Comparison of Pyrolysis Liquids from Continuous and Batch Biochar Production—Influence of Feedstock Evidenced by FTICR MS

Wolfram Buss,C Logan Mackay,Jasmine Hertzog,Ondřej Mašek,Frédéric Aubriet,Julian Pietrzyk,Vincent Carré

doi:10.3390/en14010009

Wolfram Buss, C Logan Mackay + Show 5 more

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https://doi.org/10.3390/en14010009

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Abstract

Bio-oils from biomass pyrolysis can be a resource for upgrading to chemicals or fuels. Here, for the first time, we compare the composition of bio-oils produced from two feedstocks (wheat straw, softwood) in pyrolysis units of different mode of operation (continuous—rotary kiln vs. batch) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) in different ionization modes (APPI (+), ESI (+/−)). Our results demonstrate that the pyrolysis unit design had only a minor influence on the composition of bio-oils produced from low-mineral containing wood biomass. Yet, the wheat straw-derived bio-oil produced in the continuous unit comprised lower molecular weight compounds with fewer oxygen-containing functional groups and lower O/C and H/C ratios, compared to bio-oils from batch pyrolysis. Longer residence time of vapours in the heated zone in the rotary kiln and a higher mineral content in wheat straw resulted in increased catalytically-mediated secondary reactions that favoured further bio-oil decomposition. This work shows for the first time that it is possible to produce distinct bio-oils without the need for external catalyst addition, by matching reactor type/design and feedstock.

Highlights

The transition to a circular economy brings resource re-use, recycling and recovery to the forefront of political agendas globally [1,2,3]
Softwood pellet (SWP) feedstock resulted in a lower biochar yield and higher pyrolysis liquids yield compared to wheat straw pellets (WSP) likely due to a mineral/higher ash content in the WSP feedstock
The pyrolysis of softwood with mineral contents of only ~1% produced biooils of comparable composition in both pyrolysis units, while the molecular composition of bio-oils from wheat straw with a mineral content of ~6.5% clearly depends on the mode of operation of the pyrolysis unit

Summary

Introduction

The transition to a circular economy brings resource re-use, recycling and recovery to the forefront of political agendas globally [1,2,3]. The concept of a circular economy can be applied to all areas of the economy, including agricultural and forestry where biomass residues are often left in the field or are burned with the plant-derived carbon stored in the biomass being released back into the atmosphere [4]. A promising way for biomass upgrading is pyrolysis that converts the material into non-condensable gas, liquid, and solid residue. Operating parameters, such as residence time, heating rate, and temperature, control the product yield in each fraction and define slow, fast, and flash pyrolysis [5,6]. Biochar contains aromatic carbon that is very stable against chemical and biological degradation, it is proposed as a negative emission technology [10,11]

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