Introduction
Adsorption and gas separations are two important topics in the chemical,
environmental, medical and electronic gas industries
applications.1-6 Many studies have been performed to
improve the chemical activity of different materials for adsorber and
separate gases. The technologies of gas separation include cryogenic
separation, absorption/adsorption separation, supersonic separation, and
membrane separation. 7-9 Researchers have developed
strategies to design materials to separate gas mixtures. Most of the
materials used are membranes,10polymers,11 zeolites,12carbons,13 and metal-organic frameworks
(MOFs).14
The biogas is an effective, clean and renewable energy resource. It is
obtained by process of organic matter.15-21 The biogas
is composed mostly of CH4 and CO2, with
traces of N2, H2, H2S,
and other gases.22 The separation of
CO2 and CH4 from biogas would enable
using it for various chemicals processes. Several authors investigated
materials as Co-MOF,23 Cu-BTC,24MIL-53,25 UTSA-16,26MOFs,27 Cu-MOF,28Cu-TDPAT,29 and others30 for
CO2/CH4 separations. Most of the studies
investigate the biogas purification
(CO2/CH4) as mentioned above.
Interesting to highlight that reports of
CO2/H2 separation are scarce. Soonchul
Kwon, et al. investigated competitive CO2 and
H2 adsorption on carbon allotropes such as graphene,
which has only hexagonal rings, and graphyne. They found, graphyne
provides high CO2 selectivity for gas
mixtures.31 In 2017 Zhou et al . investigated
the theoretical simulation of CH4 separation from
H2 in metal−organic frameworks
CAU-17.32 Another research group reported that
metal-organic frameworks containing strongly adsorbing sites are
excellent candidates for CO2/H2separations.33 Previous reports showed that porous
graphene membrane showed high selectivity of H2 by DFT
calculation, over several other gas molecules that often accompany
H2 in industrial steam methane reforming or
dehydrogenation of alkanes (such as N2, CO, and
CH4).34 Studies in this direction,
Arjmandi et al . have investigated the adsorption properties of
H2 and CO2 on the organic MOF-5ligand.
Their results revealed that ZnO-doped system has higher adsorption
energy values than those for the pristine MOF.35Recently, the graphydine like membrane was studied for separate a
mixture of hydrogen (H2) and carbon dioxide
(CO2) gases by density functional theory. The results
showed that the selectivity of H2/CO2 is
increased from 70 to 100% in the presence of 1,3,5 three amine
benzene.36
Synthesis and characterization of ortho-phenylene-bridged cyclic
trimeric oligopyrrole has recently been reported. These molecules have
cavities with electron donating atoms.37-38 Motivated
by the promising properties of these materials, “MPBCP”
(meta-phenylene-bridged cyclic pyrrole) was designed, to study the
ability to adsorb molecules from biogas. We investigate the effect of
coordinating the “MPBCP” with a lanthanum atom with neutral and +3
charge. The lanthanum systems were studied for adsorption of biogas
molecules. Theoretical computations have been conducted to open up
opportunities for design of materials for capture and sensing biogas.