Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin

Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 degreesC, rate of heating less than 3 degreesC/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a 'Coconut' carbon molecular sieve, but the latter has both a higher CO2 adsorption capacity and a higher coefficient of N-2/O-2 separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 degreesC/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 degreesC. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 degreesC/min. The activation of lignin-char with steam at 800 degreesC resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm(3) g(-1)) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH4 mixture. The size of the micropores was varied as a function of burn off value. (C) 2003 Elsevier Science Ltd. All rights reserved.