Ethanol extraction

Reducing CO₂ emissions is one of the most significant challenges of our time, and seeking green energy alternatives has drawn considerable attention in both industry and academia. Ethanol, the widely used fossil fuel alternative, can be produced from biomass via fermentation, but its production requires an energy-intensive distillation process. Therefore, developing energy-efficient ethanol extraction processes is urgently needed, and discovering new materials, particularly nanoporous materials (e.g., zeolites), plays a particularly critical role.

Benefiting from breakthroughs in synthesis techniques, zeolite nanosheets, two-dimensional materials with a nano-scale thickness can potentially can be a breakthrough in the ethanol extraction, but their separation performance is difficult to determine experimentally. In this regard, molecular simulations can help the exploration of the performance and design of zeolite nanosheets for ethanol extraction. In our recent computational study¹, we used molecular dynamics (MD) techniques to directly simulate the pervaporation separation process in a sandwich-like set up, as shown in Figure 1(a). Our results have demonstrated that zeolite nanosheets can possess orders of magnitude higher flux than conventional membranes, as shown in Figure 1(b). Also, two zeolite nanosheets, FER and MFI-zigzag, have been found to have outstanding separation factors of 74.5 and 136, respectively. The study has also unveiled the relationship between the separation factor and the external nanosheet surface; a more hydrophilic surface (e.g., surface having more surface silanols in Figure 1 (c) than (d)) promotes water adsorption and results in a lower separation factor.

Besides, to accelerate the large-scale screening study of zeolite nanosheets, we are also investigating the structure-property relationship to identify easy-to-compute quantities as preliminarily guidelines of the separation performance.

Figure 1. (a) Schematic representation of the simulation system. (b) Performance comparison of nanosheet membranes studied in this work with available membranes reported in the literature, including (1) silicalite membranes on inorganic supports (denoted as Silicalite); (2) mixed matrix composite membranes by zeolites and polydimethylsiloxane (denoted as Zeolite-PDMS). (c, d) Density plots of ethanol adsorption on the membrane surface of MFI and MFI-zigzag, respectively. Color bar indicates the mole fraction of ethanol (mol%) with warmer colors representing a higher mole fraction. Zeolite structures are presented by sticks and balls with color code gold:silicon and red:oxygen (Figure adopted from Zou et al. (2018)¹).

References

(1) Zou, C.; Lin, L.-C. Exploring the Potential and Design of Zeolite Nanosheets as Pervaporation Membranes for Ethanol Extraction. Chem. Commun. 2018, 54 (94), 13200–13203.