Commonly used Polymers for Separation Science

Many synthetic and organic (bio-based) polymers have been used for membrane fabrications. In this chapter, we discuss the structure and properties of some commonly used polymers, which have been used for water purification and gas separation applications. To supplement that, we discuss some characterization tools and membrane module testing conditions for performance checks.

Ionic Transport Triggered by Asymmetric Illumination on 2D Nano-Membrane

Ionic transport and ion sieving are important in the field of separation science and engineering. Based on the rapid development of nanomaterials and nano-devices, more and more phenomena occur on the nanoscale devices in the field of thermology, optics, mechanics, etc. Recently, we experimentally observed a novel ion transport phenomenon in nanostructured graphene oxide membrane (GOM) under asymmetric illumination. We first build a light-induced carriers’ diffusion model based on our previous experimental results. This model can reveal the light-induced ion transport mechanism and predict the carriers’ diffusion behavior under different operational situations and material characters. The voltage difference increases with the rise of illuminate asymmetry, photoresponsivity, recombination coefficient, and carriers’ diffusion coefficient ratio. Finally, we discuss the ion transport behavior with different surface charge densities using MD simulation. Moderate surface charge decreases the ion transport with the same type of charge due to the electrostatic repulsion; however, excess surface charge blocks both cation and anion because a thicker electrical double layer decreases effective channel height. Research here provides referenced operational and material conditions to obtain a greater voltage difference between the membrane sides. Also, the mechanism of ion transport and ion sieving can guide us to modify membrane material according to different aims.

Liquid Membranes in Catalysis

: The supported ionic liquid (SIL) membranes have demonstrated huge potential for numerous applications in current separation science and catalysis. Membrane technology allows for separation of complex mixtures of gases, vapours, liquids and /or solids below trivial conditions. Simultaneous chemical transformations can also be achieved in membranes by using catalytically active materials comprising the membrane or embedded catalysts in the custom built membrane reactors. In the present editorial, the remarkable contribution of liquid membranes in catalysis is highlighted. Some recent applications are presented and compared with conventional methods. In addition, SILs and their applications in catalysis, catalytic membranes and recent advances in membrane separation processes are briefly described.

Pumping Between Phases With a Pulsed-Fuel Molecular Ratchet

The sorption of species from solution into and onto solids, surfaces, crystals, gels and other matrices, underpins the sequestering of waste and pollutants, the recovery of precious metals, heterogeneous catalysis, many forms of chemical and biological analysis and separation science, and numerous other technologies. In such cases the transfer of the substrate between phases tends to proceed spontaneously, in the direction of equilibrium. Molecular ratchet mechanisms, where kinetic gating selectively inhibits or accelerates particular steps in a process, makes it possible to drive dynamic systems out of equilibrium. Here we report on a small-molecule pump immobilised on and near the surface of polymer beads, that uses an energy ratchet mechanism to actively transport substrates from solution onto the beads away from equilibrium. One complete cycle of the pump occurs with each pulse of a chemical fuel, synchronizing the ratchet dynamics so that the immobilised molecular machines all act in unison. Upon addition of the trichloroacetic acid fuel, micrometre-diameter polystyrene beads functionalised with an average of ~8×10exp10 molecular pumps per bead, sequester from solution crown ethers appended with a fluorescent tag. Following consumption of the fuel, the rings are mechanically trapped in a higher energy, out-of-equilibrium, state on the beads and cannot be removed by dilution nor by switching the binding interactions off. This differs from dissipative assembled materials that require a continuous supply of energy to persist. Addition of a second pulse of fuel causes the uptake of more macrocycles, which can be labelled with a different fluorescent tag. This drives the system progressively further away from equilibrium and also confers sequence information on the deposited structure. The polymer-bound substrates (and the stored energy) can subsequently be released back to the bulk on demand, either emptying one compartment at a time or all at once. Non-equilibrium sorption by using immobilised artificial molecular machines to pump substrates from solution onto and into materials, offers potential for the transduction of energy from chemical fuels for the storage and release of energy and information.

Iterative Multivariate Peaks Fitting—A Robust Approach for The Analysis of Non-baseline Resolved Chromatographic Peaks

Selectivity in separation science is defined as the extent to which a method can determine the target analyte free of interference. It is the backbone of any method and can be enhanced at various steps, including sample preparation, separation optimization and detection. Significant improvement in selectivity can also be achieved in the data analysis step with the mathematical treatment of the signals. In this manuscript, we present a new approach that uses mathematical functions to model chromatographic peaks. However, unlike classical peak fitting approaches where the fitting parameters are optimized with a single profile (one-way data), the parameters are optimized over multiple profiles (two-way data). Thus, it allows high confidence and robustness. Furthermore, an iterative approach where the number of peaks is increased at each step until convergence is developed in this manuscript. It is demonstrated with simulated and real data that this algorithm is: (1) capable of mathematically separating each component with minimal user input and (2) that the peak areas can be accurately measured even with resolution as low as 0.5 if the peak’s intensities does not differ by more than a factor 10. This was conclusively demonstrated with the quantification of diterpene esters in standard mixtures.

Membranes for olefin–paraffin separation: An industrial perspective

In the next decade, separation science will be an important research topic in addressing complex challenges like reducing carbon footprint, lowering energy cost, and making industrial processes simpler. In industrial chemical processes, particularly in petrochemical operations, separation and product refining steps are responsible for up to 30% of energy use and 30% of the capital cost. Membranes and adsorption technologies are being actively studied as alternative and partial replacement opportunities for the state-of-the-art cryogenic distillation systems. This paper provides an industrial perspective on the application of membranes in industrial petrochemical cracker operations. A gas separation performance figure of merit for propylene/propane separation for different classes of materials ranging from inorganic, carbon, polymeric, and facilitated transport membranes is also reported. An in-house–developed model provided insights into the importance of operational parameters on the overall membrane design.