2 research outputs found
Phenomena Based Methodology for Process Synthesis Incorporating Process Intensification
Process intensification (PI) has the potential to improve
existing
as well as conceptual processes, in order to achieve a more sustainable
production. PI can be achieved at different levels, that is the unit
operations, functional, and/or phenomena level. The highest impact
is expected by looking at processes at the lowest level of aggregation
which is the phenomena level. In this paper, a phenomena based synthesis/design
methodology incorporating process intensification is presented. Using
this methodology, a systematic identification of necessary and desirable
(integrated) phenomena as well as generation and screening of phenomena
based flowsheet options are presented using a decomposition based
solution approach. The developed methodology as well as necessary
tools and supporting methods are highlighted through a case study
involving the production of isopropyl acetate
A Correlation between the Activity of Candida antarctica Lipase B and Differences in Binding Free Energies of Organic Solvent and Substrate
The ability of enzymes to operate
in organic solvent is now widely
accepted and is the basis for extensive research in enzymology. The
challenge is to select the solvent media that allows the modulation
of enzyme activity. For a rational selection of a solvent, it is necessary
to understand the effect of organic solvent molecules on enzyme structure
and the enzymatic reaction on a molecular level. To gain such insight,
we combined experimental kinetics studies with full atomic molecular
dynamics simulations and found a correlation between the activity
of Candida antarctica lipase B (CALB)
[for the esterification reaction between butyric acid and ethanol
at a fixed water activity] and the binding of the solvent/substrate
molecules in the active site region of CALB. We have investigated
the influence of four organic solventsî—¸hexane (HEX), methyl
tertiary butyl ether (MTBE), acetonitrile (ACN), and tertiary butanol
(TBU)î—¸on the catalytic activity of CALB for the esterification
reaction. The solvents have been chosen on the basis of different
polarity/functional groups. Our study shows that these organic solvents
do not alter the overall conformation of CALB; rather, the solvent
effects on the performance of the enzyme may be ascribed to binding
of solvent molecules to the enzyme active site region and the solvation
energy of substrate molecules in the different solvents. Polar solvent
molecules interact strongly with CALB and compete with the substrate
to bind to the active site region, resulting in an inhibitory effect
which is also confirmed by the binding free energies for the solvent
and substrate molecules estimated from the simulations. Consequently,
the catalytic activity of CALB decreases in polar solvents. This effect
is significant, and CALB is over 10 orders of magnitude more active
in nonpolar solvents (HEX and MTBE) than in the polar solvents (ACN
and TBU). TBU molecules show an exceptional behavior because the solvent
molecule forms an extensive hydrogen bond network within the CALB
active site region suggesting that solvent molecules rich on hydrogen
bond acceptors and donors are poor solvents when used for lipase-catalyzed
esterification reactions