I am using an HPLC pump to re-circulate feed stream in a crossflow membrane module. Somewhere along this line, I have put a needle valve to induce back-pressure for permeation. Apparently, although I fix the pressure at the start of the experiment, both flux and pressure change over time (strange). Does anyone experienced this? Any suggestion why this is happening and how to solve so as to have one fixed variable and another response variable?
many thanks in advance
1/19/18
Dear Abaynesh,
I'm not sure I completely understand what you are trying to do. I assume the pressure you are monitoring is on the "feed" side of the module. If you continue to pump the feed stream through the membrane, eventually it will begin to foul, i.e., be come blocked. When this happens, the pressure will increase. At the same time, the flux will also drop. Is this what you are seeing? If so, you may have to interrupt the filtration process and flush (i.e., clean) the membrane, then continue w/ the filtration.
I hope this is formation helps you.
Bill Colonna Center for Crops Utilization Research, Iowa State University, Ames, IA USA [email protected]
Dear Colonna,
Thank you very much for your reply.
Yes exactly the pressure rise and the flux decline are due to fouling. What is strange for me that in membrane process we either operate at fixed pressure and follow the drop in flux over time to evaluate the system efficiency or fix the flux and follow the increase in pressure.
In my case, I was doing the first one, where I fix the pressure and try to follow the flux decline. Apparently, they both are changing meaning it would be difficult to evaluate the system efficiency?
1/19/18
Dear Abaynesh,
Yes, if both are changing, measuring system efficiency will be challenging. Pressure drop will always occur as the membrane fouls. Manual readjustments could be done to keep the pressure constant, but you'd have to "babysit" the system, and this would be time consuming. Perhaps you can find a pump that will automatically re-adjust and maintain the pressure at a predetermined setting. This would eliminate pressure change as a variable and let you measure only the flux change.
I hope this helps you. Good luck.
Bill Colonna
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