Low-temperature and low-pressure adsorption performance testing device and testing method thereof

Abstract

The invention discloses a low-temperature low-pressure adsorption performance testing device and a testing method thereof. The device comprises a vacuum container, a low-temperature unit, an adsorption unit, a gas distribution unit, a vacuum unit, a buffer unit and a data acquisition unit, the gas distribution unit independently provides working medium gas and test gas for the low-temperature unit and the adsorption unit; the low-temperature unit performs gradient pre-cooling on the working medium gas and the test gas; the adsorption unit is in heat-conducting connection with the low-temperature unit; the buffer unit is used for performing multi-stage pressure stabilization and flow control on the test gas; the vacuum unit is used for independently vacuumizing each unit; the data acquisition unit monitors pressure parameters. The test method comprises the following steps: vacuumizing to an initial high vacuum state, introducing working medium gas for refrigeration and temperature stabilization, carrying out gradient pre-cooling on test gas, carrying out multi-stage pressure stabilization, introducing the test gas into the adsorption unit, recording balance pressure data, and calculating the adsorption quantity. According to the invention, a stable low-temperature environment can be provided for adsorption performance testing, refrigeration vibration interference is isolated, and the stability of adsorption testing is improved.

Description

Technical Field

[0001] This invention pertains to the field of adsorption performance testing technology, specifically relating to a low-temperature, low-pressure adsorption performance testing device and its testing method. Background Technology

[0002] Adsorption performance testing is an important means of studying the application performance of porous materials (such as metal-organic framework materials, activated carbon, zeolites, carbon nanomaterials, etc.) in gas storage, separation and catalysis. In particular, in the adsorption research of gases such as hydrogen, methane and carbon dioxide, the low temperature and low pressure adsorption characteristics can reflect the microporous structure characteristics and adsorption thermodynamic parameters of the material, which is of great significance for material screening and mechanism analysis.

[0003] Currently, commonly used adsorption performance testing methods mainly include static volumetric methods and dynamic breakthrough methods, with test temperatures mostly concentrated in the range of room temperature to 77 K. For materials with large specific surface areas or strong adsorption, cryogenic testing conditions below 77 K (4.2–40 K) can more accurately reveal the adsorption characteristics of the material. To achieve such testing, an experimental system with low-temperature stability, clean gas path, and high vacuum is required. In the prior art, Chinese invention patent with publication number CN112666266A discloses a testing device for the adsorption performance of adsorbents under low-temperature and high-vacuum conditions, including a cryostat, an adsorption column assembly, a primary buffer tank, a secondary buffer tank, a vacuum pump unit, and a gas source. The adsorbent is placed in the adsorption column, which is thermally connected to the secondary cold head of the refrigerator through a copper flexible connection with high thermal conductivity. The adsorption column is mechanically fixed to the vacuum container through a fixing rod, and the refrigerator and the cryostat are sealed together using a bellows pipe. The refrigerator is fixed separately using a bracket. However, the testing device lacks pre-cooling for the test gas to match the target temperature of the adsorption unit. Directly introducing the test gas into the low-temperature adsorption unit may make it a strong heat source within the unit. The thermal shock generated by this heat source can easily cause drastic temperature fluctuations in the adsorption chamber, adsorbent, and surrounding structures, altering the diffusion rate of microporous molecules and the adsorption binding energy, thus increasing the repeatability error of the adsorption capacity test. Furthermore, the refrigerator needs to operate at high load to offset the thermal shock, increasing cooling loss and exacerbating temperature fluctuations in the cold head. In addition, the vibration isolation measures in the low-temperature section of the testing device are limited; refrigerator vibration enters the adsorption chamber through structural coupling, causing fluctuations in pressure and temperature signals and increasing the uncertainty in adsorption capacity calculation. Moreover, the gas path is mostly single-stage pressure reduction with one or two-stage buffers, lacking multi-stage throttling and closed-loop pressure regulation. -3 -10 -5Under ultra-low pressure conditions such as Pa, it is difficult to maintain a stable small flow rate, which affects the accuracy of adsorption equilibrium criteria and kinetic fitting. In addition, some systems do not achieve complete physical isolation between experimental gas and refrigeration circuit, which poses a risk of cross-contamination and pollution, resulting in decreased refrigeration efficiency, impaired purity of experimental gas, and ultimately reduced reliability of results. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature, low-pressure adsorption performance testing device and method. This invention can provide a stable low-temperature environment for adsorption performance testing through gas gradient precooling and achieve precise control of gas flow and pressure within an ultra-low pressure range, ensuring the stability of gas supply during adsorption. Furthermore, it can isolate refrigeration vibration interference through a first liquid helium cell, improving the stability of the adsorption test.

[0005] The technical solution of the present invention: a low-temperature and low-pressure adsorption performance testing device, comprising a vacuum container, a low-temperature unit, an adsorption unit, a gas distribution unit, a vacuum unit, a buffer unit, and a data acquisition unit; The cryogenic unit includes a pulse tube refrigerator, a first liquid helium pool disposed below the pulse tube refrigerator, and a heat-conducting platform that is thermally connected to the first liquid helium pool. The adsorption unit includes an adsorption cavity, which is thermally connected to the heat-conducting platform. The gas distribution unit includes a cryogenic unit gas supply branch and an adsorption unit gas supply branch, which are independent of each other. The cryogenic unit gas supply branch is used to supply refrigerant gas to the first liquid helium pool, and the adsorption unit gas supply branch is used to supply test gas to the adsorption chamber. The buffer unit is connected between the gas supply branch of the adsorption unit and the adsorption unit, and is used to perform multi-stage pressure stabilization on the test gas flowing into the adsorption chamber. A vacuum unit is used to evacuate the adsorption chamber and related pipelines. The data acquisition unit is used to monitor the pressure parameters of each unit and pipeline.

[0006] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the pulse tube refrigerator includes a compressor, a rotary valve, a valve assembly, a primary cold head, a primary cold plate, a secondary cold head, a secondary cold plate, and a regenerator. The compressor is connected to the rotary valve, the rotary valve is connected to the valve assembly, and the primary cold head, secondary cold head, and regenerator are connected to the valve assembly. The primary cold plate is located at the lower end of the primary cold head, and the secondary cold plate is located at the lower end of the secondary cold head. The regenerator is thermally connected to the primary and secondary cold plates. A primary cold head heater is attached to the lower outer wall surface of the primary cold plate, and a secondary cold head heater is attached to the lower outer wall surface of the secondary cold plate. The inlet pipe of the adsorption unit is first pre-cooled by spirally winding around the regenerator, and then suspended and spirally arranged in the first liquid helium pool. A condenser located at the lower end of the secondary cold head is provided at the top of the first liquid helium pool. The heat-conducting platform includes a first cold plate, and a first cold plate heater is provided at the top of the first cold plate.

[0007] In the aforementioned low-temperature and low-pressure adsorption performance testing device, a room temperature flange and a vacuum chamber flange are connected between the cold head of the low-temperature unit and the vacuum container, and a sealing bellows is provided between the room temperature flange and the vacuum chamber flange to achieve a sealed connection.

[0008] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the adsorption unit includes a PO tube, an adsorption chamber, an adsorption heater, an upper adsorption cover, and a lower adsorption cover; the PO tube is connected to the adsorption chamber, a vacuum unit, and a buffer unit respectively; the adsorption heater is disposed on the outer wall of the adsorption chamber; the upper adsorption cover is in close contact with the heat-conducting platform; and the lower adsorption cover is connected to the upper adsorption cover by bolts.

[0009] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the gas distribution unit includes a low-temperature unit gas supply branch and an adsorption unit gas supply branch. The low-temperature unit gas supply branch includes a helium cylinder, and a first pressure reducing valve, a first ball valve, and a first needle valve are sequentially connected between the helium cylinder and the low-temperature unit. The low-temperature unit gas supply branch is used to supply helium as a working gas to the first liquid helium pool. The adsorption unit gas supply branch includes a hydrogen cylinder and a nitrogen cylinder. A second pressure reducing valve is also provided between the hydrogen cylinder and the buffer unit, and a third pressure reducing valve is also provided between the nitrogen cylinder and the buffer unit. The adsorption unit gas supply branch is used to supply test gas to the adsorption unit.

[0010] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the buffer unit includes a first buffer tank, a second buffer tank, and a third buffer tank. A second ball valve and a second needle valve are sequentially connected between the gas distribution unit and the first buffer tank. A first capillary tube and a third needle valve are sequentially provided between the first buffer tank and the second buffer tank. A second capillary tube and a fourth needle valve are sequentially provided between the second buffer tank and the third buffer tank. A fifth needle valve, a sixth needle valve, a third capillary tube, a seventh needle valve, and a filter are sequentially provided between the third buffer tank and the adsorption unit.

[0011] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the vacuum unit includes a first vacuum pump, an eighth needle valve, a vent valve, and a ninth needle valve; the first vacuum pump is connected to the buffer unit through the eighth needle valve, and the eighth needle valve is located between the fifth needle valve and the sixth needle valve; the first vacuum pump is connected to the outside air through the vent valve; the ninth needle valve is located between the first vacuum pump and the adsorption unit.

[0012] In the aforementioned low-temperature and low-pressure adsorption performance testing device, the data acquisition unit includes a first vacuum gauge, a second vacuum gauge, a third vacuum gauge, a fourth vacuum gauge, and a fifth vacuum gauge. The first vacuum gauge is installed on the first buffer tank, the second vacuum gauge is installed on the second buffer tank, the third vacuum gauge is installed on the third buffer tank, the fourth vacuum gauge is installed between the third capillary tube and the seventh needle valve, and the fifth vacuum gauge is installed between the ninth needle valve and the adsorption unit.

[0013] The aforementioned test method for the low-temperature, low-pressure adsorption performance testing device includes the following steps: Step S1: Turn on the vacuum unit to evacuate the cryogenic unit, adsorption unit, buffer unit and each gas pipeline until the overall vacuum of the device reaches the preset initial high vacuum state. Step S2: The working gas is introduced into the first liquid helium pool through the gas distribution unit. After being pre-cooled by the low temperature unit, the working gas is cooled into a liquid working gas and enters the first liquid helium pool. The liquid working gas in the first liquid helium pool causes the ambient temperature of the adsorption unit to drop uniformly and stabilize at the target test temperature through heat conduction. Step S3: The test gas is provided through the gas distribution unit. After the test gas is stabilized in multiple stages by the buffer unit, it is introduced into the low temperature unit for gradient precooling, and then introduced into the adsorption unit that has reached the target test temperature. After the pressure of each introduction reaches equilibrium, the equilibrium pressure data is recorded by the data acquisition unit. Step S4: Based on the principle of static constant volume method, using the equilibrium pressure data recorded in step S3, calculate the adsorption amount corresponding to each equilibrium pressure point through the mass conservation formula.

[0014] In the aforementioned test method, the formula for calculating the adsorption amount in step S4 is as follows: ; in, For the first The amount of gas adsorbed in the first adsorption. For the first The initial pressure of the fourth vacuum gauge during the second adsorption. For the first The equilibrium pressure of the fourth vacuum gauge in the previous step during the second adsorption. This is the volume of the third buffer tank. Let V be the volume of the adsorption cavity. For the first The equilibrium pressure of secondary adsorption. The gas constant is... To test the temperature, This refers to the mass of the adsorbent.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The first liquid helium pool at the lower end of the cryogenic unit of this invention uses heat conduction to uniformly lower and stabilize the ambient temperature of the adsorption unit at the target test temperature. Compared with a single heat exchange mode, this results in a more uniform temperature distribution around the adsorption unit, avoiding the impact of local temperature deviations on the adsorption activity of the adsorbent. This ensures that the adsorption test is conducted in a stable and uniform cryogenic environment, laying the foundation for the reliability of the test results. Furthermore, the first liquid helium pool effectively isolates the cryogenic unit from external vibrations and vibrations generated during its operation, preventing the adsorbent from loosening, falling off, or disturbing the adsorption interface, thus ensuring the stability of the adsorption process. The buffer unit of this invention is specifically designed with multi-stage pressure stabilization and flow control functions for the test gas, effectively solving the problems of large pressure fluctuations and unstable flow rates in traditional tests. This ensures a stable pressure of the test gas entering the adsorption unit, providing a prerequisite for accurate acquisition of subsequent equilibrium pressure data. In addition, the gas distribution unit of this invention independently provides the working gas and test gas to the cryogenic unit and adsorption unit respectively, with separate supply paths for the two types of gases to avoid cross-contamination. Attached Figure Description

[0016] Figure 1 This is a system diagram of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the relevant pipeline in Embodiment 1 of the present invention. Figure 3 This is a system diagram of Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the relevant pipeline in Embodiment 2 of the present invention.

[0017] The labels in the attached diagram are as follows: 1. Vacuum container; 2. Compressor; 3. Rotary valve; 4. Valve assembly; 5. First-stage cold head; 6. First-stage cold plate; 7. Second-stage cold head; 8. Second-stage cold plate; 9. Regenerator; 10. First liquid helium tank; 11. First-stage cold head heater; 12. Second-stage cold head heater; 13. Condenser; 14. First cold plate; 15. First cold plate heater; 16. PO tube; 17. Adsorption chamber; 18. Adsorption heater; 19. Helium cylinder; 20. Hydrogen cylinder; 21. Nitrogen cylinder; 22. First buffer tank; 23. Second buffer tank; 24. Third buffer tank; 25. First vacuum pump; 26. Second vacuum pump; 27. First vacuum gauge; 28. Second vacuum gauge; 29. ​​Third vacuum gauge; 30. Fourth vacuum gauge; 31. Fifth vacuum gauge. 32. Vacuum gauge; 33. Sealing bellows; 34. Room temperature flange; 35. Vacuum chamber flange; 36. Door rod regulating valve; 37. JT throttle valve; 38. Heat exchanger; 39. Second liquid helium tank; 40. Communicating vessel; 41. Second cold plate; 42. First needle valve; 43. Second needle valve; 44. Third needle valve; 45. Fourth needle valve; 46. Fifth needle valve; 47. Sixth needle valve; 48. Seventh needle valve; 49. Eighth needle valve; 50. Ninth needle valve; 51. Tenth needle valve; 52. First ball valve; 53. Second ball valve; 54. First pressure reducing valve; 55. Second pressure reducing valve; 56. Third pressure reducing valve; 57. First capillary pipette; 58. Second capillary pipette; 59. Third capillary pipette; 60. Filter; 61. Exhaust valve. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0019] Example 1: A low-temperature, low-pressure adsorption performance testing device, such as... Figure 1 As shown, this device can test the adsorption and desorption characteristics of various gas adsorbent samples within a temperature range of 4.2K–300K, with controlled temperature and adjustable pressure. The testing device includes a vacuum container 1, a cryogenic unit, an adsorption unit, a gas distribution unit, a vacuum unit, a buffer unit, and a data acquisition unit. The cryogenic unit includes a pulse tube refrigerator, a first liquid helium pool 10 located below the pulse tube refrigerator, and a heat-conducting platform thermally connected to the first liquid helium pool 10. The pulse tube refrigerator achieves gas expansion cooling by reciprocating alternating flow of high-pressure helium gas provided by the gas distribution unit within the pulse tube. It features simple structure, low vibration, and convenient maintenance.

[0020] The pulse tube refrigerator is used to perform gradient precooling of the working gas provided by the gas distribution unit and the test gas introduced into the adsorption unit. The pulse tube refrigerator includes a compressor 2, a rotary valve 3, a valve assembly 4, a first-stage cold head 5, a first-stage cold plate 6, a second-stage cold head 7, a second-stage cold plate 8, and a regenerator 9. The compressor 2 is connected to the rotary valve 3 and provides high-pressure helium working gas, driving the circulation of the pulse tube refrigerator. The rotary valve 3 and the valve assembly 4 are connected; the rotary valve 3 converts the DC high-pressure helium flow output from the compressor 2 into an alternating flow, thereby driving the periodic flow of gas inside the pulse tube refrigerator. The valve assembly 4 is used for helium delivery, loop switching, and safety venting control. The heat transfer platform includes a first cold plate 14 fixed to the lower end of the first liquid helium pool 10. The first cold plate 14 connects the first liquid helium pool 10 and the adsorption unit, serving as an extended carrier for the cooling capacity of the first liquid helium pool 10. The first liquid helium pool 10 transfers heat to the first cold plate 14 via thermal conduction, causing the temperature of the first cold plate 14 to decrease synchronously. The planar structure of the first cold plate 14 expands the low-temperature radiation area, making the low-temperature field around the first liquid helium pool 10 more uniform. This avoids localized cold concentration and excessively high edge temperatures in the first liquid helium pool 10, providing a surrounding pre-cooling environment for the adsorption unit. A first cold plate heater 15 is located on the top of the first cold plate 14. The first cold plate heater 15 is a resistance heater, attached to the top of the first cold plate 14. Its core function is to offset the cold loss caused by external heat intrusion (such as heat leakage from the vacuum container 1 or heat conduction from pipelines). When the temperature of the first cold plate 14 falls below the target test temperature (e.g., 4.2K, 10K, etc.) due to heat intrusion, the first cold plate heater 15 can precisely output a small amount of heat to stabilize the temperature of the first cold plate 14 at the set value. Conversely, if excessive cooling occurs, the first cold plate heater 15 can also be fine-tuned to prevent the temperature from becoming too low and causing abnormal adsorbent activity. The primary cold head 5, the secondary cold head 7, and the regenerator 9 are connected to the valve assembly 4. The primary cold plate 6 is located at the lower end of the primary cold head 5, and the secondary cold plate 8 is located at the lower end of the secondary cold head 7. The regenerator 9 is thermally connected to the primary cold plate 6 and the secondary cold plate 8. A primary cold head heater 11 is attached to the lower outer wall surface of the primary cold plate 6, and a secondary cold head heater 12 is attached to the lower outer wall surface of the secondary cold plate 8. The primary cold head heater 11 and the secondary cold head heater 12 control the temperatures of the primary cold head 5 and the secondary cold head 7, respectively, thereby achieving graded temperature control of the test gas. To ensure a stable, low-temperature supply of the test gas to the adsorption unit, a pre-cooling pipeline is installed outside the primary and secondary cold plates 6 and 8 of the pulse tube refrigerator. Before entering the adsorption unit, the test gas flows through this pipeline along the regenerator 9 of the pulse tube refrigerator, undergoing gradient pre-cooling through heat exchange with the outer walls of the primary and secondary cold plates 6 and 8. This gradual decrease in temperature significantly reduces the initial temperature of the test gas before it enters the adsorption chamber 17, preventing the high-temperature gas flow from affecting the adsorbent and the system's thermal balance, and ensuring consistent test conditions. Furthermore, since this pipeline does not directly participate in the internal circulation of the pulse tube refrigerator, it does not affect the performance of the refrigerator and has a simple structure with high reliability.In the cryogenic unit, the first liquid helium pool 10 serves as the main heat insulation and cooling component, filled with liquid helium pre-cooled by the cryogenic unit's gradient. Specifically, after high-purity helium enters the cryogenic unit through the inlet, it is first cooled by a gradient through a primary cold head 5, a primary cold plate 6, a secondary cold head 7, and a secondary cold plate 8, becoming liquid helium, thus causing the temperature of the entire first liquid helium pool 10 to drop uniformly. The low temperature of the first liquid helium pool 10 is transferred to the adsorption unit through heat conduction, thereby forming a cooling environment without rigid contact. The first liquid helium pool 10 isolates the micro-vibrations during the operation of the pulse tube refrigerator, achieving zero-vibration steady-state operation and avoiding the coupling of mechanical vibrations.

[0021] The inlet pipe of the adsorption unit is first spirally wound around the regenerator 9 for pre-cooling, and then suspended and spirally arranged inside the first liquid helium pool 10. Preferably, the top of the first liquid helium pool 10 is provided with a condenser 13 located at the lower end of the secondary cold head 7. The condenser 13 is used to cool the helium gas to improve the refrigeration efficiency of liquid helium. The cryogenic unit is set inside the vacuum container 1 and flexibly connected to the vacuum container 1. Further, a room temperature flange 34 and a vacuum chamber flange 35 are connected between the cold head chamber of the cryogenic unit and the vacuum container 1. A sealing bellows 33 is provided between the room temperature flange 34 and the vacuum chamber flange 35, thereby realizing a flexible sealed connection between the pulse tube refrigerator and the vacuum chamber, absorbing mechanical vibration and thermal stress. The first liquid helium pool 10 provides a uniform low temperature field to the adsorption unit through heat conduction. Combined with the flexible connection between the cryogenic unit and the vacuum container 1, vibration isolation of the adsorption unit is achieved.

[0022] The adsorption unit is located inside the vacuum container 1 and is thermally connected to the cryogenic unit. The adsorption unit contains the adsorbent and controls the temperature for adsorption and desorption. The adsorption unit includes a P0 tube 16, an adsorption chamber 17, an adsorption heater 18, an upper adsorption cover, and a lower adsorption cover. The P0 tube 16 connects to the adsorption chamber 17, the vacuum unit, and the buffer unit, respectively. The P0 tube 16 is used to establish the reference pressure during adsorption testing and to control the introduction and evacuation of the test gas. The adsorption chamber 17 provides a low-temperature, low-pressure adsorption space for the adsorbent and contains an adsorbent support structure and a temperature sensor mounting position. The adsorbent is the test sample and can be in powder, porous block, or shaped granules. It refers to a material with a porous structure that can physically adsorb gas molecules, including but not limited to metal-organic frameworks (MOFs), activated carbon, zeolites, and carbon nanomaterials, and is uniformly distributed within a designated area inside the adsorption chamber 17. An adsorption heater 18 is installed on the outer wall of the adsorption chamber 17. The adsorption heater 18 is used for deheating or temperature control of the adsorbent. A flexible heating film is adhered to the outer wall of the adsorption chamber 17 to achieve a rapid and uniform temperature response. The upper adsorption cover is in close contact with the first cold plate 14 and is efficiently connected via bolts and a thermally conductive interface material, making the upper adsorption cover the primary low-temperature conduction path. The lower adsorption cover is bolted to the upper adsorption cover and, together with a sealing element (indium wire), seals the adsorption chamber 17. A gas inlet and vacuum connection interface are provided to ensure unobstructed gas flow and reliable sealing.

[0023] like Figure 2As shown, the gas distribution unit is connected to both the cryogenic unit and the adsorption unit. The gas distribution unit independently provides the working gas and test gas to the cryogenic unit and adsorption unit respectively. The gas distribution unit includes a cryogenic unit gas supply branch (working gas passage) and an adsorption unit gas supply branch (test gas passage). The cryogenic unit gas supply branch includes a helium cylinder 19. A first pressure reducing valve 54, a first ball valve 52, and a first needle valve 42 are sequentially connected between the helium cylinder 19 and the cryogenic unit. The cryogenic unit gas supply branch provides helium as the working gas for refrigeration within the cryogenic unit. The working gas (helium) in the cryogenic unit originates from the helium cylinder 19. After primary pressure reduction and stabilization by the first pressure reducing valve 54, the gas is controlled by the first ball valve 52, and the flow rate is finely regulated by the first needle valve 42 before finally entering the cryogenic unit. The gas flow rate of the cryogenic unit's gas supply branch is stable, and the helium supply rate can be flexibly adjusted according to the operating stage of the pulse tube refrigerator (initial cooling / steady-state maintenance). Independent gas source control prevents contamination of the pulse tube refrigerator by the adsorption test gas, achieving complete isolation between the cryogenic unit and the adsorption unit. The adsorption unit's gas supply branch includes a hydrogen cylinder 20 and a nitrogen cylinder 21. A second pressure-reducing valve 55 is installed between the hydrogen cylinder 20 and the buffer unit, and a third pressure-reducing valve 56 is installed between the nitrogen cylinder 21 and the buffer unit. The adsorption unit's gas supply branch is used to supply test gases (hydrogen, nitrogen, or other adsorption media) to the adsorption unit.

[0024] A buffer unit is connected between the gas distribution unit and the adsorption unit. The buffer unit is used for multi-stage pressure stabilization and flow control of the test gas. The buffer unit includes a first buffer tank 22, a second buffer tank 23, and a third buffer tank 24. The first buffer tank 22 is installed at the front end of the main gas supply circuit to absorb initial pressure fluctuations in the gas source, completing first-stage pressure stabilization and balancing the gas source output. The second buffer tank 23 is located after the first buffer tank 22 and is used for second-stage pressure stabilization, further reducing the gas pressure and achieving flow balance. The third buffer tank 24 is connected in series with the second buffer tank 23 in the same main gas supply circuit for third-stage pressure stabilization and fine buffering, further reducing the pressure of the test gas before it enters the adsorption unit, ensuring it reaches the set low-pressure range and preventing excessive airflow at the moment the valve opens, which could cause system disturbances. These three components constitute a hierarchical pressure stabilization system from high to low pressure, ensuring a smooth transition of the gas pressure gradient. Furthermore, a second ball valve 53 and a second needle valve 43 are sequentially connected between the gas distribution unit and the first buffer tank 22. A first capillary tube 57 and a third needle valve 44 are sequentially provided between the first buffer tank 22 and the second buffer tank 23. A second capillary tube 58 and a fourth needle valve 45 are sequentially provided between the second buffer tank 23 and the third buffer tank 24. A fifth needle valve 46, a sixth needle valve 47, a third capillary tube 59, a seventh needle valve 48, and a filter 60 are sequentially provided between the third buffer tank 24 and the adsorption unit. Among them, the fifth needle valve 46 and the sixth needle valve 47 are used for preliminary throttling, the third capillary tube 59 realizes micro-flow control, the seventh needle valve 48 is used for fine pressure stabilization, and the filter 60 is used to remove impurities in the test gas. The buffer unit is used to realize gas pressure stabilization, flow balance, and pressure buffering functions, and is an important intermediate link connecting the gas distribution system and the adsorption system. The device employs a multi-stage buffer tank and throttling pipeline for progressive pressure stabilization. The buffer unit enables gradual reduction of gas pressure and smooth flow control, preventing gas surges caused by excessively high gas source pressure or instantaneous valve opening, thus ensuring the safety and stability of the adsorption test. After flowing through the first capillary tube 57, the second capillary tube 58, the third capillary tube 59, and multiple needle valves, the test gas forms a multi-stage throttling and pressure-stabilizing channel, further refining gas flow control and maintaining a constant flow rate even under minute fluctuations, ensuring the repeatability and high precision of the adsorption experiment.

[0025] The vacuum unit is connected to the cryogenic unit, buffer unit, and adsorption unit via pipelines. The vacuum unit is used to independently evacuate each of these units. The vacuum unit includes a first vacuum pump 25, an eighth needle valve 49, a vent valve 61, and a ninth needle valve 50. The first vacuum pump 25 is connected to the buffer unit via the eighth needle valve 49. The first vacuum pump 25 provides pumping power to evacuate the buffer unit, adsorption unit, and gas path to the target vacuum level. The eighth needle valve 49 is located between the fifth needle valve 46 and the sixth needle valve 47. It is installed in the evacuation branch of the main gas supply pipeline shared by hydrogen and nitrogen, and is used to adjust the evacuation rate and for isolation operations in this gas path. The first vacuum pump 25 is connected to the outside air via the vent valve 61. The vent valve 61 ensures system safety by releasing pressurized gas during non-operational or emergency situations. The ninth needle valve 50 is located between the first vacuum pump 25 and the adsorption unit, and is used to control the connection and disconnection of the vacuum pump from the entire system, achieving overall evacuation and vacuum maintenance. Before the experiment, the ninth needle valve 50 is opened first, and the first vacuum pump 25 is used to evacuate the main system (including the adsorption unit, buffer unit and gas path) as a whole. Then, by adjusting the eighth needle valve 49, the hydrogen / nitrogen shared gas supply line can be evacuated independently to keep its internal vacuum level consistent with the main system, so as to avoid pressure difference or residual gas contamination during subsequent gas addition.

[0026] The data acquisition unit is used to monitor the pressure parameters of each unit and pipeline. The data acquisition unit includes a first vacuum gauge 27, a second vacuum gauge 28, a third vacuum gauge 29, a fourth vacuum gauge 30, and a fifth vacuum gauge 31. The first vacuum gauge 27 is installed on the first buffer tank 22, the second vacuum gauge 28 is installed on the second buffer tank 23, the third vacuum gauge 29 is installed on the third buffer tank 24, the fourth vacuum gauge 30 is installed between the third capillary tube 59 and the seventh needle valve 48, the fifth vacuum gauge 31 is installed between the ninth needle valve 50 and the adsorption unit, and the sixth vacuum gauge 32 is installed between the tenth needle valve 51 and the cryogenic unit. In addition, multiple vacuum gauges are arranged at each buffer tank and key node to monitor the pressure and vacuum changes of each buffer section and pipeline node, achieving multi-point dynamic monitoring and closed-loop regulation. This allows for real-time reflection of the gas flow status and provides accurate feedback signals to the automatic control system.

[0027] Example 2: A low-temperature, low-pressure adsorption performance testing device, such as... Figure 3As shown, in this embodiment, the adsorption unit, buffer unit, and gas distribution unit are the same as in Embodiment 1. The cryogenic unit includes a compressor 2, a rotary valve 3, a valve assembly 4, a primary cold head 5, a primary cold plate 6, a secondary cold head 7, a secondary cold plate 8, and a regenerator 9. The compressor 2 is connected to the rotary valve 3 and is used to provide high-pressure helium working fluid, providing driving force for the pulse tube refrigerator cycle. The rotary valve 3 and the valve assembly 4 are connected. The rotary valve 3 is used to convert the DC high-pressure helium flow output from the compressor 2 into an alternating flow, thereby driving the periodic flow of gas inside the pulse tube refrigerator. The valve assembly 4 is used for helium delivery, loop switching, and safety venting control. The heat transfer platform includes a first cold plate 14, a JT throttling valve 37, a heat exchanger 38, a second liquid helium pool 39, a communicating vessel 40, and a second cold plate 41. A first cold plate heater 15 is mounted on top of the first cold plate 14. The first cold plate heater 15 uses a flexible heating film attached to the top of the first cold plate 14, its core function being to offset the cooling loss caused by external heat intrusion (such as heat leakage from the vacuum container 1 and heat conduction through the pipeline). One end of the communicating vessel 40 connects to the first liquid helium pool 10, and the other end connects to the heat exchanger 38. The control end of the JT throttling valve 37 is equipped with a valve stem regulating valve 36 connected between the first liquid helium pool 10 and the vacuum chamber flange 35. The output end of the JT throttling valve 37 is connected to the second liquid helium pool 39, and the input end of the JT throttling valve 37 is connected to the heat exchanger 38. The cooling efficiency of the JT throttling valve 37 (Joule-Thomson throttling valve) depends on the inlet working fluid temperature—the lower the working fluid temperature, the greater the temperature drop after throttling and expansion. The core function of heat exchanger 38 is to pre-cool the liquid helium flowing in from the communicating vessel 40. It utilizes the cryogenic working fluid (or the cooling capacity of the second liquid helium pool 39) at the outlet of JT throttle valve 37 to exchange heat with the inlet liquid helium, laying the foundation for subsequent throttling and liquefaction. When the high-pressure helium gas, pre-cooled by heat exchanger 38, passes through the tiny orifice of JT throttle valve 37, its pressure drops sharply, causing gas expansion and work done externally. The temperature drops rapidly to 1K, flowing into the second liquid helium pool 39 for storage—serving as a stable cryogenic cold source to meet the "ultra-low temperature" (1K) requirements in adsorption testing. Heat exchanger 38 can recover the cooling capacity of the cryogenic working fluid after throttling, preventing direct loss of cooling capacity and significantly improving the energy efficiency of the entire cryogenic system. During adjustment, the flow rate of liquid helium can be controlled by rotating the lever to change the opening (valve gap size) of JT throttle valve 37—the higher the flow rate, the more 1K liquid helium is generated after throttling; conversely, the temperature increases. This adjustment enables precise temperature control at the "1K±0.5K" level, matching the stringent temperature requirements of different adsorbents (such as MOFs and activated carbon). The second liquid helium pool 39 is thermally connected to the second cold plate 41. The second cold plate 41 uses a 1K cold plate to connect the second liquid helium pool 39 to the top cover of the adsorption chamber 17 as a low-temperature reference platform, which is used to achieve efficient transfer of cold energy and provide a stable temperature reference, thus providing a stable cold-end temperature environment for the adsorption unit.Temperature control is crucial for adsorption testing—the adsorption capacity of the adsorbent is extremely sensitive to temperature. The second liquid helium cell 39 ensures that the temperature drift of the adsorption unit is ≤0.1K within a test cycle of several hours, guaranteeing data repeatability. The second cold plate 41 typically uses a high thermal conductivity material (such as oxygen-free copper, with a room temperature thermal conductivity ≥400W / (m・K)) to quickly and uniformly transfer the cooling energy from the second liquid helium cell 39 to the top cover of the adsorption chamber 17, thereby lowering the temperature of the entire adsorption chamber 17 (including the internal adsorbent) to 1K, meeting the requirements of cryogenic adsorption testing. The second cold plate 41 and the top cover of the adsorption chamber 17 adopt a "surface contact + thermally conductive interface material (such as indium foil)" design, which increases the thermal conductivity area and avoids a temperature gradient of "cold at the top and hot at the bottom" in the adsorption chamber 17 (typically with a temperature difference ≤0.2K). The adsorption activity of the adsorbent depends on a uniform temperature environment, and a temperature gradient can lead to deviations in the adsorption capacity measurement. The second cold plate 41 effectively avoids this problem. The primary cold head 5, the secondary cold head 7, and the regenerator 9 are connected to the valve assembly 4. The primary cold plate 6 is located at the lower end of the primary cold head 5, and the secondary cold plate 8 is located at the lower end of the secondary cold head 7. The regenerator 9 is thermally connected to the primary cold plate 6 and the secondary cold plate 8. A primary cold head heater 11 is attached to the lower outer wall surface of the primary cold plate 6, and a secondary cold head heater 12 is attached to the lower outer wall surface of the secondary cold plate 8. The primary cold head heater 11 and the secondary cold head heater 12 control the temperatures of the primary cold head 5 and the secondary cold head 7, respectively, thereby achieving graded temperature control of the test gas. The test gas, cooled by the low-temperature unit, is introduced into the regenerator 9 to pre-cool the introduced test gas, providing a gas source with uniform temperature and minimal fluctuations for the adsorption process. To ensure a stable, low-temperature gas supply to the adsorption unit, a pre-cooling pipeline is installed outside the primary cooling plate 6 and secondary cooling plate 8 of the pulse tube refrigerator. Before entering the adsorption unit, the test gas undergoes gradient pre-cooling by winding around the regenerator 9 of the pulse tube refrigerator through this pipeline, causing the temperature of the test gas to decrease step by step. This significantly reduces the initial temperature of the test gas before it enters the adsorption chamber 17, avoiding the influence of high-temperature gas flow on the adsorbent and the system's thermal balance, and ensuring consistent test conditions. Furthermore, since this pipeline does not directly participate in the internal circulation of the pulse tube refrigerator, it will not affect the performance of the pulse tube refrigerator, and its structure is simple and highly reliable.

[0028] In this embodiment, considering the installation between the adsorption unit, the second liquid helium pool 39, and the 1K second cold plate 41, the adsorption unit is installed with the 1K second cold plate 41 as the mounting reference. The entire unit is made of oxygen-free copper and includes a cylindrical adsorption chamber 17, a top flange, a thickened bottom section, and side air inlet and vacuum piping. The adsorption chamber 17 has an inner diameter of 60mm and a height of 30mm, with an effective volume of approximately 84.8cm³, capable of holding 10g or 20g of activated carbon, occupying approximately 24% and 47% of the chamber volume, respectively. The flange uses indium wire sealing, and the screws are uniformly pre-tightened to ensure low-temperature airtightness. Four rhodium-iron thermometers are arranged at the top and bottom to monitor temperature distribution. The air inlet and vacuum piping are connected by silver-based brazing using φ4mm oxygen-free copper thin tubes, and thermal anchors are installed at the 77K and 4K layers to reduce heat load. Inside the adsorption chamber 17, a silver-plated copper mesh and perforated guide plates are installed to ensure uniform airflow and stabilize the adsorption layer.

[0029] like Figure 4 As shown, the vacuum unit includes a first vacuum pump 25, a second vacuum pump 26, an eighth needle valve 49, an exhaust valve 61, and a ninth needle valve 50. The first vacuum pump 25 is connected to the buffer unit through the eighth needle valve 49, which is located between the fifth needle valve 46 and the sixth needle valve 47. The first vacuum pump 25 is connected to the outside air through the exhaust valve 61. The ninth needle valve 50 is located between the first vacuum pump 25 and the adsorption unit. The second vacuum pump 26 is connected to the cryogenic unit through the tenth needle valve 51. The second vacuum pump 26 is used to evacuate the first liquid helium pool 10.

[0030] The data acquisition unit includes a first vacuum gauge 27, a second vacuum gauge 28, a third vacuum gauge 29, a fourth vacuum gauge 30, a fifth vacuum gauge 31, and a sixth vacuum gauge 32. The first vacuum gauge 27 is mounted on the first buffer tank 22, the second vacuum gauge 28 is mounted on the second buffer tank 23, the third vacuum gauge 29 is mounted on the third buffer tank 24, the fourth vacuum gauge 30 is positioned between the third capillary tube 59 and the seventh needle valve 48, the fifth vacuum gauge 31 is positioned between the ninth needle valve 50 and the adsorption unit, and the sixth vacuum gauge 32 is positioned between the tenth needle valve 51 and the low-temperature unit. Example 3: The testing method for the low-temperature, low-pressure adsorption performance testing device based on Example 1 includes the following steps: Step S1: Turn on the vacuum unit to evacuate the cryogenic unit, adsorption unit, buffer unit and each gas pipeline until the overall vacuum of the device reaches the preset initial high vacuum state. In this embodiment, the first vacuum pump 25 is started, the eighth needle valve 49 is opened, and the second ball valve 53, the second needle valve 43, the third needle valve 44, the fourth needle valve 45, the fifth needle valve 46, the sixth needle valve 47, and the seventh needle valve 48 are opened; the vacuum level is monitored by the first vacuum gauge 27, the second vacuum gauge 28, the third vacuum gauge 29, and the fourth vacuum gauge 30 until the vacuum level is stable at ≤1×10⁻⁶. -3Pa, close the eighth needle valve 49. Keep the first vacuum pump running, open the ninth needle valve 50, and monitor through the fifth vacuum gauge 31 until the vacuum level stabilizes at ≤1×10. -3 Pa, close the ninth needle valve. Let stand for 20 minutes. If all vacuum gauge readings remain below the corresponding threshold, the vacuuming is considered successful. If the readings exceed the threshold, check the seal and re-vacuum.

[0031] Step S2: A refrigerant gas is introduced into the first liquid helium pool 10 through the gas distribution unit. After being pre-cooled by the low temperature unit, the working gas is cooled into a liquid working gas and enters the first liquid helium pool 10. The liquid working gas in the first liquid helium pool 10 causes the ambient temperature of the adsorption unit to drop uniformly and stabilize at the target test temperature through heat conduction. In this embodiment, a high-purity helium cylinder 19 is connected, and the pressure is adjusted to 0.3 MPa through the first pressure reducing valve 54. The first ball valve 52 and the first needle valve 42 are opened to supply helium to the compressor 2. The compressor (set pressure 1.5-2.0 MPa) and rotary valve 3 are started, and the helium is distributed to the primary cold head 5, the secondary cold head 7, and the regenerator 9 via valve group 4. The primary cold head heater 11 is started, causing the primary cold plate 6 to cool down to 80K (stabilized at 80±0.5K). The secondary cold plate 8 is adjusted according to the target temperature. If the target temperature is 4.2K, the secondary cold head heater 12 is started after cooling down to 20K, and the helium flow rate is finely adjusted to stabilize the temperature of the secondary cold plate 8 at 4.2±0.1K. If the target temperature is 77K, the secondary cold head heater 12 is started after cooling down to 80K, stabilizing the temperature of the secondary cold plate 8 at 77±0.5K. If the temperature fluctuation is ≤ ±0.05K after 1 hour of continuous monitoring, the low-temperature environment is considered qualified; if the fluctuation exceeds the range, check the helium pressure or sealing and then re-control the temperature.

[0032] Step S3: The test gas is provided through the gas distribution unit. After the test gas is stabilized in multiple stages by the buffer unit, it is introduced into the low temperature unit for gradient precooling, and then introduced into the adsorption unit that has reached the target test temperature. After the pressure of each introduction reaches equilibrium, the equilibrium pressure data is recorded by the data acquisition unit. In this embodiment, a corresponding test gas (such as hydrogen or nitrogen, with a purity ≥99.999%) is selected, and the pressure is stabilized by the corresponding pressure reducing valve (0.2 MPa for hydrogen, 0.1 MPa for nitrogen). The second ball valve 53 and the second needle valve 43 are then opened to allow the gas to enter the first buffer tank 22, where the pressure reaches 1×10⁻⁶. 4After Pa, the valve is closed. The gas enters the regenerator 9 through the first capillary tube, exchanging heat with the first-stage cold plate 6 and the second-stage cold plate 8, reducing the temperature to 85-90K and 10-15K respectively. The gas then enters the first liquid helium pool 10, undergoing spiral suspension heat exchange, with the temperature approaching the target (e.g., 4.5-5.0K at 4.2K, 78-80K at 77K). The gas then approaches the adsorption chamber 17 through the P0 tube 16, undergoing radiative heat exchange, and finally stabilizing at the target temperature ±0.5K. The pressure (1×10⁻⁶) is monitored by the fourth vacuum gauge 30. 3 -1×10 4 Pa (fluctuation ≤ ±50 Pa), temperature fluctuation ≤ ±0.5 K, pre-cooling is deemed qualified, and the subsequent pressure stabilization step can proceed.

[0033] In this embodiment, the design calculation formula for the buffer tank volume is as follows: ; ; ; In the formula, This indicates the number of moles of gas transferred between the buffer tank and the adsorption unit. The effective volume of the buffer tank. This is the universal gas constant. and These are the absolute gas pressures before and after the buffer tank is connected (at equilibrium), respectively. and These are the gas temperatures before and after the buffer tank is connected; The mass of the gas introduced into (or released from) the system. This represents an approximate molar mass of hydrogen. , To design the minimum volume required for the buffer tank, Design temperature for the buffer tank, Design the working pressure (absolute pressure) for the buffer tank.

[0034] As the working pressure increases, the required buffer tank volume decreases inversely, as shown in Table 1.

[0035] Table 1 Buffer Tank Design Table If the system operates at 2 bar (abs), the minimum buffer tank volume corresponding to 10g of adsorbent is approximately 2.07L, and for 20g of adsorbent, it is approximately 4.13L. To ensure measurement accuracy and safety margin, a nominal 5L buffer tank is selected as the primary buffer tank 22. This system is based on the principle of multi-stage buffer pressure division and micro-dosing, achieving Pa-level hydrogen supply control for the low-temperature adsorption system while ensuring safety and measurement accuracy. The overall structure adopts a three-stage series configuration: primary pressure stabilization, secondary pressure reduction, and tertiary quantitative (micro-dosing chamber). The primary buffer tank 22 (5L, 1–2 bar at room temperature) serves as the gas storage and pressure stabilization unit, supplying gas to the evacuated secondary buffer tank (0.2L) through a precision pressure reducer and flow-limiting capillary, achieving initial pressure reduction and steady-state storage. The secondary buffer tank 23 can be evacuated for a short time to adjust the pressure to tens to hundreds of Pa, forming a low-pressure gas source. The next three-stage buffer tank 24 is a micro-dosage chamber (approximately 0.8 mL), used for final quantitative pressure release. It is positioned close to the needle valve to reduce dead space and response hysteresis. During feeding, the valve from the second stage to the micro-dosage chamber is opened, and after the pressure is equalized, it is immediately closed. Then, the needle valve is slowly opened, and the flow is capillary-limited to connect with the adsorption unit, achieving stable low-pressure charging.

[0036] Step S4: Based on the principle of static constant volume method, using the equilibrium pressure data recorded in step S3, calculate the adsorption amount corresponding to each equilibrium pressure point through the mass conservation formula.

[0037] The static constant volume principle measures the adsorption capacity based on the relationship between gas volume and pressure. The adsorption chamber 17 has a fixed volume and is maintained at a constant temperature. The initial pressure of the adsorption chamber 17 is recorded. A quantitative amount of adsorbate gas (test gas) is supplied to the adsorption chamber 17 through the gas distribution unit. After adsorption equilibrium is reached upon contact with the adsorbent, the adsorption equilibrium pressure and the pressure change in the gas distribution chamber are recorded. The gas volume changes in the buffer unit (gas storage area) and the adsorption chamber 17 are calculated. Based on the law of conservation of mass, the adsorption capacity of the adsorbent at the corresponding equilibrium pressure is obtained. Gas supply continues, changing the adsorption equilibrium pressure, and the adsorption capacity is calculated. The formula for calculating the adsorption capacity is as follows: ; in, For the first The amount of gas adsorbed in the first adsorption. For the first The initial pressure of the fourth vacuum gauge 30 during the second adsorption. For the first The equilibrium pressure of the fourth vacuum gauge 30 during the second adsorption step. The volume of the third buffer tank 24, The volume of adsorption cavity 17 is... For the first The equilibrium pressure of secondary adsorption. The gas constant is... To test the temperature, This refers to the mass of the adsorbent.

[0038] In this embodiment, the adsorption amount The calculation formula is: ; In the formula, Indicates the quality of activated carbon loading; The equilibrium adsorption capacity of activated carbon is expressed by the following formula: ; In the formula, This represents the volume of 1 mol of gas under standard conditions. This represents the equilibrium adsorption capacity of activated carbon under standard conditions. The equilibrium adsorption capacity of activated carbon for hydrogen can be fitted by the Langmuir equation, and the specific calculation formula is as follows: ; In the formula, This indicates the saturated adsorption capacity (maximum adsorption capacity) of Langmuir. Indicates the adsorption equilibrium pressure. The Langmuir adsorption equilibrium constant is represented by the following formula: ; In the formula, This represents the Langmuir constant reference value (low-temperature intercept). Represents an exponential function. Represents the universal gas constant; Indicates the test temperature; This represents the adsorption activation energy.

[0039] The activated carbon adsorption capacity obtained from the above calculations is shown in Table 2. Table 2 Calculation of Activated Carbon Adsorption Capacity Next, the residual gas in the pipeline The calculation formula is as follows: The lengths of the temperature zones 77K, 23K, 4K, and 1K are 0.6m, 0.4m, 0.3m, and 0.2m, respectively. Based on the temperature distribution assumptions, the pipe temperature outside the vacuum chamber is considered to be at room temperature. Inside the vacuum chamber, the gas temperature distribution between every two temperature measuring points is considered to be linear. When calculating the amount of residual gas in the pipe, the average compressibility factor can be calculated using the average temperature at both ends of the pipe and then integrated. Alternatively, a program can be written to call refprop to calculate the numerical integral. The specific formula is as follows: ; ; In the formula, Indicates the first The residual hydrogen mass in the pipeline of each temperature zone Indicates the total number of pipelines; Indicates the first Pipeline length for each temperature zone Indicates the first Pipeline length for each temperature zone Indicates the first The temperature of each temperature zone Indicates the first The temperature of each temperature zone Indicates the first The radius of the pipeline in each temperature zone; Indicates the first The diameter of the pipeline in each temperature zone, The compressibility factor of hydrogen is shown in the table. Research indicates that at a pressure of 1 Pa and a temperature of 17 K, the compressibility factor of hydrogen is above 0.99. Therefore, in experiments ranging from 10E-4 Pa to 1 Pa, hydrogen can be considered an ideal gas. At a pressure of 1 bar, the compressibility factor changes with temperature as follows: Figure 3 As shown, the compressibility factor of hydrogen should be considered in the calculation.

[0040] The residual gas in the pipeline was obtained through the above calculations. As shown in Table 3: Table 3 Calculation Table for Residual Gas in Pipelines Then, the residual gas in the adsorption unit The calculation formula is as follows: ; In the formula, The effective volume of the cylindrical adsorption chamber 17 of the adsorption unit is represented.

[0041] The residual gas in the adsorption unit was obtained through the above calculations. As shown in Table 4: Table 4 Calculation of Residual Gas in Adsorption Unit Total ventilation Adsorption amount Residual gas in pipelines and residual gas in the adsorption unit The result is obtained by adding the three parts together, and the specific calculation formula is as follows: .

[0042] The first liquid helium pool 10 at the lower end of the cryogenic unit of this invention uses heat conduction to uniformly lower and stabilize the ambient temperature of the adsorption unit at the target test temperature. Compared with a single heat exchange mode, this results in a more uniform temperature distribution around the adsorption unit, avoiding the impact of local temperature deviations on the adsorption activity of the adsorbent. This ensures that the adsorption test is conducted in a stable and uniform cryogenic environment, laying the foundation for the reliability of the test results. Furthermore, the first liquid helium pool 10 effectively isolates the cryogenic unit from external vibrations and vibrations generated during operation, preventing the adsorbent from loosening, falling off, or disturbing the adsorption interface, thus ensuring the stability of the adsorption process. The buffer unit of this invention is specifically designed with multi-stage pressure stabilization and flow control functions for the test gas, effectively solving the problems of large pressure fluctuations and unstable flow rates in traditional tests. This ensures a stable pressure of the test gas entering the adsorption unit, providing a prerequisite for accurate acquisition of subsequent equilibrium pressure data. In addition, the gas distribution unit of this invention independently provides the working gas and test gas to the cryogenic unit and adsorption unit respectively, with separate supply paths for the two types of gases to avoid cross-contamination.

[0043] In summary, this device integrates gas supply, cryogenic cooling, vacuum control, and data acquisition. It can perform full-cycle performance testing on adsorbent materials of different forms, such as powder, porous blocks, and shaped particles. Through multi-stage buffer and pressure stabilization units, it achieves precise control of gas supply flow and system pressure. Through cryogenic units, the gas supply temperature is gradually reduced to the set value to ensure that the initial state of the test gas entering the adsorption chamber is consistent. The testing process is automatically executed by a programmed control system, which performs temperature gradient scanning, heating desorption, and steady-state maintenance, achieving full automation and repeatability of adsorption performance testing.

Claims

1. A low-temperature, low-pressure adsorption performance testing device, characterized in that: It includes a vacuum container (1), a cryogenic unit, an adsorption unit, a gas distribution unit, a vacuum unit, a buffer unit, and a data acquisition unit; The cryogenic unit includes a pulse tube refrigerator, a first liquid helium pool disposed below the pulse tube refrigerator, and a heat-conducting platform that is thermally connected to the first liquid helium pool. The adsorption unit includes an adsorption cavity, which is thermally connected to the heat-conducting platform. The gas distribution unit includes a cryogenic unit gas supply branch and an adsorption unit gas supply branch, which are independent of each other. The cryogenic unit gas supply branch is used to supply refrigerant gas to the first liquid helium pool, and the adsorption unit gas supply branch is used to supply test gas to the adsorption chamber. The buffer unit is connected between the gas supply branch of the adsorption unit and the adsorption unit, and is used to perform multi-stage pressure stabilization on the test gas flowing into the adsorption chamber. A vacuum unit is used to evacuate the adsorption chamber and related pipelines. The data acquisition unit is used to monitor the pressure parameters of each unit and pipeline.

2. The low-temperature and low-pressure adsorption performance testing device according to claim 1, characterized in that: The pulse tube refrigerator includes a compressor (2), a rotary valve (3), a valve assembly (4), a primary cold head (5), a primary cold plate (6), a secondary cold head (7), a secondary cold plate (8), and a regenerator (9). The compressor (2) is connected to the rotary valve (3), and the rotary valve (3) is connected to the valve assembly (4). The primary cold head (5), the secondary cold head (7), and the regenerator (9) are connected to the valve assembly (4). The primary cold plate (6) is located at the lower end of the primary cold head (5), and the secondary cold plate (8) is located at the lower end of the secondary cold head (7). The regenerator (9), the primary cold plate (6), and the secondary cold plate (8) are connected to the valve assembly (4). The cold plate (8) is thermally connected. The lower outer wall surface of the first-stage cold plate (6) is fitted with a first-stage cold head heater (11). The lower outer wall surface of the second-stage cold plate (8) is fitted with a second-stage cold head heater (12). The air inlet pipe of the adsorption unit is first spirally wound on the regenerator (9) for pre-cooling, and then suspended and spirally arranged in the first liquid helium pool (10). The top of the first liquid helium pool (10) is provided with a condenser (13) located at the lower end of the second-stage cold head (7). The thermally conductive platform includes a first cold plate (14). The top of the first cold plate (14) is provided with a first cold plate heater (15).

3. The low-temperature and low-pressure adsorption performance testing device according to claim 1, characterized in that: The cold head of the low-temperature unit and the vacuum container (1) are connected by a room temperature flange (34) and a vacuum chamber flange (35), and a sealing bellows (33) is provided between the room temperature flange (34) and the vacuum chamber flange (35) to achieve a sealed connection.

4. The low-temperature and low-pressure adsorption performance testing device according to claim 1, characterized in that: The adsorption unit includes a PO tube (16), an adsorption heater (18), an upper adsorption cover, and a lower adsorption cover; the PO tube (16) is connected to the adsorption chamber (17), the vacuum unit, and the buffer unit respectively; the adsorption heater (18) is located on the outer wall of the adsorption chamber (17); the upper adsorption cover is in close contact with the heat-conducting platform; and the lower adsorption cover is connected to the upper adsorption cover by bolts.

5. The low-temperature and low-pressure adsorption performance testing device according to claim 1, characterized in that: The cryogenic unit gas supply branch includes a helium cylinder (19), and the helium cylinder (19) is connected to the cryogenic unit in sequence by a first pressure reducing valve (51), a first ball valve (52) and a first needle valve (42). The cryogenic unit gas supply branch is used to supply helium as a working gas to the first liquid helium pool (10). The adsorption unit gas supply branch includes a hydrogen cylinder (20) and a nitrogen cylinder (21). A second pressure reducing valve (55) is also provided between the hydrogen cylinder (20) and the buffer unit, and a third pressure reducing valve (56) is also provided between the nitrogen cylinder (21) and the buffer unit. The adsorption unit gas supply branch is used to supply test gas to the adsorption unit.

6. The low-temperature and low-pressure adsorption performance testing device according to claim 1, characterized in that: The buffer unit includes a first buffer tank (22), a second buffer tank (23), and a third buffer tank (24). The gas distribution unit is connected to the first buffer tank (22) by a second ball valve (53) and a second needle valve (43) in sequence. The first buffer tank (22) and the second buffer tank (23) are connected by a first capillary tube (57) and a third needle valve (44) in sequence. The second buffer tank (23) and the third buffer tank (24) are connected by a second capillary tube (58) and a fourth needle valve (45) in sequence. The third buffer tank (24) and the adsorption unit are connected by a fifth needle valve (46), a sixth needle valve (47), a third capillary tube (59), a seventh needle valve (48), and a filter (60) in sequence.

7. The low-temperature and low-pressure adsorption performance testing device according to claim 6, characterized in that: The vacuum unit includes a first vacuum pump (25), an eighth needle valve (49), an exhaust valve (61), and a ninth needle valve (50); the first vacuum pump (25) is connected to the buffer unit through the eighth needle valve (49), which is located between the fifth needle valve (46) and the sixth needle valve (47); the first vacuum pump (25) is connected to the outside air through the exhaust valve (61); and the ninth needle valve (50) is located between the first vacuum pump (25) and the adsorption unit.

8. The low-temperature and low-pressure adsorption performance testing device according to claim 7, characterized in that: The data acquisition unit includes a first vacuum gauge (27), a second vacuum gauge (28), a third vacuum gauge (29), a fourth vacuum gauge (30), and a fifth vacuum gauge (31). The first vacuum gauge (27) is installed on the first buffer tank (22), the second vacuum gauge (28) is installed on the second buffer tank (23), the third vacuum gauge (29) is installed on the third buffer tank (24), the fourth vacuum gauge (30) is installed between the third capillary tube (59) and the seventh needle valve (48), and the fifth vacuum gauge (31) is installed between the ninth needle valve (50) and the adsorption unit.

9. The test method of the low-temperature and low-pressure adsorption performance testing device according to any one of claims 1-8, characterized in that, Includes the following steps: Step S1: Turn on the vacuum unit to evacuate the cryogenic unit, adsorption unit, buffer unit and each gas pipeline until the overall vacuum of the device reaches the preset initial high vacuum state. Step S2: The refrigerant gas is introduced into the first liquid helium pool (10) through the gas distribution unit. After the working gas is pre-cooled by the low temperature unit, it is cooled into a liquid working gas and enters the first liquid helium pool (10). The liquid working gas in the first liquid helium pool (10) causes the ambient temperature of the adsorption unit to drop uniformly and stabilize at the target test temperature through heat conduction. Step S3: The test gas is provided through the gas distribution unit. After the test gas is stabilized in multiple stages by the buffer unit, it is introduced into the low temperature unit for gradient precooling, and then introduced into the adsorption unit that has reached the target test temperature. After the pressure of each introduction reaches equilibrium, the equilibrium pressure data is recorded by the data acquisition unit. Step S4: Based on the principle of static constant volume method, using the equilibrium pressure data recorded in step S3, calculate the adsorption amount corresponding to each equilibrium pressure point through the mass conservation formula.

10. The test method according to claim 9, characterized in that: In step S4, the formula for calculating the adsorption amount is as follows: ； in, For the first The amount of gas adsorbed in the first adsorption. For the first The initial pressure of the fourth vacuum gauge (30) during the second adsorption. For the first The equilibrium pressure of the fourth vacuum gauge (30) in the previous step during the second adsorption. For the volume of the third buffer tank (24), The volume of the adsorption cavity (17) is... For the first The equilibrium pressure of secondary adsorption. The gas constant is... To test the temperature, This refers to the mass of the adsorbent.

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