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Influence of gas sparging on membrane performance

Farran-Lee, Sandra LU (2015) KET920 20151
Chemical Engineering (M.Sc.Eng.)
Abstract
A new oxygen barrier film that is made of arabinoxylan has been developed by the company Xylophane. Arabinoxylan is available among other things in wheat bran. But a problem with the method of extracting the arabinoxylan is that after an alkali extraction is ultrafiltration used to remove impurities and the flux during this is quite low. In this project is it investigated if gas sparging with air can improve the flux for the ultrafiltration step. But first is a study of how gas sparging a silica sol solution affects the flux made. Because silica sol has a similar density and viscosity as the alkali extraction solution from wheat bran. Two different mem-brane modules were used: a polymeric tubular membrane in the experiments with silica,... (More)
A new oxygen barrier film that is made of arabinoxylan has been developed by the company Xylophane. Arabinoxylan is available among other things in wheat bran. But a problem with the method of extracting the arabinoxylan is that after an alkali extraction is ultrafiltration used to remove impurities and the flux during this is quite low. In this project is it investigated if gas sparging with air can improve the flux for the ultrafiltration step. But first is a study of how gas sparging a silica sol solution affects the flux made. Because silica sol has a similar density and viscosity as the alkali extraction solution from wheat bran. Two different mem-brane modules were used: a polymeric tubular membrane in the experiments with silica, and a ceramic tubular membrane when treating the hemicellulose solution. The influence of air/liquid ratio, pressure and temperature was investigated.
For the silica sol study the result was that the flux improved when the liquid flow was sparged with air. The studied air flow interval did not reach the point where the flux increase levelled off or decreased. Therefore, a higher flux can be expected when using a higher air flow than the ones studied. The optimal transmembrane pressure (TMP) for the two examined concentra-tions of silica were 1 bar for the low concentration and 0.6 bar for the higher.
When the hemicellulose solution was studied air was added into the feed tank by letting the retentate flow whip the liquid surface in the feed tank, instead of directly adding it to the liquid flow as in the silica experiments. Hence the amount of air added could not be meas-ured, but the effect it had when the temperature of the solution was 80 °C was substantial. A flux increase over 200 % was reached and if the air addition was terminated, the flux still re-mained the same. When the temperature instead was 30 °C there was no increase in flux ac-companied with the air addition. After performing several analyses on the samples taken from the start of and during, the air addition it was it clear that a degradation of molecules had oc-curred at 80 °C, but not at 30 °C. This degradation can contribute to the increase in flux, but if it is the only factor can not be determined.
No examination was made regarding the effect the heat and addition of air on the arabinoxy-lan. Such effects need to be examined before the method can by recommended for the indus-try this must be examined. (Less)
Popular Abstract (Swedish)
Studier har visat att tvåfasflöde med gas och vätska kan öka ett membrans flux. I detta examensarbete har två vätskor, kiseldioxidlösning och hemicellulosalösning, luftats med olika metoder, och luftningens inverkan på fluxet har studerats.
När vätskor med hög viskositet ska membranfiltreras är ofta fluxet lågt vilket gör att filtreringen tar lång tid och att det därför behövs stora membrananläggningar, vilket är kostsamt. En metod att öka fluxet är att tillsätta gas till lösningen och på så sätt skapa ett tvåfasflöde av vätska och gas. Tvåsfasflödet kan störa den ansamling av partiklar på membranytan som sänker fluxet. I detta arbete har två viskösa vätskors flux vid ultrafiltrering med och utan tillsatt luft undersökts.
Den första... (More)
Studier har visat att tvåfasflöde med gas och vätska kan öka ett membrans flux. I detta examensarbete har två vätskor, kiseldioxidlösning och hemicellulosalösning, luftats med olika metoder, och luftningens inverkan på fluxet har studerats.
När vätskor med hög viskositet ska membranfiltreras är ofta fluxet lågt vilket gör att filtreringen tar lång tid och att det därför behövs stora membrananläggningar, vilket är kostsamt. En metod att öka fluxet är att tillsätta gas till lösningen och på så sätt skapa ett tvåfasflöde av vätska och gas. Tvåsfasflödet kan störa den ansamling av partiklar på membranytan som sänker fluxet. I detta arbete har två viskösa vätskors flux vid ultrafiltrering med och utan tillsatt luft undersökts.
Den första vätskan var en kiseldioxidlösning vars flux vid två olika koncentrationer studerades. Driftsparametrar vars inverkan undersöktes var transmembrantryck, vätskans flödeshastighet och mängden tillsatt luft. Luften tillsattes direkt in i vätskeflödet. Fluxet var alltid högre vid den lägre koncentrationen, men den procentuella fluxökningen som erhölls genom tillsatsen av luft var högre vid den högre koncentrationen. Detta beror på att vid den högre koncentrationen är ansamlingen av material på membranytan större och tvåsfasflödet har då en större positiv inverkan på fluxet.
Hemicellulosalösningen som användes i experimenten hade erhållits genom alkalisk extraktion av vetekli. Innan ultrafiltreringen förfiltrerades lösningen med kieselguhr, för att avlägsna stora partiklar. I dessa försök tillsattes luften genom att röret med vätskeåterflödet till feedtanken höjdes ovanför vätskeytan och på så vis slogs luft ner i lösningen. Två olika temperaturer på lösningen användes under experimenten, 80 och 30 °C. Innan luft tillsattes till systemet höjdes trycket över membranet stegvis tills det maximala fluxet nåtts, alltså när en tryckökning inte längre ger en fluxökning.
Vid experimenten utförda vid 80 °C ökade fluxet relativt linjärt till mer än det dubbla när luft tillsattes. Det högre fluxet kvarstod när feedtanken med lösningen hade kopplats bort från systemet under natten, och alltså ingen luftinblandning skett under denna tid. Analyser som gjordes på de prov som togs under experimentet visade att en nedbrytning av hemicellulosamolekyler skedde när luft tillsattes.
Vid ett experiment vid 30 °C skedde ingen ökning av fluxet när luft tillsattes. Ingen nedbrytning av molekyler skedde heller vid denna temperatur. Slutsatsen är alltså att det inte var tvåsfasflödet som orsakade fluxökningen vid 80 °C utan nedbrytningen av molekyler. Om det enbart är den minskade molekylstorleken som är orsaken till fluxökningen, eller om det är en kombination av storleksminskning och tvåfasflöde återstår att fastlägga. (Less)
Please use this url to cite or link to this publication:
author
Farran-Lee, Sandra LU
supervisor
organization
alternative title
Inverkan av tvåfasflöde vid membranfiltrering
course
KET920 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
chemical engineering, kemiteknik
language
English
Swedish
id
7870050
date added to LUP
2015-10-20 16:26:45
date last changed
2015-10-20 16:26:45
@misc{7870050,
  abstract     = {A new oxygen barrier film that is made of arabinoxylan has been developed by the company Xylophane. Arabinoxylan is available among other things in wheat bran. But a problem with the method of extracting the arabinoxylan is that after an alkali extraction is ultrafiltration used to remove impurities and the flux during this is quite low. In this project is it investigated if gas sparging with air can improve the flux for the ultrafiltration step. But first is a study of how gas sparging a silica sol solution affects the flux made. Because silica sol has a similar density and viscosity as the alkali extraction solution from wheat bran. Two different mem-brane modules were used: a polymeric tubular membrane in the experiments with silica, and a ceramic tubular membrane when treating the hemicellulose solution. The influence of air/liquid ratio, pressure and temperature was investigated.
For the silica sol study the result was that the flux improved when the liquid flow was sparged with air. The studied air flow interval did not reach the point where the flux increase levelled off or decreased. Therefore, a higher flux can be expected when using a higher air flow than the ones studied. The optimal transmembrane pressure (TMP) for the two examined concentra-tions of silica were 1 bar for the low concentration and 0.6 bar for the higher. 
When the hemicellulose solution was studied air was added into the feed tank by letting the retentate flow whip the liquid surface in the feed tank, instead of directly adding it to the liquid flow as in the silica experiments. Hence the amount of air added could not be meas-ured, but the effect it had when the temperature of the solution was 80 °C was substantial. A flux increase over 200 % was reached and if the air addition was terminated, the flux still re-mained the same. When the temperature instead was 30 °C there was no increase in flux ac-companied with the air addition. After performing several analyses on the samples taken from the start of and during, the air addition it was it clear that a degradation of molecules had oc-curred at 80 °C, but not at 30 °C. This degradation can contribute to the increase in flux, but if it is the only factor can not be determined. 
No examination was made regarding the effect the heat and addition of air on the arabinoxy-lan. Such effects need to be examined before the method can by recommended for the indus-try this must be examined.},
  author       = {Farran-Lee, Sandra},
  keyword      = {chemical engineering,kemiteknik},
  language     = {eng},
  note         = {Student Paper},
  title        = {Influence of gas sparging on membrane performance},
  year         = {2015},
}