• International Journal of Technology (IJTech)
  • Vol 10, No 6 (2019)

Simultaneous Absorption and Adsorption Processes for Biogas Purification using Ca(OH)2 Solution and Activated Clinoptilolite Zeolite/Chitosan Composites

Eny Kusrini, Shella Wu, Bambang Heru Susanto, Maya Lukita, Misri Gozan, Muhammad Dicky hans, Arif Rahman, Volkan Degirmenci, Anwar Usman

Corresponding email: enykusrini@icloud.com


Cite this article as:
Kusrini, E., Wu, S., Susanto, B.H., Lukita, M., Gozan, M., hans, M.D., Rahman, A., Degirmenci, V., Usman, A., 2019. Simultaneous Absorption and Adsorption Processes for Biogas Purification using Ca(OH)2 Solution and Activated Clinoptilolite Zeolite/Chitosan Composites. International Journal of Technology. Volume 10(6), pp. 1243-1250

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Eny Kusrini Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Shella Wu Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Bambang Heru Susanto Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Maya Lukita Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Misri Gozan Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Muhammad Dicky hans Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI-Depok, Depok 16424, Indonesia
Arif Rahman Department of Chemistry, Faculty of Mathematics & Natural Sciences, Universitas Negeri Jakarta, Rawamangun 13220, Indonesia
Volkan Degirmenci School of Engineering, The University of Warwick, Coventry CV4 7AL, UK
Anwar Usman Department of Chemistry, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong BE1410, Negara Brunei Darussalam
Email to Corresponding Author

Abstract
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This study examined the effects of acid/base activation and chitosan coating on clinoptilolite zeolite as an adsorbent for biogas purification from palm oil mill effluent (POME) using simultaneous absorption–adsorption methods. The effects of chitosan concentration in the clinoptilolite zeolite/chitosan (ZAC) composites were studied to determine the best type of adsorbent for purifying biogas to obtain the highest methane (CH4) concentration: the biogas produced from POME via an anaerobic digestion process had a CH4 concentration of 87% and a carbon dioxide (CO2) concentration of 13%. In this study, the Ca(OH)2 solution was used for the absorption process, and the ZAC composite was used as the adsorbent in the adsorption process. To enhance the adsorption efficiency of the adsorbent when purifying biogas, clinoptilolite zeolite (ZA) was activated using strong acid (HCl) and base (NaOH) in various concentrations (ranging from 1–3 M), calcination at 450°C for 2 h, and coating with chitosan concentrations (ranging from 0.25–1 v/v%). The ZA was coated with chitosan to increase its adsorption efficiency, as chitosan contains high levels of amine and hydroxyl groups that interact with CO2 impurities and form carbamic acid, ultimately producing carbamate salt. The composition of biogas before and after treatment was analyzed using gas chromatography. Overall, the final content of the biogas after the purification process with absorption using the Ca(OH)2 solution and adsorption in a fixed-bed column using the ZAC2-0.5 composite was 0.42% CO2 and 99.58% CH4. The purified biogas had a very high methane gas content; thus, this study’s findings suggest that purified biogas can be used as a clean energy source for wider industrial applications.

Biogas purification; Chitosan; Clinoptilolite zeolite; Composite; Methane content; Simultaneous absorption–adsorption

Introduction

The production and utilization of biogas for green energy in wider industrial applications and cleaner fuels has attracted a great deal of attention for many countries. It is necessary to purify raw biogas to enhance its energy content; this is done by removing impurities such as CO2, H2S, and water vapor. This increases the methane purity of the biogas, making it  possible to inhibit corrosion when used in pipelines and other instruments such as column reactor and machine. This also has implications for new green energy, reducing the economic losses from maintenance and operational costs for this devices and also pipelines (Bak et al., 2019).

In contrast, enriching biogas has the potential to replace natural gas in future altogether, as biogas can be used in electricity production in co-generation with heat and power (Kadam & Panwar, 2017). The amount of CH4 is increased and concentrated in enriched biogas to achieve a similar composition and the same standards as a natural gas, allowing it to be used as transportation fuel and in pipeline systems for household use. Biogas can also be converted into a liquid form using cryogenic freezing, chilling the gas to -80°C and then further chilling it to -162°C (Kadam & Panwar, 2017). This method makes it more economical to compress and transport the biogas over longer distances for further applications.

Huge increases in the price of fossil fuels since 2008 due to the economic crisis have prompted researchers to study methods of upgrading biogas since 19th century (Osman et al., 2019). Enriching biogas involves removing unwanted gases such as CO2, H2S, and water vapor to increase its calorific value and specific heat and minimize its corrosive nature caused by the acidic gases it contains (Leonzio, 2016; Kusrini et al., 2017). Its high CO2 content results in low calorific value, and further purification of the resultant gas to remove CO2 is required. Some methods for purification include pressure swing adsorption, adsorption, and chemical absorption (Ackley et al., 2003; Alonso-Vicario et al., 2010; Leonzio, 2016). Masyhuri et al. (2013) purified biogas using a Ca(OH)2 solution. Kusrini et al. (2018) captured CO2 using graphite waste composites and ceria. In terms of the adsorptive purification of biogas, researchers have used adsorbents containing physisorption, such as activated carbon and zeolite. Chemisorption efforts have utilized iron oxide and iron oxide hydroxide (Bak et al., 2019). The most-used substances for biogas purification are activated carbon and zeolite (Alonso-Vicario et al., 2010; Peluso et al., 2019).

Recently, researchers have reported the results of applying a fixed-bed column for biogas purification using simultaneous absorption and adsorption methods (Kusrini et al., 2016; Kusrini et al., 2017). However, the effects of acid/base treatments and the concentration of chitosan-coated clinoptilolite zeolite have not been reported. This paper investigates the effect of chitosan coating and acid/base activation on clinoptilolite zeolite as an adsorbent for the purification of biogas derived from palm oil mill effluent (POME) using absorption–adsorption methods. This study attempted to determine the best acid/base activation and chitosan coating of an adsorbent for biogas purification using absorption and adsorption methods simultaneously. Clinoptilolite zeolite is the most common natural zeolite; its general chemical formula is (Na,K,Ca)4Al6Si30O72·24H2O with an Si/Al ratio ranging from 4.0–5.3 and a high thermal stability of 600–800°C (Kowalczyk et al., 2006). The physico-chemical properties of clinoptilolite zeolites can be modified via thermal and chemical treatments (Kowalczyk et al., 2006). This study used biogas produced from POME; it added 10% cow feces to activate using anaerobic digestion (Kusrini et al., 2016). Anaerobic digestion is the biological process by which microorganisms break down POME in the absence of oxygen. This anaerobic digestion process produced a biogas volume of approximately 28 m3 with a high CO2 content per ton of POME (Harsono et al., 2014). Tetteh et al. (2018) reported using an organic waste source such as cow dung for biogas production. It promotes waste generation and has promising implications for green energy for use in improved economic and environmental applications (Tetteh et al., 2018).

Conclusion

This study successfully modified clinoptilolite zeolites via acid/base activation, calcination, and coating with chitosan and applied them as an adsorbent to purify biogas from POME using simultaneous absorption and adsorption methods. The modification changed the structure of the clinoptilolite zeolites, making them highly effective as an adsorbent to remove CO2 from biogas. The final content of the biogas after the purification process with absorption with the Ca(CO)2 solution and adsorption in a fixed-bed column using the ZAC2-0.5 composite was the most effective, with a composition of CH4 (99.58%) and CO2 (0.42%). The resultant purified biogas had a very high methane gas content (99.58%) and very low concentration of impurities. This study recommends that biogas produced via purification using a Ca(OH)2 solution and a ZAC-0.5 composite be used as a clean energy source for wider industrial applications.

Acknowledgement

We thank the Ministry of Agriculture, Republic of Indonesia through Grant of Kerjasama Kemitraan Penelitian dan Pengembangan Pertanian Nasional (KKP3N) No. 54.30/HM.240/I.1/3/2016.

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