Multiphase Bioreactor Design

ADVANTAGES AND DISADVANTAGES OF MEMBRANE

REACTORS

Advantages

Membrane reactors have several intrinsic advantages that make them an alternative
system to more conventional enzymatic reactors (e.g. batch, fixed and fluidized beds)
(Table 6.2). One of the great advantages of membrane reactors is certainly the possibility
of a continuous and intensive use of enzymes. This contributes to an increase in
productivity and possibly to the economical viability of the process. This aspect is
common to all continuous reactors when compared to batch systems. However, the use of
membranes instead of porous particles or beads as an immobilisation aid gives membrane
reactors some competitive edge over conventional, continuous fixed or fluidised bed
reactors

Table 6.2 Advantages and disadvantages of

membrane reactors

Advantages Disadvantages

Continuous operation possible Unfavourable enzyme adsorption

Better control possibilities Enzyme poisoning

Integration of unit operations Deactivation of enzyme by shear effects

Higher reaction rates and productivity Product/substrate inhibition at surface

Shift of chemical equilibrium Loss of enzyme activators or cofactors

Concentration/enrichment of product streams Concentration polarisation

Control of the MW of hydrolysates Membrane fouling

Multiphase reactions possible Enzyme leakage

Scale up is simple High price of membranes and modules

Improved energy efficiency Mechanical and thermal fragilness

Reduction in equipment size

(Belfort, 1989). Some of the advantages are related to the unique possibilities offered by
a membrane reactor, that enables an integration of the enzymatic process with separation
steps. Furthermore, the often occurring mass transfer limitations of conventional fixed or
fluidised bed reactors due to external and pore diffusion effects, can be reduced in certain
membrane reactor configurations, since in many cases it is possible to operate the system
with convective mechanisms rather than diffusive ones. In this way, substrates and
products can be readily transported to and swept away from the enzymes. This may be
especially important in product inhibited reactions (Belfort, 1989). This enhancement of
mass transfer could be responsible for increased productivities in membrane reactors

Multiphase bioreactor design 160