The reactions of amine, polyamine and amino alcohol corrosion inhibitors in water at high temperature

Abstract

A stainless steel reactor has been used to investigate the reactions of mono-, di-, tri- and tetraamines, amino alcohols and amino ethers in degassed aqueous solution at 240–300 °C. The predominant reactions involved nucleophilic substitutions, where the amino nitrogen acts as the nucleophile, and not solvolyses. With α,ω-diamines, cyclic and bicyclic amines were formed by inter or intra-molecular processes. Amino alcohols react by displacement of the hydroxy rather than the amino group. The material balance deficit, however, was generally significant, and it is suggested that the missing materials are polyamines arising from polymerisation that competes with cyclisation. The major product from 1,2-diaminoethane and related polyaminoethanes and ethanolamines is diazobicyclo[2.2.2]octane.

The kinetics of some of the cyclisations were studied. Reactions of α,ω-diamines and 5-aminopentan-1-ol are first order in reactant. Conversion of 1,4-diaminobutane to pyrrolidine occurs with high selectivity at 240 °C; in contrast the reactions of the less reactive compounds were less selective, probably due to the formation of polymeric materials. The relative reactivity of the substrates is discussed in detail.