CN115445401B

CN115445401B - Application of full-process green sustainable preparation ZIF-8 membrane in propylene/propane separation

Info

Publication number: CN115445401B
Application number: CN202211194449.7A
Authority: CN
Inventors: 刘毅; 刘亮亮
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2024-02-02
Anticipated expiration: 2042-09-29
Also published as: CN115445401A

Abstract

The invention discloses a full-process green sustainable preparation technology for preparing a ZIF-8 film, and the ZIF-8 film is used for propylene/propane (C) ₃ H ₆ /C ₃ H ₈ ) And (5) separating the mixed gas. Firstly, preparing a ZnO transition layer on a porous carrier through Atomic Layer Deposition (ALD) gas phase; then placing the membrane in a kettle containing only 2-methylimidazole (2-mIm) organic ligand, and growing in situ under the supercritical fluid (SCF) atmosphere to prepare a continuous compact ZIF-8 membrane; finally, the prepared ZIF-8 film is used for C ₃ H ₆ /C ₃ H ₈ And (5) high-efficiency separation. Thanks to the excellent characteristics of the coupled ALD and SCF technologies, the ZIF-8 film has the advantages of green, environment-friendly and sustainable whole preparation process, and the prepared film material shows excellent C ₃ H ₆ /C ₃ H ₈ Separation selectivity>200 The long-term elbow stopper which is difficult to achieve both sustainability of the ZIF-8 film preparation process and excellent separation performance is skillfully solved, and the industrial application prospect is good.

Description

Application of full-process green sustainable preparation ZIF-8 membrane in propylene/propane separation

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to an application of a ZIF-8 membrane prepared in a full-process green sustainable way in propylene/propane separation.

Background

Separation and purification of gases, e.g. C ₃ H ₆ /C ₃ H ₈ Separation plays an important role in the petrochemical industry. The traditional separation technology of rectification, solution absorption or pressure swing adsorption is complex to operate and has huge energy consumption, and development of a novel separation technology is needed. The membrane separation technology is paid attention to because of excellent characteristics of high separation efficiency, low energy consumption, environment-friendly process, low cost and the like. Among the numerous membrane materials, crystalline MOF (metal organic framework, MOF) molecular sieve membranes are widely used in the field of gas separation due to their suitable pore channels, excellent designability and rich controllability. In particular, ZIF-8 is used as an ordered porous zeolite imidazole ester skeleton formed by coordination of zinc ions and 2-mIm (Zeolitic Imidazolate Framework, ZIF) materials have been demonstrated to possess C ₃ H ₆ /C ₃ H ₈ The accurate screening capability of various mixed gases is achieved, and the method has great application prospect. Currently, various preparation methods based on liquid phase, gas phase or solid phase are successfully used for preparing the polymorphic ZIF-8 membrane, but the sustainability of the preparation process and the excellent separation performance are still mutually and hardly combined. In general, liquid phase processes are easy to produce with excellent C ₃ H ₆ /C ₃ H ₈ The ZIF-8 film with separation capability, but the introduction of the liquid phase solvent consumes a large amount of expensive precursor and severely pollutes the environment; the solid phase synthesis method does not need liquid phase solvent, but the film layer is difficult to show considerable C ₃ H ₆ /C ₃ H ₈ Separation capability; the problems of harsh operating conditions, expensive equipment, poor separation capacity and the like of the gas phase conversion method also limit the large-scale application of the gas phase conversion method. Therefore, a full-process sustainable green preparation height C is developed ₃ H ₆ /C ₃ H ₈ A ZIF-8 membrane with separation capability is necessary.

Disclosure of Invention

The ZIF-8 film is prepared by utilizing a metal source and organic ligand 'decoupling' strategy, such as in-situ conversion on a carrier modified by a homologous ZnO transition layer, and is a simple, convenient and efficient synthesis method. If a ZnO transition layer deposition and ZIF-8 film conversion route which does not need a liquid phase solvent in the whole process can be reasonably designed, the whole process green sustainable preparation is expected to be realized. In this regard, atomic Layer Deposition (ALD) techniques can enable vapor deposition of ZnO transition layers, while supercritical fluid (SCF) techniques are expected to convert them in situ into ZIF-8 films in green fluid media. On the one hand, considering that the deposited nano-scale ZnO crystal grains have excellent reactivity, and combining with the excellent liquid-like solubility and gas-like diffusivity of SCF, the nano-scale ZnO crystal grains are hopeful to be rapidly converted into ZIF-8 film layers and gradually bridge the residual inter-crystal defects, thereby obtaining the nano-scale ZnO crystal with excellent C ₃ H ₆ /C ₃ H ₈ Sieving ability ZIF-8 membranes; on the other hand, due to the excellent characteristics of the coupled ALD and SCF technologies, the preparation route is hopeful to have the advantages of no liquid phase solvent in the whole process, 100% recovery and reuse of chemical reagent, no need of any carrier pre-modification, membrane layer post-activation and the likeThe characteristics are further realized, and the full-process green sustainable preparation of the high-performance ZIF-8 film is further realized, so that the ZIF-8 film is pushed to be positioned in C ₃ H ₆ /C ₃ H ₈ Practical application in separations.

In view of this, the present invention provides a new process for the full-flow green sustainable preparation of ZIF-8 membranes and explores its application in propylene/propane separations. Firstly, carrying out atomic layer deposition on a porous carrier to prepare a ZnO transition layer; then placing the membrane in a supercritical kettle containing only 2-mIm ligand, and converting the membrane into a continuous and compact ZIF-8 membrane in situ under a supercritical atmosphere; finally, the prepared ZIF-8 film is used for C ₃ H ₆ /C ₃ H ₈ And (5) separating. Thanks to the excellent characteristics of ALD and SCF technology, the process of the present invention can improve both the process sustainability and C of ZIF-8 films ₃ H ₆ /C ₃ H ₈ The separation performance is excellent, the full-process green sustainable preparation of the high-performance ZIF-8 membrane is realized, and the method has good industrial application prospect.

The invention is realized by the following technical scheme:

the preparation method of the ZIF-8 membrane specifically comprises the following steps:

(1) Preparing a ZnO transition layer on a porous carrier through Atomic Layer Deposition (ALD) gas phase; the metal source required by the atomic layer deposition is diethyl zinc or dimethyl zinc, the deposition temperature is 90-150 ℃, and the deposition thickness is 20-800 atomic layers;

(2) Placing the membrane in a kettle with only 2-methylimidazole (2-mIm) organic ligand, and performing in-situ growth under the action of supercritical fluid (SCF) to convert the membrane into a continuous compact ZIF-8 membrane; supercritical CO ₂ The temperature is 35-150 ℃, the growth pressure is 7.4-30 MPa, and the growth time is 6-48 h;

application of ZIF-8 film to C ₃ H ₆ /C ₃ H ₈ And (5) separating.

Preferably, the porous carrier in the step (1) has a flat plate type, tubular type or hollow fiber type structure; the porous carrier is porous metal oxide, porous metal, porous non-metal oxide, porous carbide or porous polymer carrier. Further, the porous metal oxide is porous alumina, porous titania, porous zirconia or porous YSZ; the porous metal is porous stainless steel or porous nickel; the porous nonmetallic oxide is porous silicon oxide or porous glass; the porous carbide is porous silicon carbide; the porous polymer carrier is polyvinylidene fluoride, polyethersulfone, polyacrylonitrile or polyamide. Further, the porous carrier is a flat plate type porous alumina carrier.

Preferably, the metal source required for the deposition in step (1) is diethyl zinc.

Preferably, the thickness (apparent thickness, due to the presence of ZnO grains in vapor deposition) of the ZnO transition layer in step (1) is 4nm to 200nm, and the grain size is 4nm to 200nm.

Preferably, the concentration of 2-mIm in the step (2) is 0.0001-10 mol/l, and still further, the concentration of 2-mIm is 0.01-0.5mol/l.

Preferably supercritical CO in step (2) ₂ The temperature is 60-120 ℃, the growth pressure is 8-15 MPa, and the growth time is 12-36 h.

Preferably, the ZIF-8 film in the step (2) has a thickness of 10nm to 1 μm and a grain size of 10nm to 1. Mu.m.

Compared with the prior art, the invention has the following advantages:

1, the ZIF-8 film provided by the invention has unprecedented sustainability in terms of preparation process. The method comprises the following steps: 1) The whole process is free of liquid phase solvent preparation. The coupled ALD and SCF technology can realize ZnO transition layer vapor deposition and ZIF-8 film supercritical state conversion, and further realize full-flow solvent-free green preparation. 2) The chemical reagent is 100 percent recycled. In the preparation process, a Zn metal source (recovered as ZnO phase), a 2-mIm organic ligand and scCO ₂ The solvent can be efficiently recovered and recycled, so that zero pollution emission and sustainable utilization of chemical reagents in the preparation process are realized. 3) No carrier pre-modification and membrane post-activation treatment are needed. ALD deposition can be performed directly on porous supports without any pre-modification, such as coating with gamma-Al ₂ O ₃ Layers, etc.; the ZIF-8 film layer prepared by SCF conversion does not need any post-activation, such as solvent replacement, cleaning and vacuum additionHeat, etc., can be used directly for characterization or gas separation testing.

2 the ZIF-8 membrane of the present invention exhibits excellent C in terms of gas separation ₃ H ₆ /C ₃ H ₈ The separation selectivity (higher than 200) is far superior to that of ZIF-8 membranes obtained by most of the existing preparation methods including solution phase processes. Compared with ZIF-8 films prepared by other methods (such as electrochemical, sol-gel, chemical deposition such as atomic layer deposition, or physical deposition such as magnetron sputtering) after conversion (including solution phase, gas phase or solid phase conversion methods), the ZIF-8 film layer of the invention shows excellent C ₃ H ₆ /C ₃ H ₈ Separation performance. The method mainly benefits from the synergistic improvement of the intergrowth of the film layer by ALD and SCF technologies, and on one hand, the excellent uniformity, shape retention and controllability of ALD ensure the preparation of the nanoscale ZnO transition layer with fully exposed chemical reactivity; on the other hand, the excellent gas-like diffusivity and proper liquid-like solubility of SCF can convert the prepared ZnO transition layer into a defect-free ZIF-8 film layer with good microstructure, thereby realizing C ₃ H ₆ /C ₃ H ₈ And (5) high-efficiency separation.

Combining sustainability of preparation Process and C ₃ H ₆ /C ₃ H ₈ In view of the superiority of separation performance, the preparation method of the ZIF-8 membrane and C displayed by the ZIF-8 membrane ₃ H ₆ /C ₃ H ₈ The separation performance is sufficiently competitive in practical applications.

Description of the drawings:

FIG. 1 is an X-ray diffraction (XRD) pattern of the ZnO layer-modified porous carrier prepared in example 1;

FIG. 2 is a low-magnification Scanning Electron Microscope (SEM) image of the ZnO layer-modified porous support prepared in example 1;

FIG. 3 is an XRD pattern for ZIF-8 films prepared in example 1;

FIG. 4 is an SEM image of a ZIF-8 film prepared according to example 1;

FIG. 5 is an XRD pattern of the ZnO layer-modified porous support prepared in example 2;

FIG. 6 is an SEM image of a ZnO layer-modified porous support prepared in example 2;

FIG. 7 is an XRD pattern for ZIF-8 films prepared in example 2;

FIG. 8 is an SEM image of a ZIF-8 film prepared according to example 2;

FIG. 9 is an XRD pattern of the ZnO layer-modified porous support prepared in example 3;

FIG. 10 is an SEM image of a ZnO layer-modified porous support prepared in example 3;

FIG. 11 is an XRD pattern for ZIF-8 films prepared in example 3;

FIG. 12 is an SEM image of a ZIF-8 film prepared according to example 3;

FIG. 13 is an XRD pattern of the ZnO layer-modified porous support prepared in example 4;

FIG. 14 is an SEM image of a ZnO layer-modified porous support prepared in example 4;

FIG. 15 is an XRD pattern for ZIF-8 films prepared in example 4;

FIG. 16 is an SEM image of a ZIF-8 film prepared according to example 4;

FIG. 17 is an XRD pattern of the ZnO layer-modified porous support prepared in example 5;

FIG. 18 is an SEM image of a ZnO layer-modified porous support prepared in example 5;

FIG. 19 is an XRD pattern for ZIF-8 films prepared in example 5;

FIG. 20 is an SEM image of a ZIF-8 film prepared according to example 5;

FIG. 21 is a schematic illustration of the preparation of ZIF-8 film C from examples 1-5 ₃ H ₆ /C ₃ H ₈ Separation performance and comparison chart thereof

FIG. 22 is a graph of the single component gas permeability of ZIF-8 membranes prepared in example 1;

FIG. 23 is a graph of different operating temperatures versus ZIF-8 film C prepared in example 2 ₃ H ₆ /C ₃ H ₈ Separation performance impact;

FIG. 24 shows a different C ₃ H ₆ Feed concentration vs. ZIF-8 Membrane C prepared in example 3 ₃ H ₆ /C ₃ H ₈ Separation performance impact;

FIG. 25 is a graph of various operating pressures versus ZIF-8 film C prepared in example 4 ₃ H ₆ /C ₃ H ₈ Separation performance impact;

FIG. 26 shows a real objectC of ZIF-8 film prepared in example 5 at ordinary temperature and pressure ₃ H ₆ /C ₃ H ₈ Long-period stability evaluation of separation performance;

FIG. 27 is an XRD pattern of the ZnO layer-modified porous carrier prepared in comparative example 1;

FIG. 28 is an SEM image of a ZnO layer-modified porous carrier prepared in comparative example 1;

FIG. 29 is an XRD pattern of ZIF-8 film prepared in comparative example 1;

FIG. 30 is an SEM image of a ZIF-8 film prepared according to comparative example 1;

FIG. 31 is an XRD pattern of the ZnO layer-modified porous carrier prepared in comparative example 2;

FIG. 32 is an SEM image of a ZnO layer-modified porous carrier prepared in comparative example 2;

FIG. 33 is an XRD pattern of ZIF-8 film prepared in comparative example 2;

FIG. 34 is an SEM image of a ZIF-8 film prepared according to comparative example 2;

FIG. 35 is an XRD pattern of ZIF-8 film prepared in comparative example 3;

FIG. 36 is an SEM image of a ZIF-8 film prepared according to comparative example 3;

FIG. 37 is an XRD pattern of ZIF-8 film prepared in comparative example 4;

FIG. 38 is an SEM image of a ZIF-8 film prepared according to comparative example 4;

FIG. 39 is an XRD pattern of ZIF-8 film prepared in comparative example 5;

FIG. 40 is an SEM image of a ZIF-8 film prepared according to comparative example 5;

FIG. 41 is an XRD pattern of ZIF-8 film prepared in comparative example 6;

FIG. 42 is an SEM image of a ZIF-8 film prepared according to comparative example 6;

FIG. 43 is an XRD pattern of ZIF-8 film prepared in comparative example 7;

FIG. 44 is an SEM image of a ZIF-8 film prepared according to comparative example 7;

FIG. 45 is an XRD pattern of ZIF-8 film prepared in comparative example 8;

FIG. 46 is an SEM image of a ZIF-8 film prepared according to comparative example 8;

Detailed Description

The present invention will be described in further detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.

Example 1

Preparation of ZIF-8 film (M1) by coupled Atomic Layer Deposition (ALD) and supercritical fluid (SCF) techniques

(1) A uniform and compact zinc oxide (ZnO) modification layer is deposited on a flat plate type porous alumina carrier through ALD technology. The deposition temperature was 90 ℃. The cyclic steps for depositing a single atomic layer are as follows: the porous support was exposed to a diethyl zinc source atmosphere for 10s, followed by treatment under vacuum for 2s, followed by exposure to a water vapor atmosphere for 10s, and finally treatment under vacuum for 2s. The deposition thickness of ALD in this example was 150 atomic layers (apparent thickness 30 nm).

(2) And (2) respectively placing the ZnO transition layer modified porous carrier prepared in the step (1) and the ground solid 2-methylimidazole (2-mIm) ligand powder into a supercritical kettle, wherein the ZnO transition layer modified porous carrier and the ground solid 2-methylimidazole ligand powder are not in direct contact. Subsequently gaseous CO ₂ High pressure is fed into the kettle, and the temperature and the pressure are rapidly increased to a preset value<5min,60 ℃,15 MPa) and then CO in the supercritical state ₂ Dissolving 2-mIm powder (0.03 mol/l) under the action of solvent to form supercritical CO for dissolving organic ligand ₂ And (3) mixing the phase reaction system, diffusing the mixed phase reaction system to a region near the ZnO transition layer to carry out coordination reaction, and carrying out supercritical state growth for 36 hours to obtain a continuous compact ZIF-8 film layer through conversion.

XRD (fig. 1) and SEM (fig. 2) showed successful preparation of a uniform and dense ZnO modification layer on a porous alumina support by the above step (1).

XRD (FIG. 3) and SEM (FIG. 4) showed that a continuous dense ZIF-8 film was successfully prepared on a ZnO transition layer modified porous alumina support by step (2) above.

Example 2

Preparation of ZIF-8 (M2) by coupled Atomic Layer Deposition (ALD) and supercritical fluid (SCF) techniques

The difference from example 1 is that: the deposition temperature in the step (1) is 100 ℃; the deposition thickness was 125 atomic layers (apparent thickness 25 nm). The growth temperature and pressure in the step (2) are 75 ℃,12MPa, and the growth time is 30h.

XRD (fig. 5) and SEM (fig. 6) showed successful preparation of a uniform and dense ZnO modification layer on a porous alumina support by step (1).

XRD (FIG. 7) and SEM (FIG. 8) showed that a continuous dense ZIF-8 film was successfully prepared by step (2) on a ZnO transition-layer modified porous alumina support.

Example 3

Preparation of ZIF-8 film (M3) by coupled Atomic Layer Deposition (ALD) and supercritical fluid (SCF) techniques

The difference from example 1 is that: the deposition temperature in the step (1) is 110 ℃; the deposition thickness was 100 atomic layers (apparent thickness 20 nm). The growth temperature and pressure in the step (2) are 90 ℃,10MPa, and the growth time is 24 hours.

XRD (fig. 9) and SEM (fig. 10) showed successful preparation of a uniform and dense ZnO modification layer on a porous alumina support by step (1).

XRD (FIG. 11) and SEM (FIG. 12) showed that a continuous dense ZIF-8 film was successfully prepared by step (2) on a ZnO transition-layer modified porous alumina support.

Example 4

Preparation of ZIF-8 film (M4) by coupled Atomic Layer Deposition (ALD) and supercritical fluid (SCF) techniques

The difference from example 1 is that: the deposition temperature in the step (1) is 120 ℃; the deposition thickness was 75 atomic layers (apparent thickness 15 nm). The growth temperature and pressure in the step (2) are 105 ℃,9MPa, and the growth time is 18h.

XRD (fig. 13) and SEM (fig. 14) showed successful preparation of a uniform and dense ZnO modification layer on a porous alumina support by step (1).

XRD (FIG. 15) and SEM (FIG. 16) showed that a continuous dense ZIF-8 film was successfully prepared by step (2) on a ZnO transition-layer modified porous alumina support.

Example 5

Preparation of ZIF-8 film (M5) by coupled Atomic Layer Deposition (ALD) and supercritical fluid (SCF) techniques

The difference from example 1 is that: the deposition temperature in the step (1) is 130 ℃; the deposition thickness was 50 atomic layers (apparent thickness 10 nm). The growth temperature and pressure in the step (2) are 120 ℃,8MPa, and the growth time is 12h.

XRD (fig. 17) and SEM (fig. 18) showed successful preparation of a uniform and dense ZnO modification layer on a porous alumina support by step (1).

XRD (FIG. 19) and SEM (FIG. 20) showed that a continuous dense ZIF-8 film was successfully prepared by step (2) on a ZnO transition-layer modified porous alumina support.

Example 6

ZIF-8 membrane: c at normal temperature and pressure (25 ℃ C., 1.013 bar) ₃ H ₆ /C ₃ H ₈ Gas separation performance

The ZIF-8 films obtained in examples 1 to 5 were subjected to C ₃ H ₆ /C ₃ H ₈ And (3) gas permeation test. For mixed component gases, the feed side gas flow rate was 1:1, the purge gas is He, the flow rate is 50 ml.min ^-1 . Table 1 and FIG. 21 show that the ZIF-8 films prepared in examples 1-5 each exhibit excellent C ₃ H ₆ /C ₃ H ₈ Separation performance.

TABLE 1C of ZIF-8 membranes prepared by supercritical fluid technology ₃ H ₆ /C ₃ H ₈ Separation performance.

^* P:×10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1

Example 7

ZIF-8 membrane: gas permeation ability at ordinary temperature and pressure (25 ℃ C., 1.013 bar)

The system evaluates the gas separation performance of the ZIF-8 membrane (M1) prepared in example 1 with other smaller molecular dynamics diameter at normal temperature and pressure (FIG. 22), and the result shows that the gas permeability of the ZIF-8 membrane shows typical particle size sieving principle. In particular, ZIF-8 film C ₃ H ₆ Permeability of 75.8X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ Ideal selectivity of 246.4, exhibiting excellent C ₃ H ₆ /C ₃ H ₈ Separation performance.

Example 8

ZIF-8 membrane: c under different operating conditions ₃ H ₆ /C ₃ H ₈ Gas separation performance

The system examined the ZIF-8 membranes (M3) prepared in examples 2-4 at different operating temperatures, C ₃ H ₆ Mixed component gas C under the conditions of feeding concentration and operating pressure ₃ H ₆ /C ₃ H ₈ Separation performance (fig. 23-25), all of which exhibit high separation efficiency: 1) As the operating temperature increased from ambient to 90℃the rest of the procedure was as in example 6, C ₃ H ₆ Permeability of 69.3X10 ^-10 To 80.0X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was reduced from 205.7 to 69.0. 2) With C ₃ H ₆ The feed concentration was increased from 10% to 90% by the same procedure as in example 6, C ₃ H ₆ Permeability is 74.9X10 ^-10 To 66.8X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 Internal variation, C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was reduced from 234.7 to 123.1. 3) As the operating pressure increased from 1.0bar to 2.0bar, the remainder of the procedure was as in example 6, C ₃ H ₆ Permeability of 69.3X10 ^-10 To 123.0X10 ^- ¹⁰ mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was reduced from 205.7 to 49.1.

Example 9

ZIF-8 membrane: c at normal temperature and pressure ₃ H ₆ /C ₃ H ₈ Stability of gas separation

System evaluation of ZIF-8 films prepared in example 5(M5) Long period C under the conditions of example 6 ₃ H ₆ /C ₃ H ₈ Mixed component gas separation performance (fig. 26). C of ZIF-8 film within 60h ₃ H ₆ Permeability (-69.3X10) ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ) And C ₃ H ₆ /C ₃ H ₈ The gas mixture selectivity (-203.4) is kept stable, and the excellent performance stability is shown.

Comparative example 1 (not according to the invention)

Preparation of ZIF-8 film by coupling ALD and SCF technologies and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance: low deposition thickness (-5)

The difference from example 1 is that: in step 1, a thickness of 5 atomic layers (apparent thickness. About.1 nm) was deposited. The remaining steps were the same as in example 1. Subsequently, the ZIF-8 film thus obtained was subjected to C ₃ H ₆ /C ₃ H ₈ And (3) gas permeation test.

The relevant XRD pattern and SEM images show that no significant ZnO-characteristic diffraction peaks appear on the porous alumina support after passing through the above steps (fig. 27 and 28); accordingly, it is difficult to convert to a continuous ZIF-8 film layer (fig. 29 and 30). The gas separation performance shows that the prepared film layer C ₃ H ₆ Permeability of 2904.13 ×10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 1.1.

Comparative example 2 (not according to the invention)

Preparation of ZIF-8 film by coupling ALD and SCF technologies and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance: high deposition thickness (1050)

The difference from example 1 is that: in step 1, 1050 atomic layers (apparent thickness. About.210 nm) were deposited. The remaining steps were the same as in example 1. Subsequently, the ZIF-8 film thus obtained was subjected to C ₃ H ₆ /C ₃ H ₈ And (3) gas permeation test.

The relevant XRD pattern and SEM image show that after passing through the above steps, the preparation is carried out on a porous alumina carrierProviding an ultra-dense ZnO modification layer (fig. 31 and 32); and can be successfully converted into a ZIF-8 film layer (FIG. 33 and FIG. 34), but the gas separation performance shows that the prepared ZIF-8 film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 6.6X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 1.6.

Comparative example 3 (not according to the invention)

Preparation of ZIF-8 film by coupling ALD and SCF technologies and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance: low SCF growth temperature (32 ℃ C.)

The difference from example 1 is that: in step 2, supercritical CO ₂ The temperature and pressure of (2) were 32℃and 10MPa. The remaining steps were the same as in example 1. Subsequently, the ZIF-8 film thus obtained was subjected to C ₃ H ₆ /C ₃ H ₈ And (3) gas permeation test.

The relevant XRD pattern and SEM images showed that the dense film layer was difficult to obtain in appearance despite the weak ZIF-8 characteristic diffraction peaks on the ZnO transition layer modified porous alumina support after the above steps (fig. 35 and 36). The gas separation performance shows that the prepared film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 5.5X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 3.7.

Comparative example 4 (not according to the invention)

Preparation of ZIF-8 film by coupling ALD and SCF technologies and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance: high SCF growth pressure (50 MPa)

The difference from example 1 is that: in step 2, supercritical CO ₂ The temperature and pressure of (2) are 95℃and 50MPa. The remaining steps were the same as in example 1. Subsequently, the ZIF-8 film thus obtained was subjected to C ₃ H ₆ /C ₃ H ₈ Gas permeationAnd (5) penetration test.

The relevant XRD pattern and SEM images showed that the ZIF-8 film was successfully produced on ZnO transition layer modified porous alumina supports after the above procedure, but with apparent microscopic defects (fig. 37 and 38). The gas separation performance shows that the prepared ZIF-8 film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 10.8X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 2.8.

Comparative example 5 (not according to the invention)

ZIF-8 film prepared by converting ZnO layer deposited by ALD technology in gas phase (95 ℃ C., 24 h) and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance

The relevant XRD pattern and SEM images show that after the above steps, on a ZnO transition layer modified porous alumina support deposited by ALD technique (deposition process is the same as step (1) in example 1), it is difficult to produce a dense ZIF-8 film by gas phase conversion (reaction 24h at 95 ℃ c, no direct contact of ZnO transition layer with 2-mIm ligand) (fig. 39 and 40), mainly due to the difficulty of 2-mIm ligand to gasify and diffuse into ZnO layer and thus coordination reaction occurs. Accordingly, the gas separation performance shows that the prepared ZIF-8 film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 5042.2 ×10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The selectivity of the mixture was 1.18, indicating that no dense ZIF-8 membrane layer was formed on the porous support.

Comparative example 6 (not according to the invention)

ZIF-8 film prepared by solid phase (95 ℃ C., 24 h) conversion ALD technology deposited ZnO layer and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance

The relevant XRD pattern and SEM images show that after passing through the above steps, the ZnO transition layer deposited on the ALD technique modifies the porous alumina support (deposition process and steps in example 1Step (1) is the same), and a ZIF-8 film layer (FIG. 41 and FIG. 42) can be prepared after solid phase conversion (reaction at 95 ℃ for 24 hours and direct contact of a ZnO transition layer and a 2-mIm ligand), but microscopic defects exist, which are mainly due to the fact that 2-mIm ligand is efficiently diffused in the ZnO layer due to the lack of a proper transmission medium (solvent) under the conditions, and the formed ZIF-8 film layer has microscopic structural defects. The gas separation performance shows that the prepared ZIF-8 film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 4.6X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 1.80.

Comparative example 7 (not according to the invention)

ZIF-8 film prepared by converting ZnO layer deposited by sol-gel method through SCF technology and C thereof ₃ H ₆ /C ₃ H ₈ Separation performance

The relevant XRD pattern and SEM images show that the ZIF-8 film layer can be successfully prepared by supercritical in-situ growth (growth conditions same as in example 1) on a ZnO transition layer deposited by sol-gel method (for details of the synthesis process reference j. Mater. Chem. A,2013,1,10635) modified porous alumina support. The gas separation performance shows that the prepared ZIF-8 film C ₃ H ₆ Permeability of 29.2X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₈ Permeability of 0.6X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 47.1.

It should be noted that, compared with the ZIF-8 film prepared by converting the ALD deposited ZnO layer by the SCF technique in the invention, the ZnO layer has obvious infiltration (due to stronger sol fluidity) in the sol-gel deposition, so that the converted ZIF-8 film layer C ₃ H ₆ Lower permeability (29.2 vs 69.3 (ALD). Times.10) ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ) The method comprises the steps of carrying out a first treatment on the surface of the But the deposited ZnO has larger particle size and lower reactivity, so that the converted ZIF-8 film layer C ₃ H ₈ Higher permeability(0.6vs 0.3(ALD)×10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ) Thereby enabling the ZIF-8 film to be C ₃ H ₆ /C ₃ H ₈ Reduced separation Capacity (47.1 vs 205.7 (ALD). Times.10) ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ). In addition, a large amount of liquid phase reagent is needed in the sol-gel method deposition, and the reagent is difficult to recycle efficiently, so that the solvent-free green preparation of the film layer is affected.

Comparative example 8 (not according to the invention)

ZIF-8 films and C thereof prepared by converting a Physical Vapor Deposition (PVD) deposited ZnO layer by SCF technology ₃ H ₆ /C ₃ H ₈ Separation performance

The relevant XRD patterns and SEM images show that after passing through the above steps, a ZnO transition layer was deposited by PVD (magnetron sputtering preparation, detailed synthetic process reference [1 ]]Liu Zhiwen growth behavior of reactive magnetron sputtering ZnO film on Si substrate [ D]University of great chain chemical industry, 2006) modified porous alumina carrier, and the ZIF-8 film layer (fig. 45 and 46) can be prepared by supercritical state in-situ growth (the growth condition is the same as that of the embodiment 1), but microscopic defects exist among the crystals, which are mainly due to the fact that the size of ZnO crystal grains deposited by PVD under the condition is larger, and meanwhile, the compactness is poor, so that the formed ZIF-8 film layer has microscopic structural defects. The gas separation performance shows that the prepared ZIF-8 film shows lower C ₃ H ₆ /C ₃ H ₈ Separation performance, C ₃ H ₆ Permeability of 48.3X10 ^-10 mol·m ^-2 ·s ^-1 ·Pa ^-1 ，C ₃ H ₆ /C ₃ H ₈ The mixture selectivity was 3.5.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. The application of the ZIF-8 membrane prepared in a full-process green sustainable way in propylene/propane separation is characterized in that: the preparation method of the ZIF-8 film specifically comprises the following steps:

(1) Depositing a gas phase on the porous carrier in an atomic layer to prepare a ZnO transition layer; the metal source required by the atomic layer deposition is diethyl zinc or dimethyl zinc, the deposition temperature is 90-150 ℃, and the deposition thickness is 20-800 atomic layers;

(2) Placing the membrane in a kettle containing only 2-methylimidazole organic ligand, and growing and converting the membrane into a continuous compact ZIF-8 membrane under the action of supercritical fluid; supercritical CO ₂ The temperature is 35-200 ℃, the growth pressure is 7.4-30 MPa, and the growth time is 6-48 h;

the ZIF-8 membrane is applied to propylene/propane separation;

the thickness of the ZnO transition layer in the step (1) is 4 nm-200 nm, and the grain size is 4 nm-200 nm;

the concentration of the 2-methylimidazole in the step (2) is 0.0001-10 mol/L;

the ZIF-8 film in the step (2) has a thickness of 10 nm-1 μm and a grain size of 10 nm-1 μm.

2. Use of a full-flow green sustainable ZIF-8 membrane as claimed in claim 1 for propylene/propane separations wherein: the porous carrier in the step (1) has a flat plate type, tubular type or hollow fiber type structure; the porous carrier is porous metal oxide, porous metal, porous non-metal oxide, porous carbide or porous polymer carrier.

3. Use of a full-flow green sustainable ZIF-8 membrane as claimed in claim 1 for propylene/propane separations wherein: supercritical CO in step (2) ₂ The temperature of 60-120 ℃, the growth pressure of 8-15 MPa and the growth time of 12～36h。