membranes are applied due to its low fabrication cost, increased packing density,
easy handling and flexible fabrication steps (Zhang et al. 2013).
The metal organic framework is synthesised by bonding the metal ion and organic
linkers, and it acts as the coordination centre that enhances the flexibility and
resilience properties (Li et al. 2012). The advantages of this metal organic framework include specific surface area, unique pore volume, high adsorption capacity
and wide compatibility (Sahota et al. 2018).
9.3.5 Cryogenic Technology
The difference in condensation temperature of the gases to be separated forms the
basis of the cryogenic technology. For separating methane and carbon dioxide,
cryogenic technology uses the principle of sublimation/boiling points of the two
different gases. The carbon dioxide gas gets accumulated in the liquid phase by the
process of condensation/sublimation, and the methane gets collected in the gaseous
phase. During the condensation process, in addition to the carbon dioxide, the
siloxanes (Munoz et al. 2015) and water also get separated and can be removed
out of the unit. Carbon dioxide has the sublimation point of 194.65 K. Increased
amount of methane inhibits the normal characteristics of gas. It is mandatory to
undergo the cooling process in several steps, and so, the retrieval process depends
upon the gases to be separated.
For example, in GPP
® system, the gas is cooled to À25
C at a pressure of
17–26 bar to remove halogens, water, sulphur dioxide, siloxanes and hydrogen
sulphide from the biogas. Additional contaminants can be removed by passing it
first to a coalescence filter and then to a SOXSIA
® catalyst. After removing the
contaminants, the carbon dioxide gas is removed, and it occurs in two steps: firstly,
cooling the gas to À50
C and À59
C, where about 30–40% of carbon dioxide is
filtered in the liquid phase, and, secondly, carbon dioxide is separated in solid form.
The GPP
® plus system is upgrading its technology to generate methane in the form
of liquid. About 96% methane purity is achieved in a pilot plant in Canada
(Petersson and Wellinger 2009).
To liquefy carbon dioxide, compression and cooling must be done. The
parameters required for successful implementation of this technology includes a
pressure of 80 bar and a temperature of À170
C (Porpatham et al. 2018; Sun et al.
2015; Ryckebosch et al. 2011). Hydrogen sulphide and water must be subjected to
pretreatment to avoid freezing problem, and while methane gets separated, condensation process must be done for gases like oxygen and nitrogen (Chen et al. 2015).
The major advantages include 99% methane recovery and separation of carbon
dioxide. The limitations of this technique include high investment cost and operating
cost, need for large number of equipment, clogging (Angelidaki et al. 2018) and
high-energy requirement (Deublein and Steinhauser 2010). Green Public Procurement developed a cryogenic technology that can minimise the energy requirement
and generate pure carbon dioxide and methane in liquid form (Tuinier and van
SintAnnal and 2012; Sahota et al. 2018).
254
B. S. Dhanya et al.
easy handling and flexible fabrication steps (Zhang et al. 2013).
The metal organic framework is synthesised by bonding the metal ion and organic
linkers, and it acts as the coordination centre that enhances the flexibility and
resilience properties (Li et al. 2012). The advantages of this metal organic framework include specific surface area, unique pore volume, high adsorption capacity
and wide compatibility (Sahota et al. 2018).
9.3.5 Cryogenic Technology
The difference in condensation temperature of the gases to be separated forms the
basis of the cryogenic technology. For separating methane and carbon dioxide,
cryogenic technology uses the principle of sublimation/boiling points of the two
different gases. The carbon dioxide gas gets accumulated in the liquid phase by the
process of condensation/sublimation, and the methane gets collected in the gaseous
phase. During the condensation process, in addition to the carbon dioxide, the
siloxanes (Munoz et al. 2015) and water also get separated and can be removed
out of the unit. Carbon dioxide has the sublimation point of 194.65 K. Increased
amount of methane inhibits the normal characteristics of gas. It is mandatory to
undergo the cooling process in several steps, and so, the retrieval process depends
upon the gases to be separated.
For example, in GPP
® system, the gas is cooled to À25
C at a pressure of
17–26 bar to remove halogens, water, sulphur dioxide, siloxanes and hydrogen
sulphide from the biogas. Additional contaminants can be removed by passing it
first to a coalescence filter and then to a SOXSIA
® catalyst. After removing the
contaminants, the carbon dioxide gas is removed, and it occurs in two steps: firstly,
cooling the gas to À50
C and À59
C, where about 30–40% of carbon dioxide is
filtered in the liquid phase, and, secondly, carbon dioxide is separated in solid form.
The GPP
® plus system is upgrading its technology to generate methane in the form
of liquid. About 96% methane purity is achieved in a pilot plant in Canada
(Petersson and Wellinger 2009).
To liquefy carbon dioxide, compression and cooling must be done. The
parameters required for successful implementation of this technology includes a
pressure of 80 bar and a temperature of À170
C (Porpatham et al. 2018; Sun et al.
2015; Ryckebosch et al. 2011). Hydrogen sulphide and water must be subjected to
pretreatment to avoid freezing problem, and while methane gets separated, condensation process must be done for gases like oxygen and nitrogen (Chen et al. 2015).
The major advantages include 99% methane recovery and separation of carbon
dioxide. The limitations of this technique include high investment cost and operating
cost, need for large number of equipment, clogging (Angelidaki et al. 2018) and
high-energy requirement (Deublein and Steinhauser 2010). Green Public Procurement developed a cryogenic technology that can minimise the energy requirement
and generate pure carbon dioxide and methane in liquid form (Tuinier and van
SintAnnal and 2012; Sahota et al. 2018).
254
B. S. Dhanya et al.