Carbon Dioxide Separation by Polyethylene Glycol and Glutamic Acid/Polyvinyl Alcohol Composite Membrane

In this study, Polyvinyl alcohol (PVA) blended with Polyethylene glycol (PEG), Monosodium glutamate (MSG) and Glutamic acid (GA) was cast on a reverse osmosis membrane to form a composite membrane. It is expected that the ether group can increase the CO2 affinity of the membrane. Sodium tetraborate (Borax) as a crosslinker can increase membrane basicity and glutamic acid (salt) can provide an enhanced transport mechanism, thereby improving the permeability and selectivity of carbon dioxide. FTIR spectra show that the thickness of coating is sufficiently low, while SEM results show that PVA-PEG series have a dense surface, and particles are observed on the surface of MSG/GA series. The gas permeance and separation performance of the composite membrane was tested using a single gas. Results showed that CO2 had higher permeance (GPU) at lower pressure differential. PEG with an ether group had the greatest effect on improving CO2 permeance and selectivity. However, MSG and GA with amine groups could not effectively improve CO2 selectivity due to solubility. The best coating solution was provided by PVA-PEG-1.2. The CO2 selectivity of the composite membrane was 10.05 with a pressure differential of 1.00 bar in a humid environment and no obvious deterioration was observed over a 10-day period. Borax can improve selectivity, water absorption, and thermal stability while avoiding the need for high temperature and long crosslinking time of aldehydes, which makes it possible to be used in a PVA carbon dioxide separation membrane.

Graphene Membranes: From Reverse Osmosis to Gas Separation

Graphene membrane is a promising technology to help both carbon dioxide separation from flue gas and water desalination. This work reported the importance of membrane separation processes, the evolution of polymeric membranes before the discovery of graphene and how this material fits into this scenario. In addition, reverse osmosis and gas separations have been discussed as promising methods to reduce the occurrence of freshwater scarcity events and slow global warming. For all these separation techniques, the current state of graphene membranes technology and what advances might be brought by such one atom thick skin layer were presented, as well as the results of theoretical and experimental research. Finally, the challenges that still need to be overcome by this innovative technology as well as the perspectives were shown.

Recent Advances in Molten-Carbonate Membranes for Carbon Dioxide Separation: Focus on Material Selection, Geometry, and Surface Modification

Membranes for carbon dioxide permeation have been recognized as potential candidates for CO2 separation technology, particularly in the energy sector. Supported molten-salt membranes provide ionic routes to facilitate carbon dioxide transport across the membrane, permit the use of membrane at higher temperature, and offer selectivity based on ionic affinity of targeted compound. In this review, molten-carbonate ceramic membranes have been evaluated for CO2 separation. Various research studies regarding mechanisms of permeation, properties of molten salt, significance of material selection, geometry of support materials, and surface modifications have been assessed with reference to membrane stabilities and operational flux rates. In addition, the outcomes of permeation experiments, stability tests, selection of the compatible materials, and the role of interfacial reactions for membrane degradation have also been discussed. At the end, major challenges and possible solutions are highlighted along with future recommendations for fabricating efficient carbon dioxide separation membranes.

Small-Scaled Production of Blue Hydrogen with Reduced Carbon Footprint

This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the operation and technical characteristics of the synthesis gas generator. Its application in the creation of small-scaled plants with a capacity of up to 5–7 thousand m3/h of hydrogen is justified. Hydrogen production in the developed installation requires a two-stage method and includes a technological unit for producing a hydrogen-containing gas. Typical balance compositions of hydrogen-containing gas at the synthesis gas generator’s outlet are given. To increase the hydrogen concentration, it is proposed to carry out a two-stage steam catalytic conversion of carbon monoxide contained in the hydrogen-containing gas at the synthesis gas generator’s outlet using a single Cu–Zn–cement-containing composition. Based on thermodynamic calculations, quasi-optimal modes of natural gas partial oxidation with oxygen are formulated and the results of material balance calculation for the installation are presented. In order to produce “blue” hydrogen, the scheme of carbon dioxide separation and liquefaction is developed. The conclusion section of the paper contains the test results of a pilot demonstration unit and the recommendations for improving the technology and preventing soot formation.