DEVELOPMENT OF POROSITY UPON CHEMICAL ACTIVATION OF KRAFT LIGNIN WITHZNCL2

Chemical activation of kraft lignin with. ZnCl2 allows one to obtain h igh surface area activated carbons with a predominantly microporous st ructure. Most of porosity develops within the thermal range of 400-500 degrees C, where an increase of temperature leads to increasing micro pore volume values (up to approximate to 1 cm(3)/g) and a wider distri bution of micropore size. An increasing mesoporositiy is also observed . Increasing the impregnation ratio (ZnCl2/lignin, wt) has a similar e ffect on the evolution of the porous structure. The mesopore distribut ion remains within the low-size range even at high impregnation ratios (up to 2.3). At 500 degrees C and an impregnation ratio of 2.3, where the highest contribution of mesoporosity was observed, the mesopore v olume reached a value of 0.59 cm(3)/g. These conditions allowed us to obtain a BET surface area of 1800 m(2)/g, including the external or no n-microporous surface of 200 m(2)/g. The porous structure developed su ggests a fairly homogeneous distribution of the activating agent favor ed by the softening and partial fusion which kraft lignin undergoes wi thin the temperature range of 180-280 degrees C.