Recycling of product gas does not affect fast pyrolysis oil yield and composition

• Published in: Journal of analytical and applied pyrolysis Vol. 148; p. 104794
• Main Authors: Pala, Mehmet, Marathe, Pushkar S., Hu, Xun, Ronsse, Frederik, Prins, Wolter, Kersten, Sascha R.A., Lange, Jean-Paul, Westerhof, Roel J.M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-06-2020
• Subjects: Bio-oil; Biomass; Fast pyrolysis; Gas recycling; Reaction atmosphere; Reaction atmosphere; Gas recycling; Biomass; Fast pyrolysis; Bio-oil
• ISSN: 0165-2370; 1873-250X
• DOI: 10.1016/j.jaap.2020.104794

•The effect of recycle gas atmosphere on biomass fast pyrolysis was investigated.•Recycle gas atmosphere did not have a notable effect on the product yields.•Recycle gas atmosphere did not lead to a bio-oil with improved quality.
It has been reported that a deoxygenated bio-oil (ca. 0.12 kg kg−1 O on bio-oil basis) can be obtained simply by recycling the non-condensable gases (NCG) of biomass fast pyrolysis to a fluidized-bed reactor operated at atmospheric pressure [Mullen et al., 2013, Energy Fuels, 27, 3867–3874]. Such an unprecedented effect would (i) complicate the use of lab-scale research results obtained typically under inert gas (N2, He, Ar) atmosphere for the design of commercial scale pyrolysis units projected to utilize a recycle gas atmosphere (ii) obviate the need for catalytic pyrolysis or mild hydrotreatment processes. Considering these implications, further validation or refutation of the claimed deoxygenation effect of recycle gas atmosphere is needed.
Therefore, fast pyrolysis experiments with pine wood were performed in a bench-scale fluidized bed reactor under N2 atmosphere, recycle gas atmospheres (75 % and 90 % recycle gas volume fraction) at reactor temperatures of 430 °C and 500 °C. Mass balances were obtained and the bio-oils were analyzed using GC/MS, GPC, elemental analysis and Karl Fischer titration. No significant differences were observed in product yield and bio-oil composition (e.g. oxygen content) when going from a nitrogen gas atmosphere to a recycle gas atmosphere for both pyrolysis temperatures.