Heterocyclic Schiff base natural gas hydrate inhibitor as well as preparation method and application thereof
By preparing heterocyclic Schiff base natural gas hydrate inhibitors through modified chitosan, the problems of large dosage, high cost, and serious pollution of existing inhibitors are solved, achieving a highly efficient and environmentally friendly natural gas hydrate inhibition effect and preventing pipeline blockage.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LIAONING UNIVERSITY OF PETROLEUM AND CHEMICAL TECHNOLOGY
- Filing Date
- 2026-01-20
- Publication Date
- 2026-05-01
AI Technical Summary
Existing natural gas hydrate inhibitors suffer from problems such as excessive dosage, high cost, low recycling rate, serious environmental pollution, and difficulty in improving inhibition effect, especially during natural gas extraction and transportation, which can easily cause pipeline blockage.
A heterocyclic Schiff base natural gas hydrate inhibitor was developed by introducing 3-chloro-2-hydroxypropyltrimethylammonium chloride and pyridine carboxaldehyde into chitosan to form a Schiff base structure. This structure disrupts the cage-like structure of hydrates, improves hydrophilicity and inhibition effect, and hinders hydrate growth through amino groups.
It significantly improves the hydrate inhibition effect, reduces the dosage, lowers the cost, and has good biodegradability, avoiding environmental pollution, preventing pipeline blockage, and improving safety and work efficiency.
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Abstract
Description
A heterocyclic Schiff base natural gas hydrate inhibitor, its preparation method and application Technical Field
[0001] This invention belongs to the field of natural gas hydrate inhibition, specifically relating to a heterocyclic Schiff base natural gas hydrate inhibitor, its preparation method, and its application. Background Technology
[0002] Natural gas hydrate (commonly known as combustible ice) is an ice-like crystalline substance formed by natural gas (mainly methane) and water under low temperature and high pressure conditions. Natural gas and petroleum fluids contain low-boiling-point hydrocarbons such as methane and ethane, as well as carbon dioxide, and varying amounts of water. During the extraction and transportation of natural gas, when encountering low temperature and high pressure conditions, these gases transported in pipelines combine with water to form cage-like crystalline gas hydrates. These hydrates accumulate with the fluid flow in the pipeline, eventually causing blockages, leading to excessive local pressure, potential safety issues, and directly affecting the natural gas extraction rate and pipeline transportation speed.
[0003] To address this issue, the commonly used preventative measure against natural gas hydrate blockage in pipelines is the addition of natural gas hydrate inhibitors. However, these traditional inhibitors still have some unavoidable drawbacks, such as excessive dosage, high cost, low recycling rate, and environmental pollution. With increasingly stringent environmental requirements for oil and gas extraction, the green biodegradability of natural gas hydrates has gradually attracted attention and become a research hotspot for natural gas hydrate inhibitors, offering better economic advantages compared to other hydrate inhibitors. Currently available green hydrate inhibitors are mostly composite inhibitors, which, while having some inhibitory effect, have limited potential for further improvement. Summary of the Invention
[0004] This invention provides a heterocyclic Schiff base natural gas hydrate inhibitor, its preparation method, and its application. Utilizing the excellent green biodegradability of chitosan, a cationic surfactant and pyridine carboxaldehyde are introduced to modify chitosan, disrupting the original cage-like ordered structure of water molecules required for hydrate formation. Simultaneously, the amino groups inherent in chitosan preferentially adsorb onto the surface of hydrate crystal nuclei, hindering hydrate growth. This further improves the hydrate inhibition effect while retaining the excellent green biodegradability of chitosan itself, solving the problems of poor degradability, low inhibition effect, and high cost of current hydrate inhibitors.
[0005] The technical solution of the present invention is as follows: a heterocyclic Schiff base natural gas hydrate inhibitor, the structural formula of which is as follows: Wherein, A is the substituted ammonium chloride group, and B is the substituted pyridine carboxaldehyde group; N in B is fixed at position 1, and X is an aldehyde (-CHO) group, with position 2, 3, or 4 (i.e., ortho, meta, or para of N).
[0006] Furthermore, the heterocyclic Schiff base natural gas hydrate inhibitor is prepared using chitosan, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and pyridine carboxaldehyde as raw materials.
[0007] The preparation method of the above-mentioned heterocyclic Schiff base natural gas hydrate inhibitor includes the following steps: 1) Under alkaline conditions, chitosan is added to isopropanol and magnetically stirred at medium temperature to obtain a chitosan solution; isopropanol can adjust the polarity of the reaction system, which can help chitosan and 3-chloro-2-hydroxypropyltrimethylammonium chloride to disperse and dissolve better, ensuring that the two are fully contacted and reacted, and can also reduce the viscosity of the system and facilitate subsequent separation; 2) 3-chloro-2-hydroxypropyltrimethylammonium chloride is added to the chitosan solution and magnetically stirred at medium temperature. After the reaction is completed, the solution is cooled to room temperature and its pH value is measured. If it is not neutral, it is neutralized. Then, ethanol is added to precipitate and separate the product, and the product is filtered. 3) Under acidic conditions, the chitosan quaternary ammonium salt was added to methanol to obtain a chitosan quaternary ammonium salt solution. Methanol can help the chitosan quaternary ammonium salt and pyridine formaldehyde to fully dissolve and disperse, ensuring uniform reaction and avoiding side reactions such as excessive polymerization of aldehydes. 4) Pyridine formaldehyde was added to the chitosan quaternary ammonium salt solution and magnetically stirred under medium temperature conditions. The solution was cooled to room temperature, and then cold acetone solution was added to precipitate and separate the product. The product was filtered, washed, and finally dried to constant weight to obtain a heterocyclic chitosan quaternary ammonium salt Schiff base derivative. 5) The heterocyclic chitosan quaternary ammonium salt Schiff base derivative was dissolved in an oil-water system to obtain a heterocyclic Schiff base natural gas hydrate inhibitor.
[0008] Furthermore, in the preparation method of the heterocyclic Schiff base natural gas hydrate inhibitor, in step 1), the degree of deacetylation of the chitosan is >80%, the viscosity is 100-300 mPa·s, the temperature is 50-60℃, and the mixture is magnetically stirred for 3-5 hours.
[0009] Furthermore, in the preparation method of the heterocyclic Schiff base natural gas hydrate inhibitor, in step 2), the concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 60-70%; the temperature is 65-75℃; and the mixture is magnetically stirred for 12-16 hours.
[0010] Furthermore, in the preparation method of the heterocyclic Schiff base natural gas hydrate inhibitor, in step 4), the purity of pyridine formaldehyde is >90%; the temperature is 60-70℃, and the mixture is magnetically stirred for 10-14 hours.
[0011] Furthermore, in the preparation method of the heterocyclic Schiff base natural gas hydrate inhibitor, the mass fraction of the heterocyclic chitosan quaternary ammonium salt Schiff base derivative dissolved in the oil-water system is 0.1wt% to 2.0wt%.
[0012] The application of the above-mentioned heterocyclic Schiff base natural gas hydrate inhibitor is carried out as follows: the heterocyclic Schiff base natural gas hydrate inhibitor is added to the reaction vessel, the reaction temperature is higher than 273.15K, methane gas is injected into the reaction vessel until the pressure is greater than 2.5MPa, and magnetic stirring is turned on to carry out the reaction.
[0013] Furthermore, the application of the heterocyclic Schiff base natural gas hydrate inhibitor involves a reaction time of 10-72 hours.
[0014] The beneficial effects of this invention are as follows: 1. The heterocyclic chitosan quaternary ammonium salt Schiff base derivative obtained by the present invention through two modifications under different conditions solves the problem of poor water solubility and general inhibition effect of single chitosan. The introduction of 3-chloro-2-hydroxypropyltrimethylammonium chloride and pyridine carboxaldehyde to modify chitosan improves hydrophilicity and water solubility on the one hand, and on the other hand, by introducing the aldehyde group -CHO on pyridine carboxaldehyde to combine with the amino group -NH2 on chitosan to generate carbon-nitrogen double bond -C=N- (i.e. Schiff base structure) and positively charged quaternary ammonium salt group, it can affect the arrangement of water molecules and reduce the possibility of hydrogen bonding between water molecules.
[0015] 2. The heterocyclic Schiff base natural gas hydrate inhibitor of the present invention requires a small dosage and has high biodegradability in the process of inhibiting hydrate formation, which can reduce environmental pollution. While reducing the amount of hydrate formation, it can also significantly reduce the initial formation rate of hydrate, effectively prevent blockage of flow pipelines, improve safety, and improve work efficiency.
[0016] 3. The preparation method of the heterocyclic Schiff base natural gas hydrate inhibitor provided by the present invention is relatively easy and the cost is low, which has good prospects for industrialization. Detailed Implementation
[0017] Chitosan, CAS No.: 9012-76-4, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; isopropanol, CAS No.: 67-63-0, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution, CAS No.: 3327-22-8, was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.; 2-pyridinecarboxaldehyde, CAS No.: 1121-60-4; 3-pyridinecarboxaldehyde, CAS No.: 500-22-1; 4-pyridinecarboxaldehyde, CAS No.: 872-85-5, were all purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd. Example 1
[0018] The preparation method of heterocyclic Schiff base natural gas hydrate inhibitor includes the following steps: 10 g of 40 wt% NaOH solution is weighed, 4.0 g of chitosan is weighed using an electronic balance, and 50 ml of isopropanol is added sequentially to a reaction flask. The mixture is magnetically stirred at 55 °C for 4 h. 30 ml of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is gradually added, and the mixture is magnetically stirred at 70 °C for 15 h. After the reaction is complete, the pH value of the mixture in the reaction flask is measured. If it is not neutral, a neutralization reaction is performed until neutral. Ethanol is added to precipitate and separate the product, which is then filtered, washed, and vacuum dried at 80 °C to obtain chitosan quaternary ammonium salt. Measure 75 ml of methanol, weigh 2.0 g of the chitosan quaternary ammonium salt using an electronic balance, measure 4.72 ml of 3-pyridinecarboxaldehyde and 10 ml of acetic acid, and add them sequentially to the reaction flask. Reflux at 65 °C for 12 h. After cooling to room temperature, add cold acetone solution to precipitate, filter, wash, and dry under vacuum at 50 °C to obtain a heterocyclic chitosan quaternary ammonium salt Schiff base derivative. Weigh 1.5 g of the heterocyclic chitosan quaternary ammonium salt Schiff base derivative, dissolve it in 500 ml of oil-water solution with a ratio of 2:8, and stir until completely dissolved to obtain a heterocyclic Schiff base natural gas hydrate inhibitor with a mass fraction of 0.3 wt%.
[0019] Application Experiment: This application experiment was conducted in a 1L reactor, using methane as the gas. Before the experiment, the reactor was repeatedly cleaned at least three times with deionized water and ethanol, and then purged with gas to remove excess gas. The airtightness was checked to ensure good airtightness. The prepared solution was then injected into the reactor. The data acquisition system and the cryogenic bath were turned on, and temperature and pressure changes were recorded at 20-second intervals. When the reactor temperature reached 281.15K, methane gas was injected and pressurized to 6MPa, followed by magnetic stirring at 500 rpm. Once the gas reached dissolution equilibrium, the reactor temperature was reduced to the set temperature at a rate of 0.15K / min, and the experiment began.
[0020] Analysis of the experimental results shows that the heterocyclic Schiff base natural gas hydrate inhibitor prepared in Example 1 induced methane hydrate formation in 189 min during the methane hydrate formation kinetics experiment. Compared with the comparative example, the induction time was extended by approximately 11 times, with only a small amount of hydrate forming in the reactor, no obvious aggregation, and no impact on the normal flow of the oil-water system within the reactor. Example 2
[0021] The preparation method of heterocyclic Schiff base natural gas hydrate inhibitor includes the following steps: 10 g of 40 wt% NaOH solution is weighed, 4.0 g of chitosan is weighed using an electronic balance, and 50 ml of isopropanol is added sequentially to a reaction flask. The mixture is magnetically stirred at 55 °C for 4 h. 30 ml of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is gradually added, and the mixture is magnetically stirred at 70 °C for 15 h. After the reaction is complete, the pH value of the mixture in the reaction flask is measured. If it is not neutral, a neutralization reaction is performed until neutral. Ethanol is added to precipitate and separate the product, which is then filtered, washed, and vacuum dried at 80 °C to obtain chitosan quaternary ammonium salt. Measure 75 ml of methanol, weigh 2.0 g of the chitosan quaternary ammonium salt using an electronic balance, measure 4.72 ml of 2-pyridinecarboxaldehyde and 10 ml of acetic acid, and add them sequentially to the reaction flask. Reflux at 65 °C for 12 h. After cooling to room temperature, add cold acetone solution to precipitate, filter, wash, and dry under vacuum at 50 °C to obtain a heterocyclic chitosan quaternary ammonium salt Schiff base derivative. Weigh 3.0 g of the heterocyclic chitosan quaternary ammonium salt Schiff base derivative, dissolve it in 500 ml of oil-water mixture with an oil-water ratio of 8:2, and stir until completely dissolved to obtain a heterocyclic Schiff base natural gas hydrate inhibitor with a mass fraction of 0.6 wt%.
[0022] Application experiment: Same as Example 1.
[0023] Analysis of the experimental results shows that the heterocyclic Schiff base natural gas hydrate inhibitor prepared in Example 2 did not show significant hydrate formation in the methane hydrate formation kinetics experiment. Compared with the comparative example, the inhibitory effect is significant. Example 3
[0024] The preparation method of heterocyclic Schiff base natural gas hydrate inhibitor includes the following steps: 10 g of 40 wt% NaOH solution is weighed, 4.0 g of chitosan is weighed using an electronic balance, and 50 ml of isopropanol is added sequentially to a reaction flask. The mixture is magnetically stirred at 55 °C for 4 h. 30 ml of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is gradually added, and the mixture is magnetically stirred at 70 °C for 15 h. After the reaction is complete, the pH value of the mixture in the reaction flask is measured. If it is not neutral, a neutralization reaction is performed until neutral. Ethanol is added to precipitate and separate the product, which is then filtered, washed, and vacuum dried at 80 °C to obtain chitosan quaternary ammonium salt. Measure 75 ml of methanol, weigh 2.0 g of the chitosan quaternary ammonium salt using an electronic balance, measure 4.72 ml of 4-pyridinecarboxaldehyde and 10 ml of acetic acid, and add them sequentially to the reaction flask. Reflux at 65 °C for 12 h. After cooling to room temperature, add cold acetone solution to precipitate, filter, wash, and dry under vacuum at 50 °C to obtain a heterocyclic chitosan quaternary ammonium salt Schiff base derivative. Weigh 4.5 g of the heterocyclic chitosan quaternary ammonium salt Schiff base derivative, dissolve it in 500 ml of oil-water mixture with a ratio of 4:6, and stir until completely dissolved to obtain a heterocyclic Schiff base natural gas hydrate inhibitor with a mass fraction of 0.9 wt%.
[0025] Application experiment: Same as Example 1.
[0026] Analysis of the experimental results shows that the heterocyclic Schiff base natural gas hydrate inhibitor prepared in Example 2 induced methane hydrate formation in 217 min during the methane hydrate formation kinetics experiment. Compared with the comparative example, the induction time was extended by approximately 13 times, with only a small amount of hydrate forming in the reactor, no obvious aggregation, and no impact on the normal flow of the oil-water system within the reactor. (Comparative Example)
[0027] Application Experiment: No hydrate inhibitors were added. The application experiment was conducted in a 1L reactor, using methane as the gas. Before the experiment, the reactor was repeatedly cleaned at least three times with deionized water and ethanol reagent, and then purged with gas to remove excess gas. The airtightness was checked to ensure good airtightness. Then, 500ml of deionized water was injected into the reactor. The data acquisition system and the cryogenic bath were turned on, and temperature and pressure changes were recorded at 20s intervals. When the temperature inside the reactor reached 281.15K, methane gas was injected to pressurize to 6MPa, and then magnetic stirring was started at 500r / min. When the gas reached dissolution equilibrium, the temperature inside the reactor was reduced to the set temperature at a rate of 0.15K / min, and the experiment began.
[0028] Analysis of the experimental results shows that the induction time for methane hydrate formation in the pure water system during the methane hydrate formation kinetics experiment was 17 minutes. Significant hydrate formation and blockage were observed inside the reactor.
[0029] The comparison of the above experimental data shows that the heterocyclic Schiff base natural gas hydrate inhibitor has a better inhibitory effect on natural gas hydrates than the pure water experiment.
[0030] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A heterocyclic Schiff base natural gas hydrate inhibitor, characterized in that, Its structural formula is as follows: Wherein, A is the substituted ammonium chloride group, and B is the substituted pyridine carboxaldehyde group; N in B is fixed at position 1, and X is an aldehyde (-CHO) group, with position 2, 3, or 4 (i.e., ortho, meta, or para of N).
2. The heterocyclic Schiff base natural gas hydrate inhibitor according to claim 1, characterized in that, It was prepared using chitosan, 3-chloro-2-hydroxypropyltrimethylammonium chloride and pyridine carboxaldehyde as raw materials.
3. The method for preparing the heterocyclic Schiff base natural gas hydrate inhibitor as described in claim 2, characterized in that, Includes the following steps: 1) Under alkaline conditions, chitosan is added to isopropanol and magnetically stirred at medium temperature to obtain a chitosan solution; 2) Add 3-chloro-2-hydroxypropyltrimethylammonium chloride to the chitosan solution, stir magnetically at medium temperature, and after the reaction is complete, cool the solution to room temperature and measure its pH value. If it is not neutral, neutralize it, then add ethanol to precipitate and separate the product, filter, wash, and finally dry to constant weight to obtain chitosan quaternary ammonium salt; 3) Under acidic conditions, add the chitosan quaternary ammonium salt to methanol to obtain chitosan quaternary ammonium salt solution; 4) Add pyridine formaldehyde to the chitosan quaternary ammonium salt solution, stir magnetically at medium temperature, cool the solution to room temperature, then add cold acetone solution to precipitate and separate the product, filter, wash, and finally dry to constant weight to obtain heterocyclic chitosan quaternary ammonium salt Schiff base derivative; 5) Dissolve the heterocyclic chitosan quaternary ammonium salt Schiff base derivative in an oil-water system to obtain a heterocyclic Schiff base natural gas hydrate inhibitor.
4. The method for preparing the heterocyclic Schiff base natural gas hydrate inhibitor according to claim 3, characterized in that, In step 1), the degree of deacetylation of the chitosan is >80%, the viscosity is 100-300 mPa·s, the temperature is 50-60℃, and the mixture is magnetically stirred for 3-5 hours.
5. The method for preparing the heterocyclic Schiff base natural gas hydrate inhibitor according to claim 3, characterized in that, In step 2), the concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 60-70%; the temperature is 65-75℃; and the mixture is magnetically stirred for 12-16 hours.
6. The method for preparing the heterocyclic Schiff base natural gas hydrate inhibitor according to claim 3, characterized in that, In step 4), the purity of pyridine formaldehyde is >90%; the temperature is 60-70℃; and the mixture is magnetically stirred for 10-14 hours.
7. The method for preparing the heterocyclic Schiff base natural gas hydrate inhibitor according to claim 3, characterized in that, The mass fraction of heterocyclic chitosan quaternary ammonium salt Schiff base derivatives dissolved in an oil-water system is 0.1 wt% to 2.0 wt%.
8. The application of the heterocyclic Schiff base natural gas hydrate inhibitor as described in claim 2, characterized in that, The process is as follows: Add the heterocyclic Schiff base natural gas hydrate inhibitor into the reactor, the reaction temperature is higher than 273.15K, inject methane gas into the reactor until the pressure is greater than 2.5MPa, and start magnetic stirring to carry out the reaction.
9. The application of the heterocyclic Schiff base natural gas hydrate inhibitor according to claim 8, characterized in that, The reaction time is 10~72h.