components A and B, which component A is the more adsorbed species on a porous
material (adsorbent). So, component B has less affinity with the adsorbent and
consequently is the less adsorbed. We can also consider adsorption and regeneration
as the main stages of this process. During the adsorption stage, the binary mixture
(A + B) is fed, and a stream enriched in the less adsorbed component is produced by
the contact with the solid in the packed column. In the stage of the adsorbent
regeneration, the retained components are desorbed, so that the adsorbent can be
reused. In this stage, the desorbed gases are enriched in the more strongly adsorbed
components of the feed mixture [29, 30].
PSA technology was initially created to produce pure light products at high
pressures. In Germany, at the beginning of the 1940s was patented the first concept
of PSA, appearing later with the name “Sorbogen” for water and CO 2 removal from
the air [59, 60]. During the 1960s, more PSA patents were conceived with new
approaches and apparatus to separate mixtures in the gas phase, and the first versions
of the classical Skarstrom stripping-type cycle appeared [61, 62]. This classical
process uses a simple four-step cycle, which begins with bed pressurization with
feed, adsorption and production of the light product at high pressure, followed by the
blowdown/depressurization, and finally the purge step at low pressure. Commercially, the Skarstrom-type cycles are usually used to produce light products with high
purity and a moderate to low recovery. Recovery will be affected by the amount of
light component required to purge the heavy component at the final stage of the
cycle, as this heavy stream is normally treated as a waste stream. At the end of the
1960s, PSA technology was gaining industrial importance in hydrogen purification,
air drying, and air enrichment with oxygen. Only in the last two decades, the PSA
technology began to be exploited to the bulk separation of olefin/paraffin mixtures
[59, 63]. Considerable work has been performed combining some of the zeolites
reported above with the PSA technology for light olefin/paraffin separation [5, 10,
23, 43–46, 52, 64, 65]. In the literature, it was reported a five-step VPSA cycle
scheme to obtain propylene with a purity of 98% on zeolite 13X pellets from
0.50propane/0.50propylene mixture. However, the proposed cycle showed a low
recovery of about 19% [43, 44]. Campo and co-workers tested an enhanced zeolite
13X with an 11% binder content to produce propylene with high purity. A five-step
VSA cycle was designed and experimentally performed obtaining a purity above
99.5%, a recovery of 85% and a productivity of 1.5 mol C3H6 Áh
À1
Ákg
À1 [10]. Narin
et al., in a recent study, suggested three different VPSA cycle schemes with five steps
and using binderless zeolite 13X, to produce polymer-grade ethylene. In the cycle
that showed better performance, high recovery of ethylene, over 96%, was obtained
with an ethylene purity of 99.5% and productivity of 2.2 mol C2H4 Áh
À1
Ákg
À1 , after
13 cycles. Additionally, in the same work, two five-step VPSA cycles were also
implemented to produce propylene from 0.25propane/0.75propylene, and for the
best cycle, after 25 cycles, a propylene purity of 99.5% was reached with a
productivity of 1.0 mol C3H6 Áh
À1
Ákg
À1 , with a moderate propylene recovery of
74.6% [23]. In another study, the zeolite 4A was used to obtain high-purity propylene (97% purity and 26% recovery) also from 0.50propane/0.50propylene but
diluted in 50% of N 2 by a VPSA cycle with five steps [45]. Grande and
150
V. F. D. Martins et al.
material (adsorbent). So, component B has less affinity with the adsorbent and
consequently is the less adsorbed. We can also consider adsorption and regeneration
as the main stages of this process. During the adsorption stage, the binary mixture
(A + B) is fed, and a stream enriched in the less adsorbed component is produced by
the contact with the solid in the packed column. In the stage of the adsorbent
regeneration, the retained components are desorbed, so that the adsorbent can be
reused. In this stage, the desorbed gases are enriched in the more strongly adsorbed
components of the feed mixture [29, 30].
PSA technology was initially created to produce pure light products at high
pressures. In Germany, at the beginning of the 1940s was patented the first concept
of PSA, appearing later with the name “Sorbogen” for water and CO 2 removal from
the air [59, 60]. During the 1960s, more PSA patents were conceived with new
approaches and apparatus to separate mixtures in the gas phase, and the first versions
of the classical Skarstrom stripping-type cycle appeared [61, 62]. This classical
process uses a simple four-step cycle, which begins with bed pressurization with
feed, adsorption and production of the light product at high pressure, followed by the
blowdown/depressurization, and finally the purge step at low pressure. Commercially, the Skarstrom-type cycles are usually used to produce light products with high
purity and a moderate to low recovery. Recovery will be affected by the amount of
light component required to purge the heavy component at the final stage of the
cycle, as this heavy stream is normally treated as a waste stream. At the end of the
1960s, PSA technology was gaining industrial importance in hydrogen purification,
air drying, and air enrichment with oxygen. Only in the last two decades, the PSA
technology began to be exploited to the bulk separation of olefin/paraffin mixtures
[59, 63]. Considerable work has been performed combining some of the zeolites
reported above with the PSA technology for light olefin/paraffin separation [5, 10,
23, 43–46, 52, 64, 65]. In the literature, it was reported a five-step VPSA cycle
scheme to obtain propylene with a purity of 98% on zeolite 13X pellets from
0.50propane/0.50propylene mixture. However, the proposed cycle showed a low
recovery of about 19% [43, 44]. Campo and co-workers tested an enhanced zeolite
13X with an 11% binder content to produce propylene with high purity. A five-step
VSA cycle was designed and experimentally performed obtaining a purity above
99.5%, a recovery of 85% and a productivity of 1.5 mol C3H6 Áh
À1
Ákg
À1 [10]. Narin
et al., in a recent study, suggested three different VPSA cycle schemes with five steps
and using binderless zeolite 13X, to produce polymer-grade ethylene. In the cycle
that showed better performance, high recovery of ethylene, over 96%, was obtained
with an ethylene purity of 99.5% and productivity of 2.2 mol C2H4 Áh
À1
Ákg
À1 , after
13 cycles. Additionally, in the same work, two five-step VPSA cycles were also
implemented to produce propylene from 0.25propane/0.75propylene, and for the
best cycle, after 25 cycles, a propylene purity of 99.5% was reached with a
productivity of 1.0 mol C3H6 Áh
À1
Ákg
À1 , with a moderate propylene recovery of
74.6% [23]. In another study, the zeolite 4A was used to obtain high-purity propylene (97% purity and 26% recovery) also from 0.50propane/0.50propylene but
diluted in 50% of N 2 by a VPSA cycle with five steps [45]. Grande and
150
V. F. D. Martins et al.