CN111874881B - Method for purifying xenon by using DD3R molecular sieve membrane - Google Patents

Abstract

The invention provides a method for purifying xenon by using a DD3R molecular sieve membrane. We develop an online recycling technology of xenon in a closed-circuit medical xenon anesthesia process by using a DD3R molecular sieve membrane. Single component carbon dioxide permeability of 1.5X 10 ^‑7 mol·m ^‑2 ·s ^‑1 ·Pa ^‑1 The selectivity for separation of carbon dioxide to xenon is 570. The permeation flux is an order of magnitude higher than that of conventional membrane materials. CO due to the all-silicon nature of the DD3R molecular sieve membrane ₂ The permeability of the membrane is slightly influenced by water vapor, which is different from that the aluminum-containing molecular sieve membrane pore channel is easily blocked by water adsorption. High CO content ₂ Flux and high CO ₂ the/Xe selectivity and the long-time stability ensure the good prospect of the hollow fiber DD3R molecular sieve membrane in the on-line recycling of xenon for medical anesthesia.

Description

A kind of method that adopts DD3R molecular sieve membrane to purify xenon gas

technical field

The invention relates to a method for purifying xenon gas by adopting a DD3R molecular sieve membrane, and belongs to the technical field of gas separation.

Background technique

The preparation and purification of noble gases is an extremely challenging process. As an extremely precious rare gas, xenon has a wide range of applications in semiconductor manufacturing, optoelectronics, aviation and medical imaging and anesthesia. At present, xenon gas can only be obtained by further cryogenic rectification of air separation tail gas. Due to the extremely low abundance of xenon in the air (0.087ppmv), the energy consumption for separation is extremely high, and the price of xenon is $30,000 to $60,000/m ³ _{gas, STP} . In addition to this, the increasing industrial demand is limited by the limited supply in the xenon market. It is estimated that even if all air separation units in the world are equipped with xenon extraction units, their supply will be less than 84,000m ³ _{gas, STP} . Therefore, the development of online xenon recycling technology is the only way to ensure the effective supply of xenon.

The medical xenon recovery used in this application mainly involves a separation system of a mixture of N ₂ , O ₂ , CO ₂ and Xe. Dragerwek Aktiengesellschaft, Germany discloses a method for recovering xenon gas in anesthesia tail gas by high-pressure liquefaction method (US 005520169), the gas needs to be pressurized to >60 bar, and the xenon gas is liquefied so as to be separated from other non-condensable gases, and the content can be obtained by re-gasification It is a mixture of 80% xenon gas, 12% oxygen gas and 8% nitrogen gas; it needs to be coupled with activated carbon and molecular sieve adsorption technology to remove carbon dioxide. Italian SIAD SOCIETA'ITALIANA ACETILENE&DERIVATI SPA publicly reported a method for cryogenic recovery of xenon gas in anesthesia exhaust gas (WO 98/18718), firstly using 5-30% acetone potassium hydroxide solution to absorb carbon dioxide, and then cryogenic separation, The recovery rate of xenon is 90-92%. A method for cryogenic recovery of xenon gas has also been disclosed by Smetannikov et al. (RU 2238113). MesserGriesheim GmbH of Germany and UWS Ventures LTD of the United Kingdom optimized the cryogenic process, and disclosed methods for cryogenic solidification and recovery of xenon gas (US 006134914) and two-stage cryogenic methods (WO 2004/060459). Although recovery can be achieved by utilizing the difference in phase transition temperature between xenon and gas components, there are problems such as cumbersome separation process, extremely high energy consumption and high cost.

Hargasser discloses an anesthesia breathing system (US 2010/0258117), which proposes to use solid adsorption materials such as activated carbon, silica, alumina or molecular sieves to recover xenon gas in anesthesia exhaust gas. Advanced Technology Materials in the United States discloses a method for recovering xenon by activated carbon adsorption (US 2013/0112076). Air Products and Chemicals of the United States discloses a method for recovering xenon gas by vacuum pressure swing adsorption (US 8535414), which can be used for the recovery of 0.1-2.5% xenon gas in nitrogen. British Sagetech Medical Equipment Limited discloses a separation method combining adsorption of porous materials and extraction of supercritical carbon dioxide (GB 2574208). Zhejiang Xenon Medical Apparatus Co., Ltd. discloses a method for removing carbon dioxide from anesthetizing xenon from a mixture of solid sodium hydroxide and calcium oxide (CN 108837253). The solid adsorption or absorption method can realize the recovery of xenon gas at room temperature, but its regeneration process requires high temperature treatment, high energy consumption, and low recovery rate of xenon gas.

Membrane separation technology does not involve phase inversion, which can significantly reduce the energy consumption of xenon gas reuse; at the same time, membrane separation technology can realize continuous separation of mixed gas, and the operation is simpler, which is a more economical and reliable technical route. KlausSchmidt, Germany discloses a method for recovering anesthetic xenon by using carbon membrane (US 2010/0031961), but the membrane flux is only ~5×10 ^-9 (J.Membr.Sci.2007,301,29-38), which cannot be Meet the technical requirements of miniaturization and portability of anesthesia ventilator. Air Liquide of France discloses a method for circulating anesthesia xenon in organic membranes (US 2009/0126733).

SUMMARY OF THE INVENTION

At present, the preparation and recovery technology of xenon gas is mainly based on refrigeration distillation with high energy consumption. Increasing market demand and capacity ceilings force the development of energy-efficient xenon gas recycling technologies, such as membrane separation technologies. The invention develops a DD3R molecular sieve membrane for on-line recycling technology of xenon gas in the process of closed-circuit medical xenon gas anesthesia. The single-component carbon dioxide permeability is 1.5×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 , and the separation selectivity of carbon dioxide to xenon is 570. The permeate flux is an order of magnitude higher than conventional membrane materials. The membrane separation performance is mainly determined by the difference in the diffusion coefficients of _CO2 and Xe molecules in DD3R molecular sieves. However, the mass transfer rate of CO ₂ is significantly reduced by the presence of Xe, which is very different from the previous eight-membered ring zeolite membrane in the separation structure of CO ₂ /N ₂ and CO2/CH ₄ binary components. The molecular dynamics simulation results show that the adsorption of Xe molecules on the surface of the molecular sieve membrane forms the surface resistance for _CO adsorption and diffusion. The CO ₂ permeability and CO ₂ /Xe separation selectivity were 2.0 × 10 ^-8 mol·m ^-2 ·s ^-1 under conditions relevant to medical xenon anesthesia, i.e. carbon dioxide content below 5% and the presence of water vapour, respectively · Pa ^-1 and 67. Due to the all-silicon properties of the DD3R molecular sieve membrane, the permeability of CO2 is weakly affected by water vapor, which is different from the fact that the pores of the aluminum-containing molecular sieve membrane are easily blocked by adsorbed water. High CO2 flux and high _CO2 /Xe selectivity, as well as long-term stability, ensure a good prospect of the hollow fiber DD3R molecular sieve membrane in the on-line reuse of medical anesthesia xenon gas.

A method for purifying xenon by using DD3R molecular sieve membrane, comprising the following steps:

The gas containing xenon gas is separated by DD3R, and the xenon gas is retained on the interception side.

In one embodiment, the gas containing xenon refers to a gas containing N ₂ , Xe and CO ₂ .

In one embodiment, the composition of the xenon-containing gas is a mixture of 5% CO ₂ , 30% N ₂ and 65% Xe.

In one embodiment, the xenon-containing gas further contains H ₂ O.

In one embodiment, the partial pressure of _H2O is 2.3 kPa.

In one embodiment, when the separation is performed, the pressure of the feed gas is 1-3 bar and the temperature is 10-30°C.

The present invention also provides:

Application of DD3R molecular sieve membrane in the separation of Xe in gases containing N ₂ , Xe and CO ₂ .

In one embodiment, in the application, the selectivity to CO ₂ /Xe is 60 or more.

beneficial effect

The molecular sieve membrane method for anesthesia xenon circulation proposed in this patent can significantly increase the membrane permeation flux; at the same time, the molecular sieve membrane is a pure inorganic material with better biocompatibility and antibacterial properties, and has higher safety in medical procedures .

DD3R is a molecular sieve with oval 8-membered ring channels, and its effective channel size is 0.36nm×0.44nm. Moreover, the all-silicon property of DD3R molecular sieve makes it have a certain degree of hydrophobicity, which can effectively weaken the blockage of the molecular sieve pores by water vapor.

Description of drawings

Figure 1 is a SEM photograph of the surface (left column) and cross-section (right column) of the DD3R molecular sieve membrane used in the invention. The meaning of each area is: DD3R molecular sieve membrane synthesized under different SDA/H ₂ O ratio conditions, SDA/H ₂ O=16/4000(ab), 8/4000(cd), 3/4000(ef).

Figure 2 shows the permeability and separation performance of hollow fiber DD3R molecular sieve membranes. Among them, (a) single-component permeability and [4 ³ 5 ¹² 6 ¹ 8 ³ ] cage of DD3R molecular sieve (operating conditions are temperature 25°C, pressure 1 bar); (b) single-component (open legend) and binary CO ₂ permeability as a function of pressure in the components (solid legend) (operating conditions are temperature 25°C, pressure increased from 1 bar to 3 bar); (c) Influence of Xe molar composition on separation performance of CO ₂ /Xe mixture (feeding Pressure: 3bar).

Figure 3 is the separation performance of DD3R molecular sieve membrane. (a) Comparison of the performance of DD3R molecular sieve membrane for CO ₂ /Xe separation with other membrane materials; (b) At different temperatures, the DD3R molecular sieve membrane has different effects on CO ₂ single component, CO ₂ /H ₂ O binary component and CO ₂ / Separation performance of H ₂ O/Xe ternary components; (c) The stability of membrane separation performance of DD3R molecular sieve membrane under simulated medical anesthesia xenon gas conditions.

Figure 4 is the XRD patterns of the DD3R molecular sieve membranes prepared under different SDA content conditions.

Figure 5 is the SEM pictures of the DD3R molecular sieve membranes prepared under different synthesis time conditions. (a-b) 12h; (c-d) 24h; (e-f) 36h.

Figure 6 is the XRD patterns of the DD3R molecular sieve membranes prepared under different synthesis time conditions.

Figure 7 Knudsen diffusion selectivity (right) and ideal state selectivity (left).

Figure 8 is the performance characterization of the DD3R molecular sieve prepared by the secondary growth method, wherein, (a) SEM photo; (b) XRD pattern, using Co target Kα rays (wavelength is 0.178897nm); (c) N adsorption at _77K- Desorption curve.

Figure 9 is the adsorption and desorption curves of CO ₂ (a) and Xe (b) at 273K and 298K (data points are original experimental data, curves are single-point Langmuir model fitting data)

Figure 10 is the Virial numerical fitting of the adsorption and desorption curves of DD3R molecular sieve membrane for CO ₂ (a) and Xe (b)

Figure 11 is the isotherm adsorption heat curve of _CO2 and Xe by DD3R molecular sieve membrane

Figure 12 is the separation performance of DD3R molecular sieve membrane for _CO and Xe. (a) Separation performance of DD3R molecular sieve membrane for equimolar CO ₂ /Xe at different temperatures, with a feed pressure of 1.2 bara; (b) analysis of the contribution of Xe and water vapor to the reduction of CO ₂ permeability (operating conditions were at a temperature of 25- 150℃))

Figure 13 shows the separation performance of DD3R molecular sieve membrane for N ₂ /Xe under different pressure conditions.

Figure 14 is a schematic diagram of the DD3R molecular sieve membrane used for anesthesia xenon separation process.

Detailed ways

For the preparation process of the DD3R molecular sieve membrane used in the following examples, reference may be made to the prior art, such as CN110745839A "An Activation Process of a Defect-Free DD3R Molecular Sieve Membrane".

Single-component gas permeability evaluation of DD3R membrane separation performance

For single-component gases such as He, H ₂ , CO ₂ , N ₂ , CH ₄ , Xe and SF ₆ , CO ₂ exhibits the highest permeation characteristic, which is 1.5×10 ^-7 mol·m ^-2 ·s ^-1 · Pa ^-1 (area a of Figure 2). Due to the thin wall thickness of the hollow fiber carrier, the DD3R molecular sieve membrane supported by the hollow fiber carrier is smaller than the tubular (~0.84×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 ) and sheet (1.12×10 ^-7 mol·m -2 ·s -1 ·Pa -1 ) membranes. mol·m ⁻² ·s ⁻¹ ·Pa ⁻¹ ) supports have higher throughput (Microporous and Mesoporous Materials, 68 (2004) 71-75 and Journal of Membrane Science, 505 (2016) 194-204). In addition, the packing density of hollow fibers is higher. The ideal selectivities for CO ₂ /He, CO ₂ /H ₂ , CO ₂ /N ₂ , CO ₂ /CH ₄ , CO ₂ /Xe, CO ₂ /SF ₆ are 9.1, 5.1, 68, 201, 570 and In 1914, this was far more selective than Knudsen diffusion. The CO ₂ single-component permeability of the hollow fiber DD3R molecular sieve membrane is slightly higher than that of the 8-membered ring SAPO-34 molecular sieve membrane (CO ₂ permeability is ~1.0×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 , The ideal CO ₂ /Xe selectivity is 500, AIChE Journal, 63(2017) 761-769), which may be caused by the elliptical pore size of the DD3R molecular sieve (0.36nm×0.44nm, area a in Figure 2).

When the feed pressure was increased from 1 bara to 3 bara, the _CO2 monocomponent permeability decreased slightly (<15%, area b of Fig. 2). This is mainly caused by the decrease in _CO diffusion coefficient with increasing loading. However, the permeability of CO ₂ decreased by 50% to 0.76×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 , probably caused by the competitive adsorption of Xe. To further characterize this effect quantitatively, the gas separation performance at different feed pressures was tested. When the CO ₂ /Xe feed pressure was increased to 2 bara, the CO ₂ permeability continued to drop to 0.54×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 . At the same time, the decrease in _CO permeability is more pronounced with increasing Xe composition (region c of Fig. 2). Finally, when the _CO content was reduced to 5%, the _CO permeability was 0.24×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 ; however, the separation selectivity of CO ₂ /Xe was always around 43 , showing good separation selectivity at low _CO2 concentrations.

Membrane separation performance under simulated medical anesthesia xenon conditions. The use of membranes to separate CO ₂ /Xe is less reported. Currently, only carbon molecular sieve membranes and MFI molecular sieve membranes are used for the separation of CO ₂ /Xe mixtures (Journal of Membrane Science, 301 (2007) 29-38 and ACS Applied Materials & Interfaces, 10 (2018) 33574-33580).

The CO ₂ single-component permeability of the hollow fiber DD3R molecular sieve membrane reported in this application is 1.5×10 ^-7 mol·m ^-2 ·s ^-1 ·Pa ^-1 , which is one order of magnitude higher than the results reported in the current literature (Fig. 3a area). Therefore, DD3R will be an ideal membrane separation material for CO ₂ /Xe separation. The high permeability of the hollow fiber DD3R molecular sieve membrane will significantly reduce the investment and floor space of membrane separation equipment, and has a good application prospect for the on-line reuse of medical anesthesia xenon gas.

Figure 3 shows the industrial separation performance of hollow fiber DD3R molecular sieve membranes. Among them, (a) area is the hollow fiber DD3R molecular sieve membrane and other reported membranes, including carbon molecular sieve membrane (CMS), b-oriented MFI membrane, SAPO-34 membrane, PDMS-treated DD3R membrane PIMs membrane (PIM-1 and PIM membranes) -7 membrane) and PDMS membrane for _CO2 /Xe separation performance comparison, equimolar CO2/Xe mixture separation. (b) Region is a _CO2 /Xe binary mixture with single _CO2 permeation and saturated water vapor separation at different temperatures. Region (c) is the long-term stability of DD3R molecular sieve membranes at 3 bara for recovery of Xe in a mixture consisting of 0.76% _H2O , 4.96% _CO2 , 29.77% _N2 and 64.51% Xe.

Water vapor is often present in anesthetized exhaled breath. Due to the presence of water vapor, the _CO2 single-component permeability decreased by 37-45% (region b of Fig. 3); however, under the same conditions, the gas permeability of the aluminum-containing 8-membered ring molecular sieve membrane decreased more significantly, For example: SSZ-13 decreased by 75% (Journal of Materials Chemistry A, 2 (2014) 13083-13092), SAPO-34 decreased by 99.2% (Journal of Membrane Science, 186 (2001) 25-40). The aluminum-containing molecular sieve framework has a strong adsorption capacity for water vapor, and the adsorption of water molecules in the pores of the DDR molecular sieve blocks the diffusion of gas molecules. And our DD3R molecular sieve membrane has better hydrophobic properties, which can effectively weaken the _CO2 permeability reduction caused by water vapor adsorption. For example, in the water vapor environment, the all-silicon CHA molecular sieve membrane decreased by 88% (Separation and Purification Technology, 197 (2018) 116-121), and the literature reported that the DD3R molecular sieve membrane decreased by 68% (Journal of Membrane Science, 505 (2016) 194-204). Because the synthesis of all-silicon CHA zeolite membranes and literature-reported DD3R zeolite membranes used cationic templates N,N,N-trimethyl-1-adamantylammonium hydroxide and methyltropine iodide; this would lead to the synthesis of The cleavage of Si-O-Si bonds in the molecular sieve framework during the process forms Si-OH bonds to charge balance with the positively charged template ions. In this application, we utilize aprotic templating agents and an ionic-free synthesis solution to prepare a more hydrophobic DD3R molecular sieve membrane for CO ₂ /Xe separation in a humid environment. It has been reported in the literature that the water vapor adsorption properties of DD3R molecular sieves synthesized by this kind of template are even lower than that of Silicalite-1 molecular sieves (Zeolites, 19(1997) 353-358).

The effect of water vapor on _CO permeability and selectivity was further investigated, as shown in area b of Fig. 3 and area a of Fig. 12. In the water vapor environment, the separation selectivity of the membrane is higher than that of the dry gas. The Si-OH at the grain boundaries of the molecular sieve film layer can strongly adsorb water molecules, thereby blocking the diffusion of gas molecules in such pores. Therefore, in a humid environment, the permeability of Xe is lower than in a dry gas. The adsorption of water vapor gradually weakened with the increase of temperature, for example, it decreased by 55% at 100℃; decreased by 52% at 125℃; decreased by 42% at 150℃. However, in both wet and dry gases, the permeability of _CO2 molecules is mainly contributed by DD3R molecular sieves. Therefore, the selectivity in a humid environment is higher than that in a dry gas. It can be seen from the above that both Xe molecules and water molecules have a certain blocking effect on the DD3R molecular sieve. Taking the dry CO ₂ gas permeability as the benchmark, we compared the clogging effect of Xe and water molecules on DD3R molecular sieves (the b area of Fig. 12 ): they weakened in the order of Xe+water≈Xe>water. This shows that in the CO ₂ /Xe separation process, the blockage of the transport channel is mainly due to the adsorption of Xe molecules, while the influence of water vapor is basically negligible.

Separation and Permeability of Mixed Gas

During the anesthesia process, except for CO ₂ , the impurities in the exhaled anesthetic gas, the human tissues and organs will release nitrogen gas in the initial stage of anesthesia. In general, during the initial phase of anesthesia, the rates of _CO2 and _N2 release were 0.25 L/min and 0.02 L/min, respectively. In order to achieve online reuse of Xe, _{both CO} and N need to be removed. The nitrogen permeability of our hollow fiber DD3R molecular sieve membrane was 3.25×10 ⁻⁹ mol·m ⁻² ·s ⁻¹ ·Pa ⁻¹ , and the separation selectivity was 95.3 (Fig. 13). Although, Carreon et al. reported that ZIF-8 membrane can also achieve N ₂ /Xe separation, but in the presence of water vapor and CO ₂ at the same time, ZIF-8 will decompose to produce carbonate, thus losing the separation performance (Angewandte et al. Chemie International Edition, 53 (2014) 7471-7474).

For the recovery of xenon gas in the closed-circuit circulation system of respiratory anesthesia, we propose an online recycling system based on DD3R molecular sieve membrane (Fig. 14), and use it in a mixture of 5% CO ₂ , 30% N ₂ and 65% Xe Recovery of xenon gas. When 2.3kP water vapor was introduced, the permeability of _{both CO} and N decreased slightly (Fig. 3c). Finally, the permeability of CO stabilized at 2.0×10-8 mol·m ^{- 2} ·s ^{- 1} ·Pa ^-1 , the CO ₂ /Xe selectivity is 67±12; the N ₂ permeability is 2.4×10 ^-9 mol·m ^-2 ·s ^-1 ·Pa ^-1 , and the N ₂ /Xe selectivity is 8±2. In other words, after the selective removal of impurities such as carbon dioxide and nitrogen, more than 99% of the Xe can be effectively reused. Economically, the operating cost of the process is $1.5/m ³ _gas,STP , which is four orders of magnitude cheaper than the current market price of xenon. However, for medical anesthesia xenon, the recovery rate of other traditional recovery processes is very low, such as the recovery rate of cryogenic liquefaction is 8.95% (Anesthesia & Analgesia, 110 (2010) 101-109), the recovery rate of cryogenic crystallization is 70% (Anesthesia & Analgesia, 105 (2007) 1312-1318), the recovery rate of pressure swing adsorption is 87.5% (US 8535414 B2). The high separation performance and long-term stability of the DD3R molecular sieve membrane will significantly reduce the recycling cost of medical anesthesia xenon, making The xenon anesthesia procedure is more economically competitive.

We verified that DD3R molecular sieve membrane can recover xenon gas from CO ₂ /N ₂ /Xe mixture with certain humidity. The separation performance of the membrane is mainly determined by the difference in the diffusion coefficients of _CO2 and Xe molecules in the DD3R molecular sieve.

It can be seen from the above experiments that Deca-Dodecasil 3 Rhombohedral (DD3R) molecular sieve will be an ideal membrane separation material based on the difference in molecular dynamics size of CO ₂ (0.33nm) and Xe (0.41nm). DD3R is a molecular sieve with oval 8-membered ring channels, and its effective channel size is 0.36nm×0.44nm. Moreover, the all-silicon property of DD3R molecular sieve makes it have certain hydrophobicity, which can effectively weaken the blockage of the molecular sieve pores by water vapor.

Claims (1)

1.DD3R molecular sieve membrane is to containing N ₂ , Xe, _CO The application in the separation of Xe in the gas is characterized in that, comprises the steps: adopt DD3R molecular sieve membrane to separate the gas containing xenon gas, and xenon gas is retained in the interception side, And N ₂ and CO ₂ permeate through the DD3R molecular sieve membrane; The xenon-containing gas is a mixed gas containing 5% CO ₂ , 30% N ₂ and 65% Xe, and then 2.3kPa water vapor is introduced; During the separation, the pressure of the feed gas is 1-3 bar and the temperature is 10-30°C.

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