Microwave Optimization of the Process for Obtaining Activated Carbon from Agricultural Waste

Carbons activated from lignocellulosic residues by pyrolysis and chemical activation by microwaves and evaluating adsorbent capacity with methylene blue were objectives of the work. Optimum pyrolysis conditions: 400 ºC, 30 min, 2 g of precursor, N2 flow of 150 cm3N2/min and heating rate of 20 ºC/min, yields of 33% and %C of 44-68%. Carbons with anionic surface charges, megaporous structures and less active surfaces for adsorption. Optimum conditions for chemical activation by microwaves: 200 W, 4 min, 60% H3PO4 and 200 cm3N2/min, yields 72-96%, with %C 61-68%. Carbons with larger active surfaces, highly developed mesoporous structures, and a greater number of active sites. Chemisorption, limiting step of the process. Microwave radiation produced specific effects on the surface chemistry, increased C/O ratio, decreased functional groups with acidic oxygen, giving basic activated carbons, effective for methylene blue adsorption