Amphoteric polycondensation humic acid corrosion inhibitor and preparation method thereof

Abstract

The application discloses a kind of zwitterionic polycondensation fulvic acid corrosion inhibitor and preparation method thereof, the corrosion inhibitor is with fulvic acid as basic condensation unit, by the polycondensation reaction of phenolic hydroxyl group on its skeleton and double (2-chloroethyl) amine hydrochloride, contains one fulvic acid skeleton and one double (2-ethyl) amine hydrochloride group in each structural unit.The carboxyl group in fulvic acid skeleton shows negative electricity, and double (2-ethyl) amine hydrochloride group shows positive electricity.The preparation method has the characteristics of mild reaction condition, low energy consumption level, can change the structure of fulvic acid skeleton, improve the molecular weight of product, and give product cationic functional group.According to the zwitterionic polycondensation fulvic acid obtained by the preparation method has the function of inhibiting metal corrosion.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical additives technology, specifically relating to an amphoteric polycondensation humic acid corrosion inhibitor and its preparation method. Background Technology

[0002] Metal corrosion not only shortens equipment lifespan and causes severe economic losses, but also leads to a decline in material performance due to microscopic corrosion phenomena that cannot be monitored in real time, posing a threat to production safety. Adding corrosion inhibitors to corrosive media is an efficient, simple, and economical measure to suppress metal corrosion and extend its service life. Based on existing corrosion inhibitor development strategies, their structures typically contain heteroatoms (such as N, S, O, P, etc.) and unsaturated bonds (such as double bonds, triple bonds, aromatic rings, etc.). These special groups provide active sites for the adsorption of corrosion inhibitors on metal surfaces, which is crucial for ensuring corrosion inhibition performance. Furthermore, polymeric corrosion inhibitors have the advantages of more adsorption sites and stronger adsorption forces compared to traditional small-molecule corrosion inhibitors, representing a new trend in corrosion inhibitor development in recent years.

[0003] Fulvic acid is a class of naturally occurring compounds with abundant reserves, primarily derived from weathered coal and sludge. Weathered coal, in particular, has very high reserves in my country, but its low calorific value and high moisture content have prevented its effective utilization. The long-term dumping of weathered coal not only results in severe resource waste, but also leads to organic carbon pollution of water bodies due to the seepage of humic plants from its interior into groundwater.

[0004] Currently, fulvic acid is mainly used in agricultural fertilizers, where it has beneficial effects such as water retention, promoting plant growth, and improving soil. However, the consumption of fulvic acid in agriculture is extremely limited, and there is an urgent need to find new ways to utilize it. In the industrial sector, fulvic acid is currently modified through reactions such as sulfonation and nitration, and the modified products are then utilized. However, these modification strategies only change some active groups in the fulvic acid structure and do not fundamentally change the product's skeletal structure, thus failing to significantly improve product performance or endow the product with new functions. Therefore, the application scope of the product remains very limited.

[0005] In summary, the shortcomings of the modified fulvic acid process compared with this application are: the product skeleton structure was not changed, the molecular weight of the product was not significantly increased, resulting in a very limited range of applications for the product. Summary of the Invention

[0006] To overcome the problems existing in the prior art, the present invention aims to provide a zwitterionic condensation polycondensed fulvic acid corrosion inhibitor and its preparation method. This preparation method features mild reaction conditions, low energy consumption, the ability to modify the fulvic acid skeleton structure, increase the molecular weight of the product, and impart cationic functional groups to the product. The zwitterionic condensed fulvic acid obtained according to this preparation method has the function of inhibiting metal corrosion.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A zwitterionic condensation polycondensation fulvic acid corrosion inhibitor is disclosed. This inhibitor is obtained by the condensation reaction of fulvic acid as a base polycondensation unit with bis(2-chloroethyl)amine hydrochloride via a phenolic hydroxyl group on its backbone. Each structural unit contains a fulvic acid backbone and a bis(2-ethyl)amine hydrochloride group. The carboxyl group in the fulvic acid backbone exhibits negative charge, while the bis(2-ethyl)amine hydrochloride group exhibits positive charge.

[0009] A method for preparing an amphoteric condensation humic acid corrosion inhibitor, comprising the following specific steps:

[0010] Step 1: Dissolve fulvic acid and bis(2-chloroethyl)amine hydrochloride in water respectively;

[0011] Step 2: Add alkali to the solution from Step 1 to adjust the pH to 8-10;

[0012] Step 3: Stir the reaction system with pH 8-10 at 25-35℃, monitor the pH change of the system during the reaction, and use alkali to maintain the pH at 8-10 to obtain the crude product;

[0013] Step 4: After the reaction is complete, dialyze the crude product obtained in step 3 in water;

[0014] Step 5: After drying the dialysate, the product obtained is the zwitterionic polycondensation humic acid corrosion inhibitor.

[0015] In step 1, the mass ratio of fulvic acid to bis(2-chloroethyl)amine hydrochloride is 1:0.2 to 1:0.01. Because fulvic acid has multiple phenolic hydroxyl groups, excessive bis(2-chloroethyl)amine hydrochloride will cause a significant cross-linking reaction, resulting in an insoluble product that cannot be used.

[0016] In step 2, the alkali is any one or a combination of two of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0017] The purpose of maintaining the pH at 8-10 in step 3 is as follows: the base acts as a catalyst in this reaction. As the reaction proceeds, hydrochloric acid is produced, which consumes the base. The reaction will stop if it cannot be catalyzed. Therefore, it is necessary to ensure that the system is in an alkaline environment.

[0018] The molecular weight cutoff of the dialysis technique in step 4 is 100–1000 g / mol. It is used to remove and recover reactants that did not participate in the reaction.

[0019] The zwitterionic polycondensation humic acid corrosion inhibitor is used to inhibit metal corrosion.

[0020] The beneficial effects of this invention are:

[0021] ① A corrosion inhibitor was prepared using fulvic acid, a natural product. The chain extension and polycondensation were achieved by the substitution reaction between the phenolic hydroxyl group in its structure and the halogen in the structure of the dihalogenated compound, thereby increasing its molecular weight. At the same time, cationic groups were introduced to promote adsorption, which significantly improved its corrosion inhibition effect compared with the use of fulvic acid alone.

[0022] ② The synthesis technology provided by this invention operates under mild conditions, requiring no high-temperature or high-pressure operation. The reaction medium is water, making it green and environmentally friendly, and in line with the development concept of green chemistry. The raw material, fulvic acid, is derived from low-value-added weathered coal, and this invention technology enables the high-value utilization of low-value resources. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the synthesis reaction of zwitterionic condensation humic acid corrosion inhibitor.

[0024] Figure 2 The results are SEM-EDS analysis of fulvic acid and zwitterionic condensed fulvic acid.

[0025] Figure 3 The Nyquist impedance diagrams are for Q235 carbon steel in 1M HCl solutions containing different concentrations of corrosion inhibitors.

[0026] Figure 4 The Tafel polarization curves of Q235 carbon steel in 1M HCl solutions containing different concentrations of corrosion inhibitors are shown. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings.

[0028] Example 1

[0029] This embodiment provides a zwitterionic polycondensation humic acid corrosion inhibitor, which is prepared by the following method:

[0030] (1) Dissolve 100g of humic acid and 10g of bis(2-chloroethyl)amine hydrochloride in water respectively.

[0031] (2) Add NaOH to adjust the pH of the system to 8-10.

[0032] (3) The reaction system was stirred at 25-35°C for 8 hours. The pH of the system was monitored during the reaction, and NaOH was used to maintain the pH at 8-10.

[0033] (4) After the reaction is complete, dialyze the solution using a dialysis bag with a molecular weight cutoff of 100. The corrosion inhibitor is obtained by drying the dialysate.

[0034] raw material:

[0035] Fulvic acid is extracted from weathered coal;

[0036] Potassium hydroxide and sodium hydroxide were both purchased from Tianjin Kemeo Chemical Reagent Co., Ltd.

[0037] Potassium carbonate, sodium carbonate, and bis(2-chloroethyl)amine hydrochloride were purchased from Adamas Reagents.

[0038] Example 2

[0039] This embodiment provides a zwitterionic polycondensation humic acid corrosion inhibitor, which is prepared by the following method:

[0040] (1) Dissolve 100g of humic acid and 20g of bis(2-chloroethyl)amine hydrochloride in water respectively.

[0041] (2) Add KOH to adjust the pH of the system to 8-10.

[0042] (3) The reaction system was stirred at 25-35°C for 8 hours. The pH of the system was monitored during the reaction, and KOH was used to maintain the pH at 8-10.

[0043] (4) After the reaction is complete, dialyze the solution using a dialysis bag with a molecular weight cutoff of 1000. The corrosion inhibitor is obtained by drying the dialysate.

[0044] Example 3

[0045] This embodiment provides a zwitterionic polycondensation humic acid corrosion inhibitor, which is prepared by the following method:

[0046] (1) Dissolve 100g of humic acid and 10g of bis(2-chloroethyl)amine hydrochloride in water respectively.

[0047] (2) Add Na2CO3 to adjust the pH of the system to 8-10.

[0048] (3) The reaction system was stirred at 25-35°C for 8 hours. The pH of the system was monitored during the reaction, and Na2CO3 was used to maintain the pH at 8-10.

[0049] (4) After the reaction is complete, dialyze the solution using a dialysis bag with a molecular weight cutoff of 100. The corrosion inhibitor is obtained by drying the dialysate.

[0050] Example 4

[0051] This embodiment provides a zwitterionic polycondensation humic acid corrosion inhibitor, which is prepared by the following method:

[0052] (1) Dissolve 100g of humic acid and 1g of bis(2-chloroethyl)amine hydrochloride in water respectively.

[0053] (2) Add a mixed alkali of NaOH and Na2CO3 to adjust the pH of the system to 8-10.

[0054] (3) The reaction system was moved to 25-35℃ and stirred for 8 hours. The pH of the system was monitored during the reaction, and the pH was maintained at 8-10 using a mixed base of NaOH and Na2CO3.

[0055] (4) After the reaction is complete, dialyze the solution using a dialysis bag with a molecular weight cutoff of 100. The corrosion inhibitor is obtained by drying the dialysate.

[0056] Comparative Example 1

[0057] The only difference from Example 1 is that bis(2-chloroethyl)amine hydrochloride is not added in this comparative example; the other raw materials and preparation methods are the same as in Example 1.

[0058] Comparative Example 2

[0059] The only difference from Example 1 is that fulvic acid is not added in this comparative example, the pH is adjusted to neutral after the reaction is completed, and dialysis is not performed. The other raw materials and preparation methods are the same as in Example 1.

[0060] like Figure 1 As shown, the zwitterionic condensation polycondensation fulvic acid corrosion inhibitor proposed in this invention is obtained by the condensation reaction of fulvic acid as the basic polycondensation unit with bis(2-chloroethyl)amine hydrochloride via a phenolic hydroxyl group on its backbone. The hydrochloric acid produced in the reaction is consumed by the alkali catalyst in the system; therefore, an alkaline environment should be maintained during the reaction. Each structural unit in the product structure contains a fulvic acid backbone and a bis(2-ethyl)amine hydrochloride group. The carboxyl group in the fulvic acid backbone exhibits negative charge, while the bis(2-ethyl)amine hydrochloride group exhibits positive charge.

[0061] Structural characterization

[0062] SEM-EDS spectra of fulvic acid and zwitterionic condensation fulvic acid corrosion inhibitors were tested on an S8100 scanning electron microscope equipped with an energy dispersive spectroscopy unit.

[0063] The C, H, N, and S content of fulvic acid and zwitterionic condensed fulvic acid were determined using a German Elementar Unicube organic elemental analyzer (EA).

[0064] Two techniques were used to analyze the elemental composition of fulvic acid raw materials and zwitterionic condensation fulvic acid corrosion inhibitors. The results are shown in Tables 1 and 2, respectively. Figure 2 As shown in Tables 1 and 2, the nitrogen (N) content in zwitterionic condensed fulvic acid is significantly increased compared to the fulvic acid raw material. Considering that unreacted bis(2-chloroethyl)amine hydrochloride was completely removed by dialysis, the increased N content proves that a condensation reaction did indeed occur between fulvic acid and bis(2-chloroethyl)amine hydrochloride, with the bis(2-chloroethyl)amine hydrochloride covalently incorporated into the structural units of fulvic acid. The resulting product structure contains both a carboxyl anionic group and a cationic group in the form of hydrochloride, exhibiting zwitterionic properties. Therefore, the above results demonstrate that the zwitterionic condensed fulvic acid corrosion inhibitor was successfully prepared using the method proposed in this invention.

[0065] Table 1. Elemental composition of fulvic acid and zwitterionic condensed fulvic acid (SEM-EDS test results)

[0066]

[0067] Table 2 Organic elemental composition of fulvic acid and zwitterionic condensed fulvic acid (EA test results)

[0068]

[0069] Performance testing

[0070] 1) Performance evaluation using the static weightlessness method

[0071] The corrosion inhibition performance of the corrosion inhibitors obtained in the examples and comparative examples was tested according to SY / T5405-2019. The corroded metal was a standard Q235 steel sheet (5×2.5×0.2cm), the corrosive medium was 1M HCl, the corrosion temperature was 30℃, and the corrosion time was 4 hours. Three parallel samples were used in each test group. The specific operation was as follows: The cleaned standard Q235 steel sheet was immersed in 1M HCl containing different concentrations of corrosion inhibitor. After corrosion, the steel sheet was thoroughly rinsed with deionized water, dried, and accurately weighed. The corrosion inhibition rate was calculated using the following formula.

[0072]

[0073] In the formula: m0 and m are the weights of the sample before and after corrosion, respectively, and v 0 v and v represent the corrosion rates without and with corrosion inhibitors, respectively; s is the surface area of ​​the corroded sample; t is the corrosion time; and η is the corrosion inhibition efficiency.

[0074] Table 3 shows the corrosion inhibition efficiency of Q235 carbon steel after 4 hours of corrosion in 1M HCl solution containing different concentrations of corrosion inhibitor at 30℃. As shown in Table 3, compared with the blank sample, the corrosion rate decreases while the corrosion inhibition rate gradually increases with increasing inhibitor concentration. At an addition amount of 200 ppm, the corrosion inhibition rates of the product in Example 1 and the product in Comparative Example 1 were 94.59% and 84.57%, respectively. The product in Example 1 is the zwitterionic condensation polyfulvic acid proposed in this invention. In Comparative Example 1, since the reactant bis(2-chloroethyl)amine hydrochloride was not added, its product was essentially fulvic acid. Therefore, the comparison between the product in Example 1 and the product in Comparative Example 1 demonstrates that zwitterionic condensation polyfulvic acid, as a corrosion inhibitor, is more effective than fulvic acid alone in inhibiting the corrosion of Q235 steel in HCl. However, when Comparative Example 2 was used as a corrosion inhibitor, it actually promoted the corrosion of Q235 steel in HCl.

[0075] The comparative experiments above demonstrate that the zwitterionic condensation polyhumic acid proposed in this invention possesses excellent corrosion inhibition properties. This beneficial effect is not solely due to the use of humic acid and bis(2-chloroethyl)amine hydrochloride, but rather to the new species produced by the condensation reaction between humic acid and bis(2-chloroethyl)amine hydrochloride, which exhibits the beneficial corrosion inhibition effect.

[0076] Table 3. Corrosion inhibition efficiency of Q235 carbon steel in 1M HCl solution containing different concentrations of corrosion inhibitors for 4 hours at 30℃.

[0077]

[0078] 2) Performance evaluation by electrochemical method

[0079] The conclusions drawn from the above performance comparison were verified using electrochemical techniques. Electrochemical tests were conducted on a Shanghai Chenhua CHI660E electrochemical workstation using a three-electrode system. A Q235 steel sheet was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet as the counter electrode. The corrosion inhibition performance of Q235 carbon steel in 1M HCl solutions containing different concentrations of corrosion inhibitors was tested. The open-circuit voltage (OCP) test time was 1200 s, and the electrochemical impedance spectroscopy (EIS) test frequency range was 100 kHz to 0.01 Hz with an amplitude of 5 mV. Polarization curves were tested within the OCP ± 250 mV range at a scan rate of 1 mV / s. The corrosion inhibition efficiency was calculated using the following formula:

[0080]

[0081] In the formula R ct and R(Ω·cm) 2 (i) represents the charge transfer resistance of the blank sample and the sample with added corrosion inhibitor, respectively. 0 corr and i corr (μA·cm-2 The values ​​are the corrosion current densities of the blank sample and the sample with corrosion inhibitor, respectively.

[0082] Electrochemical impedance spectroscopy, such as Figure 3 As shown in Table 4, the obtained impedance parameters are as follows.

[0083] Table 4. EIS parameters of Q235 carbon steel in 1M HCl solutions containing different concentrations of corrosion inhibitors.

[0084]

[0085] Test results show that, compared to the blank sample, the diameter of the impedance arc increased after adding the product of Example 1 and the product of Comparative Example 1, both demonstrating a certain corrosion inhibition effect. However, the impedance arc radius of the product of Example 1 is clearly larger. Table 4 shows that the charge transfer resistance R of the product of Example 1... ct The product was larger than that of Comparative Example 1. This indicates that zwitterionic condensation humic acid has superior corrosion inhibition properties. Figure 4 The results were also verified by the polarization curve tests in Table 5.

[0086] Table 5. Polarization parameters of Q235 carbon steel in 1M HCl solutions containing different concentrations of corrosion inhibitors.

[0087]

[0088]

[0089] Therefore, although the different principles of electrochemical testing and static weight loss methods for evaluating corrosion inhibition efficiency lead to some deviations in the corrosion inhibition rate values ​​obtained by different techniques, the overall trend is consistent. That is, the zwitterionic condensation polyhydric humic acid corrosion inhibitor proposed in this invention exhibits superior corrosion inhibition performance compared to humic acid itself. This beneficial effect arises from the condensation reaction, which increases the molecular weight of the corrosion inhibitor and introduces cationic functional groups, facilitating multi-point adsorption on the metal surface and enhancing adsorption strength and density, thus providing better protection for the metal surface.

Claims

1. A zwitterionic condensation humic acid corrosion inhibitor, characterized in that, This corrosion inhibitor is obtained by polycondensation reaction of humic acid as the basic polycondensation unit and bis(2-chloroethyl)amine hydrochloride through the polycondensation reaction of phenolic hydroxyl groups on its backbone. Each structural unit contains a humic acid backbone and a bis(2-ethyl)amine hydrochloride group. The carboxyl group in the humic acid backbone exhibits negative charge, and the bis(2-ethyl)amine hydrochloride group exhibits positive charge. The preparation of this corrosion inhibitor includes the following specific steps: Step 1: Dissolve fulvic acid and bis(2-chloroethyl)amine hydrochloride in water respectively; Step 2: Add alkali to the solution from Step 1 to adjust the pH to 8-10; Step 3: Stir the reaction system with pH 8-10 at 25-35 °C, monitor the pH change of the system during the reaction, and use alkali to maintain the pH at 8-10 to obtain the crude product; Step 4: After the reaction is complete, dialyze the crude product obtained in step 3 in water; Step 5: After drying the dialysate, the product obtained is the zwitterionic polycondensation humic acid corrosion inhibitor.

2. A method for preparing an amphoteric condensation polyhumic acid corrosion inhibitor, characterized in that, The preparation of this corrosion inhibitor includes the following specific steps: Step 1: Dissolve fulvic acid and bis(2-chloroethyl)amine hydrochloride in water respectively; Step 2: Add alkali to the solution from Step 1 to adjust the pH to 8-10; Step 3: Stir the reaction system with pH 8-10 at 25-35 °C, monitor the pH change of the system during the reaction, and use alkali to maintain the pH at 8-10 to obtain the crude product; Step 4: After the reaction is complete, dialyze the crude product obtained in step 3 in water; Step 5: After drying the dialysate, the product obtained is the zwitterionic polycondensation humic acid corrosion inhibitor. This corrosion inhibitor is obtained by polycondensation reaction of humic acid as the basic polycondensation unit with bis(2-chloroethyl)amine hydrochloride through the polycondensation reaction of phenolic hydroxyl groups on its backbone. Each structural unit contains a humic acid backbone and a bis(2-ethyl)amine hydrochloride group. The carboxyl group in the humic acid backbone exhibits negative charge, and the bis(2-ethyl)amine hydrochloride group exhibits positive charge.

3. The method for preparing an amphoteric condensation polyhumic acid corrosion inhibitor according to claim 2, characterized in that, In step 1, the mass ratio of fulvic acid and bis(2-chloroethyl)amine hydrochloride is 1:0.2 to 1:0.

01.

4. The method for preparing an amphoteric condensation polyhumic acid corrosion inhibitor according to claim 2, characterized in that, In step 2, the alkali is any one or a combination of two of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

5. The method for preparing an amphoteric condensation polyhumic acid corrosion inhibitor according to claim 2, characterized in that, The molecular weight cutoff for dialysis in step 4 is 100~1000 g / mol.

6. The application of the zwitterionic polycondensation humic acid corrosion inhibitor according to claim 1 or the zwitterionic polycondensation humic acid corrosion inhibitor prepared by the method according to any one of claims 2-5, characterized in that, The zwitterionic polycondensation humic acid corrosion inhibitor is used to inhibit metal corrosion.

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