Applicability of selected methods and sorbents to simultaneous removal of siloxanes and other impurities from biogas

This paper critically reviews and discusses the state-of-the-art technologies for the removal of siloxanes from biogas, which could be used to simultaneously remove other contaminants. The reasons for purifying biogas, the scope of this purification and the recommended (depending on the biogas utilization equipment) concentrations of volatile silicon-organic compounds are presented. Established and new promising methods of removing typical methylsiloxanes from biogases from municipal landfills and sewage sludge are characterized and analyzed. Their suitability for the simultaneous removal of other trace biogas impurities and possibilities of regenerating the spent sorbent are assessed. It is shown that the commonly used activated carbon is not suitable for comprehensive biogas treatment. On the basis of the analysis, an adsorption method using halloysite (a natural zeolite mineral) as an inexpensive, universal and regenerable adsorbent is proposed. The method can be used after physicochemical treatment to comprehensively purify biogas from methylsiloxanes, hydrogen sulfide, ammonia, halides and other technically and environmentally burdensome impurities. Some directions for further research in this regard and possible environmentally safe ways of utilizing the spent sorbent are indicated.