Liquid crystals as novel process solvents for absorption

The current need to reduce CO2 emissions from power-plant flue gases demands the development of new energy efficient separation processes. A possible route for achieving this is the use of liquid crystals as a novel process solvent.

The liquid crystal (LC) state is a condensed state of matter in which molecules are arranged in an ordering between the (isotropic) liquid and the crystalline state. The attractive feature of LC molecules as process solvents is that, upon cooling, a first order phase transition from the isotropic to the LC phase takes place, leading to a step-change in thermodynamic properties such as the solubility. Given that the solubility of gases in the LC phase is lower than in the isotropic fluid, this step-change could be utilized as a ‘solubility switch’. When used in a conventional absorption/desorption cycle, this would result in a drastic decrease in the energy consumption of the desorption step.

The main goal of the project is to find LC compounds with improved solvent properties for CO2 absorption. To achieve this, a tight interplay between experimental, theoretical and molecular simulation work is needed.

The goal of the experiments is to find a LC with an optimal capacity and absorption/desorption ratio for CO2 absorption. Therefore the phase diagram of CO2 in various LC’s is measured using a Cailletet setup. The theoretical part will focus on the development of a physically based equation of state that is able to describe and predict the properties of LC-CO2 mixtures.  Such a predictive model is essential since it can be used to assist the experimentalist in defining possible candidate molecules for experiments. Next to this it can eventually be used for optimal solvent design. The molecular simulation work is needed to gain understanding of the molecular basis of the physical properties of LC’s. Next to this it can assist in the selection of candidate molecules for phase equilibria measurements and in the development of the physically based equation of state.