• No further compression is required.
• It avoids addition of chemicals/consumables (Report 2012).
9.3.4.1 Membrane Technology
It is categorised into three types based on the membranes used. They are as follows:
(a) Inorganic membrane separation method
(b) Polymeric membrane separation method
(c) Mixed matrix membrane
(a) Inorganic membrane separation method
Inorganic membrane separation method uses inorganic membranes in porous/
dense phase having high selectivity, high chemical stability, high thermal stability
and high permeability. The dense membrane is made up of zirconia/palladium/silver/
nickel/calcium titanate, and porous membranes are fabricated with silica/carbon/
zeolite/alumina (Mallada and Menendez 2008). Inorganic membranes are capable of
withstanding hard environmental problems, and hence, it is widely used for separation of methane (Zhang et al. 2013). The operational life is long for the membranes,
even though the cost of the method is high. In addition, the hydrogen sulphide and
water must be pretreated for efficient removal of carbon dioxide (Chen et al. 2015;
Sahota et al. 2018).
9.3.4.2 Polymeric Membrane Separation Method
Polymeric membranes are dense and porous in nature made up of cellulose acetate/
polyimide/polysulfone (Ahmed et al. 2010). The permeability gets altered with the
size of the pore. The basic principle lies in the convective flow, molecular sieving
and the Knudsen flow (Chen et al. 2015; Zhang et al. 2013). Solubility and
diffusivity are important for a better transport mechanism. Firstly, the gas molecules
are trapped in the membrane, and then the diffusion process is executed. The
diffusion process works on the basis of difference in pressure gradient and the
concentration (Ahmed et al. 2010).
9.3.4.3 Mixed Matrix Membrane
In mixed matrix membranes, the inorganic filler is mixed with the polymer matrix,
and so it is heterogeneous in nature with the property of high permeability, easy
scalability and economically feasible. The integration of inorganic to the polymer
membrane is done to bind the advantages of both the methods (Chen et al. 2015).
Metal-organic framework and zeolite are the most commonly used inorganic fillers
for separating carbon dioxide and methane.
The inorganic filler zeolite is crystalline in nature with tetrahedral shape and
micro-porosity. It is made up of aluminium, silicon, sodium, potassium, calcium and
magnesium. The different gas molecules can be easily separated based on the pore
size. Due to uniform pore size, it becomes easy for the zeolite membranes to
discriminate between different gas molecules. The zeolite membrane is fabricated
using flat membranes, but in large manufacturing companies, hollow fibre
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• It avoids addition of chemicals/consumables (Report 2012).
9.3.4.1 Membrane Technology
It is categorised into three types based on the membranes used. They are as follows:
(a) Inorganic membrane separation method
(b) Polymeric membrane separation method
(c) Mixed matrix membrane
(a) Inorganic membrane separation method
Inorganic membrane separation method uses inorganic membranes in porous/
dense phase having high selectivity, high chemical stability, high thermal stability
and high permeability. The dense membrane is made up of zirconia/palladium/silver/
nickel/calcium titanate, and porous membranes are fabricated with silica/carbon/
zeolite/alumina (Mallada and Menendez 2008). Inorganic membranes are capable of
withstanding hard environmental problems, and hence, it is widely used for separation of methane (Zhang et al. 2013). The operational life is long for the membranes,
even though the cost of the method is high. In addition, the hydrogen sulphide and
water must be pretreated for efficient removal of carbon dioxide (Chen et al. 2015;
Sahota et al. 2018).
9.3.4.2 Polymeric Membrane Separation Method
Polymeric membranes are dense and porous in nature made up of cellulose acetate/
polyimide/polysulfone (Ahmed et al. 2010). The permeability gets altered with the
size of the pore. The basic principle lies in the convective flow, molecular sieving
and the Knudsen flow (Chen et al. 2015; Zhang et al. 2013). Solubility and
diffusivity are important for a better transport mechanism. Firstly, the gas molecules
are trapped in the membrane, and then the diffusion process is executed. The
diffusion process works on the basis of difference in pressure gradient and the
concentration (Ahmed et al. 2010).
9.3.4.3 Mixed Matrix Membrane
In mixed matrix membranes, the inorganic filler is mixed with the polymer matrix,
and so it is heterogeneous in nature with the property of high permeability, easy
scalability and economically feasible. The integration of inorganic to the polymer
membrane is done to bind the advantages of both the methods (Chen et al. 2015).
Metal-organic framework and zeolite are the most commonly used inorganic fillers
for separating carbon dioxide and methane.
The inorganic filler zeolite is crystalline in nature with tetrahedral shape and
micro-porosity. It is made up of aluminium, silicon, sodium, potassium, calcium and
magnesium. The different gas molecules can be easily separated based on the pore
size. Due to uniform pore size, it becomes easy for the zeolite membranes to
discriminate between different gas molecules. The zeolite membrane is fabricated
using flat membranes, but in large manufacturing companies, hollow fibre
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
253