Organosilicon composite film for adsorption separation of low-carbon olefin / aromatic hydrocarbon in VOCs and preparation method thereof

Abstract

The invention belongs to the technical field of gas membrane separation, and particularly relates to an organic silicon composite membrane for adsorption separation of low-carbon olefin / aromatic hydrocarbon in VOCs and a preparation method of the organic silicon composite membrane. The invention aims to provide a novel low-carbon alkane / aromatic hydrocarbon separation technology combining a dynamic and reversible particle adsorbent and a BTESE-PDMS composite membrane, and the novel low-carbon alkane / aromatic hydrocarbon separation technology is used for realizing VOCs resource recovery of liquid chemical wharfs with high efficiency and low energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas membrane separation, and in particular relates to an organic silicon composite membrane for adsorption separation of light olefins / aromatics in VOCs and a preparation method thereof. Background Art

[0002] Volatile organic compounds (VOCs) are a class of organic substances that are easily volatile at room temperature and are widely present in industrial processes such as storage and loading and unloading of petrochemical products. Among them, light olefins (such as ethylene and propylene) and aromatics (such as benzene and toluene) are important chemical raw materials and occupy an important position in industrial production. However, these compounds often exist in the form of mixtures, and efficient separation technology is required to obtain a single product with high purity. Traditional separation methods such as distillation and extraction are not only energy-intensive and complex to operate, but also difficult to achieve efficient separation in some cases. Therefore, the development of efficient and low-energy adsorption separation technology, especially the adsorption separation of light olefins / aromatics in VOCs, is of great significance for improving chemical production efficiency, reducing energy consumption, and reducing environmental pollution.

[0003] Molecular sieves and activated carbon, as traditional adsorption and separation materials, have been widely used in the adsorption and separation of VOCs. However, these materials have significant shortcomings in practical applications. First, the pore size and shape of molecular sieves are fixed, and their selectivity for molecules of different sizes and shapes is limited. They are also prone to clogging during the adsorption process, making regeneration difficult. Secondly, although activated carbon has a large specific surface area and adsorption capacity, its adsorption selectivity is poor and it is easily affected by environmental factors such as humidity and temperature, resulting in unstable adsorption performance. In addition, both materials are prone to aging during long-term use, resulting in a decrease in adsorption performance and the need for frequent replacement, which increases production costs.

[0004] In order to overcome the shortcomings of traditional adsorption separation materials, researchers began to explore the use of organosilicon separation membranes for the adsorption separation of VOCs. Among them, polydimethylsiloxane (PDMS) silicone rubber membranes have attracted much attention due to their good chemical and thermal stability. However, single PDMS silicone rubber membranes have obvious deficiencies in selectivity. Since PDMS membranes have a certain permeability to various VOCs molecules, it is difficult to achieve efficient and selective separation of light olefins / aromatics during the adsorption separation process. Therefore, how to improve the selectivity of organosilicon separation membranes has become an important direction of current research. Summary of the Invention

[0005] The present invention aims to provide a novel low-carbon alkane / aromatic hydrocarbon separation technology combining a dynamic and reversible particle adsorbent with a BTESE-PDMS composite membrane, which can be used to realize the resource recovery of VOCs in liquid chemical terminals with high efficiency and low energy consumption.

[0006] The present invention provides an organosilicon composite membrane for the adsorption and separation of light olefins / aromatics in VOCs. The organosilicon composite membrane comprises a carrier and a PMDS-BTESE membrane. The PMDS-BTESE membrane is doped with a particle adsorbent, and the particle adsorbent is TESPTS functionalized SiO2.

[0007] Preferably, the carrier is a porous alumina ceramic tube.

[0008] Preferably, the organic silicon composite film further comprises a transition layer between the carrier and the PMDS-BTESE film, and the transition layer is zirconium oxide.

[0009] The present invention also provides a method for preparing the above-mentioned organosilicon composite membrane for adsorption separation of light olefins / aromatics in VOCs, which comprises the following steps:

[0010] (1) Tetraethyl orthosilicate (TEOS) and 3,3′-tetrasulfide bis(propyltriethoxysilane) (TESPTS) were added to anhydrous ethanol as a template and dispersed in dilute hydrochloric acid (HCl) containing 3.7% by mass to react and form an ordered structure through the template. The ordered structure of TESPTS functionalized SiO2 was then formed after aging, washing and drying.

[0011] (2) Dissolve polydimethylsiloxane (PDMS) in n-heptane, add TESPTS functionalized SiO2, and add water, 3.7% dilute hydrochloric acid, and organosilicon precursor 1,2-bis(triethoxysilyl)ethane (BTESE) during stirring to prepare tetrasulfide functionalized PDMS-BTESE organosilicon composite sol;

[0012] (3) The organic silicon composite sol is coated on a carrier and calcined to obtain the organic silicon composite film.

[0013] Preferably, in step (1), the template is one of cetyltrimethylammonium bromide (CTAB), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (Pluronic P123), and polyoxyethylene polyoxypropylene ether (Pluronic F127).

[0014] Preferably, in step (1), the molar ratio of the template, TEOS, TESPTS, water and dilute hydrochloric acid is 0.1-0.5:5-7:5-3:30-120:0.4-0.8.

[0015] Preferably, in step (1), the reaction conditions are temperature 25-40° C., time 0.5-1 h, aging temperature 60-80° C., time 12-24 h.

[0016] Preferably, in step (2), the molecular weight of PDMS is 20,000 to 40,000.

[0017] Preferably, in step (2), the molar ratio of TESPTS-functionalized SiO2, PDMS and BTESE is 1-2:5-1:5-9; and the molar ratio of water, dilute hydrochloric acid (3.7%) and BTESE is 30-120:5.4-16.2:1.

[0018] Preferably, in step (3), the roasting temperature is 100-150° C., and the roasting times are 1-5 times.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] First, by employing TESPTS-functionalized SiO2 as a particle adsorbent and doping it into PMDS-BTESE, the present invention significantly improves the selective adsorption capacity of the organosilicon composite membrane for light olefins and aromatics among VOCs. Furthermore, the introduction of a ZrO2 transition layer effectively prevents the functionalized PMDS-BTESE particles from penetrating and clogging the pores of the Al2O3 support and improves the overall stability of the composite. The sulfur bridge structure on the TESPTS-functionalized SiO2 surface not only provides hydrophobic properties but also, through π-electron interactions and a rational pore structure design, forms dynamic and reversible weak adsorption sites, thereby achieving highly efficient and selective separation of light olefins and aromatics.

[0021] Secondly, the present invention combines the dynamic and reversible TESPTS functionalized SiO2 adsorption material with the PDMS-BTESE composite membrane to form an integrated device. This design not only saves design space, but also significantly reduces energy consumption during operation. Compared with traditional adsorption separation devices and separation membrane devices, it has higher integration and lower operational complexity. By directly doping particulate adsorbents into the membrane, the present invention achieves an organic combination of adsorption and separation functions, thereby improving the overall processing efficiency. In addition, the integrated device is particularly suitable for actual liquid chemical terminal VOCs recovery scenarios. Its high efficiency and low energy consumption give this technology significant advantages in industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an electron microscope cross-sectional view of the functionalized PDMS-BTESE gas separation membrane prepared in Example 1 of the present invention.

[0023] Figure 2 This is an atomic force microscope image of the functionalized PDMS-BTESE gas separation membrane prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below in conjunction with the embodiments of the specification. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Example 1

[0026] The preparation method of this embodiment is achieved by comprising the following steps:

[0027] (1) The template agent CTAB was added to anhydrous ethanol, and then deionized water was added. During the stirring process, a TEOS+TESPTS mixture was added dropwise, and dilute hydrochloric acid (3.7%) was added. The molar ratio of the template agent, TEOS, TESPTS, water and dilute hydrochloric acid (3.7%) was maintained at 0.2:7:3:30:0.4. The mixture was stirred in a 40°C water bath for 0.5 h to form an ordered structure through the template agent. The mixture was heated and aged in an oven at 60°C for 24 h. The template agent was removed by washing with a large amount of anhydrous ethanol. After vacuum drying, a TESPTS-functionalized SiO2 with a regular and orderly structure was obtained.

[0028] (2) According to the molar ratio of TESPTS functionalized SiO2, PDMS, and BTESE of 1:5:5, PDMS with a molecular weight of 20,000 was dissolved, TEOS, and BTESE sol were dissolved in n-heptane, wherein the molar ratio of deionized water, dilute hydrochloric acid (3.7%), and BTESE in the BTESE sol was 30:5.4:1, and the tetrasulfur functionalized PDMS-BTESE sol was obtained after stirring in a 40°C water bath for 2 h;

[0029] (3) Preparation of transition layer: ZrO2 powder was added to anhydrous ethanol and ultrasonicated for 20 minutes to obtain a layer suspension. The suspension was loaded on the support by wiping method and then placed in a blast drying oven for 10 minutes. After being taken out, it was placed in a 550℃ tubular furnace and calcined at high temperature for 15 minutes. The process was repeated 8-9 times to form a transition layer to cover the macropores of the support.

[0030] (4) The tetrasulfur-functionalized PDMS-BTESE sol was coated on a porous Al2O3 ceramic tube containing zirconium oxide as a transition layer, calcined at 120°C for 30 min, and repeated 2 to 3 times to prepare a tetrasulfur-functionalized organosilicon composite membrane.

[0031] Comparative Example 1

[0032] The difference from Example 1 is that a PMDS-BTESE membrane prepared from non-functionalized silica is used.

[0033] (1) The template agent CTAB was added to anhydrous ethanol, and then deionized water was added. TEOS was added dropwise during stirring, and dilute hydrochloric acid (3.7%) was added. The molar ratio of the template agent, TEOS, water and dilute hydrochloric acid (3.7%) was maintained at 0.2:7:30:0.4. The mixture was stirred in a 40°C water bath for 0.5 h to form an ordered structure through the template agent. The mixture was heated and aged in an oven at 60°C for 24 h. The template agent was removed by washing with a large amount of anhydrous ethanol. After vacuum drying, a TESPTS functionalized SiO2 with a regular and orderly structure was obtained.

[0034] (2) According to the molar ratio of SiO2, PDMS, and BTESE of 1:5:5, PDMS with a molecular weight of 20,000 was dissolved, TEOS, and BTESE sol were dissolved in n-heptane, wherein the molar ratio of deionized water, dilute hydrochloric acid (3.7%), and BTESE in the BTESE sol was 30:5.4:1, and the tetrasulfur-functionalized PDMS-BTESE sol was obtained after stirring in a 40°C water bath for 2 h;

[0035] (3) Preparation of transition layer: ZrO2 powder was added to anhydrous ethanol and ultrasonicated for 20 minutes to obtain a layer suspension. The suspension was loaded on the support by wiping method and then placed in a blast drying oven for 10 minutes. After being taken out, it was placed in a 550℃ tubular furnace and calcined at high temperature for 15 minutes. The process was repeated 8-9 times to form a transition layer to cover the macropores of the support.

[0036] (4) The SiO2-doped PDMS-BTESE sol was coated on a porous Al2O3 ceramic tube containing zirconium oxide as a transition layer, calcined at 120°C for 30 min, and repeated 2 to 3 times to prepare a PDMS-BTESE organosilicon composite membrane.

[0037] Comparative Example 2

[0038] The difference from Example 1 is that PMDS-BTESE film directly doped with TESPTS is used.

[0039] (1) PDMS with a molecular weight of 20,000 was dissolved in n-heptane at a molar ratio of TESPTS, PDMS, and BTESE of 0.3:5:5. The molar ratio of deionized water, dilute hydrochloric acid (3.7%), and BTESE in the BTESE sol was 30:5.4:1. The tetrasulfur-functionalized PDMS-BTESE sol was obtained by stirring in a 40°C water bath for 2 h.

[0040] (2) Preparation of transition layer: ZrO2 powder was added to anhydrous ethanol and ultrasonicated for 20 minutes to obtain a layer suspension. The suspension was loaded on the support by wiping method and then placed in a blast drying oven for 10 minutes. After being taken out, it was placed in a 550℃ tube furnace and calcined at high temperature for 15 minutes. The process was repeated 8-9 times to form a transition layer to cover the macropores of the support.

[0041] (3) The tetrasulfur-functionalized PDMS-BTESE sol was coated on a porous Al2O3 ceramic tube containing zirconium oxide as a transition layer, calcined at 120°C for 30 min, and repeated 2 to 3 times to prepare a tetrasulfur-functionalized organosilicon gas separation membrane.

[0042] Comparative Example 3

[0043] The difference from Example 1 is that PMDS-BTESE membrane functionalized with phenyltriethoxysilane (PTES) is used.

[0044] (1) The template CTAB was added to anhydrous ethanol, and then deionized water was added. During the stirring process, a TEOS+PTES mixture was added dropwise, and dilute hydrochloric acid (3.7%) was added. The molar ratio of the template, TEOS, PTES, water and dilute hydrochloric acid (3.7%) was maintained at 0.2:7:3:0.4. The mixture was stirred in a 40°C water bath for 0.5 h, and heated in an oven at 60°C for aging for 24 h. The template was removed by washing with a large amount of anhydrous ethanol, and the tetrasulfide functionalized silica material was obtained after vacuum drying.

[0045] (2) According to the molar ratio of functionalized TEOS, PDMS, and BTESE of 1:5:5, PDMS with a molecular weight of 20,000 was dissolved, TEOS, and BTESE sol were prepared in n-heptane, wherein the molar ratio of deionized water, dilute hydrochloric acid (3.7%), and BTESE in the BTESE sol was 30:5.4:1, and the phenyl-functionalized PDMS-BTESE sol was obtained after stirring in a 40°C water bath for 2 h;

[0046] (3) Preparation of transition layer: ZrO2 powder was added to anhydrous ethanol and ultrasonicated for 20 minutes to obtain a layer suspension. The suspension was loaded on the support by wiping method and then placed in a blast drying oven for 10 minutes. After being taken out, it was placed in a 550℃ tubular furnace and calcined at high temperature for 15 minutes. The process was repeated 8-9 times to form a transition layer to cover the macropores of the support.

[0047] (4) The phenyl-functionalized PDMS-BTESE sol was coated on a porous Al2O3 ceramic tube containing zirconium oxide as a transition layer, calcined at 120°C for 30 min, and repeated 2 to 3 times to prepare a phenyl-functionalized organosilicon gas separation membrane.

[0048] Comparative Example 4

[0049] The difference from Example 1 is that a PMDS-BTESE membrane without particle doping is used.

[0050] (1) PDMS and BTESE sol with a molecular weight of 20,000 were dissolved in n-heptane at a molar ratio of 1:1. The molar ratio of deionized water, dilute hydrochloric acid (3.7%), and BTESE in the BTESE sol was 30:5.4:1. The PDMS-BTESE sol was obtained by stirring in a 40°C water bath for 2 h.

[0051] (2) Preparation of transition layer: ZrO2 powder was added to anhydrous ethanol and ultrasonicated for 20 minutes to obtain a layer suspension. The suspension was loaded on the support by wiping method and then placed in a blast drying oven for 10 minutes. After being taken out, it was placed in a 550℃ tube furnace and calcined at high temperature for 15 minutes. The process was repeated 8-9 times to form a transition layer to cover the macropores of the support.

[0052] (3) The PDMS-BTESE sol was coated on a porous Al2O3 ceramic tube containing zirconium oxide as a transition layer, calcined at 120°C for 30 min, and repeated 2 to 3 times to prepare a PDMS-BTESE composite membrane.

[0053] Characterization

[0054] Figure 1 This is an electron microscope cross-sectional view of the functionalized PDMS-BTESE gas separation membrane prepared in Example 1 of the present invention. Figure 1 The tetrasulfide-functionalized PDMS-BTESE polymer separation layer is clearly visible, evenly covering the surface of the ceramic support. The membrane surface is relatively flat, and the three-layer structure between the separation layer and the support layer is clearly visible: from top to bottom, the PDMS-BTESE separation layer, the ZrO2 transition layer, and the Al2O3 support layer. The thickness of the PDMS separation layer is approximately 8μm.

[0055] Figure 2 This is an atomic force microscopy image of the functionalized PDMS-BTESE gas separation membrane prepared in Example 1. As can be seen, the separation layer surface is flat and smooth, indicating that the membrane is dense, continuous, and crack-free. The surface roughness of the PDMS-BTESE hybrid membrane is low, approximately 22 nm.

[0056] The organic silicon membranes prepared in Example 1 and Comparative Examples 1 to 4 were subjected to gas testing. Propane and benzene were heated to 100°C in a molar ratio of 3:1 and continuously introduced into the membrane assembly with the assistance of N2 carrier gas. The gauge pressure on the raw material side was controlled to 0.4 MPa. After stabilization for 1 hour, the permeability and selectivity were measured. The results are shown in Table 1.

[0057] Table 1 Performance test results of membrane samples of different embodiments and comparative examples

[0058] <![CDATA[Propane permeability mol / (m 2 ×s×Pa)]]> Propane / Benzene Permeation Selectivity Example 1 <![CDATA[2.03×10 -8 ]]> 21.8 Comparative Example 1 <![CDATA[2.06×10 -8 ]]> 10.5 Comparative Example 2 <![CDATA[2.89×10 -8 ]]> 3.4 Comparative Example 3 <![CDATA[1.18×10 -8 ]]> 20.7 Comparative Example 4 <![CDATA[2.17×10 -8 ]]> 8.6

[0059] As shown in Table 1, after TESPTS functionalization, the TESPTS surface contains polysulfide bridge structures, which can promote weak adsorption of aromatic hydrocarbons through π-S interactions or polarity matching. Sulfur atoms have strong polarizability and can form weak van der Waals or induced dipole interactions with the π electron cloud of aromatic hydrocarbons, thereby improving the adsorption capacity of aromatic hydrocarbons. The incorporated silica fills some pores, and the dense structure makes it more easily adsorbed on the surface. However, the aerodynamic diameter of propane molecules is small, and a certain propane permeation rate can still be maintained. Compared with the undoped tetrasulfur-functionalized silica in Comparative Example 4, the selectivity of Example 1 is significantly improved. The unfunctionalized silica in Comparative Example 1 has weak adsorption capacity for aromatic hydrocarbons, and the selectivity is mainly improved by molecular sieving. In Comparative Example 2, due to the interaction of sulfide segments, TESPTS easily agglomerates during the copolymerization process, which makes the composite membrane prone to defects. The phenyl groups in PTES in Comparative Example 3 have a rigid and large steric structure. After the adsorption of aromatic hydrocarbons, other small molecules are difficult to penetrate the membrane.

[0060] Obviously, the above embodiments of the present invention are merely examples for the purpose of illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. However, obvious variations or modifications arising from the essence of the present invention remain within the scope of protection of the present invention.

Claims

1. An organic silicon composite membrane for the adsorption and separation of light olefins / aromatics in VOCs, comprising a carrier and a PMDS-BTESE membrane, characterized in that: The PMDS-BTESE membrane is doped with a particle adsorbent, which is TESPTS functionalized SiO2.

2. The organic silicon composite film according to claim 1, characterized in that The carrier is a porous alumina ceramic tube.

3. The organic silicon composite film according to claim 1, characterized in that The organic silicon composite film further includes a transition layer between the carrier and the PMDS-BTESE film, and the transition layer is zirconium oxide.

4. A method for preparing the organic silicon composite membrane for adsorption separation of light olefins / aromatics in VOCs according to claim 1, characterized in that: The method comprises the following steps: (1) Tetraethyl orthosilicate (TEOS) and 3,3′-tetrasulfide bis(propyltriethoxysilane) (TESPTS) were added to anhydrous ethanol as a template and dispersed in dilute hydrochloric acid (HCl) containing 3.7% by mass to react and form an ordered structure through the template. The ordered structure of TESPTS functionalized SiO2 was then formed after aging, washing and drying. (2) Dissolve polydimethylsiloxane (PDMS) in n-heptane, add TESPTS functionalized SiO2, and add water, 3.7% dilute hydrochloric acid, and organosilicon precursor 1,2-bis(triethoxysilyl)ethane (BTESE) during stirring to prepare tetrasulfide functionalized PDMS-BTESE organosilicon composite sol; (3) The organic silicon composite sol is coated on a carrier and calcined to obtain the organic silicon composite film.

5. The method according to claim 4, characterized in that In step (1), the template is one of cetyltrimethylammonium bromide (CTAB), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (Pluronic P123), and polyoxyethylene polyoxypropylene ether (Pluronic F127).

6. The method according to claim 4, characterized in that In step (1), the molar ratio of the template, TEOS, TESPTS, water and dilute hydrochloric acid is 0.1-0.5:5-7:5-3:30-120:0.4`0.

8.

7. The method according to claim 4, characterized in that In step (1), the reaction conditions are temperature 25-40° C., time 0.5-1 h, aging temperature 60-80° C., time 12-24 h.

8. The method according to claim 4, characterized in that In step (2), the molecular weight of PDMS is 20,000 to 40,000.

9. The method according to claim 4, characterized in that In step (2), the molar ratio of TESPTS-functionalized SiO2, PDMS and BTESE is 1-2:5-1:5-9; and the molar ratio of water, dilute hydrochloric acid (3.7%) and BTESE is 30-120:5.4-16.2:

1.

10. The method according to claim 4, characterized in that In step (3), the roasting temperature is 100-150° C., and the roasting times are 1-5 times.

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