2 Configuration FLAT - the active layer is a flat TUBULAR - synthesised as a continuous layer- low surface area per volume- used in flate-and-plate module and spiral-wound moduleTUBULAR- usually active layer is inside- the permeate crosses the membrane layer to the outside (feed inside)- high surface per volume- several lenghts and diameters (>10mm)
3 Membrane module – the unit into which the membrane’s area is packed. Protects membranes against mechanical damagePermits get high area in small volumeRequirements for membrane:High selectivity separation componentsHigh permeability with respects to solventM.M. have to be keep:High productivity of process,Leaktighness between stream of permeate and retentate in thehigh ratio of membrane surface to module’s volume,Facility of cleaning and sterilization,Low costs by itselfHigh resistance membrane on agressive chemical,physical & biological factors.
4 SIMPLE MODULE The module is the central part of membrane instalation. Feed composition and a flow rate inside the module will change as a function of distance.Permeate stream is the fraction of the feed stream of the feed stream which passes through the membrane.Retentate stream is the fraction retained on the membrane.
6 The choice of module configuration Based on economic considerationsType of separation problemEase of cleaningEase of maintenanceEase of operationsCompactness of the systemScalePossibility of membrane replacement
7 PLATE-AND-FRAME MODULE The number of sets needed for a given membrane area furnished with sealingring and two end plates then builds up to a plate-and-framestack
8 Plate-and-frame module Schematic flow path in plate-and-frame moduleIn order to reduce channeling- a tendency a flow along a fixed pathway and to establish as uniform flow distribution so-called ‘stop-discs’Tortous-path plateIs used to improve mass transfer,to reduce concentration polarisation by applying a proper spacer material.
9 Plate-and-frame module AdvantagesHigh allowable work pressure(high viscosity liquids)Easy to cleanEasy to replace membranesDisadvantagesLow membrane area per volume( m2/m3)Electrodialysis, pervaporation, membrane destillation
10 SPIRAL-WOUND MODULE Membrane and permeate-side spacer material are gluedalong three edges build a membrane envelope.The feed flows axial through the cylindrical moduleparallel along the central pipe whereas the permeateflows radially toward the central pipe.Pressure vessel containig 3 spiral-wound modules arranged in series
11 Spiral-wound module Disadvantages Advantages - High packing density ( m2/m3)- Easy and inexpensive to adjust hydronomics by changing feed spacer thickness to overcome conc. polarization and fouling- Low relative costsDisadvantagesDifficult to cleaning and sterilizationHigh pressure drop( kPa)- Use only for pure medium
13 Tubular module Cross section of monolithic ceramic module Schematic drawing of tubular moduleThe feed solution always flows through the centre of the tubes while the permeate flows through supporting tube into the module housing .
14 Tubular module Disadvantages Advantages Resistance for fouling Easy to cleaningDisadvantagesLow packing density (300m2/m3)ExpensiveReverse osmosis, ultrafiltration
15 Capillary moduleCapillary module consists of a large numbers of capillaries assembled together in a module.The free ends of the capillaries are potted agents such as epoxy resins, polyurethans.
16 pressure drop, type of membrane available etc. are important. CAPILLARY MODULETwo types of module arrangements can be distinguisedThe choice between the two concepts is mainly based on the application where the parameters such a pressure,pressure drop, type of membrane available etc. are important.Depending on the concept chosen, asymmetric capillaries are used with their skin on the outside or inside
17 HOLLOW-FIBER MODULEThe difference – dimmensions of the tubes, but module concepts are the same.The hollow-fiber module – highest packing density 30000m2/m3.A perforated central pipe is located in the center of the module through which the feed solution enters.
18 Hollow-fiber moduleAdvantageous to use the ‘inside-out’ type to avoid increase in permeatepressure within the fibers and it’s thin selective top-layer is better protected,whereas a higher membrane area can be achieved with the ‘outside-in’ concept.
19 Hollow-fiber module Advantages High packing density 500-9000 m2/m3 Low relative costsDisadvantagesPoor resistance of foulingDifficult to cleanDifficult to change the membraneMicrofiltration, ultrafiltration, reverse osmosis, pervaporation,liquid membranes and the membrane cofactors where the boundary layer resistancemay become very important as well.
21 Membrane foulingPolarisation phenomena are reversible processes, but in practise, a continuous decline in flux decline can often be observed.Flux as a function of time. Both concentration polarizationand fouling can be distinguished
22 Membrane foulingThe (ir)reversible deposition of retained particles, colloids, emulsions, suspensions, macromolecules, salts etc. on or in the membrane.The includes adsorption, pore blocking, precipitation and cake formation. Occurs in microfiltration and ultrafiltration.Pressure driven processes, type of separation and the type of membrane used to determine the extent of fouling.Depends:concentration,temperature,pH,ionic strenght,specific interactions (hydrogen bonding, dipole-dipole interactions)
23 rc – specific resistance of the cake Membrane foulingKozany – Carman relationship:Flux:ds – the ‘diameter’ ofthe solute particlewhere:Total cake layer resistance (Rc) - porosity of cake layerms – the mass of the cakewhere:where:s – the density of the soluterc – specific resistance of the cakelc – cake thicknessA – the membrane areaThe thickness of the layer depends on the type of soluteand especially on operating conditions and time.The growing layer of accumulates results in a continuous flux decline.
24 Membrane foulingRc the cake layer resistance can be obtained from the mass balance.In case of complete solute rejection:R = 100%The flux can be written:orJw – pure water flux
25 Membrane foulingCbPReciprocal flux is indeed linearly related to the permeate volume V for various concentrations (Cb)and applied pressures (P) in an unstirred dead-end filtration experiment with BSA as solute.Reciprocal flux as a function of the permeate volume for different concentrations (1) and applied pressures (2)
26 Methods to reduce fouling Pretreatment of the feed solution- heat treatment- pH adjustment- addition of complexing agents (EDTA etc.)- chlorination- adsorption onto active carbon- chemical clarification- premicrofiltration- preultrafiltrationMembrane propertiesModule & process conditionsCleaning- hydraulic cleaning ( back-flushing )- mechanical cleaning- chemical cleaning- electric cleaning
27 Membrane foulingAlternate pressuring and depressuring and by changing the flow direction at a given frequency.After a given period of time, the feed pressure is released and the direction of the permeate reversed from the permeate side to the feed side in order to remove the fouling layer within the membrane or at the membrane surface.Flux versus time behaviour in a given microfiltrationprocess with and without back-flushing