I have developed Graphene oxide membrane on PVDF support (pore size 0.22 micron) by vacuum (0.5 mbar) filtration, thickness of GO membrane is 20 micron. when i tested it for water flux, it shows a huge variation in time with the number of passes.
For example for 50mL water filtration for first pass it took 3 minutes and for the next pass it becomes 7 to 8 minutes, and it goes increasing with next passes. what could be the reason of variable flux ...??
pls suggest some relevant papers.....!!
Thanks
This is due to the compaction of the membrane under pressure. So, before measuring the flux, pass water through the membrane at higher transmembrane pressure, say 1 mbar for 20 min. Repeat this for three times. If the flux was the same in the two last cycles, means that the compaction is complete. Then measure the flux at the desired transmembrane pressure (i.e. 0.5 mbar).
If you can't change the pressure, you should keep the system working under vacuum (0.5 mbar) for a long period of time to achieve a stable flux.
This is due to the compaction of the membrane under pressure. So, before measuring the flux, pass water through the membrane at higher transmembrane pressure, say 1 mbar for 20 min. Repeat this for three times. If the flux was the same in the two last cycles, means that the compaction is complete. Then measure the flux at the desired transmembrane pressure (i.e. 0.5 mbar).
If you can't change the pressure, you should keep the system working under vacuum (0.5 mbar) for a long period of time to achieve a stable flux.
Relevant paper: Journal of Membrane Science 100 (1995) 155-162
http://www.sciencedirect.com/science/article/pii/037673889400263X
Compaction could be the sole contributor, but also be sure that the water being used for testing is free of particles. For example, deionization does not remove particles and microbes. Pure water allowed to stand at room temperature may develop microbial contamination that could cause filter plugging.
It is possibly due to the pore blocking by the graphene particles. Each time you use the membrane, some of the graphene particles move by the premeate from graphene layer and enter the pores. They probably plug the pores and reduce the permeate flux considerably.
It is mainly due to compaction. This trend will be continued till it attains a steady state. This will take normally 4 to 5 hours at a particular transmembrane pressure.
It is might due to pore blocking and compaction. Try to use fresh water through membrane at higher trans-membrane pressure till the compaction process is completed.
I am working on the expanded polystyrene based membranes for water purification!!!
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