A review on removal of siloxanes from biogas: with a special focus on volatile methylsiloxanes

Abstract

The occurrence of siloxanes is a major barrier to use of biogas as renewable energy source, and removal of siloxanes from biogas before combustion is needed. The siloxane can be transformed into silicon dioxide (SiO) through the combustion process in engine, which will be deposited on the spark plug, cylinder, and impeller to form the silica layer, causing the wear and damage of the engine parts, and shorten the life of the engine and affect the utilization efficiency of the biogas. This paper reviewed some methods and technologies for siloxanes removal from biogas. There are three commercial available technologies to remove siloxanes: adsorption, absorption, and cryocondensation. Other newer technologies with better prospects for development also have made a research progress, including membrane, catalysts, biotrickling filters. This work introduces the source and characterization of siloxanes in biogas, reviews the scientific progress of siloxanes removal, and discusses the development direction and further research of removal siloxanes.

Mineral Deposit Formation in Gas Engines During Combustion of Biogas from Landfills and Municipal WWTP

“…Generally the biodegradation, gas stripping and peroxidization are the three typical pretreatment methods (biological, physical and chemical ones), whereas their chemical decomposition and recovery constitute the post-purification technologies. Post-purification technologies can be divided into recovery and decomposition methods (adsorption, absorption, membrane separation, catalytic oxidation, biological degradation and photocatalysis) [3,17,18].…”

“…Modern technologies for siloxane removal from biogas are mainly based on physical adsorption using such sorbents as activated carbon, silica gels, zeolites and molecular sieves [19,20]. Above 99 % of siloxane removal efficiency in accessible technologies can be achieved, reducing their concentrations to below 0.1 mg•m -3 [3,17,18]. Adsorbing materials (carbon-based materials) with a meso-and microporous structure seem to be the most technologically, technically and economically suitable [3].…”

Biogas Upgrading Approaches with Special Focus on Siloxane Removal—A Review

“…The siloxane content of biogas from landfills or anaerobic sludge digestion is two to three times higher than that of biogas from agricultural feedstock [17,18]. The major components of siloxanes in a landfill biogas arear L2, L3, D3, D4, and D5, and they follow the order D4 > L2 > D5 > L3, and the main component is D4 constituting an average of about 60% of the total siloxanes [1,5]. In addition to siloxanes, silanols are also found in biogas but their concentration is low is biogas produced from municipal sludge digestion due to the fact that they are soluble in water [15].…”

“…Larger molecular weight siloxanes are degraded into small compounds and or volatile compounds, which eventually are found in biogas and the rest remain. The volatilization process of the siloxanes is influenced by several factors of which the mains ones are temperature, fermentation, and retention time of the substrate [1]. The biogas siloxanes amounts vary according to feedstock used and it was estimated that between 20 and 50% of D5 in wastewater and activated sludge transfers ends up in the biogas [14].…”

“…Worldwide, the community has realized that use of biogas is among the efficacious strategies to alleviate the global energy crisis. The use of biogas, which is methane rich, is very feasible and can result in the reduction of odor, methane, and other harmful gas emissions into the environment, hence improving the quality of air [1]. The gas has proved to be one of the most reliable sources of energy because it is cheap and reduces greenhouse gas emissions [2,3].…”