Hi Mark, I had a quick look at the papers on your site. If I understand correctly, you recover a gas stream with most of the CH4 at depth. You want to recover the CO2 that remains in solution, so you pump it to the surface and collect the gas, which contains some residual CH4. You then compress the mixture, liquefying the CO2 to separate it from the CH4. What you'd like is a process that collects the CO2 in the first step.
The membrane process produces H+ and shifts the acid/base equilibria from HCO3- to dissolved CO2, which is much less water soluble. Here's a plot of the equilibria (at 1 atm): http://en.wikipedia.org/wiki/File:Carbonate_system_of_seawater.svg At seawater pH most of the CO2 is present as HCO3- and CO3--. If you drop the pH to about 4, most is present as molecular CO2. If you acidified the output of the digester by running it through a membrane acidifier I'm pretty sure you'd improve the initial take-off of CO2. But I don't know by how much. It depends on how CO2 solubility and the acid-base equilibria change with pressure, and what the phase diagram of CO2/seawater looks like at pressure. In the paper by the PARC researchers they used a vacuum pump to pull off the CO2. I don't know if the CO2 would just come out of solution at the concentration/pH/T/P condition that prevails in your digester. You should also consider the cost of energy for the process - PARC measured 242 kJ/mol CO2 recovered. Forgive me if I've misunderstood your process, I've only had a quick look, cheers, john -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To view this discussion on the web visit https://groups.google.com/d/msg/geoengineering/-/rGa7HQwiTzcJ. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
