A method for separating a gas mixture using hydrates

Abstract

The present application relates to the field of gas separation, in particular to a method for separating gas mixture by using hydrate. The method for separating gas mixture by using hydrate comprises the following steps: loading a specific ice medium into a reactor, controlling the loading amount and the length-diameter ratio of the pipeline in the reactor, then charging the reactor with gas under certain temperature conditions, opening a back pressure valve to discharge gas when the pressure in the reactor reaches the required pressure for separation and hydrate begins to form, controlling the specific exhaust rate to slowly discharge gas, stopping the charging and opening the back pressure valve to accelerate the discharge when the highest temperature in the reactor is reached, closing the back pressure valve and opening another exhaust valve to make the hydrate decompose and release gas when the pressure in the reactor reaches normal pressure, thereby completing the gas separation. The method can improve the separation efficiency of the gas mixture and reduce energy consumption.

Description

Technical Field

[0001] This invention relates to the field of gas separation, and in particular to a method for separating gas mixtures using hydrates. Background Technology

[0002] Gas hydrates are ice-like solids formed from water and gases under low temperature and high pressure. Different gases require different temperature and pressure conditions to form hydrates; this property can be used to separate gas mixtures. The hydrate method for gas separation is best suited for gas mixtures where the phase equilibrium conditions for hydrate formation vary significantly, such as CH4 / H2, CO2 / CH4, and CO2 / H2.

[0003] The formation of gas hydrates is fundamental to gas separation using the hydrate method. Under natural conditions, hydrates form at the gas-liquid interface, hindering gas-liquid contact and resulting in an extremely slow formation rate; the natural formation of milliliter-sized hydrates can take several days to tens of days. To address this slow formation rate, methods for enhancing hydrate formation, including physical and chemical methods, have been developed. Since gas hydrate formation is essential for gas separation using the hydrate method, these methods are crucial for achieving this separation. Generally, the most effective method is the use of kinetic promoters in chemical methods, such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and amino acids. Some studies have used aqueous solutions of kinetic promoters to accelerate the gas separation process using the hydrate method, but this still requires several hours of separation time. On the other hand, to reduce the pressure of hydrate formation, some studies have added thermodynamic promoters to the aqueous solution to lower the formation conditions. These promoters include tetrahydrofuran and tetrabutylammonium bromide. However, these promoters only reduce the pressure of hydrate formation and their effect on accelerating hydrate formation is not significant. Overall, existing technical solutions for gas separation using hydrate methods are basically as follows: First, an aqueous solution containing additives (including kinetic promoters and / or thermodynamic promoters) is prepared and loaded into a reactor. The gas to be separated is then introduced into the reactor at low temperature. After a relatively long period, hydrate formation is complete. The gas that has not formed hydrates is then discharged, and subsequently, the hydrates are decomposed under low pressure (with or without heating) to obtain another portion of the gas. The main difference between these solutions lies in the first step, namely the different methods of hydrate formation, including using different aqueous solutions, ice powder, or water-in-oil emulsions, and the resulting differences in formation methods, such as batch reactions, bubble columns, and stirred reactors with filtration. In general, the hydrate formation enhancement technology used for gas separation using hydrate methods does not yet meet industrial needs.

[0004] The applicant's patent discloses a method for accelerating hydrate formation using an ice medium (A hydrate rapid formation medium and its preparation, application, and usage method, ZL202011351034), and mentions that this ice medium can be used for the separation of mixed gases. Similar to most hydrate-based gas separation methods, this method involves contacting the mixed gas with a hydrate-forming medium under low temperature and high pressure. After hydrate formation, the gas separates into a gas phase and a hydrate phase, with the components that are difficult and easy to form hydrates in these two phases being enriched respectively. The difference is that most methods use aqueous solutions to form hydrates, while the aforementioned patent uses a special ice medium. Overall, the problem of hydrate formation rate has been largely solved; however, hydrate-based gas separation involves not only hydrate formation but also hydrate decomposition. Specifically, the hydrate-based gas separation technology typically includes two stages: first, hydrate formation, in which components that are difficult to form hydrates are enriched in the gas phase, while components that are easy to form hydrates are enriched in the hydrate; second, hydrate decomposition, in which the gas that has not formed hydrates is quickly discharged from the reactor after hydrate formation, and then the hydrate decomposes under low pressure and releases the gas, thereby achieving complete separation of the two gases.

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

[0006] Overall, one drawback of existing technologies is their slow overall separation rate: the most common method is to use a liquid aqueous solution to form hydrates in a gas mixture for gas separation, but even with the addition of hydrate formation promoters, the hydrate formation process still takes more than half an hour, and the hydrate decomposition time is not considered. The applicant's patent ZL202011351034 uses ice as a medium to accelerate hydrate formation, thus speeding up the first stage, but it does not consider the second stage hydrate decomposition rate. Another drawback of existing technologies is high energy consumption: the first stage of hydrate formation in hydrate-based gas separation is exothermic, while the second stage is endothermic. Hydrate-based gas separation requires refrigeration; during the slow formation of hydrates, the heat of formation is carried away by an external cold source. However, hydrate decomposition requires heat, and after the heat of formation is carried away, heating is needed to accelerate the second stage of hydrate decomposition. Therefore, similar to adsorption separation, hydrate-based gas separation requires alternating cooling and heating of the reaction vessel. High pressure, refrigeration, and heating result in high energy consumption for hydrate-based gas separation. Summary of the Invention

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

[0008] This invention provides a method for separating gas mixtures using hydrates, comprising the following steps:

[0009] A) Load the ice medium into the reaction vessel;

[0010] in,

[0011] The reaction vessel includes:

[0012] The vessel body (1);

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

[0014] The jacket (2) is provided with a refrigerant inlet (3) at the bottom and a refrigerant outlet (4) at the top;

[0015] The vessel body (1) is equipped with grids (5) at both ends, thereby dividing the interior of the vessel body into pipes with a length-to-diameter ratio greater than 4; wherein, a support net (6) is installed below the grid near the lower end of the reactor.

[0016] The upper part of the vessel 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);

[0017] The ice medium is filled in the pipes separated by the grid (5) in the vessel body (1), and the volume ratio of the ice medium in the pipes is controlled to be greater than 60% and less than 85%.

[0018] B) Under the condition that the temperature of the reactor and the ice medium are both kept below 0°C, the mixed gas to be separated is introduced into the reactor through the 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, and the exhaust rate is controlled to be equal to the difference between the inlet rate and the gas consumption rate for hydrate formation; as hydrates are formed, the temperature of the ice medium rises, and when the temperature of the ice medium reaches its maximum, the inlet valve (7) is closed to stop the gas supply, and the back pressure valve (9) is opened to quickly release the unreacted gas; after the pressure in the reactor is 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 both the reactor and the ice medium is maintained at a temperature above -5°C and below 0°C.

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

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

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

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

[0024] Preferably, in step B), the method for determining that the ice medium temperature has reached its maximum is: when the temperature inside 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 completing one gas separation process in step B), the step is repeated to continuously perform gas separation.

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

[0027] The hydrate kinetics promoter was prepared into an aqueous solution with water;

[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 initial hydrate, residual accelerator aqueous solution, and remaining initial gas obtained from the reaction are cooled 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 residual accelerator aqueous solution is kept at atmospheric pressure or below, so that the gas stored in the hydrate is released, and the resulting ice-like substance is the ice medium.

[0030] or

[0031] The ice medium 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 surfactant accounts for a mass fraction of the ice medium 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 freezing point of the ice medium as the operating temperature, in wt%.

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

[0033] The present invention provides a method for separating gas mixtures using hydrates. A specific ice medium is loaded into a reaction vessel, and the loading amount and the length-to-diameter ratio of the pipes inside the vessel are controlled. Then, gas is introduced into the reaction vessel under certain temperature conditions. When the pressure inside the reaction vessel reaches the pressure required for separation and hydrates begin to form, the back pressure valve is opened to release gas. Initially, the gas is released slowly at a controlled rate. As hydrates form, when the temperature inside the reaction vessel reaches its maximum, the gas supply is immediately stopped, and the back pressure valve is opened to accelerate the gas release. After the pressure inside the reaction vessel reaches atmospheric pressure, the back pressure valve is closed, and the other exhaust valve is opened to allow the hydrates to decompose and release gas, thus completing the gas separation. This invention uses ice as a medium to accelerate hydrate formation. Simultaneously, it controls the initial venting rate of the back pressure valve and alters its venting rate at specific points (i.e., immediately opening the valve to release gas after the reactor temperature reaches its highest point, without waiting for the hydrate to fully react and form). Then, it opens the valve on the other side to decompose and release the hydrate. These steps can be completed in a short time, allowing for a larger separation throughput in a shorter period through continuous rapid charging and discharging, thus increasing the separation rate. Furthermore, the heat released during hydrate formation is utilized to accelerate hydrate decomposition, minimizing energy consumption. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the reactor used in this invention. Detailed Implementation

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0037] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0038] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0039] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, 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 to which they are incorporated.

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

[0041] A method for separating gas mixtures using hydrates includes the following steps:

[0042] A) Load the ice medium into the reaction vessel;

[0043] in,

[0044] The reaction vessel includes:

[0045] 1. Pot body;

[0046] A jacket 2 is provided around the periphery of the vessel body 1;

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

[0048] The vessel body 1 has grids 5 installed at both ends, which divides the interior of the vessel body into pipes with a length-to-diameter ratio greater than 4; a support net 6 is installed below the grid at the lower end of the reactor.

[0049] The upper part of the vessel 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 filled in the pipes divided by the grid 5 in the vessel body 1, and the volume ratio of the ice medium in the pipes is controlled to be greater than 60% and less than 85%.

[0051] B) Under the condition that the temperature of the reactor and the ice medium is maintained below 0°C, the mixed gas to be separated is introduced into the reactor through the inlet valve 7; when the pressure inside the reactor reaches the pressure required for separation and hydrates begin to form, the back pressure valve 9 is opened to exhaust gas, and the exhaust rate is controlled to be equal to the difference between the inlet rate and the gas consumption rate for hydrate formation; as hydrates are formed, the temperature of the ice medium rises, and when the temperature of the ice medium reaches its maximum, the inlet valve 7 is closed to stop the gas supply, and the back pressure valve 9 is opened to quickly release the unreacted gas; after the pressure inside the reactor is at atmospheric 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.

[0052] [Regarding step A]:

[0053] A) Load the ice medium into the reactor.

[0054] In this invention, the ice medium is the hydrate rapid 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] The method for preparing the ice medium for the rapid hydrate generation disclosed in patent ZL202011351034 includes:

[0057] The hydrate kinetics promoter was prepared into an aqueous solution with water;

[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 initial hydrate, residual accelerator aqueous solution, and remaining initial gas obtained from the reaction are cooled 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 residual accelerator aqueous solution is kept at atmospheric pressure or below, so that the gas stored in the hydrate is released, and the resulting ice-like substance is the ice medium.

[0060] The types of substances, amounts, and conditions used in each step are consistent with those recorded in ZL202011351034, and will not be repeated here.

[0061] The ice medium for accelerating the formation of gas hydrates disclosed in ZL202311089005 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 surfactant accounts for more than 400 ppm of the mass fraction of the ice medium, and the thermodynamic inhibitor accounts for less than C / 5 of the mass fraction of the ice medium, where C is the mass fraction of the thermodynamic inhibitor aqueous solution with the freezing point of the ice medium as the operating temperature, 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 will not be repeated here.

[0062] In this invention, the reaction vessel includes:

[0063] 1. Pot body;

[0064] A jacket 2 is provided around the periphery of the vessel body 1;

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

[0066] The vessel body 1 has grids 5 installed at both ends, which divides the interior of the vessel body into pipes with a length-to-diameter ratio greater than 4; a support net 6 is installed below the grid at the lower end of the reactor.

[0067] The upper part of the vessel 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.

[0068] See Figure 1 , Figure 1 This is a schematic diagram of the reactor used in this 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 mesh, 7 is the air inlet valve, 8 is the air outlet valve, and 9 is the back pressure valve.

[0069] The reactor is a fixed-bed reactor with an external jacket 2. The jacket 2 can be a water bath jacket. A refrigerant inlet 3 and a refrigerant outlet 4 are respectively provided on the jacket 2. The refrigerant flows in from the bottom and out from the top to maintain the internal temperature of the reactor below 0°C. A grid extending from one end of the reactor to the other is installed inside 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 length-to-diameter ratio. Ice medium is filled into the pipes divided by the grid. A support mesh 6 is installed at the bottom of the grid at the lower end of the reactor. Preferably, the aperture of the support mesh is smaller than the particle size of the ice medium to prevent leakage of the ice medium from the pipes.

[0070] In this invention, the interior of the vessel is divided into pipes with a length-to-diameter ratio greater than 4 by a grid 5. Maintaining this ratio facilitates gas forward propagation, thereby promoting gas separation. In some embodiments of this invention, the length-to-diameter ratio is 15. There are no special limitations on the length and inner diameter of the pipes; however, to facilitate the filling of ice-medium packing material, the inner diameter is preferably 1 cm or more; to avoid excessive pipe length, its length can be set below 300 cm.

[0071] In this invention, when the ice medium is loaded into the reactor, the volume percentage 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%, and 84%. Controlling the volume percentage within the above range has several advantages: first, it maximizes the use of reactor space and increases separation throughput; second, a higher ice medium percentage reduces the gas percentage, allowing for rapid venting of remaining gas after generation, avoiding the throttling effect and heat absorption caused by large-scale gas discharge; and third, a volume percentage not exceeding 85% provides sufficient space for expansion during hydrate formation, preventing blockage of the gas mass transfer channels.

[0072] In this invention, when the ice medium is loaded into the reaction vessel, the ice medium is controlled to be loaded 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.

[0073] [Regarding step B]:

[0074] In this invention, after the ice medium is filled in step A), both the ice medium and the reactor are kept 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 refrigerant.

[0075] In this invention, valves 7, 8, and 9 are all closed before introducing gas into the reactor filled with ice medium. During gas introduction, valve 7 is opened for charging. In this invention, the mixture to be separated is introduced into the reactor through the gas inlet valve 7 under the aforementioned temperature conditions (i.e., above -5°C and below 0°C). Preferably, the temperature of the mixture to be separated is controlled to ≤40°C; more preferably, it is controlled as follows: the temperature of the ice medium ≤ the temperature of the mixture to be separated ≤ 40°C. If the temperature is too high, excessive melting of the ice medium will affect hydrate formation.

[0076] In this 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 partial pressure of the gas 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. More preferably, the difference between the partial pressure of the gas component that easily forms hydrates in the mixed gas and the hydrate phase equilibrium pressure of the component that easily forms hydrates at the ice medium temperature is ≥0.5 MPa, and the difference is further preferably 0.5 to 2.0 MPa, specifically 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.0 MPa; if it is lower than 0.5 MPa, the driving force for generation is small, and generation is too slow; if it is higher than 2.0 MPa, the pressure is too high, and energy consumption increases. The hydrate phase equilibrium pressure of the component that easily forms hydrates at the ice medium temperature can be calculated or experimentally determined. The calculation process is relatively complex and requires a complex thermodynamic model; the experimental determination is relatively simple, and there are already mature methods for determining phase equilibrium pressure, such as using a microcalorimeter or a PVT reactor.

[0077] In this invention, the mixed gas to be separated is introduced into the reactor to the required separation pressure. When hydrates begin to form, the back pressure valve 9 is opened to slowly exhaust the gas. After the mixed gas enters the reactor and comes into contact with the ice medium, the gas in the mixed gas that readily forms hydrates forms hydrates and accumulates in the hydrate, while the other gas, which is less likely to form hydrates, accumulates in the gas phase, thus gradually separating the two gases. The required separation pressure is determined by the phase equilibrium pressure mentioned earlier (the premise of hydrate separation is that hydrates must form; therefore, this pressure must first ensure that hydrates can form, i.e., the separation pressure must be higher than the phase equilibrium pressure), specifically determined by the partial pressure and mole fraction of the easily hydrated component. In this invention, when hydrate formation begins, the back pressure valve 9 is opened to slowly exhaust the gas. The exhaust gas is the separated gas, and the proportion of the easily hydrated component in this gas is reduced compared to the original mixed gas.

[0078] In this invention, the preferred control is that the exhaust rate of the back pressure valve 9 equals the intake rate minus the gas consumption rate for hydrate formation. The intake rate is the rate at which gas is introduced into the reactor through the intake valve 7. The gas consumption rate for hydrate formation can be calculated using the law of conservation of mass; for example, consider a buffer tank A and a reactor B. Reactor B contains a certain amount of ice medium, and A and B are at the same temperature. A is pre-charged with gas. The initial molar amount N0 of the gas in A can be calculated. Then, gas is introduced from A into B to start the reaction. After t minutes of reaction, the molar amount N1 of the gas in A can be calculated based on temperature, pressure, and volume. Similarly, the molar amount Ne of the gas phase in reactor B can be calculated based on temperature, pressure, and gas phase volume. The amount of gas consumed in the reaction is N = N0 - N1 - Ne. Based on the time and the amount of gas consumed, the gas consumption rate of the reaction can be obtained. Controlling the exhaust rate at the above-mentioned level is beneficial for improving the separation effect of the mixed gas. If the rate is too high or too low, the separation effect of the mixed gas will deteriorate.

[0079] In this invention, as hydrates are formed, the temperature of the ice medium rises. When the ice medium temperature reaches its maximum, the inlet valve 7 is closed to stop gas filling, and the back pressure valve 9 is opened to rapidly release unreacted gas. Since hydrate formation is an exothermic reaction, the ice medium temperature will rise (and the temperature inside the reactor will also rise) until it reaches its maximum (and the temperature inside the reactor will also reach its maximum). The method for determining when the ice medium temperature has reached its maximum is: when the temperature inside the reactor gradually rises to a certain point and remains constant for more than 10 seconds, it is considered to have reached the maximum temperature. In some embodiments of this invention, the maintenance time is 20 seconds. When the maximum temperature is reached, the inlet valve 7 is immediately closed to stop gas filling, and the back pressure valve 9 is opened to rapidly release unreacted gas. This operation is the key point of this invention. During the rapid formation of hydrates, gas is released immediately after the temperature reaches its maximum (without waiting for the hydrates to fully react and form), using high temperature to decompose the hydrates. Through continuous and rapid gas filling and releasing, rapid gas separation is achieved, while simultaneously achieving heat coupling and reducing energy consumption. The timing for stopping the gas filling varies depending on factors such as the reaction scale and the type of mixed gas. In a laboratory reaction with approximately 10g of ice medium, the maximum temperature can be reached within 2 minutes of filling, with a reaction conversion rate of about 80%. Even on a scale of kilograms, the maximum temperature can be reached within 5 minutes, achieving a good separation effect. Therefore, the method of this invention can significantly shorten the time for separating the mixed gas and reduce energy consumption.

[0080] In this invention, after rapidly releasing gas by opening the back pressure valve 9, the pressure inside the reactor quickly reaches atmospheric pressure. Once atmospheric pressure is reached, the back pressure valve 9 is closed, and the exhaust valve 8 is opened, causing the hydrate to decompose and release gas (this gas is the separated gas, mainly consisting of the gaseous component that readily forms hydrates), thus completing gas separation. The gas discharged from the back pressure valve 9 and the gas discharged from the exhaust valve 8 can be collected separately in storage tanks, thus obtaining two different gases. In this invention, the back pressure valve 9 is the preferred valve type. If a common exhaust valve were used, operation would be cumbersome, requiring manual adjustment of the opening to control the pressure inside the reactor.

[0081] The formation of hydrates requires low-temperature and high-pressure conditions. Therefore, hydrate-based gas separation first requires refrigeration. During the slow formation of hydrates, the heat of formation is carried away from the reactor by an external cold source. However, the decomposition stage of hydrates is an endothermic reaction that requires heat. After the heat of formation in the previous stage is carried away, the rate of hydrate decomposition slows down. To accelerate decomposition, reheating is necessary. Therefore, similar to adsorption separation, hydrate-based gas separation requires alternating cooling and heating of the reactor. High pressure, refrigeration, and heating result in high energy consumption in hydrate-based gas separation. This invention accelerates the formation rate in the first stage, reducing the loss of heat of formation. Then, it controls the timing of gas release and hydrate decomposition, utilizing the heat from the previous stage to accelerate hydrate decomposition. This couples the heat of formation and the heat of decomposition, effectively improving the hydrate separation process from a temperature and pressure-switching process to a pressure-switching process only. This not only improves the overall separation efficiency but also reduces energy consumption.

[0082] There are no special limitations on the types of mixed gases applicable to the method of the present invention. Any mixed gas conventionally applicable to hydrate separation can be used, such as CH4 / H2, CO2 / CH4, CO2 / H2, etc.

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

[0084] The present invention provides a method for separating gas mixtures using hydrates. A specific ice medium is loaded into a reaction vessel, and the loading amount and the length-to-diameter ratio of the pipes inside the vessel are controlled. Then, gas is introduced into the reaction vessel under certain temperature conditions. When the pressure inside the reaction vessel reaches the pressure required for separation and hydrates begin to form, the back pressure valve is opened to release gas. Initially, the gas is released slowly at a controlled rate. As hydrates form, when the temperature inside the reaction vessel reaches its maximum, the gas supply is immediately stopped, and the back pressure valve is opened to accelerate the gas release. After the pressure inside the reaction vessel reaches atmospheric pressure, the back pressure valve is closed, and the other exhaust valve is opened to allow the hydrates to decompose and release gas, thus completing the gas separation. This invention uses ice as a medium to accelerate hydrate formation. Simultaneously, it controls the initial venting rate of the back pressure valve and alters its venting rate at specific points (i.e., immediately opening the valve to release gas after the reactor temperature reaches its highest point, without waiting for the hydrate to fully react and form). Then, it opens the valve on the other side to decompose and release the hydrate. These steps can be completed in a short time, allowing for a larger separation throughput in a shorter period through continuous rapid charging and discharging, thus increasing the separation rate. Furthermore, the heat released during hydrate formation is utilized to accelerate hydrate decomposition, minimizing energy consumption.

[0085] 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, and not for limiting the scope of the claims of the present invention.

[0086] Example 1

[0087] use Figure 1 The reactor shown uses a 15cm long, 1.2cm inner diameter stainless steel packed tube as the reactor, with a length-to-diameter 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 gas mixture to be separated is a CH4 / H2 mixture (where the molar ratio of CH4 to H2 is 0.75:0.25, and CH4 is the component that readily forms hydrates).

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

[0089] B) The temperature of the reactor and ice medium is controlled at -1.0℃ using an air bath. The mixed gas to be separated (temperature -1.0℃) is introduced into the reactor through valve 7, and the gas pressure inside the reactor is kept constant at 6.0MPa. At this point, the partial pressure of methane (approximately 4.5MPa) is greater than the phase equilibrium pressure of methane hydrate (approximately 2.4MPa). When hydrate begins to form, the back pressure valve 9 is opened to slowly exhaust gas, controlling the exhaust rate at 400mL (atmospheric pressure) / min. After 3 minutes of separation, the temperature inside the reactor rises to 6.8℃ and remains constant for the next 20 seconds, which is considered to be the highest temperature. At this point, the inlet valve 7 is closed, and the back pressure valve 9 is opened wide to rapidly release gas, instantly expelling the remaining gas inside the reactor and bringing the pressure inside the reactor back to atmospheric pressure. Then, the back pressure valve 9 is closed, and the exhaust valve 8 on the other side is opened to allow the hydrate to decompose and release gas. After 3 minutes of hydrate decomposition, the temperature inside the reactor drops to -1.3℃, and the gas separation process is complete. After step B), this step is repeated to cycle through the hydrate formation-decomposition process.

[0090] During the separation process described above, the gases discharged from back pressure valve 9 and exhaust valve 8 were collected in storage tanks and their composition was analyzed by 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 embodiment completed five hydrate formation-decomposition cycles, taking a total of 35 minutes, with an average 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 the total CH4 / H2 mixed gas throughput within 35 minutes was 590 mmol.

[0091] Example 2

[0092] This embodiment uses a reactor of a different size than that used in Embodiment 1. The reactor used in this embodiment is a cylindrical reactor with an inner diameter of 2.54 cm and a height of 15 cm, with a length-to-diameter ratio of 5.9. A 400-mesh stainless steel screen is installed at the bottom of the reactor as a support mesh. 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, and CH4 is a component that readily forms hydrates).

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

[0094] B) The temperature of the reactor and ice medium is controlled at -1.0℃ using an air bath. The mixed gas to be separated (mixed gas temperature is -1℃) is introduced into the reactor through valve 7, and the gas pressure inside the reactor is controlled to be constant at 6.0MPa. At this time, the partial pressure of methane (about 4.5MPa) is greater than the phase equilibrium pressure of methane hydrate (about 2.4MPa). When hydrate begins to form, the back pressure valve 9 is opened to slowly exhaust gas, and the exhaust rate is controlled at 1450mL (atmospheric pressure) / min. After 3 minutes of separation, the temperature inside the reactor rises to 6.8℃ and remains constant for 20 seconds, which is considered to be the highest temperature. At this time, the inlet valve 7 is closed, and the back pressure valve 9 is opened wide to quickly release gas, instantly expelling the remaining gas in the reactor so that the pressure inside the reactor reaches atmospheric pressure. Then, the back pressure valve 9 is closed, and the exhaust valve 8 on the other side is opened to allow the hydrate to decompose and release gas. After 3 minutes of hydrate decomposition, the temperature inside the reactor drops to -0.8℃, and the gas separation process is completed.

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

[0096] Example 3

[0097] The difference between this embodiment and Embodiment 1 is that the temperature of the gas to be separated is higher in this embodiment, which is 21°C, and a single hydrate formation-decomposition cycle is performed. The remaining operation steps are the same as in Embodiment 1. About 2 minutes and 30 seconds after the separation begins, the temperature inside the reactor reaches 6.8°C and remains constant for 20 seconds, which is considered to be the highest temperature. At this time, the inlet valve 7 is closed, and the back pressure valve 9 is opened wide to quickly release the gas, instantly expelling the remaining gas inside the reactor and bringing the pressure inside 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 allow the hydrate to decompose and release gas. The hydrate decomposes for 3 minutes, and the temperature inside the reactor drops to -0.9°C, completing the gas separation process.

[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 inside it is -4°C before gas inlet, the temperature of the gas to be separated is 20°C, and a single hydrate formation-decomposition cycle is performed. The exhaust rate during separation is approximately 310 mL / min. The remaining operating steps are the same as in Embodiment 1. About 3 minutes and 40 seconds after the start of separation, the temperature inside the reactor reaches 6.8°C and remains constant for 20 seconds, which is considered to be the highest temperature. At this time, the inlet valve 7 is closed, and the back pressure valve 9 is opened wide to quickly release gas, instantly expelling the remaining gas in the reactor and bringing the pressure inside 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 allow the hydrate to decompose and release gas. The hydrate decomposes for 3 minutes, and the temperature inside 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] Implemented according to Example 1, except that the initial exhaust rate of the back pressure valve 9 is set to 200 mL / min.

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

[0105] Comparative Example 2

[0106] Implemented according to Example 1, except that the initial exhaust rate of the back pressure valve 9 is set to 800 mL / min.

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

[0108] Comparative Example 3

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

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

[0111] Comparative Example 4

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

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

[0114] Comparative Example 5

[0115] The implementation follows Example 1, except that the hydrate formation time and decomposition time are both extended to 15 minutes (specifically, when the temperature inside the reactor rises to 6.8°C after 3 minutes of separation, the back pressure valve 9 is not opened immediately to release gas, but is opened after 15 minutes; similarly, when the back pressure valve 9 is closed and the other exhaust valve 8 is opened to release gas through hydrate decomposition, the exhaust valve 8 is kept open for 15 minutes), the exhaust rate is reduced to 80 mL / min accordingly, and only one hydrate formation-decomposition cycle is performed.

[0116] The results showed that the CH4 separation factor was 779, the CH4 recovery rate was 52%, and the mixed gas throughput was 127 mmol in 30 minutes. This indicates that even when using ice as the medium to generate hydrates, extending the hydrate formation time does not improve the separation selectivity; instead, it leads to a decrease in the mixed gas throughput, a drop in separation efficiency, and a corresponding increase in energy consumption per unit mass of gas separated due to prolonged refrigeration.

[0117] Comparative Example 6

[0118] Implemented according to Example 1, except that in step B), the temperature of the reactor and the ice medium is controlled at -7°C.

[0119] The results showed that hydrates were almost impossible to form, and only a small amount of gas was released from the hydrates after separation. This indicates that excessively low temperatures cannot be used for hydrate formation, thus making gas separation impossible.

[0120] Comparative Example 7

[0121] The experiment was carried out according to Example 1, except that a high-pressure stainless steel packed tube with a length of 2.3 cm and an inner diameter of 2.5 cm was used as the reactor, and the length-to-diameter ratio of the reactor was 0.92. The reactor underwent one hydrate formation-decomposition cycle.

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

[0123] Comparative Example 8

[0124] The experiment was conducted according to Example 1, except that ice was not used as the medium; instead, an aqueous solution containing sodium dodecyl sulfate of the same concentration was used. To ensure that the aqueous solution in the reactor remained liquid, the experimental temperature was 2°C. Simultaneously, an intermittent operation mode was used to separate the CH4 / H2 mixture of the same concentration: when the temperature of the aqueous solution in the reactor reached the experimental temperature, the mixture to be separated was introduced into the reactor at a pressure of 6.0 MPa and maintained constant during hydrate formation. After 30 minutes of reaction, hydrate formation was complete. Unreacted gas was rapidly discharged and collected, and then the hydrate was decomposed under normal pressure, with the decomposition gas 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-based gas separation method, demonstrating that the separation method of the present invention can achieve a more efficient separation effect.

[0126] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for separating a gas mixture using hydrates, characterized in that, The method comprises the following steps: A) filling ice medium into a reaction kettle; wherein, the reaction kettle comprises: a kettle body (1); a jacket (2) is arranged on the periphery of the kettle body (1); a coolant inlet (3) is arranged at the lower part of the jacket (2), and a coolant outlet (4) is arranged at the upper part of the jacket (2); grids (5) are respectively arranged at both ends in the kettle body (1), so that the kettle body is divided into pipelines with a length-diameter ratio greater than 4; wherein a support net (6) is arranged below the grid near the lower end of the reaction kettle; an air inlet valve (7) is arranged at the upper part of the kettle body (1), and an air outlet valve (8) and a back pressure valve (9) are arranged at the lower part of the kettle body (1); wherein, the ice medium is filled in the pipelines in the kettle body (1) divided by the grids (5), and the volume ratio of the ice medium in the pipelines is greater than 60% and less than 85%; B) under the condition that the temperature of the reaction kettle and the ice medium are both kept below 0℃, the mixed gas to be separated is filled into the reaction kettle through the air inlet valve (7); when the pressure in the reaction kettle reaches the required pressure for separation and the hydrate begins to generate, the back pressure valve (9) is opened to discharge the gas outside, and the exhaust rate is controlled to be equal to the difference between the air inlet rate and the gas consumption rate of hydrate generation; as the hydrate generates, 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 filling the gas, and the back pressure valve (9) is opened to rapidly discharge the unreacted gas; after the pressure in the reaction kettle is atmospheric pressure, the back pressure valve (9) is closed, and the air outlet valve (8) is opened, so that the hydrate decomposes and releases the gas, thereby completing the gas separation.

2. The method of claim 1, wherein, In step B), the temperature of the reaction kettle and the ice medium is kept higher than -5℃ and lower than 0℃.

3. The method of claim 1, wherein, In step B), the temperature of the mixed gas to be separated is ≤40℃.

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℃.

5. The method of claim 1, wherein, In step B), when the mixed gas to be separated is filled into the reaction kettle through the air inlet valve (7), the pressure of the mixed gas in the reaction kettle is controlled as follows: the gas partial pressure of the hydrate-forming component in the mixed gas is greater than the hydrate phase equilibrium pressure of the hydrate-forming component at the temperature of the ice medium.

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

7. The method of claim 1, wherein, In step B), the method for judging that the temperature of the ice medium reaches the highest is that when the temperature in the reaction kettle gradually rises to a certain temperature point, it is maintained unchanged for more than 10s, and it is considered that the highest temperature is reached.

8. The method of claim 1, wherein, After step B) is completed once, the step is repeated to continuously separate the gas.

9. The method of claim 1, wherein, In step A), the ice medium is prepared by the following method: a hydrate kinetic promoter is prepared into a promoter aqueous solution with water; the promoter aqueous solution is reacted with the initial gas at an initial temperature greater than 0℃ and less than 5℃ to generate initial hydrate; The temperature of the initial hydrate, the residual promoter aqueous solution and the residual initial gas obtained from the reaction is reduced to a decomposition temperature below 0°C; the residual initial gas is discharged and the frozen initial hydrate and the residual promoter aqueous solution are kept in the ice structure formed by freezing under a pressure of normal pressure or below, so that the gas stored in the hydrate is released, and the ice substance obtained is the ice medium; Or The ice medium comprises ice powder and a surfactant uniformly distributed in the ice powder; or the ice medium comprises ice powder, a surfactant uniformly distributed in the ice powder and a thermodynamic inhibitor, 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, wherein C is the mass fraction of the thermodynamic inhibitor aqueous solution with an ice point as the use temperature of the ice medium, in wt%.

10. The method of claim 1, wherein, In step A), the inner diameter of the pipe is greater than or equal to 1 cm, and the length is less than or equal to 300 cm.

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