Angelo Basile, Adolfo Iulianelli, Pietropaolo Morrone

ITM-CNR. Istituto per la Tecnologia delle Membrane – Via P. Bucci 87030 Arcavacata di Rende (CS) – Italy

Membrane per la separazione di CO2 e reattori a membrana per il suo uso

Summary

1. Membrane in gas separation: flow patterns

• complete mixing • parallel flow (co-current and counter current flow) • cross flow

2. Numerical simulation of membrane gas separation systems: • Key parameters

3. Parametric analysis:

• one stage removal • multi-stage removal

Membrane in gas separation: flow patterns

Membrane in gas separation: flow patterns

Membrane in gas separation: key parameters

Permeability:

(mol·m·m-2·s-1·Pa-1)

it is a measure of the quantity of a component that permeates through the membrane

Ni : molar flow rate of the species i (mol·s-1) l : membrane thickness (m), S the exchange surface (m2) : partial pressure of species i S membrane surface (m2)

Membrane in gas separation: key parameters

Selectivity:

(-)

it is a measure of the ability of a membrane to separate two gases

is the selectivity of the gas a with respect to b

Membrane in gas separation: key parameters

Pressure ratio:

(-)

is the ratio of the total feed pressure versus the total permeate pressure

generally, for technical applications φ ≤ 20

Membrane in gas separation: key parameters

Stage cut:

(-)

is the ratio between permeate flow rate and feed flow rate

Membrane in gas separation: key parameters

Stage cut:

(-)

is the ratio between permeate flow rate and feed flow rate

θ Increase in decrease in purity

Numerical example

Example: CO2 separation

Numerical example

Example: CO2 separation

Permeance ·1012

(mol/m2sPa)

Selectivity

α(CO2/N2)

Membrane CO2 N2 CO2/ N2

APS/MS/Al2O3(S) 470 8.3 56,6

Sakamoto, Y., Nagata, K., Yogo, K., Yamada, K. (2007)

Numerical example: effect of pressure ratio

It is not possible to simultaneously obtain high recovery and high purity

An increase in pressure ratio above 10 produces small effects

co-current mode

Numerical example: effect of the feed concentration

Lower the feed concentration, higher the decrease in purity

a pure retentate stream require high membrane area

co-current mode

CO2 recovery

recovery = CO2 captured / CO2 in the feed

Complete recovery is obtained for a value of stage-cut less than 100%

when recovery is low, purity is high

recovery = CO2 captured / CO2 in the feed

CO2 recovery

Numerical example: multi component separation

Let consider a four components mixture (CO2, H2, CH4, H2O)

Gas Permeability

(barrers) Feed

concentration (%)

H2O 10 9.1

CO2 3200 16.4

CH4 940 7.4

H2 500 67.1

Bounaceur R, Lape N, Roizard D, Vallieres C, (2006)

Numerical example: multi component separation

H2O has a negligible permeate concentration - in fact α(CO2/H2O) is very high In order to increase the purity it is necessary a second Separation Unit

co-current mode

Numerical example: multi component separation

Numerical example: two stage separation

Numerical example: multi component separation

2 stage (feed)

1 stage (feed)

Numerical example: two stage separation

Multi-stage separation unit

N2-CO2 (complete mixing mode)

x0 = CO2 feed concentration yi = CO2 permeate concentration N = molar flow rate (mol/min)

Multi-stage separation unit

co-current flow with reflux (recirculation of the permeate flow)

x0 = CO2 feed concentration yi = CO2 permeate concentration N = molar flow rate (mol/min)

Grazie per l’attenzione