left out. In addition to the amine solutions, alkaline salts like calcium hydroxide,
sodium and potassium were also added (Kougias et al. 2010; Zhao et al. 2010). The
absorption capacity of carbon dioxide is greater in sodium hydroxide than in the
amine solutions. For absorbing 1 ton of carbon dioxide, 0.9 tons of sodium hydroxide is required when compared to 1.39 tons of monoethanolamine (Yoo et al. 2013).
About 99% methane purity can be achieved through this method with less than 0.1%
methane loss (Angelidaki et al. 2018).
The advantages of chemical scrubbing include complete absorption of hydrogen
sulphide by the scrubber and high selectivity of the amine solution, and the
disadvantages include high investment cost initially, high energy requirement during
regeneration and the chemical toxicity to the environment (Yoo et al. 2013).
The amine scrubbing process is advantageous if:
• No off-gas treatment is needed.
• Plant capacity is high.
• No compression is required (Report 2012).
9.3.3 Adsorption Method
Adsorption is defined as a process in which the components of a mixture gets
attached or binds to a solid matrix which is microporous in nature but with a large
surface area. Based on the types of force, the adsorption process is categorised into
physisorption and chemisorption. In physisorption process, between the adsorbent
and the adsorbate, weak Vander Waal’s forces is involved, and in chemisorption
process, strong molecular force exists. The operational parameters for adsorption
methods include 3–8 bar pressure, 50–60
C temperature and 100–200 mbar regeneration pressure. It requires 3–5 min to complete one cycle. Cycle time, purging
pressure, adsorbent, feeding pressure and column interconnectivity are the
characteristics of adsorption techniques.
Adsorption methods are categorised into three types as follows:
(a) Pressure swing adsorption
(b) Temperature swing adsorption
(c) Vacuum swing adsorption methods
9.3.3.1 Pressure Swing Adsorption
Adsorption phenomenon of the various gas components and pressure difference are
the two key components to be considered in pressure swing adsorption method. The
adsorbing materials used are zeolites or activated carbon that can effectively adsorb
carbon dioxide. In pressure swing adsorption method, a significant amount of
methane is generated from the column, and recycling process can be undertaken
through the inlet in the pressure swing adsorption column (Awe et al. 2017). The
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
251
sodium and potassium were also added (Kougias et al. 2010; Zhao et al. 2010). The
absorption capacity of carbon dioxide is greater in sodium hydroxide than in the
amine solutions. For absorbing 1 ton of carbon dioxide, 0.9 tons of sodium hydroxide is required when compared to 1.39 tons of monoethanolamine (Yoo et al. 2013).
About 99% methane purity can be achieved through this method with less than 0.1%
methane loss (Angelidaki et al. 2018).
The advantages of chemical scrubbing include complete absorption of hydrogen
sulphide by the scrubber and high selectivity of the amine solution, and the
disadvantages include high investment cost initially, high energy requirement during
regeneration and the chemical toxicity to the environment (Yoo et al. 2013).
The amine scrubbing process is advantageous if:
• No off-gas treatment is needed.
• Plant capacity is high.
• No compression is required (Report 2012).
9.3.3 Adsorption Method
Adsorption is defined as a process in which the components of a mixture gets
attached or binds to a solid matrix which is microporous in nature but with a large
surface area. Based on the types of force, the adsorption process is categorised into
physisorption and chemisorption. In physisorption process, between the adsorbent
and the adsorbate, weak Vander Waal’s forces is involved, and in chemisorption
process, strong molecular force exists. The operational parameters for adsorption
methods include 3–8 bar pressure, 50–60
C temperature and 100–200 mbar regeneration pressure. It requires 3–5 min to complete one cycle. Cycle time, purging
pressure, adsorbent, feeding pressure and column interconnectivity are the
characteristics of adsorption techniques.
Adsorption methods are categorised into three types as follows:
(a) Pressure swing adsorption
(b) Temperature swing adsorption
(c) Vacuum swing adsorption methods
9.3.3.1 Pressure Swing Adsorption
Adsorption phenomenon of the various gas components and pressure difference are
the two key components to be considered in pressure swing adsorption method. The
adsorbing materials used are zeolites or activated carbon that can effectively adsorb
carbon dioxide. In pressure swing adsorption method, a significant amount of
methane is generated from the column, and recycling process can be undertaken
through the inlet in the pressure swing adsorption column (Awe et al. 2017). The
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
251