Membrane Technology

• Dialysis

- Applied since the 70’s.

- Low industrial interest.

- Ions & species of low MW (<100 Da).

- Ionic Membranes (just like ED).

- Driving Force: concentration gradient.

- Slow and low selective.

• Dialysis

- NaOH recovery in textile effluents, alcohol removal from beer, salts removal (pharmaceutical industry).

- Artificial kidney.

Membrane Technology

GS

MF

UFRO

HD

EDPV

• Dialysis

Membrane and module markets

Looks not very important...?.

Membrane Technology

• Electrodialysis (ED)

- Ion Separations.

- Ionic Membranes (non porous).

- Driving Force: gradient in electrical potential.

- Flat configuration.

- Hundreds of anionic and cationic membranes placed alternatively.

- Orthogonal electrical field.

- First applications back at 30’s.

- Potential: 1-2 V.

Membrane Technology

• Electrodialysis (ED)

Membrane Technology

• Electrodialysis (ED)

Membrane Technology

• Electrodialysis (ED)

- Ionic Membranes (non porous).

- Based on polystyrene or polypropylene with sulfonic and quaternary amine groups.

- ED with reverse polarization (EDR).

- ED at high temperature (60ºC).

- Thickness: 0.15-0.6 mm.

- ED with electrolysis.

Membrane Technology

• Electrodialysis (ED)

- Required membrane area

j+

VC c+

in

VC c+

out

0dczVdAj Cm Mass balance (in equivalents)

Charge flow

mdAdI

iFj

combining

i

FzccVi

FzccVNANA outinoutinC

mT

η: global electrical efficiency (~0.5 commercial equipment)

F: Faraday constant (96500 C/eq) N: number cells in the equipment

i: electric current density (A/m2)Am: membrane surface (m2)

j: cation flow (eq/m2 s)

z: cation charge (eq/mol)

Membrane Technology

• Electrodialysis (ED)

- Then the required energy, E (J), is

tRINtIUN E C2

C

as

then

FzccV

AiI outinCm

UC: potential gradient in a cell (V)

RC: total resistance in a cell ()

tRFzcV

N E C

2C

C

2C R

FzcVN P ó

P: required Power (J/s)

Membrane Technology

• Electrodialysis (ED)

Where, the required specific energy, (J/m3), is

C

2

CC

RFzc

VtVN

E E

La cell resistance can be estimated from a model based on series of resistances where the resistances to transport are considered through two membranes and the compartments concentrate and diluted.

Membrane Technology

• Electrodialysis (ED)- How to determine operational i?

t

Ficcz

DtFi DMD

M

Cation Transport

tt

cczFDi

M

DMD

If cDM+ = 0

tt

czFDi

M

Dlim

Usually: i = 0.8ilim t: transport numberD: diffusion coefficient

Cationic Membrane

Limit boundary

cCM+

cC+

cDM+

cD+

- +

concentrate diluted

Membrane Technology

• Electrodialysis (ED)- Intensity Evolution versus applied potential

i (A/m2)

ilim

Ohmic zone

U (V)

Resistance rise

Ionic water splitting

Membrane Technology

• Electrodialysis (ED)

- Fields of application: Water desalination.

- Competing to RO.

- Economically more interesting at very high or very salt concentrations.

- Other fields of application: Food Industry.

Treatment of heavy metal polluted water.

Membrane Technology

• Electrodialysis (ED)

- Examples:

Production of drinking water from salty water.

Water softening. Nitrate removal. Lactose demineralization. Acid removal in fruit juice. Tartrate removal from wines. Heavy metal recovery. Production of chlorine and sodium hydroxide.

Membrane Technology

• Electrodialysis (ED)

electrolytic Cell for the production of chlorine and sodium hydroxide with cationic membrane.

Membrane Technology

• Electrodialysis (ED)

Electrolytic cell for the production of sulfuric acid and sodium hydroxide with bipolar membrane.

Membrane Technology