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Crossflow Microfiltration of particle Suspensions - The influence of hydrodynamics and physico-chemical interactions

Huisman, Ingmar Harald LU (1998)
Abstract (Swedish)
Popular Abstract in Swedish

Tvärströms mikrofiltrering är en teknik för att avskilja partiklar med en storlek på ungefär en mikrometer (en tusendel av en millimeter) från vätskor. Exempel på tillämpningar är avskiljning av jästceller från öl, och avskiljning av bakterier från mjölk. I mikrofiltrering används membran (filter) med porer med en storlek på 0.1 - 10 mikrometer. Mikrofiltreringsmembran har i princip höga flux vid relativt låga transmembrantryck, men i praktiken sjunker denna höga kapacitet ofta ganska snabbt på grund av fouling. För att minska fouling används ett tvärströmsflöde (crossflow) som ökar partikeltransporten från membranet, och på så sätt delvis hejdar partiklarna från att sätta igen membranet.... (More)
Popular Abstract in Swedish

Tvärströms mikrofiltrering är en teknik för att avskilja partiklar med en storlek på ungefär en mikrometer (en tusendel av en millimeter) från vätskor. Exempel på tillämpningar är avskiljning av jästceller från öl, och avskiljning av bakterier från mjölk. I mikrofiltrering används membran (filter) med porer med en storlek på 0.1 - 10 mikrometer. Mikrofiltreringsmembran har i princip höga flux vid relativt låga transmembrantryck, men i praktiken sjunker denna höga kapacitet ofta ganska snabbt på grund av fouling. För att minska fouling används ett tvärströmsflöde (crossflow) som ökar partikeltransporten från membranet, och på så sätt delvis hejdar partiklarna från att sätta igen membranet. Foulingtendenser kan också påverkas av ytladdningen av både membranet och partiklarna.



Målet med forskningen beskriven i denna avhandling är att få kunskap om vilka mekanismer som bestäm- mer partikeltransport och flux vid tvärströms mikrofiltrering. Viktiga mekanismer, som Brownsk diffusion, skjuvkraft-inducerad diffusion, turbulent diffusion och transport på grund av partiklarnas ytladdning, har beskrivits noggrant. En matematisk modell har utvecklats för att beräk- na permeatfluxet. God överensstämmelse erhölls mellan modell och experimentella flux vid mikro- filtrering av kiselpartikelsuspensioner. Skjuv- kraft-inducerad diffusion verkade vara den viktigaste partikeltransport-mekanismen för partiklar med en storlek av ungefär en mikrometer, men partiklarnas ytladdning kan bidra substan- tiellt till partikeltransporten.



Inte bara mängden av fouling, men även foulingens reversibilitet beror på transmembrantrycket och partiklarnas ytladdning. Filterkakor byggda av partiklar med högre ytladdning är mer reversibla.



En ny metod har utvecklats för att bestämma mem- branets zetapotential (ett mått på membranets ytladdning). Denna metod använder vattenpermeabi- litetsmätningar vid olika pH och saltkoncentra- tioner. Från ökningen av permeabiliteten med ökande saltkoncentration kan man beräkna zeta- potentialen. Metoden har jämförts med tidigare, mer besvärliga, metoder för att bestämma zeta- potentialen och god överensstämmelse erhölls. Det visade sig att membranets zetapotential inte har någon större inverkan på foulingtendenser vid mikrofiltrering av partiklar med en storlek på ungefär en mikrometer. (Less)
Abstract
Crossflow microfiltration is a technique to separate suspended particles (or cells or droplets) from liquids by use of a membrane that is permeable for the liquid but impermeable for the particles. The permeate flow drives particles to the membrane surface, where they may be deposited and form a fouling layer. To limit the growth of this fouling layer a flow is applied tangentially to the membrane (crossflow). This crossflow causes particle transport away from the membrane surface and prevents the particles from depositing on the membrane. Other factors, such as the particle charge or the membrane charge may also influence the particle transport near the membrane surface, and in that way influence the fouling behaviour.



... (More)
Crossflow microfiltration is a technique to separate suspended particles (or cells or droplets) from liquids by use of a membrane that is permeable for the liquid but impermeable for the particles. The permeate flow drives particles to the membrane surface, where they may be deposited and form a fouling layer. To limit the growth of this fouling layer a flow is applied tangentially to the membrane (crossflow). This crossflow causes particle transport away from the membrane surface and prevents the particles from depositing on the membrane. Other factors, such as the particle charge or the membrane charge may also influence the particle transport near the membrane surface, and in that way influence the fouling behaviour.



It was investigated which mechanisms are important for the particle transport in crossflow microfil- tration. Important mechanisms, such as Brownian diffusion, shear-induced diffusion, turbulent diffusion, and particle-particle interactions, were described in detail, and based on these mechanisms models were developed to calculate the permeate flux. Model predictions were compared with experimental fluxes for the microfiltration of silica particle suspensions, obtained at well defined hydrodynamic and physico-chemical conditions, and a good agreement was observed. It was found that shear-induced diffusion was the main mechanism of particle transport governing the flux in the crossflow microfiltration of particle suspensions, but particle charges can increase fluxes considerably.



Not only the amount of fouling, but also the reversibility of fouling depends on hydrodynamic and physico-chemical parameters. Cake layers formed of stronger repelling particles showed increased reversibility.



A novel method was developed to determine electri- cal properties of membrane surfaces, based on water flux measurements at various pH and salt concentration, combined with the theory of the electroviscous effect. This method was found to be an effective means of characterising membranes. However, it was found that the electrical proper- ties of the membranes do not have a significant influence on the permeate flux in the filtration of micron-sized particle suspensions. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Bowen, Richard
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Food and drink technology, ceramic membranes, shear-induced diffusion, crossflow microfiltration, silica particles, zeta potential, Livsmedelsteknik
pages
200 pages
publisher
Food Technology, Engineering and Nutrition, Lund University
defense location
Lund Chemical Centre, Sal C
defense date
1998-05-15 10:15
external identifiers
  • Other:LUTKDH/(TKLT-1027)-84
language
English
LU publication?
yes
id
8f5159f7-b752-4259-8af2-492f871f9987 (old id 38667)
date added to LUP
2007-08-01 09:17:35
date last changed
2016-09-19 08:45:13
@phdthesis{8f5159f7-b752-4259-8af2-492f871f9987,
  abstract     = {Crossflow microfiltration is a technique to separate suspended particles (or cells or droplets) from liquids by use of a membrane that is permeable for the liquid but impermeable for the particles. The permeate flow drives particles to the membrane surface, where they may be deposited and form a fouling layer. To limit the growth of this fouling layer a flow is applied tangentially to the membrane (crossflow). This crossflow causes particle transport away from the membrane surface and prevents the particles from depositing on the membrane. Other factors, such as the particle charge or the membrane charge may also influence the particle transport near the membrane surface, and in that way influence the fouling behaviour.<br/><br>
<br/><br>
It was investigated which mechanisms are important for the particle transport in crossflow microfil- tration. Important mechanisms, such as Brownian diffusion, shear-induced diffusion, turbulent diffusion, and particle-particle interactions, were described in detail, and based on these mechanisms models were developed to calculate the permeate flux. Model predictions were compared with experimental fluxes for the microfiltration of silica particle suspensions, obtained at well defined hydrodynamic and physico-chemical conditions, and a good agreement was observed. It was found that shear-induced diffusion was the main mechanism of particle transport governing the flux in the crossflow microfiltration of particle suspensions, but particle charges can increase fluxes considerably.<br/><br>
<br/><br>
Not only the amount of fouling, but also the reversibility of fouling depends on hydrodynamic and physico-chemical parameters. Cake layers formed of stronger repelling particles showed increased reversibility.<br/><br>
<br/><br>
A novel method was developed to determine electri- cal properties of membrane surfaces, based on water flux measurements at various pH and salt concentration, combined with the theory of the electroviscous effect. This method was found to be an effective means of characterising membranes. However, it was found that the electrical proper- ties of the membranes do not have a significant influence on the permeate flux in the filtration of micron-sized particle suspensions.},
  author       = {Huisman, Ingmar Harald},
  keyword      = {Food and drink technology,ceramic membranes,shear-induced diffusion,crossflow microfiltration,silica particles,zeta potential,Livsmedelsteknik},
  language     = {eng},
  pages        = {200},
  publisher    = {Food Technology, Engineering and Nutrition, Lund University},
  school       = {Lund University},
  title        = {Crossflow Microfiltration of particle Suspensions - The influence of hydrodynamics and physico-chemical interactions},
  year         = {1998},
}