Figure 9.12 Initial reaction rate of the
reduction of hexanal as a function of
amount of baker’s yeast. The reaction
was carried out at 65°C. The total flow
passing into the bioreactor was 680
μmoles/min. The hexanal activity was
fixed at 0.05, the ethanol activity at 0.2
and the water activity at 0.57.
that initial reaction rate increases linearly for the range investigated. This linearity proves
that initial rate is under kinetic control and that internal diffusion rate of substrates is
higher than transformation rate.
Thus, the key point of this system is to optimise hydration conditions without allowing
any possible re-condensation on the catalytic material that would lead to a
gas/liquid/solid system with poor performance and poor stability.
CONCLUSIONS
Solid/gas catalysis appears to be highly interesting from the industrial point of view since
it competes strongly with other bio-processes. To date, a pre-industrial platform has been
developed for the production of esters sharing the “natural” label by solid/gas
biocatalysis, fulfilling many objectives governed by economical constraints such as
productivity from 2 to S kg of ester per hour, a condensation unit working at positive
temperature, and no consumption of carrier gas.
To this end, the process was developed as a closed nitrogen loop, in which one part
was placed under vacuum and heated for the vaporisation of substrates and the catalytic
step, while the other part was pressurised and cooled, allowing product recovery and the
recycling of clean nitrogen.
Multiphase bioreactor design 280