Abstract
This work demonstrates that the coupling of supercritical carbon dioxide extraction with pyrolysis is an effective method for the removal of extractives from forestry residues and generation of solid char with different properties from the remaining solid wood fractions. Extraction of the needles and stumps shows greater yields of resin acids, terpenes, steroids and other derivatives than that of pinewood bark, cones and branches. The char yields of both non-treated and scCO2 extracted wood fractions varied from approximately 17.5 to 38.5 wt. % on dry basis at fast heating rates. The catalytic effect of extractives is significant on the yields and morphology of solid chars in fast pyrolysis and less pronounced at slow heating rates. These results are promising as they show that both the composition and location of extractives inclusions in the interior of wood particle can affect the morphology of char samples. Moreover, the impact of alkali metals on the wood devolatilization appears to be less compared to the lignocellulosic composition in slow pyrolysis. These results demonstrate that supercritical carbon dioxide extraction can be integrated in biorefinery as a pretreatment step to control the properties of pyrolysis products by varying the heating rate.
Highlights
The transportation sector relies almost exclusively on liquid hydrocarbons as the energy source [1]
Previous results showed that the ash content of non-treated bark and bark after scCO2 extraction remains unchanged, and no differences in the ash composition are expected in other wood fractions, confirming the previous results of Philpot [26,27]
The char yields from pyrolysis of non-treated and scCO2 extracted wood fractions varied from approximately 17.5 to 38.5 wt. % on dry basis indicating the impact of supercritical extraction in fast pyrolysis
Summary
The transportation sector relies almost exclusively on liquid hydrocarbons as the energy source [1]. One reason to use liquid hydrocarbons is their high volumetric energy density and convenience of use. Both ethanol and bio-diesel are bio-based alternatives to fossil fuels. These are typically first generation biofuels, whose feedstocks (including corn and palm oil) can be utilized for food applications. With the growing interest in the production of second generation bio-fuels from waste cellulosic biomass, methanol and hydrogen produced from biomass through gasification are attractive alternatives for use in road transportation. Biomass gasification offers high conversion efficiency and the possibility to handle different lignocellulosic materials to a wide variety of applications such as heat, electricity, chemicals and transport fuels [3]. One of the major challenges in biomass gasification is the formation of tars which condense and cause the clogging of filters and reduction of the energy content of the product gas [4,5]
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