Molecular characterization of the pyrolysis of biomass

Abstract

The technique of molecular-beam, mass spectrometric (MBMS) sampling is applied to the elucidation of the molecular pathways in the fast pyrolysis of wood and its principal isolated constituents. The goal is the optimization of high-value fuel products by thermal and catalytic means. The positive-ion mass spectra shown are obtained from real-time, direct sampling of light gases, reactive intermediates, and condensible vapors simultaneously. The cellulose, lignin, and hemicellulose (e.g., xylan) components of wood pyrolyze largely to monomer and monomer-related fragments and give characteristic mass spectral signatures. Whole wood appears to behave as the sum of its constituents, with few if any vapor species derived from interaction of the main polymer constituents. An important interaction, however, is the influence of mineral matter in the wood on the carbohydrate pyrolysis pathways. Vapor phase cracking of the primary products proceeds through a stage of light hydrocarbons and oxygenates to the ultimate formation of aromatic tars and H2, CO, C02, and H20. These steps are illustrated and discussed. Consistent with these observations, a relatively simple pyrolysis reaction scheme is proposed.

Aromatic Production from Catalytic Fast Pyrolysis of Biomass-Derived Feedstocks

“…The acid catalyst can be both the heterogeneous solid acid and the homogenous organic acid products. It has previously been shown that hydroxyacetaldehyde is formed from pyrolysis of carbohydrates [25]. Trace amounts of anhydrosugars were also observed.…”

Biomass valorisation by staged degasification

“…The high amount of ash minerals in the straw will have an effect on its thermal degradation behaviour under pyrolysis conditions. Especially alkali metals are known to catalyse the thermal breakdown of carbohydrates [30,31]. Fig.…”

Lignin pyrolysis reactions

“…Coniferyl aldehyde, isoeugenol, dihydroconiferyl alcohol, 4-vinylguaiacol and vanillin are more important products (in the case of G-lignin pyrolysis). Only direct mass spectrometric analysis of the pyrolyzates from wood and lignin samples, without cooling, indicate significant contributions of coniferyl alcohol (MW: 180) and sinapyl alcohol (MW: 210) [7]. These apparently contradictory observations can be explained by the propensity of coniferyl alcohol and sinapyl alcohol to undergo secondary pyrolysis reactions, particularly polymerization reactions [82][83][84][85].…”