Enhanced mass transfer method for separating gas by hydrate method

Abstract

The invention discloses a mass transfer strengthening method for gas separation by a hydrate method, and relates to the technical field of gas separation and mass transfer strengthening, and the method comprises the following steps: dispersing mixed gas into microbubbles with the average diameter of 1-100 [mu] m through a microbubble generation module, and adding an interface microstructure regulating agent into a water phase at the same time, the regulating agent is a polyoxyethylene ether type nonionic surfactant with the HLB (hydrophile-lipophile balance) value of 10-18 and the concentration of 0.01%-0.5% (mass fraction), and inducing to form a porous or dendritic hydrate crystal structure; rapid generation of the hydrate is promoted under the conditions that the temperature is 274.15 to 283.15 K and the pressure is 2.0 to 5.0 MPa. According to the method, synergistic enhancement of remarkable amplification of a gas-liquid mass transfer interface and permeability improvement of a hydrate layer can be achieved, the CO2 conversion rate reaches 90% or above within 30 minutes, and the mass transfer efficiency is improved by 5 times or above compared with that of a traditional method.

Description

Technical Field

[0001] This invention belongs to the field of gas separation and mass transfer enhancement technology, and specifically relates to an enhanced mass transfer method for gas separation using the hydrate method. Background Technology

[0002] Gas separation technology, as a fundamental supporting unit of modern chemical industry, plays a crucial role in many key fields such as energy and chemical engineering, environmental protection, and materials science. Among numerous separation technologies, the separation method based on gas hydrates, with its inherent advantages such as mild operating conditions, high gas storage density per unit volume, high selectivity for specific components, and environmental friendliness, shows broad application prospects. It has become a research and application hotspot, particularly in cutting-edge areas such as natural gas purification, carbon dioxide capture in flue gas, and hydrogen storage and transportation. The core principle of this method lies in the fact that, under specific pressure and temperature conditions, water molecules form cage-like cavity structures through hydrogen bonding, selectively encapsulating guest gas molecules of matching size within them, thereby forming stable cage-like crystalline compounds, i.e., gas hydrates, thus achieving the separation and enrichment of target components in the mixed gas.

[0003] Existing technologies have made significant progress in improving the structural stability of hydrates and inhibiting their decomposition to promote the engineering application of hydrate methods. Specifically, Chinese patent document CN110564472B proposes a method to construct a physical barrier layer by coating the surface of hydrate particles with hydrate promoters, such as tetrahydrofuran or cyclohexane. This barrier layer effectively reduces the escape dynamics of guest molecules inside the hydrate, exhibiting excellent decomposition inhibition below the freezing point of 273.2K, and maintaining the metastable state of the hydrate above the freezing point, significantly extending its storage period and providing technical assurance for the long-term, safe storage and transportation of hydrates. Building on this, Chinese patent document CN113817443B, from the perspective of interface chemistry and materials mechanics, adopts a composite system composed of sodium carboxymethyl starch and alkyl glycoside surfactants. This system can form a protective film at the hydrate phase interface that combines interfacial tension regulation and mechanical support functions. This film enhances the mechanical integrity of hydrate particles, preventing chain reactions caused by microstructural damage and further improving the macroscopic stability of solid hydrates during storage and transportation. The common focus of the above technical solutions is the solid-phase maintenance stage after hydrate formation. Through physical covering or chemical modification, they successfully solve the long-standing bottleneck problem of thermodynamic instability of hydrates that has hindered the application of this technology.

[0004] However, with the continuous development of related technologies and the increasingly stringent requirements for separation efficiency and reaction rate in industrial applications, the aforementioned technical logic, which focuses on improving product stability, has inherent limitations at the principle level in addressing the kinetic challenges of hydrate formation. This is because hydrate formation is essentially a complex process involving the coupling of multiphase mass transfer and crystallization kinetics. The gaseous component must first cross the gas-liquid interface from the bulk gas phase, dissolve in the water phase, migrate to suitable nucleation sites, and ultimately be captured by water molecules and enter the solid lattice. In this process, the mass transfer rate at the gas-liquid interface is the decisive step in the entire reaction. To achieve final product stability, existing technologies use chemical additives or physical coatings that rapidly form a dense, low-permeability solid or semi-solid film on the surface of the newly formed hydrate nuclei during the initial stage of hydrate formation. While this film effectively prevents gas molecules from escaping during the subsequent storage stage, it also constitutes a significant physical barrier preventing the diffusion of gaseous reactants into the formation stage. This phenomenon is known as the "interface self-armoring effect," where the hydrate product layer itself hinders mass transfer in subsequent reactions. Therefore, a stabilizing layer carefully designed to improve final stability actually acts as a reaction inhibitor at the reaction kinetics level, creating an inherent technical contradiction. This contradiction causes the hydrate formation reaction to often decelerate sharply or even stop after an initial rapid pace, resulting in a series of engineering problems such as low overall gas conversion rate, long reaction cycles, and insufficient utilization of equipment volume. This fundamentally restricts the overall economic efficiency and time efficiency of hydrate-based gas separation technology.

[0005] Therefore, in the process of separating gas using hydrates, how to effectively overcome the mass transfer barrier caused by the formation of a solid layer at the interface during hydrate formation, and achieve efficient and continuous mass transfer from gas to the liquid phase while ensuring necessary stability, thereby significantly improving the hydrate formation rate and total conversion rate, has become a core technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] This invention provides an enhanced mass transfer method for gas separation using hydrates, aiming to overcome the technical bottlenecks of limited mass transfer and reduced reaction rate caused by the "interfacial self-armoring effect" during the formation process of existing hydrate methods. This invention achieves continuous and efficient mass transfer of gas components to the liquid phase by introducing a microbubble generation module with high dispersibility and an interfacial microstructure regulator that precisely controls the microstructure of the hydrate interface, thereby significantly improving the hydrate formation rate, gas conversion rate, and overall separation efficiency.

[0007] Specifically, the enhanced mass transfer method disclosed in this invention includes the following steps: The first step involves providing a sealed reactor with precise temperature and pressure control. This sealed reactor is constructed from pressure- and corrosion-resistant materials, such as austenitic stainless steel 316L or duplex stainless steel 2205 as the main material, and is equipped with an internal stirring device, a gas inlet, a liquid inlet, a hydrate slurry outlet, a heat exchange jacket or built-in cooling coil, and multiple sensor interfaces. The stirring device includes one or more mechanical stirrers, such as Rushton turbine stirrers or tilting blade stirrers, with a blade diameter-to-reactor inner diameter ratio between 0.3 and 0.6, and 4 to 8 blades, used to maintain uniform mixing of the liquid phase and sufficient suspension of hydrate particles during the reaction. The heat exchange jacket or built-in cooling coil precisely controls the reaction temperature within ±0.1K of the target hydrate formation temperature through a circulating cooling medium. The gas inlet is connected to a gas distributor, which uniformly delivers the mixed gas to be separated into the liquid phase.

[0008] The second step involves injecting a predetermined amount of pure water or deionized water containing specific dissolved substances into the reactor, and adding a predetermined concentration of an interfacial microstructure regulator. The interfacial microstructure regulator is an amphiphilic compound whose chemical structure includes a hydrophilic head group and a hydrophobic tail group. The hydrophilic head group is selected from at least one of a polyoxyethylene chain, a sulfonate group, a carboxylate group, or a quaternary ammonium salt group; the hydrophobic tail group is selected from at least one of a straight-chain or branched alkyl chain, a fluoroalkyl chain, or a polydimethylsiloxane chain with an average carbon number of 8 to 20. In a preferred embodiment of the invention, the interfacial microstructure regulator is a polyoxyethylene ether-type nonionic surfactant with a hydrophilic-lipophilic balance (HLB) value between 10 and 18, and has a polyoxyethylene chain with an average degree of polymerization of 8 to 20 and an alkyl chain with an average carbon number of 12 to 18. The initial concentration of the interfacial microstructure regulator in the aqueous phase ranges from 0.01% to 0.5% by mass. The mechanism of action of the interface microstructure regulator lies in its rapid adsorption to the gas-water-hydrate three-phase interface during the early stages of hydrate formation. Through steric hindrance, it alters the growth rate of the hydrate crystal faces, preventing the formation of a dense, low-permeability hydrate solid layer and inducing the generation of a hydrate crystal microstructure with more micropores or a dendritic, polycrystalline aggregate structure possessing sufficient mechanical strength. This specific microstructure allows gas molecules to continuously diffuse through the micropores or grain boundaries within the hydrate layer into the unreacted aqueous phase, thus overcoming the mass transfer barrier caused by the interface self-armoring effect in traditional hydrate methods.

[0009] The third step involves activating one or more microbubble generation modules inside the reactor, while simultaneously introducing the mixed gas to be separated into the microbubble generation modules at a predetermined flow rate. The function of the microbubble generation modules is to efficiently disperse the introduced gas into a large number of uniformly sized, densely distributed micron-sized bubbles with extremely high specific surface areas, thereby greatly expanding the gas-liquid mass transfer interface. The microbubble generation modules are implemented through at least one of the following two methods: The first method employs a high-shear force dispersion device. This device can be a rotor-stator homogenizer or a Venturi ejector. When using a rotor-stator homogenizer, the rotor linear velocity is controlled between 10 m / s and 30 m / s, and the gap between the rotor and stator is precisely controlled between 0.1 mm and 1.0 mm to ensure the generation of a high shear force field. The gas inlet is located upstream or inside the rotor-stator structure via a porous annular distributor, thereby forming microbubbles under shearing action. When using a Venturi ejector, a local negative pressure is generated as the liquid phase flows through the Venturi throat, drawing gas in from the side inlet and mixing it with the high-speed liquid flow. At the throat outlet, microbubbles are formed through turbulent shearing action. The throat diameter of the Venturi ejector is designed to be between 2 mm and 10 mm, and the liquid phase flow velocity is controlled between 5 m / s and 20 m / s.

[0010] The second method employs a porous membrane dispersion device. This device consists of a ceramic membrane, a sintered metal membrane, or a polymer microporous membrane, with an average pore size between 0.1 micrometers and 10 micrometers and a porosity between 30% and 60%. The mixed gas, under a predetermined pressure difference (e.g., 0.1 MPa to 1.0 MPa higher than the liquid phase static pressure), diffuses uniformly into the liquid phase through the porous membrane, thereby forming microbubbles.

[0011] Through the meticulous design and operation of the microbubble generation module described above, the average diameter of the microbubbles generated in the reactor is controlled between 1 micrometer and 100 micrometers, and the bubble volume concentration is maintained between 10% and 50%, thereby providing an effective gas-liquid specific surface area of ​​up to 1000 m² / m³ to 5000 m² / m³. The presence of the interface microstructure regulator further reduces the surface tension of the gas-liquid interface, promotes the stable generation and dispersion of microbubbles, and inhibits microbubble aggregation, thus maintaining a high specific surface area mass transfer interface.

[0012] The fourth step involves adjusting the reactor temperature and pressure to the target gas hydrate formation conditions—below the hydrate equilibrium temperature and above the hydrate equilibrium pressure—while microbubbles continue to be generated and fully contact the liquid phase. Under these conditions, the gas components dissolve in the aqueous phase from the bulk gas phase of the microbubbles through the high specific surface area microbubble interface. They then combine with water molecules and, with the assistance of an interface microstructure regulator, rapidly form and grow hydrate nuclei with a specific microstructure. Due to the presence of the interface microstructure regulator, the hydrate layer maintains a certain degree of permeability, allowing dissolved gas molecules to continuously diffuse through the microporous structure or grain boundaries within the hydrate layer, replenishing the guest molecules required for hydrate growth, thereby achieving continuous and efficient mass transfer.

[0013] The fifth step involves continuous stirring by the stirring device to maintain a uniform suspension of hydrate particles within the reactor, preventing particle settling and agglomeration, and promoting further contact between the hydrate particles and unreacted gases. When the hydrate production reaches a preset value or the gas conversion rate reaches a preset target, the resulting hydrate slurry is discharged from the hydrate slurry outlet for subsequent gas-solid separation and gas recovery. The discharge of the hydrate slurry can be performed in either continuous or intermittent operation mode. In continuous operation mode, a constant liquid level and slurry concentration within the reactor are maintained through the coordinated action of a level sensor and a pump.

[0014] The core innovation of the enhanced mass transfer method disclosed in this invention lies in the synergistic effect of microbubble generation technology and interfacial microstructure regulators. The microbubble generation module achieves precise control over the microbubble size distribution through geometric design and optimized operating parameters. For example, the rotor linear velocity of the rotor-stator homogenizer is precisely set to 18 m / s, the rotor-stator gap to 0.3 mm, the throat diameter of the Venturi injector to 5 mm, the liquid flow velocity to 10 m / s, and the average pore size of the porous membrane disperser to 5 micrometers. This ensures the generation of monodisperse or narrowly distributed microbubble clusters with an average diameter of 20 to 50 micrometers. The presence of these microbubbles significantly increases the gas-liquid contact area, raising the gas-liquid mass transfer coefficient to more than five times that of traditional stirred reactors, specifically reaching 0.05 s². - ¹to 0.2s - ¹.

[0015] The interfacial microstructure regulator, such as an alkyl polyoxyethylene ether (taking an alkyl chain with an average carbon number of 14 and a polyoxyethylene chain with an average degree of polymerization of 12 as an example), has a critical micelle mass fraction concentration (CMC) of 0.05% in water. In this invention, its CMC is typically set between 0.1% and 0.3%, slightly higher than its CMC, to ensure effective adsorption and structural regulation at the interface. The regulator selectively adsorbs its molecules onto the growth crystal faces of the hydrate, for example, onto specific growth faces of the hydrate, thereby inhibiting the rapid growth of those crystal faces and promoting the growth of other crystal faces, resulting in a more open, porous, or dendritic microstructure in the hydrate crystal. For example, under atomic force microscopy, it can induce the formation of microchannel structures with an average pore size of 10 to 100 nanometers, or exhibit a dendritic morphology with multiple branches, rather than a traditional dense bulk structure. This open microstructure significantly reduces the diffusion resistance of gas molecules through the hydrate layer, increasing the effective diffusion coefficient of gas through the hydrate layer to 2 to 5 times that without a regulator. Therefore, combined with the high specific surface area provided by microbubbles and the low-resistance diffusion path induced by the regulator, gas components can be continuously and efficiently transferred from the gas phase to the hydrate solid phase, significantly improving the overall mass transfer rate of the hydrate formation process.

[0016] In one embodiment of the present invention, for the capture of carbon dioxide, the gas component is a mixed gas containing CO2, such as flue gas. The hydrate formation conditions are set at a temperature between 274.15 K and 283.15 K, and a pressure between 2.0 MPa and 5.0 MPa. The stirring rate inside the reactor is maintained at 300 rpm to 600 rpm. Under the above conditions, the method of the present invention can achieve a CO2 gas conversion rate of over 90% within 30 minutes, while conventional methods may require more than 2 hours to achieve a similar conversion rate under the same conditions.

[0017] Furthermore, the sealed reactor can be equipped with an online gas analyzer, such as a CO2 concentration sensor based on the non-dispersive infrared principle, to monitor the CO2 concentration in the reactor outlet gas phase in real time, thereby accurately controlling the reaction process and evaluating the separation efficiency. The sensor has a measurement accuracy of ±0.5%FS and a response time of less than 5 seconds.

[0018] Furthermore, the present invention may also include a hydrate slurry delivery system that transports the separated hydrate slurry to the next processing unit, such as a hydrate decomposition unit or a storage unit, via a screw pump or plunger pump. The pump's delivery capacity can be precisely controlled to match the hydrate formation rate.

[0019] The cooling medium flow rate of the heat exchange jacket or built-in cooling coil is precisely regulated by a proportional-integral-derivative controller to maintain a constant reaction temperature. For example, the cooling water flow rate can be controlled between 5 L / min and 20 L / min, and the inlet temperature can be controlled between 273.65 K and 278.15 K.

[0020] The gas flow rate is precisely measured and regulated by a mass flow controller. For example, the CO2 gas flow rate is controlled between 10 L / min and 50 L / min to match the hydrate formation rate and prevent gas accumulation or insufficiency. The mass flow controller has a measurement accuracy of ±1%FS and a response time of less than 1 second.

[0021] The rotation speed of the stirring device is precisely controlled by a frequency converter with an accuracy of ±1 rpm to ensure the stability of the shear force field and mixing effect.

[0022] The enhanced mass transfer method of this invention overcomes the mass transfer limitations in the hydrate formation process through the synergistic cooperation of the aforementioned components and operational steps. The microbubble generation module continuously provides a large gas-liquid contact area, ensuring that gaseous reactants can efficiently dissolve into the liquid phase. Simultaneously, the interface microstructure regulator intervenes in the early stages of hydrate nucleus formation, precisely inducing the formation of a highly permeable microstructure in the hydrate crystals through its unique molecular structure and interaction with the hydrate crystal faces. This structure transforms the formed hydrate layer from a dense barrier hindering gas diffusion into a porous "bridge," continuously guiding gas molecules into the unreacted aqueous phase region. The combination of these two mechanisms fundamentally solves the problem of a sharp decline in mass transfer rate caused by the self-armoring effect of hydrates, achieving a leap in the efficiency and economy of hydrate-based gas separation technology.

[0023] Furthermore, the method of this invention can also be applied to the separation of methane and ethane in natural gas, the removal of hydrogen sulfide from industrial waste gas, and the storage and transportation of hydrogen. The required hydrate formation temperature and pressure conditions, as well as the type and concentration of the interfacial microstructure regulator, will be optimized and adjusted accordingly for different gas components. For example, for natural gas deacidification (H2S / CO2 separation), the interfacial microstructure regulator can be selected from amphiphilic polymers with high gas selectivity, such as those with specific functional groups (e.g., amine groups), to slightly enhance the capture efficiency of target guest molecules while regulating the hydrate microstructure. For H2 storage, due to the extremely small size of H2 molecules, the hydrate formation conditions are more stringent; the microbubble generation module needs to provide even smaller microbubbles to further improve the solubility and mass transfer rate of H2.

[0024] The method proposed in this invention is highly feasible for engineering implementation and has good versatility. The design of the closed reactor takes into account the needs of large-scale industrial production, and its geometric dimensions can be linearly scaled up according to the throughput. The microbubble generation module can be modularly configured and optimized according to the reactor volume and the target mass transfer rate. For example, for large reactors, multiple high-shear dispersion devices can be connected in parallel or in series to ensure uniform distribution of microbubbles and mass transfer efficiency throughout the reaction system. The screening and synthesis technology of the interface microstructure regulator is mature, and it has high stability in the reaction system. It can also be customized according to specific application requirements. For example, molecular dynamics simulations can be used to predict its adsorption conformation at the hydrate interface and its influence on crystal growth, thereby accurately guiding molecular structure design.

[0025] The method ensures the stability and repeatability of the reaction process through precise parameter control. For example, the physical properties of the hydrate slurry can be monitored in real time using an online densitometer and viscometer, and the stirring rate and slurry discharge rate can be adjusted accordingly to optimize the operation of the entire system. The online densitometer uses a density sensor based on the vibrating tube principle with a measurement accuracy of ±0.0001 g / cm³; the viscometer uses a viscosity sensor based on the rotating body principle with a measurement accuracy of ±1%FS.

[0026] During the hydrate formation process, the pressure fluctuations inside the reactor are precisely controlled by a pressure relief loop equipped with a fast-response electric regulating valve to ensure that the pressure is maintained within ±0.05MPa of the target range, preventing hydrate decomposition due to sudden pressure drops or the stability of microbubbles due to excessive pressure.

[0027] The method of this invention not only solves the mass transfer limitation in the hydrate formation process, but also lays a solid technical foundation for enhancing the application potential of the hydrate method in environmental engineering, energy storage, and chemical separation. By improving the hydrate formation rate and gas conversion rate, equipment investment costs and operating energy consumption can be significantly reduced, thereby improving the overall economic benefits of this technology.

[0028] The enhanced mass transfer method for gas separation using the hydrate process described above integrates the addition, mixing, reaction, separation, and discharge of all materials through an automated control system. This automated control system uses a programmable logic controller (PLC) as its core control unit, communicating with various sensors and actuators via industrial Ethernet for data and command transmission. The PLC system boasts high reliability and real-time performance, with a scan cycle of less than 10 milliseconds, enabling high-frequency data acquisition and feedback control of all process parameters. This allows for precise and dynamic regulation of temperature, pressure, gas flow rate, liquid flow rate, stirring speed, and hydrate slurry density. The control system also includes a human-machine interface (HMI) for operators to monitor the process flow, set parameters, and receive alarm information, ensuring the system's safe and stable operation. Through the integration of this automated control, the method of this invention achieves an efficient, continuous, and safe operating mode, further enhancing its industrial application value. Attached Figure Description

[0029] Figure 1 This is a schematic flowchart of an enhanced mass transfer method for gas separation using the hydrate method according to the present invention. Figure 2 This is a schematic diagram of the apparatus used to implement the enhanced mass transfer method of the present invention. Detailed Implementation

[0030] To enable those skilled in the art to more fully understand the technical solution of the enhanced mass transfer method for gas separation using the hydrate method disclosed in this invention, and to implement it accordingly, the technical solution of this invention will be described in detail, completely, and clearly below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described herein are only a part of the many embodiments of this invention, and not a limitation on all embodiments of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0031] Reference Figure 1 and Figure 2The implementation of the enhanced mass transfer method disclosed in this invention relies on a precisely designed, highly integrated reaction system. The core of this system is a closed reactor, which serves as the main space for hydrate formation. Its design and construction must meet stringent requirements for high pressure, low temperature, and corrosion resistance. In one specific embodiment, the main material of the closed reactor is austenitic stainless steel 316L, with a volume of 50 liters, a designed pressure resistance of 10.0 MPa, and a designed temperature range of 253.15 K to 373.15 K. The inner wall of the reactor undergoes mechanical and electrochemical polishing, with a surface roughness Ra not exceeding 0.4 micrometers. This aims to reduce random induction points for heterogeneous nucleation, ensuring that the hydrate formation process is primarily controlled by process parameters rather than the wall effect, while also facilitating cleaning and venting after the reaction. The reactor is flange-sealed using high-strength bolts and bimetallic spiral wound gaskets, ensuring excellent airtightness during long-term operation.

[0032] Inside the sealed reactor, a stirring device is installed to maintain a uniform distribution of phases within the reaction system, promote heat and mass transfer, and prevent the agglomeration and sedimentation of the generated hydrate particles. Specifically, this stirring device employs a top-mounted magnetically driven stirrer to eliminate potential leakage risks and material contamination from dynamic seals. The stirring shaft is made of Hastelloy C-276 to withstand potential acidic gas environments. The stirring blades utilize a double-layer Rushton turbine structure; the upper blades disperse gas near the liquid surface, while the lower blades primarily handle radial mixing of the liquid phase and suspension of solid particles. The ratio of the blade diameter to the reactor's inner diameter is precisely set at 0.45, and each layer of blades contains six vertical blades. The stirring device is driven by a servo motor, precisely speed-controlled via a frequency converter, with a speed control range of 50 rpm to 1000 rpm and a control accuracy of ±1 rpm, enabling dynamic optimization of the shear field environment according to different stages of the reaction.

[0033] To achieve precise control of the reaction temperature, an integrated heat exchange jacket is installed on the outside of the sealed reactor. The jacket is internally designed with spiral guide plates to ensure turbulent flow of the cooling medium within the jacket, improving heat exchange efficiency and ensuring uniform temperature on the reactor's outer wall. The cooling medium, such as a 40% (w / w) aqueous solution of ethylene glycol, is supplied by a precision refrigeration circulation unit, whose outlet temperature can be set arbitrarily between 270.15 K and 293.15 K with an accuracy of ±0.05 K. A proportional-integral-derivative controller connected in series on the cooling medium circulation pipeline, linked to an electric regulating valve, continuously adjusts the flow rate of the cooling medium based on the real-time temperature value fed back by a Pt100 platinum resistance temperature sensor with an accuracy of ±0.01 K inside the reactor. This ensures that the temperature of the reaction system is precisely stabilized within ±0.1 K of the target set value. In a specific embodiment, the circulation flow rate of the cooling medium can be controlled between 10 L / min and 30 L / min.

[0034] Material input and output are achieved through a series of dedicated interfaces. The gas inlet is connected to a mass flow controller with a range of 0-100 standard liters / minute, an accuracy of ±1%FS, and a response time of less than 1 second. This mass flow controller ensures that the mixed gases to be separated are introduced into the reaction system at a constant and precise rate. The liquid inlet is connected to a high-pressure metering pump for injecting pure water or an aqueous solution containing an interfacial microstructure modifier; the flow rate of this pump is precisely adjustable from 0.1 L / h to 10 L / h. The hydrate slurry outlet is located at the bottom of the reactor and is connected to a wear-resistant screw pump with adjustable speed, used to deliver the generated hydrate slurry to subsequent separation or storage units in continuous or semi-continuous operation modes.

[0035] One of the core innovations of this invention lies in the introduction and application of a microbubble generation module. This module transforms macroscopic gas flow into a cluster of micron-sized bubbles with a very large specific surface area, thereby enhancing the gas-liquid mass transfer process at its source. In a preferred embodiment, the microbubble generation module employs a rotor-stator type high-shear homogenizer. This homogenizer is integrated into the internal circulation loop of the reactor or directly installed at the bottom of the reactor. Its core components consist of a high-speed rotating rotor and a precision-fitted stator, both made of surface-hardened martensitic stainless steel 440C to resist wear caused by high-speed shearing. The rotor is driven by an independent, sealed explosion-proof motor, whose linear velocity can be precisely controlled within the range of 10 m / s to 30 m / s. The working gap between the rotor and stator is adjusted using precision shims and can be set between 0.1 mm and 1.0 mm. Specifically, the rotor of this homogenizer is designed with a multi-layer toothed ring structure, and the stator is also a matching multi-layer toothed ring. The mixed gas to be separated is injected into the main liquid phase through a porous annular distributor located upstream of the rotor-stator structure via a gas inlet. When the liquid flow carrying large bubbles enters the rotor-stator working head, it undergoes intense turbulence, shearing, and cavitation within the narrow gap, rapidly breaking down the macroscopic bubbles into micron-sized bubbles. By setting the rotor linear velocity to 22 m / s and the rotor-stator gap to 0.2 mm, microbubbles with an average diameter between 20 and 50 micrometers can be stably generated. At this point, the gas holdup in the reactor can be maintained above 30%, and the calculated effective gas-liquid mass transfer specific surface area can reach as high as 3000 m² / m³.

[0036] As another feasible implementation, the microbubble generation module can also employ a porous membrane dispersion device. The core of this device is one or more tubular or plate-type ceramic microporous membranes made of hydrophilically treated α-alumina with an average pore size of 2 micrometers and a porosity of 45%. This membrane assembly is installed at the bottom of the reactor. Driven by a pressure gradient 0.2 MPa to 0.5 MPa higher than the internal liquid phase static pressure, the mixed gas to be separated permeates through the micropores of the ceramic membrane, forming extremely fine and uniform bubbles on the membrane surface. These bubbles detach from the membrane surface under the action of buoyancy and liquid flow shear force, forming a microbubble cloud dispersed throughout the entire liquid phase. This method produces bubbles with a more uniform size distribution and relatively lower energy consumption, but it places higher demands on the membrane's antifouling performance.

[0037] Another core innovation of this invention lies in the synergistic application of an interface microstructure regulator. This regulator is an amphiphilic compound with specific molecular design. Its fundamental function is to change the crystallization habit of hydrates at the gas-liquid interface, inhibiting the formation of dense hydrate films from the source, thus overcoming the so-called "interface self-armoring effect." In a preferred embodiment, the interface microstructure regulator is an alkyl polyoxyethylene ether nonionic surfactant, specifically model C14E12, meaning its hydrophobic tail group is a straight-chain alkyl chain with an average carbon number of 14, and its hydrophilic head group is a polyoxyethylene chain with an average degree of polymerization of 12. The hydrophilic-lipophilic balance value of this regulator is approximately 14.5. Its critical micelle mass fraction concentration in an aqueous solution at 277.15 K has been determined to be 0.05%. In the implementation of this invention, its initial addition mass fraction concentration in the aqueous phase is set to 0.15%, approximately three times its CMC, to ensure that after the reaction begins, the gas-liquid interface and the newly formed hydrate-water interface can rapidly form a saturated regulator adsorption layer.

[0038] The mechanism of action of the interfacial microstructure regulator can be specifically described as follows: When the temperature and pressure of the reaction system reach the conditions for hydrate formation, hydrate nuclei preferentially form at the gas-liquid interface rich in dissolved gas. At this time, C14E12 molecules in the aqueous solution, in a free unimolecular or micellar state, rapidly adsorb onto the surface of the newly formed hydrate nuclei due to their amphiphilic structure. Their hydrophobic alkyl chains tend to interact hydrophobically with guest gas molecules or cage walls in the hydrate's cage-like structure, while their hydrophilic polyoxyethylene chains extend into the surrounding aqueous phase. This adsorption behavior is preferential on specific crystal faces of the hydrate crystal, thus significantly altering the relative growth rates of different crystal faces. As a result, hydrates that originally tended to grow into dense, smooth polyhedral crystals are induced to form crystal aggregates with highly complex microstructures. Observation of the generated hydrate particles using a low-temperature scanning electron microscope reveals that, after the addition of the regulator, the hydrate particles are no longer solid spheres or blocks, but exhibit dendritic or porous skeletal morphologies. These morphologies contain numerous interconnected micron / nanoscale channels ranging in size from tens to hundreds of nanometers. These channels provide low-resistance pathways for subsequent gas molecules to diffuse from the surrounding aqueous phase to the hydrate growth front. Therefore, even after the hydrate particles have grown to a certain size, their outer layer no longer constitutes an insurmountable mass transfer barrier. Gas molecules can continuously replenish the growth interface through these internal channels, allowing the hydrate growth process to continue at a high speed. This fundamentally solves the technical problem in traditional methods where the reaction rate drastically decreases due to the hydrate layer encapsulating gas bubbles.

[0039] The complete implementation process of this invention, in a specific application scenario taking the capture of carbon dioxide from flue gas as an example, can be described as follows: First, the entire system was prepared before the reaction began. The interior of the 50-liter sealed reactor was thoroughly cleaned and dried. 29.955 kg of deionized water was precisely injected through the liquid inlet using a high-pressure metering pump. Subsequently, a pre-prepared concentrate containing 45 g of C14E12 regulator was injected, and the agitator was turned on and stirred at a low speed of 200 rpm for 15 minutes to ensure the regulator was completely dissolved and evenly distributed in the aqueous phase. At this point, the final mass fraction of the regulator in the aqueous phase was 0.15%.

[0040] Secondly, a system seal check and inertization treatment were performed. All valves were closed, and high-purity nitrogen was introduced into the reactor to 1.0 MPa. The pressure change was monitored for 2 hours, and the pressure drop was confirmed to be less than 0.01 MPa, indicating that the system was airtight. Subsequently, the nitrogen was released, and the charging and discharging process was repeated three times to completely replace the air in the system and avoid oxygen interfering with the experimental results.

[0041] Next, the reaction conditions are established. The refrigeration cycle unit is started, and the outlet temperature of the cooling medium is set to 273.65 K. The aqueous solution in the reactor is cooled to the target reaction temperature, for example, 275.15 K, through the heat exchange jacket. During this process, the stirring device 2 is maintained at 300 rpm to enhance heat transfer. Once the temperature stabilizes, simulated flue gas, such as a mixture of 15% CO2 and 85% N2 by volume, is introduced into the reactor through the gas inlet until the internal pressure of the reactor reaches the preset reaction pressure, for example, 3.5 MPa.

[0042] Then, the core process of enhanced mass transfer and hydrate formation was initiated. The stirring speed was increased to 500 rpm to generate strong macroscopic mixing and suspension effects. Simultaneously, the rotor-stator microbubble generation module integrated at the bottom of the reactor was activated, with its rotor linear velocity set to 22 m / s. At this time, simulated flue gas was continuously supplied to the microbubble generation module at a constant flow rate of 50 SLPM via a mass flow controller. Under the high shear force of the microbubble module, the gas was dispersed into microbubbles with an average diameter of approximately 30 micrometers, rapidly increasing the gas-liquid contact area. Under the conditions of 275.15 K and 3.5 MPa, CO2 hydrates were in the thermodynamically stable region. CO2 molecules dissolved in water combined with water molecules, and under the action of the C14E12 regulator, rapidly generated hydrate particles with a porous microstructure.

[0043] Throughout the reaction process, key parameters are monitored and adjusted in real time by an automated control system. This system, based on a Siemens S7-1500 series programmable logic controller (PLC), integrates a 15-inch touchscreen human-machine interface. The reactor temperature is monitored in real time by a Pt100 sensor and stabilized at 275.15K ± 0.1K by a PID controller. Pressure is monitored by a pressure transmitter with an accuracy of ±0.1%FS and maintained at 3.5MPa ± 0.05MPa through a mass flow controller controlling the gas inlet and a back pressure regulating valve connected to the exhaust gas line. The exhaust gas from the reactor passes through a non-dispersive infrared (NDI) CO2 online analyzer with a measurement accuracy of ±0.5%FS and a response time of less than 5 seconds, used for real-time calculation of CO2 consumption and conversion rate.

[0044] Finally, when the online gas analyzer shows that the CO2 conversion rate reaches 95%, or when the gas consumption rate significantly decreases to a preset threshold, the supply of mixed gas is stopped, and the microbubble generation module and stirring device are shut down. At this point, a hydrate slurry with a high solids content is formed in the reactor. Through the slurry outlet at the bottom and a screw pump, the hydrate slurry is transported to a separation unit for subsequent solid-liquid separation, hydrate decomposition, and recovery of high-purity CO2 gas.

[0045] To further verify the superiority of the technical solution of the present invention, the following embodiments and comparative examples are provided.

[0046] Example 1 The apparatus and operating procedure described in detail above are used. Specific parameters are as follows: Reactor: 50-liter closed reactor.

[0047] Reaction medium: 29.955 kg of deionized water and 45 g of C14E12 regulator, concentration 0.15%wt.

[0048] Reaction gas: 15% CO2 / 85% N2 (v / v) mixture.

[0049] Reaction conditions: temperature 275.15 K, pressure 3.5 MPa.

[0050] Stirring speed: 500 rpm.

[0051] Microbubble generation module: rotor-stator homogenizer, rotor linear speed 22m / s.

[0052] Gas supply rate: 50 SLPM.

[0053] During the experiment, the gas consumption was recorded over time, and the CO2 conversion rate was calculated. The results showed that the induction time for hydrate formation was less than 5 minutes, defined as the moment when the gas consumption rate showed a significant and rapid increase. Within 15 minutes of the reaction starting, the CO2 conversion rate reached 50%; at 28 minutes, the CO2 conversion rate exceeded 90%. Finally, at 40 minutes, the reaction was essentially complete, with a total gas consumption of 35.8 moles, of which 5.37 moles were CO2. Corresponding to the initial water volume, the gas capture rate was 0.00324 mol CO2 / mol H2O. The entire process exhibited a fast reaction rate and high gas utilization rate.

[0054] Comparative Example 1 For comparison, the reactor, reaction medium, reaction gas, reaction temperature and pressure, and stirring rate were exactly the same as in Example 1, except that the reaction medium was only 30 kg of pure deionized water. The only difference was that this comparative example did not use a microbubble generation module, but instead used a traditional bubbling method, i.e., the mixed gas was introduced from the bottom of the reactor through a porous tube with a 2 mm aperture. The gas supply rate was also 50 SLPM.

[0055] Experimental results showed that under these conditions, the induction time for hydrate formation was significantly extended to 35 minutes. After the induction period, the gas consumption rate increased slowly, but at 60 minutes after the start of the reaction, the CO2 conversion rate was only 25%. Subsequently, the reaction rate decreased sharply and then leveled off, which is a typical result of the "interfacial self-armoring effect." Even after 180 minutes, the CO2 conversion rate only reached 45%, far lower than that of Example 1. The final measured total gas consumption was 16.5 mol, of which CO2 consumption was 2.48 mol, and the gas capture rate was only 0.00149 mol CO2 / mol H2O.

[0056] Data Comparison To more intuitively demonstrate the technical effects of this invention, the key performance indicators of Example 1 and Comparative Example 1 are summarized in the table below: Through direct comparison of the above embodiments and comparative examples, it is evident that the enhanced mass transfer method for gas separation using the hydrate method disclosed in this invention successfully overcomes the mass transfer bottleneck in the hydrate formation process through the innovative synergistic effect of the microbubble generation module and the interface microstructure regulator. This invention not only increases the hydrate formation rate by nearly an order of magnitude but also significantly improves the final gas conversion rate and the gas storage capacity per unit of water, thereby greatly enhancing the engineering application value and economic feasibility of the hydrate-based gas separation technology.

[0057] Furthermore, the method of this invention possesses good versatility and can be flexibly applied to other gas separation or storage scenarios. For example, in the application of natural gas removal of acidic gases (H2S / CO2), interfacial microstructure modulators with higher selective adsorption capacity for H2S, such as amphiphilic molecules containing thiol or amine groups, can be selected to further enhance the capture efficiency of the target gas while regulating the microstructure. In the application of hydrogen (H2) storage, since the formation conditions of H2 hydrates are extremely demanding and require higher pressures, the parameters of the microbubble generation module can be further optimized. For example, a porous membrane with an average pore size of less than 1 micrometer can be used to generate smaller nanobubbles, thereby utilizing the Laplace pressure effect to increase the local solubility of H2 in water and promote hydrate formation. All these adjustments and optimizations are within the technical framework constructed by this invention.

[0058] In summary, this invention, through a profound understanding of the mass transfer process, innovatively combines microscale interface control with macroscale reactor engineering design, providing a systematic, efficient, and industrially scalable solution that paves the way for the widespread application of hydrate technology in energy, environment, and chemical industries.

Claims

1. An enhanced mass transfer method for gas separation using hydrates, carried out in a closed reactor, characterized in that, The method includes the following steps: An aqueous phase containing a predetermined concentration of an interfacial microstructure modifier is injected into the closed reactor; the interfacial microstructure modifier is an amphiphilic compound containing a hydrophilic head group and a hydrophobic tail group. A microbubble generation module disperses the mixed gas to be separated into the aqueous phase in the form of microbubbles to form a gas-liquid mass transfer interface with a high specific surface area. Adjust the temperature and pressure inside the sealed reactor to the conditions for the formation of the target gas hydrate; Under the aforementioned formation conditions, the target gas component in the mixed gas dissolves in the aqueous phase through the gas-liquid mass transfer interface and combines with water molecules to form hydrates. The interface microstructure regulator adsorbs onto the surface of the generated hydrate, inducing the formation of a hydrate solid phase layer with a permeable microstructure. This allows gas molecules dissolved in the aqueous phase to continuously diffuse through the permeable microstructure to the hydrate growth interface, thereby enhancing the mass transfer process.

2. The method according to claim 1, characterized in that, The interface microstructure regulator is a polyoxyethylene ether type nonionic surfactant with a hydrophilic-lipophilic balance (HLB) value between 10 and 18. The hydrophilic head group of the polyoxyethylene ether type nonionic surfactant is a polyoxyethylene chain with an average degree of polymerization between 8 and 20, and its hydrophobic tail group is an alkyl chain with an average number of carbon atoms between 12 and 18.

3. The method according to claim 2, characterized in that, The initial concentration of the interface microstructure regulator in the aqueous phase ranges from 0.01% to 0.5% by mass fraction; the permeable microstructure induced by the interface microstructure regulator is a morphology with micropores, a dendritic or polycrystalline aggregate structure, wherein the micropores or the channels inside the structure make the hydrate solid phase layer present a connected microchannel structure, and the average pore size of the microchannel is 10 nanometers to 100 nanometers.

4. The method according to claim 1, characterized in that, The microbubble generation module is implemented through at least one of the following methods: A high shear force dispersion device is used, which generates a high shear force field in the reactor to break up and refine the introduced gas into microbubbles.

5. The method according to claim 4, characterized in that, When the microbubble generation module uses the high shear force dispersion device, the high shear force dispersion device is a rotor-stator homogenizer or a Venturi jet. When the rotor-stator homogenizer is used, the linear velocity of the rotor is controlled between 10 m / s and 30 m / s, and the gap between the rotor and the stator is controlled between 0.1 mm and 1.0 mm. When the Venturi injector is used, the throat diameter is designed to be between 2 mm and 10 mm, and the flow velocity of the liquid phase through the throat is controlled between 5 m / s and 20 m / s.

6. The method according to claim 4, characterized in that, When the microbubble generation module uses the porous membrane dispersion device, the porous membrane dispersion device is composed of a ceramic membrane, a sintered metal membrane or a polymer microporous membrane, with an average pore size between 0.1 micrometers and 10 micrometers and a porosity between 30% and 60%; the predetermined pressure difference of the mixed gas passing through the porous membrane is 0.1 MPa to 1.0 MPa higher than the liquid phase static pressure.

7. The method according to any one of claims 1 to 6, characterized in that, Through the function of the microbubble generation module, the average diameter of the microbubbles generated in the closed reactor is controlled between 1 micrometer and 100 micrometers; and during the hydrate generation process, the bubble volume concentration in the closed reactor is maintained between 10% and 50%, thereby forming a gas-liquid specific surface area of ​​1000 m² / m³ to 5000 m² / m³.

8. The method according to claim 1, characterized in that, The sealed reactor is constructed primarily of austenitic stainless steel 316L or duplex stainless steel 2205. An internal stirring device is installed within the sealed reactor to continuously stir the mixture during the reaction, maintaining the uniform suspension of the hydrate particles. An external heat exchange jacket or internal cooling coils are installed on the exterior of the sealed reactor to precisely control the reaction temperature within ±0.1K of the target hydrate formation temperature.

9. The method according to claim 1, characterized in that, When the mixed gas to be separated is flue gas containing carbon dioxide, the formation conditions of the target gas hydrate are set as follows: the temperature is between 274.15K and 283.15K, and the pressure is between 2.0MPa and 5.0MPa; and the stirring rate is maintained at 300rpm to 600rpm by the stirring device inside the closed reactor.

10. The method according to claim 1, characterized in that, The method also monitors and regulates the reaction process through an automated control system, which includes: An online gas analyzer is configured on the outlet pipeline of the closed reactor to monitor the concentration of the target gas component in the outlet gas phase in real time; A proportional-integral-derivative (PID) controller linked to the heat exchange jacket or cooling coil is used to precisely adjust the flow rate of the cooling medium based on real-time temperature feedback inside the reactor. A mass flow controller connected to the gas inlet is used to accurately measure and regulate the inflow rate of the mixed gas; A frequency converter connected to the drive motor of the stirring device is used to precisely control the rotational speed of the stirring device.

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