Studies On Modification Of Solid Super Acid SO₄～(2-)/TiO₂ And Synthesis Of Tri-n-butyl Citrate With The Catalyst

Tri-n-butyl citrate(TBC) was synthesized with solid super acid as catalyst, and the catalytic properties of the catalyst SO42VTiO2 in esterification of citric acid with n- butanol were studied. A new catalyst Tm-S04%扵i02 was prepared by modification on which the rare earth element Tm was loaded. The correlation between its structure and properties was also investigated. All these above strongly support the industrialization of TBC synthesis catalyzed by solid super acid. This paper reported the esterification synthesis of TBC under no catalyst, H2S04, or solid super acid SO421TiO2. The correlation between reaction conversion, water yield and reaction time was surveyed. The effects of initial molar ratio and catalyst quantity were investigated and the optimum synthesis conditions were found. Tri-n-butyl citrate was synthesized with solid super acid S042]T102 as catalyst, and the activity and stability of the catalysts in esterification of citric acid with n-butanol were studied. The effects of (NH4)2S04 quantity and calcination temperature on the catalysts were studied and the correlation between their structure and properties was also investigated. The results showed that (NH4)2S04 was better than H2S04 as promoter. The catalytic selectivity amounted to 99% while 20% (NH4)2S04 added and 6000C calcinated. On this condition the conversion of citric acid was 92.7%, and the ester yield was 92.3%. The formation and growth of anatase crystalline phase was the key factor in the improvement of catalytic selectivity. The deactivation of catalysts in TBC synthesis resulted from the carbon deposition and the loss of S042. In order to improve catalytic properties, Tm-SO421TiO2 was prepared by modification, the rare earth element Tm was loaded on SO421TiO2. Loading Tm effectively promoted catalytic stability, improved catalytic activity, and had no remarkable effect on catalytic selectivity. Tm-SO42VTiO2 presented good catalytic properties while 20% (NH4)2S04, 3% Tm added and 6000C calcinated. The conversion of citric acid was 94.4%, the catalytic selectivity was 99.2%, the ester yield was 93.6%, and the conversion of citric acid still amounted to 93.1% after five runs. The surface acidity and acid strength distribution, the phase structure, the state of surface SO42 and the mechanism of stability were analyzed and characterized by Hammett indicator, Py-TPD, XRD, JR. TG and DTA. The results showed that Tm-SO421TiO2 was solid super acid. 慣he phase structure remained after Tm loaded. Anatase crystalline phase formed and grew while the catalyst was calcinated from 400 to 600 揅. Raising calcination temperature led to the appearance of rutile crystalline phase. The catalyst existed two kinds of S042 ?III ? structures: chelating bidentate 5Q42 and organic sulfates. The latter predominated on the catalyst surface. Loading Tm lowered the acidity, adjusted acid strength distribution, decreased the carbon deposition of the catalyst and restrained the loss of S042. Therefore the stability of the catalyst could be improved effectively.