solid phases in countercurrent is the most attractive feature in this process, once it
promotes the mass transfer driving force, leading to more efficient use of the
adsorbent [70]. In this technology, besides the choice of a suitable adsorbent, to
perform the SMB is also necessary to deal with the selection of a desorbent capable
of displacing the adsorbed gas mixture from the adsorbent [58]. The first application
of this technology dates back to 1960s when Universal Oil Products Inc. (UOP)
implemented the Sorbex family of this process, applied to liquid-phase separations
in refineries [71]. Sorbex processes are exclusively applied in liquid-phase separations, but many studies demonstrated the feasibility of this process to be applied in
gas phase separations, namely, in more challenging situations where the separation
factor is near to unity. However, it was necessary to redesign the Sorbex process to
the gas phase, once the axial dispersion constitutes a problem in the classical
approach in which the Sorbex was implemented [72]. Several strategies were
designed for the most varied separations in the gas phase, and to the best of our
knowledge, none was implemented at the industrial scale [9]. In the 1990s, the
separation of volatile inhalation anesthetic enantiomers [73], xylene isomers [74],
and linear/nonlinear paraffins [75] was exploited by gas-phase SMB chromatography (GC-SMB) and experimentally tested at lab scale. A couple of years ago, the
development of new theories, modeling methodologies, and new operation modes
continued leading to the emerging of new solutions and concepts. SMB processes for
other gaseous separations, such as H 2 /He and D 2 /He [76] and C 3 H 6 /C 3 H 8 [77], have
been reported in the patent literature. Several authors explored this technology in the
gas phase, to separate olefins from mixtures containing the homolog paraffins, once
this technology should lead to a more energy-optimized process and olefin production with higher purity, recovery, and productivity [57, 77, 78]. Rodrigues et al.
patented a gas-phase SMB to produce high-purity propylene from mixtures with
propane, with high recovery and productivity, proving to be a strong candidate to
substitute the more traditional technologies such as distillation [79]. Since the
development of the early systems, the SMB technology for olefin enrichment gained
more and more interest, since it can be a desirable alternative to obtain high-purity
products at a similarly high recovery, even in the cases where the separation factor is
near unity [80]. A gas-phase SMB bench unit operating with a 4-2-2 configuration,
i.e., an open-loop circuit by suppression of section IV, to separate propylene from
propane on zeolite 13X with 20% binder, proved the concept by producing polymergrade olefin with high recovery [47]. For the first time it was shown experimentally
that it is possible to obtain polymer-grade olefin by gas-phase SMB at a bench scale
[47]. This latest breakthrough in gas-phase SMB applied to olefin/paraffin separation
was the basis for the polymer-grade ethylene production from ethane/ethylene
mixtures by four-zones gas-phase SMB with the recycle stream. A binderless zeolite
13X beads/propane pair was proposed as the adsorbent/desorbent pair to perform the
separation of two target mixtures with a composition of 0.22/0.78 and 0.50/0.50
ethane/ethylene. The obtained performance parameters showed the high efficiency
of that technology since ethylene was produced with a purity of 99.8%, recovery of
99.8%, and productivity of 2.0 mol C2H4 Áh
À1
Ákg
À1 from a mixture containing 50%
ethane and 50% ethylene [42].
152
V. F. D. Martins et al.
promotes the mass transfer driving force, leading to more efficient use of the
adsorbent [70]. In this technology, besides the choice of a suitable adsorbent, to
perform the SMB is also necessary to deal with the selection of a desorbent capable
of displacing the adsorbed gas mixture from the adsorbent [58]. The first application
of this technology dates back to 1960s when Universal Oil Products Inc. (UOP)
implemented the Sorbex family of this process, applied to liquid-phase separations
in refineries [71]. Sorbex processes are exclusively applied in liquid-phase separations, but many studies demonstrated the feasibility of this process to be applied in
gas phase separations, namely, in more challenging situations where the separation
factor is near to unity. However, it was necessary to redesign the Sorbex process to
the gas phase, once the axial dispersion constitutes a problem in the classical
approach in which the Sorbex was implemented [72]. Several strategies were
designed for the most varied separations in the gas phase, and to the best of our
knowledge, none was implemented at the industrial scale [9]. In the 1990s, the
separation of volatile inhalation anesthetic enantiomers [73], xylene isomers [74],
and linear/nonlinear paraffins [75] was exploited by gas-phase SMB chromatography (GC-SMB) and experimentally tested at lab scale. A couple of years ago, the
development of new theories, modeling methodologies, and new operation modes
continued leading to the emerging of new solutions and concepts. SMB processes for
other gaseous separations, such as H 2 /He and D 2 /He [76] and C 3 H 6 /C 3 H 8 [77], have
been reported in the patent literature. Several authors explored this technology in the
gas phase, to separate olefins from mixtures containing the homolog paraffins, once
this technology should lead to a more energy-optimized process and olefin production with higher purity, recovery, and productivity [57, 77, 78]. Rodrigues et al.
patented a gas-phase SMB to produce high-purity propylene from mixtures with
propane, with high recovery and productivity, proving to be a strong candidate to
substitute the more traditional technologies such as distillation [79]. Since the
development of the early systems, the SMB technology for olefin enrichment gained
more and more interest, since it can be a desirable alternative to obtain high-purity
products at a similarly high recovery, even in the cases where the separation factor is
near unity [80]. A gas-phase SMB bench unit operating with a 4-2-2 configuration,
i.e., an open-loop circuit by suppression of section IV, to separate propylene from
propane on zeolite 13X with 20% binder, proved the concept by producing polymergrade olefin with high recovery [47]. For the first time it was shown experimentally
that it is possible to obtain polymer-grade olefin by gas-phase SMB at a bench scale
[47]. This latest breakthrough in gas-phase SMB applied to olefin/paraffin separation
was the basis for the polymer-grade ethylene production from ethane/ethylene
mixtures by four-zones gas-phase SMB with the recycle stream. A binderless zeolite
13X beads/propane pair was proposed as the adsorbent/desorbent pair to perform the
separation of two target mixtures with a composition of 0.22/0.78 and 0.50/0.50
ethane/ethylene. The obtained performance parameters showed the high efficiency
of that technology since ethylene was produced with a purity of 99.8%, recovery of
99.8%, and productivity of 2.0 mol C2H4 Áh
À1
Ákg
À1 from a mixture containing 50%
ethane and 50% ethylene [42].
152
V. F. D. Martins et al.