Determination of the formation of char upon fast pyrolysis of biomass

Fast pyrolysis of biomass is a promising technique to degrade lignocellulosic biomass into smaller compounds that can be eventually converted into valuable hydrocarbon products, such as fuels, in order to reduce our dependence on fossil fuels. Three major products of fast pyrolysis of biomass are the product stream (bio-oil), non-condensable gases (H₂, CO, CO₂), and char. Char is a carbon-rich residue and has a typical yield of 12-15 %. To achieve high energy and carbon efficient fast-pyrolysis processes, it is important to understand the factors affecting the char formation and develop strategies to minimize char yield. Inorganic compounds in biomass, such as the alkali and alkaline earth metal salts, have been found to generate more char. To further understand the effect of inorganic compounds on fast-pyrolysis product distribution, fast pyrolysis/atmospheric pressure chemical ionization (APCI) mass spectrometry was employed to study the initial fast-pyrolysis products of cellobiose doped with selected inorganic salts (sodium, potassium, and calcium salts). Further, fast pyrolysis/gas chromatography with flame ionization detection (GC-FID) was employed to identify and quantify char and major volatile fast-pyrolysis products of doped cellobiose samples. The results show that, at elevated concentrations, the inorganic dopants facilitated the dehydration and degradation of cellobiose upon fast pyrolysis, causing the production of more unwanted char. This finding is significant on understanding the mechanism of char formation with the existing of metal ions during fast pyrolysis and can be used to reduce char yield to achieve high energy and carbon efficiency.

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