Study Of The Catalyst And Technology For Selective Hydrogenation Of C4 Alkyne Fractions

Technology for selective hydrogenation of C4 fractions alkyne hydrogenations used catalyst with high selectivity for removing a little of alkyne hydrogenations from C4 fractions in order to purify 1,3-butadiene. Technology for selective hydrogenation of C4 fractions alkyne hydrogenations was more advantage than traditional extractive distillation technology,so technology for selective hydrogenation was attached importance.The key technique for selective hydrogenation of C4 fractions alkyne hydrogenations was the development of higher selective catalysts.This thesis selected aluminum hydroxide modified by titanium as raw materials for preparation into support. It adopted volumetric impregnation method for preparing Pd/Al₂O₃-TiO₂ catalyst.The support and Pd/Al₂O₃-TiO₂ catalyst were characterized and evaluated of selective hydrogenation to determine Al₂O₃-TiO₂ as catalyst carrier.The alkali modified support was modified by impregnation and wet-mixing-kneading methods, and characterized by BET, XRD, NH3-TPD,Py-IR techniques. Results showed that the pore volume, average pore size and most probable pore size of support was modified by wet-mixing-kneading method were all bigger than support modified by impregnation method, the acidity and acid strength were least. The support which modified by wet-mixing kneading was more suitable as selective hydrogenation catalyst support than the support which modified by impregnated method.The effect of preparation conditon such as pH value,concentration of impregnation liquid,impregnation time and calcination condition on Pd/Al₂O₃-TiO₂ catalyst performance was studied.It determined that the optimum preparation method of Pd/Al₂O₃-TiO₂ catalyst was impregnation liquid pH=2, concentration of impregnation liquid was 0.2(wt%), impregnation time was 10min and calcination temperature was 500℃. Different assistants were added to study the effects on the physicochemical properties of Pd-M/Al₂O₃-TiO₂ bimetal catalyst,crystal size of Pd catalyst and hydrogenation activity.The results implied that the alkyne conversion rate of Pb modified catalyst decreased but the selectivity got much better;nevertheless,the alkyne conversion rate of Cu,Ag and Au modified catalyst increased obviously.It showed that the activity of catalysts improved while the selectivity of butadiene became worse than Pd /Al₂O₃-TiO₂ catalyst.The optimum process conditions of Pd-Cu/Al₂O₃-TiO₂ catalyst for the carbon four fractions selective hydrogenation were determined by investigating the effect of technological conditions on the hydrogenation activity and selectivity of catalysts. The optimum reaction temperature was 40℃, pressure was 1.5MPa, hydrogen alkyne ratio was1.5:1, liquid hourly space velocity was 8.0h^-1.