Abstract
Hydrodeoxygenation (HDO) of bio-oils obtained from intermediate pyrolysis with hot vapor filtration was investigated over Ru/C and NiCu/Al2O3 catalysts as a function of several parameters: feedstock (beech wood, wheat straw), pyrolysis temperature, catalyst and hydrotreatment temperature. Beech wood was found to be a suitable feedstock for HDO due to its low heteroatom content, whereas the high sulfur content in the wheat straw bio-oil caused irreversible poisoning of the catalysts. Ru/C generally consumed more hydrogen than NiCu/Al2O3, showing higher hydrogenation/HDO activity with higher selectivity towards alcohols and hydrocarbons, whereas NiCu/Al2O3 resulted in a higher concentration of ketones. The pyrolysis temperature affected the fragmentation degree; higher temperatures resulted in a higher quality pyrolysis oil with low oxygen mass fraction, but with decreased mass yield. By varying the hydrotreatment temperature (80, 150, 250, 350 °C), different classes of compounds were converted and different deoxygenation degrees were achieved. Overall the results indicate that intermediate pyrolysis with hot vapor filtration is a valid alternative to the more commonly used fast pyrolysis for decentralized (or small-scale) applications, especially for heterogeneous feedstocks with high ash content.
Highlights
Biomass represents the main renewable carbon resource and biomass conversion into higher value products has been the subject of much research in recent years [1]
According to the authors' knowledge, no studies have been previously performed related to the upgrading of intermediate pyrolysis oils, which is necessary for the subsequent production of transportation fuels and chemicals due to their higher oxygen mass fraction [2]
Pyrolysis oil produced from wheat straw showed a higher pH and a higher water content compared to the beech wood bio-oil produced at the same temperature
Summary
Biomass represents the main renewable carbon resource and biomass conversion into higher value products has been the subject of much research in recent years [1]. This subject still constitutes a significant challenge due to the highly complex chemical structure of biomass. Fast pyrolysis followed by upgrading is considered an economical and energetically valuable route to produce transport fuels and eventually chemicals [2]. According to the authors' knowledge, no studies have been previously performed related to the upgrading of intermediate pyrolysis oils, which is necessary for the subsequent production of transportation fuels and chemicals due to their higher oxygen mass fraction [2]. Hydrodeoxygenation (HDO), which can be indicated as hydrotreatment in this context, offers a potential strategy to decrease the oxygen content, since it can provide higher upgraded oil yield, with higher carbon recovery and better quality in comparison to alternative methods such as zeolite cracking [2,7,8,9]
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