the Si/Al ratio, the polarity increases, improving the selectivity toward CO 2 . However, the regeneration step becomes more demanding because of the strong interaction between CO 2 and zeolite [40]. The ideal CO 2 adsorbent would be the one with
an intermediate CO 2 affinity combining a relatively high adsorption capacity with
high selectivity and easy regeneration step [41]. An extensive review of CO 2 /CH 4
separation is presented by Yu et al. [35].
Some of these zeolites have been combined with adsorption-based technologies,
and highly promising results were achieved in the context of olefin/paraffin and CH 4 /
CO 2 separations. In recent years, to seek more sustainable options, there has been a
significant increase in the research activity on olefin/paraffin and CH 4 /CO 2 separation using zeolites by pressure swing adsorption (PSA) [23, 43–45, 48, 50] and
simulated moving bed in gas phase (gas-SMB) [42, 47, 51] technologies. In some
cases, the process design and optimization to the industrial scale were also proposed
[29, 52]. A few examples can be found in the literature of tests at the pilot scale and
process design. In Table 1 are presented some of the examples available in the
literature, the separation of ethane/ethylene using binderless zeolite 13X by VPSA
[23], and SMB [42]; the separation of propane/propylene mixture with zeolite 13X
by SMB [47]; the propane/propylene separation on different samples of zeolite 13X
by PSA [43], VSA [10, 44], and VPSA [23]; the propylene production using
different samples of zeolite 4A by PSA [46] and by VSA [45]; and CO 2 removal
for CH 4 upgrading on different zeolite 13X samples [29, 48, 49].
2 Adsorptive Gas-Phase Separation Processes
The backbone of the petrochemical industry is ethylene, as it is the most essential
raw material in terms of volume, number of derivatives, and sales value. Propylene is
the second product in importance as a petrochemical feedstock. Butadiene is a basic
Table 1 Examples of pilot tests found in the literature
Separation
Zeolite
Process
Ref.
Ethane/ethylene
Binderless zeolite 13X
SMB
[42]
Ethane/ethylene
Binderless zeolite 13X
VPSA
[23]
Propane/propylene
Binderless zeolite 13X
VPSA
[23]
Propane/propylene
Zeolite 13X
PSA
[43]
Propane/propylene
Zeolite 13X
VSA
[44]
Propane/propylene
Zeolite 13X (11% binder)
VPSA
[10]
Propane/propylene
Zeolite 4A (Rhône-Poulenc)
VSA
[45]
Propane/propylene
Zeolite 4A
PSA
[46]
Propane/propylene
Zeolite 13X
SMB
[47]
CO 2 /CH 4
Zeolite 13X
VSA
[48]
CO 2 /CH 4
Zeolite 13X (11% binder)
VSA
[49]
CO 2 /CH 4
Binderless zeolite 13X
Cryo-PTSA
[29]
148
V. F. D. Martins et al.