Support ionic liquid-heteropolyacid hybrid on mesoporous carbon aerogel with a high surface area for highly efficient desulfurization under mild conditions
Graphical abstract
Introduction
In recent years, the heavy use of traditional energy has caused a series of serious environmental problems [1,2]. The haze, as one of the serious environmental pollution problems, has attracted extensive attention from social and scientific research workers [3]. One of the main causes of haze is the burning of sulfur-containing fuel oil [4]. So, deep desulfurization of fuel to produce sulfur-free fuel is an important means to protect the environment [5]. At present, the mainstream technology has two types: hydrodesulfurization (HDS) and non-hydrodesulfurization. Hydrodesulfurization technology is widely used in refinery because of its high efficiency in desulfurization [6]. But, due to its limitations such as rigorous operation conditions and huge instrument investment, it is gradually replaced by non-hydrodesulfurization in industrial applications [7,8]. Non-hydrodesulfurization technology mainly includes oxidative desulfurization, biodesulfurization, adsorption desulfurization and extraction desulfurization [[9], [10], [11], [12]]. Oxidation desulfurization technology can oxidize sulfur compounds to corresponding sulfones using oxidant and catalyst under mild conditions, and then combine with adsorption desulfurization or extraction desulfurization to achieve the purpose of deep desulfurization [13,14]. Thus, in this work, we choose the extraction-oxidation method to desulfurize the sulfur compound in model fuel.
Many studies have found that organic-inorganic hybrid materials based on heteropoly acid show excellent catalytic performance in the oxidation desulfurization process due to the hydrophobic distribution contributed to organic group can reduce the mass transfer resistance and accelerate the reaction speed. Rui Wang and co-workers have reported the H2S removal with molecular oxygen as oxidant with the hybrid material catalyst in ionic liquid solutions. The result shows that the H2S with concentration of 2000 mg/m3 can be totally oxidized and removed at 200 °C, and the system has perfect regeneration ability at 200 °C [15]. Cong-Xia Xie and co-workers have prepared organic-inorganic heteropoly acid with superior catalytic activity for olefinic alkylation of thiophenic sulfur (OATS), and the conversions of thiophene (T), 2-methyl thiophene (2-MT), and 3-methyl thiophene (3-MT) catalyzed by [Bmim]H2PW12O40 all can nearly reach up to 100% under the optimal reaction conditions [16]. The hybrid materials, as homogeneous catalysts, have good activity, but they are difficult to recover from solution. To overcome the problem of recycling, the design and preparation of supported catalysts based on organic-inorganic hybrid material have attracted researchers' attention [[17], [18], [19]]. Xuan NuiPham and co-workers have introduced the HPW into H2N-SBA-15 by chemical bond, and the dibenzothiophene (DBT) can be completely removed after 120 min with H2O2 as oxidant [20]. Ivan V.Kozhevnikova and co-workers have immobilized the polyoxometalate on the surface of alkylaminophosphazene (RPN)-functionalized silica as catalyst for oxidative desulfurization of DBT in a biphasic system composed of heptane and aqueous 30% H2O2, the result shows that the most effective catalyst, PMo/BzPN-SiO2, exhibited 100% removal of DBT from model fuel at under mild conditions and could be reused without loss of activity [21]. Although the organic-inorganic hybrid based heterogenous catalyst shows good potential in fuel desulfurization, it still has some defects in application, such as the agglomeration and leaching of active components. The aggregation and leaching of the active components in the catalytic process can be reduced by selecting the appropriate carrier and load of the active components. At the same time, high specific surface area of supporter has a positive effect on the activity of the catalyst. Hence, it is important to prepare supported catalyst with large specific surface area and suitable loading amount by an appropriate synthesis method.
In this work, a kind of supported materials based on organic-inorganic hybrid was designed and prepared by simple one-pot procedure, aiming to improve the activity and reusability of the catalyst. The target products were confirmed via multiple representations and then used for extraction-oxidation desulfurization (EODS) with molecular oxygen as oxidant and DMF as extractant.
Section snippets
Materials and instruments
The materials including 4-Vinylpyridine (4VP), bromoethane, 1-bromobutane, 1-bromohexane, 1-bromooctane, 1-bromodecane, m-dihydroxybenzene, sodium carbonate and thiophene were purchased from Aladdin and used in this work without further purification. The organic solvent used in this work, such as methyl alcohol, formaldehyde (37%), dimethyl formamide (DMF), ethyl acetate and acetone, was bought from supplier.
The element contents of samples were analyzed on element analyzer (PE2400) and
ICP-AES analysis
In order to determine the loading amount of [CnVP]MoV, the supported catalysts are tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES) (Table S1). The result shows that loading amount of the active components of different catalysts is slightly different.
FT-IR analysis
The FT-IR spectra of [CnVP]Br, HMoV, [C6VP]MoV and [CnVP]MoV/CA are presented in Fig. 1. In Fig. 1a, the characteristic peaks of pyridine ring of [CnVP]Br are showed at 3020.5, 1463.1, and 1635.7 cm−1, which corresponding
Conclusions
A series of organic and inorganic hybrid materials based on N-alkyl-4-vinylpyridinium bromide and Dawson heteropoly acid were synthesized via ion exchange reaction. Then the hybrid materials were loaded on the CA with a high surface area of 1448.26 m2/g and used for extraction-oxidation desulfurization. Among all catalysts, [C6VP]MoV/CA possesses the highest efficiency of 99.63% under the optimum conditions. п-п interaction between pyridine ring and thiophene and lipophilicity of appropriate
CRediT authorship contribution statement
Yan Gao: Conceptualization, Methodology, Investigation, Writing - original draft, Writing - review & editing. Zhe Liu: Software, Validation, Formal analysis. Ruimin Gao: Formal analysis, Methodology, Investigation. Guangfa Hu: Resources, Data curation. Jianshe Zhao: Software, Validation, Formal analysis, Supervision, Funding acquisition, Resources.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank the National Natural Science Foundation of China (Nos. 21671157, 21371143 and 21501139) for the financial support. And the authors thank the China scholarship Council (No. 201906970032) for the financial support.
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