Accelerator for synthesis and decomposition process of methane hydrate

Abstract

The invention belongs to the technical field of natural gas hydrates, and discloses an accelerant for the synthesis and decomposition process of methane hydrates, the accelerant is an accelerant of a lignin synergistic graphene oxide system, the accelerant can be applied to the synthesis and decomposition process of methane, and the surface tension of a solution can be effectively reduced in the synthesis process; the induction time in the synthesis process is shortened, the time required for complete generation of hydrates is shortened, and the time required for methane consumption reaching 50 mmol / mol is shortened; meanwhile, the lignin synergistic graphene oxide system accelerant is applied to the decomposition process of the methane hydrate, and a large amount of foam is not generated in the decomposition process, so that gas release is not hindered, and the time required by decomposition can be effectively shortened. The accelerant solves the problems that an accelerant in the prior art has micro toxicity, is relatively low in accelerating effect and can generate foam to hinder gas release when being applied to hydrate decomposition, and is suitable for methane hydrate synthesis and decomposition.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas hydrates, and in particular to a promoter for the synthesis and decomposition process of methane hydrates. Background Art

[0002] Natural gas hydrate is a new type of green and efficient clean energy. It wraps up the gas molecules in natural gas through the cage structure formed by the hydrogen bonds in the water molecules, forming an envelope-type solid that looks like ice. The hydrate method for storing and transporting natural gas (SNG) is a new type of natural gas storage and transportation technology. Compared with other technologies, SNG technology has a higher gas storage density. One cubic meter of hydrate can solidify and store up to 180 cubic meters of natural gas. The hydrate is harmless to the environment during the generation process and can be released by simply reducing the pressure and raising the temperature. However, the core problem faced by SNG technology in industrial applications is how to generate natural gas hydrates efficiently and quickly.

[0003] Adding a surfactant to the hydrate reaction system is a relatively effective method, which can effectively change the critical micelle concentration of the liquid and reduce the surface tension. Currently known surfactant with a significant promoting effect is SDS, which can accelerate the growth of hydrates, but SDS is a slightly toxic material, and the large number of bubbles generated during the decomposition process will hinder the decomposition of hydrates, thereby affecting the release of gas. Therefore, the present invention proposes a promoter for the synthesis and decomposition process of methane hydrate, which is degradable, does not produce foam, is non-toxic and can effectively improve the kinetic characteristics of hydrate formation. Summary of the invention

[0004] The present invention aims to provide a promoter for the synthesis and decomposition process of methane hydrate, so as to solve the problems that the promoters in the prior art are slightly toxic, have low promoting effect, and produce foams when used for hydrate decomposition, which hinders gas release.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A promoter for the synthesis and decomposition of methane hydrate, comprising a synergistic system of graphene oxide and sodium lignin sulfonate, wherein the molecular formula of graphene oxide is C6O 11 (OH)2, sodium lignin sulfonate, its molecular formula is C 20 H 24 Na2O 10 S2.

[0007] Furthermore, when the synergistic system promoter is applied under the working conditions of 277.15K and 5MPa, the concentration of sodium lignin sulfate is 0.7g / L and the concentration of graphene oxide is 0.05g / L.

[0008] Furthermore, the promoter is applied to the methane hydrate synthesis process and the methane hydrate decomposition process.

[0009] A method for synthesizing methane hydrate by using a promoter for the synthesis and decomposition process of methane hydrate, comprising the following steps:

[0010] S1, preparing a mixed solution of graphene oxide, sodium lignin sulfonate and deionized water and then dispersing it by ultrasonication;

[0011] S2. Rinse the reactor with deionized water, and after drying, add the prepared solution;

[0012] S3, placing the reactor in a water bath, and after the temperature in the reactor is close to that in the water bath, a small amount of methane gas is charged into the reactor for purging, and the air in the reactor is exhausted by repeated purging;

[0013] S4. Fill with methane gas and stop the gas intake after the internal pressure reaches 5 MPa. At the same time, stir the solution at a stirring speed of 400 r / min.

[0014] The beneficial effects of the technical solution are as follows: the graphene oxide (GO) and sodium lignin sulfonate (SL) synergistic system promoter proposed by the present invention, in which SL is an amphiphilic surfactant, can effectively reduce the surface tension of the solution, with the maximum reduction of 31.11% compared with pure water. Adding nanoparticles GO to SL can effectively reduce the solution induction time, which can be reduced by 98.1% compared with pure water;

[0015] Under the working conditions of 277.15K and 5MPa, the 0.5g / L SL+0.05g / L GO system has good performance in induction time, T 100 、N 50 All three kinetic parameters are better than those of the 0.7 g / L SDS + 0.05 g / L GO system;

[0016] At 20°C, the SDS-GO system will produce abundant foam. However, the SL-GO system does not produce any foam and will not hinder the release of methane gas, which can effectively shorten the time required for the complete decomposition of hydrates.

[0017] Sodium lignin sulfonate (SL), whose raw material lignin is a renewable bioenergy, is extracted from waste liquid generated by recycling straw waste, so it is non-toxic and will not harm the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the experimental device of the present invention;

[0019] Figure 2Schematic diagram of the pressure change with time during the methane hydrate formation process of the SL-GO system under the conditions of 277.15K and 5MPa;

[0020] Figure 3 This is the morphology diagram of methane hydrate formation under the conditions of 277.15K and 5MPa;

[0021] Figure 4 is the surface tension diagram of SL-GO solutions with different concentrations at room temperature;

[0022] Figure 5 (a) The effect of different concentrations of SL-GO system on methane gas consumption; (b) The effect of different concentrations of SL-GO system on methane gas consumption rate;

[0023] Figure 6 (a) is the comparison of induction time between SL system and SL-GO system, (b) is the comparison of induction time between SDS system and SDS-GO system; (c) is the comparison of gas storage capacity between SL system and SL-GO system; (d) is the comparison of gas storage capacity between SDS system and SDS-GO system;

[0024] Figure 7 (a) Comparison of the time taken for complete hydrate formation between the SDS-GO system and the SL-GO system; (b) Comparison of the time taken for methane consumption to reach 50 mmol / mol between the SDS-GO system and the SL-GO system;

[0025] Figure 8 It is the hydrate decomposition morphology diagram of SDS-GO and SL-GO systems at 20℃;

[0026] Fig. 9 This is a comparison of the complete decomposition time of hydrates in SDS-GO and SL-GO systems at 20°C. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0028] Example:

[0029] 1. Experimental process

[0030] 1. Preparation of experimental materials. The names, molecular formulas, and purity of the materials required for the experiment are shown in Table 1:

[0031] Table 1 Experimental materials

[0032]

[0033] 2. Experimental Setup

[0034] Experimental setup Figure 1As shown, the device includes a data processing terminal, a data acquisition device, a constant temperature water bath, a refrigeration device, a reactor, a methane gas cylinder, a rotor and a temperature and pressure sensor. The methane gas is connected to the reactor through a gas valve. The temperature in the reactor is detected by gas phase and liquid phase temperature sensors and connected to the data acquisition device with an accuracy of 0.1K. The pressure is detected by a pressure sensor and connected to the data acquisition device with an accuracy of 0.0001MP. The refrigeration device on the left side of the water bath provides cooling capacity, and a circulation is formed through the water inlet and outlet valves to maintain a constant temperature of the water bath. The rotor in the reactor in the constant temperature water bath and the magnetic stirrer under the reactor are connected to the control device, and the data acquisition device detects and controls the rotation speed in the reactor.

[0035] 3. Experimental Methods

[0036] Because this experiment involves the decomposition of methane hydrate, methane hydrate will rapidly release heat during decomposition, causing the temperature to drop sharply. When the initial temperature is lower than 277.15K, the solution will freeze, affecting the decomposition of methane hydrate. Therefore, this experiment was carried out under moderate conditions of 277.15K and 5MPa. The experimental process is as follows:

[0037] (1) Different masses of GO, SDS, and SL were mixed with 50 ml of deionized water and then dispersed by ultrasound for 10 min to ensure that the nanoparticles and promoters were well dispersed in water.

[0038] (2) Rinse the reactor with deionized water for 3-4 times, wait for it to dry, add the prepared solution, put the reactor into a water bath, and when the temperature in the reactor is close to that of the constant temperature water bath (both reach 4°C), fill the reactor with a small amount of methane gas for purging. After purging 3-4 times, exhaust the air in the reactor, and then fill it with methane gas. When the pressure in the reactor reaches 5MPa, stop the air intake; at the same time, start the magnetic stirring through the reaction control device and stir the solution at a speed of 400r / min. Then turn on the data recording system and record the experimental data until the reaction is completed. Repeat the same group of experiments three times to eliminate errors.

[0039] (3) The GO concentration was kept constant at 0.05 g / L, and the SL concentration was changed. The SL concentration gradient was set to 0, 0.3, 0.5, 0.7, 1, and 1.5 g / L to determine the optimal SL concentration. The experiment was conducted in pure water as a control group. The other operations remained unchanged and steps (1) and (2) were repeated.

[0040] like Figure 2 The PT curve of hydrate in SL-GO system under 277.15K and 5MPa is shown. Figure 3 (af) are the morphological changes during the hydrate formation process. Figure 3 (a) is pure water control. At the beginning of the experiment, Figure 2 Stage I represents the gas dissolution period after the gas enters the reactor Figure 3 (b) and induction period, part of the gas dissolves in water, causing the pressure to slowly decrease. After the dissolution is completed, hydrate formation enters the induction period Figure 3 (c) The pressure first decreases slightly over time and then remains constant. Figure 2 In stage II, hydrate nucleation begins Figure 3 (d) Hydrate formation enters a rapid phase Figure 3 (e), hydrates are rapidly generated and reach a critical size, and the gas pressure in the reactor drops rapidly. Figure 2 In the middle III stage, the pressure and supercooling of the whole system are not enough to drive hydrate formation, and methane hydrate adheres to the inner wall of the reactor, and hydrate formation reaches the fugacity equilibrium state. Figure 3 (f) The system pressure tends to be stable and hydrate formation ends.

[0041] 2. Experimental Results Analysis

[0042] (1) Effect of SL-GO synergistic system on the kinetics of methane hydrate

[0043] As shown in Table 2, the induction time of different concentrations of SL in the synergistic growth of GO hydrate is summarized. The induction time in the table is the average and standard deviation of three experiments.

[0044] Table 2 Hydrate formation induction time in different synergistic systems

[0045]

[0046] This experiment uses pure water system as a control. From the perspective of kinetics, in pure water, the induction time of methane hydrate is about 276 minutes. When the concentration of SL increases to 0.7 g / L, the induction time is reduced to only 5 minutes, which is 98.1% less than the induction time of pure water. Figure 4 As shown in the figure, it is a surface tension diagram of SL-GO solutions with different concentrations at room temperature. It can be seen from the figure that the surface tension of SL-GO solution can be reduced to 48.65mN / m at the lowest. Compared with pure water, the surface tension reduction reaches 31.11%. When the SL concentration continues to increase to above 1g / L, the induction time increases to more than 100min, and the surface tension of the solution no longer continues to decrease. This is because the SL concentration is too high and exceeds the critical micelle concentration (CMC), which affects mass transfer and heat transfer, thereby reducing the promoter effect.

[0047] like Figure 5 The figure shows the changes of gas consumption and gas consumption rate with time during hydrate formation under different concentration conditions at 277.15K and 5MPa. Figure 5(a) It can be seen that the use of pure GO can improve the induction time of hydrates, but it cannot increase the gas consumption of methane. As the SL concentration gradually increases, the gas consumption also gradually increases, but the gas consumption is also limited by the SL concentration. In the 0.05g / L+0.7g / L synergistic system, the gas consumption is the largest, and the gas consumption increases by 180% compared with the pure water experiment. Figure 5 As can be seen in (b), after adding SL to the GO solution, the hydrate reaction rate has been significantly improved. After adding 0.3g / L and 0.5g / L SL, the reaction peak height increased to 0.0002mol / min and 0.00014mol / min, respectively, indicating that SL reduced the surface tension of the solution and significantly increased the reaction rate. After adding 0.7g / L SL, the maximum value of the hydrate reaction peak was 0.0006mol / min, and the reaction rate could reach 600% of the pure water system.

[0048] According to existing research, 0.7g / L SDS has the best hydration kinetics promotion effect under the conditions of 277.15K and 5MPa. Figure 6 The induction time and effective gas storage capacity of SL, SDS system, SL-GO and SDS-GO synergistic system were compared to further study the effect of SL-GO system on the kinetics of methane hydrate formation. Figure 6 As shown in (a) and (b), the induction time of the SL-GO system is 5 min, which is 61.53% lower than that of the SL system. The induction time of the SDS-GO system is 75.4 min, which is 59.15% lower than that of the SDS system. The induction time of the SL-GO system is 83.77% lower than that of the SDS-GO system, which indicates that the SL-GO system has a stronger ability to reduce the induction time of methane hydrate.

[0049] like Figure 6 As shown in (c) and (d), the gas storage capacity of the SDS-GO system is 80 V / V, which is only 4.37% higher than that of the SL-GO system. However, the gas storage capacity of the SL-GO system increased by 7.8% compared with the SL system, which is a more significant increase compared with the SDS system.

[0050] like Figure 7 (a) shows that the vertical axis T 100 It indicates the time required for complete formation of hydrates in the SL-GO system and the SDS-GO system under the conditions of 277.15K and 5MPa; Figure 7 (b) shows that the vertical axis N 50It indicates the time required for methane consumption to reach 50mmol / mol. As can be seen from the figure, the SL-GO system hydrates are completely generated in only 340.6min, which is 60.95% less than the SDS-GO system. The time required for methane consumption in the SL-GO system to reach 50mmol / mol is 97.5min, which is 30.18% less than the SDS-GO system. Figure 6 and Figure 7 It can be seen that the SL-GO system is superior to the SDS-GO system in all other kinetic properties except that it is slightly inferior to the SDS-GO system in effective gas storage capacity.

[0051] (2) Effect of SL-GO system on methane hydrate decomposition ability at 20 °C

[0052] like Figure 8 Shown is the decomposition morphology of the SL-GO system and the SDS-GO system at 20°C. It can be seen from the figure that the SDS-GO system will produce a large amount of foam during decomposition, while the SL-GO system will produce almost no foam during decomposition.

[0053] like Fig. 9 As shown, the time required for complete decomposition of methane hydrate in the two systems at 20°C, among which the time required for complete decomposition of methane hydrate in the SL-GO system is 234 minutes, which is 61% less than that in the SDS-GO system.

[0054] Combination Figure 8 and Fig. 9 , the foam generated by the SDS-GO system during decomposition will inhibit the release of methane gas in the hydrate, resulting in difficulty in the release of methane gas.

[0055] In summary, the SL-GO synergistic system promoter of the present invention can effectively reduce the surface tension of the solution, thereby effectively reducing the induction time of the solution; at the same time, under the conditions of 277.15K and 5MPa, the 0.7g / L SL+0.05g / L GO system is superior to the 0.7g / L SDS+0.05g / L GO system in terms of the three kinetic parameters of induction time, T100, and N50, indicating that the 0.7g / L SL+0.05g / L GO system is a better synergistic promoter that can effectively improve the kinetic characteristics of hydrate formation; at 20°C, the SDS-GO system will produce abundant foam, and the SL-GO system will not produce foam and will not hinder the release of methane gas, which can effectively shorten the complete decomposition time of hydrates; at the same time, the raw material lignin of SL is a renewable bioenergy, which is extracted from the waste liquid generated by the recycling of straw waste, so it is non-toxic and will not cause harm to the environment.

[0056] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A promoter for the synthesis and decomposition of methane hydrate, characterized in that: It includes a synergistic system of graphene oxide and sodium lignin sulfonate. The molecular formula of graphene oxide is C6O 11 (OH)2, sodium lignin sulfonate, its molecular formula is C 20 H 24 Na2O 10 S2.

2. The accelerator for methane hydrate synthesis and decomposition process according to claim 1, characterized in that: When the synergistic system promoter is applied under the working conditions of 277.15K and 5MPa, the concentration of sodium lignin sulfate is 0.7g / L and the concentration of graphene oxide is 0.05g / L.

3. The accelerator for methane hydrate synthesis and decomposition process according to claim 1, characterized in that: The promoter is applied to the methane hydrate synthesis process and the methane hydrate decomposition process.

4. A method for synthesizing methane hydrate using a promoter for the synthesis and decomposition of methane hydrate according to any one of claims 1 to 2, comprising the following steps: S1, preparing a mixed solution of graphene oxide, sodium lignin sulfonate and deionized water and then dispersing it by ultrasonication; S2. Rinse the reactor with deionized water, and after drying, add the prepared solution; S3, placing the reactor in a water bath, and after the temperature in the reactor is close to that in the water bath, a small amount of methane gas is charged into the reactor for purging, and the air in the reactor is exhausted by repeated purging; S4. Fill with methane gas and stop the gas intake after the internal pressure reaches 5 MPa. At the same time, stir the solution at a stirring speed of 400 r / min.

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