Strategies for producing biochars with minimum PAH contamination

Buss, W., Graham, M. C., MacKinnon, G. and Mašek, O. (2016) Strategies for producing biochars with minimum PAH contamination. Journal of Analytical and Applied Pyrolysis, 119, pp. 24-30. (doi: 10.1016/j.jaap.2016.04.001)

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Abstract

With the aim to develop initial recommendations for production of biochars with minimal contamination with polycyclic aromatic hydrocarbons (PAHs), we analysed a systematic set of 46 biochars produced under highly controlled pyrolysis conditions. The effects of the highest treatment temperature (HTT), residence time, carrier gas flow and typical feedstocks (wheat / oilseed rape straw pellets (WSP), softwood pellets (SWP)) on 16 US EPA PAH concentration in biochar were investigated. Overall, the PAH concentrations ranged between 1.2 and 100 mg kg-1. On average, straw-derived biochar contained 5.8 times higher PAH concentrations than softwood-derived biochar. In a batch pyrolysis reactor, increasing carrier gas flow significantly decreased PAH concentrations in biochar; in case of straw, the concentrations dropped from 43.1 mg kg-1 in the absence of carrier gas to 3.5 mg kg-1 with a carrier gas flow of 0.67 L min-1; for woody biomass PAHs concentrations declined from 7.4 mg kg-1 to 1.5 mg kg-1 with the same change of carrier gas flow. In the temperature range of 350-650°C the HTT did not have any significant effect on PAH content in biochars, irrespective of feedstock type, however, in biochars produced at 750°C the PAH concentrations were significantly higher. After detailed investigation it was deduced that this intensification in PAH contamination at high temperatures was most likely down to the specifics of the unit design of the continuous pyrolysis reactor used. Overall, it was concluded that besides PAH formation, vaporisation is determining the PAH concentration in biochar. The fact that both of these mechanisms intensify with pyrolysis temperature (one increasing and the other one decreasing the PAH concentration in biochar) could explain why no consistent trend in PAH content in biochar with temperature has been found in the literature.

Item Type:Articles
Additional Information:This research was supported by the Scottish Funding Council (SFC) (SRDG Ref: HR08004 Carbon Capture from Power Plant and Atmosphere). In addition, Wolfram Buss would like to acknowledge the financial support for his PhD provided by Derek and Maureen Moss and thank Kyle Crombie, Peter Brownsort, Clare Peters and Walter Lowe for their contributions to the experimental work.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:MacKinnon, Dr Gillian
Authors: Buss, W., Graham, M. C., MacKinnon, G., and Mašek, O.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of Analytical and Applied Pyrolysis
Journal Abbr.:J. Anal. Appl. Pyrol.
Publisher:Elsevier
ISSN:0165-2370

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