Theoretical Study of Nanoporous Graphene Membranes for Natural Gas Purification

Abstract

Gas filtration by means of membranes is becoming increasingly important for industrial processes due to its low cost. In particular, membranes can be applied to separate methane in natural gas from pollutants such as hydrogen sulfide and carbon dioxide. The recent advent of nanoporous graphene as material for membranes helped to overcome the current problems of polymeric membranes, namely the permeability/selectivity tradeoff. However, the factors that determine gas filtration through nanoporous graphene are not completely clear yet. In this work, we show that pore size, shape and functionalization severely affect the selectivity of the membrane toward CO 2 and H 2 S with respect to CH 4 . We identified that the critical diameter of circular pore for the separation of contaminants from methane with graphene membranes is 5.90 Å. An elliptical pore is discovered to select gas species having similar sizes on the basis of their shape. The more elongated CO 2 is allowed to pass though the pore while the more spherical H 2 S and CH 4 are rejected. Finally, the gas-membrane interactions are found to decisively affect the filtration performances. Functionalization with hydroxyl groups led to a higher permeability of the gas species with polar bonds while keeping an excellent selectivity.

Scale Effects in Nanoscale Heat Transfer for Fourier’s Law in a Dissimilar Molecular Interface

“…Prior studies 24 , 27 − 36 have defined boundary positions at different points during the past decades. Some researchers defined the boundary position at the innermost solid layer, 27 − 31 whereas Han et al used the midpoint of the innermost solid layer as a boundary position. 32 Furthermore, zero liquid density and the peak of the absorbed layer are also used as a boundary position.…”

Mass Transfer Through Graphene-Based Membranes

“…Note that the shape of gas molecules can also affect the transport of gases through GO and NG membranes [10,27]. The influence of the molecule shape on the kinetic diameter of molecules, and accordingly on the transport of gas through GO membrane is discussed in [10].…”

“…The influence of the molecule shape on the kinetic diameter of molecules, and accordingly on the transport of gas through GO membrane is discussed in [10]. In [27] it was shown by means of molecular dynamics simulations how the size, shape, and functionalization of pores in NG membranes affect the permeance of CO 2 , H 2 S, and CH 4 molecules.…”

Molecular dynamics study of the pore formation in single layer graphene oxide by a thermal reduction process

“…6 Several following studies proved the effectiveness of graphene membranes 7,8 and analyzed the parameters that influence their performance, stressing in particular on the impact of pore dimensions. [9][10][11][12] One of the hardest challenges, that characterizes this material, is to consistently synthe-size graphene membranes with a narrow pore size distribution.…”