Download - MEMBRANE TECHNOLOGY
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