Use of fulvic acid in gas hydrate production

Abstract

The application discloses application of fulvic acid as a gas hydrate promoter in preparation of gas hydrate and belongs to the technical field of solidified gas storage. A solution with a concentration of 0.1-3 wt% of fulvic acid is used as a gas hydrate promoter, gas is introduced into a high-pressure reaction kettle containing the gas hydrate promoter at low temperature, and solid gas hydrate is obtained after rapid reaction. The application uses natural soil organic matter, is widely available, cheap, green, environment-friendly, non-polluting, and has outstanding effects of promoting growth of hydrate, can significantly shorten the induction time of hydrate formation and enhance the gas storage density, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solidified gas storage, and particularly relates to application of fulvic acid as a gas hydrate promoter in preparation of gas hydrate. BACKGROUND

[0002] Due to the shortage of oil resources, natural gas as a clean energy has attracted more and more attention. However, compared with other fossil fuels, due to its low energy density, its storage and transportation cost is higher, which has become one of the key factors restricting the development of the natural gas industry. Recently, the solidified natural gas storage method has been widely studied, which stores natural gas in the form of hydrate, has the characteristics of low energy consumption, moderate operating conditions and non-explosive. Hydrate is a non-stoichiometric crystalline compound formed by water and small molecule gas (CH4, C2H6, CO2, etc.) under suitable temperature and pressure conditions. However, due to various limitations such as strict reaction conditions and slow formation kinetics, it is difficult to apply solidified natural gas in actual production. Therefore, some physical and chemical methods are proposed to strengthen the reaction process. Physical methods mainly increase the gas-liquid contact area by consuming energy (stirring, gas bubbles, spraying, etc.), while chemical methods mainly add hydrate promoters to strengthen the reaction. Generally, thermodynamic hydrate promoters will occupy part of the hydrate cage, reducing its gas storage capacity, while kinetic hydrate promoters can accelerate the reaction by changing the gas-liquid interface characteristics without affecting gas adsorption. Although the method of adding kinetic hydrate promoters has good application prospects, finding an efficient and environmentally friendly additive is still the focus of current research.

[0003] Fulvic acid is a red-brown or gray-black powder dissolved in water, widely exists in nature, has green, environmentally friendly and organic characteristics, and therefore has great potential for new material development. More importantly, fulvic acid has a high content of functional groups and high surface adsorption capacity, and so far still has great market and competitive advantage in plant growth agents, stress resistance agents, fluid fertilizers, pharmaceutical preparations, cosmetics and the like. The application first uses renewable and environmentally friendly fulvic acid as a gas hydrate promoter, which can significantly improve the formation kinetics of hydrate, and provides a thought and method for industrial production of hydrate. At the same time, the application uses fulvic acid for gas storage, which has important practical significance for high value-added utilization of fulvic acid, utilization of renewable resources and environmental protection. SUMMARY

[0004] In order to overcome the shortcomings and deficiencies of the traditional gas storage and transportation mode, the purpose of the present application is to provide a hydrate promoter with excellent performance and low price, which can obtain gas hydrate with fast formation kinetics and high gas storage density by using a low dose of solution. Fulvic acid, as a renewable compound containing an aromatic ring, has a good effect of promoting the formation of hydrate, and can quickly react to obtain solid gas hydrate under low temperature and high pressure conditions after being added to water to form a solution. At the same time, the molecule has a good effect of reducing surface tension, which can increase the solubility of methane in water, and the hydrophobic groups such as aromatic rings in the molecule can make water molecules arrange into a cage structure to promote the formation of hydrate. The present application has outstanding effect of promoting the growth of hydrate, can significantly shorten the induction time of hydrate formation, enhance the formation rate and gas storage density of hydrate, and has the effect of preventing the accumulation of hydrate, so it has good application prospect.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] Fulvic acid is used as a gas hydrate promoter in the preparation of gas hydrate.

[0007] The promoter is obtained by uniformly mixing fulvic acid and water, and the concentration of fulvic acid in the promoter is 0.1-3wt%.

[0008] Under low temperature, high-pressure gas is introduced into a high-pressure reaction kettle containing a gas hydrate promoter, and solid gas hydrate is obtained under stirring conditions. The temperature of the mixed system is controlled to be 268.15-283.15 K, the pressure is 0.5-10.0 MPa, and the reaction time is 0.5-12 h. The gas is any one of methane, carbon dioxide, hydrogen, oxygen, nitrogen, hydrogen sulfide, argon, krypton, xenon, ethane, ethylene, and propane.

[0009] The present application has the following advantages:

[0010] (1) The present application uses environment-friendly and green renewable fulvic acid as raw material, which has good recyclability and less harm to the environment during use.

[0011] (2) The present application uses fulvic acid as a hydrate promoter to prepare high gas storage density gas hydrate, which can significantly shorten the induction time of hydrate formation, significantly enhance the formation rate and gas storage density of hydrate, and provides an economic and sustainable method for industrial production of hydrate.

[0012] (3) The present application uses fulvic acid as a hydrate promoter to prepare high gas storage density gas hydrate, which is simple to operate, and the hydrate formed by the low dose of composite promoter can store more gas, which has important practical significance for alleviating the greenhouse effect and solving the global climate and environmental problems.

[0013] (4) The present application uses fulvic acid as a methane hydrate accelerator, and has important scientific significance and practical application value for high value-added application of fulvic acid, renewable resource utilization and environmental protection.

[0014] (5) The gas hydrate accelerator of the present application has the effect of preventing hydrate accumulation. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Figure for gas hydrate accelerator evaluation experimental device.

[0016] Figure 2 Figure for comparison of induction time of Comparative Example 1 and Examples 1-5.

[0017] Figure 3 Figure for comparison of methane absorption kinetics curve of Comparative Example 1 and Examples 1-5.

[0018] Figure 4 Figure for comparison of induction time of Example 2 and Examples 6-8.

[0019] Figure 5 Figure for comparison of methane absorption kinetics curve of Example 2 and Examples 6-8.

[0020] Figure 6 Figure for rapid formation process of methane hydrate when the hydrate accelerator of the present application is added in an amount of 0.5 wt%, the pressure is 8.5 MPa, and the temperature is 274.15 K. DETAILED DESCRIPTION

[0021] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0022] In order to study the effect of the hydrate accelerator provided by the present application on the hydrate morphology, the implementation equipment used is a visual transparent sapphire high-pressure reaction kettle and a matching system, which mainly consists of six parts, i.e. a high-pressure sapphire kettle, a balance kettle, a constant temperature air bath, a temperature and pressure measuring instrument, a stirring system and a computer data automatic acquisition system. The maximum working volume of the high-pressure sapphire kettle is 525 cm 3 (including a piston and a stirrer), the maximum working pressure is 20 MPa, and the working temperature range is -80-150 ℃. The transparent sapphire high-pressure reaction kettle is a commonly used device for studying hydrate technology, and is described in Figure 1 .

[0023] Before the reaction, the whole experimental system was cleaned with deionized water, and after vacuum drying, 100 ml of prepared aqueous solution was placed in the sapphire reactor, and the air bath temperature was set to the experimental temperature 274.15 K; when the system temperature was stable for 2 hours, pure methane gas was introduced into the reaction kettle from the equilibrium kettle, and the air in the kettle was replaced for 3-4 times, and the experimental gas with a certain pressure (less than the hydrate formation equilibrium pressure at this temperature, and the hydrate equilibrium pressure was calculated by Chen-Guo hydrate model) was introduced to reach the dissolution equilibrium; then the experimental gas was introduced into the system from the equilibrium kettle to increase the system pressure to the test pressure, the gas inlet valve was closed, and the stirrer was opened, and the stirring speed was constant throughout the experiment; as the reaction proceeded, the gas was consumed, the hydrate crystal morphology in the kettle was observed through the window, and the whole process was recorded by high-definition camera, such as Figure 6 the photo effect shows.

[0024] Example 1

[0025] The reaction system was a mixed solution of 0.25 g of fulvic acid and 99.75 g of deionized water, and the mass fraction of fulvic acid was 0.25 wt%. The solution was sent into the reaction kettle.

[0026] The experimental steps were as described above, the introduced gas was pure methane, the experimental pressure was 5.5 MPa, the experimental temperature was 274.15 K, and throughout the experiment, the hydrate was formed rapidly, indicating that the hydrate promoter had good effect on promoting the formation of hydrate, and the induction time and the final gas storage capacity were as shown in Table 1.

[0027] Example 2

[0028] The reaction system was a mixed solution of 0.5 g of fulvic acid and 99.5 g of deionized water, and the mass fraction of fulvic acid was 0.5 wt%. The solution was sent into the reaction kettle.

[0029] The experimental steps were as described above, the introduced gas was pure methane, the experimental pressure was 5.5 MPa, the experimental temperature was 274.15 K, and throughout the experiment, the hydrate was formed rapidly, indicating that the hydrate promoter had good effect on promoting the formation of hydrate, and the induction time and the final gas storage capacity were as shown in Table 1.

[0030] Example 3

[0031] The reaction system was a mixed solution of 1.0 g of fulvic acid and 99.0 g of deionized water, and the mass fraction of fulvic acid was 1.0 wt%. The solution was sent into the reaction kettle.

[0032] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 5.5 MPa, the experimental temperature is 274.15 K, and hydrates are formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrates. The induction time and the final gas storage capacity are shown in Table 1.

[0033] Example 4

[0034] The reaction system is a mixed solution of 1.5 g of fulvic acid and 98.5 g of deionized water, wherein the mass fraction of fulvic acid is 1.5 wt%. The solution is fed into the reaction kettle.

[0035] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 5.5 MPa, the experimental temperature is 274.15 K, and hydrates are formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrates. The induction time and the final gas storage capacity are shown in Table 1.

[0036] Example 5

[0037] The reaction system is a mixed solution of 2.0 g of fulvic acid and 98.0 g of deionized water, wherein the mass fraction of fulvic acid is 2.0 wt%. The solution is fed into the reaction kettle.

[0038] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 5.5 MPa, the experimental temperature is 274.15 K, and hydrates are formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrates. The induction time and the final gas storage capacity are shown in Table 1.

[0039] Example 6

[0040] The reaction system is a mixed solution of 0.5 g of fulvic acid and 99.5 g of deionized water, wherein the mass fraction of fulvic acid is 0.5 wt%. The solution is fed into the reaction kettle.

[0041] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 6.5 MPa, the experimental temperature is 274.15 K, and hydrates are formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrates. The induction time and the final gas storage capacity are shown in Table 1.

[0042] Example 7

[0043] The reaction system is a mixed solution of 0.5 g of fulvic acid and 99.5 g of deionized water, wherein the mass fraction of fulvic acid is 0.5 wt%. The solution is fed into the reaction kettle.

[0044] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 7.5 MPa, the experimental temperature is 274.15 K, and hydrate is formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrate, and the induction time and the final gas storage capacity are shown in Table 1.

[0045] Example 8

[0046] The reaction system is a mixed solution of 0.5 g of fulvic acid and 99.5 g of deionized water, wherein the mass fraction of fulvic acid is 0.5 wt%. The solution is fed into the reaction kettle.

[0047] The experimental procedure is as described above, the gas passed in is pure methane, the experimental pressure is 8.5 MPa, the experimental temperature is 274.15 K, and hydrate is formed rapidly throughout the experimental process, indicating that the hydrate promoter has a good effect of promoting the formation of hydrate, and the induction time and the final gas storage capacity are shown in Table 1.

[0048] Comparative Example 1

[0049] The reaction system is 100 g of deionized water. The solution is fed into the reaction kettle.

[0050] The experimental procedure is as described above, the experimental pressure is 5.5 MPa, the experimental temperature is 274.15 K, and hydrate is formed slowly throughout the experimental process, and the induction time and the final gas storage capacity of hydrate are shown in Table 1.

[0051]

[0052] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. The application of fulvic acid in the preparation of gas hydrates, characterized in that: Fulvic acid as a gas hydrate promoter; The accelerator is obtained by uniformly mixing fulvic acid and water, and the concentration of fulvic acid in the accelerator is 0.1-3 wt%. At low temperature, high-pressure gas is introduced into a high-pressure reactor containing a gas hydrate promoter, and the reaction is carried out under stirring conditions to obtain solid gas hydrates. The temperature of the mixing system was controlled at 268.15-283.15 K, the pressure at 0.5-10.0 MPa, and the reaction time at 0.5-12 h. The gas is any one of methane, carbon dioxide, hydrogen, oxygen, nitrogen, hydrogen sulfide, argon, krypton, xenon, ethane, ethylene, and propane.

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