Study of black carbon content in biochar obtained by different pyrolysis conditions

Resumen

Biochar is a solid material obtained by biomass pyrolysis in an oxygen-limited environment. It is used for soil improvement. Biochar's C content must be higher than 50% of the dry mass. Biochar carbon is made up of easily degradable organic carbon compounds and very stable, aromatic C structures, black carbon (BC) (Schmidt et al. 2012). According to European Biochar Certificate the BC content of biochars should represent 10 - 40% of the overall C. The aim of this study wasto determine which pyrolysis treatment (temperature and time) gives better results on Black Carbon content from different vegetal residues. As well as, determine which treatment carried out under laboratory conditions produces biochar from vines canes with similar Black Carbon content to the one performed in field (traditional procedure). Four vegetal materials (vine canes, pruning residues of pine and holm oak, and corn cobs) were pyrolyzed in a N2 atmosphere under four treatments: 400°C, 500°C, 600°C during 1h and 500°C during 4h. Also, biochar from vine canes was obtained in field by incomplete combustion or charring, based on a traditional way to obtain the so called “cisco” of holm oak, used as combustible for braziers. BC content in all biochar samples was determined by Glaser (1998) methodology which measures benzene carboxylic acids as indicators of BC, using gas chromatography and flame ionization detection. Total organic Carbon (TOC) and total Nitrogen (N) were determined by elemental autoanalyzer in biochar samples. The study reveals that biochars obtained in lab and field complied with thespecifications of C and BC contents of the European Biochar Certificate. The treatment of 600ºC 1h showed the highest BC concentrations in biochar and also referred to TOC, but for the pineresidues. The vine canes biochar obtained at 600ºC 1h showed similar characteristics to the one obtained by field traditional methodology.