Separation principles Insight in the design equations for downstream - - PowerPoint PPT Presentation

• Prof. Luuk van der Wielen, Department of Biotechnology, Faculty of Applied Sciences

Separation principles

Insight in the design equations for downstream processing

cell-disruption cell removal concentration purification formulation MARKET FERMENTER Mechanical separations (including solid particles) Molecular separations (dissolved molecules only)

let’s tackle these first!

‘0’ ‘2’ L V 1 x0 x1 y1 y2

S = Separation (extraction) factor

• appears in adsorption, absorption, stripping
• describes ratio of transport capacities
• indicates how much auxiliary phase (V) is

required per amount of feed!

• capacity of auxiliary phase goes on top

assumption: outgoing flows at equilibrium

Important concept: equilibrium stage

‘0’ ‘2’ L V ‘1’ x0 x1 y1 y2

feed raffinate extract solvent

100 Separation factor S 1 2 3

Yield %

Important concept: equilibrium stage

‘in’ via ‘in’ via’ ‘out’ via ‘out’ via feed solvent raffinate extract + = +

Solving mass balances for N number of stages, using the equilibrium relation y = K x

100 1 2 3 S Yield %

N Number of stages

L, xN V, yN +1 L, x0 V, y1 2 1 N -1 N x1 y2 x2 y3 yN xN -1

Multi-stage and countercurrent

N=1 N=2 N=5 N=10 Adding more stages increases the yield!

S à Indicates costs of auxiliary phase per amount of feedstock (V/L) and thus affects

• perational expenditures (OPEX, €)

N à Adding stages requires investment: affects capital expenditures (CAPEX, €) For a specific yield (say 99%), we can now calculate the required number of stages N for any separation factor S You have to pay both (total) Separation factor S Costs €

CAPEX OPEX total

Relating to economy – the rough explanation

CAPEX-estimates can come from

• Comparable plant (somewhere else)
• Experience or rules of thumb
• Such as: 100 M$ for 100 kton per annum liquid volume capacity
• Solids handling plants twice as expensive
• Short-cut design (back of envelope calculation)
• Detailed design
• Fundamental calculations

Increased accuracy

Relating to economy – more detail

L, xN V, yN +1 L, x0 V, y1 2 1 N -1 N x1 y2 x2 y3 yN xN -1 Try to design for most efficient solvent use (Vmin)

• feed ‘in’ = extract ‘out’

Lx0 = Vy1

• highest concentration feed

x1 = x0

• at equilibrium

Lx0 = VKx0 Smin = 1 but

Multi-stage and countercurrent

N

8

‘in’ via ‘in’ via’ ‘out’ via ‘out’ via feed solvent raffinate extract + = +

Separation factor indicates direction of transport

S > 1 product ‘moves’ with solvent V S < 1 product ‘moves’ with feed L

100 1 2 3 Yield % S

N=1 N=2 N=5 N=10

L, xN V, yN +1 L, x0 V, y1 2 1 N -1 N x1 y2 x2 y3 yN xN -1

• Use differences in S to separate multiple components
• Feed stage in between top section and bottom section
• If component A has bigger affinity for V than component B then:
• KA > KB
• A moves ‘up’ with V if:

SA (top) > 1, and SA (bottom) > 1

• B moves ‘down’ with L if:

SB (top) < 1, and SB (bottom) < 1

A B

Multi-stage and countercurrent

L, xN V, yN +1 L, x0 V, y1 2 1 N -1 N x1 y2 x2 y3 yN xN -1

stripping absorption V L back-extraction extraction L L’ dissolve crystallisation L Crystal desorption adsorption V/L Sorbent

Multi-stage and countercurrent

α depends on the choice of mechanical separation Feedstream F Contains particles (cells, crystals etc) and dissolved molecules (solutes) F Supernatant or filtrate Contains solutes = F – C – αC

Mechanical separations

Wet cells = cells (C) + cells with adherent solution (αC) including solutes C αC

L, x0 L, x1 V, y1 V, y2 V,y F,C, cF (1+α)C, c F –(1+α)C, cF F –(1+α)C, cF

Equilibrium stage for mechanical separation

αC, cF C L,x

L, xN V, yN +1 L, x0 V, y1 2 1 N -1 N x1 y2 x2 y3 yN xN -1

Same approach as for countercurrent molecular separations with: L = (1+α)C and V = F – (1+α)C + W Mechanical separations often include countercurrent wash W

100 Yield % 1 2 3 S

N=1 N=2 N=5 N=10

Design recipe (always works)

in equilibrium

• ut

mass balance

mass balance (overall, phase, local) phase and reaction equilibria (K’s) hydrodynamics mass transfer and reaction rate (k’s)

• ut

rate in

Design recipe (always works)

in equilibrium

• ut

mass balance

mass balance (overall, phase, local) phase and reaction equilibria (K’s) hydrodynamics mass transfer and reaction rate (k’s)

• ut

rate in 1+2) how much beans, water & energy?

Design recipe (always works)

in equilibrium

• ut

mass balance

mass balance (overall, phase, local) phase and reaction equilibria (K’s) hydrodynamics mass transfer and reaction rate (k’s)

• ut

rate in 3) how big of a coffee maker do you need? (even: how big a power plant to operate it?) 1+2) how much beans, water & energy?

See you next unit