technology. A wide variety of zeolites has been studied for this process, such as
zeolites 13X, 4A, and 5A. The second case study is the removal of carbon dioxide
(CO 2 ) from natural gas stream. Adsorption processes are considered a competitive
solution, once the adsorbent can be regenerated either by TSA or PSA. Concerning
the use of zeolites for CO 2 removal, natural chabazite, zeolite 4A, H-mordenite, and
zeolite 13X are the ones with more available information in literature.
In this review, we will focus on the strategy and importance of the lab/pilot scale
with perspectives of scaling up adsorptive gas-phase separations using zeolites. The
main methods adopted in lab/pilot scale studies include adsorbent characterization,
adsorption equilibrium, adsorption dynamic studies, and process simulation and
optimization.
Keywords 13X · Adsorption · Cryo-PTSA · Gas phase · Industrial · Laboratorial ·
PSA · SMB · Zeolites
1 Introduction
With the gradual increase of energy costs in the 1960s and 1970s, the petrochemical
industry was forced to find new alternatives for which distillation has become less
favorable in terms of energy input and CO 2 emissions. The adsorption-based
separation processes were implemented in the petroleum and petrochemical industry
as they offer fluid separation based on the shape, size, and chemical nature of the
molecules. The large pore surface area and the high adsorption affinity ensure the
densification of gases at moderate temperature and moderate pressure. The success
of the adsorptive technologies is intrinsically associated with the adsorbent selection.
So, the characteristics of the adsorbent, such as selectivity, cost, and regeneration
method – pressure swing, the temperature swing, purge gas stripping, or displacement desorption – must be taken into consideration, since those characteristics
determine the size and then the cost of the adsorbent bed [1]. The adsorbent materials
can be classified into three main categories: steric (molecular sieving by size
exclusion), kinetic (differences in diffusion rates), or equilibrium (differences in
adsorption capacity). The physicochemical properties of the adsorbent, as well as the
adsorption characteristics of the components on that adsorbent, are the main aspects
that determine the dominant mechanism for a given separation [2].
Zeolites are porous crystalline aluminosilicate extensively used in a wide range of
industrial applications. The synthetic zeolites have become of great importance in
the industry, especially as adsorbents, molecular sieves, and catalysts. Faujasite
zeolites (zeolites X and Y) are among the most widely used zeolites in gas separation
and purification processes. The difference between zeolite X and Y is based on the
Si/Al ratio of the structure: for zeolite X, Si/Al ratio is between 1.0 and 1.5; for
zeolite Y it is above 1.5 [3]. Zeolite X has a three-dimensional open framework
146
V. F. D. Martins et al.
zeolites 13X, 4A, and 5A. The second case study is the removal of carbon dioxide
(CO 2 ) from natural gas stream. Adsorption processes are considered a competitive
solution, once the adsorbent can be regenerated either by TSA or PSA. Concerning
the use of zeolites for CO 2 removal, natural chabazite, zeolite 4A, H-mordenite, and
zeolite 13X are the ones with more available information in literature.
In this review, we will focus on the strategy and importance of the lab/pilot scale
with perspectives of scaling up adsorptive gas-phase separations using zeolites. The
main methods adopted in lab/pilot scale studies include adsorbent characterization,
adsorption equilibrium, adsorption dynamic studies, and process simulation and
optimization.
Keywords 13X · Adsorption · Cryo-PTSA · Gas phase · Industrial · Laboratorial ·
PSA · SMB · Zeolites
1 Introduction
With the gradual increase of energy costs in the 1960s and 1970s, the petrochemical
industry was forced to find new alternatives for which distillation has become less
favorable in terms of energy input and CO 2 emissions. The adsorption-based
separation processes were implemented in the petroleum and petrochemical industry
as they offer fluid separation based on the shape, size, and chemical nature of the
molecules. The large pore surface area and the high adsorption affinity ensure the
densification of gases at moderate temperature and moderate pressure. The success
of the adsorptive technologies is intrinsically associated with the adsorbent selection.
So, the characteristics of the adsorbent, such as selectivity, cost, and regeneration
method – pressure swing, the temperature swing, purge gas stripping, or displacement desorption – must be taken into consideration, since those characteristics
determine the size and then the cost of the adsorbent bed [1]. The adsorbent materials
can be classified into three main categories: steric (molecular sieving by size
exclusion), kinetic (differences in diffusion rates), or equilibrium (differences in
adsorption capacity). The physicochemical properties of the adsorbent, as well as the
adsorption characteristics of the components on that adsorbent, are the main aspects
that determine the dominant mechanism for a given separation [2].
Zeolites are porous crystalline aluminosilicate extensively used in a wide range of
industrial applications. The synthetic zeolites have become of great importance in
the industry, especially as adsorbents, molecular sieves, and catalysts. Faujasite
zeolites (zeolites X and Y) are among the most widely used zeolites in gas separation
and purification processes. The difference between zeolite X and Y is based on the
Si/Al ratio of the structure: for zeolite X, Si/Al ratio is between 1.0 and 1.5; for
zeolite Y it is above 1.5 [3]. Zeolite X has a three-dimensional open framework
146
V. F. D. Martins et al.