Propylene/propane separation by porous graphene membrane: Molecular dynamic simulation and first-principle calculation

Removal of methanol from water by capacitive deionization system combined with functional nanoporous graphene membrane

In this article, molecular dynamics simulations were used to examine the feasibility of capacitive deionization (CDI) system combined with a functionalized nanoporous graphene (NPG) membrane for removing methanol from water. The radial distribution function of electrode-methanol and methanol-water, the self-diffusion coefficient of methanol and water, the water density near the membrane, the interaction energy between methanol and membrane, the hydrogen bond structure between methanol and water, and the 2D density map of methanol molecules near the membrane under different electric field (EF) (to simulate the effect of capacitance) were examined to evaluate the separation performance of NPG membranes with hydrogen-passivated pores for methanol. The findings show that an EF with appropriate strength can decrease the amount of water molecules near methanol, increase the self-diffusion coefficient of methanol and water, increase hydrophobicity of hydrogenated pores, decrease the interaction between the NPG membrane and methanol, and weaken hydrogen bond interaction between water and methanol molecules. All these findings suggest that an appropriate EF can improve the NPG membrane's permeability to methanol, and verify the feasibility of CDI system combined with hydrogenated NPG membrane to remove methanol from water. This study is expected to propose a potential CDI application technology, and also give a novel idea for the removal of small organic molecules in water by functionalized NPG membrane.

Computational Studies on Holey TMC6 (TM = Mo and W) Membranes for H2 Purification

The purification of hydrogen (H2) has been a vital step in H2 production processes such as steam−methane reforming. By first-principle calculations, we revealed the potential applications of holey TMC6 (TM = Mo and W) membranes in H2 purification. The adsorption and diffusion behaviors of five gas molecules (including H2, N2, CO, CO2, and CH4) were compared on TMC6 membranes with different phases. Though the studied gas molecules show weak physisorption on the TMC6 membranes, the smaller pore size makes the gas molecules much more difficult to permeate into h-TMC6 rather than into s-TMC6. With suitable pore sizes, the s-TMC6 structures not only show an extremely low diffusion barrier (around 0.1 eV) and acceptable permeance capability for the H2 but also exhibit considerably high selectivity for both H2/CH4 and H2/CO2 (>1015), especially under relatively low temperature (150−250 K). Moreover, classical molecular dynamics simulations on the permeation process of a H2, CO2, and CH4 mixture also validated that s-TMC6 could effectively separate H2 from the gas mixture. Hence, the s-MoC6 and s-WC6 are predicted to be qualified H2 purification membranes, especially below room temperature.

Adsorption-based membranes for air separation using transition metal oxides

In this work, we use computational modeling to examine the viability of adsorption-based pore-flow membranes for separating gases when a purely size-based separation strategy is ineffective. Using molecular dynamics simulations of O₂ and N₂, we model permeation through a nanoporous graphene membrane. Permeation is assumed to follow a five-step adsorption-based pathway, with desorption being the rate-limiting step. Using this model, we observe increased selectivity between O₂ and N₂, resulting from increased adsorption energy differences. We explore the limits of this strategy, providing an initial set of constraints that need to be satisfied to allow for selectivity. Finally, we provide a preliminary exploration of some transition metal oxides that appear to satisfy those conditions. Using density functional theory calculations, we confirm that these oxides possess adsorption energies needed to operate as adsorption-based pore-flow membranes. These adsorption energies provide a suitable motivation to examine adsorption-based pore-flow membranes as a viable option for air separation.

Recent Progress in a Membrane-Based Technique for Propylene/Propane Separation

The similar physico-chemical properties of propylene and propane molecules have made the separation process of propylene/propane challenging. Membrane separation techniques show substantial prospects in propylene/propane separation due to their low energy consumption and investment costs, and they have been proposed to replace or to be combined with the conventional cryogenic distillation process. Over the past decade, organosilica membranes have attracted considerable attention due to their significant features, such as their good molecular sieving properties and high hydrothermal stability. In the present review, holistic insight is provided to summarize the recent progress in propylene/propane separation using polymeric, inorganic, and hybrid membranes, and a particular inspection of organosilica membranes is conducted. The importance of the pore subnano-environment of organosilica membranes is highlighted, and future directions and perspectives for propylene/propane separation are also provided.

Computational methods towards increased efficiency design of graphene membranes for gas separation and water desalination

The potential impact of climate change is widely known as having serious consequences. The themes of water desalination and gas separation are closely related to the environment and energy industry. Graphene-based membranes are promising filtration devices for the two tasks. This review aims to supply a comprehensive overview of the recent computational studies investigating the performance of graphene-based membranes used in water desalination or gas separation. With the use of computational methods, the literature covered finds evidence for key factors, such as pore shape and density, affecting the performance of the investigated membranes. The reviewed studies are expected to act as an impulse towards more computational studies and eventually actual design of graphene-based membranes for water desalination and gas separation.

A Bibliometric Survey of Paraffin/Olefin Separation Using Membranes

Bibliometric studies allow to collect, organize and process information that can be used to guide the development of research and innovation and to provide basis for decision-making. Paraffin/olefin separations constitute an important industrial issue because cryogenic separation methods are frequently needed in industrial sites and are very expensive. As a consequence, the use of membrane separation processes has been extensively encouraged and has become an attractive alternative for commercial separation processes, as this may lead to reduction of production costs, equipment size, energy consumption and waste generation. For these reasons, a bibliometric survey of paraffin/olefin membrane separation processes is carried out in the present study in order to evaluate the maturity of the technology for this specific application. Although different studies have proposed the use of distinct alternatives for olefin/paraffin separations, the present work makes clear that consensus has yet to be reached among researchers and technicians regarding the specific membranes and operation conditions that will make these processes scalable for large-scale commercial applications.

Ultrathin Polyamide Membrane with Decreased Porosity Designed for Outstanding Water-Softening Performance and Superior Antifouling Properties

Poly(piperazine-amide)-based nanofiltration membranes exhibit a smooth surface and superior antifouling properties but often have lower Ca²⁺ and Mg²⁺ rejection due to their larger inner micropore and thus cannot be extensively used in water-softening applications. To decrease the pore size of poly(piperazine-amide) membranes, we designed and synthesized a novel monomer, 1,2,3,4-cyclobutane tetracarboxylic acid chloride (BTC), which possesses a smaller molecular conformation than trimesoyl chloride (TMC). The thickness of the prepared BTC-piperazine (PIP) polyamide nanofilm via interfacial polymerization is as thin as 15 nm, significantly lower than the 50 nm thickness of the TMC-PIP nanofilm. The surface characterization reveals that the BTC-PIP polyamide membrane exhibits an enhanced hydrophilicity, a smooth surface, and a decreased surface-negative charge. The desalination performance (both rejection and water flux) of these membranes in terms of Ca²⁺ and Mg²⁺ exceeds that of the current commercial water-softening membranes. In addition, the BTC-PIP polyamide membrane also exhibits superior antifouling properties compared to the TMC-based polyamide membrane. More importantly, molecular simulations show that the BTC-PIP membrane has a lower average pore size than that of the TMC-PIP membrane, which demonstrates an enhanced steric hindrance effect, as confirmed by desalination performance. Our results demonstrate that in the household and industrial water-softening market, BTC-PIP membrane with decreased porosity, enhanced hydrophilicity, and smooth surface is preferred alternative to the conventional TMC-based polyamide membranes.