Abstract
In the field of gas separation and purification, membrane technologies compete with conventional purification processes on the basis of technical, economic and environmental factors. In this context, there is a growing interest in the development of carbon molecular sieve membranes (CMSM) due to their higher permeability and selectivity and higher stability in corrosive and high temperature environments. However, the industrial use of CMSM has been thus far hindered mostly by their relative instability in the presence of water vapor, present in a large number of process streams, as well as by the high cost of polymeric precursors such as polyimide. In this context, cellulosic precursors appear as very promising alternatives, especially targeting the production of CMSM for the separation of O2/N2 and CO2/CH4. For these two gas separations, cellulose-based CMSM have demonstrated performances well above the Robeson upper bound and above the performance of CMSM based on other polymeric precursors. Furthermore, cellulose is an inexpensive bio-renewable feed-stock highly abundant on Earth. This article reviews the major fabrication aspects of cellulose-based CMSM. Additionally, this article suggests a new tool to characterize the membrane performance, the Robeson Index. The Robeson Index, θ, is the ratio between the actual selectivity at the Robeson plot and the corresponding selectivity—for the same permeability—of the Robeson upper bound; the Robeson Index measures how far the actual point is from the upper bound.
Highlights
Nowadays, most industrial gas separations rely on energy demanding and expensive processes such as cryogenic distillation and pressure swing adsorption
The first scientific study on membrane-based separations dates back to the 18th century, significant developments in membrane technology were made only after the World War impervious to the species; (II) to make viable for the commercial market, and in the 1960s, high-flux anisotropic membrane modules were applied for reverse osmosis applications [2,3]
A composite Carbon Molecular Sieve Membrane (c-carbon molecular sieve membranes (CMSM)) is formed used in the polymeric precursor must have an affinity with the matrix
Summary
Most industrial gas separations rely on energy demanding and expensive processes such as cryogenic distillation and pressure swing adsorption. More energy-efficient separation processes methods could save 100 × 106 tons of carbon dioxide emissions per year if applied to the US alone. In this context, membrane separation appears as a promising industrial process set to reduce the energy intensity of the separation process. Membrane technologies for gas separations have been growing ever since They present several advantages, such as continuous separation, low energy cost, easy scale-up and easy coupling with other separation processes in an industrial environment. Other separations, such as sour gas treatment, Xe recovery, recovery, and He separation separation or or sulfur sulfur removal, removal,have havebeen beeninvestigated investigated and andpromising promising results resultshave havebeen beenachieved achieved. A more detailed review review on the major on cellulose-based based CMSM is presented
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