Study On The Preparation By Sodium Borohydride Reduction Method And Catalytic Peactivities Of Cu/ZrO₂ For Dehydrogenation Of Amino Alcohol

Amino acids are the basic components of protein and one of the essential substances to maintain normal physiological metabolism in the human body,they are also widely used in industry.In the synthesis process of amino acids,amino alcohols are used as reaction raw materials,and under the action of Cu-based catalysts,amino acids are prepared by heterogeneous catalytic dehydrogenation process,which is a simple,environmentally friendly,safe and feasible process route.The disadvantage is that Cu-based catalysts are easy to agglomerate and sinter under certain temperature and pressure reaction conditions,thus losing their activity.In order to overcome the above disadvantage,On the one hand,in this paper,a catalyst with low temperature activity was prepared by using sodium borohydride reduction method and used in the dehydrogenation reaction system of amino alcohol.The optimal reaction conditions for the dehydrogenation of monoethanolamine（MEA）and diethanolamine（DEA）under this catalytic system were studied.On the other hand,a high performance liquid chromatography analysis method of amino alcohol dehydrogenation reaction liquid was established in order to quickly and accurately analyze the composition of the reaction product,and better test the reaction performance of the catalyst.Firstly,using sodium borohydride as reducing agent and sodium hydroxide as precipitating agent,a Cu/ZrO₂catalyst with small particle size,good dispersibility and large specific surface area was prepared by co-precipitation method,and the effect of the ratio of sodium borohydride,catalyst preparation temperature,precipitation time and other factors on the catalyst activity were further studied.At the same time,various characterization methods were used to analyze the morphology and physicochemical properties of the catalysts.When the catalyst preparation temperature was 45℃,the precipitation time was 8 h,and the mass ratio of sodium borohydride,sodium hydroxide and copper nitrate was 3.5:6.5:2.4,the prepared catalyst exhibited good catalytic activity in the dehydrogenation of amino alcohols.Compared with the Cu/ZrO₂prepared by the conventional method,the reaction temperature is reduced by 30%,and the reaction time is shortened by 80%.The results show that the catalyst prepared by the sodium borohydride reduction method has a larger specific surface area and more active sites,which can enhance the adsorption to the reaction solution and improve the reaction rate.The particle size of the catalyst is small,the dispersibility is good,the phenomenon of agglomeration and sintering is not easy to occur,and the service life of the catalyst is prolonged.Secondly,a high-performance liquid chromatography method based on DNFB derivatization was established to quantitatively analyze the dehydrogenation reaction solutions of MEA and DEA.And the effects of derivatization conditions（reaction temperature,reaction time,amount of derivatizing reagent,p H）and analytical wavelength on the peak intensity were investigated.The effects of chromatographic column,mobile phase type and ratio,and detection wavelength on the peak separation degree were studied.The results showed that MEA,Gly,DEA and IDA were reacted at 50℃for 30 min under alkaline（p H=9.6）conditions,using Agilent 5 HC-C18（250×4.6 mm,5μm）as the chromatographic column,ammonium acetate buffer The solution-acetonitrile system（volume ratio of 65:35）was used as the mobile phase for isocratic elution,the flow rate was 0.3 m L/min,the column temperature was 30℃,and the detection wavelength was 360 nm.MEA,Gly,DEA,IDA have good linear relationship in the range of 25～1000 mg/L,24～500 mg/L,25～1000 mg/L and 500～5000 mg/L,and the correlation coefficient（R²）all are greater than 0.997.Finally,The optimal reaction conditions for the dehydrogenation of aminoalcohols under this catalyst system were explored by using the dehydrogenation of monoethanolamine to prepare glycine and the dehydrogenation of diethanolamine to prepare iminodiacetic acid.The optimal reaction conditions of monoethanolamine dehydrogenation and diethanolamine dehydrogenation were obtained by optimizing the ratio of reaction raw materials,reaction temperature and reaction time.When the molar ratio of monoethanolamine and sodium hydroxide is 1:1.2,and the reaction is carried out at 115℃for 40 min,the dehydrogenation of MEA is the best.Under the reaction conditions,the conversion of MEA was 97.2%,and the yield of Gly was94.8%.When the molar ratio of diethanolamine and sodium hydroxide was 1:2.4,the reaction was carried out at 120℃for 45 min,the conversion rate of DEA was 99.6%,and the yield of IDA was 98.1%.Under the catalytic system of reduced Cu/ZrO₂,the monoethanolamine dehydrogenation reaction conforms to the first-order reaction kinetics law,and its reaction rate equation is r=kc₁,and the reaction rate constant k obtained according to the linear equation is 3.1×10⁷exp（-83.5/RT）.