Study On Preparation And Dehydrogenation Mechanism Of Catalysts For Preparation Of Iminodiacetic Acid From Diethanolamine

Iminodiacetic acid is an important raw material for chemical intermediates.It is mainly used for synthesizing broad-spectrum herbicide glyphosate and has wide application value in rubber and medicine.In China,diethanolamine is used as raw material to prepare iminodiacetic acid under the action of high temperature and high pressure and Cu catalyst.The commonly used Cu catalyst is Cu/ZrO2.Preparation of CuO/ZrO2 precursors by co-precipitation,impregnation,hydrothermal and other methods,followed by hydrogen reduction in a tubular electric furnace to produce Cu/ZrO2.The thus prepared catalyst has high activity and good selectivity.It is generally believed that Cu-based catalyst catalyzes the active center of diethanolamine to be Cu0,but more and more studies have shown that Cu+ plays a crucial role in the catalytic dehydrogenation of fatty alcohols to carboxylic acids or esters.Based on this,choosing the appropriate method to prepare the Cu/ZrO2 catalyst with controllable reduction degree is particularly critical for studying the mechanism of the dehydrogenation of diethanolamine to iminodiacetic acid.At the same time,the feasibility of graphene oxide as a Cu-based catalyst carrier was explored.In this paper,CuO/ZrO2 precursor powders were prepared by the reduction of CuO/ZrO2 precursor powders using hydrazine hydrate and applied to the catalytic dehydrogenation of diethanolamine to sodium iminodiacetate.Hydrated hydrazine can quickly reduce CuO under moderate temperature(40?70?)and strong alkaline environment.The degree of reduction can be controlled by controlling the amount of hydrazine hydrate to be added and the reaction time.The yield of catalyzed synthesis of iminodiacetic acid by the CZ-1 catalyst prepared by the above method exceeds 98%,and the reaction time is shortened to 2.3 hours,indicating that the hydrazine hydrazine reduction method is an excellent method for preparing a Cu/ZrO2 catalyst.The physicochemical properties of the catalysts were characterized by XRD,XPS,SEM and BET.Combined with the catalytic effect on the dehydrogenation of diethanolamine,it was found that with the deepening of Cu reduction in the catalyst,the yield of iminodiacetic acid increased first and then decreased.At the same time it has an important influence on the reaction time and the temperature of the primary exhaust.The results show that Cu0 mainly catalyzes the catalytic dehydrogenation of diethanolamine to produce intermediate aldehydes,while Cu+ catalyzes the synthesis of intermediate aldehydes.Acetaldehyde was detected in the gas generated from the reaction,and the mechanism of the formation of glycine,a major by-product,was inferred.This article examines the possibility of deoxidation of diethanolamine to prepare iminodiacetic acid sodium using graphene oxide as a Cu catalyst carrier in a strongly alkaline environment.Graphene oxide was prepared by Hummers method and GO was used as starting material to prepare reduced graphene oxide and base washed graphene oxide(bwGO).XRD and FT-IR were used to investigate the structural changes of graphene oxide in a strongly alkaline environment.The Cu/graphene oxide,Cu/rGO,and Cu/bwGO were prepared by hydrazine reduction of copper salt solution,and these three catalysts were used to catalyze the dehydrogenation of diethanolamine to iminodiacetic acid.The effects of mass ratio of raw materials and catalyst mass on the catalytic activity of Cu/bwGO on diethanolamine were investigated.For the Cu/bwGO-m-3.0 catalyst,the yield of sodium iminodiacetate can reach 57.9%.