Mixing behaviour investigation of a switchable solvent synthesis using ATR-IR spectroscopy

Abstract

A systematic study of the mixing behaviour during the synthesis of a two-component switchable solvent was carried out to assess the factors limiting the transport that influence the reaction time. Calculations on the flow regime, the Reynolds number and the resulting theoretical blend times hinted at mixing problems as a main influence. To confirm this assumption, experiments were carried out in a well-defined experimental setup where transport of the gas into the reaction mixture only occurs at the liquid surface and the composition of the reaction mixture can be measured with a mid-infrared probe. The results showed that fluctuations in the concentration can be detected which are likely caused by fluid aggregates of different composition passing the probe head in turns. The stirring speed and the pressure could be shown to influence the reaction. An increase of either parameter can shorten the reaction time significantly and reduce the fluctuations. The results were gathered in a parameter map, which illustrates areas of different fluctuation strength and allows the deduction of a criterion for the presence of fluctuations during the IL synthesis. To understand the impact of the parameters, a descriptive model for the parameter dependence was developed.