Study On Synthesization Of Tetra-2-ethylhexyl Pyromellitate Catalyzed By Solid Superacid

Tetraoctyl pyromellitate tetra-2-ethylhexyl pyromellitate (TOPM) was synthesized from pyromellitic dianhydride and isooctyl alcohol over the solid superacid. The catalyst SO₄^2-/TiO₂-Al₂O₃ was prepared, and the catalyst La-SO₄^2-/TiO₂-Al₂O₃ was prepared modified by loading La. The catalytic activity of the catalysts towards synthesizing TOPM is studied. Furthermore, the catalysts were characterized by XRD, BET, IR, NH3-TPD, TG and DES. The correlation between their structure and catalytic activity was also investigated.Above all, synthesis of TOPM from pyromellitic dianhydride and isooctyl alcohol over the solid acid SO₄^2-/TiO₂-Al₂O₃ was studied. The preparation conditions such as mole ratio of Ti/Al, concentration of H2SO4 and calcinations temperature have great influence on catalytic activity of SO₄^2-/TiO₂-Al₂O₃. The optimum preparation conditions are: mole ration of Ti/Al 1:0.3, concentration of H₂SO₄ 0.5mol·L^-1, calcinations temperature 400 ℃ By orthogonal design, optimum reaction conditions were obtained. The optimum reaction conditions are: amount of catalyst 1.8% (relative to the weight of pyromellitic dianhydride), reaction time 3h, and mole ratio of isooctyl alcohol/pyromellitic dianhydride 7:1. Under the optimum conditions, the conversion of the pyromellitic dianhydride is up to 99.6%. The use life of catalyst was studied. After being used seven times, the catalytic activity reduces to 96.5%. It is found that crystallization of TiO₂ is hold back with the addition of Al from the XRD pattern. It was found organic sulfates SO₄^2- predominated on catalyst surface from IR pattern. The surface areas of catalysts were studied. The results show that SO₄^2-/TiO₂-Al₂O₃ have more surface areas than SO₄^2-/TiO₂. It is found from the TG and EDS pattern that the SO₄^2- in SO₄^2-/TiO₂-Al₂O₃ begin to decompose at higher temperature than that of SO₄^2-/TiO₂ samples, and that the sample containing Al retained higher amount of sulfur than the sample not containing Al. NH3-TPD pattern showed that both the strength and the acid amount were increased with the addition of 23.1 %(mole fraction) Al.In order to improve the catalytic properties, La-SO427TiO2-Al2O3 was prepared by Loading La on TiCVAbOa. After be treated by La(NC>3)3 which concentration is 0.07 mol-L'1, the catalysts prepared in wide range of preparation conditions have great catalytic activity. The range of concentration of H2SO4 is from 0.3 to 0.7 mol-L'1, The range of calcinations temperature is from 400 °C to 600 °C. By orthogonal design, optimum reaction conditions were obtained. The optimum reaction conditions are: amount of catalyst 2.7%, reaction time 2h, and mole ratio of isooctyl alcohol/pyromellitic dianhydride 6:1. Under the optimum conditions, the conversion of the pyromellitic dianhydride is over 99.9%. After being used seven times, the conversion of pyromellitic dianhydride can still reach 98.3%. FTIR test demonstrates the selectivity of the catalyst is good. EDS and TG shows that the loading of La not only improved the ability to stabilize sulfur but also increase the content of sulfur on catalyst surface. NH3-TPD shows that both the strength and the acid amount of acid site were increased. Loading La had no remarkable effect on surface area and crystal form of catalyst respectively from BET test and XRD characterization. As a result, the content of sulfur and the acid site play key role in synthesis of TOPM.