Secondary Reactions of Primary Tar from Biomass Pyrolysis: Characterization of Heavy Products by FT-ICR MS

The aim of this study is to deeper understand the effect of homogeneous vapor-phase reactions on heavy components in condensed bio-oil. The fast pyrolysis of elm was conducted in a microfluidized-bed reactor (MFBR) at 500 degrees C. The primary tar formed in MFBR was immediately introduced into a secondary tubular reactor (STR), in which the secondary reactions occurred. The chemical components of both condensed primary tar and secondary products were characterized by atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI-FT-ICRMS). The results show that the condensed primary tar was mainly composed of dimers containing 3-4 oxygen atoms. Even at a low temperature of 500 degrees C, the secondary reactions would evidently promote the cracking of heavy CxHyOz compounds. More interestingly, large tetramers were generated probably by the recombination of smaller oligomers in secondary reactions. A long residence time (RT) would further facilitate the formation of oxygen-free compounds, especially for the large and condensed aromatic hydrocarbons. Van Krevelen diagrams confirm the processes (e.g., decarboxylation, decarboxylation, etc.) when the CxHyOz compounds were converted into unsaturated CxHy compounds.

Automated summary

This study aims to explore the impact of homogeneous vapor-phase reactions on heavy components in condensed bio-oil. Experimental results demonstrated that secondary reactions can promote cracking of heavy compounds and generate large tetramers, with a longer residence time further prompting the formation of oxygen-free compounds, especially for large and condensed aromatic hydrocarbons. Van Krevelen diagrams illustrate the conversion processes of CxHyOz compounds into unsaturated CxHy compounds during the reactions.