Formation of Adsorption Properties of Carbon Nanostructured Materials by Thermochemical Activation of Sludge-Lignin

Abstract

Pyrolysis is an effective way to process waste of the pulp and paper industry, in particular, sludge-lignin, which makes it possible to obtain a commercial product – a carbon adsorbent. The method of thermochemical activation using sodium and potassium hydroxides is now widely used in pyrolysis of wood waste processing. This method enables the production of carbon nanostructured materials with high adsorption properties, especially when adsorbed from the liquid phase. The paper studies the influence of conditions for the synthesis of carbon adsorbents of sludge-lignin on their adsorption properties using sodium hydroxide as an activating agent. Sludge-lignin was obtained under laboratory conditions by treating lignin-containing wastewater with aluminum oxychloride coagulant. We applied the method of the planned experiment: a rotatable central composite design of the second order for three factors. We studied the influence of the main factors determining the adsorption properties of coals, namely, temperature, pyrolysis duration and sodium hydroxide dosage, on the values of output parameters characterizing the adsorption efficiency from the liquid phase, i.e. the iodine number and the adsorption capacity of methylene blue removal. We obtained experimental data, which were used to construct response surfaces illustrating the influence of the experimental factors on the output parameters. The positive effect of pyrolysis temperature and alkali dosage on the adsorption properties of the synthesized coals was found. The following results were obtained: the adsorption activity for iodine – 300 %, for methylene blue – 1000 mg/g; indicating a developed micro- and mesoporous surface and the possibility of using these compounds for adsorption of both gases and vapors, and organic substances from solutions. Therefore, samples of activated carbons synthesized from sludge-lignin were tested as lignin adsorbents of lignin-containing wastewater. The obtained dependences correlate well with the data describing the influence of pyrolysis parameters on the coal adsorption capacity of methylene blue removal. The high efficiency of adsorbents of sludge-lignin in the removal of lignin from solutions was shown. The value of the specific adsorption was about 1500 mg/g.