Since
ethylene/ethane separation by cryogenic distillation is one
of the most energy intensive processes, it can be economically interesting
to combine it with energy efficient membrane technology. The effect
on the viability of different process configurations in relation to
the ethylene permeance (2.8 × 10–6–2.8
× 10–5 mol/(m2 s kPa)) and ethylene/ethane
selectivity (3–1000) of the membrane is investigated using
Honeywell’s Unisim Design Suite R390. Results are compared
to conventional distillation. In addition, the membrane feed pressure,
permeate pressure, and membrane surface area have been optimized to
obtain the highest possible cost savings. It is concluded that the
series configuration is the most beneficial with savings of 16% on
the total annualized costs. Hybrid membrane–distillation technology
is interesting for membranes having ethylene permeances and selectivities
beyond 2.8 × 10–5 mol/(m2 s kPa)
and 30, respectively. Increasing the membrane feed pressure toward
its critical pressure (P
c = 4850 kPa)
is always beneficial, and the optimal permeate pressure increases
to 2050 kPa with increasing ethylene permeance. For material scientists,
it is advised to focus on increasing membrane selectivity once an
ethylene permeance of 1 × 10–5 mol/(m2 s kPa) is obtained, since higher permeances beyond this point yield
less additional cost savings compared to increments in selectivity.
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