I am just wondering if someone can give a clue on the use of casting solvents to improve dense membrane performance for gas separation. These three gases - CH4, CO2 and N2 have their molecular sizes (diameters) very close to one another as compare to other light gases such as He, H2 etc. Thus designing highly selective membranes by pore size modification is challenging for separating these gases. The two prominent sites for gas transport through polymers by the Dual-sorption mode theory are the Langmuir and the Henry sites. The nature of transport in the former is by hole filling (diffusion) while that in the latter is by dissolution (solubility). Thus the permeability as well as selectivity can be improved either by improving the diffusivity or solubility or both. Literature report have shown that solubility can be improved by polymer polarity or the presence of functional groups (eg OH, amine etc) with affinity for CO2 within the polymer while the diffusion can be improved by method such as porogenation, grafting, PIM etc. The template effect documented by Kesting, which report that during preparation, the solvent acts as a transient template which controls the packing density of the final membrane material and that the permeability of polymeric membrane is directly related to the molar volume of casting solvent, is an interesting observation which can possibly revolutionize the membrane design and preparation technique. It seems solvents can be used as porogens and can perform the same function as grafting and PIM following a careful implementation. I want to think the technology of solvent preparation/synthesis is capable of opening up a new frontier for membrane technology research in gas separation. Does anyone has any opinion on this view? In order to properly manage the discussion, I would appreciate if the scope of the response is limited to dense polymeric membranes for gas separation (CO2,CH4 and N2). Looking forward to gaining from you all.
Both Ca decorated and fuorine modified graphene membrane show strong selectivity for gas separation (CO2, N2).
Hi,
Regarding solvent casting membranes generally volatile solvents are preferred such as Chloroform, Dichloromethane, MIBK, toluene, Hexane, Acetone etc. The solvent selection can be done based on the polymer properties such as polarity, functionalities, solubility parameter etc.
Regarding separation of gases with similar kinetic diameters other parameters such as polarity (dipole, qudrapole), permeability and diffusivity of the gases through polymers, chemical or physical adsorption of the gases with or within the polymeric chains etc. could be considered.
Nowadays lot of work on mixed matrix membranes with different porous particles for separation of these gases is studied which is adding huge data to the literature. You can easily get the current insights through review articles on gas separation.
PIMs and ionic liquid, graphene are the current hot topics in this work.
I think if you follow the literature then definitely you will get some new approaches of the gas separation membranes.
I hope this answers your query.
when you have gases you have automatically pressure, I'm not sure if the polymeric membrane can support this pressure , in my opinion you can use membrane ceramic or hybrid system like a membrane multilayer for to keep a hight selectivity and to support a hight pressure
Thanks Tarik.
Polymeric membranes support high pressure as high as up to 52 bar or more. Efforts are being made to develop more polymer that can withstand higher pressure than this.
Dear Jimoh,
The reverse selective polymeric membranes are one the best options to separate CO2/N2 and CO2/CH4.
I suggest one of PTMSP, PMP, or PDMS as polymeric phase.Various inorganic fillers can be used as filler such as fumed silica.
These nano-composite membranes work by solution-diffusion mechanism cohen and trenbull mechanism. The separation is done upon Tc and condensability of species which is different for these gases despite the close Vc and kinetic diameters of these pairs. These polymers have the largest free volume and permeability coefficients among the polymers. But in glassy polymers physical aging is important which must be controlled. During the solution preparation, if u choose a solvent with higher solubility for polymer and preparing more viscous solution, the final permeabilities may change.In the case of a particular polymer, more viscous casting solution, more dense and less FFV membrane.
Hope to be useful.
Regards,