2 research outputs found
Structural Behavior of Isolated Asphaltene Molecules at the Oil–Water Interface
Asphaltenes are the heaviest component
of crude oil, causing the
formation of a stable oil–water emulsion. Even though asphaltenes
are known to behave as an emulsifying agent for emulsion formation,
their arrangement at the oil–water interface is poorly understood.
We investigated the effect of asphaltene structure (island type vs
archipelago type) and heteroatom type (Oxygen-O, Nitrogen-N, and Sulfur-S)
on their structural behavior in the oil–water system. Out of
six asphaltenes studied here, only three asphaltenes remain at the
oil–water interface while others are soluble in the oil phase.
Molecular orientation of asphaltene at the interface, position, and
angle of asphaltene with the interface has also been determined. We
observed that the N-based island type asphaltene is parallel, while
the O-based island type asphaltene and N-based archipelago type are
perpendicular to the interface. These asphaltene molecules are anchored
at the interface by the heteroatom. The S-based asphaltenes (both
island and archipelago type) and O-based archipelago type asphaltenes
are soluble in the oil phase due to their inability to form a hydrogen
bond with water and steric crowding near the heteroatom. This study
will help in understanding the role of asphaltenes in oil–water
emulsion formation based on its structure and how to avoid it
Methane Adsorption and Separation in Slipped and Functionalized Covalent Organic Frameworks
Understanding atomic-level mechanisms
of methane adsorption in
nanoporous materials is of great importance to increase their methane
storage capacity targeting energy sources with low carbon emission.
In this work, we considered layered covalent organic frameworks (COFs)
with low density and revealed the effect of slipping and chemical
functionalization on their methane adsorption and separation properties.
We performed grand canonical Monte Carlo simulations studies of methane
(CH<sub>4</sub>) adsorption and carbon-dioxide:methane (CO<sub>2</sub>:CH<sub>4</sub>) separation in various slipped structures of TpPa1,
TpBD, PI-COFs, and functionalized TpPa1 and TpBD COFs as well. We
observed that the slipping improves the total CH<sub>4</sub> uptake
by 1.1–1.5 times, while functionalization does not have a significant
effect on CH<sub>4</sub> uptake. We also observed improvement in CO<sub>2</sub>:CH<sub>4</sub> selectivity due to slipping, whereas functionalization
results in decrease in the selectivity. In all considered COFs, we
found the highest CH<sub>4</sub> delivery capacity of 141 cm<sup>3</sup> (STP) cm<sup>–3</sup> at 65 bar and selectivity of ∼25
at 1 bar in 60-AB slipped structure of TpBD COF. We analyzed the molecular
details of CH<sub>4</sub> adsorption using binding energy, heat of
adsorption, pore characteristics, and expectation energy landscape.
Our results show that COFs with increasing profile of heat of adsorption
with pressure have the higher CH<sub>4</sub> delivery capacity. In
these COFs, we found proximity (∼4–6 Å) of CH<sub>4</sub> binding sites, resulting in higher CH<sub>4</sub>–CH<sub>4</sub> interactions and hence the increasing profile of CH<sub>4</sub> heat of adsorption