(388g) Thermodynamic Modeling of Gas Solubility and Transport in an Ionic Liquid Employed As Sweep Solvent during Methanol Synthesis in a Membrane Contactor Reactor

Methanol (MeOH) is an important compound finding applications today as fuel and important raw material in the chemical industry. Methanol is produced industrially by the catalytic conversion of syngas (a mixture of CO/CO₂/H₂) produced either through the steam reforming of natural gas or the gasification of coal or biomass. Methanol synthesis (MeS) is a highly exothermic, equilibrium-limited process, technically challenged by both low per-pass carbon conversions (typically, ~25%) and difficulties with heat management during reactor operation.

In place of the conventional MeS processes, our team proposed recently a novel reactive separation technology that makes use of a membrane contactor reactor (MCR)^1,2. The process employs a non-volatile, high-temperature resistant ionic liquid (IL) as a sweep fluid to remove in situ the MeS products (H₂O and MeOH). As a result, significantly improved per-pass carbon conversions and MeOH selectivity are obtained.

For optimal reactor design and operation, it is essential to have effective models for estimating the solubility and transport properties of the MeS reaction components, including CO/CO₂/H₂/H₂O/MeOH (both individually and in the mixture) in the IL (in this case EMIM-BF₄) at the relevant high pressure and temperature MeS process conditions. In the present study, the solubilities of the MeS components in EMIM-BF₄ were measured experimentally using a pressure-volume-temperature (PVT) system. To model and analyze the experimental behavior, the Peng-Robinson and Soave-Redlich-Kwong equation of states (EOS) were applied to account for the non-ideality of the gas phase, while the UNIQUAC and UNIFAC activity coefficient models were used to calculate the fugacity of the liquid phase in equilibrium with the gas phase. The modeling results are compared with our experimental solubility data, and the applied models are shown capable to predict the experimental behavior. In addition, the sensitivity of MeS-MCR model predictions to the accuracy of the thermodynamic models is investigated. Species diffusivities were measured both in a PVT cell (constant volume diffusion experiments) and also in a high-pressure TGA system.

The measured thermodynamic and transport properties are used to optimize the performance of the membrane reactor system. These experimental data are integrated in our in-house MeS-MCR models¹ and are shown capable to predict the experimental behavior.

Keywords: Methanol synthesis, Ionic Liquid, Solubility, Equation of State, Diffusion Measurements, Membrane Reactor

References:

1. Zebarjad, S.F., Gong, J., Li, Z., Jessen, K., Tsotsis, T.T., “Simulation of Methanol Synthesis in a Membrane-Contactor Reactor,” In Press J. Membrane Science, 2022.

2. Zebarjad, F., Hu, S., Li, Z., and Tsotsis, T.T., “Experimental Investigation of the Application of Ionic Liquids to Methanol Synthesis in Membrane Reactors,” Ind. Eng. Chem. Res., 58. 11911, 2019.