Alba Dieguez-Alonso

Surface Properties and Chemical Composition of Corncob and Miscanthus Biochars: Effects of Production Temperature and Method

Biochar properties vary, and characterization of biochars is necessary for assessing their potential to sequester carbon and improve soil functions. This study aimed at assessing key surface properties of agronomic relevance for products from slow pyrolysis at 250-800 °C, hydrothermal carbonization (HTC), and flash carbonization. The study further aimed at relating surface properties to current characterization indicators. The results suggest that biochar chemical composition can be inferred from volatile matter (VM) and is consistent for corncob and miscanthus feedstocks and for the three tested production methods. High surface area was reached within a narrow temperature range around 600 °C, whereas cation exchange capacity (CEC) peaked at lower temperatures. CEC and pH values of HTC chars differed from those of slow pyrolysis biochars. Neither CEC nor surface area correlated well with VM or atomic ratios. These results suggest that VM and atomic ratios H/C and O/C are good indicators of the degree of carbonization but poor predictors of the agronomic properties of biochar.

Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison

Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical-chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.

Analysis of the Product Gas Composition in Pyrolysis Processes of Single Wood Particles Using FTIR Spectroscopy

Physo-chemical reactions and transport phenomena occurring during pyrolysis of wood chips have not yet been understood to the required extent for its effective utilization for power generation. FTIR spectroscopy has been applied time-resolved to analyse the product gas composition of a single pyrolysing wood particle. A special particle reaction chamber has been built to allow for an in situ measurement of the product gas in close vicinity of the particle surface.