| Since 1990 s,the green and efficient dehydrogenation method of diethanolamine(DEA)has been applied to the synthesis of iminodiacetic acid(IDA).This method has harsh reaction conditions,complicated reaction mechanism,and produces various by-products.The lack of a detailed description of the intermediate process reaction is not conducive to the control of the DEA dehydrogenation reaction process.In this study,the contents of DEA and two by-products carboxylic acids in dehydrogenation solution were studied in depth.The DEA in diethanolamine dehydrogenation reaction solution was established and measured by a cation-exchange chromatography with a conductance detector.The influence of eluent type,eluent concentration,column temperature,solvent,flow rate,and other factors on chromatographic separation was investigated.The optimized analysis conditions were as follows: The chromatographic column was Dionex CS12 A cation exchange chromatographic column.The aqueous solution of 5.0 mmol/L methane sulfonic acid was used as the eluent.The flow rate was 1.0 m L/min and the column temperature was 40?.The results of the quantitative analysis showed that the recoveries of DEA ranged from 98.01% to 101.64%,the RSD ranged from 1.20%to 1.58%.This method is fast,efficient,and not easily disturbed.It is used for the accurate determination of DEA content in reaction liquid in actual production to calculate the reaction conversion rate.A visible spectrophotometric method for the determination of DEA content in the DEA dehydrogenation reaction solution was established by using copper sulfate as the chromogenic agent.The experimental factors such as the type of chromogenic agent,the amount of chromogenic agent,and the reaction time were optimized.The optimized derivation condition was 10% copper sulfate 1.0 m L,the reaction time was20 min,and the colorimetric method was carried out under the visible light of 650 nm.The results of the quantitative analysis showed that the standard recovery rate ranged from 99.47% to 103.70% and RSD ranged from 1.69% to 2.10%.This method has good repeatability and high sensitivity and is suitable for the determination of DEA content in DEA dehydrogenation reaction solution.Anion exchange chromatography was established to quantitatively analyze the contents of oxalic acid and glycolic acid as by-products in the DEA dehydrogenationreaction solution.The optimized chromatographic conditions were as follows: The chromatographic column is Dionex AS23 anion exchange chromatographic column.8.0 mmol/L KOH solution was used as an eluvial solution,the flow rate was 1.5m L/min and the column temperature was 40?.Under this analysis condition,the oxalic acid and glycolic acid standard curves established under this analysis method have a good linear correlation.The results of the quantitative analysis showed that the recovery rate of oxalic acid from 98.11% to 101.07%,RSD was from 0.98% to 1.29%;the recovery rate of glycolic acid from 98.06% to 101.20%,RSD was from 0.85% to1.47%.This method can directly and quickly determine the content of oxalic acid and glycolic acid in the DEA dehydrogenation reaction solution.The preliminary research of DEA content determination by high-performance liquid chromatography-indirect ultraviolet detection was carried out,and the effects of the mobile phase,background ultraviolet absorption reagent types,concentration,and detection wavelength on sample separation and analysis were investigated.The optimized analysis conditions are: The chromatographic column was HC-C18,the mobile phase is the methanol-water solution(85:15,v / v),the background reagent is0.5 mmol / L arbutin,the column temperature is 30 ?,and the flow rate is 1.0m L/min.The detection wavelength is 280 nm.This method needs to be further studied,and it is more likely to achieve accurate quantification of the content of DEA in the DEA dehydrogenation reaction solution... |
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