CN115957716B - Ag2O/SiO2@imprint composite aerogel adsorbent and preparation method and application thereof - Google Patents

Abstract

The invention discloses an _Ag2O / _SiO2 @imprint composite aerogel adsorbent and a preparation method and application thereof, which are used for removing thiophene sulfides in fuel oil and aromatic products. The specific steps are as follows: dissolving thiophene compounds with n-heptane to form a template solution, dissolving silver nitrate in water, adding tetraethyl orthosilicate and anhydrous ethanol as polar solutions, adding the template solution as a non-polar solvent, stirring under acidic conditions to form microdroplets, obtaining an _Ag2O / _SiO2 @imprint sol containing a microdroplet template, adjusting the pH of the silica sol and allowing the gel to stand, then performing an aging treatment, crushing the sol, washing with n-hexane to remove the microdroplet template, and drying at normal pressure to obtain an _Ag2O / _SiO2 @imprint composite aerogel. The adsorbent prepared by the invention has better adsorption performance than the _Ag2O / _SiO2 composite aerogel prepared by a conventional method, and has good application prospects in the field of deep desulfurization of fuel oil and aromatic products.

Description

Ag2O/SiO2@imprint composite aerogel adsorbent and preparation method and application thereof

Technical Field

The invention belongs to the technical field of material preparation and processing, and specifically relates to an Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent and a preparation method and application thereof.

Background Art

Sulfides such as thiophene (TP), benzothiophene (BT), and dibenzothiophene (DBT) in fuel oil will produce SO _x after combustion, which will cause damage to various ecosystems and human health problems, and is also one of the key causes of smog and acid rain. Aromatics are important basic raw materials for the petrochemical industry. The main products include benzene, xylene, etc. The largest use of benzene is to produce cyclohexane, styrene and phenol; p-xylene is the largest in xylene and is the main raw material for manufacturing polyethylene terephthalate plastics (PET) and polyester fibers. Aromatics mainly come from catalytic reforming and thermal cracking of petroleum hydrocarbons. Sulfides in crude oil will be transferred to aromatic products, which will cause environmental pollution during the use of aromatics and poison the catalysts in the subsequent processing of aromatics. Fuel and aromatic desulfurization has become an important research topic in petrochemicals.

Catalytic hydrodesulfurization (HDS) is a common method for reducing sulfides in fuel. This technology requires higher reaction pressure and lower space velocity to reduce the sulfur content in fuel oil, which increases production costs. Secondly, the consumption of large amounts _{of H2} also leads to increased operating costs and is accompanied by the production of toxic gases ( _H2S ). In view of this, the development of non-hydrodesulfurization methods has become a research hotspot. Among the different alternative processes such as biological desulfurization, adsorption desulfurization, extraction desulfurization, and oxidative desulfurization, adsorption desulfurization (ADS) is a low-cost alternative to HDS. Due to its advantages such as low equipment investment, mild operating conditions, and environmental friendliness, this technology is currently being widely studied in the scientific field.

Adsorption desulfurization technology is to selectively remove sulfides from fuel by adsorption through the selection of suitable adsorbents. The desulfurization efficiency of ADS is highly dependent on the type of adsorbent. Various types of adsorbents, including metal oxides, zeolite molecular sieves, MOFs, activated carbon and aerogel materials, have been evaluated for simulating fuel desulfurization. Among them, aerogel is a mesoporous material with a three-dimensional network structure formed by the mutual aggregation of nano-scale colloidal particles. It has physical properties such as high specific surface area and high porosity, and has been widely studied as a catalyst and adsorbent carrier.

In some previous studies, Zhejiang University of Technology (publication number CN 106590728 A), (publication number CN105709685 A), (publication number CN 108893138 A) prepared _SiO2 composite aerogels by doping metal ions such as Zr ⁴⁺ , Ag ⁺ , Co ⁺ , Cu ⁺ , and Al ^3+, which can have a good adsorption effect on thiophene sulfides in fuel oil, among which the silver-doped silica aerogel has the best adsorption performance. Although the doping of transition metal ions has improved the performance of the adsorbent, there are certain limitations. For example, the pore distribution of the aerogel adsorbent is wide and the shape is irregular, which affects the diffusion of the adsorbate. In addition, during the preparation of the aerogel, some adsorption active sites are buried and cannot be fully exposed, making it difficult to contact with thiophene compounds, resulting in poor adsorption performance.

Summary of the invention

Aiming at the defects of the Ag ₂ O/SiO ₂ composite aerogel desulfurization adsorbent prepared by the conventional method, the present invention aims to provide an Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent and its preparation method and application. The method uses n-heptane in which thiophene compounds are dissolved as a template solution, which is a non-polar solution. When added to a polar solution composed of tetraethyl orthosilicate, ethanol and water, it is immiscible and forms tiny droplets under high-speed stirring. The tiny droplets act as template directing agents in the sol-gel process, making the pores in the sol-gel skeleton regular. Thiophene compounds dissolved in non-polar n-heptane can be regarded as amphoteric substances. The aromatic groups of thiophene compounds are non-polar and face the inside of n-heptane microdroplets, while the S atoms in thiophene compounds are weakly polar and tend to be distributed on the surface of n-heptane microdroplets. In the sol-gel process, the S atoms in thiophene can form hydrogen bonds with -Si-OH and S-Ag bonds with Ag ⁺ , and guide -Si-OH and Ag ⁺ to aggregate on the surface of microdroplets. -Si-OH and Ag ⁺ are adsorption active sites for thiophene compounds. When washed with non-polar solvent n-hexane and the microdroplet template is removed, these adsorption active sites are enriched on the inner surface of the pores and fully exposed. Therefore, the composite aerogel prepared by the microdroplet template method can improve the regularity of the pores to improve the diffusion performance of the adsorbate. In addition, the adsorption active sites can be enriched on the inner surface of the pores, thereby effectively improving the adsorption performance of the adsorbent.

The specific technical solutions are as follows:

A method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent, wherein the composite aerogel is prepared by using a micro-droplet template method based on a sol-gel combined with a normal pressure drying method. The specific preparation steps can be divided into:

1) preparing a micro-droplet template solution: dissolving a thiophene compound in n-heptane to form a template solution;

2) preparing a gel containing a microdroplet template: dissolving a silver source in water, adding anhydrous ethanol and a silicon source, and then adding the template solution obtained in step 1), stirring under acidic light-proof conditions to hydrolyze the solution, adjusting the pH of the sol, and gelling the sol to obtain a composite alcohol gel;

3) Aging: adding an aging solution consisting of ethanol and tetraethyl orthosilicate to the composite alcohol gel prepared in step 2), and performing water bath aging to strengthen its skeleton structure;

4) Removing the microdroplet template: adding n-hexane to the gel obtained in step 3) and stirring three times;

5) Drying: The composite alcohol gel obtained in step 4) is dried under normal pressure to finally obtain Ag ₂ O/SiO ₂ @imprint composite aerogel.

Furthermore, in step 2), tetraethyl orthosilicate is used as the silicon source and silver nitrate is used as the silver source.

Furthermore, in step 1), the thiophene compound is thiophene, benzothiophene or dibenzothiophene.

Furthermore, in step 1), the concentration of thiophene compounds in the n-heptane solution is 2 mg-S/g.

Furthermore, the molar feed ratio of silver nitrate to tetraethyl orthosilicate is 1:50, and the volume feed ratio of the total volume of ethanol and water to the template solution is 12:0.5-5, preferably 12:1.

Furthermore, in step 2), the rotation speed during the gel formation process is 200 to 1200 r/min, preferably 800 r/min.

Furthermore, the volume ratio of anhydrous ethanol to tetraethyl orthosilicate in the aging solution in step 3) is 25:15.

An Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent prepared by the method.

An application of the Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent, the specific operation steps are as follows:

The obtained adsorbent was loaded into an adsorption bed device, and simulated fuel oil and simulated aromatic hydrocarbons containing thiophene compounds were introduced into the adsorber device at a space velocity of 2 h ^-1 for adsorption.

Furthermore, the simulated fuel oil is composed of n-heptane in which thiophene sulfides are dissolved; and the simulated aromatic hydrocarbon product is composed of benzene or p-xylene in which thiophene compounds are dissolved.

The beneficial effects of the present invention are as follows:

1) The micro-droplet template method proposed by the Ag ₂ O/SiO ₂ @imprint desulfurization adsorbent of the present invention uses the micro-droplets formed by stirring n-heptane in a polar solvent in which thiophene compounds are dissolved as templates, and the Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent modified by doping with Ag ⁺ is used to regularize the pores and guide the adsorption active sites to be enriched on the inner surface.

2) Compared with the desulfurization adsorbent prepared by conventional methods, the Ag ₂ O/SiO ₂ @imprint composite aerogel of the present invention not only improves the utilization rate of silver, but also avoids the energy consumption problem caused by heating during the desulfurization process.

DETAILED DESCRIPTION

The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

Examples 1-5: Effect of the total volume of ethanol and water to the volume ratio of the added thiophene micro-droplet template solution on the adsorption performance of thiophene sulfides in simulated fuel by Ag ₂ O/SiO ₂ @imprint composite aerogel.

Example 1: When the total volume of ethanol and water and the volume ratio of the added thiophene micro-droplet template (n-heptane solution of dissolved thiophene) are 12:0.5, the Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent prepared by the micro-droplet template method has the following preparation steps:

1) Dissolve thiophene in n-heptane to prepare a mixed solution with a concentration of 2 mg-S/g, which is used as a microdroplet template solution.

2) Dissolve 0.12 g of silver nitrate in 2 ml of deionized water, add 10 ml of anhydrous ethanol and 8 ml of tetraethyl orthosilicate, take 0.5 ml of the template solution prepared in step 1) and add it to the mixed solution, adjust the pH of the solution to 1.8-2.0 with 10% nitric acid, and stir at 800 r/min for 1.5 h to hydrolyze;

3) Add 5% ammonia water to the silica sol obtained in step 2), adjust the pH of the solution to about 6.8, and let it stand for 15 minutes to obtain a composite alcohol gel.

4) Add 25 ml of anhydrous ethanol and 15 ml of tetraethyl orthosilicate to the composite alcohol gel obtained in step 3), and place in a 40° C. water bath for aging for 15 hours to enhance the skeleton structure of the gel.

5) The alcohol gel aged in step 4) is crushed and washed with n-hexane. The n-hexane is replaced every 4 hours for 3 times to remove the microdroplet template solution, ethanol, water and other organic molecules in the pores of the gel.

6) The gel obtained in step 5) was dried at 120° C. under normal pressure for 12 h to finally obtain Ag ₂ O/SiO ₂ @imprint composite aerogel.

Examples 2 to 5: The preparation steps are the same as those of Example 1, except that in step 2), the amount of the microdroplet template added in Example 2 is 1 ml, the amount of the microdroplet template added in Example 3 is 2 ml, the amount of the microdroplet template added in Example 4 is 3 ml, and the amount of the microdroplet template added in Example 5 is 5 ml, so that the volume feed ratio of the total volume of ethanol and water to the added microdroplet template solution in Examples 2 to 5 is 12:1, 12:2, 12:3, and 12:5, respectively.

Comparative Example 1: The preparation method is the same as that of Example 1, except that the micro-droplet template solution prepared in step 1) is not required to be added in step 2).

Comparative Example 2: The preparation method is the same as that of Example 1, except that the template solution prepared in step 1) is a pure n-heptane solution.

In Examples 1 to 5 and Comparative Examples 1 to 2, simulated fuel and penetration adsorption experiments were used to evaluate the adsorption performance of Ag ₂ O/SiO ₂ @imprint composite aerogels for thiophene sulfides. The specific penetration adsorption experimental steps are as follows:

Fill the bottom of the glass tube with absorbent cotton, then add 1g of fresh adsorbent Ag ₂ O/SiO ₂ @imprint, and then add an appropriate amount of quartz sand on the adsorbent. Wet the filled adsorbent with n- ^heptane , and then pass simulated fuel (MF, simulated fuel composition: n-heptane + thiophene sulfide, thiophene sulfide is thiophene TP, benzothiophene BT or dibenzothiophene DBT, sulfur concentration is 2mg-S/g) at a space velocity of 2h -1. Collect the simulated fuel after adsorption at the lower end of the adsorber and perform chromatographic analysis. The breakthrough point is determined when the sulfur concentration in the effluent is 0.005mgS/g. The adsorption results are shown in Table 1.

Table 1 Summary of the performance of Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbents prepared in Examples 1-5 and Comparative Examples 1-2 on thiophene sulfides in simulated fuel oil

As can be seen from Table 1, as the volume feed ratio of the total volume of ethanol and water to the micro-droplet template solvent decreases (the amount of micro-droplet template solution increases), the penetration adsorption capacity of the Ag ₂ O / SiO ₂ @imprint composite aerogel for thiophene compounds first increases and then decreases. When the feed ratio (volume ratio) of the total volume of ethanol and water to the added thiophene micro-droplet template is 12:1, the penetration adsorption capacity for thiophene compounds reaches the maximum. Compared with Comparative Example 1 in which no template solution is added, the adsorption effect of the Ag ₂ O / SiO ₂ @imprint composite aerogel on thiophene compounds is better, which is attributed to the addition of the micro-droplet template making the pores in the aerogel skeleton more regular, thereby improving the diffusion performance of the adsorbate. In addition, the S atoms in the thiophene compound in the micro-droplet template can guide the adsorption active sites such as -Si-OH and Ag ⁺ to enrich on the inner surface of the aerogel skeleton and fully expose them, thereby improving the adsorption capacity. The adsorbent prepared with pure n-heptane as the microdroplet template in Comparative Example 2 can only make the pore regularity more regular, while n-heptane containing thiophene sulfide as the microdroplet template in Examples 1 to 5 not only makes the pore regularity more regular, but also guides -Si-OH and Ag ⁺ to aggregate on the surface of the microdroplet, thereby effectively improving the adsorption performance of the adsorbent.

Examples 6-7: Effects of different micro-droplet template compositions on the adsorption performance of thiophene sulfides by Ag ₂ O/SiO ₂ @imprint composite aerogels.

Example 6: The preparation method is the same as that of Example 2, except that the template solution selected in step 1) is a benzothiophene solution dissolved in n-heptane.

Example 7: The preparation method is the same as that of Example 2, except that the template solution selected in step 1) is a dibenzothiophene solution dissolved in n-heptane.

The evaluation method of the adsorbent prepared in Examples 6 to 7 is the same as that of Examples 1 to 5. The specific results are shown in Table 2.

Table 2 Effect of different micro-droplet template compositions on the adsorption performance of thiophene sulfides on Ag ₂ O/SiO ₂ @imprint composite aerogels

As can be seen from Table 2, the penetration adsorption capacity of thiophene, benzothiophene and dibenzothiophene in simulated fuel oil in Ag ₂ O / SiO ₂ @imprint composite aerogels prepared by adding different micro-droplet template solutions is different. Among them, when thiophene is dissolved in n-heptane as a micro-droplet template, the penetration adsorption capacity of thiophene, benzothiophene and dibenzothiophene in TP-Ag ₂ O / SiO ₂ @imprint composite aerogel is the highest, which may be attributed to the fact that thiophene molecules are smaller than benzothiophene and dibenzothiophene, and the number of thiophene molecules in micro-droplet templates of the same size is relatively large, which makes the aggregation degree of active sites such as -Si-OH and Ag ⁺ greater, thereby improving the adsorption capacity. Therefore, thiophene dissolved in n-heptane is preferably used as a micro-droplet template to prepare Ag ₂ O / SiO ₂ @imprint composite aerogel.

Examples 8-9: Adsorption performance of Ag ₂ O/SiO ₂ @imprint composite aerogel adsorbent prepared by micro-droplet template method on thiophene compounds in simulated aromatic products. The adsorbent used is the same as that in Example 2.

Comparative Examples 3-4: Adsorption performance of Ag ₂ O/SiO ₂ composite aerogel adsorbent prepared by conventional sol-gel method on thiophene compounds in simulated aromatic products. The adsorption results are shown in Table 3.

Table 3 Adsorption performance of the adsorbents prepared in Examples 8-9 and Comparative Examples 3-4 for thiophene compounds in simulated aromatic products

It can be seen from Table 3 that compared with the Ag ₂ O / SiO ₂ composite aerogel desulfurization adsorbent prepared by the conventional method, the Ag ₂ O / SiO ₂ @imprint composite aerogel desulfurization adsorbent prepared by the droplet template method has a better adsorption effect in aromatic hydrocarbons, which further illustrates that the aerogel prepared by the micro-droplet template method can improve the regularity of the pores to improve the diffusion performance of the adsorbate. In addition, the adsorption active sites can be enriched on the inner surface of the pores, thereby effectively improving the adsorption performance of the adsorbent.

Examples 10-13: Effect of rotation speed during the sol process on the adsorption performance of thiophene sulfides by Ag ₂ O/SiO ₂ @imprint composite aerogel prepared by micro-droplet template method.

The preparation steps are the same as those of Example 2, except that after the microdroplet template is added in step 2), the rotation speed of Example 10 during stirring is 200 r/min, the rotation speed of Example 11 is 500 r/min, the rotation speed of Example 12 is 1000 r/min, and the rotation speed of Example 13 is 1200 r/min.

The evaluation method of the adsorbents prepared in Examples 10 to 13 is the same as that of Examples 1 to 5. The specific results are shown in Table 4.

Table 4 Effect of rotation speed during the sol process on the adsorption performance of thiophene sulfides by Ag ₂ O/SiO ₂ @imprint composite aerogel prepared by microdroplet template method

It can be seen from Table 4 that with the increase of the rotation speed, the penetration adsorption capacity of thiophene, benzothiophene and dibenzothiophene will first increase and then decrease. When the rotation speed is 800r/min, the penetration adsorption capacity of thiophene sulfide is the best, which may be attributed to the fact that the tiny droplets formed by the non-polar micro-droplet template after stirring and the three-dimensional network structure of the aerogel maintain the most stable state. Therefore, the preferred rotation speed is 800r/min.

Claims (10)

1. A method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent by micro-droplet template method, wherein the composite aerogel is prepared by micro-droplet template method based on sol-gel combined with atmospheric pressure drying method, characterized in that the specific preparation steps can be divided into: 1) Preparation of microdroplet template solution: dissolving thiophene compound in n-heptane to form template solution; 2) preparing a gel containing a microdroplet template: dissolving a silver source in water, adding anhydrous ethanol and a silicon source, and then adding the template solution obtained in step 1), stirring under acidic light-proof conditions to hydrolyze the solution, adjusting the pH of the sol, and gelling the sol to obtain a composite alcohol gel; 3) Aging: adding an aging solution composed of anhydrous ethanol and tetraethyl orthosilicate to the composite alcohol gel prepared in step 2), and performing water bath aging to strengthen its skeleton structure; 4) Removing the microdroplet template: adding n-hexane to the gel obtained in step 3) and stirring three times; 5) Drying: drying the composite alcohol gel obtained in step 4) at normal pressure to finally obtain Ag ₂ O/SiO ₂ @imprint composite aerogel; In step 1), the thiophene compound is thiophene, benzothiophene or dibenzothiophene; In step 1), the concentration of thiophene compounds in the n-heptane solution is 2 mg-S/g. 2. The method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 1, characterized in that in step 2), tetraethyl orthosilicate is used as silicon source and silver nitrate is used as silver source. 3. A method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 2, characterized in that the molar feed ratio of silver nitrate to tetraethyl orthosilicate is 1:50, and the volume feed ratio of the total volume of anhydrous ethanol and water to the volume of the template solution is 12:0.5~5. 4. The method for preparing _Ag2O / _SiO2 @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 3, characterized in that the volume feed ratio of the total volume of anhydrous ethanol and water to the volume of the template solution is 12:1. 5. The method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 1, characterized in that the rotation speed during the gel formation process in step 2) is 200-1200 r/min. 6 . The method for preparing Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 5 , characterized in that the rotation speed during the gel formation process in step 2) is 800 r/min. 7. The method for preparing _Ag2O / _SiO2 @imprint composite aerogel desulfurization adsorbent by micro-droplet template method according to claim 1, characterized in that the volume ratio of anhydrous ethanol to tetraethyl orthosilicate in the aging liquid in step 3) is 25:15. 8. An _Ag2O / _SiO2 @imprint composite aerogel desulfurization adsorbent prepared by the method according to claim 1. 9. An application of the Ag ₂ O/SiO ₂ @imprint composite aerogel desulfurization adsorbent as claimed in claim 8, characterized in that the specific operation steps are as follows: The obtained adsorbent was loaded into an adsorption bed device, and simulated fuel oil and simulated aromatic hydrocarbons containing thiophene compounds were introduced into the adsorber device at a space velocity of 2 h ^-1 for adsorption. 10. The use according to claim 9, characterized in that the simulated fuel consists of n-heptane that dissolves thiophene sulfides; and the simulated aromatic product consists of benzene or p-xylene that dissolves thiophene compounds.