Solid Acid In The Liquid Phase Catalytic Reaction

Liquid acid is known as an essential catalyst for the production of industrially important chemicals in the field of acid catalysis.However,liquid acid has several disadvantages such as costly and inefficient separation from products,unrecylable use of catalyst,great pollution to the environment and so on.In contrast,solid acids are recyclable,environmentally friendly,easy to be separated from product,which make the migration from liquid acid to solid acid is therefore a desirable goal.Many types of solid acids such as zeolite,mesoporous material,metal oxide,super solid acid,cation exchange resin have been widely used in many liquid acid-catalyzed organic reaction,but solid acid employed as the replacement of liquid acid is still rare in the practical application.Because the selection of solid acid need to consider not only the acid-catalyzed essence of the catalyst but also the properties of acid-catalyzed reaction.Especially for the liquid-phased organic reaction in the presence of water,the effect of water on the catalyst's acid site is necessary to be considered.In this work,a series of liquid-phase organic reactions such as alkylation of hydroquinone with tert-butanol,the esterification of succinic acid,the dehydration of ethyl acetate and the acylation of 1-Methoxynaphthalene are chosen,in which SnSO₄ and carbon-based solid acid were applied.In order to know the properties of catalysts and provide foundation for their application in other acid-catalyzed reactions,the catalytic performance and stability of these two catalysts under different reaction conditions were investigated and compared with that of MCM-49 and SO₄^2-/SNO₂.The general results are summarized as following:1,A series of SnSO₄ calcined at different temperature were applied in the alkylation of hydroquinone.stannous sulfate calcined at 350℃show the highest catalytic activity compared with MCM-49(20) and super solid acid such as SO₄^2-/SnO₂.The conversion of hydroquinone is 96%and the TBHQ yield is 65%after 4h at 150℃.The reusability of SnSO₄ is excellent,After three reaction cycles,the activity of SnSO₄ drops a little compared with the original value.The structural and acidity properties of the catalyst were characterized and found that the high activity was due to its hydrophobic surface on which the acid sites were not easy to be poisoned by water during the reaction.And the high reusability may result from the weak strength of its acid sites on which less tar or polymeric compounds would be formed by the side reactions and the difficulty of leaching of sulfur species in the surface of SnSO₄.Although the acid strength and amount of acid is higher than those of MCM49(20),but the catalytic activity is lower than SnSO₄.For SO₄^2-/SnO₂,its catalytic performance and stability are both lower than SnSO₄.2,SnSO₄ was applied into other organic reaction such as the dehydration of ethyl acetate,the acylation of 1-Methoxynaphthalene and the esterification of succinic acid.SnSO₄ shows different catalytic activity and stability in different organic reactions.SnSO₄ shows high catalytic activity in the dehydration of ethyl acetate and the esterification of succinic acid.The high activity was due to its hydrophobic surface on which the acid sites were not easy to be poisoned by water during the reaction,but the catalytic activity toward the acylation of 1-Methoxynaphthalene is low.The reusability of SnSO₄ in those reactions are poorer than that in the alkylation of hydroquinone.The results of XRF show that the deactivation of the catalyst is due to the leaching of sulfur species in the surface of stannous sulfate during the reaction,furthermore,the amount of such leaching differ in different reactions.Correlating the reaction result with the properties of the reactions,several conclusions were summarized:for the organic reaction in the presence of water,the more water participating,the more amount of sulfur species leaching during the reaction.For the real organic reaction,the amount of sulfur species's leaching will increase with the increasing of the polarity of solvent or reactant.3,Carbon-based solid acid(noted as C-SO₃H) is subjected to application in the alkylation of hydroquinone and the dehydration of ethyl acetate.The study results show that C-SO₃H is seriously deactivated in the alkylation reaction,which may due to the rigor of the reaction condition resulting in the leaching of sulphonite group in the surface of C-SO₃H.But for the organic reaction in the presence of water such as the dehydration of ethyl acetate under low reaction temperature,Although the leaching of sulphonite group still happened,the amount of leaching is small.In addition,the effect of temperature and solvent on the stability of C-SO₃H were investigated in order to know the using conditions and the range of application for the catalyst and provide foundation for extending its application in other acid-catalyzed reactions.