached 88.5%, and it can still maintain a high slow-release performance, with excellent corrosion inhibition effect. The polarization curve shows that S-EPS makes the corrosion current density i The corr decreased from 13.5 μA·cm-2 to 1.69 μA·cm-2 (Table 1), which was consistent with the results of impedance corrosion inhibition, confirming that S-EPS had excellent corrosion inhibition effect under aerobic conditions.

[0040] Example 5 The influence of S-EPS in Example 1 on the corrosion electrochemical behavior and corrosion inhibition effect of EH40 steel under anaerobic conditions was studied.

[0041] Anaerobic conditions: After sterilizing the 3.5% NaCl solution, high-purity nitrogen (at a flow rate of 200 ml min-1) was used to deoxygenate the solution for 45 minutes to obtain an anaerobic experimental medium. Other conditions were the same as those in Example 4.

[0042] The experiment was carried out at a constant temperature of 30℃. Figure 3 As shown in the results, the capacitance arc radius in the Nyquist plot increased significantly after the addition of S-EPS, indicating that it can effectively inhibit the corrosion of EH40 steel under anaerobic conditions. S-EPS has excellent corrosion inhibition effect. The corrosion inhibition rate calculated by formula (1) reached 80.9% after 14 days, maintaining a high corrosion inhibition performance and showing excellent corrosion inhibition effect. The polarization curve (Table 1) shows that after the addition of S-EPS, the corrosion current density decreased from 0.5 μA·cm-2 to 0.2 μA·cm-2, which is consistent with the results of impedance corrosion inhibition, further confirming the excellent corrosion inhibition performance of S-EPS under anaerobic conditions.

[0043] Table 1. Potentiodynamic polarization curve fitting results of EH40 steel immersed in 3.5% NaCl solution without S-EPS and with 0.1 g·l-1 S-EPS under aerobic and anaerobic conditions for 14 days

[0044] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function, characterized in that: include: inoculating sulfate-reducing bacteria into a culture medium, culturing, and collecting bacterial liquid; The bacterial solution is centrifuged, the supernatant is taken, and filtered to sterilize to obtain a crude S-EPS extract; The crude S-EPS extract is dialyzed and freeze-dried to obtain the product.

2. The method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function according to claim 1, characterized in that: The vaccination rate is 1%-1.5%.

3. The method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function according to claim 1, characterized in that: The culture medium is composed of the following raw materials: 0.5-0.8 g of dipotassium hydrogen phosphate, 1-1.2 g of ammonium chloride, 1-3 g of calcium sulfate, 2-2.4 g of magnesium sulfate, 5-8 g of sodium citrate, 4-6 ml of sodium lactate, 1-1.2 g of yeast powder, and 1000-1100 ml of water.

4. The method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function according to claim 1, characterized in that: The culture conditions are static culture in a constant temperature incubator at 37° C. in the dark for 11 days.

5. The method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function according to claim 1, characterized in that: The centrifugal condition is 5000-6000 g for 10-15 min.

6. The method for extracting soluble extracellular polymers (S-EPS) of sulfate-reducing bacteria with corrosion inhibition function according to claim 1, characterized in that: The dialysis conditions are purification in a 10,000 Da dialysis bag for 72-84 hours.

7. Sulfate-reducing bacteria soluble extracellular polymer (S-EPS) with corrosion inhibition function extracted according to the method of any one of claims 1 to 6.

8. A natural green corrosion inhibitor, characterized in that: include: The sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function as described in claim 7.

9. A method for using a natural green corrosion inhibitor, characterized in that: include: Under aerobic or anaerobic conditions, the steel is placed in a solution containing soluble extracellular polymers S-EPS of sulfate-reducing bacteria with corrosion inhibition function and NaCl to obtain the product; Among them, the concentration of S-EPS is 0.1-0.3g·l -1 .

10. Use of the sulfate-reducing bacteria soluble extracellular polymer S-EPS with corrosion inhibition function according to claim 7 or the natural green corrosion inhibitor according to claim 8 in inhibiting steel corrosion under aerobic or anaerobic conditions.

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