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Combined chemical-templated activation of hydrolytic lignin for producing porous carbon

Ponomarev, Nikolai, Sillanpää, Mika
Industrial crops and products 2019 v.135 pp. 30-38
Fourier transform infrared spectroscopy, X-ray diffraction, activated carbon, analysis of variance, chemical reactions, environmental impact, lignin, linear models, micropores, porous media, response surface methodology, scanning electron microscopy, sodium carbonate, sodium chloride, sodium hydroxide, surface area, temperature
Chemical activation and template method using lignin have been considered efficient for producing microporous activated carbon. However, the limited accessibility of micropores and significant chemical consumption hinder the application of aforementioned methods. In order to save attractive properties of both activation routes and to overcome environmental impact, novel combined chemical-templated activation was investigated. A mixture of NaOH and NaCl was employed to produce carbon, which possessed high surface area and versatile porous structure. The process was optimised and described by mathematical models using the response surface method (RSM). The BET surface area and yield were selected as output performances (responses), whilst temperature, time and chemical ratio were chosen as variable inputs (factors). Macropore sizes were of the same NaCl crystal size confirmed by XRD and SEM indicating a template mechanism. Micropore origin was suggested by chemical reactions between NaOH and carbon with a formation of Na2CO3 confirmed by XRD standard patterns and corresponding FTIR peaks. According to RSM design, the most significant factor is chemical ratio for both responses. The experimental data of the BET surface area is in a good validity of the quadratic model, while yield matched the linear model well according to the ANOVA test. In this study, porous carbon was produced by new method overcoming the major challenges of templated and chemical activation and brings added value of lignin.