Study On The Preparation And Performance Of Cu/ZrO₂ Catalyst For The Dehydrogenation Of Diethanolamine

Cu/ZrO₂ catalyst was used in CO,CO₂ hydrogenation synthetic methanol, the degradation of hydrogen by methanol steam reforming, degradation of nitrogen oxides, the synthesis of amino acids from amino alcohol via dehydrogenation and cyclohexanol dehydrogenation to cyclohexanone etc. In the industrial production, the Cu/ZrO₂ catalyst prepared by traditional methods exist some disadvantages: large amount of catalyst wastage, fast deactivation, long reaction time, low reaction yield and selective. Therefore, optimization of catalyst preparation conditions is important.Based on a large number of literature investigations and theoretical analysis, with the help of co-precipitation, with copper nitrate and zirconium oxychloride solution, using 20% sodium hydroxide as the precipitant, the Cu/ZrO₂ catalyst was prepared, which was used for synthesis of iminodiacetic acid from diethanolamine via dehydrogenation. The optimal conditions of the preparation of Cu/ZrO₂ catalyst were obtained by orthogonal experiments and single factor experiments: n(Zr): n(Cu)=2:1, initial concentration of zirconium salt of 0.2 mol/L, step-feeding mode, precipitation end-point pH of 12, aging time of 5h, reduction time of 5 h. And, The optimal conditions of synthesis of iminodiacetic acid from diethanolamine via dehydrogenation: Mcatalyst∶Mdiethanolamine=1∶6, Nsodium hydroxide∶Ndiethanolamine=2.4∶1, reaction temperature of 165℃, reaction pressure of 1.2 MPa.The fresh Cu/ZrO₂ catalyst effect used for the dehydrogenation of diethanolamine was investigated, the reaction yield of iminodiacetic acid sodium was 90.21%, the reaction selectivity can reach 98.45%. Via using for repeating 10 times, the average reaction yield was 84.09%, the average reaction selectivity was 95.93%, and the one-way deactivation yield was 1%³%. The results can be included that it has a relatively stable catalytic activity and a long catalytic life.In addition, based on the potential titration analysis method, with the help of high performance liquid chromatographic method, analysis conditions of the dehydrogenation product were compared. As a result, the optimal conditions were obtained: strong anion exchange column (Hypersil SAX 5μm 4.6 mm×250 mm), mobile phase [ 0.1 mol/L (NH₄)₂HPO₄, adjusted pH=3 with phosphoric acid ], column temperature was 30℃, detection wavelength was 200 nm, flow rate was 1.0 mL/min, and the injection volume was 20μL, quota by the external standard method. And obtained the standard curve equation of iminodiacetic acid by HPLC analysis. Finally, the physical and chemical properties of catalysts were characterized by a series of modern instruments, such as: TG, TPR, BET, XRD and SEM analysis. The results show that: a BET surface area was 73.919 m2/g, the voids volume was 0.170 mL/g, pore diameter was 7.888 nm, particle size was 10⁸0 nm.