5 replies to this topic

[kougonmerlin]

I have a unique CO2 removal problem. I work in a Nanotechology company where we produce Carbon Nanotubes from Carbon Monoxide gas by a Boudouard reaction. Carbon Dioxide is a by-product of the reaction but it severely affects production. 

I need to continuously remove the Carbon Dioxide(1Kg/day) from the Carbon Monoxide gas stream. The acceptable CO2 levels are <200PPM. It is critical to ensure that the recycled Carbon Monoxide gas is not contaminated. The system operates at a pressure of 30-40 Bar (450-500PSI).

We are currently using Sodium Hydroxide/Mol Sieve successfully. The CO2 contaning Carbon Monoxide flows through a filter bed containing Mol-Sieve and NaOH. The CO2 free stream then passes to a compressor which recycles the gas. The NaOH can only be used once and it makes the process batch wise which is not efficient. I need a continuous process to remove CO2. I've been toying with a MEA but am not sure about how it can be completely removed from the recycled gas stream. 

Is there any reusable solid CO2 adsorbent that could work for this application? 

[Bobby Strain]

You can use a caustic solution to remove the CO₂ , Then dry the gas with regenerable molsieves.

Bobby

[kougonmerlin]

Hello Bobby,

I do use Mol Sieve to remove moisture in the current configuration. Instead of a caustic solution, I use Sodium Hydroxide Pellets. But I'm looking for a solid adsorbent that can absorb CO2 and then can be regenerated and re-used without having to go through any liquid circulation, pumps , dryers etc....

 

I think I found a solution. Membrane. In particular MTR Polaris Membrane, 

www.mtrinc.com/co2_removal_from_syngas.html

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That will work for me. 

[Bobby Strain]

The NaOH pellets must be wetted? If not, you can maybe switch to KOH with a bit of wetting, and just drain water periodically. I wouldn't expect that membrane would achieve removal required, and would likely still need a polishing step. Maybe you can let us know how you resolve the problem.

 

Bobby

[Art Montemayor]

Kougonmerlin,

 

What Bobby Strain has recommended is precisely what I would select as my first option in achieving what you describe: a very small, bench-size, laboratory operation.

 

If you are successful with the NaOH+Mol Sieve operation, why are you searching for something else?  I have used this method to remove this method to remove CO₂ to the ppm level in industrial applications and it should be a piece of cake in your small operation.  The system can be done in a continuous manner by using a twin-unit operation.  One unit is down and regenerating – while the second one is operating.  This is commonly done in industrial application on a much bigger scale and should be easier to apply in your case.  The solid adsorbent you are seeking for selective CO₂ removal is the Mol Sieve – which I have used to simultaneously remove CO₂ and water.  The first bulk removal step is the NaOH, followed by mol Sieve.  Please furnish a detailed flow diagram or P&ID of your process and complete basic data of the process conditions to avoid confusion.

 

I would not apply a membrane process to this small of a stream.  I would seriously look into all the trade offs involved with a membrane system and potential problems involved with the process.  You may find that the membrane presents even more process requirements and special operation – and that it is expensive to maintain and repair when the membranes fail.  I would not consider an MEA removal system as well because it can't remove the CO₂ to the levels you are probably seeking and the reboiler and process requirements make the removal of such a small stream cumbersome and difficult.

 

With a CO₂ flow rate of 1.0 kg/day, are we not discussing a main process line made of a 3/8” or ½” stainless tubing?  Correct me if I’m wrong.

[kougonmerlin]

Art Montemayor, 

 

The CO flow rate in the system is 1000SLPM, From this flow we need to remove CO2 at the rate of 1Kg/day. I've attached the PID below. 

 

http://cloud.nopo.in...31a6869bf1bbbed

 

 

 

The problem with using NaOH is that the pellets are not very efficient and needs frequent change outs. I'm yet to try decarbite or ascarite. Also the focus of our R&D is to create a process that can run autonomously. The CO2 filter is the only component that needs human intervention. That's the main reason for exploring other options. 

 

Thanks for all your inputs so far.