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In this paper, the solubility properties of the ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) were studied using a high-pressure, high-temperature set-up employing the pressure-drop technique. [EMIM][BF4] was selected for study because it is used as the sweep liquid in a membrane reactor (MR)-based methanol synthesis (MR-MeS) process recently proposed and studied by our group. The MR-MeS studies indicated high methanol (MeOH) solubilities in the IL under typical MeS reaction conditions, which then motivated this study to measure such solubilities directly under non-reactive conditions to validate the findings of the MR study. In addition, during the MR-MeS studies a concern existed about the solubility of CO2 in [EMIM][BF4], since it is a reactant in the MeS process and its dissolution in the sweep liquid would be detrimental for reactor performance. Studies, therefore, were also carried out to investigate the solubility of CO2, in addition to MeOH, in the IL. Our investigation indicates that though CO2 solubilities in the [EMIM][BF4] are high at room temperature, they become negligible at the typical MeS operating conditions (i.e., temperatures above 200 ⁰C). 

In this study a high-pressure membrane reactor (MR) was employed to carry-out the methanol synthesis (MeS) reaction. Syngas was fed into the MR shell-side where a commercial MeS catalyst was used, while the tube-side is swept with a high boiling point liquid with good solubility towards methanol. A mesoporous alumina ceramic membrane was utilized, after its surface had been modified to be rendered more hydrophobic. The efficiency of the MR was investigated under a variety of experimental conditions (different pressures, temperatures, sweep liquid flow rates, and types of sweep liquids). The results reveal improved per single-pass carbon conversions when compared to the conventional packed-bed reactor. An ionic liquid (IL), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) was utilized in the MR as the sweep liquid. The experimental results are compared to those previously reported by our Group (Li and Tsotsis, J. Membrane Sci., 2019) while using a conventional petroleum-derived solvent as sweep liquid, tetraethylene glycol dimethyl ether (TGDE). Enhanced carbon conversion (over the petroleum-derived solvent) was obtained using the IL.