Gas hydrate generation method

Abstract

To provide a gas hydrate that can be repeatedly generated by a simple technique, and a generation method therefor.SOLUTION: A gas hydrate comprises an ice block of amino acids with a frozen amino acid solution comprising hydrophobic amino acids, the ice block of amino acids comprising an inclusion gas incorporated thereinto. The amino acid solution may have a level of hydrophobic amino acids of 0.01 wt.%-1.0 wt.%. The hydrophobic amino acids may be L-tryptophan or L-leucine. The inclusion gas may be methane or carbon dioxide.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas hydrate. To It relates to a synthesis method. [Background technology]

[0002] In recent years, gas hydrates that incorporate gas molecules of methane gas or carbon dioxide gas have been attracting attention. Gas hydrates can stably hold up to 164 times their own volume inside and can be easily decomposed by decompression or heat stimulation, making them suitable for transporting, storing, and supplying gas. Therefore, development of a method for generating gas hydrates using simple procedures is being promoted. For example, Patent Document 1 discloses a method for generating carbon dioxide gas hydrate by putting powdered ice into a pressure vessel in a thermostatic bath and mixing the powdered ice with carbon dioxide gas under pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-132664 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the method of Patent Document 1, powdered ice having a fine particle size on the order of micrometers is used, so that the production of powdered ice requires a lot of time and effort. In addition, since the powdered ice needs to be handled carefully in a low-temperature room so as not to melt, it is not suitable for the repeated production of carbon dioxide gas hydrate, and mass production of gas hydrate at an actual production site is technically difficult. Moreover, such problems are not limited to the production of carbon dioxide gas hydrate, but also exist in the production of other gas hydrates.

[0005] The present invention has been made based on the above background, and provides a method for producing gas hydrates that can be repeatedly produced by a simple method. To The object of the present invention is to provide a method for producing the same. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention 1 The gas hydrate generating method according to the above aspect comprises: a step of placing an amino acid ice block obtained by freezing an amino acid aqueous solution containing a hydrophobic amino acid in a pressure vessel and cooling the ice block to -3°C or lower, and pressurizing the clathrate gas in the pressure vessel; a step of heating the amino acid ice block to a melting point or higher while the clathrate gas is pressurized in the pressure vessel, and maintaining the state in which the amino acid ice block is at or above the melting point for a certain period of time, thereby melting all or a part of the amino acid ice block; Includes.

[0011] In order to achieve the above object, the present invention 2 The gas hydrate generating method according to the above aspect comprises: a step of storing an amino acid ice block obtained by freezing an amino acid aqueous solution containing a hydrophobic amino acid in a pressure vessel, pressurizing an inclusion gas in the pressure vessel and heating the amino acid ice block to a melting point or higher; a step of pressurizing the clathrate gas in the pressure vessel and maintaining the amino acid ice block at a temperature equal to or higher than the melting point for a certain period of time, thereby melting all or a part of the amino acid ice block; Includes.

[0012] introducing the amino acid aqueous solution into the pressure vessel; The amino acid aqueous solution introduced into the pressure vessel is frozen. The amino acid ice block is then formed in the pressure vessel. and cooling the aqueous amino acid solution so as to obtain a solution containing the amino acid.

[0013] cooling the amino acid aqueous solution in such a manner that the amino acid ice blocks melt and the resulting amino acid aqueous solution is frozen while the clathrate gas is pressurized in the pressure vessel; The method may further include a step of reducing the pressure of the clathrate gas in the pressure vessel to atmospheric pressure while keeping the amino acid ice block obtained by freezing the amino acid aqueous solution cold. The concentration of the hydrophobic amino acid in the aqueous amino acid solution may be within the range of 0.01 wt % to 1.0 wt %. The hydrophobic amino acid may be tryptophan or leucine. The clathrate gas may be methane gas or carbon dioxide gas. Effect of the Invention

[0014] According to the present invention, a gas hydrate can be repeatedly generated by a simple method. To A method for forming the same can be provided. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of a gas hydrate production system according to an embodiment of the present invention. [Diagram 2] 1 is a flowchart showing a flow of a method for producing gas hydrate according to an embodiment of the present invention. [Diagram 3] 1 is a graph showing equilibrium curves and liquefaction curves of methane hydrate and carbon dioxide hydrate. [Figure 4] 1 is a graph showing the results of Raman analysis of the L-tryptophan ice block in Example 1. [Diagram 5] 1 is a graph showing the results of Raman analysis of L-leucine ice blocks in Example 1. [Figure 6] 1 is a graph showing the flow of production and decomposition of methane hydrate using an aqueous L-tryptophan solution in Example 3. [Figure 7] 1 is a graph showing the flow of production and decomposition of carbon dioxide hydrate using an aqueous L-tryptophan solution in Example 3. [Figure 8] 1 is a graph showing the flow of production and decomposition of methane hydrate in ultrapure water in Example 3. [Figure 9] 1 is a graph showing the flow of production and decomposition of methane hydrate using an aqueous L-tryptophan solution in Example 4. [Figure 10] 1 is a graph showing the flow of production and decomposition of carbon dioxide hydrate using an aqueous L-tryptophan solution in Example 4. [Figure 11] 1 is a graph showing the flow of production and decomposition of methane hydrate using an aqueous L-tryptophan solution in Example 5. [Figure 12] 1 is a graph showing the flow of production and decomposition of carbon dioxide hydrate using an aqueous L-tryptophan solution in Example 5. [Figure 13] 1 is a graph showing the flow of production and decomposition of methane hydrate using an aqueous L-tryptophan solution in Example 6. [Figure 14] 1 is a graph showing the flow of production and decomposition of carbon dioxide hydrate using an aqueous L-tryptophan solution in Example 6. [Figure 15] 1 is a graph showing the production and decomposition of methane hydrate using an aqueous L-tryptophan solution in Example 7. [Figure 16] 1 is a graph showing the production and decomposition of methane hydrate using an aqueous L-leucine solution in Example 7. [Figure 17] 1 is a graph showing the production and decomposition of carbon dioxide hydrate using an aqueous L-tryptophan solution in Example 7. [Figure 18] 1 is a graph showing the production and decomposition of carbon dioxide hydrate using an aqueous L-leucine solution in Example 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a gas hydrate and a method for producing the same according to embodiments of the present invention will be described in detail with reference to the drawings.

[0017] Gas hydrates are gas clathrate hydrates in which a polyhedral cage consisting of multiple water molecules bound by hydrogen bonds encases a gas molecule (guest molecule), and multiple polyhedra share faces with each other to form a crystal lattice. Gas hydrates are classified into structure I, which incorporates clathrate gases such as methane gas and carbon dioxide, structure II, which incorporates clathrate gases such as propane gas, nitrogen, and oxygen, and structure H, which is formed under special conditions.

[0018] The crystal lattice of structure I is a cubic system consisting of two dodecahedrons (S cages) and six tetradecahedrons (M cages). The crystal lattice of structure II is a cubic system consisting of 16 dodecahedrons (S1 cages) and eight hexahedrons (L cages). The crystal lattice of structure H is a hexagonal system consisting of three dodecahedrons (S1 cages), two dodecahedrons of different shapes (S2 cages), and one icosahedron (LL cage). When the clathrate gas is a single gas, the structure of the gas hydrate is determined by the gas molecules that are clathrated in the cages. On the other hand, when the clathrate gas is a mixed gas, the structure of the gas hydrate may change from structure I to structure II when the concentration ratio of the mixed gas changes.

[0019] The gas hydrate according to the embodiment is a gas hydrate in which gas molecules of an inclusion gas are incorporated into ice blocks (amino acid ice blocks) obtained by freezing an amino acid aqueous solution containing a hydrophobic amino acid. The particle size of the ice blocks is arbitrary, but considering the ease of handling and processing, it is preferable that the size is at least 1 mm or more. The particle size may be calculated, for example, by converting an irregularly shaped granular body into a regular shaped granular body (for example, a circle or a sphere) based on a quantity that can be directly measured as the size of the granular body (for example, a projected area, a volume).

[0020] The hydrophobic amino acid added to the amino acid aqueous solution promotes the hydrate formation reaction in the amino acid aqueous solution or the amino acid ice block. The hydrophobic amino acid is a type of neutral amino acid. The neutral amino acid is an amino acid other than an acidic amino acid and a basic amino acid, in other words, an amino acid having a carboxyl group and a functional group other than an amino acid. The hydrophobic amino acid is also a type of non-polar side chain amino acid. Unlike the polar charged side chain amino acid and the polar uncharged side chain amino acid, the non-polar side chain amino acid is an amino acid that does not have polarity.

[0021] Hydrophobic amino acids are highly hydrophobic amino acids and have the property of strengthening the local tissue of the structure composed of water molecules. Specifically, a hydrophobic hydration shell (shell of water molecules) is formed on the hydrophobic group of the amino acid in the amino acid aqueous solution, and the carboxyl group of the amino acid forms a hydrogen bond network. Even though the amino acid is hydrophobic, it is water-soluble, so it is thought that the hydrophobic hydration shell of the hydrophobic group and the hydrogen bond network of the carboxyl group promote the hydrate formation reaction during hydrate formation. Note that a hydrophobic hydration shell is also formed on the alkyl group of the alcohol (R-OH), and the hydroxyl group of the alcohol also forms a hydrogen bond network, but since alcohol has the property of not dissolving in water when the alkyl group becomes long, it does not promote the hydrate formation reaction.

[0022] The hydrophobic amino acids include paraffinic hydrophobic amino acids and aromatic hydrophobic amino acids. Examples of paraffinic hydrophobic amino acids are valine, leucine, isoleucine, methionine, alanine, proline, and glycine. Examples of aromatic amino acids are phenylalanine, tyrosine, tryptophan, and histidine. Tryptophan, methionine, phenylalanine, valine, leucine, and isoleucine are all known as essential amino acids for humans, and since they are naturally decomposed in the environment, they do not adversely affect the human body or the environment, and are suitable as hydrophobic amino acids to be contained in the amino acid aqueous solution. As the hydrophobic amino acid to be contained in the amino acid aqueous solution, tryptophan or leucine is particularly preferred.

[0023] Amino acids are classified into two optical isomers, L-type and D-type, due to differences in configuration. However, the hydrophobic amino acids contained in an aqueous amino acid solution can be either L-type or D-type. However, since only L-type exists in nature, it is preferable to use L-type considering the costs associated with acquisition and disposal.

[0024] Regarding the concentration of amino acids contained in the aqueous amino acid solution, it may be set in consideration of the solubility of amino acids in water and the promoting effect of the hydrate formation reaction. If the concentration of amino acids is too high, amino acids will precipitate from the aqueous amino acid solution during cooling and freezing of the aqueous amino acid solution or during the hydrate formation reaction. On the other hand, if the concentration of amino acids is too low, the hydrate formation reaction will not proceed sufficiently. The concentration of amino acids is preferably, for example, in the range of 0.01 wt% to 1.0 wt%. However, since the hydrate formation reaction tends to be promoted more easily when the concentration is relatively low, it is more preferably 0.01 wt% to 0.5 wt%.

[0025] The concentration of amino acids is preferably optimized for each type of amino acid. For example, in the case of tryptophan, it is preferably in the range of 0.01 wt% to 1.0 wt%. Also, in the case of leucine, it is preferably in the range of 0.1 wt% to 1.0 wt%.

[0026] After the gas hydrate containing hydrophobic amino acids releases the enclathrated gas, it can be returned to the frozen state again, and by going through the same steps as during the gas hydrate formation reaction, the gas hydrate formation reaction can proceed again. According to repeated experiments by the inventor, it has been confirmed that an aqueous amino acid solution containing hydrophobic amino acids can cause the hydrate formation reaction again even if it repeats the uptake and release of the enclathrated gas for more than half a year. Moreover, even if an enclathrated gas different from that used during the previous gas hydrate formation reaction is used, the hydrate formation reaction can proceed again. Therefore, by repeating the formation and decomposition of gas hydrates while keeping the aqueous amino acid solution in a pressure vessel, the uptake and extraction of any enclathrated gas can be performed at any timing.

[0027] (Generation System) Next, referring to FIG. 1, a gas hydrate production system 1 according to an embodiment will be described. The production system 1 is an apparatus that promotes a gas hydrate production reaction by increasing the temperature of amino acid ice blocks in a gas-pressurized state, and produces gas hydrate from amino acid ice blocks. The production system 1 includes a pressure vessel 10, a thermostatic chamber 20 that houses the pressure vessel 10 therein, and a gas supply source 30 that is connected to the pressure vessel 10 and supplies clathrate gas into the pressure vessel 10. The pressure vessel 10 and the gas supply source 30 are connected via a pipe 40 that can flow the clathrate gas. In addition, a pipe 50 that can release the clathrate gas in the pressure vessel 10 to the outside is connected to the pressure vessel 10.

[0028] The pressure vessel 10 is a vessel capable of storing an amino acid aqueous solution or amino acid ice blocks inside when pressurized by the clathrate gas. The pressure vessel 10 comprises a main body 11 having a circular cross section with an opening on the top surface thereof and storing an amino acid aqueous solution or amino acid ice blocks inside, and a disk-shaped lid 12 attached to the top surface of the main body 11 and having a bottom surface thereof in close contact with the top surface of the main body 11. A Teflon (registered trademark) packing (not shown) is disposed between the top surface of the main body 11 and the bottom surface of the lid 12 to prevent the clathrate gas from leaking to the outside. The lid 12 is provided with a temperature sensor 13 for measuring the temperature of the amino acid aqueous solution or amino acid ice blocks inside the pressure vessel 10, and is connected to the ends of the pipes 40 and 50.

[0029] The thermostatic bath 20 is a device that houses the pressure vessel 10 therein and maintains a constant liquid temperature of the medium in the bath, thereby maintaining a constant temperature of the pressure vessel 10. The thermostatic bath 20 is an example of a temperature adjustment means for adjusting the temperature of the amino acid aqueous solution or amino acid ice blocks in the pressure vessel 10. The thermostatic bath 20 includes a temperature sensor 21 that measures the temperature of the internal medium, a cooler (not shown) that cools the internal medium based on the measurement result of the temperature sensor 21, and a heater (not shown) that heats the internal medium.

[0030] The gas supply source 30 is an example of a gas supply means that is connected to the pressure vessel 10 via piping 40 and supplies the clathrate gas at an adjusted pressure to the inside of the pressure vessel 10. The gas supply source 30 includes a gas cylinder 31 and a pressure regulator 32 that is connected to the gas cylinder 31 and adjusts the pressure of the clathrate gas supplied from the gas cylinder 31 and releases it toward the pressure vessel 10.

[0031] Pipe 40 connects gas supply source 30 and pressure vessel 10. Pipe 40 is provided with a pressure sensor 41 for measuring the pressure of the clathrate gas flowing toward pressure vessel 10, and a flow sensor 42 for measuring the flow rate of the clathrate gas flowing toward pressure vessel 10. Flow sensor 42 is connected to a flow integrator 43 for integrating the total flow rate of the clathrate gas that has passed through flow sensor 42 from the start of measurement. Valves 44 that can be manually opened and closed are provided between pressure sensor 41 and flow sensor 42, and between flow sensor 42 and pressure regulator 32.

[0032] The piping 50 connects the internal space of the pressure vessel 10 with the external space. The piping 50 is provided with a gas volume measuring device 51 that measures the volume of the clathrate gas released from the pressure vessel 10. The gas volume measuring device 51 is, for example, a graduated cylinder, and is used to measure the volume of the clathrate gas generated within the pressure vessel 10 when the gas hydrate is decomposed within the pressure vessel 10. A manually openable valve 52 is provided between the lid 12 and the gas volume measuring device 51 to control the release of the clathrate gas to the outside.

[0033] The computer 60 is communicatively connected to the temperature sensors 13, 21, the pressure sensor 41, the flow sensor 42, and the flow integrator 43, acquires various measurement data, and displays the various measurement data on the display of the computer 60. The user monitors the measurement data from the various sensors displayed on the computer 60, and operates the cooler and heater of the thermostatic bath 20 and the pressure regulator 32 according to the procedure shown in FIG. The above is the configuration of the generation system 1.

[0034] (Generation method) Hereinafter, the flow of the method for producing gas hydrate using the production system 1 according to the embodiment will be described with reference to the flowchart in Fig. 2. Before starting the production of gas hydrate, an amino acid aqueous solution containing a hydrophobic amino acid and a gas cylinder 31 for storing an encapsulated gas are prepared. The concentration of the hydrophobic amino acid contained in the amino acid aqueous solution is, for example, 0.01 wt% to 1.0 wt%. At this point, both valves 44 and 52 of the production system 1 are kept closed.

[0035] First, an aqueous amino acid solution containing a hydrophobic amino acid is charged into the pressure vessel 10 (step S1: charging step). After the aqueous amino acid solution is charged, the lid 12 is attached to the main body 11 of the pressure vessel 10.

[0036] Next, the clathrate gas is supplied from the gas supply source 30 to the pressure vessel 10, and the air in the pressure vessel 10 is replaced with the clathrate gas (step S2: replacement step). Specifically, the valve 44 is opened, and the gas cylinder 31 and the pressure regulator 32 are operated so that the gas is released toward the pressure vessel 10. At the time of step S2, the clathrate gas in the pressure vessel 10 is not pressurized, and the pressure of the clathrate gas is the same as atmospheric pressure.

[0037] Next, the amino acid aqueous solution in the pressure vessel 10 is frozen to create an amino acid ice block, and the temperature of the created amino acid ice block is cooled to a first set temperature (step S3: cooling step). To freeze the amino acid aqueous solution and cool the amino acid ice block, the cooler of the thermostatic bath 20 may be operated. The first set temperature is a temperature at which the hydrate production reaction does not proceed in the pressurization step described below, and is preferably set to -3°C or lower. Furthermore, in consideration of the cooling performance and power consumption of the thermostatic bath 20, the first set temperature is preferably within the range of -3°C to -30°C, and more preferably within the range of -3°C to -5°C. Note that the amino acid aqueous solution does not freeze when cooled to about -3°C, and the freezing proceeds through supercooling release. For this reason, when freezing the amino acid aqueous solution, after supercooling release, it is cooled to a cooling set temperature that is a temperature suitable for completing the freezing of the amino acid ice block. The cooling set temperature is lower than the first set temperature, and is preferably -25°C when the clathrate gas is methane gas, and -18°C when the clathrate gas is carbon dioxide gas.

[0038] Next, while maintaining the temperature of the amino acid ice block at the first set temperature, the clathrate gas is pressurized to a set pressure (step S4: pressurization step). To pressurize the clathrate gas, the pressure regulator 32 may be operated to be further opened. The set pressure is set so that the hydrate production reaction proceeds in the amino acid ice block or the amino acid aqueous solution at the second set temperature described below, and is at least 1.033 kg / cm. 2 (atmospheric pressure), e.g. 10 kg / cm 2 ~100kg / cm 2 It is preferable that the set pressure is within the range of 100° C. to 150° C. Specifically, it is more preferable that the set pressure is set to about twice the equilibrium pressure at the second set temperature. The equilibrium pressure is a pressure at which the rate at which the clathrate gas is taken up into the amino acid ice block or the amino acid aqueous solution matches the rate at which the clathrate gas is released from the amino acid ice block or the amino acid aqueous solution. In the pressurizing step, the amino acid ice block is set to the first set temperature at which the hydrate formation reaction does not proceed, so that the hydrate formation reaction does not proceed.

[0039] Next, with the clathrate gas pressurized, the amino acid aqueous solution is heated so that the temperature of the amino acid ice blocks becomes the second set temperature, and the state in which the pressure of the clathrate gas and the temperature of the amino acid ice blocks are the set pressure and the second set temperature, respectively, are maintained for a certain period of time (step S5: heating step). To heat the amino acid aqueous solution, the heater of the thermostatic bath 20 may be operated. The second set temperature is set so that the hydrate production reaction proceeds simultaneously with the melting of the amino acid ice blocks. Specifically, the second set temperature is the temperature at which the amino acid ice blocks melt under pressure by the clathrate gas (a temperature above the melting point), and is at least 0°C or higher, preferably 1°C or higher, and more preferably within the range of 1°C to 5°C.

[0040] In the heating step, the gas hydrate generation reaction proceeds at the same time as the amino acid ice blocks melt. The hydrate generation reaction is an exothermic reaction, and the heat generated by the hydrate generation reaction promotes the melting of the amino acid ice blocks, but the temperature rise in the pressure vessel 10 is suppressed by the melting of the amino acid ice blocks. In the heating step, the hydrate generation reaction proceeds at the same time as the amino acid ice blocks melt, and the hydrate generation reaction proceeds by dissolving the clathrate gas in the amino acid water obtained by melting the amino acid ice blocks. When the amino acid ice blocks are completely melted, the temperature of the amino acid aqueous solution obtained by melting rises rapidly to the equilibrium pressure temperature under the pressurized conditions due to an exothermic reaction. The temperature rise is limited to the equilibrium pressure temperature under the pressurized conditions because if the temperature rises above the equilibrium pressure temperature, the generated hydrate decomposes and the temperature drops. The temperature of the gas hydrate then drops to the second set temperature. If all of the amino acid ice blocks have not been converted to gas hydrate at the end of the heating step, the amino acid aqueous solution without gas hydrate is left in the pressure vessel 10. Whether the hydrate production reaction is progressing can be determined by measuring the flow rate of the clathrate gas flowing from the gas cylinder 31 toward the pressure vessel 10 with a flow sensor 42 and confirming whether the clathrate gas is being taken into the pressure vessel 10.

[0041] The time required for the gas hydrate production reaction can be specified as the time from the start of the gas hydrate production reaction to the stop of the supply of the clathrate gas to the pressure vessel 10 (production reaction time). However, even if the supply of the clathrate gas from the gas cylinder 31 is stopped, the gas hydrate production reaction continues to proceed until the process of step S6 described later is performed, and cannot be stopped manually. The production reaction time may be set so that the gas hydrate production reaction proceeds sufficiently, taking into consideration the pressure of the clathrate gas in the pressure vessel 10, the amount and temperature of the amino acid ice blocks, and the contact area between the ice blocks and the clathrate gas, and may be, for example, about 30 minutes or about half a day.

[0042] The relationship between the set pressure and the second set temperature will be described below with reference to FIG. 3. In FIG. 3, the vertical axis is pressure and the horizontal axis is temperature. Referring to the specific example in FIG. 3, curves (equilibrium curves) showing that methane hydrate and carbon dioxide hydrate are in an equilibrium state are respectively illustrated. The equilibrium curves are curves on which the above-mentioned equilibrium pressures are plotted. If the pressure and temperature are set to the left of these equilibrium curves, decomposition of the gas hydrate will not proceed, so the set pressure and the second set temperature are set to the left of the equilibrium curves.

[0043] FIG. 3 also shows a liquefaction curve for carbon dioxide. When the pressure and temperature are set to the left of the liquefaction curve, carbon dioxide liquefies. When the liquefied carbon dioxide comes into contact with the aqueous amino acid solution, the hydrate production reaction is hindered, so the set pressure is set so that carbon dioxide does not liquefy in step S6, which will be described later. For this reason, the set pressure and the second set temperature may be selected from the region between the equilibrium curve and the liquefaction curve. Note that the liquefaction curve for methane is not shown because methane does not liquefy in the temperature and pressure regions shown in FIG. 3.

[0044] To explain this in more detail with reference to FIG. 3, for example, in methane hydrate, the equilibrium pressure at a temperature of 1°C is 28 kg / cm 2 Therefore, the set pressure during the hydrate formation reaction is 50 kg / cm at a temperature of 1°C. 2On the other hand, for carbon dioxide hydrate, the equilibrium pressure is 14 kg / cm at a temperature of 1°C. 2 Therefore, the set pressure during the hydrate formation reaction is, for example, 28 kg / cm at a temperature of 1°C. 2 However, as can be seen from Figure 3, if the temperature is cooled to around -18°C under these conditions, the carbon dioxide gas will liquefy, so the set pressure during the hydrate formation reaction should be 20 kg / cm at a temperature of 1°C. 2 The following settings may be used: Note that the pressurization conditions (pressure increase conditions) under which pressurization with the clathrate gas is started in FIG.

[0045] Next, the supply of the clathrate gas from the gas supply source 30 is stopped, and the amino acid aqueous solution in which the gas hydrate production reaction has progressed is cooled to a first set temperature and frozen while maintaining the state pressurized by the clathrate gas (step S6: second cooling step). This changes the amino acid aqueous solution into amino acid ice blocks, and a self-preserving effect is exhibited. The first set temperature is set so that not only the amino acid aqueous solution under atmospheric pressure but also the amino acid aqueous solution pressurized by the clathrate gas is frozen.

[0046] Next, while maintaining the first set temperature, the pressure inside the pressure vessel 10 is reduced from the state pressurized by the clathrate gas to atmospheric pressure (step S7: decompression step). Since gas hydrate has a self-preserving effect, it hardly decomposes even at atmospheric pressure as long as it is kept in a cooled state. For this reason, gas hydrate is suitable for storing and transporting clathrate gas. The above is the flow of the method for producing gas hydrate.

[0047] Thereafter, to extract the clathrate gas from the gas hydrate, for example, the lid 12 is removed from the body 11 of the pressure vessel 10 to remove the gas hydrate, which is then stored in a freezer while being cooled, and decomposed at a desired time. The aqueous amino acid solution remaining after the clathrate gas has been extracted can be returned to the pressure vessel 10 and used to generate gas hydrate. To generate gas hydrate again in this procedure, step S1 can be omitted from the above-mentioned gas hydrate generation method.

[0048] In addition, to extract the clathrate gas from the gas hydrate, the gas hydrate is stored or transported in the pressure vessel 10 while being cooled under atmospheric pressure, and the gas hydrate is heated by operating the thermostatic bath 20 at a desired timing to decompose the gas hydrate in the pressure vessel 10. At this time, the valve 52 is opened to release the clathrate gas generated in the pressure vessel 10 to the outside. When the gas hydrate is decomposed in the pressure vessel 10, the amino acid aqueous solution is left as it is in the pressure vessel 10. The amino acid aqueous solution and the clathrate gas left in the pressure vessel 10 can be used to generate gas hydrate. In this procedure, to generate gas hydrate again, the steps S1 and S2 of the above-mentioned gas hydrate generation method can be omitted.

[0049] As described above, the gas hydrate according to the embodiment uses an amino acid aqueous solution containing a hydrophobic amino acid, and can be easily produced by simply heating an amino acid ice block made by freezing the amino acid aqueous solution under pressure with an inclusion gas.

[0050] In addition, since the gas hydrate according to the embodiment uses an amino acid aqueous solution containing a hydrophobic amino acid, the gas hydrate production reaction can be repeatedly induced in pressure vessel 10 even after the gas hydrate is decomposed. Therefore, there is no need to repeatedly remove the gas hydrate from pressure vessel 10 or introduce the amino acid aqueous solution into pressure vessel 10, which reduces the costs required for transporting and storing the clathrate gas.

[0051] The gas hydrate according to the embodiment does not require additives such as surfactants derived from petroleum. Therefore, foaming does not occur during decomposition, and the encapsulated gas is easily extracted during decomposition of the gas hydrate. In addition, since no substances that have a negative effect on the environment are used, there is no risk of placing a burden on the environment, and disposal after use is easy.

[0052] The present invention is not limited to the above-described embodiment, and the following modifications are possible.

[0053] (Modification) In the above embodiment, the temperature of the amino acid aqueous solution and the amino acid ice blocks are set to the first or second set temperature, and the pressure of the clathrate gas is set to the set pressure, but the present invention is not limited to this. The temperature of the amino acid aqueous solution and the amino acid ice blocks may fluctuate within a certain range including the first or second set temperature. Also, the pressure of the clathrate gas may fluctuate within a certain range including the set pressure.

[0054] In the above embodiment, the process includes a step of pressurizing the clathrate gas (step S4), a step of heating the amino acid ice blocks to above its melting point while the clathrate gas is pressurized, and a step of maintaining the amino acid ice blocks heated to above its melting point for a certain period of time (step S5), but the present invention is not limited to this. For example, in the process of step S4, the temperature of the amino acid ice blocks may be raised to, for example, -3°C within a range in which the amino acid ice blocks do not melt.

[0055] The method may further include a step of pressurizing the clathrate gas and heating the amino acid ice blocks to above its melting point, and a step of maintaining the state in which the clathrate gas is pressurized and the amino acid ice blocks are heated to above its melting point for a certain period of time. In this case, the hydrate production reaction also proceeds in the step of pressurizing the clathrate gas and heating the amino acid ice blocks to above its melting point.

[0056] In the above embodiment, the amino acid aqueous solution is cooled to the same temperature in the process of step S3 and the process of step S6 shown in Fig. 2, but the present invention is not limited to this. For example, the temperatures in the process of step S3 and the process of step S6 shown in Fig. 2 may be different from each other as long as the temperatures are such that the amino acid aqueous solution freezes.

[0057] In the above embodiment, the amino acid aqueous solution is frozen in the pressure vessel 10, but the present invention is not limited to this. For example, amino acid ice blocks may be generated in advance in an ice maker and then charged into the pressure vessel 10, thereby omitting the process of step S1 shown in FIG. 2. The amino acid ice block may be a single block that matches the shape of the internal space of the pressure vessel 10, or may be a number of bulk pieces of ice. In the latter case, the contact area between each amino acid ice block and the clathrate gas increases, thereby improving the reaction rate and production yield of the gas hydrate production reaction.

[0058] In the above embodiment, the lid 12 of the pressure vessel 10 is removed from the body 11, the amino acid aqueous solution is injected into the body 11, and then the body 11 is sealed with the lid 12, but the present invention is not limited to this. The pressure vessel 10 may have any configuration as long as it is possible to pressurize the clathrate gas inside the pressure vessel 10. In addition, piping and a valve for injecting the amino acid aqueous solution may be connected to the body 11 or the lid 12 of the pressure vessel 10. This eliminates the need to remove or attach the lid 12 when injecting the amino acid aqueous solution.

[0059] In the above embodiment, the pressure vessel 10 is placed inside the thermostatic bath 20 to maintain the temperature of the pressure vessel 10, but the present invention is not limited to this. Other temperature adjustment means may be provided as long as the temperature of the pressure vessel 10 can be maintained constant. For example, the pressure vessel 10 may be configured to have a double structure consisting of an inner structure and an outer structure, and a medium may be circulated in the space between the inner structure and the outer structure, so that the amino acid aqueous solution or amino acid ice blocks in the pressure vessel 10 are maintained at a set temperature.

[0060] In the above embodiment, the user monitors each of the temperature sensors 13, 21, the pressure sensor 41, and the flow sensor 42, and manually adjusts the operation of the cooler and heater of the thermostatic bath 20 and the pressure regulator 32 based on the measurement results, but the present invention is not limited to this. The computer 60 may include a memory for storing a program and a processor for executing the program stored in the memory, and may control the operation of the cooler and heater of the thermostatic bath 20, the pressure regulator 32, and the valves 44, 52 of each of the pipes 40, 50 so as to sequentially execute the processes (gas hydrate generation process) of steps S1 to S7 shown in Fig. 2 based on the measurement results of each of the temperature sensors 13, 21, the pressure sensor 41, and the flow sensor 42. In this modification, the valves 44, 52 may be electromagnetic valves that can be opened and closed by an operation signal from the computer 60.

[0061] The flow of the gas hydrate generation process executed by the computer 60 will be described below. The process of step S1 in the gas hydrate generation process is executed manually, and then, when the computer 60 receives an instruction from the user, the computer 60 executes the processes of steps S2 to S7. First, the computer 60 opens the pressure regulator 32 and the valves 44 and 52 to allow the clathrate gas to flow into the pressure vessel 10, and when it detects that a certain amount of the clathrate gas has passed through the flow rate sensor 42, it closes the pressure regulator 32 and the valve 52 (step S2). Next, the computer 60 controls the cooler of the thermostatic chamber 20 based on the measurement data from the temperature sensor 13 so that the amino acid aqueous solution is at a first set temperature (step S3). Next, the computer 60 controls the pressure regulator 32 based on the measurement data from the pressure sensor 41 so that the pressure of the clathrate gas is at a set pressure (step S4). Next, the computer 60 continues to control the pressure regulator 32 so that the pressure of the clathrate gas becomes the set pressure based on the measurement data from the pressure sensor 41, and also controls the heater of the thermostatic bath 20 so that the amino acid ice block becomes the second set temperature based on the measurement data from the temperature sensor 13 (step S5). After a certain time has elapsed from the processing of step S5, the computer 60 controls the cooler of the thermostatic bath 20 so that the amino acid aqueous solution becomes the first set temperature based on the measurement data from the temperature sensor 13 (step S6). Next, when the temperature sensor 13 detects the first set temperature, the computer 60 closes the pressure regulator 32 and the valve 44 and opens the valve 52 (step S7). The above is the flow of the gas hydrate production process.

[0062] In the above embodiment, the production system 1 only produces gas hydrate, but the present invention is not limited to this. For example, the production system 1 may be configured to directly supply the clathrate gas obtained by decomposing the gas hydrate in the production system 1 to an external device that requires the clathrate gas, such as a combustion device, by connecting the end of the pipe 50.

[0063] In the above embodiment, the pressure vessel 10, the thermostatic bath 20, and the gas supply source 30 are constantly connected by the pipes 40, 50, but the present invention is not limited to this. For example, the pressure vessel 10 may be removed from the generation system 1, and the gas hydrate in the pressure vessel 10 may be stored and transported. If the pressure of the clathrate gas in the pressure vessel 10 is set to 10 kg or less, the pressure vessel 10 does not correspond to a high-pressure gas storage facility, so that the storage and transportation of the gas hydrate can be easily performed. In addition, the pressure vessel 10 and a cooling facility may be installed in a transportation vehicle, and the generation, transportation, decomposition, and regeneration of the gas hydrate may be realized at the transportation destination. Furthermore, the pressure vessel 10 after the gas is extracted from the gas hydrate may be placed in a storage facility capable of cooling the internal space, thereby generating amino acid block ice in the pressure vessel 10.

[0064] The above-mentioned embodiments are merely examples, and the present invention is not limited to these, and various embodiments are possible without departing from the spirit of the invention described in the claims. The components described in the embodiments and modifications can be freely combined. In addition, inventions equivalent to the inventions described in the claims are also included in the present invention.

[0065] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples.

[0066] Example 1 In Example 1, we verified whether the gas hydrate generation reaction proceeds in amino acid ice blocks. As the amino acid aqueous solutions, we used L-tryptophan aqueous solutions with concentrations of 0.01 wt%, 0.03 wt%, and 0.1%, and L-leucine aqueous solutions with concentrations of 0.1 wt%, 0.5 wt%, and 1.0 wt%. In addition, we used methane gas as the clathrate gas.

[0067] First, 40 ml of the amino acid aqueous solution was put into the pressure vessel 10, and the air in the pressure vessel 10 was replaced with methane gas. Next, the temperature was lowered from +20°C to -25°C to freeze the amino acid aqueous solution, and a lump of amino acid ice was created in the pressure vessel 10. Next, while maintaining the temperature of the amino acid ice block at -25°C, the gas pressure was increased to 50 kg / cm. 2 Next, the temperature of the amino acid ice block was changed from -25°C to 1°C, and the temperature was increased to 1°C and the pressure was increased to 50 kg / cm. 2 This state was continued overnight. In this process, methane hydrate was produced from the amino acid ice blocks. Next, the temperature of the amino acid aqueous solution was changed from 1°C to -25°C to freeze the methane hydrate. Next, while maintaining the temperature of the amino acid ice blocks at -25°C, the gas pressure was increased to 50kg / cm. 2 The pressure was then reduced to atmospheric pressure. Thereafter, the methane hydrate mass was taken out of the pressure vessel 10 and subjected to Raman analysis.

[0068] The results of Raman analysis are shown below. As shown in Figure 4, the presence of a crystal structure specific to structure I gas hydrate was confirmed in the amino acid ice block using an L-tryptophan aqueous solution with a concentration of 0.01 wt%. A high intensity in the Raman signal indicates a large cage, and a low intensity indicates a small cage. It was also confirmed that structure I methane hydrate was generated when an L-tryptophan aqueous solution with a concentration of 0.03% or 0.1% was used. In addition, as shown in Figure 5, the presence of a crystal structure specific to structure I gas hydrate was confirmed in the amino acid ice block using an L-leucine aqueous solution with a concentration of 0.1 wt%. It was also confirmed that structure I methane hydrate was generated when an L-leucine aqueous solution with a concentration of 0.5% or 1.0% was used.

[0069] In addition, to determine the structure of gas hydrate, methods other than Raman analysis can also be used. For example, after the completion of hydrate formation, the pressure of the enclathrated gas in the pressure vessel 10 is reduced below the gas hydrate equilibrium pressure. Then, the pressure of the enclathrated gas in the pressure vessel 10 increases and becomes constant at the equilibrium pressure of the gas hydrate. Next, when the temperature is increased step by step, the equilibrium pressures of the generated gas hydrates at each temperature can be sequentially obtained. By comparing these equilibrium pressures with the literature values, the structure of the gas hydrate can be determined.

[0070] (Example 2) In Example 2, it was verified whether the gas hydrate formation reaction proceeds even when carbon dioxide gas is used as the enclathrated gas. Methane hydrate and carbon dioxide hydrate were formed using an L-tryptophan aqueous solution with a concentration of 0.03 wt% as the amino acid aqueous solution, and the methane gas and carbon dioxide gas obtained by decomposing these gas hydrates were recovered. By calculating the recovery rate of each enclathrated gas, it was verified whether the gas hydrate formation reaction occurred. The recovery rate is the ratio of the actually measured recovery amount to the theoretical recovery amount, and can be calculated from the thermal decomposition pressure with reference to the calibration curve. The calibration curve may be created based on the measured values of the pressure and volume of the enclathrated gas obtained by repeatedly thermally decomposing the gas hydrate. The volume of the enclathrated gas may be measured with a gas volume measuring device 51 such as a graduated cylinder. For comparison, the same experiment was conducted using ultrapure water instead of the L-tryptophan aqueous solution, and the recovery rate of the recovered methane gas was calculated.

[0071] The conditions and procedures of the experiment were the same as those in Example 1 until the gas hydrate was formed. After that, while the gas hydrate was confined in the pressure vessel 10 under atmospheric pressure, the temperature of the gas hydrate was changed from -25°C to 20°C and completely decomposed. At this time, with the valve 44 of the pipe 40 closed, the valve 52 of the pipe 50 was opened, and the volume of each enclathrated gas was measured by recovering the generated gas with the gas volume measuring device 51. In the cooling process of methane hydrate, the pressurization conditions were the same as those in the case of Example 1 at a pressure of 50 kg / cm 2The temperature was set at -25°C, but in the cooling process of the carbon dioxide hydrate, the pressure was set at 20 kg / cm to prevent the carbon dioxide from liquefying. 2 The temperature was set to -18°C.

[0072] The experimental results are shown below. As shown in Figures 6 and 7, the pressure of the clathrate gas rose rapidly during thermal decomposition. When the recovery yield was calculated from the thermal decomposition pressure with reference to a calibration curve created in advance, the recovery yield of methane gas recovered from methane hydrate was 89%, while the recovery yield of carbon dioxide gas recovered from carbon dioxide hydrate was 84%. In both cases, a large amount of gas that cannot be dissolved in the amino acid aqueous solution was taken in, and it was determined that gas hydrate was generated. On the other hand, as shown in Figure 8, the pressure of the clathrate gas hardly rose during thermal decomposition. The recovery yield of methane gas recovered from ice blocks made by freezing ultrapure water was 2%. For this reason, it was determined that gas hydrate was not sufficiently generated in ultrapure water because the amount of gas recovered was small.

[0073] Example 3 In Example 3, it was verified whether the recovery yield of the clathrate gas would change when the amount of the amino acid aqueous solution put into the pressure vessel 10 was increased. An L-tryptophan aqueous solution with a concentration of 0.03 wt% was used as the amino acid aqueous solution, and carbon dioxide gas was used as the clathrate gas. The amount of the amino acid aqueous solution was 70 ml. The other experimental conditions were the same as in Example 2. When the generated gas hydrate was thermally decomposed, the recovery yield was 74%, and it was confirmed that there was almost no difference in the recovery yield when 40 ml of the amino acid aqueous solution was used. This is because, even if the thickness of the amino acid ice block obtained by cooling and freezing differs, the carbon dioxide gas only comes into contact with the upper surface of the amino acid ice block in the pressure vessel 10, and the contact area between the carbon dioxide gas and the amino acid ice block is constant even if the amount of the amino acid aqueous solution is increased or decreased.

[0074] Example 4 In Example 4, it was verified whether the gas hydrate production reaction would proceed even in amino acid ice blocks that had been left for a long period of time. 30 minutes, 15 hours, and 45 hours after freezing an aqueous solution of L-tryptophan with a concentration of 0.03 wt%, the amino acid ice blocks inside the pressure vessel 10 were pressurized with methane gas to raise the temperature. As a result, as shown in Figure 9, the pressure increased significantly during thermal decomposition under all conditions, confirming that methane hydrate was produced.

[0075] In addition, 30 minutes and 64 hours after freezing an aqueous solution of L-tryptophan with a concentration of 0.03 wt%, the amino acid ice block in the pressure vessel 10 was pressurized with carbon dioxide gas to raise the temperature. As a result, as shown in Figure 10, under all conditions, the pressure increased significantly during thermal decomposition, confirming that carbon dioxide hydrate was produced. When the temperature of the amino acid ice block was kept cooled to -18°C for 65 hours, the peak flow rate of the clathrate gas decreased, but no significant differences were observed in the convergence period of the hydrate production reaction or the recovery yield of the clathrate gas.

[0076] Example 5 In Example 5, it was verified whether the gas hydrate production reaction proceeds even when the temperature (first set temperature) at the time of cooling the amino acid aqueous solution is changed. An L-tryptophan aqueous solution with a concentration of 0.03 wt% was used as the amino acid aqueous solution, and methane gas was used as the clathrate gas. The first set temperatures were -25°C, -5°C, and -3°C, respectively. The other experimental conditions were the same as in Example 1. As a result, as shown in FIG. 11, the pressure increased significantly during thermal decomposition under all conditions, and it was confirmed that methane hydrate was produced. The recovery yields at the first set temperatures of -25°C, -5°C, and -3°C were 90%, 84%, and 91%, respectively. In addition, the clathrate gas was changed to carbon dioxide gas, the first set temperature was set to -18°C, -5°C, and -3°C, and the other conditions were the same as in Example 2. As a result, as shown in FIG. 12, the pressure increased significantly during thermal decomposition under all conditions, and it was confirmed that carbon dioxide hydrate was produced. The recovery yields at the first set temperatures of -18°C, -5°C, and -3°C were 84%, 85%, and 85%, respectively.

[0077] Example 6 In Example 6, it was verified whether the gas hydrate production reaction proceeds when the temperature (second set temperature) at which the amino acid ice block is heated is changed. An L-tryptophan aqueous solution with a concentration of 0.03 wt% was used as the amino acid aqueous solution, and methane gas was used as the clathrate gas. The second set temperatures were 1°C, 3°C, and 5°C, respectively. The other experimental conditions were the same as in Example 1. As a result, as shown in FIG. 13, the pressure increased significantly during thermal decomposition under all conditions, and it was confirmed that methane hydrate was produced. The recovery yields at the second set temperatures of 1°C, 3°C, and 5°C were 75%, 80%, and 59%, respectively. In addition, when the clathrate gas was replaced with carbon dioxide gas and the experiment was performed under the same conditions as in Example 2, it was confirmed that the pressure increased significantly during thermal decomposition under all conditions, and carbon dioxide hydrate was produced, as shown in FIG. 14. The recovery yields at the second set temperatures of 1°C, 3°C, and 5°C were 80%, 82%, and 79%, respectively.

[0078] Example 7 In Example 7, it was verified whether the gas hydrate production reaction proceeded when the concentration of the amino acid in the amino acid aqueous solution was changed. As the amino acid aqueous solution, L-tryptophan aqueous solutions with concentrations of 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.3 wt%, and 1.0 wt%, and L-leucine aqueous solutions with concentrations of 0.05 wt%, 0.1 wt%, and 0.3 wt%, were used. Methane gas was used as the clathrate gas. The other experimental conditions were the same as in Example 1.

[0079] The experimental results are shown below. As shown in Figures 15 and 16, the pressure increased significantly during thermal decomposition under all conditions, and it was confirmed that methane hydrate was produced. The recovery yields for L-tryptophan aqueous solutions with concentrations of 0.01wt%, 0.03wt%, 0.05wt%, 0.1wt%, 0.3wt%, and 1.0wt% were 89%, 89%, 73%, 65%, 67%, and 66%, respectively. The recovery yields for L-leucine aqueous solutions with concentrations of 0.05wt%, 0.1wt%, and 0.3wt% were 76%, 72%, and 55%, respectively.

[0080] In addition, the clathrate gas was replaced with carbon dioxide gas, and the experiment was carried out under the same experimental conditions as in Example 2. As the amino acid aqueous solutions, L-tryptophan aqueous solutions with concentrations of 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, and 0.3 wt%, and L-leucine aqueous solutions with concentrations of 0.05 wt%, 0.1 wt%, 0.3 wt%, and 0.5 wt% were used. As a result, as shown in Figures 17 and 18, the pressure increased significantly during thermal decomposition under all conditions, and it was confirmed that carbon dioxide hydrate was generated. The recovery yields in the L-tryptophan aqueous solutions with concentrations of 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, and 0.3 wt% were 86%, 84%, 87%, 85%, and 86%, respectively. The recovery yields in aqueous L-leucine solutions with concentrations of 0.05 wt%, 0.1 wt%, 0.3 wt%, and 0.5 wt% were 81%, 81%, 83%, and 85%, respectively.

[0081] Example 8 In Example 8, it was verified whether the generation and decomposition of gas hydrate could be repeated even if the same amino acid aqueous solution was used for a long period of time. The amino acid aqueous solution was filled into the pressure vessel 10, and then the generation and decomposition of gas hydrate was repeated a total of 31 times over a period of about 10 months from January to November 2018. As the amino acid aqueous solution, an L-tryptophan aqueous solution with a concentration of 0.03 wt% was used, and methane gas was used as the clathrate gas. The other experimental conditions were the same as in Example 1.

[0082] As a result, the recovery yield in the initial batch was 88%, while that in the final batch was 88%, and no significant change in the recovery yield was observed. From the above, it was confirmed that the reaction activity of the amino acid aqueous solution does not decrease even when the generation and decomposition of gas hydrate is repeated. [Explanation of symbols]

[0083] 1. Generator System 10. Pressure Vessels 11 Main body 12 Lid 13,21 Temperature sensor 20 Constant temperature bath 30 Gas supply source 31 Gas Cylinder 32 Pressure Regulator 40,50 Piping 41 Pressure Sensor 42 Flow Sensor 43 Flow rate totalizer 44,52 Valve 51 Gas volume measuring device 60 Computer

Claims

1. a step of placing an amino acid ice block obtained by freezing an amino acid aqueous solution containing a hydrophobic amino acid in a pressure vessel and cooling the ice block to −3° C. or lower, and pressurizing the clathrate gas in the pressure vessel; a step of heating the amino acid ice block to a melting point or higher while the clathrate gas is pressurized in the pressure vessel, and maintaining the state in which the amino acid ice block is at or above the melting point for a certain period of time, thereby melting all or a part of the amino acid ice block; A method for producing gas hydrate comprising the steps of:

2. a step of storing an amino acid ice block obtained by freezing an amino acid aqueous solution containing a hydrophobic amino acid in a pressure vessel, pressurizing an inclusion gas in the pressure vessel and heating the amino acid ice block to a melting point or higher; a step of pressurizing the clathrate gas in the pressure vessel and maintaining the amino acid ice block at a temperature equal to or higher than the melting point for a certain period of time, thereby melting all or a part of the amino acid ice block; A method for producing gas hydrate comprising the steps of:

3. introducing the amino acid aqueous solution into the pressure vessel; and cooling the amino acid aqueous solution introduced into the pressure vessel so that the amino acid aqueous solution is frozen and becomes the amino acid ice block in the pressure vessel. The method for producing gas hydrate according to claim 1 or 2.

4. cooling the amino acid aqueous solution in such a manner that the amino acid ice blocks melt and the resulting amino acid aqueous solution is frozen while the clathrate gas is pressurized in the pressure vessel; and reducing the pressure of the clathrate gas in the pressure vessel to atmospheric pressure while keeping the amino acid ice block obtained by freezing the amino acid aqueous solution cold. The method for producing gas hydrate according to any one of claims 1 to 3.

5. The concentration of the hydrophobic amino acid in the amino acid aqueous solution is within the range of 0.01 wt % to 1.0 wt %. The method for producing gas hydrate according to any one of claims 1 to 4.

6. The hydrophobic amino acid is tryptophan or leucine. The method for producing gas hydrate according to any one of claims 1 to 5.

7. The clathrate gas is methane gas or carbon dioxide gas. The method for producing gas hydrate according to any one of claims 1 to 6.

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