Date Published: February 12, 2019
Publisher: Public Library of Science
Author(s): Nurul Noramelya Zulkefli, Mohd Shahbudin Masdar, Wan Nor Roslam Wan Isahak, Jamaliah Md Jahim, Syahril Anuar Md Rejab, Chew Chien Lye, Moonis Ali Khan.
Adsorption technology has led to the development of promising techniques to purify biogas, i.e., biomethane or biohydrogen. Such techniques mainly depend on the adsorbent ability and operating parameters. This research focused on adsorption technology for upgrading biogas technique by developing a novel adsorbent. The commercial coconut shell activated carbon (CAC) and two types of gases (H2S/N2 and H2S/N2/CO2) were used. CAC was modified by copper sulfate (CuSO4), zinc acetate (ZnAc2), potassium hydroxide (KOH), potassium iodide (KI), and sodium carbonate (Na2CO3) on their surface to increase the selectivity of H2S removal. Commercial H2S adsorbents were soaked in 7 wt.% of impregnated solution for 30 min before drying at 120°C for 24 h. The synthesized adsorbent’s physical and chemical properties, including surface morphology, porosity, and structures, were characterized by SEM-EDX, FTIR, XRD, TGA, and BET analyses. For real applications, the modified adsorbents were used in a real-time 0.85 L single-column adsorber unit. The operating parameters for the H2S adsorption in the adsorber unit varied in L/D ratio (0.5–2.5) and feed flow rate (1.5–5.5 L/min) where, also equivalent with a gas hourly space velocity, GHSV (212.4–780.0 hour-1) used. The performances of H2S adsorption were then compared with those of the best adsorbent that can be used for further investigation. Characterization results revealed that the impregnated solution homogeneously covered the adsorbent surface, morphology, and properties (i.e., crystallinity and surface area). BET analysis further shows that the modified adsorbents surface area decreased by up to 96%. Hence, ZnAc2–CAC clarify as the best adsorption capacity ranging within 1.3–1.7 mg H2S/g, whereby the studied extended to adsorption-desorption cycle.
The increment of global energy demand is due to the continuous population growth, and the economy steeping up, which affected the socio-economic landscape and human welfare in the future . The renewable energy and fossil fuel are incorporated as future energy systems that control and conserve the fossil fuel used which had been discovered for future continuity demands. Hence, the sources of alternative renewable energy from the biomass resources had found as relevant continuous energy supplies based on the constant based load, control of resources and production of resources.
The impregnated CACs resulted in good capability in capturing H2S gas through several operating parameters such as flow rate, adsorbents type, L/D adsorber ratio and different gas composition compared to raw CAC. The impregnated CACs found 58–64% (ZnAc2-CAC) much better to adsorp H2S gas compared to raw CAC. Besides, characterizations of the fresh adsorbents were gathered as evidence to support the chemical and physical characteristic of the adsorbent and a guidance in preparing the adsorption-desorption operational. It showed that the ZnAc2-CAC has capable to use as H2S adsorbent for the adsorption-desorption process in several cycles. Besides, the characterizations for post-adsorption-desorption adsorbents had been done to support the behaviour of adsorbents capability degradation in the continuous system. Thus, it is suggested to improve the desorption technique to prevent further degradation on the H2S adsorbent. Hence, it will maintain the capability of H2S adsorption throughout several cycles of the adsorption-desorption process for biogas purification.