Effect of Preliminary Preparation of the Source Material and Composition of the Gas Environment on the Characteristics of Activated Carbons from Cotton Fluff with Two-Stage Microwave Heating

The effect of preliminary preparation of the source material and gas medium composition on the adsorption and microstructural characteristics of activated carbons obtained from cotton fluff by two-stage microwave heating was studied. Samples of cotton fluff were impregnated with a 5% H3PO4 solution, molded in the form of three types of cylinders: (I) without cuts, (II) with transverse cuts, (III) from crushed fluff crumbs. During two-stage microwave heating (the first stage is carbonization in Ar, CO2, or N2 for 60 s; the second is activation in air for 50 s), the fluff samples are completely carbonized and activated. It was found that the two-stage process makes it possible to achieve a higher adsorption capacity of the finished activated carbon according to the methylene blue indicator compared to one-stage microwave heating for 120 s. It has been shown that, by incising or grinding the processed samples, the adsorption capacity can be further increased. The reasons for the higher adsorption capacity of carbonized samples of type III are the higher homogeneity of density owing to grinding of the source material, which makes it possible to achieve higher carbonization temperatures in the steady state (up to 1100°C in a CO2 environment). Grinding also leads to additional surface development both due to dissection of the fiber into several fragments and due to delamination of the fiber wall during the carbonization process.