(742f) Cyclic Membrane Gas Separation Processes Assessment

for practical applications is a rather unexplored domain. One of
the main

advantages of membrane processes compared to other separations is
their ability

to work under steady conditions, without any separate regeneration
step. Nevertheless,

unique separation performances can be obtained in some cases when

a transient regime is applied. Paul explored this issue in a
pioneering study,

based on a cyclic process with synchronous valve operation.

Followed by this initial work, more theoretical and experimental
studies

about the cyclic process have been performed. Some interests and
also some

drawbacks have been defined qualitatively. A general improved
selectivity is

highlighted with respect to a conventional process, together with
a significant

decrease on productivity. Thus, the trade-off between these two
factors is the

key issue to assess whether the cyclic process is competitive with
respect to a

conventional process.

Based on Paul's process, a cyclic process for membrane gas
separations is

proposed in our study with more available operating possibilities
and less

modeling assumptions. The simulation and optimization techniques
have been applied

to different gas systems, based on reported permeability data
through a given

polymer. By simulating this process, some other unattainable
interests with

respect to conventional operations are highlighted besides the
improved selectivity,

as well as some important unavoidable drawbacks. The main outcome

of this study is, for each gas pair, a characteristic chart where
steady state and

cyclic separation performances (namely selectivity and
productivity) are compared.

An example is shown on figure 1 for the He/Ar gas pair. It can be
seen

that the cyclic operation offers a very large increase of the
process selectivity to

be possibly attained, at the expense of a productivity decrease.