Membrane separation.pptx

8/10/2019 Membrane separation.pptx

1/24

Cake Formation dan

Concentration Polarization

Dr. Subriyer Nasir


2/24

Porous and non porous Membrane


3/24

Profile Fluks terhadap waktu


4/24


5/24

Cake Formation


6/24

Fluks pada model cake formation

Jv = Fluks

P = beda tekan

= viskositas

Rm = Tahanan Membran

Rbl =Rc = Tahanan Cake


7/24

Concentration Polarization

Concentration polarization is an accumulation of excess particlesin a thin layer adjacent to the membrane surface. This

phenomenon, inherent in all membrane filtration processes,

increases resistance to solvent flow and reduces the permeate

flux; it also increases retained solids (salts) or solute

concentration at the membrane surface.

The underlyingmechanism for the concentration polarization phenomenon is

unbalanced transport of dissolved components between bulk and

membrane surface. In particular, convective flux towards the

membrane surface is prevalent over back diffusion to the bulk.

Hence, membrane separation processes are very complex andare influenced by numerous operating parameters such as the

trans-membrane pressure, nature and concentration of the

solute, and feed velocity.


8/24

Concentration polarization is a fully

reversible process in a membrane module

and it can be controlled by velocity

adjustment, pulsation or an electric field.Concentration polarization is caused by

preferential rejection of solute and removal

of solvent, creating a concentrationgradient from the bulk feed flow to the

membrane surface.


9/24

Figure 2.11 illustrated the concentration polarization mechanism on the membrane

surface.

2AC

dx

dCD

A

AB CA1

BAA NN

C

C

High Pressure

Permeate Bulk FeedBoundary

Layer

Membrane

Low Pressure

NB

NA

CA3


10/24

(sieving) mechanism and the final stage is cake filtration. In the first pore blocking

stage, the flux is similar with clean water permeation flux. For the second pore blocking

stage, the new effective "initial permeate flux" was obtained from the calculated flux atthe end of the first stage.


11/24

Polarisasi Konsentrasi

where: Cmis the solute concentration in membrane wall, Cpis permeate concentration,

Cb is the bulk concentration, Jw is the solvent (water) flux and k is the mass transfer

coefficient.


12/24


13/24

TRANSPORT

THROUGHMEMBRANES


14/24

TRANSPORT THROUGH

MEMBRANES Driving force in a membrane process is

necessary to provide the motion of the

molecules.

Membrane processes can be driven by

pressure, concentration, temperature,

electric field etc.


15/24

TRANSPORT THROUGH

MEMBRANES


16/24

Empirical Correlations Reference

dh

DSck 25.0875.0Re065.0

Belfort (1980)

dhDSck 33.075.0Re04.0 Schok (1987)

dh

DSck 33.0379.0Re648.0

Hickey-Gooding (1994)

333.075.0Re04.0 Sck Belfort (1984)33.05.033.0 Re)/(664.0 SczDSh Grober (1989)

33.033.033.0 Re)/(86.1 SczDSh Graetz-Leveque(1989)

M

hPSc

h

D

K

Kk Be

B

s 6/12/1

2753.0

Chiolle (1978)

3/12/1

2/1

Re2

065.1 ScL

hSh

spsp

f

Matsuura (1994)

33.0333.0Re09.1

ScSh

Ohya- Sourirajan (1969)

kJv

CpCbCpCmCP

pmexp

,

3/28.13 /Re1014exp NaClm ScScx

Eriksson (1988)

55.0

0

77.0

4.017.0 ),(Re63.0

P

wOPbCxScSh

f

f

S.Avlonitis et al (1993)


17/24

2.4.2.2 Cake Formation

Several authors use the term cake formation to describe the fouling and scaling

phenomenon in particular for inorganic fouling (Bacchin, et al. 2002; Kosvintsev, et al.

2002; Lin, et al. 2005).

Bacchin, et al (Bacchin, et al. 2002) proposed a model to predict the cake formation

caused by colloidal suspension in ultrafiltration process. Two parameters are used to

describe the colloidal fouling within the polarised and the deposit namely the solid

pressure and hydrodynamic coefficient. To avoid a false estimation by assuming that the

mass colloids correspond to solid volume flux towards the membrane, it was suggested

that actual mass of particles irreversible transfer to deposit is different from the mass

transferred by permeation from the solution.

Kosvintsev, et al (Kosvintsev, et al. 2002) suggested three separate periods of filtration

during the microfiltration process. The first two stages involved a pore blocking


18/24

NON-POROUS MEMBRANES

Solubility depends on the membrane

penetrant interaction

Diffusivity depends on the geometry of the

penetrant molecule


19/24

TRANSPORT THROUGH

MEMBRANES

Flux of the molecules are proportional to the

driving force by a proportionality constant:

dXJ A

dx


20/24

TRANSPORT THROUGH MEMBRANES

Chemical Potential (Composite effect of

both the pressure and the chemical activity

gradient.):

lnRT a V P


21/24

POROUS MEMBRANES

In Porous membranes, motion is assumed

to be through small pipes.

Hagen-Poiseuille model

Knudsen flow model (For gasses)


22/24

HAGEN-POISEUILLE MODEL

Assuming all the pores have the same

radius:

2

8

r PJ

x


23/24


24/24

NON-POROUS MEMBRANES

In Non-Porous membranes, solubility diffusivity

model is used.

Permeability = S x D

dC

J D dx

Documents

Membrane separation.pptx