Amino acid-activated ice and its production method, as well as gas hydrate and its production method

Abstract

This invention provides an amino acid-activated ice capable of easily and quickly generating gas hydrates, a method for generating the same, and a gas hydrate using amino acid-activated ice, as well as a method for generating the same. [Solution] The amino acid-activated ice is made by freezing an aqueous amino acid solution containing hydrophobic amino acids and dissolved CO2 gas. The concentration of amino acids in the aqueous amino acid solution containing hydrophobic amino acids may be in the range of 0.01 wt% to 2.0 wt%. The hydrophobic amino acid may be any one of leucine, methionine, glycine, phenylalanine, tryptophan, and histidine.

Description

Technical Field

[0001] The present invention relates to amino acid active ice, a method for producing the same, a gas hydrate, and a method for producing the same.

Background Art

[0002] In recent years, attention has been focused on gas hydrates that incorporate gas molecules such as methane gas and carbon dioxide gas inside. Gas hydrates are suitable for gas transportation, storage, and supply because they can stably hold gas and can be easily decomposed. Therefore, development of a method for producing gas hydrates simply and at low cost has been underway. For example, Patent Document 1 discloses a method for producing a gas hydrate in which an inclusion gas is incorporated into an amino acid ice block by supplying an inclusion gas to an amino acid ice block obtained by freezing an aqueous amino acid solution containing a hydrophobic amino acid.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The method of Patent Document 1 can easily produce gas hydrates without stirring the aqueous amino acid solution, and the amino acids used in this method are harmless to the human body and do not impose a burden on the environment, so they are easy to handle and extremely useful. However, there is room for improvement in terms of improving the hydrate formation rate for industrial use.

[0005] The present invention has been made based on such a background, and an object thereof is to provide an amino acid active ice capable of simply and quickly producing a gas hydrate, a method for producing the same, a gas hydrate using the amino acid active ice, and a method for producing the same. [Means for solving the problem]

[0006] To achieve the above objective, the amino acid-activated ice according to the first aspect of the present invention is The process involves freezing an aqueous amino acid solution containing hydrophobic amino acids and dissolved CO2 gas.

[0007] The concentration of the amino acid in the aqueous amino acid solution containing the hydrophobic amino acid may be in the range of 0.01 wt% to 2.0 wt%.

[0008] The hydrophobic amino acid may be any one of leucine, methionine, glycine, phenylalanine, tryptophan, and histidine.

[0009] To achieve the above objective, the generation method according to the second aspect of the present invention is: A method for generating the aforementioned amino acid-activated ice, A step of placing an aqueous amino acid solution containing hydrophobic amino acids into a pressure vessel, The process involves supplying pressurized CO2 gas into the pressure-resistant container to replace the air dissolved in the amino acid aqueous solution with CO2 gas, A step of freezing the amino acid aqueous solution in the pressure vessel, in which the dissolved air has been replaced with CO2 gas, Includes.

[0010] To achieve the above objective, the generation method according to the third aspect of the present invention is: A method for producing gas hydrate using the aforementioned amino acid-activated ice, The process involves maintaining the temperature of the amino acid-activated ice at the freezing temperature, which is the temperature at which an amino acid aqueous solution can freeze, while supplying an inclusion gas into the pressure vessel containing the amino acid-activated ice, thereby replacing the CO2 gas in the pressure vessel with the inclusion gas. A step of raising the pressure of the inclusion gas in the pressure vessel to above the gas hydrate equilibrium pressure while maintaining the temperature of the amino acid-activated ice at the freezing temperature, A step of raising the temperature of the amino acid-activated ice to a range of -3°C to 0°C while the inclusion gas is pressurized in the pressure vessel, Includes.

[0011] To achieve the above objective, the generation method according to the fourth aspect of the present invention is: A method for producing gas hydrate using the aforementioned amino acid-activated ice, The process involves maintaining the temperature of the amino acid-activated ice at the freezing temperature, which is the temperature at which an amino acid aqueous solution can freeze, while supplying an inclusion gas into the pressure vessel containing the amino acid-activated ice, thereby replacing the CO2 gas in the pressure vessel with the inclusion gas. A step of raising the temperature of the amino acid-activated ice to a range of -3°C to 0°C, The process involves maintaining the temperature of the amino acid-activated ice within the range of -3°C to 0°C while supplying the inclusion gas into the pressure vessel at a constant flow rate, thereby increasing the pressure of the inclusion gas in the pressure vessel to above the gas hydrate equilibrium pressure. Includes.

[0012] To achieve the above objective, the gas hydrate according to the fifth aspect of the present invention is It is produced using the aforementioned gas hydrate production method. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide amino acid-activated ice and a method for producing the same, which can easily and quickly generate gas hydrate, as well as gas hydrate using amino acid-activated ice and a method for producing the same. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows the configuration of a generation system according to an embodiment of the present invention. [Figure 2] This flowchart shows the flow of a gas hydrate production method according to an embodiment of the present invention. [Figure 3]It is a flowchart showing the flow of the amino acid active ice generation process according to an embodiment of the present invention. [Figure 4] It is a flowchart showing the flow of the temperature raising method according to an embodiment of the present invention. [Figure 5] It is a flowchart showing the flow of the pressure increasing method according to an embodiment of the present invention. [Figure 6] It is a graph showing changes in the flow rate, pressure, sample temperature, and constant temperature bath temperature of methane gas in methane hydrate production using the temperature raising method of Example 1. [Figure 7] It is a graph showing changes in the flow rate, pressure, sample temperature, and constant temperature bath temperature of methane gas in methane hydrate production using the pressure increasing method of Example 1. [Figure 8] It is a diagram showing the amino acid active ice holding time, hydrate formation time, and gas recovery rate in the experiment of generating CO2 hydrate of Example 2. [Figure 9] It is a diagram showing the amino acid active ice holding time, hydrate formation time, and gas recovery rate in the experiment of generating methane hydrate of Example 2. [Figure 10] It is a diagram showing the amino acid active ice holding time, hydrate formation time, and gas recovery rate in the experiment of generating ethane hydrate of Example 2. [Figure 11] (a) is a graph showing changes in the flow rate, pressure, sample temperature, and constant temperature bath temperature of methane gas in the experiment using 0.1 wt% L-tryptophan aqueous solution and the temperature raising method of Example 3, and (b) is a graph obtained by enlarging a part of the graph of (a). [Figure 12] (a) is a graph showing changes in the flow rate, pressure, sample temperature, and constant temperature bath temperature of methane gas in the experiment using 0.1 wt% L-tryptophan aqueous solution and the pressure increasing method of Example 3, and (b) is a graph obtained by enlarging a part of the graph of (a). [Figure 13] (a) is a graph showing changes in the flow rate, pressure, sample temperature, and constant temperature bath temperature of methane gas in the experiment using 0.05 wt% L-methionine aqueous solution and the pressure increasing method of Example 3, and (b) is a graph obtained by enlarging a part of the graph of (a). [Figure 14] This graph shows the changes in methane gas flow rate, pressure, sample temperature, and constant temperature bath temperature in the experiment using the 0.01 wt% L-tryptophan aqueous solution and the heating method of Example 4. [Modes for carrying out the invention]

[0015] Hereinafter, an embodiment of the present invention, including amino acid-activated ice and its production method, as well as gas hydrate and its production method, will be described in detail with reference to the drawings. In the embodiment, for example, the expression "T1℃~T2℃" means "T1℃ or higher and T2℃ or lower."

[0016] The gas hydrate production method according to this embodiment is a method for producing gas hydrate in which gas molecules of the inclusion gas are incorporated by supplying an inclusion gas to amino acid-activated ice. The gas hydrate is a crystalline body in which polyhedral cages composed of multiple water molecules bonded by hydrogen bonds enclose molecules of the inclusion gas (guest molecules), and multiple polyhedra share faces with each other to form a crystal lattice. The inclusion gas is a gas that is incorporated into the gas hydrate and released during decomposition. For example, CO2 gas, methane gas, or ethane gas may be used as the inclusion gas.

[0017] Next, the composition and properties of the amino acid-activated ice according to the embodiment will be described. Amino acid-activated ice is an ice block obtained by replacing the air dissolved in an amino acid aqueous solution containing hydrophobic amino acids with CO2 gas, and then freezing the amino acid aqueous solution. As a result of the inventor's diligent research, it was found that amino acid-activated ice obtained by replacing the air dissolved in an amino acid aqueous solution containing hydrophobic amino acids with CO2 gas and then freezing the amino acid aqueous solution exhibits a faster reaction rate during gas hydrate formation and a higher gas recovery rate during decomposition compared to amino acid ice blocks obtained by freezing the amino acid aqueous solution with the air dissolved in it, or amino acid ice blocks obtained by replacing the air with methane or ethane gas. The gas recovery rate is the volume ratio of the inclusion gas released during the decomposition of the gas hydrate to the inclusion gas enclosed in the gas hydrate.

[0018] The hydrophobic amino acids used in amino acid-activated ice are hydrophobic amino acids, and unless there is a particular reason otherwise, they are preferably L-type. The hydrophobic amino acids may be either paraffinic hydrophobic amino acids or aromatic hydrophobic amino acids. Examples of paraffinic hydrophobic amino acids include leucine, methionine, and glycine. Examples of aromatic amino acids include phenylalanine, tryptophan, and histidine.

[0019] Hydrophobic amino acids should be selected considering the type of inclusion gas. For example, when producing CO2 hydrate, leucine, methionine, glycine, phenylalanine, tryptophan, and histidine are suitable hydrophobic amino acids. When producing methane hydrate or ethane hydrate, leucine, methionine, phenylalanine, and tryptophan are suitable hydrophobic amino acids for methane and ethane, respectively.

[0020] The concentration of amino acids in amino acid-activated ice should be set considering their solubility in water and their effect on promoting the gas hydrate formation reaction. If the amino acid concentration is too high, amino acids may precipitate from the amino acid aqueous solution during freezing or during the gas hydrate formation reaction. If the amino acid concentration is too low, the gas hydrate formation reaction will not proceed sufficiently. The amino acid concentration should be optimized for each type of amino acid; for example, it is preferable to adjust it within the range of 0.01 wt% to 2.0 wt%.

[0021] The properties of amino acid-activated ice are temperature-dependent. Specifically, if stored below 0°C, amino acid-activated ice can maintain its activity for a long period, but if left at temperatures above 0°C for an extended period, its activity will be lost. The activity of amino acid-activated ice refers to the property that when the inclusion gas in a pressure-resistant container containing the amino acid-activated ice is pressurized, the gas hydrate formation reaction proceeds rapidly. When using amino acid-activated ice at temperatures above 0°C, it is necessary to use it quickly after raising the temperature above 0°C.

[0022] Furthermore, if the temperature is below -5°C, the gas hydrate formation reaction is less likely to proceed even if the inclusion gas in the pressure vessel containing the amino acid-activated ice is pressurized, and the heating method described later can be used. On the other hand, if the inclusion gas in the pressure vessel is pressurized at -5°C or higher, the gas hydrate formation reaction proceeds more easily, and if the inclusion gas in the pressure vessel is pressurized at -3°C or higher, the gas hydrate formation reaction proceeds almost certainly. The above describes the composition and properties of amino acid-activated ice.

[0023] (Generation System) Next, with reference to Figure 1, the generation system 1 according to the embodiment will be described. The generation system 1 is a device that generates amino acid-activated ice and also generates gas hydrate using the generated amino acid-activated ice. The generation system 1 can also extract inclusion gas by decomposing the generated gas hydrate.

[0024] The generation system 1 comprises a pressure vessel 2, a constant temperature bath 3 that houses the pressure vessel 2, and a CO2 gas supply source 4 and an inclusion gas supply source 5 connected to the pressure vessel 2, which supply CO2 gas and an inclusion gas, respectively, into the pressure vessel 2. The pressure vessel 2 and the CO2 gas supply source 4 and the inclusion gas supply source 5 are connected via piping 6. In addition, piping 7 is connected to the pressure vessel 2 to release the inclusion gas inside the pressure vessel 2 to the outside.

[0025] The pressure vessel 2 is a container capable of supplying CO2 gas and inclusion gas while containing an amino acid aqueous solution or amino acid activated ice. The pressure vessel 2 comprises a container body with an opening on its top surface for containing the amino acid aqueous solution or amino acid activated ice, and a lid that is detachably attached to the top surface of the container body and fits tightly to the top surface of the container body. A temperature sensor 2a for measuring the temperature (sample temperature) of the amino acid aqueous solution or amino acid activated ice inside the pressure vessel 2 is detachably attached to the lid. The ends of the pipes 6 and 7 are also detachably connected to the lid.

[0026] The constant temperature bath 3 is a device that houses the pressure vessel 2 inside and maintains a constant temperature for the pressure vessel 2 by keeping the liquid temperature of the medium inside the bath constant. The constant temperature bath 3 includes a temperature sensor 3a for measuring the temperature of the medium (constant temperature bath temperature), and a cooler and heater for cooling and heating the medium.

[0027] The CO2 gas supply source 4 is connected to the pressure vessel 2 via piping 6 and supplies pressure-regulated CO2 gas into the pressure vessel 2. The CO2 gas supply source 4 comprises a gas cylinder 4a, a pressure regulator 4b connected to the gas cylinder 4a to adjust the gas pressure, and a valve 4c that can open and close the flow path.

[0028] The inclusion gas supply source 5 is connected to the pressure vessel 2 via piping 6 and supplies pressure-regulated inclusion gas into the pressure vessel 2. The inclusion gas supply source 5, like the CO2 gas supply source 4, comprises a gas cylinder 5a, a pressure regulator 5b, and a valve 5c.

[0029] Piping 6 supplies CO2 gas and inclusion gas from a CO2 gas supply source 4 and an inclusion gas supply source 5 into the pressure vessel 2. Piping 6 is equipped with a pressure sensor 6a for measuring the pressure in the pressure vessel 2 and a flow sensor 6b for measuring the flow rate of the inclusion gas toward the pressure vessel 2. A flow integrator 6c is connected to the flow sensor 6b to integrate the total flow rate of the inclusion gas that has passed through the flow sensor 6b since the start of measurement. The flow sensor 6b is, for example, a mass flow meter. Valves 6d capable of opening and closing the flow paths are provided between the pressure sensor 6a and the flow sensor 6b, and between the flow sensor 6b and valves 4c and 5c.

[0030] The piping 7 releases the gas from the pressure vessel 2 to the outside. The piping 7 is equipped with a gas volume measuring device 7a for measuring the volume of the enclosed gas released from the pressure vessel 2. The gas volume measuring device 7a is, for example, a graduated cylinder. In addition, two openable and closable valves 7b are provided between the lid of the pressure vessel 2 and the gas volume measuring device 7a.

[0031] The measuring device 8 is, for example, a general-purpose computer. The measuring device 8 is connected to temperature sensors 2a and 3a, pressure sensor 6a, flow sensor 6b, and flow integrator 6c via communication cables. The measuring device 8 includes memory and a processor, and by executing a program stored in memory, it acquires measurement data from each sensor, stores it in memory, and displays it on a display. The user can refer to the measurement data displayed on the measuring device 8 and operate the cooler and heater of the constant temperature bath 3, as well as the pressure regulators 4b and 5b, according to the procedures shown in Figures 2 to 5. The above describes the configuration of generation system 1.

[0032] (Method for generating gas hydrate) The following describes the flow of the gas hydrate production method using the production system 1 according to the embodiment, with reference to Figure 2. A CO2 gas supply source 4 and an inclusion gas supply source 5 are connected to the piping 6, and all valves 4c, 5c, 6d, and 7b are assumed to be closed.

[0033] (Amino acid-activated ice generation process) First, an amino acid activated ice generation process is carried out (Step S1) in which an amino acid aqueous solution containing dissolved CO2 gas is frozen to produce amino acid activated ice. The flow of the amino acid activated ice generation process according to this embodiment will be explained below with reference to Figure 3.

[0034] First, prepare an aqueous amino acid solution with an adjusted concentration of hydrophobic amino acids (Step S11).

[0035] Next, the amino acid aqueous solution prepared in step S11 is sealed into the pressure vessel 2 (step S12). Specifically, the amino acid aqueous solution is poured into the container body of the pressure vessel 2, and the lid is attached to assemble the pressure vessel 2.

[0036] Next, in step S12, the pressure-resistant container 2 containing the amino acid aqueous solution is placed inside the constant temperature bath 3, and the pipes 6 and 7 and the sensors are attached as shown in Figure 1 (step S13).

[0037] Next, CO2 gas is supplied under pressure from the CO2 gas supply source 4 into the pressure vessel 2, thereby replacing the air dissolved in the amino acid aqueous solution with CO2 gas (step S14). Specifically, by opening valves 4c and 6d and adjusting the gas pressure with the pressure regulator 4b, a constant flow rate of CO2 gas is supplied into the pressure vessel 2. To replace the air dissolved in the amino acid aqueous solution with CO2 gas, it is advisable to repeat the process of supplying CO2 gas under pressure into the pressure vessel 2 and then letting it stand for a certain period of time multiple times.

[0038] Next, after the CO2 gas in the pressure vessel 2 is discharged to the outside through the piping 7, a gas volume measuring device 7a (graduated cylinder) is connected to the piping 7 and left for a certain period of time to bring the CO2 gas in the pressure vessel 2 to atmospheric pressure (step S15). Specifically, when valves 4c and 6d are closed and valve 7b is opened, the CO2 gas in the pressure vessel 2 is discharged first, followed by the release of excess CO2 gas dissolved in the amino acid aqueous solution. At this time, if a graduated cylinder is connected to the three-way cylinder cock provided on the piping 7, the CO2 gas is collected in the graduated cylinder, and it is possible to determine whether the release of CO2 gas is continuing. Once the release of CO2 gas from the amino acid aqueous solution stops, valve 7b can be closed again. This releases the excess CO2 gas dissolved in the amino acid aqueous solution and prevents backflow of air.

[0039] Next, amino acid-activated ice is obtained by cooling and freezing the amino acid aqueous solution containing dissolved CO2 gas in the pressure vessel 2 (step S16). To freeze the amino acid aqueous solution, the temperature of the amino acid aqueous solution is lowered to the freezing temperature by operating the cooler of the constant temperature bath 3. The freezing temperature is the temperature at which supercooling can be induced in the amino acid aqueous solution, causing it to freeze. In this freezing process, volume expansion occurs as the amino acid aqueous solution changes into ice blocks, causing the pressure of the CO2 gas in the pressure vessel 2 to rise. When this pressure rise stops, it can be determined that the formation of amino acid-activated ice is complete.

[0040] The freezing temperature varies depending on the type and concentration of the amino acid aqueous solution, but it should be set to -10°C or lower, preferably -20°C. When the inclusion gas is CO2 gas or ethane gas, considering the saturated vapor pressure, the freezing temperature of the amino acid aqueous solution should be set to, for example, -20°C to -16°C, preferably -18°C. When the inclusion gas is methane gas, there is no effect of saturated vapor pressure, so the freezing temperature of the amino acid aqueous solution should be set to, for example, -27°C to -23°C, preferably -25°C. The above is the flow of the amino acid-activated ice generation process.

[0041] (Gas hydrate generation process) Returning to Figure 2, a gas hydrate generation step is carried out (step S2) in which the gas hydrate generation reaction proceeds in the amino acid-activated ice obtained in step S1. To induce the gas hydrate generation reaction, either the heating method or the pressurization method described below can be used.

[0042] (Increased temperature method) The flow of the gas hydrate generation process (step S2) using the heating method according to the embodiment will be explained below with reference to Figure 4. At the start of the gas hydrate generation process, the temperature of the amino acid-activated ice is assumed to be maintained at the freezing temperature in step S16.

[0043] First, the inclusion gas is supplied from the inclusion gas supply source 5 into the pressure vessel 2, and then the CO2 gas inside the pressure vessel 2 is replaced with the inclusion gas by depressurizing and releasing the pressure (step S21). Specifically, valve 4c is closed, valve 6d is opened, then valve 5c is closed, and the pressure regulator 5b is set to several kg / cm². 2 The pressure is increased to a certain level. Next, the flow rate of the inclusion gas is adjusted by opening valve 5c appropriately while reading the flow sensor 6b. When the pressure of the inclusion gas reaches a preset value, valve 5c is closed and valve 7b is opened to release it to atmospheric pressure. By repeating this process multiple times, the CO2 gas in the pressure vessel 2 is replaced with the inclusion gas. At this time, if a graduated cylinder is used as the gas volume measuring instrument 7a, backflow contamination by the atmosphere when opening can be prevented. If the temperature of the inclusion gas is room temperature, if the flow rate of the inclusion gas is too high, the amino acid activated ice will melt, and the activity of the gas hydrate formation reaction will be reduced. For this reason, the flow rate of the inclusion gas is set to a level that does not cause the amino acid activated ice to melt. Note that this step is omitted if the inclusion gas is CO2 gas.

[0044] Next, while maintaining the temperature of the amino acid-activated ice at its freezing point, the inclusion gas is pressurized and supplied from the inclusion gas supply source 5 into the pressure vessel 2, thereby increasing the pressure of the inclusion gas in the pressure vessel 2 from atmospheric pressure to the set pressure (step S22). To pressurize the inclusion gas, the pressure regulator 5b should be adjusted in the loosening direction. Here again, the flow rate of the inclusion gas should be set to an extent that the amino acid-activated ice does not melt. When the inclusion gas is CO2 gas or ethane gas, the set pressure should be within a range where liquefaction does not occur. When the inclusion gas is methane gas, since liquefaction does not need to be considered, the set pressure should be increased to a range of 1 to 3 times the gas hydrate equilibrium pressure, preferably 1.5 to 2.5 times, and more preferably up to 2 times.

[0045] The gas hydrate equilibrium pressure is the temperature and pressure at which the generated gas hydrate can exist stably. If the pressure is lowered below the hydrate equilibrium pressure condition at a constant temperature, gas hydrate decomposition will proceed, and the pressure will rise to the gas hydrate equilibrium pressure at the temperature at which the gas hydrate decomposition occurred. Conversely, if the temperature is raised above the gas hydrate equilibrium pressure condition, gas hydrate decomposition will proceed, and the pressure will rise to the gas hydrate equilibrium pressure at the increased temperature.

[0046] After pressurizing the inclusion gas in the pressure vessel 2, the temperature and pressure are allowed to stabilize for a certain period of time. At this point, the temperature of the amino acid-activated ice is raised so that it passes through a range of -3°C to 0°C, preferably -2°C to -1°C (step S23). In this heating step, the constant temperature bath temperature should be set to 0°C or higher, preferably +1°C. When the temperature of the amino acid-activated ice approaches -2°C, the gas hydrate formation reaction proceeds rapidly. Note that for the gas hydrate formation reaction to proceed, the temperature of the amino acid-activated ice must be 0°C or lower, even if the constant temperature bath temperature is +1°C. The temperature raised in the heating step can be appropriately set according to the type and concentration of amino acids.

[0047] As the hydrate formation reaction proceeds and the amino acid-activated ice disappears, the temperature of the amino acid sample in the pressure vessel 2 rises rapidly and stops at the gas hydrate equilibrium pressure temperature at the set pressure. At this point, the gas hydrate formation reaction is almost complete. Once the gas hydrate formation reaction is complete, it is advisable to lower the temperature of the constant temperature bath and freeze the gas hydrate to provide a self-preservation effect. The above is the flow of the gas hydrate generation process (step S2) using the heating method.

[0048] (Boost method) Next, with reference to Figure 5, the flow of the gas hydrate generation process (step S2) using the pressurization method according to the embodiment will be explained. In the pressurization method, the flow rate of the inclusion gas can be adjusted in the pressurization step, so the rate of the gas hydrate generation reaction can be adjusted as appropriate. In the pressurization method as well, it is assumed that the temperature of the amino acid-activated ice is maintained at the freezing temperature in step S16 at the time the gas hydrate generation process starts.

[0049] First, the CO2 gas in the pressure vessel 2 is replaced with the inclusion gas using the same method as in the heating method (step S21).

[0050] Next, the temperature of the amino acid-activated ice, which was replaced with the inclusion gas in step S21, is raised to a range of -3°C to 0°C, preferably -2°C (step S22A). To raise the temperature of the amino acid-activated ice to a range of -3°C to 0°C, preferably -2°C, it is advisable to set the constant temperature bath temperature to around -2°C.

[0051] Next, the inclusion gas inside the pressure vessel 2 is pressurized and supplied at a constant flow rate to raise the pressure from atmospheric pressure to the set pressure (step S23A). The set pressure is set in the same way as in step S22 of the heating method. The specific procedure for this pressurization step is as follows.

[0052] First, valve 5c is closed, and the pressure regulator 5b is operated to set the pressure of the inclusion gas, after which valve 6d is opened. The gas flow rate is adjusted by appropriately operating valve 5c while reading the flow sensor 6b. The flow rate of the inclusion gas is preferably set within the range of 500 ml to 2000 ml / min, for example, but it may be set to 2000 ml / min or more considering the amount of gas taken into the gas hydrate. The supply of the inclusion gas to the pressure vessel 2 is continued, and when the inclusion gas pressure in the pressure vessel 2 exceeds the gas hydrate equilibrium pressure, the gas hydrate formation reaction begins. Note that the pressure at which the gas hydrate formation reaction begins is above the equilibrium pressure, but it varies depending on the rate of pressure increase, the type and concentration of amino acids.

[0053] When gas hydrate formation begins, the inclusion gas supplied to the pressure vessel 2 is incorporated into the gas hydrate, slowing down the pressure rise of the inclusion gas. If the amount of gas incorporated per unit time by hydrate formation is greater than the flow rate of the inclusion gas, the pressure of the inclusion gas in the pressure vessel 2 may decrease. If gas hydrate formation continues, the rate of incorporation of the inclusion gas into the amino acid activated ice decreases, causing the pressure of the inclusion gas in the pressure vessel 2 to rise. The amino acid activated ice maintains a nearly constant temperature until it disappears, but once it disappears, the temperature rises rapidly to the gas hydrate equilibrium pressure temperature at the set pressure, and the hydrate formation reaction is almost complete. The above describes the flow of the gas hydrate generation process (step S2) using the pressurization method.

[0054] After the gas hydrate generation is completed by any of the above processes, valve 6d is closed and the gas hydrate in the pressure vessel 2 is cooled to its freezing temperature to freeze. The frozen gas hydrate can be stored at low pressure for a long period of time, utilizing its self-preservation effect, or it can be removed and used directly. If the gas hydrate is stored as is, valve 7b can be opened at the desired time, and the frozen gas hydrate can be heated to above 0°C to decompose it, releasing the inclusion gas incorporated into the gas hydrate to the outside through piping 7. After the gas hydrate has decomposed, the amino acid aqueous solution remaining in the pressure vessel 2 can be used directly to generate amino acid-activated ice. This is because, in the generation of gas hydrate using amino acid-activated ice, stirring of the amino acid aqueous solution and the generation of powder ice are unnecessary.

[0055] As described above, the amino acid-activated ice according to the embodiment is an ice block produced by freezing an amino acid aqueous solution containing hydrophobic amino acids and dissolved CO2 gas. By supplying an inclusion gas to such amino acid-activated ice to induce a gas hydrate generation reaction, gas hydrate can be produced easily and quickly. Furthermore, since the gas hydrate generation reaction using amino acid-activated ice does not require the use of substances that have adverse effects on the environment, the reuse and disposal of the amino acid aqueous solution after use are also easy.

[0056] The present invention is not limited to the embodiments described above, and the following modifications are also possible.

[0057] (modified version) In the above embodiment, the lid of the pressure vessel 2 was removed from the container body, an amino acid aqueous solution was placed inside the container body, and then the lid was attached to the container body. However, the present invention is not limited to this. Piping for injecting the amino acid aqueous solution may be connected to the container body or lid of the pressure vessel 2.

[0058] In the above embodiment, the pressure vessel 2 was placed inside the constant temperature bath 3 to maintain its temperature, but the present invention is not limited to this. For example, the pressure vessel 2 may 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.

[0059] In the above embodiment, the pressure vessel 2 was installed inside the constant temperature bath 3, but the present invention is not limited thereto. For example, the pressure vessel 2 may be removed from the constant temperature bath 3, and the gas hydrate may be stored and transported while still inside the pressure vessel 2. Alternatively, the pressure vessel 2 may be installed in a refrigerated tank truck, and the gas hydrate may be generated and transported at any location.

[0060] In the above embodiment, CO2 gas was supplied from the piping 6 to the space between the pressure vessel 2 and the amino acid aqueous solution, but the present invention is not limited to this. For example, a bubbling mechanism may be provided in the pressure vessel 2, and CO2 gas may be dissolved into the amino acid aqueous solution by the bubbles of CO2 gas released from the bubbling mechanism. Alternatively, an amino acid aqueous solution in which the air has been replaced with CO2 gas beforehand may be poured into the pressure vessel 2.

[0061] In the above embodiment, the inclusion gas supplied from the inclusion gas supply source 5 was supplied directly to the pressure vessel 2 through the piping 6, but the present invention is not limited to this. For example, a cooling device may be provided in the piping 6 to cool the inclusion gas in order to prevent the melting of amino acid-activated ice.

[0062] In the above embodiment, the flow rate of the inclusion gas was adjusted by manually operating the valve 5c while monitoring the flow sensor 6b, but the present invention is not limited to this. For example, a flow controller may be connected to the piping 6, and the flow rate of the inclusion gas may be specified by this flow controller.

[0063] In the above embodiment, the operation of each part of the generation system 1 was manually adjusted based on the measurement data of each sensor, but the present invention is not limited thereto. The measuring device 8 may control the operation of the cooler and heater of the constant temperature bath 3, the pressure regulators 4b and 5b, and the valves 4c, 5c, 6d, and 7b so that the steps shown in the flowcharts of Figures 2 to 5 are carried out based on the measurement data of each sensor. As valves 4c, 5c, 6d, and 7b, electromagnetic valves and flow controllers that can be opened and closed by operation signals from the measuring device 8 are preferable.

[0064] In the above embodiment, the end of the pipe 7 was open to the atmosphere, but the present invention is not limited to this. For example, an external device requiring an enclosing gas, such as a combustion device, may be connected to the end of the pipe 7.

[0065] In the above embodiment, the temperatures of the amino acid aqueous solution and the amino acid activated ice, as well as the pressures of the CO2 gas and the inclusion gas, were set to constant values ​​in the amino acid activated ice generation step (step S1) and the gas hydrate generation step (step S2). However, the present invention is not limited to this. These temperatures and pressures may be varied within a certain range.

[0066] In the above embodiment, CO2 gas was supplied at a constant flow rate in the amino acid activated ice generation step (step S1), and the inclusion gas was supplied at a constant flow rate in the gas hydrate generation step (step S2). However, the present invention is not limited to this. For example, the flow rate of CO2 gas or the inclusion gas may be varied in either step.

[0067] In the above embodiment, the freezing temperature in the amino acid aqueous solution freezing step (step S16) and the temperature in the inclusion gas replacement step (step S21) were the same, but the present invention is not limited thereto. The temperature in the freezing step of the amino acid aqueous solution may be set higher than the temperature in the inclusion gas replacement step.

[0068] In the above embodiments, in both the heating method and the pressurization method, when the inclusion gas was CO2 gas or ethane gas, the set pressure of the inclusion gas was set to a range where liquefaction would not occur, and when the inclusion gas was methane gas, the set pressure of the inclusion gas was set to about twice the gas hydrate equilibrium pressure. However, the present invention is not limited to this. For example, the set pressure of the inclusion gas may be set close to the gas hydrate equilibrium pressure to initiate the hydrate formation reaction.

[0069] In the above embodiment, the amino acid activated ice generation process (step S1) and the gas hydrate generation process (step S2) were carried out continuously using the same generation system 1, but the present invention is not limited thereto. For example, the amino acid activated ice generation process (step S1) and the gas hydrate generation process (step S2) may be carried out using separate generation systems, or the amino acid activated ice may be generated in advance and stored, and the stored amino acid activated ice may be placed in the pressure-resistant container 2 of the generation system 1 at a desired timing to carry out the gas hydrate generation configuration.

[0070] In the above embodiment, the heating process was carried out with valve 6d open even after the pressurization process was completed, but the present invention is not limited to this. For example, in the heating method, the valve 6d may be closed after the pressurization process is completed, and the heating process may be carried out in this state to perform batch processing of gas hydrate generation.

[0071] In the above embodiment, a single-component gas was used as the inclusion gas, but the present invention is not limited thereto. For example, a gas containing a mixture of multiple components may be used as the inclusion gas to produce a mixed gas hydrate. Either a heating method or a pressurizing method may be used to produce the mixed gas hydrate.

[0072] In the above embodiment, gas hydrate was used for gas storage and supply, but the uses of the present invention are not limited to this. For example, since amino acids do not burden the environment and are essential nutrients for the human body, CO2 hydrate produced using amino acid-activated ice may be added to foods such as beverages and frozen desserts. Furthermore, CO2 hydrate produced using amino acid-activated ice may be used to supply CO2 nanobubbles.

[0073] The embodiments described above are illustrative, and the present invention is not limited thereto. Various embodiments are possible without departing from the spirit of the invention as described in the claims. The components described in the embodiments and modifications can be freely combined. Furthermore, inventions equivalent to the invention described in the claims are also included in the present invention.

[0074] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0075] (Example 1) In Example 1, we verified whether methane hydrate could be produced using the heating method. A 120 ml pressure vessel was used for this verification. First, amino acid-activated ice was produced using 40 ml of a 0.03 wt% L-tryptophan aqueous solution. The sample temperature during the CO2 gas substitution step was set to +20°C, and the sample temperature during the freezing step of the amino acid aqueous solution was set to -25°C. Next, a gas hydrate production reaction was performed in which methane gas was encapsulated in the amino acid-activated ice. Specifically, as shown in Figure 6, the sample temperature was maintained at -25°C, and pressurized substitution with methane gas was performed multiple times. Next, while maintaining the sample temperature at -25°C, the pressure of the methane gas in pressure vessel 2 was increased from atmospheric pressure to 50 kg / cm². 2 After raising the temperature to the specified level, it was left for 10 minutes. Next, the temperature of the constant temperature bath was raised from -25°C to +1°C. During the heating process, the gas hydrate formation reaction proceeded, and the formation of methane hydrate was almost complete in about 10 minutes from the start.

[0076] Next, we investigated whether methane hydrate could be produced using the pressurization method. First, amino acid-activated ice was produced using 40 ml of a 0.1 wt% L-tryptophan aqueous solution. Next, a gas hydrate production reaction was carried out in which methane gas was encapsulated in the amino acid-activated ice. Specifically, as shown in Figure 7, the sample temperature was maintained at -25°C, and pressurized displacement with methane gas was performed multiple times. Next, while maintaining the methane gas pressure, the sample temperature was raised from -25°C to -2°C and held overnight. Next, while maintaining the sample temperature at -2°C, methane gas was supplied into the pressure vessel at a constant flow rate of 500 ml / min, and the methane gas pressure was increased to 40 kg / cm². 2 When the pressure was increased to this level, the gas hydrate formation reaction began during this pressurization process, and methane hydrate formation was almost complete when the pressure was increased to 40 kg. From the above, it can be understood that the gas hydrate formation reaction can be induced using amino acid-activated ice, regardless of whether the heating method or the pressurization method is used.

[0077] (Example 2) In Example 2, the amino acid-activated ice retention time and gas hydrate generation time were measured for CO2 hydrate, methane hydrate, and ethane hydrate using the method of the present invention, while changing the type of amino acid used. After gas hydrate generation, the gas hydrate was decomposed by heating, and the gas recovery rate was measured. The amino acid-activated ice retention time is the time from when the amino acid-activated ice generation is completed until the gas hydrate generation reaction begins, and the gas hydrate generation time is the time required from the start to the end of the gas hydrate reaction. As a comparative example, gas hydrate was generated using the method of Patent Document 1 and compared with the case using the method of the present invention. The method of Patent Document 1 involves replacing the air dissolved in an amino acid aqueous solution with an inclusion gas, and then generating a gas hydrate reaction using an amino acid ice block obtained by freezing the amino acid aqueous solution.

[0078] In both the examples and comparative examples, six types of amino acid aqueous solutions were used for CO2 hydrate: 0.03 wt%, 0.1 wt% L-tryptophan, 0.05 wt%, 0.1 wt%, 1.0 wt%, and 2.0 wt% L-methionine. Similarly, six types were used for methane hydrate: 0.03 wt%, 0.1 wt% L-tryptophan, 0.05 wt%, 2.0 wt% L-methionine, 0.05 wt% L-leucine, and 0.05 wt% L-phenylalanine. Three types were used for ethane hydrate: 0.1 wt% L-tryptophan, 0.05 wt%, and 2.0 wt% L-methionine.

[0079] As a result, regardless of the amino acid used, amino acid-activated ice could be produced in approximately 120 minutes by cooling 40 ml of an amino acid aqueous solution at +20°C to -25°C. Furthermore, as can be seen from the measured retention time of the amino acid-activated ice, it was found that the activity that causes the gas hydrate formation reaction is not lost even when the amino acid-activated ice is stored in a frozen state.

[0080] Furthermore, as shown in Figure 8, with CO2 hydrate, the gas hydrate generation time was shortened when 0.03 wt%-L-tryptophan and 0.05 wt%-L-methionine were used, and the gas recovery rate was increased when 0.1 wt%-L-tryptophan, 0.05 wt%, 0.1 wt%, and 2.0 wt%-L-methionine were used. As shown in Figure 9, with methane hydrate, the gas hydrate generation time was shortened regardless of which amino acid aqueous solution was used, and the gas recovery rate was increased when 0.03 wt%, 0.1 wt%-L-tryptophan, 0.05 wt%, and 2.0 wt%-L-methionine were used. As shown in Figure 10, with ethane hydrate, the gas hydrate generation time was shortened and the gas recovery rate was increased regardless of which amino acid aqueous solution was used. From the above, it can be understood that using the method of the present invention results in a shorter gas hydrate generation time and an improved gas recovery rate compared to using the method of Patent Document 1.

[0081] (Example 3) In Example 3, we investigated whether the gas hydrate formation reaction could be induced even after long-term storage of amino acid-activated ice using both the heating method and the pressurization method.

[0082] First, the following experiment was conducted using the heating method. Specifically, an amino acid-activated ice was generated by freezing a 0.1 wt% L-tryptophan aqueous solution at -25°C, and gas hydrate generation was attempted using this amino acid-activated ice. Specifically, CO2 gas was replaced with methane gas, and the sample temperature was raised from -25°C to -5°C as shown in Figures 11(a) and (b), and this temperature was maintained for three nights (3918 minutes). Next, while maintaining the sample temperature at -5°C, the methane gas pressure was increased from atmospheric pressure to 40 kg / cm². 2 The pressure was increased to [a certain level], and then the temperature of the constant temperature bath was raised from -5°C to +1°C. During this heating process, the gas hydrate formation reaction proceeded. Next, the methane hydrate was decomposed, and the amount of gas released was measured, resulting in a gas recovery rate of 89%.

[0083] Next, the following experiment was conducted using the pressurization method. Similar to the heating method, gas hydrate generation was attempted using amino acid-activated ice produced from a 0.1 wt% L-tryptophan aqueous solution. Specifically, CO2 gas was replaced with methane gas, and the sample temperature was raised from -25°C to -2°C as shown in Figures 12(a) and (b), and maintained at that temperature for 3 nights (4152 minutes). Next, while maintaining the sample temperature at -2°C, methane gas was supplied at a constant flow rate of 500 ml / min, and the methane gas pressure was increased from atmospheric pressure to 40 kg / cm². 2 When the pressure was increased to a certain level, the gas hydrate formation reaction proceeded during this pressurization process. The gas recovery rate was 95%.

[0084] Next, we investigated whether the amino acid-activated ice produced using a 0.05 wt% L-methionine aqueous solution also exhibited sustained activity. Except for holding the amino acid-activated ice at -2°C for four nights (6554 minutes), as shown in Figures 13(a) and (b), the conditions were the same as those used in the pressurization experiment with a 0.1 wt% L-tryptophan aqueous solution. As a result of the above experiment, we successfully produced methane hydrate. The gas recovery rate was 88%. From the above, it can be understood that gas hydrate formation reactions can be induced using amino acid-activated ice stored for a long period of time, regardless of whether the heating method or the pressurization method is used.

[0085] (Example 4) In Example 4, we investigated whether the gas hydrate formation reaction proceeded using a 0.01 wt% L-tryptophan aqueous solution and a heating method. The experiment was conducted under the same conditions as in Example 1, except that the concentration of the L-tryptophan aqueous solution was changed. As a result, as shown in Figure 14, it was confirmed that the gas hydrate formation reaction proceeded rapidly. Furthermore, when the gas recovery rate was measured after gas hydrate formation, the recovery rate was 90%. [Explanation of Symbols]

[0086] 1. Generation System 2. Pressure vessel 2a,3a Temperature Sensor 3 Constant temperature bath 4 CO2 gas supply sources 4a, 5a gas cylinders 4b, 5b Pressure regulator 4c, 5c, 6d, 7b valves 5. Inclusion gas supply source 6,7 Piping 6a Pressure sensor 6b Flow sensor 6c Flow integrator 7a Gas volume measuring instrument 8. Measuring device

Claims

1. Contains hydrophobic amino acids, CO ２ Amino acid-activated ice is created by freezing an amino acid solution in which gas has dissolved.

2. The concentration of the amino acid in the aqueous amino acid solution containing the hydrophobic amino acid is in the range of 0.01 wt% to 2.0 wt%. The amino acid-activated ice according to claim 1.

3. The hydrophobic amino acid is one of leucine, methionine, glycine, phenylalanine, tryptophan, and histidine. The amino acid-activated ice according to claim 1.

4. A method for producing amino acid-activated ice according to claim 1, A step of placing an aqueous amino acid solution containing hydrophobic amino acids into a pressure vessel, CO ２ By supplying the gas under pressure, the air dissolved in the amino acid aqueous solution is converted to CO2. ２ The process of replacing with gas, The dissolved air is CO ２ A step of freezing the amino acid aqueous solution, which has been replaced with gas, in the pressure vessel, A method of production that includes this.

5. A method for producing gas hydrate using amino acid-activated ice as described in claim 1, By maintaining the temperature of the amino acid-activated ice at the freezing temperature, which is the temperature at which an amino acid aqueous solution can freeze, and supplying an inclusion gas into the pressure vessel containing the amino acid-activated ice, the CO2 in the pressure vessel is released. ２ A step of replacing the gas with the inclusion gas, A step of raising the pressure of the inclusion gas in the pressure vessel to above the gas hydrate equilibrium pressure while maintaining the temperature of the amino acid-activated ice at the freezing temperature, A step of raising the temperature of the amino acid-activated ice to a range of -3°C to 0°C while the inclusion gas is pressurized in the pressure vessel, A method of production that includes this.

6. A method for producing gas hydrate using amino acid-activated ice as described in claim 1, By maintaining the temperature of the amino acid-activated ice at the freezing temperature, which is the temperature at which an amino acid aqueous solution can freeze, and supplying an inclusion gas into the pressure vessel containing the amino acid-activated ice, the CO2 in the pressure vessel is released. ２ A step of replacing the gas with the inclusion gas, A step of raising the temperature of the amino acid-activated ice to a range of -3°C to 0°C, The process involves maintaining the temperature of the amino acid-activated ice within the range of -3°C to 0°C while supplying the inclusion gas into the pressure vessel at a constant flow rate, thereby increasing the pressure of the inclusion gas in the pressure vessel to above the gas hydrate equilibrium pressure. A method of production that includes this.

7. A gas hydrate produced using the production method described in claim 5 or 6.

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