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Inopor GmbH is one of the leading manu-facturers and suppliers of ceramic mem-

branes for liquid filtration. The head officeof Inopor GmbH is located at Veilsdorf/DE.The company is a daughter company ofthe Rauschert Group, which is world-wideamong the leading ten suppliers of tech-nical ceramics with approx. 1500 employ-

Ceramic Membranes in Chemicaland Pharmaceutical ApplicationsExcellent chemical and mechanical resistance make ceramic membraneseven suitable for applications, where the usage polymeric membranes isnot possible or not economical. Especially with the invention of theceramic nanofiltration membrane, a wide range of markets for ceramicmembranes was opened.

ees and 16 production plants as well assales offices around the world.The Inopor GmbH is specialized in ceram-ic membranes for liquid filtration and theonly supplier world-wide of ceramic nano -filtration types with a cut-off of 450 Dal ton[Da]. The company also works together inpartnership with the Fraunhofer InstituteIKTS/DE.

Ceramic membranes for liquid filtrationIn general, membranes can be specified bytheir chemical and material structure. Typ-ical membranes for liquid filtration are

polymeric membranes, composite mem-branes and inorganic membranes. Ceram-ic membranes belong to the group of in -organic membranes, like also e.g. carbonor metal membranes. More detailed, theceramic membranes for liquid filtration belong to the oxide ceramic membranesand are mainly made of aluminium oxide,zirconium oxide or titanium oxide. Compared with other typical membranesfor liquid filtration, ceramic membranesprovide a lot of advantages e.g:• high chemical resistance

(pH-value 0–14), even against oxidizers• high thermal resistance, even against

steams• high resistance against biological- and

microorganism• high resistance against abrasive media• easy handling and storage.Ceramic membranes belong to the groupof porous membranes, which means thattheir membrane structure consists ofpores with a defined average pore size.Typical non-porous membranes are e.g.polymeric membranes for reverse osmo-sis or ion-exchange membranes.

Keywordsliquid filtration, ceramic membranes,,micro-, ultra-, nanofiltration, cross-flowfiltration, alumina (Al2O3), titania (TiO2),zirconia (ZrO2) and silica (SiO2)

Stefan DuscherInopor GmbH98669 VeilsdorfGermanywww.inopor.com; www.inopor.de

stefan.duscher@inopor.de

Tab. 1 Available Inopor® membranes

Material Mean pore size [nm] Cut-off [Da] Open porosity [%] Dimension

Microfiltration inopor® micro

α-Al2O3

1000 800 600 400 200 100 70 40–55

Mon

ocha

nnel

and

mul

ticha

nnel

tube

s w

ith a

leng

th u

p to

120

0 m

m

TiO2

800 250 100

ZrO2 110

Ultrafiltration inopor® ultro

γ-Al2O310 5 7500

30–55TiO230 5 8500

ZrO2 3 2000

Nanofiltration inopor® nano

SiO2 1,0 600 30–40

TiO21,00,9

750 450

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The Inopor® membranes are available inalumina (Al2O3), titania (TiO2), zirconia(ZrO2) and silica (SiO2). With these mater -ials, membranes can be produced whichcover the range from microfiltration tonanofiltration (Tab. 2).The processes microfiltration, ultrafiltra-tion and nanofiltration have in common,that they are driven by hydraulic pressure,

The support defines the geometries of theceramic filter elements. Technically, cer -amic membranes can be fixed on flat sheetsupports as well as on tubular or multi-tubular supports. The flat sheet design ismainly used for lab size applications; forindustrial applications the usual design forceramic membranes is tubular. Depending on what cut-off rate shall bereached, more or less membrane layersare fixed on the support, starting with verycoarse layers – so called intermediate layers – membrane layers with decreasingpore sizes are added until the designatedpore sizes are reached; Fig. 1 shows a typ-ical structure of different layers.Because of reasons of cost-efficiency theceramic modules are designed in a waythat a maximum specific membrane areaper element is realized. On the other hand,the membrane elements has to be de-signed in a way, that they can handle alsofeed media with a high content of particlesor a high viscosity. Last but not least, thegeometries of the ceramic filter elementsare responsible that the hydraulic proper-ties during the process are acceptable allover the membrane element. Therefore,the membrane elements are designed withtubular channels; depending on the appli-cation and properties like e.g. viscosityand particle content, they are used in sin-gle-channel design or in multi-channel de-sign. Fig. 2 gives an overview of the typicalgeometries of ceramic Inopor® mem-branes.

Separation with ceramic membranesThe standard ceramic filter elements havein common, that the membrane layer isfixed at the inside of the tubes. The facessides of the ceramic filter elements aresealed to avoid, that feed or concentratecan by-pass the membrane. To guaranteemaximum resistance and reliability, thesealing of Inopor® membranes is made ofglass. Fig. 3 shows the core componentsof a ceramic filter element.The ceramic filter elements of Inopor® arecompletely produced at own productionfacility, so that Inopor® is able to supplythem in various materials and lengths upto 1200 mm. Fig. 4 shows a typical extru-sion process of a ceramic support.For the filtration process, feed liquid flowsthrough the tubular channels, pressurizedby a feed pump. Depending on the process

whereas for example processes like elec-trodialysis are driven by electrical forces.Tab. 1 shows the available Inopor® mem-branes and their separation characteris-tics.In general, the ceramic membranes arefixed on a ceramic structure, which iscalled “support” and which consists alsoof a very porous oxide ceramic material.

Tab. 2 Fields of application for micro-, ultra- and nanofiltration

Fig. 1 Typical structure of a ceramic membrane (support, intermediate and membrane layer)

Fig. 2 Typical element design of Inopor® membranes

Separation process Typical application Molecular weigth / Pore size

Microfiltration

Whey separationMilk fractioningBio-mass separationPre-filtration of liquids

>0,1µm

Ultrafiltration

Germ separationProtein separationMilk fractioningOil water separation

5000 Da – 0,1 µm

Nanofiltration

Milk fractioningWater softeningSeparation of multivalent ionsPharmaceutical separationSeparation of alcohols

200 Da – 5000 Da

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and viscosity, the feed pressure is between3 bar (microfiltration) and 40 bar (nano-filtration). With increasing feed pressure,the specific flow of filtrate (so called “per-meate”) increases, but also the risk of sedi mentation or membrane blocking in-creases and the quality of permeate de-

creases; in case of separation of bio-mass-es, increasing feed pressure also effectsdamaging of the micro organism. Ceramic filter elements are installed inhousings; typically, up to approx. 40 ceramic elements can be installed in parallelin one housing. During the phase of layout

and design, it has to be considered, that thehousing has to be designed in a pressurerange according to the working pressureand that the housing has also to be chemic -ally and thermally resistant, because thehousing gets also in contact with the feedliquid, the permeate and the concentrate.

Fig. 4 Extrusion of a ceramic support

Fig. 3 Components of a ceramic filter element

Fig. 5Cross section of a ceramic membrane

Fig. 6Flow through in a ceramic membrane element

Fig. 7 (top)Inopor® membranes

Fig. 8 (left)Inopor® membrane housing

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To realize and regulate the separationprocess, a throttle is installed on the concentrate side, so that the feed pressure effects a transport of liquid through themembrane. Because of the pore sizes, notall ingredients of the feed liquid can passthrough the membrane. The remain ingvolume flow on the concentrate side ef-fects a transportation of the separated in-gredients out of the membrane element;this flow is the reason why this type of fil-tration is called “cross-flow filtration”.Fig. 5 shows the membrane layers andFig. 6 presents schematically the flows in-side a cross-section of a ceramic element.Fig. 8 shows a typical housing of Inopor® with installed ceramic filter elem -ents.

Applications and marketsBecause of their excellent chemical andmechanical resistance, ceramic mem-

Example: Retention of germsWater is the base for a lot of medical liquids for infusions. This water – so called“water for injection” – has to be extremelypure and the treatment of this water is regu lated in the according pharmacopoeia.Fig. 9 gives a general overview of treat-ment processes for water for injection, in-cluding heat exchange (HE), reverse os-mosis (RO), membrane degasification(MD), electrodeionisation (EDI) and ultra-filtration (UF). The electrode ionisationprocess is the step where nearly all ionsare removed from the water and it worksas combined process of ion exchange anddialysis. Especially in the anion exchangeresin, micro organism can grow. To avoid,that this microorganism would pollute thepiping system and the purified water afterthe EDI stage, an ultrafiltration has to beinstalled. For this application it is highlynecessary that the membrane resists the

branes are even suitable for applicationswhere the usage polymeric membranes isnot possible or not economical. Especiallywith the invention of the ceramic nano -filtration membrane, a wide range of mar-kets for ceramic membranes was opened.So, typical applications for ceramic mem-branes are:• Separation of pharmaceutics out of

waste water (nanofiltration)• Oil water separation

(ultrafiltration/nanofiltration)• Retention of germs and virus

(ultrafiltration)• Filtration of organic solvents

(ultrafiltration/nanofiltration)• Dye separation (nanofiltration)• Filtration of acids and caustics

(ultrafiltration/nanofiltration)• Fractioning of milk

microfiltation/ultrafiltration/nanofiltration).

Fig. 9Overview treatment process for for water for injection, including heat exchange (HE), reverse osmosis (RO), membrane degasification (MD), electrodeionisation (EDI) and ultrafiltration (UF)

Fig. 10 Desinfection and cleaning of bottles

Fig. 11Result of caustic filtration with Inopor® membranes

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organism and disinfection by steam. Thisrequirements are fulfilled in an excellentway by ceramic membranes.

Example: Cleaning of causticsAll deposit bottles for beverages have tobe cleaned before their reuse. One criticalsegment of the bottles is the neck and thethread, which were probably in contactwith saliva. So, the bottles not just have to be cleaning from visual resistances,they also have to be disinfected. One stepof this process is to bath the bottles in80 °C hot caustic. Fig. 10 shows the con-

veyor belt for the bottles. Because of theconstant input of dirt and deposits of bev-erages and salvia, the caustic bath be-comes more and more polluted. To clean itwith a polymeric membrane means shortlife-times of the membranes and down-times for membrane replacement. Thecleaning of the caustic bath is done withceramic ultrafiltration membranes for Ino-pore®. Because of the excellent chemicalresistance even at higher temperatures,the membranes are working for a coupleof years. The membrane plant is installedin the side-stream – like a „kidney“ – and

keeping the COD (chemical oxygen de-mand) on a constant level. The Inopor®

membrane plant helps to safe money, butalso to protect the environment and to safeenergy, because otherwise, the causticwould be cooled down and heated up or itwould be completely disposed. With in-creasing costs for acids and caustics, therecovery of chemicals becomes more im-portant and can be done reliable and effec-tive with Inopor® membranes. Fig. 11shows the caustic before and after thetreatment with Inopor® ceramic mem-branes.

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