Pyrolysis of sludge briquettes for the preparation of cylindrical-shaped biochar and comparison between CO2 and steam activation. (15th April 2023)

• Record Type: Journal Article
• Authors: Deng, Wenyi; Hu, Mingtao; Xu, Shiyao; Hu, Menghao; Chen, Guang; Ji, Hongxian; Zhou, Piren; Su, Yaxin
• Is Part Of: Fuel. Volume 338(2023)
• Publication Date: 2023-04-15
• Subjects: Sewage sludge -- Briquette -- Biochar -- Physical activation -- Methylene blue -- Thermal regeneration; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.127317
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Briquetting showed obvious influence on sludge pyrolysis. Mechanical performance of cylindrical-shaped biochar decreased with the increase of activation temperature. CO2 -activated biochar showed higher adsorption capacity than steam-activated biochar. Both physical and chemical adsorptions played important role in methylene blue adsorption. The maximum adsorption capacity of 513.81 and 419.29 mg/g could be achieved by the CO2 and steam-activated biochar. Abstract: Sludge briquettes were prepared through briquetting (under the pressure of 25 MPa) of half-dried sewage sludge with moisture content of 30 wt%, and the cylindrical-shaped biochar (CSB) was obtained by subsequent pyrolysis (600 °C) and CO2 /steam activation (650–950 °C). Briquetting process showed great influence on the pyrolysis of sewage sludge. The temperature range for the organic decomposition increased from 150 to 500 °C for the sludge without briquetting to 150–700 °C for the sludge briquette. The mechanical performance of CSBs was greatly influenced by activation temperature. The axial compressive strength of the CO2 /steam activated CSBs were in the range of 17.8–22.2 kg·cm ‑2 at the activation temperature of 650 °C and 800 °C, but dropped markedly when the activation temperature increased to 950 °C. CSBs were negatively charged and rich in oxygen/nitrogen-containing functional groups like –OH, –COOH, amines and amides, and the specific surface area of the optimal steam and CO2 -activated CSB were 123.2 and 113.5 m 2 ·g ‑1, respectively. The prepared CSBs were applied in methylene blue (MB) adsorption, and the maximum adsorption capacity of 513.81 and 419.29 mg·g ‑1 could be achieved by the CO2 and steam-activated CSB, respectively. Both physical and chemical adsorptions played important role in the MB adsorption. Finally, the regeneration test showed that optimal samples of the CO2 and steam-activated CSB still retained around 90 % of its original adsorption capacity after three cycles of adsorption-regeneration tests, but the mechanical performance dropped by 58.1 % and 47.8 %, respectively.