Carbon Molecular Sieves (CMS)
CMS
CMS is the crucial element of any PSA-Plant for the generation of Nitrogen. The PSA process provides an in-house, indepedent Nitrogen supply at low cost for ineritizing storage tanks, piplines and tankers, for processing and storing perishable foods and beverages, for heat treatment of metals, for processing plastic and fibers, in microchip production and many other applications.
PSA process
The quantity of gas adsorbed by activated carbon depends on temperature, gas pressure, gas composition, and adsorption velocity. Pressure Swing Adsorption makes use of cyclic pressurization and depressurization steps, where more gas is adsorbed at high pressure and then released when the pressure is reduced. PSA does not require heat energy, and the desorption-adsorption conditions can be adjusted by switching pressurization and depressurization. This enables PSA to operate at a short cycle time. The figure below illustrates a typical PSA system. Pressured raw gas is directed to A, one of two adsorption vessels packed with CMS. Under high pressure, while preferentially adsorbed gas constituents remain in the CMS bed, other constituents pass through the vessel to produce purified product gas. When the vessel A has reached its adsorption capacity, the raw gas is directed to vessel B and vessel A is depressurized. Adsorbed elements are thus released and the CMS is ready for another cycle. The cycling between the two vessels enables the continuous production of purified gas.
Nitrogen-Oxygen Separation by PSA Method Using CMS
As shown in the diagram, the size differences between oxygen and nitrogen are very small. Osaka Gas Chemical's "Molcebon" has precisely adjusted pore diameters, resulting in high nitrogen and oxygen separation performance, and is used as a high-performance adsorbent for PSA.
Image showing the high nitrogen and oxygen separation performance of Osaka Gas Chemical's CMS.
Osaka Gas Chemical's CMS product range （partial list）
Related papers and publications
ACS Applied Materials & Interfaces
April 20, 2022Volume 14, Issue 15Pages 16959-18004
https://pubs.acs.org/toc/aamick/14/15
Abstract
This study was conducted with the aim of synthesizing a carbon molecular sieve (CMS) capable of efficiently and highly purely separating propylene and propane, and of elucidating its separation mechanism. Based on insights obtained from previous research (https://doi.org/10.1016/j.carbon.2018.10.021), we further carried out CMS synthesis experiments, chemical vapor deposition (CVD) simulations, and analysis using a simple model.
As a result, the following three findings regarding the separation characteristics of propylene and propane were clarified:
The separation performance can be controlled by the amount of carbon introduced during the CVD process.
Precise control of the pore entrance size of the CMS is essential.
Control of the aspect ratio of the pore entrances is also important; more specifically, a square-shaped pore entrance is preferable to a slit-shaped one.
Based on these findings, we successfully synthesized a CMS that selectively adsorbs only propylene from a propane–propylene mixed gas.
Background
The pressure swing adsorption (PSA) method is one of the gas adsorption techniques in which gas adsorption and desorption on an adsorbent are achieved by utilizing changes in pressure. Compared with the conventional method—where mixed gases are distilled under high pressure in large-scale equipment to separate and recover propylene and propane based on differences in boiling points—the PSA method enables significant cost reduction. Osaka Gas Chemicals is engaged in the development of CMS for selectively separating and recovering propylene and propane from mixed gases generated during petroleum refining and the thermal cracking of feedstock oils.
ACS Applied Materials & Interfaces
ACS Applied Materials & Interfaces is a top-tier academic journal in the fields of materials science and applied chemistry.
ACS Appl. Mater. Interfaces (published in this journal in 2022)
Impact Factor：9.5
Carbon
Volume 141, January 2019, Pages 626-634
https://doi.org/10.1016/j.carbon.2018.10.021
Abstract
To explore design guidelines for synthesizing carbon molecular sieves (CMS) for gas-phase separation, molecular behavior was simulated on a computer and large datasets were analyzed. As a result, an ideal carbon pore structure was successfully constructed, taking into account the CMS pore size, shape, and diffusion rates.
Background
CMS is a porous carbon material whose pore size is precisely designed and tuned to match the size of target adsorbate molecules. It is used in adsorption processes—specifically pressure swing adsorption (PSA)—that exploit differences in adsorption rates depending on molecular size. In order to further expand the application of CMS to the separation of various gas mixtures in the future, it is essential to gain a deeper understanding of gas separation mechanisms and to achieve optimal CMS synthesis. Therefore, establishing design guidelines for this purpose is of great importance.
Carbon
Carbon is a world-leading academic journal in the field of carbon materials.
Carbon (published in 2019)
Impact Factor：8.821
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