Synthesis and characterization of activated carbon from lignocellulosic materials by phosphoric acid activation

Activated carbons were synthesized from xylan, cellulose, lignin, mixtures of cellulose and lignin, and natural lignocellulosic materials (pecan shell and rice husk) by phosphoric acid activation. The physical and surface chemistry properties of carbons synthesized by changing independent variables were characterized by different analytical techniques.;The analytical results of physical structure demonstrated that Carbon yield is highly dependent on precursor. Detectable surface area can only be developed with the final activation temperature higher than specific values for different precursors. The pore size distribution of carbons produced from different precursors at the same conditions is different. Impregnation ratio is another very important independent variable affecting the pore formation and pore size distribution.;The carbons synthesized in this study have various types of acidic surface functional groups. The type of functional group is nearly the same for carbons synthesized from different precursors by phosphoric acid activation. However, the concentrations of these surface groups are different on carbons from different precursors. Boehm titration results show that the optimum final activation temperature is 250° for the formation of acidic surface groups on carbons from cellulose and lignin. Potentiometric titration results demonstrated that the functional groups can be classified into five sets according to their pKs: of <2.0, 2.0∼6.0, 6.0∼8.0, and 8.0∼10.0 respectively. Besides oxygen-containing groups, some phosphorous-containing groups are formed. This can be proved by FTIR analysis.;From ICP analysis results of total phosphorous content and titration results, it can be seen that the presence of phosphorous in different states contributes differently to the acidic surface chemistry of carbon samples.;Simple mixing rules based on the properties of carbons generated from the pure components of lignocellulosic materials (i.e., cellulose, lignin, and xylan) and having parameters dependent upon the processing activation temperature provide reasonable predictive estimates of the physical and chemical properties of the carbon products.