Conversion of cellulose to activated carbons for high-performance supercapacitors

E. Sermyagina¹*, K. Murashko², D. Nevstrueva¹, A. Pihlajamäki¹ and E. Vakkilainen¹

¹LUT University, Energy Technology, Laboratory of Sustainable Energy Systems, Skinnarilankatu 34, FI53850 Lappeenranta, Finland
²University of Eastern Finland, Fine Particle and Aerosol Technology Laboratory, Yliopistonranta 1 C, FI70210 Kuopio, Finland
*Correspondence: ekaterina.sermyagina@lut.fi

Abstract:

Biomass-derived activated carbons are promising materials that can be used in various applications. Current work investigates the possibilities of the cellulose-derived activated carbons in substituting the commercial alternatives for the supercapacitors’ electrodes with high efficiency, stable performance and relatively low cost. Hydrothermal carbonization (HTC) followed by chemical activation with KOH is used to convert cellulose into highly porous activated carbons. The effect of HTC parameters on the material porosity development and electrochemical properties of the electrodes is evaluated with several variations of the residence time and the weight ratio between cellulose and water during the pretreatment. The analysis shows that intensification of the HTC process (longer residence time and higher water/cellulose ratio) results in increase of the surface area of both hydrochar samples and subsequent activated carbons: with the highest surface area for the sample produced after 2 h HTC treatment with water/cellulose ratio of 6/1 – 2,645 m² g^-1. As for the electrochemical analysis, the highest values of the specific capacitance are found for the samples produced from 2 h HTC treatment: 110.3 F g^-1 (water/cellulose ratio of 3/1) and 102.5 F g^-1 (water/cellulose ratio of 6/1). Additionally, it is noted that electrodes produced from the samples treated during 4 h have higher impedance at low operation frequency. The present study proves the possibility to substitute commercial activated carbons with cellulose-derived materials, the porosity of which can be tuned accordingly already during the pretreatment step.

Key words:

activated carbon, cellulose, electrodes, hydrothermal carbonization, supercapacitors

Stabilization of persistent organic pollutants (POP) in flue gases in a biological waste incinerating facility

P. Jirsa* and J. Malaťák

Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Praha-Suchdol *Correspondence: pjirsa@tf.czu.cz

Abstract:

The article focuses on a technology of flue gases stabilization in biological and hospital waste incinerating facility. Hazardous particles and compounds formed in flue gas during the process of thermal waste degradation need to be stabilized according to an enacted legislation. The aim of the research is to examine technological process of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/F) elimination in flue gas. PCDD/F is group of persistent organic pollutants which are resistant to environmental degradation and are highly toxic for the environment in very small amounts. Experiments were performed in semi operation hospital waste incinerating plant with heating power 1.5 MW and capacity 250 kg h^-1 of incinerating material. It was observed that formation of PCDD/F exponentially grows with increasing concentration of chlorides in the flue gas, but formation varies based on type of congener. The highest concentration was measured for HxDF, 17,522 pg Nm^-3 and HpDF, 16,334 pg Nm^-3 at chloride concentration of 867 mg Nm^-3. However, concentration of PCDD congeners didn´t exceeded 4,000 pg Nm^-3 for the same level of chlorides in flue gas. Two types of activated carbon Chezacarb and NORIT were tested for capability to stabilize PCDD/F in flue gas. Results show that refining effect for both sorbent are very similar. It was observed that 0.1 g of activated carbon should be applied per 1 Nm³ of flue gas in regard to reduce 3–4 ng Nm^-3 PCDD/F under required emission limit.

Key words: