Separating Gases

What are the mixed gases?

Hi Guest.

I agree with Steve S on this one, cryogenics is your best bet.

Spencer.

We're attempting to separate CO2 from any mixture of gases. We'll look into Cryogenics, but we like to develop an inhouse solution if at all possible.

Unless your house is really blazing hot, you should be able to use a cryogenic process.

You could use molecular sieves in a pressure-swing process.

A lot depends on the pressure of your mixture, and whether you want to keep the CO2 or dump it.

What is the pressure, and the concentration of the CO2?

No one has mentioned chemical absorption/reaction. CO2 being an acid gas will react with a base in solution. These processes are well documented, look for inorganic solutions of potassium carbonate to organic processes using amines. The current practicality for this approach requires the partial pressure of CO2 to be well above the 500 - 700 ppm atomospheric concentration. Absorption is an approach if you are looking to scrub CO2 from say power plant exhaust. Then the solution is regenerated with heat, in an environment with very low CO2 partial pressure, which effects the stripping of gas from solution. Main process is a contactor (the stack). Liquid is collected, and regenerated (stripped of CO2, and other acid gases). The liquid is then pumped back to the contactor. Now what do you do with the relatively pure CO2 (after condensensing water from the regenerator overhead)?

This is the problem with recovering CO2 before it becomes a supposed green house gas. You need a market or a place to put the CO2.

You can use gas centrifuges, but then again, that's how they separate uranium₂₃₅ fluoride from uranium₂₃₈ fluoride, so naughty naughty!!!

Good point, Vermin! But I doubt he could obtain the pure nickel equipment on a scale to accomplish this! He'd be better off trying to buy some (enriched Uranium) from Iran. If the price of crude oil continues at the present level, there will be a lot more "nucleasr power reactors" around the world! One thing: The Germans synthesized hundreds of thousands of tons of crude, gasoline and lube oil and grease during WW II, from 1939 to 1945, but no one else seems to have been able to duplicate that. Here we are with all this carbon dioxide that we don't want. One would think that someone would have solved the problem of creating process gas with hydrogen to synthesize a crude oil in million gallon quantities by now!!

ps to my earlier post.

Go to the 'Zeolite absorbtion of gasses' thread here in CR4 - 'gfwhell' is asking a similar question.

I think some of the Manhattan project has been declassified. Check out those notes and have a blast.

Bob G

We are making a lab scale Pressure swing adsorption unit for a customer here

in INDIA. The purpose is to separate CO2 from N2 and O2 mixture. They will try

different catalysts for separation efficiency. Let the catalyst absorb selectively

from the pressurised mixture ,release pressure ,flush the reactor with N2, evacuate

and heat to desorb the CO2 and pump it into the receiver.That seems to be the logic.

This is a standard in the air separation industry for removal of the CO2 and H2O prior to entry in the cryogenic process. If you don't have any water, just use molecular sieve rather than alumina and molecular sieve. There are books that will help you size these vessels, determine regen flow, etc. If you get stuck, there are a fortune of companies that design this system. Are you talking large concentrations of CO2 or more like the CO2 that is in air?

If you want to separate those gasses, why don't you freeze them out? They all have a significant temperature difference for going liquid and/or freezing.

The Apollo missions used lithium hydroxide canisters to absorb the carbon dioxide exhaled by the astronauts.They also used charcoal to filter odors.

I am not aware how it is removed, but sure some process could reverse it.

Definitely cryogenics for most gases.

If it is a small mass--Go for Gas Chromatography--separate+analyze

If a huge flowrate like Natural/Associated gas ( 3>4 main molecular composition) you can separate through combination of compression,absorption,adsorption,rectification and Condensation.

Separation of Oxygen from Nitrogen and rare /Noble gases was for a long time in the domain of liquifaction/fractionation.

However - today, due to heavy demand for low-energy -consuming Oxygen in various Coal/Biomass to Ammonia/Methanol projects the search is for new routes .

To get H2 separated from 'Synthesis Gases ' at Gasifier output-- you resort to shift reactions creating safe and separable CO2 from the CO.

Fermentation gases (CH4, H2, CO2, trace H2) can be separate by using hollow fiber membrane treatment. Works well.

Paterek

The best appropiate technology to separate gases is a technology that has the best cost effective. There are several technologies to separate gases: Criogenic (fractionation), molecular sieve, membranes, absorption, adsorption, chromatography, derivatization (chemical reaction), etc....

You have to perform a study to determine what is the best economic technology for the gases to separate.