Method for separating gas mixture by using hydrate

Abstract

The invention relates to the field of gas separation, in particular to a method for separating a gas mixture by using hydrate. According to the method for separating the gas mixture by utilizing the hydrate, a specific ice medium is filled into a reaction kettle, the filling amount of the ice medium and the length-diameter ratio of a pipeline in the reaction kettle are controlled, then the reaction kettle is inflated under a certain temperature condition, and when the pressure in the reaction kettle reaches the pressure required by separation and the hydrate starts to be generated, the gas mixture is separated. Opening the back pressure valve to exhaust outwards, firstly controlling a specific exhaust rate to slowly exhaust, immediately stopping inflating and opening the back pressure valve to accelerate exhaust along with the generation of the hydrate when the highest temperature is reached in the reaction kettle, and closing the back pressure valve and opening the exhaust valve on the other side after the normal pressure is reached in the reaction kettle, so that the hydrate is decomposed to release gas. Therefore, gas separation is completed. According to the method, the separation efficiency of the gas mixture can be improved, and meanwhile energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the field of gas separation, and in particular to a method for separating a gas mixture by utilizing hydrates. Background Art

[0002] Gas hydrates are ice-like solids formed by water and gas under low temperature and high pressure. Different gases form hydrates at different temperatures and pressures, and this property can be exploited to separate gas mixtures. Hydrate separation is most suitable for gas mixtures where the hydrate equilibrium conditions of the components vary significantly, such as CH4 / H2, CO2 / CH4, and CO2 / H2.

[0003] The formation of gas hydrates is the basis for achieving hydrate-based gas separation. Under natural conditions, hydrates form at the gas-liquid interface, hindering gas-liquid contact. This results in an extremely slow hydrate formation rate. The natural formation of milliliter-level hydrates can take several to dozens of days. To address the issue of slow hydrate formation, methods for enhancing hydrate formation, including physical and chemical methods, have been developed. Because the formation of gas hydrates is the basis for achieving hydrate-based gas separation, these methods for enhancing hydrate formation are important basic means for achieving hydrate-based gas separation. Generally speaking, the most effective method is the use of kinetic promoters in chemical methods. These kinetic promoters include sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and amino acids. Some studies have used aqueous solutions of kinetic promoters to accelerate the hydrate-based gas separation process, but separation times of several hours are still required. On the other hand, to reduce the hydrate formation pressure, some studies have added hydrate thermodynamic promoters to aqueous solutions to lower the hydrate formation conditions. These thermodynamic promoters include tetrahydrofuran and tetrabutylammonium bromide. However, thermodynamic promoters only reduce the hydrate formation pressure and have little effect on accelerating hydrate formation. Overall, existing technical solutions for hydrate gas separation are generally as follows: first, an aqueous solution containing additives (including a kinetic promoter and / or a thermodynamic promoter) is prepared and loaded into a reactor. The gas to be separated is then introduced into the reactor at low temperature. After a long period of time, hydrate formation is complete. The unhydrated gas is then discharged, and the hydrate is subsequently decomposed under low pressure (with or without heating) to yield another portion of gas. The differences between these solutions primarily lie in the first step, namely, the different hydrate formation methods, which can include using different aqueous solutions, ice powder, or water-in-oil emulsions, as well as the resulting different formation methods, such as batch reactions, bubble columns, and stirred tank reactors with filtration. Overall, hydrate formation enhancement technologies for hydrate gas separation still do not meet industrial needs.

[0004] The applicant's patent discloses a method for accelerating the formation of hydrates using an ice medium (a rapid hydrate formation medium and its preparation method, application and use method, ZL202011351034), and mentions that the ice medium can be used for the separation of mixed gases. Like most hydrate-based gas separation methods, this method is to contact the mixed gas with a hydrate-forming medium at low temperature and high pressure. After the hydrate is generated, the gas is divided into gas in the gas phase and gas in the hydrate phase. The components in these two parts of gas that are difficult and easy to hydrate are enriched respectively. The difference is that most methods use aqueous solutions to generate hydrates, while the above-mentioned patent uses a special ice medium. Overall, the problem of hydrate formation rate has been basically solved, but hydrate-based gas separation includes not only the formation of hydrates, but also the decomposition of hydrates. Specifically, hydrate gas separation technology usually includes two stages: one is hydrate formation, during which components that are difficult to hydrate are enriched in the gas phase, and components that are easy to hydrate are enriched in the hydrate; the other is hydrate decomposition. When hydrate formation is completed, the gas that has not hydrated is quickly discharged from the reactor, and then the hydrate decomposes under low pressure and releases the gas therein, thereby achieving complete separation of the two gases.

[0005] However, most of the current technologies are still at the first stage (for example, accelerating hydrate formation, reducing hydrate formation pressure, and improving separation selectivity in the first stage). No technology has been found to solve the problems of the second stage, and the problems of decomposition rate and reducing energy consumption have not been solved at the same time.

[0006] Overall, one of the shortcomings of existing technologies is their slow overall separation rate. The most common method involves separating gases by forming hydrates from a liquid aqueous solution and a gas mixture. However, even with the addition of a hydrate formation promoter, the hydrate formation process can take over half an hour, and this does not account for the hydrate decomposition time. Applicant's patent ZL202011351034 uses an ice medium to accelerate hydrate formation, which speeds up the first stage but does not account for the hydrate decomposition rate in the second stage. A second shortcoming of existing technologies is their high energy consumption. Hydrate formation in the first stage of gas separation is an exothermic process, while hydrate decomposition in the second stage is an endothermic process. Hydrate separation requires refrigeration. During the slow hydrate formation process, the heat of hydrate formation is dissipated by an external cooling source. Hydrate decomposition requires heat, and after this heat is dissipated, heating is required to accelerate the second stage of hydrate decomposition. Therefore, similar to adsorption separation, hydrate separation requires alternating cooling and heating of the reactor. High pressure, refrigeration, and heating contribute to high energy consumption in hydrate separation. Summary of the Invention

[0007] In view of this, the present invention provides a method for separating a gas mixture using hydrates. The method of the present invention can improve the separation efficiency of the gas mixture while reducing energy consumption.

[0008] The present invention provides a method for separating a gas mixture by utilizing hydrates, comprising the following steps:

[0009] A) placing ice medium into the reactor;

[0010] in,

[0011] The reactor comprises:

[0012] Kettle body (1);

[0013] The outer periphery of the kettle body (1) is provided with a jacket (2);

[0014] The lower portion of the jacket (2) is provided with a refrigerant inlet (3), and the upper portion is provided with a refrigerant outlet (4);

[0015] Grilles (5) are installed at both ends of the kettle body (1), thereby dividing the interior of the kettle body into pipes with an aspect ratio greater than 4; wherein a support net (6) is installed below the grille near the lower end of the reactor;

[0016] The upper portion of the kettle body (1) is provided with an air inlet valve (7), and the lower portion is provided with an exhaust valve (8) and a back pressure valve (9);

[0017] The ice medium is loaded into a pipe divided by a grid (5) in the kettle body (1), and the volume of the ice medium in the pipe is controlled to be greater than 60% and less than 85%;

[0018] B) Under the condition that the temperatures of the reactor and the ice medium are both maintained below 0° C., the mixed gas to be separated is charged into the reactor through the air inlet valve (7); when the pressure in the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve (9) is opened to exhaust gas outward, and the exhaust rate is controlled to be equal to the difference between the air inlet rate and the gas consumption rate of hydrate formation; as the hydrates are formed, the temperature of the ice medium rises, and when the temperature of the ice medium reaches the highest, the air inlet valve (7) is closed to stop charging, and the back pressure valve (9) is opened to quickly release the unreacted gas; after the pressure in the reactor returns to normal pressure, the back pressure valve (9) is closed, and the exhaust valve (8) is opened to decompose the hydrates and release the gas, thereby completing the gas separation.

[0019] Preferably, in step B), the temperature of the reactor and the ice medium are both maintained at a temperature higher than -5°C and lower than 0°C.

[0020] Preferably, in step B), the temperature of the mixed gas to be separated is ≤40°C.

[0021] Preferably, in step B), the temperature of the mixed gas to be separated is controlled as follows: the temperature of the ice medium ≤ the temperature of the mixed gas to be separated ≤ 40°C.

[0022] Preferably, in step B), when the mixed gas to be separated is charged into the reactor through the air inlet valve (7), the pressure of the mixed gas in the reactor is controlled as follows: the gas partial pressure of the component that easily forms hydrates in the mixed gas is greater than the hydrate phase equilibrium pressure of the component that easily forms hydrates at the ice medium temperature.

[0023] Preferably, the gas partial pressure of the component that is easy to form hydrates in the mixed gas is higher than the hydrate phase equilibrium pressure of the component that is easy to form hydrates at the ice medium temperature by ≥0.5 MPa.

[0024] Preferably, in step B), the method for judging whether the temperature of the ice medium has reached the maximum is: when the temperature in the reactor gradually rises to a certain temperature point and remains unchanged for more than 10 seconds, it is considered that the maximum temperature has been reached.

[0025] Preferably, after one gas separation treatment is completed in step B), this step is repeated to continuously perform gas separation.

[0026] Preferably, in step A), the ice medium is prepared by the following preparation method:

[0027] preparing a hydrate kinetics accelerator and water to prepare an accelerator aqueous solution;

[0028] The accelerator aqueous solution reacts with the initial gas at an initial temperature greater than 0° C. and less than 5° C. to form an initial hydrate;

[0029] The temperature of the initial hydrate obtained by the reaction, the residual accelerator aqueous solution, and the remaining initial gas is reduced to a decomposition temperature below 0°C; the remaining initial gas is discharged and the ice structure formed by freezing the frozen initial hydrate and the residual accelerator aqueous solution is maintained at normal pressure or below, so that the gas stored in the hydrate is released, and the obtained ice-like substance is the ice medium;

[0030] or

[0031] The ice medium includes ice powder and a surfactant uniformly distributed in the ice powder; or the ice medium includes ice powder and a surfactant and a thermodynamic inhibitor uniformly distributed in the ice powder, and the mass fraction of the surfactant in the ice medium is greater than 400 ppm, and the mass fraction of the thermodynamic inhibitor in the ice medium is less than C / 5, where C is the mass fraction of the thermodynamic inhibitor aqueous solution with the operating temperature of the ice medium as the freezing point, in units of wt%.

[0032] Preferably, in step A), the inner diameter of the pipe is greater than 1 cm and the length is less than 300 cm.

[0033] The method for separating a gas mixture using hydrates provided by the present invention uses a specific ice medium to be loaded into a reactor, and its loading amount and the aspect ratio of the pipeline in the reactor are controlled. Then, the reactor is inflated under certain temperature conditions. When the pressure in the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve is opened to exhaust gas outward. The exhaust is first slowly exhausted by controlling a specific exhaust rate. As hydrates form, when the temperature in the reactor reaches the highest temperature, the inflation is immediately stopped and the back pressure valve is opened to accelerate the exhaust. After the reactor reaches normal pressure, the back pressure valve is closed and the exhaust valve on the other side is opened to decompose and release gas from the hydrates, thereby completing the gas separation. The present invention uses ice as a medium to accelerate hydrate formation. At the same time, the initial gas release rate of the back pressure valve is controlled and its gas release rate is changed at specific nodes (i.e., the valve is opened immediately to release gas after the reactor temperature reaches the highest point without waiting for the hydrate to completely react and form). Then, the valve on the other side is opened to decompose and release the hydrate. All these can be completed in a relatively short time. Through continuous and rapid gas filling and releasing, a larger separation processing capacity can be achieved in a shorter time, that is, the separation rate is increased. At the same time, the heat released during hydrate formation is used to accelerate the decomposition of the hydrate, thereby minimizing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0035] Figure 1 Schematic diagram of the structure of the reactor used in the present invention. DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0037] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0038] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] As used herein, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0040] In this article, when referring to the units of a data range, if the unit is followed only by the right endpoint, it means that the units of the left and right endpoints are the same.

[0041] A method for separating a gas mixture using hydrates comprises the following steps:

[0042] A) placing ice medium into the reactor;

[0043] in,

[0044] The reactor comprises:

[0045] Kettle body 1;

[0046] The outer periphery of the kettle body 1 is provided with a jacket 2;

[0047] The lower part of the jacket 2 is provided with a refrigerant inlet 3, and the upper part is provided with a refrigerant outlet 4;

[0048] Grilles 5 are installed at both ends of the reactor body 1, thereby dividing the interior of the reactor body into pipes with an aspect ratio greater than 4; wherein a support net 6 is installed below the grille near the lower end of the reactor;

[0049] The upper part of the kettle body 1 is provided with an air inlet valve 7, and the lower part is provided with an exhaust valve 8 and a back pressure valve 9;

[0050] The ice medium is loaded into the pipes divided by the grid 5 in the kettle body 1, and the volume of the ice medium in the pipes is controlled to be greater than 60% and less than 85%;

[0051] B) While maintaining the temperatures of the reactor and the ice medium below 0° C., the mixed gas to be separated is charged into the reactor through the air inlet valve 7; when the pressure in the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve 9 is opened to exhaust gas outward, and the exhaust rate is controlled to be equal to the difference between the air inlet rate and the gas consumption rate of hydrate formation; as the hydrates form, the temperature of the ice medium increases. When the temperature of the ice medium reaches a maximum, the air inlet valve 7 is closed to stop charging, and the back pressure valve 9 is opened to quickly release unreacted gas; after the pressure in the reactor returns to atmospheric pressure, the back pressure valve 9 is closed and the exhaust valve 8 is opened to decompose the hydrates and release gas, thereby completing gas separation.

[0052] [About Step A]:

[0053] A) Charge the reactor with ice medium.

[0054] In the present invention, the ice medium is the rapid hydrate generation medium disclosed in the applicant's patent ZL202011351034 or the ice medium for accelerating the generation of gas hydrates disclosed in ZL202311089005.

[0055] Specifically:

[0056] Regarding the rapid hydrate formation medium disclosed in Patent ZL202011351034, the preparation method of the ice medium includes:

[0057] preparing a hydrate kinetics accelerator and water to prepare an accelerator aqueous solution;

[0058] The accelerator aqueous solution reacts with the initial gas at an initial temperature greater than 0° C. and less than 5° C. to form an initial hydrate;

[0059] The temperature of the initial hydrate obtained by the reaction, the residual accelerator aqueous solution, and the remaining initial gas is reduced to a decomposition temperature below 0°C; the remaining initial gas is discharged, and the ice structure formed by freezing the frozen initial hydrate and the residual accelerator aqueous solution is maintained at normal pressure or below, so that the gas stored in the hydrate is released, and the obtained ice-like substance is the ice medium.

[0060] Among them, the types of substances, amounts and condition parameters used in each step are consistent with the records in ZL202011351034 and will not be repeated here.

[0061] The ice medium disclosed in ZL202311089005 for accelerating gas hydrate formation comprises ice powder and a surfactant uniformly distributed in the ice powder, or the ice medium comprises ice powder and a surfactant and a thermodynamic inhibitor uniformly distributed in the ice powder, wherein the mass fraction of the surfactant in the ice medium is greater than 400 ppm, and the mass fraction of the thermodynamic inhibitor in the ice medium is less than C / 5, where C is the mass fraction of the thermodynamic inhibitor aqueous solution at the operating temperature of the ice medium as the freezing point, expressed in wt%. The types and amounts of substances used, as well as the preparation method of the ice medium, are consistent with those described in ZL202311089005 and are not further described here.

[0062] In the present invention, the reactor comprises:

[0063] Kettle body 1;

[0064] The outer periphery of the kettle body 1 is provided with a jacket 2;

[0065] The lower part of the jacket 2 is provided with a refrigerant inlet 3, and the upper part is provided with a refrigerant outlet 4;

[0066] Grilles 5 are installed at both ends of the reactor body 1, thereby dividing the interior of the reactor body into pipes with an aspect ratio greater than 4; wherein a support net 6 is installed below the grille near the lower end of the reactor;

[0067] The upper portion of the kettle body 1 is provided with an air inlet valve 7 , and the lower portion is provided with an exhaust valve 8 and a back pressure valve 9 .

[0068] See also Figure 1 , Figure 1 Schematic diagram of the structure of the reactor used in the present invention, wherein 1 is the reactor body, 2 is the jacket, 3 is the refrigerant inlet, 4 is the refrigerant outlet, 5 is the grid, 6 is the support net, 7 is the air inlet valve, 8 is the exhaust valve, and 9 is the back pressure valve.

[0069] The reactor is a fixed bed reactor, and a jacket 2 is provided on the outside of the reactor. The jacket 2 can be a water bath jacket. A refrigerant inlet 3 and a refrigerant outlet 4 are provided on the jacket 2, and the refrigerant flows in from the bottom and flows out from the top to maintain the temperature inside the reactor below 0°C. A grid extending from one end of the reactor to the other is installed in the reactor, that is, grids 5 are installed at both ends of the reactor body 1, thereby dividing the interior of the reactor into pipes with a certain aspect ratio. The ice medium is filled in the pipes separated by the grid, and a support net 6 is installed at the bottom of the grid at the lower end of the reactor. The present invention preferably controls the pore size of the support net to be smaller than the particle size of the ice medium to prevent the ice medium from leaking from the pipe.

[0070] In the present invention, the grid 5 divides the interior of the kettle into pipes with an aspect ratio greater than 4. Maintaining this aspect ratio facilitates gas propulsion, thereby promoting gas separation. In some embodiments of the present invention, the aspect ratio is 15. There are no specific restrictions on the length and inner diameter of the pipes. To facilitate filling with ice medium, the inner diameter is preferably greater than 1 cm. To avoid excessive pipe length, the length can be set to less than 300 cm.

[0071] In the present invention, when the ice medium is loaded into the reactor, the volume ratio of the ice medium in the pipe (i.e., the pipe divided by the grid 5 in the reactor body 1) is controlled to be greater than 60% and less than 85%, specifically 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, or 84%. The present invention controls the volume ratio within the above range. First, the space of the reactor can be fully utilized to increase the separation processing capacity; second, a higher ice medium ratio can reduce the gas ratio, so that the remaining gas can be quickly discharged after the formation is completed, avoiding the throttling effect caused by the large amount of gas discharged and the absorption of heat; third, a volume ratio of no more than 85% can leave enough space for the expansion of hydrates during formation, avoiding the blockage of the gas mass transfer channel.

[0072] In the present invention, when the ice medium is charged into the reactor, the ice medium is controlled to be charged under the condition of below 0°C, more preferably above -5°C and below 0°C, specifically -4°C, -3°C, -2°C, -1°C.

[0073] [About Step B]:

[0074] In the present invention, after the ice medium is loaded in step A), the ice medium and the reactor are both maintained at a temperature below 0°C, more preferably above -5°C and below 0°C, specifically -4°C, -3°C, -2°C, or -1°C. These temperature conditions can be controlled by an external jacket and a refrigerant.

[0075] In the present invention, before air is introduced into the reactor filled with the ice medium, valves 7, 8, and 9 are all closed. During air introduction, valve 7 is opened to initiate aeration. In the present invention, the mixed gas to be separated is introduced into the reactor through the air inlet valve 7 under the aforementioned temperature conditions (i.e., above -5°C and below 0°C). The temperature of the mixed gas to be separated is preferably controlled to be ≤ 40°C; more preferably, the temperature of the ice medium is controlled to be ≤ 40°C. Excessively high temperatures can cause excessive melting of the ice medium, hindering hydrate formation.

[0076] In the present invention, when the mixed gas to be separated is introduced into the reactor through the inlet valve 7, the pressure of the mixed gas in the reactor is preferably controlled as follows: the gas partial pressure of the hydrate-prone component in the mixed gas is greater than the hydrate phase equilibrium pressure of the hydrate-prone component at the icy medium temperature. More preferably, the gas partial pressure of the hydrate-prone component in the mixed gas exceeds the hydrate phase equilibrium pressure of the hydrate-prone component at the icy medium temperature by ≥0.5 MPa. The excess is further preferably between 0.5 and 2.0 MPa, specifically 0.5 MPa, 1.0 MPa, 1.5 MPa, or 2.0 MPa. If the pressure is less than 0.5 MPa, the driving force for hydrate formation is weak and formation is too slow. If the pressure is greater than 2.0 MPa, the pressure is too high, increasing energy consumption. The hydrate phase equilibrium pressure of the hydrate-prone component at the icy medium temperature can be calculated or experimentally determined. The calculation process is relatively complex and requires the use of complex thermodynamic models. Experimental determination is relatively simple, and well-established methods for determining phase equilibrium pressures are currently available, such as microcalorimetry and PVT reactors.

[0077] In the present invention, the mixed gas to be separated is filled into the reactor to the pressure required for separation, and when hydrates begin to form, the back pressure valve 9 is opened to slowly exhaust the gas outwards. After the mixed gas to be separated enters the reactor and contacts the ice medium, the gas in the mixed gas that is easy to form hydrates forms hydrates and is enriched in the hydrates, while the other gas that is difficult to form hydrates is enriched in the gas phase, thereby gradually separating the two gases. Among them, the pressure required for separation is determined by the phase equilibrium pressure mentioned above (the premise of hydrate separation is that hydrates must be generated, so this pressure must first ensure that hydrates can be generated, that is, the separation pressure must be higher than the phase equilibrium pressure), specifically the pressure determined by the partial pressure and molar fraction of the easily hydrated component. In the present invention, when hydrates begin to form, the back pressure valve 9 is opened to slowly exhaust the gas outwards, and the discharged gas is the separated gas, and the proportion of the easily hydrated component in the gas is reduced compared to the original mixed gas.

[0078] In the present invention, the exhaust rate of the back pressure valve 9 is preferably controlled as follows: the exhaust rate = the intake rate minus the hydrate formation gas consumption rate. The intake rate is the rate at which gas is introduced into the reactor via the intake valve 7. The hydrate formation gas consumption rate can be calculated using the law of conservation of mass as follows: For example, there are a buffer tank A and a reactor B. Reactor B contains a certain amount of ice medium. A and B are at the same temperature, and A is pre-filled with gas. The initial molar amount of gas in A, N0, can be calculated. Then, gas is introduced from A into B to initiate the reaction. After t minutes of reaction, the molar amount of gas in A, N1, can be calculated based on the temperature, pressure, and volume. The molar amount of the gas phase in reactor B, Ne, can also be calculated based on the temperature, pressure, and volume of the gas phase. The amount of gas consumed in the reaction, N, is calculated as N0 - N1 - Ne. The reaction gas consumption rate can be calculated based on the time and the amount of gas consumed during the reaction. Controlling the exhaust rate within the above range is beneficial for improving the separation efficiency of the mixed gas. If the exhaust rate is too high or too low, the separation efficiency of the mixed gas will be impaired.

[0079] In the present invention, as hydrates form, the temperature of the ice medium rises. When the ice medium temperature reaches its maximum, the inlet valve 7 is closed to stop inflation, and the back-pressure valve 9 is opened to rapidly release unreacted gas. Since hydrate formation is an exothermic reaction, the ice medium temperature rises (and the temperature within the reactor also rises) as hydrates form, until the ice medium temperature reaches its maximum (and the temperature within the reactor also reaches its maximum). The method for determining when the ice medium temperature has reached its maximum is: when the temperature within the reactor gradually rises to a certain point and remains unchanged for more than 10 seconds, it is considered to have reached the maximum temperature. In some embodiments of the present invention, this holding time is 20 seconds. When the maximum temperature is reached, the inlet valve 7 is immediately closed to stop inflation, and the back-pressure valve 9 is opened to rapidly release unreacted gas. This operation is the key point of the present invention. During the rapid hydrate formation process, gas is released immediately after the temperature reaches its maximum point (rather than waiting for the hydrates to completely react), utilizing the high temperature to decompose the hydrates. Through continuous and rapid inflation and deflation, rapid gas separation is achieved, while simultaneously achieving heat coupling and reducing energy consumption. The time to stop aeration varies with factors such as reaction scale and gas mixture type. In a laboratory reaction using approximately 10g of ice medium, aeration reached maximum temperature within 2 minutes, with a conversion rate of approximately 80%. Even when scaled up to kilograms, maximum temperature was reached within 5 minutes, achieving good separation results. Therefore, the method of the present invention significantly shortens the time required to separate the gas mixture and reduces energy consumption.

[0080] In the present invention, after the back pressure valve 9 is opened and the air is quickly released, the reactor quickly reaches normal pressure. After the pressure in the reactor reaches normal pressure, the back pressure valve 9 is closed and the exhaust valve 8 is opened to decompose the hydrate and release gas (this part of the gas is the separated gas, which is mainly the gas component that is easy to form hydrates), thereby completing the gas separation. Among them, the gas discharged by the back pressure valve 9 and the gas discharged by the exhaust valve 8 can be collected in storage tanks respectively, thereby obtaining two kinds of gas respectively. In the present invention, the back pressure valve 9 is a preferred valve type. If it is replaced with an ordinary exhaust valve, the operation is cumbersome and it is necessary to manually adjust the opening at any time to control the pressure in the reactor.

[0081] The formation of hydrates requires low temperature and high pressure conditions, so hydrate gas separation first requires refrigeration. During the slow formation of hydrates, the heat of hydrate formation is taken away by an external cooling source and removed from the reactor. The hydrate decomposition stage is an endothermic reaction that requires heat. After the heat of formation in the previous stage is taken away, the rate of hydrate decomposition will also decrease. In order to accelerate decomposition, it is necessary to reheat. Therefore, similar to adsorption separation, in order to achieve hydrate gas separation, the reactor needs to be alternately cooled and heated. High pressure, refrigeration and heating lead to high energy consumption for hydrate gas separation. The present invention accelerates the formation rate in the previous stage, reducing the loss of formation heat, and then controls the timing of gas release separation and hydrate decomposition, using the heat in the previous stage to accelerate the decomposition of hydrates, thereby coupling the formation heat and decomposition heat. In fact, it improves the hydrate separation process from a temperature and pressure change process to a pressure-only process, which not only improves the overall separation efficiency but also reduces energy consumption.

[0082] There is no particular limitation on the type of mixed gas applicable to the method of the present invention. It can be any mixed gas conventionally applicable to hydrate separation, such as CH4 / H2, CO2 / CH4, CO2 / H2, etc.

[0083] The method of the present invention can be carried out continuously. That is, after processing a batch of mixed gases, the reactor is continuously charged with gas for separation. Gas separation is continuously performed by continuous charging and discharging. That is, after step B) is completed, this step can be repeated, i.e., the hydrate formation and decomposition process is cyclically performed, thereby continuously performing gas separation.

[0084] The method for separating a gas mixture using hydrates provided by the present invention uses a specific ice medium to be loaded into a reactor, and its loading amount and the aspect ratio of the pipeline in the reactor are controlled. Then, the reactor is inflated under certain temperature conditions. When the pressure in the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve is opened to exhaust gas outward. The exhaust is first slowly exhausted by controlling a specific exhaust rate. As hydrates form, when the temperature in the reactor reaches the highest temperature, the inflation is immediately stopped and the back pressure valve is opened to accelerate the exhaust. After the reactor reaches normal pressure, the back pressure valve is closed and the exhaust valve on the other side is opened to decompose and release gas from the hydrates, thereby completing the gas separation. The present invention uses ice as a medium to accelerate hydrate formation. At the same time, the initial gas release rate of the back pressure valve is controlled and its gas release rate is changed at specific nodes (i.e., the valve is opened immediately to release gas after the reactor temperature reaches the highest point without waiting for the hydrate to completely react and form). Then, the valve on the other side is opened to decompose and release the hydrate. All these can be completed in a relatively short time. Through continuous and rapid gas filling and releasing, a larger separation processing capacity can be achieved in a shorter time, that is, the separation rate is increased. At the same time, the heat released during hydrate formation is used to accelerate the decomposition of the hydrate, thereby minimizing energy consumption.

[0085] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0086] Example 1

[0087] use Figure 1 The reactor shown uses a 15 cm long, 1.2 cm inner diameter stainless steel packing tube as the reactor, with an aspect ratio of 12.5. The reactor is placed in a constant temperature air bath to control the temperature of the reactor and the internal ice medium. The mixed gas to be separated is a CH4 / H2 mixture (wherein the molar ratio of CH4 to H2 is 0.75:0.25, with CH4 being the component that easily forms hydrates).

[0088] A) Ice medium (the ice medium prepared in Example 1 of Patent ZL202011351034) was loaded into the reactor. The ice medium loading amount was 8.0 g, and the accumulated volume accounted for about 70% of the reactor volume.

[0089] B) The temperature of the reactor and the ice medium was controlled at -1.0°C using an air bath. The mixed gas to be separated (mixed gas temperature -1.0°C) was introduced into the reactor through valve 7. The pressure in the reactor was maintained at a constant 6.0 MPa. At this point, the methane partial pressure (approximately 4.5 MPa) was greater than the equilibrium pressure of the methane hydrate phase (approximately 2.4 MPa). When hydrate formation began, the back-pressure valve 9 was opened to slowly exhaust gas at a rate of 400 mL (normal pressure) / min. After 3 minutes of separation, the temperature in the reactor rose to 6.8°C and remained constant for 20 seconds, which was considered to have reached the maximum temperature. At this point, the inlet valve 7 was closed, and the back-pressure valve 9 was opened wide to rapidly release gas, instantly discharging the remaining gas in the reactor to return the pressure in the reactor to normal pressure. Then, the back-pressure valve 9 was closed and the exhaust valve 8 on the other side was opened to decompose the hydrate and release gas. After 3 minutes of hydrate decomposition, the temperature in the reactor dropped to -1.3°C, completing the gas separation process. After step B), the hydrate formation and decomposition process was repeated.

[0090] During the separation process, the gases discharged from the back-pressure valve 9 and the exhaust valve 8 were collected in separate storage tanks and analyzed for composition using gas chromatography after separation. The gas separation factor and methane recovery rate were calculated based on the composition of the gases collected in the two storage tanks. This example completed five hydrate formation-decomposition cycles, taking a total of 35 minutes, with an average single cycle time of 7 minutes. The CH4 separation factors for the five separations were 727, 675, 631, 648, and 665, respectively; the CH4 recovery rate was approximately 51%; and a total CH4 / H2 mixture volume processed in 35 minutes was 590 mmol.

[0091] Example 2

[0092] This example used a different-sized reactor than that used in Example 1. The reactor used in this example was cylindrical, with an inner diameter of 2.54 cm and a height of 15 cm, resulting in an aspect ratio of 5.9. A 400-mesh stainless steel screen was installed at the bottom of the reactor as a support screen. The reactor was placed in a constant-temperature air bath to control the temperature of the reactor and the ice medium inside. The mixed gas to be separated was a CH4 / H2 mixture (wherein the molar ratio of CH4 to H2 was 0.75:0.25, with CH4 being the component that readily forms hydrates).

[0093] A) Ice medium (the ice medium prepared in Example 1 of Patent ZL202011351034) was loaded into the reactor. The ice medium loading amount was 30.0 g, and the accumulated volume accounted for about 60% of the reactor volume.

[0094] B) The temperature of the reactor and the ice medium was controlled at -1.0°C using an air bath. The mixed gas to be separated (mixed gas temperature was -1°C) was introduced into the reactor through valve 7. The pressure in the reactor was controlled to be constant at 6.0 MPa. At this point, the methane partial pressure (approximately 4.5 MPa) was greater than the equilibrium pressure of the methane hydrate phase (approximately 2.4 MPa). When hydrate formation began, the back-pressure valve 9 was opened to slowly exhaust gas at a rate of 1450 mL (normal pressure) / min. After 3 minutes of separation, the temperature in the reactor rose to 6.8°C and remained constant for 20 seconds, which was considered to have reached the maximum temperature. At this time, the inlet valve 7 was closed, and the back-pressure valve 9 was opened to rapidly release gas, instantly discharging the remaining gas in the reactor to return the pressure in the reactor to normal pressure. Then, the back-pressure valve 9 was closed and the exhaust valve 8 on the other side was opened to decompose the hydrate and release gas. After 3 minutes of hydrate decomposition, the temperature in the reactor dropped to -0.8°C, completing the gas separation process.

[0095] The separation process took 7 minutes, the CH4 separation factor was 597, and the CH4 recovery rate was 45%.

[0096] Example 3

[0097] This embodiment differs from Example 1 in that the temperature of the gas to be separated used in this embodiment is higher, at 21°C, and a single hydrate formation-decomposition cycle is performed. The remaining operating steps are consistent with Example 1. Approximately 2 minutes and 30 seconds after the start of separation, the temperature in the reactor reaches 6.8°C and remains unchanged for 20 seconds, which is considered to have reached the maximum temperature. At this time, the air inlet valve 7 is closed, and the back pressure valve 9 is opened to quickly release the gas, instantly discharging the remaining gas in the reactor to bring the pressure in the reactor to atmospheric pressure. Then, the back pressure valve 9 is closed and the exhaust valve 8 on the other side is opened to decompose the hydrate and release the gas. After 3 minutes of hydrate decomposition, the temperature in the reactor drops to -0.9°C, and the gas separation process is completed.

[0098] The separation process took 6 minutes, the CH4 separation factor was 619, and the CH4 recovery rate was 49%.

[0099] Example 4

[0100] The difference between this embodiment and embodiment 1 is that the temperature of the reactor and the ice medium therein before air intake is -4°C, the temperature of the gas to be separated is 20°C, and a single hydrate formation-decomposition cycle is performed. The exhaust rate during the separation process is about 310 mL / minute, and the remaining operating steps are consistent with embodiment 1. About 3 minutes and 40 seconds after the start of separation, the temperature in the reactor reaches 6.8°C and remains unchanged for 20 seconds, which is considered to have reached the maximum temperature. At this time, the air intake valve 7 is closed, and the back pressure valve 9 is opened to quickly release the gas, instantly discharging the remaining gas in the reactor to bring the pressure in the reactor to normal pressure. Then, the back pressure valve 9 is closed and the exhaust valve 8 on the other side is opened to decompose the hydrate and release the gas. The hydrate decomposes for 3 minutes, and the temperature in the reactor drops to -3.6°C, completing the gas separation process.

[0101] The separation process took 7 minutes, the CH4 separation factor was 605, and the CH4 recovery rate was 46%.

[0102] Comparative Example 1

[0103] The process was carried out in accordance with Example 1, except that the initial exhaust rate of the back pressure valve 9 was set to 200 mL / min.

[0104] The results showed that the separation factors achieved after five cycles were 612, 517, 535, 561, and 533, respectively. The mixer throughput was approximately 420 mmol within 35 minutes, and the CH4 recovery rate was approximately 54%. It can be seen that the slow exhaust rate significantly reduced the mixed gas throughput. Furthermore, due to the untimely replacement of the mixed gas in the reactor, the H2 partial pressure in the reactor increased rapidly, resulting in unsatisfactory hydrate formation and reduced separation selectivity.

[0105] Comparative Example 2

[0106] The process was carried out in accordance with Example 1, except that the initial exhaust rate of the back pressure valve 9 was set to 800 mL / min.

[0107] The results showed that the separation factors achieved after five cycles were 387, 315, 361, 348, and 352, respectively. The mixer throughput was approximately 1019 mmol in 35 minutes, and the CH4 recovery rate was approximately 32%. It can be seen that the excessive exhaust rate significantly reduced both the separation selectivity and the CH4 recovery rate, despite the increased throughput.

[0108] Comparative Example 3

[0109] The process was carried out in accordance with Example 1, except that the loading amount of the ice medium was 4.0 g, which accounted for about 35% of the volume of the reactor. As the loading amount was reduced, the corresponding exhaust rate was also reduced to 185 mL / min.

[0110] The results showed that the separation factors achieved after five cycles were 809, 781, 753, 748, and 772, respectively. The mixer throughput was approximately 315 mmol within 35 minutes, and the CH4 recovery rate was approximately 53%. It can be seen that when the loading is low, the separation selectivity and recovery rate are slightly improved, but the mixed gas throughput is significantly reduced, thereby reducing the overall processing efficiency.

[0111] Comparative Example 4

[0112] The process was carried out in accordance with Example 1, except that the loading amount of the ice medium was 9.5 g, which accounted for approximately 88% of the volume of the reactor.

[0113] The results showed that the gas channel was blocked during the reaction, the gas could not pass through the filling tube smoothly, and gas separation could not be completed.

[0114] Comparative Example 5

[0115] The process was carried out in accordance with Example 1, except that both the hydrate formation time and the decomposition time were extended to 15 minutes (specifically, when the temperature in the reactor rose to 6.8° C. after 3 minutes of separation, the back-pressure valve 9 was not immediately opened to release gas, but rather the valve was opened to release gas 15 minutes later; similarly, when the back-pressure valve 9 was closed and the exhaust valve 8 on the other side was opened to decompose the hydrate and release gas, the exhaust valve 8 was kept open for 15 minutes). The exhaust rate was correspondingly reduced to 80 mL / min, and only one hydrate formation-decomposition cycle was performed.

[0116] The results showed a CH4 separation factor of 779, a CH4 recovery of 52%, and a mixed gas throughput of 127 mmol in 30 minutes. This indicates that even when using ice as a medium for hydrate formation, extending the hydrate formation time does not improve separation selectivity. Instead, it reduces mixed gas throughput and separation efficiency. Furthermore, prolonged refrigeration increases the energy consumption per unit gas mass separated.

[0117] Comparative Example 6

[0118] The process was carried out in accordance with Example 1, except that in step B), the temperature of the reaction vessel and the ice medium was controlled at -7°C.

[0119] The results showed that hydrates were almost impossible to form, and only a small amount of gas was released after separation. This indicates that the temperature was too low to form hydrates and, therefore, to separate the gas.

[0120] Comparative Example 7

[0121] The process was carried out in the same manner as in Example 1, except that a high-pressure stainless steel packing tube with a length of 2.3 cm and an inner diameter of 2.5 cm was used as the reactor, and the reactor aspect ratio was 0.92. A hydrate formation-decomposition cycle was performed.

[0122] The results showed that the CH4 separation factor was 179 and the CH4 recovery rate was 27%, indicating that the separation efficiency was significantly reduced when the aspect ratio was too small.

[0123] Comparative Example 8

[0124] The experiment was conducted according to Example 1, except that an aqueous solution containing sodium lauryl sulfate at the same concentration was used as the medium instead of ice. To ensure the aqueous solution in the reactor remained liquid, the experimental temperature was maintained at 2°C. Simultaneously, a CH₄ / H₂ gas mixture of the same concentration was separated using an intermittent operation mode: when the aqueous solution in the reactor reached the experimental temperature, the mixed gas to be separated was introduced into the reactor to a pressure of 6.0 MPa and maintained constant during hydrate formation. Hydrate formation was complete after 30 minutes of reaction, and unreacted gas was rapidly discharged and collected. The hydrate was then decomposed at atmospheric pressure, and the decomposed gas was collected.

[0125] The results showed that the CH4 recovery rate was 29% and the separation factor was 65. This comparative example is a conventional hydrate gas separation method, which shows that the separation method of the present invention can achieve a more efficient separation effect.

[0126] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for separating a gas mixture using hydrates, characterized in that: The following steps are involved: A) placing ice medium into the reactor; in, The reactor comprises: Kettle body (1); The outer periphery of the kettle body (1) is provided with a jacket (2); The lower portion of the jacket (2) is provided with a refrigerant inlet (3), and the upper portion is provided with a refrigerant outlet (4); Grilles (5) are installed at both ends of the kettle body (1), thereby dividing the interior of the kettle body into pipes with an aspect ratio greater than 4; wherein a support net (6) is installed below the grille near the lower end of the reactor; The upper portion of the kettle body (1) is provided with an air inlet valve (7), and the lower portion is provided with an exhaust valve (8) and a back pressure valve (9); The ice medium is loaded into a pipe divided by a grid (5) in the kettle body (1), and the volume of the ice medium in the pipe is controlled to be greater than 60% and less than 85%; B) Under the condition that the temperatures of the reactor and the ice medium are both maintained below 0° C., the mixed gas to be separated is charged into the reactor through the air inlet valve (7); when the pressure in the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve (9) is opened to exhaust gas outward, and the exhaust rate is controlled to be equal to the difference between the air inlet rate and the gas consumption rate of hydrate formation; as the hydrates are formed, the temperature of the ice medium rises, and when the temperature of the ice medium reaches the highest, the air inlet valve (7) is closed to stop charging, and the back pressure valve (9) is opened to quickly release the unreacted gas; after the pressure in the reactor returns to normal pressure, the back pressure valve (9) is closed, and the exhaust valve (8) is opened to decompose the hydrates and release the gas, thereby completing the gas separation.

2. The method according to claim 1, characterized in that In step B), the temperature of the reactor and the ice medium are both maintained at a temperature higher than -5°C and lower than 0°C.

3. The method according to claim 1, characterized in that In step B), the temperature of the mixed gas to be separated is ≤40°C.

4. The method according to claim 1 or 3, characterized in that In step B), the temperature of the mixed gas to be separated is controlled as follows: the temperature of the ice medium ≤ the temperature of the mixed gas to be separated ≤ 40°C.

5. The method according to claim 1, wherein In step B), when the mixed gas to be separated is charged into the reactor through the air inlet valve (7), the pressure of the mixed gas in the reactor is controlled as follows: the gas partial pressure of the component that is easy to form hydrates in the mixed gas is greater than the hydrate phase equilibrium pressure of the component that is easy to form hydrates at the ice medium temperature.

6. The method according to claim 5, characterized in that The gas partial pressure of the hydrate-prone component in the mixed gas is higher than the hydrate phase equilibrium pressure of the hydrate-prone component at the ice medium temperature by ≥0.5 MPa.

7. The method according to claim 1, characterized in that In step B), the method for judging whether the temperature of the ice medium has reached the maximum is: when the temperature in the reactor gradually rises to a certain temperature point and remains unchanged for more than 10 seconds, it is considered to have reached the maximum temperature.

8. The method according to claim 1, characterized in that After one gas separation process is completed in step B), this step is repeated to continuously perform gas separation.

9. The method according to claim 1, characterized in that In step A), the ice medium is prepared by the following preparation method: preparing a hydrate kinetics accelerator and water to prepare an accelerator aqueous solution; The accelerator aqueous solution reacts with the initial gas at an initial temperature greater than 0° C. and less than 5° C. to form an initial hydrate; The temperature of the initial hydrate obtained by the reaction, the residual accelerator aqueous solution, and the remaining initial gas is reduced to a decomposition temperature below 0°C; the remaining initial gas is discharged and the ice structure formed by freezing the frozen initial hydrate and the residual accelerator aqueous solution is maintained at normal pressure or below, so that the gas stored in the hydrate is released, and the obtained ice-like substance is the ice medium; or The ice medium includes ice powder and a surfactant uniformly distributed in the ice powder; or the ice medium includes ice powder and a surfactant and a thermodynamic inhibitor uniformly distributed in the ice powder, and the mass fraction of the surfactant in the ice medium is greater than 400 ppm, and the mass fraction of the thermodynamic inhibitor in the ice medium is less than C / 5, where C is the mass fraction of the thermodynamic inhibitor aqueous solution with the operating temperature of the ice medium as the freezing point, in units of wt%.

10. The method according to claim 1, characterized in that In step A), the inner diameter of the pipe is greater than 1 cm and the length is less than 300 cm.

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