This summary "dated October 18, 2017" by KU Leuven (University of Leuven, Belgium ) provides an answer to the question:

https://phys.org/news/2017-10-efficient-methane-co2.html

Dear Dr Nizar Matar thanks for your answer.

It depends on what it is contaminated with. If it is contaminated with H2S or Arsine you will need to be much more careful. If it is contaminated with asphalt the separation is pretty easy. If it is contaminated with ethane cryogenic and membrane separation are good candidates depending on how much and how well you need to separate.

Thanks Rick Manner for your detailed answer.

Rick Manner Based on your recommendation to use membrane separation, do you think zeolite membrane would be helpful for such purpose?

Here is an example of a membrane separator available commercially:

http://www.airproducts.com/~/media/Files/PDF/products/supply-options/prism-membrane/en-pb4030-biogas-datasheet.pdf?la=en

Dear Dr Sama Al-Jubouri as far as I know, theoretically Zeolite membrane is very promising in almost every area of gas separation, i.e., flue gas or natural gas separation. However, the synthesis of zeolite membranes is still challenging task and this is the reason that there is no commercial zeolite membrane available either flat sheet or hollow fiber membranes.

Muhammad Saad Khan I do agree with you in this aspect, however, I think a membrane incorporating zeolite (zeolite composite) would be helpful for certain applications.

Dear Dr Sama Al-Jubouri thanks for your answer, despite the existing challenges of zeolite based membranes, I do agree with you regarding the potential application especially at high temperature application like flue gas separations.

Muhammad Saad Khan Thank you for your answer.

it depends on partial pressure of impurities and flow rate and pressure (without considering cost)

Howdy,

Polaris has developed a process for the methane gas purification at low temperature, based on distillation in two columns in series (one for more lighter compounds and the other for heavier compounds).

The process is continuous and completely automated. The system can be combined with several typologies of pretreatment, depending on the pollutants to be removed preliminarily. In the latter case, a particular type of molecular sieves unit has been designed, and its regeneration is done with the same methane waste stream coming out from the cryogenic distillation unit, for reliable methane or other gasses purification.

See the URL: http://www.polarisengineering.com/blog/methane-purification.

Cheers,

Frank

Dear Prof Frank Veroustraete thanks for your answer. Indeed cryogenic distillation is the viable process for natural gaspurification by seperating methane and carbon dioxide from their freezing points. However, the process is itself quite energy intense in nature due to the very low freezing points of the carbon dioxides and hydroxarbons.

Dear Muhammad Mubashir

Dear Muhammad Mubashir

Dear Muhammad Mubashir

The Benfield process has been used to remove CO2 from H2 rich streams for over 50 years: http://wiki.olisystems.com/wiki/Benfield_process

Dear Rick Manner thanks for your answer. Absorbtion process indeed the viable technique for acidic gas removal, however, the limitations regarding high temperature and corrosive nature of the solvents are the current issues that need to be address more carefully.

An answer can be the cryogenic distillation, with a double-pressure process which avoids the formation of solid CO2. It is described in a 2017 paper by Stefano Langè, Laura Pellegrini et al. on I&EC Research: "Energy and economic analysis of a new low-temperature distillation process for the upgrading of high-CO2 content natural gas streams".

Dear Prof Giorgio Soave thank you for your response. Indeed cryogenic distillation is currently the among the most suitable separation technique for natural gas contaminants.

Dear Wajdi Alnoush agree with your viewpoint about twister supersonic separators is among the future solutions of the gas separations.

Ionic liquids were cited as a good option for physical absorption of CO2.

Dear Zin Eddine Dadach agree with your viewpoint regarding ILs as CO2 absorbent due to their excellent thermophysical and environmental properties. However, the expensiveness of ILs is the major hindrance for their commercial applications at this stage.

Dear Hassan Izzeddin Sarsak

Each process has pros and cons.The current bench mark is Amin based solvent(absorption).However, as this process has disadvantageous such as high energy requirement,tools corrosion,and solvent evaporation.Adsorption could be alternative process as it's economic process, easy to control,and required lower energy.

Dear Ahmed Almamoori fully agrees with your viewpoint regarding each technology have its own drawbacks and advantages.

You can read our review paper "Carbon capture and utilization update"

please share it!

I would like to thank all of you who dedicate part of your free time to my question. Your answers stimulate my thinking on the subject. I am also glad to get information from people from various countries of the world.

The real problem is that natural gas is not only methane+CO2, but it contains some heavier hydrocarbons (which usually make fractional distillation easier), heavier hydrocarbons and other impurities like nitrogen, H2S, COS etc.

So a treatment by basic solvents (amines, Selexol etc) or cold methanol (rectisol) may help solving the problem the best way.

See "Gas purification" by Kohl and Riesenfeld

Dear Sir Giorgio Soave appreciates your helpful answer.

Every application is different. Gas composition, pressure, temperature, desired final specification, and pant location all effect the selection process. My favorite reference materials on the subject include "Advanced Gas Treating" by Weiland and Hatcher and "GPSA Engineering Data Book". A good simulation tool will help sort out the best option. Amine, physical solvents, MRU, J-T, PSA, membrane, cryogenics - they all work and may be best suited for a particular application, but there is no "one size fits all" solution. More than one process is often required. The presence of sulfur compounds adds another layer of complexity and cost that must be considered.

Thank you Michael P O'Brien for your thoughtful answer.

Dear Mohsen Miandehy

PSA is effective for small flows, relatively low pressures and high CO2 content. It is not nearly as scalable as amine for larger flows/higher pressures.

I understand that your question relates to removal of CO2 from mehtane.

This brings to mind a similar problem of removing ethylene from Methane which was studied by our group several years ago.

We found that the most practical solution was a Pressure Swing adsorption on Molecular Sieve Type 5 A.

Here also as similar approach could provide the most cost effective solution as there is a sufficient differential between the adsorption kinetics of CO2 and the relatively inert methane. Presence of moisture if any could need to be factored in as it may influence the economic viability of the process

Dear Rustom Cursetji apprecites your contribution.

check, for the simplest approach, commercial recommendations, such as of Generon: https://www.generon.com/product/carbon-dioxide-co2-separation/, but there are plenty of such.

Dear Andras Kovacs thanks for addition.

It's available on my research gate page Andras Kovacs

thank you dear Ahmed, congratulation!

Useful contributions.Thanks

Sure guys

Dear Ahmed Almamoori thanks for sharing your relevant research.

Membrane separation seems to be the driving tech in several areas among which gas separation, especially with the incorporation of ILs and PILs to prepare pervaportaion membranes which are highly selective to CO2 due to dipole moment interaction with the cationic moieties of the ILs. Stability of pervaporation is still an issue tho.

Dear Mohanad Kamaz indeed ionic liquid incorporated membranes provide a good solution to high CO2 content natural gas streams due to higher selectivity. However, decrease in the mechanical properties (brittleness) of the membranes are the concerned in the presence of ILs.

https://books.google.com.pk/books?hl=en&lr=&id=03iaDwAAQBAJ&oi=fnd&pg=PA320&dq=info:Cnnhh4-dJ3MJ:scholar.google.com&ots=F9ieQzOqZq&sig=MaUVG9nvD538MB7ml8JKwWW9S7k&redir_esc=y#v=onepage&q&f=false

Back about 30 years ago every H2 plant had CO2 capture as the next to last step (just before methanation of trace CO). Amine were sometimes used but the most economic was called Benfield or Catacarb (2 independent inventors). The major advantage of this process was it could be regenerated with free low level heat. There are still many of these plants around. In fact they were once (and may still be). The primary source of CO2 for the beverage industry.

Dear Rick Manner appreciates your addition to the discussion.

May i ask, if using PSF membrane to separate the CO2 of biogas, how about the other contaminants like H2S, H2O, Ammonia etc? can it be separated too with one PSF membrane?

Dear Muhammad Saad Khan you can try links below:

https://www.mtrinc.com/wp-content/uploads/2018/09/MT04-Baker-IEC-2002-Review.pdf

Article Gas Separation Membrane Materials – A Perspective