| Sulfur dioxide, the primary components of atmospheric pollutants in our country, not only affect human health, but also is the main culprit for the formation of acid rain. In the traditional desulfurization process, the desulfurizing agent have a great deal of questions, for example, in the desulfurization process, many byproducts are produced and their harmless disposing and utilization of resources are very difficult, but there is a secondary pollution problems. Therefore, the development of new desulfurizing agent have becoming the focus of study. In recent years, ionic liquids due to their own good nature, has been widely applied on the investigation of new desulfurization agent.In this article, we systematically sort out the ionic liquids capable of absorbing SO2on the basis of the absorption properties. By analysis of structural properties of ionic liquids, the main factors affecting on the absorption capacity of ionic liquids for SO2are obtained, and then on this basis, design principle and related rules of ionic liquids with a high capacity for SO2absorption are proposed. A series of ionic liquids are synthesized and studied on the SO2absorption, are used to validated the proposed design rules and principles.The main results are listed as follows:1. The design rules and principles of ionic liquids for SO2absorptionTh major factors influencing the absorption capacity are functional groups(atoms with lone pairs of electrons in groups), acidity of anion corresponding acid, cation side chain length. On this base, the design rules and principles are proposed as follows:(1) The design of ionic liquids of physical absorption of SO2First, selecting the functional groups(the atom has a lone pair of electrons) with strong affinity for SO2and increaseing the number of functional groups in the structure of ionic liquid can significantly improve the absorption capacity of SO2; second, the acidity of anion corresponding acid is weaker, the absorption capacity of the corresponding ionic liquids for SO2is higher, but the acidity of anion corresponding acid must be stronger than sulfurous acid when the groups have chemical reaction with SO2, ionic liquid can show the physical absorption of SO2; moreover, after selecting anions and functional groups, increasing the length of the side chains of ionic liquid cations (to reduce the degree of cation symmetry) can also raise a small amount of ionic liquid SO2absorption capacity.(2) The design of ionic liquids of physical chemical absorption of SO2When this type of ionic liquids are designing, the structure of the ionic liquids must contain alkaline groups (such as NH2) with SO2chemical reaction, and the acidity of anion corresponding acid must be lower than the the acidity of SO2corresponding to sulfurous acid. Therefore, the selection of the groups that can be a chemical reaction with SO2play an important role in the design of this ionic liquids, the rest of the design rules and principles is similar to the design of ionic liquids of physical absorption of SO2.2. The validation of design rules and principlesIn this paper, we respectively synthesize ionic liquids of physical absorption of SO2containing three alkanolamine-based ionic liquids and two phosphate ionic liquids, and ionic liquids of physical chemical absorption of SO2containing two imidazolium ionic liquids and the mixture of alkanolamine-based ionic liquids and DBU to study the absorption SO2performance, then the proposed design rules and principles are validated. Experimental results show that, phosphate ionic liquid have higher SO2absorption capacity which is as high as2.8mole SO2per mole of IL; two imidazolium ionic liquids can absorb1.7mole SO2per mole of ILs; the alkanolamine-based ionic liquids can only absorb0.6mole SO2per mole of IL at most. Based on the analysis of structure of these ionic liquids, it can be drawn that the synthesized ionic liquids for SO2absorption performance is consistent with the proposed design of ionic liquids. |
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