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Influence of activation conditions on the properties and adsorption performance of wood-based activated carbon

Year: 2019
Type: dissertation
Abstract: In this thesis, the effects of activation conditions on the properties of wood-based activated carbon (AC) were studied utilizing experimental design. The aim was to produce suitable ACs for adsorption of adsorbable organic halogens (AOX) from pulp mill wastewaters. The activation conditions chosen as variables were activation temperature, time, and carbon dioxide flow rate. Raw material for the ACs was birch sawdust. The process was started with hydrothermal carbonization (HTC), which produced solid biochar and liquid hydrolysate as a by-product. Solid yield of the HTC was nearly 70%. The biochar was subsequently physically activated with carbon dioxide as an activating agent. Experimental design was utilized in planning the experiments and modelling the effects of the activation variables on the properties of the produced ACs. All of the materials in the process were characterized for their elemental composition. The raw material and the intermediate biochar were characterized for their composition, and the components of the hydrolysate were studied as well. The ACs were characterized for their BET surface area and porosity, and their adsorption capacities were tested with model compound adsorption using 4-chlorophenol. X-ray photoelectron spectroscopy was used to analyze the surface composition of the AC before and after model compound adsorption. Response surfaces for activation yield, BET surface area, and model compound adsorption were created based on the experimental design. Activation yield mostly varied from 16 to 22% from biochar. Highest BET surface area was 938 m²/g, but the yield for that AC was only around 3% from biochar. Adsorption isotherm of one of the top-performing produced ACs was obtained and compared with a commercial alternative. The effect of pH on the adsorption was also studied. The AC produced in this work showed slightly better adsorption capacity than the commercial one. Finally, the AOX removal ability of the AC was tested from real pulp mill wastewater. Even though the BET surface area and model compound adsorption results were promising, the removal of AOX from the wastewater was quite poor at only 11%. Furthermore, the AC dose was relatively high at nearly 1 kg/m³.
Language: English
Open Access status: green
OpenAlex ID: W3028999618
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