Preparation, Characterization And Application In Esterification Of Solid Superacid

With Green Chemistry being advocated, the brand-new concept of green catalyst has been brought forward recently. Solid superacid has many advantages such as high activity, well selectivity, and no corrosiveness, no pollution, and liability to be separating from the reaction material. A green industrial catalyst is helpful to recycling and possesses wide prospect of application. Thus, research on solid superacid has drawn more and more attention in industrial catalyst field.In this paper, we recounted the recent development of solid superacids and their appliance in esterification. Solid superacid catalyst was prepared by sol-gel method; its catalytic activity was investigated to synthesis of n-butyl acetate. The acid strength and structures of solid superacid catalyst was research. The whole process is divided into two parts that are as follow:1. Preparation, characterization and application of solid superacid SO₄^2-/SnO₂ and SO₄^2-/SnO₂-CeO₂(1) The examination of catalytic preparation and property. By uniform design, we have educed SO₄^2-/SnO₂ catalytic best preparative conditions: concentration of impregnating solutions is 3mol/L, calcining temperature is 550℃and calcining time is 3 h. The optimum conditions for the preparation of solid superacid SO₄^2-/SnO₂-CeO₂ are content of CeO2 3mol %, concentrations of impregnating solutions 2 mol/l, calcining temperature 600℃and calcining time 3 h. The temperature of calcine is the maximal influencing factor for catalytic activity of catalysts.(2) We investigated catalytic physical properties by some analytical methods, such as Hammett indicator, IR, TG-DTA and BET. Then we drew a conclusion the maximal acid strength of SO₄^2-/SnO₂ and SO₄^2-/SnO₂-CeO₂ solid superacid catalyst is -13.80. The acid centre mode of SO₄^2-/SnO₂ and SO₄^2-/SnO₂-CeO₂ is chelate structure.(3) By discussing the mechanism of catalytic losing activity. We have concluded that the main losing activity reason of SO₄^2-/SnO₂ solid superacid catalysts used in synthesis of n-butyl acetate is the accumulated carbon of catalytic surface and the loss of SO₄^2-. The loss of SO₄^2- is the main losing activity reason of SO₄^2-/SnO₂-CeO₂.(4)The catalyst SO₄^2-/SnO₂-CeO₂ was applied in the esterification synthesis of Tri-n -butyl citrate(TBC)and terpinyl acetate. We discussed the influence factors of the reactions, found out the best reaction condition. The catalyst SO₄^2-/SnO₂-CeO₂ show the good catalytic activity and selectivity.2. Preparation and characterization of solid superacid SO₄^2-/TiO2-SnO₂(1) We examined the catalytic preparation and property. By sol-gel method, we have educed SO₄^2-/SnO₂ catalytic best preparative conditions: mole ratio of titanium and tin is 3∶1, concentration of the impregnating solutions is 3mol/l, calcining temperature is 550℃and calcining time is 3 h.(2) We investigated catalytic physical properties by some analytical methods, such as Hammett indicator, IR, TG-DTA and BET. Then we drew a conclusion: SO₄^2-/SnO₂ and SO₄^2-/SnO₂-CeO₂ solid superacid catalyst had high acidity. The acid centre mode of SO₄^2-/SnO₂ and SO₄^2-/SnO₂-CeO₂ is chelate structure. The catalyst surface SO₄^2- chelated by a bidentate ligand structure together with the carrier. Loading SnO₂ has greater effect on SO₄^2-/TiO2-SnO₂. It was favorable to delay the crystallization temperature of TiO2. The surface of catalyst SO₄^2-/TiO2-SnO₂ we have prepared by sol-gel-impregnation method was far larger than that of by co- precipitation-impregnation method.(3) We discussed the mechanism of catalytic losing activity. We have concluded that loading SnO₂ stabilized SO₄^2-, and restrained the loss of SO₄^2-. Therefore, it prolonged catalyst life and improved the stability. The main losing activity reason of SO₄^2-/TiO2-SnO₂ solid superacid catalysts used is absorption of organic substances and carbon depositions on the catalyst surface during the reaction.