Rodríguez, C. (2022). Surface adjustment of biochar via gasification [Diploma Thesis, Technische Universität Wien]. reposiTUm. https://doi.org/10.34726/hss.2022.102636
E166 - Institut für Verfahrenstechnik, Umwelttechnik und technische Biowissenschaften
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Date (published):
2022
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Number of Pages:
94
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Keywords:
Vergasung; Biokoks; Oberflächenmodifikation
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Gasification; biochar; surface modification
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Abstract:
Gasification as a method for adjustment of the surface properties of biochar is investigated in this work. Uncontaminated biomass from Pinus sylvestris Scots pine is utilized as the feedstock. This material is later transformed into biochar by submission to the torrefaction process in an inert atmosphere at 300°C for 45 minutes and further activated via gasification. The main goal of the work is to obtain a product with suitable physical characteristics for a post-processing step which consists of passivation by encapsulation within a coke tar layer. Since literature findings suggest higher BET surface areas and porosity production, the thermochemical activation is performed with CO2 as the oxidizing agent. Reaction conditions such as temperature, residence time, and type of reactor are selected considering the state of the art of gasification for the activation of biochar. The parameters are varied to obtain twelve materials with different physical properties. The produced samples from the lab-scale experiments are later characterized via light microscopy, SEM analysis, and physisorption analysis. The results show that an increase in temperature and residence time produces higher burn-off values achieving 87,1% in the fixed bed and 74,2% in the fluidized bed, both experiments performed at 900°C for 25 minutes. This behavior is related to the formation of higher specific surface area and porosity, achieving surface BET area values of 904 m2/g and 516 m2 g, and pore volumes of 0,4897 cm3/g and 0,2632 cm3/g, respectively, which is significantly higher than the 0,6483 m2/g and 0,00092 cm3/g values of the torrefied biochar. SEM analysis demonstrated more significant degradation of the structure, as pores and several fragmentations appeared in the surface layer of the biochar. The main findings from the present thesis are as follows: i) Torrefaction proved to be a suitable process for biochar production; ii) Activation temperature plays a vital role in the gasification of biochar as an increase from 800°C to 900°C produces higher degradation and porosity formation, therefore, increasing the surface area; iii) Temperature, residence time, and type of reactor influences the burn-off and porosity of the activated biochar; iii) Fixed bed shows better results regarding the surface area and porosity in comparison with the fluidized bed in the conditions of 900°C and 25 minutes residence time. These results constitute the basis of further investigations where contaminated biomass can be used as a precursor in different thermochemical processes to obtain high-value-added products and unreactive and stable biochar.
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