followed by the diffusion of the gas molecules through the
polymer matrix. Finally, the gas molecules evaporate
through the downstream end (Stern 1994).
3 Membrane Materials for Natural Gas
Purification
Nowadays, there have been growing interests in the development and applications of membrane-based natural gas
separation process to tackle serious environmental issues and
challenges. Researchers have been made a remarkable
improvement in the gas separation membranes based on both
polymeric and inorganic materials for industrial application
(Centeno and Fuertes 1999; Ho et al. 2008; Mahajan et al.
2002; Noble 2011). Interestingly, new polymers, copolymers, and advanced materials such as metal–organic
frameworks (MOF) and composite materials have been
successfully used for natural gas sweetening process. Furthermore, nano-sized range inorganic materials have been
merged in polymeric structures to introduce a new class of
mixed matrix membranes (MMMs) with higher separation
performance to surpass the Robeson upper boundary limits
(Khan et al. 2018a, b, c).
Furthermore, the membrane technology has now reached
its initial stage of maturity. The following important factors
are considered for the selection of membrane materials for
gas separation such as (1) intrinsic membrane selectivity
(Thomas et al. 2017), (2) having high plasticization resistance (Iwasa et al. 2018), (3) having good mechanical and
thermal strength (Khan et al. 2018a, b, c), (4) ability to
convert materials into membrane morphology with excellent
gas separation performance under adversarial feed mixture
conditions (Zornoza et al. 2011a, b), and (5) having excellent
interaction and sorption with one of the species of the
mixture for efficient gas separation (Ismail et al. 2009).
Additionally, molecular structure, polarity, and the presence
of chemical groups in the membrane materials are other
parameters of interest as it affects the natural gas separation
performance.
Generally, the gas permeability and selectivity of membrane material are a decisive factor for high-gas separation
performance and attracted the attention of future researchers
from industries as well as academia sector. Moreover, the
scientific aspects such as thermodynamics, mass, and heat
transfer phenomena and surface chemistry at various feed
conditions are equally important to encourage natural gas
separation process. Polymeric, inorganic, and mixed matrix
membranes are used for purification of natural gas as shown
in Fig. 2. The following sections further explain the current
challenges of the aforementioned membrane materials for
natural gas purification.
3.1 Polymeric Membranes
Polymeric membranes are commercially available for various gas mixture separations such as separation of nitrogen
and oxygen from air and purification of natural gas. In the
process of natural gas sweetening, compression at feed gas
stream and low pressure of CO 2 after separation is required
to offer the driving force for permeation. Generally, glassy
and rubbery polymeric materials are used for gas separation
(Zornoza et al. 2011a, b). Glassy materials are glass-like
rigid materials and perform below their glass transition
temperatures (T g ). On the other hand, rubbery materials are
flexible, soft, and perform above their T g (Stern 1994).
Typically, the rubbery polymers give high permeability with
low selectivity while glassy polymers display vice versa.
Glassy polymeric membranes are dominating in industrial
separation processes due to their high-gas separation performance and excellent thermal and mechanical properties
(Samarasinghe et al. 2018). These membranes are further
classified on the basis of structure such as nonporous dense
membrane and microporous membrane. Microporous
membranes have a rigid morphology with connected pores
on the surface. While, the nonporous dense membranes have
a dense film through which permeants pass by diffusion
under the driving force of pressure, electrical potential, and
concentration gradient (Kanehashi et al. 2015). The separation of different components of a gas mixture depends on the
relative transport rate within the membrane, which is determined by their diffusivity and solubility in the membrane
material.
Fig. 2 Various membrane materials for natural gas purification
62
I. U. Khan et al.
polymer matrix. Finally, the gas molecules evaporate
through the downstream end (Stern 1994).
3 Membrane Materials for Natural Gas
Purification
Nowadays, there have been growing interests in the development and applications of membrane-based natural gas
separation process to tackle serious environmental issues and
challenges. Researchers have been made a remarkable
improvement in the gas separation membranes based on both
polymeric and inorganic materials for industrial application
(Centeno and Fuertes 1999; Ho et al. 2008; Mahajan et al.
2002; Noble 2011). Interestingly, new polymers, copolymers, and advanced materials such as metal–organic
frameworks (MOF) and composite materials have been
successfully used for natural gas sweetening process. Furthermore, nano-sized range inorganic materials have been
merged in polymeric structures to introduce a new class of
mixed matrix membranes (MMMs) with higher separation
performance to surpass the Robeson upper boundary limits
(Khan et al. 2018a, b, c).
Furthermore, the membrane technology has now reached
its initial stage of maturity. The following important factors
are considered for the selection of membrane materials for
gas separation such as (1) intrinsic membrane selectivity
(Thomas et al. 2017), (2) having high plasticization resistance (Iwasa et al. 2018), (3) having good mechanical and
thermal strength (Khan et al. 2018a, b, c), (4) ability to
convert materials into membrane morphology with excellent
gas separation performance under adversarial feed mixture
conditions (Zornoza et al. 2011a, b), and (5) having excellent
interaction and sorption with one of the species of the
mixture for efficient gas separation (Ismail et al. 2009).
Additionally, molecular structure, polarity, and the presence
of chemical groups in the membrane materials are other
parameters of interest as it affects the natural gas separation
performance.
Generally, the gas permeability and selectivity of membrane material are a decisive factor for high-gas separation
performance and attracted the attention of future researchers
from industries as well as academia sector. Moreover, the
scientific aspects such as thermodynamics, mass, and heat
transfer phenomena and surface chemistry at various feed
conditions are equally important to encourage natural gas
separation process. Polymeric, inorganic, and mixed matrix
membranes are used for purification of natural gas as shown
in Fig. 2. The following sections further explain the current
challenges of the aforementioned membrane materials for
natural gas purification.
3.1 Polymeric Membranes
Polymeric membranes are commercially available for various gas mixture separations such as separation of nitrogen
and oxygen from air and purification of natural gas. In the
process of natural gas sweetening, compression at feed gas
stream and low pressure of CO 2 after separation is required
to offer the driving force for permeation. Generally, glassy
and rubbery polymeric materials are used for gas separation
(Zornoza et al. 2011a, b). Glassy materials are glass-like
rigid materials and perform below their glass transition
temperatures (T g ). On the other hand, rubbery materials are
flexible, soft, and perform above their T g (Stern 1994).
Typically, the rubbery polymers give high permeability with
low selectivity while glassy polymers display vice versa.
Glassy polymeric membranes are dominating in industrial
separation processes due to their high-gas separation performance and excellent thermal and mechanical properties
(Samarasinghe et al. 2018). These membranes are further
classified on the basis of structure such as nonporous dense
membrane and microporous membrane. Microporous
membranes have a rigid morphology with connected pores
on the surface. While, the nonporous dense membranes have
a dense film through which permeants pass by diffusion
under the driving force of pressure, electrical potential, and
concentration gradient (Kanehashi et al. 2015). The separation of different components of a gas mixture depends on the
relative transport rate within the membrane, which is determined by their diffusivity and solubility in the membrane
material.
Fig. 2 Various membrane materials for natural gas purification
62
I. U. Khan et al.