Changes in char’s porosity and evolved vapours’ composition–insights from a comprehensive study of single particle pyrolysis of beech wood cylinders - Université de Lorraine Access content directly
Conference Papers Year : 2023

Changes in char’s porosity and evolved vapours’ composition–insights from a comprehensive study of single particle pyrolysis of beech wood cylinders

Maziarka Przemyslaw
  • Function : Author
Wang Xia
  • Function : Author
Almuina-Villar Hernán
  • Function : Author
Kienzl Norbert
  • Function : Author
Alonso Alba Diéguez
  • Function : Author
Vanessa Fierro
Hedin Niklas
  • Function : Author
Ronsse Frederik
  • Function : Author

Abstract

Bio-based chars are extensively used as a precursor for activated carbon products for pollutant removal. For this application, the key performance parameter is the quantity of the adsorbed pollutant (e.g. heavy metal, pharmaceutical substance). Moreover, recently the EU accepted pyrolysis and gasification solid products (biochar) for soil amendment, which will allow for their use on a large scale in agriculture. In the case of the application in the soil, the key performance parameters are water retention, microbiological colonisation and nutrient retention. All novel applications mentioned above require a specific porous structure from the bio-based material, and those originate in the material’s pore size distribution (PSD). Unfortunately, there is no comprehensive knowledge of how the amount and share of pores with a specific size (micro-, meso- and macropores) change within the bio-based char as a function of the production parameters. The presented study attempts to mitigate the aforementioned mentioned gap. The study aimed to investigate the effect of temperature on the changes in the biobased pyrolytic chars’ properties, but with a focus on assessing the whole pore size range. Moreover, particles with different lengths in the longitudinal direction were used to determine the effect of the vapour retention time within the particle on changes in the porous structure. In detail, beech wood cylinders in 2 different sizes: Ø8x10 mm (shorter) and Ø8x16 mm (longer), had been pyrolysed individually (in triplicate) at 5 different temperatures (300, 400, 500, 700, and 900 °C) in a singleparticle reactor (SPR). Next to having 2 thermocouples (particle centre and surface), the particle’s mass was recorded during the pyrolysis process. In the first set of experiments, the SPR’s outlet was connected to 2 gas analysers: a TCD gas analyser and a FT-IR for real-time recording of the composition of 14 evolved pyrolysis volatiles (CO2, CO, H2O, CH4, formaldehyde, acetic acid and furfural, among others). In the second set of experiments, the outlet of the SPR reactor was connected to a series of scrubbers filled with isopropanol (-20°C) to condense bio-oil. The obtained liquid was evaporated to remove the isopropanol. Next, the bio-oil samples were diluted in acetonitrile (4 mL) and measured with the GC-MS/FID to assess their composition. Solid products from both series were analysed toward: elemental composition, overall shrinking (micrometric screw), microporosity (CO2 absorption), mesoporosity (N2 adsorption) and microporosity/envelope density (Hg porosimetry), and the overall porosity/true density (He pycnometry). Regardless of the pyrolysis temperature, the macropores’ share accounts for less than 80 % of the total pore volume. The porosity increased almost linearly within the investigated temperature range, from 52 % for the raw wood to ca. 90 % at 900 °C. Polyaromatic hydrocarbons (PAH), being precursors of secondary char, start to appear in the pyrolysis vapours above 500 °C, but a significant increase is visible above 700 °C. An increase in the particle length from 10 mm to 16 mm caused a reduction in the micropore volume (above 500 °C). The yield of PAH (on an initial biomass weight basis) had an opposite trend. Interestingly, the volume reduction effect was not observed for mesopores and macropores. The effect of the secondary charring reactions initially induced by the higher temperature is expected to be enhanced by an increase in length (longitudinal direction) of the wood cylinders. With the conversion, the escape path of vapours is getting longer, increasing PAH retention time in the zone where char formation is thermally favoured. In the end, a longer escape route elevates the formation of secondary char in micropores at the expense of the PAH concentration in the vapours.
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Dates and versions

hal-04274226 , version 1 (07-11-2023)

Identifiers

  • HAL Id : hal-04274226 , version 1

Cite

Maziarka Przemyslaw, Wang Xia, Almuina-Villar Hernán, Kienzl Norbert, Alonso Alba Diéguez, et al.. Changes in char’s porosity and evolved vapours’ composition–insights from a comprehensive study of single particle pyrolysis of beech wood cylinders. PYROLIQ II – 2023: PYROLYSIS AND LIQUEFACTION OF BIOMASS AND WASTES, May 2023, Schloss Hernstein, Austria. ⟨hal-04274226⟩
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