MEMBRANE TECHNOLOGYBy :

Prof. Dr. Tien R. Muchtadi

DEFINITIONS

• INTRODUCTION• CLASSIFICATION OF MEMBRANE PROCESS• TYPES OF MEMBRANE• REJECTION COEFFICIENT• NOMINAL MW CUT-OFF• GENERAL MEMBRANE EQUATION

INTRODUCTIONS• Effective product separation is crucial to economic

operation in process industries• However, certain types of materials are inherently difficult

and expensive to separate• Prominent examples include :

a. Finely dispersed solids, especially those which are compressible, have a density close to that of the liquid phase, have high viscosity, or are gelatinous

b. Low molecular weight, non-volatile organics or pharmaceuticals and dissolved salts

c. Biological materials which are very sensitive to their physical and chemical environment

• A membrane may be defined as “an interphase separating two phases and selectively controlling the transport of materials between those phases

• Since 1960s a new technology using synthetics membrane for process separations has been rapidly developed by materials scientist, physical chemist and chemical engineers

• Such membrane separations have been widely applied to a range of conventionally difficult separation

CLASSIFICATION OF MEMBRANE PROCESSES

• Industrial membrane process may be classified according to the size range of materials which they are to separate and the driving force used in separations.

• There is always a degree of arbitrariness about such classification and the distinction which are typically drawn are shown in Table. 1

Table 1. Classifocation of membrane separation process for liquid systems

Name of process Driving force Separation size range

Examples of materials separated

Microfiltration Pressure gradient 10 – 0.1µm Small particles, large colloids,microbial cells

Ultrafiltration Pressure gradient < 0.1 µm – 5 nm Emulsions, colloids, macromolecules, proteins

Reverse osmosis (hyperfiltration)

Pressure gradient < 5 nm Dissolved salts, small organics

Electrodialysis Electric field gradient

< 5 nm Dissolved salts

Dialysis Concentration gradient

< 5 nm Treatment of renal failure

THE NATURE OF SYNTHETIC MEMBRANES

• Membrane used for separation process are most commonly made of polymeric materials

• Membrane have most commonly been produced by a form of phase inversion known as immersion precipitation

• This process has four main steps :– The polymer is dissolved in a solvent to 10-30 per cent by weight– The resulting solution is cast on suitable support as film of thickness ~

100 µm– The film is quenched by immersion in non-solvent bath, typically

water or an aqueous solution– The resulting membrane is annealed by heating

GENERAL MEMBRANE EQUATION

• The general membrane equation is an attempt to state the factor which may be important in determining the membrane permeation rate for pressure driven processes

• Form : J = |Δ P| - |ΔΠ| (Rm + Rc + Rf‘)µ

• J : the membrane permeation rate (flux expressed as volumetric rate per unit area)

• Δ P : the pressure difference applied across the membrane (trans membrane pressure)

• ΔΠ : the difference in osmotic pressure across the membrane

• Rm : the resistance of the membrane

• Rc : the resistance of the layers depasited on the membrane (filter cake, gel foulants)

• Rf‘ : the resistance of the film layer

• If the membrane is only exposed to pure solvent, exp water the equation become :

J = |ΔP|/Rmµ

• For microfiltration and ultrafiltration membranes where solvent flow is most often essentially laminar through an arrangement of tortous channels, this is analogous to the Carman-Kozeny equation

• Knowledge of such as water fluxes is useful for characterising new membrane and also for assesing the efectiveness of membrane cleaning procedures

MEMBRANE PROCESS

• MICROFILTRATION• ULTRAFILTRATION (U/F)• REVERSE OSMOSIS (R/O) OR HYPERFILTRATION (H/F)• MEMBRANE MODULES AND CONFIGURATIONS• MEMBRANE FOULING, FLUX RATE REDUCTION,

CLEANING AND PROCESS ECONOMICS

MICROFILTRATION

• Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 µm in size

• Dead end membrane microfiltration, in which the particle containing fluid is pumped directly through a polymeric membrane, is used for industrial clarification and sterilization of liquids

The advantage of cross-flow filtration over conventional filtration are :

a. A higher overall liquid removal rate is achieved by prevention of the formation of an extensive filter cake

b. The process feed remains in the form of mobile slurry suitable for further processing

c. The solids content of the product slurry may be varied over a wide range

d. It may be possible to fractionate particles of different sizes

MembranePermeate

Permeate

RetentateProcessing feed crossflow

Figure 1. The Concept of Cross-Flow Filtration

Figure 2. Flow diagram for a simple cross-flow system

C

b

a

Time

Membrane permeation rate

Figure 3. The time-dependence of membrane permeation rate duringcross-flow filtration : a. low cross-flow velocuty, b. increased cross-flow velocity, c. back-fushing at the bottom of each”saw-tooth”

MEMBRANE FOULING AND EFFECTS

• MEMBRANE FOULING• FLUX RATE REDUCTION• CLEANING METHODS• PROCESS ECONOMICS : EFFECT OF FLUX RATE

REDUCTION AND MEMBRANE LIFE ON OPERATING COSTS AND RETURN ON CAPITAL INVESMENT

ELECTRODIALYSIS

• OUTLINE OF MEMBRANE OPERATION• MEMBRANE TYPE AND TRANSPORT

MECHANISM• APPLICATIONS

LIQUID MEMBRANES

• TYPES• OPERATING MECHANISM• PRODUCT RECOVERY• APPLICATIONS

GAS SEPARATIONS

• MECHANISM• TYPES OF MEMBRANE• APPLICATIONS

CONCENTRATION OR GEL POLARISATION MODEL

• APPLICATION OF THE DESIGN MODEL TO THE ULTRAFILTRATION CONCENTRATION AND SEPARATION OF GEL FORMING PROTEIN SOLUTION

• CALCULATIONS AND ASSUMPTIONS

APPLICATIONS OF MEMBRANE TECHNOLOGY

• FOOD PROCESSING AND ENGINEERING• BIOTECHNOLOGY, MEMBRANE REACTORS• BIOMEDICAL ENGINEERING• PROCESS DEVELOPMENT• GROUP DISCUSSTION AND PROBLEM SOLVING

TEKNOLOGI SEPARASI MEMBRAN

• Proses pemisahan komponen berdasarkan perbedaan berat dan ukuran molekul melalui suatu membran semipermeabel, dimana akan diperoleh komponen dengan ukuran molekul besar akan tertahan (retentate) dan komponen yang melewati membran (permeate)

KLASIFIKASI PROSES MEMBRAN

Berdasarkan pada driving force yang digunakan : 1.Mikrofiltrasi2.Ultrafiltrasi3.Reverse osmosis4.Elektrodialysis5.Dialysis

Paling banyak digunakan untuk pengolahan produk pangan

What Is Reverse Osmosis?Reverse osmosis, as form of water treatment, is a technology in its infancy. The first membrane was developed in 1958. In the years following, membrane technology has grown a great deal and will continue to grow in the future. In fact, some of the membranes that are currently in use may be obsolete in a very short time, in favor of some new membrane material that is more resistant to a particular fouling contaminant.The reverse osmosis membrane is used for various applications from precious metal reclamation, to chemical reclamation, food processing nuclear waste reclamation, laboratory water purification, and on and on. We will limit our discussion to water purification and its laboratory applications.

To fully understand the technology of reverse osmosis, you must first understand the concept of normal osmosis. Simply put, in normal osmosis, water flows from a less concentrated solution through a semi-permeable membrane to a more concentrated solution (see figure 1). Reverse osmosis utilizes pressure to reverse normal osmotic flow, thus in reverse osmosis water flows from a more concentrated solution across semipermeable membrane to a less concentrated solution (see figure 2).

BAHAN BAKU MEMBRAN ULTRAFILTRASI

• Polimer (misal Polisulfon, Poliacrilonitril) dan keramik (Zirconium oxide, Aluminium oxide)

• Untuk memperoleh struktur membran dgn karakteristik tertentu selain bahan baku tadi juga diperlukan campuran pelarut dan aditif

• Karakteristik membran ultrafiltrasi : nilai MWCO (Molecular Weight Cut Off)

• MWCO batas toleransi berat molekul (BM) senyawa yang dapat dipisahkan oleh suatu membran

• MWCO 10,000 membran dapat menahan (reject) sebanyak 95% komponen-komponen dengan BM ≥ 10,000, sedangkan komponen-komponen dengan BM lebih rendah akan melewati membran

Tabel 1. Aplikasi Teknik Separasi Membran pada Pengolahan Produk Pangan

No

Teknik Proses

Tujuan Proses Pustaka

1 Mikrofiltrasi Penghilangan pektin pada sari buah apel

Zakoer and Mc. Lelan (1993)

2 Ultrafiltrasi Pemurnian isolat protein kedelai

Debra and Cheryan (1981)

3 Ultrafiltrasi Penyederhanaan proses produksi sari buah apel

Thomas, et.al. (1986)

4 Ultrafiltrasi Pemisahan komponen kasein Woychik et.,al (1992)

5 Ultrafiltrasi Penurunan kandungan bakteri pada kecap

Tien and Chiang (1992)

6 Ultrafiltrasi & reverse osmosis

Pengembangan berbagai produk tepung protein dari kacang tanah

Lawhon, et., al (1981)

CONTOH PERCOBAAN SEPARASI MEMBRAN

Tujuan percobaan :- Melakukan pembuatan membran ultrafiltrasi

dari polimer polisulfon- Melakukan annealing untuk menghasilkan

membran dengan karakteristik tertentu- Melakukan pengujian kinerja membran yang

diperoleh untuk memisahkan senyawa dekstran (Dx) (BM = 71400) dan polietilen glikol (PEG) (BM= 20000), dan

- Melakukan studi literatur apliaksi membran yang dihasilkan pada pengolahan pangan

BAHAN DAN ALAT

Bahan : polimer polisulfon (PS), pelarut dimetyhl-acetamide (DMAC), aditif nourmal methyl pirolidon (NMP), dekstran (BM=71.400) dan polietilen glikol (BM= 20000)

Alat : alat separasi membran, alat casting, water bath, HPLC waters dan detektor refraktometer

METODOLOGI PERCOBAAN• Pembuatan membran (Gambar 4)• Pengujian karakteristik membran

– proses annealing– proses separasi membran

• Pengujian selektifitas membran– mengamati prosentase rejeksi komponen

dekstran dan polietilen glikol

Polimer Pelarut Aditif

Penguapan

Casting

Pendiaman/relaxing

Pencampuran

Koagulasi

Membran sheet

Gambar 4. Diagram Alir proses pembuatan membran

Prosentase rejeksi dihitung dengan rumus :

Rejeksi (%) = [ 1-Cp/Cf ] x 100 %

Dimana : Cp = konsentrasi solute pada permeateCf = konsentrasi pada feed

• Penentuan konsentrasi solute pada feed dan permeate dilakukan dengan metode HPLC menggunakan eluen aquadest, dgn flow rate 0.8 ml/menit dan volume injeksi 200 ml

Gambar Alat separasi membran skala laboratorium

Keterangan :

A. Beaker geals pyrex

B. Tutup bagian atas

C. Tutup bagian bawah

D. Tutup pengatur tekanan

E. Aliran tekanan

F. Saluran bahan

G. Pengaduk magnetis

M. Modul membran ultrafiltrasi

O. Saluran pengeluaran

P. Disk Polietilen penyangga membran

S. Pemanas/hot plate

HASIL DAN PEMBAHASAN

• Membran dari polisulfon, pelarut dimetil acetamide (DMAc) dan aditif normal methyl pirolidon (NMP) dengan rasio 22: 62,4:15,6 hanya cocok untuk memisahkan dekstran dan senyawa lain dengan BM > 71400.

• Dengan menghitung waktu annealing saat persen 95% didapatkan MWCO membran polisulfon 71400 dan waktu annealing sebesar 6 menit.

• Annealing akan memperbesar daya rejection

• Peningkatan daya rejection diduga akibat perendaman dalam air hangat selama proses annealing sehingga pori-pori membran lebih teratur dalam jarak dan ukurannya

Hasil analisis HPLC karakteristik membran campuran polisulfon, DMAc, dan NMP pada perbadingan 22 : 62,4 :

15,6

Jenis feed Lama proses annealing

Peak area pada feed

Peak area pada

permeate

% rejection

1, PEG,

BM = 20000

Non annealing

5 menit

15 menit

16271913

16439954 16641256

4237323

2295437

2161709

73.96

86.03

87.01

2. Dx,

BM = 71400

Non annealing

5 menit

15 menit

15075104

16433516

16870494

7099627

1503613

527375

52.90

90.85

96.87

Gambar 5. Hubungan antara waktu annealing dan % rejection membran polisulfon terhadap dekstran (BM =

71400)

52.9

90.8596.87

y = 21.985x + 36.237

R2 = 0.8505

0

20

40

60

80

100

120

0 5 15

Waktu annealing (menit)

% r

ejec

tio

n

APLIKASI MEMBRAN PADA PENGOLAHAN PANGAN

Kelebihan metoda separasi membran :• Mampu memisahkan secara sempurna suatu campuran yang

terdiri dari komponen-komponen dengan berat molekul yang berbeda-beda

• Untuk memisahkan komponen bernilai ekonomis tinggi

Kelemahan :• Memerlukan biaya yang relatif tinggi dibandingkan dengan

cara ekstrasi ataupun distilasi konvensional

• Salah satu contoh komponen dgn nilai ekonomis tinggi adalah ENZIM

• Enzim : komponen protein (makromolekul) dgn BM besar (104 – 109)

• Proses imobilisasi menggunakan membran untuk enzim dg BM > 71400

• Proses imobilisasi secara fisik berarti membran akan bersifat tidak permeable bagi enzim sehinga enzim dapat didaur ulang maupun dipalikasikan untuk proses produksi secara kontinu (Gambar 6.)

ProdukSubstrat + enzim

Substrat

Produk

Enzim

Membran

Gambar 6. Prinsip separasi membran untuk imobilisasi enzim

Tabel 2. Aplikasi proses separasi membran untuk imobilisasi enzim secara fisik

Jenis proses

Jenis enzim terimobilisasi

Karakteristik membran

Jenis retentat

komponen

Jenis permeat

komponen

Pustaka

Produksi sirup glukosa

Glukoamylase dari Baciluss lichenifor, mis : termamyl

MWCO 5000 -Oligosakarida

-Glucoamylase

Sirup glukosa

Sims and Cheryan (1992)

Produksi hidrolisat protein

Protease dari Aspergillus Oryzae

MWCO 10 kDa

-protein

-protease

Asam-asam amino

Zhang et al. (1996)

Hidrolisis laktosa

β- galactocidase dari Aspergillus oryzae

MWCO > 30000

-laktosa

- β- galactocidase

Glukosa, galaktosa

Sheth et al. (1988)

Karakteristik membran untuk imobilisasi enzim tergantung pada :

1. Jenis enzim yang akan diimobilisasi2. Jenis substrat yang diharapkan akan

tertahan (retentate) pada membran3. Produk yang diharapkan melewati

(permeate) membran

HASIL PERCOBAAN

1. Enzim yang akan diimobilisasi dan retentate substrat memiliki berat molekul lebih dari 71400, dan

2. Produk hasil reaksi enzimatis (permeate) memiliki berat molekul lebih kecil dari 71400