Continuous flow synthesis of β-hydroxyethyl hydrazine in microreactors: process behavior and impurity formation mechanism

Abstract

The synthesis of β-hydroxyethyl hydrazine (HEH) via the reaction between ethylene oxide (EO) and hydrazine hydrate (N₂H₄·H₂O) suffers from a series of consecutive side reactions, leading to the generation of undesired by-products such as hydrazine impurities and alcohol–amine compounds. In this work, the process behaviors of these side reactions and the formation mechanisms of hydrazine impurities were first investigated in a miniaturized flow system. The results identify the formation of 1,2-bis(β-hydroxyethyl) hydrazine, 1,1-bis(β-hydroxyethyl) hydrazine, and tri(β-hydroxyethyl) hydrazine as notable by-products. Furthermore, the investigation demonstrates that the molar ratio of N₂H₄·H₂O to EO exerts the most significant influence on the formation of hydrazine impurities, with temperature, pressure, and N₂H₄·H₂O concentration also impacting the process. Subsequently, the components of alcohol–amine impurities were also identified, including ethanolamine, diethanolamine, and triethanolamine. A potential pathway for the formation of alcohol–amine impurities stemming from hydrazine decomposition is proposed. The influence of various operational parameters on alcohol–amine impurities formation process was investigated, finding that the impurities are more likely to form when the molar ratio of N₂H₄·H₂O to EO is maintained below 6. Moreover, the production of these impurities can be significantly reduced with enhanced mixing efficiency. The findings are anticipated to provide valuable insights into the development of comprehensive process design guidelines and optimization of reaction conditions within the industrial-scale production of HEH.