Thread View: sci.engr.chem
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Started by michaelrs
Fri, 28 Jan 1994 16:45
Diffusion/Permeation through PTFE (Gore-Tex)
Author: michaelrs
Date: Fri, 28 Jan 1994 16:45
Date: Fri, 28 Jan 1994 16:45
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Hi everybody, We are using a PTFE membrane covered sparger for aeration of a bioreactor. In principle this should give bublefree sparging. Now we find that the mass transfer (klA) is worse than ever. It is actually at 3 orders of magnitude lower. We are running at 50 ml air/min, a stirrer speed 0f 500 rpm. We checked all connections and found, that there must be some diffusion limitation. So in contrast to the claimed increase in klA we have a dramatic loss. Now that points us to question the diffusion or permeation coeeficient for air, oxygen and nitrogen thru this membrane (about 1 mm PTFE, porous). And also if there is a special pressure is required. Any ideas ? Anyone with related experience ? I would appreciate any kind of feedback, Thanx! Michael R Schuppenhauer ETH Zurich, Switzerland michaelrs@ezzeus.vmsmail.ethz.ch
Re: Diffusion/Permeation through PTFE (Gore-Tex)
Author: michaelrs
Date: Sat, 29 Jan 1994 16:44
Date: Sat, 29 Jan 1994 16:44
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In article <HaasCN-280194155839@n1-24-215-coe-abbotts.coe.drexel.edu> HaasCN@Dunx1.ocs.drexel.edu (Charles N. Haas) writes: >In article <2ibfev$96k@elna.ethz.ch>, michaelrs@ezzeus.vmsmail.ethz.ch >wrote: > >> >> We are using a PTFE membrane covered sparger for aeration of a bioreactor. >> In principle this should give bublefree sparging. Now we find that the mass >> transfer (klA) is worse than ever. > >The first thing that I would check is the possibility of membrane fouling: >have you tried this in a sterile, non-fouling system first? > >from the keyboard of: Charles N. Haas:LD Betz Professor of The system is as of today not anymore non-fouling per se as we incubated the reactor. Yet, concerning Materials & Methods: We received the mebrane, tube of 1 mm thickness on its 316LN ringsparger (diameter 60 mm) new from Bioengineering Ltd. The sparger was build in, and the reactor subsequently sterilized. This application is set forth by Bioengineering as dedicated cell culture bublefree sparging system. However they are not able to supply data about diffusion etc. After sterilization we filled the reactor with sterile Medium for cell culture (IMDM/F12) and did a sterile test for 80 h. During this time we had bubbling sparging as we supplied gas directly from the bottle at about 1.3 bara. We considered everything beeing alright ;( NOT !! So we incubated. Then we fixed our massflow controller, sealed everything and went down with the flow to 50 mln/min. No bubbling. When using nitrogen at 200 ml/min we see bubbling sparging. The time latencies to reach full saturation with air/oxygen are so large that measuring a kla is close to impossible. before it was (using same stirrer assembly & geometry) at about 25 1/h max. After realizing our failure we used a new identical sparger to sparge water and saw the same behavior as stated above. We therefore have no reason to believe there is fouling going on to inhibit the mass flow, nor is it visible. The cell concentration is right now still small and DO variations should be so low that, changes in flow should be easily visible. Therefore the question what is different when using this membrane over the ring sparger to bubble sparging without membrane. To me this points to the physical characteristics of the PTFE (Gore-Tex) membrane as to say their diffusion or permeability for gases. I hope this additional information helps, and would really appreciate your help! Michael R. Schuppenhauer ETH Zurich, Switzerland michaelrs@ezzeus.vmsmail.ethz.ch
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