Feasibility of local cotton stalks for production of activated carbon by H3PO4 on a pilot scale

ABSTRACT

Good adsorbing carbon was obitained, for the first time in a pilot scale, from cotton stalks in a locally-designed rotary pyrolyzer. Activation was performed in absence of any purging gases by imprgnation with 50% H3P04 followed by heat treatment at 420°C. Mechanically cut short sticks were soaked in diluted H3PO4 for a short duration [Batch 1] and an extended period [Batch 2] prior to thermal treatment. The derived carbons contained both coarse and fine grains with acidic effect. Porosity was characterized by N2 adsorption at 77 [o]K and the isotherms analyzed by the alpha-method to estimate total and microporous surface areas in addition to total and microporous volumes. The produced carbons exhibited well-developed porosity that was essentially microporous in composition. Several key performance parameters were altered considerably as a result of impregnation with H3PO4 and the extended chemical activation period [Batch 2]. Most of the internal porosity of both carbons was accessible to adsorption of iodine, whereas the uptake of methylene blue dye was proportional to the average size of micropores which were larger for the batch with a longer acid soaking time. SEM and FTIR investigations revealed the presence of a developed honeycomb structure and different oxygen functionalities on surfaces of the activated products which are advantageous in liquid-phase applications. Preliminary laboratory-scale experiments with Pb[II] indicate that adsorption capacity of target heavy metals compares favorably with commercially-available activated carbons. The raw material, pre-processing, and activation process prove feasible for the production of activated carbon on a large scale, thereby providing a sustainable strategy for treatment of toxic waste streams