**1. Introduction**

Gas separation and storage processes are essentially important to various aspects in human society, such as energy consumption, environmental security, and industrial production. Energy and environmental concerns are currently at the forefront of global attention. So, carbon dioxide separation is crucial to the mitigation of greenhouse effect [1–3]. Besides, separation of hydrogen and methane together with storage is indispensable for the prevalent use of clean energy. In the case of toxic gases, the separation and storage of ammonia and carbon monoxide are important for pollution control and the synthesis of industrial chemicals. The conventional gas separation technologies such as pressure swing adsorption (PSA), cryogenic distillation, etc. are very energy intensive as well as capital intensive. Also separation methods like liquid adsorbent are cost-effective. In the distillation process, the

repeated evaporating-condensing cycle of the mixture under harsh conditions is a problematical job. Also generation of liquid adsorbent is a main concern which required the heating and cooling of massive solvent medium to release adsorbed gas. Due to these negative aspects, the potential of emerging technologies based on adsorption or membrane separations is highly amiable alternative process and has been proposed as more energy-efficient technologies [4–8]. According to existing literatures, membrane-based separation technology only consumes 10% energy of that for distillation [9]. From the industrial perspective of storage and separation of different gases, adsorption-based technique is more amicable and commendable due to its superiority to other techniques like simplicity of design, easy operation, and low cost. The separation efficiency relies on internal porosity and surface properties of solid adsorbent due to their key role in gas sorption. Alternatively, molecular properties of the adsorbent such as chemical affinity or molecular size of the separated components play a vital role in the separation process. Separation and purification, meanwhile, involve the selective adsorption of particular species from gas mixtures. Also, gas storage requires elevated pressures due to volumetric capacity considerations of porous materials and the need to deliver gas at ambient pressure or above.

Nanoporous materials have attracted huge interest among the communities of materials science, chemical engineering, and chemistry due to their excellent properties such as high surface area, large pore volume, and specific surface chemistry. The term *nanoporous* refers to any material with a pore size below ~100 nm. According to the International Union of Pure and Applied Chemistry (IUPAC) guidelines, nanoporous materials encompass both the microporous (<2 nm) and mesoporous (2–50 nm) regimes. As per literature data, porous materials like zeolites, carbon, aluminophosphates, carbon nanotubes, silica gel, pillared clays, inorganic and polymeric resins, MOFs, and MOFs composites have been investigated as adsorbents. In industry some of the adsorbents are now used for different applications. In the literature, relevant reviews and monographs have discussed the syntheses process, characterizations, and the adsorption properties of these porous materials [9–14]. The importance of porous materials for different application is summarized in the literature, which can be helpful for the next-generation researcher. Among all porous material, especially in the microporous family, zeolites are the first and foremost emerging materials and attracted increasing interest because of their unique physical and chemical properties, such as high surface area, high chemical resistance, extraordinary mechanical properties, good adsorption, and catalytic properties due to specific surface chemistry [15–22]. These peculiar and amazing properties have highlighted the potential of this material in a variety of applications and particularly in the area of gas separation and storage application [23–34]. Zeolites are traditionally referred to as a family of open-framework aluminosilicate materials consisting of orderly distributed micropores in molecular dimensions. Topologically, zeolites are three-dimensional networks of corner-sharing tetrahedral TO4 ("T" denotes tetrahedrally coordinated Si, Al, or P), and different ways of tetrahedra connection lead to a diversity of zeolite framework types based on various compositions [35]. Silica zeolites consist of fourcoordinated Si bridged by oxygen atoms [36]. To date, 235 distinct zeolite framework types have been identified in natural or synthetic zeolites, each of which has been assigned a three-letter code by the International Zeolite Association (**Figure 1**) [37].

For zeolite synthesis, the well-known conventional hydrothermal method is a widely used technique. Besides the other synthesis method like sonochemical and sonochemical-assisted hydrothermal method, microwave-assisted methods are more popular and advanced synthesis process to achieve phase pure high-quality zeolites in terms of their shape, size, porosity, uniform structure, and better crystallinity [38]. Furthermore, for the synthesis of zeolite membrane on the porous support, the in-situ and ex-situ (secondary growth) hydrothermal techniques are

**97**

**Figure 1.**

*Zeolites: An Emerging Material for Gas Storage and Separation Applications*

the well known process and more popular among other synthesis routes. In the case of in situ hydrothermal process, the porous support is immersed into the synthesis solution, and the membrane layer is formed directly through direct crystallization in a suitable time period. But in this process, the probability of attaining the highquality membrane on the support is less. So ex situ hydrothermal method which is also known as seeded growth technique is an effective and accepted approach towards the development of better membrane on the support surface. This method has potential advantages in terms of achieved preferential orientation control of membrane microstructure and higher reproducibility if compared with the in situ synthesis method [39]. Extensive studies have been performed aiming at investigating potential of zeolites and derived membranes for gas separation [40–56]. Specific zeolites have a high capacity and selectivity for the gases of interest, leading to

To make this book chapter comprehensive, here three different types of zeolitic material were focused. The first one is siliceous deca-dodecasil 3R (DDR) zeolite which has elliptical pore openings defined by 8-member ring windows with an

[27, 43, 50]. Another important zeolite is silicoaluminophosphate (SAPO 34). SAPO 34, a chabazite zeolite with a composition of SixAlyPzO2, where x = 0.01–0.98, y = 0.01–0.60, and z = 0.01–0.52, has an average pore size of 0.38 nm and plays an important role for gas separation application [32]. The last one is Bikitaite (BIK) zeolite having a unit cell chemical composition Li2(Al2Si4O12)-2H2O [11, 36]. It is a small pore (diameter 0.28–0.37 nm) sized zeolite and has been studied for various applications and most notably has shown better performance in gas separation and storage application. The detail synthesis protocol and techniques used to synthesize zeolites and high-quality membrane have been discussed here.

, and it is useful for separation of small-sized gas

compact and efficient separation/storage systems.

effective size of 0.36 × 0.44 nm<sup>2</sup>

*Framework types of different zeolites [36, 37].*

*DOI: http://dx.doi.org/10.5772/intechopen.91035*

*Zeolites: An Emerging Material for Gas Storage and Separation Applications DOI: http://dx.doi.org/10.5772/intechopen.91035*

#### **Figure 1.**

*Zeolites - New Challenges*

repeated evaporating-condensing cycle of the mixture under harsh conditions is a problematical job. Also generation of liquid adsorbent is a main concern which required the heating and cooling of massive solvent medium to release adsorbed gas. Due to these negative aspects, the potential of emerging technologies based on adsorption or membrane separations is highly amiable alternative process and has been proposed as more energy-efficient technologies [4–8]. According to existing literatures, membrane-based separation technology only consumes 10% energy of that for distillation [9]. From the industrial perspective of storage and separation of different gases, adsorption-based technique is more amicable and commendable due to its superiority to other techniques like simplicity of design, easy operation, and low cost. The separation efficiency relies on internal porosity and surface properties of solid adsorbent due to their key role in gas sorption. Alternatively, molecular properties of the adsorbent such as chemical affinity or molecular size of the separated components play a vital role in the separation process. Separation and purification, meanwhile, involve the selective adsorption of particular species from gas mixtures. Also, gas storage requires elevated pressures due to volumetric capacity considerations of porous materials and the need to deliver gas at ambient pressure or above. Nanoporous materials have attracted huge interest among the communities of materials science, chemical engineering, and chemistry due to their excellent properties such as high surface area, large pore volume, and specific surface chemistry. The term *nanoporous* refers to any material with a pore size below ~100 nm. According to the International Union of Pure and Applied Chemistry (IUPAC) guidelines, nanoporous materials encompass both the microporous (<2 nm) and mesoporous (2–50 nm) regimes. As per literature data, porous materials like zeolites, carbon, aluminophosphates, carbon nanotubes, silica gel, pillared clays, inorganic and polymeric resins, MOFs, and MOFs composites have been investigated as adsorbents. In industry some of the adsorbents are now used for different applications. In the literature, relevant reviews and monographs have discussed the syntheses process, characterizations, and the adsorption properties of these porous materials [9–14]. The importance of porous materials for different application is summarized in the literature, which can be helpful for the next-generation researcher. Among all porous material, especially in the microporous family, zeolites are the first and foremost emerging materials and attracted increasing interest because of their unique physical and chemical properties, such as high surface area, high chemical resistance, extraordinary mechanical properties, good adsorption, and catalytic properties due to specific surface chemistry [15–22]. These peculiar and amazing properties have highlighted the potential of this material in a variety of applications and particularly in the area of gas separation and storage application [23–34]. Zeolites are traditionally referred to as a family of open-framework aluminosilicate materials consisting of orderly distributed micropores in molecular dimensions. Topologically, zeolites are three-dimensional networks of corner-sharing tetrahedral TO4 ("T" denotes tetrahedrally coordinated Si, Al, or P), and different ways of tetrahedra connection lead to a diversity of zeolite framework types based on various compositions [35]. Silica zeolites consist of fourcoordinated Si bridged by oxygen atoms [36]. To date, 235 distinct zeolite framework types have been identified in natural or synthetic zeolites, each of which has been assigned a three-letter code by the International Zeolite Association (**Figure 1**) [37]. For zeolite synthesis, the well-known conventional hydrothermal method is a widely used technique. Besides the other synthesis method like sonochemical and sonochemical-assisted hydrothermal method, microwave-assisted methods are more popular and advanced synthesis process to achieve phase pure high-quality zeolites in terms of their shape, size, porosity, uniform structure, and better crystallinity [38]. Furthermore, for the synthesis of zeolite membrane on the porous support, the in-situ and ex-situ (secondary growth) hydrothermal techniques are

**96**

*Framework types of different zeolites [36, 37].*

the well known process and more popular among other synthesis routes. In the case of in situ hydrothermal process, the porous support is immersed into the synthesis solution, and the membrane layer is formed directly through direct crystallization in a suitable time period. But in this process, the probability of attaining the highquality membrane on the support is less. So ex situ hydrothermal method which is also known as seeded growth technique is an effective and accepted approach towards the development of better membrane on the support surface. This method has potential advantages in terms of achieved preferential orientation control of membrane microstructure and higher reproducibility if compared with the in situ synthesis method [39]. Extensive studies have been performed aiming at investigating potential of zeolites and derived membranes for gas separation [40–56]. Specific zeolites have a high capacity and selectivity for the gases of interest, leading to compact and efficient separation/storage systems.

To make this book chapter comprehensive, here three different types of zeolitic material were focused. The first one is siliceous deca-dodecasil 3R (DDR) zeolite which has elliptical pore openings defined by 8-member ring windows with an effective size of 0.36 × 0.44 nm<sup>2</sup> , and it is useful for separation of small-sized gas [27, 43, 50]. Another important zeolite is silicoaluminophosphate (SAPO 34). SAPO 34, a chabazite zeolite with a composition of SixAlyPzO2, where x = 0.01–0.98, y = 0.01–0.60, and z = 0.01–0.52, has an average pore size of 0.38 nm and plays an important role for gas separation application [32]. The last one is Bikitaite (BIK) zeolite having a unit cell chemical composition Li2(Al2Si4O12)-2H2O [11, 36]. It is a small pore (diameter 0.28–0.37 nm) sized zeolite and has been studied for various applications and most notably has shown better performance in gas separation and storage application. The detail synthesis protocol and techniques used to synthesize zeolites and high-quality membrane have been discussed here.

After all, the performance of the developed materials was discussed elaborately for better understanding and presents the future aspect of these materials.
