Characteristics of tar formation during integrated process of biomass anaerobic digestion and gasification.

The tar problem is a bottleneck issue of biomass gasification. The influence of anaerobic digestion on gasification tar formation is still unclear. In this work, the influence of the degree of anaerobic digestion on physicochemical properties of the digestate were investigated, and consequently on tar yield and distribution. The content of cellulose exhibits the most critical parameter affecting tar yield. Minimum tar yields (2.5 wt%, 1.9 wt% and 1.6 wt% for pyrolysis, CO2 gasification and H2O gasification) was obtained in day 9 with a maximum lignin content (29.5 wt%) and a minimum cellulose content (24.8 wt%). Both gasification agent of CO2 and H2O significantly reduce tar yields. The tar distribution was always dominated by benzofuran, 2,3-dihydro- and phenol derivatives regardless of the agent. This work provides in-depth insights and clarifies the tar formation characteristic of the integrated process, which helps to realize the efficient and green conversion of biomass.