DOI: 10.5176/2301-3761_CCECP18.5
Authors: Zeyu Zhao, Xian Kong and Jianwen Jiang
Abstract:
Membrane separation is a technically feasible and economically viable technology in a wide variety of industrial applications such as air and hydrogen purification, carbon dioxide capture from coal power plant and natural gas upgrading. Molecular crystals of dipeptides with a high density of uniform open channels have received growing interest as membranes for gas separation. Particularly, crystalline hydrophobic dipeptides of Val-Ala (VA) class can form onedimensional nanoporous pores with average size ranging from 0.37 to 0.50 nm. In this work, molecular simulations have been performed to investigate CO2/N2 and CO2/CH4 separations through eight membranes composed of Ala-Val (AV), Val-Ala (VA), Ala-Ile (AI), Ile-Ala (IA), Val-Ile (VI), Ile-Val (IV), Val-Val (VV) and Leu-Ser (LS) dipeptides. To mimic practical constant-pressure-gradient separation processes, gas molecules in the permeate side were removed every 300 ps, while a certain number of molecules were added into the feed side. At room temperature and a feed pressure of 6 bar, CO2/N2 and CO2/ CH4 selectivities are up to 73.6 in VI and 120.5 in AI, respectively. Moreover, VI, AI, VA, LS and AV exhibit separation performance above the Robeson upper bound. For IA and IV, gas molecules are difficult to pass through because of their small pore size and relatively high helicity. To furthermore investigate CO2/N2 separation at a low pressure close to industrial operative condition, gas permeation was also tested at 1 bar. By comparing the separation performance of VI and LS, good selectivity can be preserved in the former with a small pore size but not in the latter with a large pore size. This is attributed to the unsaturated adsorption of CO2 in the latter. This simulation study provides microscopic insights into gas separation in dipeptide crystals and suggests the potential of dipeptides especially VI as membranes for CO2 separation.
Keywords : CO2/N2 and CO2/CH4 separation, dipeptides, permeability, selectivity, molecular simulation
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