Preparation Of Cu-based Catalysts For Diethanolamine Dehydrogenation And Development Of Continuous Processes

Glyphosate is currently the most widely used pesticide in the world.At present,Monsanto's production bases in the world use the iminodiacetic acid method?IDA?to produce glyphosate.The IDA method has a short process,high yield,good product purity,and less pollution.The production of IDA by the diethanolamine method is to use one step of dehydrogenation of diethanolamine to produce iminodiacetic acid under the action of a Cu-based catalyst.The effect of repeated use of the catalyst is poor,resulting in higher production costs.On the one hand,the stability and activity of the catalyst were improved by preparing a nitrogen-doped carbon coating structure;Co₃O₄was introduced to prepare the bimetallic catalyst,and the catalytic activity was improved by using cooperative catalysis.On the other hand,a fixed bed method was used to develop a diethanolamine continuous dehydrogenation process device.First of all,Carbon coated nano-metal particles are a new type of nano-carbon/metal composite material.Metal materials can be imparted in a small space due to the surface acidity and alkalinity of carbon-coated materials and their unique structural characteristics,which is of great significance for the dispersion and oxidation resistance of the loaded nano-metal materials.In this study,melamine was used as a carbon source and a nitrogen source to prepare a Cu-Zr O₂ nanocatalyst?CZ@CN catalyst?coated with nitrogen-doped carbon?CN?with a core-shell structure.The effect of different molar ratios of copper and melamine on the catalyst was studied.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,N₂ physical adsorption and desorption test?BET?,H₂ temperature-programmed reduction?H₂-TPR?were used to investigate the morphology and structure of the catalyst.The catalytic performance of the catalyst for the dehydrogenation of diethanolamine was investigated.When the molar ratio of copper to melamine is 4:1,the prepared CZ@CN-1 catalyst has the highest catalytic activity.The yield of sodium iminodiacetic acid is 93%,and the reaction time is shorter than that of the ordinary CZ catalyst by 40%.The yield of sodium iminodiacetic acid still reaches 88%after reusing 8 times.The results showed that the introduction of the CN layer makes the catalyst exhibit more Lewis basicity.Meanwhile,it is beneficial to the activation of hydroxyl groups and the transfer of hydrogen in the dehydrogenation reaction.The CN layer can also stabilize copper nanoparticles and improve the stability of the catalyst.Secondly,compared with single-metal catalysts,double-metal catalysts have superior catalytic performances.A Cu O/Co₃O₄-Zr O₂ precursor was obtained by a co-precipitation method.Through reduction and self-oxidation to obtain small Co₃O₄particles.Cu/Co₃O₄-Zr O₂ catalyst was synthesized with double-metal active components.The strong interaction between Co₃O₄ and Zr O₂ increased the density of active sites?oxygen vacancies?and enhanced adsorption-activation properties.Cu/Co₃O₄-Zr O₂ demonstrated high catalytic activity and stability during the diethanolamine dehydrogenation,a 96%yield was obtained.The reaction time?30 min?using Cu/Co₃O₄-Zr O₂ was faster than other catalysts.Based on various physicochemical characterization techniques,strong Cu-oxide interactions,the co-catalysis of biactive components,and the higher number of oxygen vacancies of Cu/Co₃O₄-Zr O₂ were responsible for the enhanced catalytic activity during diethanolamine dehydrogenation.Small Co₃O₄ particles improved the dispersion and stability of Cu NPs and inhibited the sintering of loaded Cu NPs.Cu/Co₃O₄-Zr O₂ shows promise for practical applications for dehydrogenation.Finally,the process of continuous dehydrogenation was designed,and a set of continuous dehydrogenation reactors was made by using a fixed bed reactor and heating outside the oil bath.The effects of the reaction liquid flow rate and reaction temperature on the dehydrogenation performance of the prepared catalyst during the continuous dehydrogenation of diethanolamine were investigated.Through the design process and the realization of a continuous process on the reactor equipment,a preliminary study on process improvement and process parameter optimization was conducted.