Environmental Engineering Reference
In-Depth Information
D.
B
IOSEPARATIONS AND
B
IOPROCESSING
Separation technologies to facilitate commercial success of biomass conversions include
those suitable for low-molecular-weight organic acids, organic esters, diacids, and alcohols;
gases such as H2; and biobased oils such as biodiesel and biolubricants. Among these,
advances in membrane technologies and in processes utilizing environmentally-benign
solvents promise especially great benefits.
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Membrane Techniques.
The development of new and/or improved membrane
materials that provide increased selectivity and specificity for the desired substances,
as well as increased flux with stability and robustness, is of central importance to the
membrane-based techniques discussed below:
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Pervaporation.
The use of pervaporation to remove either water or bioproducts
from bioreactor media appears promising. Continued support for new
membrane materials, new module and process designs, and improved
theoretical understanding and modeling of the pervaporation process should
therefore be pursued. The work of Vane and colleagues at the EPA National
Risk Management Research Laboratory (NRMRL) is a noteworthy example of
efforts in the development of pervaporation modeling and performance
prediction software.
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Micro- and ultrafiltration
. Microfiltration and ultrafiltration promise to become
major unit operations in the emerging biorefinery arena. The development of
new materials for UF and MF, including porous metals and ceramics as well as
polymers, is therefore an important priority. Similarly, nanofiltration and
reverse osmosis are becoming increasingly important, with recent
developments in nanotechnology promising to yield new materials with
significantly improved fluxes and selectivities.
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Membrane chromatography
. An improved understanding of the interactions
between culture media components and synthetic polymers suitable for
membranes would greatly facilitate the design of synthetic substrates for use in
membrane chromatography. Among those, ligand-binding and sterically-
interacting species should be investigated closely to improve the selectivity of
membrane chromatography while maintaining acceptably high throughput.
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Antifouling techniques
. Fouling is a persistent problem among membrane
technologies, with the result that methods to diminish fouling of membranes
and ion exchange materials, as well as to remove impurities such as salts or
acids that cause complications in downstream processes, are high priorities in
the advancement of bioseparations.
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Environmentally Benign Solvents
. New renewable, biodegradable solvents are
needed to support environmentally-friendly extraction processes. Supercritical CO2,
a highly compressed phase of CO2 possessing properties of both liquid and gas
phases, is one benign solvent that has already achieved great popularity and that has
the potential to contribute performance, cost-effectiveness, and sustainability to
separations of both biofuels and biomaterials.
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Integrated Modules
. Combined- or hybrid-unit operations in which a bioreactor is
integrated with a bioseparation module, as in two-phase reactor systems, are
