Extensive study on biogas trace compounds from agricultural and municipal biomass residues for downstream catalytic conversion

This study used quantitative biogas measurements from four full-scale biogas plants to determine which trace components can be expected in biogas from biogenic agricultural or municipal residues. The objective was to identify trace compounds that could damage the catalyst when biogas is used as a feedstock for a catalytic conversion. Knowing the exact composition of the biogas, including for example all sulfur-containing molecules, is therefore essential for the process's operational expenditures (OPEX). The results of this investigation add to a database of fully measured biogases and can be used to select suitable biogas purification steps. Trace compounds found in all measured biogas samples were ethanol, acetone, toluene, alpha-pinene and 3-methylfuran. However, biogases from different substrates contain distinctive trace components. The biogas from organic waste shows the highest amount of S-containing molecules (up to 14.7ppm in total), while the biogas from wastewater sludge shows higher amounts of siloxanes (50 mg m^-3STP) and the biogases from agricultural waste contain oxygenates like acetone and 2-butanone. Measurements taken at various points along the process chain indicate that activated carbon is sufficient for removing most of the trace components from biogas. However, it was observed in one plant that the activated carbon must be replaced before it reaches its adsorption limit to avoid the desorption of volatile organic compounds. Biogas or the biogenic CO₂ are well-suited to be used in downstream processes, but analytical monitoring of the biogas composition and a suitable connection between plant and downstream process are required.