Synthesis Of Tri-n-butyl Citrate Using Supported Zirconium Sulfate

As one kind of plasticizer, phthalate (or phthalate ester) accounts for the biggest market share with its popular use. It is reported that phthalate has some toxicity and may cause cancer. Therefore, production of tri-n-tutyl citrate (TBC), which doesn't possess any toxicity, attracts people's concern. At present, the traditional ways of synthesizing TBC shows disadvantages, such as environment containment, energy cost. Thus, searching for environmentally friendly catalyst is significant. Since it is report that Zr(SO4)2·4H2O has been used as catalyst for esterification of carboxylic acids, such as oleic acid, caparic acid and other fatty acids with different chain length (C4-C18), it opens a new way to the synthesis of tri-n-butyl citrate.In this paper, zirconium sulfate supported onγ-Al2O3, HZSM-5, HY, HMS or MCM-41 was prepared by impregnation method and the catalysts were used to catalyze the synthesis of tri-n-butyl citrate. The catalysts were characterized by XRD, UV-vis, SEM, TEM, TG and pyridine-FTIR spectroscopy techniques. The effects of kind of support, zirconium sulfate loading weight and calcination temperature were studied. The results showed that zirconium sulfate supported on HMS or MCM-41 exhibits better catalytic performance in synthesis of tri-n-butyl citrate. Under optimized reaction conditions, using 40 wt% Zr(SO4)2·4H2O/HMS calcined at 180℃as catalyst, esterification rate of citric acid and yield of tri-n-butyl citrate were 92.8% and 92.3%, respectively.The reuse of 40 wt% Zr(SO4)2-4H2O/HMS was studied in the synthesis of tri-n-butyl citrate. The catalytic activity was not recovered after being washed by different solvents. The spent catalyst was analysed by pyridine-FTIR, TG and ICP-OES. It has shown that the complexation of citric acid results in the leaching of Zr during the esterification, which reduced active sites and decreased the catalytic activity. TBC molecules are difficult to diffuse out from the pores of 40 wt% Zr(SO4)2-4H2O/HMS or being washed away completely, which is also a reason for catalyst deactivation.